texts:
Blocks A and B weigh 30lb and 15lb respectively, and they are both at a height 8ft above the ground when the system is released from rest. Assume the pulley is frictionless.

Determine the speed of the block A just before hitting the ground.
Determine the tension of the cord during the motion.
Determine the maximum height reached by block B

So far for part 1 I've tried to apply the conservation of energy.
Using mgh only for the initial because velocity is 0 and the kinetic energy of both blocks, plus the potential energy of block B at height 16ft for final.

This creates:

$(30+45)8=\frac{1}{2}(\frac{30}{32.2})v^{2}+\frac{1}{2}\frac{15}{32.2}v^{2}+15(16)$

Which simplifies to $v=13.10 ft/s$

For part 2,

using $T_{1}+U_{1-2}=T_{2}$

$\Rightarrow T_{1}+(W_{A}-F_{A})h=T_{2}$

$= F_{A}= W_{A}-\frac{T_{2}}{h}=30-\frac{(.5)(.932)(13.10)^2}{8}=20.003lb$

I would use the same process for the tension on B.

So to my actual question, is this the correct and easiest way to approach this problem? I don't have access the the solution and am looking for some feedback.


texts: What's the difference between tempering and aging?

texts: The processes sound really similar; I'm asking with respect to Martensite processing. Essentially the difference between Tempered martensite and Aged martensite for Steels


texts: How do train tracks handle really cold weather?

texts:
First of all, I'm interested in train track only, not the rolling stock.

How are tracks built to cope with really cold weather? An example might be some place in Canada or Siberia. Ice would accumulate all the time, changing the shape of the rail.

How does the ballast or foundation cope with the thawing tundra in summer? What about the really nasty stuff like blizzards dumping snow over the track, or sleet, or freezing rain?


texts: Logic gates for an indicator light to show the state of two sensors

texts:
I've attempted to answer the following question and I need to know if I am on the right track:

  LOGIC GATES

  Question 3

  A manufacturing plant uses two tanks to store certain liquid chemicals
  that are required in a manufacturing process. Each tank has a sensor
  that detects when the chemical level drops to 25% of full. The sensors
  produce a HIGH level of 5V when the tanks are more than one-quarter
  full. When the volume of chemical in a tank drops to one-quarter full,
  or less, the sensor puts out a LOW level of 0V. It is required that a
  single green light-emitting diode (LED) on an indicator panel shows
  when both tanks are less than one quarter full.

  3.1 Show the truth table

  3.2 Derive the Boolean expressions.

  3.3 Show how 3 NAND gates can be used to implement this

  (Consider the wording very carefully in this question)

It's question 3.1 and 3.2. The last sentence of the main question is a bit tricky. It says "Show when both tanks are less than 1/4 full."

Here is my solution:

Both inputs (namely Tank A and Tank B) need to be LOW in order to indicate a LOW output
The only logic circuit to satisfy the above is an OR circuit.
0 + 0 = 0; 0 + 1 = 1; 1 + 0 = 1; 1 + 1 = 1
From the above I believe OR operations is correct, since A and B are both LOW and thus causing the output to be low.

I was considering AND Circuit but then 0 x 1 = 0 and 1 x 0 = 0. These operations conflict with the question. The output must only show LOW when BOTH inputs are LOW.

Therefore my solution for 3.1 and 3.2 would be using an OR gate. Is that correct?


texts: The buckling stress, using the Rankine and Gordon Equation or the Perry-Robertson Equation, is always less than the yield stress of the material?


texts:
Okay, I have bought an electric motor, it has a 14mm bore, unfortunately the part I need to affix has an internal diameter of 16mm (5/8").
So, to fix this problem I call upon your experience and expertise. Is their a way to perhaps sleeve the bore with a (tiny) grub screw holding it in position? Or perhaps a better alternative that will not create vibration at around 2800 rpm?
I should let you know that I do not have a milling machine or metal lathe at my disposal unfortunate as that is, but if I did I wouldn't be asking this most likely.
I probably should mention that this project is an abrasive belt sander, of which I have already built fromantic scratch. This is in fact the last hurdle.
Thank you for your time,
Regards,
Peter


texts: Simultaneously charging and transmitting data to an android phone using usb

texts:
Dear engineers,

I have to make an engineering project which is a portable solar phone charger. One thing I need to do in it is to somehow charge the phone (android) from the battery (which is charged by solar panels) and simultaneously send data about the battery level to the phone through the same usb connection. Is this even possible to do? If so, could you please advise a way to do it? Would arduino be helpful?

I know that usb has separate lines for data and power, but I don’t know how a phone can receive this data and whether it will work while charging. I was thinking about using arduino, but it doesn’t seem to be well suited for charging a phone (maximum current output is rather low). Would it work if I made separate circuits, one for charging a phone and another for reading the data from voltmeter and sending it to the phone through the other pins on usb?

I’m sorry for such a tremendous question, I just don’t have much experience with electronics (not even a year at college), and I must somehow do all this stuff.


texts:
When you model the structure to be analyzed with a structural analysis program, indicating the beam elements, shell elements, nodes, rigid links etc... The analysis is still called Finite Element Analysis, BUT, the mesh generation is not done by the computer program in this case, since you defined the nodes yourself. Am I correct? If not, what am I missing?
In what cases, instead of modeling we have the software do mesh generation?


texts: Determine Bolt dia from Shear stress and force

texts:
The Diagram below shows a lap joint where two plates are held together by a bolt. The applied force (F) is $42~\text{kN}$ and the shear stress is $593~\frac{\text{N}}{\text{m}^2}$ Assuming that the joint will be held together by a standard metric bolt, determine the minimum diameter permissible and identify the standard bolt diameter that will need to be used.

This is my answer is this correct?

$$\sum f_x=0$$

$$V = \frac{p}{1} = \frac{42}{1} = 42kN$$

$$\text{shear Stress} = 593N/m^2$$

$$593^2 = 351.649 Kn$$

$$ \frac {42000}{351.649} = 119$$

$$ a = \frac{pi}{4} D^2$$

$$D = \sqrt\frac{4A}{pi}$$

$$D = \sqrt\frac{(4) (119)}{pi}$$

$$ = 12.309$$

Is this the correct answer, and the correct way to complete this question?


texts:
I am setting up an experimental station for which I am using a small gear pump to pump water. I have noticed that on the discharge port of the pump, a short row of bubbles comes out at high flows and low pressures.

For example, at 650 ml/min and 2 bar of system pressure I might observe a relatively long row of bubbles coming out from the port. By increasing the system pressure up to 7 bar, the row shortens and eventually disappears. The same happens if I decrease the flow. I have checked the feed, and it does not contain any bubbles.

This has led me to believe I am having some degree of cavitation in my pump, is this correct?


texts: What is the maximum efficiency of a mechanical electric generator?

texts: If we apply a simple push to rotate a system of gears to generate electricity, what is the maximum practical and theoretical power efficiency of the system, assuming the push as the only source of energy? What if the gears are to be rotated continuously?


texts: Calculating angle of attack and relative air velocity for 3DoF simulations

texts:
I am working with a 3DoF simulator to implement dynamics mentioned in this paper: "Reusable Launchers: Development of a Coupled Flight Mechanics, Guidance, and Control Benchmark" which is actually a 6DoF approach (statics+dynamics).
When they calculate the angle of attack, they use the relative air velocity, which is an inertial frame velocity minus the cross product of the earth rotation vector and the inertial frame position, and some term for wind perturbations. The problem is that in order to convert this to the body frame to get the relative air velocity for drag calculations you need to work with the body frame, which means that you need the aerodynamic angles of roll, pitch , and yaw. How else can I calculate the drag from my model which works in the local vertical local horizontal frame?


texts: Hydraulic pump choice - which produces most force

texts:
I have a choice of two hydraulic power units with specs as follows:

A. 2.2kW motor, 8lpm flow rate, 120 Bar pressure rating

B. 1.1kW motor, 2lpm flow rate, 200 Bar pressure rating

Using F=PA I assume pump B is capable of producing more force in the same system (albeit a lot slower!)

However, hearing the phrase "resistance to flow produces the pressure not the pump" many times gives me a nagging feeling.

Am I correct or is there something I'm missing?

Thanks


texts: Why is the martensite to austenite transition temperature in Shape Memory Alloys so much lower than in steel?

texts: When learning about Shape Memory Alloys (SMAs) I was told that the mechanism that allows for strain recovery in SMAs is the martensite to austenite transformation that occurs at low temperature around 90C. This transformation is named for the transformation that occurs in heat treatment in steels since the crystal structures of both are identical, although the transformation in steel occurs around 727C. My question is why is the transition temperature in NITINOL SMA so much lower than the transformation temperature of steels?


texts: How is EPD different / related to anodising?

texts:
What is the process of applying dye to anodized surfaces (specifically aluminum)?

Is electrophoretic deposition (EPD) just the process used to apply the dye to anodised surfaces?

Or is it a different type of coating?


texts: What is the difference between the wave equation and the advection equation?

texts:
I am trying to understand what is the difference between the wave equation ad the advection equation? Bot the equation seems to move a quantity. While in literature it is said that the advection equation is the simpler of the two I don't see how the wave equation is that much different than the advection equation except moving the quantity in both directions when talking in terms of 2d.

Ref :

https://www.rose-hulman.edu/~bryan/lottamath/wave.pdf
http://farside.ph.utexas.edu/teaching/329/lectures/node90.html


texts:
I want to build my own off-grid system but confused with what sizes (V, I) to get.

I want to run a 24v system powering 4.4kWh/day.  I have 4 hours of usable sunlight a day and space for panels and equipment is not an issue (within reason).

Looking at the calculations:

Electrics = 220v @ 60Hz
Load = 4.4kWh/day
Sunlight = 4 hrs

The PV array I then calculate at:

PV Array = 4400Wh / 4hrs = 1100W (10 x 100w panels)

The batteries I then work out at:

4400W / 24v = 184Ah / 80% discharge = 220Ah

A battery example [1] - 24v 220Ah deep-cycle li-ion (2000times(80%DOD))
* or if you want to go down building your own battery pack with 18650's - 7 in series (to get 24v) x 55 packs in parallel (to get 220Ah).

The calculation problems I cant find anyone explaining on Google is:

a) What size charge controller do I need?  I see options from 10A to 100A.
b) What size inverter do I need? I see options up from 100W to 3000W and more.
c) Does the PV array not need to be x2 the size so it can power the house and charge the batteries at the same time during the day?

[1] https://www.alibaba.com/product-detail/Custom-24-Volt-Solar-24V-200Ah_60670679703.html?spm=a2700.7724857.normalList.25.15c91a82Albyfj


texts: Are there materials that are good at transmitting sound but thermally insulating?

texts:
I'm wondering if there are materials good at transmitting sound but is thermally insulating? I'm trying to figure out a good material in an engine exhaust application which will pose a barrier to the high-temp exhaust flow, but allow the exhaust noise to pass through.

I'm particularly interested in low frequency sound only - 50 Hz to 350 Hz range.

The following cross-section image defines the application I have in mind a bit better. I'm trying to develop active noise control for engine exhaust noise. I'm hoping to use commercially available loudspeakers and so need to separate it from the main exhaust flow's heat & humidity. The material I'm looking for here is labelled "Material X". Sound (green arrows) will be transmitted through it, but the exhaust flow (white arrows) cannot move through.

This is somewhat opposite to this question.


texts: Do the steels 1.4404 and 1.4571 have the same corrosion resistance?

texts:
The steel type 1.4571 / (X6CrNiMoTi17-12-2, ASTM: more or less 316Ti) is commonly used in wastewater applications due to it's good corrosion resistance. An alternative is 1.4404 / (X2CrNiMo17-12-2, ASTM: 316L), which is often said to be inferior. Several steel plants published information materials to the following effect (don't have an english source, so I summarize the key points):

Heat treatment of carbon steels would lead to the formation of Chrome-Carbides, these are attack angles for corrosion. Ni and Ti are added to form 1.4571 because these elements form carbides and so prevent the formation of Chrome-Carbides.
Current (since a few decades ...) manufacturing technology allows lower carbon content in steel production, so that addition of Ni & Ti are no longer neccessary to have corrosion resistance as good or better as 1.4571 in many cases.
1.4571 is clearly superior in applications with T > 350°C

All information about the comparative corrosion resistance of these steels I found so far comes from steel plants and traders who have a vested interest in pushing 1.4404: 1.4571 is commonly used in Germany, Austria and some eastern European countries, apparantly the rest of the world moved on to 1.4404 et. al. This means german steel traders need to warehouse two types of steel.

Is, according to an independent assessment, the corrosion resistance of 1.4404 same or better than 1.4571 in most conditions?


texts: Effective ways to drive a single shaft with multiple motors?

texts:
To head off the "why not use a bigger motor" question, I'm a high school mentor for an FTC (First Tech Challenge) robotics team, with a bit of a soft mechanical / hardware background.  They're somewhat limited in what they're allowed to use, motors in particular.  Up to 8x 1.5 ft-lb 12v DC motors, max.

This year they came across the problem of needing more lifting power, which gearing could help with, but to get the lift they needed cost a lot of speed, which in a very short (~2 minutes) competition, was a costly trade off when there was a need to go up and down frequently.

Possibilities I've considered (and haven't had time to mess with yet, but I'm trying to research and get input from engineers better than myself..)

Having two motors directly driving the same gear on the shaft seems like the first obvious answer, but error prone (slipping out of sync and grinding potentially.)
Two motors driving two separate pulleys on the driven shaft, which should theoretically gain power without the gear jamming issues.

I'm planning on having the kids experiment and test, but as my ME experience is extremely weak, I'm soliciting input.


texts:
I have to make a dual blackboard like the one here, http://www.ucd.ie/physics/lhcb/contact/blackboard.jpg,

My biggest concern is what sort of mechanisms I should use to allow for smooth and easy movement of the blackboards.  The boards need to be brought up and down, and be able to stay in place once they've been moved.

I do have an idea on how to do it with weighted cords and pulleys, but I believe there are people with more experience in this area.  I'm not as certain about the mechanisms to keep the boards in place though.

Can someone help identify the parts I need to make one of the board to move up and down? Also, which parts do I need in order to make the boards stay in place after being moved?


texts: Engineering standards or testing standards for hot punched metal holes for rolled steel

texts:
So, I have a problem with fatigue cracking originating from hot punched holes. From failure forensic reviews, it seems like surface conditions contributed to some of the failures, especially where there are leftover shear marks and laps from punching operations. I did a quick research but it doesn't seem like there are well established standards regarding the finishes of holes generally in terms of hole surface quality. Am I over thinking and that nobody had the same problem previously? Or are there some standard that I am not already aware of that exists?

One of my thoughts is to establish Ra Rp Rz acceptable ranges that can be applied for the holes. But I have doubts about measurement consistency as those measurements are usually more geared towards flat surfaces. What are your thoughts on this?

Thanks for all your help!!


texts: What is the proper screwdriver for a M2 counter-sunk hex screw?

texts:
I have many M2 flush-mount, counter-sunk hex screws ordered from a variety of sources, including McMaster Carr, Ebay, etc. The Wiha 263 1.5x50 screwdriver I have does not drive any of these properly, which means I have to step down to a 1.3mm screwdriver which is too loose and causes stripping.

Can someone help me identify the proper screwdriver to drive M2 Hex screws? Numerous google searches don't seem to shed any light on this, although pages like this seem to suggest a 1.5mm hex driver SHOULD fit.


texts: What is the longest self support length a chain one molecule wide can be?

texts:
Self-support length is the maximum length of a vertical column of the material (assuming a fixed cross-section) that could suspend its own weight when supported only at the top this is an important consideration in the construction of a space elevator.  While it is unlikely a strand one molecule wide to stretch from the surface of the Earth to space, it would be interesting to know what the longest self-support length a chain one molecule wide (single-chain polymers) could be.

A larger molecule gives a larger cross section, but it is also heavier.  Most space elevator concepts are tapered  to provide additional strength where the load is greatest.

What kind of single-chain polymers can provide the longest self-support length for a column one molecule wide, and what would that self-support length be?


texts: Seeking transparent, somewhat flexible material

texts:
Looking for a material that:

Is transparent/clear - the clearer the better
Can be made to about 80cm long x 8cm wide by somewhere between 2-5cm thick (likely 2-3cm, exact details will depend on the material's properties)
Can be shaped on the cross section, either during manufacturing, or after
Is at least a bit flexible - I'd estimate no more than 20 degree bend along the length, without too much force required - i.e. something that could be bent by hand, like a plastic ruler.
Has a refractive index for visible light of 1.5 or above (higher is better)
Is cheap, or at least not too expensive
Is resistant to chipping or snapping

Can anyone help?

Partial matches to the above might be welcomed, but it would be useful to know why they are only partial matches. The key points are (1), (2), (3), (4) - other than those, the higher refractive index the better, the cheaper the better, the more resistant to chipping and snapping the better, but those are continuums rather than fixed points! The method of shaping also matters, ie something that can theoretically be shaped but in practice requires a really expensive or rare process, or hand shaping, is not practical.

For example, I have access to injection molded Polyester resin, but I understand that might not be flexible.


texts: How do Thumb instructions compare to ARM instructions for performance?

texts: A colleague mentioned that Thumb instructions were significantly slower than ARM instructions (this was for an AT91SAM7S32 processor).  Is this true?  What are the performance benefits of one instruction set over another?


texts: Abaqus Failure for I-Beam Section in Major direction only

texts:
For my 4th year dissertation in Civil Engineering I've got to investigate the difference between BS5950, Eurocode 3 and ABAQUS failures. The only thing is, in the BS5950 and Eurocode 3 the failure can only include Major OR Minor axis which is what I need. However, in ABAQUS, the software itself 'decides' in which way it will fail. It starts with Major axis but at the end it takes into account the Minor axis too which gives me an error in comparing these results with the BS and Eurocode.

My question is, is there any way you can tell ABAQUS that the only way the failure can occur is in Major axis? without taking into account the Minor axis.

I'm using BBC Basic to create the ABAQUS input files and then run them through the Command. I have already tried to put 'boundary conditions' (a maximum length it can move along) but it gave me a too high of an error between with and without the boundary conditions so I can't do that.

Has anyone ever do that kind of investigation? Any advice/ideas?

Thanks in advance.


texts: Can a simple application of two forces have two different outcomes on a rigid body?

texts:
[Summary: If two forces are such that the component of one of these forces forms a couple with the other, than which of the two cases (obtaining resultant via adding forces or obtaining moment and a resultant force via the method shown below) are correct? Read further for clear and detailed explanation]

Let two forces, F1 and F2, act on a rigid body and have a common point of application at Point A. Then their resultant force, R, can be calculated by the normal use of parallelogram as shown in the image below:

Now, since forces can be moved along their action lines in rigid bodies (statics), let the same forces be moved along their action lines as shown in the image below (Img.2):

Assume that the y-component of F2 is equal but opposite to F1. This means that the y-component of F2 and the force F1 act as a couple, and cause Moment in the rigid body, which is equal to F1 multiplied by the distance between them. In addition to this moment, we also have the x-component of F2 left over, which is the resultant force on the rigid body.

So, does this mean that, given the following conditions:

1) If any two forces Fa and Fb have intersecting action lines,

2) A line perpendicular to the action line of Fa at the point of intersection divides the plane (or rigid body) in two parts,

3) And Fb points towards a different plane (or different part of the rigid body) than Fa,

Then we have a resultant force (found by the parallelogram law) and moment at the same time?

But then what is the point of application, O, of the resultant force found in the second Image (Img. 5)?

But if this is so, then shouldn't the parallelogram be only defined in a way where the two forces are directed towards the same plane?

Or is this entire thing true? Can the forces actually be moved and resolved in a way they are here? Why or why not?

[Sorry if the post is messy and incomprehensible. I tried, as much as I can, to explain the question in the most organized fashion...]


texts: Can I keep hardened steel cool with ice while welding?

texts:
I would like to weld a piece of hardened steel but i don't want to ruin the treatment on the tip of the piece.
Can i put some ice in the middle of the shaft so the heat generated from the welding (SMAW DCEN) doesn't temper the tip?
Thanks in advance.


texts: Calculating pitch, yaw, and roll from mag, acc, and gyro data

texts:
I have an Arduino board with a 9 degree of freedom sensor, from which I must determine the pitch, yaw, and roll of the board.

Here is an example of one set of data from the 9-DOF sensor:

Accelerometer (m/s)

$\text{Acc}_{X}$ = -5,85
$\text{Acc}_{Y}$ = 1,46
$\text{Acc}_{Z}$ = 17,98

Gyroscope (RPM)

$\text{Gyr}_{X}$ = 35,14
$\text{Gyr}_{Y}$ = -40,22
$\text{Gyr}_{Z}$ = -9,86

Magnetometer (Gauss)

$\text{Mag}_{X}$ = 0,18
$\text{Mag}_{Y}$ = -0,04
$\text{Mag}_{Z}$ = -0,15

How can I calculate pitch, yaw, and roll from these data?


texts: PE exam: situations in which two question choices are close to my final answer: how to pick one?

texts:
Consider this question:

I solve this eventual question and my answer is 7.29667:

Among the question choices are 7 x 7 ft and 7.5 x 7.5 ft. Which one should I choose? I guess if a safety margin is intended, the larger choice i.e. 7.5 x 7.5 ft should be selected. Am  I right?
There are situations like this in which two question choices are close to my final answer and I'm not quite sure which one to pick. Is considering safety margin a good criterion to pick the choice? Thanks for your help!


texts: How are most sheet style nichrome-based heating elements constructed?

texts:
I have noticed that nichrome is a common resistance wire used for various heating purposes. I have seen it used inside what seem like glass tubes (like on an electric stove) and just floating in coils (like in hair dryers), but how would it be made in a sheet form?

The problem is that it is not insulated, which means that if it touches another piece of metal, the current would flow through that metal rather than the nichrome.

You would want the material it is wrapped in to be thermally conductive, but not electrically.

I've seen designs like this which put an insulator around the nichrome, but I don't see how that is effective at distributing the heat produced by the nichrome.

I am trying to achieve an even as possible distribution of heat at about 150C. My power supply is going to be a 12V supply that can do up to 15A (so current is not much of an issue here).


texts:
I am sure you all remember those prehistoric computer mouses that had a ball under it. I'm looking for any points and tips on how to create a ball and socket wheel that has an almost frictionless connection with its casing and allows for no resistance in any direction.

To clarify, this wheel should be able to move essentially with a wide range of motion in an infinite amount of directions. I am hoping to use some rubber ball that would give an ideal friction against some smooth surfaces and the base case of this is that it will not move unless a force acts on it (unless it is on an angled plane of course).

I want to know specifically if there are any technologies out there I can use for reference and if this concept is plausible, especially in simple mechanics, meaning no electronics, no moving parts or other fancy additions. Thank you for your help guys.


texts: What sensors/methods can be used from the roadside to determine if a truck is loaded or empty - without weighing it?

texts:
What sensor, using what physical principle, can penetrate a closed rectangular object like the trailer of a truck and tell if the space is empty or loaded?

Why is this question relevant? One of the biggest problems of maintaining & building roads is to understand how much load is transported over that road per time increment. A loaded truck can bring much more damage to a road than many cars can (a 18 wheeler can have the impact of over nine thousand cars). Current in-road, at-speed weighing technology can cost millions. The reason for this questions is trying to find a way to use existing low cost sensors (or a combination of multiple sensors) at the roadside to assist with estimating the weight of a truck. If we know the truck/ trailer combination is empty or full, we typically know the lowest and maximum load weight. And then can estimate the average load on this road per time increment. This is much better than current vehicle counts and is commercially very interesting.

Many thanks for staying on topic and trying to point me in the right direction.

Initial thoughts: It is easy if you can visually see the load (like on a logging truck). It is hard if it is a closed curtainsider, bulk load or container truck from a stationary roadside measurement unit.

Computer vision could be used to compare the bounce of the cab, analyze the suspension; use thermal camera to detect higher temperature of tyres or axis; acoustics of empty vs loaded. What other sensors/ physical principles should be tried like measure on an uphill stretch: slower truck of same vehicle class will be loaded truck.

Again, many thanks for sharing your thoughts on what physical principle could be tried to tackle the problem to detect if a confined space is empty or filled, from the outside without weighing it. An approximation with an acceptable error rate is fine.


texts: Is the combination of blocks and lines in this old, very long telescope an implementation of some named structure or technique?

texts:
Below are two cropped views of "Johannes Hevelius's 8 inch telescope with an open work wood and wire "tube" that had a focal length of 150 feet to limit chromatic aberration." from Harvard University, Houghton Library, pga_typ_620_73_451_fig_aa (found here) the first of which I've zoomed and enhanced the contrast.

I've used these images in two other questions in Astronomy SE:

How did Johannes Hevelius' long telescope work? Why all the round holes?
How does making a refracting telescope very long reduce the chromatic aberration of an uncorrected lens?

This answer provides a link to the original text and image but the discussion was published in 1673 and may be difficult to understand or paste into google translate.

However, the structure itself may be familliar to engineers. I'm getting the feeling that the series of square blocks with round holes and string or lines connecting them (presumably under tension?) have no specific optical function, and are purley part of a system to keep the long "telescope tube" stiff.

Is this combination of blocks and lines a recognizable implementation of some named structure or technique?


texts:
I am not sure if this is the right place to ask it, but this is a question that I thought today, and it gave me some curiosity to understand. Imagine that a car will curve, we can say the turn is a bit tight , what are the factors that can help it to flip? I was wondering about some aspects:

if the car has mass, it has inertia, so while it is curving it tends to keep the motion in the same direction that it was instants before the turn. right? So, if the car has more mass, it has more inertia, and since there is friction, one heavier car would flip easier then one lighter, considering that all other possible variables were equal.

Center of gravity, a car with an higher center of gravity would flip easier. The whole inertia of the car distributed to higher heights would be further of the tires(where friction acts), creating angular momentum.

The car being thin because it has less surface contact with the ground;

The car being lighter. This opposes what I've said in "a)", but a heavier car is more difficult to get off the road. A lighter car has more instability.

Am I wrong? In what I'm wrong? What do you think?

Thanks for helping. :)


texts: Interpolation at a face, Finite Volume Method in Computational Fluid Dynamics

texts:
I am learning CFD and I have come across an example in which the thermal conductivity needs to be interpolated at a face between two rectangular cells.

The face weighting factor is given as:

$$g = \frac{V_1}{V_1+V_2}$$

where $V_1$ and $V_2$ are cell volumes.  I expected the interpolated value, $k_{1-2}$, would be

$$k_{1-2} = gk_2+(1-g)k_1$$   (linear interpolation)

but instead the author of the example gives:

$$k_{1-2} = \frac{k_1k_2}{[1-g]k_1+gk_2}$$

In the context of finite volume method CFD, what is this method of interpolation called and why would it be preferred over linear interpolation?

(The example I am referring to above is Example 1, Chapter 8, of The Finite Volume Method in Computational Fluid Dynamics by Moukalled et al.


texts:
I can't find anything on this. Every source I can find on UV cured polymers describe the process and how they're cured using UV radiation but nothing on what the resistance to UV is once it has cured.

Specifically I'm looking at the Stratasys PolyJet (http://www.stratasys.com/materials/material-safety-data-sheets/polyjet) line of resins which are supposed to be very similar to PMMA in mechanical properties but I can't find anything on whether this extends to UV.

If anyone with more knowledge on polymers can help me out that would be greatly appreciated.


texts: How common is it to use more than two Rebar rows in a beam (bottom or top rebar)?

texts: I'm programming a drawing plugin for autocad to draw cross-section in beams and ribs. I need to know if it is worth it to add (to my plugin) the feature to add more than two rebar rows, or if I'll be covering the most use cases with two.


texts: Hanging a steel mesh without significant deformation

texts:
I have an welded steel mesh, like in  the following image.

.

Material: steel
Diameter of the wires: 4mm
Mesh: 15x15cm

I found the following information about the welds:

the minimal relative strength of welds in shear: Fms = 4.4kN

I want cut out an rectangle from this mesh (dimensions are on the following image) and want hang it on the wall, suspended by two screws.

Now I want hang to the welding points some weights. (on the image the drop-like things) :), in two scenarios:

uniformly attach to each welded point some weight (like the blue "drops")
attach one big weight to the center (the red drop)

What is the weight I can hang on the mesh (in both scenarios) without significant structural deformations (2% elongation)?
I don't want have broken welds. Will the welds fracture before the bars yield or vice versa? At what load will the first of these failure modes occur?

Also, i'm looking for some "guide" how it should be calculated - if it is possible to do in easy (read: "idealized") form, without specialized software. I would be happy to calculate it myself, but need some "how to". Understand than using finite-elemets or such will give most precise result, but is here some "easier/simpler" way?


texts: How does a stator convert velocity into pressure?

texts:
I'm looking for, hopefully, a qualitative answer to how a compressor increases pressure. I understand the equations that predict this result but I can't picture it in my head.

A rotor spins, deflecting air into the engine and increasing the air's velocity. Next, there are stationary fins that this relatively high speed flow collides with. Somehow this contact takes away velocity and adds pressure. This crucial step is the part I don't understand.


texts: Ventilation setup high sleeper night cooling

texts:
I have a high sleeper in my room (width 3,70m, length 4,50m, height 3,30m) consisting of one large plane (yellow) and one window (darker grey). The plance leaves about 80cm space to sleep. The door (not visible) is under the plane and should be irrelevant because it remains closed over night.

The space between plane and ceiling tends to get hot relatively to the room temperature because warm air rises up. Opening the window (tilt or completely) is not a problem, but the cooling only has a small effect close to the floor of the room - without moving air/wind -, and as good as none under the ceiling for hours (when I wake up at night an go down from the bed and up again I feel a significant temperature difference).

Therefore I'd like to transport cold air from outside inside the room to create a stronger/faster cooling effect. I'm considering a system with multiple small vents. Which direction of airflow would be advantageous? Blowing warm air outside? Sucking cold air in? Laying out airflow in a line (e.g. from window to bed) or in a circle? Directing the airflow close to the ground or the ceiling?

I'm renting the room and can't change the door, window or floor. The door has no joints and leaves some mm gaps at all sites. The ceiling in the build are old wood constructions which at least lets warm air pass very well in winter (I don't have to heat in the early winter because my neighbors below do that).

Construction of supports, ducts or else is not a problem because I have access to carpenter tools and expertise in the neighborhood - nor is the look of the installation/making the installation look nice. I want to figure out the engineering aspects of the setup.


texts: Differences between shell type and core type transformers

texts: What is the advantage of a shell type transformer over core type and which one has smaller flux leakage?


texts: What engineering obstacles would need to be overcometo make a hot air balloon bigger than the largest made?

texts:
Average hot air balloons have a diameter of about 18 m. The largest  out there is roughly 32 m.

My question is, are there any reasons other than fuel concerns that would prevent having a larger balloon, say around 50-60 m as a lifting body? I.e. problems with air mixing, pressure differentials, etc in such a large volume?


texts:
I have a microcontroller similar to the one in the accompanying picture. I do not want to solder wires to the microcontroller contacts

Is it some kind of printed circuit board on which a microcontroller can be placed without having to solder wires? I cannot find anything.


texts: How much strength does adding a T piece add?

texts:
If I have a flat span of steel material,  3.0m x 150mm wide and 5mm thick, and apply an increasing downward force to the middle, at some point it will fail.

But if the profile of that piece of steel was T shaped instead of a flat span, it is much stronger.

Is the Safe Working Load (SWL) for different profiles calculatable by a specific formula?

Assuming so, otherwise how could you design things like cranes, does the same formula apply to different materials e.g. aluminium v steel and different thicknesses of the same material?


texts:
If you have a saturated steam (quality=1.0) volume  that is compressed adiabtically will the steam condense to follow the saturation curve or superheat?

I found in an old textbook: The Principles of Thermodynamics (1899) on Google the following passage:

  For compression, adiabatic:

  If we start with pure saturated steam, without admixture of water, it will be superheated by compression.
  If the initial steam weight is greater than that of the water, steam is generated by the compression.
  If there is more water than steam, steam is condensed during compression.

I am still at a bit of a loss for this makes physical sense and how this is properly captured in an energy balance. (i.e., $\frac{\text{d}U}{\text{d}t} = -\frac{p\text{d}V}{\text{d}t}$)


texts: I have some university work to do based on a real world application with five or six bar mechanism, but I am unable to find such a device. Are there real applications of such mechanisms? I've considered some, such as the trigger of a gun and a locking plier, but they are all four bar mechanisms.


texts: How to create a clear bill of materials list?

texts:
I am required to create a Bill of Material for a steering system I am designing.

However, I am not entirely sure how to structure it. For example, what type of order are the parts listed as I have seen some that involve levels (I have posted below)?

I just require some knowledge from someone who has created a full list on how to write one up clearly. Also the parts circled are what I like help explaining.


texts: Difference between Linkage, Kinematic chain, Mechanism, Mechanical element, Mechanical machine and their precise definitions

texts:
Recently I started to study about "Design of mechanical machinery". Since I am a person who is very sensitive about words I want to know the difference between these notions and their precise definitions:

Linkage
Kinematic chain
Mechanism
Mechanical element
Mechanical machine

It will be very good if you introduce some source textbooks which treat these concepts very carefully and accurate as well.


texts: Positioning and size for a Joukowsky Airfoil

texts:
Joukowsky transformations are absolutely eluding me because I can't find numerical examples (I have a learning disability and formulas have always made absolutely no sense to me). I'm trying to get an understanding of how to set up a Joukowsky tranformation for an airfoil and it's positioning.
Given a thickness/chord ratio of 12%, Camber of 4%, and angle of attack of 3 degrees.
So far what I've done is trying to get the radius from the thickness/chord ratio. From diagrams it appears that to do that $$ \frac{Thickness}{Chord} = \frac{b}{a} $$
Considering that the chord is entire length making the assumption then that $ a = 100$
$$ .12*100 = b $$
This gives the chord of b as $12$
to get radius from chord $$ \frac{12^2}{12*4} $$
Giving a radius of $ 3 $
I've also seen that $$ Camber = \frac{\epsilon_i}{2a} $$
Taking again $a=100$ and $camber = 4%$
$$ .04*200 = \epsilon_i = 8$$
This is where I don't know what to do next.


texts: Difference between 'plastic yielding' , 'plastic yield strength', plastic strength' and 'plastic stress'?

texts:
I am going through a literature where these terms are regularly used and I am confused are they different and if yes then what does each term mean?
I also want to know relation of plastic strength of a rock (say granite) with pressure. I mean which equation describes this relation?


texts: Lyapunon candidate function to derive parameters estimation law

texts:
I have a system and a reference model represented in state space in the following form:

\begin{gather}
\dot{x} = Ax+Bu \\\
u = \hat{K}(t)x+\hat{k}_r(t)r \\\
\\
A_m = A+BK \\\
Bk_r = B_m \\\
K,k_r : \text{desired controller  gains} \\
\dot{x}_m = A_mx_m+B_rr \ \text{Reference Model}
\end{gather}

where my goal is to design a direct (controller gains are updated directly) model reference adaptive controller for the system $x$ to track the reference model $x_m$ when there is bounded $r(t)$ signal as reference input. By defining the error terms to be:
\begin{align}
e &= x_m - x \\
\tilde{K}(t)&=\hat{K}(t)-K \\
\tilde{K}_r(t)&=\hat{K}_r(t)-K_r
\end{align}
I have derived the system tracking error:

$$\dot{e} = A_me-B\tilde{K}(t)x-B\tilde{k}_r(t)r$$
What I want to do is derive update laws for the time changing controller parameters $\hat{K}$, $\hat{k}_r$. In order to do so I follow the Lyapunov procedure by defining a Lyapunov candidate function,computing its derivative and then trying to prove that the derivative is at least negative semi-definite. I chose the following Lyapunov candidate function:

$$V = e^TPe+|b|(\tilde{K}Γ^{-1}\tilde{K}^T+γ_r^{-1}\tilde{k}_r^2) $$

where $P$ is a positive definite matrix computed from the Lyapunov equation $A_m^TP+PA_m=-Q$ since $A_m$ is defined to be Hurwitz, $B=[0 \ \ b]^T$(sign of $b$ is known) and $Q=Q^T>0$. $V$ is the Lyapunov candidate function and the constants $Γ$ and $γ_r$ are positive adaptation gains.

$$ \dot{V} = \dot{e}^TPe+e^TP\dot{e}+|b|(2\tilde{K}Γ^{-1}\dot{\tilde{K}}^T+2γ_r^{-1}\tilde{k}_r\dot{\tilde{k}}_r) $$

Now by substituting the equation for $\dot{e}$ I have derived the following result:

$$ \dot{V} = -e^TQe+2e^TPB(-\tilde{k}_rr-\tilde{K}x)+|b|(2\tilde{K}Γ^{-1}\dot{\tilde{K}}^T+2γ_r^{-1}\tilde{k}_r\dot{\tilde{k}}_r) $$

The term $2e^TPB$ can be written $2e^T\bar{P}b$ where $\bar{P}=[p_{12} \ \ p_{22}]^T$ and since the sign of $b$ is known, $b = |b|sgn(b)$. Taking these into consideration I have reached the final form of $\dot{V}$ which is :

$$ \dot{V} = -e^TQe+2|b|\tilde{K}(-xe^T\bar{P}sgn(b)+Γ^{-1}\dot{\hat{K}}^T)+2|b|\tilde{k}_r(-re^T\bar{P}sgn(b)+γ_r^{-1}\dot{\hat{k}}_r) $$

Defining the update laws to be:

$$ \dot{\hat{K}}^T=Γxe^T\bar{P}sgn(b) $$

$$ \dot{\hat{k}}_r = γ_rre^T\bar{P}sgn(b) $$

we are left with $\dot{V} = -e^TQe \le 0$. I am writing this more for validating purposes since I am not so sure if I computed the derivatives of the transposed matrices together with the normal matrices correctly (I know it is time-consuming but anyone who is willing would really help) and also is there any other good option regarding the Lyapunov candidate function which I could consider ?


texts: Camber Diagram for Steel Girders but not for Concrete Girders

texts:
Why is it that, at least in Ontario Canada, camber diagrams are required for detailed design drawings (Not shop drawings) for bridges with steel girders, but are not required for CPCI Girders?

My understanding is that the camber drawing is required for the steel manufacture to put in a vertical curved to the beam so that when the dead load of the superstructure is added on top of the girders the whole thing bends to meet the road profile.

For concrete girder this is not done, though a similar process seems to be followed.  The screed elevation is adjusted to account for deflection of the concrete, including long term deflection from shrinkage and creep.

I would have thought a screed elevation table would be required for both steel and concrete girder designs, so why have to two different approaches for dealing with deflection to match the road profile?


texts: Determining the heat capacity of an X-Band transmitter

texts:
I am conducting a thermal analysis of an X-Band transmitter that will form part of the payload in a CubeSat. The goal is to determine how long the X-Band transmitter can operate before it will overheat.

In order to do this I need to experimentally determine the heat capacity of the transmitter.

My current plan is to apply a known heat flux to the transmitter and use it's temperature measurements to calculate the heat capacity. However, this method wouldn't take into account the convective and conductive heat losses from the transmitter (which I imagine would be significant?) These losses would lead to an over prediction of the heat capacity of the transmitter.

How can I take account of these losses in order to obtain realistic results for the heat capacity of the transmitter?


texts: Arc welder? Cheap welding device for chainmail/chainmail jewelry

texts:
I'm hoping this is the correct StackExchange for this question/request for advice.

I'm looking to buy a welder to introduce me a little to welding, my main use-case right now is the hobby projects I do with chainmail and soldering is just not good enough in my book. I'm working with stainless steel jump rings with a diameter ranging from 0.8mm to around 2mm.

I've seen on TheRingLord and Ganoksin that this can be done with an arc welder. As far as I've seen arc welders have the lowest prices and to me also seem like the least maintenance heavy since you don't need to stock up on gasses. So arc welders have my focus for now. My budged is around €200,- tops preferably from a dutch reseller, and I have no clue what to look for in a welder (my only clue so far is probably something that can be activated for short amounts). Would anyone be able to give me some advice on what would be a good welder and if I'm even looking in the right direction?

please do note that I'm not just looking for something fast and easy, I really don't mind getting my hands dirty learning how it works and getting some terrible welds in the process.

Some sites that are available for me (you might not be able to read the descriptions, but the welder device-names should still be the same):

CoolBlue
AllesVoorLassen.nl
Beslist.nl


texts: Structural analysis + thermal expansion using ANSYS static module

texts:
I am attempting to model a steel sample subjected to combined mechanical and thermal loading. The thermal loading can be quite elevated, where reduction in the elastic modulus will occur.

Does anyone know if ANSYS's static structural module automatically accounts for the reduction of stiffness?


texts: Calculating the ultimate achievable vacuum pressure of a diaphragm pump

texts:
I am looking to design a diaphragm pump for a device.  I know that I would need to achieve a (negative) vacuum pressure of ~ 350-400 mmHg.  I know from standard rotary pump design the pump rate should be dictated by stroke volume and speed, and assume this is the same for a diaphragm pump, with stroke length perhaps.

How can I calculate the ultimate achievable vacuum pressure? I am looking for an explanation of the idealized equations for calculating this property of a diaphragm pump.

This would be for pumping a water based fluid, although slightly more viscous.


texts: Finding Stress Concentration Factor when (D/d) ratio is not on a table?

texts:
So we have this homework problem, it is a rectangular filleted bar and we have to find the minimum thickness. I go and calculated the ratios but here's the problem: (D/d) = 1.375. What may the problem be? Well for this intro to Civil Engr. Course we are taught to find the stress concentration factors using a graph. This graph only has the lines plotted for (D/d) = [ 1.1 1.2 1.3 1.5 ]. How do you guys deal with this when the (D/d) ratio is not listed on a table? Is there some formula to derive the function?

I am a Mechanical Engineering Major taking an intro Civil Engineering Course (Mechanics Materials) , so I have limited knowledge in Civil Engineering terms.


texts: The internal normal force, shear force and moment

texts:
How do I determine the internal normal force, shear force and moment at the point C?

$V_c = 0$, $N_c = 0$ and $M_c=3.75 kN/m$

I have already done this:

Where is the problem?


texts: Best way to manufacture stainless steel apparatus?

texts:
Shown in the images below I have designed a small stainless steel apparatus with accompanying hollow metal cylinders ontop.

I'm looking into larger quantity production and simply CNC'ing these would be cost prohibitive. I was thinking that pressing the steel into shape would be more cost effective, but I'm unsure how I'd go about adhering the hollow pipes to the top side. Would I do some type of welding to get these on with a solid airtight connection all the way around?


texts: What system-electronic components or physic mechanism is used to modulate signals between different devices used in lithography?

texts:
I know that pattern generator device (no pattern generator software) is needed to generate a model signal system that help you use electron diffraction for wafer surface printing by the use of the TEM. These signals are templates called patterns and is generated by some electronic unknown components inside of pattern generator, maybe with an amplifier or oscillator

I don't understand what modulation system allow this "driving" signal between this different devices (TEM, pattern generator, computer..) to generate correctly template-pattern for final printing on wafer ?

To print a chip project from design (software) you need to generate a modulation to communicate with pattern generator device and this pattern generator device needs to communicate with TEM but you need still a modulation to tell what TEM should print and how to print
What type of modulation or what system/component is used to modulate different signals between this devices ?

Indeed we must generate an interference before

  Diffraction cannot be explained using a particle view of light (geometrical or ray optics); it requires a wave interpretation (physical optics), according to which any image is actually an interference pattern formed by light rays that take different paths to reach the same point in the image

But still before generating this interference to have correct diffraction electrons used to print a pattern on wafer (we use a TEM system) you need a correct modulation.
 What and how signal generating check if this modulation system is correct to ensure that the devices understand each other ?

One of technique use something like Electron backscatter diffraction


texts: How to select the correct Bolt/screw Torque for sealing?

texts:
My coworkers and I are finally testing our agriculture sensor on the field. As you can imagine, the moisture and dust are important variables to keep aside from the electronics inside our product. Therefore we now want to take into consideration the sealing more seriously.
The case of our product is made of Polypropylene, and a gasket generates the seal. We want to purchase an adjustable torque screwdriver for the sealing, but I don't have any idea of the torque range we need. Of course, we want to create an airtight seal and avoid damaging the case plastic thread.


texts: Working Out Shaft Torque in a Stirred Tank with a Cylindrical Cavern Formation (using a non Newtonian fluid)

texts:
Here is some background to the problem (in a stirred tank):

"With yield stress non-Newtonian (viscoplastic) fluids, it is possible to generate an agitated volume around the impeller, defined as a cavern, surrounded by a stagnant region where the shear stress is insufficient to overcome the apparent yield stress of the fluid."

Sometimes you can get a cylindrical cavern around the impeller, see the below image.

"By performing a force balance between the applied torque, Γ and the shear stress acting on the surface of a cylinder, we can define the boundary by setting the shear stress equal to the yield stress τ = τY. The total torque is given by:
$$\Gamma = \frac{\pi}{2} \tau_{y}H_{C}D_{C}^2+\frac{\pi}{6}\tau_{y}D_{C}^3$$

I just can't get the second term. The first term I can get by doing:
$$\Gamma_{1}=\tau_y \cdot Area_{Curved} \cdot \frac{D}{2} = \pi \cdot \frac{D^2}{2} \cdot H_{c} \cdot \tau_{y}$$

This gets me the first term...but the second term I just can't get, this is what I'm doing:

$$\Gamma_{2}=\tau_{y} \cdot Area_{Faces} \cdot \frac{D}{2} =\tau_{y} \cdot 2 \pi \cdot \frac{D^2}{4} \cdot \frac{D}{2} = \tau_{y} \cdot \pi \cdot \frac{D^3}{4} $$

Argh, so I'm getting D3/4 instead of D3/6 for the second term and I just can't work it out, if anyone can help I'd appreciate it.


texts: What is the Radius of 1 and 1/4 inch drill on a 1 and 1/4 Circle

texts: I have this figure for my engineering drawing I am currently taking this semester I am quite baffled about this $1\dfrac{1}{4}$ radius circle with $1\dfrac{1}{4}$ Drill hole. How do I do that? as a reference I have this picture.


texts: How to I determine the dimentions for a worm gear?

texts:
I have a worm gear set with no drawings. I need to model them. The only things I know are
1) The Gear ratio is 30, and the worm gear only has one thread. It is a single start as opposed to a multi start worm.
2) The diameter of the worm is 0.7 Inches, and the length of the worm is 0.852 Inch
3) The diameter of the gear is 1.007 Inches, and it has 30 teeth.

I do not know the pressure angle, diametrical pitch or gear module.

What other piece of missing information would I need to know? How do I go about figuring out the diametrical pitch? How do I figure out the module.


texts: Ansys: issue with geometry visualisation

texts:
I am new to ansys and I am running ansys 17.1 on a macbook (on a parallel desktop) and I have a problem I can't solve. When I import or create a geometry, I can only see the silhouette of it in the "Study" tab (see picture 1). The contour results are not plotted either. When I try to edit the geometry instead, the part looks just fine (see picture 2).

Has anyone ever had this problem?

Picture 1:

Picture 2:


texts: Are toasters really electrified inside of the "slots"?

texts:
My mother was born 1950. Me in the mid-1980s. All my life, she's been saying that I must never stick a metal object, such as a knife, into the toaster, because it will electrocute me.
I've always been scared of this, even though it seems highly irrational. How could they possibly sell a consumer-oriented product like that which zaps its users if they happen to touch the interior slightly as they stick a knife into the piece of toast bread to get it out from the toaster when it inevitably gets stuck sometimes? Or is too hot to use your fingers?
But then again, this world is full of dangerous things, and maybe it's considered to be such a basic security knowledge that you never put a metal object anywhere near a toaster as it is to never run a microwave oven without anything in it? Something which seems to be almost universally understood?
It still seems odd to me. Why would they have the metal parts responsible for pressing against the bread and keep it in place be having electricity going through it? When asked, my mum just says that it "may easily get electrified" as if things like that just happen. But maybe she is right? A non-cheap water boiler recently stopped turning itself off from just handling it a little too roughly, so if something potentially dangerous like that could happen so easily, maybe the toaster can also start leading electricity through its inner metal parts?
And by "inner metal parts", I don't mean that I've unscrewed it and taken it apart. I just mean the "insides"; the little hatches for the pieces of bread. The parts you can easily accidentally touch with a knife when you try to get the pieces of bread out from the oven.
And I'm primarily talking about toasters made after 1980 or so, but I'm also interested in hearing if this was different for early toasters. Usually, things back in the day used to be very dangerous and scary.


texts: What do the rectangular components of the complex frequency (s) in Laplace transform stand for?

texts:
I tried doing a quick search on this question and was very surprised that this information feels very obscure as if it is almost never discussed. Complex frequencies appear in many mathematical concepts such as Laplace Transforms and sources mention the rectangular form as $ s = σ + jω $, but fail to actually explain what the rectangular components stand for.
I saw one source mention this.
https://www.quora.com/What-does-the-real-part-of-s-in-laplace-transform-represents

the real part(sigma) is called nepper frequency it control amplitude of function and its unit is nepper/second . and imaginary part(omega) is called oscillation (radian) frequency it control oscillation and its unit is radian/second.

I just decided to ask here to know what those actually mean. Also, if some people might respond with the rectangular components being irrelevant or having little significant application I just really want to ask this for the sake of knowing.
EDIT: I am asking what σ and ω in $ s = σ + jω $ stand for and why those quantities represent the real and imaginary components of the complex frequency. The source which I cited said that σ is nepper frequency and ω is oscillation frequency.


texts:
I want to monitor how much water we're pumping out of our shallow well every day (residential). We want to figure out how many gallons per day we're using. Doesn't have to be crazy accurate.

First thought was hooking up some kind of inline flow meter to a computer.

Then I thought, hey, since the pump always outputs the same amount of water when it's running, wouldn't monitoring the amount of time the pump is running be fairly accurate as well without needing an inline flow meter?

I'm thinking a relay or something similar that's triggered when the pump turns on. What would be a simple way to hook this up to a computer? A usb trigger thingy? (don't know if exists)
Or an arduino?


texts: How to find required clamping force of bolts to prevent flange faces from twising due to torque?

texts:
I have a gearbox adapter that bolts onto a flange and I need to work out how much clamping force is needed to prevent the faces from slipping and keep the bolts in tension rather than shear when torque is applied. However I can't use the straightforward friction equation here $(F_f =\mu \cdot F_n)$ because I don't know how to work out how the force from the applied torque is distributed.

For context, the torque being applied to the flange is $9123N \cdot m$ and the flange has an inside diameter of $185 mm$ and and outside diameter of $275 mm$. There are $12$ x $16 mm$ bolt holes at a diameter of $196 mm$. The two faces bolted together are made of $1020$ mild steel.

I figured that while friction doesn't have anything to do with surface area, in this case it would be better to have the flange face diameters as wide as possible because it would require less frictional force to resist the torque at a wider radius. However this has just confused me as I don't know what/where the forces are acting on the faces.

How can I find to force from torque that is distributed over a surface such as this?


texts: How to add a gap when splitting for joint in Solidworks

texts:
I drew a puzzle like joint sketch and split a body with it for 3d printing.
But I have to add a small gap between them for the tolerance of the machine.
Any way on how to do it not manually?


texts: I'm finding difficult in implementing real time clock for pic16lf1902, wherein their are no serial protocols for communicating/interfacing with builtin LCD display. Is their a convenient way to solve the problem? For example using I2C software functions with DS1309 for LCD disply as used for PIC18 microcontrollers.


texts: How can I mesure the axial induction factor of a small propeller using a DC motor?

texts:
I am trying to measure the axial induction factor of a small aeromodelling propeller.
By axial induction factor I call the ratio of the velocity of the wind far from the propeller $V_{\infty}$ over the velocity through the actuator disk $V_{d}$ as introduced in the Rankine-Froude actuator theory.

Let us call $$a=\frac{V_{d}}{V_{\infty}}$$ the induction factor.

The experimental setup is the following :

The propeller is mounted on the axis of a DC motor
Those are placed into a wind tunnel
A resistance $R$ (of a value really close from the internal engine resistance) is connected to the poles of the DC motor and the voltage drop $U$ across the resistance is measured.

From the actuator theory we know that the mechanical power transmitted to the propeller can be expressed as :
$$P_{mech}=2\rho_{\infty}SV_{\infty}^2a^2(1-a)$$

Given that $S$ is the area of the actuator disk.
From the experimental setup supposing that the efficientcy of the DC engine is $\eta$ I have :
$$P_{elec}=2\frac{U^2}{R}=\eta P_{mech}$$

From this I can find :
$$a^2(1-a)=\frac{U^2}{R\eta\rho_{\infty}SV_{\infty}^2}$$

The issue is that the experiments do not provide a satisfying value for $a$, the values I find are really close to $a=1$ which wolud mean that the propeller does not have any impact on the flow even if it rotates really fast.

Are there any flaws either in my experimental setup or in my theory ?


texts: Why afterburners are needed instead of burning more fuel inside the turbine?

texts:
I'm reading this article on afterburners:

https://www.airspacemag.com/flight-today/how-things-work-afterburners-18481403/

It says in the article:

  A typical jet engine uses only about half the oxygen it ingests, leaving a large amount of potential energy. The afterburner, which is a long extension at the back of the engine, combines much of the remaining oxygen with jet fuel, squirted into the high-speed exhaust stream from the engine’s turbine, and ignites the mixture.

I've searched many places but I've never really understood why the engine only uses about half of the oxygen it ingests. Instead, the afterburner is needed to burn more oxygen. But why is not possible to design jet engines that burn more oxygen instead of adding another separate component, the afterburner? Why do jet engines only burn about a half of the oxygen ingested?


texts: How to find properties of supercritical CO2 as a working fluid in a system

texts:
I'm working on a process flow currently and am using carbon dioxide as the working fluid because of its heat properties and because it's an inert gas. In the reactor that I am designing I'm looking to operate at 4 atmospheres (~58.78 psia) and at around 977°F (~500°C). I know it would be a supercritical fluid at this P-T relation but can not find any information on the properties of carbon dioxide at these conditions.

How would I go about finding or calculating for the thermodynamic properties at these conditions for carbon dioxide and then be able to continue this calculation through the entire process I'm designing?


texts: High frequency ultrasound effects on viruses and bacteria

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Might anyone have any clue on how high frequency ultrasound have effect on killing viruses and bacteria on surfaces (GHz/MHz)? There have been a few articles online that say ultrasound has effect on viruses and bacteria with literally shaking the virus until inactivation.

How could ultrasound effect for instance COVID 19 or virus similiar DNA/RNA/retroviruses where destroying the outer layer or the membrane layer of the virus/bacteria etc with GHz/MHz? How is virus/bacteria protein layer strength and durability determined anyway? What units are used to determine virus/bacteria membrane layer strength?

Would it be possible to introduce for example two separate transducers, for the waves to intersect on different areas, would then allow tearing the virus apart or can changing the beam type rapidly(continuous beam, pulsed beam etc) with rotation be an effective way to twist the outer membrane of a virus well enough for it to be destroyed successfully in a short period of time?

Source:

https://www.sciencedaily.com/releases/2002/12/021216071144.htm - December 16, 2002

http://adamasuniversity.ac.in/virus-and-vibrations/ - March 30, 2020

https://www.livescience.com/7472-kill-viruses-shake-death.html February 05, 2008


texts: Rotating a lead screw with a moving magnet

texts:
Is it possible to introduce torque on a lead screw (with no magnets attached to it) with a moving magnet that can only move parallels to the screw?
(the lead screw is ferromagnetic)
Something like that:


texts: Can a gas rotameter be used for liquids?

texts:
Recently I learned a new word for what I'm looking for -- rotameter -- a device that uses a weight in a conical bore to measure fluid flow.

How can I make an uncalibrated flow meter for water flows of a few liters per hour

I've found many for gasses, but not many for liquids, and none for the range I'm looking for.

To first order approximation do I need to do more than compare the viscosity of air to that of water to use an air calibrated one for water?

The viscosities differ by about a factor of 50.  Would a 5 liter/minute gas rotometer be a 6 liter per hour water rotameter.

Caveats:  In a gas meter the bead may be plastic, which has no buoyancy effect in air, but a substantial one in water.  Indeed the plastic might float, and I'd have to use the thing upside down.  Plastic with a specific gravity of .9 would make the device 10 times more sensitive.

Depending on what's dissolved in the water, the viscosity can change somewhat.  I will be using more or less pure tapwater with about 600 ppm of assorted hardwater crud.


texts: Is it possible to calculate the shear wave velocity in lab using ultrasonic test?

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I have an ultrasonic testing equipment that can only measure the direct and semi-direct ( (a) and (b) in the image below):

I can measure compression wave velocities fairly easily, but I would like to know if it is possible to measure the shear wave velocity.

Is it possible to measure the shear wave velocity in a lab setting using this? What should the distance between the two sensors be to provide accurate measurments?


texts: I’ve been looking for a temperature sensor for my PI3 home thermostat. I’m to the point where my app is stable and running for over 20 days with the only issues relating to the temperature sensors. I have dual DHT22 sensors and those will freeze up occasionally, for which the power needs to be reset. I will try to handle this reset in code, but because this controls my home HVAC system, I would like to get sensors that will not freeze up and have greater reliability. Recommendations from someone with a current PI3 thermostat being used to control their HVAC would be appreciated. I would like to be able to rely on the sensors.


texts:
when shopping on digi-key or other electronics distributor, I can see the Torque - Holding spec, given in oz-in and mNm.

I understand Nm in a torque context when the force is applied as a lever at a distance from the rotation point (for instance when applying 1 N force on a wrench, 20 cm from the rotational point, would give 0,2Nm).

But what does it mean when we are talking about motor torque? It seems to me that it is like opposite: the motor is applying force at the rotational point, so the distance is always 0.

Does it mean motor specs are always measuring the force the motor is applying 1 meter away from it? I am trying to have a good intuition of what Nm mean when looking at motors, because tutorials online only talk about wrenches or other cases when the force is applied away from the ration point.

Thanks a lot!


texts:
A "Carbon Phase Diagram" has an upper and a lower transformation temperatures. It was my understanding that once a steel had cooled below the lower transformation temp (1333 deg F) that the austenite had changed completely to another structure (ie martensite, pearlite, cementite etc.) However when looking at the "TTT" diagram, it shows the transformation occurring between the two "C" curves. The "C" curves are below the 1333 deg F. The "TTT" diagram also shows that the transformation from austenite does not even start until the temp is below the lower transformation temp of 1333 deg F.

Can someone help me understand.


texts: Dose rate through shielding from Co-60 to verify Monte Carlo result?

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I need to calculate the dose rate leaking from sealed Co-60 sources.
Let's say the activity of a source is 7 TBq. The source is tube shaped, 2 mm radius and 10 mm in height.
There is 5 cm of tungsten and 3 cm lead in the radiation's way.
The measured dose rate according the NCRP report 102: "the maximum and the average leakage kerma rates through the housing shall not exceed 100 uGy/h"
How could I calculate if the 5 cm tungsten and 3 cm lead will be enough to limit the leakage dose rate to the 100 uGy/h range?
We have built a Monte Carlo model of the above scenario and ran the simulation.
There are a number of particles with a given energy arriving to the other side of the shielding. We save the state of these particles in a phase-space. So in this phase space we have the type of the particle: e-, gamma, position, direction, energy.
Calculating dose from the particle energies.
Dose is Joule/kg, so we need a volume with some material in which the energy of the particles will be absorbed. So we put a 1 cm^3 lead cube next to the area where the energy is the most dense in the phase space. Restart all the particles. Now we look at how much energy was absorbed in the lead cube and divide by the weight of the cube. The result is somewhat sensitive to the size of the cube because the shielding is not homogeneous.
Calculate dose rate.
Activity is 7 TBq which is 7x10^12 decays/s for Co-60 let's say that that is 7x10^12 gammas of 1.1732 MeV plus 7x10^12 gammas of 1.3325 MeV. So modelling 14x10^12 initial events would equal to 1 sec of real time. Let's say we model 1x10^9 events so now we can say have how much of real time is simulated and thus we have the dose rate.
This is what I would like to verify.


texts: What paint/spray on material should I use to insulate a metal pole?

texts:
I am not entirely sure if this is the correct forum to ask this question so please refer me on if there is a better arena.

I am creating a small weather station and I wish to measure soil temperature. I am aware that digging a hole and then burying the sensor will alter the aeration of the soil and therefore give imprecise readings. I have therefore decided to integrate the sensor into a notch in a steel tube and then drive this tube into the ground. This means that there will be minimal disruption of the soil composition and the sensor will touch the soil both inside the tube and outside.

My concern is that the steel pole will retain heat differently to the soil (both from any showing to the sun above ground and more generally below the ground) and in doing so skew the temperature readings. Can you recommend a coating that I could put on the metal to reduce its conductivity/radiative properties and therefore minimise its impacts on the sensor?


texts: Calculating a pull force between two pieces of plastic

texts:
I have an HDPE pin, 2 mm high, 2 mm diameter, that I impress into a flat plaque of hot HDPE.  It is not hot enough to melt the pin, but still hot enough that the material will shrink 4% in 24 hours.

How would I calculate the force required to remove the pin from this plaque?  The coefficient of friction being used is 0.24, and an expected value for the force might be 3600 N.

It is possible that while the pin is pulled from the plaque, due to elongation the diameter toward the top of the pin becomes smaller.

My end goal is to figure out a formula that I can use to approximate the expected pull force of this pin given varying heights, diameters, and if the pin is hollow or solid on the inside.  We cannot vary the shrinkage value.


texts: In the calibration procedure of an instrument (e.g. a pressure transducer), when we want to determine the calibration curve, is it a good choice to force the passage of the calibration curve through the origin?


texts:
I have done experiments on a grinding machine and have collected the data of grinding wheel profile (using a laser sensor).

The raw data consists of info on grinding wheel profile, waviness and
roughness (because of abrasive grains). I would like to process the collected raw data. I want to filter out the high frequency and low frequency data. (I want to apply a simple band pass filter). One cycle data is about 200,000 data units and i have them in an excel file (csv data) and would like
to perform digital filtering.

How do I filter out the waviness data separately and analyze, from this?


texts: Could a one sensor node in a cluster sense a data more the others?

texts:
I want to know if the sensor nodes in any cluster in a wireless sensor network may detect events in a different ratio i.e.some nodes could detect events more others in the same cluster, so is power consumption in these nodes will be higher than other nodes?
i want to know if there is an application in which this assumption or question is possible with take in our concentration that we can applied clustering to increase the lifetime of this network.


texts: Using magnetic field readings for linear gesture recognition

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I am thinking about using a permanent magnet as an input device for my smartphone. I have been reading some papers about it, but I really want to understand how things work. Using the integrated compass I can read the field strength along three axes. Given these readings, what property of the magnetic field could I use for gesture recognition?

To do anything I have to save the magnetic field strength along the three axes when no magnets are close to the smartphone. Then compare it with other readings.

When I place a magnet close to the smartphone in a particular position the readings will change. I can tell if the magnet is in that position when I read the same values along the three axes. This is because the magnet changes the "overall" magnetic field read by the magnetometer.

I can simulate a click when a magnet in a particular position is twisted/curled because the angle of the polar coordinates changes of about 180 degrees. This is because magnets have a north and south pole, so twisting it changes the pole and as a consequence the angle of the polar coordinates.

I would like to simulate a movement along an axis (like a slider). I can tell if I am at the beginning or at the end of it by comparing the magnetic field strength to the ones previously detected in those positions. How can I tell if I am in the middle or in any other point? The obvious solution would be to save the readings in all those points but I hope there is something about the magnetic field I am missing. Is there a law or a correlation between the points I can use?

These are some readings I recorded of seven equidistant points along the x axis:

     x,      y,      z
-39.55, -51.19, -32.67
-26.01, -41.83, -32.95
-19.94, -34.08, -33.28
-16.43, -26.62, -32.72
-15.98, -22.6,  -33.07
-15.93, -20.72, -32.96
-16.85, -18.87, -33.11

The best thing I have thought so far is to approximate the movement with a linear function but things doesn't work that well (for example the 4th and 7th position have almost the same value along x but they are in two different positions so I can't tell which one is the end and which the middle). This is one example, depending on where I am I can find myself with very different problems. How should I cope with it? Magnetic field is less strong as the magnet gets away from the magnetometer; what kind of function can describe this situation?


texts: How to determine tensile strength while the normalised tensile strength is known?

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I try to design a shaft with yet unknown diameter, i know the distribution of forces and stresses (shear, torsion and normal) in/ along the shaft. I need just one more parameter nl. the tensile strength of martial. I use Rolloff-Matek machine elements table book. In the table i choose a material with tensile stress say $1000 Mpa$, but all the values in the table are normalised for a rod with diameter $d_N=16 mm$.
May i use the tensile stress as mentioned in the tabel ? or i should find a correction factor somewhere else ?


texts:
I am a mechanical engineer who is interested in learning different processes and equipment mainly used in process industry namely, textile, chemical, sugar mill, and other food process industry.
Is there a one place to go solution available or if someone can help me and guide me to resources available online that can help me in understanding how these industries work in term of processes and equipment.


texts: Say you have two identically-weighted boxes of materials, same size, both solid, both the same temperature. The only difference is that one is made out of metal and one is made out of plastic. Why does the metal feel hotter on your hand?


texts:
What is the degree of cooling caused by air flowing from smaller diameter into a large diameter? How much does air cool as it expands?

If the air inlet was the biggest hole on the right and the outlets were the full smaller holes, would the air cool as it left each hole? Let's say that the surface area of the inlet equals the outlets.

Could these types of apparatus be linked in series to produce a staged cooling effect?

Does cooling only occur in change of pressure?


texts: How to draw an arc through 2 known points and tangent to a line

texts:
I am using AutoCAD and I was trying to figure out how to draw a circular arc through 2 known point and tangent to a line.

When I look at the circle tools I see the following options:

When I look at the arc options I see the following:

I am able to do it through a convoluted use of parametric constraints, but I cant figure out how to do it from first principals.  Is there a way?
What I figured out so far is that the center of the circle will be on the perpendicular bisector (Red Line) of the line between the known points.

Using algebra I can mathematically come up with the center for the two blue circles.  And visually I know I want the larger circle.  What am I missing to find that center point graphically?
I can do it through parametric constraints, but I thought one should be able to do this with essentially a straight edge and a compass (straight lines and circles).


texts: Torque and power for elevator with counterweight

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I need help calculating required torque and power for an elevator to select appropriate motor and gearbox.

The mass (weight of elevator plus max load) is 2000kg

The speed of the elevator is 10 m/s.

The radius of the pulley is 0,5 m

I want to use a counterweight - mass of counterweight is not specified, what is appropriate here?
I dont get it how to count when I have a counterweight in the system.


texts: Relative strength of wire mesh vs rebar for reinforcing a concrete slab

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I have a friend who is German and he says that wire mesh is much stronger than steel bars (rebar) and is mandated in Germany for reinforcing concrete slabs.

The question is, is that true, and why?

Here's a typical concrete reinforcement here (in Indonesia)

There are tied rebar beams, with rebar for floor reinforcement. Instead of the floor bars, we could instead install mesh between the beams. But what is the difference? Obviously we could buy 10.0 mm wire mesh @ 15 cm spacing, or we could install 10.0 mm bars at the same spacing (and let's say for the sake of argument that the same steel is used to make the mesh as we receive as bars). This would result in the same weight of steel per m3, However whereas the wire mesh is welded, the rebars are only tied with wire, which I guess has trivial strength.

[note, let us assume, for the sake of argument that the mesh and bars are properly placed]

Is there, in any case, an overwhelming advantage from the welds in the mesh, or can such advantage as there is be eliminated at relatively low cost, say by increasing the numbers of bars used by say 10%.


texts: Is this is a valid estimation for the mass flow required for Hyperloop air-bearings?

texts:
In Hyperloop air bearings, the air escapes through the rear cross-sectional area of each ski, you know? Yes, there is a pressure differential, but the air comes out of the skis, crashes into the tube and then is accelerated to a certain speed below 760 mph/1,220 kph and escape. The air cannot escape through the front cross-sectional area because of the ski high speed and for the same reason they cannot escape through the lateral areas (well, there will be some minor leaks). That's Couette-Poiseuille flow.

So the mass flow is rhoAc

Where c is the speed the air is accelerated to, rho is the density, and A the rear cross-sectional area.

What do you think?


texts: Will this water jet propulsion system design produce any forward thrust?

texts:
I am interested in building a very basic water jet propulsion system for a toy boat. Before I build it, I would like to know from a conceptual standpoint if this design of a water jet propulsion system will actually produce forward thrust.

Please refer to the conceptual drawing below of this water jet design. This drawing shows a top-down view of the toy boat.

An embedded motor-propeller will pull water into the pipe section coming from the stern of the toy boat and will at the same time be forcing water out of the pipe section going back to the stern of the toy boat. The force which should propel the toy boat forward should come from the dynamic pressure of the rushing water pushing against the inner walls of the two 90 degree elbow sections of the pipe. Will this particular design of a water jet produce forward thrust as expected?

Although I know that a traditional inline water jet system would be the more ideal thing to construct, I am very interested in finding out if a boat can be propelled using just the dynamic pressure(s) generated within a pipe.


texts: How much can Protactinium degrade the efficiency of the Thorium fuel cycle?

texts:
One of the counterpoints to the Thorium fuel cycle is that Protactinium, which is generated  in this cycle degrades reactor efficiency and thus needs to be removed, at least from the liquid fluoride or molten salt reactors. However, as far as I can tell, Protactinium was not removed during the functioning of the first solid-fuel Thorium reactor, which was the third core used at Shippingport; or at least I can find no mention of Protactinium being removed (during operation) in the official fuel report.

So, question(s):

Quantitatively, how bad can reactor efficiency be degraded by Protactinium not being removed?
To what degree does this degradation depend on the type and other parameters (geometry etc.) of the reactor?


texts: Looking for a device that breaks the circuit if the voltage gets too low

texts:
I'm looking for a device that breaks a circuit once the voltage of my battery gets too low. This to protect the battery.

Example: I have a 12V battery, once it reaches ~11V the huge voltage drop begins, but the device that is connected to the battery still runs and draws current. I need another device that can detect the voltage goes below 11V and then automatically breaks the circuit, preventing the circuit to draw more current from the battery. Basically, it shuts down the whole circuit.

Since English is not my native language and I'm not aware of any kinds of systems in my own language, I'm having a hard time finding something like this. Thanks in advance.

EDIT: or can I make my own?


texts: I'm in the process of designing a CNC/3d printer and I came across the term "Optical Axis rod" which seems to be the "standard" rod printers like Prusa use. But I can't find anywhere what the difference between just a "machined rod" and "Optical axis rod" actually is. Is there a tolerance difference? Is it the method it has been determined to be straight? Is it meant for optical machines?


texts: Which type of Turbine (Pelton, Francis, etc.) is most suitable to be driven by high velocity forced-air jet?

texts:
Which type of turbine (Pelton, Kaplan, Francis, etc.) would be suitable and deliver the best efficiency when driven by a high velocity forced air jet of 125-200 mph through a nozzle of 2-2.5 inches diameter? The desired outcome is maximum torque in the 300-400 rpm range.

The turbine should preferably be enclosed.


texts: How can I determine the optimal cross section of a member to correct overdesign?

texts: I am currently working on a bridge design issue. The main goal is to correct issues of overdesign. My professor said we can do this by selecting beams with different cross sections. My question is how can I determine what is the optimal cross sectional area for the force being applied to a specific beam. So far this is what I can understand. I must first calculate the amount of stress the member is experiencing using stress = force / area of the current beam used.


texts: Help in synthesizing cam profile (oscillating cam and oscillating follower)

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I am using Matlab to plot contour of the cam. So far, I understand how to use angular displacement relation between cam and follower to get the profile, pressure angle, torques etc. What I aim to do is go backwards; for a given torque vs rotation of the cam getting the profile and angle relations. How should I approach this problem?
edit1: The cam is loaded with a torsion spring that produces torque. I am considering static cases at different angles so time is not considered


texts: Design Roller Compacted Concrete Pavement Section

texts: I have been asked to consider using RCC instead of traditional PCC on an upcoming project. For a rough order of magnitude estimate, can I assume that the pavement section design will be similar? I know that the mix design and construction methods will vary, but not sure if there will be any difference in the thickness of concrete or aggregate base.


texts: How do I determine the thermal resistance of a metal box?

texts:
Suppose I have a sealed enclosure, say this one from Hoffman:

The box is 16"x12"x6", made of galvanized steel with a wall thickness of .0635" or .0785" (gauge 16 or 14).  I'm planning to put some electronics in this box, which will generate an arbitrary amount of heat. How can I use this information to estimate how much the air inside the box will heat up above ambient outside the box?


texts:
A crane is used to lower a vertical cylindrical pillar into a reservoir. The pillar has a mass of 4 tonnes and is submerged to a depth of 2.5m. It has a diameter of 1.1m.

The specific gravity of fresh water is $$1125kg/m^3$$, and $$9.81m/s^2$$.

Use a free body diagram to show the forces acting on the pillar when submerged and calculate the upthrust, the tension in the rope in air and the tension in the cable when submerged.

I have this for Upthrust:

$$ Fbuoy = Pf \cdot Vd \cdot g$$
$$\pi r^2h$$
$$3.14 \cdot .55^2 \cdot 2.5 = 2.375m^3$$
$$1.125 \cdot 2.375 \cdot 9.81 = 26.2N$$

$$Upthrust = 26.2N$$

Tension in air

$$T = w - Fb$$
$$\pi r^2h$$
$$3.14 \cdot .55^2 \cdot 2.5 = 2.375m^3$$
$$Volume = 2.375m^3$$
$$ w = m \cdot g$$
$$w = 4 \cdot9.81 = 39.24kN$$
$$w = 39.24kN$$
$$Fb = Pf \cdot Vd \cdot g$$
$$1.29 \cdot 2.375 \cdot 9.81 = 30N$$
$$T = w - Fb$$
$$T = 39.24 - 30 = 9.24N$$

$$Tension in air = 9.24N$$

Tension in water

$$T = w - Fb$$
$$\pi r^2h$$
$$3.14 \cdot .55^2 \cdot 2.5 = 2.375m^3$$
$$Volume = 2.375m^3$$
$$ w = m \cdot g$$
$$w = 4 \cdot 9.81$$
$$w = 39.24kN$$
$$Fb = Pf \cdot Vd \cdot g$$
$$Fb = 1.125 \cdot 2.375 \cdot 9.81$$
$$T = w - Fb$$
$$T = 39.24 - 26.2 = 13.04N$$

$$Tension in the cable when sumerged = 13.04N$$

Are these correct?

If not could someone help?

I have been trying to complete Archimedes Principle but just getting a little stuck on the calculations.


texts:
I have two no of motors connected in parallel of 7.5 kw max current capacity 30Amps.
The load is about 18Ton is the motor sufficient to lift this load.
The mechanical arrangement of screw jack system.

The current now taken by motor is as such,
Up movement: 37amps initial current and normal 33Amps.
Down movemenf: 20amps initial current and normal 18amps.


texts: Why do we use multiple reinforcing bars instead of one bar with a big diameter in reinforced concrete?

texts:
Why do we use multiple reinforcing bars instead of one with a big diameter in reinforced concrete?

Does increasing the number of reinforcing bars means that the reinforced concrete will have a higher tensile strength?


texts: What are the advantages of chemical oxygen generation over compressed tank storage?

texts:
Chemical oxygen generation (COG) is used in commercial airliners to supply emergency oxygen to passengers and crew if the plane is depressurized. Weight for weight it produces far more oxygen than compressed oxygen tanks.

I read the original paper on COG, several sites from oxygen candle manufacturers and the US Federal Aviation Administration document on oxygen equipment (riveting I assure you). However, most of the rest of my knowledge is from my own background as a physicist; I want to know how these methods compare from an engineering perspective.

Besides reduced weight, are there any other advantages of COG in aircraft? Does it have added safety benefits when compared to high pressure gaseous oxygen storage? The oxygen candle burns extremely hot when it goes off but I'd imagine high pressure gas canisters could be far more dangerous and prone to exploding if damaged.


texts: Soil swelling and mass/volume relationships

texts:
Given moisture content, Specific gravity of solids, initial volume, and weight. I'm asked to compute the moist unit weight, dry unit weight, and degree of saturation of this compacted soil. This is already done. This compacted soil sample was then submerged in water. After 2 weeks, it was found that the sample had swelled and its total volume had increased by 5%. Then I'm asked to compute the new unit weight and moisture content of the soil sample after 2 weeks of submersion in water.

Moisture content and total volume are known to change, but what properties remain constant during the submersion? Can S(r) be taken as 1?


texts: Byte organized and Word organized memory using memory modules

texts:
I'm currently learning about how a CPU works on the hardware level and something that keeps coming up is memory organization. From what I've learned (and please, do correct me on anything that is not right), you can have a memory organized in the following two ways:

Byte organized memory: Each address on the address bus points to a memory location where a byte (8 bit) is stored.

Word organized memory: Each address on the address bus points to a memory location where a word (multiple of 8 bit) is stored.

In other words, a byte organized memory can access any memory location that is a byte boundary while a word organized memory can only access memory locations that are a word boundary.

Now here is where I have some trouble. I am studying for a midterm comming up and I am looking at past assignments and the following question comes up:

Given a set of memory modules with 20 bit address and 8 bit data interface. We need to build a byte organized main memory of 4 MB for a 16-bit data architecture CPU.

Now I know that we need to build a main memory using the memory modules given. To start off, we need to find the capacity of each memory module, whicch is given by

2^m * n, where m is the address bus in bits and n is the data bus in bits. This gives a capacity of 2^20*8 = 1MBytes for each memory module.

Now we need to figure out how many memory modules are needed. This is fairly easy and is found as follows: 4MB / 1MB = 4 modules.

Now the part where I don't seem to understand, the memory is supposed to be byte organized, but the data bus out of the main memory is 16 bits. How can I design a byte organized memory if each access yields a word? Doesn't byte organized mean that given an address, it would be possible to access that specific byte in the memory? How is that possible when the memory modules must be designed in a way that yields a 16 bit data bus? Here is the solution for the question. Please explain to me in details why the main memory was designed this way, and how it is possible to access each bytes individually.

Answer:

Thank you.


texts:
In an adiabatic throttling process of ideal gas:

I understand that mathematically lost work is given by Tsurr * entropy generated.

But intuitively I can't understand if there is not heat exchange between system and surroundings how can the temperature of surrounding affect the work obtained by system.


texts: How to estimate a ship speed based on weather conditions?

texts: I have data from some ships, basically the base speed for a list of RPM. But it is know that this speed is not constant and it will change mainly based on whether and load of the ship. Is it any rule of thumb to stime the effect of this varialbes into a ship speed without going to heavy on the math.


texts: Which Whistle Type works with the lowest PSI?

texts:
I'm working on a project where we are trying to prototype a whistle that works at the lowest possible air pressure and still produce an audible sound.

Any suggestions on whistle type? and any additional factors or insight that might help, would be appreciated.

Assume, Open air 72 degree Fahrenheit environment using very consistent airflow of regular 72 degree Fahrenheit air.


texts: Single-phase fully-controlled thyristor converter simulation using simulink

texts:
I am trying to implement a simple single-phase fully-controlled thyristor converter using Simulink.

As load I have placed just an inductor, the firing angle is set to a=60 deg., f=50 Hz and the rms of the voltage source is 230 V. The output voltage is the one on the picture below,

Do you have any idea how can I fix the part I have circled? The waveform is supposed to be repetitive, so there should be a negative part as in the next half periods.


texts: What are the principles (if there are any) behind the conservation of bending moment in frame analysis?

texts:
I notice from this question that the moments at joint connection are somehow "conserved", or being "transferred" from one element to the others. In other words, there are no "missing moment".

Note that at joint for left image:

$$2.767\text{ kNm}=(2.37+0.397)\text{ kNm}$$

And for bending moment diagram that I examined so far (using structural software), this seems to be always the case.

So I wonder whether this relationship is true for all kinds of joint connection? Or is there a deeper physics principle behind it (such as the conservation of energy)? How can we derive it from the first physics principle, if it there is a first principle?


texts: Questions about helicopter rotors - conservation of angular momentum

texts:
I have two basic questions about helicopters. Let's say the z-axis is the vertical axis from ground to sky. I know the tail rotor is there to counteract the angular momentum effects of the main rotor, and keep the total angular momentum about the z-axis at 0.

Say the tail rotor spins about the x-axis. What keeps the body of the helicopter spinning about the x-axis in the opposite direction? I assume it's a slight tilt of the main rotor forward to balance this effect. Am I right?
How are the speeds of the two rotors are kept coordinated? I assume there must be a sensor/feedback mechanism by which rotor speeds change to counteract spinning.


texts: Accurate method or instrument to measure density of shaving cream foam or whipped cream foam?

texts:
I am currently filling a "standard" stainless steel cup of known volume with foam and then I weigh it. Then I calculate density. This method is pretty messy and I have to be careful about how I fill the stainless steel cup so that larger air pockets aren't trapped on accident. I need to figure out a less messy and more reliable method that would allow me to read or calculate specific gravity of the foam more frequently.

I tried fabricating a tube that could be filled with foam from one end and then just scrape the excess foam on both ends, but it turned out to be messier than the original method.


texts:
If I have a water pump and a fast solenoid valve (can be open or closed) and turn on my pump at a constant voltage and apply pulse width modulation to my valve. Would the resulting thrust created at the water output be constant and can it be controlled nicely by the pulse width modulation process?

What would be the equations that could model the reaction of such a setup?


texts: Why are the outter tracks of a magnetic disks more stable?

texts: In our digital computers class, the professor mentioned that the outter tracks of a magnetic disk is more reliable because the outter bit are "bigger". Isn't the packing density of a magnetic disk uniform? If we compare this with a optical CD, the inner tracks are more reliable. Why is this the case?


texts: What mechanism can make a shaft rotate in steps

texts:
I want to make a shaft rotate in 21 discrete steps, from a motor that is turning smoothly.

I am thinking of some kind of simplified clock escapement type of mechanism. Or non circular gears.

I know it could be done by programming a stepper motor. But it will be easier and more fun for me to do it mechanically with 3D printed nylon parts.

This is for a low torque low speed application. About 1 rpm and less than 0.1 Nm torque.


texts: How does Pavement ME Design handle climatic data?

texts: ME Design uses hourly climate data files (HCD) as input into the pavement design algorithm. As a user I can enter an arbitrary number of years of climate data. If I enter say 30 years of climate data and then set an analysis period of 20 years, what data does the program use? Does it use the first value in the list or the last 20 years of the file? What if my analysis period is greater than the amount of climate data entered?