texts: What is the best way to measure the helix angle of a helical cut gear? I have a sun gear from a planetary set that I would like to have custom made but I'm not sure the best way to get the helix angle, the rest of the information I can measure by myself but this one is proving to be a bit more difficult. Does anyone have a tried and true method to measure this?


texts: Type of brazing torch / gas that would be appropriate?

texts:
I'm a competent DIYer and have done a little small-scale ferrous and non-ferrous brazing in the past. It was in a professional workshop the equipment was provided suitable on request, so I didn't need to know how to choose the right gear.

So right now I'm looking at a few jobs around the home and household workshop scale personal work, and thinking that brazing is the appropriate technique. The work I have backlogged includes a copper/brass/bronze sculpture which has a brazed copper "leaf" shaped piece broken off where it was joined, small scale iron/steel/alum (<3 mm flat/5mm rod ferrous), and other minor and broken things from time to time. It's enough to be worth investing in a small brazing torch and other equipment, although I might only use it once or twice a year if that.

There is a huge amount of info out there on fluxes, techniques, and rods, so that's easy. But there is nothing solid that I can find, about torch style and gas choices, is the problem.

What I've found so far is, temps suitable for different materials (eg above ~ 500C and for copper below about 1000C from memory), temps for different gases (~1500C to 4000C roughly, from memory, sorry if my memory's wrong, the general idea is right I know). I'm also aware of the difference between flame temp and target temp and to expect that the metals and equipment will act as a heatsink. But beyond those basics, I can't find anything to guide me in choosing an appropriate brazing torch type and gas to use. (Solder yes. Flux yes. Protective gas yes. Technique yes. Combustible fuel and torch selection no.)

To an extent I can move the torch or adjust the gas flow to change the temp based on the flux and joint appearance, that's easy. But what features or spec items would make a torch suitable for my use, and which gas combinations are most sensible that more experienced brazers would go for? Should I look at heat output or gas flow to know if it's going to be adequate for brazing? I'm going to have very light use (< 1 hour/year?) and for now I'm not expecting heavy duty work, so perhaps some gas + air will be enough and makes economic sense. (Or should that be gas/LPG? No idea.) I might use it more on ferrous steel or filling, once I gain experience.

Which fuels are likely to be good for me? What makes the difference between a "not hot or consistent enough in actual use" torch and a decent budget-level torch? What sort of gear should my shortlist include (to look up "comparison of..." articles)

In all, I don't need more than a basic simple torch but I'd like to get one that can handle a little more than I'm expecting, rather than find after starting a job, that I've bought a lightweight plumbing torch that can't really pump sufficient heat into the joint. That's what I most want to learn.

Other relevant info might include common "warning signs" to help identify a cheap, poorly built  torch, and maybe also some suggestion how much gas is sensible for me to buy (0.5 L? 10 L? I don't want to run out halfway through my 2nd job and gas lasts for ages on the cupboard shelf).

Thanks for helping


texts: Right justified and left justified mode I2S

texts:
How can we check the Audio codec (wm8960) is in right or left justified mode  using raspberry-pi
I connected wm8960 audio codec to the raspberry pi and i recorded wav file i checked in the dmesg its default state is i2s mode but wm8960 codec support left or right justified mode how to change mode from i2s to left or right justified mod.
inserted link wm8960 data sheet url
[wm8960][1]
https://datasheetspdf.com/pdf/1365067/CirrusLogic/WM8960/1
Please help in this


texts:
I'm a newbie of electricity and I would like to know if a piece of tool steel connected to both positive and ground pole of a welder tend to heat up red hot.
If yes, at wich amperage?
There are some risks involved such as overheating the welder or a huge waste of electricity due to the hight resistence of the metal.
Thanks in advance.


texts: Crafting a mirrored shifting drum for motorcycle gearbox

texts:
I would like to reverse the gearing of my Husaberg FS 650e motorcycle so that by pressing the shifting pedal the gearbox changes up instead of down to the first gear.

There are many solutions on the market consisting of linkages that redirect the movement of the shifting pedal. Unfortunately this is not possible on my bike.

First of there is no ready to buy solution, secondly there is not enough free space around the shaft that would make this approach feasable.

So I am wondering if theoretically a mirrored/inversed shifting drum would accomplish this?


texts: Ideas for a simple angle adjustment/lock for a steel plate arm

texts:
I am trying to come up with a better way to adjust the angle between the two steel pieces in the picture, and lock it in place. At the moment I just have a nut and bolt that I loosen and then tighten, but it is very cumbersome.

What would be perfect is some sort of geared dial that I could turn which maintains the force between the plates so I just turn it to whatever angle I need without loosening and tightening again. I'm just not sure what exactly I would search for.

Anyone have any ideas?


texts:
When a rectangular piece of plastic (say a credit card) experiences an increasing compression force, the plastic eventually buckles. Is it possible to find the equation of the plastic's cross section once it has buckled elastically?

What I have in mind is two fingers squeezing a plastic card. The fingers are $x$ cm apart, and the card itself has dimensions $l\times b$ cm and negligible thickness. Suppose $x \leq l$ (so that the card is compressed in a direction parallel to its original length $l$. Can we find an equation for the card's deflection $y$ in terms of $x,h,b$ and (I guess) the elastic modulus?

Does the Euler column buckling result work here? That is, can we expect a solution of the form $y=A\sin(\pi z/x)$? If yes, for small deflections is it safe to assume that the arc length of the curve is equal to $l$?

I'm nervous about using this, because I'm assuming negligible thickness. Do I have to allow the card to have non-zero thickness? Can I then use this to find the value of $A$?


texts: Cheap but durable design for a quick-to-assemble, portable globe?

texts:
This question has a bit of an arts & crafts / DIY flavour, but looking at those Stack Exchanges made me feel it fits better here. I have no background in any of these things, so apologies for my ignorance, including any poor etiquette! I'm happy to improve the question if people provide feedback - or, I suppose, to remove it - but am not sure it'll be better-received elsewhere.

I'm interested in making a globe, around a metre diameter, that can be easily assembled, disassembled and carried around in a compact form. I was thinking of using 20 hexagonal and 12 pentagonal pieces, like a football - I'd prefer them to be curved, and ideally 3d printed so I can easily add colours and/or texture on the outside. But I'm not sure how best to join them together (triangular joints? hinges? struts? elastic bands? I have no idea), or what materials and thicknesses to use. My main constraints, roughly in order, are budget, weight / compactness, durability, ease / speed of (dis)assembly, and ease of manufacture.

What are some sensible approaches?

Bonus points: it would be nice if

the structural components aren't too visible from the outside
I could assemble 3-7 pieces and have that be stable by itself - so I'd prefer not to use a ball in the middle with long rods coming out, but if that's by far the cheapest solution then so be it
(extra bonus) I could attach and remove small objects using paired magnets or something similar


texts: Gear train with fixed average speed but irregular instantaneous speed

texts:
Is it possible to create a gear train whose average speed is fixed, but whose speed constantly fluctuates? I'm imagining something that would ideally always complete a single revolution in fixed time, but move irregularly along the way.

My interest in this problem is from the writings of Terry Pratchett, whose character Lord Vetinari has a clock which ticks irregularly, but keeps correct time. Numerous versions of this clock have been made using electronic control, but I'm interested in the mechanical possibilities of it.


texts:
We're making a vibration polisher for polishing laser-cut aluminum and steel parts, and we're looking for the abrasive medium to fill it with. We need about 30 liters of it - and the one we found (for jewelry use) was prohibitively expensive in the required amounts. We tried with several gravel kinds and the results were underwhelming.

What material, that would be easy to obtain and inexpensive is a common choice for a vibration polisher?


texts: How to calculate the steering ratios on multiple axle vehicles?

texts: I'm building a model of a long vehicle with 6 axles and I want to be able to steer it. How do I calculate the amount each axle should steer to minimise dragging of some wheels round sideways as it turns?


texts: Best support for a granite table top?: Flat bar 316L Stainless Steel or equal box section or unequal box section

texts: Project is outdoor granite topped table.  Table legs are two isosceles trapezoids crossed together at 90 degrees, with the legs having an internal angle of 80 degrees, made from 100 x 100 x 4mm 316L Stainless Steel equal box section. Granite top will weight either approx. 158.95Kgs (350.5 Lbs) @ 20mm thick or 238Kgs (525 Lbs) @ 30mm thick. Clearance from ground to underside of table top = 700mm. I am stuck on the support frame (which will be back 150mm from perimeter of the Granite) to be welded to the legs .  As I only have 40mm height to play with (a downstand of granite will cover the support), and given that the legs are 100 x 100mm box section, what 316L would be the most rigid/strong enough to take the weight of the granite and be welded to the legs? All answers gratefully received, but please bear in mind I have no technical knowledge whatsoever, so just a shopping list please! I have to give the fabricators a drawing that makes sense and just knowing what I want in my garden won't help them!  Many thanks in advance.


texts: Why textbooks use geometric center/centerline of the pipe when calculating/measuring pressure?

texts:
Studying Fluid Mechanics, I started to notice that almost every textbook/website uses a specific point to make calculations about the pressure in a liquid at a given depth (hydrostatic pressure): the geometric center (as shown in the images below), when presenting pressure gauges/manometers/piezometers.
Note: This happens regardless of the field to which the book is directed  (I looked in textbooks of Fluid Mechanics for Civil, for Electrical, for Mechanical...).

    Images sources: MATHalino/PennState College of Engineering (MNE)/The SensorsGuide/University of Sydney (MDP)/ScienceStruck/Chegg

        Sources: Introduction to Fluid Mechanics - Nakayama & Boucher/Mecânica dos Fluidos - Noções e Aplicações - Sylvio R. Bistafa/Chegg

One of the textbooks I looked at even draws attention to this fact, but it doesn't explain the reason for the choice:

Note the origin of the measurement of h, in the center of the tube

                                                          Source: Mecânica dos Fluidos - Franco Brunetti

A similar behavior can be identified when textbooks present liquids in motion: they use the centerline of the pipe to make calculations/measurements. Here's an example:

                                                     Source: Fluid Mechanics for Civil Engineers - N.B. Webber

So why is the choice of geometric center/centerline of the pipe so common when measuring/calculating pressure? Some hypotheses:

Maybe all the textbooks/websites are unconsciously copying each other?
Maybe is this some kind of "convention"?
Maybe it is because a point in the horizontal plane of the geometric center gives the average pressure of a tank?


texts: Shape memory alloy fibers with low Young's Modulus?

texts:
I am wondering if there exist any species of shape memory alloy fibers with low Young's Modulus at room temperature, for an application I'm working on. So far I've played with Flexinol, but it is a bit too stiff. I know Nitinol has a Young's Modulus of ~30-40 GPa. I am wondering if there exist softer fibers - I'm interested ones that might be at around ~10 GPa, ~1GPa, and < 1GPa, if they exist.

Beyond other materials, is there any procedure to make Nitinol naturally softer?


texts:
I have been testing basic circuits in SimulIDE. I created a basic exclusive or circuit that works most of the time.
There are two inputs.
When both inputs are off the bottom LED does not light up, that is correct.
When 1 of the 2 inputs are on, the bottom LED lights up, that is correct.
When both inputs are on, the bottom LED still lights up, even though an exclusive or circuit should only output ON when 1 of 2 inputs are on. In other words, if both inputs are on, the bottom LED should not light up.
I was wondering if timings could  be the problem, but I'm not comfortable enough with circuits to trouble shoot this. Why does the bottom LED light up when both inputs are ON?

(Bottom LED should be off)
Bottom LED should be offI hope this is the right place to ask, and that the tags are correct. If they are not, please let me know.
Edit 1:
So I began adding LEDs everywhere I can to test for an issue. Strangle adding an LED after the bottom OR fixes the issue. Adding an LED after the inverter also fixes the issue. The question now is, why is this happening?

(LED placed after bottom OR causes bottom right LED to turn off)

(LED placed after inverter also causes bottom right LED to turn off)
When I say "turn off" in the captions I'm referring to how that LED should behave in an exclusive or circuit.


texts: Relation between natural frequency and the thickness

texts: If I have a solid material, let's say two bricks, one of which is thicker and I do modal/vibration testing. What would be the relation between thickness and natural frequency of any of them, is there any equation that can explain it, or does it depend on the material itself?


texts: Did Otto Lilienthal ever experiment with non-human-powered aircraft?

texts: Otto Lilienthal, sometimes hailed as the first aviator, became famous for his many gliders, which pioneered new experiments in aeronautics. However, powered aircraft didn't take off - pun intended - until the Wright brothers successfully flew their powered airplane. Did Lilienthal ever experiment with non-human-powered flight? Wikipedia says he built a small engine, but doesn't say whether or not it was ever used in an aircraft.


texts: How can we determine that the flow in a wind tunnel reaches the steady-state condition?

texts: I am investigating the flow and heat transfer over a cylinder in a wind tunnel. I want to record the data that I need to calculate the flow characteristics, But how can I make sure that the steady-state condition is achieved? There are very small changes in measured parameters like velocity and we know that there is no change anywhere with time in steady-state condition.


texts: How efficient are jet engine thrust reversers?

texts: Most reasonably sized commercial aircraft rely on jet engines for propulsion.  Upon landing these aircraft use a number of means to come to a stop with the two most important being (I believe) mechanical brakes and jet engine thrust reversal.  This reverse thrust is generated by opening some small doors on the outside of the engine (shown below).  How efficient is the thrust reversal process?  For specificity, let's define the efficiency to be reverse thrust divided by forward thrust for a given engine speed.


texts: Using linear actuator in the limited space

texts:
What is most effective way to apply linear actuator to move a lift within a small sized space?

I.e. for example, for 14", which is total 820mm, to move a 330 mm lift in 740mm height box (width and depth are not limited)?


texts: What does it mean to do a "hot casting" of a brick?

texts: I was talking to someone about brickmaking and he said doing a "hot casting" of a brick requires more energy and there are alternatives that use less energy. What does that mean?


texts:
I am trying to work out the compressive stress in a material.

I have a strut diameter  of 30mm. Length is 2.5m. Load 0f 30kN.
Modulus of elasticity for the material is 160GPa.

I need to find the amount it compresses by.

I have came up with the answer: 1.130973355x10^10m

By using Stress/Strain.

I am stuck on the 160GPa. I have wrote it in the equation as: 160x10^9.

But not sure if this is correct. And it should just be 160.

And not sure if I have calculated it correctly.

Can anyone help or give advice?

Thanks.


texts: How to simulate the simply supported boundary condition in experiments?

texts:
I want to do some experiments on the dynamic behavior of the beam, plate and so on. Four boundary conditions I want to simulate:

Free
Clamped
Simply supported

For free boundary condition, I can use a string to tie the beam or plates up  and hang them on some place. For clamped boundary, I can use some bolts to fix the beam or plate on a base. But how can I simulate the simply supported boundary conditions?


texts: How to lock a wheel bearing a load in place?

texts:
I'm designing a counterweight system that lifts a single load (max 55 kg) from above. I've narrowed down what to use to link the load to the counterweight to two options:

Timing belt
Roller chain

The system will exist in two states: one where the load can freely move in either direction (up or down), and one where it is completely locked in place. This is a simple system. Currently it's only comprised of the load, counterweight, link between the two, the wheel the link runs along, the wheel's shaft, and a locking mechanism for the wheel. I anticipate that the implementation may get more complicated than this, but the primary obstacle I'm facing right now is deciding what to use for the locking mechanism.
I'm considering two options:

Pawls
Brake pads

I'm leaning towards pawls as they seem like a more reliable way of locking a wheel in place and also simpler to implement. Both a timing belt pulley and a sprocket in this case would only have their links running along the top and sides of it, leaving the cogs on its underside open to applying pawls to. That said, this is my first mechanical project, so I'm apprehensive to go that route without hearing an experienced opinion first.
For the locking mechanism there are two constraints:

A limit of 0.3 cm on braking backlash, if any (I'd consider loosening this constraint to 0.6 cm if 0.3 cm turns out to be prohibitively complex).
It should be safe enough that if someone leaned on the load that their added weight shouldn't result in its catastrophic failure.

I like the roller chain option because it seems the simplest to me, but on a site like McMaster-Carr the smallest pitch on a sprocket appears to be 1/4". This presents the potentital for about 0.6 cm of backlash when using a single pawl. Perhaps multiple pawls could be used, but it appears to add complexity, and I'm skeptical of making the integrity of the system depend on the integrity of a single cog.
Brake pads are the other option, but offhand seem considerably more complex to implement in and of themselves, but being that now I'd likely be depending on the force of a strong spring to keep the pad up against the wheel, and that how I disengage that spring is going to be done by hand, I'm figuring a new component will have to be added to the system just to enable practical contraction of the spring; increasing the complexity of this option further.
What's your take? Are there remarkably better options that I haven't included? Is using pawls on the cogs of timing belt pulleys and sprockets unsafe in the first place?


texts: Latch design for home exercise equipment

texts:
I have a latch design problem and need your help - many years in software engineering aren't helping me much here!
Two pieces of 60x30mm RHS become parallel/adjacent (on the 60mm face), with a 5mm gap, via a pivoting motion between two sub-structures. A rotary latch is installed into the bottom piece of RHS and a pin/striker in the top piece engages into the latch. All works well but this is just the initial latching mechanism to allow the user to engage a stronger mechanism - which is what I need help with: designing/choosing a suitable latch.
Firstly, it will need to hold a large force - 2275kg if I take the 7:1 leverage ratio and x2.5 safety factor into account. If this is wildly optimistic, I can use one on either side to halve that requirement. Secondly, it must be able to pull the two pieces of RHS into near perfect alignment as the rotary latch has 2-3mm of free play. There can be no free play at all once the secondary latch mechanism is engaged.
Any ideas? I attach a drawing of my current best idea - a lever laser-cut from 10mm steel plate, with a small bend, rotating on a shoulder bolt which goes through both 30mm faces of the top piece of RHS. Currently shown in the engaged position. Turning it 180 degrees anti-clockwise will disengage it. The bend is to allow it to pull the top piece into alignment before securing it. In case it isn't clear, the top piece of RHS will pivot down from top left to bottom right in the diagram (the direction the pin is pointing) and the rotary latch/striker ensure it cannot move further in this direction.


texts: Height Increase by a Floating Cylinder Over a Larger Cylinder

texts:
For a National Board Exam Review:

  A floating cylinder 8cm in diameter and weighing 950 grams is placed in
  a cylindrical container 20cm in diameter and partially full of water.
  The increase in the depth of water in the container due to placing the
  float in it is:

Answer is 3cm

So I try:

$${ P_1 = \frac{0.950kg * 9.81 \frac{m}{s^2}}{ \frac{\pi}{4} * { (20cm * \frac{1m}{100cm}})^2 } = 296.649 \frac{N}{m^2}}$$

$${ \gamma = 9.81 \frac{kN}{m^3} }$$

$${ P_2 = P_{atm} = 101325 \frac{N}{m^2}}$$

$${ P_1 + \gamma h = P_2 }$$

$${h = 10.29m }$$

What is my error? Am I using wrong approach? Wrong formula?


texts: Find a constraint relation for this Q of 3 pulleys and 2 blocks attached with string

texts:
Using any method find the constraint relation between mass 1 and mass 2.
Assumptions: No friction , massless string and pulley.
Q: Find constraint relation between 1kg and 2kg block.

what I tried so far
So, I used a method in which I consider the length of string. Length of red string is $2x_1$. Now , we can notice that one string is long joining 1kg and other joining the pulley is short. But since the assumptions are there. We can consider it like this. If you need a proof , then let me know. I shall give an example too in edit afterwards.
So , then length of string for 2nd pulley is $2x_p$.
I assume  that the Length of string for $2kg $block is $2x_2$. However, I feel this is wrong since the same string is connected to 1kg block as well.
So, I get is $2x_1+2x_2+2x_p $but my answer is coming wrong.
So, it would be helpful if you can help me just correct where my mistake is or share another method if you’d like that.
another simpler example
EDIT: an example
Here , $a_1 , a_2 , a_3 $ are accelerations of $1kg , 2kg , 3kg $block respectively.


texts: Turndown for a Post-Tension Concrete Court

texts: my father has a sports court construction business and I work with him infield and in the office. He usually almost always builds the sports courts using post-tension concrete with 4000 PSI concrete. He also includes turndowns in all the courts he builds. My question to this would be: Is it necessary or beneficial to use a turndown for the slab? The reason he uses post-tension is to avoid cracks which really does work marvelously, but is it necessary to have a turndown when there is no load on the edges of the slab? Can it actually be a negative component of such type of slab since if there is some type of soil erosion on the edges of the slab where the turndown is, this will cause an uneven load distribution of the slab itself on the edges, even though they're tensioned by the PT cables? Or is a turndown the right thing to do in this case? I'm not a civil engineer or anything but wanted to know if anyone had any insight on what would be best in this situation. Thank you!


texts: Deriving the amplitude of a coulomb (dry friction) damped spring

texts:
This is my first time posting anything, but I could not figure out the derivation of the amplitude of the spring for the 4 first oscillations. I am not acquainted with the effect and calculations of damping since I am only in high school. This is an assignment I have, I think I am in over my head, but I have invested too much time in this to change the topic. I figure that the only deviation to the classic coulomb damping where the source of energy dissipation is due to the weight sliding on top of a surface, and the force of friction is constant and does not change, is that the friction coefficient changes as more coils enter the paper cylinder which is compressing the spring. The values that I have is the frictional force of when the entire spring is within the paper cylinder, the mass of the weight, the initial elongation of the spring (x naught) and the spring constant.  . If anyone can help me with my assignment I would be eternally thankful! If not, I would gladly take any help with deriving the amplitude of the classic coulomb damping case as seen above as a backup. Moreover, If there is any rule that I am breaking with this post, let me know. This is as previously stated, the first time that I post anything, and it is due to pure desperation as I am way in over my head! Thanks in advance!
I got 15 experimental values for the amplitudes at half revolution increments for 4 revolutions, took the averages and inserted them into a graph. The graph can be seen here: https://gyazo.com/3e2d1c18b05a31d1eca88c411bdbb2cb .
To solve the equation for x(t) in the equation ma = -kz +F_r, where you would get Asin(wt) + Bcos(wt) + F_r/k, you merely need to equate it to the initial displacement to calculate B, and equate it to the derivative of displacement i.e. initial velocity to get A. A is zero if there is no initial velocity, but the question still stands, how do you get -sgn(v) so that it can be used as the value of friction over spring constant which would give the damping term. I suppose it could be gotten by taking -v/magnitude of v, but how would you calculate the magnitude of v? Since solving the equation without it would merely result in a regular cosine function.


texts: What is the voltage at the ground electrode of a spark plug?

texts: Since the voltage required to bridge the gap between the central electrode and the ground electrode of a spark plug can reach up to 40 000V and even more, my question is, how does the battery not die since the spark plug is grounded to it. Is all that energy lost in the ionization of the gas and thus the voltage reduced to ~12V?


texts:
I would like  to gather ideas to model the dynamic behaviour of a plate with variable thickness. The assumption are:

Small deformations.
The plate is all made of the same material with variable thickness.
Boundary condition can be: free edge or fixed force profile.

My goal is to have a model as simple as possible and solve it with a Matlab script. The desired input are plate physical properties and boundary conditions. The desired output is the dynamics of each point of the plate.
The main ideas I am pursuing right now are:

Write the differential equation and solve using finite differences.
Simplify the whole model with equivalent springs and point masses.


texts: Optimal control of the gradient type PDE

texts:
I recently encountered the following optimal control problem.
The purpose of the system is to find the parameter $x$ at which the maximum or minimum of the function $f$ a is reached. $x$ is unknown to us in advance.
We have gradient type PDE:
$\frac{dx}{dt}=\frac{df}{dx}+u$
where $f=\frac{1}{(x-x_*)^2+1}$, and $x_*$ - constant, at which the maximum function is reached.
Problem:  Set the cost function $J$ so that the transient process from $x(0)$ to $x_*$ in the system is exponential, i.e.:
$J = f(x,x^{'},x^{''},u) =?$
I am new to optimal control of partial differential equations. I can't seem to figure out how to find an approach to this problem, so any help would be appreciated. How to set the cost function $J$? How to generate an input control signal $u$? Do we have an analytical solution? I thank all the helpers.


texts:
I am using a nichrome wire for my project.
Q.1. I want to know which source should I use as my voltage AC or DC? I know that the average power dissipated in a resistor in one cycle(in AC source) is equal to the average power dissipated in DC source. But I want to know which would be efficient for me ... I want to use this to cut fabric.
Q.2 First of all the power dissipated in the circuit will be in the wire(which will act as a resistor). And also the wire will radiate heat energy(Stefans law depending upon emmisivity). So the temperature of the wire will increase for some time and then become constant.
I want to know if there is energy dissipating in any other form?

Edit 1: I figured out a little bit. Now please tell me if there is something to be added in place of something or not! But the problem is that e i.e. emissivity is varying. Then how to use the below formula. We are trying to find temperature but a term in the formula of temperature is itself dependent on temperature :(

$$ V^2/R=e\sigma AT^4 + mS + Something$$


texts: Is an Explosion Proof Circuit Breaker Panel Required at a Gas Station?

texts:
Check the attached photo of a gasoline station.

The two panel boxes at the center of the photo (in the corner of the station) are standard panels (IP-67), which enclose standard circuit breakers for the main gas pumps of the station.

They are less than 7 linear meters on separation.

I would like to ask you, if you have experience on electrical EX-proof facilities:

Is there any mistake here? Or is everything right according to the EX-proof codes?


texts: Order of a transfer function and its properties

texts:
I hope this is the right place to ask since I couldn't find a control systems SE.

Lets say we have the transfer function $P(s) = \frac{1}{s(s+15)(s+10)} = \frac{1}{s(s^2+25s+150)}$(completely made up numbers) of some sort of device. This is without any controller or feedback attached.

How should I look at the $\frac{1}{s}$ that's in there? Do I treat it as a separate multiplier or do I handle this as a third order system?

Without the integrator this is a simple 2nd order system with clearly defined relative damping and natural frequency because of $\frac{\omega_n^2}{s^2+2\zeta\omega_ns+\omega_n^2}$.

Technically I could treat the 1/s as an I controller with the value of $P_i$ value of 1. Would this system even have a steady state error with a simple unity P feedback? Technically it would automatically be a PI controlled system right?

If the questions don't seem clear it's because I don't really know what to ask here.

edit: I managed to read something about types of a transfer function(0, 1 or 2) which only modifies the error you will have. The transfer function shown here would be considered a type 1 because it has 1 pole in the origin(2 means type 2 and 0 means type 0 I guess). Type 1 means that the steady state error will be 0 for a step input, which confirms my speculation about the error. I still don't know if it has any other effect.

edit2:

So this picture shows the exact same thing in 2 forms. They're are functionally the same. The PID controller is C(s) in this case. Well it's a PI controller with K = 1, without me actually adding anything to the system. I've just added a negative feedback loop.


texts: Is the speed of a DC motor proportional to PWM?

texts:
I'm trying to control the speed of DC motor but unsure of the relationship between speed and PWM. I'm aware that the bigger the duty cycle, the larger the speed, but how exactly would this relationship play out?

Would double the duty cycle make the speed double too?


texts: Calculating piston force for pneumatic vs hydraulic

texts:
I'm trying to calculate piston force pressures for double acting pistons for pneumatic and hydraulic pressures.  I found the following formula for calculating both

$$\text{Force} = \frac{\text{Pressure} \times \pi  \times (\phi_\text{Bore}^2 - \phi_\text{Rod}^2)}{4}$$

It seems to me that there should be some kind of conversion factor when going from pneumatic to hydraulic or vice versa.  Is this formula valid for both pneumatic and hydraulic?

I got the formulas from the following sites:

http://www.engineeringtoolbox.com/hydraulic-force-calculator-d_1369.html
http://www.engineeringtoolbox.com/pneumatic-cylinder-force-d_1273.html


texts: What are those objects of the top of this building called?

texts:
Does anyone know what these things on the ceiling of this building are called?

I am referring to those objects with semicircle shape that act as a ceiling on the
 top of the building.


texts: Would friction forces impact a torque measurement transmitted through a gear box

texts:
I want to be able to detect very small torques placed on the end of a cantilever beam. These torques are very small - 1mg by 10cm. I am trying to make this on the cheap and use a load cell.

I plan to amplify the torque by running it through a self made very high stage planetary gear box, say like 250:1. I would apply the resulting torque to the sensor by having a rigid beam of known length hit the load cell.

Now this is essentially a static test. I will have the apparatus so that the torque on the output would be resisted so it could be measured.

Will friction be a problem in terms of accuracy? Is there an initial threshold I would need to meet for the torque to make it through the gear box?

Would I be better off with maybe using a worm gear setup?


texts: Pearson correlation of neural responses with it's linear estimation

texts:
I am trying to anderstand the following fact from this article (page 13):
How can single neurons predict behavior

Suppose I have a linear estimation of a stimulus:
$ \hat{s} = \mathbf{w}^T(\mathbf{r} - \mathbf{f}(s_0)) + s_0$

where $\mathbf{w}$ is a vector of weights, $\mathbf{r}$ is a vector of responses responses of two neurons to a stimulus, $\mathbf{f}$ is the vector of average neural responses to the stimulus, and the stimuli (angels between $-\pi$ to $\pi$) are symetric (amount and location) around $s_0 = 0$.

Can anyone see why the following is true for the Pearson correlation (where $\Sigma$ is the covariance matrix of $\mathbf{r}$):

$$ Corr(\hat{s},r_k) = \frac{\langle \hat{s}r_k \rangle - \langle \hat{s} \rangle \langle r_k \rangle}{\sqrt{( \langle \hat{s}^2 \rangle - \langle \hat{s} \rangle^2) }\sqrt{( \langle r_k^2 \rangle - \langle r_k \rangle^2) }} = \frac{(\Sigma \mathbf{w})_k}{\sqrt{(\Sigma_{kk}\mathbf{w}^T \Sigma \mathbf{w})}} $$


texts: I recently got dental braces and have been using foam earplugs to protect the inside of my lips from the braces. I place them between the lips and the braces and they work quiet well. However I am concerned whether harmful chemicals could potentially leach from the foam. Please advise.


texts: How can I find the price of a product if the manufacturer doesn't show it on their website?

texts:
I need to buy a particular brand and model of stepper motor and I have found the product on the manufacturer's web catalog, but with no price listed.

How can I find the price of device? I tried writing to the manufacturer but they haven't responded.
Why has the manufacturer hidden the price?


texts: Unusual idea for fish tank design. Unsure if plausible or not

texts: I looked through the stack exchange list of sites, hoping to find one more suitable for my question, but decided that this was the most likely place to get the answer I'm looking for. I'm not an engineer, but I'll try to explain myself as clearly as possible. Here's the set up: Two fifty-five gallon fish tanks, each on a metal shelf stand. Each tank has two holes (drilled or cut out, idk, and wouldn't mind having the neccessary steps for this explained) in their glass floors. There are corresponding holes drilled through the metal shelves that they sit on. Two U shaped glass tubes seem to hang under it, one bigger than the other, so the smaller one is above it. One end of each is set securely through the holes of one shelf and the holes of one tank, same on the other side (picture to better explain). The idea is that, when both tanks are filled with water, the tubes would fill, too, and the fish would be able to use them as highways, so they could swim freely from one tank to the other. I'm not sure how the tubes could be securely connecting, though I was imagining in the same way that the walls of the tanks are connected (I think it's glue, not sure, clarification welcome). Also, a friend proposed the problem of pressure from the water above being too much on the tubes. I really just want to know if this is doable. And, if doable, but there are some glaring obstacles, to have them explained. Thanks in advance and sorry for disrupting the well-versed engineer-y air of the site. (Side note -just because I'm intruding: This is actually an idea I came up with for a tank set up in a novel I'm writing. I've lived around fish tanks, but have never actually tried doing anything remotely like this with them- not sure how to put that. Anyway, thanks again.)


texts: Pressure drop across a damper vs rotor stator pressure increase

texts:
I am recalling from a turbo machinery course that a series of rotors and stators in a turbo machine operate like this. The air enters the machine and the rotors speed up the air so it slams into the stators and increases pressure (because it loses velocity so there is a corresponding increase in pressure according to Bernoulli equation)  and repeats this several times before leaving the turbo machine (please correct me if the general idea is incorrect).

With fans in HVAC systems, there is a corresponding pressure drop across a damper that modulates flow. If there is a constant speed can that has a modulating damper on the discharge side to control flow, what do the pressure changes look like on the fan side of the damper and the discharge side of the damper.

Maybe the two scenarios are not similar but I think I am confused as to why air loses pressure across a damper.


texts:
I'm trying to construct a stainless steel high pressure containment vessel (pressure reactor) (2000 psi or so). Yes I realize that this is a don't try this at home type of thing, and I plan to put some lexan in front of it before I do any testing.

I'm looking at 2" stainless pipe with a wall thickness of .148"(rated 4000 psi), and I'm trying to figure out the best way to seal the ends. I plan on welding one end cap on, but the other end needs to be removable. I'm not certain how to calculate how much pressure a threaded pipe end would be able tolerate, or if perhaps some sort of high pressure triclamp. I've seen some industrial pressure reactor vessels, but they are rates for something like 13,000 psi, way overkill, they are also super expensive. Looking for a DIY lower cost alternative. Any info would be appreciated.


texts:
I have two parts that should be bolted together with four M6 bolts. The tolerances of the bottom part are quite big and the holes for this part are fixed to Ø6. The tolerances of both parts are fixed due to manufacturing and lowering of costs.
I need to determine the size of the holes of the top part in order for them to fit together. I have attached a photo showing the tolerances of both parts.

I am in doubt how to calculate the size of the holes. For instance for the left side, is this the correct way?
$$\begin{align}
\text{Diameter} &= \text{Delta}_{dim} + \text{Tol}_{dist} + D_{shaft} \\
&= (211.5-210)+3.5 + 6 = 1.5 + 3.5 + 6 \\
&= Ø11
\end{align}$$


texts: Why do normal tunnel boring operations not use the dirt (from the boring itself) for reinforcement rather than bringing it from other sources?

texts:
According to Elon in this video (@13:06), he states that the reinforced segments are 70% just dirt, but in normal tunneling, they actually truck the dirt out and bring new dirt in which seems very inefficient.

Is it really that simple or is Elon oversimplifying the challenge?


texts: Managing water supply pressure to a building

texts:
I am planning to supply drinking water only (not bath or sanitation or washing)  from a tank on a 10-storey building.

The problem is that if a gravity feed is used, then the pressure will be different on each floor. For example, the estimated PSI will be only 7 on the top floor and 46 on the bottom. Ideally we want to have a PSI of 40 PSI on every floor. How can this be accomplished?


texts: Is there a standard name for a flanged threaded tube?

texts:
I have designed a custom part that I need, but it is so simple I'm sure there must be off-the-shelf versions available. However I don't know what it's called to search for it.

The image on the left is the custom part I designed, it's basically a short threaded tube with a flange at one end. The tube is 10mm long and 8mm outer diameter, with an M7x0.75 thread. Note that although it's quite dark inside the tube in the picture and difficult to see, the tube is open at both ends.

The image on the right is a kind of flanged nut type thing I found in a leather strap binding, it's similar to what I need only smaller and also too short, so I know I'm not the only person to want a part like this.

I have searched for "flanged nut", and "threaded insert", among other terms, but I can't seem to find anything like this. Is it a thing? What's it called?


texts: (Mechanics/Electronics) Anybody know DTC code for asking Air flow measurement on OBD2?

texts:
(Sorry if there's a better place for this. It's my first question)

I'm doing a final work for a Bachelor in Electronics and my work consists in making a fuel meter for a car. Its connected via OBD2 port using CAN protocol.

My problem is i can't seem to find anywhere how to ask for the Mass Air Flow (MAF). The only thing i found was trouble codes eg. faulty MAF or so.

Any help is really apreciated, as im running out of time for my project and i've found little information so far.


texts: Distribution of turbulent energy dissipation in a stirred tank

texts: Is detailed experimental information on the distribution of energy dissipation in a stirred tank(45o Pitch blade) available? I require this variation in all directions in a standard stirred tank configuration.


texts:
What are the requirements to call a controller real-time?

What are the entire standards for that?

I do not think that just rendering the output quickly before the sampling interval passes is sufficient for the real-time certification.


texts: Rigid Body Rotations and Engineering Strain

texts:
Problem

Consider the following 2D rigid body in the $x$-$y$-plane, which is rigidly rotated around the $z$-axis with the angle $\beta$:

(Image Source: Continuum Mechanics - Small Scale Strains - Limitations of Small Strain Equations - Effect of Rotations on Strains)

A point $[X, Y]^T$ will then be rotated to a new point
$$[x, y]^T = \ldots$$
$$\ldots = [X \cdot \cos(\beta) - Y \cdot \sin(\beta), \ldots$$
$$\ldots X \cdot \sin(\beta) + Y \cdot \cos(\beta)]^T$$

The engineering strains for this rigid body rotations can thus be given as
$$\epsilon_{xx} = \cos(\beta)-1$$
$$\epsilon_{yy} = \cos(\beta)-1$$
$$\epsilon_{xy} = 0$$

This means that normal strains will be induced for (large) rigid body deformations. For $\beta=90°$, they will be $\epsilon_{xx} = \epsilon_{yy} = -1$. For $\beta=180°$, they will be $\epsilon_{xx} = \epsilon_{yy} = -2$.

In a text book, I found a corresponding picture, which shows a FEM simulation based on engineering strains. As a result of the rigid body rotation, the body grew in size:

This seems to correspond to a gif I found on the German Wikipedia site (here a static version) showing the von Mises stresses:

Question

Why does the body grow in size instead of getting smaller? The normal strains are always smaller than zero, which means that the stresses are also smaller than zero (for a linear stress-strain-relationship). Would that not entail compression?
What do I miss?


texts: how to fabricate an aluminum square mesh?

texts:
I am working with a Physical Vapoor deposition (PVD) machine. I have 3*3cm Transistor Samples that I need to attach to the Sample holder of the PVD. I want to fabricate a "mesh" that will hold my sample holder.

The sample holder is a metal plate with holes for screws. The structure needs to be made of metal.

Below is a picture I drew in pain of what I have in mind, with the screw holes in the corners.

It doesn't seem to be that hard but I have no idea how to start or where to look. How do I go about doing this? are there companies that can do this ?


texts: What are these outdoors "mystery boxes" for in the USA?

texts:
While watching random videos shot in the USA (in the present time), I've noticed these little weird outdoors boxes:

What is the purpose of these? They look like they might be related to ventilation or something, but they are pretty far away from the nearby buildings. We certainly have no such "mystery boxes" where I live, and I don't even have a good guess what they might be for.


texts:
Has something like a hardware replicator ever been built? Something akin to von Neumann probes, only it doesn't have to be for space exploration?
When I say "replicator", in this context I mean a piece of hardware that can create more instances of itself.
If it has not been built, how might one go about it? At first, I was thinking that the first unit would contain a computer with a program telling it what raw materials in the environment to look for and use. But then I realized that this means the very first instance would need to have fine enough motor control to build a new machine with a new computer in it. That's seems awfully complex for a first instance of a replicator (after all, self-replicating molecules are much simpler).
So there seems to be an optimum somewhere in the middle between the following two: making the first replicator too simple may result in its lacking the ability to replicate, but if we make it too complex then it will be too hard for it replicate. But any approach that comes to mind to build this machine seems too hard for replication.
PS: Engineering noob so not sure how to tag this!


texts: What exactly is the thin wall assumption in regards to beam cross sections?

texts: What does it mean with respect to calculating stresses on a beam undergoing loading and when should it be applied?


texts: Theoretical maximum pressure from combusting LPG

texts:
I am curious how to find or estimate the theoretical maximum pressure that the combustion of a LP gas, such as propane, can produce inside of a constant volume, such as in a cylinder.
I know what the higher and lower hearing values are of propane, the reaction formula, and the flame temperature. I know it probably isn't as simple as just using the specific energy and dividing by volume because that doesn't limit that maximum pressure possible.
This is particularly fascinating to me because it is the concept is what powers the Boston Dynamics Sandflea's launcher (see: YouTube). I'm curious what the maximum power could be for this type of mechanism.
Thanks in advance.


texts: What method can I use to calculate the temperature within a house being cooled by vents on the floor?

texts:
To simplify the problem, if we just imagine a rectangle resting vertically, and on the bottom face (the one closer to the 'ground') there are slits on that face. On the opposite face to that (the one closer to the 'sky'), there are also slits. In this case I am assuming no q in or out through the other 4 faces. The reason I put 'ground'  in quotes, is because I am imagining the rectangle is not actually resting on the ground, but is instead raised off the ground through some mechanism that doesn't affect heat transfer or fluid flow of the air. Also assume the are is some T1 below the bottom face, and T2 above the top face. T2>T1.

My question is how I would go about calculating the temperature gradient within the house? The aim is to see if this is a viable way of cooling. To be clear, I am not asking for someone to work this out in detail, but rather an approach to the problem.

I spoke with a professor and he suggested using density differences to calculate the fluid flow, but I do not know how to get a temperature gradient from that information. Thank you.


texts: As the question states, do vibrations cause any influences on inductive sensors? For example, do vibrations on rail, from a locomotive, affect signalling equipment?


texts: Can the fillet radius of an edge shaped by grinding be guessed from the grit size of sandpaper?

texts:
Assumptions

Assume a small bore hole with a few mm diameter in a hard plastic plate (e.g. POM), and further assume that after drilling the hole the surface of the plate is grinded with a disk with fine sand paper (e.g. 20 µm mean grit diameter). This would remove a possible larger radius from the edge of the bore hole and sharpen it to a certain extent. How will the final shape of the edge of the bore be affected by the grit diameter?

Questions

Is it under this conditions reasonable to assume an approximate fillet radius of the bore hole's edge in the same range as the particle radius of sand paper?
If not, is the expected fillet radius more likely to be larger or smaller than the particle radius?


texts: Can air flow occur in both directions in a 2 way solenoid valve?

texts:
I'm designing a system where I need to fill and exhaust air from an an air bag. The air will be supplied from a dc motor. As of right now I've been considering placing a 2 way solenoid valve for air to flow into the bag and then open the valve without the motor on to release the air into the atmosphere.
Will this work, or does air only flow in one direction in a 2 way solenoid valve?
Sorry if it's a bit too general, I'd be happy to answer any questions.
Thanks for your help!


texts:
I'm learning about how dog clutches work particularly in sequential transmissions.

I'm having a hard time understanding the principle which ensures dogs will always mesh correctly. I can easily imagine a situation in which dogs will collide and switching gears will not work such as when the speed of the input shaft matches the speed of the intermediary shaft and dogs are aligned together or when the engine is off and the vehicle is not moving then dogs can again collide.

I'm designing my own clutch-less transmission using dog gears, because I thought they are most appropriate, so I'm trying to understand the principle, not so much the example cases I mentioned above.


texts: How to resolve the interruptions in the screw pump operation due to air trap?

texts:
In one of my application, there is a requirement to dispense the concrete paste at the required rate continuously. some technical details of the application given below

Dispense rate 5-50 LPM
Dispense should be continuous
The material is concrete paste
Solid content is up to 4 mm
delivery length is 5-6 meters
bends - 3
Hose dia 38 mm
density 1.9 to 2.2

Currently, I am using a screw pump, which can pump up to the full length of 5-6m. But with some issues.

The flow often stops, for which we had to reverse the motor few rotations and then run forward. But this operation is not acceptable.
The materials flown out of the pump was heating up by 8-10 deg.C.

We have also tried the piston pumps that are used in construction sites for concrete spraying operation. It works continuously, but there are no linear flow rate adjustments, and it is bigger in size.

The screw pump works fine, but it often stops. The reversing and restarting pumping operation is not desirable for the process.
We noticed that when reversing the motor for few rotations, the material in the hopper is raising. So we are guessing that the motor is stopping due to air trap. But supplier commenting it is because of vacuum created in the pump. because the concrete paste is not perfect fluid.

Are any screw pump users came across such situations? How did you solve it? Any suggestions to fix this issue I can get to rectify it??


texts: How to find the wear rate of materials in the net?

texts:
Are there any free online databases where I can access data for the wear rates of materials? I tried using CES EduPack, but I'm having no luck.

Maybe other free and open databases are also existing on the net? Where and how could I find the wear rate in them?


texts: What is the most efficient way to ionize air?

texts:
I have a project to convert wind energy directly to electrical energy with no moving parts.  The wind will enter a reducing tunnel for concentration, then go through an unobstructing de-humidifier, then through a multi-plate sandwich type electrode setup like that of a capacitor where the voltage would be very high to ionize the air passing through.

This ionized air molecule would then pass through a magnetic field to generate electricity.  A fraction of the electricity would be used to ionize the incoming stream again. I realize that the less the spacing between the capacitor plates, and the greater the voltage, the better the  ionization.  I was wondering what would be optimal plate spacing and voltage for dry air at STP, if a cylindrical plate arrangement would be better than rectangular, etc.  Other advise also appreciated.


texts: Azeotropic Distillation - Am I interpreting this VLE diagram correctly?

texts:
I've been looking at ways to re-concentrate a formic acid-water binary mixture with the VLE diagram below.

Am I correct in saying that to concentrate a solution of say , 40% formic acid by weight I could (excluding all recycle streams for simplicity) implement a distillation column at 1 bar to produce a distillate at the azeotrope (78%) and then pass this distillate into a second column operating at 0.1 bar to distill further to 95%?

Aditionally, would operating the 1bar column for a distillate of say only 70% (past the 0.1 bar azeotrope) then performing the remaining concentration in the low pressure column result in any significant energy savings due to less steam required at the lower pressure?

Lastly, if I was to START with a solution of 85% formic acid, already beyond both azeotropes, I could just perform simple distillation in a single column at either pressure point to obtain the 95% product?


texts: What makes scooters unstable at high speeds?

texts:
Scooters and skateboards are obviously meant for slower speeds, below 5 MPH. Typically if you go faster than that, it becomes harder and harder to control the scooter, and you will fall off. An example of this is the speed wobble, examples easily found on youtube.

What's the deal? Why is it that comparatively, bicycles can handle higher speeds with more stability and comfort?


texts: Incompressible 2D pressure-driven flow: for Navier-Stokes equations in nondimensional form, how should I express pressure boundary conditions?

texts:
*I have updated this question.

I'm using two codes for modeling incompressible, two-dimensional flow out of a tank.  My fluid dynamics experience is pretty basic; I'm using the codes to understand a chemical process.  The codes haven't been used much, so I'm running a benchmark/test (running both codes on same flow problem) to make sure I understand them.  Unfortunately, I can't post the codes.

Problem:
In the test, I want a pressure gradient to drive flow (a constant pressure at the bottom of the tank and 0 at the tank outlet).  So far, velocities calculated from one code are much higher than velocities from the other.

One code uses the Navier-Stokes equations in dimensionless form solved by Galerkin finite elements with a perturbation method (penalty formulation).  This works by eliminating pressure from the equations.  I managed to track down the developer and he ran an example for me.  Our results are identical, so I'm not making a mistake with the inputs.  The other code uses a volume of fluid method and pressure is not eliminated.

I'm now wondering if the dimensionless code (where pressure is eliminated) can handle pressure boundary conditions correctly.  If anyone has any ideas about this, I'd love to hear them.  Thanks a lot.

Edit for Dan

Here is the tank geometry I'm dealing with, plus the dimensionless groups that (according to the documentation) are used in the code that is based on dimensionless Navier-Stokes.  The dimensionless parameters are the ones with the bars over the letters. $\rho$ is fluid density; $\eta$ is fluid viscosity. I know it is possible to nondimensionalize pressure by using velocity in the nondimensionalization, but I don't know the velocity at the inlet so don't want to do that.

There is nothing in the documentation about how to deal with a pressure boundary condition.  I have used the pressure dimensionless term, but with $A$, not $a$, since I want to define an inlet boundary condition.  This gives me a pressure that is too high because it leads to velocities that are greater than in the other code.  I hope this is clear.


texts: Assessing flow rate from open sea into a container

texts:
I'm currently assessing sub sea pumped hydro capabilities, and need to use the flow rate in order to calculate power output. I can calculate the energy storage capacity using E = mgh:
$E=mgh = 25675000 \times 9.81 \times 200 = 50374 \ \mathrm{MJ} = \frac {50374\text{MJ}}{3600} = 13992 \ \mathrm {kWh}$
However, I don't know what the flow rate from open sea into the pipe would be. In the model below, the top of the pipe has a valve that will open to let seawater in during the power generation stage, down through a 90/10 Cu/Ni pipe, through a turbine and subsequently fill up the vessel, which is located 200 m below the inlet (Head = 200 m). Vessel design doesn't take into account the pressure at this depth through use of a bag seen here.
What would the best way to calculate the flow rate to use in theoretical power calculations, since the sea is an open reservoir?

Head = 200 m
Pipe Length = 1594m (assuming a straight path between elevations)
Vessel Volume = 25,000 m3
Seawater Density = 1027 kg/m3

These variables can all be changed this is just preliminary/theoretical.


texts: Difference between AT and AMT transmissions as far driving experience is concerned

texts:
Please forgive me if this isn't the right place for this question but I'm trying to understand the difference between AT (Automatic Transmission) and AMT (Automated Manual Transmission) as far as the driving experience is concerned.
Is there any difference and if yes, what are these differences ?

For example, if you trying move forward in a MT (Manual Transmission) car, when the car is parked uphill, then you will need to use half-clutch to prevent it from rolling backwards. I've heard that such a problem doesn't exist in an AT but I have no idea about AMT. This is just one aspect of the driving experience I'm trying to learn about.

If there's any aspect where they do differ, please include them in your answer.
I'm not interested in the mechanical differences though.


texts: worm gear linear motion with release mechanism

texts:
I want to convert rotational motion to linear motion. Since available space is limitation in my project, I was planning to use screw jack mechanism as a lift. But screw hack has very low efficiency - about 15% to 20% only. The rest of energy is lost to friction.

So I was thinking about using worm gear to convert rotational motion to linear motion of worm by not allowing the worm to rotate.

Is this possible and will it have better efficiencies as the contact area between worm gear and worm is much less than screw jack mechanism ?  I can use any other gear mechanism also as long as efficiency is high....

Also I need a quick release mechanism to dis-engage the worm gear from the worm. Can some one please guide me on how to disengage the worm gear ?

Thanks
Deval


texts: Why is there negative static pressure in contour?

texts:
I studied a paper about turbine and i seen that there is negative static pressure in contour. Why does this happen?

Wave Energy Harvesting Turbine: Performance Enhancement


texts: How to find the maximum misalignment from vibration?

texts:
Consider the system in the (drawn in Paint) image. Assume that there is an input acceleration at the ground defined by a PSD. This acceleration can be in any axis. Points A and B are initially aligned and just offset vertically. You are shining a laser through them and need to know what the maximum possible misalignment is to make sure your optics can handle it.

So, if I have an FEM model, I can find the displacement PSD's in each direction at both points. However, these PSD's are still a stochastic representation of the displacement. I have a few questions because of that:

Do the output PSD's represent some confidence interval? Or are they the same level of confidence as the input? (i.e. if the input is an envelope describing the maximum possible input acceleration, this describes the maximum possible output displacement)
What features of the PSD can be used to decide a maximum? Does the RMS describe this? And in that case, would it be $rms_{A} + rms_B = disp_{max}$ because each could be off by that much in the worst case? Then, you'd do some vector addition to account for the multiple directions of misalignment to get an absolute misalignment.


texts:
Someone told me to avoid over-sizing when using DC Motors. Why? Is this because of sparking and higher wear (brushes) while the motor is running at a lower power rating?

Can someone explain?


texts: Resolution of forces and state of stress at a point

texts:
Is resolution of forces similar to expressing a vector as a linear combination of some other vectors in linear algebra?
Similarly, Is the state of stress at a point in 3D similar to expressing the applied load as a linear combination of 9 other vectors(the shear and normal components along the direction of the three axes)?


texts: Positron Emission Tomography: How to get from photon count to radioactivity?

texts:
What I have learned

The detectors of the PET actually measure the photons, which are caused by the radioactive tracer injected into the patient. Then, with the help of backprojection, we get the photon count for each voxel. I hope I understood these processes right, please correct me if this is not the case.

But as final result, we get the radioactivity concentration in kBq/mL.

Question

How can the scanner convert the counted photons into radioactivity concentration?

My guess would be, that a phantom of known volume is used, with an inserted radiotracer of known radioactivity concentration.


texts: Why vehicle horns are tuned to consonant intervals?

texts:
The primary purpose of a vehicle (car, locomotive, etc.) horn is to warn other traffic units that something potentially dangerous is about to happen. And so, others must pay attention to the signal.

So, why not to tune the horns to dissonant intervals or chords (for example, several notes semitone or even quarter-tone apart, e.g. C natural, C half-sharp and C sharp sounding simultaneously), which are much more unpleasant to listen and so more "attention-payable"?

Maybe this is not a proper place for the question, but I've unfortunately not found a better one, since is more related to engineering and design (than to, for example, music).


texts: Where is Wizard in Solidworks Flow simulation?

texts: would anyone knows why my wizard in Solidworks 2016 flow simulation is missing, I am starting to learn flow simulation because of my study, I am still a beginner, I tried testing it 1 time with my created model, it works but after several days all i ever see is the image below upon switching to flow simulation tab , i cant find it, or how can i bring it back please, any help would be appreciated.


texts: Coupling in a twin engine, tandem rotor power train

texts:
Consider a transmission for a tandem rotor helicopter with two engines and two main rotors such as the one below.

Both engines are connected with sprag (one-way) clutches such that an engine's speed can underrun the rest of the system (e.g. engine failure), but normally they move in sync. The two rotors are always synchronized so they don't collide with each other as they spin (in opposite directions).

Let's assume that we know the moments of inertia for each engine and each rotor. There are accessories (not shown in the picture) which are driven by the same synchronizing shaft and there are of course mechanical losses, but we can neglect all those for simplicity. There is, however, a speed change between the engines and the rotors that needs to be taken into account.

In modeling this system, since each engine can underrun the rotors, I need to integrate the local accelerations to get the speed of the rotors and each engine separately. Generally, my question is: what torques and inertias does each "see" for the purposes for the purpose of finding an acceleration from unbalanced torques?

For the case that both engines are operating and driving (i.e. engaged clutches):

Would each component (engine 1, engine 2, and the rotors collectively) "see" all four torques and all four inertias (the four being two rotors and two engines)?
Or would each engine be unaffected by the torque and inertia of the opposite engine (i.e. due to the one-way clutch) and only "see" itself and the rotors (or maybe some portion thereof)?

For the case when an engine is being shut down and is no longer driving:

Would the shut down engine only see its own inertia and small and diminishing torque (and then you'd have to add some losses to actually get it to decelerate)?
Would the rotors "see" the torques and inertias of the rotors and the one remaining driving engine?
What about the engine that's still driving - the rotors and itself?


texts: Would Amorphous Diamond-like Carbon coatings have a fatigue cycle limit?

texts:
I'm aware that polymers like most plastics can go through stress cycles indefinitely as long as the covalent bonds are not ruptured.

On the other hand, I hear that even metals like steel and titanium do have limited life-spans no matter how small the stresses.

I'm quite interested in the application of diamond-like carbon coatings to materials. Some of these coatings can even be flexible. For example, I'm beginning to see DLC being applied to headphone diaphragms, which have to be a little flexible.

So while the plastic diaphragm that the DLC is bonded to may have an indefinite service life, I'm not sure if the same is true for the DLC coating itself. Would anyone be able to give me an insight into whether or not a DLC coating would have an indefinite life like polymers, or if it has a certain amount of cycles it can go through before it starts to deteriorate?


texts: I'm looking at this inclinometer and in the features it says "12 bit resolution." I'm looking for a resolution of up to a 1/10th of a degree but don't understand what the 12 bit resolution means.


texts: Can a horizontal foundation safeguard against earthquakes?

texts: I have not taken any course in civil engineering. What I was taught was that a broad base would prevent something from toppling. So it makes me wondering instead of nailing the foundation of a building vertically deep down into the ground, if it would make sense to make multiple buildings share a horizontal foundation.


texts: Material resistant to higher temperatures and damage

texts:
I am looking for some material which is resistant to higher temperatures (around 1000 degrees Celsius). So far, I found this:

Gypsum plaster board
Perlite board
Calcium silicate board
Sodium silicate board.

Which of this is mostly resistant to damage? Or is there any high temperature resistant material which has good mechanical properties (especially resistant to damage done on edges of boards)?


texts:
From an engineering perspective, how are the 'relieving chambers' above the kings chamber supposed to work?

The 5 layers of horizontal lintels separated by air-gaps are normally described by mainstream archaeologists as 'relieving chambers' to share and spread the load of the thousands of tons of rock above the kings chamber.
The builders obviously understood the principles of a corbelled arch since it was used in both the grand gallery and other pyramids.

They also understood the simple triangular arch, since this was incorporated in the queens chamber, and at the top of the relieving chambers above the kings chamber.

So, back to the original question, how do the relieving chambers work? (or maybe they don't?) The horizontal lintels have empty space above and below, so are presumably unloaded? The width of each chamber is constant, so can't be acting like a corbelled arch. The only elements actually doing any load spreading are the lintels that make up the triangular arch right at the top. So what's the purpose of all the layers of horizontal lintels? They must have taken a lot of additional work for no (engineering) purpose - not that I can see anyhow.

UPDATE - some theories from elsewhere on the net. A triangular arch directs the load to the side and below the bottom of the arch. For the arch to work, it needs to re-direct the load onto a secure and stable area of masonry. The most noticeable result of the 5 layers of 'relieving chambers' was to require the arch to move about 10 meters higher than it needs be.
Maybe the triangular arch was placed where it was to avoid loading the areas immediately to the side of the kings chamber? and maybe this was needed because those areas contained voids or some areas of structural weakness? A lot of 'maybes', I know.


texts:
Sawstop table saw braking system works by putting a low voltage on the blade, and when it detects that voltage shorted to ground, the blade is retracted and slammed into an aluminum block.  The claim is that it can do this in the time it takes 3 tooth to pass, and their video corroborates this.  Looks like a 60 tooth blade.

The big downside to this:  You have to replace the brake cartridge at around $60 US. and often replace or at least service the blade.  No one likes it when they lose a 200 dollar saw blade.

At 3600 rpm, that's 60 rev per second, or 3600 teeth per sec.  To stop in 3 teeth is 3/3600 or 1/1200 of a second or not quite 1 ms.  This is 1/20 of a single voltage cycle.

The second downside is getting false trips from either wet wood or from nails in the wood.

So what alternatives are technically possible?

Ran into a guy on another forum who claimed that a VFD driven 3 phase motor could stop a table saw blade fast enough that the arbor nut would spin off.

Can a VFD do this in 1 ms without destroying the motor?  (I'm thinking in terms of transient voltages) Presumably you have a big fat power resistor to soak up the energy.

The other method I was considering as a sawstop alternative:

A pair of spring loaded (think high performance engine valve spring) brake pads on a set of callipers round the bottom of the blade.

A formula 1 engine is limited to a max 18,000 rpm. 3.3 ms/rev. Valve closings must happen in  a small fraction of that time.  So the time to close is ball park correct.  Can it grip hard enough to stop the blade in 15 degrees of the blade's rotation?

The forces on the blade are considerable.  You have to stop the motor too.  Typically you're talking a 3-5 HP. These are not pick up in one hand motors.

Options for this:  My snowblower (84" wide, 48 hp PTO) has a linkage with two 4" diameter 1/8" steel plates.  They are linked with a common 3/4" machine bolt.  Hit a chunk of firewood with the snowblower, the bolt sheers.   Usually takes me longer to find a replacement bolt than to be up and running again.

The second way would be like my bushhog mower, which has a clutch between the gearbox and the blade. Some industrial sewing machines do this too.

What ways can you stop a moving device fast enough to save injury, but not damaging the machine?


texts: Maximum strength size thread for aluminium sheet per thickness

texts:
Is there a rule of thumb, or a table which helps one determine what is the maximum strength thread size to use for aluminium sheet?
I am interested in threading 3mm, and 2mm thick sheet aluminium. I am wondering what size of thread I should go for.
E.g. M3 in 3mm sheet, or could I go M4, M6?
With 2mm I would guess M3, but not M4?
I have not found an authoritive source, just answers ranging between equal to the thickness (M3 in 3mm), down to 50% of the thickness (M3 in 6mm).


texts: Why do some high speed trains have long noses, while others do not?

texts:
Why do some high speed trains like the Shinkansen E5 and E6, have really long noses while other trains, like the Eurostar and Javelin, have shorter noses?

How does the shape of the nose affect the train?


texts: How does a microbolometer (IR camera) work?

texts:
I am currently doing a project which has led me to my first encounter with IR cameras, and I am therefore quite curious as to how they operate. Specifically, I would like to know the following

How is heat converted to an electrical signal (current or voltage)?
How is the spectral bandwidth of an IR camera so well defined?
Why are IR cameras so much more expensive than color video cameras? (Color cameras have IR suppressors, right?)
How are 'regular' IR cameras different from radiometric cameras?
What is the difference between IR cameras which can detect temperatures up to, say 1000 °C, as compared to IR cameras which can detect temperatures up to 400 °C?


texts: How do measures of error or uncertainty change, when the underlying variable is transformed?

texts: If I have a measurement $A$ with uncertainty $\Delta A$, then what is the error if I do a calculation like $\frac{A}{\sqrt{3}}$?


texts:
I am looking for help with the following question please.
A piston cylinder device contains 28g of saturated water vapor that is maintained at a constant pressure of 300 kPa. A resistance heater within the cylinder heats the saturated water  by added 8 kJ of heat. At the same time, a heat loss of 3.5 kJ occurs.
(i) Show that for a closed system the boundary work Wb and change in internal energy $\Delta U$ in the first law relation can be combined into one term, $\Delta H$, for a constant
(ii) Determine the final temperature of the steam.
So far i have this for (i):
For a constant pressure expansion or compression process:
$$\delta u + Wb = \delta H$$
which is a quasi equilibrium process
I am quite stuck on this. I would like some pointers to start through this please. I'm looking to understand the problem better.
(Edit)
For (ii) i have found how to complete the question. Now could i get some help to complete the question please? How do i calculate State 1 to get 2724.9 kJ/Kg??
Once i keno this then i can place my information in and calculate the final temperature of the steam.


texts: Why do I get negative work done for adiabatic compression of air?

texts:
I am solving the following problem:

  Air having an initial pressure of 6516 kPa and an initial volume of 0.113 m3 is compressed adiabatically to a final volume of 0.057 m3. Calculate the work done by the gas as it compresses to a final pressure of 17237 kPa.

The given answer is -175.9 kJ.

I started from: $$PV^k = C$$

Work is therefore: $$W = \int\limits_1^2 P\,dV$$

$$\frac{(P_2V_2 - P_1V_1)} {(1-k)} =\frac{(17237*0.057)-(6516*0.113)} {(1-1.4)} = 615.025 \:\mathrm{kJ}$$

Is my relation correct? What am I missing and why is the answer negative?


texts: Systematic approach to design a controller

texts:
I have four different plant systems which I want to control. They are similar in some aspects (equal inputs and outputs as well as disturbances, all are thermodynamical systems). Furthermore, none of the systems tends to oscillate. The major difference are the time constants. Additionally, each system defines specific states which should be kept in bounds (e.g. restrict the maximum temperature).
Is there a systematic way of how to design a controller for these systems? Can I classify the systems in a way that I can claim that for all systems the same control approach can be used? Is there any literature for designing a controller especially with focus on which control strategy to use (there are so many and I cannot find a guide on which system I should use a certain controller e.g. PID, MPC, H_inf, Fuzzy control, integrator backstepping, LQR)?


texts:
For my racing game I am using a simplified Pacejka Magical Formula:

$\mu_{lateral} = \mu_{0} * \mu_{1} * D * \sin(C * \arctan(B * x - E * (B * x - \arctan(B * x))))$

Where:

$\mu_{lateral}$ is sideways coefficient of friction
$\mu_{0}$ is wheel friction coefficient
$\mu_{1}$ is surface coefficient friction
$B$ is wheel lateral stiffness
$C$ is wheel lateral peak factor
$D$ is wheel lateral shape factor
$E$ is wheel lateral curvature

However, I don't know what are realistic values for $B, C, D, E$. I know well the first ones and I also assume that $C$ may be around 1.1. However, what's realistic stiffness, shape factor and curvature in sideways directions for different types of real-life tires?


texts:
I read in a documentation to some adhezive: the tensile strength is 13 N/mm2. How many kilograms can the 10x10mm bonding hold?

I tried to calculate it by the following:

$$\begin{align}
F &= m/g \\
\therefore m &= Fg
\end{align}$$

the strength is in N/mm2 e.g. that is

$$\begin{align}
p = F/A \\
\therefore F = pA
\end{align}$$

substituting the $F$ in $m = Fg$, I got

$$m = pAg$$

Using real numbers,
- tensile strength = 13 N/mm2 = 13*10e6 N/m2
- A = 10x10mm (100mm2 = 0.0001m2)

$$m = 13*10e6 * 0.0001 * 9.81 = 12753 \text{ kg} $$

The result doesn't look right - the 10x10mm bonding imho can't hold 13.000kg weight.

Where did I make a mistake? So the question is: how to convert the 13 N/mm2 tensile strength to kilograms (e.g. how many kilos I can hang to the bonded 10x10mm plates?)


texts: Would too small tubing reduce the max head of a pump?

texts:
I got a mini-project: I want to automatically get rid of the water produced by an indoor air conditioner unit. Since the unit is underground, the water needs to climb ~2m to get to the outside.

I found a cheap pump online that has a max head of 3m and flow rate of 240l/h, the pipes on it have 6mm on the inside diameter. I also have some tubing left over from a gardening project but its 4mm on the inside.

I can figure out how to fit the two together mechanically but since the tubing is tad too small, wouldn't that increase the pressure requirement and thus decrease the max head?

I really don't mind if it affects the flow rate, the amount of water I need to pump out is ~2L/day max so I'm adding a microcontroller to turn it on for just a few minutes out of a day anyways.


texts: Calculating water turbine mass based on head and flow

texts:
Is there a formula, which would allow to estimate water turbine rotor mass based on head and water flow, or based on the final energy output provided by the turbine? I am interested in rough estimate, not a precise formula.

The range of parameters I am interested in is head from 0 m to 500 m, and flow from $0\;\mathrm{m}^3/\mathrm{s}$ to $1000\;\mathrm{m}^3/\mathrm{s}$. I do not know if there is very significant difference in rotor mass between the Kaplan and the Francis turbine, but ideally I am interested in rotor mass of both.

Edit: I am interested in scaling of the turbine size in general. (How big would be the turbine of 10 kW power planet? And how big for 100 MW power plant?) Turbine mass is as good parameter to get idea about the scaling as rotor diameter or other turbine size-related parameter that is used in praxis.


texts: Geometric constraints on Planetary Gears

texts:
I would like to design a single stage planetary gearbox using standard gears.
There appears to be three primary conditions to ensure the geometry of the gears will fit - correct center distance, placement of planet gears around the sun, ensuring adjacent planet gears do not interfere.
A number of the conditions depend on whether the planet gears are evenly placed around the sun or unevenly placed around the sun. What does this actually mean? Using a ring gear of 100 teeth, three planet gears of 40 teeth, and a sun gear of 20 teeth - would the planet carrier physically position the planet gears 120 degrees apart, or would two planets be positioned 33 teeth apart and one 34 teeth apart, without causing interference of the ring, planet, or sun gears?
What is a good reference for planetary gear design?


texts: How to remove potting material from an electronic package?

texts:
I have an electronic device that uses black potting materiel similar the one below to I believe to protect the electronic components from elements.

I would like to safely remove this material. This material might be some type of epoxy. There are plenty of suggestions how to remove potting material (removing potting electronics). Some indicate that the chemicals in the potting might be harmful.

How can I safely remove the potting material? Through observation can I safely narrow down the potting material?


texts: How to design a PID controller for MIMO systems in which there are more outputs than inputs?


texts: What is a "typical" in the context of control engineering?

texts:
When talking about control systems I sometimes hear the term "typical", however I have no clear understanding what it is. It's also mentioned in some codes (so far without definition), here's an example image from the DIN EN 62424 (IEC 62424:2016):

From context, I think that it refers to software building blocks or common functions of the device (sensor or actor) itself but I'm not sure. We don't have a control engineer in house whom I could ask.
I tried googling the term but typical is such a common word.
Edit to add: I wondered if "typical" is a weird anglicism, but found this in the DIN:

"Acronym and identification of a grafical diagram in a database, or group of signals or grouped PCE-tasks"
It doesnt really answer my question what a tpyical does or is for.


texts:
I need someone to confirm or deny my understanding in the following situation.

I have an empty vessel that is in equilibrium with the atmosphere and I have a pressure gauge on the vessel that displays gauge pressure. The gauge should read 0 atm, correct? If I then close this vessel, pull vacuum on the vessel to completely evacuate it (assume this is possible), then fill it with it 2 atmospheres of nitrogen, the gauge will show 1 atm, correct?

EDIT -
There is some specific volume of nitrogen that at ambient temperature will exert 2 atmospheres of pressure within my vessel. In my scenario, I mean to say I have a supply line that can deliver as much nitrogen as I need to the vessel at ambient temperature to meet this condition.


texts: Solving parallel without GUI in batch mode not working as expected (Linux)

texts:
I'm currently trying to run my solutions in batch mode because in the future I'll be running simulations which I want to be done in the background.

I've tried to adapt the code from here: https://www.sharcnet.ca/Software/Fluent6/html/ug/node22.htm

Using some additional commands from here: https://www.sharcnet.ca/Software/Ansys/16.2.3/en-us/help/flu_gs/flu_ug_sec_startup_option.html

What I tried to do was:

fluent 3d -gr -t36 < inputfile >& outputfile &

Where the inputfile has no extension and has the following content:

; Read case file
rc CoolingChannelNoBatWall3D.cas
; Initialize the solution
/solve/initialize/initialize-flow
; Calculate 500 iterations
it 500
; Write case & data file
wcd CoolingChannelNoBatWall3DRes.cas
; Exit FLUENT
exit
yes

This starts the GUI, even though I tried to suppress it. After starting the GUI it does nothing. What am I doing wrong here?

EDIT:

fluent 3d -t 36 -g -i < inputfile.jou >& outputfile.jou &

Does not start the gui, but it's also quite hard to see if anything's really happening.


texts: I've heard that the 10,000 year clock will use multiple power sources (heat differential, mechanical weight, etc.), but how are they all integrated?


texts: In Callister it says, "two modes of failure are possible ductile and brittle." Why not malleable?Furthermore why is uniaxial tensile test chosen for predicting failure?


texts: Easy nonlinear model for large deformation of a beam

texts:
I have a beam subject to twisting and/or bending forces as well as linear compression force along its main axis. It is modelled as an isotropic beam, but if anisotropic is not too far off then that's okay too. The beam is capable of large deformations such that its maximum deformations are:

140 degrees in pure bending
140 degrees in pure twisting
70 degrees bending + 70 degrees twisting

What is an applicable nonlinear beam theory I can apply to this problem using equations rather than any software-based solutions?

I like using the basic undergrad Euler-Bernoulli beam theory, but the assumptions make it invalid in this case and I'm looking for something that is in the same vein as far as calculations goes and does not require significantly more advanced mathematics.

Ideally a theory that reduces the problem to a set of equations that can be solved without requiring multiple pages of tensor calculations that are hard to follow.


texts:
I am trying to find a solution at an industrial line problem.
I have a product which is cylinder, ~40 grams, 6cm length x 2cm diameter.
The products (cylinders) are coming from a machine (output) in a horizontal rail. I can adjust the slope of the rail.
I must transfer them to another machine (packing). I must put each product (cylinder) in an vertical elevator belt.
You can understand what I want from the photo below.

My questioning is what implementation should I use between horizontal rail and elevator.
Any ideas please?


texts: Questions on Na2Cr2O7 turning to a vapor phase in 2500F furnace. And possible ways, if any, to filter it

texts:
I've looked for answers without success, so turn to the experts. At air temperature, solid-phase sodium dichromate (Na2Cr2O7) -- or the equivalent, sodium dichromate dihydrate (Na2Cr2O72H2O) -- is introduced to a 2500F glass furnace. It can be 5% or more of a ~1200 lb batch comprised largely of silicon dioxide (SiO2). Total time in the furnace = 16 h.

Much of the Na2Cr2O7 goes into solution in glass as a coloring agent. But some portion will off-gas off the glass-melt, transforming into a gas phase.

Question #1: Does the Na2Cr2O7 turn into a liquid first and then reach its boiling point and then evaporate?

Question #2: Or does it turn directly from a solid to a gas -- sublimation? Note that, mixed in the ~1200 lb batch, it goes from air temperature directly into a 2500F furnace.

Either way, gas-phase Na2Cr2O7 vapor particles rise up off the melt.

The furnace exhaust stream is estimated to be greater than 750F.

Question #3: At what temperature will the Na2Cr2O7 vapor particles desublimate -- turn back -- from a gas to solid Particulate Matter?

Question #3.A. Will they return to solid phase prior to reaching the baghouse filters?

Question #4 What size might these vapor particles be? A range in nanometers -- 30 or 50, maybe?

Question #5: Gas phase particles are not captured by normal baghouse filtration, correct?

Question #6. Filters pre-coated with lime are effective at controlling Hydrofluoric acid, for example. (Tons of it are used at this facility.) Is there any filter coating or treatment effective at capturing vapor-phase chromium?

Question #7 Is there any way at all to control vapor-phase Cr off a 2500F glass melt?

I've scoured the literature for many an hour with no luck. Now I'm turning to the experts, starting with you good folks. Many thanks.


texts: Using place command in MATLAB using different state representation

texts:
I had a transfer function

$$\frac{10s+20}{s^3+10s^2+24s}$$

and I found the state space representation of the above using MATLAB.

Using $place(A,B,[poles])$, I found a gain matrix K that corresponds to the poles.

My question is that when I tried to do this using an equivalent alternate state space representation of the transfer function (e.g. using the controllable canonical form), I got a different gain matrix K.

Why is this the case? Since the system's transfer function is one and the same, shouldn't the K matrix be the same? Does this mean that there are multiple K matrices that when multiplied with the states, would give us a desired closed loop characteristic?

Would this then be an advantage over classical control, where here we can use different kinds of controllers with different gains, whereas in classical control we can only have 1 gain value that can get us to the desired closed loop pole characteristic?


texts: How to analyse a beam considering P-delta effect?

texts:
I want to do some analysis of an axially loaded simply supported beam considering P-delta effect. I set up a non-linear load case and apply axial load to it. Subsequent analysis of live load and dead load of the beam is done linearly using stiffness matrix from the non-linear case. However, the non-linear analysis results in the beam hogging upwards, instead of sagging downwards, which mitigate effects of live load and dead load, resulting in a reduced bending moment on the beam.

I am not sure if above analysis is done correctly, or is there a way to force the beam to sag downwards in the non-linear case? Why does it cause beam hogging rather than sagging given that the beam is doubly symmetric with axial load applied to its centroid? I am using SAP 2000 v18 software for above analysis.


texts: Non-destructive Evaluation (NDE) vs Structural Health Monitoring (SHM)

texts: What do you think is the most important thing that distinguishes the non-destructive evaluation (NDE) and the structural health monitoring (SHM)? Recently there has been a tendency in the NDE community to develop a quantitative NDE and an essential part is to develop a research framework in the NDE for prediction and management of remaining service life of engineered structures. I wonder if it is necessary for the NDE considering it would be very similar to the SHM if doing so. How do think of the potential/prospect of integrating the service life management into the NDE, from the perspective of academia or industry? Any ideas will be greatly appreciated.


texts: Design review needed for novel ion trap air scrubber / purifier concept

texts:
As a side kick I came up w/ a wet scrubber / air purifier design using trapped charged water droplets.

I'm thinking about building a proof of concept but would like the community's feedback.

Schematic attached.

Existing scrubbers mix pretreat gas stream w/ liquid droplets and then collect the dirty droplets via a cyclone, mist condenser, or charged plates (for charged droplets).

My idea is to use an ion trap to hold a cloud of charged scrubbing droplets stationary against the gas influx.

This "scrubber cloud" essentially acts as a air filter but w/ much less pressure drop.

At the same time we're conserving scrubbing liquid usage and dramatically reducing reactor volume compared to a wet scrubber.

The ion trap can simply be 2 mesh screens separated by voltage diff on order of few kV
Droplets hundreds of microns
Flow velocity a few m/s
Charge per droplet a few uC
Back of env calc shows electric field force can counter air drag thereby trapping the droplets.

Over time droplets get dirty, coalesce, and may leave the trap. Then they can be captured via gravity or a demister downstream

What are your thoughts?

Thanks!


texts: FEM modal analysis computing displacements

texts:
I have an FEM model that I am doing a modal analysis of. I wanted to check that how I am computing the physical displacement is the correct way, as I've read a lot of about normalizing modes, participation factors, effective masses, etc. and I'm not 100% sure on it.

I've got the various mode shapes and frequencies but now I want to compute how much actual displacement I get if I apply a harmonic force to it. However, I don't want to compute this using the FEM tool as I want to compute a displacement in another tool.

So if I have made my FEM model using units m/kg/N/s and computed a set a modal mass normalized modes, ${\phi_i}$, whose respective amplitudes are $q_i$. The physical displacement of my model would then be:
$$
    U(x,y,z) = \sum_i  q_i\  \phi_i(x,y,z)
$$
Does this have units of meters as my modes are mass normalized or do I need another scaling factor here?

The actual mode amplitudes I compute with:
$$
    q_i = \frac{F_i}{-\omega^2 + j\ C\ \omega - \omega_i^2}
$$
Here $\omega$ is the frequency I'm looking at, $C$ some damping constant, $\omega_i$ the resonance frequency of the mode. The actual force I apply in my other tool is some factor of the generalized modal force, $F_i$. Which is just a projection of the forces I choose to apply in units of Newtons into the various modes.

Does the above sound correct?

If so, do FEM models typically output using modal mass normalization just because the calculations of displacements are straight forward like this?


texts: What is the practical application of Rayleigh number to heat sinks?

texts:
I understand that there is such a metric as the Rayleigh number which governs convective cooling in a medium.  Assume for example, a fist sized heatsink like that below in free air:-

Does the Rayleigh number mean that convection might not start between the fins?  So in effect, the finned heatsink might as well be a large solid lump? And insofar as thermal resistance goes, the thermal conductivity would only depend on the gross overall dimensions (height x width x length) and not the actual finned area?


texts: Hollow Steel Tubing: Critical Load for Sidewall Buckling

texts:
I'm looking to construct a something with hollow steel tubing (e.g. 10ga 2"x3" rectangular tubing) suspended horizontally welded to an outer frame on both sides.

I've already calculated the deflection given the loads it'll experience.

However, I know there'll be a point as I increase the load where the sidewalls will buckle/crinkle, and this point could be lower than the load where the metal bends too much.

How do I calculate this load?

I've done lots of searches, but nearly everything I can find regarding buckling loads is for metal oriented as a column and compressed, and that's not the case for this metal.


texts: Convention for spring symbols with lateral force

texts:
If you draw a diagram with a spring, is there any convention about how it should behave with lateral loads? I guess it might be either:

Rigid
Free
Elastic with bending and/or shear stiffness
Pin jointed - Initially free but as the spring rotates, it increases
stiffness due to its orientation changing.

Here's an example where it looks like we're supposed to neglect any bending or shearing of the springs. For instance, if the object moves in the y direction, only the 3 bottom springs would deflect and we wouldn't consider the bending stiffness of the other 3 springs. Is that right and common?

From http://ecoursesonline.iasri.res.in/mod/page/view.php?id=126222


texts: If a gas is pushed through a widening section of a pipe with a piston, will the pressure increase?

texts: Imagine I have a section of pipe that increases in cross-section at some point. If the gas in the pipe before this section is being displaced with a piston, will the gas increase its pressure and reduce its velocity while going through increasing area, or will it maintain its velocity and pressure at expense of energy delivered by the piston?


texts: What type of shop could make an isetta body?

texts: I am curious how car bodies were made back in the 1950s. Specifically the micro-car bodies like the Isetta. What techniques and tools were used back then? They seem fairly simple. Could a body for an Isetta be built in a small shop?


texts: Is the flow in a centrifugal pump always constant?

texts:
Found a model for a simulated centrifugal pump in the paper of Lewin:

Lewin,1993

My question arises in the simulation study the author is doing on pages 419/420.
He assumes that the pressure of the pump is given by
$$P=30+k2*F^2,$$
where $F$ is the water flow and $k2$ a time-varying resistance paramter.
Is in such a model assumed that the flow $F$ is constant?
I was wondering because considering the plot of $P$ and $F$ in figure 4 it looks like the flow $F$ is varying with time (should be the line in the middle of the plot).


texts: How does nuclear fuel reprocessing work?

texts:
As far I know, the depleted fuel cells are crushed, and solved in nitric acid.

What is coming after that? This nitric acid should probably contain a very wide spectrum of different salts (practically, all of the elements between 35-65, and yet a lot of transurans, and a lot of uranium (both of 235 ad 238), and plutonium).

To reach an efficient reprocessing, the uranium (or, at least, the actinid elements) should be somehow separated from this solution. But, AFAIK, they have very different chemical properties. How is it possible to separate only the transuranic materials?


texts: Vibration absorber design: free body diagram of a mass-spring system

texts:
Trying to draw the free body diagram of this, any help would be appreciated.
The $y$ is the amplitude of vibration of ground. Up is the positive direction.


texts: How can I learn the standards(EN,ANSI,ISO) which is related to "roller hemming method in automotive industry"?

texts:
There is a method using in automotive industry which is called roller hemming.

I have a project about this method but before beginning the project I need to learn the standards(EN,ANSI or ISO) which are related to roller hemming.

My question is that how can I learn what are these standards. When I read some articles about this method unfortunately I couldn't find an answer.