texts: How to calculate the adhesion I need to keep a 3D printed bending part straight?

texts:
3D printed parts cool down during printing, resulting in thermal contraction which causes a bending moment and separation from the printing bed.

The issue is solved by increasing adhesion to the printing bed, which however results in more stresses inside the part which can cause cracking.

The result is a poor printed part:

Provided I know the thermal expansion coefficient of a material and the Young modulus, the temperature delta causing contraction (which should be glass transition temperature minus ambient temperature) and the part length, how can I calculate the adhesion force required to keep the corners of the part sticking to the bed, or the adhesion force required to keep the layers together, without delamination?
I know that complex shapes would require different calculation. For this question I would consider only parallelepipeds ("boxes", "beams").
It may be dependent on layer height, but I think it can be regarded as second order parameter and omitted from a rough estimate.
An approximation is enough, I guess that accurate results would require a finite element analysis, which is beyond the scope of this question.


texts: Multi-stage/multi-section reinforced concrete slab design

texts:
In pre-cast bridges, one often lays beams over the columns and then places thin pre-cast "pre-slabs" over the transversal spans between the beams. These slabs already contain all the requisite positive transversal (between-beams) steel reinforcement. All other reinforcements (positive longitudinal, negative transversal and longitudinal) are then placed and In-situ concrete is poured over the "pre-slabs" up until the requisite thickness. Steel framing contained within the "pre-slabs" certifies that the pre-cast and in situ concrete work together under ultimate loads. Here's an example:

So, how does one calculate the slab's positive transversal reinforcement? The steel must be stressed so as to create a force couple with the resultant of the concrete's compression.

Now, the "pre-slab" needs to be able to withstand a load equal to its own self-weight and that of the wet in situ concrete. If this were calculated by traditional methods, a certain steel area $A_{s,1}$ would be obtained.

The additional loads (paving, moving loads, etc) are then applied as well once the in situ concrete has hardened. These loads are therefore resisted by the force couple composed of compression of the in situ concrete and tension of the reinforcing steel. If this were also calculated by traditional means, a steel area $A_{s,2}$ would be found.

Now, is the resultant necessary steel equal to $A_{s,total} = A_{s,1}+A_{s,2}$? I was initially concerned that there might be an interference in the compression regions, but given that the pre-slabs are usually less than half the total slab thickness (in the example above, a 7-cm pre-slab supports 13 cm of in situ concrete, for a total slab thickness of 20 cm), I don't believe that'd be a problem.

That being said, I'm not entirely certain of this conclusion and would like confirmation or correction on this matter. This summation of areas means that all of the steel would be stressed below their ultimate capacity in the first stage (such that $A_{s,total}\sigma = A_{s,1}f_{yd}$) and then would reach the ultimate stress under final loads (such that $A_{s,total}\left(f_{yd} - \sigma\right) = A_{s,2}f_{yd}$). Is this fine or is there some behavior I'm not taking into consideration?

Obviously, then there's the case where the compression zones of the different stages interfere one with the other, but I'll leave that for a future question.

EDIT: Here's an example of a pre-slab blueprint, including the steel reinforcement. This case is for the pre-slab including a cantilever, which explains the gap: that's where the beam's transversal steel joins with the in situ concrete. The units are centimeters. The "criss-cross" in the cross-section is a steel truss.

This site describes pre-slabs thusly (according to my rough French translation): "The pre-slab is layer 6 to 8 cm thick, creating a sort of base, whereupon once installed on the site, one must add a compression layer." It also has the following picture of a real pre-slab, where the trusses responsible for certifying that the pre-cast and in situ concrete layers work in unison are clearly visible:


texts: What type of air blower/compressor to use?

texts:
I need a way to move air which is somewhere in between a compressor and a fan: something along the lines of 20-40 cfm at 2-3 psi (500-1000 liters/minute at 10-20 kPa).

Typical small compressors (of the right power rating) seem to be approx 0.5 cfm at 30 psi.  Typical centrifugal blowers are approx 60 cfm free flow but only 0.05 psi max static pressure.

I'm having trouble visualizing what I need, let alone sourcing it.  Leaf blower?  Shopvac?  Supercharger?  Do I want a piston pump, diaphragm pump, screw compressor, turbopump, some type of higher pressure centrifugal fan, or ???

For this application energy efficiency at the described operating point is most important; size/cost/noise is much less important.  UPDATE It also needs to be oil-free.


texts:
I'm looking at linear compression dampers and finding them most commonly specified only with a "Max Force" – e.g., 270 lbs.

However, since the damping mechanism is provided by hydraulic or pneumatic resistance, the damping force must be a function of the force applied.  Here is a supplier that specifies the damping rate as the resulting "inches/second of motion given a 40lb load."

As best I can tell, neither of these figures completely describes the damping characteristics of a hydraulic compression damper.  Nor do they describe the same characteristic.

Is there some standard model or specification of such dampers that can characterize the damping resistance or speed that will result from any force (within some design range)?  (And do either of these sample specifications determine the model?)


texts: What are the charge/power connector of restaurant order pagers / buzzers called?

texts:
They look like snap buttons and used for stacking pagers for charging.
Closest things I can find are socket screws and cap nuts.


texts: What is the theory that makes this method work when dynamically balancing this system

texts:
Sorry for my bad english in advance I am not a native speaker.
I have a system similar to the one above and we are supposed to statically and then dynamically balance it. To statically balance it we are told to set two of the masses to arbitrary angles, we chose 90 degrees away from each other. We were then told to create a vector diagram, where the lengths of the vectors correspond to the mass*radius values for each of the 4 masses. By creating a complete shape we managed to find the angles of the other two masses for which to statically balance. I understand why we do this and theory behind it.

To dynamically balance it we are given these instructions

I can follow the instructions but I do not understand why this should be done and how this relates to dynamic balancing. Would someone please be able to explain why?


texts:
Here is how this artist rendered Brunel's Saltash Bridge:

Here is how it appears today.

Did the appearance change, or was some artistic licence taken in the painting?

My question is: Did this artist take some licence with the Royal Albert Bridge - or has its appearance changed?


texts:
A sawblade cuts a piece of steel which has a rectangular profile with height $h$ and width $b$. The length of this piece is given by $\ell$ (not relevant for the cutting process). I have a sawblade with length $L$ and sawtooths that have length $\Delta L$ (the sawblade therefore has $N = \frac{L}{\Delta L}$ sawtooths), peak height $f$ (the distance from minimum to maximum of a sawtooth) and thickness of the sawblate is $t$.

The sawblade is attached to the piece of metal with force $F$ and uses full length for sawing (velocity: $v$). A periodic motion front - back - front - back - ... is exerted by the sawblade.

Question 1: Which material parameters of the steel and blade determine how much the saw will penetrate through the piece of metal during ONE saw motion with full length?

Question 2: How long will it take until the piece of metal is cut?

Are there formulas to compute such things?


texts:
I am attempting to design a "flying saucer." The saucer is an ellipsoidal-ish body with a RC drone inside. I plan to allow for air access to the rotors as shown in the rudimentary diagram below:

I am pretty sure that the drag on the air flowing through the intake and through the body of the flying saucer will reduce the thrust capacity of the drone. Can anyone confirm this? Are there any other considerations I should keep in mind (maybe there's a reason helicopters don't have a big tube surrounding the lift rotor)? I want the flying saucer to behave like a slow, mellow RC drone (I don't really want high speeds or elevations).


texts: Why the variable "r" appears in circumferential force balance for a membrane

texts:
I am trying to understand a force balance for an inflating membrane (reference cited at the bottom of the post) and can't figure out why there is an "r" in the circumferential balance.
The membrane uses a cylindrical coordinate system.

"s" is arc length.
I understand the vertical balance, but not the circumferential force balance.
This is the diagram shown in the paper:

This is the resulting equation:

I don't understand the following:

T is said to be principal stress resultant, but thickness of the material is never considered here. Don't I have to multiply by the thickness as well in the first term to get force? The vertical balance did not consider thickness of the membrane either.
I understand that T1 cos(phi) is the component of T1 along the plane of interest, and (theta) is some angle in the plane. T1 cos(phi)sin(theta) is the component of T1 along the horizontal direction, and the "2" comes from integrating this from theta = 0 to theta = pi.
However, why is there an r? Why is it not just 2T1cos(phi) in the second term?

Thank you very much.
Reference: J. D. HUMPHREY (1998) Computer Methods in Membrane Biomechanics, Computer Methods in Biomechanics and Biomedical Engineering, 1:3, 171-210


texts: Will a shade hood increase a/c efficiency?

texts: Would adding a shade (i.e. a piece of plastic) at the back of an A/C increase the efficiency of a window unit A/C? I'm not talking about covering the fins but rather placing a sheet of plastic above to create shade without obstructing the air flow. Or does the forced air easily suck off the heat regardless of how much the sun is shining on the unit?


texts: Is there an FPGA which could "re-wire" itself on the need?

texts:
For example, if there is many floating point operations, it could "rewire" the area of some of its integer units to handle floating point instructions, and vice versa. Or if there isn't too many calculations, but there is many I/O need, it could parallelize its IO better.

As I know, the FPGAs load their HDL code on boot, but to me it seems not really impossible, to make it possible to reload differents  parts of a bigger HDL on the need, partially.

Does a such FPGA already exist?


texts: How does Abaqus calculate reaction force?

texts:
I wrote a UEL for one element and compared to a reference UEL (FEM), where the results agreed satisfactorily, except the reaction force. The stress, strain, strain energy all were pretty accurate.

I am unable to understand this, how does Abaqus calculate reaction force?

I am simply restraining the element in the bottom(two nodes) and applying displacement(incrementally) at the top(two nodes).

As far as I know, the STIFFNESS matrix is used to calculate reaction force in these cases, the stiffness values are quite similar in my UEL and the FEM UEL. Also if this was the case, the other parameters wouldn't have had the same values.

This is probably leading to convergence issues when I am using my UEL for more than one element, where the solutions cannot even converge for the first increment.

Would be grateful if anybody could help me figure this out.


texts: How do I form a budget for a mechanical research project?

texts:
I'm a mechatronics engineering student currently on workplacement. I've put forward a research proposal to develop an improved mechanical gripper used for automated product handling. The company likes the proposal and wants to go ahead with it, but they want more detail in the proposal, specifically a budget.

I'm a little lost in this sense, I'm not sure where to start. I'm not sure how much a prototype will cost, nor how many I will need. I have considered taking a small percentage of the overall losses caused by the current solutions but even those seem unjustifiably large.

From other professional engineers experience, what would be the usual method to develop a budget.


texts: Double-bagging problem: which bag on the inside?

texts: If you're double-bagging some groceries, and one of the bags has tears in it while the other is intact, which bag should go on the inside?


texts: Health hazards of disassembling electronic devices?

texts:
I´ve been disassembling a lot of electronic devices in order to recycle them, separating plastics, electronic boards and bolts/other metal parts.

Is there any proof of health hazards for doing it without any kind of protection?

I´m worried about possible substances used when building that could affect me by touching or inhaling them.


texts: unexpected bodies appear in ansys mechanical

texts:
I am using ANSYS Workbench 16.0, static structure analysis. An assembly is imported from NX 8.0.
In Design Modeler, I modified some parts and regrouped them, at last there are 129 bodies, and 9 parts are formed (one part contains all useless bodies and is suppressed). I renamed the bodies one by one (including suppressed ones). Everything looks fine.
But when I open Mechanical, I find one big body is missing, and many strange bodies appear randomly in 8 parts, which do not ever exist in Design Modeler.
I have renamed every single body that exists, but the unexpected bodies have raw names.
They are small parts, small faces or just empty objects with names like NX assembly and part names.
I've reset and refreshed the 'Model' step in static structure many times, but that doesn't help.
Please tell me how I can fix it?


texts: Establishing DGPS Communications With SurvCE and Novatel Recievers

texts:
I am trying to do a differential surveying project with some outdated equipment, specifically:

An old AllegroCX personal handheld computer (Win 4.1) with SurvCE loaded on it to collect data and establish communication
Two Novatel ProPak V3 Recievers (one for base, one for rover)
Two external radio communicators
Two pinwheel style antennas

I am able to establish a connection with the rover's Novatel reviever and AllegroCX using a serial cable, but I cannot get it to find the base receiver using radio communications. Is this possible wirelessly, or do I need to set up the base station via serial cable as well? Do I need to have a PC connected to the base receiver?


texts: How to have multiple copies of the same component all with different colours in Solidworks?

texts:
Regarding Solidworks 2014 (SP2)...

In an assembly I have three identical copies of a single transparent acrylic component.

How may I give them different colours?  When I change the colour of the first one to green (material...edit) they all become green even though only the first one is selected.

Clearly this change is getting pushed all the way back to the .sldprt file, but I only want this to happen at the assembly:component instance level.

I have tried to do this using a design table in the .sldprt file but I cannot figure out how to configure the columns.  Also I couldn't persuade the appearance manager to understand what I want as the "copy/paste Appearance" features seem to overwrite the Appearance rather than adding new ones.

Edit: @SBarry's suggestion worked a treat...


texts: PI-Controler: Comparison of characteristic equations

texts:
I have to design a PI-controller with zero order hold for the plant
$G_s(s) = \frac{0.24}{(s+4)(s+12)}$ to meet the specifications of $\omega_n=5\,s^{-1}$ and $\zeta = 0.6$.

I choose a $T=0.12\,s$ which leads to a approx. 13 samples per oscillation  (and $T \leq 0.125 T_d$)and applied the Z.O.H. to
$H_o(s)G_s(s)=G(s)\approx \frac{1}{1+0.5 T s}\frac{0.24}{(s+4)(s+12)}$.

With the transfer function of the PI-controller:
$G_D(s) = K_c\frac{a + s}{s}$ I get the characteristic equation with
$H_c(s) = \frac{G(s)}{1+G_D(s)G(s)}$ to $\frac{4s}{s^3 + 32.667 s^2 (314.672 + 4 K_c)s + 800.016 + K_c a 4}$.

With the desired system of:
$\frac{1}{(s^2 + 2 \omega_n \zeta s + \omega_n^2)(s + \alpha)}= \frac{1}{s^3 + 32.6s^2 + 184.6 s + 665}$ where I choose  $\alpha=26.6$ with $\alpha \approx 4 \ldots 5 \omega_n$ (hence, the $s^2$-term is equal).

Now I did the comparison of coefficents:

$314.672 + 4 K_c = 184.6 \rightarrow K_c=-32.518$

$800.916 + K_c a 4 = 665 \rightarrow a = 1.038 $

Theoretically this should be now a proper $K_c$ and $a$. But simulation shows undesired behavior (step response goes to infinity). Should I introduce another pole? Is the general approach right?

(Remark: I edited the problem considerable with help from Design of a PI controller.)


texts:
I'm new to electronics and I have a problem with timers and pulses.
I have a 24 V input signal that turns on every now and then. On every rising edge of this signal (from 0 to 24 V), I want to output a 24 V signal for 100 ms. (No retrigger.)
I've been looking into LTC6993-1 and 555 timers, however, to my understanding both of these require a constant power source to operate (which I want to avoid) and they also seem rather complex compared to the problem.
I wonder if there is an easier approach to accomplishing this without having a constant power source and just using the 24 V input signal?


texts: Do pressure regulators restrict the mass flow rate?

texts:
Suppose we have a tank containing compressed air.  If a hole is made in the tank the air will start flowing out.  The mass flow rate of exiting air will be heavily dependent on the diameter of the orifice (ie the narrowest opening on the system) - the bigger the orifice the greater the initial mass flow and vice versa.

Now, let's say we want a certain mass flow rate (x) coming out of the tank, whilst maintaining a constant pressure in the exiting gas.   We can achieve the desired mass flow rate
by making an appropriately sized opening in the tank (I'll call this opening O[i]) and adjusting the pressure using a pressure regulator.  The issue here is that the pressure regulator could have a smaller opening (O[pr]) on its inside, ie O[i]>O[pr].  This would consequently reduce the mass flow rate coming from the tank.

It's obvious that a pressure regulator can't be used above a specific desired mass flow rate.  What other devices could be used?  A wider pressure regulator maybe?

I have included a diagram of a pressure regulator, which clearly shows the small opening inside.


texts: aircraft pursuit dynamic system state update

texts:
Planar Evasive Aircrafts Maneuvers Using Reinforcement Learning

$$d=\sqrt{(x_m-x_e)^2+(y_m-y_e)^2}$$

$$\dot{d} = V_e \cos (\lambda-\Psi_e) - V_m \cos(\lambda-\Psi_m)$$

$$\lambda = \arctan\frac{x_e - x_m}{y_e - y_m}$$

$$\dot{\lambda} = \frac{V_m\sin(\lambda - \Psi_m) + V_e\sin(\lambda-\Psi_e)}{d}$$

In the state equations, $d$ is the distance between the objects $m$ and $e$. $\lambda$ is the line of sight angle between $m$ and $e$. $V_e$ and $V_m$ are constant scalars. $\Psi$ is the heading angle of an object. The picture of the geometry can be seen below.

I am interested in the discrete time state update $x(k+1) = x(k) + \delta t \times x(k)$. I have solved $d$ dotdot and $\lambda$ dotdot above. I can just plug in $\dot{psi}$ = acceleration / velocity and other variables except for $\psi_m = arctan(\dot{y_m}/\dot{x_m})$ and $\psi_e = arctan(\dot{y_e}/\dot{x_e})$, which I cannot solve using the four state variables. Please advise me how to solve for heading angles $\psi_m$ and $\psi_e$.


texts: Bar heater operating on a duty cycle - possible problems?

texts:
It's easy to obtain a room-scale radiant heater (of the order of 700-800W per bar, eg this three-bar heater) that operates very simply and easily - you turn it on, it consumes electricity, it generates heat. Convenient, cheap, simple. But they don't seem to be made in lower wattages, and my inexpert brain is wondering: what would happen if one of these were to have some electronics added to run it only part of the time? For instance, let's say I selected 75% power on one bar; it would close the circuit for 750ms, then cut the power for 250ms, repeat indefinitely.

Are there any critical downsides to a system like this?

Would this actually consume (roughly) 75% of the power and produce 75% of the heat, or would something in the behaviour of this kind of heating element change this?

Why don't heaters like this exist, with full option for any power level you choose?


texts: I wanted to know if there are any open software or even purchasable software available to predict the permeate quality through a nanofiltration module. I am designing a plant for my final year mechanical engineering undergraduate project and need to show what the results of my setup would be without actually building it.


texts: Is CNC milling on metals always followed by heat treatment?

texts:
CNC milling causes residual stresses in metals.
So, after CNC milling of a metal part, say aluminium, do all manufacturers (I'm not referring to any specific manufacturer, just generally) heat treat such parts parts after milling?


texts: Moving carbon nanotube in a magnetic field

texts: When a metal wire moves across a magnetic field, voltage is induced across it, which is equal to $BLV$, where $B$ is strength of magnetic field, $L$ is the length of wire and $V$ is its velocity. Will a carbon nanotube also exhibit this phenomenon? I am asking this because carbon nanotube is although a good conductor of electricity, but probably that is because of some quantum phenomenon (bulk carbon is bad conductor of electricity).


texts: Which US states require a bachelors in Engineering to become licensed?

texts:
I am considering moving from abroad to the US, and hoping to obtain an engineering license for employment. I have a bachelors and graduate degree in physics, but I have heard that many states require a bachelors in an ABET accredited program to become licensed.

Which states do NOT require an engineering bachelors? If they don't require this, do they have some other requirement instead?


texts: How to transfer reaction forces of beam to a weld?

texts:
I have modeled a beam as fixed-fixed. The reaction forces are -1494 lb.ft and 761 lb (vertical). There is no horizontal reaction.

Now I know this beam is welded to another element. I am trying to design the weld for the necessary forces. How do I transfer the reaction forces at the fixed end to the weld? Should I invert the directions of the reactions or should I preserve the same directions?


texts:
Is the mass flow rate constant in a thermodynamic cycle? More specifically a Rankine or Carnot cycle.

For example if the mass flow rate of the turbine is 100 kg/s, is the mass flow rate for the boiler / condenser / compressor or pump also 100 kg/s?


texts: Is there a mechanism that can turn circular motion into alternating circular motion?

texts: I'm trying to power and agitator (alternating circularly back and fourth) with a crank. I've seen a bunch of complicated mechanisms that do this, but I'm looking for the mechanically simplest method.


texts: In internal combustion engines, what determines when soft or hard gaskets are used?

texts:
I see that 4 stroke engines use hard gaskets at the cylinder heads, whereas two stroke slow speed engines that are used for the propulsion of ships or for production of electricity on land have soft gaskets.

What determines which gasket should be used?


texts:
I will try to lift up 25kg (50 pounds)(electrical child car) on a linear actuator and I know that there would be a 30cm long lever.

But my question is if there will be some lever. I think it won´t because the linear actuator will be in the middle above the load. Or am I wrong and there will be a 20cm or 30cm or 50cm lever?

Thank you for your advice.


texts: How to calculate thrust from mass flowrate and velocity

texts:
How can I calculate thrust in Newton from mass flowrate and velocity?

Please  note,I have mathematical skills of 7 year old,the most complex task I can do is multiply and divide,I dont understand any equations.


texts: Will a cyclic heat load transform my martensitic steel? How fast?

texts:
I have a plunger - that I'm using for glass forming - made out of a martensitic steel. Glass is at 1000°C and since martensite is a metastable phase, should I expect the properties of my plunger to change during its life?

If that's the case how can I calculate how fast it is transforming?


texts:
I am looking into making a strong electro magnet.
I want it to be able to hold around 100 pounds of weight or more.

Would a magnetic core like this work at all?
I'm planning on wrapping wire around one of these 'C' shaped ferrite cores.

How much current should I expect to be using?
How many turns or windings around the core should I expect?
Is 22 gauge copper solid core wire recommended?

A rough estimate would help very much.
Also If there is any formula or information you could add so that I could start to answer some of these questions I would greatly appreciate it.


texts:
I'm trying to calculate the safety factor against separation of members in a design that looks like this:

I know how to find the bolt and cylinder stiffness, but I don't know how to find the stiffness of the effective loaded area of the plates. I'm used to calculate the stiffness of hollow cones as represented here:

but this is not the case. Any suggestions?


texts: What coefficients should I use when modeling non-stationary heating of a steel plate?

texts:
I am trying to make a model of non-stationary heating on a plate, where I must use an explicit numerical method to solve the model. I decided the plate will be made of steel (0,5% C) and I found that the thermal diffusivity coefficients $k/\rho c_p$ are:

$$\alpha_{steel} = 14.74 \times 10^{-6} \:\mathrm{m^2/s}$$
$$\alpha_{air} = 1.9 \times 10^{-5} \:\mathrm{m^2/s}$$

I also have to implement a heat source but I don't know what coefficient I should use for that.

As it's a 2D problem, my solving code looks like this:

def heat_source(x, y, matrica):
if (x >= 0.8 and x <= 1.2) and (y >= 0.8 and y <= 1.2):
    if matrica[10,10]<300.:
        return 280 + randn(1)*20
    else:
        return 0.
else:
    return 0.0

dmx = (M0[iY,iX+1] + M0[iY,iX-1] - 2.0 * M0[iY,iX])/dx**2.0 # conduction in x-direction
dmy = (M0[iY+1,iX] + M0[iY-1,iX] - 2.0 * M0[iY,iX])/dy**2.0 # conduction in y-direction
M_new[iY,iX] = M0[iY, iX] + k_diffusion*dt*(dmx+dmy) + dt*k_heating*heat_source(X[iX],     Y[iY], M0)  - dt*k_cooling*(M0[iY,iX]-T_ok)

My questions are:

Am I using the right coefficients? If yes, what coefficient should I use for the heat source?
What's the difference between non-stationary and stationary source?


texts: Trying to find proper Open source CAD Software For the Automatic Tooth Comparing

texts:
I am trying to do the Automatic Tooth's CAD Compare for Tooth crowns preparation. One software for this work is the PrepCheck software and do it like shown below (YouTube video)]6

So it must be done by on the 32 Constant Geometrical characteristic for the teeth as said here.
If possible, I am asking about finding the best Open source CAD compare Software to do this automatic calculation?
I guess the CloudCompare could be a candidate, For doing it. For this, it needs to write some scripts for:

Finding every one of 32 tooth locations by Artificial
intelligence CAD Segmentation (like said here and
here) or ...,

Doing the compare by some automatic scripts for that location in
STL file.

So, The question is for finding the proper software to do this procedure on it (blender or  ...), by finding some popular Open source CAD software for this calculation I could find some sample codes via GitHub and Paperswithcode site, better.
Note:
Excuse me, If having too much information. This is because, I have tried to ask this question as a guideline to do this project, for myself or others (by adding the search links and ...),
Thanks.


texts: Thin film sheet-resistance (van der Pauw method)

texts:
A well-known method to measure sheet resistance is the van der Pauw method. Looking at Wikipedia they state that the cloverleaf configuration is the most advised. Two questions naturally arise:

Why is this the best configuration?
Why is it a cloverleaf and not a fully "filled" circle?


texts: How to periodically shut down a recirculating hot water solar thermal system

texts:
I am posed with a scenario where a hot water solar thermal system has been setup. The system comprises of a cold water tank, heating arrays and then a hot water tank. The system is closed loop and water always keeps recirculating. The system uses CPC Evacuated vacuum tubes in the link below:

http://andyschroder.com/CPCEvacuatedTube/TechnicalSpecifications/

As a part of the system's primary loop, water is drawn from the cold water tank, passed through the array and it arrives into the hot water tank.

Now the secondary loop is used to consume the energy and cool down the water in this process. In the secondary loop, Water is drawn from the hot water tank, passed via a heat exchanger and it arrives back into cold water water tank.

If the heat demand from the secondary loop is consistant and higher then the supply, everything works in harmony and the hot water tank temperature stays in control.

The problems comes in when the secondary loop no longer requires heat energy(due to a downstream low demand). Since the primary loops keeps generating energy, water in the hot water tank exceeds 95C and drain procedures are activated to prevent steam generation/excessive pressures.

The problem is exagerated by the fact that the downstream system's demand pattern is very inconsistent and the demand maybe zero for several days frequently(so I know the thermal system has been over designed but downsizing permanently is not an option)

Question:
Considering the situation above, what is the safest way to stop power generation from the arrays.

My understanding is that just stopping the recirculation would cause hot water residing inside the vacuum tubes to heat up beyond boiling point and pop PRVs on the array. Over some time this would also mean the copper tubes inside the vacuum tubes would scale and deteriorate aswell. Is this thought correct?

A solution that came to my mind was to stop the recirculation when the hot water tank has very high temperature and use compressed air to purge the water stagnant inside the array? Is this a good idea?

If air purging could be practical, I wanted to understand if there is a type of valve that would allow water to go though while preventing compressed air to go through? If such a mechanical valve exists, water could be purged through different parallel arrays without investing into automatic valves per array.

Looking forward to hearing your thoughts on how would you tackle this problem.


texts: How to determine the degrees of freedom for ball and beam system such as shown in pic below

texts: Since, motion of the ball on the beam depends on the beam angle alpha, shouldn't this system have a single degree of freedom?


texts: How can I mould a foam-core'ed carbon fibre shape?

texts:
I am trying to figure out the best way to mould/ create a closed shape (It is a 500mm long quadcopter arm) that has a foam core, and a rigid good quality carbon fibre outer.
Oh and to add to the fun, I need a hole through the center of the foam core.

Said shape must be structural and resistant to twist and bend.

My initial thought is to create 2 halves of the foam core on a 3 axis router, with the hole present, stick them together, then somehow wrap them with carbon... epoxy, jam into a mould?

Obviously there will be an amount of finishing involved, but thats OK.

The process muse be repeatable and yield a near-identical item each time.

ETA:
Further reading suggests that Vacuum assisted resin transfer moulding may be the answer. I would need to create a (very stiff) mould slightly larger than the foam core, pre-attach/ wrap the core with carbon/kevlar fabric, and then mould around.
I will need to somehow stop the central hole from filling with resin of course!


texts: Why would these hydraulic cylinders have 3 large connections?

texts:
I am trying to work out how a recently acquired Arburg 220-90-350 from 1982 works so that I can build a new control system and get it working. It's a direct clamping machine with no toggle.
The injection side is quite simple, just 3 motors or cylinders each controlled by a separate valve.
The clamp and ejector side has me confused though, there is a directional valve controlling each cylinder (simple enough) but each cylinder has a 3rd line the same size as the others connected to another single valve labelled 'high pressure'. So to summarise, 2 hydraulic cylinders each with 3 hoses, 3 directional control valves controlling the 2 cylinders.
I can't begin to draw a schematic without further disassembling the machine so I am hoping someone can give me some reasons why a hydraulic cylinder would have 3 hoses of equal size, with 1 on each cylinder connected to the same valve.
Edit:
On further investigation, I can confirm that non of the 3 hoses are connected together, i.e. there is not two in parallel.


texts: In the 1980s, did radio reporters actually carry around a clunky antenna contraption on their backs to communicate with their radio station's HQs?

texts:
I've been wondering about this ever since I saw this comedy TV show as a kid called Macken ("The car repair shop" in Swedish). Originally aired 1986 in Sweden, it features absurd situations and funny characters, but doesn't really use any "prop comedy", normally keeping the environments very realistic, which makes me ask this question.
In one episode, a local radio reporter enters the car repair shop wearing a huge metallic "backpack" with a large antenna and a microphone. It doesn't seem (to me) as if this is intended to be funny, and it seems "somewhat" reasonable to me that, even in the mid-1980s, such a thing would be required for a radio reporter to be able to "live-stream" the interview with the owner of the shop to the radio station's headquarters. Maybe it was old equipment even in 1986, supposed to indicate that the local radio station cannot afford the latest fancy gadgets?
Still, it does look rather goofy, and seems like something you'd associate with the 1950s or earlier rather than the 1980s. I cannot figure out if this was actually what radio reporters had to carry around as late as in the 1980s to "report live", or if it was seen as an obvious joke even when this was first aired.
It seems to me that, with 1980s technology, they would just need a small box with an antenna, which can be carried with one hand, but I'm obviously not an expert. And, again, maybe it was decades old inside the show's universe, supposed to highlight outdated equipment and the lack of funding.
The image shows two angles of this weird contraption from the episode.


texts:
Determine the angular acceleration of the $CD$ bar for the situation illustrated
in the figure.
The solution is $474 rad/s^2$  $counterclockwise$

I've done:
$v_B = v_A + w *r_{AB} <=> v_B= -3j$
$a_B = a_A + α_{AD}*r_{AD} - w^2*r_{AB} <=> a_B = -6j - 9 i $
But then i dont know how to finish it
My main doubt is what is the relation between acceleration and velocities of points $B$ and $C$ ?


texts: When to assume ideal gas law without incurring too intolerable error. I have the idea that it must be at high temperature and low pressure. Is there any specific values, and are there any other things to look for?


texts: How to calculate torque needed to stop a rotating beam over x seconds

texts:
I have a large boom of a radio antenna weighing $3,500 kg$ which is rotating at $0.5 RPM$. The antenna is a T shape and the boom radius is $14m$. The power to the motor is cut off suddenly and the motor acts as a rigid brake. The boom is not rigid and it continues to move/bend in the same direction for 1 second (at which points it bounces back and fourth until the forces damper out). I am trying to work out the max torque this would apply to the gearbox shaft, assuming there is no friction.

For angular movement, I have designated the centroid of each boom radius as a point load (so a point load at a radius of 7 m on both ends of the boom).

I can work out the angular moment which is $m \cdot r \cdot v$, which works out to $1750 kg \cdot 7m \cdot 0.367m/s$ or $4489.86kg\frac{m^2}{s}$

This is where I am not sure about though. I have read that torque is simply the change in angular momentum over time. So would that be $4489.86kg\cdot m $ $(44.1kN \cdot m)$?

Would this be an accurate way to determine the torque in the shaft? This is for a real scenario so If I have missed any big considerations please let me know.


texts: Are there any books which show how to design electrical coil heat exchangers?

texts: I need to design an electrically powered gas heater, but i need to do so in detail. I'm looking for a guide similar to the shell and tube heat exchanger design guide in coulson and richardson's chemical engineering design volume 6.


texts: When finding flow generated by a pump, where do points A and B go?

texts:
I tried to find the answer in past posts, but couldn't locate it.

I have a pump (100% efficient, for simplicity) that runs on 100kW and follows the equation: Power(pump) = (Specific Weight)(Flow)(Pump Head). The flow is steady, but not inviscid. We are given info for losses.

My specific question is this: Where should points A and B be located for a Bernoulli equation designed to account for the energy imparted to the fluid by the pump? I must calculate flow imparted by pump.

Should I place point "A" at the pipe entrance? Or, perhaps, right before it? I'm confused.

An illustration is attached and, as this question is quite specific, please let me know if any information is needed. I have a solution, but want to grasp the concepts enough to understand what is happening, physically.

Let me know if more info is needed, or if I've overlooked a post from the past. Thanks, everyone.


texts:
I'm a chemical engineer student and I have just started to learn about mass balance without reaction.

This is my problem -

I want to find Out the mass composition and mass flowrate of stream Y (the stream into the divider).

How am I suppose to do a mass balance around process 1 (involving the divider, before process 2) ?

From the problem , I don't know any of the compositions of the recycle 1 , I only know the flow rate .

This only tells me that the flowrate into process 1 is $50000+ 1500 $ . With this alone, how do I find mass composition and mass flowrate of stream Y


texts:
I made this kind of knurl on shaft :

but I am not sure how to be define on the drawing. I found some examples but not sure if they are correct. On the examples there type (GV) and depth of knurl and no more information.

I will be very thankful if somebody show me drawings or books with correct info.


texts: What are some overlaps between Computational Scientist and Mechanical Engineering?

texts:
I am a fairly recent graduate (I graduated December of 2015 with a Bachelor's of Science in Computational Science) and since graduating I have had an increasing desire to get involved in engineering.

What areas of engineering employ aspects of computational science?


texts:
I have a straight-line distance of 250 km between two towers and want to find the length of the transmission line that is between these two towers while accounting for the sag.

The line should be larger than 250 km. Given that the estimated sag is 60 m, how do I find the real transmission line? Can you provide me with references?


texts: Help understanding a control system represented by coefficients of theta?

texts:
I've been working with control systems and transfer functions recently, but I've come across a format that I haven't seen before using coefficients of theta, and I can't find any information about it.
Does anyone recognize the format below, used to describe a control system. As I was writing this question I realised what it is probably saying, but I'm unable to fully understand it. My thought process is written below so could somebody help me fill in the gaps?

$$\ddot{\Theta_0} + 4\dot{\Theta_0} + 68\Theta_0 = 34\Theta_i$$

I'm assuming that the dots above theta are the powers. 2 dots means squared etc. $\Theta_0$ is representing the output while $\Theta_i$ is representing the input. (The 'O' is actually a zero not a letter but I'm assuming thats a typo?). Since a transfer function is:
$$T(s) = \frac{Y(s)}{U(s)}= \frac{output}{input}$$
we could divide by $\Theta_i$ to get the transfer function. But this is where I get lost. I think this has something to do with the characteristic equation - the denominator of the transfer function when equal to $0$ - but I dont see how?


texts:
I am not sure where else to post this, so here goes.

I have a velocity profile ($v_{\phi}$) for a radial distance ($r$). From this velocity profile I am trying calculate the shear rate ($y$) which can be calculated by ( Eq 3 in Image):
$$
y = \frac{\partial v_{\phi}}{ \partial r}  - \frac{v_{\phi}}{r}  = r  \frac{\partial}{\partial r} \left( \frac{v_{\phi}}{  r}\right )
$$
Please find the image of the equation from the papers attached,

Screenshot of the equation for the paper for your kind consideration.

I have implemented the equation as such,

for i = 1: size(v_phi,1)

    y (i) = ( r(i) ) * (( ( v_phi (i) / r(i) ) - ( v_phi (i+1) / r(i+1) ) ) / ( r(i+1) - r(i)) );

    y1 (i) = ( ( ( v_phi(i) / r(i) ) - ( v_phi(i+1) / r(i+1) ) ) * ( v_phi (i) / r(i) ) );

end

However the y and y1 values calculated are very different. I am just wondering, whether I am doing something wrong in the implementation and looking for help if possible.

Many thanks.

Data >>>>

v_phi = [36.99 37.00 35.78 31.43 26.91 23.32 19.46 16.97 14.49 12.12 10.42 8.52 7.25 6.06 5.11 3.92 3.30 2.54 2.11 1.42 1.46 1.46 0.97 0.63 0.63 0.51 0.40 0.91 0.24 0.36 0.63 0.71 0.45 0.26 0.74 ];

r = [3.59 3.76 3.94 4.12 4.29 4.47 4.65 4.82 5.00 5.18 5.35 5.53 5.71 5.88 6.06 6.24 6.41 6.59 6.76 6.94 7.12 7.29 7.47 7.65 7.82 8.00 8.18 8.35 8.53 8.71 8.88 9.06 9.24 9.41 9.50 ];


texts: Shearing Stress at the Boundaries of two infinite Planes

texts:
This is a worked example on a book I am reading (Fundamentals of fluid Mechanics).

He then asks

"Can you explain the change in sign? [Hint: Sketch a sheared fluid particle adjacent to the top plate.]"

They calculate the shearing stress in the top layer, bottom layer and middle layer.
The calculate $\tau > 0 $ (in the fluid direction, they explain) for bottom layer, $\tau = 0$ for middle layer and $\tau < 0$ for top layer.
I do not understand how the shear can go be in opposite directions at the top and bottom, especially given the symmetry of the problem and the flow being in the same direction.
Hope you can help me out.


texts: Modeling high thermal expansion under fire

texts:
I am trying to use Ansys Workbench (Transient Thermal probably coupled with Static Structural analysis) to simulate behavior of a fire protection sleeve. It is used to seal the fire sectors in place where the combustible installations go through walls. Basically, as the temperature goes up, the sleeve expands (its volume goes up rapidly), it cuts out for example a plastic pipe and seals the hole.

How to model this in Ansys?


texts: Open Channel flow with pressure losses - flow depth?

texts:
In a horizontal channel that feeds off a river, does the head/pressure loss due to friction, turns etc in the channel translate to a drop in the water level between its inlet and outler? If so, could someone provide a basic insight how?

Thanks.


texts: Force required to crop/cut a mild steel bar

texts:
I have cropping/cutting wedges with a thickness of 4 mm cutting either side of a round mild steel bar (17.5 mm). Imagine two wedges being driven together with a round mild steel bar in the middle (similar to the design of bolt cutters)
These wedges are operated using 2 hydraulic cylinders (6" diameter, 2 1/2 travel) (one for each cutting wedge) to force them together (against the mild steel). The cropping wedges are made from BS 970 304S12 steel.

How can I determine the force required to crop this round bar?  What equations/formulas are relevant?


texts:
I have tried recording RF data using several different software packages: SDR Console, SDR# and HDSDR. They all seem to produce WAV files. When I open the HDSDR file in Mathematica, it says the file is "Integer16" meaning 16-bit PCM data and that the sample rate is 2400000, which I guess means 2.4 million samples per second. The data has two channels. The first 10 elements of each of these channels is:

{0.00421143, -0.00283813, -0.00268555, -0.00271606, -0.00268555,
0.00488281, -0.00378418, -0.00241089, -0.00234985, 0.00363159}

{0.00479126, -0.00332642, -0.00323486, -0.00338745, -0.00344849,
-0.00228882, 0.00415039, -0.00344849, -0.00344849, 0.0055542}

From what I understand each of these values is a composite of two bytes, but why would it be a float if it Integer16?

Also, how do I do determine the quadrature? How is the quadrature encoded?


texts:
I'm seeking a precise description of engine torque.
We talk about torque in terms of the twisting force that the piston exerts on the crankshaft with a radius equivalent of the rod throw.
Assume these two scenarios:
Engine 1: 6 cylinder, 2.5L diesel making 480 Nm torque
Engine 2: 4 cylinder, 2.0L diesel making 390 Nm torque
Cylinder volume on eng 1 is 2.5 / 6 = 0.416L
Cylinder volume on eng 2 is 2.0 / 4 = 0.5L
So its apparent that the cylindrical volume on the smaller displacement engine is larger.
How come the 6-cylinder engine produces more torque, instead of only smoothening out the performance due do less crank rotation per firing event?
I'm thinking that torque is measured with two crank rotations in mind.
Am I correct on this assumption, and if not - how is engine torque described precisely?


texts: Changing the quality of the transient process in a nonlinear system (Part II)

texts:
My question is a continuation of the topic.
https://math.stackexchange.com/questions/3910814/changing-the-quality-of-the-transient-process-in-a-nonlinear-system-in-mathemat
Unfortunately, last time I didn’t get any help, so I decided to reformulate the question.
I have a system of differential equations like this:
$\begin{cases} \frac{dx}{dt} = y \cdot \alpha \cdot sin(\omega t) + \frac{d}{dt}(\alpha \cdot sin(\omega t))
   \\ \frac{dy}{dt} + y = \frac{d}{dt}(f(t)) \end{cases}$
where:
$f(t)$ - Any function that has one extreme (minimum or maximum). For example $f(t) = e^{-(x - x_{*})^2}$
$x$ and $y$ - variables of the system of differential equations.
$x_{*}$ - the point at which the maximum or minimum of the function $f(t)$ is reached.
Let's pay special attention to the variable $x$.
Parameters: $\alpha = 0.3, \omega = 2 \cdot \pi \cdot 0.5, x(0)=1/4, y(0)=0$
The solution is to go from the starting point $x(0)$ to the point $x_{*}$ at which the minimum or maximum of the function $f(t)$ is reached.
For my system with such parameters, the solution will look like this:

It can be seen that the transition process is a transition from the initial point to the final one with a certain character, which is added to the additional sinusoidal signal $\alpha \cdot sin(\omega t)$.
It is necessary to change the nature of the transition from one point to another, making it exponential (naturally retaining an additional sinusoidal signal $\alpha \cdot sin(\omega t)$), i.e. it must be described by law:
$x(t)=(x(0)−x_{*}) \cdot exp(-t) + x_{*} + \alpha \cdot sin(\omega t)$,
Like this:

The problem is complicated by the fact that the function $f(t)$ and the point at which its minimum/maximum $x_{*}$ is located, generally speaking, are not known to us.
How to get out of the situation using the structure of the differential equation? Add additional input signal? Include an additional differential equation in the system? Use adaptive techniques?
Help! Please give at least some idea. I am desperate and my hands give up.


texts: Why are most standard bolt threads single start?

texts:
When looking at thread descriptions, one of the basic properties is always the number of thread starts.

As far as I could tell, all of the major standard bolt threads are single-start. This includes:

Unified Standard (UNC, etc.)
National Pipe Thread (NPT, NPS)
British Standard

I only found one standard thread that can also come in a multiple-starts: ACME.

What are the reasons why single-start threads are so common and multiple-start threads are rare? I am specifically interested in bolts and other fasteners.


texts: Does the aerodynamic force qualify as a viscous damping force in the Mechanical Harmonic Oscillator

texts:
When reading about a harmonic oscillator, the most common form of  damping is proportional to the velocity.
$$F_D = c \;\dot{x}$$
Without giving much thought to  viscous damping, one example I always thought of is the following. Taking my hand outside a car with velocity v. As the velocity increases the drag also increases.
However, I also know that the aerodynamic drag of a vehicle is proportional to the square of the velocity. I.e. :
$$F_A = \frac{1}{2} C_D \rho A (\dot{x})^2$$
So, either my example does not fall under viscous damping, or there is something  fundamental that I don't understand.
I would very much appreciate your insight on this.


texts:
I'm a noob if it comes to electronic components but I'm trying to achieve the following and I would really appreciate some suggestions:

I have the following requirement:

When a circuit is closed the first time (via some sort of pulse switch), an LED will receive power.
After the circuit is closed the first time, it will be open again for a long duration of time.
When a circuit is closed the second time, LED should not receive any power.
Loop continues 1-3

Basically I want a pulse of electricity to toggle circuit on every other time.
Note that during the off state, the circuit will have no power at all. So any solutions involving 555 timers etc won't work.

I have bee reading about Dual Coil Bistable relays and I was thinking to use it in conjunction with some logic gates to make this happen, but I feel like I'm going a little bit too far with this and maybe this is simpler than I make it.

Thank you!


texts: Why is a paraboloid hyperboloid shape preferred on some structures?

texts:
Why is preferred on the construction of big stadium roofs and of cooling towers, per example?

What is the advantage of this geometric figure that makes it more economical?


texts: Why is there a 5V linear regulator on this USB ATTiny85 dev board?

texts:
This dev board. 78M05G regulator, attiny85 MCU.
Similar (ON MC78Mx05) regulators' droupout voltage is listed at 2V0. USB voltage is specced at 5V0 (+0V25)(-0V55). The ATTiny85 can take 2V7 to 5V5, though for some variants the 4V45 low end of the USB spec straddles a speed grade.
By my understanding you're operating in undefined territory if you are below the sum of output voltage and droupout voltage, which would be 7V here. So why the linear regulator? Alternatively, what am I missing?


texts:
I want to power an Arduino project for several weeks on a remote location. At the location, data is gathered and sent over the internet. The project runs on 5V and draws 200mAh max. I need a power source that runs on its own, without cables.

To do so, I was looking into big batteries. My idea was to use a battery like this. It has a capacity of 50Ah and an output of 6V which I can downstep with a voltage regulator.

I have several questions:

How safe is this battery? Can directly touching the contacts cause harm?
Can my project draw 200mAh or will the battery push out more due to its high capacity?
And if it's dangerous, how can I protect myself and my system?

Hope my information in this post is sufficient, thanks for any responses.


texts:
Is design of "Budweiser's bow-tie shaped beer can " feasible & unique from engineering point of view?
Can there be a better design than it?
Like the shape of can is inclined at ten degree & appears easy to crush it? Is there any other advantage/disadvantage of this design? Please help me.


texts:
In the notes, the author stated that the shear stress is constant over the bottom face of the segment ... why in figure 7-4 , we can see that the shear stress varies ?

Which is correct ? The red circled part or the figure ?


texts: Why is the fluted edge of a twist drill bit sharp?

texts:
My intuition on how a twist drill bit operates is that the cutting is done by the end of the drill bit and that the fluted section carries away material as it's cut.

When I look at twist drill bits, though, it appears that the edge of one of the flutes is sharpened. What purpose does this serve? Does this edge actually cut material?


texts: How does a frequency to voltage converter work?

texts:
I am measuring the rotational speed of a shaft using a disk with 60 cuts and an optical fork. The signal from the optical fork is sent to a frequency to voltage converter and after that to a data acquisition system.

What is the working principle of this frequency to voltage converter? Is it counting pulses?


texts:
Hello I have this truss structure question. I understand that we need to determine the zero-force members first so that we can simplify the diagram. But I am not sure which one that I need to eliminate.
Please advise because I need to calculate the forces in each truss member and determine whether the member is in tension or compression.
edit : kn is actually kN (kilonewton)


texts: Purpose of spheres and fins on submarine propeller

texts:
On a recently launched Russian diesel-electric submarine, the rear propeller has two distinct features. You can see spheres at the base of every propeller blade:

Also, the trailing edge of the shaft has four adjoining fins in line with the axis of rotation:

Most importantly, what is the purpose and function of the spheres, and what's beneath the veil in the first image? I believe that it may differ from the second image.

It's made of a different material, so possibly a sacrificial element.

Is it to reduce noise? Is it to smooth flow or prevent cavitation?

Notice that in the first image the spheres are at the leading edge and in the second image the spheres are at the trailing edge.

There is a related youtube video.


texts: Are 3d printed gears (ABS) suitable for long term use?

texts:
i want to print a worm gear for a robot. This robot will work every day for at least 10 hours. The gears size is about the half of a sheet paper.

I searched the internet for example in industrial use. I can not find much about the life span of 3d printed gears. The only thing is that abs is good.

Are 3d printed parts applicable for industrial use?

What can i except for the life span?

Thank you.


texts: Multiple Varying cross section beam deflection

texts: How do we calculate the deflection of a cantilever with two or three cross-sections, and different forces acting at the end of each section?


texts:
I am intending to construct a small pressure vessel. It needs to be around 7 centimeters in length and width and around 1-2 centimeters in depth. It must be capable of being pressurised to 300 psi with sufficient space to contain a small amount of liquid (say 5cc)

Constraints

The body of the vessel must be made out of nickel-plated annealed brass.
The vessel will have a brass cap, held in place with silver solder.
The cap must be sufficiently thin to be pierced when it is inserted into a receptacle.

Is this design feasible?


texts: Can a load be estimated using a Kalman filter?

texts: I have a system with a motor, some masses, damping and springs. One of the masses is loaded with an unknown external force F. I want to estimate the force F using data of the motor (mainly current). There are some unknown disturbances, like temperature and friction in the system. Can this be done or are there better ways to estimate the unknown force? There will be no feedback loop. The available data will look be a time series of the current acting on the motor.


texts: Utilize multiple vehicle power outlets to increase wattage capacity of inverter

texts:
I'm trying to determine whether it would be possible to use multiple power outlets in vehicle to increase the wattage that can be obtained.

This question is driven from a desire to install an DC to AC inverter without having to connect directly to the vehicle battery. Typically, the units sold that plug into the cigarette lighter outlets in a car max out around 150 watts.  Some simple math suggests that, even with a 20 amp fuse, the maximum wattage you can draw from the outlet -before blowing a fuse - would be 240 Watts (12V x 20A = 240 W).

However, if there are multiple, separately fused outlets available, can they be connected in parallel to increase the available power?  For example, could two outlets be used to supply up to 480 watts of power?

It seems simple in theory, but I'm certain there are some more complicated aspects to be considered.  I realize that the length and resistance of the supply wires are a factor, and that if the voltage isn't balanced, then one leg will supply more amperage than the other. However, I believe this would really only be an issue as you started to approach the upper end of the amperage limit for one of the legs.  Once one of the legs maxed out, the fuse would blow, transferring the entire load to the second leg which would also blow quickly thereafter. But up until that point, both legs would share some level of the load.

I've included a simple schematic that I sketched for a visual aid.

Any educated feedback or explanation would be greatly enjoyed.


texts: Caulculating maximum shear stress at certain points

texts:
I have a structures problem I cannot solve, I have the answer and I have attempted the question. I just need to know where I am going off track. Any assistance would be highly appreciated.

My work is as follows:

At point B:

$T = Fd$, where $d = 300\text{ mm}$ and $F = 100\text{ N}$, therefore $T = 30,000\text{ Nmm}$

From torsion, shear stress $\tau = Tr/J$

$$J = \dfrac{\pi}{2}\cdot(r_1^4 - r_2^4)$$

Therefore $\tau = \dfrac{30,000 \cdot 30 \cdot 2}{\pi(30^4 - 25^4)} = 1.37\text{ MPa}$

This is the first answer listed, which leads me to believe my lecturer listed the answers for (B,A) instead of (A,B)?

However then for point A:

$T = Fd$, I believe $d$ now changes to 330 mm as you have to add the outer
radius of the bar so $T = 33,000\text{ Nmm}$

Following the same process used for B:

$$t = \dfrac{33,000 \cdot 30 \cdot 2}{\pi(30^4 - 25^4)} = 1.50\text{ MPa}$$

This is clearly not the answer my lecturer gave. I am a confused as to
where I went wrong. I am aware that I did not use the value 250mm but I
am unsure where it applies. What makes points A and B different, aside
from their distance from the force? I would really appreciate any assistance in the matter, thank you so much for reading.


texts: Spring - Piston with different extension and compression rate

texts:
I am in need of a device that extends freely without much resistance but compresses slowly.
I can provide a door closer analogy.The door should open fast but close slowly....
Do you think this can be achieved?

Basically my idea is to come up with a design for Wickets setup in Cricket.For people who have no idea what the game is...basically I need a setup for a 28 inch long wooden cylindrical stump of 1.5 inch radius to selfstand and withstand forces of a ball hitting it.Once the ball,say baseball, hits it, it should spring backwards and then comeback stand straight.

For this I am replacing the bottom 2 inch section with heavy metal so that it stands on its own and connecting this 2 inch section to the top one through a spring to handle the impact of ball.


texts: Unable to do anything with the mesh imported from blender

texts:
I made an object in Blender (default cube), then exported it to STL, then imported this STL into Solidworks.
Now I see this object just exists and I can do nothing with it.
I can't reference any face of the cube and can't scetch on it. Also I can't use Mesh Prep Wizard since it is dimmed.

What can be done here?


texts: Methods for motion tracking without a gyroscope

texts:
I am doing a project involving motion tracking using an accelerometer. I know a lot of approaches for motion tracking also involve a gyroscope, but here there is only an accelerometer available. In principle, the rotational information should also be obtainable by the linear accelerometer measurements, although the measurement error might corrupt this.
What algorithms are there specific to motion tracking using only an accelerometer? A general approach that I know is to use a Kalman filter for integration, which also attacks the integration drift problem. Is there a more specific approach for motion tracking using accelerometer data that is popular?
Should I try to recover the rotational information from the linear measurements?
Thanks


texts: Who wrote the 1990's piece about the object oriented toaster?

texts:
In the 1990's (or earlier?), an unattributed piece was written about an electrical engineer and a software developer who were tasked with building a toaster. You can view the piece in its entirety here.
It is unattributed. No copies on the Internet that I've found reference the author.
Does anyone know who wrote this piece?
Below is a quote of its introduction:

Once upon a time, in a kingdom not far from here, a king summoned two
of his advisors for a test.  He showed them both a shiny metal box
with two slots in the top, a control knob, and a lever.  "What do you
think this is?"
One advisor, an Electrical Engineer, answered first.  "It is a
toaster," he said. The king asked, "How would you design an embedded
computer for it?" The advisor: "Using a four-bit microcontroller, I
would write a simple program that reads the darkness knob and
quantifies its position to one of 16 shades of darkness, from snow
white to coal black.  The program would use that darkness level as the
index to a 16-element table of initial timer values.  Then it would
turn on the heating elements and start the timer with the initial
value selected from the table.  At the end of the time delay, it would
turn off the heat and pop up the toast.  Come back next week, and I'll
show you a working prototype."
The second advisor, a software developer, immediately recognized the
danger of such short-sighted thinking.  He said, "Toasters don't just
turn bread into toast, they are also used to warm frozen waffles. What
you see before you is really a breakfast food cooker.  As the subjects
of your kingdom become more sophisticated, they will demand more
capabilities.  They will need a breakfast food cooker that can also
cook sausage, fry bacon, and make scrambled eggs.  A toaster that only
makes toast will soon be obsolete.  If we don't look to the future, we
will have to completely redesign the toaster in just a few years."


texts: How to mount timing pulleys/belts for small DIY project

texts:
I'm building a rotating lamp for a small DIY project to learn about motors and timing belts/pulleys. As I am learning, finding parts that are small enough, fit a stepper motor shaft and reasonable priced is difficult.

I am trying to find a way to turn a lazy Susan that has a slip ring through the center within a space of about 6-8 inches. The slip ring is so that I can get electricity on the top with it still being able to freely turn.

Issues:

What are the usual increments of timing belts?  On Robotshop I found 8 in and 25in and that is it.  To me this seems like a small range.  Is this normal and have people found better supplies to offer a wide range of timing belts....in something like 1 in increments.
How much slop is in the timing belt?  When attaching two timing pulleys do you usually have to add idlers or stretch out one of the wheels to get a good fit?
How close can timing pulleys be before there is not enough threads to move.


texts: I am trying to currently model a few parts for my custom 3D Printer. I have found some flanged lead screw nuts i'm going to use, but i'm having a hard time reading the dimension sheet. Specifically, what does "D4h11" mean? I understand D4 is as per the chart, but what's h11?


texts:
I am interested how to check a nominally pined joint. Especially how to check its rotational capacity and whether i can define it as nominally pinned in structural fem model. I understand that there are criteria for nominally p. Joints but also there is a criterium that this joint must have enough of rotational capacity to accept rotation of the member.

I give an example.

Lets say i designed a nominally pinned joint according to eurocode criteria. Ran a calculation and got design forces. (shear force and maybe axial force). Joint satisfied all code checks but now i want to if this joint has rotational capacity to accept members end rotation (also calculated).

I know that there certain amount of estimation and engineering experience. But i would like to know what would do an experienced engineer when designing a joint that has stiffness somewhere between pinned and semirigid. And dont want to define it as semirigid in structural calculation.

Thank you


texts: How do products like the overheating Snapdragon CPU make it through quality control?

texts:
Almost all of the new Snapdragon CPU series (610, 810) have an overheating problem. This overheating problem may occur in the first few hours of using mobile phones that are equipped with the CPU, as we can see from the various reviews from around the web on Xiaomi mi4i, LG G4, Sony Xperia Z3+, etc.

I assume Qualcomm, a billion dollar company, has a quality control department working on (or detecting) this issue before they release the CPU. How does such a significant issue get past QC without being detected way before the launch date?


texts: Can an electric motor use reciprocating pistons like an internal combustion engine does?

texts:
Would it be possible to have an electric motor that uses an electromagnet to force a piston up and down to turn a shaft, similarly to an internal combustion engine, but without burning fuel?

Is there a name for this kind of motor?

Would there be any advantages of this style of motor compared to other electric motors?


texts:
I'm trying to find a source for this type of plastic rack gear:

This image came from this youtube video.

I can find short pieces of straight rack gear on ebay, but nothing like this.

It appears to be a vinyl/plastic type material, has 90-degree mounting flange, and is toothed on both sides.

Any information would be appreciated!


texts: Converting air flow rate between kg/s and m^3/s

texts:
Is 1 kg/s of air flow rate equivalent to 1 m3/s?

I am calculating supply air flow rate into a zone for an air conditioning system. The simulation software gives the result in m3/s but the mathematical formula that I used takes in kg/s.

Do I need to convert the flow rate, and if so, how do I convert between kg/s and m3/s?


texts: How to form a seal around a sharp moving blade?

texts:
I have a setup where I want to move a knife like blade through a body of liquid inside a container and I want to control the blade from outside the container. Apart from using magnets to move the blade, is there any way to form a dynamic seal around the blade as it moves along the container length?

I was thinking of using two long lengths of rubber that sandwiched the 1mm blade, but I am not sure how this would hold once some pressure was added to the container, especially if the blade had an oddly shaped cross section (like sharp curves that would be hard to seal).

There is a fused silica layer at the top of the container, which is in contact with the liquid.

So I am wondering if there are any seals anyone knows of that could be used in this scenario?  I'm thinking of possibly using ferrofluid as a seal at this stage.


texts: How do I batch plot drawings in monochrome without editing DWG?

texts: I'm using AutoCAD 2015, and I run into this all the time.  I'm given a group of DWG drawings, and I want to plot them into one monochrome PDF, but they do not have monochrome.ctb selected as the plot style.  Is there any way in Batch Plot to publish to PDF using monochrome without editing the individual DWG files?  If not, is there a way to edit the page setup of all the drawings together as a group?


texts:
I am attempting to mount a device by screwing into ~2" of rubber (not sure what durometer or material, but it is decently firm, maybe 70 durometer). However, I am not sure what type of anchor to use (corkscrew, wall-anchor type, ground anchor, etc). Shown below are some examples:

What are the advantages/disadvantages of each for soft materials? I assume since the material is closest to a cork, a corkscrew would likely be best (assuming there is sound reasoning behind the design of this ageless device). The worst case scenario is if the fastener tears out, and pulls out a chunk of the material along with it. I would think a helix would minimize the risk of damage, however the lack of surface area might not provide the most shear strength/holding force.

Is there a guide, or published paper, discussing the tear-out strength of these fasteners in rubber/elastomers?

EDIT: As per the comments, here is some additional information: The rack (with measurement equipment on it), is ~100 lbs. Unfortunately, I do not have access to the inside plate, or other side of the rubber layer. This is also a temporary installation (hence screws), so I cannot bond to it (epoxy), which was my initial thought.


texts: For cleaning food and objects, power scrubber vs. electric rotary toothbrush?

texts:
I'm asking about cleaning produce like potatoes and melons, NOT human organs here. This handheld power scrubber

looks like your average rotary toothbrush! Indubitably I know that a toothbrush's brush head can be far gentler than the power scrubber's. But what are other differences?

I whited out the brand name because I don't want to be accused of promoting a brand. I'm not.


texts:
I recently looked up the recommended insulation value for my area (7) and was surprised how much lower the wall insulation value was shown to be. As you can see it is almost a third of the recommended attic value. I am fairly certain that these numbers have more to do with the limited space in the typical framed wall than the actual theoretical ideal.

My question is, what is the idea ratio (can it be represented as a ratio?), or what is the calculation for the ideal spread of insulation over a house assuming you had as much room as you needed in every wall, floor, and ceiling?


texts: I am building a small robot having pneumatic system. I am using 12v car tyre inflator as my compressor.But i didn't find any 3ltr to 6ltr standardrd air tank. Can i convert my old 3ltr lpg tank into air tank


texts: Why is potential energy = 0 for ideal gases and not for non ideal gases?

texts:
Why is potential energy = 0 for ideal gases and not for non ideal gases ?
The reason is in my textbook that average between the atoms increases or decreases due to bonds being broken.So , my Q is that in case of ideal gases. Let us take two gases , $H_2$ and $He$. So , here. For hydrogen , I can say that bonds of H and H can break and average separation can increase or decrease.p even when if I consider hydrogen as ideal gas. I checked online also if I can consider $H_2$ has ideal gas and it said yes. Whereas , in case of He. I am not getting with what He would form bond with and average separation between atoms would change.


texts:
As part of a control systems course I have to implement control for a 3 DOF SISO mass spring damper model of a robotic cutter arm. The arm is to follow a 5Hz triangle wave reference which is positioning it. As you can see from the picture, the robotic arm requires damped and tracking control.

I have derived the state equations and successfully simulated the system open loop in simulink to recreate the same waveform as above. I have had success implementing full state feedback with LQR control. I have also used an integrator to achieve tracking of the output waveform. The final step is to design an estimator (since in real life not all states could be accessed).

Although I have achieved some form of control I am not entirely sure if it is correct. Does anyone have examples of 3DOF SISO with estimator, tracked and/or damped control in state space? So far all I have found is examples of active suspension:

Design of LQR controller for active suspension system

Also, here is a link for anyone who is curious about how to derive equations of motion for MBK system:

Multiple Degree-of-Freedom Example


texts: Welding rods: Why are some DC and other AC also?

texts:
The last time I welded was too many years ago in engineering school but a friend and I recently bought a welding machine and have set about trying to learn how to weld.

In researching what welding rods to buy, I found there are “sodium” rods such as AWS E6010 (High cellulose sodium) and “potassium” rods such as the AWS E6011 (High cellulose potassium). The web sites for example AWS Classifications Explained say E6010’s should be used for Electrode Positive DC (DC+) welding and the E6011’s can be used for any of AC, DC+ or DC-.

It makes sense that you would need charged particles to maintain the arc during zero crossings of the current but why should potassium work while sodium would not?  Sodium and potassium are chemically similar and everything else is pretty much the same so why should potassium based rods work with both AC and DC while sodium based rods only work with DC?

Any insights will be appreciated.


texts:
I want to do a non-linear analysis (possibly SOL 400) on Nastran. I used PyNastran (python module) to set-up the BDF file for a Linear buckling analysis (sol 105). However I feel like it might be too difficult to set everything up correctly with non-linear analysis due to the little information I found. Tutorials on the subject all recommend a pre-processor like Patran, which I don't have.

Does anyone know a free pre-processor that can actually produce the nastran input file (BDF)?

I know of salome-platform.org, but my understanding is that it cannot produce the BDF file. Or is there another solution to my problem?

Any help to solve my problem would be appreciated. Thanks!


texts: Does Eurocode allow use of Robertson chart to determine soil type based on CPT results?

texts:
It seems that use of the Robertson charts (Robertson, P.K. [1990] " Soil Classification using the cone penetration test" Canadian Geotechnical Journal 27(1), 141-8) to classify soil type based on CPT results is widely accepted practice in the Netherlands. I cannot, however find any prescriptions in the current Eurocode which explicitly allows this. I have checked all relevant standards:

EN 1997.1
EN 1997.2
NEN-EN ISO 22476-1
ISO 14688-1 and ISO 14688-2

Some of these standards are perhaps not the most recent and others do not contain the national annexes, so perhaps that is my problem. However, I cannot find a clear stipulation which allows or prescribes use of the above charts to actually determine soil type based on CPT results.

Could anyone indicate why this is allowed? Am I missing something in the standard? If it is common practice how does it not contradict the standard?


texts: In induction heaters why do metal pieces levitate in center of radial axis?

texts: In induction heaters metal seems to levitate in center of radial axis, as well as longitudinal axis (see video). Is by any chance the reason for that like in this schematic, that magnetic field lines of a metal rod, forming closed loops, move in opposite direction to the coil when going around the sides of the metal? So, repulsion at the sides, and attraction along the poles. Or, is it other reason?


texts: Established Patterns and Designs for Measuring Powder by Volume

texts:
I'm not a mechanical engineer so please be patient with my descriptions and question.

I am working on a design for a device that needs to measure out different amounts of powders by volume (not weight!), for example ground spices. Without a mechanical engineering background I am basically winging it. But coming from a software engineering background, I imagine that there must be established patterns for this type of thing in mechanical engineering as well.

What are some go-to patterns and designs for measuring out powders in mechanical engineering design?

It doesn't have to be incredibly precise. Not as precise as, for example, a gun powder measuring device. These need to be rough measures, though precision wouldn't be a problem either.


texts: Why Ceramic Capacitors Are Not Rated Directly Like Electrolytic Ones?

texts:
I want to know why ceramic or disk capacitors are not rated directly like electrolyte ones? Is it just a convention or some other reason is behind this? Like, the ceramic ones are rated as 762k. then the value of the capacitance is 7600pF. (7-1st significant digit, 6-2nd significant digit and 2=multiplying factor(100))

But an electrolyte one is directly printed like:- 3400uF.


texts: What can be the mechanism used in devising a machine that can arrange the dishes properly to make the cleaning faster in the messes/hotels

texts:
In hotels/messes the used plates are often placed haphazardly, and the workers need to pick
the plates carefully to clean them. This leads to longer washing times and longer waiting times for customers.
what new mechanical/electronic devices can be designed to solve this problem and it can arrange the dishes properly
to make the cleaning faster in the messes. I just want to know the mechanism that be used in working of such devices.
Please suggest some ideas about it.


texts: What makes a flow periodic in Turbomachines?

texts:
A quote from my textbook :

  Turbomachinery flows are steady only in a time-averaged sense; that is, the flow is periodic,
  with a period equal to the time taken for a blade to move a distance equal to the spacing
  between adjacent blades. Despite the unsteadiness, in elementary analysis all variables are
  assumed to have steady values.

Can you please explain this 'unsteadiness'? What effect does a blade moving a distance equal to the spacing between adjacent blades has on making the flow periodic?


texts: Can I make a drawing view normal to a plane in my model

texts:
I am trying to make a drawing in solidworks, with a view normal to plane offset from the top surface and at a 45 degree angle from the surface.
Here is an image showing my model with the plane. Sorry if the orientation of the view is weird from my screenshot.
I am using Solidworks 2019-2020.


texts:
Okay, my teacher said that if a filler material is added to metal it is possible with increasing filler content to observer:

Yield strength increase,
Young modulus decrease,
Resilience and elongation increase

But I thought that if young modulus decreases, wouldn’t  yield strength also decrease?


texts: i want to know if an Archimedes screw pump is more eficent that a modern screw pump to elevete clean waters 4 meters i saw many modern screw pumps smaller and  want to now about the efcency of ths two types.


texts: How do I increase negative air pressure without inhibiting airflow?

texts:
I would like to increase the vacuum power of my desoldering station. It’s a multifunction unit that includes a single vacuum pickup tool, hot air wand and desoldering gun. When using the desoldering tool or the pickup tool, the hose from the tool is connected to the vacuum port. Air is drawn in from the vacuum port and out through the wand via a hose connected to it. When using the wand tool, it works the same way, except heater located inside its housing are turned on. In order to prevent premature burn out of its heater, no tool should be connected to the vacuum port.

To increase the vacuum pressure, I am considering adding a vacuum reserve tank with a solenoid valve. It should allow the vacuum to build up negative pressure and give a stronger, momentary suction when the valve is closed for a few seconds and then opened by triggering the desoldering gun. Since I know nothing about pneumatics, I am unsure wether or not the vacuum reserve decreases the airflow when using the wand. This is only a hunch since the tank is like a capacitor which can slow down or impede the airflow.  Am I correct here? In the case that it does inhibit airflow, I also added a bypass line with another valve to circumvent the tank when the wand is in operation. Will this solve the issue?


texts: Derivation of Overall Mass Transfer Coefficient

texts:
The flux in the gas can be written as:

$$N_{1}=k_{p}(p_{1}-p_{1i})$$

And the flux in the liquid can be written as:
$$N_{1}=k_{x}(x_{1i}-x_{1})$$

And we know that $$x^*_{1}=\frac{p_{1}}{H}$$

How can I use this to find the overall mass transfer coefficient?
I know that the driving force will just be $(p_{1}-Hx_{1})$ but what's $K_{g}$ and more importantly, how is it derived?

EDIT: I'll give the best answer to anyone who can even give a hint


texts:
I'm only a HS physics student, so please bear with my lack of jargon. My question goes like this:

In the scenario of two coaxial rotors spinning independently in two different directions, each with the same amount of torque, are the thrusts produced by each rotor the same as if the two rotors were side-by-side?

My first guess was that they had to be different because of things like air displacement and pressure from the above rotor being applied to the below rotor, but it seems everything I find treats each rotor's thrust like it is completely unaffected by the one above or below it. Could someone shed some light on this? In what way is thrust from the above or below rotor affected by its companion? Thanks a lot!


texts: How much braking force do cars generate?

texts:
I've been trying to find actual figures for the braking power of cars (in order to determine things like stopping time). As I understand it this comes in two parts: the maximum force that the brakes can apply on the tires, and the maximum force the tires can apply on the road.

I'd love to find figures for particular cars (or brake systems or tires) but I would be fine with any figures for actual cars under reasonable conditions. It's easy to find math problems of this sort online but I don't expect their figures to have much in common with the real world.

If someone could point me in the right direction (car data sheets, third party testing, government regulations, etc.) I'd be very much obliged.


texts:
I'm dealing a C code here which is run on MSP430 LaunchPad. What I need to do here is modifying the program, so that at the push of the button, the micro cycles through 4 different modes:

LED1 flashes while LED2 off
LED2 flashes while LED1 off
LED1 and LED2 flash simultaneously
LED1 and LED2 flash alternatively

I quite don't understand here what I can do to make both LED flash simultaneously and alternatively. LED1 flashes and LED2 off if SW2 is HIGH and vice versa. How do the other two work?

Down here is what has been done so far:

#include <msp430.h>
#include "msp430g2553.h"
int sw2=0;

int main(void)
{
    WDTCTL = WDTPW | WDTHOLD;      //stop watchdog timer

    P1DIR  = 0x00;         //port 1 all inputs
    P1DIR |= (BIT0 | BIT6);        //set P1.0 and P1.6 as outputs (LED1, LED2)
    P1REN |= BIT3;         //activate resister on P1.3
    P1OUT |= BIT3;         //make it pull up because SW2 is active low

    for(;;)
    { sw2 = P1IN;          //read values from P1
      sw2 &= BIT3;         //mask out only BIT3 where SW2 is connected
      if (sw2 == BIT3)
         {             //if SW2 is high
            P1OUT &= ~BIT6;    //turn LED2 off
            P1OUT ^= BIT0;     //toggle LED1
          __    delay_cycles(50000);   //delay 50,000 micro seconds
         }
      else
         {             //else (SW2 is low)
            P1OUT &= ~BIT0;    //turn LED1 off
            P1OUT ^= BIT6;     //toggle LED2
            __delay_cycles(200000);   //delay 200,000 micro seconds
         }
     }
// end of infinite loop
}
//end of main


texts: How does a carrier signal work from a receiver's perspective?

texts:
for example :

Sender: A cellular signal tower(Base Station(BS)) sends data(voice, GPRS, VOIP) to the cellphone. The sender will obviously have the carrier frequency and more power(voltage+current) to generate the carrier signal.

Receiver: A cell phone which receives the data signal (voice, GPRS, VOIP) from the BS. This requires less energy because the cell phone is receiving data.

I want to know, when the receiver sends data(voice,GPRS,VOIP) to the BS, how does it do this?

Does the cell phone generate it's own carrier signal?

If yes, then how can a 3.7 volt battery be available for 8-12 hours?

OR

The receiver's signal goes on to same carrier signal which is generated by the BS.

If yes, How? Does the carrier signal use refraction/reflation properties to send data back to BS?


texts: How can I make inside a LSAW pipe uniform and smooth?

texts: I am using a LSAW 16mm(OD) pipe, and I need to have a smooth and uniform surface inside it so a piston can reciprocate easily inside it. What is the best and fastest way to remove the inside weld line? It is going to be part of a production line, therefore, the speed of this process is very important.


texts: Where does one go to produce custom metal objects?

texts:
I am wanting to produce custom mass plates for a project, very similar to those found in gyms. Here's a rough idea of what each one should look like:

This is essentially identical to mass plates one can buy online, however I am needing to produce my own, with custom specifications, sizes, etc. Most notably each plate will need a thread through the center hole.

Where would I even start looking for someone who could do this? Looking online, I get confused by all the metallurgical terms. What type of professional am I looking for? I feel clueless.

Thanks in advance.


texts: What does natural frequencies with multiplicities m=1,2 or n mean?

texts: If I have a planetary gear set consisting of one sun and N planets, what does it mean if it says that typical vibration modes of 6 natural frequencies always have multiplicity m = 1 for different N, except for the zero natural frequency? How would this multiplicities look in a frequency domain plot?


texts: Is there any more convincing exemple of the Braess Paraxod than the diamond-shaped network?

texts:
The Braess Paradox is the observation that adding one or more roads to a road network can slow down overall traffic flow through it.
This paradox supposedly applies for cars on highways but can extend to other vehicles, or other applications such as internet data or electricity within transmission networks etc...
Now the problem being that I searched examples of Braess paradox across the net, and I always find the same "example network" again and again, with :

A diamond shaped road network between 2 cities
Of which 2 branches have a constant travel time and 2 branches a variable travel time
Adding a connexion in the middle of the diamond slows down the trafic because of the variable travel time.

The problem I have with this example is that :

The diamond shaped network is not very realistic, in most place the road network was initially web-shaped before highways were added in the 1960.
All roads have variable travel time and will eventually saturate if too many cars goes through them. There is no such thing as a constant-travel-time road, but the Braess paradox relies on it
The saturation of roads is probably highly non-linear, however all examples I find it is described as "travel time is X minutes where X is how many thousands of cars takes this road", this is unrealistic

Some real-life examples where removing a highway contributed to decrease trafic are mentionned. However those might just as well have been also due to other efficient measures to reduce traffic and not solely to the highway link removal. In the end it seems every article about Braess paradox I find are just copy/pase of eachother.
It is however super-easy to do a real-life experiment for Braess paradox on a real road network, either by simulating trafic or by actually closing an real-life avenue. However I never find examples of this.
Now my question:
Is there some real-life example, not the totally unrealistic "diamond network" always given as an example, about the Braess paradox ?
IMPORTANT NODE : I'm not talking about other measures to encourage or discourage trafic, such as induced demand. Braess paradox is about how, everything else being unchanged, adding a highway will slow down trafic.


texts: Convert 1 one compound unit to another involving temperature

texts:
So, I must do the following conversion from my engineering textbook:

$0.155 \frac{m^2 * ^{\circ} C}{W}$ to $\frac{^{\circ}F * ft^2 * hr}{Btu}$

I can get as  far as:

$0.155 \frac{m^2 * ^{\circ} C}{W} * (\frac{1 ft}{0.3048 m})^{2} * \frac{1 W}{3.4123 \frac{Btu}{h}} = .39108 \frac{ft^2 * ^{\circ}C *hr}{Btu}$, but I can't figure out how to do the final conversion properly, which involves converting that from

$.39108 \frac{ft^2 * ^{\circ}C *hr}{Btu}$ to $\frac{^{\circ}F * ft^2 * hr}{Btu}$.


texts: Wire bearings on actuators on military ships

texts:
While reading about the Korvette K130 Braunschweig class of corvettes for the German navy, I noticed that almost all of the weapon systems are held in what I'd call a wire bearing.
I'd like to know what its actual designation and its purpose are.
Examples:

MASS
RBS 15
RAM


texts: Waste Foundry Sand as an aggregate for concrete mixes. I have a question regarding grain diameter and it's possible applications

texts: I'm working on a project with a company that uses sand casts during moulding processes and they provided us with samples of the sand they use before it's involved in the procedure and afterwards (Waste foundry sand). I'm wondering if there's specific parameters regarding grain size for using WFS as an aggregate for concrete mixes, my samples led me to believe that most of the WFS this company produces is about 1/2 mm to 1 mm in diameter. A brief literature review has offered no conclusive results and little information regarding specific gran diameter in WFS. Is this byproduct suitable for concrete mixing? Any help would be greatly appreciated.


texts:
The symbol:

Here is a part of the diagram:


texts: Are there diodes which can switch at multiple GHz speed? Most of them are limited up to few hundreds of MHz.


texts:
I'm looking for alternatives to measure the moisture content in a concrete mixer machine. The ones on the market are expensive, like Hidro-Mix for apparent reasons; mixers are a hostile environment for sensors.

Any information on alternative methods to measure and visualise the humidity inside a mixer or have an economical sensor brand for this purpose is welcome.


texts: Why does the microwave plate start in a random direction?

texts:
...or what type of motor is used there?

I found this type of motor - usually powered with low-voltage AC (~12V), but at times with 230V, in several appliances that require very slow rotation and sometimes a fair momentum - a color-shifting lamp, the microwave plate, an ice cream mixer...

The funny property of it is it picks the start direction at random and keeps spinning in that direction until switched off - but I never faced a situation when it would get stuck in the "unstable balance" position.

So, what is this type of motor and why does it behave that way?


texts: Simulation of motion, collision, friction and thermal expansion in 3D

texts:
I'm looking for the easiest way to simulate an array of cubes that is being pushed. Therefor I need to model the motion/collision effects, the friction with the floor and between blocks and also thermal expansion of the cubes, although that is secondary.

What libraries/packages/software do you recommend to have this simulation in place a.s.a.p.? I am familiar with python and js, therefor I've looked at pybullet & physicjs, however I'd like to hear your opinion on this.

Edit: The approach I have got in mind is to use some kind of 3D library that supports physics, which gives visualization and rapid development speed. Any other fast approach would be ok, though I will need to run many different combinations (block sizes, friction, etc) so it needs to be scriptable in some way.


texts: Microspeaker enclosure design for headphones

texts:
I want to embark on an acoustic project of designing an enclosure for some 40mm microspeakers, identical to ones found in a typical on-ear headphone solution. Are microspeaker enclosures treated in the same way as a typical loudspeaker enclosure, Just with smaller dimensions? I ask this because every acoustic/loudspeaker design book including ones with chapters on headphones in, I have read does not mention anything on enclosure design for headphones and earbuds and google is nearly a complete deadend for the level of information I am looking for...

If headphone/earbud enclosures are not treated as loudspeaker enclosures with reduced dimensions, what is the design procedure/equations for the desired acoustic & frequency response from the enclosure?

Thank you in advance


texts: Why do beverage can tabs break when bent?

texts:
Most people have had the experience of moving the tab of an aluminum can back and forth until it breaks off. It usually only takes a few complete back and forth motions before the tab breaks off.

What is the root cause of the tab breaking off?

The possible causes seem to be:

A fatigue fracture.
An overstressing of the metal.
A result of plastic deformation.

But which one is it?


texts: Pacejka's Magic Formula:Nominal vertical load on tire

texts:
To work with Magic Formula for load dependent conditions, we have to use some of additional parameters. In this link, you can find the formula about this.
What is the meaning of Fz0 (Nominal vertical load on tire)? Is it static load?
Thanks a lot,


texts: Why does flow seperation cause low pressure zone?

texts:
I know that flow seperation occurs when the fluid adjacent to a body deviates from the contours of the body . This occurs because the pressure increases in the direction of flow and velocity decreases until it reaches zero , and then , the flow reverses and a region of circulating flow develops which causes the fluid to deviate from the countours of the body ,, Is that true ?

If that's true , my text book says :" seperating flow is undesirable because it causes low pressure zones ..." how does it cause low pressure zones and the main reason for the flow seperation to occur is that the pressure increases in the direction of flow ?


texts: What considerations should I take when flame-hardening a wheel?

texts:
I'm currently trying to figure out whether or not we can flame-harden a steel wheel which was supplied with a lower hardness than expected. I'm worried, however, that flame-hardening can either deform the wheel or change its size somehow, especially given that a flame-hardening job has never been done in the company before.

The wheels are about 13" in diameter and about 6" in thick. They have a few metal details and inner holes, which I'm not exceedingly worried about since other wheels on the same machine will have different designs. The wheel will roll on a plate, although I do not know the hardness of the plate at the moment.

Ideally, I would like to flame harden the wheels from 160 Br to 400 Br, to bring it up to the design specifications, although I would be content taking it up to 300 Br, which is the hardness of some previous wheels we have tested from the same machine.

What considerations should I take before attempting to set up the flame-hardening? I have quite a few wheels to spare in case the job goes wrong, but I would also like to know if there is some quantitative analysis that should be done before starting.


texts: Autodesk Inventor Place Component with User Parameter Length

texts:
I have some user parameters which I set in "fx":

Now I need to place standard square tube ("Place from Concent Center") with a length of Tube0Length mm. How can I do this? Inventor doesn't accept the parameter:


texts: Relationship between Material cost and Labor cost

texts:
I am currently into an estimating job for a small construction company. In my previous experiences, in calculating the labor cost for a certain job,

Labor cost = material cost * 0.45

I did this to simplify the computation. Are there any other specific labor factor for different job classification for the following class:

concreting
masonry
carpentry
painting
steel
rebars, etc.

that I can adopt?

Note: This will not involve equipment in the process.


texts: I have a question regarding power electronics. What is the meaning of 'line to line voltage' what does it tell us and how can this be calculated. Say I have a three phase system how would one find the line to line voltage for this system?


texts:
So I'm given a question in which a Truck drives over a pratt truss bridge. In the question the truss is in 3D.

I'm given:
1)The loads from each axle of the truck
2)The weight of each member in the truss
3)The weight of the concrete and asphalt

The question also states that "The forces acting upon the bridge shown in Figure 3.1 can be decomposed into forces acting in the x-y plane and forces acting in the x-z plane (i.e. the forces in the lateral bracing members). Show how this observation permits a very simple analysis of the structure whereby the cross-bracing members can be simply ignored and where the truss to be analysed is a planar truss, i.e. a truss in which all members lie in one plane."

I have a few questions here, (3) being the most important:
1) How can I "show that the observation permits a very simple analysis...."
2) If the cross bracing members can be simply ignored are their weights ignored as well?
3) Considering the truss would be mirrored on either side but I am now only analysing one side (one plane), are the loads from the lorry, and the weights from the concrete and asphalt divided in half?