texts: How can I find the length of 12 gauge wire needed for a cone of if I know it's surface area

texts: So I'm working on a personal project, and I need to figure out how much 12 gauge wire (which is ~2mm thick) I would need to cover a cone shaped rubber core, which has a surface area of roughly 3,417,810 mm^2. I have no idea where to start with figuring it out and would appreciate the help!


texts: How to use sample holder on Metallography specimen preparation machine Struers Tegrapol-21

texts:
In lab we have Struers Tegrapol-21 grinding and polishing machine. I use it for sample preparation. Usually I put 6 samples at once and prepare them with sample holder. However today I need to prepare 3 samples. I checked brochure and it's not clear. Manual wasn't helping either.

I'm trying to understand why do I use two different type of holders. Ease of loading is an issue however I'm looking to learn is there a difference in grinding/polishing performance. Why and when I should choose one over the other?

Here is photo of single holder (left), sample holder(right) and Tegrapol-21.

Question

Can I use sample holder for 3 samples?
Can I use single holder for 3 samples?
If both of them is possible which one is preferred?


texts: Does screed increase the slab tension capacity?

texts:
Does a screed applied over the slab increase the slab tension capacity?

Somehow it's counter intuitive because adding weight on the slab should tension it, but do the slab and the screed behave as a whole in this scenario?

What about a floating screed?

Which is the dependency between the slab load capacity (in N/m^2) and the total height of the slab / slab+screed (if they act as a whole)?


texts: How to calculate the torque for motors for a Core XY movment?

texts:
I am trying to design a simple setup that follows the core XY movement shown:

I have been researching the statics behind this movement in order to calculate the minimum torque for the motor so I would select the cheapest one required to move a platform. I currently know the mass of the platform and the estimated dimensions for the platform. Everything else is up to me to design. I have reduced the system to this:

But I cannot find anywhere whether this is the correct method of doing this. Could someone please help me?


texts: Calculate the relative pulling force as function of size for neodymium magnets

texts:
I want to optimise the size and shape of a magnet for a desired pulling force. (Please forgive my limited knowledge of magnetism).

A cylindrical magnet fixed to an object will hold it in place by placing a steel plate underneath. There will be a plastic sheet separating them. The poles are the ends of the cylinder magnet, (I know that's not ideal for maximising force); the magnet will be encased by aluminium.

What I Would like:

I will measure the holding strength of such a cylindrical magnet (known dimensions) directly on the steel plate. Given that, I hope to:
calculate the expected holding force of a similar magnet, with the variables being the new cylindrical magnet's dimensions, and the separator's thickness.
Accuracy is not crucial. (10-20% perhaps). Ultimately I will use that to optimise factors such as cost.

Factors that can be ignored:

Grade of magnet. (Assume materials and magnetisation are identical).
Thickness of steel plate: assume thick enough to simplify calculations.

I hope this is feasible!


texts: Traction mechanisms for a robot in confined spaces

texts:
I'd like to build an exploratory robot that can fit within confined spaces1.

What traction mechanisms should I consider to propel a robot along the inside of a 4" pipe?

The pipe to be traversed will likely have fluid (assume water) within it to varying degrees from partially full to completely full.  I'm initially planning on tethering the robot with coaxial cable.

So far, I have considered a 3 and 4 point wheeled approach, such as with a Y or X configuration of wheels.  And I have considered treads instead of wheels.  The robot will need to be able to navigate 90o turns on the way in, but can be hauled out via the coaxial cable if need be.  Preferably, it will be able to back its way out for the majority of the distance it can cover.

The robot would not need to climb unassisted.  The initial use will be in a pipe that drops several feet from the access point, and then slopes down approximately 5 feet over a 60 foot run.  Retrieving the robot will be assisted by the coaxial cable or a tether line.

1 It's a rather boring application, actually.  I want to see how badly the roots are creeping into the sewer line from my house.


texts: What is the difference between implicit and explicit analysis in ABAQUS?

texts: How can I choose between Implicit or Explicit Analysis in ABAQUS for a simple rectangular composite structure with 2 layers of unidirectional lamina? I am trying to do a linear-static analysis to capture the tensile strain for the specimen.


texts:
For the problem below, I tried solving it, but I don't know where I should get the value of normal acceleration, guess I was lost.

And here's what I solved so far


texts: Can a "surface drive" propeller be submerged if induced supercavitation reduces water surface area?

texts: Assuming induced supercavitation (like Supercavitating torpedo and Juliet Marine Systems Ghost) reduces water surface area does that reduce friction enough to submerge a surface drive propeller without a reduction in thrust if the reduction in surface area equals what would be on the surface?


texts: Why would experimental Mach #s in a wind tunnel be higher that Mach #s predicted by theory (inviscid) for the same nozzle geometry

texts:
The figure below shows the mach numbers across a supersonice convergent-divergent nozzle.
Since the experimental Mach numbers (calculated from measured pressures along the walls of the nozzle) take into account viscous forces, shouldnt their mach numbers be lower than that of the theoretical inviscid predictions? Similar to the trend of the CFD (viscous) calculations?


texts: What is Radial and Thickness Mode Vibration in a Piezo Electric Ceramic Disc Transducer?

texts:
I am trying to use a Piezo Electric Ceramic Disc Transducer for ultrasonic sensing measurements for fluid levels. A Piezo Ceramic Disc with a Resonant frequency of 215 KHz or 1 MHz is under consideration. These devices specify a Radial and Thickness mode vibration configuration.

Primary Question: What is Radial and Thickness mode vibration configuration?
Secondary Question: Is Axial and Thickness mode vibration mean the same mode?

Part Specifications
Piezo Ceramic Disc 1 MHz,Thickness mode vibration

Dimensions: 15mm diameter x 2.1mm thickness
Resonant frequency fr: 1 MHz±3 %
Electromechanical coupling coefficient Kt:≥39%
Resonant impedance Zm: ≤7.6 Ω
Static capacitance Cs: 900pF±15%@1kHz
Test Condition: 23±3 °C 40~70% R.H.
fr, Zm, Kp => Thickness mode vibration
Cs => LCR meter at 1KHz 1Vrms

Piezo Ceramic Disc R 215 KHz, Radial mode vibration

Dimensions: 10mm diameter x 2mm thickness
Resonant frequency fr: 215 KHz±5 KHz
Electromechanical coupling coefficient Kp:≥60%
Resonant impedance Zm: ≤6 Ω
Static capacitance Cs: 450pF±15%@1kHz
Test Condition: 23±3 °C 40~70% R.H.
fr, Zm, Kp => Radial mode vibration
Cs => LCR meter at 1KHz 1Vrms

References:

Modes of vibration for PIEZOELECTRIC elements


texts: What does "do not scale drawing" in a drawing sheet mean?

texts:
I opened a new sheet in Solidworks drawing, in the title block, there was a field written "Do not scale drawing". What does that mean?

There is a scale already being chosen over there. It was just a new sheet and the default title box appeared. I searched the internet but could not find any simple straight description about that.


texts: Why would a train automatically derail if a signal is passed at danger?

texts:
In a recent incident in London

  Network Rail said an empty train had travelled past a red signal, which resulted in an automatic derailment. No one was injured. [link]

The derailment has caused quite a bit of damage, and a lot of travel disruption along this track.

My reading of the National Rail statement is that the derailment was a feature of the system, a response to the signal being passed at danger. While I'm sure it caused less damage than a train collision, it still seems dangerous and expensive.

Things like train stops, to trigger the brakes exist, or one could imagine diverting the train into a sand trap. Why weren't options like these used instead of derailing?


texts:
For an electronics device that I make I use a standard plastic (I think polystyrene) enclosure. This enclosure needs to be precision-drilled, ant I lack the dedicated equipment. What I think would work is to pour some kind of mould on the outside of the enclosure and bore it as needed. I would then reuse the mould for drilling other enclosures.

And to the question - what material and thickness I should aim for for the said mould ?


texts: Modifying coil spring to alter rate progressively

texts:
I want to modify the coil springs in my car to lower it 1" without raising the spring rate, so simply trimming the overall length is not an option.  My idea is to remove material from along the top edge the active coils.  Obviously, making the rod diameter smaller will make it weaker so it will compress more under a given load.  This is where I will get my lowering.  I want a progressive rate, so I'm thinking I should remove material only from the first one or two coils.  In my head, this will yield a softer ride for normal driving on average highway irregularities when the spring is being compressed those first 2 inches or so.  Yet, it will be more resistant to the compression when under more load, such as on larger dips/humps and/or when the vehicle is loaded more.

So, if I were to remove material from the spring:

(1) Will the spring compress more and lower the car without increasing firmness?

(2) Will I actually get a progressive rate if I remove the material as described?

(3) What would be the difference between removing the material from, say, one coil versus spreading it along two or even three coils?  (The spring in question has 5 active coils)

Disclaimer:  I would remove material with a flap disc for better control and to minimize heat and to create a smooth surface to avoid stress risers.  I would also gradually taper in and out of the maximum amount removed from the coils instead of immediately digging in at the start and finish of the modified areas.


texts: How to find tributary area for a column when I have a transfer slab?

texts:
If I have a transfer slab in the basement level how to find the tributary area for the columns because the columns in the upper floors have different location and tributary area than that of the basements.

Please if possible to show an example


texts: How can the ink dry so quickly after it comes out from an inkjet printer?

texts:
Every time I print a page with my inkjet printer, knowing that it literally "jets" ink all over the sheet, I'm baffled by how it's immediately dried. I cannot smudge it with my fingers even if I try. They can be instantly stacked on top of each other without anything coming off. Even large photos covering the entire standard A4 page with ink, it's still somehow all dry. It just looks wet for a bit. But it isn't really.
How did they achieve this fancy "insta-drying" ink? How long has this existed? Is this how ink always behaves? I thought it was infamous for making a mess constantly back in the day?


texts: How do cavity resonators differ from tubes of uniform width?

texts:
I read that wine bottle produces sound when u blow sideways onto its rim because
some frequencies of the white noise produced in your mouth gets amplified when they match the natural frequency of the bottle. But is the tight neck of the bottle necessary for this to happen? If I blow into a closed end tube with uniform width, can't I produce the same effect? Why do I need the small opening?


texts: How well would viscoelastic damping work between isogrid- or honeycomb-faced constraining layers?

texts:
I'm considering doing some experiments with 3D-printed surfaces and sound transmission with constrained layer damping.  I've also been thinking about using isogrid or honeycomb interior surfaces, which got me wondering:

Let's say I had a honeycomb sandwich that was cut through the middle back into two sandwich faces, each face having one side flat and the other side exposed honeycomb.  If I then sandwiched the faces back together with a thin layer of viscoelastic polymer in between the honeycomb sides, would I expect more or less damping than with the same constrained layer between solid faces of equal thickness?  Has there been any prior work on this?


texts: Strength of Plastic Underwater Domes with various thicknesses

texts:
I'm currently researching the strength of domes underwater and I went down the rabithole of material science. The basics of this research (or though experiment) is to bring a dome filled with air to the seafloor and see if it implodes or not. The specifics are as follows.

 The dome is 3D-printed
 Outer Diameter: 10 cm
 Inner Diameter: 8 cm (so the thickness of the dome is 1 cm) (this can vary)
 Material: PLA

QUESTION: What is the maximum amount of pressure this dome can take before it breaks?

I've already found the following data from this source

Properties PLA:
 - Impact strength:
   - STD: 1.8 ft-lb/in
   - MAX: 4.1 ft-lb/in
 - Compressive Strength
   - STD: 2600 PSI
   - MAX: 13600 PSI
 - Tensile Strength
   - STD: 6783 PSI
   - MAX: 9531 PSI
 - Flexural Strength
   - STD: 8970 PSI
   - MAX: 13731 PSI

It seems likely that I'll be needing the compressive strength here, because the theoretical dome is being put at the bottom of the theoretical sea. It's going to be compressed. But these numbers have very little context (at least for me, I don't have an engineering degree). I mainly worry about thickness. In my mind, when a wall is thicker, it means it can hold more weight, can withstand heavier punches and generally breaks less easily. I don't see this reflected in this number. It also doesn't take the shape of the object in mind. A sphere is supposedly  stronger then any other shape (I found this cool site selling dome bunkers). But this too doesn't seem reflected in the compressive strength value.

It might also have to do with the size effect, but that seems to weaken - not strengthen - structures and would only be applicable if I made the outer diameter variable.

If anyone can help me any further it would be very much appreciated. I really want to make clear that I'm not asking you to do my homework (this isn't really homework, but still). Pointing me vaguely in the right direction is also extremely helpful. Thanks in advance!


texts: How can i move a 5000 lb object with 1500 pound towing capacity?

texts: I'm getting a shipping container delivered to my property that weighs about 5000 pounds. Once it's delivered I will need to re-position it. I'm thinking of trying to use a number of cylindrical logs, together with some mechanical advantage to move it. My car has a towing capacity of 1500 pounds, so I'm contemplating getting a 6:1 block and tackle, effectively allowing my car to pull 10,000 pounds. I'm a little iffy on a few points though. What is the actual force that is required to pull a 5000 pound container over rolling logs on grass ( slope will also factor in) I have no idea what the coefficient of friction is here. Does the rope that feeds the pulley have to be able to withstand the full force or just 1/6 of the force? Assuming I need an anchor point, does the anchor point need to hold the full force of the pull? (any suggestions on how I can create an anchor point in a grass field .... was thinking maybe driving a steal pipe down a few feet at an angle). What else am I missing?


texts: Solar power, Battery power to mains voltage

texts:
My question is what is the most efficient way to convert 48V D.C. to 220V A.C. Not the easiest or most cost efficient but the most efficient electrically?

Also if anyone has any cheats on the best way to resupply LED House light fittings that were originally 220v supply to 48V dc I would be grateful.


texts: Is Vapor Compression Distillation inherently more efficient than a thermal-only boiler-condensor?

texts:
I'm having a hard time understanding the benefits of VCD (like Slingshot) over a conventional boiler in terms of volume of condensate produced per unit of energy input.  I've found quite a few resources explaining (in too much detail for me to fully grasp) the operation of VCDs ([A], [B]), but I haven't come across (or understood maybe) any explaining why compressing the vapor is either necessary or more than marginally advantageous.

Here's what I think I understand: inlet water comes into the system, flows through a heat exchanger to be preheated by outflowing condensate, bringing the inlet water as close to the boiling temp as practical. It's then boiled by heat exchanged from the compressed vapor (above atmospheric pressure and normal boiling/condensing temp), producing low pressure vapor that feeds into the compressor. Let me know if I've got this wrong.

I can see how this would be a closed system and could be very efficient, but it seems to me (erroneously, I assume) that a non-compression boiler could be (very nearly) as efficient. Is the higher temperature difference between the compressed vapor and inlet water the main advantage?

I've seen several sources focus on how the compression stage raises the condensation point. Beyond increasing the temp difference across the heat exchangers, it seems like this would also push the point (or zone) where the vapor condenses further downstream in the heat exchanger and a larger share of its length would be filled with vapor than without compression. Is there an advantage to this? Seems like the lower mass (vapor vs. liquid) would transfer less total heat, even with the larger temp difference.

I'm sure I'm looking at this wrong, but I can't see where. Any thoughts?


texts: How to estimate a mass-spring-damper parameters in MATLAB using RLS and OLS?

texts:
Assume that we have the differential equation of a mass-spring-damper model as follows:
$$
m\frac{d^2y}{dt^2}+c\frac{dy}{dt}+ky(t)=F(t)
$$

How it could be implemented in MATLAB to do the following steps:

First, convert the differential equation to a difference equation.

Second, finding the discrete-time transfer function of it.

Third, finding the regression equation of this system.

Finally deriving Recursive Least Squares (RLS) and Ordinary Least Squares (OLS) to estimate the free parameters of the system ($m$,$c$, and $k$).

More information on this system is available at Mass-Spring-Damper System Excited by Force F(t)

Any help is greatly appreciated


texts: What is a good non-combustible oil to be used in air compression regenerative braking/energy storage system for cars, buses, and trucks?

texts:
An important energy storage method that is being given very little consideration is gas compression.  The kinetic energy of the vehicle can drive an air pump or compressor that would compress air into a tank specially designed for pressures and heat of compressed air.  Later the energy stored as compressed air can be released through a regulated nozzle to convert to electrical or mechanical energy.

The air pump would be connected mechanically directly to the drive train or the wheels or axle to have the braking effect.  The storage process is not efficient as much heat is generated with the compression.  However, the energy can be stored in the compression tank for a very long time with little loss.  The capacity for energy storage is only limited by the volume of the storage tank and the maximum design pressure.

Special consideration has to be made for the lubricating oil used for the air pump/compressor.  It has to be non-combustible other wise it will ignite with the oxygen in the heated compressed air.  This would rule out most hydrocarbon based oils.


texts: Does Bitrate on sound files refer to bit/s or byte/s?

texts:
I'm trying to understand the bitrate calculation of a sound file(wav - uncompressed) which is showed in a mobile app. I've searched on the web and found out the bitrate calculation as below:
bitrate = sample_freq X number_of_channels X bit_depth

So if I have a stereo sound file with 48 KHz sampling frequency and 16-bit sampling depth, the result is: 48000 x 2 x 16 = 1,536,000 bit/second which corresponds to 192000 byte/second. But they represent it like 192 kb/s.
But as I know kb/s means kilobit/second and not kilobyte/second. I also used online calculators and all of them show it as kb/s.
What am I missing here?


texts: Is it possible for a bicycle chainwheel to have a fractional number of teeth?

texts:
Background

In the world of bicycle motocross, also known as BMX racing, gearing is a hotly-debated topic.

Since the bikes are all single-speed, gear ratio is a fixed number defined as chainwheel / cog (front gear divided by rear gear). Altering your gear ratio is understood as an immediately-noticeable tradeoff between acceleration and top-end speed.

Here is a series of common gear ratios:

╔════════════╦═════╦════════╗
║ Chainwheel ║ Cog ║ Ratio  ║
╠════════════╬═════╬════════╣
║         43 ║  16 ║ 2.6875 ║
║         41 ║  15 ║ 2.7333 ║
║         44 ║  16 ║ 2.75   ║
╚════════════╩═════╩════════╝

In 2012, a company called Rennen Design Group created a supposed breakthrough innovation called "decimal gearing". The claim is that through manipulations of tooth profile and ring diameter, in-between gear ratios can be created - for example:

╔════════════╦═════╦════════╗
║ Chainwheel ║ Cog ║ Ratio  ║
╠════════════╬═════╬════════╣
║ 43         ║  16 ║ 2.6875 ║
║ 45.7       ║  17 ║ 2.6882 ║
║ 37.7       ║  14 ║ 2.6929 ║
║ 43.1       ║  16 ║ 2.6938 ║
║ 41         ║  15 ║ 2.7333 ║
║ 41.1       ║  15 ║ 2.74   ║
║ 52.2       ║  19 ║ 2.7473 ║
║ 44         ║  16 ║ 2.75   ║
║ 44.2       ║  16 ║ 2.7625 ║
╚════════════╩═════╩════════╝

Note: Table is not exhaustive.

For example - a 44.2 tooth gear actually only has 44 teeth, but the tooth spacing, tooth profile, and chainwheel diameter is supposed to have been manipulated to create a larger gear.

In the world of BMX racing, the existence of in-between gear ratios like this is a Really Big Deal. Since the man behind Rennen has a Master's from MIT - and since most BMXers would rather hit jumps than do math or measure things - nobody has really ever checked up on whether or not this is valid. Some questions were asked a long time ago in the dusty corners of a BMX forum, but the testing methods didn't properly control for all variables and the thread descended into a bunch of name-calling and ad-hominem attacks.

The Actual Question

Is this physically possible?

I understand "gear ratio" to be defined as:

  For a given gear ratio x / y, one rotation of the gear with x teeth will result in x / y rotations of the gear with y teeth.

For a gear ratio of 44/16, one full rotation of the 44 tooth gear (chainwheel) should result in 2.75 rotations of the 16 tooth gear (cog).

So for a "decimal ratio" of 44.2/16, one full rotation of the 44.2 tooth gear (which again - only has 44 teeth) is supposed to result in 2.7625 rotations of the 16 tooth gear.

My biggest reservation is the fact that a chain-driven drivetrain is a TIMED DRIVETRAIN. No matter how big or small you make the teeth on the chainwheel, if they fit the chain, they're only going to push as many links through per rotation as the chainwheel has teeth.

For a true 44.2 tooth chainwheel, one would expect that 442 links get pushed through over 10 full rotations of the chainwheel - but that's not the case. Only 440 links will ever get pushed through to the cog because only 44 links get pushed through per full rotation of the chainwheel. I actually spent my whole afternoon yesterday taking video and counting links and measuring.

But I'm not a scientist. My high school didn't even offer a physics course. I'm just a racer that trains really hard and knows how to do basic math.

If this were a belt-driven system, I would completely understand how a manipulation of the chainwheel diameter would change the effective ratio - but it's not. It's a timed drivetrain, limited by the physical dimensions of the chain.

I have several hundred dollars and months of training and metrics invested in these stupid chainwheels. If someone could confirm or deny my theories, I would really appreciate it. I just want some closure.

Here's a photo of the teeth from a 41 tooth chainwheel on top of the teeth from a 41.2 tooth chainwheel - both are Rennen gears:

Here's a 41t on top of a 41.2t:

Here's the 41.2t on top of the 41t, from behind:


texts:
I have to draw a part sectional view of a valve for a project. A 3D view of the valve is supplied and a line AB denotes where the part section is to be. It says:

"The part section is to be to the left of AB"

Does this mean to section part of the area left of AB and not section the right of AB. Or does this mean to section all of the area left of AB and not section the right?

Thanks.


texts: How is the long term reactivity of implant materials evaluated?

texts:
Various materials are implanted within the human body as a result of of medical need.  Dental implants, stabilizing plates, arterial stents, and orthopedic replacements are all common examples where a material is implanted within the body.

The typical response of the immune system to any foreign body is to attack the implant.  If the immune system cannot eradicate the foreign body, then it attempts to encapsulate it instead.  This self-preserving attack from the immune system can lead to implant failure, and the likelihood of failure is, in part, dependent upon the bio-reactivity of the material.  For example, stainless steel has been evaluated to be less reactive than more base steel alloys, and titanium has been found to be less reactive than stainless steel.

How is bio-reactivity characterized, and how is it measured over the conditions of a long term implantation?


texts: I'm designing a 5 axis CNC, and preloading my lead screws has never been an issue for me,  but for the first time,  I find myself needing to preload a worm gear.  How is this done, and what's the best way to do it?  Thanks.


texts: Do cars that automatically turn off engines at idle save any significant fuel?

texts:
There are many new cars now that automatically turn off their engines when stopped at traffic lights.  They then automatically turn them on when moving off.  These systems have many names along the lines of active or eco .

The manufacturers claim that these systems are to save fuel, reduce running costs and save polar bears.  At the same time there are no published figures detailing the economies involved.  Is this just marketing hyperbole?  It seems to me that switching your engine off when it's at a warmed up idle is absolutely the last place that would generate any fuel saving worth printing.  Most cars idle at ~ 0.3 gallons per hour anyway which is nil in the context of a typical trip.  These systems also require a larger alternator, battery, and starter motor. It's a con init?


texts: How do I represent equations of motion of a dynamic system in State Space?

texts:
I'm going through some vibration theory and I need to represent the equations in state space for vibration control.

The main forced general equation of motion is:

$$\mathbf{M{\ddot q}+{\Omega_c}G{\dot q}+{[K_b+K_m-\Omega_c^2K_\Omega]q}=T(t)+F(t)}$$

$K_b$: bearing stiffness symmetrical matrix
$K_m$: mess stiffness matrix
$K_\Omega$: diagonal centripetal stiffness matrix
$T$: applied external torque
$F$: static transmission error excitation
$q$: the vector with the traslation and rotational coordinates for the sun,ring and carrier

If I'm not mistaken, for this equation the input variables would be the forces $F(t)$ and $T(t)$ plus the $q$ terms, which would form the $B$ matrix and $u$ input vector in state space form.

But for the free vibrations I have the equation:

$$\mathbf{M{\ddot q}+{[K_b+K_m]q}=0}$$

Would the input variables in this case just be equal to zero?  and the output variables just $\mathbf{{\ddot q}} $ ? I'm also trying to code this into Matlab and Maple, which can directly get me the state space form of really long equations by just inputting the equation, input variables and output variables.


texts:
Hi I am making a beam model using Abaqus. There are two beams created. I wanted to join two beams rigidly in the connection to transfer moments between beams. However, I do not know what connector or constraint should be used to complete such a task.

Here is the model I used, I created chain wire at the same point and created the following as a connector section to be assigned to this wire set. However, it does not work and give error:"Node set assembly_Part-1_Part-refpt_ has no members and will be ignored. Nodes defined in this set may have been deleted because they were not connected to any elements.".

Please help to solve this connection problem. Thank you!!


texts:
The question is not to help me get my task completed. There is the 3D statics problem that I have been attempting to solve for a long time. I have no help, hence I would like to pose you a few questions to ensure I am on the right road to end the task.
Some translations: silinder means cylinder (a kinematic pair - joint); sein is wall, and ramp stands for ramp in English. A white sphere is a vehicle, whose mass is defined as a force $F_v$ - the cylinder has it, but we neglect it, because $G_s \ll G_r $ and $G_s \ll G_v$, so we set it to be nearly equal to zero.
The task is to determine reactions at A and C.
As my lecturer states, I have to write the equilibrium equations, starting with the moments of forces. If I write the equation for moments at A about the axis $x$, then I get $R_C$. Also, he informed that the reaction at B is none or, equivalently, there is no reaction at B. Okay, we are going to determine the resultant vector of the system, given by
$$\vec{R}=\sum_{n=1}^{m}\vec{F_n}=\vec{R_A}+\vec{R_C}+\vec{F_v}+\vec{F_h}=0$$
From this equation, we get the connection between $R_A$ and $R_C$. Moreover, we find $Y_A = F_h \sin \alpha$, because $Y_C = 0$, seeing that it forms the angle $\pi/2$ with the axis $y$. - This my first mistake: $R_C$ forms the angle $\beta$ with the plane $xy$, hence $Y_C \ne 0$
Proposal 1. We can reduce the system to the point $A$ by determining the main vector and moment. Setting them to zero, we acquire equations.

Proposal 2. I tried to bring the problem to the one which I know how to solve; in other words, I know how to solve 2D beams, why not consider the problem as a complex one. That is, I wish to consider the planes $xy$, $xz$ and $yz$ separately. On which plain, I can compute moments through points. For that, I project all forces onto the planes and consider the equilibrium of each part. This might be of help to construct diagrams of bending moments in 3D beams - this is my conjecture.

For those, who are interested in the task:
On the picture, the lifting, inclined ramp with the braking vehicle is depicted. We assume that action is with the emergency load situation, where there is one lifting cylinder and one pivot (hinge) is broken. The vehicle weighs about 2.5 tons and we assume that while it is braking, the force $F_v$ become maximum $F_h = 0.3 \cdot F_v$. Ramp itself weighs10 tons and cylinder weight can be neglected. Determine reactions at the points $A$ and $B$. The width of the ramp is $b$ and the length of it is $l$. Hing $A$ and cylinder attachment $B$ are at the distance $b/2$ from the mid axis (centroid axis). The angle between ramp and cylinder is $\beta$. We also assume that the vehicle is at the distance $b/4$ from the centroid axis and at the distance $3l/4$ from the wall. At both Cylinder's ends on spherical pivot joints.


texts: Calculating the radius of a hole for a desired outflow rate

texts:
I am tasked with finding the radius of a hole at the bottom of a tank to obtain the desired outflow rate when the tank is full.

The tank is a cylinder with dimensions Height: 4.8m and Radius: 1.79m. It holds roughly 48316.6897 liters of water.

I have already determined $C_d$ (The coefficient of discharge) to be 0.6372.

The outflow rate I desire is 3500 liters per hour.

I know that $\frac{dh}{dt}= \frac{a_0C_d\sqrt{2gH}}{A}$. where $a_0$ is the radius i need to obtain, and $A$ being the surface area.

From chain rule I can get $\frac{dh}{dt}$ in terms of radius and $\frac{dv}{dt}$(The desired outflow rate)

$\frac{dh}{dt} = \frac{\Delta{V}}{\pi r^2} $

Now I let them equal each other

$\frac{\Delta{V}}{\pi r^2} = \frac{a_0 C_d\sqrt{2gH}}{A}$

This gives me the equation
$$a0=\frac{\Delta{V}}{C_d\sqrt{2gH}} $$

Now, substitute in what we know

$3500$ Litres per hour is $\frac{35}{36000} \frac{m^3}{s} $

$$ a0 = \frac{\frac{35}{36000}}{0.6372\sqrt{2\cdot 9.8 \cdot 4.8}} $$

According to this $a_0$ is $0.157304491$ millimeters in radius.

I am doubting my calculations because $3500$ liters going past a hole of radius $0.157304491$ millimeters every hour seems absurd.


texts: Controllability of $x' = Ax + Bu(t)$ implies controllability of $\left \{ \begin{matrix} x' = Ax + By \\ y'=u(t) \end{matrix} \right.$

texts:
Suppose that the system
$$x'(t)=Ax(t)+Bu(t)$$
is controllable in $\mathbb{R}^n$, where $A$ is $n \times n$, $B$ is $ n \times m$ and $u(t)$ is $m \times 1$
Show that the system
$$\left \{ \begin{array}{rclccc} x'(t) &=& Ax(t) &+& By(t)& \\ y'(t)&=&&&&u(t) \end{array} \right.$$
with the additional states $y\in\mathbb{R}^m$ and input $u\in\mathbb{R}^m$ is controllable in $\mathbb{R}^{n+m}$.

My attempt

If the first system is controllable, then the matrix
$$M = \begin{pmatrix} B & AB & A^2B &\ldots & A^{n-1}B \end{pmatrix}$$
has rank M. Let the second system
$$\begin{pmatrix}x' \\ y' \end{pmatrix} = \begin{pmatrix} A & B \\ 0 & 0\end{pmatrix}\begin{pmatrix} x \\ y\end{pmatrix}+\begin{pmatrix}0 \\ I \end{pmatrix}u(t)$$
Then, its Kalman matrix (aka controllability matrix) is
$$\bar{M} = \begin{pmatrix} B & AB & A^2B & \ldots & A^{n+m-1}B \\
0 & 0 & 0 & \ldots & 0\end{pmatrix}$$
The matrix $A$ is $n \times n$ and, by Cayley-Hamilton theorem,
$$A^{n+l} = \sum_{k=0}^{n-1} \alpha_{k,l} A^{k}, l=0,1,...$$
I mean, $A^{n+l}$ is a linear combination of the first $n$ powers of $A$. This implies that we have $n$ linearly independent columns in $\bar{M}$ at the the terms until $A^{n-1}B$ (because the first system is controllable). But I don't see how to find the other $m$ columns. What am I doing wrong?
Probably my controlability matrix is wrong, since it only can have $n$ l.i rows.

We could solve it for $y$ first and return to a system only in $x'$, substituting $u$ by some $\int u$. The Kalman matrix of first and second system would be the same and, by hypothesis, it would have $\text{rank }n$, correct? But why isn't my first approach correct?


texts: Why do stress concentrations really occur?

texts:
From doing some research I've learned that internal stresses inside an object can "concentrate" on sharp edges, as shown in the above picture. For that reason we often make fillets so that the change in diameter is smoother and we get a smaller stress concentration.

But why does the stress concentrate on sharp edges? From Googling I've found numerous inadequate answers, such as imagining "stress flow lines" getting packed at the sharp edge. Here I can see an analogy to electromagnetism, where we talk about flow lines of an electric field, but what is "flowing" here? What do the lines represent?

Intuitively, I can imagine this: If we press the object on the left in the above picture, there is a higher stress after the edge, since there is now a smaller area enduring the same force. Hence the stress is higher. But this does not explain why the stress concentrates at the edge. I mean, even with the fillet, the radius decreases anyway, so why is there not a similarly high stress on the right of the fillet?

Similar effect also occurs when we have a continuous piece of material with a hole in it. The stress is the highest around the hole.

Once again, force lines, what do they represent? Again I can see the similarity to electromagnetism. But what kind of a force field are we talking about here?

One source I found simply explained that we can use methods like finite element analysis to confirm this concentrating of stress does happen. But this is not an explanation either. Use of FEA implies there is some kind of differential equation to be solved, so what kind of theory is there behind it?

Thank you!


texts: In order to soundproof external noise, do I need to build wall stud on concrete walls?

texts:
I assume this wood framing is the wall stud.

My room looks like as follow with concrete walls

In order to soundproof external noise into my room (red circle), do I need to build wall stud?


texts: How to go about attaching a rotary table to a mounted bearing?

texts:
I'm new to all of this and am working on a project with someone. They mentioned using this kind of a rotary table, Velmex - Motorized Rotary Tables:

and mounting it on a flat horizontal surface using a mounted bearing of some kind - like this but larger, Pillow Block Bearing, Number of Bolts: 2, Ball Bearing Type, 7/8" Bore Dia.:

The descriptions that I'm reading are saying that the rotary table comes with bearing of its own? So I'm confused if this is something that's possible. I'm going to look through some more diagrams of the rotary table and see if I can see how a shaft would go through

You don't need to tell me how it can be done, just if it is something that's possible because my other idea was using an L-shaped clamp, something like this, Large L Shaped Clamp with Extra Holes for Mounting:


texts: Why does this glass tend to stick on surfaces

texts:
I have a glass here.
This is the bottom face of the glass.

Now this is on what I had kept my glass. There is a little much of water spilled on it. Let us call this thing as C

Now , when I lifted the cup. The C on which I had kept my glass also lifted up. The bottom portion of glass and the top portion of the thing were in contact. They did not leave each other.
Now , the bottom portion of the cup is flat. So, I kept my glass on that C. The cup and the C both lifted up. Why is it like that ? They should not do this.


texts: I have two abs pieces that I would like to create a waterproof seal between via compressive force via fasteners like screws. How much do o-ring/gasket compress? Certainly it is dependent on the material and how much pressure is applied, but are there any resources on this? There is a pocket on one of the abs pieces that will be mating with the other piece on the bottom with very tight tolerances, as I plan to put something in the pocket and seal it with the second abs piece.


texts: How to calculate the forces on members of a frame, due to a distributed pressure load?

texts:
I am trying to calculate the force sustained on the three labelled members of this frame (Members 1, 2 & 3). The frame will experience a uniform pressure of 1000 kPa in the area enclosed by the members. It will be screwed into walls on all 4 sides. You can imagine it as being installed in a 4m by 4m shaft. And the goal is to brace a door in the shaft, which might experience wind pressures of a 1000 kPa. Once I have found the force I will calculate the deflection in order to select the correct steel members for the frame.

For those curious, I just made up the numbers and the scenario but I am working on a similar situation and it’s been many years since I studied statics. Any help or guidance would be appreciated.


texts: Would an object at the bottom of the sea still experience buoyancy?

texts:
So I understand that buoyancy happens because the fluid exerts larger amounts of pressure from beneath an object compared to above, like in this picture

So my question is, what if the object is forced to the bottom of the container, so that no fluid is beneath it. The logic is, if there is no fluid beneath, there is nothing to push it up. So, would that object still experience buoyancy? If yes, why?

edit: interesting to see some answers disagreeing with each other. One thing to note - according to my textbook buoyancy is a force that happens because of hydrostatic pressure - it has nothing to do with density of the objects. So those who say then can will experience buoyancy because it is less dense are wrong I guess, that is not buoyancy.


texts: Derivation of beam slope for a cantilever beam

texts:
I am trying to derive the maximum beam slope formula $\theta = \dfrac{wL^3}{24EI}$ for this cantilever beam:

What method can I use for this derivation? So far I can only find simply supported beams and derivations for the $\theta_{max}$ formula at the free end (e.g., "slope at free end" column of this table). I tried doing it by hand, but I cannot seem to get to the correct answer.


texts: Cause of stepped crack up and away from lintel

texts: What are the likely causes of a stepped crack up and away from the edge of a lintel? See the diagram below.


texts: Why conduct experiment for load distribution within three triangulated structural frameworks when you can calculate theoretically

texts: So we are doing this project on conducting an experiment to investigate the Statical Equilibrium of Plane Frameworks. Why do we need to conduct such experiments when we can easily calculate by hand and by pin-joint analysis.


texts: Why are roads straightened when widened?

texts:
When widening a road, why does construction seem to inevitably include a "smoothing" out of the curves on the road, essentially making it more straight?

I've seen this personally on roads where I travel, and you can even catch a glimpse on Google satellite imagery of roads that are in the widening process: Google overlays a "ghost" lane to show where the new lanes of the road will be. It's faint, but you can see an example here on a road near Flowery Branch, GA:

Is this the engineers' way of correcting previous mistakes, or a response to devleopment that's sprung up around the road since its initial construction, or safety reasons? Or something else entirely?


texts:
If I understand it correctly in a CO2 laser engraver/cutter the laser itself is fixed in position and mirrors are used to redirect the laser to the material.

Is there some mechanism used to keep the focal point on the material or is the focal point set to the midpoint of the machine's range? Wouldn't the beam be wider at the edges of the machines travel?


texts: Metal detectors for medical applications

texts:
My group and I are currently working on a biomedical engineering project for our class. Our design idea is a wearable metal detector that uses metallic tracers in the blood to determine the concentration of glucose in the blood. There are multiple aspects of this design, but we wanted to reduce this project down to a proof of concept. We want to make a metal detector that is REALLY sensitive that can detect objects that we can make as small as possible (think iron fillings) that could simulate the tracer.

We plan to use an Arduino to read the changes in coil inductance. The main problem that we are running into is that, being biomed majors, we do not really know much about the electronics and circuits that will make this concept work. We found a few circuits for metal detectors, but we really don't understand what's going on in them. Here's a link to one that I found http://3.bp.blogspot.com/-iu_ERGb6vzQ/Ue2DyIWZYFI/AAAAAAAAAd8/yl2Wk05B37A/s1600/IMG_20130722_202500.jpg.

Main questions so far:
Can someone explain whats going on in this circuit? What would the input and output waveforms look like?
Can we use a simpler circuit and still get around the same sensitivity?
If we want a more sensitive detector would a small coil with a ton of turns be a safe option?
We'd like to use two coils concentric setup (one transmitter on receiver) would that add to sensitivity?

Thanks in advance!


texts: Injecting CO$_2$ into water: how does injection work?

texts:
I've been wanting to design my own water carbonation device for a while.
For reference, I've been looking at devices like the Sodastream, which injects pure CO$_2$ into water to dissolve it with up to seven injections per bottle. The more injections, the higher the CO$_2$ contents. I have not actually built anything yet; for now I am just trying to understand how it works.

I'm assuming that the device keeps the pressure constant, but the CO$_2$ doesn't dissolve all at once and needs multiple injections to get to the right carbonation level.

Assumption: the device opens the valve for a set amount of time with a known pressure, which releases a certain volume of CO$_2$ into the liquid.

I would assume that injecting the CO$_2$ creates a lot of small bubbles which increases the effective contacting surface area, leading to faster mass transfer.

Through calculation and use of Henry's law + an approximation for the solubility constant I've found a temperature and pressure range for my desired carbonation levels: temperature 15 °C and pressure 2 bar CO$_2$ for a desired 4 g/L CO$_2$ (perhaps with variable pressure and/or temperature to control the carbonation levels).

I have a few questions related to this:

How can I apply my desired pressure and carbonation level to a direct injection method?
How long would I need to inject, and how many times? Is there a relationship with injection pressure(preferably a formula if available)
If the desired carbonation level isn't achieved after a single injection, how far would the injection pressure need to be raised?
Is there any theoretical description of this process available?
Is direct injection of CO$_2$ an efficient method of carbonisation, or are there better/cheaper/more efficient ways to dissolve CO$_2$ in water as fast as possible?

Edit: I have a background in analytical chemistry. Any engineering knowledge is self-taught. I never received (much) formal education on subjects like fluids/gases/physics, so I hope the information I've provided is applicable to some degree.

(If you require any further information please let me know.)
(originally posted on SE Physics, they recommended me to ask here)


texts:
Which is stronger, a round sign post or a square-cross-section sign post?
I will be using one or the other to hold the top corner of a shade sail. I tried an aluminum pipe but a strong wind on the sail bent the pipe. I am about to buy a 10-foot-long sign post because they look stronger than the pipe. I found online a 2 by 2 inch square-cross-section post with a lot of holes in it. The steel is 14 gauge (0.0781 in) thick. I also found a 2 inch diameter hollow cylindrical post with no holes in it. The steel is 16 gauge (.065 in) thick. Which one should I buy?


texts:
I'm looking to rivet two sheets of aluminium together with the pop type.  I've researched that 3.2mm rivets should go into 3.3mm holes.  (Who has a 3.3mm drill bit?)  That's not a lot of clearance, which I understand is part of the concept to allow adequate development of shear capacity.

However, how do I practically do this for a row of 20 rivets?  I don't think that I can pre drill 20 holes to a tolerance of +/- 0.05mm.  Certainly not on my cheap 250W pillar drill.  The "How to Rivet" demonstrations on line only show the basic use of a rivet gun on one rivet.  How would I join two sheets with a row of pop rivets?


texts: Difference between Hysteresis, low pass filter and deadband in control theory?

texts:
I am trying to understand the fundamental difference between the following terms in the context of control systems:

Hysteresis
Low pass filter
Deadband

Are these just fancy names that can be tweaked to provide same result? By tweaking I mean some intelligent way of formulating the variables, such as using the absolute value of the output variable, instead of delta between current and previous value.

I can conceptually think of examples where the same behavior can be achieved by how we tweak any of the above three techniques. However, I am concerned that such tweaking is essentially changing the fundamental meaning of the term itself.


texts: Part load definition with respect to hydraulics

texts:
I have read that variable speed hydraulic drives have very low part-load efficiency - due to losses in the internal pumps and motors.

What is part-load?


texts: Build new home on top of 50 years old house

texts:
We have a home, which built before 50 years, now we are planning to built one more home on top [ terrace] , Is it right to go ahead & built new home on terrace ?

or do we need to check any other things before building new home ?

As the current home is 50 years old, will it survive if we build new home on top ?

Our Main intention is to keep the terrace secure....


texts: How to decode radio thermometer / hygrometer bytes to floats?

texts:
I'm playing around with a radio receiver on 433MHz and I am receiving signals from a temperature / humidity sensor.

I already figured out what bytes represent humidity, but I'm stuck with the temperature as I don't know how it is represented in the signal.
Here are some example messages I receive:

C1 | 75.2F | 70%
0001010001010011010000000100100000000100011011010111000011
C1 | 24.1C | 68%
0001010001010100100000000100100000010100010000000001000011
C1 | 24.1C | 56%
0001010001010100100000000100100000010011100001010110000011

The temperature sensor has the following readouts:

Temperature
Humidity
Unit (Celsius / Fahrenheit)
Channel (1-8)

I already figured out what the humidity is as well as what represents the channel. I also figured out a temperature range(?) [1 = ..-11 | 2= -1..-10 | 3= 0..15 | 4= 15..30 | 5=31..40]. But I have a hard time figuring out where I can find the exact temperature or the unit (F/C).

I prepared this public Google Sheet with my findings and raw data so far (sorry I don't know a better way to share on Stackexchange):

https://docs.google.com/spreadsheets/d/1q2sk5bK6Bv3gi8ahTLIUM4DaMR7AvnTVPY-NvmGMHoQ/edit?usp=sharing

(the channel with a zero based index I already figured out is violet, the humidity is in blue, some bits always stay the same hence I made them grey)

What is my best course of action now? I have been trying around with all the bits and bytes, adding them together, adding the one to the other, multiplying the temperature times 10 to get a decimal... nothing.

Yeah... Plotting is an idea, but it doesn't really help me:

Column I seems to follow the temperature in a way (negative temperature/high temperatures and the values just don't relate, look to the end of the graph), but looking at the decimal representation of I can see values such as 7,8,9 and wildly changing temperatures. I am assuming there is some kind of correlation between the temperature range and this byte but I haven't figured out yet how to achieve the calculation.

Alright I found something:

The temperature ranges in correlation with I & J seem to be the key. I & J corresponds to a value between 0-255 (I guess) for each range and represents a particular temperature value. The I & J scale seems to be logarithmic looking at the difference between 17,8C (17) and 20,8C (71) and the difference between 20,8C (71) and 22,8C (106). But that's just a guess.

So I somehow need to correlate the range (15 degrees C wide) with the 0-255 index to get a temperature. Crazy.

Converted H & I & J 12 bit number to decimal and get the following:

It does look very related, but I can't figure out a formula.


texts: Relation between burgers vector, slip plane, dislocation motion direction and dislocation line

texts:
I am really confused about the relation of this 4 entities.

I know that the dislocation line is perpendicular to the burgers vector in an edge dislocation and parallel to the b vector in a screw dislocation. I know that for a dislocation to slip, both b vector and dislocation line must be on the slip plane.

How do I know if a burgers vector [ijk] is contained on a certain plane (hkl)? Would this be the slip plane?
Knowing the slip plane (hkl), the burgers vector [ijk] and the character of the dislocation (edge or screw) how do I find the direction of the dislocation [ijk]?
Knowing the slip plane (hkl) and the burgers vector [ijk], is it possible to find if the dislocation is an edge dislocation or a screw dislocation? How?
How do the dislocation line relates to all this?

I am really trying to find the answer between them but I can't. If anyone can help me I would be very grateful. This is the exercise that created all this doubts
"Find the miller index of an edge dislocation with b=a/2[0 -1 1] and that is on the plane (111)."
What would be the miller index of a dislocation?

Thanks


texts: Turbulent boundary layer development in channel flow

texts:
I'm currently working on my Bachelor's thesis about the numerical simulation of a turbulent air flow through a rectangular channel. As part of that I'd like to compare my results to empirical correlations for the boundary layer thickness as a function of distance from the inlet for such a flow. However, I can only find correlations for a flat plate (Schlichting, White, Anderson).
Does somebody know such correlations?
Thanks!
This is the essential part of the geometry:

I study the development of the boundary layer from the tip of the plate downstream.
Simon


texts: Why do heating elements have lower rated temperatures in vacuums?

texts:
I have noticed when examining performance of various heating elements in different atmospheres that in a vacuum maximum temperatures are lower than the in air temperatures. Why is this?

(Typical heating element alloys are Nickel-Chromium and Iron-Chromium-Aluminum)

As Olin Lathrop says below the evaporation of the element becomes significantly increased in a vacuum. I found this interesting quote in an old book:

  This idea of working in a vacuum brought with it new difficulties as
  regards the construction of a furnace. The ordinary platinum
  resistance furnace proved of little value, as, owing to diminution of
  pressure, the volatility of the platinum foil, at high temperatures,
  was increased to such an extent that it was destroyed in a short time.


texts:
I am trying to discretise the PDE: $$\phi \frac{\partial c}{\partial t}+\frac{\partial j}{\partial x}=0$$ where $c$ is a function of $x$ and $t$, and $j=qc-D(q)\frac{\partial c}{\partial x}$, $q$ is the Darcy flux (function of $x$ and $t$) and $D(q)$ is the coefficient of diffusion/dispersion, and $\phi$ is a constant.

over the interval $(x_{i-1/2}, x_{i+1/2})$

My Progress

$$\begin{align*} &\phi \frac{\partial c}{\partial t}+\frac{\partial j}{\partial x}=0
\\ &\Rightarrow \frac{\partial c}{\partial t}+\frac{\partial}{\partial x}\left(\frac{qc}{\phi}-D(q)\frac{\partial c}{\partial x}\right)=0
\\&\Rightarrow \frac{\partial}{\partial t}\int_{x_{i-1/2}}^{x_{i+1/2}}c \ dx \ +\left|\frac{qc}{\phi}-D(q)\frac{\partial c}{\partial x}\right|_{x_{i-1/2}}^{x_{i+1/2}}=0
\end{align*}$$

What do I do to simplify the expression in terms of the values of the $c_i, q_i$ terms. (I am trying to get matlab to run this iteratively).

Conventions

$x_i$ is the midpoint of the $i$th interval.

$\delta x$ is the length of the interval.

$$f_i=\frac1{\delta x}\int_{x_{i-1/2}}^{x_{i+1/2}}f \ dx$$


texts: Heat Exchanger Design- Cooling a gas mixture

texts:
I am designing a process heat exchanger to cool a gas effluent stream consisting of 70% Nitrogen 23% Carbon Dioxide and 7% Water (all mole percent).

The stream is going to enter at 250 degC and 1.51325 bar (i.e. just above atmospheric pressure) and leave at 50 degC.

The stream is being cooled by an aqueous stream which has been specified as having thermal properties of water.

My question is this,
I have calculated that the partial pressure of the water in the mixture initially is approximately 0.106 bar. I used the formula Py=p to find this. P being the total pressure of the system, y being the mole fraction of component in the gas mixture and p being the partial pressure.

Is this formulation correct for the partial pressure and will partial pressure remain constant?

Also, is it correct to calculate the vapour pressure and compare this to partial pressure to check if the water in the gas mixture will condense?


texts:
How are spindle speeds calculated for a drill bit?

I've seen dozens of charts that highlight the rpm that should be used for specific drill bit types, bit diameter, and material. However, what if my chart doesn't have the particular type of material or bit that I am using? I'd also like to have some intuition to know if the chart looks right or wrong.

Upon some quick research, it appears that the "cutting speed" is what is ultimately needed for a particular material. I assume the cutting speed for each material must be looked up? Is there a standard or "go-to" place to find these? Then, information about the drill bit can be used to determine spindle speed. Again, what if I'm using a big hole saw or circle cutter, and it's not listed? How do I model the bit to use the cutting speed to determine rpm (for a given material of course)?

I'd also like to know to calculate feed speeds for a drill or mill, but there are presumably more variables. It is probably better answered in another question.


texts: Power needed to accelerate metal powder through two spinning wheels

texts:
I have a wheel which has a radius of 0.1m that needs to spin at 10000RPM. The outer surface of this wheel is pressed up against another free spinning wheel like a football or tennis ball launcher.

I am feeding metal powder through these two wheels, which I need to travel at 104.72m/s (basically the wheel needs to spin at 10000RPM while the powder is feed through). The powder is fed at a rate of 0.013 kg/s.

If I could work out the force on the wheel then I could work out the torque and hence power, however that is where I am not sure on what to do. The powder is being fed from almost standstill to a wheel traveling at over 100 m/s. It would seem the acceleration is almost instantaneous, but I know that's not the case. How would I work something like this out? Would I need the frictional coefficients of the wheels and powder?

(Assume this is operating in a vacuum and there is no air resistance)


texts:
Consider the system with unitary negative feedback such that the open loop transfer function is
$$G(s) = \frac{as + 1}{s^2}$$

a) Determine the value of $a$ such that the phase margin is 45º

b) Determine the stationary state error for the unitary ramp input

c) For $a > 0$, what is the gain margin

My attempt: My doubt is about the item (c). That what I've made:

$GM = \frac{1}{|G(j\omega)|}$ for $\omega$ such that $\text{phase}(G(j\omega)) = -180º$. In this case
$$\text{phase}(G(j\omega)) = -180º \iff \text{arctan}(a \omega) - 180º = -180º \iff \text{arctan}(a \omega) = 0 \iff \omega = 0$$

But for $\omega \to 0$, $|G(j\omega)| \to \infty \Rightarrow GM \rightarrow 0$

Is that correct?

Thanks!


texts: Rigid tensioner/turnbuckle: One side tightens, but the other side loosens

texts:
I'm attempting to make the rigid equivelent of a gate tensioner/turnbuckle. I'm doing this for a couple of reasons:

I like the idea of not fussing with cables
I'm using this experience to learn about the technology behind the turnbuckle

I've mocked up something that almost works. I've connected two hook-bolts to a threaded rod (5/16-18-36") via connectors.

It seemed like it would work in my head; I thought I would just be able to tighten one of the connectors to tension the gate. However, in practice, all I accomplish when tightening a connector is tightening one side, but then loosening the other side. The devise comes apart and fails miserably.

What kind of mechanism would it take to make this work as expected? In summary, I want to shorten the length of the device/rod by tightening a connector.

For bonus points: What is the principle called in Mechanical Engineering theory that would explain the problem where one side tightens, but the other side loosens?


texts: What is your best recommendation to optimize the torque/speed relationship of a motor?

texts:
I'm a engineering student currently taking Thermodynamics and we have this project for our finals which is a sort of reeling /towing device, the assignment consists in a reeling motor that has to tow a small car up along a slope, loaded with a certain weight, the team that is able to reel in the most weight in the shortest time will win the competition and have the maximum grade and extra credits for the semester.

The rules are:

You can only use 1 Peltier thermoelectric generator module that will deliver 12 volts to the motor of my choosing. No capacitors or energy storage devices. I could use a voltage regulator to rise the voltage but speaking to one of my professors he said that due to the fact the power is just a relationship between current and voltage, rising the voltage wouldn't really make a difference as the current would drop, so my best shot was to shop for a motor with good torque that would surely work under 12 volts in case the peltier module does not deliver its full capacity.

I had 2 options, and because I need to move the biggest load in the shortest amount of time, I had to look for a motor with a good speed/torque relationship that would work under 12 volts in the worst case scenario, but I read somewhere you can make a speed reduction arrangement to help torque like the one below:

Reducing Engine

So I went and bought two different motors,

One with high speed and comparably low torque (to see if I the reducing arrangement can help me get a better torque in the end.

BEMONOC Small DC Motor 12V High Speed 12000 RPM High Torque PMDC Motor for DIY Parts  (0.135 N.m)

And one with low speed and high torque, to test both.

Greartisan DC 12V 200RPM Gear Motor High Torque Electric Micro Speed Reduction Geared Motor Centric Output Shaft 37mm Diameter Gearbox (0.2157463 N.m)

But I was wondering if you have any suggestions as to how to improve this torque/speed relationship and get the best out of it, I really want to win this competition.

I would truly appreciate any information you can share with me in contribution to my project.

Thank you in advance and sorry for my grammar, English is not my first language.


texts: Will PVC build up an electric charge and cause a spark?

texts:
I'm working on an application in which sparks (specifically from static discharge) present a severe safety hazard.  One component in question is a piece of PVC water pipe.  It has been proposed to "ground" the pipe to minimize the risk of static shocks between humans and the pipe, and between other components and the pipe.  I am skeptical as to whether this component needs to be grounded at all; it's not conductive, so my intuition is that it isn't able to cause a shock.  Normally I would just go along with this, however the proposed methods of grounding involve expensive adhesives and coatings which also have a long lead time for ordering.

Can a PVC pipe cause a static discharge? If so, what industry practices are out there to mitigate this phenomena?

The pipe is being used in a test fixture for testing energetic materials, i.e. combustible solids. The energetic material is loaded into a length of the pipe, along with some sensors and other components. The material is ignited, after which the pipe is destroyed. The static spark concern is only during the loading process, when the energetic material could be ignited prematurely. The pipe is not used in its normal manner, like to transfer particles or fluids.


texts: Should one use multiple elements through the thickness with multiple materials?

texts:
To get realistic results from a FEM calculation, it is common (or so I've been taught by someone who may not be up to date) to use at least four or five elements through the thickness of a beam or plate. I am now modelling a composite plate bending problem, with two or three materials.

Should I use four or five elements through the thickness of every material, or can I reduce my calculation time by using one or two elements per material, as long as the total adds up to four or five?


texts:
I am trying to find out if the 12 V DC electric motors that I have are powerful enough to launch a 100 g tennis ball 30 m away. The tennis ball is put down a pipe and ends up wedged in between 2 wheels (radius = 0.05 m) driven by the two 12 V DC electric motors. The picture below should hopefully clarify the situation:

The electric motors are spinning at ~7000 RPM (no load), the motor specs are here: http://www.banebots.com/product/M5-RS555-12.html
A wheel (with mass of 0.05 kg and radius of 50 mm) is connected to each motor
The tennis ball is dropped down the pipe and ends up in between the two rotating disks
The launching angle is 20 degrees

I calculated how far the ball flies if I keep the RPM constant based on the horizontal component of the linear velocity in combination with the flying time and launching angle. However, this does not account for the mass of the tennis ball.

When the ball passes through the two wheels, the electric motors will see an opposite moment. I guess I can calculate the moment by multiplying the mass * g * radius. However, it is not clear to me how I can then accurately calculate the effect on the RPM of the motors. I can optimize the location of wheels so that the ball isn't squeezed too much, so I was hoping to ignore this in the calculation and build in some margin instead. In the end, I would like the ball to fly at least 30 m.

Does anybody have an idea on how I can calculate if the motors are strong enough to launch the ball 30 m away?


texts: Hello I am a simple rock climber, and would like to figure out how much force is applied to The lobe of a cam/the rock when the cam is loaded. So the cam lobe is circle the ramp or cam goes from 7/16”-11/16” I’m not sure that matters or if just the point of contact matters. If I ignore friction and those kind of nussance variables what is my formula if I 180lbs simply hang on the cam. (Is it a simple lever calculation)!


texts: what happens if starting arm of starter does not return to "OFF" position after a temporary supply failure?


texts: How do I select the cross section for a machine frame? Do I need to refer to the AISC steel construction manual to find the capacity of beams, columns, etc?


texts: Why does the graph of the Standard Atmosphere have temperature on the x-axis?

texts: Presumably, temperature is a function of height, so the x-axis should be the height not the temperature, but graphs like this tend to be the norm:


texts: In structural mechanics is virtual work an approximation?

texts:
In the principle of virtual work a unit virtual force imparts virtual forces on the structure internally.

When real loading is then applied the additional work done by these forces is their magnitude x distance delta.

I don’t get why we assume the virtual forces are constant as the shape deforms. Would they not change with the changing structure?

This makes me think this method is approximate.


texts: How to model heat transfer through a pressure vessel wall if the reservoir temperature is not constant

texts:
I have a closed cylinder with a gas inside at 3,000 K.

I want to find the temperature profile (over time) through the cylinder wall, something like figure (b) shown below:

In my case, however, $T_\infty$ does not stay fixed at 3,000 K over time but changes (cooling) due to heat transfer through the cylinder wall.

Unfortunately I was not able to find any solved problem like that in textbooks because any existing solved problem considers the temperature inside the bulk of gas as a constant.

How can I model this problem?


texts: how to calculate motor power for electric truck

texts:
I have a 50,500 kgs semi-trailer to modify to be electric truck.
I will mount a motor direct to differntial axis ( without gearbox ).
Differential ratio is 841 ( 5.125 ).
If I want this 50,500 kgs semi-trailer to climb a 26 % slope , what is the suitable motor power for this truck.


texts: Second Moment of Inertia (or Second Moment of Area) of Beam Section

texts:
I need to calculate the moment of Inertia Iyz but I find 0 information online about how to get it or solve it in a real problem, only that is equal to

$$\bar{I}_{yz}=\int yz\text{ d}A$$

How can I solve this in the case of an antisymmetric beam section?


texts: Maximum deflection of a beam with both ends fixed and distributed load

texts:
I'm designing a part, and I'm trying to figure out what distance a slot should be from the bottom of the part.  For simplicity in analysis, I'm approximating the region between the bottom of the slot and the bottom of the part as a beam that is fixed on both sides.  This beam will have a uniform load over the entire span.

I've found this equation to find the maximum deflection of the beam $y_{max}$, given the load $w$, beam length $l$, elasticity modulus $E$, thickness $b$, and distance between the slot and the bottom of the part (or beam height) $h$.

$$y_{max}=-\frac{w l^4}{32bh^3}$$

I'm trying to figure out what $h$ ought to be, so I rewrote it in terms of $h$.

$$h=-\frac{1}{2}\left(\frac{wl^4}{4Eby_{max}}\right)^{1/3}$$

I already know what $l$, $E$, and $b$ are, and my plan is to write $h$ as a function of $w$, but I need to eliminate $y_{max}$.  I've tried finding it using the formula for bending stress ($\sigma=My/I$), but that resulted me in an identity for $y_{max}$.  I tried finding $y_{max}$ by solving the ODE $\ddot{y}=M/(EI)$, but that got me the first formula that's above.

It would be awesome to have another formula for $y_{max}$, but a better/different method of determining what $h$ should be would be just as good.


texts: I am trying to design the windmill blades (the green part) in Solidworks but am having trouble since the radius of curvature for the blades varies at different points. I tried bending it as a sheet metal, but am having a lot of difficulty. Any ideas?


texts: How is it possible electromagnets keep a heavy maglev train levitating without forcing anything metallic to be flinged away?

texts:
I always wondered how it is possible to have electromagnets so strong that they keep a heavy maglev-train levitating without forcing anything metallic to be flinged away or to be pressed against the ceiling of the vehicle-cabin?
And how come a person inside that train which has a pacemaker implanted is not affected? With a pacemaker someone cannot have a MRI scan but still ride a maglev train?


texts:
My team is trying to build a mechanical cannon for a final project for a course and we are running into some problems with our motor stalling.
Our motor stalls when the plate hits either side of this railing (as shown with circles below) because, I think, it creates infinite tension that the motor can’t overcome. Once our DC motor is fully stalled and refuses to move in the direction of infinite tension, we try to move the motor in the opposite direction to free it up, but it stays stuck. We need to physically intervene to “unjam” the motor. Sometimes we can also press our button to move the motor backwards quickly and consecutively and it will unwind.
We don’t want to use a limit switch since we have to stay within a “required budget”, so we are wondering if there would be any other way to prevent this motor from becoming jammed. We were thinking that the jamming of the motor occurs because there is too high of a current draw when it stalls, so a solution would be to put a resistor in series with the motor driver + DC motor interface to reduce the amount of current that is drawn when the motor stalls. We have no idea if this is a robust solution that would allow the motor to easily unjam. Any ideas would be really appreciated !
Some specs for context:
DC motor that moves plate:
DC Motor Threaded Output Shaft Lead Screw 6V Motor Stepper Lead Screw Actuator Gear Motor with Long M355MM Lead Screw Thread Output Shaft
Motor has a 6V rating and a stall current of 1A


texts:
I am having difficulty with a CSWA question that asks to find the mass of the following part. Here is a link to my attempt: https://drive.google.com/file/d/162No5ugwQ-9cRkdcp-78Ohq08T8UngBd/view?usp=sharing

Can anyone identify what I did wrong? I selected answer choice A which is closest to the mass of my model but that is incorrect. Any help would be much appreciated.


texts: Finding mass flow rate and exit temperature in heat exchanger stream

texts: I'm working on a heat exchanger design project and I'm stuck at one of the first steps - energy and rate balance. In the problem, we have a hydrocarbon stream getting cooled by a water stream. We are given the following values for the Hydrocarbon stream: Vdot=200GPM, T1=135 F, T2=100F, P1=321 psia, with minimum pressure drop of 285 psig, X1=0.684 C3H6, X2=0.316 C3H8. And for the water stream we are given: T1=85 F, P1= 60psig, with an allowable pressure drop of 50psi. I found the values for mCp(T2-T1) for the hydrocarbon stream, but I'm only given values for the inlet temperature and pressure of the cooling water stream. I found the specific heat of the water stream, but I'm still left without the mass flow rate and exit temperature. Can anyone provide some advice on how to obtain one of these values so I can balance both of the streams? Any help would be greatly appreciated. Thank you!


texts: Is a 1/8" AR400F steel plate strong enough, for 4,000 lbs?

texts:
I have a Ford F350 cab & chassis and a gooseneck trailer. For the gooseneck hitch I want to use a steel plate.
The steel plate will be BOLTED to the frame, above the rear axle And the gooseneck ball will be welded to the steel plate.

The distance between the frames is about 34". So the plate Is going to be 34"long x 8" wide.

The trailer is 16,000 lbs GVWR. And a maximum tongue weight of 4,000 lbs (at 25%)

A regular A36 steel plate, 3/8" thick, will bend under load. (A36 mechanical properties: Brinell=112, Tensile=58,000 psi, Yield=36,000 psi)

So I'm thinking to use a 1/8" thick, high strength steel ASTM 514 / AR400F (Tensile Strength=184,000 psi, Yield Point=150,000 psi, Elongation = 23% in 2",Brinell Hardness = 360/444)

Is a 1/8" AR400F steel plate strong enough, for maximum 4,000 lbs?

If not, what do you think about AR400F 3/16" thick ?


texts: Max torque given in engine specification is indicated torque or brake torque?

texts: I want to calculate brake torque from indicated torque for motorcycle.


texts: Acoustic absorption of different materials? (gypsum board versus plaster)

texts:
I would assume that different materials absorb sound differently (maybe not?)

What is this called?

How can I compare the sound absorbent properties of different materials with the same surface geometry, such as plaster and gypsum board?


texts: How to power and transport air to a small hover car track

texts:
I'm trying to design a hover car track. As in, you have a 'track/circuit' that have objects being slowly moved along by the force of the air from beneath and sides. The propulsion to move the objects forwards comes from the air from the sides that are angled in the direction of the track. Picture Scalextric cars combined with air hockey.

These objects that are like carriers that hold things and are under 750 g (in total) and regarding contact with track is a circle that is 135 mm in diameter.

Track length isn't known at the moment but I think 3–5 m.

How would I effectively 'power' and 'transport' the air supply? I've looked into centrifugal fans in series and parallel and their designs and outputs but I'm stuck at calculating what the requirements would be to do this and if it can be done effectively at low cost, like something I could do in a medium sized garage.

The track will split and merge too. And there would be multiple carriers on the track.

Carriage is cylindrical in shape, weight = 750g, diameter =135mm, height 110mm

track is flat with no change in elevation. width of track would be big enough to fit a single carriage approx 150mm
The track would be like a square trench for the carriage to fit in. so the walls would be 110mm too.
The walls would be a manifold that has jets angled in the direction of the track, say 60 degrees away from the normal of the wall and parallel with the floor of the track.


texts:
I have a rf module transmitting from an antenna. As you see in Figure 1, I have a radio mast that sends waves in all directions. I don't want this. My plan for controlling wave direction is Figure 2.

How do I control RF wave direction?


texts: Ratio between heat transfer coefficient and thermal conductivity

texts:
Consider the Robin boundary condition for the diffusion/heat equation $\mathrm{u_t=a(t)u_{xx}+f(x,t)}$:

$$\mathrm{-k(t)u_x(0,t)=h(t)u(0,t)}$$

or

$$\mathrm{u_x(0,t)+\frac{h(t)}{k(t)}u(0,t)=0}$$

where $\mathrm{k(t)}$ thermal conductivity and $\mathrm{h(t)}$ heat tranfer coefficient.

My Question: Is it possible that the ratio $\mathrm{h(t)/k(t)}$ to be constant? Could anyone please help me? I have really no idea.


texts:
Do you happen to know relevant references in the literature that model the mechanical vibrations of a solid object (preferably antennas) by means of complex representations as a function of time?, i.e. can we say that the radial displacement can be modeled as

$$ r(t) = \sum_{i=1}^{N}{a_i \exp\left(-j b t \cos(\phi_i)\right)}$$

where $a_i, b,$ and $\phi_i$ are constant independent of time $t$ and $j$ is the complex number such that $j^2 = -1$.


texts: What are the engineering challenges in WIG craft development?

texts:
Wind In Ground (WIG), is an old concept.

In short: Wing-tip vortices create an additional drag on the aircraft known as the induced drag. However, when the flying craft (or bird) flies close to the ground or water, these vortices don't get enough space to develop which results in additional lift and reduced drag. This phenomenon has been effectively used in transportation vehicles to create ground effect or WIG crafts.

Although a paper titled 'Wing-in-ground effect vehicles' declares that many technical difficulties have either been solved or can be solved, according to this wiki article, there are some practical issues in using these crafts for regular passenger traffic.

Since hovercrafts also glide on air cushion, and yet they are not that rare, what makes WIG so uncommon? (Analogy wise, hovercraft is like helicopter while WIGcraft is like airplane)

Is it the engineering aspects that makes them uncommon? If yes, which aspects?


texts: Rate of flow of steam going from one pressure to another

texts:
A closed steam boiler in a coffee machine idles at around 124 °C, the steam and water inside at 1.2 barg. When a steam valve is opened, steam rushes out through a steam wand inserted in milk, to aerate and heat it.

What I'm trying to determine is the flow rate of that steam, but all thermodynamic info on steam boilers I'm finding is for industrial situations and too complex for my very basic understanding of thermodynamics.

I'm disregarding any further heating from the boiler when the valve is open and am just assuming an infinitely big boiler with unlimited pre-generated steam

I'm thinking the steam tube cross sectional area is important, as would be the length and type of tube for losses. Can someone put me on the right track as far as formulae go.


texts: Distribution of Forces into 3D Bolt Group

texts:
I'm trying to create an Excel spreadsheet that takes a 3D bolt group with x y and z coordinates, applied loading, and determines the distribution of forces into each bolt based on weighting by the distances from the centroid and bolt diameter. By "3D bolt group" I mean a pattern of bolts existing in 3 dimensions, not just in 2. I know this complicates the calculation because now there are 3 dimensions to consider. And I've seen quite a few spreadsheets that only take into account a 2D bolt group.
I found the following program (http://www.chestnutpens.co.uk/misc/boltgroup.html) that does exactly what I'm trying to do, but I'm having trouble replicating the results in my spreadsheet. I'm able to replicate almost the entire program, up until the last step that adds the forces due to direct loading and rotation. And I'm not sure why I'm getting the results I'm getting. Note: I've created in FEM the bolt group and matched the results of the program.
Has anyone ever tried to create something like this, or can help me understand where I'm going wrong? I know its a complicated method and its difficult to understand without seeing my spreadsheet. Actually, am I able to share my spreadsheet here? I'm not entire sure on all the rules here.
Thanks


texts: What makes something like water so hard to change its density?

texts: So I'm taking a compressible flow class soon, and I've been thinking beforehand about the topic. A substance like water can easily be pressurized, but its density doesn't change easily, meaning there has to be some microscopic force between molecules  in equilibrium with the pressure force. What force would this be though? Would it be Van der Waals force perhaps?


texts: Under what circumstances would one need or not need an electronic brake for a permanent magnet motor?

texts:
My company was asked to design a custom product several years ago. The original requester never bought it, but we've sold several a year through distribution. It's been a small side-line for a while, but we'd like to understand the broader use and potential market for it.

This product sits between a motor controller and a permanent magnet motor. In the event a signal is received, perhaps indicating a light curtain is broken, this unit disconnects the motor from the controller and applies resistors across the motor leads. This stops the motor. This is clearly useful primarily for safety applications. Things I'd like to understand:

What alternate solutions exist?
Who would be most likely so specify such solutions?
How can I most effectively reach those people?


texts:
How to add force in certain point. I want to see influence of point force on my structure. (See image)

That force is for example weight of some tank or something similar inside my structure. I don't have suports defined yet. How to define force on x,y,z point in ANSYS Workbrench? Is that possible? Model (geometry) will be imported as STP file  to ANSYS.

Does someone have idea how this can be accomplished.


texts: solidworks 2018 part geometry changes on scaling

texts:
See the follow file for details:  https://www.filedropper.com/filemanager/public.php?service=files&t=757744643cd3d3972ae382af4a4deb91 .  I create a spiral structure which is smooth and beautiful, then scale it up by a factor of 10.  Once it's scaled up, the geometry has changed. Can anybody tell me why, and if there is a way of avoiding it?  Thanks!

edit:


texts: How can I make a GPS traceable microchip?

texts:
I am looking for making a chip or a microchip, which can be traced with the help of the satellites. Means it is merely a chip and when I tune my satellite to a particular frequency I would get to know that this particular chip is present here and so. But it should be a chip only means no battery and all i.e. no other circuitry. I am thinking so if it is possible now and if not please suggest something similar to it so that I can use that in the similar way.
Thanks


texts: I have a water channel with a flow of 1.5 m3 per second. What would the potential energy be if I install a waterwheel with fins almost touching the sides and bottom?


texts: Vocabulary: NYC Elevated Highway & Trains, Industrial Park

texts:
I'm writing a story set in NYC and trying to describe certain industrial objects. I'm having trouble with specific technical terms for the items that I've marked w/ arrows. E.g. I don't want to use the generic term "support" or "wall" if there's a more specific word like viaduct, truss, pier, girder, silo, etc. Also specific materials (are they steel or iron, or a specific kind of design,style, type).

After extensive research, I'm still not confident which technical terms apply to these specific things. Hoping a civil or other engineer might be able to shed some light. p.s. for the Smith-9th elevated train, what's this black material and when/why was it put on if anyone knows).

Thanks in advance!

R


texts:
I'm an EE student by trade, but I've started a project that requires some mechanical analysis, and I've run up against a bit of a wall in my calculations.

The system in question that I'm looking at is an actuator, connected via ball joint to a rod, which is then connected with a ball joint to a platform. During operation, the platform will be constrained to movement in either only the x direction, or only the y direction. I'm trying to find out, based on the force of the actuator and the geometry, what the X and Y components of theses forces will be.

(Apologies for the cartoonish drawing). The actuator is on the bottom left. For the purposes of calculation, I'm assuming that the rod is rigid, has zero mass, and that the actuator does not need to move to apply any amount of force.

I'm using static equilibrium to calculate the X and Y components of the force on the upper right hand side, which will be the X and Y force that my actuator applies to the moving platform.

The actuator will apply an initial force Fa to the rod. Since both supported ends are ball joints, I know that there can be no moments on either end of the rod, only forces acting in-line with it.

In the case of $\theta_M$ being equal to $\theta_R$, the solution is straightforward: all of the force is being applied in-line with the rod, so we set the sum of forces in X and Y equal to zero, and solve.

However I'm having trouble wrapping my head around what happens if $\theta_M \neq \theta_R$.

My naive approach to solving this would be as shown below:

Break down the initial applied force into components that are parallel with the rod, and components that are perpendicular to the rod.

Here's the part I'm unsure about. Since the actuator can't move, the perpendicular force should be cancelled by an equal and opposite normal force of the actuator pushing back against the rod, correct?

However something in the back of my head is telling me that I'm missing something.

Intuitively, if we were to apply the actuator force not in-line with the axis of the rod, I'd think that there would be some kind of lever action present. An example would explain what I'm trying to say best I think. Can I not analyze a system like this statically? Or am I just completely off base?

EDIT: to make the point I'm trying to get at clear, I was able to find a mechanism that outlines what I'm talking about:

If the wheel is driving the slider, won't the output force of the slider be at its peak value when  members 2 and 3 are near parallel to one another? I feel like the same effect should be at play in my system above, but I don't know how to mathematically articulate that. Or my intuition about when the force is at peak value could be totally wrong.


texts: Development of an interstellar mission: should I design the propulsion system or the main hull of the ship first?

texts:
I am currently developing an interstellar mission for a school project. I am thinking whether to design the propulsion system (Bussard scoop) or the main hull and structure of the spaceship first. What do aerospace engineers begin with usually?

I am somewhat more inclined towards choosing propulsion first because most of the ship's mass will consist of the engine anyway and the rest can be "built around" it, whereas the engine will be optimized upon completion of the rest of the ship.


texts: How to calculate the force that a liquid creates on the wall of an underground reservoir

texts:
I would like to calculate the force exerted on the wall of an underground reservoir. The volume of rocks surrounding the reservoir creates a force equal to the product of the density of the lithosphere, the gravitational acceleration and the height above the reservoir.

What I'm trying to understand is what are the forces created by the liquid inside of the reservoir. How can I calculate these forces?


texts: Sector determination of a nonlinearity and passivity

texts:
This a not a homework or any similar task.

Regarding determine the determination of static nonlinearity, I know that one can draw two lines that contains the nonlinearity part. For instance for three cases below:

The definition for sectors is
$ a \leq \frac{f(y)}{y} \leq b $
Where $f(y)$ is shown in figure above.

For a) I draw a straight line with slipe of 1 and one line with slope of zero and for the other nonlinearities, the sectors are marked  as figures below:

The yellow area is the area that the sector should be. Regarding the sector area of the third curve. Isn't it misleading the the orange area could be accidentally interpreted as the sector area?

How would that look like for a backlash?
How do I calclulate the gain of those nonlinearity? Assume that
$gain =Sup \frac{||f(y)||_2}{||y||_2}$
When it comes to passivity, we know that $\int_0^T y^T u \geq 0$. But cant figure that out for those system and backlash. Whatever I  do I end up with all system being passive.


texts: Are there examples of spring-mass-damper system that exhibit increasing growth in an unstable way

texts: Simply, are there examples of spring-mass-damper systems that exhibit unbounded behavior or at least increasing behavior for a period of time. I am trying to do some vibrations research, but I am quite out of practice with it.


texts: Why regenerator "wheels" in a turbine engine?

texts:
Back in the early 60s, Chrysler built a turbine car powered by a turbine engine it had under development.

An interesting feature of the engine was a regenerator system to recover heat from the gases leaving the power turbine, using this heat to preheat the air on its way from the compressor to the combustor. The benefits of this were to improve fuel efficiency and reduce the final exit temperature of the exhaust. The regenerators involved some sort of rotating disks which somehow transferred the heat as they rotated. There are diagrams/animations depicting the gas flow through the engine and (generally) heat path through the regenerators, but in some ways they don't seem to make much sense.

My question is: how did the regenerator setup actually work? How was the compressor output air (60 psi?) put into contact with a rotating(?) hot surface without the pressure leaking air away to the exhaust? Why would a regenerator need moving parts at all? Could it not just be a system of tubes within tubes?


texts:
(I'm not really sure what SE to post this on, so if this is inappropriate, my apologies)

I'd like to be able to remotely control the amount of chicken feed in the feeder. Here's how I envision the setup:

 _____________________________
| Huge bucket of chicken feed |
 =============================
           |      | <--- Pipe (PVC?)
           ==Valve=---------Arduino
           |      |
          |        |
           oooooooo <---- Chicken feeder

I would guess each granule of chicken feed is about 1/3 cm cubed. I would appreciate any suggestions on the setup as well as what kind of valve to use. Thank you!


texts: Galvanized Steel (Zinc Plated Steel) vs Stainless Steel

texts:
Zinc Plating is known for its ability to prevent most corrosion, and it is done by just dipping a metal in hot pool of zinc and letting it cooldown. Meanwhile, stainless steel, an alloy that is capable of resisting corrosion.

Zinc Plating Advantages:

Cheap

Stainless Steel Advantages:

Is not coating (hence, scratching will not expose for corrosion)
Hardnesss of Material ($UTS_{Stainless} \approx 860 \frac {N}{mm^2}$) comparatively to Mild Steel ($UTS_{Mild  Steel} \approx 470 \frac {N}{mm^2}$)

Other than what is said, in what circumstance would you use stainless steel over galvanized steel?


texts:
I'm modifying a lawn tractor to pull single axle trailers in a woodland environment.    They are rear wheel drive, have enough power, but traction is our biggest issue even when using tractor/ATV tyres.

My question is - what height (in relation to the rear axle) should the tow hitch be at and why?

I have looked at tractor pulling for comparisons and

they seem to go as high as they can within the rules but I understand this is due to benefits of lifting the front of the sled off the ground.
they extend the hitch to influence front wheel lift - I guess this is to put more weight on the back axle.

Front wheels lifting on woodland slopes isn't ideal so I have always opted to go low (below axle line) as this pulls the front down and I don't see how it could reduce the weight on the back wheels.

But a physics explanation would be really helpful.

EDIT:  I also found these two links which undertake a complex analysis of sled pulling with trucks under the title 'Physics of a truck pull, using a 2WD pickup truck'.

Part I - A simplified physical model captured by a single equation
Part II - Enhancements to the dynamics of the simplified model

Thanks.


texts: What is the [PVC] tube or foam in metal springs for?

texts:
There are plenty of springs out there which have either a little PVC tube or a foam inside, when I first saw the tube I thought it was probably to prevent the metal spring from bending, but that wouldn't explain the foam that comes with others.

Is there an analysis for this materials within the springs?, in which situations shall I use this materials within the springs?

PVC Tube:

Foam:


texts: Is it possible to have a reference pulse interpolator for a CNC machine with dc drive?

texts: Is it possible to have a reference pulse interpolator for a CNC machine with a dc drive? it should work with alternating current drive but I am not sure about the direct current drive. please help me getting its answer. thanks


texts: A creep mathematical model of alloy steel for making springs

texts: I'm searching for a mathematical approach to well describe the creep （or stress relaxation）of helical-coil compression spring.I've got the spring parts and can Experiment with these parts .I need extra theoretical analysis which my experiment is trying to support.


texts: Constructing a block diagram for amplitude control of an oscillator

texts:
I'm building a Wien Bridge oscillator. The oscillation part works just fine, but it currently limits on the supply rails.

I want to add amplitude control, so I've added a precision rectifier which feeds an integrator that controls an LDR to change the gain of the circuit.

This setup makes the output amplitude oscillate. To get a better understanding of what happens I want to construct a block diagram of the amplitude control and use control theory to improve the design.

I'm already a bit stuck on building the block diagram. I've the following:

Where the 3 is the ideal gain, to compensate the $\frac{1}{3}$ of the frequency selective network. The $\delta R$ is the change in the gain resistor due to the LDR. Since the frequency selective network has 0 phase shift at the oscillation frequency I believe there is no need to put in an actual transfer function.

I've modelled the rectifier with a gain of 1, as it doesn't really change the amplitude it just presents it in a different form. The $\frac{1}{sC}$ is the integrator.

Is this somewhat correct? How can I now add the fact that the integrator output alters the $\delta R$?


texts:
I'm trying to model, in MATLAB, a membrane in 2D which has an initial triangle-like shape.

This membrane has pressure acting on it from the inside. There are also some pulling forces in random directions on the inner side. I want to analyse the behavior of this membrane over time. The way I want to model this is as follows:

I have the set of membrane points. I define the total energy of the membrane in terms of the pressure and the forces acting on it. Since this is in 2D, my total energy is actually energy per some unit length. So, the pressure energy can be modeled as $-\text{p}(\text{area under the membrane})$, and I can use trapezoidal rule to write area as $\sum_{i=1}^{n-1}(y_i+y_{i+1})(x_{i+1}-x_i)$, where $(x_i,y_i)$ is $i$th point of the membrane, and $n$ is the total number of points of the membrane. (Although it doesn't look like it, the base)

I am unaware how to model the Bending Energy of the membrane in a similar way. It has to be in the form of $x_i,y_i$ and some constant. A reference to an appropriate bending theory would also be helpful. I seem to remember some formula like $\int \chi H^2 dA$, but I can't really find a source online. Once I have the total energy of the membrane, I can solve some differential equations to get $x_i(t),y_i(t)$. How do I model the bending energy term?


texts: How to balance flow and pressure in nitrogen purged chambers?

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I have an instrument that is technically a humidity controlled chamber. It measures how much moisture is picked up by the sample through a microbalance(Zone 1). Nitrogen gas flows from zone 3 and split into 2 chambers (by a union Tee ) in Zone 2. Finally the gas is vented in Zone 1, each chamber with its own exhaust vent (tubings that vent to the back).
The Problem is that the flow is uneven. or let me rephrase, the flow is even as long as the resistance against the flow is equal for both chamber. with the slightest change in resistance at one of the vents, the flow is completely diverted to the other chamber. This happens if one of the vent tubings got slightly bent, one is slightly longer than the other, etc.. It is ridiculous sometimes
My question is: if I joined the exhaust tubings together at the end (by a Y-connection), would that equalize the pressures and gas flow in the chambers?
I'm no engineer but I can't think of a better place to ask


texts: Motor for a hydraulic pump in a hydraulic system

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I am a complete beginner to hydraulic systems, and I've wanted to learn more about this area. I'm designing a hydraulic system that involves using hydraulics to push/pull objects using pistons. I have looked at what the basic requirements are for a hydraulic system, but there is one thing that escapes me.

I come from an electronic background, and I noticed that the hydraulic pumps (for example, this one) seem to lack a motor to drive the fluid. Am I wrong? If not, I've been looking everywhere for a motor that can/should be attached to said pump, but I cannot seem to find anywhere that sells them. Is it just a simple DC motor (with correct specs), or should there be a specific motor designed for hydraulic pumps?

Looking around, I came across this, but looking through the specs, I don't see a power requirement, and being used to seeing power consumption in datasheets, I'm not even sure it is a motor!


texts: Why two identical beams without being pinned together will share half of the bending moments?

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As shown above, two identical rectangular beams are placed and NO pinned together. I know each beam has its own neutral surface but why they carry half of the bending moments? I thought the bending moments they carry are same because each of the beam is subjected same force P at the end.

Thanks