texts:
Hi I know this is a little bit of a strange one, but I’ve got a relatively cheap shelving rack that I bought to make good use of garage space.
I have included a pic, It’s footprint is 1220mm x 610mm and it currently has the standard 9mm thick particle board shelves. Although it’s been ok so far, there’s probably about 50kg on the middle shelf now (3D Printer + Laser Cutter) and I’m starting to see it bend slightly. I’m also planning to get a rotary attachment for the Laser which will add another 10kg or so.
I want to strengthen it now so it’s not an issue long term. One idea I had was replacing the 9mm shelf with a 12mm MDF one as this is the thickest I could go while still having the shelf sit flush with the frame.
I know this will be significantly more rigid, but it will probably still sag over time and does not address the issue of the frame itself potentially bending as the shelves just sit into it. To counter this my plan was to have two sections of 2020 aluminium extrusion spanning the full width which would be positioned under the board about 1/3 in from the front and rear of the rack to evenly distribute the load. I would bolt these extrusions to the frame by tapping the ends. I would also add a couple of short extrusion lengths perpendicular to the long ones to tie them together  for added stiffness.
Here comes the question: I want to use 2020 extrusion because is pretty cheap and easily available in the lengths I need. I believe I will provide plenty of strength/rigidity but my Dad doesn’t think it’ll make that much difference, and instead recommends 3030 extrusion. The problem is 3030 is much harder to get here and way more $$$.
How well would my 2020 solution work? Who is right?


texts: How to fairly distribute items when there is more demand than supply?

texts:
I have these 2 problems to solve (on the image).

I have 9 stores that want different quantities of a product. The first store asked for 62 units, the second one 10 units, etc etc.

The supplier sent a total of 138 units (case 1). I have to distribute those 138 units to all the stores in a fair way. Each box sent from the supplier has 2 units and it's better to use multiples of 2 units for each store, so that it's not necessary to dismantle the box. If it's not possible, we can dismantle the box but just in the last case.

In case 2, there are some stores who will get less than what they asked. That's ok. I just need to distribute them in a fair way so one store doesn't get everything and the others nothing.

I have a way to do this but it's really complex and full of errors so I'm trying to find an easier way like a formula or something.

What I'm doing is (I'm going to give an example for the first line and Case2):

Giving a box to every store so there is no risk to have one store receiving nothing.
Calculate: NecessityByPriority = Necessity-1box = 62-2 = 60
Calculate: PriorityEachStore: 60/sum(NecessityByPriority) =  60/72 = 83,3333%
Calculate: PriorityUnits = PriorityEachStore*(Stock-9box) = 83,3333%*(58-18) = 33,3333 [the 9box corresponde to the number of units given in the first step: 9stores*2units each]
Calculate: NumberBoxes = round(PriorityUnits/(Unit/box)) = round(33,3333/2) = 17
Calculate: NumberUnits = NumberBoxes*(Unit/box) = 17*2 = 34
Calculate the final quantity: NumberUnits+1box[given in step 1] = 34+2 = 36

In the case given there is not a great error but I am going to show you one with error above in a simulator I have done in Excel:

Here there were 3 units that remained. This is due to rounding. I can add a line to verify if there is something remaining and if so to redistribute. But I was looking for an easier way without all this formulas.

I have another process that calculates with the same formulas, everything for the first store. Then makes a 2nd iteration and recalculates everything except the first store. And on on until there is no more store. The problem is that here there is only 9 stores but sometimes there are hundreds.


texts: How effectively would a typical liquid CPU cooler cool a 15"x15"x1/8" sheet of aluminum?

texts:
I'm curious about whether a typical liquid CPU cooler (like, e.g., this Corsair H60) would be able to effectively cool a square sheet of aluminum with 15" sides and a thickness of 1/8".

I'm not even sure how to properly formulate the question so I'll describe the envisioned application. I'd attach the cooling plate to the bottom of the aluminum sheet and build a case for it with a cut-out for the fan. The result would (hopefully) be a refrigerated cooling pad for my constantly overheating laptop.

Is such an idea feasible? How powerful of a cooler would be needed to effectively chill such a sheet of aluminum?

Assume an ambient room temperature of 70 degrees Fahrenheit and that the bottom of the laptop is roughly 160 degrees Fahrenheit. I'd like to reduce the temperature of the bottom of the laptop to 120 degrees Fahrenheit. The bottom of the laptop is aluminum and about 15"x15". There is a gap between the aluminum sheet and the laptop bottom of about 1/8".


texts: I am new to abaqus and for my final year project I'm meant to simulate a force on a cylinder (testing displacement of articular cartilage) ranging from 1-15 Hz and between 15-36 Newtons but I don't know how to do it. I have all the necessary material parameters I just don't know how to apply the loading. Any help, guides or tutorials would be appreciated. Thanks.


texts: Bored Pile construction Procedures When having Water in the ground

texts:
I know the normal process of how bored piles are normally constructed, but I need to know in case we have a water table at 1.5 m under the surface level and the pile must be at a depth of 25 m. How do they prevent the water from filling into the bored pit. Because when they pour concrete they must remove the water from the drilled pit but if the water keep filling the pit and at very deep depth how could they prevent this ?

One more question I was thinking about is How much does the strength of the concrete get affected in a pile (due to the presence of water and some unwanted soil in it) ?


texts:
**Background **

I'm struggling finding how to calculate the pressure that occurs within my system and then once calculated I need to reduce that pressure.

My system

I have a 1 inch copper pipe that is 9 inches long.  Inside that pipe I have a 3/4" heating element designed for heating liquids with heat transfer oil surrounding it and threaded into the 1 inch pipe.  My desired temperature is about 450 degrees F. The system is a closed system and the fluid isn't moving so of course as I heat the oil up, pressure will increase.

Questions

Will soldered copper connections handle this pressure?  Is there a way to calculate the maximum pressure at 450 degrees F?  I believe once I know that, a pressure relief valve should help with this problem?

Thanks for the help and feel free to ask clarification questions.


texts: What is the type of hinge used in fold-down car tv's?

texts: I am trying to find out what type of hinge or mechanism is used in fold down car TV's. I need to buy one for a project I'm working on but dont know the name. See picture above.


texts: Trajectory of the center of mass of a vehicle

texts:
The problem is to find the trajectory of the center of mass of a car when it is rotating and translating (after an off center collision, for instance)
What i know as input is the trajectory of the wheels (skidd marks deposited on the surface of the road)
I also am given the geometry of the vehicle, so the distance of all four wheels to the center of mass is know, as are the Wheelbase ($WB$) and Track lenghts ($T$).
Let $y = f_i(x), i=1,..,4$ be the function describing the trajectory of the $i$th wheel, and $r_i$ be the distance of the $i$th wheel to the center of mass.
How would i go about finding a function $y = f_{CM}(x)$ that describes the trajectory of the center of mass? Assume planar motion.


texts: How do you read a blower/compressor curve with multi-curves for inlet guide vanes?

texts:
I am trying to apply an existing blower curve in a hydraulic model for a single stage blower with variable inlet diffuser vanes.  The variety of curves shown on the plot does not seem to make sense to me.  In particular, I don't know which of the blower curves I should be looking at.  The legend at the top-middle of the plot shows IGV: 10 etc. but then those same line-types are used in the plot with 12, 10, 08 etc. and no units are shown anywhere.

I looked up the ASME document referenced (PTC-10) but did not find anything in it to shed any light on how this curve was developed or how it is meant to be read.

Does anybody know how to interpret this or know of a resource that explains this style curve in detail?


texts: Is it possible to compute cutting of wood bar in Solidworks automatically?

texts:
I drew two bar parts, horizontal and vertical, then composed into single assembly. Each bar was duplicated.
The I wished to model diagonal bar and created new part just inside of an assembly. I was able to build appropriate plane and extruded the bar up to angles:

Now, how can I model cuts?


texts: Can you focus a 300W LED to a small area?

texts:
I want to focus a 300W LED into a small area, about 5mm in diameter, much like focusing the sun's rays with a fresnel lens.

I have to be like 2 meters away from the LED to focus the LED light with a fresnel lens. Why is that?

Is there a way to focus the all of the LED's light somehow onto a small area?

If it's possible, would it be akin to having a 300W laser? Mostly likely not, but why?

Thank you in advance for your answers.


texts: How do solar balloons work at high altitudes?

texts:
I am interested in the challenges that Solar Balloons face when flying.  For example, the high altitude could cause drastic changes in:

Wind speed
Temperature
Moisture

How does the unique design of a solar balloon address these challenges?


texts: Characteristic dimension for combining free and forced convection?

texts:
I have a situation that I have a combination of free and forced convection over a cylinder. Remembering back from heat transfer, to combine these I use the formula

$$Nu_{\mathrm{comb}}^n = Nu_{\mathrm{forced}}^n + Nu_{\mathrm{free}}^n$$

And that's fine. However, what dimension do I use to find $h_{\mathrm{comb}}$? Because

$$Nu_{\mathrm{forced}} = \frac{h_{\mathrm{forced}} k}{D}$$

while

$$Nu_{\mathrm{free}} = \frac{h_{\mathrm{free}} k}{L}$$


texts: Rotation around an axis outside of the mechanism

texts:
I want to design a system of linkages that will allow me to rotate the green element around the blue point/axis without entering the red circle.
The green triangle to go fully around the blue point. I only need about 120 degrees.
I have seen examples of it being done (some provided below).
I don't want to build a robot arm :), so it has to be purely mechanical, preferably with only one rotating axis as an input.
What is this idea/mechanism/process called? I have trouble googling for it.
Is there some kind of solver that would help me find relative lengths of all the linkages, etc.?

Some examples
Elephant Compliant Mechanism
https://youtu.be/iAVV_7k79ZI?t=15
Six-bar linkage for stretch and turn
https://www.youtube.com/watch?v=q8tVdjMo22E


texts: Boundary Conditions for a circular clamped plate

texts:
I've been trying to find the boundary conditions for a fourth order DE equation for a bending circular plate. I'm assuming angular symmetry and an even pressure distribution.

Displacement Equation

$$ D \nabla^2\nabla^2w(x,y,t) + h\rho \frac{\partial^2{w}}{\partial{t}^2}(x,y,t) = P(t)$$

D: Flexural Rigidity (Constant)

h: Thickness

$\rho$: Density

P(t): Pressure (Evenly applied across diaphragm)

Conversion to Polar Coordinates

$$ \nabla^2\nabla^2w(x,y,t) = \frac{1}{r^3}\frac{\partial{w}}{\partial{r}} - \frac{1}{r^2}\frac{\partial^2{w}}{\partial{r}^2} + \frac{2}{r}\frac{\partial^3{w}}{\partial{r}^3} + \frac{\partial^4{w}}{\partial{r}^4}$$

Now I need to solve

$$D(\frac{1}{r^3}\frac{\partial{w}}{\partial{r}} - \frac{1}{r^2}\frac{\partial^2{w}}{\partial{r}^2} + \frac{2}{r}\frac{\partial^3{w}}{\partial{r}^3} + \frac{\partial^4{w}}{\partial{r}^4}) + h\rho\frac{\partial^2{w}}{\partial{t}^2}(r,t) = P(t)$$

The boundary conditions I currently have

$\frac{\partial{w}}{\partial{t}}(r=a,t) = 0$

$w(r=a,t) = 0$

$\frac{\partial{w}}{\partial{t}}(r=0,t) = 0$

My goal is to discretize it with N divisions and transform the system into State Space so that I can use P(t) as a controller as well as create a Bode Plot and look at the system's resonance frequencies. I believe that I need one additional boundary condition due to the spacial derivative being of order 4.

I also plan on using central and forward/backward finite differencing of order 4 to replace the spacial differences. Possibly order 2 because that would simplify the problem.


texts: Differential equations strange 2 DOF systems

texts:
I'm trying to find state-space representation of following 2DOF systems.

I tried classic Double pendulum equations for it but I'm confused how to handle it. now I'm looking for any help and tip to solve it.


texts: How to specify and tolerance a "sharp" point?

texts:
I need to have an electrical probe machined; but I am unsure how to specify my requirements.  I am an electrical engineer with only moderate mechanical knowledge.

The probe will be machined from 0.125" diameter stainless steel round stock. The last 0.25 inch before the point necks down to a smaller diameter - maybe 0.031" - 0.062".

My question is in how to specify the pointed end of the probe. I want it to be sharp enough to dig in a little to the circuit under test but not so sharp that the point is fragile.  Also, I don't want to specify overly-tight tolerances and push up the cost. I am assuming a Swiss screw type machine will be used.

What is "sharpness"? Is it the angle leading to the point or is it the diameter at the very end?

My initial stab at it would be something like:
"a cone with 60 degree angle sides".  But this seems to imply an infinitely small point.

Should I specify a flat end of a certain diameter? (i.e. a conical frustum instead of a cone?)


texts: How does a pulley (with friction) satisfy equilibrium?

texts:
In the picture shown :

Suppose that there is a man applying a force $F$ in order to support the box using a cord that wraps over a frictionless pulley (the system is in equilibrium and nothing is moving)

Now , if we want to draw the free body diagram for the pulley, it will look like this:

We know that $T_1=T_2$ because the pulley is frictionless, and we can check that this true using summation of moments about point A = zero (assume counterclockwise positive)
$$\begin{align}
T_2r-T_1r&=0 \\
T_2-T_1&=0 \\
\therefore T_2&=T_1
\end{align}$$

Now if the pulley is not frictionless (there is friction between the pulley and the cord), then the man must apply a greater force in order to support the box (because you are supporting the box and some of your force is dissipated due to friction) (the system here is also in equilibrium). That means that $T_1$ is greater than $T_2$, but this situation will not satisfy the equilibrium equation (summation of moments about point A =zero) because $T_1 >T_2$

What is my mistake when analyzing both situations?

This is a solved example in my statics book


texts:
Background

So I am working on a project to where I am trying to heat up air within a 2 inch tube, with high air flow.  I am using 2 inch tri clamp stainless steel tubes where I basically have a fan on one end and am trying to get an inline heater so that the result is a high flow rate and high temperature (around 400F - 500F).

What I have tried so far

I have had some decent success by buying a cheapo heat gun from Harbor Freight and taking the nickel chromium array out of it, suspending it inside a 2 inch tube. I was able to get to about 400 F but after some time (an hour or so) the element seems to burn out and die. I seem to be so close to being able to achieve this goal but was hoping there is a more reliable method to heat the air without having to replace the element that often.  I would like to stay to electric heat sources if possible and it would need to be 120V, below 15A (standard house breakers in a kitchen).

Question

So I am not asking for a particular product, but rather what electric heater types out there might work for my application?

The closest thing I could find was something like this:

(Amazon link)

This one fits inside a 2 inch tri clamp tube but seems it needs to be in a liquid, not just with air flow around it? Would this more than likely just burn up too?


texts:
I am bit confused about the curve:

We could observe from the [Pump curve] that Total Head decreases with increase in flow rate, but for [System Curve], it is opposite, i.e, Total Head increases with flow rate. Why is that so? I need a detailed explanation or a link where I could understand this curve.


texts:
This is related to my recent question
Can I weaken a coil spring consisting of spring steel?. The answer here could create an additional answer there, but I do not expect that. The difference to that question is that this is about changes in the actual spring properties, so much that there could be a fully theoretical answer with no relation to empiric coil behaviour.

What changes in the properties of a coil spring if I stretch it so much that it causes plastic deformation, and cut it to restore the length?

For example, I take a steel coil spring with a length without load of 100 mm. I extend it so much that it plastically deforms, and has a new rest length of 150 mm. Now, I cut the spring to the length of 100 mm. If it had 20 windings before, it now has about 13 windings.
It does not need to be a steel spring, if a more homogeneous material simplifies it. An answer could even use an abstract material that may or may not

What is different?
How have the spring properties changed?
The mass is reduced to 2/3, how does that change the resonance frequency? Is it influenced by other factors?


texts: Contradictory units for moments of inertia

texts:
I'm looking at a motor datasheet where the moment of inertia is specified in units of "oz in sec^2". I would think that inertia should have dimensions of mass * length^2.

I did some further Googling and found that some automatic unit conversion calculators (example) let you convert between seemingly contradictory units - the site I've linked lists both kg-m^2 to kg-m-s^2 as acceptable units for moments of inertia. What am I missing here?


texts: Designing an injection molding mold for a part with a certain parting line and ejector pin location

texts: How do you design a mold to create that part? The only way I can think of is to make the parting line horizontal to the part instead of vertical. But is there any way to design the mold so that the parting line is vertical like in the picture?


texts:
I'm building a LED ceiling lamp. The idea is to mix different tones of white to get desired tone.
It will initially have 120W LEDs and maybe more later
It will probably never run at full power but I want to be able to.

It consists of two parts. Upper part where psu and electronics are, and lower part where LEDs are.
The parts are separated by sheet metal.
The dimensions are 1020x620x150
The upper parts height is 50mm
The upper part is sealed from top (by ceiling) and from bottom (by metal sheet)
The upper part will have holes in it.

I want to make the lamp as shallow as possible and for that reason I've come up with this idea for airflow generation:

Use large fans to lower noise generation.
Turn them on their side.
To force air to move in one direction block top on one side of fans, and bottom on other side of fans (images 2, 4)

Would this kind of configuration work or will I have to use small fans at high rpm?


texts: Difference between Saturated Liquid and Saturated Steam

texts: I have a (maybe stupid) question which is making me crazy: what is the difference between a saturated steam and saturated liquid state? I mean the physical difference not the difference on a Thermodynamic diagram (such as the greater entropy of the sat steam w/r/t the sat liquid).


texts:
I ran a 60 m seismic line. Energization with hammer. 12 (10 hz vertical 5 m spaced) geophones  and 5 shots (15 m spaced). Record length 0.5 s. Thanks to a borehole near a estrata of gravelly silt man-made (0.40 m) and very soft silty clay (to 5 m) and then clay improves its consistency deeper.
My seismic traces seemed to be ok, but at office the principal wave train gives 200 m/s and first arrivals refractions are that weak that can not be easily identified. I think the principal train wave shadows them.

My question: ¿What is the meaning of a 200 m/s train wave in geophysics?


texts: Wind load vs Earthquake load and R factor

texts:
I read somewhere that if for instance for a building earthquake forces are expected to be much higher than wind loads, we can increase the R (response modification factor) value, so that we bring down the design earthquake force down to wind load level.
Why do we do this? Would increasing R value not increase the cost of rebar detailing? What is the problem if the earthquake load controlled the design here?


texts: If I need a very small heat engine, should I consider external combustion?

texts:
In internal combustion heat engines, there is no heat transfer through walls required between  the source of heat and the expanding medium. With an external combustion system, we heat the expanding medium by transferring heat through the walls of some type of enclosure such as a boiler or cylinder.  The boundary layer of a gas doesn't transfer heat very fast. But for the external combustion case, consider what happens if we build larger or smaller versions of the same engine design.

Assume a scale factor $\alpha$ times each length dimension. It would appear that the ratio of surface area divided by enclosed volume varies by $\frac{1}{\alpha}$.  Then the time required to heat a given volume of expanding medium is changed by a  factor alpha. Take $\alpha = 0.1$, then you have ten times the area heating a volume of medium.

I can picture an empty saucepan on a hot stove. Dump in a quart of water. After awhile it will  heat up.  Compare to the case of dropping a single drop of water which sizzles into steam.

Now, bear with me a moment while I picture the time required to heat the gases in an IC engine  at time of combustion as being fast, something like the width dimension divided by the speed of sound in the compressed gas.  If I take alpha as smaller and smaller, the external combustion  case (boiler) gets faster and faster.  How small do we have to get before we are heating our volume of gas through the wall at speeds comparable to the IC case? Yes, I know about choking in compressible fluid flow, but small pipes may not  be needed in our external engine design.

Question #1: If I need a very small engine, should I consider  external combustion?  Let's say I'm willing to trade  some power to mass ratio to get quiet operation.

Question #2: Should I consider ganging multiple scaled-down external combustion engines  to get the advantages like quiet operation, self-starting, etc. to get any required power?

As a background comment, note the following regarding IC engine size scales:

In their book "On Size and Life", 1983, Scientific American Books, Inc., pp. 60-65, Thomas A. McMahon and John Tyler Bonner compare commercial IC engines from the smallest to the largest.  They note that larger power users such as planes and ships use multiple cylinders per engine and multiple engines per vehicle, partly because "the requirements of cooling apparatus are relatively more expensive, both in subtracted power and added mass, the larger the engine becomes".  I believe this is because of the difficulty of cooling the cylinders having smaller and smaller surface area available per unit volume as size increases.  They note that 757,778 Webra Speedys have the same mass as one huge marine engine, yet would have about 12 times the power if you could somehow link them together. It's 3.33 hp/kg for the model airplane engine, 0.27 hp/kg for the giant diesel.


texts: How to drive a gear system to wear out fast

texts:
i am designing an experimental platform to test some 3D printed gears that i am designing. i want to test the durability and what i am looking for is a way to make them wear out fast.
i will basically put 2 or 3 gears in series and form a gear train, then run them until they "fail", i am basically cehcing the vibration emitted by each gear, and i currently do it by placing an accelerometer above the shaft supporting the gear itself (above the shaft supporting bearing to be precise)

however the gears reach a point where the vibration increases no more just after running for 15 min.

Any advice on what kind of way to install the accelerometers or other sensors?
Or if i should change my DC motor, runs at 24V at 2000RPM but heating up too fast so i have to stop every 10 15 min of run.


texts: Temperature dependent electricity consumption of HVAC System

texts: I am trying to figure out if there is a decrease in electricity consumption of a cooling unit if the ambient temperature decreases from 35°C to 20°C. More detailed, a company is planning to install an HVAC system in a production hall with huge machines. Currently, each machine is cooled by a cooling unit attached to the machine. The question, will the electricity consumption of the cooling units decrease if the temperature in the production hall decreases?


texts: Is it possible to use air entrainment for air conditioning

texts:
I have seen this video pretending to decrease by 5° the temperature inside home using an air-conditioner based on the air entrainment principle (see the video here at 1m6s).

EDIT : The video is now private but you can see a picture of the air-conditioner here

Does such an air-conditioner really work?


texts: Frame element stiffness with non-axis-aligned anisotropic area moment of inertia?

texts:
I've found equations for the $12\times12$ symmetric stiffness matrix for an element of a frame (a truss with welded joints): http://what-when-how.com/the-finite-element-method/fem-for-frames-finite-element-method-part-1/ second-to-last equation, $\textbf{k}_e=[\cdots]$.
However, that assumes the area-moment-of-inertia tensor is diagonal (i.e., that the beam can have an anisotropic section, but the anisotropy must be axis-aligned). In the general case, there's an additional $I_{yz}$ term, but it's not clear where it goes. I'm guessing it goes in the $(v, \theta_y)$ and $(w, \theta_z)$ entries scaled by $3E/2a^2$ and in the $(v,w)$s and $(w,v)$s scaled by $3E/2a^3$, but for all of those, It's not clear to me what the signs would be.


texts: Convergence problem in polymer - silicon structural analysis

texts:
I'm trying to model a capacitive force sensor with a bilayer configuration of polymer - Si on Mechanical APDL 16.2 .

I have a 0.2 mm layer of Si deposited on 0.005 mm of polyimide polymer. My goal is to find out the the length change in polyimide for an exerted force of 3 mN. For that purpose, I plot the displacement curve along x direction (origin to the edge). However, I obtain a nonlinear result.

I can't understand the origin of this nonlinearity. In my opinion, the polymer has to obey Hooke's law. What could be its reason?

Here is the model code.


texts: Can Sketchup produce drawings that are adequate to manufacture components?

texts:
I'd like to design some things with bolts, fan belts, levers, motors, etc.  So I'd add a bolt here, drill a hole there and maybe take it apart and rearrange.  I'd like to do it in 3D and found SketchUp.

Can it be used to design, create and print out dimensioned components for manufacture and assembly? I'm not knocking it, but is Sketchup anything other than a really good conceptual visualization tool?


texts: Lug bolts - fully threaded or partially threaded?

texts:
Background to the question: We have been importing lug bolts under a certain tariff heading which is under dispute :

The crux of the question is whether the lug bolt ( which we have ascertained is in fact a screw ) is deemed to be fully threaded or not. The definition of this would determine the tariff heading that would be applied. Namely a separate tariff heading for a screw that is fully threaded and a different one for a screw that is partially threaded.  The question here is because of the design of this screw, namely with a seat is it considered to be fully threaded or not?

I have attached below a picture / link of the type of lug bolt I am talking about.


texts: Why don't all gas pipe flows end up at sonic speed?

texts:
According to the 1D models of compressible fluid flow, the effects of pipe wall friction and the effects of heat addition from the environment both drive a flow toward Mach 1 (i.e. the speed of sound). Whether the flow starts off supersonic (M > 1) or subsonic (M < 1), the M = 1 condition is the maximum entropy point. Wall friction will actually cause a subsonic flow of gas through a pipe to accelerate up to M = 1 (this is still counter-intuitive to me). So why then don't we find that most fluid flows through a pipe ultimately end up with sonic flow velocities?

I also do not understand what happens after the flow reaches M = 1. The textbooks I've skimmed generally say "if there is still pipe length left or heat addition past the point of M = 1, then the inlet conditions must spontaneously change such that the flow reaches M = 1 at the end of the pipe." But they do not explain what these changes are or what mechanism enforces them. What if I am controlling the inlet conditions to be a certain pressure? Then what happens at the end of a rough walled pipe if the flow reaches M = 1 in the middle? Or what if I forcibly add more heat past the M=1 point (in an initially subsonic flow) where the inlet pressure is fixed? Physically, what will happen?

TL;DR: Entropy is maximized when a fluid flow velocity through a pipe reaches the speed of sound. So why aren't all our natural gas pipelines carrying gas at the speed of sound? Or why not even our water pipes?


texts: How to infer from the volume fraction function whether a flow is transient or steady?

texts:
Hello dear engineering community.

I have a specific question about multiphase flows. I was wondering if anybody could help me with it, please.

Assume, I have a one dimensional water-air flow. Air is the dispersed phase. Let's say, it's a vertical flow. Water phase flow is incompressible.

QUESTION: if volume fraction (either of liquid or gas phase) is time dependent, then does it mean that that the flow is necessarily transient (either liquid or gas, or the entire mixture flow)? Or it can be steady?

Thank you in advance.


texts: Define inlet temperature in multi-stage adiabatic reactor

texts:
While solving some exercises for an exam, I faced a problem with a two-stage adiabatic reactor, producing methanol (exothermal reaction), with intermediate cooling. Both stages achieve equilibrium.

Two of the questions were:

Inlet temperature at the second stage
Load at the intermediate cooling exchanger

I have the inlet temperature in the first reactor, so I can couple a heat balance and a mass balance to obtain the temperature at the outlet of the first stage.

How do I calculate the inlet temperature at the second stage?

My first idea has been to suppose it equal to the first inlet temperature, but I cannot find any evidence to back it up. On the contrary, multiple charts have shown the inlet temperatures increasing after each stage. How else can I obtain it?


texts: Why do glass windows still exist? (Why haven't they been replaced by plastics?)

texts:
Glass is fragile and impractical to transport, install and repair. Even worse, glass kills and hurts people when it breaks. Falling to the streets like guillotines during earthquakes and bomb raids. During wars people put tape on their windows to prevent shattering. When that meteor exploded over Chelyabinsk, people got hurt by standing inside of a window watching the sky when the shock wave hit them.

There are perfectly transparent plastics, for example the PET material used to make coca cola bottles. Why aren't windows made out of that instead of glass (fragile ceramics)? It seems to be much cheaper, safer and more practical to handle. Is there any advantage at all to make windows out of glass? Is this a billion dollar business idea, and if so, why haven't anyone realized it yet?


texts:
The QueSST (Quiet Supersonic Transport) is a project to create a more diffuse sonic boom in order to use supersonic flight commercially without the usual abrupt 1~2 psf pressure spike damaging the environment.
I understand that traditionally jets create 2 supersonic booms, at their tail and their tip, and I assume that the new quieter jet is spreading out that pressure change over the length of the plane.
I just don't understand why the sonic booms were happening at the tail and tip to begin with, or what changed to spread them out.
Why was this problem so hard to solve, and what did NASA change to solve it?

If it helps, here are a few of the links that I looked at before hitting a wall:

https://qz.com/1049339/the-physics-behind-nasas-and-lockheed-martins-quiet-supersonic-jet-design/
https://www.nasa.gov/specials/X59/science-of-sound.html
https://www.cambridge.org/core/journals/aeronautical-journal/article/lowboom-lowdrag-solutions-through-the-evaluation-of-different-supersonic-business-jet-concepts/3045C940910ED2854DCA09C55A10EBEF
https://www.science.gov/topicpages/n/n-wave+sonic+booms


texts: Which vibration standard is the most common for transported packages?

texts:
There are several standards which all are valid when it comes to mechanical shock, bump and vibration, both for products in use and packaged and being transported.

Here are a few:

ISO 13355:2001 - Packaging -- Complete, filled transport packages and unit loads -- Vertical random vibration test
ISO 2244:2000 - Packaging -- Complete, filled transport packages and unit loads -- Horizontal impact tests
ASTM D6344 – 04 (2009), Standard Test Method for Concentrated Impacts to Transport Packages
ISTA Air ride
IEC 60068-2-27:2008 - Environmental testing - Part 2-27: Tests - Test Ea and guidance: Shock

End customer might have specific requirements, but what would a good baseline be? Is there a de facto/popular standard that everyone tests according to?

Product is more expensive than your average consumer product, but far from a space shuttle.


texts: is a cylindrical pylon just as sturdy as a cubical one of the same volume?

texts: I'm wondering if the structural integrity of a solid cylindrical pylon is just as sturdy as a cubical one of the same volume given that they're both the same height.


texts: Is the trigger of a drill a potentiometer?

texts: How does the trigger of a typical modern multi speed drill (maybe Ryobi for example) work? Is it just a potentiometer? Or is it more involved?


texts: Plain bearings (plastic) in backlash free joints

texts:
I need to design some backlash free rotational joints for slow and intermittent movements (device for human-computer interaction) for my uni project. Possibly loaded in any direction; the loads won't exceed ~100 N (fyi just to get the sense of scale) and I'd like to use plain bearings, as they should take less space and possibly have less stick-slip and smoother motion than rolling bearings. There's, for instance, that company based in Cologne, Germany that's got a really big variety of bearings - but then again, their off-the shelf preloaded bearings are really hard to move on the shaft (checked it personally), which is definitely not what I'm wanting. I was told by a salesman, that basically, as the bearings are press-fit, you can slightly alter the clearance by changing the hole tolerance. (As an example -  with recommended tolerances, a joint with 5 mm shaft would have between 0,02 mm and 0,10 mm of radial play, so choosing a more strict tolerance one can get eg. 0,01 to 0,05 mm play. Side note, perhaps can be useful for others - I was told that changing the hole tolerance generally relates 1-to-1 to the change in fitted bearing inside diameter tolerance, but I haven't checked it for myself and it's word-of-mouth, not in the catalogues).

EDIT: Below is a half-cross-section of a proposed play-free rotational joint: part 3 (with a fixed axis) is connected with axial bearing 5. Part 1, together with two press-fitted flange bearings 4, revolves around horizontal axis. It is all pressed against each other to eliminate backlash by nut 2. I think I can estimate friction caused by axial bearings, simply by defining the torque for screwing the nut.

My question is then:

are there any examples of design or scientific articles regarding play-free (preloaded) plain bearing (rotational) joints? Do you perhaps know from experience, how would such bearings (esp. plastic ones, esp. - I know I'm wanting too much - on carbon shaft) behave when given no or very little radial clearance? (by 'behave' I mean friction and 'feel' in the first place). I assume it should increase, but to what extent?

EDIT: Are such designs used at all, with this intent in mind?

I guess it is rather a matter of experience than pure calculation - but I'm lacking information on both - I'd really appreciate any hint.


texts: Nowadays deep vacuum pumps are fairly expensive, so I'm wondering: how could people reach the deep vacuum required for crookes tube or Geissler tubes in the 19th century ? (I'd be interested in building one myself)


texts: How would I do a buckling analysis with an additional fixed known lateral force?

texts:
I am using Nastran for buckling analysis, and I'm new to all of this so please bear with me.

For a linear buckling analysis, I understand that you must first apply any compressive load in the static subcase. Then solve the eigenvalue buckling problem in the second subcase using the first static subcase. The buckling load is then the amount of compressive load applied multiplied by the resulting eigenvalue.

However, I now want to apply a second fixed force of exactly 50N laterally and see what the buckling load would be with this additional 50N force. Now if I apply both the compressive load and the lateral load to the static subcase, and then solve the eigenvalue buckling using that subcase, the resulting buckling load varies a lot depending on the compressive load applied in the static subcase.

Example 1:

Apply 1N compressive force, eigenvalue is 100. So buckling load is 1N*100 = 100N
Apply 10N compressive force, eigenvalue is 10. So buckling load is 10N*10 = 100N
This makes sense, however:

Example 2:

Apply 1N compressive force and 1N lateral force, eigenvalue is 90. So buckling load is 1N*90= 90N.
Apply 10N compressive force and 1N lateral force, eigenvalue is 9.5. So buckling load is 10N*9.5=95N, which is higher than 90N.

This just proves that I am doing something wrong, and I am hoping someone can clarify what it is.
Any help would be appreciated, thank you!


texts: Is it practical to use tensile cables in a composite beam?

texts:
Many composite beams combine material that has a good tensile strength with material that has a good compression strength (like concrete and rebar).
I was wondering if there has ever been a beam that used tension cables on the side in tension. It seems to me that this might be a cheaper solution than using I beams in certain cases, though it would be more involved construction since cabling pieces would be needed (like turnbuckles).
Could this ever be practical? It seems to me that it could be in very specific circumstances, but I'd like to hear from more knowledgable people because I feel like I'm overlooking something.


texts:
I am working (as a hobbyist) on a motion system where there be electrical cable (multi-core for signaling) going to the moving part. I have considered multiple solutions to connecting the cable to the stationary base (see below). One of the options is to have a retractable cable mechanism. I am aware of mechanism that rolls the cable on a drum that is placed in the middle of the cable. I think this option is not suitable for the solution as that will add weight to the middle and the cable will slack under the weight of the drum quite a lot, which contradicts the purpose of the retractable cable. So my question -- is there any well established mechanism for retractable cable that is fixed on one end (i.e. on stationary side)?
Requirements:

Mechanical (no electronics involved)
Automatic (no manual intervention needed under normal operations)
Compact (as much as it can be I guess)
Simplicity (simple mechanisms are less prone to failures I think)

Alternatives (that I am well aware of, thus not in scope for this question):

Drag chain
Coiled cable
Sliding contacts


texts:
I apologize in advance if this is off topic - maybe it is more of an English language query... Please feel free to migrate or close if needed :)

I have seen mine cages/service lifts referred to as Mary-Ann (or Maryann/Mary Anne etc.) for example here, here and here. Does anyone know where this comes from? And is it a common term - I have heard it used in South Africa and the sources linked are Canadian, which suggests this is the case.


texts: Why a factor of 2 appears in gasket force calculation in ASME section VIII div. 1 flange design?

texts:
In mandatory appendix 2 of ASME section VIII div. 1 the following calculation is given for calculating minimum bolt load required for operating conditions of a flange joint i.e. , under internal pressure:

$W_{m1}=\pi/4\times G^2\times P+2b\times\pi G\times mP$

Where P is fluid pressure, G is gasket diameter, b is gasket contact width, m is gasket factor.

The first term is clearly understandable, it is hydrostatic pressure force.

The second term is gasket force required to maintain a leak proof joint. But it should have been $b\times\pi G\times mP$, because area of a thin annulus of diameter G and thickness b is just $\pi G \times b$ and not $\pi G \times 2b$.

Why there is the factor 2 in the second term?


texts: The difference between two load combinations in LRFD

texts:
In ASCE 7-16 there is a load combination as:
1.2D + 1.0E + L + 0.2S
but then there is also another combination as:
0.9D + 1.0E
In both of them earthquake load is the same so why would we use the second one, while the first one would create the worse combination with 1.2 instead of 0.9 for dead load? What am I missing exactly?


texts: How were gears manufactured before power tools, CNC, etc

texts:
Current gear manufacturing methods for gears usually depend on power tools, or computerised machines, or something like that.

However, watchmakers and clockmakers at one point in history needed to make gears by hand. So what tools did they use? How did they make gears (especially really tiny ones)?


texts: The title pretty much sums up the question, but basically I need to create 3 sizes of gears. I have tried 2 shapes, the first being basic rectangles. However, according to my Engineering teacher, neither of those designs will work. So now I am going to try a spur gear, but I have no idea how to get the right angle and everything else, especially seen as the shape of each spur will change with the gear diameter. So how do I go about designing a spur gear in autocad? Any (free) auto cad plugins or calculators are appreciated as well.


texts: How to simulate sound emission properties of the human body?

texts:
Is there any way to simulate sound transmission properties of the human body with solid materials?

While there are several sound sources inside the human body (heartbeat, air flow, bubbles moving inside the intestines) only a very small amount is transferred to the sourrounding air. It can however be tapped on by a stethoscope in a quite efficient fashion.

Is this process comparable to sound in and over water, where sounds sources underwater can be heard well underwater but almost nothing leaves the water?

Is it possible to create a solid body that would transmit almost no sound to the air, but can be tapped on with a stethoscope?


texts: Discontinuity in mechanism simulation: is the mechanism jammed or is my analysis wrong?

texts:
I'm designing a compact mechanism for the deployment of a mast. The idea is that the linear actuator for the deployment is on the other side of the pivot, and a slider increases the lever arm to enable the actuator to deploy the mast.

I ran through the maths (shown in details below), and wrote the code for the simulation. I want to know how the actuator force and the lever length relate, and how the force varies with the angle.

However, when I run the code I get huge spikes in the force (see below, I capped the force to 10^6 to better see the pattern), but for example I don't see why the mechanism would jam between 40 and 80°. For some reason the cross product of HP with OP (what I call the signed lever arm of F) goes through zero but I see no reason why it would given the current dimensions and angle range set. How can I fix it?

Original:

With the force capped at 200N:

And the denominator of F:

Annex

Code:

close all
clear all

%See diagram for description of variables, units are metres
a = (2+10)*10^-3;
b = a;
c = 165*10^-3;
d = 70*10^-3;
h = 180*10^-3;

m = 8; %Mass of the mast in kg
g = 9.81; %Acceleration of gravity in m/s²

%Range of the input variables
thetaMin = 0*pi/180;
thetaMax = 100*pi/180;
tMin = 10*10^-3;
tMax = 100*10^-3;

%Vectors
theta = thetaMin:(thetaMax-thetaMin)/100:thetaMax;
t = tMin:(tMax-tMin)/100:tMax;

%Solve for F
F = zeros(length(t), length(theta)); %Actuator force
L = F; %Length of linear actuator
denominator = F; %Denominator of F, or "signed lever arm"
for i = 1:length(t)
    for j = 1:length(theta)
        M = [cos(theta(j)) sin(theta(j)) 0;
             -sin(theta(j)) cos(theta(j)) 0;
             0 0 1];

        HP = M*[-t(i);
                a;
                0];

       OP = [-b;
              h;
              0]+HP;

       L(j,i) = norm(OP);

        HG = M*[c;
                -d;
                0];

        W = [0;
             -m*g;
             0];

        weightMoment = HG(1)*W(2)-HG(2)*W(1); %cross(HG,W)
        forceLever = 1/norm(OP)*(HP(1)*OP(2)-HP(2)*OP(1)); %1/norm(OP)*cross(HP,OP)

        denominator(j,i) = forceLever;

        F(j,i) = -weightMoment/forceLever;
    end
end

%Plot results
[T,THETA] = meshgrid(t,theta);

figure(1)
surface(T*1000,THETA*180/pi,F)
ylabel('Angle (deg)')
xlabel('Slide length (mm)')
zlabel('Force (N)')
title('Actuator force')

figure(2)
surface(T*1000,THETA*180/pi,L*1000)
ylabel('Angle (deg)')
xlabel('Slide length (mm)')
zlabel('Actuator length (mm)')

figure(3)
surface(T*1000,THETA*180/pi,denominator*1000)
ylabel('Angle (deg)')
xlabel('Slide length (mm)')
zlabel('Signed lever arm')

Maths: solve
$$\vec{moment}(H)=\vec{HP}\times \vec{F}+\vec{HG} \times \vec {W}=\vec{0}$$
With
$$\vec{F}=\frac{\vec{OP}}{OP}F$$
$$\vec{HP}=
\left[ {\begin{array}{cc}
cos(\theta) & sin(\theta) \\
-sin(\theta) & cos(\theta)
\end{array} } \right]
 \left( {\begin{array}{cc}
-t \\
a
\end{array} } \right)
$$
$$\vec{HG}=
\left[ {\begin{array}{cc}
cos(\theta) & sin(\theta) \\
-sin(\theta) & cos(\theta)
\end{array} } \right]
 \left( {\begin{array}{cc}
c \\
-d
\end{array} } \right)
$$
$$\vec{OP}=\vec{OH}+\vec{HP}$$
$$\vec{W}=\left( {\begin{array}{cc}
0 \\
-mg
\end{array} } \right)$$
$$\vec{OH}=\left( {\begin{array}{cc}
-b \\
h
\end{array} } \right)$$


texts: Design op-amp circuit from transfer function

texts:
What is the best way to design a circuit based on the following transfer function:

$$T(s)=\frac{9216}{(s^2 + 48s + 9216)}$$


texts: How to find the positioning of cutter machine with high accuracy with digital sensor?

texts: I have an old vertical and horizontal cutting machine that is working manually it is kind of useless because it is hard to make accurate measurements. I want to use two digital sensor (with output for any controller) to find the position with less than 1mm error on two dimensions, left-right (with rack and pinion mechanism) 0 to 2,5 m and up-down (with roller screw mechanism) 0 to 1m. What kind of sensor do I have to use under 300 euros?


texts: Does attic insulation help cool a building?

texts:
Given that hot air rises, it's easy to understand how attic insulation can help keep a building warm; say, in the winter, for example. But when winter changes to summer, does the attic insulation help keep the building cool? Or even worse, does attic/roof insulation make the building hotter by resisting the flow of heat up and out?

In the below diagram, my idea is that the R-factor of the attic insulation will resist the flow of heat up and out of the building by impeding flow from zone 1 to zone 2 in the below diagram.

Figure  1. Premise: R-factor resists heat flow from zone 1 to zone 2 thus trapping warm air inside the house in the summertime?

How would we quantify the overall effect on house temperature based on this and other competing effects? Both theoretically and empirically?


texts: Multi-position bi-stable solenoids in a small form factor

texts:
I am looking for multi-position bi-stable solenoids. So far, I have only found one vendor1 with a 3 position bi-stable solenoid.

Are there multi-position bi-stable solenoids with more than three positions? How can a 3 position bi-stable solenoid be mechanically amplified to multiple positions?

Why are these such a rare commodity? What are the alternatives other than stepper motors?

1Note, I'm not looking for a vendor recommendation, I'm trying to find out if I'm looking for the right thing.


texts: The couple of my servo motor is it powerful enough?

texts:
I am a beginner in Electronics. I am trying to make a small robot controlled by an Arduino. The problem is that I do not know how to calculate the power required to rotate a structure with a servo motor placed on its axis (see picture below).

My servo motor is a Dynamixel MX-28 T with an average stall torque of 2.5 Nm at 12 V. The product page for the servo can be found here and the specification sheet for it is here.

Do you think it is possible to rotate it using this servo motor?

Informations:

Structure weight: 2,2 kg (2200 g) (include battery-arduino-servo)

Structure Dimension: 900mm/120mm/120mm (see picture below)

Structure type: Aluminum

Servo weight: 72 g

total weight 2.2 kg will be distributed fairly. 1.1 kilo on the top and on the bottom 1.1 kilo

(click for full resolution)


texts: Is there a way to avoid reheating of steel billets in Reheat furnace and directly go from casting to roll milling?

texts: Iron ore and few compounds added will result in steel which are casted to steel billers form. this billet is again reheated to melting point of 1200c and then sent to roughing mill for desired shape. can we avoid reheat furnance and directly cast and then roughing mill?


texts: Difference in flow measurements in an open channel

texts:
I'm undertaking a civil hydraulics question.

It involves the flow of water in an open channel down a river at $5m^3/s$ until the flow is split in two by a weir acting as a sluice gate allowing flow into another stream. A weir pool is located on the upstream side of the gate. $2m^3/s$ flows into a stream not dictated by said weir and I assume we apply conservation laws so that $3m^3/s$ flows into the stream under the gate. It's stated that the gate is set to a certain height and the weir pool height is a function of the flow rate into the other stream.

The initial question pertained to finding the height of the gate above the river bed, however, the following question states that subsequent flow measurements were taken and indicate that when the gate is set at the calculated height, the flow into the stream under the weir is actually 10% less than what is calculated (I assume $2.7m^3/s$). It then asks, why could that be the case?

My first thoughts were that this could be due to frictional effects from the gate and possibly across the river bed, maybe a change in the channel geometry or possibly a change in slope. Have I covered all the possible options here or is there more that could be affecting the flow rate in this situation?

Any help would be greatly appreciated.

Cheers


texts: Simple mass spring damping system sizing K, and C factors

texts:
I have come across a problem, which has troubled me for some time now.  What needs to be done is the following:

A mass on a rod 0.6m (mass less) has a mass of 1 kg attached at the end of it. The rod needs to be rotated 60°, within t=120 sec (see image). What I would like to do is size a rotational spring (located at the pivot point) and a damping system, such that it that will damp the spring force. Thus the rotation happens within the specified amount of time.

I have written the generic differential equation of the system:

$$J\theta'' + C\theta' + K\theta = 0$$

(typical differential equation of damped spring system)

and for a critical damped system, and for $t=0$, $\theta=0$ I have the solution:

$$\theta(t)=A t \exp(-bt)$$

where $A$ is a constant, and $b$ is the damping coefficient.

My question is how can I continue, such that I can size the damping coefficient and the spring constant?

And if I can continue from here, how should I then proceed to size my system?

Please note $g=0$, no gravity.


texts: Unexpected Closed-Loop System Response of Longitudinal Aircraft Dynamics

texts: I have a closed-loop system that represents the longitudinal dynamics of an aircraft with states x velocity, z velocity, pitch rate, pitch, and x and z inertial positions. The outputs of the system (where the system response is observed) are the pitch angle and z position. The realization of this particular system is completely reachable, and so I have placed closed-loop eigenvalues at -1.5, -2, -2.5, -3, -4, and -5. I have solved for the gain matrix that gives this desired behavior. In each modal space, the modal response is as desired; no oscillations and highly damped. However, when I simulate the system response to a random unit perturbation in the state space, the system response actually has oscillations. I figured that since all of the eigenvalues are strictly negative and real, that I should see no oscillation. Is the response I'm getting what's supposed to happen or am I doing something wrong?


texts: Dictionary of standardized engineering terms?

texts: I think I once used a dictionary of engineering terms that was either a European effort or one of an (global) international standardization body - but I can't remember...


texts:
I'm reading this paper on structural members subject to both bending and compression.
In the first paragraph, in context of the equations 6.61 and 6.62, it is said:

The second two terms are modified by factors
that allow for the interaction between the different modes of
buckling.

What is meant by the interaction between different modes of buckling? How do buckling modes "interact"? I tried searching online but couldn't really find a good source. Checking a member against buckling I've understood that only the first mode is usually checked, with $N=1$ in Euler buckling equation.
$$\begin{align}
\frac{N_{Ed}}{N_{b, y, Rd}} + k_{yy}\frac{M_{y, Ed}}{M_{b, Rd}} + k_{yz}\frac{M_{z, Ed}}{M_{c, z, Rd}} &\leq 1 \\
\frac{N_{Ed}}{N_{b, z, Rd}} + k_{zy}\frac{M_{y, Ed}}{M_{b, Rd}} + k_{zz}\frac{M_{z, Ed}}{M_{c, z, Rd}} &\leq 1 \\
\end{align}$$


texts: Simscape Flexible body - modeling a busbar as a flexible component on Simscape

texts:
I am trying to model a copper busbar as a flexible body for simulating it in the Simscape Multibody environment.
I have built the model, but I am failing to generate the flexibility. I will describe the entire process. Please comment if it is the right method. If wrong, I kindly request you to suggest the actual method to be followed.
I started off by performing modal analysis on the imported STL busbar component on Matlab. The PDE toolbox was utilized. Multipoint point constraints were applied to the critical points on the body and was CB (Craig Bampton) reduced to obtain the mass and stiffness matrices. Analytically the damping matrix was also developed.
One of the points has to be considered as the reference frame, with respect to which deflections will be measured, and hence its DOFs have to be eliminated. So, as a result of rigid body modes, 6 rows and columns were manually deleted from all the matrices. Finally state space matrices were obtained.
First question, should we use an FE software like ANSYS or is it right to reduce the model and obtain the mass and stiffness matrices in Matlab using the PDE toolbox.
Once the matrices were obtained, it was superimposed with the rigid body model in simulink using joints at appropriate locations. For the rigid body model, I imported the STL file again.
Because the frames created in simulink have no inertia of their own, I split the busbar into 3 solid parts and connected each frame to the split parts. I dont see the deflection upon simulation and it stops simulating showing me an error
"Nonlinear iteration is not converging with step size reduced to hmin (1.9776e-22) at time 5.56646e-08.  Try reducing the minimum step size and/or relax the relative error tolerance."
Second question, Is this approach correct?
Looking forward for valuable suggestions.
Regards,
Goutham Sajja


texts: How do I calculate the temperature change inside a box with a heat source? What if I ventilate the box?

texts:
I have a box (as shown below). I know the temperature outside of the box (for example you could use 293K) and I would assume the temperature inside the box is initially the same as outside of the box.

I have 6000 chickens in the box. They produce a total of 15.8 W of heat with 8 W of that being sensible heat.

If the box is sealed and there is no ventilation how would I calculate the change in temperature over time? Would it be a simple case of  $Q=mcΔT$?

Obviously in the real world I would not leave 6000 chickens in a box to overheat. How could I calculate the temperature change over time if I ventilated the box at a rate of 4m3/s?

Edit: Material would be PVC coated material (like on the side of lorries/trucks). I have an found an R value of 0.16 m²K/W for this type of material and it's thickness would be around 0.75mm.


texts:
Is it possible to use an IR sensor to differentiate accurately between carbon fiber and a human hand kept on the carbon fiber surface?

I would like to move the sensor from one end of the carbon fiber object (a rectangular surface) to the other and be able to detect a significant difference in reflected intensity when the sensor passes over the hand. Will this work? If not, what are alternative sensors that I could use? The sensor will be approximately 10 cm above the carbon fiber surface.


texts:
I have been wondering, would it be possible to make an 8’x4’x’5 tank that can be put up and taken down as needed, where you would have a base, four removable corner posts, more removable posts as needed to support the walls, and a top connector.  Use either water pressure or expanders to hold the walls against the seals, and only one wall would need to be clear.  For even more extreme have the base be in multiple sections so it can fit in the back of a car.

I ask because many of my friends and myself are mermaids/mermen and we don't always have the funds to buy a massive 1000 gallon tank and the trailer to move it.  The tanks allow us to set up and entertain kids in dry environments, like a building or a fair.  I know water has the pressure to keep a car door from opening when a car goes into a lake, and I would imagine having water push against a wall will make a fairly good seal, and the bottom could be lip connector based.  I don't think it has to be 100% leak tight as it might only be set up for a few hours and something like a tarp could be placed under the tank to collect the water and pump it back into the tank.

How insane is this idea?


texts: How to calculate the steps needed for a motor to rotate a circular object in a pulley configuration?

texts:
I have a stepper motor with 200 steps per revolution and a pulleys configuration as following: 3 pulleys with 100 mm diameter each on 1184 mm PCD and are equally spaced (120 degrees) from each other. A large ring with a diameter of 1074 mm is placed on the center on the pulleys configuration (center of ring to center of each pulley is 592 mm). A belt of 3626.5 mm length and 30 mm width is positioned around the pulleys and contacts the ring. The motor is installed vertically on the bottom of one of the pulleys (concentric on the same axis). I want to know how many steps it takes for the motor in order to have a full revolution on the large ring.

Here is a simple drawing of the configuration


texts:
The Tibetan Bridge Type

I have a question regarding the bridge type called "Tibetan Bridge".
Recently close by my home town a new tourist attraction was built, the Highline 179 bridge.

It was planned as the longest suspension bridge for pedestrians in the world, but before completion it was already outclassed by
the Skypark Bridge in Sochi.

Now the Bridge is denoted as the longest Tibet-style pedestrian suspension bridge and I could not find information what a Tibet-style or Tibetan bridge is.

Other Tibetan Bridges

I could find other Tibetian bridges (e.g. Tibetan Bridge Claviere), but I could not find any information what Tibet style could be from an engineering perspective. The Wikipedia article on bridge types does not list this particular type.


texts: Why use a reference volume for leak testing?

texts: An accepted method of leak testing a test piece is by using a differential measurement between it and a reference such as in the schematic here - why might one bother doing this as opposed to just comparing your test piece alone to a predefined or recorded leak rate, or curve?


texts: Why divide the dimensions of a pressure vessel by 39.37 when calculating discharge capacity?

texts:
For a National Board Exam Review:

  A 29.53" * 39.37" pressure vessel contains ammonia with f = 0.041. Compute the minimum required discharge capacity of the relief device in $\mathrm{\frac{kg}{hr}}$.

The solution is shown as:

$$C = fDL = 0.041(\frac{29.53}{39.37})(\frac{39.37}{39.37}) = 0.03075 \mathrm{\frac{kg}{s}} = 110.71 \mathrm{\frac{kg}{hr}}$$

What I don't get is why DIVIDE? Isn't it already length and diameter?


texts: What is Byte Alignment Time in radio communication?

texts:
According to this paper, which deals with time synchronization in wireless networks, this kind of delay occurs, however I do not understand its explanation. The paper says the reciever (radio) has to determine the bit offset of the message from a known synchronization byte.

The definition from the paper is:

  Byte Alignment Time —the delay incurred because of the different byte alignment of the sender and receiver. This time is deterministic and can be computed on the receiver side from the bit offset and the speed of the radio.

If somebody familiar with this phenomenon, can you please explain it to me?


texts: What attributes of a surface are relevant to light sensors?

texts: I'm doing a study on surfaces and I would like to describe all of the surfaces that I expect to encounter in the field and determine which ones will be the most difficult to detect. To do this, I need to determine what attributes in a surface I need to consider. I have no experience in optics so I'm asking this question here in hopes that someone could save me from overlooking important factors.


texts: Calculating tensile strength for aluminium

texts:
I'm making a Z (coffee table) linkage with two interlocking C channels and a couple of steel linkage bars. While moving, they aren't load bearing but when extended, they will take a weight of around 300lbs. I need to figure out whether 3mm T66 aluminium can take that weight without tearing.

The entire weight will be spread across two bolts (10mm with bushing) and the top half of that so that's Pi x 10mm diameter / 2 because the weight is all on the top half x 2 bolts - around 31.4mm x 3mm thick = 94.2mm squared. I've found tables of properties for T66 which give figures in MPa (megapascals?) but that's where my half-remembered high school physics gives out.

How do I calculate the maximum load across a given area from these properties?

Edit: To include sketch.

The block to the left is the (fixed) seat base, along the top are Unwin rails along which the seat can slide. When not needed, the linkage around the 4 bolts can rotate it away into the floor. When they are raised (as shown), the seat+occupant, for which I am allowing 300lbs) can sit directly over the hinged section. Ignoring the rail overlap, that means that the full weight is supported by the top of the two round pivots (actually, since it's made from C channel and there are one of these on each side, that's 2x2x2x10mm bushings in 3mm aluminium).

Hope this makes the question clearer.


texts: How do stators in axial compressors work?

texts: How do the stators in axial compressors convert kinetic energy to pressure? Is this equivalent to a water hammer?


texts: Statics poblem with a pre-stretched spring

texts:
I am dealing with a statics problem in the following link. This question is from the courtesy of Engineering mechanics, Statics by R.C. Hibbeler, 13th edition.

Before applying vertical forces F and -F, 60 Ib of force causes 1.5 ft of stretch in springs. With the exercise of the two forces, springs stretch some more and this can be found from the geometry of the problem. This stretch is 0.27 ft at points C and D. Finally, again due to geometry F equals the force in one of the springs.

I sum the initial stretch and the final stretch and multiply this with the stiffness of one spring but do not arrive at the true answer.

What am I doing wrong here?


texts:
I have a flat aluminium plate and I need to mount a digital indicator[1] on it.
The digital indicator doesn't seem to have any mounting holes itself so I
think I need to use a clamp to hold it.
I don't have much experience with industry standard parts in this area and I'd
rather not make something myself if I can buy it. So is there any standard
part or way I can mount this digital indicator on a flat aluminium plate? I can
drill holes in this plate no problem.
Any help is appreciated!
[1] https://shop.mitutoyo.eu/web/mitutoyo/en/mitutoyo/01.04.04A/Digital%20Indicator%20ID-H%2C%20CEE%20AC-Adapter/$catalogue/mitutoyoData/PR/543-563D/index.xhtml


texts: Mobile Frequency and Carrier Frequency not Matching

texts:
I am using a Google Nexus 6 Mobile in India with Airtel as Network Provider. Recently Airtel has upgraded their Network to 2300 Mhz 4G. Whereas Google Nexus 6 Operates on Band 3 (1800Mhz) LTE.

When I switch Mobile to LTE Mode - I am able to use 4G Network (Internet ) but there are no Incoming Calls.

When I switch Mobile to 3G Network - I am able to get Incoming Calls but no 4G Network.

What can be the exact cause for this and possible solutions?


texts: Voltage at node A respective to the ground

texts:
I want to calculate the voltage at node $A$ respective to the ground.

$R_1=1.8\text{k}\Omega, R_2=3.8\text{k}\Omega, R_3=1.8\text{k}\Omega, R_4=5.8\text{k}\Omega, R_5=2.4\text{k}\Omega$ and $V1=4.3V, V2=2.3V$

I know that voltage $V=-V2+V1=2V$ then $R_1$ and $R_2$ in series so $R_{12}=R_1+R_2=5.6\text{k}\Omega$ then the current is $I=\frac{V}{R_{12}}=0.356\,\text{mA}$

But how do I calculate the voltage at node $A$ respective to the ground? Is it over $R_{45}$ or $R_{3}$?


texts: Does the surface roughness play any role in shock absorbing?

texts:
Consider a mass of about $130 \pm 10 $ kg, falls from height, let say $2.5 $ m.
In order to dampen the vibration and sound, I use silencer or drop pads. I was wondering if introducing the macroscopic projections, helps to reduce the thickness of the shock absorber in comparison to the classic flat surface shock absorbers.

After reading Kamran's answer:
I think the impact energy results in transversal deformation of the projected surface, that is in contrast to the vertical compression of the flat surface.  So there would be less energy transmitted to the floor.


texts: How to measure airflow going through individual server vents

texts:
*Sorry everyone for the very wordy question.

I am trying to write up a method to accurately measure the airflow through the inlet and various outlets on one of our servers in order to measure the heat output from the server partitions/cards. The boss wants to know the rate of heat production from each card, the current airflow provided to each card, and what the airflow actually should be to keep the cards running at a certain temperature. The server is partitioned into three sections and the outlet vents look similar to these:

I have purchased a TSI 9565 velocity meter that comes with a hot wire anemometer and a small pitot tube that measures down to 0.15m/s. I plan on using the pitot tube attachment to measure the air velocity, but my concern is that the velocity will vary depending on where on the vent I take it from, so I won't just be able to average it. The problem server is on site and the technician has limited time to access the server, which means he will only be able to take one measurement at each vent. We do have an exact copy of the server setup here in the main office, but the rack is quite different which means the airflow going into each server will be different.

However, I was thinking that because the server setups are the same, maybe the ratios between the velocities for each vent would also be the same. I don't have any justification for this, but if it is roughly true, I could record each individual velocity reading from each vent perforation on the server here in the office, where I have plenty of time to do it. Then I could specific a certain spot on each vent for the technician on site to take a single velocity reading from and find the factor of difference between that server and the office server. From there I could multiply all the velocity values for that vent that I recorded on the office server. It's a bit hard to explain so I've included a quick example.

My question is, is my assumption that the servers would have the same relative velocity profiles valid? If not, what would be an accurate way to measure the airflow through each vent?


texts: Shear modulus in terms of 2 Young's moduli and Poisson ratio

texts:
I have two moduli, EY and EZ, and the poisson ratio NUYZ, and the equation for the shear modulus that I am using is
$G = \frac{EY*EZ}{EY+EZ+2*EY*NUYZ}$
but I am not sure where it comes from.
I tried seeing if I could somehow rearrange the shear modulus from wikipedia: $G = \frac{E}{2(1+\nu)}$ but did not have any luck, so I was wondering if there was something obvious I am missing. Apologies if this is an easy problem, I am new to shears/Young's moduli, but if anyone could explain where my equation comes from it would be super helpful! Thank you!


texts: How to develop design criteria for subsystems in addition to the systems?

texts:
Context: 18yr fresh out of high school and have started my undergraduate engineering course at my University.
For my first ever group project, we are asked to develop a fire extinguisher vehicle. The vehicle has 4 subsystems, or 4 parts that we need to focus on. The driving, structural, water delivery part and the controlling the vehicle part.
I am tasked to develop design options for the water delivery part. It obviously needs to have a water reservoir (container), tubing, pump and some nozzle. Then, I have to a develop design criteria for these components.
The problem is that I am struggling to develop specific criteria. For example, I can come up with sustainability, safety, maintainability, economic feasibility and on and on. We all know that a pump should have all those characteristics just like any other components in other subsystems (driving etc). But how can I be specific to MY WATER DELIVERY SUBSYSTEM? I can't say water efficacy is a design criteria since this is not a criteria for tubing, pump or nozzle.


texts: A previous question here was relating wind deflection to drag creation in vehicle solar panel installations. In a residential installation drag is not the issue, but uplift is a critical concern.  Since the efficiency of solar panels is affected by temps there will need to be sufficient spacing above the roof. I'd like to know whether a solid or permeable windbreak could provide useful protection for the panels against damage from hurricane force winds or would it instead increase uplift?


texts: Which material index should be maximized for a component in a Car's manual type HVAC?

texts:
I was doing a case study on the plastic used in cars for controlling the AC in a manual type system which actually snapped in mine it just rotates according to the knob position in the dashboard, pushing and pulling with a stiff cable/rod. It finally separated as you can see in the picture. So rotating the knob effectively does nothing. I am not considering electronically actuated (Automatic type) AC in cars

Please note, the notch is indeed a design flaw as stresses are more concentrated there. I did ANSYS on a model of this however this is only a Material Selection Course that I am studying. So I need to limit myself to just that.

I went over the Ashby textbook and saw a (similar?) example in the 4th Edition.

  6.10 DEFLECTION-LIMITED DESIGN WITH BRITTLE POLYMERS

$\frac{K1c}{E}$ was derived here by substituting the hooke's law and ignoring all material independent variables.

Everything else except Young's modulus and Fracture Toughness is independent of material so we exclude that according to Ashby. And arrived at ABS, NYLON PLA as the best materials like me in the textbook too. I reckoned it could apply here too.

There are three limits for the same objective, displacement limited, load limited and energy limited. I went with deflection limited since I imagined the part would require some deflection to snugly fit during assembly.

I also put an arbitrary limit of 10% strain since any significant cant change in geometry will result in obsolete part, prices not more expensive than ABS, not weaker than ABS.

I got cardboard and paper, ABS, PLA in level 2 on CES Edupack.

The part I don't understand

Clearly, steel for example is cheaper and stronger than ABS OR any polymer, it wouldn't fail. But my problem is why do automakers around the world use plastic in all road cars when metal does the job better? Is it for lower production costs? My professor doesn't buy into the argument of "Planned Obsolesence" here.
What is a better material index here? The Young's modulus in the denominator looks suspicious, so I should just be maximizing K1c?
I should consider "Toughness" and not "Fracture Toughness" since clearly there are notches/imperfections and a better Fracture Toughness only makes things worse?

Yes, I know top trim cars have electronic actuators but I meant only on manual type AC controls

Here is the video of this mechanism

It is a mirror image to my picture because it's in an Australian car where they drive on the left.


texts:
I am tasked with the design of a helipad for a remote government facility. Annex 14 Part II (ICAO Convention on International Civil Aviation) does not clearly state what materials are acceptable.

The most common materials are concrete and asphalt.

I want to use brick pavers.

Does anyone know of any risks or restrictions in this regard?


texts: (moulded) cast properties of the untreated surface

texts:
While my research about the untreated surface of moulded cast I read that the properties such as tensile strength, 0,2% proof stress and so on are different (much smaller) from the properties you can find in the tables. That’s because the samples have a treated surface to evaluate the material properties.

Now my question is how can I determine the thickness of the surface where my properties are much smaller?

The background is that I have a bore near the untreated surface loaded with hydraulic pressure and for safety I need a specific thickness of material around the bore. And because the material properties of the untreated surface are much smaller, I will not take this area into account to my calculations. If it is needed: the regarded cast is GJS 400.

Many thanks in advance!


texts: If creep behavior can begin at 0.6T(melting) but, hot working for a pure metal starts at 0.4Tm, what is the explanation for this?


texts: How can I design a planetary gearbox with 1:20 ratio that the planets do not interfere with each other?


texts: How does 3 "liars" in Strandbeests work?

texts:
See video:
https://www.youtube.com/watch?v=75Z7-gmd_qk&t=226

This does not make sense to me. As far as I got it, bottom pipe is isolated from top 2 and just controls valve of the top 2 pipes. So, when air from bottle goes into left "liar" trough top 2 tubes of the right one it should just stop there. There is no way air can get to the middle one and also return to the right one to close/open it.

I hope somebody can explain this to me, because I'm starting to loose my mind a bit over this.

Edit:

I used Transistor's schematic to illustrate my frustration better:

See, in the video it's clearly seen that input air pipe goes only into A cylinder's input pipe. B and C does not receive air at all! Also it seems that B and C are closed initially, while A is open. And I can't really see any springs that you mentioned either. This is what really frustrates me. How B and C can operate if they are not even connected to air supply?

Edit:

OK, I'm feeling really embarrassed now. Are this tubes actually fused together? The problem is, Theo holds his finger over it almost all the duration of operation and it really seems that this 2 tubes are separate... In this case, Transistor's schematic is correct and my problem is solved.


texts:
I tried proving the condition dG<=0 where G is Gibb's free energy and instead ended up proving dB<=0 where B is exergy. Can someone please explain what went wrong with my derivation. I have attached the photo of derivation below. Thank you.

Edit 1: I looked up on the net and it said exergy and Gibb's free energy are same at NPT ensemble. I cannot understand how when both the type of energies use different Temperatures in there formula. Can someone also give an explanation for this??


texts: How do units of mm^2/mm represent the reinforcing steel area in a slab?

texts:
Whenever I've come across notation for specifying how much reinforcing steel is in a member, it is typically by giving the area of steel as a percent of the cross-sectional area of the member.

For example in this picture, you could say that the reinforcing steel is 0.02 or 2%. You could also specify the reinforcing steel given a schedule, e.g. #8 @ 12" O.C.

I recently came across a piece of software that was asking for the reinforcing steel of a floor slab in units of mm^2/mm. I cannot figure out how they came across those units. How could I calculate the reinforcement in these units given I know how much steel is in the slab in the other conventions I listed earlier?


texts:  Skogestad & Postlethwaite, Multivariable Feedback Control: Analysis & Design, Wiley, 2005 Figure 9.10 Why a negative sign on W2?

texts: Yesterday in class this question came up by one of the students in the class. Does anyone know why there is a minus sign in front of the W2 in the figure?


texts: Determine the aceleration of points B,C and D, angular aceleration of rod and the tension in rope DE when ropes AB suddenly breaks

texts:
The solutions are F(DE)=134.38N, a(D)=2.016m/s^2 , α=1.29rad/s^2, a(C)=7.828m/s^2
I agree that the FBD and the KD are these:

Then to solve this problem I've done:
$$\sum M_{c}= I \alpha_{BCD}$$
$<=> T*sen(53.13) * 5 = Iα + m*a(D)*sen(36,87)*5$
$<=> 4T = 416.67α + 150a(D)$
$$\sum F_{y}= (F(y))ef$$
$<=> T*sen(53.13) - P(BD) = m*a(Cy) - m*a(D)*sen(36.87)$
$<=> 0.8T - 490.5 = 50a(Cy) - 30a(D)$
$$\sum F_{x}= (F(x))ef$$
$<=> T*cos(53.13) = m*a(Cx) + m*a(D)*cos(36.87)$
$<=> 0.6T = 50a(Cx) + 40a(D)$
$a(C) = a(D)+α*r(CD) $
$= 0.8a(D)i-0.6a(D)j + αk * 5i$
$= 0.8a(D)i + (5α-0.6a(D))j$
and so i know that $a(Cx)=0.8a(D)$ and that $a(Cy)=5α-0.6a(D)$
and solving the system i got $T=-1032.66N$, $a(D)=7.745m/s^2$, $α=-7.125rad/s^2$, $a(C)=31.59m/s^2$, which are the wrong solutions. Comparing my equations between the FBD and KD with the resolution, my equations are wrong but i cant understand why
In the resolutions they use this equations but i still cant understand why


texts: Switch at the back of a battery eliminator

texts: I have this variable voltage battery eliminator and the "switch" to hold the wire in place is broken. Is there any specific name for this "switch" and can I buy it somewhere to replace it or can you suggest some other way to overcome this please.


texts:
Looking at the turbocharger picture below there is a compressor and a turbine side.

If you dont know the flow direction of the fluid, how can you distinguish which side is the compressor and which is the turbine? Normally for subsonic design this would mean increasing cross section area is a compressor and reverse for turbine. However, since the design is very different considering the shape of the blades between both sides there seems to be a better way to identify it. How?
Why is on the left side of the pictures every second blade shorter? What effect does it prevent/provoke?
Is there a special reason why the blades dont have a certain profile (for example NACA profiles) like in airplane turbines instead of (near) constant thickness? This part seems milled with a 5/6 axis machine, so price should not change with a profile shape design.

turbine http://www.glr.tu-darmstadt.de/media/glr/turbolader/DSC_6847_3.jpg


texts: Mathematical expression for power loss in a dielectric

texts:
I am trying to prove the equation
$$
\frac{\bar{P}}{V}=\frac{1}{2}E_0^2\sigma_{AC}
$$
which can be rewritten as
$$
\begin{align}
  \frac{\bar{P}}{V} &= \frac{1}{2}E_0^2\sigma_{AC}\\
  &=\frac{1}{2}E_0^2\ \omega\ \epsilon_0\ \epsilon^{''}_r\\
  &=\frac{1}{2}E_0^2\ \omega\ \epsilon_0\ \epsilon_r^{'}\ \tan(\delta)
\end{align}
$$
Here $\bar{P}$ stands for the time-averaged power loss which satisfies the equation
$$
\bar{P}=\frac{1}{T}\int_0^T U\ I\ dt,
$$
where $T=\frac{2\pi}{\omega}$ is the time period, $U=U_0 e^{j\omega t}$ is the complex sinusoidal voltage, and $I=j\omega\epsilon^{'}_rC_0U + \omega\epsilon^{''}_rC_0U$. The instructions say to use
$$
\begin{align}
U_0 &= E_0h\\
C &= \epsilon_r\epsilon_0\frac{A}{h}\\
V &= A\ h \\
\sigma_{AC}&=\omega\epsilon_0\epsilon^{''}_r=\omega\epsilon_0\epsilon^{'}_r\tan(\delta)\\
\tan(\delta) &= \frac{\epsilon^{''}_r}{\epsilon^{'}_r}
\end{align}
$$

The problem I face is after solving the main integral part, which is like:
$$
\epsilon^{''}_r*(F(T) - F(0)) + j*\epsilon^{'}_r((F(T) - F(0))
$$
where $F(t) = e^{2j\omega t}$ and I neglected all the constants for simplicity.
$F(T)$ is equal to $\exp(j*4*\pi)$ which is 1, making $(F(T)-F(0))$ zero.

I thought of root mean squaring both $U$ and $I$ to begin with, but this gives out $\sqrt{\epsilon^{''2}_r+\epsilon^{'2}_r/2}$ term which doesn't seem to lead to the proof result.

I have a hunch that I maybe missing some elementary calculation basics. I would really appreciate any help that you can offer.


texts: Understanding a Caterpillar Excavator Recomendation for Increasing Life

texts:
I am trying to understand / interpret one recommendation I read on a Caterpillar website for maximizing excavator life:

**

  Never dig over final drive.

**

Can anyone explain what this means? What's the "final drive" and what does digging over it mean?


texts: Will a video projector submerged in mineral oil still work?

texts: I’ve seen folks submerge computers in mineral oil to cool them- but would doing the same to a video projector profoundly throw off its internal optical aspects? I’m considering one of those small “hand held” projectors and having it project from inside an aquarium. I expect it to look cool but will it work?


texts: How does the Xbox Series X "Heat-sink chassis" work?

texts:
I understand what a heatsink does, but I cannot wrap my head around how the newly announced Xbox Series X's heat-sink chassis works. From Xbox:

Heat-sink chassis
A heat sink is a non-electronic, passive mechanical component that has a vital role in the reliability and performance of the Xbox Series X and is integrated directly into the chassis of the console. This unique component of the parallel cooling architecture helps lend to the distinctive design of the console.

The reason it perplexes me is because it seems to be lacking two main factors to be a heatsink. It does not have rows of fins or spikes to maximize surface area to the air, and it does not appear to maximize the surface area in contact with the hottest sections of the circuit boards (GPU/CPU). Is this just marketing fluff?


texts: How can I process plastic to give the impression of a leather finish?

texts:
During the '80s and the '90s, a lot of media cases were made of thermoformed PVC. I believe this trend was created by Disney and Blackbourn with their VHS cases. Then with DVDs, industrial standards for media casing have changed in favor of injection moulded PP.

For example, the latest Neo Geo AES cases are made of PP plastic but early Neo Geo AES cases were completely different. Internal trays were clearly made through thermoforming, as they have strong light reflection properties, but I'm not sure how external cases were made. They give the impression of being made of leather but are certainly some kind of plastic imitation. How were the external cases processed? Is it also PVC?


texts:
WonderBoard is a cement-based backer board mainly used for tiling in wet places. Specifically, its components are Portland cement, expanded polystyrene (EPS) beads, aggregates, and fiberglass reinforcement.

It looks like WonderBoard is also a trademark/

Is there a way to find who holds the trademark?


texts: Calculating real or more accurate specific impulse

texts:
This may fall a little under chemistry processes but I felt it has enough pertaining to aerospace to put it here. Basically, I'm in the process of attempting to develop a way to derive $I_{sp}$ as pertaining to rocket engines rather than rely on charted information.

Since specific impulse is essentially the exhaust gas velocity working against gravitational force,

$$
I_{sp} = \frac{v_e}{g_0}
$$

...it stands to reason that the ideal exhaust gas velocity equation can be substituted in here, giving something like

$$
I_{sp} = \frac{\sqrt{\frac{TR}{M}\cdot\frac{2\gamma}{\gamma-1}\cdot(1-\frac{\rho_e}{\rho}^{\frac{\gamma - 1}{\gamma}})}}{g_0}
$$

The obvious problem here is that this is the ideal exhaust gas velocity, so this is a sort of "perfect-universe" $I_{sp}$. Because most rocket engines use either hydrocarbon or hydrogen/oxygen propellants, water vapor is a major fraction of this exhaust. And as is usually taught early on in chemistry courses, water vapor is a textbook failure of ideal gas behaviors because of its intermolecular forces.

So my question is - is there a "real" specific impulse formula; something like the van der Waals equation for this application?


texts: Calculation of Activity Coefficient Model parameters

texts:
Here is the question, I am stuck on part B:

Basically, this is my thought process so far, as $x_a \rightarrow 0$, the Henry's law line becomes tangential to the actual partial pressure curve.
 Henry's law states that:
$$
p_{\alpha} = Hx_{\alpha}
$$

Similarly, using the activity coefficient model:
$$
p_{\alpha} = \gamma_{\alpha}x_{\alpha}p^*_{\alpha}
$$

Where H is Henry's constant and $p^*_{\alpha}$ is the vapour pressure of the pure component. So at small $x_{\alpha}$ values one can assume:
$$
H = \gamma_{\alpha}p^*_{\alpha}
$$

From this I can get values for the $\gamma$ (I've been given values for pure component pressure). Then I can get values for $\ln \gamma_1, \ln \gamma_2$. My next step would be to substitute in values of $x_2$ and $x_1$ into the given correlations. So, for $\gamma_1$ to be correct, $x_1$ must be very small, assume it is zero therefore $x_2 \approx 1$, therefore:

$$
\ln \gamma_1 = \frac{A \times 1^2}{\bigg( (1-1)^2\frac{A}{B} + 1 \bigg)^2} \implies \ln \gamma_1 = A
$$

Clearly, this is wrong because if I run through the same process for $\ln \gamma_2$, I get a different A value. Can someone please advise, thanks.


texts: Technical Drawing: Labelling a component that's not part of my design but integral to my system

texts:
I am creating a technical drawing of a system I created. Let's call my system, system X. System X is a mounting mechanism for already invented system Y. System Y is customizable, however, system X is a general mechanism that can be fitted to any system Y.

My question is, when labelling my technical drawing, which includes a physical outline of system Y (otherwise the paper would have a lot of blank space), how can I articulate that my general depiction of system Y is replaceable with any customized version of system Y?

I am creating other drawings that detail the mechanisms of X up close without Y, however, in the case of my question, I am trying to create an overview drawing of what system X would look like when applied.

Thank you.


texts:
Here is link of research paper in which spectrum efficiency is given in terms of dB/s/Hz. How can we define it?

https://jwcn-eurasipjournals.springeropen.com/articles/10.1186/s13638-016-0792-0


texts: Can I safely cook on High temperature paint?

texts:
Like a million others, I have a set of enameled cookware that has seen enough use that the enamel has boiled, burned, or chipped off down to the cast iron substrate.  Surprisingly, the outer painted surface that takes direct fire is undamaged.  It seems reasonable, then, that removing the inner enamel coat mechanically (grind or blast or peen) and applying a hard, high temperature coating (engine enamel or powder coat) would restore the finish and allow me to continue cooking/frying on the cookware.  It seems a simple solution that can be done in any home back yard.
However, the obvious question is whether the new coating would off-gas food-borne toxins into the food when heated.
I've searched many "Maker" websites and even asked a Major Manufacturer of one of the coatings and every answer I've gotten is, "Uh, I dunno.  So maybe not."
Is it safe to cook/fry/bake/boil food safely on a painted surface?
(and you guys thought this wasn't a technical question)


texts: Why do the fan or blower of the Air Conditioner not facing the coil flowing hot liquid?

texts:
I observed the fan on external units of air conditioners does not force air towards the hot coil containing hot liquid to make it cooler. Instead it draws air from from the direction of the coil it and blows it away. In my opinion, it would be more effective if the air from the fan was blown toward the coil rather than the fan is drawing air from the coil and blowing it away.

Then my question, why?


texts: How to find a beam for my (simple) application

texts:
I have a spanof 9m that I bridge with a (as yet unspecified) beam. From this beam hangs a load (a pipeline), right in the middle, of 4.295 kN. The beam is simply supported. I want to use an IPE steel beam. How do I go from here to specifiying the exact size? I'd appreciate a specific answer, but more importantly a walkthrough.

I understand I have a bending moment of 5.163 kNm. Now I need to divide this moment by the moment of inertia (that I can find in the right table) and I arrive at a stress. So my question is, which specific of the many moments of inertia my Lölner Stahlbautabellen list is the right one, and what is a decent assumption for  max stress, and what margin of safety to apply.

The purpose of this question is a) to arrive at a size that's no too far off, for puprpose of a drawing and maybe cost estimates, and b) to educate myself a bit. Before the structure is built, we will run this by a structural engineer, which brings me to purpose c) not to look ridiculous with a horribly under- or oversized beam.


texts: How to determine the linear and angular velocity of one end of a rod that is pinned on a track on each side?

texts:
I am working on trying to determine the velocity of one end of a rod that is pinned on both ends into two different tracks. One track is linear and the pinned end has known values. The other side is pinned to a circular track in which no values are known.

I have attempted to obtain the angular velocity first as I am using
$$ V_B=V_A+V_{B/A} $$
by using
$$ \omega = v/r $$
I have also noted to obtain $ V_{B/A} $ I need to find $ \dot\theta $ which equals $ \omega $
$ V_{B/A} $ has the equation of
$$ (\dot\theta\hat k) \times I*(cos\theta\hat i - sin\theta\hat j) $$
I am stuck at finding $\theta$ or $ V_{B/A}$ because it seems both need the other in order to get an answer.
Does anyone have a suggestion of equations to look at to obtain one of those two values with the information known?
Could I treat point A is being the center of the circle and use the formula of $ V_A = r\omega $ to obtain the value for $\omega$


texts: How do I reduce the mains spike in a switched mode PSU?

texts:
I have a switched-mode PSU for a gaming laptop.
It has a bad habit of burning out the switches on mains extension panels when I turn it on (two in the last four days).
The turn-on surge is always audible and spectacularly visible (sparks) if I plug in with the power on.
I don't think the PSU is faulty (I have two to compare), probably just not that well-designed.
I need to turn it on and off fairly regularly - it's not possible to leave permanently powered on.
I qualified in electronics (before SM-PSUs!) and write software these days, but I understand roughly what is going on.
Is there anything I can put in series on the input side to reduce the spike?
A ready made device would be great, but I'm happy to build something.
I'm guessing some sort of inductor will do the job, but I'm not sure of all the factors/trade-offs involved and I'd rather design well than just over-specify, plus I don't have any serious test equipment left.
Or is there another approach?
The PSU is specified as 100-240V / 1.7A AC in, and 19.5V / 6.15A / 120W DC out.
I am in the UK where we use the full 240V.


texts: Autocad start drawing away from the Z=0 (non-coplanar)

texts: I'm having an issue when I draw some elements. They are been drawn away from the Z=0, is causing to be non-coplanar with other elements. So, I cannot make fillets or can find crossing points. I don't want to keep flatten them or setting Z=0 manually. Does anyone know how to start drawing in Z=0 by default? Thanks in advance.


texts: What is the equation to calculate the Thrust coefficient within a set of parameters?

texts:
In the book, Design of Liquid-Propellant Rocket Engines, there is a practice problem written as such.

"Determine the design values of $(C_*), (C_f), and  (I_s)_t$ for the engine thrust chambers of the stages of the hypothetical Alpha vehicle, with the following assumed design parameters."

I am given the fuel, the fuel mixture ratio, the nozzle stagnation pressure $ (P_c)_n $, the specific heat ratio, and the nozzle expansion ratio.

I can calculate $(C_*)$ fairly easy, the problem is calculating $(C_f)$. The book says that you can derive a theoretical vacuum $(C_f)$ using a figure. However when I look at the figure its listing, It does not give me a clear path to derive the equation.

What are the equations I need to calculate $(C_f)$ or the theoretical vacuum $(C_f)$ ( I have the equation used to convert the theoretical vacuum into the actual thrust coefficient. )

Here are the pages I'm talking about.

Fig 1.17 is the referenced figure, however it does not show the equation it uses to graph its chart. What would be the equation needed to graph the chart used in fig 1.17


texts:
I am solving pipe flow problems and it came to my mind how does one find out the minor loss associated with the splitting of pipe.

Here how does one find the minor loss associated when the flow is in either direction.it is the same as contraction/expansion loss or a 90° elbow loss.


texts:
In the following paper:

  Kuhne, Felipe, Walter Fetter Lages, and JM Gomes da Silva Jr. "Model predictive control of a mobile robot using linearization." In Proceedings of mechatronics and robotics, pp. 525-530. 2004.

They have linearized the system using Jacobian:

$$\boldsymbol{\dot x}_r=\boldsymbol{f}(\boldsymbol{x}_r,\boldsymbol{u}_r)$$

Then, I am wondering

1- Is it the only way to linearize the system or are there many methods to linearize and this is only one of them?

2- If there is a disturbance $\boldsymbol{d}$, then using this method, should we calculate the Jacobian around $\boldsymbol{d}_r$ or should we calculate it around zero disturbance? Which one is more common?

3- Is linearization of disturbance in the similar way to the linearization of states and input?

4- Is there any special linearization specific to robust control?


texts: When a copper sheet is rolled into cylinder, it tends to unroll itself. Is there any name for this?


texts: Shop for process data acquisition equipment and software

texts:
I have used the Dataq products for brief data studies to troubleshoot equipment on a manufacturing environment. I am now considering a project to watch pressures, signals and other data collected from processes and issue warnings or alarms if certain conditions happen.
For instance, we are currently logging 5 channels at 100 times/second. These are pressures from pressure sensors on a pump system. We want to start issuing warnings if a pressure spikes over a certain level for more than 0.1 seconds. There are other conditions as well.
My question is what company do you have experience with when it comes to hardware and software? It seems like I could spend 100 hours creating software to do a task like a moving box standard deviation or average, rate of change or other functions to avoid spending 1k or 2k on some nice prewritten tools. I am proficient in C#.
I'd rather not:

reinvent the wheel.
buy into a lousy system because it has slick website
pay an arm and a leg.


texts: Is there a way to construct a self-centering axle?

texts:
Suppose I have a flat plate of arbitrary but connected shape.

If I try to connect an axle perpendicular to the plate it is very difficult to align it with the centre of mass, creating wobble when the axle and plate are rotated.

Is there a mechanical device that can be attached to the axle and plate that causes the axle to be self-centering to the centre of mass of the plate?