texts: Air conditioner using liquid nitrogen and a cryogenic heat exchanger

texts:
I have been trying to understand if compressor-based systems in air conditioners can be replaced to make something more economical and energy efficient.

From what I understand, the compressors primary job is to pressurize the refrigerant to bring it back into liquid state. Can't the same job be done via a heat exchanger?

Fig. 3 in this resource is an example of what I am talking about: https://www.aiche.org/resources/publications/cep/2015/september/cool-down-liquid-nitrogen#fig1

Can the existing compressor in an air conditioner be replaced by a cryogenic heat exchanger that uses liquid nitrogen to condense the liquid and pump it with a much smaller compressor? If so, how would I go about calculating the amount of liquid nitrogen needed to cool a room ~200 sq ft in size?


texts: off-scale torque measured - what is my torque arm?

texts:
I have assembled a benchtop torque measurement stand for evaluating electric motor and controller efficiency.

The motor is 49kV , 5kW brushless outrunner.

Input power reading is taken from motor controller (VESC6, FOC). Current is limited to 140A, Input voltage is 48V.

$$RPM=480$$
$$P_{input}=5800W$$
$$Q_{calculated}=\frac{P_{input}*9.549}{RPM} = 117 Nm$$
$$Q_{assumed}=0.8*Q_{calculated}=94Nm$$

The torque stand consists of two load-cells holding the motor stator. Each cell  was calibrated and tested for 5g error and is rated for 10kg load. After the motor is installed, the weight reading is offset to 0.

The rotor of the motor (shaft) is supported by the bearing and so the axial weights are compensated.

The averaged mass readings from the load-cells at peak input power are:
$$m_{topcell}=4328g$$
$$m_{botcell}=-4244g$$

I assume the torque arm: $$L_{arm}=0.065m$$
and Force measured: $$F_{cell}=\frac{(m_{topcell}-m_{botcell})}{1000}G=\frac{8572}{1000}*9.81=84N$$

And the output torque:$$ Q_{real}=F_{cell}L_{arm}=84*0.065=5.47Nm$$

Clearly, $5.47 N$ isn't even close. So either mass or torque arm is wrong.

$$L_{arm\_assumed}=\frac{Q_{assumed}}{F_{cell}}=\frac{94Nm}{84N}=1.11m$$

So, the question is - what is my torque arm?

EDIT
I have revised the approach and made $1.35m$ lever.
The mass measured with digital scale was $1520g$, which is equal to $20.13Nm$.
If I plug this into another torque equation:
$$Q=8.3\frac{I_A}{K_V}$$
I get
$$Q=8.3\frac{140}{49}=23.7Nm$$

So, perhaps the true question I should be asking is
Why cannot I apply classic torque ($Q_{calculated}$) formula to an electric motor?


texts: How do I determine the angular acceleration?

texts:
In this question I understand what we have to do to solve it and is equate the sum of moments with the moment of inertia. However I am not sure on how the LHS became negative as I see that the angular acceleration follows the same direction as the moment, so positive.

So why is the LHS negative?


texts: How to power a large electric motor from a battery?

texts:
A question I ask myself now and again is if it is technically feasible to build battery powered construction equipment, like large excavators - say 250kW motive power at the shaft of the central hydraulic power pack.

I'm not an electrical engineer so I'm not sure how the motor, battery and everything in between would look like. It doesn't seem trivial:

250 kW motive power is roughly 280kW electrical power. Most batteries deliver single digit voltage and are connected in series to deliver 12V or whatever is needed. DC motors at this power seem to need between 420 and 800V, depending on speed and torque. So I'm either talking about stacking quite a lot of battery units (with their internal resistance!) or using a DC-DC converter (do these exist for 280kW? How (in)efficient are they?) or looking at a different motor.

Provided a 250kW 12V motor exists, I'd be talking at about 23kA current. This seems quite collosal to me (but maybe I'm wrong).

Another way could be to mount several motors on one shaft, but then the inactive motors would likely act as brakes and add their own headaches (or not).

In short, for me as a non electrical engineer it's not trivial to envision such a power train. How could it look like?

An answer should:

provide a workable solution, not neccessrily the best - proof what is optimal is surely bexond the scope of an answer
list all the major components - motor, battery, converters, other major stuff I forgot - with effiencies in this particular use case
provide a decent estimate of overall efficiency (input: charging battery, output: motive energy provided)
Energy density of battery and smallest viable battery to deliver the power
ballpark estimates of weight and cost of major components are appreciated but not neccessary


texts:
software person here, venturing for the first time in the design of a mechanical system for a hobby project. Please note I have some experience in disassembling, fixing, reassembling mechanical systems, but design my own is a whole other thing.

In practice, I would need a motor (that I know how to control) to rotate a vertical pole, or mast. The motor has a wormgear reduction box similar to this:

What I'd like to avoid is to put off-axis strain on the motor in case the pole is pushed sideways; also, the pole should be able to rotate as freely as possible to the torque from the motor does not have to be excessive. The weight pushing down from the pole should also be taken care of.

My first intuitive approach would be to use two thrust bearing devices similar to this:

so that the mast will be constrained on its axis and also the weight supported. I'd mount a gear around the mast with the motor with a smaller gear on its output shaft.

Any advice, should I consider anything else? Please, let me know if a more comprehensive drawing is needed to communicate what I want to achieve, I'll try to put one together.


texts: Why Cold formed steel is becoming important for researchers?

texts: A lot of academic research is happening on CFS and it has become very popular in constructions too. Why?


texts: Torque induced regular precession/ nutation calculation and visualization out of attitude Data

texts:
I have a rocket body with given Euler Angles, Quaternions and Angular-Velocities for given time steps. And I'd like to calculate the regular precession and nutation for every time step, so that I can plot the cange of Nutation-Angle over time.

Roll, pitch, yaw and Quaternions are given in inertial-frame, while Angular velocity is given in the Body-Frame.

For some reason I read that the nutaion-angle is simply the given pitch. But I am not sure if that is really the angle I am looking for because the values dont seem to fit my prediction.

I'd like to also plot the precession. So that it looks something like this

Thanks for all suggestions.


texts:
We know that Blaise Pascal built a mechanical calculator which had a carry mechanism called a sautoir.

You can see a video of it working here, and here.

We know that Charles Babbage wrote a book of log tables.

In doing this, Babbage was inspired to create Log Tables mechanically, leading to his design of the Difference Engine.

My question is: Did Charles Babbage's Difference Engine use the sautoir carry mechanism from Pascal's calculator?


texts: Instron Test Profile -- Failure when steadily dropping the load

texts: I'm working on an Instron 5969 tester, and I'm trying to measure the residual strain in materials within their elastic zone. I'm using the test profile, which allows me to stretch the material a specific amount, hold it for a moment, release the force, and record the change in length. The problem I'm having, is when the load is removed (slowly and continuously), the machine seems to panic. It starts shaking, and the recorded values jump all over the place. I've tried multiple ramp rates (the rate at which the load is removed) to no avail. Any ideas on what else I could try?


texts: What is the maximum angle of a shelf angled brace?

texts:
So suppose I want to make a single shelf protruding from a wall and to place a heavy object on it (Figure 1). A shelf like this would fail (assuming no internal mounting that penetrates into the wall).

As such, in an ideal scenario, I would want to place a vertical column/beam directly below the shelf to help support the weight on top (Figure 2).

Yet this isn't always ideal due to other objects below the shelf. So in this case I've seen angle braces being used below the shelf (Figure 3). Now generally, from what I've seen, these angle braces are roughly 45 degrees from vertical. Why is that the common angle?

I haven't been able to find any calculations online to determine the ideal or maximum angle here. What would be the maximum (from vertical) angle that a shelf like this could support? I understand that there are many variables at play including the distance that the shelf hangs from the wall, the thickness and strength of the shelf material, the weight of the object on top of it, etc., but is there a rough calculation that could be used?


texts: How to do gold plating on Anodized aluminum and stainless steel?

texts:
I have done some research and asked in a few forums for gold plating on anodized aluminum  and stainless steel but haven't yet found the answer to my questions.

What are the chemicals for pre-processing the surface and the suitable gold solution for these tasks?

For stainless steel I believe they use Wood's nickel for pre-processing. Is it the only or the easiest method? How about anodized aluminum?


texts: Making complicated curves / surfaces in the real world accurately

texts:
There are many complex mathematical shapes like the cycloid, cissoid, umbilic torus (picture) or the shape of the Azadi tower. Sure one can design complex objects like this in CAD software today but how does one construct such objects accurately in the real world. What techniques do builders use to take an architect's zany design and accurately construct the prescribed shape?

I would like to know modern techniques to acccomplish this and also techniques used by pre 20th century engineers.


texts: What does the class 6H represent in a hole?

texts:
When using Autodesk Inventor to create a hole in a surface to fit an M4 screw in, I come across 4 parameters: size, class, designation, and diameter.
I chose the size of 4 mm, but I don't understand what class represents, and it seems that the only option for this is for it to be 6H, even though other sources online state that there should be other option such as 6G and 5g6g.

What do these represent?
What is meant by class?


texts: PID position control when setpoint does not require continuous force

texts:
I'm struggling with the practical application of a PID control algorithm when the set point does not require any external force to stay in position.

For example, I have a geared electric motor that has a mass attached perpendicular to the motor's shaft. The mass is fixed to the shaft so it will rotate with the shaft without slipping. There is a sensor on the mass that knows its angle relative to horizontal (an accelerometer in my case), which is used for error feedback. The control system attempts to drive the motor such that the mass is always balanced vertically above the shaft, as pictured below. The motor itself is attached to a robotic arm that may rotate around arbitrarily, so the motor will work to keep the mass vertical at all times.

The key thing to note here is that once the motor has achieved the set point (the mass is vertical above the shaft), it does not require any more work from the motor. No additional force is required to hold it there. In fact, there's enough back-drive friction in the gearing that even if the mass is, say, 10 degrees from vertical, it'll still stay put.

My question is in regards to correctly implementing a PID control loop for this kind of system. Here's the situation that has me confused:

Let's say the mass has come to rest deflected 5 degrees from vertical. In the PID loop, the P component is very small because the error is very small. So the integrator winds up to do most of the work of removing this steady-state error. It does its job and adds just enough power into the motor to drive the mass to the vertical position. Once the vertical position is achieved, no additional force is required to hold it there. But that integrator component still has a non-zero value and will keep driving the motor, making it push the mass passed the set point and to the other side. An inevitable oscillation about the set point will then occur.

Are there special considerations in a PID algorithm for this case? Or am I just fundamentally misunderstanding how a standard PID algorithm will react to the system I described above?

EDIT:
My original question was misusing the word "stable". Thank you to Carl Witthoft for pointing that out. The focus of my question, however, is how to properly implement a PID loop when the system requires that the control forces drop to zero as the position error approaches zero.


texts: Proper way to power/use a vacuum cylinder?

texts:
I'm considering using a vacuum cylinder in my project (like these ones) to lift sheets of cardboard, but being new to mechanical engineering I'm not at all sure what I need to attach to operate one, and the supplier's site definitely offers no details. I think I'll need a vacuum pump, but I don't know what size is necessary (for example, will something like this mini pump do?), and whether I just hook up the pump to the hole on the cylinder, or there are other parts that are required.

(I hope this is the right SE site for this; it was a toss-up between this one and the Robotics one.)


texts: Band Brake placed Perpendicular to the Diameter bisecting the Angle of Contact

texts:
I was asked the question:

  A band brake is installed on a drum rotating at 250rpm and a diameter
  of 900mm. The angle of contact is 1.5pi radians and one end of the
  brake band is fasted to a fixed pin while the other end to the brake
  artm is 150m from the fixed pin. The coefficient of friction is 0.25
  and the straight brake arm is 1000mm long and is placed perpendicular
  to the diameter bisecting the angle of contact. What should be the
  width in milimeters of a steel band with maximum tensile stress of
  55MPa and 3.0mm thick will be used?

Answer is 37mm.

I honestly see no way to solve this without any indication of power or force of some sort... here's my attempt

$${ S_{max} = \frac{F_1}{w\times t} }$$
$${ 55 Mpa = \frac{F_1}{w\times 3.0 mm} }$$

$${ \frac{F_1}{F_2} = e^{(\theta \times friction)} }$$
$${ \frac{F_1}{F_2} = e^{(1.5rad \times 0.25)} }$$

Trying to find F1 seems to be the flaw. There are just no formulas I know of which doesn't require either power, force, torque?

$${ T = F \times d }$$
$${ P = 2\pi T N }$$

Is the problem set flawed? What am I missing? Is there another way?


texts: Degrees of freedom of an internal hinge in plane beam?

texts:
What are the degrees of freedom of an internal hinge in a plane beam?

I understand that the bending moment=0, does this mean there is no slope either?

Or does it have both degrees of freedom of deflection (V) and slope (θ)?


texts: Methods to Measure Buckling without Expensive Equipment

texts:
I'm working with some flexures (circularly symmetric tube with pins at the ends).  Their bending stiffness matches my FEA.  However, I'm concerned that they are buckling, reducing their overall axial stiffness.

I don't have a way to measure the axial stiffness in situ; the flexures are part of a larger system.

I don't have a lot of mechanical measurement equipment either, but I do have:

Accelerometer
Laser distance measurement device
Oscilloscope
Masses, scales, ...

I can model the buckling, but the rest of the team relies on measurement and doesn't believe models.  So, I need to come up with a method of measuring buckling of the flexure in compression.

Ideas?


texts:
I am trying to make a simple dispenser without using any electricity. I just want to create a simple dispenser that dispenses flour with the turn of a knob. I am creating this because wherever I bake, I need so many different measuring cups for each item, so I want to make a dispenser that dispenses each item, but I will start with just flour.  Since flour is usually used in cups, I will have the dispenser dispense flour in ¼ cups. Now to get into the problems, I have a design, but I dont know how to make it.
Everything has to be in the right size since I am having the measurement of ¼ cup, so the space in between the spinning disc must be equivalent to ¼ cup. The other issue is for this to work; the canister holding the flour must be just big enough for the spinning disc to fit inside, so that means I can’t buy it online. So my two most significant issues are how do I make the disc and how do I make the canister that would fit. If anybody can help, that would be much appreciated.
If anyone has any alternative designs or ideas, they are all welcomed. I also want to mention that I dont know how to do a lot of stuff since I am still in high school.


texts: Fitting a sprocket on a small motor shaft

texts:
I have a bit of a newbie question. I've inherited a mechanical system, wherein the motor has a D-type output shaft with a diameter of 8mm.
(https://www.ebay.co.uk/itm/DC-High-Torque-Worm-Reducer-Geared-Motor-Electric-Motor-with-Reduction-Gearbox/312731356078?hash=item48d03dcbae:m:mLcgZdBy9RmkbntdUcP9aDA)

The motor is supposed to drive a component which has a sprocket (12.7 mm pitch, or 08b-1 standard, if you prefer.)

I've been trying to find a suitable sprocket, however it seems the smallest bore I could find was 10mm, in short - I need to fit a large sprocket on a small shaft. I've been looking at taper bushes, collars, etc.

Is there any way I can increase the diameter of the motor shaft, so that I can install the sprocket via a grub screw?

It is, perhaps, worth mentioning that I don't have access to a lot of tools, thus my machining capabilities are quite limited.

Many thanks in advance.


texts: How do gas flow regulators avoid choking?

texts:
According to compressible flow theory, a downstream pressure of 0.528 times upstream pressure is sufficient to choke a flow device.

So, how do industrial grade pressure regulators throttle a wide range of pressures (say 150 bar to 20 bar)?


texts: Why is -180° taken as a reference or phase margin in Bode plots? If the phase plot (grid impedance and inverter impedance versus frequency) exceeds -180° at the gain crossover frequency, then the system will be unstable in a grid-tied inverter system. So why is -180° taken as a critical point?


texts:
I'm a student currently working on a market research project on the HVACR industry, and I'm having trouble nailing down a simple answer to these questions (it may be there are no simple answers, as so far it seems like it varies on many factors of the data center).

What is the typical airflow/air exchange rate of a data center? Is it stressful on the buildings HVACR system or energy cost?
How important is humidity control in data centers?

Thanks in advance!


texts: How do I invert a system in state space form?

texts:
Suppose I have a system described in state-space form. Can I invert the system (swapping the roles of the input $u$ and output $y$)?

If we start with:

\begin{align}
\dot{x} &= A\,x + B\,u \\
y &= C\,x + D\,u
\end{align}

and $D$ is invertible, then we can use the second equation to solve for $u$ in terms of $x$ and $y$:

$$
u = D^{-1} (y - C\,x)
$$

We can then substitute that back into the original state-space description to get the inverse system:

\begin{align}
\dot{x} &= (A - B\,D^{-1}\,C)\,x + B\,D^{-1}\,y \\
u &= -D^{-1}\,C\,x + D^{-1}\,y
\end{align}

However, in typical systems $D$ is zero. What is the significance of requiring $D$ to be invertible to inverse the system? Is there a work-around allowing us to invert systems where $D=0$?


texts: What drives improvements in seismic safety?

texts:
I get the impression that a lot of old buildings fail to meet modern earthquake safety norms, and need to be rebuilt or retrofitted.  But what has changed in the last few decades that would make a building constructed today better than an older building?

For example, if you asked why modern automobiles are safer, I would say that the primary driving force (pardon the pun) is technology — crumple zones, seat belts, airbags, antilock brakes, traction control, distance sensors, alertness alarms — coupled with decreasing acceptance of drunk driving and public outrage over Ford Pintos.

If you asked why aviation is safer, I would also credit technology (e.g. TCAS), but mostly an accumulation of experience from all past mishaps.  For example, after Tenerife, the industry adopted standard radio phraseology.  After Germanwings Flight 9525, most airlines will not allow pilots alone in the cockpit again.

So, what drives improvements in seismic safety?  Exotic base-isolation schemes aside, have technology and construction techniques changed much in the last few decades?  Was there anything preventing earlier builders from making structures as strong as they could be, or today's builders from making them stronger than they currently are?  Is it a matter of decreasing willingness to risk human lives as life expectancy increases?  Increased economic prosperity allowing money to be spent on more concrete and rebar?   A tendency for government regulation to grow?

Or is the premise of the question flawed to begin with?


texts: Equation for finding the thickness of material required for tubes under radial stress

texts:
From the book "Design of Liquid Propellant Rocket Engines". Under stress analysis related pages, the author used an equation for finding the thickness of the wall needed for sphere under stress.

$$\text{Thickness of sphere wall} = \dfrac{\text{Yield pressure}\times\text{diameter}}{4\times\text{yield strength at 300°F}}$$

I would like to know the equation for tubes.


texts: How could an MGA's frame/chassis best be improved?

texts:
As an assignment for my Automotive Engineering study, I have to practice manual FEM calculations. I'm free to choose whichever existing construction, and with that I have to make FEM analyses of both the original and the improved construction. I chose the chassis of the '57 MGA i'm restoring, which is shown below:

I suppose there are several ways to improve the driveability, but I expect increased torsional stiffness to have the most impact. The rear bridge seems rather wobbly to me, but I can't really tell; I haven't driven an MGA before.
(If you have better ideas how to improve the chassis please do suggest.)

What would be a good approach to improve the torsional stiffness of the chassis?
With that, I mean what kind of construction/structure would be effective; a triangular structure between the two side beams for instance.

Please note: it doesn't have to be practically feasible or cost effective. It's just for practicing.


texts: How to install a wired sensor in a rotating bin without tangling the wires?

texts:
I want to insert couple of moisture, temp and humidity sensors in this bin to take readings from the compost.

But how do i install it without turning/tangling the wires?

Can anyone help me figure a solution I am not an engineer but I am trying hard to solve.


texts: Does a photon impart energy on a surface (to raise its temp) if it goes THROUGH that surface?

texts:
Hi so I have this senior design project involving cooling human skin as it is irradiated by an infrared LED. Human skin not only is super absorbent to IR, but that IR goes THROUGH the thickness of it really well. There are some very long path lengths of IR photons within the human body.
In my heat transfer class, we only saw radiation as dumping all its energy right at the very surface of some block of mystery meat or whatever. In that class we only cared about absorption in terms of how much radiation isn't reflected. We then treated all the radiation that got absorbed as being "stopped" by that surface essentially. After that the heat from this interaction would be distributed by conduction within the receiving block thing.
Million dollar question: What is happening to that topmost surface temperature if absorbed radiation is going THROUGH the surface? So now my deeper layers are being heated by both conduction and direct radiation?
The end goal is to figure out the surface temperature of this irradiated spot of skin, then cool it by cold air convection until a goal surface temperature is reached. Any diagrams in answers would be super helpful. I am a visual creature. Part of my trouble is photons are hard to visualize and I keep picturing bullets stopped by walls when I know photons don't have mass and it's a poor analogy. It's really tripping me up.


texts: What determines the optimal number of balls between races in a bearing?

texts:
Imagine I have an important axle in the gearbox of a motor. I want to support it with ordinary ball bearings at several places along its length. I need both the outer and inner races to stay at fixed diameters at a fixed distance from each other.

However, I can change the number of balls in between the races. I can choose any number of different bearings (though each one has to have a certain diameter, so there's actually a limit). I could squeeze an arbitrary number in, so long as that number is below the maximum and can still support the inner and outer rings.

What determines the optimal number of balls used?


texts:
Of course, this is not true for all engines (after all the pre-2014 F1 engines were 4-stroke and were rpm limited to 18,000 rpm). However, from my experience, 2-stroke engines tend to run at a higher rpm than a 4-stroke engine.

Given a 4-stroke engine only has a power stroke on every other revolution of the crankshaft, surely it would make more sense for it to in fact be 4-stroke engines that run at higher rpm, given it could theoretically run at twice the rpm for the same fuel consumption.

I guess I must be missing something here, because I fail to understand why 2-stroke engines tend to run at higher rpm to a 4-stroke engine?


texts: How to make epoxy resins dissipate static charge

texts:
I want to cast items out of epoxy resin. They  will be tools used to handle ESD sensitive devices, so they need to at dissipate static charge, or perhaps somewhat conduct. Resins used will vary depending on the part.

Unfortunately, resin suppliers seem to never give any data on electrical conductivity. I presume it's extremely low. So to have it conduct, am I right in saying I could mix in something like graphite to help conduction? I presume it would reduce strength, or at least change some physical properties, but that's fine.

I've previously experimented mixing graphite powder with non-conductive powders - No liquids or glue, and just compacted by hand in a glass tube. I found that the resistivity could not be controlled easily / effectively by varying the ratio; it seemed it either conducted quite well, or not at all, to the degree where fine tuning ratios would too unreliable.

Might that be the case with epoxy resin as well? How might I increase the conductivity of a resin? And how might it be tunable? Principles / formulas? I presume the geometry, size and other physical properties of the powder used is important, as well as, perhaps, the resin?


texts: possibility for hydraulic accumulator with no moving parts?

texts:
Some background for context only

I am in the process of designing a pressure system where my pressurized fluid needs to be kept incredibly clean, with typical contaminants at the ppt or below level. The fluid in question is more compressible than a typical hydraulic fluid, so I need to build in an expansion volume for when I cycle to lower pressure.  This expansion volume is going to look very much like a hydraulic accumulator.

The most common hydraulic accumulators are pneumatic, and the gas charge is separated from the fluid by a bladder, diaphragm, piston, or metal bellows. All of these are problems for my cleanliness requirements, as the moving parts will tend to shed metal shavings, etc.

The question

My question is, why is the separation of the two volumes necessary? In my case, this is for a fixed piece of equipment, so I can guarantee that the accumulator will always be vertical.  Can I just have a nitrogen-filled cylinder with the fluid connected at the bottom and rely on the fluid to act as my piston?  If this does work, why isn't it more common?

Edit to address some of the comments:

I'm not asking for advice on how to design a clean accumulator; I only want to know the fairly general question of whether it is possible to not separate the charge gas from the fluid.


texts: Sylvac UL 4 - USB - (Send data) reports 'no.data'?

texts:
Using the sylvac UL 4
Each time I invoke the (send data) function the sylvac LED panel reports 'no.data'.  To mention the obvious but nothing is received at the connected USB device.

My question is. . How do force the sylvac device to (have data) to send?  Can anyone explain what this 'no.data' actually means from the calipers perspective?


texts: How can I calculate uncertainty based on measurements from multiple separate runs?

texts:
I am using standard test blocks to find the uncertainty of a supermicrometer, which is capable of measuring down to 1/10 of a micron. The issue is that it measures the EXACT same length within a run of even 100 measurements. Understandably, it is suspicious to calculate uncertainty based on data with zero variation; however, the value that it consistently measures is different every time I zero the supermicrometer at a different position. For example, I may get a value of 5.0000 mm repeatedly during one run, zero the supermicrometer, and then get a value of 5.0003 mm repeatedly during the next run.

So the question is, how can I take into consideration variation between runs? Traditionally, one would use a single run to find uncertainty, but I don't think I can do that.


texts: how to find minor and major dimension after compression on ANSYS

texts:
at the begining,in this models inner diameter 2in,outer diameter 4 inc.I want to find out changes of the shape after compression as inc.

R9.jpg


texts: Statics problem ignoring horizontal reactions seems to require horizontal forces

texts: I'm an industrial engineering student taking engineering mechanics, and I'm quite confused by this problem our proffessor gave us, the chair is supposely in equilibrium, yet in order to counter the moment created by the weight pressed on the chair upward y vector vertical force on leg be would need to be eade, and cos(b) is greater than cos(a) - and she says there's no friction to insure horizntal equilibrium through resistance, could someone please show me where I'm screwing up on this, - please help! I don't want the answer I just want to see what I 'm doing wrong and fi< it, I just want to know how to solve this problem...


texts:
An object with the weight of $80N$ is balanced with the force of $F$  as seen on the diagram. What is the magnitude of $F$? (Ignore the weight of pulley and friction)

$\sum F_y = 0$

$F_y \sin 37 - 80 = 0 \implies F_y \sin 37 = 80 \implies F_y = 133.33N$

$\sum F_x = 0$

$F_x \cos 37 = 0 \implies F_x = 0$

Finally, we have

$F = 133.33N$

Am I right?


texts: MSC Nastran - BAR3/4 elements - can't assign any properties

texts:
I'm modeling a pipe in Patran, and I'd like to try bar3 and bar4 elements.
I assing the properties CBEAM to my geometry, but when I create the mesh, Patran tell me bar3 and bar4 don't support that property, and I need to use bar2.
Doesn't work even with CBAR, CROD or CPIPE. How can I use bar3 then? Seems like no properties work.

Thank you for helping me out.


texts: Fan Sensors (Tachometer vs Locked Rotor)

texts:
With regard to Fan Sensors, there are two very common methods for detecting whether the fan is doing what it's supposed to or not.

Locked Rotor- Detects when the fan is working, or when it has stopped.
(on or off voltage signal)
Tachometer- Detects the speed of the fan, to determine whether it is performing optimally.
(pulsed voltage signals)

My Question:

Q- What is the difference between using these two types of fan sensors in 'some' design?

Additional info:

I don't know what this 'design' is, but I'm asking for the practical differences if I picked either one.
I understand that both setups use different voltage signals, and require different circuitry to operate. That is beyond what I think would be the practical scope of this question.


texts: Fast and quitet linear actuator for lifting less than a kilo

texts:
I'm looking for a linear actuator that can lift a microphone of about 700 grams. It's for a goose-neck microphone (together with shock-mount) that will pop out of a small pulpit. Only the top part is bent so it will stick out a small part when at the lowest position.

The electrical actuators I have found so far are made for heavy lifting and are far to slow (and noisy). I need to be able to adjust the height quickly when a different speaker comes.

What I'm looking for would be more like a printer head carriage in an ink-jet printer. It does not have to be that fast, 10cm/second would be good enough with a stroke of +/-45cm. It would be great if it could also send feedback on its position (or if it could be driven to a specific point like a servo).

Does anything like that exist off the shelf or would I have to custom-build the whole thing? I'm planning to use an Netduino+ (with a motor shield) to drive it.


texts: Calculating the Thickness of a Glass Tube which contains a Vacuum

texts:
I am looking for borosilicate glass tubes which can be used to contain a vacuum, so the top is sealed and then there is a vacuum pump at the bottom where the edges are also sealed, effectively making a vacuum in a glass tube.

The only thing to mention is that the walls need to be somewhat thicker than normal to protect against implosion due to the fact that there will be a vacuum inside, so I need an idea of how thick the glass needs to be bearing in mind that the inner diameter is 20 cm.

The pressure outside the cylinder is atmospheric and the pressure inside is very low and can be taken to be 0.  Is there a formula or computation which would give me a good approximation for how thick the tube needs to be?  I also appreciate that there could be some shear stress due to the tube needing to be so thick.


texts:
I'm building a small microscope through which I need to pump fluid samples to image.  Currently I'm using a flow chamber from Ibidi that is perfect (length of a standard microscope slide x 5mm x 0.1mm), except that it's really not designed to be reused- one side of the channel is very thin material and cracks easily under pressure or vacuum, making it difficult to clean.

I'm also not looking to break the bank. The Ibidi channels are around $20 apiece, which would again be perfect if they were more durable for reuse.

Any suggestions?

Thanks.


texts: Why do Blast Furnace flue dust generates high rates of Zn (Zinc)?

texts: The Blast Furnace flue dust contains high rates of Zn (Zinc). I'd like to know the reason behind this. The chemical reaction of Zn inside blast furnace dust. Why it's rates becoming high?


texts: Most practical way to wirelessly transmit a single bit of information?

texts:
If I have a single Boolean value that I wish to transmit wirelessly over a relatively short distance (assume <2m) then what of the many possible options would be the most practical.

To define what I mean my practical, it is some combination of:

low cost
low power
environmentally robust
high data integrity
high reliability
low bulk/weight

All of which apply equally to both the transmitter and receiver. I assume there will be some tradeoff between these

Other concerns that might impact the answers, but are of less interest to me:

The transmission may be repeated, but not at a high frequency (assume <2Hz), although there is no penalty for higher frequency capability.
The transmission need only be unidirectional, although bi-directionality might be a bonus.
The transmission does not have any security concerns, although some level of security might be a bonus.
There is only one transmitter/receiver pair in the local area, although the ability to operate with multiple unique transmissions in the same area might be a bonus.
The transmission is one-to-one between transmitter and receiver, although the ability to transmit to many receivers, or from many transmitters, might be a bonus.
The solution should be off-the-shelf to a certain extent, although if bespoke (or high volume) options significantly improve the solution in some way then I would be interested to hear about them.
The solution should ideally be legal/unlicensed in most countries, but I'd be interested in what illegal or licensed options could be possible too.

I don't have a specific application in mind, I'm more interested as a theoretical exercise.

Note that there is a related question here, but currently unanswered and with slightly different criteria.


texts: What's the term for interchanging a frequently used machine with a seldomly used one?

texts:
I'm trying to find out the term used for the practice of interchanging/relocating/swapping 2 machines to compensate the wear and tear caused by the operation frequency differences between them. This is a practice used in machine plants where a bunch of similar machines are being utilized and where some machines get used more than the others. For example coin store laundries do swap their most used machines with the ones getting less attention because they are located at the back of these stores.

I'm told that there's a term for this practice.


texts: Why is more steam required to turn a steam turbine when electric power consumption is higher

texts:
I'm recently under industrial training at a plywood mill. My supervisor is from foreign country so there are some difficulties for me to understand what he is trying to say.

In the power plant, the turbine is speed is maintain at 5600 rpm, no matter how much is the generator output is. So, why require more steam for the turbine to rotate at the speed of 5600 rpm during high electricity usage than low usage even the rpm is the same?


texts: How do I charge titanium dioxide particles submurged in black-dyed water in home?

texts:
My first thought was to charge the titanium dioxide particles by first charging a balloon by rubbing it on my hair and then touching the balloon to the titanium dioxide powder, but that would be ineffective and the charge will escape when the powder is submerged in the water.

A better way would be to charge the titanium dioxide particles chemically after submerging them in the black-dyed water. How would I go about doing this safely, cheap and in home? (Maybe putting a non-dangerous alkaline in the final mix would charge the titanium dioxide?)


texts: choosing between v belt and round belt for fast RPM, low torque application

texts:
My pulleys are going to be rotated with a 1000-2000 RPM motor, with a constant RPM controlled by a hall effect sensor, there is going to be almost no torque as one of the pulleys just has a 100 gram optical element attached to it and all the pulleys are on bearings.

Any suggestions on choosing v belt or circular belt? Price is pretty similar and v seems to reduce risk of slipping and has better grip. Cant find a disadvantage of v belts.

I just assume slippage might become in issue with round belts at these RPMs if there isn't enough grip, no other reason to not choose them over v belts, really.

I'd imagine tooted belts wouldn't provide much advantage here besides any backlash or slippage when the system begins rotating but I don't see how it would be more precise after the speed is reached and the speed and load remain constant during operation.


texts: Question about converting 220V lamp to 110V

texts:
I have an old classic lamp (Tolomeo).
It was purchased when we lived in Singapore, so it is designed for 220V.
Since we moved to US, I have not been able to use it as the power supply here is 110V.

The adapter of the lam says:
Power Supply Type BL2UK
240V~ 50Hz TW 10ºC
For PL Lamps Type:
(then is lists some options)

Now I was wondering if someone can help me with these questions.
1. Will replacing this adapter solve my problem?
2. Will I also need to change the bulb? The current bulb it uses is: 10W
3. If adapter needs to be replaced, which one should I replace it with?

Thanks a lot for any help or guidance.


texts:
So let's say I have some heat generating machine be it a combustion engine or a fridge cooled by a fluid. I don't have a single radiator that is big enough for the amount of heat being generated but I do have a couple of smaller ones so I guess I could connect them together.
Should I put the radiators in series (one connected to the next one and so on) or in parallel (having the coolant intake pipe split into all of the radiators) and why? What would be the most efficient set up?


texts:
For moment about D , how could the FGF sin26.6 generate moment about D ?

FGF sin26.6 is located above point D , right ? How could FGF sin26.6 generate moment about D ?


texts:
I am designing my own optical rotary encoder with a non-standard number of encoder positions for a specialty application. I have gotten a 0.35mm acrylic with the pattern printed on it but now I need to punch out the center hole.
A smaller hole could be much more easily punched precisely by hand or machine.
If a punch could be designed with a small rod in the center, it would align just right with the center hole.
This method could also be used to punch out the whole disk. First a big punch with rod could be used to punch the disk, and then a smaller one to punch out the center hole.
The biggest problem that arises is where/how to get a bit that has an alignment rod in the center. Perhaps they already exist, but I just don't know how to search. I don't trust my lathe to drill out the center of a punch correctly, as the punch will likely be made of the same material as my drill bits. How can I precisely punch these holes in thin acrylic sheet?


texts: 2PL / 3PL annotation on arc in technical drawing

texts:
I found a technical drawing of a popular guitar shape online and I'm having trouble to understand a certain annotation on some arcs in the drawing. It basically says stuff like "0.43R 2PL" or "3PL" (see attached).

any idea what this could mean? My current guess is that it means that there are X PL other curves in the loop that have the same radius.

Drawing Source


texts: Calculating pressure force on inclined area

texts:
$\rho, p_o, \alpha, F_g, h, b$ are given. $F_T$ is wanted. There is a plate that can rotate around $A$. The plate measures b perpendicularly to the screen surface.

Pressure gradient

$p(z) = \rho g (2h - z)$

I neglect $p_0$ since it it's the same pressure on both sides of the plate.

Pressure Force

$$F_p = \int_{l_0}^{l_1} \int_0^b \! p \, \mathrm{d}y\mathrm{d}l$$

With

$sin(\alpha)=\dfrac{dz}{dl}$

$dl=\dfrac{dz}{sin(\alpha)}$

$$F_p = \int_{l_0}^{l_1} \int_0^b \! p \, \mathrm{d}y\mathrm{d}z \frac{1}{sin(\alpha)}$$

Now I can integrate from $0$ to $h$ since I substituted $l$ with $z$ and I get

$$F_p = b \rho g \dfrac{3h^2}{2sin(\alpha)}$$

This is the pressure force that works on the plate. To calculate its torque it has to be multiplied with its lever $l_a$.

In order to find $l_a$ I have to regard the actual torque which is

$$F_{p} \cdot l_a =  \int l \cdot p \, \mathrm{d}A$$

$$F_p \cdot l_a = \int_{l_0}^{l_1} \int_0^b \! l \cdot p \, \mathrm{d}y\mathrm{d}l$$

Again substitute $dl$ with $dz$ yields

$$F_p \cdot l_a = \int_{l_0}^{l_1} \int_0^b \! l \cdot p \, \mathrm{d}y\mathrm{d}z \frac{1}{sin(\alpha)}$$

I assume I can now insert insert $0$ for $l_0$ and $h$ for $l_1$ again. And at this point I'm unsure but I think since I integrate over $dz$ again I can insert $\frac{z}{sin(\alpha)}$ for $l$.

$$F_p \cdot l_a = \int_{0}^{h} \int_0^b \! z \cdot p \, \mathrm{d}y\mathrm{d}z \frac{1}{sin(\alpha)}$$

Inserting and integrating

$$b \rho g \dfrac{3h^2}{2sin(\alpha)} \cdot l_a = \int_{0}^{h} \int_0^b \! \frac{z}{sin(\alpha)} \cdot \rho g (2h-z) \, \mathrm{d}y\mathrm{d}z \frac{1}{sin(\alpha)}$$

$$b \rho g \dfrac{3h^2}{2sin(\alpha)} \cdot l_a = b \rho g \frac{1}{sin^2(\alpha)} \left[h^3-\frac{1}{3}h^3 \right]$$

$$\dfrac{3h^2}{2} \cdot l_a = \frac{1}{sin(\alpha)} \left[h^3-\frac{1}{3}h^3 \right]$$

$$l_a = \frac{1}{sin(\alpha)} \left[\frac{2}{3}h-\frac{2}{9}h \right]$$

$$l_a = \frac{4h}{9sin(\alpha)}$$

I'm very unsure with how I substituted and inserted. I would appreciate someone to review if I did it correctly and maybe elaborate on what I got wrong if possible.


texts: Delivering RPM from a fixed wheel to a moving wheel

texts:
I have spent the past few days thinking about a good way to get power/RPM from a fixed wheel delivered to a wheel that is able to move in a 2D plane relative to the fixed wheel. I am not too good at CAD, but I tried to make a schematic to make it easier to understand:

The orange "wheel" is fixed and is driven by a shaft. I want to get that RPM to the purple wheel in the middle. The purple wheel will be moved within the red frame (but not up/down). Some other constraint or actually simplification: I dont care if the RPM fluctuates during movement, so it can get lower/higher if the purple wheel is moving. Also the position of the orange wheel can be changed as needed, but once it is attached, it can no longer move. The orange wheel can be outside of the red frame too. The purple wheel drives a tool that needs to work against some resistance (say drilling through wood).
I was thinking about using a belt or a chain with a tensioner. My idea was to install another wheel either diagonally opposite of the orange wheel or at the bottom of the frame that is attached to spring loaded tensioner, but I failed to figure out how long my belt would have to be and how to make sure there is always enough tension to make sure the purple wheel gets enough torque to be able to deliver enough force to the tool it drives.
Are there some well known patterns for my problem? Or what would be a good way to tackle that problem?


texts: What is the proper way to handle string-to-float decimal truncation in IEEE 754?

texts:
This is not a StackOverflow question because the software engineers do not have appropriate math skills to answer an IEEE 754 question and thus must be answered by an IEEE tutor.

I had to implement my own string-to-float and float-to-string algorithms for Grisu and Unicode using C++ templates. I used the following algorithm found in the Wikipedia Single-precision Floating Point Format article:

consider a real number with an integer and a fraction part such as 12.375
convert and normalize the integer part into binary
convert the fraction part using the following technique as shown here
add the two results and adjust them to produce a proper final conversion

I am unsure what to do when the string being converted to float has more digits precision then I can store in a 32-bit (for example) float but it does not hit +/- infinity, and the proper way to round the imprecise digits/decimals. For 32-bit floating-point numbers, there is only 7 digits of precision. For 64-bit floating-point numbers, it's 16 digits of precision. Any more numbers than that must be rounded using the IEEE 754 rounding rules.

Example

Base 2 Option

We convert the integer portion first, like the algorithm in the wiki entry, by scanning to the least significant digit then parse back to the most significant digit by multiplying each digit by a power of 10 (i.e. the standard string-to-integer algorithm) and use unsigned multiplication wrap-around to detect bit overflow, round in base 2; which doesn't sound right to me and I think the Wikipedia article is not the best algorithm.

Base 10 Option

We convert every number to into exponent notation with a single most significant digit, such as converting 123456780123456789.012. to 1.234567e20 using the IEEE 754 rounding rules. Sounds like the best choice because we only have to parse the text once and we have to scan for the exponent and we can avoid the string-to-integer algorithm. Rounding in base 10 sounds the sanest due to the number still being in base 10 and you only need to read the digits and decimals once without multiplying by a power of 10. If this is the preferred method then wiki entry should be updated.


texts: Using GPU Acceleration in ANSYS Mechanical

texts:
I am attempting to solve ANSYS mechanical (via workbench) using GPU acceleration, but I keep getting the following error:

  * WARNING *                         CP =      79.594   TIME= 15:40:08
   The GPU accelerator capability is not valid when using the memory
   saving option (MSAVE command) for the PCG solver.  The GPU accelerator
   capability is disabled for this solution.

How can I turn off the MSAVE option? It seems to be default for a model this size and I cannot find the way to turn it off.

I am using V19.2.


texts: Pressure sensors - gauge vs unidirectional differential

texts:
A gauge pressure sensor measures a pressure at a port against ambient pressure.
A unidirectional differential pressure sensor measures a pressure at a "high" port against a "low" port.

Is a gauge pressure sensor the same thing as a unidirectional differential pressure sensor (simply using ambient pressure as the "low" side)?  Is this just a matter of where your reference point is?

I'm guessing you could turn a differential sensor into a gauge sensor by using ambient as your "low" side.  Can you turn a gauge sensor into a differential sensor by using a pressure port rather than ambient?


texts:
I have a question regarding inertia and friction between gears.
I have a gear which is connected to the rod at one end and an electric motor which is connected to the other end. I know the torque of the rod and I want to calculate the torque of the motor I need.
I have been told that I can't lay on transmission ration only and I also have to include the calculations of the inertia and friction between gears.

Can please someone explain me how should I do it (every example will appreciated).


texts: Airsoft BB Funnel Design - Electric funnel jam solution?

texts:
I'm working on a design to feed Airsoft BB's through a funnel. A simple gravity fed system (ie. I don't want to force them out at speed) but every now and again the BB's get jammed at the end of the funnel.

I would like to use a motor to constantly keep the BB's moving and prevent jams.

The video below highlights the issue:

https://youtu.be/eq6Sbfp9BUQ

I would welcome any tips to improve the design/make it functional.

At the moment my thought is to add ridges to the inside of the funnel, this combined with the mixing action should shift them around enough to prevent the jam?


texts: Selection of copper alloy for electrical and wear applications

texts:
I am working on a project which involves applying electrical load across a metal contact filled with lubricants (bearing applications). However, I am missing one of the blocks as attached and I cannot figure it out what material this is. Looking at the posts here, I am presuming this must be some copper alloy such as brass, however, I know that the rotating disc that this block sits on is of brass material and that can raise issues such as wear due to the presence of similar materials?

Any suggestions what material I can use for this application to not damage the discs while providing good conductivity?


texts: Is controlling humidity more precise when calculating with relative or absolute humidity?

texts:
I have a tubing system where I need to precisely control relative humidity. All my sensors are giving me temperature [°C] and relative
humidity [%].
Right now I have simple PID controller, and it's input is hooked up to the relative humidity values.

But I had an idea: wouldn't be my controller more precise if I would feed into the input absolute humidity values and not relative humidity?
My though process:

Relative humidity is dependent on temperature, partial pressure of water vapor and  equilibrium vapor pressure of water. So it is dependent on 3 values.
Absolute humidity on the other hand stated by Wikipedia is not dependent on the temperature around it.

If I would compute absolute humidity from relative humidity and temperature and feed it into PID input. Would I achieve greater precision?

I don't know if computing the absolute humidity from relative humidity and temperature would transfer the dependency of temperature or it would eliminate it.


texts: producing vibration motion of a plate (1cmx2cm) placed in water

texts:
In order to conduct a study, I need to place a rectangular plate freely placed (1 cm by 2cm) inside water and control it from outside (better wireless). I need to give oscillatory motion with specific frequency/amplitude.
At present I used LEGO Next servo motors and I could not achieve it successfully due to mechanical instability and methods to control freq and amp. Also the gear assemblies used affected the results.
May I ask people here to suggest a way to produce vibration motion of this plate with minimal interfering mechanical set up?
I can choose any kind of plate (plastic or metal) I can employ magnetic or electric methods to produce vibration.
any direction way forward will be appreciated.


texts: Why are pump action rifles so uncommon compared to bolt-action rifles?

texts:
Pump action seems to be a faster way to cycle a weapon compared to bolt action and it's a rather simple action, unlike straight-pull bolt which are more prone to malfunction. It almost seems like a direct upgrade to me.

Since we have magazine-fed pump action shotguns nowadays, It's probably possible to do the same with rifles. Even if we only had tubular magazines, the Lebel rifle actually had a tubular magazine with spitzer (pointy) bullets that was designed to prevent cartridges from firing the one in front of it in the magazine.

I know that nowadays this would be a novelty because of the availability of semi-auto rifles but why couldn't it replace bolt-action rifles?


texts:
I'm looking for the name of part which I'm pretty sure exists.  It works similar to how the seat on a exercise weight machine works.

It's a plastic band which has a bunch of connected figure 8s cut out.  Which will allow you to adjust the position of a bolt.

Can someone tell me the name of this?

Edit:  Believe it's similar to an L-Track, I basically need something with adjustable anchor points.


texts:
Could someone please explain some of the advantages/disadvantages of the wallace multiplier circuit vs a shifting and adding multiplier circuit vs an shift register multiplying circuit? We went over them briefly in class but didn't get to in depth and I'm trying to sort out which is better in what situation or even overall of applicable, and why.

The wallace multiplier is pretty straight forward and simple design (to design, the physical thing seems quite tedious) but quite huge... The shifting and adding one seems better sized and quite simple but it does have an output going back in which I guess could slow things down? But then with all the things going on it the The shift register I guess seems like a nice median but not sure if I'm missing anything there.


texts: How to measure transmit power level from LTE base station?

texts:
Can someone tell me what type of equipment is used to measure RF power levels transmitted by a cellular LTE base station? I would like to gain some insight into how the follow data was obtained.

Back Story: The local company wants to install a cellular base station in our neighborhood. They have shared the above data set indicating that the cellular coverage is poor in a certain area. But cellular service provider's web site indicate excellent coverage. Information doesn't tally up.


texts: Must rifle scopes have revealing reflections?

texts:
It's a movie trope that snipers are spotted because someone catches a glimpse of a reflection of the scope. It seems to me that this is a serious design flaw.

I also know that a good number of scopes have "lids" to protect against dirt, etc., when not in use.

My thought is this: Why is the front-most (nearest the target) lens/glass so close to the end of the pipe (as in ╞═════╪╡)? Why isn't that piece of glass hidden way inside the pipe (as in ╞═════╪════╡)? That extra bit of pipe could then block out any light/reflections apart from what is in the view of the shooter. It would also make the scope longer, but that can't be that much of a downside, can it?

If there are such scopes, how common are they? Or, put the other way around, given that reflections are undesired, how is this actually dealt with outside of the movies?


texts: I was wondering why there isn't a 9/20" diameter bolt and then realized the bolt sizes start at what ever size, the next size is + 39/1250 of an inch. Is there any reason for this? Is there any place to find a 9/20" hardware?


texts:
How do you calculate the torque on the cam, with a force placed on the follower?
Two possibilities:

Linear cam (schematic)

Radial cam (schematic)


texts: How do I conduct an experimental modal analysis with a three-axis accelerometer?

texts:
How can I compute the Frequency Response Function (FRF) if I use two three-axis MEMS accelerometer to measure the input excitation and output response?

I have read from some books that the FRF can be computed as the ratio of response to excitation, e.g., $ H(s) = x(s)/F(s)$, where $s$ is the Laplace variable. or a similar way via Fourier transform.

However, those books have not mentioned how to compute FRF when it comes to three-axis accelerometer. As there are three channels of data, i.e., X, Y, Z, should I compute the FRF for each channel separately, or I need to perform some kind of combination of these three axes before computing the FRF?


texts: What are the differences between linear and low-dropout (LDO) regulators?

texts: At a high level both a linear and LDO regulators appear to be the same. Most block diagrams appear to be the same too. Most of the device packages are three terminal packages. What are the differences between linear and LDO regulators?


texts: Limited resources for learning Fanuc Macro B programming, I need some direction as to how people learn this language

texts: Why is it that the only 2 books on CNC macro programming are by Peter Smid and one S K Sinha. Am I looking at this the wrong way? What am I missing? Is Macro programming one single thing that can be applied to CNC?


texts: Where to insulate Underfloor air distribution system in a temperate climate

texts:
I have a proposed underfloor air distribution system (UFAD) for a one level office in a temperate climate. Typically the demand for heating and cooling in this climate is about even for offices. However the building is well insulated and has a fair amount of (shaded) low U-value glazing on the sun facing elevation.

Now the question boils down to whether the thermal mass of the slab will be beneficial overall or not. At the moment I tend to have insulation within the plenum, i.e. excluding the impact of the thermal mass to create a more controlled supply, instead of having the insulation under the slab.

Based on some handwavy assumptions though, I could see some benefits of including the mass of the slab in order to reduce cooling loads (which I expect to be somewhat dominant due to the glazing and amounts of insulation).

However what would happen once the slab is fully heated, i.e. runs out of capacity? Would I night purge it? Can someone share their thoughts/experiences? When I insulate the plenum, should I include or exclude the slab?


texts: How does a digital controller's sampling period dictate the system's actuation requirements?

texts: When selecting an actuator for a controls application - e.g. choosing a servo motor for a self-balancing robot - I understand that it's important for the actuators to have fast enough dynamics that they don't significantly impact the system's linearity, and thus ensure the control algorithms function as designed. However, how much faster is fast enough? Are there any rules of thumb - c.f. Nyquist's Theorem in signal processing - for how I should choose my motor's rise time given that my controller's sample period is known?


texts: How to construct a compact linear Fresnel reflector

texts:
I have recently come across the concept of CLFRs, and I want to build one myself, as a private experiment.

I have a rudimentary knowledge of optics (which I'm sure I'll have to refresh on) - any useful links would be appreciated on bringing me up to speed.

My understanding of the technology is as follows (I stand to be corrected if this knowledge is incorrect).

A linear Fresnel reflector is constructed by taking equal width "strips" out of a parabolic mirror and "translating" the "strips" on to a horizontal surface in such a way that all the strips have bases with the same Y coordinate.
A compact linear fresnel reflector superimposes two parabolic mirrors (facing oposing directions) and decomposes them into two sets of alternating, equal width "strips" lying on the same horizontal line.

Is my understanding of the construction of CLFR correct? If yes, is there an algorithm I can use to "slice" a parabola into slices of width w, whilst preserving the reflecting angle of each "slice"?

I can think of a way of generating an algorithm, using geometry and elementary calculus - BUT, I don't profess to be an expert in this area, so I want to know what specialists in this field suggest.

A schematic of a CLFR is shown below:

In summary, how may I build a CLFR by "decomposing" two parabolas into two alternating rows of strips of width w ?


texts:
In this tutorial here

There's a current limiting application where two op amps are being used to limit the max output current.

The first differential opamp with 4 equally sized resistor values; connected to the output through a shunt resistor to measure the current draw.

The output from this opamp is then fed into the non inverting input of the second opamp while the inverting input of the opamp has a variable resistor to limit the output current.

Can anyone explain the ratio of this second opamp inverting input resistor?

Lets say I wanted to limit the current from 1-5 amps or 0-1 amps or even 2-20amps.

What's the ratio?


texts: Why doesn't a lightning strike destroy the lightning rod?

texts:
Lightning strikes have been known to cause massive amounts of damage. The stats on a lightning bolt are:

  current levels sometimes in excess of 400 kA, temperatures to 50,000 degrees F., and speeds approaching one third the speed of light

These are massive numbers, but lightning protection systems are designed to draw the lightning away from the building or structure that they are protecting. Lightning protection systems can be simply thought of as lightning rods connected to the ground via cabling (downconductor).

The NOAA specification for lightning protection requires that lightning rods be at least 0.5in (13mm) in diameter. The downconductor is a similar size copper cable (4/0 AWG or 12mm). The allowable amperage for this type of wire is only about 250A for constant current.  I realize that this is more of a heat limit rather than a instantaneous current capacity limit.

From this paper on lightning protection (page 28):

  Positive feedback on the operation of a lightning protection system is seldom documented and most often not even noticed. Only in some rare cases can it be documented that a lightning protection system has been struck if it works properly and there is no damage. There is sometimes evidence at the strike termination point which can be noted during a careful inspection, but it is seldom cost effective for the owner of a lightning protection system to obtain the expertise necessary to conduct such a careful inspection.

How can a seemingly small 0.5in (13mm) piece of metal handle a lightning strike with little or no visible damage much less without being completely destroyed?


texts: Black powder detonation analysis in ANSYS

texts:
I have an Aluminium tube that I want to insert some black powder in it and explode. This will be used as a ejection system for a high altitude rocket. It will deploy two bodies or nose cone of the rocket.

How to make a detonation analysis with ANSYS? I have used TNT instead of black powder because ANSYS does not contain black powder material. I plan to use about 3.5 grams of black powder to ejection so I used the TNT equivalency of it to make analysis. But I cannot be sure about equivalency ratio. My research says the maximum TNT equivalency of black powder based on pressure is %24 as grams. 3,5 * 24/100 = 0,836 gram and density of TNT is d = 1,65 g/cm^3. Then I calculated the volume of TNT as 0,506 cm^3 by using m = d*V equation. I designed a rectangular prism and added it to my assembly. Then I made the detonation analysis but the results of it were unrealistic. I think problems about this analysis are:

The black powder will not take place in such a tight prism as I drew in analysis.
The maximum rate of 24% causes the result to stress values much more then normal.

What should I do to make an accurate analysis? What parameters should I focus on? How can I use the black powder as a material in a detonation analysis or how can I calculate realistic equivalency TNT and black powder?


texts: What are the design principles for risers in sand casting?

texts:
Risers are added reservoirs used to feed liquid metal to solidifying casting. In the case of alloys that shrink during solidification (this is not the case of all alloys), one uses such reservoirs to make liquid metal available throughout solidification. Risers should be kept liquid throughout the solidification, which means the solidification must be directed toward the risers, which must solidify last.

What are the principles used to design such risers?

What I already know:

Their volume should be sufficient to compensate the solidification shrinkage
They should remain liquid last, so maximizing the volume/surface ratio seems appropriate

What I am looking for:

How to ensure the riser can efficiently feed the rest of the cast part?
Are there other rules (some kind of general algorithm maybe) for efficiently designing risers?


texts: Sensors / processing algorithms to emulate a human's sense of smell

texts:
A lot of research has been devoted to creating electrical devices that emulate biological sensors, including:

Visual:  Cameras, color/light intensity sensors
Auditory: Microphones, ultrasonic sensors
Tactile:  Pressure sensors, temperature sensors
Balance:  Gyroscopes, accelerometers

However, I have yet to find a comprehensive sensor/processing algorithm to detect and interpret odors.  Certainly, there are "olfactory" sensors which are dedicated to a specific purpose, such as carbon monoxide detectors, and other hazardous gas detectors.  But I have yet to find a general purpose sensor/processing algorithm that can readily detect and interpret odors within the range and resolution of a human nose.

Do such sensors/algorithms exist?  If so, what are they and how do they work?  If not, what are the primary obstacles to developing them?


texts: Can the strength of a strut be determined by deflections?

texts:
I am interesting in replacing a solid strut with tubing, but I do not want to destructively test the strut to determine its yield point. I do not want to make assumptions about the yield point based on material, because heat treatment and other factors can affect the yield point.

Can I cantilever suspend the strut and record its deflection due to a weight placed on the end, to infer the strength of the strut?

In other words lets say the strut deflects 5 inches when it is cantilevered and a weight is placed on its end. The tubing under test is placed the same way and only deflects 4 inches. Can I assume that the tubing will be an adequate replacement for the strut (ignoring factors like fatique, age microcracking, etc etc)?

I can do math that would suggest the replacement tubing will be significant lighter and stronger than the bar strut, but I am trying to find a way to actually physically test it.


texts:
How to obtain a constant pressure by a mini water pump to 9 bar?

Ex given a common engine for the aquarium, how to obtain at the output a pressure that is stable to 9 or 10 bar?


texts: How to simulate the Natural Frequencies of a Planetary Gearbox?

texts:
I have a dynamical model of a planetary gearbox of the form:

$\mathbf{M{\ddot q}+{\Omega_c}G{\dot q}+{[K_b+K_m-\Omega_c^2K_\Omega]q}=T(t)+F(t)} $

$K_b$: bearing stiffness symmetrical matrix
$K_m$: mess stiffness matrix
$K_\Omega$: diagonal centripetal stiffness matrix
$T$: applied external torque
$F$: static transmission error excitation
$q$: the vector with the traslation and rotational coordinates for the sun,ring and carrier

For the free vibrations I have the equation:

$\mathbf{M{\ddot q}+{[K_b+K_m]q}=0} $

$\mathbf{-\omega_i^2M{\phi_i}+{[K_b+K_m]\phi_i}=0} $

Where $\phi_i$ is the vibration modes.

$\mathbf{\omega_i^2M{\phi_i}={[K_b+K_m]\phi_i}} $

I know that the $\Omega_c$ term for the gyroscopic effect is neglected at first and there's no excitation input because it's free vibration. But then I don't understand where the $\phi_i$ comes from.

I have basic knowledge of vibration theory for a single degree system, but not for multi DOF which is this case.

I need to determine the natural frequencies and vibrational modes of the system from this equation but I don't know how or where to start. I have initial numerical values for Stiffness, mass, preassure angle of the carrier, sun and planet gears.

Numerically how would I know how many modes of vibration I have and how to determine them with their natural frequencies? Like I said this is the first time I deal with a MDOF system and I've read a lot but this model is far to complicated and the math is confusing me.


texts: How can I model a plane's trajectory in a simple way?

texts:
I would like to model a plane trajectory, here are my assumptions and conclusions so far:

Assumptions:

we denote the plane's speed with $v(t)$, its trajectory $x(t)$, the total trajectory time will be $\tau$
we have start and end times of flights as well as distance, so we have $\tau$ and $\int_0^\tau v(t)dt$
the plane has an acceleration phase, let's call it $p_1$
the plane has a plateau phase, $p_2$, where it reaches its cruise speed, $v_c$
the plane has a deceleration phase, $p_3$.

The plane speed over time is
$v(t) = \begin{cases}
v_1(t) & t \in p_1 \\
v_c  & t \in p_2\\
v_2(t) & t \in p_3 \\
0 & \text{else}
\end{cases}$

Let $p_1 = [0, t_1], p_2 = [t_1, t_2]$ and $p_3 = [t_2, \tau]$, we assume
$t_1 = \tau - t_2$ (essentially, same amount of time accelerate as to decelerate) and we rewrite $p_1 = [0, t_1], p_2 = [t_1, \tau- t_1]$ and $p_3 = [\tau-t_1, \tau]$.

We 'll now further assume $v_2(t) = v_1(t - \tau)$ (the deceleration shape is the inverted acceleration shape).

So at this point we are left with determining $v_1(t)$. The model has $m$ parameters for $v_1$ and $t_1$, $v_c$ (note that $t_1$ and $v_c$ can be included as a parameter in $v_1$).

My questions are:

Are assumptions realistic, make sense, anything missing?
How would you go about modelling $v_1(t)$

Possible answer 1:

Make the assumption that $v_1(t)$ is linear:
$v_1(t) = \frac{v_c}{t_1}t$.

The overall model has two parameters

Possible answer 2:

Go with a sigmoid-like function for $v_1$ but with a bounded input, I thought $\sin$ with the right phase would be good for this since it also has derivatives of zero at $\frac{dv_1(0)}{dt} = \frac{dv_1(t_1)}{dt} = 0$, this leads to:
$v_1(t) = v_c\frac{1-\cos{(\omega t)}}{2}$.

$\omega = 2\pi/t_1$

Again two parameters.

Since I don't want to have $v_c$ as a parameter/constant, I thought of introducing $\alpha = \frac{\omega}{v_c}$ thus

$v_1(t) = \frac{\omega}{2\alpha}(1-\cos{(\omega t)})$


texts: why the constants of the shear and bending are zero

texts:
In order to get the bending and the shear function using the singularity functions we integrate loading. could you please tell me why the two constants are zero.

We know that  the load is related by the bending M(x) and the shear equation using these equations: q(x)=dV(x)/dx and V=dM/dx. In order to find the M(x) and V(x) Using the singularity method I found that the constants of integration are null:
$$ V(x) = \int q(x)dx\,.$$ and $$ M(x) = \int V(x)dx\,.$$ without constants.
Could you please clarify why these constants are always null?


texts: How does the sine part i.e. $\dfrac{\ell\sin(\theta)}{2}$ appear in the calculation of shear flow ($q$)? I mean, if I'm not mistaken, the sine part is the distance from the x-axis to point D, but how is it derived?


texts: Can a sensor tell the difference between gravity vs. acceleration?

texts: Are the effects of gravity and acceleration identical to the point that no sensor can tell the difference?


texts: Synchronous machine power factor and angle

texts:
I have a 8-pole synchronous machine (as a generator), which is rated to produce 1000 kVA. Its synchronous reactance is 0.4 Ohms.
It is connected to a diesel engine with the grid frequency 60 Hz.
The load is resistive type, 500 kW, 480 V.
I need to calculate the speed, power factor and power angle.

I know the following:

Speed can be calculated by: $n = 120 \cdot \frac{f}P$  , where $f$ is frequency (60 Hz) and $P$ are poles (8)  ... and we get the result 900 rpm.
Power factor can be calculated by: $\mathrm{PF} = \cos(\mathrm{PA})$, where $\mathrm{PF}$ is power factor, $\mathrm{PA}$ is power factor angle (is that the same as power angle?)

So, how can I calculate power factor and power angle?


texts:
This high-speed video shows a cymbal's response to impact. I'm interested in how the observed vibration relates to the modes and frequencies that an eigenvalue vibration analysis would predict. My interest is not specific to cymbals, the video just illustrates a point very well.
I suspect that since excitation frequency here is much higher than the fundamental frequency of the body, and displacements are very large, eigenvalue analysis is not appropriate. Is this reasoning correct?
My guess would be that the initial response to the impact is transient (wave propagation) and would eventually converge to the combination of modes predicted by the eigenvalue analysis. Is that correct? If so, what influences the speed of this convergence?


texts:
The definition of dry steering in wikipedia

Dry steering is the act of turning the steering wheel of a vehicle while the vehicle is stationary.

https://en.m.wikipedia.org/wiki/Dry_steering

Unfortunately the article has no citation to scientific article.

So I'm curious is the "negative effects" of dry steering a thing based on real facts?

Is it now only a myth, unrelevant, since the increase of strength in materials we use in cars?


texts: Why can't we use air bearings for Hyperloop? Why isn't it feasible?

texts: Why isn't the usage of air bearings for HL feasible?


texts: Why all watches hands are stacked in that specific order ? Can it be changed?

texts:
It's just a matter of curiosity, but I find hard to justify why every single watch keep the hour hand below the minute one; from a user perspective, it seems a poorly design decision for those times when they overlap the hands.

Some manufacturers – notably Rolex with its Mercedes-like symbol – even added larger stuffs to the hour hand to be seen when such occurrences happen.

I suppose it may be done to simplify the internal gears, but I also suppose that by placing the hour-minute-seconds hands in a reverse order shouldn't be a problem…

IMO, a more reasonable user experience should show from top-to-bottom: seconds, hour, [GMT], minute hands. Isn't this achievable ?

Can someone satisfy my curiosity ? :)

Thanks in advance!


texts: Linkage between two vertically and horizontally offset wheels

texts:
I'm trying to drive a wheel with a radius of 20cm that is 20cm above the motor and horizontally offset by 20cm from the motor, similar to the following:

I wonder what a good linkage might be for a setup like this. I've considered ball joints like below, but I don't think the allowable angle of the shaft is great enough:

I didn't want to go for expensive linkages like those with universal joints. Does anyone know what might be a good linkage for the wheels in this case? The torque required will be around 50Nm.
Any thought appreciated.


texts: How do I choose a blower design for an induced draft brick kiln?

texts:
I am responsible for a brick kiln in the Punjab province of Pakistan. My government requires all brick kilns to be upgraded to match recent new standards, which include the addition of a blower near the chimney. We consulted with local engineers who presented several different blower designs and conflicting arguments regarding which design is best.
Here are the two main designs most of them agreed upon, with the fan being 52 inches in diameter and having 6 blades:
Blower Design #1

Blower Design #2

Which design will work better? I also have my doubts about the fan blades being straight. Would straight blades be appropriate for this use? What about forward or backward curved blades?
We will mount the blower at the base of the chimney, pulling hot air from cooking bricks and blowing it into the chimney. The goal is to improve the efficiency of the coal-burning process in the kiln. We refer this as a "zigzag kiln."
Here is a sketch of a similar blower configuration. Our blower will be placed above the walls instead of in front of the walls, but the airflow otherwise should be the same:


texts: how does thickness affect the maximum crushing strength and modulus of rupture of wood?

texts:
I have modulus of rupture (MOR) and maximum crushing strength of various species of wood. I am trying to understand how the thickness of wood a wood beam laid flat on the ground would affect both modulus of rupture and crushing strength. The practical application is this: We make "crane mats" which are essentially 6 pieces of long timbers bolted together. Each timber is 18 feet by 7.5" x 7.5". The entire mat therefore is 18' x 7.5" x 45". One species we use is eucalyptus grandis, and has a MOR and crushing strength of 118 and 60 MPa respectively. In contrast, red oak has an MOR and crushing strength of 75 and 42 respectively.

If my eucalyptus mat is, for example, 7.5" thick, and it lies flat on the ground, is that equal in MOR or crushing strength to a 12" thick mat of red oak?

I would be very appreciative for any tutoring. I have spent a full day trying to figure this out by myself but I'm not trained as an engineer. Thank you!


texts: How did scientists develop the stencils that made even more precise processors than they had previously?

texts:
The history of computers seems somewhat pervasive since there are so many steps in modern manufacturing and so many changes in trends with transistors over many years. Grasping how we got to our current level of processing power seems somewhat like a chicken/egg situation. How exactly were we able to create such precise processors when we only could have had more primitive tools to craft them with? For instance, take the UV stencil used on a silicon wafer to make a CPU.

How could engineers have designed a machine capable of etching out so many millions of transistors in the stencil given that they didn't originally have access to that level of processing that they are trying to achieve? Or in other words, how is it possible for computers to evolve in the process of making more precise machines from less precise machines?


texts: How to drain large tank using pump without starving pump?

texts:
Spec:

Aim: Drain a 50 litre tank of oil using a positive displacement pump (see Diagram), so that it drains quicker than gravity alone.

The pump should not be starved at any point.

The flow rate from the 50 litre tank should be at least twice the flow rate from the 5 litre tank.

Current setup:

The 5 litre tank is present because it's used to fill the 50 litre tank (in a different configuration) and also to ensure that the pump is never starved. Once the 50 litre tank is fully drained, the pump should be able to draw oil from the 5 litre tank and then the pump is switched off by a minimum level sensor in the 5 litre tank.

All hoses are 1" inner diameter.

This is where I'm stuck:

In my current setup, will the pump draw the same volume from both tanks at the same rate?

Can I do anything to ensure that the 50 litre tank drains at a much higher rate than the 5 litre tank so I don't have to constantly top up the 5 litre tank?

E.g.

If I reduce the diameter of the hose from the 5 litre tank or use a valve to restrict the flow, can I achieve a greater flow from the 50 litre tank compared to the 5 litre tank?


texts:
Does rain cause Tarmac / asphalt pot holes? If so, how?

After a period of rain in my city there are plenty of fresh new pot holes in the Tarmac / asphalt surfaces. The immediate cause is obviously axle overloading, due to appalling regulations, but these holes are fresh from a fourtnights heavy rain.

I can comprehend erosion in dirt or gravel roads as I know these substances are penetrable by water. But my impression is that Tarmac is impenetrable to water.

What process am I missing?


texts:
I have a drive way which has knick at  point ot smoothen is out i leveled it by putting loose soil

But its monsoon season and rain washed away all my soil as water comes running down slope.
In pic red is soil i am putting to level road, IS there way to stabilize this loose soil , so that water does not wash away soil


texts:
I have a 150 m deep well with a submersible pump on the bottom. As suggested I tried to get all the water out from the well. The pump engine ran for almost 2 hours and from my calculations it took 2 cubic meters of water in this amount of time. After that time the power went out, and the pump now says that I need to wait for some time before getting water, showing the message: "waiting to fill".
I made some computations about the amount of water that was inside and more or less the values of water are like the ones I supposed to.
I have tried after many weeks to get water again, but still same message. The pump tells me: wait 10 minutes. Then after 10 minutes, it shows: wait for 20 minutes.. and so on.
Could the pump be burned? I tried to check if there is water and there is


texts:
Can someone please help in finding out the phase proportion of each phase w.r.t time , cooling rate and temperature by using (mathematical model to predict phases from given cct diagram)

  Leblond method


texts:
I am designing an animatronic head, which has five degrees of freedom: pitch, roll and yaw for the head part, and pitch and yaw for the neck part.  However, the yaw movements for the head and neck are defined to be identical – if the neck rotates 7°, then the head also rotates 7° – so there are actually just four parameters determining the position of the system:

If I do this the "obvious" way, with gimbal arrangements at the two centers of rotation, that poses some practical problems for me in how to construct and drive the thing.  It occurs to me that it might be possible to instead build a linkage out of rods connected by ball joints (or similar), such that I can get the same motion by driving the ends of four of the rods along (preferably) linear tracks:

This diagram is only a rough suggestion of the sort of thing I mean (I am thinking of examples like this and this).  The idea is that the three pink nodes are attached to the head, the three green nodes are attached to the neck, and the four yellow nodes are independently driven to control the geometry of the whole system.  There would also be some number of floating nodes (not shown).
Intuitively, it seems like, with rods of the right length connected in the right topology, it should be possible to make every vector $<A,B,C,D>$ correspond to exactly one value of $<\theta_1,\theta_2,\theta_3,\theta_4>$ over a finite range.  As long as there are no problems with singularities or things like that, it would "just" be a question of translating the rotation angles into ABCD values to get any desired motion.
Given the design of the linkage, the problem of converting between the input parameters and the Euler angles is well documented, and I can use a constraint-based solver like SolveSpace to resolve the dimensions. What I don't know is how to design the linkage in the first place.
My problem is that as a non-engineer, I don't know the terms to frame my question.  For instance:

is there a general term for this kind of system (rods connected by notional ball joints)?
there are some obvious (and perhaps less-obvious) constraints on the topology – is there a name for this subject?


texts:
A reciprocating air compressor is used to fill rapidly a $3m^3$ tank at $30°c$ and $1\ bar$. The filing process is governed by $pv^{1.4}=constant$. The effects of kinetic energy may be neglected. The ratio of the final to initial mass of air in the tank is 4.
What is the work input to the compressor?
I am struck up with the problem. Please help me with how to solve this question.
Thanks
Attempted solution by OP(link in comments):


texts: Finding Derivative Gain for PD Controller

texts:
I am trying to design a PD controller $G_c(s) = K_d(s+z_c)$ with the following requirements:

No overshoot, $\zeta = 1$
Settling time $T_s = 0.0002s$

The transfer function that I am currently working with for the plant is $$ P(s) = \frac{10}{s(0.02s+1)} $$
where the closed loop transfer function of the compensated system is
$$
\begin {align*}
H(s) &= \frac{G_c(s)P(s)}{1+G_c(s)P(s)} \\
&= \frac{(50)(10)K_d(s+z_c)}{s^2+50(1+10K_d)s+(50)(10)K_dz_c}
 = \frac{\omega_n^2(\frac{s}{z}+1)}{s^2+2\zeta\omega_ns+\omega_n^2} \\
\end{align*}
$$
Given that the formula for settling time is $T_s = \frac{4}{\zeta\omega_n}$ I solved for $K_d$:
$$
\begin{align*}
\zeta\omega_n &= 25(s+10K_d)=\frac{4}{0.0002}=20 000 \\
K_d &= 79.9
\end{align*}$$
Unfortunately, this does not give me the settling time that I set in the initially, and I am not too sure as to where I went wrong.


texts:
Is there a standards organization or methodology to determine the elastic material properties of common materials?  What constants are normally used to define these properties?

More specifically, the set of equations for linear elasticity can be written as:

$$
\nabla\cdot\sigma + {F} = \rho\ddot{{u}}\\
{\varepsilon} =\tfrac{1}{2} \left[{\nabla}{u}+({\nabla}{u})^\mathrm{T}\right]\\
{\sigma} = {C}:{\varepsilon}
$$

where

$\sigma$ - Stress tensor
$\epsilon$ - Strain tensor
$u$ - Displacement
$C$ - Stiffness tensor

Using Voigt notation, we can write the stiffness tensor as a $6\times 6$ symmetric matrix

$$
C = \begin{bmatrix}
C_{11} & C_{12} & C_{13} & C_{14} & C_{15} & C_{16}\\
 & C_{22} & C_{23} & C_{24} & C_{25} & C_{26}\\
 & & C_{33} & C_{34} & C_{35} & C_{36}\\
 & & & C_{44} & C_{45} & C_{46}\\
 & & & & C_{55} & C_{56}\\
 & & & & & C_{66}
\end{bmatrix}
$$

To me, this matrix $C$ defines the elastic material properties of a material, but I've been unable to find any reference or database that lists materials in this format.  I've found a few random materials that list their properties in terms of something like the bulk and shear modulus, which then map to this tensor as:

$$
C = \begin{bmatrix}
\lambda + 2\mu & \lambda & \lambda & 0 & 0 & 0\\
 & \lambda + 2\mu & \lambda & 0 & 0 & 0\\
 & & \lambda + 2\mu & 0 & 0 & 0\\
 & & & \mu & 0 & 0\\
 & & & & \mu & 0\\
 & & & & & \mu
\end{bmatrix}
$$

where

$\lambda$ - First Lame parameter
$\mu$ - Shear modulus
$\lambda + 2\mu/3$ - Bulk modulus

However, this only works for isotropic materials.  Generally speaking, we need all 21 elements of $C$.  As such, I didn't know if there is a standards organization or methodology for determining these properties beyond the shear and bulk modulus.  Alternatively, if shear and bulk are the only parameters really needed, how are these determined and what organization standardizes these tests?


texts: What could be the downsides of leaving twist-off bolt splines in the interior of exterior columns?

texts:
I have a project where the contractor is using ASTM F1852 Tension Control (twist-off) bolts. The project is outdoors and uses weathering steel and weathering fasteners. The main members are hollow steel sections that are utilizing bolted splices.

As the contractor is tensioning the splice bolts, he is letting the twisted off portion of the bolt (spline) fall into the the hollow sections. You can hear the metal pieces ping all the way down the tower legs. There are no access holes to be able to retrieve these pieces. They are permanently in the hollow steel members.

We have used these types of bolts in other structures, but this is the first time that I have run into the situation where the splines are left in place. I have not seen an part of a specification that specifically speaks to this situation.

Will this cause any future issues for the structure?

The only possible issue that I can see is that in the future, the collection of splines will rust together and clog the weep holes in the base of the members.


texts: Can I make check valve in simple workshop?

texts:
I need a check valve ( one way valve ) for my project which has less actuation force (IDK real term. shouldn't require high pressure for inflow of fluid) and I searched in market for the valve but couldn't find one. Also I am not in place where I can easily order online.

I saw an hydraulic (can hold 2 tons ~ 7k psi. I need about 500 psi only though.) with ball valve that lifts when inflow and gets down to its seat due to gravity. It is really simple with no spring and also has no rubber or anything like that to prevent seepage of oil but it works. So I was thinking if I can make one in lathe?

There are two problems for that:

how to make a spherical hole.
despite making the structure how can I be sure that it won't leak.
Like theoretically it is possible but mostly somehow the products
don't turn out okay as planned.

I am also thinking instead of ball, a tapered one will be easier to manufacture but not sure if it will work.

Any suggestions?


texts: Find minimum horizontal force required to keep the block and wedge stationary?

texts:
In the adjoining figure, the coefficient of friction between wedge (of mass M) and block (of mass m) is μ. Find the minimum horizontal force F required to keep the block stationary with respect to wedge.

For this Q , total acc of $M+m$= $F/M+m. $

Considering inertial frame of reference , for mass M and m.FBD is as follows :

I haven’t marked N1 or N2 but can assume them according to FBD.
For mass M ,

μN1 on left means the friction from surface.

$N_m$ means normal force by the mass m which is equal to $N_M$.

For mass m ,
1 )μN2 on left is because frictional force is always in direction opposite to motion. Since the N2=0(no surface from ground for mass m) (as per Q), So $μN2=0$.
Q 1 Why did we not take $N_M$ as the normal force in μN2 ?
2 )$mg=0 $
Total F= μN1 + $N_m$ where $N_m$ = μ*N = m * acc of mass m. Since ,
μN=0. Therefore , either m or a = 0 it has to be .
So , total $F= μN$ only.
But correct answer is $(M+m)*a$ where $a=g/μ$
So , I just wish to know where am I wrong in my calculation.


texts: British tapered pipe thread; Wall thickness? & Thread designation tpd?

texts:
I have to draw two custom pipes, 1 1/4" & 2", with on one end male tapered pipe thread and on the other end parallel pipe thread. The connections are Parallel female thread with a tapered male thread, with Teflon tape as sealant.

I'm familiar with the metric tread, but the British/ Whitworth thread system is new for me. After a search on the internet and the standards: DIN 3858 / DIN ISO 228, i have the following questions:

According to DIN 3858, tapered thread largest available size is 1 1/2". Why are there couplings on the market that are larger? In my case 2".

Is the designation of "Pipe thread DIN 3858 - R 2" correct?

What is the minimal thickness of the pipes when it concerns tapered thread? Are there guidelines for this?

For the 2" connection i selected a OD = 60.3 mm, t = 2 mm. (probably too thin)
For the 1 1/4" connection i selected a OD  42.4 mm, t = 2.6 mm.


texts: What (if any) are the engineering limitations for producing "simulation" exoskeletons

texts:
To clarify the title since it cannot be said within the word limit:

A "simulation" exoskeleton, is an exoskeleton that doesn't exist to support a disabled user's movement or to help someone carry more. It is an exoskeleton that one wears in order to be better immersed into a virtual environment, either for recreation or training.

To explain further, the increased immersion is achieved using the exoskeleton for mechanical feedback, and for full body input, by matching the "rag doll" avatar's position/form to the exoskeleton you can both apply more diverse control to and experience the virtual environment in a far more immersed way. Allowing running, wrestling, climbing, carrying, etc.

That's the theory at least, and products like Dexmo achieve it on a small scale.

And there was a product in progress called Axon VR which would have been a full body experience, I can't find what happened but it seems they've decreased scope and are also doing gloves. The shtick of these gloves compared to Dexmo is that there is better tactile feedback, such as heat/texture/etc. Axon VR even has an ex-CEO of twitter invest in it so obviously the concept isn't too out there.

Exoskeletons like these that can be mounted and so don't have to lift your or their own weight, nor have to worry about batteries since then can run off the mains, should be significantly easier to make economically viably right?

So I want to know

A) Whether something is feasibly possible with a 100,000 dollar hardware budget per item at all

B) If not what is limiting it?

C) If it is, then how much would it cost (ball park numbers), and a rough cost breakdown in terms of hardware per complete item.

I understand that software for it is hard as hell, and ensuring safety within legal limits is difficult, or perhaps there isn't a big enough market that even if they were $25,000 to buy each that they wouldn't sell. By answering the above questions I hope to narrow down on the "bigger picture" of it.

From what I read online I could find upper limit of power outputs of humans reached around 2000kw (~2.5hp) or for a short period for a professional athlete, in this case cyclists. A 5hp pump can be bought for under \$1k off the first site I found, even if you had to go as high as 10hp to not only stop but also "reverse" any actions of a "sprinting" human, which probably wouldn't be safe anyway and wouldn't be a feature, as well as being extremely rare, that's sub \$2k.

After that you have material for a frame, ~40 cylinders/hydraulic motors (total), hoses, sensors, and (most expensive as far as I know) ~40 servo valves, and I'm sure some other things. (~40 estimated as 3 for each shoulder and hip joint (+12), 2 for each upper and lower arm and leg (+8), a few for each wrist/ankle, and 5 for each hand (+10)). Now I admit servo values can be PRICEY, but in bulk and many of the 40 not under much stress like the ones for fingers I figure the price should stay WAY under \$250 a valve + cylinder, which even then becomes \$10000 which for what you're getting isn't too high in my opinion. And that's an all out all motion one, I imagine most people could have lots of fun with just hands, feet, and waist "simulation".

I mean there are already exoskeletons on the market that can walk people who can't walk! On battery, against the force of gravity, within a reasonable price range. I'm honestly mostly wondering if I'm crazy more than anything, wondering why we don't have simulation exoskeletons already, maybe I am just vastly over estimating their market value.


texts:
The adhesion between two solids is characterized by the adhesion energy. If you have two solids adhered at an interface and you want to pull them apart, I understand that you have to supply the energy described by the surface energy (J/m^2) times the area (m^2).

Intuitively, it seems like there should also be a minimum adhesive force. If I try to separate two materials at an interface using a tiny force, it is never going to act over a distance so it will never do any work. There is then, presumably, some minimum amount of force required to separate them. This force would of course be specific to the angle at which it was applied (pulling vs peeling, for example). Is this adhesive force a property used for analysis? Is it generally extensible, ie, if I double the surface area of an interface does the specific adhesive force (N/m^2) stay the same?

Secondarily, what is the relationship between the force and work required to de-adhere to materials at an interface? If the energy required is characterized by a adhesive energy, $E$, and I pull them apart with force $F$, what is the characteristic length over which the work is done? $\int dE/dF$? Is the adhesive energy you might look up in a table not actually appropriate for finding the required force?


texts: How is the YAW angle calculated by an IMU sensor?

texts:
Say a body rotates by 90 degrees, then the yaw angle will be 90 which can be calculated using the data provided by IMU.
Now from that point, the body traverses some distance and is again rotated by 90 degree in the same direction. What will be yaw angle shown by the IMU? Will it be 180 degrees or 90 degrees?
In a nutshell what I want to ask is that, is the angle measured from the initial starting point or from the last reference point?

For Roll, Pitch, Yaw, please refer to the above diagram.


texts: How you calculate the temperature scaling factor?

texts:
Used to obtain the corresponding pressure at ambient temperature. Example when testing Proof or burst pressure to a given value at 300°F, but you will test with corresponding pressure (higher) to ambient temperature.
Example. Proof Supply Pressure @ 300°F = 1161 psig
Proof Supply Pressure @ AMBIENT = 1161 X Temperature Scaling Factor
= 1161 X 1.15
= 1335 psig
     Burst Supply pressure @ 300°F = 1251 psig
     Burst Supply pressure @ AMBIENT = 1251 X Temperature Scaling Factor
                                     = 1251 X 1.24
                                     = 1551 psig

Please note different values for TSF for Proof and Burst pressures. Are these values obtained from the material the part is made off? Is there is a calculation, what it is?


texts: How would one determine if a fluidised bed (with liquid flow) is determined to be a stable fluidised bed, which subsequently doesn't form a plug or bed at the top of a column (bounded by frits), when under pressure?