texts: Calculate proper stepper torque to convert clay extruder from compressed air to leadscrew actuator. Is this the correct way?

texts:
First time poster here. First of all please excuse my english mistakes but most of all my terminology and ignorance on the subject.

Now to the question! A friend of mine asked me if I could help him convert his ceramic 3d printer extruder from compressed air to a piston system (driven by a leadscrew linear actuator). As of now, he told me, he uses 4 bar of pressure to make the clay extrude at the desired rate and that's all I know plus the nozzle and cartridge internal diameter (respectively 1 and 65 mm). What I'm looking for is a stepper motor/lead screw combination that can exert enough linear force to move the clay through the nozzle (the rate of extrusion would be given by the stepping rate of the motor).

Here is what I've done as "homework" but I'm a firmware developer so I'm hoping to get some guidance in solving this problem. Since the nature of this problem is not only practical but also not needing particular precision, what I've done are essentially ballpark, or back of the envelope, calculations.

converted bar to N/mm2 (4 bar -> 0.4 N/mm2)
multiplied N/mm2 by the cartridge cross sectional area ($0.4\text{ N/mm}^2 \cdot 32.5^2\pi\text{ mm}^2$) to get the total force exerted on the clay of ~1320 N (I'll round this to 1400 N to have some margin)

Knowing the force needed I picked a lead screw from a catalog to get some specs for the next calculations, what I chose is a screw of 10 mm diameter and 2 mm/rev lead

using this Wikipedia article, I calculated the needed torque to raise a load of 1400 N, assuming that's the clay's resistance according to step #2. (I used the raise formula with the stainless steel coefficient of friction to purposely oversize the system a bit to have some overhead). So the terms were:

$$\begin{alignat}{2}
F &= \text{load on the screw} &&= 1400\text{ N} \\
d_m &= \text{mean diameter} &&= 0.01\text{ m} \\
\mu  &= \text{coefficient of friction} &&= 0.2 \\
l &= \text{lead} &&= 0.002\text{ m}
\end{alignat}$$

$$
\text{Torque} = \frac{Fd_{m}}{2} \left( \frac{l+ \pi \mu d_{m}}{ \left( \pi d_{m}- \mu l \right)} \right)
$$

As a side note I also used the formula with the lead angle and angle of friction to be sure of my results for which I used:

$$\begin{alignat}{2}
\phi &= \text{angle of friction} &&= 11.3° \\
\lambda &= \text{lead angle} &&= 3.6433°
\end{alignat}$$

$$\text{Torque} = \frac{Fd_{m}}{2} tan(\Phi + \lambda)$$

for a total result of 1.86 Nm of torque (from both formulae!)

Well that's all nice and gives an answer that I like (a torque of 1.9 Nm is quite common for steppers).

But the fact that I like it doesn't mean that it's correct!

What makes me suspicious is that 1400 N of force is more or less what's needed to hold up a 140 kg man (please bear with me on that... I'm trying to use some "everyday experience" to get to a correct answer) and I can extrude the clay from the cartridge with my bare hand... I'm sure I'm not able to put 140 kg on that!

So what I'm asking is essentially if I followed the right path in tackling this problem.


texts: Can we engineer detergent micelles to pick up Microplastics?

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I'd like to know if I could get micelles to pick up microplastics in water. I read that microplastics are sometimes charged, so can we make the lyophobic end to pick up microplastics, so that they can then be collected on the water surface and be easily disposed? This is the idea I'm planning to pitch this for a science fair, is this actually feasible? I read that detergent micelles work well even in hard water, so can we use such detergent micelles to pick up microplastics?

Thanks!


texts: How to introduce the CONSTITUTIVE equation into structure mechanics

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Suppose I have stress and strain relationship and it can be simplified to the equation $\sigma=Function(\epsilon)$. This is the CONSTITUTIVE equation of the material I want to do research.

Assume that I need to do the finite element analysis and it has dynamic(nonlinear) deformation, I have the model and I have the CONSTITUTIVE equation which I mentioned the 1st paragraph.
How can we put those things into a structural equation to do the simulation and what structural equation I need to use?

Can we put this CONSTITUTIVE equation into the following equation $\nabla\cdot \sigma =Force $? Then we can get $\epsilon$, we get displacement and $\sigma$ explicitly.

Also, I think the above is the linear equation, what about nonlinear equation?

Thank you very much.


texts: Has a specific type of alternative intersection been shown to reduce congestion & accidents?

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Localities in the US have different road layout and setups.

For example the Michigan Left, Jersey Left/Jug Handle, vs a standard 4 way stop with left turns at the intersection.

Have any of them come out as clear winners?


texts: What is the simplest way to convert this oscillating angular motion to (incremental)rotation? and some Q on viability of lin. wind energy extraction

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Intro;
I'm currently obsessing over linear energy extraction from wind; a surface to extract the maximum amount of energy from wind in one stroke, then rotating/changing shape on the aerodynamic return stroke. I feel like this is useless and stupid but I cant rest until I know why.
Main Question;
To make a small concept of this idea using a flat rotating surface I'm trying to come up with a mechanical printable design (no electrical components) that directly rotates the surface 90 degrees in the same direction each stroke without adding bulk to the oscillating surface.
The only solutions I've found involve ratchets or other bulky/inefficient/complicated mechanisms.
The picture shows the desired motion, intended as a large structure but also working for a small proof of concept, Any ideas to achieve this translation are much much appreciated.
Additional info clarifying the image:
(a) sequence of changes in positions, the surface needs to quickly rotate 90 degrees reaching each end of the stroke.
(d) concept of power extraction with a flexible cable passing through a generator to a mirrored version of the mechanism offset by one stroke (b)

Concerning viability of linear energy extraction instead of rotation;
As far as I know rotating windmills can be ~60% efficient at most while I'd imagine a flat surface (or a air version of those Peltier wheels that theoretically remove all kinetic energy) could surpass that ~60%
with the  complication of returning this surface to its original position.
I would love any insight whether/why this is wrong or unachievable.
Apologies for the messy writeup, I'm not used to discussing these concepts/terms in English.
Thank you for reading, I look forward to replies and will clarify anything if requested the upcoming weeks.


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A pinned system comprising bars of the same material and cross-sectional area is subjected to a vertical load P.

I am required to form a relationship between FAB and P.

The first part of the solution is as such,

$cos\theta=\frac{\delta_{AB}}{\delta_{AC}}$

But how is the angle $\theta$ the same after deflection? Shouldn't it be smaller?
And I can't seem to form a relationship without assuming the theta as the same.


texts: Is Scrooge's giant glass dome feasible in real life?

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In an Uncle Scrooge (or Scrooge McDuck, not sure of the translation here) comic named "Treasure Under Glass", Scrooge orders a giant glass dome to be manufactured in order to aid his endeavours exploring a 17th shipwreck containing a valuable treasure.

The giant dome, which is Donald's idea is described in the following image by a fine engineering drawing since I couldn't find a pdf of the comic :

The primary objective is to clear the area of sharks so it can be explored on foot.

From the comic, I made the following rough estimates :

The spanish galeon is 60m long (based on the Neptune), which would make the dome bottom diameter approximately equal to 100 m
We will assume the dome is a perfect half-sphere (assuming from the drawings in the comic)
Dome height estimated at 50 m according to the previous statement
The dome is tightened to the bottom of the ocean with several ropes as in the drawing, each rope being fixed into the wet sand at its end.
According to the comic, we see that there are 5 ropes extending from one side to another, distributed in an even fashion.
Following 3., the estimated depth at the bottom of the wreck is 100 m

Following these assumptions, would such a thing be feasible from an engineering point of view, assuming close to infinite funds and that Scrooge agrees to pay the bill ?

In particular :

What kind of tension would each rope have to withstand ? Would
regular ropes be enough or should they have used steel cables ?
How would those be tighten into the sand in a reliable way ?
What kind of tremendous forces would the dome have to withstand ?


texts: Difference between min/max clearance and min/max tolerance and relation between them

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Recently I have seen a question as follows:

Dimension of the hole is $50 +.02/-.00$ mm and shaft is $50 +.02/-.00$ mm.The minimum clearance is?

My answer is .00 but the correct answer as per the website is -.02

Where am I going wrong?

Please help me.


texts:
Case 1
The development of Case 1 of this problem in which the axes of the prisms intersect at right angles, is shown in Diagram 1. Note that inter-edge lines are required for the development of both solids, their positions being found by projectors drawn from the different views of the drawing to the full view of the end.
Case 2
Case 2 of the problem in which the axes intersect at 45°, is developed in a similar manner. The projections for this are shown on the plate at Fig 1(a). In order to avoid confusion of lines, projectors are sometimes drawn as shown on this plate, that is, only their starting points are indicated, as between the two views of the octagonal prism in this drawing. First, reproduce the projections. Next, develop the stretch outs for the solids on the lines MN and M'N', and draw edge and inter-edge lines through their respective points. The positions of the inter-edge lines are found by projecting the point A in the plan across to the full view, as shown in (d) afterwards locating the points x and y at x' and y' in (d'); then they are projected to the elevation and carried to the development in the usual manner, the resulting figures at (b) and (c) completing the development of the solids.
Question
What I need to know is, should both drawings be drawn in an elevation and plan way? And where exactly is the problem in both cases that should be developed?


texts: Is using a 4x4 bolted to the face of 2x12 enough?

texts:
I am working on a project that has three 2x12’s supporting a load of 12,000 lbs. similar, but not exactly, to how joists support a house.
The 2x12’s are supporting about 6,000 lbs. on each end.
The three 2x12’s are:
a) Each cut to 90in.
b) The load takes up 24in. from each end of the 2x12’s leaving 42in. of free space in between.
c) The three 2x12’s are spaced parallel to each other, with one 2x12 being 24in. in front of the other.
d) The 6,000lb. (On each side) load is laying on a thick wooden plank (on each end) that is perpendicular to the three 2x12’s.
e) The two thick wooden planks on each end of 2x12’s (mentioned in “d”) is securely fastened to the 1.5in. part of the 2x12’s, as well as having blocking and other bolted wooden members that leaves (as stated in “b”) 42 in. Of free space in between.
f) The three 2x12’s are only 12in. off the ground.
Everything is stable and strong without any issues except for one.
I need to lift this so that it is 14in. off the ground (lifting it 2 in. in total).
Removing the load; as well as dissembling is not an option.
This will have to be lifted with the three 2x12’s and everything above (including load) remaining intact.
My best option is to lift (with a hydraulic jack) the front most 2x12 to 14in. and then lift the back most 2x12 to 14in.
-I’ve done this before with no problems.
The only problem, that I have now, is that directly under the 2x12 is things that I can not remove and is not strong enough jack it from.
The saddle of the jack is 2in.
All wood is Douglas Fir #2 or better.
My plan is to bolt a 4x4 cut to 42in. (to fit in the free space mentioned in “b” and to better distribute the force of the jack).
This 4x4 will be bolted (3 bolts spaced almost equally apart) to the outward face of the 11.25in. part of the front most and back most 2x12’s.
Questions:

Do you think is strong enough to support the load plus force of the jack or do you think it will just rip the 4x4 off of the 2x12; while also destroying the face of the 2x12’s?

Do you think maybe adding a 4x4 on the inward faces of the 2x12’s (these will not have the jack touch it) will provide any more strength to make this process acceptable?


texts: Is the Crimean Bridge in danger of collapsing?

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Some sources point to difficulties which may destroy the bridge, so the Wikipedia article on the Crimean Bridge e.g. has:

"The geology of the Kerch Strait is difficult: it has a tectonic fault, and the bedrock is covered by a 60 m (197 ft) layer of silt.[44] About 70 mud volcanoes have been found in the area of the strait.[44] More than 7,000 piles support the bridges; these piles have been driven up to 91 m (300 ft) beneath the water surface.[44] Some of the piles are at an angle to make the structure more stable during earthquakes.[44]

Some experts have expressed doubts that the construction is durable, given the tectonic and sea current conditions in the strait.[44][45]

Pollock, Emily (6 July 2018), Europe’s Longest Bridge Spans Troubled Waters, Engineering.com, archived from the original on 13 October 2018
Kerch Strait Bridge may collapse at any time – expert, UNIAN, 12 October 2018


texts:
I've got a quick question related to ASME B31.3.
In my system I plan on making connections in the field for deploying the system(ie think air products LN2 tanker showing up on site and deploying flex hoses). Is there any way to escape the leak test requirements for the new connections I'm making
The way I understand the code is that for a pneumatic leak check I would have to perform it at 1.1 x design pressure, which really isn't feasible in the application.
Common sense is telling me that leak checking at operating pressure should be OK, just don;t know if that is in compliance with ASME B31.3


texts: What program to implement mathematical models?

texts:
I am an engineering student and recently came upon some articles that provide numerical models that relate electromagnetic fields and temperature. I want to test out these numerical models but am unsure how to begin.

It was suggested to use either MatLab or Python. Are there any resources that will teach me how to use either to solve numerical models that include differential equations and system of equations?


texts: Methane Gas Density in Adiabatic Compressible Flow

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Hi.. The question above is one of the tutorial question from fluid mechanics textbook. In the textbook solution for this question, the density of the methane gas stream at downstream was computed with the ideal gas law equation.

What I don't understand is it possible for us to compute the density of the methane stream at downstream with the equation on below provided we know the density of methane gas and mach number at downstream.

From datasheet, the density of methane gas = 0.678 kg/m^3 and Mach number at downstream, Ma= 0.4537

The answer from the textbook solution was 2.858 kg/m^3


texts:
So, glassmakers were tasked with building parabolic mirrors for telescopes. I imagine that process is now entirely done in heavily automated factories.
How does one make a mirror and then carve it into a parabolic shape?


texts: Convergence problem in RANS simulation of unsteady flow

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I am simulating an air flow through a two dimensional rectangular channel. The channel splits into two channels, one of them is followed by a 90 degree bend downwards and leads into a cylindrical volume through which the air flows out of the geometry.
Here is a picture of the geometry:

For the simulation I use the RANS approach with the k-omega SST model. However, the solution doesn't really converge. I located the problem in the area of the transition from the channel into the cylinder where the jet bends towards one side but doesn't completely stabilize there. Instead, it keeps flapping around which can be seen in an animation of a velocity contour over a few hundred of iterations:

I assume that such a flow situation is indeed pretty unstable not only numerically but physically too. My question is the following: Given the transient nature of the flow shouldn't the RANS model just average out these fluctuations? Can a transient flow lead to instabilities in a steady RANS simulation? Do you know papers about this topic?
I would really appreciate your help!


texts: Modeling Vehicle Acceleration - Simulink

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Hello I am modeling a vehicle that has a seperately excited DC motor as the power plant utilizing the constant-torque and constant-power regions for traction.  The acceleration is governed by the following equation
$$
M \frac{dv}{dt} = F_t -(\beta_1+\beta_2v^{2}+\beta_3v)
$$

The problem with my model is that the $\beta_1$ component, the rolling resistance, is a constant value and causes the velocity to go negative for the first 0.7 seconds when the model is executed . Any suggestion on how to fix this issue?


texts: Why are engine blocks so robust apart from containing high pressure?

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Lately, I've been pondering why some engine blocks are so bulky, I always thought intuitively it was because they had to last a long time whilst containing thousands of combustion cycles but the more, I look into the reality of engine design that understanding doesn't always hold up to the design of an engine.
It seems cylinder walls have a set thickness which makes pretty good sense, then there is a water-jacket chamber for coolant which again, makes sense but then there is an outer shell of material that is sometimes even thicker than the cylinder walls themselves. This is where I become confused (An example image below)

Surely, this outer shell doesn't need to be as thick as it is. In my mind all it's doing is containing a pressurized coolant which can't amount to more pressure than the combustion of the engine itself. So why is it sometimes as thick as the cylinder wall?


texts: How to solve mesh error for narrow surfaces in Ansys Meshing?

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I am simulating a spherical grooved bearing….e.g. A bearing that has spiral grooves on the ball. Please see the following figures.
There is a kind of lubricant between ball and cup, so as to prevent metal-to-metal contact (Full film lubrication theory). The dimension of groove and gap between ball and cup are in (mm) and (micron). For example, Value of groove depth is equal to 0.006 mm and also, areas of some surfaces are too small.

Fig1:

Fig2

Now in Ansys meshig, when I tried to mesh, I got following error(Fig 3,4,5,6). I want to mesh be structure.

Fig3

Fig4

Fig5

Fig6

According to the following Fig, I increase number of cell in edges and change dropped option to kept option in mesh method and the error is only as follows:

Fig7

In Fig5 is explained about narrow surface. What do these errors happen? I am grateful that guide me in this case.

Thanks.


texts: Can you tell me (for USA) which code (or standard or guide) and in it where exactly I can see the distance required for the raft foundation, as far as how much it should extend horizontally beyond the outermost columns of the building? (In other words, how much larger it should be (as a minimum or a specified ratio etc...) than the building footprint as defined by the outer columns) I checked ACI 318, IBC, NEHRP document and cannot see it. Unless I missed it. Please help.


texts: Is there a danger to a human that is linked to ground wire of home electrical system?

texts:
Assume that a person is touching a bare wire when the person is connected directly to the ground system of a home electrical system.

If a hot wire from, say, a washing machine, suddenly shorts to its chassis, doesn't that route to ground, and isn't our human suddenly now part of a deadly circuit involving the hot wire?

This question came about from hearing about people who do this on purpose. Many people now practice "earthing", physically linking themselves to the earth ground plug of their home's electrical system.  They go as far as sleeping on mesh wire sheets plugged into ground to protect from stray EMF.

This question is not to be a commentary on the earthing theories.


texts: When current is injected into a Peltier device/thermo-electric cooler, it heats up, when the current is reversed, it cools down. Why does it takes less time to heat up than to cool down?


texts: Asymettric stiffness matrix for a generator-gearbox-turbine system

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I need to model the system in figure, where turbine, shaft1 and gear1 are a unique rigid body, while shaft2 can be modeled like a torsional spring. Using as coordinates Theta1, clockwise angular displacement of the turbine, and Theta2, anticlockwise displacement of the generator, i obtain these equations of motion

where tau is the transmission ratio of the gears and J0 the equivalent moment of inertia of the turbine-shaft-gears block.
The stiffness matrix is not symmetric and it should be impossible, where am I wrong?


texts: Is it possible to extract mechanical energy using Turbines behind PulseJet engine?

texts: Pulsejet expels pulse of hot gas (unlike turbojet engine) which create some thrust(Not good enough for ). These gases are hot, fast and pulsed. Is it possible to convert kinetic energy of these gases to mechanical energy using Turbines? (Assuming hot gases are not too hot for turbine blades to melt down). My concern is about Pulsed gases. What kind of problems/challenges it may cause in an engine perspective?


texts: How can batteries in electric/hybrid cars charge at such a high rate?

texts:
If I were to look at "normal" batteries online, they often have charging C-rates of less than 1. However, with a car that uses regenerative braking, obviously such a low charging rate would not be acceptable, as this would mean very little energy can be recovered by this process.

For example, F1 cars can deploy 160 horsepower for approximately 33 seconds per lap from the battery system (4MJ). Given Lithium-Ion batteries have a specific energy of up to 0.875 MJ/kg, this means the 20kg battery can only have a maximum possible capacity of 17.5 MJ. Therefore, a deployment of 4MJ in 33 seconds would mean a discharge C-rate of around 25. This is without even considering the extreme charging C-rate that would be required to recharge the battery during such heavy braking (little time) as in F1.

Therefore, my question is how electric/hybrid car batteries can handle the charging/discharging demands of regenerative braking?


texts: Which equations of a state space model influence the poles and zeroes?

texts:
In regulation, if we represent a system with a state space model, we end with three matrices A, B and C (without taking into account feed-forward part) that define a specific part of the following equation:

$\dot{x}=Ax+Bu$

$y=Cx$

Is it also possible to define the transfer function $G=\frac{N}{D}=C(sI-A)^{-1}B$?

If we want to find the poles, we search when the denominator ($D$) is equal 0 and for the zeroes when the numerator ($N$) is 0.

My question is, if we want to define which part of the state space model influence whether the poles or the zeroes. I would say by looking at the previous equation that $A$ is the only one to influence the poles and $B,C$ act on the zeroes.

Unfortunately, the corrections made to my exam gave a different answer: $C$ influences the poles and all the matrices the zeroes.

I don't understand, why is that the case?


texts: I want to dissipate 3 kW of heat with an air conditioner. How big of an air conditioner do I need?

texts:
So the title says it all.
I have a room (4 m x 4 m x 2.5 m) which is closed.(Actually there is a window and I could add a 50 cm panel fan if needed as an exhaust if that will help.)
I have some devices that need to be under 60°C they manage to do that now but it is still cold here. (Average temperature outside is about 5 to 15°C ± 3°C and I leave the window open, they devices are actively cooled with heat sinks and small fans that work up to 50 - 80% of their speed.)
The total power consumption of the devices is about 3000 watts.
How big of an air conditioner would I need to maintain about the same thermals if the outside temperature gets to like 20 to 35 degrees outside?


texts: Continuation of learning CAD/CAM/CAE packages

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Don't know about you but here in Spain, in the practice lessons we use some software related to the field (for example, ADAMs for Multibody Systems in MechE, right now). Then when the course ends, we don't mention / use the software until you start working in a company and you might don't remember anything at all or you just don't know enough.

I'd like to know what can I do in order not to miss this knowledge and really master all this software we are supposed to know. Do we really need to master all the software or a few are enough?

Practical example: I used MATLAB in few practices, but if I had to use MATLAB in a company I don't know how I should proceed.


texts: Are there any 'clever' mathematical techniques for testing a micrometer?

texts:
I've just inherited a vintage British 25 mm micrometer, and it's precious to me.
You can test a spirit level by reversing it, and similarly you can for an engineer's square.  We can test a right angle via the 3-4-5 formula. Absolute verticality can be proved with a rock on a string. And NASA can detect the constituents of exoplanet atmospheres thousands of miles away just by peeking at them.  Is there some mathematical 'trick' that we can perform to test the accuracy of a micrometer?
I'm quite prepared to accept no.

This question excludes expensive gauge blocks.


texts: How to design an enclosure around the load cell (Beam type)?

texts:
Hardware and Electronics Used: Arduino UNO, HX711 ADC Load cell amplifier, Load Cell (2Kg);
Currently, I am working on a project which requires me to put load cell along with the other circuitry in an enclosure to make it water-resistant... But while doing so, the weighing platform and the base come in contact (as shown in picture 2). This messes up the readings.  I 3D printed various loading styles and tried out a few different configurations but none of them seem to work. The configuration that is shown in Image1 is an ideal one that yields precise results irrespective of where you place the load on the weighing platform. The configuration in Image2 yields fluctuating readings which make no sense whatsoever. Can you suggest to me some way by which I can design a proper enclosure around the load cell and the circuitry in order to get proper readings and also keep it water-resistant?


texts: Does anyone know how would one use "mutexes" in fortran user subroutine so that I can run abaqus job via parallel processing?

texts:
I really would like to run my abaqus jobs (that have user subroutines attached to them) very quickly. I have read some sections in documentation about calling a utility subroutine called "MutexInit". I didin't understand when i could use it so that there will be no errors!!!

Could anyone please direct me to anywhere where I can have an idea of what to type in my subroutine files so that I can use cpus 4 or higher to run my abaqus jobs super fast?

Please and thank you very mch!


texts: Terminology for ponding behind a bridge during a flood

texts:
I have read a specific term to describe the process when water pools behind a restriction such as a bridge during a flood. I cannot for the life of me remember what the word was.

The term specifically refers to the process of the ponding of water upstream of a restriction during a flood creating an area where the water pools higher and velocity is slower. Essentially the flood version of localised water detention due to a outlet restriction.

If anyone could help me out with the exact terminology that would be great. Have been searching all over to no avail.


texts: Pavement ME, Version 2.5.5 and PCC Longitudinal Cracking?

texts: In Pavement ME, Version 2.5.5, why is there a tab for "PCC Longitudinal Cracking" calibration factors since longitudinal cracking prediction is not part of the current Pavement ME?


texts: How was surveying for maps done before lasers?

texts: I understand that you can have a device with angular measurements for rotation and elevation, and use trigonometry to calculate the distances... but only if you have some distances to start with. How did they accurately measure the first straight-line distance over any distance significantly long enough to give usable angles? And wouldn't the error in other distances calculated from this very quickly accumulate out of control?


texts:
I have a project that includes some standard AISC clevises on threaded rods in pure tension. I am trying to find guidance on how best to address the possibility that the rod could rotate with respect to the clevises over time, causing the clevis to eventually disconnect from the rod. My belief, and that of the engineer on the project, is that this is not a likely problem unless the rod was expected to ever see near-zero loads, and we have specified a jamb nut in any case, just to be conservative. All the same, I am wondering if there is any code or documented standard practice that would back us up for situations like this where pretension is not controlled.

Ideally, a code would answer this question in the general case, but some specifics of our application are as follows:

The material is ASTM A36 for both the rods and the clevises. The rods theoretically experience around 3 kips of tension under dead load only, and about 10 kips under the code maximum live load (controlling). They only experience a load reversal (go into compression) during a code-level seismic event. The threads on the rod are right hand at both ends (not turnbuckle style.) The clevis is AISC #3 size with a 1" DIA rod. Both clevises are themselves restrained against rotation. The axis of the rod is plumb. At installation, we will be able to verify that each rod is substantially loaded, but not necessarily that they are sharing the load equally.

I have looked at some other clevis assemblies like this used for diagonal bracing of frames, and they don't have even a jamb nut, but I doubt they experience the same sustained tension, and they aren't in the same orientation.


texts: Vibe Table: Increase Peak Force Capability?

texts:
I'm driving a small, benchtop vibe table (shaker) with two Crown DSI-1000 PA's, and also cleaning my signal with a DBX 231s EQ. Currently running the system at 6.8 GRMS, but I'm looking to increase my overall driving level.

With the test article mass/ test levels I'm shooting for, I'm conflicting with the specified peak capability of my shaker.

To be more precise, I would like to drive a ~5.5 lb object to ~10 grms (random vibe). According to my back-of-the-envelope calcs (Eqn 1), I don't think there is much I can do besides purchasing a larger shaker. This shaker tops out at 200 lbf. However I figured it would be worthwhile to probe the community for ideas in case there is some sort of engineering voodoo I can employ. Will also post in EE stack exchange.

TL:DR, Is there any way for me to increase the peak driving force/ capabiltiy of my shaker table without the risk of damaging it?

My PA's and EQ are also getting close to their maximums, at just 6.8 grms.

Desired profile: NASA GEVs STD-7000a:

Eqn 1: GRMS = [PEAK_SHAKER_FORCE / (ARTICLE_MASS + ARMATURE_MASS)] / 2 . --> GRMS = (200 lbs/ 13.5 lbs) / 2 ...................................................................... --> GRMS_MAX = 7.4


texts: Polarity of a relative angle - Knee joint angle

texts:
I'm wondering if it's correct to write:

$$ \alpha = \theta_{lg} - \theta_{th} $$

EDIT: the theta angles are defined positive in counter-clock direcction, instead alpha in clockwise direction. My goal is to find a relationship between the three angles I wrote above (the relationship should be valid at any time istant).

Thank you for your time.


texts: What's the usefulness of maximum stress calculated on Secant's formula for buckling?

texts:
For comparison: in Euler's formula, we calculate the critical force such that when the column is subjected to it, it buckles. As far as I understand, the yield strenght of the material doesn't really matter.

However, when facing eccentric load, secant formula is used and a maximum strain is calculated, instead of a critical force. Does it makes sense then to use yield strength as a maximum admissible strength?

Edit: also, when derivating the formula for the maximum strain, one already considers the compressible strain and the bending combined. Thus, when calculating the maximum strain, I don't need to further make any considerations about their interations, correct?


texts: Is it standard practice to use a pressure relief valve as a pressure regulator?

texts:
I'm attempting to understand the difference between a pressure relief valve and a pressure regulating valve. From my research far, I've come to the following conclusion:

Pressure relief valves are primarily used for limiting pressure build ups and are often safety related. Pressure relief valves vent the fluid when the pressure exceed some setpoint.
Pressure regulator valves on the other hand are used to regulate a pressure via step-down. These regulator are typically non-venting.

So I'm somewhat confused as to whether or not I should be using a pressure relief valve or pressure regulator in my application. It seems like a pressure relief valve would do the same exact thing as a regulator except it would vent the gas. Do pressure regulator offer better regulation than a relief valve?


texts: How to derive fixed end moment of a beam fixed at both ends with a point force not in the center

texts: So this is as far as I have gotten. The formulas written in green are the formulas that I have to find/ derive but I am hitting a wall. I know I am supposed to integrate but I am not sure where to go from here to get to the end formulas. If someone could please help explain/ walk me through this, I would really appreciate it.


texts: How to calculate required air mass flow to keep CPU below certain temperature?

texts:
I have been assigned to work out how much air flow is needed through each partition of our servers in order to keep our processors at (or below) 60C (333K).

I have worked out the current mass flow rate going through each partition, and the heat flow rate, and I know the temperature of each processor from the system logs.

However I don't know how to calculate the required mass flow rate to bring down the temperature of the CPU's to a certain value.

For example, let's assume on one partition I have found:

air mass flow rate = 0.01 kg/s
heat flow rate = 150 J/s
temperature of inlet air = 298K
temperature of outlet air = 308K
temperature of CPU = 353K
Goal CPU temperature = 333K.

So I need to reduce the CPU temperature by approximately 6% (1 - 333/353).

Does this mean I simply need to increase the airflow by 6%? I originally figured this could be true because a decrease in temperature of the CPU would be a linear decrease in the heat flow. So according to the heat capacity formula (q=mc$\Delta$T), where q is the heat flow, m is the mass flow, c is the heat capacity at constant pressure, and $\Delta$T is the change in temperature:

1.06 * 150 J/s = 1.06 * 0.01kg/s * 1000J/kgK * (308K - 298K)
Therefore the mass flow rate needs to be 0.0106m/s.

The problem with this is I am assuming the outlet temperature remains the same, which I don't expect would happen. And the mass flow increases by such a marginal amount. I just don't feel like an increase in mass flow by 6% would decrease the CPU temperature by 20C.

Could someone please show me how I should be doing this? (Please note the goal is simply to find how much I need to increase the airflow)


texts: How do you find the resultant hydrostatic force on a curved surface which is not exactly semicircle

texts:
Assuming this is a pressurized chamber with hydro-static force acting on a semi circle stuck in a surface:

To find the resultant force, I would first divide the semicircle into half. Pressure on curve surface is equivalent to pressure on projected surface form the curve. Therefore, I can find the resultant force (F1) from multiplying water pressure (P) with radius of the circle (R):

Where $F_1 = P \times R$
Considering the other half of the semicircle, my free body diagram should look like this also:

Where $F_2 = P \times (R-r)$
Therefore, my resultant force should equals to $F_1 - F_2$.
I would like to know if this is the correct way of calculating the resultant force for such scenario.


texts:
I'm going to make such a stool:

Originally it's made of thick plywood, and I want to switch to a thinnest possible OSB to make it as cheap and light as possible.
It's a bar stool of 70 cm height, 33 cm width. Front plate is 16° inclined from vertical.
My gut tells me that the weakest elements are regions on the sides of the opening(The left one is encircled on the image). I have to keep the opening, it's bottom edge acts as a footrest.
At the narrowest point the width of this area is $b=5$ cm, opening height is $L=28$ cm.
I calculate that $h=12~\text{mm}$ OSB would suit me.
My first question: Can I consider it as centrally loaded column?

I calculate slenderness ratio:
$$\lambda = \frac{L_{eff}}{r}=\frac{L_{eff}}{\sqrt{I/A}}$$
where $I=\dfrac{bh^3}{12}=7200~\text{mm}^4$. So $\lambda={28~\text{cm}}/{\sqrt{7200~\text{mm}^4/(50~\text{mm}\cdot12~\mathrm{mm})}}=81$. It tells me that it's a long column. So the load would be limited by buckling.

Critical load $F=\dfrac{E_{OSB}I\pi^2}{L^2}=\dfrac{3~\mathrm{GPa}\cdot7200~\mathrm{mm}^4\cdot\pi^2}{(28~\mathrm{cm})^2}=270~\mathrm{kgf}$

Second question: Am I right that the stool made of 12 mm OSB would be able to hold over a ton of static load?
Third question: You can notice screwheads on the picture. How can I estimate the load they need to withstand?


texts: can a design table be created -only- for colours in solidworks?

texts:
exactly what the title says.  and, what is the easiest way of doing this?  I can do it clunky and manually by first creating a design table with only one dummy variable then adding the colour colums..

edit: this https://help.solidworks.com/2018/English/SolidWorks/sldworks/t_inserting_file_design_table.htm , with the correction that the A2 cell must be named "family", as described here (not where I originally found it) https://help.solidworks.com/2011/English/SolidWorks/sldworks/LegacyHelp/Sldworks/Configuration/Formatting_a_Design_Table.htm is what I was looking for..


texts: Subsea galvanic corrosion protection by paint

texts:
In submerged conditions galvanic corrosion effects exist between metals with dissimilar nobleness and the presence of seawater as electrolyte.

Does reducing the contact area by using an nonconducting paint on the interface layer between the two metal parts help delay this process? Or is any the solid contact electrical route, e.g. via a bolt or so, enough to make the deterioration speed limited by the electrolytic process c.q. the surface area in contact with the electrolyte?


texts: Difference between a positive and negative adjustable voltage regulator (LDO's)

texts:
I am having trouble understanding the difference between positive and negative adjustable voltage regulators (LDO's). There are circuit diagrams for the positive LDO's such as the following:

I am not able to understand what a circuit diagram of a negative voltage regulator looks like or how different it would be from a positive voltage regulator.


texts: In a control block diagram what does a block with an angled arrow through it mean?

texts:
I have been looking at papers describing how to do non linear control with neural networks. A lot of these papers have block diagrams with a symbol I don't understand. There is a block with an angled arrow drawn through it. The tail of this arrow is an output of another part of the block diagram.

The sample is from a paper called "Nonlinear System Control Using Neural Networks" by authors Jaroslava Žilková, Jaroslav Timko, and Peter Girovský.

A link to their paper is here:Nonlinear System Control Using Neural Networks


texts: Where is the resistance in my DC hub motor coming from?

texts:
I'm designing an electronic speed controller for an electric bike and I recently mounted my wheel and performed some tests. The wheel (an old 24V brushed DC motor) works pretty much exactly how I expected it to EXCEPT there is a large amount of mechanical resistance both when I attempt to turn it by hand and when I hook up my ESC. Here are the values of a preliminary test with the bike mounted (no load):

The weird part is that there is a little bit of "give" (low resistance) when the wheel is turned by hand for about 6 inches or so. I uploaded a video to youtube of me moving the motor by hand to show this clearly (sound on!). The video doesn't exactly show this but the housing of the wheel is not rubbing anywhere on the fork of the bike.

Does anyone know if the mechanical resistance of the motor might have something to do with the brushes? Or maybe how the wheel itself is mounted? I appreciate any and all answers!


texts: When using digital signatures, what does "capable of verification" mean?

texts: Numerous state regulations adopt the NCEES model language for the use of digital signatures.  This language says, among other things, that the signature must be "capable of verification."  It is not clear to me what this means, though I can make some guesses.  Is there any authoritative answer as to what, exactly, must be verifiable when using a digital signature to sign an engineering document?


texts: ANSYS Workbench - Support type when lifting

texts:
Which type of support should I use when trying to simulate stress in structure that is lifted. Lifting is done by using four lifting lugs and chain angle is 45 degrees. What type of support to use on this surface:

Lifting chains (ropes) are not modeled.

EDIT

Structure is loaded with force of 20 000 [N] acting on plate shown on picture. Lug will be welded to plate.


texts: When were the japanese yellow/white/blue/silver paper steels introduced?

texts:
The steel series called kigami/shirogami (yellow/white paper steel, high purity carbon steels in different grades), aogami (blue paper steel, a tungsten alloyed tool steel series), aogami super (a refinement of the aogami series), gingami (silver paper steel, a rudimentary but pure and apparently precise stainless series) are commonly used for quality japanese hairdressing, kitchen, gardening, woodworking and shaving tools.

Such tools are, in the west, usually marketed as very traditional.

Nowadays, it seems these steel types are proprietary to the hitachi subsidiary "Yasugi Special Steel Works"

When were these steel types introduced? English language internet research yields no clues except that YSS was founded in 1899 and merged multiple times, and that some rather old YSS-steel based razors exist with S2 and A2 as part of their inscriptions, and that these steels use some kind of electric crucible process and are made from iron sands, and that the highest carbon grade of "white" steel (shirogami #1) is considered similar to traditionally made "tamahagane" sword/knife steel in material properties.

Were these steel types an invention of YSS; if not, who introduced them when; if yes, when did they introduce them? What preceded them in the relevant markets?


texts:
What is the fastest possible slot car one can build? What are the limiting factors?

Obviously, we have to require that the motor is aboard the car and that it's propelled by the wheels (we don't want a particle collider or a rocket), and we want a closed track and go many rounds (we don't want a drag racer).

I guess we would build a large looping, but at which speed will it break from centrifugal force? How much energy can we pump into the car before the track melts? Can we cool the whole race track down to use superconductors? Do we want to evacuate the whole track to avoid sound barrier effects or do we need air for something (cooling? aerodynamic control surfaces on the car?)?


texts: What's a good way to equalize pressure between 2 spaces without allowing gas exchange under normal circumstances?

texts:
I have a reaction chamber where gasses are injected to maintain a certain mixture. The container is sort of like a bell, where the bottom is submerged in water to make a seal.

The issue I have is that when injecting new gas into the chamber the excess has nowhere to go, so the water level is forced downward. I would like to maintain the water level difference inside and outside the chamber of <0.1in.

This rules out most kinds of check valves, because the pressure differential is too low. What I'm currently doing, is intentionally leaving a small hole open in the reaction chamber to allow pressure to equalize. Gas is injected at a very slow rate, so this works ok, but unwanted diffusion is always occurring through the hole.

Does anyone know of a mechanism that will allow the pressure to equalize, but which will not allow significant gas exchange once the pressure is equal? I'm thinking something similar to a water trap, but with even lower pressure drop.


texts: Reference book for hydraulic systems design

texts:
I'm looking for a good reference book on the topic of fluid dynamics/hydraulics systems engineering.

I'd like a reference for simlpe/estimate calculations on things like major losses (pipes), minor losses (bends, orifices, expansions, contractions, etc). The media that I most frequently work with are water, glycol, hydrogen and air.

I know that CFD and exact value calculations can be quite cumbersome in fluid dynamics, and that is why I am looking for an engineering reference book for estimate calculations that can help simplify the calculations when I need to make system design estimates (>100 different calculations).

Please let me know if you have any suggestions!


texts: Are equilibrium values of a differential equation uniquely dependent on its constants?

texts:
I have a dynamic model which undergoes two distinct stages. The system starts out with certain initial conditions and once a specific point is reached in stage 1, these ending conditions are used as the initial conditions for stage 2, and the remainder of the solution is calculated. I am attempting to solve for the steady-state equilibrium point by taking the derivative of the potential energy with respect to each generalized coordinate, setting equal to zero, and solving. For stage 1:
$$
 V_{im} = \frac{1}{2}k_1y_1^2 + \frac{1}{2}k_2(y_2-y_1)^2 + k_r \theta_o^2+m_1gy_1 \\
    +m_2g(y_1+y_2)+2m_3g(y_1-l \sin{\theta_o}) +\frac{1}{4}k_{1n}y_1^4+\frac{1}{4}k_{2n}(y_2-y_1)^4
$$
and for stage 2:
$$
    V_{de} =  \frac{1}{2}k_1y_1^2+\frac{1}{2}k_2(y_2-y_1)^2+k_r\theta^2 + m_1gy_1 \nonumber\\
    + m_2g(y_1+y_2) + 2m_3g(y_1-l\sin{\theta}) + \frac{1}{4}k_{1n}y_1^4
    + \frac{1}{4}k_{2n}(y_2-y_1)^4
$$
where $ \theta_o$ was a constant while $ \theta$ is variable. Still, these reveal the same two derivatives:
$$
\frac{\partial V}{\partial y_1} =  k_1y_1+k_2(y_1-y_2)+g(m_1+m_2+2m_3) +k_{1n}y_1^3-k_{2n}(y_2-y_1)^3=0
$$
and
$$
\frac{\partial V}{\partial y_2} = k_2(y_2-y_1)+m_2g +k_{2n}(y_2-y_1)^3= 0
$$
Therefore, I would assume that both stages would have the same steady-state position, but this is not always the case once I run the entire simulation numerically in MATLAB (details not shown). Sometimes the steady-state of stage 1 matches the calculated value and not stage 2, and sometimes it is the opposite way around. What could be causing this discrepancy?
For comparison, stage 1 and stage 2 position graphs as described are below:

The values of the constants are the same throughout the simulations.


texts:
I have to calculate a ratio of a planetary gear set. It's an existing gear set and had been already implemented for years ago(works fine). Somehow it does not fit the general formula of planetary gear set which is

R = 2*P + S (number of teeth)

On my gear set:
R = 62
P = 21
S = 18
62 != 21*2 + 18

So how can i calculate the correct ratio?


texts:
I've found this video on YouTube:

https://youtu.be/hWK8Gv0JHqk?t=220

Watch from 3:40 to 4:20.

I'd like to learn more about this linkage that makes that link alternate between hitting and missing the sliding link.

I've searched for the animated movements from 507 Mechanical Movements superficially and found nothing.

Thanks in advance.


texts:
I was wondering what is the 3D software being use ( picture below )
Thanks in advance!


texts: Canonical approach to experimenting with a gearbox design

texts:
I'm hoping to design a simple gearbox for a 1-seater car for kids. So far I'm only using discs of paper I cut out and rotating them by hand. I wonder what the canonical approach is to prototyping/experimenting with gearboxes. I guess the prototype won't need to be big, but just 10CM or so?

Should it be done virtually in a CAD software instead?

I'm very new so any tip will be appreciated.


texts: Why use two tower cranes on one construction site?

texts:
I am fascinated by construction. My university is building a new facility, and they are using 2 tower cranes in the construction.

Why would a contractor choose to use 2 cranes on one construction project? Is it simply a matter of saving time by having the two cranes work simultaneously? What are some other considerations that might be taken into account?

EDIT: after checking your answers, I agree that it is most likely that using two cranes in this situation was mostly done to increase productivity/throughput, and the positioning of the cranes depends on the building design and ease of loading materials to be transported by the crane.


texts: Liquid Vacuum Filler machine using Venturi Pump

texts:
We are currently using a liquid vacuum filler machine that vacuum fills nail polish. There is a Gast 1/4 horsepower motor and a Gast rotary vane pump that according to the gast website pulls 20" of vacuum at a flow volume of 4CFM.

I wanted to know if it is possible to switch to a Venturi vacuum pump to accomplish the same thing.

There are four filling heads on the machine.


texts: What are exact location of Integration Points in STRI3 element in ABAQUS?

texts:
Introduction

I have a file with .rpt extension from ABAQUS which is output of a model. This .rpt contains stresses of elements and displacements of nodes in plane text format. There is an item with this file which i was not able to find in ABAQUS manual fluently. I wanted to find out stresses in this . this is original model and it is completely with STRI3 element.

This is a section of output file:

This does give S11, S22 (normals) and S12 (shear) stresses in defined location.
I believe each element does have 3 points which for integration are used. These points are also known as "Integration Points". In the text file above it seems each element does have 3 integration points.

Actual Question

What are exact location of integration points of an STRI3 element, if this STRI3 element does have 3 nodes: N1, N2, N3 with known coordinates (X1,Y1,Z1), (X2,Y2,Z2), (X3,Y3,Z3).


texts: Comparing the precision work of plane surveying and geodetic surveying

texts:
In geodetic surveying, we consider the spherical geometry of the surface though the surface is not perfectly spherical.
In-plane surveying, we consider a small surface area which is considered as a plane or flat surface whose results upon surveying do not get affected.
But can't totally neglect the curvature of the earth's surface so the assumption of flatness must affect results to some extent.
I know that geodetic surveying has great precision than plane surveying. However, both will be accurate though.

If both survey methods were performed for an area then what would be the "precision difference"(in terms of significant figures/numbers) between these two surveying methods for the same area?
I am questioning about the "closeness of the results" of plane surveying to the actual/real parameters. So what is reality then? This is what we are trying to achieve with well equipped, periodically improved and advanced technology for great accuracy and precision that hadn't been achieved before.
I want to compare their precision because I think results from geodetic surveying are very close to reality so "comparing these readings with plane surveying allows us to find out the extent to which the assumption of flatness affects results?"

And generally what is the precision (in numbers) for these(individual) methods when performed in their standard confined areas? I think this question can be answered with some experimental readings and experiences.


texts: How to remove protective valve cap from CO2 cylinder?

texts:
I have received a CO2 cylinder from an online seller fitted with a protective cap over the valve:

I understand these should unscrew, but this one appears to be stuck very firmly.  Is there a standard or recommended way to remove these safely?  The biggest challenge seems to be securing the cylinder itself to stop it slipping while attempting to turn the cap with a strap wrench or similar.  Any tips?


texts: How to calculate the moment of inertia of a worm gear?

texts: Should I consider them as a cylinder to find their inertia? Any tips will be helpful.


texts: What's the meaning of 'Total acceleration effective'?

texts:
I'm reading a document describing the procedure to do a random vibration test. In it, a PSD (Power Density Curve) curve is defined, and there's a note at the bottom of the curve:
Total acceleration effective: 50 to 500 Hz = 2.0G

What does it mean? Thanks.


texts: What is the difference between NPT and pipe diameter?

texts:
I am confused about the difference between NPT, outer diameter of a pipe, and nominal pipe size.

Let's say I have a 1/8" NPT pipe. Does this mean the outer diameter of my pipe is 1/8"? Is the nominal pipe size equal to the outer diameter of the pipe?


texts: Device to remove condensate, without creating a hazard (EX) zone

texts:
I have gas pipeline with biogas, low pressure - approx 40mbar over atmosphere. I want to remove a small amount of condensate, inside a building, without creating an ex-zone. Small amount: I honestly don't know but it should be next to nothing. But I create a low point and want to be sure I don't block my pipeline.

What is a valve that I can build into the pipeline at the low point, that allows me to ex-filtrate gas without creating an ex-zone?

No need for an actual supplier, but some terms to aid my googling my writing of the RFQ would be great. Plus the technical info to decide if it's the right gadget for my problem!


texts: If this is submerged in water, and contracts and squeezes itself together, does it rotate?

texts: With 9 blades that are in a slanting axis so that they roughly follows a spiral around the center, would this device be similar to a pump, and turn (rotate) and gently pump the water down along the central axis as it contracts and squeezes itself together?


texts: Relation between armature voltage and mechanical power in electrical Engineering

texts:
I am searching for an effect chain that leads to the mechanical power $P_{mech}$ of a DC motor, starting with the applied armature voltage $U_{A}$. My request also includes all the electrotechnical quantities with cause, effect and linking formula, which are created 'on the way' between $U_{A}$ and $P_{mech}$.
Thanks in advance!


texts: Ideas on optimization of DRA and energy consumption of a pipeline

texts:
I have a 200 mile pipeline with a few pump stations in between.  I am trying to find ways to optimize the electricity and DRA consumption, and was wondering if anyone has ever done something similar before?

Currently, I am building models of the outlet flow rate as a function of energy and DRA. I am also building models of the flow normalized by energy as a function of DRA usage, vice versa.  Is there any other more proper ways to do this optimization?

The formal problem would be: How to achieve optimal flow rate with least DRA / electricity usage.

Data

Flow rate at the beginning and end of the pipeline
Current of the pumps at the intermediate pump housing
DRA ppm  at several pump stations


texts: connecting wheels to dc motor directly or with gears

texts:
In which case speed of car will be faster: if wheels are connected to dc motor directly or with gears?
We are making battery powered car in which case our car will be faster?


texts: Find the system response given the initial condition

texts:
I am given these sets of equations for a gantry crane:

1) $M\frac{d^2x}{dt^2}+D\frac{dx}{dt}-mg\theta =u$

2) $ml\frac{d^2\theta }{dt^2}+mg\theta +m\frac{d^2x\:}{dt^2}=0$

3) $y=x+l\theta $

Where $x$ is the position of the trolley; $M$ is the mass of the trolley; $m$ is the mass of the payload; $\theta$ is the angular position of the payload; $D$ is the damping coefficient; $y$ is the payload position; $u$ is the force applied to the trolley; $l$ is the cable length.

Based on the equations above, I have found the transfer function of this system to be $G\left(s\right)=\frac{y\left(s\right)}{u\left(s\right)}=\frac{s^2\left(l-1\right)+g}{Mls^4+Dls^3+\left(M+m\right)gs^2+Dgs}$

Now, I have to find the system response if $u$ is zero and the payload is shifted by an angle of $10^{\circ }$.

What this means is that we must now consider the initial condition of a $10^{\circ }$ angle when we do the Laplace transform; however I can't figure out how to incorporate the initial condition in my equations.

Also, if $u$ is zero, how is it mathematically possible to find $y(s)$ to be not zero, given that $y(s)=u(s)G(s)$?


texts:
I'm a beginner in chemical engineering so apologies in advance if this question is very basic!
The Problem
You are required to measure the mass and volumetric flow rate of a slurry stream. The slurry contains only water and solids. You take a bucket and stop watch and measure the time taken to fill the bucket. From these measurements, the following information is obtained.

The stream fills a 10 litre bucket in 13.5s.

A sample of the slurry weighing 767g is filtered and dried. The dry solids weigh 148g.

The density of the solids only is known to be 3200kg/m3.
TASK: Calculate the mass flow rate of the slurry stream.

My Attempt

I converted the rate at which the slurry filled the bucket to m3/s.

10L / 13.5s = 0.01m3/13.5s = 0.000741 m3/s

I calculated the density of the slurry by adding together the relative densities of its dry solids and its water.

density of slurry = (ratio of dry solids:slurry stream)(density of dry solids) + (ratio of water:slurry stream)(density of water) =(0.148/0.767)(3200 kg/m3) + (0.619/0.767)(1000kg/m3) = (0.193)(3200 kg/m3) + (0.807)(1000 kg/m3) = 1424.6 kg/m3

I plugged in the respective values into the equation mass flow rate = density * volumetric flow rate.

mass flow rate = 1424.6 kg/m3 * 0.000741 m3/s = 1.055 kg/s
Correct Answer
According to the answer key, the answer is supposed to be 0.854 kg/s.
I'm not sure where I went wrong.


texts: How should I position two shelf supports for the best distribution of load?

texts:
I'd like to mount a shelf on the wall. I have two shelf supports to do so, like this:

Relative to the shelf, where do I place the (blue) supports to achieve the best distribution of load?


texts:
How to convert Joules(kinetic energy) plot chart into watts?
Anyone know how?


texts:
I thought my electric car charging unit uses 6.6 kW of power. However, I found the label and it actually says 6.6 kVA. When I saw this I thought something along the lines of...

  Well, $ P=VI $, therefore kVA must be the same thing as kW... strange, I wonder why it's not labelled in kW.

So a quick Google search later, and I found this page, which has a converter that tells me 6.6 kVA is actually just 5.28 kW. The Wikipedia page for watts confirmed what I thought, that a watt is a volt times an ampere.

So what part of all this am I missing, that explains why kVA and kW are not the same?


texts: Decoding pump- valve analogy for medical instrument

texts:
I am referring below diagram where pump and valves are used to allow waste, diluent water control in biomedical instrument.

But I am not able to get how single pump can have multiple port, I have seen pump with one suction inlet and one pressure outlet.

Can someone explain me how pumps here having different ports (P1,P2,P3,P4,P5,P6)? I am not asking for flow, because it's dependent on application and no one can tell me by just looking at above image. But my question is about multiple ports for pumps.

Thank you in advance.


texts: Sizing the air duct that comes after a fan

texts:
I'm sorry if this sounds like a beginner question. I've tried to search around, but I may be looking for the wrong terms. I have basic knowledge of fluid-dynamics, but not enough to properly measure a ventilation system.

I've been redirected here from Physics Stack Exchange - I hope this is the right place for my question.

I want to build a fume extractor. Basically, I will have a fan sucking air into a flexible duct, which I will send out of the window, approximately at the same height as the fan, or possibly slightly higher (no more than a couple of meters).

I've learned that if I use a duct that is too small (with regards to cross section) the airflow of the fan will be limited to the point that air may even be pushed back towards the fan. However, I'm afraid that, if I use a duct with a cross section much larger than the section of the fan, inefficiencies may arise and limit the air intake of the system.

I'm already thinking of a larger fan (140 mm instead of the usual 120 mm), but what should be a good size for the duct? Would it be bad to use a 150mm one? Should the sizes match? Should it be larger? Does it matter how long the duct is?

I'm also aware that a rigid duct would perform better than the flexible one, but I'm not really trying to optimize the performance. I'm just trying to discover most of the stupid things I should avoid doing. Thanks for understanding.

EDIT: More details

Here's simple schematics for my project:

The fan is secured to a box (made of cardboard, or possibly 3D-printed plastic), and at the other end a duct guides away the extracted air, out of the window or into a carbon filter. In a separate room of the box, cables and electronics don't interfere with the air flow to avoid turbulence.

Does the size of the box matter? Should it just fit the fan and the duct, or could it be any larger? Should it be tapered?

Does the shape of the folds in front of the fan have any importance? Are they really helpful or should I skip them?

I may be overthinking this: I see many people who just glue some cardboard to a fan and they're done. But I see their designs sometimes don't actually extract air well, and I would like to make sure I'm not overlooking important details. Again, I'm not trying to squeeze any little bit of performance out of the system.


texts: How does humidity, specifically using a humidifier, affect the filtration of PM2.5 particles from a room?

texts:
I live in a very smokey and dry area where people are advised to use air purifiers. Since it's also dry I'm curious what affects, if any, adding a humidifier to a room with an air purifier would have?
When I looked into it, it seems like moisture can affect pollution and actually bring it down to the ground level e.g creating smog, so it seems like adding a humidifier to a room with an air purifier must have some effect but what that effect would be is hard to figure out.

Would the increased humidity cause particles to stick to the water and be easier to pick up by an air filter?
Would it just help my body absorb the pollution better and not the filter at all so it's actually worse?
Nothing, something, else?

Any concrete advice would, of course, be appreciated too, like:

Do NOT run a humidifier
Run a humidifier but only if it's an atomizer
Run a humidifier but only in front of your air purifier to pull pollution out quicker
Etc

Thanks for the time!


texts: Is heat transfer = potential energy in formula of 1st law of thermodynamics?

texts:
According to my textbook ,
1st law of thermodynamics is
Change in internal energy of ideal gas = K.E + P.E = Work done = $F_{ext}$ * displacement$_{walls}$
= n * degree of freedom * R * $\delta$T / 2 + 0.
Change in internal energy for any gas = W$_{macroscopic}$ + W$_microscopic$ or Thermal. W= work done here
= W + q
= $\frac{n * degree of freedom * R *$ \delta$ T_{diff}}{ 2}$ = P$_{ext}$($V_i$ - $V_f$) \delta$ is macroscopic work + q is microscopic work(No formula )
My Questions :

Here , if we are finding change in internal energy , why do we write macroscopic + micro work. Both should be microscopic right.

So , $\delta$ E for ideal gas was = $\frac{n * degree of freedom * R *$ \delta$ T_{diff}}{ 2}$ and so is same for the 1st law. Shouldn’t we have had added + P.E ?

Can we say this formula of 1st law on external + internal system because of the formula of work done ?.


texts: What does the Torque vs Frequency plot mean for a stepper motor

texts:
I found this motor which I believed had interesting specs, but when I checked out the data sheet, the torque-speed graph was replaced by a torque-frequency graph! I do not know what it means. How does it intuitively translate to torque at a given speed?

Thank you so much!


texts: What's the optimal solution for a candy dispenser that will dispense one candy at a time despite its size?

texts:
Non-engineer and terrible googler here, apologies.

I'm building an arduino project that will dispense candy when the time is right to take it. I am having problems with the physical aspect of the gadget, as I don't know how to dispense one candy at a time (given that different medicines have different sizes).

Imagine you have a simple container like this

|        |
|        |
|        |
---------

and you can fill it with candy (of every different size, but each set of candy is the same size), e.g.

|**     |                   |        |
|*******|                   |     @@@|
|*******|                   |@@@@@@@@|
---------                   ----------
(small size candy)      (bigger size candy)

Now what could be done so that only ONE container like this can handle one candy falling at a time?
If the candy were always of the same size, this would not have been a problem. However, with different sized candy, this is problematic


texts: What is up with the spaced rudders on the SMX-31/Barracuda?

texts:
You can see it in the video here for the Barracuda: https://youtu.be/_NZKyvQVRd0?t=124

And here's a pic of the SMX-31: http://www.hisutton.com/images/Fr_SMX-31_cutaway.jpg

What are the advantages of this rudder layout over a more conventional one without the gap?


texts: How to manufacture cutting dies for metal foil?

texts:
I am making a die for cutting arbitrary shapes from thin (0.1–0.5 mm) copper foil/sheet using a manual arbour press. The product will be an oak leaf shape, approximately life-size, for use as part of a sculpture project.

I am pretty experienced at general fabrication and metalwork and have access to a well equipped fabrication workshop including TIG welding, lathe, manual die grinding, manual forging and heat treatment, etc. (but not CNC milling). However, I don't know what would be an effective and reasonably low cost way to make a die for this sort of process. Is there a reasonable way to make this in-house or is it better to just get a die made by a specialist?

Accuracy of sizing isn't that important, the main priority is aesthetically smooth and well-finished edges. Visual appearance and minimal finishing are the main goals. I will be cutting in batches of around 700.

The outline will be a stylised oak leaf, so a continuous loop with various lobes, where my first priority is smooth transition between radii rather than exact tolerances.

The options I've considered so far are:

A knife-type tool (perhaps pressing onto a rubber block)
A shearing tool with a positive and negative die (like a hole punch)—in this case I am particularly interested in how to work out the optimum tolerances between the top and bottom tools for a given sheet thickness (probably 0.1 mm annealed copper)


texts: What thickness of steel sheet do I need to achieve a given strength?

texts:
I have a customer that originally bought 0.0351" thick sheet steel, CSA grade, G90 zinc coating.  They moved to 0.0236" Grade80, G90 to cut costs.  The thinner, harder steel satisfied their customer's strength requirements.  Their customer would now like a heavier zinc coating (G110) for corrosion protection but our customer wants to keep the total metal thickness the same meaning the base metal thickness will need to decrease.  Strength is determined by the base metal thickness, not the zinc coating!  What is the formula to determine how thin I can go and stay within the strength requirements of my customer's customer?

Now-  Here is where you are going to beat me up.  I do not know the strength requirements yet of my customer's customer.  If I assume that requirement to be 'x', I could still calculate strength.


texts: How could an absorbent material be emptied?

texts: I have been thinking about this for quite some time: Given a foam or other absorbent material saturated with a solvent, how could you draw all the solvent to the top of the foam (basically how could you 'empty' the foam and draw all the liquid out of it)? I think a strong enough vacuum at the top of the foam should do the trick, but am not sure. If there are any publications regarding this problem, please link them in your answer as well; I have not been able to find any.


texts: What calculation to find how much force before tipping over?

texts:
I was thinking of building a free standing structure out of plumbing pipe that would go flush against the wall to hang jackets and other items.

Attached is a sketch of the general thought of what the structure would look like.

Picturing it in my head, it seems like it should be all good. But then I just got curious about that actual math to get a rough idea of what force it would take to tip it over.

This is assuming that the pipe is strong enough to hold.

I started looking into the calculations for levers, but it seems to be like there are a couple levers chained together. At that point it became beyond me.

Note: I plan on taking other safety precautions like attaching to the wall. But I am more curious theoretically now.


texts: How do I start determining the forces in the 3 bars?

texts: For part A I have $\Delta$A + $\Delta$B = $\delta$. For part B I've tried summing forces at the joints but keep getting lost. Any help is appreciated my final is on Friday.


texts: I am looking to buy a centrifugal monoblock pump for my laboratory. The suction and discharge sizes are mentioned as 12mm x 12mm. Does anybody know what does it mean? Does it mean 12mm OD, or does it mean 1/2" BSP?


texts: On steam locomotives with six driving wheels, why are the rear set of wheels placed further apart from the other two?

texts:
So, as the question states, on steam locomotives with six driving wheels, the rear wheels are farther from the middle wheels than the front wheels are. You can see it in these pictures:

It's sometimes less obvious, but this detail always appears to be present, even if it's really subtle and hard to see. In this picture, if you look closely, you will see that the rear pair of wheels is slightly farther back than the distance between the first two pairs of driving wheels.

I've noticed that this doesn't appear to be the case for locomotives with eight driving wheels. (Alternatively, it is present, but it's super subtle and I haven't noticed it yet.)

So, what is the reason for this and why does it only seem to apply to steam locomotives with six driving wheels?


texts: What is the lifting force of a Helium balloon in air?

texts:
I am trying to solve the problem:

  What is the lifting force of in kN for a 10 m diameter spherical balloon with helium inside at 101 kPa and 320 K surrounded by air at 101 kPa and 298.15 K?

The given answer is 5.28 kN.

I start from the Buoyancy Formula:

$$F_{b} = (p_{air} - p_{gas})*g*V$$

And Ideal Gas Law:
$$PV = mRT$$
$$P/RT = m/V$$

Density of Air: $101/0.287*298.15=1.18$

Density of He: $101/0.287*320=1.10$

Volume of Helium Balloon: $(4\pi/3)*(10/2)^3=(500/3\pi)$

Substitute:

$$F_b = (1.18 - 1.10)*9.81*(500/3\pi)$$

I get 0.4101 N; am I missing something or is the given answer wrong?


texts: I'm trying to simulate a purifier in Aspen Plus in a cryogenic system. This purifier is just meant to change the pressure of the outlet stream based on the inlet flow and pressure (we are using the purest xenon money can buy and making it several orders of magnitude purer, so I'm just modeling it as pure xenon hence the purifiers only being pressure changers). I have tried using calculator blocks around different components (namely compressors and pipes) but none are allowing me to simulate a pressure drop the way I'd like. I figure the correct way to simulate this pressure drop would be with one of the custom user models, namely User2 (I've been eyeing it because I already have an excel sheet with the relevant formulae), however I'm sure any user model would work. I'm not exactly sure of how these user models work, however. Could anyone walk me through how to create a custom user model in Aspen, or point me to a tutorial? The section of the User Models documentation relevant to User and User2 hasn't been especially helpful to me.


texts:
Consider a mechanical setup, in which there are two concentric tubes, both to rotate counter to each other ie in a contra rotating fashion. Inner tube runs clockwise, and outer tube runs counter clockwise. Is there any kind of bearing that I can use between the tubes to ensure smooth functioning of mechanism. Or just a plain bearing is effective to put in between the tubes, for smooth running.
The rpm of inner tube is 1000 rpm, and outer is about 10000 rpm. So can I put any
bearing with capacity of about 11000 rpm, work in this scenario, ie can i install
any bearing in between the tubes, or are there specific application bearings to be used for the concentric contra rotating tubes.


texts:
I wanted to evaluate the safety of a walking aid device (walker). For example, if the way it is constructed and whenever I handle it, there are no risk of rotation, around its center of mass, turning over, i.e imbalance/instability.

For example, a walker with 4 wheels. A person performs around 20% of its body weight for holding the handles of the walker. When the person pushes the walker, will it be a possibility for the walker to turn over, is it unstable?

So, there is a theoretically way to calculate that? And virtually? Can I use ANSYS to check that?

Thanks!


texts: What is the maximum actuator strength allowed by physics?

texts:
What is the strongest actuator (that can exert a controlled amount of force & be able to start/stop) that an infinitely advanced civilization (e.g. only limited by the laws of physics) could create, and how would it work?
The size and mass must be macroscopic (e.g. human-sized).


texts: Why would a SMD (spring mass damper) model of steel break down?

texts: Under what conditions would steel be able to be modelled as a 3D SMD model, and under what conditions would the model break down?


texts: Difference between Precipitation Hardening and Tempered Martensite

texts:
The textbook "Materials Science and Engineering An Introduction" mentions that:

  "Precipitation hardening and the treating of steel to form tempered martensite are totally different phenomena, even though the heat treatment procedures are similar; therefore, the processes should not be confused. The principal difference lies in the mechanisms by which hardening and strengthening are achieved."

I read through both chapters but I cannot see the difference. Both processes work by a solubility difference of B in A at different temperatures, then quench it to prevent the solute from diffusing out and then speed up the aging process through heat, which allows precipitates of the solute (any solute or Cementite in the case of Martensite) to form, which impede the movement of dislocations and thus make it very hard, yet through being in a rather ductile matrix improving the overall toughness. Where is the difference between the two?


texts: Schematic Diagrams for Mechanical Systems

texts:
Is there some sort of equivalent standardized schematical (topological) diagram -such as Piping and Instrumentation Diagram, Electrical Schematics, Process Flow Diagrams, etc.- for the realm of mechanical engineering? I just need to draw the overall architecture that would describe the main components of the system and how they are connected, without going into too much detail. I have seen some diagrams but they seem to be ad hoc, as they have no fixed resemblance to each other.

Image 1: I'm looking for something in this complexity.

Maybe there is more than one way to do this but it would be nice to be more universally understood. Looked into OMG SysML but that didt at first glance seem to have what i was looking for.


texts: Reynolds transport theorem and eulerian material derivative

texts:
The problem as well as my work so far are in the image.

I begin with equation (2.23) and use the divergence theorem to express the second term as the surface integral part of the problem equation. From there I quickly end up with what appears to be an equation stating that the partial derivative of the scalar field at x is the same as the full derivative. This would imply that the integral of the convective part is zero. Since this is a general case I don't think I can make that statement. Either I've made a mistake somewhere or I am not seeing how to proceed from here.

Would appreciate help in figuring out which of those two it is and how I should proceed from here.

One thing that caught my eye repeatedly is the definition of the function for the problem. By definition and context I believe it is assumed that small x is always a function of time and initial position X, as in equation (2.20). Also, I do not fully understand why the second term of the final expression in (2.20) has to be evaluated at x.


texts: Are ceramic materials suitable for making locking lugs for guns?

texts: Since ceramics are resilient to shear loads, could one make locking lugs in a gun out of them or will tensile loads also be present leading to failure of such lugs? Also, could those tensile loads be decreased by decreasing the aspect ratio of the lugs?


texts: Converting Linear Motion into rotary motion

texts:
I'm looking at designing something using the same mechanism used in this pepper grinder. As far as my knowledge goes, it is converting vertical Linear motion (the push button) into horizontal rotary motion (the ceramic grinder).
I would like to understand how this is achieved, especially in such a small vessel.
I'm an amateur when it comes to this stuff, and was hoping someone here could explain it to me.
I appreciate all answers.
Thanks, Beau


texts: Tricks for controlling process with logaritmich characteristics over 20 orders of magnitude

texts:
I'm building a machine that operates over 20 orders of magnitude with logarithmic process characteristics. I have tried regular PID and also all sorts of variations of PID and did not get good results. What other alternatives to PID I have?

I start with 21% oxygen in a closed vessel (at high temperature) and pump it out ion by ion down to log10(pO2)=-20 of original amount. I have sensitive enough sensor, pump and power supply for it. This part all works great if I set pump currents by hand or babysit the process. To go up in concentration I just lower the pump current and leakage takes care of adding oxygen.

But as you see, in context of trying to automate the control with PID, what works well at one region is completely unsuitable at another region. It does not help that the full loop of measurements takes about 10 seconds.

I have limited the current used to 500mA, and at worst conditions the current needed to cope with the leakage is 700µA, so the range for the current is not so huge. Nor is the range for sensor voltage, which is about 100mV to -1V.

Maybe I could control pump voltage instead of pump current. Current results directly to change in amount of oxygen (which is logarithmic). The resistance of the pump depends on temperature, and most of all the oxygen gradient, and would yield much more linear and automatically regulated response.


texts: How to know which constraints suffer from 'nodes are used more than once as slave node' in abaqus?

texts:
I have been struggling to find which node and constraint suffering from 'nodes are used more than once as a slave node' in abaqus error message.

Please help me resolve this problem
Thank you


texts:
I am looking at a control system which has an unstable pole in the process. The transfer functions of process and controller are the following:

G = 10/((s+10)*(s-1));
K1 = 4*(s+1)/s;

where G is the process and K1 is the controller. I have found with the Routh Criterion that the closed loop is stable for $K>1.125$ and so I have chose the value 4 since it gives good performances. Now, when I plot the root locus of the closed loop:

T1 = K1*G/(1+K1*G)
figure;
rlocus(T1)

I get the following:

What I don't undestand is from where the zero that cancels the unstable pole comes from, since the closed loop transfer function is:

$\frac{(40(s + 1))}{(40 - 10s + 40s + 9s^2 + s^3)}$

can somebody help me?


texts: Pressure-force limiting blocks or relief mechanism for avoiding excessive pressure over a piece

texts:
I am looking for some device that can be used for blocking a sheet of glass or other materials in position. On one side of the glass (blue sheet in the diagram) is applied a force if the force is above a certian value the upper block is released and the glass is free to move upward.

I am looking for a kind of force limiting relief device but I can't find anything already on the market? Am I missing something? Is there any conventional name for such devices?


texts: Are there different solar panels for recapturing energy from household lighting?

texts:
I have been investigating recapturing energy from house lighting using solar panels.

Are there solar panels specifically designed to capture indoor lighting with a higher efficiency?

If so, what are the differences between the outdoor and indoor solar panels designed for this purpose?

References:

Solar Efficiency Limits
Can Solar Batteries Charge Using Incandescent Light?
Can solar panels charge from street lights, during the night? As it does charge from the sun during the day!


texts: Why home Air Conditioning AC compressor insulated

texts: Compressor is hot due to gas compression, and the gas then cooled in condenser. AC installed in tropical climate. Why compressor have insulation barrier?


texts:
I am trying to mill a spherical recess into stock on a 3-axis mill. I am generating the G-code in Fusion 360. I need some guidance on the best tool path generation option in Fusion 360 as every attempt i simulate shows the tool spinning in the air for extended periods.
This is what I am trying to cut out.

What I am struggling with is getting the recess cut away gradually. I can cut it in one pass but the tool plunges deeper and deeper as it spirals to the center. I want it to gradually plunge layer-by-layer. When I select multiple passes by means of axial offset passes, it cuts the entire recess multiple times starting higher than the level of the stock and shifting down 1mm after each complete mill. This way i get a gradual cut away but the tool spends most of its time in the air.
The crux I am trying to figure out is how to get it to optimally cut the recess without spending so much time in the air but same time doing it gradually without plunging so deep towards the centre.


texts: Has anyone used Freescale's (now NXP semiconductors) small engine ECU development kit? If so, please give me pointers on which model to choose to tune a 50cc Yamaha GY6 engine. Also as I'm still in college will the difficulty be too high ( i.e, would I require High level knowledge).


texts: Why/how normal shear stress is zero in thin-walled beams?

texts:
Please explain how the normal shear stress (shear stress normal to the cuve, C, defining the cross-section of a thin-walled beam) is zero. I have attached a screenshot from a book which says that the outer surfaces of the beam are stress free. This cannot be true except in very special cases. Right?

Now consider the following image. Here axis $1$ is the axial direction of the beam, and axes $2$ and $3$ define the cross-section of the beam. For the normal shear stress to be zero in the member $A$ of the cross-section, the shear stress $\sigma_{21}$ should be zero on the lateral face $1$ which is possible only if there is no axial force on the lateral face $1$. Am I right?


texts:
I once saw on TV a factory dipping a product into a tank of paint and it magically emerged with a crisp pattern. (It was an Archery bow, and the pattern was army-style camouflage).

Was I deceived or is it actually possible?


texts: What is the difference between capacity use factor (CUF) of solar power plant and plant load factor (PLF) of coal based power plant? Can we compare both since they seem analogous?


texts: How do automotive engineers determine the manufacturer rated towing capacity?

texts:
My layman’s understanding is that the limiting factors for towing capacity are usually the brakes, engine work capacity, and the transmissions ability to handle the prolonged torque without overheating. Are there other factors I’m not considering? Perhaps vehicle weight?
I’ve noticed that rated towing capacities on cars can vary significantly from one year to the next or between models. I’m assuming the reason is that manufacturers are avoiding liability.
For example the 2006 Subaru Legacy has a 2700 lbs towing capacity, while the 2006 Subaru Impreza with the same engine and transmission is 2000 lbs, and the 2006 WRX which is basically an Impreza with a more powerful engine and brakes has a 0 lbs rated capacity.


texts:
I am trying to figure out some ways in which a ZigBee network can be monitored. As is the case in any network, here we have a central coordinator and several slaves joined, however, there seems to be a tendency for the established links to break during operation.
I'm not entirely sure why this happens, but I was wondering whether there is a means in ZigBee to monitor the 'strength' of connection. Repeatedly pinging is of course, one way to do so, but are there any other, possibly less demanding options?


texts: How do you determine flow distribution at a dividing T-Junction?

texts:
So I've been trying to find out how to determine what proportion of fluid will flow down a given path when a main line branches into two lines at a 90 degree T-Junction and I can't find anything helpful.
Lets just assume water at room temperature in steady-state conditions.
It seems that pressure losses will have an effect on proportion of distribution. If the two paths have similar designs, ie; the same energy losses, the flow will split roughly 50:50. However, if one path has more energy losses than the other, then < 50% of fluid will go down that path. So there is a relationship between the proportion of pressure losses in the line to the proportion of flow down that path. What is this relationship? Is there a numerical model to determine this?
Also, intuitively, at a 90 degree T-junction, momentum/inertia should have an effect. Obviously the fluid would prefer to continue on straight rather than take a 90 degree turn, especially at high speeds. Do we consider this when determining flow division? Is there a numerical model to help me determine it's effect on how much flow will go down a given path?
Any answers or resources guiding me in the right direction, or numerical models to help me determine flow distribution at a T junction would be greatly appreciated!
Thank you in advance.


texts: If gypsum has been added into clinker during the production of cement,is curing process still needed to be carried out?

texts: Gypsum is used to prevent immediate stiffen and reduce heat loss of cement. If gypsum has already been added into cement,do we still need to undergo curing process after that?


texts: Unknown value in solution of continuity problem?

texts:
I've been stuck on this for an hour. (Probem is below)

The problem is with part b. I understand its the basic mass flow in - mass flow out with air. The equation being $$\rho_{air}A_4V_4 = \rho_{air}A_0V_0$$ where we are trying to solve for $V_4$ or the speed of air coming in through pipe 4.

We rearrange to $$V_1=\frac{\rho_{air}A_0V_0}{\rho_{air}A_4}$$

Everything should cancel to

$$V_1=\frac{A_0V_0}{A_4}$$

The issue, what on earth is $V_0$???!

In part b, $\frac{dh}{dt}=0.1910\;\frac{ft}{s}$ and is the value I ASSUMED would be used for $V_0$ in this case but no, it gives a value of $27.5 \: \frac{ft}{s}$ which is not correct.

The value supposedly used for $V_0$ is 0.1484

What is this value?
Where does it come from?

The only thing I can think of is that it has something to do with 'average velocity' as stated in the part b question.

Yet I'm drawing a complete blank. And have been for more time than I care to admit. Especially considering the solution is right in front of me.

Help is VERY appreciated at this point.


texts: How to prevent deposition of dust on ceiling fan blades

texts:
It is well known that dust gets deposited on a rotating ceiling fan because formation of a boundary layer over fan blades. The air layer next to blade surface is stagnant due to no-slip condition and the presence of a strong viscous force.

How could I modify the blade design to prevent the blades from accumulating dust? Is it possible to make the blade's surface so smooth as to prevent deposition?


texts:
I am implementing a second order filter.
It simulates hydraulic servo on an airplane. Its about 35-40 years old.

What confuses me is the notation. Like "2(.7)(52)S", what does it mean? If its just products, why then not write the resulting number?

I tried with doing 2704/(S^2+72.8S+2704), but it seem a bit slow.


texts: Theoretical maximum generated power for a given torque

texts:
Being an electrical engineer, I'm hoping someone will help me double-check my math. I have a small circuit that I want to power for years that consumes an average 10uA at 3V.

I'd like to power this circuit from a small water turbine with a magnetic coupling that can sustain at most 1 oz-in of torque before slipping.

If the turbine runs 1hr/day at 100rpms (and 1 oz-in of torque), and assuming the generator and regulation circuit run at 100% efficiency, could it power that circuit. I think it's close.


texts: How can I measure correctly with a ruler?

texts:
When measuring with a ruler divided into mm lines, should I include the lines by themselves or only in between them?
I illustrated the problem. (I took an example of measuring of 10 mm with two long lines just to make my point, but my question is also about 1 mm, 2 mm, etc).


texts:
It is a known fact that beams and spheres have the ability to carry relatively high loads.
Beams are seen in bridges and other structures even since the days of ancient roman architecture.
Spheres have even more impressive abilities. Eggs, for instance, can deal with great compression loads without breaking while their shell is ridiculously thin. Pressure chambers also usually have domes at their ends - being able to resist much higher loads than plane surfaces.

I assume the trick is that there are almost no shear stresses - most of the stress is tensile due to the shapes geometry. Generally, materials can withstand loads more easily this way (bending is more destructing than stretching).
Can someone shed some light about this mechanism? How the stresses are arranged in a tension-compression pattern? If find it quite challenging to visualize it.


texts: Can cameras+display screens with window/mirror-like optical behaviour exist?

texts:
Display screens connected to cameras are significantly different from windows or mirrors.  Looking through a window or mirror, we can focus on infinity, and we can move our vantage point to see a little different.  With a display screen showing live camera footage, we see the field of view from a single point (the camera location) and our focus is on the screen.

Would it be possible to develop a screen + camera that is much closer in behaviour to a window or a mirror?  I think the screen and camera would need to have the same surface area.  Both would be sensitive to direction, and when camera pixel $(C_i, C_j)$ on the camera receives a photon with frequency $\nu$ from angles $(C_\phi, C_\theta)$, the screen would send a corresponding photon at frequency $\nu$ from position $(S_i, S_j)$ to direction $(S_\phi, S_\theta)$, where $(S_\phi, S_\theta)$ are calculated from $(C_\phi, C_\theta)$ mimicking either window- or mirror-like behaviour.

Is such a device theoretically possible?  If yes, would such a device be technically feasible today?  If yes, has there been any serious work on such devices?  If it's theoretically possible but not feasible today, what would need to be developed before such devices may be on the horizon?

It should have a wide range of applications in telepresence, augmented reality, automotive engineering, and surely a lot of other fields.


texts: Effects of constructed tubular/annular beam upon moment of inertia

texts:
I would like to construct a hollow beam using either 2"x4" or 2"x6" structural lumber.1  My thought is to take 4 boards and butt them against each other in order to form a square beam2 with a hollow core.  The boards would be glued and mechanically fastened with screws in order to keep the beam from separating.  Likewise, the beam would be clamped under significant pressure while the glue dries.

My question is about the resulting moment of inertia for the beam.  My understanding is that moment equations for beams assume a homogenous material.  My concern is that's an assumption that I'm likely approximating but not actually meeting.

Am I okay to use the standard moment of inertia equations as is?

Or is there some sort of de-rating that I should apply to the beam since it is a composite material instead of a homogenous material?  If I should de-rate, how would I apply that within the standard calculations?

1 Please note, these are nominal dimensions.  Actual dimensions are approximately $\frac{1}{2}"$ smaller.
2Nominally, that would be a 6" or 8" square, but would be 5" or 7" once actual dimensions are taken into account.
3Please also note that these beams will not be used in a load bearing manner in which anyone could be injured.  I'm building a pergola and I want to run electrical wire through the center of the beams.


texts: What foil profile(s) does the MIT Decavitator (or similar vehicle) use?

texts:
I'm looking for some kind of "standard" hydrofoil profile suited for a water vehicle comparable to the MIT Decavitator (similar weight/speed/power/etc.), so I can use it as a base to get started with my own simulations/experiments. As far as I can tell, the team behind the Decavitator didn't publish details about their foils in more detail than the following:

The larger 60$\times$2.35-in / 1520$\times$60-mm
(span $\times$ mean chord) wing is placed about 6 in / 150 mm below the
pontoon bottoms, and the smaller 30$\times$1.4-in / 760$\times$35-mm
wing is placed another 6 in / 150 mm lower. [...]
The wings employ a custom 14%-thick airfoil which has been tailored
for the operating Reynolds-number range of 150,000 -- 400,000,
using the design principles and numerical simulation methods
employed for the Daedalus wing airfoils [Drela_JA88,Drela_SV89].
The structural merit of the relatively thick
airfoil allows smaller wing areas and less overall drag than
the 10-12%-thick airfoils more commonly employed at these
low Reynolds numbers.  The thick airfoil also gives the rather
wide usable lift-coefficient range $0.2 < C_L < 1.1$ , which
translates to low wing drag over a wide range of speeds.

(yes, I checked out those references, they are very general and don't have any hydrofoil example)
I have found some details on the design of foiling surf boards, but as far as I can tell they usually heavily restrict the wing span (for safety/maneuverability reasons I guess) to the detriment of efficiency so they aren't useful to me.


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I'm trying to identify the pictured fastener. It's a single piece around the arm of a gas spring, allowing it to pivot. I've had to replace the spring, but the screw is size M8 while the eyelet on the spring arm, is only big enough for an M6. Is there another way to achieve the same function?

Any assistance would be much appreciated


texts: Optimal method of attaching commercially-available heavy bag mount to finished ceiling with least risk of structural damage

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Admittedly, this question is related to an earlier one on the same subject.  I would like to mount a heavy bag using a system detailed in the attached picture (FirstLaw Fitness Shock Mount).  The system is designed to be mounted between and directly to 2 joists that are 16" on center with included lag bolts. My garage ceiling is covered with drywall with a bedroom above.  I assume (hope) that the gas strut on the mounting plate will somewhat help with noise and vibration, but my largest concern is mitigating unsafe loading conditions on the ceiling.  I saw an earlier post where a structural engineer suggested not attaching the mount directly to the joist. Was this to provide mitigation for vibration/noise?

Can anyone provide a "safer" installation idea or are the instructions adequate? Based on an earlier answer, could I further distribute the load if I attached a 2x6 or 2x4 on the ceiling so that it runs under the floor joist for a couple of feet, do the same to the next joist over and then attach the mount perpendicular to and on the 2x6's?  If this is acceptable, what size and length of lag bolts would be required since they would need to go through the 2x6 and into the joist? When attaching the mount to the 2x6's, would the lag bolts also need to go into the joist?  And finally, if this idea provides for better load distribution/safer install, is there concern that it does require more holes being drilled into the joist?

If anyone has a better/easier/safer idea, I would be most interested.  A diagram with dimensions would be great.

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