texts: Peak flow calculation using rainfall data

texts:
I am trying to use the Curve Number Method to calculate the peak flow over an area. The precipitation is provided in a table, with the first column being the time (hr), second column being the incremental rainfall at each time (inch.), and the third being the cumulative rainfall (inch).

If I am calculating the peak flow, should I just go with the highest incremental rainfall during the period (which is 0.75 inch at 1 hr), or the highest cumulative rainfall (which is 2.25 inch.)?


texts: Difference between direction of ramming in hydraulic press?

texts:
In Printed circuit board/Plywood lamination Hydraulic Press machines (seen here).

The ramming action comes from bottom in all the machines I saw so far. For such action from bottom, excavation has to be done. Is such excavation mandatory in ramming from bottom?

Will there be any difference if we do such ramming from top ?


texts:
The job site requires welding both aluminum and steel (each to themselves only) for different areas of the project.  The contractor has a dual purpose wire feed welder (aluminum and steel) but I am unsure that a dual purpose welder will be optimal for both types of metals.

Can you get quality welds from a multiple metal wire feed welder, or do you need separate units for steel and aluminum?

I'm looking to understand any potential differences between the three types (aluminum, steel & dual) of welding machines and the welds they produce.  Likewise, any testing results that indicate the strength of welds for both types of metal using both dedicated and dual purpose welding units would be useful.


texts: I want to have water source on the 2'nd floor of our house so I can wash stuff there without going down to our 1'st floor... Is there a way to make water rise from 1'st to 2'nd floor?


texts:
I have an old 7,000 lb. blacksmith table (I had it weighed at truck stop). Similar to the one this man has:

Sorry for the size of the pic.
I need to lift one end the way he is doing and I have a farm jack that is capable of doing it. The problem the table top is too high for the farm jack to reach. My shop floor is not fully level so when I put something with a wide enough base to put the farm jack on; everything becomes wobbly. Using the farm jack alone is fine but I don't feel safe putting something under the farm jack to make it reach the height of the tabletop.
Under the tabletop is a 5in.x5in. solid square steel brace that is welded between the legs (brace is 52in. in length). When I got the table the previous owner told me that those braces were solid steel square bars. Also the previous owner, or whoever welded the braces in, cared enough to engrave a warning on these braces that stated DO NOT REMOVE.
Now I would just jack one side of the table from under the steel brace but the underside of the braces is not fully flat and the farm jack's claw does not fit securely and eventually slides out after a few pumps. (I guess the previous owner used these when working on stuff)
Each brace has a total of 6 holes:
2 holes are in the center and aligned vertically (2-1/2in. on top of each other)
2 holes are on each end and are 40in. apart (on each end the 2 holes are aligned horizontally 3in. between them).
I only have some thin steel in my shop nothing that would be suitable for this.
When I came to the site I saw some guy post a question that was similar to what I need (I was laughing so hard because it sounded almost dead on what I was going to ask) but the answer he got wasn't suitable for me.
Seeing that I do have 4x4's (wood) laying around and A LOT of grade 8 bolts. I am thinking of trying what that guy did or is planning on doing (he didn't update his post). I am going to bolt the 4x4 to the brace and the farm jack's claw will fit securely under the 4x4 and I can lift one end of the table like the man is doing in the picture.
Should I bolt the 4x4 to the 2 center vertical holes?...meaning I cut the 4x4 at 5in. (the width of the brace) and make the 2 vertical holes align with the 2 vertical holes in the brace. The cut ends of the 4x4 will be facing up and down; the smooth ends of the 4x4 will be facing left and right.
Or
Should I bolt the 4x4 length wise?...meaning I cut the 4x4 at 40in. (the length of the brace) and make the 2 holes on each side (4 in total) and bolt it to the brace. The cut ends of the 4x4 will be facing left and right; the smooth ends will be facing up and down.
Thanks in advance.


texts:
A pulley system has mass moment of inertia of 1.4kgm^2. If 8kg block is released from rest from S=1, by using energy approach what is angular velocity at S=2? Radius of pulley is 250mm. Note S is from the pulley centre.
This is what I did:
$$T_1+V_1=T_2+V_2$$
$$0+ 8(g)(1)= \frac{1}{2}(8)w^2(0.250)^2 + \frac{1}{2} Igw^2 - 8(g)1$$
Then rearranged for W and got 12.85rad/s?? Am I on the right tracks please?
The mass is at the bottom and it is originally 1m away. The mass then moves down to 2m away from the pulley from this original position of 1m away.


texts: I was trying to compute the fixed end moment for the beam (given below) using equilibrium equation for x, y displacement and moment but there are 4 unknown variables reaction and moment at both ends but I have 3 equations only, vertical equilibrium and moment about both ends. could someone help me to get the answer $-Pab^2/L^2$?


texts: Can Voyager 1 or 2, theoretically, return to earth if given instructions before their electronic instruments shut down in 2025?

texts:
According to the NASA Website, the Voyager probes will begin powering down electrical components soon with all electronic functions ceasing some time around 2025.

With no ability to transmit back to earth and thus of 0 value in the Interstellar Medium...

...could either one (or both) of the Voyagers be directed back to Earth at all before electronic shut down?

If not; do aerospace engineers have any idea where either (or both) of the probes may end up?


texts: How to sanitarily measure vacuum in milk?

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I would like to measure the vacuum inside of a tube which will contain air and milk. A vacuum pump attached to the tube will maintain a vacuum of around 15 inHg.
Are there inexpensive sensors I can use that will work in a milk environment and can be cleaned easily? I have never personally used an electronic pressure transducer and I worry that the milk will get into the inner workings of the transducer and either (a) ruin the transducer or (b) be inaccessible for easy cleaning.
I have found many inexpensive transducers on NXP.com, for example this one:
https://www.nxp.com/docs/en/data-sheet/MPXAZ4115A.pdf
My concern with the sensors above is that the ported variants will be too difficult to clean and the non-ported variants look like they might have a small hole on the top of the sensor in which milk could get into (hard to tell from the line drawings if that is an open hole or a closed membrane).


texts: Build Device for Emitting Weak Air Bursts at Specified Frequency

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I'm a neuroscientist interested in building a device to replicate the following study.

https://www.nature.com/articles/s41598-018-24924-9

Essentially, they sent air through a nose catheter to stimulate mechanically sensitive cells of the nose. They had 8 seconds of continuous air, followed by 12 seconds off (0.05 Hz). This was to mimic the breathing associated with deep meditation, and they report it induced alterations to consciousness.

I'm interested in building a device that can replicate their paradigm, as well as send air bursts at an arbitrary frequency of my choosing. Ideally the range should be between very slow (~0.05 Hz) and higher frequencies (~100 Hz).

I understand pulsing most standard pumps won't work for those higher frequencies. My mechE friend proposed some two way valve that would be able to pulse between two directions, the nose catheter, or just out to the air. I could then just use a standard continuous pump or fan.

I'm unfamiliar with the terminology and haven't been able to find such an electrical valve. Does anyone know of any such valves, or perhaps has a better design in mind?

Thanks everyone!


texts: Simulink analysis of data parallel to generation

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I would like to simulate the following scenario with Simulink/Matlab(/Stateflow): A random number generator is running. Every 10 seconds the numbers that were generated during the last 10 seconds are added up. If the sum is greater than 50 the system is put into an unsafe state (simply a variable 'state' that initially is zero and then gets changed to one). Otherwise (sum <= 50), the state remains unchanged.

My problem is how to implement the 'parallelism' of keeping the random number generation going while analysing the generated data in the background. Any hints of how to do this are greatly appreciated!

This is how I would like the simulation to somehow look:


texts: Mounting a pcb at a different angle than mold direction

texts: We have a problem with mounting a PCB at a different angle than the mold direction angle. I have graphic below to help explain. If we were to build standoffs at the same angle as the mold direction but we need that PCB to be 90 degrees from the ground plane. What is the best method for mounting this? Any help would be great.


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What simple machines have an ability to make a part that is more precise than any available part within a machine?
This is partly related to history about how early machine parts improved in precision. But modern science might have discovered shorter paths to it, those answers are also of interest.
Simple geometries like a ball, screw rod, cylinder, are likely to be the easiest to bootstrap in precision. If you think other shapes like a flat plate or rectangle bar are important, you can describe a path to improve them too.
For example, assuming the first screw is made crudely, by hand. Then screw cutting machine may use this screw to cut another screw, but because screw in the machine may be flipped or shifted, errors of the crude crew will be averaged out, while general structure, the thread, will still be applied. New screw will have higher precision than the initial screw. If you have examples of a simple chain of machines fulfilling the same job, those are also of interest.
https://en.m.wikipedia.org/wiki/Pantograph is often mentioned in discussion on this topic, but I dont think it is quite helpful, because it cant make parts well as big but more precise, or its own parts, such as straight rods or bearing. Or if it can, help me understand how.
My main interest is scale-less geometry precision, so that if error was 1% surface roughness to max length, new version is to have 0.1% surface roughness to max length, regardless if it is bigger or smaller. Exact size match, like making a ball exactly 3cm dia is of interest too, but less so.
TLDR: how would you recreate more precise geometry for a ball, screw, cylinder, if you have only crudely made machines at hand?


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I need help with the following factor of safety.

This is the infomation to apply to the equation.

Tensile Strength = 460MPa

Shear Stress = 280MPa

Bolt Diameter = 8mm

Angle = 50 Degrees

I need to determine the tensile stress and shear stress in the bolt.

I have the equation for Shear stress.

$$\frac{Ultimate Stress}{Allowable Stress}$$

So far i have this.

201.061mm^2 being Area of the 8mm bolt.

$$\frac{9kN}{201.061mm^2} = 0.04476\frac{kN}{mm^2}$$

$$x1000 = 44.76\frac{N}{mm^2}$$

$$= 44.76MPa$$

$$\frac{280MPa}{44.76MPa} = 6.255MPa$$

So Shear Stress = 6.255MPa

And i think i work it backwards to work out tensile strength?

$$\frac{Ultimate Load}{Allowable Load}$$
The problem i have is how to apply the 50 degree angle. I have read to multiply the equation by cos or sin. But i am really stuck on this part.

Could anyone help me please?

Thanks.

Attached diagram. Sorry for not attaching this before.

a is 50 degrees. And is what i am stuck on. I do not know how to apply the degrees to the equation.


texts: Translating the name of a type of beam from Russian to English

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I am trying to translate the name of a special kind of beam from a set of Russian-language drawings.

The dictionary translates the name as simply supported beam, but it's not that simple. There is a slight difference in two kinds of beams. First - what is called a simply supported beam:

  A beam that lies freely on two supports and covers one span.

Second - my beam. This one is different from the previous that it lies on multiple supports and covers many spans.

Important note: both of the beams are not continuous; i.e., they are parts of one long beam.

The question is, what would I call the second beam?


texts:
I'm building a machine to make drinks and I would like to be able to put a straw into the cup. To achieve this, I need to build some kind of mechanism, that will be able to feed me with one straw on demand.

What I was thinking about is some V-shaped box where all the straws will be stored, with a hole at the bottom, but there will be a gear blocking the hole, so the straws will not fall out of the box. However, the gear will have a cut in it and will be rotating. So each turn, one straw will fall into this cut. Something like this:

Will it work? Or is there any better way of achieving this?
Thanks.


texts: Determining RTK parameters for runoff analysis

texts: I am examining a watershed and determining runoff using the RTK method. I basically use a 'guess and check the hydrograph' method right now. I've seen calibrators that use a mutation and convergence criteria using root mean square but I've had limited success using them. How can I perform this analysis more efficiently than using my 'guess and check' method?


texts:
I need to design a pivot arm which is pulled up by a float (buoyancy force). In the upper positions of the lever arm, there's a mass trying to pull down.
The reason that I'm presenting this problem is to consider all the variables (most significant) in order to build a low-cost prototype.

The variables that I consider are:
1.- Volume of the float, the material is polypropylene. I need a low density but high volume float in order to generate more buoyancy force, is that correct?
2.- The distance between the force applied and the pivot "d1". If I generate more torque, more will be the force generated by the buoyancy, right?
3.- The angle of the arm A.

This is my first attempt presenting this problem, so any suggestion will work.  The goal is to achieve a bigger force than the 95 N generates by the "object x" in order to reach the 'sealed position' denoted by "d2".


texts: How do I connect a 3mm water tube to a plastic box?

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I need to connect a 3mm inside-diameter tube from a solenoid valve to a plastic box. The box wall thickness is 4.5mm. The purpose is to empty water in the box when needed.
How should I connect it so that it is water-tight (very low pressure - around 70mm water depth)?

The photo shows the valve and the plastic box.


texts: Why do some cars have flow channels in their bodies to decrease drag?

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From my understanding, the more surface area the flow passes, the more drag happens due to skin friction.

An example of this is the new Ford GT, which has a converging cockpit and separated side body panels. I did some research and the answer I found is related to decreasing the frontal area of the vehicle, but when I compare it with the increase of the surface area it's almost double the area of similar cars.

Image source: ford.com


texts: How to formulate a 3D version of the Navier-Stokes equations in 2D for numerical solution?

texts: I'm considering a topology optimization problem where the design domain is a rotating annulus (in $\mathbb{R}^2$). One of the adjoint equations of the Navier-Stokes system whose solution is to be used in the sensitivity analysis has a weak form with righthand side: $$\int_{\Gamma_{\text{out}}} \rho(r\times u) \cdot \omega)n\cdot v + \int_{\Gamma_{\text{out}}} \rho(r\times \omega \times r)\cdot \omega)n \cdot v + \int_{\Gamma_{\text{out}}} (\rho(\omega\times r)\bigotimes u)n\cdot v,$$ where $v$ is a test function, $r$ is "perpendicular to the axis of rotation" (I've assumed that this is a position vector, see below), $\omega$ is the angular velocity (which is constant, say $|\omega| = 500$), $\Gamma_{\text{out}}$ is the outflow boundary (the outer boundary of the annulus), $n$ is the outward normal to $\Gamma_{\text{out}}$ (i.e. $n(x) = \frac{x}{||x||}$), $u$ is the velocity computed by solving the Navier-Stokes equations, and $\rho$ is the mass density (scalar). I'm wondering how I can formulate this problem for a 2D problem. What I'm doing now is writing $$r(x) = \begin{bmatrix} x_1 & x_2 & 0\end{bmatrix}^\top,\\\omega(x) = \frac{500}{||x||}\begin{bmatrix} -x_2 & x_1 & 0\end{bmatrix}^\top,$$ and so on, treating every 2D vector as a 3D vector in the $xy$-plane, doing the computations by hand and then coding them explicitly (since of course the PDE software I'm using doesn't know how to interpret a cross product of vectors in $\mathbb{R}^2$ either). I'm wondering if this approach is correct or there's some other way of formulating this problem that I'm missing. I'm also not sure that I'm interpreting $r$ or $\omega$ properly, so if there's anything I'm missing there I'd be grateful for some feedback. I'm not an engineer or physicist by training, so I'm not aware of the conventions for these things!


texts: How do temperature and pressure influence the rate of evaporation of water in a closed vessel?

texts:
I am trying to solve a fairly simple question but I'm kind of stuck on the technicalities:

  Imagine that water is evaporating into initially dry air in the closed
  vessel shown schematically in Fig. 8.1-1(a). The vessel is isothermal
  at 25 °C, so the water’s vapor pressure is 3.2 kPa. This vessel has
  0.8 l of water with 150 cm2 of surface area in a total volume of 19.2 l. After 3 min, the air is five percent saturated. What is the mass
  transfer coefficient? How long will it take to reach ninety percent
  saturation?

The answer starts with this: $$N_1=\frac{\text{Vapor concentration}\cdot\text{Air Volume}}{\text{Liquid Area}\cdot\text{Time}}$$

So far this makes sense. The solution then goes on to do this:

$$N_1=\frac{0.05\cdot(\frac{3.2}{101})\cdot(\frac{1\ \mathrm{mol}}{22.4\ \mathrm{liters}})\cdot(\frac{273}{298})(18.4\ \mathrm{liters})}{(150\ \mathrm{cm^2})(180\ \mathrm{sec})}$$

I understand the denominator but the numerator I'm not sure of. Overall there are 18.4/22.4 mol of gas and 5% of that will be water vapor, I get that. But what's with the temperature and pressure adjustment?


texts: Best software for 3D modeling and simulation semiconductors?

texts:
Need to design 3D model of photodiode and calculate it (interaction light with semiconductor). What software product would be better for this objective and why?

Important criteria:

Big library semiconductor elements.
Comfortable interface
Small expensive CPU\GPU (high speed of calculate).
Price of product.
Ability to import geometry from autocad\solidworks etc.


texts: Energy density of "heat storage ceramic" vs. NMC li-ion batteries

texts:
I was intrigued to read about so-called "heat storage ceramic" and was wondering how the energy stored in such way compares to energy stored in a NMC Li-Ion battery, if the latter is used to generate heat (the article lists it a 230kJ L-1). I know it is not an apples-to-apples comparison, but I am curious about any ballpark assessment, especially in terms of energy stored per kg.

The main reason for my interest is potential use in electric vehicles in cold climates. I drive an EV in Quebec, and I know that when the temperature is significantly below freezing, I can expect to spend 5-7KWh per 100km of driving simply to heat the interior. If energy density of "heat-storage ceramic" is significantly higher per weight or volume, it could make sense to install heat storage "batteries" alongside electrical batteries.


texts:
A patent that I read that stated:

"  Coating tungsten with nickel then with aluminum, will stop oxidation in open air environments. And even pass the melting points of both the tungsten and nickel, the metals doesn't seem to melt"

Will this hold up in a real engineering application, even if it goes past the melting points of nickel and aluminum?

Heres the patent:
https://www.google.com/patents/US2682101


texts: Do adhesives have a minimum thickness (bond line) to be useful?

texts:
Background

I have always assumed (or heard) that adhesives require a minimum thickness of adhesive to function properly. One example of this is not clamping two pieces of wood together so tightly that all of the glue squeezes out.

This assumption seems to be backed up by the following articles on minimum adhesive bond line:

From MasterBond:

  Bond line thickness is one of the important factors to be considered in designing a bond joint. Most commonly used bond line thicknesses in a bond joint range from about 0.002 to 0.007 inches.

From Epotek:

  Minimum bond line thickness often receives special attention in part specifications but, is often overlooked and seldom controlled or monitored during process and manufacturing engineering. The risks of inadequate bond line could be low strength...

Why this might not be the case

I ask about this because recently a machine shop that was fabricating a part for my design asked about adding adhesive to the connection of two components where no adhesive was specified.

The part is a press (interference) fit between two steel components.

The machine shop was offering to use a product that specifically states that it is used in interference fit situations. The idea of a minimum bond line seems to directly contradict the use of an adhesive in an interference fit. This is a white paper from the supplier that also talks about the use:

  Retaining compounds are used ... for interference fitted joints: • added to existing interference fit designs to increase joint strength and reliability; ...

So which is it?

Do adhesives have a minimum thickness (bond line)?
Do adhesives in an interference fit have a use?


texts: How Can I do punching of 0.22mm in stainless steel sheet (Sheet thickness 0.5mm)

texts:
Wanted to press punching of 0.22mm dia (Bottom) and on (top) 0.6mm dia

Please suggest how can I make such die?


texts:
Suppose that a ball bearing has axial and radial force ratings of 300N. If the bearing is to hold a 1m long shaft in its bore with a 1kg load on the end of the shaft, will the ratings be exceeded? The torque due to gravity is 10Nm, but how should torque be compared to the bearing's force ratings?
Thanks in advance.


texts: First millennium BC Egyptian rudder systems

texts:
Hello I am researching first millennium BC Nile freighter rudders. They sailed upstream and came  back down with the current. The Greek writer Herodotus tells us that going downstream they were towed by a raft  and towed a stone behind, no doubt to provide steeridge way. Most had twin quarter rudders but a recent excavation had two closely spaced holes in the keel.  Amongst other possibilities they may have been used for a pair of rudders with blades on one side only with one facing forward and the other facing aft.

In use they may have acted as a reversable rudder and skeg. The rearward blade was lashed amidships when going downstream with the ship presenting her stern to the current and the forward rudder would be used. When sailing upstream the forward rudder would be lashed and the rearward one used. Overall length of the rudders is unknown as is the profile. Do you think the hydrodynamics could act to make it function as a single foil given that the blades were flat.  The  vessel was around 26M in length

Q


texts: What does "crs" mean in structural engineering / construction?

texts:
In the realm of structural engineering, construction, foundation design, what is "crs" when talking about piles/posts? Is it an abbreviation? Does it refer to some sort of size?
Some examples:


texts: Why did my result show "more blades on turbine = more RPM"?

texts:
I placed a normal cooling fan 45cm away from a small turbine generator. i had 3 turbines, one with 4 blades, 8 blades, and 12 blades.

The one with 12 blades always rotated the fastest, even after changing any possible variables such as height or distance from the fan.

I did some research and apparently turbines with higher number of blades rotate more slowly.

So why did my experiment show that more blades on a turbine gives more RPMs? Any ideas?


texts: Simple Finite Element Modeling of Wall Piers

texts:
I'm working on analysis of a bridge wall-pier for dead and live loads. When modeling the pier in finite element software (LARSA), I'm running up against several modeling questions:

Is it valid to model the wall as a single column element? (Going to a plate mesh seems like overkill for a run-of-the-mill highway bridge.)
How should the connectivity be modeled between the girders and the wall pier? Are rigid links appropriate? Joint constraints? Beam elements with really high moments of inertia?
If I wanted to run modal analysis, would this change the modeling considerations?


texts: Software options for simulating oil flow in small diameter pipes

texts:
I'm looking for 1D software packages that can simulate flows of oil (lubricant) in pipes of a small diameter (typically between 1mm to 12mm in diameter) and have found around 10+ possible candidates, but pretty much all of them seem to be designed for water flows, and much larger pipes.

Can anybody recommend a software package in which I can build a model in a GUI and input the pump and pipe characteristics in order to find the outflow at multiple outlets?

Full CFD seems like overkill, I'm keen to hear from any body that has experience with simulating lubricant flows, particularly in compact networks.

Note: I couldn't find similar questions (re: software recommendations) elsewhere on the engineering SE, please let me know in the comments if this isn't good practice, and I will remove the question.


texts: Winding a wire heating element after a few uses

texts:
I bought recently 10 meters of Kanthal A1 AWG18 wire, which is a type of heating element (FeCrAl alloy). I intend to make a coil out of it, but it's no use doing that right now, I need more of it for my project (electric furnace), have ordered more of it online and am waiting a couple weeks till it arrives.

My question is this, if I use the heating element a few times in a different project (assume here that the wattage is the maximum possible), in a way that I won't twist or wind it in any way, will this affect the physical properties of the wire in ways that might make it harder for me to turn it into a coil later on, for my initial project? (I'll be winding the coil manually, it will be between 5 and 10 mm of diameter)

I ask that because heating elements tend to get more brittle with time, but I don't know how long it might take for such changes to happen.


texts: Is a pneumatic cylinder in general a linear or rotary actuator?

texts:
I've just begun to learn pneumatics and I'm really confused where the pneumatic cylinder falls under in the categorization of what kind of mechanical motion it is suppose to produce. I've seen one source say that it is rotary and for analogy the motor is its linear counterpart. But I haven't seen any other sources to back this up definitely. I understand that it might be possible for there to be both types.
What is the classification of the one that's most commonly discussed when like someone is new to pneumatics?


texts:
Internet search results don't give much results of real life examples of bladeless turbine. Has anyone ever seen a working real example of Tesla's bladeless turbine, in some industrial or other application? How did it perform? What was the application?

Marino


texts: Low accuracy current feedback measurement in motor control

texts:
Given a very low accuracy current sensor in a 3 phase inverter (in my case used for motor control) what is the best way to tackle the issue and keep reasonable performance and robustness at the same time of my feedback loop? The manufacturer of the sensor provides a low accuracy. Specs for my current sensor are the following:

Sensitivity: 33mV/A
Accuracy over full scale range: 12.8%
Full scale range $\pm$ 40 A
Offset is 1.65 V ($V_{cc}/2$, where $V_{cc}$ is 3.3 V)

Getting to how much this corresponds in A (assuming the full scale is on the analog V side) is about 1A, so I assume $\pm 0.5$ A as error.
The manufacturer does not state whether this is normally distributed error or anything else. I fear it might be a systematic accuracy error.
This is extremely course. Solutions that came to mind to close the loop without losing stability and keeping some sort of reasonable performance:

real time estimation/reconstruction of currents, given I have 3 sensors, one for each current (this is probably not doable because the switching frequency required for the application is too high and there is no time for digital filtering or estimation)
robust control ($H_2$ or $H_{\infty}$). My doubt on this is about the error modeling. As far as I understand robust control deals mainly with modeling the plant's parameters uncertainty and disturbance rejection.

Any idea to overcome this issue?


texts: Stopping metallic construction held by a threaded rod from wobbling

texts:
I am working on a 1.5m satellite dish with a custom feed. The problem is that the feed is being very wobbly once slightly pushed, as shown here: https://www.youtube.com/watch?v=rAFGbEhhDZ8 (it swings back and forth, which would not be a good thing on a windy day).

Would adding a second thick plate to the back of the feed (where it's held on by the threaded rod (24M)) make the feed any stiffer and reduce/stop wobbliness? I had this problem with my previous thin rod (see Stopping/reducing wobbliness in threaded rod), but I fixed it by increasing the diameter of the rod. What could I do with the feed?


texts: Does a one way clutch for motorized cable reel exist?

texts: I am newbie in the area of clutches. I am making a motorized cable reel (DC motor) which I needed to make it easy for anyone to pull the cable reel out manually without much effort. Only pulling the cable out is manual. The retraction of the cord is done automatically via the DC motor. So, based on my research online, one way bearings mounted on my DC motor sprocket seem to be the way to easily/freely pull the cord reel out manually without too much effort. But based on my understanding of this one way bearing, I would need disengage this one way bearing clutch while I need to retract the cord back in the opposite direction. If this statement is correct, I was wondering how I should disengage this clutch for retracting the cable back in. Do I have to use a powered electromagnetic clutch (something like this) while will get disengaged while powered, and thus allow the cord to get retracted back in easily? Is this the only way of doing this?


texts: How is a carbon fiber chassis made one piece?

texts:
How is such a one piece car chassis from carbon fiber made at one piece?
Do they make the parts individually and bond it some way that it is extremely durable bond?
What bonds are really durable for carbon fiber that they can allow for carbon fiber to behave in stress tests as one piece?
Since carbon fiber needs to be vacuumed to be cured, doing this one piece has some challenges how can this even be possibly made one piece?
NOTE: Any book or resources on this topic would be greatly appreciated it


texts: Measuring wire damage using strain gauges

texts:
We need to determine the physical damage in some area of overhead lines that can't be inspected visually. The damage's in general caused by short circuit and air pollution (mostly sulphur compound).

Our idea is to attach strain gauges to the area and measure the change in strain which should be increase as wire's damaged.

Was wondering if I could get some opinions on whether this could potentially work and are there any issues we should considering?


texts: Is the reliability of automotive sensor technology impeding the success of self driving car?

texts:
The reality is that sci-fi KITT is almost here.

Recently I read articles Delphi car driving itself across the country as well as Tesla cars will be self-driving this summer. As of 2013 four states (Nevada, Florida, California, and Michigan) have enacted some type of legislation to permit autonomous vehicles. This indicates legislators recognizing the emerging technology.

Also these autonomous vehicle have many sensors to gather data real-time which are processed by complex software algorithm. Radar technology is one such used in front and rear cross traffic alert systems.

Among the many potential advantages, few traffic collision is one of them. Likewise there are many obstacles too. Among them are disclaimer such as the one by Toyota "Do not rely exclusively on rear cross traffic alert or blind spot monitoring systems. These are driver assist devices and are not a substitute for safe and attentive driving "

Question:

Is the reliability of systems such as rear cross traffic alert system, in a self-driving car the primary obstacle impeding the success of self-driving car with human as fall back option?

References:

Self-Driving Cars: Are we ready? - KPMG
Tesla cars will be self-driving this summer
Automobile sensors may usher in self-driving cars
Driverless Car to Begin Cross-Country Trip Sunday
Sudden unintended acceleration


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Is there a DIY method for calibrating thermometers in the 200 to 250 degree Celsius range?
In a moment of boredom I decided to put all five of my wife's oven thermometers side-by-side in the oven and set it to maximum. After waiting for them all to stabilize they all disagreed with each other over a 70 degree (C) range of values.
How can I know which one is right? (or even just 'least wrong'?)
I know I can calibrate the zero value against melting ice, and can calibrate 100 degrees against boiling water, but non of my thermometers actually go this low, and even if they did, the temperature range I'm interested in is 200 - 250 degrees.
Any ideas?
UPDATE - I'd prefer to do this without spending too much money, hopefully no more than any of the thermometers cost in the first place. I'm looking for a solution with prove-able results. Simply buying another oven thermometer, even a top-rated one begets the question 'how do I know the new one is any more accurate?'
Incidentally, I googled various oven thermometers reviews, and non of the comparisons even mentioned accuracy, they were more concerned with ease of use and the size of the dial rather than whether or not they worked properly!
UPDATE - apparently sugar melts at 184-186 degrees - pretty close the sort of temperatures I'm interested in. This has some advantages a) I already have sugar! and b) unlike solder, I'm not going to worry about it being potentially toxic and contaminating the oven.


texts: What is the curing process for polymer concrete if it doesn't use any water?

texts: The curing process for regular cement concrete is sprinkling water fog or using a moisture retaining fabric. I was wondering what the process is for polymer concretes because they don't use any water.


texts: How could I automatically agitate water by blowing warm air over its surface?

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I want to increase the evaporation rate in a tank by blowing warm air over the surface of the water in the tank; this will (hopefully) agitate the water, increase the airflow in the tank, and maybe heat the tank slightly. How could I do this?

The main goal here is not to heat the tank, but to agitate the water in the tank. The fan/device/whatever works has to be somewhat small, in addition, and it should blow without human assistance.

Thank you for any and all help!


texts: Will laser cutting render my galvanized sheet metal susceptible to corrosion?

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Firstly, pardon my ignorance about this topic because I am an electronics engineer.
I designed a 3 mm thick mounting bracket for one of my products. For this, I need to cut a galvanized metal sheet  and bend it 90 degrees.
Maybe I am being over cautious, but (per my reasoning) since the galvanized coating is only in the outer section of sheet metal, the 3 mm wide edges will be uncoated, therefore susceptible to corrosion.
Also the 90 degree bent part will be stretched, so coating thickness will be reduced.
Are these effects real? Do they make any practical difference?


texts: Impact force with unknown deformations or time duration?

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I expected to find more documentation on analytical solutions to determine the contact force between bodies, where deformations ($\delta = \delta_{1} + \delta_{2}$) and impact time ($t = t_{f} - t_{i}$) are unknown.

The time interval begins at contact between bodies (with $m_{1}$, $v_{1,i}$, and $m_{2}$, $v_{2,i}$) and ends at the instant $v_{f} = v_{1,f} = v_{2,f}$.  Without deformation, $d = 0$: $d = \frac {v'-v}{2}*t$ and $\mathrm {dP} = F\mathrm {dt}$ require the time interval $t = 0$ and $F \to \infty$.
Avoiding deformation analysis, is it possible to apply $\lim_{t \to 0}$ or $\lim_{d \to 0}$ to calculate a finite, average contact force?
If not, how is deformation ($\delta = \delta_{1} + \delta_{2}$) or time duration ($t$) calculated?

While accurate solutions are readily obtained by Finite Element Methods (continuum mechanics), as shown, do analytical solutions exist?

Many engineering texts do contain partial solutions (for axial, bending, and torsional impact), where deformation is calculated for the impacted body only- they do not account for deformation in both bodies.  This results is a conservative estimate of contact force and stress.
Contact forces and stresses are well documented (ex. Contact Mechanics); however, they require that contact forces are known.  Please explain how these might be introduced to solve for deformation in both bodies.

My incomplete solution follows.  I am interested in critiques and/or practical, analytical approaches to this type of problem.
Conservation of Momentum: $$m_{1}(v_{f} - v_{1,i}) = m_{2}(v_{f} - v_{2,i}) \; \Rightarrow \; \therefore v_{f} = \frac {m_{1}v_{1,i}-m_{2}v_{2,i}}{m_{1}-m_{2}}$$
Without a known force, deformation is solved with respect to energy.  For the ideal case, bodies are linear elastic (with stiffness $k = \frac{EA}{L}$ where $E$ is the Modulus of Elasticity, $A$ is contact area, and $L$ is the length perpendicular to contact area).  Certainly, these large assumptions result in error; regardless, they allow for an estimate.
$$\Delta E_{Kinetic} = E_{Deform}$$
$$[\frac {1}{2}m_{1}v_{1,i}^2 + \frac {1}{2}m_{2}v_{2,i}^2]_\text{i} - [\frac {1}{2}(m_{1} + m_{2})v_{f}^2]_\text{f} = \frac {1}{2}k_{1}\delta_{1} + \frac {1}{2}k_{2}\delta_{2}$$
I am unable to complete the system of equations- I know that both bodies:

Deform during the same time interval

Have equal contact forces/surface stresses

Can this problem be solved analytically?


texts: Can a neutrally bouyant helium balloon be suspended in air using magnet entrapment?

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The above picture is a basic concept of how a levitron toy works.

Could the top floating peace stay entrapped in the magnetic field without having to spin if the edges of the balloon keep the top piece from flipping over?

The balloon is neutrally buoyant with the small piece inside and secured not to flip over.

I do know the spinning causes gyroscopic stabilization and keeps it from flipping over to attracting poles. The opposing poles of the 2 magnets creates the lift. The shape of the base magnet keeps the levitation entrapped.

Youtube video
In other words could I replace the spinning with a balloon?

I tried to find support to that theory using current models and I am blown out the water wrong because those model were electronically stabilized.

Why would a balloon make a difference?? In this model the difference is the helium balloon may make it weigh less and allow the top to be pushed higher by the base. Like a sail ship mast the buoyancy of the helium and the weight of the secured to balloon top would be kept up right entrapped.

Will not know until I try it. Unless it has been tried some where else this way?

How does a Levitron work?

Where on Earth is the magnetic field intensity stronger?

Could a satellite levitate above the magenetic fields of Earth?

Could a city be built out of Balloons?


texts: Exact procedure to mount a blanking spade near a butterfly valve

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This is a follow on to my previous question about blanking spades. There's a gas pipeline with a butterfly valve mounted between to flanges. I want to work on one side (call it the inert side) and need to close his side with a blanking spade to the other side (gas side). To enter the spade I have to close the valve and open a few bolts so I can push the spade in. But the moment I remove bolts, the force (What's Kraftschluss in english) between the valve and the flange on the gas side is weaker and I get a leak. At least that's what I think happens.

Depending on pressure on the gas side, I either have a gas leak and a potential hazardous atmosphere in the working area, or  air infiltration into the pipe and a potential explosion hazard there.

So far all no butterfly valve I've seen could be mounted as a headpiece.

So either there's a trick to it or a short time hazardous atmosphere is accepted (and can be worked around with appropriate safety measures).

So what is the actual procedure to enter a spade into a pipeline in light of this?

P.S. I don't do or supervise these works. I'm just curios how the folks doing it (should) go about it.


texts: How can I calculate the discharge flow rate of compressor of 1 HP?

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Outlet nozzle - 1 1/4 inch
Cut off pressure - 8 bar
Tank capacity - 35 ltrs

How can I calculate the discharge flow rate?
Based on the outlet nozzle, discharge rate will vary.


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Can someone explain what this sentence means?

"The mean power produced in this plant is 100 MW with a mean productivity of 5100 kWh/tcoal."

Specifically what does 5100 kWh/tcoal and 100MW mean?


texts: Why are hydropower plants always wheel-shaped and not flat?

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Question:
Why are there no flat power generators like in the picture below, that work on the surface of shallow, but steadily flowing rivers ?  (As a floating micropower plant.)

The picture shows a conveyer belt with vanes/blades(?) attached to it. The water flow moves the conveyer belt. A generator could be attached to the front and back "wheel" of the belt.
Here's a video of something similar. I would just build it on a larger river.
Why would I ask this?
There are much more flat rivers than waterfall-like structures on this planet. Using them looks like a much more non-nature-inversive, cheap solution. Having a longer surface should supply better drag by flowing water.


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I am studying the thrust distribution of jet engines.
But I'm now a bit confused.

In Rolls-Royce's "The Jet Engine" book,

http://aeromodelbasic.blogspot.com/2012/05/thrust-distribution-distribution-of.html

  At the start of the cycle, air is induced into the engine and is compressed. The rearward accelera- tions through the compressor stages and the resultant pressure rise produces a large reactive force in a forward direction. On the next stage of its journey the air passes through the diffuser where it  exerts a small reactive force, also in a forward direction

I understand the first part of the paragraph that the compressor is providing forward thrust, as it is pushing (so compressing) air rearward. But why is the diffuser also providing forward thrust?
And also why the nozzle is providing rearward thrust?

The similar conculsion is also shown here:
http://www.pulse-jets.com/phpbb3/viewtopic.php?t=2183, that the diffuser is providing positive thrust by calculating the pressure force.

From my understanding of basic fluid mechanics,
shouldn't a nozzle be providing forward thrust, like the sprinkler in the garden or a fire hose?
And shouldn't a diffuser be providing rearward thrust, as the outlet speed is slower than the inlet speed, and so m dot X (v - u) is negative?

What's wrong with my understanding?

It seems like I don't know when I need to add a pressure force term P_out A_out - P_in A_in, in addition to the change of momentum term (m dot x (v-u)), while calculating the force of a control volume.


texts: What is the angle of twist in end point A?

texts: Can anyone please explain this question to me? I am okay with answering a gear assembly with 2 gears at a time. But the third one here is confusing me.


texts: How would I calculate a force on a spring? Or more specifically the weight of an object that spring is supporting

texts: I am trying to create a simulation for car suspension and tyre physics and to do the tyre physics I need to know how much weight is over the friction point that is under the spring.


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I have built a small, simple linear generator. It works, but I'm sure it could be more efficient because I didn't know how many windings of magnet wire to use.  I know there is a formula I could use to determine how many windings but have been unable to find it. Can someone provide me the formula or where I can find it?

Now for more details of the project in case that somehow helps. I have a cylinder about 2.5 cm long and about .4 cm inner diameter. I have a cylindrical neodymium magnet that just fits inside and is about .2 in height. Of course, when I hold my fingers at the ends and shake back and forth I get a small current. I would like to be able to light an LED (hopefully a super bright). I realize it will strobe on and off - which is exactly what I want. I haven't yet used it with an LED, but did connect it up to a multitester to see that I was generating a current. Perhaps I will need to upsize the magnet/change the cylinder size (diameter or length). I'm hoping I will not need to change things too much as I have space limitations. But I could change things a bit if needed. If anyone has thoughts, I would be happy to hear them, although the winding issue is more what I'm hoping to have answered.

Thanks


texts: What boundary condition should I use for the edge of a blind flange?

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When testing a pressurized pipe with off-standard flanges, often times the materials available to fabricate a blind flange of the correct size are limited to what is around.

I've made it a habit of referring to Roark's formula's for stresses and strains, and going to the table for large deflection circular plates for these.  I use the area inside the bolt circle.  They have three boundary conditions available:

Simply supported (neither fixed nor held)
Fixed but not held (no edge tension)
Fixed and held.

Bolted connections are unusual - especially since I have a full face flanges.  I've designed to both simply supported and fixed but not held.  The simply supported works, the fixed but not held does not.  However, due to the flatness out to the OD of the face, it seems like the rotation of the edge should be 0, so it should be fixed but not held.  I'd like to make these thinner, so it would be nice if someone can demonstrate an accurate boundary condition (or perhaps that 80% of the fixed + 20% of the simply supported would be conservative via FEA).  I'd like to see better research into the mechanics of design for blind flanges (which is rarely covered in the context of the Boiler and Pressure Vessel Code, or elsewhere).

The main question is: what boundary condition for the edge should I use?


texts: Solidworks Loft error (guide curve not intersecting with profiles)

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I am trying to add 'finger grooves' to my model of a brake lever and want to use a loft to do so. I have created (to my knowledge) all required sketches for the loft but SW gives me an error when trying to select a guide curve... (please see image below), which is strange since I drew the sketches such that the edges of the profiles should intersect with the guide curves... I am not sure what I am doing wrong...(I get a similar error when I try to select the other guide curve instead)
The error:

The file: https://forum.solidworks.com/servlet/JiveServlet/download/244266-1-225417/Saint+lever+extended+5.SLDPRT.zip
Another weird thing which (I think) is causing some issues with creating the guide curve (the one highlighted in blue) properly: There is a transition at a certain point in the model where I applied a fillet to round off the lever surface, before applying the fillet there was no transition after there was... very weird.. please take a look at the image below.

I made a very simple drawing (see image below) of the part (before adding the aforementioned fillet), I've dimensioned the 'curvy' bits to try to make the shape (which parts are straight lines) clearer.

Would you know of a way to get rid of said transition (and what may be causing it)? Would it be possible to get rid of the transition whilst still using the fillet feature for the rounding of the handle? Or would I have to use a swept cut instead of a fillet to eliminate this transition? Is there a way to create the desired 'finger cavities' without getting rid of the transition?
The result of the loft should look somewhat similar to the image below (but the shape will be repeated more times/and will be slightly more 'rounded' than the shape seen in the picture)

I have added the file as an attachment
Any input is greatly appreciated, thank you very much!


texts: What is the advantage of using GPIO pins as sinks instead of sources?

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I'm following this tutorial on how to control Raspberry Pi GPIO pins with Python scripts.  Instead of connecting the test circuit (LED + resistor) between the ground and the GPIO pin however, they connect it between the +3v pin and GPIO (see section 4, last paragraph).  The author says this is to have the current come from the 3v pin rather than the GPIO pin.  However, from my limited understanding of electricity, the magnitude of the current through the GPIO pin should be the same regardless of how the polarity has been set, the only difference would be its direction.

Am I wrong about the current?  Is it actually better to draw power from the 3v pin instead of the GPIO pin?


texts: How can the linear relationship between curvature and bending moments be verified?

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As part of an experiment, I'm verifying the existence of a linear relationship between curvature and bending moments for three beams using different materials. The plotted data can be seen below. Visually, there is a very strong positive linear relationship. Visually, the residuals are small. Of the three populations of data, the lowest Pearson coefficient is 0.9998, the highest is 0.9999.

In terms of verifying this linear relationship in a lab report, need I discuss anything other than the regression lines being visually straight and the residuals being visually small? Is it necessary to calculate the Pearson coefficients? Should any other statistical tests be carried out such as the coefficient of determination?


texts: Converting grams of fuel per kWh of energy

texts: Is there a database showing how many grams of a particular fuel generates how many Kilowatt hours of electricity?


texts: Are all pressure-volume processes polytropic?

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I was searching for information about pressure-volume processes when I read, in a heat engineering book, "The process is polytropic with $PV^n = \text{constant}$."

How can I know that a real life process follows this model? Are all processes related to this heat engineering, pressure-volume, etc., in fact polytropic?

And if they aren't then how can I tell when that model is valid?


texts: Problem with Energy Transfer Rate Conversion

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Given the question:

  Calculate the energy transfer rate across a 6 in wall of firebrick with a temperature difference across the wall of 50 °C. The thermal conductivity of the firebrick is $0.65\ \frac{\text{Btu}}{\text{hr ft }^\circ\text{F}}$ at the temperature of interest.

The correct answer is 369 W/m2

I used the following approach:

$${ x = 6in => 0.5ft }$$
$${ \triangle T = 50^oC => 122^oF }$$
$${ k = 0.65Btu/hr-ft-F }$$

$${ \frac{Q}{A} = \frac {k\triangle T}{x} = 158.6Btu/hr*ft^2 => 500W/m^2 }$$

But I did not calculate the correct answer.  Is there a step that I am missing?


texts: Is air density calculated using Total Pressure (Dynamic and Ambient) or just Ambient?

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I have some wind tunnel data and static and dynamic pressure are logged (temperature too).
I need to calculate lift and drag but I’ve been confused whether to use only ambient pressure to calculate density ($\rho = P/RT$) or both ambient and dynamic, which I have no idea how to combine to get the density. I know that dynamic pressure is given by $P_{dyn} = 0.5\rho u^2$.


texts: Accidental Torsion and Equivalent Static Load for an irregular structure

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Important note: I am writing a structural FEM software from scratch, so I won't able to use existing commercial FEM package. I would need to know how all the important quantities are calculated from the first principles.

I would need to determine the accidental torsional effect ( UBC97, 1631.5.6, pp-27, this accidental torsion effect is needed for both response spectrum and linear time history analysis) for seismic dynamic analysis.

$M_t=F_xe_y$

Where

$F_x$ is the equivalent lateral static force in $x$ direction

$e_y$ is the accidental eccentricities in $y$ direction

Take note that all these involved quantities are evaluated on floor basis.

My structures are quite irregular and general, such as this:

For a cantilever column or an one dimensional lumped mass model, the term on floor basis is easy to interpret because there is only 1 node per floor, and the $F_x$ can only be applied on this node itself. Compare this lumped mass model with the above 2D structure FEM model and you can see the difference:

But when you have such a 2 dimensional irregular structure, analyzed using FEM, calculating $F_x$ and $M_t$ is no longer easy:

How should we obtain $F_x$, given that it is lateral static force, but we are doing dynamic analysis?
There are so many nodes on a floor, so on which node(s) should the $M_t$ be applied?
In FEM, each beam, column, wall and slab are multiple-node elements. And each node has a internal force value  resulted from FEM analysis, what should I do with all these forces at different nodes? The comment here says that I should sum up all of the forces on each related node in order to obtain the correct $F_x$ ( I'm not sure whether I interpret it correctly or not). But I am highly skeptical of this approach, because won't that make $F_x$ dependent on the number of nodes, an artifact of how we mesh an element? How can a real physical quantity increases with the number of nodes we decide to mesh?
If 3) is true, then what about the $F_x$ on the wall above a particular floor? Should we sum them in? What about the internal slab and beam? Do they have this force also?
How should we intepret $M_t$? Is it internal member force to be resisted by beam/slab? If yes, if there are many slabs and beams into $x$ direction, then how should this $M_t$ be distributed? Or is it an external static force; so one would have to apply this external force on the structure in order to calculate the individual internal member force induced by it ( via the FEM equation $ku=F$)?

So the question is, how to calculate and interpret accidental torsion in a FEM model? I've tried to obtain a general way to reduce a 2 Dimensional general FEM structure into 1 Dimensional lumped mass model, so that I can apply the above formulation easily, but I was told that this wasn't possible.


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I am taking a graduate course in Digital signal processing with no prior knowledge in DSP. So I am struggling because I don't have the foundational knowledge. Please I need help with the following.

Assume we have the following difference equation $y(n) = y(n-3) + w(n)$ where $w(n)$ is the white gaussian noise. The transfer function of the system is given by $ H(z) = \frac {Y(z)}{W(z)} =\frac{1}{1 – z^{-3}}$. The question is, how can we determine the $z$ transform of $W(z)$ assuming the white noise has zero mean and variance $\sigma^2 = x$.

Should I perform my analysis in the frequency domain by transferring the transfer function from z domain to the frequency domain. I read that to do that we need to replace $z$ with $e^{j\omega} $
Any explanation will be greatly appreciated.


texts: How to maintain a static negative pressure in a valve?

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My target is to create a valve with multiple inlet capillaries. And my output is a pipe of a larger diameter. I do not want to use any electrical systems, and at the same time, I want to maintain enough negative pressure inside the valve to influence the flow of fluid to be from capillaries to the pipe and not the other way round. The pipe-capillary system is evacuated and the fluid inside is at a higher than atmospheric pressure (we can assume 4-5 atm). I also wish the flow to remain laminar and avoid turbulence.

I looked into kinds of pumps which, in principle, achieve this... But I could not find any self-controlling system which does not require external power to maintain the pressure force required. Pneumatic systems like the flow valve looked promising but I could not figure out a way to achieve the requirement I am aiming for.
I was thinking of inserting a high pressured section inside the valve which would push a diaphragm with constant force. And that force can be used to maintain the negative pressure that I want. Another idea with having a vacuum instead of a high-pressure fluid to achieve the same (effectively the inverse mechanism). But from a design perspective, I could not figure out a way to avoid leakage of the high pressure over time. My idea was inspired by the action of a syringe. I tried to design a CAD model for the same to simulate it... But could not figure out how to implement all that I read on this topic.

Does a valve or pneumatic system exist that achieves this (am I missing some information that I should know)? And if not, how can I make such a valve?
I need to manufacture this as well, so simplicity/availability of resources is important. But any theoretically sound solution will also be greatly appreciated :)

Thanks in advance


texts: What is the best heat and moisture resistant adhesive?

texts: I have to join metal to metal (Aluminium or SS piece onto a vertical SS wall) that could take a shear load of say, 600gm with an area of contact of around 2cm^2. The environment is above boiling surface of water. So, the adhesive should be resistant to 100 deg C temperature, and moisture - with water droplets. Check the image for setup. What are the best adhesives for this purpose? I have checked Araldite, but specs say its max temp is around 65 deg C. Any suggestions? Also desirable is if the adhesive is semi-permanent: If I need to remove it and make the joining at any other location, it shouldn't be terribly difficult.


texts: What is a Velocity, Pseudovelocity, Acceleration, Pseudoacceleration response spectrum?

texts: I would like to know what is a velocity response spectrum, PseduoVelocity Response spectrum, and how they are different from one another? Could you also do the same for acceleration and Pseduoacceleration? Also the explanation of this graph:


texts:
I am currently looking for materials, which return into their relaxed form/ position after intense bending/ stretching.

Could you please let me know what is the name of this mechanical property, so that I could search further on this topic?

Do you know any examples for such materials? Perhaps some polymers?


texts: Is there a name for a process of constructing gradient/smoothly distributed material density?

texts: Are there conventional processes by which one can construct a material that gradually transitions from one alloy or molecular density to another? For instance if I wanted a material that gradually transitioned from steel to cast iron or from rubber with one molecular density to another, I'm sure it's different for different material, but is there at least a name for that type of process?


texts: Why not use Sodium Hydroxide mist to precipitate carbon dioxide from hydrocarbon combustion exhaust

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Much of the currently used techniques of scrubbing the carbon dioxide from power plant exhaust uses sophisticated amine and other organic compounds.  These compounds are then forced to release the CO2 with electric current or heat so that the concentrated CO2 can be pumped underground or otherwise sequestered.
Why not just spray the power plant exhaust with a finely atomized Sodium Hydroxide mist to directly precipitate out the CO2 as Sodium Carbonate or Sodium BiCarbonate?  The carbonates can be sold as carbon credits and/or be useful products.  Sodium Hydroxide can be obtained in quantity cheaply from electrolysis of sea water and other methods.


texts: Interpreting roots of a cubic EOS with 3 phases (VLLE)

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I would like to know how to interpret the roots of the Peng Robinson equation of state for vapor-liquid-liquid equilibrium.

I know that if two phases are present, the largest root is taken as the compressibility factor of the vapor and the smallest root is taken as the compressibility factor of the liquid.

What does the smallest root represent if two liquid phases are present (in addition to the vapor)?  Is it meaningful?

And how can I determine the compressibility or molar volume of each liquid phase?

Ultimately my goal is to be able to calculate the fugacity coefficients for components in the vapor phase, liquid phase 1, and liquid phase 2 in order to calculate the K factors for use in a multicomponent equilibrium algorithm - but I believe that I need the molar volume of all three phases in order to do this.


texts: Are graphene and carbon nanotubes superconductors under atmospheric pressure? What are their critical temperature and current density for superconductivity?


texts:
I have a question about modelling a nonlinear 2nd order ODE for an impact of a sphere on a thin plate in Simulink. Depending on the solver and solver options, my results in Matlab vary a lot. Some are physically reasonable, some not. Strange enough, refining the time step makes the solution less plausible from a physical point of view. Now I thought about modelling the ODE in Simulink an see which results I can get there.The problem is the dimensionless ODE for the indentation of a sphere in a plate:

$$\frac{d^2 \sigma}{d \tau^2}+\left( 1 + \lambda \frac{d}{d\tau}\right)\sigma^\frac32 = 0$$
Where $\sigma$ is a dimensionless displacement and $\tau$ a dimensionless time. $\lambda = 110 = constant$. The initial conditions are: $\sigma\left(\tau = 0\right)=0$ and $\frac{d\sigma}{d\tau}|_{\tau=0}=1$.

Unfortunately, I do hardly have any experience with Simulink. Does anyone have any experience/tips for modeling this kind of problem in Simulink?


texts: Electromagnetic compatibility (EMC) filter and power line filter leakage

texts:
I have some questions regarding Electromagnetic compatibility (EMC) filtering  and power line filter leakage.

What will be the effect of leakage current of power line filter (2A)  when both power line and telephone line filters are installed on same enclosure having common ground and no RCD or GFCI device installed in the facility.  Will it create a hum in the phone lines?
What should be the line to ground capacitance of a power line filter for a 50Hz telephone line filter?
What should be the line to ground capacitance of a telephone line filter?


texts: Is it a good idea to intentionally discharge lithium batteries to 80%

texts: Manufacturers recommend keeping lithium batteries between 40 and 80 percent charged. I tried, but sometimes I let my phone get higher than that. Then I try to bring it down  soon as possible, either by playing graphic intensive apps or by charging some other device off my phone via USB-c. Is there a point in bringing it down once it already has overcharged. Which method is better/worse?


texts: What's the definition of concept of inversion in architecture? Can you also give some example for this and explanation?

texts: It's one of questions for my exam, and I couldn't find anything about inversion related with architecture on the internet. Thanks for help!


texts:
does any one know how to derive the deflection equation of a continues beam of three span of equal length and equal UDL load
Here's a link

these two pictures shows my tries to solve the question


texts:
I want to look at the thermal heat plume of a human in still air in a room. So I have a tank of water with a heating coil/cylinder in it. How do I calculate what the heat output of my heating coil will need to be in order to mimic that of a human's ($100W$) in air?

This is based on dimensional similarity between water:air, Reynolds' number and Reyleigh number. The Rayleigh number, which governs buoyancy is given by: $\dfrac{g\beta}{\nu \alpha \kappa}q x^4$, where:

$\alpha=$ thermal diffusivity
$\beta=$ thermal expansion coefficient
$\kappa=$ thermal conductivity
$\nu=$ kinematic viscosity
$x$= distance from the heated surface

But I don't really understand if the Rayleigh number is the right value to be attempting to maintain similar between both scenarios. Any help would be much appreciated.

EDIT:

So using the Q* formula to get similarity between the two media

$\dfrac{Q_{air}}{\left(\rho C_pT_{\infty}g^{1/2}x\right)_{air}}=\dfrac{Q_{water}}{\left(\rho C_pT_{\infty}g^{1/2}x\right)_{water}}$

and rearranging to get Q_water:

$Q_{water}=Q_{air}\dfrac{\left(\rho C_pT_{\infty}g^{1/2}x\right)_{water}}{\left(\rho C_pT_{\infty}g^{1/2}x\right)_{air}}$

Then substituting in:

AIR: $\rho=1.225kg/m^3$, $C_p=1.005kJ/kg\,K$, $T_{\infty}=21^{\circ}C$, $x=0.1m$, $Q_{air}=100W$.

WATER: $\rho=1000kg/m^3$, $C_p=4.19kJ/kg\,K$, $T_{\infty}=8^{\circ}C$, $x=0.1m$, $Q_{air}=?W$.

I get $Q_{water}\simeq 1.2\times10^4W$... But this seems much too high. Can this be right?


texts: How to calculate the torque created by a rotating motor?

texts:
I have watched this video where the speaker explained how the vertical spin of a quadcopter is stabilized, and how it could be unstabilized to make the drone rotate.

Here is a screenshot of the video, with:

In green: motors
In red and blue : rotation sense of the motors
In brown: arrows for the force exerted by the motors on the quadcopter (3rd newton law)

I do not understand that much the principles, so I would like an explanation with this question: What is the formula of the force momentum created by one of quadcopter's motors?

My thinking is:

I imagine it is not the value of the torque used by the motor to rotate, otherwise it would be independant of the speed of the motor.
It should not be either the lift force created by the motor (momentum would be zero in respect of the force vector's orientation).

What bothers me in the video is: Why are there only two sides of each motor where there is a force (brown arrows)? There should be four since the torque is applied all around the axis. And if there are four forces on four sides (i.e. infinite forces around the axis), then how is the difference of force (and thus torque) created?

Then how is this torque (on the drone's vertical axis) created by each of the motors?


texts: How does an ultrasound device determine where the reflection is coming from?

texts:
When the ultrasound transducer emits a signal and the signal comes back to the receiver how does the software or hardware determine where it came from? I understand it finds distance or depth by delay.

For example when you see an ultrasound of a baby and it has the 2D spread, how does it determine if the reflected wave is from the right or left side of the spread.


texts:
I'm looking at a teardown of a Masterlock. The guts look like this

What's strange to me is the black, plastic pinion that appears to be smooth and a strangely shaped cam:

Here's the cam magnified:

The motor doesn't seem to be encoded in anyway to prevent stall and the PCB only has one microswitch, but it's for the spring-loaded, shuttle-like metal piece rather than the cam. So I wonder how the motor knows when to stop without stalling. There doesn't seem to be a current shunt on the PCB either.

My take is that the square groove of the cam (top facing) faces down in the housing. The round groove on the right of the square groove is where the plastic pinion contacts. That leaves the two not-so-visible grooves facing the mat (ie those facing away from the housing). Does anyone know how the cam is turned? The bottom groove of the cam appears round, so it could probably grip on the black plastic "pinion". But then, if cam shaft is the axis of rotation, that round face can't be the contact face with the pinion.

Does anyone know how how the shaft is rotated or how the motor is encoded such that it won't stall?

I'll also magnify the black plastic pinion here:


texts:
Let's say that I have the following continuous system:

$$G(s)= \frac{2}{1+s}$$

I could convert it to a discrete system using for example the Tustin approximation https://en.wikipedia.org/wiki/Bilinear_transform

So I replace s with:

$$s \rightarrow{}  \frac{2(1-z^{-1})}{T_e(1+z^{-1})} $$

Hence I get the approx. discrete transfer function:

$$G(z)= \frac{2}{1+\frac{2(1-z^{-1})}{T_e(1+z^{-1})}}$$

Now my question is, how can I compute its frequency response ?

In the end, I would like to be able to compare the discrete approx. freqe. response with the  freq. response of the continuous original transfer function.


texts: Approximating a Gimbal using Springs and Dampers

texts:
I recently asked a question about odd results from a transfer function, and while looking over my work, I conjectured that maybe I'm having a more fundamental problem. Since this is a design problem I don't expect anyone to give a full-fledged answer, but any hints or prodding in the right direction would be appreciated. Here goes.

I'm looking to model a one-axis gimbal in Simulink, which requires a transfer function to plug into my simulation. The gimbal has the following properties that I need to capture in a transfer function:

Pushing the gimbal (giving it an impulse $\delta$) will move it some finite distance $x$. This is equivalent to having an impulse response that converges to a finite value.
The gimbal has a resonant frequency of $\omega$. Since I will be using active PID control on it in Simulink, if I attempt to drive the gimbal with a forcing frequency near $\omega$, I should expect high amplitude oscillations in the position $x$.

These two responses combined will produce a very realistic expectation: pushing on the gimbal will move it (though damping will slow it down to a halt if the force is removed), but if you get near the resonance frequency of the structure, you'll excite the first elastic mode and have large-amplitude oscillations.

Below is a picture of what I thought the system should look like, approximated with springs and dampers (because finding the transfer functions of these elements is easy to compute):

My rationale is as follows: imagine just the mass $m$ and the damper $c$. This will produce the first response required, having the impulse response converge to a finite non-zero value. To force the resonancy condition, I should attach to the mass a spring-and-dashpot so that I can use the simple equation of:

$$\ddot{x} + 2\zeta\omega\dot{x} + \omega^2x$$

However, if you look at the link I've provided, I'm having a whole host of problems reproducing the two required conditions in my model. I think something is wrong with how I've modeled the system, but I don't quite know what's going wrong.

Any help would be greatly appreciated. Further, if anyone knows of papers that describe modeling of one-axis gimbal systems (I've found plenty on two-axis gimbal systems, but those are way too complicated for what I'm trying to accomplish here), that would also be helpful.


texts: Suppose that I want to transport gases in a tube in only one direction. Can a liquid check valve be used in place of a gas check valve or is there a specific reason to use only a gas check valve?


texts: How were the sequence of bar widths assigned to digits 0-9 for UPC barcodes?

texts:
UPC barcodes are comprised of a series of black and white bars. Bars can range in width from 1 to 4 (1 being the thinnest and 4 being the thickest). Each digit, 0 through 9 is encoded using exactly 4 bars:

Digit | Bar Thickness Sequence
  0   |        3-2-1-1
  1   |        2-2-2-1
  2   |        2-1-2-2
  3   |        1-4-1-1
  4   |        1-1-3-2
  5   |        1-2-3-1
  6   |        1-1-1-4
  7   |        1-3-1-2
  8   |        1-2-1-3
  9   |        3-1-1-2

How were the bar widths assigned to the numbers 0 through 9?  I notice that each series of 4 bars sums to 7, but other than that I am not seeing an obvious pattern?

(Note: The numbers a UPC barcode encodes can have special meanings (product classifcation, vendor, checksum, etc.)  This question is only about how the bar widths (the barcode encoding) was derived.

Here is one of the references I found: All About UPC Barcode & EAN Barcode


texts:
I have 2 pipe lines, both water . that combine to heat up water.

Assuming at steady state ,

Heat gained by cold water = heat lost by hot water

Let's say , according to formula , I calculated the combined temperature to be 62.94 degrees C.

However , the temperate transmitter tells me that it's 63.06 degrees C, slightly higher than 62.94.. why is that the case ?


texts:
Measuring pressures have many different applications which require proper encapsulating of the sensors, but at the core there is a limited amount of techniques.
To my understanding, the two leading technologies in high accuracy pressure sensing are:

Measuring resonant frequencies in e.g. quartz crystals
Piezo-electric elements

And there are two leading technologies in pressure transfer from ambient pressure to the pressure sensing element (force collectors)

Diaphragm
Bourdon tube

I found a easy to understand reference to precision and accuracy of pressure sensors Pressure sensor fundamentals: Interpreting accuracy and error.
Here they divide Accuracy into the following categories

Nonlinearity
Hysteresis
Nonrepeatability
Zero point error
Span error
Temperature impacts
Long term drift

Most high accuracy sensors promise an accuracy of 0.01% of full scale, but how does this distribute among the different types of errors?
Are there any sensors promising significantly better accuracy?
Is there some technologies that are better than others on e.g. hysteresis or temperature impacts?
Has there been scientific comparisons between different sensors to measure these errors which constitute the total accuracy?
What is the best way of going about to find the sensor best suited for my purpose?


texts: What are the numbers on the other side of vernier caliper

texts: I have an old German caliper. It works and look like any other caliper but on the other side it has a series of numbers ranging from 0 to 61653. What are these?


texts: What does 0.1D  signify in this cotter joint. I meant is it denotes spacing between pin and hole. I am new to machine drawing , kindly let me know. Thanks in advance


texts: Is it possible to build a building with 3 levels, with the 2nd and 3rd levels having areas with clear spans (no columns) of 130 ft length and 85 feet width? There can be columns outside of this clear span area and on the first (ground) level.


texts: What is the difference between Bluetooth Low Energy and Bluetooth BR/EDR in Park mode?

texts:
It is known that Bluetooth Low Energy transmits data only during short time intervals called Connection Events. Connection events occur regullary with predefined period. The rest of the time Bluetooth LE device is does not transmit nor receive data. That is how low energy consumption is reached.

Meanwhile, classical Bluetooth BR/EDR has Park state. In this mode the parked slave wakes up at regular intervals to listen to the channel in order to re-synchronize and to check for broadcast messages. The rest of the time Bluetooth BR/EDR device is does not transmit nor receive data.

So, why Bluetooth LE consumes less energy?


texts: Assign a name to surface in CAD STEP file

texts:
I have a CAD model designed in FreeCAD and need to export it to a STEP file (neutral CAD format) to be used in numerical anaysis software. I would like to assign names to selected surfaces in order to later define analysis boundary conditions on them. Is there a way to

Define surface names directly in FreeCAD so that they are kept by the STEP export and seen by the analysis pre-processor after import, or
Manually edit the STEP file and inject the names at approproiate places

Regarding the second option, I am able to identify the relevant surface and the definition looks like this

#885 = CYLINDRICAL_SURFACE('',#886,53.);

I tried adding a name between the apostrophes but this didn't seem to make any difference

#885 = CYLINDRICAL_SURFACE('mySurfaceName',#886,53.);

A link to a detailed description of the STEP format would be very useful too.


texts: I have a small piece of stainless steel that I need to remove 1-2mm of material. The hardness is 200. What type of file do I need to get?

texts:
This is a part of a mounting system for an Olight pistol flashlight.  The universal adapter that they include isn't so universal when it comes to a Canik handgun.  I've talked to the people at Olight and their engineers say its made of stainless steel with a hardness of 200.  I need to remove 1-2 mm of material off the adapter for a proper fit but I don't know what type of file I need.  I think I can accomplish this with a hand file and time with the proper tool.  I know that some metals are softer than others, thats why I'm asking.  I don't want to purchase a file that won't scratch this hardness but it works wonders on gold/silver or aluminium.  I also have a dremel rotary tool if you think that might work better than a hand file.
Any advice would be greatly appreciated.  Thanks in advance for all your help


texts: Why there are no jets (missile or aircraft) faster than Mach 3.3?

texts:
Fastest plane ever built: SR-71 ,Max Speed: 3.3 Mach , Development - 1950s

Fastest drone ever built: Lockheed-D21 ,Max Speed: 3.3 Mach, Development -1960s

Fastest cruise missile ever built: Brahmos , Max Speed: 3.3 Mach, Development - 2000s

Why Ram/turbo-Ram jets got stuck around 3.3 Mach? Is there any technological challenge beyond 3.3 Mach like heating or combustion instability or low thrust?


texts:
I'm new to beams and I'm struggling to find the correct vertical reactions forces at support C and E.

The correct answer is 8.58 kN for $V_c$ and -3.58 kN for $V_e$

However, when I calculate the sum of the moments and set equal to 0 I get

$$\begin{gather}
1.5 + 2V_c - (3\cdot3) + (2\cdot(2+\frac{2}{3}))= 0 \\
V_c = 2.4\text{ kN} \therefore V_e= 2.6\text{ kN}
\end{gather}$$

What is it that I'm doing wrong in my calculation?


texts: Can you use the kinetic energy of air to power a car?

texts: In my fluid mechanics class, I've learned that a fluid traveling in a pipe will generate a force when the exit area is smaller then the entrance area. Suppose a pipe is attached to a car that will use the kinetic energy of the air passing over the vehicle. Assuming that the car is moving at a constant velocity and the pipe is straight and the exit area is 1/4 the size as the frontal area, is it feasible for a moving vehicle to generate enough force from the air to reduce energy use?


texts: What is the accuracy of direct metal laser sintering (DMLS)?

texts: They've printed jet engines with it that work after polishing.  So how is the accuracy measured and how accurate is the DMLS process?  I can't find the required info anywhere.


texts:
Is there a big difference between salt water and normal tap water in terms of thermal properties (heat capacity, for example)?

If so, can anyone give me a table of thermal and thermodynamic properties of salt water?


texts: Selectively rotating (engaging/disengaging) one of 80 couplings on a small shaft?

texts:
I've been working on this problem for years (literally) and haven't yet found a workable, scalable, pragmatic, and cost-effective solution that would allow me to selectively rotate one or more of 80 discs closely aligned on a single, rotating shaft.

Basically, I have 80 identical "discs", each of which is approximately 2 mm wide, spaced out with approximately 2 mm between each disc, concentrically mounted along a shaft (which can be anywhere from 5-20 mm in diameter).

Unfortunately my background is in electronics and not in mechanics or mechanical engineering, and I'm unaware as to whether or not this can be considered a "solved problem" at this scale.

I have tried a number of different approaches (both conceptually and in prototype) but have constantly been stymied by the tight specifications.

Conceptually, something as simple as a gear translating rotation in one axis to another (perpendicular) axis, attached to each "disc" and actuated by a linearly-moving motor would do the trick:

One attempt I've used is to have a rotating "indexer" fixed to a spindle in the middle of the shaft (with the rest of the shaft being free to spin around the spindle), then moving that linearly while subjecting it to rotational movement when aligned with the disc in question (with a matching cutout in each disc mated to the shape of the shaft/indexer), but the need for extreme precision in order for it to move freely along the axis made it unworkable (along with the fact that the shaft/spindle now needed to be twice the width of the working surface. In the example below, the indexer would be 9b, used to rotate 11H without rotating 11G or 11I:

I know one solution would be a clutch of sorts - if one exists that would fit on/in each of these discs. Then the clutches could be mounted directly to the shaft, and the clutch for each disc (somehow, as of yet that's a big question mark) engaged or disengaged as needed when the shaft is turning to translate that motion to each disc.

I had an idea to use a "magnetic clutch" (if that is a thing) where rectangular strips of magnets would be mounted into channels in the shaft, then tiny magnets would be embedded around the periphery of the cutout in each disc. The idea was that when not "locked" in place by some external mechanism, each disc would (by magnetic force) rotate with a spinning shaft. When externally locked, the disc would then hold in place with the "clutch" disengaged as the shaft spun freely under it. Unfortunately, it seemed that even with neodymium magnets, the friction from the entire system was too much for the magnets and the discs were permanently in an "unlocked" position and would not spin with the shaft.

There is also the obvious solution of using pure friction. I have leeway in what material the discs and shaft are composed of, but I'm not sure if that's something that can be considered a reliable solution as it should last for hundreds of thousands of "disengaged rotations" without wearing out or losing friction.

I feel like I might be overcomplicating the problem. Bottom line: tiny discs, one rotating shaft. Selectively (preferably in parallel, but one-at-a-time is fine) rotating each of the discs, without needing tolerances only achievable in a factory and at a affordable price (let's say under $100).


texts: Can a Foucault's current brake be used on the rails themselves to brake trains?

texts:
Your typical Foucault's current brakes operate on a disk, which is placed in an electromagnetic field in order to transform kinetic energy into heat without friction. The problem is that the disk still overheats, just like an usual disk brake. In the case of railways this also needs that the wheels have adherence to rail.

Theoretically, it would be as simple as to place two huge magnets around both rails in order to brake the train. A simple mechanical design could move the magnets up and down whether we want braking or not. The magnetic field would turn kinetic energy into heat, but this would not overheat as the heat would advance along the train itself. Also this would not require any friction, and as thus, no mechanical parts have to be changed due to use. (Friction braking is still required for stopping the train once a low speed would has been attained with Foucault's current braking).

This would have the following advantages :

Braking doesn't rely on rail adherence
Since permanent magnets can be used, no electricity needed to operate the braking device (work on non-electrified railways, or in emergency when there's damage to the overhead lines)
No risk of overheating in the long run since the dissipated heat moves along the rail.
Don't damage brake pads, and don't damage rails as does the usual emergency brake which applies friction to the rails.

The only major problem I'd see with such a system is that the magnets would also attract the rail itself (made from steel) - but if magnets on both rails are in reverse directions each force will cancel the other, so the magnets just have to be very solidly attached.

Is such a system possible or have I missed something ? If it's possible, why isn't it more widely used ? Or would the magnets needs to be too strong for this idea to be any effective, and this would have effects on passengers or their belonging ?


texts: Oceanic stirling engine: pressure difference between atmospheric and ocean depths would make engine work?

texts:
Given that the deeper you go into the ocean the higher the pressure, could this pressure difference between atmospheric (above water) and a certain depth in the ocean be used to run a stirling engine?
The piston would have to have an open facing to both or either the water at a certain depth (high pressure side) or the atmospheric end (low pressure side.)
In typical stirling designs the high pressure end uses heat in a fixed area which increases the pressure and moves the piston. What if the heat were the same and constant? Would that still work? The ocean depth would be a fixed pressure and that is why I ask.
Instead of heat difference we would be using pressure difference between two areas to drive the stirling engine.
Just a thot
edit
I appreciate the responses so I came up with a possible workaround for the high pressure side (in the ocean.)
Let’s say for the high pressure side there is a open ended cylinder that is facing upward. In this cylinder, when the piston is fully extended upwards it goes halfway the distance of the cylinder length. On the downstroke it goes the opposite direction which would be towards the bottom of the ocean floor.
So as some commenters have pointed out, when the high pressure piston has the upstroke, it is pushing against the depth of the ocean.
A possible workaround may be to introduce air right before the upstroke on top the high pressure  piston so the piston is pushing a bubble of air out the end of the cylinder instead of the pressure of the water. The bubble would rise and be like a buffer until the piston reaches its furthest extension from which point the water fills the cylinder and the pressure difference from the atmosphere and the depth of the ocean drives the piston downwards again.
I imagine a lot of cavitation would happen in such a setup so you would need very strong materials.


texts: Transparent, hard material that lets infrared through

texts:
I am trying to build a protective enclosure for Microsoft's Kinect v2, which emits (and perceives) IR in the 827–850 nm range. In order to fully enclose the device without blocking those signals, I need some transparent and hard material that will let infrared pass through.

I have tried acrylic, glass and crystal from the local glass cutter, but I can't get good results from any of those materials.

The best result I got was when I stuck the pane flush to the Kinect's front, otherwise the IR camera just can't see anything. However, technically I can't do that because I need to allow the Kinect to tilt, and I can't have the pane always flush to the Kinect.

The enclosure will be completely opaque apart from the front pane (which is what I'm looking the material for).


texts: What is the best method to model the input of an electro-mechanical system for control design and simulations?

texts:
In particular, say I have a dynamic model of the inverted pendulum / cart as described here. Instead of using the error difference in force to input into my controller, I want to take into consideration a motor driver (voltage input) to a DC motor for the force.  Would the best method then to analytically describe the force relationship to the voltage input?  If so, then would I need to include a voltage state variable so that I can build a controller based on that signal?

My motivation for asking is that I feel I have a fundamental disconnect with controls engineering.  In my studies I've gone over classical and modern theory without the benefit of actually applying theory to application.  Most of what I participate in deal with electromechanical systems, but most books, articles, etc I come across don't really delve into the physical interpretation of the plant input.  I would appreciate any feedback on the matter.


texts: Why does Experimental Modal Analysis need a reference signal?

texts: I need to conduct a vibration experiment with 3 accelerometers for a gear box. I'm reading the theory of mainly how to perform the vibration analysis but I don't understand why EMA needs a reference signal, and what it means by it? Also, is it the same for operational modal analysis?


texts: Is there a concept of gain and phase margin for a strictly open-loop transfer function?

texts:
I'm new to control systems, and I'm attempting to analyze the stability of an open-loop transfer function. I know that by checking the locations of the poles (and ensuring all poles are in the LHP) I can ensure that my transfer function is stable.
However, I'd love to know how stable this transfer function is. Reading textbooks like "Modern Control Engineering" by Ogata and watching Brian Douglas YouTube videos, I've learned about the concept of gain and phase margins, and their application to determining how resistant a system is to changes in the gain or phase. This would be helpful in my design, as there are many elements of my system that are approximations, and I want to ensure that the TF will be robust even with these errors. From my understanding though, the math behind using Bode/Nyquist plots to determine stability margins relies on the fact that you're analyzing the stability of an open-loop system in the case that it was closed with unity feedback.
Is there any similar concept for strictly open loop transfer functions, if I truly don't care about ever closing the loop? Or do I have some fundamental misunderstanding of the concept of stability?


texts: Is it possible that entropy generation decreases with decreasing turbine efficiency(First Low efficiency )?

texts:
I simulated an axial turbine(Wells turbine). Now I have faced with strange problem.

Performance of any turbine can be improved if the losses are identified and minimized. Several losses can be defined by flow separation, small or large vortices creation or flow circulation, etc.

In fact, when the turbine have lower efficiency than others turbines, it means that this turbine have more losses than others. In other words, the mentioned turbine have more flow separation, vortices or flow circulation than others. This again means that mentioned turbine have more entropy generation than others because entropy generation include velocity gradient terms and when separation and circulation(losses) increase, entropy generation also increases. Is my statement right?am i right?

Now, i designed an improved blade and a thicker blade(constant cord) than to base blade. . My results show that the Improved blade have better efficiency and lower entropy generation than to base blade. These results are logical. the thicker blade have lower efficiency and more losses than base blade(thinner blade) . And so, this cause higher entropy generation. But according to my results,  the thicker blade have lower efficiency(it is logical) and lower entropy generation(I think that it is not logical) than to base blade. Is it possible that entropy generation decreases  with decreasing efficiency?

I am grateful that guide me about this case.


texts: Does a tank of liquid nitrogen increase in total internal energy after emptying?

texts:
Suppose there's a 10 liter perfectly-insulated sealed tank of saturated liquid nitrogen at 4 bar. Therefore the fluid has properties,

$\rho=740 \,\frac{\text{kg}}{\text{m}^3}$,
$m=7.4 \,\text{kg}$,
$\hat{u}=-93\,\frac{\text{kJ}}{\text{kg}}$,
and $U=-690\,\text{kJ}$.

If you drain all the liquid from the tank, then eventually in the tank you'll have 10 liters of saturated nitrogen vapor at atmospheric pressure with properties,

$\rho=4.6 \,\frac{\text{kg}}{\text{m}^3}$,
$m=0.046 \,\text{kg}$,
$\hat{u}=55\,\frac{\text{kJ}}{\text{kg}}$,
and $U=2.5\,\text{kJ}$.

So the total internal energy has increased, despite removing most of the mass! Have I made an error in my calculations, or is this correct? Is there an intuitive way to think about this phenomenon?


texts: What thread to use in tapping a hole for a 2-56 Helicoil insert?

texts:
Helicoil from McMaster-Carr 18-8 Stainless Steel Helical Inserts 91732A201  calls out a specific tap to use, but I cannot find out what thread this tap is putting into the hole for the insert.  I want to call out the tapped thread on a drawing, and put the 2-56 insert in later.
I cannot find what the thread should be.  This would be the outside thread of the helicoil.  I know the drill size is #41 = 0.0960 but what is the thread size?

Thanks.


texts: What is the name of the substance that underwent the ductility test in the YouTube video Ductility Test?

texts:
In the YouTube video Ductility Test, I saw a black substance undergo a ductility test. It appeared to be as ductile as silly putty although silly putty is just a very viscous liquid. It seems that it can keep being pulled thinner and thinner. I couldn't find the name of the substance in the video. I just want to know the name of that substance. Once I learn the name of that substance, I can ask another question about the properties of that substance.

I'll ask whether it's a solid unlike silly putty. I know it started off as a liquid but I'll ask whether it got turned into a solid or just a very viscous liquid. I'll ask "If it's a solid, what is its yield strength?" If it has a higher yield strength than the typical chromium steel, it could be very revolutionary because it cannot sustain crack propagation and therefore cannot be weakened much by the presence of a crack.


texts: How can I get final value of $V_{out}$ at $t=∞$ in RC circuit?

texts:
I can obtain the transfer function in this RC circuit.
$$ \frac{V_{out}}{V_{in}} = \frac{1}{(RCs+1)} $$
When $V_{in}$ is set to $10V$, how can I get final value of $V_{out}$ at $t=∞$?
I tried to use the final value theorem but I can't get the answer.


texts: Designing a non-circular radial o-ring seal

texts:
I am working on a design that has some pretty tight space restrictions. I've got a rectangular plate (with rounded corners, inside R0.12") that needs to seal a housing. The sealing requirements are IP66.
I know that using an o-ring in a weird-shaped groove is common for face seals. However, I don't see any guidelines when doing a radial seal. I've toleranced it the same as if it were a circular seal - about 12% squeeze on the o-ring
My question is - What is going to happen in the corners? Could some weird loading cause the o-ring to be stretched or squished in the corners and seal poorly?
I don't exactly have space to stretch the dimensions enough to convert it to a pure face seal. Might it work fine as-is? Or can I change the design to mitigate risk? My only thought is to reduce the groove height so that the o-ring is constrained axially as well as radially and just kinda gets squished from both directions. Axial position of the cover plate is not important.


texts: Is it possible to derive velocity vector form position vector without unknown such as: position vector of A = (0.8)i + (1.2)j?


texts: Using electromagnetic induction to fire a neuron

texts: In order to make a neuron fire via an external electrode, the electrode must input some electrons in the extracellular space(just outside of the neuron). Imagine a straight conducting wire touching a neuron and other end free in the air. If you move a strong magnet near the wire, such that the wire cuts the magnetic flux, then voltage will be generated at the two ends of the wire. In this case will the neuron fire? or equivalently, will there be flow of electrons to the neuron? Note that the wire is in open circuit i.e. other end is in the air. If there will not be any flow of electrons, can some simple modification on this setup will make it happen?


texts:
A fan that consumes 20 W of electric power when operating is claimed to discharge air from a
ventilated room at a rate of 0.25 kg/s at a discharge velocity of 8 m/s. is this claim reasonable?
I am getting maximum possible velocity of air around 12.64 so it's reasonable to me but all solution available on internet says maximum possible velocity of air is 6.3,so it's not reasonable.
Please help
The internet solution for the question:


texts: What are reasons to use cutting speeds different from recommended?

texts: In my experience, many companies do not use the recommended cutting speeds for materials.  In general, it seems they opt for lower cutting speeds.  Is there a reason they typically do this?


texts: How do I interpret the curing pressure of a composite from this data sheet?

texts:
A question asked about the necessary curing pressures for a composite resin in the autoclave. Looking through the corresponding datasheet (HexPly F155), I'm confused:

  Cure Procedure

  Apply vacuum of 22 inches (74 kPa) Hg minimum.
  Apply 85 + 15 – 0 psig (586 + 103 – 0 kPa) pressure for laminates.
  Apply 45 + 15 – 0 psig (310 + 103 – 0 kPa) pressure for sandwich.
  Vent vacuum bag to atmosphere when pressure reaches 20 psi (138 kPa).
  During cool-down when the part temperature falls below 140°F (60°C), pressure can be released and the test panel removed from the
  autoclave and debagged.

The first step is clear, but not the next steps, for instance 85 + 15 – 0 psig (586 + 103 – 0 kPa) is causing me a headache and I can't make sense of it.

I'd guess that one is the external positive pressure and the other is negative vacuum pressure under the sheet, but I couldn't for instance have a 103 kPa vacuum.