texts: sudden expansion in wind tunnel diffuser design

texts:
I have a question regarding my wind tunnel design. Originally the system had a 90mm dc fan pulling air, upon testing I find the design unsatisfactory as air movement was very "weak" ( I used my hand to feel the air moving at the front end ). So I decided to replace it with a 140mm noctua ippc fan, an extra adapter had to be design to fit the new fan.
My question is how severe will air flow be affected by the sudden expansion at the end of the diffuser originally meant to mount a 90mm fan? I am also willing to start over with a new design if that's easier than fixing this. My design is based on this paper
Below are pictures of my design:

Sideview of the wind tunnel, 140mm fan is represented as the box at the end of the wind tunnel, with the adapter preceding it. Missing walls at the testing chamber and diffuser will be covered with thin transparent plastic.

2.Angled view of the wind tunnel

3.Front view of the adapter, connected to diffuser

4.Rear end of the diffuser, connected to 140mm fan

5.Cross-sectional view of the adapter, the angle of expansion was first decided at a constant 22.5 degrees then "smoothen out"

Thanks for reading through all these, would appreciated any input.


texts: Does anyone know how to create the Verilog code for low pass filter in FPGA? I have no idea from where to start the project. Can anyone help?


texts: Self Weight in Moment Distribution (Hardy Cross)

texts: When applying the moment distribution method also known as the Hardy Cross method, how do I take into account the self-weight of columns? In the case of the beams, I can just apply the weight load laterally. However, for the column the load is axial, therefore causing 0 fixed end moment even when there is a difference in the support bending moment reaction.


texts:
I'm looking for a vacuum fryer and so far the only ones available to buy are large, industrial machines.
Is there some technical consideration that makes small scale machines economically unfeasible?
This guy makes his own from a pressure cooker and a pump:
https://www.youtube.com/watch?v=-oSJ3b3KwGU&t=2s
Is a small vacuum fryer for home use feasible? How would the condenser work without using dry ice?


texts: Do non-linear passive pneumatic throttles exist?

texts:
On of the more simple throttles is a channel, which is described by the Hagen-Poiseuille equation:
$$\Delta P = \frac{8\mu L Q}{\pi r^4}$$
This equation, when rearranged, tells us that the Flowrate $Q$ is linearly dependent on $\Delta P$. Do passive non-linear pneumatic devices exist, which are not linearly dependent on $\Delta P$?

For example, is there a pneumatic equivalent to the Thermistor - which has a non-constant $R(U)$-dependency, and as such a nonlinear Flow vs Voltage curve?


texts: What constitutes AGILITY where Behavior-Driven and Unit Testing are concerned

texts:
This morning I had a presentation on PHPSPec which the official website describes as follows:

  A php toolset to drive emergent design by specification.

As defined within an adjective context the word "emergent" is defined as follow:

  the process of coming into being

On the other hand PHPUnit is said to focus on quick code commits and asserting that no code regression occurs in other parts of the code.

With that being said the argument that came out of presentation is that PHPSpec is still a unit test framework which I did, in no way disputed that, but mine I think was more on what the tool really focuses on which is design.

The differences among these two tools is succinctly explained in this article on Laracasts.

Now comes Agile Methodology  which is explained here and here. The latter article on Agile Methodology highlights mentions why this methodology is better (see below for an excerpt).

  When you take the aggregate of agile principles, implement them in an
  agile framework, leverage collaboration tools, and adopt agile
  development practices, you usually get better-quality applications,
  faster-developed applications, and better technical practices (aka
  hygiene).

The view is that PHPSpec offers nothing that PHPUnit does not. However, if we look into the Engineering discipline and what it is about we can almost see the mention of tools (see below excerpt):

  It encompasses concepts, principles, theories, techniques and tools
  that can be used for developing high-quality professional software.

Looking at all this within the perspective of Continuous Integration tools include, in that context, things like PHPSpec, PHPUnit, Behat, Codeception and so forth for achieving varying test strategies. Within an engineering context all these tools have roles to play. However, it does seem that one cannot use the other, particularly PHPSPec, within an Agile environment. What I think lacks is a real-world context where one can really drive Test-Driven and Behavior-Driven Design using these two tools in particular.

I might be wrong in how I have been seeing things within the context of Agility coupled with Software Engineering strategies to deliver high quality code and so forth. I do not claim to be Mr Know-it-all mine is to try and become better and knowledgeable within my profession and thus improve on my skills.

Can somebody please help me understand Agile Methodology when mixed with Software Engineering within the context of PHP and how one can go about implementing a Software Product Development process taking advantage of readily available testing tools and strategies out there? Thank you in advance.

EDIT

This question has been moved into the Software Engineering space. I apologise for posting it here I did not know any better. Thanks


texts: Nonlinear observer of an unknown variation state

texts:
consider following diff equations
$$
\dot{v} = \frac{f_x}{m} = \mu g\\
\dot{\omega} = \frac{T}{J} - \frac{Rf_x}{J}\\
\dot{R} = \eta
$$
where the input is $T$. There is a help equation for slip ratio. The unknown variation is $\dot{R}$.where $\eta$ is a state and variable that I declared. $f_x$, $J$, $m$ and $g$ are known. $R$ is known at the beginning but then it varies.
$$
\lambda = 1-(\frac{R\omega}{v})^n, \:\: n=\left\{-1,1\right\} $$
What I have done is to define some state variable:
$$
x = [x_1,x_2,x_3]^T = [\omega, v, R]^T \\
u = T\\
y = [x_1, x_2]$$
When I build the system I end up with a singular matrix. What kind of observation approach does work on such system to observe $$x_3$$. I really want to use a slide mode observer. Otherwise everything else works.

I would appriate it alot if someone gave me a hint.


texts: Is it possible to measure the "noise level" of an area without using actual microphones which can record actual audio?

texts:
In a way, I wish that the government had put up noise level measuring equipment in every populated area of the country, allowing me to see on a map which areas are the most quiet and peaceful over time.
Sadly, this screams "surveillance nightmare" to me, as these devices probably would be, or could act as, microphones, and thus record the actual sounds/conversations rather than just checking the noise level.
Is it possible to make devices which only measure the noise level, but cannot record/pick up actual speech or human communication? And if so, are those cheaper than the microphones, or would they have to be specifically manufactured for more money? (And thus very likely not be done.)
Is this a "thing" which exists? Or would it have to be expensively invented and then have surveillance-prone people convinced to use them instead of microphones?


texts: How do AC/DC Adapters (Wall Wart) prevent AC Noise Coupling to DC?

texts:
I am wondering if AC noise (EMI) gets coupled to the DC side of the AC/DC adapter,  what are the design methods used to isolate AC noise getting coupled to DC output in an AC/DC adapter. What are the relevant AC/DC adapter (Wall Wart) specifications that can help identify the quality of AC/DC adapters?
Thanks in advance for your help!


texts: Why are there no mufflers for water plumbing?

texts:
People who live in multi-unit apartment buildings often need to be careful not to bathe late at night, because their neighbors will be able to hear the sound of the water going through the pipes.
As I understand it, this sound is made by turbulence which occurs when the water moves through a small orifice such as the valve of a faucet or shower. The vibrations caused by the turbulence travel through the pipes and this is why they can be heard in a neighboring unit.
I have long wondered why we don't prevent this sound transmission by installing mufflers in water plumbing. They would be installed upstream of the constriction point and could consist of any number of shapes encouraging sound to reflect back toward the source. For example, replacing a section of pipe with a pipe of a larger diameter should create two points where sound can reflect, diminishing transmission. Inserting an "S"-shaped segment should have a similar effect. These principles are also used in designing air ventilation ductwork which blocks sound transmission.
Automobile exhaust mufflers come in a variety of shapes and sizes, such as in this 2007 patent or this 2012 patent:

Can anyone explain why the principles that we use to block transmission of sound through tubes of gas, such as the exhaust system of an internal combustion vehicle, or ductwork for a home theater system, aren't useful to create silent plumbing?


texts: Bridge terminology - railing-like parapet

texts:
If a bridge has a parapet that is nota fully solid block and resembles railings with posts, as the following image

What is this type of parapet called?
What are the top, bottom, post, and hole of the railing-like structure called?

Thanks!


texts: Adding phase error to a system based on phase margin

texts: I have a MIMO transfer function and referring to a research work, I have found a phase margin for this MIMO system. I want to check and see the system blow when a phase error greater than the phase margin is introduced to the system. But I cannot think of how to do that either in time or the Laplace domain? Any help or other source to read from is highly appreciated , thanks.


texts: How does a Vibratory Pump ("Schwingankerpumpe") work?

texts:
in my aquarium Ive got a little pump for bubbling air through the water so it is substained with enough oxygen. Internaly the pump works fairly similar to old door bells, where the mains is flowing through a coil thus creating a magnetic field which moves an armature, which again presses air thorugh a hose and underneath the water's surface. (As from the German Wikipedia, https://de.wikipedia.org/wiki/Schwingankerpumpe)

Now one day I looked at my pump as I found out that its housing  is very tight so that air cant come to the inside. I wrapped it up completely in plastic foil, but the air output didnt reduce. I followed the hose with my eyes, but it (obviously) didnt show any holes in it.

Still, I can use the pump (without any possible air input) to fill up a balloon.

How is that possible?

Greetings,

~Cr0n


texts: What happens, when the pump discharge velocity is faster than 3 m/s?

texts:
I am doing a gerotor pump application design.

I know the velocity of the suction port should be 1 ~ 2 m/s to avoid cavitation. Since I have enough space for suction port, it is not a problem.

Yet, the discharge port's diameter must be 16 pi because of the space and sealing problem. I read that discharge velocity should be 3 m/s, but I found the discharge velocity goes up to 4.5m/s when I calculated it with diameter 16.

What would happen if the discharge velocity is over 3 m/s?


texts: How to go from a Lagrangian to an Eulerian description of the velocity of a particle

texts:
Let's say that a fluid is undergoing a one dimensional motion with the following velocity field: $\mathbf{U} = V(x,t)\mathbf{i}$.

The problem asks to find $V(x,t)$ given that the position of a particle initially at coordinates $(x_0,t_0)$ is $x=(x_0/t_0)t^2$.

I first wrote the langrangian derivative of $\mathbf{U}$ and equated it with the acceleration of a particle $2(x_0/t_0)$. This led me to a transport equation and ultimately to a wrong result.

So, I've been thinking about it for hours and I'm really getting nowhere. Any help is appreciated.


texts: How to find phase proportion at equilibrium - from iron-carbon diagram - Leblond

texts:
{Equilibrium proportion P, this is the proportion which is reached at a constant temperature after an infinitely long time:P is also the austenite proportion in the case of extremely slow heating. It is determined by the fact that the free enthalpy of the pearlite-austenite mixture is a minimum at the temperature T for this particular proportion P. It can be read from an iron-carbon diagram (incorporating effects of alloying elements).}

above {Equilibrium ....} read from journal paper.
My question is how to find P from the iron-carbon diagram??
Explain in detail if possible with example.
Thanks


texts: What is the pressure of water-dew resulted from cooling of atmospheric air down to dew point temperature?

texts:
Suppose, In a room, Air is at 1 atm presssure. So should be the pressure of any water surface in the room. If the room temperature is cooled downed to dew point temperature, vapor (moisture) will start to condense at Tdp (dew point temp) and Pv (vapor pressure). In this phase changing process, the temperature and pressure of both saturated vapor and saturated liquid will be same and constant. (Tdp, Pv).
So, the pressure of dew (saturated liquid) is Pv or 1 atm ? suddenly changes like jump discontinuity? what am I missing?


texts:
I need to calculate the tonnage a medieval wood screw press could generate. In particular I’m speaking of a press used to squeeze water from newly formed sheets paper in-between layers of felt (see picture) however medieval wood screw presses used to extract olive oil or juice from grapes are identical.

I am not an engineer but I will be giving a PechaKucha (a short 6 minute 40 second lecture) to a group of hand papermakers in a few months from now in which I will include the concepts of simple machines like the lever and the inclined plane to gain mechanical advantage.

Such presses exist in museums throughout Europe however being over 500 years old we are unable to use these to test the actual force. Here’s what I already know. The formula for calculating the ideal mechanical advantage on jack screws is straight forward which includes the advantage gained from length of the lever and the pitch of the thread. The much more difficult part is allowing for friction.

I’ve read that even well-lubricated jack screws have efficiencies of only 15% - 20% but that’s for a machined iron screw. The threads on these wooden screws were chiseled by hand with the most difficult part being the inside threads of the nut.

So my question is – is it possible to calculate the efficiency of a hand carved wooden screw? Presumably the upper limit of efficiency would be less than the 15% noted above (and is this 15% figure is correct in the first place)? But what might be the lower end of efficiency be?

Here are the dimensions of the wood screw


texts: What Goes Into Making a Variable Field Magnetic Motor?

texts:
(I feel it is necessary to mention that I am not an electrical or mechanical engineer; I just like to build fun things.)
I've already got a good explanation of the concepts involved in a variable field magnetic motor, but how is it achieved? It surely can't just be a DC motor with a retractable stator, right?
Here's an example of what I'm trying to make: https://www.youtube.com/watch?v=olnXy-J48SY
It really does look like a simple DC motor, but every one of these I've seen has that brown padding at the top of each armature loop. Is it something vital to the contraption?
I've scoured the internet, but there isn't a whole lot that goes further into this than the concepts involved. I realize this may force you to dead-reckon, but I'm desperate for information by now.


texts: How much seawater could be desalinated using the waste heat from a powerplant?

texts:
I've done some rough calculations on how much water could be produced by using the waste heat of a powerplant to boil seawater.

I'm interested in a ballpark figure and would like to know if I have a major flaw in the calculations.

A 1MW plant with 1/3 efficiency can boil 17 moles of water per second assuming that the water is at the BP and it takes 40KJ/mol to boil it.

17 moles of water is 300g.

In one day the plant boils 26 tons of water.

One acre foot is around 1200 tons.

California uses 110,000 acre feet per day.  This is 132,000,000 tons per day.

This could be produced by 5,100,000MW.

It seems like this potential source would be a drop in the bucket in terms of meeting water needs.


texts: What sort of plastic is this? What would you call this color scheme?

texts: I saw this plastic on a baby changing station and was wondering what sort of plastic it was. It seems like injection molding plastic but I'm not sure which one and also what pepper color scheme that is.


texts: Can a propeller be used as a balancer by spinning it perpendicular to ground?

texts:
This is a unique idea of mine. In the above image, the torque reaction propeller is rotating clockwise producing a side-thrust of 40N. With its reaction torque alone, it has to balance the moment generated by the payload on the other side. So...

Regarding this, I put my arguments as follows. Please choose one of these as correct one or create your own concept to solve the issue I'm having.

Argument 1
I've also read somewhere that the yawing torque of a motor is the torque of the motor itself. If this is the case, the torque of the propeller will be:

This result is based on the assumption that the relation
Rotational power=torque×angular velocity holds true in this case where a propeller involves.
The torque so obtained will not be enough to balance.

Argument 2
If this torque is considered to be leveraged by the distance from the pivot upon which it acts, units on both sides of the equation doesn't balance.
Refer eqn.1 in image 2 where the LHS would be in N.m and the RHS would be in N.m-squared if considered to be leveraged

Argument 3

In this case, at the mentioned distance of 8.75cm, the frame will be level.

Argument 4
Here, the torque we obtained from eqn.2 in image 3 is considered as a rotational force acting at a distance, which is the propeller's mean radius, from the centre of the hub.

In this case too, like in the previous, the propeller torque reaction will be able to hold the frame level albeit at a greater distance from the pivot.


texts: Special Considerations for Steel Plate Marketed for Laser Cutting

texts:
A contractor working for me on a steel construction project is using a steel product they refer to as 'laser plate' which is marketed as specifically as having good performance on laser cutters. This doesn't appear to be a trade name, but a colloquial term. Looking at the material, it has little to no mill scale, but doesn't look quite as clean or shiny as other plate I've seen sold as 'hot rolled, pickled and oiled.' The contractor assured me that the plate conforms to ASTM A36, which is all my project requires, and I'm requesting a mill certificate to confirm that.

Provided it is certed for A36, are there any special concerns I should have about this special steel? In general do steels marketed for lasercutting have a different chemical composition, or do they just have the mill scale removed? The closest source I've been able to find is here, (PDF) which suggests that lower silicon may have some influence but mostly just in how it affects mill scale adhesion.

To be clear, I'm only asking about the type of material. I'm familiar with concerns relating to laser cutting as a process and am not concerned about it.

The plates they are using range from 3/16" thick to 1/2" thick and the plates will be welded according to AWS D1.1.


texts: Can I benefit from using a real axle as a shaft of a brushless motor on my RC car?

texts: I'm designing an RC car and considering two options now. I can put some gears into it, so that I would have a certain gear ratio between motor and axle, or I can remove shaft from the motor and, instead, put in the axle with wheels on. I want to avoid overheating of the motor primarily, and if it's ok, it would be great to raise the output power. So I want to ask whether the motor based on the axle would overheat or not, and is this way beneficial in terms of speed and construction?


texts:
I want to build a bitcoin "flip-clock" price ticker.

I want to build a physical number flipper, with numbers from 0-9. I was thinking about LED matrix, or e-ink display, but that's not as exciting as a real flipper
The price would get updated every 5 or 10 minutes, by checking some public API
Everything would be controller by Raspberry Pi, Arduino or similar single board computer

I want to make as many things as possible from scratch.

Design the 3D parts
Print the 3D parts needed
Wire and assemble things together
Write the appropriate scripts

I chose this project, because it would be something cool to have on a desk, and would serve a purpose. Plus it involves a lot of different fields I want to play around in, but at a fairly light level:

3D printing
3D designing
Engineering
Programming

Now here's the problem... I have no idea where to start.
I'm good at fixing things, taking things apart and putting them back together, had quite some experience with 3D programs like 10 years ago, have some experience with programming (php, js). But I never built anything from scratch.
So, I'm not sure whether this is the right place, but I want to start a thread to continuously ask questions, and progress forward.
First things is first is probably choosing the setup?
I was thinking Raspberry Pi or Arduino? I would only need a simple computer which would be able to connect to the internet (preferably wifi) and fetch the price every once in a while.
Maybe having a Raspberry Pi would be an overkill? As I only need a simple operation. And preferably I wouldn't want to rely on SD card (maybe I am wrong, but I think they might die off after a while, since this ticker would be on 24/7)?

Any thoughts, comments, suggestions are welcome!
Also, if I am in a wrong board / site, I appreciate if you would point me to the right direction.

UPDATE
I found a good open-source split-flat project: https://www.tindie.com/products/scottbez1/split-flap-display-kit-4-characters/


texts: Convection and radiation heat transfer coefficients

texts:
I have a problem where we have given conditions:

Inner temperature is: 20 celcius
Outer temperature is: -5 celcius

Between these temperatures we have a wall, made of:

50mm of mineral wool with thermal conductivity of $\lambda=0.04\frac{ W}{mK}$
and 270mm of tile with thermal conductivity of $\lambda=0.6\frac{ W}{mK}$

Tile is on the inner side of the wall and mineral wool is on the outer side.
Now I need to figure out the heat transfer coefficient of convection and radiation.
I have tried to take Gr and Pr from VDI Heat Atlas table for properties of dry air. With that I got $R_a = Gr*Pr = 127 000$ and Nu = 0.092 *127 0001/3 = 4.6.
Then I calculated the coeffiecient of convection (a):
$$a = \frac{Nu * λt}{  Lt},\qquad jossa \quad \lambda t = \frac{4.6 * 0.6 W/m·K}{  0.27 m} = 10.22… \approx 10.2$$
and for coefficient of radiation (b):
$$
b = \epsilon \sigma(T_{p2} – T_{y2})(T_{p} – T_{y})$$
$$b = 0.93 \cdot  5.67\cdot 10^{-8} \frac{ W}{m^2K^4} \cdot  (287.952 + 293.152) \cdot  ( 287.95 + 293.15) $$
$$ b= 5.173… \approx 5.17 $$
I took the value from emissivity from a website that specified emissivities for different types of tiles, not sure if it's right.
Now, shouldn't thermal resistance for inner surface be 0.13 and reciprocal of total heat transfer coefficient. With my values, it isn't:
1/(10.2+5.17) = 0.065 != 0.13
What is wrong with the calculations?


texts: Does gear diametral pitch have to be an integer? (teeth/diameter)

texts:
I'm doing a gear design project, and I'm using a multivariate mixed integer non-linear optimization suite known as Couenne distributed by COIN-OR. Within Python, I use this solver to solve for all aspects of the gears in a 2 ratio reverted gear-train given 2 target gear train ratios (4.3 fwd, 9.1 rev). My classmates are telling me that the diametral pitch for each gear pair must be an integer value, or a value with a well known fraction in decimal form. Is this true? I've found that placing this constraint makes it much harder to approach the 2 target ratios. Perhaps it was a consideration about manufacturing, because It would be exceedingly hard to machine a diameter that is an irrational number. However, couldn't the same be said for any diameter? Manufacturing shouldn't depend on the dimension because for any given manufacturing precision we will never know what is after the decimal place. For both irrational and integer diametral pitches, the manufacturing error would be the same. So why would gear diametral pitches have to be integer values?

Without this constraint, I'm able to achieve a total gear train ratio error of 1.3*10^-8 percent from the target ratios.

EDIT: when I refer to "diametral pitch" I am referring to the gear module, number of teeth per inch


texts: Creating holes in the assembly in Solidworks

texts: I have 2 parts in an assembly that I am trying to connect using 2 bolts. I want to create the holes by creating 2 circles on a surface and by cutting through both objects using the circles. If I do this using the Extruded Cut option in the Assembly Features, I am able to create the holes in the assembly but the original objects don't get updated with the holes, so I cannot export them as STLs (they only exist in the assembly). If I try to create the holes with the Edit Components option, I can edit one of the objects, but it doesn't affect the second object at all (the hole only goes through the first object and disapperas on the second object). I am confused. I need to do that change on the assembly, because it is difficult to align the holes if I edit the parts separately. What am I doing wrong?


texts: Safety of suspended (drop) clay ceiling tiles

texts:
Drop (suspended) ceiling tiles are of course quite common, but I am in the process of trying to evaluate the long term safety of a specific kind of suspended tile made of fired clay.

When installed it looks like this

The tile measures about 12 inches x 9 inches and weighs 2 kilograms.

Now the important point is that the tile is supported only on two ends and therefore a single breadthwise fracture causes it to lose all support. In such cases it has been observed that it may sometimes "hang in" for a few days before it falls out, but I don't think that is necessarily true. This type of tile has been widespread in its use in India for over a century now, and also in parts of Europe. Experienced engineers and architects of repute think this is as safe as any other type of suspended tile ceiling. From its design it seems that is not true. However its widespread usage seems to indicate that I am missing something. Does any structural engineer on the forum have an opinion or observation? Is this really as safe as any other suspended tile? If so what makes it safe despite the observations above? Thanks!


texts: Acoustical Design considerations for Active Noise Cancellation Project for Air vent

texts:
I am working on ''Active noise cancellation for air vent'' project. I am using NI myRIO1900 it has FPGA module(Xylinx Z-7010) , Audio Technica ATR 3350 omni directional microphones and Tevion Loudspeakers. I have done the programming using LabVIEW . I am using sinusoidal noise source of (200-500 Hz) as test noise signal to simulate the noise.

I have implemented LMS(least mean squares) algorithm on LabVIEW, as a preliminary results I am getting around 8dB noise reduction but these results are pretty random in a sense only at certain volume levels( if I adjust very carefully), the noise cancellation is happening and the variation in step size is not giving any decent change ( again I have to make volume level changes to see some results).

Over all, I am getting some results but I don't have control over the results.

This is my set up

[the pipe length is 1 meter]
I know I have to consider secondary path modelling and feedback modelling. I have actually completed the coding of FBFxLMS(Feedback Filtered x LMS Algorithm) also but I don't have any reasonable results with this also.

I have read in 2-3 places that without proper acoustical design it is not possible to reduce the noise effectively. Quoting from this paper page 5

  ''If the acoustical design of the system is not optimized,the digital
  controller may not be able to attenuate the undesired noise
  adequately.''

I am using this paper as my major reference.
The only point I am aware of is using low frequency noises (<= 500Hz) to consider the sound wave propagation as plane acoustic wave. I am completely unaware of any other details on how to better my acoustical design.

I am wondering how to improve the acoustical design of my setup for effective noise cancellation?
What are the problems using just cardboard material to simulate the environment of air vent ?

Please help me if some one has experience with ANC or Acoustical design.

Edit:
I am just using this model as prototype to demonstrate effective and controlled Active Noise cancellation.I don't have any practical model to compare to(right now!).
I am looking for some useful references or previous works dealing with acoustical design of Active Noise Cancellation(ANC).

Edit2:
More details:
1.In the picture the Anti noise speaker has just been inserted without proper sealing.


texts: Inconsistencies with units for thermodynamic identities

texts:
I am working out the temperature for an Ideal diesel cycle:
Based on the isentropic properties for an ideal gas.
$$T_f = T_i * r^{k-1}$$
Where $T_i = 50 ºF = 510ºR$
If I use ºF, then $T_f = 172.9ºF = 632.9 ºR$
If I use ºR, then $T_f = 1763 ºR = 13030 º F$
It gives me completely different temperatures; how am I supposed to determine which one is correct?


texts: How do you exclude the connections between mechanical shaker and specimen?

texts:
to apply any kind of vibration, shock input using a mechanical shaker to any specimen, you first need to connect the speciment to the shaker, that sometimes needs some connectors that could weight as much as the specimen.
This means that the shaker, would need to apply more force to move the specimen ( like in case of imposed displacement). How is the effect of the excessive connector omittable ?


texts:
I'm an EE, but I'm working on a project at work where I need to venture into materials science & chemistry.

My question is, does thermoplastic, Polybutylene terephthalate (PBT), fall into any of these material categories?


texts: Does a Mechanical equivalent of an Integrator exist

texts:
In electrical domain, we have resistors, capacitors, and inductors as fundamental constitutive elements. Similarly, in mechanical domain, we have masses, springs and dampers.

In most of the literature, we can immediately see that they have the one-to-one relation, perse i.e., we can go from one form of representation to other, or even mix them up (mechatronics). However, the problem I see is, in the electrical domain, we have the inductor which is an energy storage element, representing an integrator, collectively speaking. In contrast, when we look it up in the mechanical domain, all we have are mass-spring-damper equivalent, and there is no explicit representation for an inductor.

So, my question is this, does there exists a fundamental equivalent for an inductor in mechanical domain i.e., a mechanical equivalent of an integrator with a physical meaning in itself. If so, how it is called?

I have tried a lot of literature to find one but failed in the quest. So, all your help and suggestions are welcome.


texts:
I have this example:

$M_k$ = 80 Nm
$d_1$ = 30 mm
$d_2$ = 20 mm
$a$ = 600 mm
$b$ = 500 mm
$G$ = 8,5e4 MPa

I want to know the twist at free end of this shaft. I am using the formula:

$$\phi = \dfrac{M_k \cdot a}{G \cdot \dfrac{\pi d_1^4}{32}} +  \dfrac{M_k \cdot b}{G \cdot \dfrac{\pi d_2^4}{32}}$$

It gives me 0,037 rad.

But the result in the book is 0,013 rad. Where is the error?


texts: Can someone please explain why the top left image is correct and the bottom left image is not? Both of these images have the bolts on the lower half of the wood beam (tension) side.


texts: Inline ducted fan/air turbine blade design to maximize output torque

texts:
I've currently got a mechanism that is powered via a shaft connected to a ducted fan. The ducted fan is powered by an existing air flow through the duct. I am looking to re-design the fan to increase torque/performance. The fan will be injection molded and is about 2" is diameter. With no-load, the current fan spins at 10k RPM. I need to make measurements under load, but it's significantly slower.

How can the parameters of the fan blades be adjusted to maximize the output torque?


texts: Determining required torque for a chain and sprocket conveyor belt

texts:
I am working on a project for an electronics class, but need some help with one of the mechanical details.
My job is to program a stepper motor to move a conveyor belt back and forth as specified. The "belt" will have a chain and the shaft of the motor will have the sprocket. But before I choose my stepper, I need to know what the required torque for my stepper motor is. Unfortunately my physics knowledge isn't great, so I googled to find the equation I should use. This is what I came up with.

I also found this equation which comes out to be similar to the above equation except this one doesn't have the efficiency and gear ratio involved.

So I have 3 questions:

what kind of force would I calculate for F? If the object is laying flat horizontally, what kind of force would be pushing against it east to west?
the two equations give me very different results due to the efficiency and gear ratio. when would I use one equation over the other?
where would the required speed come into the picture? if I want to move my object quickly vs slowly, would this affect the torque needed?

If you are still reading this, I thank you for your time, and hope you could help me with any or all of my questions...

Thanks :)


texts: How can a clutch engage gradually without wearing away very quickly?

texts:
Here's an animation of a gearbox and clutch from Wikipedia.

I learned to drive recently, and was surprised at how the clutch worked, engaging gradually as I moved the pedal by fractions of a millimetre.

How is this possible? It looks like the gears would be pretty quickly stripped away.


texts: Can we use an open expansion tank in solar water heating system?

texts:
We all  know that in an indirect (closed loop) hydronic system, an expansion tank is needed ,to deal with thermal expansion of the circulating water, that can be either open expansion or closed expansion tank however I've mostly seen indirect solar water heating systems with closed expansion tank.
Can we use open expansion tanks in this type of system?


texts: Isentropic Flow and Conservation of Mass

texts:
I have some doubt on fluid mechanics that need some confirmation. I am on the section that discusses about compressible flow and the effect of variation of flow cross section area.

It stated that that an isentropic flow would obey conservation of mass and what I wonder about is that any chance that an isentropic flow would disobey conversation of mass?

What made me wondering this was I was considering the mass flow rate of isentropic flow in converging-diverging nozzle. If my understanding towards isentropic flow is not wrong, the mass flow rate of an isentropic flow would always be constant no matter of what position it is in the nozzle.


texts: Is nonlinear control slower than linear control?

texts:
Is there any scientific comparison between linear and nonlinear systems?

I often hear that

  Nonlinear control is more sluggish than linear control.

which makes sense. But is there any research or any claim based on practical experience which supports this claim?


texts: Why does flow separation cause stall when it creates a low pressure zone?

texts: In an airfoil, a low-pressure region forms in the turbulent wake created when the flow separates. Wouldn't this cause an increase in the net vertical force acting on the airfoil since the pressure at the top decreases?


texts: How to know whether the flow is supersonic in a nozzle?

texts:
For a project I had built a convergent divergent nozzle designed for Mach number = 3. In that project, I could know the flow has gone supersonic by seeing the manometer fixed between the throat and the divergent section (drop in pressure, as the divergent section acts like a nozzle for the supersonic flow).

However, this got me thinking, If I am to build a nozzle for the propulsion purpose (or any practical purpose), it is not desirable to have holes in it for the manometer in order to maintain the uniform strength. My theoretical calculations tell me that the flow should go supersonic and no shock in the nozzle, but while building, the surface finish, geometric tolerances and supply pressure might not be what I expect. In that case, how do I know if the flow has gone supersonic?

I thought about following ways. So far I haven't tried any of them.

Using a Pitot tube might not be useful since there will be a bow shock in front of the tube if in case the flow is indeed supersonic (as shown in the figure),  which will increase the total pressure. We can use Reyleigh pitot tube formula, but how to compute static free stream pressure without affecting the flow / nozzle?
Schlieren Photography: If we see oblique shocks / shock diamonds, then the inference will be: 'flow is supersonic'. This will work only when the shock features are super clear.


texts: How does this one-contact solar cell work?

texts:
I am unable to grasp how this only-rear-contact solar cell works. From what I understand the solar cell produces electricity by making the top and bottom side of solar cell complementing each other (that's why putting Al and Ag paste on both sides could be completing the circuit)
Thus, for this, how?


texts: Method for determining pump characteristics

texts:
I have a rotary pump and want to gain knowledge about its characteristics. I have an uncalibrated flow meter. At best I want to get a flowrate/pressure-diagram.

I understand, I need to analyse the flow sensor in advance.

Things I have:

Voltage and current measurement equipment
Counter and/or microcontroller for evaluating rotary sensor pulses
oscilloscope
vast set of tubing and fittings which can be connected to the pump and the flow sensor.
graduated beaker

Things I don't have:

Pressure sensors
calibrated sensors
calibrated pumps.

My questions:

Can I gain pump characteristics without usage of pressure sensors?
How can I calibrate the flow sensor without a calibrated source of flow rate?
What is a setup for getting the full Q/P-Diagram without?


texts:
I know there are some aspects we can try to apply this surface area to volume ratio to say physical chemistry in order to see reactivity of chemicals. However I am very confused in my structural engineering elective course, it states that surface area to volume of high rise tower like structures is very important. I do see that the SA:V ratio of certain shapes in general give a very interesting and neatly simplified expression once computed, but I do not see what the application of SA:V ratio is when building structures of towers (Eiffel tower CN Tower etc...).

Can anyone help me explain the significance of SA:V ratio when building high rise structures (I would appreciate technical details as engineering is not my major of study i want to understand alittle better)?


texts: What is the appropriate type of controller for this system?

texts:
I am given this transfer function for a system:
$T\left(s\right)=\frac{9.81}{s^4+0.5s^3+11.2815s^2+4.905s}$

Now, I want to design a controller that will make the closed loop system have an overshoot due to a step input equal to $5\%$. A controller with a proportional gain $K_p=1$ gives me this step response of the closed-loop system on MATLAB:

As you can see, the overshoot with this proportional gain is way bigger than $5\%$. As K increases, the response becomes weirder.

Here, I have tried $K_p=6$:

PI, PD or PID controllers give a similar response to the figure above. So, it seems the best I can do is a controller with $K_p=1$, which is not acceptable in my case.

What would be the appropriate type of controller for this system to get a small overshoot?


texts: Does westinghouse braking system prevent using anti-lock system?

texts:
This question concerns the Westinghouse braking system. If I understand correctly this video, in an emergency braking (e.g. in case of failure in main air pressure line) the pressure in the main pressure line decrease rapidly (main pressure line vented to the atmosphere), triggering the brakes. Brake cylinders are then pressurized with no modulation in brake cylinder pressure.
Anti lock systems are important on slippery rail track, especially due to fallen leaves as explained in this article (fr) and this article (fr). If I understand correctly, anti-lock braking system works by modulating the pressure in braking system. In case of emergency braking, the anti lock system must modulate the pressure in the braking cylinder.
The modulation in braking system pressure needed for anti-lock system seems to not be compatible with the emergency brake feature of the Westinghouse air braking system.
Can anti-lock system be fitted on a Westinghouse air brake systems? If so, how does it works in case of failure in main pressure line?


texts: Why is finite elements method not part of electrical engineering curriculum?

texts: The question is straightforward. FEM is a third year course in mechanical engineering but not generally taught in electrical. Why is this?


texts: Material with strongest grip on Aluminium 6061

texts:
Attached is an example picture of a clamp that will be attached to a pipe made of Aluminium 6061-T4. The clamp should have very tight grip on the pipe and prevent it from slipping or rotating but the Aluminium pipe is fragile and so the clamp cannot be tightened too much. Thats why I am looking for a material for the inner surface of the clamp that will provide a firm grip on the Al pipe without requiring too much tightening force.

The clamp-pipe interface material (shown here as the black rubber-like thing) should have a very high coefficient of static friction with Al6061 in order to provive a tight grip. I want to know what materials are best suited for this purpose? Which material has the highest coefficient of static friction with Al6061?

My research so far:

The best material I could find is rubber that supposedly has a coeff of static friction of 0.8 with Aluminium. (source: http://atc.sjf.stuba.sk/files/mechanika_vms_ADAMS/Contact_Table.pdf)
Surprisingly the coeff of static friction between Aluminium-Aluminium is 1.05 !! So does it mean I should use aluminium in the inner surface of the clamp instead of rubber? sounds counter intuitive. (source: http://www.engineershandbook.com/Tables/frictioncoefficients.htm)
If I use a material like rubber or silicone, should I consider any texture on the surface? Are treads better than a smooth surface?

I am not an expert in these things and so I would greatly appreciate if someone can either suggest me a meterial or educate me on how to select the right material that will have the best grip.

Edit 1: To visualize, imagine the pipe is held vertically by the clamps and a weight is attached to the bottom of the pipe, what material at the pipe-clamp interface will allow me to hang the heaviest weight?

Edit 2: The surface of the pipe is smooth to touch with matt finish, not mirror polish. Its actually anodized. Any damage to the pipe like denting or clamping marks is absolutely not acceptable. Also the pipe needs to be re-positioned occasionally, to do so, we loosen the clamp, slide the pipe to position and then tighten the clamp again


texts: Modelling gas desorption from a still solution (e.g. a beer)

texts:
The common way to model or estimate gas (e.g. CO2) desorption rate from a liquid solution is by using an equation similar to this one

$J_{CO_2} = -k_L a(H·C^G_{CO_2} - C^L_{CO_2})$

where $J_{CO_2}$ is the molar (or mass) flowrate, $k_L$ is the mass transfer coefficient, $a$ is the specific contact surface, $H$ is one of the many expressions used for Henry's constant, and the G and L scripts stand for gas and liquid phase respectively.

The problem with this approach is that all the correlations I know used to estimate $k_L$, $a$, or most commonly $k_La$ imply that there is a gas stream with a given gas velocity (e.g. aeration or sparging).
How could I estimate $k_La$ for a still solution, for instance a glass containing beer where the gas bubbles are stripped slowly? Furthermore, if I wanted to assess the effect of stirring the beer with a spoon, how could I estimate the effect?


texts: Why are the processes called "Precipitation Hardening" and "Solid Solution Strenghtening"?

texts:
Does precipitation hardening really only make the material harder while Solid Solution strengthening makes it stronger altogether (thus increasing the area under the stress-strain-curve edit: excuse the mistake here: the area under the stress-strain curve denotes the toughness, not strength)? If so, then what is the reason behind this? Don't both mechanisms work by impeding dislocation gliding (one through precipitates and the other ones through introduced strains)?

In this link, it is mentioned that "The high tensile strengths of precipitation hardening stainless steels come after a heat treatment process [...]", which suggests that hardening indeed also increases strength. Is there a specific reason for why the names were chosen in this manner?


texts: Difference between Reactive power input and Reactive power consume by Load?

texts:
In a power electronics converter is there any difference between reactive power input to the converter and reactive power consume by converter? (In case source current waveform is square in nature).
If yes then how we can calculate the difference between the two reactive powers?


texts: periodic rotational conditions in Fluent

texts:
I have one question:

In Fluent, should be generated same mesh in rotational faces for creating periodic rotational conditions?

Is there a way that unmatched meshes are applied for creating periodic rotational conditions?


texts: Determining steady flow between two reservoirs with two different pipes in between

texts:
Two reservoirs are connected by two pipes with different diameters in series. The elevation of Reservoir A is 40m and Reservoir B is 35m to respective water surfaces. The first pipe is 500 m long with a diameter of 0.075m and the second pipe is 2000m long with a diameter of 0.1m. What is the flow between the two reservoirs? The absolute roughness is 0.01 for both pipes and teh pipe elevation is constant.

What I have tried so far is by trial and error in the Moody Diagram find a Friction Factor to use with the Darcy-Weisbach Equation. However, I cannot get a number matching my first guess of the Reynolds Number. The pipes have different diameters so that means I have to do a trial for each pipe. Also when calculating I cannot use the Head loss of 5m but of 1m since that is the correspondent Head Loss for that length of pipe? How do I go about solving for the problem above?

Thank you for your help.


texts: What is the name of optimizing space between laser cut parts?

texts:
When we send some drawings to laser cut operation, they use a proprietary software (usually specific to the laser machine) to duplicate the drawings per request, with the spaces between parts optimized. It's a bit like "panelizing" operation in PCB manufacturing.
What is the name of this optimized assembly operation? (How can we find a proper software to make it by ourselves?)


texts: Can PWM be used to control the flow of a solenoid valve?

texts:
Most cheap pump can achieve, according to the Amazon page, around 5 PSI and I would need something a way higher that can still be controlled.

I have this solenoid valve.

Can I use pulse-width modulation (PWM) with a longer time period to control the flow of a pressurized liquid? Will that  damage the valve? What is the accuracy of the valve?


texts:
I have an EtherCAT loop with a servo motor that is controlled at 2kHz. An outer loop running at 1kHz has to calculate the demanded torque for the servo motor and send it through UDP.
The motor needs to respond to a request that includes demands for position, velocity and acceleration.
I need to implement a control loop that is able to convert the three parameters (position, velocity and acceleration) in a torque number. If I calculate the force starting from the velocity, then I need to control overshoots and promptly reduce the demanded torque without undershooting. If I calculate the force from the position, then I loose the velocity and acceleration component.
What are the best resources to read to start this project? Or what block diagrams are best suitable for this use?
Let me know if I need to be more specific
EDIT: The load applied to the motor is human force changing between 0daN and 60daN. The lever length is 0.2m with an angle that can be approximated to 90deg for the whole travel

Some numbers: the motor has a gear ratio of 1:8 and the travel limit is 27 deg (216 deg at motor shaft). It needs to be reactive enough to change velocity (at gear output) from 125deg/s to -50deg/s in 60ms with a tolerance in demanded position of 10%. The motor itself has a specified maximum velocity of 720deg/s and max continuous torque of 240Nm at gear output. The servo drive runs at 8kHz


texts:
I need to get another component like this but I can't seem to find any manufacturers / retailers.

To describe it:
It is spring mounted on a shaft and retained by bushing on the top and an enlarged shaft diameter bottom. E-clip on top is for securing shaft in place. Spring pushes the pin down.

If anyone knows what they are called, I would like to know.


texts:
I am working at a construction site and came accross this issue. a borehole needs to be expanded in length inside a container-office. Working space is as little as 6m x 3m (19ft by 9.5ft). Height of the container is about 2m (6'6"). Heigt can somehow be altered up to 5 meters (16'5"). Borehole diameter is 150mm (6"). Current depth of the borehole is 30 m (98 ft). The depth should be increased to 42m (138 ft). See the attached sketch for details.

The borehole was bored before the containers were placed. It is used to measure water levels with piezometric sensors inside them. Water levels have dropped lower than expected and the borehole needs to be expanded in depth to reach lower groundwater deposits. Containers cannot be moved, and the location cannot be changed since this specific borehole is in a sensitive location, so please do not offer boring a new borehole outside the container.

What method or which equipment can be used to work in a small container space and can reach such depth.


texts: Why use rectifier / inverter in locomotives?

texts:
Image Source

Why not just take the AC from the alternator to the motors? Why go AC to DC to AC again?


texts:
I'm solving this problem in mechanics,

Two cylinders A and B, weighing 100 lb and 200 lb respectively, are connected by a rigid rod curved parallel to the smooth cylindrical surface shown in Fig. P-329. Determine the angles α and β that define the position of equilibrium.

I already understood that the relation between $\beta$ and $\alpha$ is  $\cos \alpha = 2 \cos \beta$ by doing summation of moment with respect to O and equating to 0. What I don't get is how come the angle from this picture becomes 90 degrees?


texts: What happens in Thermal boundary layer in a flow with cooled plate?

texts:
All the notes on Thermal boundary layer(TBL) explains the growth of TBL over a heated flat plate ie cooler fluid is flowing over a hotter plate (heat is flowing from the plate to the fluid).
How does the thermal boundary layer develop over a chilled plate, where hot fluid flows over a chilled plate. Also, Can you please direct me to any notes or text that deal with this?


texts: What are the regular holes in poured concrete walls called?

texts:
These holes are caused by bars that are put through the frame before the concrete is poured and then clamped, so the mold can't swell outward.

Is there a name for these holes though that is widely recognized?


texts: Mechanics of Solids / Strength of Materials

texts: I have shared a question from mechanics of solids and my solution with it, as you can see I am trying to take the derivative of the stress equations to find the min, max points but its going wrong. I need to know why my solution is wrong.


texts:
The conventional wisdom consistently holds that "oil (or grease) attracts dirt", giving rise to the need for seals and dry-lubricants.

But I've always considered that to be loose thinking, the truth being closer to "oil retains dirt (dust, grit)" and that there are no electrostatic, magnetic, or gravitational forces at work actually drawing loose particles into an oil film.

Is my intuition correct or does an oil or grease film actually exert some attractive force on airborne particles?


texts: Most efficient fillet design given an envelope (for stress)

texts:
If one has a specified allowed X length and Y height, into which a fillet can be placed to reduce stress concentrations, is there an equation which can be used to determine the optimal shape of the fillet?

I have looked into Baud Fillets and Thum-Bautz fillets, but I find that although these fillets work fantastically for a desired y height OR a desired x height, these don't work well when one has constraints on both of these dimensions. Furthermore, it seems scaling the fillet shape along the axis does not work well, in many cases ending up worse than a circular fillet.

If it is relevant, this is for fillets that are to be placed on the ID or OD of steps in tubing.

I know one option is various shape optimization algorithms, but I was hoping that there was some kind of out of the box solution that I could use to hopefully avoid this.


texts: With which parameter can you specify whether a metal is ductile or brittle

texts:
I have to do a durability approval of feather key (shaft-hub connection) and the formulas are dependent if the shaft respectively the hub is ductile or brittle.

But what is the decision about to say it is ductile or brittle.

My norm for feather key isn’t saying anything how to distinguish if the metal is ductile or brittle.
The norm for pressfits uses the parameter fracture elongation and reduction of area.
And the literature is talking about brittle metal when the Maximum Stress Theory is valid $(\sigma_{limit}/\tau_{limit}=1)$ and ductile metal when the Shear Stress Hypothesis is valid $(\sigma_{limit}/ \tau_{limit}=2)$.

$\sigma_{limit}$ is tensile strength
$\tau_{limit}$ is the strength when plasticity begins

Okay, there are many possibilities… But which one is the right possibility? Or is there a connection between my findings that I’m not aware of?

Thanks in advance for your help.


texts: How can I connect F=ma to Drag=1/2*Cd*(rho)*V^2*A?

texts:
I previously posted a different question that was very vague.  I have kept working on the problem, and now I have a different question.  Please let me know if I should have just added it to the old one.

I am trying to find the drag that a go-kart sees using a coast-down test, in which you accelerate then allow the cart to decelerate on its own (without using the brakes.)  I have data on the speed of the cart vs. the time.

For a cart that is decelerating due to drag, my data is saying that the velocity is proportional to the square of time (a parabolic curve of velocity vs. time).  I have looked at the data of other people's coast-down tests (I found them online), and their velocity appears to follow the same trend that mine does.

The above would mean that the derivative of velocity, the acceleration, would be linear if plotted against time.

Given these two relationships:

$$v \propto t^2$$ $$a \propto t$$

it would follow that:

$$v \propto a^2$$

My understanding is that you can calculate drag using $F=ma$, where  is the drag force $F=D$.

This would mean that
$$D \propto \sqrt{v} \quad (?)$$

However, I have read that drag is proportional to $v^2$.  The data that I have looked at from other people's tests also shows the relationship that drag is proportional to $v^2$, but I can't figure out how they got that relationship when their velocity curves are parabolic with respect to time.

What am I doing wrong?  I can't figure out how these two equations can both be true.

I guess my main question at this point is: should the velocity vs. time plot for a decelerating vehicle have a curve fit of $$t \propto v^2$$ or $$t \propto \sqrt{v}$$?

Thank you for any input.

I've attached an image of my data to show what I'm seeing.


texts: How do I implement scientific experiment to derive a equation called Gerber Line?

texts:
How do I implement scientific experiment to derive a equation relevant to subject of stress and fatigue called Gerber Line equation?

May you also provide some historical context to that?


texts: Evaluate "damping" of higher-order transfer function - something similar to settling time without the discontinuities

texts:
I have an 11th order transfer function in the continuous domain (simplified linearized model of a grid-forming converter) and I'm looking for a way to characterize it with a single number for evaluation of a parameter sweep. I've so far been using settling time because that's a typical requirement in grid codes, but there are discontinuities in a parameter sweep (when a peak moves past the threshold the function jumps). That for example makes the use of search algorithms difficult and also makes it harder to define an optimum over all operating points (the location of the discontinuities of course varies depending on the operating point). There also wouldn't really be a point in linearizing if I end up evaluating something that I can extract from a nonlinear model :)

So I'm looking for something that is similar to settling time, but without the discontinuities. I have several pole pairs in close proximity to each other and to zeros, so simply evaluating the damping ratio of the dominant pole pair won't do. I know that I can weigh pole pairs by frequency, but that would still neglect the zeros. I need to somehow incorporate the zeros as well.

I hope my problem is comprehensible. Any hint in the right direction is appreciated!


texts: Why is 14.5° a commonly used pressure angle in gears?

texts:
In gearing, according to Wikipedia and Dr. Rainer Hessmer's involute gear generator, the most popular pressure angles in the industry are 14.5°, 20° and 25°, with 20° being the most abundant. I can appreciate why 20° and 25° might be common values since they are nice round numbers. This then brings up the question; why 14.5°?

I understand that the lower pressure angle of 14.5° will come with some advantages over 20°, such as keeping the lines of action of the forces on the teeth further from the gear axis, reducing the reaction force of the shaft for the same torque transmitted. What I don't get is why a rather peculiar, un-round number such as 14.5° is a common choice? Was there a practical reason behind it, such as the minimum pressure angle before undercutting occurs for gears of a typical number of teeth, or was the value applied when a large quantity of these 14.5° gears existed prior to a standard pressure angle having existed? Perhaps it is a relic of an older standard of gears?


texts: Why are CO2 analyzers much more expensive that CO detectors?

texts:
This question emerges from Earth Science SE since recently there was asked this. There so far no one had the engineering/ measurement device expertise to answer this.

I am aware that these are fundamentally different in the case that the purposes of CO2 analyzer is to accurately monitor the levels of CO2 in the atmosphere probably in making a difference between a few parts per million (ppm) in air (as there is currently around 400ppm in the atmosphere and it is a well mixed gas in the atmosphere). On the other hand CO sensors probably need to be able to tell when the concentration of CO exceeds some predetermined threshold where it is safe for humans to breathe.

I would like to hear the answer on why and what causes the large price difference. My guesses are: complexity of manufacturing of CO2 analyzer, parts or the large scale production of CO sensors. It is probably the sum of many but from an expert on this or an enlightened opinion I would like to hear from this more accurately.


texts: How to calculate strength for titanium wire

texts:
I'd like to use a titanium wire to make some jewelry. I ordered two kinds of titanium wire, 0.3mm thick and 0.5mm thick. Both of them are grade 1 titanium.

How do I calculate the strength they'll have, i.e. the amount of weight they could lift before snapping?

I know that titanium grade 1 has an ultimate tensile strength of 240 MPa, but I don't know how to use that information to get the amount of force needed to snap the wire.


texts: Determination of a Joukowski airfoil chord (demonstration)

texts:
I'm currently studying Aerodynamics, and one thing that I noticed is that the maximum and minimum $x$ coordinate of the airfoils (which are necessary to compute the chord) on the transformed plane (let it be $z(x,y)$) correspond to the transformed intersection points of the circumference on the original plane  (let it be $\zeta(\xi,\eta)$) with the real axis. I don't find any proof of this statement, and so I tried to do it by myself. The problem is that it got too complicated to be solved analytically (too many different powers of trignometric functions). So I'm requesting someone to try demonstrate this too. I think that there's a simpler way to do it.
There's my introduction to the problem:

Consider the original circumference defined on the complex $\zeta$ plane:

where $a$ is the circumference radius, and $b$ the intersection of the circumference with the real positive axis, $\xi$. The parameter $\beta$ is the angle between the horizontal line and the line that links $\zeta_0$ to $b$. The center of the circumference is:
$$\zeta_0=-b\varepsilon+ia\sin(\beta)=-b\varepsilon+i(1+\varepsilon)b\tan(\beta)$$
So, this circumference is defined by:
$$\zeta=-b\varepsilon+b\frac{1+\varepsilon}{\cos(\beta)}\left(e^{i\theta}+i\sin(\beta)\right),\hspace{15pt}\theta \in [0,2\pi]$$
Now I need to show that for the Joukowski transform $z=\zeta+\frac{b^2}{\zeta}$ the $x$ coordinate (real coordinate on the plane $z$) has
a maximum on $\zeta=b$ (intersection of the circunference with the positive real axis) and a minimum on $\zeta=-b(1+2\varepsilon)$, (intersection of the circunference with the negative real axis).


texts: What type of fastener / rivet is this please?

texts:
I think I may have worked this out but I would love it if a real engineer could confirm it please?  Is the fixing shown in the photos a shoulder rivet?  Semi tubular?  For the record the pictures show a collapsible music stand, the metal legs shown are both about 5mm thick and the fastener / rivet's diameter is approx 10mm on both visible ends.  The two metal leg parts both freely pivot on this fastener so it’s essentially a hinge (bearing?) allowing the stand to fold up, but are also securely fixed together by it so there is no wiggle and it’s really sturdy, so it’s the perfect tightness.
I’m trying to prototype a similar part by hand so might struggle with a heavy duty machine rivet if that’s what it is, is there a locking / screwing equivalent I could try?  Any other advice on securely fixing two movable flat leg parts is most appreciated.
Thanks!


texts:
I am trying to build a reed instrument played by the wind (kind of like these aeolian instruments: Eerie musical instruments played by the wind from around the world but using reeds rather than strings), but given the necessary pressure to make the reed vibrate, I am having difficulties. For example if I place a reed instrument such as a duck call near a fan, it has not enough power to drive it. I tried to place a funnel in between, but still had no luck.

So, I have two things to consider:

To find the most suitable type of reed or make one from scratch (something similar to these, but all the online examples are too narrow to capture actual wind: Hypotooter -- a Mini-musical Instrument) that starts vibrating in the weakest possible wind
To direct the wind through a funnel-like piping (maybe not a usual funnel shape, but a different shape?), so that the reed is exposed to more power, if this is a good idea at all.

I am stuck at this point and don't even know if this is possible at all. I have heard of wind whistles or flutes played by the wind, but only when the wind very strong, however I am looking into a reed instrument because of its different sound quality + the ability for it to be played by lighter winds as well. Is this possible or is there any directions that you could suggest for me to experiment?


texts: What is the retention time distribution in an STRcascade when the reactors are of uneven side and we have some recircultion?

texts:
Consider 2 or 3 stirred tank reactors as a cascade. The sizes are different. A part of the throughput is recirculated from the last to the first. The mean hydraulic retention of course is straightforward to calculate. But what is the residence time distribution?

I think this is a solved problem, but for some reason the solution is not in any textbook I've consulted so far. Only the classical case of stirred tank reactor (STR) (all same size, no recirculation).

What is the effect of recirculation on the RT distribution? Logic says the distribution will be closer to a single vessel, but how to quantify?

Is there a significant effect on the HRT distribution of a STR cascade when the tanks have different sizes?

As stated above, I'm sure this is a solved problem - I just haven't been able to find the solutions.


texts: How would you move a sail boat with no wind or paddles

texts: If I stood on a sailing ship and had a very strong pair of lungs (possibly motorized) then if I blew the sail would I be able to move the ship forwards?


texts:
I am simulating an known as , using CFX as a solver.

This turbine have 8 blades((360/8)=45 deg=pitch angle). Due to the circumferential symmetry, only one eight of the annulus has been computed, imposing periodic boundary conditions (periodic rotational) in the tangential direction. The computational domain has been restricted in the axial direction to four chord lengths upstream and six chord lengths downstream of the blade.

Computational domain is as follows:

Also, these are set with specified e. Reference pressure is 1 atm. At the inlet I input a normal speed and at the outlet I have Static Pressure SST as turbulence model setting advanced turbulence controls such as curvature correction and production limiter. Frozen rotor interfaces connect the domains. Rotation domain rotates wit and No-slip boundary conditions are imposed on blade and hub and casing in stationary and rotation domain. and also Rotation domain is set as follows

Also, the values of production limiter and curvature correction and conservation target are default values and

My problem is as follows, there is an error in end of set up in CFX.

Also, Set up of passages in 360 is as follows:

I am grateful that guide me about above cases.


texts: How to use Spectroid app to measure low frequency vibrations?

texts:
Need to measure how low frequency (vibration) changes when going through different materials. The only possible way found is by using Spectroid app. However, have no idea of what settings to set up. Test environment would be:
Subwoofer, pointing to the top, inside an isolated box with a wooden board on a top (to mimic
real life floors of the apartment). On the board - material that will be tested. And on the material the phone with Spectroid app running.
Can anyone tell what settings to use? Vibrations will have low dB values (almost silence to humans, but still can be felt with the body (if f.ex. laying on the board)).
Here are the settings currently available in the app.
Can anyone guide me how to use all that...?


texts: Electric Motor Sizing : Understanding how much torque I need given Force

texts:
Physics has never been my strong point... I have a task to size a motor. The question is:  Based on information below, how do I calculate required motor torque to accelerate a mass with the information below? Please explain the formulas and where they originate from. I understand how to calculate the force required. I don't understand how I compute the required torque to achieve this force.

Variables:

Motion Direction:  Horizontal - Perpendicular to gravity
Mechanics:  Ballscrew & Linear Slide mechanism.

(W) Weight of Load to move:           100KG
(D) Distance load should move:        1 m
(A) Speed load should move:          .04 m/s
(C) Coef of Friction of Mechanism:    .003
(p) all Screw Pitch:                 2.75 mm
(d) Ball Screw Dia:                   20mm
(T) Min motor torque required:         ?

*Please arbitrarily choose variables for any missing information and declare them in your post.

Thank you for your time.


texts: How were these candlesticks made in the 1800s?

texts:
"Candlesticks" for this question are really just a stand-in for axisymmetric silver, brass, etc structures, possibly hollow and made of thin sheet material?

Examples:

From my research, today we would use metal spinning for sheet material, possibly casting, or turning with a lathe from solid stock are also possible. Hammer forming has certainly been around a long time. But in the late 1700's and early 1800's, it seems like metal spinning was not in common use, and these candlesticks are so ornate that they couldn't have been done only on a lathe. What techniques were commonly used? Where can I learn more about this type of work?


texts:
I have a question about work measured in foot-pound.
Let's say we have a 10 pound-mass ($10$ $\text{lb}_m$) object. Then
since that 10 pound-mass ($10$ $\text{lb}_m$) object gives 10 pound-force ($10$ $\text{lb}_f$) due to gravity, if we raise that object
2 feet, the work is 20 foot-pound ($20$ $\text{ft}\cdot\text{lb}_f$).
I was wondering if I am right.


texts: What ASTM standard would be appropriate for testing the breaking strength of nylon ropes

texts: ASTM D4268-93 would appear to be the relevant testing standard, but this was withdrawn in 2002 and is no longer active. Is there a current standard?


texts: Can a thing resonate whilst exposed to white noise?

texts:
Imagine some thing put in the presence of loud pure white noise, say at a level that might come from a teenager's HI-FI set to annoying. And the thing is like a champagne glass, sheet metal box or other thin walled vessel.  I'm not considering anything like a cannon ball or anvil.

I can foresee two scenarios:-

The thing vibrates at it's natural self resonant frequency, but only with limited amplitude as the power content of white noise at a specific frequency is relatively small.
The thing does nothing whatsoever as all the various frequencies present in the white noise induce vibrations that cancel each other out.

Which is it, or might there be a third possibility?


texts: Implicit and Explicit finite difference discretization of steady state heat conduction equation

texts:
I understand what an implicit and explicit form of finite-difference (FD) discretization for the transient heat conduction equation means. But I am not able to understand if it is possible to categorize the discretization of steady state heat conduction equation (without a source term, i.e Laplace equation) as implicit or explicit scheme as well?(or is it just implicit form of discretization as we use iterative solvers?)

Edit: Whenever I try to understand the meaning of explicit an implicit solvers, the notes and other resources always explain them using a (transient) time-varying equation. According to such resources For a transient equation if the solution for the next time step is given in terms of current time step values (which we already know, either by initial condition or by previous calculation) it is called as an Explicit solution, and it could be solved for directly without forming a system of equation. If the solution for next time step value is given in terms of current time step values (which we know) and next time step values (which we don't know) it leads to an implicit solution and this gives us a system of equations which is solved for by iterative solvers.

My confusion is, if we take a steady state equation there are no time steps involved (so there is no current and next time step) so what would be an explicit and implicit solution? and why would an explicit solution require an iterative solver as they can be solved for directly?


texts: Is the order of operations in jacking a cable relevant?

texts:
If you have a prestressed concrete beam or slab and are jacking a cable from both ends, does the order of operations alter the result?

For a symmetric curve, the tension diagram along the cable's span after friction losses is always shown as symmetric.

Is this the case regardless of whether the ends were jacked simultaneously or one after the other?

If the ends are jacked simultaneously then the symmetric friction loss makes perfect sense. However, if the cable is jacked first from the left and then from the right, I'd expect the tension profile to be asymmetric.

When jacking from the left, the cable is pulled and on its left end the cable force is equal to $P_0$, the jacking force. On the right side, the cable force is $P_0 - \Delta P$, where $\Delta P = P_0\left(1-e^{-(\mu\alpha+kL)}\right)$ is the friction losses. The left side is then anchored (disregard the anchorage slip losses for a moment). The right side is then jacked. Effectively, this jacking adds a force of $\Delta P$ to the right end, so that it too is now at $P_0$. However, wouldn't the left end also be affected with an increment equal to $\Delta Pe^{-(\mu\alpha+kL)}$, such that the diagram is asymmetric?

What about if one considers the fact that when the left side is anchored, anchorage slip losses occur? So the diagram should go: friction losses from jacking the left side, anchorage slip losses from anchoring the left side, friction losses from jacking the right side and then anchorage slip losses from anchoring the right side.

EDIT
After a few honest-to-God minutes freaking out thinking I was the biggest idiot on Earth I realized that what @sanchises commented doesn't rule out my question.

The cable in my question does remain in static equilibrium, as can be seen here:

When jacking from the left, the cable suffers at its left extremity a force of $P$. Friction losses along the way ($\Delta P$) cause the right extremity to end up with $P - \Delta P$. The right extremity is then jacked, which effectively applies a force of $\Delta P$. Friction losses also apply here, now with a value of $\Delta\Delta P$, such that the left anchor is additionally jacked with $\Delta P - \Delta\Delta P$.

This results in the left anchor with a force of $P + \Delta P - \Delta\Delta P$ and the right anchor with only $P$. These are not, however, the only forces acting on the cable: the friction losses are what keeps it in static equilibrium. Globally, we have to the left $$P + \Delta P - \Delta\Delta P +  \Delta\Delta P = P + \Delta P$$ and to the right $$\Delta P + P - \Delta P + \Delta P = P + \Delta P$$ both of which equal the total jacking force (first $P$ on the left and then $\Delta P$ on the right).


texts: What type of tires and wheels do I need to make a PVC beach cart?

texts:
I would like to make a beach cart that supports 200lbs and uses this design

What type and dimension wheels and tires should I buy? I have a budget of $100.00 for the tires and wheels. I cannot afford expensive sand tires like Wheelez. Will All Terrain Tires (AT) sufficiently work in sand with the expected load?


texts:
I was reading documents about energy importation and came across the following:

The import was of 5,915.87 MMtoe

I wonder if  MMtoe = $10^6*10^6$ toe  = $10^{12}$ toe.
First time coming across a unit expressed like that.


texts: Sheet Metal Bending: stuck on calculating the minimum radius required

texts:
I'm used to calculate the minimum radius required for bending operations on both aluminum and steel sheets, given the following parameters: https://imgur.com/a/7akHC

Problem statement:

  For a sheet metal stock with  inch thickness, determine the minimum
  tool radius for both the steel and aluminum alloys that will not tear
  the material. Assume the sheet of material is in pure bending (i.e.,
  no additional tension is applied during forming).

I have already learned about the following formulas:

R = 1/k
k(y) = e(y) / (h/2)
e(y) = k.y

Given that R = 1/k, the next step is to find the maximum curvature k for each sheet.

The problem is that I don't know how to find the maximum curvature, and I'm still stuck.

Any thoughts?


texts: Angles Measurement to control (move) a robotic arm

texts:
I am working on a robotic arm, I am going to use servo motors, those are going to be controlled from the PC with command (it is a chess-game arm) so the command will be some thing like move piece from A1 to E7 for example.

How can I calculate the angle that I am going to pass to the servos for each specific command?


texts: Hydraulic Brakes - Why motorcycle brakes more powerful than bicycle brakes?

texts:
I was wondering why motorcycle brakes have so much more stopping power than bicycle hydraulic brakes (Than can be found on mountain bikes for example).

The rotor has a bigger size which gives better leverage for the brake pads and thus more stopping power.

But I don't understand the following:

If the moment (force times lever length) exerted on the brake lever (by the rider's hand) is the same (is this a correct assumption) and the total amount of lever travel is the same... the amount of clamping force the hydraulic brake's caliper's pistons exert on the pads must be equal (I think)(since the same amount of energy is used at the lever.

Or is the free travel (the distance the pads have to travel before they hit the disc) much smaller on a motorcycle disc brake resulting in a shorter (free throw) of the lever which means there is more percentage of the lever travel that can be used to 'build pressure' meaning a smaller piston can be used which would give more clamping force at the pads?

The brake pads are much larger on motorcycles but then again because of the increased surface area one would have to exert more force on the bigger brake pads to get the same pressure/area.

Are my conclusions incorrect?

Is the pad material a lot softer on the motorcycle brake pads?
What design changes would enable higher clamping force with the same lever throw/force exerted on lever (if any design changes could accomplish this)?

Another example (light motorcycle vs heavy motorcycle):
my motorcycle (Suzuki gn250, 140 ish kg wet weight) has a hydraulic front (disc) brake. A Honda Goldwing (very heavy motorcycle , 380 kg wet weight) also has a hydraulic front (disc) brake. What would be the main differences that enable the Goldwing's front brake to have so much more power?

Another question:
The Goldwing has 2 discs/2 calipers in the front. There is more pad material indeed but the same thought (more surface area of pads means more force needs to be exerted in total on the brake pads in order to get the same force/area on the contact patch between pads and disc surface).
Is even softer material used on the brake pads for 2 rotor front brake systems?
Or am I missing something?

Some disc brakes have 2 piston calipers, some have 4 piston calipers. It is suggested that the 4 piston caliper variants have more stopping power..
Is it true that the 4 piston calipers have more stopping power in general? If so, what is the reason behind this?

Thank you!


texts: There is a missile guidance algorithm called proportional navigation. Is there an opposite algorithm for missile avoidance? Something that tries something other than escaping in the direction of a homing missile that doesn't work when the escaping object has a little less power?


texts:
Which is more economical to improve or change the soil that is used to build a structure?

my answer is that it depends on each case, but I would like to get more information, or where to search about it.

Thank you.


texts:
I have a simple linear translation stage that is driven by a screw, and I would like to attach a stepper motor to the screw drive.  The axis of the screw and the axis of the motor are approximately colinear.  The issue is that, as the screw turns it recedes away from (or advances towards) the motor.  The spacing between the motor shaft and the screw drive can change by as much as 10 mm.  A diagram of the problem and an example of the type of stage are shown below.

How can I couple the stepper motor to the screw drive in a way that allows for this expansion/contraction of the space between the two?


texts: Determining If A Test Article Is Suitable For X RAY Following Shock Testing?

texts:
I am interested in putting a small (3"x3"x2") assembly under X-ray, following a shock test, in order to evaluate failures of an internal ceramic piece. Unfortunately, this assembly utilizes quite a bit of potting material (epoxy) and as such, cannot easily be disassembled.

I'm considering reaching out to some local dentist practices to see if I can purchase X-ray time from them, however, I'm concerned that the material makeup of my assembly will not allow adequate penetration and will result in a poor image.

The general makeup of the assembly from the outside and moving inwards is...

0.125" thick aluminum outer casing
0.25" to 0.5" foam-like epoxy
some small (but strong) magnets
a ceramic "skeleton" structure (this is what I'm most interested in evaluating for failures)

Should note that the magnets are not necessarily in the line-of-sight of the ceramic, so 'penetration-ability' of those is a non-issue.

However, regarding the aluminum, with a HVL of 0.06" at 120 keV (source), I'm worried that I may not be able to sufficiently penetrate the outer shell and produce a good image.

MY QUESTIONS ARE:

Penetration aside: Is it reasonable to suspect that I will be able to gather useful information and identify fractures in the ceramic?
Google tells me that the typical energy capability of a dentistry x-ray is <200 keV. For someone with experience in the radiation field, do you expect this would be sufficient to penetrate my test article and produce a good image?


texts:
I am working on a vent. The vent is attached to a box and is designed to extract air out of the box using the venturi effect. Air is made to flow over the vent which creates a significant pressure difference between the face of the vent and the inside of the box making air to flow out. I have performed the Analysis using Fluent and trying to figure our the flow rate(mass flow rate) of the air escaping from the vent outlet.

I am new to CFD and want to know how to find that out from my analysis?

Please find attached a photo which shows the setup.


texts:
I've been studying the design of turbopumps and their impellers, all the design equations and what-not; this question concerns the contours of the impeller vanes. I'm going to attempt to enter aerospace engineering in the future, so I figured I might as well start getting exposure to the concepts now.

I'm currently attempting to design an impeller in CAD to test my knowledge of the equations as well as get better at CAD, but one of the facets of the design rather baffles me.

As you can see here (source, page 208):

The calculation of the radial contour of the impeller (that is, concerning $\beta_1$ and $\beta_2$ should be relatively easy given the other content in the paper, but radial impellers in turbochargers and other such equipment almost always appear to have a "lip" or forward facing top edge near the eye of the volute or casing inlet.

Here is an example of what I'm referring to:

You can tell that the vanes are backwards-curved, but near the top of the impeller vane closer to the eye, the curvature reverses and flares forward to approach near-flat slope.

My questions are:

What is the purpose of this axial contour (forgive me if that isn't the proper term)?
Are there specific design parameters associated with that contour? The Rocketdyne text above didn't seem to make any mention of the axial profiles of the impeller, other than the diagram to the left describing the dimensioning of the shrouds.
Where can I find an explanation and source of design information for how to design the contour?


texts: I want to build my own 4 point bending tester. First, I need to see what parts are available for sale. Can anyone tell me if the circled L-shaped part has a name I can use to search with, and if so what? Alternately, any suggestions as to parts I could use in a similar fashion would be useful.


texts:
As I was studying about  differential equation,then I got a question in my mind that we are taking out general solutions for a differential equation.
Like for example -
Q) $\frac{dy}{dx} = \left[\frac{1}{(1+x^3)}\right] – \left[\frac{3x^2}{1 + x^3}\right]y$
Solution:
⇒$\frac{dy}{dx} + [\frac{3x²}{1 + x²}] y = \frac{1}{1+x³} $
Comparing it with $\frac{dy}{dx}  + Py = 0$, we get
$P =\frac{3x^2}{1 + x^3}$
$Q= \frac{1}{1 + x^3}$
Let’s figure out the integrating factor(I.F.) which is e^(∫Pdx)
⇒$I.F  =  e^{\int \frac{3x^2}{(1+x³)}dx}=e^{\ln(1+x^3)}$
⇒$I.F. = 1 + x^3$
Now, we can also rewrite the L.H.S as:
d(y × I.F)/dx,
⇒ d(y × (1 + x³)) dx = [1/(1 +x³)] × (1 + x³)
Integrating both the sides w. r. t. x, we get,
⇒ y × ( 1 + x³) =  x
⇒ y = x/(1 + x³)
⇒ y = [x/(1 + x³) +  C
But how do we get that differential equation (as given in the above question -> $\frac{dy}{dx} = \left[\frac{1}{(1+x^3)}\right] – \left[\frac{3x^2}{1 + x^3}\right]y$
from our real life ?


texts:
I'm afraid I'm completely out of my depth here.

I would like to use a tungsten filament to radiatively heat something near to it (in vacuum).  My issue is I cannot figure out the easiest and/or cheapest way to control the power to the filament.  The answer I keep circling around is something involving an SCR and maybe a transformer to step down the line voltage.  But some things I've read (Chromalox's product materials, mostly) indicate that I don't need a step-down transformer, or if I did I just need a phase-angle fired SCR.  Other places I've looked (product literature from other people, such as Omega) indicate that an SCR, even phase-angle fired, can't drive an inductive load reliably. I've also considered putting the transformer first, but most SCRs I've seen require line voltage input (either for auxiliary electronics or for their own operation).

Another point of confusion is that I am not sure how, if at all, I am controlling the current in the filament (high temperature resistance=0.1 ohms ~= 15x low temperature resistance).  The SCR just turns the output on and off, after all, to produce some sort of average power, right?

Does anyone have experience with this sort of system or goal?  The filament in question is designed to be driven at 7-ish volts and up to 62 amps, although I assume I could always drive it with higher voltage.  I would like to plug into a 120V single phase wall socket.  I am not wedded to the SCR, or really any element of the design, as long as it can be computer-controlled eventually (and get real hot).

Thank you!


texts: How to build multiple large scale fish tanks with water at different temperatures

texts:
I am wondering at a high level what are the material components that might be used in building several large scale fish tanks that are temperature regulated like on a fishing farm.

For example, what I am imagining is something like this:

 __________________________________________________
|                |                |                |
|     Tank 1     |    Tank 2      |       3        |
|                |                |                |
|________________|________________|________________|
|                |                |                |
|                |                |                |
|       4        |       5        |      6         |
|                |                |                |
|________________|________________|________________|
|                |                |                |
|                |                |                |
|       7        |       8        |      ...       |
|                |                |                |
|                |                |                |
|________________|________________|________________|

Where each tank is let's say 10 meters by 10 meters. There could be potentially a hundred or more of these tanks.

The reason for the many tanks are twofold:

To separate certain species of fish from one another.
To create different environments (salinity, nutrients, and most relevant, temperature).

The question is how you would keep these tanks at a certain temperature. Perhaps, let's say, they are indoor. Or if it can be answered both ways, then including outdoor would be interesting to know but I imagine there are too many additional constraints in that case. So let's say they are indoor.

I am not an engineer, I do software development, but I am  interested in learning how to build real stuff too.

I would imagine that these are built with concrete, then somehow perhaps the concrete is heated or cooled with some technology. Or perhaps instead of regulating the temperature of the concrete, the water is cooled somehow directly. I would like to know how this cooling process would work, so I can understand how something like this could be built. Right now I can imagine the structural components for the most part (reinforced concrete, for example, and digging the dirt, etc.), but I don't know how the actual temperature regulation would work at this scale. Also would be interested to know (if there are multiple ways), what the best vs. the most cost effective way would be (or just if this type of thing is considered expensive or not). But if that's too much to ask, just knowing generally how you would implement this sort of thing would be the main question.


texts: Calculating speed, forces and pressures when extending a cylinder

texts:
So I have the following circuit:

And the first question is, if DV1 is pushed all the way to the right, what speed will the clamp cylinder attain and as it extends what will be the pressure at P1.

Similarly Once the clamp cylinder has become fully extended, if the button on DV2 is pressed, what will be the speed of the piston of the lift cylinder and the pressure at P1?

The specifications are as such:

Clamp cylinder -> Bore = 20 mm diameter, rod of 15mm diameter and a stroke of 1m.
Lift Cylinder -> Bore = 200mm diameter, rod = 15mm diameter, stroke = 1m
Clamp cylinder has a resistive force of 2.5kN that opposes motion
Lift Cylinder moves a mass of 50kg and no resistive forces
The relief valve is set to 20 MPa
Pressure valve, PV2 is set to 10MPa
Pump -> 5mL/rev and 1440 RPM
no pressure losses in line or components or internal leakage

So my thoughts are;

The pump is pumping at 5 *1440 = 7200mL/minute.

I'm going to just ignore PV1 as it's just a pressure relief valve, so it will just limit the system to whatever it is set to (20MPa).

I think we can ignore PV2 and everything beyond for the first question too. Or since this flow goes back to tank, I think it may mean that the system can't be more than 10MPa?

Now I think we calculate the Area of the head of the cylinder which is A = (0.2/2)^2 * pi = 0.0314 m^2.

So from here I think we can just put it into the formula Vext = Qp / A.

So 7.2*10^-3 / 3.14*10^-2 = 0.2293 m/s

Is this correct, or do I have to subtract some flow that would go to the other parts of the system (towards flow 2 and PV2).

Then the pressure at head should be P = F/A. This is my main problem, as 2.5*10^3/0.0314 = 80MPa which is way higher than any of the possible answer choices. Not to mention higher than what PV1 is set for.

So where have I gone wrong and how can I solve these problems?


texts: How are thermodynamics properties of gases and liquids calculated numerically?

texts:
I was wondering how the values of thermodynamic properties as enthalpy, entropy, internal energy, specific heat, specific volumes ... etc, of gases and liquids are calculated using programming libraries such as cantera and thermopy as an example.

How are steam tables made for instance? How do we get all these values of properties if not experimentally?


texts: Steady state value, a possible shortcut?

texts:
I have this differential equation:

$\dot{\eta (t)}=\frac{-2\eta(t)}{C(\widehat{R}+\Delta R)}+\frac{K^2 L}{C E^2 (\widehat{R}+\Delta R)}+K$

which, my book says, correspond to a LTI system, asymptotically stable with a constant input:

$\frac{K^2 L}{C E^2 (\widehat{R}+\Delta R)}+K$

It says also that the steady state value of the variable $\eta (t)$ is

$\tilde{\eta (t)} = \frac{K C(\widehat{R}+\Delta R)}{2} + \frac{K^2 L}{2E^2}$

The book doesn't say how to get this, but I reached the same result solving the differential equation (after a change a variable it can be solved separating variables) and calculating the limit for $t\rightarrow\infty$.
My question is: is it really necessary to solve the differential equation or is there any property I can use to avoid it? I'm asking this because looking at the expression of the steady state value you can see that is equivalent to the ratio of the input and the coefficient of $\eta(t)$.  Is it random or am I missing something?


texts: Mounting an antenna base on a roof using only double sided tape?

texts:
I want to put a vertical antenna on top of my roof. The antenna is basically 4 meters of PVC pipe and 5 meters of 19mm aluminium tubing.

The roof at my house is corrugated sheet metal, and I want to avoid drilling (and even touching the current screws as much as possible).

Here's a render of my idea:

The mast itself will be, of course, held by ropes. Will double sided tape (3M VHB) be able to prevent the base from sliding around during installation? Will the tape hold up to thermal expansion of the corrugated sheet?

The main idea of this support is being able to pivot the antenna in case of very strong winds, or servicing it (it has a coil in the middle).


texts: Calculating the torque required by an Archimedes screw pump

texts:
Given an Archimedes screw pump (shown below) how would you go about calculating the torque required to operate it?  I'm assuming a situation where you have to design for a given flow rate, Q (m^3/s) and the diameter, angle of incline and head are known.  The fluid to be pumped is water.

I believe the power required to lift water in such a pump is just the hydraulic power, which we have all the variables for:

  P(hyd) = rho * g * Q * H

 (Power = density * gravity * flow rate * head )

But I'm struggling to conceptualise how this translates into a value for torque.

Any help would be appreciated!


texts:
In the past few weeks I've seen several European steam locomotives in museums. I noticed several of them have a box in the driver's cabin, similar to the one in the picture I've attached. Several cables or tubes leave this box in a circular arrangement and I wonder what this box is doing. So, what is it?

(Engineering.SE seems to be the best fit for this question; if there's a better one, please let me know.)


texts: How to calculate torque required to rotate assembly about the center

texts: The image is a hollow cylinder: 2in OD, 1.76in ID. Connected is an angled bracket, 45 deg, that weighs 3lbs. The top rectangle piece connected to the bracket is 10 lbs,the dimensions are 31.1in x 14.1in x 1.97in . The bottom of the cylinder has a bracket where the motor will attach to. I am planning on using a continuous rotation servo motor. I am trying to figure out how to calculate the torque required to rotate the assembly about the center, vertical axis of the cylinder and am not sure where to start. The biggest part I am stumped on is getting the moment of inertia of the assembly due to the awkward shape of it.  Even just a general idea of how to calculate it/procedure will be greatly appreciated.


texts: What are cascaded and parallel PID loop and what are the differences between them. I searched on google and came across few websites but still i don't understand the the two types of control loops ?


texts: How to find required size of AC gear motor for planetary mixing application?

texts:
I want to find a suitable AC or DC gear motor for concrete paste mixing. The application details are given below

Material type - concrete paste
RPM - 30-200rpm
Qty of material - 30Liters
Mixing style - Planetary
To understand the type of mixer, you may consider bakery mixer.

Can somebody help me how to calculate the capacity of gear motor that I have to select for this application?


texts: Regulating pressure down inside vessel as it increases

texts:
I want to keep the pressure inside a balloon (effectively - a rubber vessel) constant, as the balloon is compressed. I'm wondering if a regulator like this (wiki page here showing mechanism - I believe) can do it? They're designed to regulate a higher relatively constant pressure (eg large volume at 30bar) down to <1bar in a smaller vessel to keep that constant. I think these are one way tho - if the pressure starts increasing in the outlet the inlet will close off, rather than dissipate that increase back to the source, whereas I want to effectively use it to do exactly that. Would this work? Or is there a better way to do this?

Thanks for all help given!