texts: What's the current nomenclature for "English" system of units?

texts:
Is the term "English units" still in current everyday use? I do hear this term among other engineers I work with but I'm unsure if this is a localized usage or is consistent with the wider community.

Mainly I'm focused in the HVAC field but I don't know if terminology would be different in other areas. I noticed that ASHRAE uses the term "IP" or "inch-pound" to refer to what could also be called "English" units, e.g.:

  "The ASHRAE Handbook ... is available in I-P (Inch-Pound) or SI
  (System International) units of measurement."

Formerly I had thought "US customary" was the appropriate term to use.

There might be some subtle technical differences among how "English", "IP", "US customer", or any other scheme is defined. But what I'm interested in is understanding which term mechanical engineers are likely to use in everyday discussion or writing where those technical differences are generally not relevant.

I don't have the impression these units are widely used outside the USA, but I do have an international "audience" in mind so international differences would be interesting, if any.


texts: Explain each of the values output by HEC-RAS

texts:
I am looking at a Flood Risk Assessment that uses HEC-RAS to model the predicted levels of flooding on a piece of land. As shown in the attached image, the report lists a number of variables with abbreviated names and I would like to know briefly what each one means and which one of those values shows the predicted height of flood water.

I found this document: HEC-RAS Output Variables which gives the full names of the abbreviated variable names. But the actual significance of each variable still make little sense to me.

Thank you in advance for any help you can give me.


texts: Why use steam water and not other fuild in steam engines?

texts:
Given this answer, I understand the importance of phase change (liquid --> gas) for the fluid used in a steam engine. Thus I understand it is important to use a fluid that is liquid at pressure and temperature this engine may work in (between 600 and 1000hPa, between -20°C and 50°C (I may take large margin for extreme climate condition including high altitude mountains)).
Thus, we may use any fluid that is liquid in this condition and easy to boil (I'm thinking of ethanol that has a lower boiling point but other fluids may be suited).

My question is: why water and not other fluids such as ethanol?

Edit: I cite ethanol but I don't want the answer to be focused on this fluid in particular. It can be any fluid that is liquid in normal temperature and pressure condition and easy to boil. I have no idea what fluid can meet this requirement.


texts: Why is it easier to run an STA on a CPLD than an FPGA?

texts:
I am aware that it is easier to run a static timing analysis on a CPLD than a FPGA, but why is this?

Any information would be greatly appreciated.


texts: Heuristics for Efficient Structure (Shed) Design

texts:
Are there any heuristics / thumb-rules to evaluate whether a shed-structure has been efficiently designed?

To be specific, I have an industrial shed, 12 m tall, 270 m2 floor area (longest span 10 m)  & the structural design submitted needs approx. 22 tons of structural steel.

Are there any thumb rules to judge if this is reasonably efficient? Or has the designer lazily just submitted an overly conservative design?

Being a non-snow location with no roof access & no winches / gantry cranes the roof loads ought to be really light. Intuitively 22 tons seemed a lot of steel for this to me.

If adding more details or even the entire design would help judging I can do that.

Perhaps others can give me numbers from other projects?


texts: Are there any specific plans for the other parts of the 747s scavenged to make the Stratolaunch carrier aircraft?

texts:
I'm not sure quite how many people are familiar with the Stratolaunch project, so I'll give a quick summary.

Paul Allen and Burt Rutan (of Scale Composites) teamed up a few years ago to create a rocket that would be air-launched from an airplane - in fact, the aircraft with the largest wingspan ever. This airplane, affectionately dubbed "the Roc," will, if things go well, have two fuselages, six jet engines and a 385-foot wingspan.

The airplane took several parts from two 747-400s, including its engines. Wikipedia states

  The aircraft will be powered by six 205–296 kN (46,000–66,500 lbf) thrust-range jet engines, that are planned to be sourced from two used 747-400s that will be cannibalized for engines, avionics, flight deck, landing gear and other proven systems that can be recycled to cut development costs. The two aircraft have been purchased and have arrived on site as of March 2012.

Stratolaunch has two pages on the purchases, but I can only find a small bit of relevant information.

Are there any specific plans for the unused parts of the 747s?

By the way, I believe this is our first aerospace question (and our 100th question!).


texts:
The site states that Tin cannot be welded, but after I made some research, I discovered that tin, when alloyed with copper or used as a protective coating for steel, can be welded.

My question is why pure Tin isn't weldable? What are its properties that made it non-weldable?

I have no prior background to welding and is just starting to study the metallic materials that is used in engineering. I also tried to research answers to this question first before I posted it here, but I can't find anything, if possible could you also include a link/book reference so that I can read it.


texts: Rotating four cylinders with one motor/actuator

texts:
I have a setup with 4 cylinders placed next to each other in following configuration. The cylinders are made of .2mm stainless steel. I would ideally want to rotate them along their axis using a single actuator/motor. What would be the best mechanism to do so?

I'd like to keep the cylinders as close to each other, due to space constraints. Any references would also help.


texts: Show all sides of a solidworks part in a solidworks drawing

texts: I'm new to solidworks, and I built my part and would like to put it into a drawing. Its a small square box-like base with one side of the base having holes in it. When I put my parts into the drawing, it shows 2 sides of the base, a bottom view, and an isometric view, but it never shows the side/plane with the holes on it. My question is this, how do I have a solidworks drawing show a different plane or side of the base?


texts: What purpose do the "angled tabs" on a PCIe bracket serve?

texts:
In the PCIe specification (see page 75), the "short arm" of the bracket has two cutouts; one for the slot that the retaining screw fits in, and another square cutout that has additionally had the sides bent back at a diagonal angle. Actual brackets also have these features. However, at least some slot covers omit the diagonally-angled bends.

What is the purpose of this cutout, and especially, the bent bits?

For bonus points, what is the purpose of the round hole at the opposite side of the bracket that some brackets have, and some don't?


texts: Can I use a water-pump to lower pressure and boil water?

texts:
I'm trying to figure out what kind of pump I should use to boil water at low temperature. Here is my idea of the setup:

The dark blue water comes in, the pump sucks down the light-blue water. This will reduce the pressure in the top, forcing the dark blue water start boiling.

The water then condenses and gets pumped out.

An important condition is of course the temperature of the incoming water. This can be calculated using the Antoine equation,

$$p =10^{\left(8.07131 – \frac{1730.63}{233.426+T}\right)}$$

where $p$ is pressure in mmHG, and $T$ is temperature in degrees Celsius.

I'm trying to figure out what how I can translate the boiling of water to psi. I get confused because as some water gets pumped away, that will be replaced by newly condensed water, thus increasing the pressure again.

I'm assuming I should use a positive-displacement pump. Please let me know if this is a bad idea for some reason.


texts: Do you adjust gas flow rate (SCCM) to volume of chamber?

texts:
If I am carrying out a reaction by flowing 200 SCCM of a gas in a 20mm diameter pipe at 100mm length, if I change the pipe diameter to 10mm:

Do I adjust the mass flow rate of the gases?
If so, how do you calculate this?

Thank you for helping. Looking to learn.
Cheers


texts: The banana clips attach to a multi-meter out of view, the power supply wires are correctly in place, and the resistors are correctly in place. Would putting the red left-hand banana clip and its respective wire into the H15 tie node place the multi-meter in a correct--i.e. series and not parallel--position to measure total current out?


texts: Gear that prevents another gear spinning freely

texts:
My Lego model has a winch on the front. It's a simple spindle with a reel on it with a rubberised cog for winding at one end and two cogs at the other (as shown below).

Is there a technical name for the cog/gear on the blue spindle that stops the cog on the grey spindle spinning freely? Is this a common mechanism in real machinery?

Also, assuming this relies on friction and that the effectiveness will be reduced with wear and tear, how would that be mitigated in real equipment?


texts: Heat Transfer in Different Wire Configurations

texts:
I am trying to create a program which estimates the final temperature of a magnet made of copper wire. I have different configurations in mind, but I will start off with a straight square wire with a circular cooling channel inside of it. Inside runs water which cools it off. The coil is wrapped in some type of electrical insulator. The wire is exposed to air. I am trying to model this using unsteady-state conditions and run it up to a steady state position to calculate the final temperature of the inside (middle if it makes it easy) of the wire, the temperature of the outside of the wire as well as the final temperature of the water coolant.

I have been at this, and coming up with some equations, but I have not taken heat transfer before and am struggling somewhat on this problem. I know that for unsteady state heat transfer

  ∂T/∂t = α ∇^2(T)

where the partial of temperature versus time is the laplacian of temperature times a factor alpha. There are some numerical methods to go about doing this and I am able to include a convective heat transfer coefficient, but I am not sure how to add in the rest of the geometries nor how to include a heat generation term. It just seems like there re so many things that have to be simultaneously solved and I am not sure where to go. I am not sure if the textbook I am reading is not sufficient or if I am not seeing where to go in general. Thanks in advance.

The wire is square with an inner cooling channel. A layer of insulation wraps around the wire which may be neglected for now. I'm trying to reconcile both the convection from inside the wire, the convection outside the wire and the conduction inside the wire. No temperature is fixed which makes this very difficult for me to try to design around.


texts:
What are the tolerance specs on the major diameter of imperial bolts?

Specifically, a 1/4-20 imperial bolt has a major diameter of 0.25in, but what is the tolerance on that dimension. I (and everyone I've asked) have always taken that value to be exact, but that's obviously incorrect.


texts: Why does the thermal boundary layer(TBL) thickness increase with decreasing Prandtl number?

texts:
Consider a liquid flow in which, keeping all else constant, we can vary the thermal conductance(K). Now, if we increase the thermal conductance of the fluid the Prandlt number will decrease. I read that as Prandtl number decreases the thermal boundary layer thickness becomes larger than the velocity boundary layer.
What if we have to compare the boundary layer thickness of liquid with lower K and higher K?Will the liquid with higher K( lower Pr) have thinner TBL than the liquid with lower K (higher Pr)?
I am asking this because I think higher value of K should cause heat to diffuse more easily. If heat diffuse easily then in the TBL the temperature should reach the free stream temperature in a shorter distance. So shouldn't the thermal boundary layer be thinner for higher K.


texts: Is a single large impact better than several small impacts for breaking ice

texts:
I'm designing a device that uses impact to remove ice from sidewalks. I have a question about how to best design the impact mechanism.

I can design it to deliver several light impacts or fewer harder impacts. The energy will be the same in both cases.

Which is the best way to go?


texts:
For a mechanical design, I would need a small/light axle, having high precision (as less loose as possible and reduced drag). With precision, there is not a very strict definition, however, I target ~0.2º of radial rotation (axial movement is not that an issue).

The length of the axle is around 24mm, on which I would attach a few elements (~50g).

The first idea is to use a bearing on each side of the axle, but I am not sure what is the good practice for attaching the bearing.

Following is my current sketch:

The closest example of what I am doing is the axle in the actuator of a Hard-Disk, however, the bearing there is internally tapped for fixation. Most of the bearing I found on the market are not tapped. My feeling is that tapping the bearing is not a good idea.

My question is:

What are the commonly use pieces, practices, terms and fixations for this type of problem?

I understand is a quite broad question, but either I miss terminologies and in any case I did not found answers online. Also, I do not need a deep answer, but some indications of where to look further.

Others possible tags: axle, matched-set


texts: How to prevent static buildup in an electric burr mill coffee grinder?

texts:
Every morning when I get up, I use this coffee grinder to grind beans for my morning coffee.

When I remove and subsequently open the top of the bin, I often find that enough static electricity has built up in the grounds/bin that particles of coffee will literally fly out of the bin and onto my hand and the counter, making a mess. Coffee will also be stuck to the sides of the bin to varying degrees, making it necessary to rap the bin on the counter in order to dislodge the particles from the sides. Of course, more then fly out and increase the mess on my counter.

I have made some observations of a few factors that seem to affect this:

It happens to some degree with most beans, but I've noticed that the darker the roast, the greater the static charge. It's the worst with French Roast (my favorite), which is also oily since they add oil to the beans in the roasting process.
The coarseness of the grind doesn't seem to matter except that a coarse grind produces heavier particles which don't tend to fly as far.
Cleaning the bin had no observable effect on the static.
Waiting a while after grinding doesn't seem to do much to alleviate the problem. I've ground the beans and waited 10-20 minutes before removing the bin and observed no apparent decrease in the amount of static.
It is worse in winter when the air is dry, but I don't really let my house get too humid.
Google reveals that this problem is not specific to any one brand or model of grinder, but seems to plague most burr grinders.

My questions are these:

What is the cause of this static charge in the grinding process?
What modifications can the end-user make to either the grinder or the process to prevent static buildup?
How could this be eliminated in the design itself?


texts: Is a Geodesic Dome (fuller dome) that floats possible? What material or engineering effort would it take?

texts:
Buckminster Fuller has popularized Geodesic Domes (invented by  Dr. Walther Bauersfeld who based it on the use of convex polyhedrons), and thus, making buildings with a very large roofs that don't need pillars.
In popular science magazines it's said that if you just make the Geodesic Dome large enough, it would float by it self because the air pressure underneath the dome would be bigger than the weight pressing it down, and so, it would float.

Question:
Has there ever been an serious attempt to prove that this was theoretically or even practically possible?

In the sense that has there ever been a serious paper published about this, at a university or institute?


texts: Electricity generation via piezoelectric roads, stairways, is it plausible?

texts:
I've been wondering if roads and stairways laced with piezoelectric generators be a viable method in clean energy generation?

I'm currently unfamiliar with all engineering aspects of piezoelectricity except for the fact that it generates electricity given differences in pressure. We generate pressure all the time using our bodies, dropping our feet downstairs, and our automobiles generate pressure on our roads all the time.

Q1. So I'm wondering if current piezoelectrical generators could be able to generate electricity through the transmitted pressure of our paved roads?

Q2. If that is possible, would the generators be able to stand such pressures casually?

Q3. How much electrical generation could I expect from a 50 step stair ladened with such a device?

Q4. If it's plausible in terms of engineering, is it economically viable?

I would love to hear an answer, thanks!


texts: How would one describe the difference between measuring and gauging? As I understand it at my company, we use a fixed tool to gauge something, but we will use a set of calipers to measure something. Is this a correct understanding?


texts: How metal fittings seal connection without rubber gaskets?

texts:
I am well familiar with the concept of gasket. From my non-mechanical engineer perspective, I can understand how a standard rubber gasket works in various plumbing and automotive applications (such as O rings etc). However, working on both auto engines and residential plumbing over years I have noticed some fittings forming a sealed metal-to-metal connection without using a rubber gaskets. Some examples are galvanized or copper unions that look like this:

In metal-to-metal connections like this that require a high pressure seal, what insures that small cracks in the connection (that a rubber O ring would be conforming to due to its soft texture) do not leak?


texts: Please explain this flatbed microwave design

texts:
Here is a Galantz flatbed microwave

The waveguide is smaller than a wavelength.

1)Usually apertures of less than a wavelength are considered to block EM wave but not here, why ?

2)The width of the waveguide is 6 cm and the height about 2 cm, does that polarize the EM waves alonf the 6cm axis  ?

Here's the inside of the oven :

3)What's the purpose of that metal bulge in front of the magnetron output ?

Here's the bottom of the oven, the ceramic plate is lifted to reveal the wave stirrer

The wave stirrer is removed to show the opening for the waves entry and the shaft of the stirring plate

4) can you explain the geometry of the disk and the reason designers chose to make the waves enter the oven from below the stirring disk?


texts: If I have a water pump positioned horizontally where the diameter of the inlet and the outlet of the water is equal: Din = Dout. If the volume flow rate is know experimentally by measuring the time taken to fill a container with a known volume. Is it possible to calculate thrust force of the water pump based on these information? If possible how? If not why?


texts: Do linear actuators need to stay powered once in place? If not, how can I lock them?

texts:
I want to build a small remote-controlled submarine, and have been thinking about how to handle the ballast tanks. The simplest option seems to be a piston shaft, which fundamentally needs some kind of (sealed) linear actuator with sufficient force to overcome water/air pressure at reasonable depths (say 0m to 50m).

The problem is I don't have an infinite supply of power available on-board and all the linear actuators I found use ludicrous amounts of it, such as over 1 amp at 12 volts... but I only need to move the piston every now and then, most of the time it just needs to sit wherever I tell it to and not move.

My question is, once  a linear actuator has been "actuated" into place, can I de-power it and expect it to hold up to its maximum rated load? Does it depend on the design of the actuator? If not, what are some engineering approaches I can use to mechanically lock the piston into place until I need to unlock it, so that I can trade off precious electrical power for mechanical strength?


texts: What are the meanings of `B.C. 3/8"` and `6-11/32"`?

texts:
I'm totally ignorant in this area, and probably didn't know how to properly google my question - sorry..

I found this specification here: (https://si.shimano.com/pdfs/ev/EV-RH-IM10-2045B.pdf). My guess is that M10 is the about the metric thread specification (https://en.wikipedia.org/wiki/ISO_metric_screw_thread). But what is the meaning of B.C. 3/8" then?

Another question about this spec: (https://si.shimano.com/pdfs/ev/EV-FH-2200-2202B.pdf) - what would be the meaning of 6-11/32" - it can't be a range, or can it?


texts: What is the advantage of statically indeterminate structures?

texts:
Most of the real life structures are statically indeterminate.

What is the benefit of designing a statically indeterminate structure instead of a statically determinate one?

I don't mean only beams and trusses.Per example, the shaft of a merchant vessel is considered as a typical statically indeterminate structure.


texts: What allows a lock to be unlocked from the inside without a key?

texts:
I understand how a pin and tumbler lock stops you from opening the door unless you have the key that aligns all the pins with the edge of the plug, allowing it to turn. But I can't find anywhere how the opposite side of the lock works!

How does turning the lock from the inside unlock it if the pins are blocking the plug?


texts:
Alright, for this data is it correct to get young modulus as 16GPa please and resilience as 14j/mm^3??
For resilience is it just 1/2(stress)(strain at yield)?
Stress is first column in MPa
Cheers lads
[![stress is first column in MPa  ][1]][1]
[1]: https://i.stack.imgur.com/Zy26y.jpg![enter image description here](https://i.stack.imgur.com/DdUou.jpg)


texts: Fluid energy mills with powdered reactive metals

texts: Can fluid energy mills manufacture spherical powdered metal of size ~5 micrometers in cases where the metal is quite reactive, like with lithium and aluminum, if the fluid used is a non reactive gas like argon or helium?


texts: Pipe diameter, Flow Rate, Pressure & Velocity for water

texts:
I am hoping for some help with calculating the size of pipe for a given length.
The system design is a 10000L supply fills a 5 tonne water tank that then feeds a variable speed pump. The pump sends the water around a 150M loop/ring of pipe then returns to the 5 tonne water tank. The return pipe will be approximately 600mm from the inside base of the tank, so it will be in the water creating a closed loop.

I need to move the water at a velocity of above 4.5 m/s to decrease biofilm on the pipe surface. along the 150M loop there will be 4 take off points, 1 of which requires 2000 l/h output, the other 3 require 500 l/h output. So if they were all open at the same time a total of 3500 l/h is required. However in the future the loop/ring will be increased to double its size to 300M with similar outputs, so a total of 7000 l/h.

How can I calculate the pipe size for:
A - 3500 l/h @ 150M lenght (with bends)
B - 7000 l/h @ 300M length (with bends)

Also once A is calculated, would increasing the pump speed and pressure increase the flow rate to achieve B?

I think the math will be a bit beyond me, so please can you go gentle with me.


texts: Difference between verification and validation

texts:
The words "validation" and "verification" frequently appear when reading the results of a paper. A Google search of these words left me even more confused:

verification: The process of establishing the truth, accuracy, or validity of something.

validation: The action of checking or proving the validity or accuracy of something.

Example: I constructed a mathematical model of real-world system. I compared the model results with actual values and found that the model had an acceptable error.
Did I verify or validate my model?


texts: What's the process for starting an ISO or IEEE standardization?

texts:
So, I just saw this question on the Statistics SE site, about how in artificial intelligence/machine learning some people use a particular set of terms in one way, and other people use the same set of terms in the exact opposite way. It got me thinking that this confusion might be resolved if there was an official standard by a body like the ISO or IEEE regulating things.
So, what's the official process for starting the process of creating an IEEE or ISO standard? If you wanted one of these big engineering organizations to make an official standard on the topic, what would you need to do?


texts: Is there any application of control engineering to the study of algorithms stability or computer science theory?

texts:
I am an undergraduate student in Electrical and Computer engineering. In our 5th semester we have a obligatory "Introduction to control systems course". I was wondering if these bunch of math theories is applicable to other directions of my school rather than the obvious (in the next semester we choose majors and there is one called signals and automation which basically involves every "advanced" control theory module, but I want to know if it is useful other than that).
I like the ideas of the course, but I am not really into the hardcore applications of it. I think I want to follow a more theoretical path which involves math applicable to computer science. So if I do not go for the "automation and signals major" but into computer science, hardware and math major, is there any chance I find it useful? For example because it involves the stability, I have seen some advanced graduate seminars where people talk about the convergence of algorithms ...maybe some control theory theorems are useful there?


texts: Rapid acceleration and deceleration of Space X's BFR

texts: Given that momentum is the product of speed and weight (Velocity x Weight) would rapid deceleration or acceleration in weighless space, of Space X's BFR have an impact on its passengers. I ask because if it is to travel at 27000km/h most of its journey would be spent accelerating and decelerating very much limited by earthlike g forces as airliners do, therfore minimizing on the reduction of travel time. Would most of the braking and accelerating have to take place in space at zero gravity?


texts: Screw Cap design for high pressure surge vessel

texts: I'm designing a pressure vessel with a relatively large cap that provides access into the vessel, what recommended thread specifications is needed to maximized locking and safety against faliure or popout.


texts: How can I find the emission power of a WiFi mobile phone antenna?

texts:
I need to find the emission power of a WiFi mobile phone antenna. I have checked the IEEE 802.11 specifications but it says that the power transmission is variable and depends on the mobile phone fabricant and power saving options.

I also searched for information about some specific mobile phones but the datasheets available on the Internet seem quite weak and do not say anything about WiFi power transmission.

Is there a complete datasheet of mobile phones? How can I determine the transmission power in the WiFi antenna of a specific mobile phone?


texts: Exact anlytical solution for beam-lifting problem constrained by crane capacity

texts:
I have been trying to calculate the analytical solution for the following problem but have not succeeded to reach an exact solution. Can anyone propose a way?

A concrete beam is to be lifted by two cranes. The beam is 20 m long and weights 900 kN. The cranes have lifting capacities of 500 kN and 400 kN. What are distances $a$, $b$, and $c$ in the scheme below so the cranes are not overloaded? (position of cranes are marked with | |)

            <---- a----> <----- b -------> <--- c --->
            ===========================================  <-- the beam
                        ||                ||
                     A = 500 kN        B = 400 kN

A & B: reaction forces of cranes
distributed self weight q = 900 kN / 20 m = 45 kN/m
$a + b + c = L = 20\text{ m}$

The beam is statically determinate.

My attempted solutions:

I started from the equilibrium equations of the sum of bending moments about the left and right ends which are equal to zero:

$$\begin{align}
\sum M_{left} &= 0 = Aa + B(a + b) = \dfrac{qL^2}{2} \\
\sum M_{right} &= 0 = Bc + A(b + c) = \dfrac{qL^2}{2}
\end{align}$$

A third equation is needed; I have tried $a + b + c = L$, but I arrive at the "apple = apple" situation, which implies that the three equations are not independent.

I also tried to add an additional constrained by putting any of the $a$, $b$ or $c$ values equal to a constant value. The issue then is that each of the equilibrium equations become dependent on only one of the two remaining unknowns, as in the following case, where I have put $b = L/3$:

$$\begin{align}
\sum M_{left} &= 0 = \dfrac{qL^2}{2} = Aa + B(a + L/3) \\
\sum M_{right} &= 0 = \dfrac{qL^2}{2} = Bc + A(c + L/3)
\end{align}$$

And thus, each solved unknown will not satisfy the other equilibrium equation.

I have run out of tricks in my sleeve ...


texts:
I am looking for the following mechanism:
A pair of gears initially in side-by-side arrangement.
The shaft of the first gear is fixed to a first plate. The shaft of the second gear is fixed to a second plate.
The first and second plate are connected by a hinge. The plates are initially in a flat side-by-side configuration. The shafts are initially parallel.
The first plate is held stationary. The second plate moves freely on the hinge.
As the first gear is rotated it rotates the second gear. It also pushes on the second gear causing the second plate to pivot on the hinge.
As the first gear rotates through a partial turn (e.g. from 0 to 120°) the second gear also rotates through an equivalent partial turn (e.g. from 0 to -120°). As the gears rotate the second plate pivots a small angle (e.g. from 0 to 40°). Thus the shafts of the gears are parallel in the initial position and tilted relative to each other in the final position.
Is such a mechanism known or possible?
Here a rough illustration of the idea:
[
[


texts: How to calculate heat and mass transfer rates from an enclosed box?

texts:
I'd like to know if it's possible to calculate the heat and mass transfer rates from a small volume to the environment.

Let's assume there is a box with a small opening at the top. The air inside the box is hot and humid (65 °C and 100% relative humidity). The air outside the box is cooler and drier (25 °C and 50% relative humidity).

How should I proceed? I've tried using Fick's law of diffusion but the rate of transfer was too low. There must be something I am missing. I've thought about free convection but it does not fit for my situation I guess. Could Boussinesq equation be used?

Thanks in advance for any help.


texts: Can an embedded system be designed to support electrical manufacturing testing?

texts:
Background
Desktop computers and laptops can be configure to dual boot. Example: Ubuntu and Window on the same computer/laptop.

Question:
Can a similar concept be applied to embedded system? If so this can greatly benefit electrical manufacturing testing. Electrical manufacturing testing depends on high throughput. So booting a complete for example Embedded Linux system is not efficient and almost never done in electrical manufacturing test environment. So with some type of electronic switch/signal (may be provided by the tester) is possible to load very fast a minimalist set of software that already program to the processor that will enable testing of the board. For example verify the external crystal (XT) is correct and functioning.

Per @ouflak comment: I am aware of a particular NEC V850 micro-controller based application, where all micro-controllers were programmed using a gang programmer before been placed on the PCB board. During Electrical manufacturing test, the tester would force micro-controller to load very small program and communicate to the PCB board via the CAN bus to activate sections of the embedded system for testing purposes.

Similarly I would like to investigate how a beaglebone black like PCB running Android architecture/design can be modified to boot from a section of the flash for electrical manufacturing test only. There is no point loading and testing the graphic controller for TI Sitara as vendor TI as already done perform this function. All that is need is to test and verify the PCB manufacturing process.


texts:
A way to find the modes propagating in a resonator of length $L$ is to write the field as $E(x,y,z)e^{i \omega t}$ and calculate $E(x,y,z)$ inside an equivalent periodic lens structure. Then imposing self consistency on the round trip $E(x,y,z+2L)=\sigma E(x,y,z)$ we find modes.
Can you explain the concept behind this technique, for example, what is the meaning of E(x,y,z) when $z>2L$?


texts: How to determine the banking angle of a quadcopter/helicopter due to unbalanced load along the X-axis?

texts: What theories/equations can be used to determine the banking angle of a quadcopter/helicopter due to unbalanced load, given that the load will only shift along the X-axis


texts: force required to bend .375 thick aluminum tab

texts:
We are trying to determine the force that was needed to bend an aluminum tab on a piece of our aircraft equipment.
The tab is deflected 2 inches and is 3 inches in length.    load was at the tip (3 in moment arm)
Material is .375 in thick, 1.5 width and as mentioned was 3 inches long, with the load hitting the end.   load was cantilever.    6061 aluminum


texts: Is activated sludge process efficient for industrial waste water treatment ? why if isn't?

texts:
The main raw water has following parameters, water comes from a soap manufacturing factory

pH 7.1
BOD 520 mg/L
COD 4890 mg/L
TSS 360 mg/L
No Oil & Grease

if you need expected treated effluent data
 - pH 6.5-8.5
 - BOD <50 mg/L
 - COD <30 mg/L
 - TSS <250 mg/L
 - Oil & Grease <10 mg/L

Is activated sludge process efficient for industrial waste water treatment of this kind of raw water? what are the reasons if it isn't a good way to treat such raw water. Any recommendations with reputable sources such as research papers etc?

my proposed process is initial sieve filtration --> airation --> addition of floc (bacteria and protozoa) --> settling tank --> gravity filtration

I'm really new to this and trying to understand it.

please letme know if I asked it in a incorrect way. thanks


texts: How does expanding gas in isobaric process move a piston?

texts: If we have a simple adiabatic cylinder with a piston on top and we heat the gas from the inside, the gas starts to expand and move the piston up. This process is isobaric; but if the pressure on the piston doesn't change, how does it move up?


texts:
I have a load of almost 15 kg.
Both the pulley diameter = 0.6m
Distance between the center of both the pulley is 0.8m.

Loads are permanently attached to the belt.

i will use a HTD belt for this system.

Can anyone help me find the torque required for the motor?
Thinking of using a stepper or servo motor to rotate it in steps of 10cm.

i dont have any knowledge about the frictional losses


texts: If I made a incandescent light bulb filament smaller what would happen?

texts: If I took the filament in the bulb and made it smaller, and also increase the thickness of it, what would happen?


texts: Calculate heat transfer for a partly hollow cylinder?

texts:
What is the general approach for calculating the heat transfer through a body? In this special case I want to calculate the $\Delta T$ (i.e. the temperature difference between the side and the top/bottom) for a given $P_{heat}$ through the following cylinder:

The heat power is applied on the side of the outer cylinder (equally distributed), and is distributed both on the upper side and on the lower side of the cylinder. Without the trench in the cylinder I know the formula, but how does it change with the trench? (The trench is not going through the whole cylinder, only through half of it resulting in a common base).
The formula for the whole cylinder is with $S_m$ the average way from side to the base, $A_Q$ the area covered by the heating source on the side, $A_B$ the area on the bottom of the cylinder and $\lambda_{Al}$ the heat transfer capacity:
$$\dot{Q}=\frac{\lambda_{Al}\cdot(A_B-A_Q)}{S_m\cdot\ln\left(\frac{A_B}{A_Q}\right)}\cdot \Delta T$$
Btw., is that formula correct, or are there other ways to calculate that?


texts: How can "mpg" be high under low engine load?

texts:
Let's say a car at 60 mph requires roughly 20 hp to maintain its speed (i.e., to overcome rolling resistance and drag).

If this car makes 240 hp and gets about 34 mpg (not too unrealistic), how is it getting 34 mpg if the engine is only at 0.05 efficiency? I know modern automobiles are supposed to have an efficiency limit near 25-30% thanks to Mr. Carnot:

Chart from here.

I feel like gearing must be part of the answer but I'm having a hard time understanding just how the gearing allows the engine to generate 20 hp while clearly be at a higher efficiency than indicated on the chart for low engine loading.

Maybe I'm not getting exactly what the engine loading is referring to?


texts: What's the difference between thermocouple grade and extension grade wire?

texts:
We got a bunch of yellow thermocouple wire which the Omega web site says is type K extension grade wire. They also sell thermocouple grade wire which looks to be brown.  What's the difference?

I was speculating that the thermocouple grade is super pure and gives voltages that are in agreement with what's expected and extension grade will need to be calibrated but probably won't be too far off.

Does anybody have an experience with this?  How far off will it be?

Thank you for any ideas.


texts: Hydrostatic transmission to directly translate movement

texts:
I have been thinking about small hydrostatic transmission to directly translate movement of stepper motor (NEMA 17-23 size, geared with 3:1 or 5:1 ratio).
My design currently involves 2 identical radial piston motors/pumps with 3 cylinders all connected to central crankshaft and individual hydraulic lines connected pair of cylinders (pump<->motor), so there are no extra valves, reservoirs, etc.
Each hydraulic line (3 in case of 3 cylinder pump/motor combo) is filled and purged separately, after that it should be (theoretically) sealed maintenance-free system able to precisely translate bidirectional movement of pump-driving stepper motor to actuator.
There will be obviously friction losses, but given that continuous power requirements for the whole system are quite small (4-5W) and the driving motor has safe max operating power level at least ~5 of that, it should be ok.
Rough sketch of the concept (pump/motor internals like conrods/crank not shown):

Do you see something obviously wrong with the design, why it won't work as envisioned ?


texts: How to make holes in granite without electrical or iron tools?

texts:
I see granite blocks in ancient Egyptian temples with perfect holes drilled into them. The historians say at that time (2500BC) they did not possess iron tools or the wheel and certainly no electricity. The most capable metal tool was made of copper.

One theory suggests that a two-man saw with a flat copper blade was used to make horizontal cuts in granite by throwing sand at the cut line; the silicon quartz pushed by the blade make cutting granite possible. But this process yields something like a 1/2 inch deep cut after many hours of sawing (impractical).
I assume they may have employed a copper hole-saw or tube-like tool using the above method. But it still seems very tedious and impractical.


texts:
Sutherland's Law seems to be a fairly well-accepted relationship between dynamic viscosity and temperature and was originally created to work for ideal gases, though it is often extended to be used for atmospheric air.
$$
\mu = \mu_{ref}  \frac{T}{T_{ref}}^{3/2} \left(\frac{T_{ref} + S}{T+S}\right)
$$
$T_{ref} =$ reference temperature
$\mu_{ref} =$ viscosity at $T_{ref}$
$S =$ Sutherland temperature
My question is there any data or evidence to show that this formula is applicable for other gas mixtures and if so, what type of error should be expected?  Also, I'm not totally sure what the Sutherland temperature is here
My specific application is in the development of lifting surface designs for Mars and for Titan atmospheres which are very much not representative of Earth's.


texts: How much foam is required to fully absorb the impact of dropping a barbell?

texts:
I’m working on a project for my home gym. I want to be able to drop a loaded barbell without bothering my downstairs neighbors. My main approach is to use 2 blocks of dense foam on which to drop the barbell (when loaded with weights, barbells have 2 contact points to the ground). Ideally the foam absorbs the full impact of the weights, letting no vibration travel through the the floor.

I’ve learned that dense foam is expensive! A 4” tall block of decent foam costs $106.

To help me determine what material to buy, is there an equation that calculates how much force foam of a given density and thickness can absorb, without any force passing through to the floor?

Some initial values:

Assume barbell weighs 250 lbs, so 125 lbs dropping on each foam block
Barbell is dropped from 72 inches above foam.
Foam comes in densities of 0-8 lbs per cubic ft, escalating in price substantially.
The contact point between barbell and foam pad is the width of the weight plates, an average of 7 square inches.

I’m looking for a way to find the optimal trade off between foam density and thickness. For example, a dense foam costs more, but requires less volume to absorb impact.

Thanks for any assistance!


texts: How do electric vehicles' motors run at high speeds above 10000rpm?

texts:
For example, for a squirrel cage induction motor, the speed of operation is given by
Ns = 120*f/P
depending on the number of pole pairs and supply frequency. Now the supply frequency is 50/60Hz while the minimum number of pole pairs is 2. This limits a squirrel cage induction motor to a maximum speed of 3000/3600 rpm. However, Tesla's AC induction motors can run above 10000rpm. How is this possible?


texts: How to create an algorithms for fitting a network of tubes into a cube?

texts:
How to create an algorithms for fitting a network of tubes with a range of diameters into a cube, with maximum volume in the tubes? Assume:

30 cm minimum square side
1 cm minimum pipe diameter
1 mm pipe wall thickness.
Cube edge length $L$
number of different diameters $n$
volume Pipes $= \pi r^2\times\text{length}$.

The tubes form a network in the sense of a continuous network of connected Tubes.

Tricky parts:

Finding the ideal number of different radiuses of pipes to use.
accounting for curves in the pipes. May be worth assuming straight pipes with U-turns at the ends? Obviously square pipes would be ideal. But we are restricted to circular pipes.

Best to break down the problem into components:

assuming (one) 1 cm diameter pipe, how to fit most volume pipe into 30cm cube.
assuming (multiple) diameter pipes: 1 cm and 5 cm diameter pipes, how to fit most volume pipe into 30 cm cube.
how to determine the optimal number of diameters
i. given limited number or radii,
ii. given unlimited number of radii.


texts: How can I model beam column connection that doesn't connect at centerline?

texts:
In direct stiffness method, the beam and column connection are  assumed to be done through center-line beam and column:

And hence we can represent them easily using frame elements ( 1D element) and do not have to model the surface contacts or using area elements.

However, in reality, beam and column may not always be connected via centerline: eg: such configuration is not uncommon

It is easy to see that the offset of beam shall induce additional moment on the supporting column.

How should I modify my stiffness matrix in order to accommodate the offset of beam from the column center location? The frame representation of beam and column is just too convenient to give up.

For the purpose of this question, assume that I am writing a frame analysis software from first principle ( yes, from the equations on the wiki page that I link to), and hence can't make use of any existing software package


texts: Which will require more force? small or big scissors?

texts: Which will require more force (kgf)? small or big scissors?


texts: Can concrete lose strength during curing?

texts:
We cast a bridge's concrete deck and kept samples for concrete strength tests at 7 and 28 days.

We took a test at 7 days, and the test result were over the design strength (designed for 30 MPa, result was 33 MPa). The control engineer insisted that we have to also do the 28-day test.

This seems pointless to me, as I believe concrete gains strength during curing, and doesn't lose it. Can the results of the 28-day test be worse than those of the 7-day test?

I am asking this question because I want to get paid for the job. The control engineer (who signs the documents) is the one who is insisting that we have to wait until the 28-day test.


texts:
QUESTION

For a business project, I'm looking into the viability of a greenhouse situated in Canada's far northern town of Iqaluit. The problem is how to mathematically simulate the internal air temperature of the greenhouse.

WHAT I ALREADY HAVE

detailed 3D renderings of the greenhouse
all materials with their corresponding thermodynamic values such as K-values
climate data that shows the approximate intensity of solar radiation in Iqaluit, angles of sunlight throughout the day and hourly temperature data.
data for the required environment for certain crops to thrive, such as humidity, required sunlight, temperature fluctuations, pH, etc.

CONTEXT

What make this greenhouse investigation unique is that the greenhouse is a much smaller affordable design that is meant to grow a small supplementary source of fresh produce for low-income families which often suffer from food insecurity in northern towns such as Iqaluit due to prohibitively high costs for fresh produce.

We would also like to strive for simplistic, mechanical systems that are easier to maintain and less prone to failure. A major concern of the group as of now is by how much could the internal air temperature plummet by at night?

GOAL

The goal in mind is to use the information we have so far to determine:

Is it possible to grow vegetables such as leafy greens within the current design WITHOUT an external power source other than sunlight? (A greenhouse that does not require electric heating is a major goal) How does the internal air temperature vary with the current design?
In the case that the current design is not sufficient for healthy crop growth, what modifications are necessary? (Many potential solutions have been considered):

Have a solar powered heater that charges through the day and intermittently provides heat through the night.
Greatly increase thermal insulation surrounding the greenhouse through the use of a thick air-inflated wrap that surrounds the entire structure in addition to thicker polycarbonate panels for construction.
Use a setup of concave reflective panels surrounding the greenhouse to increase the amount of heat collected during the day. I have already done some calculations but my numbers ended up far off. Equations I have worked with so far are $Q = mc\Delta T$ and $\dfrac{Q}{t} = \dfrac{A\Delta T}{\text{Thermal Heat Transfer Coefficient}}$.

CONCLUSION

I think the problem demands looking at every single material and also examining the characteristics of the air inside as an ideal gas, as well as the poly-carbonate and it's emissivity/albedo (black body) characteristics.

Any steps or hints in the right direction with equations or methods of calculation would be greatly appreciated!


texts: What causes opposite motion in Newtons third law. Or is the mottion matter independent?

texts:
For every action, there is an equal and opposite reaction. Sample case me doing a push up I force myself to move up by pushing against a rigid body ( the floor ).

There goes I can not push myself sideways by thrusting my hands forward but as the case of a pushup. Or if I hit the water with an open fist it feels painful because the movement causes the liquid to feel like a rigid body( instantiating rapid opposing motion on a body ).

So with that, moving to rockets, their motion ( in earth ) is caused by a heavy surge of air simulating the hard body ( with the open fist slap on water logic ) and when enough causes the rocket to move in the other direction.

My current logic in this argument is for the opposite reaction to occur, there is an opposing opposite matter that causes makes the opposite reaction to recache in the other direction?
As I am trying to understand how something would move in a vacuum. In the case of a bird also it pushes air down for it to go up... My mechanical physics is not that great I am tackling this in a more logic-based approach.So, a case scenario definition of all the definitive forces and direction of reaction would be well appreciated and is this logic correct ( for a motion to occur there must be something resisting movement ).


texts: How can large bridges be made resistant to earthquakes?

texts:
How can large bridges, with spans on the order of 1 km, be made resistant to earthquakes?

I'm no expert on quakes, but there are at least two kinds of shaking: lateral and vertical. The vertical shaking in particular really worries me. I don't know how any kind of shock absorbtion can be built into a massive, tall structure like a building or bridge tower.

(I was originally going to ask about suspension bridges, but then I read that suspension bridges are not great for heavy trains. The background of this question lies in my exploring the idea of a Bering Bridge (from Alaska to Siberia, crossing the Bering Strait), which would be primarily a train bridge. And it would need to handle freight trains, the heaviest of all sometimes exceeding 100 tons per car.)

So I will just ask the question about large bridges in general.

I think the largest quake in Alaska was a 9.4 Richter Scale in 1964, hitting Fairbanks. (I don't know how to convert to Moment-Magnitude scale). Is it possible to build large bridges that won't collapse from that? Ideally, we want the bridge to not collapse during a quake even if it's under full load.

P.S. I know it's not cost effective to build such a bridge. For one thing, far east Siberia has no rail network (or much civilization in general). There was a tunnel project proposed which I think they said was cheaper than a bridge, which I couldn't understand because digging through tough rock seems a lot harder than driving a pile in 50-m deep water. The tunnel project was suspended IIRC, no surprise.

Anyway, I'm just exploring if such a bridge is technically possible and can be quake-resistant. If you need something closer to reality, I suppose we can look at the Golden Gate Bridge in San Francisco. I saw here they were working to make it safe in quakes up to 8.3, but it didn't go into the details. And keep in mind the Golden Gate Bridge does not handle freight trains.

Anyway, is it possible to quake-proof or seriously resist quakes in large bridges loaded with a freight train? The bridge would not necessarily have to remain completely undamaged. I just don't want it to snap and drop the train in the ocean.

Is this possible?


texts:
If my understanding is correct, Roe averaging is supposed to be a linearization of the nonlinear flux jacobian.  For the Euler equations, one can compute the roe average as depending on density, velocity, and enthalpy.
Why is it enthalpy?  How would I derive that from a parameter vector approach, and how would I compute a different roe average for a system that is fundamentally different from the Euler equations?


texts: How do I physically protect solar panels from snapping when dropped?

texts: I am creating a system that I drop from 20m to the ground and I want it to be solar powered. Weight is an issue so I am trying to minimise it as much as I can. How can I ensure that the solar panels remain intact and don't break upon being dropped if they are attached to this system? I was thinking foam insulating to both hold it in place and absorb the force, but are there any other suggestions?


texts: How to determine the number of effective anchors in a base plate?

texts:
The situation is a steel baseplate that has to be anchored to concrete to resist lateral loads.

The lateral load on the base plate is great enough that more than one or two anchor rods are required. The base plate has room for 8 anchor rods.

The holes in the base plate will be somewhat over-sized per AISC to aid in setting the base plate over over the anchor rods. The anchor rods have already been cast into the concrete. The nuts on the anchor rods will not be tightened enough to consider the connections to be slip-critical. There will be some movement of the base plate required before it engages the anchor rods.

Variations in the placement of the anchor rods and the hole locations will mean that not all of the anchor rods will be engaged at the same time.

In this situation, how do you determine how many anchor rods can be considered to be effective in resisting the load? The number of anchor rods will directly effect the size of each anchor rod.


texts: What is the name of my feedback procedure in control system that I am using?

texts:
I have created a self balancing robot. It uses PID control to control its pitch angle and gets the feedback from gyroscope and accelerometer. But I have not used any sensor to feedback the displacement to the controller. I have just approximated the voltage applying to the motor to the displacement through programming (let suppose 5v to the motor will make the motor to rotate for 1 rev/s and after integrating it , it will give the displacement covered). Through which I was able to maintain the robot at a single position. But now its time write the report and I do not know what to call this type of feedback of displacement.
Thanks


texts: How fast can Jansen's linkage driven walker go?

texts: I've seen videos of Theo Jansen's linkage driven walkers, and they all walk really slowly. Is it because they want to showcase leg movement or these things actually can't move fast?


texts: Different results for every cloud compare aligning module

texts:
I have tried cloudcompare and the aligning ICP module like this:

and give transformation matrix lie this:

For one STL file twice and get different result for under 0.1 value in max distance like show at below pictures:
first one :

Second aligning try:

The above cloud compare bin file could be acceptable from here.
so i like to know why this difference in results happen? does every time which i use align module it create different transformation matrix ?
Question asked also here:
https://www.cloudcompare.org/forum/viewtopic.php?f=9&t=4625
Update:
My guess is that happens because of difference between The reference STL points and the aligned target points, which  here for reference is almost 26,000 point and target almost 200,000 point. which needs to select random point based of reference points in target STL file for aligning.
Thanks.


texts: I have mode shapes and eigen frequencies from FE simulation. I have modal matrix and eigen frequencies corresponding to each mode. The mode shape is mass normalized.  I am required to correct each mode for  damping, i.e to add 1% modal damping to each mode. Can anyone help , how can I add 1% modal damping to each mode.


texts: How to improve a PID control loop by adding feedforward?

texts:
Assume you have a system model that is controlled by a PID controller (feedback). You want to add feedforward to improve the characteristics of the controlled system. How can you design the transfer function of the feedforward?
(Cf. this image)

On slide 18 of this presentation, it is suggested to use a gain and a lead-lag filter:

  K*(T1*s+1)/(T2*s+1).


texts: Will expanding metal disrupt my motion sensor?

texts: I am trying to install a door motion sensor in a environment that will get very hot for our work. So the door could heat up to temperature of 150-200°F. We built the frames and door to handle the expansion but what can we do about the motion sensor? In guess with temp that hot it will expand causing the alarm to constantly go off.


texts: What should I learn/study to start building ROVs (remotely operated underwater vehicles)?

texts:
I'm a software developer with no experience in building physical devices/hardware.
I did ~15-20 beginner-to-medium-level projects with Arduino (following some tutorials), but I wouldn't count this as an electronics experience.
Even though most of my life I've been developing software, I've been always passionate about the idea to build some physical device which would somehow interact with surrounding environment.
I've just got some free time from my work (about 6 months) which I would like to dedicate to some project. Ideally, I would like to build some simple underwater vehicle which I could control from outside and which would be able to do, lets say a photo while being underwater.
My question is basically where do I start? What kind of knowledge is actually required for building such a device? I believe my path should be something like:

Quick recap of school algebra classes
Quick recap of school physics classes
Dive into Electronics
Learn about how to do the communication with underwater device (some isolated cable should work I guess)?
???

I'm also trying to understand how do I build (or I just buy?) the parts for the vehicle. How do I learn to build something that can swim underwater? Could you please give me a direction?


texts: How/where to take moments to solve a static equilibrium equation

texts:
A 200×250 mm panel of mass 20 kg is supported by hinges along edge AB. Cable CDE is attached to the panel at C, passes over a small pulley at D, and supports a cylinder of mass m. Neglect the effect of friction.
For those who cannot see the picture. The axis are oriented as follows, x+ is pointing out and to the right, y+ is pointing up and z+ is out and to the left.
$A=[0,0,.25]$ $ B=[0,0,0]$ $ C=[.2sin(\Theta),-.2cos(\theta),.125]$ $ D=[.2,.1,0]$
I have $\sum F_x=0=A_x+B_x+\frac {mg}{\lVert CD\rVert}(.2-.2sin(\theta))$
$\sum F_y =0=A_y+B_y-192.2+\frac {mg}{\lVert CD\rVert}(.1+.2cos(\theta))$
$\sum F_z=0=A_z+B_z+\frac {mg}{\lVert CD\rVert}(-.125)$
I am having trouble deciding where I want to make my moment in order to create a system I can solve for m in terms of $\theta$.


texts: Sunlight-powered device set to change world: will it work?

texts:
Vast areas of desert sand are being shone on upon by the sun. Now that's some ENERGY!
Using this proposed apparatus:

Sunlight over large area is concentrated on steam chamber, where water turns into vapor.
The high temperatures of the gases in the steam chamber will push on the loose piston, compressing the air above it right into the air canister.
Air canister is carefully sealed and removed from the apparatus.

The air canisters can then be used for refrigeration, as placing them inside an insulated chamber (the "fridge" with food in it) and releasing the gas outside will significantly reduce temperatures. Repeated with enough canisters, I believe the internal temperature of the "fridge" can reach below 0 degrees Celsius temperatures?
Can some kind soul explain to me the efficiency and possible limitations of this apparatus?


texts: Light transmittance of acrylic with temperature

texts:
I have a 2 mm piece of UV transparent acrylic sheet. The datasheet defines it as 80% transparent at 300 nm. However, when I use it with different temperatures (4-50°C), the transmittance characteristics are totally different. It is much more transparent at higher temperatures.

Does anyone know if this is true - that the light transmittance of acrylic varies with temperature? And what might be the reason?

To be more specific, I am interested in the 250-600 nm wavelength range.


texts: Degrees of Freedom for Complex Pulley Systems

texts: I'm trying to understand DOF clearly, but this pulley system has me doubting myself. When I try to determine the degrees of freedom, I sum the DOF of each object, and subtract the constraints. for this system, I have four pulleys (1-4, in order of the masses, 1 2 4 3 left to right, not labeled on the diagram) and four masses. That means there are a total of 8 bodies, all restricted to 1 DOF motion each, so 8 DOF for the bodies. However, I understand that the motion of pulley 3 is constrained to mass 3, and pulley four is constrained to mass 4. There is an additional constraint in that the rope is constant length. This would lead to 3 constraints, and 5 DOF, however, I believe there are further constraints that I am missing, namely between the pulleys and the masses attached to the rope directly. What is a good methodology to determine the DOF of this system?


texts: How does a cable-laying ship retrieve a partly-laid cable?

texts:
I was reading an article in the press this week about a project to lay an undersea cable across the Tasman Sea. The ship had had to return to port for repairs and return to complete the job later.

This got me wondering: how does the ship secure the end of the laid cable, and how does it retrieve the cable to continue the cable-laying operation?

In this instance it was a fibre-optic cable for telecoms use - would there be differences for other cable types?

Similarly, I imagine that very long cable runs (e.g. trans-Pacific) would need to be laid in more than one piece. Would similar techniques be used, or would some different approach be used for planned breaks?


texts:
A pretty simple question, but one that's weirdly confusing me:

I'm working with an equation for total water demand (Q) were w is the allowance for water wasted. w is typically 30%. Most books therefore present the equation (I'm simplifying it here by replacing the bits irrelevant to my question with x) to...

$$ Q=x(1+w) $$

The first equation makes sense to me. One book (also by a recognized authority on the subject) however factors in the loss in efficiency this way:
$$ Q=\frac{x}{1-w} $$

Could someone help me reconcile the two?


texts: How to ensure uniaxal and uniform force application on uneven samples using pressurized fluids

texts:
I am trying to apply a compression force to samples using air. I do not want to directly apply my loading since my samples are irregular. I do not wish to process them with a flattening step. I hope to use fluid and pressure to get a single compression force with even distribution across the surface. In the left example I have a spacer that has a negligible poisson's ratio so i will neglect expansion orthogonal to the applied pressure. In the right hand example I would have pressure on the side correct?

Based on the cartoon below I am hopping to have the pressurization of the air transfer to the samples. Assume the vessel is air tight with the exception of the flow restriction to control pressure levels.

Can I make this assumption?


texts: Strand layout in prestressed concrete girders: is a partially filled bottom row acceptable/advisable?

texts:
My state (USA - Nebraska) uses "NU" type prestressed girders (though the question should equally apply to all geometric variants of prestressed concrete "I" girders).

There are 6 "rows" available for the prestressing strand. Moving from the bottom row upward, a maximum of 18, 18, 12, 6, 2, and 2 strands can be accommodated in each row.

I understand that theoretically the most efficient design will result when the rows are filled from the bottom up.

Virtually all the plans I've seen fully fill that bottom row. However, I consistently run into cases where I'm not inclined to fully fill the bottom row.

Case 1. I need less than 18 strands total.

Case 2. I need 18 or more strands total, but the principle of "fully fill the bottom row first" requires debonding to satisfy the stress limits at transfer. Whereas, if I strategically partially fill several rows I can avoid debonding.

An example of one of my strategic layouts is below (shown at midspan; the orange strands are harped at 0.4L and 0.6L):

The question initially arose because the standard drawings require that specific strands in the bottom row be extended into the concrete diaphragms at supports (see the top figure). If the bottom row isn't full, how will the contractor decide where to place the strands and which (if any) strands should extend into the diaphragms?

More generally, is there any problem with partially filling rows?

I'm also interested in rules-of-thumb for strand layout.


texts: Plot zero-pole from frequency response matrix

texts:
I've represented with Matlab a system with three degrees of freedom. I'm trying to plot a pole-zero map from my Frequency Response Matrix H(w) in the case of Damped-Forced :

w=0:0.01:30;
for ii=1:length(w)
    FRF=inv(-w(ii)^2*M_gen+1i*w(ii)*C_gen_approx+K_gen);
    FRF11(ii)=FRF(1,1); FRF12(ii)=FRF(1,2); FRF13(ii)=FRF(1,3);
    FRF21(ii)=FRF(2,1); FRF22(ii)=FRF(2,2); FRF23(ii)=FRF(2,3);
    FRF31(ii)=FRF(3,1); FRF32(ii)=FRF(3,2); FRF33(ii)=FRF(3,3);
end

Does anybody know if it is possible do this directly with some possible solution or do I have to get values of my FRF end, then generate pole-zero maps?


texts: Get electricity generation data for Europe

texts: I am looking for electricity generation data (hourly at least) including renewable energy generation, for European countries. From as many years back as possible to the present. Where can I find this information?


texts: Influence of a diagonal fold on a web + double fold situation

texts:
I need to build a steel frame with a steel web in it, as illustrated below.
Flanges of the frame will be welded, as well as the web, along its whole perimeter.

Would adding a diagonal fold to the web allow this structure to whistand a bigger load? Or, for an equivalent loading, would the fold allow me to use a thinner web?

Addendum:

Considering the doubly folded strap of the web material welded on the ends to the frame, is there a critical angle for this double fold, where, at some point it is stronger to have no folds at all, rather than two folds.

Intuitively and I may be wrong about this, concentrating matter close to the diagonal tends to make the web behave as a truss. However shear flow must be disrupted as well with two folds of very obtuse angle. See illustration below.

Is this case can it be assumed that one single fold, whatever the angle of the fold, weakens the structure, but two diagonal folds, whatever the angle, makes it stronger?


texts:
What is "redundancy," exactly? As far as I know a system/component is redundant if critical components are being duplicated to ensure a higher safety level while reducing availability.

Lets take a look at a sensor. If it is a redundant sensor it has 2 channels, right? I have seen that some manufacturers say that their components have triple redundancy with 3 channels. How is this possible? As far as I get this triple redundancy means that there should be 4 channels working independently.

Example here.


texts: Mdf cutting seems to require absurdly low spindle speed for the right chip load

texts:
I've been trying to calculate the correct spindle speed and feed rate for my setup and it took me to some absurd settings. Can you do the math and check the sources hand in hand with me, plase?
My spindle is 2.2kW with up to 24k rpm.
I am trying to use a 6mm (1/4inch) straight flat flute end mill on an 25mm (1 inch) MDF.
My machine is specified (by the suplier) only for up to 3000mm/min cutting speed (and 6000 in rapid movement).
I used this site for reference on desited chip load (https://www.cutter-shop.com/information/chip-load-chart.html)
It says I should cut a chip of .013” (0.3302 mm) at the minimum.

When I entered this number into Fusion 360 it resulted in feed rates so high that I had to reduce spindle speed to 1 / 8 of what it is capable of:

Please tell me, is that right or what else could be wrong? I'm also a bit worried that the pulse driver spindle may not have enough power on such low speed.


texts: Rules of thumb for sizing an air pump piston?

texts:
I am working on a design for a small air pump that uses a single piston.

When choosing a piston I have two parameters diameter and stroke. So, I can make it fatter and shorter, or skinnier and longer, for the given volume of air that I want to move per stroke.

Are there any rules of thumb concerning how to make this choice?


texts: Why are different tractor trailer hitch configurations used in different regions of the US?

texts:
This may not be the best SE site for this question but I figured there had to be some engineering insight behind it- I've noticed in the western US tractor trailers have much longer hitches, like below, as compared to the east.
http://www.capitaltruckbody.ca/images/PupTrailer2009V5009.jpg
It seems whenever I've been west of the Mississippi, most of the large general construction trailers have these extended hitches. The majority of the trailers I've seen up and down the east coast have shorter hitches, like this: https://dealer-cdn.com/media/offshore/IMG_9655.JPG
My apologies if the wording isn't correct, I'm not familiar with the terminology. The hitch length of western trailers seems to be consistently longer than necessary based on what I've seen on the east coast.
Secondary question that seems independent of trailer length as commented already, why do trapezoidal framed trailers with long tongues like this seem so prevalent in the western US:

I'm acutely aware of reason for their design but I'm just confused why I've never seen any like this on the east coast, even with plenty of mines/quarries around.


texts: Could I define an isothermal efficiency?

texts:
There's an adiabatic efficiency because real processes can't be adiabatic.

I want an isothermal compression (yes, I know an adiabatic compression consumes less work, but my pressure differential is too high and a high temperature rise is undesired).

I know real compressions can't be isothermal because there will always be a higher or lower temperature rise.

How could I define it? Something like this?

$\eta_{iso}=1-\Delta T/Factor$

But how could apply this to my compressor? I can't apply it directly as if it were the adiabatic efficiency, which is based on theorical vs. real enthalpy jump.

I just came up with this idea: What about multiplying the isothermal work by $1+\Delta T/Factor$ to get the real compression work?


texts: How can I calculate the z-transformation of this transfer function of a time-discrete controller?

texts:
I am currently preparing for an exam where on part is control theory. This is one task from a former exam where I don't know how to solve it (translated from German):

  Calculate the z-transformed transfer function $G(z)$ of the time-discrete plant ("Ersatzregelstrecke"). The time-continous plant $G_s(s)$ is given. The sampling rate $T_A$ should be viewed as given.

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

  Note: $$\mathcal{Z} \left \{\frac{a^2}{s \cdot (s+a)^2} \right\} = \frac{z}{z-1} - \frac{z}{z-e^{-aT}} - \frac{aTz \cdot e^{-aT}}{(z-e^{-aT})^2}$$

I know that I can simplify $G_s(s) = \frac{1}{(s+1)^2}$, but this is obviously not of the form $\frac{a^2}{s \cdot (s+a)^2}$...

How can I calculate this?


texts: What causes circular hydraulic jumps in kitchen sinks?

texts:
My understanding so far is that a jump occurs when the Froude Number $\left(Fr=\frac{v}{\sqrt{2gh}}\right)$ of the radial flow falls with a decreasing velocity due to friction and viscosity; and the jump occurs at the critical point where $Fr=1$.  However, I also learnt that the height of the jump is dependant on the difference in $Fr$ before and after the jump which contradicts the former theory where there is no difference.

Could somebody please explain and help correct my understanding?

Sources

http://thatsmaths.com/2014/01/09/white-holes-in-the-kitchen-sink/
https://en.wikipedia.org/wiki/Hydraulic_jump#Tabular_summary_of_the_analytic_conclusions


texts:
I have a heating system with which I heat up 10 liters of water by 24.2°C in 610 seconds.

My system consumed 0.5 KW of electric energy in this time.

Now I used this formula:
Specific heat of water * volume * temperature difference / time

and I get 1,66 KW (created)

efficiency 332%

Is this correct? Or must I use some other formula to calculate efficiency?


texts: What is the kinetic energy required to impact the surface of asphalt roads?

texts:
I am trying to find estimates of the minimum kinetic energy required to impact the surface of asphalt roads as a first-order impact assessment of road functionality to rockfall (i.e. boulders hitting the road and creating a hole/crater). What I am really interested in is some sort of fragility function relating the kinetic energy or dynamic pressure with a measure of impact – e.g. probability of "perforation" or hole on the road surface.

I haven't found much on that in the Natural Hazard literature and was wondering if anyone here could suggest any Engineering reference.

Thanks!


texts: irregular shape basement as part foundation for two story timber frame house

texts:
A 3 m deep basement has a two story timber frame house above.

They share a side, however both have parts "outside" of the other, as can be seen in the sketch below. The red dash is the basement, the blue is the house.

Can a basement form part of the foundations for the house in conjunction with other foundations not part of the basement?

Are there any risks or known issues with this concept?


texts: shear stress at particular point in beam

texts:
In this example, I suspect the selected A' (area) is wrong... From the notes, A' is the "portion of the member's cross sectional area above the section where t is measured". But, in the example, we could see that the selected area is located to the right of the point where shear stress is calculated. Are the notes wrong?

I believe the selected A' should look like this (refer to green shaded part). Am I right?


texts:
I was browsing for Gibraltar strait tunnel where due to greater depth it is not being build.
Question popped up as to why tunnel building is difficult at lets say 1000m. we have coal mines which go deeper than that, than why not tunnel?


texts: Is it possible that an electronic device "half-works" when the power adapter supplies too much voltage?

texts:
I work in a lab, and I've been trying to replace a lost AC-DC power adapter. I got one recently that has the exact specs that I need, which are apparently pretty rare (15V, 400 mA). However, when I test the power adapter with a voltmeter, it's actually outputting ~22V, despite what it says on the plug.

Now, when I plug in the power adapter, the camera "turns on" because the green LED on it comes on. However, when I try to run the camera software, it behaves exactly as it does if I have the camera unplugged or turned off. So the software is not "seeing" it, even though it's plugged in, and plugged into the  firewire port on the PC (yes, it uses firewire... ugh).

So now I don't know why the camera is not actually working. My hypothesis -- is it possible that the camera is not really working because the power adapter is bad, and that the specs are too far off from what it wants? Even though the LED light turns on, maybe the voltage/current is close enough to make something work, but not close enough for it to actually function properly?? Is this stupid?

I'm just not sure if this is a software or hardware problem...


texts: Can nuts safely be removed from bolts where the threads have been intentionally damaged?

texts:
On old bridge plans I have occasionally seen a note to "burr threads after installation". This was done to keep the nuts of bolted connection from loosening all the way and falling off of the bolt.

An example of this practice can be seen in this Google Books excerpt from Bridge Engineering, Volume 2:

  Nuts on the floorbeam hangers have a tendency to work loose; this we generally remedy by putting on check nuts where the thread is long enough to permit; if not, we burr the thread after adjusting.

That book is from 1916, but I have seen this on much more recent bridge plans. Sometimes the note is along the lines of "intentionally damage threads ...".

The practice of damaging the threads is still an option per this AISC response.

This isn't such a big issue for normal bolted connections where the bolt could be cut (or otherwise destroyed) and replaced with a new one. This is a problem for anchor bolt connections where one end of the anchor bolt is embedded in concrete. These bolts can not be easily replaced.

The intention of damaging the bolt thread is to keep the nut from working loose. The expectation seems to be that with enough torque the nut would effectively re-tap the bolt as it is removed.

Is it feasible to back the nut off of the bolt without destroying the bolt?
Would there be any confidence that the anchor bolt could be reusable after this procedure is complete?


texts: In a planetary gearset is it possible to move both carrier and ring gear at the input speed while holding sun gear stationary?

texts:
A friend and I were in a discussion and can't seem to find the answer to the question above. I said it was possible and he said it isn't and now we are both confused so could anyone help here?

Also would it be possible to spin carrier and sun gear while holding ring gear stationary?


texts: Is an Adjustable Stiffness Flexure Spring possible?

texts:
I have recently discovered flexure springs (see image below), and I am interested in using one in an amateur project I am building.

However, I would prefer if I am able to adjust the "stiffness" of the flexure spring, to allow the spring to bear different loads.

Despite extensive searching online, I have not found a flexure spring design that provides flexible or adaptable stiffness.

Is it possible to have a flexure spring, the stiffness of which, can be adjusted?


texts: Can I oversize my air conditioner if I use a two speed compressor?

texts:
The upper floor of my house has a split A/C, three-ton. When the temperature gets up above about 95 Fahrenheit, the unit can't keep the upstairs cool. That means that for a few weeks a year, my kids' bedrooms are still almost 80 F when it's time to put them to bed. That's not really acceptable. Multiple technicians say there's nothing wrong with the unit. I understand that A/C units are sized to keep you comfortable 99% of the year, so it looks like I'm just struggling with that 1%.

My attic has an approximate R value of 32. Not super, but the calculators I've seen indicate that upgrading to 49 won't pay for itself in less than twenty years. So I don't think insulation is the main issue.

The house is about eleven years old, so I expect the compressor to require replacement any minute.

I could upgrade to a larger unit, but then you run into
short-cycling issues.

What if I got a larger unit with a two-stage compressor?

For example, I could get

a Goodman GSX14 three-ton as a direct replacement.
or I could also get a GSXC16 four-ton.

Would the ability to run at half-speed compensate for the short-cycling concerns, and allow me to have a higher peak rating without the downside of lost dehumidification?

An alternate solution would be to get some portable 12,000 BTU units
and just use those during the peak temperatures.

I'm not sure if that might have other side-effects.


texts: Projection of a given view to produce another views

texts:
First as a beginner in Technical drawing, I'm required to project two other views from the given views. In the first image the original object was not given and I'm required to produce the third view. I felt there should be the original object to be able to get dimension. Unlike the second drawing where the original object was shown so it becomes a little easier.
All I need is a correct way of approaching this kind of drawing in order to be guided accordingly.
Thanks in anticipation


texts:
Could anyone please explain what is the difference between active and passive earth pressure when we talk about weight retaining walls.

Both are lateral pressure exerted by the soil on a retaining wall, but why do we call one active and the other passive ?


texts: What is the 'application standard' referred to in EN 1993-1-7

texts:
I'm using the Eurocodes for some structural analysis and am looking for the limiting value of deflection of a plate.
EN 1993-1-7, Section 8.2 states:
For limiting values of out of plane deflection w see application standard.

I'm not sure to which application standard this is referring.

Can anyone point me in the right direction?

Thanks


texts:
So I have this problem, every Sunday we have about 200 kids come over to our house in town, and they make a LOT of noise. We also have mildly nice neighbors that do not like noise Sunday afternoon when they are trying to watch a movie on their front porch. They live directly across the street, with only two vine-covered fences on either side of the road. They are getting somewhat fed up with all the noise, (imagine 100/200 kids yelling at the top of their lungs) and my dad had the idea that we build a brick wall to stop the sound. So my question is, how high would this have to be to be efficient, and is it worth the cost? (a 7ft wall would cost about $200-500) Or would it not work at all?

I previously posted this question as an acoustics physics question, it was closed for being off-topic, they suggested engineering as better, so I posted it here.


texts:
I have been trying to determine the response coefficients for seismic analysis of Non building structures in ASCE 7-10 and found that the value of R, the response coefficient, is larger in case steel connections are detailed using AISC-341 than AISC-360, this would imply a larger design load in case of AISC 341 than AISC 360.

So basically,

AISC 341 -> Large seismic design load
AISC 360 -> Smaller seismic design load

Does that imply AISC 341 design results in a more conservative steel connection than AISC 360 or is there a difference in steel design philosophy?


texts: How to change the direction of the force with a high resolution

texts:
I have a sample of 600 milligrams which is supported by a rope. So the force is in the vertical direction. Now I want to change the direction to the horizontal direction while keeping the force equal(1 microgram accuracy). The first idea would be to use bearings. But if you calculate the resolution which is caused by friction, it would correspond 0.6 milligrams accuracy while I want a resolution of 0.001 milligrams.

Do you have any ideas how to change the direction of the force while retaining a high resolution?

Kind regards

Bearing converting force to horizontal plane.


texts: Calculate FTIR-system response functions from measurements of a calibrated black body

texts:
I need to find the response of my FTIR spectrometer. I do have a calibrated black-body source (area-emitter) which I measured at various temperatures.

The system operates in inverse cm, cm-1. My approach so far was the following:

1) Measure spectra at temperatures $T_i$
2) Scale the spectra i.e.

the x-axis $x_{in~um} = 1e4/x_{in~cm-1}$
the y-axis, $y_{in~um} = y_{in~cm-1}/x_{in~cm}^2$
to account for the dispersion relation between measured energy spacing and desired wavelength spectrum. At this point an example for scaled measurement (blue) and theoretical blackbody (orange) at the same nominal temperature looks like this (CO2 and H2O lines are at the correct positions):

3) calculate the response function $R=I_{BB}(T_i)/y(T_i)$ (I think, here in a first approach I assume that the background radiation does not contribute significantly. I would have expected similar response functions for the different temperatures; however what I get looks like:

The "response function" drifts with temperature. I am unsure now if I have a misconception in the defintion of the response function, or if I picked up an artefact. I hope someone with more experience can help me out?


texts: How does pressure drop occur across a pipe

texts: Consider a pipe in which flow is taking place.A textbook says,when there is a valve or heat exchanger or resistance to flow between two points in this pipe,pressure decreases from one point to another.It occurts to me that when there is resistance to flow, velocity decreases and hence kinetic head decreases which implies pressure head increases (according to Bernoulli's equation).Could someone clarify?


texts: How to trace a square with a reuleaux triangle

texts:
I am trying to trace a square (with rounded corners) using a reuleaux triangle and a single (circular rotation) motor. I've seen many animations (example) of this but do not understand how to make it.
A diagram or geogebra file in the answer would be extremely helpful. Thanks!


texts: How are the location of Gausian points determined in Finite element theory?

texts: From the finite element theory, what is remained a bit unclear for me, is that how do we know the location of gausian points where the integration is done for each specific type of element ? it is not indicated in many FEM books, but if someone could explain it here , it would be fantastic


texts: Why isn't air added to the primary reformer in ammonia production?

texts:
Is there an energy related reason why, in the production of ammonia, air is not introduced in the primary reformer? In this case we don't need the second reformer. I could think of a few reasons like the fact that in the secondary reformer hydrogen gas is needed to react with the oxygen to water, which can react with $\text{CH}_4$.

But this is not really energy related?


texts: Relationships among turbo jet rpm and compression ratio and thrust

texts:
A question about performance of a turbojet.
Why are compression ratio and thrust are not in linear but increase exponentially with RPM?


texts: What kind of bearing should be used for free rotation under load?

texts:
Let's say I have a 300 rpm motor and a roller connected to it's shaft and I would like to use it for pulling fabric from a printer-kind machine. But think that printer's printing speed is changing according to printed surface and I want this motor's shaft to spin freely when opposite load occurs on this roller by fabric.

So basically, if printer prints 100rpm long fabric, 200rpm of motor will spin freely as printer pull other side of fabric. When printer prints another length of fabric, motor will roll again. Roller (or idler?) should be able to spin asynchronously.

I don't know much about bearings and mechanical parts so my question might be weird, but I heard some kind of bearing can solve my problem. I tried to explain but sorry if it's nonsense. Thank you for your help in advance.


texts: How to evenly heat stainless type 304 steel bar to approximately 200F?

texts:
I need to heat stainless bar stock prior to bending in a forming machine.  I would like to reach approximately 200 degrees F.
The material is stainless type 304/304L, 3/16" thick.
We are heating it to temporarily lower its tensile strength for a challenging bending application.  Heating works quite well allow it to bend without distortion.
We are heating it in a kitchen-type oven set to 400F (and it really measures approximately that hot), yet the stainless bars never seem to reach more than 160F, no matter how long they sit in the oven.
We need to make thousands of these and they are, so using a blowtorch would be too slow and not practical given the size of the part.  Any ideas for a better way to heat these?


texts:
I need a motor for my project. My aim is to move a 10 kg mass using a belt pulley system, with a velocity of 15km/hr to a distance of 3.6m. The maximum time for moving the same is 1.5 sec.
Can somebody please help me with the calculation and finding out the right motor, that is the max power and max rpm of the motor required?


texts: Lifting a cabinet using actuators or scissor lift

texts:
Disclaimer: I am not an engineer - just a DIY guy looking for some advice or help please, so please forgive me if I use incorrect terminology :)
I am building a cabinet that has a hidden inner cabinet that is meant to rise up out of the former. The inner cabinet needs to rise 500mm and needs to support a maximum weight of 40kg (including the weight of the inner cabinet carcass itself).
I am on a budget with this build at home, so I'm trying to use either parts I already have or low-cost ones. I figure that I have 3 options available:
1. Motorised Scissor Lift

This will just simply be 2 pairs of arms, where the bottom pivot points are connected to a shaft that rides horizontally along a 16mm stainless steel threaded rod (powered by a small geared 12V DC motor). The top and bottom pivot points will ride along steel rails on bearing wheels. The arms will be made from 50mm wide mild/carbon steel with a thickness of 5mm.
2. Poor-man's Linear Actuator

Off-the-shelf linear actuators are horrifically expense where I'm from, so I took to understanding the mechanics involved and sought to try building one myself. My small proof of concept using the same 16mm stainless steel threaded rod (riding inside a seam-less steel pipe for sturdiness which is not shown in the image above), connected to the same motor works. However, I'm uncertain if the motor is powerful enough to turn the rod.
3. Scissor Lift alternative

The above is an alternative although I'm not convinced this will be as sturdy as the first option. Plus the motor will have to ride up and down.

With each option, I aim to ensure that the inner cabinet slides along some sort of linear rail to avoid any "wobbling" as it rises and drops.

The motor I'm using rated as follows:
DC GEARED ROUND BRUSH MOTOR, 12VDC, 0.6A, 1:30 REDUCTION 270RPM, 2KG/CM

I fear that my motor might be under-powered to achieve the necessary lift, so would truly appreciate the community's help on this and the which of the above options would be suitable. Also, please advise me if the standard stainless steel threaded rod is okay, or if a trapezoidal lead screw would be more suited.
My sincerest thanks in advance.
PS - sorry for the long post!


texts: What is $V_{IH}$ and $V_{IL}$ in datasheets? I found High-level input voltage and Low-level input voltage on the datasheet?


texts: Should I use ST or LT values for extruded rod?

texts: In MMPDS for AA7075-73511 (extruded rod) the Table 3.7.10.0(g3) show both ST and LT values for transverse directions. For a rod with circular cross section there is really no Short and Long transverse directions. Which one should i choose? Do not want to be uneccassary conservative and choose ST-values if it is not applicable. In my case I'm looking at the higher end off the table with diameters around 4in.


texts: What will the strain energy stored in the bar due to centrifugal effects?

texts:
I having trouble with this problem for a while now. Each time I land with same solution but it's not matching with the given answer.
My answer: (6 ρ^2 Α L^5 ω^4)/(5Ε)
Given answer: (2 ρ^2 Α L^5 ω^4)/(15Ε).


texts: How can I get a quick 2B shine on grade 316 stainless steel?

texts: I have a stainless steel (316) 2B finish strip.  I tried buffing the material for a shiny surface but it takes lot of time to finish my production.  So, I want to know if there is any chemical available or any more simple process which I can do in-house to get a shiny surface on SS316 material?


texts: Are crushed cement stones and additional digging necessary when repaving a road?

texts:
These days the city is repaving the main road close to my office. Looks like the rainwater drainage system is being upgraded and curbs and drains are added to manage the flow of rain water. Few casual google searches helped understand some of basic cross section for a new asphalt road. An image of the search is attached below.

Below is a picture from the current repaving of the road, where an excavator is scoping out the dirt and trucked out. Then the dirt is replaced by different types of crushed stone.

Questions: What is the engineering explanation for all this additional rework? To begin with was the road sinking? To the casual user the road appeared to be perfectly in good shape, thus a waste of tax payer money. How can the additional cost be justified?

References:

Roman Roads
Storm drainage systems
Roadside ditches? - Coventry Township


texts: Design a Jig and Fixture for 3-axis CNC Milling Machine

texts:
Newbie Here!!!
This is my assignment task. I am required to design a Jig and Fixture for 3-axis CNC Milling Machine. The workpiece will be a simple aluminium block and it will be cut and shaped into a flywheel.
I had searched online about Jig and Fixture. Most of them stated that jig is used for guiding the cutting tool for operation such as drilling, reaming, tapping and boring operation. The Fixture is used to hold and support your workpiece.
The question is.....

Why do I need Jig to guide the cutting tool for a simple drilling operation? Can't a 3-axis CNC Milling Machine perform the drilling process automatically itself?

Is Jig actually placed on the workpiece or milling table instead of getting clamped to the milling table? (I google searched, I saw some mentioned that Jig is not clamped to the table!!) Is it true, won't the Jig get moved during the cutting process?

What else can I use the Jig for in my assignment?


texts: Can pressure rise due to heat flux in a pipe?

texts:
I'm talking about a:

  smooth circular pipe without any valve at inlet or outlet
  without pressure losses due to friction
  subjected to a constant heat flux from outside on the entire pipe external surface which makes temperature rise from $T_i=973.15[K]$ to a $T_o=1073.15 [K]$
  in which air flows at pressure of $p_i=10 [bar]$

this doubt was born studying the momentum balance:

  $\rho*v^2|_{out}-\rho*v^2|_{in}=p_{out}-p_{in}$

expressed using the perfect gas law $\rho=\dfrac{p}{R^**T}$

and using the conservation law $v=\dfrac{\dot{m}}{\rho*A}$

where $A$ is the cross sectional area of the pipe.

Replacing those in the balance and if I assume mass flow, composition, and cross sectional area constants, I get:

  $\dfrac{\dot{m}^2*R^*}{A^2}*\left[\dfrac{T_{out}}{p_{out}}-\dfrac{T_{in}}{p_{in}}\right]=p_{out}-p_{in}$

because the block outside of the parentheses is constant, this bring me to a fractional second order equation, in which $p_{out}$ is the only unknown. The numerical solutions to this equation are (if I put the outside block equals to 1 for simplicity):
$1*\left[\dfrac{1073.15}{x}-\dfrac{973.15}{10^6}\right]=x-10^6$
that I can rewrite as $\dfrac{1073.15}{x}-\dfrac{973.15}{10^6}=x-10^6$
again as $\dfrac{1073.15}{x}-\dfrac{973.15}{10^6}-x+10^6=0$
and definitively as $\dfrac{1073.15-\dfrac{973.15*x}{10^6}-x^2+10^6*x}{x}=0$
denominator simply exclude $x=0$ as possible solution
while solving numerator equation bring me this two (and both numerically valid) solutions:

  $x_1=-0.00107315$
  $x_2=1000000.0001$

we can easily exclude first result because it has not a physical meaning because can't exist negative pressure, so definitively $p_{out}=x_2=1000000.0001[Pa]=1.0000000001[bar] > p_{in}$

This result makes me weird because it's the first time I heard about this pressure behaviour. I don't understand why!


texts: Controlling hydraulic cylinders with variable delay

texts:
Electro-mechanical systems typically used in robots have very low delays and are quite simple to build servo controllers for.

Hydraulic systems are much less common in robotics and have delay due to the length of the hydraulic lines. This delay may vary considerably depending on the system conditions.

What methods exist for dealing with this variable delay when designing a position or velocity servo controllers for hydraulic cylinders?

Update:
I have spent some time checking academic literature and have found the following books:

Introduction to Time-Delay Systems - Fridman
Nonlinear Control Under Nonconstant Delays - Bekiaris-Liberis and Krstic

I have not had a chance to read these enough to have a clear answer to my problem yet. Hopefully this can provide others with a starting point at least. Both authors have many papers on topics regarding control with time delay systems that are nonlinear or varying.


texts: How to calculate stopping distance with grade?

texts:
$$d = \dfrac{V_1^2-V_2^2}{2g\left(\dfrac{a}{g}\pm G\right)}$$

I am wondering if the car travel on the road of a sag curve or crest curve, there is two gradients of the curve. (G1, G2). Which gradient value should be used in the formula ? The one with larger gradient?


texts: Is a #4 nylon washer the right size for a 4-40 nut?

texts: I need nylon washers to sit between a 4-40 nut and a circuit board to insulate the nut. I'm assuming a #4 washer would be similar in size to the nut.