texts:
Hello everyone this project is for my aquarium.

I have a big bucket beside it on the floor and I was planning on using it for the water changes. Will be a neocaridina shrimp breeding aquarium so my goal is to maintain water parameters stable with very slowly changing between water changes.

So the main goal is to pour the new water into the bucket and slowly geting it released to the aquarium at a constant and even dripping rate so water never overflows on either side as well. Basicly the water will be forever flowing from one to the other.

Moving the water from aquarium to bucket is easy thanks to gravity but uphill.... how can I do it with a dripping system at the end at 2+ meters high? I guessed If I just use a tiny water pump with a airline tube leading into the aquarium could work but water pressure worries me caused by the dripping output...

What other materials must be used? Is this idea viable or just a waste of time?

Thank you so much.


texts: Meaning of "no mechanical delay required" in packer description (oil drilling)

texts:
This description of the Reflex Lite packer by Reactive states the following among its advantages:

"No mechanical delay required"

What could that mean? The packer has no built-in system of delayed activation or delayed swelling control? Or "there is no need for complex procedures when installing the packer"?


texts:
I am searching for some software to simulate the behaviour of soft bodies like cheese in an quantitive way. For example I want to know the forces in the body during the simulation.
I thought of programming one by myself but this would probably take way too long. And I'm confused about all the programs I found on google.

So does anyone know some software to simulate things like cheese?


texts: Usage of the three-sigma limits in calculating minimum force

texts:
I have carried out 10 cantilever sample tests that provide a braking force as follows (in kN):
22.1, 20.98, 21.03, 20.7, 21.03, 21.09, 20.98, 21.08, 21.24, 21.19
The goal is to recommend the worst case breaking force
The mean is 21.14 and the STD is 0.37.
If I use the 3-sigma rule, the minimum force is 20.04kN (mean-3sigma). I feel like the 22.1kN sample is skewing the minimum data.
Whats the best way to recommending the worst case scenario for the breaking force?


texts:
I wanted to ask that if we are given the ratio of rotor length to radius to be 2 and asked to find the TSR for a 3 blade rotor, will we use the following expression:
$$          \lambda_{optimal} = \frac{4\pi}{n}     $$
where $n$ is the number of blades.


texts: Matching Air blower CFM vs HEPA filter CFM, and ΔP in WG, for laminar flow design

texts:
I am trying to build a laminar flow box using instructions at these YouTube links for design and build.

They recommended getting a Dayton squirrel cage air blower model 1TDU2 rated at 1202 CFM. The performance sheet for this air blower ( CFM vs. in wg) can be seen at this link I've already purchased this... (can be returned)

I am now considering buying one of these HEPA filters from Ebay:

A. CAMFIL FARR. 855023669, PX-21.75-44.00-9-40-FU-00-00-0 MEGALAM PANEL HEPA FILTER (link) = 0.40 in W.G. / 100FPM / 554CFM

B. CAMFIL FARR 85502A548 MEGALAM PANEL P7-23.12-47.12-5-08-00-7D-00-0
(link) = 0.58 in W.G. / 100FPM / 704CFM

C. CAMFIL FARR 855024774 MEGALAM PANEL P7-18.00-48.00-2-03-SR-00-00-0 PACK OF 2
(link) = 0.71 in W.G. / 105FPM / 550CFM

My requirement for maintaining microbial sterility are

(i) minimum 90 FPM

(ii) minimum 99.99% air purity

The help I seek is in the form of your answers to my questions below, please:

I know there is a large mismatch between air blower CFM rating and any of these filters recommended CFM rating.

1. Are any of the filters listed above matched with my air blower in terms of CFM rating? I guess not, but I want to be sure.

2. Is matching of the air blower CFM and filter CFM done at zero pressure, or operating pressure drop water gauge (which varies across these 3 filters) ?

3. FYI, I will be using a pre-filter to get rid of large particulate matter, that contributes additionally 0.3 in WG pressure drop

4. If at total WG pressure drop, the air blower CFM is X, and the rated air filter CFM is Y, then for maintaining filter integrity, I know X < Y and X = Y is OK (where X > 90FPM). But how high can X get when X > Y ? 20% , 30% , 100% - something else?

5. What are the consequences of X >> Y ? Will it blow out the HEPA filter? And more air means exceeding capacity to capture particles, so more air, but partially dirty air, right?

6. Can anyone help me with who to read and interpret a Camfil Farr HEPA filter's label, especially the description e.g. PX-21.75-44.00-9-40-FU-00-00-0, P7-23.12-47.12-5-08-00-7D-00-0, P7-18.00-48.00-2-03-SR-00-00-0 etc.?

7. I was told that for my application, a "high flow" (~1000 CFM) thicker HEPA filter (11 5/8 in) is better than a "standard" thinner one (5 7/8 in) with only ~ 500 CFM. Is this a valid piece of advice, given my goals?

8. From Ebay or elsewhere, do forum users have friendly advice for a (an equally or more) cost effective alternative to these Camfil Farr HEPA filters?

Thanks, in advance. Have a great weekend!


texts: Civil Engineering - Detailing of free draining backfill and modelling of hydrostatic pressure in retaining walls

texts: It is considered best practise to specify free draining backfill material (eg gravel) to be placed immediately behind a retaining wall. Supposedly, this alleviates hydrostatic pressure on the wall, allowing more economical designs to be achieved. But the free draining material typically only extents 300mm behind the wall. What prevents the soil behind this free draining material to saturate, impose hydrostatic onto the gravel and then transfer the hydrostatic pressure onto the wall?


texts: Determing the optimal dimensions for hydrocyclone water/sediment separation

texts:
OK, let's be clear: I'm a software engineer (retired), not a physicist, hydrologist, or hydraulics person, so please be gentle.

Back Story:

In the process of developing an open source system for monitoring water column
height in our well and of house / irrigation water usage (we're in N. CA), I discovered we had a substantial problem with sand and silt in our well water. We hadn't noticed it before because other components of the system (e.g. our 3,000 gal holding tank, ozone system, and calcite filter) were removing most of it before it came out of the kitchen tap. But that's not what they were meant to do. (Well, the ozone is sort of meant to help with clumping, but not the other 2.)

After going through several variations on filters -- paper, steel mesh, etc. -- it became clear that they all clogged up, requiring frequent flushing / cleaning.

After reading a lot of stuff which is waay outside my area of expertise, it is clear what we need is a hydrocyclonic filter. User rul30 mentioned Solid-Liquid Seperation by Ladislav Svarovsky. Chapter 6, Hydrocyclones appears to be exactly what I need. Except I don't know how to go from the formulas and academic description to a specific set of dimensions I could use with a 3D printer or other fabrication method.

Problem Statement:

I have a well pump that is throttled to 3GPM to minimize silt migration into the well. This flow level is substantially below what all commercial hydrocyclonic filters require (mostly 10GPM and higher). We have a mix of heavy sand (which is easy to get rid of with even a half-assed cyclonic filter), and a fair volume of material that is as small as 50 µm. I have plenty of pressure available, so we can create significant velocity, but the specific dimensions of the upper cylinder, the lower cone shape, and the depth of the vortex finder are based on equations that are beyond me.

Help?


texts: How to find the balance position of valve downstream a tank?

texts:
We have a tank which has a constant inflow of water (Qi). The level (h) of water in tank is controlled by opening/ closing (l) a valve downstream of the tank. Overflow height of the tank is 4 meter. I want to find the position (ls) of the valve, mathematically, such that inflow and outflow through tank becomes constant.

Also how can this be done using simulink.


texts: How do large turbines deal with asymmetry and beat arising from those?

texts:
A large turbine used in an electric plant can easily have 10+ meters in diameter and rotate at 70+ RPM. Should any asymmetry occur the rotating turbine will produce beat which will sooner or later destroy the plant. Crafting a turbine that large and perfectly symmetrical looks like a tough challenge.

How is this problem solved? Why doesn't the beat from turbine asymmetry cause mechanical damage?


texts: When teaching separation processes, which one should be introduced first? Distillation or absorption?

texts:
I am preparing a basic course on Separation Processes (5th semester, BSc Chemical Engineering). I can see that many well-known textbooks (e.g. Seader & Henley, Wankat) start by teaching in detail distillation and only then, the chapters on absorption/stripping are presented. As a student, I think I was taught exactly the opposite: first absorption and then distillation, which I believe it is a natural way as absorption is significantly simpler than distillation. My question is, what are the pros and cons of teaching first absorption and then distillation?

My own list would be:

Pros

Absorption/stripping equilibria are often described by Henry's law (or similar). It is an easier first step than complex VLE expressions
It's a good way to introduce McCabe-Thiele algorithms
No condenser or reboiler. Therefore, no need to do energy balances at first (only when vaporization heat is very significant)

Cons

Distillation is the most relevant separation process and it is important to allocate a lot of time to its thorough study


texts: How do turboshaft engines maintain a constant rpm regardless of load?

texts:
I understand that most turboshaft engines tend to run at (or close to) their most efficient rpm all of the time, and it is the load that is changed e.g. the pitch of the blade pitch on helicopters.

If everything else is kept the same and the load is increased, the rpm would obviously drop. Therefore, I assume that to maintain the constant rpm, the fuel flow must be increased as load is increased.

How exactly does the engine set the correct fuel flow to keep the engine at its most efficient rpm? I guess that on modern engines, this is probably done by a computer system, but is there also a mechanical way to do this, as would have been used in older engines?


texts:
Not sure if anyone would know this, but was discussing it with friends, and it seems like quite the puzzle. In short, how is nuclear fuel in reactors handled?

Logically, the nuclear fuel must be transported to the site, then placed into the reactor, then - once fully used - removed. But given the strength of the radioactivity of the elements, how on earth is this done?

Using the Chernobyl disaster as an example, the guys who had to clear up the mess weren't able to be close to the source for more than ca. 60 seconds without it being deadly. Even with lead protection, electrical circuits broke, so robots seem not to be an option. Just seems like a really difficult task to be able to transport, install, remove and dispose of the uranium without there being major hurdles.

Anyone know who it is done?!

Also, on a related topic: if a nuclear power station is decommissioned, how is the core dismantled? How can you safely remove the irradiated graphite, for example?

My friends and I spent ages debating how it could be done and we would love to know the answer!!

Thanks in advance.


texts: One dimensional U-Factor Calculation - How to determine indoor / outdoor film resistances

texts:
Can someone clarify the ASHRAE Fundamental 2017 (SI Units) (See Below) Indoor and Outdoor film resistances.  The manual states that it comes from Table 3 and in the description of table 3 it states "Table 3 provides effective resistance values for plane (i.e., generally flat) air spaces that are enclosed within an assembly."  So the values listed below should be found in the table.

How do you determine the direction of heat flow (I'd assume for a wall it's horizontal)
What mean temperature do I use
What air space to use?

Give the values 0.030 and 0.120 I figured I could reverse out the logic.  But 0.120 is not even listed in Table 3?


texts: What is the ideal metal sheet thickness used in a 1 tonne atv/tractor dump trailer?

texts:
What would the ideal thickness of the dump trailer bed be, so it can withstand loading rock from a height of 1 meter?

The spacing of ribs is yet to be decided.

The goal is that the trailer be as light as possible, whilst being strong enough to withstand hauling rock every once in a while.


texts: Technical Analysis to determine optimal Cellular to transmitter location

texts:
At a very high level what are required technical analysis to

determine the need to for a new 4G LTE cellular transmitter in US?
find find the optimal location for the transmitter in US?

Back Story: The leading US based cellular service provider wants to install a cellular  transmitter in our neighborhood on public property. The residence are oppose to the idea. In all accounts 4G LTE cellular coverage is very good. Below is coverage map from the vendor.

The vendor during public hearing claimed that that cellular signals are very poor and shared a some measurement data including Reference Symbol Received Power (RSRP) data for 4G LTE. It appears that the vendor is not upfront of all a facts, only shares selected information.


texts: Ideas needed: how to tilt a panel side to side

texts:
requirements:

a panel of wood 4 ft long by 2 ft wide laying flat
this panel should be able to tilt side to side (2 way)
the weight on the panel will be about 250 lbs up to 400 lbs.
controlled lift of each side should be max 3 inches

Solutions investigated:

pneumatic cylinders (price unknown)
air suspension (for cars) (roughly $250)

Any ideas how this can be done without breaking the bank?


texts: How to connect a motor with a 4mm shaft to a propeller that takes 1/2 inch shaft?

texts: I have a motor with a 4mm shaft. I've purchased a propeller that's designed to fit a 1/2 inch shaft. How can I securely couple the two?


texts: Does air flow rate of an air pump imply the same rate when using it to pump water via air pressure?

texts:
I want to build a machine that pumps liquids (roughly density of water) out of an enclosed cannister. The cannister has for one inlet for air at the very top and has an outlet (near the top as well) that feeds a tube down to the bottom of the bottle. Both these in/out-lets are sealed with silicon and the one that allows air in has a one way valve for the air.
The outlet is connected to a manifold with valves that lets me choose when to allow liquid to flow out.
I want to use an air pump to pressurize the cannister and then control the liquid output (on/off, not flow rate) via the manifold valve.
In addition when the manifold is open the air pump will be constantly pumping to replace lost pressure.
I am considering a pump like this which claims to have an air flow rate of 3.5 liters/minute. Does this mean that if I keep the manifold open and pump I air at 3.5 liters/minute it will flow liquid out of the outlet at the same rate? Or is there something i'm not considering that is going to make it flow at a slower rate?
Such things that might be of concern is the the liquid is acting against gravity (not much, it's being pumped up maybe 6 inches to the manifold) as well as the inner diameter of the fittings on the cannister (0.095 inch).
Pump in question:
https://smile.amazon.com/NW-5V-6VDC-Miniature-Vacuum-100KPa/dp/B078H8V563/ref=sr_1_2?dchild=1&keywords=air%20pump%205v&qid=1609264991&sr=8-2
And a diagram of my intended design:
https://i.imgur.com/f0w5H5j.png


texts: What kind of sensors to be used to measure the carbon dioxyde concentration?

texts:
I'm planning a thought project for measuring the C02 in a room (at office namely), and communicating its results to a computer.

But I'm blocked at the early stage: which sort of sensor and which is the mechanism to measure the CO2 concentration in air ?

I saw devices for sale, not communicating with computers, only LCD screens, and there were no indications on what is the system/mechanism used.

Any idea ?


texts: How is a highway prevented from being buried by sand in the desert?

texts:
When I happened to see pictures of a highway in the desert, the question arose in my mind. The highway will probably be buried if a sandstorm rages. So is there any solution to this problem?
https://www.sciencenews.org/blog/wild-things/algal-blooms-created-ancient-whale-graveyard


texts: What is the best method to generate heat from a compressed air canister?

texts: I want to convert the pressured air exiting a valve to heat. I know that a vortex tube can be used to do this, but I am wondering if I need to make modifications to the vortex tube to make it more efficient or if there is just another, more efficient, way to generate heat.


texts: How to backfill vacuum chamber with low pressure gas

texts: I have a vacuum chamber that I would like to backfill with 15 mTorr of argon.  The problem with accomplishing this is that most pressure regulators can't do pressures that low.  Are there regulators that accurately regulate mTorr level pressures, or is there some other approach to backfilling a vacuum system at low pressure?


texts: Why is the yield strength of steel assumed to be less for a thicker element?

texts: The above image is part of table 3.1 of Eurocode steel design standard. Looking for example at the first row (steel grade S 235), we see that there are two values for yield strength $f_y$, one for element thickness $t < 40mm$ and another for thickness $t > 40mm$. But why is the yield strength less for the thicker element? I am aware that the yield strength depends on the manufacturing process of the element. For example, in hot rolled steel there are residual stresses due to uneven cooling of the steel element after hot rolling process. But I would assume that thicker elements require less rolling, and therefore less residual stresses. So why do we assume the value to be lower for these elements instead? Am I misunderstanding something? Thank you!


texts: We are designing a button panel at work, made out of glass and are running into some issues. Glass, of course, can shatter. But we noticed that when dropping a steel ball in the center of the glass it is far less likely to shatter than when the same experiment is performed near the corners. It almost always shatters. Why is that? Is there something we can do with the geometry of the panel (currently rectangle) that will alleviate this issue? Maybe rounding the corners to be circular? Does anyone have a link to some research on the topic (i.e. how thick the glass should be to survive a ball of mass $m$ being dropped on it from height $h$)?


texts: Continuous vs Discrete system simulation in Python

texts:
Normally, when you discretize continuous system with zoh method, your continuous system output with the corresponding discrete inputs passed through zero-order hold should be the same at sampling instants. But here in my code it is not the same, but I can't understand why? Here we have a second order system, and I apply discrete PID control to the discrete system and simulate it in for loop. Then I take the discrete input values and for simulating continuous time system output I accumulate (many) shifted and weighted (by discrete input values) step responses of the continuous system to get the output. Here is the code:

import numpy as np
import matplotlib.pyplot as plt
import control.matlab as cn

sys = cn.tf([1, 1], [1, 4, 5])
Ts = 0.01
sysd = cn.sample_system(sys, Ts)

print(sysd)

# prints:
#
# 0.009851 z - 0.009753
# ---------------------
# z^2 - 1.96 z + 0.9608

ref = np.ones(1100)
Kp = 10.
Kd = 1.
Ki = 1.

y = []
y.append(0.)
u = []
u.append(Kp * (ref[0] - y[0] ) + Ki*(ref[0] - y[0] ) + Kd*(ref[0] - y[0]))
y.append(0.009851*u[0])
Acc_Intg = ref[0] - y[0]   # Accumulator for Sum of errrors for Integral term Ki.

for i in np.arange(1, 110):
    Acc_Intg = Acc_Intg + ref[i] - y[i]
    u.append(Kp * (ref[i] - y[i]) + Kd * ((ref[i] - y[i]) - (ref[i - 1] - y[i - 1])) + Ki * Acc_Intg)
    y.append(y[i]*1.96 - y[i-1]*0.9608 + u[i]*0.009851 - u[i-1]*0.009753)

T = np.arange(0, 0.8, 0.01)
u = np.array(u)
yc, TT = cn.step(sys, T)
yc = yc*u[0]
for i in np.arange(1, T.size -5):
    yaux, TT = cn.step(sys, T[0:(T.size - i)])
    yc[i:] = yc[i:] +  (u[i] - u[i-1]) * yaux

y = np.array(y)
plt.plot(np.arange(0, y.size * 0.01 - 0.0000001, 0.01), y)
plt.plot(T, yc)
plt.show()


texts: How to measure the unbraced length of lateral torsional buckling for negative moment in a W-shape steel beam?

texts: I have a W-shape steel beam that is fixed-fixed and the top flange is fully braced for lateral torsional buckling. The negative moment at the end controls the design and there is no lateral bracing for the bottom flange. What will be the unbraced length ($L_b$) for the bottom flange? Also, if I provide brace points at the points of moment inflection then what will $L_b$ be? In general, what is the rule for measuring $L_b$ for bottom flange under negative moment? If possible, please provide proof from AISC code.


texts: Wire heating and heat transfer in a cylindrical pattern

texts:
I have a series of copper coils with ¼” cooling plates between each coil. The cooling plates will be manufactured from aluminum and cooled using copper tubing. There are seven in series, and a plate in between each but theoretically this should be able to be expanded to any number of these plates in series. A picture is below of the setup. I went through a similar exercise with a different configuration which was very similar, but I am not sure if I got the final process correct.

There is current flowing through all of the copper coils and the resistance and current are known. What I originally came up with was that the final temperature of the copper would be Tc=P*R_th +Tw where R_th is the total thermal resistance and Tw would be the temperature of the water. the thermal resistance would just be the addition of the thermal resistance due to the water (convection) as well as the resistance to travel the width of the insulated plate and the copper along the axis, but I am not sure how to go about this when all of them are in series and are simultaneously heating and cooling.

Getting the convection coefficient for the coil cooling is something that I am not worried about, I am just trying to get the equation that would describe this. I am looking for the final temperature of the coil (red) after everything has settled to it's final temperature. I don't know if this can be achieved in steady state or if a transient process must be taken.

Here is the cross section of the cooling plate in between each wire coil. The plates are in the white spaces shown. The black represents the circular cooling plate. The red is the geometry of the cooling tube which sits in each plate and carries flowing water.

The schematic of heat generation and thermal resistances is down below, but would be in series with almost 7 others of the same variety. Note that the pipe carrying the water does not cover the whole area so it may not be beneficial to look at the problem as all the heat traveling through the piping (hence the two plate resistances) or if there is some way to reconcile that.


texts: What's the difference/advantages/disadvantages to a tower with a moving jib, vs a flat jib

texts:
Apologies if I've got the terminology wrong, I'm in now way involved in engineering, but I work in a high rise in a city with a lot of construction going on.  I see a lot of different types of cranes, and it's got me wondering.

The two most common types I see are (I think) both tower cranes, however Some have the classic T shape, where the arm stays level, whilst the others have an are that raises up and down.  Both types seem to be working on the same types of sites, so I've been wondering what the difference between the two types are, and why you'd pick one over the other.

Here are examples of what I'm talking about:


texts: If the emergency brake in a train is broken, do the passenger car brakes still work?

texts:
Scenario:
Suppose the emergency brake button in the cab of a train is not working. Would the emergency brake cords / buttons in the passenger cars still work?

This question is inspired by this question on the SciFi StackExchange, asking why the passengers in the train fight scene from the movie SpiderMan 2 did not simply pull the emergency brakes.

In that particular scene, a R46 City Subway Car was rendered "unstoppable" by ripping out the speed control lever in the car, which also happened to disable the emergency brake button (see 16 seconds into the video).

With movies, we suspend our disbelief in order to enjoy the story that is presented.  But the above SciFi question got me to thinking about how emergency brake systems are designed for trains.

Given trains significant mass and momentum when moving, it seems like there would be multiple, redundant safety systems to provide braking capability for the train.

My Question:
Is there a common safety design used for the braking system of trains?

Does that design account for portions of the system failing and allowing other portions to compensate for the failed components?  (ie. would the passenger car emergency brakes still work?)


texts: Can it be more efficient to pump heat into warmer water than cooler air?

texts:
About this time of year in my region people often look at the air conditioning compressor pumping heat to the outside air on one side of their house while their swimming pool heater tries to pump heat into the water on the other side, and wonder why they're paying twice to move heat.  Inevitably someone thinks of submerging their compressor coils, but then they run the numbers and realize that it won't be too many days before their swimming pool is uncomfortably hot.

But this leads to an interesting engineering question: What is the practical breakeven point between air-source and water-source heat pumps (for cooling indoor air)?  I.e.: Is it possible, due to its higher thermal conductivity, for a water sink at a higher temperature to be more efficient for cooling than an air sink at a lower temperature?

More specifically: Suppose we have an outdoor compressor with surface area x pumping y BTUs of heat.  I am assuming that because water has something like 20 times the thermal conductivity of air that it would be a more efficient heat sink even when it's somewhat hotter than the air sink.  (Is that correct?)  But how much more efficient?  I.e., at what temperature differential is air as efficient as water?

(Or is this not a practical question?  For example, we run fans to force more air through air-cooled compressors.  That takes energy, but maybe it raises the effective thermal conductivity to the point that it is breakeven with a convective water sink ... even including the energy to drive the fan?)


texts: How to find strain in an inclined member of a struss

texts:
I'm working through an FEA problem and I'm stuck.

Question: How can I determine the strain in member 3 from displacements known at node 3?

It's at 45 degrees, I know I should be using some $cos\phi$ and $sin\phi$, and given the displacements I suspect there to be a negative strain (indicating compression), however, I'm not entirely sure how to find the strain in the inclined member using both displacements.


texts: Equivalent spring of beam supported by springs

texts:
My professor gave us yesterday a problem to calculate the equivalent spring of the system shown in the attached figure. The problem: a cantilever beam supported by two springs $k_1$ and $k_2$ located at distances $a$ and $b$, respectively, from the left end. The beam has length $l$ and flexural rigidity $EI$. The idea is to approximate the motion of the mass in the vertical direction by a simple one degree of freedom system, so the first step on it is to calculate the equivalent stiffness coefficient of the system.

I am having some trouble to understand his solutions, because I don't agree entirely with what he said. His approach to the problem:

Given the deflection equation of a cantilever beam with a load $P$ applied at the tip,
$$
v=\frac{-Px^2}{6EI}(3l-x)
$$

he says an equivalent spring $k_{eq12}$ substitutes the springs $k_1$ and $k_2$ at the right-end of the beam. To calculate $k_{eq12}$, the total potential energy is
$$\begin{align}
U&=\frac{1}{2}k_{eq_{12}}y_l^2=\frac{1}{2}k_{1}y_a^2+\frac{1}{2}k_{2}y_b^2\\
k_{eq_{12}}&=k_1\left(\frac{y_a}{y_l}\right)^2+k_2\left(\frac{y_b}{y_l}\right)^2
\end{align}$$
where $y_a$, $y_b$ and $y_l$ are the deflections of the beam for a load located at $a$, $b$ and $l$. He claims $y_a$ and $y_b$ are the deflection of the springs.

Therefore, for a unit load,
$$\begin{align}
y_a&=\frac{a^2}{6EI}(3l-a) \tag1\\
y_b&=\frac{b^2}{6EI}(3l-b) \tag2\\
y_l&=\frac{l^3}{3EI}       \tag3
\end{align}$$

Now, if $k_{eq_{12}}$ is an equivalent spring at the right-end of the beam, then the equivalent spring of the beam is in series with this equivalent spring, so the equivalent spring of the entire system supporting the mass is,
$$
\frac{1}{k_{eq}}=\frac{1}{k_{eq_{12}}}+\frac{1}{k_{beam}}
$$

Substituting the deflections $y_a$, $y_b$, $y_l$, and the equivalent stiffness of the beam being $k_{beam}=3EI/l^3$, we get
$$
k_{eq}=\frac{\left( k_1\left(\frac{y_a}{y_l}\right)^2+k_2\left(\frac{y_b}{y_l}\right)^2 \right)k_{beam}}{k_1\left(\frac{y_a}{y_l}\right)^2+k_2\left(\frac{y_b}{y_l}\right)^2+k_{beam}}
$$
which can be simplified, substituting $(1)$, $(2)$, $(3)$ and the $k_{beam}$, to
$$
k_{eq}=\frac{3EIk_1a^4(3l-a)^2+3EIk_2b^4(3l-b)^2}{l^3\left[k_1a^4(3l-a)^2+k_2b^4(3l-b)^2+12l^3EI\right]}
$$

That is the answer he gave us. Particularly, I don't agree with a few steps along the way, but the key point here for me is that we cannot use the deflection equation for a cantilever beam a tip load at the end, because this beam is not exactly a cantilever beam, but it has two extra supports, the springs.

My approach to this problem would be to, given an applied load $P$ at the left end, find the deflection equation for the system with the springs and the approximate the equivalent stiffness with the new equation. The deflection equation now would have to be calculated from the $EI\frac{d^4v}{dx^4}=w(x)$ elastic curve. A much harder work, because it is a cantilever beam supported by two springs, and it is a statically indeterminate beam. Is this line of though correct or was his approach correct?


texts: can a new foundation be dug alongside an existing house with a deep foundation without compromising the structural integrity of the existing house?

texts:
Can a new foundation be dug alongside an existing house with a deep foundation or cellar without compromising the structural integrity of the existing house?

Subquestion: should I leave rebar or sth sticking out from the existing foundation to join it with the new foundation?

existing house (not built yet):

foundation 1.8m deep (wall)
foundation is on a pad of compacted crushed rock that creates a 1m perimeter around the house. The perimeter above that is filled with sand up to ground level
wood framed, some brick walls

new addition:

walls and pipes will be joined to the existing house
will have the same type of foundation and frame
dug into ground, that is fresh - that is never compacted or dug into before.


texts: Why do car-seats have an expiration date?

texts:
My wife and I are expecting our first child, and therefore are expecting to purchase a car seats. My wife and I have discovered that car seats have "expiration dates": a car seat, no matter how lightly used, is deemed unsuitable for use after a particular date. We wonder why.

A car seat which has been in an accident could be compromised in ways that simple visual inspection could not confirm. I am not asking about these car seats. I am asking about the car seats which have experienced the repeated loading/unloading which comes from placing a small human child in and out of the seat and driving them about in a driving style that could only be described as "not aggressive."

Attempting to look up answers for this question have not yielded any satisfactory results! So I ask you, engineering stack exchange, why do infant and child car seats have expiration dates?

I have a few possibilities, but I have issues with all of them:

The car seat is designed to withstand a number of cyclic loads, and critical car-seat parts have a fatigue life which the manufacturers base the expiration date on. This seems the most likely, but babies are really small and the materials are meant to protect them against high-speed crashes for the entire product life!
The car-seat manufacturers are greedy, using social pressures and the label of "unsafe" to force parents (as a group) to buy car seats at regular intervals and deny the second-hand market any 'viable' material.
Something in the car seats really does degrade with use, heat, or sunlight and therefore actually expires. (This seems unlikely, but terrifying!)
Safety standards are expected to update after some amount of time. This particular explanation seems very odd to me: safety standards are set be governments and industry groups, and I doubt car-seat needs have evolved so much that a regular update every few years is entirely needed, or that those updated industry safety standards will always render old products unsafe.

Or maybe it's something else! Sources are welcome!


texts: Minimum drum wall thickness when rope wrapped around it

texts:
I need to design a hollow drum that holds steel wire rope under tension. The wire rope gets pulled from both ends with a force of 200kN, it is wrapped around the drum 5 times. The outer diameter needs to be 1m and I was thinking of using S355 for this application.
My question is: How would I go about calculating the minimum wall thickness of the drum, as to withstand the ''crushing'' pressure of the wire wrapped around it?


texts: Application of Bernoulli's equation between stationary and moving reference points

texts:
I'm working on a pipe design problem using Bernoulli's equation, from first principles. The pipe is from a water storage reservoir (point 1) and discharges into a river (point 2). These are my two reference points respectively.

Now I know that the velocity at the reservoir is zero (point 1) as the water level is assumed to be stationary, but is the velocity at point 2 equal to the speed of the river?

This seems to make sense from my understanding as the movement of water in the river would carry some energy which must be considered.


texts: Fix plastic tub (leak) and resist applied forces

texts:
I hope I'm not too much off topic here. I'm hoping it can make sense as a mechanical engineering question.

There is a crack in the front of the tub of my front loading washing machine.
As you can see in the drawing #1, there is a weight attached right where the crack formed. Seeing the machine do the spin cycle, I assume quite a bit of force is applied, noted as F1weight and F2weight.
I'm thinking of putting epoxy glue but I think F1weight will destroy the joint.
What I think I should do, is put some kind of fiber with a high tensil strength into the epoxy glue. When it dries, the glue will fix the leak and hold the fiber in place. The fiber will be responsible of ensuring the integrity of the glue and resist F1weight.
I'm thinking something like glass fiber fabric that would sink in the epoxy?
Any idea what could be used here?


texts: How can thin wire in generator windings carry the high output current?

texts:
I observed the rebuilding of a 12KW, 120V gas-powered generator.  I was amazed at how small the generator portion was (roughly the size of an electric motor you might find in a major home appliance).  The windings were pretty thin magnet wire, like you would find in an appliance motor.

Getting the 100A generator output to the breaker box requires heavy-duty wire.  That same current originates in the generator windings.  How is the thin wire in the windings able to carry 100A (which far exceeds what wire that size is rated for)?


texts: Difference between "Design Dwg." and "Mfg.Dwg."

texts:
From an Inspection and Test Checklist for flange heaters (the number is the same on both lines):

I wonder what the difference between "Design Drawing" (or is it "Drawings"?) and "Manufacturing Drawing(s)" is. Is it that Mfg. Dwg. merely represents some part of Design Dwg. (sheet no.3) that is copied for use in the production shop? Or are there some additions\changes?

Sorry if this is a very basic question. I tried to translate this document and dropped the translation because I found it quite hard to understand many of the terms used, especially in the condensed context of a checklist. But I remembered some terms, and it made me curious.

P.S. I was told on a translators' site that it could possibly mean "Manufacturer's Drawing Number" in this context. I wonder if that's true.


texts: Why is the acceleration of wedge and block equal like this

texts:
No friction at all anywhere. Let me explain the diagram in steps and the Q.

green colour let us start with. It represent a wedge on which there is mass of 10kg (red colour). That’s it the first picture.

dotted line in white represent when the block touches the bottom of the wedge.

represent the dotted yellow line which represents the direction of acceleration for 10 kg mass. Which is kind of like unknown or not in a symmetry.

Where the Q lies

The Dark yellow line represent displacements. Below one is AC I.e displacement of the wedge. Now , only thing in this Q what I don’t understand is that why is Displacement of mass 10kg BC even though the direction of acc for 10 kg is the dotted line.
If you wish to know why the dotted line , there is an example in my textbook which tells us that. Also , tells us that because of the dotted line kind of acceleration, we use pseudo force for solving such questions.
EDIT: Where a different concept and answer is also used.


texts: How to protect a pressure gauge from condensation in a vacuum steam boiler?

texts:
Pressure gauges are protected from steam condensation in a regular boiler by using a siphon where steam condenses and prevents steam from going further up to the gauge.

However in a vacuum steam boiler when the boiler is re pressurized after use the pressure would push the water in the siphon up to the vacuum gauge.

I currently dont use any siphon and my vacuum gauges are far off (from condensation I guess) after a few boils, how can I prevent that ?


texts: how to calculate required torque and rpm to through a 160 gram cricket ball horizontally at 160km/h velocity?

texts:
I am going to design a bowling machine. In this design, I'm going to use two motors that are being placed vertically and their shaft are attached with two horizontal identical wheels with a space of ball in between these two wheels.

The wheen diameter is 360mm and the weight is 3kg each. the ball is 75mm dia and the weight is 160 grams. I need to calculate torque and rpm required to throw the ball at 170km/h velocity. The cricket pitch length is 22 meter = 2200mm

Required Torque:

The required acceleration is a need to throw the ball at 170km/h means 47.22m/s

$v^2=u^2+2fs$ where intial velocity is $u=0$

So, $f = v^2/2s$

accleration $f = 50m/s^2 $

The force required $ F = ma$ where $m =$ total weight of two wheels + wight of ball $= 6+0.160$ $= 6.016$ kg.

So, $F = 308N$  i.e, $154N$ in each wheel.

Assume rubber to leather kinetic friction $u = 0.4$ it's not actually

kinetic Frictional force $Fr = 1.4 * 154 = 215.6$

Required torque $Ta = F * r$
$= 215.6 * (0.36/2) = 36.8 Nm$

Required RPM:

If the linear velocity of the ball is $v=47.22m/s$
The velocity of the ball is an average velocity of two-wheel $v = (v1+v2)/2$

for the maximum velocity of the ball with no spin, the velocity of two-wheel must be the same.

so, $v1 = v = v2$

ao, the angular velocity of each wheel should be $v = d × w × 0.001885$

So, $w = v/(d * 0.001885)$RPM

$=2510$RPM

Please let me know I am right or wrong?


texts: How do I solve an optimal control problem where the dynamics depend on some function of the state?

texts:
A typical optimal control problem with state $x(t)$ and control $y(t)$ can be expressed as $$\max_{x(t), y(t)} \int_0^{t_1} f(t,x(t), y(t)) dt$$ subject to $x'(t)= g(t, x(t), y(t))$ and boundary conditions for $x(t)$.
I want to solve a problem that looks very similar, but the dynamics are $$x'(t)= g(t, x(t), y(t), z(x(t)) ),$$ where, the sequence $z(\cdot)$ is to be chosen although it's argument is the state.
I'm not sure where one can look for solutions to this non-standard problem. How can I approach this problem?


texts: How Much Efficiency is Lost in a Gear Train

texts:
I want to get a rough estimate for the transmission efficiency of two different gear trains. One is a one-stage gear train with 11.67:1 ratio (140/12 teeth) and the other is a compound two-stage gear train with overall gear ratio of 18:1 (72/12 + 36/12 teeth).

I read in a forum that one can expect a 10% loss per stage of gear train in this case but I wanted a second opinion. Any help would be greatly appreciated.


texts: Solidworks Long Term Transient Heat Transfer

texts: I have a cylinder with water, containing an arbitrarily shaped (i.e. a free surface), but still a primarily cylindrical object. The setup is subjected to transient heat loading (dT +20 -10C at room temperature), for a period of 6 months. I have a dataset regarding the temperature for the whole period and I am interested in simulating the temperature within the object. Now obviously running a coherent simulation with such a detailed dataset is beyond the computational capacity of mine, and I was wondering if there is a way to tweak heat transfer parameters and/or the setup to get my answers relatively accurately.


texts: Will an empty spray can maintain a vacuum?

texts: If I were to remove all the air from a canister of WD40 so that it was a vacuum inside, and reinforced the walls so that it won't collapse in from atmospheric pressure, what would happen when I pull the trigger? Will it now suck like a vacuum cleaner?


texts:
For any testing that a part is suppose to pass a test, let's say the leakage test of a seal flange.

How should I individualize the cause?

I know there is root cause analysis and for different cases I probably need Design of Experiment (DOE) analysis for considering all cases of test to find the root cause?

I have not seen any papers that talks about doe analysis and root cause analysis at the same time.


texts: Why is this overdefined? Can't I move right vertical line to the rright?

texts: Why is this overdefined? Can't I translate eveything yellow horizontally to the right?


texts:
If we give a sinusoidal $\cos(\omega t)$ to a 1/s, it means that you just integrate the given input.

What if we have the same input but Transfer Funtion with a pole, let's say 1/(s+1), what will be the output of the system ?

Edit #1

According to my hand calculations, I guess there no way rather than dealing with Laplace Transform.

Hint: As you may know,

$$\begin{gather}
\cos(\omega t) \rightarrow s/(s^2+w^2) \\
h(s) \rightarrow 1/(s+1)
\end{gather}$$

output --> multiply them, and then apply partial fraction expansion, and then Laplace^-1

P.S.(Took approx. 30 min)


texts: Can someone explain how the output of this control system is derived?

texts:
I understand equation (1), but I really don't see the connection between equation (2) and the picture.
For starters, shouldn't the $b_0$ constant be multiplied by
$$net(n)-(a_1 \cdot net(n - 1) + a_2 \cdot net(n-2))$$
Edit: Honestly even an "I'm not sure" would be helpful


texts: analysis of PD controller vs static-gain

texts:
I have a plant $G(s)$ which gives position and velocity as output
$$ G = [G_{ru}(s)\quad G_{vu}(s)]^T $$
where $G_{ru}$ is the integral of $G_{vu}$, and $u$ is the input to the system. Now if I want to control the system with a proportional-derivative law I can write

$$ u = C e_r $$, with
$$C = (k_p +s k_d)$$ where $e_r$ is the error with respect to the reference position (e.g., a step command),

I can build the sensitivity and complementary transfer functions as

$$ S = (1+G_{ru}C)^{-1} $$

$$ T = G_{ru}C(1+G_{ru}C)^{-1} $$

When I instead consider the system as having 2 outputs,

and I define a new controller as

$$C_{2} = [k_p\quad k_d]$$,

and the corresponding sensitivities as
$$S_2 = (I_2 + GC_2)^{-1}$$
$$T_2 = GC_2(I_2 + GC_2)^{-1}$$

we can see that $S_2$ and $T_2$ are now $2 \times 2$ transfer matrices.

The question is: why $T_2(1,1)$ differs from $T$ since they have the same controller and represent the same thing (in this case the how the position behaves given a step command)?

The corresponding bode plots are depicted here below. Only the dc gain is the same, but the transient is quite different. Why does this happen?


texts: Affect of Cast in Pipes in a 1m thick Raft Slab on shear

texts: I am designing a 1m thick raft slab and the drainage guys have thrown in 100mm diameter cast in pipes all over the raft. See Attached images 1 & 2. Wondering how this will affect the shear in the raft and how i can go about calculating required shear reinforcement for a) the column and b) the pipes. I have read the presence of the pipes can be ignored however this doesn't seem right to me especially when columns are surrounded by pipes. Any feedback or pointers to get me in the right direction would be greatly appreciated. the Raft has an H20-150 Basic Matt throughout T&B.


texts: How to measure signal period with Arduino?

texts:
I am trying to use an Arduino Uno R3 as a tachometer (It is going to measure the RPM of my motorcycle). Basically it only has to count how many times an input pin goes HIGH in one second.
The problem is pulseIn is too slow for it...
The pin will be on for up to 230 times/ second (14.000 RPM).
So that would be 1000/230 (approx. 4 ms per rotation, i believe).
What is the easiest way to do the job? I can't figure any solution yet...


texts: SMD Bread board and electrical simulation software

texts:
I am designing a DC-DC boost converter using an SMD LM2623 and an inductor which is also SMD of 4.7 μH. I want to first build a prototype but I can't use an ordinary breadboard. Could someone please advise me whether there is a way I can mount SMD components for testing?

Secondly, I have failed to get an electronic simulator having LM2623, does someone know any simulator which can help me do my circuit analysis?


texts: Why are typical UART baud rates not in multiples of 1000?

texts: Why are typical baud rates not in multiples of 1000 instead of being in multiples of 300 i.e. 4800, 9600, 19200, 115200, etc...? Is there a mathematical or electrical reason behind this?


texts: When an elevator has two buttons next to it, ^ and v, what do they actually mean?

texts:
Both as a kid and as an adult, I've encountered elevators lined up next to each other, or single ones, which have two buttons on each floor (outside of the elevator):

^

And:

V

Pressing one of them makes it light up. Not understanding what the arrows/pointers symbolize, I always pressed both. They would stay lit until the elevator arrived. I have no idea if I made myself wait longer or caused issues for others by doing this.

As far as I can tell, there is nothing whatsoever which explains what the buttons do. No instructions of any kind. This was apparently considered so obvious that even the dumbest person could figure it out. But clearly, they had not thought about me...

To me, the most likely way in which they are meant to work is:

  Pressing "up symbol" means "I want to go up", and pressing "down symbol" means "I want to go down". That is, you are just implying that you want it to arrive at your floor ASAP, but the information you input is where you want to go. Correctly telling the elevator system this information supposedly helps it perform optimally for everyone, and potentially even shortens your own wait time.

However, if that's what it means, then why am I allowed to press both buttons, which then both stay lit? Shouldn't it then disable the other button since you pressed the first? Since you can press both, that gives zero useful information to the elevator system. Unless that means that there are people standing in line who want to go up and others who want to go down... but that sounds too complex of a setup.

Another possible interpretation is:

  Pressing "up symbol" means "I want the elevator to go up, stopping at my floor, because it's currently below my location", and pressing "down symbol" means "I want the elevator to go down, stopping at my floor, because it's currently above my location". Since each person can see where the elevator currently is (on a separate series of lights, above the elevator), this is quite possible, albeit perhaps slightly less likely.

So... which is it? Or does it work in some entirely different way? Am I the only person in the world who manages to get confused by those buttons?

Wouldn't the best design be to have just one button per elevator entrance which simply means "bring the elevator here ASAP"? At least that cannot be misunderstood.


texts: Seismic Design Changes between ASCE and UBC Code?

texts:
what is the difference between the seismic design between ASCE and UBC code?
from load combinations to loads applied to the history between the sudden shift or change in the code. and which one of the codes does it result in over-reinforcement  (or overdesign) i mean what code for example will give column dimensions >> than the other one ...

Thank you in Advance.


texts: I'd like to ask you if a C mex s-function model in Simulink can get the dSpace execution time lower, rather than having a model with blocks and functions.


texts: PID control of a DC motor with PWM from Raspberry Pi - how to cross dead area?

texts:
I'm driving a DC motor (actually a linear actuator) with a Polulu motor controller from a Raspberry Pi. The motor drives if you ask for anything between 20 and 100% duty cycle, so there is a dead zone between -20% and 20% duty cycle.

I'm using a laser distance sensor to measure position of the actuator, and I'd like to make the actuator track a desired position using a PID controller.

The problem I'm facing is that as the position crosses over from being too low to too high, the PID controller takes a load of time to cross through this deadband, after which the position is completely wrong!

I've tried creating a lookup table for the motor speed based on the requested speed, but this doesn't help a huge amount. I was thinking of creating two lookup tables, one for when the position is above setpoint and one for when it is below which cross over instantly from -20 to 20 and vice-versa.

Any thoughts on this problem (or just what it is called so I can Google it!) would be much appreciated.


texts: Force in a string attached tangential to a servo

texts:
If I'm using a servo with a string attached to it (while the string is attached to another object) the string is attached tangentially at about 1.5cm from the centre of the servo and the servo draws 270 milli Amps and has 5V supplied to it (while having an angular velocity of pi/10) can I find the force in the string by doing the following: using P=IV find the power of the servo  then using angular velocity = linear velocity x radius work out the linear velocity of the string, then using P = FV find the force in the string?
Thanks for helping out!


texts: Why aren't these kind of drivers used in loudspeakers?

texts:
This is a driver in a headphone. These can produce every sound and beyond that humans can hear. I understand that there are full range speakers that are sometimes used, but they work in a very different way. The drivers that are used in loudspeakers use rubber surrounds, rather than an integrated plastic surround with the ridges seen here.

Could someone explain to me why drivers like these can't be up sized to produce a more durable full range speaker?


texts:
Why does DSG have low torque capacity? They are very simillar to manuals but manual transmissions can handle greater torque. Why js that?

What determines the torque capacity of transmission?


texts: Humidity in home is much higher than outside

texts:
We have a two year-old, two-story town house with:

fiberglass insulation in the walls;
a Tyvek vapor barrier under foam board on the exterior walls;
blown cellulose insulation in the attic;
stucco outside;
and a refrigeration cycle air conditioning.

We live in Phoenix, AZ (desert climate) and our indoor humidity levels are consistently 20% to 35% higher than outside. During the summer we consistently have humidity levels in excess of 80% (not 70%), even with the damper fully open. It has been so humid inside that the tile floors had sweat on them.

We have no indoor plants or water features. Our dryer vent is operational, and our exhaust fans from the bathrooms are vented externally through the roof. There are no unusual ceiling vaults and we do have ceiling fans to stir the air. Ours is an end unit, so we have one shared wall with a neighboring town house, which has no vapor barrier.

We have had the builder heavily involved for warranty work to determine the root cause of the humidity sources. We have tried:

Slowing the AC blower motor down to allow the water in air to condense;
Looking for water leaks with an infrared camera (FLIR);
Looking for blockages in the vents in the eaves;
Calibrating the thermostat (Ecobee);
Balancing the air flow by adjusting the vents inside with flow meter hood;
Adjusting the air conditioner refrigerant cycle pressures;
Fully opening the damper to let in dry air;

- Increasing the exhaust fan to run for 30 min in a 60 min cycle.

The problem hasn't gone away and we're not sure what to do next. Is there anything else we can try before we resort to installing a whole house dehumidifier, or adding additional attic ventilation?

What are your thoughts on the RH trend over time?

Also, I did a rough calculation that the home needs to express ~350 pints of water per day (ASHRAE) psychometric chart corrected for altitude, but the HVAC company measured the AC system is operating properly and measured the AC will remove 77 pints of water per day.  I read that whole home dehumidifiers typically remove ~100 pints per day.  What are your recommendations on how to best ventilate the attic while controlling cost?

  Historical Indoor RH and Temp. Including limited outdoor data


texts: Why is there no heat-affected zone with water jet cutting?

texts:
On Wikipedia it states that the main benefit of a water jet cutter is that there is no heat-affected zone.

I am wondering about the physics behind this. I have found experiments supporting this, but I cannot produce a theoretical argument. Am I wrong in assuming that by the time it would take to heat up the material, a new influx of cold water keeps the temperature down?


texts: Why cannot series DC motors self regulate its speed?

texts:
When load increases on shunt DC motor, the speed decreases resulting in a downfall in back-EMF. This in turn, causes the net voltage, and hence the current to increase causing an increase in torque and thereby increasing the speed. Thus, it achieves a constant speed.

Considering that there is no difference in the relations when it comes to series DC motors, except that the torque is related to the square of the current, why wouldn't a series DC motor be able to self regulate its speed ?


texts:
I want to perform a RULA based analysis on a set of participants and in order to calculate the RULA score I would need the upper arm(shoulder) angle. My question is would the upper arm angle be based of the trunk or the vertical axis?

For example, if the person had a bent back and if he was not aligned with the vertical axis, then the upper arm angle would be calculated with respect to the back or the vertical axis?

In the RULA assessment sheet: https://i0.wp.com/www.ergo-plus.com/wp-content/uploads/RULA-2.jpg the vertical axis and the back are both aligned with each other. But what if they were not? With what other line, ie, the back or the vertical axis, we would obtain the upper arm angle?

I have so far tried both the methods and both yield decent results but I dont really know which one would be the one RULA actually suggests to use!

Thank You!


texts: Why don't we often use polymerics for large scale structures?

texts:
Other than higher creep and relaxation moduli, why are polymerics rarely used for large scale structures, architectural, oil rigs, pipes, or other? It seems like, although they have weaker mechanical properties, they have better corrosion resistance etc.

Are polymerics just cheaper?


texts: How to display an adiabatic boundary condition in a diagram?

texts:
I want to create a diagram. It will consist of a plate with a uniform heat load, a heat sink, and an adiabatic boundary condition. I thought of displaying the sink as a rigid attachment (as in mechanical problems).

My question is: how do I display the adiabatic boundary conditions?


texts: What is the influence of precipitation on pavement performance in both jointed plane concrete pavements (JPCP) and asphalt concrete pavements?

texts:
How are the integrated climatic model as discussed in Enhanced Integrated Climatic Model Version 2.0,  and the thornthwaite moisture index (TMI) used to calculate erosion, suction, and frost heaving in Pavement Mechanistic-Empirical Design?

Specifically interested in how precipitation affects pavement performance within Pavement Mechanistic Empirical Design (PMED) software.


texts: I think this is an electricity question:  When I start my microwave, it starts normally the motor revs down drastically, then back up to normal, then stops.  ..a total of about 10-15 seconds.  Thinking the microwave was shot, I bought a new one.  Same results.  What could be the cause?


texts: Find transfer function from step response and root locus?

texts:
I am given a step response of magnitude of 3 and the root locus and I have to find the transfer function of the system. The function I find gives me the step response(magnitude of 3 again) of the last diagram.

I'm a beginner at this so I've done something stupid probably but I have trouble finding answers regarding control engineering on the internet. This is what I tried doing:
I found the poles and the zeros from the root locus. z=-5,+4 p=-6,-10,-3
I think my transfer function is given from this formula but I'm not sure if we have an H(s) in the feedback and it is not stated : $$ T(s)=  \frac{KG(s)}{1+KG(s)} $$
From the poles and the zeros my open-loop transfer function G(s) is :
$$ G(s)= \frac{(s+5)(s-4)}{(s+10)(s+6)(s+3)}$$ Doing the calculations I find : $$ T(s)= \frac{Ks^2+Ks-20K}{s^3+(K+19)s^2+(108+K)+180-20K}$$
From the step response(final value is 4) and the final value theorem I find $\frac{-20K}{180-20K}=-4/3=>K=5.14$  I divided 4 by 3 because the first step response is of magnitude of 3. With this K the step response is the one in the third diagram.It's close to the first one but it's not the one I'm looking for.

What am I missing here?


texts: Matlab Code Debug: Trapezoidal and Simpson's Integration Rule

texts:
Hey so I am having issues some issue with this code:
~

function
    format long;
    %Knowns
    a = 0;
    b = 2;
    n = logspace(1,6,20)
    TrapError  = [];
    SimpError = [];
    QuadError = [];
    QuadSegs = [];
    RVal = (sin(2)./2)+(sin(6)./6); %real value
    tol = logspace(-1,-16,20);

    %Calling Functions and Finding Error
    for x = 1:length(n)
        TVal = TrapezoidalIntegration(@fhandle, a, b, n(x))
        SVal = SimpsonsIntegration(@fhandle, a, b, n(x));
        [QVal num] = quad(@fhandle,a,b,tol(x));
        TE = abs(RVal - TVal);
        SE = abs(RVal - SVal);
        QE = abs(RVal - QVal);
        QuadSegs = [QuadSegs num];
        TrapError = [TrapError TE];
        SimpError = [SimpError SE];
        QuadError = [QuadError QE];
    end

    %Plotting
    loglog(n,TrapError, 'kx' );
    hold on
    loglog(n,SimpError, 'bo');
    hold on
    loglog(QuadSegs,QuadError, 'r+');
    grid on
end

%Create a function for the equation
function [y] = fhandle(x)
    y = cos(x).*cos(2.*x); %define the function
end

function[val] = TrapezoidalIntegration(fhandle, a, b, n)
    h = (b-a)/n; %finding step size
    vec = linspace(a, b, n+1)
    f0 = fhandle(vec(1));
    fn = fhandle(vec(end));
    tot = sum(fhandle(vec(2:end-1)));
    val = (h./2).*(f0+2.*tot+fn);
end

function[val] = SimpsonsIntegration(fhandle, a, b, n)
    h = (b-a)/n;
    vec = linspace(a, b, n+1);
    if mod(n,2) == 0 %check if there are an even number of segments
        f0 = fhandle(vec(1));
        fn = fhandle(vec(end));
        SumOdd = sum(fhandle(vec(2:2:end-1)));
        SumEven = sum(fhandle(vec(3:2:end-2)));
        val = (h./3).*(f0 + 4.*SumOdd + 2.*SumEven + fn);
    else
        f0 = fhandle(vec(1));
        fn = fhandle(vec(end-3));
        SumOdd = sum(fhandle(vec(2:2:end-4)));
        SumEven = sum(fhandle(vec(3:2:end-5)));
        %use Simpsons 3/8 rule for the last 4 points
        Other = (h./8).*(fhandle(vec(end-3)) + 3.*fhandle(vec(end-2))+
        2.*fhandle(vec(end-1))+ fhandle(vec(end)))
        val = (h./3).*(f0 + 4.*SumOdd + 2.*SumEven + fn) + Other
    end
end

'''

Currently, the error is incorrect for all points expect the first and second. This is my plot:

and this is the correct plot:

if anyone has any suggestions I would greatly appreciate it.


texts:
I have a 43-ton tractor. The tractive effort force [N] (TEF) required for a given rolling resistance (RR) coefficient of 0.06 is determined by the formula:

$${TEF}=(c + Grad\%)mg$$

where Grad% is the gradient percentile of incline, c is the RR coefficient, m is the mass of the tractor and g is the acceleration due to gravity.

At 5% incline the TEF is 46,401.3 N. So the tractor will require 46,401 N of force to move up a 5% incline. As the gradient increases the TEF increases as well - which makes sense.

But say for example I have 275 kW engine delivering max torque at 2300 RPM = 240.8 rad/s (P= τω; τ= P/ω = 275,000/2300 RPM = 275,000/240.8 = 1142.02 Nm <- is this calculation even right?).

How can I find the maximum towing capacity of the tractor at a given gradient? I.e, how much additional mass can I pull?

The weight I can pull will go towards "0" as the angle/gradient of incline increases. This is because the engine will be using more power going up hill then on a flat incline.


texts: I am asked to design a pile cap which also serves as a collision barrier. What special design considerations need to be addressed in order to raise pile caps above ground level?


texts: What does a higher eject force do in a clutch?

texts: I am looking at two clutches and the details on both are identical. The only difference is the eject force. One is 3300 and one is 3600. Does a higher eject force mean higher performance? And also does it have any drawbacks? Like is the clutch harder to press or something? I would appreciate any help :)


texts: Converting multiview drawing to isometric drawing

texts: Please help me answer this. There is more to this but I just need to know the trick so I can answer the rest please.


texts: Deflection of constrained rectangular plate

texts:
Does a standard formula exist for calculating the (maximal) deflection of a constrained rectangular plate that is loaded with a evenly distributed pressure?

I found this Useful tables of mechanics, however I'm not sure if it's correct:


texts: Rayleigh damping in Finite Element Models using beta-coefficient only

texts:
I am modelling a railway track in ANSYS where the different soil layers have different material properties (including different damping ratios).

Since I know what frequency of vibrations to expect in the track, I can model the damping ratio using beta-damping in the soil elements only. I do not want to use alpha-damping, since it is defined globally in ANSYS and therefore would apply to all other materials for which I do not want to include damping.

I have no problems in the results, but I need to justify why it is okay not to include the alpha-coefficient. I have found a report online that says "In many practical structural problems, the $\alpha$ damping (or mass damping) which represents friction damping may be ignored ($\alpha=0$)."

However, I need either a published paper or relevant textbook, or a detailed justification why beta-damping is a good approach, and I have been unable to find it so far.


texts: Can the same diaphragm pump be used to pressurize a container?

texts:
If the output of a diaphragm pump is impeded in any way, or meant to be at higher pressure than the input of the diaphragm pump, will it work, or will it stall out and fail to pump?

In addition to this, are there reversible diaphragm pumps?


texts: Is it better to throw used domestic cooking oil in toilet or within the garbage?

texts:
I recently asked a friend how I should recycle my used deep frying oil because I just don't have enough oil to justify taking my car, drive 20 minutes away to the waste collection site for few liters of oil.

So my friend advised me to just throw it within the garbage. The oil has to be burn anyway so it will be burned at the recycle station and generate electricity and heat from it.

One other solution, is to simply throw the oil in the sink. When it reaches the wastewater treatment plant, settling basins will separate the solid, the liquid and the floating oil.

So I propose here three solutions, and I would like to know which one is the most adapted for someone that want to eliminate about 5 liters used cooking oil per year.

Store it in the basement then go to the waste collection site located 20 minutes away by car and get rid of the oil once a Year.
Save that storing space by throwing 1 liter within the regular garbage 5 times a year in a sealed container.
Throw the used oil in the toilet and throw away the shrank empty plastic container in the prepaid garbage bags (I have to pay 3$ per 35l bag).

These propositions have to come with goals:

Most energetically viable solution
Less environment impact
Most convenient solution


texts:
Everytime I try this question I keep getting 93.75 mm. I was just wondering where I'm going wrong. Here's my work:

$$
BC=\dfrac{FL}{AE}=\dfrac{1500000\text{ N}\cdot 1250\text{ mm}}{100000\text{ mm}^2*200\text{ MPa}}=93.75\text{ mm}
$$
For deflection to be in $\text{mm}$, all units have to be in $\text{N}$ and $\text{mm}$, right?


texts: How to make a mechanical elevator with rotation?

texts: How can I make an elevator that goes up while twisting like in this video? (The man that made this used an old printer)


texts: Multiphase Flow - Energy Coupling Parameter

texts:
I have a general question regarding energy coupling in multi phase flow.  My question comes is based on the text from this book:

https://books.google.co.uk/books?id=CioXotlGMiYC&pg=PA33&lpg=PA33&dq=thermal+coupling+parameter+continuous+dispersed&source=bl&ots=s9uWpatRmM&sig=-aRSlKoQXHc7gTlZTsl30ROncfo&hl=en&sa=X&ved=0ahUKEwjh6-DfhdzSAhVELMAKHfKOBHAQ6AEIGjAA#v=onepage&q=thermal coupling parameter continuous dispersed&f=false

(page 33)

This is kind of obscure so I'll provide a quick background:

Basically, the premise of the question is that there is a flow of fluid, the fluid has a continuous phase, and within the continuous there exists a dispersed phase, so something like water flowing with little droplets of oil inside the water. The idea is that, suppose the water is flowing through a pipe and into a control volume. The coupling parameter will compare the effect of the dispersed phase on the control volume to the continuous phases effect. So, a flow of fluid with a continuous phase containing n drops per volume flows into a cubic control volume of length L (a volume of $L^3$).

Energy coupling is related to temperature. So, in energy coupling the two things that are to be compared are:
The energy (heat) released by the droplets (the convective heat transfer from droplets to water)
The energy provided by the continuous phase (the heat energy of the water)
Thus, the coupling parameter will be:
$$
\Pi_{\text{Energy}} = \frac{\text{Heat Released by Droplets}}{\text{Enthalpy Flux from Water}}
$$
The heat released by the droplets comes from Newtons law of cooling:
$$
mC_d\frac{dT_d}{dt} = Nu k_c \pi D (T_c - T_d)
$$
D is the diameter of the droplet, Tc and Td are the temperatures of the continuous/dispersed phases. Nu is the Nusselt number. Again, there are n droplets per unit volume therefore the total heat released from the droplets is:
$$
nL^3Nu k_c \pi D (T_c - T_d)
$$
The heat flux due to the continuous will just be:
$$
\rho_c u C_c T_c L^2
$$
Which is the density of the continuous phase multiplied by the volume flowing per unit time multiplied by specific heat capacity and it's temperature. The coupling parameter is therefore:
$$
\Pi_{\text{Energy}} = \frac{nL^3Nu k_c \pi D (T_c - T_d)}{\rho_c u C_c T_c L^2}
$$

Ok, so that's all fine and dandy. The issue is when they simplify the above formula. So there exists a thermal response time constant (I do not believe it matters where it comes from, this is basically an algebraic exercise at this point):
$$
\tau_T = \frac{\rho_dC_dD^2}{12k_c}
$$
This can be included in the above equation such that :
$$
\Pi_{\text{Energy}} = \frac{nL^3Nu k_c \pi D (T_c - T_d) \rho_d C_d D^2 \tau_T}{\rho_c u C_c T_c L^2 \tau_T }
$$
This can be cleaned up, Nu/2 can be approximated to 1 at low Reynolds numbers. piD^2/6 multiplied by density of a droplet (spherical) gives the mass of that droplet, multiply that by n and you end up with the total droplet density per unit volume. The above equation simplifies to:
$$
\Pi_{\text{Energy}}= \frac{T_dCLC_d}{uC_c T_C \tau_T } \bigg(1-\frac{T_c}{T_d}\bigg)
$$
Where C is the ratio of total dispersed phase density and continuous phase density.

Here is the problem, the book quotes the final result as:
$$
\Pi_{\text{Energy}}= \frac{CL}{u\tau_T } \bigg(1-\frac{T_c}{T_d}\bigg)
$$
Which implies that:
$$
\frac{C_dT_d}{C_c T_c} = 1
$$

I don't see any justification for that though...does anyone know where the extra terms went?

Thanks.


texts: How would a w shaped tunnel system drain water?

texts:
My DnD group recently had a scene where we were escaping a tunnel system under a lake. My character used a bag of holding to slow drain the lake until we were at the bottom near the entrance of a tunnel. Picture a sink with the drain at the bottom. The tunnel system basically snakes down and up like an exagerrated W, with a pocket of air at the top and us starting on the right top side.
My idea was that I should be able to elevator us down and then up each bend by swallowing / releasing water from the bag. The DM figured that the water on the other side of the bend would stay up and collapse onto us as we reached the bottom of the first bend. How would the water behave in this scenario? Does it depend on whether the space between bends is air-tight or not?


texts: How to secure a rotating disc so that it has no wobble

texts:
For a 3D printing application, I need to have a spinning disc(that I will rotate via geared stepper motors) that will wobble as little as possible. By wobble, I mean that it will only rotate around it's axis and not shift side to side.

The goal is to build a 3d printer that uses polar coordinates rather than traditional Cartesian coordinates. Instead of using leadscrews, I want to instead rotate two discs. Disc 1 is mounted to disc 2 which is mounted to an immobile surface. If I can precisely rotate both, I should be able to 3d print. So the question is how can I mount them such that they don't require much torque to spin and also spin accurately around their axis?

I have ordered some lazy Susan type bearings from McMasterCar, but they wobble too much under use. I've heard that there are axial and thrust bearings and that the ones I ordered are thrust. Should I use a combination of the two (and how would you suggest mounting it?) or should I use the diagonal type that has both combined in one assembly?

The disc is 8 inches in diameter and I would like to keep the assembly thin. The disc is spinning parallel to the ground; if I were to mount the bearing underneath, it would be in compression.

Here is a sketch showing one of the axis:

This sketch shows an overview of the whole system:


texts:
Intensity of RF wave at a distance from source can be calculated by using inverse square law. But imagine an RF energy travels a distance $d1$ before being perfectly reflected from a metal surface. How much is the energy intensity at a point B, which is at a distance $d2$ from the point of reflection?

1) B lies in the line of reflection.

2) B is not located at the line of reflection. It forms an angle $\theta$ with the line of reflection.

My though process is following. Intensity must be much more along line of reflection. Probably , it should follow inverse square law along line of reflection, but i am not sure.


texts: How to determine / control if a conveyor belt runs straight?

texts:
I'm spec'ing out a conveyor belt and want a control mechanism to make sure that it runs straight. I know there exists a product for this since I've seen the function in an older tender, but don't have a clear idea how the device looks like and what it does - googling *"Geradelaufkontrolle Förderband"' didn't yield anything helpful.

Is there a device that gives me an alarm when the belt runs off course, what is it called, and how does it work?


texts: Why are/were sewers made large enough for somebody to walk down in there?

texts:
Today, I have been reading a lot about sewer systems on Wikipedia, in the hope that I would find information or at least photos showing what I think of as sewers, namely somewhere under the streets in a city where you can climb down through manholes with ladders and then walk around on little pavements down there, with rivers of sewer water flowing calmly around and the walls being made of rocks or something.

That's what I think of when I hear "sewer". But I found none of that.

I read about ancient sewers (with very few photos or illustrations of any kind) as well as saw a photo of some modern sewer pipe which definitely doesn't let you walk around in it. Nowhere could I see the "real" sewers, which I associate with Victorian-era England.

Basically, I wonder: why did they have to make them so large-scale? Why do humans need to go down there? And if they had to back in the day, then why don't they now, or in ancient times?

A ton of details are missing in my understanding of sewers. I've also always wondered how they could afford to do this everywhere in a large city. It seems like an insane amount of work just to transfer away some turds. Yes, I realize it's a crucial necessity to prevent diseases and provide for modern/convenient living, but still, it seems so wasteful (no pun intended) to build them so "roomy". Maybe that was only done for certain sections or something?

I especially wonder how in the world they were able to do this when the city was already made. Seems like you'd have to tear down all the houses if you want to make massive sewer systems, and then rebuild all the houses. Did they really do that?


texts: Generating electromagnetic signal using CPU clock

texts: Laptops have processors running on few GHz clock. Is there a way to generate electromagnetic signals in that range using some software or coding? Say generating 2.4 GHz signal if the CPU runs at 3 GHz.


texts: Maximum Normal Stress From Mohr's Circle

texts:
Given This Diagram, I am to:

Determine Principal Stresses
 (My Ans: 92000 and -8500kPa confirmed with Answer Key)
Determine Max Shear

(My Ans: 50500 kPa confirmed with Answer Key)
Find the Angle between the plane of the maximum (positive) shear stress and the original plane of stress.

(My Ans 28deg Answer Key -61.8deg)

My Mohr's Circle has C=42,000 and R=50,477 It is my understanding that my original point would be at (84,000 , 28,000) and the max shear stress is at the highest Y value of the circle (42,000,50,477)

As such I calculate:

cos^-1(42/50.5) = 33 deg
90deg-33.7deg=56.2deg
56.2deg/2 = 28.1 deg

Where am I going wrong?


texts: How can a non flowing fluid have kinetic energy?

texts: I am currently studying engineering thermodynamics from Cengel and Boles and there it is given that total energy of non flowing fluid per unit mass basis is given as $e=u+\frac{v^2}{2}+gz$.But if the fluid is non flowing how can it have macroscopic kinetic energy$\frac{v^2}{2}$?


texts: Designing RLC circuits at specific frequencies for teaching use

texts:
I need help designing simple circuits that resonate around specific frequencies. Basically I am looking for recommendations as to what size capacitor, inductor, and resistors I should get. Sorry if this is not the right forum - I am new to all of this!

We will use them to model neuronal resonance in an undergrad course. Each student group would get a breadboard + components, simple audio / function generator (adjusting input frequency) and measure resulting AC voltage with a multimeter. They will estimate the resonant frequency range by noting which input frequency produces the highest voltage response on the multimeter, and then change out components of the circuit to see how their properties affect this output.

I was hoping to create circuits that resonate around 8 Hz, 16 Hz, and anywhere between 30-35 Hz. These don't have to be exact.

Thanks for your help.


texts: Combustion Chamber Back Pressure due to gas injection

texts: I am trying to calculate prior to testing the expected back pressure resulting from injecting gaseous oxygen through an injector orifice (choked) into a rocket combustion chamber before ignition. I have tried using the Borda-Carnot equation with the assumption that the chamber mean flow is sufficiently low and that the pressure differential between the chamber and atmosphere is sufficient to drive the same mass flow through the nozzle that was injected into the chamber. Calculating the delta P under these assumptions yields an unreasonably small delta P across the nozzle. Is there a hand-calc method available that would provide some insight to this? I know that there are highly localized dynamics in the gas flow that are likely going to cause significant deviation from the analytical values, but I am mostly looking for a first-order estimate.


texts: Why are the two acceleration considered as a1 and a2 here and find acceleration of 6kg mass?

texts:
Why are the two acceleration considered as a1 and a2 here? What is the reason for this even though the tension of both the strings are same.
T is equal to 5gTcos 53 for left side and 5gTcos37 for the right side


texts: What is the deflection of planet-ring Gear Mesh along the pressure line and the position of the Plant gear?

texts:
For a Sun-Planet mesh in a planetary gear train, there will be a deflection $\delta_{sn}=\delta_{s}-\delta_{n}$ along the pressure line and the position of the planet will be determined by $\psi_{n}$, and by looking at the geometry of the picture the sun-planet mesh angle will be $\psi_{sn}=\psi_{sn}-\alpha_s$, where $\alpha_s$ is the pressure angle of the gears.

As for the Planet-Ring mesh, I can't find any literature defining the deflection and meshing angles, considering the ring is an internal gear, how would the geometry work here?


texts: Calculating force transferred from pinion gear to rack

texts:
I am really challenged as I need to fit a bunch of motors in a 6" box acting as linear actuators. I was looking for linear actuators (most I found were brushed DC) at first but the ones I found that would fit in 6" didn't have a suitable speed torque curve for my application. I started looking at steppers and continuous spin servos, combined with a rack and pinion to transfer the rotational movement into a linear motion.

I need to calculate a linear force resulting from a torque applied on a rack from the pinion gear attached to the spinning motor. Let's say I have a servo applying a torque of 29 kg-cm on the rack, how is this force going to be transferred on the linear rack? (I do not know the pitch and size of rack and pinion yet, but I want to know how big the gear could be to make the rack move faster at a given motor RPM).

Thank you so much!


texts: Suppose there is a rod, on the wall or at the centre, in a pressurized vessel, the pressure inside the vessel being P. The rod has a shear strength of S. Is it true that the rod will break, in shear, if P>S, otherwise it will not? To me it seems so, but I am not able to get my head around it.


texts:
In a sensor project I'm involved with, we have a requirement to bypass the airflow from one sensor while it does some further measurements. To do this, I implemented a flap driven by a standard servo which rotates the flap through approximately 90 degrees, opening one port and closing another.

I'd like to try and improve this with a better, less leaky, mechanism. The first thing I've thought of is a cylinder rotating within another:

The green outer cylinder contains three ports to which the inlet pipe and two outlet pipes (~20mm dia) are connected. The inner cylinder (~30mm dia) rotates to select one or other of the outlet pipes - thus it has either a really elongated inlet port or four ports. I figure I can place the servo in the centre - this dictates the inner cylinder diameter.

Is there an existing off-the-shelf product that would do this for me or will I have to try and 3-D print it (or find two waste pipes that will fit appropriately)?

Is this a reasonably way to do airflow selection or will it turn out to be even more leaky than the airflap (which wasn't particularly well done as it happens - it can be improved)?

Edit: As an addition in the OP rather than as an answer/comment: This is another way of doing this. Once you know "pneumatic" is the term you can add terms like "servo valve" to google image search and get all sorts of neat ideas (including little lego valves!):


texts: Can anyone verify this wall thickness of a pressure cooker?

texts:
I am working on designing a pressure cooker. I've have tried to find, using two different models, the wall thickness based on the following assumptions:

Cylindrically shaped container
Made of stainless steel
Internal pressure of 20 psi
The  internal pressure is what sets a lower limit on the thickness

From the two aforementioned models I have found a wall thickness of 0.1mm and 0.05mm respectively.

The wall thickness I get seems to be very thin. My guess is that the internal pressure is not what makes ordinary pots thick but actually it's the resistance to impacts occuring during regular usage that sets the limit on how thin the walls can be. Is this correct? Is there a rigorous framework for estimating the required thickness from this criterion? I haven't been able to find litterature on this.

The models are as follows:

Simple pipe: $\sigma=\frac{pR}{t}$

Annaratone: $s=\frac{p D_e}{2f+p}$

$p$ - pressure
$R$ - radius
$t$ - thickness
$D_e$ - Outer Diameter
$f$ - basic allowable stress


texts:
I have a basement which floods, the water comes through a drain in the floor. I am therefore looking to use an HFT Pipestoppers to stop the water coming in

I think the water comes from an old tank (B) (which I can't find).

Does anyone know what pressure I would expect in the pipe to the basement (x)
and advise if this is a good option.


texts: Why is building houses over train tracks way more difficult / expensive?

texts:
The question is already in the title, but I guess some context might be interesting:

I'm living in Munich (Germany). It is the area in Germany which is probably most expensive to live. Even the surrounding area is way more expensive. Building higher is only partially possible due to construction regulations (e.g. in the center nothing is allowed to be higher than the Frauenkirche; roughly 100m).

Most desired are the areas close to S-train stations, especially close to the ones that are highly frequented (I'd guess about one train every 2 minutes or so).

Almost at the center, there are buildings next to the train tracks. For example the Munich Google office. However, I have never seen buildings over the tracks (except for bridges). And the tracks cover a lot of space which is super central. To give you an impression, look at the screenshot below:

North of the tracks, east of the yellow-colored bridge, you can see the Google office. the building isn't huge, but it's not small either.
The big building in the top of the screenshot is Paketposthalle. It covers an area of 20.000 m².
We're talking about 2200 EUR/m² to 4200 EUR/m² (source)

For this reason, I wonder why I haven't seen any buildings directly over train tracks. Is insulation against the noise the problem? Is safety a problem, e.g. if a train derails? Is it the vibrations that might damage the house? Building safety exits? Is there not enough area below where one could build the support structures for the building?

There are way more expensive areas around the world than Munich. I guess Hong Kong / Tokyo / Shanghai might be one extreme example. Do they have buildings over train tracks? I'm not talking about underground ... but thinking about it, I'm not quite sure if there would be a difference if the city grows over the train tracks.


texts:
I would like to ask about the boundary conditions to be considered in a stepped beam. For a cantilever beam wherein the one end is fixed while the other end is free to oscillate along the z-axis, we can set the deflection equation to be W(x). The boundary conditions at the fixed end are W(0)=0 and W'(0)=0 while at the free end, W''(L)=0 and W'''(L)=0.
I would just like to ask about the boundary conditions or continuity equations that will exist at x=L1, or the boundary between the thick beam and the thin beam. What underlying equations will exist here?
Thanks a lot for your information. :)


texts: Resistive force sensor: some basic questions about its functionality

texts:
I want to know what the circular force sensor outputs when it is connected to the breadboard (with resistor). Does it output force measured in grams? When I slightly touch the sensor with a finger, the output value varies around 500-600.

Another question: Do I need to somehow calibrate the output values in order to use them for other measurements?


texts: How efficient is the opposed cylinder combustion engine design?

texts:
The Opposed cylinder design for gasoline engines is rather uncommon, though several have been made in the past.

The expansion forces in an opposed cylinder engine are balanced. For ever force there must be an equal and opposite force. Thus V shaped cylindar arrangements create forces that cause the engine block to vibrate. This seems like waste of energy.

Napier Deltic engines, a type of opposed cylindar engine,  are described as "high strung" and require more maintenance. I would expect the same of any opposed cylinder design due to the use of gears instead of a single crankshaft. Ignoring the maintainence issue, is the opposed cylindar design more efficient at burning fuel?


texts: Steel vs Bamboo strength types/ weight and in various directions & orientations? Specific, Tensile, Compressive, Shear, Lateral etc?

texts:
Why bamboo is the ‘green steel’ of 21st-century Asian architecture
Bamboo fibre is stronger and cheaper than steel, says Dirk Hebel
Carbon Fiber Vs Steel Vs Aluminum Vs Bamboo Pros and Cons
Is bamboo stronger than steel?

How are their comparative strengths in various directions and orientations?

I've been reading a lot online but can't seem to find definitive comparison that talks numbers and specific comparison of numbers in various directions.

Are there specific experiment(s) or research whose findings can be outlined here?


texts:
Here is a picture of a caliper that I found:

Calipers are such basic tools, but I have trouble understanding how they work. Here the main scale says "mm" at the end, and the Vernier scale says "0.05mm". I've read some explanations saying that if the Vernier constant is, say, 0.1, on the Vernier scale the "1" is at a distance of 9/10 from 0, so that if an object that is 0.1mm thick is measured, the "1" on the Vernier scale is moved 1/10 to the right and the "1" is aligned with the "1" on the main scale, and therefore the measurement is taken to be 0.1mm.

But here we have a Vernier scale with 0.05mm as the constant. Shouldn't this mean that the "1" of the Vernier scale should be 0.05mm short of the "1" on the main scale? But this is clearly not the case, the "1" spacing is clearly much larger than the "1" spacing on the main scale. So how does this caliper function?


texts: I want to understand this pneumatic circuit

texts:
I have trouble understanding the following pneumatic circuit diagram:

I am new to reading circuit diagrams and i am unfamiliar with some of the symbols. I would appreciate if somebody could explain them to me. In particular I have the following questions:

What does the dotted line in bottom left of the directional control valve mean?
Why is a control valve with 5 ports used? Isn't one of the port on the left of the valve redundant and a 4/2 valve could be used instead?
Why are there four ports on the actuator? I am only familiar with actuators with two ports (which would correspond to the top two ports). What are the bottom port and the right port used for?
What does the symbol in the top right mean?
What do the triangles on top of the lines mean? Why is one white and one black?

I realize that these are a lot of questions. But as I said, I am new to this. I would also appreciate if anybody could link a free source, there such diagrams are explained systematically. So far I used the Wikipedia page, but there are a lot of symbols/subtleties which are not covered there.


texts: How can I calculate the shear modulus (Gxy) for the material of a composite laminate [10/-10/-10/10] using test data?

texts:
I have the data from a tensile test including axial displacement, force, and strain, as well as E1, E2, Nu12, and Nu21 for the carbon fiber prepreg. I am trying to use this axial data to calculate Gxy for a 4-ply laminate with the angular orientations [10/-10/-10/10]. How can this be done.

I am confused since the Q matrices and Q bar matrices depend on Gxy so I don't know how to use those if we are solving for Gxy. Also, I do not have any data from the transverse directions, only in the direction of the applied load.

The test coupon I used was 12" long by 2" wide.


texts: Simplest Way to Make A Pressurized Water Reservoir

texts:
I have a vapor system that requires a 50 psi feed of DI water. Without getting fancy, is there a simple commercial off-the-shelf part I can buy, fill with water and hand-pressurize? Or something with an NPT inlet & outlet that I could pressurize with nitrogen or some other inert gas? At maximum, I think I'd need a 10 gallon reservoir - something that can sit on a lab bench.

The alternative is to slap a small pump in the reservoir, but that seems like overkill.


texts: Frequency shift keying uses at least two different frequencies. How much should be the difference between the two frequencies so that the receiver reads the signal properly reliably? Is there any theoretical law or empirical norm?


texts: Stop Spa-to-Pool Siphoning Thru Spa Pump

texts:
I have a partially above ground Spa and an in-ground pool.  When the spa is filled to spillover with pumps off, water siphons through the spa pump and into the pool until the spa water level drops about 13 inches.
What confuses me is that the Spa drain is about 12 inches below the pool returns and the highest pipe in this circuit is about 5 inches above the highest spa water level.

I cannot figure out why siphoning is occurring or how to stop this.  Instinctively I'm guessing I should raise the highest point 13" (since the water drops 13"), but don't really want to make the change only to find out it doesn't work.  Suggestions how to analyze and solve this?


texts: Can you convert a histogram of linear separation of lines into a distribution (histogram, PDF, PMF) of their lengths?

texts:
I have an image of lines (they're actually crystal defects viewed through an SEM)

What I'm really after is a histogram of line lengths, but as can be seen from the above micrograph, most lines exit through the image area, making measuring a histogram of their lengths impossible. Also these lines are very long, and taking a much larger picture would reduce the ability to resolve closely spaced lines, and stitching together many pictures of this resolution is generally prohibitively time-consuming.

What can be measured easily is the spacing between lines (say, the black lines), and a histogram made from these. One could draw many perpendicular lines randomly through the lines, then measure the length between each intersection, for example. I think there should be a relationship between this line spacing distribution and the line length distribution, given that the lines are randomly placed and parallel.

Any ideas on how I could extract some kind of distribution of line lengths from a line separation histogram?

Edit: I essentially believe that there is a measurement or set of measurements that I can do to extract a length distribution. For example, the measurement offered above. Now, this measurement may contain information on not just the length distribution, but the position distribution of the lines (vertical and horizontal), and their orientation distribution (these are distributions based on the set of info of a line: length, x and y positions, and orientation). Thus, if we assume random positions and parallel orientation, there is one distribution left, that being length distribution, which may be extractable given the measured distribution. To clarify, I think the measurement offered would give the set of 4 distributions just by a kind of "solution by extremes": Imagine changing lines position so that they are all in a row or a column, changing the lengths so that they are either very short or very long, or changing the orientations so that some are nearly parallel to the measurement direction. This all intuitively changed the shape of the measured distribution for me.

This is all my intuition, so I am asking if anyone has relevant know-how, or can point me in the right direction on how I may be able to, first show that this is possible, and second extract a line length distribution from some measurement(s). I may just post this in the math stack exchange


texts:
I have a fastener with an accessibility problem.  At the time of installation, the fastener is at the bottom of a crowded box with obstructions varying stiffness (Metal Plates and harnessing).  It is possible, but very inconvenient to position and drive the fastener using a pick up tool, then drive the fastener with a long set of 1/4" drive socket extensions.

I'm thinking that a better solution would be a permanently installed drive tool which extended the fastener to the top of the box.  The solution I am imagining would leave the fastener placed permanently, or rather at an earlier stage of assembly, then allow the fastener to be driven without having to fish for the fastener from the top of the box.

Design Considerations

The grip length of the fastener is unchanged
Driving the fastener is the primary consideration
A secondary consideration is positioning, the fastener remains in a slot and needs to be positioned in the slot to capture the thread on the far end.
A bonus would be if the coupling allowed the screw to be driven without changing the depth of rod where it is being driven.  This would seem to require a coupling which could trasfer torque and also be telescoping.

To assist in imagination, I'll say that this is an 10-32x2" socket head fastener, driven from 18" away.

Possible Solutions:
 - Use an adhesive to bond a hex driver to the fastener then run a dedicated socket or bit extension to where it can be reached at the top of the box.
 - Weld a steel rod to the fastener.

Looking for better ideas and/or products which would make this easy to implement.


texts: How do I compute/plot the open loop transfer function of a system given its state-space description?

texts:
Suppose I have a dynamical system with a continuous time state-space description given by the matrices A, B, C, and D, under full-state feedback u=Kx (where x is the state and x is the control input).

How do I compute the Bode plot of the open-loop system, as I would do in traditional frequency-domain analysis?

As a simple, concrete example, consider the problem where the plant is a mass on a spring, on which I can exert a force $F_{ext}$. Suppose I use a PID controller to control the position of the mass.

A state space description of the plant (with an adjoined integrator state to be used by the controller) is:

A = [0, 1, 0; -k, -g, 0; 1, 0, 0];
B = [0; 1/m; 0];

And the PID controller can be realized through full-state feedback with the matrix:

K = [kp, kd, ki];

Meanwhile, in the frequency domain, the plant has transfer function $G(s)$, and the controller has transfer function $H(s) = k_p + \frac{1}{s} k_i + s k_d$.

In frequency domain analysis, the transfer function $GH$, the open loop transfer function is of interest. This is what we example, for example, to determine gain margin and phase margin.

How do I obtain $GH$ given $A, B, C, D$ and $K$?


texts: Does the plant transfer function of a system change with variations in the reference variable?

texts:
I am designing a PID controller for a system that requires several step changes in the reference variable (concentration of solute in a tank) over a set period of time. I can find the plant transfer function experimentally, by applying a step change in the input (flow rate) and measuring the resulting changes in concentration over time.

What is not clear to me is: does the plant transfer function change each time I apply a different step change in the input variable (e.g. from 0.1 L/hr to 0.08 L/hr then after a while from 0.08 L/hr to 0.05 L/hr), or is the plant transfer function fixed for a given system (regardless of changes in the reference/input variable)? Thanks in advance.


texts:
While browsing a local news site, I stumbled upon this picture of a broken bus door. The glass was fractured due to a rock impact. As far as i know there are no heating elements on the window section in the picture. Now, what interests me is the apparent periodicity and structure of the fracture pattern.

Are periodic fractures something commonly encountered in tempered glass?
Is the mechanism that generates such fractures understood?
Is it a consequence of the manufacturing process?
Perhaps the way the glass is affixed to the door?

Thanks in advance