texts: Can a bridge's towers be used as wind turbines?

texts:
I come from a fairly remote island where we need a 150 min ferry ride to reach the mainland.

While the island has few resources that would encourage a government to investigate the possibility of a large bridge such as the Denmark-Sweden one, there is one resource that we have in abundance - wind.

Would it be possible to combine a mega-bridge with an offshore wind-farm? With turbines in the bridge towers. Possibly also wave-generators underneath? Or is this just fantasy?

If this is a realistic possibility, then maybe, just maybe, we could at least get someone to consider this rather than laugh-out any suggestion of connecting us to the mainland.

The shortest distance is 23-24 km. An alternative would be a total distance of 29Km, but hitting a small island after about 20Km.

I suspect it's just fantasy, but it'd be good to know.


texts: Is there a 5% range CO sensor with a response rate higher than 1Hz?

texts:
I'm building a portable emission analyser which measures emissions from a tailpipe, to aid in troubleshooting and tuning an engine. For this, I need a $\text{CO}_{2}$ , a $\text{CO}$, and an $\text{O}_{2}$ sensor.

While these sensors are widely available, I am in search for the type of sensor that has the lowest response time, while being able to measure in the range of 5-10% (gas dilution is not an option for my application). I already found a $\text{CO}_{2}$  and an $\text{O}_{2}$ sensor that are able to do so, but I can't find a $\text{CO}$ sensor with these capabilities.

Those all seem to have a response-time of around 30 seconds, and most are only able to measure up to around 2000ppm. I need a sensor as fast as 1 second or faster and able to measure at least 5% $\text{CO}$.

So, Is there a $\text{CO}$ sensor on the market that is able to measure in the range of 5%, while responding within 1 second?


texts: What is the required torque to rotate a 50mm aluminimum plate of weight 100g?

texts:
I have a aluminium plate of radius 50mm and thickness 4mm. How much torque is needed to rotate it?

In case additional information is required :

I have a RS 380 motor, but I guess torque required is irrespective of motor.
How do you calculate torque of other round plate sizes? Like 60mm or 55mm.

What is approximatively the exact torque for 50mm?

[![motor][2]][2]


texts: Question regarding calculation of angular velocity connected to coordinate transformation

texts:
So i need to calculate the angular velocity of the dark disk, $w^*_3$.
In the master solution they state it is : $w^*_3 = w_3 + \overline{w_3}$
with :

$w_3 = \frac{|\dot{r}|}{4a}$

$|\dot{r}| = v_a + \overline{w_3}\cdot a$

$|\dot{r}| = v_b - \overline{w_3}\cdot 2a$

$ \Rightarrow|\dot{r}| = 2a\cdot (w_S+w_R)$

$\overline{w_3} = \frac{1}{a}(|r|-v_1)=\frac{1}{2a}(v_b-|r|)=\frac{1}{3a}(v_b-v_a)$

$ \Rightarrow \overline{w_3} = 2w_r-w_s$

$ \Rightarrow w_3^* = \frac{5}{2}w_r-\frac{1}{2}w_s$

So, the question I have is that if I understood correctly,  $w^*_3$ is the angular velocity of the disk itself (in its coordinate system) if you look at it from the disks center. So shouldn't be $\overline{w_3}$ already be my $w^*_3$? Because it is the angular velocity with which my disk is actually spinning?(in it's coordinate system)


texts: Why is the bending moment equation for a uniformly distributed load (w) across a length x on a structure given by w(x)(x/2)?

texts:
So for any structure, simply supported beam, three hinge frame, cantilever etc. where there is a uniformly distributed load. For example, for a simply supported beam with uniform load of w along the length of x. Why is the bending moment equation w(x)(x/2)? I understand that the magnitude of the force is given by w(x), but is the reason for the (x/2) is because the magnitude acts halfway through the load?

Now I know that shear force and bending moment are related, with the shear force being the derivative of the bending moment, so I can just integrate the shear force equation to get w(x)(x/2), but I want to confirm through fundamentals as to why the equation is as it is.

Thanks.


texts: Why isn't it possible to build a car moved by wind power?

texts: So, first of all, I am a High School student and I wanted you to explain me something (in a more "concrete" way, if you know what I mean): I had an idea the other day to make a car with a wind turbine attached to it, so that the more the car runs, the more wind gets into the turbine and more energy is generated, wich powers the car. I know this is some kind of "moto perpetuo" so it wouldn't work anyway, so I asked my physics teacher about it and he said It cannot work because of the first law of thermodynamics, and he asked me a way to calculate the energy generated by the turbine. I just wanted a concrete way of showing it doesn't work, like, using data from wind turbines that exist, cars that exist and so on. But how do I calculate the energy generated?


texts: Is there any device that can capture a picture into 3D model?

texts:
I am currently wondering is there any way or device that can transform a picture into 3D model automatically?

or a machine learning thing to learn from picture (2D) into 3D model?


texts: Discrete measurement - continuous observer design

texts: I have to design a controller for the above system where the two pulse generators (red blocks ) are synchronized (measurements are only available at discrete points). However, my understanding is that the controller and measurements should have faster dynamics than the system in order for it to have good performance, but in my system I cannot increase the measurement sampling alone since its synchronized with the fixed pulse generator (input to system). Can I use an observer to estimate the values between two sampling points of measurements hence provide continuous input to the controller? In other words, can I use both real measurements and estimated ones for the same variable? How can I design the observer in this case? Is there any other possible solution?


texts: How to straighten an aluminium extrusion?

texts:
The extrusion shape is a simple square tube. If I set it down on a perfectly flat surface with its curvature upwards, the middle raises up by around 5mm over the length of 1m.

So far I tried to just put a weight on it while its laying on a glass pane (my perfectly flat surface) but after 24h that did just about nothing.. maybe if I left it there for a year? I'm not that patient.

Are there any other options for me to straighten it without specialized tools? I could heat it up with a torch if that helps..?


texts: How to adjust magnification when mounting camera on microscope

texts:
I apologize in advance if this is the wrong site for this question.  If this is the wrong site, would some kind soul point me towards the correct site?

I have a couple of Vision Engineering TS4 microscopes in my lab (both purchased used from eBay).  One came with a camera attachment with a completely unknown camera mounted.  No documentation, no cables, no power supply.  Luckily, the microscope has a standard "C-mount" attach point.

The TS4 microscope has an optical zoom range from x6 to x40.  This is a great range when working with surface-mount components on circuit boards.  These microscopes project the image onto a view screen rather than forcing the user to sit hunched over a pair of eyepieces.  Current listing on eBay: Vision Engineering TS4 Stereo Dynascope

I removed the existing camera and instead installed a 2.0 MP camera, also purchased from eBay.  Wireless Control 1080P HDMI HD Industrial Lab C-mount 2.0MP Microscope Camera US.  I've used these cameras previously when modifying simple lens-based microscopes with great success.

The problem that I'm having is that the image on the monitor driven by the camera has far too much magnification as compared to the optical screen mounted on the microscope.  So much so that the resulting image simply can't get small enough.

What I know about optics and lenses might fit on the head of a very small pin.  I don't have any idea how or what to change to bring the image size seen by the camera down to something similar to what is displayed on the native view screen.

Guidance appreciated.


texts: Can a cellulose sponge be used as an actuator to shut off flow of water temporarily?

texts:
In non-recirculating hydroponic systems, we want to fill containers with nutrient rich water  let's say up to an inch, let the plants take up the water , give the plants some air time for a few hours, and then restart a filling cycle.

I was thinking a sponge could be used as a sensor and actuator.  The sponge valve would be dry and open.  As the water reached an inch the sponge would get wet and expand in a cylinder and push something that blocks the flow of water in a 4mm irrigation tube.  As the water gets absorbed by the plants, the sponge would dry out and the pressure lowers and eventually it becomes low enough that the water starts flowing again, for a new cycle.

Is a cellulose sponge realistic for this. In particular would the wetting and drying state of the sponge be sufficiently stable or would it rapidly deteriorate?  Is there another material that would be better suited?

Thanks


texts: Mechanism to transfer power between a button on a panel and a button several inches distant

texts:
I have an application where a single board computer similar to a Raspberry Pi is rigidly mounted inside a box.  There is a power button on the board that I want to press "remotely" by pressing a button on the outside of the box.
Our previous solution for this problem is failing due to the holes in the boxes not always aligning 100% according to spec.  I was wondering whether there might be something like a remote shutter release cable (allowing flexibility in where the button on the box is mounted) that could be mounted on the wall of the box and connected to the button on the board in such a way that pressing the outside button presses the inside button.
A stiff, extended plunger seems like it would be prone to alignment difficulty.
If this is an x/y problem, I'm also open to other suggestions.


texts: How do i figure out what the wing area/sqft needs to be for a functioning wing-flapping ornithopter? Lets say for example there is 500# of force moving the wings up and down, and the wings and passenger combined weighs 250#. What is the minimum needed wingspan/area to climb through the air?


texts: What is the term for diagonal bars which are making rectangular frame more rigid?

texts:
For example in yellow:

if all bars were rectangular, the entige frame would tend to skew. To prevent this, these diagonal bars are mounted.
What is the term for them?


texts: During truss fabrication, the truss member are usually connected by welding does behave like fixed joints not pin joint so how will that behave like truss without pin connection?


texts: Flex and Static Bend Radius of a Cable: Which one should be larger?

texts:
I am looking for a cable to be placed in a drag chain that is moved multiple times per minute. Therefore, the cable needs to have a flex lifetime of over 1M times. Since the space is also tight, the bend radius is of interest. However the datasheet mentions:

  Flexing bending radius: $5\phi$
  Static bending radius: $10\phi$

where $\phi$ is the diameter of the cable.

Shouldn't the flexing bending radius be larger than the static bending radius? I would expect that a cable flexing all the time would have more restrictions on the bending radius than one that never moves.


texts: What are the calculations required to design transmission system for an Electric Kart ( i.e Go Kart)?

texts:
There is a national level competition Ecokart (Electric kart design & manufacturing) has been held every year in Delhi, India. there are some rules for making the kart which are specified in the rule book.

ECO KART SERIES


texts: Why don't we just build a giant wind turbine?

texts:
The power generated by a wind turbine is given by:

$$\mathrm{Power} = \frac{1}{2}C\rho AV^3$$

Where:

$\rho = \text{Air density}$
$C = \text{Coefficient of performance}$
$A = \text{Frontal area}$
$V = \text{Velocity of the wind}$

In other words, the power is proportional to the square of the length of the blades and the cube of the velocity of the wind. As we know, the velocities of winds are high at high altitudes. So instead of building many smaller wind turbines, why can't we just build a giant wind turbine that is, say, 1000 m tall? That may be an engineering challenge at first, but won't that be more economical in the end? After all, the Burj Khalifa in Dubai has been 828 m tall.

Why can't we build three instead of one pillars to support such a structure? Why can't we build one at the sea?

  The Vestas V164 has a rated capacity of 8.0 MW, has an overall height
  of 220 m (722 ft), a diameter of 164 m (538 ft), is for offshore use,
  and is the world's largest-capacity wind turbine since its
  introduction in 2014.


texts: Find additional heating and cooling needed by having a specific wall

texts:
I need some help to a design problem at my university. The design work is about designing a prefabricated wall panel. I calculated the U Value of the external wall and it is 0.0136 W/m2K. The thickness of the wall is 0.353 m and total area equal to 3 m x 6 m = 18 m2 (assumed no openings).

What I need to do now is to estimate how much energy do I need to maintain the inside temperature. I know that the maximum summer outside temperature is 30°C and the minimum in winter -20°C. How can I calculate the additional cooling and heating I need by having this wall?

It is basically a whole design project with the purpose of creating a prefabricated panel that can meet the needs of a specific country that was given. It was entirely flexible, nothing was given, just a city to make it fit there!  I divided my work as I thought it would be better and one part of it was the thermal properties.I tried to choose materials that can meet a rigorous U value of 0.13 and now I would like to show how much better it is in terms of operational energy (cooling and heating). After a research I did I found that probably I could calculate the heat loss and heat gain (the simplest I found with the data I have is by this Ht = A U (ti - to) and then according to my results propose a heating system or cooling etc. But I am not sure if this is the right way to do it.. this is why I asked some help.


texts:
Our question is what size and alloy aluminum tube can be used to replace steel tube in a vertical load application. Our current spec is 1.5” OD STD steel tubing 7 feet long. We will use 6 poles attached to steel footings to support vertical stacking of containers that each weigh 1500 lbs. the bottom container will see 4500 lbs. from vertical stacking.  the containers are 45” wide and 87” long. There is one pole in each corner and 2 in the center on each side. Six tubes of steel 1.5” x 7’ steel is to heavy. Can we use aluminum tube round hex or square and what alloy ?

Thank you


texts: Does plastic expand at colder temperatures?

texts: After placing a dry solid block of nonporous plastic material in the freezer for a while, I was surprised to find out when I retrieved it that it had expanded globally by a few inches. Which type of plastic must this be and do plastics expand at colder temperatures?


texts: Name of protocol used to communicate with Fuelling Station Dispensors

texts:
I am trying to figure out the actual (Range of ) communication protocols used to communicate with Fuel Dispensers at fuel retail outlets.

I see them write 2-wire protocol which is not specific as there are a bunch of communication protocols that communicate over 2 wires. I am suspecting it to be CAN but not sure.

I will be glad if anyone can assist with even further information on communication with fuel station devices


texts: LTE channel characterization from Time Domain waveform

texts:
I am currently interested into the diverse Downlink LTE channels broadcasted over air after some (QPSK, 16QAM...) modulation. More precisely their waveform.

I would like to know if, with a good filtering of the noise, we could characterize the LTE signal in time domain, so we could correlate a waveform with a specific downlink channel.

In another words: is the LTE signal waveform dependant from the data it is carrying or the antenna it comes from? And if yes, which part of the signal in time domain?

I will distinguish two cases here, first the channels carrying information (sequence of bits), and the Reference Signal (RS) which exists only at PHY layer.

We know that transport channel like PBCH are periodic in time (i.e occupying 1st to 4th symbol of the #1 slot in each RF, repeating the same MIB during 4 RF -> %40ms). This is the same thing for the PDCCH controlling channel, with the specificity that the number of allocated symbols can vary from 1 up to 4 symbols (which i guess makes the potential correlation harder).
I find these channels potentially interesting because of the redundant data they will carry over time (at least i think it's redundant for PBCH - information about the antenna configuration for PBCH, less sure about the PDCCH). Unlikely to the PDSCH channel which carries variable data over time in its payload, and therefore that I'm judging more difficult to characterize (maybe i'm wrong?).
RS is also redundant in time. It's used to help UE figuring out the DL power. Thought, I don't know what we can expect of its waveform.

I don't forget SSCH and PSCH, broadcasted every 5 Sub-Frames. Maybe they are also characterizable?

Should it be relevant, I don't have the MathWorks® LTE System Toolbox, even though I'm pretty sure it could be helpful.


texts:
Is it possible to constraint a line on another line by way of a perpendicular constraint? This also includes center points on other objects.
What I am trying to accomplish is to move a rectangular array to a set distance from another object (all in sketch) at the center points. So basically, I need to move this array to a set location from the corner or another object (inside the object which is a rectangle)
I have been trying to get this to work in different ways for the past 3 hours with no luck or even trying to find additional help on the Autocad inventor forums.
Please keep in mind, I am VERY new to Inventor (started with Fusion and, YUP, there are a ton of differences). Are there even guidelines? I will not be able to use the grid as my measurements are not a whole number and precision is 3 places.
Hopefully, I have explained what I am trying to accomplish, If you need any further information to assist me in answering this question, please do not hesitate to ask. :)
Attached is a sample of what I am dealing with. the column of objects HAS to be x, y from the top and right sides of the outer rectangle. The additional lines outside of the rectangle in the upper right are directional lines for creating arrays only.

Thanks in advance.


texts: What is this "johnson controls" device on the wall in airport?

texts: I was passing column in waiting area of Pearson airport when my sweater cought some kind of device on the wall. Device was without cover and looks like old thermostat. When my sweater caught it, it fell off and started to blow air (I think). Maybe someone knows what is this device and why it blows compressed air? Yes, I informed airport employee.


texts: Some questions about the specific speed (Ns) of hydro turbines

texts:
So we all know the basics behind specific speed Ns of hydro-turbines.
$$N_s = RPM \cdot  \frac{ \sqrt{(P)} }{ H^{1.25}}$$
where P is the power output and H is the head. The theory is that once you know the Ns for that model of turbine, you are able to find out either the RPM, power output or head if you are given absolute values for 2 of the 3 mentioned variables.
Let's say I have a turbine with a known Ns. If my head increases but my power output remains constant due to say, reduced flow, then the RPM will increase since Ns is fixed. So far, so good.
However, if my head remains constant but my power output increases due to increased flow, then my RPM must decrease since Ns is fixed. But if we think about it that doesn't make sense...the RPM must be increased for a larger power output, no? Is there something wrong with my understanding of Ns?


texts: Good estimates for torque generated while turning a dial

texts:
I'm trying to design a little device which is hand-driven and which involves turning a bevel gear pair. I want a small gear pair but I don't want it to be weak. The forces involved will be small (it's attached to a pinion along which will slide a rack < 1 kg), but of course I still need to check the safety factors involved. So here's my question:
Since it's hand-driven, what torque value can I enter for the strength-calculations? I search for "typical torque values human hand" (and variations on this), but I keep receiving maximum human turning strengths which are definitely not going to turn up with this device. The dial has a ~3 cm diameter.


texts: Does a diesel-like (ignition by compression) engine running on gaseous fuel exist?

texts:
I think, it could lead to, for example, very environment friendly and very efficient urban traffic.

But I also think, it required very precise part construction.

Do such things exist? At least in plan?

Extension: Clarification added, waiting for acceptable answer again.

Extension #2: Despite the "common sense", diesel engines aren't so simple. Although there is no spark, there is a part which injects the fuel in exactly the perfect moment into the piston. This happens with around 2000atm pressure. Maybe this would be hard in case of gases.


texts: Is it possible to design solid slabs on ETABS 2016?

texts: My graduation project involves designing several buildings with flat and solid slabs. I already know that ETABS can design flat slabs but is it possible to design solid slabs?


texts: Number of Holes punched through a Plate of SAE 1010 Steel

texts:
Reviewing for a National Board Exam:

  How many 5/16 inch holes can be punched in one motion in a steel plate
  made of SAE 1010 Steel 7/16 inch thick using a force of 55 tons. The
  ultimate strength for shear is 50 ksi and use 2 Factor of Safety

Answer is 5.

This is a common strength of materials question given among problem sets in engineering. Here is my attempt:

$${ S_{plate} = \frac{F}{N\times d \times t} }$$

$${ 50ksi = \frac{ 55tons \times\frac{2204.622lb_f}{1ton} }{N \times \frac{5}{16}in \times \frac{7}{16}in} }$$

I get N = 17...

I think what I'm getting wrong is the conversion of tons; I've tried UK Tons, US Tons but nothing. Is there a correct conversion factor?


texts: What machinery should I invest in for tapping and threading?

texts:
I've found myself tapping and threading a lot lately, and doing so with hand taps and dies.  What would be the next step up from using a drill-press to cut holes for tapping, and a lathe for turning parts to diameter for threading?

What are options for making this easier and more precise short of a 6-figure screw or CNC machine?


texts: How does this mechanical heat click work?

texts:
I own this vaporizer: (product link)

It has no electrical parts. To use it, you take off the cap at the left, put some "herbs" in it to smoke (vaporize), and put the cap back on. Then you heat the cap with a torch lighter until it says click. The click indicates that the cap (made of stainless steel) is at the right temperature. Then you can inhale from the right part and hot air with vaporized herbs will enter your body. It will click again when it has cooled down. (video)

How does this click work? Can I make this myself with a CNC machine?

The click system is at the end of the cap.


texts: Some cell phone cases have a waterproof rating of IP-68, often specifying that they can tolerate immersion to 6 feet for 30 minutes or 3 feet for 60 minutes.  My understanding, however, is that a good seal (like an o-ring) would fail near a certain water pressure without much time dependence.  So, why the strange time dependence?  This makes me wonder about diffusion of water across a poor seal being a factor, but I am guessing instead that these numbers are simply conservative times used in final manufacturer QC checks.  Anyway, is there a theoretical predictive model to determine the expected "waterproof time vs depth" scaling?


texts: Advantages/Disadvantages of two-bladed windmill?

texts:
The vast majority of wind turbines I have ever seen feature 3 blades, as shown here:

Recently while driving through western new York state, however, I passed by several turbines featuring only two blades, as shown here:

What advantages and disadvantages would a 2-bladed wind turbine have over 3-bladed versions?


texts: Does an electric vehicle going downhill recover energy?

texts: I have to model the behavior of an electric car. For this, I use these equations and I can observe by "playing" with parameters that, when going downhill at constant speed, the car has a negative consumption (i.e. recovers energy). I was wondering if this is realistic?


texts:
I am calculating the transmit power for $K$ single antenna IoT devices in an Indoor scenario. The receiver has 64 antennas. I am trying to minimize the transmit sum-power, i.e., $\sum_k p_k$, where $p_k$ is the transmit power of $k$-th IoT device. The noise power is -168dBm/Hz. The BW is 180kHz and the transmit frequency is 2.4GHz. I have a minimum requirement for the SNR.

Upon solving I am getting a transmit power in range of -60 dBm to -70dBm. Is the transmit power feasible considering the noise is too less and the path loss is minimal considering a room size of 10m, i.e, the max distance between transmitter and receiver is 10m?


texts: Is sitting on a double-decker bus's upper deck more hazardous than sitting on its lower deck?

texts:
Many people online allege feeling more 'wobbly' or 'unstable' while seated on the upper deck, than on the lower, and that in an accident, sitters on upper floors are more likely to be ejected out through the windshield even if they're wearing seat belts. Are these allegations true?

Now I no longer sit in the front top seats,apparently and not surprisingly the most dangerous seating position in a double decker bus crash.

Quora distinguishes the physics of the upper deck from lower deck.
Accordingly, the upper deck undergoes more lateral movement and so people standing upstairs are more likely to be thrown sideways.
The upper deck of bus,in comparison to lower, is high. Due to this fact the torque produced in upper deck is larger than the lower one. One standing in upper deck frequently experiences great push and pulls during acceleration and breaking. One can get injured. So, in fact travelling in upper deck of the bus is dangerous.
Many bus operators do not permit standing on the top deck because standing raises the centre of gravity and the force is applied further from the fulcrum.


texts: Instrumented Bolt - Conversion of measure strain/stress to clamping force

texts:
As part of some experimentation on a bolted joint, I have used an instrumented bolt with a number of strain gauges.

The testing has produced results of strain with respect to time. By using the Elastic Modulus of the bolt I can easily convert this into mean stress in the bolt. My question is how this relates to clamping force in the joint.

Is it as simple as averaging this stress over the loading area (i.e. bolt head and nut clamping surfaces) to attain a clamping load?

Thanks


texts: Can a water pressure switch be used as a low-water cutoff means for a steam boiler?

texts:
Steam boilers obviously need to be protected from the catastrophe of running out of water -- you then either get a meltdown if the boiler is fired unwatered for an extended period of time or a boiler explosion if the water returns before then, neither of which are good.  Hence, automatic low water cutoffs are required on steam (and hydronic, but that's beyond the scope of this question) boilers in all modern boiler codes.

Current low water cutoff technology consists of two types of cutoffs: probe and float.  Floats have the advantage of not requiring an external electrical power source to work, but can get hung up due to deposits (scale), causing them to stop working.  Probes lack moving mechanical parts, but require external electrical power to work, as they use the conductivity of the water as part of the switching circuit, and can also be fouled by boiler scale.

However, there are other properties we can measure to determine how much water's in the boiler -- one of them being the static head (pressure) of the boiler contents.  This can be done either as a partial head measurement, measuring the pressure of the water above the minimum waterline with respect to steam pressure and cutting out at 0 differential, or as a total head measurement, measuring the static pressure of all the boiler water with respect to the boiler steam pressure and cutting out at a differential equal to the static head of the water at the minimum waterline.  In both cases, the pressure switch would have a trapped steam line piped to it as well as the connection to the boiler water volume, and it would be wired as is typical for low-water cutoffs, opening the fuel control circuit when it trips.

How well would such a cutoff scheme work at protecting a boiler?  Would a pressure-switch based safety be more or less vulnerable to failing hazardously (due to fouling or mechanical malfunction) than the existing float-type or probe-type cutoffs?  Are there other flaws in this scheme I should be aware of?


texts:
I was asked to solve the following problem on my test:

A tank is filled up to height H with a liquid having specific gravity 1.6. The rest of the tank is filled with air. A pressure gauge attached on top of the tank measures the pressure to be 11.5 m of water and another pressure gauge attached at the bottom of the tank reads 16.8 m of water. Now, what is the value of H?

I don't know where to start. I have solved U tube manometer problems but never faced something like this one. I don't have a single clue. Even the total height of the tank is also not given. Is it really possible to solve the problem with only single data (the SG of the liquid) ? What do you think?


texts: Safe temperature thresholds for #2 HDPE and #5 PP plastic

texts:
It would be convenient to use a temperature adjustable heat plate (element)/mug warmer for the massive amount of blender bottles accumulated over the years.
What are safe thresholds to safely warm the contents in seemingly, relatively safe plastic containers, BPA- and Phthalate-free, without leaching chemicals into the contents. Is plastic even a safe or effective, heat conductor long term?
It seems the type pf plastic they use is made with High-density polyethylene (HDPE) & Polypropylene (PP). The melting point of HDPE and PP is respectively 267.44°F and 340°F. High-density polyethylene is a relatively poor heat conductor with a value of .42-.51.
Porcelain and better yet Stainless steel have much higher thermal conductivity values, 1.40-2.27 and 16.3-24 respectively.
Not sure if this is a more suitable question for the other stack sites (i.e. Coffee, Seasoned Advice or Physics), it seems most aligned with a chemical/materials engineer.


texts:
I use Labcenter Proteus Circuit simulation - you create circuit design, then apply current and see simulation in action - for example leds are blinking, or motor is rotating. If there is microcontroller - say AVR, you just load compiled hex file for it and see simulation live - again, if it was programmed to blink led, and there is one on pin, it will blink, or you can simulate button pressing and see what happens, etc.

Now, I know SolidWorks have SolidWorks Electric, SolidWorks Simulation, SolidWorks CircuitWorks (are those all?), is there any way to have such functionality in it? I mean, if I have added motor to project, then created circuit with avr microcontroller in SolidWorks electrical, is there a way to somehow combine those two, set .hex file for avr and run simulation to see how motor moves? Or Any alternative, how do engineers do such things?


texts: Cheapest way to measure gas flow (mass)?

texts:
I understand that there are quite a few fairly simple and cheap methods to measure the flow of gas in terms of volume, allowing you to get a flow rate in terms of litres per minute for example.

However, what would be the cheapest method to measure the mass of gas flowing along a pipe, so that differences in pressure etc. don't impact the results taken?


texts: How would you calculate the eigenfrequency of such a cantilever?


texts: Can ultrasonic sound pass through solid medium?

texts: For my electronic project, I have been searching the internet for a non invasive flow meter that does not require disassembly. I have found an ultrasonic measurement technique that use the clamp on method (just fitting on to the pipe) for flow measurement of liquid though a pipe. But when I search through internet I found that ultrasound can behave like light as it is reflected back from a solid surface. Is this true? Or it is like ordinary sound that can pass through a medium?


texts: silicone injection molding - making a flexible ring

texts:
I am working with silicone injection molding as a hobby and I am wanting to make a ring.

I have tried with 100% silicone and the results are a clear ring that is not quite the consistency I want. I would like to experiment with making it more or less elastic if possible, as well as different swirled colors.

How can I change the elasticity of a silicone ring and how can I introduce swirling colors into it as well?

I searched around for other existing things, and this silicone ring is close to what I want to make.

https://groovelife.co/products/silicone_ring_breathable_groove?variant=13528608580&gclid=CjwKEAiAkajDBRCRq8Czmdj-yFgSJADikZggxMT5d91MuDELqOKU6eFGvRvJWkAbHWH1_Gxu9of58RoC9oDw_wcB


texts: What tension/compression loads does aircraft wing skin experience?

texts:
Ok so thinking about aircraft like the 787, which have some quite drastic wing flex (upper image), I was wondering what the loads are that are placed on the skin on the the upper and lower surfaces of the wing (not considering torsion from control surfaces etc...) - considering tension and compression only.
So naturally, one would assume that the upper skin panels experiences compression, and the lower skin panels, tension due to the different radii of rotation they both follow. However, does, for example the lower surface of the upper wing skin experience tension, not compression, due to the material thickness (I'm thinking about the principle in the lower image).


texts: Type of electronic lock for a garage door?

texts:
I would like a lock for a garage door (roll up style). I would like the lock to be something I can control electronically, and also I would like it to retain it's state when the power is removed.

The power requirement seems to rule out any type of electromagnetic lock, and I considered a solenoid, but I'm not sure if I can get one that stays in the current position when the power is removed.

I think there are two types that will work - one with a latch on a solenoid (https://www.adafruit.com/product/1512) or possibly a small linear actuator that could be extended through a plate to lock the door. Are there any other options I'm overlooking?


texts:
Steam at 1 MPa, 300°C flows through a 30 cm diameter pipe with an average velocity of 10 m/s. The
mass flow rate of this steam is:

A) 0.731 kg/s B) 2.74 kg/s
C) 3.18 kg/s D) 3.78 kg/s

Can anyone help me out please?

I thought I had to use m=PVA
P=1000 pa
V=0.2579 (property table)
A= pi*15^2
So m=1000*0.2579*((pi*15^2)/1000)= 183 kg/s which is not correct.


texts: compute the maximum resisting torque that can be overcome by the system at the shaft axis

texts: A 2Nm motor M is used to drive the system through a gear drive and a chain drive. the overall reduction ratio is to be between 16:1 and 18:1, and at an output speed of 6rpm.


texts:
Let me state I was once an Engineering student but am now a professional software engineer working on a side project that involves something similar to the question below.

I have a box hanging from a beam and the box weighs 200 pounds. The beam is parallel to the ground and it can safely support the weight of the box.

My question is does the ability of the beam to safely support the weight of the box change as the box moves from one end of the beam to the other. Does the speed at which the box moves affect the ability of the beam to support the weight? (for example, 1 mph vs. 300 mph).

Basically if the beam supports the weight of the box when it's not moving, is it safe to assume it will continue to support the weight when it's zooming from one end of the beam to the other?


texts:
Note: This question originally appeared on the Physics site (see here) and was closed for being off-topic. Whoops!
If ships at sea can tack in a zigzaggy pattern by converting backwards force from the wind (using the sail) into sideways force, then that sideways force into forward force by bracing against the (stationary) water via the rudder...

source: another stackexchange question
...couldn't the same principle be true with the roles of the wind and water reversed --- as in a river with stationary air above it? That is, can a riverboat tack upriver as long as the air above the river is not moving? Are there any rivers with the right conditions to make this happen? If the air won't work, could zigzagging cables stretched across the river do it?


texts: Expressing Derivative of Cable Tension Component

texts:
I am looking at Hibbeler's section on a `Cable Subjected to a Distributed Load' in Engineering Mechanics - Statics, Ed13, as shown in the attached images.

I am getting stuck deriving equation (7-7). I derive the horizontal equilibrium equation just fine;

$$
|\vec{T} + \vec{\Delta T}| \cdot \cos(\theta + \Delta \theta) - |\vec{T}|\cdot \cos(\theta) = 0
$$

I rearrange to describe horizontal tension component as a function of $\Delta x$ (given $\Delta T$ and $\Delta \theta$ are ultimately functions of $\Delta x$);

$$
|\vec{T}|\cdot \cos(\theta) = |\vec{T} + \vec{\Delta T}|\cdot \cos(\theta + \Delta \theta)
$$

Then I express the differential;

$$
\frac{\Delta(|\vec{T}|\cdot \cos(\theta))}{\Delta x}
=
\frac{|\vec{T} + \vec{\Delta T}|\cdot \cos(\theta + \Delta \theta)}{\Delta x}
$$

Then when I go to express the derivative, I come up with a limit which does not exist.

$$
\frac{d(|\vec{T}|\cdot \cos(\theta))}{dx}
=
\lim_{\Delta x \to 0}\frac{|\vec{T} + \vec{\Delta T}|\cdot \cos(\theta + \Delta \theta)}{\Delta x}
$$

Further to this, it is not obvious to me how the resultant force from the distributed load acting over $\Delta x$ can be defined as $w(x)\Delta x$ (in line 8) as the author suggests. I feel it should be defined as;

$$
\Delta F = \int_{x}^{x+\Delta x}w(x)dx
$$

becuase the loading intensity function is not constant. Any pointers as to where my errors are? Appreciate any advice offered. Thanks.


texts: Why GPS receivers are more sensitive than GSM or WiFi receivers?

texts:
GPS receivers are able to operate at signal level of -150 dbm or less, but mobile phones need far more than -115 dbm level signal. Why GPS receivers are so much more sensitive than GSM or WiFi receivers? See these receivers

GNSS L86
Wi-Fi FC10


texts: Is it possible to make a tunable coherent light filter with 1.8 nanometer bandwidth for visible light?

texts:
On January 1991, the esteemed Swedish professor of optics filed a patent titled "Coherence filter", that blocks coherent light regardless of laser light wavelength using destructive interference and lets through ordinary incoherent light. Sometime in 1999, several University College of London professors published "Detection of coherent light in an incoherent background"which uses both optical and digital signal processing with an interferometer to measure the self-coherence function of the incident radiation to produce an interferogram which is subsequently narrow band filtered to yield a sinc envelope.

I was wondering if it is possible to make a tunable coherence filter with 1.8 nanometer bandwidth for visible light which lets through ordinary incoherent light with less than 5db loss. The reason I chose a bandwidth of 1.8 nanometer is because Edmund Optics manufactures part 87293 which is a spectrophotometer with that wavelength resolution.

In certain applications, sensing , filtering and protection from laser radiation is required for protection of eyes.


texts: Is it possible to simulate the electric power output of a linear alternator using finite element analysis software?If yes, which?

texts: We need to build a small (1-2W) linear alternator for a project in engineering school. Is it possible to use finite element software to finetune our design instead of actually building real life models? If yes, which software should we use? We are using AutoCAD fusion 360 to design our 3D-model.


texts: How can the wobble of a rotating cantilever shaft be reduced?

texts:
I have a cantilever shaft 6inches in length supported on one end using a ball bearing. I am having problems of shaft wobbling in the bearing. I cannot have support on the other end.

How can I help this situation?

The shaft is made of aluminum, rotating at around 120 rpm.


texts: Required clearance for moving part (Push Button)

texts:
I'm designing a push button made from most likely ABS but possibly TPE, it presses a surface mount button on a PCB with 0.9mm travel.

The ABS button is 8x8mm Square and travels through 4mm of polycarbonate

I want there to be very little (if any) wobble and as little gap around the edges as possible for aesthetic reasons. But I cannot have the button snagging or jamming as the product wears and the inevitable dirt build up.

How big should the cut out be?


texts: Is it true that points of root locus only satisfiy the angle condition?

texts:
So , I was reading a course book : ''Modern Control Engineering '' by Ogata and I came forward this statement that made me skeptical:
''The points of root locus only satisfiy the angle - condition. Closed - loop poles are the roots of the characteristic equation and therefore satisfiy both the magnitude and angle condition. If , we want to find the closed - loop poles for a given gain value K , then we have to ...''
I am not sure why does not every point of root locus correspond to a closed - loop pole for some K. Is it true? And if so , these points that are not closed - loop poles for any K , do they have any meaning/ physical/geometrical/control theory  ?
I even have an assumption to this: Maybe he means , that if K has to be integer ( K may has to be integer , in ''real world applications''(?))? Then of course , root locus would have a discrete-represantion graph , so he means that if K - is integer ,  in root locus we connect the dots (to have a continoous represantantion) and thefore not every point of it is closed-loop pole and everything would make sense.
I even graphed, a root-locus in python : If you click an any point python returns the corresponding K for this point (which may be float) . So is this the reason?  Let me know if I am wrong/right


texts: O-Ring Design for low pressure applications

texts:
I'm trying to figure out how to create a seal for a very low pressure gravity feed system. Essentially its a low pressure solenoid valve. Is there any equations to estimate the amount of force you would need on a o-ring to seal it from any leaks of pressure $p$ its placed in a spring solenoid combination so I need to have this as low pressure as possible. Any ideas on what force I would need from the spring to seal a liquid the pressure is due to a height of about 40mm with a liquid like water. So if my math is right that's
$$
\rho g h = 997 kg/m^3 * 0.04m * 9.81m/s^2 = 391.22\ pascals
$$
at the o-ring so pretty small amount of pressure.

Also what material would you suggest for the O-ring I have considered, I have used 50 Durometer with no success and am thinking about moving to a silicone based O-Ring. I can't increase the force of the spring because a solenoid will need to overcome it and i'm limited on space.


texts: Friction factor for wormgear design materials

texts:
I'm working on a database which involves geometric design parameters, forces analysis and efficiency and losses for wormgear reduction design systems.

To determine the tangential and axial forces applied to the gear reduction system, I need to relate the Sliding velocity with the friction factor for different materials combination.

I found this graphic chart in a technical paper. This graphic is exactly what I'm looking for, but I need a curve for steel worm and a polymer (Copolymer Acetal precisely) worm gear:

I would be grateful if someone can help to find that material curve.


texts: Is it possible to use a vehicles own carbon emissions to shield it from wind drag?

texts:
Let's say a cargo ship uses a large amount of fuel while on a voyage. Could you direct the exhaust i.e. Carbon dioxide into a chamber utilising a check valve so the emissions don't backflow into the engine? Allow the gas to travel through a hose towards the front of the ship and release through a gas control valve which regulated that the gas is at a specific pressure. Before releasing it so that it blocked the wind and cleared the ship essentially eliminating or reducing frontal drag?

Could this method also be utilised on planes and other vehicles? the gas wouldn't weigh much due to heat from just being emitted from an engine so I can't figure out why this isn't used in formula one cars and so forth?


texts:
The CNC spindle is supposed to operate its single shaft in two different modes:

high RPM (30,000-80,000 RPM), variable, possibly quite high torque, a straightforward PID to maintain the RPM as torque varies ("work mode", RPM control).
very low RPM (exact value doesn't matter), nearly no torque (just friction of bearings), rotation of shaft to precise angle. ("optical scan of the tool, from all sides", angle control).

The first is achievable through a good AC or DC motor. The latter would be achievable through a stepper motor with microstepping. I can cut off any of the motors (leave it idle) and drive the other to achieve either of the modes.

But I don't think typical stepper motors are capable of surviving 80,000 RPM applied externally - and I'd prefer to avoid a mechanical clutch decoupling the stepper.

Are there steppers that can just survive these kinds of speeds? Or other neat solutions that don't overly increase the mechanical complexity?


texts: Extracting Uncertainty from Numerical Solution

texts:
I am performing numerical and uncertainty analysis for an oblique shockwave angle function:
$$
\tan(\delta)=\frac{2}{\tan(\theta)}\frac{M^2\sin^2(\theta)-1}{M^2(\gamma+\cos(2\theta))+2}
$$
where $\delta$ is deflection angle, $\theta$ is shock angle, M is mach number, and $\gamma$ is the ratio of specific heats. In our observation, $\delta$, $\theta$, and $M$ all have uncertainty. $\gamma$ is assumed to be exact.
Our unknown quantity is $\theta \pm \sigma_{\theta}$. If it was possible to solve for $\theta$ analytically, it would be trivial to propagate uncertainty (excluding covariances):
$$
\sigma_{\theta}^2 = \left( \frac{\partial\theta}{\partial M}\sigma_M \right)^2+ \left( \frac{\partial\theta}{\partial\delta}\sigma_{\delta} \right)^2
$$
The question is: how do I define $\theta$ so that I can take a derivative of it with respect to $M$ and $\delta$ for uncertainty analysis? Or maybe there is a way to approximate $\theta$ and take a numerical derivative? I am probably overthinking this.


texts: 74141 BCD-to-decimal converter lighting wrong/multiple LEDs

texts:
I'm having trouble with a 74141 IC while building a nixie clock. At the moment I'm testing it with 10 leds and a 4K7 resistor, expecting them to light up one at a time as per schematic: NTE74141 Integrated Circuit TTL − BCD−to−Decimal Decoder/Driver 16−Lead DIP Type Package

Trouble is, both output 0 and 2 lights up no matter what input I set (by connecting ABCD input pins to 5V or ground). Is the IC corrupt or did I miss some detail?

Schematic:


texts: Why do we use simple bending equation when bending moment is caused due to shear force?

texts: Simple bending equation is derived assuming pure bending(when a couple is applied onto a beam with no shear stress).We tend to use the above derived equation when moment is caused due to shear stress?How far is this correct?


texts: ANSYS Design Modeller more significant figures

texts:
I need to just get the volume from ANSYS Design Modeller but I would like a higher number of significant figures rather than just 5 (See picture).
How do I do this?
Thank you for your help!


texts: Derivation of expression for strain in a beam that experiences transverse vibrations

texts:
I was watching
this video (the link to the video is https://www.youtube.com/watch?v=AoxTyIJprg8&list=PLMXj6GKKnHI6Lftj7CXr9WusMkXi5s9yH&index=60) which is part of a course on mechanical vibrations. Can someone explain how the expression for strain is derived in the video? Why is strain the derivative of u(x,t)?


texts: Why have cascading vessels in the 'B' part of the 'AB' wastewater treatment process?

texts:
The AB process is wastewater treatment process that works like this:

'A Stage': Wastewater is (after mechanical treatment) subjected to a high load activated sludge process where also a lot of contaminats are adsorbed on the sludge.

'B Stage': Low load activated sludge process with further BOD destruction and nitrification and denitrification in anoxic zones.  A part of the effluient of the B vessels (before settlement tanks) is recirculated to the beginning.

Each stage has it's own set of settlement tanks and return sludge, so the biology is adapted to the specific conditions.

Now my question: I've seen the claim (and actuall don't doubt it) that the B-stage is more effective (Per volume available) when the effluent of the A-Stage is added in a cascading way: Say (in a rectangular, long tank) 50% of effluent at the inflow end, 50% in the middle. Return sludge is all added at the beginning of the B stage. A carbon source can be added if required.

What is the process reason why cascading is more effective? In a cascading low load reactor, is there still recirculation?


texts: Calculation of beams in flat roof structure

texts:
Beams 1 to 7 carry the load of the roof (for example 200N/m2)
The maximum bend of these beams is 5mm
How do I calculate the forces working on these beams?


texts: "Heavy-duty" or not, can my drawer slides really support this weight?

texts:
Okay, so recently I got a Dewalt 735 Thickness Planer.

It's great at what it does. (It even LOOKS like it's ready to consume the tender flesh of lumber, like some twisted Victorian lumberjack... though, maybe that's just me).

Anyway, the problem I've been experiencing with the tool is that, while planing, should a board exceed a certain length, such that the midpoint of the piece is no longer supported while some portion of it is still being cut, the board tips, resulting in snipe (a gouge in the board, resulting from the angle shifting mid-operation).

Okay, no problem: I'll just build some supports. Now, I just so happen to have some Heavy Duty 22" full-extension 150-pound-rated drawer slides - about a dozen of em - from a different project. Cool. I'll run a roller bar between em and make the whole deal extendible at need. I can even add flip down leg supports if needed (though if the slides are strong enough, I'd rather not).

As I was doodling this out, my son walks in and asks what I'm looking at. I muse aloud that it's a shame I don't have longer slides. 22 inches isn't terribly huge for infeed/outfeed.
Then he asks me: "So why can't you just hook two together? Just stick another piece between em so you can screw into both sides of that." Heh. From the mouth... of... babes?

Now, intuitively, this seems like a bad call (certainly without the leg support). But I'll be damned if I can figure out WHY or what to tell him. Some long-forgotten, niggling memory of similar suggests this is a Static Equilibrium problem, which - despite it having been decades since I've looked at any of this - I have some vague recollection on how to calculate. But it's the addition of the strut that hooks the two slides together I cannot account for.

Now, although the finished version of either approach will have two slides with a bar spanning them, I'm reducing this to two dimensions for my own old brain to walk through.

HOW do I figure out how much load would be put on the roller if I were to take his approach?

COULD a 150 lb capacity (well, two combined, for the 2d example we're using, per side - four total in actual implementation) support a portion of the mass of a single, call it 25lb board?

WOULD it need legs?

Edit additional clarification: the dimensions of the mobile base are 38" wide (the axis perpendicular to the force) by 26" deep (the axis parallel) by 30" tall (including the locking steel casters it rests atop).
It is constructed of the better part of a full sheet of 3/4" Baltic Birch plywood (call it 75 lbs), and contains a small cabinet containing various bits and bobs (~30 lbs). Also seated alongside the planer is a cast iron bench top jointer (~65 lbs), which itself has 2 drawers beneath it containing various sleds, jigs, and blades (~20 lbs). This is all in addition to the four 4" steel casters (~2.5 lbs ea.) the fixture rests atop, and the 105 lbs. planer itself. This accounts for an approximate total weight of ~300 lbs and change. I've been simply treating it as the proverbial "immovable object" in the equation, Archimedes be damned, but that is, I admit, simply because it hadn't occurred to me it's stability might be compromised.


texts: Relative inefficiency of doorless fridges at supermarkets

texts:
It appears to be a waste of electricity to keep a bank of refrigerators wide open with no doors or covers whatsoever on them.

They seem to be just blowing cold air out into the supermarket.

They are not turned off at night when the store closes.  Even the "green" Whole Foods-type places do this.

But is it really that inefficient to operate them that way?
  What is the relative efficiency between a refrigerator with a door and one without a door in a supermarket?


texts:
I am planning on buying a kitchen stand mixer with planetary action.
One important factor to consider is the type of gears the mixer uses, they can be plastic, composite or metal.
As far as I know metal gears are the best and plastic the worst in terms of durability and handling stress.
However I don't know what are composite gears and how they fare, compared to metal or plastic.


texts: What is the frequncy range of seismic vibrations?

texts:
I'm working on a structure which needs to sustain common seismic vibrations due to earthquakes. So I want to do some modal analysis to find natural frequencies of the structure and make sure they are out of the range of seismic vibrations. I'm being told that if the natural frequencies of the structure are beyond 17 Hz it should be fine. However, I can't find any reference approving this specific number.
So I would appreciate if you could help me know what is the frequency range of seismic vibrations, providing engineering or scientific references. Thanks for your support in advance.


texts: Getting the elevation of a specific point of a elevation gridline

texts:
In a highway Project, I have to design a road connecting to roads together. The map I have on AutoCAD is a elevation gridlines map and I have x, y and z coordinates
but I don't know how to get an elevation for a point that is not exactly on a clear grid point, as the points where the grid lines intersect, the elevation is given.


texts: Watching Apollo 13 and rereading Lost Moon, Jim Lovell's exciting recollection of the events on the crippled spaceship, I began to wonder. Why does NASA maintain the gasses at the triple point? A pressure vessel designed to handle very high vacuum (which H2 and O2 triple points are near complete vacuum) and low temperatures is thicker and more dense then a pressure vessel designed to handle modest amounts of pressure. Why wouldn't they store these gasses at higher pressures, at or near atmospheric pressure?


texts: Rapid Cooling System for Commerical Freezer

texts:
I have a bit of an ambitious project on hand and was looking for some advice/ideas.

My team and I are working on a project that involves retrofitting a commercial grade freezer (model MasterBilt IHC-48) into an environment chamber that would be used for HASS testing. HASS testing involves perform a rapid temperature cycling test and vibration/shock test, which would be used to stress electronic products.

As an example this rapid temperature cycling might involve going from +65C to -10C in 2 minutes and vice versa.

The medium inside the chamber would be air.  The dimensions inside the freezer are 27"x58"x46" (0.686m X 1.47m X 1.17m).

The gray area for me is how to achieve this rapid cooling.  What I am looking for are ideas/suggestions on how to retrofit this freezer to achieve this rapid cooling.

Any ideas/comments are welcomed.


texts: Is it known how streamlined the Shinkansen 800 bullet train is when on rails?

texts:
This question is different from What is the optimal streamlined shape?. That question is probably about an ideal situation of flowing through space with no gravity in a fluid with zero viscosity and infinite bulk modulus. This one is about a real bullet train which is not an ideal situation like that. https://www.youtube.com/watch?v=7ccoEmlxlks shows a video of a Shinkansen 800 bullet train. It looks like a shape that will not produce much turbulence at the back end. That's based on my guess that that would be a kind of streamlined shape. My question is

Is it known for different speeds, what the force of air resistance divided by the density of air,  divided by the crossectional area of the train, divided by the square of the speed of the train is when it is on rails?

I know that if atoms were infinitely small and air had the same density but with an infinite bulk modulus and zero viscosity and the train had an infinite strength and shear modulus and bulk modulus as well, that number would be constant because the laws of flow of a fluid in an ideal situation like that are preserved under a slowing down or speeding up of the process. However even if the laws allow it, we could not in general reverse the process of flowing through a fluid with turbulence because there is a forwards arrow of time because there was a beginning of time, just like if you call one heptagon in a hyperbolic heptagonal tiling the central point and start there doing a random walk, where you will be next give where you are will always be random but where you were last given where you are now and where you started will never be fully random.
12:00 into the video https://www.youtube.com/watch?v=5zI9sG3pjVU, you see the flow of air around a smooth sphere. It appears to have a jet of air a little behind the sphere nearly stationary in the frame of reference of the sphere. And the kinetic energy of the air in that jet in the frame of reference of the rest of the flowing air probably converts into kinetic energy of the eddies. So for  speeds large enough to have a high enough Reynold number to be turbulent and a low enough speed to not be a high fraction of the speed of sound, for that sphere, the force of air resistance divided by the density of air, divided by the crossectional area of the sphere, divided by the square of the speed of the sphere should be very close to 1. I believe an ideal shape similar to the shape of the Shinkansen 800 in an ideal situation of going through a fluid would have zero resistance. However if it's flowing through space without gravity or real wheels like a train and no opposing gravity against a normal force like a real bullet train, there might be exponential growth in the fluid pushing it out of its original orientation.
I know almost nothing about engineering. I'm looking for a simple answer that can just satisfy me with knowledge. Then I'll leave it to other people to invest in new research based on the answer if they want to. I'm not trying to design anything myself. However, I cannot figure out an algorithm for determining in advance given what the answer is, whether it will satisfy me. When somebody is working on something, they don't propose a concrete algorithmic plan from the start. They feed themselves ideas and trust themselves to think for themselves later how to use them. Similarly, a good answer to this question would come from somebody who can function as if they are a future self of me and uses their discretion to figure out what type of answer will probably be a good answer that satisfies me.


texts: Tool Clearance at Bottom of Milled Thread

texts:
Hi,

So I have a large piece that I want to thread (the entire region in blue), but I am not sure how much space to leave at the bottom for retraction of the blade (region in red), see above image.

For example if I have a M55 x 2.0 thread, should the little box the in red be the size of one thread?

Meaning: Width = pitch , Height = (Major Diameter - Minor Diameter of thread).

Or can it be smaller while ensuring that the entire blue region is threaded?


texts: How can a car can be lifted using hydraulic press?(Pascal's Law)

texts:
The above pic is describing the system how the car will be lifted if car is placed on the larger piston. But if the small piston is moved through 1m (say) ,then the piston is merely moved by millimetres. Then how, in practical life,small piston can actually be used to lift a car in a carwash station. If helpful, please suggest books, E-books or a few good articles.
The following portion is edited area after the question was declared answered
My question was very nicely answered and now my confusions have been eradicated and I'm grateful for that. I have hit upon a conclusion in the light of answer given and want the experts to confirm my following statement: If small multiple displacements "h" are not considered(see the answer with figure) and only stroke of the smaller piston is considered,
THEN more fluid enters the large piston than fluid lost by by smaller piston and vice versa (on pushing small piston) i.e more fluid will come out of the larger piston than fluid gained by smaller piston upon pulling the smaller piston upwards.
Note: I also wrote similar text in comments section but now I edited question thinking I followed wrong approach


texts: Using python to send automated commands through a serial-usb-cable adapter

texts:
I have an old peristaltic pump with a 9 pin male sub-d socket labeled Gilson Serial Input Output Channel (GSIOC) that connects a master device to devices with RS422A specifications, or RS485 specifications. The GSIOC implements RS422A/RS485 transmitters and receivers.

Could any computer serve as a master device by simply connecting the pump and computer directly through a serial to USB converter with proper specifications?

Building from here could serial commands be written on and sent directly from the computer to the pump in order to control speed/rotor direction...etc? Or am I missing important conceptual understanding on how to remotely control the pump?


texts: Operating a load cell below excitation voltage

texts:
I currently have this load cell, which has a 10V excitation voltage. However, there is a very nice/convenient load cell amplifier that works with an excitation voltage of 5 VDC.

What are the consequences of operating a cell at a voltage lower than the normal excitation? Just increased noise in the signal?


texts: DC and AC Simulation on Ansys Maxwell for calculating the core and winding losses in an Inductor

texts:
I want to simulate the core and the winding losses in an inductor using Ansys Maxwell when imprinted with a triangular pulse(positive RMS Current). I am doing a DC simulation to get the inductance matrix to get an equivalent inductance(To get the ripple current). Then an AC simulation with the current harmonic (3 harmonics)of the triangular pulse.
Is there any way to have a complete automation of the AC And DC losses, such that the simulation is optimized using parameterization?  What I want to do on Ansys is: optimize the dimensions of the inductor core and the windings so that I get the lower losses and no saturation in the core. So for each dimension, there is a DC simulation and also AC simulation to calculate all the losses, and accordingly, there is a parametric sweep and we get an optimum configuration of the inductor considering the AC as well as DC losses together.


texts:
With folding barriers like the one below, how does the orange bar get turned by the green mechanism? What's inside the yellow triangular part?

https://www.youtube.com/watch?v=LF8kSTCZIxw


texts:
I'm looking for an elegant mechanism for restricting the movement of the wheel cradle in the picture.

The wheels are intended to be able to swivel around +-5° but not more.

The initial idea is to have some kind of pin and a slot in the front plane. Is there an established way of making the axis itself somehow reduce the swivel?

The axis needs to be round in shape (no hump); there'll be tightening clips around it
The forces to the rotational direction are minimal, i.e. just gravity


texts: Can turbine engines really run on "just about anything"?

texts:
I often read that turbine engines can run on almost any fuel source. I understand that turbine engines are less "picky" in terms of the fuel source that they can use, but surely there would still be some limitations as to which fuel source can be used e.g. a certain range for flash point, auto-ignition temperature etc.?

Likewise, could a turbine engine be built from scratch to run on a fuel not normally suitable for turbine engines? And if so, would this engine be less efficient?


texts: Coefficient of Friction, Passive Magnetic Bearing

texts: While comparing magnetic bearings to others ceramic bearings, a rough first point maybe to compare would be the two different bearings' coefficients of friction. This is just a thumbnail comparison apart from load bearing, and rpm, and any other metric that one might have with the application in concern. Is there a rough estimate for passive magnetic bearings, for an example to compare with a ceramic bearing might have 0.2, steel bearing 0.8, or this bearing called an Autonomous Decentralized Bearing" : 0.0027, any numbers for a passive magnetic bearing, or for reference any numbers for a similar active magnetic bearing?


texts: Convective heat transfer coefficient in finite difference method boundary conditions

texts:
Suppose there is a cubic material with an internal heat source ($\Delta q / \Delta t =$ Constant), and is immersed in a sufficiently large amount of water. Now I would like to use finite difference method to simulate the steady state temperature distribution.

I think a natural convection boundary condition within the range of laminar flow can be assumed, and the maximum temperature should not exceed 100 $^\circ$C. As the surface temperature distribution is not uniform, each surface node should have its unique convective heat transfer coefficient ($h$), as this parameter depends on the temperature difference between the solid wall and the fluid.

But by looking up some heat transfer textbooks, I have never seen people address to the problem in such a way. I only found some treatments and correlation equations on the scenario of uniform temperature distribution of different geometries, while in my simulation, the temperature of different surface nodes are different. Giving it a second thought, I realized that convection heat transfer coefficient is dependent upon fluid properties, which will make it extremely complicated.

So is it possible to perform such calculations with finite difference method? Is there a method to at least estimate the convective heat transfer coefficient?


texts: How to find the diameter of bolts in a flanged joint?

texts:
So I'm given this question with the following diagram:

Two sections of a pipe are joined in a flanged joint as shown in the Figure below. The difference in pressure from interior to exterior is 2 MPa.

The joint is connected with 12 off bolts, equally pitched around a pitch circle diameter of 350 mm. If the maximum allowable tensile stress on the bolts is 300 MPa, what diameter do the bolts need to be?

My working out

First I find the area of the section that the bolt's diameter takes up:

$A = \pi (0.175+r)^2 - \pi(0.175-r)^2 $

$A = 0.7\pi r\ $

Then I find out the force acting on that area of section and divide by twelve to obtain the force for a section that has one bolt.

$F_{12} = (2\times 10^6)(0.7\pi r) = 14 \times 10^5 \pi r$

$F_1 = 366519.1429r$

I then sub this into the stress equations since I know the maximum tensile stress for 1 bolt:

$A = {F_1 \over \sigma_{max}}$

$\pi r^2 = {366519.1429r \over 300 \times 10^6}$

$Diameter = 0.039 m$

But the answer I'm given says it is supposed to be 5.9mm. Is there anything wrong in my thinking?


texts: Optimum Moisture Content and Maximum Dry Unit Weight

texts: Anyone know how to solve for the OMC and MDD using mathematical solution? The book says its OMC is 13% and MDD of 2020. I tried using $a+bx+cx^3$ and getting its maxima but its far from 13%


texts: How to test connectivity between wire and piezo-ceramic transducer

texts:
I have mounted a piezo-ceramic ultrasonic transducer (MODEL # SMD10T2R111WL, Vendor Website: PIEZO CERAMIC DISC 10X2MM R 215 KHZ WIRE LEADS) under a plastic tank using epoxy. Please see the below picture.

I am trying to confirm that the wire did  not get detached from the transducer while mounting. Is there a way to test it. The two wires that are soldered to the transducer are not connected so there is no way to check the continuity of the wires using multi meter short circuit test.


texts: What is the theoretical relationship between sound and mass with respect to the sound barrier as a max velocity?

texts:
First post here, forgive me any faux-pas. In regards to compressible flow and accelerating a mass flow, such as in a converging nozzle, I know that you can't accelerate a mass past the speed of sound (Mach 1, that is, the velocity at which an infinitesimally small mechanical wave would propagate itself through the same medium, i.e. the mass of air itself). So, you need a diverging section to allow you to continue to de-pressurize the mass and continue to convert its enthalpy into kinetic energy (velocity).

I know how this works, via the following equation (and its analogues):

and I understand choked flow and all sorts of analogies for how much mass flow could be possible (traffic jams, etc). My question is more of a why. Why is the speed of sound the max velocity of some given mass at the throat?

At first, that was my question, then, I recognized that sound is just a wave of pressure difference - so then, I asked, what is the relationship between pressure and mass? Well, pressure is force over area, and force is mass accelerated - so is that the key to the relationship? But pressure has no mass - so then do I have to treat the mass flow as a wave (like in wave-particle duality for matter)? I think by this point I've gone way too far and missed something simple.

So, why the "speed of sound"? Why pressure waves, instead of electromagnetic waves, or some arbitrary constant with respect to the medium? What does the velocity of pressure have to do with the velocity of matter in this context?


texts: Why does a vortex at a tube's entry causes a contraction below a discharging container's short tube?

texts:
While discharging water from a short tube, I noticed that a vortex began to form on the top of the discharge tube causing the jet issuing from a short tube to contract (less than the cross sectional area of the short tube).

My question is why does the jet contract below the short tube?

When the vortex forms the velocity is at a maximum:

$$A_1v_1=A_2v_2$$

So, the area must be a minimum.

I also observed that the contracted jet maintains this state until all the water is discharged from the container. Could this be explained in terms of head loss caused by the vortex?


texts: How to select a low flow rate diesel flow meter

texts:
I need to select a precise flow meter for the following application condition:

Flow range: 0-150 liter per hour
Medium: Diesel

There are so many meters on the market that I am a bit lost. How do I determine whether a flow meter is acceptable for this application? If there are many acceptable flow meters, why should I choose one over the other?


texts: How/why lubricating a rolling bearing would make them spin less time (dissipate energy faster)?

texts:
I have lubricated the ball-bearings of two hand spinners (the anti-stress toys) and contrarily to my expectation the time they keep on spinning has been divided by four.

One fact I have noticed, the rolling bearings now makes almost no more noise at all: they were really noisy before.

I am trying to explain myself why/how the energy in the two hand-spinners would dissipate so much faster ? It is contrary to my intuition.

Any idea ?

When I say divided by 4, it is an estimation:

I have an anti-smoking anti-stress technique that involves a short meditation, and I was using two hand-spinners, one in each hand for a duration of roughy 2 minutes, a bit more, (repeated numerous time for one year or so).

But after lubricating them this afternoon with WD-40, the duration falls to 30 seconds at most.


texts: Bearing to allow a sphere to roll freely

texts:
I want to know what bearings might allow a sphere (5cm diameter) to roll in-place most freely.

The closest mechanism that matches what I might want to achieve is a "ball transfer", I believe the term is.

I have been unable to find:
 - an explanation of the internal mechanisms they use
 - if there are different implementations
 - how freely the ball can roll, and in what motion relative to the base.

My goal is to have a mechanism that supports a ball the size and weight of a snooker ball, so it can be used as a trackball (to replace a PC mouse, or touchpad). An optical sensor from an optical mouse would be placed underneath, to detect the movement of the ball, so spinning on that point is not necessary, but the sphere should have the lowest possible friction when its surface sweeps over the sensor.

The reason low friction is required, is it would allow the user to transverse a large screen distance by giving the ball momentum, and then stopping it would allow the user to resume precise placement.

One solution I considered was to have extremely small castor-wheels, three of which would be placed around the base of the ball. But I have not found any such castors; their wheels would have to have a diameter of around 1cm or less.

Another idea was to use a number of ball transfers to support the sphere itself, but again, ball transfers seem to be rather bulky, their balls having a diameter around 2-3cm, plus a rather large mechanism surrounding them. And I do not know how much friction they would still have, since they seem to be made to support far heavier loads (>20kg) than that of the snooker ball (250g)

Can anyone give me any other solutions, and/or highlight pros/cons I need to be aware of?


texts: Relationship between output mechanical power and max pressure for a pump?

texts:
If an air pump needs to able to generate a particular pressure at a particular flow rate.

How do we size the electrical motor for this particular scenario? The electric motor would be coupled to the pump shaft in this case.

I mean how do I calculate the mechanical power the motor shaft has to deliver to achieve this?

Does the pump technology have any bearing on this I mean diaphragm, piston etc.

Lets take an example pressure of 1 psi at a flow rate of 10 liters / min.
I need to know the wattage of the motor that would be a suitable fit for this specification.


texts: In an air conditioner, how does the released air get cold so quick?

texts:
As I understand from reading about air conditioners is that the way they work is that air sucked in from the room is passed by the cold evaporator pipes and then the air is released again.

My question is how does the air sucked in from the room change temperature so quickly since it passes very quickly by the cold evaporator pipes and released again?


texts:
I am not a mechanical engineer, so just trying to figure this out. I want to attach a servo to my telescope focus, but the servo only has about 180 degrees motion, whereas you need to turn the knob about 540 degrees for the full range of focus. It has a rack and pinion gear, so my plan was to find a pinion gear with more teeth (maybe 48?) to get the full range in 180 degrees.

The pinion gear has 16 teeth and an outer diameter of about 8mm. I measured 10 teeth on the rack which was about 15mm. The diameter of the shaft is about 5mm. My question is, what size gear would I need, how many teeth, what pitch? Does it exists? My best guess is 48 teeth would be needed, but I am not sure about my pitch. Also, if the gear exists, do they make them to attach directly to a servo? Or will I need to get a shaft and a shaft to servo coupler?

Thanks


texts: Choice of Datum Features and Number of Datum Features

texts:
Consider a rectangular stock section with a dowel hole and other features of size (FOS) on it. The dowel hole serves to locate the entire part.
Should my choice of datum features be what is most convenient for the machinist or for the Q&A engineer? Given that it is rectangular, it is easiest to set up the datums as the 3 orthogonal faces/edges of the part.
But the external faces/edges serve no engineering purpose and is pointless to dimension any FOS from the edges. They should be dimensioned from the dowel hole instead since this determines the part's final position/orientation during assembly
In this scenario, can I have more than 3 datum features, i.e. including the dowel hole as a datum FOS to give 4 datums?


texts:
Given ist the following framework:

$$E=210 \frac{\text{kN}}{\text{mm}^2}$$
$$ EA \to \infty $$
$$ I_1 = 80000\text{cm}^4 $$
$$ \frac{I_1}{I_2} = \frac{3}{4} $$
$$ I_3=I_1 $$

Using the principle of virtual work, I'm suppossed to figure out by what angle $\varphi_i$ beam 2 and 3 are skewed. Shear forces can be omitted.

In my virtual system, I apply a moment at the joint:

How can I determine the reaction forces needed in my virtual system? I assume that the moments in 1 and 4 need to be 0, but there is no way to cancel out the moments at the ends of 2 and 3 and still have a force equilibrium.

Or is my understanding of a balanced virtual system flawed?

Any help is greatly appreciated. Thanks!

In case someone wants to work through the problem themselves, here is the solution and what I've calculated so far:

Solution:
$$\begin{align*}
\varphi_2&=0.009\text{rad}\\
\varphi_3&=0.007\text{rad}
\end{align*}$$

Calculation:

$$EI_1 =EI_3= 210\cdot 80000\cdot 10^4\text{kNmm}^4=168\cdot 10^9\text{kNmm}^4 = 168\cdot 10^3\text{kNm}^4$$
$$ EI_2=\frac{4}{3}EI_1=224\cdot 10^3 \text{kNm}^4$$
Reaction Forces:
$$ \begin{align*}
A_x &= -126\text{kN}\\
A_y&=-42\text{kN}\\
B_x&=-42\text{kN}\\
B_y&=\hphantom{-}\text{42kN}\\
G_x&=\hphantom{-}42\text{kN}\\
G_y&=-42\text{kN}
\end{align*} $$

Since we ignore shear forces and $EA\to \infty$ we only need to consider moments.

The moments can be calculated to:
$$\begin{align*}
1:&-q\frac{x^2}{2}+126x=-\frac{21}{2}x^2+126x\\
2:&-42x+336\\
3:& -42x\\
4:& 42x-168
\end{align*}$$


texts: LTE to 3G IRAT Handrover: What happens afterward

texts:
Let's say that there has been a handover from LTE to 3G of a particular UE. Once the handover is complete, the MME is no longer required to maintain the sessions/bearers that has been established for that particular UE. I have found the following call flow in a reference, which is not so reliable.

1.  eNB  ⇒  MME     S1AP    S1      UEContextReleaseRequest
2.  MME  ⇒  SGW     GTPv2   S11     Release Access Bearers Request
3.  SGW  ⇒  MME     GTPv2   S11     Release Access Bearers Response
4.  MME  ⇒  eNB     S1AP    S1      UEContextReleaseCommand
5.  eNB  ⇒  MME     S1AP    S1      UEContextReleaseComplete
6.  SGSN ⇒  MME     GTP     Gn      SGSN context request
7.  MME  ⇒  SGSN    GTP     Gn      SGSN context response
8.  SGSN ⇒  MME     GTP     Gn      SGSN context acknowledgement
9.  MME  ⇒  MSC     SGSAP   SGs     SGsAP-EPS-DETACH-INDICATION
10. MSC  ⇒  MME     SGSAP   SGs     SACK SGsAP-EPS-DETACH-ACK
11. MME  ⇒  SGW     GTPv2   S11     Delete Session Request
12. SGW  ⇒  MME     GTPv2   S11     Delete Session Response

Given the scenario, some of these calls make sense to me. For an instance, once the handover to 3G is done, there is no point of having the access bearers S1 between eNB and S-GW and S5/S8 bearer between S-GW and P-GW and so forth. So, the Release Access Bearer Request in 2, and Delete Session Request at 11 are sensible.

What I particularly don't understand is that, why are calls 6,7 and 8 there? What purpose do they serve? Or is this entire flow blatantly wrong? If it is blatantly wrong, where can I find something sensible to read about what really happens? I have combed through the 3GPP specs for weeks now, but still couldn't find answers to the questions above.

EDIT-1

Okay, after looking at some PCAPs, the purpose of the calls 6,7 and 8 is also clear. Upon falling back to 3G, the SGSN is going to require the UE context at MME, in a format that SGSN can understand. To an SGSN, MME looks like another SGSN. So it requests, the context from there over S3 interface. However, the call flow above says the message exchange between MME and SGSN happens over Gn, that which contradicts with the the 3GPP spec, that which according to, the Gn interface is used to establish the connection between SGSN and GGSN. Now, the new question is going to be on the accuracy of the flow. Is this call flow accurate?


texts: Why is using steam to rotate a turbine more efficient?

texts:
For example i have an exhaust pipe with very hot air from burning biofuel, and i have a turbine at the end of the exhaust that rotates and generates electricity.

Why is it more efficient to use the heat to boil water then use the steam produced to rotate the turbines? As in why is more electricity generated by using steam to rotate the turbines as opposed to not using steam when burning the same amount of biofuel?


texts: Why do we use linear transformation of states in linear control technique

texts:
Just to leave some space here I link to an introduction of linear transformation of state. How is it useful? Can nayone provide an example where it is indeed useful and has to be done?
http://www.staff.ul.ie/burkem/Teaching/st-tr.pdf


texts: Why is there a side walk in the ditch in between two highways?

texts: I noticed what looked like a side walk in the ditch in between the freeway. It repeated for a few miles. At the ends of the sidewalk were small gray slated boxes about 6” or so. The length of the sidewalks were from about .2 miles up to about a mile or so. Construction crews were building more. What are these for?


texts:
After reading some docs about Electric Vehicles (EV), I learned that there are 4 differents charging modes.
For example, let's consider a slow recharge, where EV is connected to a single-phase domestic wall socket: its battery will absorb 16 A, so (considering a voltage of 230 V) about 3.7 kW.
3.7 kW is, often (depending on the type of contract with the grid operator), a value near the maximum power rating of an household.
So, I  guess that 16 A is only the maximum current value allowed by that precise "charging mode", and that it's also possible to recharge the EV with a smaller value of current (so a smaller power).
Otherwise, during EV charging, no other electric equipment (such as TVs, applicances, ...) could be supplied, without generating an electric overload.
Am I guessing right?
If it's possible to recharge an EV with a smaller power than 3.7 kW (in my case), how, and by which device, is this power value determined? Will this value be the maximum power value which doesn't cause an electric overload?
Is there anyone who could clear this?


texts: How does an oscillating sprinkler like this change directions?

texts: I'm trying to understand how an oscillating sprinkler like this, is able to change directions. Does it still use a four bar linkage mechanism like a traditional oscillating sprinkler?


texts: How can I power a driveshaft while also allowing it to freely spin when not under power?

texts:
I'm designing a drill powered vehicle that needs to be able to drive uphill and downhill. The drive train roughly looks like this. The drill locks up when it's not running so I need something that will allow the shaft to freely spin when the power is off. I looked into centrifugal clutches but my drill doesn't produce high enough rpm for that to work.

Is there anything else that I could purchase or manufacture that would make this possible?


texts: Determining the required specs of Stepper Motor

texts:
Being a non-engineering type, I'm trying to calculate what power and torque I would need from a DC stepper motor to execute a particular task.  I'm certain that my question will open me up to potential observations regarding my lack of knowledge in this field. That said, if your critical observations use humor to make the point, I will appreciate them for that. However, I do expect to gain some good knowledge from this group.  Here goes nothing.

I am building a device that will be used to lift, and hold 200 pounds approximately 2 feet in elevation.  The mechanical elements of this device are 100% the same as a standard worm-shaft driven, scissor jack for a motor vehicle.

Envision a letter "A" as the two arms on the top of the scissor, and the left arm is anchored to the substrate, and the right arm is attached to the threaded block that travels along the worm-shaft. As the worm-shaft is rotated, the threaded block will travel along its axis which will in-turn cause the "A" to get taller and skinnier. This achieves the lift needed for the device.

Question 1:
In order to achieve the required power and torque to lift and hold 200 lbs without having to manually turn the worm-shaft (as one would when jacking up a car), should I couple the motor to the worm shaft concentrically, or use one gear on the motor shaft, and one on the worm-shaft?

Question 2:
Depending on the direct-couple method, or the gear ratio method, how do I determine the power and torque of the motor?

I really appreciate any help I can get with this challenge.


texts: What is the opposite of an uninterruptible power supply called?

texts: The question title says it all. I'm looking for the opposite of a UPS, ie it won't turn back on if there is a power outage. I know they exist but, I can't remember what they are called or find them on Google.


texts: Automatic Shifting without Electronic throttle

texts:
I need to design an automatic shifting system, for a FSAE car. Clutch and shifts are electronically engaged and disengaged using a Pi Innovo engine control unit (ECU).

The issue I am worried about is downshifts, I would like to rev-match, for quick, clean downshifts and clutch life.
There is no possibility of my team using an electronic throttle, therefore I can not "blip" the throttle electronically.

My idea is when a downshift is needed, I send a signal to FULLY disengage the clutch electronically, then when the engine RPM reaches what is consider matched, I send a signal to shift.

Would allowing my engine to rev while the clutch is fully disengaged damage the clutch? Also, how is important is rev-matching? We already replace our clutch after a week of racing, would not rev-matching be that much of an issue?


texts: What are these mechanical components called? (assuming they are standard components)

texts:
These parts were salvaged from a special mechanical calibration rig. I don't see anything that looks like that in McMaster-Carr, but perhaps I don't know where to look.

The aluminum part is probably custom but the rod (300-series stainless steel) and the plastic (acetal, I think) threaded part with the brass handle look like standard parts. The aluminum part has an internal thread so the depth of the plastic part can be adjusted by screwing it in or out. The plastic part has a conical lead-in and a bore that fits the stainless steel rod with some play. I believe it acted as a pivot with springs to take out the play.


texts: Need advice on how to detect an object in the way of a closing door

texts:
I have a system design with a 149oz-in stepper motor for opening/closing a drawer style door. My cross sectional dimensions of the door opening are 20" width by 15" height. The motor actuates linearly inward and outward via remote user control. I'm trying to install various safety protocols, one of which is for physical interference during the state of which my system is closing or retracting the motor driven door. I need to efficiently handle the detection of such off-nominal events, where a human hand/finger or other interfering object is inside the opening during this state of operation. I want to immediately stop the motor (or shut off the entire system) upon sensing any physical interferences during the closing state in order to prevent crushing the impeding object with the retracting door.
For a reference point, the most relatable application to mine that I can think of is a kitchen dish washer door opening/closing via a remote controlled motor. I've looked into light curtain sensors, but I am unsure if these are suitable for my smaller sized cross section. To me, it seems that this would also be quite hard, if not nearly impossible, to incorporate something like this into such a limited space opening as well.
Thougths?


texts: Physical meaning of increment in static problem in abaqus

texts:
When we use Abaqus to solve the static problem, one step is to set:

Time period, the number of increments and increments size.

But since the static problem is not time-dependent, there is no time, which means the above time is virtual time. Then I was wondering how we look at those parameters in the static case.

Can we think that way:
The Time period is the real/physical total deformation time for the static problem and is scaled to 1. And its substep which from Time period/number of increments comes from the sub deformation which is also scaled.


texts: Is radius of gyration same for both types of moment of inertia?

texts:
We know that moment of inertia is commonly known as second moment of area. Which is $\int_{}{} y^2 dA$.

However there another moment of inertia called as mass moment of inertia given by $\int_{}{} r^2 dM$

Also we know that radius of gyration is by definition,

$r_{mass} =\sqrt{ \frac{ \int_{}{} r^2dM  }{\int_{}{}dM} }$

Similarly

$r_{area} = \sqrt{ \frac{ \int_{}{} r^2dA  }{\int_{}{}dA} }$

So my question is whether this $r_{mass}$ and $r_{area}$ are same for any arbitrary object? Of course the axes about which integral is evaluated are the same.


texts:
I am using a Magnet like this in an assembly and I am trying to calculate the torque in point P2 (see picture below) resulting from the attraction force F between my magnet and the steel part.
As I assume that the magnetic force is a volumetric one, I am not sure which distance to point P2 to take for my torque calculation.
In the case of an equidistant gap (no tilting) between the rotational symmetric Aluminium part which is carrying the magnet and the Steel part, I think the resulting Force can be seen as it is applied in the center of the magnet which is in a distance of L1 to P2?

Therefore, in this case the resulting torque around P2 would be: M=F*L1.
Please correct me if I'm wrong.
But in the case of tilting I am not sure which distance (L2 or LP) to consider for torque calculation.
As P1 is the only contact point between the two parts it might be the point where the load on the steel plate is applied?
This would lead to M_tilt = F*LP.

Thanks for your help!


texts: Evaluating a developed system by application of a case study

texts:
I am looking to the evaluation of a developed system to provide validity to my research. The system consists of manufacturing processes, procedures etc. and the plan is to implement the system at an industrial partner and manufacture certain products as cases for real-world evaluation.
Is this in fact a case study approach?
Myself as the researcher will obviously be involved in the implementation and operation of the systems, does this contradict the definition of a case study?
Are there other better-suited research methods for such an evaluation that I am missing? Possibly action research?
Are there research methods that can be applied prior to real-world implementation to assess such a system. In a type of hypothetical/prospective/illustrative manner?
Any input is appreciated.


texts: Joining two 2020 aluminium profiles to make a 2040profile

texts:
I recently bought a 2020 profile and after I got the product I realised that I needed a 2040 profile instead.

So, I was thinking of buying one more 2020 profile and connecting it with the 2020 profile parallel to each other to make it a 2040 profile.

I am trying to find a way I can do this using a joining plate so that I can easily assemble and disassemble it whenever required.

If someone can guide how? and where? I can buy the parts it would be great.


texts: Forces on a wheel during braking (Quarter Vehicle Model)

texts:
I have created a simple xcos simulation for quarter wheel using the equations given at the bottom of the image.

I understand the total torque on the wheel will be the braking torque and the friction torque. My question was right till the end the friction torque is really high( I am calculating mu from Burckhardt tire model). Even as the velocity goes to zero, the friction force gets higher (mu*mg). Is this realistic? Will a tire right up to the point it actually stops experience such high torque?
Thanks!


texts: I am attempting to cover an old half pit in a service station and convert the space into a paint booth. If i put a grid of 2ft x 4ft under the steel, how thick of sheet steel would I need to support up to a 10,000 lbs vehicle driving on it? Understanding that the load is divided between the four tires.


texts: Aren't there infinitely many orientations some given gyroscope angles could represent? (Generally understanding gyroscopes)

texts:
With two gimbals, the angles of the gimbals can effectively move to allow the flywheel to point in any direction with respect to the frame. This much is clear to me, since the flywheel direction is only one vector (as opposed to a coordinate system) and you only need two angles, like yaw and pitch or spherical coordinates, to rotate a vector to any direction.

I think the third gimbal has to do with the fact that, because the flywheel's direction is 'just' a vector, the flywheel's direction with respect to the frame orientation is not unique. You could rotate a given local coordinate system around the flywheel direction and every rotation would be a possible orientation with respect to the global coordinates (for a given flywheel direction in local coordinates).

I am not clear in how a third gimbal would fix that, though. Although in my head I can understand that yaw-pitch-roll rotation steps each occur by rotating one of the gimbals, and that together they give a well-defined orientation, I can't seem to reconcile that with the aforementioned fact that the frame's orientation should not be uniquely determined by the flywheel's direction.

Does that issue, as I suspect, have to do with the concept of gimbal lock? (which I am also having a bit of trouble fully understanding) At first I was under the impression that the main practical issue with gimbal lock was requiring very fast, frictionless movements (or even flips). I wasn't sure about the implications of "losing one degree of freedom" (I could see one angle was made redundant, but I thought without friction everything would still be normal after moving away from 90° pitch*). Now, my intuition says even under in an ideal, frictionless environment, going in and out of gimbal lock will mean that we may suddenly have switched to one the wrong orientations (as in, even if the flywheel direction is correct in local coordinates, the yaw-pitch-roll reconstruction of our orientation based on gimbal angles would be wrong).

What I've said so far may be somewhere between a little and completely off, but if it's close to correct, then my last question is: what prevents us from going into an incorrect orientation when not gimbal locked. For instance, if initially the flywheel is pointing along the roll axis**, then what prevents angles of, say, 0° yaw, 45° pitch, 0° roll from drifting to 45° yaw, 0° pitch, 90° roll (in both cases the flywheel direction would be the same in an aircraft's local coordinates).

P.S. It's hard to google for gyroscope because a lot of the results are about the sort of spinning top device that is also called gyroscope or about the gyroscopic effect.

 * In the case of using angles yaw-pitch-roll, applied in that order, to describe positions.

** If my understanding is correct, angles, starting from the initial/zero-angle orientation, are applied from inner gimbal angles first to outer gimbal angles last. Assuming the flywheel is in the inner gimbal, and considering the inner gimbal axis must be the yaw axis, it should be okay to have the flywheel pointing along the (initial) roll axis (and what would not be okay would have the flywheel pointing along the yaw axis, since it must be perpendicular to that).


texts: Can I use an optical fiber to direct a laser cutter?

texts: Specifically, a 100W CO2 laser. Are there any considerations other than the maximum power for a fiber?


texts: What constitutes progressive engineering experience?

texts: Many states require that a PE applicant have some number of years of "progressive engineering experience". Are there details as to what qualifies? For example, if an engineer is working in sales and not design, I would tend to think that would not count. But that's just my impression. Are there defined rules? General guidelines or standards of practice?


texts: PID tuning of a classic voltage controlled three-phase rectifier

texts:
I have a three-phase synchronous active rectifier

I need to control it with a voltage oriented scheme like this:

But I have no idea of how to tune multiple PIs, I'm trying to do it by trial but I need a "systematic" method.