texts: How do you calculate Mcr (critical buckling moment)

texts:
When designing a steel beam, the resistance to buckling is related to Mcr; the elastic critical moment for lateral-torsional buckling.

However the Eurocodes give no advice about how to calculate this parameter.

How would you calculate it?


texts: What is the best graph type to show a comparison value between two cases?

texts:
In that graph, I want to show the two values and the error percentage from the comparison between two values. I am using microsoft excel.

can anyone give me any idea which best graph for this case?
Thank you


texts: Wrap a geodesic dome with a poly sheet: Minimize overlap & loose areas

texts:
I want to make a geodesic dome greenhouse (16ft wide, type: 3V 5/8).

Source: http://geodesicdomes.ca/wp-content/uploads/2009/12/domes-fullsize.jpg

I would cover a geodesic dome frame with clear poly plastic sheeting.

I can purchase clear poly plastic in almost any rectangular dimension (either as narrow house wrap or as wider greenhouse poly).

Problem:

When I've researched this sort of setup online, I've found lots of photos of attempted wrapping jobs. Unfortunately, when the poly is wrapped around the dome, it ends up looking as ugly as sin. There ends up being lots of overlap and/or loose areas, which have the added disadvantage of being noisy in wind.

Example:

Source: https://www.instructables.com/id/20-Geodesic-Dome-Greenhouse/

Question:

What method of wrapping a geodesic dome would result in the least amount of overlapping and loose areas?


texts: In simple pendulum problem, how to change Initial boundary conditions polar into cartesian coordinate

texts:
The problem is

Using the equations of motion for the simple pendulum in cartesian coordinates (Eq.(3.7)), numarically integrate the trajectory for the initial conditions

(\[Theta][0], \[Theta]'[0]) = (0.1, 0)

Plot the pendulum angle theta[t] and the pendulum length l[t]=sqrt[x[t]^2+y[t]^2] as a function of time.
The equation (3.7) is

x''[t] == (-x[t] x'[t]^2 - x[t] y'[t]^2 + x[t] y[t] g)/l[t]^2
y''[t] == (-y[t] x'[t]^2 - y[t] y'[t]^2 - x[t]^2 g)/l[t]^2

At first i try to make EOM(equation of motion) only express for x[t] and y[t]. So use l[t]=sqrt[x[t]^2+y[t]^2]]. And in this problem the initial boundary condition expressed polar coordinate, sine i try to change IBC(Initial Boundary Condition) as

\[Theta][t] == ArcTan[y[t]/x[t]];
Tan[\[Theta][t]] == Sin[\[Theta][t]]/Cos[\[Theta][t]] == y[t]/x[t]

Since,

y[0]=Sin[\[Theta][0]]
x[0]=Cos[\[Theta][0]]

Actually I don't know that another two IBC correctly.

there is my process by using Mathematica and solutions what i want to plot. Actually I just try to make to plot similarly to solution. So i was assumed the one of IBC.

That is, I want to know method of changing IBC, and i want to plot the graph in solution.


texts: Can tensile strength be the same as yield strength? Can Flexural Yield Strength be related to the yield strength of a material in any way?


texts: Only merging features can be patterned error Solidworks

texts:
I am trying to make a circular pattern of the following feature in this Solidworks file.

I received the following message: 'Only merging features may be patterned. If appropriate, make a pattern of bodies instead.'
Can anyone tell me how to fix this error? Thank you for any help.


texts: Why does collector current increase with base current in BJT?

texts:
The base current in the BJT is due to the recombination of holes and electrons. To neutralize the p region an electron leaves the p region. If we take it the other way round, the larger the base current the greater is the recombination, so the collector current should reduce, but $\beta$  $I_c/I_b$. $I_c=\beta I_b$, which shows that $I_b$ is directly proportional to $I_c$.
I am searching for the physical essence of this thing. As we know that in MOSFET voltage controls the drain current by changing the channel width, similarly the BJT is said to be a current-controlled device, so I am eager to know how exactly the base current controls the collector current.


texts: Can bending moments for a combination of loads on a simple beam, be calculated by adding the individual B.M. of each load?

texts:
This problem is about bending moment of a simple beam subject to a mixture of 4 or 5 UDLs and point loads. The beam is assumed to be rigid enough that deflection of the combined load is "small".

Solving this analytically for all load combinations simultaneously, in order to graph the result, is a tricky formula.

I'm wondering if, in this kind of simple case without significant distortion, one can simply use standard formulae for bending moments for single UDLs and point loads on a simple beam, and sum the results, which would be a much easier approach.

Intuitively, it should work. But is this actually a correct intuition? Can bending moments be summed in this way for multiple loads acting on a beam, to generate a graph of total bending moment acting at different positions on the beam?


texts: Path of least resistance misunderstanding

texts:
I was always taught that electricity flows through the path of least resistance.

The problem that I'm having is that I've seen/done this:
Take 3 wires have one wire break off into the 2 other wire (like a fork in the road) and put electricity through the first single wire.

Now I take a multi-meter and test the end of each of the wires that forked from the original wire. Both wires show current/energy.

How can this be possible, this happens even if I use 2 wires with different conductivity.

The ending output might differ between the wires, but both wires are getting energy, even though one of them is more resistant.

Can someone please explain this to me?


texts: 2 complement code and Carry, Zero, Overflow and Negative Flags

texts:
Assuming I have a negative 8-bit number represented in 2 complement code, let's say -12, what number can I add to it to set all flags mentioned in the title (Zero, Negative, Overflow and Carry), or at least 3 of them?
My understanding now is that 8 bit 2 complement code can only represent numbers from -128 to 127, so when I have -12 I can add +12 and I will set the carry and zero flag. The other way would be to add a negative number to -12 that will be equal to a positive 8 bit number(e.g. -12-120), which means I will set my overflow and carry flags.
So is there a way to set all of the flags or at least three of them ?


texts: Is it possible to measure x & y displacement components with a single point (out-of-plane) vibrometer?

texts:
Originally I was going to use accelerometers, but they are to big for the disk I'm trying to measure.

Basically I have a set of planetary gears for which I need to measure the vibrations in the x and y components, mainly. I´ll be performing modal testing with an instrumented hammer and a laser single point vibrometer.

Since my gears are straight teeth spur gears I didn't take into account the "z" coordinate or vibrations of the system for my dynamic model, so if I point the laser perpendicularly to the gear´s plane the vibrations being measured by the laser will be those in z, which I'm not interested in.

I read that if I had two Laser Doppler Vibrometers I could measure the in-plane motions I'm looking for, but since I only have one I was wondering if there´s a way of decomposing the projected component by pointing the laser at certain angle?


texts:
I'm designing a gear system which is 1 motor(drive gear) will drive the last gear(driven gear), and there will be a few gear between the motor and output gear. I understand that the gear ratio between motor and output gear didn't change even I add how many gear in between, and even I change the size of gears in between. As long as I keep the input and output.

Here the link reference for above explanation http://www.wikihow.com/Determine-Gear-Ratio

My question is, what happen if I add cluster gear in between, does it change the ratio between drive gear and driven gear? As what I understand, it will not change the gear ratio, but a few engineer's friend told me different thing. I cannot found solid explanation on this.
Please refer attached image for what I mean.

Thank you.


texts: where to find / what to call a 3/4 inch air valve that can be opened/closed electrically?

texts:
I'm looking for something like this air valve:

(as discussed in https://engineering.stackexchange.com/a/12404/12007)

But I need to tube to be wider (3/4 in), the tube to be shorter (the shorter the better), and I would like it if the mechanism for opening and closing the valve wasn't so bulky. This is a picture of an air valve at a much larger scale:

https://www.homedepot.com/p/Suncourt-12-in-Normally-Closed-Automated-Damper-ZC112/204268743?cm_mmc=Shopping%7cVF%7cG%7c0%7cG-VF-PLA%7c&gclid=CjwKCAjwlIvXBRBjEiwATWAQIp6R6KVXc7l3PrZILy2NjFr2LsexUXmn6eohfsIsHXPDVXo3r9prZBoC_QgQAvD_BwE&dclid=CIXgsZqh2toCFQN6fgodAd8ElA

I'm hoping to find something like that at a 3/4 in scale, where the mechanism is proportionally smaller also.

I only need the valve to be able to withstand the pressure of a person exhaling, which I think is like 3 psi max. So I'm hoping something less bulky than the solenoid in the first link could be used.


texts:
We have a ton of ergonomic data in STL files. We would like to use that data to define a basic shape for our designs. So what i am looking for an algorithm or software solution that is able to scan the data and calculate an average shape. I have looked into generative design but that doesnt seem to be what im looking for.
Do you guys know of any way to tackle my problem?
Also, if this is the wrong place to be asking these questions, im very sorry! Could you point me the right way?
Bonus points:
It would be great if it shows which files are further away from the 50th percentile and which are further towards the 1st and 99th percentile.


texts: Part to "increase" the diameter of a small shaft, what is is called?

texts:
In my lab we have dressing tools for sharpening grinding wheels. The tools are diamonds mounted on a steel shank and the shank fits into a custom holder with a set screw in our machine (pictured).

The hole in the tool holder is rather large so that it can fit a variety of tool shank diameters. We have a tool with a shank diameter much smaller than the hole diameter, so it has this metal ring wrapped around it to increase its diameter so that it fits tightly in the holder hole. The ring has a gap on one side so that it can be tightened on the shaft.

My question is: What do you call this piece of metal used to increase the diameter of a small shaft? My first thought was to call it a "split collar" or a "split ring" but that doesn't yield anything similar on a Google search.

The reason I am wondering is that we have other dressing tools that are too small to fit in this holder and I would like to buy more of these metal pieces so that we don't need to keep re-using the one we have. But I can't find it if I don't know what it's called.


texts: What are the limitations of active noise cancelling?

texts: Let´s pretend there is a source of homogenous noise. Up to which decibel level could active noise cancelling be viable to decrease the volume of this noise significantly? Is it like 10, 50, 100 dB?


texts: How can a sensor detect the traffic lights?

texts:
I am working on an idea for my capstone project. I am trying to get an idea of a device, sensor or reader that can detect the front traffic light situation. so that it can tell when the light is green or red. I am still not sure what is the best way to detect the light? Is there any possibilities that the sensor can tell the light color without using any corresponding sensors or devices in each single traffic light? I was trying to find how driverless cars can see the traffic lights but still no ideas yet.

I appreciate your participation.


texts: What is the difference between a bogie and a chassis

texts: Both bogie and chassis seem to define the part of a wheeled vehicle that describes how the wheels are linked together. Are these terms interchangeable? if not how are they different?


texts:
I have plant,
$$P(s) = \frac{1-s/5}{(s^2 + s/4 +1/4)}$$
I am taking a mixed sensitivity approach for that I have chosen $V$,$W_1$ and $W_2$ as follows:
For bandwidth, $\omega$ =1 so I chose M as,
$M = s^2+ s.\sqrt(2)+1$
$D = 1/s^2$
So, $V = \frac{s^2+ s.\sqrt(2)+1}{1/s^2}$
and the remaining values, $W_1=1$  and $W_2=0.1$
My code is as follows:
s=tf('s');
P = (1-(s/5))/(s^2+s/4+1/4);
M=s^2+sqrt(2)*s+1;
G=[M/s^2 P;
0 0.1 ;
-M/s^2 -P];
G=minreal(ss(G));
nu=1; % u has nu=1 entries
ny=1; % y has ny=1 entries
C=hinfsyn(G,ny,nu); % default rel. tolerance 0.01
K=tf(C) % so

L=P*K;
T=L/(1+L);
% bandwidth(T)  % 0.9963
S=1-T;
figure(1)
bode(T,K*S,P*S,S);
legend('T','KS','PS','S');
grid
figure(2)
step(T,K*S,P*S)
legend('T','KS','PS');
grid

I am not getting and controller $K$ for this code. I would really appreciate if you give some suggestion about choosing $M, W_1, W_2$ or anything that might help me get a controller $K$


texts: A uniform block is in the form of a square ABCD of sides 2 m and a unit thickness. E is a point on AD such that ED = xm. The portion EDC is then removed from the block. What is the maximum value of x such that the block will not topple?


texts: How to cast and mold melt plastic to a shape and design you want?

texts: I am trying to use plastic for a cheap and easy casting but I'm having trouble in molding it to any given shape. I'm trying to see if I can make a spark plug and want to cast out a model for measuring and getting a feel for the design. But I never worked with plastic. I'm using HDPE plastic.


texts:
In a gear you normally have a center hole for the shaft to be put into. Why do some gears have holes surrounding that center hole?
Is it for weight reasons? Does it add stability? Is it so you can add special parts?


texts: How to minimize ozone production while ionizing air?

texts: Right now I am using nine components intended for home air ionizers in parallel, I'd like to build one big one.  I've heard that if one keeps the discharge voltage at -4kV, this produces negative ionization with a minimum of ozone, but I'd like to know more than that, e.g., where that voltage arises from, whether and how it changes with temperature and/or current applied, et cetera.  And I'd like to keep it as simple as possible, though I probably can still pull out my long-ago calculus if I must.  Suggestions?


texts:
I don't understand the fixed end moment AE and also fixed end moment EA ? shouldn't they be the same ?

For the fixed moment AE / fixed moment EA , shouldn't it = -10(2) +5(2) = -10 , for fixed end moment , we always assume clockwise as positive and anticlockwise as negative , right ?


texts: How is mechanism used in modern projector different from intermittent mechanism used in conventional one?

texts:
Do modern projector used for digital class works on same  old conventional intermittent mechanism and blocking of light
during change of frame.
What is principal used in modern projector?


texts: How to account for pistons inside a free body diagram?

texts:
If you have taken basic statics classes you'll remember the free body diagrams used to calculate the forces inside a mechanical system; such as a beam structure consisting of pivots, rollers, fulcrums and fixed points.

One area of study that is not covered in great detail however is the addition of lateral moving parts in these systems, such as pistons.

In the system that I am calculating a piston is conected to a secondary beam at a pivot, the secondary beam is connected at the opposite end to a primary beam by a pivot. and the primary beam is connected to a fixed position by a pivot again. The purpose of this system is work as a mechanical gripper pulling in and pushing out on the primary beam.

My question is how to calculate the forces acting in the system giving the changing shape of the system given a known force value of the piston.

Note: I apologise for not uploading an image to provide clarity, but I am unforetunately unable to do so at work. Additionally I apologise for being vague, I am just looking for a starting point to determine the rest, researching the topic so far has been a futile effort.


texts: Why are there rivets on the drum case of a band brake

texts:
Ive seen some images of band brakes and I notice there are usually two rivets (or screws) on the drum casing (encircled in the image below). What are the rivets riveted to? And why are they riveted?
Are these rivets present only in simple band brakes or are they also present in other types of drum brakes?

Image from Wikipedia. Usage licence: CC BY-SA 3.0


texts:
Shear areas have been obtained for a few different cross-sections. I-sections usually define their shear areas as equal to the product of the height of the section and the thickness of the web (assuming they fall under the thin-walled category).

However, what would the shear area for these sections be (assuming thin-walled theory applies)?

Should we adopt the smallest width which gives a continuous rectangle? But then the section to the right would have zero shear area.

Or should we adopt the width which gives the largest continuous rectangle by area?

Or is there some other method?


texts:
Does anyone have application experience with harmonic gear drive efficiencies as opposed to planetary or parallel axis reduction systems?

I'm looking into drives with about a 25:1 reduction, and it seems the efficiencies go down as reduction ratio decreases.

Interested in using something with a smaller footprint than a multi-stage planetary, if possible.


texts: Convert Load Deformation (Extension) Data to Stress-Strain Curve

texts:
I am trying to manipulate some data that were obtained from a three point load experiment on a porcine tibia.

I would like to obtain a stress-strain curve for the various specimens; however, the only data that was given from the Instron three-point loading set up was Load (N) vs Deformation/Extension (mm).

My question is: how do you convert the Load vs Deformation curve to a Stress-Strain curve?


texts: Problems with shear force diagram in beam model

texts:
I am starting to learn how to use ANSYS APDL. So I don't have much knowledge in the software.

I have modelled a cantilever beam (with beam188 elements) and the only load that i have applied was the self weight.

When I ask for the shear force diagram (element table) and plot the results, the SFD looks like this:

Shouldn't it be linear? What happened?


texts: Simply Supported beam with multiple point loads and distributed load

texts:
How can I solve this problem using FEM (longhand calculation)? I want to find deflections at each load point. This is not a homework problem. This is related to a project that I and my brother is doing for the conveyor. The distributed load is conveyor and point loads are some features that we are trying to add to it. I tried to solve this by Integrating moment function but if I try to add/remove point load from this, I have to do that integration part again and in some cases, the distributed by leg supports instead of any beam.
I was thinking this problem can be generalized through FEA.

1) I want to find deflection at each node point (where the loads are) and maximum deflection

2) I tried to solve this by double integration method but that method will only be specific to this beam that is why I thought of the FEM

3) In this example, conveyor is resting on the beam that is the distributed load and when conveyor is supported by leg supports, there is no need for calculation as they are standard

4) I do not have FEA software package.

$E=300\times10^6\text{ psi}=2068\ GPa\quad,\quad I=500\text{ in}^4=2.08\times10^{-4}\text{ m}^4$.


texts: How to increase the air flow rate through a dust-separating cyclone?

texts:
I'm making a dust extractor for a desktop CNC milling machine.  My design process was very crude: I looked at some DIY dust-separating cyclones, and it seemed like they just work without any advanced calculations, so I visually copied some of those designs at a smaller scale, sat a large PC cooling fan over the top, and put the whole thing in a coffee can:

My reasoning was that (1) the 18W fan blows out a lot of air, (2) the only place for that air to come from is through the hole at the top of the cone, and (3) the only way air can get into the sealed cone / dust receptacle (the bottom can) is through the tube at the side.  So, it would have to suck a reasonable amount of air through that red pipe.
It does work to some extent (video), but not as well as I hoped.  You can see that it barely picks up sawdust through a 1-inch hose, and ideally I'd like it to draw in dust at a range of 20-50mm or so-- I can't position the inlet any closer than that to the point where the dust is created. Plus, I'd like to fit a dust filter over the exhaust hole, which will reduce the air flow even more.
My question is basically "how can I make it suck harder?".  But more specifically, how do I start to analyse what's happening, and what determines the amount of air pulled in?
Most Google references are either way over my head, or talk very specifically about pumps in volute casings; obviously I removed the volute casing from my fan in order to fit it in the enclosure.  If I understand correctly, the point of the volute is to make the fast narrow stream exiting the fan into a slower, wider stream at higher pressure (why?), and I guess that something similar happens in my can:

A) incoming air spirals down; dust is thrown out and drops through bottom of cone
B) clean air spirals up through fan inlet
C) fast air exits fan circumference
D) ...and expands into volume below, losing speed and increasing pressure
E) higher-pressure air blown out into atmosphere

Stage C/D is the part I'm most uncertain about.  The rest of the design comes from recipes, but I've changed the way air exits the fan and would like to understand how this might affect things.
Edit 4 Feb 2016:
Per @ericnutsch's suggestion, I made rough measurements of the air flowing into stages A and C, and got a figure of about 0.009 m3min-1 at both points.  I also found the manufacturer's data for the fan, which suggests I should be able to do better-- the stated max is 1.09 m3min-1.  For comparison, my crappy handheld vacuum scores around 0.024 m3min-1.  I've ordered a pressure sensor to investigate further...


texts: Stress Concentration Factor – Why a Specific Range?

texts:
I was trying to find the stress concentration factor for a specific situation and I found two different resources for it.

Ref: Shigley's mechanical engineering design

Ref: Roark's Formulas for Stress and Strain
However, I found both resources were only applicable for d/w <0.3
Why is it data can only be found in this specific range? The example I have has a value of 0.5 and is therefore outside the range so I am unsure how to proceed and what the implications are of it being outside the stress concentration factor range.
Any help is greatly appreciated, thanks


texts: When does torque applied on a shaft produce bending and when does it not?

texts:
In both cases in the picture above torque is applied to the shaft, however in the first case the force $F_{c}$ also produces bending across the shaft. So my question is, how do I know if a torque should be shown with a force like in the first example, or with a torque vector like in the second example?

My best guess is that it depends on what produces the torque. Some ways do produce bending (like conic friction plates for example), while some don't.


texts: Elastic (Young's) Modulus relation to the Eigenfrequency

texts:
I would like to compare the shape of the frequency spectrum of a plastic and aluminium component. Now if we assume that the plastic and aluminium component only differ in the material, while the mass and stiffness stay the same (I know, large assumption), how would generally differ the shape of the frequency spectrum from each other? Obviously, the damping plays a major role here and would be much higher in case of plastic, therefore the response amplitude would be lower, the resonance zone wider and a shift (which is many times neglected) towards a lower frequency would be made... Could I in a very simplified version, just for the sake of understanding, draw it like this?

Another question would be the temperature dependence of the elastic modulus. If the temperature rises, the modulus is reduced which also affects the eigenfrequency. In case of aluminium not so much, but in case of plastics, the difference can be enormous. My understanding is that in case of elevated temperatures, the damping increases; in case of plastic much more than in case of aluminium. Could I visualize this as:

Any constructive answers are much appreciated!
Kind regards,

Luka


texts: Do spiders *actually* get into a house through the sewer/water pipes?

texts:
Every time I have seen a spider at home, in the bathroom, whether it was in a house or in apartments, whether on the bottom or upper floor, I always immediately assumed that it had come "through the pipes"; that is, crawled up through the drain pipe leading into the bathtub, or the drain hole in the floor which takes care of any water that spills out on the floor.

Or even that it had swimmed all the way up through the water toilet.

Luckily, it hasn't happened for quite some time now (knock on wood...), but this thought was especially present in my mind when the spider was sighted in the actual bathtub.

My question is: do spiders actually crawl up such pipes, into homes? Or is this a false assumption? Don't spiders tend to come in from opened doors and windows? Not through pipes?

I mean, it's not like the drain pipes lead directly down underground with dirt and creatures living there. It's still connected to the bigger sewage pipes, no? I cannot imagine any creature surviving not only the oxygen-less, long trip through these large sewage/water pipes, but to also have the strength to stop and actively push themselves up and keep crawling all the way up to my apartment/house's bathroom.

But maybe I underestimate those vile creatures of pure evil.

On the other hand, it seems unlikely that a spider would come from the outside, though a window or door, only to find itself crawling into the bathttub and be sighted there, so that talks against my theory that it's impossible for insects to enter through these drain pipes...


texts: How exactly do respirators seal out pathogens?

texts:
A "respirator with a rating of P100, has been tested to be proof against oil, and tested to filter 99.97% of all particles 0.3 microns in diameter or larger.'

As you know, an atom is 99.9999% empty space. So even if a respirator's edge is touching your face, why can't pathogens cross and sneak past the face seal? See the green arrows in my pictures below.
To wit, how can we guarantee that the gap between your face and a respirator's edge is smaller than any virus or pathogen?

N95, P100: What do all these mask numbers mean and how do I know it's keeping me safe? - SFGate

  If the mask isn’t sealed around your face, you’re just breathing through the edges, and it doesn’t filter much at all.  Men with beards cannot get the full benefit of a mask, and many men have looked at shaving it off for the sake of their lungs.

  3M writes in this handy but rather complex guide: “Do not use tight-fitting respirators or loose-fitting facepieces with beards or other facial hair or conditions that prevent direct contact between the face and the edge of the respirator.”

The left is a 3M P100 respirator.


texts: Should we use ELF or ULF for very deep metal detection and which specific frequency?

texts:
We are trying to design a metal mineral deposit detection system using  low frequency radio waves.  I am not sure on the physics of why the ultra low frequency electromagnetic radiation can penetrate the earth and sea.  We need to be able to scan to a depth of 3 miles from the surface.

Wikipedia classifies ELF (Extremely Low Frequency) radiation as between 3 Hz and 300 Hz, and ULF (Ultra Low Frequency) from 300 Hz to 3 kHz.  Both ranges can penetrate the earth, but I don't know which would be better for our application.  Which frequency would yield the most precise, accurate and reliable results for this depth?


texts: Automation: steady state error calculation block diagram

texts: Hello I have a problem determining the value of K in this block diagram, to calculate this value, I applied this method, but the value at the end of K I is different from 216, you could explain to me where I'm wrong


texts: What will happen if I run a submersible pump without water?

texts:
I have a submersible pump and it's clearly stated in the user manual that it should not be operated without water.

But what will happen if it's not adhered to? The obvious answer is that it will malfunction. But I want to know what causes the malfunction to occur. I am trying to use it for some other purpose that does not require it to be submerged.


texts:
Can this formula be used to evaluate the minimum thickness of a spherical pressure vessel that holds hydrogen gas at 10 ATM for a long time?

$$\sigma = \dfrac{p r}{2 t}$$

I was told, "As long as you don't need to hold the pressure for a long time or above room temperature, which will cause creep." It would seem that the person is trying to say that the container will fail over time due to creep. Is this true if the container will never go above room temperature? If yes, how should the design of the container change to address this problem?


texts: experiment with interlacing to achieve 3d effect

texts:
I am going to attempt an experiment to achieve 3d effect.
I read about autostereoscopy on wikipedia.

I am trying to do this,

I have already processed image in that format. see the image

every alternate pixel is of particular eye image.

If I create a black - transparent impression on a sheet then it would show a correct image of either left eye or right eye.

I am thinking of printing image(for example) shown below and cut the white areas on the paper.

after that process I will align that sheet in front of my monitor.

I wanted to ask is this a good idea or I am doing something wrong ?


texts:
I'm designing a small system where typically a ball valve is used to divert water through a heater when desired. I've noticed the ball valves designed for this situation result in a hard 90 degree turn when diverting the flow, and also lowers the diameter of the pipe by approximately 10%. The inside of the valve is manufactured such that it will create a significant amount of friction and turbulence even when it's in the straight/bypass position.
.
I'm considering an alternate plumbing approach that uses a standard ball valve and tee wye bend fitting. When the ball valve is closed, water will be diverted through the tee wye bend. I suspect this will result in less resistance and higher flow than the aforementioned three way valve will allow, but I'm unsure if I need to be worried about turbulence or other factors that will constrain flow while the system is in either of the two possible states.

The valve will be open to bypass the heater the majority of the time. Will the tee branch lead to a significant amount of friction or turbulence that will impede the flow in any considerable amount?
Can someone with a better understanding of the fluid dynamics at play here verify that my alternate approach is more efficient (or at least not significantly less efficient) in terms of flow than the design with the three way valve?


texts:
Is it possible to "pump" a powder the same way liquids can be pumped?

If so, what are the challenges? If not, what are some alternatives?


texts: Is my understanding of the roles of transistors in this circuit correct?

texts:
THE CIRCUIT'S FUNCTIONING
This circuit is a rain water sensor circuit that buzzes when there's water on a probe.I found it on net.1
CIRCUIT COMPONENTS

3 Volts Battery
BC 558 Transistor(PNP)
BC 548 Transistor
330K Resistor
A Water Prob
10K Resistor
.01 Microfarads Capacitance
Any Speaker

MY UNDERTANDING OF TRANSISTORS ROLE
If NPN transistor(BC 548) in this circuit is working properly,emitter should have less current than collector,which is enough for speaker.Collector-side gets a high voltage which gets grounded by PNP transistor's collector.(BC558)
If there's a problem with Bc548 then emitter will have lots of voltage,thus collector will have less.Which means PNP transistor on there is used to shut down the circuit if there's a problem.(If a PNP transistor gets low voltage from base,the current from emitter starts to flow to collector which means shutting down the circuit,causing all coming current to go to grounding for avoiding burning the speaker.)
Is my understanding of transistors roles correct?
Thanks for the help.
1-https://www.elprocus.com/simple-electronic-circuits-for-beginners/


texts: How should one model a structural model with both line elements and area elements?

texts:
I am modelling my structure using FEM, and my structure contains line elements (1D) such as beams and columns and area elements (2D) such as walls and columns.

My question is that, how can I proceed to do modelling, and how can I interpret the results for stress and strain, especially at the places where 1D elements meet the 2D elements? Take for example,

A beam's Center of Gravity might not be located within the slab, but in reality the beam and slab are still touching each other. In other words the beam is offset from the slab
A wall's center of gravity might not be located within the slab,  but in reality the wall and slab are still touching each other. In other words the wall is offset from the slab
A beam and a column are supposed to be connected together, except that now the beam is offset in left and column in right. If going by line element, they are no longer touching, although in reality, they still are.

Is this a solved problem? Any research literature that I can refer to, or any software packages that you can recommend that handle this gracefully?


texts:
I was informed today by one of the on-site operators that they saw the colour of the stack flue gas change from colourless to a yellow/purple gas for a short period (~5mins) before returning back to colourless
It's a heavy-fuel oil steam boiler (~4ton) @ 10 bar.
I know the that the colour is heavily dependent on the chemistry of the fuel being burned but has anyone come across such behaviour? I'm trying to find a place to start before jumping into a full investigation.


texts:
So I'm looking at performance curves for thermoelectric coolers, and it seems like these curves are so misleading as to be useless unless I'm missing something fundamental.
Suppose I have a thermoelectric cooler, and I manage to pump it with enough current to achieve a given temperature differential between the two plates. This temperature differential will itself cause heat to flow back through the semiconductor that makes up the thermoelectric cooler. For the one I happen to be using, based on the thermal conductivity of bismuth telluride (assuming this is the semiconductor involved) which has a thermal conductivity of ~1.2W/(m*K), and the dimensions of my TEC (20x20x3.6mm), it looks like I should have a thermal resistance of about 7K/W. This means that anything below the line that starts at the origin and has a slope of 7K/W will always be unachievable, but this region isn't specified in the thermoelectric cooler's datasheet, nor is its thermal resistance.
When I actually try to drive the TEC with a known current (4.5A), if the datasheet's operating curves are to be believed, I should be able to get a $\Delta T$ of about 50C between the two plates when I am not pumping any heat. In practice, though, I only get to a temperature differential of about 20C (despite having nothing on one side of the TEC except my tiny temp sensing IC and the other side attached to a massive heatsink I keep at room temp). It seems like the quoted $\Delta T$ is complete nonsense, because what will ultimately constrain the maximum achievable temperature differential is the thermal resistance of the TEC. Anything below the line of thermal resistance of the TEC is not achievable, and the quoted $\Delta T$ doesn't actually mean the maximum achievable temperature differential, but is just the intercept if you extrapolate the operating curves to the x-axis.
Am I missing something?


texts: How are high gear ratios achieved in a small space?

texts:
I have a very basic understanding of how gears work, and while trying to learn more, I've run into a small point of confusion.

If a 2:1 gear ratio is achieved by having twice as many teeth on one gear than the other, then how are 250:1 ratios achieved? Certainly there aren't gears with 2500 teeth on one gear, and 10 on the other...

For example, here's a very tiny motor with a 250:1 gear ratio: DC Motor with Gearhead


texts: Optimal gear combination with the same ratio

texts:
Summary: In a gear train, with given target ratio and configuration (eg. number of gears and how many compound gear steps are involved), what are the considerations when trying to select the optimal size (number of teeth) of the gears?
Full story: I have a small lathe with manually adjustable gear train for the power feed. Manual means that I have a selection of gears to choose from and I can decide which 3 or 4 of them to install to achieve the required final ratio. There are three shafts altogether, out of which the driver shaft and the driven leadscrew have fixed position and the middle one is adjustable (this can accommodate a single idler gear or two as a compound).
Now I basically understand how to calculate the gear ratios that are needed, but I have many gears and I can achieve the same final ratio by several different configurations. For the sake of the argument, please ignore that some of the theoretical configurations might be physically impossible to fit.
Example: My leadscrew has a pitch of 1.5mm, and say I would like to cut a 0.75mm pitch thread, so I need a 2:1 gear ratio. With 3 gears, the size of the idler in the middle does not affect the ratio so I can use (driver/idler/driven) 20/X/40, 30/X/60, 40/X/80, the idler being anything between 20 to 80 teeth as long as I can fit it. In a similar fashion, with 4 gears where the idlers are compound on the same shaft, I can use something like 20/30/60/80 or even 20/80/60/30 to achieve required final ratio.
Obviously some of the configurations are more optimal than others considering stresses, wear, and maybe for other reasons. I would like to know if some basic thumb rules can be used like "more teeth are the better due to stress distribution" and "try to avoid great differences in number of teeth". Another issue is that the gears have actually been made of different materials, most being POM but some aluminum and the smallest ones with 20 teeth are from steel. I have a feeling that the differences in strength might affect this for a greater extent than the differences in teeth.


texts: Elevation / pipeline Elevation calculation

texts:
We do inspections using a robotic camera in the pipeline. It’s tractor type camera. (Ref. photo)

While driving the camera through the pipeline it gives us the camera tilt degree output.

The camera System gives us output as below,

could please help me to calculate the elevation/altitude of each meter. Using camera tilt degree value.

As below.

Awaiting for your answers. If you need any further info. Let me know.


texts: What kind of math do engineers really use?

texts:
I am from the mathematics StackExchange section, many of my students are engineering students at University. I was wondering what kind of calculus do you real engineers use? I have known two engineers. One from airplane design and another from metrology. The former used very very little calculus, some ODE's with constant coefficients by linearization. The latter used only basic math, no calculus, with some excel.  I want to be honest with any engineering student so they know what awaits them.

Also, a follow up question. Did you find it beneficial to have about four semesters of calculus? Maybe you do not use anything from it, but it does enhance your mathematical reasoning, which does have a positive externality on your engineering skills?


texts:
I recently went on a tour of a glass manufacturing facility who produce bottles for the prestige alcohol market. I was informed on the tour that red glass cannot be directly produced - any bottles that I have seen had made by applying a spray to a plain finished bottle as opposed to adding the colour into the molten glass.

Why is this?


texts: If I make a sandwich of wood, thin plastic, carbon-fiber tow (cut to about a foot long) impregnated with epoxy to the right ratio, thin plastic, and wood, and clamp it together and leave it, will I end up with a structure similar to a pultruded carbon-fiber rod?  Will it have anywhere near the compressional strength of a product like these [1]?  ..I'm not the first to consider this.. [2]


texts: Why shouldn't dark area analysis be used to estimate carbon content on high carbon hypoeutectoid steels?

texts:
I had this thought with me for quite some time, that you can't use the usual formula for estimating carbon content on a Nital etched hypoeutectoid sample (DarkArea*0.77) if the steel obviously has more than around 0.6% carbon.

I am pretty sure I read that somewhere, but I can't find that, and I might have been operating in a false premise for some time now.


texts: Can vacuum balloon become possible with this idea?

texts:
As it is well known, a vacuum balloon using the materials we have at our disposal is not possible, because of the sheer force they have to resist from the air outside.

I asked this question on Physics stack exchange and haven't got an answer yet.

I have an idea and I want to know if there is anything that makes it impossible.

Build a balloon out of graphene which is very light and it is conductive too.
Since graphene is not airtight, cover graphene (that is not yet inflated) with a good electrical insulator which is also airtight.
Now make the graphene store electric charge.
This would exert force from inside as the electric charges on the graphene repel each other.
This causes the balloon to inflate while having a vacuum inside.

Now my question is there any theoretical problems (not engineering problems) with this model?


texts: Mating a round surface with a flat surface

texts:
I have a small flat surface (~80mm x 80mm) that needs to adhere to a round surface (radius = 100mm). Does anyone know how to mate the two surfaces together using tape to give a good enough bond?

Any thought appreciated.

EDIT: The part with the flat surface (~250g) is supposed to be hung on the round part (a lamp shade). Both parts are plastic. I'm hoping to avoid causing damage to either part. The whole assembly will be kept indoor.


texts: Sea waves: Having trouble visualizing the difference between group celerity and celerity

texts:
What I know, if I'm not mistaken, is that group celerity is the speed at which the energy is transferred and celerity is the speed of the waves themselves.

Since sea waves basically transfer energy and the particles won't follow along much, I don't understand why they need to be so different, specially in deep seas. And I also don't understand why the group celerity in shallow waters tends to $\sqrt{gd}$ if we use Airy's linear theory (yes I know it's not very appropriate for shallow waters).

Any explanation will be much appreciated, thank you


texts:
I know a PID controller. Recently, I heard someone mention a PIAD controller. What is this? Is it a kind of extension of a regular PID controller?

In the control engineering litterature, I have only found a $\text{P}\text{I}^λ\text{D}^µ$ controller yet.


texts:
This device is about five feet tall.  It is located in a ground-floor alcove in the exterior of a commercial building on a public street in Santa Monica, California.

Each of the chained manual valve handles seems to also be attached to some sort of electric switch.  (The junction box for the cables is visible on the wall behind the pipes in the upper-right quadrant of the picture.)

The small black attachment in the lower left quadrant is a water flow or
volume meter.

Our best guess is that it has something to do with fire suppression.  But what?

Why is it located on the outside of the building?  What are the valve handles for?  Presumably the chains are to prevent tampering by passersby, but why are the handles there at all, if the apparatus is outside the building?  Who is expected to use them?

What are the two seemingly disconnected pipes at the bottom for?  Some sort of drainage?  The two bottom pipes seem to be linked by some sort of feedback apparatus; is this right?  What is it for?

The more details in your answer, the better.  I am totally mystified.

Thanks.


texts: Determining gas properties in a steam and air gas mixture

texts:
I have a gas mixture (steam and air) contained in a tank.
I know the tank pressure ($P$), temperature ($T$) and the massic air fraction ($x_a$).

I would like to determine the density of both gases to perform some calculations afterwards.

Intuitively, I would have done the following :

$$
\rho_{steam} = IAPWS97('rho\_PT', P,T)
$$

i.e. asking IAPWS tables to provide me the density of steam at the tank conditions.

However, it seems based on available ressources that this is wrong. The correct way do do it would rather be

$$
\rho_{steam} = IAPWS97('rho\_PT', P_{steam},T)
$$

Therefore taking into account the partial steam pressure to compute its density within the tank rather than the total tank pressure

Why is that ? Intuitively, I would use total tank pressure because it seems to me that both steam and air experiences the total tank pressure and not only their partial pressure and therefore I would use total tank pressure to compute their properties.


texts: Diesel or Gasoline? Which one is more dangerous to our health?

texts:
I have an overall question that's been bothering me for years. Which is more dangerous for our health, a diesel car or a gasoline car?
This is quite a cliche question and I can find a lot of newspapers reporting that diesel is way more dangerous, but I would like to hear a more engineering/scientific/economic approach to this. Can anyone help me with this? I have a series of other questions that would help me to answer this overall question. Here is goes...
In this article, they write:

Diesel fumes are significantly more damaging to health than those from petrol engines, according to research which shows that related air pollution contributes to lung disease, heart attacks, asthma and other respiratory problems.

And they are referencing a nice report written by Department for Energy and Climate Change.
So it is agreed by many that Diesel is more dangerous than gasoline. But at the same time, the diesel engine has a higher efficiency.
Q1: Is the efficiency also reflected in the amount of gases getting out? In other words, an engine with a higher efficiency releases a lower amount of gases?
Then there is a second question, which might sound a bit stupid but,
Q2: Why are people so much for buying Diesel cars (especially in Europe)? They are way more expensive, and yet so popular in Europe.
Q3: Is the lower price of Diesel fuel really making a difference? Or is it the power and reliability?
At the same time, the regulations in US are more strict to Diesel cars.
Q4: Is it because of the emissions or is there another reason for this?
Q5: Is really NOx worse for our health than COx?
Q6: What are the engineering limitations in reducing the NOx's?
I know that some question are not strictly related to engineering, but I want to avoid posting the same questions in other places. However, I would appreciate if you could answer to any of the questions. I would highly appreciate any help in understanding this.
I think this is a very important issue, because most of people (like me) are unaware of these issues.


texts: Applying full state feedback on DC motor with torque load

texts:
I tried to apply full state feedback on DC motor (with no load) and it works fine in the simulation on Simulink

But the question is if I have a load applied on the motor (let’s say constant load or any thing else) the system in this case has two inputs voltage and torque load (Tl).

I can control only one input (voltage) and I have no control on the other input (Tl), So in this case what can I do in order to be able to perform full state feedback ?


texts: What is the maximum temperature that could be achieved by a heat-pump and will it affect its efficiency?

texts:
I did some research and found out that one of the applications of a heat pump is as a water heater which means that it could achieve a temperature of about 100-degree Celsius.
Will changing the refrigerant or the compression ratio of the compressor lead to an increase in the temperature? (R718 refrigerant showing to reach 200-degree Celcius)
If yes what is the maximum temperature that could be achieved? and also will this affect its efficiency?


texts:
My project team and I delivered the design of a 14ha urban infrastructure development in Sydney for a Client. The project was to hand over the development at a Tender level of design, which would be tendered upon by a number contractors. The succesful bidder would then take on the rest of the project as a Design and Construct contract, and complete the works.

As a part of our deliverables, we issued all engineering plans in pdf and AutoCAD dwg, and all design files including the 12d data terrain models and design strings. We have now had a request from the winning contractor to provide the entire 12d '.project' file, which includes all functions, modifiers, appliers and range files. Providing this would save the contractor a significant amount of time, even considering all of the design strings and models which have already been issued.

Our involvement in the project has been completely handed over, and we consider all of our responsibilities departed. There are a number of people in our team who consider it not appropriate to provide the .project file, whilst there are a number of people who don't see it as an issue.

Has anyone run into this issue before, or has anyone got any guidance on whether it should be provided? Are there any risks in sending the information? Does anyone have any thought's on where our Client's ownership of the data ends and our Intellectual Property begins?


texts: Car which can climb the ramp of higher inclination

texts:
Two automobiles both of which have the mass center located midway between the front and rear axles,are identical except that one is front-wheel-drive and the other is rear-wheel-drive.The cars are driven at constant speed at ramps of various inclinations.The question is to judge which car could climb the ramp of higher inclination angle from a theoretical point of view.

My idea was that the front wheel drive would be more effective if more weight acts on the front wheel.But in this case the center of gravity is midway between the rear and front wheel axles .I couldn't see how I can approach this problem.Any ideas?Thanks.


texts: Why is it useful to scale seismic ground motion data

texts:
I am learning by myself structural dynamics but confused about the concept of scaled ground motion data. I can't get the reason why the acceleration data should be scaled. I mean, isn't it better to use the original data "as it is" to compute the response of structures so that the results can reflect actual response of a specific structure?

EDIT : Is it the case that when we design a structure, scaled data should be used, while unscaled data can be utilized when we conduct post-seismic-analysis of a structure?

Could someone please summarize the situations when we should use scaled or unscaled data?


texts:
In this case, L, theta and P are given, there will be 4 reactions at the wall? (2 horizontal and 2 vertical).

$$\begin{align}
\sum F_v &= 0 \therefore F_{v,B} + F_{v,A} = P \\
\sum F_h &= 0 \therefore F_{h,B} = F_{h,A}
\end{align}$$

What will be the tensile stresses along AB and AC?

However, I do not know how to obtain the other 2 equations to solve all the reaction forces at the wall and the tensile stresses? Can anyone please help? One of those equations are from the moment?


texts: One way/locking mechanism without springs or flexible members

texts:
There a few neat mechanisms that allows only one way motion without the use of a pawl or ratchet.  This is one of them:

https://www.instructables.com/id/LEGO-Technic-One-Way-Gear-Mechanism/

What I'm looking for is a mechanism that can't be undone once it has gone from one position to another (without taking it apart; i.e., removing a pin) after it is rotated.  This could be useful in certain applications, but my search turns up nothing like I remember.

I can think there might be a four or five-bar mechanism that has a critical point where the mechanism can't undone, but can't remember (or where to search for it)!

I do remember seeing one many years ago at one of my first engineering jobs, but can't recall the details other than "that was neat!"  The mechanism I saw had I believe 3 to 4 moving parts.

There are some other mechanisms that don't use springs or latches; a search for this turned up something also nifty, but not quite what I was looking for:

https://www.youtube.com/watch?v=E4cMyPqE3lg

Any thoughts on this?

No magnets, no springs; this was a strictly mechanical thing (nothing hidden; I could take it apart, and the mechanical lock was fascinating).  The closest analogy I can think of is to those Sokoban games (and perhaps this is a way to think about it) where if you perform a certain order of operations, you lock up the puzzle.

This is one solution I came up with this morning, but I'm wondering if there is a list of them, a search term I'm missing, or other examples.

In this example, a plunger enters from the left; I'm not too sure of the geometry, but I think this is an example of how it could work.  When the plunger brings the two locking elements behind it, it can't go back, because of a stop at the end of the plunger, prevents the linkage from reversing.

Even cooler - I believe the mechanism I saw had no linkages - just a series of Sokoban-like moves where the system went from one state to another, but couldn't be reversed without taking a part out of the 2D plane it was in.


texts: How to manufacture parts with complex air channels inside?

texts:
I am designing a part that requires multiple air channels with an intricate structure inside. I would like to know if there is any state of the art injection molding technique or other technology that will enable that solution.

Amount of air channels: 14.
Volume of the design: 40x40x40mm.
Distribution: curved and some channels are connected with others, others not.

I can not show the design, I signed an NDA agreement.


texts: There are the "consumer" negative ion detectors which are about 50 USD, reviews appear to indicate that they are not measuring very much at all.  Then there are the professional ones which are $800 and up.  As I understand it the customary standard measurement is in millions of ions per cubic centimeter; the precision needed is not great, 25% or 20M/cm3 will do, range 10 to 300 would be very helpful.  Any ideas?


texts:
I was wondering about the main difference between using heat pipes and a fluid-based cooling system. In both cases the heat is transported away from the heat-generating area to a place where the heat is dissipated. What is now the advantage of using a fluid instead of heat pipes? Is it the lack of heat transfer points (a fluid has no heat exchange points, except of the radiator and thermal pad, while heat pipes have to be connected)?
Thus, when is it more beneficial to use a fluid cooling system instead of heat pipes?


texts: Flywheel is used to store energy for the non power producing strokes of an IC(internal combustion) engine,  do we use a fly wheel in an motorcycle and if yes what is it's size and where is it placed?


texts: Easily accessible material for maximum grip on a prosthetic hand?

texts:
Currently in the process of developing a 3d printed prosthetic hand and I am in need of advice on the type of rubber (or other material) we should use at the finger tips to give it more grip. The hand is capable of closing with a good amount of force, but it has a hard time holding heavier solid objects (like a glass cup, for instance) due to the lack of friction. I figure we only need small patches of some material at the contact points on each finger tip and potentially some in the palm, but I'd like to get insight from people who know more than I do.

We are considering using the inner tube of a bicycle and cutting it into small patches, but we are not sure if we would be better off with something thicker to allow the clutched objects to sort of sink in to the rubber more.


texts: Visualization/Verification software for interacting parts e.g. Gears etc

texts:
Not sure if there is any software that would model the movements of physical parts, or if even they can move with the given configurations ( software engineer background, no idea the lingo used here ).

For example, at the start  this video it shows modelling of gears simulated, do CAD programs have this capability or this is something else? are there programs that are able to determine if parts were made (for example) from plastic, then they would break, or if they were made of steel then they would require too much torque that the stepper motor wouldn't be able to handle.

Basically, what are the current limitations of modelling and simulation software for mechanical systems?


texts: RV HVAC and Fridge Freezer on the same coolant loop?

texts: Given the space, weight, and power constraints of an RV it is useful to make as much use as possible out of every component.  Is there an engineering reason why a refrigerator / freezer and an air conditioner could not share a single compressor and condenser?


texts: Why do domestic electric oven do not use thermal insulation?

texts:
Domestic ovens doesn't have any form of thermal insulation AFIK, and even have vents to circulate fresh air.

It would be more energy efficient to add thermal insulation to prevent heat escaping from oven. As a second benefit, it will be reach temp faster, reducing cooking times.

So, why doesn't anybody does this?


texts:
I am trying to decipher some as-built drawings for an old wood frame building. The purpose is to generate a preliminary load takeoff. I cannot figure out what the following is saying:

It looks like "3 Ply Built up roof " but the rest makes no sense. Any seasoned structural engineers can tell me what this says?


texts: Origin of barricade tape color combinations (allegedly OSHA)

texts:
Various sources (e.g., Wikipedia and WorkSafely) claim that the seven color combinations commonly used for barricade tape (a.k.a. caution tape) and safety markings in North America (yellow and black for physical hazards, green and white for first aid supplies, etc.) are specified by the US Occupational Safety and Health Administration (OSHA). OSHA standard 1910.144 ("Safety color code for marking physical hazards") is often mentioned. However, 1910.144 states only the following regarding color:

The color red should be used to identify fire protection equipment, sources of danger, and emergency stop controls.
The color yellow should be used to mark physical hazards.

Are the seven color combinations specified in another OSHA standard? (If so, I haven't been able to find it.) If not, where did they originate?


texts: Keeping rpm stable with input of floating rpm

texts:
How can I create a gear system which keeps, say, 60 rpm stable on output wheel, when I don't care about force? I am using a hand-turned crank as an input wheel.

I know a flywheel could be used, but it is weak to small accelerations and slowdowns over time.


texts: Why is my Venturi pump much weaker than expected?

texts:
I'm trying to make a simple Venturi tee which will have air flow through it while sucking some water from down below (like paint sprayers do).  I want the device to pull the water to a height of 1 meter.

That means that I need 0.1 atmospheres (104 Pascals). The dynamic pressure equation states that $P_{a}=\frac12\rho v^2$, meaning that $v=2P_a/\rho$.  The density of air is $1.22 kg/m^3$,  $P_a$ is 104 so  $v=128\ \mathrm{m/s}$.

I experimented a bit with my air pump and found out that with a nozzle of ~5 mm in diameter I can fill a 10 litre bag with air in ~7 sec. That should mean that the velocity is around 60 m/s.  With those results I took a hose of 16 mm in diameter, stuck my pump nozzle inside (from one side) , made a small hole juxatoposed to the nozzle from above (maybe 3-5 mm diameter) and stuck a straw in it.  When I turn the apparatus on, hovewer, the straw (placed in a bottle of water) lifts the liquid for no more than several millimeters.

Why does my Venturi pump not work?


texts: How to judge the character and sign of a dislocation?

texts: I do understand that $ \mathbf b||\mathbf t$ for screw dislocation but I am unable to judge the sign of the dislocation. Again if $\mathbf b \perp \mathbf t$ how do I judge its sign? Any formula which explains the sign and magnitude (to some extent) will be highly appreciated. Here, $\mathbf{b}$ is the Burger's vector and $\mathbf{t}$ is the tangent vector.


texts:
I started with a book (pdf see here: https://www.pdhonline.com/courses/m104/m104_new.htm)

In this book there is the following formulla found
$$f_0 = 170 / \sqrt{M_1 * t  / (1 + M_1 / M_2)}$$.
The page i refereing to is 4-2 (added below) but can also be found on this link(called page 28)
http://buildingcriteria2.tpub.com/ufc_3_450_01/ufc_3_450_010032.htm
For text related to this figure see page 27 of the same link.

I assume the situation it decibes is showed in situation B of figure 4-3

It is not a difficult formula but still i have some difficulties with it... The for here most importand one is as follows. When try to convert the formula to metric i run into a unit problem...
So the unit version is as follows. $$f_0[1 / s] =  170[?] /  \sqrt{[lb / ft^2] * ([ft] / 12) / (1 + [lb / ft^2] / [lb/ft^2] )}$$
With
$(1 + [lb / ft^2] / [lb/ft^2]) = [-]$ and $[lb / ft^2] * ([ft] / 12) = [lb / (ft * 12)]$ resulting $1/[sec]  = 170[?] / \sqrt{[lb / ft]}$ (i ignore the factor $1/12$ for now).
This would mean the unit (of the 170) of the numerator should be $\sqrt{[lb/ft]} /s$ while i would expect that it should be related to the speed of sound(and thus in $ft/sec$. The denumerator is would have $ft$ as unit).

So my question is as this:
Where is this formula come from how is this formula build up. AND maybe a pointer to a paper where this formula comes from.


texts:
I am trying to write code for the buckling of composite plates using the Ritz approximation but I can't understand something. According to Reddy (Mechanics of laminated composites), this is the equation of the principle of minimum potential energy (since we are concerned with buckling, q = 0 and the frequency omega = 0):

And the Ritz approximation

But after substituting 6.6.5 in 6.6.4 we get

It seems that delta w_0 has been substituted with X and Y but with indexes p and q, but it seems we do not sum over them. If that is the case, how do we go around solving this? Do we iterate over them but for some reason it is not written explicitly?


texts: If a water pipe has a large diameter at the start and a small diameter at the end what part of the pipe would the water flow faster?


texts: Which lubricant (oil or not) to use if I want to prevent sticky/gummy buildup?

texts:
I am currently tinkering with typewriters and two things striked me when I started to read about their maintenance:

They are supposed to run almost completely dry, except for a very tiny amount of lubricant at very specific points;
Gummy or sticky gunk buildup - usually due to over-oiling + dust buildup + passage of time - is one of the main causes of typewriter malfunctioning.

As an avid cyclist I am, I have already noticed some oils have a tencency to get sticky as they dry out and mix with dust (e.g. gearbox oil), while others seem to be very stable and somewhat "repel" dust, mostly automatic transmission fluid - ATF, power steering fluid, or suspension oil. I believe these are somewhat intended to remain fluid and to actively repel dust, which seems to "fall out of the way" instead of get increasingly mixed with the oil and the working surfaces.

I know a lot of typewriter folks use sewing machine oil (Singer, mostly), but I wonder if its characteristics are suitable for this need of not getting gunky as the years pass.

So que questions are:

Given the considerations above, would some type of oil or non-oily lubricant be more adequate than sewing-machine oil?
Is the hydraulic fluids hypothesis a good one?
Any other relevant consideration?


texts: Quick Solidworks question: How to cut a 3D part along a line in a sketch?

texts: I'm not having luck with the Trim Entities feature, which is just for sketches. I just want to shave the top part off completely at the angle that I've drawn.


texts: Find the differential equation to the closed-loop system

texts:
I know that the closed-loop transfer function is equal to
Y/Ysp = (P controller * DC motor) /(1+(P controller * DC motor)) then I am struck.  Can anyone give me some hints on how to proceed?


texts: Example of real-life problem solved with numerical methods?

texts:
I hope this is a suitable question to ask here.

Well, I'm taking Numerical Methods this semester (also called 'Numerical Analysis' in some places).

The term-assignment is to find a real-life problem which is solvable by numerical methods. And then present two different methods to solve it.

It doesn't have to be something new, simply presenting someone else's solution is acceptable.

This seems like an incredibly easy thing but I'm having a hard time finding something of reasonable difficulty to use.

Any ideas or suggestions?


texts: Can a reinforced hose develop an internal restriction due to thermal expansion?

texts:
The type of hose involved is the thinnest one on the right in this picture. This hose contains an external rubber layer, a textile reinforcement layer, an inner rubber layer and a nylon lining.

The hose has been ziptied to a plastic electrical conduit and it serves as a discharge hose of an automotive air conditioner, so it gets warm during the system operation, and internal pressures are high (the reason for the reinforcement layer).
Also, it's located not very far from the exhaust plumbing.

Can the zip tie and the conduit possibly restrict the hose internally due to thermal expansion as the hose warms up, or would the zip tie expand together with the hose? Can the reinforcement layer prevent the hose from developing a restriction except in the case of a lining delamination?

Here's an exemplificative picture of the arrangement:


texts: Pulse Oximetry, does the decimal matter?

texts:
I work in a sleep research lab. We have a couple of Masimo pulse oximeters that report pulse oximetry values in terms of integers (e.g. 90, 91, 92, etc.).

Now our principle investigators used to use an Ohmeda Biox 3700 that reported data via analog output in a nice (noisy) curve (e.g. after filtering, 90, 90.1, 90.3, 90.4, etc.).

There's some discussion that because of the lack of decimal, the Masimo is useless for data reporting. The Ohmeda though is from the 90s and I can't find any documentation that indicates if taking the decimal is even acceptable for the device's resolution. Any thoughts?


texts:
Most of finite element calculations are performed with an orthogonal mesh (Cartesian coordinate system). From this calculation, we get two values of required steel area per linear meter: $Ax, Ay$ ($cm^2/m$) for each direction. However, my slab is circular, so the steel reinforcement have to be put in orthoradial direction. How do I convert the reinforcement from orthogonal to orthoradial?

Thanks,


texts: Moment placed off-centre on a rotating body

texts:
Imagine a body which is allowed to rotated around its centre of gravity. I place a rotating moment, $M_d$ on a point which is a distance d from the body's centre. $M_d$ is only required to put the body in motion, i.e. overcome the friction and intertia required for the body to start rotating around its centre of gravity.
Compare this moment to a moment $M_0$ located at the centre of gravity. Same conditions apply for $M_0$, it only has initiate rotation. Is $M_0 = M_d$? Or is one bigger than the other?
Theoreticaly they should be the same but intuitively when compared to screwing a screw, it is easier to screw the screw if you apply the moment directly on the screw axis of rotation.
Could someone please explain if there is a theoretical difference or if it is only my intuition which is wrong.


texts: How to calculate the register draught/draft loss (RDL) of a burner?

texts:
I am aware this is a vague question but it is something which has been on my mind.

Would anybody know the steps used to calculate the draught loss across a burner in the furnace of a boiler?

Would it involve using parameters from the forced or induced draft fan?

What other values would need to be taken into consideration?

Thanks!


texts: does payload weight distribution affect rolling resistance?

texts:
Recently came across the following 2-minute YouTube video that claims A Balanced Rig Saves Fuel

While nicely done, it is a marketing video.  Does anyone know of any unbiased studies that support the claim?


texts: Best way to attach a square tube to a flat surface?

texts: I have an aluminum square tube (diameter 1/2") that I would like to attach to a flat aluminum surface which has a circular hole of smaller diameter in it for water to flow through at low pressure. Would welding a flange to the square tube (with screw holes for going into the surface) be the best option, or are there better ways for making this kind of attachment? This is not a high pressure system so I don't think there will be any complications there.


texts: How is a shear pad of remote compliance device formed?

texts: I am researching on mechanical design of remote compliance devices (RCC)†. In the RCC, manufactured by ATI, they use shear pads for lateral compliance. They mention that shear pads are elastomers bonded with metal shims. I couldn't find how it is being made. Are there layers of elastomers between wedging pieces (shims) or something else? How is adhesion being achieved?


texts: Measuring the distance to an object with RF resonance

texts:
Assume I put an RF antenna in front of an object (typically the face of someone sitting in a chair, so able to move about +/- 10cm in all directions) at a typical distance of 1m. If I consider the system antenna/face as a resonant cavity, I'd get a fundamental resonant frequency of about 150MHz.

I have a general physics education but no experience at all with RF antennas and resonators, so I have no orders of magnitude in mind. I realize such a 'resonant' cavity would be extremely poor, but how poor? My question is: is it conceivable to have enough resonance with basic antenna and processing electronics to be able to measure the mean distance to the face with a precision of say 1cm (i.e. measure the mean resonance frequency with about 1.5MHz precision), or is it an obvious and complete no go?

If it were conceivable, how 'clean' would the background need to be? Assuming there could be many unconstrained background objects (typically at a distance twice larger) all in a small room, could I just pick up the main resonance frequency around 150MHz for my measurement or would all the reflections / interferences with the other objects + room walls mess the signals completely up?

Note: I'm not expecting a detailed solution to my problem (although I'll happily take it if it comes :) I'm more looking for an "expert's feeling" like "yes, people have done that for decades", "maybe, you'd have to try" or "No way dude, you're completely dreaming".

In any case, if anyone sees any other (as cheap as possible, and most importantly automated and non intrusive) way to get such a measurement (+/- 1cm at 1m distance) please let me know.


texts: Can I Calculate The Discharge of a Capacitor If All I know Is Algebra

texts:
Since my last post on Engineering-Beta, I have composed a few simple simple circuits involving capacitors(super-caps specifically), resistors and LED's.

The following image is of a branch from a circuit I designed,which highlights the discharge of a capacitor through a resistor and LED. I will be using this as a reference to all my questions:

The moment That I allow current to flow from this circuit, Voltage will begin to drop, and current would begin to drop also. I know that the addition of resistance into the circuit can slow the loss of charge at the capacitor...

I wrote a bunch of stuff regarding all this, but it seems trivial now. Basically, I'm dealing with a rate of change that is not constant,  and I'm trying to find precision in my circuit, I would like to be able to calculate the time duration of the discharge but, I believe that:

"Calculus is concerned with things that do not change at a constant rate"
-TheMathPage.com

Sum everything up, all I know right now is intermediate algebra, and from all my google searches about this topic, they keep talking about derivatives and calculus. So, how can I figure out the rate of discharge of a capacitor? Or have I answered my own question already?


texts: What does reactive power translate to in terms of torque?

texts: Say I'm trying to connect an AC generator to a circuit containing an inductor and a resistor, powered by a steam turbine. I understand that because of the resistor, I'll be dissipating energy and therefore I'll need to drive the generator with a certain torque. But what about the inductor? Obviously there's no dissipation of energy. Rather it is given and taken from the inductor. So does this mean that I'll get pulses of torque in the generator shaft? I mean, sometimes the inductor will pose a torque that opposes the rotation of the shaft, then the next moment it will produce a torque in the same direction. Have I understood this correctly?


texts: Torque acting on a rotating wedge due to a linear force parallel to the axis of rotation

texts: Let's say I have a wedge which can only be rotated about a fixed axis perpendicular to the ground. There is a cam follower mechanism constrained to vertical movement with a ball roller on the end which is applying a vertical force on this wedge at a fixed distance L from the center of rotation. As a function of F, theta, and L, how do I find the resultant torque? This is not schoolwork, it's based on a nutating mechanism I'm designing for my job.


texts: Do I need a feedback loop while testing PID controller?

texts:
This is a homework for my university course control theory.
The task is simple: Test the P, the I and the D controllers separately to see the effect.
We don't have to connect the controllers to a system it means IN -> controller - out, but the instruction doesn't say if we have to use a unity gain feedback loop.
Does it make sense ( practical use ) to test a PID controller without a feedback loop?
The inputs are step function for P and I controllers and a ramp function for the D controller.
And I do everything in Simulink.


texts:
I have a concrete steel ceiling. The calculations show the ceiling is designed for 1,5 kN/m² in addition to it's own weight and traffic loads including snow. So I assume I can hang 1,5 kN/m² from that ceiling, provided I use suitable anchors.

However, when I hang any load from that ceiling, I apply discrete point loads. I probably cannot simply say: Well the room is 2x4m, so I can hang 2m x 4m x 1,5kN/m² = 12kN in the middle of the room. Which is probably wrong.

So how do I arrive at the point loads I can apply?


texts:
Can anyone point me to a calculation or formula that would tell me what percentage an 6061 T6 aluminum tube OD should be able to be flared to, using any or all of the following: OD size, Wall size, yield strength, ultimate tensile strength and elongation?

I have a 3" long sample that has a 2" outside diameter with a wall size of 0.090". The method of flaring is utilizing an Instron tensile testing machine. The part is being forced down onto a 60 degree cone with a flat surface at the top. There is not a predetermined speed or force that the cross-head must move. The T, Y & E properties fall into the middle of the tolerance for the alloy and temper.

I realize the calculation couldn't be precise, but I'm wanting a ballpark figure to work with as my customers include a minimum flaring percentage that the part must make and I don't know where they're getting their data from. They are coming from steel so I want to make sure they are not just bringing that measurement straight across.

The typical part is anywhere from 2" to 3.5" OD with a wall in a range from .075" to 0.100".. The customer's spec for minimum flare percentage is from 10% to 15% depending on the part.


texts: Nitinol FEA using Advanced Simulation NX

texts: Is there a tutorial on how to do non-linear FEA using Siemens Advanced Simulation NX (not remap) with Nitinol, preferably using sol 601. An example would be very helpful, I searched online but most just have Ansys or abacus examples.


texts: How much weight can a floating vessel carry before submerging?

texts:
Source: http://www.cbc.ca/news/canada/new-brunswick/friday-flood-new-brunswick-2018-1.4647979

Is there a way to calculate how much weight a vessel can carry (in fresh water) before it submerges?

Assumptions:

The water is not disturbed (no waves or wind) and the cargo does not move
The vessel weighs 200 lbs when empty
The vessel's volume is 60 cubic ft


texts: I have a project that involes electrochromic materials and I am wondering if it's possible for an electrochromic material to turn from white color to black and vice versa. If the answer is yes, can you name that material?


texts: Good material for friction disk for a torque hinge?

texts:
What kind of material(s) would make a good friction disk, or disks, for a friction hinge, or torque hinge? This will be for the hinge on an arm that needs to be adjustable and also hold it's position with 1 to 10 pounds on the end. The hinge may be a vertical tilt hinge or a horizontal swivel joint.

The two pieces that will swivel against each other are flat metal with 2 surfaces of 1.5 inch diameter of overlap where the friction disk will be. I plan to use a bolt with a spring washer to supply the pressure.

The specifics above are to give an idea of the scale of the forces. My question is generally about what materials are used for friction disks.

Brass or nylon washers are sometimes used for hinges or joints when you don't want friction. I want the opposite of that - I want friction.

I want something durable enough that won't wear out quickly or disintegrate, and grippy enough to hold without slipping. The hinge may be repositioned several times per day. The worst thing would be a hinge that slowly slips over time.

Ideally, the materials would slide without making noise, like scratching or grinding sounds.

Edits: I reduced the weight from 40 down to 1-10 lbs.


texts:
In this question , I dont understand why the KBC is 4EI / L .... I was told that for the far end pinned or roller supported , the K = 3EI / L , so shouldn't the KBC = 3EI / L

In the 3rd photo , we can see that for far end pinned supported , k = 3EI / L , not 4EI / L

What are the difference between the example in photo 2 and photo 3 ?


texts: Will strong electric field damage electronic components?

texts:
Electronic components like transistors, diodes etc have maximum voltage ratings which when exceeded damages the respective component. Is voltage sufficient to damage a component or there must be a sufficient current? I mean one may place these components in an external electric field (static field not dynamic) such that the voltage between two points exceeds their rated voltage capacity. However, there is no current supply as the component is in an electric field(in air), and not connected to a power source. Will the component be damaged?

Note that the electric field is strong enough to exceed components voltage rating but not high enough to cause dielectric breakdown of air or semiconductor material.


texts: Transfer function into block diagram and matrix form

texts: I'm reading a book on Control System Design and running into the same issue I had in Kinematic Design. When things are presented in a format without any numerical examples it just appears as gibberish to me and always has (I do have a learning disability which maybe my issue.) So I'm working the problems and trying to take the problem statement of $$ H(s) = \frac{(s+2)(s+4)}{(s+1)(s+3)(s+5)} $$ and place it into a block diagram as well as a matrix. The issue I'm running into is that the only examples I'm seeing involved $$ H(s)= \frac{b_0s^k+b_1s^{k-1}+b_k}{s^k+a_1s^{k-1}+a_k} $$ which is makes absolutely no sense to me. Any help would be appreciated.


texts: What are the major differences between Engineering degrees and Engineering Technology degrees in terms of employability?

texts:
What difference in education occurs between two graduates, one with an Engineering Technology degree (be it Civil, Mechanical, Electrical...) and the other with the equivalent Engineering degree "proper?"

Assuming both degrees are 4 year degrees and both are able to become PEs, how do potential employers feel about the different degrees? Is there a difference in pay?

What options does the graduate with an ET degree have to advance his/her education? For example, can one earn a masters with an ET degree?

I'm looking for advantages/disadvantages of either degree in terms of employability and career progress, from the point of view of an engineer who has hired people with these backgrounds.


texts: Anisotropic constants and progressive failure along-side ANSYS Mechanical model

texts:
I am modelling a CMC plate bolted to a superalloy plate in ANSYS Mechanical. I set up the orthropic material properties of the CMC from literature (x,y,z modulus and max stress), and I am using the maximum stress failure criterion. My degradation rule currently constitutes a 0 compressive stiffness degradation (fibre/matrix), a full stiffness degradation for fibre tension, and a partial degradation for matrix tension according to the material bilinear model.
My degradation model is inspired from literature, and I am assuming that matrix degradation leads to partial stiffness reduction according to stress-strain experimental data.

I know that using the TB,ANISO and TBDATA commands I can somehow
input specific bilinear plasticity data, but how can I do this along
side ANSYS Mechanical with a command?
Also, to extract load-displacment data I ran a basic parametric analysis and increased loading. How
can I run this iteratively until full failure of the CMC part?


texts: Can I increase the range of a howitzer by using more propellant?

texts:
The muzzle velocity of a firearm can, all else equal, be increased by lengthening the barrel of the weapon which can theoretically be extended up to the point that friction and air resistance would overcome the benefit of pressure buildup in the barrel.

I think that the range of a howitzer be increased simply by adding more explosive propellant. Why is this not used? I would think that this would be a straightforward way to increase the gun's effective range. Any ideas?


texts:
Gearboxes usually have a reducing ratio like 200:1, which means that they take a high-speed input and convert it into a high-torque output.

Would they work if I connected them in reverse?

Is there an approximate ratio at which a human could no longer power one in this configuration (without the use of a large lever)?


texts: Tethered Balloons vs Towers for Wireless Communication

texts:
If we use tethered balloons (aerostats) with wireless gateways fitted on them (let's say for Cellular or LPWAN communication), they can provide much more coverage owing to the height they can reach (e.g. while towers usually reach a maximum of 2000 feet, tethered balloons can usually reach a maximum of 4.5 km). And increasing the height of a gateway can increase the coverage surprisingly, since at a sufficiently good height, the Fresnel Zone gets good clearance giving clear line of sight. And it has been recently demonstrated using LoRa when someone created a record of 702 km coverage with a high-altitude balloon.

I wonder why are tethered balloons then not used for communication?

While there are many instances of high-altitude balloons (like Google's Project Loon, Space Data SkySite® or this question on this StackExchange), I could find scarce resource on low-altitude tethered balloons. What I could find was this work done in 2008 (IEEE Conference Paper) by a  research lab. Another recent conference paper (2016) is this from another lab. The first paper also demonstrates that the tethered balloons turn out to be lower cost in the long run.

Some reasons that directly come to mind are:

Balloons would require more maintenance (and may turn out to be expensive)
Cost of balloons would increase dramatically as the weight of the wireless equipments is quite high
Balloons would struggle under winds (however since they'd be tethered, exactly how would wind affect them?)

What I would like to know is some solid engineering answer on this, with some numbers to back the claim. What exactly restricts their usage from RF, Communications, Aerodynamcis or Mechanical point-of-view, as compared to fixed towers? Or perhaps is it just that beyond 2000 feet (maximum tower height), you do not get any benefit in Fresnel Zone clearance?


texts: What is a "compression stop" for a tongue & groove joint?

texts:
I came across this snippet in a vendor manual for gaskets for a flanged joint for vacuum duty (tongue & groove). What exactly is a compression stop? Is it evident in the sketch below?

http://www.flexitallic-gmbh.eu/wp-content/uploads/2015/02/Gasket_Design_Criteria.pdf


texts: What would be the disadvantage if any to placing evaporator casement beneath furnace for central forced air HVAC sustem?

texts:
I have only been in the HVAC business for 3 years and I have already encountered 2 cases of leaking air conditioning evaporators.  In both cases the evaporators were located above the central furnace in an up-flow forced air system.  My diagnosis is that while the evaporators may have been designed to withstand the hot air temperatures leaving the furnace heat exchanger and flowing through the evaporator, the repeated expansions and contractions of the metallic evaporator coils due to these extreme temperature fluctuations shortened their lifespan.  In other words, if the AC evaporator did not have to contend with the heat from the furnace it would last much longer and less prone to develop leaks.

So, for a better design where both furnace and AC evaporator have to share the same forced air system, wouldn't it be smarter to place the evaporator and its casement beneath the furnace but above the forced air fan?


texts:
I am currently working on creating a tool to calculate the maximum heating rate on a re-entry vehicle given starting conditions and coefficients. I am using Re-Entry Aerodynamics by Wilbur L. Hankey as my current source. On page 30, he introduces the following equation as a way to calculate the heating rate:

The problem is that I do not understand the equation. The way I interpret it is:

What doesn't make sense to me is the ρ^m in the equation. If you attempt to solve for the units of ρ^m, you get it as K s^3/m^4, which makes no sense to me.
My researching myself has been unable to lead me to an origin or explanation for the equation, and neither my coworkers or my student friends have ever seen it before. If someone is able to give me some idea what I'm looking at, that would be great.


texts: What ramping constraints for gas plant - CCGT, combustion and steam turbine?

texts:
I am using the publication Current and Prospective Costs of Electricity Generation until 2050 to source ramping constraints for an economic model of three different gas power plants - CCGT, combustion turbine and steam turbine. As I'm not an engineer I have the following questions:

The model is a little simplistic. For that reason, I cannot use
three different time and cost parameters for hot, warm and cold
start. For a gas power plant with load factors of between 10 and
60%, which start would you think is most relevant (i.e. most often
done): hot (shut down 8h or less), warm (8-50h) or (probably not)
cold start (more than 50h)? Would you apply something in between hot
and warm start?
Regarding start-up time, there are not many studies for steam
turbines (p.71 in pdf numbering). Someone advised my to use a rather
slower start-up time for steam than for combustion. So could I use a
value similar to CCGT, for example?
For the "ramping load gradient limit in %-Pn/min" (p.74 in pdf numbering), I have the same issue with steam turbines as described in 2).


texts:
I'm currently investigating fault recovery in a UAV using MATLAB.
I've been given several variables:

phi = the roll angle
psi = the yaw/heading angle
beta = the side slip
p = roll rate
r = yaw/heading rate
delta_r = angle of the rudder
delta_a = angle of the aileron (the aileron is currently inactive).

My input is the rudder angle.
I've simulated a step fault in the yaw/heading sensor and I'm trying to recover from it.
To detect that there was a fault in the heading sensors: I compared the actual side-slip with the modeled side slip. If there is a difference between the "real' system and the model in heading angle, but no difference in side-slip, then the heading sensor is faulty.
To recover from this fault: I want to reconfigure the side-slip so I can use it to determine the heading/yaw angle. In order to do this I need to multiply the side-slip by the transfer function between side-slip and heading/yaw angle.
We've been given the following equations:

I'm having some trouble coming up with a transfer function between side slip and heading angle.
I figured the best thing to do, as I am using a simulation filled with arrays, is to turn all the derivatives into their discrete equivalent - of course this is means I'm not using a transfer function, but an equation. Taking the equation for the derivative of beta and discretizing it...

When I plug this in, the system doesn't recover.
I even tried doing Laplace transforms, but I get stuck here:

And I'm not sure how I could apply that in MATLAB
Is there a mistake in my logic or approach? How would I turn the discrete system into a transfer function?


texts: Membership of professional societies/associations for electrical and electronic engineers

texts: Membership of which professional organizations for electrical and electronic engineers are recognized globally?


texts:
I'm trying to design a kind of water valve with inexpensive materials as a first prototype.
The water flow from the PVC pipe (1) reach the body of the valve and pass through an aluminum grid (3) to the water tank. When the water level goes up pushes the float closing the water intake at point (2).

How can I calculate the buoyancy force needed to stop the water flow? And, what will be the mass of the float?

Let’s back to the basics; here I present the problem and some math that I been doing, I would like your opinion:

Connected to the PVC pipe (2) I have a garden hose with a water flow pressure of, let's say... 49 kPa (I need to check this with a manometer), and I attached a 25 mm diameter and 0.5 m long PVC pipe. Let’s pretend that the float seals the other side of the PVC pipe, so I need to calculate the force generate the water flow pressure against the float.

Please take in consideration that I'm not a fluid mechanic expert.

When I open the garden hose, the PVC pipe starts to fill, so based on this situation:

$$P_1+\dfrac{\rho gh_1+v^2\rho}{2}=P_2+\rho gh_2+\dfrac{v^2\rho}{2}$$

If I took the height of $P_1$ as the reference, $h=0$, and the diameter of the PVC pipe and the garden hose pipe are the same (25 mm), the water flow velocity at those points are equals:

$$P_1=P_2+\rho gh_2$$

So, if the garden hose pressure is 49 kPa:

$$\begin{gather}
49000\text{ kg}/\text{ms}^2=P_2+9.8\text{ m}/\text{s}^2\cdot 1000\text{ kg/m}^3\cdot 0.5\text{ m} \\
P_2=53900\text{ kg/ms}^2 \\
P_2=53.9\text{ kPa}
\end{gather}$$

Ok, assuming this math is correct…now I have to calculate the force against the bottom of the PVC pipe at point 2:

$$P=F/A$$

In order to simplify this example, I took the diameter of the PVC pipe as the contact area.

$$\begin{gather}A=\pi r^2=\pi\cdot0.025^2=0.002\text{ m^2} \\
F=107.8\text{ N}
\end{gather}$$

If the pressure of the water flow generates a force of 107.8 N, I need an opposite force with a higher value to counteract it. Is that correct?

My goal is to find a material (mass; area) that generate enough buoyancy force to stop the water flow through the valve and seal the water intake, and when the water level goes down, the float valve will let pass the water flow to continue to fill the water tank.


texts: Does tunnel lining made of cast iron tubings actually accept all the mechanical loads?

texts:
Here goes a recently opened underground railway station in Moscow, Russian Federation (image is from here)

On the left is an undecorated (just painted and it will likely remain this way) tunnel wall. The tunnel wall is lined with cast iron tubings - specially crafted pieces of cast iron connected with thick steel bolts and having the seams sealed with cement. This lining forms a huge pipe which holds the ground from collapsing and the shot is made from inside the pipe.

The cast iron is something like 30 millimeters thick.

Is there actual ground right behind that (not very thick) cast iron? What if the ground underneath is not hard enough and the loaded pipe has to bend downwards?

Does the cast iron hold all the possible mechanical loads alone or is there anything else in the structure?


texts: Thermal oil in Boiler not reaching desired temperature

texts:
The thermal oil Feroline U in Boiler is not gaining the desired temp of 240 Degrees. We have physically measured the temp using digital thermometer at a distance of 20 cm where the boiler temp sensor is installed. 40 degrees are lost in 20cm insulated area.
The boiler is well insulated with Rockwool & oil quality is good (recently tested).

What could be the reasons? Any solutions please?


texts: Machine Analysis Problem: Finding the vertical force at joint K

texts:
Help me in determining the right solution in this problem. I already have an initial solution here but when I compute, my answer does not match to the answer key. I would like to know where did I create a mistake.
(By the way, this is not a homework.)

These are my initial equations:
Knowing that member BC is a two force member and it is a duplicate so I arrive to this equation. I dismember the member BC and pin J from the body.
$\sum M_J = 2F_{BC}(\frac{80}{80\sqrt(17)})(60) + 2F_{BC}(\frac{320}{80\sqrt(17)})(440) - 2000(200) = 0$

After I solve the force in member BC, I use that value to solve $F_{Ky}$. I dismember the member HL and member BC from the body.
$\sum M_H = -2000(1700) + F_{Ky}(1100) + 2F_{BC}(\frac{320}{80\sqrt(17)})(280) + 2F_{BC}(\frac{80}{80\sqrt(17)})(1440) = 0$
I got a value of around 2500 N but the answer key states that the answer is around 403 N. I am thinking that the condition that HL is connected to the truck can affect in the computation.


texts: One large fireplace flue versus two smaller ones

texts:
I am a mason contractor whom specializes in Rumford Fireplaces. I am helping design a fireplace that had a problem fitting in a single 18" x 18" flue pipe. So I installed two 13" x 13" pipes adjacent to each other.
They start at the smoke chamber tight together with a smooth as possible connecting partition.  I'm cutting out the connecting flue walls some 12" down from the chimney top so as to form a plenum in order to avoid pressure variations from wind on one side more than the other.

The two flue pipes will be equal in height and length and have the same amount of masonry surrounding them to keep temperatures even.  They will be centered in the smoke chamber and their total area is 256 $in^2$, which is nearly equal to 1/9th of the 48" x 48" fireplace opening as required by all codes.

My masonry teacher built a design like this long ago as have I, and I have had no problems. However, I am being told on certain blogs that this design will cause turbulence and double the drag resistance.  I'm also told that I should have used a single 13" x 20" flue with a inside area of 192 $in^2$.

I believe that having my pipes connected at the top and bottom prevents turbulence from pressure and flow differences.  And that having more cross sectional area from the combined flues should easily compensate for the added drag of the extra 12" of smooth tile partition.

I also believe that in a smoke chamber, a intermittent vortex exists below the damper blade and never rises into the flue area because the flow changes to laminar flow before entering the pipes and the parting divider.

Normally, I don't use double flues.  However, I really can't see how two pipes connected at both ends and being larger in combined area will hurt flow via turbulence to a point of where you would see enough flow loss to generate eddy's in the flow.

If anyone can help verify if two flue pipes is sufficient or not in this design, I'd appreciate it.

To summarize my thoughts: I don't believe the air flow will be negatively affected from using two flue pipes instead of a single flue pipe because of the connection between the two pipes and having a larger overall combined area within the pipes.


texts: Statics problem: Finding resultant force angle measured counterclockwise from positive x-axis

texts:
I have this diagram:

And I have done these calculations:
$$\begin{align}
R_x&=-20\sin(30)+30\cos(35)+80\cos(45)=71.14\text{ lb} \\
R_y&=20\cos(30)+30\sin(35)-80\sin(45)=-22.04\text{ lb}
\end{align}$$

The magnitude of this resultant force is then:
$$|R|=\sqrt{71.14^2+(-22.04)^2}=74.48\text{ lb}$$

Here's the part I need help with. I can get a theta angle for where the resultant force's angle is, but I want to figure out how one would get this angle measured counterclockwise from the positive x-axis:
$$\theta=\tan^{-1}\left(\frac{-22.04}{71.14}\right)=-17.21°$$

How can I get this angle measured counterclockwise from the + x-axis? I don't get this and would really appreciate some help. This comes up a lot and I do not understand it.