texts: Can the continuity equation and Bernoulli contradict each other?

texts:
Please bear with me - I'm a lapsed mathematician and I'm self-studying these concepts.

A question asks the following:

  Water flows in a pipe of diameter 5 m at a velocity of 10 m/s. It then
  flows down into a smaller pipe of diameter 2 m. The height between the
  centre of pipe sections is 5 m. The density is assumed to be uniform
  over the cross sections. The gauge pressure at Boundary 1 is 120 kPa.
  Calculate the velocity at the smaller pipe section.

There is no reason I can see to assume mass flow continuity doesn't apply, and using $v_1A_1 = v_2A_2$ one obtains $v_2 = 62.5$ m/s. However, using the Bernoulli equation while assuming atmospheric pressure at the smaller section, one gets
$$
\frac{p_1}{\rho} + \frac{1}{2}v_1^2 + + gz_1 = \frac{p_2}{\rho}+\frac{1}{2}v_2^2 + gz_2
$$
$$
120+ 50 + 5g = 0 + \frac{1}{2}v_2^2 + 0
$$
$$
v_2 = 20.93,
$$
and in fact this is what the textbook answer gives. I am quite confused as to why mass continuity applies in other situations, even with changes in pressure, but doesn't seem to apply here.

My question is: is this textbook question then ill-posed? I feel as though by providing too much information about the pipe section without checking the calculations, the question is bound to create a contradiction. The 5m/2m diameters don't actually make it into the final answer.


texts: What is the meaning of vorticity and circulation?

texts:
In fluid kinematics I can't understand the meaning of these terms : vorticity and circulation.
Can somebody give me a description of these terms so that a lay person can understand them easily?


texts: What grade of titanium are "memory titanium" glasses made of?

texts:
I've worked with different grades of titanium. Mostly with grade 5, and also grade 1 which is ductile.

I know that some glasses are made of titanium and are called "memory titanium", I guess because they bend back to their original shape?

My question is, which grade of titanium would that be?


texts: Does excitation matter in a time-domain simulation/computation of a transfer function of an LTI system?

texts:
Let's say I am running a FDTD simulation of a wave-equation to determine a transfer function of an LTI system:

\begin{equation}
H(f) = \dfrac{Y(f)}{X(f)}\
\end{equation}

where $Y(f)$ and $X(f)$ are Fourier transforms of signals measured at some point in the FDTD grid for a grid with an "obstacle" inserted and an empty grid, respectively. Assume that it's an acoustic wave simulation and that the "obstacle" is modelling a fully reflective object.

My question is: does the type of an excitation signal matter in that kind of problem? For example, how broadband the signal is? And if does matter, then - how? My intuition tells me since in the end we're computing a relation of two signals, any propagation issues of the input signal will be the same in both simulations and therefore cancel each other in the above equation. The only issue that I can think of is the SNR.


texts: What are the raw materials for water filter housing production?

texts:
I want produce water filter housing (like below images)
who can tell me what are need raw material for these?
Best Regards


texts: Correlating relative humidity outside and inside an enclosure

texts:
I am building a device and I tried to Google an answer to this question but I am an electrical person and lack knowledge in this field.

I need to know what the relative humidity inside an enclosure (of my device) will be for a given ambient temperature. If I know:-

Relative humidity outside the enclosure (95% RH)
The ambient temperature (40 deg C)
The air temperature inside the enclosure (60 deg C)

Since the air inside the enclosure is hotter because of the electronics I know the RH inside will be lower but I do not know how to go about quantifying and justifying it on paper.


texts: Calculating gain of an overall system. Analogue electronics

texts:
Our professor has given us a review for a upcoming exam. But he has never done anything like this question and it has stumped a quite few of us. We are hoping someone can walk us through this so we can understand, as he will not assist.

"A modular two amplifier system consists of a first stage amplifier with an open loop gain of 100, an input impedance of 25kΩ and an output impedance of 2kΩ, and a second stage with an input impedance of 2kΩ and an open loop gain of 50 and an output impedance of 500Ω.

Calculate the gain of the overall system.

Using a single op-amp, specify a third modular amplifier, using the original two in the order or otherwise, such that the input impedance of the overall system is 20kΩ, the output impedance is 2kΩ, and the magnitude of the overall voltage gain is 2000."

I thought you could just multiply the gains (gain = - Z2/Z1) of each op amp together, but some classmates disagree with me.

Should I approach it with op amps or signal circuit equivalents? Does a voltage divider have anything to do with it?

I can attach screenshots of circuit diagrams we have tried.


texts: How does a graph with tensile stress-strain curve and compressive stress-strain curve superimposed look like involving true stress and true strain?

texts:
If you have a graph with a tensile stress-strain curve of a typical metal or alloy and you superimpose a compressive stress-strain curve on it (from same metal or alloy), how would this look like if you had to sketch it?

I know that when you talking about engineering stress and strain, you will get a typical metal stress-strain curve for tension and then in comparison the compressive one follows same path for the elastic region and then after that rises above the tensile one.
And you will notice three differences:

compressive one will have no necking and thus no maximum/tensile point.
it will fracture differently and with way higher strain
like mentioned before; F needed for compression is higher than for tension in the plastic region because of the increasing area and so engineering stress will be higher as well.

Now how would tensile look like versus compression if we talking about real stress and strain? Especially regarding point 3, will compression still rise above tension curve in the plastic region?
So in other words will delta F be higher than delta area in compression? Will the extra rise in Force for compression with respect to tension be compensated by the fact that for compression the area increases and for tension it decreases and thus true stress will be equal?

If it not much to ask, could someone sketch a true stress and strain curve with both tension and compression for a typical metal?


texts: How many Technical Rescue: Collapse Units are there in the US?

texts:
In a story about today's Miami bridge collapse, I saw this photo:

In the upper left, there is a white box truck which seems to say "MIAMI DADE FIRE RESCUE / TECHNICAL RESCUE / COLLAPSE UNIT," even though the start of each line is obscured by a pole.

First responders, including another fire truck, are visible on the scene and one of the crushed passenger vehicles' headlights are still on. (Reports indicate the crushed vehicles were stopped for a red light).  The disaster scene looks pretty fresh, though clear of bloodied victims and easily clearable bystanders.

However, collapses like this are supposed to be quite rare.  The impressive observation that such a specialized unit got there so quickly got me wondering, how many of these units are there?

Recognizing that collapses might be more common in countries with weaker building codes, and thus Collapse Units like this might be more necessary there, I'm primarily restricting the scope of this to the US.

Photo by Joe Raedle, Getty. I do not have original image credit/permission to relicense this under CC-BY and thus am not re-uploading it, but asking the question seems like a fair use exemption.


texts: How to calculate screw pullout strength?

texts:
I am designing a system where a beam is acted on by a horizontal force. I intend to hold the beam in place with a set of screws, although I am uncertain how much force they will be able to withstand.

What method can I use to determine the holding force of screws?


texts: Why would the flow go horizantally not vertically in the tube?

texts:
I was curious about this. If i have a tube which has water flowing in it. and mounted vertically a small extension tube with a loop. The water will go horizantally and only a few drops will go vertically. Why is that? and how can u determine how much water will go vertically? I tried to search for a scientic explaination but didn't find anything. What if I want to design a tube with this loop but I don't want any water to go vertically?

Here is a diagram if you don't understand:

Is there anyway to prevent the water from going verically if the tube is blocked?


texts: Why are words bit-shifted for an Atmel SAM4S SPI slave?

texts:
I have discovered a problem when using the SPI peripheral in slave mode on an Atmel SAM4S.  Occasionally words can become bit-shifted.  I can force this condition by enabling the peripheral some number of clocks after NSS goes active.  I do this by waiting for NSSR, then using a delay loop to wait a specific time before I enable the peripheral.  I have confirmed on a scope that when the peripheral is enabled n clocks after NSS goes active, the words are shifted by n bits.

When the peripheral gets in this state, the only way to recover is to perform a reset (i.e. set the SWRST in the control register).  Disabling and re-enabling is not sufficient.

This issue has also been observed on a SAM9G45 MPU.


texts: Why is soot produced in diesel exhaust, since diesel runs lean?

texts:
Since diesel runs lean, why is soot produced in diesel exhaust?

Soot is carbon particles due to incomplete combustion. But, since diesel runs lean with plenty of oxygen, why does this happen?


texts:
I have the following robot arm:

Now how do I obtain the equation of motion:

$$ M \ddot\theta + \vec{b} + \vec{g} = \vec{\tau} $$

I am familiar with forces, torque, velocity and so on. I know that this equation follows from force and torque equations. However, I don't know how to establish these force and torque equations.

The torque is applied by motors in the joints, so that the arm does not move. No payload is attached to the end-effector.

As far as I understood, $\vec{\tau}$ contains the two scalar torques for each of the two joints. $\vec{g}$ should be the force vector in negative y-direction, although I am not quite sure. I have no idea what $\vec{b}$ might be.


texts: How can I find the Transfer Function in Z-domain?

texts:
This is my signal;
$y[n]=x[n]+0.8x[n-0.2]$
When I take Z-transform I get;
$Y[z]=X[z]+0.8z^\frac{-1}{5}X[z])$
Then I found the Transfer function as;
$H[z]=\frac{Y[z]}{X[z]}$
$H[z]=1+0.8z^\frac{-1}{5}$
I want to extract the numerator and the denominator parts of this $H[z]$, but all the examples I see have integer z exponentials as -1,-2 etc. How can I save the function from 0.2 exponential?


texts: Why is manganese steel non magnetic in as cast condition?

texts: Is it because of some ferrite stabilizer or something?A detailed explanation to this is most welcome.


texts: What are the non-practical features of a sterling engine that cause the internal combustion engine to be used instead?

texts:
What are the non-practical features of a sterling engine that cause the internal combustion engine to be used instead (in a car)? (e.g. price, size, the power to weight ratio, etc.)

Can you name any that aren't as obvious as those stated above?
Please provide answers that aren't obvious but are still relevant.


texts: Are there pumps that can vary their pressure and flow rate, while maintaining the same power?

texts:
To avoid the inconvenience of buying compressed "air" cleaners and scavenging quarters for refilling tires, I'd like to get a pump that can do 72 PSI (vapor pressure of difluoroethane minus atmosphere pressure) at ~2 liters/minute for dusting, and 35 PSI @ ~40 L/minute for filling tires (I calculated to pressurize a 33L tire @30 PSI to 35 PSI, 10.4L of uncompressed air is needed, and I'd like to do this in 15s). The dilemma is that I can't seem to find any portable pump that can operate at both these 2 points.

I have one of those 12V portable pumps that can go up to 250 PSI, but the time it takes to fill a single tire is painfully slow (and loud). The problem is that at a low pressure of like 30 PSI, the flow is pretty much the same (I measured about 6 L/minute with a balloon) as at a higher pressure like 80 PSI. In other words, the motor isn't delivering it's full power at low pressures. This is just like the limited power band on diesel and gasoline engines.

Are there pumps that have a wide power band that would meet my requirement?

Or do pumps in general have limited operating points? Here's the impression I got:

(top - high pressure, low flow)

piston
diaphragm
centrifugal pumps
axial pumps / propellers

(bottom - low pressure, high flow)

One idea is to make a piston pump with a large bore volume coupled to an electric motor with a constant power curve (torque = power / RPM). That way, it can operate at both high flow, low pressure (high RPM, low torque on the motor), and low flow, high pressure. But I don't think a constant power motor exist, so you'll end up needing a transmission, which will make it complicated.

Other ways?


texts: Could a magnetic audio tape recorder/player be made using a vibrating permanent magnet?

texts:
Cassette tape players use a read head where the magnetic field from the tape is directed through an induction coil. The induced current in the coil is then amplified and sent to the speakers. Now I'm wondering if magnetic tape technology could also work with a permanent magnet that vibrates from the changes in magnetic field in the tape (for playback) or that is made to vibrate externally to create a changing magnetic field on the tape (for recording).

Obviously this is just a theoretical question as I'm not going to use a permanent magnet tape player for anything. I am just wondering if this would be possible with any level of sound quality.


texts: I purchased a pergola kit and realized afterwords I'm not happy with the placement of the center post.  If possible I'd like to eliminate it.  After searching for a while I haven't been able to find any information regarding span lengths for such a small load.  The inside dimensions of the sleeve surrounding the  horizontal 16' span is 1 3/4 x 5 7/8.  Can anyone help point me in the right direction or recommend a solution?


texts:
I have a system consisting of 4 magnets rotating at speeds between 200 and 6,000rpm, which are facing 4 other magnets with a 0.5mm gap between the two sets. The set-up looks like this:

Both sets of magnets have their noth pole facing out so that they repel each other (the 0.5mm gap is maintained by other means). The resulting effect is that when the bottom set starts spinning, the top set follows because the top magnets naturally fall (radially) between the gaps of the bottom ones.

What I'm trying to do is work out what the decoupling torque provided by this set up is. In other words, if the bottom part is spinning, how much torque do I need to provide to stop the top part from rotating?

The diameter between the centres of the magnets is 17mm, they are 90 degrees apart, and I have the following (very basic) information on the magnets themselves:

Diameter: 6mm
Performance: 5,900 Gauss
Vertical pull: 1.4 kg
Slide resistance: 0.28kg

Can anybody point me in the right direction? I have made the following attempt, but I don't think that's right:

T = 4 * (8.5e-3 * 0.28 * 9.81)  = 0.093 Nm


texts: Power decreases as the diameter increases

texts:
I have a question about the use of a servo motor.

I need to lift a load of $130\ kg$ with two servo motors with $13\ Nm$.

The diameter of the shaft is $Ø40\ mm$, ie, $r=\ 20mm$.

$1\ N = 1\ Kg\ *\ 1\  m/s^2$

$1\ Nm = 1\ Kg\ *\ 1\  m/s^2*\ 1\  m$

Therefore:

$25.506\ Nm = 130\ Kg\ *\ 9.81\  m/s^2*\ 0.02\  m$

By my reasoning, two servo motors could raise this load if the point of application of the load is exactly the diameter of the shaft.

If I use a cable that every time its diameter increases inside a pulley, at some point I will not be able to lift that load anymore?


texts: Vehicle emergency high-deceleration braking and steering system

texts:
I wish to investigate an active vehicle braking method for use in extreme situations. Very high accelerations are acceptable in situations where this would prevent the much worse accelerations present in a collision.

I was thinking of a system that will use ejected gas/liquid to reposition the position of a car and/or assist in braking. We know that ejected mass (gas or other) create a propulsive force. I was thinking to utilize this mechanism to create a force that will decelerate the car. Or maybe change its position/trajectory (eg. when it moves out of the road in a steep turn).

Would such system be viable?
What parameters would such system have?
eg to decelerate a car travelling at 30m/s within 3 meters
(about 15g deceleration!).
How much mass should we eject and at which speed?
Have such systems being proposed/researched/built?


texts: What are air barrels (with regards to oil pipelines) and why are they a problem?

texts:
I read an article about Alberta, Canada losing millions per day from air barrels and am now doing some research, but having a hard time finding information.

I am curious to know more about air barrels and why they occur. Are there better systems out there that prevent air barrels or is it a constant, inevitable issue for pipelines? In particular, I am interested in the economics that result in air barrels, as well as the infrastructural issues or limitations that companies use to justify the purchase of air barrels. If you happen to know anything else about them, please do tell.


texts: In many application, the knowledge of the orientation of a body is essential for control purposes. There are several representations, where one is the Euler Angles and another is the Quaternion represenation, where the Euler Angles suffer from gimbal lock. My question is, how can one use the Quaternion represenation for control the angular position in space? If this would be possible, then why are the Euler Angles so widespread?


texts: First/Third angle projection symbol in drawing sheet format

texts: is there any inbuilt feature in Solidworks to appropriately add the symbol for First/ third angle projection into the sheet format as per our selection?


texts: Power a microcontroler with a motorcontroller?

texts:
I have a motor controller that operates at 10-50V and draws 5A controlling a 3V motor that draws less than 1A.
I had a an idea where I want to try to use a microcontroller to control this set up.
The motor controller has an auxiliary 5V output that can support loads that draw less than 10mA.
If I find a suitable microcontroller, can I use the motor controller to power it? Should I use the motor controller to power it?
More info: I am working on a design for a robot build. My system currently has two motors one that runs at 48V (and around 3A) and the aforementioned one (3V) both using the same type of motor controller. I'd prefer not to have two power supply lines running, so can I run the smaller motor system on the motor controller powered at 50V? Is that safe? (the motor controller can take a 56V max)
Thank you for reading, any input would be highly appreciated.


texts: Mounting outdoors camera using aluminum 5052

texts:
I designed a simple U shape 2mm sheet metal bent mount for a 4kg outdoors CCTV camera. The mount was accidentally produced from 5052-H32 Aluminum instead of 6061-T6.

Is it common to use 5052 aluminium for such structural use-case? Or it is better to reproduce the mount? A static linear analysis shows that there is a factor of safety of 1.6 with g factor of 12.


texts: I often seen printers like this in offices and schools. Considering how we can have printers small enough to fit on a desk, why are these printers taking up half a room? What are they capable of doing, and why do they need to be that large?


texts:
A thermistor, which has a Negative Temperature Coefficient (β) of 3300 (K) and a resistance ($R_o$) of $10\text{ k}\Omega$ at a reference temperature of 21ºC, is used to measure the temperature of an industrial process. If the resistance of the thermistor (RT) is reduced to $2\text{ k}\Omega$, calculate the temperature of the process.

Here's what I got, it's not finished because I didn't know how to continue, and I also don't know if it's even correct:
$$\begin{align}
3300K &= \dfrac{T_2T_1}{T_2 - T_1} in(R1/R2) \\
3300,000 &= \dfrac{T_2T_1}{T_2 - T_1} in(10K/2K) \\
3300,000 &= \dfrac{21T_2}{T_2 - 21} 1.61 \\
2049689.441 &= \dfrac{21T_2}{T_2 - 21} \\
2049689.441(T_2 - 21) &= 21T_2
\end{align}$$
Like I said, I don't even know if I'm using the right formula.


texts: Does anyone know how to derive the deflection formula $\delta = \dfrac{-0.0068wL^4}{EI}$ for a continuous beam spans over 4 supports?


texts: Which kind/model of sensor is appropriate for detecting vibration at one end of 1000 m steel block?

texts: We have to detect vibration/sound produced at rail track for upcoming train at 1000 m distances . So which sensor is appropriate here? thanks.


texts: How can Geothermal heat a home using the ~55 degree heat source of underground to a more usual 72 degree inside temperature?

texts:
It has bugged me for a while. If the earth is a constant 50-60-odd degrees several tens of feet beneath ground, and houses (I assume; ours at least does) don't drop down to lower than those temperatures often, how come a geothermal unit isn't just using supplemental electrical resistance heating (and not the ground loop heat source?) all the time?

Is it because the above ground equipment is actually a heat pump (extracting more heat out of the circulated liquid than the temperature it comes out of the ground at)?


texts: A radar that is not an OTH detection distance

texts:
Let's say that we have a radar that is not an OTH on a boat, and it is placed 30 meters above the ground. Is there a way for it to detect an offshore platform 152 kilometers away from it, since the Earths curvature should prevent it from doing so?

The reason why I'm asking is that I saw a flat earth video where the guy is in the north sea and this is the supposed setup of his radar. Because the curvature of the earth the offshore platform must be 1376 meters high for it to be detected by the radar. Is there any way for a radar to extend its range over the horizon?


texts: How can I build a electronically controlled valve for a 1/4 inch tube

texts: I'm looking for a practical efficient way to open and close a 1/4 inch gravity fed hose. Initially I was thinking of using a Solenoid, but can't find anything suitable. My second thought was using a servo and valve. I was also looking into some sort of piezo valve but they seem very specialized and expensive.


texts:
What I did was I found the $I_{short circuit(AB)}$ = 10/5 = 2A by shorting AB.
How am I supposed to find $R_{AB}$ in order to solve for $V_{Thevenin}$? It can't be 5//10 right?


texts: Is there any method or formula that can be used to find the operating voltage of a coil using the resistance of the coil? If so, is it also applicable to AC coils or any other technique?


texts: Ball Screw or Roller Screw : what is the best option for noise level and fatigue performance?

texts:
I had some talks with a supplier about the noise level of both technologies.
I wanted to have a wider opinion.
Regards


texts: Mathematic modeling of an overshot water wheel

texts:
We're working on a project that require some mechanical engineering and electronics engineering. In this project we've to model this overshot water wheel (so the water comes from the left top side and flows over the wheel to a lower place, so that the wheel will spin at a certain velocity).

But we've to get a startup to model this mathematically, we're looking for a so complete model (we're looking for as much as important inputs and as outputs we're looking for the torque and the power of the wheel).


texts: Materion sells 4 types of amorphous metal alloys,it cost huge amount of money,1000 dollar per kilogram.My question is,why would anybody choose it over lets say titanium 6al-4v?


texts: Is displacement the most important factor in determining a motorcycle engine's overall performance?

texts:
This is a simple question to follow up the question from the thread below:

Engineering formula to relate engine displacement and power

Motorcycle manufacturers tend to show the displacement value in mass production motorcycles incorporated in their names such as Honda Wave 125i, Suzuki Raider 150, Kawasaki Z1000, etc. Most of these are below 200cc displacement. (Exceptions are Yamaha YZF-R1M, Kawasaki Ninja H2, etc).

The question is: If power is not determined by the displacement alone based on answers and comments on the thread above, does this imply that the displacement is the most important factor in determining the engine's overall performance?


texts:
I found the following paper and am attempting to put Saturated Pressure and Saturated Temperature into excel. I got Saturated Pressure to work, but can't get saturated Temperature to work.

Saturated Steam Equations Paper

Saturated Pressure (working)
=(B18+273.15)/647.096 [cacluates Tr from C]
=EXP(9.56756 + 5.39806*LN(B19) - 6.16183*(LN(B19))^2 + 1.49572*(LN(B19))^4 + 0.433*B19^5 )

Saturated Temperature (not working)
=B15/22064 [calculates Pr from kPa]
=EXP((0.00937817 + 0.000498951*B16 + 0.0000111049*B16^2 + 0.000000334995*B16^3 + 0.0000000344102*B16^4)^(-0.4))

I thought maybe it was outputting in K, but that did not solve it.

Either I didn't correctly translate the equation, or the equation is wrong. Thoughts? Thanks!


texts: Fastening a Nut on threaded rod from the middle

texts: Does there exist any type of Nut, that can be screwed on a threaded rod that can slipped in without having to go to the ends of the threaded rod?  I can sort of imagine a Nut that was a U shape instead of O shape, or perhaps two C shapes that could interlock some how.  Does anything like this exist?


texts: what is the name of this wheel found in toys which rotates freely?

texts:
I have tried doing search by image on few popular Internet search engines but could not get it. (sorry, it picked up lot of dust and a bit ugly to see).
I want to know the name of such wheel and where can I probably purchase it by mentioning parameters. Are there any alternate designs?


texts: How do you determine the accuracy of a measurement device?

texts:
Lets say you have a measurement device of which you do not know the accuracy, and a reference measurement device. Both measure a variable $x$. The range of interest is $x_0<x < x_1$. How do you determine the accuracy of the unknown device in this range?

My course of action would be to gather values for both devices from $x_0$ to $x_1$ and building a distribution of errors. The accuracy could then be the error span, $\pm3\sigma$ or something similar - is this correct?

Assumptions:

The reference measurement device is calibrated and has virtually no error


texts: I have an electrical connector made of zinc-aluminum alloy (exact mixture unknown) that I would like to braze to a steel tube. Can this be done, what kind of material(s) would work for this application?


texts: Longitudinal impact of steel rod on a steel plate to verify the contact duration

texts:
So I'm doing an experiment to verify the contact duration when a steel rod (Material: Mild Steel) is allowed to free fall longitudinally on a steel plate. The arrangement is real simple:

The rod is allowed to fall longitudinally on the plate, resulting in a number of impacts. I will only be considering the first impact.

Now here's the problem I'm facing: During the first contact and off-contact, the oscilloscope reads a much higher than expected value for the contact time. Same procedure is repeated for three lengths of the rod (200mm, 350mm and 475mm), all resulting in the same anomaly. Here are the results:

As clear from the plot, the experimental values are similar to the theoretical values except for an offset (found to be about 121 µs). Any idea why this is happening?

P.S: The theory used is that of elastic waves produced on spherical contact where the impact results in the creation of a compressive wave that travels to the end of the rod and returns as a tensile wave which pulls the rod off contact. As such the contact time t=  2l/(wave speed). Wave speed = 5000 m/s.


texts: I am thinking of building a house with basement next to some existing structures. Are there rules of thumb on how closely/deeply you can excavate next to an existing structure? By moving farther away from the existing structure do I reduce the potential need for temporary retaining?


texts: Why are creeks sometimes piped underground in urban areas?

texts:
I live in Melbourne, Australia and a lot of the creeks here have been diverted through underground storm water pipes. I guessed that this is because land is highly sought after for development, and a lot of these creeks have been built over, however there are also a lot of cases where there is nothing built over the top of them at all. They simply carry the normal water flow through a small concrete pipe, leaving an empty valley on the surface which would only carry flood waters during heavy rainfall. What's the reason for going to the cost and effort of doing this?

Is it a safety concern having creeks in residential areas? Do creeks have some effect on the land which would affect nearby buildings? Is it just for the convenience of being able to cross them without a bridge?

Example

Dandenong Creek in Bayswater area @ -37.836524 lat, 145.254465 long (water flow goes from the right to the left of the image):

I've also seen a creek which briefly goes both above and below ground. The rushing water of the underground section could be seen through an overflow while the topside creek was mostly just stagnant water. It seemed completely pointless and made no sense to me.


texts: Difference between Allowable Bearing capacity Service and Ultimate?

texts:
When we calculate the dimension of a foundation we always use the allowable SERVICE bearing capacity (lets call it qs) and all the necessary checks are based on this value qs.

My question is why does the geotechnical report calculates the ultimate bearing capacity (lets call it qu)?

In my own research I stepped upon an article that says that when the geotechnical engineer calculates the ultimate bearing capacity it calculates the ultimate load by multiplying the service loads with a safety factor (lets call it Fs) now for a structural engineer (such as i am) we use different load combinations to calculate the ultimate load (especially when we have seismic and wind) in a simple case for example the most famous load combination in the ACI Code is 1.2D + 1.6L if in a certain case the Live Load is >>>> than the Dead Load the use of a simple Fs will not work to calculate the ultimate load combination.

Is that Explanation for this topic is feasible ? and what do you have other suggestion to the difference of qs and qu ? and where do we use each one?

Thank You in Advance.


texts: If I replace a flow orifice with a Coriolis flow meter of the same size do I need to worry about pressure drop with the new Coriolis meter?

texts: I have a 3 inch line with a 1.5 inch flow orifice. If I take out the flow orifice and put in a 1.5 inch coriolis meter will the pressure drop be the same or better with the new coriolis meter than with the flow orifice?


texts:
I am trying using pump to promote circulation of latex solution in a latex dipping tank. Is there any pump that suits this purpose? Also, is there any better ideas to promote circulation of the latex in the latex tank without handling the solution vigorously.
The explanation of main process can be found in this link.
https://www.youtube.com/watch?v=oTIADlYOkNc


texts: Does a 3-phase electricity grid need to be synchronised and are the phases split between houses?

texts:
Note: This may be UK-specific, I'm not sure.

I overheard part of a conversation about 3-phase electricity, one guy was saying that mains generators use 3 coils (or something) and as it spins it produces 3 different waves of alternating current that are 120 degrees apart. That's why the power lines often have three (or six) sets of cables, one for each phase. He said that if different phases are electrically connected then bad things happen, and sometimes if only one phase goes down, every third house on a street could lose power.

This raised a few questions for me:

Does that mean all power stations have to be in sync with each other? If so how is this achieved?

Is it true about every third house, I've never seen this?

Does this mean we effectively have 3 grids overlaid on top of each other?


texts: What is the cross-sectional shape in blue called? The shape, used on the shafts, is used for torque transfer, gears or similar. The three arcs are same diameter as the ball bearing ID, so bearings rest centered perfectly, but flat parts are used for engagement of sliding gears. Because of the shape and surface of engagement is much stronger than standard cut out keyway.


texts: Can wifi signal reception be improved by opening a door?

texts:
A wifi user is in a different room than the router. The computer is having a hard time connecting and receiving the wifi signal.

Can the wifi signal from the router to the computer be improved by opening a door to the room where the computer is?


texts:
I have a few questions relating to a multiple layered spinner that uses ball bearings to reduce friction, kind of similar to a fidget spinner. The image below is an example of the multilayered bearing spinner.

My questions are as follows:

Does having multiple layer of bearing rings decrease the overall friction on the outermost ring and allow it to spin for a longer period of time?
Does increasing the number of ball bearings in each ring decrease friction?
Are there any formulas or relation that would allow me to calculate the overall run time of the outermost ring for a given tangential force?


texts: Computing the stress field of a structure made of 4-nodes shell elements (accounting for membrane action, bending and shear)

texts: I am trying to implement my own FE code for shell structures. Most literature provide formulations and strategies on how to compute shell element stiffness matrix. I can already compute deformations using my FE code, but I don't know how to get the stress field. Can somebody direct me to the right paper/textbook?


texts: Question on fluid flow measurement uncertainty

texts:
Say you are trying to measure the liquid flow rate (mass or volume) through a pipe and you want to get the best measurement possible, and you have two flow meters. In one scenario, you put one flow meter and leave the other out as a back up. In the other scenario, you split the flow up into two pipes, put a flow meter on each, and then join them back up later. In the final scenario, you hook them up in series on one pipe only.
My instinct is that using two measuring devices instead of one is always better, and I'm fairly sure that the series case is the best scenario. However, what happens if you can't put them in series? Is it better to just have one, or to split the flow up if you can?
For the purposes of these scenarios, I'm always calibrating the whole unit end to end, so I would always calibrate both meters as one.


texts: What is the optimal shape of a beam subject to three point bending?

texts:
Assume we have a beam with density $\rho$ that is subject to three-point bending according to the image above. The beam cross section is rectangular with the variable height $H(x)$ and constant width $B$.

What function describing the non-constant height, $H(x)$ will yield a minimal total mass of the beam assuming a maximum allowed deflection of $\delta$?

The mass of the beam can easily be described as:

$$m(H) = \int_0^L \rho BH(x)\text{d}x$$

I started off trying to solve this using Euler-Bernoulli beam theory but later realized that this formula is only valid for constant second moments of area. Any ideas how to solve this problem?


texts:
Is there a technology in Laser Tape Measures which differs from the ones in Laser Range Finders (ToF or Triangulation)?
It seems that Laser Tape Measures are less expensive than any Laser Range Finder which I can find with equivalent accuracy (3 mm).
It is common to find tape measures with 3 mm accuracy up to 50 m for 30€, while the range finders I could find with an accuracy below 5% are all above 100€.
I'm only interested in the sensor and not in the whole device. One option would be to reverse engineer a laser tape, such as HERE, but I believe that there must be a more elegant solution for that. Am I looking for the wrong kind of sensor?
Thank you for your help!


texts: What about the natural convection heat transfer coefficient (*h*) at low Delta-T?

texts:
In a system I am modeling for personal research, I have a sphere (S) submerged in air (A), initially at the same temperature Ts = Ta.

Then the temperature of air is slowly increased (or decreased), by something like 0.5 °C/h. In these conditions the Delta-T = Ts-Ta is necessarily low.

But, would h be so low that the main heat transfer mode is not convection anymore?

UPDATE: It is a sphere of say 20 mm radius, made of steel, and exposed to ambient air - which means the temperature of air will change with the diurnal cycle; 0.5 °C/h is a rough estimate based on the observed diurnal excursion in a certain locality.

In light of the informative comments & answers below, I would then like to ask how is the conductive heat transfer coefficient defined for this case.


texts: Advice on suitability of corner joints in welded frame

texts:
I'm designing a frame for supporting some agricultural equipment that will be composed of welded square hollow section members. The top of the frame will be a rectangle of SHS members, with four vertical SHS legs - one in each corner.

When it comes to the corner joints, I'm not sure which is the best way to go: (A) weld the top members together with 45° mitred corners, then weld it on top of the vertical members, or (B) weld the horizontal members in between the vertical members, and cap the ends of the vertical members. See the following image for a comparison.

My feeling is that B (on the right) would be stronger, but I'm not sure why. I'd like some information - perhaps what terms I should be searching for - so that I can come to an informed decision based on the requirements of my application.


texts:
I would like to know with which existing types of power plants(thermal,wind,etc.) can compressed air energy storage(CAES) be used efficiently? And how can it aid power plants like thermal(a brief explanation is sufficient)?

As far as I know it requires multiple compressors and hence can be used with a gas turbine power plant. But why would a gas turbine need CAES since it can readily obtain air and compress it at any time?


texts: Rotating Multiple Solar Panels with One Motor

texts:
I am designing a system to have solar panels track the sun, but only with one axis of rotation that will tilt the panels from east to west.

I want to connect the panels together so that one motor could rotate multiple panels. I was thinking of a something like a bicycle roller chain and sprockets. Where a long chain goes around, say, 5 sprockets that each rotation a solar panel, and wraps around again forming a loop.

I am not sure if the chain will have enough contact with the sprockets, especially on panels that are in the middle of the chain system. The chain would basically be resting on those sprockets from the weight of gravity.

Is this a good design choice for such a system? Is there more cost effective way to accomplish the same thing? Should I supply tension to system so it has good contact with all the sprockets?


texts: Solar Array Frame Design / Statics Design Problem

texts:
I need some help with a statics design problem. I am tasked with designing a solar panel frame to mount on a building and am the only engineer on staff so I don't have anyone else to ask the simple dumb questions. Since I have no real experience doing wind load calculations I figured I would assume a load normal to the solar panel face. My idea is to use two square aluminum tubes mounted along the long side of the three solar panels stacked vertically along the tube. My analysis involves the support structure for one side, of one array column. As of right now I am hoping the solar panels themselves will suffice as cross-member connections. The details really don't matter, in fact the wind loading really doesn't matter either. It is the method I am having trouble with.

Want it to be able to withstand 125 MPH gusts. That appears to equate to 30 lbf/square foot. Given 18.47 sq. ft./ panel * 30PSF * 3 Panels + 135 lb panel wt = 1797 lbf. That's 1800 lbf total distributed load accross all three solar panels in one array column. Since there will be two support structures per array column that's 900 lbf distributed load per support structure or 4.48 lbf/inch. (Not sure where I got 6.2 on my drawing)

I know I need to determine the reactions at each pin joint, do shear and moment diagrams and then I will do a buckling failure analysis on each support strut member. Any guidance would be appreciated, started doing some calcs on my own and things just weren't coming out right.


texts: Does the turbine outlet affect the power generated by the turbine ?

texts:
In my text book , it is written
"Power generated by the turbine can be increased by using a gradual expansion at the turbine outlet"
The picture below explains the meaning of gradual expansion at the turbine outlet

i.e the cross sectional area of the pipe at the turbine outlet is increasing gradually m, causing gradual expansion..

How does this thing cause the power generated by the turbine to increase ?


texts: How To Obtain The Correct Differential Gears With Motor Shaft Adapters

texts:
My knowledge in gears in limited to their types (bevel, spur, etc).  I am trying to combine the power/torque of two DC motors using a differential gear.

I have a good handle on the idea and design from here and here

The problem I am having now is finding the correct differential gear to use (in term of shaft size, etc).

For a PoC I don't mind using Lego or plastic.  Eventually these two motors will connect via another differential to two other motors (which have their own differential) for a total of 4 to hopefully turn the drive shaft of this kettcar.

My overarching question is:

How/where do I choose the correct differential to use?
How do I scale up/down the motor's output shaft to fit into whichever differential gear I end up using?

As to "why" do this:

Learning
Learning
Fun

That said, if this approach is bat-crap crazy, then please feel free to say so and suggest an alternative.


texts: How to determine whether a particular velocity vector will result in a laminar flow?

texts:
Lets take the substance to be water. To my knowledge , the only condition imposed on a velocity profile to distinguish between laminar and turbulent force is the Reynold's number. For lets say I have been given this velocity vector :

V = (xy) i + (yz) j + (xz) k

Now how will I determine whether water, with this velocity profile , can have a laminar flow or not ?


texts: What is the formula for deflection of an end-loaded cantilever rod beam?

texts:
For a cantilever beam of circular cross section, loaded at the end, how does the deflection of the free end vary as a function of beam length and diameter?

I expect the answer will be something like:

$$\dfrac{L^2}{D^3}$$


texts:
Most of the windows in our rooms are mostly rectangular.

Why don't we chose any other shape like circle, triangle or trapezium? Does it affects airflow through room? Is the reason is that they look fancy or some specific reason?


texts: Basic dimension relationships in a valveless pulsejet engine

texts:
I'm willing to take my own shot at the construction of a blast supercharged valveless pulsejet, a holy grail among DIY jet enthusiasts.
However, since my idea is not very compatible with the geometry of most popular pulsejet engines, im going to have to build a custom valveless pulsejet first.

To that end, I need to know these basic design priniciples:

The ratio of the main exhaust pipe length to intake pipe length
The ratio of main exhaust pipe diameter to intake pipe diameter
The appropriate amount of flare in the main exhaust pipe
Any properties of combustion chamber that have to be kept in a defined relationship to the two pipes

I know there's a remarkable amount of variation in existing designs, therefore im only asking for a rule of a thumb for choosing those parameters.
I would have asked on the pulsejet forum but im still awaiting account activation


texts: How to generate a synthetic infrared and red LED signal for SPO2 calculation

texts:
There are multiple algorithms out there for generating synthetic EKG signals (for test and validation of heart rate estimation algorithms). All you plug in is the desired heart rate, and the algorithm outputs an EKG signal with the desired heart rate.

I need to create a similar algorithm - but for pulse oximetry. I would like to implement a signal generator which generates a synthetic infrared and red (photodiode) signal based on a user-specified/pre-defined SPO2 rate. I then want to take the synthetic red and infrared signal and let them be processed by an SPO2 estimation algorithm. If the algorithm outputs an SPO2 estimate which is close to the pre-defined (i.e. the true SPO2) SPO2 value, then I know that the algorithm works.

How would I go about creating such a signal generator?


texts: Thick walled cylinder theory - Stress/strain in ballooned out tube

texts:
I want to work out how much I can expand a piece of rubber tubing before it ruptures. The wall is 0.75mm and the ID 5mm. Hence I am working out the stress/strain from thick-walled cylinder theory using these pages.

In Lame's equations (derived on those pages), are the radiuses in the formula the original radiuses before expansion, or those resulting from expansion? Does the same go for the radius under investigation?

many thanks for your help


texts: I have inherited a product with inconsistent designs sharing the same part number. What do I do?

texts:
I am now in charge of a product line my company has been shipping for a decade. One of the previous product engineers was... shall we say, less than conscientious about sustainability and proper documentation. We have shipped hundreds of units, of multiple design variants, under the exact same part number. The manual presently reflects only one variant, meaning many users can't use it. And we've had multiple instances where a user has tried to reorder a unit by part number, only to find that what we ship them does not match what they already had.

Obviously, this is terrible. One does not change the specs or user interface of a product without also changing the part number. We will avoid such things in the future. But my question is about the past.

We have, on paper, documentation indicating what design variant each serial number corresponds to. My thinking is to create a spreadsheet, and name each variant retroactively, so we can at least support users that call in or place reorders. We would then create proper manual(s) so that the user can, based on their serial number, understand the operation of the units they have.

But I'm just making up that solution. It occurs to me that there may be formal, industry-standard methods of dealing with such things. Is there a procedurally-correct way to handle my existing install base?


texts: What is the technical name for temporary construction fences?

texts:
My structural engineering friend and I passed a construction site years ago, and he called those temporary fences a technical name. Now I ask him the technical name he said those years and he doesn't even remember the moment, understandably, and is not sure there is even a technical name to begin with. I googled "what is the fence built around ongoing projects called" and 'temporary fencing" came up.

This is my final straw to chalk it up to a distorted memory or finally learn that elusive name (every few months I remember that moment and still don't remember the name). So is there any technical name for temporary construction fences just as we have aggregates for sand, gravel, etc? If there is, please for the love of sanity, what is it?


texts: 1m3 water container and ice damage prevention

texts:
I was looking for data on ice resistance for these kinds of 1000 litres containers. I believe they are made of polyethylene with an outside aluminium structure. Given the physics of ice expansion, what could be the safe level of water inside if subjected to icing conditions ?
Does adding a half inflated bike tube inside could allow relieving pressure from ice ?


texts: Why is the Current to Motor less than Motor Rated Current?

texts:
I have a motor for a submersible pump with a Rated Current of 8.4A as given in the motor's electrical data. However, when it is running, I record a current of 3.4-3.9A. Is there a fault I am supposed to look into, or is this normal?
Why is the rated current so much more than the measured current.


texts:
Can someone help me with the dimensioning convention used here?Usually the coordinates are given as cartesion X,Y,but I am unable to understand this convention.
Also each individual hole size is not mentioned,so how does one find the hole size if they are close in diameter.Here the sizes are quite disparate,so it is visually obvious.

Cheers & TIA


texts: How effective are pancake motors as generators and why

texts:
Using a motor as a generator but  looking to test something
Why would or would they not be good generators
thanks


texts:
I am having a very difficult time identifying this thread. This part is a plug that I am trying to replace because the threads were stripped.

The best fit for pitch is 11 threads per inch (imperial), but the major thread diameter is 32mm. It does not appear to be tapered and the rubber seal would support this observation.

I have looked through many standard thread size charts and have been unable to locate a match. I thought BSPP-16 was close enough (at 33mm) but when I tried, the BSPP plug was too large to fit the associated female thread.


texts: Measuring flow of polyol with ultrasonic flow meter

texts:
Our company is installing flow meters on an old polyurethane foam machine.
After some research, ultrasonic flow meters were chosen as they have no moving parts and are easy to clean.  Polyurethane foam is produced by mixing polyol with isocyante (not as bad as it sounds) at a fairly precise ratio.  However, the ultrasonic flow meter will not work with the polyol.  The polyol we are using is the polyether type.

According to the manufacturer any polyol should not be a problem, nor should the viscosity be a problem.  Apparently they have used the same flow meters for honey and glycerin and they work well in those applications.

Why would the flow of polyether polyols not be able to be measured in an ultrasonic flow meter?


texts: How to make a micro water dripping pump with little or no electrical input?

texts:
I would like to make/obtain a micro water dripping pump, as a component of an item I am designing, to irrigate a plant with a water drop every few seconds in a closed loop.

With "micro" I mean few cm³ in size. I imagine this should not be bigger than a walnut.

I insist on a closed loop, meaning the system isn't connected to a water input like water tap or such.

What technology is available? I would prefer a system with no or little electrical input.

Would such pump come ready-made or would I have to make it myself from scratch?


texts: Pressure delivered to an object under a pneumatic press

texts:
I'm hoping some kind person can tell me if I have this right or not.  I swear this isn't a homework problem.

I'll be using a heated pneumatic press to heat seal lidding to plastic containers (imagine I'm sealing yogurt containers).  I need to verify that the machine I'm looking at can deliver a certain psi at the interface of the plastic and the lidding.  That interface has much less area than the total area of the heated platen applying the force.

From what I understand I take the pressure delivered to the machine, subtract the ambient air pressure, multiply by the surface area of the cylinder and then add the total weight of the platen to get the full downforce the machine is capable of.  From there I divide that by the surface area of the contact between the object under the press and the platen.

Please enjoy my wonderful art below (these are just random numbers):

So in this case the total downforce of the platen is:
(100psi - 14.7psi) * 1 sq in + 10 lbs = 95.3 lbs

And the force experienced by the red object under the press is:
95.3lbs / 2 sq in = 47.65psi

I feel like that's right but all my attempts to google for this answer only lead me to finding the total downforce of the press and not the force experienced by a smaller object under the press.  Do I have it right?  Thanks!


texts: How do you calculate the measurements for an hourglass?

texts: I'm trying to build an hourglass, but I don't know what all the specs are that determine exactly how long it takes a given volume of what material to finish within a certain time. Are there any hourglass equations anywhere?


texts: Definition of buckling as a sudden deformation

texts:
On Wikipedia, buckling is defined as follows:

  In engineering, buckling is the sudden change in shape of a structural component under load such as the bowing of a column under compression or the wrinkling of a plate under shear. If a structure is subjected to a gradually increasing load, when the load reaches a critical level, a member may suddenly change shape and the structure and component is said to have buckled.

Why do we define buckling as a sudden change in shape? This definition implies that a column is perfectly straight until we apply a load over a critical limit, after which the column suddenly curves sideways. But in real life, columns are not exactly straight and loads are not applied exactly to the center lines of columns so there is a bending moment on the column (and therefore everywhere in the column) for any load, not just a load above a certain limit.

Classical Euler buckling assumes a perfectly ideal column, and for that buckling appears as a bifurcation solution after a critical load is reached (and not before), but a real life column is not ideal and any eccentricity on the column or the load means that a bending moment is technically present for any load, however small.

So are real life instances of buckling not strictly speaking buckling according to this definition?


texts: What do we call these corrugated board sleeves put upon cardboard boxes to provide additional strength?

texts:
This kind of a sleeve from cardboard put upon a cardboard box is called обечайка (obechaika) in Russian. What do we call them in English? I was told on Proz.com that we call them "cardboard shells", is that so?
I was translating a text in which medical products were packaged into cardboard boxes with such additional shells to provide additional protection.
Such shells provide additional strength but sometimes such shells are made from decorative paper with fancy design and are put around, for instance, a box of chocolates to make it look more refined. These are also obechaikas in Russian.
Here, a cardoard box is slid inside an obechaika:

Here's another use of the term obechaika, a decoratice paper shell around a food product in a plastic container:

In this usage obechaika is more frequently called shuber, for some reason. The word is yet absent from Russian dictionaries, might be a new coinage.


texts: meaning of 1" baseplate fitting to mount to a standard 1" feedthrough port

texts:
I was looking at this page to figure out how I would install a manipulator onto my chamber.

It says 1" baseplate fitting to mount to a standard 1" feedthrough port"

So, I would have to have a tapped hole of 1 inch in diameter. I am not sure what the thread turn number is going to be.

In solidworks, I see that I have 1-12, 1-14, and 1-8.

Should I be able to assume one of the three just based on what they call "standard?"


texts: How to calculate the pressure a pipe can withstand?

texts:
I was looking at high pressure pipes and their pressure ratings. I'd like to know how these pressure ratings are determined.

I assume that pipes are tested until failure, and the failure pressure is multiplied by some safety factor to determine its 'rated' pressure, but is there a formula to calculate what the failure pressure should be before testing it (based on the material, wall thickness, diameter, or other measurements of the pipe)?


texts: I am trying to simulate multiphase fluid flow (gas-particle) through a electrostatic field. Are there any ways to do this in ANSYS?


texts: How can I match the angle of projection from a book illustration?

texts:
I have translated the part illustrated below into Solidworks but I haven't been able to match the angle of projection used in the illustration.

How can I identify that angle used in the image, so that I can reproduce the figure as closely as possible?

The drawing is from an old book by Thomas French.


texts: What is the definition of Ecm in equation 7.10 of EC2?

texts:
In the old British standard we use a time dependent modulus of elasticity of concrete to calculate crack width, which is usually about half of the 28-day Ec for long term modulus. In Eurocode EN 1992-1-1:2004, from clause 3.1.3, it seems that Ecm is defined as the 28-day modulus of elasticity of concrete.

Is this definition correct, or should the formula be interpreted as Ecm(t) instead?


texts: What sensors should be used to analyze vibration of a hard disk?

texts:
What kinds of sensors can be used to monitor the condition of a hard disk?

We want to be able to detect when a hard disk is not operating correctly.

Unexpected vibrations may be caused by spindle problems (probably low frequency), or by head crashing (high frequency).


texts: Is there any way to test a two-stroke carburetor for blockages?

texts:
I have problems with two stroke carburetors which I often end up solving by buying a whole new carburetor and replacing the old one. I think that somehow the orifices get clogged.
I have tried disassembling them and cleaning them in an ultrasonic cleaner, but it does not work.
Is there any way to test a small carburetor and make sure all the orifices are clear? The problem is that when I look at the carb it is basically a block of steel with a bunch of different holes in it, and it is not clear to me which hole connects to what so I have no way to tell if it has a blockage or not.


texts: Residual stress in circular shaft subjected to torsion

texts:
I am reading Mechanics of Materials by Beer and Johnston.The author points out if the torque in the shaft is removed the resulting reduction of stress and strain at a point considered will take place along a straight line .As was the case for normal stresses the shearing stress will keep on decreasing until it has reached a value equal to its maximum value at C minus twice the yield strength of the material.

Can anyone throw some insight into it?I am not aware regarding normal stresses as well.Thanks.


texts:
Just curious and working on some hypothetical problems on my own...I'm currently studying for my PE license.  Also, trying my best here with the Latex stuff.
Let's say there's a crude oil pipeline and it somehow gets a hole in it and begins to leak.  If you wanted to calculate the flow rate through the hole, my understanding is that you would approach the problem in the following manner:
$$ Q = CA_0\sqrt{2g_c\frac{P_1-P_2}{\rho}}$$
Where:
$A_0$ = cross-sectional area of orifice (leak hole) = $\frac{\pi*d^2}{4}$ = $\frac{\pi(2)^2}{4}$ = $3.14 in^2$
$P_1$ = 1,000 psi (pressure in pipeline)
$P_2$ = 14.7 psi (atmospheric pressure on outside of pipe)
$\rho$ = density of crude oil = 870$\left(\frac{kg}{m^3}\right)$ $\left(\frac{2.2 lb}{kg}\right)$ $\left(\frac{1m}{3.28ft^3}\right)^3 $ $\left(\frac{1ft}{12in}\right)^3$ = $\frac{0.031lb_m}{in^3}$
$g_c$ = 32.2$\frac{lb_m*ft}{lb_f*s^2}$ = 386.4$\frac{lb_m*in}{lb_f*s^2}$
So I get the following:
$$Q = C3.14in^2\sqrt{\left(772.8\frac{lb_m*in}{lb_f*s^2}\right)\left(\frac{\frac{985.3lb_f}{in^2}}{\frac{0.031lb_m}{in^3}}\right)}$$
Is this the correct approach?


texts: What mechanism do safety belts use to engage?

texts:
Earlier today I came across a creep testing machine that uses a safety belt as a mechanism for stopping loads from hitting the ground. It is probably the first time I saw a safety belt roll outside of a car and it got me wondering how do safety belts work?
What is the primary mechanism that they are using for engaging and disengaging? I expect it to be entirely mechanical in nature, however I can't put my finger on it.
Is it at all similar to the ratchet or the freewheel mechanism?


texts: Active noise canceling for CNC enclosure

texts:
this is my first post here! I wanted to share my ideas for this and get some input on them.
My parents were kind enough to let me put a cnc machine in the loft. (shapeoko 3 xxl)
In order to make them not regret their decision, I need to go to some extreme measures for sound deadening which are

Dual Pane extruded acrylic windows with a helium filled 3/4" gap in-between.
Active Noise Cancellation.

Helium, in as little as an 8mm gap, can provide tremendous sound dampening properties! up to 20db of suppression. the windows will be sealed with a nitrile adhesive as nitrile has a low permeability to helium. search "tech ingredients helium vs sound" on youtube to see demonstrations on helium's incredible sound suppression properties! you can also check out his active noise canceling demonstration too.
Active Noise Cancellation I will place electret-type mics on each wall of the enclosure with a piece of soft foam in-between the mic and the wall to decouple the microphone from the surface transducer which  will be mounted on the outside of the enclosure on each wall. the microphone signal gets sent to an amp, which then drives the transducer which makes the wall vibrate. we then wire it so the signal is out of phase thus canceling the vibrations. I already ordered two transducers and a two channel 50w amp (cheap class d one from amazon) and will begin testing this weekend.
Basically I need some input on the design as well as a few questions answered.

will the fact that the cnc machine is moving around the enclosure (the source of the sound is constantly shifting) cause any issues with the overall performance?

will the helium leak out at an inconvenient rate?  there will be two valves on the top and bottom of each window for helium filling and re-charging. all I need to do is use helium filled balloons as my helium source. Not sure about the permeability of extruded acrylic is to helium. the nitrile glue is supposed to be one of the best gasketing materials for helium as it isn't very permeable to helium. im hoping ill only have to "recharge" the windows every few months.

any general input and ideas would be much appreciate!


texts: Prolong frozen ground conditions (to trick fruit trees into flowering later)

texts:
There is a common problem with fruit trees in temperate climates where the trees flower before the last frost. Generally speaking, if the tree has flowered, and the temperature drops below freezing, the flowers die and do not produce fruit.

This is certainly not a new problem. It's my understanding that the problem affects almost the entire fruit farming industry in temperate climates.

I've heard that fruit farmers have large-scale commercial techniques that they use to mitigate the issue, such as:

Covering
Fog or smoke
Wind Machines
Sprinkling
Heating

While these methods might be practical for commercial farmers, not all of them are practical for small-scale urban farmers like me.

One technique that us gardeners often wonder about is:

Instead of actively protecting the open flowers, would it be possible to trick fruit trees into not flowering as early? In other words, keep the ground frozen longer than it would be naturally, to delay flowering (I'm making an assumption that trees don't flower when the ground is frozen).

While such a technique would likely be impractical for large-scale farmers, it might be resonably practical for small-scale gardeners.

Note: I imagine that there are more factors at play than just ground temperature. For example, the amount of sun, angle of the sun, and the temperature of the air might also be factors when it comes to the flowering timing.

I suspect that prolonged frozen ground conditions could significantly delay the tree from flowering (maybe by a couple of weeks) which would make a huge difference when it comes to avoiding late frosts from killing flowers.

Can I prolong frozen ground conditions to trick fruit trees into flowering later?

Idea:

An idea would be to insulate the ground around the tree with snow. The theory being that the insulation would prevent heat from the sun from warming up the ground where the roots are.

However, an obvious problem with snow is that it melts, and not always when you want it to. From past experience, I'm guessing that this pile of snow will mostly melt before it is helpful to me (before late spring).

Edit:

I'm dealing specifically with plants in the prunus genus:

Examples:

Prunus tomentosa
Prunus besseyi x prunus salicina hybrids
Prunus avium x prunus salicina hybrids


texts: To Which distance Punching Shear Reinforcement is placed in Mat Foundation?

texts:
As I know, a thinner mat may be possible by providing a nominal amount of vertical reinforcement as compared to a mat without vertical reinforcement, the vertical reinforcement is used to resist punching shear at d/2 from columns or shear walls at foundation level.

Now my question is to what distance (or offset) from the column to stop placing these vertical reinforcement is it at a distance d/2 ?

Please if possible provide reference in ACI Code.

What i need is the critical section outside slab shear reinforcement from which distance from the column ?


texts: What was that?! Quantifying the impact of a martial arts strike

texts:
Measuring things like a martial artist's strike can be challenging because it is a complex motion and common vernacular will use imprecise or incorrect terms.  This question is an attempt to identify the applicable measurements (quantification) and the correct units behind those numbers.

Background:
In a recent question of mine, I asked for sensors that could be used to measure a martial artist's strike, such as a kick or punch.  My primary intent was to demonstrate to the student how their technique improved their strike.  The answers there are great, and definitely addressed my question.

What led to this question is that I received a follow-up, clarifying comment asking if I wanted to measure force, energy, or power.  To which I responded that I simply needed something measurable to show the difference or improvement to the student.

There was a subsequent comment* that got me thinking:

  From what you write here, I would like to add that it is neither force nor pressure nor energy that you actually want to measure.

*The comment has since been deleted, but I started this question shortly after it was left.

What got me thinking about that second comment is while I've seen many references using units of force, there are other ways of quantifying a martial arts strike.

For example:

This reference prefers to use 'force' and condemns using 'pressure'
This reference also uses force, but mixes up their terminology when describing acceleration and velocity, so their usage of terminology is suspect.
This reference focuses on velocity, momentum, and energy.
This reference uses $lb_F$ for their measurements.  Coincidentally, this is the series that started me down my original line of thought with the other question.

My question:
What is the correct terminology for measuring (quantifying) the magnitude of a martial artist's strike versus another strike?

The measurement should be applicable across a variety of strikes (punches, kicks, elbows, etc...) and valid for different practitioners.  Likewise, I'm not worried about defining good versus bad; I want to be able to quantify the strike.  This ties into basic process improvement - we measure the process we want to improve and compare the measured results.


texts: Criterion to neglect poles of higher order

texts: If I am having a fifth order system,  it is said that the dominant two poles nearer to the jw axis  determine the nature of the output, is there any criterion to neglect the other three poles , should we neglect them even if they are just to the left of the dominant poles...


texts: Relation between engine's displacement (cc) to its power

texts:
I have looked at small engines. Once I saw Mitsubishi G350L (made around 1986), the displacement is 141cc, but it maximum power is only 3.5HP at 2200RPM. I saw another engine, Honda GX200, 196cc, 6.5HP at 3600RPM. And another amazing Bajaj (automotive maker from India) with its Qlue, the engine is 200cc but can produce 13.3HP at 5500RPM. Indeed they are different. But the difference looks to be too much.

My question is how come the engine power so different? What is the relation between the piston's displacement and its power? Those 3 engines are relatively close in the cylinder displacement.


texts: Equating $\frac{dp}{dt}$ and $F$ at a hydraulic jump?

texts:
A journal I am reading about circular hydraulic jumps provides the equation and I quote:

$H$ Depth after hydraulic jump, $h$ depth before hydraulic jump, $V$ velocity after hydraulic jump, $v$ velocity before hydraulic jump, $R$ radius of hydraulic jump.
The condition for conservation of momentum can be written as
$$\frac{dp}{dt} = 2\pi R\rho HV^2 - 2\pi R\rho hv^2 = F_1-F_2$$
where
$$F_1 = 2\pi R \rho g \int_0^hx\cdot dx = \rho g\pi Rh^2$$
$$F_2 = 2\pi R \rho g \int_0^Hx\cdot dx = \rho g\pi RH^2$$

I understand that units for $F$ and $\frac{dp}{dt}$ are both $kg\ m\ s^{-2}$, and that they are equivalent.
But I don't know how, in this example, $F_1$ and $F_2$ are derived i.e. where $g$ and the integrals come from.  Could somebody please explain?
Page 4 from: On the circular hydraulic jump


texts:
https://www.maxongroup.com/maxon/view/product/251601

https://www.maxongroup.com/maxon/view/product/gear/spur/gs45/301171

Consider that this motor-gearbox combination is backdriven so that the motor acts as a generator. My goal is to try and make a relatively accurate simulation of the losses/damping that occur due to the fact that it's driven in reverse. From what I understand, the total inertia of the motor felt by the output of the gearbox (now used as an input) can be calculated by the equation below where $I_{gearbox}$ refers to the mass inertia of the gearbox.

$I_{total}=r^2I_{rotor}+I_{gearbox}$

I know that motor cogging torque needs to be considered as does the friction in the gearbox, but I am unsure as to how this is done. My impression is that the most resistance comes from the friction within the spur gearbox as it is occuring to the point that it takes grown man strength to get it turning at all.

Are there specially designed gearboxes which are designed to work somewhat equivalently in reverse as well? I know that "planetary gearheads up to two stages or spur gearheads" should work but the efficiency is still low. https://drive.tech/en/stream-content/dc-motors-as-generators

Or would I be better off making a simple gear train with two/three spur gears? The driving torque would be quite low.

Thanks in advance for any assistance


texts: How to select a micro controller for a low power applications?

texts:
I am interested in a microcontroller for a low power application. I have been advise to look at MSP430 or Microchip PIC microcontrollers. I also wonder if ARM-Cortex-M0 is a good choice too.

At a high level the system will have two analog sensors, few GPIO to control LED, and actuation mechanisms. The systems is intended to be powered with standard batteries.

What are the critical parameters that warrant attention in researching for a suitable low power micro controllers?

Note: I posted this question on engineering SE and have not received any responses. I believe the question might be better suited for this forum.


texts: Am I calculating the power required and power out for a peristaltic pump correctly?

texts:
I am trying to design a peristaltic pump, in a spreadsheet where I can alter the tube and casing diameter, pump RPM and some other parameters, I'm wondering if anyone can spot anything odd in this method as in some conditions it seems to give a reasonable answer, and others not (ie: Power delivered greater than power required). My process currently is:

Calculate volume per revolution:

$$V = \pi^2\cdot\left(\dfrac{\phi_{tube}}{2}\right)^2\cdot\phi_{case}$$

Calculate discharge per occlusion:

$$Q = V\cdot\dfrac{2\pi\cdot RPM}{60}$$

Calculate flow velocity:

$$v = \dfrac{Q}{A_{pipe}}$$

Calculate Reynolds number (where $\nu$ is the dynamic viscosity):

$$Re = v\cdot\dfrac{\phi_{tube}}{\nu_{water}}$$

Calculate flow friction coefficient using Nikuradse’s experimental equation:

$$f = 0.0008 + \dfrac{0.05525}{Re^{0.237}}$$

Calculate flow frictional head loss using Darcy Weisbach equation:

$$H_l = \dfrac{f\cdot\ell_{pipe}\cdot v^2}{2 \cdot 9.81 \cdot \phi_{tube}}$$

Calculate torque required (where $\mu$ is the coefficient of friction):

$$\begin{align}
T =& (\mu_{roller} \cdot \text{tube re-expansion force} \cdot \phi_{i,tube}) + {}\\&(\mu_{roller} \cdot \text{tube re-expansion force} \cdot r_{crank\ shaft})
\end{align}$$

Calculate power required to drive pump:

$$P = T \cdot \dfrac{2 \cdot \pi \cdot RPM}{60}$$

Calculate total head loss assuming both ends open to atmosphere, using Bernoulli's equation:

$$H_t = \dfrac{v^2}{2g} + H_l$$

Calculate total power out (wher $\rho$ is the density):

$$P_t = \rho_{water} \cdot Q \cdot H_t \cdot 9.81$$

Seems to agree with similar projects to mine, but I get some odd results. Anyone got any ideas?


texts: I'm trying to replace connections between a trunk cable and drop cables in a DeviceNet system. The system is in a high humidity environment, so the current clamps used now are not holding up with the harsh conditions. The plan is to replace the cable with a round cable with t-port taps. The taps are IP67 rating, which can handle full submersion in water for 30 mins. I'm wondering though if it will still hold up in the high humidity environment which is constant. My question is asking if IP ratings correlate with a products ability to tolerate humidity.


texts: Dc motors for controlling wheels of a wheelchair

texts:
I am doing a project on controlling wheels of a wheelchair.
The diameter of the wheel is about 25-30 inches, the weight which the wheelchair is supposed to carry is upto 80 Kgs and it should run at a speed of 0.5-0.7 metres per second.
I thought of using a 24V dc motor, what speed and Power must the dc motor provide to move a wheelchair at above specifications.


texts: Trouble with Base circle and meshing with spur gears

texts:
I am a novice who is trying to make some gears. I have followed the formula's but sadly something seems to go wrong and the gear's don't come out right. Below is some dimensions and pictures.

Gear 1

Module(Diametral Pitch)(P) = 3,

Teeth(N)                   = 12,
Pitch Diameter(PD)         = 36,
Addendum(A) = MODULE       = 3,
Deddendum(B)               = 32.529,
Outside Diameter(OD)       = 39,
Root Diameter(RD)          = 28.5,
Base Circle(BC)            = 33.82884,
Circular Pitch (CP)        = 9.4248,
This produces a gear that looks "right" (small gear on right)
here is a link to my CAD file
https://cad.onshape.com/documents/e67e4eedf7e94a76c439bef0/w/4a5cb0732a0c5ca585fb5d87/e/2a98076fc77593239bb0eaa7

Now when i apply the same formula's to gear 2 i get a issue.
Gear 2

Module(Diametral Pitch)(P) = 3,

Teeth(N)                   = 40,
Pitch Diameter(PD)         = 120,
Addendum(A) = MODULE       = 3,
Deddendum(B)               = 116.529,
Outside Diameter(OD)       = 123,
Root Diameter(RD)          = 112.5
Base Circle(BC)            = 112.7628,
Circular Pitch (CP)        = 9.4248,
Pressure Angle             = 20 (for both gears)
Here is link to the CAD file
https://cad.onshape.com/documents/e67e4eedf7e94a76c439bef0/w/4a5cb0732a0c5ca585fb5d87/e/2a98076fc77593239bb0eaa7

The base circle and root diameter are practically the same ?!
The gear teeth look different but i have used the same formula's for both gears.
Here are the formula's i have used, just in case there is a massive error!!!!

Module(Diametral Pitch)(P) = 3 (Saw this number used so stuck with it!)

Teeth(N)                   = 40, (Wanted to try a bigger number)
Pitch Diameter(PD)         = 120, (Teeth x Module) (40 X 3)
Addendum(A) = MODULE       = 3,  (I hope this is true !)
Deddendum(B)               = 116.529, (1.157 x P(Module) = 1.157 x 3 = 3.471 =120 - 3.471 )
Outside Diameter(OD)       = 123, (Pitch diameter + Addendum)
Root Diameter(RD)          = 112.5 (Pitch Diameter - (2.5 X Module) = 120 - 7.5)
Base Circle(BC)            = 112.7628, (Pitch Diameter x COS (20pressure angle)
Circular Pitch (CP)        = 9.4248, (PI x Module)

Here are some pictures

The diameters you can see on the pictures are in order from the top of the tooth to the centre:
Outside diameter,
Pitch circle(pitch diameter),
Base circle,
Root diameter,
The images show the bigger gear with its base circle and root diameter practically on the same diameter. The smaller gear seems more in proportion
I set the Module(diametral pitch), which in this case is 3. I only used this number because I saw it used in a example Involving 12 and 24 teeth gears.
Does anyone think I should have change it as one gear is quite big (gear 1 is 12 teeth and gear 2 is 40 teeth) or is it just personally preference?
Did I use the module of 3 incorrectly for these gears?
I sadly forgot to mention in the original question the centre distance between the gears, which is 78mm. I am not sure if you would set the module (diametral pitch) based on the centre distance.


texts:
Consider two streams of air flowing through the nozzles to an unlimited volume with atmospheric pressure.

The flow is the same, but the cross section areas of the circular nozzles and the speeds differ, so the flow through the smaller nozzle is proportionally faster.

Intuitively, the stream which is faster at the nozzle would transfer the air farther.

Is there any empirical rule which can be used to measure air stream dissipation rates given the initial speed and nozzle cross section area?

I am aware of Lattice-Bolzmann numerical methods, and can run the experiments too, but as i am new to air dynamics, may be I am overlooking something obvious.


texts: Generating NACA airfoils with three digit maximal thickness numbers

texts: I have two wind turbine blades, one that that consists of NACA 44xx airfoils and the other NACA 63-2xx airfoils. Some sections of these blades have airfoils whose maximal thickness are specified by three digits, such as .247c (where 'c' is the chord length). Is there any program that will allow me to plot such an airfoil?


texts: Different calculations for values of thermodynamic properties

texts:
While deciding what tool (library) to use for a simulation of a hybrid gas turbine plant, I found that different libraries/tools of thermodynamic properties yield different values than the other.

I made a simple test to calculate $c_p$ of air at $300\ K$(same goes for enthalpy by the way) only for simplification and comparison and here are the results.

Source              |    Cp at 300 K (J/kg.K)
--------------------------------------------
Thermopy  (python)  |   1004.89
Cantera   (python)  |   1010.06
CoolProps (python)  |   1006.627
EES Software        |   1005
Engineering Toolbox |   1005
Incropera's book    |   1007
Cengel's book       |   1007

What do you think is the reason for the difference in values?

Apparently the one closest to the properties sheets from Incropera and Cengel is CoolProps but is this level of accuracy sufficient?

The case might not be convincing for $c_p$, but it did occur to me once while calculating adiabatic flame temperature of some fuels and the error were in hundred Celsius range!

Link : used Python code


texts: Can a system with a response Y(x) = ax + c be called linear?

texts:
I made a DC-DC converter its  ideal transfer function is:
$$  V_0(D) = DV_i  $$

I took measurements of its response and then made a linear regression, I got this result:

$$ V_0(D) = 0.98DV_i -0.42 $$

Quite similar to the expected value. Now, can I say that the system has a linear response?

strictly speaking, the system response should be zero when the input is zero, but in this case, if D = 0:

$$ V_0 = -0.42 $$

What would be the correct way to refer at the response of this system?

Edit:

Here is a plot of the theoric response, red, vs experimental values green.
The 0.42 basically represents an offset because the losses of the system.


texts: Thermistor - Steinhart-Hart Coefficients

texts:
In order to identify Steinhart-Hart coefficients for a thermistor, three known temperatures may be used to find three resistances.

What is the best way to choose these temperatures to calibrate from?

Is it more beneficial to use three temperatures within the typical operating temperature of the thermistor, or to take a broad range of temperatures (say 0, 50, and 100°C)?


texts: Why are moulds sometimes dimensionally larger than the metal components they make?

texts: I have this question and I can't seem to find any sources which I can used to determine a potential answer.


texts: How do british standard pipe parallel (BSPP) (G) threads seal?

texts:
I realize that there must be some sort of o-ring, gasket, or washer, but from an engineering standpoint it is not clear how to know what fitting will seal to what without having the parts in front of you and experimenting.
Most plumbed components from outside the US come in this standard, but there are never any o-rings provided or recommended. Surely there must be some specifications for each type and their respective pressure ratings.

This pipe thread comparison article indicates using a copper
crush washer at the male face.
Wiki shows a fitting with a rubber o-ring at the root of the
male threads.
ISO 228 exists, but like all these standards to have to buy it.


texts: How do the constraints imposed on a material increase the stiffness?

texts:
As the title of this post says, how do the contraints increase the stiffness. For example, I was doing an exercise where I had to calculate the deflection on a rubber block with and without deflection and they mentioned that "the constraint increases stiffness by a factor of 1.33 (for v=0.5)" where v is the Poisson's ratio. So, where does the 1.33 come from and what are the effects of the constraints.
I understand that imposing constraints will make it harder to stretch/bend, but I do not understand how they came up with 1.33
Thanks!


texts: Why doesn't stovetop glass crack from thermal shock?

texts:
I have a feeling that if my stovetop was made out of regular glass, it would have cracked from rapid cooling/heating a long time ago – especially if you consider accidental water spills. What kind of glass is able to withstand such abuse?
(I am just looking for terms to google for further reading.)


texts: Gradient of refractive index at very short distances

texts: I have only taken standard (basic) level math courses in high school and had learned only the fundamentals of wave and ray optics in physics classes. Therefore, Im asking only for a very general answer: Is it possible that lens consisting of a flat plate with a very high refractive index gradient (maximal n=2.7, minimal n=1) going across the plane of the lens, with thickness equal to 20 wavelengths be used to refract a laser beam, or is the scale too small for the behaviour of the light to be predicted from the law of refraction?


texts: Question about how to couple round servo shaft to flat shaft

texts:
I'm looking to control a commercial deadbolt using a small servo, motor, or gear motor. The deadbolt has a common Schlage cylinder such as this one that has a flat shaft that runs through a slotted hole in the deadbolt. In this diagram the shaft is labeled 'tailpiece' and is connected to the thumb-turn on the inside of the door.

Most servos and electric motors come with short, round shafts on the end of them. Presumably in common usage a gear or cam is mounted to that shaft with a screw. For this situation, it would be convenient to couple the two shafts directly together inline, such that the motor would replace the thumb-turn.

I'm not in any way a mechanical engineer, so I'm really grasping at straws but I think what I need is a shaft adapter/coupling? Something that would encase the round shaft of the servo on one side and the flat shaft of the lock cylinder on the other and clamp down on both.

Alternatively the server / motor could be mounted perpendicular to the flat shaft and two gears could mesh to make a 90 degree angle. I don't have anything to measure torque properly, but I know the thumb-turn is not quite an inch in radius and it takes more force to turn it then it takes to pull a stiff trigger, so probably 5-10 lb inches? I feel like the gear-based option might not stand up to that. Then again, the whole lock set could do with some grease. It's an old house.

Another thought I just had was a through-hole motor. Or servo. Do they make through-hole servos?

This is a one-off solution for home application, but I'll document it and share that documentation so it'd be nice if the solution was broadly applicable to common lockset configurations. I'm leaving the standard keyway on the outside of the door for power outages. It may be hard to turn due to the servo on the other end, but it would be infrequently used.

Now that I've disassembled it and refreshed my memory of what it looks like on the inside, I realize there's a second option. The thumb-turn engages the lock cylinder via a component that I don't know the name for. On the thumb-turn side it's a washer with an oblong inner diameter. On the door side it's a collar with a matching outer diameter.

Here's some photos of the actual parts: https://imgur.com/a/wX0BDVf

I could potentially make a wood part that fits over the door-side collar and could screw into the arms of a servo motor. Might be easier than a shaft-coupler.


texts:
I would need to stick two opposite edges of a sample on two small metallic plates (as it were a bridge).
The sample is Silicon and on top an high temperure superconductor which is Temperature sensitive. This means that the procedure is done at -40 degrees maximum.
I tried to use U300 epoxy, but this does not work since the reaction of the two components is not activated at this low temperature.
Do you know a special glue that can work? Please be aware that I will perform experiments at few Kelvin, so the glue (or whatever) should be cryo.


texts: Would it make sense to have a 12V lighting circuit in a house?

texts:
Modern LED bulbs must convert the standard household supply (for example $240\text{V AC}$ in the UK) into a DC supply at a lower voltage (usually $12\text{V DC}$ I think) for the LED array. This is done on a per-bulb basis.

Does this waste much power in the conversion?
If all of your bulbs are LED bulbs, would it make sense instead to have a $12\text{V DC}$ circuit for lighting around the whole house and LED bulbs without the per-bulb conversion?


texts: How to sense displacement without using any camera?

texts:
I am working on a hand-held prototype model in which I need to fix motor RPM below a certain displacement. For example, if overall displacement is within 5 mm then the motor should be running at a fixed RPM.

After getting this done (I mean if displacement is > 5 mm) I wish to work on sensing the linear acceleration of the hand-held prototype. I will use this data to control my motor's RPM again. Typical hand-held displacement range would be around 5 cm to 30 cm in 2 sec.

Someone suggested to use IMUs to sense acceleration and rotation but I am not sure how to design my prototype to utilize an IMO. How can I select an IMU and determine an appropriate sensitivity level? References to relevant literature would be very helpful.


texts:
I was reading about Automotive Brakes (Chapter 52, Automotive Mechanics by William H Crouse, Donald L Anglin, 10th edition). And in a section about drum-brake self-adjusters, it is said that the incremental self-adjusters are attached to the secondary shoe of a duo-servo brake; The adjustment is made when the vehicle is moving backwards and the brake is applied. And then the mechanism of how the adjusting lever and adjuster spring follows the text.
What I don't understand is why the secondary shoe? It only seems reasonable since the adjuster is doing its work while the vehicle is in backward motion. But then, why the adjustment only happens in backward motion?


texts: controlled depositing of goo with a syringe

texts:
I was thinking about this kickstarter project where they print circuit boards, and later they show it printing solder paste.  I've seen other liquid or paste dispensing systems like this too, maybe for medical or chemical uses.

My question is how do you make a system that dispenses a known amount of paste like that?  I get that I can run a motor and put pressure on top of a syringe and goo will come out of it. Maybe a stepper with some gearing?

Is there a feedback mechanism?  It seems too small to have some kind of flow meter there.  Are these kinds of things just open loop and you calculate the volumes ahead of time and just crank down the motor accordingly?

You must have to get it to some baseline first though, like a home position where paste is at the bottom of the nozzle.

Just curious how these things work.


texts: What controls the gain in a BJT amplifier, and why does this circuit have a gain of unity?

texts:
In the case of the first circuit, The ratio between the input voltage Vin and the voltage at the collector and the ratio between the input voltage Vin and the voltage at the emitter are supposed to be around 1.

In the case of the second circuit, the ratio between the input voltage Vs and the voltage at the output Vout is around 30.

My understanding of the circuit (please correct me if this is incorrect):

I know the purpose of the resistors in the center region of circuit 2 is to bias the transistor and make it operate at a specific Q-point.
The purpose of the 10uF capacitors is to filter any DC component of the input and output signal, as well as to prevent changing the biasing.
The capacitor across Re is a bypass capacitor, which is supposed to prevent the AC component from affecting the gain through negative feedback.
The purpose of the emitter resistor is to provide negative feedback.
The purpose of the collector resistor (and I am not sure about this) might be to limit the current from the source.
The purpose of the resistor at the output (I am not 100% sure about this either) might be to work as a load
The resistor next to the input signal Vs is used to step down the voltage of the signal, as to use a small signal model in the circuit instead of having to use the large signal model.

Assuming the following: a beta (Ic/Ib) of around 250, R1 of 75k and R2 of 33k for both circuits, and an input voltage Vin of 4 volts peak to peak with a frequency of 1khz for the first circuit,

What controls the voltage gain in circuit 1 and 2 at the collector, and why is the gain in the first circuit only 1?


texts:
This is about linear time-invariant, stationary problems.

According to Donald Kirk's book Optimal Control Theory, for minimum-fuel problems on page 299, I was told that if there exists a singular arc, then the controllability matrix is singular or the system matrix $A$ is singular. However, the controllability matrix being singular (or the system matrix $A$ being singular) does not imply a singular arc's existence, according to this source on MIT OCW.

On the other hand, for minimum-time problems, on page 296, the system is controllable if and only if there are no singular arcs (it is also mentioned by the MIT OCW lecture notes). How can one mathematically prove these?

I have seen the proofs of singular arcs being the sufficient condition, but how can one prove that it's a necessary condition for minimum-time (but not for minimum-fuel)?


texts: What is the relation between the Biological oxygen demand and the depth of water tank?

texts:
I need a relation between Biological oxygen demand and depth.

The ultimate [BOD] is known, and I need to calculate a [BOD] at any depth of water tank; temperature is constant. The tank is two meters deep and the incubation lasts seven days.

Ultimate biological oxygen demand is 0.05 mg/L.

I need constant-rate equations for deoxygenation and biological oxygen demand.


texts:
Let's say that I have $14$ regular matrices of order $4$.
I'd like to compare the data of each matrix
with all 13 others to see if there's a match

Is there an algorithm that can accomplish this task?

I'm more interested in the algorithm and not any particular
programming language.

[EDIT]
In response to the first comment, a match would be if all rows and columns of the matrix are the same, small 2x2 example.

 m1       m5
|00| === |00|
|00|     |00|

 m3       m1
|00| =\= |00|
|01|     |00|

 m2       m1
|10| =\= |00|
|01|     |00|

 m2       m4
|10| === |10|
|01|     |01|

It would continue like this for 16x16 but in the end I could get a list of matrix that maches
m1 matches m5
m2 matches m4
m1 doesn't match m3, etc...


texts: Why are there no fully diesel electric cars?

texts:
Diesel electric locomotives seem popular, even these days.  The UK's Type 45 destroyers have tried integrated electric propulsion, and I think that there are hybrid motor-generator cars that can recharge their battery.

There clearly seems a steady move towards transforming more and more power train components to electricity in all sorts of vehicles. Assuming that we don't attach over head wires and a pantograph system to Volvos, the next best thing seems fully diesel electric power. No?


texts: Average Nusselt number or heat transfer coefficient to compare better heat transfer?

texts:
I'm simulating different arrays for cylinders in a simple cross flow heat exchanger (cylindrical pipes) as shown below:

Inlet temperate(300K) is constant and the cylinders are at constant temperature(400K).

I'm simulating different arrays for cylinders.

I've calculated average Nusselt on each pipe then summed all of them and finally divided it by the number of cylinders (9).

This gives me an average Nusselt number for heat exchanger. Let's call it $Nu_{av}$.
$Nu_{av}=\frac{\sum Nu_{cylinder}}{9}$

I also calculated the heat transfer coefficient of heat exchanger using the following equation:
$\dot{m}c(T_o-T_i)=UA(T_s-T_i)$

$\dot{m}$: Mass flow of fluid passing the heat exchanger

$c$: Specific heat of fluid

$T_o$: Average outlet temperature

$T_i$: Average inlet temperature

$U$: Heat exchanger coefficient

$A$: Total surface of all cylinders

$T_s$: Cylinders surface temperature

I've simulated a lot of arrays. In some cases, the average Nusselt number($Nu_{av}$) is bigger and in some others, the average outlet temperature and so, the heat exchanger coefficient($U$) is bigger.

My question is: Which one should be my criteria to compare cases? Average Nusselt number or heat exchanger coefficient?


texts: What criteria to focus on when selecting a BLE module?

texts:
I am trying to select a BLE module for low power application. I have looked into different BLE modules from different chip manufacturers. For example:

ISM78G1D Bluetooth Low Energy SIP from Inventek
Blue Gecko BGM13S Bluetooth® Module - SiP from Silicon Labs
SimpleLink Multi-Standard CC2652R Wireless MCU from TI
EZ-BLE and EZ-BT Bluetooth Modules from Cypress
nRF52840 from Nordic Semiconductor
Samsung ARTIK™ 020

I am in the process of learning strategies on selecting a BLE module given a few choices. The application will be used in a low power application which includes a sensor to detect objects. We plan to connect the BLE module to the host micro-controller controlling the sensor. The BLE module will communicate to a Gateway (currently being defined) that will transmit the data to the cloud.

Appreciated if someone can provide some guidance on what criteria to use when selecting a BLE module. Thanks for your help!


texts: Why does column buckling occur when the load is parallel to the column?

texts:
I'm studying Euler's work on structural engineering from a book out of curiosity and it is mentioned that he developed a mathematical theory describing the buckling of columns under a parallel load (the weight-force of the load is directed down along the column). The theory is covered quickly without much motivation.

But this got me thinking; why does a column "buckle" in the first place? If the load presses the column down, why does the column even start deflecting sideways? I know this happens in real life since this fact is easily confirmeable with household objects, but theoretically, why do objects start deflecting sideways instead of just compressing under loads? This might be something obvious and maybe I'm just overthinking but I find this curious nonetheless.