texts: Difference in shear stress - one bolt vs two

texts:
So i have a little diagram to visualize:

So lets say i have a 20 mm plate connected with two M8 bolts, and i apply a 30kN force in the direction shown in picture. Question is - would the force be equally distributed between bolts - i.e., each bolt will have a 15kN of shear stress? Or each bolt will still take full stress of 30kN?


texts: What's the best material to use for my project

texts:
I need to get a piece of stiff material cut and drilled for a project I'm working on.  It has the following requirements:

1.6mm thick
should be stiff (similar to PCB material, aluminum, fiberglass)
about 12" x 3"
6 holes need to be drilled (all around 5mm in diameter)
will be making ~500 of these plates
material type is not important - just needs to be about as stiff as PCB material/fiberglass
conductivity doesn't matter - metal or non-metal is fine - my PCB will have plastic board supports spacing it off of the mounting surface.

I'm trying to figure out the best material that will yield the best pricing were I to outsource this to a machine shop or manufacturer of some kind.  In other words, what combination of material and machining process will cost the lowest.  I was looking at having a PCB manufacturer use PCB material (because this will be the mounting plate for my PCB and they'd already have all the tooling), but I'm open to use fiberglass, metal, plastic, or any other material.  I was hoping that someone here might have done projects with various machine shops or manufacturers and be able to provide some recommendations as to the best materials and processes to use.

UPDATE

Just to provide a few more details - I am manufacturing a PCB and I need a mounting plate on which to mount DIN rail clips.  So, the PCB will have board supports (which allow for a loose-ish fit) which hold it to a mounting plate (of some material type), and the mounting plate will have DIN rail clips attached to it.  The reason for the plate is to provide something to which the DIN rail clips can mount to.  I do not want the PCB directly attached to DIN rail clips because I don't want twisting forces applied to the PCB during DIN rail mounting/removal.


texts: Thermal efficiency of a furnace reactor?

texts: I'm doing plant design and one of the reactors is a furnace that uses methane to burn. I want to calculate the amount of methane that is required. I have the energy needed and the calorific value of methane but now I need a average thermal efficiency. Just to be clear I want the ratio of energy produced over how much was put in. Thanks


texts: I have seen some theories saying stress is a scalar. I don't understand why. Anyone can explain.


texts: Transfering moment through internal hinge

texts:
My professor says, the internal hinge can not transfer moment:

But can we calculate $\Sigma M_A=0$ for whole beam ( without cutting it or something) this way?:

$\Sigma M_A=0  ===\Rightarrow M_A+(D_y \times 4m ) + 3KN.M =0$

with this equation we literally transferred the 3KN.M moment to point A while my professor says the internal hinge can not transfer moment.

Something is wrong, and I don't know what it is.


texts: Solving single phase no load transformers questions

texts:
1000/100 V, 10kVA, single-phase transformers impedance referred to HV side given as (5+j10). The no-load power of the transformer is given as 300W. What is the efficiency of the transformer at full load with a power factor of 0.8 lagging?

A)90.9 B)92.6 C)96.4 D)None

I stuck about no-load power. Is it equal to Pi or Pi+Pc ? I mean 300W is Pi or Pi+Pc ?
My solution


texts:
I am trying to fabricate a very small elliptical nozzle; if possible, 10um x 20um. I am almost certain that this cannot be achieved with regular machining. Ideally, the material would be corrosion resistant (e.g. stainless, brass) although that is not absolutely necessary.

The depth of the hole would depend on the material. I need to have small deflection with a pressure differential of 80kPa. Therefore, a stronger material like SS would maybe have 1-2mm of depth.

The tolerance is less important than the smoothness of the edges. A hole that is a couple of microns off spec is better than one that has edges with roughness of 1-2um.

Could it be done with laser cutting? Are there any other methods that could achieve such feature size? Thanks.

Edit: added material and tolerance requirements.


texts: Scanning and modeling my personal vehicle for aerodynamic simulation

texts:
I have this pickup truck that I love dearly. I often change the aerodynamic configuration of the truck when I use my camper shell, or roof top tent, etc.

Is there a reasonably easy way to create a mesh model of my truck from images so that I can use ANSYS to model the aerodynamic effects?

Thanks!


texts: What FDA compliant plastics can have contact with alochol (wine)?

texts:
I am able to find that the class for materials that can be in contact with wine (~10-15% alcohol by volume) is called Class VI-A and Class VI-C, but I am not able to find a list of materials that are approved for those classes. Does anyone have experience with navigating the FDA for a list of materials that are approved for a certain class of use?

https://www.fda.gov/RegulatoryInformation/Guidances/ucm081818.htm


texts: What action does a 3 axis gyro stabiliser do to stabilise the drone?

texts: A gyro measures the angular velocity of a drone around 3 axes: yaw, roll and pitch, but what physical change does it make to the drone after measuring this value to give it stable flight? As it is a gyro chip, and not an actual gyroscope, would it still precess? does it change motor speed etc.? Thanks in advance.


texts: What is the umbrella-like thing surrounding this new structure?

texts: Recently this water tank was constructed (poured concrete).  (I presume it is a water tank, as they laid blue plastic/PVC water pipe, perhaps 24 in. dia., in the vicinity at the same time.)  After the outside was finished, they erected this dark (almost black in the picture) inverted umbrella-like screen around the base.  I have never seen such a thing, either during construction, or around a finished tank.  What is its purpose?


texts: What is the best resolution obtainable by ultrasonic non destructive testing? I understand it depends on frequency.


texts: Hi there, When I was very little I came up with this idea for a power station and I recently remembered it and was curious about the viability. The way it works theoretically is that a voltage supply is temporarily provided to an electric motor to get it spinning up to speed. The motor has a magnet on its armature that spins in a coil to generate electricity, this will generate output electricity. This output is taken from the generator and split, some will go as an output from the power station and some will be fed back in to the system. The portion that is fed back runs through a rectifier to convert it from ac to dc voltage and then through a dc amplifier to get it up to whatever the voltage supply to the motor initially was. The output of the amplifier then becomes the new power supply for the motor as the temporary voltage supply is cut off using a switch. This could potentially leave the system self sufficient. I understand that a small amount of electricity would still have to be used to power the amplifier and it won't be greatly efficient but it was just an idea that I had when I was little. I highly doubt this design will work but if anyone could explain to me why or provide improvements to the design then I would be very grateful.


texts: Isn't a pin support supposed to prevent translation both horizontally and vertically?

texts:
I know that pins prevent horizontal and vertical translation and that rollers prevent only the vertical one.
Therefore, what I do not understand here is that while the support at B reacts with two forces C support has only one, even though both look like pins to me.Where am I going wrong here?

(I could not find anything on the site about whether I can upload images this way. I hope there are no copyright issues related to my post because
 I do not own the images. If there is, please notify me and I will immediately take them.)


texts: Heat Exchanger Design (Log Mean Temp Difference or Epsilon NTU Method)

texts:
I am trying to design two heat exchanger interfaces (shell and tube) that transfers heat to and from an intermediate heat pipe. The picture below gives a general idea of the problem I am trying to solve, although the system would look differently. That is, the red pipe would transfer heat to the yellow pipe in a separate shell and tube heat exchanger (HX-1), and the yellow tube would then transfer heat to the blue pipe in another separate shell and tube heat exchanger (HX-2). All different colored fluids are different. Here we will assume that the end of the yellow pipe is connected to it's inlet. (Like a loop)

Specifically I know the inlet and outlet temperatures of the blue and red fluids, along with both of their mass flow rates. I also have the temperature (outlet temperature of the first heat exchanger and inlet temperature of the second heat exchanger) of the yellow fluid to be $340 ^\circ C$ as well. The unknown parameters I would like to find are listed below:

Mass flow rate of the yellow fluid
Inlet temperature of yellow fluid to HX-1 (or outlet temperature of yellow fluid to HX-2 since they're assumed the same)
Required contact surface area between the red and yellow fluid
Required contact surface area between the yellow and blue fluid.

Of main importance is the required surface areas. I am not sure if I should apply the log-mean temperature difference or the epsilon-NTU method. I am also pretty sure there will be some iteration/numerical methods involved.
Does anyone have experience in this, and would it be possible to get a rough step-by-step procedure to finding these values?
Apologies for the vagueness of the question, I've been stuck on this forever. I'd appreciate any help possible.
Thank you in advance.


texts: What is the reason for the instant loss of a vaccum through the sealed glass tube after shuting off a pump?

texts: A pump is connected to a glass tube to evacuate it. The reading shows 0.4 mbar when the pump is on because of a vacuum. As soon as the pump is turned off, the pressure in the tube becomes equal to atmospheric pressure.


texts: Rapidly cool a flue gas without water circulation

texts:
I am a newbie at this!!

For an experiment, I have a diesel generator that releases hot flue gases at 150-160 Degree Celcius.

I want the output gas to be at less than 75 degrees for a duration of ~ 1 hour without 'circulating' water. I'd like to do this with static water tank/bath (because 1 hr is usually the maximum time of operation at once for a generator.)

-The location I am in is where ambient temperature is ~ 18-30 degree celcius.
-Exhaust diameter is 4 inches

I want to be able to design a kind of heat exchanger:

Can I just fill a tub of water, and divide the output exhaust into 4/5 tubes, take them through a tank of water? (like MUX-DEXMUX)
What's the amount of water that'd be required for the setup to be able to give that much heat reduction, for ~ an hour?
What sort of geometry should I build to not have much back-pressure on the gas flow.
What'll likely be the best material to build these pipes?

What's the best direction/references/designs to look into for design such, water bath/non-circulating type heat exchangers?

My experiment till now.


texts:
I am designing a stainless metal base plate to mount an orientation critical sensor. The sensor has two 6H7 6mm deep holes to align it. One of the holes is a slot to allow for adjustment.

The sensor manufacturer prescribes a 6g6 pin (loose fit) but that would result in a nonstandard transition fit on the hole in my plate if I'm correct. Could I simply use a spring dowel instead?


texts: Variable speed conveyor / frequent stop and start

texts:
I'm working on an application which requires varying the speed of a conveyor that will frequently need to stop and start.
More specifically, we need to first set the speed of the belt, and then have frequent cycles of 3-4 seconds on and then stop for 3-4 seconds.

I had initially thought a simple 3-phase conveyor with a VFD (for speed adjustment) and then a contactor (for start/stop) would be fine... But a few google searches seemed to indicate that this would probably damage the VFD in a short order, since the VFD needs a few seconds to start correctly.

So is there a canonical way to set up this sort of system ? The conveyor load is low (few kgs) and the speed is also low (around 1m / 10 seconds).


texts: How can we derive the formula of the centroid?

texts:
In order to find the coordinates of the center of an area, we can use this formula:
$$\begin{align}
 \overline{x} &= \frac{\int x\text{d}A}{A} \\
 \overline{y} &= \frac{\int y\text{d}A}{A}
\end{align}$$

How can we derive this formula? Can you help me understand it so it becomes intuitive?


texts: How do I determine the reactions at the base of a tethered T-frame?

texts:
I received a tricky bonus question today in my engineering class:

I've begun by equating all moments and forces to zero, about an arbitrary point, which I labeled at $C$. Finally, I attempted to solve for $C_x$ and $C_y$ without examining $M_c$. However, my answers for $C_x$ and $C_y$ were incorrect, and I'm unsure as to the process for solving $M_c$.

How do I solve for the reactions at the base of a T-frame that is subject to various point loads, including a fixed tether at one end of the top bar?


texts: Effects of rolling resistance on wheel angular and vehicle longitudinal speed

texts:
The differential equation for wheel speed can be given as:

In here, $T_t$ is driving torque (not braking), $F_x$ is longitudinal force of tyre, $J_w$ is wheel inertia, $\dot{w}$ is angular speed of wheel and $Frolling$ is rolling resistance force.
According the equation, if we increase the resistance force, $\dot{w}$ should increase. Increasing of angular speed may cause higher slip ratios. As long as longitudinal slip ratio increases, it is possible to have higher longitudinal tyre forces according to Magic Formula.
In here i have a confusion: High rolling resistance makes possible to have higher longitudinal force according to this differential equation. How can it be possible? How can $F_x$ increase with higher values of rolling resistance? If $F_x$ becomes high, it is impossible to decrease the vehicle. With the help of the positive and high $F_x$ force, vehicle cannot decelerate.
Thanks,


texts: Will a fan that is composed of several fans fixed inside rotating tube work?

texts: I want to design a custom 3D printed fan that would be made of several axial fans that would be connected (fixed) to their cylindrical casing. I am planning to rotate the whole assembly (the cylinder with fixed - nonrotating fans inside) using one engine on one axle only around it’s axis. I am hoping to achieve a higher static pressure (sum of individual static pressures of fans). Do you think this will work?


texts: Calculating Load On Winch From a Distributed Load?

texts:
I am in the process of building an antenna mast that can tilt from horizontal (down) to vertical (up). The mast (arm) is 360" and weighs a total of 105 lbs. I need to calculate the amount of force placed on a winch in order to lift the mast (arm) from the down to up position. All the formulas I am finding are for calculating the force required to lift a weight at the end of a leaver. It seems to me that this will not work in my case since the weight is distributed evenly over the entire length of the arm.
I have two options (plans) on how to place my winch. I need to determine which option will require the least effort but also the most stable.
Can anyone shed some light on this? I have attached a diagram.


texts: How does concrete perform in an Insulated Concrete Form (ICF) house?

texts:
From: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4033560/

I can see that concrete can really go bad after a few hundred freeze and unfreeze cycles:

If an ICF house has insulation from the inside of the house, then the concrete will be cold, if the outside temperature is cold too.

More detail on the layers: insulation for the ICF is grey EPS, 15cm outside, 15cm concrete, inside: 5cm

The question: for how many years can concrete survive without any issue in an ICF house?

I think, because of the 5cm grey EPS insulation from inside, the concrete will receive many freeze/unfreeze states and will go bad earlier/deform/crack?. Living in ~eastern EU, winters are max -10C. But it goes about ~60 days under 0C yearly.


texts: Is it important to have a good behaviour inside internal loops of a cascaded PID controller?

texts:
A cascaded PID controller is depicted in following image (courtesy of controlglobal.com):

The primary PID tracks the setpoint $SP_1$ and delivers a setpoint $SP_2$ to the secondary PID.

I wondered if it could be a problem if the secondary PID does not have a nice behaviour w.r.t. tracking its setpoint, while the total result of the cascaded PID controller is OK. This would mean that the overall tracking of $SP_1$ is OK, which is the goal of the total controller, while some internal controllers are not tuned too well.


texts: Which joint is providing the force to a bipedal robot to move the body forward?

texts: This is related to construction of a bipedal robot. I have a doubt regarding the stages involved in walking of a biped. In the one leg support phase, when the body moves in a circular path about one leg, who is providing the force? How can the joint at the knee or hip provide the force for the body to rise and move forward?


texts: Do structural engineers carry insurance for catastrophic errors?

texts:
A friend of mine is a structural engineer and he often complains to me about how little sleep he gets at night worrying over whether or not he accounted for all the little details involved in his design.

For all the double and triple checking one might do, buildings are very complicated structures.  Sometimes its impossible to account for every possible situation.  Of course, one does to the best of their ability to try to account for everything.  But if something goes wrong, say a building either collapses or some other less severe problem causes injury or death, I would assume that the engineers can be held accountable.

Are they covered by some sort of malpractice insurance in a similar fashion to doctors?


texts: Is a chair with N+1 wheels ever less stable than a chair with N wheels?

texts:
My workplace has a policy to provide standing desks upon request, but no policy to provide chairs of matching height.  (I work for the government...)  We can buy our own, or build our own.  However they added a stipulation that the chairs must be bought or built with five or more wheels.

Since five is an awkward symmetry to measure and to sit in, I'd probably build my chair with six wheels.  Or perhaps eight because I can start with a square and lop off the corners to make an octagon base.  Or maybe make the base a perfect circle and line the bottom with innumerable tiny wheels?

This set me to wondering:  is there any situation in which a chair with N+1 wheels is strictly less stable than a chair with N wheels?

To make the question interesting and rule out trivial answers, assume that the wheels are more-or-less at the chair's perimeter and more-or-less evenly distributed.  Assume the floor is flat.


texts: Steam Turbine - is it possible to run starting ejector and main ejector simultaneously for better efficiency?

texts:
In a steam turbine, is it possible to run the starting ejector of the surface condenser along with the main ejector?
Will it improve the efficiency of vacuum generation?


texts: What's the minimum area ratio required to achieve choking in Converging nozzle?

texts:
Is there any equation for minimum area ratio (Throat area (At)/ Combustion Chamber area (Ac) ) required for choked flow in convergent nozzle (just like equations for minimum Pressure ratio and Temperature ratios)?

While searching online for minimum Area ratio required, most of them are related to CD nozzle. But in my case I'm looking for Convergent nozzle only so that I can get an estimate how wide combustion chamber should be to the exhaust area.

I tried to derive equation from mass flow continuity equation but it is dependent on flow velocity inside combustion chamber which is generally assumed to be near zero. (and I got stuck here.)


texts: Measuring intensity of a radio wave reflected from a metal plate

texts:
I am building a Project that can pinpoint location of a pen or any object (something as small as 0.5 mm radius sphere) placed on a flat screen.

I am using a ultrasound sensor (initially but i can switch to a different sensor if the situation demands) attached to one side of the flat screen ( on top edge). I'll be attaching a metal ( aluminium or copper) film on the object whose location I want to detect. I'll be using two ultrasound sensors to measure the x and y axis distance and pinpoint the location

I am trying to find a way wherein I can measure the intensity and direction of the reflected wave from the metal film to detect location. However I can't find a way to do so yet.

Is it possible to do so and if it is will ultrasound suffice ?


texts: Measuring a pattern size on a flat surface

texts:
I want to manually measure the dimension of a pattern printed on a flat surface, with an accuracy of about 0.1mm. For simplicity sake, let's say this is a black rectangle, printed on a white background, and i want to measure its width and height. The dimension can be between 20cm and 80cm.

I have tried with a vernier caliper, but placing the caliper accuratly enough on the rectangle borders is impossible, especially since the caliper jaws do not lie flat on the surface.

What kind of measuring instrument could i use? Is there something dedicated to this task, or a way to use a standard instrument to do that?


texts: What is expected back pressure at a constant flow rate?

texts:
There is discrepancy between 2 labs regarding what the normal pump back pressure should be given the following dimensions of an LC system flowing at a constant rate.  I have searched for equations to determine this and check if the software read back is correct but I have been unsuccessful at determining an appropriate equation.

System dimensions and set up are as follows:

1.254m of PEEK tubing going from the pump to the MS inlet with a single 2uM PEEK filter attached in-line (no column).
The inner diameter of the PEEK tubing is 127 um.
Flow rate 1mL/min
Solvent = 84% Acetonitrile in water with 0.1% formic acid.

In this instance, assume an open ended system in which the end of the tubing is disconnected from the MS inlet and collected into beaker.

Is there an equation to determine what the pressure should be?


texts: I seem to be getting conflicting information. Shigley's Mechanical Engineering Design textbook states that, "proof load is the maximum load (force) that a bolt can withstand without acquiring a permanent set". Other sources online say that proof load is approximately 90% of yield strength. Based on Shigley's definition, a bolt begins to yield before reaching the yield point?


texts:
These days I'm designing a 5-DOF parallel manipulator with Autocad. Though I know that some people might say that Autocad is not a proper software for robot designing but I only have access to this software at the moment. So here is my question (and I thank you in advance for your help) :

$\textbf{Parametric constraints:}$ Unfortunately I do not know how to put geometrical constraints on my parallel manipulator though I have searched a lot on net and watched some videos about it on youtube. By geometrical constraint I mean putting some restrictions on for example two 3d objects that they can make some restricted moves with respect to each other. For example I have a spherical joint in my robot which I want it to perform some rotations without actually leaving its socket (as depicted in the following basic picture).


texts: What is the difference between aeronautical and aerospace engineering?

texts: Every time I search for "aeronautical engineering" on Google I see a few results about aerospace engineering. So they must be similar, but what is different about these careers?


texts: dSPACE compiler linker error -- fscanf undefined

texts:
I'm dealing with a somewhat intractable problem. We're running dSPACE 7.4 (RTI 1006) on MATLAB 2011a, which I understand uses the dSPACE DS1006 C Compiler v. 2.2. When I try to compile one of our models, I wind up with a linker error claiming that fscanf is undefined (it's being invoked in a custom function). I have verified that stdio.h is where it should be in the system hierarchy and that it contains a definition for fscanf. Following are the steps I took to try to resolve the problem:

linker initially complains about undefined fscanf()
extra definition inserted in model-specific file where I know it will be compiled causes linker to complain about inconsistent definitions for fscanf()
commenting out fscanf() definition in stdio.h then allows successful compilation/linking
inserting stub definition into stdio.h and commenting out original (and stub in model-specific file) results in 'multiple definitions of fscanf' errors (this is the weirdest part of the whole story)

The stub definition (I am assured by a higher-up that this shouldn't break our model but I haven't yet had a chance to verify this) is as follows:

int fscanf(int a, char *cp, void *b, ...){return 0;}

So, if I'm reading it correctly it's a version of fscanf that won't actually do what fscanf is supposed to do. In summary, I have to hack my compiler's library to get this model to build, and I'm not entirely confident that it will run on our hardware at present. I also don't want to tell everyone in the office to modify their dSPACE installation and break fscanf unless I know that it works and it's the only way forward.

Can anyone give me some insight on this?

UPDATE: It does indeed run on our hardware. But I don't like breaking fscanf(), so I'd still like to figure this out.


texts: Calculate thermal flow for air flowing through a tube, with fins

texts:
I have the same problem as described in this question:
How to calculate the resulting temperature for a stream of air through a hot tube?, but I want to increase the transferred heat by adding fins onto the inner side of the tube, parallel to the flowing air. Is that useful? If yes, how does the formula mentioned in the answer (https://engineering.stackexchange.com/a/5536/2844) change?
Furthermore, how do I get from the temperature difference to the transferred heat power?


texts: Bicycle headlights with different low beam reflector types

texts: What makes second reflector different than first one in terms of efficiency and correct beam distribution (brighter below cut-off line, dimmer closer to the ground)?


texts: How to contain air ions inside a chamber without loosing their charge?

texts: I would like to create an experiment where I would hold ionized air molecules. Most likely negative O2-1 ions. I am looking for the most appropriate enclosure so that the ions do lose as little of charge to the surroundings as possible. I couldn't find any suggestions... Any help would be greatly appreciated.


texts: How do I measure mercury in a graduated cylinder?

texts:
Convention says to measure at the bottom of the meniscus, but I think the cohesion/adhesion balance of mercury results in it "bulging out"

Do you measure at the top of the bulge  (near the center) or the bottom (near the edges)?


texts:
As mentioned in the question above, I am working on a clinker silo, I want to know if the forces applied on the cone of the silo are exclusively coming from the weight of the material stocked or their any other source that I need to consider specifically in the emptying phase.

I stay available for any information required for you to answer my question.


texts: what is the actual meaning, role and aim of $p_0$, $V_{a_0}$ and $V_c$ for Mach-meter?

texts:
Roskam, book "Airplane Aerodynamichs and Performance" at subparagraph: "2.5.2 HIGH-SPEED AIRSPEED INDICATORS (COMPRESSIBLE FLOW)" uses the following three equations:

a) $\left(\frac{\gamma}{\gamma-1}\right)\frac{p}{\rho}+\frac{1}{2}V^2=\left(\frac{\gamma}{\gamma-1}\right)\frac{p_t}{\rho_t}$

b) $\frac{p}{\rho^\gamma}=\frac{p_t}{\rho^\gamma_t}$

c)  $V_a^2=\gamma\frac{p}{\rho}$ ,

and, after some steps, it reachs $M^2=\frac{2}{\gamma-1}\left[\left(\frac{p_t-p}{p}+1\right)^\frac{\gamma-1}{\gamma}-1\right]$  (called eq.n (2.44) )

At this point the book says: "...From this equation it can be seen that when $(p_t-p)/p$ is measured, the Mach number can be calculated. An instrument which measures both $(p_t-p)$ and the static pressure, $p$, to indicate the Mach number through Eqn (2.44) is called a Mach meter. Note, that a conventional airspeed indicator will only measure $(p_t-p)$.

When, in the calibration of an airspeed indicator, $(p_t-p)/p$ is replaced by $(p_t-p)/p_0$ and $V_a$ is replaced by $V_{a_0}$ , the resulting airspeed is called the calibrated airspeed, $V_c$ ...."

After some steps it yelds an equation with $M^2$ depending by variables $\gamma$, $\delta$ * , $V_c$ , $V_{a_0}$ and it tells that Fig 2.6, obtained with this last equation, represents a plot of true Mach numbers versus calibrated airspeed for constant pressure altitudes.

My QUESTION is: what is the actual meaning, role and aim of $p_0$, $V_{a_0}$ and $V_c$ ? I suppose Roskam considers they play an experimental role to set the MachMeter before it will fitted to use, but I have to understand exactly how to use those variable. How to obtain them?

Note that equation with calibrated variables is not something realistic about the flight because for example we have $\frac{(p_t-p)}{p_0}$, so we have in the same formula $p$ and $p_0$, something is changed and something is not changed, so it's not represent a specific physical situation but only something artificial in order to calibrate the Mach-meter, I suppose. But ... can someone explain me the details?
Maybe that Machmeter is measuring $V_c$ every moment during flight?

$\delta$ is $p/p_0$


texts:
How can i calculate the weight bearing capacity of a section of aluminium box section? Known variables of section: Dimension, thickness, distance from load and supports.

A pictorial example might help:

Let me know if there's anything else needed to solve this problem


texts: How to disassemble this eccentric bushing

texts:
This eccentric bushing:

belongs to the hand crank of this machine:

It cannot be seen clearly in the photo, but the small blocking bar inside the bushing is not hovering over but rather, is sunk into a notch in the same surface which contains the thread.
I would like to disassemble the bushing, because the crank is badly aligned. How can I do this? Should I remove the small blocking bar inside in order to disassemble? Do I need a special tool?


texts: Convert angular acceleration from (S/100Hz) to (RPM/s)

texts:
I'm writing a script that converts from a customer's preferred unit of $\frac{RPM}{s}$ and a device's input/output of $\frac{s}{100Hz}$ My Logic is as follows:
Converting $\frac{RPM}{s}$ to $\frac{s}{100Hz}$:
$$\frac{RPM}{s}=\frac{Revolutions}{(s)(min)}$$
$$\left(\frac{Revolutions}{(s)(min)}\right)\left(\frac{1 \;min}{60 \;s}\right)=\frac{Revolutions}{s^2}=\frac{Hz}{s}$$
$$\left(\frac{Hz}{s}\right)^{-1}=\frac{s}{Hz}$$
$$\left(1\frac{s}{Hz}\right)\left(\frac{100\;[1Hz]}{1\;[100Hz]}\right)=100\frac{s}{100Hz}$$

Answer:
$$\left(\frac{RPM}{s}\right)^{-1}\left(\frac{60 \;s}{1 \;min}\right)\left(\frac{100\;[1Hz]}{1\;[100Hz]}\right)=\frac{s}{100Hz}$$
Therefore, I understand that my inverse function would also be:
$$\left(\frac{\;s}{100Hz}\right)^{-1}\left(\frac{100\;[1Hz]}{1\;[100Hz]}\right)\left(\frac{60 \;s}{1 \;min}\right)=\frac{RPM}{s}$$
To me this FEELS wrong as, per these equations
$1\frac{RPM}{s} = 6000\frac{s}{100Hz}$
AND
$1\frac{s}{100Hz} = 6000\frac{RPM}{s}$
Meaning I just need one equation to covert betweeen the two units. Am I missing something or do I really need to only do half the work?


texts: How do I know when to use an upward or a downward curve when I'm drawing a bending moment diagram for a uniformly-distributed load (UDL) and what's the most reliable way of identifying the maximum bending moment?


texts: Young's modulus for composite auxetic material

texts: If you look at the screenshot you will see a composite auxetic material. How would you calculate the E-modulus for it? Is it as simple as the rule of mixtures, E = V1 * E1 + V2 * E2? Or is it more complex because of its structure?


texts: Calculating how big a base to attach to a chair to prevent it toppling

texts:
I have a pair of cinema seats that are designed to be bolted to the floor.

I don't want to do this so instead I have made wooden feet and bolted the seat to them and they are quite stable.

I know that an object won't topple if its centre of mass lies within its base, so I simply made the feet extend to the rear of the seat back and the front edge of the seat base when folded down. Now they look quite large, so I'd like make the feet as short as possible. The seats do not recline.
I'm pretty sure the centre wooden foot has no effect on front/back stability so can be reduced to be just a few CM longer than the metal plate it is bolted too (for aesthetic reasons).
For the 2 outer feet, can I experiment with the tipping point by standing the chairs (with feet attached) on other wooden blocks with I can move forwards and backwards?
I also have another pair with no feet attached yet, and they will tip backwards if stood up, but with someone sitting in them they will freestand, and are quite difficult to tip backwards but relatively easy to tip forwards, which tells me that they only need to extend perhaps 10-15cm backwards.
Question: How do I calculate how short the feet can be without sacrificing stability?
Assume 2 normal sized adults.


texts: Is inverse hall-petch relation valid crystals larger than nanocrystalline?

texts:
The image shown here is of ceramics, where they varied the grain size and measured the strength. For example, let's take Al2O3. There we observed that strength first increased from 3 μm to 95 μm. But after 95 μm, strength was decreasing (dislocation slip can explain this behaviour).

Q 1. Why does strength decreases is we reduce the size from 95 μm to 3 μm, (many people have suggested looking for inverse hall-Petch relation but that is valid for nanocrystalline material)

Q 2. Why do TiO2 and Nb2O5 are behaving very different?


texts:
What is the best way to test the weld strength of a cross wire weld? For example, a wire grid with .212 dia wire x .212 dia wire.
I cannot find any solid information online for testing cross wire welding (projection welding). I have seen a  picture of someone using a torque wrench to test individual intersections.


texts: An induction cooktop has a high frequency power source that is applied to a coil. I was wondering if you could take the high frequency electronics from a cooktop or even buy / design a high frequency power source and instead of a coil take a 50 or 200 foot long wire and attach to rebar to heat it to a temperature of only about 30 degrees Celsius in an environment that is -30 degrees Celsius?


texts: how much power is needed to move a linear axis

texts:
Ι need help calculating the power usage for a linear axis motor. it must move  up and down at a maximum speed of 0.5 m/s a load of 50 kg
What I did so far:
The load (i.e. weight) acting on the motor is:
$$F = mg = 50 * 9.81 = 490.5 [N]$$
where:

F-force [N]: weight of the mass

m - mass [kg] mass of the  arms + mass of the belt + estimate of the mass of the moving parts of the axis

g - gravitational acceleration [m/s2]

Calculation of the power required to be performed by the engine
$$P = F * v = 490.5 * 0.5 = 245.25 W$$
where:

P: work [W]

F: force [N]

v: linear speed [m/s]

Given an engine efficiency of 0.8 it will be obtained that the required power is:
$$P_{t,η} = \frac{P}{ η} = \frac{245.25 }{ 0.8}  = 307 W$$
And when a safety factor of Ν=2 is taken into account it will be obtained that the required power is:
$$P_{t, s} = P_{t,η} \cdot N =  614 [W]$$
The problem that I have is how to take into calculations the inertia or the acceleration I need? What other formulas i need?
I searched the web and did not find what I need.


texts: How to reduce Engineering Bill of Material Cost for electronics products?

texts:
What is an effective method to re-engineer a current product to reduce engineering bill of material (EBOM) cost?

This is a continues improvement project for a current product in electronics space. Attached is an example of a PCB board. The product consists of many similar boards. The BOM includes active and passive electronic components such as capacitors, resistor, microprocessors, transistors, PCB boards, connectors etc.

What is an effective method to tackle this engineering cost reduction problem?


texts:
I would like be able to measure LED brightness using a cost effective instrument.

What are the available instruments to measure LED brightness and respective cost effective techniques?

Background: I'm interested in converting what the customer thinks is acceptable brightness to actual LED brightness specification?.

Reference:

How can I measure the brightness of a LED?


texts: Is cauchy's stress tensor symmetric always?Does this symmetricity  hold in accelerating and non-zero cross velocity gradient flow field?


texts: How do extra building levels affect the foundation design apart for the extra load?

texts:
I have been talking to some structural engineers trying to find one to design foundations for my contemplated bespoke building based on hi-cube 40-ft shipping containers. The initial concept is just two containers on concrete slab with garage space between them:

Ultimately, I would like to build extra levels on top of the containers. But at this point I do not want to design that. For now I just want what is on the picture, albeit with foundations strong enough to carry the extra load of say 2 additional levels.
I have been trying to explain the above to structural engineers, specifically mentioning that any extra levels will not be directly connected to the concrete foundation but to the containers only (which would be reinforced if needed). Essentially, the containers will be the foundations for the extra levels.
But so far I have been told that they need the design of the extra levels.
Can someone please explain: why is it not sufficient to just assume extra load on the containers to calculate the concrete foundations? Why would the exact design of the extra levels make any difference (as far as the containers' concrete foundation is concerned) beyond its weight?


texts: Discrepancy of calculated critical compressibility factor in Peng Robinson EoS

texts:
The Peng Robinson Equation of State gives a better approximation of the critical compressibility factor $Z_c$, where experimental data ranges between $0.24$ and $0.28$ (Source). Since the calculated value should be $0.307$ for any substance (Source), I'd expect to obtain a rather close number by re-applying numerically the Equation of State, given a point $(T_c,P_{c})$ on the Clapeyron's Diagram.

However, when I try to solve the Equation of State for $Z_c$ it gives $Z_c=0.321379$ (Mathematica), a solution with discrepancy of $4.6\%$ from the theoretical value.

Also when I use sightly different parameters for this EoS from Wikipedia, the numerical result with the same code is $Z_c=0.311155$.


texts:
My drafting program outputs a .dwf format file. In it, arcs are encoded as

(Circle 602331619,844923003 537072960 32715,65588)

where my so-far affirmed interpretation is (Circle, X-center,Y-center Angle Unknown1,Unknown2).

The image for the arc is shown below (highlighted in Gold):

Hence, each arc has its center and radius given. Are the pair of points at the end the starting and ending angles?

If you take (32715,65588) as (3.2715 rad,6.5588 rad), the output starts making sense. Is this correct?


texts: How often do you need to check torques on bolted flanges?

texts:
Due to the fact that pipe flanges rely on bolts, and bolts rely on friction, it seems obvious to me, as a manufacturer of piping, to recommend that bolt torques need to be checked every so often, to ensure piping doesn't leak.  I've got a few questions about this, but here is the first one:

How often do you normally check torques on bolts at a plant?  In other words, what is a good industry standard preventative maintenance schedule when it comes to threaded fasteners that are loaded below yield?  I would prefer that answers provide a reputable source for reference.


texts: How to drive 12V servo motors using 5V PWM or 3.3V PWM using ARM MCU?

texts: I have to drive several 12V servo motors. So I wanna to get 12V PWM Controller (12V Logic Controller). I have MCU as Atmel SAM3X8E arduino due board. It has 5V PWM outs. Is there any Controller IC available for this task?


texts: What is the compressive strength of carbon nanotube reinforced polymer?

texts:
What is the range of compressive strength of carbon nanotube reinforced polymers?

Although CNT's themselves have phenomenal (oriented) compressive strength, and one can find references to that, CNRP's incorporate CNTs in the polymer matrix and polymers are not known for their compressive strength.

There is a lot of materials data on various carbon nanotube reinforced polymers but it all seems focused on applications where compressive strength isn't limiting.


texts: "Barbed" fastener, ideally with a release

texts: I'm trying to identify a fastener or type of fastener.  I have a stud/post that comes up through a board and the fastener is something that would push on and hold in place.  Ideally it would be removable.


texts: beam cross section modeling by extrusion on proe

texts:
I would like to create beam models having various cross sections on ProE tool.

Can I create a beam model like below by only extrusion?

Can anyone explain what is the best way to model various cross sections of beams?


texts: Total lateral pressure from clay soil when hydrostatic pressure is also present

texts:
I'm stuck with how to work out the total pressure and centre of pressure in this example.

At an outdoor boundary between two properties there is a stepped change in ground level of the clay soil. The ground abruptly changes level by H (roughly 0.9 - 1.2m if it matters). A vertical retaining wall is present, whose design is not relevant here. The soil's depth is much greater than the wall height so there are no relevant local boundaries or property changes in the soil below the retaining wall (however deeply it is embedded in the soil). There are no buildings or other sources of pressure on the soil other than its own weight and soil mechanics, and hydrostatic effects of any water it contains. There is considerable rainfall at times, so the soil will periodically become saturated.

I'm ignoring for now, any other issues, such as bearing, shear and other failure modes, but for safety I should probably assume active rather than passive pressure, I think. I want to find the maximum design lateral pressure such a wall must resist in the presence or absence of built-up hydrostatic pressure, and the height above the lower ground level at which that pressure should be taken as being exerted for calculation purposes.

Specifically I think what I'm trying to find is the maximum design lateral pressure exerted by the soil and any ground-water on the wall, and the point at which that pressure is exerted for calculation purposes (a) if there are ample weepholes/drainage, (b) if there are no weepholes/drainage. I'm expecting the answer to depend on the characteristics of the specific clay to an extent, but I can't work out which characteristics are critical and how much they affect the answer.

Update Sketch as requested:


texts: OpenFOAM simpleFoam calculation of flow around object leads to strange result

texts:
I calculated the flow around an object using OpenFOAM's simpleFoam and wanted to evaluate it's drag coefficent. Actually the drag coefficient is in a reasonable range for the object so I thought the simulation went well. However when I looked at the flow fields they appear to have some strange diagonal artefacts in them.

The mesh I used looks like this where the flow is coming from the left. It is refined near the object

The resulting pressure field looks for some reason like this:

And the velocity field like this:

The flow is coming from the left with a uniform velocity of ~0.03. This corresponds roughly to a Reynolds number of 800 for the object. The calculation was done in laminar mode and the following interpolating schemes where used:

ddtSchemes
{
    default         steadyState;
}

gradSchemes
{
    default         Gauss linear;
    grad(U)         cellLimited Gauss linear 1;
}

divSchemes
{
    default         none;
    div(phi,U)      bounded Gauss linearUpwindV grad(U);
    div(phi,k)      bounded Gauss upwind;
    div(phi,epsilon) bounded Gauss upwind;
    div(phi,omega)  bounded Gauss upwind;
    div((nuEff*dev2(T(grad(U))))) Gauss linear;
}

laplacianSchemes
{
    default         Gauss linear corrected;
}

interpolationSchemes
{
    default         linear;
}

snGradSchemes
{
    // Korrigiert für Non-Orthogonalität
    default         corrected;
}

wallDist
{
    method meshWave;
}

For the solvers the following set-up was used:

solvers
{
    p
    {
        solver          GAMG;
        tolerance       1e-8;
        relTol          0.01;
        smoother        GaussSeidel;
    }

    Phi
    {
        $p;
    }

    U
    {
        solver          smoothSolver;
        smoother        GaussSeidel;
        tolerance       1e-8;
        relTol          0.1;
        nSweeps         1;
    }

    k
    {
        solver          smoothSolver;
        smoother        GaussSeidel;
        tolerance       1e-8;
        relTol          0.1;
        nSweeps         1;
    }

    epsilon
    {
          solver          smoothSolver;
          smoother        GaussSeidel;
          tolerance       1e-08;
          relTol          0.1;
            nSweeps         1;
    }

    omega
    {
        solver          smoothSolver;
        smoother        GaussSeidel;
        tolerance       1e-8;
        relTol          0.1;
        nSweeps         1;
    }
}

SIMPLE
{
    nNonOrthogonalCorrectors 0;
    consistent      yes;
}

potentialFlow
{
    nNonOrthogonalCorrectors 10;
}

relaxationFactors
{
    equations
    {
        U               0.9;
        k               0.7;
        epsilon         0.7;
        omega           0.7;
    }
    fields
    {
        p               0.8;
    }
}

cache
{
    grad(U);
}

What could cause these strange diagonal patterns?

EDIT: As suggested by the comments, I increased the distance between the object and the surrounding walls. However I still got the same issue with the diagonal fragments.


texts: Spring-like device with anisotropic k value

texts:
Is there a device that acts like a spring (i.e. $F=kx$) but the spring constant, $k$,  has different values in compression and tension?

For example, if $k_c > k_t$ (where c and t refer to compression and tension), then the spring would quickly compress und a compressive force but would slowly expand under a tensile force.

I imagine you could design a hydraulic system like this with some check valves and control valves. Is there a single device that does this? Or alternatively, are there practical engineered systems that do this?


texts: Why do 2 points on a mechanism not have the same angular velocities?

texts:
Could someone please explain me why the velocity of point P and P' aren't the same? Appearently it is because the angular velocity of point A and B aren't the same.

We are only given that the angular velocity of A is 10rad/s clockwise.

Why? I would think that, as these two elements are connected , they would all rotate with the same angular velocity. If A rotates with a speed of 10rad/s it would be logical for me that point B just follows and rotates with the same angular velocity.


texts: How do hooks/bends cause bearing stresses in reinforced concrete?

texts: Can someone please explain the exact mechanics of development of bearing stresses in concrete on account of bending of steel reinforcement and/or providing of hooks at the beam-column junction for anchorage? Would there be no bearing stresses if the rebars are not bent at the said location? In other words are the bearing stresses a direct consequence of bending the rebar or introduction of hook?


texts: I hope this is not off-topic. I’m wondering if someone could please provide some examples of a basic mechanism (I’m thinking something like a bevel/spiral gear, but open to anything) that is attached somewhere to a vehicle, and uses the rotation of the wheels as a timer/measure to perform a task. As a fake example, maybe it would be something attached to an axle and every 10m rings a bell. I’m talking totally mechanical, not involving electricity or computers. Thank you


texts: How can I improve traction on a wheeled vehicle yet reduce friction?

texts:
This is inspired by a project I undertook for my Physics class last year; I'd like to apply it in the future.

Background: For the project, I and a few classmates were required to build a small car powered by any of a number of sources; we opted for a mousetrap that turned two rear wheels on a four-wheel car as it was released. Our group's goal was to make the car go as far as possible.

One problem was that the power source was not constant. The lever arm of the trap lifted in an arc for about five seconds, then returned to its resting position. During this time, it propelled the car. The car then coasted for the rest of the way.

In the powered stage, we wanted to increase traction. The wheels were CDs (because we had a $5.00 budget), which have a tendency to spin out. So we attached pieces of cloth to them to get better traction. On the second stage, however, we found that this cloth slowed down the car quite a bit because it dramatically increased friction (as we found out after several hours of testing different combinations).

Other groups used duct tape to cover the wheels, and some used records, which seemed to do slightly better than CDs (though that violated the size restrictions). Cloth seemed to have the best traction, though - we didn't have many spinouts. The tests were done on a typical classroom floor (I'm not sure what it's made of - linoleum? - but it's the same as in almost every school, at least in America).

In a wheeled vehicle in general - obviously not just a small car powered by a mousetrap - how can I substantially improve traction on the wheels while the power source is on yet reduce friction while it coasts? Is it as simple as choosing certain tires, or is there a bigger and better engineering solution?

As a final wrap-up: My thought would be to have a shifting center of mass for the vehicle, where the powered wheels have a lesser tendency to slip and the front wheels are nearly frictionless. During the powered stage, the center of mass would be near the back, while in the coasting stage, it would be near the front. This could help reduce the normal force on certain wheels and thereby produce or avoid extra friction.


texts: Force and Kinetic Energy on a Speed Bump

texts:
I have done a basic calculation of the force at an angle on the speed bump when the car makes a contact on it (please check the attached image), now I wanted to calculate the kinetic energy that I can get from this considering the vehicle is 1850 kg and travelling at 15 mph from this force. I have also calculated the potential energy that I can get from the car just using gravity and the mass. Once I obtain that how do I add both the energies? Can I just add them or is there an equation for it?

The main aim here is to calculate the energy that I can get when a car at 15 mph hits a speed bump.


texts: Best angle and length for a diagonal wood support for a pull-up bar

texts:
I want to construct a freestanding pull-up bar like the one described here.

But I was wondering what would be the best angle for a diagonal support considering that the things I care are:

That it doesn't fall over when doing a muscle-up or swinging from the bar.
That it uses the least amount of floor space, i.e. a diagonal support attached at a height of 4 feet at 45 degrees needs a base of 4 feet but a diagonal support at the same height but 30 degrees from the column that holds the bar (or 60 degrees form the base) only needs a base of 2.3 feet. By base, I mean the horizontal beam that closes the triangle between the vertical column and the diagonal support. So I prefer a base of 2.3 feet because it uses less floor space.

So I'm trying to develop an equation with variable angle and height to minimize base length but that it can support the forces for muscle-ups or swinging from the bar. I weight between 130-140 pound and I don't foresee anyone over 200 pound using it.

It's been a long time since I've done any static/dynamic analysis, so I don't really know where to start.


texts: What is the equivalent moment of inertia of a two-pivot pendulum?

texts:
I am working on a system that consists of a hanging-pendulum thrust balance with two pivot points, one in the front and one in the back There is a heavy weight applied in the front. I can change the position of the center of gravity by applying counterweights on the rear part. See attached image.. The position of the center of gravity is known as well as the moments of inertia with respect the pivot points

I would like to simplify this system to an equivalent physical pendulum with one pivot point. However, because I have two pivot points, I have two moments of inertia, one with respect to each one of the pivots.

In the beginning I thought about taking the mean average of both, and then calculate the period of a physical pendulum or compound pendulum, just as Hyperphysics suggests: $T=2\pi\sqrt{\frac{I_{y}}{mgLcm}}$, where

$I_{y}$ is the average moment of inertia,
$m$ is the mass of the system,
$L_{cm}$ is the distance pivot-center of mass.

but this just does not seem right. Can somebody give me a hint on how to do this? Better, is it even reasonable to do such simplification? Shall I use a matrix notation? My purpose is to study how the thrust balance will respond when a force is applied upon it.

I have analyzed the oscillations of the system for several counterweights. From the study of those oscillations I can obtain the damping coefficient $\zeta$ and the natural frequency of the undamped system $\omega_{n}$, but I still need $I_{y}$ to complete the equation $\omega_{n}=\sqrt{\frac{k}{I_{y}}}$.


texts:
Why do we design foundations at SLS and not ULS?

If we use ULS wouldn't we be taking a higher factor of safety?

SLS = Serviceability limit state. It considers how the structure is actually expected to behave, generally by using partial factors of 1.

ULS = Ultimate limit state. It considers complete structural failure, utilising partial factors to increase loads and decrease strength.


texts: How do you ensure that a beam is loaded through the shear center?

texts:
Reading about shearing stresses in beams, it is commonly stated that it is necessary to load a section through its shear center, so no twisting is applied to the beam. This is specially important in thin-walled open section, that have very weak torsion strength.

But how do you desing a beam in such a way? For example: if I'm designing a floor beam with a C-shape section, how do I enforce that the shearing forces act through the shear center?

Thanks!


texts: I'v been preparing a seminar related to vibrations_damping systems when it come to the two topics: the active controller systems and the passive ones, could anyone please tell the simplest definitions and differences between them both, thanks in advance.


texts:
I am looking for a weight sensor which has a range from 2000 kg to 30000 kg to measure the weight of passing trucks.
Accuracy is not very important. Power use is very important, typically 3.3v.

Do there exist these kind of sensors?


texts:
I have to solve this question, and I've tried multiple things with the angle and displacement but I just cannot figure it out.
I started with a M/EI diagram and i went from there.
Any tips on how to tackle these problems?


texts: Thermal transfer function of an isotropic material

texts:
Consider a piece of material of infinite extent (i.e. no boundaries) with a point source of heat at its center which oscillates at frequency $\omega$ about the mean temperature $\langle T\rangle$.  If I place a temperature sensor somewhere else in the material at a distance $r$ from the heat source, what will the transfer function between the source and the sensor be?

From experience I expect it to be a single pole low-pass filter of the form
$$
  \frac{T_{sns}}{T_{src}}=\frac{1}{1+\tau s},
$$
where $s=i\omega$.  I also expect that the time constant $\tau$ will be a function of the thermal conductivity $\kappa$, the distance between the source and the sensor $r$, and maybe the heat capacity $Q$.  Naive dimensional analysis of these quantities shows that
$$
\tau\propto \frac{Q}{\kappa\ r}
$$
has the correct units of seconds.  Can anyone give a more rigorous answer?


texts: Is understanding tensors a prerequisite for understanding plastic deformation (metal forming) equations, plane stress, plane strain conditions, etc..? If so which book should I use to understand tensors?. Because on the internet people suggest that a good resource to learn tensors are the physics books that deal with relativity, etc. So I am not sure whether that perception will be suitable for studying the stress tensors.


texts: What manufacturing process could be used for this part?

texts: How might the "shell" in this picture be manufactured? What process could be used to achieve this geometry? It is made from plastic.


texts: Failure of wire flattening pinch rollers

texts:
I have 0.13 mm stainless steel wire flattening pinch rollers

that are mechanically pressed by two bolts. I need to press them very hard to get good flattened wire.

The problem is, the bearings got very very noisy and they broke and the pinch rollers shaft was broken, so how I can solve this problem?


texts: Optimising driving speed of stepper motor for maximum acceleration by trial and error

texts:
I'm writing code for a microcontroller that will ramp up the speed of a stepper motor as quickly as possible, for a jig that I'm building, that moves a workpiece from one position to another along a linear rail.

This question is not about modifying the mechanical or electrical system around the stepper motor, but simply the rate at which the stepper motor is stepped.

Given a desired speed, it will ramp up the speed of a stepper motor (and so the speed of the workpiece) from stationary. (The stepper motor will not have any kind of feedback to the controller other than a switch at each end so it can periodically establish its position, and stop if it's lost/gained too many steps in one direction).

So, I'll need to implement/write a function which gives the optimal speed $s$ (revolutions per second) at time $t$ for maximum acceleration. (Where $s(t=0)=0$) which the microcontroller will use to determine how fast to accelerate the workpiece / stepper motor.

The function might look like this:

$$s = kt$$

Where $k$ is an optimized constant, $t$ is in seconds, $s$ is revolutions per second.

The maximum maximum acceleration will be specified by choosing a value of $k$. It will be determined by experiment rather than calculation.

What I want to know is:

One (or more) formulas that I might use. I would then attempt various contants, varying them so I find values that result in good acceleration.
A strategy for determining those constants.

E.g. using the above formula:

start with some value of $k=k_0$
Attempt #1: Run the motor with that value of $k$, starting from $t=0$. Record the speed at which the motor failed to accelerate.
Attempt #2: Double $k_0$, call it $k_1$. Repeat step 2.
Attempt #3: Use half of $k_0$ as $k_{-1}$. Repeat step 2.
If $k_1$ gives the highest speed, double it as $k_2$.
If $k_{-1}$ gives the highest speed, half it as $k_{-2}$.
If $k_0$ gives the highest speed, followed by $k_1$, take the average as $k_{0.5}$
If $k_0$ gives the highest speed, followed by $k_{-1}$, take the average as $k_{-0.5}$
Repeat step 2.
And so on

Further thoughts

I think the above formula might work well assuming there is the equivalent of a flywheel attached to the motor, and:

there is zero friction
the motor exerts constant torque at any speed

Is that correct?

Similarly assuming:

the motor and system has zero mass / inertia
the motor exerts constant torque at any speed
the only resistance to movement is friction

Then the motor can still accelerate to full speed immediately. (So $k$ could be infinite). And if there is inertia, assuming friction forces are constant, (ie independent of speed), assuming I'm correct so far, then the formula is still good; $k$ will just be a lower value.

But that leaves questions:

What is a typical relationship between stepper motor speed and torque? Clearly it tails off as speed increases, otherwise there would be no limit to its speed. So it clearly won't be taken into account by the above formula. I am investigating this link which goes into much detail, but perhaps there are factors which are more significant than others, or there are more basic models that give good approximations.
What other factors could be significant that would can not be modeled within the above formula?


texts:
Throttles, chokes, dampers, and valves all restrict fluid flow. Aside from specific terminology/usage in internal combustion engines, are these really interchangeable terms, or do they have some specific meaning? Perhaps choke and throttle only apply to internal combustion engines and have no standard meaning outside that context? Damper might then be a special case of valve that applies to gases?
Dictionary definitions are not tremendously helpful. From Wiktionary:
Choke: 1. A control on a carburetor to adjust the air/fuel mixture when the engine is cold.
Throttle: 1. A valve that regulates the supply of fuel-air mixture to an internal combustion engine and thus controls its speed; a similar valve that controls the air supply to an engine.
Damper: 1. Something that damps or checks:
A valve or movable plate in the flue or other part of a stove, furnace, etc., used to check or regulate the draught of air.
Valve: 1. A device that controls the flow of a gas or fluid through a pipe.
2. A device that admits fuel and air into the cylinder of an internal combustion engine, or one that allows combustion gases to exit.


texts: Best way to create separate heating zone for basement

texts:
I have 2 heating zone in the house: one for the upper floor and one for main and basement. Both zones split from the main duct into their own ducts and use a damper to close/open.
Now I want to separate the basement in its own heating zone and wondering what is the best way to go about it.
The heating ducts are separated for each of the main and basement heating vents, so my first thought was to buy dampers for all the upper vents/ducts and configure the basement zone to close those when blowing air into basement, but keep open the rest of the time.
Would this be something that could work or are there better ways to go about this?


texts: Retaining Wall: Saturated Soil & Hydrostatic Pressure

texts:
I understand that Hydrostatic pressure and Soil pressure exist concurrently. I'm curious how these separate loads interact with each other.

Full disclaimer: I am not an engineer nor do I pretend to be one. I recognize that these are very broad & elementary questions; I am at the early stages of my understanding. Please be assured I am not, and will not, attempt to engineer  actual structures.

Does the pore size limit, in any way, the surface area available for
hydrostatic loading on the back of a retaining wall? I assume it
does not. It would stand to reason that water under pressure would
suspend the soil particles and push its way to the point where most
of the surface area on the back of the wall was under a hydrostatic
load?
Soil particules become suspended in water while a hydrostaic load is
present. Does this (or any other water related factor) affect the
overall soil load or does it remain the same?
Is the total load on the wall simply $\frac{H^2}{2}(\gamma_s K_a + \gamma_w)$ (Where $\gamma_s$ and $\gamma_w$ are the soil and water densities, respectively)?


texts:
How do I recognize a good Hydraulic Servovalve? It is probably the frequency response but what do I have to look for in these diagrams?

Is it correct to assume that the higher the frequency at a given amplitude ratio (i.e. -6dB) the better the dynamic behaviour?

What about the phase shift?


texts: Why did Jersey barrier bridge rails become the dominant type of highway bridge rail?

texts: Although it's different in each state, most highway bridge rails used to contain either poles or elevated concrete slabs. Very few were just solid concrete. Then, in the mid to late 1970s (some places a little earlier), solid concrete walls resembling Jersey barriers took over in practically every state as the predominant bridge rails. Why? Was there some study that came out around this time that determined these to be safer?


texts: Is it possible to use direct air capture technology for CO2 on a non-commercial level?

texts:
CO2 is used as fertilizer in aquariums where it's brought into the water with diffusors from compressed form in cylinders. Direct Air Capture machines for CO2 have been presented for experimental geo-engineering purposes.
I was wondering whether it's possible to use the technology on a much smaller scale which allows one to supply the fertilizer as a constant CO2 stream (a few g per hours) or somehow compress the CO2 into a cylinder to produce it at home. This should avoid the the need for at least transport and energy for compression and allows to near endless supply for free.
Could I emit CO2 certificates? Just kidding...


texts: How to calculate if a motor is strong enough

texts:
I am building a machine for a project that should slowly tip a screen forward about 95 degrees, hold for a couple of seconds, and then slowly return to vertical.  The design I am working on uses two stepper motors connected to the screen with a belt drive.  I can change the gear ratio of this drive to anything up to 2.8.

I need to select the smallest motor that will provide enough power for this application.  I have the torque - speed charts for the motors, as well as the weight and moment of inertia of the screen.  Is there a formula that I can use to calculate if the motor will be strong enough?

The screen will begin vertical, rotate forward about 95 degrees, and then return to vertical. The weight of the screen assembly is ~5.7 lbs. It will rotate about an axis ~2.75 inches below the center of mass. The screen assembly consists of a display surrounded on all sides by 1" t-slotted aluminum.  The axis of rotation runs through the center of the bottom aluminum rail.  There are two small stepper motors mounted just below this rail as well.The aluminum frame is 11.75" wide by 10.0625" tall.  The motors and mounting plates extend an additional 1.66" down.  Specs for the family of motors I plan to use can be found at automationdirect.com.


texts:
While visiting Vancouver, Canada recently, I noticed there is a lot of construction for apartments and condos.  Attached is a photo of one of many of those sites, and at these sites, I noticed something unusual to me: temporary columns on lower floors appeared to support floors above, and all floors are made of concrete. In my photo, three of the uppermost floors were supported by floors beneath them. This seems fairly consistent across several construction sites.  So my question presumes that this practice is structurally sound, Canada is not a country that is devoid of competent architecture design.  I just don't know why it is sound.

I understand that concrete has very little tensile strength, and so perhaps the concrete flooring used in these buildings are reinforced - presumably with rebar.

My question is, why only 3 floors?  If the concrete is not reinforced, wouldn't all floors from the ground up need to support the floors above it?  And if the concrete is reinforced, why is there a need at all to support the floors above?

It would seem to me that the 4th floor in the photo is bearing the brunt of all of the support above it, as it is not being supported by anything underneath it.

I'm further curious about what happens next: will each of the floors be given a permanent support?  If so, why hasn't it been done already?  If not, what will happen when those temporary supports are removed?


texts:
I have a formula to compute the deflection of a beam.

When I have computed the deflection I get a vector with non-negative elements representing the deflection in each position on the beam.

When I am plotting the deflection vector I get a downwards parabola since the elements are positive.

But now I found this plot somewhere else

I guess the plot illustrates how the beam is bending at positions where loads are placed.

Is it correct to get negative deflections? I wonder if I need to multiply my elements in my deflection vector by -1 in order to obtain the same plot as shown here.


texts: Schaeffler, De Long, and WRC welding diagrams - which steels can be used?

texts:
I am working on a simple program that would help welder to count how much ferrite, austenite etc. there is in weld. I am focusing on stainless steel.

I have decided to use 3 graphs: Schaeffler, De Long and WRC. What I don't know is for which materials can I use each of these graphs, to get reliable results.

I believe, that in each of those charts I can use only Cr-Ni steels. Am I right? Also, standard in my country (PL) that concerns stainless steels splits them into groups like: ferritic steel, austenitic steel, ferritic-austenitic steel, martensitic steel and heatproof steel (hope I translated it right). So which group of steels can I use in three diagrams I mentioned?

TL;DR
Which groups of steel can be used in Schaeffler, De Long, WRC diagram to get phase composition of weld?


texts: Shaft which can independently rotate and translate axially

texts:
I would like to mount a sensor onto a shaft which can be translated axially as well rotated independently. This arrangement permits me to capture a 360 deg scan and then translate the shaft axially to scan at a different height.

How should one use a lead-screw and stepper motor coupled with some other mechanism to achieve this (non-helical) motion ? Thanks for any tip.


texts:
I am trying to solve this but I am stuck; I have watched loads of YouTube videos but still don't understand how to complete it:

A mass of $m=0.12 kg$ of air has an initial temperature of $T_1=500°C$ and pressure of $p_1=0.8 MPa$. If the air is expanded according to the law $pV^{1.2} = c$ to a final volume of $90\ litres$, determine

i) its initial volume, $V_1$

ii) its final pressure, $p_2$

iii) its final temperature. $T_2$

For air, take $R_{specific} = 287 Jkg^{-1} K^{-1}.$

I have got these equations which i believe i need to use.

$$pV = nRT$$

$$n = \frac{p  V}{R  T}$$

Are these the correct equations to use?

I also think the fixed amount of gas is the constant?

I have been looking at Boyle's law. And Charles' law.

Any help appreciated.

Thanks.


texts: How to analyze a bent beam: Stress concentration?

texts:
I am analyzing a beam, that has a bend in it. Intuitively and inspecting FEA results using a linear solver, there is a stress concentration at the bend of this I-beam.

The part was not a straight I-beam that was later bent. Instead it was made with this bend by welding a curved web onto two flanges constructed of formed pieces of sheet metal. While there was some plastic deformation in the forming, the I-beam has mostly not gone through any yielding. My question is more related to, what stress concentrations arise from this modified geometry. Most analysis of beams pertains only to straight beams.
When I was learning about stress concentrations in Shigley's, they talked about notches and holes, but not bends. Is there a factor one should apply for an x degree bend?
Any thoughts?


texts:
I am trying to find a part number for this pad ( see attached). 4" wide, 6" long, 1.3" thick. Very coarse.
I know this is a weird question and will probably be closed. Anyways, we have used those, but do not have the original box, and do not know where it came from. I did a google picture search and nothing matched. I contacted McMaster Carr and 3M, but they didn't know. Maybe someone knows and has a comment before this is closed.
Thanks


texts: Defining appropriate test function spaces for the finite element solution of Euler's fluid equations

texts:
I have the following coupled equations for the conservation of mass and momentum of a compressible fluid

\begin{equation}
\rho_t + (\rho u)_z = 0,
\end{equation}

$$
(\rho u)_t + (\rho u^2)_z + \tfrac{1}{k}\rho_z = \left(\frac{dp}{dz}\right)_f + \rho g
$$
over the domain $[0, 2L]\times[0, \infty)$ for density and velocity $\rho = \rho(z, t)$, $u = u(z, t)$ respectively. Note that
$$
g = g(z) = \begin{cases}
9.81 & \text{if } 0 \le z \le L
\\
-9.81 & \text{if } L < z \le 2L
\end{cases}
$$
and that $\left(\frac{dp}{dz}\right)_f$ is a frictional pressure term that is non-linear in $\rho$ and $u$.

The weak variational problem is: $\textit{find $u\in V_1, \rho\in V_2$ such that}$
\begin{equation}
\int_0^{2L} v\rho_t - v_z\rho u dz = 0
\end{equation}
$$
\int_0^{2L}q(\rho u)_t - q_z\rho u^2 - \tfrac{1}{k}q_z\rho - q\left(\frac{dp}{dz}\right)_f - q\rho gdz = 0
$$
$\textit{for all test functions $v, q$ in spaces $V_1$, $V_2$ respectively.}$

I am then discretising these equations in time using an implicit backward Euler discretisation for implementation in the finite element solver software Firedrake (this is a standard approach when using Firedrake).

The problem I'm having is that the Firedrake solver does not converge with the inclusion of $\left(\frac{dp}{dz}\right)_f$, and gives the wrong solution when $\left(\frac{dp}{dz}\right)_f$ is excluded.

So in order to narrow down the causes of this divergence, my question is: are there specific spaces for $V_1$ and $V_2$ that should be used for this kind of variational problem?


texts: eDrawings Displays Text Differently Than Spinfire

texts:
I am generating a very simple DXF file with the netDXF library. The DXF is a polyine box with text in the middle. When I open the file in SpinFire and DWG Trueview the text is centered (image with H aligned center). However, when I open it in eDrawings the text is way off (image with H off center).
Does anyone know what could cause this? I wonder if I am missing something in the header or what could cause these viewers to show the same file differently. My best guess is that eDrawings does not respect the alignment property. Any insight is greatly appreciated.


texts: Did I wire these solar panels correctly?

texts:
recently I bought 3 solar panels rated at 5V 200 mA each. I want to use them to charge a 5V battery bank to charge a phone. Thinking about the proper way to put them, I thought i can connect all in parallel to get maximum current, but realized that if the sun light was a little weak it will no generate full 5v thus preventing charging. So I decided to put 2 in parallel to give the equivalent of one 5V solar panel, connected in series with the 3rd panel to give the equivalent of 10v. sacrificing a little current to get higher voltage, to allow the charging to happen on a wider range of sun light power. The following picture shows the wiring and the schematic I intend to replicate.

Now that I have an equivalent of 10v, 400mA solar panel. I used a 7805 voltage regulator to cut down the excess to 5v.

Final step, I added a standard diode to prevent the panels from leaking the battery in the shade.

and now measuring:

Questions:

I didn't think about this before putting the diode, but is it okay to put the blocking diode on the ground wire? because I know some applications do not use the ground except for safety (i.e. 3 phase system). it would be helpful also to avoid the 0.7v drop across the diode before the regulator.
according to previous calculations, I'm supposed to get a maximum of 10v output before regulation, and considering that the sun was pretty shinny today, why was the reading I got not more then 6v? I have measured across each panel seperatly and got around 5.5V, are the connections right?


texts: How does punched card computer circuit design work?

texts:
I am trying to understand the underlying process of computer circuits from the beginning. I am reading about punch cards. I have come across several youtube videos and articles which are useful.

reference article: How did punch cards work? Specifically, what is the reading mechanism?

Can someone explain me back in time when punch cards were used. Punch cards with holes were entered into a reader and the holes lead to completion of circuit, how does completion of circuit helps to compute something? How was that circuit designed? Please refer some article to understand some examples about this.


texts: why is the outside of an electromagnet not magnetic?

texts:
On the electromagnet setup pictured below, only the core part is magnetic (when powered, it attracts a piece of steel) but not the 2 "wings" outside that are supposed to channel the magnetic flux.

Why is that?


texts:
Sorry if this is the wrong exchange, if it is could you point me in the right direction that'd be awesome!

I have a bit of a problem locally that I think there could be a simple solution that we're not seeing. I'm part of the local volunteer group that cleans the river running through the town but a lot of rubbish is thrown in. We have litter pickers to get the close bits and what is in the weeds, nets to get the closer litter that floats on the surface, and hooks to try and get the heavy items out from under water, but that's where the problem is.

A lot of the items that get thrown in take a lot of energy and time to get out. They may include things like shopping trolleys (carts), we recently pulled out part of a car exhaust, car and bike tires, large metal or wooden poles, children's toys, chairs, wrought iron bench ends, and so much more! On the edge of the water there are thick reeds to promote biodiversity in the river, and wooden beams to support the bank. The hook very often gets caught on these and gets stuck, meaning we have to put our selves in danger to free it. I would happily jump in the water, because hey its just a bit of water, but the medical team that follows us has strongly advised us not to as there are a lot of rodents around and we could contract diseases such as weil's disease. The hook we use is attached to about 5 meters of rope which allows us to throw the hook in and attempt to catch the items, but if we miss then we just have to keep trying.

Below is a model cross section of the river that may help you visualise the area.

I have thought of a potential solution to this that may help. We use one or two people either side of the river who hold a guide rope which the hook is freely attached to. Each side then has a rope attached to the rope so that they can pull the hook across the guide rope. The guide is lowered into the water to hook the item and then the attached ropes can be pulled to pull the item out. If the hook or item becomes trapped or free we would simply pull the hook in the other direction to reattach or free the hook again. A model of this is also attached below.

What are your thoughts on this? Could this be a valuable solution or am I just getting it completely wrong?

Thanks in advanced,
Shaun.


texts: linearizing a non linear state space equation

texts:
I have this 1-DOF helicopter simulator.

The motor's armature resistance is $R$, inductance $L$ and motor constant $K$ and reaction torque on the motor shaft is $τ$. $T$ is equal to $k_1w_2^2$ and $\tau$ is equal to $k_2w_2^2$.

$$w_1 = \dot{\varphi}_1$$

$$w_2=\dot{\theta}$$

Τhe differential equation for the current is:

$$\frac{\partial I}{\partial t}=\frac{E - RI - K_1w_2}{L}$$

in which $E$ is the input armature voltage and the equation for the torque is

$$\frac{\partial w_2}{\partial t}=\frac{KI - K_2w_2^2}{J} $$

in which $k_2w_2^2$ is the load torque and finally for the last equation I used lagrange method to derive equation of motion of mass $m$ and $M$.

$$ T = \frac{1}{2}mb^2\dot{\varphi}^2 + \frac{1}{2}M\alpha^2\dot{\varphi}^2 + \frac{1}{2}Jw_2^2 $$

$$ U = mgb\sin\varphi - Μg\alpha\sin\varphi $$

which finally gives

$$ mb^2\dot{w} + M\alpha^2\dot{w}_1 + bmg\cos\varphi - Mg\alpha\cos\varphi = -Tb = K_1w_2^2b $$

$$ \frac{\partial w_1}{\partial t} = \frac{-k_1w_1^2 + Mg\alpha\cos\varphi - mgb\cos\varphi}{M\alpha^2 + mb^2} $$

I wanna know whether everything here is right and how to linearize it around $\varphi = 0$ cause when I try to do that $\dfrac{\partial w_1}{\partial t}$ becomes a constant which is:

$$ \frac{\partial w_1}{\partial t} = \frac{Mg\alpha - mgb}{M\alpha^2 + mb^2} $$


texts: How to calculate if a motor is fast AND strong (torque) enough?

texts: I’m working on a prototype and I’m having trouble picking out a motor for that job. I need it to be able to move a rope that is about 2-4 mm thick outward (like a winch in reverse almost) and I also need it to be quick. Quick being about 0.025 mm per second. How would I determine this exactly? Unfortunately, math has never been my strong suit and while I have been looking over datasheets I’m not understanding them too well. What I’m asking is how do you determine if a motor has enough torque AND enough speed for an application.


texts: What can I coat on Stainless sheet (316 L) plate to achieve high thermal reflectivity?

texts:
I was thinking of using some Aluminum coating/blanket but the temperatures can reach 550C+ in the Chamber I work at. I am concerned about melting.
Let me know.
P.S: I am an entry level Engineer. Please no judging.


texts: How do I define settling time vertical line on root locus?

texts: I want to understand how in process of design of a controller I have to meet requirements using root locus method. I know that for the given damping ratio I need to estimate the arccos of it and everything below that angle is the desired region of my poles and zeros. But how about the settling time when it's said that it should be less than 1 second, how do I find the region (the vertical line) that corresponds to that requirement?


texts:
Is it possible to generate power from fruit juice, using a device with a simple circuit which charges a battery using juice from fresh oranges?

If so what would be the ratio between emf emitted and juice from orange?

if the device used rechargeable cells charged by the orange juice, would there be enough force to cut oranges automatically with a small blade connected to a battery powered motor?

I am hoping to collect and store energy collected from the juice in a rechargeable battery, would this be possible? of so would be energy stored be enough to power a small motor to operate a knife which would cut through the fruit?

the device would cut oranges into quarters at the press of a button, it would use a collection tray beneath the cutting area which collects juice residue from the cutting process and convert this into electrical energy stored in a battery.


texts: What is this pneumatic connector called?

texts:
I'm looking into fitting ball-type inflatable equipment (eg bike tires, yoga balls, basketball ball, etc) to a 2/4 silicone tube. This will be to measure the pressure inside the inflatable, so the other end of the tube goes to a pressure sensor.

The top valve seems to have a schrader valve compatible threading.

The bottom end seems to be called descriptively (hose fitting, air pipe fitting, tube connector, pneumatic fitting, etc), are there any DIN or other names for this?

How is each end named of how does one goes about finding such component?


texts: How Can I Determine Multiple Discharges from a Pipe Network? (Knowing the Inlet Conditions)

texts:
I have little/no experience with pipe networks and have been searching for a methodology to calculate the discharge from multiple outlets of an oil pipe network with a single inlet. As far as i can tell I have too many unknowns to use something like the Hardy Cross method (and often i don't have loops, just multiple branches and outlets as shown below), and Hardy-Cross seems to be used to find flows in pipes with known inflows and outflows, which I don't have.

A good example may be something like this:

Inlet flow rate is known
Fluid Properties are known
Geometry of all pipes/bends/outlets are known
The height above a datum of all pipes and outlets are known
Flow is each pipe branch is UNKNOWN
Discharge from each outlet is UNKNOWN (ext. pressure can be assumed ambient)
I have target outflows, and could modify pipe length/diameters to obtain them

See my very crude diagram:

Can anybody suggest an analytical method I can use to calculate the outflows and/or optimise the pipe lengths to obtain a set of target outflows?

A worked example of a similar problem would also be appreciated.

The person who tried to solve this problem before me just divided the inflow up based on the area of the outlets, without considering losses, bends or even the lengths of the pipes anywhere in the network. I have been searching for a while with limited resources for a worked example or solution method for this.

I will probably write a code to solve these problems if I find an appropriate methodology. (I'm aware commercial software does exist that could calculate this, but I don't have access).


texts: Is it safe to slightly cut the edge of RCC beam for passage of AC Vent and wiring?

texts:
My electrician made a cut in the wall and the beam as in the image in my absence. The cutting is done with hammer and chisel and it is around 1.5inch deep..I'm really worried that it might impact the structural strength.

Beam appears to be larger than 9inch by 9inch.

Is it safe to do it? If it is not, what could be done to fix this?

Thanks a lot!


texts:
I'm trying to make an evaluation of the available 3D printing options of polypropylene and I'm having difficulties comprehending material characteristics that make PP PP-like.
I realize this sounds a bit non-exact, but please bear with me. Polypropylene is very beneficial for this specific product because it handles repeated large plastic deformations very well and won't break. When you look at the material properties and compare them to other plastics for injection moulding, one characteristic stands out - elongation at break, which can be up to 150% or more for PP for injection moulding (this value is from a generic database, actual materials have similar values).
When I checked the HP's PP mateiral and Stratasys's Durus PP-like mateiral, their elongation at break was very low, around 20%, which is less than PA11 for SLS 3D printing.
Maybe elongation at break is not a good parameter to evaluate the response to large plastic deformation I mentioned. Maybe someone has more insight into this.
EDIT: I tested the PP printed part for bending fatigue. The part was printed on a HP fusion jet printer and the results are very similar to the injection molded part.


texts: How does dynamic braking work with railway locomotives?

texts:
General Electrics boasts that its Evolution series diesel-electric locomotives are capable of dynamic braking. Dynamic braking uses the electrical traction motors on the locomotive axles - motors are switched into generator mode and convert kinetic energy of the locomotive into electricity which is then directed either into large resistors (most common) or into charging batteries.

Sounds good but a typical scenario is having two or three diesel-electric locomotives pulling a train of one hundred carriages. A typical locomotive has up to ten axles and weighs up to two hundred tons, so three locomotives have up to thirty axles and weigh up to six hundred tons. They together pull around one hundred carriages and each of those has four axles without any motors (so unable to implement dynamic braking) and weighs around one hundred tons each (when fully loaded). One hundred carriages together weigh about ten thousand tons total - about 16 times more than the locomotives.

So it looks like if the locomotives use dynamic braking and the carriages don't use any braking at the same time then the whole train should "compress" and either derail or collapse into the locomotives because of inertia. So the carriages should use air brakes each time when the locomotives use any brakes so that the whole train slows down evenly.

This means that dynamic braking can only be used to slow down the locomotives, not the entire train and the carriages have to use air brakes every time the locomotives use any brakes.

Can dynamic braking be used to slow down the entire train or does it only slow down the locomotives?


texts: Parts needed for controlling vacuum line pressure with pressurized nitrogen

texts: I'm trying to assemble a simple setup where a line which is typically under vacuum can be pressurized by an external nitrogen supply, with this pressure regulated to less than 1 bar absolute (let's say 700 mbar). This nitrogen supply comes from the building and is at ~6 bar. What kind of regulator would let me do this? Would a conventional regulator which just reads gauge pressure work? As an additional note, there would not be any flow to or from a process occurring in this line while it is being pressurized or at the nominal 700 mbar regulated pressure.


texts:
I am having a bar and surface (made of aluminum). I need to attach some material to the end of the bar so that, if I apply any force (25 N-sideways) to bar it has to stick with the surface.

Force is applied normally to the flatter surface of the bar. I need to select a material at the end of bar so that the force applied on the bar is minimal.

What methodology should I choose to find an answer?

Aim is lowest necessary force to keep the rod intact (with a material added to rod end)


texts: do prestressing tendons located in the compression zone contribute to compression reinforcement?

texts:
when doing the normal RC design of an RC beam, it is determined that compression steel reinforcement is required, does a prestressed tendon in the compression zone contribute to the area of compression steel?

Possibly it could contribute, but with a reduced contribution because it already has an axial load within it.


texts: How does the relative valency of the impurity and host metals affect solubility in a substitutional solution?

texts:
I have a book that claims:

  A metal will have more of a tendency to dissolve another metal of higher valency than one of a lower valency.

I interpret this as saying that a metal with higher valency will dissolve more easily into a host metal than it would if it had a lower valency. For example, $\textrm{Fe}^{3+}$ as impurity atoms and $\textrm{Na}^{+}$ as host will work better than vice versa.

But then in the summary of the chapter it says:

  A valence that is the same as or less than the host material will have more appreciable solubility.

Which of the two statements is correct?


texts: Independent constraints - Procedure to verify it

texts:
I am wondering if there is a procedure to verify that the constraints of a system of rigid bodies are independent.

Here there is an example of a system with dependent constraints: L beam - Strange result

Thank you for your willingness.


texts: Standard parameters for machining aluminium?

texts:
Sorry for the weird question but I was wondering about the standard machining parameters for Aluminium (if there is even a standard). Particularly the values for a CNC process (preferably in SI) for a rough volume milling and one for a finishing cut. Google searches doesn't seem to be very helpful as I only need rough values for testing purposes. (CAD Package is CREO Parametrics 2.0)

Thank you for your help!


texts: Problem while solving for the moment of a cantilever beam

texts:
As in the first image,
Moment at any point between C and B should be 0.

But when I try to solve it by substituting equal and opposite forces at end C so that anti-clockwise moment of $F(l-a)$ and force $F$ act at C, moment diagram comes out different.
Why is there discrepancy?


texts:
I am working on a design for a small lathe that could double as a horizontal drilling machine like a Westhoff.

My plan is to have specific geared speeds, rather than continuously variable speed.

I am wondering what the best type of motor would be. Cost is no object, but it needs to be compact, no more than 6" in diameter and hopefully less.

Startup torque is not required, because in this type of application you can always start the motor unloaded; in fact, even if the motor had zero startup torque I could potentially add a small starter motor to start the main motor, if that would be better.
It would run on normal AC household current
My thought is to find a motor with a high peak torque rating and then just run the motor at that ideal speed, using gears to adjust speed as necessary
Obviously, the more horsepower the better

What type of motor best fits these characteristics?


texts: How to cut evenly spaced uniform holes in a plate of metal?

texts:
I've looked everywhere for this seemingly simple question, but I cannot for the life of me find out how to easily cut a specific amount of holes in a plate of metal with my cnc. Am I going to have to make each individual hole, or is there a program that automatically generates an svg, g-code, stl, etc. for evenly spaced holes?

I'm attempting to cut a grid pattern using a Shapeoko and a Grbl Arduino shield.


texts: Finite difference discretization of the Cauchy-Riemann PDEs

texts:
I made a forward fd-discretization of the Cauchy-Riemann PDEs but I am struggling to implement this in python.
I have a quadratic mesh with heighτ = $2*\pi$. The dirichlet boundary conditions are at $u(x,0) = f(x) = \cos(x)$ and $v(x,0) = g(x) = sin(x)$. And I have periodic boundary conditions: $u(2\pi,y) = u(0,y)$ and $v(2\pi,y) = v(0,y)$.

My code:
import numpy as np

import matplotlib.pyplot as plt

from mpl_toolkits.mplot3d import Axes3D

#meshsize

N=100

U = np.zeros([N,N])

V = np.zeros([N,N])

# dirichlet bc

x = np.linspace(0,2*np.pi,N)

for n in range(0,N):

    V[N-1,n] = np.cos(x[n])

    U[N-1,n] = np.sin(x[n])

# recursion

for i in range(1,N-1):

    for j in range(0,N-1):

        U[i,j] = U[i,j+1] - V[i+1,j] + V[i,j]

        V[i,j] = U[i+1,j] - U[i,j] + V[i,j+1]

        #periodic bc

        dx1 = x[j] - x[i]

        dx = np.mod(dx1, xSize * 0.5)

        V[i-1, 0] = dx

        U[i-1, 0] = dx

        V[i-1, N-1] = dx

        U[i-1, N-1] = dx

# coordinates

x = range(N)

y = range(N)

x, y = np.meshgrid(x, y)

# for interactive plot

%matplotlib notebook

# create plot

fig = plt.figure()

ax = fig.add_subplot(111, projection='3d')

ax.plot_surface(x, y, U, rstride=1, cstride=1, cmap='viridis', edgecolor='none')

I expect the plot to look like the complex e-function $u (x, y) + i\;v(x, y) = exp (ix − y)$ but when I plot U or V there is only the integral of sinus or cosine respectively plotted. I am not sure if my nested for loop does what I want or if I have a lack of understanding how to plot this right. Does anyone have an idea how to solve this?


texts: Where do I start with learning how to transfer data via RF

texts:
So I literally have no idea where to start but I know what I want to make.
The goal is to somehow transmit 25mb/s of data across 15km with high penetration. Acceptable for reaching through trees and rocky areas in the mountains.
I would like to focus on lower frequencies like 1.3ghz or 2.4ghz but I know there are limitations to that frequency. I really don't have a clue where to start if someone could point me in a good direction that would be amazing.
I was thinking it would be cool to use 1.3ghz and transmit on multiple channels, then combine them all to get the desired data rate.
Again i'm super noob at this kind of stuff so please excuse my ignorance.