texts: Minor Losses Pipeflow Momentum vs Steady Flow

texts:
First post in the engineering forum

The Problem Statement
I have designed a prototype agitator tank - its a circular square duct like pipe filled with incompressible liquid (acetone/water) which spins on a vertical axis.

I had intended to build fluid momentum thru viscous action (achieving something akin to solid body rotation) then rapidly stop the pipe body hoping the fluid momentum will continue to circulate a flow for a time until viscosity degrades it

I have calculated all the minor and major losses in the 'circuit' and they indicate that viscosity should degrade quite slowly but experimenting it appears that the fluid stops flowing almost immediately.

My Question

Have I miscalculated the losses as the K-values I have used as they appear derived from steady flow.

$h_{Minor loss}= K.\frac{v^2}{2g}\ $

Is there a difference in how the relative velocity $v^2$ to the pipe is developed

NB: Interestingly it does not require any more force to stop the full tank than the empty one so I'm really confused as to where this fluid momentum is going.
Additionally no matter how well I fill it (displacing all air , putting under pressure) I can still hear 'sloshing' when I stop the body, is there some sort of cavitation going on ?


texts: Biological process in wastewater treatment

texts: Biological process is the secondary stage in most of wastewater treatment plant. Is there any wastewater treatment plant without undergoing biological process?


texts: How to handle modal combination in response spectrum analysis for member forces for member with more than 1 element?

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My textbook says for mode combination, the peak value $r$ of each response quantity is determined by combining the peak values $r_n$ of the modal contributions to the same response quantity.

From what I understand, this means that we have to calculate the response (be it displacement, the difference in displacement, the forces or moment) for each mode first, before we apply the modal combination method such as SQSS, CQC and ABS in order to obtain the total response.

This is also verified by the numerical example in the textbook.

However, in the textbook example, all the members are 1-element members, easy to interpret the above clause in the textbook. What about members (beams, columns) that are of more than one element? In FEM we often create a single member out of multiple elements.

Do we combine the element response into member response on per mode basis first, before we combine all the member modal responses into total member response?

Or do we combine the total modal response for each element, and then only combining the element response into member response?

In other words, is the modal combination done at element level or at structural member level?


texts: How is the detailing of the intersection between two RC beams perpendicular to each other?

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In the below picture I want to design B4 and B6 but I am not sure which one does support the other and how the detailing of the area of intersection between these two beams?

Is it better that B6 supports B4 because B6 have the shortest span?


texts: Temperature change during phase change of water

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Suppose we have a mass of water at room pressure and temperature, then we started heating the water.
What will happen to the temperature if we decreased the pressure while the sample of water is undergoing phase change from liquid to vapor(keeping in mind that heat is being added all the time)?
My book ( thermodynamics by Yunus A. Cengel) says that the temperature would drop but the book does not provide explanation.


texts: Driving many parallel shafts from one motor

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Is there a preferred solution to the problem of driving parallel rotary shafts from a single motor?

I have six shafts that I want to drive from one motor. The shafts are all:

rotating the same direction
parallel
planar (although this is not a hard constraint)
low speed and moderate torque (~100W/0.1HP)

If I were to wrap one timing belt on pulleys around each shaft, most of the shafts would have very low contact angles and would likely slip. Running six timing belts, one from each shaft to the motor, is ungainly and expensive. Gearboxes would be difficult to align, have low efficiency (40-80% from my research), and require frequent maintenance (lubrication).

This seems like it must be a solved problem, but none of the solutions I can find seem very elegant. Any suggestions?


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I have an underdamped control system for a DC motor. It is only a mathematical model so I can't visualise the motor.

I can change the value of the "k" or compensator. I have noticed that changing this value changes the frequency of oscillation in the step response.

I was wondering what the effect of increased oscillation in a control system would be on a DC motor?

Thanks!


texts: Is there a way to permanently change all the decimals in AutoCAD to 2?

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For example
1.5678
I would like to change to
1.57
Permanently, meaning that every time I open another project, all the digits are in 2 decimal places only.
is there a way to make it like that?


texts: How is the attractive force between two magnets changed when they are separated by non-metalic solids?

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I recently encountered the following practical problem. We have a system of several layers:

a neodymium magnet; a disc, dimensions and grade to be determined
1 mm of 925 sterling silver; we can suppose that this is a disc, diameter 15 mm
0.5 mm of paper or tissue (cotton)
1 mm of the same silver disc
again, a neodymium magnet

How can I estimate the attraction force between these two magnets in this system based on their dimensions and grade? I found several estimators online (this one, for example) but they all assume that there is nothing between the magnets.

Even being able to estimate "X mm in diameter and Y mm in thickness would yield at least Z grams of pull" would be great.


texts: How To Assign Different YoungsModulus To A Multi-material Mesh?

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I have a mesh designed in Blender and I am using SOFA Physics engine simulator (based on FEM), however, I don't know how to assign different YoungModulus to a mesh like mine since each parts are interwined. It would be easier if I have two separate meshes e.g. encapsulation.
Do anyone has any idea how to assign different E for a multi-material mesh?


texts:
I'm planning to drive a small linear guide (4cm long) with a servo in a setup like this:

I wonder if the ball bearings inside would sustain too much stress due to the vertical forces exerted by the links whilst driving it linearly. AFAIK ball bearings can support reasonable radial load, but I'm aware that these guides are usually driven by lead screws instead. Is it a good idea to drive the guide the way presented above?


texts: Can I use a ultrasound sensor to measure water level?

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If I use an ultrasonic sensor will it detect the water level?

I was thinking about a product to read water level on water boxes (common in Brazil). I researched about instrumentation for this measure, and I think that an ultrasonic sensor is the best option. Will the water correctly reflect  ultrasound and not change the normal measurements against a solid obstacle?


texts: Should a welded connection between strut and waler be designed to take compression load?

texts: Temporary structures are usually constructed in a less precise manner than permanent structures. This is more so in a braced deep excavation where the walls are in constant motion as the excavation progresses downwards. During the assembly of walers and struts, there could be a small gap between the strut-waler connection due to fabrication imperfections. How does one decide whether the fillet weld connecting the strut to the waler need to be designed against compression due to possibility of such a small gap?


texts: Inductor/Transformer core design - reducing losses from eddy currents

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From what I know, the key to reducing losses due to eddy currents in a core is to reduce the path that they take, as is shown in this diagram illustrating solid vs. laminated cores (courtesy of Wikipedia).

Would taking this one step further and making the core a bundle of wires/rods instead of a stack of laminations reduce the losses further? If so, then why aren't there any commercial designs using it?


texts: How does load force impact load inertia?

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I am trying to simulate a winch as a speed-regulated motor that works through a gearbox to lift a mass. The output of the gearbox is a drum, which rotates to accumulate cable.

I feel comfortable converting the mass to a moment of inertia and I also feel comfortable with converting that moment of inertia (output-side) to the moment of inertia "seen" by the motor (input-side) with the gearbox ratio. With a simple simulation, I have no problem writing the equations of motion.

My complication comes when I want to model "stretch" in the cable. I thought I could do this by simply putting a spring of arbitrary stiffness between the winch drum and the mass, as pictured below.

With this model, for the sake of simulation, I'm assuming I know the "drum height", which would be how far the drum has turned multiplied by the drum radius, and the height of the load. The spring force would be $k(\phi r - y)$, but how do I apply this to the motor?

I have a motor model:

$$
\frac{\Theta}{V} = \frac{K_T}{R_a Js+K_T K_b}
$$
and a PI controller model:

$$
\frac{V}{\Theta_\mbox{error}} = \frac{k_p \left(s + \frac{k_i}{k_p} \right)}{s}\\
$$
where $\Theta$ is the motor speed, $V$ is terminal voltage, $J$ is the inertia of the load and machinery, and $R_a$, $K_T$, and $K_b$ are the motor armature resistance, torque constant, and back EMF constant, respectively.

The interaction I'm interested in studying occurs when the PI controller is tuned to the anticipated load inertia $J$, which would be found with the motor, gearbox, drum, and load mass, but the system actually "sees" the springy-mass.

Simplification is done by setting the $k_i/k_p$ ratio equal to $K_TK_b/R_aJ$, giving:

$$
\frac{\Theta}{\Theta_{\mbox{error}}} = \frac{V}{\Theta_{\mbox{error}}}\frac{\Theta}{V} =
\left(
\frac{k_p \left( s + \frac{K_TK_b}{R_aJ} \right) }{s}
\right) \left( \frac{\frac{K_T}{R_aJ}}{s+\frac{K_T K_b}{R_aJ}} \right)
$$

(Note I can leave $k_p$ as variable because the ratio $k_i/k_p$ can be set to whatever I want via $k_i$ as long as $k_p$ isn't zero.)

So, in an ideal world, where the value of "total" inertia $J$ is known in advance, the pole cancels, and the entire system reduces to:

$$
\frac{\Theta}{\Theta_{\mbox{error}}} =
\left( \frac{k_p}{s} \right) \left( \frac{\frac{K_T}{R_aJ}}{1} \right) \\
$$
$$
\frac{\Theta}{\Theta_{\mbox{error}}} =
\frac{1}{\frac{R_aJ}{k_pK_T}s}
$$

Finally, $\Theta_{\mbox{error}} = \Theta_{\mbox{ref}} - \Theta_{\mbox{out}}$, so, with algebra:

$$
\boxed{\frac{\Theta_{\mbox{out}}}{\Theta_{\mbox{ref}}} = \frac{1}{\frac{R_aJ}{k_pK_T}s + 1}}$$

So, kind of sorry to shotgun so much detail, but I wanted to impress on anyone reading that I feel confident with all of my steps so far and that I have spent considerable effort working on this problem. Now, again to my question - I want to simulate stretch in the cable between the drum and the load, but I'm not sure how to use the spring force to modulate load inertia.

One thought I had was to try to fake an "equivalent mass", by assuming:

$$
F = m_{\mbox{equivalent}}a \\
m_{\mbox{equivalent}} = \frac{F_{\mbox{spring}}}{a} \\
$$

but this doesn't feel right, and I'm not sure what I would use for acceleration $a$.

I'm frustrated to be this far along on the problem and getting stumped by what seems like should be an easy issue, but I really can't think of a way to approach this problem. I think if I could frame it correctly I could work out the mechanics, but it's the force-to-inertia conversion I feel like needs to be made that has me stumped.

Finally, for the record, I have also tried back-tracking my motor model to include the load torque. This gives seemingly-reasonable results, but in the end I subtract the load torque from the motor torque to get net torque, then apply that net torque to the total inertia to get motor acceleration. That feeds on down the line and, again, I'm not sure that I'm treating total inertia correctly.


texts: Boiling Point, Pressure and Distillation

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I have a line in my text that states the following:

"For systems with low boiling points (e.g. Ethane-Ethylene, propane-propylene etc.), high pressures are used so the vapour leaving the column at the top is cooled by water."

I don't understand the utility of high pressure over here. Isn't usage of water in the condenser already the case?


texts: is it possible to find all the support reactions of this continuous beam using fourth order equation without using principle of superposition?


texts: Stresses exerted by cutlery on a cylindrical utensil holder

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What forces of torsion, compressive stress, and tensile stress are exerted by cutlery on a cylindrical utensil holder?

Also lets suppose that the holder is tightly packed. Is there a maximal tensile strength it can withstand?

I really don't know how to approach this question quantitativly....


texts: Measuring viscosity with tools other than viscometer

texts: I would like to measure viscosity, but do not have access to a viscometer. If possible, I would like to avoid having to purchase one. I have access to many other  flow measuring devices, including flowmeters, pressure sensors, and a turbidimeter, and was wondering if taking measurements with these would somehow allow me to make, at the very least a proportional measurement to viscosity (I only need relative measurements between different fluids, exact specifications are not necessary). I dont have reason to believe these liquids would behave significantly non-newtonian, and they would likely all be water with additives such as salt and detergents.


texts: Low maintenance device to trade flow rate for lift height?

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Is there a compact device which can trade flow rate for lift height without too many moving parts?
My particular application is a 10 meter deep and 10 centimeter wide well with shallow water level, therefore the usual high-powered well pumps run dry too quickly. Submersible pumps with low flow rate, high working lifetime and sufficient pressure do not seem to exist. But even if such pumps did exist, I would still be interested in an answer from an academic point of view. Maybe there is a solution without any moving parts at all? That would be neat!
Ideas I discarded so far:

A hydraulic ram pump seems to requires a high flow rate and long feed lines.

Daisy-chaining multiple small pumps with low pressure multiplies failure rate. (I tried five pumps of type AD20P-1230D with a head of 2 meter each, but the rated 50,000 hours lifetime is highly optimistic.)

A water wheel driving a chain pump sounds like a maintenance nightmare due to the mechanical nature of the chain pump and it is also not very compact (disregard the cow in the following illustration).


texts: Are rocket engines practical for commercial aircraft?

texts:
What are the prospects of seeing rocket engines become the standard for commercial aircraft?  It might be a dumb question; I really don't know all that much about the topic.  The reason I ask is that rocket powered aircraft are much faster—and who doesn't like speed?

My concerns are:

I don't know whether there any designs that would be economical.  I understand rockets burn a tremendous amount of fuel and that is obviously a limiting factor.
There could be safety concerns.  Just because we can do something doesn't necessarily make it a good idea.  We have seen the struggles Musk has had with his rockets.

We keep hearing about all these super trains that can get us from Chicago to NY in an hour, even though the whole idea of traveling on a track at those speeds seems quite dangerous.  However, up in the air there is nothing to hit, which is a different story.


texts: The oil spill in Mauritius would be caused by cracks in the hull. How can this happen? Is it possible to be caused solely by rough weather?


texts:
I prototyped this attractive wooden sit/stand laptop stand

but ran into a problem keeping the legs tight enough to hold their position. There are 1/16" thick EPDM washers between the oak legs - the washers are almost 1.25" in diameter with a .25" hole for a threaded tension rod. If I want to resist about 15 lbs of force on a 8" lever arm, that's only about 10 ft-lb of torque that I need to resist. What the hell, let's say 20 ft-lb.

I tried to find a toothed washer that I could use in pairs, each one epoxied to one of the oak legs, but couldn't find a suitable design. (For example the Nord Lock wedge locking washers won't work because they are directional. They will work on one side, but on the other the rotation will be in the wrong direction.)

What alternative material(s) should I use which might resist that rotation?


texts: we currently need some help in analyzing the real (!) content of our design files of Solidworks 2018. Recently we are faced with ghost-parts within our assembly files. Unfortunately, support is not able to solve the issue by now. Since version 2015 the files are no more based on MS-CFB (Compound File Binary File Format). Does anyone have an idea how to explore the file contend? Greetings


texts: Solving for stiffness matrix numerically by a set of measurements

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Is it in general possible when you have a mechanical structure (in this case I am referring to the structure in this post) and you want to determine the global stiffness matrix of this structure, to solve for the matrix based on measurements?

More specifically, I have a structure where parts are connected by springs. I apply a known force to one of the parts and measure the displacement. In this way I get $n$ force/moment - displacement/rotation pairs.
Is it possible to solve for a matrix $K$, for

$F = KX$,

with $F =\begin{bmatrix}F_x & F_y & F_z & M_x &M_y&M_z\end{bmatrix}$ and $X= \begin{bmatrix}dx & dy & dz & \theta_x &\theta_y&\theta_z\end{bmatrix}$?

Is this feasible from a mechanical point of view, because e.g. this "stiffness matrix" $K$ may not be unique according to the load applied?
Are there any constraints or requirements regarding the measurements?

P.S. Applied forces are rather small (within the elastic range of the spring) and the displacement is restricted, so no large deflections should occur. This is why I assumed a linear approximation.


texts: Does kevlar (composite materials ) have elasticity?

texts:
Can we use kevlar, a composite material in leaf springs.  I mean does it have the properties which are essential for a leaf spring (like resistance to bending, elasticity)

if it has, are(properties)  they sufficient in case of heavy vehicle leaf springs?


texts: Maximum hole size in brickwork before a lintel is required

texts:
Holes are made in brickwork walls for all kinds of reasons including gas flues, to route cabling and to fit windows. At some point that hole gets large enough that a lintel is required to support the brickwork above.
My questions are:

My theory is that the height of the hole is not relevant as to
whether additional support is required. The only important factor is
the width of the hole. Is this correct?
Is a circular or rectangular hole preferred?
Does the type of construction i.e. cavity wall, double leaf solid wall, single leaf wall make a significant difference?
What is the maximum width of the hole before additional support is
required?


texts:
Basic Googling on the mechanical generation of oscillating motion (moving something back and forth in the manner of a windshield wiper or a flapping wing) from a source of circular motion comes up with a concept known as a "four-bar linkage" or "crank rocker".  For example, this video shows very clearly a simple way to create a windshield-wiper motion:

Crank-Rocker Four-Bar Linkage

The problem is, this doesn't look anything like a windshield wiper.  It has a bar attached to the tip of the "wiper" pulling it back and forth along its arc.  But in an actual windshield wiper (or wing, for that matter) the moving force comes from the base, not the tip.

So how do you go about generating oscillating motion from the base of the oscillating device, windshield-wiper style?  Assume you're starting with a motor providing circular motion, as in the video.


texts: Will circulating air within a sealed ductwork system cause it to implode?

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Referring to the pasted in ductwork diagram, if an inline ventilation fan with a high CFM airflow was used to circulate air within a sealed ductwork system, would the fast moving airflow result in a significant pressure drop within the ductwork and cause a section of it to implode?

Or since it is a sealed system and air can neither leave nor enter it, would the result be that the fan would essentially just be circulating pressurized air around the ductwork and there would thus be no pressure drop within the ductwork? Referring to the ductwork diagram again, would static and dynamic pressure (in PSI) at points A, B, C, and D be approximately the same if measured first with the fan turned off and then measured again with the fan turned on?

Although this appears to be a homework question, it is not. I am contemplating running ductwork from my house to my garage and I want to make sure that what I construct will not implode.


texts: Shear rate of a fluid in a container with a sliding PTFE top plate. Will the liquid move with the plate?

texts:
I am trying to work out how a liquid inside a container will be affected by the back and forth sliding of a Teflon coated plate such as the one in the picture.

I know how to work out the shear rate of a fluid between two plates moving at different velocities using the v/h equation, but it doesn't take into account things like the walls on my container, or the fact that the plates may be hydrophobic.

My goal is to move the plate (which is in contact with the liquid) back and forth without the liquid moving. So my question revolves around firstly whether it is even possible to move the screen back and forth without significantly displacing a certain liquid it is in contact with underneath, and secondly how I would go about calculating to what extent the liquid would be disturbed.


texts: How and WHY does the tension in an arch dam or bridge change as the degree of curvature and radius of curvature change?

texts:
Arch bridges operate according to the following (I am assuming arch dams are the same):

Tensional force in arch bridges are virtually negligible. The natural curve of the arch and its ability to dissipate the force outward greatly reduces the effects of tension on the underside of the arch.
The greater the degree of curvature (the larger the semicircle of the arch), the greater the effects of tension on the underside of the bridge.
(Source)

WHY does a greater degree of curvature results in more tension? A diagram would be useful if possible.

2. How does the changing the radius of curvature affect the tension and compression in the dam, and ultimately the strength of it.


texts: Will lightning strike an aluminum rod in a pot on my balcony?

texts:
I have some tomato plants on my balcony (4th floor in a 7 story building). The balcony is a recessed one.

The building has lightning protection on top.

To support them, I put a 2 m long aluminum rod into each pot. At the tip of the rods I put some isolating tape, so that it covers the tip of the rod.

Will these rods attract lightning?


texts: Dimensions of a bar when it is subjected to axial pull

texts:
Determine the change in dimensions of a rectangular bar of length 2 m, width 200 mm, and thickness 100 mm, when it is subjected to an axial pull of 20 kN in the direction of its length.

Take $E = 2\times10^5\text{ N/mm}^2$ and $\mu = 0.3$.

I have gotten up to $\delta L = 0.01$. Then using $\mu = \dfrac{δb/b}{δL/L}$, I got $\delta b = \dfrac{\mu bL}{δL}$, which is 0.3×200×2000/0.01 = 12million!

I don't know where I have mistaken but it is frustrating me.


texts: Ash size particle dependency of initial coal particle size in fluidized bed combustors

texts:
I'm looking for information on coal ash size in fluidized beds. How dependent is it on the initial coal particle size? Would I expect ash from 5mm coal particles to be significantly larger than ash from 0.1mm coal particles? Or does the abrasion from fluidization cause the ash size to become small no matter what. Also, I'm not talking about ash that is vaporized and then reformed (fly ash), but just the mineral ash component of the coal itself.
Also does anyone know of any good literature on ash size?


texts:
So I have a set of data, units purchased per month over a 4 or 5 year period.  I have about 3000 different items, but here are 2 examples of what Ive done:

Item 1: Mean 24 STDEVA 18
It has purchases practically every single month of each year.

Item 2: Mean 12 STDEVA 15
It has at least 1 or 3 months with purchases of 0.

I do understand that stdev doesnt treat 0's differently than it does outliers.  So for example, if most numbers are 1, then a 0 now and then wont increase your std dev.  But if most numbers are 100, then a 0 now and then will increase it, right?

My question is, how can I determine which items are safer to purchase (inventory) such that I wont be so affected by large stdev?  Iow, 18 of 24 is still a pretty big number.  Its telling me that 68% of all values in that set are +/-18 units away from 24.  That could be as low as 6 or as high as 42.  On the other hand, 15 of 12 is just as bad.

How should I use the std dev to determine my safety level of purchases for a given year?

Set 1: 14,80,14,52,12,71,23,12,32,9,14,28,2,9,13,74,25,62,18,58,19,21,14,11,6,25,37,1,46,48,83,29,8,26,50,15,26,66,19,65,93,4,16,98,62,24,0,0,6,5,33,0,1,70,0

Set 2:
4,4,13,30,22,50,16,4,60,16,31,35,10,10,10,8,10,23,0,3,18,0,10,8,37,73,2,11,9,18,4,0,3,11,19,3,7,0,3,0,0,2,0,4,4,14,11,0,0,0,0,4,0,0,0


texts: Industry standard dimensions for a 5-gallon water cooler?

texts: I'm designing a product to accept a 5-gallon water jug. This is the light blue, transparent plastic kind for potable water that you can buy, swap, or fill at grocery stores. I can take measurements of jugs I own, but I'd like to ensure the product will accept any jug conforming to the standard. Does such a standard exist, particularly for the mating surface of the cooler?


texts: About glass transition temperature in a DMA scan of an unknown material

texts:
Dynamic Mechanical Analysis, otherwise known as DMA, is a technique where
a small deformation is applied to a sample in a cyclic manner. This allows the
materials response to stress, temperature, frequency and other values to be
studied.

DMA works by applying a sinusoidal deformation to a sample of known geometry.
The sample can be subjected by a controlled stress or a controlled strain. For a
known stress, the sample will then deform a certain amount. In DMA this is done
sinusoidally. How much it deforms is related to its stiffness. A force motor is used
to generate the sinusoidal wave and this is transmitted to the sample via a drive
shaft.

Modulus values change with temperature and transitions in materials can be
seen as changes in the E’ (elastic modulus) or tan delta curves (tan delta = elastic modulus / loss modulus). This includes not only the glass
transition and the melt, but also other transitions that occur in the glassy or
rubbery plateau. The glass transition (Tg) is seen as a large drop (a decade or more) in the storage modulus when viewed on a log scale against a linear temperature scale.  A concurrent peak in the tan delta is also seen. The value reported
as the Tg varies with industry with the onset of the E’ drop, the peak of the tan
delta, and the peak of the E’ curve being the most commonly used. This is a typical output from a DMA scan in temperature with a ramp rate near 5 °C:

Question:

The image below shows the results from a DMA scan.
In black there is the elastic modulus, in gray the loss modulus and in brown the tangent delta or damping. What is the meaning of the two tangent delta peaks?

Is the material changing its property during the DMA scan? The x-axis is temperature, while modulus and tangent delta have different units on the y-axis. And what is the meaning of the increasing elastic modulus?


texts: Difference between light and heavy cracking of hydrocarbons?

texts:
Cracked gases usually are quenched after cracking reactions.

Why for lighter gases like ethane, indirect quenching is used,

But for cracking of heavier naphtha or gas oil, most cooling is performed by direct quench.

I understand that cracked heavy gas oil contain a larger amount of fuel oil and vice versa but why.


texts: How does galvanised steel culvert withstand abrasion from solid particles in the stream?

texts:
Zinc-coated roofing steel loses its zinc coat after about ten years because of being exposed to elements and it has to be painted. Zinc-coated powerline posts lose zinc too and experience corrosion, however they are built of thick parts which are "eaten up" slowly and once enough cross-section is lost they are replaced.

However I've recently seen a culvert assembled from pieces of corrugated steel with coating looking like zinc. Parts were something like 5 millimeters thick and connected with numerous bolts and the culvert diameter was about 1,5 meters.

The water passing through a culvert bring sand and other particles which surely grind the surface. I assume this should remove the coating from the submerged part of the culvert within several years and then corrosion will start and eat the not so thick steel rather quickly.

How is abrasion by solid particles addressed in culverts made of galvanized steel?


texts: What is the difference between work hardening and strain hardening?

texts: I have come across the definition somewhere,"Work hardening, also known as strain hardening, is the strengthening of a metal or polymer by plastic deformation. This strengthening occurs because of dislocation movements and dislocation generation within the crystal structure of the material."Now I have been told by my professor that strain hardening and work hardening are different.I would like to have a detailed answer on this.


texts: What kind of connection allows rotation at only one end?

texts: We are looking to connect a non spinning coolant pipe to a spinning drill pipe. The connector needs to spin on the end with the drill pipe but be stationary on the end with the coolant pipe. Is there some type of bearing you know of or some other connector?


texts:
I have a peltier (TEC) device capable of 400W Qmax, a 160W thermal load that I'd like to keep at ambient, and this water block running at about 1.5 gpm w/ room temp water. I think this system is right on the border of what is possible, but I'm struggling to determine the exact efficiency of my peltier unit.

The datasheet for my peltier indicates a Qmax of 400W and claims that maximum applied power is about 690W -- does this mean that I have a 57% efficiency? To me that seems extraordinarily high for a TEC.

Because I don't believe 57% is right, let's assume a 30% efficiency. In that case, my peltier will need to be operated at around 533W in order to dissipate the 160W load + the load from the peltier. And now, I have 693W total being dumped into my water block.

Am I doing this calculation correctly?

Other notable factors:
- This system will be operated in a vacuum environment so convective cooling is a no-go.
- There is a thin (~1/8") aluminum plate between the heat load and the peltier.


texts:
What determines the maximum torque of a DC motor?
How is this related to the equations

$$E=k\omega$$
$$T=kI$$

where

$E$ is electromagnetic force / voltage (V)
$\omega$ is rotational speed (rad/s)
$T$ is torque (Nm)
$I$ is current (A)
$\phi$ is flux (Wb)
$k$ is the motor constant (V/(rad/s)=Nm/A) such that $k=K\phi$


texts: Can I use a pipe of any material other than copper in a counter-flow heat exchanger?

texts:
Why are copper pipes used in counter-flow heat exchangers?

Could I enhance heat transfer by using a pipe made of any other material?


texts: I have a tiny reactor, and the volume I need is 425ml. If there is no/few other reactants, then the volume in hydraulic retention time is clear: reactor/container's volume. and hrt is V/u(V is 425ml, u is flow rate) But if I fill 80% of container with something like lime mud, the real volume of water is only 20% left -- 85ml. How is my V should be? 425 or 85ml? IOW, the volume in hydraulic retention time is of reactor/container or liquid?


texts: Theory of steady state error and dynamics of error for automatic control systems

texts:
I'm currently studying control systems specifically the mass-spring-damper system.

Which is described by:

$$\ddot{y}=(b/m)\dot{y}+(k/m){y}=(b/m)\dot{u}+(k/m){u}$$
Where

$b:$ coeffiecient of friction

$k:$ coefficient of stiffnes

$m:$ mass of spring

From class we were told that
$$error = e(t) =y_{ref}-y(t)$$
Taking the first and second derivative
$$\dot{e}(t)=-\dot{y(t)} $$
$$\ddot{e}(t)=-\ddot{y(t)}$$
After this we substituted with $e(t)$
$$\ddot{e}(t)=-(b/m)\dot{e}(t)-(k/m){e}(t)+r(t)+d/m$$

Then $r(t)$ is defined as $r(t)= ky_{ref}+mk_pe(t)$

What I don't understand is where does the term $r(t)$ and $d$ come from. The example is taken from Ogata's book, but the dynamics of the error isn't covered in the example of the boook. Where can I read more about this so I can understand this equation.


texts: Calculate energy (kW, or kJ) from Vapour Expander Generator

texts:
I'm a student of Integrated Water Management, and looking at a geothermal bore that is producing potable water for a town's water supply.

The bore water reaches the surface at $50$ $^oC$, and flows at 1.6 million liters per day.

It's suggested a vapour expander engine could convert this heat to useful work, but such an engine may not commercially exist.  Nevertheless, I'd like to calculate the energy potential.

Can anyone help with the Excel formula I'd need to calculate this?


texts: My contractor did not the work properly on the structure of my house.  He did not support the beam correctly.  I hired an engineer to check it and he sent his recommendation.  I asked my contractor to correct his work as per the drawings and he said he will send his expert to check it.  I was wondering what kind of expert can overule the engineer recommendation? If this expert says that everything is fine, who is responsible?


texts: Finding Neutral Axis of a simple shape undergoing axial load

texts: I know that the neutral axis occurs where the sum of stresses (bending + axial) is equal to 0. I have found the stresses and drawn a diagram to represent forces. How do I determine the neutral axis?


texts:
I have the following problem most of which I have calculated but have a difficulty with the beam under angle. The angle is 56,30 degress. I just cannot figure out how the forces there are acting - the equations I am making have three unknown variables in two equations, which cannot be calculated, so apparently there are forces I "cannot see" there as well and the equations are wrong.

The disributed loads have been replaced with concentrated loads: the point where they act is indicated.

Thank you very much for advice.


texts:
These are suction-mounting hooks. I want to visualize and understand how do they stick on walls.
After these hooks stick on wall. Like we compressed them. How? Since gases are compressible up to a good finite limit. What makes it difficult for them to come off if I pull them. It should be easily able come off also. Online , it says that the air gets enclosed inside . But I am not getting exactly what it means by that. How does that air enclosed creates a way in which it becomes difficult for us to pull the hook off.


texts:
I am trying to calculate the velocity in a pipe with length $L$ and diameter $D$, which is connected to bottom of a pressurized vessel. The vessel dimensions are known and the level of the liquid inside the vessel is known.

I need to figure out the mass flow rate as a function of pressure inside the vessel.  We can ignore the friction losses in the pipe, and the vessel is filled with water.  Also, how can I find new pressure inside the vessel after the valve has been open for 1 second.


texts: What is error in action? And why is it called error "in action".


texts: Relation Between Distributed Load and Shear

texts:
I saw the following extract from Hibbeler's 'Mechanical Engineering - Statics, 13th Ed';

The general result $\frac{dV}{dx} = w(x)$ seems to rely on the shear forces at the interface acting in opposite directions. If my force distribution function along the top of the beam is linear with gradient 0, then my $\Delta F$ would act in the centre of $\Delta x$ and the shear force at the right and left interface of $\Delta x$ would be identical vectors, both acting downwards. My vertical force equilibrium would then be described as follows;
$$
\Delta F - V - (V + \Delta V)=0
$$

This then breaks the general relationship described by (7-1). What am I misunderstanding?


texts: Weight distribution on sliding or “pocket” doors

texts: Does anyone know if hollow sliding/pocket doors have a weight/more dense wood at the bottom of the door to prevent from swinging?


texts: Why does accuracy of temperature PID controller drop over time and how to eliminate it?

texts:
What am I trying to control?

I have a container with approximately 3*2*6 meters (width, height, length).
I am controlling through PID the Temperature 2 (temperature inside a tubing system) to get Temperature 1 and 3 (temperatures near floor and celling of the container) to the desired values (see graphs below).
Temperature 2 is coming from a sensor inside a tube system through which the air is circulating and Temperature E. is coming from a wooden box inside the container.
Box and tubing is a closed system with some minimal temperature leaks.
The PID’s output is connected to PWM of triacs which heat the air in the tubing system.
EO% is describing how much % of 1 second (the PWM period) the triacs will be set to True = therefor making heat. So if EO is 50, then the triacs will be making heat exactly 0.5 seconds

Sketch of my system:

Step response of the system (X axis format is HH:MM:SS):

What have I tried so far?

I am running the software on PLC from local distributor (not an Arduino board) where I have implemented this PID model from Arduino library.. But in the future I will be using Beckhoff PLC's.
I have tried implementing the basic PID controller with little accuracy.
Then I have tried implementing PID controller with proportional on measurement and derivative on measurement and my accuracy went higher (link is to a blog talking about the two methods).
Now I can control temperatures with precision to almost 0.5 °C and little oscillation.
PWM frequency is 1 HZ and PID sample time is 2 seconds.

What is the problem?

You can see on the pictures below that I slowly increment my PID setpoint through time (PID’s setpoint is the black line).
When my system has a temperature in a range from 20 to 55 °C my accuracy is quite good.
But once I get above 55 °C, PID’s is not able to control the temperature accurately anymore and the PID output always result in a spike and therefor even larger inaccuracy.

What can I do to eliminate this problem? And what is causing this behavior? Are there any better methods then the simple PID controller?

Other observations:

I think the problem lies in the I component of the PID controller.
When the temperature is low the P component manages to control the temperature just right. But when the error is getting bigger and bigger the I component is cumulating and then it overshoots.
When I am running the PID on all temperatures (25, 40 even 58 °C) the accuracy is as I said 0.5 °C and oscillation is minimum. The problem only occurs when I slowly increment the PID’s setpoint and therefore increase the temperature.

Pictures (X axis format is HH:MM:SS):
Picture 1 and 2 (temperatures and the PID's output):

Picture 3 and 4 (temperatures and the PID's output):


texts: What are displacement field and Deformation field?

texts: I am studying mechanics of materials while I came across these terms called the displacement fields and the deformation fields. I am not able to understand the difference between them. Can someone explain it to me.


texts: ANSYS: Why do I have a choice of choosing TOP/BOTTOM under contact/target shell faces?

texts: When ever I try to use a surface to surface contact, i.e. 2D shell elements to 2D shell elements, under the option Contact/Target shell face, either I can pick TOP or BOTTOM. Why is that? How is that going to cause trouble if I don't choose it correctly? Why is that important and how can I pick the correct shell faces?


texts: I'm using an F2802x microcontroller and I saw in Embedded Coder in Simulink that I have Digital output block. When I use this block, how does it work?


texts: Flexural modulus for a beam fixed at one end

texts:
For a beam supported at both ends with a mass in the middle, the flexural modulus is given by:

$$E_b = \frac{F L^3}{48I d}$$

with I as the area moment

$$I = \frac{1}{12}wh^3$$

How does the expression for modulus change if we have one fixed end as in the diagram below?

ja72 states in this answer that

$$E_b = \frac{F L^3}{3I d}$$

But I'm not clear on the derivation.


texts: A room 10"x10"x17" lxbxh respectively to be heated 397F if a heater is placed inside the room (2 kw) how many heater are to be required to heat the room from room temperature to 397 F in 1 hour.


texts: Joule Thompson Effect and Isenthalpic Processes

texts:
We are trying to compute the Joule Thompson (JT) coefficient for air going through a valve from P1 to P2 (where P2 is a much lower pressure).  Beginning this we were thinking that the water in the air was going to cause the flow to freeze when going through the valve but upon learning more we found this JT effect and coefficient.  Apparently this takes into effect the friction and isenthalpic (same enthalpy) characteristics of this flow to show how the temperature/energy changes through this.
My question being, does anyone know how to determine this coefficient for a process?
Thank you!


texts: Best traffic control device/system for given situation

texts:
I am familiar with the round-a-bout/traffic light pros and cons, however, I've been tasked with deciding on a solution for the given parameters below.

Currently, there is a two-way (four lane) road with a speed limit of 35 mph. Rough traffic counts for peak hours are 580 vehicles in the morning (primarily North bound), 660 vehicles mid-afternoon (North/South split), and 400 evening (primarily South bound).

Access to a new facility will create a need for an access road resulting in a 3-way intersection. Access road will be to the East and for the most part only North bound traffic will make right turns to enter the facility. Less than 10% of the North bound traffic is expected to use the facility at any given time. Once finished at this facility, it is expected that the traffic will leave via the same access road and make right hand turns to continue North bound. However, as much as 20% of this traffic will need to make a left turn to return South bound.

Assume a community with some, but very little experience with round-a-bouts, and a primary desire to keep North and South bound traffic flow steady.

Giving your opinions and reasons, would you consider a round-a-bout or traffic control device utilizing a camera system for the left turn lane on the access road to be better?


texts: Identify plant transfer function to design PID controller

texts:
I am trying to find the transfer function of a plant that contains numerous equipment including a heater, several tanks, pumps, membranes etc.

I need to design 2 PID controllers: the first one to control the temperature of the stream entering one of the membranes, and the second PID controller needs to maintain the solution concentration in one of the tanks.

I have seen that there is a system identification tool in Matlab that I can use to find the plant transfer function. The problem is, I am not clear on exactly what the plant transfer function should describe. Should it represent the whole plant (e.g. all the tanks, pumps etc.) or only the part of the plant that I am interested in to be able to design the controllers (e.g. resulting in two different plant transfer function equations for each controller).

Thanks in advance.


texts: Using XFoil to generate data for various Mach numbers

texts:
I am attempting to use XFoil to generate a list of coefficients of a given airfoil at a range of speeds.
The first issue I faced is that it appears with XFoil, you give it a Reynolds number (which varies by speed) and an Angle of attack, and it outputs the Coefficients of Lift and drag etc.
What I need, however, is to input a range of subsonic mach numbers (or various reynolds numbers) and for it to output the:

Lift Coefficient
Drag Coefficient
Max AOA (Departure)
Maximum possible Lift Coefficient

How would I go about this using XFoil or any other similar program?


texts:
Could anyone tell me what the variables in this formula are?

$$\tau=\frac{S\;a\; \bar{v}}{I\; t}$$

I believe it is used for shear stress and that $I$ is moment of inertia but unsure on the other variables.


texts: What does "'LBLMY" mean on the side of a railcar?

texts:
In this photo, what does 'LBLMY signify? Seeing it directly under the capacity, and 5000 pounds lower, I'm guessing it's a "limited capacity" of some sort. But I can't come up with anything that would abbreviate to 'LBLMY.

The only things I've found while searching for "lblmy" look like OCR errors.


texts: Trying to shed some weight on my design, any thoughts?

texts:
I am trying to design a lifting mechanism and I would love some insight/opinions as to how I can shed some weight off it.

The current weight I have for my mechanism is 187.5kg, however, this is supposed to be something that is "easily transportable"

I am using stainless steel. Originally we had 20.3m of steel with a cross section of 40mm x 40mm and 10mm thick. Seeing as 187.5kg is quite high I am looking to reduce the weight. I will admit the material and cross section were chosen relatively arbitrarily, but we wanted to be sure that our structure could hold any load without actually worrying about the calculations for that.

The main stress that will be exerted on the beam is bending, as the structure is built like a table, and will have a weight suspended from the middle. I looked up that the yield stress for stainless steel is 193 MPa (I took the lowest value I could find for safety reasons) and I have applied various different cross sections for the steel.

For my original dimensions 40 by 40 by 10mm thick:

$$\sigma\text{ (bending)} = \dfrac{My}{EI}$$

Assuming my table top is completely made of a hollow rectangle of stainless steel:

$$\begin{gather}
M = 200\cdot9.81\cdot500\text{ (lifting 200kgs 50cm away from it)} = 98100\text{ Nmm} \\
I = \dfrac{40^4 - 20^4}{3} = 800000\text{ mm}^4 \\
y = 20\text{ mm} \\
E = 193\text{ MPa} \\
\therefore \sigma_b = 0.0127\text{ MPa}
\end{gather}$$

I worked in mm because 1 kg/(mm*s2) = 1 MPa

A reduced, solid cross section of 20mm gave a bending stress of:

$$\begin{align}
M &= 98100\text{ Nmm} \\
I &= \dfrac{20^4}{3} = 53333\text{ mm}^4\\
y &= 10\text{ mm}\\
E &= 193\text{ MPa}\\
\therefore \sigma_b &= 0.0953\text{ MPa}
\end{align}$$

I know stainless steel is a very strong metal, which is why I leaned towards using it originally. I would just really like to know if the logic behind all of my calculations make sense? Am I on the right track for this or have I done something horribly wrong that I am unaware of? I am aware I did not include self weight, but did not see the need for it.

Thank you for reading, I would appreciate any thoughts on this.

Edit: this is for a university project, I am mainly looking for pointers on my conceptual design and work.


texts: Why is there tension in outstand flanges of compressed elements?

texts:
Above table is from Eurocode. According to the table, the stress distribution in a flange of a beam can be negative in part of the flange when the part is subject to bending and compression. Why is this?
If we have a beam that is compressed and bent at the same time, shouldn't the stress vary from positive to negative as a function of distance from the neutral axis (in vertical distance in the picture), not as a function of distance from the web, along the flange as in the picture? Why does the stress vary like that, from the "bottom" of the web to the tip of the flange?


texts: Distribute 6 inputs to 9 outputs with pipes

texts:
I have the task to connect 6 input sources of fluid with 9 output (sinks) sources. Each input should be connected to each output. Each input should be able to distribute the fluid to only 1 output at a time. I have straight pipes, Y connections and valves, that I can use. I should use the MINIMUM amount of valves and Y connections as possible.

Is there a standard approach to reducing the number of components required for a design like this?

This is the best I could get to so far:


texts: How to make an annular metal to metal snapfit?

texts:
I am designing a watch case and would like to know how to make an annular snap fit for the backplate. The material used is stainless steel. I could find references for Metal-plastic snap fit but I need both parts to be metal. I have seen a similar design in a Withings watch.

PFA image link: https://www.wareable.com/media/images/2015/01/img-6044-1421770737-9RIG-full-width-inline.jpg

For plastics I used : http://fab.cba.mit.edu/classes/S62.12/people/vernelle.noel/Plastic_Snap_fit_design.pdf


texts: Is systems engineer an IT profession or an interdisciplinary field of engineering?

texts:
The term Systems Engineer has always interested me as it generally involves many different fields of engineering.

Systems Engineer - Interdisciplinary

The definition I'm familiar with is usually defined as an interdisciplinary profession of engineering, where the engineer has experience in a number of fields and uses this during the design of a system.

Systems Engineer - IT related

After searching for jobs here in Australia, I've found many systems engineer positions. However almost all of them are relating to IT jobs, referring to the programming of computer systems at the system level.

Question

Why is there a conflict of these two definitions?
Which one was first?
And is Systems Engineer no longer valid in the interdisciplinary sense?

Notes

Please forgive any mistakes and assumptions I have made, I'm new and ready to learn.


texts: Why are some submarines using liquid oxygen for combustion?

texts: I think som submarines like Kockums use liquid oxygen instead of compressed air for driving their combustions engines. Is it more energy efficient to oxygen enrich the air before burning it compared to using common air?


texts: How does one calculate degrees of freedom in a reactor with parallel reactions?

texts:
Some time ago, I was going through some exercises and I came across a odd question, for which my atomic species degrees of freedom did not match my degrees of freedom using molecular species. I showed my lecturer and he couldn't see why this was the case. The (summarized) question is as follows:
2 reactions occur in a reactor:

\begin{align}
\text{C}_2\text{H}_6\text{O} + \text{H}_2\text{O} &\rightarrow 2\text{CH}_3\text{OH} \\
2\text{CH}_3\text{OH} &\rightarrow \text{C}_2\text{H}_4 + 2\text{H}_2\text{O}
\end{align}

The input feed of water and $\text{C}_2\text{H}_6\text{O}$ is specified and the selectivity of the first equation. Reactions do not go to completion.

So, there are 4 unknowns ($\text{H}_2\text{O}$, $\text{C}_2\text{H}_4$, $2\text{CH}_3\text{OH}$, and $\text{C}_2\text{H}_6\text{O}$).

Doing the atomic analysis:
$$\text{DoF} = 4 - 3(\text{C},\text{H},\text{O}) - 1 (\text{Selectivity}) = 0$$

Doing the molecular species:
$$\text{DoF} = 4 + 2 - 4(\text{H}_2\text{O}, \text{C}_2\text{H}_4, 2\text{CH}_3\text{OH}, \text{C}_2\text{H}_6\text{O}) - 1 (\text{Selectivity}) = 1$$

Do you see where the problem is?


texts: Is a beam is subject to axial load, does it mean that deformation is the same in each point?

texts:
If we look at a cross section at any point, stress will be the same $\sigma=F/A$ and the hooke law says that $\sigma=E*\epsilon$

It means that the deformation will be constant throughout the beam, which obviously can't be correct. So what am I missinterpreting here?


texts: How to interpete the formula: $I_{G}\alpha = \dot{\vec{H}}$?

texts:
I am having hard time to fully undestand what those formula's actually mean. I know the meaning of each element:

I : moment of inertia
H : angular momentum
$\alpha$: angular acceleration
$\omega$: angular velocity

$I_{G}\alpha = \dot{\vec{H}}$

$I_{G} \dot{\vec{\omega}}= \dot{\vec{H}}$

Could someone explain the meaning and/or give and example/context to clarify things?


texts: Maximum deflection of a beam, fixed in one end and concetrated load at free end

texts:
A 2 m long beam fixed in one side with a 2000 kg concentrated load at free end. Profile of the beam is HEB100 material S235.

I would like to know if the beam will break under this load. If yes, what is the maximum load it can handle and how do you calculate it?


texts: Why did Volkswagen use special software ONLY during emissions testing?

texts:
As we all know, Volkswagen is in the middle of a scandal centered on its use of special software to lower tailpipe emissions during standard emission testing protocols.

What I don't understand is why this software needed to be switched off in other circumstances. Why can't the car always operate in low-emission mode? Is there some negative effect on performance, component life?


texts:
While learning about normal and tangential stress, we had a task, where I had to calculate the cross sectional area of a beam that could withstand the force applied to it, if the beam was sliced in the middle on an angle (Like two 90 deg trapezoids glued together).

I hope this makes sense.. having a language barrier here.

I was given the maximum allowed normal and tangential stresses under which it would not break.

As we know, Maximum tangential stress = 0.5 maximum normal stress.

I was given two values. For example, the max normal stress was 7.6 MPa and the tangential stress was 4.1 MPa and according to the rule, if tangential stress is 4.1 then the max normal stress can be 8.2 MPa. So the calculations are done based on the lowest value, since it can't hold any higher...

But if I'm only basing on one of the values and they're both connected to the equation, why does the task give me both? Is it just for the task, or in real life there are there materials that somehow have specifications for the tangential stress and normal stress boarder values which are different when using the equation?

I hope any of this makes sense.

The question basically is-  How can the same material have two different values of stress it can withstand? Is it just for the task or..?


texts: Methods for External Antenna Detection - RF systems

texts:
I’m designing an RF device that should be able to use multiples sets of antennae, one a low-gain internal PCB antenna and the other an external high gain antenna attached via an SMA connector.

I’d like to be able to automatically detect when the external antenna is connected and disconnected (so that I can electronically switch between antennas) be able to switch to using it automatically.

I have come across ways of doing this by adding a known resistance to the antenna and then simply detecting this resistance through the use of a potential divider. This however would require the antenna to be precisely calibrated and be a short circuit antenna. Ideally I would like to be able to detect any kind of antenna attached to the SMA connector.

How might I go about doing this? Are there any other electrical properties of the antenna which could be exploited to detect its presence? (For example, would it be possible to somehow detect the capacitance of the antenna when it is connected or would this change in capacitance be insignificant?)


texts:
Recently I was weighting stuff with my dad and as I was playing with one of the old 2 kg weights I felt with my fingers number "5". After cleaning and upon further inspection it turned out the writing on the weight says "5Φ". We checked and it indeed weights 2 kg as my dad remembered. It was done with a simple balance scale by comparing with another weight of similar age that is properly marked as "2 kg". There are no other marks on that weight. On the opposite side is a bulge but it's an irregular blob - I think it's remainder of sprue.
So, question that arised in my head is - what does that Φ mean? Is it some rare unit of mass? Some sort of preferred series or standard for weights?
I was looking for answers and found nothing. I ruled out pounds that was first thing that came to my mind because the difference was to big (5 pounds is approx. 2.26 kg) - though there are some signs of wear and corrosion it's in rather good shape and I don't believe it weighted 0.26 kg more originally. Also, considering I'm from Poland and the weight is really old it probably was made during the soviet era (maybe even in USSR) - so that phi could be actually cyrilic fe - but that also gave me no results.
As a last resort I decided to ask here - maybe some member of that community will know the answer. Below is a photo of the weight in question.


texts: How to determine materials and torque for a flat setscrew that won't loosen, slip, or mar

texts:
I'm a non-engineer doing a little design project.
I'm going to be running some M5-ish (have some flexibility) setscrews into a shaft of about 6mm. There's no reason why the shaft can't be flatted off a bit so I'm presuming I'll do that.
There's no motors or electronics involved and the ends of the shafts are getting a pretty minor (I don't have numbers, sorry, I know I'll need them at some point and will need to do testing to get there) amount of force applied from a distance 20-30mm away. The setscrew connection must be highly resistant to slipping or loosening over extended (could be effectively permanent) use but also must be re-settable occasionally. When it does get reset, it could be right in the area of prior settings on the shaft, and it will have to be done with high accuracy (say down to a resolution of .02mm ideally), so I want to avoid marring as much as possible. (If this isn't possible then the whole thing will have to use a pinch bolt instead of a setscrew.) The shaft can be any material, within reason.
The part will have some exposure to vibration but I don't intuit that it will be more than blue loctite will protect against.
How do I do the math to determine what exact materials to use and the torque on the setscrew to avoid the screw loosening, slipping, or significantly marring the surface of the shaft?
Any recommendations for reading on the topic would be great.


texts:
I have a question about the characteristic dimension.

Q1
The drag on an airship is known to depend on the air density, ρ , dynamic viscosity,
μ , speed relative to the air , V , and a characteristic dimension, L . An airship is to
operate at 20 m/s in air at standard conditions. A model is constructed at 1/20 scale
and tested in a wind tunnel at the same air temperature to determine drag.
(a) Perform a dimensional analysis to determine the criterion which should be
considered to obtain dynamic similarity.

like the question said for the characteristic dimension L, How can i know what dimension is L.


texts: How to calculate the start-up cost of a natural gas boiler

texts: How I can calculate or find a value for the start-up cost of a natural gas boiler? The boiler will have a capacity of about 700 kW and is intended for heating the water for a greenhouse.


texts:
can someone tell me how to calculate the bearing forces of the two bearings?
I can't get any further because I don't have the angle for the second bearing.
I don't have an idea anymore.

F =   20KN
q0= 2000N/m
a =   1000mm

At the bottom under Lösungen are the results.

Thank you in advance.


texts: Build and visualize Pitch, Roll and Yaw from 9dof data offline

texts:
I am trying to build pitch, roll and yaw from sensor readings of a 9 degree of freedom sensing device.
The data look like that (in a .csv file):

TIME,ACC_X,ACC_Y,ACC_Z,GYRO_X,GYRO_Y,GYRO_Z,MAG_X,MAG_Y,MAG_Z
2313992204,-1.694118,-2.053042,-8.886943,0.006272,-0.004091,0.000682,-48.200001,-68.400002,13.000000
2313992204,-1.674976,-2.029114,-8.886943,0.006545,-0.003682,0.000682,-48.500000,-67.599998,11.300000
2313992204,-1.674976,-2.033899,-8.882157,0.006136,-0.004091,0.000273,-47.799999,-67.500000,12.300000
2313992204,-1.703690,-2.033899,-8.882157,0.006818,-0.003682,0.000409,-47.700001,-68.099998,11.800000
2313992204,-1.694118,-2.053042,-8.877372,0.006409,-0.004500,0.000682,-47.900002,-67.400002,11.200000

I am not familiar with building this measures from these data and also I am not familiar with quaternions.
This question is the only thing I have found to be related to mine questions (Calculating pitch, yaw, and roll from mag, acc, and gyro data), however, it is not using all the axis.
Ideally, I want to build this vector and be able to visualize them in 3D (like cube animation that is made live from 9dof sensors and Arduino). Moreover, I want to be able to compute the heading from this data.

Can anyone help me, I have all my pipeline in python so it would be helpful to have advice on how to do that with python?


texts: How deep are utilities typically buried?

texts:
What are the recommended or relevant standards for US city planning with regards to depth ranges for various utilities such as water, natural gas, and power, as well as for subway or rail, etc...?

For example, water and gas lines should be buried well below the frost line to prevent damage from ground movement.  What standard(s) dictate those depths?

I am primarily interested in standards applicable to major cities such as Atlanta, Boston, Chicago, Dallas, Denver, New York, San Diego, Seattle, Washington, etc...  My assumption is that there are enough similarities between the cities that a standard would have been developed.


texts: How does a monitor arm hold the monitor in place after rotating to a new position?

texts:
Not sure if an example is needed, but here is one.

I'm curious as to how the joint connected to the monitor itself "remembers" the last position the monitor was moved to. In my naiveté, I imagine the rotation being enabled by grease, so how is it that the monitor does not always rotate back towards the direction of gravity's pull?


texts: How much an unevenly heated glass plate bows?

texts:
In relation to this question about 3D printing, I wonder how much a 200 mm square glass plate heated only in a central 15 cm square region would bow upwards or downwards.

According to the thermal expansion of glass, the linear expansion for 15 cm and 100°C deltaT would be 0.05 mm.

Using the formulas provided in https://planetcalc.com/1421/ I input 200 mm as chord length and 200.05 as arc length. The result is 2 mm height which seems a lot to me. Using 150 mm and 150.05 mm I get 1.7 mm which is still a lot.


texts: How to draw isometric view of this shape?

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I'm having trouble drawing an isometric view of this shape:

I've only just started an engineering course and so far it's involved a lot of drawing which I usually can do but I can't seem to figure out how to 'place' this object to make an isometric view. Am I able to make the base of the object in my drawing whichever face I want?, as I feel perhaps if I rotate it so that the face with the hole is facing the ground might make it easier to draw, or do I have to use the 20x20 square as the base like it is in the current view.

This is also kind of confusing me as well in regards to drawing it in parallel oblique view but that's another issue I guess which I'll probably be able to figure out once I wrap my head around how to attempt the isometric view.

The other shapes I've drawn (see example) felt a lot easier to simply start and don't mess with my brain like this particular shape does. It isn't being marked but I still want to understand how to do it since I'll probably have to deal with these types of shapes later on anyway and would rather have the basics down now.

I'm sorry if my explanation doesn't make sense but I'm not really sure how to word my issue at the moment.

Any help would be greatly appreciated, thanks.


texts: How to calculate specimen strain in split hopkinson pressure bar?

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I want to plot the stress-strain chart for a specimen after a test.
In the output file of excel, I have "Strain of transmitted bar" and "Strain of the incident bar"
I also have Young's modulus of the bar which is 209 GPa, other data are:

Diameter of the bar = 21 mm
P wave velocity = 5100 m/s
Length of the striker = 200 mm

I do not know how to get the specimen strain from these data so I can have the whole "strain" and then plot the chart?


texts: Unequal water level in connected containers - Aquarium Sump

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I have recently designed and had fabricated the following two sumps for my Aquarium (See image).

I have a pump in the right hand container (section 4), and the return is coming back into the left hand container (section 1) - both flowing at equal rate (~1000lp/h).
Two 32mm flexi-pipes connect the two containers.
I was expecting the water level in both containers to equalise, but the left container is consistently running near to maximum whilst the right container water level is - as I would expect it to be - at the baffle height for 'section 1'.
Why am I not seeing equal water heights in both?
See below a picture of the situation occurring with RED lines indicating water height, BLUE lines indicating baffle heights, GREEN arrows indicating water flow direction. Please ignore the fact that I currently have one of my bypass valves turned on - it's all I can do to drop the water height in the left container a few centimetres.

Note - Reducing flow rate, and removing water from the system does not seem to have any positive effect on the left hand container. Filter sponges/socks etc were added after this effect was happening. The system has been running stable for 24 hours with this effect visible.


texts: How is sand blasting different from abrasive jet machining

texts: All I know is sand blasting is used for cleaning and etching purposes and abrasive jet machining (AJM) is used for making cavities and slots. But I think AJM can well also be used for cleaning and etching since it involves spraying abrasive particles just like sand blasting. If thats true isnt sand blasting a type of AJM process? How are they different? Are they different in machining procedure, or the equipment used?


texts: How to remove unwanted line from 2d trimming?

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I have a problem when I'm extruding a trimmed surface, it's look alright in isometric view, but in 2d view it shows unrelated line due to the trimming of the circle as show in the photo below, any idea to remove it so that the 2d view looks normal which how it should be

Sample image unwanted line


texts: What does 'Open Flow' mean for a pump flow rate?

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I have specifications for a positive displacement pump where, in the data table on the last page, the given flow rate is referred to in the column header as 'Open Flow.'

Is this the maximum flow generated by the pump?


texts: Cantilever beam with disc at end (structural mechanics)

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I am trying to figure out how I can assemble multiple finite elements to obtain the system mass matrix $\boldsymbol{M}$ and the stiffness matrix $\boldsymbol{K}$.

The situation is depicted in a picture (see below, assume the left side is not fixed). Now, I thought about splitting the body into a cantilever beam and a disc. The beam has four degrees of freedom in a planar analysis. I will refer to $q_1$ as the vertical displacement at the left side of the beam and $q_2$ is the deflection angle at the left side of the beam. At the right side of the beam, the vertical displace is denoted by $q_3$ and the deflection is denoted by $q_4$.

For the disc, I assume the degrees of freedom as depicted in the picture below. Hence, $q_{\text{S},1}$ and $q_{\text{S},3}$ for displacements and $q_{\text{S},2}$ and $q_{\text{S},4}$ for the angles of deflections (double headed arrow). It is obvious that $q_3=q_{\text{S},3}$ and $q_4 =q_{\text{S},4}$.

If I set up the mass matrix $\boldsymbol{M}_\text{B}$ for the beam I see that it has the format $4\times 4$. The same goes for the stiffness matrix $\boldsymbol{K}_\text{B}$. Assume that the mass matrix of the disc is given by $\boldsymbol{M}_\text{D}$ and the stiffness matrix is given by $\boldsymbol{K}_\text{D}$. How can I assemble the system mass matrix $\boldsymbol{M}$ and the stiffness matrix $\boldsymbol{K}$ from the previous matrices?

Feel free to write down the procedure on a sheet of paper, that would be good enough :). I also appreciate a resource that is explaining this procedure.


texts: Why did the Plexiglass on the Bathyscaphe Trieste crack?

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After passing 9,000 metres (30,000 ft), one of the outer Plexiglas window panes cracked, shaking the entire vessel.  (Wikipedia)

Why did the first layer of plexiglass Window panes crack on the Bathyscaphe Trieste while descending down to the Mariana Trench? Weren't they tested under such amounts of pressure? As far as I know, plexiglass can hold pressure of up to 20,000 PSI before it can actually crack.

  Related cross-post: https://physics.stackexchange.com/questions/353497/why-did-the-plexiglass-on-the-bathyscaphe-trieste-crack


texts: Which material is most efficient for the skin of a solar balloon?

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Quoting from the Wikipedia article:

  A solar balloon is a balloon that gains buoyancy when the air inside is heated by the sun's radiation, usually with the help of black or dark balloon material.  The heated air inside the solar balloon expands and has lower density than the surrounding air. As such, a solar balloon is similar to a hot air balloon.

What material would be the most efficient (minimize material mass, maximize payload, maximize heat retention) for weaving the skin of a solar hot air balloon? I want to consider thermal conductivity of the outer surface, radiance of the inner one, and structural strength. I want to achieve the 60 metric tons payload lifted to at least 200 meters over tropical sea level.


texts: How to transition from battery to USB in a microcontroller?

texts: I am designing a 3V battery-powered simple micro-controller to collect sensor data in RAM. How can I avoid a conflict with the 5V of a USB when it comes time to upload the data? Disconnecting the battery would lose the RAM. The solution needs to be very simple as the PCB is very small.


texts: Two railway locomotives connected one after another

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I am relatively new (not in terms of registration but in terms of activity) on this site. I don't know if this question is suited here.

I have seen two rail locomotives connected one after another and those two (assuming) hauling the rakes. While this is true, I didn't see a loco-pilot (In India, the engineer who drives a train locomotive is called a Loco-Pilot) in the second locomotive.

If we assume that second locomotive is on neutral gear and not throttling at all, then it makes sense.

If its a case of two locomotive hauling the rakes together, is it a valid assumption that the two have synced to the same speed?

EDIT: The real question is in regards with, how the amount of power required to haul the rakes is divided among the number of locomotives connected?


texts:
Time to empty a pressurize oxygen tank through a regulator.
The tank contain 12oz of oxygene at 3000psi (room temp.)
The regulator is set to 120psi.
The exit pipe is a 14inch pipe with 2mm inner diameter.
The experiment stop when the tank reach 120psi.
I may change the tank size and the regulator output pressure.


texts: Variables Relating to Atmospheric Water Generation

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I am interested in discovering a method to relate air flow to temperature reduction efficiency.

The purpose of this is in application to atmospheric water generation.

The apparatus will involve a fan (with a CFM rating), a long coil that will be externally cooled, and the temperature it is cooled to with perhaps another post processing stage. That would involve the narrow diameter pipe opening into a larger diameter "dew point chamber" or a way to cool the air further by narrow to wider expansion.

All of the condensed water will be collected into a collection reservoir.

So, the question is: How can I relate the CFM (cubic feet per minute) of air flow, the diameter of the pipe, the length of the pipe, the temperature of the pipe, the diameter of the expansion chamber --> the amount of water collected?

I am not an engineer. I am a simple person with aspirations to design a viable atmospheric water generator. I do not want to discuss energy requirements. I only want to discuss the variables I have outlined.

EDIT: I understand the idea of relative humidity vs. water available to "mine" from the air via condensation. My question pertains to the apparatus itself and how the variables relate. My concern is a high air flow will only have a certain rate of cooling based upon the length, diameter, and temperature of the pipe. My goal is to develop, with someone's kind help, a sort of formula for determining the temperature of the starting air (ambient) and the output temperature based on the variables.

Thank you, my fellow smart humans!


texts: I am a fourth year civil engineering student at IOE pulchowk, Nepal. In our syllabus one practical based curriculum called Project Engineering has been added. I, along with 5 friends, are interested in bridge project( mailny RCC slab bridge). Design and cost estimation are mandatory. Along with design and estimation, we want to make this project research based. What can be areas which we can consider regarding this matter?


texts: How accurately are moveable span bridges balanced?

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Movable span bridges (bascule and lift) typically employ a counterweight to help reduce the amount of energy and size of motor required to move the span. Due to variations in the the construction of the bridge and counterweight, the theoretical balance of both the span and the counterweight may be off.

After a movable span is complete, how close to perfectly balanced do the span and counterweight need to be?


texts: Material thickness to withstand Pressure

texts:
Let's say I have a Sphere made out of Acrylic, with a diameter d meters.

And I want to submerge it down in the ocean. The depth is such that it reaches up to p PSI.

How thick does the Sphere have to be, in order to withstand pressure of up to p PSI?

(I used the variables d and p so I can be given a formula that I can learn/understand instead of a raw answer.)


texts: Can somebody explain how this equation(based on conservation of mass of a fluid) came about?

texts:
This is taken from Versteeg and Malalasekhara CFD book.
δx, δy, and δz are given as the dimensions of the sides of the fluid element under consideration along the three axes respectively.

On the other hand, I've read the same mass flow rate derivation in Anderson's Fundamentals of Aerodynamics and understood it perfectly.


texts:
I have a second order system with open-loop transfer function
$G(s)={a\over(s+b)(s+c)}$, $a,b,c$ are already known.
This system has unity feedback.

I am interested in the time consant of this system, but I need to know should I calculate based on the open-loop or closed-loop transfer function?

The second question is how to calculate the time consant of a second order system? On this webpage (Second Order Systems), it says a second order system may be the combination of two first order systems. If the time constant for the two first order system is $\tau_1$ and $\tau_2$, the time constant for the second order system is $\tau^2=\tau_1 \tau_2$. Can I compute according to this equation?


texts: Energy required to liquify gaseous oxygen?

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Does anyone know where I can find some documentation of a real-world liquification process, and the energy costs?
I can calculate the heat that must be removed from O2 gas to get to liquid, but how would this translate to an amount of electricity (kWh) required to operate the cooling equipment?
I hope that my basic thermodynamics calculation are correct?


texts: I have a hole that contains metal shavings after I have tapped it. Is there a common method to clean out metal shavings from between the threads of the tapped hole?


texts: Metering pump that is either computer compatible or microcontroller compatible?

texts: I'd like to write something in Python to automate and maintain a specific dosing formula for a couple of our processes. We need a dosing pump that either has a USB port that can interact with a computer or a microcontroller. Do any manufacturers make pumps like this? Thanks!


texts: Maximum slope of the road for a car pulling a trailer

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I have a five meter long, 2.40 meter wide, 200 kg portable catamaran I've built at home. To transport, I bought a semi-finished trailer, just the running chassis; and built the upper structure, namely the supports for the catamaran.

Normally they build trailers for a typical mono-hull boats where most of the weight is on the rear side, so they build the chassis such that the wheels and the axle are closer to the end rather than being near the middle of the length.

However, my catamaran is uniform in weight along its length and most of its weight is on the front part (before the axle). Having the axle in the middle seemed more reasonable, so I changed its place:

I measured the amount of weight exerted on the coupling, it was as low as 30 kgs. Not a problem, but when I tested launching the boat (on the ground), with just about half a meter sliding the catamaran backwards, the trailer's bow took off into the air.

It needed about 10 kgs to come down to the ground. If I stayed on the trailer during the launch it would not be a problem, but this caused me to think of another possibility - possible instability during driving uphill.

I tried to formulate the problem in terms of forces and moments. There are two critical pivot points: The trailer wheels (axle) which I believe initiates the unstable action, based on the net moment on the axle. And the coupling which may cause car wheels to take off if the moment is non zero on it.

What maximum incline uphill would cause this instability?  Can an equation be provided with a variable axis position so I can optimize the stability using this equation?


texts: Drawing documentation: Is possible to keep the original drawing valid when revised version is released?

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is possible (by European standards) to have two (or more) valid drawings with same drawing number but different revision indexes?
For example:

DRW-001 = Some Bolt M20x50
DRW-001a = Same bolt but length
changed (M20x60)

And then BOM(s) where both (DRW-001, DRW-001a) are used for bolts M20x50 respectively M20x60?
I know this is far from good solution, but it is even legal/valid?
(My 6th sense tells since a new revision is released, all previous versions became invalid. But can't find any stamdard citation supporting my feeling.)
Thanks


texts: what design features allow a milling machine to withstand lateral pressures against the bit

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I need to cut a slot 4mm wide by 25mm long in aluminum tube with a 2.2mm wall thickness and a 35mm O.D.  The tube is 250mm in length.

It seemed a drill press with a fluting bit might suffice for this "one-off" task, in combination with a sliding table. But I don't have a lot of experience with bench tools and was advised that a drill press is not really designed to handle lateral stresses and that I should get a milling machine instead.

Whether or not a drill press could handle this task, what features make a milling machine better able to do it? Do milling machines have a different kind of spindle bearing? Higher bit-rotation speeds? More rigidity overall and tighter tolerances?


texts: How to calculate the required thickness of a material to withstand a certain force or acceleration?

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I am using a sheet of a certain material to dampen a product. Now, I have been looking at different soft dampening materials, and they're all defined by their durometer scale and other factors.

Which factor should I look at and how should I use it to determine how thick the sheet should be to withstand a certain amount of vertical force or acceleration?

Thanks in advance.


texts: Friction losses between spur gears: less teeth are better than many teeth?

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In my project, a little Nema11 stepper motor turns for max +/-90° an handle. When the windings of the motor are not energized, the handle can be manually rotated by a human operator.
The load is not big: the stepper offers max 19 N x cm of torque and the max load in the handle is around 3 Kg. The gear ratio is around 1 to 4.
My goal is to reduce as much as I can the bad feeling of "clunkyness" and friction/resistance added by the gears when rotating the handle by hand.
What is the better? An "high" number of small teeth, or a small number of "big" ones? (I.e. a small m value versus a big m value, while keeping the pitch diameter the same.)
From an intuitive point of view, I could think that many small teeth have more probability to stay in close contact, increasing friction. While few "big" teeth stay more "away" one from the other. But I could be wrong...
I've read somewhere that efficiency of spur gears is substantially independent from the value of the modulus. It is strongly related to the value of the pressure angle α instead.
Is this true? It seems that I can simply choose almost the value m that I like more to build the gears (in acetal/Delrin).


texts: How does corrosion occur at a temperature below 0 degrees Celsius?

texts: The ISO 9223 standard indicates that there should be no corrosion at temperatures below 0 degrees celsius. Independent researchers have however proposed to lower the minimun temperature stated in the standard to lower values in order to account for the actual corrosion observed in Nordic climates. What is the explanation for the observed corrosion at temperatures below the freezing point?


texts:
So I've been drilling standard 1/4" aluminium in a small (250W) consumer drill press.  I've used a little oil to help, but I'm not sure if I'm doing it right.  The holes seem okay though. They're 10mm diameter.

Judging by the swarf coming off the bit, am I doing it right or is there room for improvement? The edges of the swarf seem 'ripped' with little tags visible. And one side is dull, the other polished.


texts: transformation matrix from the original reference to the main reference

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Consider the state of tension in the neighborhood of the point $ P $ represented in the Figure.

Determine the principal directions of the stress state in $P$ and write the transformation matrix from the original $S(O,\vec{\imath},\,\vec{\jmath},\,\vec{k})$ reference to the main reference $S(O,\vec{e}_\mathrm{I},\vec{e}_\mathrm{II},\vec{e}_\mathrm{III})$.
I already got that $\sigma_{yy}=42.67$.
The solution is
\begin{aligned}
\text{}\\[2.75ex]
\begin{cases}
\vec{e}_\mathrm{I} &= \cos\theta_\mathrm{P} \vec{\imath} + \sin\theta_\mathrm{P} \vec{\jmath} + 0 \vec{k} \\
\vec{e}_\mathrm{II} &= -\sin\theta_\mathrm{P} \vec{\imath} + \cos\theta_\mathrm{P} \vec{\jmath} + 0 \vec{k} \\
\vec{e}_\mathrm{III} &= 0 \vec{\imath} + 0 \vec{\jmath} + 1 \vec{k} \\
\end{cases}
\end{aligned}
I know that 1$\ \vec{k}$ is one of the main directions of the state of tension because we got that $\sigma_{zx}=\sigma_{zy}=0$ and therefore
\begin{cases}
\vec{e}_\mathrm{III} &= 0 \vec{\imath} + 0 \vec{\jmath} + 1 \vec{k} \\
\end{cases}
However i can't understand why $\vec{e}_\mathrm{I} $ and  $\vec{e}_\mathrm{II} $ are that expression.
Could someone explain it to me?
So the rotation matrix about x and y axis (not needed in this exercice) will be: \begin{alignedat}{1}R_{x}(\theta )&={\begin{bmatrix}1&0&0\\0&\cos \theta &\sin \theta \\[3pt]0&-\sin \theta &\cos \theta \\[3pt]\end{bmatrix}}\\[6pt]R_{y}(\theta )&={\begin{bmatrix}\cos \theta &0&-\sin \theta \\[3pt]0&1&0\\[3pt]\sin \theta &0&\cos \theta \\\end{bmatrix}}\end{alignedat}
right?


texts: I am designing an enclosure, and top and bottom should be linked thanks to snap fit. I have to use 3D-printing to make both parts. The material is ABS. I made some trials, but they keep breaking. I am using the design in the following picture.  Do you have any idea about how I can strengthen them or something else to prevent them from breaking ? Thank you for your help !


texts: Looking for a common term for "non-circular pipe"

texts:
In Russia, there's a special term for a pipe that is not circular in its section: "a profiled pipe" (профильная труба). There's even a Wikipedia page for it: профильная труба. Such pipes come in a wide variety of sizes and usually have an oval, square or rectangular section ("profile" in Russian), but other kinds of sections are possible.

I wonder what is the common cover-all technical term describing "any kind of non-circular pipe".

Example of usage:

  Pervouralsk New Pipe Plant produces a range of non-circular pipes, including pipes of variable cross-section.

(Also asked on ELL SE)


texts: Building drone transceiver module with 2 recievers onboard to switch gates ON/OFF to turn motors On/Off

texts:
I'm looking for any resource that can help me build a radio (no infrared) controlled circuit with two receivers onboard a drone. The purpose of this circuit is for research and education. Whenever transmitter sends :

a signal to receiver 1, the receiver 1 circuit module should close switch a, and
a signal to receiver 2 module, it should open switch B (which is normally closed)
A) How can I differentiate between the two received signals so that there is no false switching ?
B) Which module will work best with low weight & long range as primary objective ?
If anyone knows where I can get parts for such transceiver RF circuits or even a tutorial or schematic that would be really appreciated.

I'm looking for is something to get me started in the right direction to build RF wireless circuits or use an available module. Thanks!


texts: Difference in energy consumption between empty fridge and fridge filled with bottles of water

texts: I have about 12 bottles of water. If I want to minimize the energy consumption of my refrigerator, should I put these bottles in the fridge or leave them out?


texts: Modelling acoustic instruments — predicting frequencies, decays, levels, and phases of modes of a circular membrane (drum head)

texts:
I have been working on some acoustic synthesis software for modelling several acoustic instruments. I am using the principle of modal synthesis, where every mode of vibration is individually synthesized, generally using a resonant bandpass filter (or sine wave). I have used this approach to get great results on stringed instruments like guitar/cello where the relationship between modes is simple and reasonably predictable. However, I am struggling with drums.
As a 2D circular membrane, the vibrational properties of a drumhead (and even more so, a two headed drum with a drum shell between) are much more complicated than a simple string. However, I still believe this should be possible to synthesize well given modern computing power. With the correct data, I can easily synthesize 500+ modes simultaneously to give a likely good sound.
Imagine a simple 2D circular membrane excited by a strike of energy at its dead center. The information I ideally need for each mode is:

Frequency ratio relative to the fundamental (0,1) - this is easily given in an ideal circular membrane by the Bessel zeros. Things would be different in a "nonideal" membrane, but this is easy to get from any program like ANSYS either way, and I would prefer an "ideal" simulation first.

Maximum amplitude of sound of each mode relative to the fundamental (0,1). If a point of reference is needed, let's say we are measuring sound at 2-3" from the center of the excited membrane.

Decay rate of each mode, where decay rate is given by time to reach 1/e amplitude relative to that mode's highest initial amplitude, or alternatively in dB/s.

Time delay from excitation to beginning of a mode's oscillation in milliseconds or in radians/degrees for that mode's frequency.

If I have a table of that data for the first 500 significant resonances of a circular membrane (or full drum model), I can easily put that into synthesis to see what I get.
ANSYS is okay even in simple usage for providing basic modal frequencies (#1). But I am uncertain if/how it or another program can possibly provide #2-4 on that list.
Is this a very simple or challenging set of data to try to get? How would you approach it, ie. with what program or modelling technique?
Alternatively, the biggest component of the "sound" besides the frequency ratios is the decay rates. If you are aware of any equation that can, using an arbitrary damping coefficient $c$, express the theoretical decay rate of any (m,n) mode from a given decay rate of (0,1), that would likely work well enough too. It was easy enough in strings to work in this way, but I don't think it will be so easy in 2D. I'm sure such an equation can be derived, but I don't know it, and I'm not sure anyone else does either. I am hoping to be able to work that relationship out from modeled data if I can get modeling working.
Thanks.


texts: Are linear controllers inadequate for nonminimum phase systems?

texts:
Based on the following publication:

  Kouro, S., Perez, M.A., Rodriguez, J., Llor, A.M. and Young, H.A., 2015. Model predictive control: MPC's role in the evolution of power electronics. IEEE Industrial Electronics Magazine, 9(4), pp.8-21.

Available here, it is said that:

  MPC can be also used with nonminimum phase plants, which usually appear in rectifiers connected to the grid, avoiding linear controllers, which, in these cases, have a very restricted performance [76], [79], [83].

Dose it mean that linear controllers are not adequate for nonminimum phase systems? If yes, why?


texts: I have water being diverted from underneath my foundation in one specific area from an unknown source. It's causing my foundation to settle and I have already had it leveled with piers.  I have confirmed that it is not a plumbing leak.  It only happens when it rains really hard.  I spoke to a plumber who told me he ran across this kind of issue before and after his customer investigated where their utility lines were, AT&T's lines were causing the problem and they ultimately were responsible for installing a sump pump to resolve the issue.  I know absolutely nothing about how utility lines run underground and how this could cause water to be diverted under a slab.  Does this make any sense to anyone?


texts: Why are so many things around us rectilinear?

texts:
If you look at the man-made objects around you, you will see that almost all of them are either rectangular, or parallel and perpendicular. There are a few circles here and there, but the overwhelming trend in basically everything humans make now is the rectangle. This is true from the computer user interface that you're looking at now and the typography in it all the way up to the shape of building blocks in your city, and if your city is completely planned, to the shape of large sections of it as well, and the fields around it. Even some administrative borders are also rectangular, which seems like the only geometric trend with these.

The product and graphic designers apparently only follow this trend and make everything rectangular because that's what it looked like when they started to work with a particular medium. They didn't probably set the trend.

You could argue that rectangles are easier to pack together, but triangles and hexagons are just as easy to pack, and there are numerous other shapes, polygonic or curved, that pack perfectly well.

The concept of rectangles even applies to the third dimension and there most things are box like, our fridges, houses etc.

If a list were to be prepared of the primary motivations for such rectangular practise, then what would top that list ?

Moreover, the question also applies to the relevance of such motivations in the current age of 3D printing, and modular and adaptive architecture.


texts: How feasible is a 200km long tube with no curvature?

texts: By no curvature I mean not following the earth's curvature. Would it be easier to tunnel the middle through the earth or raise the ends out of the earth? Is there anywhere that this kind of construction has been made and if so how much did it cost?


texts: Bonding steel plate to fiber cement sheet effectively

texts:
I've been trying to produce a cheap panel using fiber cement and zincalume sheet. There is a research paper that I read about bonding steel plate to concrete to increase their tensile strength by reaching a fully composite state when they are bonded with epoxy.

I've calculated the cost of bonding those two materials with epoxy and mechanical fasteners. I found out that if I cover the entire surface with epoxy the cost is too high. I wonder can I just make a Square and X shape ( [X] ) with the epoxy adhesive and reach the same benefit as covering the entire surface? Or is there an alternative solution to this?


texts: How is a merge left or a merge right chosen?

texts: Recently a certain 2 lane exit ramp changed from merge right to merge left, but the entrance ramp immediately preceding it is merge right. Why was this changed? In a given circumstance, what dictates a merge left rather than a merge right?


texts: Applying PSO for tuning a compensator for double integrator plant

texts: I was reading a book on control systems by Richard Dorf and he lists procedure for designing a lead compensator for a double integrator plant. Using the method I developed models in Matlab and it works fine. But I am unable to to tune the system with constraints for time and frequency domain performance. I would like to tune the system for specific rise, fall , zeta, bandwidth, phase and gain margin requirements. I was thinking of PSO algorithm, but it requires an objective function in the first place. I require guidance for deriving the objective function for the constraints listed above.


texts: Whats the correct name for the filament driving mechanism used in 3d printer extruders and MIG wire feeders?

texts: Looking for the correct terminology to for the cable/filament feeding mechanism used in 3d printer filament feeder where the filament is gripped between a bearing and a gnarled gear tooth driven by motor - also seen in MIG-welder wire feeders. Would like to be able to do some searching to find out more on integrating similar mechanism to retract either stainless steel cable or Dyneema rope in something I am working on.


texts: Results for Bending Moment using BEAM188 on ANSYS APDL

texts:
I'm doing a static analysis on a uniformly loaded cantilever beam in ANSYS APDL. I'm using BEAM188 with all the default options, so it uses linear form. for the element behaviour, which I think means the bending moments and tensions are linear within the element.

I want to plot the bending moments along the beam with an area contour, for that I'm using:

ETABLE,MI,SMISC,3
ETABLE,MJ,SMISC,16
PLLS,MI,MJ,1,0

This are the axial stresses due to bending, it looks very similar to the bending moment, it shows discontinuities between elements and for each element it shows the same value on both nodes.

Why does MI=MJ? Shouldn't there be a linear variation of the moment in the elements? Does it make sense for it to be discontinuous between elements? Or is this just a bad plot and I should plot the values on the nodes I get with PRESOL,M as opposed the plot each I and J node values for each element.

The results overall seem good, but I'm not sure if this is a correct representation of the behaviour of the elements.

I'm sorry for such a basic question. I hope I wasn't too confusing.


texts:
My question might seem a simple one, but it has been troubling me for a while.
How many hours in a day do conventional electrical generators work (the ones in large power plants)?

Do they by any method conserve or store the power before it reaches the consumer?


texts: Which design to maximize friction for a device standing on concrete?

texts:
I have a device 4cm X 5cm X 15cm that stands on asphalt/concrete/road. So, the device is taller than its base which makes contact with the asphalt.

I want to maximize the friction so that the device stands as well as possible without any attachment.

I'm considering a thin rubber add-on attached at the bottom of the device and I'm wondering what is the best design for such rubber to maximize the friction with asphalt.

I selected rubber because it has the highest friction coefficient with asphalt - there is a reason why tires are made of rubber...

But how should I design the bottom side of this rubber part that will be in contact with the asphalt? Here is an idea which I got inspiration from a bathtub mat. What is the best pattern possible? And what should be the pattern size (small or big relative to the 5cm X 4cm area)?


texts: I was trying to understand this stress curve in the notch effect. $\sigma_y$ I can understand but $\sigma_x$ and $\sigma_t$ not. Could you please explain?