texts: How to calculate miter angles for an angled stretcher

texts:
See the image below:
When I lay this out in Fusion, I can get the angles but I can't figure out how to calculate it mathematically.
The goal is to have the angled stretcher fully contact the upper 45"-long support and the floor(even though there will be excess to remove.)
I'm looking for a formula for calculating the stretcher angle(35.8 in this case) and the length that the 2x4 would have to be.


texts: Draw the third view and the points on each view. In the first picture you have what the exercise has given us and in the second what I have drawn. I have turned the page so that the first view is the one on the left, the horizontal one is the one on the right. Is that OK? Should I use the one at the right as a lateral view?


texts: Secant modulus is defined as the slope of a line connecting the origin and a specified point (like yield point) in stress-strain diagrams. Instead of elastic modulus, which is the slope of the tangent line at origin, the secant line connects the origin and yield point. But what is the purpose of this method? I know this is used to approximate the behaviour of materials at the nonlinear region, but why do we use secant modulus instead of tangent modulus near the yield point? Tangent near the yield point would probably approximate much better. The secant modulus method seems hugely inaccurate to me.


texts: Does downdrag affect cantilever pile retaining wall design?

texts:
Downdrag
Downdrag in foundations occurs when soil layers consolidate and settle under additional load. This typically occurs when additional fill is placed on top of the existing soil. The actual downdrag force comes from the friction of the soil against piles as the soil moves down. It is assumed that soil settlement goes along with downdrag.

Retaining Walls
The controlling load for cantilever retaining walls is usually the lateral earth pressure. Any vertical load on the sheet pile or soldier pile is usually so small that it is ignored.

This retaining wall is designed to retain additional fill over consolidating soil. The piles are embedded below the consolidating soil and will not settle. Would the downdrag or settling soil affect the calculation of the horizontal soil forces?


texts: Deflection of a fixed-fixed pvc pipe under self weight

texts:
I would like to start by saying I am not an engineer, so I apologize if this question seems simpleminded.
I am making a manual tarp reel from pvc pipe, and I am trying to decided whether to use Schedule 40 or Schedule 80. I need to know which one will sag, deflect?, the least amount under its own weight. The pipe will be 10ft long and in a fixed-fixed position.

Type
Outer Diameter
Inner Diameter
Weight
E

Schedule 40
1.315”
1.049”
.32 lbs/ft
400,000 psi

Schedule 80
1.315”
.957”
.41 lbs/ft
400,000 psi

When I used $\frac{wL^4}{384EI}$ , I got 4.683 for Sch 40 and 5.233 for Sch 80. Is this even the correct formula? The Sch 40 doesn’t visually seem to sag 4 inches.
Any help and explanations are much appreciated! Thank you!


texts: How to mechanically attach a compression spring to a flat surface

texts:
I am working on a new project right now and I was wondering if anyone had any ideas on how to keep a spring fixed and connected to this flat plastic piece [image shown below].
Our goal is to keep the spring erect and allow for an upright, linear compression.
I was wondering if there was a mechanical method of attaching/fixing these two pieces together without using glue, epoxy, or other such products.
The best solution that we have been able to come up with so far is to add a custom threading into the plastic such that the spring can just screw into it, but we are afraid that this wouldn’t be too robust. Another downside is that the spring is winded in a counterclockwise manner so I am not sure how it would even be able to “screw” it in.
If anyone has a clever solution to this problem, I would really appreciate it.
Thanks,
Ryan


texts: What's the rationale for closely spaced standard LVL sizes?

texts:
Generally LVLs in the US seem to conform to heights that were historically used for solid lumber. e.g., 5 1/2" is the height of a nominal 2x6. This makes sense because presumably LVLs had easier adoption this way.
However there are a few sizes which don't follow this pattern and also are pretty close to others - specifically I'm thinking of 9 1/2 vs 9 1/4 and 11 7/8 vs 11 1/4. Especially with the first pair which differ very little, what's the reason for this?
Here's a table of common sizes from https://webstructural.com/beam-designer.html:
Name            Grade   Width   Height  Moment (ft-lbs) Shear (lbs)
Microllam LVL   2.0E    1 3/4"  5 1/2"  2125            1830
Microllam LVL   2.0E    1 3/4"  7 1/4"  3555            2410

Microllam LVL   2.0E    1 3/4"  9 1/4"  5600            3075        *
Microllam LVL   2.0E    1 3/4"  9 1/2"  5885            3160        *

Microllam LVL   2.0E    1 3/4"  11 1/4" 8070            3740        **
Microllam LVL   2.0E    1 3/4"  11 7/8" 8925            3950        **

Microllam LVL   2.0E    1 3/4"  14"     12130           4655
Microllam LVL   2.0E    1 3/4"  16"     15555           5320
Microllam LVL   2.0E    1 3/4"  18"     19375           5985
Microllam LVL   2.0E    1 3/4"  20"     23580           6650


texts: Restricted Rotation using electromagnets

texts:
I was wondering if I could restrict the rotation of a part over another in one direction alone using an electromagnet but allowing me to have a continuous rotation if forced (maybe by using some leverage?) to rotate in that direction.

The concern with using a ratcheted device is intermittent restriction- what I am looking for is a continuous restriction - at any angle of rotation.

I would like to add an image to the question, but not sure how. thus attaching a google drive image. url is https://drive.google.com/file/d/1ugcji9pDeVQiaCE9BgmFnaj6gt8gPMcf/view

Here, 1 will rotate clockwise or counter cw based on an input (not shown) and 2 rotates w.r.t 1, but need an electromagnet that can stop its rotation in counter clockwise direction unless otherwise turned using a 20 kg force (that is leveraged from elsewhere)


texts:
I've recently visited an old (about 60 years old) micro hydroelectric standalone installation. Total electric power is about 3 kW A/C.

A local told me between generator + fly-wheel and turbine there is a clutch.

Question is: what is the role of a such mechanical part in this system?

NB: local was not an expert.


texts: Finite element welding simulation with commercial software?

texts:
I am looking forward some libraries/add-ons to perform welding simulation (thermomechanical coupling, steel alloys) using commercial software, like Ansys or Abaqus. My aim is to determine better welding patterns that minimize residual stresses and/or distortion, in an industrial setting. As far as I know this issue has been addressed in the research literature (using complex heat source patterns, phase transformation material properties and birth/death of elements), but I have found very little to no reference in commercial software, and the company I work with cannot afford to fund a university-type research group.
Thanks!


texts:
I major in chemical engineering, and I'm solving a example of unit operations.
The textbook is Warren L. McCabe, Unit Operations of Chemical Engineering 7th ed.
Here is example 24.1.

And this is its solution.

From this, it says that the density of air is 29/369 × 492/620.
But it omitted the untis, so I can't understand the equation.
I assume that this equation is probably ρ = PM/RT, since molecular weight of air is 28.97 g/mol when I searched for it.
But the numbers 369, 492, 620 are still mystery. What is those?


texts: I need a solution to a problem. I could not figure out myself how to do it

texts: I was trying to solve this problem. But I could not figure out how to do it. Please help or provide a hint how can I solve it?


texts: Mathematical connection between systems of particles and rigid bodies

texts:
This question goes right back to the first principles of mechanics, so to speak. I'm confused as to the nature of forces applied to rigid bodies. Mathematically, a force acts on a particle of a known mass, but I don't see the mathematical connection that allows a rigid body of the same mass to behave similarly under the influence of the same force.

I understand that a rigid body can be obtained by extending the idea of a system with only a finite number of particles to a system with its number of particles tending towards infinity. Thus each particle in a rigid body will have a differential mass.

Therefore, what I don't understand is how a force applied at a particular location on a rigid body doesn't lead to an infinite acceleration due to the infinitesimal mass of the point at which the force is applied. Obviously this is not the case in real life, however this is what occurs when I try to take the definitions that surround systems of particles and try to build up rigid body mechanics around it.

So, does a force applied to a rigid body simply imply that this force is spread over the body? This would mean that the definition of a force on a rigid body is different to that of a force on a system of particles (since if it is acting on the rigid body as a whole it is not acting at a single point), right? What am I missing?


texts: In the buildings designed with strong column weak beam concept, the columns will remain elastic, their plastic deformation will be limited. but this is not true at the base of the building. i mean i understand why at the base of building earthquake force is largest but why do we let plastic deformation there?


texts:
I'm looking into plane strain and I'm a little confused about the concept. If we assume the material is much longer in the $z$-direction, the typical assumptions I see are
\begin{equation*}
|\varepsilon_{12}|, |\varepsilon_{13}|, |\varepsilon_{33}| \ll 1
\end{equation*}
where $\boldsymbol{\varepsilon}$ is the strain tensor. Even if we suppose those terms are zero, it seems to yield the following stresses are nonzero:
\begin{equation*}
\begin{split}
\sigma_{33} =& C_{1133} \varepsilon_{11} + C_{2233} \varepsilon_{22} + C_{3312} \varepsilon_{12} \\
\sigma_{23} =& C_{1123} \varepsilon_{11} + C_{2223} \varepsilon_{22} + C_{2312} \varepsilon_{12} \\
\sigma_{13} =& C_{1113} \varepsilon_{11} + C_{2213} \varepsilon_{22} + C_{1312} \varepsilon_{12} \\
\end{split}
\end{equation*}
In practice are the $\sigma_{i3}$ typically ignored or assumed to be small? This formulation seems to imply we have $\sigma_{33}$ is not necessarily small even in the case of isotropy, for instance $C_{1133}$ or $C_{2233}$ $\gg 1$.  As we already have three (hopefully independent) equations for $\sigma_{11},\sigma_{12},\sigma_{22}$ in terms of $\varepsilon_{11}, \varepsilon_{12},\varepsilon_{22}$ we could I suppose rewrite $\sigma_{33}, \sigma_{23},\sigma_{13}$ in terms of $\sigma_{11},\sigma_{12},\sigma_{22}$, but I wonder if I am perhaps missing a core assumption of plane strain. For instance we assume $\frac{\partial u_1}{\partial z} \approx -\frac{\partial u_3}{\partial x}$ since $|\varepsilon_{13}| \ll 1$, but would it be wrong to strengthen this and assume $\frac{\partial u_1}{\partial z} = \frac{\partial u_3}{\partial x} = 0$, where $u$ is the displacement?


texts: Does the Rim of a wheel handle all the compressive force?

texts:
Consider the wheel of a bicycle .

Now from what I understand, all the spokes that are above the upper half of the wheel happen to be in tension as the hub of the wheel hangs on these.

What I don’t understand, however, is the loading (tensile or none) experienced by the spokes that are in the lower half of the wheel.

So, is all the weight of the bicycle  supported by the rim of the wheel, as that is where the Normal Force acts at vertically upwards ? Are rims then designed to undertake compressive loading ?

And if so, then why ? Why not instead use tubes or rods instead of spokes which can handle both tensile and compressive loading ?


texts: Could a vacuum tank ever be light enough to be boyant in air?

texts:
Given futuristic materials, could a structure ever be strong enough to contain a vacuum, yet light enough to provide buoyancy under standard atmospheric pressure?

Obviously "futuristic materials" is highly ambiguous because we don't know what exists in the future... but what properties would it take? Are there theoretical materials that provide the right properties that are at least compliant with the laws of chemistry?

So, for example, if you created a woven carbon fibre bag and then somehow impregnated it with seamless industrial diamond, would that be sufficient?


texts: Is there a way to distinguish between U.S. Customary and British Imperial volumetric units?

texts:
I am used to the metric system where everything is simple and consistent. I can do quick conversions between metric and imperial in my head, but especially when it comes to volumetric measures, I cannot be sure if British or US Customary units are used. Here I refer to units such as gallons, pints, etc. not cubic-linear units.

Questions arising from this confusion is how to know which unit is being used.

In technical publications, will the author or publisher note the applicable units somewhere?

For everyday use, is there a convention that says U.S. gallons or otherwise must be specified, or is it up to the whims of the manufacturer? If not, how can I reduce my chances of making an error if I cannot ask or measure?


texts: How can a mechanical pocket watch wind itself from movement, and does it really get damaged if wound "too much"?

texts:
Today I received the mechanical pocket watch that I had recently ordered. It was this one: https://www.trendhim.se/guldfargat-mekaniskt-retro-fickur-p.html#full-gallery
I find it extremely fascinating to just stare at the mechanism. It's hypnotizing. But the instructions (consisting of one small square-sized little piece of paper) worry me a lot. They mention two things in particular:

The watch can be wound either by movement or by using the "knob" or "crown". But why do the manual winding if it winds itself from simply you walking around with it? Can that really wind it up to any significant degree? And how does that work mechanically? I don't understand that.

They make a bold point of claiming that you must never turn the crown/knob more than five rotations or until you "start feeling a resistance", or else you "may damage the watch". This has me extremely worried because it's very unclear to me when it supposedly "gives resistance", and I must have turned it more than five rotations several times already now, in spite of reading that warning. I'm now paranoid that I may have already damaged the fascinating but apparently fragile thing. If I have indeed ruined it, will that show immediately, such as it just stopping suddenly, or will it result in slow and gradual degradation of the time-keeping or something along those lines?

I thought I was very careful, but I just can't tell (so far) when it's supposedly "fully wound up". I don't understand why it would get damaged from getting "too" wound up, nor do I grasp why it's necessary to begin with if it auto-winds itself from movement. (Except after you've slept, perhaps.)


texts: Melting point of copper is around 1000 C. If you put a thin copper wire say 50 micron or so over a gas stove flame, it will break immediately. Has its melting point been reached? or, some other phenomenon is at work?


texts: Why aren't elastomer suspensions still used on economy cars?

texts: Classic Mini Coopers used a hollow rubber cone as a combination spring and damper in a pushrod suspension. Why aren't simple elastomer springs still used in cheaper cars? Formula 500 cars use an even simpler rubber spring: a small "hockey puck" with adjustable preload.


texts: Turbulence model for low reynolds problem

texts:
I'm simulating the flow in a capillary with a sudden expansion. The small capillary has a diamater of 250 µm. The big capillar has a diamater of 1000 µm. My flow rate ist $ 1\frac{ml}{min} $. Using standard properties of water I have a Reynolds number of 85 in my small pipe. For my mesh I choose one similar to this case: https://openfoamwiki.net/index.php/Sig_Turbulence_/_Dellenback_Abrupt_Expansion. I am using a low-Re mesh. I simulated it laminar first, but it seems unphysical to me, because I couldn't see any vortex, but because of the high expansion ratio one would expect a vortex after the sudden diameter change. Now I'm using k-omega-SST and getting similar results (no vortex at all). My simulation is converging well.

Do I have to use a special turbulence model for these situation? Or am I wrong in expecting a vortex in this situation?

Best Regards,
Gesetzt


texts: Use two passive CPU coolers on one single CPU?

texts:
I aim on building a silent, completely passively cooled PC, with no moving parts at all (I am aware that it is cheaper to go for an inaudible computer instead, using low speed fans. This is not the point.).

I came up with the idea to install not one but two CPU coolers, of which in theory one alone should keep a high performance CPU cool only using natural convection, but not in practice. For this I thought of using a triangular shaped piece of copper, with thermal compound between each surfaces.

Will this improve heat dissipation compared to a single heat sink or is the thermal resistance of the copper block a problem?
I sketched the idea below:


texts:
I am simulating a axial turbine and number of cell are about 3000000.

Under relaxation factors are as follows:

Pressure: 0.1

momentum:0.1

Turbulent kinetic energy: 0.5

Turbulent dissipation rate: 0.5

Velocity formulation is relative.

Turbulence model is K-E relizable. The convergence of solution is monitored by checking the residuals of the numerically solved governing equations. Moreover, in order to judge the convergence, the behaviour of other quantities, such as the total pressure at the inlet and outlet boundaries, and torque coefficient generated by the rotor, are also monitored. Here, the default convergence criterion of each residual is reduced in order to allow the monitored quantities to stagnate at consistent values. It seems that convergence is ok but there is reverse flow!! why?

residuals :

torque coefficient:

total pressure at the inlet and outlet boundaries:

Mass flow rate:

I continued this run and is as follows:

Residuals are almost constant. What is the reason?

Is convergence OK?

I am grateful that guide me about this case.


texts:
A motor is used to drive a shaft that is geared through 1:1 bevel gears to a propeller. The shafts are mounted on bearings in a hard casing that is attached to a 2nd ground. I want to know if the 2nd ground needs to react any of the torque produced by the motor, to stop the whole casing rotating? If so, how much? Any help would be greatly appreciated. I have tried sketching the system below for clarity.

Many thanks


texts:
Ok, so I am pretty confused at the moment with a question that I have been given to work out by my lecturer and was wondering if I could get some guidance with it. I will attach images of the question and diagram of the circuit while trying to say how I believe it should be worked out. I have not yet had the classes for this question yet but wanted to get a better understanding of it before I go into the class.

But I guess my main question would be this, is there a calculation that I could use to get a measurement of $I_b$ reliably without having to randomly guess numbers to get to 10 micro Amps and with regards to the results I have currently would you say I am on the right track? As I feel like I am complicating the question more than I should be.

So the question says "Using Figure 8 adjust VBB so that the base current is set at 10 micro Amps, and complete table 4."

Straight away I see that $I_b$ going to the base of the emitter has to be reading 10 micro Amps, I have a multi meter in place to make sure it is the reading I am getting but to do this I have to change the VBB voltage to make the multi meter read the right amount of Amps. So for me I have literally been spending 5 minutes trying to find out what 10 micro Amps is every time and id assume there is a much easier way to find this than spending 5 minutes doing 0.556677, 0.556679, 0.556683 etc until I find the right value.

I had also took note that I am given VCE which tells me if I change VCC to say 0.6V I will get the same reading on the VCE meter of 600mV and I have to work out $I_c$ which is the measurement on the multi meter from the transistor collector to VCC.

For some reason the attaching a imgur link wont work through the link section so I will leave the link below for the gallery of the 4 images.

Image 1

Image 2

https://imgur.com/gallery/6PdgPZo


texts: Dc motors: relationship between PWM frequency and Torque

texts:
I am experiencing serious reduction in torque when using PWM to reduce speed - I'm temporarily resorting to 10Hz, and even then, 50% mark-space gives me (at most) half the torque of fully on. I'm assessing the torque by seeing what weight can be lifted via a worm gear. I've tried up to 1kHz and it gets worse with higher frequencies. Yet supposedly PWM should give the full torque.

What in theory could be causing this? I bumped into something mentioning inductance of windings, but inductance, when driving a 6000 RPM dc motor with 10Hz PWM shouldn't have any effect on torque?

If it is the inductance, then I suppose I'll need to drive the motor with a constant current source, which I suppose will mean driving the motor above its rated voltage for low speeds, assuming it won't die.


texts: During a lecture my teacher told me that the UPSTREAM in ADSL is very much affected from near end crosstalk due to DOWNSTREAM, while DOWNSTREAM is not affected by this  phenomena. This lead to the decision to dedicate lower frequency to the UPSTREAM and higher frequency to the DOWNSTREAM. Is this correct? In case it is, how is the DOWNSTREAM not affected by near end crosstalk effect?


texts: Pressure drop in very low reynolds number flows

texts:
The wikipedia article for the Darcy Weisbach pressure drop equation states that "In effect, the friction loss in the laminar regime is more accurately characterized as being proportional to flow velocity, rather than proportional to the square of that velocity: one could regard the Darcy–Weisbach equation as not truly applicable in the laminar flow regime."

What pressure drop equation would be more appropriate for flow with Reynolds numbers 1-100?


texts: Most efficient heat exchanger for dirty air/water medium?

texts:
It's been a long time since I went over heat exchangers and even then it was all theoretical. I'm looking for anyone with real world experience with different types of heat exchangers.

I'm looking at building a external wood burning stove. Most of the designs are pretty much just a firebox surrounded by water which is a step up from just putting a pot of water over a stove. They a bit overpriced/simple for what they are and most are 'dumb' devices. Temp too cold, turn on fan, temp too hot, turn off fan.

Most of my combustion experience is with events that occur multiple times/second rather than in hours. I think there is a lot of room for improvement starting with a proper heat exchanger.

Rough initial estimates:

Air Temp: ~1500F | ~800C
Water Temp: <212F | <100C (Not making a boiler due to safety).


texts: How can I determine the overall acoustic impedance of a string with different core and winding materials?

texts: Violin strings are either single core materials or of the wound variety with a single core of one material wound with a helix of another (usually heavier) material to give the string a lower resonant frequency. In analyzing the acoustic impedance of a wound string, which part will determine the acoustic impedance of the string , the core or the outside helix material? Or will the overall impedance be somewhere in between the two?


texts: What is the difference between base shear and pseudo lateral load in seismic analysis of buildings?

texts: What is the difference between base shear and pseudo lateral load in seismic analysis of buildings or are they the same?


texts:
I’m curious about the sound made by some types of high powered electric motors and related control devices. Many (but not all) large electrical motor systems make high pitched sounds that correlate to acceleration. How to describe this sound? It is essentially a mid-high tone that rises in pitch as the drive system accelerates, and drops somewhat in deceleration.

One example is subway trains and streetcars, specifically modern electronically controlled electric motor unit “EMU” trains. As operators add power to move the trains forward, the tone rises in proportion to motor speed (and therefore overall vehicle speed).
Older pre-war trolleys seem not to make these high tones, or if they do, they are drowned out by other noises. This seems to be associated with modern high power electronic switching devices, and not necessarily with the motors they drive.

Other electronic devices that make high tones are VFD motor controls, and going back a few years, camera strobe flash units that made a high rising tone as they recharged.

To generate a sound, some physical matter has to vibrate, and push adjacent matter until landing on an eardrum. I’d really appreciate knowing the precise source of these particular tones (i.e.: going beyond “well, high power electronics make sounds”).

Question 1: generally which specific types of component vibrate, and what force causes the vibration (e.g.: capacitors, thyristors, magnetism, etc)?

Question 2: are there associated structural considerations? Does the vibration cause any strain or mechanical fatigue to the device itself or surrounding wiring or mounting surfaces? Other interesting effects?


texts: How does the efficiency curve of a well pump shift with speed?

texts:
Well pump manufacturers publish "efficiency curves" for well pumps, such as this one (the curve that is most sharply convex down, whose Y axis is read from the "% EFF" scale on the right hand side):

The well pumps are usually sold with a name that reflects the flow rate that yields peak efficiency. So this one is called a "33GS" because it is most efficient at 33 GPM.
These pump curves typically presume a motor speed of 3450 RPM. How might I expect the curve to shift or stretch if the motor speed changes? I'm particularly interested in the range from about 2800 RPM to 3600 RPM.


texts: What is the behavior of unpowered FPGA pins on I2C bus?

texts:
The development board for the touchscreen chip we got is too good ;)

The chip provides the readouts over I2C, passes it to FPGA (I could provide the model if I find a magnifying glass... but I'd prefer a more generic answer anyway) and the FPGA passes the data over RS232 to an FDDI which connects over USB to the PC.

Except I don't want the signal over USB or RS232, I need it in I2C.

There's a jumper that allows me to remove power from the FPGA, and there are convenient test points on the I2C bus which I can connect to the bus with my device, but the FPGA still remains connected.

What kind of problems/interference can I expect from it - present on the bus, unpowered?


texts: How to measure the stiffness of a rectangular beam, and compare it to a triangular beam?

texts:
I'm an amateur at engineering, working more on musical instruments, and I'm often in confusion regarding what exactly constitutes stiffness of a beam for a load applied on it so it could resist deformation, for example on googling for a rectangular beam I get the basic definition that it is proportional to breadth × square of height.
But the moment of inertia is proportional to breadth × cube of height/12.
And for a triangular beam there's even less information (think the general shape of a guitar brace with the base of the triangle taking the load and the point hanging freely downwards).
Please give me some simple formulas to calculate both if possible, the load will not be uniformly distributed on the beam but for the present consideration, the load may be applied either downward at the middle of the beam (like a violin) or pulling the beam upwards (like an acoustic guitar). If possible please provide both scenarios.
I'd like to add pictures of the forces acting on the bracing (or beam if you will) so you could get a better picture of what stiffness I'm seeking. The red colour defines the beam and the blue is the location where the load will be applied on the beam, the arrow pointing towards or away from the blue marker shows the direction of the force being applied to the beam


texts: How to calculate heat transfer between two solids in a medium?

texts:
If I have a cuboid block of metal and there is a cylindrical source of heat input (A) and I want to determine the heat energy at B (also cylindrical) how would I do this?

I understand considerations must be given for transfer from A to the block, the transfer of the block to surrounding air and then the transfer of the block to B. So, how would I calculate this?

I am only looking for a very rough approximation to the solution as this is to help me with a project of mine. I just need to find an answer I can use to provide a comparison between designs.


texts: How do you actually control the cooling level of AC?

texts:
I'm hoping this is a relatively simple question to answer, but I just couldn't find it on Google.

With regard to air conditioning (or any cooling system that relies on compressing/evaporating), how do you actually control the 'cooling' temperature? After compressing/pressurizing the refrigerant, I understand that it becomes cool due to releasing heat, however, how do you control the level of coolness?

Is temperature directly related the amount of pressure being applied to the refrigerant? I.e, more pressure leads to lower temperature, less pressure leads to higher temperature?

Thank you!


texts:
I am trying to see if I can generate a plasma from an induction coil that is wrapped around a glass jar under vacuum. Tons of induction coil heatering circuits are on ebay for forging that can supply up to 1000W and operate at a frequency of 100khz.

I am feeding in 30V at 5A to my circuit with the copper coil wrapped around my bell jar under vacuum (~100mTorr) though I am not getting any plasma. Any suggestions? I should be able to ignite that with that pressure and the power in the coil?

induction coil link: link


texts: How to simulate an exhaust fan condition in ANSYS Fluent?

texts: I'm trying to simulate a model which has one inlet and three outlets, and I'm passing air through it. Now, I want one of the outlets to have exhaust fan. I see options of exhaust fan and outlet-vent in the boundary conditions. So how should I simulate for this condition? And previously, I had done the simulation with all the three outlets which were given the outflow factors as 0.4,0.3&0.3, and the case I'm referring to, what outflow factor I need to give and simulate while one being used as exhaust fan/ outlet vent and the rest being the regular outflows?


texts: Why does a radial engine need a master rod? Why can't slave rods be the only rods? Would this spider bearing (around 1:05 in the video) work for an IC engine, why or why not?


texts: What is the strongest known *metallic* material which can be used on Earth?

texts:
The discovery of nanotubes and graphene has pushed the limit
of material strength high enough that building a space elevator
could be managable. But most of the new materials are created
from carbon or other non-metallic substances (silicon, boron).

What I would like to know: What is the strongest known metallic
component and what advancements had been made in this regard ?

In the former question I was too imprecise because I erronously
assumed that it may be deduced what I mean with strongest metallic
material. So you get know my complete list of conditions:

After I perused the literature, I decided now that I want the
material with the highest "tensile toughness" meeting the other
conditions (in J m^-3). This solves elegantly the problem of
desired ductility because strong brittle and weak ductile
materials are ruled out.
While I suppose the first condition will leave only metals,
in case it does not: Allowed are alloys and half-metals (B,Si
etc.) as long as the end product shows the characteristic metallic
luster if polished.
The material does exist and it can be provably synthesized on Earth.
Theoretical materials are not allowed.
The material exists at standard NIST conditions: 293.15 K and
a pressure of 101 325 Pa. It exists in Standard Dry Air.
It is also stable during a human lifetime, it does not dissolve, break
apart or lose more than 5% of its strength when stored in Standard
Dry Air.
Given unlimited resources (money and processing) I expect that I
would get a 10 g ingot of the material within a week.

What are the material parameters (Yield strength, compressive strength,
shear strength, tensile strength) in contrast to e.g. V2A steel ?


texts:
This question got into my mind when I am cleaning my motorcycle.

If spring shock-absorbers like the one below absorbs shock from road imperfections, reducing strain in the motorcycle body as your drive, then why does car manufacturers use rigid bumper for cars instead of semi-rigid or flexible bumpers?

Isn't it good for the car that its bumper dissipates some energy in collision so that the time of impact increases, therefore reducing impact force? What are the pro's and con's of this idea?


texts: speed measured by pitot tubes is that of the wind speed relative to the aircrafts. Now, this itself depends on weather conditions which can affect wind speeds. So, then why employ pitot tubes at all if they can give deceiving readings? Can not satellite imaging be used rather for measuring accurate speeds?


texts:
Adjustable selfie stick are two separate tubes that combined together... but how can they be able to lengthen and shorten... I want to know how it is made in the inside?

Already googled "how adjustable stick work" & "how adjustable selfie stick work" but couldn't find any explanation...


texts: Aluminum square tubing capacity question

texts: I have an awning that I am attaching to the corner of the house. I needed to extend it so I got a piece of 6063 square aluminum tubing. It's 1 inch wide with .125 wall thickness. It has about 2 feet sticking out. I'm wondering if this will be strong enough. I originally had some Home Depot .0625 thickness made out of God knows what as far as alloy. It broke after about a week or two when it got windy. I'm wondering about how many lbs stress this new material will handle. It's 6063 but not sure what temper it is but I believe it is tempered.its a high quality tube from a specialty shop that seems to specialize in aluminum tubing


texts: Help finding connector to fit 1 3/8in / 35mm mounting flange on horn driver

texts:
My project is a DIY talkbox using Monacor KU-516 compression driver.

I'm having a hard time finding the right connector to fit the hose to the driver, M35 is a rare size it seems.

There's one option of M35 x 1.5 looking through the tables for metric-thread sizes.

There's no information on TPI threads per inch on the datasheet for the driver. I read a tutorial from another builder, he 3D printed a part with 18TPI and didn't fit perfectly.

If anyone knows any item I could buy to solve without 3D printing a custom please let me know. (I've searched tap/hose adapters with no luck)

If I have to 3D print a part how should I measure the TPI accurately to make the correct thread?

I'm assuming the 18 TPI fitting didn't work as 25.4 (1 inch) / 18 = 1.41

If the flange is M35 x 1.5, at 18TPI would the fitting not snug enough?


texts: How much does an evaporative cooler cool down a room

texts:
So I'm trying to create a system that automatically runs evaporative coolers to keep a warehouse at a desired temperature, given the internal and external temperature and humidity. I can get the coolers to run automatically and read the data I want quite easily.

Here's what I need to know: is there a way to calculate how much a cooler cools down a room? I can find out the volume of the room and the airflow of the coolers, so an equation that requires those will be fine. Is there an equation that describes how much a cooler cools a room down?


texts: Tracking location and direction without GPS?

texts:
How can I track a device's location (x,y,z coordinates) as well as the direction the device is facing (north, south, up, down, etc.)?

Standard accelerometers are not precise enough for very small scale (personal hand-held devices) and tend to drift.

In addition, satellite GPS is not available in the location where this device would be used.


texts: Can you use an electromagnet to break the connection of a permanent magnet?

texts:
At first, I had a particular goal, but I'm starting to doubt feasibility which has led me here.

Original Goal: Create a small (3in²) electromagnet with 100% duty cycle capable of holding at least 50lbs for 1-2 hours at a time.

I haven't fully killed this idea off, but I'm starting to think heat may be a significant issue here; so I'm considering a different approach.

New Question: Can I use a permanent magnet with holding force of +50lbs and use an electromagnet to disrupt the holding ability, which would then release it?

The idea here being that I could possibly use a magnet capable of holding hundreds of pounds, but it'd always be "on" so to speak. If my original electromagnet idea is plagued by heat problems; maybe I could leverage a powerful electromagnet at < 5s intervals to separate a metal object from a permanent magnet.

Does any of this make sense? Am I speaking jibberish? I'm not sure exactly which direction I can go, but my end goal is that I need to hold ~50lbs for 1-2 hours and then release it... with a magnet that won't become overwhelmingly hot.


texts: "u" vs "n" orientation of channel profiles: why difference in strength?

texts:
For example, metal tape measures can be extended and stay straight when in a "u" orientation, but collapse the other way round.

I presume the same phenomenon is why metal shelving has sheet metal on top, and flanges on the bottom rather than the top.

Why is this?

I'm guessing: it's because of the direction of compression/tension, and buckling. Since a long piece of material being compressed is more likely to buckle than a short piece. In one orientation, the buckling can only happen when the walls buckle across their height but in the other orientation, the compression acts across the entire length of the channel?

Both a common-sense approach, and a mathematical approach are welcome; I assume formulas are well established, using "moment of inertia" values for beam profiles or similar.


texts: How to connect a pneumatic cylinder to a door?

texts:
I have this pneumatic cylinder that I wish to connect to a wooden door in order to make it kinda like a Star wars door.  I'm wondering what the best way to connect the cylinder to the door would be.

The cylinder has a threaded rod at the end. Looks like the one attached.  I was wondering if there are components like a bracket that can be screwed onto the door and has a threaded loop to which the Rod could be screwed to?


texts: Fit NRTL parameters for an immiscible system

texts:
Problem description:

I need to know the liquid-liquid eqilibrium behavior of a THF-water-toluene system. I need to use NRTL because UNIFAC does not predict THF-water systems accurately.

I have NRTL parameters only for THF and water. UNIFAC is predicts THF-toluene, so I could simulate that system with UNIFAC and fit NRTL parameters to the UNIFAC results.

This leaves toluene-water parameters. Since toluene and water are immiscible, VLE data does not exist, only VLLE data or LLE data. I have heard that it requires some special expertise to fit NRTL parameters to LLE data.

Main question: How can I fit toluene-water NRTL parameters?

Related side question: According to Wikipedia, there can be two sets of NRTL parameters: 1.) for LLE prediction and 2.) for VLE prediction. My thermodynamics textbook doesn't discuss this. To what extent can parameters fit to VLE data be used for LLE? Please link to a reference that discusses this, if you know of one.


texts: What are the necessary qualitative criteria for the existence of limit cycles

texts:
The literature on the existence of limit cycles is replete with complex and abstract mathematical analysis. Or for specific systems of specific structure, specific mathematical criteria that determine the existence or non-existence of limit cycles. But (for many years) I've not been able to find any references that address, in more general, qualitative (non-mathematical) language, what minimum physical elements are necessary in a system for a limit cycle to exist.

My thoughts are a system must be structured (1) to contain at least two different states in which energy can be stored and which is able to flow periodically between them, and (2) to contain a non-linearity that facilitates regular orbits without either growth or decay and (3) sufficient initial amount of energy or else constant net energy such that input balances loss.

Nonlinearity is a key element since you cannot practically realize an oscillator without decay or growth.

Are these the essential key elements or can the necessary elements be described more in a more fundamental way?

Anyone know of references that treat this question?


texts: What is the relationship between the strain in different directions?

texts:
A cube made of an isotropic material is subjected to a tensile stress as shown in Figure 2. What is the relationship between the strain in different directions ?

There is an elongation in $z$ direction and contraction in $x, y$ directions. So $\epsilon_x, \epsilon_y < \epsilon_z$. Is my reasoning correct ? Since they say material is isotropic, can I say anything else about $\epsilon_x, \epsilon_y$ ? (Like $\epsilon_x = \epsilon_y$). Please explain how someone can arrive at a conclusion about $\epsilon_x, \epsilon_y, \epsilon_z$.


texts: How do I use FEM to derive the torsional constant of an arbitrary shape?

texts:
In this question I ask about how to perform a first-principle derivation of the torsional constant of a section. It appears that there is no such analytical derivation for torsional constant, so my question therefore becomes: what about FEM derivation for torsional constant of arbitrary shapes section?

Note that I am not interesting in just using a FEM package without actually understanding the basic principle. I want to be able to derive the FEM formulation from first principles.


texts:
Hello I was searching net but can find information. I am doing a hobbyist project. I would like use shaft with metric triangular thread as a leadscrew. Can I do that? I know ACME will be loads better but they are not easy to get my hands on where I live.
Also if it helps I am trying to create very miniature milling machine, controled by hand and maybe with a lathe built-in. I would of course not use it for anything too precise. Just for milling out in aluminium and wood for artistic purposes. Or to make precision tabletop drill ( here it shouldn't interfere right ? )


texts: Why is the current that can be drawn from an electric generator constant?

texts:
In an answer to this question, for a motor used as a generator, the following was said:

  The maximum current that can be drawn from a generator is generally a fixed value that is not determined by speed.

What equation(s) show this?


texts: Why do we analyse frequency response for step inputs?

texts:
In my class I'm in, our lecturer presented frequency response methods such as the nyquist plot and bode diagrams. Then when designing a lead compensator later, he said one of the specifications should be a steady state error to a step response below a certain value. Why do we consider step responses? I have been reading ogata's book and the first sentence in the frequency response chapter says that frequency response is specifically for the case of sinusoidal inputs.

It doesn't make sense to me to analyse the frequency response over a large range of $\omega$ either since a non repeating signal has an infinite frequency anyway?

If someone could explain this it would be helpful, I can't post my lecture slides here, but I hope I was clear enough.


texts: What are the type of Equations that can determine if parabolas are better shapes to support structure or hyperbolas?

texts:
So it is taught that arches are good to support structure and most bridges are build out of arches, so I am curious to know how we can determine the internal forces of such complex shapes. Is it only done by numerical methods such as FEA or there are analytical equations that help prove it.
Can you point to any famous analytical equations?


texts: Inertia Relief and Buckling SOL105 in Nastran

texts:
Has anyone ever tried running buckling simulations in Nastran where inertia relief is invoked? I am just using a simple plate and I am getting "funny" modes (unrealistically low eigenvalues which correspond to in-plane deformations - no buckling). I went through the documents and they do not seem to suggest that it should be avoided or anything of the sort. In fact the following is stated under PARAM,INREL,-2 that "This method leads to indeterminate matrices which are not supported by buckling. If attempted the solution will fail."

But i am using PARAM,INREL,-1 and the model runs through. The *.f06 files looks ok too (OLOAD, epsilon, strain energy and so on..)

Can anybody shed any light or suggestions on how to proceed with this?

Thanks!

PS:

I have a plate modeled with CQUAD4s referencing a PCOMP and i am trying to find its eigenvalues. The loads on the plate are a combination of all in plane loads (Nx, Ny, Nxy). Due to the existance of in-plane shear, the setting up of the boundary conditions is not a trivial task and that is the reason inertia relief was considered. Also, with inertia relief in the model and along with the "funny" modes, i also get realistic ones, the eigenvalues of which match those i get with ESAComp and ESDU 81047. So to summarise:

If i could get the eigenvalues ESAComp and ESDU 81047 gives without inertia relief i would gladly do it
The fact that the first realistic eigenvalue i get with inertia relief in the model matches those from above suggests (imo) that it is somehow doable.


texts: I am a senior in high school and have been accepted into multiple engineering schools, and the top engineering school I'm looking at is OSU(industrial and systems engineering). I have noticed that there is no Calculus 2 and the only programming class required is an intro to Java. I understand that OSU has an impressive engineering program, but I am unsure what courses will be necessary. Could someone please help me understand what mathematics and programming skills are needed in industrial engineering?


texts: How do you calculate the Enthalpy of a geothermal resource?

texts:
Enthalpy seems to be commonly used to characterize geothermal reservoirs, but how is it calculated? I have an example here where the enthalpy is cited as 800 $kJ kg^{-1}$ for a reservoir with a temperature of 190 °C. In that case the enthalpy was apparently just taken to be the specific heat of water (4200 $J kg^{-1} °C^{-1}$) multiplied with the temperature, something like $H = c\Delta T$ (meaning that the reference temperature must be 0 °C).

Is that the correct way to do it? And if yes, is this really the enthalpy in the thermodynamical sense and why is the reference temperature 0 °C?


texts: DIY device to repeatedly depress and release gas pedal on a vehicle

texts:
The pedal needs to be depressed about 1/2 to 1 inch, once every three minutes.  I believe the best way to do this will be with a rotating arm of length 2 to 2 1/2 inches that has rollers on each end, rotating at 1/6 rpm.  The device needs to be powerful enough to overcome the moderate amount of tension in the pedal spring.  It will preferably plug into a standard 120-volt outlet.  It needs to be portable, so I plan to anchor it to the floor by putting a heavy weight on top of the base of its frame.
So my main question here is, where can I find an electric rotating arm of length 2 to 2 1/2 inches that's powerful enough to overcome the spring tension in the pedal?  Is it easy to find an electric motor with a 120-volt plug that one can easily attach an arm to?  Finding something that'll work for the arm, attaching rollers to it, and building a proper frame will be easy.  It's mainly just the motor that I'm unfamiliar with selecting and obtaining.
There is plenty of clearance above the pedal, so an arm of up to about 6 inches would work.
A small eccentric cam was my first thought, but rollers are easier to attach to an arm than a cam.  A piston-like device also came to mind, but that seems way more involved than a rotating arm.  Any suggestions/ideas for accomplishing my goal will be greatly appreciated!


texts: Work calculation in a thermodynamics cycle process

texts:
To calculate work in a cyclic process (say Carnot cycle) we find area under p-v curve,or use net heat transfer= net work done.
Why won't we simply add work calculated in each process of a cycle,like in Carnot: W1 +W2 +w3 + w4


texts: Can radiant induction heat thermally decompose wood

texts:
Is it possible to thermally decompose an indicator like wood in a induction heating container made of stainless steel if the induction frequency is low enough to heat the container about 1000°c.

Would the radiant heat from the steel cause the wood to heat to a point where they could break down and combust?


texts: Why can't I see my phone screen in landscape with sunglasses?

texts:
I'm using a OnePlusOne and while using my sunglasses I can see the phone screen in portrait mode, however if I rotate the screen to landscape I can't see anything at all.

My sunglasses are polarized.

What is the reason for this?


texts: Why are negative frequencies included in the nyquist plot?

texts:
What is the physical meaning of using negative frequencies while making Nyquist plots?

I know that we do a mapping from $s-$ plane to $f(s)$ plane, and we move along a contour. What I don't get is that Is the Nyquist plot purely a mathematical construct? Is there no relation between the frequency on plot and actual frequency? If there is, then what is the point of plotting negative frequencies,Is it just so that we could count the number of encirclements?

I am not able to grasp the idea behind it.


texts:
I want to measure a tube's diameter with a precision of about 0.1 mm. I have a caliper but sadly the tube is wider than my tool.

I would like to know what methods exist to precisely measure a diameter. Ideally, without buying any (expensive) tools.

A few ideas I have are:

Tape measure the circumference. Then divide by 3.1416.
Roll the tube once and measure the distance traveled. Divide by 3.1416.

I'm not sure if I would be able to achieve the desired accuracy with one of those methods. Any ideas will be appreciated.

Edit: Why I can't use my caliper:


texts:
I've been looking for a way to size an electric motor for a vehicle that could be assumed as a box-shaped load with a mass of 60 kg, up a 10° incline, at 1.6 m/s, using continuous tracks with 1 motor per side, but for some reason while searching for the answer I found different formulas for this and all of them gave me different answers.
What is the actual formula I should use to find the power required to move this load? As detailed as possible since it's for a practical application not only a theoretical question.
The last one I found is:
$$P = \frac{F_t\ v}{\eta}$$

Where $F_t = Rolling\;Resistance\; +\; Gradient\; Resistance\; + Air\; Resistance$
and $\eta = Transmission\; Efficiency$.
Is this the correct formula I should be using? Am I missing something? Should I consider Air Resistance since the vehicle is not moving too fast? I noticed both rolling resistance and gradient resistance have a friction coefficient, do I use the same one on both equations?


texts: What are the benefits of a diaphragm pump vs a simplex pump?

texts:
What are the benefits of a diaphragm pump

over a simplex pump?

Is there any specific design criteria that should be used/stated in an engineering specification for a diaphragm pump?


texts: If aircraft are pressurised, why do our ears pop during liftoff and landing?

texts:
Something hit me during my last flight: our ears feel that the pressure around us changes quickly during liftoff and landing, they hurt more and more until we make them pop. However, the cabin must maintain a level of oxygen higher than outside the aircraft because it isn't dense enough at ~10km to breathe normally.

Does that mean that the aircraft merely takes air from the outside, heats it up (it's  around -40°C outside at 10km) and adds oxygen to it before blowing it inside? How else?


texts: I search and read about Ferranti effect online, but none seems to be clear enough for me to understand how it actually happens. I must say, I do not have much prior knowledge about inductive/capacitive nature of the transmission lines - thus, it makes it harder to understand if the voltage drop is about these, or if it happens through the transmission line because of the no LOAD at the recieving end. I will appreciate if someone can explain "ferranti effect" giving enough, detailed explanations of the other factors as well (eg. current of the transmission line, etc.)


texts: Pneumatic Actuators - System Reversibility. Is it possible to use an actuator to store energy?

texts:
I'm very much new to pneumatics and I was wondering if there was such a thing as a reversible pneumatic actuator?

I'm designing a system that has to be lightweight, pneumatic and use a mechanical input to store energy in a pneumatic manner. The system must then be able to translate this energy back to kinetic energy.

From my research I have found that there are no pneumatic motors that can be back-driven to run as a compressor, and the addition of a compressor adds weight to the system so I'm trying to avoid this. Essentially, I was wondering if I used a generator/motor to convert the mechanical input to electrical energy, would an actuator have the ability to convert electrical energy into a source of potential energy?


texts: Analytical six-bar linkage trajectory solution

texts:
Six-bar linkage is shown on the image:

It has one degree of freedom, so if one of the variables is constrained, it's possible to calculate the positions of all the joints. In this specific case the point C is of interest. It is required to derive a function which describes trajectory of point $C$ (red line on image 2), as $x = f(y)$. Constant values are positions of fixed joints $A$, $H$, $G$ and links' lengths $L_{AB}, L_{BC}, L_{FD}, L_{FE}, L_{GE}, L_{HF}$.

What I can do, is assume the angle $\phi_1$ and then use trigonometry to derive positions of points $F$, $E$, $D$, $B$ and finally, $C$. The math behind that is next:

Define:
$$\begin{align}
R(\phi)&=[\cos\phi, \sin\phi], \arctan(A) = \arctan(A_y/A_x) \\
F&=H+L_{HF}R(\phi_1) \\
\phi_2&=\arctan(FG) \\
\phi_3&=\arccos\left(\frac{|FG|^2+L_{FE}^2-L_{GE}^2}{2|FG|L_{FE}}\right) \\
D&=F+L_{FD}R(\phi_2-\phi_3) \\
\phi_4&=\arctan(AD) \\
\phi_5&=\arccos\left(\frac{|AD|^2+L_{AB}^2-L_{BD}^2}{2|AD|L_{AB}}\right) \\
B&=A+L_{AB}R(\phi_4-\phi_5) \\
C&=B+\frac{L_{BC}}{L_{BD}}BD
\end{align}$$

That wasn't too hard to derive. Now, the real problem is, angle $\phi_1$ is unknown, instead the $y$ coordinate of point $C$ is given.
What I can think of, is combing all the equations into one, expressing $C_y=f^1(\phi_1)$ and trying to inverse the function into $\phi_1=f^2(C_y)$. That way I could pass $C_y$ to $f^2$, get the angle $\phi_1$, pass it to the initial formulas and get $C_x$ as the result. But this seems nearly impossible. I can write down the equation for $C_y$ and it will have just 4 summands, but those will contain sines of $\phi_{2-5}$ which in their turn are arctan or arccos of fractions which contain other angles which are again some invert function of other huge expression... Expression for $\phi_2$ isn't very big, but for $\phi_3$ it's enormous and $\phi_4$ is getting out of my hands. Inverting all that is something I can't imagine.
Are there any sane methods to calculate the six-bar linkage and get an analytic solution for the trajectory?


texts: I am trying provide Customs with a tariff code for a helical spring of steel wire. The Harmonized Tariff Schedule asks for the "cross-sectional dimension" of the spring. I have been told that this is not the same as the diameter. Does anyone know how i can find the "cross-sectional dimension" of a spring with an inside diameter of 4.7 mm and an outside diameter of 5.3 mm? Not sure you would need it, but the height is 12.4 mm. Any help would be greatly appreciated. Thank you.


texts:
I was watching a video that derives the forced vibration response of a beam. The link to the video is https://www.youtube.com/watch?v=6VuLZDgRhZ4&list=PLMXj6GKKnHI6Lftj7CXr9WusMkXi5s9yH&index=56

In the derivation, why is it correct to use the expressions for $w_n$ and $U_n$ (natural frequencies and mode shapes) that were derived based on free vibration of a beam?
These expressions were derived using the method of separation of variables by equating the first two terms in the equation of motion (EOM in the image above, with f equal to 0 for free vibration) and then equating them to a constant. The two separate equations, one that depends on time and another that depends on position, are set equal to 0 and boundary conditions are used to find the natural frequencies and mode shapes.

But why is valid to perform these steps when the right side of the EOM is not zero?


texts: Examples of situations where using classical control methods are better than modern methods

texts:
I'm doing some reading on control systems at the moment and when reading pages on classical control methods, some sites state that they are preferred in industrial applications.
I've read that simple SISO systems such as temperature control for air conditioning can be achieved faster and more efficiently using classical methods. Through my reading, I've generally only found smaller-scale applications for the classical methods. I was just wondering if there are any larger-scale situations in the industry that benefits from using the classical methods over other methods.
Thank you in advance.


texts:
The Gibbs Phase Rule indicates that for a two phase, single component thermodynamic system we will have one independent intensive parameter.
Given that the Degree of Freedom is $1$ means that fixing one intensive parameter would fix the entire state of the system.

Any property $x$ is just a function of one other property say $y$, i.e. $x=f(y)$. This gives for two phase system $P=f(T)$, but why isn't $v=f(T)$?

As we know $v$ can have a value anywhere between $v_f$ and $v_g$. Are there any assumptions for the Phase Rule, other than equilibrium, which would explain this?


texts: Why does Bourdon tube measure relative pressure?

texts:
From Wikipedia:

  Bourdon tubes measure gauge pressure, relative to ambient atmospheric pressure, as opposed to absolute pressure;

But looking at pictures such as the one above, it seems there is only one connection into the tube, the one where the gas whose pressure is being measured enters. It would seem that the deformation of the tube is only dependent on the pressure of the gas. So why does the Bourdon tube measure gauge pressure relative to atmosphere instead of absolute pressure?


texts:
I have two 3 by 4 foot roof windows facing south and want to keep the heat out in summer.
What I did on the hottest days was I opened them a bit and strapped cardboard on top. That way a bit (hot) wind came in but the sunlight stayed out.
Of course there are electric shutters, but I guess they will not last ten years, if at all, in these harsh conditions. In summer you can fry eggs on the roof and in winter it's covered with snow and ice.
My best bet was to permanently glue aluminum foil from emergency rescue blankets onto the glass but I do not know what the best removable glue would for that, since these things will also not last forever, but are cheap....
What is your suggestion here? Thanks in advance :-)


texts: What parameter to lower elastic elongation of a rod under tension

texts:
Let's assume I have a rod under tension that is only elastically deformed. What parameter can I change to decrease is elongation. $T_{current} < T_{critical}$

decrease Temperature
increase hardness
increase Young's modulus
increase tensile strength
increase the diameter of the rod
increase yield strength

I figured Young's modulus because a higher one means more stiffness?
Does a higher yield strength change the elongation for a given applied force?
But I am really not sure about the other parameters.


texts: Why didn't the Fukushima turbine supply electricity to the residual heat removal system?

texts:
Instead the pump relied on the diesel generators, why didn't it just use the residual heat to generate electricity?

P.s. The question is very specific to the residual heat generated after inserting the control rods and the cooling pump which failed to cool down the system since it has no electricity when the diesel generators failed.


texts: How to add friction to a rope without using abrasion

texts:
I have a pay-out winch. It is a spool of rope that has a disk brake attached to it, so I can control the torque required to rotate the spool.  When the torque is very large, however, the rope begins to bury itself into the rope that is still on the spool, and this causes a lot of abrasion and wear on the rope. I tried a different winding pattern, but the rope still cuts into it.
I'm using 1 mile of 400 lb test kevlar. The spool diameter is 4 inches.
Does anyone have a suggestion?  I was wondering if I can thread the rope through a mechanism as it leaves the spool to add friction (pink box in the picture). Are there any off-the-shelf solutions? For example the rope could go back and forth between two rows of pulleys, each of which has a little friction.  The point is to avoid wearing out the rope with a lot of heat or abrasion.
Can you suggest a way to prevent the rope from burying itself?  I guess I could make the spool larger and wider (decrease the depth of the rope still on the spool).


texts: How do I calculate how much weight an iron cylinder can support?

texts:
I would prefer an equation.
The premise is that I'm trying to calculate how thick an iron cylinder using a screw jack would need to be to support 20kg of weight for engineering class. We haven't learned anything along these lines and I'd really like to know.

Thanks!


texts: What is the technical name for a water reservoir that retains its contents via vacuum and ambient air pressure?

texts:
This is a strange question for me because this is so extremely common, but I have never heard a name to describe exactly what it is.

This is commonly used to provide water to animals from a trough or tube at a constant water level without dripping. As the water in the trough is reduced in height from drinking, air bubbles enter the reservoir which then releases sufficient water from the container to refill the trough and stop further air from entering the container.

The remaining liquid is held inside the container by the vacuum above the water, and atmospheric pressure holding the water up in the evacuated space, even though the bottom remains open.

And this reservoir container is formally called a.... ?


texts: Can e-paper capsules be made larger in size?

texts: Can I buy individual (larger in size) e-paper capsules from somewhere? (for an electronics project for example) and is it even possible for such large e-paper capsules to be engineered?


texts: What are some different sealing methods?

texts:
I'm trying to join two different parts together but it's hard trying to find the best method.

I cannot weld them because they must be able to be removed easily. I  can't use any nuts or bolts because then it won't be interchangeable and for what I'm trying to fit my part on, there are hundred of different variations.

I need out to have a very strong seal like I bolted or welded it on but without having to really do so. It also must be extremely air tight. I need a lot of creation on this one. I thought about making a suction effect but didn't know if it would be strong enough and hold it like bolts would. I'm trying to fit my own cylinder head to a little engine I have.


texts: How to convert *.3OXZ CAD files to *.STL?

texts:
We are using one dental scanner (Vitality Scanner)

and the output format is in 3doxz Format,So we need to change it to stl for some analyzing on it, So i need to find out any software for this CAD format Converting.

For example one of it's 3DOXZ Format is here:

3DOXZ CAD Example

Thanks a lot.


texts: How does anything actually cut anything, since we all know stuff is made up of atoms and molecules, which can't be touched together (It Requires Binding Energy). So how come we see things all around us being cut so easily?


texts: Reducing vibration coming from the floor while at sleep

texts:
having an interesting issue here. Imagine you live above some mental dude who starts a vibrating device and frames it against its ceiling - my floor (for your imagination, see example of this at the bottom), or just plays a sound speaker on low frequency. Vibration in my apartment barely feels when siting on a chair, however it does feel quite a bit when I am in bed - it either stops me fall as sleep, or wakes up. This is my nightmare for the last couple months.
Had all kind of tries (f.ex. truck tires under bed ^^), but nothing helped, apart of a temporarily solution - sleep in a different place every night (meaning - no bed, only mattress on a floor).
Need a real solution. My tired head brings one idea - a hanging bed (seriously). Some frame stands on a floor and on that frame my bed hangs. Yes that means I sleep kinda in a ship, but waving effect could be smaller if bed hangs on V shaped ropes (not vertical). See my art drawing example bellow (red is rope, blue is frame, black is bed).
My issue now is - would this even work? Any better ideas? If not, maybe an advice on what materials could be used? I live in Europe - so don't suggest bamboo sticks etc. Willing to find reliable and cheap materials (since I wont be living like this forever :)
If you don't like the idea of a "bad neighbour" problem here, imagine I live close to rails and same issue happens - vibration when train goes by.
Help guys, this is a real issue.
p.s. estimated total weight I would say 300kg. (no other person in bed except me, obviously...)
p.p.s. found an interesting idea from @broccoli here. Though a bit in doubt that that small vibration would cause bed to move instead of shake. If anyone could elaborate on this, would be great too.

Edit:
Answer from @Fred sounds reasonable, but adding an image of the tire chamber. Tried to put these 4 under the bed, but vibration reduction was too small. Also had vibration pads under the tire chambers.
Thats why hanging bed looks as a 'best' option for me :)


texts: How can traffic signal controllers handle multiple conflicting preemption requests of equal priority without dropping one?

texts:
Let us assume that we are North American traffic engineers, and have the (hypothetical, plausible, yet pathological) intersection configuration depicted (not to scale and lacking lane lines, sorry -- I did not have time to build the model to scale or paint it!) below on our hands.  Both intersecting roads are four-lane, arterial roads with an AADT of 10000, a 40' bus or tractor-semitrailer for the design vehicle, and 35mph speed limits, while both railroad tracks are signaled, mainline railway tracks with 20+ trains per day, albeit also speed-limited to 35mph through the curves due to cant and curvature.

The traffic signals (not shown in the diagram) are standard 8 phase signals with pedestrian heads and leading protected left turns controlled by a NEMA TS-2, while the crossings are protected by flashing lights with cantilevers and gates controlled by grade crossing predictors.  The nearest crossing (west approach leg) provides 200' of storage space, and the far crossing (south approach leg) provides 300'.

This configuration has been in service for several years after a road-widening project on the north-south road.  However, a near-miss happened recently at this intersection where a car had to dart off onto the shoulder to evade an approaching train as it had queued onto the west approach crossing, so preemption is being considered for this location. But, there's a problem -- it's possible that a train move on the south crossing could preempt the intersection, then another train could show up on the other track, causing a second request for preemption before the traffic signal has finished servicing the first preemption request.

How can we handle this situation? I can see that dropping the second preempt request on the floor, which is the default behavior as I understand it of a traffic signal controller during preemption, could cause undesirable results including:

No track clearance green for the second train, leaving a possible queue on the track
Queues tailing back into the intersection from the second crossing, possibly causing track clearance to fail for the first track due to the  queue from the second direction obstructing the intersection approach from the first direction direction.
Illogical turn movements during the preemption hold if limited service operation is used -- these shunt cars into a queue waiting for the second crossing to clear
Driver befuddlement at intersection operations with multiple trains present

However, simply servicing the second pre-emption request doesn't work either, because it could yield a track clearance green that allows movements that queue waiting for the first train, or worse, cut off the first train's track clearance green prematurely, leaving queued cars stranded on the tracks.

The railroads involved both are more than happy to give you all the advance preemption time you want, and are both providing 12-wire preemption interconnects to you.  Furthermore, there's enough traffic here that everyone wants limited service even during a double preemption, and enough trains here that double preemption would occur every three months or so based on data logged by the GCPs.


texts:
There are many videos on Youtube about opening of new dams, where the water is already ready to go though the dam.
What I wonder is how engineers moves water to a new dam.
To me it seams as a chicken and egg problem.

Are explosives involved?
And how do you prevent the water from hammering into the new dam and destroy it?
How did they get e.g. the water to Hoover Dam?


texts:
We are considering to build our family house. Where I live, people build either:

Concrete beams for the structure and then thermal bricks for the external walls; or,
Heavy duty steel structure and then some drywall system for the exterior.

In both cases, there is a concrete slab at the base.
I love the look of the steel structures, their design, speed to construction, insulation capabilities, etc. However, I am wondering about their lifespan. For concrete and brick houses, it is not uncommon to have a house renovated at 50 years and look like new.

What is the lifespan of residential houses built with steel structure?
Can I expect to grow old in the house and that my children will inherit it, or should I consider that in 50 years they would have to demolish it and rebuild?


texts: Understanding the total energy in a AA battery

texts:
AA batteries have about 4 watt-hours (14400 joules, 10620.9 pound-feet).

Ignoring losses, does that mean a AA battery could theoretically lift 10,620.9 pounds, 1 foot high?

You'd need an electric motor, some sort of crane or lift, the right gearing, and a fair amount of time. What's the best efficiency you could hope for? Even with 50% loss, you should still be able to lift a pickup truck, but this feels wrong (impossible).


texts: Creating a constant internal temperature that is negligible to the external environment

texts:
Okay, Hi there Engineers! I am a newbie to this site, and to engineering.
So, I wanted to make this post to get all the help I can get. I have been set a task of creating a prototype of the following;
I have been given a device (the device being a Rubidium Atom Clock/Standard. Pictures are provided below.)
The fault with this device is that different internal/external temperatures will affect the clock. So what I need to do is; somehow make the interior temperatures a constant, where ever the device is (so if it is in Iceland, the internal temperature must be the same as it will be if it was in the Sahara Desert.)
Oh yeah, and the interior temperature must be within -20°C to +65°C.
If you need any information before you can help me, please go ahead and ask. Also, as I've stated above, I am new to engineering, so if you are trying to help me, please explain as much as you can so I can understand. And, I won't have advanced tools available, just assume that I have the tools in a workshop.
Bear in mind, I have very little space to work with in the device, and watch out for voltage, I don't want any systems like fans or something to affect the power supply.

Specifications
(Not exact to the device I am using but I will get that as soon as possible, they are pretty similar):

Device Images:
...That is rather annoying. I can't upload more pictures due to my account not having 10 reputation. If you are looking for the device, just search up "Rubidium Oscillator PRS10B"


texts:
So I need to calculate how big geothermal heat pumps I need for a building. Heat pump is used for heating and to heat used water.

If I know how many kW's are needed for heating the building and the calculated flow rate of used water, what is the simplest and quickest way to calculate how much power is required from the pump(s)?

Let's say AC heating requires 20 kW, underfloor heating requires 5 kW and flow rate of used warm water 0,3 l/s. And I know dT for AC heating is for example 35 and underfloor heating is 10 and used warm water leaves the pump at 58 degrees celsius.

How should I calculate it? And how do I convert this all to annual kWh used?


texts: How is the kinetic energy change during a throttling process negligible?

texts:
The throttling process is a constant enthalpy process, in which the pressure decreases. So,

h1 = h2

u1+p1v1 = u2+p2v2

If the pressure is decreasing and if we consider the Joule-Thomson coefficient to be such that the temperature is decreasing too(so internal energy, u will decrease), then the specific volume will increase. If the specific volume increases won't it cause a change in velocity and so the kinetic energy? Why is it said that there is a negligible change in kinetic energy in a throttling process?


texts: Torsional rigidity D vs torsional rigidity factor k vs torsion constant J

texts:
I have a physics background so apologize my ignorance.

I'm confused by the constants $D$, $\kappa$, and $J$ when it comes to torsion of beams. From what I understand $\kappa$ and $J$ are the same thing, $J$ is (usually) for round beams with isotropic materials while $\kappa$ is for beams with unusual shapes and/or material properties.

What I really don't understand is how you get from $D$ to $\kappa$ though. In a paper, call it paper 1, I found, in the case of an orthotropic beam with rectangular cross section, they derive equations for torsional rigidity $D$ then mention equations such as

$$
\kappa=\frac{D}{2ba^3G^0_x}
$$

where $b$ and $a$ are the height and width of the beam while $G^0_x$ is the shear modulus. Where did this equation come from? Is it a standard result? Did they derive the equation for $\kappa$ from FEM simulations?

Then in this paper (call it 2), which deals with torsion of arbitrarily shaped orthotropic composites, they talk about the torsional rigidity $GJ$, which makes me doubt my previous statement about $J$. One of the equations that they give is that the torsional rigidity factor $\beta$ (which is $\kappa$, right?) is

$$
\beta=\frac{GJ}{ab^3G_{zx}}
$$

From what I can tell $GJ=D$ from paper 1 and like I said $\beta=\kappa$. So once again I wonder how $D$ (or $GJ$) and $\kappa$ (or $\beta$) are related.

I should explain that the reason why I'm looking to understand better these relationships is because I'm 3D printing springs. I'm looking to find a relationship between the shear moduli of an orthotropic material and the spring constant of a coil spring.

One method that I found is to relate the energy stored in a spring to the energy stored by a beam under torsion $\frac{1}{2}kx^2=\frac{1}{2}\kappa \theta^2$, where $k$ and $x$ are the spring constant and deflection, and $\kappa$ and $\theta$ are the torsional constant and angle of twist of the material.

The two big problems that I have are that my springs have square cross sections (because they're easier to print) and are orthotropic. Hence why I'm having so much trouble.


texts: How to chose production process of copper electrical connector, Extrusion vs Die casting

texts:
I want to get manufacturing done for custom designed copper connector which I am planning use it in my home automation project. I created design of the connector in Freecad . I have exported the designs in PDF and published to local manufacturers.

To be frank I am from software background and it is first time I am creating designs and getting them manufactured.

After publishing my designs I got few replies. One of the reply asked me which production process to be followed extrusion or die casting.

I have no idea of this, tried google to search for any clues which would help me deciding .

After browsing few pages I got to know only one difference one of process involves melting the metal and other  one include forcing cold metal to shape it in desired design.

Can someone please help me deciding.how to chose the production process which would suite my application?


texts: How to weld a copper flange with a Nickel alloy pipe?

texts:
I have a copper flange and I want to weld it to a nickel alloy pipe.
Normally, which welding technique is used to join these two parts?
Also what is the filler material to be used to weld a copper part with a nickel alloy part?


texts: Does negative pressure inside the barrel affect low-powered railguns?

texts: Just something I was wondering about when I've seen this on reddit today. Unlike in firearms where the pressure propels the projectile, in a railgun, wouldn't the pressure ahead/behind of the projectile slow it down instead? If so, would it be by a significant amount?


texts: Loadcell / strain gauge sizing for a joist

texts:
I am looking to use some load cells (foil based type) to detect presence for home automation within in a room. I was looking to mount some loadcells to the joists for the floor (UK Based house so around 6x2" Joists around 13ft long on 400mm (1.3ft Centres) to try and measure deflection.

I'm not bothered for Exact measurements, but knowing the difference between a small dog and a human may be useful or determining more that one person.. but again not a real issue..

What size loadcell would people recommend, I've seen very small sensors used for deflection in steel components such as suspension components on cars..  this makes me think that I dont need large sensors on timber joists that 'should' move more?

For mounting I was thinking of bonding / gluing to the side of the joist, near the centre of the span and sanding it smooth first..

Thoughts, suggestions, help?

Thanks


texts: How to apply static failure criteria for bending stress in an angled cylindrical surface?

texts:
Let’s say I have an irregularly shaped bearing with a cross section that looks like the angled surface of a conical frustum, shown below.

If a bending moment is applied which causes the inside diameter to ‘cave outwards’, how would I perform a static loading failure analysis to see at what bending moment the shape would cave outwards? How would I determine the second moment of area and distance from centroid values required to apply the bending stress formula sigma = My/I? Or is there a manufacturing method in the form of some sheet metal bending formula that would be more helpful in looking at failure mode in a cylindrical cross section instead of a planar one.

EDIT: The end goal is to have the curved surface completely vertical, as if it was the surface area of a rod. If there is an easier method of calculating the forces required, let me know!


texts:
If we are able to create a fusion reactor so there is a net gain in energy how can we turn the heat into electricity.

I know how it is done normally for fission, steam, but how could this be adapted for a fusion reactor where all of the heat is confined?

Are there any concepts for the stage after fusion becomes net positive?


texts: High pass filter and differential equation relationship

texts:
Consider the problem stated as follows:
A signal y passes through a high pass filter $\frac{s}{s + ω }$. A high pass filter with cutoff frequency ω isolates the variations of this optimized variable from its average value. The state that represents the high pass filter is denoted by η.
In the literature, the equation is represented as: $\frac{d η}{d t } = - ω  η + ω  y$.
My question is, which principle did they use to arrive at that equation.
I know that the inverse Laplace transform of $\frac{s}{s + ω }$. will result in a differential equation, as it is being multiplied by s. However, I don’t know how to compute $\frac{s}{s + ω } * y$.
I have attached a screenshot of the control diagram. I will really appreciate it if someone can please explain this concept to me.


texts:
Does the module of 2 meshing spur gears have to be the exact same value ? What is the allowable difference?

So basically my module is off by 0 01 and my coworker made a model and it works. So I'm just wondering what the allowable difference  is ?

Ps these are custom made gears.


texts: High pressure water pumps filling a container. How long does it take to obtain P pressure?

texts:
The problem I have at hand is the following: I have a container C with a given volume V. I need to fill it with water, fast, up to a given pressure P. I have a number of high pressure hydropneumatic pumps to choose from, but they are expensive and take a while to get here. I don't even have such pump readily at hand to test the equations. The flow rate for these pumps is easily calculated as:

$$
Q = Q_{max} - K_{b} P
$$
$K_{b}$ is a pump parameter per datasheet. Obviously pressure $P$ won't go higher than $Q_{max}/K_{b}$, the pump stops working. Now I start simplifying things: I consider no thermal factors, no sudden pipe diameter change, no turbulence, no back flow, constant ambient pressure, always the same fluid; basically no hydrodynamics. And the longest shot, I consider the pressure per volume rate of the container constant:
$$
\frac{P}{V} = K_{t}
$$
I treat $K_{t}$ as some sort of elasticity constant which in reality comprises the actual container elasticity,water compressibility, container's volume, etc. It's the only empiric data I have: how many liters of water I stuffed in the container to get the target pressure. Taking differentials, and considering t=0 the moment the container is full with P = 0, I get:
$$
P(t) = \frac{Q_{max}}{K_{b}}(1-e^{-K_{t}K_{b}t})
$$
Which makes sense for a single pump. But I can't find a way to adjust it to multiple pumps in parallel with different parameters. I need an equation to later iterate and get the best combination of pumps possible. Trying to get an "equivalent" pump, the flow rate is the sum of flow rates as in: $Q(t) = Q_{1}(t) + Q_{2}(t) ...$, easily resolving to an equivalent pump having parameters $[\sum{Q_{{max}_i}},\sum{K_{{b}_{i}}}] $, but that does not make sense with the equation above. Keep in mind this is for pressures up to 2000 Bar.


texts: How to measure a laser diode's Wavelength

texts:
I have some laser diodes. I want to know how to measure the wavelength of laser diodes ranging from visible to near infrared? (300 nm to 1100 nm)

What type of instrument/meter do I need to use? spectrometer, spectrophotometer, wavelength meter, reflectometer, oscilloscope or what and how?


texts: I am working on designing a set of gears for 3D printing. I have not done any gear design before - how should I improve the design to prevent gear slipping?


texts:
I have an object that weighs approximately 10 grams = 0.022 pounds. I know it can hold at least 45.1 pounds without breaking. It's a cube-like object so I placed many books on top of it and weighed the books.
I want to compare the strength of the object to steel to see how strong the object is.

How do I calculate the strength to weight ratio of this object?

I think it can hold 2,050 times its weight based on 45.1/.022=2,050.
I read that megapascal's (MPa) are used to assess how much force an object can withstand.
A megapascal (MPa) is a metric pressure unit, mostly used in hydraulic systems that gauge high pressure ratings, that equals 1,000,000 newtons per square meter (which is a pascal). 1 MPa is equal to 10 Bar.


texts: Design of Gating & Runner system in Gravity Die Casting

texts:
How to design gating and runner system in permanent dies so that material flows smoothly throughout the design without spilling back from the gating channel.
What should be the shape of gating system and how the volume of gating system be related to the volume of the piece that is required to be casted through gravity die casting?


texts: Batteries AA - industrial R6 vs normal LR6

texts:
I have the following issue:
One year ago or so I bought a toy for my kid. Worked fine, then the battery got low (still working though but under performing). I checked the battery type, see is an AA (3 of them). Went to the store and bought some.
Replaced the batteries and the toy won't start at all. Put the old back, toy worked so I checked what went wrong.
Noticed the toy had Industrial Panasonic R6 batteries and I bought Normal Duracell LR6. So I have to questions:

Are industrial batteries safe for children (I think yes their main purpose being stability afaik but I must ask :) - kind of like my kid)?

Considering the fact that both type of batteries are AA, both have same nominal voltage (1.5) and according to https://en.wikipedia.org/wiki/AA_battery the LR6 has actually higher capacity... why is the toy not starting?


texts: Deflections Of Statically Indeterminate Structures

texts:
When analysing and then designing a rigid jointed, statically indeterminate structure, I can solve for all the forces and moments using the Hardy Cross (Moment Distribution) Method.

However, I am unsure about how to solve the deflections on the beams and columns. I need these values in order to design based on serviceability limit states and verify deflection checks.

Can you please demonstrate (or point out) a method to quickly and effectively find the displacements in a multi-storey, statically indeterminate structure.


texts:
I have a question about intravenous flow rate controllers, which are controlled using microprocessors. For example:

I want to control the IV flow rate, the flow is in range from 0 to 300. So, I just put a number between 0 drips/minute to 300 drips/minute in a 10 scale from the computer interface, and the microprocessor would control the flow rate to the desired number. For example, when I put 60 drips/minute on the computer interface, the microprocessor controls the mechanism until the flow rate reaches 60 drips/minute. The tubing used by the IV dispenser is a form of PVC plastic.

I've been trying to use a pinching mechanism like in the picture below. I'm using that kind of mechanism because it is easier to insert and remove the tube from the device when required. But, the mechanism still doesn't give the precise output that is specified, also it is unstable.

So, how can the flow rate be controlled just by using motors such as a servo motor or a motor DC and microprocessor?


texts: How do I determine what hardness to change the bearing or the track?

texts:
We have a project that requires us to use a qty of 4, Ø2" yoke roller bearings mounted two per side on a trolley that roll on a steel track. The maximum total weight that we estimate on the track at any given time while in service will be between 8k to 12k lbs. This will be distrubuted too the 4 rollers which each have a capacity of 8,000 lbs each. So there would about 2k-3k per roller.

We will be using standard yoke roller bearings that have an outer ring hardness at 58-62 Rockwell C or 58-62 Rc. Our Track is hardened to 52-58 Rc. Knowing that the track has a hardness less than that of the bearing, wouldn't it stand to reason that the track will wear out before the bearing? This is unacceptable for this project.

We need a solution so we can make the bearings the wear item on this project. The track would take many man hours to replace , where a bearing would take very little time to replace and cost much less than a new track.

We would need to increase the track hardness to slightly higher than the bearing or lower the hardness of the bearing to make the bearing the wear item instead of the track. The downside to this is that I would sacrifice bearing L10 Life by lowering the hardness of the outer ring.

We would love some help solving this issue if anyone has had any experience with this problem.

****UPDATE 1/14/2020*****
Since I posted this question, I have spoken with quite a few other mechanical and manufacturing engineers who specialize in bearing and track design. They all pretty much explained me the same thing that using a a track that is 40-58 Rc will work just fine with a yoke roller that has an outer ring hardness of 58-62 which is the industry standard for that type of bearing. The bearing internal rolling elements and seals will wear out long before the track or the OD of the outer. Being that the track is 52-58 Rc it should endure many yoke roller swap outs over the years with the loads and application this is being used with. I'd like to thank everyone for your time and effort put into helping us come to a conclusion of this issue.


texts:
Recently, I visited industry where they produce steel coils (rebar + plain coils). At the end of the production process, I discover that rebar coils are getting sprayed by water:

Whereas plain coils are not getting sprayed by water. What's the purpose of spraying water on rebar coils but not on plain coils?


texts: Simulating fluid dynamics for Generative Design of water turbine in Autodesk Fusion 360

texts:
I am trying to use Autodesk Fusion 360's generative design feature to produce more efficient turbine blades for hydroelectric power generators.

How can I simulate the load of water-fall on a turbine and use it to optimize the shape of the turbine? Also where can i obtain a starting shape model of a turbine?


texts: Is "pitch diameter" the same as the distance between the centers?

texts: I am designing gears in FreeCad, and printing then on a FlashForge Finder. I want to know if the pitch diameter is the same as the distance between the centers of the two gears. Both gears are external spur gears.


texts: How can I use 2 motors to increase rpm on one wheel?

texts: I want to add power of both motors in such a way that it increases the RPM on a wheel, to be used in a tricycle.


texts: timing pulleys setup for children's pedal car

texts:
I want to convert my son's pedal car to electric. The car is meant for 3-6 year old children.

So far I got the following:

50W, 3300 RPM electric motor with 8mm round shaft (no keyway or shaft groove)
10mm threaded rod made of some fairly soft metal to use as a shaft

I was thinking to connect the motor to the shaft with XL timing pulleys. With a 10 teeth pulley connected to the motor and a 100T one on the shaft, I would get a 10X RPM reduction and with 10-inch wheels, I calculate that the max speed of the car will be ~15KM/h. Probably still a bit to high but I could do further electronic limiting.

Now I have a few questions:

Would there be issues if I combine the smallest pully in the range with the largest one? It seems XL-10T is the smallest and XL-100T is the largest.
Considering these easily available pulleys are almost always mounted with set screws would the grip be sufficient for this application?
What is the required belt length if the distance between shafts is ~90mm?
What is a practical way to tension the belt for something like this?
Is 10mm thick enough for this belt?


texts: Looking for a loading code for use in the design of a small scale private bridge? (4.5m span, one lane)

texts:
I'm currently designing a small reinforced concrete bridge on private property. The project is in Scotland.

It's very small scale, a single lane, with a span of around 4.5m.  Service life is taken as 120 years.

Using Eurocode design for standard road bridges seems far too over-the-top (there will not be any lorries crossing this bridge for example), so I'm looking for a good load design precedent (with backup documentation). The largest vehicle that may foreseeably cross the bridge would be, say, a 30 tonne concrete mixer.

If there's a good code that relates to, say, loading on temporary works or construction traffic loading then we feel that would be perfect for use on this bridge. Lest we over-engineer the thing and it costs a fortune...


texts: Which coating best exploits "darker when wet" phenomena

texts:
This "practice calligraphy" paper has a special coating that amplifies the contrast between light/dark when a wet brush is applied.

The physics behind this effect has been explained:

Why do wet objects become darker?
Why does paper become translucent when smeared with oil but not (so much) with water?

From my understanding the refractive index of the liquid and roughened surface should be as close as possible (Eg: Glycerol 1.4729, and PMMA 1.4896) in order to maximize this effect. But this Pilot paper works better than any of my trials.

Can anyone suggest how it's made, or what materials/chemistry would work best?


texts:
I would like to show at high level that, in principle, the spectral efficiency (SE) of frequency division duplex (FDD) equals the SE of time division duplex (TDD) and both of them are half the SE of full duplex (FD).

Recall that in FD, the downlink (DL) and uplink (UL) transmissions utilize the whole spectrum for the whole time. On the other hand, in FDD these transmissions utilize half of the spectrum for the whole time and in TDD they utilize the whole spectrum half of the time.

Let us assume that an FD system transmits $b$ bits in total (i.e., DL + UL) in $T_{\text{FD}} = T$ seconds. Hence, the aggregated data rate is $R_{\text{FD}} = b/T$ bits/s. The bandwidth utilized for the DL and UL transmissions is $B_{\text{FD}} = B$ Hz. Therefore, the SE is $\text{SE}_{\text{FD}} = R_{\text{FD}} / B_{\text{FD}} = b/BT$ bits/s/Hz.

An equivalent FDD system would also need $T_{\text{FDD}} = T$ seconds to send $b$ bits and, therefore, would have an aggregated data rate of $R_{\text{FDD}} = b/T$ bits/s. To this end, though, it would utilize a spectrum of $B_{\text{FDD}} = 2B$ Hz. Thus, the SE of this FDD system would be $\text{SE}_{FDD} = R_{\text{FDD}} / B_{\text{FDD}} = b/2BT = \text{SE}_{FD}/2$ bits/s/Hz.

Similarly, an equivalent TDD system would need $T_{\text{TDD}} = 2T$ seconds to send $b$ bits and, therefore, would have an aggregated data rate of $R_{\text{FDD}} = b/2T$ bits/s. For the DL and UL transmissions it would utilize a spectrum of $B_{\text{TDD}} = B$ Hz. Hence, the SE of this TDD system would be $\text{SE}_{TDD} = R_{\text{TDD}} / B_{\text{TDD}} = b/2BT = \text{SE}_{FD}/2$ bits/s/Hz.

We see that, in principle, FDD and TDD have the same SE, which is half the SE of FD.

Is my reasoning correct or some of my assumptions is wrong? Does indeed TDD achieves an aggregated data rate that is half that of FDD (but, of course, the same SE as FDD since it uses also half of the bandwidth)?


texts: Water flow down a 9% grade for 750' then fills tanks before traveling up 20' over 175'

texts:
I'm in hopes that someone far smarter than myself can tell me the answer to my questions.
I am setting up a water capture system for a spring. The spring drains into a pond where I am installing a 525 gallon tank that will essentially be underwater. That tank will feed a 2 inch pipe running 750 feet down a 9% grade where it will fill two consecutive 1700 gallon tanks. The 2 inch pipe will then continue it's run another 175 feet but now going up 20 feet in elevation in that 175 feet before entering the house.  Once inside it will downsize to 1" pipe.
The two 1700 gallon tanks will be sealed.
Will I have enough pressure from the long 750 foot drop or will I need to put in a pressure pump?
What will the pressure be once it enters the house?
Thank you to anyone who works on my problem and is able to answer my questions.
Be well, Mark


texts: Industry standard for AC wall electrical box space

texts:
Are there any industry standards (Engineering Specifications) for the minimum / maximum space required for the electrical box that holds a regular AC wall plug?

The problem I am trying to solve is quite simple - are / is there any local (USA, Canada, or EU) industry standards that require, or set, dimensions in the Height, Width, and Depth (in inches or centimeters) of the space required to be used by the electrical box for an AC wall plug as shown below:


texts: What do Rear-End Collision Avoidance System do on Ice?

texts:
I read on itworld.com:

  Companies such as Volvo and Mercedes are working on crash avoidance systems. Radar measures the distance to obstacles ahead of the car, and if one comes too close the system will warn the driver. If the driver fails to act in sufficient time to stop the car safely, the cars computer takes over and applies the brakes.

Is anyone working on making the cars respond sooner at colder temperatures, or when the road appears to be in slippery conditions? (car has less traction, etc.)


texts: How much force/torque act on a wheel of a vehicle when vehicle moves a constant speed and suddenly got a bump or jerk?

texts:
I am working on disturbance rejection technique in a vehicle of a wheel. Suppose our vehicle moves with a constant speed 15 km/h. Since roads are uneven in nature, suddenly vehicle got a bump or jerk. Is there any method or relationship to find out the force or torque applied by the jerk or bump?

Assume mass of a vehicle is M (kg) and radius of wheel is r (cm).