texts:
I am developing a model for the respiratory system of a neonate (newborn child) for a BME project by using pressure/volume data of the lungs. To model these, I plan to use a rubber balloon. However. the calculations are more difficult than I thought (especially because rubber behaves non-linearly and with a hysteresis effect, but I will ignore these effects).

I will assume the balloon is perfectly spherical, that it behaves linearly and that the strain is dependent on the radius relative to the original radius ($R_0$).

Here are the equations for the basis of my model:

$$
V = \frac{4}{3} \pi R^3_1 \\
R_1 = \left( \frac{3V}{4\pi} \right)^\frac{1}{3} \\
\sigma = \frac{pR_1}{2t} \\
\epsilon = \frac{R_1 - R_0}{R_0} \\
E = \frac{\sigma}{\epsilon}
  = \frac{pR_0R_1}{2t(R_1-R_0)}
  = \frac{pR_0}{2t\left(1-\dfrac{R_0}{\left(\frac{3V}{4\pi}\right)^\frac{1}{3}}\right)} \\
$$

My conclusion is: $$E \propto \frac{p}{V^\frac{1}{3}}$$

Is this correct?


texts: How to calculate torque required by a motor depending on load?

texts: I want to know whether the torque required by motor depends on load. If it does, then how can I calculate it?


texts:
My background is in Environmental Science, although I have recently been taught in the basics for energy engineering especially for solar panels.
I'm currently using PVsyst to build solar panels on a given building at a given location. However, I'm finding it difficult to explain and understand this diagram with my limited circuit knowledge.
Can someone offer a detailed explanation of the components along with what they represent in the network and what the entire picture means?  I know that 1. represents a diode, and it looks to me that 2. represents a European-resistor, I partially know this because of basic practice in LtSpice.


texts:
I was wondering how to mount a small rotary encoder to a platform in order to measure how far a small treaded robot has traveled. We're using this tread/wheel set:
We've tried epoxying the encoder shaft directly to the end of an extra gear wheel, but it broke off quite easily. I'm thinking about grinding down the encoder shaft until it can just squeeze into the axle hole of the drive wheel and then using the epoxy inside the wheel. It would then be driven off of the tread.
Like this:
However I'm not sure this would be the best idea, and other suggestions would be appreciated. Especially with keeping any assembly either coupled to the drive shaft or to a tread.
Note: Its for an EE senior project, and none of us have much experience with construction skills. Its going to be the platform for an automated robot on Aruino.


texts: PLEASE ANSWER Sterling vs Combustion Engine

texts:
This may be difficult to answer but, theoretically, if you had a car with a sterling engine that produces say approximately 300 horsepower how much of any specific heat source would need to be used if the car had a mass of 1.5 tonnes in order for the car to travel 100 km. Furthermore, what would a combustion engine that produces the same power in a car that has the same body and mass use in terms of fuel compared to the sterling engine?

What are the requirements for a sterling engine to perform at the same level as a combustion engine in an automobile?


texts: Is it possible to do purification of Sodium Sulphate and which companies do this?

texts: If Sinter filter generates lots of Sodium Sulphate and then is there a way to make purification of this and which companies are already do this process?


texts: Is it possible to silver solder a reliable grounding connection to a stainless steel ultrasonic cleaner tank?

texts:
My ultrasonic cleaner has a stainless steel tank with a threaded grounding stud for fastening a mains earth wire. I tried to tighten nut that fastens the ground terminal to the stud, but the stud sheared cleanly off the tank.  It appears it was either spot welded, soldered or brazed on.
Unfortunately, I can't think of another way to reliably ground the tank. I'm considering silver soldering or brazing the stud back on, but I fear a couple of issues:

The brazing or soldering material could corrode over time since they're likely to be dissimilar metals.
The ultrasonic cleaning vibration could compromise the resulting joint over time leading to failure.

Should I be concerned with any of these issues? Is there a better alternative to these methods?


texts: Galvanic corrosion in a non-corroding environment

texts:
If we submerge a welded structure of, for example, Duplex (1.4462) and Stainless Steel (1.4301) in water, which is normally not a threat for either of these materials alone, do we see corrosion in the Stainless Steel due to galvanic coupling? Is there an electric potential difference between these materials in water or does it depend on the substance they are submerged in?

I can see that in a corroding environment where the materials would trade electrons with the environment, then the electrons lost by the more noble material (Duplex) would be replaced by electrons from the less noble material (Stainless Steel).


texts:
I already know solution, I just want to understand something in part b.

A vertical cylinder fitted with a piston contains air initially at 120kPa and 100 celcius. The piston is restrained by a set of stops. The piston diameter is 0.1m, its mass is 5kg, and the ambient pressure and temperature are 100kPa and 20 celcius. The cylinder is then cooled as heat is transferred to the surroundings.

a) At what temperature does the piston fall below the stops?

b) How far down (as a fraction of its initial height) has the piston moved when the contents of the cylinder has cooled to the ambient temperature?

a)
So this is assumed to be a 3-step process:

$ P_2 = P_{external} + \frac{mg}{A} $

Volume is supposedly constant from 1 to 2:

$ \frac{P_1 V_1}{T_1} = m R = \frac{P_2 V_2}{T_2} $

So $ \frac{P_1}{T_1} = \frac{P_2}{T_2}$

$ T_2 = T_1 \cdot \frac{P_2}{P_1} $

b)

Since 2 -> 3 is supposedly a constant pressure process:

$ \frac{P_3 V_3}{T_3} = \frac{P_2 V_2}{T_2} $ or $ \frac{V_3}{V_2} = \frac{T_3}{T_2}$

So $ \frac{V_2 - V_3}{V_2} = \frac{\delta h}{h_2} $

So my question is, if the ideal gas equation is:

$ P V = mR \cdot T$

$m$, $R$ are constants

and if the temperature changes, then on the left hand side either pressure of volume can change, how is it known that from process 1 to 2, volume stays constant?

The problem postulates that heat of system will be cooled down by the surrounding temperature (20 C), nothing's said about neither pressure nor volume. So either of them can change... how does one know that volume stays the same from process going from 1 to 2?


texts: Why does India have more than 1 MCC (Mobile Country Code)?

texts: I was checking the list of MCC (Mobile Country Codes) on Wikipedia and found that India has two MCC: 404 and 405. 404 contains only GSM/UMTS/LTE operator bands and 405 contains both GSM/UMTS/LTE and CDMA operator bands. The problem is that I do not understand the reason for having 2 MCC for the same country. We also have mobile network code (MNC) to differentiate between various operators, circles and the bands.


texts: How to determine if mass transfer convection is natural or forced?

texts: I know that forced convection requires some external bulk flow, but is there an equation to determine which form of Convection is dominant? I looked around and found the Richardson number $\mathrm{Ri}=\frac{\mathrm{Gr}}{\mathrm{Re}^2}$ but I don't know how to interpret the number or if it even applies to mass transfer.


texts:
I just watched this video: https://www.facebook.com/HigherPerspective/videos/1162007547164896/

I don't understand what I see. If the spinner's magnetic, the bowl is made of iron and that the wood piece is magnetic too. Shouldn't the iron bowl mess the magnetic field? Can someone explain how this works?

Another similar image from Wikipedia:


texts: Is it possible to use Ammonia vapor in steam turbine

texts:
I am currently designing a prototype. I have asked to use low boiling point liquid to run a steam turbine. So i am thinking of using liquid ammonia.

What are the complications involved when using vapor ammonia in a steam turbine. Is it possible to run a small steam turbine using ammonia vapor?


texts: Hot neutral in UPS devices in battery mode

texts: I have faced a problem with ITYS E-3KVA UPS device. While operating in the in-line mode the measured neutral-ground voltage is almost equal to zero. However, during the battery mode the neutral-ground voltage is equal to 102 V. Knowing that the UPS is properly grounded and the wiring network was checked many times and everything was ok. This neutral-ground voltage caused a serious damage to the medical devices we use. Could you please provide me with a thorough analysis, from your point of view, and tell me how to overcome this problem. Thanks in advance


texts: Light bulbs with highest energy efficiency

texts:
Most specs for light bulbs list luminous efficiency (or, more accurately sometimes, luminous efficacy) but not energy efficiency. Luminous efficacy tells you how bright the light is as observed by a human eye per unit of input electricity. Unfortunately, the human eye is terrible at measuring power and its very hard to convert between lumens/spectrum/human eye/radiant power.

I'm curious as to which types of lights have the highest energy efficiency, which I'm defining the amount of energy that would be absorbed by a perfect absorber surrounding the light bulb divided by the electric input. In this metric, the light is just a one form that the energy takes between electricity and its absorbed form (eg, heat). Obviously the exergy is degraded in this process, but I'm not worried about that here.

I would expect that incandescents are near 100% efficient by this metric since the only losses should be conduction/convection from the element through the near-vacuum and wires. This weakly scientific analysis suggests that LEDs are probably only 40% efficient by this metric because all their luminous inefficiencies are thermal losses in the cells. I think fluorescent lights might be extremely efficient by this metric but I can't really find any data.

I found the phrase "radiant efficiency" somewhat useful but still can't find much in manufacturers data sheets. Is there a better name for the metric I've described or a good database for what values might be?

In response to comments: I am interested in the power radiated away from the light bulb in the form of electromagnetic radiation divided by the electric power that goes in to the lightbulb. I don't care about the wavelength of the light (even though I understand that it changes both how much you can see and how much can be recaptured in another form later). I do care about thermal losses inside the bulb that don't radiate power across a distance.


texts: How can dross/slag formation be reduced during aluminum recycling?

texts:
I have furnace for aluminum recycling wherein dross formation is a major issue. It reduces the yield by about 10-12%.

I am looking for change in process parameters or other solutions through which I can reduce the dross formation.


texts:
I'm going to simulate an automotive radiator . The method called $\varepsilon$- NTU , suggests following steps to calculate the heat rejection,$Q$, of a heat exchanger:
1-calculate $U$(overall heat transfer coefficient)
2- calculate $NTU$
3- calculate $\varepsilon$ and finally calculate $Q(W)$.
My question is about calculation of $U$ in automotive radiators. We can neglect fouling and wall resistances and write:
$$
 \frac{1}{UA} = \frac{1}{\eta_aA_ah_a}+\frac{1}{A_wh_w}
$$
$U$: Overall heat transfer coefficient. $A$ : Air side or waterside area. $A_a$ : Air side heat transfer area$A_w$: Waterside heat transfer Area $h$ : heat transfer coefficient $\eta_a$ air side surface efficiency.I want to use Shanoun & Webb formula to calculate the first term of the above equation(Air thermal resistance). They propose following equation for automotive radiators:  $$ (\eta Ah)_a=(\eta_f Ah)_{l} +(\eta_f Ah)_{S1}+(\eta_f Ah)_{S2}+h_eA_e$$  You can find regions named louvered(l),S1,S2 and e in following image:   This is image of a fin between 2 flat tubes.Question:  Shanoun and Webb just enter areas relating to one fin in their equation. So when we want to calculate $UA$, we account total surface of water$A_w$ but just a small surface of air side$A_a$. It makes the answer wrong. How can we use this formula to calculate $UA$ ?


texts: What is a "window of length N" in a signal processing algorithm?

texts:
I am reading a scientific paper in which an algorithm for evaluating an electromyography signal is described and I just don't get the meaning of the word "window" in the following part of a sentence: (First full paragraph of page 4)

  "Fig. 5 shows ... signals ... over two windows of length N = 500 "

What is window supposed to mean here?


texts: Is Solidworks Motion capable of finding the torque of the planet carrier (output) in a planetary gear set when in steady state? The sun and ring gears are both inputs and all gears are rotating at a constant angular velocity.


texts: Applications for Rankine, Coulomb, and Terzaghi horizontal earth pressure theories

texts:
All of these theories are in use today, and anyone can look up the definition of each theory in a textbook.

But what are the practical applications for each theory, or said another way, in what situations should one theory be preferred to the others? Compilation of a general list would be most useful.


texts: Machine that can paint a bulk of small objects all over

texts: What type of machines are used to paint a bulk of small objects all over... things like buttons, keys, ping pong balls, paperclips etc.


texts: How does one create a draft in a room (with a single window)?

texts:
There is a room on the south side of the building, which doesn't have any ventilation vents, but does have a window.

Opening a window doesn't cause good air circulation (by which I mean that the air in the room is still hot, and the air on the street is still cold).

How does one create good air circulation in a room --with a single window- without using a fan or air conditioner?


texts:
I recently read about a newly proposed 'burger' lane across a roundabout.

burger lane plan http://www.gloucestershirelive.co.uk/images/localworld/ugc-images/276271/Article/images/29745204/15574035-large.jpg

From what I can see,  it bypasses the main point of a roundabout, a continuous circle of traffic with well defined rights of way. The only reason I can imagine one is to stop a tributary to the roundabout clogging the other entrances,but I don't understand how that would be achieved.

What's the purpose of a 'burger' lane in a roundabout?


texts: Dominant parameters in the dynamical response of a linear oscillator

texts:
I am working with a very simple 3-DOF damped LTI spring-mass system. As an exercise I am altering two parameters simultaneously (stiffness and damping coefficients connecting mass 1 to mass 2) to see which combination minimizes:

Settling time
Overshoot

The objective is to determine which parameter has the greater effect on the performance, either the stiffness or the damping.

My question is: How can I determine if changing stiffness or damping is having more of an effect on the aforementioned criteria ? Is there a way to quantify how they contribute to the performance ?


texts: Head loss from rectangular slot orifice flowing up?

texts:
For sizing purposes I'm trying to calculate head loss for a level spreader outlet for water, where the water is being supplied from below by pressure. It's essentially a reverse slot drain—instead of water flowing down the slot and leaving, it's entering from below and leaving up through the top of the slot. There's no outlet pipe; everything leaves through the slot for the purposes of this calculation. Here's a sketch showing two views of it (I left off the inlet pipe):

Once the water leaves the slot, vertically, I know it can be modeled as weir flow, so I can calculate the height it would have to reach for a given flow rate for a sharp rectangular weir of its length. From that I know I need at least enough head/water height to reach that height above the slot: $D_{pipe} + H_{slot} + H_{weir}$.

My question is, how do I model the friction losses from the slot itself? I imagine the width of the slot to be significant, at least for small enough widths. I found a rectangular submerged orifice equation from this site (using cfs & square feet):

  $Q = 0.61A \cdot \sqrt{64.4 \cdot H} $

and there are definite similarities: the top of the slot in my problem is also a rectangular opening that, once enough water is flowing, will have water on all sides. However, it's turned 90 degrees, so I feel that the above equation might not be appropriate. I imagine the equation above takes into consideration the need for additional head to drive enough horizontal flow, which might be different from the vertical flow in the slot I'm considering.

What's an appropriate way to calculate the head loss from the slot opening itself?


texts: Has anyone built a heat powered vapor compression cooler?

texts:
I've had this idea in my head for a refrigeration cycle which is powered by heat, uses only one fluid, and whose only moving part is the fluid.
I would like to know if my idea is new, or if it's something which was tried and abandoned.
I'll describe my idea in terms of water and steam, but other fluids would likly work just as well.
The system starts with the boiler, where external heat is added, to turn the water passing through into steam.
Some of the steam from the boiler is used to power an old fashioned "steam injector" which is to pump water into the boiler.
The rest of the steam from the boiler is used as the motive fluid for an aspirator (one of two).
The condenser receives steam from the steam powered aspirator, rejects waste heat into the envionment, and turns steam into water.
Some of the water from the condenser is injected into the boiler, the remainder is used as the motive fluid for our second aspirator.
The water powered aspirator sucks in cold steam from the evaporator, and spits it into a gas/liquid separator.
Water from the separator passes through an orifice tube into the evaporator; steam from the separator is sucked out by the steam powered aspirator and discharged into the condenser.
If my idea is in fact new... I would love to know if any thinks it would work, and how it's efficiency might compare with a typical absorption system.
I'm not mechanically inclined, and have no means of testing this myself.


texts: Transfer pump suitable for air, water and their mixture

texts:
I need a pump that can remove water from certain volume (~300ml). Water mixed with washing agent (soap) is pumped into this volume using another pump ~5-20L/minute. This volume is not completely sealed - air can get inside (sometimes easily, sometimes in very limited quantities). I need to guarantee that water will not spill out of this volume. In my understanding I need a water transfer pump, but such that can run dry for a while and work as vacuum pump. I looked what market has to offer, but didn't find anything like that.

So the question is - does such pump exist at all? If so, how it is called, so I can search for it online?


texts: Why are freezerless refrigerators more efficient?

texts: Why are freezerless refrigerators more efficient and just out of curiosity, about how much energy can I save per month per cubic feet by going all-refrigerator?


texts: How can I compute the thickness of a pole of a given material that is needed to carry a given load?

texts:
I want to compare those values for different materials, e.g. wood (pine, cork) and plastic polymers (HDPE,PP). So I want to compute the max load for a given material and cross section. Can I say that the max load is prportional to the cross area? and is this also true when I use hollow poles?
Another question is what happen when the pole is loaded for limited amount of time. Can I tell when a pole that is loaded with, say, 20% more then its max load, will crush when loaded for 30 minutes every day?

And a question I'm very interested in is which cheap material will give me max strength per its density?


texts:
It is possible with a microphones array to isolate a sound coming from a direction. Is it possible with an array of photo diodes to isolate a light signal coming from one direction?

For example having 4 photo-diodes oriented at the same direction, spaced by 2 cm, and facing lamps at the ceiling, is it possible to isolate the amplitude of each light source reaching the photo-diodes from different directions (different lamps). What would be the algorithm or the method used for doing such thing?


texts:
I have heard it said that the Laplace transform has "many applications". But the only "applications" that I ever came across are those that require one to solve either some kind of differential equation.

Can you provide an application of the transform, where the transform of the function allows one to solve a problem, but which is not differential equation related.

For example, the Fourier transform has applications to signal processing, where one sends/receives signals by transforming and inverting them afterwards. This application with the Fourier transform has no interest in any differential equation solution. Is there a similar application for Laplace?


texts:
I am simulating a furnace as follows:

Is it possible to capture temperature distribution in this furnace without designing intake fan? Which kind of boundary conditions can replace with intake fan?
In this model, there is a electrical element for generating heat (in fact, transferring heat to air flow). How can I set this element as a boundary condition?

In addition, There are four cylinder in this model and they rotate. I want to obtain temperature distribution around these cylinders.

This problem is unsteady an 3D. Firstly (t=0), temperature in furnace is 25 but when air flow cross air duct and electrical element, temperature in exit of duct is equal to 200 C. All of furnace walls are adiabatic. Therefore, We have two kind of work(electrical work and mechanical work) and Q=0.

What information (pressure, temperature, heat flux, power and ...) should I have for boundary conditions in parts of Fan and element?

Major goal in this simulation is to find that temperature distribution (inside the furnace) is uniform or not (i.e 200 C).

I am grateful that guide me and give me useful links and documents in this case.


texts: If an aircraft's wing blows air downwards, how is the momentum conserved in level flight?

texts: An aircraft's wing generates force of lift by directing the oncoming airflow down. How is this momentum balanced when the aircraft is not climbing, but maintains level flight?


texts: Calculation for heat transfer rate / cooling capacity for air cooled solid

texts:
I have a pipe which is channeling air flow from a compressor with a known mass flow rate and temperature. I can adjust the mass flow rate (power setting) and measure the delta T for the temp of air coming out the nozzle for each setting. It's for a cooling application and I want to maximise mass flow rate and minimise temperature of the flow. How can I optimise this system?

The air is channeled perpendicular to the disc solid with a gap between the nozzle and the solid to allow the air flow to dissipate. The nozzle and the disc are fixed.


texts:
i'm trying to apply free body diagram to simplified excavator consept.

As you see, earth drill causes moment on  the arm. If we know the "L", we can find F = M / L. But let's say ground friction is very very high. The F force cant move the excavator. Then the arm is going to try take excavator down. Because the arm comes from upper not the ground level.

So the problem is how can i find the force and its moment arm which causes taking down?


texts: What is the maximum force needed to move the roller block from point A to point B and where does that maximum force occur?

texts: Hello everyone. This project is for a very specific application and I am trying to determine the force necessary to get the block from point A to B. Specifically the maximum force necessary and at what point it happens. Ideally this would be solved parametrically so that I could determine the force needed at any point along the travel (x axis), but I have included all of the measurements as well. A few things to note: the rolling block is securely fixed to a track with a quality bearing system. As the block is pushed forward, the platform increases in angle. The system is static at point A, then as the block moves forward most of the force is on the x axis, and then of course at some point in travel the majority force is transferred to the y axis. I do not have a coefficient of friction for the bearing system, and of course this will increase as more force is transferred to the y axis, but hopefully someone who can answer this will be able to address how to handle that in a general manner. It would be fantastic to have a differential equation derived for force as a function of the travel distance, but if anyone could show me how to simply determine the maximum force needed that would suffice. This is not a homework or exam question and I am not a mechanical engineer, obviously lol. I made this with Paint 3D. If you get really precise with the measurements I've given you will see that the trig doesn't exactly work out, but it's close. I simply need to know the method so I can dial in the measurements later. Thanks in advance!


texts:
I want to build an electric motorcycle ( more of an electric bike, actually), but i don't want to use a conversion kit.

I want to take out the pedals and put a motor there (either 12v DC or 220v AC).
My problem is how to transfer the power from the engine to the rear wheel:
Do I need some sort of gearbox?
Let's say I would use a 0.7kw, 3000rpm 220v AC motor:
How do I connect the spinning rod of the motor to a chain or belt (it doesn't necessarily have to be chain driven€

Is this a bad idea? Can the motor drive the wheel directly? The whole thing (including the rider) would weigh less than 150kg. 0.7kw is enough for the speed I desire. (I am interested in building a dirt bike actually...)

Excuse my English, I am not a native speaker.


texts: What are the moisture related issues in the use of Stucco and EIFS in the building construction Industry?

texts:
I am investigating the use of stucco masonry versus Exterior Insulation and Finish Systems (EIFS) in the construction industry. I have no knowledge or training in this matter and my knowledge is limited to what I have read in the past few days.
Stucco

As I understand it, both stucco and EIFS have a long history in the building construction industry. I have also read that there are two type of EIFS, PB (polymer-based) and PM (polymer modified) systems widely used in the building construction industry.
Exterior Insulation and Finish Systems (EIFS)

Question: What are the moisture related issues in the of Stucco and EIFS with regards to mold buildup with respect to corrugated aluminum siding? Once again my primary interest is with to respect to moisture and mold.

References:

How do I mitigate moisture problems when putting up drywall over stucco with torn tar paper?
Exterior insulation finishing system
EIFS vs. Stucco: What’s the Difference?
Stucco System


texts:
I have to determinate the power (Watts) for an oven to reach the Temperature Reference. And I have been given only the function to apply power to the oven and read the temperature.

I've reading the Ziegler-Nichols method. And the first step is to obtain the tangent in the inflection point, and then check the values of:

L : The point where the tangent intersect the x axis
T : The point where the tangent intersect the reference line

But I do not understand one thing, the range of the power I can apply power from 0 to 10,000(W).

Do I have to calc this tangent for a static random Power? But which value, because it will be the same in "production mode", when the power is vary because of the controller?


texts: Control each axis separately - quadcopter

texts:
I would like to know why axis can be controlled independently in a quadcopter. I mean, I was told that you can control $x$ and $y$ independently but I couldn't find a demonstration
Edit: the testbench that is used when you want to see how the response of a quadcopter would be is a one arm quadcopter (i.e, just 2 propellers like this:

That testbench can be used because you can control how the response of the $x$ axis is and then use the $y$ axis. And, when you put both axis together, each axis response would be as they were in the testbench
How can we demonstrate that?
Or, the question would be: why you can use a one-arm testbench for a quadcopter?


texts: I'm looking to design a push button mechanism similar to the soda gun where water is forced to pass through a single passage based on which button has been pressed. What are the different approaches I can take to solving this problem? This is a purely mechanical design problem, without the aid of electricity.


texts: Torque sensitivity of a VFD induction motor through a gearbox?

texts:
I have an application that requires torque limiting and I need to determine if VFD torque limiting will provide sufficient protection. I have used VFDs for torque limiting through gearboxes before with success, but I am hoping to find a way to calculate the result as opposed to just gut feeling.

10HP motor
1775 rpm
69.5:1 gearbox reduction (im assuming 50% efficient)
25.5 rpm at driving sprocket

I have looked at some frequency drives to get an indication of their torque/amp sensitivity. Ive seen 0.1A, 0.01A, 0.1% of torque and 0.01% of torque as control resolutions, but have not found any literature specifically addressing if this resolution can be reasonably expected.

In this situation I am gearing down, so inertia, backlash and controller reaction time will not be an issue.


texts: When calculating a car's suspension caster, after turning the steering wheel 20 degrees, why multiply by 1.5?

texts:
To calculate caster of one side of a vehicle, the steering wheel is turned 20 degrees to the left, and the camber is obtained; this represents the 'in' value of the front right tire. Then the steering wheel is turned 40 degrees in the opposite direction; this is the 'out' value for the front right tire. The two values are subtracted from each other, and then multiplied by 1.5, to obtain the caster, for that particular side of that car.

If the steering wheel is turned by 15 degrees, instead of 20 degrees, the constant is 2.0 instead of 1.5.

For 10 degrees, the constant is 3.0.

I'm wondering how these constants, 1.5/2.0/3.0 are obtained? I presume it has something to do with the unit circle?


texts:
This is probably a fairly basic question for seasoned Siemens NX users, but I can't find a solution anywhere.

I have a large assembly and I would like to set certain components to wire frame view, while still viewing other parts as solid bodies. I know it's possible, because apparently I've done it before, but I can't remember or find how I did it.

I can set the entire assembly to wire frame easily enough, but I would like to set only certain parts to be.

Also, when I go into the part (the limit switch in this case) the part default is NOT wire frame but a solid body. I'm assuming (hoping) there is a setting in the assembly that I can toggle off/on per part as needed. Solidworks had something very similar, but I'm not using NX and am still inexperienced with the available tools.

Hopefully this is an acceptable forum to be asking this!


texts: How thick does my stainless steel table top need to be?

texts:
I need to construct a table that will hold a water tank. The filled tank will weigh up to 1300 pounds. I have the table leg frames worked out to hold 2500 pounds so no worries there. (Here is a link to details.)

They are just a 28" x 34" rectangle. The tank itself has a footprint of 30" x 38" and is made of molded polyethylene, so don't count on its rigidity for support. The table top will be 36" x 48". (It is bigger than the tank solely because I can buy it off the shelf at that size without any fabrication cost.) There will be no motion to account for nor any rapid changes in the weight. So my question is how thick does the stainless steel table top need to be to safely bear 1300 pounds?


texts: How to connect butted or overlapping fiberglass insulation

texts:
We are working on a project requiring a temperature-controlled oven for melting lead, tin and other low-temperature metals.  The inner cylinder is aluminum.  The heat comes from Kanthal wire, for which we needed an electrical insulator capable of withstanding the heat.  The problem is, something must hold the fiberglass in place.  We just tried to melt the stuff end-to-end (does not hold) and with an overlap (gets blackened, shrinks, but does hold a tiny bit).  We have thought of a couple of alternative ideas:

Add glass powder, sand, or broken glass to the area of the joint and have more glass available to melt
Get some kind of glass fiber and "sew" the layers together somehow
Some kind of chemical adhesive that can handle the same extremes of temperature

The plan is to wrap a thin layer of fiberglass around the inner aluminum, then wrap with Kanthal wire.  Then wrap more fiberglass around that and cover with aluminum, and do enough layers that the outside is not hot to the touch.  An Arduino will control the circuit, and slowly bring the inside up to exactly the temperature we want using a thermocouple.

How can we hold the fiberglass insulation in place without interfering with or shorting out the Kanthal wires that will go around the fiberglass?


texts:
What is the meaning of clutch fill?
See for example this paper.


texts: How to add Beam cross section properties to imported mesh in Ansys?

texts:
Ansys Workbench 17.1

I have a mesh that was imported from Abaqus into Ansys but the beam cross section data is missing. As a result the structural model omits the beam elements.

How do I access the beam cross section data in Ansys? I cant find any way to do it in the FE Modeler, Mechanical Model or Mesh modules so far.

EDIT: There appears to be no way of directly doing this in Ansys Work Bench or AIM. I had to write some code the alter the *inp files to include the missing information prior to importing to Ansys.


texts: How to draw a shear force diagram when two forces are acting at the same point

texts:
I am working on this question on my statics assignment:
Approximately at point B there are two forces, 20kN and 50kN.So far, I have only calculated global equilibrium and got the following values:

$D_y=(\frac{80}{7})kN$
$D_x=(\frac{20}{\frac{\sqrt{13}}{2}})kN$

$A_y\approx89.094 kN$

My question here is, when I'm drawing the shear force diagram do I sum up the 20kN force and the 50kN force into one resultant and graph it? Or, do I draw them separately. I need help.


texts: I have build my own bridge from paper and i want to know the elastic module for the bridge, my bridge is flat all over the way and cylindrical from the sides.


texts: What is the test procedures for a flame arrester?

texts:
A flame arrester is basically a heat exchanger in front of the tubulure. It conducts the heat of flame to some other place (to the liquid and/or the container especially if the container is built from a metal material), thereby extinguishes the flame before getting into the container.

I built a simple flame arrester with a tea strainer in front of the bottle and dumped some drops of denaturated alcohol into the fire. A controlled experiment demonstrated that the flame arrester works and if there is no flame arrester, an explosion is inevitable.

However, I don't think I should use this approach in a real-life situation because I can't know how much flame the arrester could arrest in a real case.

How can I test a proper flame arrester if it is produced correctly?


texts: Solar Radiation Environmental Test Duration

texts:
I am designing an outdoor sensor and I need to test it for continuous outdoors service. One of the test I wish to perform is a solar radiation test for the actinic effect (like procedure 2 in MIL-STD-810). I want to examine how the sensor will behave under continuous thermal radiation from the sun.
The problem is that MIL-STD-810 states that I have to make a 56 days long test, which is not practical. If I go to civil standards like IEC60068-2-5 then they do not suggest a test duration at all.

How would you test an outdoors unit to validate it's integrity under long time solar radiation?

Thanks in advance!
Eli


texts: Can this SpaceX Starlink ground station antenna's gear mechanism move it in both altitude and azimuth?

texts:
Ars Technica's Teardown of “Dishy McFlatface,” the SpaceX Starlink user terminal links to the YouTube video Starlink Teardown: DISHY DESTROYED! and a screenshot from there is shown below.
There are three 45 degree bevel gears; the two on each side connect to motors and the one in the center seems fixed relative to the mounting posts.
Question: I'm wondering if by driving the substantial-looking motors in the same versus opposite direction this kind of mechanisms could both rotate around the shaft (azimuth) and point up and down (altitude or elevation)?
This answer to How should we point our SpaceX Starlink ground transceiver antennas? in Space Exploration SE confirms that even the current dishes move somehow but it's not specific. The antenna is not parabolic reflector like a "direct-TV"receiver, but instead is an array antenna. It seems that in order to maximize exposure at all angles they've decided to articulate the array mechanically for at least some of the satellite tracking, rather than use electronic phasing of each element alone. This way the antenna can always present near-maximum area to the StarLink satellites as they pass back and forth across the sky every few minutes.

click for larger view or watch the linked video


texts: What is the difference between direct and indirect reading instruments

texts: I need to know the difference between a direct and indirect reading instrument. Would a caliper be a direct and a gauge block be indirect? Is a direct instrument something with a variable measurement and indirect something with just a fixed measurement?


texts: Volumetric oil pump efficiency goes up when viscosity goes down?? Strange behaviour

texts:
Riddle me this : we are driving an external gear pump (this kind) at a fixed RPM.
At start, when the oil temperature is low (and viscosity high), the volumetric flow is much less than when the oil starts to warm up.
For exemple, we have a ratio of around 5 in volumetric flow when the oil goes from 10°C to 80°C.
Every pump expert we've talked about has told us that this should be the other way around (and definitely not in that proportion, more like 5-10%) because the slip of a less viscous fluid will degrade the volumetric efficiency of the pump.
Nevertheless, we ran the tests and even made some volume/time measurement (to remove a flowmeter error from the equation) and they are consistent...
Also, the circuit is super simple (tank-pump-restriction-back to tank) and there's really nothing that could explain that...
Thanks for your feedback!


texts: Determining stability of a current souce from the datasheet. How to?

texts:
Is there any way to calculate the stability of an instrument such as current sources and digital voltmeters from their datasheet?
Let me provide one example. My application requires stable current sources (better than 100ppm for a few hours) capable of feeding a probe with 10 mA. In principle, I could use the Keithley 6221 to do so. If I check its datasheet, I find this:

For 10 mA, the accuracy would be +/-(0.05% * 10 mA + 10 uA) = +/-15 uA (1500 ppm with regard to 10 mA). Of course this is accuracy and not stability. But then, with the information above, how could I tell whether this instrument is or is not appropriate for my 100ppm stability specs? Can I reach any conclusion just based on the typical noise? If so, how to?
Thanks, folks, Take care.


texts: What technologies prevent drones from being as efficient as birds?

texts: We have large scale aircraft with long endurance and much higher speed than birds. But it seems that aircraft of comparable size to birds (i.e. drones) have much lower endurance, top speed and flight range. What technologies are currently limiting us from achieving this?


texts: How is it possible that it took until the 1950s or even longer before they started using car belts and neck-supported seats?

texts:
I've spent a large amount of my life thinking back on past times, both long ago and "recently", meaning ~1950s to me.

A lot of things make sense, but some things just fundamentally baffle me. One of those things is the seemingly total disregard for safety when driving cars.

People were not idiots a few decades ago. Well, at least not the ones who invented and manufactured large machines such as cars. They must have very quickly, long before the 1950s, had tons of evidence of people dying in traffic accidents, or getting seriously hurt. How did it not occur to them to have some kind of belt or any other safety measure?

It's not like the safety belt wasn't invented, and used in various military contexts. And even if that weren't the case, it's a very obvious invention. We aren't talking about hi-tech sensors and air bags all around the passengers and refined safety measures like that -- we're talking about a basic belt around the humans so that they don't come flying through the window and become a pulp of blood and guts.

And those seats, leaving the whole head part "free", seems just silly as well. Who felt safe driving like that? Even at a low speed, you can feel it in your neck when there is an unexpected stop and there is nothing supporting your back of the head. These two things seem like they would've been implemented at the latest months after the modern car was invented in what I assume must've been around 1900 -- long before the 1950s when they (well, some) seemingly started to even consider human lives and health in the making of cars.

I can understand if they didn't bothered with seat belts in a wagon powered by one or two horses, but even then, they probably had some kind of handle or something to grab on to. When you introduce powerful engines, well, it just seems to go without saying that you would have to think about the consequences.

Is it possible that I'm somehow over-estimating the amount and seriousness of car crashes and traffic accidents in general? Did people really not care whatsoever about whether they were alive or dead or in a hospital for the rest of their lives, as long as they got to drive a car without any safety measures whatsoever? I don't understand this mentality, and I'm having a hard time understanding it.

Again, many other things can usually be explained in a satisfactory way, but this especially just doesn't make sense to me.


texts:
I ran across the diagram below in the mindtomachine blog post describing an homebrew arc welder.   It shows two transformers with inputs in parallel and outputs in series.   Is there some advantage to this arrangement rather than a single transformer with a doubled turns ratio?

Perhaps it's just what he had at hand, but I wanted to confirm with someone having EE background.

P.S.  I'm not planning on building this, just curious.


texts: Fan starts making noise and air flow is reduced considerably

texts:
Yeah.. I dont know if this belongs here, I coulnd´t find a proper stack exhange site for this but it sort of involves physics I guess so... yeah.

Basically, I have a ventilator, that after a few mins of functioning starts making this weird noise, like if the air is somehow trapped, and indeed the air flow is reduced considerably.

Feels like if something like a curtain got glued behind the fan, however there is nothing there.

No idea how to even approach this problem, all I know is that this sound comes along with an air flow reduction of about 75%, which sucks.

Any suggestion is very welcome.

Thanks.

This is the ventilator model: https://http2.mlstatic.com/D_NP_627075-MLA29187536462_012019-Q.jpg

Also if I turn it off and wait until the blades stop spinning, then turn it on again the problem goes away for a few seconds/minutes. It´s like it resets.


texts:
I'm encountering some troubles while trying to solve this exercise.

Let us consider a radio link between a geostationary satellite and a ground station. We send a binary signal (represented by two voltage levels), which got filtered by a rised cosine filter, frequency modulated to $f_p = 4~\text{GHz}$ with modulation index $I_f = 9$. We have to guarantee a signal-to-noise ratio after demodulation (let's call it SNRAD) of 15 dB.

The exercise asks to determine the bandwidth $B$ of the modulating signal known that:

At the receiver input the noise power, in the same bandwidth of the received signal, is $W_N = -100~\text{dBm}$;
The system temperature is $T_s = 290~\text{K}$;
The text of the exercise recalls that the bandwidth of the whole frequency modulated signal is 4 times the Carson's Bandwidth: $B_{tot} = 4B_c = 4B\left(I_f + 1\right)$.

Do someone have any suggestions about how to solve this exercise?

EDIT. I've tried to use the SNRAD information to obtain the SNR of the received signal, but I don't know if it is a correct way to use this information. By the way, as you will notice, the number that I obtain in this way seems incorrect since it is too low.

$SNRAD=3 I_f ^2 SNR = 3 ~ \cdot ~ 81 ~ \cdot ~ SNR = 243 ~ \cdot ~ SNR$

which in dB becomes

$ SNRAD_{dB} = 15 \text{dB} = 23.86 \text{dB} + SNR_{dB}$

from which I obtain something strange:

$ SNR_{dB} = 15 \text{dB} - 23.86 \text{dB} = -8,86 \text{dB}.$

A second approach I thought to calculate the bandwidth is to use the information given about the noise power level in the same bandwidth of the received signal. Again I don't know formulas which link the two things (noise power level and bandwidth) and the SNR obtained before seems too low.

EDIT2. I forget to try the classical formula which link the noise power level with the bandwidth considered. In this case we have:

$W_N = F k_B T B$

where $F = \frac{T_s + T_0}{T_s}$ . Now we have another problem, we have two unknown variables: the received signal power level (S) and the bandwidth of that signal (B) which need to find to solve the exercise. In fact:

$SNR_{dB} = -8.86 \text{dB} = S_{dB} - W_{N,dB}$ .


texts: What will be the effect of torque and wheel diameter on the stability of a robot?

texts: I'm building a self balancing robot and would like to know how the wheel diameter and the torque provided by DC motors, would affect the overall stability and response of the robot. The balancing bot is based on the principle of an inverted pendulum.


texts:
I am making a sandwich design. I designed two parts that fit well together and assembled on Solidworks.
Top part:

bottom part:

The two parts are attached like two LEGO pieces. I want to pump water through one of the middle holes at the top part and exist through the other. My first plan is to glue the two-parts together. However, I feel that water will leak at the points where the two parts meet. Is there a smarter method in the 3D printing community ?


texts: What does 1 x rpm or 2 x rpm or 3 x rpm in vibration analysis mean?

texts:
a description for virbation monitoring of industrial bearings states:

  peak amplitues at 1 x rpm

should be an indicator for a fault in my case. Can somebody explain me what I have to understand under 1 x rpm. My chart (FFT) shows Amplitude in m/s^2 on the y-axis and Frquency in [Hz] on the x-axis.

Do I need to know how much rotations my bearings do in one minute? If somebody can give an example, also was 2 x rpm mean and how I calculate this value?

Thanks in advance!


texts: How do I solve for the mole and mass flow rates in a system?

texts:
I've been trying to solve this problem for a while with no success.  I think I figured out that $m_1$ is $420 kg/hr$ and that $n_{3,A} = 3 kmol/h$ using the mass balance equation:

$input-output+generation-consumption=accumulation$

where steady state conditions mean there will be no accumulation and the lack of a reaction means that there will be no generation or consumption.

Everything else I've tried to solve for the remaining values has led me to a dead end (420=420, 16=16, etc.)  Any help would be greatly appreciated!


texts: Mechanical Linkage Question - Velocity Diagram

texts:
Can someone confirm the velocity of B, given point C has velocity of 3 units/s down and point A has a velocity of 5 units/s upwards?

My approach has been to resolve for the tangent velocity component of B with respect to A, and tangent component of velocity B with respect to C, then found the resultant B using the two aforementioned tangents?

Any thoughts?


texts: How do the dimensions of a ductile iron casting change as it cools?

texts:
I am designing a pattern for a sand casting. It has only one critical dimension which is a 4" inner diameter cylinder. If I use a 4" core, will the casting shrink away from the core? In other words will the inner diameter of the cylinder end up being 4.1" or something like that? What kind of shrinkage can I expect for ductile iron?

The cylinder needs to be a sliding fit on a 4" diameter painted, mill finish steel column. The inner diameter of the cylinder should end up being no more than 4.05".


texts: Unexpected jamming of a misaligned assembly

texts:
I have a small assembly with several parts misaligned. By turning the grey wheel, the grey block is to rotate about its axis (Axis 1). The problem I have is that the grey wheel can't be turned further anti-clockwise given the current position. It seems to be jammed.

The red connecting rod can freely slide in the yellow bore, which itself can rotate with the rod in the grey bore. I'd expect the red rod to extend further and turn the yellow connector.

Does anyone know why the wheel might be jammed or how it could be modified to allow continuous rotation?


texts: Does the frequency of input voltage in induction motors have to be continuously altered?

texts: I understand that for magnetic lines of the rotating magnetic field to cut the windings of the rotor (and induce current), the field has to rotate at a slightly higher rate than the rotor. But if we assume the motor starts from zero RPM, at what speed does the field rotate at this moment in time? Do we have to somehow sense the rotating speed of the rotor and adjust the frequency of the 3-phase input voltage somehow? I think this is not what happens, since such a requirement seems somewhat complicated to achieve, especially given that induction motors have been around for quite a long time. So what am I missing?


texts: Specifications of Tensile Test Specimen?

texts:
I am Currently Working on Measuring Various Mechanical Properties of Metalic Materials using Universal Testing Machine (UTM) at Various Temperatures. I know that for Testing at Ambient Conditions, ASTM E8/E8M is followed.
By Literature Review, I have Identified the Specimen Dimensions for My Experiments.
Due to Lack of Adequate Experimental Data, I am Unable to Identify the Specimen Dimensions with respect to ASTM E21 and ISO 15579 for Testing at Elevated and Low Temperatures respectively.
Since, These Standards are Quite Costly to be Purchased Individually, Should I take the Specimen Dimensions at Room Temperature for Experiments at Low and High Temperatures ?
Is there a Major Difference in the Dimensions presented by these Standards or Can I Complete the Analysis using My Assumptions ?


texts:
I have some laser-cut filing templates, about the size of a business card, made from 3mm-thick 1095 carbon steel. These parts will be used to guide a round metal file when filing odd shaped holes in aluminum. They will be clamped onto 13mm-thick aluminum and used as a filing "stencil". Thus the parts are not structural, but they need to withstand light pressure from a file without themselves being substantially filed. Aluminum is very soft, and I believe that with only light filing pressure, if the steel stencil pieces are hardened properly, the file will "skate" over them so they last essentially forever.
This is the process I was given by the laser cutter for hardening the 1095 steel:

Coat pieces with boric acid to prevent scale and decarburation. Heat the pieces up until they don't attract a magnet
Immediately quench the pieces into light oil, brine, or water (how do I choose?)
Immediately temper at 200C for 1 hour and allow to natuarally cool

From what I can tell, the last step is designed to prevent the parts from being excessively brittle, but may slightly reduce surface hardness. Since the parts aren't structural anyway, and I am trying to achieve maximum hardness, is there any benefit to performing the tempering step?


texts: What's the difference between a vacuum regulator and pressure regulator?

texts:
When browsing through pneumatic parts, I notice that some vendors specify different components for pressure regulator and vacuum regulators. SMC for example does this.

I'm curious why vendors would actually need to differentiate vacuum regulators from pressure regulators. It seems like a vacuum regulator is simply a pressure regulator whose inlet port is connected to something wished to be vacuumed, and the outlet port is connected to a vacuum supply.

Is there more going on here?


texts: Where did I go wrong conceptually when attempting to calculate the maximum force on a truss at a given joint?

texts:
In the problem statement below, the question states to find the maximum load $\vec{P}$ that the truss can support. My method of approach was:

Draw a FBD for the entire structure.
Generally I would identify all external forces, however for this problem I felt it was unnecessary because I felt they weren't needed if I knew already the forces in each member.
So I then dove straight into joint $D$, and assumed each member connected to $D$ was in tension and experienced the maximum tensile force $\vec{T} = 1500$ lb.

However, this led to the wrong answer when solving for $\vec{P}$. The solution manual instead found each external force in terms of $\vec{P}$ and started at joint $A$ to find $\overrightarrow{AD}$ and $\overrightarrow{AB}$ in terms of $\vec{P}$. In addition, in order to get numerical values, the solution manual assumed member $\overrightarrow{AB}$ was experiencing the maximum compression force of 660 lb. However, when I assume that member $\overrightarrow{AD}$ is experiencing the maximum tensile force, it doesn't work out the same.

My question is, conceptually, why must I find each each member's force in terms of $\vec{P}$, and why must one assume $\overrightarrow{AB}$ is experiencing maximum compression (but not $\overrightarrow{AD}$ in maximum tension)?

EDIT: I want to note that I do not need help with solving this problem, nor the math required. I simply am just looking for a conceptual answer as to why my approach did not work (i.e. only analyzing joint $D$).


texts: Linear actuator with low vibration and low noise

texts:
Which kinds of linear actuators offer the lowest levels of noise and vibration?

I am looking for an actuator with these properties that can push a load vertically on the cm scale. Velocity, accuracy and max force are secondary. I'd be very glad for a hint to the specific category of actuators that might meet these requirements.


texts: What causes the sound coming from electrical vehicles?

texts:
All the electrical vehicles I've ever ride make that humming sound (either cars or trains).

What exactly causes that sound? Is it drag force in the gears? Is it a fan?

Or is it because of the coils (see coil noise)?


texts: Simplifying head loss across a piping network

texts:
I am tasked with designing a compressed air piping network,with  and would like to determine the pressure loss across the different layers of instruments

-now here is the 3D layout of the network. The blue circles are instruments I want to deliver air to. They are in parallel with each other and connected in rows parallel to each other. L connotes pipe length (and in some contexts also the vertical elevation) while d is the diameter.

-I would like to find the maximum possible head loss (from point 1 to point 2) given that a proportion of the flow is teed off at each branch.  I would also like to find consequently the proportion of flow teed off in each branch.

Am I correct in assuming points 1 and 2 (below) and going about the normal head loss calculation? How do I account for the tees and wyes branching off?

Assumptions

Flow is turbulent

The pressure drop across each brand is designed to be constant (with regulator valves -otherwise they differ due to elevation - maximum between the bottom and the top being 35 meters).


texts: How to calculate a global strain from a field disitribution

texts:
For an arbitrary articulated structure subject to non-affine (non homogeneous) deformations, the components of the strain tensor are defined locally. Is there a way to calculate a numerical strain tensor that represents the whole volume? Can a Poisson's ratio be determined for such situation?

My first guess is that the volume average of the fields should do it, but I'm not sure if this is the right approach.

I'll appreciate any help.


texts: Suggestion to control a gimbal bldc motor for positioning

texts:
I try to understand what the PID controller of a gimbal stabilizer boards
(e.g Storm32BGC) does influence?

From the IMU we get position and velocity after sensor funsion. The input variable of the plant seems to be the speed of the gimbal motor (since its driven by 3 sine waves), not the voltage as usual in a brushed dc motor setup. So one can not just implement a torque control for holding the position. When I investigated the Storm32BGC, it looks like the PID does influence the position and the speed at the same time: Fast movements leads to fast speed corrections, but also the deviation from the stationary position leads to a given speed. This two speed signals seems to add up. Has anyone an Idea how this is done? I could not find any papers about this topic.


texts: Laser Cutting backing material instead of grid?

texts:
My research group recently purchased a 40W CO2 laser cutter. We work in the biosensing field and some of the materials we wish to cut are very thin nano/micro fibers that will be cut into relatively small pieces.

When cutting the material we hope to keep the samples as clean and uncontaminated as possible. So the current grid is not the best option as it will most likely get contaminated by other materials we cut and also the small samples will most likely fall through the grid anyway.

Can anyone suggest an alternative solid material that can be used instead of the  grid? Ideally the material should not be affected by laser cut at all or at least not give off any smoke, particles or other contamination. Also the material should not reflect the laser back towards the sample.

Thus far I have tried two options on an external laser cutter before we got our own.

1st) Ceramic tile as I was told that it would not reflect any of the laser underneath the samples and also not get cut by the laser. BUT after testing it was found that a whole lot of molten ceramic was deposited on the samples.

2nd) Stainless steel metal sheet that was orbital sanded to reduce reflection. This was a little better than the ceramic but I think there was some reflection of the laser under the laser that reduced the quality of the cut. I only assume this because there was a little burnt material left on the steel after cutting the material.

I'm thinking possibly glass above the grid but I have heard that even glass can be etched and so if the sample material retains heat this may cause the glass to etch or shatter? We are yet to setup and switch on our new laser cutter and some experimentation and optimization is needed.

Thanks in advance for any advice!!


texts: How to calculate how much compression is needed for a spring to buckle

texts:
First off; School was many years ago and I know little of the mathematics behind all the physics and engineering stuff. So if you have an answer, please explain it like I'm 5?
The goal: I aim to be able to create a buckling spring switch (like the old IBM keyboards) compacted into any form factor that the calculations might allow.
The problem: How can I calculate which spring I should use to produce the buckle?
My research so far: So I've found out about the slenderness ratio of springs. If I make sure that the free part of the spring has a mean ration of above 4 the spring will likely buckle. But how do I know how much compression I will need for the buckle to occur? Meaning; Given spring X, how many millimeters of compression will be needed for the spring to buckle?
My search-skills does not serve me well here.
To iterate: I want the spring to buckle. If you know about the IBM Model M (and the like) you probably know what I want to be able to do.


texts: How to implement a Monte Carlo Simulation for studying uncertainty in dynamic stiffness?

texts:
I have a dynamic mechanical system of the form:
$$\mathbf{M{\ddot q}+{\Omega_c}G{\dot q}+{Kq}=F(t)}$$

and I need to introduce some uncertainty for the $K$ parameter, which is a symetric matrix of $q$ degrees of freedom.

I did a bit of research of Monte Carlo simulation but I´m a bit confused of how different textbooks approach the problem.

For example , my actual stiffness value is of $1e8$, and I wish to generate values uniformly distributed between $K_l = 1e6$ and $K_u = 1e12$.

I found that I can do this by applying:
$$\lambda_i = \mu_{\lambda_i} + \epsilon_i$$
where $\mu_{\lambda_i}$ is the mean value of $\lambda_i$ and $\epsilon$ is a random parameter, and also
$$\sigma_{\lambda_i}^2 = E[{(\lambda_i-\mu_{\lambda_i})^2}]$$

I would be using Matlab for running the simulation , with the command rand I can generate a randomly distributed numbers between 0 and 1.

The problem I find with this is that I don't know know to input the boundaries of the $K$ stiffnes values I want.

Then I found another text book that explains how to generate random variables using:
$$ X_i = A + (B-A)R_i$$
Where $R_i$ is the random number which can be generated by Matlab with rand command to generate a new random variable $X_i$, with lower and upper limits $A$ and $B$. So in matlab I would do a for loop like this:

for i=1:num
    Ki=Kl+(Ku-Kl)*rand;
end

My main question would actually be, what is the difference between these two methods and for the first one, would $\epsilon$ just be a random 0-1 number adding to the average designated value?

Thanks


texts: Hello I am a high school student and I am curious about how street light is arranged along the road. Is there government laws to install street light on the road or is the arangement of the street light that is the most efficient to its road? If it is, how are the lights arrangement? Is it by some sort of software?


texts: How to connect Arduino to brushless motor through only 1 digital pin

texts: I know how to connect motor to Arduino with 3 wires: 5v, digital pin and ground. As I know only digital wire need to control "speed control" of my motor. So, if my Arduino connected to computer and it is not needed to get this 5v from "speed control". So I decided to remove useless 5v and ground wires. When I remove ground wire, it is okay. But when I remove 5v wire, my motor works about 3-5 seconds on random frequency and then die. So, can I use only 1 digital pin to control my motor?


texts: Custom heavy gauge machine table to support clothes dryer

texts:
Background
Looking to build a table for a dryer to fit inside a laundry closet. The table must be assembled inside the closet, as such it has three parts: two legs and a metal sheet for the table top. Here's a picture of the table outside the closet:

Here's a picture of the dryer on top of the table:

Weights, Measures, and Materials
Dryer

Dimensions: 65.5cm x 60cm
Weight: 50kg

Table

Dimensions: 106cm x 63.5cm
Material: Steel alloy

Same, but without the wireframe:

Without the table top to show the supporting flaps:

Problem
I'm concerned that the table thickness will be insufficient to support the load. A flat plane deflector calculator is useful for calculating the total load applied to center of plate, but doesn't quite tell me if the distributed load of the dryer (not a point load) will be structurally sound.
In comparison, commercial heavy gauge machine tables support over 900kg, so it looks like the design is sound.
Question
Are these calculations reasonable? (Especially pertaining to the forces imparted by the dryer?) That is, will a 1.25cm (approx. ½") steel alloy table top outlast the dryer?
Related Links

https://www.engineersedge.com/beam_bending/beam_bending3.htm
https://www.engineersedge.com/calculators/flat-plate-deflection.htm
https://www.engineeringtoolbox.com/young-modulus-d_417.html
https://www.engineeringtoolbox.com/poissons-ratio-d_1224.html


texts: Why design a cable stayed bridge with pylons inclined towards the obstacle being spanned?

texts:
Here's a YouTube video with a concept of a bridge which is currently under construction in Saint Petersburg. The bridge largest span is cable stayed and designed to drive traffic over the Neva river fairway.

The largest span rests on two pylons placed symmetrically such that they are inclined towards the fairway axis. Something like this:

This differs much from "usual" design where pylons are built upright. They may have "A" shape but still don't have inclination along the road axis.

The usual strategy of building cable stayed bridges is that you first build the pylons and temporary supports, then assemble the deck on those supports, then mount the cables, then remove the temporary supports. Maybe the pylons become evenly loaded once construction is complete but clearly building those inclined pylons of dozens tons of reinforced concrete poses a challenge - both the pylons and their foundations need to support the extra loads that appear simply because the pylons are inclined. Building an upright pylon looks much easier.

It looks like this design just asks for extra problems and doesn't provide any benefit compared to pylons built upright.

Why design a bridge with pylons inclined towards the river fairway instead of upright pylons?


texts: Best PID autotuning algorithm/library for simple heater problem

texts:
It's the 21st century, anything is possible. Except for PID autotuning for a simple problem, heating/cooling system - make robust and ready to use solution. I've found only one library for PID autotune: https://github.com/br3ttb/Arduino-PID-AutoTune-Library, but even its author says that it is not a robust approach. My question is:

What types of algorithms for PID autotune for a simple heater/cooler application exists? What are their pros and cons?
Is there some open-source libraries for PID autotune?


texts: Live motion simulation with respect to electromagnetic field software

texts:
Totally numb question from non-engineer, so sorry about that. For my little home project I need to create a matrix of solenoids, so I need some kind of simulation. I wish to be able to create metal rod of specific volume and mass, and coil with specific number of turns, so being able to apply current source to coil, see rod movement, if it occurs, to be able to experiment with voltage, coil turns or rod mass. I have no experience with CAD software whatsoever I must say.

I saw some demo videos with solidworks where there was Newtonian Cradle simulation using motion analysis, is there the same 'simple' and 'intuitive' type of simulation for motion analysis with electromagnetic field? For example so I can create electromagnet, place some metal on it, then turn on current and it will attract (or repell) in live?

I saw such motion simulations in solidworks and inventor, also comsol multiphysics looks promising, can anyone suggest some?

thx.


texts: Do beams in a structure transmit to piers?

texts:
Sorry if the question is confusing as such, here's an image that makes it hopefully clearer:

So let's say this building consists of two elevated concrete slabs. The first elevated slab is supported by the 9 massive reinforced concrete piers arranged at even intervals of 5m x 5m, and connected with massive reinforced concrete beams. Thus the building is 10m x 10m in dimensions.

The second concrete slab is supported by eight of the 9 massive concrete piers, the ones around the perimeter,  but the concrete pier in the middle is only one-storey high. Instead two less massive piers (labelled A & B) start from the height of the first elevated slab and support the second slab.

In this case, my questions are

is this design potentially safe & practical as a way of supporting the top slab?
does this  mean that the beam along the junction of A-B requires extra reinforcement compared to a design where the top slab is supported by the same (extended) pier as the bottom slab.
are there any other major ways that the forces differ, e.g, in terms of the forces transmitted by the lower columns, or the loads experienced by the lower slab?


texts: Is there a male and female valve that is closed until connected together?

texts:
I'm trying to make a quick release male and female connector similar to the one shown here.

One connector is attached to the bottom of a container filled with liquid. When it is not connected it is closed and none of the liquid can flow out of it. However when it is in contact with another connector it then opens and allows the liquid to flow out of it. Any ideas where these kind of connectors can be found or made?


texts: Why not drive an air source heat pump domestic heating system with an auto engine?

texts:
Theses are my thoughts on the question. I can't find an answer to "why not?". It there something I am missing, or are auto manufacturers simply too focussed on cars only?

The automotive industry has been developing internal combustion engines for many decades. They are now routinely capable of running for 20,000 miles service interval, which is a simple oil and filters change.

20,000 miles will be around 2000 litres of fuel, which is comparable to the oil required to heat a house in the UK for a year using an oil  boiler.

Air source heat pumps are only just capable of offering cost savings to a UK household, compared to an oil-fired boiler, because of the inefficiency of the power stations and electricity grid in delivering electricity to the house, compared to burning the fuel locally. A local heat-pump gain of 4+ has to be multiplied by electricity generation and distribution inefficiency (around 0.5? Not sure).

The auto manufacturers' investment in internal combustion engines in under threat from electric vehicles. They have made the investment to mass-produce engines, and ought to welcome another possible use for much the same.

So, why don't the auto manufacturers develop an domestic air source heat pump based on an auto engine?

The water cooling system would be the house's central heating system. Auto cooling normally runs at 90C. Domestic heating systems normally run at no more than 70C for safety reasons, and often as low as 30C for thermodynamic efficiency reasons. Would this be a problem?

I don't know what fraction of a car's fuel is lost as heat via the exhaust pipe. In any case, some (large?) paer if this could be reclaimed via a heat-exchanger, as with a condenser boiler.

The rotary motion the engine generates could either directly run a compressor, or run a generator to provide electrical energy for the house with excess sold back to the electricity utility. Unlike solar panels, this energy would almost by definition be generated at times of maximum demand (in the UK, the coldest weather. In hot countries, the hottest weather, for cooling).  So this would automatically be a benefit to utility companies and they might offer a good price even without the government forcing their hands.

An auto engine can provide a range of power levels, so the system could easily modulate its output to match demand.

I'd guess that an auto engine driving a heat pump, directly or indirectly, could have a heating efficiency of 2-3. Heat pump efficiency for driving a hot water central heating system is typically 3, so that lower figure allows for some losses. A modern boiler's efficiency is 0.85. I'm guessing that overall electricity utility plus heat pump is around 1.5

Annual servicing would be an oil and filter change. By using a larger oil supply and larger filters, it might be straightforward to push this to 2, even 3 years. Costs not a lot more than oil boiler servicing. Also a fixed installation should be a more benign environment than a moving vehicle.

I know that a petrol engine can also run on natural gas. Presumably a diesel could be modified to run on kerosene. If not, this would require a household without a gas supply to use diesel as heating fuel. Governments might worry about leakage of tax revenue from the heating oil tank into a car's fuel tank. However, in any case, electric cars are going to destroy that revenue in coming decades. (In the UK, farmers use low-tax "Red diesel" for tractors and heating.  This fuel is dyed red so auto fuel tax evasion can be detected).


texts: What is the down-stand beam called at an edge of a surface bed or raft foundation? It is not exactly a grade beam or stem wall. It is more like a toe.


texts: How do I create nano-scale mesh electronics in Solidworks?

texts:
I'm trying to complete a project for my solidworks course and it involves nanoelectronics. The idea is to create a mesh array of field effect transistors (FETs) that will monitor the firing of neurons in a microfluidic device. My design is inspired by science articles like this one:
https://iopscience.iop.org/article/10.1088/1361-6528/ab3534

I've already had some problems with using Solidworks for nano-groove technology as 72k features is too much for my computer to handle, but there won't be a need for as many nanotubes and circuits for the mesh. I can make a 3D image of what I want, but my professor wants me to make an electrical simulation to verify my design works. My professor is also not too available to me at the moment, so I'm limited on asking him what to do.

There's no need to worry about how I will shape and orient the nano-scale wires. I just need to know how I would build a new electronic part from scratch. If I just make copper and carbon tubes, is that going to be enough to properly simulate?

Here are some images to help clarify what I want to make:


texts: Water & plumbing pipes vs gravity or air pressure

texts:
I'm sure there is a simple answer here, so I apologize in advance for the unchallanging & low level question, but here it is:
 Why does the water at water oulets, through out a building, stop their water flow near instantly when the Rising Stem Gate valve at the out side water main is shut closed, But will trickle and trickle with little flow for almost an hour when the indoor building main ball valve, downstream of RSG valve, is shut closed.
Building has 3 floors.
Anything helps.


texts: Is possible for a silt soil to be compacted hard as a rock?

texts:
I had been told that a silt soil, when professionally compacted (from all the laboratory essays to the compaction with a vibratory roller), ends hard as a rock, and when hit with a metal bar it makes a metallic noise.

I find that hard to believe. Is it true? What is the common reality?

I mean the question from the viewpoint of a earth pavement construction, or as a subbase for another type of pavement.

I have interest in the answer from the viewpoint of a fast checking of the quality of the compacted soil (before any essay to check the level of compaction)


texts: How can we assume that structural supports are rigid?

texts: In engineering classes we made the assumption that structural supports (fixed, roller, etc.) are rigid. Thus, the displacements of a beam ,for example, at a fixed support are set to zero in the horizontal and vertical directions as boundary conditions. However in real situations shouldn't there be some displacement due to deformation in the support? Wouldn't that affect stresses/strains in both the beam and the support considerably?


texts: Engineering in Kazakhstan and Rainfall Intensity

texts:
We are about to commence a large project in Astana, Kazakhstan worth several hundred million dollars. The design of Stormwater quantity, quality, and hydrology will be a large component of our works, and I am having an issue locating rainfall Intensity-Frequency-Duration (IFD) tables for the region. Similar to those which one might use from the Bureau of Meteorology on any site in Australia and are crucial to the design of stormwater.

My question is, has anyone completed drainage design for this region, or can anyone provide pointers on where I might find IFD tables for this region? More generally, does anyone have pointers on designing stormwater systems in freeze-thaw conditions.


texts: What are the disadvantages of PDDD controller

texts:
I have a system that has the following transfer function:

$G(s) = \frac{1}{s^2(s^2+4+1)}$

As can be seen it is a 4th order system.
This is the bode plot of the system:

I need to use a lead compensator in order to generate sufficient phase margin. If I use a tame PDD controller I am limiting my crossover frequency around the position of the green arrow, as the double derivative action can theoretically only provide 180 phase lead. However if I use a tame PDDD action I can place my crossover frequency in the vicinity of the orange arrow. This also means that I can make my system infinitely fast, if there is no limit on control action...

My question is: is it realistic to use a triple tame derivative action? I can't find a similar controller anywhere on the internet!

Thanks in advance!


texts: Critical Buckling Load for a Spring Supported Bar

texts:
The above is a past exam question from an introductory structural analysis course, one in which although we have studied the Euler buckling load equation, we have just been given parameters for the equation based on the standard end support conditions (fixed/fixed, fixed/pinned, etc.).  I don't think the above example fits any of the standard end conditions and am therefore finding it difficult to derive an equation for $P_{cr}$
I have tried to use the bending moment equation by including torque (that opposes bending) from B and the net load (due to spring C) as follows:
$$
T_B = \beta_r \theta
$$
Taking a small deflection x in the vertical direction and y in the horizontal:
$$
tan\theta = \frac{dy}{dx} \approx \theta
$$
$$
\therefore T_B = \beta_r \frac{dy}{dx}
$$
Using the bending moment equation:
$$
M=-EI\frac{d^2y}{dx^2}
$$
$$
\therefore \sum M=-EI\frac{d^2y}{dx^2} + \beta_r \frac{dy}{dx} = Qy
$$
The net load $Q$ can be expressed in term of the force P and the reaction force due to the spring at C as:
$$
Q = P - \beta dx
$$
Leaving the final second order equation:
$$
EI\frac{d^2y}{dx^2} - \beta_r \frac{dy}{dx} + (P-\beta dx) y = 0
$$

This is beyond the scope of our course, so I have no idea if:
a) The above equation is correct or solvable (and if so how one goes about solving it)
b) There is a different approach using more basic techniques (which is more than likely the case)


texts:
Recently, tube steel manufacturers in the US have begun using the new ASTM A1085 specification for forming tube steel (a.k.a. hollow structural section or HSS) shapes, as opposed to the existing A500 specification.

From what I've read (here and here), the A1085 material spec has the following benefits over the existing A500 spec:

tighter tolerances (no need to take reduced wall thickness for design)
identical yield strengths for all types of tube members (as opposed to A500, in which the yield strength differs for round and rectangular shapes and depending on the grade)
set maximum yield stress of 70 ksi (useful for seismic applications, though I am not well versed in this area)
standard Charpy V-notch requirements corresponding AASHTO Zone 2 (I assume useful for the transportation industry for fatigue reasons)

These benefits come with a small premium - I've read 7% to 10% increased cost depending on the mill.

I primarily work as a structural engineer in the nuclear industry.  Most of the work I do is in services, where we perform mostly small modifications to plants (i.e., no design of large buildings for the most part, but smaller supports, platforms, and the like).

If I have no need to restrict the maximum yield strength of the material and I have no fatigue concerns, is there any benefit to specifying the newer A1085 tube steel material over the existing A500 specification?  For practicing engineers in non- or light-seismic zones, have you realized any benefit using the new A1085 spec?


texts: Adjusting the pressure of the condenser and the evaporator

texts:
The picture below shows a refrigeration unit

I was reading the operation manual of this unit. It is written that the pressure of the condenser is controlled by the water flow rate. Reducing water flow rate will increase the pressure of the condenser.

On the other hand, the pressure of the evaporator is controlled by the refrigeration load or cooling capacity (Q dot L). Increasing Q dot L is acheived by adjusting the voltage of the electric heater. The pressure of the evaporator is increased by increasing Q dot L.

Can you explain to me how could reducing water flow rate cause the condenser pressure to increase ? And how could increasing the cooling capacity cause the pressure of the evaporator to increase ?


texts: How to solve system's general stability from transfer function?

texts:
I have a homework which should solve by me. My problem is questions are really simple or should I think outside of the box? Like, bode diagram, nyquist or etc.? And, are my answers correct?

Thanks.

Question-1

  $$G(s) = K\dfrac{As+1}{Bs+1}$$

For which values $K, A$ and $B$ is the system always stable? Should I look directly to the pole of the system?

$Bs+1=0$
$s=-1/B \implies  \text{So, must } B>0$

Is it enough? Or, anything else? What about K, A?

Question-2

  $$G(s) = K\dfrac{As+1}{(Bs+1)(Cs+1)}$$

For which values $K, A, B$ and $C$ is the system always stable? Should I look directly to the pole of the system or anything else?

$$Bs+1=0 \wedge Cs+1=0$$
$$s=-1/B \wedge s=-1/C$$
$$\implies  B>0 \wedge C>0$$

Is it enough? Or, anything else? What about $K$ and $A$?


texts: What is the correct pipe size for a 2inch pipe?

texts:
I'm was looking into the ASME B16.5Pipe flanges and pipe fittings and it has 2 dimension tables metric and inches.

What I found was rather strange for me. I was looking at a 2 inch welding neck flange, and the hub diameter must match the pipe size.

For the metric table this is 60.3mm and it is the same in all pipe sizes charts that I have available. When I look at this dimension in the Inch table, it is 2.38in when I convert this to mm this varies from the metric table..
2.38in * 25,4 = 60,452mm

So there is a ,152 difference between these values. What is correct? These differences are to be found on more flanges then just the 2" flange size.


texts: Why use bushings of different material than what they contact?

texts: I've heard that materials that need to slide against each other should be of different materials. Why is that?