texts: How does fan airflow relate to its RPM setting?

texts:
A fan can run at 600 - 2000 RPM, at 2000 RPM it has 50 m3/h airflow.

0% = 0 RPM

100% = 2000 RPM

At 50% = 1000 RPM is the airflow halved to 25 m3/h?


texts: How to solve stress/strain constitutive equation for system of springs and dampers with a Coulomb friction element added in?

texts:
I am attempting to solve the stress/strain constitutive equation for a system of springs, dampers, and a Coulomb friction element. Basic examples for such constitutive equations can be found in this article on Viscoelasticity. These expressions are made in terms of stress (σ) & strain (ε).
The goal is a final equation with all the stress terms on the left side and strain terms on the right side. For example, if you only had $E_1$, $E_2$, and $η_2$ in the following diagram (3 elements), it works out to:
$σ + \frac{η_2}{E_2}\dot{σ}= E_1ε + \frac{η_2(E_1+E_2)}{E_2}\dot{ε}$
Here is the system I am trying to solve:

The first branch is a simple spring. The second branch is called a "Maxwell element" which is a spring and viscous damper in series. The third branch is called a "Jenkins element" which is a spring and Coloumb friction element in series. This is where I'm having trouble.
This article provides all the Jenkins arm equations I have to work from.
Maxwell only derivation (for comparison)
Here is an example of the correct solution for constitutive equation of the same system but with no Jenkins elements, with the branches as $A$ for $E_1$, $B$ for $E_2$, and $C$ for $E_3$:

Stress ($σ$) relationships:
$σ = σ_A + σ_B + σ_C$
$σ_A = σ_{E1} = E_1ε_{E1}$
$σ_B = σ_{E2} = E_2ε_{E2} = σ_{η2} = η_2\dot{ε}_{η2}$
$σ_C = σ_{E3} = E_3ε_{E3} = σ_{η3} = η_3\dot{ε}_{η3}$
Strain ($ε$) relationships:
$ε = ε_A = ε_B = ε_C$
$ε_A = ε_{E1}$
$ε_B = ε_{η2} + ε_{E2}$
$ε_C = ε_{η3} + ε_{E3}$
Solve stress of each branch ($A/B/C$), eliminating individual element stresses and strains:
$\dot{ε}_A = \dot{ε}_{E1}$
$\dot{ε}_B = \dot{ε}_{η2} + \dot{ε}_{E2}$
$\dot{ε}_C = \dot{ε}_{η3} + \dot{ε}_{E3}$
$\dot{ε}_A = \frac{1}{E_1}\dot{σ}_A$
$\dot{ε}_B = \frac{1}{η_2}σ_B + \frac{1}{E_2}\dot{σ}_B$
$\dot{ε}_C = \frac{1}{η_3}σ_C + \frac{1}{E_3}\dot{σ}_C$
$\dot{ε} = \frac{1}{E_1}\dot{σ}_A$
$\dot{ε} = \frac{1}{η_2}σ_B + \frac{1}{E_2}\dot{σ}_B$
$\dot{ε} = \frac{1}{η_3}σ_C + \frac{1}{E_3}\dot{σ}_C$
$\dot{ε} = (\frac{1}{E_1}\frac{d}{dt})σ_A$
$\dot{ε} = (\frac{1}{η_2} + \frac{1}{E_2}\frac{d}{dt})σ_B$
$\dot{ε} = (\frac{1}{η_3} + \frac{1}{E_3}\frac{d}{dt})σ_C$
$σ_A = \dot{ε}\frac{1}{(\frac{1}{E_1}\frac{d}{dt})}$
$σ_B = \dot{ε}\frac{1}{(\frac{1}{η_2} + \frac{1}{E_2}\frac{d}{dt})}$
$σ_C = \dot{ε}\frac{1}{(\frac{1}{η_3} + \frac{1}{E_3}\frac{d}{dt})}$
Sum total stress:
$σ = σ_A + σ_B + σ_C$
$σ = \dot{ε}\frac{1}{(\frac{1}{E_1}\frac{d}{dt})} + \dot{ε}\frac{1}{(\frac{1}{η_2} + \frac{1}{E_2}\frac{d}{dt})} + \dot{ε}\frac{1}{(\frac{1}{η_3} + \frac{1}{E_3}\frac{d}{dt})}$
Final Solution:
$σ + (\frac{η_2}{E_2} + \frac{η_3}{E_3})\dot{σ} + \frac{η_2η_3}{E_2E_3}{σ_{tt}} = E_1ε + (\frac{E_1η_2}{E_2} + \frac{E_1η_3}{E_3} + η_2 + η_3)\dot{ε} + (\frac{η_2η_3}{E_2} + \frac{η_2η_3}{E_3} + \frac{E_1η_2η_3}{E_2E_3})ε_{tt}$
The Jenkins Problem
The Jenkins arm equation (given by (6) in the article) is, written in these terms:
$\dot{σ}_C = \frac{1}{2}E_3 \dot{ε}[1- \text{sign}(σ_C^2 - μ_3^2) - \text{sign}(\dot{ε}σ_C)(1+\text{sign}(σ_C^2 - μ_3^2))]$
Here, $μ_3$ is the "maximum Coulomb friction force" of the Jenkins element, and the $\text{sign}$ function is:
sign(y): -1 for y<0, 0 for y=0, 1 for y>0
My problem is this: I don't know how to rephrase this Jenkins arm equation in terms that allow me to sub it into $σ = σ_A + σ_B + σ_C$ like I did in the Maxwell solution.
I would need it as:
$σ_C =$ ... terms of $E_1, E_2, E_3, η_1, η_2, μ_3, ε, \frac{d}{dt}$ only ...
Or I can't substitute it into the overall stress equation and solve it.
I think the $\text{sign}$ functions make solving this the same way impossible. My thought is perhaps the only way is to develop multiple constitutive equations - one for each "condition" of the Jenkins arm.
But even this I don't think will solve it, because that would require me to know $σ_C$ to determine which equation I am using, and I won't know that. I need this in terms solely of $σ$, $ε$ and the constant coefficients, just like the Maxwell solution.
Is there any way this can be solved?
Thanks.


texts: Standard specification for direction of lateral load for beams

texts:
I have always thought that lateral load is horizontal and not vertical in direction. For example, from this MIT notes and many others:

  The lateral load resisting systems for earthquake loads are similar to
  those for wind loads. Both are designed as if they are horizontally
  applied to the structural system.

But the textbook I have (Mechanics of materials, 7th edition, Gere and Goodno, page 412) shows a vertical load on a beam and says it is lateral load. Here is the page:

Is there a convention for loading directions and the authors happens to use different one or should not Q above be called transverse load?


texts:
I know that radiant barriers (i.e., reflective films applied over or under insulated spaces) don't technically have R-values (because they primarily reflect heat, instead of primarily slowing convection and conduction as does traditional insulation), but they do have some insulating effect, which could be quantified as equivalent to an R-value.

E.g., if I put a radiant barrier under R-19 insulation, what equivalent insulation will that space experience?  Holding conditions constant, an HVAC system will see a reduced load after the addition of the radiant barrier.  One could find the pure insulation level that matches that load reduction – perhaps it's R-30? – and based on that say the radiant barrier is "functionally equivalent to R-11."

Amendment: Yes, there are good theoretical reasons why radiant barriers are not assigned an R-value.  However, as one user notes, we only ever talk about "R".  For example, where I live the standard for home insulation is R-30.  Can I reliably achieve that through a combination of blanket insulation and a radiant barrier?  MIMA, hardly an objective trade organization, did a test in Florida 30 years ago which, while highlighting shortcomings of radiant barriers, did note reasonably consistent heat flow reduction from properly installed barriers.  I would assume that with the benefit of 30 years of knowledge and increased emphasis on insulation we can say something useful about the functional value of adding a radiant barrier to an insulation stack.


texts: Can I use a 1500 lb winch to pull a clamp on wheels that weighs 20,000 lb?

texts: I need to be able to pull a blow molding clamp out of the machine onto a temporary frame for maintenance. The clamp weighs 20,000 lb but the starting force to get it moving is only 365 lb, so can I use a 1500 lb winch to pull the clamp out onto the roll-out frame? The clamp is sitting on 8 V-Grooved wheels and running on rails.


texts: Upper limit of force required to pull a trailer

texts:
I am looking to calculate the force that would be required to pull a single axle 12000 lb box trailer with a 72 sq ft frontal area up a 10% grade at 80 mph.
It has been quite a long time since I've done any engineering and I want to make sure I'm not way off.  I am only looking to find a comfortable upper limit for potential force required to pull any trailer.  My numbers estimate a heavy trailer going up a very steep grade faster than one probably should.
For this example I'm estimating 1200 LB of strain from pulling the weight of the trailer and another 1200 LB from the drag of the wind.  Is this a fair rough estimate or am I way off?


texts: I’m trying to find out if it’s possibly to form a cylinder or tube with a diameter of 1 inch using some kind of curling die for a press brake. I’ve seen dies that make small 360 degree bends like that but they always have additional length of sheet metal extending from the tubular section. Does anyone know if it’s possible to form just a small tube without additional material extending out? This tubing would be used for handles to lift something, similar to a handle bar on a bicycle or something.


texts: formula for M(x) - Shear Force and Bending Moment Diagrams

texts:
I've watched the video "Understanding Shear Force and Bending Moment Diagrams" from "The efficient engineer" and i got a doubt in this exercise
For $4<x<7$ I arrive to $V=-6x+42$ and by doing sum of the moments equal to zero I got $M-21-18x-6(x-4)(x-4)/2 = 0$ which simplifying is equal to $M=3x^2-6x-51$ which is different from the formula of the solution from the video
I already understand that the formula for $V(x)$ that I arrive is right but I can't understand if the formula that I arrive for $M(x)$ is right or not..
could someone explain it to me?

My diagramm was:


texts: Why one big cargo ship is more efficient than 10 or 100 smaller ships?

texts:
Given the fact that small container ships are easier to manufacture than big container ships.. then why is it considered better to build bigger ships instead of many smaller ships?
And to see why manufacturing is easier at smaller scale - consider the smallest and largest scale - I can build a 1 meter toy ship myself, but i can't build an OOCL Hong Kong like ship by myself. By induction this should be true for all levels. The biggest ship looks like this:

In this interview : https://youtu.be/Opnk-cPOM50?list=WL&t=776 - Elon Musk explains that is more efficient to have a big rocket rather than a small one. And gives this example of big trucks and big ships.
But to me doesn't realy makes sense. With smaller size, manufacturing is easier, mass producing is possible, faster and cheaper, and materials can have greater strength for the weight. So much that at smaller size even plastics can be used.. at bigger sizes steels can be used.. and at extra big sizes - like a 10km long ship - nothing can be used since no such materials exist. So how come that bigger is better?
Indeed when we go to extremes then other things play a factor - factors like super small ships are smaller than the waves, and 1km long ships might not fit in port etc..  but outside of such non fundamental limitations, in principle, when we consider the cargo ship case, say this 1 ship in the picture above with 2500 containers vs 10 ships with 250 containers each. Why is it better to go with the 1 big ship in this case? Seems to me is easier to build 10 smaller ships than one which is 10x bigger. Or even better - have 100 ships, each carrying 25 containers. So why am I wrong?
Does the same reasoning applies to trucks.. and why it doesn't apply to rocket engines? Why having 28 small Raptors for Starship is better than 5 big F1 engines like Saturn 5? How to properly think about this?


texts: I'm practicing some questions for my upcoming exam and I need the formula for super elevation when you've been given the coefficient of lateral friction in the question


texts: Fusion 360: Measurement issues to Slicer Software

texts: So I made a design for the Autodesk Competition but for some reason, I have never had this issue, but when I export to .obj and open in S3D, it doesn't convert the measurements. My meaning: I have a 3.5x3.5x10 inch design but in S3D it reads as 3.5x3.5x10mm and I do not know how to fix this. Any help would be great!


texts: I've never seen this type of flexible coupling, can someone tell me what it's called?

texts: Putting together a project, I've found this clutch but I've never seen this type before. It has a sort of flexible plate connecting the two parts, attached to both in two places corresponding to where the four teeth are. It seems to be working but I have no idea what torque it's ok for and how much I should compress it, if at all. Sorry for the shitty photo quality.


texts: How can different torque levels be measured at a single rpm using a chassis dyno?

texts:
I've been struggling with this for days trying to make sense of a rpm vs torque chart I've seen recently.

The chart states the engine load was measured 100% 70% 40% 0% and at 1000 2000 3000 4000 rpm. How is this done if using a chasis dyno?

I attached the chart for reference.

That's my question, but below I'll elaborate on my thinking and hopefully there will be a clear error in my understanding...

I think part of my problem is that I'm unsure what the throttle is doing when these charts are produced using the dyno.

Am I right in thinking that to get the 100% load points over each rpm, the test is started with the engine idling then pushing the throttle to 100%? The RPM will increase rapidly up to redline and the engine torque at each RPM can be estimated working back from wheel RPM and transmission ratio etc. They measure at 4 discrete RPM though, suggesting they might have control over the dyno resistive force?


texts:
I am a civil engineering undergraduate. I have an interest in Biotropic Design and sustainable energy and am working on a new conceptual design. I would like to know what analytics may be done to prove the efficiency of the system  in a proof of concept for local government. I don't know how to calculate any of the results that I will likely be asked such as:

What volumetric size is the system likely to occupy?
What is the estimated power output?
How much is it going to cost to run?
How much water will it need to run?
What pressure needs to be maintained to keep the system free of condensation before the turbine?

Add any other questions you think you'd ask if you were expected to spend £5 million on building a new powerstation for your city and answer it with the necessary equations to back up a positive attitude towards getting the job done.

The system works on the principle of negative pressure as opposed to energy intensive positive pressure.

There are two tanks in a closed system. Tank A is the wet tank and Tank B is the dry tank. A contains water at nominal room temperature but this may vary depending on weather conditions and may decrease to no less than 278K. Tank B temperature is unknown.

Between A & B is a turbine that unrestrained operates at an estimated 99.9% efficiency {take this as fact}. I would like to calculate energy output at 50% efficiency under load producing 1GW minimum.

Tank A pressure is 3psi.

You can choose the minimum size tank to maintain that will maintain negative pressure maximum of 10psi for 24 hour period. The maximum size is immaterial as it will tie up with another system for another purpose that is kept in negative pressure for permanent operation at a maximum of 8psi.

A proof of concept research system has already been made and works. It uses a Tesla turbine. The Tesla design is being improved but there are patent design modifications I cannot reveal with that aspect. Tank A measures 348K and system depressurised to 25 inches of mercury (ultimately 28.5inches). Tank B is easily 278K, if not lower. The turbine output is estimated at 1kW. It is a closed system. Eventually it will be designed to extract thermal energy from naturally heated water. That water may be up to 380K.

The idea is to get water to boil at 272K and keep a constant supply available. The incoming water will have a minimum temperature of 278K.

I don't know anything about any equations relating to this question.

How can I calculate the amount energy extracted with all the above
information?
What equipment would I need to measure energy and power?

If there is anything else you think should be added to the list, do edit and suggest rather than comment. I would like this question to become a permanent example for reference.

(no, this is not a university exam question.)
Cold Steam Research


texts: Damp vibration on phone attached to car seat

texts:
I'd like to create a 3d printed system to damp the vibrations on the phone when we are on the road. The idea is to be able to hold the phone for my little kid when we travel
First I tried a spring system that connects the fixed part to the phone holding part, with no success, the vibrations were not only eliminated but increased.
Also tried inserting sponge/rubber material in between the phone and the phone holder, but seemed useless.
At this point I don't know what else to try, and I didn't find any commercial product.
How would you do it?


texts: Isotropic materials and levels of stress

texts:
I was wondering if I was to have two objects both made of isotropic materials such as steel and aluminum and the two objects were the same geometry and I was to apply the same load and boundary conditions to each, would one of the materials have a higher stress?

My understanding is that because stress = load / area then the stress for steel would be exactly the same as for aluminum.

But then there is the relation between Young's modulus $E = \frac{\mbox{stress}}{\mbox{strain}}$. So it is difficult for me to justify my first thought.

It would be interesting to hear some thoughts on this.


texts: What would happen if I tempered aluminum of aeronautical use (Al 2024)?

texts: What would happen if I tempered aluminum of aeronautical use? Being more specific, an alloy of 96% of aluminum and 4% of copper, without modifications and 2% of impurities. (Al 2024)


texts: How to find the reaction forces, moments and the displacement of the fixed beam with a link?

texts:
The beam is fixed on both ends and there is a link in the middle. There is a force F on the link.

My approach to solve this problem:

A free body diagram is cut at the link and made into 2 systems.

Horizontal forces are ignored.

Sum of force in vertical direction for system 1 on the left:

$A+L(link)-F = 0$ (1)

The sum of moments about A:

$ Ma+L*l-F*l=0  $

For the Right side I do the same as above.

The problem is I keep getting nowhere and running in circles. I calculated the displacement for the left side and also the right side.

I equaled them to tr and solve for unknown variables, as the displacement at the link (length l) has to be same for both the sides, but still can't cancel out the variables to solve for the reaction of the forces. My goal is to solve in terms of F for the reaction forces.


texts: Best way to build kick start lever for motorcycle

texts: Let's say I want to build a new kick start lever for my bike, what's the best way to make one? Is it (Hot/Cold) Forging or Casting? I'm looking for the materials too, do you think chro-moly steel a good choice? Thanks!


texts: Determining length of interstage cooling coils for removal of heat

texts:
I'm currently trying to determine the length of cooling tube required to remove a specific amount of heat from my exothermic reactor in stages.
I'm aware I need to use the equation $Q = UA \theta_{lmtd}$, and $Q = mc_p \Delta T$.
I have the kJ values of heat I need to remove, and my research has led me to believe that water at 100C to use vaporization in my favour would be ideal.
If I'm working at just a touch more than atmospheric pressure, and working with water at 100, what's the U value for this - water alone is between 3-35 [W/m2C], which would mean the length of my cooling coil (at a diameter of 3 inches) would be over 1700m.
Any help would be greatly appreciated.
I feel like I'm stuck on something very basic.
Thank you.


texts:
I choose an AC motor (IEC) with frame number 71. The key on the shaft of the motor is $5mm,$, $4.23 mm$ and $6 mm$ in diameter. At other hand i cant't find a safety coupling (torque limiter) with exactly the same dimensions as the key way on the  motor. They are all a bit smaller or bigger but they have the same  diameter as the motor. for instance $4 mm$, $2.23 mm$ and $6 mm$ in diameter.

what can i do ? Is it possible to use a slightly greater safety coupling or the dimensions of the both, should exactly be the same ?


texts: Heat press of vinyl on 100% polyester fabric

texts:
I want to customise a piece of fabric that is 100% polyester (exclusive of decorations, wash at 30º) with vinyl. My idea is to use a vinyl cutter (such as Silver Bullet) to cut a pattern on the sheet, remove the background, transfer to a transfer sheet, and use a heat press to adhere the design to the fabric.

I have seen good results of this method on cotton and I am not sure if a heat press would work on polyester.

How can I transfer a digital design onto 100% polyester fabric?


texts: What kind of professional(s) build/design factories?

texts:
I have a small self-built food processing unit (500sqft) but it is very labor-intensive. I want to make a larger unit (45,000sqft) with 100x more output using factory machinery (automation, conveyor belts, etc).

My current unit is composed of a lot of electrical components and plumbing systems; it's not top notch and beyond my expertise to scale into something larger. It is a food manufacturing and processing plant with many chemical inputs.

I am not exactly sure who to contact regarding this build or where to begin my search.


texts: What is the difference between mechatronics and robotics, if any?

texts:
When explaining to someone what mechatronics is, I ususally end up stating that it is synonymous with robotics. While I think it is mostly true, are there any subtle differences between the two?

The obligatory google search suggested that robotics is a subset of mechatronics involving autonomy. I'm not sure I completely agree. Is there any qualifier that would for sure separate a system into one or the other? Or is it just a different label?

I've also noticed some schools will have a robotics undergraduate degree but mechatronics graduate degree. Does this make any difference?


texts: Chemical Engineering Question using Raoult's Law

texts:
A liquid mixture containing 35.0 mole% acetone and 65.0 mole% water is to be partially vaporized to produce a vapor that is 70.0 mole% acetone and a residual liquid that is 30.0 mole% acetone.

(a) Suppose the process is to be carried out continuously, and at steady state the feed rate to the evaporator is 10.0 kmol/h. Calculate the molar flow rates of the product streams and the temperature (°C) and pressure (mm Hg) of the system.

How do you calculate the temperature and the pressure?


texts: How to find a dimension that isn't explicit if there are tolerances

texts: For a part like the one shown, let's say I wanted to find the dimension labeled 3", if it wasn't already labeled. Since there are tolerances already on the part, how would I determine the 3" value along with its tolerances? Can I just add and subject the tolerances? For example, 4.00 +- 0.3 - 1.00 +-0.1 = 3.00 +- 0.2 ? What if I wanted to find the distance from the right end of the hole to the right face of the part, assuming diameter D = 1" +- 0.01? Could I simply do 3.00 +- 0.2 - (1/2) +-(0.01/2) = 3.00 +- 0.2 - 0.5 +- 0.005 = 2.5 +- 0.195? Thanks for the help!


texts: Holonomic constraint forces using Lagrange multipliers

texts:
Consider a multibody robotic system with Lagrangian $$ L =\frac{1}{2} \dot{q}^{T}M\dot{q} - V $$ and equations of motion of the form
$$M(q)\ddot{q}+C(q,\dot{q})\dot{q}+A^{T}(q)\lambda+N(q)=0 $$

where $N=\frac{\partial V(q)}{\partial q}$  and $\lambda$ represents the Lagrange multipliers for the constraint forces (MLS pg. 269; pg. 287 in pdf). $A$ is the constraint matrix from the Pfaffian form $A\dot{q}=0$. We are concerned with holonomic constraints, which can be differentiated to obtain the Pfaffian form.
$ C=\sum_{k=1}^{n} \Gamma_{ijk}  \dot{q_{k}} $ where $\Gamma_{ijk}$ are the Christoffel symbols of the first kind.

The Lagrange multipliers can be calculated using the formula (MLS pg. 270, pg. 288 in pdf)
$$\lambda =-(AM^{-1}A^{T})^{-1}AM^{-1}(C\dot{q}-N)$$

This gives the holonomic constraint forces $A^{T}\lambda$.

I would like to see some examples of this method for calculating the holonomic constraint forces for planar systems.

I have seen this method being applied to calculate the tension in a simple pendulum (MLS pg. 270, pg. 288 in pdf), but I would like to see examples of planar systems with more degrees of freedom.

I'm specifically interested in the case of a 2R manipulator shown below.

The equations of motion are on pg. 164-165 (pg. 182-183 in the pdf) in MLS.

My objectives are:

Apply the holonomic constraint $\theta_{1}(t)=0$ and obtain the holonomic constraint force.
Show that we get the dynamics of a simple pendulum for the
constrained system for initial conditions $\theta_{2}(0)=0, \dot{\theta_{2}}(0)=0$.

I have done the calculation for the constraint $\theta_{1}(t)=0$ but I'm not able to show 2. The expression I get for $\lambda$ is

$$\lambda=
\begin{array}{c}
 \frac{g (d \text{m2} \text{r2} (\sin  \text{t2})-\text{m2} \text{r2} (\cos  \text{t2}) ((\cos  \text{t2}) b+d))+b d (\sin  \text{t2}) \dot{\text{t2}} \dot{\text{t2}}}{d} \\
\end{array}
$$

where $(t1, t2)=(\theta_{1},\theta_{2})$ and $a, b, d$ are the geometric and inertial parameters $\alpha, \beta, \delta$ described in MLS (pg. 165; pg. 183 in the pdf).

Suggestions for other methods to calculate holonomic constraint forces would be helpful too.

References:

MLS refers to

  Murray, R. M., Li, Z., Sastry, S. S., & Sastry, S. S. (1994). A
  mathematical introduction to robotic manipulation. CRC press.


texts: Lightweight substitutes for machined aluminum parts

texts:
I have machined parts that are made of aluminum and anodized black.  The reason that I chose aluminum is because:

It can easily be machined and is low cost and is common, so easy to buy
It is light weight compared to steel
It can take heat
It is easy to finish with oxidation

The parts are used on a CNC machine so being lightweight is important so that the machine can move faster.

But, I need my part to be significantly lighter weight, so would like to switch materials, but not pay a lot to get a prototype made.

Is there another metal that is a good substitute?
Can a plastic laminate be used? For example, plastic parts that I can get machined then add a high temperature tape to reflect heat?


texts: Would if be possible to have an efficient, diagonal heat sink to save vertical space?

texts:
I need a heat sink for my Peltier cooling fan but also need to saves as much vertical space as possible. I've been exploring various Heat Sink options but many of them extrude outwards making compact variants hard to find. I've found compact options such as Flared Fin Heat Sinks:

However it would really be optimal if the fins just went to one side for my application as need the heat dispersal to be concentrated in one direction. My question is could something like this be at all effective for my peltier TEC:


texts: 6082 Aluminium softened by brazing. How to harden?

texts:
I've started playing around with brazing pieces of extruded aluminium sections to join them together for strong joins as an alternative to bolting them.

The pieces are made of 6082-T6 aluminium alloy. I've found that the heating needed to braze softens the aluminium enormously, to the point where 3mm thick sections can be effortlessly deformed with pliers.

I've done a lot of searching and I need to either naturally or artificially age-harden it (precipitation hardening). But how long it takes to naturally harden, or the precise process needed to artificially harden it (temperature & time) escapes me. Also, quenching might help, but I haven't found any definitive answers.

How can I re-harden the alloy?


texts: Find same modulus z plane poles of over damped system

texts:
I am asked to find two poles of a second order discrete over damped system that have the same magnitude (0.4, to be exact) in the Z plane. From what I understand, that is not possible since over damped systems have two distinct negative real poles at the S plane and, using $z=e^{sT}$
, the two poles in S become two real, distinct and positive poles in Z. This means that poles z1 and z2
are:
z1,z2=a,b
with a≠b, a,b>0 and a,b∈R
So they can't both have length 0.4. Am I missing something here?


texts: How can I find the amount of force needed to bend and break a magnesium cylinder?

texts:
I want to determine how much force in Newtons will be need to bend a solid cylinder of magnesium.  The cylinder is (x) cm in diameter,  and it is (l) cm long.  The density of normal magnesium alloy is 1.8 grams per cubic cm. The yield strength is 130 MPa, the tensile strength is 220 MPa, the Young's modulus is 45 GPa, and the melting temperature is around 615 degrees Celsius.  All the information about magnesium alloy can be found here.

How can I calculate the amount of force needed to bend a magnesium cylinder with variable diameter and length, or the minimum force needed to break the magnesium cylinder by bending? If I had a general formula, I could then use Newton's law to find how much mass can be put on the cylinder in order to bend it or break it by bending, based on the gravity of the planet Earth.


texts:
I'm attempting to find the equations of motion (and eventually transfer functions) for a mass-spring-damper system, but one that is slightly different from your generic damped system example.

Below I've given a picture of essentially what the system looks like.

There is a large box with mass m and spring k inside of it. This box is damped by damper c to the left-hand wall of the room. I apply a force F(t) to the side of the box, causing both the box and perhaps the mass inside to move. x is measured from the left-hand side of the room to the center of mass, so x will increase both when the box moves and when the mass inside the box moves.

What I imagine happens is that for low frequency forcing functions, the spring is essentially nonexistent and the equation of motion looks like:

$$F(t) = m\ddot{x} + c\dot{x}$$

When the forcing function frequency approaches the resonance frequency of the system, not only will the box move to the right, but the mass will vigorously experience motion inside of the  box. I'm not quite sure what the equation of motion looks like for this case.

I'm looking for one differential equation that captures both of these - low frequency and high frequency forcing functions. At the end of the day I really want a transfer function to use in Simulink.

$$\frac{w_n^2}{s^2 + 2{w_n}{\zeta}s + {w_n^2}}$$

This transfer function doesn't seem to model what I want, even though it's the generic second order system transfer function.

Any help would be greatly appreciated. ^^


texts: How would I determine if an upward flow of liquid at 100 bar forces a bed of porous solid upwards or flows through without affecting the same bed of material? Is it related to bulk density and pores?


texts: Is there any ecological modifier which can be added to PLA to make it not brittle, and good for some heavier-duty outdoor food-grade use?

texts:
Is there any modifier which can be added to PLA to make it not brittle, and good for some heavier-duty outdoor food-grade use?
The criteria is that adding the modifier still keeps the material biodegradable.


texts: Grate that does not cause air rush noise?

texts:
I have an air supply grate that is making a roaring noise. It has rectangular slats.

I know the sound is coming from the grate, not the duct, because when I remove the grate, the duct is silent. It is only when the grate is in place that it is noisy.

Is there a shape I can make a grate that will generate little or no noise when air passes through it?


texts: How do you interpret a pneumatic regulator symbol?

texts:
I'm an EE trying to interpret a pneumatic schematic and have a few questions regarding the symbols being used.

I've come across two different regulator symbols (or so I believe them to be regulator symbols). I'm curious if someone could break down the difference between each.

Here are my interpretations and questions for each symbol:

I believe this symbol represents a pressure regulator. The spring indicates that it is a pressure regulator valve. However, I'm somewhat confused as to what the dashed line is meant to represent. Is it just meant to represent a feedback line for regulation purposes?
This symbol is similar to symbol 1, however, it differs in how the arrow is oriented. What is the significance of the arrow direction?


texts: How can I use the bending stiffness of corrugated cardboard to determine maximum stacking heights of pallets loaded with glass bottles?

texts:
I am doing a project at the moment which involves improving the packaging operation at work. Right now I am looking at ways to improve packaging selection based on engineering principles, rather than guess work, which is what's being used currently.

We make many shapes and sizes of bottles and a major problem that we have is pallets which collapse because of poor packaging selection. The main problem is shown in the below image - the bottles in my (crude) sketch show a cross section of 1 stack of bottles.

As you can see, the 'void' in the base of the bottle, which we call the 'push' is often large enough to allow the neck of the lower bottle to move a considerable distance in to it. This causes the corrugated board to be pinched between the 2 bottles and in effect is a 4-point beam loading situation, with the orientation of the forces flipped 180 degrees (relative to their orientation in the testing standard).

I'd like to know how I can relate the values from a 4-point bending stiffness test (BS ISO 5628:2012) and use these values to select an appropriate corrugated cardboard grade, based on the expected 4-point loading situation for each bottle.

From my limited knowledge of beams, I think I would need to:-

Define a maximum load based on the expected mass of bottles above the
point at which the maximum load is expected (i.e. on the neck of the
lowest bottle in the stack.)
define a maximum allowable deflection to
work back and find a stiffness that would correspond to this
deflection.
input the lengths and positions of the forces based on
the bottle geometry.

Some sticking points that I haven't been able to address:-

Is my fundamental assumptions of this being a 4-point bending
situation correct? We make round and square bottles which vastly complicate the loading situation. Obviously in my model I am only considering a cross section to relate this to a 4-point loading test.
There are many bottles on each layer of a pallet. In my approach I
have opted to simplify the model by only considering the mass
directly above a single bottle. I am not sure, for example, how
significant the contribution of the frictional forces from the
surrounding bottles is.

EDIT: We do not used cardboard boxes. We used either pads or trays. In either case, the loading is always normal to the flat face of the cardboard. Edge compression never occurs with our packaging.

I'd really appreciate any feedback. Thanks.


texts: Stone Retaining Wall Water Seepage Issue?

texts:
Hi all,
A boundary retaining wall we have is seeping water in a couple of places at the very bottom only after a downpour. This lasts for days and will eventually dry up with enough time but the water pools near the wall as can be seen in the pic. From what I can tell, the wall is part of a soak-away system and is approximately 30yrs old. It's a double leaf wall? block/concrete internally with Stone on both sides and pilasters along the construction. Should I be concerned or is there anything I can do to remedy this?
TIA,
Derek


texts: Determine the range of values for a PI controller

texts:
This is a basic control theory question, since Control Theory is a part of applied mathematics but also of engineering I was unsure whether to ask this here.

The question says:

Given the transfer function of a system is $G(s)=1/(s^2+3s+2)$, consider the design of a PI closed loop control system with unit feedback using proportional gain $k_p$ and integral gain $k_i$, both of which are positive. Determine the range of gain for which the closed loop system is stable.
What I did was this, I went the Routh-Hurwitz way:

After completing the Routh table, I went ahead and reasoned a little about what conditions need to be met in order to avoid sign changes on the main column, however it seems that these conditions are never met! I get that $k_i$ should be less than zero when the problem clearly specifies it will always be positive.
Have I done something wrong? Is my reasoning right? Is the answer "The controller is never stable"?


texts: How is steel tempering addressed when installing pre-heat rivets?

texts:
AFAIK when you heat up a piece of steel to high temperature and let it cool down slowly (as opposed to shock cooling by say submerging it into water) steel gets softer - that's called tempering. Steel getting softer means it can bear less load without getting deformed.

Suppose we connect parts of steel skyscraper with steel rivets. We heat them up in fire and then put them into holes and deform their tails. While the rivet is inserted inside a rather cool surrounding construction (and being deformed) it cools down which more or less resembles tempering process.

So it looks like installing rivets leaves them tempered and so rather soft and prone to deformation.

How is this process of rivets getting softer and "weaker" accounted for?


texts: How do you account for buckling in a brick and mortar structure?

texts:
I was thinking about this question from quite a while back about height limits of a brick and mortar tower. One answer pointed out that, due to the high compressive strength of brick, one could build a tower 7.4 km high without taper before individual bricks fail in compression. So it seems highly likely that a high brick structure will fail in another way. One candidate for a failure (the other two that come to mind would be lateral forces and accumulated errors in the masonry) is buckling pr more precise self buckling. Wikipedia gives a formula for self buckling but for the purpose of this question the simpler case of critical stress to cause buckling is more interesting (because the formula is simpler):
$$\sigma = \frac{F}{A} = \frac{\pi^2 E}{(l/r)^2}$$
The crucial element is, I think, Youngs' modulus $E$, which represents stiffness in tension. You often hear the statement that the mortar or rather the connection brick - mortar - brick has practically no strength in tension. Intuitivly, a structure build from several parts should be worse at resisting buckling than a monolith - So the formula given above for buckling would give an upper limit to the maximum stress. However quite slender brick structures, like catalan vaults or tall chimneys, where built and withstood the test of time.
My ultimate question is: $E$ is a material constant. Strictly speaking a brick tower is a a structure made of bricks and mortar. How is the effective $E$ determined in this case?
*


texts: How to Find the Magnitude of Force and Direction

texts:
Give me some tips on how I can find the magnitude of $F_3$. The hint maybe is the angle of inclination of w axis such that the force components are equal along that axis, my instructor once told me. However, I can't still figure it out on how to solve for that angle.
The problem stated that $F_1$ is resolved in u and v axis, $F_2$ is resolved in v and w axis, while the $F_3$ is resolved in w and u axis. It is also stated in the problem that the components of $F_1$ and $F_2$ are equal along the v axis, the components of $F_2$ and $F_3$ are equal along the w axis, and the components of $F_1$ and $F_3$ are equal along the u axis.
Original problem


texts: Pneumatic valve clicks but doesn't actuate

texts:
I am trying to build a door to a hidden room and want to use pneumatics to open the door. I have purchased some equipment to test with, namely a 12 inch Parker air cylinder and a U.S. Solid 5 way 2 position valve. After hooking everything up I have the following configuration:

When I connect the barrel plug to a 24v 5amp DC power brick, attach to pressure (currently have the compressor set to somewhere like 5-10 psi but have tested with 20-30), and run a simple "turn the pin on and off" Arduino code the relay clicks as expected and the valve sounds like it is engaging, however the airflow doesn't change. It remains coming out of the A output. I contacted U.S. Solid and have already got a replacement valve but the same issue occurred with their replacement so I'm beginning to think I'm doing something wrong.


texts: What is the definition of Building integrated photovoltaics?

texts:
What is the definition of BIPV?
Building integrated photovoltaics emerged as a new way of reducing energy consumption. However, the question is how do these systems work?


texts: Small building basement foundation moisture: permeable vs impermeable

texts:
I understand that moisture is the enemy of interiors.  I know that the standard basement foundation for a house-sized building uses moisture barriers on the outside of concrete retaining walls to reduce seepage and uses a drain with a sump pump to remove any moisture that does come in.  This is a reasonable method but it strikes me as inelegant.
Furthermore, I know that ancient people often lived in pit houses that were dug anywhere from 0.5 m to 2 or 3 m into the ground. Anthropological documentations of indigenous homes sometimes even show pit houses containing wood paneling and soft goods like hides or cloth that would be ruined by moisture. More recently, houses in the past few centuries often had basements before cement was an accessible building material; dry-stacked or adobe-mortared stone foundations facilitated basements that were dry enough to allow long term food storage.
So, my questions: Is a permeable foundation feasible in a modern home? Would a certain amount of moisture be guaranteed or could adequate considerations (siting, design, materials) be made to keep the place from flooding, molding, or excess humidity during the wet season?  What means might ancient people have used to keep their pit houses from excess moisture?


texts: How difficult is attaining EIT certification?

texts: I'm currently filling out an application for the Massachusetts FE & EIT certification. Section 22 requests information regarding memberships to professional organizations. Unfortunately, I'm not a member of any and I'm afraid of leaving this section blank. Is anyone familiar with how leaving this section blank would impact my chances of getting certified?


texts: Heat resistant material for Nickel Chromium Wire?

texts:
This should be a pretty straight forward question but I can't seem to find the type of material that is used..

So I am making my own heating coil out of Nickel Chromium wire. I plan on using two bolts in a frame that hold the entire thing together. Obviously the bolts themselves are conductive so my plan is to wrap the bolts in the "heat resistant cardboard" that I see inside of hair dryers and other heating devices that use the same wire. Does anyone know which type of material this is, as I am sure normal cardboard would simply ignite...


texts: Edge sizing control is applying number of divisions and biasing unexpectedly

texts:
When I generate Mesh elements in Ansys Fluent, they aren't generated as expected with the edge sizing control.
I've set the Edge Sizing control of this edge with these settings: (Number of Divisions: 20 and Biased):

With these settings it's expected to see on the edge: 20 mesh elements and with their size biased.
But it's not the case: Their sizes are not biased and they are not 20 mesh elements.

These are the Mesh general settings:


texts: Replace mercury with silicone oil in diffusion pump

texts:
We have obtained an old mercury-vapor diffusion pump for high vacuum. However, we do not want to operate it with mercury in our lab due to health concerns (which is presumably the reason it was scrapped by the original owner).

Instead, we plan to fill it with a silicone oil of the DC-704 type or similar. The pump has thermal regulation and a large baffle to stop oil vapor counter-propagation.

Has anybody tried replacing mercury with oil? What are possible problems with this approach?


texts: A mechanical system with coupled oscillators and dampers

texts:
I found here Coupled oscillators, the last one on this page, a system named by the author "Vehicle Suspension System". But I am not sure this modelizes a suspension for a vehicle.
I am interested to find and describe appropiate physical phenomena modelized by mechanical systems of this type and any other bibliographical references would be of help. Is it somehow related to a vibration reduction system in civil engineering?


texts: How wasn't Thames Tunnel flooded during construction?

texts:
I have read the Brunel's shield directly exposed ground which was then excavated by the workers. But the construction was done just a few meters under the seabed. How wasn't the tunnel flooded immediately?

I think of small pits that children dig on beaches in the sand near the water. As soon as water level is reached, the hole is flooded very quickly. Shouldn't the same have happened to the tunnel? Was the soil water-tight enough so that the water didn't seep so fast?


texts: is this a picture of a plate girder train bridge or a deck truss train bridge?

texts: Is this a picture of a plate girder train bridge or a deck truss train bridge?


texts: Sensor Fusion under translational movement

texts: There are many sensor fusion algorithms available like the complementary filter or the EKF. They all do a decent job for rotational movement attitude estimation, but what happen when I have a translational movement? For example the complementary filter does rely on the accelerometer alone when there is slow angular movement, which is the case for translational movement (no angular movement at all). So, the estimated angle is wrong and I get a deviation from the real position. Is there anything I can do to avoid this drift? Would a Kalmanfilter compensate for that? If we take as an example a quadcopter, where often a complementary filter is used. How does they avoid this drift? There is a lot of translational movement in this kind of application.


texts: Why does aluminum clad steel wire have high corrosion resistance?

texts:
Why do aluminum clad steel wires have high corrosion resistance despite being two dissimilar metals?

Does the aluminum act as a protective & sacrificial layer similar to zinc in galvanization or is there some other mechanism going on?


texts: When reconditioning of a pneumatic cylinder, which fit between piston and cylinder is required? and how much tolerance between mating parts is required?. Will surface finish inside of cylinder play a major role?.


texts: Will coefficient of discharge remain same when it is used for measuring either liquid or gas flow rate?

texts: I would like to measure air flow rate. I have a orificemeter but do not know its coeficient of discharge. Will the Cd remain same for both the liquid and gases or it will be different.?


texts: Can I lift 15 tons on air bearings with 0.2 kg air/s?

texts:
The air is at 13 kPa and 400 K. I can raise both the supply temperature and the pressure if necessary. No problem with that. I could get 1.7 kg/s for the air bearings, but I have no more air.

I thought levitation this way was possible, but I'm doubtful now because there's an Australian engineer who's skeptical.

Elon Musk said it was possible, but Hyperloop critics deny it.


texts:
What kind of Freon air conditioner would work upside down? Or somehow make it cut off and start working again when upright?  I have a small cabin so it can be electrically driven. I know they have an air conditioner for fighter jets but, I need a cheaper aftermarket one, if cheap is possible?
Related: https://aviation.stackexchange.com/questions/24441/do-jet-fighters-have-air-conditioning-systems


texts: Thermal expansion during the course of melting (in metals specifically)

texts:
The question is with regards to Thermal Expansion at the point of melting.

My basic understanding is that a material will generally undergo linear thermal expansion until some phase change occurs (crystal formation, melt, etc) that changes the material behavior. Take Aluminum, for example. It has a linear expansion coefficient of ~23E-6 /K when solid, but might go as high as ~98E-6 /K when melted. What I can't find, however, is how much expansion occurs over the process of the melting transition itself? It seems like if a solid metal with a poisson ratio of 0.35 (compressible material) transitions to a liquid with poisson's ratio of ~0.5 (incompressible), there must be some large amount of expansion as it fully "decompresses" to that point. Kind of how water which we all learned in elementary school counter-intuitively expands when frozen, I would assume metal behaves more intuitively with a large expansion when melted.

Is there any formula to predict this expansion amount during melt, assuming all heat is contributing to phase transition and not increasing temperature?


texts: How to input amplitude on a second order transfer function?

texts:
I have some samples of readings from an accelerometer (unit: g) and I did a FFT (on MATLAB) on the vector generated from these samples to see its frequency spectrum. Then I have isolated the peaks and located its frequency.
OK, now the control theory question.
Let's say, to simplify the example, the only peak is 2 g at the frequency of 10 Hz. The accelerometer acquired the samples over a vibration system, so I assume it is undamped oscillating endelessly at a natural frequency of 10 Hz. My transfer function would be:
$$F(s) = \dfrac{(10\cdot2\pi)^2}{s^2 + (10\cdot2\pi)^2} = \dfrac{3948}{s^2 + 3948}$$
I multiplied by $2\pi$ before raising because it's given in Hz and I have to convert it into rad/s (right?)
I intend to make a PID control (on Simulink) to analyze some parameters, as overshoot, settling time, etc.
The REAL question is: how do I "tell" the system that the amplitude of it is 2 g?
Is it like a gain that I insert before the transfer function block?


texts: Which is better: Defog a car windshield with cold or hot air?

texts: So i had this experience when driving in a cold night, where my windshield just got all blurry. I knew that on the drivers manual they say you should turn the hot air and soon it will go off, but my friend that was on the passenger seat said the cold air will work too. We turned the AC off and re-experienced the fact. I got the chronometer and and got the time of both situations, defog with hot and cold air and there were really small diference btween them. How can i explain this in terms of thermodynamics?


texts: I'm working on my university project but I can't find a proper  synthesis method for 5 bar mechanism. I'm working on underactuated mechanism. It's a slider crank with the connecting rod divided into 2 links with a pin joint. Thanks!!!!


texts: Statistical approach to defect detection and prioritization

texts:
My company has over 100k communication devices deployed. We collect failure information from the devices. We have two type of data failure count per hour for each device and we use that to calculate failure percentage. We are developing a pro active monitoring system which will help us better maintain the system. One of the challenge is to prioritize devices using failure count or failure percentage. Is there any statistical or mathematical theory which will help us create a priority list using both count and percentage?

Edit 1: All the devices are not the same. But for this process we will consider to be same. To have a good system performance we have to prioritize our troubleshooting.


texts:
In a statics exam I had the question in the picture attacehd and I had some trouble understanding it. The question is so

Under the effect of torque Mo rotates a wheel (radius r) with constant velocity around point A. A brake jaw presses on the wheel (height c) . The brake jaw is connected to a tilted brake handle with inclination angle α . The break handle is articulated at point B and horizontally binned. On the other side the brake handle is supported by a sliding shoe against a vertical wall ( corfficient of friction µo) . The friction coefficient between the rotating wheel and the jaw is µ. The weight of the brake handle is neglected. The system in the above described state is in equlibrium.

I translated the question myself so execuse me if the formulation was a little bit messy. I have also attached a photo of how the answer should be.

What i don't understand is

1) why there is no reaction at the point B  (the movable bearing)

2) why is the anticipated direction of brake handle motion is upwards and how the rotation of the wheel causing this motion

3) which component of the reaction of the wheel on the brake handle responsible for this motion ( normal or friction )

4) why is the moment at point A  Mo=Rr, isn't the opposing moment by the friction force supposed to be less than Mo because the wheel is in motion and if the opposing moment is equal to Mo doesn't that mean the wheel is at rest


texts: What is the mechanical element that holds a worm gear shaft in place called?

texts:
Here is an image of a worm gear. What is english word for mechanical element (two of them will be necessary for a worm gear) in which the worm shaft will "lie" and rotate?

Here is one photo of the element where it is part of a housing; I need it as separate mountable element (I will mount it on plate):


texts: Finding the Torque, RPM and power required to move an object

texts: If I have an object of 90kg, moving along the ground with motors attached to wheels, how would I calculate how much torque, rpm and power those motors would need to have to accelerate the object to 20 mph in 10 seconds? If you have any resources like videos or readings, or just an explanation of how to do it, I would appreciate it. I realize this may be a duplicate question, but I cannot find something that explains this simply. I am a novice to this sort of thing and through all of my googling I just can't figure it out.


texts: What is a method to export a SolidWorks part (with distinguishing between materials) to a voxel cloud?

texts:
i'm doing a simulation in matlab which uses a 3D matrix as input, i.e. the matrix has the form (xDim, yDim, zDim).
With a simple STL export and a voxelization of this STL file i can get only a matrix with all elements be either one or zero.
But my part has four different materials which i need to distinguish in matlab.
One single slice in the matrix should look like:

0 0 0 0 1 1 1 1 2 2 2 0 ...
0 0 0 1 1 1 1 2 2 2 0 0 ...
0 0 0 1 1 1 1 1 2 2 2 2 ...
.
.
.

As a first step: in which format should i export my part to preserve the materials as some value?


texts: What are these parts on these Soviet tanks?

texts:
I'm sorry if this is not the right site but I really don't see another more suitable on Stack Exchange. Some Soviet tanks have these canister-looking things that hang down off the sides of the hull, very near the wheels. Some of them appear to be tilted. Here's a photo of them ...

Further, here is a 3D model of an IS-3 so you can get a really good view of these. The ones that are tilted on this one are different. They appear to be different on each one:

3D Model

Here is another 3D model where you can see these. Again these are different ones.

3D Model

Do these things just become loose and end up twisting? What do you think they could be?

Also, if you look at the first photo, on many of these tanks the left side of the suspension and wheels are set back slightly from the right side. It's quite subtle, and strange. Does anyone know why this is? This offset I'm speaking of is really subtle. The first model has it, the second model doesn't. The first one being obviously more accurate.

Edit: Someone has suggested it looks like a shock absorber, here is a screenshot from a good position.

Also, someone pointed out that in the first model I linked some of these are missing above some wheels, about 3 or four. In this picture you can also see some missing. I'm really confused about this.


texts:
How can I encode a quantized vector in matlab ?

This is a part of a problem where I am asked to implement a communication block using matlab.


texts: Why don't car engine piston-rods (or similar parts) fail as often as other car parts?

texts:
Anyone who has owned a car has ultimately dealt with failure of a sensor (parking), or A/C failure, battery shutdown or a tyre puncture. Part breakdowns like these are pretty common, at least relatively.

In a car however, the most stress (mechanical and thermal) is faced by the engine and engine-parts. If you think about it a little more, you could see that the most stress is faced by the piston-rod and connecting shaft. Those and related parts face constant tensions and compressions, on the order of many times a second, and not to mention the higher temperatures.

Despite that, I rarely hear of such failures (in proportion to other common failures mentioned above). What could be the reason for this? Are those engine parts over-engineering to never fail (almost, 'cause nothing is certain), over the lifetime of the vehicle?


texts: Will pressurizing container slow moisture permeation?

texts:
I have some electronics housed inside a sealed plastic enclosure, which will be used in a very humid environment. The environment can be assumed to be 100% humidity at a constant temperature, all the time. Plastic is permeable to water, so over time water diffuses through the plastic and the humidity inside the enclosure gradually increases. Within a few weeks the humidity inside the enclosure exceeds 80%.
Can I slow or stop the permeation of moisture by pressurizing the air inside the plastic enclosure? Is there a relationship describing how the rate of moisture transmission changes with pressure?


texts: Quite often while calculating angular velocity we come across the quantity radians per second. How do I treat radian dimensionally?


texts: How to cut Silicone and leave smooth edges?

texts:
We've got drawings for a prototype that we're trying to mimic by altering an original mold of the product.  For us to mold it would be quite expensive to just test it to see if it works or not.  We're trying to see if there's way to cut the Food Grade Silicone in a uniform way that would leave the edges smooth? This would allows us to test our drawing in the real world and get feedback.

We haven't had any success so far.  I'm not a materials guy so this is new to me.  Looking for any advice.


texts: What is the difference between turbo wastegate and variable geometry turbo?

texts: I don't see what the difference is between turbo wastegate and variable geometry turbo. Both seem to allow some of the gas flow, without turning the turbine, ie. bypassing the turbine, have I understood correctly? The only difference I see, is that the wastegate allows the gas to flow before the turbine, while the variable geometry, after the turbine. Any idea?


texts: Effect of Pressure on Combustion efficiency (of hydrogen) in excess air

texts:
Can somebody explain relation between combustion efficiency and pressure in lean mixtures using any kind of chart or mathematical equations?

At first glance I thought, combustion efficiency increases with pressure initially and then gets constant. But not sure by how much amount it varies based upon pressure for different fuels.

Then I tried to derive a formula to calculate or estimate Combustion Efficiency using Collision theory. As per my understanding, more collisions need to happen between reactants for better combustion efficiency. But collision theory alone is not sufficient to calculate or estimate Combustion Efficiency.

Also does Combustion efficiency varies between simple fuels like Hydrogen and methane under similar conditions? If so, why and at what margin?


texts:
In the notes , I dont understand that flange is thin , and the top and bottom surface are free of stress , can someone help to explain please?

Secondly , why the q' is assumed to be q '  throughout the flange is assumed to be 0 ? why are they stress free ? We could see that , the shear force V is applied to the top of the beam right ?


texts: Mechanism of a manual Crank Adjustable Height Standing Desk

texts:
I am trying to figure out the lifting mechanism of a manual Crank Adjustable Height Standing Desk. Please see the image below:

My question is what it is inside the metal frame (check the red marked area)
that is causing the entire system go up and down when I move the crank?


texts: Calculate the temperature stability of wavelength demultiplexer

texts:
Hi ive been given this question:
A wavelength demultiplexer (DMUX) used in a DWDM communication system has a
channel spacing of 100 GHz. The operating pass band of each channel is 50 GHz. The
transmission wavelength response of the DMUX depends linearly on temperature with
a sensitivity /
= 0.12 nm ℃−1
.If a laser of wavelength 1531 nm is centred in the pass
band of the DMUX, calculate the required temperature stability ∆ of the DMUX.
The given answer is +-1.63 degrees celicius however ive tried to work it out as follows:
Allowed change in wavelength = 3 *10^8 / 25GHz = 0.012 m
Allowed change in temperature = change in wavelength/sensitivity = 0.012/0.12*10^-9 = 10^8
The answer im getting is very wrong, so any help would be much appreciated!


texts: How can I calculate a robotic arm's maximum reach?

texts:
I have the Fanuc robotic M-2000iA/2300 data sheet in which it is being told that its maximum reach is 3734 mm and its payload capacity is 2300 kg, so how is its maximum reach being calculated and in respect to which axis?
Also, what will the load capacity be at that point?

Datasheet


texts: Why is the thin-walled cylinder more likely to experience failure along its axis than along its hoop/circumference?

texts:
I was watching a YouTube video  to understand the concepts of hoop/circumferential stress and axial/longitudinal stress in thin-walled cylinders and their formula derivation.
So the formula of the Hoop Stress: $$\sigma_{hoop}=\frac{(p * r )}{t}$$
where $p$ is the internal pressure of the cylinder, $r$ is the internal radius of the cylinder, and $t$ is the thickness of the cylinder,
The formula of Axial Stress: $$\sigma_{axial}=\frac{(p*r)}{2t}$$
My question is: They have mentioned in the video that since the axial stress is less than the hoop stress, then the thin walled cylinder is more likely to experience failure along its axis than along its circumference.
I still don't agree that just because the stress along its axis is smaller than that along its hoop, then it is more likely to undergo failure along its axis.
The stress is meant to resist deformation, and to resist the applied force. The axial stress is smaller just because the internal pressure applied along the axis is smaller than the pressure applied along the hoop.
So yes the axial stress is smaller than the hoop stress, but on the other hand the applied internal pressure is less along the axis than it is along the hoop of the cylinder.


texts: Is it possible to increase the heat output of a gas stove by connecting two gas supply canisters to it at the same time, and is it safe to do so?

texts:
Here's a typical outdoor gas stove:

It is fed by a low-pressure gas supply in the form of a camping cartridge or via an LPG cylinder connected to a low-pressure regulator (around 30mbar) like this one:

My question is: is it possible to increase the heat output of the burner by connecting two low-pressure supplies in parallel via a T-piece like this one?

Would this actually result in double the gas flow/double the heat output, or would the stove itself impose some limitation on the maximum pressure of gas able to flow through it (excluding the obvious extreme cases of catastrophically high pressure where the stove or pipes might crack)?

How dangerous is it? Obviously I assume it's not a recommended procedure and it probably has safety considerations, but for example would doubling a low-pressure supply from 30mbar to 60mbar pose a serious risk, or are appliances in general built to withstand far higher pressures than this? I know standard gas hoses, for example, can withstand pressures of 20 bar (100x higher than low pressure canisters).

Is there a way of determining whether an appliance will be able to handle higher flow?

I've seen this done on cheap/flimsy camping stoves so I assume it's not a catastrophic risk especially with better-made burners.


texts: Thermal expansion of a hole in a plate with a temperature gradient

texts:
I have a rectangular metal plate with a hole in it (with diameter of 300 mm). The plate has a temperature gradient going from one of its short sides to the other, I can measure the temperature anywhere in the plate.

I want to compute how much the hole is deforming from its round shape.

I know that I can calculate the expansion of the hole at uniform temperature with $\frac{ΔL}{L_0}=αΔT$ . So I was wondering if it is correct to measure a bunch temperature points at the edge of the hole and just apply that formula to each of them independently. But since there's a temperature gradient I'm assuming that there will be mechanical stresses between hot and cold zones working against the expansion, is this the case?

Is there a way to compute this by hand?

In the picture $T1>T2$.


texts: Why no hydraulic piston gas compressors?

texts:
I've been looking at solutions to compress gases and getting stunned by the cost and maintenance requirements of existing systems to fill cylinders (whether for SCBA or chemical storage) to 2000-4000psi:  The cost of entry is over 4 figures, with commercial systems like those used in fire stations and SCUBA shops running into 5 figures.  And, as far as I can tell, they are all direct mechanically driven multi-stage pneumatic pistons.

Meanwhile, sitting in my garage I have a manually-driven hydraulic bottle cylinder that can lift 20 tons, and typical hydraulic systems circulate hydraulic fluid at 5000-10000psi.

So I have in mind a very simple gas compressor: a single piston sealed on both ends.  On one side it is driven by a single hydraulic pump line.  On the other are two gas valves: An intake and an output.  Operation is simple:

Hydraulic pressure shut off.
Gas intake valve open.
Hydraulic flow reversed until piston has drawn in the maximum capacity of gas.
Intake valve closed.
Hydraulic pressure run until piston has reached maximum compression
Output valve opened (if not one-way and hence automatic), then closed once pressure equalized with output cylinder.

If the piston lacks the compression ratio to reach the desired psi, then the charged cylinder is switched to the input line and another cylinder to the output.

Am I missing a reason this won't work?  Or does it already exist in some form close to this?

If not, where and under what name might I find a long two-sided piston with pressure fittings on each end?


texts: What are design features of impact type screwdriver bits?

texts:
Modern screwdriver bits, marketed for impact tool use, have "torsion" control, apparently implemented with a necking of the bit.

Does this feature reduce the delivered peak torque?

Practically, does it reduce bit failure?


texts: What are typical manufacturing constraints when producing (conical) springs?

texts:
Small background: for a project of mine I need to develop a (very light) conical spring.

While there are plenty resources out there for regular springs I really struggled to find anything on conical springs (non-linear and telescoping conical springs, to be precise).

Since the main constraint for my spring are its dimensions, I tried to calculate the wire diameter needed that can accomodate for compression force of around 5 cN.

After some digging I managed to find this paper and made some calculations according to it.

D_1 = 0.003 m    # upper mean diameter
D_2 = 0.011 m    # lower mean diameter
n = 10           # number of coils
H = 0.0055 m     # height of spring at rest
G = 79.3 GPa     # steel shear modulus
F_C = 0.05 N     # full compression force

  $ F_C $ is the load for which the smallest active coil (with local
  spring diameter $ D_1 $) reaches its maximum deflection $ H $

  $ F_C = \frac{Gd^4H}{8D_1^3n} $

Hence, $ d = \sqrt[4]{\frac{8F_CD_1n}{GH}} $

Given the inputs above, I calculated that wire diameter should equal approximately d = 0.12544 mm. (By the way if you can see it's wrong, I'd greatly appreciate some directions)

However, when I approached some manufacturers with these numbers, several of them said it could not be done.

Could you please tell me what kind of constraints are typically taken into consideration when manufacturing such springs?

Is it that it's impossible to create a spring of this shape that will hold its properties or are they simply lacking proper machinery?


texts:
Is there any emitter/receiver (passive or active) systems that allow distance estimation in the range of 1~2 meters with an accuracy of few centimetres and don't need to have a direct line of sight as optical systems mostly do?

I was thinking about using such sensors as nodes to put on a suit that a human can wear. As a result, a graph can be obtained where each node represents one of those sensors and each edge describes the distance from this node to the other nodes. Using graph optimization techniques, the graph would converge to the correct joint position of the human. Such a system could replace expensive motion capture methods using calibrated external cameras.


texts: How to force creating a conformal mesh interface between zones in Fluent?

texts:
I am trying to perform simple 2D CFD analysis on Fluent having 3 adjacent zones(inlet, porous and outlet).

The problem I have is whenever I select non-equilibrium thermal model in porous zone in Cell Zone Conditions (as follows)

I get the following error:

A duplicate of this zone cannot be generated automatically, as it
contains a non-conformal mesh interface.
You must manually make a copy
the porous fluid zone and define it as a solid zone before you enable
the non-equilibrium thermal model.

AFAIK, a non-conformal mesh interface is an interface which does not have equal number of nodes on both sides, but it seems to me (visually) that I have an equal number of nodes on both sides (between zones):

So how can I make sure that I have conformal mesh interface between the fluid zones and the porous zone?


texts: Finding the sampling period to avoid loss of signal

texts:
We have:
$$ s(t) = 4u(t)−u(t−1)−2u(t−2)−2u(t−3.5)+2u(t−4) $$
where $u$ is the Heaviside function.

I had to draw the graph and find the minimum sampling period so we wont have loss of signal. I have drawn the graph.

$t=kT$
where $T$ is the sampling period.So $T=t/k$ so how do I find T?


texts: I am trying to understand what the dynamic factor $K_v$ describes. I know that a low $K_v$ factor results in quieter and smoother work of the gear but what exactly does $K_v$ tell me?


texts: Develop linear parametric model of a third order plant

texts:
Consider we have the third order plant described by the equation:

$$ y = G(s)u $$

where $\ G(s) = \frac{b_{2}s^{2}+b_{1}s+b_{0}}{s^{3}+a_2s^2+a_1s+a_0} $

If we assume that all parameters $\ a_0,a_1,a_2,b_0,b_1,b_2 $ are unknown then we can develos a linear parametric model of the form:

$$ z = θ^{*Τ}φ $$

where

$\ θ^*=[a_2\ a_1\ a_0\ b_2\ b_1\ b_0]^T $, $\ φ = [-\frac{s^2}{Λ(s)}y \ \ \ -\frac{s}{Λ(s)}y \ \ \ -\frac{1}{Λ(s)}y \ \ \ -\frac{s^2}{Λ(s)}u \ \ \ -\frac{s}{Λ(s)}u \ \ \ -\frac{1}{Λ(s)}u]^T $ ,

$\ z = \frac{s^3}{Λ(s)}y $

Now, let's suppose that the parameters $\ a_2,a_1,a_0 $ are known and their values are:

$\ a_2 = 3 $

$\ a_1 = 1 $

$\ a_0 = 2 $

How can we develop a linear parametric model of the plant considering these parameters known and as a result the vector $\ θ $ should be $\ θ^* = [b_2 \ \ \ b_1 \ \ \ b_0]^T $ ?


texts: Upper bound for von Karman Vortex Street?

texts:
I'm trying to see if I can find any literature on this specific question, but a few days of scholarly digging has been fruitless.

Given a 5" round pipe with a bluff body inserted, is there an upper bound for the Reynolds number at which the von Karman Vortex Street is no longer discernible? It seems to me that the vortices would be shed so close to the bluff body that they would be covered up by eddies in a turbulent flow (Say, Re >=100,000).


texts: What development possibilities could yet exist in water desalination?

texts:
I am thinking mainly in $\frac{kWh}{m^3}$ and $\frac{\$}{m^3}$.

In the past some decades a wide range of surprisingly efficient water desalination plants were built, mainly in desert regions (Middle East). These plants use reverse osmosis via a system of multiple pressered membranes. This solution seems to be very effective in the sense of energy usage.

But it is not enough. Comparing the desalination prices (coming mainly from energy costs) to the alternatives, a further 60-90% reduction is yet needed.  Comparing them, what development potential is there in water desalination?

I think water desalination has probably a theoretical energy limit, which could be maybe calculated from entropy and binding energy formulas.  How near are we to this theoretical limit?


texts: Confused about internal hinges for calcualting reactions

texts:
[]
I'm really confused about internal moments.
Regarding image 1,
When taking moments about D (the hinge), why does the book only consider the right side? Could you technically consider the left side (-Va x (L1+L2) - (Vb x L2) = 0) as well? By technically i mean unrealistically because i understand that considering the left side would introduce unwanted unknowns into the 4th equation (first 3 are sum of x,y,moment about A) as the equation would become:
VcL3 - P(L3+L4) - Va x (L1+L2) - (Vb x L2) = 0 am i right???
Regarding image 2,
Why must the triangular distributed load be split as shown to calcualte Ma? I got the question wrong when i assumed the UDL was concentrated at its centroid (right of hinge) as a single force. I feel this contradicts with image 1 (3) because Vc is also a single force on the right hand side of the hinge?
My understanding is that normally (without hinge) the whole triangular load would act at the centroid of the whole triangle?
I do understand that internal hinges don't restrict moments and that only shear forces are transferred across but this doesn't make sense.
Thank you and sorry for the long quesiton.


texts: Analytic expressions of the kinetic and potential energy

texts:
A homogeneous rigid circular disc (radius R, mass ms, center point S) rolls without a slip on a plain with a small angle of inclination alpha against the horizontal. A point mass MG is fixed on the disc in a distance e to the center point S. The motion of the disc can be described by the angle phi between the vertical and the connection line SMG.

Please see the figure for reference.

I am trying to calculate Kinetic Energy and Potential energy of the given problem (pic #2) and I have considered both masses as one system but I am not sure if that's correct or not. Also, I am not sure if the h term in potential energy (mgh) is correct here. So I would be glad if someone could throw some light on this. Thanks in advance!


texts:
Complete hobbyist here. I have two questions I have a problem figuring out.
I have hard time finding information about axis and types of connections they have. For example take this worm gear reducer:

It has axis connection with small extrusion on one side, where motors usually have shaft with one flat side. I found this adapter :

on the site it's called Axle sleeve but I haven't found this part by this name elsewhere, so maybe there is another more precise term?

Is there a beginner friendly resource I can study to get more familiar with this system? What both types of connections are called etc.


texts: Stepper motor holding torque without coils energized?

texts:
I want to know what torque a stepper motor can hold when stationary. They seem to only have one figure in specifications for holding torque which, I presume, is while coils are energised.

How is this normally handled in usage of stepper motors? Is there a way of calculating holding torque while coils are not energised? I know braking can be done by shorting the coils, but it's obviously not as effective as just holding one coil energised to maintain position. Is one coil usually just kept energised to hold position with maximum torque? Is there a limit to how long one coil can remain energised?


texts: Pressure drop in a CFD simulation of an air flow too small

texts:
I am simulating a turbulent air flow through a rectangular channel with the goal to match measured velocity profiles and the static pressure at certain points. My problem is that the pressure drop in the channel is not as high as in the measured data. Below you can see a diagram of the static pressure at the measurement points:

The black line represents the measurements, the red line the simulated data. As you can see the pressure drop is too small. As a result the simulated velocity profiles lag behind the measured velocity profiles more and more as can bee seen in the following pictures for position 1 and 4:

One possibility to increase the pressure drop would be to increase the wall roughness but then the boundary layer gets too thick. Which boundary conditions can I change to increase the pressure drop without increasing the boundary layer thickness?
Thanks!


texts: How to optimise feed-forward control of a process based on a prediction using the prediction confidence?

texts:
I'm looking for a control method for a production process with the following characteristics:

1 control variable
many process parameters (+-50)
1 resulting variable
continuous measurement of resulting variable with 30-90 second delay
complex physics that govern the process and numerous factors that determine the (non-linear) relation between control variable and resulting variable

With constant process/input parameters, the distribution of the resulting variable is normal.

The control method should ensure that the resulting variable should be above a set minimum and that the average of the resulting value should be as close to the limit as possible. Being above the lower limit makes the product more expensive, being below the lower limit however is more expensive: the product is scrapped.

Now I want to try the following: I have want to make a statistical model using some process parameters as input predicting the control variable that leads to the desired value for the resulting variable. Next to the value of the control variable, I also want to determine the 'confidence' or distribution of that value. Then I want to state a portion of the time the control variable must be above the lower limit (i.e. 3 sigma). Consecutively I'd like to set the setpoint for the control variable at the such a value that I achieve the given portion above the lower limit. To illustrate what I envision I made the illustration below.

Do you think this setup makes any sense? Am I missing any obvious alternative solution that is much simpler? Is this a known approach?


texts:
What forces are relevant when it comes to a davit lifting arm with a support? I'm not sure how to take the weight of the davit into account or how to calculate the max stress/strain on the system.

The davit is set on a beam and it lifts a 979 lb lid off of a tank. There is a support coming from the vertical piece about three-fourths of the way up that reaches over to the horizontal piece about half way.


texts: How to derive deformation gradient or displacement gradient?

texts: In one of my project, I need deformation gradient or displacement gradient for some elements in my model that made by ABAQUS software and I can't find it directly, any suggestion or help would be appreciated.


texts:
Mechanics books always highlight that the main advantage of bearings is to reduce friction, especially when we talk about them in rotational motion applications. The example of ball bearings is always mentioned. The balls prevent and regulate the contact between the inner and the outer rings in which they reduce the friction between the two.

Would that be the main philosophy behind bearings? If that is true, then would not be better off just to remove the whole setup and have the axis of rotation free from bearings so that there are not any inner or outers rings and therefore the friction problem would be removed from the beginning?

However, I always see that the friction treatment is secondary to a main purpose of bearings ( that I have not realized yet ). Should not be there a more fundamental reason of bearings?


texts: What signal formats are used for VSAT systems

texts: Which signal formats do the VSAT communication systems use? I am currently reading the book "Satellite Communications" by Timothy Pratt but the content seems too confusing. Can anyone specifically tell me the names and types of signal formats used in VSAT systems?


texts: Why is the saturation pressure of the refrigerant desired to be slightly greater than atmospheric pressure in an evaporator?

texts:
I read that it "is a positive pressure
against the environment". But I am not too sure what that means.


texts:
I am building a pneumatic shear to cut .135" C1018 round wire. We will be holding the wire in a hardened thimble and using a heat treated beveled cutting knife.

How much force do we need to be able to produce?


texts: Is Fusion 360 compatible with SolidWorks?

texts: I.e. can I save a model in Fusion 360 that can then be opened in SolidWorks?


texts: What are some techniques for improving stabilization given a mechanical time constant?

texts:
Problem: I have a self-stabilizing system that utilizes an intertial measurement unit (IMU) attached to the hull of a vessel. The system self stabilizes by performing matrix rotations based on the output of Euler angles of the IMU, effectively driving the motion in the opposite direction to compensate for the motion of the vessel.  In simulation, and with a system that has a large maximum acceleration and velocity, the algorithm works great. The issue is that there exists a very real lag in the motion of the physical output of the drive.
Question: What are some techniques for compensating for this lag?
Current Attempt: I characterize the motor/output drive by analyzing the amount of lag given a set of velocities. That is, I run the motor at various velocities and measure the difference between the expected position and the actual position of the output drive. From these measurements I deduce a polynomial equation (second order) which effectively predicts the lag of the motor given a certain velocity. This is worked into an ABG filter, which estimates the current velocity and acceleration of the system given positional input. As the IMU data comes in, it is passed through the ABG filter and the coefficients derived from the aforementioned polynomial is applied as a velocity feedforward, which adjusts the output proportionally to the rate at which the roll and pitch are adjusted.  Adjusting the coefficients of the ABG filter, heuristically, should theoretically alter the predicted path such that the IMU output is seen as an "adjusted" or otherwise contrived value intended to force the motors to perform a velocity/acceleration larger than the actual (unadjusted) output of the IMU would require, effectively reducing the error between the desired position of the motor/drive and the actual position of the motor/drive.
The lag of the motors/output appears as a phase difference between the IMU output and measured position of the output drive. It seems to always lag by about 200 milliseconds. My assumption was that by increasing the target position, the motor would effectively move quicker. To some extent this works well, but there's a lingering error between where I want to be and where I am at any given point in time.
Further Considerations: After reading some research papers on the topic, it appears that use of a PID loop is preferred over the use of the filter/feedforward in my original question.
https://ieeexplore.ieee.org/document/7375580
Any help is much appreciated.


texts: How deep would a water bottle have to be submerged in the sea to burst?

texts:
Assume the water bottle is the most sturdily built standard water bottle one could acquire in an american supermarket.

This is the first question I've asked, so I'm sorry if I'm not in the right place or asking it the right way. If I may I'd like to throw in these follow up questions:

Is there a good way to approximate how good an object would be at serving as a long term floatation device, like a pontoon or bouy?

Is there a way to calculate what the optimum size or shape of a 'water bottle like structure/material' (pocket of air encased in plastic) would be for displacing weight lifted out of the water by the buoyancy?


texts: Find electronics in wilderness; or, "I dropped my cell phone in the woods!"

texts:
Imagine I was working in the woods and dropped my cell phone somewhere in a large area where it is now hidden beneath dense vegetation.  By calling it I confirm that either it has powered off or its battery is dead.  How can I find it?

A consumer metal detector (induction magnetometer) will easily find it if I can get within a few feet of it.  But there must be more efficient means of finding electronics in a wide wilderness area given their unique and unnatural characteristics.  For example:

They contain dense, refined metals.  There is easily more copper, nickel, and perhaps a few other elements in a phone than in an acre of wilderness almost anywhere.
They contain antennas.  Even when powered off, the electronic structures are there to receive and transmit signals efficiently in a particular spectrum.

Can radar be used to discriminate either of these characteristics and provide a practical means of scanning a large area to zero in on the device?  Are there existing systems that do this?


texts:
Spring Design

In spring design, there a a variety of parameters to consider. Some of the parameters are solely physical (wire diameter,  coil diameter, length, etc.) and some are determined from the physical dimensions in combination with the material properties (spring constant, allowable stress, etc.).

Spring Set

One physical characteristic of a spring is whether or not it will experience set. This is a permanent deformation of the spring after it has been compressed. Whether or not set is an issue depends on the level of stress that the spring undergoes versus the material's tensile strength.

The common  rule of thumb is that set is not a concern if the spring only experiences 40% or less of its tensile stress. If the spring experiences between 40% to 60% of its tensile stress, then the set can be compensated for during manufacturing. Above 60% of the tensile stress, set cannot be controlled.

The reason that spring set can be compensated for is that it occurs after only a few cycles and then the full amount of set has been reached.

Creep

Creep is a separate phenomenon from set. Set happens immediately, but creep happens with constant load over time. Since the metal is under stress, it should exhibit creep. Creep is also affected by temperature.

I want to know how a spring is affected by long-term constant load. I have not been able to find any information about creep in springs or how to calculate it during spring design.

How is the long-term creep of a spring determined?


texts: Do fine grit sand papers and wax polish bars and pastes have a universal color code?

texts:
Im talking about 10k 5k 2k 1k 800 400 grit papers, wax polishing bars and polish paste.

Do they have a universal color code which corresponds to grit?

Many times the letters are either not on the paper or hard to read.


texts: Is there a CE mark requirement for positive control logic?

texts: I am looking into any requirements to obtain a CE mark that require control logic to be positive. In other words, if an electronic circuit has logic that either resets or turns the circuit off, is there a requirement that the control line activates the reset/shutdown by a low (ground) to high (such as TTL) transition or state change?


texts: The behavior of the stress-strain curve of metal, containing a void

texts: Let's assume that in a metal sample without any dislocation, there is a void. Then we conduct a uniaxial tensile test.


texts:
Two questions on wireless transmission, packed into one.

First: I am confused about the meaning of the term 'Bandwidth' in a wireless transmission environment. The two most common definitions I could find are:

difference between the upper and lower frequencies in a continuous band of frequencies
the maximum rate of information transfer (bps) across a given path

How do I reconcile these (assuming they are reconcilable)? In other words, why does the difference between the upper and lower frequencies in a frequency band equal the maximum rate of information transfer across the path transmitted? Can someone kindly explain the connection in a clear, visual way if possible?

Second: what is the relationship between 'Bandwidth', 'Capacity', and 'Throughput'? I have seen a bunch of analogies saying that the Bandwidth can be thought of as a pipe and that the throughput can be thought of as water flowing through this pipe, implying that the Bandwidth is some theoretical maximum transmission rate and that the throughput is the actual transmission rate (which can be lower due to various overheads). Is this the analogy right, and if so, what does 'Capacity' mean?

I would greatly appreciate answers to these questions if possible. Thanks.


texts: What are the differences between compressor stations, pump stations, and booster stations?

texts:
I am doing some research on impacts related to natural gas compressor stations. In some states, I've received data for compressor stations alongside other facilities in the oil and gas world. These booster stations and pump stations.

Before filtering out these other types of facilities, I'd like to make sure that I understand the difference between the facilities. Could someone outline key differences across these facilities?


texts: Why is friction force is not considered as centripetal force?

texts:
This is a solved example in my text book"Engineering mechanics dynamics. R.C.Hibbeler" :

The 3 kg disk is attached to the end of a cord.  The other end of the cord is attached to a ball and socket joint located at the center of the platform.  If the platform rotates rapidly,  and the disk is placed on it and released from rest,  determine the time it takes for the disk to reach a spead great enough to break the cord.  The maximum tension the cord can sustain is 100 N..  And the coefficient of the kinetic friction between the disk and the platform is 0.1

when the free body diagram of  the particle was drawn,  the friction force was considered in the tangential direction,,  but it wasn't considered in the normal direction(tension was only considered) why?  I was expecting that there is kinetic friction in the normal direction,  since the disk is moving relative to the platform.


texts: Configuring UART Port to 115200 on Renesas RX130 using Code Generator

texts:
Does anyone have insights into configuring UART port on Renesas RX130 microcontroller for a bit rate of 115200? I have successfully configured for a 9600, 19200, and 38400. I can read from the MCU and write to the MCU via terminal programs such as tera term. I am using the code generator available through e2Studio IDE.. I am using Serial Communication Interface SCI1, from which I have configured RXD1 / P30 (Pin 18) and TXD1 / P26 (Pin 20). Note P30 is port 3 bit 0 and P26 is port 2 bit 6.
Below is the MCU package configuration view enter image description here

Below is Code Generator software component configuration view SCI1 enter image description here

Has anyone run into similar issues? Thanks for your help!
Note: I am open to exploring Firmware Integration Tool (FIT) to configure UART ports


texts: calculating the efficiency of a microwave oven

texts:
If I want to calculate the efficiency of a microwave oven, I have the input Energy (= power (watts) x time (s)) and the output which I measured using temperature difference (q=mct).
So do I divide output/input x 100 or do I find the difference between them (=work) then divide it by the input energy?


texts: Should I model the load from a pool at the top floor of a multi-story building as live or dead?

texts: I am designing an aquatic center on the top floor of a multi-story building. The critical beams and columns to be designed are supporting a 25 m lap pool and I am wondering whether to apply a live-load or a dead-load safety factor to the water load acting on the structural elements.


texts:
I have slightly inclined (50 cm over 6 meters) metal roof over my studio. The roof has bad thermal insluation -- 15 cm of mineral wool between sheet metal.

The location is Kiev, Ukraine. Ambient temperatures extremely rarely exceed 32 °C, and most of the activities in the studio occur after 6 p.m., when it's never over 30 °C. I lived through a year without AC, with only fans for air intake and circulation.
With ventilation turned off the hottest time inside is 7 to 8 p.m.. With ventilation on, and 20 people inside the temperature inside is 1-2 °C more then ambient air.

I want to cool the inside for a few degrees by pouring a water on the roof.
My questions are:

Can I hope for outside roof surface to get as low as a wet-bulb
temperature? The graph gives me 25 °C at warmest hour of
ambient 32 °C 55 % humidity.
Which method of water distribution is more effective:
  a) Drip tube. Would be easiest to install. The drawback being the risk of water joining into a few streams instead of uniformly wetting the surface.
  b) Misters.
  c) Sprinklers.


texts: What type of fan would I need to induce the lift of a 200 lbs object?

texts:
I know this might sound ridiculous, but I am attempting to make a fan designed to induce lift of a 200 lbs object. By 'fan', I mean like the fans that lift a drone off the ground. I can only have a maximum of 3 fans.

I am trying to lift the object at least 5 feet of the ground.

Do you know what type of fans I would need, and/or the RPM of the fans? I am little bit confused on what to ask since there aren't any other questions like this. Also I am a beginner to engineering.


texts: Do micrometer calipers have any advantage over vernier calipers?

texts: Micrometer calipers measure thickness. Vernier calipers can measure both thickness and inside diameter. For the same least count and accuracy, both are similarly priced. Do micrometers have any advantage over verniers (besides size- micrometers being compact)?


texts: X-form and cross-form rudders in underwater control

texts:
What are the advantages of using X-form rudders in comparison to cross-form rudders?

Why do some submarines, torpedos and underwater autonomous vehicles use X-stern control?

X-stern:

Cross-form:


texts: What is the smoke made by the fogging machine? Is it harmful to humans?

texts:
What is the principle of a fogging machine ?
on what process a fogging machine depends ?
distillation or vapourization ?
what is the harmful effect of fogging machine ?


texts: Should long-term prestressed girder camber always be upward?

texts:
When considering long-term prestressed girder camber (for a bridge), what are the implications (if any) of long-term downward deflection on girder performance? Should prestressing be designed to ensure that long term camber is always upward?

I'm using the PCI multiplier approach to calculating long term deflection.

  Utah DOT Structures Design and Detailing Manual page 14-30
  https://drive.google.com/file/d/0B8QRVMpaE6oYWTg3WU5ISDhkRGM/view


texts: Thermal conductivity listed in the rather complicated Btu/s-in.²-°F/in - am I converting this right?

texts:
I'm currently working through some rather old documentation which gives the thermal conductivity of a material as 9.8 x 10⁻⁶ Btu/s-in.²-°F/in. There are many typical ways to give a thermal conductivity in imperial units, but this does not appear to be one of them - in fact, I cannot find any other instance of thermal conductivity being expressed this way, and even the document I'm working with only uses it a handful of times, none in specifying a known value or constant I could check against another unit of thermal conductivity.

I've worked through the units, and it seems most likely to me, though I'm far from confident in this, that this unit is equivalent to 2943641 watts per meter kelvin, making the given value equal to 28.85 W/mK (which seems like a plausible value).
However, I'm far from confident in my calculation here, in particular about the meaning of the dashes and period in the unit.
Is 1 Btu/s-in.²-°F/in = 2943641 W/mK the correct conversion factor? How would one read this unit aloud - "BTU per second-inch squared-degree farenheit per inch"?