texts: Submersible sump pump life in pit without water?

texts: What can happen to a pump in a pit without water for many months, then the fall heavy rains start adding water to the pit, will the pump be efficient to do its job? Should water be added to the pit to exercise the pump? If yes, what would be the recommended frequency?


texts: Finding fraction of liquid and solid from isomorphous alloy phase diagram

texts:
if alpha of 82% B and liquid of 57% B are in equilibrium in an alloy of 73% B,the fraction of liquid is?
I know formula for it, but confused in finding property.
Any help will be of great use & will be highly obliged. Thanks


texts: is there any relationship between endurance limit and tensile strength for thermoplastics?

texts: i want to know about  the relationship between fatigue strength and tensile strength for thermoplastics especially PPSU (POLYPHENYLSULPHONE)@23 DEG.


texts:
First of all I am just a starter in Matlab, so the program is not optimized. For now I just want to get it running. This is a 3D heat problem with boundary conditions. Fixed temperature from the north, insulated from the bottom, and we have convection on the 4 surrounding sides with the same h. when I run it it does not give me the right convergences. I have the analytical and the solidworks approximations, so I know the results I get in Matlab are wrong. Could someone advise me please. Your help is appreciated.

==============================

%===Solution of the problem of 2D in the bookmarks:Case2a=====
clc;
close all;
clear all;

DX=0.01; % step size
DY=0.01;
DZ=0.01;
Lx= 0.6; %length along x-axis in cmn
Ly=0.4;   %length along y-axis
Lz=0.3;   %length along z-axis
Nx=Lx/DX+1;    %Number of nodes along x-axis
Nx=floor(Nx)+1; % I shouldn't add 1. I should get it automatically
Ny=(Ly/DY+1);    %Number of nodes along y-axis
Ny=floor(Ny);
Nz=(Lz/DZ+1);
Nz=floor(Nz)+1;

K=2;
h=500;
T_inf=20;

X=0:DX:Lx;
Y=0:DY:Ly;
Z=0:DZ:Lz;

T=zeros(Nx,Ny,Nz);

% I added imaginary nodes outside then it gave me numbers

tol=1;
s=0; %s=2000 could be set as the maximum number of allowed iteration for
example
err=1;
T_old=1;

while err >=tol %&& s<2001
    s=s+1;

%------------boundary conditions------------------------------------------

%====North temperature (Boundary)
T(:,Ny,:)=90;
%===South Boundary "insulation" ==============
for k=1:Nz
    for i=2:Nx-1
   T(i,1,k)=0.25*[2*T(i,2,k)+T(i-1,1,k)+T(i+1,1,k)];
  %T(i-1,1,k)=4* T(i,1,k)-2*T(i,2,k)-T(i+1,1,k);
    end
end
%================Back Boundary "Convection" ================
for j=2:Ny-1 %changed
    for i=2:Nx-1
  T(i,j,1)=0.5*K/(h*DX+2*K)*[2*T(i,j,2)+T(i-1,j,1)+T(i+1,j,1)+2*h*DX*T_inf/K];
    end
end
%================Front Boundary "Convection" ================
for j=2:Ny-1
    for i=2:Nx-1
  T(i,j,Nz)=0.5*K/(h*DX+2*K)*[2*T(i,j,Nz-1)+T(i-1,j,Nz-1)+T(i+1,j,Nz-1)+2*h*DX*T_inf/K];
    end
end

%================West Boundary "Convection" ================
for j=2:Ny-1
for k=2:Nz-1
  T(1,j,k)=0.5*K/(h*DX+2*K)*[2*T(2,j,k)+T(1,j,k-1)+T(1,j,k+1)+2*h*DX*T_inf/K];
    end
end
%================East Boundary "Convection" ================
for j=2:Ny-1
    for k=2:Nz-1
  T(Nx,j,k)=0.5*K/(h*DX+2*K)*[2*T(Nx-1,j,k)+T(Nx,j,k-1)+T(Nx,j,k+1)+2*h*DX*T_inf/K];
    end
end

% The interior nodes
for k = 2:Nz-1 % I think it needs to go loop by loop(pairs of loops)
    for j = 2:Ny-1
        for i=2:Nx-1
    T(i,j,k)=0.25*(T(i-1,j)+T(i+1,j)+T(i,j-1)+T(i,j+1));
        end
    end
end
err=max(max(abs(T-T_old)));
T_old=T;
end

T=rot90(T)


texts: Understanding redundant pharmaceutical packaging

texts:
I ran across an interesting combination of packaging for some medicine the other day.

The medicine in question was a prescription migraine medication.  The exterior, cardboard package that it came in was fairly typical.  The interesting part was that the medicine's outer packaging consisted of a thick, foil envelope, and the inner packaging consisted of a thick, foil single blister pack.

Which got me to thinking - both layers of packaging appeared to be equally effective at blocking light and moisture from seeping into the underlying pill.  Using such extensive packaging would appear to be more expensive that traditional packaging techniques.

What properties of a chemical (pharmaceutical) intended for general usage (consumption) would merit the double layer of packaging and additional expense?  Or to be a bit more specific, what is it about a medication that causes it to need such extensive protections?  Or am I completely off-base, and it's more of a manufacturing concern in making sure the pill isn't damaged before being delivered to the consumer?


texts: is there a command to make pdfattach becomes editable like the command of pdfimport?

texts:
The difference between pdfattach and pdfimport commands is that, I can click multiple pdf using pdfattach, but it seems that I cant select any geometry out of it? But by using pdfimport, I can select the lines out of it. It has geometries.
sample pdfattach

Sample pdfimport


texts: Control system for a temperature controller

texts:
I have adapted a refrigerator to create a temperature controlled environment for brewing beer. I have mounted an electric heater coil inside the fridge and configured a basic controller to maintain a constant temperature inside the fridge. When the temperature at the temperature probe, $T_p$, is below the target temperature, $T$, the heater is turned on. When $T_p$ is above $T$, the fridge compressor is turned on. The target temperature, $T$, is in fact a small range to stabilise the system.

$$ T_p \lt T-c \ \ \rightarrow \ \ Heat  $$
$$ T_p \gt T+c \ \ \rightarrow \ \ Cool  $$

My question is this:
I am trying to decide, more for interest than anything else, whether it is more effective to probe the temperature of the air inside the fridge, or the liquid (beer) inside the plastic vessel inside the fridge?

My instinct says that I should probe the air temperature, because the temperature of the beer will follow the temperature of the air, subject to a time delay, and by probing the temperature of the beer I could get unstable feedback due to this delay? Would the answer change if I were to put the fridge outside, where the air temperature is subject to much more variation? I suspect in this case it might be better to probe the beer so that the controller can over-compensate with air temperature and limit temperature variation of the beer.

For the purposes of this application, the control system is fixed as I'm using a fixed controller ie. heating and cooling are binary on/off functions. However I'd be interested to learn of any control techniques that could be implemented with a raspberry pi, if they were suggested!

Thanks in advance.


texts: LQR control and system dynamics linearization

texts:
I recently finished a project that simulated the dynamics and control of a 6DOF quadcopter model using a state-space LQR control approach, but I had a few questions that I wanted to ask that might help me develop the model further. From the literature, if we have a general nonlinear dynamical model of the form,

$$\dot{x}(t) = f(x(t),u(t))$$

then the "standard" approach to control engineering is to linearize the nonlinear system dynamics into the form,

$$\dot{x}(t) = Ax(t) + Bu(t)$$

where,
$$A = \frac{\partial f}{\partial x}, \space B = \frac{\partial f}{\partial u}$$
are constant matrices that have been evaluated at an equilibrium state $x = x_{eq}$ and $u=u_{eq}$ (for a quadrotor this equilibrium state is a hover with pitch, roll and yaw equal to zero and control inputs being enough to counteract gravity). Once this is done, we can then use our $A$ and $B$ matrices to find the "optimal" LQR gain matrix $K$ by solving the Riccati equation (or equivalently using MATLAB's lqr function), and use this gain in a control law of the form
$$u(t) = -K(x(t)-x_d(t))$$
to find our control inputs $u(t)$, that allow us to track a desired state trajectory $x_d(t)$ by applying $u(t)$ to our full nonlinear system dynamics $\dot{x}(t)=f(x(t),u(t))$.

This approach worked pretty well for the quadrotor simulation, but I was wondering why we're required to linearize our system dynamics about an equilibrium point. Wouldn't it also be possible to have a time-varying state-transition matrix $A(t)$ and time-varying control matrix $B(t)$, that would be computed using the same linearization process above, except that instead of linearizing about the hover equilibrium state we would linearize about our current state $x(t)$, which would then allow us to re-compute the LQR gain matrix at each time-step? This would then give us a time-varying gain matrix $K$, and would presumably give us better tracking capabilities since our next state $x(t+1)$ would be close to our previously linearized state. Any advice would be much appreciated, since I'm struggling to find out why linearization always occurs around static equlibrium points, and not about current states.


texts: A metallic cube of side 10cm, density 6.8gm/cc is floating in liquid mercury (density 13.6gm/cc), with 5cm height of cube exposed above mercury level. Water is filled over this to submerge the cube fully. What is the new height of the cube exposed above the mercury level?


texts: How to prove that during loading session of glass container, which will happen first - overstressing or buckling - via FEA?

texts: How do I prove that during a loading session of a glass container, between two failure modes, overstressing or buckling, which will happen first via FEA? Is there any scientific way of approaching this problem? Possible references will also be appreciated.


texts: What is the cycle of simulation editing?

texts:
So this is very general, but... How are simulations for vehicles done? I know that computational fluid dynamic simulations are used, but why are repeated tests of actual hardware done too? Obviously this is because there are some things that are found through actual physical testing. So this leads into my question. Are simulations refined from the actual test data? how are phenomena from the actual test translated into simulation? Eyeballing things? just gathering data, making a hypothesis, and then running the simulation again from the top?
I guess what my question ultimately boils down to is: What does a simulation cycle look like?


texts: I am unsure of how to interpret the uncertainty given for a Multimeter I have been using. Everything is listed as follows ±(0.8%+10). I have never seen uncertainty listed this way, with a +"x" after the percent uncertainty. What range does this correspond to exactly, -10.8% to 10.8% or is it -0.18% to 0.18%? Here is a link to the datasheet: Digital Multimeter Datasheet. Thanks!


texts: If in both cases if there is an application of Shear Stress then why do we have Screw dislocation in one case and Edge dislocation on the other?


texts: How to characterize a system given several curves

texts: We have a system that heats up when voltage is applied, temperature is then measured against time. We have several different data plots of temperature versus time at varying voltages. We need to develop a PID controller to control the system. How would we find the system equation?


texts: Flat root spline vs filet root spline: what's the difference

texts:
I'm looking at a hobby micro servo, which has a 5mm splined shaft output. Specifically, this is a Tower Pro model SG90 or clone.  Close-up photos of the shaft below.
I've found online diagrams for both a 30 degree Flat Root Spline shaft, and a 30 degree Filet Root Spline.   Can someone please explain the difference between these spline designs?

I'm adding a drawing approximating the photos (and a hub) of a 21 tooth spline with a 5mm pitch circle and 45 degree pressure angle.  (To simplify, I've not used involute teeth.)
I have filleted the exposed corners of the teeth at 0.06 mm.  Is it these that make it a fillet root spline?
I've also added a fillet to the empty spaces joining the faces.

P.S.  here's a link to my in-progress CAD model.   Feedback welome.


texts: Flow through an Annular Orifice for Pintle Injector

texts:
Our rocket team is trying to finalize the design of our injector for a small liquid rocket engine.  The current analysis challenge is verifying the correct pressure drop across the annular orifice leading to the combustion chamber which the Kerosene flows through.

The current equation we are working with is this one provided in Mathwork's documentation.
https://www.mathworks.com/help/physmod/hydro/ref/annularorifice.html

Because we know the inner diameter of the annulus (the pintle body OD), and the properties of the liquid flowing through the reservoir leading to the injector orifice, we were able to calculate an orifice OD of 1.11inches.

The reason we are suspicious of this equation is because it makes reference to laminar flow, where we have a pretty high mass flow, and hence high flow velocity.

Are there any simple (undergraduate level) resources that can further inform us how to either directly calculate diameter, or could let us converge on a discharge coefficient and diameter through numerical methods?

Thanks!  Here is a quick picture of our injector if that helps.
https://i.imgur.com/BUb8DG3.png


texts: Question about length of commercial augers

texts: I am planning on buying a 16mm auger for a project of mine. I was wondering if the length given (such as 460mm) included the shank and tang or if it just specified how long the business end of the auger was?


texts: What is a thermodynamic process that is not polytropic?

texts:
In discussion under another question, it was pointed out: "Not every process is polytropic; that is just a special case when $pV^n$ is constant" Must have missed that in school.
What is a real life example of a non-polytropic process in a closed system (energy transfer yes, mass transfer no)?
How are non-polytropic processes simulated/calculated?


texts: How to furnace-melt bismuth oxide into optical glass?

texts:
I have been experimenting with a furnace at my house and am looking to attempt the more difficult process of creating bismuth-oxide based optical glass for the purposes of creating optical elements (think lenses and reflective glasses).

I'm having trouble finding what the raw material inputs to create the best mixture should be, as well as best practices for an amateur such as myself. Most of the literature on how to produce good results are either pay walled or too esoteric for me to understand. I was able to find a helpful paper, with the following excerpt:

  The raw materials of tellurium dioxide, TeO2 (Aldrich 99.5%), and
  bismuth (iii) oxide Bi2O3 (Aldrich 99.0%) were used to synthesize the
  glass sample. The glass sample was prepared by using a melt quenching
  method [32,33]. The bismuth (iii) oxide, x = 5, 8, 10, 12, 15 in mol%
  was added into the tellurite oxide and was weighed using a digital
  weighing machine with an accuracy of ±0.01 g and then mixed together
  by using a mortar and pestle. The mixture was poured into an alumina
  crucible and put into an electric furnace set at 100 °C for a period
  of 30 min. The alumina crucible was used because it can withstand high
  temperatures and does not react with the raw materials during the
  melting process as opposed to porcelain crucibles. The temperature was
  then increased by 10 °C/min until 900 °C and the then maintained for 2
  h. When the melting process was completed, the molten liquid was cast
  into a stainless steel cylindrical shape mould which had been
  preheated at 400 °C for 30 min. The sample was annealed at 400 °C in a
  second furnace for 1 h, then the furnace was turned off. The glass
  sample was cut at a thickness of about 2 mm for the required
  measurements [33].

I have pulled a few assumptions from this paragraph which it would be helpful for me to verify before testing this out:

I'm assuming the passage

  the glass sample was prepared by using a melt quenching method [32,33]. The bismuth (iii) oxide, x = 5, 8, 10, 12, 15 in mol% was added into the tellurite oxide

is simply stating that the end concoction consists of a combination between 85-95% TeO2 and 5-15% Bi2O3, correct?
What is the purpose of annealing for in this context? My end case for the result pieces are simply for prototyping, but my guess is I will have to polish the pieces with cerium oxide without destroying them so they can not be too brittle. Is annealing required?
I'm lost for understanding what the quenching method is, results online are sparse and the linked papers are pay walled. What is the process for this like?

Are there other things I should know? I have this furnace and have had success with simple metals but not sure what else I need to know for something a bit more chemically involved like optical glass.

Thank you.


texts: How does a closed loop control system actually work?

texts:
I'm currently taking classical control theory and have some questions regarding basic concepts related to closed loop systems.

Let's say I have a simple servo motor controlled by an electric current. Using a PID controller, my block diagram is as follows:

Now, I'm still struggling to understand some things:

At what point is my loop actually producing a signal that my servo can use? And how would I extract it from my control loop?
Why can I simply take my PID'ed error signal and plug it into a plant requiring current as an input? If I had a set current I could calculate the torque on my motor, from which I could then determine the accerleration and thus get the position by integrating that value twice. How do I do such a calculation if I only have a value that tells me to either increase or decrease my current by some factor?
Why is the positional output calculated by my plant reconnected to my sensor in the feedback loop? Why is there an output in the first place? Shouldn't the sensor simply deliver continous data and the loop respond according to my error term?

I would be very glad if somebody could answer these basics questions for me, I just can't quiet wrap my head around the basic mechanics of a control loop like this.

Thanks in advance!


texts: Why do we still scuba dive with bottled air?

texts:
Breaking down water into H2 and O2 through electrolysis takes 241.8 Kj/mol. According to howstuffworks.com, the average person uses 550L of pure oxygen per day, which equates to about 24.6 moles of pure O2.

The new Tesla car batteries are 85 kWh, which (in a perfect world) would be enough energy to extract about 1265 moles of O2 from water through electrolysis, enough oxygen to breathe for 51 days! Even a system at 1% efficiency would be able to provide enough oxygen to breathe for 12 hours. Current scuba tanks only last a fraction of that (using bottled air).

Why do scuba divers still use bottled air rather than generating their oxygen through electrolysis, in a world where batteries have enough capacity to generate plenty of oxygen through electrolysis?


texts: How can I make a rudimentary sunspotter?

texts:
This is similar to my Physics.SE question Microtops sunphotometer sun target optics - there I was asking about the optics principles (the answer is no good for my understanding, but I have been able to figure it out myself).

The purpose behind a sunspotter is to show when a device is lined up in direct view of the sun - vital for fields such as sunphotometry etc.

This question is given that I now understand the optics principles involved (similar to a magnifying glass, but smaller and does not burn when focused) - what method can be used to make a rudimentary sunspotter?

In particular, I am interested in:

a suitable material that would be used for the sun target (as per the Microtops picture on the linked page).
the same orientation of the sun target being perpendicular to the incident light.

What I am not interested in:

any device how to make a device that allows viewing of things like eclipses.


texts: What are the LENOVO YOGA 3 USB-like inlet 20V 2A wiring/signal/voltage specs?

texts:
I have an unknown-history Lenovo Yoga 3 Fold-Back Keyboard Laptop that I am trying to charge/test/repair I and don't have a OEM or aftermarket power adapter.  The power input site looks like a usual finger-thick usb power inlet but with an additional small "wing," however it will physically accept a regular USB male.  The bottom of the laptop says "20V 2A."
I have searched the web looking for the power spec I should input in order to power up the laptop, but I found nothing. Nor did I find a name this connector may be called (USB-Wingy? USB-Flaggy? USB-Perky!?).
I tried wiring a common USB male pigtail (having presumably the Red +5V power, white -Data, green +data, and Black -Ground) to a 70W 20V DC power supply (from a generic Universal Laptop Power Supply kit), and the following attempts failed (meaning no light on the "Battery" light on the laptop):

Red to 20V+, Black to Ground
Red and white to +20V, Green and Black to Ground.

What are the correct specs and wiring, and what is the name of this connector's shape so that we can put a name to talk/query about it?
Pic attached of the input site and the common USB pigtail I used.

Update Here's a better pic  and the Model is 80JH Lenovo Yoga 3.14 and yea there are another two stor shorter pins deep in on the side of 1 and 4 for a total of 6.
[]


texts: Why don't we use principal maximum stresses when designing a structural element?

texts:
Consider a concrete column is under compression from top loading and also carries some shear stresses.

If take a plane 2d element in the column with these stresses and rotate it to the point it gives out the it maximum normal stress then rotate it to give out maximum shear stress which both values should be higher than our original calculated stresses.

Why don't we compare those value to the concrete's compression and shear strength instead?

I apologize if my question is too simplistic, I'm still a civil engineering freshman.


texts: Rate of Cooling of a Black "Polymer" Handgun

texts:
I need to understand some basic concepts about the cooling characteristics of a black "polymer"-and-zinc-alloy handgun (specifically, this one).

If this gun was left on the ground under daytime sunlight, I assume that both the ground and the gun would get warmer.  I assume, also, that after the sun went down, both the ground and the gun would begin to cool.  My questions are:

1) would the gun warm under sunlight to a higher temperature than the ground, because it is black and/or because of what it's made of?

2)  after sundown, would the gun cool at the same rate as the ground?  Or, would the rate of cooling be different?

Edit:  I should clarify that the surrounding ground is essentially brown dirt/mud.


texts:
How to measure torque in a bicycle?
how much newtons will produce by the pedal of the cycle ?


texts:
I'm interested in knowing whether or not submerged welding can be done in fluids other than water, specifically mineral oil in this case. The reason I want to know is that I'm looking into designing an extrusion 3D printer for metals that works on the same principle as stick welding, like these ones:
https://hackaday.com/2020/03/31/3d-metal-printer-uses-welding-wire/
https://3dprint.com/226829/researchers-develop-low-cost-metal-3d-printer/
However, I don't want the metal to oxidize, and the machines in these examples produced very poor surface quality due to the metal overheating and melting. I know that the oxidization could be prevented by surrounding the entire print in an inert gas, like argon, carbon dioxide, or sulfur hexafluoride, but I wanted something that would be easier to recycle without getting contaminated, plus a fluid would help to keep the print cool. Water isn't an option because it rusts metal and its conductivity makes it dangerous to use with electricity, so mineral oil seemed like the best option, as it is also used to cool transformers.
My major concern with using oils of this kind is, obviously, that they are flammable when heated to high temperatures in the presence of oxygen, so for this question I'm assuming the welding is taking place either in an airtight box (but expandable to account for the oil evaporating), or in a swimming pool full of mineral oil big enough for the heat to dissipate into safely. I was also wondering if the oil might decompose into toxic chemicals at welding temperatures or introduce unwanted inclusions or contaminants into the weld. Anything you can tell me would be helpful. Thanks.


texts: How to estimate the required thickness of a transfer floor

texts: I am examining a high rise building project of 30 floors with a podium underneath and 2 basements. The structure in the tower and the podium varies between flat slabs, steel structure for wide spans, a huge shear wall around the tower's core, etc. The basement space has become inefficient as a parking area so I'd like to transfer this whole structure to an 8x8 or 16x16 grid of columns by using the transfer floor/slab. How can I estimate the required thickness of the transfer floor?


texts:
I am an engineering student. I want to get into microscopy research and bio-science. So I want to buy a fair enough compound microscope. I searched for them and there are so many variants from different manufacturers. So, I couldn't select one.

My budget is $1000. I know that sounds way too overkill for entry level, but just say that this is total amount I have to spend for a good microscope. I am currently in India and associated price for variants of major manufacturer is not mentioned here so if anyone can mention price(as in India), would be appreciated.

Which manufacturer and which variant should you recommend specifically?


texts: How to choose order and cut-off frequency for low-pass Butterworth filter?

texts:
When using IMU data (accelerations and angular velocities), many papers use a 4th order low-pass butterworth filter with a cutoff frequency of 5 Hz. However, none of them really justify why those filters have been chosen.

Can anyone please explain how the order and cutoff frequency are chosen for a filter of this nature? My data has a sampling frequency of 125 Hz


texts: Oil recovery by thermal expansion of rock

texts: Does rock expansion play a role in increased recovery of oil when heat is supplied to the reservoir at the hands of steam or hot water ?


texts: Is there any hardware to use in GPR applications?

texts:
I want to make a radar system which needs to send EM wave and receive the reflected wave from the ground.

I am looking for a ready to use RF signal processing hardware but can't be sure which is applicable.

As I found that, the required frequency range for us is approx. 700 - 1000 MHz. So, we need to process this frequency of signal. I talk to somebody who told be that we need ADC having double the frequency we use which is 2GHz or something. I am not sure what we need else and what should be looked for.

I need to visualize beneath the ground with spatial image created from the signal read.

I searched for articles but couldn't find sufficient data about the hardware that we can use.

I suppose it is ok to have some ready to use evaluation boards from IC companies if they fit. Such as this.

Thanks


texts: Fluid dynamics of non interacting tanks in series

texts:
I have a system like this:

and I have to estimate the height of the lower tank.

First of all, I'm considering that I have a non-viscous, incompressible fluid in steady flow.

Base apertures

The outlet velocity of liquid when draining a tank or a container can be expressed as:
\begin{equation}
v = C_v \sqrt{2gH}
\label{eq:baseAperture1}
\end{equation}
where $v$ is the outlet velocity $[m/s]$, $C_v$ is the velocity coefficient (water: 0.97), $g$ is the acceleration of gravity ($g=9.81 m/s^2$) and $H$ is the height $[m]$.\
The volume flow can be expressed as:
\begin{equation}
V = C_d A \sqrt{2gH}
\label{eq:baseAperture2}
\end{equation}
where $V$ is the volume flow $[m^3/s]$, $C_d$ is the discharge coefficient ($C_d = C_c C_v$ where $C_c$ is the contraction coefficient (sharp edge aperture: 0.62, well rounded aperture: 0.97)) and $A$ is the area aperture $[m^2]$\\
I know the volume flow and the height, so, using the first equation I get the outlet velocity $v$. Using the second equation I can get the area A of the outlet hole (I have two possible results because I don't know if the hole has a sharp edge aperture or a well rounded aperture).

Bernoulli

\begin{equation}
\frac{d}{ds} \left(\frac{v^2}{2} + \frac{p}{\rho} + g h\right) = 0
\end{equation}
where $v$ is the flow speed, $p$ is the pressure, $\rho$ is the density, $g$ is the gravity and $h$ is the height.\
From the previuos equation, I get:
\begin{equation}
\frac{v^2}{2g} + \frac{p}{\gamma} + h = constant
\end{equation}
where $\gamma = \rho g$\
For a tank with a small orifice in a lateral, close to the bottom, I have:

Bernoulli part 2

Making a lot of maths, I get these two equations:
\begin{equation}
\dot{h}_1 = -\frac{A_{d1} \sqrt{2g}}{A_{D1}} \sqrt{h_1} + \frac{K_P}{A_{D1}}V_P
\end{equation}
\begin{equation}
\dot{h}_2 = \frac{A_{d1}\sqrt{2g}}{A_{D2}} \sqrt{h_1} - \frac{A_{d2} \sqrt{2g}}{A_{D2}} \sqrt{h_2}
\end{equation}
where $h_1$ is the height of the upper tank, $h_2$ is the height of the lower tank, $A_{d1}$ is the area of the orifice of tank 1 and $A_{d2}$ is the area of the orifice of tank 2, $g$ is the gravity, $A_{D1}$ is the area of the upper tank and $A_{D2}$ is the area of the lower tank, and $V_P$ is the voltage of a pump. In my exercise, $Q_P = V_P K_P$ where $Q$ is the discharge. Is $Q_P$ the volume flow?

I know how to linearize that equations, using the Jacobian, and solving that equations but I don't have the areas $A_{D1}$ and $A_{D2}$.

How can I get $A_{D1}$ and $A_{D2}$?


texts: Describe the magnitude of a force using real-life comparisons instead of numbers

texts:
I already asked this on physics.se, I got a suggestion to ask here, but the question became too old to migrate before I decided to do it. I did also receive an answer, and I am grateful for it but
still hope someone has another idea.
I need to describe the relative magnitude of a force using real-life comparisons instead of numbers.
At work, we glue some Devices onto a flat horizontal surface and my task is to periodically check how stable the Devices are. Specifically, I push them with my hand to see if they will tilt, spin, rock or move etc. I now need to provide a report. There is no specific method for checking the Devices, or for the subsequent reporting, but I am trying to improve our practice, and introduce some sort of convention.
The Devices are roughly the shape and size of a box of six eggs, or 500 grams of margarine. The largest face is horizontal.
The best way I can describe it for now:

Option 1

The first Device only moved/tilted when I applied the force needed to tip over a washing machine.
The second Device moved/tilted when I applied the force needed to tip over a 5ltr/1gal bottle of water.
The third Device moved/tilted when I applied the force needed to tip over a 500g/16oz tub of butter.

The above examples sound silly and totally unsuitable for a professional report.
Option 2

A normal Device only moved/tilted when I applied the force needed to tip over a washing machine.
The second Device moved/tilted when I applied around a tenth of the force needed to tip over a normal one.
The third Device moved/tilted as soon I applied around a hundredth of the force needed to tip over a a normal one.

The above examples avoid silly wording. But they are overly accurate: my hand's estimate of the force applied is nowhere near the accuracy implied by the numbers like a tenth and a hundredth.

My intuition is that a convention must already exist for this, perhaps in the field of health and safety to describe how much resistance/support a barrier is supposed to provide? As you can hopefully see, I only need to provide an indication of the order of magnitude.
A measurement in absolute terms would be great, but a nicely worded description in relative terms will also be enough.
Another area where this problem might be common is the specification of adhesive products (we do indeed use builder's grab adhesive to install our devices). Something like "glue 1 will hold the weight of a person, but glue 2 will only hold the weight of an A4 clip-frame".
In an ideal world we would have categories or an agreed system with three levels of stability, where everybody knows what level 1/2/3 is. I'm afraid I'm probably not important enough to try and establish any such categories though. I am hoping that this problem has been resolved in one industry or another and there is a solution I can adopt.
I am conscious this question can be seen as opinion based. If more people think this is an issue please let me know and I will try to edit my question to make it more appropriate for stack exchange.
Finally, I am not aware of any sort of instrument that performs my "test" and measures the force/effort/torque required. Any suggestions would be most appreciated, even if product recommendation is a controversial subject on the wider stack exchange.


texts:
I have a base with 4 wheels, the rear axle is a motor which drives the base forward or backwards, this contains a diff, so there's no problem there.

The front axle is a steering axle like that in a car, except where the steering column would be extends vertically, and not at a diagonal in a car.

In spare parts, I have an arm which is capable of pushing and pulling (depending on which way the DC current goes), and this is affixed to a plate at the rear of the wheel base, and points at 90 degree angle from the plate, towards the steering column. The arm is affixed 20cm to the left of the steering column. I want to use this arm to turn the steering axle.

If I fit another (fixed, non extending) arm onto the steering axle so it can be pushed and pulled, what could I do to connect the two arms so that the extending arm can turn the steering axle? Would the non extending arm also need to be extendable (like a piston)?

Below is a very poorly drawn diagram that I've rushed a bit. The yellow section is the extending arm, the blue bar is the bit for steering. The black bar that extends from the blue bar is the steering column (with the proposed fixed arm pointing left)

Thanks.


texts: Harvesting thermoelectric energy from computer graphics cards

texts:
During CES2015 a well know Graphic Processor Unit (GPU) manufacturer introduced a new GPU. These GPUs need complex thermal management to keep the processor cool. Most GPU accelerator card manufacturers develop new graphics accelerator cards that use primitive thermal management technology compared to today's advanced technologies. Most of us know this technology as fans that manage this unwanted thermal energy, as seen in this image of a graphics accelerator card:

What barriers do engineers need to overcome to convert this wasteful thermal energy to useful electrical energy?

Below is a temperature profile of a GPU card.

References:

A Thermoelectric Generator That Runs on Exhaust Fumes
Small Thermoelectric Generators
Thermoelectric Technology Overview
Extend Your Video Card's Life With Custom Auto Fan Speed Settings


texts: How to Find Drag Force from Skin Friction

texts:
Just wondering if someone can please can give me some idea, as to how I can solve this question that is not related to current study. I haven't been able to work out where to start with it just yet.

Air flows parallel to the surface of a smooth flat plate 10m long. The boundary layer has zero thickness at the leading edge. The Reynolds number at the trailing edge of the plate is 10^7.
Calculate the total drag force due to skin friction on one side of the plate per unit width?
Assume that for a laminar boundary layer, up to Rex = 5_10^5, the skin friction coefficient is Cf = 1.328 (Rex)^-1/2 and for turbulent boundary layer Cf = 0.074 (Rex)^-1/5. Take the density of air as 1.2 kg/ m^3 and its dynamic viscosity as 1.8_10^-5 kg/ ms.


texts: In a rectangular waveguide, how can one determine if any propagation modes exist?

texts: I'm currently studying microwave engineering, and I came across the query mentioned above. I know that rectangular waveguides use TE(m,n),TE and TM modes, but I do not understand how these modes came into being. Can someone please help me?


texts: How to repeat on ABAQUS FEM simulations without reloading the mesh?

texts:
I would like to perform several FEM simulations on a given mesh with ABAQUS, where only the orientation of an element set would change in between.

Currently, I'm just generating several inp files (see an example below) and I run them one after the other. But this has the inconvenience to reload every time the mesh, which takes time due to its large size.

Would there be a way to load the mesh only once, perform the simulations, save the results in a file, modify the orientation (orientation label going from ORI_1 to ORI_X), reperform the simulation, save in another file and so on?

I thank you in advance,
Regards,
R.B.

*HEADING
TEST
*INCLUDE,INPUT=Mesh.inp
*INCLUDE,INPUT=PARAMETERS_MATRIX.inp
*Solid Section, elset=AllE, material=Matrix, ORIENTATION=Matrix
*INCLUDE,INPUT=PARAMETERS_CRYSTAL.inp
*INCLUDE,INPUT=ORIENTATIONS_LIST.inp
*Solid Section, elset=MID, material=CRYSTAL, ORIENTATION=ORI_123

*Step, NLGEOM=NO, name=Step-1
*Static
1., 1, 1e-05, 1.
*INCLUDE,INPUT=MESH_BC.inp
*Output, field
*element output, POSITION=CENTROIDAL, elset=AllE
S,E,EVOL
*End Step


texts:
I've written a program to generate gears and write them to dxf files. I thought all was well until I looked at the mesh of two gears.

From everything I've read there should be no backlash when the pitch circles touch. So I'm ether reading wrong, or my calculations are skewed. If I drop the pressure angle to like 8, the teeth fit nicely. The image is with the angle set to 14.5 This is the actual code, I derived it from here

//angle of involute to outside circle
//see fetch.pdf, equ (6),(7) then from...

//polar_radius = base_radius * sqrt( 1 + t^2 )
//where t is the arc AB
//the limit of polar_radius is the outer_radius

//   so solve for t at the limit
// t= ( ( outside_diameter / base_diameter )^2 - 1 )^1/2

//for the end point of the involute arc
double Dop= gp.od / gp.bd; //ouside diameter / base diameter
double t= sqrt( Dop * Dop - 1 ); //angle of tangent to involute arc, at limit
double Ac= t - atan( t ); // angle of involute arc, at limit

then I create a line string for the involut curve as:

for( size_t step= 0; step <= ITERS; ++step )
{
    double arc= t / ITERS * step;
    *ls+= bg_point( base_radius * ( cos( arc ) + arc * sin( arc ) ),
                    base_radius * ( sin( arc ) - arc * cos( arc ) ) );
}

And thinking about it, how could you not have backlash when the teeth arc from the base circle, the point where the line starts at half a tooth/space distance. But I'm just not sure.

Also, I'm planing to put all the code on GetHub and will do it sooner than later if needed.

UPDATE:
The fix is in and now it looks like it should. This is with a 20 degree pitch.

I've uploaded to GetHub using the MIT license. If I think this useful, maybe others will also. The user interface needs a lot of work, gear params are still hard coded. Only these two files have any thing to do with gears.

gear_gen.h

gear_gen.cpp

The rest is a CAD drawing interface. Thanks again SprocketsAreNotGears!!


texts: Is it necessary to consider temperature effect on waling?

texts: Many text book literature on braced excavation mention the necessity to consider additional load due to temperature effect on struts. But nothing is mentioned about waling. Why is this so? Wouldn't axial load in waling be significant for waling with large cross sections? Is the consideration any different from struts? How would such effect be considered for waling, if temperature is a necessary consideration?


texts: What engineering advances paved the way for "modern" computers?

texts:
By "modern computers," I mean electronic programmable computers such as those that were developed about the middle of the 20th century.

My understanding is that early computers such as Charles Babbage's "calculating machines" worked mainly on mechanical principles, like a modern "abacus". Apparently later machines were more electronically based. I'm talking about computers that evolved from using vacuum tubes, to transistors to integrated circuits, and ultimately silicon chips.

What engineering advances enabled the above transition to occur from physical means (e.g. vacuum tubes) to electronic means (e.g. transistors) when it did (middle 20th century)?


texts:
I am currently attending a radio technology course. We continuously work on radio sets that are sometimes used as manpacks by the Army. In order to learn how to operate them we work in close proximity to the sets and their antennas.

The antennas are generally whip type or long rods. Such as these :

The radio sets generally output around 25-50W in the 30-90MHz frequency range. Can that possibly cause damage to my iPhone?


texts: Under defined sketch - inner rectangle for chessboard

texts:
I am working on chess board using SolidWorks 2016 and I've created two rectangles, outer one and inner one with 8x8 grid using Linear Sketch Pattern:
Why is my sketch under defined?

ADDENDUM:
It seems I've managed to manage relations of inner rectangle - I've added dimensions between lines and added Perpendicular relation to base two lines in centre of coordinate system - so I think now it is fully defined, however, whole sketch is still under defined:

Why?


texts:
I want to use a mix of polyurethane and acetone to coat some polyester fabric. I have the choice between using a PU glue or a PU foam but because polyurethane isn't a single material with a fixed composition but rather a range of chemicals sharing similar chemistry, I wonder which one would be better.

I want the lightest coating possible it should be water proof as well as UV resistant one.

So here are my questions:

● Should I go with a PU glue or a foam?

● Will the UV resistant property of the foam would still work once it is dissolved in acetone?


texts: Is circular water cooling reliably more efficient than static air cooling?

texts:
I'm looking into developing a system that supplies wasted heat of the transformer of my aquarium LED light (which is always quite) to the aquarium water in order to save resources. The heat which is currently emitted into the room ought to be transported from the transformer into the aquarium water using heat exchange and the water flow in tubes which are already available because of the filtration setup.

It's gonna be a hobby project, but I was planning to design a 3D printable enclosing for the transformer and the transmission of heat into the circulating water for different sized transformers in order to increase reusability.

I know from PC hardware cooling systems that water cooling is generally more efficient than air stream cooling (the LED transformer for this project works without moving air). However, I'd like to check what to consider during design of the heat transmission in order to ensure that the water cooling always is more efficient than the static air cooling so that I and potential other users don't risk damage on their transformers.

The following details reduce reusability, but I guess it's fine to develop the prototype localized at first: In the hottest summer (Berlin, Germany) the aquarium remains below 23 degree whereas I'd like to have it at 25 constantly. Thus, I assume that the water can always take all the heat of the transformer.


texts: What should be the material and thickness of front pillars to stop car (~1,847kg and ~262 km/h) without killing the driver?

texts:
"Tesla Model 3 owner died in a tragic accident with a semi truck. The Model 3 went under the truck’s trailer resulting “in the roof being sheared off as it passed underneath,” which is known as a “side underride” accident."
Is it possible to stop the car?


texts:
I'm interested in the development of electric small airplanes with 4 or 6 seats, that could really happen in the following decades.

One of the main problems related to this project would be the specific energy of the batteries used on these airplanes. Batteries should have a good energy storage to make the range of the aircraft reasonable, and they also need to be light, to make the lift possible.

I saw in this article that the specific energy of the Li-ion batteries could reach 300 Wh/kg until 2030, but it's still a little bit low for a small aircraft. I did some more research, and I found that new different type of batteries are being developed, like lithium-air batteries, that in practice can get a specific energy of 1700 Wh/kg (just read this).  I found also that glass batteries could be a thing too (read this), which could have specific energy several times greater that the recent Li-ion batteries and could work at low temperatures (which is good for high altitude flight).

I've little knowledge about chemistry of batteries, and so I'm requesting someone that has good formation in this area to share an opinion about the possibility of existence of batteries like lithium air or glass batteries at 2030 for example, and which value of specific energy could be a good prevision around that year.


texts: Can the two columns and little triangle thing be removed?

texts: Can the two columns and triangle thing be taken off so I  can add a porch.Is it a major job?


texts: How to make a choice between rolling element bearing and journal (plain) bearing?

texts:
I wonder if there exist a formal guideline to help engineers choosing the right type of bearing.

Except in some few cases, this is not very evident to me.
As far as i know, the plain bearing systems are really simple, so why bothering to design the rolling element bearings? I guess there is a reason, but i don't see it.

I've done some research on the web, besides the economic factors and some other vague statements i couldn't find anything useful.


texts: Why boiling occurs when vapour pressure equals the local atmospheric pressure

texts: When we increase the temperature of water in an open container, the vapour pressure increases.But boiling (phase transition at constant temperature and pressure) occurs only when the vapour pressure equals atmospheric pressure.My understanding is, till that point the atmosphere can hold the water vapour like a cover or lid but when equilibrium partial pressure of water vapour(vapour pressure) tries to increase beyond atmospheric pressure, the atmosphere cant hold the vapour and boiling starts.Is this right?


texts: What standards exist regarding diagnostic systems in automotive engineering?

texts:
I'm designing a diagnostic system that simulates an environment and user input for a dummy vehicle. All possible critical situations are simulated in order to find out whether any errors are triggered, or if the software contains any faults or bugs.

It's a vehicle for state defense, it doesn't have OBD like normal cars, but a display with buttons with which you can seek and troubleshoot errors. I have to design a procedure for testing each new software release. I was wondering if any standard exists for testing/validating software. Just like driving cycles(NEDC, WLTP) exist for emission tests.

Do any standards(SAE, DIN, etc.) exist for this kind of thing?


texts: Calculating the force and/or torque required to pivot an arm from one end

texts:
I'm trying to design a two-stage "arm" which articulates from an attached base. The arm uses a pulley and cable at the "elbow" and a hydraulic cylinder mounted on the lower stage to lift the upper stage (similar to a boom truck).

For a given arm length $L$, pulley diameter $D$, and maximum weight $W$ at the end of the arm (obviously the arm itself has some weight too), how can I determine the maximum required hydraulic cylinder pull force ($F$) required to lift the arm from a horizontal orientation?

If there's a formula where I can plug in the values, I can experiment with different arm lengths, pulley circumferences, and weights to hopefully find a sweet spot in relation to available hydraulic cylinders and pulley sizes.

Here's a rough drawing. Thanks for any pointers, links, etc.

UPDATE:

So I found this document which clearly expresses the formulas used to calculate forces required to lift a weight on an arm.

From this document, I understand that $F = ma$, and $T = Fd$.

So am I doing this right?

Let's assume 225 kg weight to be lifted, and an arm length of 6 m, and a 30 cm pulley diameter.

$$\begin{alignat}{2}
F &= 225 \times 9.81 &&= 2207.25\text{ N} \\
T &= 2207.25 \times 6 &&= 13243.5\text{ Nm}
\end{alignat}$$

So pulley radius actually becomes the length of a lever, right?  So the same torque would need to be generated by applying a linear force to a 15cm lever?

$T = 13243.5\text{ Nm}$ and $d = 0.15\text{ m}$, so $N = 88290 N$

So in this example I would need a cylinder that would be able to generate 88,290 N pull force (or roughly 20,000 lb pull), and a cable that could also withstand more than 20,000 lb strain?


texts: Wind resistance inside turbulent flow ("prop wash")

texts:
I have an object that is launched from the side of a plane (it is a flare).

The question is: what does the flare do while it is proximate to the plane?  Will it hit the tail?

After accounting for the motion of the aircraft, I have the motion of the flare decently understood and plotted, according to wind resistance without accounting for the propeller wash.

Then it occurs that the flare will be in the prop wash of the aircraft while it is in motion near the plane.

Understanding that the prop wash will be turbulent, and assuming that I find a way to estimate the wind speed of the prop wash, what will be the effect on the force of wind resistance due to the prop wash?

I.e., how will the turbulence of the prop wash mitigate the increased wind resistance due to the airspeed of the prop wash?

To expand on this, and the flexibility of the answer, the parameters are:

The velocity of the prop wash is an estimate of the upper bound of the average velocity of the prop wash
The purpose of this is to verify that an object coming out of the side of the plane will not hit the tail
It is necessary simply that I establish an upper bound on what the wind resistance conditions are going to be, as I already have a code written for the position estimate, relative to the aircraft geometry, speed, altitude, etc.

My current solution is as follows (not ready to post as an answer):

Get an upper bound on power output of the engine (~1900 kilowatts for the turboprop in question here)
Multiply the watts by the reciprocal of the forward velocity of the aircraft and reciprocal of area affected by the propeller to get a force per sq meter
Solve for $v_w$ in the equation $F = \rho A_{prop} v_o (v_w - v_o)$, which is a correction to the estimate in response 3 of the linked forum thread.


texts: What does the steel grade "11SMn30" mean?

texts:
I am starting to use steel in some of my designs, and while trying to learn more about this material and its properties I have realized that there is so much more to it than I thought.

How does the grading system used for steel work? For instance, what does "Grade 11SMn30" mean, and how does this affect the properties of the material?

Answers/comments indicate there are multiple standards, which I did not know, but I've found out that this is an EN grading.


texts: Ceiling mounted punching bag without compromising structure or floor above

texts:
This question is regarding the safest way of installing a heavy punching bag of 100 lbs from the basement ceiling. Above the basement ceiling is a wood floor. The goal is to sleep soundly at night knowing that we don't have to worry about damaging the ceiling/floor structure.

QUESTION 1:

Is one of these methods, or another method, the best and safest for hanging and using a 100 lbs punching bag and not having to worry about it damaging the floor structure or the floor above over time?:

(a)

Adding 3 or 4 beams parallel between the existing basement ceiling joists
Adding a perpendicular beam that will screw into those parallel beams (so that the weight is distributed amongst those beams)
Attaching the ceiling mount (Note 1) to that perpendicular beam

(b)

Adding a beam parallel between the basement ceiling joists
Attaching the ceiling mount (Note 1) to that one parallel beam

(c)

?

Note: The ceiling mount is designed to absorb the shock produced by hitting the bag. The bag hangs from the ceiling mount, which is screwed into the ceiling beam.

QUESTION 2

What is the best way to secure/install the parallel beams?

QUESTION 3

My assumption is that hanging anything from the existing joists, or even making holes in the existing joists, is best avoided so as not to weaken them or tamper with the existing floor structure. Is this a valid assumption?


texts: Is it possible to build a DIY RLC circuit for a classroom demonstration?

texts: I was describing the mathematics of RLC circuits to my students, and was wondering if it's possible to build an actual RLC circuit with coils of wire and an inductor and a variable capacitor. The closest thing I could find is this ferrite core circuit. But instructions are sparse, and it's not clear if I can use an amplifier and listen to it on my headphones.


texts: Mechanical device to simulate hinge axis external/off of part

texts:
Take a horizontal bar 10' pinned on the right end, so that there is a hinge point on the right end. Space requirements dictate that the bar must be cut in down to 5' (cut in middle and keep the left side, discard the right side) and yet it still must pivot as it did before. To accomplish this a mechanism must be constructed underneath/around the shorter bar, but must not extend out to where the original hinge point was, as that would defeat the purpose.

This mechanism is relatively straight forward to construct out of curved track that the bar rides along, where the curved track has a radius equal to the distance from the bar to the original hinge point. However I want to know if it's possible to construct a mechanism only out of linkages and straight track.

I have created such a device in solidworks using only linkages and straight track that gets very close to simulating the external hinge point, but is not perfect. There is only a very small range of motion where the simulated hinge point is relatively stationary; for the rest of the motion the hinge point is not stationary at all. This leads me to believe this is not possible to construct; for the mechanism to perfectly simulate the external hinge point for a small range of motion, it must also perfectly simulate it for all range of motion. This is similar to how no two different functions, when graphed, truly overlap. If the functions perfectly overlap at all, then you know that they must be the same function. (This is not true for negative power function, which partially overlap with their positive power function counterparts. However, these functions are discontinuous, whereas the motion of linkages and track is continuous...)


texts:
I have to calculate the slope/tilt from a 6 axis (3D Accelero, 3D Gyro) IMU. Are there open source libraries that help one do this or should I build it on my own? How do I get started?

Is there an open source library to calculate slope, tilt, collision, shock, turning intensity of a vehicle using an IMU? There are great FWs for flight control from which I can derive many things, but couldn't find one for automotives.


texts: RF Engineering - Cascading a 3 Port S-Parameter Network into a 4-Port S-Parameter network

texts:
I have been trying to cascade a 3-port scattering parameter network into a 4-port scattering parameter network that will ultimately be terminated by another 3-port network (as can be seen below).

The ports are not all terminated to a common impedance (for reasons pertinent to the work being done). For the sake of the mathematics, the SnP matrices are fully populated with non-zero values (i.e. there are loops caused by the cascade).
I have been able to find a lot of material online about how to cascade 2-port networks together but nothing on cascading non-2-port s-parameter networks.
Could someone possibly explain the general mathematical process for cascading these s-parameter networks into one another as described in the diagram?


texts:
I have to write a matlab code using finite element method to solve this problem. I have solved it as follows but I dont know how to apply it in matlab.

I have to write a matlab code using finite element method to solve this problem. I have solved it as follows but I dont know how to apply it in matlab.


texts: How much is too much control valve cycling?

texts:
In a textbook on process controls, I read that when tuning a controller there must be a balance between performance and excessive control element cycling. My question is, what corresponds excessive cycling?

To narrow down the question, assume we have a control valve with linear characteristics. What is the minimum time the controller should take to move the valve 5% of the controller output? For a typical set point change, how many cycles (up and down) of the valve are too much prior to reaching the final valve position?

I suspect there is a process specific part of the answer (minimize disturbance, smooth operation criteria), but what I am after is: what is too much cycling to avoid damaging the valve itself or to prolong the valves lifetime?


texts: Wouldn't it be most effective to insulate a house with just an air space?

texts:
It is my understanding that of all three states of matter, gases have the lowest thermal conductivity.

If this is the case, why are solid materials, such as fiberglass and polyurethane, used for this purpose?

Would it not make the most sense to simply fill the space with air?


texts: Go-to resource for open hardware engineering resources?

texts:
If you would search for open source software projects, you'd probably run into GitHub and BitBucket.

Is there a similar site/community around open hardware to share and version CAD files, curcuits, etc. (not modeling software but an open hardware product oriented)?


texts: Is it possible to reduce the divergence of a red laser pointer beam from 40 degrees to 1 degree?

texts:
I would like to find out if it is possible to reduce the divergence of a red laser pointer beam from 40  degrees to 1 degree.

@Ruslan wrote on October 3 2013 that because the active zone of a red diode laser has diameter of order of several micrometers the divergence of a red laser pointer beam is currently 40 degrees.

Due to Heisenberg's uncertainty principle $\Delta\times\Delta p \gtrsim \hslash/2$, one can't really make a quantum have zero momentum in any direction. So you can't say that photons go in the same direction - this is just a simplified description of laser operation. In reality, the thinner the beam, the higher the divergence.

Compare e.g. a DPSS laser (e.g. green laser pointer) with a diode laser (e.g. a red laser pointer).

In a DPSS laser the active material will have diameter of order of hundreds of micrometer, and the exiting beam will start from even smaller diameter for various reasons. The divergence is quite small: if you remove the collimating lens, your light image from a green laser pointer will be several centimeters after the light goes several meters. Divergence angle would be $\lambda/d = 532\ \mathrm{nm}/100\ \mu\textrm{m} \approx 0.3°$.

If you try doing the same with a red laser pointer, you'll see that its light diverges quite a lot: after going several centimeters in direction of propagation, it'll already give image of several centimeters. The reason for this is that active zone of diode laser has diameter of order of several micrometers. This makes output beam quite thin, making Δx small and thus Δp high, and this is what leads to high divergence. Divergence angle would be $\lambda/d = 640\ \mathrm{nm}/1\ \mu\textrm{m} \approx 40°$. Actual angle would depend on which transverse direction you select, because active zone is ∼10× longer in one direction than in another.

In general, the thicker your starting laser beam, the more collimated it is, so if you manage to make a (visible wavelength) laser with beam starting at 1cm thickness, you'll have almost perfectly collimated laser beam.

I would like to know if there is a method to enlarge the active zone of a red diode laser from a diameter of several micrometers to 30 micrometers. Also, could a lens with short focal length be used to reduce the divergence of a red laser pointer beam from 40 degrees to 1 degree?


texts: Because adiabatic processes would lead to a high temperature rise due to the high reduction in pressure (from 1 atm to roughly 0 atm).


texts: Is a wing that runs the length of an aircraft viable?

texts:
I was thinking about fighter aircraft like the Harrier which have thrust vectoring and computer-controlled stabilisation nozzles. Also an anhedral angle on the (small) wings. The aircraft relies so much on the computer stabilisation, and flies like a brick if the engine fails, so why have those wings at all? Couldn't you get as much lift from wings of the same area that run parallel to the fuselage, that is much shorter (left-to-right) but deeper (front-to-back) wings? And wouldn't this create much less drag reducing the thrust requirements?

Having thought about this I realised that for fighters it's probably not a good idea as they would lose a lot of pitch-maneuverability, but for passenger jets, would a roll-stabilised approach with a short wing that runs the full length get the same lift while reducing drag? Is such a wing viable?


texts: Two storey brick building without using wood or steel

texts:
Is it possible to build a two storey building just using bricks (no wooden beams, steel beams or steel reinforcement) to suspend the floor of the second storey?

I'm aware that using wooden beams is an option, however because of the environment of the build (tropical rains, humidity, termites, ants, beetles and millions of other insects), I would much prefer to use only brick - if this is possible.

Ideally there will be no intermediate supports; the floor structure will span from one external wall to the other.

I have an intuitive feeling that an efficient structure can be built using just bricks - but I can't quite articulate it.

Has this been done before - is this even possible?


texts: "Intermediate profile #2 could not be solved. Consider editing the relations and dimensions of the original sketch."

texts:
this should work.. surely..  I even tested it in another file with another solid body present but not connected..

moved the operation to the very beginning of the design tree, suppressed everything else, same problem.  it must be something about the file..


texts: I have a planar object whose center of mass is not at the geometric centroid, and I want to roughly estimate the magnitude of four hypothetical point masses that at the four corners that would result in the center of mass. In summary, I want to backsolve the center of mass equation with reasonable assumptions. I currently have 2 equations for the center of mass in the x and y direction, but I need two more equations to be able to solve for all four.


texts: How to connect to heating networks both with sources and consumers into one network?

texts:
We need to connect two distinct heating networks on a wastewater treatment plant into one. So far I've only seen heating networks with one central heat source or one central manifold that all heat sources feed into, but this time we have distributed sources.

Here's the state the system is now in:
network 1:
Natural gas boiler, several smallish consumers (two adjactant buildings)
network 2:
oil boiler, sewage gas CHP, several smallish and one big consumer (sveral buildings, spread aout about 100m apart)

Target state:
both networks (about 100m apart) are connected,
Manifold 1:
one additional gas CHP, one additional largish consumer
Manifold 2:
no change

Manifold 1 should supply power to manifold 2 when needed, never the other way round.

My idea is to have connect both hot and cold sides and have pumps (hot side manifold 1 -> hot side manifold 2, cold side manifold 2 -> cold side manifold 1). The "hot" pump will be controlled for delta T between both manifolds, the cold pump should ensure hydraulic balance but I dont know a good control scheme for this.


texts: Why is there limited use of Y (Wye) fittings in a refrigeration system?

texts:
I'm a Mechanical Engineering intern currently working in HVAC and Refrigeration for grocery stores.
I'm looking into ways, with lower energy losses, to encourage equal flow distribution at liquid pipe junctions. I'm wondering if anyone can give me insight as to why there is limited cases of using copper wyes or "Y" junction fittings in refrigeration systems, and why there is only "T" junctions.
I've read somewhere that it has to do with the "Y" design not performing well in high pressure scenarios but I haven't been able to find any other information on the subject.
FYI I'm based in Sydney, Australia. If things are different overseas I'd love to hear your input too!
Thank you all in advance.


texts: How to solve power surge caused by curing oven PWM cycle?

texts:
I have a Despatch LBB 1-69 lab oven in my shop. It is a single-phase, 110-volt, 30-amp unit. It is wired to a 220 volt, 2-phase, 40-amp panel (on a single 110 volt phase), which is fed by the 100-amp main service. All wiring is appropriate or larger for the task at hand.

During operation, the element is switched on until the unit approaches the set point, then switches to a 1 or 2 Hz (approximate, not measured) pulse and maintains this mode until the heater is switched off or the set point is changed. The "on" period is substantially shorter than the "off", perhaps 10% or less of the period duration. It makes for a very stable temperature but I'm experiencing a nasty side effect.

Once the sun has gone down, there's a noticeable flicker in the garage's florescent lights, that coincides perfectly with the oven's operation, pulsing away. More problematically, every light on the same phase throughout the entire place displays the same behaviour. This is unacceptable, especially heading into the darker winter period.

If this were a fluid circuit, I'd add an accumulator to reduce some or all of the pressure fluctuations but clearly it's not. Would an appropriately sized capacitor (or bank) be a solution? Could they act as a sufficient reservoir to smooth out the fluctuations?

I'm not sure if this plays in to anything, but the voltage in the facility is quite high - on the order of 123 to 126 VAC at any given time.


texts: Closed loop guidance and control: how to tune a system with multiple feedback controllers?

texts:
I'm trying to design a closed-loop guidance system for rockets - something that can be implemented in Kerbal Space Program, for example. To do this, I'm following the design process described in Ashish Tewari's Advanced Control of Aircraft, Spacecraft and Rockets. His approach breaks the system up into a guidance controller for trajectory tracking and 3 attitude controllers for pitch/roll/yaw control:

The controllers are designed with a state space approach. The attitude controllers send gimbal angle commands  to the engine to maintain attitude control (zero angle-of-attack), while the guidance controller also has a feedthrough term  to make trajectory corrections in order to follow a preset nominal trajectory .

He then demonstrates how to tune each of the controllers individually using LQR, but leaves integrating them as an exercise to the reader.

As a first step, I tried implementing the guidance and pitch controllers individually in Simulink, then combining them as prescribed. However, while the individual performance is very good (as expected), their combined performance is abysmal (see below image). The pitch and guidance controllers' commanded gimbal angles start 'fighting' each other immediately, saturating the gimbal actuator and resulting in zero control over either the trajectory or angle of attack.

With all that said, my questions are:

Is there a fundamental error with this controller architecture, or is the poor performance I'm getting resolvable with a better controller tuning?** My theory is that the main issue here is that both the guidance and pitch controllers directly feed commands to the gimbal actuator; in other examples of hierarchical control systems, the outer 'guidance loop' only seems to set the setpoint for the inner 'actuator loop' to follow.
Could this also be a consequence of tuning the controllers individually, then combining them, as opposed to the other way round?** In a controls problem where the linearized system comprises multiple sets of weakly coupled dynamics, can the controllers really be tuned individually with LQR, or do we still need to consider the full system when performing LQR?


texts: Is there a reason why both plasticizer and vulcanizing agent are needed during processing of rubber?

texts:
According to this Wikipedia page, vulcanization is an important process to make rubber harder and more durable. However, another Wikipedia page says that plasticizers play a significant role in rubber manufacturing, acting as a softener.

Is there a reason why both are needed when processing rubber? It seems to me that they exhibit an exact opposite effect on the rubber being processed and hence only one is needed.


texts: How important is an ABET-accredited Engineering Degree in the EU (like Germany) or other countries that is not in North America?

texts: I have an option to either attend Middle East Technical University - North Cyprus Campus (non-ABET accredited) or Mapua University (ABET accredited) in the Philippines to study Chemical Engineering as an undergraduate. I would personally prefer to study in (METU NCC) than in Mapua, but have been reticent due to the Chemical Engineering program there not being ABET accredited. I have a feeling, however, that ABET accreditation mainly pertains to engineers in the United States. How important is the ABET accreditation if one wants to pursue a job in the EU or other countries NOT in North America after their bachelors in engineering? How will this affect my job prospects? If you have any experience in this, please don't hesitate to share them. There seems to be a lack or contradictory information in the internet regarding this matter. Thank you so much!


texts: Spreading vacuum load using stacked perforated sheets

texts:
I am thinking of playing around with food in partial vacuum conditions (ie water boiling at room temperature). But, as it is more a curiosity, I'd rather not spend too much money right now. That inspired me to be a little creative with stuff I already have.

I have a pressure canner (heavy duty aluminum), an AC vacuum and sheets of 3/16" acrylic. The acrylic would be nice to use as I can keep an eye on what is happening.

I don't think the acrylic is thick enough to withstand the pressure, so I was thinking of ways to combine them somehow.

Here is a proposed solution. For the first sheet on the low pressure side, drill some holes in the sheet to reduce the pressure, but make the holes small enough that it is not able to come to an equilibrium while the pump is in operation. Then another sheet is placed on top of it with a gasket to keep them separate. This next sheet would have smaller/fewer holes in order to .. In theory, this could continue indefinitely, then an unperforated sheet at the top.

Here is an illustration (note, I missed gaskets around the vacuum outlet):

a=pressure canner
b=sheets of acrylic
c=gaskets
d=vacuum outlet
e=larger holes
f=smaller holes

I am not particularly sure I want to do this, but I am curious if the general concept is sound.

One possibility is that it could work, but the holes would be smaller than I could reasonably do in my home shop. Acrylic isn't great for drilling.


texts: Equation for comparing force delivered to road at wheel based on varying gear ratios?

texts:
By introducing many new gears and changing the tire size I am altering the torque delivered to a rear bicycle wheel from an electric motor. This then changes the "power where rubber meets pavement". "Forward thrust?" I don't know what the proper name is!

I have googled around, but find myself just plain confused and unable to sort through how to evaluate this by using the information I have - which consists of the ratios and wheel sizes. This web page seems to explain it all, but for the life of me I can't follow it.

Yeah, I guess I'm a dummy.

I do not have an actual measure of the motor's starting torque, yet. Have yet to figure out how to affix my torque wrench to the motor without hurting the motor or myself. Motor torque will be a variable named in the equation, so a value won't be needed at this point.

I need to determine how much MORE torque I am applying to the wheel with the new gear setup versus the original gear setup. This is so I can decide if I have increased the delivered torque enough to accomplish the goal of moving ~180lbs with relative ease compared to the original gearing. The original gearing and wheel size was insufficient for the task and by looking at the percentage or ratio of the increase I should be able to ballpark whether I have the design right to move the weight.

The current ratios were set up so that the max speed of the wheel in high gear at the motor's preferred speed of 2700RPM will be at the legal limit of 22KPH/15MPH. I thought that that should put my starting power in the lowest gear somewhere good enough to get the bike and the weight rolling along - but I cannot figure out how to verify that.

Original Gearing/Wheel setup:

Motor > 5.81 reduction direct mount on a 11.5" diameter wheel (that's
actual rolling diameter, it is nominally a 12") .
New Gearing/Wheel Setup:

Motor > 5.81 reduction > 3-Speed transmission reductions >
final-drive 1.5 reduction fixed to 20.5" diameter wheel (that's
approximate rolling diameter - it is nominally a 21").

3-Speed gearing ratios are 1.33, 1, and .75 - these are not
changeable.

New gearing combined ratios:

1st gear - 11.05,

2nd gear - 6.68,

3rd gear - 8.86

all fixed to the same 20" wheel.

If I should be calling torque 'power' when I talk about it at the wheel instead of the motor, please let me know what the distinction is and if I need to make them distinct in the equation.

Again:

I am looking for an equation to use that allows me to vary the 5.81 reduction and the 1.5 final reduction and see the changes in torque/power at the wheel.

At its core the question is:

How much more starting grunt do I get with XXX ratio and Xwheel than I did with AAA ratio and Awheel?


texts: Are storm drains put after road has been finished and asphalted?

texts:
Local government has been doing main capital city road reconstruction for a year now (had to be done in 3 month originally, but it is out of budget and out of time as usual).

They have finally opened it few month ago.
But now they are closing it down again, reason is to put down storm drains or drainage wells. As you can see from the photos, there is some major work being done.

We (vocal citizens) feel this stinks and either it was a trick to make money, or a stupid mistake. Non of these is great.

Government is claiming that this is how it is done. First you make a road, then you break it to put down drainage.

I googled around for road making timelapses, looked at various articles, but non had detailed this procedure. I would like to know if there is truth to this.

I wonder if there is a civil engineer out here, who has experience in these things and can shed light on the matter.

This youtube video clearly shows manhole is being put during asphaltation phase: https://www.youtube.com/watch?v=yJFFY-8TV_E


texts:
I'm writing a fusion360 adding to model windmill blades. My first goal is to model the NREL Phase IV in which the airfoils (S809) definitions come with thickness and also span station (wich I¿dont know what is):

Right now, I'm able to calculate the max thickness. as shown in the next picture as the difference between the max point on the upper surface(y-direction), and the min point(y-direction) of the lower surface. I'm not really sure if this is correct, and then I don´t know how to modify the entire airfoil with the new thickness definition in the table above.


texts: What is the name of this mechanism for raising and lowering the impression cylinder of a printing press?

texts:
It is like a cam that has an off-center hole, and it rotates in its fixture with a knob to lock it in place. The purpose is that you can loosen the knob and rotate the piece to slightly raise and lower the shaft that is connected on the other end.

Does this have a name? Is it a commonly-available part or is it something that has to be custom machined?

This is for a printing press, used to adjust the vertical position of the impression cylinder a couple thousandths of an inch.


texts: Determine volume of liquid in a fluid bladder

texts:
I am trying to determine if it is possible to "physically" determine the volume of liquid (such as water) in a non-solid container like a fluid bladder like this or this?

Assume that it is not possible to keep accurate track of the difference between how much fluid is placed in the bladder and how much is taken out, and that a "physical" measurement must be made (where "physical" can include using a sensor, or using some sort of actual measurement of the dimensions of the bag to compute the volume).


texts:
So I've got a problem here in fluids. It's driving me insane but I know I'm missing something simple.
Up until now we've worked with Newtonian fluids resulting in the "normal" NS equations in Cartesian coordinates (ie 1). those apply only to non-compressible, Newtonian fluids. We were specifically given the general tensor version of the equations( i.e. ), and some data about the shear stress vs the shear rate, and told it was a power law fluid in this question (so non-Newtonian).
I understand from the derivations for how we get from the "general" NS equation (the screenshot) to the "normal" equation I showed first above, but I cannot figure out how to apply the general form to this power law fluid (which behaves as a pseudoplastic given we have a n < 1). I've searched literature and our textbooks and no one goes through the derivation. Any help?


texts: How can I find deflection in a member that doesn't have a constant area moment of inertia?

texts:
I'm trying to calculate the maximum deflection in a simply supported member with a uniformly distributed load. The trouble is this member does not have a constant area moment of inertia. I've drawn a simplified version of the specific problem I'm trying to solve:

I'd like to treat this problem like this case except I don't know how to account for the changing I.

So clearly the maximum deflection will occur at the center, but what methods can I use to account for the changing value of I?
I see that the problem could be broken up into chunks. The back plate and the first two inches of the rib are constant along the length, and then the part that changes could be broken up into three sections. First section would be the increasing slope of the rib, second section is the long constant portion of the rib, and the third section is the decreasing slope of the rib. I've found examples online about how to deal with connected beams of different I values, but the issue here is I changes as you go along the length for sections one and three.
I've found a guide here that gives the formula v"=M(x)/(EI(x)) and then you integrate and solve for boundary conditions, but my I value is more complicated than the first two examples on that site.
I've also tried to look into Castigliano's Theorem but I'm already a bit confused without even getting into the fact that M and I are both dependent on x.
The actual geometry of the part I'm working with is slightly more complicated than the example I've given, but I think I'd be able to adapt the solution for this problem to my actual problem. I'd like to solve this problem using Excel or MATLAB/Octave because there are other sizes I need to solve for. Ultimately, I need to use this solution process to optimize for an ideal rib length which is why I plan to use Excel or MATLAB/Octave. I have access to ANSYS Mechanical, but my intuition tells me once I figure out how to solve this, future calculations would be done much quicker in Excel or MATLAB/Octave instead of ANSYS.
Any tips or ideas of how to approach this would be very appreciated. Thank you.


texts: Understanding input shaft torque for a motor without a shaft

texts: I'm looking through this catalog at the motorized rotary tables and it says on page 114 that the maximum input shaft torque is 150 oz-in.The rotary table doesn't have a shaft so I'm confused as to how I should interpret this. Does it just mean that the maximum torque exerted by the motor is 150 oz-in or is there something else I need to be considering?


texts:
This is the question please:
1 kg of steam is at 100 bar and 375 °C expands reversible in a perfectly thermally insulated cylinder behind a piston until the pressure is 38 bar and then steam is dry saturated. Calculate the work done?
So, I got the answer for this question as -169.7 kJ/kg but this is what I don’t get please:
If it’s 375 °C it’s super heated? So it is in front of the saturated vapour line. It says it expands to become dry saturated but shouldn’t it compress to become dry saturated?


texts: What is the sequence of exams to become a Professional Engineer in California?

texts: I'm in school for electronics engineering.  Would someone lay out the high level steps in becoming a professional engineer (PE) in the state of California?


texts: Difference between a spring's k-value and rate constant?

texts:
As everyone learns in physics class, Hooke's law states that a spring's force is proportional to the distance it is stretched/compressed.  The constant of proportionality is usually referred to as $k$.

I am currently working on a project for which I need a spring and I found online that I should probably use a "K25" spring for my application.  I assumed that this K is the same $k$ that is commonly used to represent the spring constant.

However, when I actually started shopping for said spring I have found that it seems to be different.  Springs are listed with both a "rate constant" and a K-something value.  See this catalog list* from McMaster (the K-value is at the end of the part number, i.e. 9637K25).

The two numbers don't seem to be related.  For instance there are two K25 springs, one has a rate constant of 28.53 and the other has a rate constant of 83.

So what's the difference between these two numbers, what do they represent physically, and what is their relation to the spring constant $k$ from Hooke's Law?

*For some reason McMaster's website doesn't allow me to link to a subsection of springs, I am looking in the "Cut-to-Length Compression Springs" category.


texts:
The motor in a washing machine oscillates at set frequencies as compared to a motor that spins very fast in a fixed direction in a blender/mixer.

What I don’t understand however is : Don’t they both have the same job to perform -To mix a liquid (usually water) with solid stuff ?

The more friction the motors can create between the solid materials( food or clothes ), the more rubbing action there would be, hence a faster operation.

So, why don’t the motors of a mixer spin like that of a washing machine ? Or are there those types of mixers as well ? If so, which one does the job faster ?


texts:
I would like to control the locking of a gear, using a solenoid.  My original idea was to simply activate the solenoid to pull back the lock (a tooth that sticks into the gear), but that means that I'd need to keep applying current to the solenoid as long as I want the gear unlocked.

Now, I'm thinking it would be better to have a mechanism between the solenoid and the gear, so that a pulse to the solenoid would unlock the gear, and another pulse would lock it.  Kind of like the mechanism in a click type pen.  What would be a good choice of mechanism to accomplish this, considering how solenoids have a very short stroke distance?


texts: Most efficient way for finding the rotation angles after moment distribution (Cross method)?

texts:
First of all, I have taken a look at the Grinter's method, which is similar to Cross, but balancing angles instead of moments. My question assumes that we are using the Cross method, and not the Grinter's method.

The literature explaining the moment distribution (i.e: Cross) method for statically indeterminate structures tends to affirm that the designer needs the moments rather than the rotation angles, and therefore all books and references I checked don't pay any attention at all at getting the rotation angles. I think that's a false affirmation, because the designer needs to check both ULS and SLS requirements (with SLS being quite often more limiting than ULS), and you need to know the rotation angles in order to find the maximum deflection and be able to check it.

It's a bit surprising, because the "we just need the moments" affirmation seems to suggest that engineers didn't check the maximum deflection in structures designed with the Cross method, which allegedly was broadly used from the 1930s to the 1960s. I find it hard to believe that they didn't check the maximum deflection in their structures.

I'm wondering what would be the most efficient way of finding the joints rotation angles after you apply the Cross method. Do you really need to apply the Grinter's method instead of Cross? Is it not possible to get the rotations starting from just the Cross solution?

The only solution that came to my mind is to integrate the moments diagram twice, but the conditions for solving the integration constants would depend on the structure topology, and I wouldn't call it "efficient"...


texts: How can I set up a reverse osmosis water system to use a pressure tank?

texts:
Most home reverse osmosis water systems use a low pressure bladder type tank that has 5-10 PSI. That way the back pressure on the RO system is not too high.

I want to use a glass-lined tank of the type used for people with well water and have it pressurized to a faucet-type pressure of around 30 PSI. The only way I can figure out how to do this is to have two tanks, one unpressurized and the other pressurized. So, the RO system would drip water into the unpressurized tank. Then a pump would draw water out of the unpressurized tank and force it into the pressure tank.

Is this the only way to do this, or is there a simpler solution?


texts:
The input signal is limited and lies in range $[-U;+U]$. $U$ - unknown.
The output signal must be rescaled to be in the range $[-1;+1]$, i.e. is $+1$ if the input is at steady-state $+U$, and $-1$ if the input at steady-state $-U$.
Between $-1$ and $+1$ the output signal must also occupy some rescaled value.

What can be used as a block $ ??? $ for such a conversion? Is there a linear / non-linear filter that does this, and such and which is described by the differential equation?
Remarks:
Red line, just my fantasy about how the input signal changes


texts: Determine two values of σ22 for which the maximum shear stress is 80 MPa

texts:
Determine two values of $\sigma_{22}$ for which the maximum shear stress is 80 MPa
i know that
\begin{equation}
\sigma_{ij} = [\sigma]^\top =
\begin{bmatrix}
\sigma_{11} & \tau_{21} & \tau_{31} \\
\tau_{12} & \sigma_{22} & \tau_{32} \\
\tau_{13} & \tau_{23} & \sigma_{33}
\end{bmatrix} =
\begin{bmatrix}
90 & 0 & 60 \\
0 & \sigma_{yy} & 0 \\
60 & 0 & 0
\end{bmatrix}
\end{equation}
and i also know that $\tau_{max}=(\sigma_{I}-\sigma_{III})/2$ <=> $80 = (\sigma_{I}-\sigma_{III})/2$
but in the solutions appears that
Case 1
\begin{equation}
\begin{aligned}
\sigma_\mathrm{I} &= 120~\mbox{MPa} \\
\sigma_\mathrm{II} &= -30~\mbox{MPa} \\
\sigma_\mathrm{III} &=~? \\
\end{aligned}
\end{equation}
\begin{equation}
\begin{aligned}
\tau_\mathrm{max} &= \frac{1}{2}(\sigma_\mathrm{I}-\sigma_\mathrm{III})
= 80~\mbox{MPa} \Leftrightarrow \sigma_\mathrm{III} = \sigma_\mathrm{I} - 2\tau_\mathrm{max}
= -40~\mbox{MPa} \\
\end{aligned}
\end{equation}
Case 2
\begin{equation}
\begin{aligned}
\sigma_\mathrm{I} &= ?~\mbox{MPa} \\
\sigma_\mathrm{II} &= 120~\mbox{MPa} \\
\sigma_\mathrm{III} &= -30~\mbox{MPa} \\
\end{aligned}
\end{equation}
\begin{equation}
\begin{aligned}
\tau_\mathrm{max} &= \frac{1}{2}(\sigma_\mathrm{I}-\sigma_\mathrm{III})
= 80~\mbox{MPa} \Leftrightarrow \sigma_\mathrm{I} = \sigma_\mathrm{III} + 2\tau_\mathrm{max}
= 130~\mbox{MPa} \\
\end{aligned}
\end{equation}
\begin{equation}
\therefore \sigma_{yy} = 130~\mbox{MPa} \vee \sigma_{yy} = -40~\mbox{MPa}
\end{equation}
Is the solution right? If its right could someone explain me why is this true?
\begin{equation}
\begin{aligned}
\sigma_\mathrm{I} &= 120~\mbox{MPa} \\
\sigma_\mathrm{II} &= -30~\mbox{MPa} \\
\end{aligned}
\end{equation}


texts: What is the best thin/light material to kill/absorb sound? Sorbothane?

texts:
I am currently building a box filled with electronics and I now look to isolate the sound a bit with the lightest and best material out there.

What I am looking for is a thin, lightweight and very soundproof material. I came across a material called Sortbothane and it seems like a very good fit.

Sorbothane Acoustic & Vibration Damping Film 40 Duro

0.04" of Sorbothane Will Absorb up to 4 dB

That number is pretty impressive I must say and the material seems to be reasonable light and thin as well.

So to my question, do you think Sortobothane is the way to go or is there any other materials out there with the same/better soundabsorbing?

I am also thinking to combine a few materials to make it very solid. For instance I am planning to use a small layer of silicone as well.


texts: Questions about a controlled demolition video

texts:
I came across the following Youtube video which shows the controlled demolition of a chimney.
https://www.youtube.com/watch?v=Sb62_QesDTw
The construction of the chimney appears to be reinforced concrete, with the reinforcing bars in both the axial and circumferential directions.
From the video, around the 0:24s mark, you can see some explosions at the base of the chimney, to the right of the chimney, which then collapses to the right. Can someone please explain how the location of the charges determines the direction of the fall?
How does the type/construction of the building, the explosives used (detcord, cutting charges etc.), charge placement (placed in drilled holes, superficial to structure, etc.), prevailing wind (yikes!), pre-existing damage to the building, affect the outcome?


texts: Why do race cars — such as Formula 1 cars — use two brake master cylinders?

texts:
In Derek Seward's Race Car Design and in some of the videos on race car braking systems, such as this one, it is mentioned the use of two master cylinders, one for the front brakes and one for the back.
The bias between front and back being set using different lever length between the pedal and each master cylinder.
Why is this configuration preferred over a single master cylinder of same surface area and a bias valve? Is it safety requirement to keep both front and back hydraulic systems entirely separated or is there any technical benefit?


texts: Lowercase phi (φ) seemingly used for diameter in diagram instead of Ø?

texts: On a technical drawing for resistors, the lead diameter was given as $\varphi 0.55\text{mm}$. Since they also specify the wire is 24 SWG, and 24 SWG is a diameter of 0.559mm, did they simply use φ (phi) when they should have used Ø, or is this actually accepted notation? And if it is accepted usage, does the usage of φ differ from Ø?


texts: Equilibrium concentration of point defects in solids at sufficiently elevated temperature

texts: Equilibrium concentration of point defects in solids is defined as $\chi=\exp(\frac{\Delta s}{k_B})\exp(\frac{-\Delta h}{k_BT})$. At high temperatures, may be even higher than melting temperature of the solid, does the entropy become undefined meaning there will be no equilibrium concentration for point defects?


texts: What do they call that elegant triangular scaffolding often used in future-oriented architecture?

texts:
I'm a 3d artist and I'm trying to produce a type of scaffolding within a biodome.

For lack of knowledge in technical terms, I'm having a hard time learning about the design pattern/structure that I must follow (I suspect just making a triangle-array would be ignorant).

What is the technical term for the triangular scaffolding often used in future-esque projects? I've seen it used to hold up giant solar arrays as well as biodomes, etc.

If I only knew what it was called I could go ahead and research it!


texts: How can we tell if a press mold need more stages?

texts: I was asked to design a simple press mold for a 0.5mm sheet metal part. It has some small but rather deep sinks (5-7mm) which has made me wondering if it can be done in a single stage or it needs more stages. I guess there should be a table to help me through without the hassle of FEM with Ansys or other softwares. I read some books on metal-forming but I couldn't find my answer.


texts: Interference between direct signal and reflected signal

texts:
A laptop's antenna receives signals from a Wi-Fi router in two ways:

signal falling directly on the antenna from the router, say 1 m away
signal coming from same router but bouncing off the walls and traveling some distance, say 10 m.

Therefore, at any point of time, the antenna receives multiple signals at the same frequency. How is the resulting interference taken care of?


texts: Flow in a T-Junction with pipes of different diameters

texts:
I have been trying to model a complex pipe network recently and have come across something I can't find any information on. In my model, I have been assigning equivalent lengths of pipe to various fittings, but I commonly encounter fittings such as this:

Inlet to T: 10mm diameter pipe
t-through: 10mm diameter pipe
t-branch: 1mm diameter pipe

Essentially I have a T junction where the branch is also a sudden contraction, but the dominant flow direction is perpendicular to the branch. Does anybody know a method of calculating equivalent length of pipe in a case like this?

I don't think a regular vena contracta, as described by normal theory for sudden contractions, would occur in the 1mm branch, since it is perpendicular to the main flow and not coaxial with the main 10mm pipe.

But I have various instances where this occurs, and the amount of the contraction varies (e.g. the branch pipes can be 1,2 or 5mm) but the normal method of equivalent pipe length for a t-junction does not account for the changing area. I need something that will account for it.


texts: Planned power outage and backup generator

texts:
In a few days, there will be a power outage that will probably last for 8 hours. We had this issue before, but then only our part of de building was affected. It was temporarily resolved by using 2 industrial extension cords. But in this case, the whole street won't have power. So that's not an option.

Because we've done it before with extension cords, we where wondering if we can do it again using a power generator. I've counted about 15 computers. Assuming they use an estimated 250 watt average. But I'm aware this is a big guess.

What are the things to keep in mind when choosing a temporary backup generator?

The equipment we want to supply:

Mail server, file server, firewall and all other primary network devices use an APC
Other devices (8 computers, 8 27" screens) will be powered off. They are both on 2 power loops (hope I'm using the correct terminology). Once these are connected to the temporary power supply, the devices can be switched on again.


texts:
I'm working on a design project that will require a flexible component that will be operating at temperatures from $0^{\circ}$C to $-200^{\circ}$C. Are there any thermoplastic polymers that remain flexible at the lower thermal extreme?
If the temperature range was closer to near zero I would just use silicone tubing, but the lower limit for silicone seems to be around $-70^{\circ}$C to $-50^{\circ}$C typically.


texts:
I recently became curious why some lights flicker in some videos, and I read some explanation about it, and I still have some questions.
1. Does every light have to have a frequency? can it have an infinite frequency? (= can it possibly light continuously without "flickering")
2. From what I understand, the lights in the video flicker when the camera frequency rate is higher than that of the lights. So, does that mean the lights won't flicker when the camera frequency rate is higher than light frequency rate? (but they still don't align perfectly) is there any visible difference between the camera frequency rate being higher than the light frequency rate and the two frequency rate being exactly the same?

Thank you very much!


texts: How much power could a turbocharger generate?

texts:
I can find many figures online for the extra power generated when a turbo is fitted to an engine. However, I can't find any figures on how much energy the turbocharger turbine actually takes out of the exhaust stream.

I do know however that in Formula 1 they have an "MGU-H" system, which take rotational energy from the turbocharger turbine and converts it to electrical energy.

My question is how much power could be produced by a generator fitted to a turbocharger turbine and could it be more effective to use this power to drive the wheels, rather than use it to spin a compresser as with a conventional turbocharger system?


texts: How to model a double transfer function in Simulink?

texts:
I'm trying to model an actuator in Simulink based transfer functions previously derived.
One of functions is $$\omega_p=G_2(K_cG_1V_c-c)$$ where $$G_1=\frac{K_e}{\tau_es+1}$$ $$G_2=\frac{1}{c+K_cK_wG_1}$$
where $K_c,K_w,K_e,c,\tau$ are constants. I'm not really sure what it means to have a transfer function inside another and how to model it. We tried substituting $G_1$ into $G_2$ directly but the result didn't seem right. Would really appreciate if someone could explain what it means, how to model it in Simulink or point me in the right direction.
Thanks in advance.
Update: The other part of our system seemed to have been the one causing problems instead of the transfer functions it turned out.