texts: Low cost, compact cable strain relief for laser cut sandwich case

texts:
I have created the following PCB design:

On the right is a USB port, on the left are a number of pads for connecting a round multi-core cable. There will be between 3 and 10 connections, depending on what is being connected. The cable will most likely be soldered directly to the PCB, although a connector could be used. The large number of pads is to allow for different configurations, only 7 to 12 will be used at any one time.

The board is limited to 50x50mm for cost reasons.

My plan is to use a low cost "sandwich" enclosure, basically two acrylic laser cut parts, a top and a bottom, with screws and spacers to hold the PCB in the middle. The case can be larger than the PCB if required.

How can I add effective but cheap strain relief to this design? I was considering extending the case by 10mm to the left, and adding a couple of holes to thread a cable tie though. Alternately I could thread more screws through and bend the cable around them, but that would require more space. Perhaps some kind of slot in the bottom and top case parts would allow a rubber strain relief grommet to be fitted.

This is a hobby project, doesn't need to be commercial grade.


texts: PV Diagram Pressure temperature volume increasing what is net effect on output?

texts:
I am not properly understanding this question. please help!
Most of the process on PV diagram have this kind of curvature

But in the question above, its bit weird.
My thoughts:
Pressure, temperature and volume all increasing.
So It looks like combustion process than expansion.
I am unable to figure out answer for it. They all seems correct.
There is definitely net work (-ve may be but there is net work)
Not sure about Net heat output.
As expanding density might decrease but pressure is increasing so it might increase.
And enthalpy is more likely to increase as all the quantities are increasing.
Please clarify the above thoughts and explain the answer.
I searched a lot all over the internet. Did not found any process look similar to this!


texts:
I know that a redundant link is a link that doesn't affect the motion of the mechanism even if it is removed . But how could we recognize these links ?

I was solving a problem abuout finding the mobility of a mechanism. I have noticed that the mechanism is negative , although the configuration of the mechanism appears as if the mechanism is able to move , so this is a contradiction. Is this method used to investigate if there are redundant links ? (By finding the mobility first and checking whether the mechanism is able to move or not )

After this step , I think we must recalculate the true mobility , by first removing the redundant links . How could we determine these links ? Is there a certain method ? or I must check all the links , by imagining what will happen to the motion of the mechanism if each link was removed ?


texts: When heating a house, does the water flow slowly decrease as the difference in temperatures approaches 0?

texts:
So let's say you set your thermostat to 20 degrees centigrade, and the current room temperature is 10. A flow of water will gush into the radiators. What I'm wondering, is this flow constant the whole time, or does it slowly descend as the room temperature approaches 20 degrees?

Another way to put it, in the same scenario as above, will the room temperature get to 20 degrees faster if I put the thermostat on 30 degrees? Or will it take the same time?


texts: How to use the linear momentum equation to determine the forces required to hold a nozzle stationary?

texts:
This is the problem I'm trying to solve:

I'm looking at the worked-out solution from my professor and it shows that the sum of the forces in the x-direction is equal to:

[d/dt(momentum) in the x-direction, out] - [d/dt(momentum) in the x-direction, in]

I don't understand what is meant by momentum out vs. momentum in and why one is positive and the other is negative.

Also, I apologize if this is a dumb question.


texts: Laplace Equation -- Heated Plate -- Heat Flux Boundary Condition

texts:
I am having a problem with transferring the heat flux boundary conditions into a temperature to be able to put it into a matrix. I understand that
deltat = deltax*q''/k but I do not know how to code it so that I can loop it into the matrix in MATLAB. I have not had heat transfer and it is a steady state problem, so it should be relatively simple.

How could you index code to be able to loop through since deltat = T(i,j) - T(I+1,J)?

Thank you for any help!


texts: Polar plot direction with increase in frequency

texts: If the angle corresponding to the open loop transfer function of a system at infinite frequency is smaller than that at zero frequency, the polar plot curve in the clockwise direction with increase in frequency. Why is it so ?


texts:
I have a question regarding valves: Let's assume a district heating system where you want to control the mass flow in a sub-station with a valve.

Is (in normal cases) the diameter of the valve (fully open) smaller than the diameter of the pipe that is going to the house (substation)?
Is this the reason, why a valve has a nominal pressure drop at full opening? Because when the diameter of the pipe and the valve would be equal, then the valve would have no pressure-drop when it is fully open right?


texts:
I read something about defining hand gesture, which include mid-air hand gesture (e.g a peace sign with the two fingers moving one after another), touch-based gesture (e.g. on touch screen), and motion gesture - manipulating the device (e.g. tilting a mobile phone sideway, pointing a mobile phone towards a person).

But I am not sure about how to categorise these gestures according to the following axis dimensions.

Some definition I saw were;

  Single-axis Motion occurs around a single axis

  "No matter the gesture is done in the mid-air context or on a surface,
  if the movement is done only in one of the three coordinates, X, Y, or
  Z, it is single-axis."

  Double-axis "If the gesture is performed on a surface, for example on a tabletop application, then the gesture has Double-Axis
  dimensionality."

  Tri-axis Motion involves either translational or rotational motion, not both.

  "If only either of translation or rotation occurs in a gesture which
  is performed in 3D space, it has tri-axis dimensionality."

  Six-axis Motion occurs around both rotational and translational axes

what if I flip down a phone along one axis, it can be considered a rotation in 3D space? if yes then it would be tri-axis even it is movement done in one single axis?
for sliding a phone along a plane and in a straight line, is it a tri-axis motion as it is translation n 3D, or is it a single-axis movement as it moves along one axis only?

Any examples would be very helpful. Thank you very much!

references

*definition in quote is from here: TAXONOMY OF GESTURES IN HUMAN COMPUTER INTERACTION

definition not in quote signs is from here:
http://doi.acm.org/10.1145/1978942.1978971*


texts: Stress Analysis on a Bogie Frame Structure using ANSYS

texts:
The error is "There is at least 1 small equation solver pivot term (e.g, at the UY degree of freedom of node 2144). Please check for an insufficiently constrained model."

This error occurs while applying forces on a bogie frame structure in ANSYS mechanical APDL.

How can I correct this error? because the charged data is correct


texts: What's the easiest way to count high speed pulses?

texts:
I need to count digital pulses with a width of 30 ns and display the updated count to the user every second. The pulses have already been through a comparator and a pulse shaper. Resolution isn't a concern, my only concern is the counting the number of 30 ns pulses while picking up minimal noise.

Is there an easy way to use a PIC microcontroller or a special circuit to execute the count? Could I use a PIC or circuit to execute the count and relay the count to a raspberry pi for further processing/display?


texts: what is the best way to communicate among multiple raspberry pi boards?

texts:
so i was planning to make a project were a system of computers( in my case raspberry pi's) need to communicate to do a certain job. And i am having a trouble choosing a way of communications. so i would like it if any one has some thing to offer.

here are my needs, and thoughts,

Needs

i want a data to be transferred between multiple raspberry pi boards. The data includes videos frame by frame, and some sensor data.
i want it to use the smallest amount of time possible for transferring data. since the boards are going to be attached on moving objects i need to have a fast communication in order for each of them to make decision depending on the others data.
i want each board not to be dependent on the other during network fails

Thoughts

Use a computer as server or the man in the middle to handle data transfers and also do some computations.
use WiFi or Bluetooth modules to create connections.

those are my thoughts and needs so, suggest me any design principles you now, their advantages, and disadvantages.


texts: How to prevent movement in this 3 DOF setup?

texts:
I have a 3DOF platform that I'm trying to make more stable. It's difficult to explain in words what the issue is so I've added a GIF below.

Any ideas of how I can get rid of this wobble? The DOF arm tends to cave inwards. I know it's being caused by the very small gap between the screw and the channel but is there any way to prevent this? Since the servo's I'm using don't have a dual shaft going through and through I can't modify the servo arm to be a inverted-U attached on both ends of the servo.


texts:
Hooke's Law defines a linear-elastic relationship between stress and strain.

$$ \sigma = E\epsilon $$

Steel behaves very much like a linear-elastic material, following Hooke's Law closely. It does, however, display non-elastic behaviors such as relaxation. Relaxation is the behavior wherein a member under constant strain displays variable (and reducing) stress over time.

My question is: is relaxation plastic? If the relaxed member were released, how would it behave? Would it follow a path defined by its elastic modulus? If this is the case, then it will end with a plastic deformation, no? After all, when stressed, the member will have reached $\left(\sigma_1, \epsilon_1\right)$. After relaxation, it will reach $\left(\sigma_2, \epsilon_1\right)$. Once released, it would have to reach $\sigma =0$, which implies in $\epsilon = \epsilon_1 - \dfrac{\sigma_2}{E}$ and since $\sigma_2 <\sigma_1$, that implies in a nonzero $\epsilon$.

Or is there some other behavior? Does the elastic modulus change to allow for a return without plastic deformations?


texts: How much weight can my stepper motor rotate?

texts:
I'm building a 3D scanning (photogrammetry) device with a rotating platform, a bunch of wheels and a stepper motor. What I want to know is how much weight that motor could rotate on the platform.

Currently the platform weights just over 2kg and is just under 40cm wide (see the image below). I estimate that the objects I will be scanning will weigh no more than 5kg (just to be safe).

So the link to that servo motor says it has a 'stall torque' of 15kg - cm at 6V. I have no idea what that means. Is that enough? Will it be able to rotate the my platform?


texts:
I am using 123D Design to build a model for 3D printing.  What I want to build is a large 2D rectangle with several smaller rectangles inside. Then, I want to extrude the larger rectangle, but leave the smaller ones as holes.

I thought that I could subtract the smaller rectangles from the larger one and then extrude the remainder.  However, when I use the subtract tool, I cannot select sketches - just solids.

Any ideas on how to do this?  I would very much like to know how to do it 2D first, and then extrude the remainder.  However, if I must transform this to 3D first, I'll be willing to learn that instead.  Much appreciated!


texts:
The exercise is taken from linear algebra and its applications, prof. G. Strang

Exercise 2.4.8 Truss
I have already found that: m=n=8 → system is statically determinate, therefore solvable by equilibrium equation.
A is a 8 by 8 square matrix.
Also we know, there aren’t any rigid movements since the truss is fixed. Also, because 8-8 is 0, we're expecting 0 solutions to Au=0
I wrote the forces eq. equilibrium:
$f_{H_1 }=-y_2-y_4 cos30$
$f_{H_2 }=y_2+y_5 cos30$
$f_{H_3 }=-y_7-y_5 cos30$
$f_{H_4 }=y_7+y_4 cos30$
$f_{V_1 }=-y_2-y_4 sin30$
$f_{V_2 }=y_2+y_5 sin30$
$f_{V_3 }=-y_7-y_5 sin30$
$f_{V_4 }=y_7+y_4 sin30$
How should I continue and say something regarding the stability of the system?


texts: Torque required to move the skid steer robot

texts:
I have a 4 wheel skid steer robot. My motor can deliver up to 6 Nm with a gearbox efficiency of 70% up to 170 rpm. I want to find out whether I will be able to make a pivot turn and move.

So I assumed that pivot turn force = force to move the blocked wheel.

The force required to move a 100 kg weight is F = c * m*a = 0.02 (friction, not a rolling friction as I am taking worst case scenario) * 100 * 9.81 = 20 N.

The wheel will be placed 10 cm below the weight so the torque required is 0.1 * 20 = 2 Nm. Is that correct?


texts: Automatic translation of either-sided rotation to fixed directions?

texts: Is there a purely mechanical device that takes in clockwise or counter-clockwise rotation 'indiscriminately' and outputs in both cases clockwise rotation?


texts: Books and resources for an entrepreneur inventor?

texts: What books would you recommend for an inventor entrepreneur?


texts:
I asked the same question in electronics sub, but since it is more general I am asking it here again. I bought the Sharp dust sensor GP2Y1010AU0F. Below are the graph of readings indoor for ~5 minutes, it seemed quite smooth to me. The peak at the 10th second is done on purpose for showing the max reading. The ug/m3 values are created using the reference graph in the data-sheet.

I want to compare my readings to some references, there are some papers giving the measurements for smoke, candle, deodorant etc. However, it would be better to create and environment with known PM information.I don't have any reliable machinery for creating or measuring the environment PM density. So far, I though of creating a chemical reaction in a 10-20m3 closed room and periodically increasing the reaction parameters. I need your suggestions for testing the sensor with a known input.


texts:
I have a Structures question about determining strain energy that I am unable to solve. I have attempted it and I have the answer, I would appreciate if if someone can just tell me where I am going wrong.

Q: A solid conical bar of circular cross-section is suspended vertically. The length of the bar is $L$, the diameter at the base is $D$ and the weight per unit volume is $\gamma$ (equivalent to density x gravity). Determine the strain energy of the bar due to its own weight.

$$\text{Answer} = U = \dfrac{\pi D^2 \gamma^2 L^3}{360E}$$

My work is as follows:

$$\begin{align}
U &= \dfrac{\gamma((1/3)\pi r^2 L)^2)L}{2E\pi r^2} \\
U &= \dfrac{\gamma(\pi^2r^4(1/9)L^2)L}{2E\pi r^2} \\
U &= \dfrac{\gamma\pi r^2L^3}{9\cdot2E} \\
U &= \dfrac{\gamma\pi(d^2/4)L^3}{18E} \\
U &= \dfrac{\gamma\pi d^2L^3}{18\cdot4E} \\
U &= \dfrac{\pi d^2 \gamma L^3}{72E} \\
\end{align}$$

I am incorrect by a factor of 1/5. Where in my working/logic did I go wrong?

I know:

$$U = \dfrac{(\rho gAL)^2L}{2EA}$$

I assume:

$$AL = \text{Volume (of a cone)} = (1/3)\pi r^2 h$$

I am confused as to whether the A in the denominator is the base of the
cone or the volume divided by the height.

I can derive the correct numerator, however I am not sure how my
lecturer arrived at 360E for the denominator.


texts:
The gas $(A)$ is diffusing into the solid sphere $(B)$, The sphere phase is assumed to be stagnant so we have no bulk movement, $(A)$ is being consumed in the sphere by a rate of $KC_A$ which $K$ is a kinetic constant and $C_A$ is concentration of $A$ in the sphere, $C_A$ in sphere as a function of $r$ (radius) is desired.

By the species continuity Eqn. we have :

$\frac{1}{r^2} \frac{d}{dr}(r^2N_A)=-KC_A$

By definition of $N_A$ we have:

$N_A=y_AN_t-D_{AB}\frac{dC_A}{dr}$

which $N_t$ is zero by the stagnant assumption. By substituting $N_A$ in the first Equation and differentiating we obtain:

$C_A''+\frac{2}{r}C_A'-\frac{K}{D_{AB}}C_A$=0

I just don't know how to solve this differential equation, maybe there's a need for a simplifier assumption that I didn't make, anyway I welcome any advice from you guys helping me find the answer.


texts:
Bending moment diagram from shear force diagram

We all know that $$\tau = VQ/ It $$
how to determine the shear stress at G ?
I'm having problem of finding Ay
centroid if the solid that i found earlier is y = 98.5mm

so , my working is
Q = Ay = (250x10^-3)(50x10^-3)( 50+125-98)(10^-3) = 9.63x10^-4

I'm considering the area above the G .

Is my concept correct ?
edited : There's a dashed line from G to the bottom . It's making me confused . for Q , should i consider the area either to the left or right of the G ?


texts: How to calculate propulsive force of gas ejection

texts: How can I calculate the propulsive force produced by ejection of a gas? I suppose it depends on the gas, the velocity with which it ejects, the amount of gas, and some other parameters, like the geometry of the nozzle for example. I would like a calculator to play with the gas density, the gas velocity etc, and see the various propulsive forces generated.


texts: What is the name for a removable sewn bag stitch?

texts:
This stitch is composed of a single string/thread and is common on dogfood and grain sacks. It can be removed by just pulling on the end. Here is an example I found on youtube.

Thanks!


texts:
Speed breakers are safety devices that keep check on the fast-moving traffic. But
what does the speed breaker do when the vehicle is already slow approaching.
Is there any better breaking system design approach which keeps the fast-moving vehicles in check but
eases the travel of the slow-moving vehicles?


texts: Which polymers are used to make polymer concrete?

texts: I was going through the wikipedia page on polymer concretes. It seems like a good type of building material. I was wondering which types of polymers are used in the concrete, since I cannot find any online besides epoxy.


texts: Here's one for any of you electronics experts. On the 2nd story of my house, I have a TV antenna. It reaches a height of about 5 ft above the house, and the mounting bracket is attached to the back wall of the restroom. The downlead cable runs into the attic, through a preamp and on to the tv's throughout the house. Now...here is the puzzler...anytime someone goes up to the restroom and opens the door, the picture on all of the tv's will start tiling badly...before that, it was crystal clear....once the person comes out, opening and closing the door again, it will become clear. Now, why in the world would opening and closing the door of the restroom affect the signal from an antenna mounted behind the restroom and at least 5 foot higher than it's roof? I thought the family was nuts when they first told of this...I have tested and retested, it makes no sense at all, but I can't deny that it does happen.Anyone have a theory?


texts: Does Pavement ME Design output the tensile strain beneath an AC layer?

texts: I'd like to know the tensile strain beneath the asphalt concrete (AC) layer in my design structure. Usually, the strain is used to calculate the number of axles (Nf) that the pavement structure can take before failure. Do you know how/where I can find that?


texts: How are the conditions after the shock calculated for a shockwave formed on a cone?

texts:
How do oblique shockwaves differ from 2D to 3D problems? More specifically, how are the conditions after the shock calculated for a shockwave formed on a cone (e.g. the inlet cone on a ramjet)?
I am familiar with the process/calculations of the after-shock conditions of obliques shockwaves at a ramp, namely for the deflection angle:

where  is the deflection angle,  is the angle between the shockwave and the normal,  is Mach number and  is the ratio of specific heats.
Firstly, is there a difference in the conditions when the ramp is revolved into a cone? Secondly, if they are different, what are these differences, specifically in the calculation of the deflection angle and velocity after the shock?

EDIT: Looking at the link suggested and a few textbooks, I found Modern Compressible Flow: with Historical Perspective by John D. Anderson explained conical flow very clearly. To summarise, the ODE to solve is the following:

Finding the solution of the flow involves being given either the cone angle and surface Mach number, or the shock angle and the surface Mach number, and then numerically integrating the ODE above.
As for the other conditions after the shock, the shock wave relations for immediately after the shock still hold. Similarly, after the solution to the Taylor-Maccoll equation has been found, the usual isentropic relations for density, pressure, temperature etc. can be used.


texts: Practical setup to measure angular velocity

texts:
I have got a spinning top from a Canadian manufacturer, and I am deeply amazed by how neatly it spins.

My interest in physics has led me to try to find out at what top speed I can spin the top and how that compares to other tops made from other materials and other shapes.

I have glued a little sticker to it and recorded it with my phone's camera but the frame rate is far too slow to be able to count the number of rotations over time.

I don't have access to specialized equipment but I can measure or approximate the volume, mass, density, temperature and probably also the moment of inertia. How do I measure the angular speed of the top?


texts: The boundary condition(s) for a continuous beam

texts:
I have a continuous beam across a center column (not sure whether I've draw it correctly or not)

The Displacement and force diagram is as shown:

The first diagram is the bending moment, second the axial force, the third is the displacement.

Now, what is the boundary condition at $R_A$, $R_B$ and $R_C$?

From what I can infer, it seems to be

$w(0)=w(L)=w(2L)=0$ (corresponds to the deflection at the three support)

$M(0)=M(2L)=0$, or $\frac{d^2w(0)}{dx^2}=\frac{d^2w(2L)}{dx^2}=0$ (corresponds to the moment).

But I suspect that I am still missing some boundary conditions in order to derive the complete displacement/force diagram for the continuous beam. Are there any boundary conditions that I've missed?


texts: How to grind into concrete ( not core drill )

texts:
I have a very specific and weird task I need to accomplish.

I have a concrete wall that I need to get samples of the concrete dust to grind and get them tested, i plan on using a plunge router with a vacuum collar type setup with a grinding head of some sort ... problems are

needs to be in-situ ( i can't do a standard core then chop it up )
I can only find one grinding head that appears to do what i need https://i.imgur.com/4IhxHMW.png
needs to be about 50-70mm diameter sample area and not miss any of each "layer"
i need to do this about 50 times and i'm not sure a vacuum bezel head will last long?
i need to drill in 0.5mm increments each sample of the dust

i thought id check and see if anyone else has an idea of an easier way I could accomplish this! Surely i'm not the only one who has encountered something like this.

Cheers


texts: What is the name for a low pressure, low volume air reservoir?

texts:
I'm working on a project that requires very precise, but low pressure controls. I'm using a pump to charge a chamber to <15kPa, then a manifold of proportional valves to control output pressures from a few channels at around 3kPa with low flow. I've been using the tubing from the pump to the manifold as a reservoir, but I'd like more volume, in the range of 0.2-0.5L. I'd imagine such a reservoir exists for <$50.
A squeeze bottle with some barb fittings is in the ballpark, but I'm curious if there are other ideas. I'm hoping someone can help me find the right terminology here, as all I can find are large tanks when I search 'reservoir' or 'accumulator'.


texts: At How Many RPMs Would Aluminum HDD Platters Shatter?

texts:
I'm using hard drive platters to create a Tesla Turbine. I'd like to get as much efficiency out of it as possible. That being said, for safety concerns, I'd need to know a generic range at which they'd shatter.

If there's no range that anyone has found, then how could I (safely) test what speed they shatter at?


texts: Ride Comfort Estimation using Accelerometers

texts:
I've been trying to find established/novel methods for calculating ride comfort using accelerometers and recently I came across this paper which uses ISO 2631 standard to get an objective measure of ride comfort.
Upon reading the paper, it highlights that the standard objective ride measure does not correlate strongly with the subjective ride measures. Hence, the authors use NN to figure out a better correlation.
The objective measure the standard uses, as discussed in the paper(I did not buy the ISO standard yet), is the running root mean square(RMS) of acceleration to calculate weighted acceleration($a_w$). This method considers the occasional shock and transient vibration through the use of a short integration time constant.

(I think the equation is wrong because the power outside of integration should be half)
My questions:

Has anyone here used ISO 2631 to estimate ride comfort?
When I perform running RMS on 20,000 acceleration data points, instead of getting smoothed 20,000 points, how do I get a single/cumulative RMS or $a_w$ to estimate ride quality using table 5?


texts: In circular motion , why do we say this is centripetal acceleration

texts:
Let us say a particle is moving in a circle  with Uniform circular motion .
Then , if I take an equation like this .
$\theta$ = S(Arc length or Total distance covered ) / Radius of circle *( time taken to cover this distance ) = $\delta$ v ( final - initial velocity ) / v final or initial *( Time taken )
= Velocity of particle / Radius of circle = Centripetal acceleration/ Radius of circle .
So , I am not getting is why do we get centripetal acceleration here.
Why not tangential or total acceleration?


texts: I am having trouble finding a 3.4 µH through hole inductor that is in stock right now. I was wondering if I can just place 2 inductors that add up to 3.4 µH in series to solve this problem. I am not sure if this would introduce any problems, if so what kind of problems and how can I mitigate them.


texts: Selection of corrosion resistant material for mechanical testing apparatus

texts:
I want to build a 4-point bending apparatus for operating within a corrosive environment, using EXCO type corrosion solution as seen in ASTM Standard G46. Thus, in this highly corrosive environment, I need a very stiff material to act as the testing apparatus. Obviously, metals would be preferred.

Can anyone suggest a metal that would be immune to corrosion, and/or an easy method to coat a more generic metal, say tool steel, such that it is immune?


texts: Cannot understand an equation related to impedance. (Power system analysis)

texts: Can someone explain how can we find |Z| term and also from where does the cosine term arrive at the final equation.


texts:
I'm trying to find the maximum bending moment and deflection for this symmetrical simple beam. The formulae I can find, deal with either cantilever beams with one fixed end, or continuous beams without cantilever ends, not this kind of situation.

I've tried to model the beam as two fixed-end cantilevers, on the basis that symmetry demands the middle of the beam is horizontal, and then modelled the loads as separate loads superimposed. But I'm not getting anywhere and not sure how I'd tell whether my answer was correct, if I did. I don't know if the fact that the beam can rise or fall in the middle (depending how F compares to W) is the problem, or if it's something else.

The beam won't be exposed to non-linear behaviour. It could bend either way, as I don't know whether the 2 point forces will be larger or smaller than the UDL, or the exact lengths involved.

Is there an easy way to work out the maximum deflection and B.M. of this beam, and if so, what are they?

Note, this isn't homework or coursework (I haven't had those for many years!). It's part of a real-world practical design I'm trying to work on.


texts: Why does prestressing in trees make them stronger?

texts:
In "Structures: or Why Things Don't Fall Down" James Gordon talks about trees being prestressed with the outside in tension and the inside in compression. Why does it make a tree stronger to have it in tension on the surface and compression at the core and how do I read the graph in the first picture below?

Also, in the third pic it talks about doing the reverse with a concrete beam. How do you create tension using rebar?


texts: Damped harmonic motion with dry friction

texts:
So I'm a hobbiest who loves doing and learning about different subjects. Often I run into difficult problems that I normally can find solutions to however this one stumped me, I have reviewed many physics journals on the problem but either they are two complex or tackle the much easier version of 'viscous' friction.(p 2/54)
Essentially when I even begin a solution I yield to this:

Ma = sign(v) * mg*mu - kx

This would be simple if the friction didn't change direction. Does anyone have a suggestion on how to approach this problem? I'm not looking for someone to solve it I just want an idea on how to start it. Thank you


texts:
I did a Civil Engineering course some years ago and from my textbook I had a question on a pump with hoses. Unfortunately I haven't been able to find a solution to this yet.

A pump feeds two hoses, each of which is 45 m long and is fitted with a nozzle. Each nozzle has a coefficient of velocity of 0.97 and discharges a 37.5 mm diameter jet of water at 24 m/s when the nozzle is at the same level as the pump. If the power lost in overcoming friction in the hoses is not to exceed 20 per cent of the hydraulic power available at the inlet end of the hoses,
calculate (a) the diameter of the hoses, taking f = 0.007, and (b) the power required to drive the pump if its efficiency is 70 percent and it draws its water supply from a level 3 m below the nozzle.

These are the calculations I have so far

a) Head lost in friction Hf = 4 * f * L * v^2/ D * 2g, where L = Length of hose, D = Hose diameter, v = hose velocity and f = friction coefficient

If H = Head at inlet to pump and hoses

Head at nozzle Hp = H − 4 * f * L * v^2/ D * 2g
or Hp = Head at inlet to hoses - frictional head loss in each hose.

If jet velocity = V and Cv = 0.97 Jet Velocity V=Cv √(2g ∗ Hp), where V = 24m/s

Hp = V^2/(2g ∗ Cv^2) = (24^2) / 2g * (0.97)^2, so Hp = 31.208 m

For continuity of flow, flow from hoses = flow from nozzle, so 1/4 Pi * D^2 * v = 1/4 * Pi * d^2 * V, where d = jet diameter

v = V * (d2/D2) = 24 *(0.0375)^2 / D^2 = v = 0.03375 / D2.

I have then put this in the frictional head loss formula 4 * f * L * V2/D * 2g = 4 * 0.007 * 45 * (0.03375 D^-2)^2 / (D * 19.62) = 1.43521875 ∗ 10−3 ∗ D−4/ D ∗ 19.62 = 1.43521875 ∗ 10−3/ (D5 ∗ 19.62).

Note 2g = 19.62

If power lost in overcoming friction in hoses is not to exceed 20 per cent of hydraulic power available at inlet end of hoses, then H = 5 * 4 * f * L * v^2/ D2g
so Hp = 5 ∗ (4 * f * L * v2/ D * 2g) - (4 * f * L * v^2/ D2g) = 4 * (4 * f * L * v^2/ D * 2g) = 4 * 1.43521875 * 10^-3/ (D^5 * 19.62)
Hp = 5.740875*10^-3/ (D^5*2g)

So 2g * Hp = 5.740875 * 10^-3/ D^5 = 19.62 * 31.2018 = 612.1798m

D^5 = 5.740875 * 10^-3 / 612.179, so D = (5.740875 * 10^-3/ 612.1798)^0.2 = 0.09872m

so Hose Diameter = 98.72 mm
IN MY TEXT BOOK ANSWER WAS GIVEN AS 98.5mm, WOULD THIS BE DUE TO ROUNDING?

(b) Power from pump P = w * Q * Hp,
where w = unit weight of water, Q = flow through pipes and Hp = Head from pump

Now we have to use Bernoulli equation with pump head term in it as well as head loss

Z1 + P1/pg + V1^2/2g + Hp = Z2 + P2/pg + V2^2/2g + Hf

In this formula we assume that P1 ands P2 are atmospheric pressures at entry to the pump and exit of the nozzle, so P1 = P2 = 0

Z1 = 0 and Z2 = 3m

V1 = velocity in hoses and V2 = jet velocity from nozzle = 24m/s

We have to calculate velocity in hoses and then frictional head loss

From before v = V * (d2/D2) so v = 24 * (0.0375^2)/ (0.09872^2) = 3.463m/s so V1 = 3.463m/s
Now we have to put V1 into frictional head loss formula Hf = 4  *f * L * v2/ D * 2g
so Hf = 4 * 0.007 * 45 * (3.463)^2 / (0.09872 * 19.62) = 7.80m

Now we have to put values in Bernoulli equation to find head from pump

so using Z1 + P1/pg + V1^2/2g + Hp = Z2 + P2/pg + V2^2/2g + Hf

0 + 0 + (3.463^2)/2g + Hp = 3 + 0 + (24^2)/2g + 7.8 Hp = 3 + (24^2)/2g + 7.8 - (3.463^2)/2g = 3 + 29.3578 + 7.8 - 0.611 Hp = 39.5468m

Flow from one hose Q = 1/4 Pi * D^2 * v = 1/4 * Pi * 0.09872^2 * 3.463 = 0.026507m^3/s

Power from one hose P = w * Q * Hp = 9810 * 0.026507 * 39.5468 = 10284W = 10.284kW as there are 2 hoses, total Power from hoses P = 10.284 * 2 = 20.567kW

as the pump has an efficiency of 70 per cent then Power from pump = 20.567/ 0.7 = 29.382kW

IN MY TEXT BOOK THE ANSWER WAS GIVEN AS 31.1kW, IS THERE SOMETHING ELSE I SHOULD TAKE INTO CONSIDERATION?


texts: Stepper motor torque calculation based on pulleys ratio

texts:
Say a stepper motor has fixed value of "units", given as a holding torque related to distance of the center of its shaft. Like 1kg/cm or 14oz/inch.

I have a GT2 16-teeth pulley on the motor shaft. (I'm using a 5mm GT2 belt as a load transfer if that matters) Knowing that the motor can hold 1kg weight, 1cm away of the center of its shaft, and the 16-teeth pulley "outher-teeth" diameter is 9.7mm, I can easily assume that it can hold about 1kg of load safely (at least trusting manufacturer's datasheet).

But, what if I add a GT2 48-teeth pulley on the load part (I don't know the outer diameter)?

Is there any algorithm I could use (to atleast roughly) calculate load capabilites of the motor, based only on the pulley teeth count?


texts: Effect of varying diameter bolts on shear stress under eccentric loading

texts:
In my mechanics of materials class we are required to be able to solve problems with bolts in shear. Unfortunately our textbook doesn't cover this subject we only had a little bit of information given on slides and I am having trouble finding other resources that expand on this concept.

Here's an example question for context:

So far these problems are straight forward. The total shear on a bolt is equal to the direct shear plus the torsional shear. First you get the direct shear component by distributing the force evenly on each bolt so $\displaystyle\tau_D=\frac{P}{4A}$ where $A$ is the cross sectional area of the bolt parallel to the force. Then you calculate the torsional shear by finding the torque $T$ of the force $P$ about the centroid of the bolts and $\displaystyle\tau_T=\frac{Tc}{J}$ where $c$ is the distance of the bolt from the centroid and $J$ is the polar moment of inertia of the bolts. The direction of the torsional shear is found perpendicular to a line from the centroid to the bolt in the sense of the rotation of the torque.

I have no trouble doing these types of problems but I'm curious what happens if the bolts are not all the same diameter.

What I'm guessing is that the torsional shear will change because the centroid and polar moment of inertia will change but the torque stays the same. Is that correct? Is the force in the direct shear component still evenly distributed on the bolts?

In the above example if one bolt has a larger diameter than the others would the direct shear on the bolts still be $\displaystyle\tau_D=\frac{P}{4A}$? (obviously $A$ is now different in the larger bolt) or would the force in the direct shear be proportional to the relative size of the bolts?

Can anyone explain this to me to verify if my line of thinking is correct?


texts: How to calculate torque requirement for vehicle with Mecanum wheels?

texts: What are the changes specific to mecanum wheels when calculating torque requirements for a vehicle. I have the data for the vehicles mass, top speed and top acceleration.


texts: Why do we need to condense steam in the rankine cycle?

texts:
In my admittedly naive understanding of the rankine cycle, steam is condensed back into water after passing through the turbine.  Why not reuse the steam instead?  It would seem to require less effort to reuse heated steam than to intentionally condense the water only to reheat it once again.

I'm sure i'm misunderstanding something about the process.  Why do we have to condense the water at all?


texts: Epoxy that can withstand up to 800C and is optically transparent?

texts: I'm looking to use an epoxy in a high-temp environment like 800C, and one that is optically transparent at 450nm (not below 90% transmission). But i'm having trouble finding one. It can be made of any material, as long as it can be cured in a mold.


texts: Determine Cp of an oil from density and temperature?

texts:
I suspect I know the answer to this, but hoping someone may know something I don't here.

Is there a way I can determine the specific heat capacity at constant pressure (Cp) of an oil if I know the density, temperature and viscosity?

The oil I am interested in: http://www.bakerprecision.com/neo/75w90rhd.htm

The company is only small and hasn't got a value of Cp as far as I can tell, I have contacted them. They are unlikely to have tested it in my experience of dealing with them.

As far as I know this could only be done by experimental correlation, and there is no universal equation.

Is there any theory you know that can estimate the value of Cp of an oil from basic properties without experimentation?

I know:
Dentity, viscosity and surface tension at room temperature. Plus viscosity at various other temperatures.


texts: This device is used in washing machines to dispense water and cleaning solution in the right amounts. What is the working principal of it?

texts: The following device is generally used in washing machines to dispense water and cleaning solution in the right amounts whenever needed. How does this device work?


texts:
I am building a table with four legs which must support a dead weight of 250 kg, and possible peak dynamic load of 1000 kg (A 200 kg person climbs onto and off of it).  The legs come straight down from the box, rigidly fixed to an aluminum tubing frame.  They flare outward and end in free-rolling wheels.  Dimensions are as shown.

The application is very weight-sensitive.  Would legs made from 6061-T6 aluminum round tubing, 1.0" OD x ".093 wall be sufficient or should I bite the weight bullet and go with steel tubing?


texts:
I am trying to assemble the parts of Plummer block and draw the half sectional views from the front as given here
I am facing some trouble understanding a few sectional views. In this view
I am unable to understand why there are two different radii R32 and R34 marked in the front view of base.
In this view
I am unable to get why there are two different radii for brass shown R32 and R30. Also which component R38
represent in the front view.
Thanks.


texts:
I’m trying to understand how anti-squat works in motorcycles and how the geometry plays a major role.

I don’t understand, however, the reason why the force from the tires that is transmitted to the chassis of the bike via the swing arm is always along the axis/centre line of the swing arm and not parallel to the ground.


texts: value of $\gamma$ in the H-infinity norm

texts:
Suppose I have the system:

$\dot{x} = Ax+Bu$

$y=Cx+Du$

and the following Hamiltonian matrix:

$H=\begin{pmatrix}
A & \frac{1}{2}B^TB\\
 -CC^T&-A
\end{pmatrix}$

I want to find the value of $\gamma$ which is the bound of the $H_{\infty}$ norm, so it is the value such that $\left |T(j\omega)  \right |_{\infty }<\gamma$.

I know that for the bounded real lemma, if the eigenvalues of $A$ have negative real part, and $I\gamma^2-DD^T>0$, then the Hamiltonian have no eigenvalues on the imaginary axis. I also know that if the eigenvalues of $A$ have negative real part, then $\left |T(j\omega)  \right |_{\infty }<\gamma$ holds.

But my question is : how do I find the value of $\gamma$?

I have been told the result is $\gamma=0.5$ but I really can't get to this result. I have tried using the Shur's complement to see if this matrix is negative definite (so before doing that i switched sign to the Hamiltonian). In this way i thiught that if the A matrix is negative definite, it has all eigenvalues with negative real part, so the resulting value of $\gamma$ form the computation would have been the searched value. But I don't find the desired result. Maybe I am missing a point and doing something wrong, or maybe I am complitely on the wrong path.

Can somebody please help me? Thank's in advance.


texts: Typical tolerances for valve lift using a camshaft?

texts:
I am working on a linear actuator for a valve.

Wondering if anyone out there can point me towards the tolerances that are used for valve lift in a typical internal combustion engine using a camshaft?
i.e. what is the plus/minus range that the valve lifts to?

Thanks!


texts: How to create a Liquid tight cable seal in a fuel storage tank

texts:
I am working on a telemetry system where a liquid level sensor (Hydrostatic pressure sensor) is used to monitor the volume of fuel (gasoline / diesel) in an underground storage tank.

The sensor has to immersed in the fuel and has a cable that is to exit the tank and then be connected to an acquisition unit housed in a panel.

The main problem i will like ideas on is that, the sensor cable needs to form a liquid-tight seal at the point it exits the tank.

I have come across a component called a CordGrip / Cable gland but will like to know if any other methods exist

The final solution should take into account that the exit point of the cable is exposed to the outside environment of sunshine and rain


texts: How would you mechanically model an Earth-Moon like orbit?

texts:
I'm hoping to make a small mechanical demo (~10cm tall) that models an orbit that is similar to the Earth-Moon orbit - that is, only one side of the Moon faces Earth. I'm trying to keep it simple, so here's my idea so far:

where the blue and yellow represent Earth and Moon, respectively. These are meant to represent a different planet and its moon though.

The orbit of the Planet (blue) and its Moon (yellow) has the following differences:

Planet is eccentric
Only one face of the Planet and see its Moon, i.e. the horizontal bar on each disc should remain parallel. The bars are for explanatory purposes only.
Planet's rotation axis may shift (vertically along the green bar), but the Moon's orbital axis is fixed, i.e. Moon should be always in contact with the outer ring housing

My question is: how should the two discs be connected in order to to have the above properties? I've thought about using springs, but I think it'd be quite flimsy though.

I know about orreries, but typically they don't self-adjust orbits though. Also, I was hoping for a simpler mechanism given that there doesn't need to be empty space between the two discs. I'm only hoping to model the motion on just one plane.


texts:
I'm trying to add a cavity in part A using part B in an assembly. I'd like to expand the cavity uniformly away from the B around each feature. Instead, the cavity seems to be expanding from the center.
All of the "scale about" options produce similar results. The origin of part A and B are at their centers.

Edit:
From the comments, it looks like offset is what I should be looking at. I created an offset surface but I'm not sure how to trim or cut it from the part.


texts: How to find the minimum shear area of a rectangular thread

texts: I am trying to find a method of calculating the minimum shear area of the following rectangular thread form. It is a 4.125" square thread, 8 T.P.I., straight, right-hand thread. The thread is loaded in the axial direction, thus I would like to calculate the minimum thread shear strength.


texts: Relationship between Heat Flux and Engine RPM

texts:
I'm doing a project that involves knowing the average steady-state heat dissipation rate of a single cylinder air-cooled engine (through the engine wall and fins) at a given RPM. The problem is that I cannot seem to find any research regarding the same. Most of the data available out there revolves around the measurement of the peak heat flux across different components(piston, wall, etc.) at various crank angles.

At this point, even a rough value would be good enough.


texts: How to avoid contact penetration in Ansys?

texts: I am trying to simulate contact between a flat rigid plate and a sphere. I am applying a load on the flat rigid plate and the sphere is flexible. How can I avoid this flat from penetrating into the sphere?


texts:
How do you design against an earthquake?
Do one initially consider earthquake in early design stages or is earthquake mitigation considered later in the design stage after conceptual stage?

What are the advantages and disadvantages of the above-mentioned approach?

I am unable to find enough material online on this topic can someone guide me on this so that I can further my research.


texts: double effect roller bearing or two needle roller bearing

texts:
Good morning,
I need to source 30 or 50 bearings such as the picture. This is a double effect roller bearing and the mid washer is drilled as you can see.

Shaft diameter: 17mm

Height: 22.26mm

Speed is not an issue

This is not standard and very hard to find.

Instead, I was thinking to put 2 AXK1730 needle bearing + 2*2 AS1730 washers and make another mid washer with the 2 holes

What do you think about this?


texts: Automatic door, linear actuator or stepper motor

texts:
I need to build a device that has motorized a door with a hinge on top, similar to cat doors:

Between these options, which one makes the most sense:
- use an actuator on the side to push the door up
- put a pulley on the door hinge and drive it with a stepper motor through a belt
- put an anchor above the door, on the same plane, and pull a string on a reel with a stepper motor
- or, any other idea :)

What makes the most sense from a mechanical point of view? it's for a small device where the door is roughly 7x7" and weights about 0.6LBS.

The actuator seems the simplest so far, but before I order parts I would like to have opinions from people that understand this stuff :)


texts:
Sorry I'm having a migrane and can't think rn, which is why I am posting such a basic question for confirmation...

The above diagram shows two sprockets on a beam which is attached to a driven gear.
The Red sprocket doesn't rotate (it is fixed). The orange sprocket is at the other end of the beam and can spin freely. Theres a chain between them (not drawn)
Relative to the gear/beam, the red sprocket is rotating in reverse.
So would I be correct in saying that the orange sprocket will turn with the opposite angular velocity of the Driven Gear?


texts: I'm confused as to what is the difference between the above said stresses and their corresponding strains. If possible can anybody explain in detail what is engineering stress


texts: Distribution of energy absorption in inelastic collision

texts:
Object A has mass $m_A$, and is travelling west with velocity $v_A$.  Object B has mass $m_B$ and is travelling east with velocity $-v_B$.  The objects collide in a perfectly inelastic collision so that the velocities of the two objects after the collision are the same.  Prior to the collision, the objects are made of uniform, identical materials and shapes.

How much of the kinetic energy is absorbed by deformation of object A, and how much of the kinetic energy is absorbed by deformation of object B?

If there is not a unique solution to this question because of a lack of necessary constraints, please answer the question with some examples for the unspecified constraints.

EDIT: when I said same shapes, I meant they are both cylinders or prisms or spheres or something.  The dimensions and masses of the shapes may be different.


texts: Multi-Directional Rack and Pinion Drive - Vehicle Motion Using Helical Wheels

texts: I have a vehicle with 4 wheels. Say I replace the wheels with large helical gears (pinions). If I set the vehicle on linear helical racks, it should be able to travel in one dimension. Say I replace the racks with a similarly toothed ground surface, could the vehicle travel in 2 dimensions (without rotating the body of the vehical)? I think it would be possible with opposing front and rear wheel drives. It should operate like a "screw" in the second dimension. Would the ideal helix angle be 45 degrees (to support movement in both directions)? How will speed, Torque, and service life be affected?


texts: is there a formula to determine if a structure will topple over

texts:
as a child all of us have built a tower out of Lego. we built it as high as we could but then eventually it topples over.

is there a formula to calculate how wide and heavy the base has to be for the tower not to topple


texts: Linearly Damped Harmonic Motion with Sliding Friction

texts:
In Problem 2/54, I have come up with a solution only one decimal place off from the books results. I am posting to see if someone can look over my solution to see if it is correct.

To begin the equation given:

a = u*g - (k/m)x

Only works in cases where it only moves in a direction where the friction force is strictly positive (i.e. the block is moving leftward).

To solve the case of motion in the opposite direction must be considered, the equation for motion opposite this direction is:

a = -u*g - (k/m)x

Now using the relationship in the book:

vdv = ads

Integrating and noting that each starting and stopping point has zero velocity:

(1) 0 = u*g(xf - xi) -(k/2m)(xf^2 - xi^2)

(2) 0 = -u*g(xf - xi) -(k/2m)(xf^2 - xi^2)

Now using (1) the first stop start point occurrs at:

xf = .23866m

On the way back however the motion is reveresed and equation (2) is used to find:

xf = .022666m

The solution in the book was: 23.3mm

Did I make a mistake or why is there such a seemingly slight difference in the answer?


texts: What are the available options to create plastic bumpers?

texts:
I want to know the list of options to make a plastic bumper. Currently I can think of moulding methods:

Injection moulding.
Blow moulding.

Questions:

What are the other moulding methods?
Is there any other methods that are not considered "moulding", that end up giving me a plastic bumper?


texts: Is it acceptable to paint weathering steel?

texts: Weathering steel is not typically painted, because it produces a thin rust layer that protects the rest of the steel from further corrosion. Would painting weathering steel be an acceptable additional line of protection, or would this cause some unforeseen complication?


texts: When producing a set of engineering drawings for products we tend to specify the materials used for the part in the notes. For example if it's a moulded part we'd specify PA6 GF20 and then the manufacturer and the manufacturer's code. We then store the TDS for this material in the technical file. We have a new QC guy who is now insisting that we put the polymer TDS on the engineering drawing now - literally paste it into the drawing. This seems wrong to me for several reasons but I'd like to know if anyone else considers this as correct or not.


texts:
Does any one here know of an authoritative source (ASME, ISA, NFPA, OSHA, etc..) that gives a definition for the following in one of their standards or codes and the number for that standard or code:

LO (Valve Locked Open)
LC (valve Locked Closed)
CSO (Valve Car Sealed Open)
CSC (Valve Car Sealed Closed)

I'm not looking for an explanation, I'm looking for a citable code.


texts: Longitudinal axis (x) is the axis orthogonal to its lateral directions (y and z), but what is transverse direction? Is transverse just another term for lateral?


texts: ansys workbech structural- difference between pressure and surface force application

texts:
In Ansys workbench , structural module, in modelling, what is the exact difference between pressure and surface force application? Is surface force applied in same manner as that of pressure application or different?
In more detail, I want to know how the total force is applied on the surface equally?


texts: stability/controllability of a finite time linear quadratic regulator

texts: If I have a linear quadratic regulator (quadratic objective function with linear dynamics) and use an open loop control - are there stability/controllability requirements on the system?  I know that there would be these requirements if I were to implement a closed loop control but I can't find any corresponding requirements for open loop.


texts: head coefficient and volume coefficient for centrifugal pump

texts:
If I need to calculate the head coefficient using $c_h=\dfrac{gH}{N^2D^2}$ and the volume coefficient using $c_q= \dfrac{v}{ND^3}$ while keeping $N$ (impeller rotational speed in rpm), how can I make the units cancel out and have a dimensionless answer?

I am measuring $D$ (impeller diameter in meters), $g$ (gravity m/s^2), $H$ (total pressure head in meters), $V$ (volumetric flow rate in m/s).

I made it dimensionless by changing RPM to 1/s, however I have been asked to keep RPM and change the other units, can someone plz help.


texts: Design compensator to improve yaw rate control performance for aircraft

texts:
I am trying to design a compensator to improve the yaw rate ($\dot{r}$) control performance of an aircraft. The lateral dynamics for this aircraft is given in steady space form as following:

where A (4x4) and B(4x1) are both known. I am also given a set of closed loop and observer poles (6x1). I tried to construct a set of equations to incorporate the washout filter and rudder actuator ($\delta_{r}$) by creating the steady-space model for the aircraft, obtaining the transfer function, and finding the closed loop transfer function of the system including the rudder actuator and washout filter. In order to perform pole placement in MATLAB using the place() function I needed to have a state space model, so I used the tf2ss() to obtain the new state space model. However, the A matrix in this case was 11x11, but my system has only 6 states. Also, the rank of the observability matrix was 6. I am really confused on what I should do next to compute the compensator's transfer function.

The programming language I am using is MATLAB, so if you have any suggestions please include the MATLAB code.


texts:
In your experience, what items that should be in geotechnical reports are sometimes missing, and what do you do in that case, can you provide example? Do we look at codes or make best guess and based on what? Or do we need to make our own soil testing? Please give example / examples from your experience or what you know, if you could...

Edit: This question was closed by the moderators stating that it is opinion based. However, this is the nature of this question. Missing items in geotechnical reports occur often and the only way to discuss this is through opinion of experienced engineers. See the answer below, which was given before the moderators closed the question, which provides a very informative answer. This question should stand open which would provide valuable information to readers. This question is a useful discussion for geotechnical and structural engineers. Asking for typical missing items can not be a fact based question in nature in the first place. Experiences are also valuable.


texts: Calculate exhaust with expansion chamber muffler

texts:
I have a book with the formulas to calculate the length of engine exhaust pipe, but these formulas don't take into account the muffler.
If I add an expansion chamber, how the calculated length change?


texts: what's wrong with this robust control scheme?

texts:
I'm learning how to control a double integrator with $H_\infty$.

my model is simply

$$\begin{gather}
\dot{r} = v \\
\dot{v} = F/m \\
r(t_0) = 0\text{ m}, $v(t_0) = 0\text{ m/s}, m = 1000\text{ kg}
\end{gather}$$

so I want to be able to track a step command. I have noise on measurements of position, velocity and force, assumed with a noise having a std of 0.02 m, 0.01 m/s and 0.2 N.

I want to have closed-loop bandwidth equal to 0.2 Hz with a steady-state error of 0.1 m, and a sensitivity peak at $f_{p} = 1$.

The scheme I implemented is the following:

The weigthing functions are the following. Since I want to track low-frequency changing signals, I imposed
$$W_{ref,r} = \frac{1}{s/\omega_{lpt} +1 }$$
with the low-pass tracking function $f_{lpt}$ equal to $2\pi f_{lpt}$, and $f_{lpt}$ equal to 0.2.

The noise weighting functions are constants corresponding to the values mentioned above, while there is no feedforward contribution, so $W_{ref_F}$ is equal to 1, and so does $W_{ctrl_inn}$ (perfect inner dynamics). If I understand the theory correctly, the functions $W_{p_r}$ and $W_u$ play a similar role as the matrices $Q$ and $R$ in LQR, except that we can shape them frequency-wise, and that we are minimizing the $\infty$ norm instead of the Euclidean one. So, as recommended by Skogestad in his wonderful book I specified
$$W_{p_r} = \frac{s/M+2\pi f_{p}}{1+2\pi f_{p} A}$$
with $A = 0.1$, $f_p = 1$, and the peak for the sensitivity transfer function M equal to 2.

The transfer function for control performance is a high-pass filter needed to penalize high-frequencies such that the controller does not waste efforts in trying to control high-frequency dynamics (in my case > 10 Hz)
$$W_u = \frac{3+ 2 \pi f_{hpf}/2}{1+2 \pi f_{hpf}}$$
with the high pass frequency $f_{hpf}$ equal to 10 Hz.

I get this bode plot of the inverses of $W_{p_r}$ and $W_u$, so at small frequency the sensitivity tf $S$ is small, and at large frequency $KS$ is small, that is, no big control efforts.

If I synthesize the Hinf with matlab I get a $\gamma$ equal to 10. I would expect a small value because we want to make the z output small for the expected exogenous inputs. Can someone tell me what I'm doing wrong?

P.S. I'm getting the generalized plant by using linmod on the above specified Simulink model to get A,B,C,D and I transform it into P by doing

P = ss(A,B,C,D)
P = minreal(P)

P.P.S. The step response also diverges.


texts:
One of the benefits of electric cars is that many parts can be eliminated, simplifying the overall system. Could EVs eliminate brakes as well by slowing the car down using reverse torque from the motor?

I know this is a horrible idea for a number of reasons, but I'm wondering if there are any fundamental reasons why it couldn't be done. E.g. perhaps axles would fail from the torque required for extreme braking.

EDIT: I'm specifically asking about the case where the car provides a retarding torque using the motor that exceeds the amount that can be effectively used for regen braking. Or is regenerative braking torque limited by something that can't be solved with more power?


texts: I need a mechanism/method to control a shaft that can rotate at different speeds. (faster clockwise and slower anti-clockwise)

texts:
I need to develop a mechanism - Where in I have a shaft that needs to rotate at different speeds. Lets say at a higher RPM clockwise and a lower RPM anti-clockwise.
This shaft is attached to my machine, so I can't have 2 shafts.
If i have 2 motors to the same shaft, I'm afraid there'll be feedback on the other motor, while one is running.

For example, like the image attached. Both the motors are connected to the lead screw. The motor (and the lead screw attached to it) on the left rotates at a higher rpm and this motion is used to lift my system. Similarly from the other side but to drop it quicker (the reason for the speed difference).

Any ideas? Thanks :)


texts: Solid mechanics: Deflection of a rectangular elastic membrane

texts:
I am trying to solve for the deflection $w$ of a rectangular membrane with tension $T$ acting on two opposite edges. These two edges are fixed i.e. $w = 0$. The other two opposite edges are free. The size of the membrane is $L$x$L$. There is a pressure $P$ acting on an area $\frac{L}{3}$x$\frac{L}{3}$ at the centre of the membrane.

A schematic is presented below:

If the tension was acting on four edges and they were fixed. The equations and boundary conditions could be written as:
$$T\frac{\partial^2w}{\partial x^2}+T\frac{\partial^2w}{\partial y^2} = p$$
with boundary conditions:
$$w(x=0) = w(x=L) = w(y=0) = w(y=L) = 0$$

I do not know how to modify these equations and boundary conditions for my problem.


texts: Von Karman mixing length $l=k \frac{du/dy}{d^2u/dy^2}$

texts:
In a fully developed turbulent flow of an in-compressible fluid inside a pipe of radius $R$, velocity at the center is $U_m$. If we define $U^*=\sqrt{\tau_0/\rho}$, where $\tau_0$ is the wall shear stress and $\rho$ is the density, then find the velocity distribution as a function of $y=R-r$ distance from the wall.
  Consider the $l=k \frac{du/dy}{d^2u/dy^2}$ as Von Karman mixing length.

Now, if we write $\tau \approx \tau_0=-\overline{\rho u' v'}= \rho l^2 (du/dy)^2$, then we get $$(U^*)^2=k^2 \left(\frac{du/dy}{d^2u/dy^2}\right)^2 (du/dy)^2$$ and $$U^*=k\frac{(du/dy)^2}{d^2u/dy^2}$$ Now let $p=u'$ to get $p'/p^2=k/U^*$. Integrating twice gives $$-1/p=\frac{k}{U^*} y+C_1$$and $$u=-\frac{U^*}{k} \ln \left( \frac{k}{U^*} y +C_1\right)+C_2. $$

Now, one of the conditions for finding $C_1$ and $C_2$ is $u(y=R)=U_m$. What will be the other condition? This is the problem I encountered solving a similar problem:

  In a pipe with diameter $0.8 \ m$ water is flowing (turbulent) and velocity at $y=0.2 \ m$ is $2 \ m/s$. If the relation $u/U^*= C_1 \ln(y/R)+ C_2$ is true, then find $C_1$, $C_2$, and wall shear $\tau_0$ (notation is as same as above).

Should we relate this to viscous sub-layer somehow?

Note: I have posted this in the physics site also. If I get my answer in one SE site I'll delete the question in the other one.


texts:
I am currently working on a project that involves CFD simulation on ANSYS and i need some help as it has got me stuck. I am designing a faucet atomizer and it's functioning is similar to a nozzle.

I have designed it on CATIA and am trying to analyse it on ANSYS Fluent.

I am using the following conditions:

-Pressure based solver, absolute velocity, steady flow

-Flow characteristics: Laminar at inlet, turbulent at outlet

-Boundary conditions: inlet velocity: 0.041 m/s, inlet pressure: 300000 Pa,outlet pressure: 0 Pa

-Fluid: water(liquid)

I have the following doubts:

1.)I read that turbulent models give accurate results even if flow is laminar but not vice versa so i chose turbulent but which turbulent model should i apply?

2.)My geometry has swirl, complex curves and rotational flow and i read that k-epsilon, k-omega models do not handle such flows and curves well so which model should i adopt(my geometry is very small in dimensions so swirl may not matter?).

3.)How should i do the meshing of my model? I did it multiple times according to my understanding but due to some reason the solution didn't converge and diverged a couple of times as well. My system also does not have a lot of computational power hence less elements and nodes in mesh.

I am attaching some images of my geometry with sectional views, extracted volume and also the meshing done by me. Kindly take a look.

I will be able to share the geometry file with you if you require.

I will be very grateful if you can help me out.

Thanks


texts:
I was trying to use the new interface of ANSYS Workbench to couple ANSYS with Excel without learning Python. I'm having problems because I can only set one parameter in Excel, like one cell. Once I managed to put an array, but I can't do this right now.

What I want to do is this:

My problem has: input x, input y, output z, output w. What I am doing is using the interface in ANSYS, exporting the data, copying to another Excel spreadsheet and after that passing to Origin for better graphs.

What I want to do is have four columns in Excel, put something like 20 values in input x, input y, then update the Workbench project with all design points, and my other two columns in Excel get filled automatically.

Since I can't put an array as a parameter in ANSYS, I am missing the automation of what I want.


texts: Force P required to slide the door if one of the wheel becomes frozen

texts:
I am solving problems from the book: Meriam Kraige Engineering Mechanics statics vol 1. The problem is as follows:

The sliding door rolls on the two small lower wheels $A$ and $B$. Under normal conditions, the upper wheels don't touch their horizontal guide. The question is to find out the force $P$ required to slide the door at a steady speed if wheel $A$ becomes "frozen" and doesn't turn in its bearing. The coefficient of kinetic friction between a frozen wheel and the supporting surface is $0.3$ and the center of mass of the 64 kg door is at its geometric center. We have to neglect the small diameter of the wheels.

My attempt

I calculated the normal reactions at the two wheels to be equal to $32g$ each. I then applied $P=0.3N$ which gave me the incorrect value of $P$ .I couldn't get where I am wrong.Any help shall be highly appreciated.Thanks.


texts: How to calculate load bearing capacity of a floating pavement?

texts: Given tire load of a vehicle, how do I calculate load bearing capacity of a non-reinforced concrete pavement floating on a layer of heat insulation material, which is on the RC base? I can't figure out how to use (or if I can use) soil mechanics models because I don't have any information on cohesion etc. I just have nominal carrying capacity of insulation foam (200kPA) and how much it collapses at a given load. (We want to use the roof as a garage, which was not designed as a garage.)


texts:
Stiffness, k, is defined by
$$k=\frac{Force}{deformation}$$
if you insert this into formula
$deformation = \frac{\text{Force}\times\text{ Length}}{AE}$
you get
$$k=\frac{A.E}{L}$$
where E is elasticity, A is area and L is length.
But from before I remember that we wrote just the E values in stiffness matrix. Even many people use elasticity and stiffness as if they are the same thing, which is wrong. Why do we write elasticity values in stiffness matrix, or what am I missing here?


texts: Bolt circle indication on angled ellipse

texts:
Ok so I am a machinist, not an engineer, but figured someone here might be able to provide some insight into my situation.

The part is 2.75" diameter and is on a 3.3* angle in the X axis on my mill. I have milled the surface flat at 3.3*, and now I need to indicate center to drill a bolt circle, accurately. tolerance is +-.005"


texts: Effect of centripetal acceleration on angular acceleration

texts:
$a_t$ = $\frac{dv}{dt}$ = $\frac{d(r*\omega)}{dt}$ = $r $* $\alpha$.
$a_c$ = r*$\omega^2$ = $\frac{v^2}{r}$
These are almost all the variables and values associated with centripetal and tangential acceleration in case of circular motion.
The Q 1 : is to find angular acceleration of particle when it’s speed changes from $2$m/s to$ 4 $m/s in 4 seconds where r of the circle =0.5m.
$a_t$ = $\frac{dv}{dt}$ where $dv=4-2$ and $dt=2$.Therefore , $ a_t$=$0.5m/$ $s^2$.
Then used $r $* $\alpha$ = $a_t$= 1 rad /$ s^2$
My Q’s are that why did we not need to use the formula of centripetal acceleration here( in Q:1)to find angular acceleration. But instead used formula of tangential acceleration.
If I take a situation in which there are 3 different values of centripetal acceleration. For example , 4 , 5 ,6 m/$s^2$ and take the same values of the above Q 1 only for dv,dt and r. Then , still Angular acceleration would be having same result since there is no mention of centripetal acceleration.
Why do I think it is not possible :

Doesn’t centripetal acceleration also affect the angular acceleration. We have $\omega$ in the formula of centripetal acceleration which is stated as amount of $\theta$ covered per unit time. Then , it means there has to be centripetal acceleration relation with $\alpha$ or angular acceleration also.

My confusion in brief is that ,  we know net acc = $a_t$ + $a_c$ . Right. So , I am thinking that both formulas when combined together should give angular acceleration
EDIT: Regarding a= $\frac{dv}{dt}$.


texts: What is the axial temperature distribution for a electric heating tube

texts:
Is the axial temperature distribution uniform for a simple and cheap electric heating element such as shorturl.at/tEJSU
I understand that the current that is passed is same along the tube but not sure if the temperature would be uniform.


texts: A humidifier before a heater and after a heater

texts: What is the difference between installing a humidifier before a heater and after a heater?


texts: What is the protective part of a staircase handrail called?

texts: Below the handrail of a staircase is some kind of gridwork to prevent people or objects from falling off the staircase into the space below. What is the term for this gridwork? - perhaps "handrail grating"?


texts: Bevel gear friction and inertia calculation

texts:
I want to calculate the friction and inertia between 2 bevel gears with straight teeth.
I know how to calculate those parameters between regular gears with straight teeth.
Is there any difference for bevel gears?

Thanks,


texts: Is it possible for laptop speakers (versus external speakers or headphones) to pick up radio signals?

texts:
Heard a strange sound a couple of times last week while web browsing. It sounded very much like I was listening to someone's microphone (e.g. the sound was static-y, it sounded like papers were rustling and then music was playing, etc.) but the sound ended abruptly, without me touching anything. I couldn't investigate it before it ended, and I couldn't see anything in any of my tabs that indicated something had played. It also definitely did not sound like an ad....

Researching the problem a bit, I've seen something similar reported relatively frequently, with the explanation being that the person's speakers or headphones had picked up some AM radio signals, a baby monitor, etc. The small catch is that I only ever saw external speakers or headphones being discussed, rather than laptop speakers. My question, then, is whether the speakers being a laptop's internal speakers would make a significant difference, e.g. due to being more "insulated".

I'd very much like to chalk up what I experienced to an explainable physical phenomenon rather than, for example, a trojan that has evaded all of my anti-malware scans somehow. Figured that here seemed like an appropriate place to ask, though if I've misjudged this and another place would be better, I'd be happy for suggestions.


texts: Why a technology like freewheeling not used in cars to save fuel? We all know that when we move to neutral gear (coasting), the car travels farther than when it is in gear because there is no engine braking effect. I understand there is a safety issue there - but is that the only reason for not using it? What I am trying to say is - when the foot is off the gas pedal, stop engine braking effect using some technology to achieve better mileage.


texts: Could railway overhead wires be used for long distance electricity transmission?

texts:
Most electrified railway in Europe operates at 15 kV 16.7 Hz AC or 25 kV 50 Hz AC.
Power is typically produced between about 2.3 kV and 30 kV and stepped up to 115 kV to 765 kV AC for long distance transmission (Wikipedia).
If the railway overhead wires were fed by a single power source how far from this source could the rail network extend?
Is there a limit to the number of users that could connect to the railway overhead wires?


texts: Does a Peltier device conduct heat when turned off?

texts:
If I put a Peltier device between a heat source and a heat sink (Peltier turned off),
How well will it conduct heat? as opposed to lets say a copper block?
Thank you


texts: What bending test and torsion test standard are recommend for a surfboard?

texts: I wish to find a bending and torsion test standard for a surfboard (non-prismatic) that is roughly 2000mm long. The closest I've found for bending test is probably those ones that are designed for concrete where the specimen is really long and thick.


texts: How would you measure the electrostatic field of a celestial body from its surface?

texts: If we need to measure the Electrostatic field of a celestial body due to its interaction with space plasmas, What kind of instruments can be used to achieve this?


texts: Do 3 blade wind turbines generate more power than a 9 blade, all else being equal?

texts:
After doing some research, I have come to the realization that 3 blade design horizontal turbines have the greatest maximum coefficient of performance. Most sources seem to agree a Cp of ~0.45 at TSR=7 is optimal for 3 blade designs.

The power output of a turbine is P=0.5*CprhoA*V^3. So what I cannot wrap my head around is why, all other things being equal, more blades (of course up to a limit) does not equal a greater coefficient of performance and thus more power. How is only 3 blades this limit on something 200m in diameter?

It seems there would be a significant portion of the air passing freely undisturbed through the rotor.

I welcome any answers and explanations, but preferably backed by formulas.


texts: How to provide lateral support for adjacent masonry during installation of steel UC in an old cavity wall?

texts:
I've got a structural engineer ready to provide calcs on this job, but there is a specific aspect where I'd like a heads-up what the normal approach would be, before I raise it with him, in case he says it's a matter for builders to decide (which it probably isn't!).

The building

The property is a pretty typical London UK suburban 2 bedroom terrace, early 20th century. The wall is 2 x 100mm old London brick, with a 50mm unfilled cavity. The aim is to install a steel 203x203x46kg steel moment-resisting frame on the ground floor (USA:1st floor), as part of sorting out inadequate support for the rear wall as part of an extension. The rear wall is 6m wide and the opening will be about 2800 H x 6000 W resting on the original trench foundations, so there will be a horizontal load spreader, and 3 vertical columns (both sides + middle).

I've sketched one side of the frame and related wall:

I'm pretty confident about installing the horizontal load spreader (I've cut out below a cavity wall and retrofitted lintels/RHS below it, elsewhere). But for this frame, I can't mount the vertical columns against the wall - I need to cut a slot through both leaves of the rear cavity wall, and fit the UC into the slot.

The space for the slot isn't wide (maybe 220mm wide - the width of a single brick), but it is quite tall.

The problem

My concern is the lateral bracing shown in the top-right sketch. While most of the load on the removed brickwork is vertical and removing 200mm width isn't an issue, the masonry probably also provides lateral/torsion/racking support to the adjacent rear wall and party wall. I'd be happy if the slot was only a metre or so high, but I'm worried that a 2.8m slot might be too much to trust without appropriate lateral bracing, while the UC is being installed.

This is surely a very common situation for domestic extensions. What should I expect to be told as the usual/proper way to brace the slot, to make absolutely sure there can be no adverse lateral freedom or movement affecting the adjacent wall, during the few days it'll take for the 2.8m slot to be cut and emptied of brickwork, and the UC being installed and mortared in place?

My thoughts so far

I have a couple of ideas, sketched below, but I can't find a definitively good answer.

My own ideas revolve around using short (200mm vertical) steel sections to brace the wall laterally, and hold the slot open properly while the column is installed. Once the column is in, the braces become redundant and can be cut away or left in place.

I'm thinking of either using RHS and slotting the new UC inside it - then it just needs moving sideways to fit - or creating heavy duty "U" shaped sections with 20mm steel bracing at their "open" end, which can be selectively opened and closed one at a time, to allow the UC to be installed. But I've never seen a description of a "proper" or safe way to do this, so these are just guesses.

Questions on my mind:

What is the realistic risk?Realistically, how significant is the lateral movement/racking/twisting risk in this situation? How much/how likely is it that there really is a problem?
How severe and what direction are the non-vertical forces/moments likely to be?Assuming "normal/ordinary" construction, what should I expect for typical/relevant non-vertical forces/moments and their directions, to help anticipate what the engineer/builder needs to counter?
What is the usual way this is done safely, and are my ideas any good?What is the usual way to install UCs without exposing this risk? How heavy duty is this bracing typically, if bracing is needed (Are my ideas adequate, or are there better/cheaper ways?)


texts: What is the maximum length of oil pipelines?

texts:
This is inspired by the discussion and controversy surrounding the Keystone Pipeline.

The main part of the Keystone Pipeline system is about 3,400 kilometers long, stretching across a large portion of the United States. The Keystone XL extension would add another long section to it. Altogether, the length of all the segments would be . . . oh, something very big, I imagine (though I acknowledge that none of the oil will travel through all sections).

What is the practical limit for how long an oil pipeline can be?

In the interest of narrowing this down, I'd like to focus on two sub-questions:

Is the structural integrity of the pipeline at risk the longer it gets?
Is there any possibility of adverse effects on the oil over longer spans?


texts: ∂p / ∂s ds Component in Euler's Fluids Equation

texts:
For the last hour I have been trying to understand what $\dfrac{\partial p}{\partial s}ds$ is in Euler's equation but I have a problem. You can see this image:

I know that
$p\ dA = \text{Force}$

$γ ds dA = mg$

but what is $\left(p + \dfrac{\partial p}{\partial s} dA\right)$?


texts: Standard bicycle spoke tensiometers are too large for use with small wheels, the kind used on recumbent bikes and folding bikes. Could a small adjustable or beam-style torque wrench be used to gauge spoke tension with something like the apparatus in this sketch, a socket with a couple of J-bend spokes welded to it?


texts: Are there steam tables for subsaturated steam?

texts:
By Googling I can find basically two types of steam tables for water. They are either saturated steam tables, which I understand are for steam in saturated state. Here pressure are temperature are fixed together as saturated steam states form a curve in water phase diagrams. Then there are some tables for superheated steam, where temperature exceeds critical temperature for water.

But what if I'm interested in values for water vapour/steam that is neither superheated nor saturated, that exists under the saturation curve in water phase diagrams?

Why are we specifically interested in saturated steam?


texts: Turning an engine over with engine compression

texts:
When you compress a bicycle pump and seal the opening, the pump will automatically return to it's initial position when you release it. I suppose this is how air suspension works as well?

if you have a internal combustion engine without any gas and turn it over - for instance with a kickstarter, until the piston reaches the very top on the compression cycle - why doesn't it return to the bottom by itself by the air compression alone? Is there anything blocking this, or is the air simply not powerful enough to turn the engine over?

See comments from Physics StackExchange


texts:
I'm building a tracker for a high altitude balloon but some of the components are out of stock and may not be in before our launch date. I'm good with an iron but have limited engineering knowledge. Here is the list of components for reference:

Multilayer Ceramic Capacitors MLCC - SMD/SMT TDK
Thick Film Resistors - SMD Panasonic
Schottky Diodes & Rectifiers - ON Semiconductor
Multilayer Ceramic Capacitors MLCC - SMD/SMT Murata Electronics

I'm wondering how people go about finding suitable replacements for out of stock parts. I realize that there may be many factors in finding replacements and that this is too broad a question for a quick answer but I just wanted to start somewhere.


texts: Are there any variable frequency drives that work digitally?

texts: By this I mean can any DC to AC variable frequency drives invert digitally (no moving parts) and if so how do these work? Is this possible for both sine and square wave inverters?


texts:
I am designing a functional replica of the Apollo FDAI (aka 8 ball).
See pics Real FDAI Another view

  From the Apollo 8 Flight Journal:
  The FD/AI (Flight Director/Attitude Indicator) or "8-ball" is one of the most important instruments in the spacecraft. Designers had originally intended to give the crew three separate displays to show their attitude; one each for roll, pitch and yaw. Being pilots, the crews quickly threw out the three displays for a development of the artificial horizon familiar from aircraft instrument panels.

Here's what I have so far (I know, those aren't steppers, it's only V1)
V1_ball V1_view2

V2 will rely on three stepper motors to position the ball. Previously I put the motors more or less in line with their respective axes. Unfortunately, this introduced the challenges of dealing with rotating electrical connections, balance of the ball, motors turning the weight of other motors... Etc.

So, why not eliminate these issues at the cost of increased mechanical complexity!
V2 sketch (please excuse the humanCAD)

My plan is to use gears (and belts potentially) to move the control axes to be colinear with the roll axis. All control axes will be concentric and will have its own shaft (two of which will be hollow). Basically like the three hands on a clock. This will allow all the motors to be outside the moving ball mechanism.
The problem with this is it demands more performance of the motors.

For example: if I wish for the ball to pitch, I have to move the yaw motor in tandem with pitch to prevent the yaw bevel gear from moving relative to the pitching platform. Furthermore, if I want to move pitch and yaw at the same rate, the yaw motor must move twice as fast as the pitch motor.
This issue is even worse if I want to roll, requiring compensation in both pitch and yaw axes.

I don't expect this to be a problem at low rates, but it severely limits the maximum rate of the ball. The pitch motor must be able to move at least twice as fast as the roll, even worse, the yaw must rotate 3x as fast as the roll motor. I'm not willing to sacrifice the accuracy of the instrument, so simply gearing the motors "faster" is not a solution.

I believe that an elegant mechanical solution exists, but I'm stumped. I think if I had a mechanism that behaves in a "I can turn you, but you can't turn me" manner might go a long way.


texts:
I'm trying to lift a platform with several guides using a linear actuator, but off the centre as follows:

The load on the platform will be around 100kg, which is just within the linear actuator's 120kg load capacity. The platform will be around 50cm*50cm. My plan is to use 2-4 rods as guides with linear (or tapered?) bearings at each corner (or opposite sides if 2 rods) of the platform. Does anyone know if this would be a good idea? Would the linear actuator wear out more rapidly if the actuation was off-centre?
Any advice appreciated.


texts: What is the minimum diameter necessary for 2 linear motion shafts to deflect less than 0.05mm when a 2kg weight is in the centre?

texts: I am planning to build a large scale 3D printer that will utilise 2 1000mm linear motion shafts that each have a young modulus of 210 GPA. The ends of the shafts will be secured in a block of plastic and will not be able to move and the distance from one usable end to the other will total 900mm. Due to the large size of the parts being used I have concerns over possible deflection that could occur. Therefore I need to calculate the minimum required diameter necessary for 2 shafts to support a 2kg weight in the centre while deflecting less than 0.05mm (my layer height is going to be 0.1mm). Thanks for any help I am not an engineer so I have not the slightest clue how to do the calculations to determine this.


texts: What are some robust method to detect or repel lizard?

texts: I am working on a HVAC project where lizard in going inside the electrical unit and causing wire damage and short circuit. I need to find some solution to detect or repel lizard before any catastrophic situation. Since lizard are cold blooded species, I cannot use IR head index measurement methods or PIR sensor. Also, lizard are very small creature so method need to be foolproof.


texts: Why is the point of failure load lower than the peak load?

texts: In a tensile test the peak load was 69kN, but the point of failure load was 60kN. Why is it lower?


texts: Relevancy of (neutron energy loss and atomic weight) and the material selection of fast and thermal nuclear reactor

texts:
From this https://www.nuclear-power.net/glossary/neutron-moderatoraverage-logarithmic-energy-decrement/, I have found that the relationship between atomic weight and neutron energy loss can give the number of collision between a neutron and nucleus to slow down (average logarithmic energy decrement.)
I was wondering if this can be a good factor of selecting materials for fast and thermal reactor. I have not found the any relevancy between the relationship mentioned above and the material selection of the reactors.
Can anyone please explain how the relationship between atomic weight and neutron energy loss can be relevant to the selection of materials between fast and thermal reactor? Or, can anyone give me any link/sites to know about it more?


texts: Why does the water pressure initially drop then stabilize when pressure testing a valve?

texts: Sometimes the dropping goes on so long(10-15 minutes) that the test is thrown out and the valve is opened and filled with water for a longer period of time. Pressure testers claim that it is because of air, but when I ask why does air in the valve cause a bad test, they can't answer me. Some technicians seem to think that it is because air is more compressible, but this doesn't make a lot of sense to me because some of our products are tested with nitrogen. I feel like it is possible that the system is not in equilibrium and air bubbles are sort of crawling around making their way to gather with a larger pocket of air in a stable pocket of the liquid.


texts: Cooling Down Fridge Encased in wooden box

texts:
I'm currently working on a project which involves a small fridge encased in a wooden box.  It's designed for hotels and the boxes vary slightly, but one common trait is that the box has an open vent towards the back which is meant for ventilation.  Unfortunately, the hotels like to jam the box up against a wall, which prevents the vents from working properly.  We have no control over how the wooden box is manufactured (in fact, the fridge was made to fit inside this box) and the vent hole varies in height from hotel to hotel.

The point is, the hotels demand that we be able to cool down the temperature inside the box, without any added electricity.  I have already looked at Thermoelectric Couples and the temperature difference is about 18°C between the ambient interior of the box and the compressor which isn't enough to run a small fan.  I have attached some passive heat sinks to the compressor itself, which did reduce the ambient temperature, but increased the temperature inside the fridge.  I'm stuck, and I am thinking of using aluminum foil extending from the fridge to outside of the box to help conduct the heat away.  Can anyone suggest any other ideas?


texts: Measuring gas flow from a low-output device

texts:
My lab uses a home-built biomedical instrument that acts as a ventilator for test-subjects. In other words: our device combines nitrogen and oxygen gases and pumps them down the line at a specified rate. The actuation is controlled with three parameters: breath rate (breaths/min), inhalation duration, and breath hold duration. While it is running, it considers these parameters and actuates accordingly.

In order to calibrate our device, we have regulators on each gas line that control their pressures. This obviously changes the gas volume output at the end of the line. What is an easy way for us to measure the volume of gas flow out of the system? I'm trying to avoid buying any devices if I can.

EDIT:

This device is very low output, approximately 0.25 mL/breath or ~40 mL/min. I had originally thought to use a small syringe, but the backpressure was too much for the ventilator.

Our current method for measuring volume output is to fill a bucket with water, place a water-filled graduated cylinder on the surface, and then have the ventilator actuate several times to displace the water in the cylinder, measure that, and then divide by the number of actuations to get volume/breath.


texts: What valve to use to divert incoming air from a pipe to another pipe stream?

texts:
There's an 4 inch exhaust stream that's emitting air at 2000CFM, I want to divide the exhaust in a 'Y' kind of outlet with two pipes.

If State 0- Exhaust out through one pipe.

If state 1- Exhaust out through another pipe.

What electrically actuated valves should I look at?

Thanks in advance.


texts: how can i find Spectral Acceleration (Sa(T1; 5%))?

texts: I want to do incremental dynamic analysis (IDA) for my project and for hunt and fill algorithm i need the 5% damped Spectral Acceleration at the structure’s first-mode period (Sa(T1; 5%)) . Can i find it by using Seismosignal software directly ? if not how can i calculate Sa(T1; 5%) ?


texts: Why are toilets not equipped with exhaust air vents?

texts: Aerosol and gaseous emissions are generated in toilets. Drawing exhaust air from the ceiling ensures effective dissemination of airborne contaminants. Why is the exhaust air not drawn from the toilet instead?


texts: Is there a way to calculate mass flow rate of an axial compressor?

texts: Is there a rule of a thumb equation for the mass flow rate of a stationary axial compressor at sea level, using intake area and RPM? Or do other factors like blade geometry make too much of a difference for such an approximation to be possible?


texts: What stainless steels are good for induction heating?

texts:
I'd like to know which stainless steels are good for heating on an induction stove. Wikipedia notes that the surface resistance resistivity is a good figure of merit. However, that article only lists the surface resistance resistivity for two types of stainless steel -- the better being 432. However, I cannot find 432 from my favorite supplier, although they do have 430.

Will 430 have a similar surface resistance? Is the a resource where I can find the surface resistance of other stainless steels? I have searched around but only found results for the two stainless steels that wikipedia lists.

EDIT: Looking at the IEEE article that underlies the wikipedia article, I think that the wikipedia article should use "surface resistivity" instead of "surface resistance". I was using the terms in the wikipedia article. Sorry for any confusion. I will edit the wikipedia article if appropriate.


texts: Couette-Poiseuille flow between non-parallel plates

texts:
I have a Couette-Poiseuille flow (both flows combined) where the plates are not parallel. So h, the thickness of the flow, changes along the x axis.

Can I use a mean h to calculate the viscid stress? Is this procedure correct?

$τ_v=-μ_a  v/h+|∆p_L |h/2L$ (I know the Poiseuille equation for parallel plates includes the y coordinate, but I substituted for h, the height I'm interested in to calculate the stress.

$τ_v=-1/(h_1-h_2 ) ∫〖μ_a  v/h〗 dh+1/(h_1-h_2 ) ∫|∆p_L |h/2Ldh$

The integration limits are $h_1$ and $h_2$ and the former is greater than the latter. Both are the thickness limits and I'm still too new to this forum, so I can't put them where they should be.

This is the result I got:

$τ_v=-μ_a  v/(h_1-h_2 )  ln(h_1/h_2 )+|∆p_L |(h_1+h_2)/4L$

Right or wrong?


texts: How to compute the performance of a refrigerant?

texts:
As I understand it, there are 5 key factors that determine the performance potential of a refrigerant gas:

Vapor density
Enthalpy of vaporization
Thermal Conductivity
Critical temperature
Specific heat

What are the relevant equations or calculations to weigh these factors? In other words, if we consider the following performance metrics:

amount of energy required to perform a specific amount of cooling
speed at which cooling take place
pressure required

How can I relate these 3 metrics to the 5 molecular characteristics above? Note that the answer is complex because, for example, item #1 above is a curve. For example, in other words the amount of energy required may not be constant for different rates of cooling (#2).

(Note that in this analysis I am ignoring safety issues, long-term maintenance issues like corrosion and leak tendency, and secondary performance issues, like dielectric strength; I am only considering primary performance.)


texts:
Usually, the frequency of a computer's CPU is expressed in GHz.
But does this mean that the individual transistors etched on the chip also switch on and off billions of times per second? Or are the high frequencies of CPUs achieved thanks to some "group effect" ? (since there are billions of transistors in a CPU, they may not need to switch at gigahertz frequencies themselves).

Note: For sure, this kind of information can easily be found for "macroscopic" scale MOSFETs. But I am absolutely not sure that they can be compared at all to their nanometric counterpart.

Thanks


texts: How to determine the force to empty a syringe containing high-viscosity fluid?

texts:
I am trying to determine the force it would take to fully empty a syringe using a long nozzle, that contains a high-viscosity fluid.
Specifications I'm using:

I'm trying to determine the force through Hagen-Poiseuille equation:

However the results I am getting from physical testing show are very different. I have tested with 3 different flow rates, and difference between them is minimal, while Hagen-Poiseuille predicts it will be substantial, especially at higher flow rates:

Physical testing showed results around 1kN lower than expected. I must be missing something. Syringe and nozzle are both highly polished - is there a way to take it into account?
Any thoughts would be welcome.


texts: Exactly what makes steel-concrete composite beam better than pure steel?

texts:
A composite action beam may have a concrete section the top, carrying the compression load, and steel at the bottom, carrying tension.
But I have always thought that concrete had lower strength for a given mass then steel, compressive or otherwise. So why do engineers build steel concrete composite action floor systems at all? How could it possibly save weight?
To clarify; What are the practically significant advantages of s composite beam of steel and concrete over one made of purr steel?


texts: Deflection of thin plate with 1 free edge and deflection > thickness

texts:
I have an thin uniform rectangular steel plate supported on 3 sides and free on one, and  supporting a uniform load.

I'm trying to determine what thickness of plate I need to keep deflection below a given value, but the deflection may not be "small" compared to the plate thickness, so standard formulae for maximum deflection may not be accurate, and I'm stuck on how to check my answer, or how to calculate it more accurately.

Data:

The plate is a flat rectangular plate (stainless 316 or mild, undecided) anything from 1.5 -15mm thick with an unsupported area at its edge of 1250x500mm total 0.625m^2. It is simply supported along the 500-1250-500 edges and free on the other 1250 edge. The unsupported area carries a static load of 4800 N/m^2 (approx 360kg spread uniformly over the unsupported area) plus its self weight.

The 3 supported edges are unrestrained simple supports that can slide or rotate; they don't resist any movement except in the Z-direction (a bit like it's resting across the  3 edges of a "u" shaped pit).

My question is the thickness of steel plate I need, to ensure maximum deflection (at the middle of the free edge?) stays under possible values of 3mm / 5mm / 10mm (the most likely permitted deflections or at least a good selection to choose between)

The problem is that I am guessing solutions could be thicknesses around 1.5 - 5mm, which means that the deflection might not be "small" compared to its thickness and the usual simple calculation may not be very accurate or trustworthy. But I'm not sure....

Thanks - and any hints how I can work this out myself appreciated but not essential :)


texts: Determining depth of flow in open channel flow

texts: Open channel flow in a circular pipe has a maximum flow Q_max at a flow depth approximately 93.8% of the pipe diameter. Calculating flow Q from depths 92.5% and 94.9% both give the same value for Q. So, if we know that the flow is Q, or if we are designing for a flow of Q, how do we determine which flow depth be correct in practice?


texts: How are non-continuous internal threads plastic injection molded?

texts:
I'm trying to figure out how the heck some of these plastic bottle caps are injection molded. By having the thread on the inside of a cap, this obviously creates an undercut.

Now I've watched some videos on Youtube on the process, and I can see that a metal threaded core is twisted into place (automatically or manually by an operator). The mold is closed, plastic is then shot into it, the mold opens, and then the threaded core is twisted out of place to allow ejection.

Some caps have split threads (as seen below) and use a collapsible core.

And some caps use a long continuous thread (as seen below) which makes sense for ejection (one continuous spin).

But this other style cap uses a long but non-continuous thread (as seen below).

My question is, how is this achieved? How does the threaded core spin out of place without colliding into the threads since the thread has an ending. In my mind, when this spins out of place, the feature on the core called out with the arrow below would collide into the freshly molded threads on its way out.