texts: Is the viscous friction coefficient of a BLDC motor dependent on the system inertia?

texts:
I have to model the required torque to move a system composed of several mechanical parts such that this system performs a motion profile. It is a Maxon drive composed of an ECX Speed 16L BLDC micro-motor with a mounted GPX gearhead.

I am confused as to how to calculate the viscous friction coefficient for this drive, which is not indicated in the datasheet. However, the datasheet does indicate the "mechanical time constant" and digging in a robotics book (Robotics by B. Siciliano, Springer), I found that the mechanical time constant is simply:

$$
\tau = \frac{I_m}{F_m}
$$

$\tau$ being the mechanical time constant. The book states that for an electrical rotary actuator, "$I_m$ and $F_m$ are respectively the moment of inertia and viscous friction coefficient at the motor shaft".

The "at the motor shaft" portion of the phrase confuses me. Does this mean that the inertia at the motor shaft is the whole system inertia? This would mean that the inertia of all the parts combined will first have to be reflected through the transmission (in this case belt-pulley transmission + gearhead). If this is the case, I do not see how $\tau$ is a mechanical constant for the BLDC motor since the system inertia could change if parts are added.

Is $I_m$ simply the rotor inertia of the BLDC motor? Or do I have to take into account the gearhead too, making $I_m$ the drive inertia?


texts: What are these reflective triangles on the sides of train track rails for?

texts:
Last night while waiting for the train at South Yarra station in Melbourne, I saw these reflective triangles stuck on the sides of the train track rails. They were evenly spaced a few metres apart for as far as I could see down both ways of the tracks. They could only be seen on the far pair of tracks, and the tracks on the other side of the platform also had these little triangles on the far pair of tracks. I'm assuming that there are also triangles on the near pair, but stuck on the other side of the rails where I couldn't see them.

There is a picture of the platforms and tracks on the Wikipedia article for South Yarra Station from 2014 which shows they weren't present then.

I can't work out what these reflective triangles might be used for. What is their purpose?


texts: System Identification 1-d altitude control

texts:
One dimensional altitude control of a hovercraft. The model's dynamic equations that I came up with are, I treat the hover craft as a rigid particle and my goal is to have it hover at or reach a certain desired height.

$$F = ma$$

$$X(t) - mg = ma$$

$$ma + mg = X(t)$$

Taking Laplace Transform yields

$$m \cdot s^2 \cdot Y(s)  - mg \cdot U(s) = X(s)$$

$$Y(s) = \frac{X(s)}{m \cdot s^2} + g \cdot U(s)$$

where X is the input thrust and Y is the output and U(s)  is a constant unit step. However I can not seem to isolate for $$Y(s)/X(s)$$. I think it may have something to do with me including the gravity force in the dynamics equation when it may act as a disturbance but I am not sure.

When creating a dynamic model of a system How do we handle the constant force of $$mg$$ do we treat it as a disturbance, and if so how do we go about doing that?


texts: First Moment of Area - Meaning of Sign/Sense

texts:
I was trying to find the moment of area about point A on the following figure:

I prefer to use integration, since it can be extended to different shapes, and did this:

$\displaystyle Q_z=\int_{-25}^{25}\int_{-23}^{35}y \, dy \, dz=-17400 \:\mathrm{mm}^3$

However, the solution I have been given states that $Q_z=17400 \:\mathrm{mm}^3$

This made me wonder about two things:

What is the meaning of the sign (if there is any)?
What have I done wrong in my calculation (aka "What am I not understanding here?")


texts: Melt plastic powder bed with radiant heat?

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I want to melt a bed of plastic powder so that the powder bed once melted and then cooled forms a solid sheet of plastic.

In order to melt the powder I'm thinking of passing a nichrome (Ni80/Cr20) wire over the bed without the wire touching the bed. With the direction of motion of the wire perpendicular to the length of the wire.

The heat from the wire should radiate from the wire and pass into the plastic powder in order to melt the powder. Is this possible? Is it possible to to melt plastic powders through heat radiation from a nichrome wire.

Conditions:

As an alternative to melt the bed with radiation, one could heat the bed's platform. But I can't do that because the  bed's platform is made of plastic and might begin to melt if I heat it. So heating through radiation is the only viable option I've thought of.
Bed dimensions: 30 cm X 15 cm.
I can use a wire of any diameter. Single wire or multiple wire in parallel.
Melting temperature of plastic powder  used is 270-300°C.
Any distance between the wire and the powder bed is possible. Close distance between the wire and powder is preferred.
If not nichrome any other material can do the job.


texts:
I am a novice in control systems and just learned about PID controller.

So after watching tons of youtube videos I realized that the input of my plant is actually defined by the error. For the case of PID, when a gain multiplies to the error plus the integral of past errors plus the rate of change of error is the new input of my plant.

But what if my error is zero and plant works ideally? meaning there is no history of error being anything other than zero. So three terms have been and will be zero.  Does that mean the input of my plant is zero? That means that the desired output of each plant always should have an input equal to zero so that it would be equal to the setpoint?


texts: Calculation of the specific CO2 emission of a cogeneration plant for the produced electricity

texts:
Suppose I have a cogeneration plant that runs on natural gas and produces heat and electricity. The heat effeicieny is $\eta_{th} = 0.4$ and the electricity efficiency is $\eta_{el} = 0.4$.

The burning of natural gas produces 215 g/kWh of CO2.

For the calculation of the CO2 emission of the generated electricity from the cogeneration plant, one could now calculate $\frac{215}{0.4} = 537.5$ g/kWh.

However, I would like to calculate the CO2 emissions for the electricity generation of the cogeneration plant, taking into account that CO2 emissions are saved because another heat generator has to generate less heat.

A natural gas boiler with an efficiency of $\eta_{th} = 0.9$ is taken as a reference for heat generation. So the 1 kWh of heat is generated with $\frac{215}{0.9} = 238.88$ g of CO2.

How do I calculate the CO2 emissions for the electricity generation in this case?

My calculation attempt:

First I would calculate how much CO2 emssions the boiler has for 0.4 kWh:

$238.88 \cdot 0.4 = 95.55$ g of CO2

Then I would subtract this value from the previously calculated co2 emission of the electricity:

$537.5 - 95.55 = 441.95$

The electricity generated by the cogeneration plant would then have a CO2 emission of 441.95 g/kWh.


texts:
I have some questions about overhead line and substation equipment in high speed line.
My first question is about if all the overhead voltage is the same for all the intervals of speed? I mean for 250, 300 and 350 Km/h is it 25 Kv?
My second question is about if we want to increase speed of line, for example, after 5 years, should we change all these equipment  related to its consumable power? Since when the speed increases, it needs more power? What can we do to have a cost-effective solution?

Thank you in advance


texts: Clamping force of a bicycle quick release skewer

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In brief: between a standard quick-release skewer and a bolt-on skewer, which will provide greater clamping force?

More detail:

Modern bicycle wheels are held in place by clamping skewers that run through hollow axles.  The typical "quick release" design has a built-in lever on a cam that you close with you hand to secure the wheel, like this:

If you prefer not to have the quick-release mechanism on your hub for whatever reason, it's possible to retrofit your axles with "bolt-on" skewers which forego the cam and lever for simpler hex heads:

The torque spec for bolt-on skewers is generally 7 N-m, while Shimano recommends 5.0 - 7.5 N-m tightening torque on their quick-release skewers.

My question: How would these torque values applied through their respective systems (7.5 N-m through a cam versus 7 N-m through a threaded fastener) compare?  Which would likely result in a higher clamping force (if we're assuming proper lubrication with no contamination, etc.)?

Generally, people seem to believe the bolt-on design clamps down better, but I've seen some people insist the opposite is true.  Conventional wisdom in the bicycle world is notoriously dodgy, so I was hoping to get some expert insight.


texts: Finding Transfer Function between specific points

texts:
Hi I have this block diagram:

Now, I want to reduce it to such a block diagram:

How do I find  H ?
I am looking for a general method, of how to approach such problems.

Here is what H should be:


texts: What makes suspension bridges unsuitable for railways?

texts:
I recall reading in an old issue of Model Railroader an article about railroad bridges.  In it, the author mentioned that you shouldn't have a model suspension bridge for a railroad track on your layout because no such arrangement would be prototypical.

In his own words, "suspension bridges and trains don't mix."

I realize that the author probably wasn't an engineer (at least in the sense of this site), but his remark did get me thinking.  I am somewhat of a railroad buff, and I can't think of a suspension bridge for trains - the closest thing that comes to mind are the trolley tracks that were on the Brooklyn Bridge*.

I understand that there wouldn't be many suspension bridges for trains, since other bridge types would be better suited (cheaper, easier to build, etc.) but why are they so rare?

*Bear in mind, though, I live in the US, and am pretty unfamiliar with foreign railroad infrastructure.


texts:
Question: How is shelf deflection determined?  More specifically, how is the deflection determined when one or more edges of the plate have reinforcing edging applied to them?
I have been able to find plate deflection equations in a number of places, but of the resources I have found, they are limited to plates without any edging at all.
I have found a shelf sag calculator which happens to be well known and loved by woodworkers.  But their calculator only handles a single side of edging, and they don't provide any explanation of the formulas that are used.  And depending upon what deflections I find, I may need to be able to evaluate the deflection in a lattice structure with a supporting skin.
I would assume that the edging can be treated as simple beams supporting the plate, but I don't know how to apply that support to the plate.
Is there a standard set of equations and / or plate geometries that can be applied to estimate what the shelf deflection may end up being?  Or is this getting into the non-trivial end of analysis and design?

Background:  For a hobby project of mine, we need to build shelving to support a variety of items which cover a range of shapes and sizes.  Some items are large and comparatively lightweight (e.g. a student's desk).  Others are small, dense, and kind of heavy (e.g. concrete block).  And of course, there are some in the middle for both size and either side of the weight spectrum.
We're planning on building several sets of shelving to accommodate the various sizes of things that need to be stored.  And while we do have to design for the unknowns of the future, we're still trying to optimize costs through the amount of material used.


texts: Differential equation of the vertical displacement of a cable

texts:
Given a cable (totally flexible) fixed at both ends, subjected to a vertical force $f(x)$ in his plane, with variable area $A(x)$, and variable elasticity $E(x)$ I want to find the differential equation of the vertical displacement $y(x)$ in his equilibrium position.

I think the differential equation is:
$$\frac{d}{dx}\left( E(x)A(x)\frac{dy(x)}{dx} \right) = f(x)$$
But I can't get to that or something similar.

I have tried the following:
The tension of the cable will be $\vec{T} = T\vec{u}$ where $\vec{u}$ is the vector tangent to the cable. Setting equilibrium in the direction of the cable we get:
$$ \vec T(s+\Delta s) - \vec T (s) + \vec f(x) = 0$$
so:
$$ \frac{d \vec T(s)}{ds} + \vec {f} (x) = 0 $$
For the basic equations of elasticity we know that
$$ T = A(x)E(x)\epsilon $$
But I don't know how to combine this information to get an equation with $x$ as an independent variable and $y$ as the dependent one.


texts:
I finished taking my control theory course, and I want to build an RC car that has cruise control. So I started off with the force analysis, and I got external forces that are constant. For example if the road is sloped, then the gravitational force is holding the car back. Another force is rolling resistance. I believe these are the only two considerable forces that will resist the car's movement; however, this does not provide a stable system.

Doing a little research online, I found that most models, if not all, say that the external forces are proportional to the velocity of the car. I understand how that can be related to the spring-damper model, but I don't see why the external forces are proportional to velocity when all the forces are constant. For instance, rolling resistance only depends on the weight/normal force of the car--not velocity. So how can I say they are variably dependent on velocity?

Also, let's assume that the forces are proportional to velocity, then how would I figure out that proportionally constant?

I am trying to create a model in simulink with some sort of controller, probably PID, then later transfer it into reality. And I am already stuck with the main system. Thanks for any help!


texts: What kind of pressure switch can I use for pressures up to 5-10 tons/cm^2?

texts:
I need a pressure switch for an electric circuit that has to be closed once a piston is compressing at a pressure of (approximately as we haven't specified how much force we have to use, and maybe it will be greater) 5 tons/cm^2 (75000 psi). The problem is that I can't find any model that satisfies these characteristics due to either

them not being as common as to be talked about in the sites I can access
my abilities at intelligent Google search are not good enough or
them not existing.

I can't believe a component like that doesn't exist and I'm very confident about my intelligent Google search skills so, can someone tell me if there's a chance I can get to know about components like that?

I would be very thankful if anyone could give me a model or a brand or any reference or recommendation to find such information (or about why I won't).


texts: What is the feedback signal used in the speed control of a brushless DC motor?

texts:
In a brush-less DC (BLDC) motor the commonly used speed is sensed using the feedback from Hall effect sensors and the back or counter EMF. The linked article on Wikipedia also mentions that 'Other sensorless controllers are capable of measuring winding saturation caused by the position of the magnets to infer the rotor position.'.

Are these the only possible sensors used to sense the speed? Additionally, how can we estimate the load torque in a practical and commercially available BLDC motor?


texts: What is the difference between TE and TI?

texts:
I have done some research about the subject but I can't find the difference between Temperature Element (TE) and  Temperature Indicator (TI)

Here is an image of the P&ID of the project am working on if it can help clarify my question.


texts: What is the deepest bridge pier in the world?

texts:
I have tried searching for this, but I am unable to find a good answer.  There is all sorts of stats about the longest bridge in the world, the highest, the longest span, but I think one of the most difficult things is the depth of the pier.

From my internet search I found a San Franscisco article that says the deepest pier in the world is on the Bay Bridge at 242 feet (~74m).  This was built in the 1930's, so does the feat of engineering still remain at the deepest, or has it been superceded?

I initially wondered about this because of Boris Johnson refloating the idea of the idea of a road bridge between England and France.  At 26 miles, that would not be a world breaking engineering challenge, but it seemed to me the depth of the piers.  The Straight of Dover deepest point is 68m, so this does seem like a feasible project from a engineering point of view, but I think the question remains whether it is an efficient use of resource.  Particularly when the Channel Tunnel is only running at 48% or so.


texts:
I have 5/8" PEX piping (I.D. .475") throughout house.  Am connected to city water supply (@ 40# psi)
all new PEX pipe, all new valves....no leaks

In April, 57,000 gallons reportedly flowed thru the house.
In May, 37,000 gallons reportedly flowed thru the house.
In June, 11,00 gallons reportedly flowed through the house.

History, In January, February, and March...only 2000-3000 gallons flowed each month.  From July to Dec, the flow rate was back to 2000-3000 each month.

Based on the 5/8" PEX pipe diameter, with the 40 psi pressure, how many gallons is possible to flow in one hour?   With a 30 psi, whats the flow rate per hour?  With a 50 psi, whats the flow rate...in gallons per hour for the 5/8" PEX?

How do I figure the flow rate, (gallons per hour) coming to/through the 5/8" PEX depending only, on knowing the cities psi at the time?  The psi could be a variable.


texts: why did my ceramic matrix composite turn out brittle as snow?

texts:
I have attempted making a ceramic matrix composite (cmc) by wetting glass fiber cloth with waterglass and baking it at 200°C. The resulting material disintegrated on touch. Unwetted fibers did not change their properties after baking.
How can this be explained?
Did suction caused by evaporation of water pulled apart pieces of sodium silicate attached to fibers, ultimately pulling apart cracks on the fiber surface?
Shouldn't glass fiber surfaces be "crackless"?


texts:
So I am working on a personal project that involves an IV pole. In a standard IV pole with lockable casters, there is still some give in the vertical section of the pole. If you apply a force to the top of the pole, it will move a small distance.
How would I calculate the force required to push the IV pole a set distance?
If it makes a difference, I am going to be pushing the pole with a slider-crank mechanism driven by a motor. Really, I want to figure out the torque required for the motor, but I can calculate that myself once I know the force.
I tried to make a force diagram, but I must be forgetting some stuff from school. Can I just assume that the force has to be greater that the weight of the section of IV pole that moves?
Thanks for the help and let me know if you need any clarification on anything.


texts: I'm looking for the simplest way to increase rotational speed from 120 to 5,000 rpm for a light duty device

texts:
I'm currently designing a device and want to increase speed from 120 to 5,000 rpm. Device is lightweight, hand operated, free spinning, low torque in/out. Picture a cheap fertilizer spreader from Home Depot. They increase speed maybe 2 or 3:1, I'd like to up that to 40:1 or so.
I'm currently sketching a chain & sprocket, bevel gear set (need to redirect 90 degrees), and a spur set arrangement to achieve the increase, but wondering if there's a better/simpler way.
I'd like to use all off the shelf parts as I can't afford to custom design anything. I'd like to find an existing speed increaser, but and I've found are super heavy duty and will not work for my application.
This is a home project and I want to keep costs minimal, hence replacing gears with chain & sprocket to reduce cost. Interested to hear what ideas I may not be thinking of for this, thanks.


texts: Air Conditioners: Compressor Explosions?

texts:
In this piece of news it is said that an Engineer and Blogger named Utpal Chakrabarti has died after explosion of air conditioner compressor.

My question is, how dangerous air conditioners are? Which is more dangerous: Window Type ACs or Split Type ACs?


texts: Choosing a proper BLDC motor for lab centrifuge

texts:
I'm trying to make a swing rotor centrifuge and find a proper BLDC motor to reach 6000G with capacity of 4x50ml Falcon tubes. I did the calculations roughly but I'm not so sure about them and also couldn't find a proper motor for my calculations.

My rotor will be something like this;

Well for my calculations;

Mass of the system : 250gr (50gr for body and 4x50gr for tubes)
Radius of the body : 6.5cm (I'm trying to minimise it to minimise the inertia)
RCF : 6000
Ramp-up from 0 to 6000G : 10s

And probably my supply voltage will be 12V or 15V and my custom ESC can deliver up to 20A.

And from those inputs I get;

Inertia : 0.000528125 kg*m^2
Angular Acc. : 95.1056763541775 rad/s^2
RPM : 9100
Torque (with %20 safety margin) : 60.27mNm
Power : 57.4W

But for example when I go and search for a motor such as 200W High Power Brushless Outrunner DC Motor Bldc Motor Price

It seems the torque is well within specs. But to get 9100RPM I need to supply 10.1V which may cause decrease in torque (?).

Also taking Torque Constant into account I get; 5.7A and it seems too low to me. I mean can I really make this thing spin from 0 to 9100RPM  in just 10 seconds with just 10V and 5A?

And there is also Back EMF which I still didn't quiet understand. For the motor in the link, BEMF constant is 0.0011V/rpm and when I calculate torque producing voltage I get 0.6V, does this mean that I actually drive this with 0.6V? If so, than I need 95A to spin it with 9100RPM? But with terminal resistance involved, my available current is 0.6/0.1 = 6A, so I can't drive this with 95A, because of terminal resistance?

As you can see, I'm really confused and I'm really new at this things, so any help would be great.


texts: How do I verify the reaction forces of an FE model due to a response spectrum

texts:
In the case of a static calculation of a structural model, one can verify the model by checking the applied and reacting forces to be equal zero.

I would like to adapt the same principle for a structural model with a response spectrum as an input.

Is it correct to do the following:
1) perform a frequency extraction procedure to obtain 90% of the eigenmodes contributing to the mass and rotational inertia.
2) calculate the mass of structure being excited and multiply it by the peak acceleration amplitude given in the response spectrum, eg 20g.
3) its not clear what this step should be... is there something I can do with the modal participation factors to help me calculate the total reaction load?

Any suggestions will be welcome.

Best Regards


texts:
I am searching for information on how finite element code (abaqus /ansys) could be used to model the contact stress behaviour between 2 bearing surfaces?

The key point is that there is an additional hard coating n both surfaces so as to reduce wear.

How would one model this additional hard layer?

Would this hard layer be represented by an additional layer of elements with a higher elastic modulus?


texts: what kind of welding setup to mig weld high-temp stainless

texts: In my initial foray into welding I am looking at welding some 300-series stainless tube, no thicker than 1/4" and more likely 1/8".  I have not yet purchased a welding machine, and wanted to get some feedback on how the metal composition impacts what kind of welder I need.


texts: Why don't cable cars use multiple cables?

texts:
I was reading up on cable cars, and it struck me as odd that they only use one cable. While the system isn't likely to fail, and there are contingency measures (e.g. brakes) in case something happens while a car is going downhill, it seems odd that the designers of, say, the San Francisco cable car system didn't add in at least a second cable.

Why is this?

My guess is because of turning (explained here) - if there were two cables, one would have to go faster for a given turn (unless the "let go" method was used).


texts:
I am solving problems through Fox and McDonald.Here is the problem

I tried by finding out the torque due to viscous forces which is $$\tau_1=\mu(2\pi Rh)\frac{R\omega}{a}$$ and the torque due to mass m1 as $$\tau_2=m_1gR$$ Writing into equation $$\tau_2- \tau_1=m_2R^2 \frac{d\omega}{dt}$$ integrating this and using boundary condition $\omega=0$ at $t=0$ I got $$\omega=\frac{m_1ga}{2\pi Rh\mu}[1-exp(\frac{-2\pi \mu htR}{am_2})]$$ . However I am missing $m_1+m_2$ instead of $m_2$ in the exponential part.Any ideas? Thanks.


texts: Can you get the ratchet mechanism out of a socket wrench by itself? Anyone know where if so?

texts:
Title pretty much says it all; looking for a reversible ratchet hub for a special latch that I'm designing.  Definitely open to any ideas/sources that the community at large might have.
Thanks!


texts: What material properties matter when selecting a material to withstand a specific pressure (as a sealed tank)?

texts:
I want to design a tank to hold liquid propane. The proposed tank would have one inlet valve, one output valve, and no sharp edges. I've read that the pressure required to maintain propane in a liquid form at 100 degrees Fahrenheit is 177 psi.

An example analogous to my case; I have a spherical, 40 sq. in. tank in which I want to store liquid propane. If propane must be held at a pressure of 177+ psi to remain in liquid form at 100 degrees Fahrenheit, then the tank must be able to withstand 177 psi * 40 sq. in. = 7080 lbs at all points of the tank's surface. What material properties should I look at to find a material suitable to withstand that force? I want to think tensile strength, but would like an expert's advice.


texts: Switching batteries from series to parallel - technical solution

texts:
I'm thinking of developing a pocket 'power bank' that could provide both 6V and 12V - a charger to charge either a phone (with 6V) or a notebook computer (with 12V).

The electrical diagram is simple enough; switch attachment of the terminals like below.

The schematics is not everything though. I'd like the charger to have two sockets, one providing 6V, the other - 12V, and to "sense" what to serve by having a plug in either of the sockets (let's say using both at a time is forbidden; I can place them in such a way that both plugs won't fit at a time, say, a slider that opens either of them but never both).

Best if the "sensing" was done in the simplest, mechanical way (e.g. there are sockets that provide an extra "sensing" contact that shorts to mass if the plug is in), but if that would prove too difficult or mechanically complex, a more complex electronic solution would work too, providing it won't drain the batteries when nothing is plugged in. (and of course the circuitry must accept external charging current - accepting only one of the two, either 6 or 12V is fine).

And of course while just cutting one of batteries off for 6V would be the easiest solution, it would halve the capacity for 6V application and cause parasitic charging issue when switching to 12V after the 6V power has been depleted, so it's not really an acceptable solution.

So, how to build such a circuitry - that provides power from two batteries, in series or in parallel depending on which socket was used?


texts: What is this "clamp" place on a piece of bar stock while turning it in a lathe for?

texts:
I am watching a Youtube video depicting someone machining a crankshaft for a miniture rotary engine. Around the 4:27 mark after preparing some bar stock the person in the video places some sort of clamp on the stock before putting it into a lathe to machine further.
What is the purpose of this clamp?


texts: galvo scanner + rotating off-axis mirror for beam offseting?

texts:
diagram:

Assuming

1) the scanner can angle a beam anywhere on the circular off-axis mirror and

2) the off-axis mirror can be rotated as an the diagram to any angle needed,

can the beam shooting at any point on it from the scanner be made parallel to the middle beam bounced off of the off-axis mirror?


texts: What is the model name of this two-stroke carburator?

texts:
There is a two-stroke engine carburetor that is found in many two-stroke engines made between 2000 and 2015. For example, you find it in hedge trimmers, weed wackers, chain saws, etc. Who makes this carburetor and what is its model number or series?

I found out the answer to this question. If the question gets reopened, I will post the answer.


texts: addition of non paralle shearing forces and stresses

texts:
I would like to ask for help regarding the summation of non parallel shearing forces acting on an elastic body.
In the image force F (Left to right direction,in yellow) acts on the top horizontal surface "A" of an elastic cuboid body that is attached to the table only at its bottom surface.  I know how to calculate the stress and strain. But what happen if a second force "F_vertical" (in black) acts on the top portion of the vertical surface facing the reader, again direction left to right. how do I add the stress and strain imposed by both forces.
(I am a physician not an an engineer or physicist ).

thank you
Yehuda Raveh


texts: which type of casting will give higher cooling rate, casting in thin water-cooled copper mold or casting in thick copper die?

texts:
It is will known that increasing cooling of a metal casting will lead to finer micro-structure which mean higher mechanical properties.
 If I have 2 molds one is thick copper die ,& second is just thin-walled copper cup or mold cooled by water. which one of them excepted to cool the molten metal i.e. aluminium faster ?

the calculated heat diffusivity of copper is : thermal conductivity x specific heat x density = 385 x 0.385 x 8960 = 1328096 m²/s

while for water it is just : 0.6 x 4.2 x 1000 = 2520 m²/s only !!

so, the copper can transfere heat 527 times faster than water.

by calculations it seems that copper die have higher cooling power as it has higher thermal diffusivity , but in real life it seems water have more cooling power. I am so confused.


texts:
In preparation for a Fluid Mechanics experiment, I am looking for a simple commercial ready made
apparatus to generate a linear velocity trend to prove a new theory:

https://aip.scitation.org/doi/abs/10.1063/1.4964761

The load is around 10kg starting from rest to reach linearly say a 0.5m/sec within a distance of say 0.5m..
Any hints ? :)

72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13

The Leading Edge theory: a new insight into the laminar Boundary Layer by Mohammad Gabr

The Abstract :

The flow properties at the leading edge of a flat plate represent a singularity to the Blasius laminar boundary layer equations; by applying the diffusion equation where the velocity of a moving flat plate in a stationary fluid is diffused to the far field, the leading edge velocity profiles are studied. Experimental observations as well as the theoretical analysis show an exact Gaussian distribution curve as the original starting profile of the laminar flow.To conclude; the main key results are as follows: [1] The velocity profiles at the leading edge of a flat plate are Gaussian Curves that grow in space and time; whereas the Blasius velocity profile is a part of the general Gaussian curves solution. [2]A new method to calculate the friction drag is successfully tested, based on the displacement area of the leading edge velocity profile. [3] In order to obtain the final physical proof of the new theory it is recommended to carry out experiments using an ultra-thin flat plate moving in a stationary fluid and measuring the velocity profiles at the leading edge with different measurement techniques.


texts: Effect on pavement by light tracked vehicles with rubber inserts

texts: Is there data available to quantify the effect on pavement by light tracked vehicles with rubber inserts.  One example of such a vehicle is the M113 armored personnel carriers shown below.


texts: Advantages of quadruple motor electric car

texts:
When Tesla introduced the dual motor model s it had better range and performance (so better in everyway except price).

Would a quadruple motor car (one per wheel) have even better range and performance?
Or
Was the increase in range and performance not due to the number of motors but due to the ability to remove the rear drive shaft etc?


texts: Calculate amount of evaporative coolers needed to cool down an area

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I have a task to create a software that calculates how much evaporative coolers are needed to maintain a certain temperature in a given room. I need to create a simple form, where variables are next :

1 - Location (i can fetch dry and wet bulb temperatures) 2 - Desired Temperature 3 - Air changes per hour 4 - Area of the room (m2) 5 - Number of people in the room

I am working with AOLAN evaporative coolers, and i have all the specification from them for the devices used. I just can't wrap my head around the calculations. So my question(s) are rather simple : How do i calculate the amount of coolers needed to cool down an area with all the given parameters up there.

I would love if someone could give me guidelines into how to achieve this.


texts: Piezoelectric matching/backing layer materials

texts:
To maximize the piezoelectric transducer reception/transmission power we must choose the correct backing/matching layer materials, I'm working on a project to measure a steel tank liquid level (non invasive from the bottom, sensor must be glued) and we have the electronic board finished and the ceramic piezoelectric disk, but we are lacking of knowledge of choosing this material that I mentioned.

The tank that we'll measure is a 3 meters tall, 8mm steel bottom wall.

As far as I read the material selection must take in consideration the acoustic impedance, am I right? Also someone recommend using closed cell foam as backing material and stainless steel as matching layer, but we're not sure about the thickness.

Do anyone have recommendations regarding the correct materials/layer thickness for this application?


texts:
I am trying to figure out how to calculate either the distance or angle of 2 Idler Gears in a Timing Gear Configuration like so:

I have been able to eyeball things, so they are approximate. I would like to come up with an equation to get an exact number for either dimension A or B. I came up with an angle for A of approx 44.7 deg where all the teeth mesh.

UPDATE:

I was able to use CAD to figure out how this needs to be done. Now I just need to figure out how to calculate all of this:

Basically what I ended up doing is all the angles are multiples of the tooth angle for each gear. Next I took a line at the tangent points of each gear perpendicular to a connecting line between each angle. See the blue lines in the above picture.

In this problem the tooth angle can not be used to calculate the spacing directly because of the gear mesh as seen on the bottom of the 22 tooth gear as seen in the top picture. The meshing actually takes place off of the tooth angle.

Just to clarify I am using 64 pitch gears, the diametrical pitch is calculated using standard gear equation:

Dp = N/P

Where:

N = Number of teeth

P = Pitch


texts: What's the term used for machine parts orientation naming on the sagittal plane and from inside the machine?

texts:
I know that the current title can be hard to understand. Let me try to explain our problem: We do manufacture and service industrial machines and we are currently updating our spare parts manuals for our distributors. In those manuals we do name some of the parts based on their placement for different planes on the machine like "top-bottom" part, "front-back" part, and of course the most problematic one "left-right" part. (It's problematic because people tend to name parts on the sagittal plane from their standpoint which reverses the placement of the parts. "Left" and "Right" do switch in that case.) When we name the parts on the sagittal plane (I'm not sure of the term for the plane. I've just looked it up) we use the driver's seat orientation which means we imagine ourselves standing in the machine facing its front side and deciding on the left-right nomenclature based on this position.

We need to educate our worldwide distributors and service technicians about this nomenclature and every time we explain it with sentences like the one above.

I'm trying to find out if this orientation has a standard naming which is accepted worldwide. Terms like "Driver's seat placement" or "Driver's seat orientation" doesn't do the job most of the time and needs further explanation.


texts: How to attach a metal rod to an air cylinder?

texts:
I have signed up for  an engineering class, and the first project is purely mechanical. I've never done mechanical work, so this is quite interesting to me. I have come up with the following project - create a snack box that can only be unlocked by someone standing far away from the box. Here is the image with the basic idea:

The problem I am having has to do with the rod attachment to the air cylinder. I can bend the metal rod to enter the hollowed out wooden piece attached to the lid, but how do I keep the rod firmly connected to the cylinder?
This is my purchase list - https://www.amazon.com/hz/wishlist/ls/ONWDBSI72VQ6?ref_=wl_share.
Since I am completely new to this - if you have improvements on the design, or better purchase suggestion please let me know.


texts: How can I calculate pressure change due to reaction?

texts:
I'm studying a reactor, that can be imagined simply as a pipe in which a reaction advances.
In this reactor, the inlet and outlet flow are constant as is the temperature.

If that reaction is equi-molar no pressure change happens, otherwise in a reaction like steam reforming, where product moles are greater than reactant ones, I should expect an increase in pressure.

$$CH_4+H_2 O \rightleftharpoons CO+3H_2$$

How can I calculate the pressure change due to change in the number of moles?

PS: In a closed system (like a vessel) I'd use the ideal gas law: $pV=nRT$ ... but this is not the case!

I was thinking about:

steady state grants me $\dot m|_{in} = \dot m|_{out}$
I can express mass flow as $\dot m = \dot n \cdot MM$ where MM is molar mass
and as  $\dot m = A \cdot u \cdot \rho$ where A is the cross sectional area (constant) u is mean speed and $\rho$ is density
I express density with ideal gas law $\rho = {p \over {R \cdot T}} \cdot MM$
finally I get $\dot n = A \cdot u \cdot {p \over {R \cdot T}}$
now, since A,R,T are constants
taking the reaction abovementioned, if $\dot n$ rise up $u \cdot p$ have to follow this trend.

How, who, what, does make pressure constant while speed rise up ?


texts: What is the physical interpretation of the eigenvalues of the stiffness matrix in the finite element method?

texts:
Given an equation of motion of an undamped system $\mathbf{M}\mathbf{\ddot{q}} + \mathbf{K}\mathbf{q} = \mathbf{f}$, $\mathbf{M}$ indicates the mass-matrix, $\mathbf{K}$ the stiffness matrix, $\mathbf{q}$ the time-dependent displacement, and $\mathbf{f}$ the applied force. The roots, $\omega^2$, of the equation $det(\mathbf{K} - \omega^2\mathbf{M}) = 0$ indicate the vibration frequencies.

My question is: what is the physical interpretation of the eigenvalues of the stiffness matrix $\mathbf{K}$?


texts: Is there a universally accepted way to refer to choosing a more powerful motor for an application?

texts:
One antonym word I can think of is "derating".  If I say "derate motor for pump X", it can mean "select a motor with lower power output, since the pump doesn't need a more powerful motor".

But what about selecting a more powerful motor?  How can I say "I want to ____ the motor for this pump" and mean "up" the motor, "bump up" the motor, "choose-a-stronger" motor?

I am looking for a phrase or single word, that can be used to speak of this concept clearly.  For example when explaining the concept to the sales team or to the customer (user of the engineering application).


texts: How to do section classification for a plate or flat bar?

texts: When doing section classification to calculate buckling of a plate subjected to some bending and compression on its edges, do we consider the plate width as outstand of flanges "c"? What are the limiting values for plate and bar in section classification?


texts: 321 stainless electrode corrosion factors? (arc erosion resistantance)

texts:
I am looking to lengthen the life of 321 stainless Steel electrodes (arcing through quartz glass).

If I seal off the electrodes from oxygen (thermally conductive potting compound) will this increase the high-temp / high-voltage corrosion rate?

I thought keeping out humidity would help long term, (current electrodes are rusted out even though they are stainless), but I read about how the SS metal may need oxygen to heal the surface?


texts: Could Tesla have REALLY shaken a building with a little oscillator?

texts:
I came across this story while reading about Nikola Tesla ground-power scheme. Supposedly, he created a little oscillator that could be plugged into the ground, tuned to the right (resonant) frequency, and clamped on to an entire building to shake it down. Could this work? Tesla often exaggerated or lied about his inventions to bring in investors (and therefore became a "New Age Cult Hero"). Yet resonant oscillation can be really powerful -- as seen in the oft-mentioned Millenium Bridge debacle, or in the wine-glass-breaking-scream trick, or a person on a swing set (Side note: I knew someone who said that he once went the full circle!). However, it can only work if more energy is put in than is lost with each cycle. Would the energy lost from the oscillations of the structure be more than covered by Tesla's little vibrator?
Also, his idea to "break apart the Earth" with resonance couldn't work... could it?


texts:
I am currently a project intern, working on Light Fidelity (Li-Fi). Most part of the project deals with development of software for Renesas Micro controller.

I have a simple doubt regarding timer and interrupt programming.

As a part of my project, I have to generate an interrupt as soon as the timer overflows. I am trying hard and finding it difficult to achieve it . Also. I need to know about how to calculate the timer overflow value, so that an interrupt is generated.

It would be great help,if these questions are solved and explained in detail.

Thank you!


texts: How do you get a closed vessel to >90,000 psi internal pressure

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Im trying to build a cold isostatic press with a internal vessel area of 300mm3.
A cold isostatic press forms green metal components using pressures greater than 90,000 psi.
Using an oil or water/emulsified oil solution do they use a high pressure pump and connect it to a hydraulic intensifier?
Any direction is greatly appreciated thank you.


texts: What is the advantage of using D'Alembert's principle when dealing with dynamic systems?

texts:
In our dynamics class, it is highly recommend to us to use D'Alembert's approach rather than the traditional approach to solving dynamic problems. For example, consider the problem of a block resting on a surface (we know the cof): Rather than calculating the frictional force of the block on the slope and comparing that to the component of weight acting down the slope, we draw the free body diagram including the inertial force and directly solve for a, which will tell is if the block is moving or not. My question is why this method is recommended over the traditional approach? It seems the answer is usually with regards to making it easier to solve more complex problems, but I don't quite understand why this trivial manipulation of Newton's second law makes it much easier to solve problems?

I'm sorry if this has been asked before, but I couldn't quite find a satisfactory answer online!


texts: What is the minimum height of a chimney needed in a camper?

texts:
Like a lot of people nowadays, I'm fitting a log fire into the back of a camper van but can't find the minimum height above the roof for the chimney. Ideally, it should be as low as possible for aerodynamic and roof clearence purposes.

Building regs state that the pipe should be 2' above the highest point on the roof and I've seen people blindly follow this with their conversions (which is ridiculous) but nobody says why. Air flow? Safety for thatched roofs? The most recent paper I've found on the subject was published in 1946 and doesn't address this issue.

The venting for the stove is entirely different anyway with a 30cm cubed combustion chamber, a 130mm internal sized flue, a 500cm straight pipe to the roof and a 3-5Kw output.

Is there some formula for a minimum chimney height above the roof? Or a university compartment specializing in combustion?


texts: Heating circuit: Galvanized steel with press fitting vs welded steel pipes

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What are the downsides for galvanized steel pipes + press fittings vs. welded steel pipes in a heating application? Diameter would be DN25/1".

Background: The customer specifies only steel, only welded connections for heating pipes starting at this size. The contractor wants to use press fittings, presumably because this way the installation will be easier. The rooms the installation will take place are rather full.

Are there good technical reasons to avoid galvanized steel pipes + press fittings? Corrosion, longevity, others?


texts: Why don't we use other substitute of cement while building a roof for thermal proofing?

texts:
Cement heats up like crazy. I live in the top floor and the heat is unbearable. Also it has a high carbon footprint.

Why still cement is vastly used? When there are so many better alternatives?


texts: How can I measure the vibrations of a solid object?

texts:
I want to measure the vibrations of a solid object (a tuning fork, a bone conducting headphone, the chest during singing) and to isolate them from the vibrations of the air. So I am looking for a meter that will pick those vibrations only when it's in contact when the vibrating object (hence a meter that just reads frequency probably won't work for me)

I've tried to use a smartphone's accelerometer but it didn't pick anything. I've also to use a phone's sound meter in order to see whether it's picks more sound when in contact with such object but the reading was the same.


texts: Calculating and Designing a Ring Gear for LEGO

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I'm working on 3d printing a planetary gear for LEGO. I've got a constrained set of planetary + sun gears and was looking into designing a custom ring gear.

I've read a little bit into the design of gears but am currently confused. This is what I've found.

Sun gear: 20 teeth, OD=21.3mm
Planet gear: 12 teeth, OD=13.38mm

In both cases, module (m) = 1 (for the gears to mesh the module has to be the same?)

Pressure angle = 20 degrees.

I was just wondering how I would go about designing such a ring gear in CAD, i.e. figuring out the number of teeth, tooth size, height etc. Thanks in Advance.


texts: What happens if an entire country turns off all lights and electric devices during peak consumption hours?

texts:
I've been reading about smart grids but I studied Computer Engineering and my already limited knowledge of power systems is very rusty. I keep hearing that traditional power stations have to adjust production to match demand, but I don't understand how this is possible. What happens when there is more demand than production? Who runs out of power? What if there's more production than demand? I read that power stations look at historical demand levels to increase production during peak consumption hours, but what if they increase production and everybody turns everything off, driving demand to zero? What happens?
EDIT
Just to clarify, I want to know what happens if demand goes up and down while production remains constant. What happens if demand goes to zero in a second? Does the power plant break down? How? What if the demand doubles in a second? Do the lights in my house lose half of their brightness?


texts: Max horizontal momentary load of vertical steel tube

texts:
I have sections of steel tube I want to set up for use as zip line anchors and was wondering what the allowable load would be on the vertically mounted tubes. I read that a zip line could have momentary tensions of up to 8,000 lbs put on the anchoring structures. The tubes are rolled, welded steel, 0.83 inch wall thickness (14 ga.). The end anchor point I was planning on was 10' long buried 2 feet in the ground in an 18" diameter concrete pier. The anchor point for the line would be 4 inches from the top so 7 ft 8 in. above ground.

The start side anchor post would be the same steel tube but buried 3 feet down in 15" a pier. The anchor point will either be at 9 feet above ground or 15.5 ft. Depending on my ability to brake the trolley. The start side tube will have another one directly behind it at 22" center to center that I could hook up a guy wire between to beef it up since there will obviously be more deflection.

Your thoughts are muchappreciated!


texts: Designing a "ratcheting" spinning wheel with ferrous metal bits

texts:
I'm trying to design a freely spinning wheel that will "lock" into a few different configurations. I'm planning on placing a rare earth magnet near a certain point on the wheel, and inserting bits of ferrous metal into the wheel so it will stop at those locations.

Two questions:

1) Any thoughts on the general viability of this design, and

2) How can I find ferrous metal bits? I tried searching on hardware sites for pins and small dowels, but they're usually of a fairly nonmagnetic steel alloy. Are there any specific search terms I could use, or types of items that are highly magnetic that I could repurpose?


texts: How much air gap is required in a storm pipe?

texts:
I'm studying the design of storm sewers and I had two questions relating to air gaps in storm pipes:

According to sources I've come across, flow through storm pipes
require an air gap so as to maintain open channel flow. Do I need to
maintain a specific amount of air gap? Or will any amount of air gap do?
Also, does it really matter whether or not I have an air gap? Do we
maintain an air gap so as to prevent a partial vacuum and self siphonage within the pipes? In which case why would it matter? Furthermore, since
storm sewer manholes (inlet pits) are open to the air, wouldn't that alleviate  any pressure differentials?


texts: Machinability index for ferrous and nonferrous material

texts:
What are the machinability index for ferrous and non-ferrous materials?
Please help me so that I can learn more about it. Thanks


texts: Small water pump powered by wind turbine : what type?

texts:
I need to aerate a small pond in my garden. I would like to build an autonomous system with a small water pump. The power would come from a small vertical wind turbine I will build. Since my pond is tiny (only 150 L), I will only need to pump small amounts of water, that too at a low height (20 cm is enough). The idea is to make some sort of a fountain.
The pump would only have to work when there is wind, because the pond is capable of staying in good shape without constant aeration by design (lots of plants, no fish). The flow rate could vary depending on wind speed.
I see two options :

make an all-mechanical system, with the windmill directly powering a mechanical pump,
make an electric system, with a windmill producing electricity (say, 12V) to power an electric pump.

For option 1, I would prefer to keep the design as simple as possible. Ideally I'd connect the pump directly to the shaft of the windmill. Since I know nothing about pumps, I'm wondering what type would be suited for this option. I assume that it would have to be able to pump from low speeds, and its torque would have to be fairly low (my wind turbine is going to be quite small). I was considering this, but the manufacturer says it needs 600 W to work.
For option 2, I'm worried about the fact that the pump might receive power on and off a lot, and I assume (perhaps wrongly) that these motors like to get constant power. If that is not a problem, then I'd probably get a small waterpump (like this).
Any advice welcome.


texts: What are the drawbacks of inceasing the bandwidth of the system?

texts:
I have a doubt concerning the closed loop frequency responce of a control system.

Suppose I have the following situation:

in which is plotted the frequency response of a system with different badwidths. In this case I know that in generale the performances are good as the bandwidth of the closed loop increases and I know that the price to pay to increase the bandwidth is a high control effort, but is there some other drawbacks in increasing the bandwidth of a system?

I was thinking abouth the noises, which are at high frequencies, this if the bandwidth is at high frequencies, and the system does not roll off fast, the noises enter into the system.

But I am not sure about what I said.

I know that as the badwidth increases, also the reference tracking gets better, but I also see that the roll off is not smooth, I so I was interpreting also this as a fact that there are worse performances with respect to the noise rejection.

Also, I know that there are some limitation of increasing the bandwidth of a system. So, considering a stable and minimum phase system, I know that the limit in bandwidth ig given by the hardware.

But if I increase the bandwidth is there some other limitation? By doing some experimentaition I have see that the disturbance rejection gets worse after a certain frequency, is it due to noise?

Can somebody please help me?


texts: HVAC Condensor Liquid Level/Ratio Estimate

texts:
Let's say I have a simple condenser inside of a HVAC system with 1 point of entry(Super-heated Vapour) and 1 point of exit(Saturated Liquid) for my refrigerant r134a.

A pipe passes through it with water for heat transfer reasons. I know at all times the $\dot{m}_W$ (mass flow rate) of that water and the EWT (Entry Water Temperature) and LWT (Leaving Water Temperature) via sensors.
The condenser is an isobaric process, so pressure at entry $P_1$ = pressure at exit $P_2$. Pressure is known at all times via sensors.
I also know the entry temperature $T_1$ via sensors. Its enthalpy $H_1$ and entropy $S_1$ at entry are known via tables.
Because I know the pressure at exit $P_2$ and its a saturated liquid, I know other thermodynamic data: $T_2$, $H_2$, and $S_2$.
Lastly, I know control measurement like compressor speed and guide vane opening, so I assume, I can estimate the mass flow rate entering my condenser (not sure how?). I also have access to geometric data of condenser.

To my understanding, inside the condenser, that gas becomes a liquid via heat transfer, and the condenser container is at all times, partly filled with R134a liquid and gas.
Given the above info, how would I use energy/mass conservation, fluid equation/ Bernouilli equation to calculate the depth of water inside my condenser tank?
I want to make a least-square/Gauss estimator of my liquid level given known measurements, and that predictive equation to compare with an actual sensor we already have. It's to get liquid level feedback signals for my control system when its value is outside of my liquid level sensor measuring range.


texts: Making a three phase squirrel cage induction motor in PLECS?

texts:
I was just curious if I was to make a Three phase squirrel cage induction motor connected to a
mechanical load System Block Diagram in PLECS with a rated frequency of 60hz, 6 poles, 220V rated stator voltage and a Friction coefficient of 0.25. Would I just be using an asynchronous machine in place of the three phase motor?


texts: What is the name of the vertical lines in groundwork plans

texts:
When producing groundwork designs especially in Bentley software, I noticed people like to produce them with contours and vertical lines or even tadpole-shaped lines instead of simply doing triangulation. Example:

What is the name of the vertical lines?


texts: How to resolve Keil uVision 5.0 compilation errors?

texts:
In an effort to learn Embedded System Programming I recently installed Keil uVision 5.0. I am using a STM32F development board. At this point all I am interested in is getting STM32 L1 Tutorial #1: Hello, World! (LED Blink) code complied and loaded into the microcontroller. While attempting to build the code I got the following errors. What is the cause of this error?

*** Using Compiler 'V5.06 update 3 (build 300)', folder:
'C:\Doc\Programs\Keil52\ARM\ARMCC\Bin'
Build target 'Target'
Error instantiating RTE components
Error #540: 'Keil::Device:Startup:1.0.0' component is not available for target 'Target'
Target not created.
Build Time Elapsed:  00:00:00


texts:
Consider a rod with a length of 150 [mm] and a diameter of 44 [mm]. At the left boundary the rod is fixed to a wall. At the right end a torque of 1000 [N m] is applied. The remaining boundaries are free to move. As a material a S275 steel is used. Thus Young's modulus is given as $Y=210000$ [N/$mm^2$] and Poisson's ratio is $\nu=0.3$.

A reference solution for the maximal displacement suggests it should be around 0.1103 [mm] and the maximal von Mises stress should be about 103.6 [N/mm^2]. In this Solidworks tutorial the same thing is done, but with different values than the reference I used (which is also based on a Solidworks example).
The problem I have is that the finite element simulation tool I use does not have a direct way to specify a torque as a boundary condition. One can, however, specify a boundary surface pressure. I'd like to convert the given torque into a surface pressure. Here is how I did the conversion. I created a vector field that gives the direction of the pressure load in the $x$, $y$ and $z$ direction and converted the torque value into a pressure. As a vector field I used:
{0, Sin[ArcTan[y, z]], -Cos[ArcTan[y, z]]}

A plot of the vector field looks like this:
VectorPlot[{Sin[ArcTan[y, z]], -Cos[ArcTan[y, z]]}, {y, -1, 1}, {z, -1, 1}]

Then I converted the $1000$ [N m] into $1000*10^3$ [N mm]. To get a pressure I think I'd need to use something of this sort:
$$M_t / q * 1 / (\pi r^2)$$
where $M_t$ is the given torque value. I would like to convert the torque into a force by dividing the force by a length. The $q$ is the part I am uncertain about what to use. I tried $q=\sqrt{y^2 + z^2}$ such that it gives the radius to the axis but that does not give correct values. Then I divide by the area of the surface to get a pressure.
I think I am making a mistake in the conversion. If someone could point me in the right direction...
Update:
Here is a different approach: Based on this we start from
$$M_t = \frac{J_T}{r} \tau$$
where $J_T$ is the torsion constant, $r$ the radius and $\tau$ the maximum shear stress. We solve for $\tau$ to get
$$\tau = \frac{M_t r}{J_T}$$
The torsion constant can be computed with
$$J_{zz} = J_{xx} + J_{yy} = \frac{\pi r^4}{2}$$
With this approach I get a maximum displacement of $0.111035$ [mm] and a maximum von Mises stress of $104.277$ [N/mm^2], both close enough for government work.
A plot of the von Mises stress:

In principal, I think, this approach could be used for other surfaces, then one would need to compute the area moments of inertia for those surfaces.


texts: How to write the equilibrium stress equations for a hollow, rectangular beam?

texts:
I have a system consisting of a hollow, rectangular cantilever beam (pictured below). I'd like to write the equilibrium stress equations à la the Cauchy Stress notation.

How do I account for the hollow section in the equation? How is it represented in a free-body diagram of the system?


texts: How is sandpaper grit size (the FEPA number system) defined?

texts:
Sandpapers are labeled to show their coarseness according to different standards. The CAMI system is used in e.g. the USA, and the FEPA system in Europe. I am interested in the FEPA system. It labels sandpaper with a number such as 220, 360, 500, 1000 etc. where higher numbers indicate finer coarsenesses. Exactly how does this number tell coarseness? I am interested in the FEPA number definition only.

I found this website. It states that:

  [...] by the FEPA standard for macrogrits grade F180, no more than 3% by mass of the grit can have a particle size larger than 90 microns, and at least 94% must be larger than 53 microns. In F220 (a “microgrit”), no more than 3% can be larger than 75 microns, at least 50% must be in the range 50.0 to 56.0, and at least 94% must be larger than 45 microns. See the Standards section below for detailed information.

So:

180: Grain sizes mainly within $[53;90]\;\mathrm{\mu m}$
220: Grain sizes mainly within $[45;75]\;\mathrm{\mu m}$

This indicates that the FEPA number (I don't know why they call the numbers F; they are usually denoted with a P) indicates a range of grain sizes.

Do anyone know more and can confirm or better explain the definition and for example know where to find an overview of more FEPA numbers?

Many websites, such as this, explain how to understand the standard but not how the number relates to a physical value. The Wikipedia article is not of much help as it doesn't dive any deeper into the definition details than other websites I can find. And the FEPA website is of no help either since it seems to require payment for the information.

Thank you for you help.

Update

I have been looking into sandpaper types.

FEPA P220 equals CAMI 220. Labeled grain size: $68\;\mathrm{\mu m}$
FEPA P500 equals CAMI 360. Labeled grain size: $30\;\mathrm{\mu m}$
FEPA P1000 equals CAMI 500. Labeled grain size: $18\;\mathrm{\mu m}$
FEPA P4000 equals CAMI 1200. Labeled grain size: $5\;\mathrm{\mu m}$

If the number is the number of grains (e.g. 220 grains when the number is P220) that stacked reach some height (for example 1 inch which is 2.54 cm) lengths would be:

The P220 gives ~1.5 cm and the CAMI 220 gives 1.5 cm.
The P500 gives 1.5 cm and the CAMI 360 gives 1.08 cm.
The P1000 gives 1.8 cm and the CAMI 500 gives 0.9 cm.
The P4000 gives 2 cm and the CAMI 1200 gives 0.6 cm.

There is no system and none come close to for example one inch (not even the American system). Otherwise there must be gaps and spaces counted in as well that I am not aware of. From these quick calculations, the number does not seem to be a "number of grains per length" value or alike.


texts:
Hi I don’t understand this question, can someone please explain what it is asking?

An electrochemical cell with two electrodes of iron and copper at 25°C. The standard reduction electrode potentials E0 of Fe ion (2+) to Fe metal is ‐0.44 V, and Cu ion (2+) to Cu metal is +0.34 V.

If this is a standard spontaneous cell, calculate the standard cell potential, draw the electrochemical cell and justify anode (oxidation), cathode (reduction) and direction of electron flow.

Okay so I tried this so far:

Fe2e+ 2e = Fe
Cu2e = 2e + Cu

But where do I go from here and is this even right?


texts: Can the production rate of labs-on-a-chip ever reach the production rate of silicon chips?

texts:
Labs-on-a-chip and silicon chips both have the potential - and in some cases have already reached the potential - to drastically scale down tasks, in these cases performing chemical reactions and performing computations.

Part of the appeal of silicon chips is - besides their size - is that they can be easily mass-produced. Labs-on-a-chip have tremendous potential, but they are in the early stages of development.

Can labs-on-a-chip be mass-produced in the same way that silicon chips are mass-produced?


texts:
I'm looking to design a system that can control a solar panel through an electrical actuator for a range of motion of -45 to +45 degrees for maximum solar exposure. The panel will be mounted on a 10 feet pole and will be attached at the center of that pole. This means that either the mechanism will be at the pole's top or at least some kind of bearing to allow for the movement.

The caveat in this case (because the panel is attached high up) is that due to security reasons the system must be designed in such a way that the panel will be held stable (mustn't rotate and mustn't fall off) without relying on the actuator itself, in case of power failures.

I've started looking around for actuator mechanisms but haven't yet found anything that talks specifics about similar security requirements. I'm looking for pointers / ideas as I'm not yet experienced in such cases.

PS: For anyone who would be interested in numbers the panel weighs about 150 kg and will possibly receive a horizontal wind force of 300N. Also a torque of 100Nm will need to be applied in order to change its facing direction.


texts:
I would like to ask a specific conceptual question which bothers me for quite some time! First of all i do know the difference in between reversible and irreversible processes. What is thought in Thermodynamics courses is the maximum work can be obtained via reversible processes. Now please consider the following example.

Air (assume as ideal gas) at 5 bar and 298.15K (25℃) is expanded to 1 bar and 298.15K by a mechanically reversible processes: Heating at constant pressure followed by cooling at constant volume.

When one considers the corresponding PV diagram , the work is calculated as the area under the curve which is obviously larger than the reversible isothermal expansion.

Here are my questions

1) How many different reversible paths can be drawn in between two different states at the same temperature (there can be infinite number of irreversible paths)?

2) How can heating an ideal gas at constant pressure and cooling at constant volume be a reversible process (these are not adiabatic or isothermal)?

3) Is it possible to say that : There can be many different reversible paths between two specified states, all of which will give larger work than corresponding irreversible paths but also vary in between themselves so that it is not possible to state which reversible path will give the highest work before specifying the path itself.

Thank you all in advance for your sincere help and answers.

UPDATE: From MIT thermodynamics course notes: the reversible one produces the maximum work of all possible processes between two states.

If so there should not be more than one reversible process between two states. Then how can the process path given in the question be reversible as we can already perform the same change with isothermal expansion.


texts:
I am working on a project that requires a wing to be rotated and I need the rotation mechanism to be fail-safe -- if power fails, the wing will stay in place and not move around.  My thought was to use a worm drive since they are not reversible.  However, worm drives typically reduce speed.

Would there be anyway to make this reduction in speed from the motor to the gear as little as possible using a worm drive?
Should I just forget the idea of a worm drive and use a motor that can hold its position even if turned off (if so what type of motor could do this?)?


texts: Determine Stiffness (k) and Mass (m) of a system from impulse response

texts:
I have a test sample (Piezo Diaphragm) which I am actuating with a voltage supplied to the sample to assess the impulse response.
When this voltage is supplied to the sample a deformation per unit voltage occurs and the diaphragm undergoes a deflection (displacement).
Once the voltage is removed, the diaphragm (sample) undergoes damped oscillations until it returns to its initial condition before the voltage was supplied.
The displacement over time is measured with a laser vibrometer and results in a damped oscillations plot.
From this plot I am able to determine system characteristics using the log decrement method such as natural frequency and damping ratio.
My question is whether it is possible to determine system characteristics such as Stiffness (k) or Mass (m) solely using the displacement over time data and the damped oscillation plot?


texts: Can concepts like “critical damping” or “resonant frequency” be applied to more complex systems than just a spring and damper in parallel?

texts:
I am trying to do some modeling analysis by representing materials with parallel systems of springs and dampers. In the simplest case with just one spring parallel to a damper, we have the traditional "damped oscillator":

The fundamental resonant angular frequency is given by:
$$ω = \sqrt{\frac{k}{m}}$$
Critical damping is calculated from the equation of motion:
$$mx_{tt} + cx_t + kx = 0$$
$$ms^2 + cs + k = 0$$
$$s= \frac{-c ± \sqrt{c^2-4mk}}{2m}$$
There are then three conditions:

$c^2 <4mk$ (under damping)
$c^2 >4mk$ (over damping)
$c^2 =4mk$ (critical damping)

The damping ratio is then expressed by $\frac{c}{\sqrt{4mk}}$.
I am trying to figure out how to apply similar concepts to more complex models such as the following:

The equation of motion where $σ$ is stress (force) and $σ$ is strain (stretch, analogous to $x$) is as follows:
$$σ + (\frac{η_1}{E_1} + \frac{η_2}{E_2})\dot{σ} + \frac{η_1η_2}{E_1E_2}\ddot{σ}= (η_1+η_2)\dot{ϵ} + \frac{η_1η_2(E_1+E_2)}{E_1E_2}\tag{1}$$
I have been thinking about this problem, and my inclination is that in a more complex system, there will not be one single frequency of oscillation, but rather multiple frequencies.
Critical damping is the damping coefficient which leads to the most rapid extinguishing of oscillations.  If a complex system has multiple harmonics, perhaps such a simple concept cannot be applied. Perhaps you would need to pick a specific harmonic to address, and then you could calculate the damping coefficient that would extinguish that harmonic fastest (eg. the fundamental).
I presume such a thing should be possible. It seems reasonable.
How would one predict the fundamental frequency or various frequencies/modes of vibration from an equation of motion like (1)? Then let's say I can calculate a given fundamental frequency of $f$. How would I then go about establishing the damping coefficient that would most rapidly extinguish it?
I presume this is solvable as springs and dampers are commonly used to model physical objects, but I'm not sure how to go about it.
Thanks.


texts: What engineering concepts are used in EV3 programming/ a Mindstorms robot?

texts:
If possible, could someone please compile a list of the engineering concepts associated with EV3 programming and Mindstorms robots.

Thank you - your answers are much appreciated.


texts: Summary of major outage management works needed in the 4th decade of a nuclear reactor?

texts:
I've noticed that quite a few commercial nuclear reactors have an extended outage (they close down for several months) some time late in their third decade, and the maintenance works during the closure involve significant investment. This cost has been high enough in some cases that the reactor has permanently shut down rather than undergo the works (e.g. the Vermont Yankee, Dec 2014) because the business case just didn't stack up.

What are the works involved, in terms of scope and cost; how much do these vary depending on the type of reactor (PWR, BWR, ...)?


texts:
Subtitled: Ah, strong am I with the Force, but how do I measure it?

With all due apologies for paraphrasing Yoda, I am trying to measure a force.  Fortunately, it's an easier force to measure than midi-chlorians.

When I tutor others in karate, one of the things I emphasize is a focus on the technique behind the basic strikes.  Experience has shown that the proper technique can yield a lot more force behind any strike.  The problem I run into is that even though a student claims they can "feel" the difference in a strike being more powerful, they often revert back to their incorrect technique because they haven't convinced themselves that the difference is truly there.

I would like to design a system that measures the force behind a strike.  In particular, I need to identify some sensor at the point of impact that can be used.  National Geographic has done something very similar, but the equipment they use, such as crash test dummies, is prohibitively expensive.  Likewise, I don't need the resolution or accuracy provided by that equipment.  Whether someone hit with 100 or 101 lbf of force is immaterial.  I want to demonstrate when then go from 100 to 200.

What sensor or system could I use in order to measure the force at impact from various karate strikes?  Ideally, I could mount the device in a  focus mitt, or similar, and be able to attach the pad to an adjustable system so various strikes could be measured.

My principle design constraints are:

low(er) cost
repeatable measurements
range of 0–2,000 lbf

I'm not looking for a complete system design, which would include all the monitoring electronics.  I'm just trying to focus on a sensor that can provide a measurable output of some sort, such as voltage.

Also note that I plan on running wires to the device, so I already have an easy way to power the system.  I may go wireless at some point, but I would use a battery then and I want this question to remain focused on the sensor itself.


texts: What should length of copper coil be to heat fluid from Temp A to Temp B?

texts:
I'm building a milk pasteuriser.

The milk in the cooling tank has a starting temperature of 4°C. It should then be heated to 72°C for 30 sec, then cooled back down again to 4°C as quickly as possible (if I understand the process correctly).

I've got 2 bulk tanks, one with a heating fluid of 90°C and another with cooling fluid of 4°C.

My question is this: What should the length of each of the copper induction coils be to heat/cool the fluid to the appropriate temperature for the required length of time. (I'm looking for a formula if such exists)

**Side note: I'm not an engineer. I'm a home hobbyist with background in maths/programming.


texts: Sliding mode surface derivative exact matrix format (ds/dx)

texts:
Is there any suggestion on sliding surface state  derivative matrix (ds/dx) format?

ds/dx = [ds/beta,ds/dalpha,ds/dp,ds/dq,ds/dr,ds/dphi;
         ds/beta,ds/dalpha,ds/dp,ds/dq,ds/dr,ds/dphi;
         ds/beta,ds/dalpha,ds/dp,ds/dq,ds/dr,ds/dphi];

or

ds/dx = [0,0,ds/dp,0,0,ds/dphi;
         ds/beta,0,0,0,ds/dr,0;
         0,ds/dalpha,0,ds/dq,0,0];

problem described below

In the article Controller Design using Bifurcation Map for Aircraft Spin Recovery, the sliding surface derivative is obtained using a numerical method.

The steady space system is defined by the following equations:

$$\dot{\underline{x}}=A(\underline{x},t)+B(\underline{x},t)\underline{U}, \\
\underline{x}=[V,\alpha,\beta,p,q,r,\phi,\theta], \\
s=\left[\begin{array}{c}
\dfrac{d}{dt}(\phi-\phi_d)+\lambda_1(\phi-\phi_d) \\
\dfrac{d}{dt}(\alpha-\alpha_d)+\lambda_2(\alpha-\alpha_d) \\
\dfrac{d}{dt}(\beta-\beta_d)+\lambda_3(\beta-\beta_d) \\
\end{array}\right]$$

where $\lambda_1$, $\lambda_2$ and $\lambda_3$ are positive real numbers.

The article states:

  The control law from reaching law in Eq. (6) can be derived
  as:
  $$\dot{s}=\dfrac{\partial{s}}{\partial{x}}\dot{x}=\dfrac{\partial{s}}{\partial{x}}(A+Bu)=-Qsgn(s)+Kf(s).\tag{8}$$

  By solving the above equation (8) for u (3 x 1), one gets expressions
  for u as:

  $$u=-\left(\dfrac{\partial{s}}{\partial{x}}B\right)^{-1}\left[\dfrac{\partial{s}}{\partial{x}}A+Qsgn(S)+Kf(s)\right].\tag{9}$$

  The matrix $\frac{\partial{s}}{\partial{x}}$ is computed numerically.
  The control inputs computed are subject to position and rate
  constraints on control surface deflections as listed in the Table 1.

How would be the exact form of matrix of $\dfrac{\partial s}{\partial x}$ (element of $\dfrac{\partial s}{\partial x}$ in columns and raws)?


texts: How do cordless lawn mowers determine lawn density?

texts: Some cordless lawn mowers have a feature that causes the motor to cut off when the mower is rolled over a driveway or over a section of lawn where the grass is very sparse.  How does the mower sense this condition?


texts: Transmitting power over long distances what is better AC or DC?

texts:
I found this answer to a related question. The part of the answer that's confusing me is:

  Transmitting DC power over a long distance is inefficient. Thus AC supply is a far more efficient to transmit power.

According to Siemens it's quite the opposite:

  Whenever power has to be transmitted over long distances, DC transmission is the most economical solution compared to high-voltage AC.

Also, from Wikipedia

  HVDC transmission losses are quoted as less than 3% per 1,000 km, which are 30 to 40% less than with AC lines, at the same voltage levels.

Is the posted answer correct?

- - EDIT - -

Chris H made a very important observation (see his comment below): The context of the post I mentioned was of low voltage whereas I was blindly thinking of high voltage. Indeed I learnt loads by the answers and comments. Thanks.


texts: System model for motor controlled inverted pendulum with rotating motor body (used in camera stabilizer application)

texts:
I'm planning to build a head-mounted camera stabilizer for pro GoPro camera. The idea is that when I tilt my head the camera would stay at a user-set angle.

I'm using an accelerometer and a gyro to measure camera angle $\theta$ and angular velocity $\dot{\theta}$, and some motor to control the camera angle. I derived the following differential equation for the system (which is basically an inverted pendulum) where $l$ is length of the rod, $\theta$ is the angle of the camera due to gravity, $m$ is the mass, $g$ is the gravitational acceleration, $b$ is damping coefficient (due to friction) and $\tau$ is torque. $\tau_{motor}$ will be the input of the system.

$\tau_{total} = \tau_{motor} - \tau_{gravity} - \tau_{friction}$

$I\ddot{\theta} = \tau_{motor} - mgl\sin\theta - b\dot{\theta}$

$ml^2\ddot{\theta} = \tau_{motor} - mgl\sin\theta - b\dot{\theta}$

$\ddot{\theta} = \frac{1}{ml^2}\tau_{motor} - \frac{g}{l}\sin\theta - \frac{b}{ml^2}\dot{\theta}$

From here I'll continue designing the control algorithm using state-space methods such as state-feedback control (I choose camera angle $\theta$ and angular velocity $\dot{\theta}$ as states and $\tau_{motor}$ as input).

Now here's the question:

I want to test how my control system behaves when a person tilts his head (I'll be using Matlab and Simulink). How should I incorporate the tilting of the head (or rotating of the body of the motor since the motor will be attached to head) into my control design? I guess it can be thought as a disturbance to system (or another input)? How should it be incorporated to the system model (meaning the differential equation above)? Should there be maybe more differential equations? I thought it would be nice to give the system the the angle of the body of the motor (meaning the angle of the head) as function of time and observe how the control system works. In other words I would like to see how the controller works if I tilt my head for example back and forth.

On the other hand, is this a good approach or should I just use another torque $\tau_{disturbance}$ to test the controller? I'm pretty sure that it isn't the same as tilting the motor body, but would perhaps lead to good enough model for the controller?


texts:
The book "Instrument Engineers' Handbook vol. 1 - Liptak" said that for the first-order system forced by a step or an impulse, the time constant is the time required to complete 63.2% of the total rise or decay; at any instant during the process, the time constant is the quotient of the instantaneous rate of change divided into the change still to be completed.

How can I express the last sentence mathematically?

Thank you very much.


texts: What is the difference between pipe section, hot-finished, and cold formed circular hollow section?

texts: I was reading a steel catalog and saw that it categorizes steel sections separately into pipe section, hot-finished circular hollow section, and cold formed circular hollow section. Given the same design strength, for example S355, is there any fundamental differences when designing a section of say, 610mm depth and 10mm thickness, using steel material from these three categorizations?


texts: Conservative rebar dowel hole sizing and embedment depth

texts:
My question concerns the hole sizing and embedment depth of post installed rebar which is secured with epoxy mortar into a hole in a reinforced concrete slab.

Hole diameter sizing

My assumption #1 is that the minimum and maximum size of the hole depends on the minimum and maximum thickness of the epoxy mortar. Playing around with the Adhesive Anchor Volume Calculator on the Hilti website suggests the following hole sizes:

+----------------+----------------+
| Rebar diameter |   Hole size    |
+----------------+----------------+
| 10 mm          | 9/16" (14 mm)  |
| 15 mm          | 3/4" (19 mm)   |
| 20 mm          | 1" (25 mm)     |
| 25 mm          | 1 1/4" (32 mm) |
| 30 mm          | 1 1/2" (38 mm) |
+----------------+----------------+

For the purposes of this example consider HIT-HY 200 Injection Mortar.

Question 1 - what deviation from these hole sizes is permitted? If a 16 mm hole is accidentally drilled then can the 10 mm rebar still be used with full strength?

Hole depth sizing

My assumption #2 is that the required embedment depth of a rebar dowel depends on the bond strength of the epoxy mortar  and the load that the rebar is required to carry.

Conservatively consider that M10 rebar is required to have a pull-out resistance equal to the force that would yield it at 500 N/mm².

Rebar area $= π \times 5^2 = 78.5 \text{ mm}^2$

Rebar circumference $ = 2 π \times 5 = 31.4 \text{ mm}^2$

Conservative pull-out force $= 500 \text{ N/mm}^2 \times 78.5 \text{ mm}^2 = 39.25 \text{ kN}$

For C25/30 concrete the design bond strength of HIT-HY 200 Injection Mortar for any rebar diameter is given by $2.7\,\text{N}/\text{mm}^2$

Bond-strength per mm of M10 rebar $= 2.7 \times 31.4 = 84.78 \text{ N/mm}$

Required embedment depth $= 39250 \text{ N} ÷ 84.78 \text{ N/mm} = 463 \text{ mm}$

Question 2 - Is this a conservative methodology for determining the required embedment depth? Will an embedment depth of 463 mm provide full strength in the case of M10 rebar secured with HIT-HY 200 Injection Mortar in C25/30 concrete?


texts: Are there other finite element types besides the usual?

texts:
By finite element type I specifically mean element geometry.

I am aware of Beam/Strut, Quad, Tri, Tet & Hex but are there other types, eg a hexagonal prism, rhombihedral etc.. ?


texts: How can I do engineering projects for money at home?

texts:
I am a M.Sc. graduate in mechanical engineering and I have experience with engineering software, like MATLAB, CATIA, and ABAQUS.
I want to know how I can find industrial projects like finite element analysis or wave propagation to do at home and make money.
I will have to give the finished project to the company using Email.


texts: Stainless steel corrosion resistance in seawater

texts:
Stainless steel comes in several qualities.

AISI 303 (1.4305) (Stainless Steel A1) approximately 304 but more machinable due to sulfur.
AISI 304 (1.4301) (Stainless Steel A2) comprises of 18% chromium and 8% nickel.
AISI 316 (EN 1.4401) (Stainless Steel A4) is 16% chromium, 10% nickel and 2% molybdenum.
AISI 316L is the low carbon variant to enhance weldability.

For seawater 316 quality is often advised. I'd like to understand:

By what process does molybdenum make the metal more resistant to corrosion in seawater?
How do the material loss rates compare between these grades of stainless steel, as well as to ordinary structural steel (S235, S275 or S355)?


texts: What does C20019 IN PAIRS AT 900 MAX CTS WITH 2 ROWS OF BRIDGING AT 1/3 POINTS mean in a technical drawing?

texts: Specifically, does in pairs mean that there are 2 C20019 members per indicated line on a technical drawing?


texts: Heat Deflection VS Coefficient of Thermal Expansion?

texts:
I was looking at a spec sheet for a photopolymer and saw these two different subsections under the "Thermal" section. I tried Googling around as I usually do, but no site could give me the clear difference between the two and some simply defined the two as the same. I have a hard time believing that since there are two distinct test methods indicated by the ASTM. Could someone please clarify what the difference is?
PS - To further clarify, I mean the difference between the two results, not the ASTM test methods.


texts:
I have a question regarding how are the vertical forces on a spur gear shaft are supported. I am currently doing my undergraduate (in final year) and have only dealt with gearboxes where the shafts axis lies in a horizontal plane. I am designing a device that requires the shaft to be vertical.
I understand how the bearing would support the axial and radial forces but what about the vertical forces, how could I support these (from the weight of the shaft and gears).


texts: How to filter outside air during wildfire to safe breathable level?

texts:
I've had an experience of having outside air heavily polluted by wildfire smoke, and now I'm reading up on the wildfire happening in Southeast Asia. When the air outside got too polluted to breathe, I covered a plain old fan with a wet cloth and closed all windows. That helped me filter out the air somewhat, but I would like to know if there are more effective measures to take in such situations.

The CDC's site says you should use air conditioner's air filtering function if you can't relocate. Let's say you can't, what can you do to make the air in your home breathable?


texts: What is the percentage of direct workers in an automotive production plant compared to all the employees?

texts:
I am not asking for specific numbers of any production plant. I want to know the general direct worker/employee ratio of a plant.

Example: if there are 1000 employees working usually 700 of them are direct workers etc.

I am looking for estimates backed up with sources or personal experience.
Also there may be multiple shifts in a production plant so I am looking for the ratio in a single shift since all the jobs may not get a night shift. The plants I am interested in are the ones that mass produce for international brands. Including the country the plant is in would also be helpful for categorizing the information.

Direct worker means a worker directly working on the production line while employee means all the the people getting paid in that plant.

Edit: Added more information.


texts: Does electromagnetic shielding using conductor metal sheet enclosure attenuates magnetic field as well?

texts: Does electromagnetic shielding using conductor metal sheet enclosure attenuates magnetic field of the electromagnetic wave as well? If yes, what is the relation? I know it does attenuate electric field of the electromagnetic wave.


texts: Understanding Stagnation Pressure Head in non-compressible fluids

texts:
Does the stagnation pressure head in a pitot tube allow for the calculation of dynamic head at a point in the tube, given that the static pressure head at the point is known?
For example in the diagram below:

The stagnation pressure head can be given by: $\frac{p_{2}}{\gamma}$ or $\frac{p_{0}}{\gamma}$
Assuming the 3 points are at the same elevation can the Bernoulli equation be expressed as:
$$\frac{p_{0}}{\gamma}=\frac{p_{1}}{\gamma}+\frac{v_{1}^{2}}{2g}=\frac{p_{3}}{\gamma}+\frac{v_{3}^{2}}{2g}$$


texts: Linear force multiplication (or division) without hydraulics

texts:
Gears are used to transfer power between two rotating shafts, either by increasing or decreasing the angular speed, with a corresponding inverse change in the torque. If I want to do the same for linear motion, I see only two options in front of me:

Use Pascals law for liquids and connect pipe of varying diameters to multiply (or divide ) the force, as is done in car jacks, or,
Connect the input linear drive to a rotating shaft, connect it to a step-up or step down gear, and then convert rotary motion back to linear.

Hydraulic cylinders are kind of costly and keeping the fluid at a higher pressure is not quite convenient. Also using a linear-rotary-linear power transfer is easy to build but quite inefficient. Is there another way to do this?


texts: How could we calculate the coefficient of a PI controller (ki - kp) which regulates the voltage of the DC bus link of a three-phase inverter?

texts:
From my calculations I arrived at a non-linear equation :
$$ C\frac{dV_{dc}}{dt} = 3e_q\frac{I_q}{2}V_{dc} - \frac{V_{dc}}{R_{dc}} $$
I have calculated the operating points which are $I_q = 9.58A$, $V_{dc}=400V$ and $R_{dc} = 65.6$
but I got stuck on the next step to find the transfer function of this equation .


texts: Can foil strain gauges measure strain normal to the plane of the sensor?

texts: I'm wondering if anyone in the community has experience with foil strain gauges used to measure strain components that are normal to the plane of the sensor? If the strain gauge were pressed between two large flat plates, for example, would there be enough deformation of the conductive path to cause a measurable change in resistance?


texts: Calculating deflection for a home built trailer

texts:
I am designing a 4'x12' trailer frame.  8' of it will support weight, the balance will be the tongue.  My area of concern is bending at the ends of the long supports.  There will be a wheel assembly located 4' from the frames end that will support all but the tongue weight of 100 -120 lbs.  I plan to use commercial steel tubing so the moment of inertia ($I$) and Section Modulus ($Z$) are known quantities.

What I need is a formula that is suited to this design - ie. something that will tell me how much the frame might bend under load.  I have some knowledge of simple design as well as an AISC and Machinery's handbooks

Its going to be a 4' x 8' with a 4' tongue, the tongue weight should be 50 to 80 lbs. I'm designing it to keep the weight below 900 lbs.  I want it to have 15" wheels.   I'm using components for a design weight of 2000 lbs. and plan on using axle-less wheel hubs.  There will be a close to a uniform load spaced over the wheels.  The wheel assembly will be off center to improve tracking.

I'm looking for a suitable "Beam Diagram" to ensure I stay within a reasonable deflection.   I have seen them designed with 2" x 2", and 2" x 3" tubing.


texts: Need advice answering this kinetics of particles energy method dynamics problem

texts:
Problem 3/155 The light rod is pivoted at O and carries the 2kg and 4kg particles. If the rod is released from rest at $\theta=60°$ and swings in the vertical plane, calculate (a) the velocity $v$ of the 2-kg particle just before it hits the spring in the dashed position and (b) the maximum compression $x$ of the spring. Assume that $x$ is small so that the position of the rod when the spring is compressed is essentially horizontal.

The part I am most confused about it part a) as I am not sure how to come up with the energy equation using angular motion instead of linear motion. Trying to solve the question I assumed I had to use $\frac12I\omega^2$ instead of $\frac12mv^2$.The height for GPE of mass a and mass b I am also unsure how to calculate.

In addition to part a, I assumed the energy equation: $GPE_a=KE_b-GPE_b$ where GPE is gravitational potential energy and KE is kinetic energy. The kinetic energy of A = 0 since it is initially at rest, and GPE of mass b is negative due to loss of GPE where I took the vertical plane as the datum.

I may have the wrong assumptions and I am open to other answers people may have.


texts:
Can anyone help with this Impact problem? It does not seem very difficult but I am having trouble putting all the parts together.
Thanks,


texts:
I am looking at a rod that has an acting force along one end that's pinned into a frictionless track. The other end is pinned into a track that has friction. I am trying to determine the contact forces at each end of the rod, as well as the friction force on the end that's in the frictioned track.
$$ \vec{\dot{\omega}} = 0.1 $$

I am looking at using the equations $ M_{cm} = I_{cm} $ and $ F = mA_{cm} $
I've worked the force equations to equal
$$ F_x = mA_{cm} $$
$$ 5-cos(\phi)F_b = sin(27.65)98.1N $$
and
$$ F_y = mA_{cm} $$
$$ N_A + sin(\gamma)N_B+cos(\phi)=cos(27.65)*98.1 $$
and the momentum equation
$$ M_{cm} = I_cm * \vec{\dot{\omega}} $$
$$ M_{cm} = 10 * 0.1 $$
I'm having difficulties figuring out the angle for $ F_B$ as well as determining how $M_{cm}$ is playing a role in here at all.
Any suggestions would be appreciated.
$$ I = 1.41 $$
$$ s = 0.5 $$
$$ b = -0.5 $$
$$r = 1$$
$$c = 2$$
$$X_A = 1.25$$
$$V_A = .5$$
$$A_A= 0.25
$$


texts: How can I calculate "bendability" of aluminium tubes?

texts:
Disclaimer: sadly not an engineer (I hope this is the right place for such my question. Please let me know if it isn't).

I'm designing a tent. I know most of the dimensions of the first prototype I want to build, but I'm struggling with the poles.

Don't mind the short lines

When inserting the poles into the rings at the extremities of the tent base (groundsheet), they bend to form the shape of the tent, as we can see in this Naturehike Cloud Up 2 pitching video.

In my design, I need to be able to predict how much (how far) the poles will be able to bend. I'd love to use Easton's Syclone poles, but I doubt they'd sell them to me. So I'm interested in aluminium poles such as these:

Knowing this is essential for my project, because the bendability of the poles will determine lots of aspects of the design (such as pole parts length for example).

So, my question is: how can I predict (or simulate [that'd be awesome]) the bendability of my poles? Any suggestion is immensely welcomed.


texts: Can tritiated water be separated from regular water with a centrifuge?

texts: Tritiated water should weigh more than regular water. Can they be centrifugally separated?


texts: Scalability in the context of optimization and control systems

texts:
I am having a hard time trying to make sense of the phrase "Scalable optimization". I read from a few papers discussing that some global optimization solvers like BARON, ANTIGONE, etc. do not scale well with the number of scenarios.
I quote from "Languages and Tools for Optimization of Large−Scale Systems":

Model scalability means the granularity of the model behaviour should be easy to change, without the need to re-build the model.

My very basic understanding and experience with optimization is that optimization would not work well if scaling of the problem is not done properly, and computational time increases with problem size or dimension (large scale system). As to model scalability, I thought a model is built for a specific subject/process and its granularity/level of detail cannot be changed unless we rebuild it?
Can someone shed some light on this?


texts: Which will be stronger for securing a cantilever umbrella in a deck

texts:
I am securing a cantilever umbrella baseplate to a deck. The decking timber will be reinforced with a pine nog between the deck joists.
The options that I have are to use 10mm stainless steel coach screw that will be embedded into a 70mm nog.
Alternatively I can use a 10mm bolt, washer and nylock nut that will be secured through a 50mm nog.
The timber will be the same grade wet H5 pine. The deck plate is the same size and thickness, as is the material of the screw / bolt.
Which method will be stronger. I can't use a longer bolt due to the limitation of space under the decking timber in order to fit the nut.
Thanks


texts:
While I’m studying about a fired heater (furnace) in chemical engineering , I learnt that the process fluids enters from the convection section and leaves at the radiant section of the furnace.

Why is this the case ?

How is this linked to the temperature of the hot flue gas rising up? The temperature of the hot flue gas is lower in the convection section. So how does it link to why the process fluid is entering from the convection section and not radiant section ? Thanks.

The picture shows the process fluid entering from the convection section and leaves at the radiant section. So to clarify, my question is asking why does it enter from the convection section and not the radiant section. ?


texts: Sun light illumination on a lower floor vs high building closely

texts:
there is an investor that wants to build very close to our building. In case we agree, the buildings will stand like on the pictures below, 3 meters apart from each other. I tried to draw them in proper scale so I hope that is more or less correct. This is in 43.20 latitude.

My question is, in case we agree for one reason or another, is it possible to ensure enough sun light during the day on our floor?

The immediate idea I've got was to request them paint the wall facing towards us in white pearly  paint. I am wondering though if this is going to be good enough as well whether there are some other clever ways to direct sun light to our windows.

Any good products or services available in Europe would be welcome (hope this will be alright according to StackExchange rules).

The matters are subject to negotiation and I expect investor to be helpful in case any measures involve their cooperation, even slight building design changes might be possible.

Thanks a lot for any insights!


texts: What is the "tl" unit of weight measurement?

texts:
I recently purchased a digital scale from eBay.

According to the listing it can weigh in the following units:

  Multiple Weighting Units: g, oz, tl, ct.

Screenshot of that page:

Now I know that "g" is grams, "oz" is ounces, and "ct" is carats (and the figures displayed agree with that) however what is "tl"?

If I measure a 10g reference weight it shows as 0.853 tl, thus 1g is 0.0853 tl. Allowing for slight measurement errors (the last significant figure changes a bit with different measurements) I can't find any unit of weight that "tl" could correspond to.

The closest in name I could find is "tael" but the conversion factor doesn't agree. (10g is 0.264555 tael).

The unit also measures in grains (gn) although that is not advertised.

The device only measure up to 200g, so I imagine that whatever "tl" is will be some sort of measurement of jewellery or similar.

So, my question is: What is tl?