texts: External diffusion: calculation of surface concentration

texts:
I am struggling a bit with an external diffusion problem.  I am trying to calculate the concentration at the surface (as well as surface reaction rate) and would like some help or guidance.

Here is what I have thus far.

The reaction taking place, is

I want to calculate the concentration of B at the surface of a spherical catalyst particle.

Flux:

Now, from the diffusion equation:

.

R_A can be approximated by the first order reaction rate

so

(just ignore the "2" after the =)

Now, the boundary conditions that I think I should use, are

Note, at all times, I already have the values of all components' bulk concentrations, and I also have values for D_i,j and D_i,mix for all i,j.

Are my boundary conditions chosen correctly for solving for the surface concentration of B (i.e. c_B or y_B or P_B, which are all related)?

Edit:

I need surface values for calculation of the effectiveness factor. I can use any way to calculate surface values with the values that I already have.

I chose r to be any point in the radial direction, even "past" the sphere (when going from r=0, the centre), delta = the thickness of the boundary layer.

Edit 2:

It seems I may have over-complicated it. Based on this video, the control volume considered is only the gas part - the boundary layer. This is correct, since the reaction is assumed to only take place on the catalyst surface and not in the gas phase itself.

In that case, $R_B=0$

$\therefore \large{ \frac{\partial }{\partial r}\left ( r^2 \frac{2cD_{B,\text{mix}}}{y_B-2} \frac{\partial y_B}{\partial r} \right)=0}$

So, at $y_B(0)=y_{B,\text{surf}}$ and $y_B(\delta)=y_{B,\text{bulk}}$

!! Ahh, I've just realized a mistake in my boundary conditions. At $r=0$, we are at the center of the sphere, so that boundary condition is incorrect. !!

So, let's try again:

At $y_B(r=r_{sphere})=y_{B,\text{surf}}$ and $y_B(\delta)=y_{B,\text{bulk}}$

From Matlab: $\large{y_B= 2+{\left (y_{B,\text{bulk}}-2  \right )} \left ( \frac{y_{B,\text{surf}}-2}{y_{B,\text{bulk}}-2} \right )^{\left (\frac{r_{\text{sphere}}\left ( \delta -r \right )}{r\left ( \delta -r_{\text{sphere}} \right )}  \right )} }$

Now what? How do I get the surface concentration values? Since I do not know the thickness of the boundary layer ($\delta$)?


texts: Looking for a compression spring alternative with 10x lifespan

texts:
I'm working on a project where 100k spring cycles is gonna last a few months
Any recommendations on an alternative? I considered magnets but their sprigabilty isn't great (also, will they get demagnetize with constant repel forces?)
I'm working on a linear motion like that:
https://www.pinterest.com/pin/337136722090812189/

The spring will be 2cm in length and 3-4mm in diameter.
Also, I can design it for a tension spring, will this make a difference?


texts:
I need to find blank sheet of a Double-Curved sheet metal part. There are some functions in CAD softwares like Solidworks, Catia, Nx, 3dQuickForm (solidworks Add-in) and etc for flattening a surface, it looks like that they use iFEM to find the flatten sheet, But the answer is not the same in every software! it is obvious that there are some errors involved! I do not have access to details of configurations of iFEM in those CAD sofwares and Ansys is much more reliable for FEA. Despite the fact that it is very common question to find the flatten sheet metal, I could not find any clue to do this job in ANSYS.
My surface is made by LOFT feature in Solidworks and due to very large radius of curvature, deformation is elastic.
Is there any feature in Ansys to solve this problem?
*this picture is in Solidworks.


texts:
I know that the King Post and "Truss Web" or "braces" are there to make the whole truss "stronger", but can someone explain what are they actually supporting if there is no load on the bottom chord/tie beam?

If you do a truss analysis with loads on the "upper" nodes, the kingpost and webbing are 0 members. I'm guessing you can't actually do a truss analysis on this (altho it is called a truss) because the majority of forces are bending forces? the braces are there to keep the rafters from bending and the kingpost is there to keep the bottom chord/tie beam from sagging?


texts: Converting a light switch to a Boolean toggle switch

texts:
I have a system in which there is a screw with an electrical contact on it. When the screw is in all the way, one electrical connection is made. When it is out all the way, another connection is made. If it is in-between, no connection exists and my circuit doesn't work. I can adjust the endpoints which determine what is "in" and what is "out". The piece is from a garage opener that I am trying to repurpose. Here is a picture of the system.

I can control my unit with this setup, however I would like to use a light switch, since turning a dial really isn't as easy as flipping a switch. The lightswitch, unfortunately toggles between on and off. I would like to control between connections 1 and 2 instead, since another switch gives power to the unit. Is there a way I can do this or am I just going about this entirely the wrong way?


texts: Why does fatigue crack growth require unloading?

texts: When a crack has been initiated in a material, further loading of the material causes stress concentrations at the crack tip. This high stress causes the material to break at the tip and the crack grows. As the material is loaded again, another stress concentration occurs and the crack grows again. But why do we need to unload the material in between? Why doesn't the crack just propagate immediately from the initial notch?


texts: Cheap electrical motor that can spin freely in both directions when unpowered

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I am looking for a cheap (preferably under 2000 USD) electrical motor that can spin freely in either direction when the motor is unpowered. The motor will be used as an alternative source of power to a hand-cranked ferry.

There are three cranks: one on the ferry + one at each docking station. All three cranks are connected - when one turns, all turn the same direction.

At this point, we're just looking for a quick proof-of-concept hack that interferes minimally with the current operation of the ferry. What we have in mind is a small electrical motor mounted near each of the two cranks on shore, directly connected to the crank axles using belts or bike chains. To keep it as simple and cheap as possible for this quick proof-of-concept, we were hoping to find a motor that spins with minimal resistance in either direction when unpowered.

Our first idea was to use a direct drive brushless motor designed for bikes, since they presumably do not need a clutch to spin freely, but from what I have read, such motors don't like high load at low RPMs, so they don't seem ideal for our use-case. Our cranks will spin at about 30 RPM. The load varies depending on the weather, but rarely more than an adult person can crank with one arm.

Does anyone know of an off-the-shelf product that meets our requirements?

I have googled for a geared motor with an internal magnetic clutch that automatically releases when the motor is unpowered, but I've found no good candidates so far.


texts: Strategies for cable vibration: eigenvalues are suitable?

texts:
This is a theoretical question.
It is known that in "classic" vibration analysis natural frequencies can be found by solving an eigenvalue problem, from the undampened vibration equation like

$\mathbf{M}\mathbf{\ddot{u}} + \mathbf{K}\mathbf{u} = \mathbf{0}$

where $\mathbf{u}$ is the displacement vector.
But, with reference to this situation

I started to wonder if this type of analysis is not correct here because $\mathbf{K}$ (stiffness) of the cable is not constant but $\mathbf{u}$-dependant (equal to zero when $\mathbf{u}$  is a displacement of compression).

So I would like to ask if someone could suggest me another strategy, or show why the eigenvalue analysis could be used also in this case.
Thank you all.


texts:
I'm building a mount for a small IR sensor which will look very similar to this, minus the large camera.

I am wondering whether or not it would be necessary to do calculations to ensure that the structure is safe and will not collapse.

The potential problems I see are the bending moment due to the weight of the top motor. Would I calculate this and compare to the yield stresses in the bolts of the bracket? Potential buckling? Would it be worthwhile to use a software such as Ansys to run a stress simulation? The weight of the camera is very small and would not effect any calculations. I am using aluminium. Thanks


texts: Impact of mold material in carbon fiber part finish

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Does the material with which I make the mold for carbon fiber parts affect the finish the part will get? If it does, I would like to understand how a given material may affect the finish.

Another thing that is confusing me is the exact definition of finish. Does it refer only to the smoothness of the surface of the final part, or does it also refer to gloss and polish?


texts:
I have a simple, practical engineering question.

I'm trying to design a hot water circulation system with a constant flow rate of 1.3 L/min. I'm having trouble finding any pumps that will do the job at the temperature (80-100C) for a reasonable cost.

Essentially, I'm trying to Development of a Consistent and Reproducible Porcine Scald Burn Model

Does anyone know:

Where to search for for reliable, inexpensive, high-temperature water pumps? I tried McMaster Carr, but they didn't have anything that fit the bill.
Another way to adjust the flow rate? I thought a nozzle might work, but I'm worrying about too much back pressure damaging the pump, or worse, that a restricted area wouldn't even reduce the flow (RTT)?


texts: Failure in Hollow, Thin Beam due to Collapse of Cross Section

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I'm having trouble figuring out how to predict the failure of a hollow channel due to bending. If I'm correct, for a beam with a static second moment of area, $I$, the following equation could be used to find the bending moment needed to cause yielding in a ductile material: $$\sigma _{b}=-\frac{My}{I}$$
However, for a square, hollow extrusion (for instance) with relatively very thin walls, it seems likely that the side walls (perpendicular to the torque vector) would first buckle and start to bow outwards, bringing the top and bottom walls (parallel to the torque vector) closer together. This would "squish" the cross section and significantly reduce its second moment of area as a function of the applied torque.
In other words, if you applied a bending moment to both a hollow beam and a solid beam with equal second moments of area, I hypothesize that the hollow beam would yield under a lesser bending moment due to the deflection in the lateral walls of the cross section.
That being said, I've searched to no avail for any method to model the premature failure of a hollow beam. I would like to be able to relate failure due to yielding to the applied bending moment for an arbitrary hollow, thin cross section, and I would appreciate any help. Since this scenario involves buckling within bending, I anticipate that it would be complex to model analytically. For that reason, I would be content with any sort of approximation, such as introducing a modification to the value of $I$ in the above equation.


texts:
One of the places I frequent recently had the curb and sidewalk rebuilt by the city.  Previously, there was a roughly continuous transition from the street to the rest of the private drive next to the building.

After the rebuild, the sidewalk was leveled out which created two sloped areas coming from the street.  The problem with this new design is that even at reasonable speeds, vehicles are somewhat bottomed out from the up-down-up motion created by the two slopes.

If it matters, this is a transition point from a public street and sidewalk onto private property for a non-residential building.

This is what the entryway looks like now:

What it used to look like:

Please note, I have exaggerated the slopes in the illustrations in order to clarify what I'm asking about.

Is there a common term used in roadway design that describes the double slope?  I would like to be able to research the term to see if there was any code violation.  At a minimum, I'd like to use the correct terminology when I ask the city about rectifying the problem.


texts: What is the justification for working on such large stretches of road?

texts:
I live and work in the UK, a country known for relentless roadworks.

Last week I drove through roadworks on the M1 that lasted for 18 miles, necessitating road users driving at 50 mph. Of course, almost all of this impressive stretch was simply coned off, with active work only present on one or two small sites. Signs indicate that work will continue into next year.

What justification is there for keeping such a large section of road cordoned off for improvements? Is it a safety or economical consideration? It would seem prudent to close off mile sections at a time to increase traffic flow and reduce the number of cones/signs/average speed cameras in use, but perhaps there is an underlying reason I am missing?


texts: Do modern, easily-opened tincans have the same "life expectency" as the classic, hard-to-open tincans?

texts:
Growing up, canned food was opened by using a hand-operated (or automatic, if you were rich) "tincan opener". It was a pain to get the damn thing open, and when you did, you were lucky if you didn't cut yourself in the thumb on the sharp edges and fiddling with the little metallic thing with a razor-sharp cutting edge.

Nowadays, really just in the last few years, all the tincans I see have these little "soda can" opening things which require no external tools and opens the whole lid very easily.

"Classic"/traditional tincans are said to hold up a very long time if stored properly. Maybe hundreds of years, possibly?

What I wonder is if the easiness in opening comes with a price for the modern tincans, namely by cutting its "edible until" date closer to when it was manufactered? Maybe they are even deliberately designed such, so that people are unable to "stack up" on emergency food and keep having to buy new tincans as the olds' contents become rotten and inedible?

On the other hand, I remember eating slightly expired cans of various food, sealed with the classic method, and they were absolutely disgusting when opened... But maybe I was just unlucky?


texts: What if project requirements depend on discoveries while designing?

texts:
I asked a question where a comment pointed out:

  Requirements are things that you should be drafting to figure out what you want, before you know exactly how you are going to solve it.

I was doing it backwards. I was going to define requirements after I had investigated design ideas to weigh up compromises that might be made. What I called requirements were flexible, depending on the cost vs effectiveness of design ideas.

If I do not know what I want before I consider design ideas, if the possible criteria are not requirements, then what are they?

The problem is the product fits into a larger system, ultimately the goal is profit from a business perspective, but considering the whole system's economics while designing the one product would be too complicated, so the requirement for "maximum profit" doesn't help!


texts: When a frame structure is analyzed using a FEM computer software, does the program still generate mesh, even as a line mesh, on frame members, or we must do it ourselves?


texts: Why are drill bits always slightly undersized?

texts:
I have found that drill bits are always slightly undersized. For example, 10mm bits tend to be more like 9.8mm diameter. And in aluminium, the hole ends up being about 9.9mm. The same seems to be the case for conical stepped drill bits

I've found it useful for inserting ball bearings, since they can be hammered in place without being damaged and will stay firmly in place. Also, bolts tend to be slightly undersized so will have a more snug (but still loose) fit.

What's the actual reason for drill bits being undersized?

Oddly, hole saws tend to be slightly oversized. A 15mm hole saw's teeth outer diameter measures to be 15.05mm and makes a 15.3mm hole.

Is there a term for drill bits which are slightly oversized instead? Or hole saws which produce slightly undersized holes? (assuming they exist)


texts: Screw type associated with COM port/DB-9

texts:
DB9 female port often have female slots for two screws to secure the male plug onto it. What is the type of this screw?

Word 'screw' is mentioned 7 times in Wikipedia DB-9 article but not the type.

Same port is a COM port on computer. Old school mouse port too.

At least Farnell, parts distributor have these screws categorized under: d-sub-jack-screws, and many items say M3 that being the type of the thread and the size both, 3 millimeters.

However, I have an unknown screw that fits into the mentioned female slot, and I have a legit M3 type screw, and the threads are way denser on the standard M3 screw. They have the same thickness tho.

Two leftmost ones fit, and are of the type of which I want to know the designation, the one on the right is M3


texts: Which part of the LED is affected when it is exposed to liquid nitrogen? I have seen experiments showing LED's brightness increasing and color shifting, when the LED is submerged in liquid nitrogen. I have also seen one where the color went DOWN in frequency, how can you explain this inconsistancy?


texts: Can I get some help solving this statics reactions problem?

texts: I'm working on this reactions problem. I know M(ay) is equal to 0, but I haven't been able to figure out how to solve for the tension in cable BC, forces A(x) and A(y), or moments A(x) and A(z). I've tried summing moments and forces every way I can think of, but keep coming up short and could use some help!


texts: Difference in the properties arising from precipitates and intermettallics

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What are the key differences in the mechanical properties caused by precipitates and intermettallics in metal alloys?
So far I've found that intermettallics are larger phases, and are usually hard and brittle.
Could someone explain why please? Are there other key differences?
Thanks!


texts:
In context of machine design, what is mean fatigue strength? (as I am thinking I am mixing it up with midrange strength)

In my class we deal a lot with steels and this is a low strength steel, but I can't find those three words "mean fatigue strength" put together followed by a definition and/or formula...


texts:
I had a PC Mountable Wet/Wet Differential Pressure Sensor
I used it to measure a pressure difference , I don't know how to convert its output to pressure !


texts: Why was air conditioning so early and wide-spread in the USA specifically?

texts:
As far as I understand things, air conditioning was standard in cars in the USA as early as by the mid-1950s or so. Perhaps even sooner.
In the late 1990s, our car (common model of Volvo, albeit a few years old for sure) in Europe had no air conditioning at all. It was often very hot to sit in in the summer. (Just as it was very cold in the winter.)
I've endured the last 20 years worth of hot summers without air conditioning. Actually, in 2016 or something, I did have it briefly, in the form of a portable unit which was located indoors and hooked up to the window in a very problematic manner, because it was clearly not made for windows which open inward (it expected slide windows), to the point where I had to get rid of it since it kept coming loose all the time, driving me absolutely insane. (But the coldness it produced, for the short bursts when it was working as intended, was Heaven-like.)
In the USA, it seems as if even the cheapest possible place where you can live still has air conditioning as a "minimum standard of living", since what seems like decades at the least.
How come this wonderful invention is basically unheard of here, in spite of it being so unbearably hot, whereas it's extremely common in the USA?
I did notice even as a kid that the fancy houses had AC units on the outside, so it definitely did exist, but seems to have been (and remained) something of a luxury product which by no means is standard or even common in apartments.
Why is this?


texts: In the early days of steam engine powered ships, wouldn't a system that intermittently injects high pressure steam above a wide column filled with water, thereby displacing the water and expelling it through a nozzle connected at a 90° angle with the bottom of the column offer better efficiency than ungeared steam turbines? A valve would then open letting the steam escape and the water surge back in to the previous level and the cycle would repeat.


texts: Program for creating a cylinder given its axis, center and radius?

texts:
I have data with the following normalized values:

Unit vector for cylinder axis:
-0.00270666, -0.01226211,  0.9999212

Normalized coordinates for cylinder center
0.01412114, 0.01074875, 0.00017004

Normalized cylinder radius
0.12903491

Is there any program I can use to display a cylinder with the following parameters? I know of programs like OpenSCAD that accept height and radius for a cylinder which can them be translated,rotated, etc. but I'm not sure how to use the unit vector of the axis to get the height (I assume for rotation I can use trignometric functions to derive the angle of the cylinder).

Thanks


texts: Is there a general rule of thumb for how accurate a gauge should be in compared to the parts being checked? In my chemistry class, I remember making standards where the instrument needed 1 more significant figure in compared to the standard solution we were creating. Is it the same rule for gauges?


texts: link text (note) with mass property in Solidworks for different configurations

texts:
I have a SolidWorks assembly with 2 configurations. I want to display the mass of each configuration in the model itself as a note (text). An illustration is shown in the figure below.

I have two doubts as follows:

I want to know if it is possible to link the note with the mass property so that when I switch over to next configuration, the note automatically updates with the new mass of the 2nd configuration.
Is it possible to indicate the mass of only a sub-assembly in the note.


texts: Equations of motion for a motor supported by a spring resting at the centre of a beam

texts:
Assumptions from this:

Sum of forces on the beam to be calculated
Sum of moments on the beam to be calculated
Sum of forces on the motor to be calculated

As:

F=-kx = kθL^2

Equations of Motion

Beam

Question:

Would anyone be able to explain why the + and - L/2theta are the way they are?

I believe I understand why k1 is positive and k2 are negative as taking moments about the centre, assuming clockwise is +ve, means that k2 opposes and k1 follows rotation but I don't understand how to assign L/2 a + or -.


texts:
My next door neighbor's car backed into my wooden fence and knocked down a section.  I want to protect the fence from a future accident.  A steel pipe filled with concrete would cost more than PVC.  A pressure-treated 6x6 could also work.

I want to do it up right.


texts:
How would you go about solving the following problem. I believe Bernoulli's equation needs to be employed, but I'm not sure how.

  Find the magnitude of the force that needs to be applied to a piston of a 20ml syringe with 1cm diameter tube to drain it in 20 seconds through a 40mm length needle of 0.2mm inner diameter. The fluid inside the syringe is water.

Force = ?

Volume of syringe = 20 ml = 0.00002  m^3

Syringe diameter = 0.01 m

Length of needle = 0.04 m

Needle diameter = 0.0002 m

Time to drain syringe = 20 s

Fluid density of water at 20 degrees celcius = 998.21 kg/m^3

Dynamic viscosity of water at 20 degrees celcius = 0.001002 Pa.s


texts: Can a dry-pipe or preaction valve be used to create a branch off a wet pipe sprinkler system?

texts:
Individual-head (i.e. not deluge) sprinkler systems come in three flavors:

Wet-pipe systems have water pressure at the head at all times -- they are the quickest to respond, but can't be subject to freezing conditions and are too risky for water-sensitive spaces
Dry-pipe systems have compressed air in the pipe between the head and the dry-pipe valve -- when the head fuses, the dry-pipe valve is opened by the pressure change and delivers water to the system.  This can be used when a freeze risk exists, but is slower to respond.
Preaction systems are used to provide external confirmation (from say an alarm system) before the sprinklers activate -- the alarm system must open the preaction valve before water can flow onto the fire.  This is used when accidental discharges must be controlled at all costs.

This raises the question: under NFPA 13/13R/13D, can individual fire zones be protected by a dry-pipe or preaction system while the remainder of the building has wet-pipe sprinkler protection? For instance, the attic, garage, and unfinished basement in a home could be dry-pipe protected to avoid freeze-ups while the finished spaces are protected by a conventional wet-pipe system.


texts: How to calculate flow rate and direction in system with multiple blowers

texts:
I have an odour control system where foul air is being extracted from multiple sources and then pushed into a scrubber vessel. Normally, all my designs look something like this:

https://ibb.co/58YSdpc

With this arrangement, I'm able to maintain negative pressure at all sources which ensures that the foul air is being sucked into the treatment system, and that it doesn’t escape into the air through any openings.

However, I currently have a project where one of the sources is a sludge buffer tank that is being mixed through pressurised  air. The system looks like this: (Fans A/B are duty/standby arrangement with rating: 4650m3/hr @1500Pa)

https://ibb.co/bj04pBB

The compressor blows air into the tank from the bottom through the water, and the water level in the tank varies from 1 m to 4 m. This means the pressure in the headspace could range from 10,000 to 40,000 Pa (The way I did this is that  I subtracted the pressure of a water column 1m to 4m deep from the 50 kPa). I would like to know how the air flow rate directions and relative magnitudes  would be like in this system, and whether there will still be negative pressure in the sources. Thanks!


texts:
If I need to get a pressure of 6 bar at the exit of a nozzle for cleaning purpose, how can I determine the following (assuming nozzle outlet dia to be 5 mm):

The pump capacity to provide such a pressure.
The diameter of pipe connecting pump to nozzle assuming total 5 m length.

I'm not looking for mathematically precise answers, but just need to get overall idea of how to calculate the pump and connection specifications.

Some additional information:

The working fluid is water.
The nozzle is used to clean a plate which would be kept at distance of 200mm from the nozzle exit.
The working pressure is specified as 6 bar, which I believe is the stagnation pressure at the nozzle exit.
The nozzle dia is 5 mm


texts: Describing values as being 'assumptions' or 'assumed' - what is the correct approach in academic papers for civil engineering?

texts:
I am a language editor of academic papers in civil engineering (typically written in English by Poles).

I frequently encounter the term 'assumption' being used to describe a value that is adopted for the sake of calculations.  For example, an author might not precisely know the original thickness of a corroded steel shell of a silo, but makes a decision about what it might have been in order to perform calculations/modelling.  This would typically be written as something like: "assumption for thickness of steel shell = 6 mm".

I really feel uncomfortable with words like 'assumed' and 'assumption' on the basis that they are, almost by definition, unscientific.  What would be the correct way to describe the above example?


texts: How much rain water run off do I need to power an LED greenhouse

texts:
My question essentially is how much water to power green house LED lights. Specifics bellow :

Say I have a warehouse with a flat roof with a bunch of water tanks or the whole thing being a water tank. Using say 30 feet High and 20'Lx20'W. How much power could I generate utilizing the roof to store water?

One lighting fixture could run 400 watts.

I was pondering these last few days on this, I've googled a couple of equations but not sure I used the right ones. Thanks for your input in advance.


texts: How to calculate the thickness of a circular plate centrally supported?

texts: I wanted to calculate the required thickness of a circular plate of radius 0.06m made of A-36 steel. The plate is supported by a rod at its center welded together with the circular weld of radius 6mm. A uniform load of 981N is applied on the top of the plat. I wanted to calculate the minimum thickness of the plate so that the plate may not bend. Any help would be highly appreciated.


texts: Is there a drill adaptor or attachment tool for cut a metal solid cylinder

texts:
I need to cut a 7mm solid Aluminium plug (Non-hollow and non-threaded) to replace a part in my car.

Is there a simple drill adapter tool to cut a solid metal cylinder (Plug) from an Aluminium mass ?

(Hole saw cutters are not in small sizes like 7mm)

Edit:

Commercially these plugs are called "Solid Aluminium Rivets". But 7mm size is not available commercially (Available maximum size is 1/4" or 6.4mm). Actually head part of the rivet is not necessary for the function. It is needed for remove the plug for rebuild. But practically, that head got damaged when I try to remove it by a plug remover. So I had to drill-out the plug. So there is no photo to show. So, since the head is useless, I just need to make a plug to close the Idle port of my old carburetor.


texts: Calculating stresses of section with varying depth

texts: I'm trying to solve the question attached below (please note the handwritten values are ones that I calculated/not part of question) I am assuming that to find the load $q$ I need to get the bending stress (which from my calculation was $45\text{ N/mm}^2$) and substitute into equation of Bending stress $= \dfrac{My}{I}$ to solve for M which should be equated to $\dfrac{ql^2}{4}$ then find $l$, however I think I messed up in the first part of the question because I'm not taking the area of part A into consideration, can you please advise me on how to approach depth-varying beams?


texts: What is this nut on a micrometer head and what is the tool for removing it called?

texts: My apologies for a likely very simple question. But what is this nut which I have on a micrometer head called, and what is the tool for removing it called?


texts: Why was Freon used in spray cans before it was declared a threat to ozone?

texts:
I've heard that in the past, spray cans (aerosol cans) contained Freon. I found that the Montreal Protocol made the usage of Freon illegal due to its effect on the ozone layer, but I can't find the reason for why Freon was used in the first place. I understand its role in refrigeration systems, but I fail to see a functionality for spray cans.

So why would anyone use Freon in spray cans, what was its contribution? I assume that it affected the pressure inside somehow, but it's just a guess.


texts: How can the Microsoft and the Facebook Fibers reach 160 Tbps between Virginia and Bilbao?

texts:
According to this article, Microsoft and Facebook have completed a 160 terabits cross-Atlantic cable. Based on my calculations, this doesn't seem probable, so what did I miss in my calculation?

The maximum frequency that a mono-mode fiber can reach is roughly:

$F_{max}=(1/\lambda)*\sqrt{\frac{c}{DL}}$     $(1)$

$D$ is the dispersion parameter.
$L$ its length.
$\lambda$ is the central wavelength.

For $\lambda$=1500 nm , $D$ = 100 ps/nm/km and $L$ = 10 km.

I find: 10 GHz

Assuming 400 wavelength channels, 2 polarizations,  8 fibers, without relays under the ocean and a bit of magic I cannot reach 160 THz.  What am I missing?

$(1)$ is obtained with the definition of $D$ assuming that the dispersion of a pulse of angular frequency $\omega_0$ , angular line-width width $\delta \omega_0$, duration $\delta \tau_0=2\pi/\delta \omega_0$ is $\delta \tau_1=L(1/Vg(\omega_0+\delta \omega_0 /2)- 1/Vg(\omega_0-\delta \omega_0 /2)=LD\lambda^2/(\delta \tau_0)$. $Vg$ is the group velocity.

The maximum frequency is such that:

$F_{max}=1/\delta \tau_0$

and

$F_{max}=1/\delta \tau_1=\frac{\delta \tau_0}{LD\lambda^2}$


texts: Is there formula to calculate the compressive force required to achieve x% of squeeze in an O-ring? I have referred the Parker O-ring and Apple Rubber Handbooks, but they provide just approximations. I am trying to calculate the linear force per length for a 4 mm o-ring and I want to achieve 25% squeeze.


texts:
I want to use a round-over bit on a CNC router after cutting a profile with a 3mm (1/8") bit. So the round-over bit needs a shank thinner than that. I could only find shanks with 6mm (1/4") diameter.

Do round-over bits with shanks thinner than 3mm (1/8") exist? If not, what is the physical limitation that prevents it?


texts: Do regulations in the United States limit the size of aerial wind turbines?

texts:
What with all the work done by the FAA recently on regulating drone usage, I thought it would be nice to turn my eyes to the sky for another, less-known type of aerial denizen: the aerial wind turbine.

Wikipedia has all the relevant information, so I won't rehash it here. The most important thing here is that aerial wind turbines - and I'm mostly interested in aerostat-based designs - are free-floating, just like certain types of tethered drones, which have given the FAA headaches because they're not like most aircraft.

I did find this article, which says

  Regulations and technological restrictions suggest it may not happen very soon, or at all, but some researchers believe aerial turbines will be tapping high-altitude winds for power generation sometime in our future and perhaps within the decade.

and

  That said, companies currently working on the project seem very loosely formed. They are in the development phase and are aware of federal airspace restrictions.

Here's the relevant FAA page.

I suspect that FAA regulatory measures on drones cover aerial wind turbines, but I'm not positive, and I'd like to see some specific mention of them in regulations, if possible. I assume they're treated as (tethered) drones, but I haven't been able to find any direct mention.

Getting to the point: Aerial wind turbines are, in general, much smaller than typical wind turbines. There are obviously some factors that make it easier for wind turbines built on the ground to be larger (support, for instance). But larger turbine blades, while a source of trade-offs, can be much more helpful.

What regulations (in the United States), if any, limit the size of aerial wind turbines?


texts: I'm taking statics, and I'm stuck on this truss problem, how do do I solve this?

texts: I'm an engineering student, our professor assigned us this truss problem I found $A_y$ and $L_y$ by using the moment about l, and found ab, now what? It seems like I have too many unknowns to solve for after that...


texts: Can superhydrophobic surfaces be used to reduce drag?

texts:
I am mainly interested in reducing drag in aircraft and I have an idea that I want to learn more about...

Can a superhydrophobic coating reduce drag in water-craft such as boats and submarines?

If that is the case, could a superhydrophobic coating decrease the drag coefficient of aircraft making them more aerodynamic? Or would some other material that's phobic to air be needed for this, and does it exist?


texts: Is there any way I can be sure a wall is NOT load bearing?

texts:
I've Googled the hell out of this and it doesn't seem to be, i.e.

It's structured like a standard stud (not reinforced top)
It doesn't run along a floor joist
The uprights are pretty badly cut and not snug

But it looks to me like the remains of an attic support structure (it an attic conversion/extension into a dormer-like structure) and to my untrained eye, it seems like a lot of roof (80" from nearest edge to back wall) to support itself.

I was planning on building a stud wall on the outside edge and running a support beam along the length to be safe but is there any way I can be sure that the support isn't even needed?


texts: How to choose between two possible arrangements of tapered roller bearings?

texts:
I don't know how to decide between the $X$ and $O$ arrangement, i don't have any specific example at this moment, but i want to know.

Catalogues offer only some basic calculations. I'm not quite sure if there any guidelines or instruction exist, i have already consulted many books, but so far my researches failed to help me justify the choice between the two arrangements.

Source: https://debearings.se/wp-content/uploads/2016/08/12-Tapered_roller_bearings.pdf


texts: How can I limit a simulated aircraft's angle of attack?

texts:
I am making an aircraft in a simulator (using JSBSIM). Note that I am not a professional.

The manual states that it is limited below certain calibrated airspeed to a certain positive angle of attack.

I have tried different schemes to make this work, but I have not been successful.

For example the simplest was to just freeze the elevator when the limit was reached. But in for example a loop, the alpha will increase even with frozen elevators as the plane goes through the loop.

Another was to use a feedback of the exceeded alpha with a gain into reducing the elevator actuation. But that makes the plane pitch jerk. It should be smooth.

I hope someone can help me out. I prefer a solution that does not use PID controller as they are a pain to calibrate. Block diagrams or text help is very appreciated.


texts:
Hi guys, can someone explain how to do this question? This question is under Geometric Dimensioning and Tolerances and I am clueless on how to tackle problem like this.
EDIT

This is the explanation given in textbook regarding MMC and LMC situation.


texts:
I'm trying to design a jewellery  box, with a mirror in the lid. When open, the lid should rest at an angle of about 135 degrees from original closed position.

I've been learning about 4 bar mechanisms, they sound appropriate (frame = box, coupler = lid) BUT in my case, the crank won't go through a full 360 degrees.

I've been using a simulator with crank=150, coupler=160, rocker=frame=225 but I need a way to model the start / finish positions to ensure everything lines up right.

Is there an app, or even a page full of math, covering the use of 4 bar mechanisms as a hinge? (I'm new to the mechanical engineering field, any help appreciated)

EDIT: The techniques of designing joint positions are apparently what I'm looking for. Mechanism synthesis (2- or 3-position synthesis) is the term to look for. It would seem I'm also going to need a full-blown CAD program, as compared to simple web-based apps I've been using


texts: How to state the PSD value (random vibration)

texts:
In random vibration analysis, the load is given as a PSD (power spectral density). The values are often $G^2/Hz$, but I have an example where the PSD is a pressure $Pa^2/Hz$. The value is written as $(100 N/m^2)^2/Hz$ which brings me to these questions:

Is that value $(100 \;N/m^2)^2/Hz$ equal to $10000 \;(N/m^2)^2/Hz$? (The results of the analysis imply that the answer is Yes, but I want to confirm my understanding.)
Are both styles of writing the value acceptable? Is one style more common or acceptable than the other? For example, I have never seen an acceleration PSD written as $(5 \;G)^2/Hz$ to represent a value of $25 \;G^2/Hz$.


texts: Save money with using a refrigerator correctly - blowing cold air to the back of it?

texts:
We are heating up our houses in winter to ex.: 21C to then have an insulated box inside the house, which we cold down to 5 and -15C, and we call it a refrigerator.. :)

The situation:

we would buy a new refrigerator and put it in a house having 21C constantly
we would also have a "heat-pump boiler" for heating water.
the "heat-pump boiler" outputs colder air than what is there in the house normally, that is how "heat-pump boilers" work, ok.

Like if I would put out the whole refrigerator to outside, where there is ex.: day: 5C night: -5C, I would be sure that the electricity consumption (operation cost) would go down, because it wouldn't have to battle with the indoor 21C.

The question: would blowing cold air from the "heat-pump boiler" to the back (to the bottom or top of the back?) of a refrigerator help reduce the operational cost for the refrigerator?


texts: Shear force and bending moment for continuous span

texts:
It's given that L1 = 5m, L2 and L3= 7.5m, w = 8.9kN/m , I am asked to find the bending moment using these coefficient.. Prior to this , i need to have the value of shear force first.Shear force = coefficient x force.I having problem getting the force for support 2 and 3 .... I think that the 'bottom'shear force for support 2 should be = F x Cs = w x L1 x Cs = 8.9 x 5
x 0.66 = 29.4kN, while 'top'shear force for support 2 should be = F x Cs = w x L1 x Cs = 8.9 x 7.5 x 0.484 = 32.3kN, am i right ? Correct me if i am wrong.


texts: Would outside reinforcement increase thermal shock resistance of a glass cyllinder?

texts:
Would a glass cyllinder reinforced on the outside with tensioned glass fiber be more resistant to thermal shock than an unreinforced one?
I understand that the failure happens when the glass starts to cool down and contracts, and reinforcement that limits the expansion in the first place should prevent the cracks from forming


texts:
Which position of the water pump in the below diagram provide maximum water output to the overhead tank?

Each floor is 12 feet in height.
I already have the pump (Centrifugal Regenerative Self Priming 1HP Peripheral Type, Self Priming - 180sec At 3m STATIC SUCTION LIFT) and would like to know which is the best location to install it for maximum water intake to the overhead tank. The water Supply is only available for a limited period everyday and the goal is to achieve maximum water to the overhead tank.
The Water supply line provides water from a bigger (8inch) main line but water pressure from it is not adequate to pump up water on top level. (Water pressure only enough to supply water to first floor and that too with reduced pressure.)
The water pipe from main supply to pump and from pump to overhead tank is 1/2 inches wide.


texts:
A spool has a mass of 500 kg and a giration radius of $k_G = 1.30m$. The
spool lies on the surface of a conveyor belt, the static coefficient of friction  is $\mu_S=0.5$.
The spool is not moving at the beginning.
Determine:

the largest acceleration $a_T$ of the conveyor belt, such that the spool does not slip.
the pulling force in the rope.

The equations I have are:
$$I_G = m \cdot r^2 = 500 kg \cdot (1.3 m)^2 = 845 kgm^2 $$
$$\sum_i \vec{F_i} = m_G \cdot \vec{a_G}$$
$$\vec{N} + \vec{T} + \vec{F_z} + \vec{F_w} = m \cdot \vec{a_G} $$
After projection I get:
\begin{equation}
\begin{split}
T - F_w  & = m_G \cdot a_G \\
N - F_z  & = 0
\end{split}
\end{equation}
For the moments I get:
$$\sum \vec{M_G} = I_G \cdot  \vec{\alpha}$$
\begin{equation}
T \cdot 0.8 - F_w \cdot 1.6 = I _G \cdot \alpha \\
\end{equation}
Other relations are
\begin{equation}
\begin{split}
-a_G + 1.6 \cdot \alpha & = a_T \\
a_G  & = -0.8 \cdot \alpha \\
F_w  & = N \cdot \mu
\end{split}
\end{equation}
The solution from the teacher is:

This solution does not satisfy
$$a_G  = -0.8 \cdot \alpha$$
My question is: "Is this last equation wrong?"


texts: How do I calculate voltage at an LED in parallel?

texts:
I have this circuit:

If D2 was a resistance, I could just combine it with R2 to get some composite resistance that I could put in series with R1. That way, I could calculate the resistance of the entire circuit and, thus, the total current.

Now, this is not the case here but I know a few things here:

whatever voltage drops at D2, also drops at R2
the current through R1 is the same as through R2+D2

But I do not know the current from the beginning, so I cannot calculate the voltage drop at R1. And the diode is non-ohmic, so I cannot find out anything about it.

In this way, I do not see how I could apply Kirchhoff's laws or any other methods because I seem to be missing information... where do I start here?


texts:
This is the top part of a basic sit/stand base I'm making.  It is a monitor platform and sliding keyboard tray.

Instead of the large base with 2 rods on each end (like this design see video at bottom of page) I'm looking for another way to raise and lower the desk.

The one issue with the base design, is that in the lowered position, the platform is already 4 inches up off the desk and will then have to sit on top of the base another 3.5 inches or so. The addition of a base anymore than an inch or so would be too high...(unless the platform does not have to sit on the base)

I'm looking for some sort of electronic or manual jack that could fit under the over-hanging portion of the platform. Perhaps a small one on each of the 4 corners.... or maybe 1 longer one for each side? (The platform is 33"X18")

I would like to raise the desk about 12 inches from where the top sits now. Also will be in an office setting so can't be too loud.

Are there any type of devices that could be engineered... or purchased... or somewhere in between, that can work for this application or have been use for something similar in the past?

Some other random ideas I have had: some sort of accordion or scissor lift that attaches across to the bottom of each vertical leg of the platform....or maybe air bags?

Here is a close up of the leg and edge hanging over.

Update1

or for a more manual design, I came up with scissor sliding rods with rails. On one side, it would have a sliding rail attached to the top of the over hang, and then a rail attached to some sort of base - that would fit beneath the over hang:

Has something like this ever been proven to work decent?

The only problem with the scissors as a whole unit is that the top would need to be attached to the legs of the platform...and not sure how many inches it would add..in addition, the whole desk would move forward and back, along with up and down (and I have no idea what the kid is saying...probably some thing like I'm 8 and smarter than you).


texts: How to get this hydraulic system working and help identifying parts and their function

texts:
I have recently acquired a 1982 Arburg 220-90-350 injection moulding machine, mainly just as a hobby to further my knowledge on injection moulding machines and control systems as I plan to modernise the control system by redesigning it from scratch using a PLC and HMI.
This is my first proper project involving hydraulics at this scale, the hydraulic pump motor works but I have no pressure at the hydraulic valves. There are two proportional valves on top of the pump, the pump has two large pipes connecting to the manifold and one small one.
What is the purpose of the proportional valves and do I control both at the same time, just one, if so what one? What is the small pipe doing, it is the small rubber hose connecting to the lower side of the pump?
I'm sure the control valves on the manifold are standard hydraulic valves and not proportional, is this right?
I'm thinking all I have to do is work out what the proportional values do on the pump and then control them and then control the valves on the manifold. Is this the right way of thinking?


texts: Relation between ride frequency and wheel deflection of a car

texts: I am not able to understand the relation between ride frequency and wheel deflection of a car, as per given in Race car vehicle dynamics book by milliken. Is it something to relate with harmonic motion of a forced oscillator? I still don't get why there is a 188 in the numerator.


texts: How to get a transfer function from this block diagram?

texts:
Pardon my paint skills, I did my best

My attempt is short and seems to fail, I have no idea why:
$$\begin{align}
\alpha &= in - a_{1}\beta - a_{2}\gamma \\
\beta &= \alpha z^{-1} \\
\gamma &= \beta z^{-1} = \alpha z^{-2}
\end{align}$$
inputting 2nd and 3rd equation into the first one I get:
$$\begin{align}
\alpha &= in - a_{1}\alpha z^{-1} - a_{2}\alpha z^{-2} \\
in &= \alpha + a_{1}\alpha z^{-1} + a_{2}\alpha z^{-2}
\end{align}$$
I can write the output as:
$$\begin{align}
out &= b_{2}\gamma + b_{1}\beta + b_{0}\alpha \\
out &= b_{2}\alpha z^{-2} + b_{1}\alpha z^{-1} + b_{0}\alpha
\end{align}$$
I have output and input in terms of alpha, but I can't figure what to do from here.


texts: Derivation: Entropy of Vaporisation using Redlich-Kwong EoS

texts:
The part I'm stuck on is the last part. Basically, the question is to obtain the following equation for the entropy of vaporisation using the Redlich-Kwong equation:
$$
\Delta S = R\Bigg[ \ln \frac{V_2 -b}{V_1 - b} \Bigg] + \frac{0.5a}{bT^{1.5}}\ln \Bigg[ \frac{V_2(V_1-b)}{V_1(V_2-b)} \Bigg]
$$

Solution Attempt:

I think I should start by using the known fact that at equilibrium, the free energy of both phases must be the same. Using Gibbs free energy:
$$
dG = -SdT + VdP \implies -S_1dT + V_1dP = -S_2dT + V_2dP
$$
Therefore, I can write an equation for change in entropy due to vaporisation:
$$
S_1 - S_2 = (V_1 - V_2)\frac{dP}{dT}
$$
However when I simply differentiate the given EoS and multiply by $V_1 - V_2$ I don't get the same result. Clearly, in the answer they have integrated wrt v at some point but I just don't get why or how. Any help will be appreciated, thank you.


texts: New electrical engineer seeking advice on electrical design for hotel!

texts: I am a recent graduate who is working on a brand new hotel project. I am helping to design the electrical system. I was wondering if anyone who is in the field would be willing to help me by giving me step by step advice on the entire process of designing an electrical system for a commercial building (A hotel in particular)? Any advice and guidance will be appreciated. Thanks!


texts: Effects of Solar Shield on Electronics Enclosure

texts:
I am designing a prototype of an electronics package that

will sit out on a pole in the sun 24/7 with a
max ambient temperature of 50˚C and
at 30˚N latitude.
It produces 50W of internal heat and the electronics are rated to 70˚C.

Currently, it is all housed in a grey polycarbonate box (approx. 18"x12"x6" hwd).   I have room for a 100W air-to-air heat exchanger (I need to keep the box watertight which also precludes most vents) but from back-of-the-envelope calculations I can already tell that the solar loading will likely overwhelm the exchanger.
So, from the outset I have planned on putting a solar shield around the enclosure, but now that I have reached that point in design I realize that my heat transfer skills are more than a bit rusty and I'm having trouble fitting the solar shield into my thermal model.

I am just wondering if any of you have any tips, suggestions, or resources on how to incorporate solar shields and what their actual effects are on the cooling of enclosures.
Do any of you have any experience with solar shields?
I have contacted the major enclosure companies for white papers and did some Googling but it all seems very surface-level with not much being given to the driving theory or secondary considerations such as sky temperature or ground reflections.

I am currently leaning towards some sort of aluminum "shell" with an air gap because of its high reflectivity and corresponding reduction of emissivity inwards towards the enclosure, but I have no idea how to translate this concept into harder numbers to make sure I can actually reduce the solar loading to the point that the exchanger can handle it.

I should note that I work at a startup so my resources are a bit limited (in terms of consulting and labor) so I've found myself straying outside of my skillset quite a bit.

I appreciate any responses, let me know if I need to include more info.


texts: Aircraft Longitudinal and Lateral Transfer Function Terms

texts:
The figure shows input and output variables for both longitudinal and lateral stability transfer functions.

I completely understand what each term stands for but I was wondering what would be the best way to physically interpret the relations. I am having trouble visualizing  the relationships.

For your reference:

$\eta$ = elevator control
$\epsilon$ = thrust pertubations
$\xi$= alieron control
$\zeta$ = rudder control
$u,v,w$ = translation velocity in $x,y,z$ axis respectively.
$p,q,r$ = angular rate in $x,y,z$ axis respectively.
$\phi,\theta, \psi$ = roll, pitch and yaw respectively


texts: Using RC scale-down model to pre-test aircraft design

texts:
I'm a bit involved into building an actual airplane. And while the guys go conventional ways, I'm trying to look around to see other solutions.

One of that is to try and use and RC scale-down model (easier and cheaper to build) to test and find flaws in the design and also possibly to give pilots some training before flying the actual plane.

So the question is - what will and what will not be similar in a model's behavior (say 90 cm and 180 cm wingspan versions) compared to full scale airplane (about 9m wingspan). I've already found answers related to Reynolds number on Physics SE, so it seems aerodynamics test (if we do any on the model) should be run in a pressurized tube. It's also obvious that power-to-weight ration in a model will be much higher, but possibly that can be solved by depowering the engine.

So if I build a 1:10 or 1:5 scale RC model, will it in some way be useful for actual aircraft design, building and pilot training?


texts:
I'm a novice in mechanical engineering and I'm having some troubles to find a pipe that change from one section to other. In this case I want to connect a circle section to a rectangular section. I google it but only found the second Figure. Water is going to be used with a pump of 4 HP.
The diameter of the circular part is $d_{int}=90 mm.$ and the dimensions of the rectangular side are less than the $d_{int}$. So basically, I want to know how to search them or are there any mechanism that can replace what I'm trying to do?


texts: Particularly in an Electric Arc Furnace I have seen carbon boil occuring . I understand the reaction is very vital but what is it's utility? A detailed answer to this is most welcome. The internet says that it promotes slag metal reactions and temperature homogeneity. But my question is how that is it.There are many elements present but why particularly do I need to boing carbon? Why not Si, P etc. This is where the problem seems to be very confusing for me.


texts: Is there a way to visualize or quantify atomic clusters in crystalline materials?

texts:
For multi-component crystalline materials, can we detect atomic clusters containing just 2, 3, or 4 atoms?
Take a material $A_4B_3C$ for example. Can we detect clusters of A with 2 atoms (pairs), 3 atoms (triangles), or 4 atoms (tetrahedrons)?


texts: What is this V-shaped strut on the landing gear for?

texts:
On this video from Captain Joe, you can see that the landing gear of the airplane has got some sort of v-shaped strut connecting the two moving parts.

I think that I saw the same thing on some vespas with a suspension in the front wheel.

What are they for ?


texts: How is modulated the Primary Synchronization Signal in LTE?

texts:
PSS is based on 62 values from a Zadoff-Chu sequence. Three different sequences can be used by an LTE Cell, to represent the Physical Cell ID within the Cell ID group.

The formula is the following, $u$ being an index $[0;2]$ corresponding to a Physical Cell ID.

$$\begin{cases}
\partial u(n)=e(−\dfrac{j\pi}{63} un(n+1))&\text{ for }n=0,1,…,30 \\
\partial u(n)=e(−j\pi u(n+1)(n+2)63)&\text{ for }n=31,32,…,61
\end{cases}$$

Now my question: is there any kind of QAM or QPSK applied to each of the 62 values we get from the sequence, before they are mapped to the time/frequency grid (Radio frame)?

I know that Secondary Synchronization Signal (composed of 31-length
M sequence) is modulated by BPSK before being mapped.
I've found that and OFDM subcarrier has for formula $s(t) = A\cos(wt     + \Phi(t))$. I still haven't found yet where this intervenes.
For a 1.4 MHz bandwidth, a 126 points IFFT is performed, if you
know what that really means (physically speaking) beyond switching
from frequency to time-domain.

In the end I would like to get the proper antenna output signal carrying a PSS, to study it.


texts: What's the smallest hydropower plant that can blackstart a grid?

texts:
One of the most underrated capabilites of classical, large-scale hydropower plants is their ability to "black start" a dead electric grid.  I'm not going to go into details on the blackstart process here, or why hydroelectric plants are better at it than other types of power plants (whether fuel-burning or renewable), but suffice it to say that hydroelectricity provides a significant portion, if not the lion's share, of blackstart capacity in many, if not most, grids worldwide.
However, not all hydroelectric plants can provide blackstart power.  Clearly, "micro-hydro" systems relying on DC generation and inversion to AC are incapable of blackstarting a grid, size aside, as the inverter simply won't try.  Some micro-hydro systems, as well as most larger "mini-hydro" systems into the dozens of kilowatts, use induction AC generators and capacitor banks instead of DC generators and inverters.  These systems can't blackstart either, as the capacitor banks used will not provide enough reactive power to the generator for it to come up mains frequency and voltage on its own no matter how much you spin it.
This raises a question, though, given that the emphasis in modern hydropower development is on smaller-scale systems (tens or hundreds of kW), often configured in a "run of the river" fashion, over massive, multi-MW to GW investments with equally massive impoundments.  How small can one make a hydroelectric plant while retaining its capacity to supply blackstart power to the grid it's connected to? Is there some lower limit below where the use of synchronous AC generators is no longer feasible? Or could one theoretically build blackstart capability into small hydropower plants, whether they are based on impoundment or "run of the river" techniques?


texts: heavy duty cargo bike - which direction to choose

texts:
I would like to build a heavy duty cargo bike. Heavy = approx 200Kg of load on the front rack.

I want 2 front wheels.

Basically, there are 2 options that I know of:

the front wheels are fixed to the front rack/ load and the whole part is moving when I want to turn. This uses a single pivot. This seems appropriate, but I'm worried about the single pivot and the tube size (regarding the tube between the bottom bracket and the pivot)
The rack is fixed with the chassis, everything including the wheels can move without moving the rack/load. This includes the whole load is not always in the same plan, and it worries me because i'm not sure it's a good idea to move 200kg, it is a lot of inertia

What's your opinion?


texts: Why would "quality of the gearbox" affect torque of a machine tool?

texts:
I read a manufacturer's web site which has the following statement:

  Some manufacturers promote their higher horsepower as a selling
  feature over competitors. However, it is critical to recognize that
  horsepower is not the determining criteria on saw performance, but
  instead it is how much torque is delivered to the band wheels. The
  amount of torque delivered to the wheels is based on the quality and
  ratio of the gearbox. Today, the higher technology saws can both run
  more efficiently and deliver more torque to the band wheels, with
  lower horsepower than on older saws.

I understand the importance of the gear ratio. Higher gear ratio, more torque. However, why would the "quality" of the gearbox make any ddifference to the torque. If the gearbox is 24:1, then it is same whether it is an expensive high-quality gearbox or a cheapo gearbox, I would think. Why is the manufacturer saying that the gearbox quality affects the saw performance?


texts: Motorized 4 part extension column mechanism?

texts:
I'm a programmer working on a project where we will be controlling a crane's boom for motion control. We are currently a year out from having the actual crane in house, but are doing the software ahead of time as we can 3d simulate a lot of it. I thought it would be a fun idea to make a little miniature version to play with (and it would be a fun toy for the office). Our crane boom consists of 4 segments and to scale it down somewhat proportionally each square tube will be 1.5 feet long and the first extension will be 2 inch outer diameter, with each inner tube getting 1/4 smaller. Making a little mechanism to pan and tilt the boom is simple, but I'm not sure how to go about controlling the extension with a motor.

Ideally I'd like to control the extension with just one motor I can mount at the base of the boom. My question is, is there a mechanism that can create this collapsible column with just one motor?

I realize the easy solution is probably 4 separate motors that use a rack and pinion to extend each segment, but I don't think Ill have the space for the motors at this scale.

Another option I've pondered is using a spring and then having the motor just wind up a string that pulls to compress the spring but I feel acquiring a spring of the right diameter, length and strength would prove challenging as at full extension this will be about 4 feet, though I'd like to make it as small as possible.

Hydraulics and pneumatics are completely out of my ability.

In this, each segment should move the same amount as the boom extends. I feel like there has to be some sort of mechanism for this but I can't think of anything else. I think our actual crane uses a bunch of pulleys but I'm not sure how that works. My boss is designing the crane, but I'd like to do this as a surprise for him so I don't want to ask him for his input.


texts: the possibility of a breakwater/seawall preventing the beginnings of a landslide-formed tsunami

texts:
. . A thought recently crossed my mind which I cant seem to find any studied material on. It occurred while hearing a story about a potential future landslide in Kauai causing a large tsunami aimed at Japan; similar to this July 2017 landslide in Greenland [1].

The story made me wonder, can a breakwater/seawall built around any potential landslide area prevent the future buildup of a tsunami; or maybe a significant portion of its energy transfer?

To clarify, I am not writing about defensive measures that articles mostly seem to speak of [2]. Instead, I'm interested in preventative measures for controllable instances. Thanks for any insight.


texts:
Time history analysis of earthquakes for structures, is a NON-LINEAR dynamic method correct?
Then why is there also something called "LINEAR response history analysis"? What is the difference of this from non linear time history analysis?


texts: Fixed end points optimal control problem

texts:
Given two points $(t_0,x(t_0)=x^{0})$ and $(t_1,x(t_1)=x^{1})$ in the $(t,x)$ plane, the objective is to find an optimal trajectory $x^{*}(t)$ such that the cost function
\begin{equation}\label{eq:1}
J(x) = \int_{t_0} ^ {t_1} g(x,\dot{x},t) dt \tag{1}
\end{equation}
has a relative extremum with $g$ being a function with continuous first and second partial derivatives with respect to all its arguments. In this case where the end points are fixed, the necessary condition for minimizing the functional $J(x)$ is obtained by means of Euler-Lagrange equation
\begin{equation}\label{eq:2}
\dfrac{\partial{g(x^{*},\dot{x}^{*},t)}}{\partial{x}} - \dfrac{d}{dt} \dfrac{\partial{g}(x^{*},\dot{x}^{*},t)}{\partial{\dot{x}}} = 0.\tag{2}
\end{equation}
Next, as I was studying the same problem (from Modern Control System Theory by M. Gopal) with the modified constraint - terminal time $t_1$ fixed but $x(t_1)$ free, I encountered a bit of difficulty (highlighted in bold texts) in understanding the flow of arguments. It goes as follows.
Given $x$ be any curve in the admissible class $\Omega$ and $\delta{x}$ represents the variation in $x$ which is defined as an infinitesimal arbitrary change in $x$ for a fixed value of variable $t$.
The first variation in $J$ is given as
\begin{equation}\label{eq:3}
\delta{J}(x,\delta{x}) = \dfrac{\partial{g}(x,\dot{x},t)}{\partial{\dot{x}}}\delta{x(t)}|_{t_0} ^ {t_1}+\int_{t_0}^{t_1}\Bigg\{\dfrac{\partial{g(x,\dot{x},t)}}{\partial{x}} - \dfrac{d}{dt} \dfrac{\partial{g}(x,\dot{x},t)}{\partial{\dot{x}}}\Bigg\} \delta{x}\ dt. \tag{3}
\end{equation}
For an extremal (minimal or maximal) $x^{*}(t)$, we know that $\delta{J}(x,\delta{x})$ must be zero. In the following we show that the integral in \eqref{eq:2} must be zero on an extremal.
Suppose that a curve $x^{*}(t)$ is an extremal for the problem under consideration; $t_1$ specified and $x(t_1)$ free. The value of $x^{*}(t)$ at $t_1$ is say $x^{*}(t_1)=x^{1}$. Now consider the fixed end-points problem with the functional $J$ in \eqref{eq:1} and the end-points $(t_0,x^{0})$ and $(t_1,x^{*}(t_1))$. The curve $x^{*}(t)$ must be an extremal for this fixed end-points problem and therefore must be a solution of the Euler-Lagrange eqn. \eqref{eq:2}. The integral term in \eqref{eq:3} must be  zero on an extremal and
\begin{equation}\label{eq:4}
\dfrac{\partial{g}(x^{*},\dot{x}^{*},t)}{\partial{\dot{x}}}|_{t_1}\delta{x(t_1)}=0.\tag{4}
\end{equation}
Since $x(t_1)$ is free, $\delta{x(t_1)}$ is arbitrary; therefore it is necessary that
\begin{equation}\label{eq:5}
\dfrac{\partial{g}(x^{*},\dot{x}^{*},t)}{\partial{\dot{x}}}|_{t_1} = 0. \tag{5}
\end{equation}
Equation \eqref{eq:5} provides the second required boundary condition for the solution of the second-order Euler-Lagrange equation.

Now my question is- why should one consider a fixed-end points problem for this case? I am stuck at this problem for quite some time now and therefore sincerely appreciate any thoughts, or suggestions.


texts: When dealing with powders, metal or otherwise, it is often stated weather the powder grains are spherical or flakes. Is it the grinding process that determines the shape of the powder, or is the shape obtained through some other means?


texts: Why are entry-level CNC mills cheaper than entry-level manual mini mills?

texts:
Having used some big, old, manual Bridgeports in school, I was looking into getting a small mill (manual or CNC) for hobbyist home use on metal and wood.  I was surprised to see many CNC milling kits on Amazon for quite cheap ($200-600 USD) whereas the the cheapest manual mini mills seem to be roughly 400-1000+ USD.  My question is why the cheapest CNC mills cost less than the cheapest manual mini mills?  (I am presuming the entry level for manual and CNC mills are the same except obviously the key automated part --- ie that RPM, vibration, stability are similar, but please comment on that in your answer if that's a confounding variable).
EDIT: My question originally had two parts with the second asking if there was also a performance difference between entry level CNC and entry level manual mills, but since none of the answers addressed that in much detail and it's sort of a separate (but only possibly related) question I have removed it.


texts: AC Harmonics on a system appearing as DC

texts:
I have a theoretical question about harmonics and DC.
Given I have a circuit which has a power supply providing an AC input(230Vrms @ 50Hz), this then goes into a load which, takes this supply rectifies it to DC and performs a DC to DC conversion for a DC load.
If the system (load)imposes some DC onto the AC supply it will be seen as a DC offset for instance 1V DC offset. If I were to measure the DC voltage over the Line and neutral going into my load.
Could this hypothetical DC offset be caused by harmonics in the load say the 2nd,3rd,4th harmonic but, appearing as a DC offset.


texts: Is it possible to create a hard slick non-stick non-degradable substance?

texts:
I once read on a web page I can no longer find that corundum is a covalent network. I'm guessing that's because despite the fact that the electronegativity difference between aluminum and oxygen is more than 1.7, corundum has exactly 2 valence electrons per bond so its valence orbitals hybridize into one orbital for each bond each of which is filled with 2 electrons making the substance really strong like a covalent network. Since it's a covalent network, if you replace each aluminum atom with a silicon atoms, would you have excess electrons some of which random walk to the surface atoms filling their outer shells and making nothing adhere very strongly to the surface?

There could be so many practical applications for it when it's etched nanosmooth. According to this article, diamond has high friction with itself in an ultra high vacuum and according to this question, super smooth surfaces have high friction with each other so I'm guessing that because of diamond's strong adhesion to itself from forming bonds between the surfaces, even when the normal force is tiny, the force of friction per area between the surfaces is almost as high or higher than the sheer modulus of diamond so the two diamond surfaces undergo the stick-slip phenomenon contributing to wearing out.

On the other hand, when you have 2 smooth spheres of corundum with some of its aluminum atoms replaced with silicon atoms sliding against each other even in an ultra high vacuum, the force of friction between them per area of contact will be much smaller than the shear modulus of the material so they should slide smoothly and not wear out. Also, a nanosmooth frying pan made of that material would be so revolutionary. It would not chemically degrade over time. All sorts of food would have so little adhesion with it. Maybe soft solids like squash though won't roll off because they have some adhesion to it and lack the ability to flow like a liquid and roll off and would have to be rinsed off. We could make tongs out of the exact same substance for those pans and have the food not stick to the tongs either and the tongs would not scratch the pan because the pan is made of such a hard material and they're both smooth and the tongs would not undergo the stick-slip phenomenon with the pan. Also, according to the Wikipedia article Fracture mechanics, brittle materials are weak because they have surface cracks and it takes a smaller amount of tension to magnify the tension to the breaking point at the tip of the crack and the longer the crack is, the less tension it takes to crack the material but if it's etched nanosmooth, its strength will probably be a significant fraction of its sheer modulus but according to this answer, the strength a material needs in order to not break on collision varies as its sheer modulus to the power of $\frac{4}{5}$ so it should totally resist breaking from colliding as long as it doesn't hit something rough in the collision like a rock and get scratched. Also, because it's so nonstick, it could be etched smooth and when it's pulled out of the etching liquid, the liquid will not cling to it and evaporate redepositing the material it dissolved away as a rough surface so it will remain nanosmooth after it's etched.


texts: How to build a transparent double hollow helix at home

texts:
I'm building a product prototype for a client. We are trying to figure out the best way to build a hollow helix capable of transporting liquid at home. Something similar to this:

So far our best idea is to use standard tubing and try to use rings mounted on the side of a support cylinder which the helix loops through but this seems almost impossible to pull off at a small scale, and wouldn't look too good.

We have also considered heating sand and using that to bend acrylic tubing, but this certainly still doesn't feel ideal.


texts: Problem with performances of a control scheme

texts:
I am trying to prove with Matlab that if I have an improper system and I place poles at higher and higher frequencies the performances of the system improves. In particular I am considering the following two degree of freedom scheme:

where $C_{f}= \frac{(1+s)(1+0.05s)^{2}]}{(1+\tau s)^{3}}$

My code is the following:

s = tf('s');
P = 1/[(1+s)*(1+0.05*s)^2];
C = (s+1)/s;

tau_1 = 0.1;
CF_1 = [(1+s)*(1+0.05*s)^2]/((1+tau_1*s)^3);

tau_2 = 0.01;
CF_2 = [(1+s)*(1+0.05*s)^2]/((1+tau_2*s)^3);

tau_3 = 0.001;
CF_3 = [(1+s)*(1+0.05*s)^2]/((1+tau_3*s)^3);

T1 = (C+CF_1)*P/(1+P*C);
T2 = (C+CF_2)*P/(1+P*C);
T3 = (C+CF_3)*P/(1+P*C);

figure;
bodemag(T1,'r',T2,'b',T3,'g'),grid
legend('tau = 0.1','tau = 0.01','tau = 0.001')

so what I expected is that the performances with respect to the reference tracking increse as tau gets smaller, but if I do the Bode plot, what I get is:

from which I don't really see much of an improvement. Moreover if I change some values:

which is somenthing that to me does not makes sense because I should have that with $\tau =1$ I should have better performances than with $\tau =10$, this because with $\tau =1$ the pole is at higher frequencies that with $\tau =10$.

Can somebody please help me solving this problem?

Thanks in advance.

[EDIT] If I plot the step responses I see the same problem:

[EDIT 2]For completeness, I post the image of the step response for the first choise of tau's:

for these values of $\tau$ there is a clear improvement for overshoot and a faster response.

I also tried other values smaller than 1 for $\tau$ and all of these show what I expected in the step response. While for values bigger than 1, I obtain something similar at the other situation.

Does somenone know why this happens? Thanks.

[EDIT 3] With the last one, so values of $\tau$ smaller than 1, I have also noticed an increase in phase margin, so this should mean that the system is performing better.

While, if I consider the values $\tau=1$ $\tau=10$ i get that for the first one the phase margin is 125 deg and for the second is 170 deg. So this should be in according to the fact that $\tau=10$ performs better.


texts: How long does it take for two initially seperate fluids to reach a certain homogenity across their container?

texts:
Imagine the following initial condition:

Two completely miscible fluids A and B with different dynamic viscosities $\eta_A$ and $\eta_B$ are seperated in a container with fixed Volume $V_0$ and length $L$. The temperature $T_e$ is constant across the container, the time is $t_0=0$. The mass fraction $w_B(x)$ at this point in time is a step function (or a convenient approximation of it), as shown in the sketch below.

With those definitions in mind, what is the time $t_m$ at which the mass fraction $w_B$ is within $\pm \delta \%$ of its equilibrium value across the whole container?

The first thing which came to mind was the diffusion equation:
$$\frac{\partial\phi(\mathbf{r},t)}{\partial t} = \nabla \cdot \big[ D(\phi,\mathbf{r}) \ \nabla\phi(\mathbf{r},t) \big]$$
From there, I probably 'just' need an approximation for $D(\phi(\mathbf{r},t))$ and solve the differential equation. Is this the right direction? What approximations would be appropriate?

The Stoke-Einstein-Equation enables me to calculate $D$:
$$ D = \frac{k_\mathrm{B} \cdot T}{6 \pi \cdot \eta \cdot r}$$
but I don't know the radius $r$. I just dont know how to move on.


texts: How to control the level in multiple connected tanks at the same time?

texts:
In a coupled tanks system, what is the control strategy to simultaneously control the level in multiple tanks. In this case the actuators influence multiple control variables. The system is as shown in this diagram

The variables to be controlled are the liquid levels in each of the tanks. The actuators are the valves on the pipes as well as the inlet flow q0. The problem is that the same actuator e.g. V1 influences both h1 and h2. I tried to 3 different PIDs for each tank. Each controller receives the height in the corresponding tank and sends the control signal to the corresponding outlet. So, PID1 receives input h1 and controls only V1; PID2 receives input h2 and controls only V2...


texts: When analysing a structure using traditional methods (e.g. Hardy Cross, Slope Deflection, Force Method, etc.), it is a first-order elastic analysis. My question is, how would one analyse a statically indeterminate frame by hand but taking into account the second-order effects. This is more from an academic perspective and that is why I am asking for hand calculations using traditional methods or even direct stiffness method.


texts:
I read that a human

https://www.google.co.uk/search?client=ms-android-samsung&ei=l0_EWNjsHKXEgAafuIUg&q=john+stapp+45+g&oq=john+stapp+45&gs_l=mobile-gws-serp.1.0.0.6460.9902.0.10829.15.14.1.8.8.0.185.2085.0j13.13.0....0...1c.1j4.64.mobile-gws-serp..1.14.1112.3..35i39k1j0i67k1j0i10k1.tC-NnmcrLLw

Can survive 46g force so what type of rocket and how much fuel would be best to stop a human falling at terminal velocity without exceeding this g force limit.

I also read spacex use rockets not parashutes for the weight advantage so would a short (i think 1 second) burst rocket be better in anyway to a parashute (despite such deceleration causing injury(yet non permanent)).

Or would the rocket and fuel be far too big.


texts: Assist for vertically telescoping support?

texts:
Two questions.

Has anyone had experience in retrofitting consumer (locally-available) square aluminum tube as telescoping structural support?  Ergo; with 0.125" wall thickness square tube at an outside dimension (OD) of 1.5", would minor superficial sanding and end beveling of an inner square tube with OD of 1.25" enable a telescoping pair?

Furthermore, could said pair be capable of implementing a gas spring internally for vertical assist?  See image below, noted: gas spring improperly sketched upside down.

Loads and dimensions can be provided if necessary.

ADDITION:
Is there an implied ideal mount offset for a gas spring in this circumstance relative to the load distribution (please see 2nd attached image below)?


texts: Power torque and rotational speed of a not running yet DC motor

texts: If the power $P = C\omega$, so how a DC motor powered by $P = 10\text{ W}$ can work as $\omega$ is of course 0 rad/s at first, because if $\omega = 0$, then $P = C\omega = C\cdot0 = 0$?


texts: I have a problem with my representation of roll in Simulink

texts:
I am currently an engineering student and a member of the aerospace club of my engineering school (ESILV) which is called LéoFly. We’re a team of 12 students and are building a Fusex (Experimental Rocket) for the launch campaign of the CNES in partnership with Planète Sciences association. The goal of our experiment is to counter the “natural” roll of the rocket after the boost-phase. I am the one who must program the algorithm that counters the roll using a gyroscope and four solenoid valves (2 for the clockwise direction and 2 others for the counter-clockwise direction). I decided to use Simulink to develop the closed loop control using the following image, equations and data.

The image is the cross-section of the rocket with the four fins. This is an example of a “natural” roll in the counter-clockwise direction, so the program gives the order to the two solenoid valves of the clockwise direction to eject gases and cancel the roll of the rocket.

Here are the equations we have started with:

$$\begin{align}
\sum C = J \dot\omega &= J \ddot\theta \\
2F_a R_1 + 4F_b R_2 &= J\ddot\theta \\
\dfrac{1}{J}(2F_a R_1 + 4F_b R_2) &= \ddot\theta \\
\omega(t) = \ddot\theta(t)t + \omega_0 &= \int \ddot\theta(t)\text{d}t
\end{align}$$

The $C$’s are the torques considered in the experimentation (Thrust torque and Roll torque), $J$ is the inertia, $\theta$ is the angle and $\theta$ equals the derivative of $\omega$ in the time domain. After that, $F_a$ is the force of thrust, $F_b$ is the force of roll, $R_1$ and $R_2$ are two different radii of the rocket.

Here are the data, taken from our experiments and our rocket.

Then, in Simulink, I’ve crafted the closed loop thanks to the schematic representation, the equations and the data. We don’t want roll, so the input is 0 (in radians per second) and the output is the roll of the rocket (in radians per second). This is a closed loop because of the gyroscope, and the dynamic subsystem is composed of the thrust torque and the roll torque which is the disturbance in this problem.

Thêta-lim is the saturation block that represents the max roll that the rocket can have physically. The White-Noise block is here to add randomness in the representation of the roll torque. The roll torque can be clockwise or counter-clockwise and is never always at the maximum of him (here the Roll Torque block is approximately 10 N.m so the disturbance which is added to the thrust torque is between 10 N.m and -10 N.m). Thrust Torque is approximately equal to 0.29 N.m and the inverse of Inertia is equals to 90 m2.kg-1. The switch subsystem is here just to permit a better implementation in the Arduino to pin the solenoid valves in the program (which will be generated from Simulink). The PID has the next values: $P = 114$ and $I = 28$. I didn’t use the auto-tuner because it gives the values for a step of 1 while we don’t want a step of 1 but an input of 0. Thus, here is what the scope gives me.

It is what we wanted for our roll control system: counter the “natural roll” and converge to an angular velocity of 0 radians per second. Of course, it is a student Fusex so we don’t want to have a perfect curve that converges to 0, we don’t have the time and the money to do that!

But the problem is at $t = 0^+$: I put in Simulink (in the integrator block) a “natural” roll (angular velocity) of 2 radians per second. How is it possible to go from 19 rpm to approximately 0 rpm in 0 seconds? It does not seem physically possible, and we don’t know if it is a problem due to Simulink or if it is a problem in our blocks, if our closed-loop is poorly conceived or if the starting equations are not good. One of our professors told us that it can certainly be the problem of Simulink (because of the side effects apparently).

Thus, what are your impressions about this and what do you recommend me to resolve this (these) problem(s)?


texts: How to Compute Total Strength of Composite Tensile Bars

texts:
In this question about combined tensile strength, all of the tensile bars are of the same material. But what if the case that they are made of different materials?

Say we have $200$ bars of $A=10 (\rm mm^2)$.

$100$ bars of steel with $E=200 \, (\rm {GPa})$, at tensile limit,  $\sigma=200\, (\rm {MPa})$, $\eta=20 (\%)$.
$100$ bars of aluminum with $E=60 \, (\rm {GPa})$, at tensile limit,  $\sigma=80\, (\rm {MPa})$, $\eta=10(\%)$.

What is total strength (the maximum force capacity) of the bars? Assume that one end is fixed and the other is a rigid body moving in longitudinal direction, so that all bars have the same change in length.

Note: We have to assume that the material is of plasticity, and will not hardening after yield. (The tensile limit is the same as the yield strength.) This may be beyond the text book of elasticity theory.


texts:
okay so I am really struggling to see how to resolve the Normal reaction force and Weight into the r and theta direction please? Why is it that the angle is taken to the left of N and right of mg please?
Can someone give me some tips on this please? And why isn’t the N force resolved with the angle to the right of it attached to the theta line please?


texts:
So, I'm doing a group project for a materials and manufacturing engineering class, where our job is to make a product using injection molding. For our project, we chose a sphere (keeping it simple)

I'm in charge of calculating cooling time for the part while its in the mold. Herein lies the issue:

I have to figure out how heat (power) flows through our mold, Which can be represented by a hollow sphere in a perfect cube.

The equation for thermal conductivity is (K)(A)(T2-T1)/(L), Where L is the parallel distance of hard object in which the heat has to flow. This equation is set up for a solid, uniform plate, The problem is that the object in which the heat must flow is NOT a uniform object!

So what do I set L as?

I have Schaum's outline for college physics, and it allows me to define the rest of the parameters. I just need L.

Also, another question: Our mold is being 3-D Printed, to where the mold isn't truly a solid object; a certain percent is plastic (Given by % infill) and the rest as air. I believe I got the K-value correct for this part but I would like to backcheck -> ((%infill)(K-PLA)) + (100-%infill)(K-air) = K-incomplete_infill


texts: Heat transfer in a fin with constant volume and given efficiency

texts:
Assume we have a cylindrical fin which has the effective length of L and its efficiency is given by the equation: $$η=exp(-0.32mL)$$ where $$m=\sqrt{\frac{hP}{kA}}$$ where P is circumference and A is the cross sectional area of the fin.

If the volume of the fin remains constant, which of the following statements is true?

By increasing the length of the fin ...

Heat transfer increases.
Heat transfer decreases.
Heat transfer increases then decreases.
Heat transfer remains constant because the volume is constant.


texts: Selection of correct DC gearmotor with given load

texts:
I am designing an Actual working extendable welding station for my college project. The idea is to lift the unit up/down with the help of 2 lead screws and 2 DC gear-motors, one on each side. The total weight needed to lift will be around 500 lbs. I want to select suitable dc gear-motor for that. Lead-screw will be 3/4" diameter of 0.2" pitch.

I want the torque calculations done to select a dc motor.

I have done this much so far:

$F = m \cdot a = 227 \mathrm{kg} \cdot 9.8 \mathrm{m}/\mathrm{s}^2 = 2224.6 \mathrm{N}$

But, we are using 2 motors to drive this, so i just divide the force/2 = 1112.3 N.
I need the table to lift 15". So, the lead screws can be around 20" long.
Considering 20" long lead screw:

$T = F \cdot r = 1112.3 \mathrm{N} \cdot 0.508 \mathrm{m} = 565 \mathrm{Nm}$

But, that is the absolute minimum torque just to keep the system in steady state right?

So, I need assistance in finding the real torque required and how to assume the minimum acceleration needed to find the real torque.

Also, how to calculate Power for the motor.
Based on this calculations, I will be buying the motors to actually install it in my design so I need the calculations to be accurate! Thanks to all in advance.


texts: Is there a solution for USB Multiplexing, i.e. passing data between different devices by sharing/splitting a USB connection?

texts:
Forgive me if my title is vague, I will attempt to explain my issue. I don't know if such a solution exists and I have tried searching without any luck.
I would like to utilize a passive USB protocol analyzer, a la the "Beagle" to sit in between an embedded hardware device, which will be fuzzing another embedded device (running a Linux-like OS), and a PC controlling the fuzzing device, as well as performing analysis on the data the Beagle will be collecting.
I need to be able to control the fuzzer from the same PC that acts as the analyzer (receives the USB packets) as well as connect the fuzzer AND the Beagle to the target. Does a solution like this exist?
I don't think that the USB splitters will work for me because I think that the splitters also act as chargers and will only send data from one end at a time. I don't think USB hubs, that act like switches, will work either. Instead, I am looking for a device built specifically for my issue. If I have to do something custom, I am also willing to try that as well if I can get some guidance.
I have drawn a diagram that hopefully explains what I want the setup to be as best as I can. Original.  I haven't drawn any technical diagrams before, so please excuse me if I am missing some details.

If there is a better stack exchange community where my post is better suited, please let me know.
Looking forward to getting some guidance.


texts: Is a MSC Adams simulation with smaller steps always more reliable?

texts: In a given simulation in MSC Adams, if I use a 1 or 0.1 step increment, I get the (favorable) result I intuitively assumed would occur, but if I use step increments of 0.01 or 0.001 a different (and unfavorable) result occurs. One would assume the finer-detailed result would generate fewer simulation false-result-inducing artifacts. Should I always assume the more granular simulation will result the more realistic and reliable result?


texts: How to choose an electronic connector/cable that works in a vibrating environment?

texts:
We are designing a diagnostic electronic tool for a vibrating table.

In our PCB there are a gyroscope, an accelerometer and a bluetooth module.
Our PCB is attached to a vibrating table that works at 12 Hz with 10 mm peak-to-peak amplitude. It has to work for at least three years "always on".

When we are choosing the power connector, what are the technical elements we have to check before buying one? Are there special connectors for that specific use? "Vibrating-environment connectors"?

We are going to pot the pcb.

Our fear is that with that amplitude and with that frequency a normal soldered connector would fail and break itself.


texts: ESD-safe tweezers have a black coating on the handle. If I am grounded to a work bench, and normal tweezers are already conductive, then what is the point of the conductive black coating? Screw drivers sometimes have handles which may be insulators, but tweezers are all metal. Are they not as conductive as I am expecting? Maybe an oxide layer?


texts:
My friend and I are working on a project requiring for us to propel a syringe forward in a small container with significant force. We are debating whether to use an elastic band wrapped around the syringe (in the form of a small hand slingshot) or a flat piece of spring steel that upon activation will revert into its original, curved shape, pushing out on the syringe.

Is there such a type of spring steel that will be able to do this effectively and with a large force? If so, are there any downsides to using it as opposed to an elastic band? The goal is to make a product viable on the market for long-term, one-shot use.


texts: How to deal with a point force acting right on the hinge of a beam?

texts:
I have been attempting to solve a question where there is a point force acting on the hinge of a beam. Here is the problem:

I am not sure how to deal with the 2 kN point force at $C$ ($C$ and $E$ are the hinges). If I split the beam into three parts, $\overline{AC}$, $\overline{CE}$, and $\overline{EG}$, I don't know where that 2 kN force should go. If I include it in both of the equilibrium equations of $\overline{AC}$ and $\overline{CE}$, then the sum of $F_y$ will be imbalanced. I believe this problem is statically determinate but I am just stuck at this point. I don't want to attach my workings here yet as I really would like to tackle it myself with a little bit of clarification and help.


texts: Choosing of repeating variables in Buckingham's Pi theorem

texts: What are the criteria for choosing repeating variables in Buckingham's Pi theorem in dimensional analysis? In many problems, it's solved by taking D,V,H (Diameter, Velocity, Height) as repeating variables. Why do they take the above variables as repeating variables, when the problem also contains the following variables g,u (acceleration due to gravity, viscosity)?


texts:
Could anybody provide a resource for finding or researching historic construction methods?

My current need is for a typical vaulted or dome ceiling construction methods circa 1992 in the US but I think it would be a helpful resource to have for the community in general. It is easy to find modern typical methods but I am interested in how the methods and processes have changed over time.
Any help is appreciated!


texts: Why do we dig holes and fill them in with concrete?

texts:
I'm watching construction of a new building across from my office. The old building has been demolished and the demo team has completed taking everything away and a new company has come in to start working.

The new building will have a five floor underground parking lot and 19 floors above it. The site used to be an industrial area and sits on what used to be marsh.

Now for the question: The excavators are digging holes maybe 6 to 10 feet deep (hard to tell from my vantage point), supporting the hole with vertical walls and filling them with concrete then covering them with dirt. Several of these are along the perimeter but at least one is in the middle of the construction site. What are these for?

The only thing I could add that might help is to say that they appear to have surveyed for underground utilities and appear to have marked telco and sewage pipes judging by the orange and green markings. At at least one spot they indicated 14'. I'm not sure if it's at all related to the holes though.


texts: Difficulty to reach Mach 1 by blowing into a small converging-diverging nozzle?

texts:
I'm learning about the basics of converging/diverging nozzles in my thermodynamics class, and it has me curious. Could you theoretically blow into a tiny converging/diverging nozzle and break the sound barrier, or do other effects prevent that from happening?

Assuming one could blow 10MPH, dividing by the speed of sound in Wolfram gives me:
M=0.013
Using an online calculator I get
A/A*=45
Using the width of a straw being 7.5mm (sorry for mixing units, but M is unitless so no harm done) I get
A*=1.25mm, or ~
D*=1.25mm

Which seems like something you could realistically 3D print. I saw somewhere that Lulzbot claims an xy precision of .05mm, so I would imagine the tolerance would be a manageable issue. However, I assume there's something I'm missing. I've heard somewhere that there's a fourth power relation between the width of arteries and the ability to push blood through. Is that an incompressible substance relation, or can I apply that here?

I also notice that my textbook uses a few assumptions, such as ideal gas relations and isentropic flow. I believe air should behave ideally in this range, but isentropic implies frictionless (right?), and I'm not sure this would apply with such a small 3D printed part, or such a large change in speed.

TL;DR can you reach choke flow through a converging/diverging nozzle with Ai = Ae = the cross sectional area of a straw?


texts: Computing winch input torque for certain pull capacity

texts:
I am trying to calculate the input torque for my mechanical winch to pull 5000kg. I want to setup a slip clutch on the input shaft and adjust the springs to slip exactly on 5000kg to avoid any damage to the rope. My winch is a PTO driven by input shaft coming out from the transfer case. Winch gear ratio is 38:1, drum diameter is 0.10m (10cm) and rope is 0.01m (10mm) plasma rope.
I am using this formula: Torque = Force X Arm
Where Arm = radius of drum + radius of cable
Arm = 0.05m + 0.005m = 0.055m
Torque = 5000kg x 0.055m = 275kgm
input shaft torque = 275kgm / 38:1 = 7,23kgm = 70,9020795 N-m is this the right torque to setup the slip clutch at ?


texts:
I have answered the following questions, however I’m unsure if they’re correct.

1.) For this question do we consider gravity force, I have used it but I’m not sure if this invalidates my overal derivation. Since the flow is one-dimensional and in the x-direction, must we only consider the momentum and forces in that direction? So must I remove pg?


texts: How to perform 3 point bending test by using force instead of displacement in ABAQUS?

texts: I know you can apply displacement to a rigid body (cylindrical rod) to perform a 3 point bending test in ABAQUS. Is it possible to apply force to the rod (e.g. rod with super high young's modulus so it wont deform). I am trying to apply topology optimisation on a structure, so the displacement will change when material is removed at every iteration.


texts:
I really need some help identifying this diode.  I contacted ON Semiconductor's technical support and they couldn't tell me what it is, even though it is a Fairchild Semiconductor diode (ON owns Fairchild now I guess).

I am attaching a picture of this diode.  It has a Fairchild logo "F" followed by three lines of code "523" "IC" and "F8."

If you can help me out with this, or point me in the direction of someone who can, I would be very thankful.

Thanks for your help!


texts:
I'm looking for a solution to selectively engage and disengage a drive shaft with a number of output pulleys, one-at-a-time, like a clutch. Speed would be around 1000 RPM, and torque less than 20 inch-lbs (about 2 Nm). Clutching must happen when unpowered.
My first thought is to emulate how a manual transmission gear selection works (with a dog clutch and a yoke), but a quick google search doesn't turn up any packaged solutions that do this, which leads me to believe it may not be a popular solution to a common problem for a good reason.
How are these sorts of things usually done in mechanical systems? If you have one source of power and multiple powered devices which may be on or off, how are they engaged?


texts: Read holes schematic drawing notation. How to? Particular case

texts:
I am asking here for your help and advice on how to read holes schematic notations.

On the attached picture I've marked with a green color part of notation that I don't know how to read / understand. And will be thankful for any advice on how to interpret this notes.

With the red color I've marked a holes with countersinks. But I'm failing to pick up necessary details from the sketch to understand the size/angle/depth of this countersinks. (I understand that they can be missing, but I tend to think that they might be in the notations that I don't understand)

Thank you for considering this question!

source: the drawing was taken from this youtube video - link


texts:
Just by taking a train ride across my home city I can see truss bridges like the one in above picture everywhere. There are numerous variations, but the most common design seems to be this. But why are they built specifically this way?

I can intuitively kind-of see why such a design probably is strong, but is there any kind of in-depth reason? I would be interested to know the answer as much from the physics side of things as possible. Googling didn't help much; I could find information on the different variations and many examples, but none really covered what is it about this design specifically that makes it so popular.