texts: How problematic is it to run vapor saturated liquid through a scroll pump?

texts:
I see that scroll pumps often have "Vapor ratings" of something like N Liters of water per hour. I know in rotary-vane pumps, it's a big no-no to run any kind of vapour through them and you need a cold trap. On the other hand, I know you can run vapour through a diaphragm pump, but it's generally regarded as a bad idea.
Are these vapour ratings just for whatever doesn't make it into the cold trap, or do they actually allow you to skip out on the need of the cold trap all together?


texts: Cheaper alternative to silicone rubber sponge?

texts:
Is there an alternative for silicone rubber sponge? The reason I was thinking of this material was because I needed something that was

Flexable
Thermally Conductive
Electrically Insulated
Waterproof

Silicone rubber seems very expensive, so I was looking for a cheaper option that would still meet the above requirements.


texts:
My question has two parts.

What is BSc engineering and Btech engineering ?
Which has the highest validity in electronic and computer fields?

 PS : Specially in North American region.


texts: Looking for locking "lanyard" reel mechanism

texts:
I'm working on a system that requires a small cord (~3ft long) to retract up into a reel and lock in place so it cannot be pulled away from the reel. Sort of like a seatbelt mechanism after it's been pulled too far or too hard.
I'm hoping to find something off the shelf that is small and lightweight (~100g) before building my own solution. I've found industrial spring reels like these, that are of the correct size and construction, but none have the locking functionality I'm looking for.
Does this mechanism sound familiar to anyone?


texts: how are these radial piston rotors machined

texts:
A typical radial piston rotor can have simple holes machined from the outside through the inner diameter to create flow channels for hydraulic fluid to actuate the pistons.

I came across this model and I was wondering, how would something like this get machined?


texts: How much should I put effort to refine a Response surface?

texts:
A response surface that I have obtained from a DOE analysis with multiple variables, show small irregularities when I plot 2D variable-vs-variable curves . like somewhere it should be exponentially and only reduce, it changes the gradient in some points.

I assuem it's from the impreciseness of the fitting of the Response surface. How much effort shouldI put to obtain a more precise curve ?


texts: How to scale a 3D object on 2 dimensions only?

texts:
How can I scale a 3D object only on 2 dimensions with Autocad?

For instance, I would like to scale a complex object whose maximum dimensions are 50x30x10 (on axes x, y and z, respectively) obtaining an object whose maximum dimensions are 75x45x10, i.e. I would like to scale it up to 150% on x and y axes only, leaving unchanged the z dimension.


texts: Why does blood pressure cuff size matter?

texts:
There are a number of sources that confirm blood pressure cuff size can have a significant impact upon the measured reading.  (See 1, 2, 3, 4)  The most succinct description I have seen is this:

  The error that is introduced by too small a blood pressure cuff is a reading that is too high and the error can be 50 mm and this is not rare. ...
  Too large a cuff introduces the opposite error, an artificially low reading but not nearly the magnitude of the too small cuff error.

Disclaimer, I haven't reviewed the material too closely on the site I quoted, so it's likely they're trying to sell something.  But their summary is in alignment with other non-commercial sites I've found.

What I'd like to understand is why the blood pressure cuff size affects the measured reading.

From my simplistic understanding, a blood pressure cuff squeezes against the brachial artery.

The compression of the brachial artery temporarily stops blood flow and allows the practitioner to measure when flow commences again.

Assuming the cuff is large enough to stop blood flow, I would like to understand the physiological principles that are affecting the read measurement.  And I think this is a valid engineering question as I'm interested in the interaction between the measuring device (blood pressure cuff) and the system being measured (blood pressure via the brachial artery).  In other (much bigger) words, what biomedical engineering principle is at work to cause the measured blood pressure to differ?


texts:
I'm planning to build an air-dropper for a small drone - a device to release small payloads hanging under the drone.

This is a commercial example of such a system, used with a much bigger drone - for heavier payloads, pretty heavy itself, and using the drone's built-in systems for control:

https://www.youtube.com/watch?v=e81eQ0pYLCs

(7:18 - system in action. 5:44 - the part, for which counterpart I'm asking.)

I'm planning to build something similar, but much smaller. Payloads of up to 100-150 gram (but often smaller too), a completely independent control system. I already have working remote control electronics capable of outputting 3.3V at 40mA (driving a tiny coreless motor like this; I also have such motors), under 10 gram together with the battery.

I still have no idea what sort of actuator I could use to release the payload. I'd prefer it to remain unpowered when 'latched', needing only power to open (drop the payload). It should be as lightweight as possible, because any of its weight takes away from payload capacity of the drone. And not being very expensive would be a big plus.

For the ideas I had so far:

Most servos I've seen are rather on the heavy side, or provide so little torque I'm afraid any latch I come up with won't suffice.
I considered pairing a permanent magnet and an electromagnet that would cancel out the magnet's field, but first I'm not sure if I can output a field strong enough, and then the cancellation won't be perfect and if my payload is very light, it won't drop.
I don't think I have the current to drive a linear electromagnetic actuator to unlatch a hook (not sure about that though).
I don't have means to build more complex gearboxes to convert the high RPM of the tiny motor to torque - at least from scratch; if something of that kind is commercially available and small enough, it might be good.
...also, it would be great if it was fully reusable and safe. I seriously considered just a small relay to put full current from a battery through a resistive spiral to burn through the line with the payload. I'm not enthusiastic about this idea.

I'm not specifying the housing, 'hook', line, attachment methods etc here - these are to be made such as required for it to work.

(also worth considering: a fully mechanical connector with no electronics; disengaging on a maneuver not encountered in normal flight, e.g. a rapid drop. I can't generate negative-G, but I can make the drone -almost- drop out of the sky. If this could disengage the hook, that would also be a workable solution. This is not as preferable as it requires considerable vertical space and is rather risky.)


texts: What is the gain and time constant of a system with a constant output?

texts:
For example, if your transfer function is defined as :

$$\frac{H(s)}{Q(s)} = \frac{1}{5s}$$

What would the gain and time constant be in this case (since it's usually in the form of $\dfrac{k}{Ts+1}$ where $k$ and $T$ are the time constant and gain, respectively)?

(This is the transfer function for a tank being filled, but the exit stream is a pump so it is constant. Where $H$ and $Q$ are deviation variables for output and input, respectively)


texts: Air flow optimization in a small opening

texts:
I have a 36 x 6 cm opening from where I need to pull fresh air. I need to optimize for air flow as well as noise. I considered using 6 Noctua NF-A6x25 fans which would give me a total of 175,2 m3/h at 19.3 db/A with 1,61 mmH2O of static pressure per fan. Since the air flow was a bit on the low side and I thought of using 4x Noctua NF-B9 redux-1600 fans with an 36 x 6 cm to 36.8 x 9.2 cm air guide, which would, in theory, give me a total of 257,2 m3/h at 17.6 dB/A with 1,61 mmH2O of static pressure per fan. There will only be a dust filter on the opening. The fans are oriented horizontally thus directing air from the bottom up.
Having said that, I have a few considerations:

What is better, 6x 6cm fans or 4x 9.2cm fans with an air guide given the importance to air flow?
How much of the air flow is hindered when using 4x9.2cm fans on a 36x6 cm opening?
What would be the optimal height of the air guide?
Can an internal structure of the frustum help with optimizing airflow?


texts: In the general case of the plane motion of a rigid body, the resultant does not pass through the G of the body. Why is that?

texts:
My book, Vector Mechanics for Engineers: Statics and Dynamics 12th Edition,  states in the plain motion of a rigid body, the motion of the rigid body is completely defined by the resultant force and resultant moment about G acting on the body. But it also states

We also note, as we did earlier, that the system of the external forces
does not, in general, reduce to a single vector m¯
a attached at G. Therefore,
in the general case of the plane motion of a rigid body, the resultant of the
external forces acting on the body does not pass through the mass center
of the body.

Is it because the resultant moment is not zero at G in general, and if the resultant force doesn't pass through G, we can replace it with  the same vector attached at G and the couple ? Is that right?


texts: How can you calculate wear of steel pipe that is transferring sand laden fluid under pressure?


texts: Can a vacuum in a room increase the pressure in a tube?

texts:
Ok, So I work as a Marine Engineer but I do not have an engineering degree so I am having a hard time wrapping my head around this problem.
So currently on my ship we had a minor spill overboard from our black water collection tank (lower left) where air was drawn in from our grey water (lower right) tank. The air that was drawn in agitated whatever liquid was in the black water tank, causing it to foam and go overboard.
Background Information
The grey water tank is in a machinery space that is very well sealed in case of a fire, lets make the assumption that it is a sealed box. The water from our sinks, showers and drains gravity feed into this tank. When the tank reaches a certain level the pressure head from the sensing tube will cause the valve activator to send a signal to our vacuum discharge valve to open. This will allow our vacuum collection system to draw water from the grey water tank. The vacuum discharge valve will close when the pressure head in the sensing tube goes down to a certain level.
A vacuum in the system is provided by a pump recirculating the liquid in the BW Tank through an educator.
The Problem / Proposed Cause

The proposed cause of air being drawn into the Vacuum Collection System was due to an exhaust fan in the space being set to high while the intake fan remained at low. This caused a vacuum in the machinery space which apparently caused premature pressurisation of the sensing tube tube to act as if the pressure head was great enough to cause the Valve Activator to open the Vacuum Discharge Valve eventually allowing in air.
What I cannot wrap my head around.
I can't seem to understand how a vacuum in the space would cause over pressurization of the sensing tube? I would think a positive pressure in the machinery space would cause that.
Is there some sort of law in physics that can explain this for me? Or does the proposed explanation have flaws?


texts: How can one reliably prevent pedestrian access to a parking garage, but allow vehicular access?

texts:
Consider a typical private parking garage for a condominium or apartment building.

There is currently a typical garage gate that opens and closes (slowly) to allow vehicles to pass safely through the gate.

What is the optimal method for preventing access into this garage by pedestrians/foot traffic, but ensuring the same safe entry/exit for vehicles?

The goal is to make sure people cannot enter/exit through the same gate that vehicles may enter/exit.

Practically implementable solutions only, please.  Cost need not be a factor.


texts: How to Pull Heat Quicker from a Thermo-Electric Cooler using an Aluminum Heatsink

texts:
I just purchased an aluminum heatsink that I am using to "wick" away heat from a Peltier; however, I was wondering how I can pull heat from the hot side of the peltier quicker.

I have purchased large, small, medium sized aluminum heatsinks and have not been able to explain why one works better than the other. This is the root of the problem: what determines how fast a heatsink can wick heat away from the hotside of the Peltier?

I was thinking adding copper heat pipes, such as the ones on a laptop heatsink-fan combinations; however, I would need to thermally attach the copper heatpipes to the same heatsink to cool them. I am afraid this might kill the efficiency of the heatsink.

Thank you, and I am looking forward to hearing your suggestions


texts:
I am working on a school project that requires me to build a machine. I have designed the machine but I am stuck at torque calculation. The problem goes like this, the machine supposes to rotate a stack of trays (5 trays stacking up vertically) at a constant speed.

Below is the information:

Mass of each tray: 8 kg

Tray Radius: 0.3 m

Moment of inertia of each tray: 0.333 kg m^2

Let's just say the friction is very small and can be neglected. The rotational speed should reach 1200 rev/min in 5 seconds. How do I calculate the torque required to rotate the stack of trays?

Any help would be appreciated!


texts: How does a nuclear powered rocket engine work?

texts: Nuclear power always require some way of converting the energy from nuclear to electrical or mechanical to be useful. For example, in a nuclear power generation facility, this is done through heat/steam which drives mechanical generators. What is the mechanism used to convert nuclear energy to rocket power?


texts: Why do we need flow rate measurement devices?

texts: When we can manually measure the discharge flow rate,what for have we developed the concept of venturi meter or orifice metre?


texts:
I'm trying to make some code to predict the performance of a sounding rocket I want to build.  To do this, I need the atmospheric density at any point in the flight for the time-step simulation I made.

I got my atmospheric density in slug/ft^3 from https://www.engineeringtoolbox.com/standard-atmosphere-d_604.html and put all that data in this python script, under the assumption that the function that would best describe this data would be a negative exponential.

from scipy import optimize

import numpy as np
import matplotlib.pyplot as plt

def fxn(x, a, b, c):
    return a*np.exp(-b*x) + c

altitudes = np.array([0,5000,10000,15000,20000,25000,30000,35000,40000,45000,50000,60000,70000,80000,90000,100000,150000,200000,250000])

density1 = np.array([23.8,20.48,17.56,14.96,12.67,10.66,8.91,7.38,5.87,4.62,3.64,2.26,1.39,.86,.56,.33,.037,.0053,.00065])

altitudeLinSpace = np.linspace(0,500000,500000)

#Popt returns a array containing constants a,b,c... etc for function 'fxn'
popt, pcov = optimize.curve_fit(fxn, altitudes, density1, p0=(1, 1e-6, 1))

print(popt)

#Plots data
plt.grid(True)
plt.ylim((0,25))
plt.plot(altitudes, density1)
plt.plot(altitudeLinSpace, fxn(altitudeLinSpace, popt[0], popt[1], popt[2]))
plt.show()

Which gives me this graph when I plot the solution ( Altitude ft (x), density in slug/ft^3 * 10^-4 (y)):

The orange curve is what python found as a solution, blue is the plot of the data I used to curve fit.  Because of the poor fit, my guess is that the data is actually not a negative exponential, but I'm not really sure how to determine the kind of function this might be...

I'm not looking for perfect, but using a polynomial is a less than ideal solution here as the 'wiggles' give too much error at higher altitudes.

Any suggestions on how I could fit this data better would be greatly appreciated!

Solution from Math SE: https://math.stackexchange.com/questions/3009560/curve-fitting-atmosphere


texts: Can be used a lab on a chip device as a nuclear fusion device?

texts:
This is what a lab on a chip is
https://en.wikipedia.org/wiki/Lab-on-a-chip
I ask if could be used as a nuclear fusion device , that could rise the number of nuclear fusion per atom, knowing that microchannels can mix better substances?
Microchannels could be made by engineering means, like photolithography , already are made microchannels at the size of few micrometers
Microchannels could be working either by light either by small electromagnets
I think that could work because the nanochannels or microchannels could be used one time, as pellets are used in the laser driven nuclear fusion.
Could be used, burnt , and replaced with another pellet like usual pellets are used in the laser driven nuclear fusion.
It's just needed that a continous flow of pellets like this to be used
Notice that i spoke about a microchannel that works either by light either by small electromagnets.
The substances , or in this case of fusion, the ions could be moved by a magnetic field
As far as i know ions could be moved no matter how small a channel could be , by a magnetic field
Laminar flow would not be a problem since the number of molecules involved in fusion would be small


texts: What are the best materials to use for producing drinking water from the Air?

texts:
There are several companies producing equipment that produce drinking water from the air. They use dessicants, hygroscopic brine, or deliquescent salts, to adsorb water from atmospheric humidity.  Then they use a heat source to evaporate the adsorbed water to be condensed and funneled to a collection point. Some systems use solar photovoltaics (PV) to run fans and controls, and solar heat for de-adsorption. One system claims to use the process's downward flow to create a lower pressure for de-adsorption, which makes it more efficient at lower temperatures.

I'm looking for information on electronic controls, the core of which is probably a delta-humidity-inside/outside sensors; the best adsorbant material (quantity and configuration), and the material to use for the condensation surface.


texts: Why are concrete bridges more prevalent than steel bridges in the United States?

texts:
According to the United States 2014 National Bridge Inventory the number of concrete bridges far outstrips the number of steel bridges.

Reinforced Concrete: 253,336

Prestressed Concrete: 148,333

TOTAL CONCRETE: 401,669

versus

TOTAL STEEL: 181,095

Why would concrete bridges outnumber steel bridges?

Basis for Categorizing By Material Type

The concrete and steel totals are based on the "Main Structure Type" inventory code from the NBI Recording and Coding Guide. This is a three digit code defined as shown below.

Motivation for Question

In the state where I work we often design steel and concrete "alternates" for each bridge. However, we consistently see the concrete alternate (usually prestressed) selected instead of the steel. I'm trying to understand why this would be since steel seems to offer quite a few benefits...quick construction in the field, predictable material properties, often lighter than concrete girders, damage is usually readily inspectable, etc. etc. I've always chalked it up to some sort of inertial regional preference (when I was in Chicago we saw tons of steel, but in California and Nebraska it's mostly been concrete) and thought I'd see if there were some more substantive reasons.


texts: Transistor choices for switching high speed data communication lines

texts:
So here's my situation: I'm a mechanical engineering student working on a product innovation for one of my courses. The product itself is fairly heavy into embedded programming, which I'm comfortable with. What I'm less comfortable with is the small electrical engineering bit I need to do.

Essentially, I need to be able to control (turn on or off) a high-speed (USB) data line via transistor (or SSR, if you want to be pedantic). When a high signal is sent to the (base or gate), the line is enabled, and data can flow. When there is a low present, the communication is disabled.

Because I'm dealing with very low current flow, my inclination is to use an NPN transistor, mostly because I have a few handy. Is there a better transistor or special rating I should be looking for for this application?


texts: Why are there multiple ways to save polygonized 3D model data?

texts:
In CAD, there are multiple file formats only for the scope of saving polygonized models in three dimensions.

For example, there is the Object File Format and furthermore, there is the much more famous STL format.

What are the different (most important) use cases and reasons to use especially one of them?


texts:
I was surfing through the web to find any article about why boxers don't like headgears. Then some random website claimed that a headgear doesn't absorb the punches moreover they limit vision. So I thought of a headgear that may prove useful to absorb punches. So the idea is actually using a little modified headgear with a face cage. I'm quite sure some of you have seen Pain in Naruto. So I will put some button like metal on my face cage that may make me look like a silly Pain. Then these buttons will be connected to some hollow metal tubes with spring that will only contract if the force projected on the cage exceed a certain value. The hollow tube will support headgear's structure, then these hollow tubes will be connected to some more buttons situated at the back of the head.  These buttons will act as a delicate pressure regulator we see in pressure cookers. These buttons will also be connected with the tubes with springs.
What do you think of this? Is it possible to build a headgear like this which will prove useful according to the intended way?


texts: Why are earthfills fully covered in concrete where they join bridges?

texts:
Here's how a typical earthfill carrying a roadway joins a typical bridge

Parts of the earthfill slopes are greenish - that's grass - and parts are whitish - that's concrete.

The earthfill slope is fully covered in concrete where it joins the bridge but the rest of the earthfill is only partially (lower part only) covered in concrete, the rest of the slope is grass-covered.

This photo is of a 20+ meters high earthfill and lower earthfills' slopes are usually not covered in concrete at all except where they join bridges - the join is usually fully covered regardless of how high the earthfill is.

What's so special in that part where the earthfill joins a bridge that this part is fully covered in concrete while the rest of the earthfill is either partially covered or not covered at all?


texts: Why are the synchronous reluctance motors not self-starting?

texts:
I have been studying synchronous reluctance motor since a month. I am curious to know why is this motor not self starting?
If used with an inverter, this motor can be made self-starting. Or by adding conductors bars on the rotor just like an induction motor, to make it line-start motor.
Synchronous reluctance motors do not have conductors or permanent magnets in their rotors. It is just iron with flux guides/barriers. There is no opposing force in this motor as present in PM motors. I am aware that if position sensor and inverter is not used, the rotor may rotate in any direction that is undesirable. Is there any other reason that this?


texts:
I know how a 3 Transistor CMOS camera pixel works. As I understand, 4T CMOS pixels have one additional transistor that connects the photodiode to a so-called floating node.
What is that floating node and what is it good for? Seems like a storage for photo-generated electrons, but I thought CMOS pixels give you voltage, not charges (light CCD's...).
Maybe it's good for multi-integration to reduce readout noise (think I was reading that somewhere)?
Any help is welcome, including good hints for further reading on the principle of camera pixels.


texts: Is strain energy the same as potential energy, or something differen?

texts:
Sorry for this stupid, basic question. But I got hung up on it.

We know from Clapeyron's theorem that the strain(internal) energy of an elastically deformed body is equal to half the work

$$
U=\frac{W}{2}
$$

What I'm effectively confused about is, where does the rest of the energy from the work go? From conservation of energy the other half of the work has to be somewhere. Can you say that the other half is potential energy? Or is strain energy and potential energy effectively the same? Or am I thinking about this all wrong?


texts: Are stator magnets in brushed DC motors radially magnetised?

texts: In an electric motor like this one, are the stator magnets radially magnetised, as in, each of the two magnets has opposite poles on the inside and outside diameter?


texts:
I'm working with a custom made mini computer, am335x based.
It comes with 2 GPIO ports that we use to provide services to our customers.

I want to change one of those specific ports, that is already being attached to a specific device, to use an internal pull down.

The port is always with value 1 when no voltage is provided, and I need to change that because when that device provide no voltage, it has the same internal state has when it provides 0V.

This is the information of the specific pin:

    root@be905g:~# cat /sys/kernel/debug/pinctrl/44e10800.pinmux/* | grep "pin 20"
    pin 20 (44e10850.0)
    pin 20 (44e10850.0): 48302180.eqep (GPIO UNCLAIMED) function pinmux_eqep1 group pinmux_eqep1
    pin 20 (44e10850.0) 0000002e pinctrl-single

I saw that the "0x2e" value that is associated to the pin should be "0x27".

I've modified the DTS file and recompiled, and even with 0x27 in memory the port behaves as having a pull up.

I've used the command:

    mem_util 0x44e10850

and it returned 0x27, but still.

This is how the pin description in the ".dts" file I decompiled from the shipped ".dtb "looks:

    pinmux_eqep1 {
                pinctrl-single,pins = <0x50 0x2e 0x54 0x36>;
                linux,phandle = <0x40>;
                phandle = <0x40>;
            };


texts: How to edit content center data (Inventor 2018)?

texts: Example: I want to use an M8x20 bolt in Inventor and edit the data of the file to get it right in BOM. I was able to do it in Inventor 2017 and earlier but not any more. I have tried to untick "read only" in the content center properties etc. Any suggestions?


texts:
I am getting confused with the maths in the max distortion strain energy part of the question. Plus there is a misprint as the formula for distortion should be a^2 +b^2-2ab=(yield stress)^2, here they have missed the 2 in 2ab. Or maybe I am wrong

Can someone please solve it correctly showing the working(maths). I just need a step by step working as I am making some error solving it myself. And the one solved here is missing steps.
*F.S=1 that's why not mentioned.

Thanks


texts: Trapping a particle in a laser beam (optical tweezers)

texts:
So upon watching videos and reading articles i understand few things. For one when the laser beam is focused to a tight enough point when placing a material in there (people use crayola markers) it will trap and burn that particle for a little while.

My question is how can i do this without  having to touch a marker to it? Can I achieve a particle effect through something else or atleast something that wont burn off the particle right away. Also is this effect as easy as talking a 405nm laser, focusing it with some sharp lenses and then having that particle get trapped. I have seen a few diagrams but still it is unclear all the equipment they use and then in a video it is just a laser focused to a point.
Such as these:

UPDATE: Upon reading more i see the mW required is only around 5mW which isnt bad at all. I also see people use graphite but im not sure how ling that particle lasts? Forever until the beam is broken or only for a certain amount of time. To use graphite could i simple take a block of it and wave it in front of the laser at its lowest density point to capture the particle? My other confusion is the lens required what is so special? Is there maybe an equation that includes a class of particles, wavelength, power, and focal length of lens to see where i stand with this. I know this isnt what stack overflow is for but i just want to set this up and see it and understand it rather then just read so maybe a good diagram that i or any member coming here could understand in order to setup this experiment.


texts: Help me guesstimate the loads I can apply to a little PE block welded to a PE wall

texts:
I want to mount some equipment into a polyethylene (PE) shaft. I can't bolt or drill directly into the walls, but the supplier of the shaft can weld little PE blocks onto the wall: 50x50x50 mm, with bolts pressed into the blocks.

I have about 30kg worth of piping and valves etc, most of the weight will be borne by the ground actually but I need an additional attachment point higher up. My idea was to have two of these blockse mounted on the walls, with a steel rail between them paralell to a section of pipe to attach the pipe via one or two hangers. The shaft is 1 m across, the horizontal rail will be about 0,8m. I will have shear on the blocks but no moment. The wall thickness of the shaft is at least 10mm.

At this point I don't need exact structural calculations, I need to know if this is feasible so i can leave it to the contructor to figure out, or if I need to spend more brainpower on the issue.

I understand there are plate welds and butt welds in the PE world? In either case, how much load can expect one my little blocks to bear?


texts: Reasons for bending direction of rebars in beams

texts:
When we do detailing for RC structures, the rebars in a beam have to anchor into a column. For an external column (not at the roof), the rebars are usually bent in 90 deg to provide sufficient anchorage length.

When I read the design manuals, books, etc, the rebars are always bent to the far face of the beam. E.g. The top bars in the beam bend to the bottom and the bottom bars bend to the top.

May I know why is the bending direction always like that?


texts: If I have an I beam which I subject to some bending load, how can I calculate when the thinner middle part of the I beam will buckle? I though I could use Euler's critical load formula here, but it's unclear to me how exactly I calculate the compression load of the middle part of the beam


texts: Would 6061 or 5052 Aluminum have lower rate of creep?

texts: I am making a device which uses a bent thin sheet of aluminum as a spring which provides a constant force.  It must be made of aluminum.  Over time the material will relax and the force of the spring will decrease.  I am wondering if there would be a significant difference between the rate of creep in 6061 vs 5052.  The material will be at room temperature and the force will be well below the yield strength of both materials.


texts: Eulerian and Lagrangian descriptions of velocity

texts:
I feel as if I understand the conceptual difference between Lagrangian and Eulerian descriptions. But I can't seem to follow the math. I have one example that I would greatly appreciate an explanation or full calculation for

  The motion can be expressed as:
  $$\left\{\begin{align}
x_1(X_1,X_2,X_3,t) &= X_1 \\
x_2(X_1,X_2,X_3,t) &= X_2 + \dfrac{X_2 v_0 t}{h_0} \\
x_3(X_1,X_2,X_3,t) &= X_3 \\
\end{align}\right.$$
  velocity in Lagrangian description:
  $$v_i = \begin{bmatrix}
0 \\
\left(\dfrac{X_2v_0}{h_0}\right) \\
0
\end{bmatrix}$$
  in Eulerian description:
  $$v_i = \begin{bmatrix}
0 \\
\left(\dfrac{x_2v_0}{h_0 + v_0 t}\right) \\
0
\end{bmatrix}$$

I am entirely on board on the velocity in the Lagrangian description. I cannot for the life of me figure out how the Eulerian description is computed nor why.

Can someone show me how the Eulerian description of the velocity is calculated?


texts: Home made microscope using donated objective lens and camera-ocular-adapter

texts:
I have a bunch of nice objective lenses from an huge old microscope set, and would like to make a microscope body tube with just one objective and one ocular lens. Without using trial and error to determine the right distance between the lenses, how might I calculate the correct distance between them. I'm then going to make a tube with this length and with a thread so I can mount the objective lenses. For the ocular lens I want to use an adapter from AmScope (CA-NIK-SLR) which mounts directly onto a DSLR camera.
I've tried to use a rolled up paper to determine a good distance from the objective lens to the camera, but I can't tell if the image is focused correctly on the camera sensor. Even if I could tell, I can't easily measure it then. Trial and error for this would take a lot of time and money and so I'd prefer it if I can get a formula or something like that.

If anyone knows how to do that, I'd be really happy to hear it!


texts:
I am wondering whether and how superfluids (possibly at room-temperature, if that is possible at some point) can be of any practical use in mechanical or electrical engineering or other fields.

I would be delighted if you could provide me with some thoughts about hypothetical or even practical (at low temperatures) realizations of machines that use superfluids and might have a huge impact.


texts: Calculating final drive force from engine torque and tyre spin ratio

texts:
Trying to build a simplified physics simulation for cars, along the lines of "Car Physics" by Marco Monster. I'm stuck at straight line acceleration. I don't know if I understand the processes correctly or not:
I'm using engine torque, gear ratio and throttle input to calculate the "potential drive torque" on the axle. From this, I directly calculate the angular acceleration of the drive wheels. Then I compare the actual speed of the vehicle with the angular velocity of the wheels to get the longitudinal slip ratio. If too much power is used, the result indicates that the tyre is spinning by a certain amount. And here's where my confusion starts. I then use the spin ratio and the load on the drive wheels to get the final drive force.
Am I correctly using the spin ratio curve by plugging in the spin ratio and using the resulting force directly as the final drive force?
This feels wrong, over time there's a discrepancy between the angular velocity of the wheel (calculated from engine torque) and the car's speed (calculated indirectly from load on the wheel, the only input that was carried over from the engine calculation before is the spin ratio). The difference between the two speed values gets larger as long as I accelerate.
Edit: Adding my current pseudo-code
var engineTorque = getEngineTorque(engineRpm, throttleInput)
var loadOnRearWheels = getLoadOnRearWheels(...)
var maxTireTraction = frictionCoefficient * loadOnRearWheels
var potDriveTorque = engineTorque * gearRatio
var potDriveForce = potDriveTorque / wheelRadius

var driveWheelAngularAcceleration = potDriveTorque / rearAxleInertia
driveWheelAngularVelocity += driveWheelAngularAcceleration * dt
driveWheelRpm = driveWheelAngularVelocity * 2 * PI
var slipRatio = getSlipRatio(driveWheelRpm, wheelRadius, speed)
var driveForce = getForceFromSlipRatio(slipRatio, loadOnRearWheels)

var totalForce = driveForce - resistanceForces - brakeForce
speed += dt * totalForce / mass


texts: What are the limits of small 3D printed gears?

texts: How much tangential force should I expect a 10~20mm pitch diameter/1.5mm gear module 3D printed rack and pinion system to support without breaking nor sliding?


texts:
In my limited engineering knowledge, and limited research skills, I couldn't find a complete answer for the reasoning behind the chosen tones for DTMF. I did find a hint that said something about resonance/interference, but that's not enough details to satisfy my curiosity.
On a possibly related note, could there be "Tri Tone Multi Frequency" signals? Or even Quad? Is there a limit?


texts: how to calculate the speed ratio (Rotational speed to advancing speed) in friction stir welding

texts:
I am a student and I work in the friction stir welding of a hardened aluminium alloy 7075-T6, and I want to confirm about this information before I put it in the article.

I found in the literature that there are two ways of calculating the ratio of speed:

ratio=advancing speed/(rotational speed*pin diameter)

and the other is:

ratio=Rotational speed/advancing speed

what should I choose?


texts: Gaps in derivation of thermodynamic property equations

texts:
If $h=h(T, P)$.
Does $ dh = c_pdT + \left[v - T\left(\frac{\partial v}{\partial T}\right)_P \right]dP \Rightarrow h_2 - h_1 = \int_{T_1}^{T_2} c_pdT + \int_{P_1}^{P_2}\left[v - T\left(\frac{\partial v}{\partial T} \right)_P\right]dP $ ?
If so, how?
I apologize for this, but I just haven't been able to find an appropiate justification for this operative behavior in any of the Calculus, Differential Equations and Thermodynamics books in my possession. I'm particular bugged by the "integration of differentials" and how it, before me, seems to damage the symmetry of the first equation in the statement.


texts: How to increase blast furnace top gas temperature?

texts:
Why does blast furnace (in Iron & Steel works) top gas temperature stays low and what are the fixes for that to increase without using a burner?

The top gas temperature goes below 80 degrees (celcius) and the system requires a burner to increase the level of temp. Why we would need a burner, there should be a different way for not to decrease its temperatures.


texts: Controller to maintain a stable amplitude

texts:
I am recording a channel before and after injecting current into that channel. I control the current injection using a switch, when the switch is on current goes to the channel, when the switch is off current is off.
My aim is to have a similar amplitude in the channel before and after the current injection.
So currently, I am storing data from the channel before the switch (X), and store data after the switch (Y). I want the data before and after the switch to equal each other (X=Y).
The more the switch is on , the higher the amplitude (Y) is in comparison to A, and the opposite is true.
The duration of the switch being ON is what I can control in order to have the amplitude before and after equal.
Would using a PID control be a right way to start?


texts:
Let us we are moving in a car. There is a wall in front of us, we need to decide can we go around it or not. It is known that width of the wall is $w$ and our speed is $v = const$.

What is a simple approach to set formally conditions upon which it is safe to go around?

I understand that there are many possible details such as traction, weight of car etc. and will be glad even for the most simplistic analysis. If you can provide a source, that too is great. Thanks.


texts: Does the pressure due to corrosion in concrete depends on degree of corrosion?

texts:
I am trying to relate the degree of corrosion with the pressure exerted in surrounding concrete. My common sense tells me that higher the degree of corrosion, higher should be the pressure exerted, but my equation tells me it is constant. Obviously, I am making a calculation mistake but could not figure it out. What mistake am I making (figure attached)?
Consider unit length along the rebar:

Area after corrosion is $A_1=A_0(1-p)$, where $p$ is the percentage of corrosion.

The volume occupied by rust if there was sufficient space is given by converting the volume of steel to equivalent volume or rust: $A_2=A_1+pA_0\dfrac{\rho_s}{\rho_c}$.

Initial volume: $V_1=A_2-A_1$
Final volume: $V_2=A_0-A_1$
Change in volume: $\Delta V=V_1-V_2$
strain: $\epsilon=\dfrac{\Delta V}{V_1}$

Solving, we get $\epsilon=\dfrac{-\rho_c + \rho_s}{\rho_s}$. There is no $p$.

What am I doing wrong?


texts: Best way to dent a pipe from the inside?

texts:
I am currently trying to redesign a pipe with 2 dents from the inside.
What is the best way to manufacture something like this, also how would i go about describing this process in a drawing?

In the pictures you can see the pipe before and after the dents are placed. The sides on the pipes are welded on, so it is possible to acces the inside before doing this.

The cutout is present on both pipe, but this is also an extra process that could be done after the denting process.

Material is 3mm AISI 304

EDIT: The design is meant to be used for a prototype, demanding production solutions will not be optimal.


texts:
From google, I got this meaning of Wire rod:

Wire rod is a long steel semi-finished product manufactured by hot
rolling billets on  continuous rolling mills.

Here is the stack of steel coils:

Why steel coils are called Wire rod?


texts: Is youngs modulus a derivative of stress and strain?

texts:
From This page it can be seen that young's modulus is given by,
E = (Δstress) / (Δstrain)

Which means E is a point function,  that changes as the strain in member is increased.

I am feeling skeptical about this definition, as I haven't read E as derivative anywhere before.


texts: Best way to go about "HiPot" testing setup

texts: What is the best way to set up a dielectric strength test?  I am planning on using two threaded copper rods for adjustable movement that will receive the voltage.  In between the two rods will be the dielectric (wafer/thin film).  Any insight on how to create a platform for testing consisting of two copper rods and a place to put the dielectric would be appreciated.


texts: What does "Lg" mean when defining form of screws

texts:
The context of this question is the Form, Fit and Function (FFF) rule defined in ASME. It states that form is used to define any product with reference to its size, mass, shape, dimensions, and other visually identifiable features. For example "SCREW, PAN HEAD, M3 x 0.5, 2mm Lg, 316 SS". I am guessing this is Lag length based on some research i.e. the length from the head where the thread starts.

Q) What does Lg actually mean? Please quote resources for more reading


texts: Mass inertia tensor for rod non-symmetric regarding coordinate system origin

texts:
I want to express the inertia tensor of a rotating rod (total length $L_1$) to use it in Lagrange mechanics for expressing the kinetic energy associated to the rotation with angular velocity $\dot{\theta}_1$. I know the moment of inertia regarding the center of mass $m_1$ as $1/12\cdot m_1 L_1^2$ and with the central axes theorem I obtain
$$
J_{1yy} = J_{1zz} = 1/12\cdot m_1 L_1^2 + m_1 l_{c,1}^2
$$
So I can express the the kinetic energy as
$$
1/2 \cdot \dot{\theta}_1^2 (1/12\cdot m_1 L_1^2 + m_1 l_{c,1}^2)
$$
Is that right?

The rotation is constrained to the horizontal plane around the origin ($\vec{x}_i = \vec{0}$)


texts: How to avoid dyed liquids staining reflective/transparent surfaces

texts:
I'm dealing with some hydrocarbons (diesel, gas oil, kerosene, ethanol) where I'm putting them in a chamber and shining light through them to hit a sensor on the other side in order to measure their colour. Unfortunately what I'm finding is that the lenses and reflective surfaces in the chamber that I'm using for these optical measurements are being stained by the products and subsequently affecting the measurements. When the chamber is emptied, small amounts of product remain clinging to the internal surfaces. As this dries a residue is left which remains on the surface.

I've tried a couple of different materials: stainless steel reflectors, transparent Grilamid plastic lenses, a stain-resistant transparent potting and regular glass. All of them end up with a residue that clings to the surface that needs to be wiped clean. Unfortunately, for my application I'm not going to be able to get access to the internal surface to clean it so I need to find a way to prevent this residue from clinging to the internal surfaces.

The main restriction for me is that the system needs to basically be 100% maintenance free, and unfortunately I can't control the fluid coming in and out and therefore can't rinse the system out.

I was wondering if there are any products (both transparent and reflective) that are basically completely "hydrophobic" but for hydrocarbons and will prevent the product clinging at all to the surface and staining the lenses and reflectors?


texts: "bubbles" forming after heating my Thin film transistors

texts:
I am fabricating Bottom gate Thin-film-Transistors.

The Gate is 60nm Molibdenum. The dielectric structure changes with the table below. The temperature represent the annealing temperature after having deposited the IGZO semiconductor.

sample  Structure temperature
1       SiTa      300
2       SiTa      180
3       SiTaSi    300
4       SiTaSi    180
5       TaSi      300
6       TaSi      180

after heating the samples, I am getting these bubble-like formation on the gate structure.

what could be causing this issue?
Prebake SiTa-300

Postbake SiTa-300

Prebake SiTa-180

Postbake SiTa-180

prebake SiTaSi-300

postbake SiTaSi-300

Prebake SiTaSi-180

Postbake SiTaSi-180


texts: What is the characterising difference between a riser and a runner?

texts: The image given below shows a bolster with a series of riser and runner. What I really do not understand is which is the riser and which is the runner. Also a detailed explanation to why multiple risers and multiple runners are being used will be highly appreciated. In general what is the distinguishing feature between a riser and a runner? Out of the two rods in the periphery why is one relatively thick and the other one thin?


texts: Building a machine from an ideal physics problem

texts:
I have a physics professor for whom I'd like to build a machine. Featured in a problem he is notorious for assigning students, originally from Kleppner and Kolenkow's "Mechanics," the machine causes all three blocks to accelerate, including the large block M1. A picture is featured below.

This problem features frictionless surfaces, massless ropes, and massless frictionless pulleys. I'd like to build the machine for the professor as a thank you gift, but I ask if anybody has suggestions for how to get relatively close to the frictionless and massless constraints above with objects I can realistically build with, e.g. teflon and steel for low-friction surfaces.

Thanks for any advice and suggestions!


texts: What material is used to make gas pipes?

texts:
What is the most common material gas pipes made of?
I read in a unreliable website it's steel, is it true?

Also how good is steel at stopping or slowing down the leaking of gas?

The gas I am using or planning on using is Argon which is denser than air.


texts:
My understanding of swash plates led me to believe that the pistons in a swash plate pump rotate around with the driving shaft along with the chambers in which they aspirate (e.g. M&S Hydraulic Youtube video on swash plate plumps).  As the axial position of the pistons change, the piston chambers draw and expel fluid.

However, I just watched a training video from "Our Virtual Academy" (which costs money to view unfortunately) where the pistons do not rotate with the shaft; instead, the swash plate rotates causing the pistons to move axially.  The angle of the swash plate is varied by forcing pressurized fluid into the control chamber (here is an example).

I can't imagine why one would use this latter form of swash plate pump.  What are the reasons for the different approaches? (What is the correct terminology to distinguish the two so I can carry on my own research)


texts: Is there a way to quantify or graphically represent noise immunity? Is noise immunity different than noise margin? If yes, how?

texts: Generally, there is a talk about noise margin and noise immunity in digital circuits. Both terms seem interrelated but some texts differ from this. My query is whether these two are entirely different terms? If so, then is there a way to quantify noise immunity?


texts:
I have to tune a state space model for certain parameters in Matlab.
The transfer function has to be
$$T(s)=\frac{k_q(1+0.162s)}{s^2+8.23s+67.7}$$
Using the place command, I have been able to place the poles at $$p_{1,2}=-4.115\pm 7.12i$$ with a full state feedback gain of $-280$ and $-28$.
However, I now have to place the zero using a prefilter such that the zero is at $s=-0.6653$ and the system tracks an input signal properly.
I fail to see how a prefilter would affect the enumerator such that the location of the zero can be altered. How can I place the zero?


texts: Can the structural integrity of bridges be measured in real-time for safety?

texts:
As a follow up to this question, I wonder if structural integrity monitoring information can be provided real-time and to a sufficient degree that safety decisions can realistically be made from the information.

To put things in context, in the USA and other parts of the world federal, state, and local governments regularly receive structural integrity reports on infrastructure, including bridges. These reports are the results of assessments that are performed on a scheduled basis, and it can be many months or possibly years between assessments.

Bridges are an important part of federal, state, and local government economy since they provide critical infrastructure.  It is also important to protect historical land marks such as the Golden Gate Bridge.

Golden Gate Bridge, an iconic bridge in the United States

And the consequences of insufficient information can be quite severe.  For example, in August of 2007 the I-35W Mississippi River bridge collapsed, which resulted in the loss of many lives.

I-35W after the collapse

Question:

Are there technologies that could provide real-time status such that they would help forewarn federal, state, and local governments of impending bridge failures? For example, is there something that could have predicted the I-35 collapse and notified the public in order to avoid the loss of life?  It seems like this wireless sensor to monitor structural integrity of bridges would work, but I'm not certain as the domain is outside of my experience.


texts: Why do most centrifugal fans found in laptops have tiny blades?

texts: If you were to use a centrifugal axial fan instead, won't you be able to achieve higher flow rates and better pressures? It seems like the efficiency of these motors are very low.


texts: How to determine the choke point in a compressed gas system?

texts:
I have a pressure regulator bringing an inlet pressure of 150 bar down to 10 bar which is then lead into a plenum followed by a nozzle of area 340 mm^2, exposed to atmospheric conditions.

Weirdly enough at both points the necessary condition of pressure ratio for choking is satisfied!

The critical exit pressure below which choking occurs (p*), is 5.8 bar at the nozzle exit and 79.7 bar at the regulator exit. How do I explain the fact that the flow chokes only at the nozzle?


texts: Simplest software for making 2D and 3D visualizations(animation),

texts:
I have to do simple visualization or animation of movements for simple hand prosthesis. There are no validation or calculations required. I just want to show concepts working principles (movements mainly) with animation.

What's the fastest way to do it?


texts: I have the following differential equation and I need to obtain the transfer function of Z / P but there are constants so I cannot factor to obtain the relationship, how could I obtain the transfer function of Z / P?


texts: Why do transport containers for wafers open clockwise?

texts:
In the semiconductor industry and research, silicon wafers are transported in round plastic sample containers with a screw lid.

Other than any other screw top though, the lid always opens (releases) when turning in the clockwise direction, as opposed to e.g. a bottle cap that opens counterclockwise.

Is there a practical reason for this? Why are they made like this even by different brands?


texts: Do all ductile materials experience necking before fracture?

texts:
This stress-strain curve presents a linear elastic range, followed by yielding and accompanied by a decrease in toughness the material goes into the plastic region. As it strains more and more the material then suddenly snaps! Without necking...

Fracture occurring without necking isn't something I would expect from a ductile material, in fact it's a trait of a brittle material. But, the material can't be brittle with all that strain in the plastic region.

So which is it?
Question: Would this material fall into a "mostly ductile" category instead of ductile?

I have four stress-strain curves i am working with at the moment. Three of them are similar to this one however, they show a decline in stress when necking before fracture. This diagram does not decline in stress before fracture. They were all tested on the same tensile stress machine (a Shimadzu machine i believe). Part of the assessment is to determine the possible types of materials each curve could be.

Question: Because this material doesn't neck so i'm wondering if there are any materials which have a stress-strain curve such as this. I was thinking some metals may strain and then just snap or perhaps timber. I'm really not sure.


texts: How do I define properties orientation in a 2D short random fibers composite? ABAQUS

texts:
I generated different 2D microstructures with different fibers volumetric fraction (basically a square representing the matrix and a lot of small rectangles inside, with different measures and random orientations, representing the fibers). I'm attaching a figure to be clearer.
To run the simulations using Abaqus I need to define the properties of the fibers (the rectangles), but how do I set the properties according to the main axis of each fibers considering that I have random orientations? I cannot manually set the axis orientations for each fiber, it would be too timeconsuming considering that I have configurations with 40% of fibers (more than 400). I need to find a way to set the properties according to the main axis of the fibers (rectangles).
To be more specific, I created an RSA alghoritm in Matlab to create the random distribution of fibers. Then, I create the main square (representing the matrix of the composite) in Abaqus and I create the fibers by partion, importing the generated fibers distribution as a sketch.
Thank you all for your attention.


texts: Technical drawing for a part with complex (non-line, non-arc) geometry

texts:
I've been making technical drawings for various parts I've designed. Since these parts were meant to be 3D printed, this is mainly just to have them in my portfolio so I have something to show/talk about at the upcoming career fair (I'm an undergraduate ME student).

I've encountered difficulty with one particular part, which is designed to hold the motor for a perpetually spinning top. Because the motor ran a little hot when turning the rather heavy disc it was attached to, I used the SolidWorks wrap tool to remove portions of the cylindrical casing in order to encourage heat dissipation.

As you can see in the image, SolidWorks is unable to annotate the resulting dimensions, at least not using the basic tools I'm familiar with. So my question is: how would the dimensions of this part be represented on a technical drawing? Relatedly, since it probably determines the answer: by what process could a part like this be machined, if 3D printing was not an option and the arguably unnecessary complexity could not be removed?


texts:
I've recently been on Rügen and I have seen this:

Does anybody have an idea what this is?

(To give Google a chance: A ship with four "towers" made out of steel on it. They looks a bit like high-voltage electrical towers.)


texts: Fan placement effect on pressure in chamber

texts:
I am building an air-hockey table. Essentially, a rectangular wooden box with holes on the top surface.  I am fitting a blower fan on the bottom and wondering how affects the airflow, if at all.

From my understanding, air is sucked from under the table and pushed in the box, increasing pressure and forcing air out of the holes on top.  Is pressure uniform within the box with air flowing in? Or will the area around the fan have a higher pressure compared to the corners, for example?


texts: How to design and build a pulley system for a given purpose?

texts:
I am a high school student wondering if the pulley system described below will work, and if so, how to go about it.

Basically, I have a small system where as you pull back an object, it causes two lengths, labeled $d$ and $p$, to move forward. $d$ is dependent on many factors other than just the pulley system, but $p$ is just growing linearly as the object is pulled back. I've determined that the relationship between $d$ and $p$ is: $$p=\sqrt{A+Bd^2}-C$$
Where $A$, $B$, and $C$ are positive constants.

Here is a diagram to visualize how $p$ is connected to the system:

The length $p$ is the distance from the smaller block to the edge of the base. As you pull the object back, the string is pulled which pulls the spring and increases the length $p$. My question is, is there any sort of pulley system or just general construction I can insert between the object you pull and the pulley which is connected to the smaller block such that as you pull the object back, $p$ does not increase at a linear rate, but instead increases at the exact same rate of $d$.


texts: Confused with supercritical airfoil transonic condition analysis

texts:
I am a high school student learning to analyze aircraft models in Autodesk CFD for the first time.
My current project is  analyzing a supercritical airfoil on Autodesk CFD (that was designed in Autodesk Fusion360).
Can I get help with the following :
I researched several turbulence models(https://knowledge.autodesk.com/support/cfd/learn-explore/caas/CloudHelp/cloudhelp/2019/ENU/SimCFD-UsersGuide/files/GUID-E9E8ACA1-8D49-4A49-8A35-52DB1A2C3E5F-htm.html#:~:text=Turb.%20model%20%20%20Turbulence%20Model%20%20,model%20wi%20...%20%206%20more%20rows) and I chose the SST k omega turbulence model, with a 250 m/s inlet velocity, 0 gauge pressure , unknown outlet and a compressible flow , I am getting a lift to drag ratio of approx. 4.3.I think the lift to drag ratio is too low. I am suspecting the analysis conditions are to blame.  Are these the correct input parameters? Am I missing anything else?
Thank you.
Here is a screenshot of the analysis:<img src="https://i.stack.imgur.com/w1bsv.png" alt="I ran the airfoil analysis at angle of attack=5degrees
" />
The following image is my mesh along with the convergence plot after working with the suggestions.


texts: Long term engine issues by using Active Exhaust?

texts:
Looking to install OEM active valve mufflers on my 2019 Mustang EcoBoost.
Wondering if the valves opening and closing, thus changing exhaust back-pressure would cause the engine to run lean/rich and do long term harm to my bone stock car.
Long term reliability has priority over sound for me but if it has ZERO effect then I will go ahead and do this.
Thanks in advance


texts:
I am looking for a (rather cheap) low RPM controllable motor. If it could turn in both directions (also controlled) that would be a huge plus. Any ideas?
Right now I'm using a disco ball motor at 1 RPM.  It works fine but the problem is I have with this is that sometimes I might want 2 or 5 rpm (especially when lowering it the option to speed it up would be very handy).  The disco ball motor has a set RPM of 1 and I cannot alter it on the fly.
Secondly when I power the disco ball motor it turns clockwise, and the next time I power it, counterclockwise, and so on... I have worked around this problem, but if I could somehow control the direction also, that would be a huge plus.
I would like to change these options (speed and direction) by using a lever/knob/handle/whatever on the unit itself (not by using pc or anything).  Anyone know of a unit that does this?


texts: How do I attach an electric motor to a trailer wheel?

texts:
I have an electric motor which is intended for a bicycle/scooter and has a 11-teeth chain sprocket.
I plan to use it to spin a trailer wheel (which have 4 holes for bolts about 3'' from the center). In these cases, do I have to design a mount to attach the wheel to the motor or is it possible to buy a mount that would fit my needs?

Any advice would be appreciated. Thank you.

Wheel: http://recstuff.com/trailer-tires-wheels/tire-wheel-combos/8-tire-and-rim-packages/4-80x8-loadstar-trailer-tire-lrc-on-4-bolt-galvanized-wheel/


texts: Rubber that remains Elastic in Hot and Dry Application

texts:
I work for a valve manufacturing company and our customers have an application where very large volumes of hot (200F), dry air pass through our valve.  As a consequence, the rubber (carboxylated nitrile) sealing surfaces within the valve harden, eventually leading to the valve being inoperable.
While I am no polymer expert, is seems obvious to me that the plasticizers are being “cooked” out of the rubber.  I am looking for a cost-effective alternative rubber material that will remain elastic/pliant in this challenging application.  We offer valves that use PTFE, but this would be unacceptable to our customers from a cost perspective.
Any thoughts or guidance would be greatly appreciated.


texts: How much power does a stepper motor draw when holding weight?

texts: I want to lift something in the air with a stepper motor. If the object is 1kg and I want to keep it in the air for 12 hours. Is it a good idea to keep the power on the motor all that time? Will it draw excessive amount of power? Ideally I would like to cut power to the motor when the movement is done, but then, will the motor be able to hold its position?


texts: How do you model a real-life truss in structural analysis software?

texts:
I am trying to recreate the following model of a wooden roof truss provided to me by a truss manufacturer:

My question is twofold:

What is the common/correct way to model the boundary conditions and internal fixity conditions (pin pin?) for the elements as well as the structure itself?
Given generic roof loading in pounds per square foot, how should I distribute the loads to the truss? It seems to me that applying distributed live and dead loads for the top and bottom chords on truss elements poses a stability problem, as it was under my impression "idealized" trusses can only resist axial loading and thus loads can only be applied at the nodes. However this is a real truss, so I expect things may be different.


texts: Why build a cell lattice tower with square cross-section instead of triangular cross-section?

texts:
First, a neat image from Wikipedia

Here the cell tower has three vertical (or maybe slightly inclined to the inside) thicker pipes which are located at angles of a triangle and those three thicker pipes are interconnected with numerous thinner pipes and this yields a lattice tower with triangular horizontal cross-section.

Clearly you need at least three vertical pipes to make this happen. The design above with triangular cross-section is very popular.

However sometimes cell towers are built with square cross-section - they use four vertical pipes located at angles of a square instead of three pipes. It looks like waste of steel and design complication - what can a tower with square cross-section do what one with triangular cross-section cannot?

I could imagine there're was a difference when a tower had notable load concentrated in one direction. Yet I'm asking about cell towers that carry rather lightweight equipment and mostly have to withstand wind loads.

Why are square cross-section cell towers used instead of triangular cross-section towers?


texts:
I need to draw this in orthograhpic views. I'm a bit confused about the weight of lines I should use to draw. Like ,for the pat (I pointed the arrow at) you can see it's sticking out a bit, would I use just a regular weight line or what?

Also. We've been given some dimensions like 30mm and 70mm. And the thing also says the drawings need to be done on a 1:1 scale. What does this mean? DOes this mean I need to draw exactly at 30mm and 70mm, not make it bigger ration?


texts: What is the rationale for a 6x6 truck chassis with 2 axles front vs. 6x6 chassis with 2 axles rear?

texts:
What is the rational for these two different 6x6 truck chassis arrangements? Is it merely a matter of intended distribution of weight across the chassis while in use?

As in, two axles up front to support a heavy engine, two axles in the rear for heavy cargo, or for towing a trailer?


texts: How is train speed calculated in OpenRails?

texts:
I have been playing OpenRails Train SImulator recently and I thought i made my own train(which i did), then the physics part came up. It required me to fill in a lot of parameters, like braking, sanders, and of course, engine. Now the engine part is confusing me, it requires me to enter:

Mass(KG), Max Power(kW), Max Force(kN), Continuous Force(kN), and Max Velocity(mph).

Now the Mass, MaxForce and MaxContinousForce is easy to find, but what about the rest? In order for me to know more about what i am doing, i would like to know how the speed in the game is calculated using all these values? Because i thought the speed of the train was only calculated using the MaxForce and the Mass value, but all these values seem to have some connection as if one of those listed values is changed, speed is different. So how would I calculate the speed of a train using these parameters(What is/are the formula('s)? And how are the horsepower values and force values related to each other in terms of final speed?(As again, i though kW didn't matter in speed)

Can someone explain me?

Thanks!

Edit:
So mainly what i want to know is:
Is the calculation of speed in general affected by horsepower/kW(does it have anything to do with speed/force at all?)


texts: Is there a particular reason the Moléson funicular is built as a giant bridge?

texts:
So I live in Switzerland and there is lots of funiculars in my country. Most of those were built between 1890 and 1930, and for most of those the line is on the ground most of the time, there is bridges only where necessary, just like a regular train line.

The Moléson - Plan-Francey funicular is very particular in that not only it was built much more recently (in the late 1990s), but also the line is basically a huge bridge, the funicular never stands on the ground.

I think this is very weird and should have made the line much more expensive to build for no reason at all. Why is this line built on a giant bridge rather than on the ground with bridges only where necessary? Bridges would have made sense in order to make the line straighter (and thus shorter/faster), but the line is not even straigt anywhere !

Video of the funicular here.
Detailed photos and technical explainations about the funicular here


texts: How to calculate the Torque required to rotate two bars perpendicular to each other

texts:
This question relates to a previous question (How to calculate the required torque in a static equilibrium system) where I have enquired about the start-up torque required to rotate a system. However, the parameters have changed slightly since then, and as a result I am not entirely sure if the system is still considered to be in "static equilibrium" - somehow I believe it still is, and I am speculating that the only factor that has changed is gravity, considering the additional weight added.
However, I do not know what other forces are now at play in the new system.
Question: What is the required start-up torque to rotate the system with the parameters provided below ?
This is what I have:
2x bars perpendicular to each other,  intersecting each other at their centres. Something like this:
                  10kg (F3)
                    |
                    |
                    |
                    |
10kg (F1) ----------+---------- 10kg (F2)
                    |
                    |
                    |
                    |
                  10kg (F4)

Bar weight      : 0.5kg (500g)
Axle weight     : 0.5kg (500g)
Max RPM         : 3 RPM
F1, F2, F3, F4  : 10kg each
Time to Max RPM : 10sec

*** Ignore Friction and Drag.

The motor torque specification is given in kg.cm.

A motor (whose start-up torque requirements I need) is attached to an axle. The motor is required to turn the axle at a constant speed of about 3RPM. What is the required start-up torque to reach 3RPM after 10 sec ?
(I am hoping to hear from Kamran again)


texts: I have used 250 watt DC motor, for DIY electric potters wheel. Motor rated with RPM 3300 and geared reduction to 330 RPM. The issue I am facing is wobbling of the motor head. This issue is with the motor head/shaft and not the disc. How to fix it?


texts: Why does pressure during a hydraulic transient phenomenon like fluid hammer goes below the line pressure?

texts:
I am trying to understand why the pressure fluctuations during a hydraulic hammer phenomenon would go below the line pressure (Pmin < Pi) I thought there will just be a rise in pressure and then the pressure would came back to the settling pressure but thats not the case as the pressure seems to go well below the settling pressure too (which could cause cavitation if the pressure drops below vapor pressure). I know there are multiple peaks because of the pressure wake being reflected back and fourth in the hydraulic line (and that the pressure at any point in the pipe at any given time is a superposition of all the wave, incident and reflected, at the point).
I am not able to understand how the pressure can go below the line pressure as surge is suppose to be a compression wave. The Pmin suggest that a expansion wave is travelling behind the compression wave. Any material to understand this better would also be helpful.


texts: Control Systems: Why is this system unstable?

texts:
I am currently doing a control systems course and I was lead to believe that if a pole lies on the imaginary axis in the s-plane (i.e s=0), then the system was marginally/critically stable.

However, I come across this transfer function and plotted it in Simulink.

Analysis shows that there are 3 poles at s=-1, s=-3 and s=0. So because there is a pole at s=0, the system should be marginally stable right? But the output of the transfer function shows this:

To me, that is showing the system is unstable because the output is getting bigger and bigger as time goes on. Is this correct? Or is my understanding still flawed?

If the system is unstable, then why aren't any of the poles in the right half of the s-plane?

Thanks


texts: how do i formulate a kalman filter for an upwash coefficient?

texts:
I want to make a kalman filter that will estimate the upwash coefficient $C_{\alpha_{up}}$

my state vector: $ X_k=[u \ v \ w \ C_{\alpha_{up}} ]^T $

My measurement vector: $ Z_k =[\alpha_m \ \beta_m \ V_m]^T $

My control input vector: $ U_k =[\dot u \ \dot v \ \dot w ]^T $ where $ \dot u ,\dot v,\dot w $ are unbiased and noise free.

I have dataset with $ \dot u,\ \dot v, \ \dot w ,\alpha_m ,\ \beta_m, \ V_m $ vectors where each vector contains Nx1 elements

Following are my equations:

$$\begin{align}
\alpha_{true} &= \tan^{-1}\left(\dfrac{w}{u}\right) \\
\alpha_m &= \alpha_{true} (1 + C_{\alpha_{up}}) + v_\alpha \\ \\
\beta_{true} &= \tan^{-1}\left(\dfrac{v}{\sqrt{u^2 + w^2}}\right) \\
\beta_m &= \beta_{true} + v_\beta \\ \\
V_{true} &= \sqrt{u^2 + v^2 + w^2} \\
V_m &= V_{true} + v_V \\
\end{align}$$

$v_\alpha, v_\beta \text{ and } v_V$ are white noise sequences

My approach:
$$ \begin{bmatrix} \dot u \\ \dot v \\ \dot w \\ \dot C_{\alpha_{up}} \end{bmatrix} = \begin{bmatrix}
0 & 0 & 0 & 0 \\
0 & 0 & 0 & 0 \\
0 & 0 & 0 & 0 \\
0 & 0 & 0 & 0
\end{bmatrix}
\begin{bmatrix} u \\ v \\ w \\ C_{\alpha_{up}} \end{bmatrix} +
\begin{bmatrix}
1 & 0 & 0 \\
0 & 1 & 0 \\
0 & 0 & 1 \\
0 & 0 & 0
\end{bmatrix}
\begin{bmatrix}\dot u \\ \dot v \\ \dot w \end{bmatrix} $$

Assuming I can obtain a linearised non-null Observation matrix $H$ size 3x4 .

Have I defined my state matrix $ \Phi $ properly? If not, what is the mistake?
With a null $ \Phi $ and non-null $H$, I would get the system to be unobservable, violating the condition of Kalman filter

$$O = \begin{bmatrix}
H_{k+1,k} \\
H_{k+1,k} \Phi_{k+1,k} \\
H_{k+1,k} \Phi_{k+1,k}^2 \\
\vdots \\
H_{k+1,k} \Phi_{k+1,k}^{n-1} \\
\end{bmatrix}$$


texts: Why people experience more jerk or shock sitting in the back seats of a bus?

texts: Those sitting in front and mid part doesn't experience much shock, while those those sitting in back does. Why?


texts:
So I am in the process of working on a rather strange and specific project. I am looking to capture as much energy as possible from a small steam turbine using a DC motor and then use that to power another DC motor.

Essentially my idea was to charge a capacitor using the first dc motor until a specific voltage and then discharge it as fast as possible into the other dc motor. The only part I am not sure of is creating the circuit that will allow me to flip the switch when a certain voltage is reached.

Also as a secondary question what would be the advantages and disadvantages of using a battery vs a capacitor in this situation?

I apologies if this is a simple question, I am still new to circuit design so any recommendations would be super appreciated.


texts: How does the S-N curve (or Wöhler curve) of a material change with frequency?

texts:
How a Material fatigues can be characterized by a Wöhler curve where each datapoint corresponds to a failure with the stress on the y-Axis and the number of cycles on the x-axis. An example is the following Wöhler curve:

How does this curve change with the frequency with which a cycle count is reached?


texts: I don't understand how bending moment is being calculated in the problem mentioned in the above link. I understand the parts after that i.e. calculating elastic potential and partial derivatives but I am just not able to understand the bending moment part. I would be glad to receive some responses on this.


texts: Specific Questions about Traffic Signal Preemption at Grade Crossings

texts:
Several questions, regarding traffic signal preemption at a grade crossing

Is the preempt relay, which triggers the preemption sequence,
located inside the bungalow which houses the grade crossing
predictor, or is it located inside the cabinet which houses the
traffic signal controller?
It is my understanding that the speed of an approaching train
determines the length of time that the preemption sequence will be
provided for. Is that true? And if so, does the crossing predictor
calculate the train's speed, determine how long the preemption
should be provided for and then tell the traffic signal controller
to provide it for that amount of time?


texts:
If we have the following forward converter:

when $Q_1$ is on we have:

Why is it that the Diodes $D_1$ and $D_3$ are off?

Similarly when $Q_1$ is off why is Diode $D_2$ off?


texts: How to calculate the thickness of the residual stress layer generated by a machining process

texts: Machining a metal part will create residual stresses on its surface due to the deformation that the process introduces to it, is there any model to estimate how thick will this stress layer may be?


texts:
The electrolyser used in the process at 25°C and 10.0 bar exhibits a global yield of 82% with a potential of 1.481 V. Determine the electrical energy that can be electrolyzed by year in order to get molar flow of hydrogen: $F(H_2) = 12.016 \times 10^6\ mol/h$.
So, can anyone help with the calculation of energy required for this electrolysis ?

Update:
Yes, it's homework. I actually calculated the needed energy but i don't know if it's true.

Electrolysis: $\ce{2H_2O + Electricity -> 2H_2 + O_2}$.

The half-reaction is: $\ce{4e^- + 4H_2O(l) \to 2H_2(g) + 4OH^-(aq)}$ .

the molar flow of electrons is: $F(e) = 2F(\ce{H_2})/0.92 = 12.016 \times \frac{10^6}{0.92} = 14.653\cdot 10^6 \pu{mol/h}$.

Then, $1F(faraday\ constant) = q(e)\ Na = 1.602 \times 10^{-19}\times 6.023\times10^{23} = 96488.46 C/mol$.

$F(e) \ F = 14.653 \times 10^6 mol/h \times 96488.46 C/mol = 1413838.6 \times 10^6 C/h$

$I(current) = q/t = 1413838.6 \times 10^6 C/h \times 1h/3600s = 392.74 \times 10^6 A$

$E(energy) = UIt= 1.481 \times 392.74\times 10^6 \times 31536000s  (1 year) = 1.834\times 10^{16} J$

Your formatting was hard to read, so I formatted with MathJax.  Please check it out to make sure I got the correct syntax.


texts: Charging a single-phase EV with three-phase power

texts:
So last month I bought my first EV (Škoda Superb iV PHEV) and it comes with single-phase charging. I immediately noticed that the provided home charger will only draw 8A from my 16A fused phase supply (the main fuses are 20A).
OK, I can understand that: somehow the logic finds that full 16A would load the fuse a bit too much or that the phase as a whole is incapable of delivering so much current and thus reduces charge current to the only lower available setting, which is 8A.
But I have run into many situations where having the battery charged in 3 hours instead would give me more electric range. e.g. you come home from work, but have to go shopping later in the afternoon. Naturally this makes me want to have an option of charging the vehicle faster, but I also have a condition of future-proofing my purchase since wallbox prices hover around 1000€.
So I see my options as thus:

Buy a charger that will be more adaptable to grid conditions and will charge at e.g. 14A if full 16 is deemed too much - should be relatively cheap.
Increase main house fuses and the particular socket fuse so that the charger will recognise it as 16A capable - this one comes with added monthly costs because of increased capacity, even if the actual consumption is ultimately the same.
Buy a wallbox that can fuse three-phases into a single phase.

I find option 1 a bit ridiculous: I already have a home charger and replacing it with a different one that would be a bit more adaptable seems somewhat funny.
Option 2 is risky and expensive long term. Risky because I have no idea what makes my home charger choose 8A over 16A. 25A main fuse & 20A socket fuse might not cut it.
So option 3 seems the best, especially if I want to future proof my investment (next car  will probably be a BEV and will thus require a good wallbox). But I just can't seem to find a wallbox that would match my requirements. I found this one, but AFAIU, it's not future-proof as it ONLY does 3 phase to one phase conversion. It can't become a 11kW three phase power supply for my next BEV.
Do I expect too much of my would-be wallbox? Or has someone run into the same issue as me and built a true adaptable three phase wallbox that can, when needed, also merge the phases to a single one? Alternatively, build my own with the help of my better electrically educated friends?
Edit: clarification on the limitations I'm facing:
Currently my house is connected to the grid via 3x20A main fuses. This costs 15€ per month just to be connected + actual power usage. Increasing main house fuses to 3x25A would increase the connection cost to 20€ monthly + actual power usage (not to mention the change itself which would be a few hundred €).
The wiring I'm using is fully under my control, and currently I'm using 2.5mm2 wires that should be able to carry 16A. Can replace easily if needed.
The general idea with option 3 is to actually lower the current demands on the phases: if I only need 16A (max charging current of my PHEV), that means a bit over 5A per phase... I do realise that even future proofing the wallbox with a 3-phase-capable one would introduce the same issue with a true BEV with 3-phase charging capacity.


texts:
I was reading that for a type-2 system the value of acceleration constant
$$K_a = \omega^2$$ where $\omega$ is the gain cross over frequency. This means that the units for $K_a$ should be $(\frac{rad}{sec})^2$. But I found in the datasheet of AD2s83 that the units for acceleration constant are defined as $(\frac{1}{sec})^2$. There seems to be some conflict in the units. Clarifications are required in this regard.


texts: Minimising permeation rate of hydraulic fluid through hydraulic hose

texts:
I am designing an experiment where the hydraulic hose is going to be subjected to relatively high internal pressure for prolonged period of time and it is absolutely imperative that the rate of permeation is minimised. I have found one great book that deals with gases but nothing on liquids or liquids under elevated pressure. I am unable to find any data regarding the permeation rates of hydraulic fluids and/or water through the hydraulic hoses or more generally through various polymers.

The length of time is in years and the pressure in tens of MPa so I am assuming that the permeation will not be negligible.

How can I determine the permeation rate of a fluid through the hose before running my experiment and minimise the permeation rate if it is not negligible?


texts: Is it possible to have the load cell signal as feedback to the servo drive of the servo motor?

texts:
In my project, I have to control the linear motion in one of the two modes. It will  be either in position control or load control.

for the displacement control, The servo motor takes the quadrature encoder input as a feedback signal to control the displacement and getting the very accurate displacement control.

Same way, for the load control mode, I want to control the motor, based on the load cell signal as a feedback input. I could not find a possibility of to do so without having an intermediate controller.

In a servo drive, there is a torque mode control mode. But there is no feedback input in the drive. In this case, I think, the servo drive is controlling the motor torque may be through the current consumption of the motor. Rather, is it possible to control the motor based on load cell signal as a feedback input? If there is a solution to connect load cell input for the torque control, then intermediate controller for load control can be avoided.


texts: How can permeation units in Darcy be converted to the SI form. For example, how would 9.0 x 10-6 darcy be converted to SI units of permeation? How would it also be converted to the permeation units: (cm^3 . mm)/m^2 . d . atm ?


texts: Trapping heat by curing of concrete under plastic sheets

texts:
Although curing of concrete under plastic sheets is a recognized technique, I have some doubts about it.
I think that the plastic sheets may trap heat coming from the exothermic reaction, which will result in important temperature rise in fresh concrete.
I am concerned about heat coming from inside and not outside.
My question is: is this a real issue?


texts: Why is it more common to use ceiling fans instead of air pumps?

texts:
As the title suggests, why not use high-powered air pumps instead of ceiling fans to inject hot air from the ceiling down to the cold, bottom floor?

I understand it may seem silly (especially since it may require a lot of energy), but wouldn't it work better than a series of fans in a large, tall warehouse for example?

Wouldn't the pressure differential in air pumps be sufficient to force the hot air at the ceiling down to the floor further and faster than ceiling fans?


texts:
I've a Rigol DS2072A. It works great except for an offset problem that I noticed the past few days.

Channel 2 always shows a DC offset. This is independent of any settings such as channel coupling, internal termination resistance or bandwidth limiting. The input connector only has a 50 Ohm terminator connected.

It's a constant height above 'zero' on the screen, independent of vertical scale. This means that for higher ranges, the scope calculates that there is more offset. (e.g. 80mV@1V/div vs. 8V@100V/div).

I noticed that the offset lowers when the scope warms up.

Only for the lowest scales (in the millivolts range) the offset changes with the scale setting, but there is no sound of relays for these scales, so it's probably software scaling what we're looking at in these regions.

I attached a picture where you can clearly see the offset:

Running any calibration commands doesn't change anything.

Is there a way I can fix this? Or does this indicate that the scope is broken?

Is this a case of 'you get what you pay for' or just bad luck?


texts: Is there a way to obtain a circuit of some sort given a Nyquist plot?

texts: I have some transfer functions and I was wondering if it would be possible to approximate this to an electric circuit equivalent. For example, given the Nyquist plot below, is it acceptable to hypothesise that a circuit with RC components can represent this Nyquist plot since we know that the Nyquist plot of a low pass (RC) filter is circular such as the one below?


texts: Which imperial units of measurement use vulgar (simple) fraction numbers?

texts:
All values of metric units are expressed in decimal or scientific notation. Some imperial units, use fraction numbers as primary notation (3/4" for 0.75 inch).
As far as i know, only inch and foot values are using this notation. Are there any other units using this notation?

Update

My question is about the written form
IMO it is not about language but more engineering related. To be more specific: the background of my question is about how to store those notations in digital form (so maybe ask this at stackoverflow?). In other words: what data type should be used for number values of specific units of measurement. Millimeters can always be stored as decimal. For inches this is weird, and a fraction number is expected.
We have a system, used to store a lot of technical data (characteristics of technical components). We are wondering if the data type should be dependent on the System of Measurement used, imperial or metric:

metric: data type = decimal
imperial: data type = fraction BIG question: for inch and ???


texts:
I'm an software dev and my job is to convert a .dxf file into a .svg file
My code actually works, but there are some issues with the dimensions or something similar. Unfortunately, i have no background in technical drawing whatsoever.
The finished .svg looks different from what expected.
When using an online .dxf to .svg converter it works. The .svg looks as expected from the customer.
My guess is that there seems to be something in the header of the .dxf file that I'm ignoring.
I've read through several documents but i can't figure out why my .svg looks different.
Expected:

What i am getting:

Its much smaller and its flipped. Ignore the color, i filled every hexagon on purpose!
Looking at the converted .svg in detail, all coordinates are different from what it says in the .dxf
This is the header of the .dxf file:
header:
$ACADVER: "AC1012"
$AUNITS: 0
$CELTYPE: "BYLAYER"
$CLAYER: "0"
$DIMALT: 0
$DIMALTF: 0.0393700787
$DIMASZ: 3.5
$DIMBLK: "_FILLED"
$DIMCEN: 5.346
$DIMDLI: 22.572
$DIMEXE: 1
$DIMEXO: 0
$DIMGAP: 0.625
$DIMLFAC: 1
$DIMLIM: 0
$DIMSCALE: 1
$DIMTFAC: 1
$DIMTM: 0.01
$DIMTOL: 1
$DIMTP: 0.01
$DIMTXT: 3.5
$DWGCODEPAGE: "ANSI_1252"
$EXTMAX: {x: 594, y: 420, z: 0}
$EXTMIN: {x: 0, y: 0, z: 0}
$HANDSEED: "CEF6"
$LIMMAX: {x: 594, y: 420}
$LIMMIN: {x: 0, y: 0}
$LTSCALE: 32.67
$PDMODE: 3
$PDSIZE: 0.05
$TILEMODE: 1
$VIEWCTR: {x: 297, y: 210}
$VIEWSIZE: 420


texts: What causes rechargeable batteries to age? What can be done to extend life of these batteries?

texts:
These days most of modern electronics use rechargeable batteries as a power source. Also, these days most modern rechargeable batteries are Lithium Ion or Lithium Polymer based. Like any other devices, over time these rechargeable batteries lose the ability to recharge, retain and discharge energy thus users have to replace the devices or rechargeable batteries.

It is my understanding that the rise in battery internal resistance is the primary cause the rechargeable battery aging. Is this accurate? If so what can be done to lower or eliminate the internal resistance in rechargeable batteries.

If my understanding is inaccurate what is the cause for rechargeable battery aging?

If the causes for battery aging are understood, how can electronic engineers design charging and discharging circuits to extend the rechargeable battery life?

References:

Battery University
All About Batteries, Part 1: Introduction
All About Batteries, Part 2: Specifications & Terminology
All About Batteries, Part 7: Lithium Thionyl Chloride


texts: What is the physical interpretation of the second term in the viscous stress tensor in the Navier-Stokes equations?

texts:
I have been searching for this answer for awhile. I've read numerous texts and even watched some lectures online, but often times this is never explained and just given. The viscous stress term in the Navier-Stokes equations looks like

\begin{equation}
\nabla \cdot \tau = \nabla \cdot \mu \left(\nabla\vec{u} + (\nabla\vec{u})^T\right)
\end{equation}

Now the term $\nabla \cdot \mu \nabla\vec{u}$ is easy enough to understand as it is just velocity diffusion, but I have a hard time coming up with a physical interpretation of the term $\nabla \cdot \mu (\nabla\vec{u})^T$. After I expanded this term I ended up with

\begin{equation}
\nabla \cdot \mu (\nabla\vec{u})^T =
\begin{pmatrix}
\frac{\partial}{\partial x} \nabla \cdot \vec{u} \\
\frac{\partial}{\partial y} \nabla \cdot \vec{u} \\
\frac{\partial}{\partial z} \nabla \cdot \vec{u}
\end{pmatrix}
\end{equation}

which seems to imply that this effect is not present in a divergence-free velocity field, but I still can't come up with or find any physical intuition about what this term actually means. Does anyone understand what this term physically represents?


texts: What's the difference between critical load and yield stress, and failure in general?

texts:
So far, I have learned of three quantities that are related to the failure of a beam (axial and longitudinal loads). The first illustrates the stress under which balsa wood will undergo plastic buckling:

where m is a constant (estimate =2 for balsa, sigma ys is yield strength, and rho s is 1500 kg/m^3. rho is obviously density.

The second is a graph of compressive failure strength of balsa wood at varying densities:

And finally Euler's Critical Load equation: "The critical load is the maximum load which a column can bear while staying straight."

Here, E = elastic modulus, I = area moment of inertia, K is a constant varying from 1-2 (based on whether the member is pinned or not on ends, estimate =1), L is the length, and Pcr is the critical load in Newtons (I believe.)

The first two are from this research paper, and the last is from Wikipedia. My question is, if there is a length at which the load will not bend the beam, then why is there a plastic buckling stress, which only depends on area? Shouldn't the beam not buckle under any load as long as the length is small enough? I believe there is something I am missing with the fundamental definitions of these. If stress is F/A, then the first equation could be changed to F = A *... which does not include length, as Euler's equation does. And how does failure, as shown in the graph, play into this?


texts: Thermal Conductivity? Units On a Data Sheet

texts: I've been trying to find the value of thermal resistivity for some linear disc resistors. I know that Thermal Resistivity is the reciprocal of Thermal Conductivity but the thermal conductivity on the data sheet is given in W/cm^2.C/cm     which is the units for the heat transfer coefficient per cm not conductivity if the "period" is actually a multiplier and not just a period? Is this some convention I am unaware of on data sheets like this? I do have the thickness of the resistor disc in use so I think I can get the actual conductivity by multiplying the value given by the thickness squared?


texts: What LOS is used by AASHTOWare ME for the traffic capacity cap option?

texts: In AASHTOWare ME, when using the traffic capacity cap option, what is the LOS that the software assumes for this calc? Is it "F"? (Not covered in the Help function)


texts: Torque required to start rotating a wheel about its center

texts:
Assuming i have a circular disc of a significant mass and diameter. Neglecting friction, if a motor is put at its center how do i calculate the torque required for the wheel to just start to rotate?
Since the center of gravity is at its middle point, the only vectors i can work with dont provide any moment
i've seen in posts such as this saying a very low torque can rotate the wheel but how low?


texts: Fat hexagonal M3 nuts, with outer diameter greater than 6 mm

texts:
This is a follow on from my previous question, Will standard M5 T-slot nuts fit these different 2020 aluminium extrusions?

The extrusion has this profile:

and here is a more in-focus photo, of four, in a 2 x 2 configuration:

The gap, between the bottom of the flange and the top of the circle, is about 4.4 mm high. The M5 hexagonal nuts are 3.85 mm thick, and 7.85 mm wide.

I have been using these 2020 extrusions with regular M5 hexagonal nuts (and M5 bolts, obviously).

However, I have recently found a need to use M3 bolts as well (to secure PCB mounted mechanical switches and endstop holders to the extrusion, for a 3D printer, see Complete list of fasteners for the Sintron Kossel).

The width of the slot is 5.4 mm and regular hexagonal M3 nuts are also around the same width (5.38 mm), and hence slip out of the slot. I guess that I could use a wider washer to hold the nut in place, but does anyone know of a "fat" M3 nut that is available, preferably one that is the same size as an M5 nut, but with a smaller M3 bore?

The problem has arisen because I should be using "European" 2020 aluminium, which takes T-nuts, and those come in a range of bores (M3-M6).  However, I have been unable to obtain any, in Bangkok.


texts: Why are coils used to generate magnetic fields

texts:
I understand that coils have properties over a single wire in producing a magnetic field.  But I'm a hobbyist not an expert.  I know electricity was discovered from a wire carrying a charge when presented in a magnetic field.  So I wonder if that is why we use wire and wire coils to pass through the magnetic field.  (Because that's what was used at the time of discovery.)

Solid copper presents a massive magnetic field, as seen when dropping a strong magnet through the inside of a length of copper pipe.

Has anyone tried using solid copper plates to generate magnetic fields instead of coiled wire?  Would that work or not?  Why?


texts: in linear optimal control,linear quadratic regulator,we have a system of the form: x=Ax+Bu,the optimal control law U is a state feedback,it's a function of the riccati equation solution and the state vector.I'm asking about stability,is the optimal control law U always stable?is the system is always stable? Can you give me some references about the demonstration?


texts: Inefficiency of intermittent burn in rockets

texts:
Imagine I have a combustion chamber with a nozzle. There is a high pressure oxygen bottle and a high pressure gaseous fuel bottle connected to the chamber. Would the fuel efficiency be lower if I performed combustion in a series of many very short burns than if I emptied the tanks in one go?
Since at the end of any burn there's a period where pressure decreases, I imagine that the total impulse of the engine will be lower for the intermittent combustion since it will go through many of these periods instead of just one, leading to increased fuel consumption.


texts: How to join between two PBX telephones wirelessly?

texts: I have two PBX telephones. Each one has a line cables to the houses, but there is no connection between these two pbx telephones, neither wire nor wireless. How can I join between them wirelessly? What equipment should I buy?


texts: Is it structurally sound to cut an I beam to a T on one end?

texts: I'd like to confirm whether the replaced beam in the attached picture is structurally sound given the end was cut to a T instead of an I. I had a qualified structural engineer approve the work but I'm curious about the engineering properties of the final result.


texts: Do all supersonic airliners have a high angle of attack when landing?

texts:
The Concorde had a famously high angle of attack (and pitch angle) when landing. This led to its famous droop nose:

The Concorde's Russia counterpart, the Tupolev Tu-144, had the same issue.

These are the only two supersonic airliners to have been built, so there is, admittedly, a small sample size. The Tu-144 has also been derisively called "the Concordski", as some claim that its designers stole plans from the Concorde. So there are clear similarities.

However, there are some supersonic airliners on the drawing board. Will they, too, have high angles of attack when landing? As a follow-up question: Will they, too, be fitted with droop noses?


texts: Driving a lead screw using a universal joint

texts:
I have some issues regarding a lead screw.

It's used as the main driving system for a scissor lift which requires about 2Nm torque to operate.

This is the exact part if it matters:

https://www.amazon.co.uk/TOOGOO-Optical-Housings-Aluminum-Coupling/dp/B07PFQKQV6/ref=sr_1_2?keywords=200mm+opticalis&qid=1583887143&sr=8-2-spell

due to space constraints in the design I have to use a universal joint and place the motor at a very slight angle to clear a few things:

https://www.amazon.co.uk/sourcing-map-Rotatable-Universal-Steering/dp/B07H9ZKBSB/ref=sr_1_4?keywords=6mm%2Bto%2B8mm%2Buniversal&qid=1583887292&sr=8-4&th=1

Regardless of how much I tighten the grub screws, they will eventually come loose (only on the lead screw end, not the motor end) and slide over the the lead screw. I've tightened them so much that even one of them became stripped and I had to replace it.

I have a bottle of medium strength loctite, does using that for the grub screws solve the issue or are there better ways of doing it?

Another idea was using a file to make a flat spot on the lead screw but I'm not sure how well that'd work or if it makes things worse. Since I only have 1 lead screw, I thought it'd be best to ask before destroying it.