texts: How to calculate scarf ratio or lap overlap for composites?

texts:
I'm building a plane, and one of the solutions I've thought of for connecting the wing spars to the fuselage involves connecting carbon fiber parts.  As mentioned in this answer, I found this explanation for how to calculate the scarf ratio:

  The scarf ratio is determined by the ratio of fiber tensile strength
  and the shear strength of the resin. If your fiber takes 3000 N/mm²,
  the resin transmits 20 N/mm² and the fiber content is 60%, the ratio
  is 1:90, so a 1 mm thick composite layer would need to be joined over
  a length of 90 mm.

I have tried to find more detailed explanations, but have not yet succeeded.  I am interested in knowing where this information comes from.  I have at least two specific questions:

does the answer depend on how the composite layer was prepared?
For example, does the answer change if the composite layer is a pultruded carbon-fiber strip? The fiber ratio is similar to what is claimed above as ideal, but the curing temperature is higher.
It is proposed above that the resin transmits 20N/mm^2 - this square mm,  which is a surface, how is it oriented?
If this was 20 N/mm^2 per mm of overlap of two composite layers, it would seem to make more sense. That's what seems to be being calculated. So is it a typo, or is there something more fundamental that I'm missing?

I think what I'm missing is that I'm thinking of lap-joints, also mentioned.
I think that the orientation of the 20 N/mm^2 surface in the above discussion is parallel to the scarf surface, the surface along which the composite layers are joined.  In this case, is the 20 N/mm^2 a tensional strength, or shear strength?  looks like it's a combination of both?  it would be a shear strength in the case of a lap joint, a tensional strength in the case of a but joint.

A similar question about lap joints is here.


texts: Solution diverges for Converging-Diverging Nozzle

texts:
I am trying to run a CFD simulation for an ASTAR nozzle but cannot get the solution to converge.

These are the steps I took to try and run the simulation. I made the geometry in Solidworks and imported the Parasolid file into the geometry (careful to to select 2D for the analysis type) and generated it. In the meshing I applied edge sizings (with bias toward the walls) and face meshing to get a decent looking mesh with skewness below 0.6 for all parts. For the setup conditions I did:

General: changed type to density-based

Models: turned on Energy

Materials: in the fluid air I changed density to ideal-gas and viscosity to sutherland (with default settings)

Boundary conditions: set outlet to pressure-inlet at pressure of 3e5 Pa, pressure-outlet at 0 Pa, and walls are no-slip condition

I left all the other settings as is, initialized it and ran it for 500 iterations, but it just blew up and I'm not sure what could be going wrong. Any ideas or tips on what to check for this? I've attached an archived work file that has all the setup and information in case this proves useful.

Thanks!

Files can be found here: https://studentcommunity.ansys.com/thread/solution-diverges-for-converging-diverging-nozzle/?postbadges=true


texts: What mechanism do I use for this pen-like design?

texts:
I am trying to make a pen-like product that moves out fluid from its tip for some special chores, but I am having issues about the motion of the clutch. The picture you see is a sectioned concept because my thought isn't fully fleshed out.

Legend: Black stripes - fluid, Yellow - Button, Orange - Body, Pink - Spring, Teal - Clutch, Green - Clutch ring, Blue - Plunger, Red - Cap, Grey - Cartridge

Goal: When I push the button once, the plunger pushes up the red cap, which pushes up the fluid in the cartridge. As more liquid is expended, the red cap moves up until it reaches the top, when there's no liquid. Each time the button is pushed, I want the plunger to move and stop in accordance to the level of fluid left in the cartridge. For example, if the liquid is halfway, the plunger will be more upward.

I have a clutch system where the clutch ring is press fitted inside and a clutch has a tight fit against the clutch ring, to force the clutch to hold on to the plunger as it moves upward. This way, the plunger can move up then stay still without any external force acted on it (the button being pressed).

Main problem for me: After a certain level of fluid is gone but fluid still remains, the button won't be able to touch the plunger no matter how much I press the button. I tried introducing a small connection between the button and the clutch, so the plunger can still move even if the button doesn't have contact with it, but that introduces more problems.

You may notice more problems but the bottom line question is: will this mechanism work? If so, how can I resolve this main issue and if not, what other mechanism(s) will work? I'm not looking for specific numbers, but just needed to be point in the right direction (mechanism choice) to use.

I appreciate any and all responses!


texts:
I'm seeking an explanation in reference to the photo below. I'm unsure how the solution within the red box calculates the max tension of the Aluminium beam and the max compression off the Aluminium beam.

How are you able to differentiate whether the Aluminium is in tension or compression within this scenario?

As well as how they are able to make the statement that "the steel is entirely compressive bending stress and the max bending stress is at the top of the flange"

Thankyou!


texts:
4.3 is the diameter of the hole in mm. But I don't understand the 4- part. Usually that's like a screw size but I haven't seen it like this before.
edit: as one commenter said I think it's just to indicate there are 4 holes


texts: How to size proper Transformer (3phase quesiton)

texts:
I have a question regarding the sizing of a proper transformer. I have a source voltage and load. See the following:

Primary Source: 480VAC 100A (3phase)
Secondary: 415 VAC (3phase) Load: 2 parallel AC-DC units 10kW, Power Factor = 0.8 (ea).

How do you go about sizing a proper transformer to interface between the source and the load?


texts: Arranging members within a truss efficiently

texts:
A wide variety of trusses exist for bridges and roofs. There are many different permutations when it comes to arranging the internal truss members. Depending on the direction, a diagonal member may be subjected to either compression or tension. Using this outline of a truss top chord and bottom chord, for example:

How does one goes about searching for the most efficient arrangement of internal web members within the truss, without going through a tedious trial-and-error process?


texts:
I am a little confused about how a 2-bit adder works. For 1-bit adder, my understanding of it is fine and I am able to draw out the truth table for it. However, if lets say I have a 2-bit adder, I can't seem to work out how the display shows the sum of both binary.

For example,
1st full adder - A1 = 1, B1 = 0, Cin = 0 => sum = 1 and carry out = 0. The carry out then goes to another full adder hence, for the 2nd full adder A2 = 1, B2 = 0, Cin = 0 => sum = 1 and carry out = 0.

Does this mean that my binary representation is 11? Based on looking at the both the sums, however I know that 01 + 01 = 10. I am pretty sure I am understanding something wrongly here and hopefully someone can help me out.


texts: Is the Qmax of an T-Beam equal if calculated both above and below the neutral plane?

texts:
I was doing a question involving a T-Beam question wrong since I was selecting the wrong area to use for $Q_{max}$ when trying to maximise the shear stress.

$$\large{\tau}= \frac{VQ}{It}$$

A friend argued that the area both above and below the Neutral Axis should be equal but despite trying multiple times, I have been unable to get the same result.

Is this statement correct? (and if not, why)

It would seem by argument of equal values both above and below the beam that perhaps it would be correct, even if the beam is unsymmetrical.


texts: What's the thermal bounds of a typical computer case fan?

texts:
I'm thinking of repurposing computer fans (case fans and/or CPU/GPU fans) for a hobby steam turbine project. So the idea would be to use the fan rotors in the turbine to drive the shaft (discarding their electronics.)
However, this means that the fans would run in quite high temperatures; 100 degrees celsius I suppose, since it's steam.
Hence my question, what's the upper temperature limit of a typical, plastic computer fan? Will it survive steam?


texts: What type of bearing could be used to keep a utensil level while being moved from plate to mouth?

texts: I need a bearing that the inner bore will stay level and balanced when the out ring is rotated. My son with autism lacks the motor function to feed himself with a spoon. He can turn his wrist, when the spoon goes to his mouth its 90 degrees off. I need to be able to insert bearing into a handle and have a spoon in the bore that will stay level.


texts: Thermal efficiency affected by hertz (Gas turbine)

texts: Take the LMS100 gas turbine for example. Why does the efficiency change when generating power in 50 or 60hz waveform?


texts: Practical rugged method for elevating water 7 feet high?

texts:
At a very low-tech, rustic forest camp, I've built a 'water tower' connected to a gravity-fed water filter to provide something like a clean water faucet. It's basically a 5 gallon bucket on top of a ~6' high platform, with a 1' long hose running down from it connected to a filter. It is idle for long periods of time and then used for a period of 1 to 9 days, receiving apx. 3 gallons of moderately turbid, acidic water input each day.

I want the end of the filter (i.e. the clean water spout) to be about waist high (way easier to work with than a spout only a couple inches above the ground). To accomplish this I could either shorten the filter's hose or raise the bucket, and thinking that height/gravity was important for a gravity fed filter, I opted to raise the bucket. This presented two challenges: I need a taller platform, and I need a way to fill the bucket when it's at or above head height. The taller platform was easy enough to build, but a sturdy enough ladder to carry water up to the bucket is harder to craft. How can I get water from ground level up in to a bucket that's rim is about 7' high?

The conditions on site are very rustic and remote. It's a long drive to get there, then a bit of a walk to camp (lugging gear in a backpack and by hand), and currently the only dry storage is makeshift via tarps (not reliably dry). I don't always go there with a large vehicle, so transporting a ladder back and forth isn't a great option, and if I leave a steel ladder there it will be exposed to extreme temperature swings & moisture. I'm envisioning some relatively primitive technology like a pulley, an Archimedes screw, or more compact easier-to-transport modern technology like a small hand-pump with a hose, but I know very little about the details of those options. So I ask Engineering.SE: what practical rugged method can I use to elevate water 7 feet high? If some kind of pump, what specs to look for and what other equipment will I need to make it work?

Bonus if the method can be scaled or setup in series so to move water further distances. As of now, to get water to the ground next to the water tower, one has to carry water by bucket up a steep ~100' slope that has ~75% grade.


texts:
Can anyone tell me how to go about this problem?

There is a square shaped laminate (polyethylene fiber and epoxy resin composite) that is constrained on one side. A gun is fired and the bullet hits the laminate. What kind of stresses result in the laminate? How should I go about their calculation? When I say stresses, I mean the stress tensor components $\sigma_{i,j}$. Also, can the strain tensor components $\epsilon_{i,j}$ be calculated?

Textbooks and other sources don't show or tell how the stress components are measured. Also, in the above problem, the mass and the velocity of the bullet are known.


texts: Modification of Beam Equation for Thin Sheet

texts:
I am trying to determine the modulus of elasticity (Young's Modulus) for a rigid paper sheet. The issue I am having is that my results for the Young's Modulus change depending on what orientation (length extending out or width extending out) I use to measure it.

The material of the paper is not trivial, and as a result I am not able to find a datasheet on the material itself. Instead, I did some simple tests to calculate the Young's Modulus, especially since it is a thick sheet that behaves more like a sheet of metal than floppy paper.

I took the sheet, fixed one end, and measured the deflection at the other end (and other relevant parameters). I did this with both the length and the width extending freely over the fixed end. I accounted for curvature in the sheet when measuring the deflection in order to make the measurement as representative of an ideal beam as possible (there were some assumptions I made about the curvature, but I will not go into details about how I eliminated the effect of curvature in my deflection measurement unless I have to, as I believe the problem lies elsewhere). I then used the Euler-Bernoulli beam equations for distributed load, $q$, (in this case, the distributed load was due to gravity) to arrive at the Young's Modulus, $E$. $$E = \frac{qL^4}{8I\delta_{gravity}}$$ $q=$ distributed load, $L=$ the length of the paper extending over the fixed end, $I=$ second moment of area, which changed depending on orientation, and $\delta_{gravity}=$ deflection after removing effects of curvature.

The results I achieved were consistent ( within 0.3 GPa of each other), but changed drastically, by almost an order of magnitude or more, when changing whether it was the width of the paper that was modeled as the "length" of my beam, or the length of the paper.

I am wondering what caused this big change in the Young's Modulus, since I don´t know if it is typical for Young's Modulus to vary by such a large amount between orientations (10-90 times difference). Paper is an anisotropic material (thank you, alephzero), so it could be related to this fact. I believe I am missing some factor in the equation that is depenedent on orientation, such as a correction factor for structural stiffness due to sheet curvature, or something with the Poisson ratio, but of course, this belief can be misleading me.

Things to note:

The material is foamboard, only the outside of the material is made of paper in the strictest sense. The inside is made of foam.

I changed the distributed load, $q$, depending on the orientation, since the weight/length changes depending on whether the width or the length. I did the same thing for the second moment of area, $I$.

For the second moment of area, $I$, I modified the equation to more precisely model the shape of the curvature, but it did not change the value of $I$ significantly.


texts: At what temperature do I risk altering the structure of steel?

texts: If I have structural or tool steel that has been treated to some standard (ASTM, SAE, ISO -- e.g., for hardness) but I don't know the details of the treatment, is there a "safe" temperature below which I can work the steel without affecting its performance characteristics?


texts: Derivation for bridge natural frequency estimate in Eurocodes

texts:
The Eurocodes gives the following equation for estimating a "simply supported bridge subject to bending only"*:

$$n_0 = \frac{17.75}{\sqrt{\delta_0}}$$

Where

$n_0$ is the natural frequency in hertz
$\delta_0$ is the deflection at mid-span under permanent actions in mm

The equation is seemly plucked from thin air, and there is no explanation as to where the constant 17.75 comes from. As an engineer I'm loath to use a formula I don't understand, but more than that it would be helpful to learn the fundamentals behind it so that I can see if it can be altered to work with other support conditions.

Can anyone provide a derivation / fundamental origin to this relationship?

*Full reference is: EN 1991-2:2003 6.4.4 [Note 8] (Equation 6.3), if that helps.


texts:
I'd like to make an oven for curing adhesives that require an elevated temperature for a proper cure. I'd like for the temperature to be settable from 60 degrees C to 75 C plus or minus 5 degrees over time, and over the volume of the container. I'd like for the volume to be about 6" x 6" x 6" or 15 cm x 15 cm x 15 cm.

Primary objectives are to keep the cost down and to make the oven out of easily available materials from home depot or mcmaster carr or similar. Ideally would prefer to repurpose some home appliance. The ideal for me might be just repurposing a toaster and adding a temperature controller to it, but I worry about a toaster having consistent temperature through its volume.


texts:
This morning, as with every morning, I had my coffee. However, today it was burnt, because I slightly overfilled the water. I use an Italian Percolator on a gas top.

Normally, you put it on to boil, and once you hear the water bubbling, the coffee is ready, and chamber C will be full of coffee.
As you can see, you fill chamber A with water, loosely fill B with coffee, and the water then rises through B, up through the red pipe, and flows over into C. However, as the picture shows, there is a small valve on A. If you fill the water above this valve, you get horrible coffee. When you hear it bubbling, very little coffee has risen into chamber C, and you have to wait a long time for it to do this, while water also escapes from between chambers B and C (which screw together).

Why does this happen? I cannot think of why there should be a valve to release what is presumably steam. Surely the machine should work regardless? Why does the steam have to be released for the mechanism to work properly - is it linked to the pressure of the system?


texts: How do I make my balloon annotations circular instead of oval-shaped?

texts:
I'm getting oval balloons for my annotations instead of circular balloons even though I selected the circular setting.

Is there any way to edit/revert this annotation to become a normal circle?


texts: Calculating the link budget of antenna and receiver with free space-path-loss formula

texts:
I really know that the real calulation of the range of UMTS, GSM or LTE antennas is depending on a lot of issues, reflection, and other stuff which makes it really complex.

I need only a rough model which I can calculate the range of them, so I thought I use the free-space path loss formula and look for the "r" in the formula. Is there anything wrong with my idea? Despite the fact that of course in really you'll almost never have just a free space but rather buildings,hills and other stuff but lets say, for my model I say there is nothing that disturbs my signal.....

If I can use the formula, my question would be so the only difference of those systems would be the frequency and the transmitted power or received power of the mobile phones, is that correct?

https://en.wikipedia.org/wiki/Free-space_path_loss


texts: What is the correct type of stainless steel for transporting argon gas?

texts: What is the correct type of material, 304L or 316L stainless steel tubing, for transport argon gas? Is it required to be an electro-polished finished?


texts: Historically, how did tram switches work?

texts: Historically, the switches on regular railways were switched manually using a lever by dedicated staff to route trains correctly before getting replaced by an automatic electronic system. A similar system is in place for trams in modern times, but how was it done before this was possible, with horse-drawn trams and at the beginning of electrification? It would obviously not be possible to have separate staff be responsible for switching the switches like on railways in cities as they are often located in the middle of roads, in addition to being very numerous in more complex systems. How did tram switches operate before being equipped with an automatic electronic system?


texts: Modern equivalent concrete strength to 'Class Ws 3/4" '

texts:
Consider the following extract from a UK reinforced concrete detail drawing dated 1970:

What is the modern equivalent to this concrete class?


texts: What is the mechanism of the blades movement

texts: this is deblistering machine by Stripfoil. I wounder to know the mechanism of blades movement ( equally ) with one? screw. when the operator rotates the handle, all blades move with the same distance.


texts: I have a small pump that does 6L/min flow-rate. With a pipe size of 0.5 inches and 3 nozzles spaced at a distance of about 1m each, is it possible to do effective misting? My total pipe length will be 4m. I have been trying out calculations from various references but it keeps driving me nuts. What am wondering is, is the pump fit for that job? I have seen similar pumps online with equal flow-rates and pressure ratings of about 130psi. What matters most?


texts: How to calculate monosymmetry index of an unequal angle?

texts: I saw some formula involving integration. Is there a straightforward formula to calculate this instead given b, d, t and alpha angle between x-x and u-u axis?


texts: Steel Continuous Beam Structural Diagram

texts:
Here's an image of my structural plan that my group and I are designing for a university assignment. It is a 7-story steel structure with bracing at the two ends and at the verticle core near the center.

Our professors have suggested that we use continuous primary and secondary beams however we are unsure what they are. All of the structural calculations (bending moment, shear, deflection check) will be done with a computer program however we must first understand the structural diagram of a continuous beam in order to enter the proper information into the program.

What would the continuous beam structural diagram look like for the primary and secondary beams of this structure? Is the diagram below correct?

Any explanation of how a steel continuous beam works in a multi-level structure is greatly appreciated. Thank you for your help.


texts:
I'm currently looking around for a new bike and I've noticed lots of load-bearing carbon parts (frames, cranksets, forks etc.) with an interesting finish like this:

and I was wondering what this type of carbon cloth is called and why it's used. I've seen it used on parts (e.g. forks) where the forces are predictable (laterally during cornering or longitudinally during braking) and thus unidirectional or woven cloth would appear to be the best option from a specific stiffness perspective. It does look pretty cool and thus presumably has marketing value but other than that, I'd appreciate any ideas!

Additional image:


texts: What is the minimum diameter for vertical bars in a column according to ACI?

texts:
What is the minimum for vertical bars in a column according to ACI and I am looking for a particular condition where diameter must be greater than 0.625 in.
(when using S-concrete for column design it gives a warning that diameter must be 0.625 in. but I couldn't find anywhere in the ACI that include this condition)

If any article or in any clause in ACI refer to this condition please share.


texts: Industrial applications of vector calculus

texts: I'll be teaching vector calculus to mechatronics engineers, and I'd like to provide them with industrially relevant examples, especially of the use of vector fields.  Can anyone suggest either an example application that they have personally used or a text that I can use to glean some examples from?


texts: How to equalise the water distribution in a leaky pipe irrigation system?

texts:
I have a 200 litre water butt and plenty of 22 mm plumbing pipe and fittings and I want to build an irrigation system for my vegetable patch so that I can open the tap after a few dry days and ensure all my plants get equal amounts of water from the butt.

The end of the patch is about 5 m from the water butt and at the same level, so the head is only the depth of the water-butt (1 m) plus about 10 cm as it sits on a small platform I built. I will bury a hose 20-30 cm under the ground to the end of the vegetable patch, where it will come back up to the surface and split into 4 rows of pipe about 15 m long each with holes drilled to release the water.

I think I should taper the holes so that the ones at the start will be smaller and the ones at the far end will be bigger, but given the low pressure I don't know how small these should be or what the size-difference in holes I should use from one end to the other to ensure that water gets all the way along and is evenly distributed?


texts: In an incremental nonlinear FE procedure does the material stiffness matrix need to be updated?

texts:
A typical nonlinear FE problem can be given by:

\begin{equation}
\mathbf{R} = \mathbf{K}\rho + \mathbf{F}_{NL}(\rho),
\end{equation}

where R is the vector of applied forces, K is the material or linear stiffness matrix, $F_{NL}$ is the nonlinear force function and $\rho$ is the vector of displacements.

The tangent stiffness matrix is:

\begin{equation}
K_T = K + \dfrac{\partial F_{NL}}{\partial \rho}(\rho)
\end{equation}

If an incremental procedure is applied, $\dfrac{\partial F_{NL}}{\partial \rho}$ will need to be updated at load application step, since it is a function of the deformed configuration.

But why does the material stiffness matrix $K$ not need to be updated? $K$ is formed by rotating local stiffness matrices and assembling them into a global frame of reference. Surely when the geometry becomes deformed $K$ will need updating also, even if it is the linear stiffness matrix?


texts:
There's a EU EN standard 1822 for air filters  that has seen several iterations. The pre-2009 versions of EN 1822 (which seems to have come out in 1998) were pretty confusing as they allowed poorer filters to be labeled as H or HEPA; e.g. a "HEPA 12" filter would filter 99.9% of particulates, but this is strictly inferior the US HEPA which filters 99.97% of particles of 0.3 um (assuming Wikipedia is correct about this). The 2009 revision of EN 1822 somewhat fixed this as anything below 99.95% is now called "EPA" instead, so the "HEPA 12" from EN 1822:1998 is now "EPA 12" under EN 1822:2009.

I'm still not sure if the two standard are really comparable though. I don't know what the particulate size is for EN 1822, nor am I sure what is the difference between "integral value" and "local value" for the emissions under EN 1822. The latter in particular is somewhat worrisome because it carries a footnote that allows manufacturers to change this by agreement with the purchaser, which I suspect some may turn into a sort of click-wrap agreement.

So is HEPA 13 under EN 1822:2009 (integral value ≥ 99.95%, local value ≥ 99.75%) approximately the same as US HEPA or does one need to move to H14 for that (integral value ≥ 99.995, local value ≥ 99,975)?

Or maybe there's something else that I'm missing because I've found a comparison that puts the Mil Std 292 numbers below those from EN 1822, so I guess there's a difference in testing methodology that accounts for this. Does someone know the details to clarify?

This latter table surely refers to pre-2009 versions of EN 1822, as no year is stated anywhere in the document and has "H12" and so forth in it. A similar version but using the newer EN terminology can be found on the website of a different manufacturer, but oddly there's a E11 but H12 in there. These tables don't inspire much confidence because I'm not sure 292 is even the US Mil. Std. number for HEPA filters, (the 292 standard is about rockets). Different documents state it as Mil Std 282, which is indeed about fitlers for protective cloting... but otherwise the equivalence stated is about the same [H]EPA 12 being the same as the US HEPA of 99.97%.

Is this correct though, and if it is what in the testing method explains the difference?


texts:
Can someone please help me with the symbol for background shear? To give you a bit of context, I am referring to background shear as in the following sentence taken from Hussian et al.:
Vorticity magnitude has been widely used to educe CS and represent vortex cores. However, this approach, though fairly successful in the free shear flows investigated so far, may not always be satisfactory since vorticity magnitude does not identify vortex cores in a shear flow, especially if the background shear is comparable to the vorticity magnitude within the vortex


texts: Building a coffee maker - food grade, heat resistant material?

texts:
Background
I want to build a drip-style coffee maker for fun. My "design" features a sealable cylindrical housing for the water and heating element. Silicon tubes will carry boiling water from the cylinder to the coffee grounds. I plan on using a cheap water heater element that I can power using a 120V household outlet. A valve will be installed on the side of the cylinder to allow steam to escape. By partially closing the valve, I think I can modulate how quickly boiling water is pushed through the silicone tubing to the coffee grounds.

Question
What material can I use for the cylinder? Right now I'm looking for easy and cheap. I have access to a drill press and welding station, but not a mill/lathe.
Options that I'm considering:

3D printing using a food-grade filament. Not a great option. It seems there aren't a lot of good filaments that can withstand boiling water for long periods of time.
CPVC piping. I think this would work, but I'm seeing mixed answers online. A few answers say CPVC is rated for 200 F, not 212 F. Another resource rated CPVC for much higher temperatures.
Copper tubing. This would be safe, but it's an expensive option. And I guess I would need to worry about welding/threading the top and bottom.


texts: Manual vs Fusion360 calculation of natural frequency of beam

texts:
I'm trying to uncover the natural frequency of a mass-less beam with 2 masses attached but getting different answers from Fusion360 vs a hand calculation.

L1=1m, L2=2m, m1=10kg, m2=20kg, Young's=21010^9Pa, H=0,04m, B=0,02m I=H^3B
My current way of calculating the natural frequencies via matlab is:
alpha11 = 2*L1^3 / (6*E*I);
alpha12 = L1^2*(3*L2-L1) / (6*E*I);
alpha21 = alpha12;
alpha22 = 2*L2^3 / (6*E*I);

A = [alpha11 alpha12
     alpha21 alpha22];

K = inv(A);

M = [m1 0
     0 m2];

omega_n = sqrt( eig(inv(M)*K) );
omega_1 = min(omega_n);
omega_2 = max(omega_n);

f1 = omega_1 / (2*pi);
f2 = omega_2 / (2*pi);

This results in f1 = 3,18 Hz & f2 = 28,57 Hz
When running the same beam in fusion the downwards natural frequencies are f1 = 29,4 Hz & f2 = 10279 Hz.

In fusion the beam had to be given a minimum density of 0,001 g/cm³.
What could be the cause for the natural frequencies differing this much? What am I doing wrong? Any help is deeply appreciated!
EDIT
To clarify the fusion setup. The beam is constrained against xyz-movement in the end. The masses are added as point-masses in the middle of the beam (only acting on a small area)


texts: How do I read this schematic drawing notation for a drill hole?

texts: It's for an NX part. I can't figure out the depths and such. I just know the placement of the 4 holes and that the diameters are 10 mm each.


texts:
I have some doubts about a quick-release mechanism that I'm working on and I'd like to run it by you.

I have hollow tube in which there's a spring-loaded rod. Part of it is made wider and there's a metal round pin that restrains the entire mechanism as shown below:

The spring rate is 1.23 N/mm its free length is 135mm but it is compressed to 35 mm.

I'm using a servo quick release mechanism similar to this:

It is driven by a servo with a stall torque of 9.8kg/cm

My question is, would the lateral force the rod is exerting on the pin be a problem for the motor? E.g. the friction between the pin and the hole of cylinder being so great that the motor won't be able to move? Is there a way to mitigate this?


texts: Is there a formula to relate the axial length of a nozzle expander with its radius?

texts: I know the inlet, throat and outlet areas for a nozzle expander. Is there a formula to know its axial length? Something like L= f(A) = f(D).


texts: How can I calculate backward extrusion force

texts:
I am interested in finding a way to calculate the force necessary to do a backwards extrusion. Typically these would be for forgings 0.5 to 3" in diameter (or square) of different kinds of steel. The diagram below shows a typical type of forging I might want to do:

This would be die formed in A2 steel by backwards extrusion using a hex-shaped punch. The forging would be done with the work piece at its forging temperature.

I want a way to calculate the force (forging load) necessary do such extrusions.


texts:
Could you please tell me why the singularity function is one when x=0
I mean $<0> ^0=1$

Thanks you in advance


texts: What is the stiffness modifiers for a prestressed slab?

texts:
According to ACI the stiffness modifier for moment of inertia for flat plate and flat slabs is 0.25 (ACI318/318R-02 10.11.1) to mitigate for the cracked section.

But in a prestressed slab (post-tensioned) the crack is controlled can the stiffness modifiers be taken higher than 0.25?

My professor suggests that it could be taken between 0.6-0.8, can anyone suggest any article or document or even a discussion about this topic to be sure about this problem ?


texts: How much force can a pole in ground take before falling?

texts:
Consider I have a pole stuck in the ground as illustrated below:

When a force F1 is exerted on the pole, its bottom end will push against the ground it's stuck in; the ground then exerts a resistance force. Intuitively, if F1 is very strong then the pole's upper end will move in F1's direction and if F1 is very weak, the ground resistance Fr keeps the pole in place.

Given some measures of the pole, specifically, how deep it is (L2) and what radius r it has (it is a cylinder), I would like to be able to determine the magnitude required by F1 to move the pole's end.

I have asked a similar question, with more physical details on another stack exchange site, too. Here is the link.

Update:

Assume that the ground is made of only one material, with uniform density, disregarding any "dirty" effects, such as moisture, or temperature. The length of the pole, its radius (it is a cylinder), and its depth L2 are all constant.

Let's view the pole as a lever with its pivot where air, ground, and pole meet. Then we have F1 * L1 = F2 * L2 when the lever is in balance. Now, I would like to find out at what force F1 the pole starts moving; the pole is moving when F1 * L1 > Fr* L2.

The problem would be solved if we find a means to compute Fr. My idea was that as the pole (in the ground)pushes towards the right at every height 0 > L >= L2 (L = 0 on dotted area where air and ground meet), there is a resistance force Fr(L) at each height (view illustration here). For big L this force is small while for small L the force grows. I assume Fr(L) must grow in a linear fashion as it does with levers (F1 * L1 = F2 * L2). Assuming that, Fr could be computed by F2 = 0∫L2 Fr(L) dL.

The solution need not be that exact, the force need only be computed approximately: the force will be used by game simulation the physics need only appear real. All that is required is a means to compute what resistance force Fr the pulling force F1 must overcome to move the pole.


texts: Where can I find how good given aluminum is for machining?

texts:
What kind of resource provides summary data on how given kind of aluminum yields to machining? Are there norms, or such?

Explaining:

Different kinds of metals yield to machining differently; e.g. MO-59 brass has a small addition of lead, which makes it leave a clean, smooth cut; in contrast pure copper will pull, crease, drag into threads; where the milled surface of brass left a mirror shine, copper left a fleece-like mess of metal turned into myriads of tiny wires.

The data for a few materials I worked with, I got through word-on-mouth, or own experimentation. I know resources exist, from which professionals learn this in an organized manner, but I don't even know what keywords to look for.


texts: Why is the JPCP CTE default value in Pavement ME 4.9 when the ME Pavement Design Guide Manual of Practice recommends 5.5 for unknown?

texts: The default value for JPCP CTE in v2.5.5 (and v2.3) is 4.9.  However, per Table 10-5 on page 152 of the ME Pavement Design Guide Manual of Practice recommends 5.5 if unknown.  Moreover, there is only one aggregate type with recommended CTE below 5.0, whereas most common aggregates are at least 5.2 or higher.  So how could it even be that on average, the global calibration used 4.9 or that the default should be 4.9?  Why was 4.9 selected?


texts: oscillation motion from DC motor (computer fan)

texts:
I intend to make an oscillating motion from a simple computer DC fan (say 5V).

My question is: could a signal generator with a sinusoidal signal of (say voltage 5V  and frequency of 5 Hz) be used to power such a DC fan to produce the oscillating motion ?

Second question:
it is related to Oscillations in motor control systems.
Will there be a damage for a low frequency and low voltage input to the fan ?

For additional info, the load is lightweight, and the mechanical rotation is about ±45 degrees.


texts: Which floor is likely to collapse during the earthquake?

texts:
I'm currently working on resonance frequencies of buildings and have to do a practical work/experiment on which floor of the building is likely to collapse during the earthquake. I have the slight idea on how it will work but I have no idea how I should do an experiment to show and prove it. My guess is the top floor as it will move more distance in same time (therefore move faster) and it is higher than the center of the gravity.

I have quite a variety of apparatus such as the amplifier, signal generator, arbitrary function generator, vibration generator, sliding platforms and some metal plates for building structures.

It would be great if I can get some insights and tips on how I should go about doing the experiment. Some equations relating to thus would be great.


texts: Does a concrete slab (deck) cause compressive load in a wall beneath it?

texts:
Let's say you build a square reinforced concrete deck at height of, say, 3 meters, with the deck supported by its own steel reinforcement and by four reinforced concrete piers (call them, A, B,C, and D) below each corner of the square.

If you then build four infill walls, A-B, B-C, C-D, D-A, are those walls under compressive load? From one side, the weight of the concrete slab would say yes, but on the other side the fact that deck was supported prior to the walls, maybe not?

Is there a difference, in the context of the loads transmitted to a wall below, between a vertical stack as follows:

wall - reinforced concrete ring beam - slab

and

wall - reinforced concrete deck with reinforcement designed to support the deck by itself and the piers alone.

Here's an example, without the ring of beams:


texts:
In mechanics, we have the so called compatibility conditions, which quarantee that when a body deforms, the strains are "compatible" in such a way to no discontinuities or gaps for inside the body as it deforms. Intuitively, this means that infinitesimal pieces of material connected in the undeformed body stay connected, and won't end up inside one another.

From Wikipedia:

  ..In the continuum description of a solid body we imagine the body to be composed of a set of infinitesimal volumes or material points. Each volume is assumed to be connected to its neighbors without any gaps or overlaps. Certain mathematical conditions have to be satisfied to ensure that gaps/overlaps do not develop when a continuum body is deformed. A body that deforms without developing any gaps/overlaps is called a compatible body. Compatibility conditions are mathematical conditions that determine whether a particular deformation will leave a body in a compatible state.

Reading the Wikipedia page, these equations/conditions are developed:

$$ \frac{\partial^2\epsilon_{11}}{\partial x_2 ^2}-2\frac{\partial^2\epsilon_{12}}{\partial x_1 \partial x_2}+\frac{\partial^2\epsilon_{22}}{\partial x_1 ^2}=0$$

They are derived by stating that

  ..there are six strain-displacement relations that are functions of only three unknown displacements. This suggests that the three displacements may be removed from the system of equations without loss of information.

Firstly, sure, the above statement does make sense, but what does it have to do with compatibility, as I described above? Why is it that when a few variables are removed from the system, we are now guaranteed to have a deformed state where no material overlaps or develops discontinuities?

Most of other material that I've read online just state the same intuitive idea of compatibility, and then just state that the deformation is compatible when the strain is integrable and proceed to find conditions ensuring that. Alternatively,  it is proven that the solution to this equation can be found:

$$\epsilon=\frac{1}{2}[\nabla u +(\nabla u)^T]$$

Again, sure, we need to know that this equation can be solved to have a sensible strain field, but how do we know the solution strain field is compatible, in the intuitive sense described at the beginning?

Why simply being able find a solution displacement field, or being able to integrate the strain field imply that the strain is compatible?


texts: i am trying to make a small, simple 3d printed robot with humanoid characteristics. i am working on its arm at the moment. it is being driven by a small sg90 servo motor which pulls the forearm about a pivot towards the upper arm using a pulley made from fishing wire. this works well enough. however i am having trouble getting it to go the other way. i have tried adding an elastic band from point A to point B on the diagram. this works but it is not very smooth. i have researched into springs and it seems that the torsion variety are exactly what i need but they are jaw dropingly expensive(whats the deal with this? other spring types are quite cheap). could anyone offer an alternative solution to my problem? i am aware that this is a very basic question so hopefully it wont be too difficult for you folks to solve. thanks!


texts: Which mounting bracket to use with a geared box?

texts:
Which 90 degree bracket would you use for this one? Do you have any suggestions for what i should be looking for, I find it very hard to find something. It is 5cm between all the outer holes.

Would love to use something like this, but that doesn't works for my uneven, off-centre, geared dc motor.


texts:
I would like to know what mechanical parts can be used to convert a rotation movement from an axis to another.

For example: You have the shaft of a motor rotating vertically, but you need to rotate a part horizontally.

I already found the worm drive assembly but I would like to know if an "exhaustive" list exists somewhere with pro/con for each.


texts: What material characteristics are most important for heating element material selection?

texts:
I want construct a heating element by screen printing a flat coil pattern of conductive paste onto an insulated substrate. This conductive paste consists of a powder of conductive metal contained in a viscous epoxy paste. The pieces of metal are held together by the paste to form a conductive pathway. There are several options for the type of conductive metal filler - so far I have found silver, silver and copper mixed, carbon, graphite and nickel.

What material characteristics should I be looking at in trying to assess the best filler material? I want to make a heating element that will heat up as quickly as possible with the least amount of electric current being put through the heating element. The max temperature of the heating element will be 100 C.

I am thinking that the two most important qualities for generating heat with the least electric current are Resistivity and Thermal Conductivity. Is this correct?

These are the specs on some pastes I have found. It seems like the Nickel paste would be best - is that right?

Nickel Volume Resistivity <0.004 ohm. cm Thermal Conductivity 1.44 W/M-K

Graphite Volume Resistivity 0.004 ohm. cm Thermal Conductivity 0.24 W/M-K

Silver Volume Resistivity 3.00 E -3 ohm. cm Thermal Conductivity 1.45 W/M-K

Carbon Volume Resistivity < 40 ohm. cm Thermal Conductivity 0.25 W/M-K

Silver/Copper Volume Resistivity 3.70 E-2 ohm. cm Thermal Conductivity 1.15 W/M-K


texts: On the steam locomotives, why was the driver's cabin not located in the front of the boiler for better visibility?

texts: I always wondered how the drivers of steam locomotives could observe the road.


texts:
Is there an adhesive that works well with ceramic and is heat-resistant? The application is a teapot that should sustain temperatures up to 100C-105C.

The Devcon 5-minute epoxy worked, but easily detached when 100C water was poured in. This is getting hard to find for non-industrial uses.


texts: What type of pneumatic valves would represent the valves in the schematic?

texts:
What type of pneumatic solenoid valves would represent the valves in the schematic?

Specifically, the lower valves could be represented by a 5 port 4 way 2 position valve. This is because there is only one port with bidirectional flow for each side.

However, I'm not sure how to realize the upper valve system since there are 2 ports with bidirectional flow. Is there a way to realize this system with multi-port valves or does the upper system need to utilize direct acting (not pilot spool) valves?


texts: What's the longest lasting tubing in air?

texts: What's the longest lasting tubing for use in low pressure air systems?  I'm looking at building a greenhouse with double or triple layer ETFE panels and the tubing would be run through the metal pipe structure, so it would experience exposure to air an either steel or aluminum with low (a couple PSI or so at most) air pressures.  It would be a much bigger pain to replace the tubing than the ETFE panels so I'd like something which goes significantly beyond the 30-40 lifespan of the ETFE panels.


texts: Converting accelerating linear motion into constant rotational motion

texts: Suppose there is an accelerating mass along a straight line, and you would want to convert that linear motion into rotary motion. Is it possible to convert that accelerating linear motion into constant speed rotary motion? Could you suggest mechanisms that I can use?


texts:
I'm trying to build a table with 4 swivel legs that can be locked into arbitrary angles so that it can stand over one to three rows of storage crates in my garage:

As you can see, the legs aren't reinforced or braced to prevent wobbling or shaking. In fact, the fixtures to the table top are simply pipe flanges which might sustain too much stress on their own:

If the maximum load is 100kg, will this design be adequate? I'd appreciate any advice on improving the structural integrity.
Thanks


texts:
So we are trying to build an AC generator, an alternator, if you will. We are using a 5" PVC pipe for the body with a hole drilled diametrically, through which a bolt passes. Inside of this pipe, on the bolt, we have a six pole rotor magnet, which rotates as we rotate the bolt. We then have 18 gauge, plastic coated wire wrapped around the pipe. We used a drill to spin the magnet at respectable speeds, but were not able to get any electrical outputs. Are there any glaring issues in this design? If so, how can we address them?

The first image is of the inside of the generator, showing the rotor magnet (apologies for the image). The second is of the outside of the generator, showing the wire wrappings. The bare copper wire is shown there to test an unprotected wire and is not used in the actual design.


texts: How do I hook these components together to get my desired functionality?

texts:
I have a big button http://store.2xlnetworks.com/thebigbutton/ and a display counter Microframe Model 265 https://www.microframecorp.com/d0265-6-digit-rugged-computer-controlled-display .
I want the push button to make the display counter go up one digit every time its pushed. Any idea how to go about this problem ?


texts: What tool does one use to inspect pipe bevel angles?

texts:
My translation of a document published by the Pervouralsk New Pipe Plant:

Inspection of pipe-end root face (“face ring”)
Inspection of this type is carried out as required by the regulatory documentation using a ruler or a gauge.
Bevel angle inspection
Inspection of this type is carried out as required by the regulatory documentation using a [protractor? goniometer?] or a gauge.

What tool do we usually use to inspect bevel angles at the end of a pipe?
The Russian word used is "угломер", literally "angle-measurer". According to Multitran, it could be translated in dozens of ways.
(I'm translating the word "truba" as pipe despite some saying that "tube/tubing" is a more proper word: the reason is, the plant uses "pipe" throughout its English-language website)


texts: Establish a controlled rotation on gears

texts:
I am a 3d designer trying to build a simple device for my project and I have a problem. As you can see in schema below, point G has weight on it and it needs to be a controlled, vertical rotation. I am afraid that when I build this, it will go faster or slower on sides. Rotation needs to be stable and I need rotation to stop where it is, as soon as motor stops.

Can a mini motor achieve this and what kind?
Do I need to add extra parts to the device and what are they?

Thanks in advance and I am looking forward to answers.


texts:
I've been studying this topic for a couple of days now. I started by asking some questions regarding output Torque and gear ratios relations.
Now I came with the whole picture and some calculations that I been working on. My goal is to find out if I'm in the right direction, and also point-out relations between equations that I'm not sure of.
To make this more clear and clean, I divide the system into three sections; A, T and B.

In section A its the electric motor and worm/spur torque transmission.

On another topic with a lot of help, I realise that the power provides by the motor is crucial to generate the output torque and angular velocity that your system requires. No matter the radius, ratios or N of teeth of the spur; if the power isn't enough, the gate won't move at the desired velocity.

So, the problem in question:
My goal is to find out if this system will be able to move a gate of 600 kg with a velocity of 0.33 m/s, and how much time it will take to reach that velocity.

The technical data of the motor is:

P = 1/2 hp ; RPM = 1450 ; 220V/50Hz

SECTION A:

P = 0.5 hp = 373 (kg * m2 /s3)
Pin = Tin * win

win = 1450 rpm = 151.84 (rad/seg)

Tin = 373 (kg * m2 /s3) / 151.84 (rad/seg) = 2.456 N*m

This, of course, is in an ideal situation, without considering losses. (how can I add an estimation of electric motor losses?)

The worm/spur system has a gear ratio of 23:1.

Considering the efficiency of the system of 80%, we have:

Tout = 23 * (0.8 * Pin) / win = 45.2 N*m

Now, Tout also can be calculated by Tout = 0.8 * Pin / wout

angular velocity applied on the spur is:  wout = (0.8 * Pin) / Tout

wout = 0.8 * 373 (kg * m2 /s3) / 45.2 N*m = 6.6 rad/sec --> 63 rpm

To consider real circumstances, its the moment of inertia has something to do within this case? I mean, is this Tout enough to accelerate the spur to 63 rpm??

SECTION T:

In this section, I'm wondering what happens with force transmitted in the distance "d" to the pinion. I'm not sure if I need to consider losses in this section.

SECTION B:

Here I have a lot of question about what's happening.
The Pinion has 17 teeth and is module 4.

From gear design, I understand that module, and axial pitch determines the Lead and lead angle of the gear. This has a direct relation with the surface contact (involute) in the system and frictional forces.

Is the torque Tout the same as calculated for the worm/spur system? What about the radius of the pinion? If I increase the radius, the Torque will increase as well?
The radius of the pinion is = 0.025 (m)

Tout = F * r

F = 45.2 N*m / 0.025 m = 1808 N

Does this mean that the force applied to the rack is 1808 N? Is this force enough to accelerate until 0.33 m/s?

F = m * a = 600 kg * 9.8 m/s2 = 5880 N ; here I need to consider a friction factor according to the wheels and ground. (0.1)

F = 5880 N * 0.1 = 588 N; this means that I need to generate 588 N force to move the gate, but what about the acceleration? if the gate has 4 m, how much time will take to reach the 0.33 m/s

I need a last push to understand this system entirely.


texts: How is the neutron capture cross-section increased in thermal breeder reactors?

texts:
The related Wikipedia article says:

  A breeder reactor is a nuclear reactor that generates more fissile
  material than it consumes. Breeder reactors achieve this because
  their neutron economy is high enough to create more fissile fuel than
  they use, by irradiation of a fertile material, such as uranium-238 or
  thorium-232 that is loaded into the reactor along with fissile fuel.

Thus, a breeder reactor somehow solves, that the thermal neutrons in it create equal or more $^{239}\rm Pu$ (by the neutron capture of $^{238}\rm U$, which decays to $^{239}\rm Pu$ in two steps), than the fission (of $^{239}\rm Pu$ or $^{235}\rm U$) wastes.

Now my question is, how do they reach this?

In a thermal reactor, the neutrons are thermal (i.e. their kinetical energy is roughly the same, than the medium around them). Thus, also the cross sections for neutron capture are roughly fixed. And these are far smaller, which would be required for breeding (as far I know, roughly half of it).


texts: Adding an R2R Digital to analog converter inline with TRS connector

texts:
I am trying to create a simple R2R DAC, maybe 8-16 bits.

I want to be able to that type of DAC inline to a headphone line.

Since the an 8 bit R2R DAC will need 8 pins, how exactly do I wire up a TRS connector to that?

Do I have to put an analog to digital converter inline first?

3.5mm TRS analog audio player output ->
[create analog to digital output] ->
[apply the digital signal to my 8bit DAC] ->
output to 3.5mm TRS analog


texts: How to create a mechanical equivalent to dropping object onto steel floor

texts:
(I was informed on the Physics board that this is an Engineering question, therefore they closed it there, and I moved it here)
First, I have next to zero formal physics training... I opted for all math & electronics electives back in my 1970s high school curriculum.
Goal:
My goal is to create a replacement for a "vertical drop test" by accelerating an impact mass in the horizontal plane.
The existing Vertical Drop Test machine that I want to replace drops a small product 1 meter onto a steel plate, but the orientation of the product is not predictable, and it needs to be.
By creating a Horizontal impact machine to substitute for the vertical drop, the product can then be pre-positioned on the machine so that the impact happens at a precise location on the product being tested.
My main challenge is understanding how to calculate what mass to accelerate at the "product", and at what velocity.
My example follows:
Assuming the object being dropped vertically is a 100g solid plastic ball.  I calculate the impact speed of a 1 meter vertical drop to be 4.429 m/s, resulting in 0.98 J kinetic energy.
On my proposed horizontal impact machine, I would have the same ball resting on a horizontal shelf (without constraint), and impact it horizontally with a given mass/velocity. The "ball" will then move away from the point of impact, just like it would bounce when dropped on the floor.  If that horizontal impact mass is 250g (with essentially no deflection) moving at 2.8 m/s (which is still 0.98 J Kinetic Energy, I believe), are the impact forces equivalent to the vertical drop regardless of the "give" (deflection) the "plastic ball" may have?
I know that if the "ball" were stationary, and I moved an infinite mass (the floor) up towards the
ball" at the same speed as the ball being dropped vertically, the impact would be the same. (right?)
If I use a lower impact mass, I would need a higher velocity to equate to the same impact Force, is that correct?
Does the impact mass need to be many times (10x or greater) the mass of the product being impacted, in order to cause the equivalent impact Force?
I love to learn, but again, my physics background is minimal... I'd appreciate any lay-language help, with formulas (or even a link to a web site with a calculator for such a problem).
/edit/
A bit more "detail".  This is for testing watch buttons... it's called a "Button Focused Drop Test", and is not an ISO regulated test.
The problem with the "normal" way of performing this test, is that the machine releases the "sample" as it's falling, but well before it impacts the target... which in this case is a steel plate. The watch almost always tends to "tumble", making the impact point/position unpredictable. In addition, when watches are "square", and have multiple buttons on a flat side are tested, it's very hard to isolate a specific button. Also... once it's dropped and impacts the steel plate, it bounces elsewhere, possibly incurring additional damage not related to the initial impact.
If the watch is laid on a horizontal "shelf", and the impact device is pre-aligned so that the impact position is precisely controlled, and once the impact occurs it falls into a padded receptacle, the initial impact is all that happens... and the results are extremely predictable.


texts:
I used to calculate the power needed by a pump using Bernoulli equation,

$ W =(p_2-p_1) + {1 \over 2}\rho(u_2^2-u_1^2) + g\rho(h_2-h_1) + R $

where $\rho$ is fluid density (and assuming it is constant), subscript 1 is inlet, 2 is outlet, $p$ is pressure, $u$ is speed, g is acceleration of gravity, $h$ is and $R$ are pressure drops (see EDIT2).

In this formula fluid properties are represented by $\rho$. What will happen if I change the flowing fluid? e.g. water for mineral oil.

With water, I need more power than to flow the same amount of mineral oil, due to its lower density.

How this assumption could be right/complete!? Since does not appear the property of viscosity of the fluid anywhere and that's just the resistance of a fluid to the deformation/movement?

EDIT1: fixed the Bernoulli formula; add $\rho$ assumption;
EDIT2: clarify $ R$ term:  since we are talking about a pump, losses are lumped, not distributed, we are not talking about losses in a pipe, thus they are not Reynolds dependants. Thus $R$ does not depend on fluid properties but relies only on inlet/outlet pump geometry;


texts: A Variable Valve Timing (VVT) engine with exhaust GT added, with and without Turbo Charger applied to the crankshaft?

texts:
This topic is the follow-up to the original topic:
Why are turbo compound engines not more widely used?
Why are turbo compound engines not more widely used?
Please, do understand that I am a pure dilettante, and I ask these questions to understand more about modern trends with Internal Combustion  Engines (ICEs). I upfront apologize for my ignorance, and maybe mechanical conceptual errors.
According to what was said and written there, I tried to find answers to the following questions.
The original lines which initiated these questions:

So when you design an engine you have a few
choices. For instance, you can either increase
engine efficiency, or sap energy from the exhaust
line. If you employ variable valve timing, for instance,
you can extract much more of that exhaust energy
and put it into the crankshaft without a turbo. If you
instead add a turbo, you've added another set of
gears, more moving parts, taken up more space,
and added more weight.
Now the turbo might be slightly better at extracting
energy than the variable valve timing, but does it
offset the additional cost, weight, and reliability?

[1] Why not employ a variable valve timing engine with the addition of the turbocharger?
The rationale behind this will be that the combustion is almost ideal, so even more exhaust gas energy will be deployed to the turbocharger Exhaust Gas Turbine (EGT)?
[2] What about variable valve timing engine with EGT addition which directly applies additional momentum to the crankshaft (probably with the additional CVT gear mechanism in between a ICE and EGT, to synchronize the effort of the ICE engine + EGT)?
This is the one with EGT without turbo charger, rather to use all the EGT energy as mechanical energy (I could not find this patent, and it should be somewhere)?
Furthermore, no (google search) evidence that this one was ever used in the automotive and truck industry?!
[3] Seems that [2] is somehow cheaper than [1], but with a few percentage less efficiency... Is this a known fact (pointing to some papers proving such a hypothesis)?
Thank you all very much in advance,
Zoran


texts: Ethernet to serial converter using TM4C129EXL

texts:
I need help regarding the lwip stack with tiva c, I am building UDP to serial converter, the function is working correctly, but I have some concerns:

When I receive the UDP packet buffer, I directly echoed it back if UART  is busy sending the previous UDP, is this correct because I am not sure what is the type of the allocated buffer?
When UART is not sending, I put the data on array and send it to the UART function, is there any other efficient way to perform this ? i.e using ring buffer or any other techniques?

the code for udp callback function for receiving packets:

void Udp_Receive(void *arg, struct udp_pcb *pcb, struct pbuf *p,
               struct ip_addr *addr, u16_t port)
{

uint8_t *pui8Data;
uint32_t ui32Idx;

//
// If packet more than 128 bytes drop it
//
if((p->len) > 128)
  {
    pbuf_free(p);
    return;
  }

//
// check UART and if it is sending just echo the UDP
//
if(uart_status == 1 )
{
       //
       // Send the echoed message.
       //
       udp_sendto(pcb, p, addr, 1234);
       pbuf_free(p);
}
else
{
    //
    // Received Packet information and send it to serial
    //
    udp_length = (p->len);
    pui8Data = p->payload;
    udp_to_serial_counter++;
    //
    // clear the payload array to receive new one.
    //
    for(ui32Idx = 0; ui32Idx < udp_length ; ui32Idx++)
       {
        udp_payload[ui32Idx] = 0;
        }
    //
    // fill the payload from buf into the array
    //
    for(ui32Idx = 0; ui32Idx < udp_length ; ui32Idx++)
       {
        udp_payload[ui32Idx] = pui8Data[ui32Idx];
       }

    pbuf_free(p);
     //
     // Allocate a new pbuf for sending the response.
     //
     p = pbuf_alloc(PBUF_TRANSPORT,udp_length, PBUF_RAM);
     if(p == NULL)
     {
         return;
     }
     //
     // Copy the the received  packet payload into  the udp_payload
     //
     p->payload = udp_payload ;
     p->len = udp_length ;
     //
     // Send the echoed message.
     //
     udp_sendto(pcb, p, addr, 1234);
     pbuf_free(p);
     set_uart_send_status();

}

The uart send function is :

UARTSend( uint8_t *pui8Buffer, uint32_t ui32Count)
{
    // Loop while there are more characters to send.
       while(ui32Count--)
       {

     while(!(ROM_UARTSpaceAvail(UART6_BASE)));

     ROM_UARTCharPutNonBlocking(UART6_BASE, *pui8Buffer++);

   }
          while((ROM_UARTBusy(UART6_BASE)));

}


texts: So in my bachelors and throughout my engineering degree, we did everything in MATLAB. But I've heard that many companies use python over matlab. Trying Python out for myself, it seems harder to use in every way; you have to load in modules while in MATLAB they're included by default, plotting is not included by default, indexing starts at 0 (okay cool, but why?), there is no transfer functions by default, and there is no nice way of carrying everything over between MATLAB and something like SIMULINK... So MATLAB pretty much seems superior in every way, why do so many companies apparently use Python instead?


texts: I have seen many times that people gets the frequency response function using DTFT. Can I use the Fourier series, and when I do that?


texts:
I am studying this problem:

  The rigid bar ABC shown in Fig. P-212 is hinged at A and supported by a steel rod at B.
  Determine the largest load P that can be applied at C if the stress in the steel rod is
  limited to 30 ksi and the vertical movement of end C must not exceed 0.10 in.

So the solution is:

QUESTIONS:
1. Why is the elongation distribution in the length of the beam a triangle?
2. Why is the elongation $\delta_{st}$ computed as the elongation in the cable?

Can somebody please explain the solution?


texts: Can isotropic materials become anisotropic under elastic deformation?

texts: Are there solid materials that begin as isotropic materials (i.e. isotropic elastic parameters) in their natural (i.e. unstressed) state, but that become anisotropic under sufficient stress/strain?  What would it take to modify an existing material with isotropic elastic properties to have anisotropic elastic properties?


texts: So I’m driving down the highway in my sedan on a speed of lets say 60 mph. Why is it that my car sways just before it passes or it passes me? Almost always where the semis first tire is (closest to the hood)? What forces are acting upon it? What could be a possible explanation to why it happens? Why is it only at that spot that the car sways?


texts: Meaning of a symbol for a hole specification in a drawing

texts:
A very simple question, so sorry for this, but I have searched many online docs and cannot find a simple answer. I have a hole specification of 3.4 + 0.13 (picture attached).
What does the +0.13 mean?
[


texts: rotating mirror system for shifting a beam?

texts:
I am looking for some mirror setup where rotation one or more elements in the mirror setup will allow to shift the beam along its axis.

Two mirrors in a galvanometer scanner type setup work well for controlling the angle of the beam.

Rotating risley prisms can be used to only offset the beam without changing its angle but the possible positions are limited.

Dove prisms are great for rotating the beam along itself or rotate in a circular fashion if prism center is shifted.

But as for offsetting (shifting) a beam along its axis from a (-1,-1) position to (1,1) without changing the angle of the beam, I can't find any setup which involves a rotating mirror rather than shifting mirror. But I feel there may be something missing from my limited optics knowledge.

4 rotating galvo scanner mirrors may do this but this may be an overkill and the size of the mirrors on the last two will increase to impractical sizes for decent 45 degree FOVs or more. So I'm crossing this one out.

In case not clear, https://i.imgur.com/3qkvRpS.jpg


texts:
I am trying to understand how to turn a basic click button into something that behaves like a pressure sensitive button, meaning the harder you press it the greater the value.

There are PWM modules that you can use to get different current but I am thinking of something like a button.

Could I do this with a micro-controller, a click button and some software or are there special buttons that do the job and send signals in a range based on how hard/ fast it's pressed?


texts: Is hydrostatic pressure a dead load or a live load?

texts: I have a structural analysis question.  I want to know if the hydrostatic pressure in a water tank is a live load or a dead load and why?


texts: Evaluating performance of heat sink designs without finite element simulation

texts:
I have the opportunity to do a few metal 3D prints for just the material cost, and would like to experiment with the performance of heat sink designs (mostly for fun).

Since I have no experience designing heat sinks, I would say that the expected failure rate when just printing what I have in mind and testing it will be quite high, so I need a good way to evaluate the performance of a design before creating a prototype.

Now since this is just for my fun, I do not want to invest in pricey finite element simulation tools. I could not find anything free that is useful, since I think it has to take into account airflow and thermal radiation. How can I get an idea of how my design will perform before printing a prototype and without using finite element simulation?

I am planning on a 4 cm by 4 cm 120 W Peltier element (ceramic surface), the heat sink should be  stainless steel, though I am hoping the relative performance of two heatsinks doesn't change with a different material (one day I hope I can use copper).

I am not so sure about temperature differential here but I am assuming 25 °C ambient temperature.


texts: Room with computer racks, with or without ventilation

texts:
I have a room of computer rack that with 2750 watt power needs, which according to this site, I need 9000 BTU/h AC. I'm deciding if I should put a vent in the room or not. When there's a ventilation, it will look like this:

Note that there are two wind turbine ventilators on the roof. Also the attic is cool because of the good air circulation.
Question for this scenario:
1. Will the AC and the grill vent vanquish the humidity from the air outside, which is warm and humid?
2. Will dust enter the room via vent despite the fact that the airflow is upward to the wind turbine ventilator?
3. Is 9000 BTU an optimum number? Is it too much or too little? I'm thinking most of the heat is drawn to the vent.

The second scenario will look like this:

In this scenario, instead of a ventilation with a chimney, there is a ducting that caries heat, which escapes to the attic and goes to the wind turbine vents. Question:
Will this give faster heat reduction whereas there is no way humid air will come to the room?

regards


texts:
In an assignment we had to build a Clock D-Latch and give the boolean function and the truth table for the states $Q_1$/$Q_1^*$ and the following states $Q_2$/$Q_2^*$.

The latch looks like this:

I've got the functions but I don't know how I proceed with the truth table for the states $Q_2$ and $Q_2^*$.  At first I thought I could just replace the $Q_0$ in the boolean function with $Q_1$ and could calculate the states, but that doesn't work.

Functions are: $Q_1 = Q_0^* (D+ {\sim}CK)$ and $Q_1^* = {\sim}Q_0^*({\sim}D + {\sim}CK)$ where $\sim$ means not.

To be more specific: With $Q_0 = 0$, $D = CK = 1$ we get $Q_1 = Q_1^* = 0$. But the state two is $Q_2 = 1$ and $Q_2^* = 0$. I don't understand how we get from 0,0 to 1,0?


texts:
We've been given a DWG file from a topographic survey of our garden. It looks great but when I try to measure dimensions of objects in Autodesk I know the real world size of, they're off by a factor of about 6 which means I cannot actually use it.

Here in the UK I would expect everything to be in metres but how can I check, because something seems screwy?


texts: How to achieve Bi-directional Clutch Transmission

texts: I understand that Clutches are used as One-way Clutch. Any idea on something where clutch can be used for bi-directional rotation. I mean allows input torque transmission to output in both CW and CCW direction but it stops transmitting from Output to Input. Basically to prevent Back driving of Prime mover due to external load on the Output side?


texts:
I've been studying mechanical simulation with nastran/patran, nowadays.

I knew weight density is used in imperial unit system, instead of mass density.

I feel using weight density is tedious, because I have to put a conversion factor to change weight density into mass density, when I perform dynamic simulation, always.

I just had used SI unit in my whole life, so that I don't know which advantage there is in using weight density, compared to using mass density.

Could anyone explain why weight density is used in imperial unit, instead of mass density?

And then, what is the advantage of weight density, compared to mass density?


texts: How to calculate what size steel RHS to use?

texts: I am welding up a rack to support a distributed load of up to 1000kg, what is the process to work out what steel section size I should use? Many Thanks.


texts: calculate torsion in a diffrent sized shaft

texts:
first of i know it seems like a homework assignment but it does not, it is calculations i need to do at work and it has been a long time since i studied this material. so I need help to calculate if a given clutch can handle a given torque but I'm not sure if my calculation are right.
what I did so far

on the left there is a motor on the right is the cluch with a connector.
ive build a FBD:

and ended up with this eq:
$$\tau_{max} = \frac{T*r_1}{J} = \frac{2T*r_1}{\pi*r^3}=\frac{2*2.5}{\pi*(6.05*10^{-3})^3} = 7.2 [MPa]$$
but I don't know if this is the way to calculate and I don't know how to calculate if the point connecting the two diameters is strong enough.


texts: I have one tile that came off. I got a replacement tile, and some grout. But the online guides say you need mortar to glue the tile to the ground. Can I use the grout as mortar? I want to save money so I only want to buy one thing.


texts: When NOT to use Bessel's Correction for Standard Deviation

texts:
I can not find a clear explanation for when NOT to use Bessel's correction and use N instead of N-1. As I understand it, Bessel's correction would apply to things such as clinical trials, sampling from a production line, voter polling, etc.

I am performing an experiment analyzing mass flow rate into 3 entry points. I want to analyze the deviation of the distribution into those 3 entry points and compare it to an ideal perfectly even distribution of a (relatively) known mass.

I believe I know the "true population mean" in this circumstance - its an even distribution so if I reduce everything to percentages, it would be X = 1/3 = 0.333. I believe I need to use N instead of N-1.

The complicating factors are that while I think I know the starting mass for the experiment, my scale has an instrument error associated with it. Also my measurement of mass flow rate versus time has multiple measurement instruments associated with it as well!

I guess if I boil down the question.... I need to figure out if I need to use N or N-1 for standard deviation. Does the error inherent to the measurements necessitate N-1 or does knowing my "ideal distribution" allow me to use N?


texts:
I have 2 questions related to NASA CEA's Isp values in the output file.

When looking through the output of NASA's CEA tool, I am trying to understand the difference between its "Ivac" output and its "Isp" output. What is the difference between these two outputs?
While the concept of a vacuum Isp makes sense to me, I don't understand why it is output in the context of  the inputs I put in; I gave the CEA code a finite value Pc/Pe number, meaning Pe was not 0. So what is Ivac mean in this context?


texts: What are the governing equations solved in FEA for structural mechanics?

texts: In CFD we focus on the NS equations as the governing equations (together with other equations) and solved them using Some numerical method (usually FVM). What are the governing equations (counter parts of the NS equation) in solid mechanics?.


texts:
I posted this question on electronics SE, but was suggested that I post it here.

I basically having three heaters (serpentine pattern) on a PCB (fiberglass board), as the following image shows:

The ones at the end would be heated to 95°C, the ones next to it at about 50-55°C, while the middle one to about 72°C. They are spaced 0.3mm apart.

The problem is because the 55°C heater is between heaters with higher temperatures, the heat gets transferred onto that area and goes well beyond 60°C, which I'm not able to control.

I tried removing the area between the heaters to see if it would help somehow, but the problem persists.

What can I do to "confine" the temperature to the heater area?


texts:
I would like to take a deep dive into the world of jewel sourced watchmaking components (including, but not limited to, bearings) but I am having trouble finding any textbooks on the subject. Are there any watchmakers/horologists/jewelers who can kindly point me in the right direction?
This all started when I decided to design a very tiny rolling scotch-yoke mechanism & thus required an equally tiny bearing. Here is a figure showing a regular & rolling scoth-yoke on the left & right, resp.

The only jewel bearings I have found are optimized to be fixed externally s.t. an internal pivot can freely rotate within its bore. I want to know if there are any other jewel sourced components optimized for my immediate use, or any other future uses I might have.


texts: What's the difference between Strain tensor and deformation gradient tensor?

texts: Why do we need to define the strain tensor if we already have a tensor that describes the deformation between relative particles in the continuum which is the deformation gradient tensor?


texts: Using a controller to remotely alternate the direction of a peristaltic pump

texts:
I am working with a peristaltic pump to move liquid to/from a reservoir through a closed loop of tubing. The motor can rotate clockwise or counter-clockwise when set with either of the directional buttons below.

The direction of rotation can also be controlled remotely using contacts #1/2 in the green barrier strip below:

I have little experience with this kind of work. Would this be a simple enough task to connect, program and use a controller to alternate the direction of the motor for some time interval?

Even if someone could describe the process for me in simple terms, it might be helpful in my understanding of how to approach the challenge.


texts: How to add a controlled amount of a nutrient solution to a water line

texts:
I have an existing water supply system for the cattle on my farm whereby 6 troughs located in different fields are all fed from a common header line.
The pressure in that line ranges from 3-5 bar (It’s well water supplied from a submersible pump).
Water is supplied to each trough based on the water levels using a mechanical ball-cock system.
Currently I need to visit each of those 6 troughs each day to manually add a liquid mineral solution (to provide extra nutrients to the cattle at this time of year).
That solution comes in the form of plastic drum.
Currently I distribute about 350ml of that solution in total daily which covers 60 cows

I would like to automate this process in some way so that I can feed the solution directly into the header line.
What would be the best way of doing this to control the supply of the nutrient solution?
I only want to add the solution when there is flow in the header line.


texts: Can the critical buckling load from non-linear FE calculation be higher than the one from linear?

texts:
Let's consider a FE buckling calculation without plasticity.

Is there theoretically any chance that the non-linear analysis will give a higher buckling load than the linear one?


texts: Do all structures deform if put a load on them?

texts:
Suppose I have a concrete wall in front of me and I push on it, now it seems that I do work and the energy has magically disappeared.
I am trying to figure out how this works, the explanation I thought for it is that the wall compresses just a little (similar to how a spring does) and my energy gets stored in increasing the energy of the structure of molecules of the wall. Now, the molecules want to go back but I simply can not observe them because the magnitude of the oscillations are that low.
For the above analysis to be correct, I need that that all bodies are necessarily compressed by some amount when put under a load. Is this statement true? In sense has there been studies on this?


texts: Strength of a welded steel gate with vertical bars vs. crossed diagonal bars

texts:
Looking for some hints on how to create a rough estimate for the following problem.

Given two steel gates with the same dimensions, same material - e.g. everything is the same.  The only difference is that the middle parts have different structures.

When applying some force to the top, the gate will start to be more and more deformed, and at some force the gate will touch the ground at the place where the blue arrow points.

I'm looking for a rough estimate of how much more force is needed for the second gate - i.e. how much more "sturdy" is the second gate.

I really don't need any exact calculation, but probably will need some material data, so:

common steel thin-walled beam (25mm x 25mm x 2mm wall thick)
each joint point is welded, we can be simplify and assume that the welds are exactly as strong as the material itself
the suspension points can hold infinite force
and any other possible simplification - this problem isn't for any rocket-science but for solving an evening talk with a friend.


texts: How to calculate the coupler length in a crank rocker mechanism

texts:
I'm trying to learn a bit about building kinematic mechanisms by building a small project. The goal is to be able to open and close a box programmatically via a servo motor.

I have a small box that I've reproduced in fusion 360 and I'm trying to design a crank rocker mechanism to open and close the box. After reading up on the crank rocker concept (I have no background in engineering so I'm brand new to all of these concepts) and building a couple of free standing proof of concepts (I put them up on thingiverse) I tried to start fitting the linkages into the box model.

The issue I'm running into is that, given the size constraints of the box and the length of the servo's horn, I'm not sure how to calculate the correct coupler link length.

I know that according to grashof's law I need to make sure that the sum of the shortest and longest links are less than the sum of the other two links; $s + l < q + p$.

I started by modeling the rocker arm ($q$) first so that I could figure out the length of the sliding slot (not sure what to call this) I would have to add to the lid so that the arm could actually open the lid. I placed the points for the rocker arm on the box and the lid so that there was room for the rocker arm to move without hitting the back of the box when the lid was fully opened, so it was kind of an arbitrary placement choice.

I already know the length of my default servo horn so I was going to stick with that (though I can 3d print a new horn if necessary).

I figured that between:

The positioning of the servo and the bottom of the rocker arm (making the grounded link $p = 55.228mm$
The length of the rocker arm $q = 60mm$
The length of the crank arm $s = 25.53 mm$

I could just calculate the length of the coupler arm ($l$).

$$25.53 + x < 55.228 + 60$$

The part that I'm not sure how to figure out the correct X value. It seems like, if I understand all of this correctly, I have a range of values I can pick from and the top of that range is $89.698 mm$. I know that the bottom of somewhere around $68.081 mm$ (I don't actually know the proper way to calculate this, I just closed the lid on my model and measured the distance between the end of the servo horn and the top of the rocker arm :| ).

I know I can figure it out by noodling around with the coupler arm length until I find one that will let me fully extend the lid, but I'm trying to use this all as a learning exercise/introduction into these concepts.

Is there a way of determining the ideal coupler length?
Am I even right on the way that I've approached it so far?
Am I missing anything super obvious?

Thanks in advance for the help!


texts: Why does removal of ventilation of a sewage pipe lead to backflow from the toilet?

texts:
A building where three toilets (toilet + urinal each) are connected to the same sewage pipe under the building. The pipe is DN 100 and should have (according to old plans) a gradient of 1:50. Two floor drains are also connected to this pipe. It empties after a few meters into a DN125 sewage pipe that collects the water from a dozen showers. This empties after 6m or so in a larger pipe outside the building.

The branch of the network near the toilets hade a ventilation pipe straight up through the roof, that was errouneously removed during recent refurbishments.

Since then, at certain shift changes when the toilets and showers where heavily in use, the floor drain overflowed and sewage from the toilets flooded the area. The whole network was checked with cameras. There's no blockage, only a slight sag near the toilets. It was observed that when you flush a toilet, the urinal in the same stall by will empty partially.

In the same building, in a nother branch of the sewaer pipe network, the ventilation pipes where removed also. Here, we have a lot of pipe upstream of the toilet and so far no problems occured.

Now, our assumption is that due to the removal of the ventilation, we have this backflow problem. I want to check if my reasoning here is correct & if we are not solving the wrong problem by installing a new ventilation:

When flushing the toilet, I have a plug of water in the pipe and an area of underpressure behind until air can pass over this plug.
When the, downstream of the toilets, the pipe is relativly full because the showers are in use, the water from the toilets flows off slower and the time till equalization is longer
Hence backflow and overflowing floor drain


texts: Can the hysteresis phenomenon be considered as a (type of) friction

texts:
I was wondering whether the hysteresis (in particular, mechanical motion systems) can be considered under the class of friction.

From theory, I know that the frictional forces are direction, and velocity dependent. In the same sense, they also possess memory in the special cases of frictions. So, is it correct (without abusing any definitions) to consider the hysteresis observed in motion systems to be under the class of friction. Because the hysteresis in motion systems also characterises the same characteristics.

Simply put, under what conditions one can classify the hysteresis under the frictional nonlinearity, and if not, under which conditions this fails to do so?


texts: Do longer gun's barrel improve accuracy?

texts:
I have been reading a lot about guns in Wikipedia. I know much of the terminology of firearms. However, I was wondering why some firearms such as shotguns and rifles have very long barrels opposed to small handguns such as revolvers and pistols, that normally have shorter barrels.

I know, there are functional differences between the types of weapons I described: Shotguns normally shot shogun shells with pellets, Rifles have "rifling" inside their barrel, pistols are made to be held with the hand without shoulder support, revolvers have a cilynder of cartridges that rotates. (This descriptions is rough and doesn't intend to be a very accurate defintion of every gun type).

Nevertheless, shotguns rifles and snipers normally have longer barrels than pistols and revolvers (althought there are handguns with long barrels).

Here there is an article about the subject

The question is:
What advantages and disadvantages come with differences in length of the barrel? And does a longer barrel improve accuracy?

I have made up some hypotheses. I list them here. :

-Longer barrels are used for higher explosive ammo because the barrel can contain the expanded gases and made them push the bullet over a longer barrel, giving the bullet more energy.

-Longer barrel means the sight is further and thus one can make more precise shots because the two aligning marks are further, and thus in order to seem aligned to the eye they have to be in "more aligned" than with a shorter barrel.


texts: Is Matlab old versions usable with Win 10 on core i3

texts: About Matlab (a software very useful for engineerinng, too), Is "Matlab 2008" or "Matlab 2012a" usable on laptop with core "i3" with "Win 10 Home"?


texts: What's the most cost-effective cutter bit material that can be used to machine aluminum oxide?

texts:
Al2O3 is a hard, white material used for making firebricks and numerous molded ceramic parts.

Say I had a firebrick, took a core out of it using a thick-walled diamond hole saw and a drill press.

What lathe insert material would I then use to machine the outside of the Al2O3 cylinder assuming I could take care of all the holes using diamond hole saws?

My budget for one cutting bit would be $500.  But that would take me many hours of work to raise, so I prefer something less expensive, since I'm probably going to break it, hence cost effective.


texts:
I need help to figure out the torque needed by a motor to lift an arm with fixed weight at the end like in the picture....

Where the green circle is the fixed motor and the arm is welded to the motor shaft and the movement is only 90 degrees goes from vertical to horizontal.

The arm length is 55cm, arm weight is 4kg and the fixed attached weight is 13 kg

I wanna know what is the torque (n-m) required to rotate the arm from a vertical to horizontal position.


texts:
What is a Butterworth filter?

I have raw X, Y, Z acceleration sensor data that I need to smooth them from noise. I have read that a Butterworth filter is one of the most appropriate for the specific kind of job I am working on.

Is that filter being applied directly on the raw data (time-amplitude domain) or I need to translate the data to the frequency-amplitude domain (using FFT)?

Is IIR any kind of a Butterworth filter?

What do I make with the result from that filter? Do I multiply it on my data in order to filter them out?


texts: Transient overvoltage protection by varistor

texts:
Using a varistor is a common practice  in alternator excitation system. It is used with rotating rectifier diode.
Is it used for transient overvoltage protection?

Is it protecting diode or rotor winding.
How this overvoltage may occur?


texts:
I have a question that goes thus. At what angle $\theta$ must the $500N$ force be applied in order that the resultant $R = 1000N$. For this condition what will.ne the angle $\beta$  between $R$ and horizontal
I got
$ \theta =97.9^\circ$ and $\beta=34.1^\circ$
But I'm not sure that's rightly done. I need help with verification of result

Here's my solution


texts:
While building the foundation of a house, the concrete columns were built 15cm (6 inches) from the planned position, which is reducing the space for a door.

The position that should have been there is shown below. But, C2 is shifted to left by 6 inches, and the column shown at the bottom of pic is shifted 6 inches to right. This leaves no space for the door to be placed as expected. Need a workaround.

In below pic, the upper column is shifted to left by 6", and lower 6" to right, leaving just 2'6" for door rather than required 3'6".

So we need to shift the column by 6 inches. How to do it? It's built up to the ground level only yet, and beam isn't  built over it.


texts: Flux Cored MIG on unknown steels, what is this stuff?

texts: Welding on some unknown Steel, I made the weld, and this stuff formed. It looks like a fast shutter speed shot of smoke or something for me but it's a solid material that has formed. It almost seems like millions of little Fibers at all flowed along with the hot air and gases coming off the weld. Has anyone seen this stuff before and does anyone have an idea what it is?


texts: How do I get the closed-loop transfer function of the system, fitted with a PID controller, if the input valve has a transfer function?

texts:
How do I get the closed-loop transfer function of the system, fitted with a PID controller, if the input valve has a transfer function given by:

$ \frac{Q(s)}{P(s)} = \frac{Kv}{(Tv*S+I)} $

Where Kv is a constant of proportionality between the steady-state discharge and the pressure on the input valve. Tv is the time constant of the input valve.

I'm not sure how I'm meant to use the input valve transfer function to work out the closed-loop system transfer function.

Could anyone help explain the steps?


texts: Calculate the specific surface area of a mesoporous sample

texts:
I'm a nanoengineering student who's been stuck on the following problem for a few days. I've gone back over my professors slides, watched podcasts from an old professor, etc. etc., but don't understand it any more than I did when it first came up. All I know is that it deals with the BET Isotherm, which there isn't a tag for...

Calculate the specific surface area of the mesoporous sample described below.
Assume the effective cross-sectional area of one N$_2$ molecule is 0.18 nm$^2$, and 1 mole of gas occupies 20 L at standard temperature and pressure.

I'm then given the following graph and table:

I'm not 100% sure where to start, so I just have the following equations from my notes written down:

slope (m) = $\frac{c-1}{cN_m}$

y-intercept (b) = $\frac{1}{cN_m}$

$c-1=\frac{m}{b}$, $c=\frac{m}{b}+1=e^{\frac{\delta H_{des}-\delta H_{vap}}{RT}}$

Area (A) = $N_m*N_a*A_0$

$A/m=$ specific surface area.

Where Na is avogadro's number, A0 is the N2's surface area, and m is the mass of the nanoparticles.

Thanks so much for your help!


texts: Translation of vibrational motion in the 15-20 Hz range

texts:
Is anyone familiar with how to create a "shaking" fluidized bed. With vibrational amplitude in the 2" range and Hz 15-20?

I'm constructing a vibrational fluidized bed dryer for the purpose of drying shredded coconut. This machine, as far as I can tell, is generally a continuous process - however my team and I are trying to construct a batch type system.

We have two 1/2HP vibrating motors running of a VFD, mounted the the rigid frame at the center of the machine, which is attached to a series of 6 springs - 110 lb/in, 7n, 6" coils evenly spaced throughout the structure. We have had success translating the motion evenly in the 40-50Hz range to achieve a fluidized bed. But it's our understanding that the fluidization will be superior in a shaking system. However when we run tests the coconut consistently goes to a certain side, depending on the vibrational force settings and the exact Hz.

Is it possible to translate this motion to the purely vertical plane and keep this amplitude consistent while still using springs? Or is a different dampening mechanism needed.

(Note, there are also about 20 15 lb/in springs added evenley throughout the structure to stablilize vibrations, are these necessary?)

Thanks!


texts:
Need confirmation for this question please: A pulley with Radius of 90mm and a mass moment of inertia 0.28$kgm^2$ about its central axis is subjected to a torque of 50Nm about this axis. What is angular acceleration of the pulley?
Soo, I did this: $\tau=I_o \cdot alpha$, therefore angular acceleration alpha= 50/0.28= 178.6rad/s^2??
Isn’t that number too high for a pulley please? What am I missing?


texts: Can Zinc/Aluminum coated anchor rods be used in concrete?

texts:
Bolts and anchor rods that are very high strength ($F_u$ > 150ksi) are not supposed to be galvanized.  This is because of concerns about hydrogen embrittlement. This includes ASTM A 490 bolts and ASTM A 354 Gr. BD anchor rods.

The project in question has very high lateral loads and is outdoors. Typical ASTM F 1554 Gr. 105 anchor rods end up being very large in diameter. This is why ASTM A 354 Gr. BD rods (2.5 inch diameter) are specified. There is no space for more anchor rods.

Since the project is outdoors, a corrosion protection coating is required. The only coatings that can be used are Zinc/Aluminum coatings such as ASTM F 1136 Grade 3.

There is a history of aluminum not being used in contact with concrete because of corrosion concerns. This seems to be specifically with solid aluminum.

Do I need to be concerned with the aluminum content of this coating reacting with the concrete that the anchor rods are embedded in?


texts:
How come axial compressors always narrow and turbines always widen towards the rear? From what I know:

The speed of sound of air increases with temperature, therefore increases (decreases) as it goes through the compressor (turbine).
The compressor and turbine blades at each stage should be meeting the air at just below the local speed of sound (more precisely critical Mach number).
The rotational speed of all stages of a given spool is constant.
The cross-section through which the air is flowing is $\pi(r_e^2-r_i^2)$, where $r_e$ and $r_i$ are the exterior and interior radii, respectively.

So shouldn't compressors widen and turbines narrow towards the rear, with the interior varying more than the exterior? And shouldn't turbines be much larger (~2x) than the compressors they drive?

You can obviously see civil engines don't look like this:

RR Trent 1000 (Courtesy of aviationgazette)

GE GEnX (Courtesy of www.mikejamesmedia.com)

Anything I'm not taking, or taking too much, into account in my analysis?


texts: Why does the tapered part of a Wing have such high coefficient of Lift?

texts: If we take a Trapezoid wing shape as an example and see that it has low $c_l$ near the root of the wing and very high $c_l$ at the tip. The Lift generated, however, is reversed to the that of the $c_l$.


texts: What happens when pumps are blocked off?

texts:
What will be the result if the pipe losses is greater than head produced by the pump?

What will be the result if outlet is closed?


texts: Wifi modulation and standard interoperability

texts:
I've been reading this summary(info.tek.com) of Wifi standards from Tektronix, which seems to do a pretty decent job of explaining things, but has left me with a couple of questions:

For access points that support multiple standards, how are the beacons transmitted? I would guess they use BPSK, but it's not clear whether this would be DSSS or OFDM (e.g. 802.11n devices don't support DSSS as far as I can see)
When both the access point and end device support multiple standards (b/g/n seems pretty common) how do they decide which standard to use? I guess they let other devices know what they support through broadcasts/probe requests, so do they just default to the one offering highest data rates?


texts: How can one make the beam angle smaller on an ultrasonic sensor?

texts:
I'm trying to create higher resolution data with a beam angle of 5> degrees (as close as 1 degree as possible). I have been experimenting with creating using an aluminum casing around the sensor input. Are there any other or perhaps better ways of doing this?
CH201 datasheet.