texts: d40cy1 refrigerator compressor speed control resistor values

texts:
I have a bar fridge with a d40cy1 compressor in it.  I can't find an manual for it.  I would like to bypass the thermostat and speed control and force it to run continuously at its lowest speed.
I only have experience with danfoss bd50 DC compressors, with them you can use a jumper for low speed and increasing resistance will make the motor run faster.  I'm hoping the same is possible with this little AC unit.
cheers
BTW I'm remote and have no access to buy a DC compressor or all the other better stuff I could be using, just need a solution with what i have on hand


texts: Why is it said that the flange of an I beam carries most of the moment?

texts:
It is often said for I beams that the flange carries most of the moment subjected to the beam, while the web carries most of the shear force. The latter is obvious from pictures like above, showing the distribution of shear stress.
But why does the flange carry most of the moment? The normal stress on a beam is linearly proportional to distance from the neutral axis. So why is it assumed that the flange carries the bending moment?


texts:
It's given that the applied force is 10kN at F and 25kN at E . I have trouble of finding the other real force in the member of the trusses .
So , i start by drawing the FBD at F . I have 10kN point downwards , so the reaction is 10kN upwards  , so it's in equilibrium . But , i really have no idea how the author get the reaction 15kN ( in tension) pointing to the left and to the right . Can someone explain about it?


texts:
Background

The normal space elevator (that reaches from the Earth's surface to a counterweight beyond geostationary) needs a material that's strength/weight ratio is better than any material we have available.

I've another idea, that I assume isn't possible either, but I'd like to know what makes it impossible?...

The idea

What if, rather than starting the tether from the Earth's surface, it starts from 2000km above the Earth? This will massively reduce the necessary strength/weight ratio of the material. Not only is the part closest to Earth experiencing the greatest gravitational force (per unit mass) but there's a sort of vicious circle: To add a metre to the length of the tether we need to strengthen the whole tether (above this new segment), which means making it heavier, which means making it stronger, and heavier, etc.

I found, using the numbers for Zylon, it works.

"How's it stay up?"

This elevator, unlike a real space elevator is in 'proper orbit', or at least it is, on average. The part that hangs towards the Earth will be suborbital (indeed will be going quite slowly relative to low-earth orbit), while the part that extends beyond geostationary will be at superorbital speed. It is in orbit.

"But how do we get to the start of the tether if it’s 2000km up?"

Going up into space is easy, getting into orbit is the expensive bit. A rockoon might be a neat way to get to the 2000km mark with a very modest rocket (the rocket equation means that we can use a very small rocket to get to 2000km, compared to the rocket required to get to 2000km orbit) - about 3kg of propellant per kg of payload, I think.

"But won’t you pull the whole thing down as you climb it?"

Yes. To correct for this, ion-engines will be arranged on the tether for station-keeping. Some of the payload can be used for refuelling these (they have a specific impulse 10 times better than a rocket launcher, and the rocket equation helps here, so hopefully we’ll need far less fuel!)

Numbers

I wrote a python script with a few assumptions (that it's 'suspended' from something geostationary, so it has a length of 27415km), it ends 2000km above the Earth's surface. It has a tensile strength of 5.8GPa and density of 1.54 g/cm^3 (Zylon). It can hold a 400kg payload at the bottom of the tether. I found it needed to have a total weight of 2100 tonnes and a maximum diameter of 10.4mm.

Questions

caption: simulated space elevator - plotted every two minutes. Not sufficiently high to be geostationary, and I suspect either the initial conditions or modelling errors mean that it failed to remain orbital!

Does this work? I've modelled a simple 7-segment tether, but I need to tweak the initial conditions a little to get it into a good orbit. I worry that something weird happens with orbital mechanics that means this isn't going to be a stable object? Can a tether stay 'vertical' without too much station keeping?

If it does work, it's neat, as it'll take less than 100 flights of the falcon heavy to get it up there, and after than geostationary orbit will be cheap :)

Code for the model and mass calculations.

Edit #1

To look at @kamran's point that "The system is...doomed to...pull the higher eleveation parts into lower/ heavier orbits and crash eventually." It does seem it's inherently overly sensitive to initial conditions, if it is slightly too low, then the gravitational force on it scales much quicker than it would if the object were a point mass. I wonder if this can be mitigated by shortening the tether: The centre of such a contraction would be the centre-of-mass, thus it would 'pull up' the centre-of-gravity out of the gravity well a little. Maybe this would be the mechanism to control this effect? But it does feel like it's not in a stable state and will require active control. See 'fall-to-earth' scenario below!


texts:
I've been going down the rabbit hole as far for pipe vs tube and have ran into the same statement from co-workers and on the internet. That statement is

"TUBE IS STRONGER THAN PIPE"
https://www.metalsupermarkets.com/difference-between-pipe-and-tube/

Which makes no sense to me, shouldn't how strong they are be a function of wall thickness and pipe ID? It seems like it's just comparing apples and oranges. Anybody got some insight on this ?


texts: How can Engineering Equation Solver solve both equations and a table?

texts:
I don't know why they tried to ruin EES by doing this, but what people want to do is have the solver recognize an equation with a variable, and then take that same variable and plot a table of it with varying values in a separate parametric table.

The problem is it the software states a conflict between assuming two definitions of the variable at once, so unlike competently designed software, users have to choose between either a table or the equation solver, not both. How can this be fixed?


texts: How do hybrid cars achieve greater fuel efficiency?

texts:
In this question I’m comparing non-plug-in hybrid fuel/electric vehicles with fuel-only vehicles. Also, I’m not disputing that hybrid cars are more fuel efficient, I’m just trying to understand how.

If I remember two things from high school physics, it’s:

Creating energy from nothing is against the law.
Converting energy from kinetic to stored energy and back again is always less that 100% efficient - you end up with less kinetic energy than you put in, the rest being “lost” to the environment in the form of heat or whatever.

Both a fuel-only car and a hybrid derive all their locomotive energy from the fuel (ok, and gravity, if you’re going downhill, but let’s ignore that). But the hybrid involves an extra conversion to/from stored energy on the way, i.e. charging and discharging the battery, which according to the second principle above should make it less efficient.

Furthermore, the battery entails additional mass, which, if it were dead weight, would reduce the power/weight ratio of the car, reducing efficiency.

So to achieve greater efficiency, the hybrid engine must somehow make use of energy that would ordinarily be lost in the engine of the fuel-only car. In order for the hybrid to be more fuel efficient than the fuel-only engine, it needs to do this in a way that overcomes the above inefficiencies and then some.

So my question is, what broad physical/mechanical techniques does a hybrid engine use to achieve this, and (in rough numbers) how much of the efficiency gains come from the different techniques?

I know there’s regenerative braking, but how efficient is this in practice? I.e. how much of a car’s kinetic energy that would otherwise be lost through braking is actually captured and re-used as locomotive energy? And is this basically it, or are there other techniques that significantly contribute to the efficiency of a hybrid?


texts: Is a granite block tunnel longer lasting than reinforced concrete?

texts:
Assumptions
Building Process exists
Waterproofing is able to be replaced

Notes

Please answer yes or no with the science backing.
This question is only about the strength and lifespan.
This question is NOT about cost, or process.
Additional material may be required. Please include in your answer if it can overcome an obstacle.

Potentially Relevant Values

Compressive Strengths:
Granite: ~200MPa
Concrete: ~70MPa


texts: How to determine how large each terrace should be on a multi-level retaining wall?

texts:
I am making a concrete sleeper wall and am unsure of the current structural integrity (I am not a civil engineer) specifically regarding the width of each terrace.

My retaining wall will be made from concrete posts, and sleeper slats with rebar as a reinforcer:

I hope that my rudimentary drawings provide enough information.

I have a 5 degree lean back on each terrace of the wall, and each post, and slat is reinforced. However, I do not know how to determine if 4' for each terrace will cause integrity issues. If possible, I'd like to go down to 3' per each terrace. Is there a way to calculate this, or a rule of thumb for these types of retaining walls? Is there a point where I have to use geo-grid reinforcement?


texts: Can we change steel properties by application of magnetic field while quenching?

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Austenite is non magnetic while $\alpha$-ferrite and pearlite are magnetic. (Magnetic properties of pearlite vary as a function of carbon content)

If a strong magnetic field is applied in a particular direction while the steel is being quenched (rather, austenite is being quenched!), would the grain structure change? Is it possible to get superior grain structure and hence tougher steel by application of cyclic magnetic field?

My speculation is that, at the eutectoid point while quenching the steel, as low carbon zone of pearlite has more permeability, that zone should align itself to the strong magnetic field by pushing the carbon in orthogonal direction, so grain boundaries should take a different shape.

Will it actually happen?


texts: Does surface finish affect steels strength properties? If so, how does strength increase or decrease with the type of surface finish applied?


texts: Why 'battery storage power stations' use mainly liion batteries?

texts: As I understand liion batteries have lower lifetime, than LiFePO4. Why would such big stations use liion batteries then? Wouldn't replacement cost large amount of money? And how long those liion battery storage power stations last, before batteries are no longer usable?


texts:
I am interested in the kinetic energy T and the potential energy U of a three dimensional Timoshenko beam.

For a 2D Timoshenko beam the energies read:
$$ T = \dfrac{1}{2} \int\limits_o^l \left( \rho A \left( \dfrac{\partial w}{\partial t} \right)^2 + \rho I \left( \dfrac{\partial \Phi}{\partial t} \right)^2 \right) dx$$
$$ U = \dfrac{1}{2} \int\limits_o^l \left( EI \left( \dfrac{\partial \Phi}{\partial x} \right)^2 + kAG \left( \dfrac{\partial w}{\partial x} - \Phi \right)^2 \right) dx$$

But in these formulas $w$ and $\Phi$ are just defined in the x-y-Plane. How can I derive the energies for bending in both direction (x-y-Plane and y-z-Plane) and torsion (around x-axis)?

EDIT: I figured out a part of the question by myself: Because Timoshenko beams are a linear theory, one can simply add the energies of two deformations and get the energies of the superposition of the deformations. Therefore:
$$ T = \dfrac{1}{2} \int\limits_o^l \left( \rho A \left( \dfrac{\partial v}{\partial t} \right)^2 + \rho A \left( \dfrac{\partial w}{\partial t} \right)^2 + \rho I \left( \dfrac{\partial \theta}{\partial t} \right)^2 + \rho I \left( \dfrac{\partial \Phi}{\partial t} \right)^2 \right) dx$$
$$ U = \dfrac{1}{2} \int\limits_o^l \left( EI \left( \dfrac{\partial \Phi}{\partial x} \right)^2 + EI \left( \dfrac{\partial \theta}{\partial x} \right)^2 + kAG \left( \dfrac{\partial v}{\partial x} - \theta \right)^2 + kAG \left( \dfrac{\partial w}{\partial x} - \Phi \right)^2 \right) dx$$
Where $w: \mathbb{R} \times \mathbb{R}^{+} \rightarrow \mathbb{R}$ is the deflection in the x-y-plane and $\Phi: \mathbb{R} \times \mathbb{R}^{+} \rightarrow \mathbb{R}$ is the slope in the x-y-plane. Respectively $v$ and $\theta$ for the y-z-plane. Can someone please confirm this?

Still the energies for torsion are missing. Can the theory of Saint-Venant applied here?


texts: What is the name for a digital height measuring device?

texts:
What is the generic name of the electronic hand-held device that measures the relative height of two different points (altitude, etc.)?

As an example, suppose I'm climbing a tree. I turn on the device, put it in my pocket, and once I've climbed 15 feet from the ground, the device should indicate "15 feet" on its display. When I climb further up to 20 feet, the device should indicate "20 feet" on its display.

I used to measure different levels using a Dumpy level and total station "distant measurer-laser." I need a different kind of device that can take levels more quickly but I don't know what this device is called or how to select a particular model. In addition to the name of the device, what properties of the device should I be looking at in order to take measurements more quickly?


texts: How are the thermodynamics of CPUs and other chips handled?

texts:
I hear that designing the thermal efficiency of such systems is very difficult. I'm not sure why, though, and I am interested.

On the one hand, I bet the heat is somehow a function of the total power in the system. On the other hand, as individual bits are flipped, I imagine the heat migrates around the die.

How does heat move around the die, and how does this affect the cooling of the CPU? Are specific compensations made to accommodate the movement of heat?


texts: In the image below,only 4 quadrants are mentioned but my intuition says there should be 8, please clarify me?

texts: I am learning engineering drawing and confused on this.


texts:
I have a circuit that consumes enough power to keep running from a powerbank. However, to save energy I'm putting it in low energy mode at night.

Problem with powerbanks, they turn off when not enough power is consumed. My proposed solution was creating a separate low-power circuit that times how long the powerbank is off and at the right moment provides a short burst of power. The devices in my circuit then turn on, the powerbank detects this and also turns on.

All the devices in my circuit are Arduinos or Arduino compatible running on 5V. The circuit pulls a maximum of 200mA. I have no physical input on the system as it is placed in a different location. Everything needs to be automated. It preferably has to use the powerbank due to portability and the desire of having no external wires.

What is a safe method for an external circuit, to turn on another circuit in an automated way?


texts: Need help identifying component on hydraulic schematic

texts:
I'm relatively new to hydraulics, and I'm trying to understand this schematic. I've got the majority of the system figured out, but I cant for the life of me understand what the symbols at positions 18/20/23 represent.

The unit actively controls a constant pressure in the two cylinders attached using an electronic pressure switch. Its the control unit of a hydraulic tensioning system in a ski lift. My feeling is that 18/20 may have something to do with electrical pressure cells?

Thanks


texts: What actuators do the me-shifter gear shifting system uses?

texts:
I have a shifter kart (125ccm kz2) with 6 gears.
What I want to do is to change gears from the steering wheel. Like in the system mentioned in the question.

I have the electrical and electronic system needed but I need a fast and powerful actuator (using 12VDC or 5-6VDC, 3 cm travel, going both ways, about 30Nm)

I was thinking about using just the actuator from one of these systems (don't have that much money to spend on it), but I don't know what it is.
This is the website: http://me-shifter.com/

Any help would be appreciated.


texts: How can I ensure steady flow to all the valves?

texts:
I've set this up for my hydroponics water distribution system. The water is pumped up,  and is distributed via the valves. I can manual control the valves so that each outlet has a steady flow of water.
However, the pump is on a timer and when it turns off and back on. The flow isn't even. Certain sections have water flowing through them, while some have none.
I'm thinking adding a check valve that would prevent backflow when the pump is off. Will this ensure steady flow to all the outlets? What causes the uneven distribution?
Thanks


texts: Effect of flow through a static hydraulic pump on its RPM

texts:
What happens when fluid flows through a static hydraulic pump? Will there be a negative RPM to impede the flow?
By static pump, I mean a pump with initial RPM = 0.0 and is not driven by external forces during the transients of flow.


texts: Can strain gauges radially be mounted on 8 mm diameter shaft for torque measurement for effective result?

texts: I need to measure a torque on an 8mm shaft of an electrical motor on a prototypical device. The expected torque is ~15 Nm and for the data processing I intend to use an Arduino. One requirement which excludes commercially available torque sensors, is the available installation space in the device as well as weight limits and the price. Due to the small diameter, I am afraid that the curvature of the shaft could be too high for the strain gauges - is there any recommendation or best practice how to handle that?


texts: Drawing conclusions about 3d truss from 2d model

texts:
I am on the task of analysing the load capacity of a warren-ish truss bridge similar to this one. I do not, however, have the software or skill to model and analyse a 3D structure.

I was wondering wether or not i could analyse a 2D simplification and still come to a somewhat credible conclusion. What considerations should be made when approximating a 3D truss as a 2D truss? What would be the limitations of such an approach? Thank you.

Edit:
I do not have to know the exact maximum load. My only goal is to figure out where the truss will fail first.


texts: Degassing silicone solution with negative pressure

texts:
I am planning to use polydimethylsiloxane (PDMS) to create a phantom for mimicking tissue for imaging. For this, I plan on using SYLGARD® 184, which is a viscous liquid. When adding other components to it, air bubbles will be introduced.

I have learned that one way (available to me) to remove bubbles / de-gas the solution is by using a vacuum pump to create negative pressure. What negative pressure is sufficient to remove the air from the gel-like solution?


texts: Why does aircraft reverse thrust actually work?

texts:
Please note that the question is "Why", not "How".

For sure I'm getting this wrong, but I'm stuck and I don't know why! If a reverse thrust is applied during an aircraft landing wouldn't the total amount of work necessary to pull the air inside the turbine (hence pushing the aircraft forward) be canceled by the amount of work used to push the air forward (i.e. pushing the aircraft backwards)? I mean, why does it work? Why does the net work push the aircraft backwards and help to stop the plane?


texts: How the 3M Aura 9332+ masks filtrate airborne particles/virus?

texts:
The 3M Aura 9332+ mask is labeled FFP3 which means that it filters at least 99% of airborne particles.
This article mentions that N95 masks (which filtrate 95% of airborne particles) filtrate the airborne particles with some materials (wool, glass particles, and plastics...)with 1-2 percent copper and/or zinc.

I looked at the  3M Aura 9332+ datasheet and I couldn't find any information about their (possible) content in copper/zinc. They only mention that the filter is made of Polypropylene (cf. p2).

So my question is: if the 3M Aura 9332+ doesn't contain copper/zinc, how does it filtrate the airborne particles? Do they work like HEPA with a combination of diffusion, interception, impaction, and electrostatic attraction? If yes, how is it possible because the masks are much thinner than HEPA filters?

Side question (which depend on the answer ― special pandemic):
Can this mechanism be destroyed by humidity (breathing) and/or sweating (salty water)?


texts: Why is it so hard to find DICOMs with Inversion Times recorded?

texts:
I've been searching for MR Images of anything that comes in DICOM format and have Inversion Time. I tried getting the Facebook fastMRI data set, the NIH Visible Human Project and the UTA4 Dataset and NONE of them had DICOMs with Inversion Time recorded. Does anyone know why this is the case?
I'm about ready to give up on this project but I wanted to ask on here to see if anyone knew where I can get DICOMS with Inversion Time recorded.


texts: Managing precipitation in cooling process

texts:
Are there standardized ways of dealing with precipitation in chemical engineering continuous flow processes? I have an application in which I need to cool a fluid via a heat exchanger and the fluid will precipitate some solid on cooling. The two specific issues I predict are:

I need to select a type of heat exchanger that won't clog from the precipitate. Probably the best cases are something where the precipitate can just fall out by gravity or it is carried out by the fluid. What types of heat exchangers are good for this? Single pass shell-and-tube?
I need an automated way to remove the precipitate from the fluid. What pieces of equipment are used for this?


texts: How is drilled shaft lateral resistance calculated using LPile?

texts:
The AASHTO LRFD Bridge Specification, Section 10.5.3.3 says "shaft lateral resistance" should be checked at the strength limit state (i.e. factored loads). How is shaft lateral resistance determined using an LPile model? Is it the lateral load required to form a plastic hinge in the shaft?

If I'm dealing with a very short shaft (light pole foundation) am I likely to be governed by service limit state deflections & overall stability instead?


texts: Is the silicone oil used in a diffusion pump oil special?

texts:
I have obtained two diffusion pump stages from a pair of very old Vacuubrand high vacuum pump. The rotary vane pump in one of them was dead and another overheating. So, I salvaged only the diffusion pumps. I pan to set it up with a rotary pump to build my own high vacuum pump. The inside of the oil diffusion pump was quite burned up due to lack of proper maintenance. I cleaned it up with Toluene and detergent and now it's almost clean.
I have presently have two types of rotary vane vacuum pump  oils with me i.e., a clear looking hydrocarbon based mineral oil and another one is a brownish thick oil (could be polyester based or something). The latter is quite viscous also. I managed to borrow a rotary vane and tried using the brownish vacuum pump oil and it was a bad idea. Once heated the entire room stank. Took it apart and cleaned again.
My question is can I used the clear mineral oil or it must be a silicone oil? I currently only have like 25mL XT 704 silicone oil with me that a friend gave me. Is it mandatory that only this particular silicone oil must be used or any type of regular silicone oil will do the job?
Here are a few pictures of the oil diffusion pump (the second unit is also same) below:


texts: Advantages and disadvantages of bevel gears

texts:
What are the advantages and disadvantages of bevel gears?

This is what I've already found:

Advantages:

possibility to change operation angle

Disadvantages:

must be precisely mounted
shafts' bearings will be exposed to significant forces
limited gear ratio < 5

Do you know any other? Especially advantages.


texts: Design op-amp circuit from transfer function?

texts:
What is the best way to design a circuit based on the following transfer function: (0.0364*s)/(0.0002*s + 1) ? I am trying to design the derivative stage of a PIDF controller using op-amps

EDIT: This is part of a bigger problem where i have to design a PIDF controller to achieve the minimum possible settling time for the plant function: $$\ G(s)= \frac{100*20*100}{(s+10)(s+20)(s+100)}$$


texts: What does the accuracy and precision values for a pipette mean?

texts:
Is the accuracy interval the tolerance for the instrument?

Does the precision interval indicate a single standard deviation? And more importantly, does the precision assume a perfect operator (so the variance is due simply to randomness) or does it take into account an operators reading/technique?

The reason I ask is because I did a bunch of measurement using a 1 mL micropipette with a "precision" of 0.002 mL and got a standard deviation of 0.0026 and am curious if that additional 0.0006 error is because of my poor technique compounding upon the instruments "inherent" uncertainty.


texts: How much power will 4 germicidal lamps use?

texts:
I was wondering if this portable power supply will be sufficient for running 4 UVC lamps all at once. If so, for approximately how long?

Power Supply: SUAOKI G100 27000mAh /3.7V Power Bank Station 100W AC, Type-C Quick Charge 3.0 USB, Solar Rechargeable Portable Power Generator for Travel Outdoor Use for MacBook Smartphone Camera

UVC Lamps: UV Linear Clean & Germicidal Lamp Kit for up to 100 sq. ft. Room with 5ft Cord and Plug (Ozone Free)


texts: Craig Bampton Model Order Reduction on Ansys

texts:
I am in the process of modeling a component as a flexible body in Simscape Multibody environment (Simulink). I need to superimpose rigid body model with the deformation model.
The deformation model is the state space matrices derived from a FE model. I tried the FE approach available on Matlab using the pde toolbox, but this did not give me accurate results.
Hence I need to perform the FE analysis of the component on Ansys, perform the Craig Bampton Model Order Reduction and extract the Mass and Stiffness matrices of the reduced boundary nodes.
I do not have much of an experience working on Ansys.
It would be really nice if you can advice the right approach to follow in Ansys to achieve the result.
Thanks and Regards,
Goutham Sajja


texts: Are there robotic 'worms' that can burrow in soil and detect metals (e.g. gold), possibly via X-ray?

texts: I looked it up didn't find anything. I was reading about mining and wonder if it's a technology that's used, as I didn't see any mention of it. I suppose the worms would have to be relatively large, maybe between large-dog-breed sized to automobile-sized because of the need for a sufficiently high-capacity battery, if not petroleum-powered.


texts: How to control precisely the wall temperature of a tubular reactor?

texts:
I have modelled a multi-tubular reactor performing a Fischer-Tropsch synthesis of alkanes and I was wondering about the stability of such a reactor. Even a very tiny deviation of the wall temperature can lead to a potential destruction of the catalyst if not more...

The Fischer-Tropsch synthesis I am modelling as an adiabatic temperature around 1200 K. This is the result I get when the wall temperature varies from 201.000 °C to 201.470 °C.

So theoretically a variation of less than 0.5 K can lead to a reactor temperature variation of more than 150 K.

How to control the temperature along the reactor (it can be more than 10 meter long) as precisely as let 0.1 K say of difference to avoid such unpleasant drift leading to a potentially bad situation?


texts: Log Mean Temperature Difference of a Counterflow Heat Exchanger

texts:
I am solving the following problem:

  A liquid-to-liquid counterflow heat exchanger is used to heat a cold fluid from 120 °F to 310 °F. Assuming that the hot fluid enters at 500 °F and leaves at 400 °F, calculate the log mean temperature difference for the heat exchanger.

The given answer is 232 °F

I used:

$${ LMTD = \frac{\triangle max - \triangle min }{ ln( \frac {\triangle max}{\triangle min} ) } }$$

$${ \triangle max = 500-120 = 380 }$$
$${ \triangle min = 400-310= 90}$$

I plug them all together and I got 201.3383331.

What am I doing wrong?


texts: Transistors and diodes have (reverse) breakdown volatge ratings. What is not specified in datasheets are how long such voltages must be applied for breakdown to occur. Suppose a diode has reverse breakdown voltage of 100V. Will applying 100 V (appropriate bias) for duration of 1 ps, 1 ns, 1 us, 1ms or 1s cause breakdown ? How long breakdown voltages must be applied for breakdown to occur?


texts: What is the meaning of these two inverted triangle water table symbols in a borehole record?

texts:
Consider the borehole record below (in particular the Water Depth column).

There is a white inverted triangle at a depth of 3.20 m. What is the meaning of this symbol?

The white inverted triangle indicates the depth at which water was struck.

There is a black inverted triangle at a depth of 2.50 m. What is the meaning of this symbol?

The black inverted triangle indicates the depth to which the water rose after 20 minutes.

My new question is why does the water rise above where it was originally struck? What is this implication of this? Is the location of the black inverted triangle the true location of the water table within the soil? Why was water struck lower than this?


texts: How can I get the Zoom button to be visible while I'm on the Home tab?

texts:
I'm using AutoCAD 2015.  While I'm drawing, I spend most of my time on the Home ribbon tab.  I like the Zoom ribbon button, but it is on the View tab.  Is there any way to move the Zoom button to the Home tab, so I don't have to switch ribbon tabs to hit it?  Alternatively, is there any way to add the Zoom button (or at least just a Zoom Extents or a Zoom All button) to the bottom toolbar, or somewhere where it will be visible all the time?

I am aware that I can do a Zoom Extents just by typing "Z-Enter-E-Enter", but I like my toolbar button.  :)


texts:
I'm trying to understand the double stub matching impedance using Smith Chart.
Here is the diagram for the double stub impedance:

The impedance on the right has to appear purely resistive.
So admittance $Y_2=-jb'$ and admittance $Y_b=1+jb'$
and the admittance at $Y_1$ is elected to be at $3\lambda /8$. Why is this distance chosen to be $3\lambda /8$?
And to get the impedance at this location isn't it enough that I rotate $Y_b$ by $270^0$, why do I have to rotate the whole circle by 270?


texts: Should I apply Force or Pressure, Ansys Static Structural

texts:
I am working on a project where I must find the maximum principal stresses on an object subjected to impact loading condition. I know the velocity of the object (the one which will hit the test object) and its weight. My questions are:

For analysis should I apply force or pressure to the area of impact?
How do I calculate the force/pressure?


texts: What is the difference between a single-stage pump and a centrifugal pump?

texts:
Here is the small $12 \; V$ pump that I am looking at. The manufacturer called the product as DC brushless centrifugal circulation small water pump but under its description it mentions that it is a single stage pump.

I wonder what the difference is? Is it a misleading description or title or do those terms are used interchangeably?


texts:
The front shaft support bearing on my front deck lawnmower keeps burning out its seal.

Typical scenario:  PTO coupling catches long strands of grass which wraps around the PTO coupling, and also around the splined shaft between the coupling and the bearing.  Friction heats up the plastic seal, it falls out, then the back up metal retainer falls out.  Soon after the bearing is history.

The bearings are cheap, but it takes about 2 hours of awkward work to replace them. (I'm considering using a split pillow block to make the replacement easier.)

Only recently figured out the connection between long grass and bearing failure.  On this particular occasion, the failure was about 2 hours after the long grass.

Q1:  What do I ask for to get a bearing with a seal that withstands more abuse?

Q2:  Are there other ways to protect the bearing seal?

Edit:  As per request:  Grasshopper 1995 721D

Rear bearing never winds grass.

Mower is NOT used for a lawn, but to maintain aisles in a tree farm.  Some of this is done with a John Deere MX-6 rotary disk mower (6 foot wide; run by a 55 HP Deutz Tractor.  The grasshopper is in effect being used as a 'trim' mower, and is used for certain classes of weed control once a year, as well as mowing trails in the woods. (Snowberry, currants, raspberries, hazelnuts, baneberry, elderberry  It also mows lots of gopher hills.  Part of it's task too is to mow the oil lease access road twice a year -- another mess of clover, alfalfa, thistles, and grasses of types that embarrass  creeping red fescue as being a weakling come lately.

I am not trying for a manicured lawn.  I'm trying for a 'trimmed pasture'


texts: I have a question about the design principle. To explain my problem I made the sketch "wheelbarrow". To minimize wear, which design is preferred?


texts: I'm looking for some advice on what study of engineering I should pursue. I want to be a PLC / SCADA programmer, but with all these engineering titles I am lost on what to even look for. I was thinking electrical engineering and then take some smaller programming courses. If anybody has any experience in the field or knows anybody and can guide me in the right direction it will be appreciated.


texts: Torque needed to keep a wheel spinning at high RPM

texts:
I have a treaded wheel which is 16'' diameter and 4'' across (trailer wheel).

If I want it to spin constantly at 2750 RPM, what amount of torque do I need to apply to combat friction and air resistance?

I need to find this out for one of my projects and I am only knowledgeable of ideal world physics. Is there an equation for measuring non-conservative forces on a spinning wheel (like F= b*v^2)?

Any advice would be appreciated. Thank you.

Edit: Thanks for all the insights. I wanted to get an estimate because I have to choose the proper motor to use in this situation. Much cheaper to know which motor/wheel to go for now than to realize the motor/wheel combination is too weak.
In case I have been misunderstood, I purely want the force to keep the wheel spinning. The wheel isn't moving an object body. So, would any drag (v^2) still apply?


texts: Determining stiffness of a beam w/varying moment of inertia

texts:
I need to calculate $K$ or equivalent stiffness of a beam that has a varying $I$ across its length. $I$ has been given to me as a function of $x$, or length.

I have been unable to find a proper equation or set of equations describing how to obtain $K$ for this situation. I've found equations for constant $I$ values across the length of beams. Is there an equation I am simply unaware of, or some general procedure for deriving $K$ for variable $I$ values?


texts: Can we currently achieve 55 MPG on Non-Hybrid vehicles using internal combustion engines?

texts:
With recent debates, one frequently hears that it's currently not possible for car manufacturers to meet the 55 MPG energy efficiency rating required by 2025.

So, is there something physically impossible about meeting this standard? Is it achievable within the next 5 years? If not, what is preventing it?


texts:
This question is a bit general but hopefully someone can point me in the right direction.

If you have a metal container, welded shut that's fitted into a hole that is say 10 meters wide and 30 meters deep.

This has the volume of about 21,205

If you pump pure oxygen into the tank until all the water was pushed out of that cylinder, what would be the pressure of the oxygen in the tank. How much oxygen would be in the tank?


texts: What does "28" and "27" mean on my metric thread pitch gauge?

texts: I have a metric thread pitch gauge that came in a tap and die set, it has pitches like $0.75$, $0.8$, $1.25$, etc. which is the distance between each thread. However there are two gauges that say $27$ and $28$ - I thought maybe it means $0.28\text{ mm}$ or possibly $0.28\text{ inches}$ if they threw in some non-metric ones, but it is neither of these (it's about $0.9\text{ mm}$) what are these?


texts: If my electronics are outdoors in a ventillated NEMA 4 enclosure, should I conformal coat my circuit boards?

texts: I'm considering putting a circuit board in a ventilated NEMA 4 enclosure outdoors. I'm a little concerned about humidity and condensation inside the enclosure. Do I need to conformal coat my circuit boards, or take any other precautions?


texts:
I'm trying to understand bolt preloading. I found this analogy on Wikipedia. I understand that as the spring is loaded to some pretension and the block is inserted, as we apply an external load to the hook the spring won't move unless the load is bigger than the preload, since the resultant force is then towards up.
From Wikipedia:

When an external tension load is applied, it relieves the compressive strains induced by the preload in the clamped components, hence the preload acting on the compressed joint components provides the external tension load with a path (through the joint) other than through the bolt. In a well designed joint, perhaps 80-90% of the externally applied tension load will pass through the joint and the remainder through the bolt. This reduces the fatigue loading of the bolt.

I still don't understand why only a part of the tension load goes through the bolt. The bolt is the only fastener in the joint, the components don't have any kind of adhesive or anything, how can the tension have "a path" through them?


texts: Are there reversed rotation direction in generators (as back EMF in MOTORS)?

texts:
There is a back EMF in a motor, due to current flow in a magnetic field.

So, in a generator, is there a reverse rotation (opposed to original rotation) due to a current flow in magnetic field?

I think there is, and this reverse rotation is zero when there is no load connected to generator (no current flow).

As the load connects to a generator, reverse rotation will arise, this will lead to a rotation speed down (slow down output frequency and voltage)

Am I correct?


texts: How to detect what wattage that my Windows laptop is receiving via USB-PD?

texts:
I don't know too much about USB-PD. I understood that USB-PD requires negotiation between the charger and the receiver. So probably my Windows laptop (Dell XPS 9570) should be able to know the current wattage input it's receiving. Windows probably also know since it's popping up saying slow charging. So I'm curious to know what wattage is my Dell is getting and is it getting the 100w it supposed to get?

My setup is a Dell XPS 9570 connected to Razer Core X Chroma eGPU. I've tried two cables, the Thunderbolt that came with the Razer Core X and the Apple Thunderbolt 3 0.8m, both of them still give that slow charging pop up.

Cheers!


texts: Can a 2 HP motor move a 1,000 lbs flat-bottom boat across a flat material surface?

texts:
There is a small 13' long x 6' wide, 1,000 lbs (total weight of everything) all-fiberglass white pontoon boat with dual flat-bottom fiberglass pontoons. (Each flat pontoon bottom is 2' in width, with an empty 2' space between the two, running the length of the pontoon boat). The boat is in a lake and sits with 2.5" of it being below the waterline.  There is a 2 HP electric motor mounted on the back of the boat. It is tiltable and extends beyond the 13' length of the boat itself. Its propeller is on shaft that places it nearly two feet below the water line when submerged.

The boat needs to be driven on to a foam-filled drive-on/drive-off floating dock. The floating dock is secured to a bulkhead at one end and tapers/slopes downward for about a foot at its loading end, where the two pontoon noses of the boat would commence movement on to the dock. The dock has a flat top surface area of 13' x 8' and has 3" of freeboard (i.e., height of dock that is above the water line) without the boat on it. The rigid top surface area of the floating dock has a permanent friction-reducing industrial coating or surface. (The co-efficient of friction would approximate that of outdoor carpeting.)

QUESTION: Will the 2 HP electric motor be sufficient to power/drive the 1,000 lbs, 13' boat on to the floating dock? If so, how much of the computed capacity margin to do so will be needed to do the work?

ASSUMPTIONS:

(1) The 2 HP motor must drive at least 12' of the 13' long boat on to the floating dock. Power is controlled with a throttle handle.

(2) Although the boat could approach the dock with some kinetic energy, moving at 2 or 3 MPH, the worst case scenario is that the boat is static in the water, with its nose only several feet from the sloped end of the dock, before the 2 HP motor starts its attempt to drive the boat on to the dock.

(3) The expanded polystyrene (EPS) foam filled dock is rated to keep up to a 1,500 lbs load entirely above the water line. With a 1,000 lbs boat on it, the dock would still have freeboard of 1".


texts: Do I use alternating, mean or max/min stresses for Miner's rule?

texts:
I am trying to work out fatigue life of a part using Miner's rule, however I am having some trouble working out which stress values to use. I have seen some examples but there seems no rhyme or reason to the values they have used in the accumulative Miner's rule, where fatigue failure occurs when :

$$\sum_{j=1}^{j=k}\frac{n_j}{N_j}=1$$

Where $n_1, n_2...n_k$
 represents the number of cycles at specific overstress levels and $N_1, N_2...N_k$ represent the life (in cycles) at these overstress levels.

The example below just used the maximum positive values, with no regard for negative values, even if they were nearly the same as that maximum positive value. Surely this negative stress would have some impact on fatigue, more so than a zero based loading?

So if I have a stress vs time plot (shown below) that varies from positive to negative quite randomly, where do I get these overstress levels from? Are they the alternating stresses, mean stresses, or max/min stresses that are over the endurance limit of the material?


texts: Finding the enthalphy of Helium given internal energy

texts:
I am trying to find the enthalphy of Helium if its internal energy is 200 kJ/kg. The answer is given as 333.42 kJ/kg, but I keep getting the wrong answer.

I've tried the following:

$\begin {align}
H &= U + PV \\
H &= U + mRT \\
\end {align}$

Universal Gas Constant, $R_u = 8.314 \:\mathrm{\dfrac{J}{K \cdot mol}}$

Individual Gas Constant, $R_i = 8.314 \:\mathrm{\dfrac{J}{K \cdot mol}} \div 4 \:\mathrm{\dfrac{g}{mol}} = 2.0785 \:\mathrm{\dfrac{kJ}{kg \cdot K}}$

$\begin {align}
H &= 200 \:\mathrm{kJ/kg} + 1\:\mathrm{kg}*2.0785 \:\mathrm{kJ/kgK}*273.15 \:\mathrm{K} \\
H &= 767.74 \;...\\
\end {align}$

Why is my answer different?


texts: Center line to centerline of pivots for two 16 diametrical pitch gears. One gear 72 tooth other 36 tooth

texts: I have two spur gears, each of a diametrical pitch of 16. One gear has 36 teeth and the other 72. I need to know what the distance should be center line to center line of the gear set. This would be the distance between the two shafts that the gears would rotate on.


texts: What is the twisting rate to reduce capacitance load on DC power transmission line?

texts:
I need to carry dc (direct current) electrical power from a solar array to point of use.  I know that an undesirable capacitive load will develop if I just run the power and neutral wires parallel to each other for a long distance.  For this reason, the transmission wire pair would need to be twisted around each other to introduce an inductive load to offset the capacitive load.  This is a form of impedance balancing with the goal of net 0 reactive load, where reactance encompasses both inductance and capacitance.

I know there is a formula to calculate the wire twisting rate in twists per meter needed to cause enough inductance to zero out capacitance but I have had trouble finding it.  I think it is based on the total length of wire, size of wire, voltage, and width of insulation among other variables.  Any help is much appreciated.


texts: Can large capacitors allow power plants to run at full load and store excess electricity?

texts: We know that demand for electricity is not constant. Power plants are not operated under full load conditions. What if power plants were operated under full load condition and excess electricity was stored in capacitors? I have read that capacitors of 10 kF capacitance are available. Could the use of such capacitors make it reasonable to operate power plants under full load at all times?


texts:
I've been asked to describe the physical significance of a dimensionless group (Biot Number) . I understand the definition of the group but I am unsure what the term "physical significance" means in the context of engineering.

Thanks for helping.


texts:
Is it possible to simulate a layer of dust deposited on top of a PV cell in a controlled manner?

One potential method I had was to put a given weight of a particulate/powder (chalk powder, talcum powder, etc.) into water, and pour the water on top of the solar panel, letting it dry and thus leaving the powder on top of the panel. Would this be viable, and if so, what would be the best powder to use?


texts: How this radio knob converting a rotation into a straight-linear motion?

texts:
Few months ago I opened the boards of an old, scrap radio-cum-tape-recorder (Philips DR183); whose tuning knob (that adjusts the gang); was very peculiar.

( * I did not found its datasheet on web)

The channel-indicator is a narrow rod at the tip of red plastic-thing. That indicator moves along a straight-linear segment when I turns the wheel.

However, it is just a rough sketch.  I could not figure out, what mathematical principle/ geometric theorem being used in this mechanic. It is neither like pulley and rope; and nor-like a piston-with-crankshaft. My question is, on what-basis they have chosen the angles, distances and ratios to make such movements?
 Or, For say if I try to make one with cardboard etc; what angles, lengths, ratios etc I have to choose, and in which logical basis?

Here I've provided some of its allowed conformations.

Please feel free to move this question if it is more appropriate for any other SE site, such as mathematics.SE .


texts:
The Poisson ratio of the material equals 0,33. If I load a cube or a cylinder that is fixed at one end with compression force in ANSYS I can confirm that the ratio is 0,33 by dividing the lateral by longitudinal strain.

But when I load a geometry that is hollow with changing cross section the lateral/longitudinal ratios across the geometry change in unreasonable intervals that make no sense to me, because I was convinced that the ratio is always constant and does not depend on cross-section or shape. My question is, what does the ratio depend on and how? If somebody could direct me to some useful literature, it would be greatly appreciated.


texts: Intuition behind pressure losses in pipes

texts: From standard pipe-loss equations we know that features in piping systems, such as wall surface roughness, or valves along the pipe system, cause major and minor pressure losses respectively. However, my intuition of how such features actually cause pressure losses seems to be incorrect, as I would have thought that surface roughness and valves would actually increase pressure along the pipe system as they tend to cause more restrictions in the flow. Could someone explain on an intuitive level why such features actually cause the opposite to take place?


texts:
So I have laser cutter. And I am thinking about buying a control unit (this one, to be exact).

But my concern here is the following: If the input DXF file contains splines, they will be converted to lines (G01) and arcs (G02 or G03), since these are all the entities G-Code has.

Since have absolutely no knowledge about motors or controlling them, the question is as follows:

Does the control unit from the link do the same? Does it convert DXF to G-Code?
If yes, is there a control unit that would quide my laser cutter over a spline from the DXF and NOT on some series of lines and arcs?
This webpage says that only Z axis is controlled with PID. Why? How are other axis controlled. Does this mean I could in general choose between PID and G-Code?


texts: Which states offer PE licensure for Software Engineering?

texts:
Which U.S. states offer Professional Engineer (PE) licensure for software engineering?

In my research, few of the state licensing boards listed on the NCEES site include the Software Engineering discipline.  Most focus on engineering disciplines such as Civil, Chemical, etc.

When I checked with NCEES, they recommended contacting each state individually!  Yuck.


texts: The water held underground in a geothermal system is under high temperature and pressure. Are pumps used to raise the very hot underground water to the surface or does the water rise under its own pressure? One source says that the water is pumped up: https://energy.gov/eere/geothermal/electricity-generation while another says that it rises on its own: https://www.youtube.com/watch?v=kjpp2MQffnw I am not sure if I am just misunderstanding the wording. Does anyone know which is correct?


texts: What type of sensing element is used in Water Quality Monitoring Meters?

texts:
What type of sensing element is used in Water Quality Monitoring meters such as those pictured below? I might not be using the correct search terms.

Some of these meters monitor Total Dissolved Solids (TDS) or pH levels in water.

I suspect there is an electro-chemical sensor. I have not been able to locate any information on the sensing element or the mechanism. I intend to build a simple water quality meter using a simple microprocessor and respective sensing element.


texts: I just learned about signed magnitude ,1's complement and 2's complement representation and I want to make sure that I understood them

texts:
So if I have the number 17 ( 8 bit code), the signed-magnitude representation is : 00010001
For -17 : 10010001
For 1's complement 17 = 00010001
For 1's complement -17 = 11101110
For 2's complement 17 = 00010001
For 2's complement -17 = 11101111
Please I need someone to tell me if it is correct.
Thank you in advance.


texts: How to run a steady state dynamics, Modal step based optimisation using TOSCA?

texts: What design responses must be given in the TOSCA gui. I chose volume reduction as an objective function with the constraints of displacement. Is this approach correct?


texts: How to calculate the force required to move this water bot with certain speed

texts:
This is my project where I have created a river cleaning machine. It works fine but no actual calculations have been done regarding the power requirement of motors(A software engineer ). The machine is half-submerged in water.
I want to know how to calculate the total amount for the force required to move this machine. Is there any formula that tells how much force is required to exceed the resistance of water and attain a certain speed.
Kindly ignore the white PVC pipes attached on the side of the machine. I added that because of some balancing issues which I will solve and thus the pipes will be removed.
My target is that even if I make a bigger model then using these same calculations I should be able to select the motor accordingly.
Waiting for your amazing answers. :)


texts: Typical IMU accelerations and angular velocities for lower limbs

texts:
Is there a dataset out there right now that shows the typical acceleration and angular velocity values for sensors attached to the thigh, shank, and feet for standard walking?

Or literature/textbook that describes what these typical values should be?


texts: I disassembled a usb wifi adapter. I was surprised to see a 40MHz oscillator, when wifi works at 2.4GHz. How the output of the oscillator is scaled to the required frequency?


texts: Does pressurization speed affect the tensile stress in the vessel wall

texts:
Does it matter whether you pressurize a vessel from zero to 4000 psi in 40 millisecond or 10 hours? Will that affect the response of the tank wall in terms of the tensile stress in the wall during or after full pressurization.

Given I have a scenario where I'm making a large amount of gas in a closed chamber by reacting some chemical compounds. If the reaction takes place so fast that the vessel went from zero to 4500 psi in less than 1 second, how can I calculate (or at worst estimate) the thickness of steel wall of the vessel that can take the pressure surge and still remain intact with the gas contained. If you need further details, I'll be happy to provide.


texts: Is there a relationship between depth/diameter/etc... of meteoric craters and the strength (eg:compressive strength) of the target material (sand...)?

texts:
So I am trying to write a high school research paper (3700 words) on the topic above. I am not sure if there is such a relationship, but I think intuitively we can agree that different materials will react differently to a meteor impact (especially in small lab size experiments since they are in what is called in the strength regime as opposed to gravity). I think a relationship exists because of the Newton-Laplace equation :

So perhaps someone can shed light on how impact craters inform us about the target material's mechanical properties ?


texts: How to measure the luminance an unevenly lit object?

texts: I need to measure luminance vs angle characteristics of an led lamp. I have access to a lux meter and a luminance meter. The problem is, that the luminance meter can only measure luminance within 1 degree, and the lamp is about 100cm x 2cm with LEDs about every 4cm, so the diffusor is not evenly lit. How should I go about measuring the luminance of the whole surface? Should I do many measurements along the lamp and do some kind of average? I even have a robot that could move the luminance meter by increments of 1mm or so. Or maybe should I measure the light with the lux meter and somehow calculate the luminance from that and the surface area?


texts: How can I keep a free spinning range finder pointing down?

texts: I have a rod mounted inside of a 2x4 that is allowed to freely spin inside of its hole. Attached to that rod's head is a range finder. I want the rod to reliably point down at the ground at all times to accurately read the 2x4's distance from the ground. The rod cannot be fixed in place. The 2x4 will be hoisted into the air and lowered by hand to about 8 ft max. My first idea was to weight the range finder so that it spins around and points down, however playing around with it, it's not as consistent as I would like. The 2x4 allows for free spin but isn't frictionless and I have to tap it a bit by hand to get it to fully position itself downward. I thought about adding a vibrator or something to the rod. Are there any other suggestions I may not be thinking of?


texts: Can not boot BeagleBone Black with 4D LCD touch screen using pre-built Android images

texts:
I am using a BeagleBone Black, Revision B with a 4D Systems LCD touch screen. The screen worked initially with a stock Angstrom or Debian distribution but I want to use Android instead.

I tried to use all of the pre-built Android images from Texas Instruments for the 4D screen, but I can not boot anymore. There is nothing on the screen. I tried to boot on the 4D screen via HDMI.

I am writing the image to the SD card with ./mkmmc-android.sh /dev/sdb.

Additional details:

4D System LCD is of model 4DCAPE-43T
Android distribution is 4.2.2 (Jelly Bean)
Ubuntu is the host system
Android Pre-built Image can not boot

Click on image for a larger version of the image.

Note: This is a screen capture from above e2e.ti.com forum link


texts: Unexpected Results from my Transfer Function

texts:
I have a system that can be modeled with the following picture:

There is a mass $m$ connected to a spring $k$ and a dashpot $d$. These are both connected to another dashpot $c$. A force $F(t)$ is applied at the junction.

After some effort tackling a system of linear ODEs, I've found a transfer function that describes this system:

$$\frac{X(s)}{F(s)} = \frac{ds + k}{(mc + md)s^3 + (mk + cd)s^2 + (ck)s}$$

I'm almost certain this is correct considering I've checked over the math multiple times (and the units check out, which is always a plus).

The system has certain parameters: $m = 1$, $Q = 20$, $\omega = 50$ Hz.

From this we can calculate the following parameters: $k = m(2\pi\omega) = 98696$ N/m, $d = \frac{sqrt(mk)}{Q} = 15.7$ Ns/m.

I estimate $c = 4$ Ns/m.

Given these parameters, I expect the following:

Impulse response that asymptotically approaches a value.
Step response that grows without bound.
Bode plot that has a peak at around 50 Hz.

The first two are true, but this is what my Bode plot actually looks like:

The reason I expect a peak at 50 Hz is because when $F(t)$ has a frequency near $\omega$, the amplitude of motion of the mass should rapidly increase.

Is there something that I'm modeling incorrectly here? Or is there some major misconception about how I think this system operates?


texts: Angular acceleration and the moment of inertia

texts:
The wheel is made from a 10-kg thin ring and four 0,5-kg slender rods. If the torsinal spring attached to the wheel's center has a stiffnes $ k = 2 N*m/rad$, so that the torque on the center of the wheel is $ M = (2* \theta)*N*m$, where $\theta$ is in radians. The wheel is rotated two full turns, $\theta = 4*\pi$ Determine the angular velocity when the $\theta = 0$ and determine the angular acceleration immediately after release, just before the movement begins. Determine the angular acceleration at the moment when the wheel is back to its original position.

I have calculated the angular velocity but I have problems calculating the angular acceleration. Where to start?

$w = 10.9 rad/s$ and $\alpha_1 = 9.5 rad/s^2$ and $\alpha_2 = 0$


texts: solving short electricity interruptions with an UPS

texts:
Context

A plastics factory with installed power of about 500 kVA. Most of the consumption is represented by motors and resistances.

Problem

There are several (8+ a day) power interruptions, lasting usually less than 50 seconds each. There's a diesel power plant and an automatic transfer (of which they have damaged two already). Usually the plant "enters" when the power is restablished, which doesn't solve the problems caused by the interruption and instead causes the transfer to suffer. In very unstable days, they prefer to override the transfer and have it in "manual" to avoid damage. Interruptions beyond 18 seconds require a complete stop of some of the machines and the consequent generation of considerable waste.

Proposed solution

There are large UPS (500+ kVA), often used to serve datacenters and the like. Their prices range around USD 200k for a 500 kVA one. The idea is to set up the transfer to take on for larger outages (say in excess of 120 or 150 seconds) and to have the UPS as the main source for shorter ones.

Doubts and Questions

I'm not sure if the inductive nature of the load and their start peaks can be effectively handled by the UPS. I don't know if it's robust enough for the task at hand (in lack of a better word). What protections should I consider for it?

In one UPS specs sheet I read that it can handle 150% load for one minute (that will be 750 kVA) and 125% (625 kVA) for 10 minutes. Does that mean that it can keep the plant running for those times? What should I consider to avoid the UPS not performing to expectation?

Do you see a better solution?


texts: Is it possible to remove Staedtler ink from a paper?

texts: I am practicing engineering drafting and sometimes I am near on finishing my work but suddenly I make a mistake. Is it possible to remove the ink? If yes, how? Where can I buy such tools? I am using a Staedtler's Mars Matic 0.5mm.


texts:
"By mounting a gyro on a set of gimbal rings, the gyro is able to rotate freely in any direction. Even though the gimbal rings are tiled, twisted, or otherwise moved, the gyro remains in the plane in which it was originally spinning"

Now I've seen that statement in several different textbooks, but I'm having trouble understanding the terminology used. It's stating that the gyro is able to rotate freely in any direction, but then it also says that the gyro remains in the plane it's rotating. If it can rotate freely in any direction, then it isn't in it's original plane of rotation. So if anyone could simplify that, it'd be helpful.

Also the gimbals allow things to rotate around it while the gimbal doesn't rotate, but then wouldn't you need the gyro to move for precession to take effect?

For an example if I said that I applied a force with regards to precession taking place, would the gyro maintain it's plane of rotation but that force would take affect on the gimbal?

Thank you!


texts: How can I estimate blocking window distance in an sCMOS sensor setup?

texts:
I am trying to establish an appropriate distance between a spectrograph output window and a CMOS sensor.

The spectrograph creates a focused image on the CMOS sensor but I am trying to restrict the light as the initial pixels are capturing light of higher intensity from 0th order wavelengths. Post processing is possible, but I would rather physically restrict the wavelengths.

I need to block out some of the pixels in the border. Therefore, I need to determine at what distance the blocking window needs to be placed.

I hope the image below will illustrate my problem.

The setup is:

Motor operated scanning mirror
Headwall VNIR Spectrograph
PCO Edge VNIR 2560 x 2160 pixels sCMOS sensor

I am trying to "see" 2560 spatial pixels and 500th-1600th spectral pixels. So, I am thinking the horizontal window dimensions would remain the same (at 16.64 mm), but the vertical dimension is unknown. For example, vertical dimension would be 7.15 mm if the window is placed EXACTLY on the sensor. I am trying to establish how far to place the window. I can place the window anywhere between 5 and 10 mm from the sCMOS sensor.


texts: How to manage two control loops as safety when BPCS is shared?

texts:
I am trying to wrap my head around some excerpts from:

CCPS Layer of Protection Analysis
CCPS Guidelines for Independent Protection Layers and Initiating Events
IEC 61511

I am trying to understand how to apply Approach B and use two functions in the BPCS (e.g. a control loop and an alarm) as independent Protection Layers (IPLs) in a LOPA, when the CPU is shared.Guidelines are very vague about it.
What parameters should be looked at, to decide to apply Approach B?
Note: I understand that, if the guidelines are not clear to me, I should not apply Approach B. The request comes from a client who is trying to consider as many safeguards as possible before having to update their BPCS and SIS.


texts: Why do electric cars claim "instant torque?"

texts:
I was at a well-known electric car company today and they claimed "instant torque." The quote was something like the following:

  Driving this car is very different from a gas-powered vehicle. For example, it has instant torque when you press the accelerator. Unlike a gas vehicle where there is a slight delay.

My question is, where does this "instant torque" come from? Is the explanation as simple as the fact that electrons/electricity travel/s at the speed of light. But it takes time for an internal combustion engine to convert chemical potential energy into kinetic energy via thousands of tiny explosions? Or is there something else that could illuminate this explanation?

Edit: I just found this related question on a separate SE. Can anyone add more of a "fundamental physics explanation" to the set of answers?


texts: Why doesn't epoxy stick to silicone? Is there a type of epoxy that does?


texts: What kind of pump not limited by atmospheric pressure?

texts:
Most pumps like centrifugal pumps are limited by atmospheric pressure. This is because the pump simply create a vacuum where the atmospheric pressure pushes the water into it. Hence there is a limit of 10 meters of waters it can acquire due to gravity.
What kind of pump where it is not limited by atmospheric pressure so it can acquire say 20 meters of water?
If there is none in production. Then theoretical. Like for example in certain explosion, great vacuum is created. This can make it suck more than 10 meters of water, right?  Or other techniques not limited by existing technology. I just want to have idea how such pump can operate. I googled but didn't get the answer.


texts: Can photopolymers from 3D printer be fused together like for thermo plastics?

texts:
I'm considering getting a SLA 3D printer, but the big uncertainty is whether I can build large things like propellers by printing them piecewise and fusing them together like you can with ABS and acetone (or butanone).

The resins are proprietary, so I guess that's why I can hardly find any information on this. But according to Wikipedia, photopolymers are thermoset, so that rules out melting them. But are there any solvents that can fuse them?


texts: What do the parameters k1 and k4 adopted in crack control tables in EC2 refer to?

texts:
Referring to page 123 of the code in EC2, BS EN 1992-1-1:2004, note 1 above Table 7.3N indicates that maximum bar spacing for crack control is derived based on $k_1$ parameter being 0.8 and $k_4$ parameter being 1.0. According to crack width calculation in clause 7.3.4(3), $k_1$ is 0.8 and $k_4$ is 0.425. Under stress limitation clause 7.2, $k_1$ is 0.6 and $k_4$ is 1.0. So, what do $k_1$ and $k_4$ refer to in Table 7.3N?

I need to know precisely what the parameters mean because I want to verify my crack width calculation based on clause 7.3.4 to see if they match with what is presented on the table.


texts: I have the yaw rate, rear wheel speeds, and the radius of tires, how to find x and y speeds?

texts:
I only have these 3 data sets:

rear right and left wheel speeds (they change with time)
yaw rate (also changes with time)
constant dynamic rolling radius

How am I supposed to find the directional speeds of the vehicle? I know that yaw rate is equal to (the difference between the rear right and left wheel speeds)/(the distance between the rear wheels)

and

therefore the distance between the rear wheels should be equal to (the difference between the rear right and left wheel speeds)/(yaw rate) right? But when I work with the data sets and do this calculation, I see that the distance is not constant when it should be!

And also, how to find the directional speeds with these given parameters only???


texts: Determining intermediate pressure between two turbines

texts:
A steam power plant employs two adiabatic turbines in series. Steam
  enters the first turbine at 650 C and 7000 kPa and discharges from the
  second turbine at 20 kPa. The system is designed for equal power
  outputs from the two turbines, based on a turbine efficienct of 78%
  for each turbine. Determine the temperature and pressure of the system
  in its intermediate state between the two turbines. What is the
  overall efficiency of the two turbines together with respect to
  isentropic expansion of the steam from the initial to final state.

How should I determine the pressure between two turbines?I have the solution from a solution manual (prob. 8.6) but I just can't understand why it takes pressures around 700 KPa and does an interpolation.
what we know:

$S3=S2=S1$ (if working isentropically) ($S$ is entropy)

$x$ (Quality of exiting vapor)

Note:we could determine properties of the intermediate flow properties using one property($S$) just if it's two-phase, but it's assumed that the intermediate flow is superheated.

I'm sure of problem's data and that's all we have.


texts: Amount of programming needed to become a decent industrial engineer

texts: I am interested in becoming an industrial engineer. I know the basics of Java and Python but I cannot program well. I am wondering whether it is still possible for me to become an industrial engineer.


texts: Calculating stress from elementary tension and bending formulas

texts:
I need help with this problem.
Suppose we have a cantilever with width $-c \leq y \leq c$ and length $x=l$ fixed at $x=0$. We know that it is loaded by uniform shear along the lower edge with magnitude $S$ and the upper edge and the end $x=l$ are free from load. I know how to find the stresses using the airy stress function, but could you please tell me how to find $\sigma_x$ and $\tau_{xy}$ using the elementary tension and bending formula so that I can compare?

The depth of the beam perpendicular to the x axis is 1.


texts: Why is the spin velocity of a gear irrelevant if perfectly balanced?

texts: Going through some theory about epicyclic gears I came accross a comment that says that the spin velocity of the gear irrelevant if perfectly balanced, I don't understand why this might be true, is it because it would be constant and thus can be measured without variations?


texts: What is the difference between wake and recirculation region?

texts:
If we place a obstacle in the fluid flow, fluid will be circulating behind the obstacle. What is this called?

This might be a wake or recirculation region. What is the difference?


texts: Undamped forced vibration for a multi dof system

texts:
I'm trying to determine the amplitude vs the excitation frequency of a multi dof dynamic system. I'm very confused from reading different methods, although I understand there's a very general one, which is not giving me the results that I think should be when plotting the response.
Considering a system with no damping  $\mathbf{M{\ddot x}+{Kx}=F(t)}$, and by assuming the harmonic excitation of the force is a cosine the system becomes $\mathbf{-MX{cos(\omega t)}+{KX}cos(\omega t)=fcos(\omega t)}$. From here the cosines get cancelled out so
only $\mathbf{[K-M{\omega^2}]X=f}$ remains. By solving for the $X$ vector in the end I get $X = \frac{F/M}{|\omega_n^2-\omega^2|}$.

So with Matlab I wrote the following code, with parameters I found on an example from brown.edu, in which the explanation is not complete, my system is actually a 24 DoF system, so I need the code a bit automated:

    k1 = 2;
k2 = 1;
k3 = 1;
m1 = 1;
m2 = 1;

M=[m1 0; ...
   0 m2];
K=[k1+k2 -k2; ...
  -k2 k3+k3];
F=[1;...
   1];

[V,D] = eig(K,M);
D     = diag(sqrtm(D));
frequencies   = (D);
[rows,~] = size(V);

f=linspace(0,0.7,100);
omega=2*pi*f;
Mag = M\F;
Xt = zeros(rows, length(omega));
    for i = 1:rows
        for j = 1:length(omega)
            Xt(i,j) =  abs((frequencies(i)^2 - omega(j)^2)\Mag(i)) ;
        end
    end
figure
    for m = 1:length(frequencies)
        plot(omega, Xt(m,:));
        set(gca,'YScale','log')
        hold on
        axis tight
    end

Where the main part is the  Xt(i,j) = (abs (frequencies(i)^2 - omega(j)^2)\Mag(i) ); , which follows the determined formula for the displacements of each degree of freedom.

When plotting what I get is:

which shows the masses vibrations being at resonance, but from what I understand there should be more peaks and some antiresonance.

What am I missing in the general math?

EDIT_1: I changed the bit of the code to calculate the absolute values of the equation like: $$X(\omega) = \left|\sum_n \frac{F/M}{\omega_n^2 - \omega^2}\right|$$ but I get the same when plotting. I found another solution but I don't understand how its determined or why choose it.
From ${M{\ddot x_i}+{Kx_i}=f(t)sin\omega t}$ the steady state solution is $x_{iss} = x_{is} sin \omega t + x_{ic} cos \omega t$ , where $i = 1,2$ , then
$$ \begin{bmatrix} \mathbf{-(\omega)^2M+{K}} & \mathbf{0} \\ \mathbf{0} & \mathbf{-(\omega)^2M+{K}} \end{bmatrix} \begin{bmatrix} \mathbf{x_{ic}} \\ \mathbf{x_{is}} \end{bmatrix} = \begin{bmatrix} \mathbf{0} \\ \mathbf{f} \end{bmatrix} $$
 which is then solved to get ${X_{i}} = (x_{ic} + x_{is} )^{1/2}$
First, I don´t understand very well if just $x_{iss}$ is substituted in ${M{\ddot x_i}+{Kx_i}=f(t)sin\omega t}$ for $x_i$. And is this just assuming a sum of $cos$ and $sin$ instead of my first approach of only $cos$? Then, do I need to consider adding the transient response also, which I´m actually not sure how it would be.

EDIT_2: I think I figured out what I was doing wrong. I changed the equation from $$X(\omega) = \left|\sum_n \frac{F/M}{\omega_n^2 - \omega^2}\right|$$ to $$ X = [K-M\omega^2]^{-1}F$$ which mathematically I though they were the same??? The code part that changed is as follows:

for j = 1:length(omega)
       Xt(:,j)  =  abs((K-M*omega(j)^2)\F);
    end
figure
    for m = 1:length(frequencies)
        plot(omega,Xt(m,:))
        hold on
        axis tight
    end

And the result plot is:

For my extended MDoF system I got:

In which I excited all DoF, even when I only excite a single one, it is still very hard to notice what's going on, is there a better way of analysing the response?


texts:
Used to connect the chain for a window actuator to a U-shaped window bracket.

The threaded end screws into a bolt hole (M5.5 female thread) on one side of the U-bracket. The tip of the fastener fits into a 3mm diameter slot on the other side.

The end of the chain pushes and pulls perpendicular to the axis of the fastener on the unthreaded section between the two connections.

Dimensions: Total length: 34mm.
Threaded section length: 6mm.
Unthreaded section: 3mm diameter.
Threaded section: 5.5mm diameter.

What type of fastener is this, and how do I go about procuring a replacement, short of resorting to a bespoke service?

The unthreaded section can be thicker to some degree, or be threaded, as long as there is a 3mm diameter tip of at least 4mm length to connect to that side of the bracket.

For example, a M5.5 bolt with a 3mm diameter dogpoint would do the job. However, as far as I understand, there are no bolts standardized to a M5.5 diameter.


texts: I am working on a flywheel currently, and I was wondering what is the force needed to recenter the flywheel when it is spinning and it is nudged slightly off axis? Is it related to gyroscopic precession?


texts: What is the most cost efficient way to cool a tank of oil with water?

texts:
I have a tank of oil which I plan to heat 24/7 with constant 15 kW. I want to dissipate this energy using water as a coolant. I have the outside unit of an out of order split type air conditioner that could be used as a radiator to heat the environment.

Can I dissipate this much energy on such a radiator?

How should I exchange heat between the oil and the water? I thought of a heat exchanger used in floor heating. I saw some rated 70 kW and above. But I can't imagine how it works seeing it's small size.

The tank is about (1*1*1) m, filled with oil. I would use only as much oil as needed to immerse the electronics I want to keep cool at <50 °C. The energy to be dissipated is constant 15 kW.
The A/C radiator with a fan is installed ~5 m above ground, the tank being on the ground.
I want cooling to work also in the hottest summer, topping at about 40 °C on the hottest days of July.
The system must be closed, because I don't have infinite amount of water.


texts: Farting sound when connecting power amp with to the pre amp

texts:
As what the title says
When I connect my designed preamplifier,which is in a breadboard,
unto a power amp kit (Acoustic 50W Mono) with a speaker, there is a farting sound, as if it is a pulsating DC. And if I directly connect my music or mic to the power amp the output of the speaker is fine but very weak since there is no preamp.

In addition, the farting sound is always present, meaning with or without an input of music or mic the farting sound is there.

From what I could think of right now is that it is due to the bias also going to the poweramp or too much low frequency that I'm not aware. And I need help in solving this problem.

And here is an image of the preamp.


texts: How does the central lock mechanism in articulated arm (magic arm) works?

texts:
does anyone know how does the central lock mechanism in articulated arm (magic arm) works?

The magic arm usually used to hold camera, with only 1 knob, it can lock all sides. How?


texts: What limits a power plant's load gradient?

texts:
Each power plant has a load gradient characteristic, describing to what extent it can change the output of its generators in a given timeframe. Reading the literature, I know that, for example, a gas turbine power plant has a vastly higher load gradient than a one that uses coal as its primary energy.

However, I cannot find a description which parts of the plant contribute the most to the load gradient. I can imagine that a gas-powered plant can change its output faster because there's no mill involved as in a coal power plant, but where does its gradient exactly come from?

More specifically: What constitutes the load gradient of

a gas turbuine power plant,
a Lignite (brown coal) power plant
a bituminous coal power plant
a nuclear power plant?

And why is there a difference between lignite and bituminous coal power plants?

I'd very happy to read up on the details if one could name a book. I've read several books that describe how these plants work, but fail to mention what creates or limits their load gradient.


texts: Stress yield of a specimen, result confusion

texts:
I am trying to calculate the static yield stress of a specimen using the
0.2% offset line on a stress strain curve. I found the static yield stress of the specimen to be the number in bold (104.1239). Given the shape of the
graph and how close the static yield stress appears to be to the UTS, I was wondering if this value actually looked correct? Or could I have accidentally calculated the dynamic yield stress instead?

The material I used in this test was a "low grade aluminum"... which is throwing my thought process off.

I would really appreciate any insight on this.


texts:
In control theory, according to the definition of matched uncertainty, the uncertainty enters the system through the same channel as the control.

If we consider the system:
$$\dot x = F(x)+G(x)u+Δ(x, t),$$

where $F$ and $G$ are known functions comprising the nominal system and $Δ$ is an uncertain function known only to lie within some bounds. For example, we may know a function $ρ(x)$ so that $| Δ(x, t) |≤ ρ(x)$.

If we require that the uncertainty $Δ$ is of the form:
$$Δ(x, t) = G(x) · \barΔ(x, t)$$

for some uncertain function $\barΔ$, this form is called the matching condition because it allows the system to be written as:
$$\dot x = F(x)+G(x)[u+ \barΔ(x, t)]$$

where now the uncertainty $\barΔ$ is matched with the control $u$, that is, it enters the system through the same channel as the control.

What are the physical examples for matched and unmatched uncertainties?

(Levine, William S., ed. The control handbook. CRC press, 1996.)


texts: What are fluids or "goos" called, that increase friction?

texts:
I have a shaft inside a bushing, the shaft has a gear on one end that is supposed to provide resistance to other gears it is driven with.

I'm having a hard time finding the correct term for the sort of grease or fluid, or in more lay-man's terms a "goo", that will provide increased friction between the shaft and the bushing, rather than reducing friction, as it is with regular oil or grease.

Essentially a tar-like substance, that isn't as messy as actual tar. Perhaps also similar to tree-sap, except more manageable in terms of putting it into a mechanical device. Also tree-sap gets hard over time, I'd like to keep its mechanical properties, like viscosity, etc.

In case you're wondering, this is going to be part of a soft-open gearing, such that a small door doesn't fling open when the lock is released, instead it provides some resistance.


texts: How to store gas on little pulsejet plane?

texts: I am thinking about building small plane with a pulsejet but the engine would need to be roughly 2 cm in diameter. Is it even possible to fit something to store gas on that sized plane? At least for like 10 seconds of running.


texts: Do the floorboards in timber beam floors have a structural function?

texts:
Timber beam floors with perpendicular timber floorboards as indicated in the drawing below are common throughout northern Europe. The floorboards are nailed onto the beams and are quite substantial with a thickness of around 25-30 mm. The floorboards are typically connected with one another with longitudinal tongue and groove joints.

I wonder if the floorboards serve a structural function? Specifically, I could imagine that they could serve to distribute loads or to brace the beam structure.

Image source

--
EDIT:
As pointed out by Solar Mike the floorboards are indeed typically connected with one another with longitudinal tongue and groove joints.


texts: Estimation of cutting torque for circular saw device

texts:
How could I estimate the required torque for cutting through wood using a blade, say 180 mm in diameter?
I am not too sure how to approach this.


texts: Why do some diesel engines run on diesel fuel and others on fuel oil?

texts:
Trucks and smaller vehicles with diesel engines run on diesel fuel which looks more or less like kerosene - less flammable than gasoline, low viscosity liquid. However larger diesel engines like this 120 thousand horsepower marine engine have more or less the same design but use fuel oil which looks very different from diesel fuel - much higher viscosity and I'd guess igniting fuel oil at room temperature is a challenge.

How does it happen that engines of the same design use two different fuels? If one of them is superior to the other then why won't they all stick to that superior fuel?


texts: Is there any recommended/suggested/required penetration rate for a miniature cone penetrometer? A 20mm/s is for a standard size of cone penetrometer, what about for miniature one?


texts: Why are automotive brakes set inside the wheels, and not on the axles?

texts:
In most (maybe all?) automobiles, the drum or disc brakes are positioned at the end of the axles, inside the wheel. This increases unsprung mass, which reduces handling performance.

Would it not be just as effective to move the brakes inboard, positioning them on the axles themselves, somewhere under the chassis in between the suspension arms? It seems that this would have the same effect, but would eliminate the brakes' contribution to unsprung mass.

I've seen it done this way on go-karts with a solid rear axle. Does the fact that automobiles have sprung suspension systems necessitate the brakes' placement inside the wheels? Are there other engineering tradeoffs at play?


texts: What limits my Courant number in Implicit Density based Solver?

texts:
As from the derivation we are able to see that the implicit density based solver (such as BTCS) is unconditionally stable for any courant number. So what is it, which limits the upper boundary of CFL while using it in practical applications?

I need this for simulations in ANSYS Fluent.
I have been told that non-linear effects start coming in, but I don't know what exactly are the non-linearities?


texts: Can cross correlation be used to see if filtering of a signal has changed it too much?

texts:
I am filtering a signal, and want to check if I am not over filtering it , I wanted to use cross correlation , but I am not sure if it is a good technique. usually I get something like the following as Cross Correlation between the signal itself and the filtered one. i sit a good criteria?:
The filter is 4th order Bessel, lowpass filter, with 250Hz pass band for a 512Hz signal. no time lag between filtered and original


texts: Do you think these power distribution joints would suffice or should I improve on them?


texts: What does L mean in Uncertainty Measurement Result U(E)=0.08+1.2L ;k=2?

texts:
I'm calculating the combined measurement uncertainty u(c) of a measurement for a length displacement sensor. Amongst other factors, one individual uncertainty affecting the error of measurement is the uncertainty of the gage block I'm using. In the calibration certificate of the gage block the uncertainty of measurement is expressed as:

$U(E)=0.08\ \mathrm{µm}+1.2\ \mathrm{L}$

With the coverage factor $k=2$.

The nominal thickness of the gage block is 10 mm and usually uncertainty is expressed as just  ±0.08 µm. In this case, what does $L$ stand for?


texts: How is rolling resistance accounted for in the Pacejka Curves?

texts:
I am simulating the acceleration of a car (FSAE) in a straight line. I have data of the Pacejka Curves ($F_x$ vs. $SR$) of the tire we will be using. The thing is that the curve doesn´t pass through the origin ($F_x=SR=0$). Instead the curve is shifted horizontally meaning that $F_x(SR=0)\neq0$. I have troubles finding the explanation. I am pretty sure it has to do with the rolling resistance of the tire.

My model (simplified) is as follows:

The driving torque on the axle is resisted by $F_x(SR)$ which causes a countertorque. Resultant torque is what accelerates (rotationally) the axle. $F_x$ is what drives the car forward.

Can anybody explain me the meaning of a shifted Pacejka Curve?


texts: Air - rectangular membrane system vibration and natural frequency

texts:
I'm struggling with the following problem:

The boundary conditions are $w(x,y) = 0$ around the edges.

I am supposed to find the natural frequencies of the system as a whole, and find the solution for $w(x,y,t)$ based on the inout $p_{in}$. The air can be perceived as a 1-D continuum to simplify the equations.

There is a body of air above the membrane with the pressure at height L above the membrane being defined as $p_{in} = p_0 e^{jwt}$
I know how to solve this problem for the membrane alone with some initial conditions but I'm lost as how to work with this problem as a whole.
I don't see how could I use the known equation $\frac{\partial^2 w}{\partial t^2} = \frac{\sigma_1}{\rho}(\frac{\partial^2 w}{\partial x^2} + \frac{\partial^2 w}{\partial y^2})$ to find the solution.

So my guess would be that I have to find the solution for a 2D wave equation with a source, then write a boundary condition equating the pressure in the air at the surface of the membrane to the source in the membrane equation and go from there.
Meaning  $\frac{\partial^2 w}{\partial t^2} = \frac{\sigma_1}{\rho}(\frac{\partial^2 w}{\partial x^2} + \frac{\partial^2 w}{\partial y^2}) - \frac{p(x,y,t)}{h \rho}$ and $p_{air}(x = L, t) = p(x,y,t)$.

Any help, insight or link to relevant materials will be greatly appreaciated.


texts:
Given a beam ($\rho, A, l$) rotating with angular velocity $\omega$, find the maximum stress in the beam and its location.

I think the maximum stress occurs at the base, because the resultant force is the entire axial force. The total axial force is:

$$F = \int_0^l\frac{m}{l}\omega^2r\ dr = \frac{m\omega^2l}{2}$$
$$m = \rho Al$$
$$\sigma_{max} = \frac{F}{A} = \frac{\rho\omega^2 l^2}{2}$$

Did I do this right?

The follow-up question is, what happens when the beam is extremely thin: $t << l$

I don't know how to answer the follow-up.


texts: Small gearbox PM gears tolerances allowed

texts: We have a small gearbox design for fire prevention louvres to be opened when a fire is detected by computer software calculation, with PM gears, but the tolerances calculated are very tight. What general tolerance range could we allow for small dimensions ranging from 5mm to 14mm


texts: What does it mean that a ball bearing can handle thrust load but a roller bearing can't?

texts:
I can't wrap my head around it so if someone could explain this to me. According to http://www.vncbearing.com/roller-bearings-vs-ball-bearings-major-differences/
ball bearings can handle thrust loads but roller bearings can't. Now I understand that ball can rotate around all axis and roller around only one, but still... If you put a shaft on those bearings it's meant to rotate, you don't allow a shaft to go through a bearing, it's always fixated in one way or another. So what's really the point of that statement?


texts: How do I add a resistance to mechanical movement in both directions, apart from friction?

texts:
What options do I have for creating a resistance to a mechanical movement apart from simple friction?

Assume I have a lever, which will result in either circular or linear motion.  I want to be able to apply a resistance to this motion, so that the user will have to apply extra effort to move the lever in either direction.  I could use a spring, which would resist motion in one direction, but this would then result in a restoring force when the initial displacement force was removed.  I want the extra force to act in both directions, so that the lever is "heavy" to move, but will stay in its new position when displaced.

I want the force to be able to be calibrated and remain constant, so I don't want to have something like a brake pad, which will wear, or just a nut to do the joint up tight, as this will be too difficult to achieve a calibrated force.

Is there something that could be done with a spring or pneumatic air muscle or by using hydraulics?


texts:
I have a question regarding gasturbine energy balance,

the total energy that flows into the gasturbine is given 12 MW and the power needed for the compressor is 4.4 MW and the turbine power is 9.3 MW. So the net output is 9.3-4.4 = 4.9 MW which is around 40% efficiency.

But what happened to the 12-9.3 = 2.7 MW, where it is lost ?

It also says, 60% losses but actually 4.4 MW of the turbine power is needed to run the Compressor which I dont think is a loss, how would you explain this ?

At last, how do I create a Sankey Diagram of this energy flow ?


texts: Where to connect the tubes on the refrigerator compressor to operate by using hand?

texts:
I am trying to operate the compressor of a refrigerator using my hand. I have opened the case of the refrigerator compressor and removed the part responsible for the compression. I have made a gearbox and connected it to the rotor of the compressor as shown in the figure below.

I have connected the condenser, dryer, capillary tube and evaporator using copper tubes in the mentioned order.
I am able to see two tubes(marked by green and orange circle) coming out of the compressor as shown in the figure but not able to understand on which tube of the compressor I should connect the high-pressure vapour part and which tube to the low-pressure vapour part.

I also want to know how to fill the tube with the refrigerant so that upon rotating the crankshaft I could obtain the refrigeration cycle.
Please help me with my project and correct me if I am doing something wrong.


texts: How to reverse the direction of rotational movement on the same axis?

texts: I want to make a "gearbox" that will transform input rotational movement to an output rotational movement with the same speed but in the different direction (clockwise / counterclockwise) on the same axis. How can this be done?


texts: Mohr's Circle explanation in detail in simple languagr

texts: Someone please explain me Mohr's circle in detail in a simple language


texts:
From an engineering perspective, what limits the maximum speed you can reach with a regular car? I understand that some of the faster cars are for safety reasons limited to not run faster than say 250 km/h, but that's not my question.

I can think of several reasons, but not sure which of these is relevant:

Is the limit set by some part (which?) breaking if I increase the rpm, as suggested by red marks on rpm meters?
Or is it rather that you cannot get in fuel fast enough to keep increasing the rpm?
Or is it that friction/drag increases as you speed up and the engine cannot overcome this as it can only generate a maximum amount of force/torque? If yes, what does this amount of torque/force depend on?


texts: MIMO control: static inverse plant decoupling

texts:
I am using techniques explained in the book of Skogestag, Multivariable feedback control, for feedback control of a MIMO plant. In this book they explain the phenomena of static inverse plant decoupling in which the interaction of the off-diagonal terms are eliminated.

I have a triangular MIMO plant in which one of the off-diagonal components is zero. Is it still usefull to apply static inverse plant decoupling in this case?


texts: direction of shear flow to cancel out the moment

texts:
In the figure , we can notice that the moment due to Pe is counterclokwise , but moment due to shear flow is also counterclockwise , How can the Pe prevent the twisting of the beam ?

Or is the direction of the shear flow wrong ? Should it flow from the below to the top ?


texts: What is a material that allows air to pass but not water vapor?

texts:
What are some materials that allow air to pass but not, or to a lesser extent,  water vapor?

Here are two materials I am aware of:

Teflon is a material that allows water vapor to pass, but not air. Water itself can't pass.

What are some other sourceable substances which have this feature? What are some defining terms and measurements used to identify this property in a material, and how can the rate of water vapor / air transfer be manipulated in such a substance?


texts: Linkage of two shafts that need to rotate different angles

texts:
I have two switches that have different throw angles the switches have shafts coming out of them which are connected the the cams that can be seen in the attached pic. One needs to rotate 95 degrees to throw and the other 83 degrees to throw, the motion of the left shaft will be limited to 95 degrees via a pin in the cam and is drived via an external handle however the right shaft will not have this pin and will be driven via a link as seen in the photo, the distance between the two cams is 255mm.
I need help calculating the length of the two small arms that will connect the shaft to the link.
I have looked at both using gear ratios using the angles to estimate the length of links 1 and 3 as well as completing analysis for a 4 bar double rocker mechanism however got stuck with the calcs as it has been a while since I studied this and can only find examples where all link lengths are known and angles are to be calc'd (happy to supply my calcs).
I have attached a basic diagram of the system, any advice would be great, thanks!


texts: What is the common filler used in plastic injection moulding?

texts:
What are the common filler materials used in PP, PE, LDPE, HDPE, and PVC-moulded materials?

To give a background - I own a limestone quarry and selling calcium carbonate in powder form. I want to make value added products from CaCO3, which I came across the filler master batches. But I am not sure what type of plastics use that. Answer to this will help me identify a particular sector and do targeted market analysis as I understand different end users require different grades of CaCO3 fillers.


texts:
I am looking for a kitchen salt grinder.
I know salt is an aggressive compound and it needs a little bit of attention when we design products.
Since most of grinders have plastic-made or stainless steel-made parts (I'm talking about grinder mechanism), and corrosion is virtually unavoidable,
As engineer, I have one (+bonus) question:
I know salt can corrode metals, is it true for plastics too?
Bonus. Concerning about health, is preferable to have metal corrosion (rust) or plastic corrosion?


texts: Is there an analogy between mechanical vibrations and electromagnetic waves

texts:
Recent questions about analogies between mechanical and electrical systems and about electromagnetic waves from a conductor made me wonder whether there is an analogy between the mechanical vibrations of a single degree of freedom (dof) system which are induced by external excitation of the base (see below)

and the electromagnetic waves from a conductor.
More specifically the post stated that :

To my understanding every conductor reemits a bit of electromagnetic waves induced in it by radiation.

I have to admit that I do not know how well does that statement hold, but I am certain that there is at least some truth (so I'll welcome any assessment of the validity of this statement).
In any case, the way I interpreted the above statement was that in both cases it seems to me that there is an external source of "wave-like" energy (notice the quotes), which results in a portion of the energy to absorbed and reemited from the system.
Although, I am somewhat familiar with the mechanical aspect, the rf aspect is uncharted territory for me. If someone can fill in the blanks on the analogy (if such an analogy exists at all), it would help me understand better the electromagnetic aspect by mapping my existing knowledge.


texts: What does it mean to design something by using "first principles"?

texts:
A fan of Elon musk but have hard time understanding his engineering approach when he says use "first principles". Could anyone elaborate on that ?

When we got a problem at hand what is the first principle way to solve the problem ?

Reference
www.youtube.com/watch?v=NV3sBlRgzTI


texts: Why aircraft refrigeration uses a centrifugal compressor in place of reciprocating compressor?

texts: Why aircraft refrigeration uses a centrifugal compressor in place of reciprocating compressor and a gas turbine in place of reciprocating expander?


texts:
I've run some stress simulations but I keep getting some unexpected results. I have 3 parts connected using 4 bolts as follows:

A torque of 1N is applied to the hole on the right to simulate a hung weight. After running several stress simulations, the two highest points of stress concentration appear to locate at the bottom of the part with the hole, specifically at the end of the fillet on the outer surface:

As you can see, there are two hotspots along the end of the fillet -- equal distance away from the edges. Does anyone know what might cause the stress at these two locations?

EDIT: Here's an overlay of the mesh over the stress hotspot:


texts:
I am installing an acrylic shelf, 75-1/4" L x 10" W x 1-1/2" deep.
It is fixed to the wall at the short ends. Should I be worried about deflection in the center of the shelf when weight is added? Is there anything I can do to calculate this?