texts: FEM 3D truss analyzer produces forces that do not sum to zero at joints

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I am writing some code for the analysis of 3D truss structures. The program is a typical implementation of the direct stiffness method for truss elements. While testing it and comparing results to other FEM programs, I encountered the following problem.

When I have a joint with zero-force truss elements (for example a joint where 3 non-coplanar truss elements meet), the forces in these elements do not equal zero, which contradicts the joint equilibrium equation. This only happens for space trusses. When I consider plane trusses and add zero-force joints (for example a joint where two non-colinear truss elements meet), everything works out okay.

I cannot see what causes this problem. Perhaps some additional form of static condensation is needed for the 3D-case?

My thought process is that if the force in an element equals zero, that means that $u_{i} - u_{j} = 0$, where $u_{i}$ and $u_{j}$ are the axial displacements of that element, expressed in its local coordinate system. Simply stated, no elongation means no force. Of course, the whole element can be displaced in a rigid-motion-manner only, if at all.

The problem seems to be the following. Assume you have a 3D truss defined, with no zero-force members. Attach 3 elements to it (i.e. a tetrahedron, which is stable by itself) so that the entire truss is stable again. Assume the joint where these elements meet is unloaded, hence all the forces in the added elements must equal zero. Of course, the other displacements and forces in the truss are not affected by this - it just acts the same as without the added three elements. Hence, the truss would somehow need to "know" that it must be displaced in such a manner that none of the three members is elongated (or contracted), i.e. they can only be displaced as a whole, rigidly.

This seems pretty weird  and it hints that perhaps such situations should indeed be treated before the analysis. Then again, the direct stiffness method is, as far as I know, completely general and should be able to calculate any truss.

Further on, for 2D trusses this situation does not seem to arise at all; the zero force members are always recognized correctly by the direct stiffness method.

Below is an example of a truss where I encounter the problem. The image represents the element and node labeling of the truss.

From equilibrium of node 10013 (the upmost node), it follows that the forces in elements 112, 114 and 116 must equal zero. But, the program only calculated zero force in element 114. The forces in elements 112 and 116 are of order of magnitude similar to the other forces in the truss.

When I remove elements 112, 114 and 116, all the forces in the truss are calculated correctly when compared to another FEM solver (up to 3% difference, as mentioned above).


texts:
I designed this ball feeder for my robot however I'm experiencing frequent ball jams as the ball is stuck against the wall of the hole entry or just a ball being moved left and right not entering the.
I was thinking of maybe adding a wall to one side of the opening to guide the ball into the opening. However since the balls are on top of the moving disc they could fall on th other side and get stuck there.
I should mention that this is implemented using a single servo motor so only 0-180* movement is possible.
I'm open to any suggestion either ne design or improvement.


texts: Are there any differences between using nylon or ABS for RF electronic cases?

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I want to contain a very small PCB (roughly a square centimetre) in a casing. For demonstration purposes I want to 3D print a couple of those casings as well.

The most obvious method available would be using ABS for the printed casings. However, nylon appears to be smoother and tougher. Those traits are often a plus during demonstrations. However, since the PCB contains a S band antenna I'm slightly worried about the RF properties of the material used.

Are there any downsides to switching from ABS to nylon that I'm not seeing?  I'm especially interested in the RF characteristics in 2-4 GHz range. Cost is not an issue.


texts: How to get similart Geomagic two stl file deviation in free Cloudcompare software?

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I need to compare two STL (Dental model Scanned) files and find the deviation between their points, SO this two STL files have different boundary, so i already used the GEOMAGIC Control software for comparing STL files, one sample output file would be like this:

I found these two like:

Are there any open source alternatives for geomagic?

How to compare/quantify (populate) two .stl models having shape difference to see result as color stl file and bar telling plus and minus changes?

useful for finding free alternative software for Geomagic, So i installed the Cloudcompare in my Linux OS, and aligned two stl file  and used the compute cloud/mesh distance icon and get this output picture of stl which shown geomagic output above:

So in the CloudCompare output i have 1 aria which i don't want to be.
How could i solve this problem?


texts: Why do herringbone/double-helical gears have a stable and unstable configuration?

texts:
I understand that double-helical gears are used over regular helical gears to balance axial forces in a shaft but, depending on the direction, it seems that these balanced forces can be either compressive or tensile.

A quick Google search shows that many suppliers recommend the compressive configuration over the tensile one when installing these gears, because it is more "stable." However, most of the websites I have looked at have similar wording when saying this, and I have not yet found any source that is credible (academic textbooks, well-know suppliers, etc.). This makes me suspect that this is either not a very important consideration, or it is not true. From what I understand, if the forces are compressive, they will correct any axial misalignment, but I would think that tensile configuration would also correct the misalignment. In other words, I can't really picture the "unstable" scenario.

Moreover, I do not understand how both the pinion and the gear could be both in a "stable" configuration, since any compressive forces in the gear would have to cause a tensile force in the pinion. If one direction is truly "stable," which of the two (pinion or gear) should be stabilized?

If anybody has any credible online sources or intuitive explanations on this stability problem, that would be a great help


texts:
I am currently developing an AHU for all weather conditions.
I need the design process for calculating coil capacity and air discharge rate.

Issue is that, while plotting the process on psychrometric chart, you can give only 1 outside air condition.

So you would need to plot 12 different charts for a year (considering that the temp. is averaged out for a month, which I think is not the correct way to design) and choose the highest required capacity as design requirement.

Hence for all year air conditioning how can I design coil capacity and air discharge?? Any other methods?


texts: Help finding a thixotropic suspension with specific properties

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I currently doing research on 3d printing on circuit boards. The technique we are using is to put a conductive material, I.e ceramics/metal in a gel/polymer, to print the suspension and then when is complete to sinter away the gel/polymer. The problem I am having is the suspension needs to be thixotropic. Furthermore it must have a high viscosity i.e 500 cpa under low shear and to quickly drop to low viscosity as the shear increases

So far the closest thing I have been able to find is in this paper but if you look at the graphs none of them have a high enough viscosity and more importantly the drop to low viscosity under increasing shear is too shallow.

I have tried to use models like the ones in this paper but I am finding it quite difficult.

Does anyone have any suggestions to find more materials like the one I require? Thanks


texts: Is there a standard for where treelines are drawn?

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On surveys and site plans, I've often found treelines. These look like the below image, and serve to delineate in a very approximate way the areas full of trees and those that aren't:

Is there a standard for where the line should be drawn, in terms of either tree trunks or canopies? For example, in the image below, should line A approximately run down the canopies of the trees closest to the outside? Should line B approximately run down the trunks of those trees?

I am aware that these lines are all very approximate and one should never read too much into them. However, before approximating something, no matter how roughly, I'd like to know what the target to be aiming at is. (And likewise for interpreting someone else's approximation.)


texts: Contrradicting answers for relation of speed of a motor with current

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For a DC motor, speed of the armature is inversly proportional to current.

But at the same time, we know that torque of the armature is directly proportional to the armature current. Since speed can be increased by applying torque, this means that speed is directly proportional to armature current.

How is this possible ?
Where have I gone wrong ?


texts: A board or mat that we can detect a push at an exact point

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Is there any kind of board or mat that when we place it on the floor and wire it, a self-made connected device can read these data when it is being pushed and holding onto it, at multiple points?

Location where the force is applied onto. Something working similar to a touchscreen, or a trackpad, or at least a keyboard. Except it's not any of those :-D
Magnitude of the force

I need to build a footstep detecting device consisting a board that can be wired and detect point of pressure and how much amount it is. It is something working like a capacitive sensing device. But able to handle greater pressure.


texts: Can the phrases “carbon fibre reinforced polymer composites” (CFRP) and “carbon fibre-epoxy composites” be used interchangeably?

texts: Does the "polymer" in CFRP directly and unambiguously imply the use of an epoxy resin?


texts:
I have a quick question related to the topic of mechanics of materials.

If I were to have a beam that is fixed at both ends and has a central point force, do moments develop at the fixed supports?

e.g.

I was thinking, wouldn't there be an absence of moments at the fixed supports since the balanced vertical reaction forces at both ends would prevent the development of a moment?


texts:
I am currently trying to validate a shadow flickering algorithm against some data generated by Openwind. The goal of this validation is to have a code that we know that is correct and modify it to asses the influence of wind turbine blades on the energy yield of solar farms, since their objective is different and placing environmental sensors on their software is not really scalable.
I have seen some documentation from other sources than Openwind (which lacks details about the implementation) stating that normally the rotors are modeled as spheres, which leads to conservatives estimates. But when I try to simulate an obstacle at 100 m to the West of an observer I get significant differences. I am using the same algorithm for the Sun's path as them* (NREL, according to their manual), and I get good results if the flickering is happening before 13 h or after 15 h. My best attempt so far is shown below. On the x axis there is the hour of the day given by Openwind for the beginning (blue) and ending (orange) of flickering for a given day. On the y axis there is the value given by my code. I already tried:

Tinkering with the coordinates precision
Tinkering with the turbine position
Considering/not considering the altitude for the Sun position
Considering/not considering the apparent diameter of the Sun in the sky
Modeling the rotor as a disc facing the Sun's azimuth
Modeling the rotor as a disc facing the wind
Modeling the rotor as a disc with fixed orientation
Modeling the rotor as a sphere
Using the apparent elevation instead of the elevation from the output given by pvlib for the Sun direction

*Since I'm coding in python, I am using the implementation given by pvlib
I don't know what else to try, so any ideas are welcome.


texts: How to divide the water flow into outlets with equal flow each?

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I'm designing a machine that uses water to boost fish in one phase of a process. My main concern is how to split the water flow that I get from a water pump in to $N$ outlets with same flow rate. The image below shows this graphically. I need to use PVC pipes. I posted same question on Physics but they redirect me to this page (https://physics.stackexchange.com/q/579522/274594)

Update 2020-09-17:

Flowrate from water pump is constant.
Diameters on the figure are not physically representative, it's a simple conexion diagram.
$D_{pump} > D_{outlets}$
$D_{outlets}$ are equals

I'm also concerned because I don't know too much about this and when I Google it I can't find anything related: equations.


texts: I need help identifying a special kind of coupling

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I found this switchable coupling in Rollof/Matek machine elements, i have never seen this kind of coupling before.

According to the dutch edition its name is:

  Tweevlakskoppeling

Which literally means Two-surface coupling

After some research on the web i couldn't find any reliable information, i thought the translation is wrong, then I checked the original edition in german, apparently, the name is correct. The original edition:

Can someone identify this coupling?


texts: What device would you use to set angles in two plates?

texts: I am studying gauges for measurements and I can't find the answer to what device I would use to set angles in 2 plates.


texts: Terminology for motors with custom bearings

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I am interested in buying electric motor components separately so I can add my own bearings, not use a motor with sealed OEM bearings.

I do not know the correct terminology for this type of application, so I do not know how to search for it.

How can I find motors like this?


texts: carry over factor in beam ( moment distribution )

texts: In the solution , we notice that the 2823.6 is the result of carry over factor from BA to AB . Why we dont need to do the same thing for BC to CB ?


texts: Shear force expression for singly supported triangular load

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From equilibrium: $$C_y = \frac{w_0L}{2}$$

And the load is given by: $$w(x)  = \frac{w_0}{L}x$$

Thus the expressions for shear and moment are given by: $$V(x) =\int{-w(x)dx}=-\frac{w_0}{2L}x^2 + C_1\\M(x) = \int{V(x)} = -\frac{w_0}{6L}x^3 + C_1x + C_2$$

How are $C_1$ and $C_2$ determined?.

Cheers


texts:
What are the best foundation type for a construction in the city and earthquake prone area?
If bored pile foundation is the best, which type is the best, square, circle? what are the considerations of that type?


texts:
A hydropower plant uses a river to generate electrical energy. It has a drop of $107m$ and the flow rate of water is $275$ $m^3$/$s$. The flow rate of the water is the same in and out of the system.

I was asked to determine whether the system is open or closed.
Ans: open

And to simplify the general energy balance for the system

$Q + W = ΔH + ΔE_k + ΔE_p$

here is where I am a bit uncertain as to how to simplify it, I think that only $ΔH$ can be removed from the equation since the enthalpy won't change. Is that correct?

And so if $Q + W =ΔE_k + ΔE_p$ how can I use that to calculate the maximum amount of electrical energy that can be generated?


texts:
Can I use a conical head at the bottom for a small diameter steam manifold ( Schedule 40- 3 inch dia. and 2 inch dia. ) that needs to operate at high temperature (~450 deg Celcius) and High design pressure (25 bars = 363 psi)

Since this is a steam distribution and condensate removal manifold, I want the (bottom) head to allow all liquid condensate to be drained via a trap at the bottom.

Can I use a conical head in such a high pressure case? Or are they reserved for lower pressure applications?

Should I stick with Elliptical head?

Also, which would be cheaper and easier to manufacture?

Thanks in Advance.


texts: What is the unbraced length of a pile in soil?

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When analyzing a pile or drilled shaft as a beam-column, how do you determine the unbraced length of the portion that is in the ground? Typically, the braced points on a beam or column are well defined, e.g. there are connections at discrete locations.

A pile in the ground will have some resistance to movement because of the soil. Is this resistance enough to consider the pile to be continuously braced (Lb = 0)?

Another way of considering the situation might be to look at the deflection diagram. Should the braced length be based off the first or second point where the deflection crosses zero? Or similarly where the moment diagram crosses zero?


texts: making a leak proof thread for my keychain idea

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I have been designing a prototype for a keychain that sprays perfume. I have a metal keychain piece which has a female thread and the plastic sprayer screws right into it and has a male thread.

I want to get these manufacturers ASAP but I need to be ensured it wont leak. I think I will switch my straight thread to a tapered thread, will that help?

What can I do to ensure that it will not leak?

Thanks!!


texts: Complementary filter in MPU_6050 is giving me the wrong answer when the system is accelerating

texts:
So I am using a complementary filter to find the attitude in my quadcopter, doing the following
$$\text{angle} = 0.98\cdot (\text{angle}+\text{dt}\cdot \text{angle_rate})+0.02\cdot \text{accelerometer_angle}$$
Now the problem is that the angle is wrong when my system(quadcopter) is accelerating, do you know how to solve the problem, or it is normal not to get accurate values when accelerating even if one is using the complementary filter?


texts: Electrochemical protection for corrosion

texts: When we have a part that tends to corrode; Is it possible to apply an electrode on it to sense the excess or deficit of electrons on it that make it prone to corrosion and accordingly send a current that will drive that excess or deficit of electrons away? So that it will protect the part from corrosion?


texts: What material (preferably relatively inexpensive), can I use for absorber in a fresnel solar concentrator

texts:
I am thinking of building a prototype for a solar generator using a fresnel lens to concentrate sun rays to a relatively small area, for the purpose of harnessing the thermal energy.

The problem with this is that the temperature at the concentrated point, temperatures as high as 3000F are possible.

What (preferably inexpensive) material can be placed at the focal point of the lens, to transfer the heat away to do some useful work?


texts: Moment of inertia calculation at different axes

texts: I have moment of inertia at 2 different axes orientation. How to calculate the angle between the 2 axes?


texts: Is it possible to make commercial (or not) IC´s with FPGA?

texts:
I am working as TV repairer but some "IC jungles for TV's" are from China without almost information and often they are impossible to find.

My question is : Is it possible to do a IC jungle for TV, LCD, plasma, etc by aplying FPGA.

I know by microcontroller I can't do it because they are not so flexibles as FPGA's.

For example look this IC is from a TV and it's impossible to find out because is from China:

And this is the diagram:

Is it possible to do most IC's impossible to find (because they are from china mostly) by FPGA?


texts: What area should I use when calculating induced voltage?

texts:
I am trying to build a low power output generator with 12 pole pairs and 9 stator coils. The design will be similar to the one described in this link Basic Principles Of The Homebrew Axial Flux Alternator  , but at a different scale/size. I am trying to find some way of estimating the number of turns I will need in the coils to produce an output voltage of 6.5V. The generator should produce this voltage at 100rpm. I am getting very confused about how to use Faraday's law to do my calculations.

$\varepsilon = N\frac{d(BA)}{dt}$

Faraday's Law as explained in this example where the area used is that of the magnet, while Faraday Law of Electromagnetic Induction  states at the bottom that A is the area of the coil. Does this difference have to do with when the magnetic field is stationary while the coil is moving versus when the magnetic field is moving relative to a stationary coil? Also, should I be using $$\varepsilon = N\frac{d(BAcos(\theta))}{dt}$$ instead? Thanks very much in advance, and apologies if I am missing something very obvious here.


texts: In what order turbojet engine parameters are calculated?

texts:
As I see it, if you're going to calculate a twin-spool turbojet engine, you

Determine expected max aircraft speed, and engine thrust at that speed and when stationary.
Calculate peak mass of air flow
Calculate energy needed to propel this mass of air
Calculate bypass ratio
Calculate compressor properties

And from here I have no idea where to move on. Some books I've read just go through the engine from compressor to exhaust nozzle, but none explains which parameter of the engine is primary and where do calculations start and how they're performed.

Would you give me a clue?
Thank you!


texts: How can I make a motor powered hammer swing more naturally than a Leonardo cam?

texts:
Most people are probably familiar with Leonardo hammer cams. But I'd like to make a motor-powered hammer that swings more like this (apologies for the crude diagram):

The hammer would fall due to gravity, then get dragged along the ground on its way back up.

Of course, this diagram does not work, because the hammer on the way up needs to make a >= 90 degree angle with the wheel radius in order to fall (step 2), but needs to collapse to < 90 degrees in step 4 in order to drag along the ground.

Is this doable with simple, hardware store components?


texts: Ansys Workbench, defining ambient temperature correctly

texts:
this is probably a beginner's question. I have a simple solid material, lets say wood wall. I am performing transient-thermal analysis. On one side, I have elevated temperatures (after 30 minutes, I already have some 750 degrees Celsius). On this side of wall I defined convection and radiation. Film coefficient is constant, the ambient temperature I defined using a table with values. The same I did for the radiation (in this case I defined constant emissivity and used same temperature table as for convection).

On the other side I have only ambient temperature. So, the temperature at time 0 is 25 degrees Celsius and should go up over the time. This is defined under Initial temperature. I also specified convection and radiation of the wood on the other side, and here is the problem. I defined convection again (this time the film coefficient and temperature is constant, 25 degrees Celsius) and radiation as well (again, the temperature and emissivity are constant).

Since the elevated temperatures of the first side are getting pretty high over the time, it is logical to expect higher temperatures on the other side of wood wall (on its surface at least). However, when I got results, the temperature stays at 25 degrees Celsius whole time.

Is there a way to define just the initial ambient temperature on the "cold" side of wall? I do not want to limit the temperature on the cold side, on contrary, I want to see how high the temperature can get on that side.

Thanks.


texts: Settling of unevenly loaded storage tank

texts:
Suppose I have a concrete tank, round, vertical, diameter in the range 16m-24m. One half the floor is filled with gravel or concrete to a height of maybe 2 meters. When the tank is empty, that will mean I have about 5 tons per m² more weight on this half, when the tank is full (with water or a slurry that's mostly water) it's still 3 tons (assuming 2.5 t/m³ density which is exact enough for my ballpark). Most of the times (>90%) it will be full. The tank will be above ground, 8-10 m high.

I want to know if the tank will tilt during its lifetime, say 20 years. I'm not a civil engineer and I have no feeling for the numbers involved. My gut feeling is that my tank will tilt visibly in a matter of a few years and that my idea is not feasible as is. Can someone weigh in and comment on ...

Will I have tilt/uneven settling problems? At what magnitude over the tanks lifetime?
What's the easiest (=cheapest) remedy, leaving the tank interior alone?

Clarifying points: The tank is not yet built or even planned. It's just an idea I'm thinking about that calls for half filling the tank to create a sort of funnel. I wonder if this idea is worth pursuing, and uneven loading/settling is one issue want to consider. I'm not in the "call a structural engineer and let him calculate the static" phase, I'm in the tossing around harebrained ideas in my skull phase. I'm sure such a tank can be built to last for 20 or 200 years, but at what price?


texts: Negative gain in Ziegler-Nicholas Oscillation Method?

texts:
For a plant G(s), the transfer function is given by:
$$G(s) = \frac{(10s+50)}{s(s^2+20s+2500)}$$

Using Ziegler-Nicholas method to get the parameter: $k_p = \dfrac{-1000}{3}$ and $w =-28.868j$.

Is it correct? what should I do in case of negative $k_p$ and how do I calculate the PID parameters?


texts: Sort of a general question, but does there exist or might there exist a sort of thermal switching material? A material that could be switched from a thermal insulator (maybe more of a thermal insulator than air) to a thermal conductor by some means like through electricity, light or magnetism? Kind of like a thermal switch? It would be a useful material a device had to remain hot or cool off quickly, without using a fan.


texts: What Are The Procedures To Get a US Professional Engineer License?

texts:
I am a Civil Engineering professional having around 7 years of field experience and is now working for a govt. agency. All I want is to get a Professional Engineering (PE) License. But at present, I am living outside the USA and planning to be at USA on the next year.
I will arrive at the USA just 10 days before the exam and will leave the USA after 5 days sitting in the exam.

Questions:

Can a non-resident USA visa holder apply to attend in the PE Exam?
What precautions/preparations I need to take to pass the PE Exam on the first attempt?
I have read many articles on PE Exam. I have heard that https://bookscivil.com/pe-civil-reference-manual-16th-ed-michael-r-lindeburg-pe/ this book is necessary to pass Civil Engineering PE Exam. Is that true?


texts: Can the thickness of a guard post be derived purely from energy principles?

texts:
Consider an ordinary staircase with a banister rail supported by a wall at one end and a steel post of constant profile at the other end. The base of the post is embedded rigidly in the fabric of whatever structure the stairs are part of.  The post must not bend beyond a set (small) amount, permanently deform, or fail to support the guard rail, in the event that someone falls downstairs or against it, and the maximum deflection of the post in the event of a fall is in any case to be small compared to its length (rough indication: 0.5–4.0% or say ~5–40 mm vs ~1000 mm).

The rail and post, and any fixings, are each thick enough and well enough secured, that they will not shear or become loosened by any plausible impact of a person (or persons, including anything they carry) falling down the stairs and against them at any point.  Within these criteria, it's desired to make the post with a narrow profile, and therefore minimally thick.

From a pure engineering perspective (ignoring any building codes for now) is it sufficient to reason that any collision/impact will be elastic and therefore the minimum profile for the post can be derived by:

Estimating a maximum KE and PE for the falling persons,
Setting a maximum desired deflection of the post.
Reasoning on a pure energy basis that the post can be treated as a simple/ideal deflected cantilever beam, and its minimum profile is that which satisfies strain energy of the steel at maximum desired deflection >= maximum KE+PE of likely falling objects?

It seems to make sense and yet I am not too familiar with impulsive impact (more familiar with statics), and I'd like to check if there's a reason this would be an underestimate or must be treated with caution. (For example maybe a falling object would have CoG slightly higher than the actual rail height? Or other reasons might exist that this would lead to an insufficient result?)


texts: UAV 5-Channel Multispectral camera vs. modified RGB camera that resolves NIR

texts:
Looking into purchasing a drone. One has a dedicated 5-channel multispectral camera (Micasense RedEdge) the other has a modified Sony RGB camera that resolves the NIR spectrum. Can someone sum up the pros and cons of each of the above systems?
Can one filter spectral data taken with a modified camera ?

Here is the manufacturer's description of the modified camera:

We specifically modify our cameras internally and externally to ensure we have technically appropriate 3-band data for either

NIR vegetation mapping - To use NIR mapping effectively, one
processes the imagery via algorithms such as NDVI (Normalised
Difference Vegetation Index), which is a ratio of the NIR band and
other visible bands.
Natural colour mapping (RGB)
Underwater mapping - designed specifically for water penetration
and underwater bathymetric mapping

All with the SAME modified camera, but simply screwing the appropriate filter onto the lens (we supply the 3 special filters after the camera modification).

To me, it suggests that the "3 bands" are not collected simultaneously as one needs to change filters. Am I correct?


texts: Meaning of energy method in control theory

texts:
What qualifies a energy method in the context of control theory?

Citing from a paper to give the context in which this expression came to my attention:

One of the challenging problems of the double inverted pendulum is its swing-up from the downward position to the upright position. The swing-up of the double inverted pendulum can be performed by using an energy method and by separating the swing-up into three steps: first stabilizing the first pendulum in the upright position, then swinging-up the second pendulum while stabilizing the first, and finally stabilizing both pendulums in upright position [11]. However, this control method requires considerable time before both pendulums reach the upright position.

I know that in MPC their exist something like an energy cost function meaning that the terms in the cost function are the values with sign not the absolute values. Is the term related to that?


texts: Dependency between load capacity for reinforced concrete slab and thickness

texts:
How does the load capacity for a reinforced concrete slab depend on the thickness of the slab?

Example:

Let's suppose that we have the following constants:

concrete quality (including the maximum compression resistance)
same rebars (E.g.: mash of 4/100 mm)
the rebars are at 35 mm from the bottom of the slab
the load is constant in every point of the slab

Firstly let's suppose that the slab has a thickness of:

100 mm and supports a constant load (permanent: screed, ceramic tiles + temporary: objects, people) of 250 kg/m^2 (2.5 N/m^2).
150 mm
200 mm

How to determine the load capacity for points 2 and 3 based on point 1?

P.S.: The example is just to emphasize the idea. I'd like to have a more general solution.


texts: How big does hail need to be to damage auto body panels?

texts:
I am trying to determine under what conditions falling hail will dent automobile panels. For example, is it determined by the size of the hail, the speed of impact, force, energy, etc.?

I know there are many variables that must be taken into account to get to an answer, such as the material strength, angle of impact, thickness of material, alloy compound, age of car, etc. but surely with the global automobile market worth over $9 trillion there must be some useful rule or heuristic for designing these panels to resist hail damage.

I have read The Numerical Prediction of Panel Dent Resistance Incorporating Panel Forming Strains but it does not take hail as a main force into account. I am not an engineer so I don't know how to get a figure from this paper.


texts: Considerations for switching from Conc. Sulphuric acid to Oleum

texts:
First off - this project is still in the early planning stages. The basic scope is that a plant want's to switch from using conc. sulphuric acid (~98%) in its process (nitration) to oleum.

I questioned why they would do this and their reasoning is supply shortage of sulphuric acid causing downtimes. Apparently an alternative supplier is not possible and they want to use oleum to supplement their shortfalls.

I'm conducting a high-level review of this idea.
From my brief assessment it would seem that in most cases sulphuric acid and oleum are interchangeable, and, in cases where equipment is designed for compatibility with sulphuric acid it should also be compatible with oleum.

Some of the points that have I have flagged so far...

storage tanks -- material compatibility seems fine, but generation of fumes (SO3) may not be compatible with the scrubbing system

pumps/handling -- oleum (depending on concentration) can have significantly different viscosity and freezing points which in the local climate might cause issues.

nitration -- nitration reaction kinetics would likely be affected when switching to oleum...this would require labscale investigation and cannot be predicted accurately. The presence of dissolved SO3 might affect the reaction?

reconcentration -- there is currently a system in place designed to reconcentrate spent sulphuric acid (vacuum distillation), what changes would be required to re-concentrate oleum

It would be appreciated if anyone with experience could contribute other concerns or comment on the above.


texts:
I'm a little confused by the differences between LQR control and numerical optimal control (such as direct multiple shooting, direct collocation and pseudospectral optimal control). It seems that LQR uses linear system dynamics to minimize a quadratic cost function and can find a solution rapidly, so it's suitable for on-board control. Whereas numerical optimal control uses full non-linear system dynamics to minimize a cost function (not necessarily quadratic), but requires a fairly good initial guess to achieve convergence to the desired solution, and can take a relatively long time to find a solution, so it isn't generally suitable for on-board control.

Having had some experience implementing numerical optimal control algorithms, I'm hoping to try and implement an LQR controller in similar simulated problems to see how each differs. If, for example, we consider the problem of minimizing the fuel used when vertically landing the first-stage of a rocket back on Earth, using 3-DOF dynamics in a Cartesian coordinate system, we get the following output for the system's states, $s = (x,y,v_{x},v_{y},m)^{T}$, and controls, $u=(u_{x},u_{y})^{T}$, versus time (the weird jagged control inputs that occur for most of the control profiles are due to the rocket's engines being turned off (coasting) and so control input is arbitrary since it has no effect on the rocket's trajectory).

Our required final state is zero x- and y-velocity $(v_{x}(t_{f}),v_{y}(t_{f}))=(0,0)$, and, if we consider our landing site to be at the origin of our coordinate system, a final x- and y-position of $(x(t_{f}),y(t_{f})) = (0,0)$. As can be seen, given our initial conditions, numerical optimal control produces a trajectory made up of a series of "waypoints" every few seconds, giving the control profile required to achieve the desired final state (a two-point boundary value problem), and simultaneously tries to minimize the fuel used to achieve such a trajectory.

Now, does an LQR controller act in a similar way, where I only have to give it my system's initial conditions, and it'll work out the series of control input values to use in order to meet the desired final conditions whilst minimizing fuel use? It seems almost too good to be true! I feel like I'm missing something fundamental to my understanding of their differences.


texts: Were steam locomotive fitted with centrifugal governor?

texts:
Wikipedia states that steam engines were fitted with centrifugal governor to keep a rotational speed almost constant.
For steam locomotives, Wikipedia speaks about regulator but nothing about the automation of this regulator. I imagine this device is less needed in the case of a locomotive because of the greater moving mass. Nevertheless, automating the locomotive speed regulation might be useful. That way, there is less risk of over-speed in case of unexpected sliding (traction control?) or when the track goes downward.
Was there any steam locomotive fitted with a centrifugal governor or any other device whose purpose was to control steam flow based on locomotive speed without human intervention?


texts: Balancing flywheel and coupling shaft at home

texts:
I am rebuilding a mini soil compactor roller.

I replaced the old 8 hp Kubota diesel engine unit with a new Dongfeng unit. I want to weld the coupling shaft, which is built from 2" pipe with rubber damper at one end, to the hydraulic motor.

How can I ensure the shaft is balanced after we weld it to the flywheel? We would like to do this cheaply if possible.


texts: Maximum tensile and compressive stress in a T-beam

texts: Where does the T-beam come from? There's just a straight beam resting on two supports. And where do 10 and 80 come from? I am so confused.


texts: What power lasers can be used to heat fabrics to 70 degree Celsius?

texts:
For a project that I was building I wanted to heat fabrics to 70 degree Celsius using lasers.
Since fabric is a very wide term for now I was looking to draw heat patterns on 100% cotton T-shirt and the colour of the T-shirt is black.
The project is similar to many laser engraving projects (on wood and plastic) but the key differences are:

I do not want the fabrics to be cut, engraved or damaged by the laser.
I would want to heat the area under laser dot to 70 degree within minimum possible time.
The laser would go over the entire T-shirt but wherever heat is not needed it would remain off

Could anyone please suggest what power laser would be suitable for such heating project ?


texts: How can I confirm nL Volume Measurement for Pump and Sensor Calibration

texts:
I'm dispensing around 1uL of volume with 1% accuracy. Although I'm confident in my pump, I'd like to be able to routinely confirm that I'm getting the exact volume I'm requesting every time.

How can I reliably measure volume at this small scale? I've tried a precision scale, but the evaporation rate for the fluid is quick and I'm losing non-negligible volumes while waiting for the scale to settle.


texts:
I am reading B. P Lathi, Modern Analog and Digital Communication.
In it, there is a topic where the author says that maximum information rate is two pieces of information per second per hertz.

Now I am a little confused as according to the sampling theorem, we need a minimum frequency of 2B samples per second.

Why does then the author say that only a maximum of 2*(maximum frequency) independent pieces of information per second can be transmitted, error free, over a noiseless channel of bandwidth Bhz.


texts: How can I measure the thickness of a sedimentation layer in a closed tank?

texts:
Biogas slurry often contains sand and grit and organic matter that eventually sediments. Clearing thetank from sedimentation is expensive (plant downtime, additional equipment) and dangerous. So it would be interesting to know how much sediment there is.

Typical tank heights are around 8m, so I think opening a hatch in the roof and poking with a long stick is not an option. What are other ways to do this?

Liquid level gauging is done with a pressure sensor mounted in the lower part of the wall, or a radar sensor on the roof.


texts: How can I determine the code changes in an Atmel ASF update?

texts:
Atmel's ASF (Atmel Software Framework) is periodically updated by Atmel.  When an update is available, Atmel Studio notifies you and asks if you want to download the update.  If I install the update, this does not update any code in my existing projects.

I want to determine what code changes have been made in the new ASF compared to what I previously used in a project.  And ideally I'd like to be able to cherry-pick the changes that I want to incorporate (and exclude those I don't).

The only way I know to do this now is to create new project with the updated ASF (using the ASF Wizard to add all the drivers I used previously) and manually diff the files against my existing project.  Then manually copy/paste from the files I want to include.

I thought I heard that Atmel uses an internal git repository for their ASF.  Is there a way to get at this directly and view the changes?  Or is there a better way?

It would also be nice to view the changes before installing the ASF update.


texts: Finding the diameter of a material using tension stiffness and Young's Modulus

texts:
This question is similar to a question I am stuck on, but I have changed it to get an understanding how to works.

A spring is being made by pulling a 12cm long cylinder of material in tension with a desired stiffness of 6200kN/m.

It has a density of 2.9 g/cm^3, an ultimate tensile strength of 375 MPa and a Young's modulus of 70 GPa.

What should the diameter (in mm) be for the metal "spring"?

So, my question is how can I go about solving this question?

I have looked at the Young's Modulus and Hooke Law's formulas.  But keep getting stuck with material displacement.  Do I need to know the amount of length the object changes to work out this solution, or am I on the wrong track?

Can I assume: $\Delta L = 1$ if I used the following formula to find the $A_0$, which I can then calculate the diameter from:
$$
F = \frac{E A_0 \Delta L}{L_0}
$$

Any help will be most appreciated.


texts: Why do all high-speed trains run on electric track (as opposed to normal track with diesel-electric trains)?

texts:
AFAIK, all high speed trains (200+ kmh) run on electric track.

Why is this? Is there something about a diesel-electric engine that makes high-speed trains more difficult?

Here's some other data, and correct me if I'm wrong:

Electric track is high-maintenance. Using a pantograph to pick up power from overhead wires is also non-trivial at speeds of 200 or 300 kmh. The electric system is much more prone to failure in bad weather (storms, snow/ice, etc.).

I've often heard the claim that electrified rail is more energy-efficient than a diesel-electric. However, I've never seen numbers showing exactly how much more efficient it is compared to diesel-electric. Maybe someone knows a source on that.


texts: How can I convert volume as a function of time to mass or mole as a function of time for a dissolving drug particle?

texts:
I have been given a spherical drug particle that dissolves by surface erosion into the bloodstream. The rate of dissolution is proportional to the exposed surface area of the particle. I have to model the volume of the dissolving particle as a function of time, which I did, and I got

$$V(t) = \left(\dfrac{3V_0^{1/3} - kt}{3}\right)^3$$

where $V_0 = V(t=0)$, the initial volume of particle. When I plot using Excel with $V_0=100$, I get a reasonable downward sloping curve which reaches 0 in about 3 sec.

Now I have to derive the rate of drug release as a function of time (g/s or mol/s) from the volume function. There is no other information given. How do I do this? Please help!


texts: Damage differences in frontal collision of two vehicles and their speed

texts:
Please check this newspaper article and its pictures and the video in it: Article

It contains photos and a video of a frontal crash between two vehicles of a trolley line. From the photos, it seems like one vehicle suffered much more damage the the other. Judging by this photos, what can be said about the speed of the two vehicles? Can the difference in damage be attributed to much different speeds of the two vehicles?


texts: Are AC generators more efficient than DC generators?

texts:
I've been doing some research into AC and DC generators, and I was wondering if AC has any advantages in terms of efficiency.
Given that AC generators are usually brushless while DC generators generally have brushes, along with DC generators requiring several components to convert a pulsating direct current to a 'pure' one, it seems reasonable to me that AC generators are generally going to be the more efficient of the two.
But as always, I'm open to hearing the thoughts of others and ready to be proven wrong, so if anyone has any ideas to pitch in that would be great.


texts: Rust formation on Cold rolled carbon steel(SPC 270D)

texts: We are using Cold rolled Carbon steel(SPC 270)grade. We have observed rust formation due to exposure to air(8-12hrs). The rust analysis resulted 1.6% chlorine whereas allowable limin is <0.01%. Air ppm shows 4ppm for 24hrs. We would like to know the allowable chlorine ppm in air which will cause rust and reasons for it.


texts:
I'm using the Ansys ACT Api with C# to create an extension for Ansys (Mechanical).

When developing the extension I need to build a dll file from C# code (using Visual Studio). My problem is that every time I want to test my extension with a new build, I need to restart Ansys Workbench so that the dll of my extension can correctly be replaced.

This is rather time consuming, and I assume there must be a work around, but can't find anything in the documentation or online.


texts:
I've watched a few videos explaining how actuators work and it seems to me that a regular, non-blocking, actuator would freely move if not powered. But theory and practice are rarely the same thing.
I've never owned an actuator, and nobody on the entire internet have tried to push on an actuator that is not powered, hence this question.

To give a bit more clarity, I'll describe my application and what I want to use the actuator for. There's this door that I often forget to close. I want the door to close after some time, if open.

I don't need the actuator to ever open the door, just to close it, if open for more than, say 5 minutes. Edit: The closing mechanism has to be on the "pull to close" side of the door.
I want to be able to manually open and close the door, as that will still be the primary mode of operating the door.
The logic part will be done using an arduino and some sort of sensor that figures whether the door is open or not.

An actuator seems to fix my problem, but only if the shaft can freely move when not powered. So, can a cheap actuator like this be moved freely when not powered? If not, what would my options be?


texts: What type of bearing used in swivel arm?

texts:
To model a swivel arm on column that rotates by hand
What type of bearing should i use
Should it support radial and axial load or just supporting axial load is enough ?


texts: Realistic Value for the Rotational Inertia of a Gate

texts:
Don't worry guys i won't ask how to calculate the moment of inertia of the gate. I already have, but i have no experience in real life engineering, so i would be thankfull if any of you could review my result.

The Door wieghs about 90 kg Has a length of 3000 mm a height of 1115 mm and a width of 40 mm

I Calculated the Moment of Inertia on the hinges and the result was 227.5 kgm². I added a Picture so you can get an idea of how the gate looks like.


texts: is there any other ways to refine mesh size in particular place without making a partition?

texts:
I am currently making a corroded model in Abaqus, but not all locations are suffering from corrosion. As shown in the picture there are some parts (the blue parts) that do suffer from corrosion, so since the picture is only part of the overall bridge structure, I am wondering whether there exists many ways to make finer mesh size in corroded locations only without creating a partition?

Please comment if you know how to resolve this problem.

Thank You


texts: Does a spillway failure have different consequences versus dam failure?

texts:
I noticed this Tweet about the Oroville Dam concerns this week:

Seems most media is not emphasizing/noting the distinction.  Is there a difference in the consequences of a spillway failure?  Seems intuitively that the release of water might be slower due to what may well be a smaller gap.

But is that true?  And would unmitigated spillway failures generally add concern that additional stress/erosion can result in full dam failure shortly thereafter?


texts: Does it matter what direction a herringbone gear turns?

texts:
Obviously, the forces and pressures should mostly be the same, but just in reverse. But when play, flex, and such are accounted for, are there any subtle differences to having a herringbone gear turn in different directions?
Intuitively, I might suspect that it would be preferable to turn towards the centerline, so that the first point of contact on each tooth isn't near either edge.


texts: Is it possible to measure the concrete workability by a mobile app one day?

texts:
After studying all methods that can measure the concrete slump, I found 62 devices that service this purpose at the same time these devices are expensive and not practical enough, for this reason the mobile applications will be better than devices in this field.
From here I discussed a new idea for an app to measure the concrete slump without any physical efforts or wasting time by using some numerical methods,and to advance my research I need to see the different comments on this idea.
Please check this link to see the small draft.


texts: I have implemented a PI compensator for an integrator plant through floating point variables and everything works fine. The design intent is tracking filter and it does not track well the input signal. In simulation, everything works well. What could be the problem and what is the workaround?


texts: Design of fan pipe for propelling glitter

texts:
I am trying to create a prototype for a glitter shooting mechanism. It is worth mentioning that I have no experience with mechanical engineering or fluid dynamics. I think the below image describes the situation very well:

The fan is considerably wider than the diameter of the pipe so I just visually designed a connecting pipe from the fan to the PVC pipe. The goal is to have the fan blow glitter up through the longer section of pipe and out the top. The glitter will initially be stored in the bottom of the bend, not blocking the air passage completely.

Currently, the issue I see is that a lot of air is coming back out through the inlet shooting almost sideways out once it leaves the fan. I was considering adding a pipe section with the same dimensions as the fan to direct the flow into the inlet and prevent the air from squeezing out through the sides (i.e. forcing it against the air being sucked in). Would this work?

How can I maximize the ability of the fan to push glitter given access to more PVC pipe and a 3D printer?


texts: Steady-state tracking error has to equal zero, what values do I need?

texts:
A block is used to model instruments with limited capabilities to provide inputs to the plant. A seen below:

The output of the block  is related to the input  with the following input-output relationship:
$$u_a = \begin{cases}
-M & u < -M \\
u & u \in [-M, M] \\
M & u > M \\
\end{cases}$$
The control system can be seen below:

Given that $D(s)=15\dfrac{s+0.1}{s}$ and the transfer function of the plant is $G(s)=2(s+0.8)/(s+4)(s+36)$
How can I find the smallest value of  to guarantee that the steady-state tracking error is zero when the reference input is a step function with amplitude 8 ?
I have calculated the transfer loop equation $L(s)=\dfrac{30(s+0.1)(s+0.8)}{(s+4)(s+36)}$ but I am completely stuck.


texts: How does the shape of CPU/GPU fan blades affect their performance and loudness?

texts:
I need to replace the fan on my graphics card. The original fan is exactly like this one but there is another fan that seems to be a new revision of the same model number from the same manufacturer (NNTG vs. NNTM). The main difference seems to be the shape of the blades:

Neither I nor the DHGate seller can find any data about the fans (CFM, noise) so that's why I ask here.

To make up my mind I need an answer to both questions:

Which blade design is likely to cool the GPU the most?
Which one is likely to be the quietest?

The safe choice would be to get the exact same one (NNTG) but if the new design can be more efficient with the same noise, or as efficient but quieter, I'd prefer the new one.

Note that I don't want to buy an aftermarket fan (even if the prices are similar), I just want a replacement for the old one.

EDIT 2015-04-26 : Finally I bought both and, unlike what I said in the comments, I found a way to quickly switch the fan without taking out the whole heatsink assembly, allowing me to test both fans.

Despite the general consensus that NNTM was supposed to cool the GPU better, temperature with NNTG is actually 5°C cooler than with NNTM (after 10 minutes of running glxgears in full-screen). Maybe the motor doesn't match the power needed for the redesigned blades of NNTM, I don't know.

Anyway, if you need to replace a GA512SL fan for a RadeonHD like I did, buy the NNTG model :-)


texts: Determine shear flow direction in profile/beam section

texts:
I have been looking at the location of shear flow centers for profiles for my mechanics of materials course.

I am trying to figure out how to determine the direction of the shear flow in a given beam section with a shear force which is either directed up or down (aligned with y-axis). In my lectures it has been said that 'the shear flow in the web of the beam section must always follow the same direction as the shear force'.

I have found some examples where it appears this rule does not work though:

https://www.youtube.com/watch?v=zs_dEtwgxSM
Interpretation of shear flow/shear center of L-profile

In these 2 examples the shear flow direction in the web of the beam section is drawn in opposite direction of the shear force. I do not know why the aforementioned rule does not apply to these examples. Is this rule (shear flow direction in web must follow shear force direction) correct?

How do I determine the direction of shear flow for these 2 examples/in general?


texts:
I have a question about air conditioning and the probable modes of failure.

I recently installed a Nest thermostat in my home. I've noticed that it seems to prefer to have the air conditioner's compressor on for multiple short durations instead of one long period. This got me thinking...

1) This is going to kill the starter capacitor of the air conditioner more quickly than normal.

2) I wonder why they made the control system like this... It MAY extend the life of the compressor.

Here's my thought process:

The AC compressor is effectively a non-linear constant-Q source (i.e. you pump energy into it (by compressing the freon) at a rate (which is technically a function of the temperature differences involved) and it heats up until the energy coming in (from the compression) equals the energy going out (by the blower)).

If you were to run this continuously, the compressor itself would get really, really hot, always running at its maximum temperature (i.e. the crossover point between the efficiency-drop of the compressor at the high temperature vs the convection-cooling of the compressor). If you work it in smaller increments, you can keep the temperature down of the compressor.

The starter capacitor is an annoying $100 capacitor... but the compressor dying can effectively total the AC.

So: how much of the wear on the compressor is due to over-heating? Is this actually going to make an appreciable difference, or is Nest just unnecessarily eating my starter capacitor?


texts: Determining damped frequency and damping ratio from time domain data

texts:
I have some time domain data which are responses of an aircraft to various inputs (example: time vs. bank angle for lateral stick pulse input). I need to compute the effective damping ratio and damped frequency of these "signals".

I considered several options but none worked as well as I hoped.

Computing instantaneous frequency and damping ratio using Hilbert transform: This does not give single frequency and damping values. Also, I get negative values sometimes.
Finding approximate second order system and using its parameters: Works for some test cases but I have test cases where the signal can not be represented well with second order system.
Simply detecting the peaks (minima/maxima) in the signal and using them: In some test cases I don't have oscillations, i.e. no peaks. Besides I am not sure how to use the peaks to compute the damping ratio.

Is there any robust method to do this type of analysis?


texts:
I understand bevel gears are used in situations were a 90 degree change is required, but I can't visually understand why. Why can't we just use standard spur gears at 90 degrees, what do we actually benefit from using a bevel?

Essentially I'm asking how the engagement between gear teeth react if we just used spur gears for a 90 degree change, rather than bevel gears.


texts: I am designing a lifting device for practical use which is powered by a dc motor with worm gear. The lifting device should be able to hold the load in place at a certain height.however, i read that wormgears are self locking only in situations where shock and vibration are not present, in other words, if the lifting device is not perturbed in any way, the self-locking feature will probably perform as intended. This could present a problem for security reasons and functionality if the lifting device is intended for use in varied conditions. My question is, should I consider others options, like different types of gears or persist with the worm gear


texts:
It's known that the positive displacement pumps are self-priming, however can I operate the pump without water in its casing?

I know that I can use the positive displacement pumps as a priming pump for the centrifugal pump, however will I need to fill its casing with water before the priming process?


texts: How was it possible to beat a soldier with a full plate armor?

texts:
From my point of view, it seems that a soldier armed with a full metal plate armor was almost invulnerable at the time their opponents yielded swords, spears or bows. I understand that it couldn't be the case, but I'm not sure about the physics behind it.

More specifically:

How could an archer beat this soldier? An arrow shooted with full power would have enough kinetic energy to penetrate it?
How could a swordsman or a spearman beat this soldier? Would the impact of these weapons suffice?
Just out of curiosity, a modern gun would penetrate into the plates that easily? One headshot would do?

I'm thinking on a soldier wearing an armor like this one below, or even  bulkier.

[1]

[1] Courtesy of Wikipedia


texts:
I am working on analyzing a few problems, but have not really come across this type of stress concentration problem. Does anyone know where I can study the analysis of this situation?

Pressing ball through hole with smaller diameter with some force F

Another problem involves modelling a structure like so, and attempting to find the shear experienced at the connection E:

Bodies 1, 2 and 3 connected (maybe bolts) at lines B and E, if force F_ab acts on body 3, what shear force experienced at connection E? Is it simply summation of forces? Would the geometry changes not matter?

Any guidance would be much appreciated!


texts: What causes the hiss from one audio source but not another over long cable?

texts:
I have pulled some CAT6 through the ceiling from one room to a nearby cupboard, for line level audio signal.

See wiring:

I haven't used a balun or DI box, and there isn't TOO much hum and hiss, it's manageable.

But something strange is happening with the audio from Alexa, it sounds really bad: a lot of hiss and distortion. When you turn the volume down, the signal to noise is so bad that the hiss is really high, also the distortion doesn't really disappear it just gets quieter.

When I unplug the Alexa and swap it out for audio from my phone, it sounds really clean. So you'd think it's a problem with the Alexa. But...

I tried another Alexa and the same problem happens.
I turned the Alexa up (and mixer input down) and vice versa, this didn't help
So then I plugged the Alexa directly into the amp and it sounds really good
I plugged the Alexa back and tried it in a battery pack, rather than into the USB power supply, and the problem is still there.

What is the reason for this?

Should I be using baluns, or a DI box or something like that?

I've heard it's fine sending line level signals over CAT6 - indeed with the phone plugged in, it's all good.


texts: Material to absorb very low frequency radio

texts:
Is there any material that will absorb very low frequency radio light? I know that stealth aircraft use radar absorbant materials in their design that absorb radio light best at certain frequencies, but I cannot find any information on materials that are explicitly stated to absorb very low frequency radio light.

I am not looking for any aspect of geometry such as faraday cages - only materials.


texts: Why not use fire-retardant plastics everywhere?

texts: Some plastics will sustain a flame. Others won't. Not spreading a fire is obviously preferable in almost every circumstance. What advantages do combustible plastics have over non-combustible plastics, and in what circumstances?


texts: What is the difference between fault tolerance and robustness of a system?

texts:
I am trying to understand the difference in the definition of "fault tolerance" and "robustness" when it comes to system design.
For instance, what would be the main design considerations or what would be the definition of the terms when looking at engineering problems?  In particular, how do those terms apply to mechanical or electrical power engineering?
I found some definitions but they were centered on computational engineering. The document didn't give much insight in how to define those terms in other engineering disciplines.

Robustness: The capability to cope with unknown errors during execution and provide the system services all the same.
Fault-tolerance: The capability to tolerate a certain set of errors defined during the development of a system.

Source
What would be the difference between a fault tolerant and robust design?
Can a hard distinction be made?
Which techniques or design principles are applied to ensure a fault tolerant design, and which are applied to ensure a robust design?


texts: Is static determinacy regardless of the number of reactions?

texts:
source
I assume those supports in the first figure are pins so there are 4 reactions in total.
And as shown in the second figure, there are 3 reactions in total.
I thought for a structure in plane to be statically determinate, it must have only 3 reactions, but these are quite contradictory to me.


texts: Do we need to check punching shear when a drop beam is connecting columns?

texts:
If we have a series of columns as shown in the picture below and to reduce deflection of the slab between two columns that are 11.7 m apart we placed a drop beam 30 x 100 cm (the slab is 35 cm thick) do we need to check the punching shear for these two columns ? and if we need to check the punching shear do we use the beam thickness (100 cm) or we use the slab thickness (35 cm)

I am asking this particular question because in SAFE for columns C5 through C12 does calculate the punching shear


texts:
What would be the typical efficiency of a large industrial single-stage squirrel-cage air blower?

For example how many kilograms of ambient air (STP) would be moved per second by such blower which needs 20kW of electric power to turn its impeller (assuming 90% electric motor efficiency, make that 18kW of mechanical power at the impeller).


texts: How much energy do all the world's emails use?

texts:
I have heard high level statistics and headlines around

blockchain uses more energy than the Netherlands

I am interested to compare this quantitatively to other utilities, for example email and social media.
How much energy does all the world's emails use?
Another way to think of this: how much energy would be saved if everyone immediately stopped sending emails, and they didn't use any substitute for emails?


texts: Manual transmission: Why downshifting is less smooth than shifting up?

texts: Today while driving I had to make a quick shift to a lower gear that was not as smooth as it should've been. I've been taught that while shifting to a lower gear you have to be more careful when releasing the clutch than while shifting a gear up. Why is this? I understand the basic mechanism of transmission and clutch. When shifting up, the car can "bump" slightly if the rotational speeds of the engine and wheels are far apart. But why does this effect seem more noticeable when shifting down?


texts: Calculating Minimum Pipe Pressure Requirement for an Irrigation System

texts: I am setting up an irrigation system for my ranch and I have a hard time calculating the minimum pipe pressure requirements to reduce cost. I need to know the maximum pressure the pipe has to cope with. The pipe would transfer water from a high elevated pond (with enough water to feed the line constantly) to a barn down below. There is a 166 meter height difference between the inlet and outlet. I can easily calculate the upper bound pressure as 16.6 bars, however as I get it, the friction loss plays an important role too. The pipe's length is 1200 meters and made of polyethylene (Absolute roughness of 0.007). We need to open and close the faucet on the exit pint on demand (important) so the water head may reach the full height of 166 meters when the outlet is closed. The question is: do I have to order the 16.6 bar pipe or a lower grade pipe would do?


texts: How much noise does a road noise barrier block?

texts:
I am from The Netherlands, where noise barriers like these are commonly built along motorways:

Now I live in England, where such structures are almost non-existent.  In The Netherlands, living 200 metre from a motorway, I experienced far less noise than I do in England, living roughly 1.5 km from a motorway.

How much noise does a motorway noise barrier typically block?  I realise the answer will depend on a lot of factors, probably primarily noise barrier design and distance from motorway, and likely others.  The extreme case would be to completely bury the motorway, which should reduce noise to essentially zero.  Ideally, I would like to have a map like the England noiseviewer where the user can toggle on or off a basic, intermediate, or advanced noise barrier and observe how noise at particular distances gets reduced, although I expect such a map does probably not exist.


texts: Visibility/Height Requirements for Plumbing Air-Gaps (Commercial Building)

texts:
Are there any visibility/height requirements with regards to plumbing air-gap design/installation?

We're looking at using an air gap device to allow HVAC condensate drip to enter a buildings drainage system.  I've seen this before on residential applications where the washing machine drain and HVAC condensate drip are combined into a single box using a product such as:

http://www.siouxchief.com/products/supply/access/laundry-boxes/oxbox-washing-machine-outlet-box?template=P3Technical

or

https://www.ferguson.com/product/lancaster-pump-34-x-1-12-in-fip-x-mip-multipurpose-air-gap-lg175/_/R-4376003?skuId=4376003

or

https://www.freshwatersystems.com/p-328-mr-drain-air-gap-md-10a-15-or-2-standpipes.aspx

Customer is requesting that air-gap boxes be located below counter level with cutouts in the back of the installed cabinets.  Condensate from units on second floor too low for air gap to be installed in second flow.

Here's the concern behind my question.  What happens if there is a system backup due to a clog and my air-gap is the lowest point?  Obviously it would result in an overflow.  If the air-gap is visible this would result in simple cleanup.  If the air-gap is hidden behind cabinets or in a wall then the overflow would go unnoticed for a period of time and result in a much larger (expensive) cleanup.

Seems like there should be code requirements that prevent hidden air-gaps or require them to be located above a nearby sink or other drain that is visible so that an overflow is "contained" in a visible area.

Thanks.


texts: Can a speedbump safeguard a pipeline located below?

texts:
Recently I noticed a concrete speed bumper created near my parking. On enquiring the purpose, the committee who took the decision told me that the purpose of the bumper is to safeguard an existing pipeline below the bumper from heavy vehicles. Some significant points:

Existing road in the complex is made up of concrete and is plain. The road has not suffered any damage from any heavy vehicle in past.
The pipe is made up of polypropylene or some similar material. The diameter of pipe is about 6 inch. It is there to direct the water collected from roofs to rainwater harvesting reservoir.
Speed bumper is solid and made up of concrete.
Heavy vehicle here is a water tanker truck with capacity in multiples of kilolitres (Usually 5KL) filled to the top with water.

Question Is it necessary to raise such a speed bump to prevent any harm to pipeline below concrete plain road? Is it helpful, has no effect or worse in avoiding impact on the pipeline below?


texts: basic physics: does pulling on a hook place greater stress on it than passively hanging from it?

texts:
Sorry for such a basic question, but it is a safety concern that brings me here:

We have a hook installed on the ceiling. From it a rope chair (examples) hangs.

Assuming good form and no wild swinging, will doing pull-ups on this hook place a greater stress on it than me sitting on the rope chair?


texts: Does it matter the type of motor used ? Couldn't the wiring be changed to achieve high starting torque?

texts:
A series DC motor has a high starting torque thanks to its field wiring consisting of thicker wires and fewer turns resulting in high starting torque. And a shunt DC motor do not have a high starting torque because of a field winding consisting of thinner wires and more turns.

But why couldn't wiring be made a choice depending on the use so that it does not matter which motor is being used ?


texts: How would a person be able to rebuild modern machining?

texts: In a post apocalyptic setting, rebuilding humanity's technologies would be a pretty prevalent idea. I am in the process of becoming a mechanical engineer. Something that I have noticed is most classes don't teach how to make persion tools from scratch. How would someone, given unlimited raw resources but no references(rulers,tools,ext) be able to build something like a persicion lathe or a vernier scale?


texts: How would I put a barcode of other scannable code on a coffee cup?

texts:
I am interested in mass producing a reusable coffee cup (à la KeepCup) with a scannable id on it.

Cup will be plastic or glass, ideally glass.

ID code will need to survive being washed regularly.

I was thinking it could be put on by whatever method is used to put beer names on pint glasses, but I really have no idea how any of this is done. Onte thing I was wondering about was if I need to print in two colours (black and white for example) or if frosting some lines on it would work.

The reason I am interested in any of this is I want to assess the feasibility of giving out takeaway coffee cups which can then be returned to a 'cup bin'. The barcodes are needed to identify which cups have been returned.

And the codes have to be unique for each glass.


texts:
I'm trying to think of limitations or disadvantages of LTI systems in control theory, however, I can't think of many. The only one I can think of is that not every system is an LTI system.
Linear time-invariant systems (LTI systems) are a class of systems used in signals and systems that are both linear and time-invariant. Linear systems are systems whose outputs for a linear combination of inputs are the same as a linear combination of individual responses to those inputs. Time-invariant systems are systems where the output does not depend on when an input was applied. These properties make LTI systems easy to represent and understand graphically.


texts: How standardized are step pulleys/gear speeds on machines tools?

texts:
Edit/Note: This is NOT "the X/Y problem". The question I have asked here is exactly the question I need an answer to.
I'm not asking how to selected the correct RPM for a given situation (that's irrelevant to the current problem, and besides I already know how to do that), but rather asking about what RPM settings are available on machine and how standardized those settings are from model to model.

I have a project I'm working on where one of the parameters is spindle speeds on manual machine tools that that only run at discreet speeds. For example gear head lathes or Bridgeport clones with step pulleys. Part of the project would work much better if the numbers I pick, happen to exactly match what's offered by the machine tools other people are using. Is this even remotely possible? Are there a few standard sets of speeds offered or does each machine more or less end up with a different selection?
As a starting point; I have a Bridgeport clone that lists it speeds of: 80, 135, 210, 325, 660 1115, 1750 and 2720rpm. I'm also finding a number of images online that list the same numbers, so that seems to be at least one standard.
Are there other common sets of speeds for other kinds of mills? What about for geared head lathes? Etc?


texts: Why does filter efficiency decrease with thickness?

texts:
I understand that the most important parameters for a filter are basically pressure drop and thickness, both of which affect efficiency. However why does thickness cause a change in efficiency?

I'm particularly interested in the use of nanofibers as filters, and why decreased diameter increases efficiency.


texts: I am looking for some basic mechanical parts to build structures(prototypes)?

texts:
I am looking for something like this to make my robot ideas as prototype. But I don't know it's name! Also if there are better options I will happy to know.

(source: instructables.com)


texts: Efficient processing waste water with pigments and dyes to reduce cost

texts: Although ink waste (mixed colors of different inks for printing) is 90% water, separating the inks appears to be problematic. We have tried membranes, RO, electrolysis, boiling, and solidifying with kitty litter. Membranes do not trap the dyes, electrolysis is slow and expensive, boiling is expensive and messy, and litter makes too much waste. I would like to separate out the water and decimate (reduce by 90%) the waste. Any other process ideas? I have worked on precipitating the ink but I am not much of a chemist and there are all kinds of different components.


texts: Structural Analyses of Trusses, method of joints

texts:
Symmetrical truss is given:

I have issue with the sign convention for joint H.

See below the solution for joint I. As you can see, when calculating equilibrium in y (vertical) direction, forces that act upwards are written with "+" sign, and forces acting downwards with "-" negative sign.

Yet for joint H below, forces acting downwards are written as positive, which is why $F_{HJ}$ turns out to be a negative force (compression force). But it's not consistent with the solution for previous joint.

How would you go about finding force in member HJ?


texts:
There are many Lithium Ion and Lithium Polymer rechargeable battery related accidents. Are some of these accidents are battery design related? Are some of them misuse of rechargeable batteries.

What is the chemical composition of Lithium Ion and Lithium Polymer battery?
Why do rechargeable Lithium Ion  & Lithium Polymer batteries explode or catch fire?
Why cannot the rechargeable battery explosions and catching fire be prevented?

References:

What causes laptop batteries to overheat?
Complete Guide to Lithium Polymer Batteries and LiPo Failure Reports
Why lithium batteries keep catching fire
Why lithium-ion smartphone batteries keep exploding


texts: How does a two dimensional elevator work?

texts:
If you watch this video, you can get a sense of how an elevator can operate in two dimensions. But, what I can't figure out is how it is driven.

If you consider a conventional elevator, there is a car and a counterweight connected by steel rope. The motor only has to oppose or resist the difference in weight between them (at most half the load, because it can be counterweighted to the car plus half its rated load). This limits the work the motor has to do when lifting the imbalance, and limits the energy it has to remove when lowering an imbalance. Also, the work is done by fixed equipment (typically at the top of the shaft) which doesn't contribute to the weight of the car.

But in the two-dimensional ropeless system, there is no counterwieght, the motor is part of the car (and adds to its weight), so has to drive all that weight going up, and get rid of all that energy going down. It also has to do it without risk of runaway/freefall. And, it shouldn't just burn off all that energy as heat (terribly inefficient). So my question is, how is it done?


texts: What are grads used for on a scientific calculator?

texts: Every scientific calculator I've come across has a DRG button that controls whether trigonometric functions use units of degrees, radians or grads yet I've never seen or heard of any system that actually uses grads. When is the grads setting useful?


texts: How to calculate the power/torque/force needed to move a 4 wheeled vehicle?

texts:
I am trying to build a "mule": it s basically a go kart chassis with a 12v dc motor (I figured it would be easier to use). Now I need to determine how powerful should the motor be...

It is going to have 4 small wheels (15 cm in diameter - maximum), and be rear wheel driven, and it's going to do some soft kind of off roading (backyard terrain)
It is going to carry up to 150 kg at low speeds (5km/h max). Should I use a torque converter? I was thinking of using 2 cordless drills to do the job...

Do I need torque or power in this case? I'm thinking I'd need plenty of torque as it is a pretty heavy load and the project requires low speeds...

How can I determine the needed power / torque for future projects? Is there a formula (considering air friction 0).


texts: Can the pitch circle of a gear be farther out than the intersection point of the involutes on opposite sides of a tooth?

texts: I'm trying to make an involute spur gear generator but can't seem to get it right. I know that the diameter of the base circle of the involutes is equal to the pitch diameter * cos(pressure angle). But this means that as I increase the number of teeth and the pitch circle gets larger, its scale relative the base circle also increases. And at a certain point, the pitch circle passes the the intersection point of the two involute curves that will make up the sides of a tooth! (My tooth sides are made of an involute in standard position, and one that is mirrored and rotated by an appropriate angle)


texts: What should be the relation between flange length and web thickness for an optimum I - beam?

texts: While learning about I-beams I became curious to know if there is any relation between the flange length and web thickness of I-beams or if its arbitrary.


texts: In the Apollo 13 mission, how could the batteries have "no Volts" with two Amps of current?

texts: In the movie Apollo 13 there's a scene when the LEM is losing power; when they switch the module on, one of the astronauts reads the levels and says that one battery has no Volts but 2 Amps. What did he mean?


texts:
If you carefully look at LED in flashlights, they are blinking at fast rate despite the batteries are DC. It's even more obvious on flashlights with separate R,G,B LED (to allow the control of color) when you move it fast.
Why is it so ?

( It's also the case for "power on" indicators in many devices, but here it could just be a low quality DC low voltage from AC 220V. )


texts: Hinge joint for flat panels that can also flex horizontally?

texts:
I have to design a science display board consisting of 20 panels 2m x 2m high and wide, which can fold up as a giant pamphlet.

The difficulty is how to load and unload them from a lorry in less than an hour. The display boards fold out of the back of a lorry and down a ramp where they have to go oblique to one another.

Do you know a strong, simple, stable hinge which is fast to unfold from a lorry, which doesn't make the panels fall over?


texts: How to identify low quality electronic components early?

texts:
Our component sourcing organization purchases large amount of electronic components from suppliers. I believe this is through a bid process. Engineering provides the sourcing organization specification, and they purchase these parts for the plant to use in manufacturing. The issue is that recently the plant has been receiving a increasing amount of capacitors which might be defective. This is causing our products to fail. I have checked the few new incoming capacitors using fluke multimeter, and the measurements are with in specification.

It is not practical to continuously inspect these capacitors, and I have been tasked to recommend the solution. How does one technically address similar issues?


texts: Can a plate under bending be designed using its plastic section modulus?

texts:
I am designing an end plate connection. My lecture notes show its bending capacity is calculated using elastic section modulus. For class 1 I-beams, we can use its plastic section modulus. I wonder whether plates could be designed this way since it's capacity would be 50% higher.

For info, I'm using Eurocode.


texts: Tightest bend radius of circular acrylic rod light pipe for total internal reflection

texts:
I want to channel light from an LED indicator through some clear, circular acrylic rod. I want a rough-ish idea of the smallest bend radius through which the acrylic can be bent and maintain TIR. I will be experimenting, and would like an equation to guide the design.

The surrounding medium will be air. I don't know if there are different acrylic grades that need to be factored in, hopefully not because retailers don't seem to give further information.

The wavelength will vary, but only visible light is of interest. So I'd like an equation to give minimum bend radius, given a particular wavelength and rod diameter.


texts: Why do single speed RC cars use a gearbox?

texts:
Being a mechanical engineering novice (I stick closer to solid state electronics), when I look inside of any toy-grade RC car, I see a series of different-sized gears between the motor shaft and the drive axle.

Why does a single-speed RC car require a gearbox?
Instead, why can't a gear on the motor shaft connect to a gear on the axle?

So far, two of the plausible explanations I have come up with are that

The motor turns at a different RPM than desired by the axle, thus
conversion is required.
To put protection between the spinning of the axle and the
spinning of the motor.

I ask because I am setting out to make my own Lego car driven by a DC brush motor and have no idea what to do for a single speed gearbox other than hook one gear to the motor shaft and one gear to the axle and let it go.


texts: Is a permanent platform that is hanging and moving a dead load or a live load?

texts:
If a permanent room or platform is suspended from a larger structure (say, on a cable that is attached to a hook on a track in a ceiling) and designed to be in constant but not necessarily repetitive motion, does the load that the room/platform places on the larger structure count as a dead load or a live load?

On the one hand, it is permanent and won't ever be removed (like a dead load,) but on the other hand, it moves (like a live load.) I'm not talking about the loads that would be incurred by its motion, only by its weight.


texts: How to produce aluminium powder by E. J. Hall method

texts:
I have watched videos on YouTube producing Aluminum powder by mechanical methods. Like this one. It uses Aluminum foil and coffee grinder:

There are similar videos which use the same basic method but with some sort of ball mill:

Is there any reference to produce Aluminum powder by any metallurgic (non-mechanical) method like Everett Joel Hall method?


texts: What do we call these "transport frames made of wood" (обрешетки in Russian)

texts:
I'm translating a document in which there is a mention of обрешетки used for preparing goods (medical equipment of large size) for shipment. This term derives from reshetka (решетка) - lattice, and means "custom-made frame of wooden planks built around a load destined for shipping". It's kind of a rough crate built around the product intended for shipping, not pre-made.

I wonder what the proper term in English might be. Multitran provides a long list of options, but without describing them much, so it's hard to distinguish.

There's a whole National Standard document in Russian that describes how these "frames" must be built, with many pictures. However, it provides the wrong translation there in English: "roof boarding" (because the same Russian term is also used for roof lattice).

I'm submitting my translation in an hour, so I'll stick with descriptive "wooden frames" but I'd be glad to learn the formal term if it exists.


texts: Do scaled models reflect strength characteristics of full size

texts:
Lets say you want to build a bridge out of carbon fiber. This has never been never been done before, and it's super expensive stuff. So your goal is to use as little material as possible, but obviously your bridge still needs to have enough strength.

To start you look up how strong is carbon fiber, and the online data sheets tell you that a 10 oz cloth has a tensile strength of 800KSI.

After running the math this sounds perfect and should give your bridge enough strength for it's uses.

However, before you start a super expensive project that's never been done, based on nothing more than datasheets you found online and equations that might not fully apply to your material you run a sanity check.

Before you start building your full sized bridge, you build a small one that's 1/10th the size.

Assuming this small bridge is exactly the same as the large one, just using 1oz fiber instead of 10 oz fiber would your small bridge endure 1/10th the load of the full sized one?

I don't mean to apply this question to carbon fiber alone. With anything in engineering if you scale up a model perfectly using the same materials would the strength scale up proportionally, or is there some kind of real life nuance that blows all this mathematical beauty out of the water?


texts: Is this refrigeration cycle thermodynamically possible?

texts:
This is a screenshot of a lab where we were experimenting Vapor-Compression Refrig. Systems.

I am trying to understand what is happening between points 1-2 because I thought that because of max isothermal efficiency the gradient of the line shouldn't be more than the constant entropy line between the two points.

Also I am not sure how to explain the dip between points 5-1.


texts: Water distribution through N x Needle orifices

texts:
Consider a water distribution setup consisting of a feeder line blocked at one end but having 100 needle outlets all the same size. The feeder line cross sectional area is much greater than a needle cross sectional area so the flow from any needle is very close to one hundredth the overall flow into the feeder line. I think the feeder line would act like a massive reservoir which is being topped up at the entry point. Lets say that the flow into the feeder line is 1L/sec. Then the flow out through any needle is 10mL/sec. Assume that the system is in steady state with all needles happily delivering their 10mL/sec.

Scenario A

At the entry point of the feeder line we introduce 100mL of red dyed water. Assume that this does not affect the water characteristics other than it's now red. How is this red water distributed through the needles? Intuitively, I'm thinking that the first needles (the lower numbered ones) will get more of the red water than the later needles. But is this true? Does anyone have any mathematics that could describe this? I briefly considered that it was like an impulse function; but this would only be so if the steady state of the system changed. It doesn't. It's still water with the same characteristics, just red. It's like being able to tag electric current with a colour - it's still electric current...

Scenario B

At the entry point to the feeder line we install a water switch. The water can be switched to either blue water or red water. If we have the switch set to BLUE and we have all needles delivering their 10mL/sec of blue water and then switch to RED. How long does it take the system to be delivering 10mL/sec of red water from all of the nozzles? Assume that the switching action has no effect on the system itself other than changing the colour of the water. I'm hoping to find some sort of mathematics to describe this.

Otherwise I might have to build the thing and see what happens!


texts:
In these units: cm³.20μ/m².24hr.atm - (definition) cubic centimeters for a 20 micron film thickness per square meter per 24 hours under a pressure difference of 1 atm.

My question is what does the "Pressure difference of 1 atm" mean?


texts: What voltage are these hydraulic valves and how to I control them?

texts:
I am building a new control system for an injection moulding machine, the last part I am trying to work out is the main pump.
It has two proportional valves on the output, one labelled throttle valve and one labelled pressure limiting valve.
The throttle valve is connected between the pump outlet and the pressure limiting valve is connected between the pump control line and the tank return.
I think that you use the throttle valve to control the pump pressure and use the pressure valve to control the bypass pressure which is just like an energy saving thing. Is this the correct way of thinking?
The main question is though was voltage is do I use to control the valves and what is the pinout for the 3 pin feedback connector on the end on each valve?
Pictures of the pump and valves:


texts: How to sample Mean-Time-To Failure values from a Weibull Distribution with shape 1.5?

texts:
I have a mean time to failure (MTTF) recorded from 100 systems which is 6.5 years. The shape parameter of my component is given with k = 1.3 (based on a list the from literature).

Now I want to sample (generate) further failure times based on a Weibull distribution. Can I use 6.5 years (=MTTF) as a scale parameter?

I would like to do this in python code, if anybody knows a solution for this.


texts: What are alternative to installing LTE / Cell Tower to address capacity issue?

texts:
One of the cellular vendors wants to install a 180 foot monopole antenna in our neighborhood.  They claim that there is significant growth in LTE consumers. So in order to better serve the customers they need to install a new monopole. Following are two reasons that they provided recently.

The current towers are over capacity thus cannot reliably serve the
consumers
The cellular signal is weak therefore consumers cannot make phone calls

Question: What are the alternate ways to solve this problem beside installing a new monopole?  Are there new  LTE/Cellular technology that can help reduce cell tower capacity as well as permit the consumer to make phone calls reliably using cells phones?  What are any future technology that might address this issue?


texts: Ethernet extender kit claims to send data through power cables - Is this correct?

texts:
I own an ethernet extender kit which has two devices connected to mains. Its data sheet claims that the device "your homes electrical wiring to extend your broadband network anywhere in the house". An informative youtube video also suggests that the data is transferred from your mains.
The little I know about 3 pin power sockets makes me think that this is impossible. I strongly suspect that both devices have receivers and transmitters within them that transmit the data. Is there any way I can prove/disprove this?


texts: mass-friction-spring system with closed loop

texts:
My professor told us that it is possible to see the friction in a mass-friction-spring as the contribution of a closed loop control system. He wrote the following formulas:
Transfer function:
$$G(S)=\frac s {s^2+\frac k M}$$
gain:
$$\rho=h/M$$
where k=spring constant, h=friction constant, M=mass
Can you recognize these formulas and give me some indication about this method?
I think it would be useful to understand what is the meaning of the transfer function is this case?


texts: Alternative to heater cartridge for 10mm deep hole?

texts:
In a design for a heated block I am working on I only have the space for a 6mm X 10mm hole for my heating element to be inserted into.

Originally I had planned to use a 40W heater cartridge but the smallest I can find is 6mm x 20mm and the extra 10mm that would stick out the block would be inconvenient as I want to insulate the area around this from the heat.

Is there a good alternative to a heater cartridge that would fit my specs?


texts: Temperature vs Material Properties - ABS

texts:
I'm working on a design that uses fairly large plastic components (ABS, ~400mm longest dimensions). I'm looking at adding a steel component that encapsulates this plastic part. And, the steel part needs to be tight against the ABS part.

Because of the thermal properties of ABS, the plastic part will change size fairly drastically relative to the Steel part. Since the steel part needs to tightly encapsulate the ABS part, I've been considering cooling the ABS part to around -10 to -20 Celsius before attaching the steel which would be at around +20 Celsius.

My question is, with ABS cooled to that temperature would riveting the steel part to it still be an option, or should I expect fracturing from the rivet? I've tried looking into the hardness, brittleness, and Younges modulus of ABS as a function of temperature but I can't find any good data.

Rivet would be a 7/32 sized rivet through a 3mm thick piece of ABS.

Any help would be greatly appreciated.


texts: How do I extrude a region in autodesk inventor?

texts:
I'm a beginner at autodesk inventor.
For some instances when I click a region to extrude it doesn't come alone.

The screenshot below illustrates something even stranger.

What should I do to make this not to happen?


texts: Design a beam that is straightened with force on one end

texts:
From here, I read that if you have a straight beam, bend it with force at one end, and then create a beam with the resulting curvature, the equal and opposite force won't make a straight beam.

What is the shape of a curved beam that will become straight given a point force on the end?

Assume the cross section is rectangular.

Either a closed solution or a way to approximate the shape will do.

Edit:

I'm trying to design a spring for a 3d printer.  For technical reasons, printing a 3d helix is difficult.  A design that has a constant cross section in one axis is best.

One design that I've seen is an zigzag-shaped spring.  It seemed to be, however, that the stress isn't evenly distributed, with more strain on the corners and less on the straight parts.

My thought was to make an eye-shape with pointed corners that compresses to two flat lines.  My intuition is that, if the shape compresses to a flat line then it's spreading the tensile forces evenly and won't break at a weak point.

From the link above, I read that I can't assume a constant $I$ in the Euler-Bernouli beam equation:

$${\frac {\mathrm {d} ^{2}}{\mathrm {d} x^{2}}}\left(EI{\frac {\mathrm {d} ^{2}w}{\mathrm {d} x^{2}}}\right)=q $$

This PDF claims that the neutral axis of a curved beam isn't the same as in a straight beam (where it is just the centeroid).  There is a formula for distance of the neutral axis from the inside of the curve:

$$ \text{Height of Neutral Axis} = {\frac h {\ln(r_o / r_i)}} - r_i$$

And the radius of a function $y$ at point $x$ is:

$$R =\left| \frac { \left(1 + y'^{\,2}\right)^{3/2}}{y''}\right|,
\qquad\mbox{where}\quad
y' = \frac{dy}{dx},\quad y'' = \frac{d^2y}{dx^2}$$

With those, I hoped to find the shape that, at rest, looks like an eye and when squeezed becomes two flat lines.


texts: How to determine heat exchanger equation?

texts: What is the equation to determine the inside surface temperature along the length of the counter flow heat exchanger?


texts:
I was wondering if there is any equation that helps to calculate flue gas velocity through a pipe? Can I use the Poiseuille Equation to solve this problem by assuming the flue gas is acting as a newtonian fluid?

The pipe diameter is 3.66m, change in pressure is 3atm, length of the pipe is 10m, density of the flue gas is 0.811kg/m$^3$ at 150 ˚C, and the viscosity (C$_p$) is 0.0232.


texts: Rule of thumb for choosing a best sampling rate

texts:
I have a discrete control system with known dead time and time constant, where a process variable is sampled at regular discrete time intervals and fed back to the controller. I want to find out an optimal, or at least good, sampling interval.

I came accross a few websites saying that "Sample time should be 10 times per process time constant or faster", e.g. sample-time-is-a-fundamental-design-and-tuning-specification/
But I cannot find any theory supporting this statement, so I guess it may be a rule of thumb.

Is this statement correct? and can someone explain it?

====Edit====

This Edit is after Jeffrey's answer.

I want to provide more details about my control system. It is a discrete system with a reference input. The goal is to keep the output close to the reference input (like a room temperature control system). The difference between the output and the reference input is the error fed to the controller, so the controller has control output accordingly. The system has a dead time, as well as a time constant, both at the scale of $1$ to $10\mu s$. The fastest sampling interval of the output is at the sacle of $0.1\mu s$.

My question is: is the fastest sampling rate good enough to achieve a stable control?