texts:
I am new to the field, most of the papers I have searched directly conduct CFD simulation but skipped the calculation. I hope to get an estimation by calculations.

I am designing a small scale horizontal overhead air curtain covering a 0.5m x 1m (Width x Height) area.

Assume no temperature, air density difference between inside and outside air, no winds or other kinds of draught. Considering an ideal case, and the air curtain is blowing vertically downward,

$b\times h$ = outlet cross-sectional area
$L$ = throw distance
$v_0$ = initial velocity
$v_L$ = velocity at $L$

Is there an equation or other numerical methods to determine the relationships between $b$, $h$, $L$, $v_0$ and $v_L$?
Also, is it possible to find $b_L\times h_L$ (cross-sectional area of the air stream at $L$)?
How to determine optimal outlet cross-sectional area $b \times h$?
How to determine optimal air speed vL? (to minimize leakage but also turbulence) (2.5-3.5 m/s for most of the currently existing products)

Are there any relevant considerations I should consider?

What references/sources would be good to read?


texts:
Enclosed within a consumer electronic, I would like to spin a small balanced load.  The device will be rotated relative to gravity, but no other direct forces will be applied to the load.  A coreless DC motor (e.g. often used for pager vibrators) will be used, but in contrast I would like to minimize noise/vibration.  Here is what a current prototype looks like:

If I just hang the bare motor by its wire leads and let it spin the balanced load, there is low noise/friction relative to the above assembly.  I believe this is because the above assembly adds rotation resistance via the shaft hole and acts as a 'vibrational conduit' to the motor.  However, because the device will be rotated w.r.t. to gravity, and the load is of moderate mass (2-4g), I think there will need to be some sort of shaft support to prevent radial play.  There are two basic designs I can think of to achieve this:

External shaft hole (as seen in above image)
Bi-axial motor (seen below):

The main criteria to decide between the two should be:

low noise/vibration
low axial/radial play
easy to assemble/difficult to incorrectly assemble

Given these criteria, it seems to me that using a biaxial motor is the way to go.  However, there is one catch: they are not commonly produced, and I can only find one source.  Furthermore, the only model I could find operates at 24V (vs typical 3.7V), which will require stepping up logic voltages.  So, if using a biaxial motor is indeed preferable for this application, would it be reasonable to expect a manufacturer to make me 'custom' biaxial 3.7V motors of quantity 5-10K?  If such a customization is not feasible for this relatively low order quantity, does it make more sense to develop a shaft support assembly for a uniaxial motor, or work around the non-ideal electrical characteristics of the 24V biaxial motor?


texts: Calculating estimated Overall Heat Transfer Coefficient

texts:
I have problem where I'm trying to determine the Overall Heat Transfer coefficient of a heat exchanger that uses the latent heat of vaporization of water in the process.
I know the Q value I'm trying to get to, the heat transfer area, and the temperature differences.
I'm aware the standard equations being used here would be
Q = UAT and Q = mcpT
for a normal heat exchanger, but I'm not sure how that works alongside vaporization.
Any help would be greatly appreciated - thank you.


texts: Inertial Forces while analysing forces on a Piston in a Slider - Crank Mechanism?

texts:
I get that we are analysing the Piston in a non-inertial frame of reference, but the point of my question is that according to D'Alembert's Principle, whenever an inertial force comes in the line of motion of the object the net Force on the body becomes zero and the body is in a state of Dynamic Equilibrium. But even then, we write:

$$F_{net} = F_p -F_f - F_i$$

where

$F_p =$ Force due to combustion/pressure
$F_f =$ Frictional Force
$F_i =$ Inertial Force

Due to the occurrence of inertial forces, shouldn't $F_{net} = 0$?


texts: Deformation gradient tensor from particle displacements in an inflating material

texts:
I don't have a mechanics background, but am trying very hard to read and understand how to approach this problem. I am struggling with understanding what's "correct" or the basic process of going from what I have to understanding the steps I need to take next.

Here is the system:
An initially flat material clamped in a circular aperture is inflated in a bulge test. I cannot use any of the common spherical cap equations (I've done this already, but am trying to move to a better measurement). The shape that is formed is more of a mountain-like shape and not a hemisphere. I also don't want to assume pure bending with a plate approximation, as the deflection reaches about 4-5 times the thickness. I think it probably undergoes an initial bending stage and then transitions to stretching. It definitely goes beyond the elastic regime as the material eventually ruptures.

I have 3D images that give me a view of the shape, as well as the x,y,z coordinates (and hence displacement vectors) of hundreds of particles embedded in the material as it undergoes deformation.

My big questions are below (note that I don't mention what I "need" yet because I am not sure how this problem is commonly approached):

1) First, what is the general protocol for tackling a problem like this? Is there a normal flowchart that people work through when they see a problem like this?

2) Is there a way to get stress field if you figure out strain field first? How do you go from strain to stress?

3) With respect to figuring out the strain field:  I have the displacement vectors for every particle throughout the experiment.

3a) Is it possible to get the deformation gradient F just using this collection of displacements? I don't know what function (if any) relates the coordinates of the point pre-deformation to the position post-deformation.

3b) Suppose I am able to get deformation gradient F. Just looking at F, all the information is in terms of the x, y, and z axes. But given that my shape goes from being a plate to a mountain, it doesn't seem like information in these three directions make a lot of sense in terms of "useful" information. Suppose I was curious about how much tranverse shear there is, or lateral shear, or just tension at different locations on the shape? But xz shear/xy shear doesn't mean anything if I have a mountain shape, right?

In that case, isn't it more useful to know the deformation gradient along a different axis oriented with respect to the important directions on the curved mountain shape?
Like, suppose at any point in this mountain-like shape, I decide on 3 local orthogonal axes - one that is normal to the surface, one that is pointing "up" the mountain, and one that is tangent to the circular contour: and then I somehow got the deformation gradient with respect to these three axes at any point:
Would this be meaningful in terms of answering my question of lateral/transverse shear on the shape vs tension?

Is this a stupid/wrong method?

I would be grateful for any guidance here -- even if I just know whether the direction I'm going in sounds right or would give meaningless information.

Thank you!


texts: Solidworks - parametric conical helix antenna on a dielectric

texts: I'm stuck half way through construction of parametric conical helix antenna on a dieletric. I have created the intersection line but I'm struggling to make it a planar surface on top of the conical object as shown in the picture attached. I also have attached the Solidworks file.


texts: Is it likely that a 3d printer will ever be able to print a copy of itself?

texts:
3d printers are still at a relatively basic stage and currently not capable of printing entire complex machines that require multiple materials. Is it possible that they will ever be capable of printing copies of themselves? Or are there essential components which probably will never be possible to print.

If essential parts cannot be produced directly, could machines to make them be produced by 3d printing?


texts: Required mass of wood to produce 20 Watts/Hour

texts:
Requirements:

I need to produce $20\ \mathrm{W}\,\mathrm{hr}^{-1}$ by burning wood.
The specific energy of wood is $21\ \mathrm{MJ}\,\mathrm{kg}$
Find the required mass of wood to produce $20\ \mathrm{W}\,\mathrm{hr}^{-1}$
Assume ideal conditions

What I tried:

$P=E/T$ where $P = 20\ \mathrm{W}\,\mathrm{hr}^{-1}$ and $T = 1\ \mathrm{hr} = 3600\ \mathrm{s}$, which yields $E=72\ \mathrm{kJ}$ when rearranged.

Now I know that wood has a specific energy of $21\ \mathrm{MJ}\,\mathrm{kg}^{-1}$, thus specific energy is $E/m$ where $E=72\ \mathrm{kJ}$ as found above, which yields $21\times 10^6 = 72\times10^3/m$.

Solving for $m$ gives 3.4 milligrams of wood. I appear to have missed something.

What have I missed?


texts: How can you calculate the torque and speed of a single output gear being driven by two different input gears?

texts: I am building a gearbox that needs to lift around 50lbs very rapidly. I already have a single planetary gearbox that does the job in around 7-10 seconds, but I would like to cut this time down significantly. In order to do this, I have heard that I should be using a gearbox with multiple input motors as this will be stronger. However, I don't know how I would calculate the torque provided or the speed with which the output shaft will be turning.


texts: Data logger via modbus hardware solution

texts:
I have 3 programable logic controllers and other one which isn't part of my solution but I can access usefull data via modbus. I've setup windows service on a remote server to gather data and store it in a SQL Server.
But the problem is if the Internet fails? So I'm searching for a hardware data logger solution.
I saw a schneider scadapack but I think it doesn't support modbus as client.
Everything I'm seeing is hardware with I/O for digital and analog input/outputs but I have already that in PLCs. What I need now is to gather data from the PLCs via modbus RTU/TCP/UDP. After the service detects connection errors it registers the begin date and end date. After it detects PLCs are reachable again it downloads the usefull data that it missed from the hardware data logger solution.

Which solutions support this?

Yokogawa MW100
Schneider scadapack models

Both this are data acquisition systems via I/O and probably not via modbus.
I'm lost. Help?


texts:
I've got a damascus steel knife, which I accidentaly broke the wooden handle. I teared it apart and all I was left was a bare blade. I've created a new wooden handle, but while making it, I've also brushed the blade a bit, while fine sanding the wooden handles while attached to the blade.

Is there any option I could re-etch the blade again, and if so - what acid should I use (I've heard for Ferric III Chloride (Fe3Cl)) but I don't know the concentration neither the time or temperature of etching or the whole procedure.

So, how do I etch a damascus steel knife?


texts: A latch that’s easy to open under lateral pressure

texts:
My middle schooler is building a catapult that’s supposed to hurl a ping-pong ball 5 meters:

The problem is that the pressure on the latch is so high that the kid just cannot trigger it:

The door latch used as a trigger is being under so much pressure that it just wouldn’t slide out. I doubt that adding lubricant would help enough.

Thus the question: what latch design could you suggest so that it would operate smoothly under lateral pressure?


texts: For how long could a plane handle turbulences?

texts:
Some days ago, I took a plane (Airbus A330) for a pretty long flight - around 8hrs. During the flight, we experienced some turbulences and I thought : what if the turbulences last the whole flight?

How would a plane react to 8+ hrs under mid to heavy turbulences during the whole flight?


texts: Low cost molds. Can such molds be produced?

texts:
I recently found the following link https://anglingai.com/224b-4-4-blood-line-swim-bait-mold/.
There you will see that they sale hundreds of different aluminum molds related to fishing. These molds are really inexpensive (from 50 up to 200 USD). How they are producing them? I though that molds cost thousands of dollars.

I am currently in progress on designing a product and I will need a mold for the enclosure of the product for low production runs (no more than 200-300 items per month). The enclosure will need to be either from ABS or some other kind of strong material that is not brittle. Probably also, the material will need to somehow be manually injected in order to reduce the total cost.

Where can I find someone to produce me low cost molds (like the above) for a product design that I will create with Fusion 360? Can this be done or I am really naive? I am mostly interested for the outside finish of the enclosure. Inside it there will be electronics that will be potted with special type of resin in order to protect them from the elements. As such, the inside will be as simple as possible.


texts: Mount thermal imaging camera on ordinary optical microscope?

texts:
Anyone tried mounting thermal imaging camera on ordinary optical microscope?

I know it is unlikely to work. Because of different refraction index and possible absorption of IR radiation by the lens.


texts: Simple Thermal Analysis for sealed Aluminum box with 3.7 Watts of heat generation internally

texts:
I am looking for a starting back of the envelope calculation to determine if an aluminum box with just free convection can dissipate 3.7W of internal heat generation or if I need to think about adding a heat sink into design.

The way I see it the heat generating electronics would be radiating heat via convection to internal air of box and then heat would travel into box and via free convection into atmosphere. I'm fine neglecting radiation and am not sure how to approach this problem after reading for the last couple hours on thermal stuff.

T ambient = 50C
T max for electronics= 40C
T Internal starting =20C
Q generated by electronics = 3.7W
Box dims = 75mmx75mmx100mm , Area=.0412m^2, Vol=.0005625 m^3
Box thickness= 7mm
Box material is aluminum
R_aluminum=200
R_air =.0262

Thanks for any help on how to approach this


texts:
Good morning/afternoon/evening,

I am working on a project in my spare time, and was wondering how this effect is created.

and

I am going to assume this is more than just a cutout with an LED behind it, but if I wanted to do a simple LED indicator, not shapes, how would that be done? My initial guess is that a piece of black translucent polycarbonate with an LED behind it would do the trick. Would this produce a nice little circle?

Thank you!


texts:
I was going through some literature in power electronics relating to sliding mode control. I noticed that they have separately dealt with the reaching condition and then the existence condition for the sliding mode.

Question: Doesn't it imply that if the reaching condition is met, the existence condition is also automatically met?

If $s$ is the sliding surface, Reaching Condition: $s\dot{s} \leq 0$

Existence Condition: $\lim\limits_{s\to0} s\dot{s} \leq 0$


texts: How to calculate actual efficiency of a steam turbine

texts: What are the parameters required to calculate the overall efficiency of a steam turbine and how to calculate. Is there are certain assumptions to be made while calculating the overall efficiency of a steam turbine.


texts:
I need to set up a system with a DC motor that will cause it to run for a small period of time, then stop, and then be able to repeat this until disconnected from its power source.

Any ideas of how I could achieve this would be greatly appreciated!


texts:
I am working on a problem at the moment and would appreciate some of your expertise regarding this issue. If you see the image below,  I am trying to calculate heat transfer from a fluid entering a vessel/tank on the grey cuboid within. To begin with, I am focussing on side C.
I would like to understand how we would work out the Velocity of the fluid at point C when water is pumped in at A (intake), and, when discharging from point (B), i.e A flow, B return.
The overall problem I am trying to solve is how long it would take to heat the cuboid from convection heat transfer (forced + also natural). At the moment I am calculating (Re) and need to determine velocity.

It is not a home work question, it is for general research. There is no actual question I’m working from.
I would like to understand how to work out velocity at C when there is a flow into A and out of B. This will allow me to work out Re at C.


texts: Heat Transfer in A Cylinder of an Internal Combustion Engine

texts:
I am new in engineering, could anyone explain the approach to calculate the max heat generation, the heat transfer from the cylinder to the atmosphere and from cylinder to the piston.

I am also wondering about how does changing L3 affect the max heat generation which is allowed and why

the picture is the cross-section of the engine.


texts: How to prevent algae in water cooled laser tubes?

texts:
I recently got a laser that is water cooled via a couple of clear plastic tubes (about .5 cm diameter).  I have heard it can happen that algae or other undesirable inhabitants can get into such tubes and cause problems.  I have also heard that wrapping the tubes in something dark to keep light out can help with this issue.  However, I have not heard of a good material for wrapping the tubes with, and I am looking for suggestions.

Ideally I would like to be able to slide a sheath of some opaque material over the tubes.  Something like heat shrink (unshrunk) might work.  I have also seen braided nylon sheaths for covering cables, but they don't look very opaque.  What's the best option?


texts: How should I set the turbulent prandtl number in a turbulent compressible flow simulation?

texts:
I'm working on simulating compressible fluid flow over a flat plate with turbulence.  The energy equation for compressible flow with turbulence requires modeling a turbulent heat flux of the form

$$q_T=\frac{\mu_T c_p}{Pr_T}\frac{\partial T}{\partial x_j}$$

where $\mu_T, c_p,Pr_T$ are the turbulent viscosity, specific heat (constant pressure) and turbulent Prandtl number.  Clearly, all three of these paramters vary throughout the domain and require a model to determine their values as a function of the flow variables (density $\rho$, velocity $u$, pressure $p$, and temperature $T$.  The turbulent viscosity is estimated using the variables of the specifically chosen turbulence model.  The specific heat $c_p$ is a function of temperature, and can be estimated by interpolating over the most recent temperature values.

However, I have no idea how to estimate the turbulent Prandtl number as a function of the temperature, velocity, density, or pressure.  The only relevant discussion I've found on this issue is in Wilcox (2006)'s Turbulence Modeling for CFD (chapter 5, section 5.4.2, pg 250), where it states

  A constant value for $Pr_T$ is often used and this is usually satisfactory for shock-free flows up to low supersonic speeds, provided the heat transfer rate is not too high.  The most common values assumed for $Pr_T$ are 0.89 or 0.90, in the case of a boundary layer.  Heat transfer predictions can usually be improved somewhat by letting $Pr_T$ vary through the boundary layer.  Near the edge of a boundary layer and throughout a free shear layer, a value of the order of 0.5 is more appropriate for $Pr_T$.

While modeling $Pr_T$ as a constant is OK for some cases, I want to know if there is a standard model to prescribe its value as a function of the flow variables $T,u,\rho,$ and $p$.  Preferably, this model should ascribe values near 0.9 within the boundary layer and 0.5 throughout a free shear layer, as described by Wilcox.  How should I prescribe the turbulent Prandtl number throughout the domain as a function of the flow variables?


texts: Simple cantilever beam deflection - what is the simplest way to add a damper?

texts:
I am looking at a simple cantilever beam deflection:

I understand the general expression for deflection/force would be:
$y_s = \frac{Fx_s^3}{3EI}$
$F_p = \frac{3y_sEI}{x_s^3}$
If you were going to add viscous damping to the bending of the beam, would it be as simple as:
$F = \frac{3y_sEI}{x_s^3} - cEIθ_t$
Where the equation for the angle of deflection is $θ = \frac{FL^2}{2EI}$?
I have seen some suggestions that simple damping of cantelever beams is done by applying viscosity to the rate of angle change with respect to time. Is that generally correct?
I have had some strange behaviors trying this so I'm not sure what the ideal simple solution is.
Thanks for any help or answers/ideas for either question. It is appreciated.


texts: Two dimensional plasticity with radial return

texts:
Note - This is a duplicate of the question I asked over on Physics which hasn't received any attention.

What is the proper method to scale deviatoric stresses back to the yield surface in plane stress 2D?

I cannot get the radial return method to produce the desired results under plain stress conditions in 2D. I'll show this using an example in both 3D and 2D in the hope that my mistake might become apparent.

Three Dimensions

Assume an arbitrary trial Cauchy Stress tensor of:

$\sigma_{tr} = \begin{bmatrix}
    90 & 20 & 0 \\
    20 & 90& 0 \\
    0 & 0& 0
\end{bmatrix}$

Then the hydrostatic component is given by:
$\sigma_{tr,hyd} = \begin{bmatrix}
    50 & 0 & 0 \\
    0 & 50& 0 \\
    0 & 0& 50
\end{bmatrix}$

And the deviatoric component by:
$\sigma_{tr,dev} = \begin{bmatrix}
    40 & 20 & 0 \\
    20 & 10& 0 \\
    0 & 0& -50
\end{bmatrix}$

We will use the Von Mises criterion to determine whether the stresses are still in the yield surface. This calculated as (for general plane stress):

$\sigma_v = \sqrt{\sigma_{11}^2-\sigma_{11}\sigma_{22}+\sigma_{22}^2+3\sigma_{12}^2} = 86.6025$

For the sake of argument let's assume a yield stress of $\sigma_y=80$. In which case the deviatoric stresses need to be scaled back by a factor of $\alpha={\sigma_y}/{\sigma_v}=0.9238$. So the new deviatoric stress is given by:

$\sigma_{dev}=\alpha*\sigma_{tr,dev}
= \begin{bmatrix}
    36.95 & 18.48 & 0 \\
    18.48 & 9.24& 0 \\
    0 & 0& -46.19
\end{bmatrix}$

And the scaled back

$\sigma=\sigma_{tr,hyd}+\sigma_{dev}
= \begin{bmatrix}
    86.95& 18.48 & 0 \\
    18.48 & 59.24& 0 \\
    0 & 0& 3.81
\end{bmatrix}$

If we calculate the corresponding Von Mises stress we get $\sigma_{v}=80$ indicating that the scaling was correct.

Two Dimensions

I haven't repeated a lot of the text here for brevity. Check page 157 here for confirmation of hydrostatic stress in 2D, it's just $(\sigma_{11}+\sigma_{22})/2$. Assuming plane stress then:

$\sigma_{tr} = \begin{bmatrix}
    90 & 20 \\
    20 & 90 \\
\end{bmatrix}$
$\sigma_{tr,hyd} = \begin{bmatrix}
    75 & 0 \\
    0 & 75 \\
\end{bmatrix}$
$\sigma_{tr,dev} = \begin{bmatrix}
    15 & 20 \\
    20 & -15 \\
\end{bmatrix}$
$\sigma_v = 86.6025$

The problem is that scaling the deviatoric stresses ($\alpha$ is the same as before) results in:

$\sigma_{dev}=\alpha*\sigma_{tr,dev}
= \begin{bmatrix}
    13.86 & 18.48 \\
    18.48 & -13.86 \\
\end{bmatrix}$

And then:

$\sigma=\sigma_{tr,hyd}+\sigma_{dev}
= \begin{bmatrix}
    88.86& 18.48  \\
    18.48 & 61.14 \\
\end{bmatrix}$

Calculating the Von Mises stress gives a value of $\sigma_{v}=85$, which is outside the yield surface. What is the problem here? What is the proper method to scale the deviatoric stresses back to the yield surface in 2D?

Update
I am slowly coming around to the ideal that this radial return method is only appropriate for full 3D or plane strain (in which case the $\sigma_{33}\neq0$). Page 25 of this seems to also indicate that this is the case, but I am still unsure.


texts: What is the difference between grout and mortar?

texts: As I know so far, mortar and grout are mixtures of cement paste and fine aggregates, but both of them play different roles in the construction site. Is it true that grout has more strength compared to mortar? What are the differences between them?


texts: Pressure-volume relation of thin-walled shell

texts:
Attempt to edit into a more specific question as suggested by moderator:

I would like define the shape and material properties of a 3D thin-walled shell/membrane-like structure (for instance a baloon). Then I would like to approximate the pressure volume-relation (PVR) of this structure - what pressure will we obtain when increasing the internal volume?

I'm planning to create a mesh of 2D triangular elements for a 3D shell with volume V0 and internal pressure zero. After defining the stiffness matrix for the material I should be able to compute the nodal forces, geometric configuration and internal volume for a certain internal pressure (the plan is to use an iterative approach searching for a configuration where all resulting nodal forces equals zero, that is where expanding forces arising from the internal pressure equals constricting forces arising from displacement).

To do this I need to calculate the nodal forces created by 1) displacement from the original V0 configuration and 2) from the internal pressure. I think I can figure out the first one, but I do not know how to transform the internal pressure (acting perpendicular on the triangular elements) into nodal forces. Any ideas?


texts: I studied many papers and I face with concept of  numerical diffusion,but I don't understand it. Can someone explain briefly about numerical diffusion?


texts: Accounting for blank registration within CAD design

texts:
How do CAD designers account for the fact that a blank may have to be flipped to a different side in order to allow the piece to be completely milled through a CNC system?

For an example, let's use this car made from a rectangular block of pine:

It appears that three planes need to be surfaced in order to mill the object.

The bottom plane of the block has a slight concave shape
The side plane has two hollowed out shapes that would not be accessible from either the top or bottom planes
The top plane has a slightly concave inflection applied to the slope

And there are several cuts that go all the way through the blank.

It seems easy enough to mill the bottom shape first, including any through cuts from the bottom.  This work on the bottom wouldn't significantly affect the overall shape of the blank, and there shouldn't be any complications moving to the next plane.

But after you complete the bottom, milling either the side or the top would appear to create problems for flipping the blank to the final plane.  Specifically, the outline of the original blank would have changed significantly enough that prior mill registrations would be thrown off.

I suspect that this is a somewhat common problem as complex shapes are fairly commonplace.  And I'm more interested in the general approach to solving this problem than I am about how the example car would be designed.

So how does a CAD designer account for the fact that the edges of the blank will be changing during milling and that those changes may (will) complicate the milling process?

Disclaimer: My knowledge of CAD design and CNC manufacturing is fairly limited.  My knowledge comes primarily from what I picked up at University and has been supplemented by advanced DIY projects.


texts: In horizontal axis wind turbines, why does axial component of absolute velocity stay constant (wake rotation theory)

texts:
I am having hard time understanding how does the axial component stay constant through the rotor. Every resource i look just says it is due to mass conservation but never gives the actual conservation equation and i can't write it.

For clarity, i am talking about wake rotation theory and not the simplified 1D momentum theory.


texts: High frequency TIG welding and Bluetooth or WIFI frequency

texts:
I need to work on a project where multiple objects need to exchange trough wireless protocol and they are near to High frequency TIG welding machine.
All objects works by pair (one emitter and one receiver) and they are up to 20 pairs in the same area (something like 30 or 50 square meter)
Each pair do not have to interfer with other pair of objects and they have to not be interfered by the TIG welding machine.

Should I better use WIFI or Bluetooth protocol?
Range is not an issue as each object of a pair is not far from the other object of the same pair.

For what I found, High frequency TIG welding is given to 1Mghz


texts: Are tube fittings a feasible way to create tight seal?

texts:
I'm doing an experiment where 2 electrodes are inserted into 2 openings in a cylinder holding electrolytes to measure its impedance. We want the openings to be tightly sealed because the cylinder holding the electrolyte will be pressurized. Our idea is to insert the electrodes through the holes of tube fittings. The tube fitting will screw onto the threaded cylinder and it will lock into the electrodes. Will this work, and what type and size of tube fitting should I use for this? Please give any other suggestions.

Here's a picture of what it looks like. The cylinder will be remade with only 2 holes. That's the electrode with a rod attached. We're hoping the tube fitting will dig into the rod. The diameter of the rod is about 1/4 in.


texts: Equation of the parabolic suspension bridge cable when the deck mass is known

texts:
I'm reading the derivation of the equation of the hanging catenary from Wikipedia:

https://en.wikipedia.org/wiki/Catenary

In the same article the parabolic equation governing the shape of the main cable of a suspension bridge is discussed, and its equation is obtained as following:

$$y={\frac {w}{2T_{0}}}x^{2}+\beta$$

Here $w$ is the density of the deck and $T_{0}$ is the horizontal tension on the cable at lowest point.

Let's say I'm designing a suspension bridge with the length and density of the deck and its other features are known. I would be interested in knowing the equation of the main cable to calculate the length of the secondary cables (the vertical ones). But how do I get $T_{0}$?


texts: Difference between VC-130 and VC-131 steel

texts: I am a draftsman. I make project of mechanical pieces and machinery. Some pieces works like knifes or sleeve, so to reduce the friction we design the ideal material to manufacture this pieces. The steel Vc 130 or 131 are options of choices. What is the usage of steel grades VC-130 and VC-131? What the difference in applications between them, on tools and gears projects?


texts: Why is the rear wheel of the Penny-farthing so small?

texts:
I see a lot of people asking why the Penny-farthing's front wheel is so big, and I think I've read enough materials to understand why (at least, at the most basic level). But even so, I feel that the rear wheel is too small — not just compared to the front one, but actually really small.
Is there a specific reason why?

Also, why would this front-big-rear-small design not be used for other vehicles (for instance, I know some trucks have smaller front wheels and larger rear wheels, which is the exact opposite of penny farthings)?


texts: How to switch between two cores (inside the coil) in a simple brushed DC

texts:
I am going to build a very simple brushed DC motor. The rotor will not be enclosed in a stator (the rotor will be built on a bench with free space around it), and I will using permanent magnets to make the external magnetic field.
I plan to compare the torque generated on the rotor with a non-iron core, with the torque generated on the rotor with an iron core (the two cores will have the same dimensions). I will do this at stall torque, and I think this will help me find the permeability of the iron core (assuming the non-iron core has a known permeability). The permeability isn’t constant in a ferromagnetic material such as a material made up of iron but knowing the permeability at stall torque should be enough for this assignment.
The best way to compare the two different torque values would probably be to just build a single rotor with a single coil and have the ability to just interchange the cores since this hopefully will eliminate some error when comparing the torque. This would mean that the coil can't be permanently attached to the first core, although the coil also has to be attached strong enough so that it doesn't fall off when the rotor spins. I got this suggestion from an electrical engineer, but I can't get in touch with him anymore. I could also build two different motors and try to make them as similar as possible to eliminate error, but the first option I think is better if it's possible to accomplish.
The dimensions of the cores will be 30x28x90mm (it's a rectangular shape, I couldn't find a cylinder), and I have the ability to cut and drill the iron core that I’ve bought, although I can only cut and drill across the short end. I plan to put the axis of rotation across the short end, but I don’t know if I should make the axis by drilling a hole (and inserting a small steel rod), or by cutting the core into two pieces and attaching each piece to a bigger prebuilt axis. This decision could influence my main issue, namely how I can switch the cores.
Any help is greatly appreciated, and please let me know if the question is unclear or badly formulated, and I will explain more about my assignment.


texts: What is the significance of a diagonal input in a control diagram?

texts:
I have seen several block diagrams with diagonal inputs, drawn with an arrow through the block.

 and others like that (via Google image search)

What is difference between this and a typical signal input? What are the dotted lines signifying?


texts:
The shortest connection between two portals would be a tunnel with constant gradient. Why do long tunnels instead rise from both portals to a culmination point, introducing unnecessary steep gradients?
Some thoughts: If it is for drainage, this could as well be done to one portal only. Shortening of service tunnels cannot be a reason, as they are often not connected at the highest point. Problematic bedrock could as well be circumnavigated laterally.


texts:
I'm studying the possibility to read an engine RPM by reading the vibrations of it. Basically an engine is "oscillating" on a car chassis on all 3 axes (X, Y, Z) but mostly on the Y one. When ignition is produced on a cylinder, then there should be like a "spike". Considering for a 4 stroke engine that the crankshaft has 2 revolutions per ignition, if I can "read" ignition then I can do the math and get RPM.
Because my expertise in electronics is quite limited I ask here for an advice of how to approach this. Which accelerometer to use? What is range and sensitivity / resolution that I should look for?
Any advice / hint is really appreciated
Thank you in advance


texts: What is the highest-temp castable refractory cement available?

texts:
I very much ruined 3 $10 diamond hole saws making this ceramic insulator out of a firebrick and Ryobi drill press.  Drilling out the large core took 1-2 hours and a lot of arm strength.

Therefore, I will turn to custom ceramic shops or my own castable refractory molds. I am concerned that the custom ceramic shops will be too expensive though.

So what is a refractory cement available to me that can withstand the melting point of titanium?  I.e. there is a Tungsten hotnozzle about 6mm x 10mm that goes at the bottom of this ceramic tube.  It's for a 3D printer that prints metal (hopefully!).  So, I don't need the entire piece to withstand that temp, but just at the end point and radiating around that.

However, when I search for castable refractory cement, it seems like only one product type comes up.


texts: What's the purpose of cavalier and cabinet in oblique projection?

texts: I really don't know why one person should create cavalier and the other one should create cabinet when it comes to oblique projection, are there any reasons why one should use cavalier instead of cabinet and vice versa?


texts: Is it possible to use Plain Cement Concrete post for fencing?

texts:
I am in need of around 700-800 posts to fence my farm in a semi-arid area in TN state, India. In my place granite posts mined from quarries are normally used. It costs around Rs 300-400 per post(6-7ft). I want to use plain cement post instead of the costly granite post. As it has no rebar, it costs around Rs 170-200, and as it has no iron, it can have long life without corrosion. The posts are used to tie 6-7 nos of GI barbed wire to safeguard the property.
I want to know , whether its feasible to use PCC post for fencing. If its not, how to incorporate iron rebars without the risk of corrosion in the long run. Please suggest.


texts: Characteristic length for the given problem of heat transfer

texts: In the following problem of heat transfer, what does characteristic length actually mean? In this problem, they have found the heat transfer coefficient (h) separately for the vertical and horizontal surface with the characteristic length being the height and width, respectively. Is it okay to take the length of the duct as characteristic length? If yes how should I proceed to solve this problem?


texts: Why is the head loss in submerged pipe is 0

texts:
Looking at this question :
Point C head loss is 0 according to the author
Bottom right
Can’t understand why , any good explanation for this claim ?
Look at page 33 at the top


texts: From a pie in the sky approach, similar to the question of whether a jetliner could be theoretically solar powered, what are the limiting factors on the magnitude of lifting capability of a controllable blimp? At what point would the control surfaces be so large that they would be impractically massive? What size would be too large for the fabric? Does a blimp with slightly heavier than air properties have the capacity to be much larger than its lighter than air brother? Anything you can supply would be appreciated.


texts: Is the PID just an outdated control method and state-space is superior?

texts:
So I've been wondering this for a while; is PID just a simple but slightly outdated control method / isn't state-space (SS) a far superior method in pretty much every way?
SS allows for MIMO, PID just SISO. SS allows for non-linear models, PID does not do non-linear models. SS allows you to see and control the states of your system, this is kind of lost in the laplace transform of PID... So given this; why do I encounter PID everywhere? Is it simpler and cheaper and good enough if it works?
I've asked this question to my mechatronic systems design professor, but I did not really find his answer all that satisfying: "State space is not going to do magic if loopshaping way of designing PID reaches its edge. State-space is time domain to design linear control while loopshaping is frequency domain. With both you can design PID."
His research group is focused on the high-tech side of things, and has made a 'fractional order' PID controller toolbox (FLOreS - Fractional order loop shaping MATLAB toolbox, essentially you place a bunch of zeros and poles close to each other to mimic something which is between e.g. s^1 and s^2). In any event, I think he might be biased so I wish to get some perspective.


texts: Interface level between 2 components in Liquid-Liquid Extraction, What does it mean?

texts: In LLE physical processes, there is this level (interface) between the 2 components  (for example) that is being separated as shown in the picture. I know that the height of this level from the reference point (0%) tells us the efficiency of separation. I don't understand the mechanism of what this inferface level means and how does it tells us the efficiency of the process. What does it tells us if it is more or if it is less than the opitmal level (given by engineers) ?


texts: How to compare small and large scale model of an IC engine to predict force, torque, rpm etc generated by actual engine?

texts:
I have this 6 cylinder radial engine designed in Solidworks.

Rendering

Blueprint (Source:Inventor Wizards)

And I want to perform some motion analysis on this engine to make some prediction about it's feasibility.
So by now I have successfully completed the motion study simulation and generated plots of piston acceleration against time.

Plotted for a crankshaft speed of 200RPM.

Can i use some method or this data to predict acceleration of large scale model of this engine?


texts:
Following situation: I need to mount a console holding a load to the edge of a 25cm concrete plate. I want you to check my reasoning. This is the situation:

My thinking is: The load is 170kg, which amounts to 1.67 kN. The length of the cantilever is 600 mm. So the tension load on the upper two fasterners (of four, installed in square patterns) is a total of 1.67 kN * 600 mm / 150 mm = 6.69 kN.

Looking the specifications of a likely system, I see that 2 M10 fasteners at embedment depth 100mm offer me 2 * 8.7 kN tensile load, which contains decent margin of safety. The shear load per fastener is in the same range, there's 4 fasteners, so even considering 10 or 20 kg for the console (likely too much) this is ok.

I'm out of school too long. Is the above  correct?


texts: What is the best insulation wall for a house? ACC wall, Cavity wall, etc

texts:
Normally, people use Autoclaved Aerated Concrete (AAC) to build a concrete house because ACC is a good thermal insulation brick that easy to buy and not expensive

And another way i've heard about insulation wall is Cavity wall. IMO, it rarely find a house that use this kind of wall.

Then the main topic of discussion here might be

Autoclaved Aerated Concrete (AAC) wall vs Cavity wall which one is the best thermal insulation wall?

Note that another method can be purpose if it better than ACC wall and Cavity wall


texts: How do DC motor parameters scale with motor size?

texts:
Consider the following DC motor parameters:

Rotor resistance, $R\ [\Omega]$
Motor constant, $k_t\ [\mathrm{V/rpm}]$
Inertia, $I\ [\mathrm{kg\cdot m^2]}$

How do they scale with motor size? Do $R$ and $k_t$ depend on $I$?


texts: I have seen several forums related to this question about the difference between observers and estimators in control theory and could not understand it clearly. I wanted to know how the state estimators and observers originated in first place. What was the motivation behind this concept? Does it have any relation with statistics?


texts: Is the metacentric height independent of heel angle?

texts:
when the sides of a pontoon are verticle, BM(distance between center of buoyancy and metacenter) is given by I/V

As well as for a small angle that expression is true. But when the heel angle increases what heppens to the BM?


texts: Sign of torque in torsional vibration of a shaft

texts: In the example problem below, how were the signs of the torques at x = 0 and x = L found? At x = 0, the direction of pulley rotation is unspecified but the direction is assumed to be positive. And at x = L, if you use the right hand rule the torque is applied in the positive x direction but the author states that torque is negative by the right hand rule. Is this because the shaft is stationary and must supply the same torque in the opposite direction at x = 0 and x = L?


texts: Rules of thumb in the design of stringers and frames for hull design

texts: In the design of boat hulls (and aircraft) reduction in material thickness is important and the hull is usually made as an assembly (welded or riveted) with stringers and frames. The design of stiffened panels is a complex problem. Are there a set of simplified rules for the design of stringers and frames for boat hulls?


texts: How much cm needed for airflow? - optimal window shutter distance

texts:
I am thinking that air (if it is still) is a very good insulator.

So why aren't we putting the window shutter far away from the window?

It would have more air between the window and the shutter and the Question:  it would cause better insulation?

Or above a few centimeters thickness, the airflow would start anyways by itself and it would just only backfire?


texts: How can I generate smoke (or mist) that leaves no residue?

texts: I have to visualize flow over some designs in my wind tunnel. However, my advisor has stated that previous students have wrecked the machine when they have used oils and I think Dry Ice might interfere with the results owing to its different density and the fact that it will probably sink to the bottom of the tunnel (it is the horizontal kind).


texts: How to find all the parameters in weight vector in Levenberg-Marquardt Algorithm?

texts:
I already had a data for corroded thickness distribution (in matrix form) for corroded surface model in Abaqus with mesh size 5 cm
I want to create thickness distribution with bigger mesh size (e.g 50 cm) but I dont want to use average thickness to obtain the smaller matrix size,
I want to use effective thickness by utilizing the equations in the picture.
But till today I still have no idea how to use those equations.
Does anyone have any idea?

Thank you


texts: Calculating the Structural Forces Required to Support a Robot on an Overhanging Beam

texts:
this is my first time posting on here and I have a question regarding the structural properties a beam will need in order to fulfill some requirements we have for our robotics team. The scenario is as follows: Our robot has two wings that drop to our sides in order to support two other robots in order to simultaneously lift all three. The situation results in the lifted robot applying a large amount of force on the top of two beams supported only from the side of the wing held against the robot frame. The current wings we have are made out of 1/16in aluminum tubing, which has ended up being heavy and not sturdy enough for our needs.

We have been doing research on potentially using fiberglass or carbon fiber rods. We think that 3/4in OD solid fiberglass rods will be strong enough for what we need, but are not sure. I understand that fiberglass is very flexible, and while this normally would be good we only have room for about an inch of bending. This is because all three robots must clear 12 inches while being lifted, and we lift ~15 inches up. This only leaves 3 inches of clearance, and we would like to keep as much wiggle room as we can for any tilting/unbalancing after lifting.

Because of this, we looked to hollow carbon fiber tubes. We can afford .625in OD .515in ID Pultruded rods, but after doing research we believe these will be ineffective, as they focus on tensile and compression strength, while the force we are dealing with is transverse on top of the tube. As roll wrapped rods are quite expensive, the largest tube we can afford is .422in OD .372in ID twill rods. I understand because the way the fibers are directed, roll wrapped rods are much stronger in dealing with perpendicular or twisting forces, but believe the size we will need to support the robot is outside our price range.

Obviously this quite a lot and I dont expect anyone to completely solve our problems. I have presented all this information in hopes someone can provide the methods we can use to calculated the type of rod we will need and its amount of deformation, bending, breaking point, etc. We are currently planning on using the previously mentioned 3/4in OD solid fiberglass rods from goodwinds composites, held by an aluminum holding piece that attaches the rods to the frame. Below I will attach some pictures and diagrams to better express the forces involved and our setup. Keep in mind that weight is a huge factor as well, but we think we any composite used will be lighter than our original wing. Currently each one is around 5lbs

Thanks guys!

J

https://imgur.com/a/ECNzz


texts: I'm looking to determine the difference between the two yield strengths on a Matweb material property table for DuPont Performance Polymers Zytel® 105F BK010 PA66. The top is for "50% RH; ISO 527-1/-2" per the comments and the bottom is "DAM;ISO 527-1/-2". I need to know what 50% RH and DAM mean so I can make an informed decision. Any help would be appreciated.


texts: Pendulum clock, escapement pallet mounting position

texts:
Im interested in creating a 3d printed pendulum clock,
all the diagrams and files I can find are mounting the pallet at the top of the escapement wheel which causes more complex design to avoid pendulum rod with the rest of the clock,
why cant the pallet be mounted downwards from the escapement wheel? is there any particular reason?


texts: Boundary conditions for Stream function-Vorticity method

texts:
I have used a MATLAB finite difference code to solve a lid driven cavity flow, based on a Stream function-Vorticity formulation of the viscous, incompressible Navier Stokes equations. Details about the method can be found here.

I want to change the code to simulate the flow around a square box in a rectangular domain, where the flow is uniform on the left side, and the flow is limited by the horisontal walls on the top and bottom. However, on the right side of the domain, where the flow exits, I have no idea how to express the boundary conditions.

How can I express the boundary conditions on the right side? Is it even possible for this method?


texts: How long does it take for dust to settle out of the air?

texts:
In order to make this a manageable question, let's add a few simplifications.

The dust particles can be well described as uniform spheres of radius $R$ and density $\rho$.
The space is enclosed and there is no bulk flow, i.e the air is still in a macroscopic sense.
The air is at the standard temperature and pressure (STP); $T=20\ ^\circ\mathrm{C}$ and $P=1\ \mathrm{atm}$.

Under these conditions, what is the settling time for dust particles?  At what size/density does Brownian motion of the air become important?


texts: Typical cycletime of an industry pid controller for servomotors

texts: I am wondering the following. What are the typical cycletimes (or timesteps), that are used in real industry-standard pid-controllers (for example for assembly-robots on a car-production-line). I didnt find anything specific in the literature, just the theory. Therefore I am asking here. Often, these information is not published by the vendors of these pid-servo-controllers, so maybe someone has some experience here. Thanks.


texts: Uncertainty Calculation of LVDT displacement transducers for length measurement

texts:
I have to calculate the uncertainty of measurement for an LVDT Linear displacement transducer used for measuring length. Uncertainty calculations are ruled by ISO 17025 but there are no (at least haven't found) specific guidelines for the mathematical procedure of uncertainty for LVDT sensors. There are many guides for more common measuring instruments like head micrometers and calipers though.

Is there any official document to which I can refer to for the requirements and maths for calculating the uncertainty of measurement for this kind of sensors?


texts: How would you refer to a bolt mounting slide as opposed to a simple hole?

texts:
I'm writing a patent application and my device incorporates a similar design as what I've seen used on Dovetale plates. However, instead of a preset hole for positioning a bolt to mount to, a grooved slot is machined into the part so the bolt can be positioned at any point along the slide.

Is there a canonical technical name for this?


texts: Do high votlage transmission lines disturb other electrical devices?

texts:
I had the question myself it those high voltage transmission lines, disturb other electrical devices? Let's say I have an high voltage next to a mobile basestation, does it effekt the electrical components in the base station or the wireless communication of the antennas ?

Is there any way I could calculate that?


texts: Internal stress tensor associated with centrifugal/centripetal load

texts:
I have some trouble to understand the relationship between internal stress tensor and the external traction force (in this example, the traction force is a volumic centripetal force). Consider a cube made of a very high elastic modulus homogeneous material (which can be approximated to a quasi-rigid body), it is rotating about axis-z in a constant spin speed $\Omega$. For sake of simplicity, the three axes are attached to the cube.

In its stationnary configuration, with respect to the attached rotating reference, the centrifugal force on any point in this cube should be equilibrated by an internal elastic force, in order to keep the cube from falling apart. Given the coordinate of a generic point $P$ in this cube as $\boldsymbol{x} = [x\;y\;z]^\text{T}$, the centripetal force density can be given by
$$\boldsymbol{f} = \rho [\boldsymbol{\omega}]^2 \boldsymbol{x}$$
where
$$[\boldsymbol{\omega}] =
\begin{bmatrix}
0 & -\Omega & 0 \\ \Omega & 0 & 0 \\ 0& 0 & 0
\end{bmatrix}$$
My question is how to express the corresponding true/cauchy stress tensor on this point for equilibrating the centripetal force density as
$$\boldsymbol{\sigma}_{\boldsymbol{f}} =
\begin{bmatrix}
\sigma_{xx} & \sigma_{xy} & \sigma_{xz} \\ \sigma_{xy} & \sigma_{yy} & \sigma_{yz} \\ \sigma_{xz}& \sigma_{yz} & \sigma_{zz}
\end{bmatrix}$$

Thanks for taking a look!


texts: Why is conservation of mass holds on filling balloon with gas?

texts:
Given a ballon and only one inlet, where some gas enters at a constant rate and the control volume of the balloon changes with time, why does conservation of mass hold?
To give some background, this is an example problem in the Raynold's Transport Theorem section.
What I don't understand and looking for clarification is that, since the mass is added to the system, how is the mass of the system constant. It changes with time, is it not? So how is the conservation of mass holds $\dfrac{dm_{sys}}{dt}=0$? (See "comments" section of the below image)

Here is the original question:

Where eq. 3.1 is $\dfrac{dm}{dt}=0$,
and the eq. 3.16 is the Raynold's Transport Theorem:
$$\frac{d}{dt}(B_{sys})=\frac{d}{dt}\biggl(\int_{CV} \beta \rho d\mathcal{V}\biggr) + \int_{CS} \beta \rho (\mathbf{V_r} \cdot \mathbf{n})dA$$
From this book:

Thank you in advance!


texts:
I know that for a system to be BIBO stable the eigenvalues need to be stable so real(lambda)<0
so get that is only valid for 4
but how can i find out the other systems which are BIBO stable?


texts: how do tilt-shift DSLR lenses and video projector lens shift lenses work?

texts:
For photography there are tilt-shift lenses.
For video projectors there is lens shift lenses.
With video projector lens shift I get perfect, undistorted video projected up to 100% above, below, left or right from center of the lens.
Same with the shifting function of tilt-shift camera lenses, the offset changes but photo is undistorted from that, so several photos can be taken and stitched together in photoshop.

I've never had chance to look inside either tilt shift camera lenses or video projection lenses with lens shift feature. Both are too expensive for me to attempt to disassemble. Nor have I had luck finding info on someone else doing it or explaining what's inside.
My only guess has been that either all some lens elements are physically shifted along the DMD or LCD but I haven't been able to understand how that won't cause distortion as center of lens changes for other lenses and DMD/LCD.
The only place I've found any info on this has been a youtube video for a DIY video projector where someone used a (fresnel) lens tilting, not shifting.
https://youtu.be/Rp8HIf5eUpo?t=4m45s
The projector in that video is the only one I've seen where someone attempts to use fresnel lens tilting to do keystone correction optically rather than in software, and nothing is done for shifting.


texts: How can I calculate the total signal level (noise) of PC fans?

texts:
I have a fan on a PC case running at 100% speed making 40dB/A of noise (sound pressure). Then I add a second fan right next to it running at 100% speed making 30dB/A of noise.

What is the combined noise level?
What happens if add and extra 50dB/A fan?
And then 10 more 30dB/A fans?

Forget about space, treat them as sources coming from the same point in 3D space.

EDIT

The total signal level from sources with different strengths can be calculated as:

Lt =  10 log ((S1 + S2 ... + Sn) / Sref)

Where

Lt = total signal level (dB)

S = signal (signal unit)

Sref = signal reference (signal unit)

Source

I can't directly use this formula because it requires the sound power of fans instead of the sound pressure manufacturers such as Noctua typically provide. How can I convert it? What will I need?


texts: Different measured strain in beam experiencing pure bending

texts:
I have a beam experiencing a pure bending moment. The setup is similar to this image from these lecture notes (with different values).

Using the flexure formula, we can determine that the stress (and thus the strain) at any point along the top of the beam between C and D should be the same:
$$
\sigma_{max} = \frac{Mc}{I}
$$
where $M$ is the moment, $c$ is the distance from the neutral axis, and $I$ is the area moment of inertia.

However, I've a couple of strain gauges along the top of the beam measuring strain in the axial direction. These gauges are reading different values at different locations between C and D.

Is this expected? Is it a limitation of the model or are the gauges malfunctioning (or laid up improperly)?


texts:
Let’s say I have moving cart with velocity U .
And water from pipe flows at velocity V with respect to ground
The question asks to use Bernoulli equation , pressure is atmospheric in the top
If I use Bernoulli equation relative to the cart I get hight h different than that when being on ground . Why ?
V3 = 2V relative to Cart
Using Bernoulli equation I can easily get the hight
But when moving to the ground frame and using Bernoulli I get different answer
Which one is true ?


texts:
I have a car moving in straight line with certain time-varying acceleration and there is another car moving in a curvilinear way along some curved path with some time-varying acceleration. The inertial reference frame is say fixed at some point in space. The relative velocity and acceleration at any instant is calculated.

Why is the relative velocity of the car moving in curved path from the point of view of the car moving in straightline, different from the relative velocity of the car moving in straightline from the point of view of the car moving in the curved path?
I know that in mathematical formulation this will involve the instantaneous angular velocity of the car following the curved path. But that is not very intuitive to me. Is there any way I can understand this situation clearly and more intuitively,i.e., Visualize it.


texts: Material Properties: Does bending reduce iron rebar's strength?

texts:
I'm reading an introduction to structural engineering book and there's a fundamental concept I'm trying to relate to real life:

In construction, we regularly bend iron rebar into a variety of shapes and rebar stays locked in whatever bendy shape we give it.

As I understand it, if the rebar holds its deformed position that means it's behaving plastically and not elastically. When a material transitions from elastic behavior to plastic behavior, doesn't that mean it has yielded?

If it has indeed yielded, shouldn't bent rebar exhibit vastly reduced bearing capacity, particularly about the areas it has been bent?


texts: Method of Calculating pressure of failure in a cylindrical container?

texts: Is there a formula or method to calculate the pressure of failure of a cylindrical container of known material, thickness, and size?


texts: Advantages of a commuter train instead of a vehicle travelling in a straight road

texts:
Most large cities these days have some sort of metropolitan commuter train system. What are the reasons for the commuter trains, why couldn't we instead of having train tracks why not clear a large distance of straight road and have a vehicle, such as a large bus riding on it?

Looking at the speed of trains (in my city they go at an average of around 70 km/h) surely the speed alone is not a factor since it would probably be feasible to have some sort of large vehicle achieve this speed. Trains also require large infrastructure such as tracks and power lines. On the other hand, such large vehicles would probably be safer on tracks instead of roads, and a train on tracks would probably be easier to automatize than a vehicle with wheels.

I can think of a lot of reasons for and against trains over wheeled vehicles, but what are the real reasons why commuter trains are so popular a choice for cities?


texts: Why are 4-stroke diesel engines preferred in new developments?

texts:
2-stroke engines seem to offer a massive advantage over 4-stroke engines.  In the case of gasoline engines, there is a need for forced induction, but in the case of large diesels (which invariably have forced induction anyway) it seems that their advantages outweigh the disadvantages.

So why is it that all newly developed diesels (not counting large ship engines and research designs such as Achates Power) are 4-stroke?


texts: Launching a ball with springs or with elastic bands

texts:
I’m a student and have to create a machine that can launch a small bowling ball to knock over some pins.

I was thinking that I could use elastic potential energy to launch the ball but I’m not sure if I should use springs or elastic bands.

The problem is that I don’t have a lot of space to work with because it can only be 0,5m x 0,5m x 0,5m. And for that reason I am leaning towards springs but I’m not entirely sure.

Thanks in advance, if you need more information about the project just ask.

Edit: For the project I have to launch a ball 12 meters away and knock over 5 bowling pins. I am not allowed to use pneumatics or explosives. The ball has to stay on the ground and the goal is to knock over the pins like in a bowling match so I need a way to aim my system to hit a different pin when I only hit a few of them, but I already have an idea for this.
I thought about only using a ramp but when I calculated the speed it would have it would not be enough to consistently knock over bowling pins. Then I thought about adding springs or elastic bands or something like that to give it some extra speed.


texts: Alternative approach to reference geometry to mirror a swept cut

texts: I am looking for a way to mirror the swept cut shown in the figure below about the object's midplane, which is parallel to the right plane. Can you do this without reference geometry, for example is there a way to select the midplane of the object without creating a new plane?


texts: Gear Ratio of a Stepped Planetary Gearset

texts: I was looking into planetary gearsets, and came upon the concept of a stepped planetary gearset. In the image shown above, if my input was the blue sun gear, the output was the planet gear, and the ring is assumed to be fixed, how can I go about deriving what the gear ratio would be?


texts: What type of pump is recommended for pumping gasoline/petrol in vapor phase?

texts: I would really like to know your input, perhaps there are regulations on this that I'm not aware of that can help out regarding the overall safety of the process.


texts:
I meant to get a countersink for wood. Then in the hardware store, beside the countersinks, I saw a glass/tile drill bit set, which as a pack, is not so much more expensive than a single countersink. So, I got those glass/tile bits.
Now, I have a problem whether these bits would actually last. I suppose these are Tungsten Carbide & perhaps cut more so with it's hardness (chipping at the ceramic or glass) than with a sharp edge. I haven't opened them, but I assume them to be sharp. So if I used these & the sharpness wears away on its intended use, it's still good for the intended use. But, for wood, without the sharp edge obviously, it won't bore well.
Am I wrong here?


texts: I general, if you model a system (pendulum for example) and you do not include damping into the system (maybe caused by friction): Is it generally possible to tune a PI or PID controller for an second-order-dynamical system that is undamped? Because without friction/damping no energy can leave the system, and therefore I am wondering, if PID-control can generally work for these systems or if this will lead always to oscilations or unstable control?


texts:
In this flow control simple experiment in the lab, i am made to control the flow through the pipe and at the same time record down the output given by the sensor in voltage. I am told to record down values for increasing output and decreasing output.
The lowest flow is 0cc/min, and highest flow is 3000cc/min. Just wondering why must i take datas for both increasing and decreasing output. Is this so that i can determine the recommended operating range of the sensor? which will be the min. value to the max value of the both sets of outputs (increasing and decreasing) ?

The Objective of this experiment is by the way to investigate the linearity and hysteresis of the flow sensor.


texts: What is the best approach to fix empty pockets in a concrete slab/wall

texts:
What is the best approach to fix the pockets seen below:

The pockets were due to the stones in place which did not allow to pass the concrete material, and later on gravity made it's way.

Options on my head:

Fill with liquid cement, although it won't be as tough.
Fill with concrete, can't guarantee it will make it into every spot of the air pocket, nor sure how to do it well without failing miserably.
Fill with liquid cement and little pieces of rock (one of the 3 components that concrete uses) so it can fill as much as possible and the pieces of rock can fill the big part.

Cutting down the affected parts are not an option.


texts: Boundary layer is not captured well in axial turbine blade simulation

texts:
I am simulating an axial turbine, I tried different mesh topologies and all give me almost the same number. In fact, Boundary layer is not captured well, Reynolds number is equal to $4.4 \times 10^5$ and according to mentioned formula in the following link, I computed $y_1$ (First cell height) by using $y^+ = 30$ and $y^+ = 60$.

But in the two cases($y^+=30$ and $y^+=60$), the boundary layer is not captured well (Why?). In the other words, according to the following figure, there is no adjacent wall. And also, I studied the following link:

For this reason, performance parameters are not validated well. In fact, there is a difference with the experimental value. This difference is not big but it is not good! I think that it is difficult to capture BL by using low Re number turbulence model (for example,  $k-\epsilon$ turbulence model).


texts: An Argument from Kelvin’s Circulation Theorem

texts:
Page No. 318, John Anderson’s “Fundamentals Of Aerodynamics”.

The author here states from Kelvin’s circulation theorem that the initial circulation around a closed loop including the airfoil when the flow is stationary, which is 0, must be equal to the final value of circulation in that closed loop once the flow has reached a steady state.

Okay. So far, so good.

But then, he argues that the starting vortex’s negative circulation is the reason for the formation of the positive circulation around the airfoil.

Now, the above can only be true when the airfoil, once steady-state flow has been reached, is still a part of the closed loop formed by those initial fluid elements.

But, here’s the thing. Those initial fluid elements have by now, crossed the airfoil. There’s no obligation that the airfoil must at all times remain enclosed in that loop, made by those very same fluid elements.

If so, then Kelvin’s circulation theorem simply cannot be applied in the way the author presents it for the airfoil.

If so, then the starting vortex should  not be the reason for the development of circulation around the airfoil, or should it ?

Some clarity needed.


texts: How can I calculate headphone driver excursion?

texts:
I'm a headphone enthusiast, and once I tried to open up my headphones to see how much they move when I play my music.

However, I was really surprised to see that the sounds that I could "feel" actually came from a driver that didn't have any visible motion at all! The only way I could see even the smallest motions was by turning the volume up to extremely high levels that I would never listen to.

I tried to use the calculator I found here to calculate the motion that my headphones would make, and the results I got seemed to make sense, but this calculator was made for large speakers, not small headphones.

Could anyone tell me if this calculator should scale down to a headphone level (45 mm)? If not, what is an estimate for how much motion a headphone driver should be making at moderate volumes in terms of mm traveled?

Thank you!


texts: 3D Representation of Magnetic Field Lines

texts:
There are several tools available for monitoring electrical metrics (voltage, current, resistance, frequency). I have recently acquired all that I need for these studies.

What tools are available for monitoring magnetic metrics (force, flux, reluctance, intensity, density)?

What I am really looking for is a tool that can give me a 3 dimensional representation of field lines. I am looking for a tool that (perhaps) uses the Hall effect to generate a 3D digital plot of potentially complex field interactions involving multiple magnets (possibly in motion). Are there off-the-shelf tools available within the budget of an average hobbyist? If not, could I build a 3-dimensional array of Hall effect sensors that could be arranged around my experiment to capture fields and field changes over time? I am good with writing software but new to circuit creation.

Add-on question: Are there other tools you would recommend for magnetic studies by a hobbyist?


texts: How can deflection and spring constant of cantilever beam stack be calculated?

texts: How can I calculate some properties of a stack of 2 bonded cantilever beams like in the image? Especially I am interested in the spring constant and deflection with force on random locations. However, what confuses me is their lengths are not same. Otherwise I would recalculate the moment of inertia according to cross section of beam stack and then results can be acquired with well known formulas.


texts: When doing Mohr's circle, why do we rotate by twice the angle?

texts:
On page-3 of these MIT OCW notes, it is said that if we want to find the stresses when the square element is rotated by $\theta$ , then we should rotate diamter of mohr circle by $2 \theta$ and read of the numbers from the ends of diameter.
Is there any intuitive reason as to why we have to use twice the angle?


texts:
I need to design some custom involute gears for a project that I am working on and this is my first dive into gears.

I worked out how to calculate the size of gears by the required numbers of teeth and module.

This gear dimensions:
Module = 1mm
Teeth  = 36
Clearance = 0.1
Pitch Diameter = 72mm
Outside Diameter = 74mm
Whole Depth = 2.1mm

As you can see it's a tiny gear and I'd like to be able to make the blade to cut this gear myself.

With a standard pressure angle of 20 degrees, how would I calculate the angle of the cutting surface to make this gear profile?


texts: Why are 0-10V signals de-facto standard in HVAC applications, when 4-20mA is more common in other applications?

texts:
I've been involved in a few projects with HVAC systems, where sensors etc. generally used 0-10 V signals, and looking at catalogues of Buderus and other suppliers this still appears to be the standard.
In other industrial applications, you typically see 4-20 mA for analogous signals. When checking the Endress & Hauser catalogue at random, some sensors aren't even available with 0-10V signals.
Why this discrepancy?


texts: How can I create a small pump that can pull fish to a higher elevation without killing them?

texts:
(for the record, I already attempted to ask this in the physics stackoverflow)

I'm attempting to create something similar to a vertical multi-siphon. The device would pull water from multiple sources, at multiple elevations (a total range of about 5 feet) up to the top source so it can redistribute down again.

This could be simply accomplished by (a) pump(s) or a mini-turbine, but the transfer medium should be about 4 inches diameter: about large enough for a Betta fish to move up.

I can't use a multi-siphon going down and just out-pump the down flow of water, this means the fish would have to fight against the current up the piping so this isn't really an option.

Chemical and thermal lift are also not feasible to move the fish.

I'll take you quickly through some research. Anyone reading this knows that (after priming) a siphon attempts to equalize pressure which equates to leveling out the water involved.

While I can't find any examples of this, reason should stand that with a sufficient priming force, you can pull from multiple sources.

You should even be able to do crazy things (to a point).

So when you attempt to siphon vertically, it requires a pump.

And it stands to reason that a (properly calibrated) pump system could be used to supply multiple sources.

So the question becomes, how do we safely lift a fish that went down a siphon back up to its original level?

The only thing that is currently coming to mind, is use airline tubing connected to a pump to pull the water from the point at which the "siphon" was primed.

Continually applying negative pressure might be enough to pull the water at a rate that isn't going to vacuum a fish. Though, I'll admit I'm concerned it might need a series of pumps like this to imitate a caterpillar propulsion system.


texts: Block Diagram Reduction: Is it necessary to do it stepwise?

texts:
Just a short question: Is there any usefulness in doing block diagram reduction piecewise?

The reason I am asking is that I find it much (!) easier to just find the final $\frac{output}{input}$ transfer function using mathematics (the brute force method), but my professor does it stepwise.

If I am to do it stepwise, I still feel like I have to do it mathematically, rendering the stepwise reduction pretty useless as far as I can tell.

I realize this seems like a banal question, but I cannot find anything answering this question is my controls book.


texts:
This may be a dumb question, but is a solid block 100% of the time stronger than a 'strategically hollow' part. Strategically hollow meaning, the internal structure is design in such a way to support the loading direction?

My thinking is originating from both 3D printing internal supports but also from bio-mimicry designs. Looking at the internal structure of bones, they aren't solid, would they definitely always be stronger if they were solid? Intuitively I would say 'obviously' however could an internal structure is designed in such a way that the surface energy, and load paths create a stronger structure than a single solid block?

If there is a way to design the internal structure, how would you go about designing/analyzing this, if not is there a way to prove that it's not?


texts: Universal joint vs Double Universal Joint (CV configuration) kinematics

texts:
Concerning this subject, I consulted the following Wikipedia page: Universal joint

where the elementary kinematics equation of the U-joint is stated.

But, a little bit further in the article Double Cardan Shaft

where the configuration described consists of 2 U-joints, the previously mentioned equation is reversed, i.e:

$\tan \gamma _{1}=\cos \beta \tan \gamma _{2}$,

$\tan \gamma _{2}=\cos \beta \,\tan \gamma _{1}\qquad \tan \gamma _{4}=\cos \beta \,\tan \gamma _{3}$

I do not intend to doubt the validity of the info on the article, but this hit me as a pretty weird thing.

Are these relationships correct?


texts: How to align the assembly in Siemens NX?

texts:
I rotated the assembly somehow and when I try to make a technical drawing of the assembly this happens:

As you can see, the cylinder ( assembly ) makes an angle.
How can I fix it ?


texts:
While reading about airplane engines on the internet, it is common to find figures of their thrust, in kilo Newton. However, in the case of ships and naval vessels, when talking about the engine, the only parameter mentioned is the horsepower of the power plant driving the propeller.

So, my question is, what is the typical thrust generated by a large naval ship (such as the nuclear-powered USS Enterprise aircraft carrier, with a power of 210 MW)? How can this be calculated?


texts: Round beam deflection under its own weight

texts:
I'm trying to calculate how much simply-supported round beams of several materials and diameters deflect under their own weight plus an additional weight in the middle.

I know the material densities so I can calculate weight of the entire beam, and I know the material Young's Modulus so I can calculate Moment of Inertia.

I've got the deflection due to an added weight calculated correctly, but I'm stuck on deflection due to the shaft's own weight.

Several places have given the formula:

$$\delta C = \frac {5 q L^4} {384 E I}$$

eg: https://en.wikipedia.org/wiki/Deflection_(engineering)#Uniformly-loaded_simple_beams

But I am not sure what q represents.

Wikipedia describes that as "Uniform load on the beam (force per unit length)" and I see other sites mention it in Newtons.

Is that gravity's acceleration (9.80665 m/sec^2) times the beam's own weight in kilograms to get Newtons of downward force?

eg: https://en.wikipedia.org/wiki/Newton_(unit)#Examples

For example, a 102g beam would exert 1N of downward force, so q would be 1?


texts: What are the design trade-offs in the different rocket engine cycles for liquid propulsion systems

texts: Liquid propelled Rocket engines work on various cycles such as pressure-fed, pump-fed(gas generator,staged combustion, expander, etc) and these have various design trade-offs between complexity, reliability, operational simplicity, development cost(?) etc. What are the various trade-offs between these cycles?


texts: Derive a heat equation for a shrinking nanoparticle

texts:
I consider a spherical nanoparticle (NP) that is shrinking, for instance due to a melting process. I know that the pressure $p$ is proportional to $1/R(t)$, where $R(t)$ is the radius of the NP at time $t$. Conservation of energy states
\begin{equation}
\rho\frac{\partial u}{\partial t}=\nabla\cdot\vec q,
\end{equation}
where $\rho$ is the density, $u$ is the internal energy and $\vec q$ is the heat flux given by Fourier's law,
\begin{equation}
\vec q=-k\nabla T.
\end{equation}
The classical heat equation is obtained by assuming that the volume is constant along the whole process, which leads to $du=c_vdT$. Under constant pressure, a similar equation holds, derived from
\begin{equation}
dh=du+d(pv),
\end{equation}
where $h$ is the specific enthalpy.
In this case, where neither the volume nor the pressure is constant, in which way could the internal energy be related to the temperature to obtain an equation involving only $T$? The only quantity which is kept constant in this case is the density, but I don't know how to go on...
Any help would be appreciated!


texts: What properties can be plotted on an Ashby diagram?

texts: I am having trouble interpreting Ashby plots. Usually, I am given the plots with the shapes but I am asked to identify where each material (metal, ceramic, composite...) fits. Can someone provide me with a complete list of all the properties I must know of these basic materials in order to be able to fill in any usual Ashby plot?


texts:
I'm building a hovercraft, which transfer function i have to find for further control. The hovercraft can be found in the following

As you can see, the hovercraft has 2 motors for direction. I have been given an advice to apply a step to the system, via the direction motors, and determine the transfer function, from the stepresponse. For this several questions comes to my mind:

A step on the motor, meaning for example 5V on the motors?

What should the ouput of the transfer function represent? (should i monitor velocity, acceleration, position after x seconds?)

Best regards


texts:
A steel parallelepiped with a square cross-section fits exactly into the cavity.
it's loaded from the top surface(see picture).
how can I calculate the stress in X- and Y-direction if the strain in X- and Y-direction is zero.


texts: Where could I find, or what is a material that could be used with 30 GHz pulsed DC current to produce 30 GHz pulses of light?

texts: I need to produce pulses of light that turn on and off for equal intervals at 30 GHz. I know there are lasers that are capable of this frequency, so I need to know what materials they use to produce pulses of light at that frequency within those lasers. How could I search for them?


texts: Rectangular hollow section vs square hollow section

texts: Which is better to use in contructing ceiling frame? RHS or SHS? And why?


texts: What is the most efficient way to convert a fuel into electrical energy?

texts:
Large steam engines seem to get pretty good efficiency, but there are other options such as combustion turbines.

Ignoring all other considerations, what methodology can extract the most energy out of a given amount of fuel?


texts: How split-flap display rotates by exact angle

texts:
In a split-flap display there is a barrel which rotates by a small angle N times to get to some next display element. However I fail to understand, how it is possible that the barrel rotates exactly by some desired angle? How is the rotation error after each flip is not accumulating? The only explanation I can think of is that it has sensors that sends signal back to the the motor to stop it.

Or is it possible that a motor can make exact rotations without error accumulation? I don't think it is possible unless the motor itself has built-in controller systems which resets the position each time to eliminate the error.


texts: Could a gold/{second metal} crown be created that would pass the Archimedes test cost effectively?

texts:
Many people are familiar with the story of Archimedes submerging a crown in water to identify if the volume of the crown was consistent with the volume of the same amount of gold.  The test was to see if a lighter cheaper metal (like silver) was included in crown.  If the crown maker substitutes silver for some of the gold, they make a sinister profit at the risk of their life.

Platinum is heavier than gold, silver is lighter.  Using the values as of January of 2015, could any combination of metals be used to create a crown that would have the same volume as a solid gold crown, with a cost effective benefit for the crown maker?

Using the values of metals in 287 BCE – 212 BCE, could it be cost effective for the crown maker?


texts: Calculation of Clamping force from bolt torque

texts:
I'm trying to calculate the clamping force resulting from torquing a nut and bolt to a particular level.

I have found this formula in various forms in a lot of places.

$$T = KDP$$

$T$ = Torque (in-lb)
$K$ = Constant to account for friction (0.15 - 0.2 for these units)
$D$ = Bolt diameter (inches)
$P$ = Clamping Force (lb)

I applied this to my problem

$T = 0.6\text{ N-m} = 5.3\text{ in-lb}$
$D = 3\text{ mm} = 0.12\text{ in}$
$K = 0.2$

This gives $P = \dfrac{T}{KD} = 220\text{ lb} = 100\text{ kg}$.

So, I have two questions.

The result seems way too high. I'm using a tiny M3 bolt, and not much torque. I can't see how this would result in 100 kg force. Can anyone see the error?
The formula doesn't take account of thread pitch. I would expect a fine thread to give more clamping force for the same torque. Is there a formula that accounts for thread pitch?


texts: How to structurally bind bamboo stems for loads?

texts: I would like to begin a case study in structural design using bamboo, which has currently become available to me. The design instance I would like to structurally copy is the Rogue RM-6 "Monster Rack" and a simple bench. Knowing that bamboo is used in scaffolding there must be details on structural reinforcement when binding stems together to make a structure. I would like to apply these kinds of principles to this rack design making necessary modifications where compromise is necessary. I do not know a good source to learn how make such structural binding techniques, so I thought to ask here if anyone here knows of one.


texts: Finding good and effective solution for overhead RCC slab spalling due to corrosion in Rebars

texts: Please suggest some effective repair solution for spalling overhead slab due to high corrosion in rebars.


texts: Variation of LED light as a function of distance

texts:
I'm trying to use LED's as a point source of light for a project I have.
a crucial idea is that the intensity of the light of the led falls off as 1 over the distance squared as we move away from it. i.e. it should obey the inverse square law.
I ran some measurements on an LED and tried to fit the results on a curve but did not get that result,(the intensity was more proportional to $1/d^3$).
my measurements could be non-accurate.

I haven't found any helpful sites that point out that LEDs actually follow the inverse square law, but I'm still skeptic that it does.

so my question is, can an led be used to some extent as a point source? how does an LED light vary with distance and with direction? if unfit, what other light emitting circuit components can be used instead if any?

I appreciate any kind of help.


texts:
I bought a 4 W Electromagnet to collect aluminium cans laying on the floor. A can weighs around 0.015 kg. I read aluminium is only paramagnetic. And playing manually with the current magnet, I cannot appreciate any force being exerted to the aluminium can.

How powerful should a magnet be to be able to pick the cans from the floor?
(let's say, from 10 cm away?)


texts: Do the hole patterns drilled in laps really help ensure uniform expansion and contraction?

texts:
Some laps have patterns of holes drilled into them - two examples are below. In both cases the user claims that the holes (among other techniques) help ensure that the laps stays close to round when they're adjusted. I've seen it in enough places that I'm willing to believe there's some truth to it. Beyond vaguely saying that it redistributed the stress, I just don't see how though.

How do these hole patterns help ensure roundness when the lap changes sizes?

Examples of the claims (time to start on the relevant sentence):

https://www.youtube.com/watch?v=H2SeLcbcYkE&feature=youtu.be&t=188
https://www.youtube.com/watch?v=AEsaSN4LLU4&feature=youtu.be&t=178

Examples of the laps:


texts:
I have a zinc lock box that looks like this:

where there's a top and a bottom part. Notice that there're two interesting features (circled in red):

After cutting it up slightly:

The section view (of the right feature) looks like the following:

And the part circled in blue previously looks like:

Are those features results of some staking operation? If so, is it common for staking to produce such clean, squarish dents (red arrow) even on the lower part? My guess is that these might be designed for holding the two parts together.

UPDATE

I've now cut another piece off to hopefully aid better understanding:

The features highlighted by red arrows don't seem to be regular shapes. The corners of the deformations in the upper component seem to have very small radii, but the features in the lower component that "bite" into the upper component look quite rough. Could this mean that the dents in the upper part were part of the cast and not deformations created by staking into the lower part?


texts: Is there a positive displacement compressor that can rival axial compressors in terms of air mass flow to weight ratio?


texts: Rotate rack while keeping it engaged with gears

texts:
I am trying to design and construct a working replica aircraft instrument (a Horizontal Situation Indicator to be exact) but am facing a couple of issues. The first one can best be demonstrated with the below picture.

The inner disk (brown-ish, including the white markings) can rotate freely around a central axis. The orange bar is fixed to that disk, so it rotates with it. At the same time, the bar should be movable along the slot on the lower part, so with the disk orientation depicted in the picture it would be able to move left and right.

I thought the easiest way to move that bar is using a rack that moves left and right. However, I don't see a way to keep that rack coupled with its driving mechanics throughout the rotation. The goal is for it to be moved completely independently of the rotation.

The first solution that comes to mind is fixing the motor that moves the rack to the disk so it rotates with it and the coupling between the rack and its pinion remains stationary, but that comes with other drawbacks as I'd have to incorporate a slip ring for the wiring and have to deal with the extra torque that is required to rotate the disk to begin with.


texts: How to calculate strain from maximum bending moment and stress?

texts: How can I calculate the strain in a simply supported beam from having the maximum bending moment (25kNm) and the maximum bending stress (45MPa)?


texts: I'm doing an optional review sheet before a test and I'm stuck on this one problem. I really don't know what it's asking. Can someone help lead me in the right way? Thank you


texts: Sum up the loads at same position on a deflected beam

texts:
I am computing the deflection of a beam.

If the length of the beam is 10 m and I have load at the position 4 m from left with force 5 N.

Now I add another load at the exact same position with force 4 N.

Can I just sum up the forces and write 9 N instead of 5 N?

It's a school exercise in which I'm told to plot the deflected beam and show all the loads. The only clever way to show the loads is to plot arrows at the positions and annotate the arrows with the load force. But if I have many loads at the same position, it will be quite messed up.


texts: Equation for Axial flow compressor blade/stator vein geometry?

texts: I've read through many PDF's on the web but can't seem to find the equations I'm after, I am trying to make a small model axial flow compressed jet engine, a little smaller then a shoe box. Any good online resources I can read up on? Much appreciated.


texts: How does stiffness/rigidity affect the bending moment of a beam

texts:
My question may sound silly as it’s mainly good sense but I may be mixing things up.

Let’s consider a flexible cantilever beam of a given length and material is fixed at one end and free at the other end.
Let’s suppose a dead weight is put at the free end.
This results in a bending moment at the fixed end of say 10 Nm and a given deflection at the free end of say 1 cm.

Now let’s suppose the beam thickness gets increased and as a result stiffer. The deflection at the tip will be reduced for sure, but what about the bending moment at the fixed end? Is making the beam more rigid going to reduce the bending moment?

Looking forward to your thoughts!
Many thanks

Thanks for you answers, much appreciated.

I get that the bending moment caused by a static load applied at the free-end does not depend on the elasticity of the beam. Only the deflection does. I would have thought that the greater the deflection the higher the bending moment... Can you confirm this isn't true? Imagine a 100 m long vertical monopile support structure looking like a slender cylinder anchored in the seabed and subjected to dynamic wave loadings exciting all the cylinder modes. The thinner the cylinder wall is, the more elastic the cylinder gets and the greater the deflections at the top get. I would think that the maximum bending moment would be reached when the deflection is the most significant and therefore making the cylinder more rigid with thicker wall would both reduce the deflections and the max bending moment, wouldn't it?


texts: How to do Blade Element Momentum Theory Analysis for NACA airfoils?

texts: I wanna perform BEMT analysis on blades of different geometry and not just symmetric thin airfoil. How to do this?


texts:
I recently saw a video where a glassblower was making something, and one of the first steps was to push the wad of molten glass down into a shaper with a number of vertical spikes, such that the result vaguely resembled a gear.
I am aware that gears can be made of plastics and wood (e.g. https://woodgears.ca/gear_cutting/index.html) as well as metals, but would glass (perhaps a stronger variant such as tempered or borosilicate glass) be suitable to make gears out of? Are there any historical examples of this?
Obviously with modern materials and techniques steel is probably the best choice in an industrial setting, but I am curious as to it's suitability as an intermediate step between cheap but quickly worn down wooden gears for rapid prototyping and metal gears for serious use. I would imagine it could be a lot easier and cheaper to melt glass in a home workshop and pour it into a mold or shape it appropriately as compared to doing the same thing with metals (keeping in mind equipment costs e.g. having to build a foundry capable of melting steel).


texts: What is the difference between BOR and POR micro-controller reset modes?

texts:
I have been reading about embedded systems, and particularly the reset modes. As I understand a microcontroller can have several reset modes.

What is brownout reset (BOR) and power on reset (POR)? What is the difference between BOR and POR?


texts: What is a round steel bar called with straight grooves running its length called?

texts:
I have a variable speed controller that has a knob that's a push fit. The knob is pushed onto what I would describe as being a rod that has grooves like a thread but the grooves run the length of the rod, rather than around it.
What is this type of rod called? And if I were to want to extend it, are there fixtures designed to essentially connect two of those types of round bar together?


texts: What is the logic to solve this cantilever problem?

texts:
I solved it using the logic that the vertical link of the beam is basically there to make the beam act like a cantilever.
So I think it is a cantilever problem.

Therefore,
$$EI\frac{d^2y}{dx^2}=-px=M$$

and further integrating it we get
$$y_{max}=\frac{PL^3}{3EI}$$

But the book people say that the answer is wrong and the answer it 4 times a this answer. Why?


texts:
I have the situation from the following drawing:

It represents a model for measuring the torque of a generator.
There is an arm connected to stator and, the other end of the arm to a bending type load cell. I want to model this system and have as an input the torque of the generator rotor and as output the torque that reaches the load cell. I want to model somehow how is the transfer of energy from the rotor to the load cell.
The load cell type is Hottinger Z6FC3.
The system is connected like in the figure below.

I am new at this and don't know much mechanics. I don't know how to write the motion equations for the two bodies and connect them.


texts:
Ok so what happend is that i started to think about Submarines and why exactly you cannot open the bottom heatch at lets say the Challenger Depth. At least i am pretty sure you cannot do that. Right ?
Because, i was told that if you were to open the Heatch, water would still rush in and kill you rather fast. But why ? All of the Water and thus all of the Pressure is above you. Here is a bad illustration of what i mean
My theory: In theory you can do that, but now, since there is no floor, all the Pressure from above is resting on the Water below. Which itself is the support for the Submarine. And with no floor, the Water gets forced in. So what happens is that the Air is acting like the Floor that is missing. But while the Floor could resist the Pressure from above pusing it against the support from below, the Air cannot. And thus gets compressed.
Is that right ?


texts: How to design a transfer function for a Model Rocket?

texts:
I am building a roll stabilized model rocket. I am beginner at controls systems. How do I find out the transfer function of the rocket. Although, I am aware of definitions and stuff of control systems. I just a need a nudge in the right direction.

Also what your thought on using State Space Analysis?

Thanks so much! :D


texts: What level of vibration testing should I perform on my product?

texts:
I'm trying to determine a level of vibration testing I should perform on my product. I understand electrical stress/life testing and I'm looking for a mechanical equivalent.

I have a DC motor running in my application that generates a certain level of vibration. I'm planning to do some environmental testing to my electronics and one of the tests is vibration, so I plan to subject the electronics to the level of vibration above what the motor produces, my thinking being that a higher level may be equivalent to electrical life testing. My product needs to last ten years so I'd like to know that the vibration I see now won't cause problems in several years time.

For instance, I can put an accelerometer on my electronics and measure ~2 g. To simulate over the product's lifetime should I be applying a higher level of vibration, say 3-5 g?


texts: Conveyor Truss Analysis Problem with loading

texts:
I've been working on a schematic and its been going beyond my comprehension; so i thought i should consult better structural engineers here. (I'm a fresh Civil Engr Graduate though)

i have this scheme shown below, where the task is to design a truss carrying a conveyor mechanism. i'm able to calculate trusses of any type with correct loading parameters, but this scheme has been eluding me for hours.

so i simplified it to this for proper analysis

The issue is that, i know trusses cannot carry load on their members as done in the scheme where 7.3 KN is applied. This is where the problem is, am i missing something? this is my first conveyor truss analysis, i really hope this QA site will shed a lot more light on this matter. Thanks


texts: Which type of motor can I use for my project?

texts:
I am working on a project of linear positioning where a bed is coupled with a motor driven high pitch multi-start back driving lead screw. I need the bed to be freely moving when the motor is not energized.

Currently I am using a NEMA 23 hybrid stepper motor of 1.8 Nm torque with gears since it has significant detent torque. But i need to eliminate the gears.
What kind of motor will be suitable for me?

The approx specs needed are as follows:
Torque: 0.7-1 Nm
max speed: 200 rpm

PS: I read about variable reluctance stepper motors but was unable to find any manufacturers or distributors for it. Can someone please direct me to one, also I am open to consider any other types of electric motors.