texts: How do I calculate the max flow rate for a pump with no power restrictions?

texts:
Let's assume we have a pump and it can draw as much power as it needs. As the pump speeds up, it creates vacuum in the intake. At some point it draws the gas/liquid so fast, the intake pressure is so close to 0. At that point, no matter how much power we put into the pump, the flow rate doesn't increase.

I figured out it strongly depends on the intake size and shape, the type and design on of the pump etc.

On what other factors does it depend? Is there a way to calculate or at least estimate the maximum? Is it even a valid question?


texts: Need to produce vibration amplitude of 200 um (approx) at natural (resonant) frequency, can be any frequency between 100 to 150 Hz

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In order to conduct study, I need to produce controlled vibrations with amplitude (maximum) approx 200 um (micro) at frequency between (100-150) Hz. Vibration amplitude must be controlled with input voltage (Battery operable) while frequency remain constant.

I tried many things :

1) Eccentric Motor - frequency and amplitude, both varied with voltage.

2) Solenoid - difficult to control with voltage. (If any way exists, please suggest me).

3) Voice Coil Motor - Its very costly, I need solution around 10-20 $ max. as project constraint.

4) Linear Resonant Actuator - It is the best solution, but I am not able to find any LRA which can produce vibrations in um (micro metre).

Please suggest me any product exists or ways to produce controlled vibrations.


texts: How to calculate deflection of a cantilever beam subject to point loading

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I am trying to solve the following beam deflection problem:

  The cantilever beam is subjected to the point load at C.

  Generate the equation for the elastic curve by using the double integration method.
  Find the maximum deflection and slope if L = 3 m and P = 10 kN acted at 2 m from A.

  Ans: $y_{max} = -46.67/{EI}$

For part 1, my answer is $EI\dfrac{d^2y}{dx^2} = - Px$.

For part 2, my answer is:
$$\begin{gather}
EI\dfrac{dy}{dx} = -\dfrac{Px^2}{2} +c_1 \\
EIy = -\dfrac{Px^3}{6} +c_1x +c2
\end{gather}$$

at $x= 0$, $y = 0$, so $c_2 = 0$
at $x = 0$ , $\dfrac{dy}{dx} = 0$, so $c_1 = 0$

So, $EIy = -\dfrac{Px^3}{6}$.

$EIy$ max occurs at $L=3$, so $EIy_{max} = -\dfrac{10\cdot3^3}{6} = -45$, but the answer is  $EIy_{max} =-46.67$. What have I done wrong?

For the slope at x = 2, my answer is $EI\dfrac{dy}{dx} = -\dfrac{Px^2}{2} =  -\dfrac{10\cdot2^2}{2} = -\dfrac{40}{EI}$.


texts:
I'm trying to find a suitable shock absorber for a small ATV with a specific value (to be determined later). But everywhere I look, no one seems to be giving the damping ratio of the shock absorbers.
I'm not expert in this field, so I'm wondering if I'm missing something, and that in reality I don't need the damping ratio to select a proper shock absorber, and that the damping ratio in fact can be controlled by some other means?

All I have is the intro to vibration degree course where the damping ratio was always given.

Thanks for the help in advance.


texts: How to make machined plastic part slippery for small dry particles

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We have a plastic part that is a receptacle for small ( < 1mm ) particles. It is a disk with a shallow cone shaped indent made using a drill. When a particle is placed in the receptacle it should fall to the centre, but sometimes it stays on the side due to friction.

The particles can be spherical, globular or circular flat, and are made of calcium carbonate :) They are dropped in one by one and the slope of the cone is about 20 degrees.

To fix this, we are thinking the receptacle should be metal with teflon coating. However, is there any other coating we can apply to the plastic to increase its slipperiness? Perhaps rubbing graphite or a pencil lead in there?


texts: Is there a pressure relief mechanism that operates faster than sound in a material?

texts: In the event of an explosion through a high pressure gas pipe, is there a way to vent the pressure wave, in order to protect downstream objects? The mechanism must be faster than sound; pressure relief valves and even rupture discs are actually too slow and will not respond to such a "fast" pressure wave.


texts: How to negate rotation of a rotating linear guide rail on a carriage?

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We would like a carriage mounted element (CME) on a rotating linear guide rail (LGR) that negates the LGR rotation and thusly remains rotationally stationary relative to the LGR's pivot affixation surface.

Here is a diagram to illustrate what is desired for just three example angles and three example distances from the pivot superimposed (but all angles and legal distances should work - even right up to the pivot itself, though that is less important). P denotes the pivot and the CME has a notch on it to indicate constant orientation relative to the surface the pivot is affixed to:

The axis of rotation is the same for both the LGR and CME in question. This axis is the axis you'd intuitively imagine when imagining a LGR rotating, which is to say the axis that pierces through the top of the carriage and into the LGR, although that is only describing the direction of the axis, the origin/pivot doesn't follow the carriage; it is in a constant position near the end of the LGR.
I've already attempted various solutions, but most fail because of their inability to function with a dynamic distance from the pivot due to the carriage's linear freedom of movement.
One solution that could account for the carriage's dynamic distance from the pivot was to use sensors to measure the rotation of the LGR and a servomotor to rotate the CME to the desired angle. I will begrudgingly use this solution if nothing better is found, but I'd much prefer something with good old gears/pulleys/chains/etc. to ensure there's no "lag" and to keep costs down, etc.

Sorry for being cryptic, I am working on a prototype for something and my partner in crime is paranoid that their idea will be stolen. If you have any queries relevant to finding an answer I'll be happy to answer them.
edit: There will be two carriages on the LGR, each with their own CME, differing to the diagram. Both needing to negate the rotation of the LGR as already described. This is one of the things my partner would have rather withheld if you are wondering why I didn't say it sooner.


texts: What is the logic behind combustion air requirements?

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Combustion Air is the air that is required to provide complete combustion for a fuel source. Enough oxygen is required so that there is not an issue with carbon monoxide. This is an issue in houses and anywhere that has a furnace, water heater, boiler, etc. that isn't electric.

All of the codes and references (1, 2, 3) that I have seen use either the volume of the room that contains the equipment or an area of free-flowing vent from the outside in a ratio to the BTUs or Watts of the equipment.

Neither of these measures seem to be directly related to the chemical equation of combustion.

Comparing the volume of the room doesn't seem to take into consideration a replenishment of the oxygen from anywhere.
Specifying an area of vent seems to ignore the speed of air through the vent. It also doesn't seem to relate to the size of the chimney.

What is the logic behind either specifying a room volume or vent area for combustion air?


texts:
If I have a tank of nitrogen gas at 2000 psi (13.79 MPa) and a pipe of 10 mm cross sectional area and 1 meter long how long would it take to fill another, initially empty tank, to 5 L at 1000 psi (6.89 MPa)? Assume to 2000 psi (13.79 MPa) never drops and the initial source is unlimited
I have tried a couple of things so far:
Renouard Equation: p2i−p2f=46,742 $ρLq^{1.82}D^{−4.82}$⟹4391.11 L/s unreasonable
Panhandle Equation: -12166 L/s unreasonable
Weymouth Equation: 1066 L/s better but still an awful lot
Tried using experimental data: with this I know at the initial condition of 2000 psi (13.79 MPa) I have 228 ft3 (6.456 m3) and in 5 seconds the pressure drops to 1750 psi (12.066 MPa) but I no longer know how much gas is left.
Any help is much appreciated on this, thanks.


texts: How does LTE eNodeB set the Base Station output power?

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I'm interested into the power radiated out of an eNodeB (LTE/4G) radio base station: which parameters does this power depend on, if they are constant or relying on the environment...

All of this in order to be able to predict the rated power transmitted out of the BS antenna.

I've been seeking in the 3GPP technical requirements and sheets, but nothing conclusive about it until now, specificaly for LTE signals.

It shall differ from the others radio standards such as GSM or UMTS since LTE uses OFDM which implies multiple carriers instead of one. My guess is that those multiple carriers should in theory reduce the rated power per carrier.

I still have some certitudes about it, those being that the output power depends on the cell size, also that traffic-load, somehow, is taken into account (potential small cells may be deployed for capacity boost).


texts: Recovering mechanical energy from natural gas water boiler

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Is there any heat energy lost to the mechanical force of pushing a piston in a combustion engine?

In other words, would a natural gas burning as a flame produce more heat than the same amount of natural gas that was burned when driving a combustion engine?

The context of this question is around fuel efficiency of natural gas water boilers.

My current understanding is that a naked natural gas flame is burning inside the unit, and heats water that is contained within a series of pipes, which in turn is cooled in a heat exchanger, and that same heat exchanger heats the incoming cool water.

I'm wondering, would if it make any sense at all to burn that natural gas inside a combustion engine and use the heat of the combustion engine used to heat the water to the same extent as a naked flame.

More generally my goal is to solve the question, can we heat water the same extent by burning the same amount of natural gas and get free mechanical energy?

Thanks


texts: How to determine the stiffness matrix for finite element matrix

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I'm having difficulty understanding how the stiffness matrix for finite elements is obtained. I am only having a difficult time understanding how to obtain the matrix values for K from the given information, but understand how to do everything up to and after just get stuck on this.

I don't understand how the 8, -8 are obtained in the K11, K12, K21, K22 positions yet 3, -3 is obtained for K22, K23, K32, K33 following by the 18 in K33, K34, K34, K44.
Every direction I look at it falls apart at another section.
Though I just figured one thing out, but I'm not sure if it's correct or only works for this situation.
For $$ K^1 = 24/12 * 4 = 8 $$
For $$ K^2 = 24/8 * 1 = 3 $$
For $$ K^3 = 24/4 * 3 = 18 $$


texts: Can crosshead movement be used to measure strain in tensile testing instead of an extensometer?

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I am trying to design and build a low cost tensile test machine for plastic specimens. Most machines I've seen measure strain data using an extensometer, either the clamp-on type or the noncontact type (using video). However, both options are expensive to implement, so I was wondering if it would be a good idea to measure crosshead movement vs. time to use it as elongation data, and the correlate it with cross-section area and force vs. time data to obtain a stress-strain curve. Would this be feasible, if extremely precise results are not required?

Since so many machines use extensometers, I assume there must be a good reason not to use crosshead movement as elongation data. If so, why are crosshead movement and specimen elongation different? And how significant is said difference? Would much would test results be affected if crosshead movement were used as elongation?


texts: Plastic failure evaluation of steel using FEM

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I would like to evaluate failure in steel using FEM, especially in geometries with stress concentrations (notches etc.).

One possibility is to calculate the stress distribution using a purely linear equation of state (elastic = Hooke's law) and evaluate the von Mises stress, using appropriate stress concentration factors (plastische Stützzahlen in German). The drawback is that you need to know (or approximate) the appropriate stress concentration factor(s).

Another possibility is to calculate the stress distribution using a nonlinear equation of state. For steel I read that the bilinear elasto-plastic model is realistic enough for most cases. However, I'm unclear what to evaluate as failure criterion. I noticed that when I change the load to a certain model by a factor of two, the maximum von Mises stress does not change significantly (once it is in the plastic region). I suppose this is due to the values of the two moduli (elastic modulus and tangent modulus) being at least one order of magnitude apart (210 GPa vs. 1-10 GPa). My assumption is that I can use the maximum strain or maximum plastic strain as failure criterion, however I was unable to find a reference supporting this assumption.

Please note that I am interested in failure from a single loading event only. I understand that the fatigue failure mechanisms (when load cycles are applied) are quite different.

So the question is: What can I use as failure criterion, and why? Please support your answer with a (link to a) book chapter or publication - thanks.


texts:
The part is a clevis and was insterted in a steering rack . Part was in Tension, torsion and bending. It failed at the end of the threaded bolt part. Is it a common problem for bolted joints ? How can it be resolved ?

At first a bend was observed in the threaded part in the direction in which it is kept in the picture before failure.


texts: What is the analytical approach for a fiber cutting machine?

texts:
Folks,

so today in the Lab I came up with this problem (see picture). It shows a cross section of a cutting machine. There's a blade moving with a constant speed $\frac{dx}{dt}$ towards the center of the roll made up of wood. This roll is turning with a adjustable speed $w$. Let's assume we keep $w$ also constant. So the questions I ask myself are as follows:

How does the rotational speed w influence the thickness of the thickness of the fibers being cutted?
What is the mathematical function of the contact point (roll/blade)?
Do the fibers have a constant thickness?

Through careful consideration of the problem, I found the answers to 1) and 3).

Yes the thickness is influenced by $w$. For 3) it can be said that after one rotation of the roll, the fibers have a constant thickness. By observing the contact point on the wooden roll it can be seen that the point makes a spiral towards the center. Basically what is missing now, is the analytical/mechanical approach and mathematical formulation for this spiral.


texts: Determination of thermal expansion of a hollow cylinder

texts:
I have a heater rod inside a brass rod, which is wrapped by PTFE insulation. The dimensions of the assembly are:

Heater diameter = 9.5 mm
Brass rod diameter = 25 mm
Insulation diameter  = 100 mm

When the heater heats the assembly, will the assembly get tighter or looser? The final temperature that the brass rod would reach is 100 °C and the initial temperature is 20 °C.


texts:
I am working on a project to bring light into a bunker. The bunker is 3-4 meters below the ground.

I am looking into bringing natural light into the space, instead of using electricity. The space is difficult to access and light must therefore be transported by flexible cable for about 20 meters from the surface to the areas I want to light up. I am thinking of pipe around 1 cm diameter maximum.

I am looking into a cheap solution to create an optical pipe that is effective at transporting light.

I am wondering what techniques are typically used.
What kind of pipes would you use ?
Is it possible to fill the pipe with other materials to increase its effectiveness ?


texts: I am an electrical engineering student that wishes I could have taken some civil engineering courses. Anyways I'm trying to design a pvc structure that I will use as a somewhat complicated room divider. I have the basic design drawn out, but I'm not sure how to design for stability and loading (eg, how many supporting beams to build). I'm familiar with Solidworks and should be able to sketch up a design to do stress testing if that's something useful? I did some basic mechanics from first year, and know how to setup equilibrium equations but I'm not sure if that would be of any help in the design process. I'm open to learning new mathy thing and would love to treat this as a learning experience to solve a practical problem. A nudge in the right direction would be appreciated. Thanks!


texts:
My classmates are making mousetrap cars to go 10 feet, and whoever goes the fastest wins. How a mousetrap car works is by attaching a lever arm to the snapper (the part of the mousetrap that shoots forward). The lever arm has a string attached to the end of it, and it is wrapped several times around the axle of a car. When you let go of the lever arm, the snapper goes 180 degrees, spinning the axle and making the car go forward. Here is a link for more information: https://www.wikihow.com/Build-a-Mousetrap-Car

I have an idea for a car, but want to make sure it's sound before building it. I plan to have six wheels. The back wheels will be adopted for distance, so it will have a longer lever arm and a thinner axle. The middle wheels will be adopted for speed, so it will have a thicker axle and a shorter lever arm. There will be two strings attached to the lever arm. One will be at the end, and will be wrapped around the distance axle, while one will be near the middle and attached to the speed axle. My reasoning is that the middle wheels will provide a lot of speed, and at the same time make it easier for it to start moving. The back will make sure it keeps going once the speed boost wears off.

What I want to know if doing this will work, or if it would be better to just have two pairs of wheels that are moderate thickness and moderate distance from the mousetrap. This is my concept sketch:


texts: Given 3 force measurements, what are estimated forces at other locations?

texts:
Given three unequal force measurements spaced equally 120 degrees apart on a circular plate at F_R, F_C, F_L,  I need to calculate what the estimated force measurements would be if taken at positions F_NW,F_NE,F_R, and F_L (90 degrees apart).  All forces are perpendicular to the plate surface (straight down) and I'm treating downward as a positive force (into the screen on top view).
I have tried a few different techniques but nothing is giving me a sane answer.  Any help or techniques are appreciated.  Hopefully my question is clear.


texts: Rotating two shafts together - coupling rod?

texts:
Are there any established (compact and simple) solutions for turning two 5mm rods/shafts side-by-side together by driving a singe motor? The torque is about 5kg-cm. The one I'm thinking of is the coupling rod:

Are there disadvantages to this solution compared to others, e.g., gearing?

If the coupling rod is a good solution, where could I get my hands on those "tabs" where the coupling rod connects? Is the coupling rod supposed to be connected using some small shoulder bolts and nuts?


texts: Placing an accelerometer on arbitrary position and define this as the new coordinate system

texts:
I'm working on a small home project and I'm looking to use an accelerometer for tilt sensing. I would like to be able to place it anywhere on the object. If I place it in a way that the coordinate system on the device is not aligned with the object I would like to rotate this to match it.
Do I need to calculate a rotation matrix between the coordinate system I give the object (lets say I would like to have Y axis of the device be Z) and the coordinate system of the accelerometer itself?


texts: How are components printed onto chips in lithography?

texts:
When making chips using lithographic techniques, How are the transistors and capacitors and other components "printed" onto the board?
When we print one we use things like UV or E-beam to print out the shape we want (using some kind of mask), but after we're left with the desired shape, how are the transistors, capacitors, resistors (and so on) placed? Are they there all along somehow?
I bet this question has a simple answer but I must be mis-interpreting some concept which doesn't let me understand.


texts:
Why do we need to shut down power generators if we are producing more power than the grid requires?

How it will damage the system if they are not shut down?


texts:
Internal Combustion Engine powered cars need multi-speed gear shifts since their power is highly dependent on speed and engines have narrow usable power/speed bands.

Some electric vehicles are also coming out with gear shifts. We have Antonov already working on a 3-speed gearbox for electric motor drive, and the new Exagon Furtive eGT is said to be coming with a 4-speed gearbox. Why multiple speeds on an electric vehicle? The reasoning is the same as for an engine. It is to allow lots of torque in first gear to start but also to eliminate the need for the motor to run insanely high RPM's when you're going 80 mph on the freeway.

Metal band saws also come with some form of mechanical speed control (CVT or* gear shift) since you will want to cut softer stuff using high gear, but you will need low gear to cut iron, steel, etc. There's Clausing Industrial who have put two xor THREE speed controls: a belt-drive CVT, 4-speed gearbox, and possibly an infinitely-variable** inverter motor, in their V4014H vertical band saw!

But what's odd is that many tower cranes also have gear shifts (on the hoist winch) even though they're electric!

For example, the hoist winch on the Liebherr 357 HC-L 12/24 luffing boom tower crane appears to have a 3-speed gearbox immediately after the motor. Using a 215-horsepower (160 kW) motor and 1-fall operation, the maximum no-load lifting speeds are (capacities based on halving the capacities of 2-fall operation):

330 m/min (3rd gear) maintainable up to 1,500(?) kgf
185 m/min (2nd gear)
113 m/min (1st gear)

And the maximum full-load line speed at 12,000 kgf (even on third gear, I presume) is 68 m/min.

The smaller 147-horsepower (110 kW) hoist winch also, apparently, has 3 speeds (these are again on 1-fall operation):

261 m/min (3rd gear) maintainable up to 1,100(?) kgf
157 m/min (2nd gear)
91 m/min (1st gear)

And the maximum full-load lifting speed (again, on any gear) is 45 m/min.

NOTES:

"No-Load Speed" is at zero hook load (when the crane is lifting only the hook-block)
kgf = Kilogram-force
*Logical OR
** "Infinitely-variable" = "Continuously variable down to zero speed"

My questions are:

Despite the fast lifting speeds often encountered and the high load capacities, shouldn't the working range of a tower crane be smaller than that of a car?
If electric motors do so well on cars without a gear shift, why would you need such a thing on a winch? In this case, a crane hoist)


texts: Why do steam and diesel engines have differing cylinder configurations?

texts:
Consider a fixed steam engine, such as in a Lancashire cotton mill or pumping in a Cornish mine.  Then consider a fixed diesel engine such as a large generator or ship's engine.

Why does the steam engine have one or two large cylinders with long stokes, but the diesel has many cylinders with relatively short strokes?


texts:
I'm asking this question as an early computer science student who is beginning to get way more interested in really low level stuff/computer/electrical engineering. I am very unfamiliar with hardware, and even after watching numerous videos and reading numerous articles there is still something I can't seem to grasp.

You write a program, compile it, it is loaded into memory, and then...???

I know a transistor can be made to store one bit of data. Okay, fair enough....

But when you load a program into memory, what is...happening? I'm familiar with logic gates and all of that, but what does it mean to be...In memory?

If you have a program loaded into memory, it's in its machine code computer readable format and being processed, how do those values translate from "being in memory" into transistors being on and off? From my understanding, the program counter is reading these pieces of data into your memory, so when you're in memory, does that automatically mean there's this on-off process going on? Is that the last step? How do physical hardware chips "read" this data that is in memory?

I think what's throwing me off is that every video I've seen representing how a transistor stores a bit of data shows a guy switching wires into different holes on a board demonstrating it. But there isn't a little man inside the computer switching wires around. How does that process take place?

Please help me out here, I am ignorant and want to learn.


texts: Selecting edge of a circle in Solidworks

texts:
When I am drawing things (Assembly) in SolidWorks, on some parts which I work on, I can select the edge of a circle and then measure the dimension to a line, like shown below:

But the problem is that on some others I simply can't. It won't allow me to select the Edge of a cirlce when I hold down the SHIFT key. If I "insist" and drag the measurement to an edge, it jumps to the other end, like shown below:

I think I'm doing everything right: Doubleclick Sketch to edit it, select a line, then hold SHIFT and then try selecting the edge of a circle. I already searched on the internet around, but no one had really a solution for it. The closest I came was this.

Why does it work on some projects and on some others it don't?

Any help is greatly appreciated.

EDIT: I'm using SolidWork 2016 Premium x64 (SP 0.0)


texts:
I'm recreating an old mechanisme in 3d modeling software. The idea is that this triangular shape rotates around an off-center axis. This will create 4 phases. first (like in the picture) the construction L is down and stay stable in that position (which means the parts of the triangle thing that touch the construct L are partially circle. In the next phase the construction moves up, then it is stable again and in the last phase it moves down.
Questions are: what is the mathematics involved in the shape assuming it never looses contact with the construct L. Initially I made the sides out of 6 circular elements (arcs), but I'm not sure if that is even the correct shape. Once I have the shape, what is the position of L as function of the rotation of the object?


texts: Potentially fatal near miss: Due diligence in tool selection

texts:
I recently outfitted a crew to build scaffold in preparation for an upcoming turnaround at our plant.  Among the tools requested were canvas buckets for manually hauling material and tools up and down scaffolds.  In sourcing these I went through a reliable well established industrial supplier with a know brand.  I ordered bags rated for 100 lbs which above the maximum load for manual hoisting permissible on our site.

Several days after arrival on site one of these bags failed with a 27 lb load in it.  Nobody was hurt but it could have easily turned out differently.  We immediately pulled all bags from use.  In investigating it was discovered that when used outside in winter conditions that the plastic parts of the bag bottoms become brittle.  No temperature restrictions were offered in any documentation related to these bags and these tools were being used for the purpose they were designed for.

I feel awful that a decision I made put people at risk.  Is there some aspect of due diligence in tool selection that a reasonable engineer would have been expected to take that I had missed?


texts: How to get a wheel pump to deposit water near the top of the wheel?

texts:
Suppose I have a wheel, about 6 feet in diameter, with empty soup cans affixed around it, powered by a big windmill. This drawing only has four spokes, but there will be more:
                      ___
                      ___| <-- tin can
          ...   \       |       /
    .... <--bamboo chute| <--spoke
...               \     |     /
<--water is sent that way    /
                    \   |   /
                     \  |  /
 __                   \ | /                  |  |
|  |-------------------( )-------------------|__|
|  |                  / | \
                     /  |  \
                    /   |   \
                   /    |    \
                  /     |     \
~~~~~~~~~~~~~~~~~~~~~~~~|~~~~~~~~~~~~~~~~~~~~~~~~~ <-- water
                        |__
                       |___ <--water is picked up here

The water needs to be dispensed into a chute, or aqueduct, made from bamboo, cut in half. The water is sent down the chute to another higher pool of water.
The first problem I'm running into with this design is that there isn't any way to position the chute in a way that catches the water pouring out of the cans. If I position the chute under the can, it falls within the radius of rotation, and blocks the turning.
How can I get the water from the cans to spill out into the chute, at ideally the highest point possible?


texts: How do I import an .inp and an IGES together into Ansys workbench?

texts:
I have an .inp file of Ansys that is basically a mesh, that could be imported into Ansys APDL and converting to .cdb file.

But I also have another .IGES file that I should import in the same model and assemble on the first one. How do I do that ?


texts: Improving PMMA adhesion on Gallium Arsenide wafer pieces

texts:
Firstly, I'm unsure about the scope of this stack, but let's try.

I'm doing electron beam lithography on semi-insulating GaAs wafer pieces. And I have a hard time getting the PMMA to stick onto the GaAs. It detaches from the surface, and makes EBL possible.

My initial approach was cleaning in U/S acetone, then rinse with IPA. Secondly, I tried rather long cleaning steps (30 minutes of sonication time), and longer solvent bake of the PMMA (solvent: chlorobenzene).

I've had limited success with 60s etch in ammonia, followed by a 3 hour solvent bake, after spin coating. Limited success means that the thin film did not entirely peel off, in the vacuum of the SEM.

I'm aiming for a 100nm PMMA layer, and I need to produce features of down to 200nm in linewidth.

Do you have any pointers, or ideas for surface cleaning/etching? I'm contemplating the standard RCA cleaning procedure, but it's also a rather significant step up in complexity and work safety considerations.


texts: How to calculate adiabatic air temperature loss caused by increase of humidity?

texts:
I'm searching for an approach on how to calculate the adiabatic temperature loss of air when increasing its humidity by a humidifier.

Assumed we have the following setup:

Air measuring position 1 (before humidifier):

$T = 30{ °C}$

$x = 10\text{ g/kg (absolute humidity)}$

Air measuring position 2 (after humidifier):

$T = \text{? °C}$

$x = 20\text{ g/kg (absolute humidity)}$

The question now is: How can I calculate the air temperature at measuring position 2? With a Mollier-diagram it would be easy to figure out, but I want to solve it the analytical way.

I guess there is something possible with the enthalpy of air:

$$h_1=h_2$$

$$Q_1\cdot x_1\cdot T_1=Q_2\cdot x_2\cdot T_2$$

$$\frac{Q_1\cdot x_1\cdot T_1}{Q_2\cdot x_2}=T_2$$

What is missing? :-)


texts: What is a good way to bond stuff to silicon nitride?

texts:
I am currently looking into attaching a wire onto Silicon Nitride igniter, which is being used as a resistive heater. The problem I am experiencing is that the Silicon nitride is extremely hard to bond things on as is, and in addition, the bonding agent has to be able to tolerate temperatures up to 1K Celsius. I have already experimented with ceramic epoxy and found difficulty.
Alternatively, we have already considered using a silicon Carbide igniter, however, all commercial igniters have bases that are too big for our uses.
It is possible for us to use filaments and create a base, however, we would like to avoid the hassle if possible.
What would be a good way to do this?


texts: Virtual Work - Determining Relationships in deflections

texts:
I'm having problems understanding the worked answer for this problem:

Here's part of the worked answer:

I don't understand why $\delta_C = \dfrac{4}{9} \delta_A$ . Can you please explain that part of it?


texts: Equations for stress in a hollow prolate spheroid under external pressure

texts: Are there analytical expressions (functions of geometry and applied pressure) for the stress in a hollow prolate spheroid, like there are expressions for the stress in a hollow sphere/cylinder?


texts: which kind of accelerometer/vibration sensor are suitable for sensing vibration of building floor caused by human foot strike?

texts: I want to count human presence in a room through vibration sensing of concrete floor. For this I want an accelerometer with low frequency detection capability. I have used ADXL-345 which is not much sensitive for floor vibration sensing. Also piezo (see figure) sensors are not much sensitive.


texts: Adhesion of Super Glue (containing ethyl cyanoacrylate) and PVDF (polyvinylidene fluoride) film

texts:
Would it be considered safe to use super glue, which contains ethyl cyanoacrylate, to attach a PVDF film to a metal alloy?

It says super glue is not recommended for polyethylene or polypropylene. However, I am not sure about the hazards for polyvinylidene fluoride.

Thanks!


texts: How do I keep my bit from wandering on a drill press?

texts:
I punch metals before I start a bit in them, but with small-diameter bits I am finding that they wander inside the material.  E.g., drilling a 1/8" hole in 1/2" of aluminum the (titanium-coated HSS) bit will come out the other end a measurable distance to a side (orthogonal to the drill feed direction) from where it entered.

To be clear, the bit starts where I want it to since I punched the metal. But the bit appears to be flexing within the material, causing the resulting hole to be angled.

How can I prevent this?  Is there something about the material that I need to understand in order to prevent the bit from wandering and causing the hole to be skewed?  I'd like to know the mechanics behind the materials that is causing these skewed holes.


texts: Removing water and nitrogen from reactor effluent

texts:
I wish to remove water and nitrogen from my reactor effluent in order to decrease downstream equipment sizes and subsequently capital costs.

Stream composition:

${H_2S}$.................5.6%

${SO_2}$.................3.3%

${S_2}$.................9.2%

${COS}$.................0.9%

${CS_2}$.................0.1%

${CO_2}$.................1.3

${H_2}$.................1.4%

${H_2O}$.................34.5%

${N_2}$.................43.7%

Removing these components would result in a approximately 90% less flow rate.

Restrictions:

The sulphur MUST stay above melting point, $\pm$130 $^\circ$C at 1 atm.
ZERO sulphur compounds must leave the water or nitrogen streams. (meaning that if these compounds are in the water or nitrogen streams, they have to be removed at a later stage as well.)

What I have done thus far:

I used the Clausius-Clapeyron equation to solve for a pressure where the dew point of water is higher than the melting point of sulphur.  I found that at 3.5 atm of pressure and approximately 130 $^\circ$C, liquid water forms but sulphur stays liquid, and density separation can be performed with the added bonus that sulphur is insoluble in water.
However, I cannot think of way to remove the nitrogen or a cheaper,more efficient way to remove the water.


texts: Recommendation of different materials for 3D printing flexible parts

texts:
I am planning to 3D print this part from solidworks.
I am hoping to achieve a good level of flexibility with the clasps in this part.

Thin circular arc in the Top drawing.

and

Wider circular arc in the Front drawing.

The only flexible materials I have access to currently in the lab I work are nylon and polypropylene. I'm not sure which is a better, so I would like to get some recommendations. The flexibility I am looking to achieve is similar to that of the handle on a pen cap. I want the clasps to be able to flex enough to snap onto a circular tee without breaking, and if necessary be pulled open to take the part off again.
The thickness I am thinking of printing at is 0.1 mm thickness but I also need to be able to have the labels and tick marks be clear enough.
Ultimately I'm only interested in which material is best. Thanks.


texts: Smart fastener for male thread in solidworks

texts: Is it possible to add nut using smart fastener feature in SolidWorks as shown below. Presently I have added nut using toolbox feature. I want to know if we can add nut and a washer to male thread directly using smart fastener feature rather than separately adding nut and washer from toolbox


texts: What is the theory behind Eurocode 1 - Part 2: Traffic loads on bridges?

texts:
I'm interested in some theory Eurocode 1: Actions on structures - Part 2: Traffic loads on bridges. How were the limits chosen (e.g. maximum deck acceleration = 3.50 m/s2)? Why is the lower limit of $n_0$ governed by dynamic impact criteria and given by the following?

$$n_0 = \begin{cases}
80/L, &4m<L<20m \\[2ex]
23,58L^{-0,592}, &20m<L<100m
\end{cases}$$


texts: Does temperature affect the colour of the light emitted by an LED?

texts:
Suppose you have an LED that emits a spectrum of colours such that the resultant colour emitted is white. Will changing the temperature if the LED itself change the composition of the light's colour spectrum, hence changing its resultant colour?

My immediate answer to this is no but after a bit of research, I came accross this graph:

The website states that:

  Figure 9 shows the light output of several LEDs as a function of junction temperature. The temperature dependence is much less for InGaN LEDs (e.g., blue, green, white) than for AlGaInP LEDs (e.g., red and yellow).

As the graph clearly shows, the relative light outputs of the red, white and blue light changes at different rates as temperatures increase. This shows how the intensity of the light overall changes with the temperature of the LED system. However, does this mean that the colour composition of the emitted light changes with temperature as well?


texts: Torque required to rotate object around axis using Stepper Motor for Kinetic Machine

texts:
Hey all,
I'm creating a machine to rotate a socket wrench using an arm attached to a motor shaft in order to make clicking sounds from the object therefore I'm trying to choose an appropriate stepper motor with sufficient (holding?) torque to be able to rotate a socket wrench around an axis point. My understanding that in order for the motor to adequately pick up and rotate the object about the axis, the holding torque >= Force required to lift the load. I'm also neglecting the mass of the arm and the friction of the force needed to 'click' the ratchet when it's moving in the non-locked direction.
Referring to the image above, the mass of the socket wrench is 1.2 kg and its length is 0.475 m. My calculations in the image indicate that I would need a motor that could provide >= 5.6 N-m...
Also, I'm not sure if adding the arm to the shaft of the stepper motor actually decreases the required torque - it seems that even while I decrease the required force to turn the socket wrench by applying force at the end of the object (towards the handle) that I'm also decreasing the holding torque from the motor.
Does this seem right? I feel like 5.6 N-m is a lot of torque - most DIY steppers (e.g. for 3D printers and what not) are somewhere in the range of 0.5-1.2 N-m. Are my calculations correct? Does anybody have any ideas on better ways to go about creating this kinetic mechanism?


texts: How does pressure change with depth in earth?

texts:
I've learned in school that pressure in water changes like

$$p(h) = \rho g h$$

where $h$ is depth in meters, $\rho$ is density (e.g. 1000 $\frac{\text{kg}}{\text{m}^3}$ for water) and $g$ is gravitation acceleration ($\approx 9.81 \frac{\text{m}}{\text{s}^2}$) and $p$ is the pressure in Pascal.

I guess there is no similar law for pressure in earth as it is to different, depending on where you are. But is there a rule of thumb? What do engineers who build tunnels / underground stations do?


texts: Small scale aluminium tubes manufacturing

texts:
Our startup needs short aluminuim tubes (max. ~70 cm [~27.5 inches] long / less than 1 cm / 0.4 inch diameter) such as these:

We'd prefer to manufacture them ourselves rather than buy them from a s

Are there small scale solutions (machines, etc.) that would allow us to do this?


texts:
I am looking to purchase some new Vernier calipers, but I am overwhelmed by the amount of specs which are being offered.  I need help in understanding how to evaluate them.

I do not want a dial or digital set of calipers, but rather am interested in any additional qualities such as the accuracy that these may offer which Vernier calipers can not.

Accuracy is the most important quality that I am looking for.  For the sake of the question, assume that I have budget around US $2,000.  What aspects of the Vernier calipers should I be looking at in order to have a high degree of accuracy?  What else should I be examining with the calipers as part of this purchase?

I have some specific sub-questions that I haven't been able to figure out.

Graduation

A common amount is 0.02 mm, does this mean we can advance each measurement by a minimum of 0.02 mm? Therefore cannot get any closer a measurement from any 1 point on the scale?

Parallax-Free

I have read somewhere online that parallax-free aids the readability of calipers, thus allowing for less human error - If this is true, does this parallax-free attribute come at a cost? Do we lose some accuracy? (I think I read parallax-free Vernier calipers do not have a separate upper movable ruler like some of the others.)

Metric

I'm having a hard time identifying what's standard.  What are common units offered?


texts: shear stress at nail at different points

texts:
In this notes , i dont understand how the Q=(Ay) of the is considered ...

I think the both Q at part C and part B should be = (60)(15)(mm^2) ... i have redrawn the structure , i am not sure whether it is correct or not...
From the definition of shear flow , A is the cross section area of segment that is connected to the beam at juncture where the shear flow is calculated .


texts: ~121:1 speed reduction; are more gears better?

texts:
Taking a 1750RPM 110VAC appliance motor down to about 60RPM, maybe a little less. It's a home project on the cheap, so dropping a few hundred dollars on a ready-made gear box is to be avoided, and I'm working with the kids as a school project and so creating by hand as much as possible.

1/2" plywood for an initial prototype/proof of concept, with a planned move to 3D printed gears afterward. Assuming a tooth pitch of 18-25mm, and that we play with the tooth count between the gears to spread out the wear and tear, which would be better for durability, chatter, noise? Fewer gears with larger reduction ratio at each step, or more gears with a smaller ratio?


texts: Does a house heating system affect perceived and true indoor air humidity?

texts:
Does a house heating system affect indoor air humidity?
Or to be more precise, does it affect your perception of how dry the air in the house feels (for instance dry is your mouth waking up)?

(I searched for this but could only find explanations from furnace company websites)

Every (lay)person I ask this seems to think house furnaces make the air drier (at least the perceived dryness). One friend claims that the air gets even dryer than the outside air.

My intuition is that heating can only increase the evaporation inside the house (from the little surface liquid water sources (shower, taps) there may be), therefore making humidity go up.

I suspect people think this because furnaces are only on in the winter when the outside air is dry leading to dry air inside as air exchanges. Thus it could be due to this spurious correlation.

Another possible explanation is that the higher air temperature increases the air's water carrying capacity, which in the absence of an abundant water source, extracts water from your body faster. Therefore increasing perceived dryness. Even if these two countervailing effects are true, can we use first principles to bund which effect dominates?

EDIT (after seeing the answers and discussions below):
Perhaps perceived humidity is too loose to define. What if we define the water loss of a human over a period as our measure? But my ideal answer would have two numbers to compare:

Baseline_loss = how much water does a person looses sleeping in a cold sealed room (say at 1C temperature) with 100% relative humidity and no air movement.
Total_loss = how much water does a person loses if the same sealed
room was heated up to 22C (a nice in-home temperature).

Then Heating_induced_loss = Total_loss- Baseline_loss


texts: How to configure strain gauges for tension measurement?

texts:
I have a machine which has belts with three pulleys, one of them is connected to the motors,the one in the middle moves to tighten the belt, and the third is idle pulley. This belt assembly sits on a plate and a strain gauge is attached to the plate. The function of the belts are such that they will pull a fiber by gripping on it and the strain gauge is for measuring the tension in the fiber.  The engineer who designed this is no longer available and I don't know how to convert the readings from the strain gauge into tension. I have attached the assembly image, can anyone tell me how to calculate tension in the fiber that is being pulled by the belts from the strain gauge measurements?

Please let me know if additional details are needed.


texts: How to constraint with objects out of sketch plane?

texts:
I would like to constraint the centers of two rectangles to be exactly across the part central axis (shown in the middle of cylindrical hole)

Is it possible?

Rectangles should be as wide as circular hole


texts: In what context is 50 threads per inch common?

texts: I recently found a loupe with a thread pitch reticle displaying common UTS thread pitches... except that rather than 40, 48, or 56 it has a 50. What would this be used for? It doesn't appear to date from earlier than the 1960s - the housing and dioptre lens are plastic, the reticle and retaining ring are glass/metal.


texts: Location of breakdowns in power transformers

texts: Where exactly are breakdowns occuring in power transformers? Means, between which components exactly?


texts: Determining mass flow rate and exit velocity of compressible flow

texts:
This one's a bit of a doozy, so please feel free to comment on any one single part or parts to this problem.

The setup is simple--I have a container (an empty bottle) which I fill with a certain pressure of compressed air through a car tire valve assembly attached to the top of the bottle. On the bottom is an orifice made crudely by forcing a heated paperclip through the bottom of the bottle, small enough such that a thumbtack can fit snugly through it, effectively sealing the hole. The whole thing is attached to a small toy car; Removing the thumbtack releases a stream of air that acts as a thrust force. I'm running this trial with a 2 L bottle at room temperature, and for incremental pressures of 10 psi from 30 psi to 60 psi.

As an assignment, I have to determine a few things:

1. THE NATURE OF THE FLOW: My understanding is that adiabatic flow is different from isothermal flow is different from compressible/non-compressible flow, etc. Unfortunately, this is literally the first time that I've heard any of these terms, and while I researched and understand their definitions I cannot tell which of the following my setup is. Would anyone with a more professional of experience know which my setup might be, and why? This affects which of the equations I can use to find...

2. MASS FLOW RATE & THRUST FORCE: I did see this link on calculating the flow rate of air through a pressurized hole: https://physics.stackexchange.com/questions/131032/calculate-flow-rate-of-air-through-a-pressurized-hole

However, my understanding is that the Bernoulli equation described in the link above does not apply because if the ratio of outside pressure to bottle pressure is lower than 0.528, then the flow is choked. This, however, opened up another can of worms, in that I had trouble finding an equation that does work concisely.

I've found quite a few, but I am the world's worst researcher and am probably missing something very helpful. I need to know the BEST one given my setup. The ideal scenario would be a time-dependent one; I found this website (the equation is towards the bottom of the page) that split the mass flow rate into a time dependent equation that had a time-dependent pressure equation and time-dependent temperature equation as part of its components. I tried plugging values (pressure of 30 psi) into the pressure equation and received some pressure marginally different from 30 psi for a time of 10 seconds into the trial. This seemed to conflict with the fact that a lot of air sounded like it was coming out of the bottle in the first 10 seconds when I ran the trial. OR, if this equation is absolutely right, am I doing something wrong with plugging in my variables or failing to account for a certain variable or effect with my experimental setup? For plugging in, I used the temperature in absolute kelvin, the gas constant R = 287.058 J mol^-1 K^-1, gamma = 1.4, orifice area in m^2, volume of bottle in m^3, and pressure in psi.

Given the nature of my setup, what specific mass flow rate equation would apply best, and why? THERE ARE A LOT, and trying to look for the right one myself has gotten me nowhere the past few days. Note that my setup involves something that is time-dependent, as pressure, mass, velocity of the gas being expelled are changing over time as air is expelled.

3. VELOCITY OF GAS THROUGH ORIFICE: Again, I've had trouble researching this. I know that I can relate this exit velocity to mass flow rate, since:

Mass flow rate = (gas density)*(Area of orifice) *(exit velocity), so if I solve for the former three I can easily determine exit velocity. This would be made much easier, however, with an equation describing the escape velocity. This is, again, better as time-dependent and pressure-dependent, as changing pressure means changing gas density and changing exit velocity.


texts: Why don't refrigerators have parts outdoors?

texts:
I've always wondered why refrigerators don't have some of their parts located outdoors like an air conditioner.

In warm weather, it seems like it would make sense to have the condenser outside like an AC unit to avoid heating the room. In cold weather, it seems like it would be much more efficient to have the condenser outside to cool down faster. Why is the condenser still indoors?

First, does this exist in some places? Have I personally just never seen it? Maybe for large commercial, refrigerator/freezers?

If not, would the cost simply outweigh the benefit? Is it cheaper to have the AC cool the room down after the fridge has heated it slightly rather than install another condenser outside? In cold weather, is the fridge acting as an efficient space heater, so putting the condenser outside not really get you anywhere? I'd be interested to see if a cost/benefit analysis has been done.

Finally, is it just convenience? Is it simply much easier to just move the fridge in, plug it in, and be done?


texts: How to make an Idol always strictly face the rising Sun?

texts:
I recently came to know that the Sun rises on a different place in the horizon everyday : https://astronomy.stackexchange.com/q/39670/14624 To me the change in the direction of Sun rise seems significant in certain months, as detailed in the question.
What can I do to ensure that an Idol is always strictly facing the rising Sun?
As an aside, I also wonder based on what were the idols in Asian temples placed. Looks like its a general East direction. I think mostly because the effect of this change in the direction of Sun rise isn't as significant in countries closer to the equator, they got away with it. But how can this be achieved in countries further away from the equator (example Australia)?


texts: How can I finish a round hole so it has 90 degree corners (flat bottom)?

texts:
I have a 10 mm depth x 5 cm length 99% Tungsten rod.  How can I machine the described hole so that instead of having a bevel from the tip of the main drill-hole bit, it has a perfect 90 degree corner all around as if the tip of the drill bit were like a flat router bit?

If this is not feasible, I can think about a design that doesn't use this larger hole.  For this design, the inside of the large hole will be filled with an AlO3 ceramic tube that snuggly surrounds 1mm D of round stainless steel wire that flows through the center.


texts: How do I to connect aluminium profiles with 60 and 120 degree angles?

texts:
I would like to construct an aluminium profile frame which includes connections with stiff fixed angles at 60 and 120 degrees.

What options do exist for creating those connections, preferably without having to further process the profiles themselves?

There are many ways for connecting elements at 0 or 90 and sometimes 45 and 135 degrees, but even with exact cuts at different angles (which I would like to avoid) there do not seem to be many tools for creating other connections available.


texts:
I was watching a video on the ti products out currently for wireless microcontrollers, and they mentioned a "multi-standard" CC2650 mcu here http://bcove.me/uekqgi7q. What makes a microcontroller "multi-standard"?

Thanks!


texts: Can steel be replaced with aluminum alloy in reinforced concrete?

texts:
Can aluminum alloy be an alternative to steel for reinforcement in terms of the same forces encountered by reinforced concrete beams? Will it be economical and feasible?

Are there organizations who already practices the use of aluminum alloy reinforcement as a replacement to steel?


texts: Am I estimating thrust of a ducted fan correctly?

texts:
I'm asking if I'm doing this correctly.
I've estimated the thrust of a ducted-fan model aircraft neglecting pressure changes across the duct as follows:

$$F = Q * \rho * (V_e - V_0)$$

$$= Q * rho * (Q/A_e - Q/A_0)$$

$$  = 131 [cu. ft. / sec] * 0.00237 [slug/cu. ft] * (131/0.74 -131/0.92)$$
$$  = 0.31 * (177.03 - 142.4)$$
$$= 0.31 * 34.6$$
$$= 10.7 lbf$$

where

F = Thrust,
Q = volume flow rate of air = 131 [cu. ft. / sec],
$\rho$ = density of air = 0.00237 [slug / cu. ft],
$A_0$ = an circular inlet area = 0.92 [sq. ft],
$A_e$ = an exit area = 0.0.74 [sq. ft].

That seems an awfully high value for thrust to me. Am I missing something?


texts:
I'm trying to mathematically model an actuation system and it comes down to relating the pressure across the pump and the actuator as shown in the picture. Assuming no friction in the pipes and the inlet and outlet flow rates are the same (both equal Q3), how can I relate P1, P5 to P2, P4?
I tried considering the hydraulic analogy and use Kirchhoff's voltage law but didn't know what to do with the actuator. Would really appreciate it if someone could point me in the right direction.


texts: What kind of impeller pump is this? (photo)

texts:
First, what kind of impeller and pump is this? I mostly see centrifugal impellers in the net.

I googled about this but didn't find direct reference to it. Most are about centrifugal pumps. Although I managed to find a video that discussed something similar to it. But in the following, the vane is flexible and the upper wall seals it and the presenter says it creates negative pressure right at the part pointed by the screwdriver. However, in the impeller above, the vanes are solid and not flexible, so where is the negative pressure created that suck the water and how is the cavitation performance of the above?


texts: Is it possible to engineer water-walking boots?

texts:
A naive question, yes, I know, but it's something that has plagued me for a long time. Whether by secreting a substance, controlled vibrations, metamaterials, or powered systems, is it possible to make something that would otherwise sink, not sink, preferably to an extent where (possibly with extra wide soles) boots may allow walking on water, even if only for a short period of time?

It's a hypothetical contemplation, so anything goes, including things that react explosively or otherwise violently with water, high-tech materials, experimental tech, etc.


texts: Why does the BlueROV2 have three clcokwise and three anti-clockwise propellers?

texts: If we look at the Bill of Materials of BlueROV 2 they have written the thrusters separately as clockwise and anticlockwise. Why not use Reverse config. ESC instead of anticlockwise propellers?


texts: Why does a system with zero resultant moment turn after temporarily force-tilted?

texts:
Say a beam, 3m long from end to end, has a pivot placed at its centre of mass, at half its length i.e. 1.5m. Objects with weight 200N each are placed on both ends of the beam. The system is in equilibrium and thus no turning effect.
Now a force of 30N is applied on one of the ends until the beam turns 15deg to the horizontal. When this force is removed, the moments on both sides are balanced. But, the beam turns, until it becomes horizontal?! If resultant moment is zero, how can the object turn?
Is the moment really not zero, or is there some potential energy transferred to the beam which converts when the force is released?


texts: Reinforced Concrete Columns - Interaction Diagram Question

texts:
I'm confused about some concepts concerning interaction diagrams for reinforced concrete columns. Hopefully somebody will be able to answer these:

Point with zero tensile strain, but before uniform compression (no moment)

In the calculation for this point, I see that the distance $c$ (distance to neutral axis from extreme fiber) is assumed to be the height of the cross section. I understand that the strains are all compressive which means that no tensile zone will exist below the neutral axis, but why wouldn't it be assumed that $c = d$ (distance from extreme fiber to last layer of steel). Since the analysis of columns with axial + moment is essentially an extension of beam analysis, why would the concept of effective depth not be used? In other words, I think the strain distribution for this point should act from the extreme fiber to the last layer of steel.

Stresses in the steel layers are computed based on

a) An assumed value for $c$ (for the zero tensile strain point with moment)

or

b) A calculated value for $c$ (for the balanced point and below)

Based on this value of $c$ when the stress in the steel layers is computed it can come out to be less than, equal to, or greater than the yield stress for the corresponding reinforcement. I don't understand how this can happen. In beam design a strain distribution is assumed (under, over, or balanced), and forces are computed based on the stress in the steel. The assumption you make determines whether you initially know the stress in the steel or if it has to be computed. Either way since the steel is assumed to be elastic-perfectly plastic, the stress in the steel is never going to be greater than the yield stress. Based on this concept, how can the stress in the steel come out to be greater than the yield stress when forming the interaction diagram. From what I can tell if the stress in the steel comes out to be greater than the yield stress, the stress in the steel is set equal to the yield stress for the purpose of computing forces. Can someone explain this iterative process for computing the steel stresses?


texts: How to make a stepper motor retract on power loss with arduino?

texts:
I am trying to make a stepper motor rotate a poster down (like a motorized projected screen) upon the Arduino receiving power, when the Arduino loses power for it to retract. The reasoning behind this is to connect it to a smart plug, so I can activate it via my google home. This is my first Arduino project, so I apologize if it seems really basic. I was thinking that I could use a capacitor or something to charge on power on which could be discharged on power loss by powering the motor, but I'm unsure how/where to connect a capacitor to the Arduino board.
For reference what I will be using:

Arduino Uno board with AC power adapter plugged into smart plug
CNC shield
Driver
Nema 14 Stepper motor

If there is a better solution or something else I could use (I saw in someone's projector screen project that they used a potentiometer) I'd love to hear about it.


texts:
I have the following problem
E= 210 MPa
d = 40 mm
n = 20
y = 1.5
a =1
calculate the maximum allowed load for the system
I am confused on how to solve the problem, I really need advice.


texts: What's the difference between annealing, curing and sintering?

texts: All these processes sound like structural change caused by heating.


texts: Physical Significance of Max Shear Stress in a Rod in Compression

texts:
For a rod in compression, the max shear stress at a point is $\pm\sigma_x/2$, i.e. half the compressive stress applied at either end.

This value is obtained using the equation for $\sigma_\theta$, the longitudinal stress at any point in a material if it is subjected to a set of stresses (equivalently represented by normal and shear stresses), then rotated through an angle $\theta$, while these same stresses remain in place.

So, does this max shear stress in a rod in compression refer to when the rod is rotated by 45 degrees such that it experiences max shear stress under the same compressive load? Or is this a value that the rod experiences at all times as a result of weaknesses in the material along different axes? Because at an angle of 0 degrees, there wouldn't be any shear stress in a perfectly homogeneous rod under compression, would there?


texts: Can you perceive similar kind of "humanizing" of technology in other fields of engineering than computer science?

texts:
So I've noticed that computer science has actually been developed so that it has become more human and less technological in the sense that development has raised the abstraction level up to a "more human" level. A modern computer scientist is able to think about computing in very "humanly" ways, rather than as merely machine-like ways. That's because programming languages have become to be able to express concepts more naturally, rather than as some sort of memory address manipulation.

Is a similar kind of phenomenon observable in some other fields of engineering?


texts:
I have the following parameters in my project.

enter link description here

I submitted a paper. Now, one of the Reviewer's comments is as follows:

Validation is not enough and convincing. The CFD results should compared with static and dynamic torque and efficiency performance with LES simulations available in the literature and or experimental measurements.

What is the exact meaning of "static and dynamic torque"?
I am grateful that give me useful links and papers in this case.

My used turbulence model in my project is K-W SST(RANS simulation). Also, there are not any LES simulation available in this my field. My work is a 3D turbine.

Thanks.


texts: Maximum compressive force for pipe vs solid cylinder

texts: If I have a pipe with external radius R and internal radius r. Maximum compressive force will be given by the same formula Fmax=σS as for cylinder or different? where $S = πR^{2}-πr^{2}$, and σ is compressive strength of material. In other words, if I have some shape with the same mass per meter length as cylinder, maximum compressive force will be the same or different? For example, if I have solid cylinder from steel with 10 cm radius, area will be 314 square cm, and if I have pipe from the same steel with external radius 20 cm and internal radius 17.32 cm, area and mass per meter length will be the same as cylinder 10 cm radius. What can handle more compressive force pipe or cylinder or it will be the same? If it is different, maybe someone can give me useful links and formulas?


texts: How to calculate and common capacity factors for gas power plants

texts:
I am wondering the following, and didn't find anything online or here in the forum:

1) How is the capacity or load factor of a gas power plant calculated: (GROSS electricity generated)/(maximum capacity x time period) or (NET electricity generated)/(maximum capacity x time period)?

2) What range is common for a gas power plant capacity factor (gas turbine, steam turbine, CCGT) when the plant is operated at a profit?


texts: How to cut a pipe such that water comes out evenly across the length?

texts:
I am trying to build a wetland filter for a pond. Basically, you dig a big hole, fill it with rocks (large at bottom, small at the top), and pump water deep under these rocks, so the water slowly trickles upwards. My main problem is finding a way to make sure the water from the pond is pumped underneath the wetland filter, in an equally distributed amount. I can't have the water pouring underneath in one or two spots, it should be equally distributed.
                                                                   X
                                                                 x |  X <-- flowers
                                                                  `()/
                                            |~~~~~~~~~~~~~~~~~~~~~~||~~~~~~~~~~~~~~~~~|
|~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~| |................(wetland filter).........|
|                   (pond)                | |ooooooooooooooooooooooooooooooooooooooooo|
|                                         | |                                         |
|     <-|-|-|-<                           | |                                         |
|_________________________________________| |_________________________________________|

A big pump is dropped in the pond, and a pipe leads it underground under the wetland filter. Its basically a space with big rocks, with water in between.
  ___    water flow--->              hole
 [   ]_________                       |
 [   ]_________\                      V
 [   ]         \\______o____o____o____o____o___o____o____o___o___o___
/     \         \____________________________________________________] <--cap on end
    ^                          ^
    |                          |
   pump                      2" diameter PVC pipe

I need to get the water dispersed evenly underneath the wetland filter area. Some other people recommended using PVC pipe, and simply drilling holes in it. The water should go out through the holes. But those suggesting had a 5 ft wide wetland filter, mine is 150 ft long, so I don't know if that solution scales.
My concern, because I have a larger-than-typical design, with the pipe being almost 150 feet long to reach all of the bog, how do I insure the water is evenly distributed to each of the holes?
Will the water pressure equalize and cause the same amount of water to go out of each hole? Does that require carefully making sure the total accumulated size of all of the holes equals the flow rate?
Do I need to make the holes incrementally get bigger towards the end of the pipe? If so, how do I scale the holes along the distance?


texts: Free falling fluid pressure distribution

texts:
Consider a free falling tank of fluid. The goal is to find the pressure distribution.

My intuition says that there should be no pressure distribution; the pressure should be uniform since the container is also accelerating at the same rate and direction as gravity, so there is no upward reacting force on the fluid to create a hydrostatic pressure distribution. This is also previously supported by others: https://physics.stackexchange.com/questions/4619/water-pressure-in-free-fall

Previous questions and answers, however, are entirely handwavy and also based on intuition. How can we prove this mathematically?

I start with Euler's equation in the downward direction of acceleration, let's say the $z$ direction:

$\rho a_z = -\frac{\partial P}{\partial z} - \rho g$

and the fluid is accelerating downward with acceleration $a_z = -g$.

Substituting into Euler's equation yields

$ \frac{\partial P}{\partial z} = 0$

thus proving that the pressure in a free-falling fluid is uniform.

Is this correct? Can I apply $a_z = -g$ in the fluid equation of motion even though gravity is already accounted for?


texts: equivalent full hours of heating equipment

texts:
I would like to know if there is a standard way of calculating the equivalent to a capacity factor but for heating equipment. That is the ratio between the amount of heat delivered during one year divided by the amount of heat that could be delivered by the equipment (capacity x time in a year). Or otherwise, the equivalent full load heating hours divided by the number of hours of the year.

I thought of an approximation, dividing the average annual heating degree days by the maximum annual heating degree days of the city where the building is situated.  I would like to compare it with other ways of estimating the same factor.


texts: Explaination for a stepwise load displacement curve

texts:
An experimental study to compare the stability of different plate systems made of titanium to fix fractures of the lower jaw (mandible) made of resin material.

The load displacement curve I have obtained was step wise both in the elastic region and in the post yield region. Is a step wise load displacement curve normal? How can it be explained, are there similar cases, and what is the references?

 explained


texts: How is heat transfer calculated for an aqueous salt solution?

texts: I am familiar with using $\dot{Q}=c_p\cdot\dot{m}\cdot\Delta T$ to calculate the heat transfer rate of a fluid given a singular value for specific heat capacity (such as with water), but how do I go about calculating heat transfer rate for an aequeous solution such as $MgCl_2 (aq)$? Do I somehow use the heat capacities of both water and salt together?


texts: how do i keep static deflection in a spring at a minimum upon applying gravity in a mass spring system without altering the response?

texts:
i modelled a simple mass spring damper system (with a vertical orientation) with base excitation in solidworks. After applying all necessary parameters, i plotted responses with and without gravity applied. I noticed that the steady state responses were equal but the positions were different which is in line with theory. In the response with gravity applied, the bodies overlapped which is undesirable. How can i prevent the bodies from overlapping while maintaining the same response?
Is the different positioning due to the static deflection of the springs? if so, when i increase the value of "k" the response changes. Or am i also to increase the damping coefficient? How does it work? i need some clarification please
Thanks in advance
added pics for reference

no gravity

with gravity


texts: My output is much lower than I expect it to be for my transistor-zener diode voltage regulator

texts: I have created this simulation ( see below) of a transistor and zener diode voltage regulator. The output is supposed to be a steady 5 V. But it is like the top bit s cut, to an approx 4.4 V value, then it plunges to the minimum voltage value. I really dont understand why and how to fix it


texts: What temperature required to alloy copper and aluminum?

texts:
According to this phase diagram, the melting point of 30% copper aluminum bronze is around 548°C.
Lets say I create molten aluminum at 680°C, can I add small pellets of copper and swirl them around to create a molten alloy? or will the alloying process not start until Copper's melting temp has been reached at around 1080°C?


texts: Is there a way rotate a wheel in a single direction but have opposing motions every 180 degrees?

texts:
In order to give you a good idea of what I want to accomplish suppose you have a telescope mounted on a single rod extruding from the ground. The telescope is free to move such that you can tilt it to point at a particular altitude but can never point towards the ground. In order to move the telescope you have a wheel which can only be rotated in a single direction (say clockwise). Is there a gear configuration that would make a point alternate rotations every 180 degrees? and also have it configured such that the power loss is consistent throughout the entire cycle so that no half a cycle takes more power than the other?

Here is an illustration


texts: How are circular portholes mapped onto cylindrical hulls?

texts:
When portholes are put into a cylindrical hull, such as of a submarine or an airplane fuselage, is the glass window curved to match the curvature of the cylinder?

And if so, is the porthole wrapped around the cylinder so that orthographically it would appear wider than it is tall, but it retains the area of a circle,

OR

is the porthole projected onto the side of the cylinder, so that it looks like a circle when viewed orthographically.


texts: Is there a relation between porosity and PPI density in porous media?

texts:
I've seen two methods to describe porosity of porous media (specifically metal foams):

Porosity $\epsilon$ which is a ratio between volume of voids and total volume of the medium.
PPI (Pores Per Inch) which is the number of pores in one linear inch.

Unfortunately while reading some papers about the relationship between volumetric heat transfer coefficient and porosity in metal foams, some authors describe the range of porosity they used with $\epsilon$ while the others use PPI density, so is there any relation to connect both terms?

There is a similar question on cfd-online and someone answered with this formula but I am not sure where it came from or if it's even correct:

$$\text{Pore density (ppcm)}=\frac{300}{D_{particle}}\sqrt{\frac{(1-\epsilon)^2}{\pi\epsilon}}$$


texts:
What kind of automatic transmission would be the best to connect an electric engine with the rear axle of a RWD car?

Specifications:

200HP, 3000rpm electric motor
top speed 220km/h

The automatic transmission should have higher output RPM and be able to bring the car to top speed of 200km/h.


texts: Controlling the temperature with high precision

texts:
I need to control the temperature with high precision, and for this task would be good a temperature controller with pt-100 sensor, something like this one PID Temperature Controller ITC-100. As I see that, it can be very simple: there is an input (pt100 sensor), an output - to the heater element (my heating element needs 12V supply). However, I still have some things which are unclear for me:

Is it generally supposed that there is a power source for the heater
element which I also put in the circuit or usually the temperature
controller gives the voltage at the output ? Or is that voltages
supposed for the external SSR, not my heater?
In many sources I have seen circuits with external SSR. However,
such temperature controllers already have internal relay. Should it
be possible without any problem just wire output to my heater
(because in all schemes output goes to the external relays)?
Wires soldered to the pt sensor shouldn't influence much to the
measurement, right?


texts: Are light coloured roofs more durable? If so, why aren't they more common?

texts:
If I run Google search for "roof" the pictures are typically of medium or dark gray, medium or dark green, medium or dark brown, brick red and other not very light colors - very rare are clay or sand coloured or similar colours roofs.

Neat image from Wikipedia:

Roofing materials nowadays are typically engineered (plastic coated steel, etc), not natural materials such as straw, and can have whatever color you please.

It looks like light coloured roofs absorb much less sunlight and so heat up notably less and this should prolong their lifetime. In my experience the key reason of dark ruberoid degradation is evaporation of resin because of sun radiation - it loses elasticity, basically turns into cardboard and then inevitably tears into pieces. I assume similar degradation processes happen in all materials that are either coated in plastic or rely on elastic resin for their properties.

Why are lighter coloured roofs not more popular? Is there any engineering reasoning behind this, or is it simply a design aesthetics choice? Does a light color roof provide any significant benefit from durability standpoint?


texts: incompressible fluid approximation and fluid vs sound velocity

texts:
consider the following case:
A straight tube, with a constant mass flow rate of water $\dot m_{in}=\dot m_{out}$ , and with a linear power entering in it $\dot Q [\frac W m]$. And the water is the liquid phase in all the tube.

My professor told us that in this case the incompressible fluid is a good approximation if the velocity of the water is much less than the velocity of the sound. Can you explain me why this should be a good criteria?
In particular what confuses me is that the density should change depending on the temperature region.


texts: Solidworks freezes when creating an angle mate

texts: When I try to create an angle mate in an assembly by pressing shift and choosing the angle option in the menu that appears, a green and white mouse appears next to the arrow and I cannot access any other options or set the angle. What key should be pressed to set the angle?


texts: Latent heat of fusion of water near triple point

texts:
When a thermally isolated vessel of liquid water is depressurized to vacuum, part of water will evaporate, remainder will freeze - total heat being split between latent heat of ice and enthalpy of vaporization. I wanted to calculate the proportions - how much will evaporate, and how much will freeze.

The problem is the values of latent heat and enthalpy of vaporization wander quite a bit with pressure, and they are quite hard to find for anything else than 1 bar. I managed to obtain the value for steam (2501KJ/kg), but I'm still not successful with ice - there is a multitude of tables and documents that list a variety of materials at 1 bar, so if there is one that follows the pressure, I was unable to find it.

So - what would be the latent heat of fusion of water at about 612 Pa?


texts: System curve for use in determining pump operating point

texts: What is meant by a "system curve" that is used to determine the operating point of a pump. I know what a "pump curve" is, but I often hear about a "system curve" being generated so that the pump operating point can be determined by where the pump curve and system curve intersect.


texts:
Why Heat Exchangers are preferred to work in Constant Pressure Process than Constant Volume Process?

Mostly, all problems are solved in Constant Pressure Process


texts: How can we model a full depth reclamation (FDR) layer with emulsion (wet FDR layer) in a pavement design?

texts: So far, I have only been able to model dry layers as I've only been able to represent the FDR layer with one modulus value.


texts: determine if the flow is laminar or turbulent

texts: what would be the the type of flow if the water flows through stainless steel channel? would it be a laminar flow or turbulent flow. I assume the adhesive force of water to stainless steel is minimum.


texts: How is the simplest Ampere's law formula for cylindrical surfaces?

texts:
Current would only flow through the cylinder walls, not inside the cylinder. The cylinder is hollow.
I need the formula in order to calculate the magnetic field produced and see if it's lower than the critical magnetic field strenght of a material.


texts:
So I want to tap a super small hole on grade 5 titanium alloy with M1.8x0.2 (which should be possible according to this Quora's answer. But is there any tap available for me to do this job? I mean M1.8 with grade 5 titanium, the normal tap should break very easily. Since it's a super small hole with super tough material.

Also, can it be done by normal CNC, like the one you'll find in a normal company? Since the document looks like some scientific research which might be using some advanced machines. And can it be done on CNC engraving and milling machine or it needs a CNC lathe?

Last, why you should tap titanium with CNC but not by hand?


texts: Is there a valve design or system that can do this?

texts:
I am trying to come up with a way to bleed air from a tube to avoid air (gas) from reaching the other end of the tube. Is there a way to do this automatically? It must be able to work in all orientations and it shouldn't leak any fluid when it is shaken or turned upside down. I've thought about trapping air by raising a section of the tube before it reaches the end, sort of like what's pictured here:

However, this can only last so long until it becomes an air lock and fluid stops flowing, and I didn't think that it could work when it is upside down. Is there a way I could use this concept but continuously remove the gas out of the tube?
A design that could differentiate gas and liquid in a tube and can make them flow in different pathways would be the best solution (if this even exists).
I would appreciate any ideas and concepts that could be used to come up with a design. Thank you in advance!


texts: How to construct rcc column footing on rock?

texts: I am constructing my house on a rocky plot. Some of the columns will be placed over rocks and we were not able to dig deep in the rock. So, these column footings will be on the surface. Is it safe?


texts: How to find the 'reaction speed' required in a valve for a certain application

texts:
I know this is answerable but I'm not sure I know where to start:
You have a pump (constant volume flow) supplying the primary side of a heat exchanger with hot water (flow). The temperature of the flow is adjusted by mixing in cold return with a three way mixer (valve). The temperature of the medium on the secondary side out of the HX $t_{so}$ is measured, as is the flow temperature (primary side in) $t_{pi}$. The goal is a specific value $T_{so}$ for $t_{so}$ (lowercase letters: actual measurements, uppercase letters: setpoints).
I see two principal control strategies (and within each the question if one uses PID controls or simpler schemes):

control valve directly for $t_{s}$
control valve for a given $T_{f}$, if $t_{s} > T_{s}$ for a given length of time, adjust $T_{f}$ downwards and vice versa

My question is: If there's a sudden jumps in temperature or flow on the inlet of the secondary side - say 10K in 5 seconds, or flow drops to 75% within 2 s,  and I have a certain parameters - say $t_s$ must never be higher then $T_s + 5K$ or $t_s = T_s +_- 0.5 K$ 60 s after the disturbance is registered, how do I know how fast acting the three way mixer must be (from 0-100% in 120s?)? The numbers are of course just indicative.
Analytically, the required $t_{pi}$, can be calculated iterativly using the following ($\dot m$ mass flows on primary and secondary sides, $c$ respective heat capacities):
$$ t_{pi}=t_{po} - \frac{\dot m_s c_s}{\dot m_p c_p} * (t_{so} - t_{si})$$
NMech provided a closed form:
$$ T_{p,i} = T_{s,o} - \frac{
 Q }{A k} ProductLog[-\frac{A k(T_{p,o}-T_{s,i}) e^{-\frac{A k }{Q}(T_{p,o}-T_{s,i})  } }{Q}]$$
Where:

$ProductLog[x]$ is the Lambert W function.


texts: How do I measure the time taken for a laser to cut a metal?

texts: I am a placement student and was given a project asking to measure the time taken for the laser to cut a metal and send it to Excel into a spreadsheet automatically. I am a computer science student and am unaware of how I should begin this project or how to do it. How do I measure the time taken for the laser to cut each metal?


texts: Detachable tubing connections (joints) for frame assembly

texts:
I am looking into fabricating a steel tubing frame that needs to be dis/assembled (applies to many larger furniture like bed, shelving unit, wardrobe, cupboard, cabinet, ...).
What are the variants of the steel equivalent of a butt-joint and their pros/cons?
I have only found information on joints for construction steel (think skyscraper-sized double-T section) so far.
I have not found anything for closed sections in DIY sizes like 20/30/40 mm or 1 inch (easily available in hardware stores).
I am certain there must be something in literature. I might not be searching with the right terms.
Ideally, the connectors would be "invisible", i.e. hidden inside the tubing (square or rectangular).
I am considering welding a bolt to one part and a cap onto the other - one hole for the bolt, and another to enable tightening a nut inside the tubing:

Drawbacks: only one fastener, bolts may be too small, assembly of the nut very "fiddly".
Pros: does not weaken tubing (depending on load/bending moment).
Another option:

Drawbacks: profile not tensioned, "snug" fit depends on availability and tolerances of tubing.
I'm also interested in connector-hardware made for this purpose.


texts: Unknown circuit component with glass encapsulated contacts

texts: This is an unsoldered circuit component that had two metal pieces that weren't making contact inside a thin glass tube. What is this? I haven't seen anything like it before.


texts: Relationship between thermal conductivity and reaching the steady temperature?

texts: The diagram is for three materials with different thermal conductivities. I think number 1 is the material with higher thermal conductivity because it transfers the heat faster so it gets to the steady temperature sooner than the other two. Am I right? If not or if my reasoning isn't correct, I appreciate your help.


texts: Why do I need to place car cabin filter according Air flow label

texts:
in most of car cabin filters (for example MANN filter) I see that I need to place it according the "Air flow" label?
But why I need to do that?
What will be wrong if I will put it in opposite side of "Air flow" label?


texts: Absolute Digital Encoder Speed measurement

texts:
I am using a 16-bit absolute magnetic encoder and I get the position from SSI 3 wire, I mean digital outputs for my position control application. I have a problem with getting accurate speed data. I am trying to get speed data from position derivation with a digital filter but nevertheless, my speed data is not accurate and there is too much noise, hence I am not controlling the motor as well.
I have checked some articles and forums but I couldn't find anything about speed measurement with digital outputs. There are a few methods like the T method and the M method but they are using for pulse outputs. Is there any method for estimating or calculating the speed for absolute digital outputs encoders for low-speed applications?
Thank you!


texts: Solidworks gear representation in drawing

texts:
I have an assembly in Solidworks with gears that I want to make a sketch from it.
I want to hide the gears teeth and represent the each gear teeth only as center line, like in the picture below on the left:

I have tried every button in Solidworks, but didn't find how to hide the unnecessary tooth at the end.

Thanks for any help.


texts: What is the longest lasting modern building material?

texts:
Historically the longest lasting building materials seem to be stone. But I was wondering what material modern technology can create that would last longer under various conditions.

The various things the material would need to be tolerant to would include extreme heat, cold, water, wind, plants, animals, sunlight, earthquakes, as well as a determined effort by people to deface, damage or destroy.

I had considered steel blocks with a coating of an alloy or metal that would not react to air or water, or maybe an advanced form of composite glass or plastic such as bullet and bomb resistant glass that would be multiple feet thick and reinforced with metal as well.

I was planning to ask this question in an architecture stack, but all I could find was home improvement and I thought engineering may have more people versed about materials science than do it yourselfers.

So, if a modern team was going to build a pyramid and wanted it to last much longer than those of Egypt what materials would likely be used?


texts: Why were engineers negligent in the 1981 Hyatt Regency walkway collapse?

texts:
I was recently reading up on the 1981 Hyatt Regency walkway collapse.  It was a tragic loss of life and haunts many to this day.

The linked article does a better job of summarizing things, but here's a summarized version of what led up to the collapse:

The engineering firm (Gillum & Associates) designed the walkways to be supported on really long, threaded rods.  The company supplying the rods (Havens Steel) didn't like the specified rods because they were going to be expensive and likely to be damaged during construction.  Havens Steel sent an alternate design to Gillum & Associates which was used for the construction.

The alternate design didn't meet code, catastrophically failed, and led to the loss of many lives.

The Missouri Board of Architects, Professional Engineers, and Land Surveyors found Gillum & Associates guilty of negligence and revoked all of the engineering licenses assigned to Gillum & Associates and its employees.

What I'd like to understand better is why Gillum & Associates was held liable for the disaster.  Wasn't it really Havens Steel's fault for proposing the alternate design to begin with?  If Havens Steel had built according to the original design proposed by Gillum & Associates, then the disaster never would have occurred.


texts: construction joint in shear wall passing through vertical bar splices

texts: Usually in cores and shear walls, one extends vertical bars above the construction joint a distance at least equal to the lap splice length to allow for splices away from the construction joint. But is there a problem if the splice does occur at the construction joint (such that part of the splice is below and part is above the joint)?


texts: Purpose and name of fine pitch marks on a cast metal part

texts:
I have seen this kind of mark on various cast metal parts. This is an image of the base casting of a hard disk drive made by HGST.

What are these marks for?
What are they called?


texts: Force applied by fan under inviscid & incompressible flow

texts:
I have a wind tunnel (subsonic flow of air) which consists of a fan inside (and ahead of) a long cylinder of cross-sectional area of $A_e$, followed by a diffuser of $A_o$ c.s. area ($A_o>A_e$).

The fan maintains a velocity of $V_e$ inside the tunnel.
Assuming the flow inviscid and incompressible, I want to find the amount of force per unit area that the fan applies.

I chose the entire inside of the tunnel (fan included) as the fixed, non-deforming control volume.

Applying Conservation of Momentum for the c.v. (gage pressure used):

$$F=\rho(V_o^2A_o-V_i^2A_e)=\rho V_e^2A_e(A_e/A_o)$$

The volume integral was dropped since the flow is steady.

The last transition was done with the help of Conservation of Mass which yields:

$$A_eV_e=A_oV_o$$

The correct answer should be $(\rho/2)V_e^2A_e(A_e/A_o)^2$ and in the available solutions to me, Bernoulli was used on the stream line that begins after the fan and ends outside the tunnel at atm' pressure, and Momentum Conservation was applied to a control volume enclosing the fan alone.


texts: Lift and drag force measurement in a flume

texts:
I'm trying a test a hydrofoil in a low Reynolds flume, but struggling to find a way to mount the hydrofoil in the flume and measure the lift and drag force.

I have some idea of using a load cell but not sure how to set it up and connect it with to hydrofoil, as the hydrofoil span across the width of the flume.


texts: Why don't flight recorders transmit only when they receive a ping?

texts: I was surprised that flight recorders only have enough battery to send out signals for 30 days. I'm guessing that it blindly sends out signals that help it to be located. But instead, why aren't they made to only send out a signal when they receive a ping? Surely, then, they could last for years?


texts: connectedness between the output voltage and input voltage

texts:
Given this circuit

I want to deduce the relationship between the output voltage $U_A(t)$ an d the input voltage $U_E(t)$ using Kirchhoff's current law. We're allowed to assume that $R$, $L $and $C_1$ and $C_2$ are given to us.

My solution so far:
$$ U_E = U_R + U_{C1} $$
$$ U_{C1}=U_L+U_{C2} $$
$$U_A = U_{C2} $$
$$ \rightarrow  U_E = U_R+U_L+U_A$$
At point $K$, i want to use Kirchhoff's current law:
$$I_R=I_{C1}+ I_L= I_{C1}+ I_{C2} $$
Is my last step correct? How to continue?


texts: Why is the color gamut of an RGB monitor triangle-shaped?

texts:
Relative to the CIE chromaticity diagram, it is usually said that rgb monitors can't actually reproduce the entirety of colors in that diagram. The best they can do is cover a triangular region inside the "horseshoe".

On the subject I read this:

"An additive colour space defined by three primary colors has a chromaticity gamut that is a color triangle, when the amounts of the primaries are constrained to be nonnegative."

My question is: why is that the amounts of the primaries being constrained to be nonnegative leads to a triangle? Is the triangle a projection of a slanted slice in another color space? (I'm rusty on my math, just trying to understand this point).


texts: This is a gear that transfers force from a motorcycle kickstarter to the transmission. What method should I use to repair the missing teeth.


texts: Engine Combustion Cylinder Wall Thickness

texts:
Been referencing this website for some time but now need to seek specific help.  I am not an engineering student but rather a DIY hack who loves engineering and machining neither of which I am particularly good at yet!! :(

I am currently looking at a project to design an aluminium cylinder head for an engine.  The engine block is an existing cast iron one with a 92mm cylinder bore.  The strength of the block is not in question.

I am specifically trying to understand how to calculate the thickness of the aluminium combustion chamber walls in order to minimise deflection (else the head gasket will fail) and to ensure sufficient strength so as not to fail.  To simplify lets assume the cylinder head is a flat plate sitting on top of the block.  It is bolted down with a bolt spacing of 95mm across the block and 102mm along the length (not sure if this is relevant or not).  I realise that a real cylinder head will have braces and other features that will provide strength but that is too complicated and this simple model will give me a starting point.

The pressure within the combustion chamber is expected to get as high as 1500psi (race engine) at which point lets say the volume of the combustion chamber will be 90 cubic centimeters (the piston will already be travelling back down the cylinder).

I have tried to use the formula I found on this site below;

S = PD / (2 x Tw)

or

Tw = PD / (2 x S)

Wikipidea shows the yield strength of aluminium (6061) to be 35,000psi so lets be safe and use 25,000psi as a working strength.  The formula becomes;

Tw = (1500 x 3.622) / (2 x 25000)
Tw = 0.10866in or 2.76mm

Firstly, I am not sure I have the thickness correct in terms of being strong enough not to fail as it seems very thin.  Secondly, this does not take into account the bending of the head.  I really do not know how to calculate for that.  I would say 0.001 - 0.002" for deflection is the max.

I want to research and learn for myself but this one has beaten me.  Any help would be hugely appreciated.

* UPDATE - EDIT *
Not sure the best way to address concerns in the answers so shall do it here.

Not sure what in-cylinder temperatures will be but understand that it should be included.
I didn't make it clear as to which thickness I am looking at.  The cylinder walls are cast iron and are from an existing engine so I do not have any concerns about their ability to withstand the forces.  I am only concerned about the aluminium plate on the top.
What I am designing will be almost a flat plate on top of the cylinder block so this calculation should provide indicative results.
I agree that 356 is a common alloy for engine use.  6061 is almost identical and available to me here in Australia.  Maybe I need to use something like SimScale to analyse stresses.


texts: Can we use a gas cylinder made of A6061, meant to carry air up to 300 bar, with Hydrogen up to the same pressure? If not, what is the maximum pressure that one can safely use hydrogen with?


texts: Can I connect a power supply main (SPH) and inverter main (SPH) with common neutral to a TP MCB?

texts:
I have limited knowledge of MCBs and just doing research to secure my kitchen.
I want to connect my power supply main and inverter main with common neutral to a TP MCB. This MCB will be placed in the kitchen. The idea is to isolate the kitchen from power supply and inverter with a single MCB in case something goes wrong or manual action. Can I do this with a TP or I need two MCBs to achieve the result.
My expectation:

MCB in question: https://www.havells.com/en/consumer/switchgear/circuit-breaker/miniature-circuit-breaker/mcb-tp-c-curve-(1).html
Thanks in Advance
More information added:
My connection at the moment shares the neutral and unfortunately it can't be changed easily. That is why I am looking at TP MCB so that I can isolate the Kitchen completely.
I did some research and looks like everyone is saying TP is used only where the power supply is 3 phase line. But in my opinion the MCB is 3 pole (not phase) and should trip whenever there is a problem in any pole. I have checked DP MCB and the symbol for the connection is same. It is just one extra pole in TP MCB. My understanding is, if we can connect live and neutral in DP MCB then why we can't add one more pole and achieve the same result with TP MCB.

Please suggest!


texts: Finding all members using method of joints

texts:
Well, I'm having a hard time finding the forces through summation of moments in figure 4.14, the problem is, there's 3 hinges, which means there's 4 unknown forces. It's kinda hard to find the forces.

I tried researching about it but I can't find anything similar to this one.
Do you have any advice or do you know the right process to do so?

I really don't need the specific answer to the image below, I just want to know how to find the 4 unknown forces.