texts: ANSYS Fluent - Using Patch to set initial conditions, should I set the pressure and velocity or only one property to generate shock waves in a pipe?

texts:
I am fairly new to CFD and I am working in ANSYS Fluent.

I am trying to model two specific shock waves in opposite directions in a length pipe. The shock waves need to be traveling at specific Mach numbers and I am trying to generate the shock waves at the boundaries of the section with the Patch command. I just wanted to ask whether I need to specify the pressure and velocity of each shock wave or if I should just specify one property of each shock wave?

Any help, links, or feedback would be greatly appreciated. Thank you for your time.

Edit: Also, I was wondering if it would be recommended for me to create small zones next to the boundaries and apply the patch to these zones (instead of applying the Patch directly to the boundaries)? Thank you again!


texts: Calculating the flow rate of a siphon system

texts:
What i am looking for:

I am looking for a formular to calculate the water output in $l/s$.
My goal is to match a pump (pumping the water back up) with the following setup, to keep it going with as few corrections as possible.

Where i am at the moment:

Currently i have Torricelli's law for an ideal system.

But with this i am not sure if i have to take $h = h_2 - h_3$ or $h = h_2 - h_3 + h_1$?

Restrictions:

The pipe is flexible.

I don't know:

The friction of the pipe.
The angles.

My setup:

An upper water tank with a water level $h_2$ mm (which is consistant!).
A lower water tank.
A pipe with it's intake $h_3$ mm above the upper Tank bottom. And it's outlet $h_1$ mm below the upper tank bottom.
The pipes diameter is $d$ mm.
The pipes length $l_1$ mm.
The water flow is started by sucking (like stealing fuel).


texts: What type of liquid flow control could this device use?

texts:
I am trying to figure out what kind of device is being used to stop and start the flow of liquid inside this device. Below is a link to the device. It looks too small to be a solenoid or a pump. How else would they do it?

I heard somewhere it may be a Venturi system but how do you electronically control a Venturi system that is that small?

http://www.wunderbar.com/dispensing/beverage-dispensing/liquor-dispenser/skyflo


texts: Transfer of angular velocity in Oldham's coupling with the centre disc not sliding

texts: In Oldham coupling,is it possible that the same angular velocity is transferred from one shaft to the other when the centre disc is not sliding?If so,why do we want the centre disc to slide?I know that the shafts are misaligned but it is occurring to me that the same motion is possible when the centre disc is held back from sliding?


texts:
I am not an expert in the signal processing!
I working on a simulation the interpolation ( upsampling and filter). The interpolation process was divided into two stages:

stage 1: FIR - filter ( upsampling factor N) and "bypass" ( factor 1)
stage 2: FIR - filters and "bypass" ( factor 1)

Could someone explain what bypass filter is?


texts: I am unable to find it again but I once heard of a type of air pump that involved a pair of offset archimedes screws inside a cylinder. The point of the device was that as the screws would turn against eachother it encapsulated air into pockets (like how a centrifugal fan would) but then these pockets would compress their contents as the screws turned against eachother. What was this pump called?


texts:
Does 200lb/in of load on a S12x31.8 over 15 feet seem reasonable? I'm having a tough time trusting the numbers.

Two story house with an attic as below. Dotted lines show load bearing walls W1 and W2. There is currently a single wood 4x6 rough hewn girder running the entire 36 feet bowing 1-2.5 inches between lally columns spaced 8ft apart (see the red highlighted areas with greatest negative deflection (up to 3" from level). I've started raising slowly (1/4" every 4-6 days), and I'm thinking just replacing the wood girder with steel in the basement (unfinished). And using 24x24x18" poured, rebar reinforced supports over packed calcareous sand which should support 9000-12000PSF.

Right now, I am guessing that center girder needs to be rated to 160-190 lb/in. For S12x31.8, my numbers are showing I can span up to 15 feet (180in) and still maintain an acceptable L/360 deflection:

Unit Load - q : 200 (lb/in)

Total Load : 36000 (lb)

Length of Beam - L : 180 (in)

Moment of Inertia - I : 218 (in4)

Modulus of Elasticity - E : 29000000 (psi)

Distance of extreme point off neutral axis - y : 6 (in)

Support Force - R1 : 18000 (lb)

Support Force - R2 : 18000 (lb)

Maximum Stress - : 22294 (psi)

Maximum Deflection - : 0.432 (in)

This is attractive because I can use two supports and span the entire structure, perhaps using three separate sections. Does this seem right?

I'm considering running three evenly spaced girders using three sections each, because I'm worried there needs to be more support for the tired floor joists. See the image below option 2. This would seem to make 120lb/in more than adequate and even single center load @ 10 tons looks like it would be acceptable (especially near W1, which would fall middle of the girder). I'm having a hard time believing these numbers. Does this seem right?

Total Load : 20000 (lb)

Length of Beam - L : 144 (in)

Moment of Inertia - I : 218 (in4)

Modulus of Elasticity - E : 29000000 (psi)

Distance of extreme point off neutral axis - y : 6 (in)

Support Force - R1 : 10000 (lb)

Support Force - R2 : 10000 (lb)

Maximum Stress - : 19817 (psi)

Maximum Deflection - : 0.197 (in)


texts: Why do monocrystalline solar cells have rounded/cropped edges?

texts: What is the meaning of this croped part? Why do they crop it, rather than let it be full square?


texts: Help interpreting dimensions from this drawing

texts:
Why there are different dimensions for the same measurements on this drawing?
For example 0.127mils and 0.097 mils pin to pin. Or highlighted 405 and 385 mils.
I can't find anything on the datasheet indicating the difference?? Is this typical and max? Or typical and min? (some actually say max)

Need to know highlighted distance so I know where to place this part on the PCB. I could just make it 405mils to be safe, but I still want to know why they did this on the drawing?

Complete datasheet link below drawing. Thanks.

https://www.mouser.com/datasheet/2/418/NG_CD_1218434_D1-1234416.pdf


texts: Determine the reactions at A and C, knowing that α = 30º

texts:
QUESTION(see image attached):

Really need help here can someone help me show how we get the solution as shown in the image file attached above.

okay since I was asked by one of the users commenting asking me to show what I had done; please see attached image file below

Thank You.


texts: What measurement accuracy/precision is required to detect a 10% relative change in the measured quantity

texts:
I'm trying to design a measurement system, the primary objective of which is to reliably detect a 10% change in the the volume of fluid flowing through a pipe.

I'm struggling to come up with a required accuracy/precision for the system based on something on something other than "This is simply as accurate as I could make it".

Note I am only really interested in relative change, i'm not sure how this effects the system requirements in terms of required precision/accuracy. For example, there two primary sources of error:

Measurement error (accuracy)
Estimated internal diameter of the pipe (precision)

I'm assuming I can completely negate the error introduced from the estimated internal diameter of the pipe and place the requirements solely on the "measurement error"

Is there a statistical technique to determine the accuracy required to reliably detect X change in some variable?


texts: External indeterminate vs internal indeterminate

texts: What are the difference between these two ? Here's my notes , The author just stated the formula without explaining much . Can someone explain further what 's their difference ?


texts: Artificial gravity with accelerating elevators enclosed in a gigantic sphere

texts:
If we could be able to construct a gigantic hollow sphere, multiple elevators/chambers can glide in the interior of the sphere, accelerating and decelerating without colliding, providing artificial gravity of 1G. The sphere of course has to be gigantic so that the angular acceleration would be significantly less than the acceleration of the chamber, in order to minimize the coriolis effect. Could a solution like that to the artificial gravity problem be feasible?

[EDIT]
Ok let’s simplify it a bit. Instead of a sphere, imagine a giant ring structure in space which stays still (doesn’t rotate). In the internal surface of the ring there is an elevator that can move along the circular path of the ring’s interior. The elevator starts to accelerate forward with 1G (following the circular path). Because of the huge proportions of the ring, the centrifugal force will increase but slowly. The key concept is to satisfy the following equation: forward acceleration + centripetal acceleration = 1G. So as we reach higher speeds, the forward acceleration of the elevator has to be reduced. When the  centripetal acceleration reaches 1G, the forward acceleration has to be 0. At this point the coriolis effect will be most severe. From that point the elevator decelerates but the equation: backwards acceleration + centripetal acceleration = 1G, still applies. Another important thing is that there is a distinct chamber that floats inside the elevator, so that it can rotate and stay in the same position for the person that is inside.

A more concrete question is how big has to be that ring structure in order to provide 1g artificial gravity for 1 hour (30 minutes accelerating and 30 minutes decelerating the elevator)?


texts: Practicality of energy recovery from HVAC systems?

texts: I've been thinking about ways to maximize efficiency in large buildings, and one thing I thought of was to place some sort of turbine in the exhuast vents or smokestacks of factories, power plants, and large office buildings. Is there a reason that this hasn't been done? We're expending energy to move the air, so why don't we try to recover at least some of it? It seems like it's basically free energy.


texts: What is the explanation why Pulse and Glide is more energy-efficient for trains

texts: I read that trains in pratice instead of acceleration to a certain speed level and holding the speed, they accelerate and then cost, accelerate again, und keep this pattern. This was shown by experiments. What is the explanation why this way of driving is more energy-efficient?


texts: Is there a lighter-than-air foam material?

texts:
Soap bubble foam made with helium floats up, but due to extreme fragility hardly counts as "material". There are many solid foam materials though - PUR foam, or styrofoam to name the most common. They typically use carbon dioxide for inflation though (usually produced from precursors of the foam, as a desirable side effect of their reaction).

But it shouldn't be too difficult to make solid foam filled with helium (or hydrogen) in proportions assuring positive buoyancy in air, and I can imagine desirability of it, at least as a filler in applications where mass costs a premium (transport, aviation) even if its structural properties were to be too poor for any other purpose.

Is such material produced? Is it used anywhere? Or if not, why?


texts: Why increasing the coefficient of friction results in evenly distributed load in rolling machines?

texts:
I'm designing a rolling machine for reduction of steel ingots of $5 mm$ to $1.96 mm$ thick. I can convince myself using equations why increasing the coefficient of friction (in case of lubrication system fails) results in evenly distributed load in rolling machines, but i can't describe intuitively why this happens.

As the friction coefficient increase, normal forces increase as wel and i expect the peak to move upward, but why it moves to the right as well ?

The horizontal axis, represents the angle of contact zone, and the vertical axis shows the dimensionless stress. $\frac{\theta}{\theta_0} = 0$ means exit angle(reduced) and $\frac{\theta}{\theta_0} = 1$ means entry angle.


texts: How can I improve water flow within this diagram?

texts:
I'm hoping I'm asking this in the right place. I'm trying to determine how I can improve the water flow within a project I'm working on.

The flow starts out at the large water pump on the bottom left, flows through a radiator and into a water to air intercooler. Cooling the water to air intercooler should warm the water which will then flow to a tee where a part of the water will flow through normally and a small portion of the water gets sucked in by a smaller pump, pushed through an ESC and electric RC motor and continues back to the original pump.

The large pump flows 500GPH
the small pump flows 90 GPH

The Diameter of the large pump and hoses is 3/4"
and the diameter for the smaller pump is 5/16"

The water should be at 80*F (Or ambient temps) exiting the radiator and probably 170* after the intercooler, ESC, and Motor. (This are estimates as I don't really know the temps post radiator)

I have a small radiator I could place between the small pump and esc to cool the water more if needed.

My gut feeling is that the Tee's with the reducers are a poor choice thus why I'm asking how I could improve this system.


texts: I am not a professional in engineering and was wondering what I could use to add traction to a wheel. (I have to make a small self-car for a school project) I was wondering if there was a cheap or almost free material I could use for it. The wheel is going to be made of wood, it is going to drive on ceramic tile and the car is not very heavy, maybe around a pound. I am not necessarily looking for a product, just a way to increase traction.


texts: How does the articulation system on a fiberscope work?

texts:
A fiberscope is the snakelike, fiber-optic camera that doctors use during an endoscopy. The tips of these scopes can articulate: you can control the rate at which they bend in one or more directions.

For instance, the tip on one end of this fiberscope can bend in various directions and at various angles. You control this via the controller on the other end.

How is this done? I'm assuming it involves a sort of spring/flexible tube and some sort of cable system that controls the rate at which the spring/tube bends, but I can't imagine how this would work.

Edit: This image from this article refers to a (or possibly four) "tip bending control wire(s)".

(here's another one)

I guess the question is: what do these wires do? Do they bend the tip by contracting/expanding? Is there some sort of mechanical device in the "bendy" part that is controlled by these wires?


texts: I’m a civil engineering consultant, and I am analyzing different properties across US to develop long-term property maintenance plans

texts:
I am looking for some pretty specific tasks to be carried out by a software program.  I’m currently using Civil 3D, but I can’t help but think there is a better program (or at least a better Autodesk based workflow).

Here is an overview of my project, followed by the requirements I’m looking for.

Overview:

Approx. 40 locations/sites
Use hi-res raster aerial images (most obtained via UAV) to analyze properties
Looking to identify obvious problems such as poor drainage, inadequate parking, deteriorated pavements, potential future growth areas
The properties are mostly commercial or industrial
Based on the owner’s vision and property maintenance budget, develop a rudimentary 5-10 year outlook (i.e. install underground storm detention and adjacent pond in 2020, add a loading dock in 2022, etc.)

Needs:

Create polygons around problem areas or items of interest
Ability to assign a polygon to a layer or tag (there will be 10-15 total layers or tags that every markup will fall under
Automatically change the appearance (color, transparency) depending on the layer or tag
Quantify square footages, # in each layer or group
Generate a report in .csv or .txt format for each location

Note: Final deliverable would hopefully be web-map based (think google maps JavaScript APIs).


texts:
I basically need to replace these valves with a modern equivalent

It’s a pneumatically actuated three way valve for high pressure and flow rate (200 bar, 50 liters/minute). The liquid is basically glue and has a high fouling potential.
What is this type of valve called. Is a high pressure 3 way ball valve suitable here?


texts: Is it ok to use a "4-cycle only" fuel in a 2-cycle motor with mixed oil?

texts:
I have some Tru-Fuel, which is an ethanol-free gasoline. Ethanol free gasoline is needed in small engines because ethanol can degrade rubber gaskets and cause other problems like gumming up carburetors.
However, the Tru-Fuel says "for 4-cycle engines only" which is kind of crazy because most small engines (chainsaws, weed wackers, lawn mowers, etc) are two-stroke engines. Are they just saying this because they have a separate product that has pre-mixed oil, or is that some legitimate reason why I can't mix the Tru-Fuel with oil and put it in a 2-cycle engine?


texts: Optimal plumbing layout for 3 storey building?

texts:
I'm trying to design a plumbing system for a school project, and I want to verify that my initial piping layout from water source to outlets is logical before I start making calculations and programs for the system.  Here is my drawing, thanks to Rhodie:

The green curve represents a hill that the building is on.  My logic for this design was that by minimizing the number of fittings I have in my system I can reduce the required head I would need to generate by the pump and save some money.

Any advice or comments would be greatly appreciated!


texts:
all. The top beam is subjected to uniformly distributed load. FYI, the column is 5m in length.  As you can see, the major axis of column is connected to the beam with moment connection on top. However, in the minor axis of column, there's nothing to connecting them.
For the major axis, the buckling length shall be 0.7*5 = 3.5m (K = 0.7 for bottom pinned, top fixed condition) ,
For the minor axis , the buckling length shall be 2*5 = 10m , right ?? (because in minor axis, it's cantilever , nothing to restrain the column on top) . However, the program detect the buckling length as 5.0m.
So, my question, for the minor axis, is it considered as cantilever ? Or since  in the major axis, it's already gt the moment connection, in minor axis of connection, there's really doesn't matter whether the minor axis of column in restrained or not...


texts:
What am I measuring if I set my multimeter to AC voltage readings and take the black probe out of COM? It seems that I am getting higher readings when I go near a light or my computer screen. This measurement seems to get more sensitive (I think) when I make a circular loop with an ordinary copper wire and connect the red probe with the loop.
What am I measuring in the two cases? Are they measuring the same thing?


texts:
I was studying a book on control systems where I read that a block diagram is a specialized high-level type of flow chart.
What is the difference between a normal flow chart and a block diagram?


texts:
I'm buffing the years of built up dirt off a aluminum grain tipper trailer, using a woolen buffing pad mounted on a angle grinder. I'm going in a upwards & downwards motion with great success, however, that's the pattern it's leaving. 1st I thought I'll finish by doing a 2nd, lighter buff or polish in a sideways left/right direction.

But I've remembered advice of cleaning a motorbike frame, to only work in one direction (probably with the frame in the case of a motorbike).

How can I buff and polish aluminum to get the best finish, without leaving a pattern? (Directional buffing/polishing in particular.)


texts: What are some things to keep in mind when searching for a step motor where a lot of torque is required?

texts:
I want to build rotating arms of length around 2ft that can hold up to 30 lbs of weight and am wondering what kind of motor to get. I'm thinking of getting a step motor so that I can know exactly which angle the arm is at.

The key requirement is that it needs to be a high torque delivering system. Gears would be good to achieve this but as a beginner, I don't have a lot of experience with constructing my own gear-motor combinations.


texts:
I have a background in mechanical engineering but HVAC is not my specialization. I am trying to properly size an axial fan to get a determined airflow from a duct. Both inlet and outlet are at atmospheric pressure. You can see in the diagram that it is a very simple system with 1 inlet and 1 outlet. I have a main filter at the inlet with the given pressure drop at the CFM i am trying to achieve. I also have a secondary filter with much lower pressure drop. Assuming a laminar flow condition and negligible pressure losses in the duct (I can check these assumptions on my own), what would be the way to determine the required pressure from the fan to achieve the desired CFM output?
Thank you
I


texts:
I am studying embedded systems and microcontrollers and now I have to face the interrupts. I understood the main concepts around them and how to implement them inside a C code, but I want to know how they work at hardware level.

I found this scheme on the internet:

But I cannot understand it at full. Can you explain me a bit? Don't worry to use technical terms, I think that I will understand them. However I prefer to search some terms that I don't know rather than limiting your knowledge while answering.

Nice engineering at everyone!


texts:
I'm a bit confused about all the different "definitions" of uncertainty?
One can calculate "uncertainty" of a single measurement by simply checking how accurate the tool that is being used to do the measuring is.
One can also calculate "uncertainty" of a group of measurements by finding the standard deviation which means that any more measurements made will have a 70% chance of being within one standard deviation of the "true value".
Finally, there is also standard error which is also a measure of "uncertainty", but I'm not sure what it says.

Which "uncertainty" do I have to find in the following problem and would I go about finding it?

A particular 1.00-kg bag of rice consists of 2.00% "supergrains", each of which contains 5ppm of arsenic and the rest of the grains contain no arsenic. What is the average concentration?

A grain of rice weighs 20 mg. What is the uncertainty in the concentration due to sampling if a 10.00 g sample is taken for analysis from this bag?

If the entire contents of the bag were ground to spherical particles 100 micrometer in diameter, what would the uncertainty be if a 10.0 g sample were taken for analysis?

The first part is pretty straight forward. I calculated that the average concentration of arsenic in this bag of rice is 100ppb.

It's the next two questions I don't understand partly because as I said in the beginning, I'm not sure what "definition" of uncertainty they are asking for/about. How would I go about finding it?

Please correct any assumptions or definitions I've made if they are incorrect in any way. I'm really trying to learn and I know how important precision of language is.


texts: Why did they move ancient Egyptian temples to prevent them from water damage instead of encircling them with a dam?

texts:
Specifically I'm talking about Abu Simbel temple and Philae temple. Which are close to a reservoir created by Aswan dam.
It seems to me easier to build a dam than to move a temple.


texts: Where can I find an Electrical Engineering master or phd student for my GPR radar project

texts:
I want to make this project but lacking manpower and knowledge. I want to include one having knowledge and excitement. Where should I find one? I am just graduated. So no money I can offer. I can share the gains and knowledge in all means. I have networks to get some investment if I could build a prototype etc. I need someone to work with.

I didn't know where to write actually. I didn't want to write in quora so that I can stay silent due the people I know for now.


texts: Why do we increase the minimum beam/slab depth if we increase the grade of the reinforcement to control the deflection

texts:
I've just started to study reinforced concrete design and I came across this

 in the "Design of Concrete Structures" by Dr.Nilson.
and I was wondering why do we increase the minimum thickness if we are using stell grade more than 60 ksi instead of decreasing it?


texts: What happens if I use a 240v clothes iron in USA?

texts: Since all it really is is a heating element, what happens if I use a 240v/50Hz clothes iron with a 110v/60Hz supply?


texts: how to find torque from force due to pressures that change as a function of z

texts:
My teacher is very strict about copying his work so I will have to explain it.
We have a wall with two fluids of different constant densities and depths. The wall is 'L' long. The wall has a section that goes sideways a certain depth in and then down all the way to the bottom of the tank. We have already solved for the pressures as a function of z on both sides. Previous exercises had us find the resultant force on different sections of the wall. Now we are asked to find the torque on the lower portion of wall about point P.
I see that 2 things will be changing with z - the pressure force exerted from both fluids and the moment arm. I am not too great with integration - If I could get pointers on where to start with my integration that would be appreciated. .


texts: Hi so I recently learned about dew point and rainning. From my understanding, dew point is the temperature at which the air can hold the amount of moisture present. And when the temperature decrease, the air can hold less moisture, so some of it must condenses, which come down as rain. So with this fact, does the rain usually happens when the temperature decreases? Then how can we describe the rains starts during noon(when it’s the hottest of the day) ? Is there any other factors that causes rain ?


texts:
Given the following system:

$$\dot{x} = \begin{bmatrix}1 & 1 & 0 \\ 0 & 1 & 0 \\ 0 & 1 & 1 \end{bmatrix}x + \begin{bmatrix}0 & 1 \\ 1 & 0 \\ 0 & 1 \end{bmatrix} u$$
$$y = \begin{bmatrix}1 & 1 & 1 \end{bmatrix} x$$

I need to find the minimal realization of the system. I know that the minimal realization means controllable and observable.

The system given is not controllable and not observable.


texts: equivalent deduction of Non-mechanical thermodynamic work

texts: "Work (as in Thermodynamics) is said to be done by a system if sole effect on the surroundings could be the raising of a weight." So, how is non mechanical work like : Chemical work, Magnetization work or even electric current flow work be reduced to the same?


texts: Let's take a 2009 Camry as an example. It runs on a 2.4l, 2360cc to be exact, engine with 4 cylinders. This means that the capacity of all the 4 cylinders combined would be around 2.4 litres in volume. I have noticed with Japanese cars after around 3.0L they add two more cylinders and make the engine a V6. Why can't you have a 3.0L I4? Or a 2.4L V6? How does it change the engine? I'm assuming that for a 3.0L I4 the cylinders would have to be larger to hold the extra volume. Would that mean that it would take them longer to burn the fuel inside and lead to slower acceleration maybe? Finally does it matter if the car is a 4WD or a 2WD?


texts: calculation of tension in curved chain for chain fountain (Mould effect)

texts:
https://royalsocietypublishing.org/doi/10.1098/rspa.2013.0689

A chain of some sort goes upwards, turns in a half circle (according to the drawn diagram), and goes back down.

Focusing on the half circle, the equation given by the paper to account for its centripetal force is

"In our initial analysis, we assume the curved region at the apex of the fountain is small enough, and has tight enough curvature, that the centripetal acceleration is much larger than the gravitational acceleration (v2/r≫g). The centripetal acceleration is then provided by the tension in the chain. If the (local) radius of curvature is r and the tension in the curved region is Tc" Also the lambda is mass per unit length

Why is Tc divided by r in the left half of the equation? If it was force per unit length then I would expect Tc to be divided by (pi)r instead of just r.


texts: Why are Chinese aircraft carriers conventionally powered?

texts:
China has nuclear-powered submarines, which means China is able to manufacture portable nuclear power-plants.
Then, why is the latest Chinese aircraft carrier Shandong conventionally powered?


texts: How hot does a rocket nose cone get during launch?

texts:
More specifically, I'd like to know if unmanned rockets need to be specially designed to withstand the heat generated from air friction and shock waves during launch.  I found the diagram below on the NASA website which shows some fairly high stagnation temperatures, but the problem is that I don't know how fast a typical rocket travels on its way to, say, low earth orbit.  I also don't know what the velocity profile looks like, i.e. Mach number vs. altitude.

Most of the information I've found only talks about orbital velocity and reentry temperatures, neither of which is very useful.


texts: What is the best way to model a beam and slab bridge?

texts:
I notice bridges designed by bridge engineers in my company invariably uses two models. One model for seismic load case and another for other load cases. I was told that some bridge elements, such as the slab and the walls have to be modelled differently, using plate elements, to capture the actual stiffness. But because it is not easy to extract the output such as bending moment, these have to be modelled as beam grillage in the non-seismic model.

As the models are different, additional effort is required to extract and combine the outputs, before processing them for design. If you are a bridge engineer, I would like to know if you have found a simpler way to model a bridge.


texts: Why do some guyed towers come to a point at the bottom?

texts: Why do some guyed broadcast towers come to a point at the base. It seems that it would be more stable if each vertical bar was anchored separately rather than being balanced at one point.


texts: DIY thermally insulating construction material

texts:
I need to thermally insulate two metal (say aluminum) parts, the first of which is at 200-400 °C (473-673 K), and the second one is at room temperature. It should be possible to screw the parts together or something, to form one solid assembly. The typical dimensions are like 10-40 mm. The insulator should be able to be created in a DIY setting.

The insulation material has to be reasonably stiff/strong to enable a rigid compound construction, so all plastic foams etc. are out and, due to the high temperatures, almost all (easily available) solid plastics are also out.

Comparing thermal conductivities I have found that all mineral-based materials are reasonably insulating at ~1 W/(mK) when compared to metals (~10^2 W/(mK)).

What has come to my mind (in order of ideation):

porcelain
glass
gypsum
fine-grained concrete

Anything obvious I have missed?

Gypsum seems very practical in that it can be easily cast with very fine structures. However I am not so sure whether it resists the heat (crystal water? gets more brittle at higher temp?). Anyway it is certainly a bad material for threading a metal screw in.

Glass is stiff and temperature resistant, but it is also sensitive to high temperature gradients and breaks easily under mechanic stress.

Fine-grained concrete (don't know if this exists at all as a product) - probably similar to gypsum, but a little stronger. But the question remains, if it can resist repeated heating/cooling/dehydration.

Porcelain (or other sintered minerals): sounds perfect, but can I reasonably expect to create a shaped part with threads/holes etc. at home?

Are there any best industry practices for parts like that?


texts: Cheap material and construction to insulate balcony during the winter?

texts: It's a long shot, but I was wondering whether there is any material I can wrap around my balcony to be able to use it like a sun room during the winter. A plastic-like material that I could span around my balcony and somehow seal to the outside of my balcony door, thereby allowing me to keep the balcony door open. It would need to be cheap and fairly easily removable.


texts:
I have a small table-like platform with two legs. Underneath each, I need to measure the amount of force. I want to use the difference between the two force measurements to estimate the platform's center of gravity.

What's a good sensor to use for this? Looking through suppliers Digikey, all the sensors that can handle a large amount of sustained force are either enormously expensive or way too large. Is there another way to measure force without bulky discrete sensors?

As a cheaper alternative, I was thinking of placing the platform on a low-profile seesaw, with a rotary potentiometer at the fulcrum, and springs under either end. The seesaw would tilt in proportion to the offset of the platform's center of gravity, and this could be measured with the potentiometer. It could do the same measurement as a $200 force sensor at a fraction of the cost. The only problem is that most potentiometers distribute their range of values across 360 degrees, whereas I need all those values within the range of 1 degree.


texts: Liquid Limit of Soil through Atterberg Tests

texts: My lab is evaluating the liquid, plastic, and shrinkage limits of some soil samples and we are following this video provided by the Missouri University of Science and Technology. The video indicates we should conduct at least 3 tests where it takes 15-20, 20-25, and 25-30 hits of the Casagrande Apparatus to close the gap that we make via the grooving tool. And this video also explains that the liquid limit is defined as the moisture content in which it takes 25 hits of the Casagrande Apparatus to close the divide made by the grooving tool.  We have been doing our best to turn our soil sample into a "uniform paste" through adding water as the video indicates, and even when that is the case, on a consistent basis, it takes fewer than 10 hits for the gap to be closed. Bottom line: My question is could there be soil samples where their liquid limits are lower than what the Atterberg Limit and Casagrande Apparatus method could detect? I do recognize the possibility of user error on our part, that we can continue to refine our technique on making the soil sample a "uniform paste." Thanks in advance!


texts:
I want to make a drone system which can recognise when fruit has dropped in our orchard, and pick it up and put it in a basket before theyve rotted on the lawn. I'm thinking buy a drone off amazon, attach some sensors, a camera and some fruit grabbers to it and bastardise the remote with a microcontroller and receivers, so falling fruit is recognised, and the drone can guide itself to pick it up. I was wondering if anyone could help in any way with the 2 bits (large bits I admit!) I don't yet know how to do:
1: how to recognise fallen/falling fruit

I was thinking an image recognition system using a pi?

2: how to have the drone fly itself to pick it up and return it to a predefined location

no idea yet besides accelerometers... Do I need to read up on missile guidance systems lol?

Any help much appreciated!


texts: Power assist mechanism for double pendulum?

texts:
I'm making a double pendulum for an art installation, and I would like to add energy to the system to compensate for friction and air drag losses so it can run more or less indefinitely.

The design so far has the top pendulum connecting to an axle at the top which is parallel to the ground and can rotate freely. So far I've sketched out a design which uses a rotational position sensor and a microcontroller to determine the pendulum shaft's current speed and position. A small, reversible electric motor will connect to the axle with a somewhat "limp" drive belt around the consistency of a rubber band (to lessen the impact of rapid chaotic changes mismatching with power input direction). As the axle rotates unpredictably, the control software will reverse or advance the motor to add a slight force in the current direction of rotation. Once tuned, the hope is that it will not perceptibly interfere with the natural motion of the pendulum while adding enough energy to keep the pendulum swinging with the same total energy as it started at.

Questions:
1) Are there mechanically simpler ways of adding energy to such a chaotic system?
2) Will energy added to the top pendulum distribute to the bottom pendulum in a way that would leave a casual observer unaware, or would the system develop obviously unnatural motion?
3) How can I roughly estimate (+-50%, to size the drive motor) the average energy input required to overcome friction and drag losses?


texts: What type of positive displacement pump is used for vacuum liquid extraction?

texts:
I would like to learn what type of positive displacement (PD) pumps are used to remove liquids from vacuum applications. I have been searching for an example application, but it seems to be a rare case.

So, imagine you have a liquid trap in a large vacuum system. The flow of water accumulation is so high that it warrants an extraction pump to remove the water. The pressure is about 90% vacuum. The goal is to remove the water to dump so it only need be pumped back up to ambient.

Is there a type of PD pump that is better at this application? From what I have found, very few pump manufacterers publish performance for vacuum operation.

Does anybody have an example of a vacuum application where a PD pump is used to extract liquid?


texts: How to correctly size the blades for a small educational wind turbine?

texts:
I want to design a small wind turbine that can be easily carried out of the classroom into the sports field in relatively low-wind conditions (5-15km/h) that can power a small ultra-bright 5V LED - just enough to show that it works.

How do I calculate the power I can get from different blade diameters in these wind conditions, and the power needed to drive a small DC motor/generator enough to light the LED?


texts: Where should I start to be a control system engineer?

texts:
I am a telecommunication and network engineer working as a programmer and data analyst. One of my dreams was and still to be a control system engineer and to design and program a smart robots and systems.

I have a background in programming and matlab. Where should I start ?

I get a book from Amazon for Norman S. Nise. The book is very technical and there is lots of things that I can't understand.

Where should I start and what electronic kit should I buy to start with and do experiments.


texts: Thermodynamics of gas exchange between gas cylinders

texts:
A synthesis gas mixture ($\text{H}_2:\text{CO}$ with molar proportion 2:1) is needed for methanol synthesis. The final mixture must be available in a gas cylinder of 50 L, say cylinder $M$, which contains, initially, pure $\text{H}_2$ at 5 bar. The carbon monoxide which will compose the final mixture is available in a smaller cylinder (20 L), say cylinder $m$ in a volumetric proportion of 9:1, at 120 bar. Both cylinders are, initially, at 303 K. A 1/8” steel tube must be used with a globe valve placed 1 m from the small cylinder $m$ and 4 m from the cylinder $M$.

How can one calculate the pressure and temperature of both cylinders in the process where the gas transfer is done opening totally and suddenly the globe valve, after 15 s? The dynamics of the problem seem to be difficult to implement.


texts: How is the equivalent spur gear diameter of a helical gear equal to (d/cos^2α)?

texts:
The book I've got says that the equivalent spur gear radius(re) =
(Semi-major axis)^2/(Semi-minor axis) of the ellipse made by the cut-section normal to the teeth of the helical gear.
There is no explanation provided for the given relation and is what I seek.


texts: How can I model a hysteresis curve from data?

texts:
I have the task of modeling the current to torque mapping for a given motor. I have an experimental set up where I can retrieve current, torque pairs.

Now my initial approach was to model the relationship with a regression curve, but I realized that the motor certainly shows some kind of hysteresis.

How would I be able to compute a current to torque mapping that also includes hysteresis from the data I obtained


texts: How do I calculate the ideal travel distance of the ball screw per revolution of the stepper or per step for the following hardware?

texts:
Question How do I calculate the ideal travel distance of the ball screw per revolution of the stepper / per step for the following hardware (I believe this is called the lead)?
Background I have a pre-built 100mm Ball Screw Drive Linear Slide purchased from Amazon.
The specifications of this assembly are as follows.

Material: Aluminum

Boundary dimension: 40mm

Shaft diameter: 12mm / 0.47inch

Rated vertical load: 40KG

Rated horizontal load: 60KG

Accuracy: 0.01mm

Effective stroke: 100mm / 3.9inch

Ball screw length: 165mm

Sliding block: 60 x 80 x 30mm / 2.36 x 3.15 x 1.18inch

Pitch-row width: 68mm (max)

Pitch-row length: 60mm

Screw: M6

Slide table size: 190 x 40 x 20mm / 7.48 x 1.57 x 0.79inch

Weight: Approx. 1432g

The stepper motor included with this module is 42BYGH48.

Looks very similar to the ones defined here with the same wire out colours. Looking into this I found multiple sources refer the desired number this as the lead (lead is the linear distance traveled by the nut or screw after one full rotation). Page 2 of this source talks about this but I don't really follow where these numbers have come from.

Can anyone suggest a good source to help explain to me what I need to calculate this for myself? What values am I missing from my setup to calculate this?

Sorry, I suspect I'm thinking about this all wrong and look like an idiot! had a long day at work and just spent an hour digging around and made no progress! I was certain someone here could point me to exactly what I needed!


texts: How Infinadeck Omnidirectional Treadmill works

texts:
I have seen this paper about the Omnidirectional Treadmill With CAD model ( with tiny rollers on it):

Which compered its prototype with infinadeck as shown below:

but don't see those  roller in infinadeck as seen here:

So does the rollers in infinadeck (more zoomed video) are so small that can not be seen or that company use another mechanism for this device, for example like this:

Update:
By seeing this video i guess Thanks, infinadeck don't have tiny rollers and only have the chain show in the CAD model of paper like this:

But i don't know i am right?!
Thanks.


texts: How to accurately measure mass flow through server vents using an anemometer

texts:
I have to work out the air mass flow coming out each vent on a server and have proposed to use a hot wire anemometer to measure the air velocity at each vent by placing it slightly inside one outlets of the vent (it is a grid pattern), then multiply that by the vented area and air density to find mass flow.

My concern is that I am instructing technicians to do it on site, and I am worried that the measurements may vary significantly depending on where on the vent they are taken from i.e. if they take it from the corner or side of the vent it may be different from the centre.

This is my first time trying to measure something like this and was wondering how others in the industry do it. Is there a better way of doing this?


texts:
I have read on many sites that for lift to occur, the pressure below a wing must be higher than the pressure above it. This happens by somehow moving air faster over the top of the air foil so the pressure above the wing decreases.

What I can't understand is: Why does the air above the wing have to move faster? Because on many sites it is stated that there is a misunderstanding that air moving upwards has to flow faster to reach the end at the same time with the air moving downwards. But that is wrong: https://m.youtube.com/watch?v=6UlsArvbTeo

So why else would the air upwards want to move faster? Why don't they both move at the same speed?


texts: I have got 19.6 as the answer for (a) but the book tells 14 is the answer. Can someone tell what mistake I have done or is there in the book.


texts: Is there a specific term for the car loops at an airport?

texts: I notice that many airports allow cars to loop around the arrivals/departures. Is there a specific term for this design feature in airports?


texts: Upper frequency limit of transmission line

texts: How would I determine the upper frequency limit of a transmission line from these plots? I plotted these in matlab after being given some RLCG values. About all I can seem to understand from these plots is when I can start using the high frequency approximation formulas for calculating characteristic impedance and etc, which is around 30MHz.


texts: Determining the transfer function of cruise control given characteristic equations

texts:
During my time revising for my control engineering module, i've come across this question

The automatic cruise speed control for a vehicle is described by the following equations

$\bigl( 1\bigl)$ $m \frac{dv_0(t)}{dt} + Fv_0(t)=u(t)$

$\bigl( 2\bigl)$ $u(t)=K[v_0(t)-v_r(t)]$

where m is the mass of the car, 1000$kg$, F is the frictional constant 50 $Nm^{-1}s$ and $u(t)$ is the throttle actuator force and K is the proportional gain control for the actuator.
Also $V_0(t)$ is the actual speed while $V_r(t)$ is the desired speed.

There are two parts to this question, and im a bit confused on both of them.

part 1 says to draw a block diagram of the speed control system. In the control engineering module we generally draw the block diagrams as related to s, so i thought i'd get the laplace transform of the function (to get the transfer function) and draw it from the general model of a control system

This coincided with part 2, which wants me to show that the transfer function in terms of K is given by

$\frac{V_0(s)}{V_r(s)} = \frac{K}{1000s+50+K}$

I went about working it out and eventually ended up with this

$\frac{V_0(s)}{V_r(s)} = \frac{-K}{1000s+50-K}$

Can anyone help me figure out where i went wrong?

Also, i attempted making a block diagram in the t domain for this system, however since there are two equations with equal outputs (not summed) i was completely stumped on how i would display that as a model that is accurate, without making assumptions like equating K with the system gain of the other equation


texts: How does the second Motor operate in this diagram?

texts: The two motors are mounted in parallel as you can see in the picture and each one of them is connected to a gearbox through an elastic coupling. My question is : how do they operate together ? is one of them supposed to be off ? if you have any book or any website that discuss such transmissions I'd be thankful.


texts: How to create intersected conical copper coils?

texts:
I'm looking to create something like this:

But the problem with solid copper wires is it tends to spring back into it's original shape and this construction will flatten.

I've tried creating a wooden cone and wrap the copper around it; however, after leaving it for 24 hrs, it still flattens when I take it off the wooden cone.

Any help is appreciated, thanks!


texts: Assessment of a concrete beam being strengthened by an additional steel member

texts:
Hi there (from Europe),

I am completing what should be a relatively quick assessment for the client, but I have started to second guess my self and would like some reassurance.

Essentially the job involves removing a portion of an existing 2.6m x 1.22m concrete slab in order to install a manhole (1.2m x 0.75m). I've taken the fairly rudimentary (and conservative imo) approach of simply reducing the existing slabs moment capacity by reducing it's width. For example, for assessing the moment capacity of the current slab I took a width of 1.22m, but it's reduced capacity would be based on a width of 1.22-0.75=0.47m.

With an original moment capacity (89kNm), and reduced moment capacity(37kNm), we know the difference between these two (52kNm). My idea was to simply take two Square Hollow Sections and attach them to the underside of the slab, on either side of the manhole, and size them such that each was capable of holding half the difference in moment, 26kNm.

This is a fairly simple approach but the more I think about it the more I'm beginning to reconsider and instead consider assessing the steel and concrete as a single composite section to Eurocode 4.

This is a small scheme with a low budget and I lack experience of Eurocode 4 to quickly assess this.

My question is thus:
Is my approach conservative enough to safely size steel members or is there something fundamental that I am missing in composite design that makes my solution inaccurate and dangerous?


texts: Can a Tesla Powerwall 2 be rate limited?

texts:
Can a telsa powerwall 2 be rate limited (discharge/charge)?

I have access to realtime electricity rates (30 min update interval) and also access to 12 hour predicted look ahead. So I wish to limit the charging (if the buyback rate is high) and limit the discharging (if the buyback rate is low).

I can see that I can basically just use an on/off controller by literally shutting the powerwall off entirely (the api supports this). But it would be nicer to rate limit it.

Is there any public (or private) api that could allow me to achieve this?

edit: I found this API however it doesn't appear to have figured out any rate limiting. Tesla Powerwall 2 - Local Gateway API documentation


texts:
I am wondering if, at all, the wave equation, or the heat equation, is ever used in engineering? I think this equation is of theoretical, rather than, practical interest. For example, by solving the wave equation over a circular membrane we get all the possible standing waves on it. This is a theoretical result. But when engineers construct things do they ever rely on this equation?

I would like to see an explicit example in engineering when the heat equation (or wave equation) PDE is set up and explicitly solved by the eigenvalue expansion.


texts: Recommendations on a rigid connection between materials

texts:
I am trying to construct a torsion pendulum/balance for a physics experiment but the research papers are always missing specifics on how the certain connections are made.

I am looking for recommendations on rigid connections for:

How to attach a glass mirror to tungsten wire.
How to attach tungsten wire to torsion pendulum/balance beam.
How to attach PLA to glass.
How to attach glass to glass (I do not have the capability to melt them).

Here is a link to an example experimental setup. The balance beam I am using is actually quartz glass tube. The wire is tungsten. The plastic components are 3d printed and are PLA. The total weight is about 22lbs suspended from the tungsten wire.

(I posted this in the Physics exchange and they closed it claiming it is an engineering problem)


texts: Is there any National Pipe Thread Straight (non-tapered, requires O-ring or compression olive) that is compatible, even loosely, with a machine thread threaded rod? I want to put a reducer on the end of a pipe threaded with NPTS and reduce to like 1/4 inch NPTS nominal and have that reducer ride on a 5/16-18 threaded rod.  So it's like a shoring jack or lolly column, but really cheap, and the threaded rod can fit through a small clearance and guide the end of the pipe to the bearing point.


texts: Is "Modal Response Spectrum Analysis" the same as response spectrum analysis? How about modal superposition analysis? This is the same or different? Or all are same?


texts: Determining the magnetic reluctance of a straight flux path

texts:
Currently I run into an issue understanding the following. The bottom part of this magnetic circuit is made from steel which has a finite relative permeability. However, the flux paths is made out of 3 parts, namely lt1, lt2 and lt3.
How could I determine the magnetic reluctance of the bottom part of the circuit since it is made of 3 parts.
Can I add the flux paths lt1, lt2 and lt3 and use ht as width, or do I have to do it in parts?


texts: Shape memory alloy fibers with low Young's Modulus?

texts:
I am wondering if there exist any species of shape memory alloy fibers with low Young's Modulus at room temperature, for an application I'm working on.  So far I've played with Flexinol, but it is a bit too stiff.  I know Nitinol has a Young's Modulus of ~30-40 GPa.  I am wondering if there exist softer fibers - I'm interested ones that might be at around ~10 GPa, ~1GPa, and < 1GPa, if they exist.

Beyond other materials, is there any procedure to make Nitinol naturally softer?


texts: How are wind tunnel models used when designing supersonic aircraft?

texts:
There are two things involved: wave drag and boundary layer separation. The wave drag depends on the Mach number while the latter depends on the Reynolds number of the flow. It's easy to maintain the incoming Mach number as it is independent of the geometry; however, the Reynolds number depends on the geometry of the model.

$$ \text{Re} = \frac{\rho u d}{\mu}$$

If air is used as a medium, then assuming that the flow is to be maintained at a constant Mach number, $\rho$ and $u$ will be fixed by the gas dynamic relations. $\mu$ is pretty much out of our hands, so the only non-fixed parameter is $d$.

Since $d$ is much smaller for a model than for a real aircraft, the flow will have a lower $\text{Re}$ than a real aircraft would. This will give different flow separation characteristics for a model than for a real aircraft.

In subsonic testing, only thing that matters is $\text{Re}$, which can be fine tuned to match with the actual size by tweaking $u$ for given $d$. But in supersonic flow, we do not have that luxury, as $u$ is decided by the Mach number of incoming flow.

So how are wind tunnel models used for design of aircraft, spacecraft and missiles? Are there correction techniques to predict flow separation better? Can the same techniques be used for dealing with CFD data?


texts:
Draw the FBD of the entire frame, assuming that friction and the weights of the members are negligible. How many unknowns appear on this FBD?

This is what I've tried so far. I have four unknowns. They are F1, F2, F3, F4


texts: Clarification of cover definition in Eqn 7.11 of EC2 for calculating crack width

texts:
In EC2 clause 7.3.4(3), cover c is defined as the cover to longitudinal reinforcement. Say for a beam with cnom of 40mm and outer links of 16mm, the cover to longitudinal reinforcement will be 56mm. However, from clause 8.2.2 of PD 6687-2:2008, it states that the cover c should be taken as cnom. My understanding for cnom is that it is the nominal cover to the outermost bar, which is the outer link if it is present.

Since crack width depends very much on the concrete cover, why does PD 6687-2 propose a different definition for the cover? Should the calculation for crack width include outer link diameter? OASYS Adsec seems to include link diameter in its calculation.


texts: How does Electric arc welding compared to gas welding?

texts: While focusing on Quality and strength of welded joints produced but both methods..


texts: Can a crisscrossed metallic skeleton resist earthquakes for buildings?

texts:
To follow up with my previous question on the seismic design of buildings, I would like to ask if it makes sense to support buildings with strong thick 'crisscrossed' metallic frames.

I have the impression that an 'X-structured design' provides good structural integrity, as commonly seen in construction sites. Would it be wise to construct buildings out of a metallic 'skeleton' that is formed throughout by intersecting the diagonals of squares?


texts: Calculate whether a polycarbonate plate can withstand a certain force

texts:
I need to calculate whether a polycarbonate sheet can withstand a certain maximum force. The force is an impact force on any one point of the sheet at any given time. All I have are the Young's modulus and the dimensions of the sheet. Any ideas how I can go about calculating the maximum force the sheet can withstand? This polycarbonate plate is placed vertically and held on all edges by a frame.

Thanks!


texts: Need help in deriving components of forces when they depend on lengths and angles. (2 questions)

texts:
I am having difficulty with two questions from a book I am studying about statics. I have seen the answers but it did not help me understand how the answers are derived. I want some advice on how to think about these types of problems and whether there are any tricks which help to solve them.

Question 1 (1st image);

A small probe is gently forced against a circular surface with a vertical force F (the red vector). Determine the n- and t-components of this force as functions of the horizontal position S.

Question 2 (2nd image);

Determine the x- and y-components of the tension T which is applied to point A of the bar OA. Neglect the effects of  the small pulley at B. Assume that R and alpha are known.


texts: How to model the inside of a server for CFD and thermal studies?

texts:
At my workplace I have been assigned to create an accurate 3D model of our Dell PowerEdge R820 servers so we can insert our custom cards and run a CFD and thermal analysis on them. The end goal is to have an exact understanding off all the airflow and heat transfer within the servers and server racks to help in designing future systems and fix overheating issues we are having with some of our current ones.

My problem is that the insides of these servers are quite complex and it is going to take an era for me to reverse engineer all the parts with a pair of verniers and find out how much heat is produced and where.So I am wondering if anyone else has come across something like this before and how they created an accurate CFD of their system.

Would 3D scanning be an option? I am concerned that 3D scanning will be too accurate, in the sense that what should be a straight edge might be turned into 200 different vertices etc. And I am not sure of how much cleanup it would require. I plan to do the CFD in Solidworks which requires solid modelling - it may have issues with the surfacing of the scans. Would like to hear from anyone with experience regarding this.

On the other hand, does anyone have experience with getting 3D CAD models from companies like Dell? I work at a large company and we buy a lot of their products for our projects but I wouldn't have a clue what department to call to see what needs to be organised to get CAD files. Would welcome any input here.

Lastly, for the thermal modelling, my plan of attack is to use some IR cameras to see where the heat is being produced. But I don't know how to work out HOW much heat is being produced at these spots so I can model the heat production from these processors in the CFD. What do people normally do for this?


texts: How can I translate a pressure boundary condition to a velocity boundary condition for incompressible, viscous flow?

texts:
I have been working with an old code for modeling incompressible, 2D viscous flow out of a tank to understand a chemical process.  There isn't much documentation and I'm not a fluid dynamicist, so I have been trying to check that things are working as they should by comparing results with those from another code.  The comparison is great when I use a velocity inlet condition.  However, there is a major discrepancy when I use a pressure inlet condition.  In both cases, the outlet pressure is zero.

I have spent several weeks trying to figure out what the problem is with the pressure inlet condition (and have an active question about it) because I have pressure inlet values that I want to use in my problem.  I don't know velocity inlet values.  But I have to acknowledge I've hit a wall with figuring out my pressure inlet boundary condition problem.

This may be a dumb question, but I would really appreciate it if someone would help me confirm if I can transform my pressure values into an inlet velocity condition.  If I can, maybe I can simply use an inlet velocity and my problems will be over!

I understand that:
$$P = \dfrac{1}{2}\rho U^2 + \rho gz$$

where $\rho$ is fluid density, $U$ is velocity, $g$ is the acceleration of gravity, and $z$ is depth of the tank inlet below the tank outlet at 0.

So if I simply plug in my inlet pressure value and rearrange, will I get a valid inlet velocity that I can use for a velocity boundary condition?  My concern is that I'm dealing with viscous flow and I think this expression is related to the Bernoulli equation, which does not account for viscous flow.

If I'm right and I can't use this expression to calculate an inlet velocity, does anyone know if there's an alternative?

The reason I say I probably can't is that I've tried it and the results from the two codes don't match.  I'm just trying to figure out where my problem is--if it's likely to be a bug in one of the codes, which code is the problem, or if I'm making some mistake when inputting my boundary condition values.


texts: How to control the timed release of small bubbles in a liquid?

texts:
I'd like to have electronic control of the open/close timing of a source of air at the bottom of a tank of liquid such that I have control of when a single bubble is formed.

Experimentation would be required but I expect the open period to be at most 250ms - the more scope for lower period options the better.

The process of bubble forming would be repeated over and over again - with a 50% duty-cycle the frequency of new bubble formation would be a minimum of 2Hz.

Let's say 5~10Hz would be ideal.

Multiple bubbles will need to be formed in close vicinity (~10mm) so the device would either have an appropriate form-factor, or some kind of tubing system would be put in place.

I will have close to arbitrary control over the control signals, but I expect some form of digital control per 'channel', preferably parallel and direct, i.e. 0=closed, 1=open, as opposed to some kind of interpreted data stream.

Although I understand that the dynamics of bubbles will be all over the place, in terms of control I'd expect low latency.

Question: what kind of devices am I looking at here?

Are there off the shelf components that can do this?  Cost is a concern at some level but is not necessarily the overriding requirement.


texts: Trouble with an actuator on a Robotics SolidWorks design. Any ideas why?

texts:
I am in the process of developing a robotics design on SolidWorks.
The goal of this design is to tilt a platform using 2 actuators.
My design utilizes 2 indirect actuators that are separately powered and operated to tilt the platform on each end.
Each actuator has a fixed rotational joint at the top, that should rotate along the hinge as it gets pushed up with it's actuator, thus lowering the other side at the same time.
(See MODEL 1 below, which contains a brief 360 and identifies the actuators on my SW model).
Please note the 2 rotational joints at the top of each actuator, and notice that they have full rotational capability at any stage.

However, when I attach a metal plate onto my rotating joints and try to animate my SolidWorks design, it ends up pulling the opposite actuator, and keeps the metal plate level the entire time. It does not move the rotational joint at the top of it's actuator at all. Which does not make any sense because the rotational joint should account for the actuators push.
As the actuator moves up one one side, both joints should rotate by the same angle, and the plate should tilt. However this does not happen at all, both actuators move together, and the plate remains flat.
Can anyone please explain why this is happening and what I can do to fix this issue?
Is this a problem with SolidWorks perhaps?
Any input would be highly appreciated, I can provide more information if needed.
Thank you for your time
(See MODEL 2 below, which contains the problem, a brief 360, and identifies the actuators with the metal plate on my SW model).


texts: What are the technical differences between flexible and rigid solar panels?

texts:
During a recent search I discovered the existence of flexible solar panels. Besides the obvious differences of low weight and flexibility what are the high level technical differences between flexible and rigid solar panels? What is the typical Lux VS Current curves for such solar panels?

The available technical specification for the above solar panel are listed below

Technical Specifications:

Power Output: ~6V @ 1W (~160 mA)
Output Type: DC Voltage
Dimensions: 100mm / 3.94" x 198.43mm / 7.81" x 0.77mm / 0.03"
Operating temp range: +32 to +158°F (0 to +70°C)
Weight: 27.93g

References:

Amorphous Si Solar cells
Solarmade
Powerfilm solar
Flexible 6V 1W Solar Panel
Solbian

Disclaimer: I am not endorsing any of these products.


texts: How can I check whether a nonlinear system is zero-state observable?

texts:
Given a nonlinear system, such as:

$$\begin{align}
x_1' &= x_2 \\
x_2' &= −x_1^3 + u \\
y    &= x_2
\end{align}$$

How can I check the zero-state observability of the system?


texts: Document Feathering Tolerance on Drawing

texts:
I am recreating an engineering drawing package from old quotes for a large assembly. In the quote they say "All length edges not to exceed 1/32" deep feathering". For some context this is for a bunch of graphite blocks which were cut to a constant cross-section.

First what exactly does feathering mean in this machining context? Secondly what is the best way to denote this tolerance on an engineering drawing?


texts: Dimensioning holes through a hollow shaft

texts:
I have three types of holes in a hollow shaft that are perpendicular to the shaft. The first type of hole go only through to the centerline. The second type go all the way through (i.e. out the other side). The third type go all the way through, but are not a mirror image of each other. They are patterned at 160 degrees, instead of 180 degrees. How should I best show these in my drawing?
For "through to centerline" I've seen THRU used. (in this first example)

So how would I show this if it really did go through everything. How would I call this 160 degree pattern out? I tried to show this with several cross sections but it looks terrible.


texts: what is 1P frequency in rotor (wind turbine)?

texts: In wind turbine, Is the number of revolution taken in 1s is called 1P frequency? If not, is it possible to find the 1P rpm from rpm measured for 1 hour (that is, I have 60 rpm data points from tachometer)?


texts: If I were to fully fill a sphere with water without any air trapped inside, how to find the pressure of the water at, say, the center of the sphere?


texts: Is there a need to consider the moment generated by horizontal water pressure in a pool?

texts: Suppose there's a pool  which is supported by 4 beams (Perimeter beams)and 4 columns. When designing the beam should we consider the moment generated  due to the horizontal water pressure? (I'm using BS 8110 for designing)


texts: Is it necessary to preheat an investment casting mould when working in a vacuum?

texts:
Normally, in investment casting, the mould is preheated before pouring the liquid metal in to reduce thermal shock from rapid cooling.

In a vacuum, the heat transfer due to gas convection is reduced to zero, which will also reduce the thermal shock. Does that mean that, if performing investment casting in a vacuum, I do not have to preheat the mould?


texts: Cylinder's surface condition of gas springs (gas struts)

texts:
I've discussed part of these question somewhere else, but realized I have to be more specific about it. I'm new to this site and hope I'm doing the right thing.
I'm planning to manufacture gas struts used in kitchen cabinets; therefore, firstly, some guide books or standards about the needed cylinder surface (surface finishing and tolerance) and compatible o'ring and rod seal of this cylinder-piston mechanism would be very helpful.
The gas strut is filled with 6-7 bars Nitrogen and the cylinder have 14mm ID and 12cm length. The piston consists of a steel rod and a plastic piston head. Obviously, there is a rod seal between the rod and cylinder, and an o'ring around the plastic piston head. I cannot use seamless tubes since the end price would not be able to compete with current gas struts. I've been suggested plug draw welded pipes(tubes) in order to eliminate the weld seam inside the tube. How close would the inside surface after drawing be to the desired surface? Is this the most efficient way?


texts: Why Sony headset's charging station doesn't charge other NiMH batteries rather than which came with it?

texts:
I've got a Sony MDR-RF4000 wireless headset, which is already 7 years old, so obviously its NiMH battery (Sony BP-HP550-11, basically a pair of AAA NiMH rechargeable batteries tied together) shows the signs of age.
The battery compartment has a note that explicitly says: "You cannot charge any rechargeable battery or dry-cell battery other than the supplied battery". And it doesn't lie. I'm using a pair of Eneloop batteries, which are also rechargeable and also NiMH. And they do provide power to the headset just fine. But the cradle station doesn't charge them, as described.
What is the technical reason behind that? How could Sony even achieve that, be that for an evil purpose or not? I'm using NiMH batteries in place of NiMH batteries after all, why do they refuse to charge? Are there many different kinds of NiMH batteries incompatible with their respective charging stations?


texts: Why do microwaves get louder when the timer goes off?

texts: With most microwaves I've used, I've noticed that once the timer goes off, there is a couple seconds where the "microwave sound" gets louder and it seems to be cooking more intensely before it actually shuts off. Why is this?


texts: Do flexible water hose cause pressure drop with constant flow?

texts:
My dad has a tub by a lake.
He has a water pump in the lake to pump up water into a tub.

He claims that if he use a flexible hose, the pressure in the hose at the top will be lower than if he use a rigid hose. The pump has to keep a flexible hose stretched, causing a pressure drop, he says.

I say that if the diameter of the hose doesn’t change while the pump runs, there will be no pressure drop, so once the pump is fully running, it doesn’t matter if the hose is flexible or not.

Who is right?


texts: Why does public transport uses compressed air to open doors instead of electromotors?

texts: System with compressed air seems more expensive and harder to build and integrate neither using simple electromagnetic drives to open public transport doors.


texts:
Chainsaws use oil to lubricate the chain. The usage is quite minor, probably less than 1cc per minute of work. The oil is normally supplied from a refillable compartment to the chain only when the chainsaw is running.

How is the delivery managed?

A pump? The capillary effect?

If it's a pump, I'd be interested in details - I mean, I have a hard time imagining a pump this slow (<1cc/min) supplied from the high-RPM engine... or does it use an extensive gearbox to slow down? A separate motor?

[note: I mean the oil used for chain lubrication, not mixed with fuel for the two-stroke engine of motorsaw]


texts: I have a situation where a 5mm steel rod needs to be in contact and rolls over segments of a 80mm steel pipe's inner face. Would it be a good idea to loosely slip a Teflon bushing over the rod and use it as a roller? I haven't seen loose fitted bushings, so I'm not sure if it'd be right to let a bushing rotate like that.


texts: What metal material to use for stove exhaust pipe?

texts: If biofuel is burnt, for example wood, and the stove I am building is made of metal, what is the most appropriate metal material I should use to avoid excessive corrosion in the exhaust pipe of the stove?


texts: How to integrate ∫vᵢ(uᵢ² + vᵢ²)dA in calculating monosymmetry index of an angle?

texts: I saw this question asking about calculating monosymmetry index of an unequal angle. What I need is a formula to calculate $\int v_i{(u_i}^2 + {v_i}^2)\text{d}A$, given the depth $d$, breadth $b$ and thickness $t$ of an angle. $A$ is the area and $v$ and $u$ are the coordinates of each small element $i$ of the section. Is there a simplified method to derive the above, neglecting root radius and toe radius?


texts: How does conductivity $\sigma$ of salt-water depend on salinity?

texts:
In what way does the electrical conductivity $\sigma$ (or conversely, resistivity $\rho = 1/\sigma$) depend on the salinity $S$ of the saline- (or sea-) water?

I know they must be in some way proportional since the more free charge carriers (ions in this case) available, the more electric current is possible.


texts: What loads does the safety factor apply for?

texts:
As is well known, a safety factor is often applied for engineering structures as a measure of precaution.

I would like to ask for which loads (if not all) does the safety factor apply for.

For instance, take an aircraft wing. The safety factor will need to be applied for the aerodynamic loads but does it need to be applied for any other loads such as the self-weight of the wing or the weight of the powerplant?


texts: How the sizing of electric motor is done for a electric vehicle?

texts:
I have calculated the resistances encountered by the vehicle. Now to find the required power i used formula

                    Required power= Total resistance force * Max. velocity

I came out with around 50 kw.....but this is the power required by vehicle.

How to calculated the motor power?

I don't think 50 kw powered motor is required to propel a vehicle with gross weight around 700 kg


texts: Will a TV with a Sateillite Input work with Cable TV (In Europe)

texts:
I am trying to work out whether a TV is able receive Cable TV in my apartment without having the TV itself to test it with.
The TV has a sateillite TV coaxial input. Is this equivalent to Cable TV? Will it be able to tune the channels in the same way? The Cable TV socket is also coaxial.
The TV is a Philips 58PUS8535/12. TV is Tele2 (formerly ComHem) in Sweden.


texts: impulse input and discontinuity in initial condition after

texts:
Consider a dynamical system as bellow that is subjected to an impulse input:

$\sum_{n=0}^N {a_n x^{(n)}}= f_0 \delta(t-t_0)$

the initial values are non-resting (all non-zero):

$x(t_0^-)=x_0\hspace{0.2cm} ;\hspace{0.2cm} x'(t_0^-)=x_1\hspace{0.2cm} ;\hspace{0.2cm} ... \hspace{0.2cm} ;\hspace{0.2cm} x^{(n-1)}(t_0^-)=x_{(n-1)} $.

How can I write the correct initial values for $t=t_0^+$? This is ambiguous since integrating the differential equation above, yields:

$ \sum_{n=1}^N a_n  \big[x^{(n-1)} (t_0^+)-x^{(n-1)} (t_0^-)\big] = \sum_{n=1}^N a_n  c_{n-1} = f_0$

where $c_i$s are the jumps in initial conditions. In literature, it is said that only the highest order will undergo a discontinuity, yet it's not clear for me why.


texts: Difference between static water level and water table level

texts: Can anyone please explain to me the difference in the levels of static water and water table?


texts: How can I calculate the temperature rise of a circuit board for a given power dissipation and area?

texts:
I have a PCB of approximately 4" x 4". It has a single long spiraling trace on it. The trace is 50 mil 4 oz copper, so nominally it's good for something like twenty amps before it overheats. But this board overheats much faster. My supposition is that the windings being so close to each other has a compounding effect on the heat.

Now, presumably I could increase the surface area of the PCB, and thereby dissipate the same power with less temperature rise. My question is, how does one calculate such? What is the relationship between the power dissipated by my copper plane, its temperature rise, and its surface area? Assume still air.


texts: Degree of Freedoms in a Node of a 3D Frame/Beam Element

texts:
I recently took a quiz for my Matrix Methods of Structural Analysis Class, in which I encountered the following MCQ. My answer of '6' was justified, in my opinion, by the size of the stiffness matrix for a general 3-D beam element, which is 12x12 (6 for each node).
I am pretty sure I am correct but I would like confirmation on whether to approach my instructor with this.


texts: How to choose reference signal in a state space model?

texts:
I am a bit confused about choosing reference signal in order to control state space models.

I have read(however without deep math explanation) that one has to scale his reference signal for to make system to be able to track input signal. Also there is a function which gives a scaling coefficient Nbar, so I have to multiply my reference signal by it:

s = size(A,1);
Z = [zeros([1,s]) 1];
N = inv([A,B;C,D])*Z';
Nx = N(1:s);
Nu = N(1+s);
Nbar=Nu + K*Nx;

In my particular case there is the model of a pendulum on a one dimensional cart with arbitrary chosen poles. My state variables are
${\vec{\textbf{x}}} = [x\ \dot{x}\ \theta\ \dot{\theta}]^{T}$.

Below is matlab code:

clear all;

M = 1;
m = 1;
l = 1.5;
g = 9.8;
I = m*l^2;
b = 0.05;

denom = M*(m*l^2) + I*(m + m);

a22 = -(b*I + b*m*l^2)/denom;
a23 = (g*(l^2)*(m^2))/denom;
a42 = -(b*l*m)/denom;
a43 = (g*(M+m)*l*m)/denom;

b21 = (I + m*l^2) / denom;
b41 = l*m / denom;

A = [0 1 0 0; 0 a22 a23 0; 0 0 0 1; 0 a42 a43 0];
B = [0; b21; 0; b41];
C = [1 0 0 0];
D = 0;

% Check for controllability
co = ctrb(A, B);
fprintf("%f\r\n", rank(co));

% POLES
P = [-1.5 -0.9 -2.5 -3.5];

% Placing poles
K = place(A, B, P);

% Reference signal rescaling
sys = ss(A, B, C, D);
N = rscale(sys, K);

My simulink model:

And position plot:

Everything works like a charm. However I totally miss the intuition behind that.

Imagine standard PID control, in this case if I would like to control position I would set the error to ´current_position - desired_position´ and apply standard PID formula to that error. From the above it is intuitively clear why position is controlled and if I want to control, for example, velocity I will just set error to velocity divergence.

However in a state space I have some coefficient which arises after calculating dot product between my state and gain matrix. And for some reason after subtracting it from a scaled version of u I get controlled position. Why is a big secret for me. And how would one control any other state variable in this case, like velocity for example?


texts: Replacing PID with Lead–lag compensator?

texts:
I have a vehicle (I bought it and it proprietary and I have no information about any internals) which I want to integrate into my simulation environment. So far I have a physical model of it which I gained by driving around recording data and building a physical model from it. Now I'm at the point where I want to model the internal controller. I though that it might use a PID but I think now that something else is used instead.
First I ran (around 30k) simulation with the physical model as basis to come up with the PID constants. In the simulations I let the vehicle move around the way as I did with the real vehicle and compared the response of my controller with the measured response of the real controller. In the image below you see the best PID which my brute force parameter search came up with.

As you can see my PID (red line) does not respond as fast as the real controller (green line) So my question is now:

What kind of controller could have been used here ? And how can I model it ?

It is definitive not a PID. Ten year ago I had lectures on control and system theory but since then I did not need to build a controller so I have not much experience. I looked into the literature and found the Lead–lag compensator which look promising but I have no idea where to start or how to implement it. To get the constants here I again can run simulations in a try an error manor. Maybe another different approach has been used but I have no idea what.


texts: DWG specification document for parsing a DWG file?

texts:
I am extending the Apache Tika parser for DWG files so that I can parse text out of DWG files.
Currently someone else has written some basic metadata parsing which is great. But the newer versions of DWG are not yet supported.
I would like to add that support, and extend what is possible to parse.
I read around online and the Spec for DWG file format is proprietary as far as I can tell, so does that mean there is no open specification document?
Any help anyone can contribute to help me parse DWG files would be appreciated!


texts: What is the difference between incremental and cumulative error?

texts:
In a description for ballscrews on a CNC, I saw two types of error listed:

Incremental error: < 0.0006"/ft
Cumulative error: < 0.0008" at 35"

What are these types of error measuring? What is the difference between them?


texts:
I am currently designing a small weather station that will be suspended from two fiber optic cables and a power wire. You can imagine for now a three point attachment to each wire with a wind vane suspended below, like so. I need some help figuring out the best way to support it while allowing rotations.

Basically, I would like to be able to have the device adjust its pitch so that if one fiber gets pulled vertically, the wind vane will stay level. The yaw adjusted by the force from wind. I am not sure how important roll will be to add in, so for now I have not considered it too much.
The reason for controlling pitch is that as the fibers are pulled up in the air, one may be

My basic idea now is to have a rod go through a small hole in the top part of the device, where the device can rotate, adjusting the pitch. You can see the 3 holes for inserting that rod; here is a video of the device. I would choose one nearest the center of mass (to be determined). For a sense of scale, those holes are about 1.5 mm in diameter. The whole device is small, and should be about 100-200g total.

I plan to have a clevis structure attach to that rod; what my fingers do in the video. After that it will have to go to an assembly above that will allow yaw rotation (not designed yet).

The problem I find with this design for pitch is there is no damping, so the device oscillates upon disturbances instead of finding an equilibrium point. Also, I have had some trouble finding rods and other parts at this size.

Any suggestions on how to best design this and parts that may be useful would be great.

Thanks!

(P.S. I tried putting the third image, but stack exchange limits me to 2 links until my reputation score is at least 10.)


texts: How to calculate the force required to lift this deck?

texts:
I want to build a folding deck. both sides are on wheels.
Trying to wind my head around how to calculate the required force for the hydraulic piston to be able to pull the deck into a folded position..
Any ideas?
Each side is around 67 KG.


texts: What is the meaning of 'ergodic capacity' of a wireless communication channel?

texts: I have a simple question: in the research literature on wireless communications I often see the term "Ergodic Capacity" of a channel. What does it mean?


texts: How can I change the type of extrusion output in Siemens NX 12?

texts:
I´m new to Siemens NX 12 coming from Fusion 360. I´m having problems with the extrusion command in NX 12. I´ve created a sketch where I want to extrude one big body and then add with the second extrusion some parts to it. When I select the lines of the sketch and then look at the output of this operation I only get walls with no thickness but not a solid body. How can I change this behavior?
thanks for your help :)


texts: How can I connect mismatched solar panels in parallel?

texts:
I have two solar panels, a Sanyo HIT 240HDE4 (35.5 V and 6.77 A at max power) and a Panasonic (SANYO) HIT VBHN245SJ25 (44.3 V and 5.54 A at max power).

These panels are mismatched in both voltage and current, so aren't ideally suited to being connected either in series or parallel.

Can I add a voltage regulator/converter to one of these panels to bring the voltage in line with the other, therefore allowing me to connect them in parallel?

For example, if I bring the 240 W panel up to 44.3 V.

Then I can connect both to my MPPT controller and not waste energy.


texts: Fender Telecaster outer body measurements

texts:
I appreciate this may not be the best forum to pose this question but...
I've been attempting to model a copy of a Fender Telecaster electric guitar in SketchUp. I've been mainly working from a PDF document which provides the measurements for the hardware routing and the neck pocket but provides nothing regarding the measurements and radii of the actual body shape.
I've had a good look around online but am struggling to find anything.


texts: How are blanking spades entered into gas pipelines?

texts:
I often see specifications for refurbishing works on gas pipelines calling for blanking spades, to separate the area worked on from the rest of the gas system. This is in addition to closing valves.

Googling showed me some pictures of how blanking spades look like, but I don't yet understand the process of installing them. The most straightforward way would be to mount them between flanges, after a section of pipe has been valved off and flushed. How are blanking spades actually used?


texts: Lens to "stretch" or enhance vertical resolution in a photo

texts:
I'm trying to measure water elevation as a function of distance in a water tank, viewed through the glass wall, as shown here:

The height variations that's of interest to me is very small. Would anyone know of a lens that can be placed in front of a camera to stretch the image vertically? This will help enhance the vertical resolution of the photo. Other suggestions are also welcome.


texts: Turbulent Boundary Layer Thickness as Velocity Increases

texts:
I'm attempting to find the highest free stream velocity over a flat plat before a sensor placed 'delta' away from it experiences turbulent flow. When I plot this in Matlab it seems that the turbulent boundary layer thickness decreases with velocity. This seems pretty counter intuitive to me, am I thinking of this in the wrong way? Or am I making a silly coding error?

These are the governing equations

$$\begin{align}
\delta &\approx \dfrac{0.37x}{Re_x^{1/5}} \\
Re_x &= \dfrac{\rho u_0x}{\mu}
\end{align}$$
Source

EDIT : Do not include any 'clear' or 'delete' code when posting, because many people do not want their workspace cleared.

Matlab Code

% clc
% clear all
rho = 1025;   % density of water
mu = 0.00108; % dynamic viscosity
x = 65e-3;    % distance from leading plate edge
U = linspace(0,10); % Free Stream Velocity
Re = (rho*U *x)/mu;
turb_lay = (0.382*x)./(Re).^0.2
lam_lay = (5*x)./(Re).^.5
plot(U,lam_lay,U,lam_lay2,U,turb_lay)
xlabel('Velocity (m/s)')
ylabel('Boundary Layer Height (m)')
legend('Laminar Boundary', 'Turbulent Boundary')


texts: Is learning VLSI design useful for a control/automation engineer?

texts: I've known of a few universities that include a class about VLSI design as a part of their control/automation engineering programs. I undestand VLSI design to be about creating integrated circuits with millions of logic gates. Is this actually ever done by control engineers in real life, and if so, in what sort of situations? Or is there any practical reason for taking a VLSI design course? I assumed microcontrollers, PLCs or PCs were used for practically all automation projects, and I can't really picture a situation in which a controls engineer would have to design a VLSI circuit him/herself, but I find the topic interesting and would gladly try to learn about it if it is actually useful.


texts: How do you determine equilibrium altitude of helium enclosure?

texts: How does one determine the equilibrium height/altitude of an enclosure of helium, given payload, weight of enclosure, and net lift?  What is the formula that will help calculate roughly at what altitude the enclosure will reach equilibrium with the surrounding atmosphere?


texts:
How small/compact can a pump or other mechanism be, that would allow compressing gas (or liquid) to pressures of excess of 10GPa, continuously?

Throughput may be minuscule, of order of milligrams per hour; even lower is acceptable. Also, for "size of the device" let us count all the necessary infrastructure: if it requires energy of a nuclear power plant to operate, it's not compact. Let's say we have some 30 watt of energy "for free"; anything above that goes out of our "compactness budget".

Input gas is pressurized to "reasonable" levels - order of 30KPa; if more pressure is required, the container goes into "compactness budget" with at least 20kg of the gas inside.

There's abundant heat sinking capacity, but any extra heating goes out of our "budget". Operating (ambient) temperature - choose anything between 40K and 400K as you like. It should have operational lifetime of at least a year, preferably ~10 years.

(clarifying: "continuous" - we can assume a small "buffer" container on the output side, emitting the pressurized gas at rate that is the average of the intake speed, so short "discontinuity" like piston motion is fully acceptable - simply keep the "buffer" above 10GPa with losses of order of assumed average input (1mg/hour, or less if required, but fairly constant).)


texts: Viscoelasticity and Hyperelastic model, history and difference

texts:
Actually, I see some papers use viscoelasticity or hyperelastic model for the same materials. It seems to me that those models were invented in different eras, and the hyperelastic is a newer model than viscoelasticity. Am I right?

What's the difference?

What is the best way to decide which model to use when we want to simulate a material?


texts: What liquid crystals are used most frequently in displays?

texts: Is there a specific chemical that is used frequently in the production of liquid crystal displays? During my internet research so far, it seems as if the specific chemical composition of the liquid crystal does not matter very much. This website gives a list of apparently commonly used LCs. Are there one or two chemicals that are used in practically all common LCDs?


texts: Is there fire suppression in some phone batteries, and if so, how does it work?

texts:
I recently saw a rugged smartphone, three or four years old, with a ~5000 mAh battery, suffer a major impact to its back. This wasn't a fall, it was a fast impact with a heavy object. Immediately there was this loud hissing sound, and clouds of what looked like white and very-light-brown smoke came out of every aperture in the sides of the phone. The "smoke" was not acrid, did not disturb my (quite sensitive) lungs, and smelled only like slightly peculiar burning, not even strongly plasticine. There were absolutely no flames visible at all, the phone was warm and not hot to the touch within 30 minutes, and although the back of the phone had meltage visible, much of it was intact.
To me the above looked a lot like some sort of fire suppression system I had never heard of, which perhaps released a whole lot of CO2 or perhaps something else, to prevent anything more dangerous from happening. Anyone know if this is true, and if so, how it works?


texts:
I am trying to design a heat source for use with testing the functionality of an infrared thermometer. I am happy with my circuit, I have a surface heated to a nice, constant 50°C (as constantly monitored by a thermocouple).

The surface is just an aluminium alloy, which I have sprayed with a matt black paint. Unfortunately, finding the exact emissivity of the surface is proving difficult. I am unsure whether to keep this as my surface, or find something else. The matt black paint is supposed to have an emissivity of 0.93-0.97, yet aluminium alloy has a very low emissivity.

A table can be found HERE which shows the emissivity of different surfaces.

Thermal conductivity of different materials can be found HERE.

The reason I chose aluminium was because it is easy to get hold of, it is not expensive and has good thermal conductivity. Because of its low emissivity though, I had to paint the surface in order to test the infrared thermometers.

I did a lot of research on the subject and there are so many places that specify using a black surface to get the best emissivity (as in closer to 1.0), yet there are some black surfaces which have a very poor emissivity as seen HERE. That document also shows some white surfaces as having good emissivity, and white is the furthest from black you can get!

There are other articles such as this one HERE that look at the effect of the smoothness of a surface, which I found interesting as some materials with smooth surfaces have a good emissivity, even if not black.

So my question is: What is more important when it comes to emissivity (getting closer to 1.0), colour or surface finish? Do different colours or surface finishes affect the wavelength of the thermal radiation? If so, why and how do these factors have an effect?


texts: Efficiency of a fully-engaged friction clutch

texts:
I'm wondering whether there are any notable losses in a typical automobile clutch when fully engaged.

Only losses that come to mind:

material twisting with torque changes
slipping due to imperfect friction

Are these even significant and are there any more? What is a typical energy efficiency of a fully-engaged clutch?


texts: What material for DLP/SLA 3D printer bottom window?

texts:
What material is used for the bottom window of 3D printer that the cured resin layer does not stick to and that it is transparent to the uv (365 nm) light?
And what material is used for the top plate where the model should stick.


texts: How do you calculate the work of a Carnot Heat Engine using entropy?

texts:
The problem given is as follows:

A Carnot cycle has a heat engine fluid efficiency of 30%. The heat transfer to the fluid in the boiler Qh happens at 270 centigrade. At 270 centigrade, the entropy of saturated vapour and liquid water are 6.001KJ/(kgK) and 3.067KJ/(kgK), respectively. Determine the net work produced by the Carnot engine.

I am pretty sure to solve it you need to use the Carnot efficiency equation so 0.30 = W / Qh but I am not too sure how to get Qh from the information provided.  Please explain or put me on the right track if you can!

Thank you in advance!


texts: What is friction head loss through a pipe mean?

texts: If water goes through a pipe and ends up at higher elevation, what does it mean for the water to have friction head loss?


texts: Is the strain in the pre tensioned steel after cutting of tendons compressive or tensile in nature for pre-stressed concrete?

texts: When we cut the tendons of the pre-tensioned steel, the steel undergoes compression, therefore the steel should have compressive strain. But when we calculate the residual strain, the strain in steel and the compressive strains in concrete due to shrinkage/creep are considered opposite in nature.Why?


texts: I recently was at the Naval Air Museum in Pensacola Florida.  There are lots of models of aircraft carriers, including the latest class (Gerald Ford class as I recall).  This latest class has electromagnetic rails instead of steam catapults to launch the jets.  However it still has arresting cables. So I got to thinking that with the sophisticated servo systems we have today, it seems possible to have a servo system on rails on the landing strip that follows the jet as it lands and automatically grabs the tail hook and has a controlled deceleration. On the Science channel show "Outrageous Acts of Science"  there was an amateur inventor who created a servo system to follow his dart throws to give him a bullseye every time. A servo system would improve the chances of a successful landing. I read astronaut Scott Kelly's autobiography and he said one time as a Navy pilot in bad weather at night he had to try dozens of times to land because his tail hook would not grab a cable. Also, the servo approach would eliminate the scrapping of steel cables.  From what I have read, steel cables get replaced fairly frequently due to wear.  Am I missing a fundamental flaw for this idea?


texts: How to measure number of strokes in a small space

texts:
I have read about a device called drumometer, which measures the number of strokes of hitting drum stick.

I think this is almost the same, but instead, I would like to measure the number of strokes/impacts made when I shake a very small object inside a very small container.

To give an example, imagine a cube where one face is removed, hence making a hole. Then, I put the end (say X) of a stick inside that cube and hold the other end  (say Y) from outside. I then start vibrating (I mean like stirring movement) the stick so that the X end hits all faces of the cube. Then I want to measure how many times the X end of that stick hits not necessarily all faces but at least one face (since I will shake it randomly anyway).

The cube could be as small as 1 cm^3 (it might not even be a cube, just something with a hole that small where a stick can be put inside and shook from outside), and the stick is just long enough for me to hold it and small enough to get through the hole.

Thus, in relation with that drumometer, it kinda looks like an even smaller "drumometer" is needed. What do you think?

I don't have good background in measurement, only have some elementary freshmen undergraduate physics background instead. This is gonna be very helpful in my experiment once I know how to measure the number of strokes.
*feel free to edit my tags if not related


texts: Is it possible to build an air compressor with no moving parts?

texts:
Is it physically possible to build an air compressor with no moving parts? I'm envisioning a thermodynamic cycle capable of compressing air with no moving parts and operated in a stationary way. There is no limitation on the compression factor, provided it is significantly greater than one (1.1, 2, 100...) but the design must be realizable.

Zero moving parts is a big constraint. You can interpret it as the absence of pistons, crankshafts and other complex mechanisms that will wear out over time. If some moving parts are needed, what are the minimum required moving parts, with the lowest maintenance requirements?