texts: How can a piece of steel rotated without any power input?

texts:
Currently I am trying to rotate a piece of steel >90 degrees without any power input. The piece of steel is attached on the wall. A servo is also attached on the steel.

This question addresses turning the piece of steel if the servo fails to work. A battery is not supposed to be used. Generally like a servo may do it with power the rotation should be performed without power whilst in this case the rotation has to take place only once.
The trigger is a toggle switch that will drop,if pushed, a weight on the right side (see picture) in order to rotate the piece of steel. This rotation has only to be performed once. Doing this currently the required rotation >90 degree does not take place.

The remaining questions are:

Where has the weight to tip the steel ideally so that the piece of steel can be moved/rotated with the least amount of force? I was thinking that the edge of on the right side of the steel would be most beneficial location to tip with the weight. Am I right?
What weight must ‘the object’ be in order to move a 8cm x 2cm x 4cm piece of steel >90 degrees. Hereby I have to know the required force on the steel in order to rotate it.

Do I think too naively and have any mistake on my thoughts?


texts: Is it possible to change a 'relaxing length' of edges for 8 node hexaedral element in 3d FEM

texts:
I am using 3D FEM with 8 node brick element to model a certain type of growth/expansion, which is not a plastic deformation. First, I apply a pressure/load and I get displacement and new position of nodes and calculate stress/strain. Next, I would like to change the 'edges' relaxing length (different edges by different factors) of an 8 node hexaedral element. Such change in relaxing length would be due to addition of a new material, resulting in expansion of a mesh. My question is, whether in such a model I can calculate sort of relaxing length for a brick element edges after application of pressure and consequently change it to get new nodal positions? I can imaging doing so for e.g. 1D string, but I am not sure if it makes any sense for 3D hexaedral element.

I would be grateful for any helpful suggestion/comments

Denis


texts: State observer for speed estimation from encoder

texts:
I try to implement a state observer (Luenberg Observer) to estimate the speed of my motor. Only the absolute position of the motor can be measured and I want to take into account also the target velocity as the input.

So my derived state space model looks like this:

The states are position, velocity and acceleration
$$
x = \begin{pmatrix}
p \\
v  \\
a
\end{pmatrix}
$$

The Input is the velocity target vi minus the estimated velocity state:

$$
u=(v_i-v)
$$

The system matrices looks like this (T is the sampling time):
$$
A = \begin{pmatrix}
1 & T & \frac{T^2}{2} \\
0 & 1 & T  \\
0 & 0 & 0
\end{pmatrix}
$$

$$
B = \begin{pmatrix}
T \\
1  \\
\frac{1}{T}
\end{pmatrix}
$$

$$
C = \begin{pmatrix}
1 & 0 & 0
\end{pmatrix}
$$

$$
D=0
$$

When I move the input -v into the A matrix, it looks like this:

$$
x_{k+1} = \begin{pmatrix}
1 & 0 & \frac{T^2}{2} \\
0 & 0 & T  \\
0 & -\frac{1}{T} & 0
\end{pmatrix} x_k + \begin{pmatrix}
T \\
1  \\
\frac{1}{T}
\end{pmatrix} v_i
$$

$$
y_k= \begin{pmatrix}
1 & 0 & 0
\end{pmatrix} x_k
$$

So I tried to place the poles of the error dynamics with a Luenberg observer by choosen L for:

$$
A-LC = \begin{pmatrix}
1-L_1 & 0 & \frac{T^2}{2} \\
-L2 & 0 & T  \\
-L3 & -\frac{1}{T} & 0
\end{pmatrix}
$$

I placed the poles in matlab as follows:
$$ |\lambda_i|<1$$
 at [-0.5,-0.55,-0.6]

Which gave me for L:

$$
L = \begin{pmatrix}
2.65 \\
2.92 \times 10^3  \\
-1.9 \times 10^5
\end{pmatrix}
$$

So I embedded this observer in the real system, but the results are actually very bad. So I think I did something wrong with the state space model, especially the input u seems not to be a good idea. Has anyone an idea how else I can model this system, especially about the input u I'm very unsure. Should I use the actual current as input for u, since this is proportional to the torque and so the acceleration?

Edit: What i further see is, that state a is not observable (Observability matrix has determinante different from zero), but since I don't want to observe the acceleration (I give this directly as an input), I think this should not be a problem, right?

Edit 2 Well, my Luenberger gains are pretty high, so I think that might be a problem. I update the state as follows:

$$
x_{k+1}=(A-LC)x_k + B v_i + Ly_k
$$

y is my measured position at instance k, so let's say this is 4000 (12 bit encode resolution). Initially my states are zero. Then the acceleration will be directly 4000*(-1.9 * 10^5), huge! So  I think I really messed up something here.


texts: Does Poisson's effect explain why the necking effect is more apparent in some materials during a tensile test?

texts: I know the ratio at which the cross sectional area changes to length is Poisson's ratio but is this why necking is more apparent in some materials than others or is the necking effect only dependent on the material's ductility?


texts: Calculating required torque of stepper motor for manipulating blinds

texts:
I have a outdoors wooden window blinds and currently I am raising/lowering them manually - by pulling/releasing a rope that's hooked on them using pulley. It's the most basic setup but still I can't understand how the calculation of torque works.
I know the formula is Torque = Length x Force and Force is gravity pull (mass x 9.81 N*kg-1) (+ some friction). But I am not sure what "Length" is in this case. And where in this formula is considered the motor shaft diameter and step size. From what I understand the torque should be bigger when using microsteps.
So, what is the correct formula in this setup to estimate required torque for the step motor to be able to pull the blinds all the way up and back?


texts:
I need to spin a threaded rod to raise a picture on a frame. The weight of the picture + the parts that it hangs on will be around 6 pounds. Two motors are going to be used to lift it via threaded rods (like in 3d printer platforms) but I need them to lift about 8" in less than 4 seconds.

I am unfamiliar with the differences between a DC and stepper motor and my worry is that when the picture is coming back down, a DC motor could overrun or would it not have enough power to strip the rod or nut (even over time)?

With a larger stepper, say like a 128oz/in and an M8x1.25 rod (.31" with 20 threads/in) is it reasonable for me to use steppers or should I go with DC and rely on timing to stop the lowering motion?


texts: What is the current limiter for SEPIC LED driver?

texts: I have designed an LED driver with SEPIC converter for 220 volts line. I hear  starting current for 3 or 4 cycle is very high in the branch of switch and second inductor(18 A). I want to reduce it to less than 1 amp. What is the way that I can apply to limit startup current of SEPIC?


texts: Smallest possible controlled chain reaction-based nuclear fission reactor?

texts:
I think, it could be a reactor utilizing californium-242 (or, at least, weapon-grade U-235) cooled and moderated by heavy water.

Essentially, it were similar to an atomic bomb, but - of course - it would be optimized for stay around the equilibrial state.

The result were probably a very strong neutron source.

I think, it could be used for various things, mainly in the space applications.

Does any cost/size estimations about this ever created?


texts: How long can I reasonably expect my external USB HDDs and memory sticks to last?

texts:
I have a number of external USB HDDs (nearly all of them 2.5") in my fireproof safe. They are between 7 and 9 years old. (For a period of two years, I bought one almost every month until I had enough for me to feel as if it was not logically possible for all of them to die on me at the same time.)
There's also a bunch of USB memsticks, not much younger than the HDDs.
I take them out on a rolling schedule and sync new data to a couple of them from my main computer, then put them back. It's a chore, but I pride myself on not willingly uploading my data to some "cloud" storage. (One would have to be a fool to assume that they can't, or won't be able to later, break current encryption.)
For years now, I've had a nagging feeling in the back of my head that I should be replacing the old ones, or at least prepare a couple of new ones to take their place when they inevitably die on me.
Other than the purely practical problems of cost and getting them here (long story), it just feels weird to me. This might be a sign that I'm getting really old, but it feels like I just bought these disks. They certainly don't feel almost a decade old! Furthermore, I've barely used them according to myself. They've mostly been resting in their cozy safe, only regularly getting any "action" in the form of I/O. It feels like I've not been "wearing and tearing" on them nearly as much as would be the case if I, for example, was some kind of GoPro action adventurer who has a backpack of HDDs with him on his wild trips into the mountains, where he constantly transfers large video files and exposes them to heavy impacts from rocks and the ground and whatnot.
I have seen and heard absolutely zero signs of them starting to die on me. I don't remember how long the warranty was, but I suspect something ridiculous such as 2-3 years or something. I cannot imagine buying a hard disk which dies after 3 years. I frankly feel as if these are going to last for hundreds of years at this pace, but who knows? Maybe all of them die on me now, and there goes all my data... A frightening thought in many ways, given my empty existence.
On the other hand, if this were the year 2000 and I had a HDD from 1991 (-9 years), I would've seen that as ancient back then...
Is there a non-hard disk company-sponsored report or general advice for how long these things can be expected to last in reality?
There's also the problem of barely any physical space left inside the safe to put any further disks, so I'd ideally have one of them die on me, then replace that, then another dies, and I replace that, etc. But what if they all go at once? Planned obsolescence?
Everything always comes down to money. I just cannot afford some kind of "tape system" for long-term proper archiving.


texts: Where to learn programming for mechatronics and overall?

texts: I have recently finished Matriculation and currently trying to build up certain skills I think will be useful. I have applied for university and one of the courses I am looking at is mechatronics. I was wondering if anyone had information on what programming languages to learn and where I could learn them (hopefully in a form that best fits a busy schedule and allows for me to pause and resume learning at my choice such as a video series on YouTube or something).


texts: Determining behavior of heat exchange system

texts:
I'm trying to develop a thermoelectric (Peltier tile-based) beverage cooling system. Ideally, I'd also like a device to solve the warm beer problem if the thermodynamics give me any confidence.

First, I'll detail my thought flow in the theory sense and then I'll get to my specific setup that I had in mind.

Obviously, if one immerses a 100 W, 10% efficient Peltier tile in a glass of water at 298 K (let's say, containing 10 mol exactly), if the container system is assumed to be adiabatic in nature, to drop the temperature to 274 K (roughly 35 °F) requires:

$$
Q = m \, c_p \, \Delta T = 180.2 \times 4.1813 \times 24 = 18083.3 \:\mathrm{J}
$$

Then, since the efficiency gives the nominal "heat transfer" power to be 10 W:

$$
t = \frac{18083.3\:\mathrm{J}}{10\:\mathrm{J/s}} = 1808.33 \:\mathrm{s}
$$

So, the cooling would take about 30 minutes to chill the glass down, much more when you consider that a glass of water doesn't adhere closely to adiabatic behavior.

The actual setup (poorly-drawn hand sketch follows):

Now, obviously there are four sets of values to consider here:

The specific heat and thermal conductivity of the beverage itself
The specific heat and thermal conductivity of the glass container holding the beverage, easily approximated by making the assumption that the glass can be characterized by fused silica
The specific heat and thermal conductivity of the water transfer fluid, well-established
The specific heat and thermal conductivity of the 6061 aluminum working chamber, which is again well-established

My problem is how to model the system and get model calculations for the transfers between each step, so, for example, solving the equation so I know if I use a given cumulative wattage of Peltier tile, it'll reduce the temperature of the system by a given amount in a certain amount of time.

As before, I'm willing to concede, for the purposes of discussion, that this system can be assumed to be adiabatic with respect to the external environment; that is, no heat is absorbed from the environment during the cooling process.


texts: Is active noise cancellation useful in vehicles?

texts:
The cabin noise of vehicles is a large concern in the luxury market. Why haven't any automakers used the same techniques as are employed in active noise cancelling headphones.  In these devices a microphone is used as an in-loop sensor to suppress low frequency ($f\lt500\ \text{Hz}$) pressure fluctuations in the enclosed space near the ear.

Why isn't similar technology used in vehicles?  What technical improvements are required over the standard vehicle sound system to implement it?  Given the increased volume of the system, what differences can be expected between vehicles and headphones?


texts: Does speed matter while one steel part is pressed into another?

texts: If one press some steel part into steel hole to get unsplittable assembly, does this operation speed matter? Is it better to hit by hammer, or to slowly jam with vice? Does it relate to steel type (e.g. soft or hardened)?


texts: Are there basic rules to properly design vein channels?

texts:
I am trying to model a prototype resembling a section of vein channels. I am wondering if there are some basic rules for such fluid channels, for instance when a vein splits in two capillaries, is there some quantity conserved (area of the section or else)?
I observed that with my current design (which is done by hand just imitating pictures I saw) the fluid I pump in tends to flow very fast in some channels and very slow in others. I'd want some sort of common front to advance.
I am a mathematician and have ZERO education on fluid dynamics or else :) any help is much appreciated!

EDIT: I saw the comment answer and I apologise because I am not sure I will be able to formulate my question in a decent way for engineers :). I am printing my model in rigid plastic and the application is scanning its section in the X-ray CT lab. Here's a couple of pics that I hope will clarify my position:

The idea is to have a viscous fluid (honey+iodine) put in the top "funnel" and start measuring in the CT lab, observing it flowing into the bottom channels.
Observe that the channels have a rectangular section.


texts: How can I block ultrasound from an automotive transducer at about 8'?

texts:
We are testing a new ultrasound product using a Texas Instruments PGA450 automotive transducer.

Three of us are sharing a lab and we need some kind of ultrasound-blocking partition walls around each product to prevent interference. Think cubicle walls that absorb ultrasound.


texts: Mean diameter of the collar when calculating the raising torque

texts:
TL;DR

Is it possible to calculate the mean diameter of a collar?
Can I ignore the collar's component when calculating the raising torque?

I have been trying to answer this question, Z axis: Stepper motor and lead screw torque calculation, over on the 3D Printing site.
I obtained an equation for the raising torque from
Torque Required to Raise Load (TR) Calculation and the full equation, for both thread and collar, is given by:
$$T_R = \frac{Fd_m}{2}\left(\frac{l+\pi\mu{d_m}}{\pi{d_m}-\mu{l}}\right)+\left(\frac{F\mu_cd_c}{2}\right)$$
Neither of the mean diameters for the square thread, nor the collar were given.
However, I found that the mean diameter of the square thread can be  determined from the pitch, $l$, and nominal diameter, $d_n$, by
$$d_m = d_n-\frac{l}{2}$$
However, I do not know how to calculate the mean diameter of the collar. I was hoping that it would simply be
$$d_c = d_n+\frac{l}{2}$$
but, I think that might be incorrect, although I am not sure - as this would seem to be the formula for calculating the major diameter of the screw, when given its mean diameter.
Looking at a series of tutorials, I see that the mean diameter of the collar may need to be provided. For example, from Solution 10.3

After reading around the topic, I see that often the component relating to the collar's friction is discarded (or, as the tutorials state, considered to be eliminated). Why is that? Is that a common simplification?  The OP had this simplified version of the above formula in their question,
$$T_R = \frac{Fd_m}{2}\left(\frac{l+\pi\mu{d_m}}{\pi{d_m}-\mu{l}}\right)$$
So, do I actually need to worry about the collar's mean diameter?


texts: Mini freewheel / overrunning clutch for stepper motor

texts:
I am looking for a mini freewheel, one that I could mount on a standard NEMA 17 stepper motor (or similar stepper). I want to use it with a pulley, such that it starts the motion of a wheel, which can then continue to rotate on its own.
Does anybody have an idea where I could get such a freewheel? Most of what I have seen is either for bikes or cars - I just need a very small version.
Any tips are appreciated!


texts: How is the shift map of an automatic transmission constructed?

texts:
Figure 2 in this tutorial represents the shift map/schedule of an automatic transmission. How is this map constructed? I want to know how to design a shift map myself for another transmission.

The shift map is below:


texts: Is it acceptable, with reinforcement, to notch a floor joist more than 1/6 of the depth?

texts:
IBC 2308.8.2 states a rule of not notching more than 1/6 the depth of a wooden joist (emphasis added):

  Framing details. Joists shall be supported laterally at the ends and at each support by solid blocking except where the ends of the
  joists are nailed to a header, band or rim joist or to an adjoining
  stud or by other means. Solid blocking shall not be less than 2 inches
  (51 mm) in thickness and the full depth of the joist. Notches on the
  ends of joists shall not exceed one-fourth the joist depth. Holes
  bored in joists shall not be within 2 inches (51 mm) of the top or
  bottom of the joist, and the diameter of any such hole shall not
  exceed one-third the depth of the joist. Notches in the top or bottom
  of joists shall not exceed one-sixth the depth and shall not be
  located in the middle third of the span.

Would it be acceptable to notch a joist more than 1/6th of the depth if adding a steel plate or sistered wood beam (going the full length) or some other method (short of putting a column in the middle)? I need to cut about 2.5" out of a 9.5"-deep beam to get an HVAC duct through.

The joist is between the basement and first floor. Above is, I believe, the living room.

The joist spans 10'.


texts: If these modern factories are so highly automated, why must they still be in China?

texts:
Recently, I bought a cheap mechanical pocket watch. Turns out that, in spite of how nice it looks and feels (and functions, so far), it's some kind of noname Chinese-made thing. The price I paid was just above $50 USD.
How can such an intricate mechanical device be so "cheap" (considering the worth of today's fiat money)? I of course suspect that it may break down in a few months, but I could just as well see it lasting my entire life and beyond. It's pretty obvious that, to sell to me for that little money and still make a profit for the store as well as whoever actually manufactured it in China, it was made 100% automated by sophisticated, modern machines. It wasn't some guy in Switzerland sitting for many hours manually placing the little objects into it -- then it would've cost 10x or 100x that price.
Considering how insanely advanced and efficient modern factories evidently are, why must everything still be made in China to "keep costs low"? Why not set up the exact same factories locally and let them produce the same items in the same automated manner here at home, skipping their added premiums and the shipping costs all the way from China?
I can understand that it was cheaper to buy essentially slave labor from China when things had to be done manually with human hands and eyes, but, as I understand it, there aren't even humans working in these factories anymore, except to maintain the machines that do all the actual work. But today, for example to make my mechanical pocket watch, why did they not just make it in the West?
How can it (apparently) still be cheaper to have things automated in China and shipped here with their "cut" included? Or are there other reasons besides money?


texts: General solution for the most critical pattern of live loading

texts:
From ASCE 7-05 code:

  ASCE 7-05 Section 4.6 states "The full intensity of the appropriately
  reduced live load applied only to a portion of a structure or member
  shall be accounted for if it produces a more unfavorable effect than
  the same intensity applied over the full structure or member."

The article then goes on to demonstrate how can we calculate the pattern of live loading for a few simple, text-book cases.

The problem now is, what if the configuration is not as simple? In real life the beam configuration, the support condition can be very different than from textbook examples.

How to obtain the most critical pattern of live loading for the most general situation? Is there an algorithm for this?


texts: In Digital Signal Processing, why is the spectrum of a signal with 'real' samples better than the spectrum of the same signal with padded samles?

texts:
Say we have number of samples to be 128 and a signal sin(2*pi*1000*n*Ts)+sin(2*pi*2000*n*Ts) sampled at 8kHz.

Now say we have same signal but only N = 64 samples. But in order to create 128 samples, we pad the signal with 64 zeros.

Each of these scenarios the frequency resolution is 8000/128 = 62.5Hz, but the spectrum of the first one is much better, as in, you will have two clear peaks. Why is that?

Thanks in advance


texts:
Does anyone know why product picking carts like this, commonly found in warehouses and supermarkets, are mostly just 3 or 4 shelves high?

Is it because of ergonomic issues or mechanical ones? Couldn't these carts be twice as tall and have their capacity doubled?


texts: How do enginners build highway interchanges ? Are highway interchanges build based on a mathematical theory such as braids and knots theory?

texts:
I am trying to find how do enginners build roads especially highway interchanges.
Are they relying on any topology theories such as braids and knots theory?
Is there any connection or link between topology and designing interchanges ?
I can't find any article explaining it.
Thanks a lot.


texts:
in the first photo , it's stated that the dy/dx at center = 0 , however , in the second photo (website) , it's stated that the dy/dx at the boundary = 0 ,which is correct ? I'm confused now
http://www.geom.uiuc.edu/education/calc-init/static-beam/support.html


texts: How I can compute cutting processes with continuum mechanics?

texts:
In YouTube I have seen various videos where someone cut with a sword into hard objects and has cut that into pieces. For example:

https://www.youtube.com/watch?v=EVCWGwvctt4

Given the mass, the velocity and the material of the cutting blade, how I can compute whether some material is cut by it completely or not? Which basic equations should I use? Are there theories that model mathematically such things?


texts: Why do I see stresses on the fixed support face of a solid body in FEA?

texts:
Below, I have shared pictures of a simple model in FEA. As it can be seen that the face onto which the fixed support is applied, there exists Von-Mises stresses. I cannot comprehend why. Since the nodal deformations are equal to zero there, but still there exists stresses. I am aware of the fact that there must be a transverse reaction force on that face due to poisson's ratio effect, but still why would I see stresses there.
In reality, if a face of a solid body is extremely rigid because of how it is supported, should I still expect stresses on that face?


texts: Materials which withstand high temperatures, and are relatively soft, for chuck jaws

texts:
I need to modify a chuck's jaws so they can handle high temperatures, but will not scratch the workpiece. (Glass). The load will be very small.

I will probably use aluminium jaws and either coat them with, or attach to them, this material.

Example items being held:

Borosilicate glass tube, 30mm long, 6mm diameter, 5g weight
Borosilicate glass tube, 50mm long, 30mm diameter, 50g weight

The tube will be held horizontally by the chuck, and should be supported such that the other end will not droop by more than 2mm. That end is held in a propane bunsen flame, on the edge of the hottest part of the flame: a cone 15-20mm height, with a base ~12mm, 1200-1400°c.

I do not have figures on what the chuck jaws will have to withstand, but the air passing over the tip of the jaws probably wouldn't be more than about 250°c, and the temperature of the glass at that point will be about the same.

Of issue might be the heat radiated from the flame - so a heat reflecting material will help.

Also, since the rest of the chuck will be barely above room temperature, it may help to have thermally conductive material to dissipate heat from the tips of the jaws to the chuck.

Plastics seemail like an obvious choice for softness, but high temperature plastics seem hard to find. Silicone (260°c) and PTFE (204°c) are barely temperature resistant enough, but so far seem like the best choice, since higher temperature polymers like Vespel (300-400°c) are very hard to come by.

What alternatives are there? Metals? Composites?

The only other approach I might use is a heat shield directly in front of the chuck, but it would be awkward, as it would have to fit quite snugly around the workpiece, different shields would be needed for different size workpieces, and would be time consuming if batches of workpieces need to be processed. I can't imagine how this could be automated for large batches. Even then, scratching the workpiece could be a problem.


texts: Anyway of converting this to outputting digital readings?

texts:
is there anyway of converting this machine into giving me digital readings?

I bought it on ebay the other day and I am planning on cleaning it up and getting it looking good as new.


texts: How to make a wire turn with a turbine head

texts: I have an outer pipe and an inner pipe a lot smaller than the inside of the the outer pipe, and the head of the (mini) turbine will be connected to a metal rod. There will be wires connected to the head and it will be turning to the wind. How should I set up the wires?


texts: How do I transition to legit freelancing, coming from a background of unethical projects?

texts:
I am a recent electronics engineering graduate, currently legally working as an embedded software engineer in a company.

In the future, I would like to become a freelancer, like signing up on a freelancing website and getting hired to do real projects.

Currently, as a side/weekend gig, I help engineering students with their diploma projects. It's obviously illegal but it's a very common practice around here. But frankly, it's a great opportunity for me to earn good money and learn my trade with real hands-on experience.

In the future, when looking for real customers, they will likely ask for a portfolio of my work. What am I going to show them? Some diploma projects of random people that I supposedly made? I'm afraid that would look very unprofessional.


texts:
I bought sunglasses in China that claims to have UV400 protection. I'd like to test this as my eyes' health is on the line :)

Is there any way to check the maximum UV amount these glasses can protect me against?


texts: How to get natural frequencies from accelerometer measurements?

texts:
I will be performing some tests and measuring the vibrations of a planetary gearbox. The accelerometer I will be using stays attached to the gearbox and saves the data into a log, which is available after the test is finished.

My main objective is to extract the natural frequencies of the accelerometer data and compare them with a simulation derived from an analytical model.

What is the best method for the signal conditioning of the accelerometer data?
I don't understand if the steps between, do I need to have an Integrator for determining the velocity and displacement also, or will a direct fourier analysys like the fft will yield the natural frequencies?


texts: What is "Yale Key, 10½ Section, change 900"

texts:
The specs say:

  Admittance shall be by means of a
  locked door and/or key operated switch,
  which in order to provide compatibility
  within Local Authorities, shall be a Yale
  Key, 10½ Section, change 900. Access to
  level 1 facilities shall be gained without
  opening the main controller door(s).

What exactly is the meaning of the bolded section? I guess it defines some kind of key (and associated lock), but how do I read it? How can I even begin searching for a lock fulfilling these specs?


texts: Calculating Thrust for Contra-Rotating Propellers

texts:
How do I calculate the thrust of ducted contrarotating propellers?

Is there any formula or website calculator or would it have to be done through experimenting with scale replicas?


texts: Adding tension to a model of a Timoshenko beam?

texts:
I am interested in modeling a Timoshenko beam: https://en.wikipedia.org/wiki/Timoshenko%E2%80%93Ehrenfest_beam_theory
However, I would also like to add tension to the beam so that it can vibrate like a string as well as a beam.
The Timoshenko beam is described at that link by two coupled equations, where subscripts are derivatives of that variable:
$ρA w_{tt} = κAG(w_{xx}- φ_x) + q\tag{1}$
$ρIφ_{tt} = EIφ_{xx} + κAG(w_x- φ)\tag{2}$
Where $ρ$ is density, $I$ is second moment of area, $E$ is Young's Modulus, $G$ is the shear modulus, $κ$ is the Timoshenko shear coefficient, $A$ is cross sectional area, $w$ is transverse displacement, $φ$ is rotation of a segment, and $q$ is external force/load.
To solve a unified equation of motion, they isolate $φ_x$ from equation (1), take the $x$ derivative of equation (2), and then substitute in various derivatives of the $φ_x$ from equation (1) into (2).
This also helps to eliminate $φ$ which would be hard or impossible to solve for in a finite difference approach.
This gives a final equation of motion of:
$EIw_{xxxx} + ρA w_{tt} - (ρI + \frac{ρAEI}{κAG})w_{xxtt} + \frac{ρAρI}{κAG}w_{tttt} = q + \frac{ρI}{κAG}q_{tt} - \frac{EI}{κAG}q_{xx}\tag{3}$
Now let's imagine a very simple model for a vibrating string:
$ρA w_{tt} = (T + σA)w_{xx}\tag{4}$
where $T$ is basic tension and $σ$ is the extra stress on a given segment from lengthening (strain).
How could I combine these two systems? My idea is to just add these terms into equation (1) so I'd have:
$ρA w_{tt} = κAG(w_{xx}- φ_x) + q + (T + σA)w_{xx}\tag{5}$
Then I could just combine (5) with (2) to create a new version of (3).
But I'm wondering if this makes sense. Wouldn't these tension terms also affect equation (2)? Ie. Wouldn't I have to add something to equation (2) also?
Thanks for any ideas.


texts: Pneumatic Can Crusher (Number of holes allowed for crushing plate)

texts: Hi I'm designing a pneumatic can crusher for my course, and came across a problem.  How many allowable holes would be ideal to relieve pressure on the crushing plate of the device?  Are there ways to go about it formula wise that may be useful?  The clearances between the crushing plate and the housing would be enough to alleviate pressure built up I'd imagine but I was curious if there was a way of figuring it out anyways.  Thanks in advance


texts: How to represent a load supported at multiple points on multiple beams?

texts:
I have a frame, similar to a container frame, with two vessels inside. Each vessel is supported at four points on two beams, as shown in this mockup:

I am using ANSYS to simulate the loaded frame. How should I represent the impact of the weight of the vessels on the frame so that my structural analysis is correct? Should I divide the total weight of the vessels by four and place that force on each supporting plate or use remote force to represent the weight of each vessel?

I know only the mass and center of gravity of vessels. I don't have full models of the vessels, just a model of the frame.


texts: Pipe wall thickness and production tolerances

texts:
I made a calculation for a pipe that needs to handle 1 MPa pressure. I based my calculation on ASME VIII div1

My calculation says that my pipe needs to be 3 mm thick. But do I also need to account for the tolerances pipe manufactures have on the thickness?

This should be 12,5% according to a colleague of mine (sorry I don't have the source) but I am quite confident he is correct about this.

I can't find a note in the ASME VIII div1 about this maybe I over-read this.

So the question is: do I need to add the pipe wall thickness tolerance to my calculated thickness to be theoretically correct according the ASME VIII div1?


texts: Input-output representation to state space

texts:
How do you create a state space representation of the following input/output equation:

$$ \dot{y} = -ky + u + a\sin(ωt) $$

where the parameters $k$, $a$, and $ω$ are unknown.

The end goal is to create a model reference adaptive controller (MRAC) using only the measurements of the input and output of the system. I believe the first step of this process is to create a state space model for the system from the equation given above. Without the addition of $a\sin(ωt)$ this would be a simple problem but that additional sine term is throwing off my calculation.


texts: Different results when applying equation

texts:
The system shown in the Figure is guided by two blocks in A and B, that move in the fixed grooves. If the speed of A is 2m/s down, determine the speed of B at time θ = 45º

In the textbook they said w = 14.1rad/s (counterclockwise) and v(B)=2m/s
i consider counterclockwise moment positive
if i use the vector BA
$$v_B=v_A+w_{BA} x \vec{r}_{BA} = -2\vec{j} + w_{BA}\vec{k}  \times (-0.2cos(45)\vec{i}+0.2sin(45)\vec{j})$$
$$= -0.141w_{BA}\vec{i}+ (-0.1412w_{BA}-2)\vec{j}$$
and since $-0.1412w_{BA}-2=0\Leftrightarrow w_{BA}=-14.1rad/s$ (since is negative, the direction is clockwise) and $v(B)=2i$.
But if i use the vector AB:
$$v_B = v_A+w_{BA}\times r_{AB} $$
$$= -2\vec{j} + w_{BA}\vec{k}  \times (+0.2cos(45)\vec{i}-0.2sin(45)\vec{j}) $$
$$= 0.141w(BA)\vec{i}+(-2+0.141w(BA))\vec{j}$$
and since $$-2+0.1412w_{BA}=0 <=> w_{BA}=14.1rad/s$$ (since is positive, the direction is counterclockwise) and $v(B)=2i$.
So I got two different results for w(BA) when using vector AB or BA. Which vector should I use when I apply the equation v(B)=v(A)+v(B/A) and why?
Similar case
in this case i use the vectors AB and BD, and i got the opposite signals for the angular speed of the connecting rod BD and for the piston speed P (although the value in module is correct) Should i had used these vectors?

we know from the exercice that w(AB)=209.44rad/s, β=13.95 and we want to discover v(P) and w(BD)
w(AB)=209.44rad/s
v(B)=v(A)+w(AB) * r(AB)
=0+ w(AB)k * (0.075cos(40)i+0.075sen(40)j)
=0.0575w(AB)j-0.0482w(AB)i
=-10.1i+12.04j
v(D)=v(B)+w(BD)*r(BD)
=v(B)+w(BD)k * (0.2cos(13.95)i-0.2sen(13.95)j)
=(-10.1i+12.04j) + 0.194w(BD)j+0.0482w(BD)i
=(-10.1i+0.0482w(BD))i + (12.04+0.194w(BD))j
12.04+0.194w(BD)=0 <=> w(BD)=-62.06rad/s
v(P)=v(D)=-13.09i


texts: What is the difference between "Crushed Stone" and "Crushed Gravel" aggregate?

texts:
Crushing Question
While reading a material specification for crushed aggregate, the text mentions both "crushed stone" and "crushed gravel" are acceptable. These materials sound very similar, but they are mentioned individually. I assume that this means that they are not the same.

What is the difference?
How can I tell the difference if I see them on-site?

Example
This specification from Michigan is an example:

Aggregates shall consist of clean, sound, durable particles of crushed stone, crushed gravel, or crushed slag...


texts:
I'm developing a Frictionless Braking System for 2 wheeler using electromagnet. My questions were

How can we overcome the problem of braking at Low speeds. This type of braking tends to fail.
How can I solve the problem of Emergency Braking without deviation in path (For Example: If my motorcycle is travelling at a speed of 50kmph with a load of 120 kg and if there is an obstacle, how do I provide leverage to this brake)
How do I mount my Electromagnets onto the brake calliper and what type of electromagnets should I use?(looking for specifications of electromagnets)
How do I calculate Braking Torque, Force at the front and back wheels of the 2-wheeler, efficiency and other important parameters? (Looking for formulas or Calculated examples)

I had tried to use a relay/ SMPS for the point 2 stated above.
I am using an Aluminium T6 6061 plate of 3mm thickness and 35 cm diameter.
PLEASE HELP


texts: How to attach a wheel to a turning axle for a ball machine

texts: I'm trying to make a DIY tennis ball machine. However, I'm not quite sure how to attach the wheels to the steel rods, which will be attached to the motors. In other words, the wheel and the rod should become like one single object, so that rotating the rod will rotate the wheel too. The design is something like the picture below, but the wheels I'll be using can be found here. What are your suggestions?


texts: Git, Mercurial, others -- what's the best system for an engineering team new to version control?

texts:
I recently started working with a new team doing detailed energy modeling for all flavors of building projects -- commercial, industrial, residential, new construction, renovations, additions. As the team has been growing, we've been discussing three particular problems that I believe version control could help with.

Our challenges

Coordinating multiple people working on a single energy model. Each building model involves different components -- geometry, envelope, HVAC, lighting, etc. For time-crunched projects different people may work on different components simultaneously. To bring each person's work together at the end can be complicated and time-consuming.
Keeping track of "known good versions" for a particular application. To streamline our work we create templates for various building components. Each template may only be ready to use for certain building types (say, HVAC template #n is working for commercial buildings but not tested for residential). When starting a new model we review release notes to make sure we apply the appropriate template, until our periodic review when we test/update templates for all use-cases. Both the tracking of historic versions, and the periodic integration of updates, is complicated and time-consuming.
Reproducing results from a report sent to a client. During model development we periodically prepare reports for clients. Each report is tied to a version of the model and templates which is archived on our server. This way we can re-open the old model to address any questions the client has, even as model development has continued. At times we also need to change aspects of the old model to answer specific client questions, before a model update is ready. At this point, the task of integrating two separate streams of model changes becomes... complicated and time consuming.

All of these processes can be improved with version control -- but nobody here has ever used version control!

I'm wondering if others here have been in a similar position, and implemented a version control system. What did you use, and how did it go? What best practices can you share?

Some details about our team and our work

All engineers use Windows 10
All of our modeling tools are Win32 applications (eQuest, Open Studio, TRNSYS), but modeling source files are stored as text-based files (not binary)
We're considering Git, Mercurial, and Bazaar
We do not currently have a server where we could run something like SVN, so we'd prefer a distributed system which could store files on a shared drive (such as a networked drive, SharePoint, DropBox, etc).


texts: Combined uncertainty of two different measurements

texts:
I am an electrician apprentice in charge of the analytical measurements at the power plant I am hired at.
In certain parts of our process we have redundant pH measurements that feeds into our SCADA system. The measurements are continuous and are not sample based.
I have identified the uncertainty to be +/- 0,10 pH per pH instrument with a confidence level of sigma 2.
Let's say I have three redundant instruments that are freshly calibrated and adjusted and which gives me the following measurements from my process:

Instrument 1: pH 4,00
Instrument 2: pH 4,05
Instrument 3: pH 4,10

The true value, with 95% confidence, then must lie somewhere between:

Instrument 1: pH 3,90 - 4,10
Instrument 2: pH 3,95 - 4,15
Instrument 3: pH 4,00 - 4,20

We of course assume that the process media is homogeneous in it's pH level throughout and that the different pH values arise from the instrumentation itself (for example each pH-sensor reacting differently to changes in temperature, pressure, linearity and so on and so forth)
So now I am suddenly confused and my logical reasoning would make me conclude one of two things:

The uncertainty is actually much larger than I thought (3,90 - 4,20) or
I can exclude the extremities... and so only the overlapping
parts of the interval must represent my uncertainty (3,95 - 3,15)
which however still leaves me with twice the uncertainty compared to
the uncertainty of each individual instrument (0,20 vs 0,10).

Any ideas on how to tackle this?
By the way, this is a real practical issue I am facing. Even though my pH instruments agrees equally with my reference (buffer solutions) down to 0,00 they still differ slightly between each other when inserted into the process media. Usually up to pH 0,05.
Thanks in advance.
/David


texts:
I'm trying to make a project with keil uVision 5, for DA14580 (Dialog Semiconductor).
http://www.keil.com/dd/chip/6853.htm
But in Select Device dialog there's no device from Dialog Semiconductor.
As you see in the photo, i dodn't found Dialog Semiconductor MCUs.
The Question is: How can i start a Project with some selected mcu?
All examples that i can found is for TI microcontrollers or Atmel.

Also, Device missing from Pack Installer too:

The only information about the device that I'm looking at is in device database in File Menu:

I tried to "Add" the device but, when I'm creating new project for a specific Device, (Photo No1) I cann't find the device in the list.


texts: Mechanically increasing RPM of ac induction motor

texts: If you spin the stator of an AC induction motor than would the rotation of the rotor increase? Or would it have a different affect such as moving with a higher force?


texts: Servo, control, rpm sensor in high g environment

texts:
I've used a few types of mechanically actuated variable pitch props on my boat, so I know their performance is good.  However, their strictly mechanical and also self-contained nature makes their operation unreliable.  I'm looking into the feasibility of an electrically actuated one for my own use, and I have a few questions.  Since a prop must bolt on to an existing shaft drive, it has to be fully self-contained- no levers or wires connected externally.  Lots of challenges here, but the biggest that I'm having trouble finding info on is the g-force question.  At 4k rpms, say 2" off center, that's suddenly 900 gs of acceleration.  Will any servo or controller be able to handle that?

I'd like to measure the RPM internally as well, though potentially I could mount a magnet on the drive to count passes/rpms that way.  But an accelerometer on board would be neater.  Again, could it handle the gs?

I'll certainly entertain discussion of moving everything to the center (not ideal), but even then any part of a component that extends to 1" from center would see 500 gs.


texts: Calculating reliability of a parallel redundant system

texts:
I'm trying to calculate the reliability of a system that has proven to be a bit more complicated than I thought. Here is the block diagram for the system:

Every single component in this diagram is a Line Replaceable Unit with a mean downtime of 2 hours. If any of A-F fail, that's a failure for the "subsystem" indicated by the dotted line. The entire system will successfully work as long as only 1 of the dotted line, A-F, "subsystems" has failed. Because of the mean downtime of 2 hours, if two of the dotted line subsystems fail within 2 hours of each other, the system fails. This subsystem highlighted in green is not particularly difficult. What's throwing me off is the inclusion of components G1 and G2, routers that fail when either A (UPS) or B (DC power) fails. This makes up the subsystem highlighted in red. The entire system fails if both routers (components G1 and G2) fail, within 2 hours of each other of course.

Basically, I thought that the reliability of the whole system can be calculated with Bayes Theorem which would give the reliability of the system as:

Reliability of green subsystem * probability that G1 and G2 do not fail

PLUS

Reliability of red system * probability that another of the dotted line subsystems does not fail

PLUS

reliability of red system * probability that the other red subsystem does not fail

Unfortunately, I think I'm vastly misunderstanding Bayes Theorem and maybe the system as a whole. Can someone lead me in the right direction to how the inclusion of these G components affects the system reliability? Maybe I just need to re-read up on Bayes Theorem?

Thanks!


texts: Naming of 1P4A or 5A layer configurations

texts:
Glass is brittle and easily damaged. So, a new kind of glass material is made, in which it's layers are made of hexagonal tablets (made of borosilicate glass) arranged in 1P4A or 5A, as happens in natural nacre. This synthetic glass proves to be more resistant to impact.

More about is given in this link.
https://science.sciencemag.org/content/364/6447/1260/tab-figures-data

Now my question is, where does the terminology "1P4A" or "5A" come from? I cannot find it on the net.

I also don't know if this is the right place to post this question. Please guide me.


texts: Is the formula $T=2qA$ valid for both open thin-walled and closed thin-walled members, where $T$ is torque, $q$ is shear flow, and $A$ is the area?


texts:
I have been reading a lot on flexure bearings, but it's still not really clear what they are. From everything I've seen, it seems like a flexure bearing is just a spring.

Can someone give me a simple explanation of what they are and their use?


texts:
I build an awesome skating rink for the kids. Now I have to flood it. I have the rink built 450 feet from the lake. The rink is 7 feet higher than the water. I have a 1.5-inch polyurethane rigid hose running from lake to rink (100% sure no air leak). I have that hose connected to a brand new, Flotec FP5172 1-1/2 HP Self-Priming High Capacity Pump running on 115V, and then from the pump a 15-foot hose to irrigate the rink. With the show about to start, I plug in the pump and it’s not siphoning water. The guys that sold the pump to me did it was ample strength.

Should I have the pump at the lake pushing the water uphill versus my current setup of pump beside rink and pulling it through 450 feet of hose? There’s barely any suction at the lake end when I pull out the hose from the lake.


texts:
I know that friction helps car to move forward. The engine of the car turns the wheels, and the tyres have to grip the road in order for the car to start moving forward. If there is no friction, tyres cannot grip the road! It is similar to a geared wheel moving on the ground

But I can't imagine how does friction act as a centripetal force when the car is turning on a roundabout? What is happening at the point of contact between the wheel and the road ?


texts: How can I draw Voronoi regions in curved surfaces in AutoCAD?

texts:
How can I automatically compute and draw/display the Voronoi diagram of a given set of vertices on a surface in AutoCAD?

A "Voronoi Sketch Generator" is the best I could come up with on a google search.

Quite close, but:

It doesn't seem to work for curved surfaces, only flat 2d planes
It is a plugin for Fusion360, not AutoCAD
It doesn't let me define the set of vertices of the diagram (it generates them randomly)

It is my understanding that I can import an AutoCAD drawing to Fusion360 and then export it back to AutoCAD. Maybe tuning up this plugin for this task would be my best choice?

Being a telecommunications software engineer I have near zero experience with AutoCAD, so I apologize for my absolute ignorance on the topic.


texts:
I need to make this structure:

from this other:

but I don't figure how, I tried to "Convert Entities", but doesn't work. Can you help me?


texts: How do automotive engines differ for longitudinal vs. transverse applications?

texts: Sometimes engines are described as being intended for a particular orientation, e.g., "The 4.6 L; 278.6 cu in (4,565 cc) LD8 (VIN "Y") is a transverse V8 for front-wheel drive cars." What exactly does that entail? Why would an engine function differently with transverse instead of longitudinal mounting?


texts: Deriving the First order response of a sensor

texts: I'm trying to derive the first order response of a sensor with step input. However, I'm stuck at step just before conducting the Laplace transform. In the following image, how is the left side equal to the right side? I know the right side equation is necessary to obtain to perform Laplace transform.


texts:
I have a setup in which a bolt threaded on two ends with an unthreaded shank in the middle will be rotated by the unthreaded shank area. That is, the bolt's axis of rotation is roughly the red cross:

I wonder if there's a small part/connector that I could fit over the unthreaded shank so that a shaft could be connected to the connector such that the bolt can be rotated. Perhaps, something like below where the top is a hex/square hole and the bottom is a threaded hole?

Alternatively, are there low-profile setups where a bolt can be rotated around the centre?


texts: Is it possible to make AR500 steel at home by just melting its components and applying appropriate heat treatment?

texts: Would it need hot forging or hot pressing before heat treatment to be equal in strength and toughness to commercial AR500 steel plates?


texts: Inventor: How to replace static part with articulation?

texts:
I have downloaded the following part file of a servo motor as IGES from the vendor:

I have then built an assembly that uses several of these motors, as well as a number of idlers/hubs, brackets, machine screws, and whatnot. I've used the standard "constrain mate to face" and "constrain mate axis" constraints, as well as inserting bolts from content center, and bolted connections for bolt+nut.

Now, as it turns out, the "horn" part of this servo (the aluminum wheel on the front with the eight threaded holes) is modeled as a static part of the mesh in the IGES file. But, in real live, this moves/articulates. I'd like my model to move/articulate the same as the real thing.

How can I get there with the minimum amount of re-work?

The closest I can think of right now is to break off the horn from the motor housing, and create two part files, then create a sub-assembly out of those part files, and then delete each of the motors in the bigger assembly and re-add them. Given the amount of constraints and bolt connections on those things, that would be about as bad as starting over from scratch.

Is there an easier/better way to achieve what I want?


texts: Fluid allocation for shell and tube heat exchanger

texts: I'm designing a shell and tube heat exchanger with a hydrocarbon stream (31.6% propane and 60.4% propylene) entering at 135F and 321psi, and leaving at 100F being cooled by water at 85F and 74.7 psi. As of now I have the hydrocarbon stream on tube side and water stream on shell side, mainly due to the high pressure of the hydrocarbons and it being at a higher temperature. Is this a decent enough basis for my decision? Any help would be greatly appreciated, thank you!


texts: CE Marking on low budgets: conforming to EMI / EMC requirements in ELV and mains circuits

texts:
For one-off, bespoke electronic products, or ventures on low budgets, what is the cheapest way of ensuring the product conforms to EMI/EMC requirements of CE marking? This can be at design time and / or  throughout the manufacturing process.

Examples:

A small-run, electronic microprocessor based controller (using a CE-Marked zero-cross solid state relay) intended to switch on or off a 2 kW load such as a consumer grade 240 V, 2 kW blower heater.
A one-off CNC machine that utilizes CE-marked, low voltage motors and servos, and is controlled by a microcontroller and miscellaneous circuitry
A new venture into producing LED lighting with controllers - typically switching 10 W loads; using PWM to control brightness; controlled by a micro-controller; using SMD LEDs, and a CE-marked switched-mode 24 V, 3 A PSU.

Obviously there must be logical principles which one can apply to allow one to bypass other expensive conforming methods.  For example,  connecting two CE-marked appliances to each other where they are intended to do so would most likely not need any further testing.

The problem is that for more complicated scenarios getting products approved by external companies that provide CE-marking assessments can be incredibly expensive. Also, I have not found any particularly affordable equipment/methods to carry out EMI/EMC testing - and not being an expert in EMI/EMC means I would not be confident about using such equipment effectively.


texts: how to avoid a clash of magnetic charge and electric charge

texts: now I'm working on a project which involves a dc motor and high voltage. I'm developing a machine consists of a motor to rotate a platform disc and high voltage will be applied during the rotation. The problem is when I supply a positive high voltage at motor shaft during rotation, the motor stop working. Do you guys have any idea, how I can supply the high voltage properly the high voltage supply?


texts: I'm very new to designing shapes in multi views and drawings and got a homework problem on this. I have to draw an isometric from this multiview drawing. I have no clue where to start and am not totally sure what all the lines on the drawing mean. Any help is appreciated!


texts:
So ive got the moments of :

B:

Vertical : $\sin(75)AB + \sin(45)BC = 33\text{ lbs}$
Horizontal : $\cos(75)AB = DB + \cos(45)BC$

D:

Vertical: $\sin(60)DC + \sin(65)DE = 100\text{ lbs}$
Horizontal: $\cos(60)DC + BD = \cos(65)DE$

A:

Vertical: $W_F = \sin(75)AB$
Horizontal: $\cos(75)AB$

E:

Vertical: $W_B = \sin(65)DE$
Horizontal: $CE = \cos(65)DE$

How do I solve this truss problem with multiple unknowns? It seems every possible manipulation leaves me with at least one unknown.


texts: Having the Power/Torque-RPM curves of a vehicle, how can we derive the engine power equation and the torque out of these curves with respect to time?


texts: How to calculate load on roller to create given deflection?

texts:
I am trying to calculate what loading on a fixed roller will create a predetermined maximum deflection. I ran some calculations, but the values I'm getting are significantly lower than I would expect.

Attached are the calculations.

Thanks!


texts: Is it possible to have circulation without vorticity?

texts: Both circulation and vorticity have to do with rotation of a fluid element.How are vorticity and circulation are related.


texts: What is the idea behind an expansion valve?

texts:
I am watching this video(https://www.youtube.com/watch?v=gVLhrLTF878) and beginning at around the 2:20 mark, it explains the significance of an expansion valve with the following ideas:

Restricts refrigerant flow to lower refrigerant pressure.
Decreasing surrounding pressure $\lt$ liquid(refrigerant) pressure implies boiling liquid.
Decreasing surrounding pressure around a liquid allows the liquid to evaporate. The evaporation takes some of the kinetic energy from the liquid which consequently lowers the temperature of the liquid.

I have listed the ideas as to how I have understood it, but number 2 and 3 seem contradictory to me. Maybe temperature and pressure do not have a linear relationship? Please, anyone, clarify any misunderstandings I have.


texts: time interval selection for RMS of vibration

texts:
What is the general practice for selecting time interval for RMS calculation for vibration data (mm/s)

Should it be linked to the the frequency of the motor or the sampling rate?

Thanks!


texts: Office Complex Foundations/Base Depth and Undeground Water

texts:
I have a school case study to prepare a (business) plan for office building construction with at least one level of underground parking. I have it pretty much done, but I still need to clarify one thing (teacher is not available):

(1) What is implied by "Underground water level varies from 5-6m" for the construction? Currently I ignore it. Does it affect the underground parking if I consider only 1 level? Does it have (any/significant) impact on building costs?

(2) What would be depth of typical base/foundation for an office complex building (3 stories, 50k sqm)?  Does the underground water interfere in any way?

Tried googling for relation of underwater level and foundations, but couldn't really find anything.


texts: Which diameter and thickness pipe to choose

texts:
I'm building a roller for a "pool" cover I got at home. The cover weighs 10kg (8kg but I'm considering some weigh added by the water present on it). I have a bosch profile structure where I will support it.

Now I need to choose a pipe. I don't know which pipe to choose. Will a steel 35mm diameter with 1.5mm thickness pipe does the job without deflection? Should I increase the thickness or the diameter? The tube lenght will be 4m.

Thank you


texts:
I am trying to measure the height [level] of the water in a box that goes from -3°C (saltwater) with water and 150°C dry. Objects will be placed inside the box but will not take up the whole area.

I need a sensor that is robust enough to go through those temperatures and measure accurately. I was thinking of using a float switch on a worm gear, but the motor couldn't stand the heat...

What other methods/sensors are there? I also have a clear tube that runs outside of the tank meant for visually inspecting the height of the water.

Can I use a ultrasound sensor to measure water level? is a closely related question but focuses upon ultrasound.  That won't work for my particular case because the contents of the box are effectively unknown.  And capacitive techniques won't work either as the box will be grounded.


texts:
Sequencing batch reactors let sludge settle before drawing off the supernatant. For this, decanter arms are often used. An example is here.

The challenge is to draw off the supernatant without creating turbulence, which would disturb the sedimented sludge and lead to sludge in the supernatant.

I'm willing to compromise on the amount of supernatant I draw off, say only 20% of fill level. Can I use a simple standing pipe for this, or will I get excessive sludge?


texts: Single Split Air Conditioner & Supply/Exhaust Fan

texts:
First Question

Does single split AC (the type with evaporator indoor and compressor outdoor) vent or exhaust air outside and thereby create negative air pressure in the room?

Reason being I am trying to ventilate my home gym room through the door gap with a wall mounted supply fan in the living room outside the gym room, so the gym room needs to have negative air pressure. Installing an exhaust fan in the gym room defeats the purpose since i would like to work out in an air conditioned gym.

Second Question (assuming the answer to the above is yes)

In another room (outside the living room as well), a master bedroom, i am planning to install another wall mounted supply fan but due to space issue, it has to be on the same wall as the air conditioner, right beside it.

Does this then mean that the air vented by the AC compressor unit would immediately be sucked back into the supply fan, introducing the hot and high concentration of CO2 back into the room, defeating the purpose?

Would this then mean that having a bigger CFM supply fan in the living room would be better than having 2 smaller units one in living room and another in bedroom?

As the unit in living room will not be affected by any AC and the air will still be able to travel to the gym room & bedroom via the small door gap provided that the AC is on and is able to create negative air pressure in the rooms?

Thanks.


texts: How is a 25-year-old can of soda now empty without having been opened or poked?

texts:
I just discovered in my parents' basement a Sprite can from 1995* and also a Coca-Cola can probably from the same year.

Both cans are unopened and have no visible damage or holes. The Coca-Cola can feels "normal", but the Sprite can is empty!

You can hear in my video that there is no liquid sloshing around in it.

I can't find any way that the soda could have escaped.

We also don't see any mess near where the cans were, but I don't know for certain that the cans stayed in the same place for 25 years, so maybe there could have been a mess of liquid leaked out somewhere else if the cans had been stored somewhere else earlier. But nothing feels sticky or looks like there has been a leak of any kind.

What are possible explanations for how a carbonated drink could disappear from a sealed aluminum can?

*I had kept it as a "collector's item" from when the Houston Rockets won their second championship.

Note: I originally posted to https://physics.stackexchange.com/q/532731/46543 , but the moderators closed the question and said it belonged in Engineering. Also, I followed advice of commenters there and refrigerated the can and then later submerged it in warm water, but as you can see in this video, there were no bubbles revealing any holes!

Also, many people suggested that the can never had liquid in it, but that seems extremely unlikely since neither I nor anyone in my family remember ever encountering any can ever that was sealed but empty.

UPDATE

Video of opening the 25-year-old Coca Cola can
Video of opening the 25-year-old Sprite can that felt empty


texts: Air demand for powder fluidization system

texts:
I need a good estimate of the air demand for a system to fluidizde a powder. We a have silo with a 60° cone and a rotary cell feeder attached to the opening in the cone. The powder (fine powdered activated coal) shall be fluidized by blowing some compresses air into it. Perrys chemical engineering handbook gives some tables and nomogram for full fluzidization (air velocity of 0.15 - 6 m/s over free area of silo). However, I really only need fluidization near the walls of the cone, so I should be able to get away with less.

Silo diameter is 3-4m, mass flow rate up to 60kg/h

How do I estimate the air need for fluidization?


texts: How to calculate saturated steam flow rates?

texts: It has been a while since I had thermodynamics and am attempting to solve this problem for work. I need to figure out the other two mass flow rates. I worked it out with specific heats, but don't really trust it. Seems like there should be a simple way to do it with enthalpy; the process just escapes me. Thanks for the help!


texts: Drawing the Connection of 2 Arcs with Radius

texts:
I am supposed to be re-drawing this image to scale
 However when I Try to connect the arc R11 with arc R26 using the radius R22 I get a negative # in my calculations. i.e. R26-R22=(-4)

Is there a different way to draw this? I have tried nearly everything and have completed the rest of the drawing except this one point, Am I missing something here?


texts: Do triangular/area coordinates offer computational advantages for numerically integrated triangles?

texts:
Isoparametric triangular finite elements can be formulated using "triangular coordinates" $(\zeta_1, \zeta_2, \zeta_3)$, also sometimes called area/areal/barycentric coords, or using "Cartesian coordinates" $(r,s)$ defined on a master element. These two systems can be related to each other without difficulty, and seem to be functionally equivalent.

It seems that several texts and journal papers use triangular coords  $(\zeta_i)$ exclusively, particularly those that are more recent and/or mathematically oriented. On the other hand, I have older textbooks and use certain commercial FEA packages that consistently present element formulations with $(r,s)$ coordinates. I have a feeling that this might be due to historical reasons, but perhaps there is more to it.

Provided that the element geometry is restricted (straight sides, and any side nodes are uniformly spaced), I understand that triangular coords may be useful because they lend themselves to analytical integration, and thus avoid potentially costly numerical integration procedures. However, when these conditions are not met, numerical integration must be used. In that case, is there any benefit from using triangular coordinates, conceptual or computational?


texts: Neutral axis in canteliver beam at support

texts: First, I thought the neutral axis would just be the y bar which can be obtained from the centroid of the cross-section but is different. I have tried letting the net moment at the wall = 0 and the reaction force I got is 1kn * 1m. But I am kinda lost on how to continue.


texts: What material can wick up fluids while not allowing micro-organisms to pass?

texts: I'm looking for a material that can wick up a solution containing nutrients and sugars. The dirty side of the wick should touch a medium to draw up the solution, on the clean side of the wick sterility should be maintained. Do you know of any material that will allow wicking of the fluid while stopping micro-organisms? Antibacterial properties of the material are a plus.


texts: Deflection of parallel rods with force at an angle

texts:
As in the picture below, there is a static force $A$ being applied at 45 degrees to a rigid rod attached to a rigid plate. The plate is supported by two rods of length $B$ and diameter $D$, each of circular cross-section, which are fixed at their ends opposite the plate. The force is applied halfway between the two rods. The weight of the objects are negligible.

See here for a more precise diagram, but note that there should also be a bending moment at the point where the load is applied due to the parallel-axis theorem.

The objective is to determine the deflection in each of the two rods. Assuming no other parts in the picture other than the two rods deflect, how do I determine the deflection of the two steel rods?

Edit: I think a better way to visualise it is that it is kind of like a cantilever; where the two fixed ends are like attached to a wall. This was how I saw the problem.


texts:
I have a situation where I have two water supply lines and both need to be the same pressure. One of the lines is normally always a little higher than the other, but by different amounts depending on circumstances.

Is there a special kind of valve that will automatically restrict the high line so that it always matches the pressure of the low line?


texts: Mechanical solution for keeping a vertical stack under pressure

texts:
I'm looking for a solution for keeping a vertical stack of small boxes under tension. I will use the device in the attached picture to hold the boxes which will have a lid on the top, and the boxes will be pushed towards the front by a linear actuator. So far I've thought of an extension spring which will be attached to the back end of the device and the bottom platform, but not sure if it's an optimal solution.

Thanks,
George


texts: What is the Brinell hardness of ATSM A786 steel?

texts: This steel is often used as a floor plate.  I could not find the Brinell hardness rating.


texts: clamp force or torque for non-steel screws - brass or aluminum

texts:
It is common for screw tightening to have the relationship between torque and clamp force defined by:

$$T=kFD$$

However, all the calculators seem to assume the screw is steel.  How can this be adjusted if fastener is brass or aluminum?  Is it correct to scale results from calculators by youngs modulus.  Ref https://www.engineersedge.com/torque.htm


texts: Why are flyovers/metro rail tracks much higher than traffic?

texts:
To pick a specific example, a flyover that goes over a ground-level road/rail need only be as tall so that the tallest vehicle travelling in the outermost lane can clear it.

Or another, an elevated road/metro rail that runs along a ground-level road need to be as tall as the tallest vehicle.

But why are they made much taller than that?


texts: How do I compute combined tensile strength?

texts: If I know the tensile strength of a pin, how do I compute the total strength of multiple pins?  That is, 2 objects are connected by multiple pins, evenly distributed, each with a height of $2mm$ and a cross sectional area of $3.33mm^2$.  For some reason the answer of just multiplying the tensile strength of each pin by the number of pins, doesn't make 100% sense to me.


texts: Setting up a radiation heat transfer problem

texts:
I am trying to solve a radiation heat transfer problem. The problem is set up like this: Two spherical shells of radius R whose surfaces are separated by a distance R. One shell, call it A, has a steady heat flux of Q and the other, call it B, does not. Both also radiate to ambient ('surface' C) at 0 C.
To solve this I use these equations:
$$ \dot{q}_i = \frac{\varepsilon_i A_i (E_{b,i}-J_i)}{1-\varepsilon_i} \quad \text{for } i = 1.. N $$
$$ \dot{q}_i = A_i \sum_{j=1}^N F_{i,j}(J_i-Jj)  \quad \text{for } i = 1.. N $$
So for sphere A, the left hand side of both equations is Q and for the others it is zero. The view factors are as follows:
FAB = 0.0294
FAC = 1-FAB
FBA = FAB
FBC = FAC
FCA = FAC*SurfaceAreaA/SurfaceAreaC
FCB = FBCC*SurfaceAreaA/SurfaceAreaC
FBC = FAC
Since the temperature of C is set, I have 6 equations in 5 unknowns (TA, TB, JA, JB, JC).  When I try to solve this in matlab using the nonlinear equation solver I cannot get a solution.  Did I make a mistake in setting this up?
Below is the matlab code I am using for equations 1 and 2.
function F = TWO_SPHERES_AMBIENT(J)
% Function called by FSOLVE

sig = 5.670374419e-8;    % S-B constant [W/m^2*K^4]
r = 0.1;                 % Radius of Balls A and B [m]
R = 10;                  % Radius of "Ambient" sphere
g = 50000;               % Equiv. Internal Generation of Ball A [W/m^3]
vol = 4*pi*(r^3)/3;      % [m^3]
sa = 4*pi*(r^2);         % Surface Area of Balls A and B [m^2]
SA = 4*pi*(R^2);         % Surface Area of "Ambient" Sphere [m^2]
totgen = g*vol;          % Total Heat Generated in Ball A [W]
flux2surf = totgen/sa;   % Total Flux to the Surface of Ball A [W/m^2]
eps1 = 0.7;              % Generating ball emis.
eps2 = 0.5;              % Nongenerating ball emis.
eps3 = 0.99;             % "Ambient" emis. (1, Except Div. By Zero Below)
FAB = 0.0294;            % View Factors
FAC = 1 - FAB;
FBA = FAB;
FBC = FAC;
FCA = FAC*sa/SA;
FCB = FBC*sa/SA;
FCC = 1 - FCA - FCB;     % Plays no role in equations below. (J(3)-J(3)=0)
FBC = FAC;
% BELOW IS IS THE RETURN TO FSOLVE. J IS WHAT FSOLVE PASSES IN, F IS
% RETURNED BACK.
% J(1) IS BALL A RADIOSITY
% J(2) IS BALL B RADIOSITY
% J(3) IS 'AMBIENT' RADIOSITY
% J(4) IS BALL A TEMPERATURE
% J(5) IS BALL A TEMPERATURE
% J(6) IS "Ambient" TEMPERATURE
% EQUATIONS 1, SET TO ZERO AS REQUIRED BY FSOLVE.
F(1) = sa*(FAB*(J(1) - J(2)) + FAC*(J(1) - J(3))) - totgen;
F(2) = sa*(FBA*(J(2) - J(1)) + FBC*(J(2) - J(3)));
F(3) = SA*(FCA*(J(3) - J(1)) + FCB*(J(3) - J(2)));
% EQUATIONs 2, SET TO ZERO AS REQUIRED BY FSOLVE
F(4) = eps1*sa*(sig*J(4).^4 - J(1))/(1-eps1) - totgen;
F(5) = eps2*sa*(sig*J(5).^4 - J(2))/(1-eps2);
F(6) = eps3*SA*(sig*273.15.^4 - J(3))/(1-eps3);


texts:
Stepper motor should drive a frame to tilt, but not 360 degrees, but only within 20 to - 20 degree.
What simple machine elements do you use to restrict the freedom of movement?
It must be a mechanical solution, not a software one.
Can it be only done through gear elements and no further addition elements?

Something like the following
https://www.youtube.com/watch?v=w7v2lVsjH4g

Thanks


texts: Can different analog and mixed signal devices be combined on a single chip

texts:
Say I want N-ADCs, M-amplifiers, K-filters, and why not, an oscillator too. Is there a platform to combine whatever device i need, and that this platform is implemented on a single chip?

I know an FPGA has a pool of logic gates and flip-flips, and so anyone can implement a huge number of functionalities with some coding. But is there something similar in the analog and mixed signal domain of electronics? If so, how do you build your system? is it like a drag and drop sort of thing, where you choose whatever device you need from a library and place it in a layout, and then fab it? Could this be ASIC? can I layout my own ASIC using, for example, Cadence?

Please some details!


texts: When reaming a hole to fit a bearing, can I get an underfit by icing the workpiece?

texts:
It's my first time working with bearings, but this is a necessary part of my robotic arm project.  I have some $10 bearings that are 24mm OD.  I want to fit these tightly in a hole, ideally getting a press fit or interference fit (steel bearing, aluminum block).

I ordered a reamer that's 24mm and plan to ream the hole on a lathe, but I am worried - what if the bearings are themselves OD undersized (I don't have any fancy measuring calipers by the way).  I think ideally I want a hole of maybe 23.99mm.

Thinking ahead, if I run into this problem, could I cool the workpiece in ice before placing it on the lathe?  This way the workpiece would be reamed in a shrunken state, and then expand as it warms up to room temp?  The last thing I want to do is break a tool, but this seems like it could work.

Wikipedia says aluminum has a volumetric thermal expansion coefficient (av) of 69,  and for Silicon Carbide (the reamer is made of this) 8.31.


texts: How can I reduce the computation time required to simulate a brain tissue penetration model?

texts:
I am trying to model the strain generated by inserting an electrode device into brain tissue. I've had some success in doing this in ANSYS Explicit Dynamics. Here's a link to a GIF showing the penetration.

My issue is that I had to do a very fast insertion (10 m/s) in order to have a faster computation time (~18 h). The actual insertion speed is on the order of 0.1 mm/s, which ends up being 5 seconds of simulation. 5 seconds of explicit dynamics simulation is days of computation on my computer! My question is, can I do this sort of slow penetration/ballistics model in ANSYS transient dynamics or some other implicit model? Or am I stuck with Explicit dynamics and the super long computation time?


texts: I am currently working on a design for a beer pump (liquid dispenser) of (15 kg approx.), that will be clamped to a table with 2 clamps. This component has a handle attached to the top, where approximately 150 N will be applied each time the beer is to be poured. I need to determine how much clamping force is required for the component to stay rigid into the table without falling. I am new to this field, hoping someone can guide me towards the right answer.


texts:
In Ernest Cline's novel Ready Player One, the main character lives in the "stacks" - a dystopian vision of what a trailer park may look like in the future.  The "stacks" are primarily composed of trailerhouses stacked

  ... at least fifteen mobile homes high (with the occasional RV, shipping container, Airstream trailer, or VW microbus mixed in for variety).  In recent years, many of the stacks had grown to a height of twenty units or more.

and

  The trailers on the bottom level rested on the ground, or on their original concrete foundations, but the units stacked above them were suspended on a reinforced modular scaffold, a haphazard metal latticework that had been constructed piecemeal over the years.

There's also a great picture from the cover which helps visualize:

I'm curious how feasible this actually is.  Can a typical mobile home support that much weight?  Can standard steel scaffolding provide enough support?  Can the ground support that much weight without a better foundation than typical for a motor home?


texts: Nickel Chromium Wire for high temperatures

texts:
I've been trying for months to find a way to heat moving air inside a tube to high temperatures.  The closest to success I ever had was using an element from a heat gun. It would achieve the desired temperature but over time would burn out.

This has led me to believe making my own coil is probably the best approach.

Parameters

So my desired temperature in the tube is about 450 degrees F with around 400 CFM going through it. At 1500 watts of power,  what diameter and length nickel chromium wire would I need for this?


texts: How do you maintain a constant pressure in a pipe with multiple outlets?

texts:
I've seen in piping and ventilation systems, when they branch off, the continuation of the main trunk gets smaller.  Presumably this keeps the pressure (sorta) constant along the whole length of the main trunk.
So I wanna do this with a swimming pool pump return.  My current outlets are about 9' off the pool bottom (very old in-ground).  This causes a dead spot in the middle of the pool where cr*p collects and it's also the hardest to reach with the vacuum.
My thought is a single pipe running vertically down the sidewall with a number of holes drilled into it - try to get the water flowing "differently" than it does now.  Ideally I eliminate this dead spot.
I'm not interested in lowering the diameter of the pipe so much as much changing the size of the holes (presumably smaller holes at the top where the pressure is higher).
Anyhow, there's gotta be an equation or method for determining this, but I'm only a lowly electronics engineer.. I never took any fluid dynamics classes! So I don't know what this principal is called so I can't even Google it effectively.   Anything is better than me just guessing at it, so what'cha got??


texts: Question on sketching nyquist plot of transfer function with poles on imaginary axis

texts:
I have encountered some issues with sketching the nyquist plot for the following loop transfer function:

$L(s) = \frac{25K}{S^2+25}$

I know that you first take:

$L(\omega=0) = K$

$L(\omega = infinity) = |0| e^{-180}$

For the larger part of the D contour, as for the smaller section of the D counter, I sub $\omega = \epsilon e^{\gamma}$ to represent a number with small magnitude and phase, if I substitute that into the transfer function, that is $L(\epsilon e^{\gamma}) = \frac{25K}{25} = K$ as $\epsilon e^{\gamma} + 25 \approx 25 $

From this information I can do a rough sketch of the nyquist plot, but when I plot it out on matlab I get something very different. Is my thought process on this correct?


texts: Is the convergence of solution ok in Fluent?

texts:
I am simulating an axial turbine by using Fluent. The convergence of solution is monitored by checking the residuals of the numerically solved governing equations. Moreover, in order to judge the convergence, the behaviour of other quantities, such as the total pressure at the inlet and outlet boundaries, and torque coefficient generated by the rotor, are also monitored. Here, the default convergence criterion of each residual is reduced in order to allow the monitored quantities to stagnate at consistent values.

Now, according the following figures, Is the convergence of solution ok? and particularly about residuals? As you see in sixth figure, residuals increase and decrease!!! I want to know that this event is logical or not. I already thought that residuals should decrease decidedly because of convergence. But in this simulation, residuals increases and decreases!! What is reason for this event?


texts: Why do boiler exhaust stacks use tapered transitions?

texts:
We have a boiler exhaust stack with a base dimension of 120" ID and an overall height of 84'.  21' up, the stack begins a slow transition to 7'6" ID.  The transition takes approximately 35' to reach its smallest diameter in the stack.

In designing the new stack I was wondering if I could just make a straight stack or if the transition is actually performing a function.  Why would a boiler exhaust stack be tapered?

The existing stack is manufactured of Alloy 5052-F and I want to make the new one of CS construction.


texts: Lab Equipment for Monitoring Sub Zero Temperatures

texts:
I am doing research on objects frozen with liquid nitrogen then seeing how they thaw.

I need to monitor objects temperatures as they thaw. Ideally getting the variance of the external and internal temperatures.

What strategy or equipment would you recommend to get this data.

Thank you.


texts: Distribution of water through a pipe network

texts:
I have a network of stainless steel pipes that are distributing water throughout a building.

I know the flow rate of water entering the system is 600 IGPM, but am unsure of how this water will be distributed. I have attached a simplified schematic of what the pipe network looks like.

Is it safe to assume the flow rate throughout this network will be the same, even though the diameters change, based on the continuity equation?

A1*V1 = A2*V2


texts: Combining critical speeds for a shaft of variable cross-section

texts:
I am looking to determine the critical speed for a shaft with universal joints at each end, where the halves are joined by telescoping profile members. I can calculate the critical speed of each member individually, but I'm running into problems determining how to combine these numbers to get a critical speed for the whole assembly.

The shafts do operate at variable lengths, but I can prescribe the maximum length, so I will know the configuration at the worst-case scenario. The shaft can be divided into 3 sections, one with the inner member, one where the inner and outer member overlap, and one with the outer member. I have lengths and area moments of inertia for each cross-section, so I could calculate individual critical speeds, but I can't assume these simply combine linearly since the deformation of one section will contribute to the next.

I have tried some calculations using the Dunkerley equation -

$$\frac{1}{\omega^2}=\frac{1}{\omega_1^2}+\frac{1}{\omega_2^2}+\frac{1}{\omega_3^2}$$

but the numbers I got didn't seem to square with my experience in reality. Is this the correct way to do this, in which case I should look at other factors to address my vibration concerns with these shafts? Or is there another way to combine the three critical speeds to obtain a max speed for the whole shaft? (Note also that I don't need an exact answer necessarily - if there is a straightforward way that will give a decent estimate or the form of an equation, I can use existing data and experience to improve that estimate.)


texts: What could be the reason for these sections not agreeing?

texts:
I have two results that don't seem to match up and I can't figure out why.

I built a hollow square section (HSS) using two different structural analysis softwares (they both agreed). However, they don't seem to agree with the AISC steel table despite the dimensions being identical. It seems to be the Torsion Constant (J) which is slightly off in the table.

What could be the possible reason for this as I am totally stumped?


texts: Is a geared motor better for a DIY wind turbine?

texts:
I have decent electronic understanding, but I've not much idea about motors.
I plan to make a small wind mill which should be enough to power a couple of LED lights for like an hour every day. I was thinking of buying a motor, and these are the options I have:

Ebike MY1016Z 250W 337rpm Geared DC motor (GB)
Ebike MY1016 250W 24V 2650RPM DC motor

My idea is to buy a 24 volt DC motor, and then with decent wind, I'm assuming it would give at least 12 volts, so I'll attach a charge controller and 12 volt battery.
The thought process is this: I'll probably be able to generate 10-14 volts on a windy day. So I'm assuming my battery would be charged nicely when that happens.
Questions :

Can I use a 24 volt motor to charge 12V battery with above assumptions? What can go wrong?
Is a geared motor better suited than a normal e-bike for the purpose?
Is this experiment worth pursuing?


texts: Stopping force exerted on a rope. (Checking if rated strength is sufficient)

texts:
I have a 23 kg dog, and a rope lead that is rated to 50 kg.
If the dog is running away at say 6 mph and I pull on the lead to decelerate and stop the dog within say half a second or say 0.5 meter what is the maximum force that could be exerted on the lead?
There are obviously a lot of unknown variables in this,  but as one could imagine in a real world scenario how can I calculate roughly if my lead is going to be strong enough.  Is there a formula I could use to get a rough idea the maximum weight in kg that the lead would be likely to experience.


texts:
So is there a standard rule of thumb, or equation about the distance the end of a screw will travel per rotation?

Conversely, how many turns it will take to travel a specific distance?

Say I have an M3 screw and I want to make absolutely no more than 3mm into an object and avoid hitting electronics. Looking at the M# screws in my toolbox they appear to have a standard pitch ratio for the threads?


texts: What's the smallest pin-like hole I can machine into a piece of tungsten using a metal lathe and common carbide tools?

texts:
I am going to machine something out of a small 40mm long x 8mm diam tungsten rod.  The majority will be hollowed out using a larger bit, but at the very tip, I need a small hole, the smaller the better between .05mm and .6mm.  I understand an L/D for that small hole should be less than 60%?  Did I get that right?

Can this be done with a standard micro carbide bit?  I guess the length of the hole can be adjusted to make this work out.

The purpose of the nozzle will be to pour out accurately micro amounts of melted steel.  My parts include the ability to push steel wire at the rate of 1/27 mm^3 / step (of a stepper motor), so as you can see a tiny amount!  But if not possible, I can bump that number up some.


texts: What does P0.35 stand for in a Tech drawing for a Bolt

texts: Got a Tech Drawing today with measurements and all that. I understand everything except for one part where they've specified a bolt with M4 P=0.35. The M part I get but what does the P specify?


texts: Is there no longer such a thing as varying quality of hardware for USB memsticks?

texts:
I'm trying to buy a new 128 GB memstick, for the first time in a very long time. It's going to store important files, and while I will have at least one "copy", I still don't want either of them to just die.
But when I look at the products on offer, I find only two kinds:

Extremely cheap ones.
Extremely expensive ones, but with no stated benefit besides built-in encryption. (Which I actually consider to be something bad!)

It seems like I cannot "pay a bit more to get something which is less likely to die on me". It seems like the most expensive ones only have encryption and certifications, but no actual difference in what materials or production methods have been used to create it.
Are USB memsticks or flash memory in general so "stable" at this point that they simply cannot make them any better, or won't for some reason?
I find this frustrating. The cheapest 128 GB stick now costs the same as my total expenses for one day, and I live very cheaply. I find it psychologically difficult to trust it, or even two of them.
And even if it's cheap to buy numerous ones, it's not problem-free to deal with the setting up (encrypting) and then constant backing up to them. That part cannot be underestimated. I've found that as time goes by, I become increasingly less willing to take them out from their hiding places to update the data on them. It's a major chore, so I want as few of them as possible but with reliable quality.
Can somebody explain the situation?


texts: How to use lsim in matlab for a closed loop system

texts:
I have designed a system using a minimum realization.

I have the A, B, C matrices and I have assigned closed loop poles for the system.

I used the place command to find my K matrix.

I am wondering if it is possible to use the lsim matlab command to simulate my closed loop system (A-B*K)?

$$x' = Ax+Bu$$
$$u=-Kx$$
$$x' = (A-BK)x$$
$$y=Cx$$

All examples I have found for lsim use the system transfer function or the open loop system.

I have seen examples such as this:

t = 0:0.01:10;         % simulation time = 10 seconds
u = zeros(size(T));    % no input
x0 = [0.1 0.1 0.1];    % initial conditions of the three states
sys= ss(A,B,C,D);
lsim(sys,u,t,x0)

But I am not sure how to use this with the closed loop (A-B*K) system.

Any help would be appreciated! Thank you.


texts: I have to inspect a sphere on a CMM, and the standard states that the "Sphericity must be within 0.02mm". I am using a Zeiss CMM, and it does not have a 'sphericity' inspection method, but it does have a 'profile' inspection method. Since profile is essentially ensuring a tolerance band that would cover the whole sphere, would this suffice?


texts:
On a recent project for a outdoor shed the roof support structure did not look like one of the conventional roof truss designs I have encountered. See snapshot below. (The span is 10 m with the support members 250x125 mm beams)

Is this still a truss? Or what is this sort of support framework called?

It looks like a textbook King Post Truss (to me) but without the vertical member.


texts: I was wondering how to design this circuit in depth, since I have no idea what to do.


texts:
My instructor said that if a joint has reaction support attached to it, then it is not a zero force member. However I saw in this figure that joints E and A are attached to a pin and a roller, respectively but it is indicated in the answer key that members DE and AE are zero force members. What is your insight about this?

source: Engineering Mechanics - Statics (R. C. Hibbeler)


texts: Can I hook up pressurized hydrogen to a gas piston engine and have it work as is?

texts:
I am looking to try some type of hydrogen conversion to get better gas mileage but also want to work on something new to burn some extra time.
I was mainly looking to see if I could power the entire car with a hydrogen combustion engine alone.
I am not an engineer or car person so sorry if this is a dumb question.


texts: Display element coordinate system using Ansys Mechcanical APDL

texts: Is there any way to display element coordinate system in ANSYS Mechanical APDL GUI (the same way the global coordinates system is displayed)?


texts: How to design the most hydro/aerodynamic shape for a 'vehicle' that goes back and forth (using ANSYS)?

texts:
I am interested in making a very small scraper blade that moves back and forth along a submerged surface, however I need to make it as hydrodynamic as possible so I disturb the liquid as little as possible.

I understand I can model different things such as wings in ANSYS, however most of the tutorials only focus on those that have one direction of travel. I need to design the most efficient shape that will be moved in both directions in a liquid.

I know there are a lot of variables to deal with, but I need some sort of starting point on how to approach the problem. Can anyone offer any suggestions?

Edit: included a picture to explain a bit better.


texts: How do I model the friction on a rolling pulley wheel, which holds weight, on a horizontal cable?

texts: I am currently designing a motorized zipline trolley that will carry a person on a horizontal cable, so I am trying to calculate the friction on the wheels to determine what kind of motors I need. I initially approached the problem using a static friction model using the coefficient of static friction between two steels. However, my professor told me to replace my model with a rolling friction model, so I took the coefficient of rolling friction between two steels. This greatly reduced the calculated value of friction; however, I feel like there should be more friction because the weight of the person will cause deflection in the cable, so a portion of the wheels' circumference will be in contact with the cable. I want to assume no slipping for the wheels, so I don't know how to account for the static friction while keeping the rolling friction model. How can I calculate the additional frictional force that I am not modeling?


texts: 200A tig welder enough to weld 8mm thick steel flat bar/stainless steel sheet/tubing

texts:
I would like a tig welder. It has to be able to weld 8mm thick steel flat bar so we can fix the front gate if it breaks.

I also want to be able to do stainless and aluminium  for projects.

It seems my budget can only get me at most a 200A machine.. My budget is £500

so would a 200A machine be enough?

also why do people say tig without argon isn't good?


texts: what is the degree of freedom of a pair of gear wheels?

texts: Two gear wheels A and B are touching each other and they can rotate about fixed points P and Q respectively. how to calculate the degree of freedom of the system by using gubbler's equation?


texts: Conversion from LSB to mg not making sense for accelerometer

texts:
I have a BMI088 and am trying to get an accelerometer reading.

The data sheet and specs for Bosch Sensortec are here:

The sensitivity per range is this (its a 16 bit signed integer):

± 3 g: 10920 LSB/g
± 6 g: 5460 LSB/g
± 12 g: 2730 LSB/g
± 24 g: 1365 LSB/g

Yet, the formula they give to calculate the force in mg is this:

mg = accel_int16 / 32768 * 1000 * 2^((range register value) +1)

Where the range register has the following values:

± 3g  = 0x0
± 6g  = 0x1
± 12g = 0x2
± 24g = 0x3

If we do the math on that and plug in the highest value (+32768) and highest range register value (0x3), we get a force of 16000mg or 16g, so a range of -16g to +16, not -24g to +24g.

So what is the correct conversion?

If we do simply, accel_int16 LSB / 1365 LSB/g we get a maximum value of 24g for 32768 which is intuitively what one would expect. Going by the same logic of a linear response, we might also say, each value (LSB) represents a LSB/mg, which would be

32768*x = 24000mg

x = 0.7324

In this case we can take a reading, multiply by 0.7324 to get our mg.

What am I doing wrong or not understanding? Why does the data sheet formula not give me the correct range?

The second part to that question, is, I  want to have a scale factor to convert from LSB to to meters/second/second, so intuitively one would think it would be:

scale = 0.7324 * 0.001 * ~9.8m/s/s

Again, if we follow the datasheet formula we get

scale = 0.4883 * 0.001 * ~9.8m/s/s

Am I misunderstanding something fundamental here? Or does a 24g accelerometer only measure in a 16g range for some reason?


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