texts:
I am trying to code a simple FEM problem. A bar is fixed at the bottom edge, and a displacement is applied at the top. I want to apply the displacement gradually , so I have divided it into a number of steps. A rough outline of the code looks like this:

 %********************************************************* %
> Newton-Raphson Control parameters
> %*********************************************************
>
> uload=5;         % the total displacement
  numu=10;         % number of steps
  du=uload/numu;   % step size
  tu=0;            %initial value
> tol=1e-2;

>   for ii=1:numu  %Loop over total number of steps
>
>       iter=0;
>       tu=tu+du;  %increment displacement at each step
>

>          while(error>=tol)  %Iteration
>            iter=iter+1
>            Ku=sparse(sdof,sdof);    %Initialize stiffness matrix
>            [Ku] = Kmat(Ku);  %Create stiffness matrix by user defined function
>               Ru = sparse(sdof,1);  %Initialize residual force vector
>            [Ru] = Rvec(Ru,u);  %Calculate residual force vector by user defined function(consists of internal force only)
>            [Ku,Ru] = applyBC(Ku,Ru); %Apply BCs by user defined function

>            delu = sparse(sdof,1) ;  %Initialize solution vector
>            delu = Ku\Ru ;   % Calculate displacement
             u=u+delu; %   %Increase displacement value
>            error=norm(Ru)  %Calculate Error (This step is probably causing the divergence due to selection of improper criterion)

>          end %iteraion
> end %step

This code won't compile in MATLAB because all the functions are user defined and the input data is not provided. I just wanted to portray a rough outline of what I am trying to do.

This algorithm, works fine if I only have a few elements(suppose 100) defined. If I decrease the mesh size, the solutions tends to diverge, the error keeps on increasing. I figure that is probably because the way I calculate the error is not useful for this simple case.

Now my question is what can be the best convergence criterion for this problem? Since the problem is simple linear elastic, no non-linearity involved, I think the values calculated in the first iteration is correct, so no need for further iterations. But later I would like to extend this code to perform non-linear static analysis, so is there a convergence criterion that can be used for both? If not, then what can be used for each case?

P.S: I have modeled a similar problem in a commercial code, where obviously it works, but when I check the details of the solution, it says that it has used one iteration per step(which is expected). In my code with more elements, the iterations keep increasing after the 2nd step. Thus my doubt regarding the choice of convergence criterion.


texts: What is the fraction of power transmitted to the generator in full-hybrid cars?

texts:
In full-hybrid cars like the Toyota Prius, usually both internal combustion engine (ICE) and electric motor produces mechanical power to the wheels at cruise. But some of the mechanical power produced by the internal combustion engine is converted to electric power through a generator.

I would like to know typical values for the fraction of the total power generated by the ICE, which is transmitted to the generator at cruise.


texts: How to create a buffer along a curve in Rhinoceros 5?

texts: Say I have a line (0,0)<--->(1,0) and I want to make a rounded "buffer" along it (or any curve, just keeping it simple) in such a way that I now have a closed curve with radius 0.5 so that I end up with a rectangle with semi-circles on each end that is 1 unit in height, and 2 units in width.


texts: How is response spectrum result used for earthquake analysis

texts: For simpler buildings we can use response spectrum analysis. How is this used? The maximum acceleration we get from this , is simply multiplied by the mass of the building to get F=ma , total earthquake force on the building? Simple as that?


texts: What type of stainless steels can resist 6 months under the sea?

texts:
Resist means without catastrophic corrosion here.
We assume that there is no coating or anodic protection.
The steel can be mirror polished and passivated.
To make it more difficult, the shape is not a perfect sphere but a mechanism with some very bad water stagnation.
Since all seas are different let's say that the part is a few miles away from San Francisco seashore.
We are 50 meters underwater. There is no source of heat in the mechanism.


texts: Is there a limit to the size of ships that can have hydrofoils (would an aircraft carrier work)? Would there be cavitation if the load was high enough, and to what extent would using larger foils help, and would they stop providing any advantage over non-hydrofoils at some point?


texts:
Can someone explain why the M is assigned to be anticlockwise here ?

When i assign it as clockwise , i will get -P(δ -v) , which is different from the author ...
If i do so , then , all the sign will be different
Can i do so ? Why ?

or the second example here , i can understand that M = -Pv , since M+Pv = 0 at either end when it's in equlibrium.

P/s : I know the the sign convention of the bending moment of beam is positive when the beam upwards as shown ...

For the first example  , i gt M+P(∂-v) = 0 , so M = - P(∂-v) .
I am not sure whether is my concept correct or not .


texts:
I am trying to design a musical locket which includes a slowly (28 rpm) rotating component.
The two things that make this a challenge is:

Very limited space. The motor and the reduction system should fit in a cylindrical space of radius x height = 7.5cm x 2.5cm (3x1 inch).
It must be as quiet as possible
I don't have a specification for torque, but because of the lightweight components and the large reduction, I believe any solution sort of a watch mechanism will be overkill in that aspect

What I've got until now: Most motors and/or gearboxes readily online are very noisy. So my current plan is to use a computer fan, which is really silent. My first try was to use a 2-step worm reduction, but I noticed that although the motor itself was silent, the gears and the bearings their axles were on started producing large noise. So my current plan is to use a 1-step pulley reduction.
Now, I need to squeeze as large a ratio as possible from this, and then the rest of the reduction will come from feeding a PWM signal to the motor for descreased rotational speed. What I have not found anywhere is information on minimum pulley diameter at such scales.
How small a diameter can a pulley be, if it is using a 2mm(~.01 inch) cross-sectioned "belt"? Light scientific backing will be very appreciated.


texts:
I want to secure a box (roughly 20kg in total) that contains electronic equipment to the underside of a flat steel structure. We can weld onto the underside.

The steel structure has a high chance of receiving mechanical impacts from above (for example, large rocks falling onto it), so I'd like to find ways to dampen the mechanical shock and vibration reaching the box.

I have seen shock mounts/isolation mounts before (like moulded rubber mounts), but they seem to be designed for supporting objects that rest on top of the mount -- in other words, the mount is designed to be under compression.

What options do I have if the object is "hanging" from the mount?


texts: Can high alloy tool steels be quenched in brine?

texts:
It is will known that most of tool steels are quenched in oil to prevent cracking and distortion which appears when quenching in water due to non-uniform cooling caused by formation of insulating vapor blanket "film boiling".

but according to some  literature 1 using 14% brine solution or 1% polymr solution eliminate this vapor blanket so we can expecting more uniform cooling compared to water quenching.

according to another literature 2 the probability of quench crack formation
at first increases to the maximum value, and then decreases to zero.

increasing cooling rate is possible by using strongly circulated brine quenching
bath, and using brine eliminate vapor blanket which ensure uniform cooling.

so, can we excepting maximum hardening depth, minimal cracking and distortion and eliminated fire hazard by quenching high alloy tool steels by quenching in circulated brine instead of oil ?


texts: Mathematical relation between shear stress and temperature

texts:
I have recently started research in mechanical engineering. Currently I am working in the field of friction stir welding. During my study I came across a point where I have to find the mathematical relation between shear stress and temperature during plastic deformation of material. I tried to find out about it on google but did not get satisfactory answer. Can anyone please explain about it?

To be specific, I am performing Friction stir welding on aluminum during which the temperature is going to be in the range 473-700 Kelvin.

It is a difficult question for me hopefully not for others.


texts: Can you suggest a motor that would be suitable for these parameters?

texts:
I am trying to specify a motor, but I don't know where to start. I need it to be able to:

Lift a weight of $200kg$,
through a height of $2m$,
Using a lead-screw with the following dimensions:

$$OD = 26mm\\ Pitch = 5mm\\ Core =21mm\\ Mean\ Diameter=23.5mm$$


texts: Why does local derivative and convective derivative only apply to spatial descriptions?

texts:
In continuum mechanics, why does local derivative and convective derivative only apply to spatial descriptions?
Is it because in the material description, the motion focuses on the particles, and not on fixed spots in space, and in each particle's motion the time and space are simultaneously changing, so we can't perform derivative w.r.t time and space separately?


texts:
I want to build myself a pull-up bar. I am confident enough that I can guesstimate how much material I need for it to be strong enough, but this time I would like to challenge myself to properly calculate all the strengths needed.
However I am stuck at the first point -- how do I properly estimate the loading on such a thing? By this I mean only the maximal instant force that my body would apply to the bar, safety factors will be added later.
Is there some standard that tells you what dynamic forces to expect from a human body?
My best guess so far goes something like this: I can hang on single hand, but not with another person pulling me down, so the max total force that I can apply to the bar will be somewhere between 2x and 4x my body weight, anything more and my hands will certainly slip. Therefore I design for 4x my body weight and add safety factors on top of that. Does that make sense?


texts:
Let's assume a DMM is specified to have accuracy "0.1% FS +/-0.02" when used on the 50 V range.

I get that 0.1% FS means the true value will lie somewhere between measured value - 0.05 and measured value + 0.05. But what does +/- 0.02 mean here?


texts: How to set up the boundary between volumes in a simulated turbine

texts:
I am simulating a turbine and I have some doubts about the correctness of my approach.

In this turbine, there are three volumes:

The two volumes are the piping before and after the blade and the other volume contains the turbine blades. The domain containing the blades rotates at 2000 rpm = 209.43 rad/s while the other two volumes are stationary.

I modeled this turbine in Gambit.

In this case, are there any problems? Gambit is weak for modeling this stage.


texts:
A Hazardous Chemicals Waste Recycling company & KOH production, ABANDONED the site, they cut (looks like with a diamond saw) the concrete floor (25cm height) at about the middle of the warehouse, in the size/shape of a bed, for what reasons?  and, some Circular Cuttings (diameter of a round plate)?

What would be the PURPOSE of ALL these CUTTINGS?

They also did cuttings on the asphalt floor outside the building, rectangular shape (approx 400m2 & 300m2 area), and replaced it with NEW ASPHALT. Few months after they left the site, the NEW ASPHALT is covered with rusty powder. How is the RUSTY powder forming? chemical reaction??

There is also BLACK OIL forming above the OLD asphalt floor? How come it's rising from the floor? chemical reaction??


texts:
I am exploring whether a diamond based capacitor could be made for powering a drone. From my initial research, it has the right material properties (thermal conductivity, strength to weight ratio, dielectric strength), but I know from experience that doesn't mean it can be made. I found that the only practical way of making the near flawless diamonds are through chemical vapor deposition techniques. Since the capacitor would need to have conductive plates that sandwich the diamond, it would make the part a composite.

So I am here to ask the question:

What would make a composite chemical vapor deposition diamond hard to make?

From my initial thinking about it, it seems that mating the two layers chemically would be difficult, as diamond is quite inert and doesn't want to bond to the conductive metals needed for the electrodes. But, if carbon, like graphite or graphene is used, I think it could work since the whole capacitor would essentially be the same element, just configured differently. The size of the capacitor would be 0.1 cc, so I think most vacuum chambers already in existence would be able to make the part.

Is this doable with current technology, or are we missing something that makes this not possible currently?


texts:
Background

For a washing process after a crystallization we want to know how much filter area we would need and if said area will work for our fixed volume flow.

Calculation

$\dot{V_F}$ has a given value

Velocity $u$ should be the     superficial velocity and is at a fixed value we found in our mechanical engineering script.

With $\frac{\dot{V_F}}{u} = A$ we can calculate our needed  filter area. Question is, will that area work for our volume flow.

With $\dot{V_F} = \frac{A \cdot \Delta p}{\eta_F(\alpha_w \cdot L )+ f_M}$

we can then calculate $L$.

$\Delta p = \Delta p_{filter medium} + \Delta p_{filter cake}$

$\Delta p_{filter cake} = \frac{(1-\epsilon)^2}{\epsilon^3 \cdot x^2_{32}} \cdot 150 \cdot L \cdot \eta_F \cdot u$

Now we insert $L$ in the equation for $\Delta p_{filter cake} $ and we get the exact $\Delta p_{filter cake}$ that we originally assumed when calculating $L$. Actually we expect to get a different value in order to find all variables via iteration.

Somewhere we made a mistake in our assumptions I think, but I can't see where right now.

I know that $\dot{V_F}$ is a function of $L$ however we can't change $\dot{V_F}$. And we insert it anyway in our equation for $L$ so I think that assumption is valid.

English is not my mother tongue, so please excuse any spelling / grammar mistakes. Furthermore this is not a given tasks, but a problem we stumbled upon during our group project (designing a plant).


texts: At what (outside) temperatures is it efficient to run my windowbox heat pump?

texts:
I am an electrical engineer that took two semesters of Thermodynamics about 4 decades ago.  I am aware of the theory behind the Carnot cycle and such.

I live in a condo in the Boston area that is all-electric (except for a fireplace I am not using and has its flue closed up).  Recently, I replaced the windowbox A/C with a windowbox A/C and heat pump.  I have been using the heat pump solely to heat the apartment while the outside temps have been above 40 F.

The other heat is simple resistance heating, which I will call "100% efficient" even though the electricity was generated at a plant somewhere with a heat engine of far less efficiency.  I look at the heat pump as being a way to recover some of the heat lost in that inefficiency because, theoretically, it is better than 100% efficient because the heat coming out of it is the sum of the electric power running it plus whatever energy taken from the outside air.  I also know that this efficiency decreases as the outside temperature falls.

But now as winter is starting to close in, outside temps will become consistently below freezing.  At what point is it not worth it to run the windowbox heat pump?  Just asking if some HVAC sorta people know a rule of thumb regarding this.


texts: What is Experimental and Operational MODAL ANAYLIS?

texts:
EMA and OMA are two methods used for determining the mode shapes of the natural frequencies of mechanical systems. I understand it until that point. I know that for EMA we need an artificial excitation like a hammer and measure the response.
But what is the final objective of these methods? Is it to model the dynamical system or to obtain the parameters? Or maybe it is a vibration analysis or measurement method? It´s not quite clear what the answer is.


texts:
I've just started to learn Gate, Globe, Ball, and Butterfly valves.

I'm thinking about "dirty services" now.

Which types of valves are most suitable for dirty services, and what characteristics must the valves have?


texts: Can FSI analysis be linear on the solid part?

texts: Is the FSI analysis always considered Nonlinear or the solid part analysis can be linear too?


texts:
As a follow up to this question, I have a question about rivet hole management in Autodesk Fusion 360.

I've got two pieces, a flat sheet of aluminum and an inverted hat channel that I want to rivet together. The easy (and naive) way would be simply to specify a bunch of rivet holes in each piece while being careful to match the holes sizes and distances from each other.  And that works until I need/want to make changes to the rivet hole sizes or layout, then I have to go remember to change them on both pieces.

I am skeptical of any practice that relies on me remembering to do something in lots of places. I'd much rather create a kind of master rivet hole pattern that each piece inherits from.  That way, I make one change to the master and it's automatically propagated to all the places I need it.

How do I link the rivet hole sizes and pattern together so if I change it one place, it changes it in the other?  I've seen "Project geometry" but can't seem to figure out how to make it do what I want.


texts: Linear pneumatic actuator opening time - pressurise connection pipe

texts:
I would like to estimate the time needed to open a linear single-acting pneumatic actuator.
The actuator's piston is loaded with a spring pushing downwards and the operating fluid (air or nitrogen) pushes upwards; other forces like weight and friction are present.

The operating fluid is provided by a large tank (ideally infinite) with stagnation pressure $P_\infty$ and stagnation temperature $T_\infty$.

If the tank is connected directly to the actuator, balance of forces, with fluid force depending on actuator inlet mass flow rate, leads to an ODE which I can solve numerically.

Since tank and actuator are actually connected by a long pipe, $\frac{length}{diameter}\approx 1000$, I need to estimate the time to reach the equilibrium state in the pipe ("pressurise the pipe"). Initial conditions for pipe and actuator are $P|_{t=0}<P_\infty$ and $T|_{t=0}=T_\infty$.

Does anyone know a way to estimate the time required to reach the equilibrium state in the pipe, maybe based on some dimensional argument or some typical time related to the pipe?

If not, I must determine the evolution of pressure, temperature and mass flow rate inside the pipe.

I have been reading literature for compressible flow in pipes, usually coming from natural gas distribution applications, but the problem of transient compressible flow in a pipe, be it isothermal or non-isothermal, leads to a system of PDEs.

The model verification examples I found led me to suppose that the PDE was

  requiring some sort of boundary condition also at the exit of the pipe. Since I do not know the pressure / temperature / mass flowrate entering the actuator in advance, I am missing something.

but since the PDE is hyperbolic, it actually requires boundary conditions at the inlet only, besides initial conditions.

Any help or suggestion would be appreciated.


texts: Have tunnel boring machines been mass produced? What are the difficulties in mass producing a tunnel boring machine?

texts: Tunnel boring machines are a common tool in deep tunnel construction. I am curious if they have ever been mass produced in specific types. What are the possible problems in (a possible) mass production of such machines?


texts: Can chemical vapor deposition chambers be used to lay down thick layers of metal?

texts: Can CVD Chambers be used to lay down thick (~1 mm) layers of metal?


texts: Applications with combination of high friction and low wear?

texts: What would be some common applications involving high friction and low wear rates? for example, gear-driven mechanisms which require high friction between the gear teeth but ideally low wear between them.


texts: Design automation using fluid dynamics simulations

texts:
I have a question about design automation or generative design.

There is a company that creates pumps. Their work-flow is following:

1)  create design of a pump using CAD

2)  create mesh for computer simulation

3)  perform simulation (usually fluid dynamics)

4)  using results of a simulation, decide if the design is good enough

5)  if not, go back to step 1

They are doing all these steps by hand. I was wondering if there is any possibility to automate any of these steps.

For example algorithm or software that takes the design and tries to change important parameters (for example length or width of something) based on simulation results automatically (= performs some kind of optimization of the given parameter).

Is this something that generative design can accomplish? I am completely new to this field (however I have a background in CFD simulations). I will I really appreciate any help, introduction or link, so I can learn the basics.


texts: Specificities of satellite AOCS (Attitude and Orbit Control System) engineering

texts:
I'm still a graduate student in aerospace enginneering, in Europe. I specialised in control systems, and I'm interested in working in the satellite manufacturing industry. I'm especially curious about satellite's AOCS (attitude and orbit control system), and what I painfully lack at this point are real accounts of engineers working on this field. Of course I understand what this field is about, but I have no idea what an AOCS engineer actually does on a daily basis.
The thing is, up until now my control courses have been very general in their scope. But I know that the way control engineering is carried in practice varies drastically depending on the field : the temperature control of a heating system won't look anything like the roll control of an airliner (different environment, different physics, different mathematical tools, different concerns driving the control decisions..), and although both are technically control engeneering jobs, from an engineer point of view, on a daily basis they look like completely different jobs.
I know the same can be said of every engineering discipline to a certain extent, but I've been led to believe that this variety is nowhere as prevalent as in control engineering.
So my question is : what are some specificities of AOCS design compared to control engineering applied to other fields ? Is there anything I should know about it, like aspects of control that are especially essential in AOCS compared to other fields, or on the contrary aspects that are not as important in AOCS as in other fields ? What are the main things that are on the mind of an AOCS engineer, the main things to take into considerations that are due to the specificities of this field (space environment, etc.) ? What does an AOCS engineer actually does on a daily basis ?
Thanks.


texts: Shear forces along a beam using singularity functions

texts:
$\newcommand{\a}[1]{\langle#1\rangle}$
As you can see, the left end of the beam is fixed, and a distributed load is applied to the beam. I calculated the shear forces by conventional means, but when I calculate it with singularity function I get weird results. Here are my calculations:

$$q(x)=-3000\a{x-0}^{-2} + 3000\a{x-0}^{-1} - \frac{2000}{3}\a{x-0}^1 + \frac{2000}{3}\a{x-0}^0$$

The first term comes from reaction torque and the second term comes from reaction normal force. The shear force is just the integral of the $q(x)$.

$$v(x) = 3000\a{x-0}^{-1} - 3000\a{x-0}^{0} + \frac{2000}{6}\a{x-0}^2 - \frac{2000}{3}\a{x-0}^1$$

As you can see the results are false. I'll appreciate any help.


texts:
I am making a project where i need to put a water valve below the tank and then need to open it automatically but the problem is that already available brass electric valves aren't good enough to handle the 120C temp besides i heard that brass isnt good for something that will be consumed by Humans later.
And that overtime brass get mixed up in material and it will be consumed.
what's the best solution for this problem ?

i was thinking maybe is there anyway that i can put a motor or something on this steel valve and remove this handle and then open it with that motor or something


texts: What is the difference between shaft power and brake power?

texts:
I know little about internal combustion engines and I feel a little confused about brake and shaft powers. I read a book that only talks about shaft power, and other that only talks about brake power, without making a proper definition of the physical meaning of these quantities. I'm now thinking that they both mean the same thing: useful power on the crankshaft (the power produced by the engine cylinders less the losses and the power that is used in accessory components).

For example, in Mechanics and thermodynamics of propulsion (1992) (Hill Peterson), pag. 155, the the brake specific fuel consumption uses shaft power in its definition, and not the brake power (as the name suggests it).

I would really appreciate some clarification, or some book suggestions, since the ones that I read are too vague.


texts:
I have a small drum that will be immersed half way in a water bath (drag). The drum will contain some 500ml of photo chemicals (weight).

The questions:

is there an easy way to calculate the gear ratio to get between 35 rpm and 75 rpm?
OR is there a gear ratio that will keep the rpm of the motor (variable speed motor)?
considering drag/weight should I worry about stress on gears? Should I use bushes (brass/nylon) or small bearings around shafts?
what kind of electric motor do I need (DC motor for toy or drill?)
do I need a lot of torque to obtain durability?
using gears, is there an easy way to calculate the necessary motor power/torque vs weight of drum (if I use a bigger drum)?

See drawing for general concept.

Thanks for helping me to learn!


texts: How do you calculate the best gear reduction for max speed?

texts:
I know that a gear reduction would decrease the RPM if the motor ran at constant speed, but in reality its speed is a function of the load.

I first tried turning a wheel with a direct drive system, but the motor started getting warm (burning off the lubricant inside) and was spinning much slower than without a load because it didn't have the torque required. I know that a gear reduction would cause less stress (torque) on the motor, which in turn, would allow it to [possibly] go faster. I am essentially looking for the highest speed I can get, so how would I determine the proper gear reduction ratio to use?


texts:
Note, as I have my degree in chemistry, I denote "=>" as the next step in the equation. Also, sorry for any obvious mistakes that I made - as I mentioned, my degree is not in engineering. Thanks!

I am considering a design for a PET spherical toy ball. The ball will have a radius of 0.07 m that will have pressurized air in it at a pressure of 5.81 atm (588698.3 Pa). Also, the ball will include a 35 nm coating of Reduced Graphene Oxide (RGO) as a durable coating on the outside of the ball.

To get the thickness of the walls of the ball, I know that the ultimate tensile strength of PET is 55 MPa. Because I want a 15% safety factor for the ball, I do the following calculation:
$$(1-15\%)\cdot55 = 46.75\text{ MPa} = 46750000\text{ Pa}$$

I then use the reduced ultimate tensile strength to find the thickness of the wall using the formula for a thin-walled sphere where $p$ is pressure, $t$ is thickness, $r$ is radius, and $\sigma$ is stress:

$$\begin{gather}
\sigma = \dfrac{pr}{2t} \\
46750000 = \dfrac{588698.3 \cdot 0.07}{2t} \\
\therefore t = 4.41\times 10^{-4}\text{ m}
\end{gather}$$

I can calculate the burst pressure of the sphere $P$ for pressure (gauge) inside sphere, $FS$ for factor of safety, $\sigma$ for allowable stress and additionally $R_i$ for inner radius, $R_o$ for outer radius:

$$P = \dfrac{(R_o^2-R_i^2)\sigma}{(R_i^2)FS}$$

For calculation of bursting pressure, we take $\sigma$ as ultimate stress for a given material and put $FS=1$.

Note here that I chose the express the ultimate tensile strength of PET as $5.5 \times 10^7$:

$$P = \dfrac{((0.07 + 4.41 \times 10^{-4})^2 - 0.07^2)\cdot 5.5 \times 10^7}{0.07^2 \times 1} = 695183.67\text{ Pa} = 6.86\text{ atm}$$

I now want to calculate the volume of PET needed to create a sphere of the desired dimensions:

$$\begin{align}
V &= \dfrac{4}{3}\pi \left(\left(\dfrac{d_o}{2}\right)^3 - \left(\dfrac{d_i}{2}\right)^3\right) \\
&= \dfrac{4}{3}\pi \left(\left(\dfrac{0.140 + 4.41 \times 10^{-4}}{2}\right)^3  - \left(\dfrac{0.140}{2}\right)^3\right) \\
&= 1.36 \times 10^{-5}\text{ m}^3
\end{align}$$

I now want to calculate the volume of Reduced Graphene Oxide (RGO) to apply to the surface of the sphere:

$$\begin{align}
V &= \dfrac{4}{3}\pi \left(\left(\dfrac{d_o}{2}\right)^3 - \left(\dfrac{d_i}{2}\right)^3\right) \\
&= \dfrac{4}{3}\pi \left(\left(\dfrac{0.140 + 4.41 \times 10^{-4} + 35 \times 10^{-9}}{2}\right)^3 - \left(\dfrac{0.140 + 4.41 \times 10^{-4}}{2}\right)^3\right) \\
&= 1.084366 \times 10^{-9}\text{ m}^3
\end{align}$$

Can you see any mistakes in my calculations?

Please do not ask why I am using PET as a material or other design decisions like that. There are good reasons for them.


texts: Rule of Tens/Ten to 1 Rule in Measurement and Inspection

texts:
I'm trying to clarify my understanding about the requirements [read: best practices] for measurement resolution and measurement confidence.

The "Rule of 10s" is a commonly tossed around guideline for measurement resolution that, to the best of my understanding and searching, suggests the following:

That your measurement systems should be able to resolve to a level of 10% of your total tolerance.

However, regardless of whether you consider "tolerance" to refer to the product or process tolerance, there still seems to be some confusion among those I've talked with.

As an example, take the following dimension:

125mm +/- 10mm

In this case, the total tolerance range is 20mm.  Ten percent of 20mm would be 2mm.  Therefore your measurement system should be able to resolve down to a 2mm level which would get you roughly 10 distinct "categories" into which your results fall.

An alternate theory that I've come across however, is:

That the measurement resolution should be "ten times greater than your specification/tolerance as written.
This is the "move the decimal place" approach and is more a "significant figures" discussion.

Taking the same previous example where the tolerance is +/- 10mm, increasing the resolution 10X would imply that measurements should be obtained at the 1mm level.

I don't believe this latter approach is the intent of the "10 to 1" rule, but I'm looking for some general consensus.

To complicate this question slightly, consider a scenario with an engineering drawing which defines a length as follows:

468.2mm +/- 6.48mm

(THIS is where the team arguments begin.)

The total tolerance is 12.96mm (6.48mm x 2), of which 10% would be 1.296mm.  Being a good inspector, and dropping the decimal places to utilize a 1mm resolution measurement method, this still seems to be contradictory to the intent of the dimension.

Where the dimension or tolerance is specified out to multiple decimal places, should the "move the decimal place" method be invoked? If a dimension is specified out two decimal places, it would only make sense to be able to resolve it to 3 decimals.

Appreciate anyone who takes the time to read through this and give your thoughts!


texts:
Consider a sliding cursor C that is fixed to the disk which has a constant angular velocity counterclockwise at 4 rad/s. Determine the angular velocity and angular acceleration of the AB bar at the instant shown. [0.667 rad/s (counterclockwise); 3.84 rad/s2 (Clockwise)]

to solve this exercise I draw the two axes

I've done
$$\begin{align}
v_C &= v_O + \Omega_{OC} \times r_{OC} \\
&= 0 + 4k * (-0.06\sin(30)i+0.06\cos(30)j) \\
&= -0.12j-0.2078i \\
v_C &= v_A + \Omega_{AC}r_{AC} + v_{rel} \\
&= 0 + \Omega_{AC}k\cdot 0.180\cos(60)i + 0.18\sin(60)j) + v_{rel}\cos(60)i + v_{rel}\sin(60)j \\
&= (-0.156\Omega_{AC} + 0.5v_{rel})i + (0.09\Omega_{AC} + 0.866v_{rel})j
\end{align}$$
and therefore i got $v_{rel} = -0.2079\text{ m/s}$ and $\Omega_{AC}=0.667\text{ rad/s}$ which are the correct results
$$\begin{align}
a_C &= a_0 + \alpha_{OC}\times r_{OC} + \Omega_{OC}\times (\Omega_{OC}\times r_{OC}) \\
&= 0 + 0 + 4k(4k(-0.06\sin(30)i + 0.06\cos(30)j)) \\
&= 0.48i-0.8312j \\
a_C &= a_A + \alpha_{AC}\times r_{AC} + \Omega_{AC}\times (\Omega_{AC}\times r_{AC}) + a_{coriolis} + a_{rel} \\
&= 0 + 0 + \alpha_{AC}k(0.18\cos(60)i + 0.18\sin(60)j) + (-0.44i - 0.069j) +(-0.139j + 0.24i) + a_{rel}(\cos(60)i + \sin(60j)) \\
&= (-0.156\alpha_{AC} - 0.2 + 0.5a_{rel})i + (0.99\alpha_{AC} - 0.208 + 0.866a_{rel})j
\end{align}$$
and therefore i got $a_{rel}=0.56\text{ m/s}^2$ and $\alpha_{AC} = -6.156\text{ rad/s}^2$, which is the wrong value for $α_{AC}$.
is it possible to solve the exercise using the 2 axes that I draw?
because I can't understand where my resolution is wrong


texts: What type of exhaust is vented from the rooftop of this apartment?

texts:
I recently signed a lease for a high-rise an apartment unit that directly overlooks the rooftop of lower floors.  That is, my apartment is on a smaller floor plate than the units below it, and I could theoretically open the window and walk out onto the roof of the lower floors.  Unfortunately, I don't have any pictures.

The roof has several small vents that look like this:

And some larger ones sort of like this:

I can't remember what kinds of pipes I saw, if any.

Do I have to worry about the air coming from the roof vents?  Would there be any bathroom/sewage ventilation on a rooftop like this?


texts: What should the size difference be between a lid and a container?

texts:
I am designing a box and lid (for a home-made micro computer). Using Autodesk Inventor (Student Version), I've created my box which looks something like this:

I plan on 3D printing (ABS Plastic) the box and lid in the end.

And I am going to create a rectangular lid to encapsulate the contents. I know accuracy will be important to the printing, so I want to make sure I have the sizing right. If it helps you answer my question, the dimensions of the top of the box are 3in by 4in and I want my lid and its outer lip to be around 0.1in thick. I would like the seal to be pretty tight (won't fall off easily) but if it's too small I risk breaking the ABS Plastic when putting on or taking off the lid.

My question, however, is what should the difference in size between the outer rim of the box's top and the inner rim of the lid be?


texts: Computing winch maximum line pull (torque vs lift capacity)

texts:
I am trying to ascertain the maximum line pull for an old winch I have in my workshop and I am arriving at values that are considerably higher than what is in the original manufacturer's manual. I am not sure if I am doing this right and want to validate my calculations.

The winch is rotated hydraulically with a motor. The motor shaft is connected to a wet brake which in turn is connected to a planetary gear hub. This hub is then connected directly to the drum.

Some specs:

If the motor builds up 3000 PSI and has 38 LPM of flow it produces a torque of 295Nm with 316RPM. (or 30.08163KGm)

The wet brake disengages and produces negligible friction.

The ratio in the gear hub is +53.58:1

The diameter of the drum on the winch is 0.81m

The diameter of the cable used to pull is 0.0202m

From what I understand, to find linear force for a winch I must use this formula: Torque = Force X Arm

Where Arm = radius of drum + radius of cable radius drum = 0.81m/2 = 0.405m radium cable = 0.0202m/2 = 0.0101m Arm = 0.405m + 0.0101m = 0.4151m

Where Torque = Torque of motor X ratio of gear hub Torque = 30.08163KGm X 53.58:1 = 1611.7737354KGm

Therefore Force = Torque / Arm Force = 1611.7737354KGm / 0.4151m = 3882.856505420381KG

Am I correct to therefore say that the maximum line pull before the winch stalls is 3882.85KG? Therefore We can say it can lift anything bellow this weight?


texts: Why is there this perforated pipe inside this vertical construction joint in a reinforced concrete wall?

texts:
The picture below shows a veritcal construction joint of an approximately 50 years old reinforced concrete industrial structure. The expansion joint was likely originally sealed with a flexcell which due to age and water ingress has deterioriated and come away from the joint exposing a peforated metal pipe.

My question is does any one know why the pefortated pipe was installed there originally approximately 50 years ago? Does it have a drainage purpose? The joint should have been waterstopped. Is this a second line of defence? If so where do you expect it to drain to? Has anyone seen a similar detail to this before?


texts: How can I determine pressure leakage in a pneumatic system?

texts:
I am an engineer currently designing a system in which the leakage of a hose is tested. The system consists of the following components:

An air data system used to generate a pressure inside the hose.
An automated pressure measurement device used to measure the pressure in the hose.

The goal of the test is for the air data system to exert a pressure on the hose and make sure that the pressure doesn't drop while the system maintains that pressure. The air data system will maintain the pressure and the measurement device will periodically read the pressure over a length of time. After some time has passed there is a limit to which the pressure should have changed. If that limit is exceeded the test will be considered a failure otherwise considered a pass.

The pressure measurement device is not perfect and leaks a small amount of pressure on its own. Is there a way to account for how much pressure is leaked by the pressure measurement device? I'd like to do this in order to get a slightly more accurate value for pressure in the hose.

If it helps, here is some other information I know about the system:

The air data system is +/- 2% accurate.
The air data system can be detached from the pressure measurement device and measure its own pressure it's putting out.

Is there a way where maybe I can measure the pressure of the air data system in isolation, and then with the pressure measurement device attached... in order to maybe obtain some sort of mathematical/physical relationship or system of equations? I am thinking that something along those lines might work.


texts: Finding the components of a vector along two other vectors

texts:
Using only the diagram above (Not using the questions in the diagram), i am asked to find the components of F2 along F1 and F3.

I am having trouble with this question. I can easily resolve any of the vectors into their x and y components but I am not 100% certain how to resolve it along the other vectors. Am I correct in saying that to resolve F2 along F1 we draw a line down directly from the head of F2 to F1 and then take 750*Cos(45) to get the component parallel to F1. What should I do to resolve F2 along F3?

The answer is given as 1240N and 884N. Any hints on how to get to those answers would be much appreciated. Perhaps I am not understanding what is meant by resolving a vector along another vector?


texts: Will drilling a hole in a pane of glass reduce it's structural integrity?

texts:
I've got a glass box that measures 900mm x 450mm x 450mm.

The width of the glass is 6mm thick.

If I drill, cut, or grind a small hole in/through one of the faces; will it significantly affect the structural integrity of that piece of glass?

I'm concerned it might become prone to cracking, if for instance, I pick it up to move it.

I thought there might be some kind of ratio, or formula I can use to determine a safe size for a hole, a safe distance from the edge, and so on.


texts: What happens when you put the wrong type of fuel in an internal combustion engine?

texts: What happens to the working of petrol engine when it is emptied and filled with diesel or to  a diesel engine emptied and filled with petrol? Will the engine be able to operate and, if not, why not?


texts: giga/tera hertz timer? super fast spinning disc?

texts:
How would I go about detecting a very small amount time dilation

I want to accelerate something and measure the time dilation even if I reach 1km/s time dilation is very small but it looks just barely within reach.

I'm currently thinking a spinning disc, but the numbers are all just a bit beyond what I know how to build. For the timer I obviously want maximum resolution.

I could spin a 0.6m diameter disc at 1000hz(60,000rpm *fixed conversion error).. I suppose... in a vacuum...errrrmmm... I'm trying not to kill myself.....

I want to test a hypothesis...

cosmic inflation redshift destroys energy

cosmic inflation create new space

new space has vacuum energy

HYPOTHESIS 1: expansion red-shift of certain energies(eg photons) has space-energy conservation. space to energy / energy to space conversion is occurring, and if you factor in space as energy there is conservation.

I roughly calculated the energy the numbers and they fall within reasonable range, but I cant think of a way to test it except correlating expansion rate with radiation energy traversing various regions of spacetime,

So I while I'm working on that I moved on to hypothesis 2, which is much more of a long shot, because relative velocity redshift doesn't have lost energy, the energy is conserved as momentum. But I figure is one form of redshift involves space-energy conversion then perhaps so do the other types of redshift.

Hypothesis 2 : All red/blue shifting includes an energy to space conversion. While traveling at high speed if light is emitted forward it is blue shifted and converts some space into energy, emit light backwards and it creates space.

So my plan is to arrange a time dilation test by accelerating a time counter. Sandwich it between 2 powerful LED arrays, one facing forward and one facing backwards. check if time dilation is affected when light is emitted forward and/or backwards. (try both pointing at the counter and both pointing, always aligned so lights are pointed parallel to motion vector)


texts: Tubing for explosive gas or hydrogen transfer

texts: Recently, I heard that there is a law/ OSHA/ ASME piece of regulation dictating that hydrogen should be transferred (suppose from a tank of hydrogen to another location) by using specially approved tubing. Is this true?


texts: How does Rule-1 guarantee cylindriccity in GD&T?

texts:
If I have defined the size tolerance of a shaft, how is the maximum cylindricity tolerance automatically specified by rule-1 of GD&T?

I mean when a shaft shoulder diameter is defined (e.g. 33g6) then it is usually checked by measuring the diameters at multiple axial locations. What is the guarantee that each of the measured sections at various axial locations will lie between the coaxial cylinders as required by the cylindricity tolerance?

Any ideas?


texts: Define Free Air Delivery for an air compressor

texts:
Free Air Delivery (FAD) is a common measure of the capacity of an air compressor. I have a question that comes at the end here. My question is a little different from what you might be expecting. So first, let me establish some basics so that we don't just get replies giving a version of the standard answer.

FAD is a flow rate of air derived from measurement at the outlet of the compressor, defined at the corresponding outlet pressure, e.g. 300 litres per minute @ 700kPa. However, FAD is not simply the raw flow rate measured at the discharge at this raised pressure. The measured flow at the outlet first has to be converted back using a formula, to be the equivalent flow rate that would be obtained if the pressure and temperature were the same as at the intake.

Put in other words, here is a quote from a guide put out by the German compressor manufacturer Kaeser:

  The air delivery of a compressor (known also as the free air delivery or FAD) is the expanded volume of air it forces into the air main (network) over a given period of time. The correct method of measuring this volume is given in the following standards: ISO 1217, annex C and DIN 1945, Part 1, Appendix F. ... Proceed as follows to measure FAD: the temperature, atmospheric pressure and humidity must first be measured at the air inlet of the compressor package. Then, the maximum working pressure, temperature and volume of compressed air discharged from the compressor are measured. Finally, the volume V2 measured at the compressor outlet is referred back to the inlet conditions using the following equation ... The result is the free air delivery (FAD) of the compressor package. This figure is not to be confused with the airend delivery.
  $$ V_1= \frac{V_2 \cdot P_2 \cdot T_1}{T_2 \cdot F_1} $$

Source: Kaeser "Compressed Air Engineering: Basic principles, tips and suggestions."

Note that F1 is a factor where

$$ F1= p_1- (p_p \cdot F_{rel}) $$
where

p1 = inlet pressure

pp = vapour pressure

Frel = inlet humidity

For teaching purposes, that is a quite a lot to take in at once. It would be good to state an initial, approximate, concept that can then be qualified and refined.

So, to my question. Is this not virtually the same as saying: "Aside from leakage losses, FAD is equivalent to the flow rate of air being sucked into the intake of a compressor that is working against a certain backpressure." Is that a legitimate statement?


texts:
I'm designing a funnel/bottle for a powder. My goal is to have all of the bottle's powder contents come out when inverted. However, the powder has a tendency to stick to itself (like flour or brown sugar) and so I will run into a chance that the powder will not fall into the bottom vessel by gravity alone.

To make matters more complicated, this is not an open funnel on the top. It will be more like a plastic water bottle in that when it's rotated to dumping position, the top isn't open to the air and venting doesn't currently appear to be an option.

My question is, what funnel surface type will increase the flow to help dispel the powder contents? Some ideas that come to mind are smooth, vertical guides, or stepped stairs. Note my funnel outlet is fixed in diameter.

Smooth

This one makes the most sense as it's a "smooth" flow. However, I've been surprised by how air and water behave in relationship to fluid dynamics (ex: golf ball dimples or pickup trucks being more aerodynamic with the tailgate up).  And although fluid dynamics doesn't cover powders, I would imagine there's some similarities.

Vertical Guides

In theory, these ridges would break up the powder clumping on the way down.

Stepped

In theory, these steps would add turbulence on the way down and help break up the powder on each "step down."

Extra question: Regardless of the features in the funnel (or lack thereof), what's the minimum angle from vertical that would be ideal for a funnel to dispense powders by gravity alone?


texts: buying a mounted bearing determining radial vs axial load it can bear

texts:
Can anyone tell if these bearings load ratings are for a radial load or an axial load ?

Bearing designed for an axial load is (sometimes?) called a "thrust bearing".

Based on its mounting, I guess this is a thrust bearing for an axial load.

https://pgnbearings.com/collections/ucf200/products/ucf206-20-pillow-block-square-flange-mounted-bearing-1-1-4-bore
( those links work at time of posting )

Based on its mounting, I guess this is for a radial load.

https://pgnbearings.com/collections/ucp200/products/ucp206-20-pillow-block-ball-bearing-1-1-4-bore

The basic specifications are given in a table and include static and dynamic load ratings (images include a detailed mechanical drawing).

The mechanical drawing may indicate how the bearings are situated within the mounting.

For someone with more knowledge the mechanical drawing may allow you to determine if the bearing is designed for an axial or radial load.

-- EDIT --

After jko answered I looked again at the mechianal drawings provided in the specifications, for illustration here is another bearing   https://pgnbearings.com/collections/fr-series/products/fr8-zz-meatal-shielded-flanged-ball-bearing-1-2x1-1-8x5-16   appears to be a radial bearing meaning designed to bear a load perpendicular to the axle on which it is mounted.    As I understand it the bearing balls themselves are mounted (inside the casing, if any, of the overall bearing ) on two surfaces, those surfaces determine how the bearing is designed to carry a load, the surfaces are perpendicular to the direction of load, or one could say the load is applied to those surfaces    in my original question as i look more closesly at the mechanical drawings provided in the specs, i now see the surfaces on which the ball bearings themselves roll appear to be perpendicular to the axis on which the bearing is mounted meaning both are thrust bearings   in the link in this comment, in the mechanical drawing the surfaces on which the bearing balls roll are parallel to the axis of the bearing so that this would be a radial bearing.

This isn't an attempt to answer my question but giving my own understanding and also a comment directed towards those who may have already answered asking for clarification.


texts:
I have the problem following. There is a deformable sphere with radius r. It goes inside a constriction channel with d*d cross section. Assuming that the sphere volume is constant and the sphere shape after squeezing is a rectangle cube, what is the value of force or pressure exerted on a wall? Is there any analytical solution and how should I calculate the force?

Many thanks for your time.


texts: Can combined cycle turbines be small enough for trains?

texts:
Combined Cycle Turbines are a gas turbine whose exhaust heat powers a second turbine running on steam. These can get thermal efficiencies greater than 50%, whereas a plain turbine would get 30 to 35%. Large power plants tend to use combined cycle for obvious reasons.

But I want to know if this can be small enough to power a train?

Example of a very small jet engine, which is very similar to a gas turbine.

Desired specs:

Fuel: either natural gas or kerosene
Horsepower: ~4500 (taken from a typical diesel train engine (GE Dash 9))
Max volume: 25 x 3 x 6 meters (about the volume of a train car)
Max weight: 100 metric tons

I'm assuming a fuel car can follow behind the engine car. The turbines would generate electric power sent to the car wheels, which is what a modern diesel-electric train does. I was imagining combined cycle turbo trains for freight and passenger services, but at "normal" speeds (100 - 150 kmh).

So can this be done with today's technology? The engine would still need to be insulated enough and efficient enough to retain 50+ % thermal efficiency.

BTW, I'm aware of this failed example from Amtrack starting in the 1970's. I don't think those were combined cycle turbines, and I could not find an explanation for why "The high cost of operating the trains led to their withdrawal from the Midwest in 1981." But I did notice those were tiny trains, 5 cars total (2 engine cars, 2 coaches, and a food car). That is probably far too small to get economy of scale.


texts: Is it possible to look at exposed chip and know the components and the circuit involved?

texts: Typically a chip is packaged to protect it and to make it easier to handle. Is it possible  to look at exposed  chip (see images  here https://electronics.stackexchange.com/questions/56649/what-is-a-die-package) under microscope and know the components and the circuit involved?


texts: Stretching material accurately with a machine

texts:
I am currently making software to interact with a conductive rubber cord. I am very interested in figuring out the percentage of a stretch of the cord, to determine how the resistance changes.

Example:

Stretch the cord 1 cm, see the difference in the resistance:

Stretch the cord 3 cm, see the difference in resistance:

Programmatically, I can tell this change. When I use my hands, I can see the resistance flow change as my pressure increases on stretching the cord. However, as my hands are probably not the best instrument for accurate stretching, I am in need of an alternate machine to do this for me.

Does a such device exist, which can hold one end of this material for me, and pull the other end 1 cm? 3 cm? etc.
Since I am a software engineer, and certainly lack in the field of mechanical engineering, is a good approach to take here to use motors and a raspberry pi to possibly create my own stretch machine?


texts: How to model robotic wires behavior in solidworks

texts:
I'm trying to create a block or anything else in soildworks that I can move and see the compression of the lower wire further from the arm
Something like this

The example show just one joint but I want it for a long array of joints
But I have no idea how to go about it
Can you give me a direction on how to do it?


texts: Scalable alternatives to CNC router and laser cutter

texts:
I am doing calculations on costs for alternatives for manufacturing this children's toy I invented, a puzzle where letters in plastic fit into wood.

I have been using a CNC router to carve subtract the letter shapes from wood and a laser cutter to cut those same shapes in plastic (with some clearance). I have a good idea of the costs involved in manufacturing it myself, hiring someone to supervise the machines, or hiring a service bureau. My understanding of manufacturing at scale is much more limited.

I think it would be possible to get similar and cheaper results by moulding Medium Density Fiber or Perspex. Is that possible? Can you think of other scalable alternatives?


texts: Why is the partial derivative of stress in the circumferential direction equal to zero in axial symmetric bodies?

texts:
I've come across this phenomenon several times and never found any real reason for this.

When I consider a cylindrical object like a rod, I need to calculate several things. One of those is the stress tensor in cylindrical coordinates represented by $r$, $\theta$, and $z$ directions.

Now, in many books and in my lecture notes there's always this one line that says:

$$ \frac{\partial\bullet}{\partial\theta}=0$$

I know that when compressing a steel rod (assuming there is little to no friction at the contact points) the steel rod should get compressed in the $z$-direction and expand in the radial direction.
Why is there no stress in the circumferential direction?

I've looked in many places and I hope that I didn't accidentally miss the other SE question with respect to this specific topic.


texts: When recording VHS tapes from analogue TV back in the day, was the "Teletext" data also recorded?

texts:
Ever since I was a kid in the 1990s, I've been wondering about this. I have never been able to verify/test it in a conclusive manner.
It may be almost forgotten now, but in those days, each TV channel (at least in Sweden) had a "hidden interface" in the shape of "Text-TV" ("Teletext") which would show a fullscreen "terminal"-style dump of information, allowing the user to "surf" this primitive "Internet for poor people" by entering numbers such as "123". You then had to wait a certain amount of time and then could see that "page".
Obviously, this was accomplished by some sort of hidden metadata being sent along with the video/audio data, and the waiting was necessary because it only sent some "pages" of data at a time due to bandwidth limitations.
My question is: if you recorded such a broadcast onto a VHS tape with a normal VCR, then later looked at the video tape, would the TV allow you to enter and "surf around" the Teletext, just as if it had been "live"?
Or was this data scrapped and never made it onto the VHS tape? Or was it included, but some other reason made it impossible to (easily) "surf" it later?


texts: Large deflection of a non prismatic cantilever beam under distributed load

texts:
Here's what I got trying to calculate the large deflection of a cantilever beam with two different cross sections under a uniformly distributed load:

From the figure, the shear force is:
$$
V(s) = q(L-s)\cos(\theta)
$$
$\theta = \theta(s)$ being the deflection angle.
from the beam theory, the bending moment is:
$$
M(s) = EI(s)\frac{d\theta}{ds}
$$
we have:
$$
\frac{dM(s)}{ds} = V(s)
$$
we get:
$$
\frac{d}{ds}(EI(s)\frac{d\theta}{ds}) = q(L-s)\cos(\theta)\\
E\frac{dI(s)}{ds}\frac{d\theta}{ds}+EI(s)\frac{d^2\theta}{ds^2} = q(L-s)\cos(\theta)
$$
where:
$$I(s)=I1+H(s-L1)*(I2-I1)$$
in which $H(x)$ is the Heaviside function defined as:
$$H(x) =
\begin{cases}
0,  & \text{if $x\lt$ 0} \\
1, & \text{if $x\ge$ 0}
\end{cases}
$$
and
$$\frac{dI(s)}{ds}=\delta(s-L1)*(I2-I1)$$
in which $\delta(s)$ is the Dirac delta function defined as:
$$\delta(x)=
\begin{cases}
0,  & \text{if $x\neq$ 0} \\
1,  & \text{if $x=$ 0}
\end{cases}$$
so, finding the deflection boils down to solving the boundary value problem of the nonlinear second order differential equation for $\theta(s)$:
$$EI(s)\frac{d^2\theta}{ds^2}+E\frac{dI(s)}{ds}\frac{d\theta}{ds}-q(L-s)\cos(\theta)=0$$
with the boundary conditions:
$$\theta(0)=0\\
\frac{d\theta}{ds}(L)=0$$
and the deformations in the y and x directions respectively:
$$y(s)=\int_0^s \sin(\theta)ds\\
x(s)=\int_0^s \cos(\theta)ds$$
Can anyone confirm these results? Thanks.


texts: Weird texture on faces when using Shapeoko CNC

texts: when I run an operation that mills a face down on my CNC, it leaves this weird texture. It's hard to describe, so I attached an image. What is it caused by and how do I fix it?


texts:
So, this is the truss I have to solve, more precisely I have to find forces in all of the members of the truss. That is why I used method of joints. I started from the joint A and realised without calculating that members attached to it (Fab and Fal) are the zero force members.

PICTURE ON THE LEFT: After that I continued the process with joint B and calculated forces in members Fbl and Fbc. If I have made a mistake here, I will appreciate  you also point that out.

PICTURE ON THE RIGHT: The only joint with 2 unknown members that has left after calculating members of joint B is joint L. But here is the problem. Since I can only use 2 equations - sum of the forces in the X and Y direction (in method of joints), I don't know how to find Flk and Flc, since those are not neither vertical nor horizontal forces. I know I should split those into their components  (vertical and horizontal), but since they are both unknown members (so are the components), I don't see way to calculate any of them.


texts: What if ammonia is used as a refrigerant for a refrigerator?

texts:
I have a refrigerator whose compressor configuration is:
power- 10hp
compression ratio- 10:1
I do not have expertise in this field, but I am curious if I use ammonia as a refrigerant instead of HFC-134a then what will be the temperature in the hot side of the refrigerator?


texts: Best insulation material for pipes @ 500℃

texts: What will be the best thermal insulation material for insulation of pipe lines having temperature of 500℃. Mineral wool and Calcium Silicate can be used but here we have a constraint of both weight and space.


texts: Can cyclonic separators be used to separate heavier and lighter gases?

texts:
I'm trying to increase the Helium detection capabilities of a sniffer unit. Could a cyclonic separator, like that used in the oil/gas industry, with enough fluid velocity move the heavier gas molecules in air (O2, N2, Ar, CO2) to the sides of it while keeping the lighter elements (He, H2) in the center to be detected by a sniffer?

We're trying to detect leaks of helium from refrigeration systems on an assembly line. we're designing a positive air box to prevent any outside contamination from the filling and recovery stations. The box will have a blower attached to it to pull the volume of the box in 10 seconds. because most of the gases in the box are not our trace gas we have a very low mbar l/s level (allowable is 9e-7) that is on the borderline of the minimum of our sniffer unit we are looking to use. The sniffer unit has the precision of 1e-7 mbar l/s at 300 SCCM and 1e-6 mbar at 3000 SCCM. We are going to have an array of sniffer heads in the center of this conic that will sample the air at the center (with the thought that the lighter elements would be there) leading to a more accurate reading because it is sampling less of the non-trace gas. This process of sampling and detection along with the lifting/closing of doors and shifting of the equipment is done on a conveyor belt within a 40 second time period.

The current system is a person at the assembly line with a hand held sniffer going around the connections, but are getting readings that there are leaks even though there might not be, probably due to the helium charging station only 3 feet away from the leak testing area. we are looking to automate the process for less false readings and quicker turn over time in the process.


texts: Source-Sink pair with different strength

texts:
I know when I have a source-sink pair with equal strength in a uniform flow, I get the rankine oval.
Lets say that my source is know +1.25*Q and my sink is -Q, would I still get some sort of "oval body"?
I think I'd still get flow over a closed body, correct me if I'm wrong.


texts: Why is pressure head ignored in open channel flow?

texts:
Also, what does this excerpt from Wikipedia mean

However, since with open channel flow, the water surface is open to the atmosphere, the pressure term between two points has the same value and is therefore ignored.


texts: A region of attraction analysis using invariant sets

texts:
How can I find a region of attraction for given system? $k<0$

$$\begin{align}
x' =-kx+x^3\\
   \end{align}
    $$


texts: Is it okay to replace pressure with point loads for structural analysis?

texts:
I am trying to analyse a wing structure in Ansys static structural. In most examples I have been through the lifting pressure is uniformly applied under the bottom of wing or it is simplified to point loads. I have 2 questions regarding this,

Is it okay to apply pressure loads on bottom wing as - (lift*load factor/wing area)
How can I apply pressure loads accurately taking into account coefficient of pressures at the wing
surface?

EDIT 1: the wing is divided in 3 parts, the middle parts has a spar box which acts as a slot for the spar extensions of outer wings. knowing the stresses at this junction is critical


texts: Train decelerations in no power condition

texts: Suppose a train is running at 30kmph and suddenly the power is switched off. How do we calculate the reducing velocity at intervals and what factors will affect the change in it?. Further how much time will it take to stop from that position and the distance it will cover before coming to halt?


texts: Is there a more efficient transducer to convert mechanical energy into electrical energy than electromagnetic induction?

texts: I know piezo film has one of the lowest efficiency to date when it comes to converting mechanical energy (or stress in the context of piezoelectricity) and motor (magnet and coiled copper wire) seems to be quite efficient. But is there something more efficient than electromagnetic induction? Thank you.


texts: Help avoiding damage to perforation wheels

texts:
I have an application in which I need to adjust the position of 2 perforation wheels along the y axis to regulate their distance from a film web edge.  Though the speed of this positioning will be quite slow (low FT), I am concerned about damaging the perforation wheels as they are pressed against a steel roller with significant force to ensure cutting.

I figure there a couple ways to prevent damage:

1) Reduce force (Fp) on perforation wheel during movement.
-Interrupts continuous operation of the machine

2) Spin the perforation wheel about the z axis proportionally to the speed of movement along the y axis, sort of like steering.  I would need to sync the two wheels together.

3) Do nothing: The wheel self corrects by deflecting in the y direction by some small angle

Context: The total travel of the perf wheels is unlikely to exceed an inch in total.  I do not currently know the pressure on the wheels, I don't know of an easy way to measure it either.

As the machine in its current form is in continuous use at the moment I cannot really trial many things for real.  Thanks for the advice.


texts: Dead mans brake on a hand-pushed wheelchair

texts:
Would it be possible to install a dead-mans brake on a wheelchair?

I have been calling around and wheelchairs do not seem to come with a dead-mans brake. With that i mean the brake found on airport trolleys: you let go the trolley stops.

The problem that needs to be solved is that we are often pushing a grown man on a steep hill. If the person pushing the wheelchair were to stumble and release the chair, it would probably end in death as the road is not only steep, it is also full of bends and has irresponsible, speeding cars and buses.

Would it be possible to install one made from off-the-shelf parts?

I have seen this: https://casterconnection.com/dead-man-brake-system.html

But this is part of a set of small wheels, i'm not sure if that would be the right solution. If i replace the front wheels with this braking pair, would the chair not flip over?


texts: What happened to the projectile in Hypervelocity Impact tests?

texts:
I recently saw a tweet about Hypervelocity Impact Sample and someone ask how is it possible to shoot a projectile at that speed and what happened to the used projectile when hitting the shield.

I found that it was probably shooted by a Two Stage Light Gas Guns but I didn't found anything about the projectile.

I only found this:

  They got their name because hypervelocity impact produces local
  pressures in the target and projectile that greatly exceed the
  material strength of these materials, the material behaves as if it
  has no strength, i.e., like a fluid, or hydrodynamic behavior

  Handbook for Designing MMOD Protection

What happened to the projectile ?

Does the projectile melt with the shield ?
At this speed, does the projectile melt before hiting the shield ?

EDIT: deletion of the last question, test done in vacuum.


texts: Demagnetize neodymium permanent magnets at < 60 degrees C

texts:
I have 10 cylindrical neodymium permanent magnets about 5mm in diameter, 5 mm long, embedded in a thermoplastic polymer.    I want to demagnetize them without removing them, or heating them above 60 C - they must remain motionless, +/- 1 mm.

Note that the magnets are NOT all aligned in the same direction.

I can move a demagnetizer within 5 inches of the assembly, or place the entire (1m x .3m x .2m) assembly within a demagnetizer.

Yes - I thought about melting the plastic and replacing them - but all the other stuff must stay invariant :(


texts: Feedback Control Question: Finding compensator numerator (B(s)) and denominator (A(s)) polynomials to satisfy a specific requirement

texts:
I wish to find the polynomials B(s) and A(s) in the following compensator equation:
A(s)D(s) + B(s)N(s) = F(s)
Given,
$$N(s) = s - 2$$
$$D(s) = s^2 - 1$$
$$F(s) = s^2 + 3*s + 4$$
Condition
The degree of B(s) should be less than the degree of A(s)


texts: How can I efficiently find the root cause of validation failures?

texts:
Within most engineering development processes, product testing and validation is an integral part of the product development process.

All prototype / engineering development samples are tested. And all failures are handed over to product engineering with failure reports, which includes test data documented in various forms (paper, word documents, excel tables, etc). The product development team then gets 1-2 weeks to perform root cause analysis and develop corrective action before the product goes into production.

The current root cause analysis / corrective action process that I'm working with can be characterized at best as chaotic, brute force, or uncoordinated. Needless to say, some product comes back as warranty returns or field returns.  We'd like to drive the return rate down.

The business conditions, competition, and resource levels don’t permit the luxury of additional time for root cause analysis and proper (the way I prefer) corrective action. We do understand there are areas in the engineering development process that can be improved, and plans are underway to implement these improvements.  Currently, we are following waterfall project management methodology. And it's worth noting that I am responsible for the electrical engineering component only.

Question: What is an engineering product develop process strategy that will help bring order to the current chaotic, brute force, uncoordinated root cause analysis and corrective action processes?

We currently have a few suggestions on the table, but would like to probe the community for additional insight.


texts: Can one build a custom Android TV by buying different components of the system?

texts: With a spec as good as Nvidia Shield plus one with a build in TV tuner?


texts: Consequences of Inextensibility of an in-plane line in Euler-Bernoulli Beam Theory

texts:
The Euler-Bernoulli beam theory is based on the hypothesis that the beam deforms such that a straight line normal to the beam axis before deformation remains

inextensible
straight
normal to the beam axis

after deformation.

I am trying to find out the consequences of these assumption number 1 and 2 for displacement field. In the following discussion, $x_1$ is the axial direction and $x_2$, and $x_3$ are in-plane directions. Similarly, $u_1$ is the displacement along axial direction, and $u_2$, and $u_3$ are in-plane displacements. The coordinate system is placed at the centroid of the cross-section of the beam.

Assumption 1: A straight line normal to the beam axis before deformation remains inextensible after deformation.

Consider a straight line $\overline{AB}$ in the cross-section of the beam as shown in Fig. 1.. The length of the beam before deformation is given by

$$l_{AB}=\sqrt{(x_{2A} - x_{2B})^2 + (x_{3A} - x_{3B})^2}$$

where, $x_{ij}$ represent the ith-coordinate of jth point. For example, $x_{3B}$ is displacement along $x_3$ direction of point B.

Similarly, the length of line $\overline{AB}$ after deformation is given by

$$l'_{AB}=\sqrt{(x_{2A} + u_{2A} - x_{2B} - u_{2B})^2 + (x_{3A} + u_{3A} - x_{3B} - u_{3B})^2}$$

Since the length of line $\overline{AB}$ cannot change, i.e., $l_{AB} = l'_{AB}$, therefore,

$$\sqrt{(x_{2A} - x_{2B})^2 + (x_{3A} - x_{3B})^2} = \sqrt{(x_{2A} + u_{2A} - x_{2B} - u_{2B})^2 + (x_{3A} + u_{3A} - x_{3B} - u_{3B})^2}$$

which is possible if and only if $u_{2A} = u_{2B}$ and $u_{3A} = u_{3B}$.

Since, points A and B are arbitrary points on the cross-section, therefore, we can conclude that the $u_2$ and $u_3$ displacement will be same for all points on the cross-section of the beam. In other words, $u_2$ and $u_3$ are functions of $x_1$ only.

$$u_2(x_1, x_2, x_3) = u_2(x_1)$$
$$u_3(x_1, x_2, x_3) = u_3(x_1)$$

Assumption 2: A straight line normal to the beam axis before deformation remains straight after deformation.

This is possible if and only if the line translate as rigid-body along axis $x_1$ and rotate as a rigid-body about axes $x_2$ and $x_3$.

Rigid-body translation: If the line moves as a rigid-body along $x_1$, its displacement along $x_1$ is given by $\overline{u_1}(x_1)$.

Rigid-body rotation about $x_2$: If the line rotates as a rigid-body about $x_2$, the displacement of any point on the line along $x_1$ is given by $x_3  \phi_2(x_1)$, where $\phi_2(x_1)$ is the angle of rotation about $x_2$.

Rigid-body rotation about $x_3$: If the line rotates as a rigid-body about $x_3$, the displacement of any point on the line along $x_1$ is given by $-x_2 \phi_3(x_1)$, where $\phi_3(x_1)$ is the angle of rotation about $x_3$.

So, the total displacement along axis $x_1$ is given by
$$u(x_1, x_2, x_3) = \overline{u_1}(x_1) + x_3 \phi_2(x_1) - x_2 \phi(x_1)$$

Owing to the reasoning mentioned above for both assumptions, are the conclusions made sensible and correct?


texts: Electrical component most likely to fail in window AC unit after power surge?

texts:
I have a window AC unit, 115 VAC, 10 amps. Power went out earlier in the week due to the big storm on the east coast and once it came back on every LED on the control panel was lit (not typical) and would run for a few seconds once I turned it on before shutting off and wouldn't turn back on. My house is older and the only grounding provided by the outlet is contact with the mounting screw on the face plate. It has a GFI power cord that will reset and stay on test fine so there's nothing wrong with the outlet itself or the breaker, other devices plugged into the same socket work. The unit is only 2 months old and was working fine beforehand so I'm thinking any surge when the power came back on either blew a fuse or capacitor. I was able to remove the cover as much as GE wants the end user to be able to, but it only provided access to the PCB for the control panel and everything there seemed to be in working order. It seems that whatever potentially failed dangerous components on the compressor driver PCB are tucked further back in the unit that would require serious tear down.
It's a week until a repairman can come to inspect it for a $100 service call and whatever mark-up is on the replacement part. I was wondering if there's a likely culprit that failed that would only be a few bucks off of Digikey.


texts:
I read an article in a textbook which says stiffer rubber increases vibration damping and softer rubber increases vibration isolation.

Can anyone explain this how?

What is the difference between vibration damping and vibration isolation..?


texts: Solar Heat Gain/Outside Temperature Effects on a House

texts:
I'm currently a sophomore Mechanical engineering student and need some help with an equation for my project. I am coding a simulation in Matlab and have been given a very short time frame to do it. I chose to model the thermal efficiency of a house with the main output being cost to run heating/cooling system per day. Due to time constraints I tried to simplify the analysis a bit. I am neglecting heat transfer through siding, framing, the roof/ceiling, the floor, people inside, and appliances. Basically just four walls of insulation. I am looking at windows and solar heat gain from them. Since I am ignoring siding I am also ignoring solar heat gain transfer to it. Currently I have the program written to produce an output on a graph, but my equation to calculate the new inside temperature doesn't seem correct. I am using conduction through the insulation, convection from the ambient temperature inside, and solar heat gain due to the windows. I have restricted the size of the house to a 30'X40' single story with 8ft walls. The walls were also 1ft thick. So I ended up with the following:

Q_(conduction) + Q_(solar H.G. from windows) = Q_(convection due to ambient inside temp)
Where:

Q_(conduction) = -kA(T_wall-T_outside)/(Thickness of wall)
[A = total surface area of walls on house]

Q_(solar H.G. from windows) = (Area of window)(Shading Coefficient)(Solar Cooling Load Factor)

Q_(convection) = hA(T_wall-T_ambient)
[A = total surface area of walls on house]

From there I solved for the new temperature of the wall inside (T_wall). T_wall was used to show how the house's inside temperature changed from the desired inside temperature due to the outside temperature and solar heat gain. I'm currently finishing up my first thermodynamics class so this information is still relatively new to me. What information I could find for solar heat gain was from this website: Solar Heat Gain

Ten years of outside temperature data was pulled from the usclimatedata website. Does this equation look correct? Thanks in advance for any helpful advice/help!


texts: Mohr's circle: maximum normal stress tensor

texts:
Given:

$$
   \sigma_{ij}=
  \left[ {\begin{array}{cc}
   -20 & 60 \\
   60 & 90 \\
  \end{array} } \right],\quad i,j=x,y
$$

I want to find the principle stress tensor $\sigma_{ij}^{pr}$.
Using the Mohr's Cirlce, I get:

$$\sigma_{max}=116.39,\sigma_{min}=-46.39$$

the points where the circle intersects with the $x(\sigma_{xx},\sigma_{yy})$ axis.

From there, how do these points make up the principle stress tensor?

Is

$$
   \sigma_{ij}^{pr}=
  \left[ {\begin{array}{cc}
   116.39 & 0 \\
   0 & -46.39 \\
  \end{array} } \right],\quad i,j=x,y
$$
correct?


texts: How do we define the durability as per density?

texts:
We define the durability with the equation as seen below.

$$x\propto \frac{\text{Cross-Sectional Area}}{\text{Cross-Sectional Area}\times \text{Length} }$$

Hence

$$\therefore x\propto \text{Length}^{-1}$$

This equation was only for matters which has same density. Let us imagine that there is a tree with $3\text h$ and an iron pole with $3\text h$. Now we see that our equation doesn't work in this condition. The iron pole will be more durable than the tree even if they have same lenght. Then, how do we define the durability as per density?

According to our equation,

$$\text {Tree} = \frac {1}{3h}$$

$$\text {Iron Pole} = \frac {1}{3h}$$

It seems like their durabilities are same. However, Iron pole has greater density than tree. By the way, Iron pole is more durable. How do you explain this? or Is there any equation that we can use when there are two matter which doesn't have same density?


texts: (CAD) Inventor - Extrude rectangular pattern of circle sketches

texts:
[

Hello, I try to extrude a lot of circle sketches but I can't select all of them and when I try, there is so many lags. Does someone has a solution ? I am sorry I'm a noob in CAD. Thank you so much ! :)


texts: Can you use an accelerometer to measure beam deflection under static loading?

texts:
With an appropriately collocated accelerometer is it possible to retrieve lateral deflection of a beam under static loading.
The beam will be loaded and then deflect until it reaches equilibrium with external load. Could one integrate accelerometer signal twice to obtain how much has a point been deflected?
This theoretically in the framework of an Euler-Bernoulli beam under pure bending.


texts: How should I position two shelf supports for the minimum deflection?

texts:
The above is the shelf that I'm intending to put up.  It will have two symmetrically placed supports. This is probably a simple question that really should be answered in all DIY shops but...

Assuming a uniformly distributed load across the entire shelf, what should the value of x be to obtain the minimum deflection anywhere along L?


texts: Why is the truss member between two fixed supports zero?

texts:
If i first assume the member(far left) to not be zero and use method of joint at both points of constraint, with both constraints having unknown vertical reaction, it cannot be solved.

Load and lengths are known, horizontal reaction can be found.


texts: How do I determine the temperature inside a transformer vault?

texts: I am trying to determine the temperature of an underground concrete vault buried 10m underground. The vault has the following dimensions: 2640mm x 5995mm x 2640mm with a wall thickness of 250mm. The transformer has the following dimensions: 2083mm by 1702mm by 1257mm. It has heat losses of 2080W to 11000W. How can I determine the temperature inside the vault? How would adding mechanical ventilation change the temperature inside this vault?


texts:
I thought I understood what a proportionality was, but it was recently called into question. I want to make sure I fully understand how the term is generally used in the engineering world. The basic explanation of proportionality is that two variables are related by a constant multiplier such that a change in one of them results in a change in the other, scaled by this constant of proportionality. So we could say:

$$
A(x_1, x_2, ... x_n) \propto B(x_1, x_2, ... x_n)
$$

or

$$
A(x_1, x_2, ... x_n) = cB(x_1, x_2, ... x_n)
$$

where $A$ and $B$ are the proportional variables and $c$ is the constant of proportionality.

My question deals specifically with what restrictions are placed on this constant. In my previous description, $A$ and $B$ were functions of a number of variables, they are necessarily the same variables. Is this the case?

Additionally, in engineering, few things are every truly a constant, so our constant of proportionality could be a function of a number of parameters:

$$
A(x_1, x_2, ... x_n) = c(y_1, y_2, ... y_n)B(x_1, x_2, ... x_n)
$$

However, it is my understanding that when discussing proportionality it must be assumed that all of those $y_n$ parameters must be held constant within your system. This is where my understanding starts to come into question. It was suggested that $c$ need not be independent of $A$ or $B$ and this is still a proportionality:

$$
A = c(B)B
$$

Now, I had always assumed that this is a prime example of a situation where $A$ is not proportional to $B$. But upon thinking about it further, I came up with 3 limited domain cases given the following relationship:

$$
A = (e^B - 1)B
$$

case 1: $B < -10$

case 2: $B > 10$

case 3: $-\infty < B < \infty$

It seems to me that for case 1, we could perhaps say that $A \propto B$ given the small change in the coefficient. But for cases 2 and 3, would it ever be reasonable to consider $A \propto B$?

To clarify my questions: Is anything about my understanding as outlined above wrong? Are there any situations where it is correct to say $A \propto B$ and that the constant of proportionality is a strong function of $B$? Does this answer change if we can consider $B$, and therefore $A$ to be nearly a constant? Is that a useful situation to consider?


texts: PID controller - Counterproductive derivative

texts:
I'm having trouble understanding the derivative part of a PID controller, because it sometimes seems to react the opposite way that I would like.
Let's use a simple example where :

the controlled variable is a vehicle position, on a 1 dimension axis (in m)
the actuator signal is the vehicle speed (in m/s)
the setpoint is 100 m
the sampling time is 1 s

Now let's analyze two cases:

The current position (at t = Ns) is 80 m, and the previous position (at t = (N-1) s) was 60 m.
Hence, we've made 20 m of progress toward the setpoint of 100 m (we're going the right way).
The current error is (100 - 80) = 20 m, while the previous error was (100 - 60) = 40 m: this gives a derivative error of (20 - 40)/1s = -20 m/s.
The current position (at t = Ms) is 140 m, and the previous position (at t = (M-1) s) was 120 m.
Hence, we've made 20m of regress from the setpoint (we're going the wrong way!).
The current error is (100 - 140) = -40 m, while the previous error was (100 - 120) = -20 m: this gives a derivative error of (-40 - (-20))/1s = (-40 + 20)/1s = -20 m/s.

In both cases, the derivative has the same value, so the controller's derivative behavior will be the same. But the situations are very different: in the first case we're getting closer to the goal, while in the second we're getting away from it.
Why is the derivative part making the same adjustment for two situations that are so different?


texts:
In the real world, would this pinned frame exhibit a deflection in the fixed, left hand side column?

Arguments from peers largely surround:

1) There wouldn't be left-column horizontal deflection because the moment cannot apply through the pin to the column.

2) There would be left-column horizontal deflection because although the moment doesn't travel through the left-column pin, in reality the right side will sag and pull the left-column towards the right.

Exceptional answers will explain if points 1) & 2) are correct; provides additional information we haven't considered; and the inclusion of visual diagrams if relevant.


texts: Would connecting 100's of small telescopes into one huge telescope make for a significantly better telescope?

texts:
Not sure if this is a Physics related or Engineering related question, but imagine that we would take 100's of small hobby telescopes and somehow managed to point them all at the same point in the sky at the same time. We would than digitally process this image.

Would we be able to combine these images and get image quality of a much larger telescope? We assume that all of them would point at a same part of sky at the very same time. Do you think we could get a significantly improved image compared to individual telescopes? And if so how much of a better image would we get?


texts: How could you produce large quantities of metallic hydrogen?

texts:
Could you somehow crush hydrogen atoms with magnetic fields in order to produce it? Or maybe someday someone will invent a material capable of withstanding 500GPa and we'll have giant machines that crush atoms together?
Given that diamonds can be synthesized as well I don't think it would be too hard.


texts:
I've been working with a team of 'designers' that are highly concerned over a potential failure mode of ABS plastic. Their theory is that under a static load well under the yield point of the material that a plastic ABS part will eventually stretch and fail.

The specific example is a handle that I've calculated to hold over 190 lbs before yielding is being loaded to 30 lbs and held there for seven plus days.

The only type of failure I can think of that this could be would be creep, but since we're working at constant room temperature, constant load, evenly distributed load over a wide surface (3 square inches) and so far below the yield point I can't imagine that this test would produce any useful results.

Can anyone think of anything this test would show? Is there a failure mode that I'm not thinking of (specific to ABS or not)? Or is this more likely a test in futility?


texts: Can current passing through a wire potentially ignite gasoline? If not, why?

texts:
I am doing some restauration on my old Vespa and since the fuel indicator doesn't work, I took the fuel gauge system out of the tank and tried to understand how it works to repair it.

Apparently, 3 wires go to the tank, one is ground while the other two should be live (12V RMS voltage I think). Now, looking at the gauge, there is an empty plastic piece which stays on the surface of the gasoline and moves a potentiometer which can be also submerged by gasoline (when the fuel tank is full) but in practice it is often not submerged.

The tank is, of course, closed but air can go inside it (in order to let gasoline come out to the engine).

Now, at first I didn't even think about it but my father asked me:

  Isn't it dangerous to have current (and possibly a spark) inside your fuel tank?

So far the number of Vespas I saw blowing up is zero so it probably isn't dangerous, but still, I don't understand why. My reasoning is the following:

The current passing through the potentiometer may be very low and therefore not cause much heat being dissipated.
The risk of a spark between contacts is probably low due to the low voltage and since the electrodes should be always in contact.

Needless to say I'm not satisfied with my explanation and I'd like someone who knows about physics to explain me why the risk of explosion is very low (or non existent hopefully).

In case you are wondering, the gauge is the following


texts: How I can controller the reach of WIFI antenna?

texts:
I would like to know, which antenna 802.11 model, it your reach can be controlled.

In a some researches, I'm discovered a tool called "iwconfig", native on some Operation systems Unix Like. It is used by own OS to manager interfaces wireless.

Some options of tool:

interface essid {NNN|any|on|off}
interface mode {managed|ad-hoc|master|...}
interface freq N.NNN[k|M|G]
interface channel N
interface bit {N[k|M|G]|auto|fixed}
interface rate {N[k|M|G]|auto|fixed}
interface enc {NNNN-NNNN|off}
interface key {NNNN-NNNN|off}
interface power {period N|timeout N|saving N|off}
interface nickname NNN
interface nwid {NN|on|off}
interface ap {N|off|auto}
interface txpower {NmW|NdBm|off|auto}
interface sens N
interface retry {limit N|lifetime N}
interface rts {N|auto|fixed|off}
interface frag {N|auto|fixed|off}
interface modulation {11g|11a|CCK|OFDMg|...}
interface commit (Para salvar alterações)

I'm using an device USB TP-Link N TL-WN823N, 2.4 Ghz

But this devices is basic. I can only set some settings like, Mode of operation (ad hoc, monitor, manager), channel, essid...

I believe that I can control your reach, I should to manager the txpower or sensibility (sens). When I try to set it, the system returns that operation is not supported by device. Possibly is because this device is not dedicate to used like access point.

So, I would like to know if are some antenna 802.11 that the reach can be controlled by txpower, sensibility or something
physical to break the reach


texts:
I'm designing a coordinate measuring machine for my FYP. I need to know what is that black zigzag flexible cover usually made of. Is that leather, rubber or some other material? And how is it fabricated?

It is called a ‘Ball Screw Cover’, they are available in just nylon or fiber coated plastic-
Sometimes, you just need the term for the component to get going down the right path: “Ball Screw Cover”


texts: How is any kind of structural reliability achieved if the probability of annual wind speed exceedance is 0.02?

texts:
Above is the definition of fundamental basic wind velocity from Eurocode 1. According to its instructions, wind loads on building are supposed to be calculated based on this velocity. It says that this velocity needs to have an annual risk of being exceeded of 2 %. But isn't this quite a risk? If we design our building's extreme wind loads according to this value, doesn't that mean our building has 2 % chance of failing? To me that seems quite high.
Also according to Eurocode, in reliability class RC2, we should have a reliability index of at least 4.7, which approximately corresponds to probability of failure less than $10^{-6}$. This is much lower than 2%.


texts: Help with closed loop heat controller (for a non engineer)

texts:
I am interested in setting up a controller which can modulate the output of 2 hotpads based on input from an infrared thermometer. The hotpads have their own dials, but I am considering controlling them by voltage instead. So my question is, what is the simplest method for modulating voltage (or rotating dials) based on temperature? One problem in particular that I am unsure about is how to account for the gradual propagation of heat through my system, since I am heating a large (2' diameter, 1" thick) rotating aluminum disk. I have a laptop at my disposal, and minimal funding.

I would prefer to avoid wiring my own sensors, so any recommendations you have on how to achieve this would be great. I could handle a breadboard at best with my experience, and I have only an introductory level understanding of electromagnetism... But I can code in C, Java, and Matlab, and I have experience assembling PCs, so I am hoping this is within my abilities.


texts: I am not sure if this is the best place to put this, but if I'm in the wrong place please tell me where I can go. So I know a peltier module is not the most efficient, however my goal is to make a hand warmer / cooler with a petlier module. My operating temperatures will be around 60f to 90f, nowhere near the max of most peltiers. My first question is can it be powered by a small battery? Second, would I need a heatsink with this kind of temperatures that I want to produce and if it's required, is there any passive cooling I can use without being thick? Third, is this idea practical?


texts: Determining the torque needed for a servo motor

texts:
I'm looking for a bit of clarity on a design I have in mind. Please bear with me as I have no background in physics, engineering and this is part of my first real DIY project, so the knowledge base upon which I write this question is fairly low.
I'm trying to rotate a hollow bamboo gardening stake (30cm long, 2.5cm diameter, denoted by B in the image below), with a servo motor. I plan on mounting the servo with a rounded mount (denoted by A) that will be printed to fit snugly inside the stake. There will be "fingers" attached to the gardening stake (represented by the light grey cylinders) upon which a PVC cable will rest (represented by the orange line). We will be hanging some light objects (max weight 0.15kg /item) on the cable, between the cylinders.
The goal is to rotate the stake such that the cylinders move from position 1 to 2, and the cable slides off, then rotating the stake back to its original position.
I've done some reading about torque and think the calculation I need to perform is summing the torque required to turn each weight (or force) hanging down on the cable, for its respective distance from the servo. Alas, being a newcomer to the world of physics and engineering, I have no idea if that's right, and prefer to try and be precise than overcompensate by purchasing unnecessarily powerful servo motors.
How would I go about determining the torque required by the servo motor? Or does a simpler design exist to create the desired motion, that I've not thought of?
Thank you in advance.


texts: What is the specific heat capacity of corrugated cardboard?

texts: I am testing out different materials with different specific heat capacities and their correlation with soundproofing (e.g. wood, cork, styrofoam, etc.) but I can't seem to find the specific heat capacity of cardboard anywhere (the average S.H.C. of regular corrugated cardboard).


texts: Reasonable expected yield strength of A513 steel

texts:
I'm looking to build a fish-tank stand for a decently large fish tank (300 gal).  I'm looking at building it out of A513 steel because that is easily available locally.  However, I am having trouble finding a good yield stress to build my design on.  A513 does not have a maximum yield stress requirement, so the measured results I find on the internet are all over the place!
Is there a reasonable estimate for maximum yield strength for A513, short of going to the company providing them the steel and asking them which specific supplier they are using, and then getting data from that supplier?


texts: Import Coordinate System as Marker in MSC Adams

texts: A very simple question, yet I couldn't find an answer: I created a simple part (e.g. in SolidWorks) with one solid body and two Coordinate Systems. I would like to place my Joints, Revolutes, etc. in Adams on the already existing Coordinate Systems from SolidWorks. Therefore, it would be necessary to import the two Coordinate Systems as Adams Markers. How can I do this?


texts: Why in paper space of AutoCAD 3D are colors of object shade not displaying

texts:
I am using AutoCAD 2016. In model space, I draw a colored 3D object. Then I made an isometric view of that object in the paper space (layout page). In the 'Appearance' section of 'Drawing View Editor' I selected the 'Shaded with visible lines' option as below.

In spite of that, in the layout page, the shade of the object, and its color is not displaying.
I also make it confirm that in the 'Page Setup' window, the 'Display plot styles' checkbox is unchecked.
I did many things to have shade colors in layout, but nothing became successful.
Can anybody suggest me a solution?


texts: How to derive Darcy's law only in the case of saturated soil without derived all cases?

texts:
How to derive Darcy's law only in the case of saturated soil in mathematical/theoretical way without having to derive all the cases?

I can only find the generalized theoretical proof for all cased but not its more simple version.

Here is its simple version I ask you to derive(This is coming from Introduction to geotechnical engineering by Das):

$$v=ki$$

Where $v$, $k$ and $i$ are the discharge velocity, hydraulic conductivity and hydraulic gradient, respectively.

Darcy's law is a constitutive equation that describes the flow of a fluid through a porous medium. The law was formulated by Henry Darcy based on the results of experiments on the flow of water through beds of sand, forming the basis of hydrogeology, a branch of earth sciences. But then I was only able to find the theoretical derivation of the generalized Darcy's law


texts: What is the significance of hinge in the internal structure of the beam?

texts: I had come across a question on shear force and bending moment diagram where a cantilever beam with a roller support at point C is given and the portion beyond point C in overhang. Does this hinge act as a internal release point in the structure? If yes then the does this mean bending moment about point B is zero.


texts: Shouldn't steam be compressed water in SAGD?

texts: I am doing some labor work on a rig and am confused about something. I heard from my superiors that we are injecting steam at 180°C with the wellbore pressure being 2 MPa. If I look at these conditions on a steam table, shouldn't the steam be compressed water?


texts: How to find the smallest change in voltage

texts:
You are comparing different A/D converters that will have 3.2 V and -3.2 V as their positive and negative reference voltages, respectively. Out of the following, converter _ can resolve the smallest change in voltage, which is approximately_  . (m = milli and u = micro)

(A) 16-bit, 100 kHz

(B) 8-bit, 1 MHz

(C) 15-bit, 512 kHz

(D) 19-bit, 256 kHz

(E) 17-bit, 330 kHz


texts: Why aren't turbos/turbines controllable pitch?

texts: I am wondering why turbines are not implemented with controllable pitch blades (on the rotor system)?  I assume the reason is that the coupling between the stator and rotor systems posed by typical controllable pitch mechanisms poses an unacceptable frictional loss for such a high speed/ low torque application.