texts: What is "Bernoulli-Lift", and why does it only account for 20% of an airplane's lift?

texts:
Whenever the question "Why do airplanes fly?" is asked (e.g.
»What really allows airplanes to fly?«,
»How an airfoil works?«) at a certain point the following is cited:

  Bernoulli's principle accounts for 20% of an airplane's lift…

In a very general formulation Bernoulli's Principle states

$p_\mathrm{total} = p_\mathrm{dynamic} + p_\mathrm{static}$

Assuming low ( $M\ll0.3$ ) velocities this can be written as (resulting in an error of 5% at $M=0.3$ due to density change):

$p_\mathrm{total} = \frac{1}{2}\rho u^2 + p_\mathrm{static}$

When Bernoulli's Principle is defined as that. Then ( in case of $M\ll0.3$ ) it does account for 100% of the lift, since it describes how the static pressure difference between suction and pressure side results into drag and lift (neglecting skin friction).

Which additional assumptions have to be made to come up with a lift which is only 20% of the actual lift? Is this the lift one would calculate when the lift-force is based on the equal-transit-time-assumption? Or is this an error occurring when a delta wing also features vortex system so that the definition of the total pressure might be difficult?


texts: What are the Singular Values of a dynamic system and how are they calculated in the *sigma* function in Matlab?

texts:
According to Matlab documentation:

sigma plots the singular values of the frequency response of a dynamic system.

bode creates a Bode plot of the frequency response of a dynamic system.

I am reasonably familiar with Bode plots and dynamic systems but I don't understand what the singular values of the system are or how they are calculated. Are they related to the magnitudes of the system (which can be outputted by bode)?

For reference, I have a discrete state-space system which I am attempting to model as a reduced order system. One of the papers I have been using to accomplish this mentions using the sigma function to compare the two models. The paper is 'Dynamic Mode Decomposition with Control' by J.L.Proctor.

Any help with understanding singular values or this sigma function would be appreciated.


texts: Best way to communicate data wirelessly with specific conditions

texts:
So I need two modules to give each other data with the following conditions:

They are relatively short range. They need to be near each other to transmit the data, say around 5 cm.
They are relatively small.
Battery powered, preferably ready to transmit the moment its turned on with a switch.
The data they receive should be sent via bluetooth to another device (There is a reason I can't use bluetooth directly)


texts: Bounds to prove exponential stablity for given Lyapunov function

texts:
Problem 3.6 in Khalil's Nonlinear Control: Use given Lypunov candidate function to prove that the origin is exponentially stable. The system is
$$\dot{x}=\begin{bmatrix}x_2\\-h(x_1)-2x_2\end{bmatrix},\hspace{0.5cm}h(x_1)=x_1\left(2+\frac{x_1^2}{1+x_1^2}\right)$$
and the given Lyapunov candidate function is
$$V(x)=\int_0^{x_1}h(s) ds+\frac{1}{2}\left(x_1+x_2\right)^2$$

To prove exponential stability, we need to find four positive constants, $k_1,k_2,k_3,a$, such that
$$k_1\lVert x \rVert^a \le V(x) \le k_2\lVert x \rVert^a$$
and
$$\dot{V}(x)\le -k_3\lVert x \rVert^a$$
We can write the Lyapunov function more explicitly as
$$V(x)=\frac{3x_1^2}{2} + \frac{1}{2}\left(x_1+x_2\right)^2 - \frac{1}{2}\ln(1+x_1^2)$$
and its time derivative as
$$\dot{V}(x)=-\left(\frac{x_1}{\sqrt{2}} + \frac{x_2}{\sqrt{2}}\right)^2 - \frac{3x_1^2}{2}-\frac{x_2^2}{2}-\frac{x_1^4}{1+x_1^2}$$
It is relatively clear that we can use $a=2$, and that there exists some $k_1,k_2,k_3$ that will hold.
But how do we find suitable values for the $k_i$'s ?


texts: How does Work behave in two different refrigeration setup?

texts: Does work behave the same way for all temperature range while in a refrigeration setup. When quality of heat changes with the temperature, Does it apply to work also. IF we consider refrigerator Source-sink of 1000-500k and 300-250k, Does 1KJ of work input have the same effect or the effect is different. My doubt may be a very silly, i might be missing something. Any input is appreciated. Thank you.


texts: What made bronze the first widely used (non-ornamental) metal in human civilization?

texts: I recall learning about the bronze age in school. Why was bronze so important to the technological development of humans?  Why not some other metal?


texts:
I am working on a model city.

Suppose I have utility poles A, B and C (brown) that go around a sharp corner. Looking from above, how do I connect the poles with power lines (gray, solid)?

Are the crossarms of utility pole B rotated correctly with respect to the direction of the lines? Do the crossarms of pole B the correct length, or do they need to be longer than normal? Are there any other problems I should keep in mind?

Thanks.


texts: Explanation on negative voltage to microcontroller

texts: How does negative voltage damage the pins of my PIC16877A microcontroller. Could anyone explain to me? Thanks


texts: Can I use a NPT fastened device to vacuum or 10^-2 Torr?

texts: I am designing a flange to be use to maintain a pressure of 10-2 Torr for at least 3 months. I am using an o-ring seal from my (device) to the product weldment. I am looking for feedback on using NPT fittings in a vacuum system. I have heard it is unwise. However what I find readily available online is only NPT fitted gauges. I was thinking of using Teflon tape or Loctite. I should add there is a fitting I am using to adapt from NPT to conflat which will be welded.


texts: Would a PE-pipe filled with concrete make a good pillar?

texts:
An idea that keeps popping up in my head, that I don't know enough structural/civil engineering to know if it's good from a technical point of view.

Take a piece of polyethelene (PE) piping, fill it with concrete, let the concrete bind. My understanding is that under compression, a concrete (or other) pillar will 'want' to shear apart in a plane 45° to the direction of the compression (assuming we don't bend our pillar). This is an outward movement. This shear force could be contained by the surrounding pipe, since PE is quite good in tension. Othe materials for the pipe might work the same, I say PE because it's quite corrosion resistant.

I know everyone is building concrete pillars with rebar inside, I don't claim my idea is superior. I'm not interested in understanding why everyone is building pillars the way everyone is building them, I want to understand the flaws and limitations in my idea. Some thoughts:

I think it's useful to think as pressure in the pipe, as we have that data easily available - if we use PN10, it can take 10 bar, etc., and we don't need to think about the thickness of the pipe and it's yield strength. But how would the compressive force translate into pressure on the pipe? The concrete is no liquid, so pressue will be less than compressive load / pipe area. How much? I think understanding this will tell us how much, or little, our pillar will carry.

Another possible issue is that PE is quite smooth. The pipe can't take forces via friction and in my mind that translates to point loads at the places where the concrete happens to deform most.


texts: How to use more CPU cores in SpaceClaim?

texts: This is a more technical rather than professional question. I have a hyper-threaded quad core CPU. While building models in SpaceClaim I noticed that it only uses one logical core. A single core will be on a very high usage percentage while the others are nearly idle. How can I set SpaceClaim to use more cores and make better benefit of the CPU?


texts: Why are most jigsaw blades designed to cut on the up stroke and have teeth that point towards the shank?

texts: Why are most jigsaw blades designed to cut on the up stroke with teeth that point towards the shank? Why are reverse teeth jigsaw blades less popular?


texts: Calculation of natural frequency in a hinged beam

texts: What I tried: Using the conjugate beam method to find deflection and hence stiffness of the beam, but I am unable to find reactions in the conjugate beam.


texts: Cad file for turnstile mechanism/ one-way clutch/ one-way rotation?

texts: I am writing my first 3D cad-file and I want to place into it a turnstile mechanism (a mechanism that allows a fixed axis to rotate only one way, and not in the opposite). Are there cad-templates for devices I can find in some online-platform for engineers? I found this cad-file, though it looks too large and complicated, I want to place it in a device that is 20cm*20cm*20cm. As an engineer, where would you look for a template of a device you want to create physically? Or any suggestions how to create my own simple turnstile cad-file?


texts: Why do the anti-resonant filters in servo controllers operate on the velocity output and not position?

texts: I've been looking into implementing a cascade controller for a motor control application that has a position, velocity, and torque control loops. Because the system we are positioning can experience some mechanical resonances, we are considering an anti-resonance notch filter implementation (possibly multiple notches). In my reading most anti-resonance filters acting on the velocity. Isn't the vibration that we are trying to remove happening due to oscillations in position? Why then would we not filter on the position so that certain frequencies in the position response are dampened?


texts: When are overshooting controllers preferred over asymptotic ones?

texts:
Disclaimer

Designing the behavior of controllers is an important task for many applications. Every application needs its own requirements fulfilled. For example a CNC machine needs a controller with a strict asymptotic convergence to the set value. An overshooting behavior can’t be tolerated due to the fact that once removed material can’t be replaced by the same tool. Other examples for devastating results with an overshooting controller behavior are autopilots landing an aircraft or shuttles docking the ISS.

Question

Are there any real applications where a controller with an overshooting behavior can not only be tolerated but leads to an overall suitable performance for the system? I am looking for a specific example not just field of tasks where it might be the case.

Thoughts of my own

There are systems where an overshooting control behavior can be tolerated. Like if a robot needs to stay on a specific path on the way to its destination with a given tolerance. A controller that controls the distance to this given path can let the robot wiggle a little around the given trajectory as long as it keeps it inside the tolerance. But if you can design a controller with an asymptotic converge to its trajectory you would prefer it to get rid of this wiggle. I can’t think of any real application where you would prefer an overshooting controller over an asymptotic one if you had the choice.


texts: I've been trying to get this sweep to work for a while now. It works with a solid circle. It doesn't work with an annulus. I can provide more info if necessary. I made sure the order of the features matched what I've seen in other threads about this issue but that doesn't seem to help. Every time I try to build it, I get the error "The intermediate profile # 2 could not be solved."


texts:
Exercise

The building is the following:

The exercise is to basicly calculate everything (forces, reactions, ...) and draw several free body diagrams, given $a,h,\vec{G},(\vec{g})$. $2$ is a frame, $1$ is a bar, $6$ is a heavy disc with weight $G$ and the rest parts are rods.

Problem

Now my problem is drawing the free body diagram for the component 6. I got the following:

This would result in:
$$\sum F_x=0 : cos(\alpha)4=0$$
$$\sum F_y=0 : -y_3-y_5-sin(\alpha)4-G=0$$
$$\sum M_{(3)}=0 :  aG+3a\cdot (y_5+sin(\alpha)4)$$

However the first equation would result in the force $4=0$, which doesn't really make any sense for me. If I think about it I would say, that rod 4 should take some force and make the building stronger...

Can you tell me, wehere my problem is? :)
Thanks


texts: Why is the unit for torsional twist in radians?

texts:
It's easy to understand the formula for the twist angle in a section due to torsion, and all the units neatly cancel out leaving a unitless number.

It might sound like a very simple question that it's stupid, I mean the result is very intuitive but I still can't make out how people know that the result would be in radians.

I reckon it has something to do with torque in the formula since it's the only variable with something to do with circles but I can't figure out the relationship.


texts:
I'm an electrical engineer building a pump system to transport various disinfectants from large drums into smaller bottles for my parents' family gym business.  I've realized that I need something that's made to transport chemicals, probably magnetic drive, otherwise the seals and/or diaphragm may dissolve. I'd also like it to be usable in a sprayer application for spraying gym equipment, so a higher psi is needed. I was looking at this pump, but the psi is very low.
Here are some additional questions:

For isopropyl or ethyl mixes, what type of pump internal materials should I look for?
I'm also considering this, which contains 13% alkyl dimethyl benzyl ammonium chloride, 13% alkyl dimethyl ethylbenzyl ammonium chloride, and 73% other (probably inert)
Should I be looking at diaphragm pumps or something else?
Any disinfectant mixes other than alcohols that you could recommend that might work with more pumps on the market?

Desired specs:

Ideally, the pump would support up to 100psi so that we can use it as a sprayer for some equipment and surfaces.
Ability to run dry, or just shut off if dry
Not gigantic in size


texts: Where to place fans for maximum effectiveness in sharing air conditioning between rooms?

texts:
I have a split-type inverter air conditioning unit in one room placed near the ceiling. Assume that the cooling capacity is met, and I'm using the correct CFM of fans. I would like to share this air conditioner with the adjacent rooms. My plan is to install two fans for each room to be cooled. There will be four fans in all.

Questions: Are the following implementations correct?

I install one exhaust fan to blow cold air from the colder room near
the floor to the living room (hotter). This is because cold air
tends to settle to the floor and this makes it easier for cold air
to be moved from one room to another.
I put one exhaust fan at the higher point (directly in front of
split type air con) which is pulling hot air from the other room
back to the colder room. My thinking is that in the other room which
is hotter originally, hot air rises. So putting the exhaust fan at
the higher point makes it easier to move hot air from the hot room
to the colder room.

Thus, #1 and #2 complete the heat exchange cycle and cools the other room. I repeat the same implementation for the other room. What do you think, does this make sense?

Some people suggest the reverse. This way putting the exhaust fan to pull cold air to the hotter on the top (near the ceiling) instead of near the floor. Since its easier for cold air to falls to the floor thus more efficient. Is this a better scenario?


texts:
I want to break this PCB with some know force of X newtons in the bottom left tip of the PCB. The problem is that in Static Dynamics I just get infinite deformation and in explicit dynamics I really don't know what to do.

Anyone knows how to do this? I want to see the part crack away from the board.


texts: Why does my piezoelectric actuator stick at low temperatures?

texts:
I use a piezoelectric actuator on an experimental set up. At low temperatures (Lower than 0 Celsius), the piezo will freeze. Meaning, it will actuate about half way, and then stop moving. Other than the temperature, other conditions have changed.

It is possible that this sticking is in fact some lubricant in the device. I

Can someone comment upon any possible physical origin for a piezo to stick like this?


texts: Can Compressed air be used as a thrust component in a spacecraft to propel the craft through space or to orient the craft?

texts: Hello I was watching a video recently about aircraft carriers and how they use compressed air to propel aircraft off the ship. It go me thinking if I had, maybe a 50cm x 50 cm x 50 cm spacecraft that was put into orbit. Would I be able to use compressed air as thrust to orientate the space craft? or even better would I be able to use it to give the space craft a greater distance from the Earth?


texts: Force to compress flexible elastic tubing

texts:
How would one work out the force required to compress flat, using a flat bar on top pressing down, a thick walled (15mm OD 10mm ID) piece of flexible plastic (PVC) tubing i.e. so reducing the x-sectional area inside the tube to 0?

Just looking for any way to approximate the real situation without having to use an FEA simulation.

Many thanks for your help!


texts: First glance: structural integrity of this roof

texts:
There's a rooftop we recently discovered with a great view, and it's easily accessible for us. Obviously we'd like to go up there a bit more, particularly in summer with a couple of fold up chairs or something. I was thinking of getting someone in to look at it properly to assess the structural integrity of the roof, but I figured it might help posting on here first to get an early opinion from anyone willing to offer some advice.

The roof feels solid. As with any metal roof, there's obviously a few minor creeks here and there, but as a whole it does feel strong with 3 people up there. It's also reassuring to note that workers go up there quite often, and hence the walkways that have been setup on it so far. We want to set something up similar to the current walk ways - a slab of plywood for instance that will distribute the weight evenly across the vertical seams when standing or sitting on the roof.

The roof area is 6.25x8.50m and here are some photos we took:

The advice anyone gives on here will not be taken with absolute authority - I understand there's only so much you can do with the limited data I've provided. All advice will be considered general and not relied upon, but whatever thoughts you have to share would be greatly appreciated. I'm particularly interested in comments of absolute rejection to us going up there, along with a reason of substance explaining why it's profusely dangerous for us.

Someone also talked about running the structure in the opposite direction to the support beams. Would this be better, from the point of view of safety?

Cheers!


texts: In ASD do you divide elastic or ultimate strength?

texts: In Allowable Stress Design (ASD) method, to find the allowable stress, do you divide the ultimate stress or the elastic stress (where the material becomes plastic) by the factor of safety? For example when using ASCE 7?


texts: Can an angular momentum vector be a couple vector?

texts: In my book, Vector Mechanics for Engineers_ Statics and Dynamics, sometimes angular momentum vectors and their derivatives are noted as a couple vector. there are not a single explanation about it anywhere though. A couple vector is defined by two equal, opposite force vectors, if I'm not mistaken. So I looked up on other books like Engineering Mechanics_ Dynamics, but there is no such expression in the book. I don't know what the author of the first book I mentioned here intended to say.


texts: Equation for the spring constant of an orthotropic, rectangular wire spring

texts:
I hope I can get some help with this problem as I've been struggling with it for a long time. I have a helical tension spring with radius $R$ and a square wire cross section and made of orthotropic material. I'm trying to derive an equation for the spring constant $k$ by equating the energy stored by the spring $\frac{1}{2}kx^2$, where $x$ is the distance stretched, with the energy stored $U_t$ by a shaft of equivalent length so
$$\frac{1}{2}kx^2=U_t$$

As explained in the title, I have a particular situation because the material is orthotropic and the cross-section of the shaft is a rectangle as shown in the image above. I already have an expression for the torsional rigidity $GJ$ of an orthotropic rectangular shaft with shear moduli $G_{zx}$ and $G_{zy}$:
$$GJ=a b^3  G_{zx} \beta$$
where
$$\beta=\sum_{n=1,3,5...}^{\infty}\frac{32 c^2}{\pi ^4 n^4} \left(1-\frac{2 c }{\pi  n}\tanh \left(\frac{\pi  n}{2 c}\right) \right)$$
and $c=\frac{a}{b}\sqrt{\frac{G_{zy}}{G_{zy}}}$. When I equate
$$\frac{1}{2}kx^2=U_t=\frac{GJ}{2 L}\theta^2$$
I can plug in $\theta=\frac{x}{R}$ (the angle the shaft has been twisted by is roughly equal to the angle each coil of the spring gets stretched by) so
$$k=\frac{GJ}{L R^2}$$
where $L=2\pi R N_a$ and $N_a$ are the number of active coils in the spring. To me the equation looks complete but the problem is that when I enter values like $a=0.005$m, $b=0.0025$m, $G_{zx}=1159.1$MPa, $G_{zy}=974.3$MPa, $N_a=5$, and $R=0.01$ I get $k=632.642$ instead of $k=2780$, which is the right answer.

Since I have that the torque on the shaft is $T=ab^3G_{zx}\theta\beta$ I tried other equations for $U_t$ where $U_t=\frac{1}{2}T\theta$ or $U_t=\frac{1}{2}\frac{T^2 L}{GJ}$ but none of the answers come even close, $198.75$ and $62.4393$. Am I doing something wrong when equating the two energies?


texts: Is the center hole important on car wheels?

texts:
I came across with this discussion about this topic, however it doesn't address the answer clearly.

What is the safety role of center hole (A) on the vehicle wheels? Is it supposed to carry the weight on the wheel and take the stress over from the wheel lugs?

Or, is it there only to help on assembly of the wheel?


texts: Rotary to linear motion - how to make upside down “hammer” mechanism?

texts:
I’m not an engineer, however I think this place is the best one to find an answer to my question.

So my problem is as follows: I need to create a mechanism, preferably driven by a dc motor, that will hit the surface above it as hard as possible for a small DC motor. Like a sort of hammer, that is supposed to hit the surface above it (above is the keyword, I found DaVinci’s hammer mechanism, but it works based on gravity, which is not really helpful in the opposite direction). I’ve tried to research rotary to linear mechanisms, but all of them look like they will stop when the linear part hits the surface above and cannot go further. Can you suggest something?


texts: Creating an extrude in creo parametric 5

texts:
I’m trying to create the following extrude.

I have created a crankshaft based on the following sketch:

I then removed material as follows, which is placed on the rear surface of the shaft.

The material is removed successfully, however my final result has a thick extruding circle around the top of the crankshaft.

What am I doing wrong ?


texts: How determine the compression of a beam with a concentrated end load in the x axis?

texts:
I'm studying Electronics Engineering so I have almost no background in mechanics, just a little of statics and dynamics. I have recently started an internship in an investigation center where they make microelectromechanical systems (MEMS). I was asked to know the deformation in $y$- and $x$-axes for a cantilever beam with a concentrated end load. I have more interest in the vectorial mechanics rather than the material mechanics.

I have done research in Minhang Bao's book Analysis and Design Principles of MEMS Devices, where I found that the maximum displacement at the free end is:
$$w(L) = \dfrac{4FL^3}{EI}$$
if the load is on the $y$-axis.

But I couldn't find any information related to the compression in the $x$-axis. I came up with the idea of using a similar triangles approach but think that won't be so accurate.


texts: Why does the stress-strain curve decrease?

texts:
This is a stress-strain diagram

I have noticed that the curve decreases between points C & D and between E & F.
Why does that happen? I expected the curve to always increase since the tension force in a tensile test is always increasing and the cross sectional area of the specimen decreases, which means that the stress is always increasing.


texts: Motor shaft mounting with clamps and bushings

texts:
If I'm in the wrong section of stack exchange, please help me go to the right place.

I am trying to find out if this combination of motor shaft and clamps will work out.

I found these clamps/bushings

https://www.maedler.de/product/1643/1621/spannsaetze-com-b-bohrung-6-bis-100mm

and I'm curious if they will work out with the kind of shaft on this motor

http://mehatron.rs/step-motor-nema-34-86x155-60a-130nm-sa-duplom-osovinom

The main problem is that the shaft of that motor is machined and the clamp relies on the full surface of the shaft.

By the way, those clamps work for the motors with a shaft containing removable key ( for example MiGE 130ST-M15015 ).

Aliexpress is full of these shaft couplings, but i do not believe that they are sufficient to hold these kinds of torque levels, for example :

https://www.aliexpress.com/item/32967906911.html?spm=a2g0o.productlist.0.0.2f2c46a1ZWZH4p&algo_pvid=0a5001e7-7d75-4397-9a01-0e5d64cde7cd&algo_expid=0a5001e7-7d75-4397-9a01-0e5d64cde7cd-9&btsid=deae1df8-64c1-479e-9d65-e967ef04e93f&ws_ab_test=searchweb0_0,searchweb201602_8,searchweb201603_53

or these :

https://www.aliexpress.com/item/32956726953.html?spm=a2g0o.productlist.0.0.2f2c46a1ZWZH4p&algo_pvid=0a5001e7-7d75-4397-9a01-0e5d64cde7cd&algo_expid=0a5001e7-7d75-4397-9a01-0e5d64cde7cd-8&btsid=deae1df8-64c1-479e-9d65-e967ef04e93f&ws_ab_test=searchweb0_0,searchweb201602_8,searchweb201603_53

The good thing about these sahft couplers is that they can be made to fir the shaft perfectly, with 2 screws for the 2 machined parts i was talking about.

The forces are around 10 Nm and I want to avoid any kind of slipping.


texts: In freecad, how do you copy a sketch geometry from one plane to another?

texts:
I'm using FreeCAD, and I would like to copy all the geometry in a 2D sketch to another plane. So you have a 2D drawing on XY, and you want the same geometry to be copied to XZ. I can't seem to find an good way to do this.
One way I have tried is to copy the whole sketch, create a cube, and then map the geometry of the new sketch copy to the cube object face. It's quite a clunky method however and I doubt it's the most efficient way to do this.


texts: If I want to run an abaqus job (in Linux redhat) with user subroutine on parallel processors, how do I do that?

texts:
I work in Abaqus 2017 a lot. I have noticed that when I submit any abaqus job (that does not contain any subroutine!) via parallel processing (aka cpus=4 or 8), it runs just fine!

But, when i submit an abaqus job that contains a user subroutine with it via parallel processing, it won't run at all. It will not abort, or terminate, or do anything. The job will freeze.

The only way to run an abaqus job that has a user subroutine with it, is to run the job with single processing. This takes up a lot of time.

I do use the allocatable arrays for the job, and define them in my subroutine. Is there something I should include in my subroutine?

Could you please tell me why is it that the abaqus jobs (with user subroutines) get completely stuck with cpus of 4 and higher? Please?

Thank you very much!!!


texts: Temperature Control on and Induction Cooktop

texts: Many induction cooktops for sale have the option of controlling the temperature instead of setting the heat.  How does the temperature control typically work?  Is it an open loop or closed loop control system?  Is the temperature measured using an infrared sensor, or by some other means?


texts: Lift produced by an airplane wing is related to airspeed - this much is clear; a plane moving too slowly will stall. But what is that relation? Linear? Quadratic? Exponential? I don't need the exact equation, which is surely quite complex, just the character of the relation.


texts: How to make pivoting arms move symmetrically towards each other?

texts:
I have a basic design of two arms which need to be brought together. But I tried the design using a test setup and it did not work successfully. Here is a diagram of my design -

What I observed is that arm 2 moves up before arm 1. I want both of them to move towards each other to cause a compression, and away from each other to cause expansion. Is there any way in which that could be achieved using minimal design requirements?


texts: How the COP differs for a Vapor Compression Chiller without the U*A values of Evaporator/Condenser?

texts: I am trying to find the COP of a VCR system. I can reach the COP with using the EES(Engineering Equation Solver), without dealing with the UA values, i.e. just with the energy balances for the cycle. How the COP can differ, if I incorporate the UA values of the Heat Exchangers into the model? Is there any need for this?


texts:
I'm coming from the software engineering world (please don't rip me to shreds here), and I'm somewhat unfamiliar with the manufacturing process when it comes to cut and bend steel.

To provide broader details, we're making a pretty simple steel enclosure (basically a box), that will house some electronic, and need to build a relatively low number of them (a few hundred).

So my question is:

Are there CAD tools specifically created to allow for the design of a folded steel enclosure?
If I needed to provide a standard design document to a variety of manufacturing places to get quotes, which should my document look like? What info should it have about the enclosure?
What are my best resources to find a vendor to help us build something like this?

Sorry about how noobish this all sounds, I'd love to learn more about this process, any help is very appreciated.


texts: Are there any cold-expandable materials of significant expansion factor?

texts:
There are thermo-shrinking plastics, commonly used in electronics, which stay shrunk after cooling down. There are thermally expanding foams. The closest to 'expanding when cooled' I know is water, with ice expanding, but only by a small margin, a scarce couple percent.

Is there a material that would start expanding significantly when cooled? May shrink back when heated, or may stay expanded. It doesn't need to be as forceful as ice (which can explode rocks) but it should have at least 30% expansion ratio, the more the better.


texts: How can we prove that Thrust-to-weight ratio depends by max speed?

texts:
Raymer (see source below) affirms "Thrust-to-weight ratio is closely related to maximum speed". Why? How can we demonstrate it?

Source: Daniel P. Raymer Daniel P. Raymer "Aircraft Design: A conceptual Approach" Chapter 5, Paragraph 5.2 "THRUST-TO-WEIGHT RATIO" Subparagraph "Statistical Estimation of T/W" page 80.


texts: What 's the function of COMP pin(Pin 3) in LM5030 - Push Pull IC?

texts:
I'm a student. Now, I am learning to use LM5030 IC to design a Push-Pull converter. So, I read LM5030's datasheet and can not understand the function of COMP pin (Pin 3). The red line is Feedback circuit, input its connect to VOUT, output its connect to COMP pin.

Following the info in the datasheet, it's said: " The comparator polarity is such that 0 V on the COMP pin will cause a zero duty cycle". The duty cycle is to switch on/of 2 MOSFET. And in above figure, the output of the feedback circuit will make COMP = 0 when VOUT > 0, it means the duty cycle for 2 MOSFET will be zero.
That makes me can not understand. Did I miss something?

P.S: LM5030 datasheet


texts: Optimization: Most efficient way for multiple people to move boxes

texts:
We are moving house in a few weeks and have a couple of people helping moving the boxes. My previous experience from moving is of queues building up in small hallways and people getting tired from walking up and down the stairs, so this time, I intend to make this as efficient as possible.
Intuitively, it feels like specializing the labor assignment (e.g. one person offloading the truck, another walking boxes to the door, the third only walking up and down stairs) would improve efficiency, in that it reduces queue-building because people never run into each other. A rotation could then be made for assignments to reduce fatigue.
On the other hand, maybe the monotony in this, that I so carelessly disregard, will actually lead to a increased overall time - regardless of how many pizzas I buy them afterwards.
I did some googling to see if there is a more efficient algorithm for this; my thinking is that this must have been discussed to death when coming up with the car assembly lines in the early 1910s, but there is very little discussion around this on the internet - perhaps no one cares.
My question is therefore to: are there any other optimizers out there that have figured out the ultimate moving algorithm?


texts: Do contiguous laser curtains exists? and if not are there any lenses that could spread a concentrated beam into a "planar" beam

texts: The first photo is an example of a light curtain. I am certain that every individual beam is from an individual laser and receiver pair on both cases. Would it be possible to have one laser beam perhaps be directed from the top or side of the case to create a contiguous light "plane". Hopefully the picture below could help you visualize what I have in mind. The receiver end would have to be able to detect fluctuations of the laser beam at a reasonable resolution.


texts: What is "flow instability" in porous media?

texts:
Pressure drop across a porous medium can be described by the Forchheimer extension to Darcy’s law:
$$-\frac{dp}{dx} = \frac{\mu}{K_1}\cdot v + \frac{\rho}{K_2}\cdot v^2$$

where $K_1$ and $K_2$ are permeability coefficients that depends on medium geometry (Pitz-Paal
et al., 1996).

I just came across this paragraph in a paper studying the flow stability in porous media in solar volumetric receivers, which I couldn't digest at all:

  In the flow through a porous sample, the mass flow density is determined by the pressure difference between the two sides of the sample. The pressure drop is produced by a blower. Instability occurs when a pressure drop causes different mass flow densities

What blower? and what makes pressure drop cause different mass flow? (Keeping in mind previous equations)


texts: Fluid is flowing from nozzle in upward direction

texts:
If a nozzle is projected upwards with water flowing with a certain flow rate
then in how many ways can you find the diameter of the jet of water at a certain
height from the nozzle exit?

One approach- We can find velocity at that height and we know the discharge so we can find diameter from here
Do you have some other approach


texts: How are these springed ball connectors called? Can not find them without right name.


texts: How to determing convergence in a CFD model

texts:
I am simulating an axial turbine. Under relaxation factors are default.

Residuals are as follows:

And also, mass flow rate, torque (in direction of Y) and inlet and outlet total pressure are as follows(in order to judge on convergence):

Torque (in direction of Y):

Inlet and outlet total pressure:

Mass flow rate in inlet and outlet:

Now, I have some question about Residuals:

As you see in first figure, residuals decrease until about iteration of 1500 and then after iteration of 1500, residuals increase. I want to know that this event is logical or not. I already thought that residuals should decrease decidedly because of convergence. But in this simulation, residuals increases and decreases!! What is reason for this event?
According above figures, Is solution converged?


texts:
I'm trying to design a metal surface with micro-perforation for a product and light it from other side with LED, such that the perforated pattern appears only when lit.

In my previous prototype, which used laser drilling (20 micron holes) for perforation, there was considerable warping of the metal film (around 0.3 mm thick) which rendered the prototype unusable (aesthetically)

Another problem I had with the prototype was that the light was not getting through perforation evenly i.e., I was not able to see the light from different angles.

On initial research about laser micro-drilling I found that the thermal conductivity of material plays important role in heat affected zone, which could result in warping. The material used for prototype was stainless steel, which has comparably lower thermal conductivity than aluminium.

What care needs to be taken to avoid or reduce the HAZ and hence the warping?
For the visibility of light through perforation, will the hole size and spacing directly affect this?

I am trying to achieve the appearance like shown below

Misfit Shine fitness band; the micro-perforation on dial is invisible when unlit.


texts: What screw to use with 1.8mm thick countersunk brackets?

texts:
I have a few brackets that are 1.8mm thick with 4.5mm countersunk holes like this:

The countersunk machine screws that I've found have head heights of at least 2.2mm (some 3.2mm). This is taken from https://www.mcmaster.com/screws

Anyone know what sort of countersunk screws should be used with these brackets? I can't seem to find any common ones with a head height of ~1.5mm.

Thanks


texts: I have a bucket full of water with a hole in bottom, lying on a spring like in the picture I have attached. Is this system considered to be linear or not?


texts:
I'm interested in whether a flat rubber washer or equivalent is good enough to replace an o-ring in a low pressure application (edit: I meant low pressure differential. My bad.). The reason is that flat washers might be easier to design for if you have a dynamic seal application where one tube has to "air lock" against another tube.

The application is to mount an air sampling tube in such a way as I can automatically sample air and then, later, automatically heat the tube to 200C and pull the vapours.

The tube is just a thin walled (0.25mm) steel tube 6mm or so in diameter and 40mm or so long). Here's how I initially imagined the system:

So some sort of automatic airlock connector tube could move out, seal against the o-ring and then stop at the green washer. The green washers might be something like mica or teflon, something able to take the 200C while insulating the holder - I want to heat just the tube, not everything connected to it! Here's a cross section:

I have some issues with this - firstly I'm not convinced that a metal to metal seal (tube against holder) will air seal properly, even when pushed by the automatic connector. Perhaps another o-ring is necessary?

Secondly, mica washers aren't flexible (I think) and getting a washer into a groove like I've shown might not be possible. If I replace the washer with some form of flat seal which captures itself against a lip, perhaps this type of form:

As I would have to make the connector by machining or other process, perhaps this would make the design easier. But is such a v type seal effective at air sealing? The difference is that in the O-Ring, positioning is all that is necessary but with a flat washer type, you need force too (related link: What are the common failure points of waterproof cases?)

EDIT: Clarifications:

I believe I tried to present too much information at once and missed the important points!
The pressure differential should not be very high. I'm considering a flow, from outer atmosphere, of a few litres per minute through a sorbent. If the pressure diff was more than 1/2 atm I'd be surprised.
The green washers are really to provide heat isolation, not air sealing. If the sorbent tube is 200C I didn't want the entire system to try and be 200C too!


texts: Safety standards involved in building a zipline

texts:
I'm a ropeway engineer with a lifetime of experience. I would like to build a zipline in a public place (officials agreed to support me).

Where can I get safety standards for constructing a zipline? I live in Georgia (country) and it's a new thing here, so I was thinking about adopting European standards.

I just don't know where to find it or which company to contact.


texts: How can I attach a rotary encoder to a retractable dog lead?

texts:
I need to know how I can attach a rotary encoder to something string/wire that I can pull and it retracts automatically

My idea was to take apart a retractable dog lead leash and affix it to it somehow, but I'm not seeing how I could make that work.

I've included a picture of the dog leash(right) and the rotary endoer(left).

The only goal here is to measure distance/velocity of a retractable string/wire. I'm not tied down to using a dog leash or rotary encoder, open to any suggestions.

Is there any other solutions that are not very expensive?


texts: Boeing 737NG pickle fork cracking. What determines the fastener layout?

texts:
Boeing 737NG aircraft are currently being checked for cracking in the "pickle fork" assembly that attaches the fuselage to the wings. The affected joint has 4 fasteners that attach the fork to the wing. It's intended mostly to resist shear loads, as the fuselage twists relative to the wing. Boeing's inspection data is available at the FAA. That includes this image:

There is much discussion of this problem at the pilot's forum pprune.org Someone there states that the fasteners are meant to be an interference fit in holes that have been reamed and cold worked, and that the cracks have occurred because holes were drilled 6 thou oversize.

Why would this arrangement - 2 large fasteners and 2 small fasteners - have been chosen?
Boeing refer to the small fastener area as the "fail-safe strap". In what way might this be regarded as fail-safe?
Where is it appropriate to use interference fit fasteners in these specially prepared holes?
Why would drilling the holes oversize lead to the observed cracking?


texts: How do I calculate Pressure drop across relief valve and then force on piston?

texts:
So, I'm designing a basic downhole hydraulic tool cutter of an OD = 5 1/2 in., and my tool contains a relief valve and a piston. I am trying to calculate pressure drop across the relief valve so that I can calculate the force on piston that activates the knives. Please help me how can I achieve this.
Q, flow rate =  30 L/s
Pressure = 25 MPa

I haven't completed the drawing yet, but I'm referring to this design. I was suggested to add a valve and a spring.


texts: How to rebuild and lubricate worn plastic parts?

texts:
I'm hoping to rebuild a joystick (sidewinder strategic commander), though the parts inside it are a bit too wobbly because they have been worn beyond tolerances. Due to this wobbling on one (rotation) axis, the sliding action is rough on the x/y plane.

Any recommendation on how and what to use, if there is a compound I can apply to make up for what was lost through friction?

How can I bring the plastic mechanisms back to spec? Also what lubricant is suggested afterwards?


texts: What mechanism in the radar that enables the switch between transmission and reception?

texts: I think there is a mechanism that switches off the transmitter in order to turn on the receiver in the antenna. Do you know the technical terms by which this is done?


texts:
I'm struggling to confirm the Velocity in an open channel flow with 0 percent slope.  Water enters the channel from an open pipe.  The rectangular channel dimensions (66' Long x 3.33' W x 6.75' D) and Q (15 MGD) are known.  The channel is concrete and empties into a larger basin via free fall (i.e. no weir at end).  I would use mannings; however with no slope I'm stumped.  Any help would be appreciated.

P.S. This is a real world problem at a waste water treatment plant I'm working on.

Thanks in advance.
C


texts: How to estimate the tensile strength of inch diameter steel round?

texts:
The tensile strength for 1045 TGP Precision Steel Round is said to be 91 ksi. Although, different diameters must be a factor, right? Would a 1" diameter rod be 104.5 ksi or 1045 ksi?
Say I want to make a seven foot barbell, requiring about 150 ksi. Is it possible to get there by hardening some sort of steel? Or will that make it too brittle for lifting weight plates?


texts: How can I prove the location of centre of gravity of centroid?

texts:
In a book, There is chapter of "Centre of Gravity" before "Moment of Inertia" and in the chapter Centre of Gravity, the list of some centroid and it's location of C.G (i.e x̅ and y̅) is given. You can refer similar table from wikipedia. And with the help of it, the examples of finding the location of C.G is explained.

But I want to prove the location of C.G for that centroids. For example, I want to prove that y̅=4r/3π for the semicircular. How can I prove it?


texts:
While architectural features are oftentimes more aesthetic than they are technically complex, this still seemed like a suitable question for here.

I am working on a project for an industrial type facility that will include one or more large exhaust air stacks. These stacks are part of an odor control system, so while the air will be clean, the final step is to get the air high over the area for the purposes of dispersion.
The facility will be in a relatively nice part of town so the residents don't really want to see the stack. Are there proven ways to hide such a structure or to make it more appealing similar to what is done with cell towers disguised to look like trees?


texts: How to Make an Object Able to be Screwed In/Out With a Sideways Knob

texts:
I am trying to make a device that can go up or down a screw by twisting a knob, kind of like a wing nut, but the wing would be sideways (I suppose). To clarify what I mean by this, please see a simplified version in a diagram below.

I think this type of engineering has already been used in various devices, such as a microscope, where the course adjustment knob will raise or lower the "stage" of the microscope.

Does anyone know where a part/device like this could be found, or how I would go about making something similar?

Thank you so much for your time and kindness,

Kelsey Nealon


texts: How to design a magnet to handle a known force?

texts:
There is a metallical structure. I can estimate how much steel are in it. I would like to know how tall/strong a magnet should be to maintain a certain object to the metallical structure.

The object is not that heavy, but it is submitted to multiple forces, like air flood, so it need to be sufficiently strong.

Knowing the force to handle, how could I know the size and optimal disposition of the magnet?


texts:
I understand that for a rectangular c-s the shear stress distribution is parabolic and the max shear stress occurs at the neutral axis and has a value of 1.5V/A. Where V is the 'applied shear force' and A is the cross-sectional area.

But this in turn then means that the shear force at this point is equal to 1.5V ( 1.5 times larger than the applied shear force) - which seems a tad strange physically.

Is this due to the fact the the average shear force (average shear stress x cs area) is equal to the applied shear force? This is the only way it makes sense to me.

Thanks!


texts: classify ECG signal using neural network

texts:
I am looking to classify ECG signal using with neural network. I have never done signal analysis before.

From the samples of data I have, I have noramlised, transformed using the FFT , get the pics, amplitudes and the frequencies.
Now, How do I feed those values, to my ANN (Artificial Neural Network)? This looks like a tuple(pair of value) for each row.

Sorry. I have no much experience in engineering but I am recently challenge myself on area that is not particularly mine.


texts: some kind of gearbox for driving a removable shaft; is there a name for it?

texts: This is a noob question, please don`t be too harsh on me. I would like to use a motor for turning a mixer. The shaft of the mixer should be removable and I though of 3d printing a case which holds the motor and a gearbox in place. I made a very simple drawing of how it should look like (or how i can imagine it). I was wondering if such a thing already exist but I do not find it because I do not know the name. It should be easy to remove the shaft. Some sort if quick release/fix. The motor will run at 300 to 1000 rpm at low torque.


texts: How to model a driven wheel with no slip

texts:
I'm working on a design problem, and I'm having trouble figuring out how to model the torque needed to drive a bike tire at a set acceleration.

Let's say I have a tire with normal force between tire and ground Fn, coefficient of static friction between tire and ground u, and diameter d.

What is the necessary axle torque to drive the tire at desired linear acceleration a from standstill without slipping? How great can a be if you want to avoid slip?

Also, the problem doesn't give me a tire mass or moment of inertia. Is this problem possible without those?


texts: How to estimate the time cost of interrupting a task and picking it up again later

texts:
In terms of personal productivity (single machine scheduling) when a task is interrupted before being done in order to switch to a different task, it incurres a 'tear down' time cost - putting tools, files, materials away etc. It also incurres a set-up cost when you pick it back up again - getting the tools, files, materials ready, reviewing the work that was previously done etc. Given a limited set of information about the task, how would one estimate the tear-down and set-up cost associated with interrupting a task?

Let's say that we have the following information:

Initial total estimated time to complete task.
Current estimated remaining time to complete task.
Task value (this could be an amount in $ or some other measure of importance)

Is there a good, recognized, heuristic to evaluate the time cost associated with interrupting a task? Maybe something as simple as "10% of the task's total estimated time".


texts: What is the opposite of "parallel" in engineering?

texts:
The two towers of the Verrazano Bridge are not parallel: they are [???] to account for the curvature of the earth.

What is that word?


texts: How can the bearing capacity of an existing tarmac road be determined?

texts:
From a typical ground investigation borehole log the tarmac thickness is recorded but no tests have been carried out on the road surfacing or formation level. I'm after an approximate bearing capacity of the road surface, including the contribution of the surface itself and the sub-formation under it.

Obviously heavy vehicles can be resisted, can I take a typical heavy vehicle and assume a minimum bearing capacity from the bearing stress under the vehicle or is there another/better more reliable method?

I can't carry out further insitu tests.


texts: Are there any precedent designs for a mechanically-delayed pressure release valve?

texts:
I need to release pressure of around 50psi, after 3-4 seconds of initiating, from a vessel using a mechanical switch. I had considered a pneumatic solenoid, but I want to forgo the inconvenience of charging the device with electricity in addition to the air, as well as save the space that would be needed for the bulky solenoid, circuitry, and battery.

I therefore need what would essentially be a "mechanical-fuse" that releases pressure after a delay when triggered. I considered a screw-type piston that gets forced along a track by the air in the vessel itself, which at a set psi could guarantee a specific time of release. I also need the system to be no longer than 5 inches along the axis of released pressure. Does a "screw-fuse" sound like a viable idea? Does anyone have any other sources for a mechanical fuse of this type, or an idea of their own?


texts: What are characteristic values for a piston pump?

texts:
For a piston pump you can calculate/measure things like,

Average Volume flow rate (m³/s)
Geometric Values (Surface)
Pressure over time
closing times of the valves
energy conversion efficiency $\eta$

besides those, what charateristic values are there?

 (example of a type of piston pump source)


texts: The relationship between the I control and the stability margin

texts:
While I'm reading the paper, it said
"The I control can makes the phase lag, so it can makes stability margin reduced."
Words are not same as that, but the meaning is the same.

How the I control makes the phase lag in the PID controller?
If the plant's transfer function is $G_p (s)$, the open-loop transfer function $G(s)$ is
$G(s) = \left(\frac{k_i}{s} + k_p + k_d s\right)G_p (s)$
when we use the PID for the controller. After substitute $s=j\omega$,
$G(j\omega) = \frac{\left(k_i-k_d\omega^2  \right)j+jk_p\omega}{\omega} G_P (s)$
So, how can I find that the I controller makes phase lag?
How the phase lag makes stability margin reduced?
In the paper, it wrote "stability margin". I think that's phase margin. Anyway, how can I get the relation between 'stability margin' and 'phase lag'?

Thank you for advising!


texts: Can temperature gradient keep concrete wall below 100% RH in 100% RH atmosphere?

texts:
Consider a high and wide concrete wall of say 30 cm thickness, covered with a sheet of vapor barrier on one side, and a sheet of say 30 cm thick and effective insulation on the other side.

The vapor barrier completely blocks water vapor. The insulation lets water vapor through and leads away any condensed water downwards where it is drained away. The concrete lets vapor vapor through, albeit slowly.

The air on the vapor barrier side (the inside of a hypothetical building) is 25°C with 50% Relative Humidity, and the air on the insulation side (the outside of a hypothetical building) is 10°C with 100% RH. See illustration above which shows the wall from above.

According to some vendors of basement insulation, a setup like this will cause the concrete wall to become relatively dry due to vapor pressure towards the insulation in which the water vapor will condense and allow the water to drip down and then be drained away.

But I can't make myself understand how this process works from a physical point of view. I thought an infinite source of water vapor spreads out until all air is saturated with water, so I would expect the wall to end up having 100% RH.

Will the wall end up relatively dry, at say 70% RH? If yes, how exactly?


texts:
I recently learned the basics of automotive clutches, more specifically friction clutches. Here is a simplified version of their operation explained to me (the car starts at rest): The engine and the transmission are connected via friction plates. When the clutch is pressed down, the plates are separated. When to clutch is released slowly, the plates press harder together and the friction between them causes the car, via transmission, to gain speed.

But what confuses me is this: The car weights many tonnes, and the engine spin very fast. When the plates are coming into contact with each other, they are slipping until the car begins to move. Isn't this causing a huge amount of heat to be produced? And most of all, how are the friction plates manufactured so that they don't "smoothen out" very quickly, reducing the friction coefficient between them? I understand that they do wear out and need to be replaced sometimes, but considering the high torque and speed of the engine, you would think they'd wear extremely quickly.

Also, isn't the force needed to press the plates together enormous? Considering the large mass of the car, how kind of mechanism is used inside to car the press the plates together? And how can a person then, using only one foot, be able to again separate these plates? I assume the clutch pedal is connected to some kind of hydraulic system to amplify the force?

I've Googled a lot and watched several Youtube videos on the matter but they all simply show that friction holds the plates together and pressing the clutch releases them.


texts: How to compute the transfer function from a response graph

texts:
I understand that the model for a first order system is
$$G(s)=\frac{k_m*e^{-\tau s}}{T_ms+1}$$

In this case $\tau=3$ and the system gain $k_m=10$, correct?

I need to calculate the transfer function and after that I can calculate the poles by solving for $s$ in the transfer function's denominator. Am I on the right track?

How can I calculate the transfer function given this graph? I don't have access to a book.


texts: How does polygonal effect affect the effect of angular synchronization in car engines' timing train drive?

texts: Is a regular roller train drive used in most car engine's timing chain drive? If so, wouldn't the polygonal effect affect the accuracy of strict angular synchronization between the camshafts and the crankshaft?


texts: Did the pressure unit "bar" change definitions since the 1930s?

texts:
I don't see anything in Wikipedia about it, but (from this question) when I try to reproduce the equations in this 1933 paper, I get values 106 away from the values in the paper.  When I reproduce this equation, for instance:

I get 5×10−11 bar

Likewise, it says:

Sound intensity and pressure are related by acoustic impedance of air Z0 = 400 N·s/m3.

So

1.9×10−16 W/cm² ↔ 2.7×10−5 Pa
71 dB below 1 bar = 2.8×10−4 ⋅ 1×105 Pa = 28 Pa


texts: Calculate hydraulic torque from motor HP, hydraulic pump and gearbox

texts:
I am curious about the design considerations for a hydraulic system.

Let's say you have a 3HP 1200RPM motor
you also have a hydraulic pump that's rated 4LPM and pressure of 40MPA rated for 40RPM MAX

You can put many different types of gear box on the 3HP motor to get it to operate in the N-40RPM range

Let's forget about the power loss through heat when using the gearbox.

I am trying to understand the relationship between HP and RPM of the electric motor, Pressure of the system and output Torque.

Let's say I am working at 200Bar, electric motor doing 40RPM and the hydraulic motor running at 4LPM.

How would that compare to say going to 20RPM and keeping 200Bar and 4LPM.

I do understand that raising the pressure would increase the heat and possibly require cooling.

Any suggestions on how to calculate these relationships?


texts: How is the wattage of an incandescent light fixture determined?

texts:
I've seen light fixtures with varying wattage rating. From 30W to 100W even though the actual socket is the same.

What is the limiting factor, why can't I put say a 75W bulb in a fixture rated at 50W?


texts: Sign convention for deflection and slope of beam?

texts:
What is the sign convention for deflection and slope of a beam as shown in the diagram below?

When I derive the formula using Euler-Bernoulli for deflection and slope myself, I end up with - deflection at y, - slope at A and + slope at B.

However, using formula I found, for the same scenario:

$$y=\frac{Px}{12EI}\ \left(\frac{3l^2}{4}-x^2\right)$$

$$θ1=θ2=\frac{Pl^2}{16EI}\ $$

Gives + deflection at y, + slope at A and + slope at B.

What is the convention here?


texts:
In my text book it's written that head losses in elbows is produced by secondary flows..
I have looked for the meaning of secondary flow,  and I found that :
The primary flow is parallel to the main direction of fluid motion and the secondary flow is perpendicular to this..
But I didn't find why does it occur.. Can you help me?


texts: Solidworks export the 3d points of a spline

texts:
Is it possible to ( how do you ) export a series of points along a spline.
A spline has been created in 3d from various segments.
I would like to export a table of 3d points along the spline starting at one end and every mm or so along the spline.

The result would be a file with Z,Y,Z points that are every mm along the spline.
I want to end up with lots of little line segments that approximate the spine.

I have seen a few tutorials on how to export intersection points but that in not what I am looking for.

Thanks


texts: How does the Nest Learning Thermostat bezel rotate without bearings?

texts:
Looking at both the Nest iFixit teardown and this Nest bezel replacement tutorial, it looks like the Nest stainless steel bezel mounts directly to the PCBs and displays inside.
The Nest bezel is able to rotate freely though (and very smoothly, I should add) while the components inside remain fixed - how is this possible? I was under the impression that this smooth, frictionless connection between a rotating body and a stationary body was only really achievable through ball/roller bearings.


texts:
I recently saw this kind of "end of tube fixation design" on a website (see picture):

I am more specifically interested to the "fixation head with 3 screws". Basically, this is an end clamp for a tube, that allows to mount the tube perpendicular to a surface with 2 screws.
I cannot find such a part online easily. Do you know if it has a name / where I could find it?


texts: I am thinking on analog circuits, whose circuit design could be read (or, at least, significantly altered) from software. Do they already exist?


texts: Are latest software engineering methodologies, such as Agile, being adopted by other engineering disciplines?

texts:
I know comparatively little about general engineering methodologies, but it strikes me that the (now outdated) "waterfall" method is possibly very apt for mechanical engineering. Perhaps advances in rapidly changing software engineering could also be applied.

Are software methodologies influencing other engineering disciplines? Or vice versa?

Wikipedia's page on engineering says:

  Koen argues that the definition of what makes one an engineer should not be based on what he produces, but rather how he goes about it.

Which vaguely implies that development processes are to some degree ad-hoc, given that neither the methodology section of that page, nor the problem solving subsection of the engineering page make any references to development stages in the precise ways that is widely encouraged in software engineering.

So why the apparent lack of processes?


texts: mounting a transducer under a polycarbonate jar for fluid level detection

texts: I am working with a tdc1000-tdc7200 evm board for water level detection. I am trying to mount a steminc 1MHz ultrasonic transducer under a polycarbonate jar to measure the water level in the jar. According to TI's recommendation (source) I am using Cyanoacrylate for transducer mounting. I am wondering is there other options of adhesive that I can use for mounting? I am looking for an adhesive that does not react with water. Also TI recommended using hot glue over sensor which also absorbs. Is there a better alternative that does not hinder transducer performance?


texts:
I was reading about the new Intel Xeon Phi processor on Intel's site

https://software.intel.com/xeon-phi/x200-processor/remote-access

and ones of its features is:

Highly-parallel performance: Features up to 72 cores with deep out-of-order buffers.

I was looking for a basic description of these buffers that highlights maybe their purpose (ie parallelism) and behavior. Are these buffers used in the cache?


texts: What is the purpose of grid-like details on engine blocks?

texts: It is common to find this kind of detailing and patterning on engine blocks and related parts. Older engine blocks display much more flatter and simple geometry and this kind of mold work must come with a considerable production cost. What is it's purpose?


texts: Heat loss calculation and Energy Balance

texts:
The image shows the CAD model of the annealing zone in a galvanization simulator. The zone is electrically heated with a AC current of 5597A at 2.09V. This whole zone is surrounded by insulating material. The power input is 11.7kW. Electrical energy is converted into heat energy. The sample rods are inserted into the heating pipe for annealing.
We calculated various heat losses/power losses in the system which are as follows:

The heat loss into the sample rods, measured in the cooling water is 2 kW
The heat loss into the top and the bottom flanges, measured in the cooling water is 3,4 kW
The outside area of the Zone insulation is 78°C in average, the area has 0,65 m². Estimated heat loss should be about 0,7 kW (according to housing heating tables for 1-plate heaters)
Heat losses in sum: 0,7 kW + 2 kW + 3,4 kW = 6,1 kW

The consumed electric power to heat the Zone is 11.7 kW
In principle, the input energy (electricity) should be equal to the out energy (heat).
I wanted to find other heat sinks or power losses (e.g. electric losses). What are the various heat losses in the system?
What am I missing here?


texts: Gas cleaning in activated carbon filters - How much moisture is needed and why?

texts:
Biogas and sewage (typically around 60% CH4, rest CO2) gas is typically treated in activated carbon (ac) filters to remove H2S and siloxanes. The ac filters need a small amount of oxygen (>0,4%) to work. Additionally, the moisture content needs to be controlled. This is where the confusion starts.

It is logical that the gas may not be saturated with water, as condensation in the filter would cause ac particles to clog and would lose filter surface. But I've seen different statements about the optimum moisture content: One source claims 50% relative moisture is optimal, others go for drying the gas as much as economically sensible (10-30% rel. moisture). So far I've found no reason given for why water is even beneficial.

What is the role of water in gas cleaning by ac, and how much is actually optimal?


texts: What is an effective method of turning polyurethane foam into a powder?

texts:
I want to grind flexible polyurethane foam to a size of about 50-100 microns.
The feedstock is shredded 1.5 lb/ft^3 polyurethane foam.

I tried a commercial meat grinder, which works but is very slow, and
I tried a hammermill, which works, especially if it's mixed with ice, but nothing's really been effective.


texts: Accessing parameters in HEX file (ECU program) using A2L file

texts:
I was given the compiled program from an automotive ECU by my colleagues in HEX-format, as well as the corresponding A2L-file. For my project I need to read the applied parameters from that HEX-file.
I want to do this automatically, via a MATLAB function, as the parameters are used as inputs in a Simulink model.

Now as an example the HEX-file looks like this:

[…]
:2001C00000000000000000000000000000000000000000000000000000000000000000001F
:2001E0000000000000000000000000000000000000000000000000000000000000000000FF
:2002000054710780809A0780809A0780809A07808C530680000011A0140011A000000000D4
:200220000000000000000000000000000000000000000000000000000000000000000000BE
:2002400000000000000000000000000000000000000000000000000000000000000000009E
:2002600000000000000000000000000000000000000000000000000000000000000000007E
[…]

(please note that it is just an exemplary excerpt)

The address for a certain parameter can be read from the A2L for example as ‘0xA0143B0B’.
From the specification on the XCP-protocol I know that the address in the A2L is 40-bit long  (32-bit address and 8-bit extension).
As you can see the address I read is 64-bit.
Now if I got it right in my exemplary address ‘A01’ is reserved, ‘4’ is the address extension and ‘3B0B’ is the actual 32-bit address.

Can anyone confirm this or correct me if I am mistaken?

Reading the data from the HEX-file in position ‘3B0B’ is incorrect. My colleagues exported the data for me in a text file to verify my results, and they clearly differ.
Are the ‘:’ counted when the position is addressed?

Edit: I just found out that 'A01' defines the RAM-Segment the data is written in. But how can I find this Segment within the HEX-File?


texts: Change material properties of elements in named selection in Ansys workbench using APDL commands

texts:
How to change the material properties, i.e. Young's modulus and Poisson's ratio, of a set of elements which is defined by a named selection in Ansys workbench using a command snippet of APDL code?

The named selection is denoted steelElements.
An appropriate material, named Structural Steel is defined in an "engineering data" system.


texts: How do I create a graph of the phase angle and response of a harmonic excitation in Matlab?

texts:
In my course of dynamics of structures, I am struggling with some basic principles. As a practice, I am plotting (or attempting to plot) the curves that are shown in the course book, with the help of Matlab. For example, I want to plot the phase angle theta as a function of beta, the dimensionless frequency, for a damped SDOF. The code I have is the following:

%Stiffness of the spring in [N/m]
k = 1;
%Mass in [kg]
m = 1;
%Damping constant in [Ns/m]
c = 0.1;
%Initial displacement in [m]
u_0 = 0;
%Initial velocity in [m/s]
v_0 = 0;
%%
%Resonance frequency in [rad/s]
omega_res = sqrt(k/m);
%Resonance frequency in [Hz]
f_res = (omega_res)/(2*pi);
%Eigenperiod in [s]
T_res = 1/f_res;
%%
%Critical damping in [Ns/m]
c_c = 2*sqrt(k*m);
%Damping ratio in [/]
xi = c/c_c;
%%
%Damped eigenfrequency in [rad/s]
omega_d = omega_res * sqrt(1-xi^2);
%Damped eigenfrequency for strongly damped system in [rad/s]
omega_hat = omega_res * sqrt(xi^2-1);
%%
%Timevector
t = 0:0.1:100;
%Betavector
beta_v = 0:0.001:4;
%D as a function of beta
D = 1./sqrt((1-beta_v.^2).^2+(2*beta_v.*xi).^2);

plot(beta_v,D)
axis([0 4 0 10])
xlabel('Dimensionless frequency [-]')
ylabel('Dynamic amplification factor [-]')

%theta as a function of beta
theta = atan((2*beta_v*xi)./(1-beta_v.^2));

figure
plot(beta_v,angle(theta),'m')
axis([0 4 0 pi])
grid on
xlabel('Dimensionless frequency [-]')
ylabel('Phase angle [rad]')

But plotting gives me the curve of an undamped SDOF. The curve I get:

The plot I am supposed to get:

Does anyone have a clue what is wrong in my approach?

A second struggle occurs when you want to plot the the response for a particular beta. The curve I achieved was not what I expected. My code is the following:

%Response
beta_a = 0.2;
D_a = 1./sqrt((1-beta_a.^2).^2+(2*beta_a.*xi).^2);
theta_a = atan((2*beta_a*xi)./(1-beta_a.^2));
p_hat = 1;
omega = beta_a.*omega_res;
u_p = p_hat/k.*D_a.*exp(i.*(omega.*t-theta_a));
B = u_0 - p_hat./k.*D_a.*exp(-i.*theta_a);
A = (v_0 + xi*omega_res*B - p_hat/k*D_a.*i*omega*exp(-i.*theta_a))/omega_d;
u_h = exp(-xi.*omega_res.*t).*(A.*sin(omega_d.*t) + B.*cos(omega_d.*t));
u = u_p + u_h;
figure
plot(t,real(u))
grid on
xlabel('Time [s]')
ylabel('Displacement [m]')

Can anyone help me with this line of thought? What's wrong?


texts: Why does exit pressure match back pressure in Converging Diverging Nozzles?

texts:
I am trying to understand why normal shocks are caused in Converging Diverging Nozzles. My textbook explains that since the exit pressure must match the back pressure, the normal shock is the only mechanism that can make this happen, which I understand.

However, why does the exit pressure have to match the back pressure? What if it did not? Then simply the jet of fluid exiting the converging diverging nozzle would expand or contract under the pressure driving force induced with the back pressure.

Any clarifications welcome.


texts: Modeling composite material fibers orientation in a FEA

texts:
I am looking for guidance for analyzing composite materials that are reinforced by fibers of some sort. A good mental model would be bars of steel in concrete. The concrete will have its own physics that is essentially isotropic where the steel only plays a significant role in a given direction.
My actual problem has more than one orientation but if I can at least understand how they do this in principle I may be able to take it from there.
I am not sure how to specify a "fiber" and give it a length and orientation. The papers I have been reading do not seem to explicitly model the fibers but some how capture this anisotropic behavior in the elements. I am somewhat of a novice on this space and the papers I have seen thus far assume a level of competence to fill on the gaps.
Any advice or reference to a tutorial that does something similar would be much appreciated.


texts: I have an 80 ft metal tower, that is cemented into a dirt ground, that houses two antennas to send and receive Wifi. The tower's power source is not a home. It has a dedicated line, that runs directly to it's own power meter. The tower is about 300 feet from a concrete home. The internet company says, that since the tower is buried in dirt, it is "already naturally grounded". I have other people who are saying it is extremely dangerous to not have it properly grounded with a copper rod. What are the potential dangers if lightening were to strike the tower?


texts: Material for suspension that stiffens in higher speeds?

texts:
I was hoping there exists a material like hard rubber used in bushings, but has the property to stiffen when exposed to vibration with high frequency.

So, my application is something like a small dampening suspension on a system with stiff wheels so in high speeds the dampening will get stiffer due to the higher frequency vibrations that occurs from the small wheel rolling on a surface like asphalt. So the system is soft in low speeds and stiffer in higher speeds. Do you guys know of any material or system with these properties?

Update:
Honestly, I was looking for something small and hopefully something not reliant on a power supply to change the ride characteristics of a skateboard/longboard truck depending on its speed. My theory is that if the bushing on the truck gets stiffer in higher speeds the ride is more stable and less prone to speed wobbles. ( Stiff bushings/dampener requires more weight to turn the board = less wobble in higher speeds)

I guess this is not that difficult to make using something mechanical with an electric speed sensor, but a better solution would be if such a material exists or if its possible to make a bushing molded in some material that stiffens when a small electrical current is applied.


texts: For a small valve in a fluid system, what is the relationship between pressure and flow rate?

texts: The specific example I have in mind is a car tire with a small leak in it.  As the pressure increases, does the outflow of air increase linearly, i.e. $v\propto P$, or does it have some more interesting behavior?


texts: Principle of Virtual Work vs Castigliano's (Second) Theorem

texts:
I had a look online and into some literature however I did not seem to find a good comparison for the two different methods. They are both used for determining displacements and slopes (rotation by theta) at a point in a continuum.
Former uses a virtual unit force which equals to the strain energy in the element (when multiplied by displacement of interest) and latter uses differential with respect to a virtual force that tends to zero.

Which one is more efficient and which one is more accurate? Why would one choose Virtual Work over Castigliano's or vice versa?


texts: Evaporation of water using a vacuum pump?

texts:
Is it possible to boil the water simply using vacuum pump?

Also, is there any chances of ice formation?
If yes, then how we can calculate the heat given to the water to avoid ice formation?


texts: How many train passes can railway tracks endure?

texts:
I know that the rubber on car and truck tires wear, and the road concrete wears out. I wondered:

While steel is hard and elastic, it still causes friction (interaction
between molecules) and therefore abrasion.

Let's say we have on average 20-30 wagons with four axles with a full load of 50-60 tons on each wagon and a traction vehicle. How many train passes can a railway rail endure before it must be replaced? What is the equivalent time frame in which this number of passes is achieved on average?


texts: Calculating Strain gauge Values in a tensile Test

texts:
I got a question on an online quiz which leaves me clueless.
I gave my best to translate the question as accurately as possible:

There's a strain gauge placed upon a tension rod with a rectangular cross section in transverse direction. Which Value does it show at the onset of yielding?
The steel used is mild steel S235 with an E-Module of $E = 210000$ MPa, $µ = 0.3$, yield stress $R_e = 235$ MPa and UTS $R_m = 490$ MPa

Dimension of the Tension Rod: 100mm x 13,4mm x 7,4mm (Length, Width, Depth)


texts:
What are the nominal voltage ratings and operating tolerances for 60-Hz electric power systems above 100 volts up to a maximum system voltage of 1 kV in Brazil?
I am looking for a document like ANSI C84, that describes typical distribution service and equipment nameplate voltage ranges and tolerances.

I know about 60% of the population is served by a 127 Volt system and a minority is served by a 220V system and both systems use the same type N plug.

For example is the 127 Volt system split phase 127/256 like North American 120/240?
Is the 220 Volt system split phase 220/440 ?
What are the standard three phase voltages, 220Y127, 380Y220 ?
Thank you


texts:
I was watching this Feynman video and (as usual) his explanations make a lot of sense.

Now I just took a train, and am not so sure anymore. Looking at the train wheels they did not appear cone shaped to me. Also, if the train was running on cone shaped wheels I would expect that there is very little contact area between the wheel and the rails. However the rails looked completely shiny on the top suggesting that the wheels are in contact with all of the rail (i.e. flat wheels).

Are modern trains using a different method to deal with this problem or are the cones almost flat anyway (what angle)?


texts: How can pitot tubes give us local velocity in a flow

texts:
I am studying about static pressure,dynamic pressure and the principle behind pitot tube.

However in pitot tubes we apply Bernoulli equation between two points which are not on the same streamline. So this should not work for rotational flows. I understand that the very application of Bernoulli equation requires there be no friction and hence no viscosity. So if the fluid was not rotating beforehand it has to be irrotational for us to apply Bernoulli equation.

Is there any way to do this for a rotational flow with or without viscous effects.


texts: Quick return mechanism for spring-loaded screw

texts:
Looking for a way to convert rotary motion to linear, but it should take less energy to get back to initial position than when going from initial position to the end position.

Specifically, a screw mechanism pushes a spring with multiple of full motor rotations. Then it stays in this ending position for a while as screw prevents the spring from pushing the mechanism back. Now, I'm looking for a mechanism that will retract back to the initial position with less work than before, f.i. with a single motor turn in the same or opposite direction.

For example a lipstick mechanism works with a cam and a pin. Imagine that this mechanism pushes a spring and you can draw the pin out of the cam so the spring will push back. The problem is how to do that with a single rotational motor.


texts: Why are lasers used for concentrated light applications instead of incoherent light sources?

texts:
Some laser applications consist simply of concentrating light into a small spot.  Two example applications are laser welding and cutting. In these cases a CO2 laser is often used which needs a regulated power supply, a water cooling system, and a supply of CO2 gas.

Why do these applications use a laser instead of a simpler (i.e. incoherent) light source such as an AC powered arc lamp?


texts: How much energy is needed for the USA to only use desalinated water?

texts:
What amount of energy would it take to replace the entirety of America's water consumption with desalinated water? And how does it compare with the country's current energy generation capacity?
By "water consumption" I generally mean things that one usually thinks of when thinking of using water, including but not limited to household, commercial, agricultural, mining, and industrial uses. I'm not talking about filling reservoirs for recreation, hydroelectricity generation, or outflows meant to preserve fisheries. If there is another case worth considering, feel free to ask, or simply note it in the answer.
By "amount of energy", I mean to take seawater and turn it into usable water, not to pump such desalinated water from, say, San Diego to Denver. This would clearly be a non-trivial amount, but I think it would be too hard to calculate with much precision. (I guess the lower bound would be the current hydroelectric generation capacity of the USA, and a reasonable upper bound would be 10x that amount.)


texts: How to deal with rotation of an element in theory of elasticity?

texts:
As you know in linear theory of elasticity equations for strains are given as (according to picture):

But what will be if an element will just rotate (strain equation is on the picture):

Intuitively i think there should be no strains. The main question is how to deal with it?


texts: Generating practical power without an iron core, but with high RPM

texts:
Here's what I'm proposing - a small turbine directly coupled to a permanent magnet that's spinning at, say, 150k RPM. The magnet is enclosed one or several wire loops parallel to the axis of rotation.

Generated EMF is proportional to the magnetic flux and its rate of change. Without an iron core, the flux would be a lot smaller, but it would be in part compensated by the much faster rate of change. There would also be no core losses as well as no eddy current losses. Is something like this practical? Why is it said that driving generators from turbines without any gear reduction is inefficient?

Are iron cores added to generators to increase their specific power or their efficiency? Is it both?


texts: Is it more energy efficient to use cloud storage or connect a raspberry pi to an external hard disk? How can we quantify this?

texts:
I am thinking about where to store my digital files for backup.
I want to have the lowest carbon footprint.
(I'm going to use energy usage as a proxy for carbon emissions to make the problem simpler.)

I could use cloud storage such as Google One. https://one.google.com/about

I could connect a 4 TB external hard drive to a raspberry pi and connect it to the internet, making my own private version of the same thing.

https://medium.com/@aallan/adding-an-external-disk-to-a-raspberry-pi-and-sharing-it-over-the-network-5b321efce86a

Intuitively, I feel like using a google data center would be more more eco-friendly because of economies of scale.

How could I quantify this intuition?
Which solution is more energy efficient?
How much more energy efficient is it?


texts: How does a pressure vessel fail when the interal pressure exceeds the yield stress of the material?

texts:
When we design a pipe or pressure vessel, we look at hoop stress and longitudinal stress and then look at the material properties. We assume that the material reacts to the load as a solid. However This answer and comments claim:

Wall thickness doesn't matter if you try to contain a pressure that's greater than the yield strength. The material will permanently deform no matter how thick it is.
It's like i'm trying to contain a gas bubble in a soft mud. No matter how much mud I add around it - i can't contain it.

Is this true? Do metals behave significantly different when subjected to pressures beyond their yield strength?
This could be tested experimentally: To arrive at a very thick walled pipe we could  drill a hole into a block of gold (ultimate tensile  strength 220 Mpa). Build the block large enough and the pipe wall thickness should withstand the immense pressure - So when we pressurize the hole to something > 220 MPa (a pressure common in water cutting, but at much other places.)
If the statement cited above is correct, we should see a different failure mode than a thin walled bursting vessel - for example creep. Or not, if material behaviour is dictated by the stress in the vessel material, not in the medium contained.
If we look at the pressures involved for even a soft metal like gold, we see that this a mostly academic question - for the vast majority of applications, the pressures encountered are well below the yield strneghts of the materials so we simply don't need to consider additional failure modes.
The above experiment is just an example, to show that such a situation could indeed be engineered. I'm sure other experiments can (and have) been done. My intution is that the material will start to flow in some way (towards the least resistance) but I'd like to know for certain.


texts: I've seen some of the robotics competitions use pneumatic actuators for brute force actions ( like a hammer or lift ), but nothing precise. Is it possible to use pneumatics in a more precise scenario?, I'm assuming this is how pneumatic robotic arms operate, but I'm a little unclear on how they operate so precisely.


texts: What are the different methods to join 2 parts so that one can rotate 180 degrees around the other?

texts: Let's say we have one simple box and its bottom has been cut in a circular shape. We want to attach another box to this box that can rotate 180deg around the first one. What mechanism can be used to join these two boxes?


texts: When calculating the deformed radius of a pressurized thick-walled cylinder, why is the hoop strain used rather than the radial strain?

texts:
The context

I’ve taken an interest in the design of pressure vessels for use in submarine applications. From a cursory survey of what is used in industry, it seems the de facto standard housing is a thick-walled cylinder (rather than a thin-walled cylinder which would be prone to buckling when loaded in hydrostatic compression). While the equations for stress and deformation in a thick-walled cylinder subject to internal and external pressures are well established (Young, Norton), I’ve also read that prestressed compound cylinders can result in a housing with a greater strength to weight ratio (Kharagpur, Sun).

As a result, I’ve been trying to understand the derivation of the thick-walled cylinder equations to better understand how they can be applied and optimized.

The question

With the help of multiple online sources (primarily Kadapa and Katna), I’m confident that I understand the derivation of Lamé’s equations

$$\sigma_r = C_1 + \frac{C_2}{r^2}$$
$$\sigma_\theta = C_1 - \frac{C_2}{r^2}$$

This is where things get interesting. In both sources mentioned above, and indeed everywhere else I can find it, the equation for the change in radius of a differential shell is calculated from the hoop strain, rather than the radial strain as I would expect.

$$\varepsilon_\theta = \frac{\sigma_\theta - \nu \left( \sigma_r + \sigma_z \right)}{E}$$
$$u = \varepsilon_\theta r$$

While I’m satisfied this is correct, I don’t understand why. Why doesn’t the radial deformation result from the radial strain as I expect it should, according to

$$\varepsilon_r = \frac{\sigma_r - \nu \left( \sigma_\theta + \sigma_z \right)}{E}$$
$$u = \varepsilon_r r$$

What I've tried so far

I’ve tried evaluating both equations for $u$ for the simple case of a single cylinder subject to internal and external pressure (the boundary conditions given in every textbook).

While I haven’t compared the values to a more reliable source, the equation with hoop strain always produces deformations in the direction of the pressure differential (an external pressure causes the cylinder to contract). The equation using radial strain has so far always produced deformations of differing magnitude and in the direction opposite the pressure differential (an external pressure causes the cylinder to expand).

In both Kadapa and Katna, it is offhandedly mentioned that  and $\varepsilon_r$ and $\varepsilon_\theta$ are equal on the bases that

$$\varepsilon_r = \frac{u}{r} = \frac{2 \pi u}{2 \pi r} = \frac{\delta\ circumference}{circumference} = \varepsilon_\theta$$

While I can’t find fault with this statement, I think I have shown that it is only true for thin-walled cylinders where the hoop stress is assumed to be constant throughout the wall as below:

  Based on the methods presented in Kadapa, Katna, and others,

  $$\varepsilon_r = \frac{du}{dr}$$
  $$\varepsilon_\theta = \frac{u}{r}$$

  Assume that

  $$\varepsilon_r = \varepsilon_\theta$$

  If so,

  $$\frac{du}{dr} = \frac{u}{r}$$

  This first order linear ODE has the solution

  $$u = kr$$

  As a result,

  $$\varepsilon_\theta = \frac{u}{r} = k$$


texts:
On my belt sander, there is a small cast aluminum drive pulley/wheel about 1.25" diameter that slips over a 5/16" shaft. Two flats on the shaft mate with two flats inside the bore.  The internal flats in the bore have sheared off, so now the wheel just spins on the shaft instead of driving it.

The manufacturer no longer makes the cast aluminum wheel, and no parts stores via google have any old stock left.

I have two ideas for fixing it 1) mill keyways (too expensive) or 2) drill a hole for a 'shear pin' (spring pin, roll pin; which is my plan at the moment).  I'm open to other suggestions.

For the pin, what is the optimum diameter and what metal?  If it is small, it'll likely shear under normal use. If it is large, then the shaft will be weakened too much.


texts:
I have a part made from 5mm alloy plate and I need to cut a large cutout in the middle of said part:

As seen above I intend to use a small cutter to cut through the stock (not necessarily plunging as shown here) and cut around the inner diameter of the part instead of roughing out the entire area of the cutout which would take a lot longer.

My concern is that when the cut is complete the large piece of internal cutout could get caught by the cutter and thrown around the machine enclosure, wreaking death and destruction as it goes. Is this something I should be worried about and if so, what's the usual strategy for making this type of feature?


texts: How do I make sure I don't damage electrical components (L293D, RaspberryPi, & DC Motors)?

texts:
I have a RaspberryPi that will control 4 DC motors. I will be using 2 L293d ICs. The 2 ICs will be powered by a 24v 5A Power Adapter.

Question:  What other components do I need?

I imagine I would be needing resistors so the ICs don't burn but I am not sure what power rating. I am also worried that I might damage my RaspberryPi. Also, the motors will be connected through a long wire (about 1.5m long) and I am worrying about too much power being lost due to the long wire.


texts:
A double shear butt joint is shown below in the diagram 4 plates are held together by two bolts. The applied force is 42KN. Determine the shear stress within the joint

$$\begin{align}
a &= 2 \frac{\pi}{4} d^2 \\
&= 113.0973355 \\
\frac{42}{2} &= 21 \\
\frac {21}{\pi/4\cdot12} &= 20.05352283\text{ kN/mm}^2
\end{align}$$

Is this correct?


texts:
I can not really understand how people decide what tolerances to set for a part or assembly. For example:
When can I choose 0.2 mm and when 0.002 mm; and if I choose 0.002, why didn't I choose 0.001 or 0.004 or any other number?
Is there a Handbook, a standard, or is it mostly about experimenting and experience?"


texts: Can the Sabatier reaction power a vehicle?

texts: The Sabatier reaction converts CO2 to methane. Can a vehicle that burns methane recover it (at least some part) from the exhaust gases via the Sabatier reaction? I am interested to know how this would be implemented, and whether such a vehicle has ever been built or prototyped.


texts: Is it possible to cast copper around another metal

texts:
So i have seen these super conductor rods around (which appear to be copper around titanium/niobium).

Now I am wondering (for a maker usecase) if its possible to create something similar by for example casting copper around rods of another material, i.e. iron, nickel, stainless steel, or even just titanium.

What is the science behind this, is it possible to just cast 2 different metals together so they become fused?


texts: When beverage can stay-on tabs are lifted do they depressurise the can by lifting the rivet?

texts:
I understand that the inside of a carbonated aluminium beverage can is pressurised. When the tab is pulled up,a rivet is lifted. Does this cause the can to depressurise? So then the can can be pierced with less force.

Thanks.


texts: Can I use AutoCAD to learn mechanical engineering by DOING (like programming)?

texts:
I would like to learn mechanical engineering as a side project. But, I would like to learn in a way similar to programming. Learn by doing.

Of course I understand I can't build things automatically just yet as I have no 3D-printer and they aren't advanced enough for most things (right?)... but Autodesk has simulation software which may do what I need.

Can I learn mechanical engineering by using AutoCAD for real projects?


texts: What does it mean that the mass of a propellant tank is at premium?

texts:
I am reading the rocket propulsion elements book by sutton and I came across the following statement: "Because the propellant tank has to fly. its mass is at a premium and the tank material is therefore highly stressed."
I am just learning, and have no strong technical background, so I will appreciate the explanation!
Thanks!


texts: Molding thermoplastic over sensitive components

texts:
I have an electronic assembly that is heat sensitive. Due to the incorporation of a CR3032 coin cell battery, it can survive being heated to a maximum of 60 degrees C.

I want to coat this assembly in a biocompatible, waterproof plastic. This layer will be the ultimate barrier to moisture between my device and a biological environment.

At the moment I am using parylene-C, which performs admirably, but is very expensive.

Various species of thermoplastic promise to perform just as well, at dramatically lower cost, but I don't know how I'd apply them without damaging my battery.

My question to you is, how could I coat my circuit in a thermoplastic without thermally damaging it, and without spending more than a few dollars per unit?


texts: Advantages of hydrogen gas turbine over fuel cell

texts:
In the setting of large-scale electricity generation, I was wondering why one would want to burn hydrogen in a gas turbine instead of using it to power a fuel cell. Aren't fuel cells  more efficient because they're not bound by the Carnot limit? Two reasons I can think of are:

Fuel cells are limited in their power output
Fuel cells can't be started as quickly as gas turbines

Are these points correct and relevant? I guess the second point is only relevant for peaking power plants.

In a similar vein, I've read in one of Smil's books that fuel cells are somehow limited (in what sense I'm not sure anymore but I believe it was power output) by their "active area". I'm having difficulties learning more about this "active area". Can someone maybe expand on that?

Thanks a lot.


texts: Whats a reliable way to measure the amount of rope going out of a coil?

texts:
I am an undergraduate researcher and I am working at enhancing a calibrating system for a hydrographic surveying system that my supervisor uses on his hydrography course. The rope is used to lower a bar check system, and it comes out of a coil. I want to find a reliable way to measure how much rope has come out of the coil.

Currently the rope has markings on it at every meter so that the person deploying it can know how much rope has been used by counting the number of markings that passed.

I was wondering if there is a more reliable way to measure how much rope has come out of the coil, preferable by some sort of measuring device. The most obvious idea would be some sort of pulley system that records the number of rotations of the pulley, but that is prone to slipping and the error could add up over 30 something meters. Do you know of such a device or idea that could help with that?

(p.s.: this is a very minor aspect of the whole design, and doesn't affect at all my work, it would just be a "nice to have" thing in the design)


texts: Qualitatively how does the O-wind turbine function?

texts:
Recently the O-wind turbine won the James Dyson award for innovation, the item is essentially a compact wind turbine which unlike traditional wind turbines can harness wind from multiple directions, the wind is converted to kinetic energy to then generate electrical energy.

However I am struggling to understand how this works as a concept. From what I've read the spherical shape is fitted with vents which has a large entrance hole and small exit holes. I am unsure of how this could initiate the movement of the object in the presence of wind.


texts: Why are railroad tank cars bent in the middle?

texts:
I recently noticed that the cylindrical shape of a railroad tank car is not completely straight but has a bend in the middle. The entire tank is a bit lower there. What's the reason for this bend?
This is also visible on the drawing of a DOT 117 tank car on Wikipedia (the red nearly-horizontal lines were added by myself).
I first thought it had something to do with pressure containment, but the model 117 is apparently used for non-pressured goods only.


texts: Physical meaning of some earned values using DePriester Chart

texts:
Using DePriester Chart and Given one of mole fractions ($z$), pressure and temperature we can acquire K-values for that properties and bubble and dew properties.

Now there are sometimes that we get some K's and using the summation of $y/k$ we get some quantities that are not 1, like 0.9 or 1.2. My question is about those values, are they showing some physical property?

If I wanted to calculate the dew point pressure at a given temperature and I take arbitrary pressures (including the dew point pressure) I get the following results.

[p] = psi    sum of y/k
- - - - - - - - - - - -
   100         0.828
   126         1.000
   150         1.174

Do the values for the pressures above and below the dew point pressure have a physical meaning?

For example, showing us that we are in two-phase, SH vapor or SC liquid region?
Or are they just showing there isn't VLE with that given property?