texts: Moment equation from dynamics differs with equations from physics & statics. Where did I go wrong?

texts:
In my dynamics class, we're being asked to solve the following problem:

My Attempt:

Since I'm given the initial velocity, final velocity, and distance, I solved for the acceleration of the plane using kinematics:

$a = \frac{v_f^2 - v_i^2}{2d} = \frac{(55.6 m/s)^2 - (16.7 m/s)^2}{2(425m)} = 3.31 m/s^2$

Now this is where my approach starts to differ from the formulas recommended by the class. I decided to set the moment about point A equal to zero, because the plane is not rotating as it moves down the runway. I seem to remember from both statics and physics that if a body is not rotating about a given point, you can simply set the moment around that point to be zero.

Let N be the reaction force at B. Combining the above assumption with Newton's second law in the x direction, I get:

$\Sigma F_x: R = ma = (140000kg)(3.31 m/s^2) = 4.63 *10^5 N$
$\Sigma M_A: -(15m)N + (2.4m)mg - (1.8m)R = 0$

Solving for N gives me:

$N = 1.64*10^5 N$

According to the solution guide, this is incorrect.

Solution Guide's Explanation:

The guide uses a formula which was introduced to us in the textbook, which is as follows.

For some point P fixed on a rigid body with center of mass G, the moment about point P is given by:

$\Sigma M_P = I_G\alpha + ma_Gd$

where:
$I_G$ is the moment of inertia of the rigid body about G
$\alpha$ is the angular acceleration of the rigid body about G
$a_G$ is the acceleration of G
$d$ is the moment-arm distance, from P to G, of $ma_G$

The book cleverly chose a point C on the plane through which both R and A (the reaction force at wheel A) pass. See below:

Using the moment equation above and setting $\alpha = 0$ (because the plane isn't rotating) gives:

$\Sigma M_C = ma_Gd = (15m)N - (3m-1.8m)mg$

Finally, using $a_G = 3.3 m/s^2$ and solving for N, they got:

$N = 2.57*10^5 N$

Why I'm Confused:

From the physics and statics classes I've taken in the past, I've always been taught that $\Sigma M = I\alpha$; there was never that extra "$+ mad$" term thrown onto the end. That term is basically saying that an accelerating body with no rotation can still have a moment about a point. By contrast, in my physics and statics classes, I recall using the fact that if a body is stationary (no angular acceleration), we can set the moment about any point on the body equal to zero to help us solve.

My Guess at Where the Inconsistency Lies:

Here's my guess at where the inconsistency lies: in my statics classes, we assumed that the rigid bodies we were analyzing had not only zero angular acceleration, but also zero linear acceleration. (It's statics, after all!) In dynamics problems such as this one, however, there is a nonzero linear acceleration which must be accounted for. The "+mad" term must come from the fact that for any point object, the moment about some fixed point O is given by:

$\Sigma M_O = \vec{r} \times \vec{F} = \vec{r} \times m\vec{a}$

As I'm writing this, I think the intuition totally makes sense. It seems the formula used by the solution guide accounts for both rotation of the rigid body about its center, and linear acceleration of the body with respect to some point P outside the center of mass of the body.

I'll still post this though, in case anyone would like to correct me, add anything, or use this for their own reference.


texts: Building a half-arch of a specific height, while consistently using an angle divisible by 90

texts:
I am trying to construct a lift handle in the CAD Sketchup. The circled part of the image shows the arch I'm referring to.

The program, Sketchup, has a 'tool' called push/pull, and another tool called rotate. I have a video uploaded on streamable demonstrating this, but I'm not sure if it's within the site's rule to do so. Here's a brief clip partially demonstrating it in action: https://i.imgur.com/pgVRw9d.mp4

I use the push/pull tool, to raise the face of the object by 250 mm, and the rotate tool, to rotate it by 15 degrees. $90/15 = 6$. The arch ends up with an overall height of 1074 mm.

I repeat the task 2 more times, but with the angle of 7.5 and 30 degrees.
With 7.5 degrees, the arch looks much curvier, but the height is 2032 mm. With 30 degrees, the arc sides are noticeably pointy, but its height is more acceptable, 591 mm.

Here is an image of all 3 arcs together:

The dimension of each side on the inner part of the arc, are all 250 mm.

My question is, what equation may I use, so I end up with an arch that looks curvy enough, in this case 15 degrees or lower, and has a height of 508 mm from the 'ground' (or x-axis)?

I tried the following, with no success:

Circumference of a circle $C=2\pi r$

The arc in this case represents 1/4th of a circle; so $C_{arc}=2\pi r/4$

$$\begin{align}
2\pi508/4 &= 797.96 \\
\dfrac{797.96}{90/15} &= 132.99
\end{align}$$

I push/pull the face of the object by 132.99, and rotate its top face by 15 degrees. I repeat this process 5 more times. The 6th arch rotated, is perfectly perpendicular to the x-axis. Unfortunately, the height is 571 mm, instead of 508 mm.


texts:
In case of Uranium, things are lot easier, because $UF_6$ is gaseous from around 60 $\,^{\circ}\mathrm{C}$.

I know, that in most cases, plutonium isotope separation is not needed, because there is no need to separate its fissile isotopes. But there is an exception: radioisotope thermoelectric generators (used to power remote devices such as spacecraft and unmanned polar equipment) need ${^{238}}Pu$.

I think, Plutonium can be separated from the depleted fuel cells with chemical methods, but how to separate ${^{238}}Pu$ from the result?


texts: What is the correct method to remove or tighten this splined "nut"?

texts:
This photo shows the input shaft of an air compressor head.
The splined cog-looking disc around the shaft is actually a sort of threaded nut which screws into the larger disc around it. It serves to hold in the bearing on this side.
It may be that this part requires a unique, specialized tool - but I suspect there may be something that is "standard" but perhaps uncommon instead. In many environments a compressor head doesn't require such frequent maintenance that a totally unique tool would be inconvenient.
Note the bolt heads around the splined part don't allow for very much clearance - about 3/16" or ~5mm.
I think given some brute force it probably could be unscrewed using a punch or even a screwdriver used as a punch, but I don't want to damage it.
Possibly an adjustable pin spanner might fit - but the only ones I have are pretty lightweight. Also I think the pins would probably pop out of the grooves (they are usually used in holes instead).
This compressor head is vintage, I think about 70 years old.


texts: I saw a video where a person was measuring hardness of a material with Shore durometer type D and was comparing it to steel. The screen on durometer showed 96.5 HD and I was just wondering, how much would that be in Brinells? (or alternatively Rockwellss or Vickers)


texts: Are M8 screws double the size of M4 screws?

texts: Found some printable M8 screws on Thingiverse (https://www.thingiverse.com/thing:4805480), which made me wonder if I can get M4 screws, just by resizing them factor 0.5.


texts: Is there any entrance losses in this particular Pipe design?

texts:
Let’s say this odd design, the arrow is the direction of water flow (don’t ask why because I’m just curious about it)...

I drew this out and just wanted to ask if water were to flow into the pipe like that, will there be entrance losses ?

I know if water were to flow the opposite direction, and the exit pipe goes into the water as a submerged exit, there are exit losses.

But now I reverse the direction of flow and now, so is there entrance losses ?


texts: We are looking for a solution to hold two Power cables on a 3D printed part. This part is installed in a vibrating environment. So we need the cables to be pressed not to move and not to transfer vibrations to electrical components. We have thought about a C shape holder, but it would surely not maintain cables enough. We also looked for components sold on the market but nothing meets our requirements. Here is a picture to help you to understand. Thank you in advance !


texts: When is the Equal Pressure Point in a Typical ICE?

texts:
My question refers to a typical bog standard normally-aspirated 4-cylinder petrol/gasoline engine.

Let's say it's a 2.0 litre engine (10:1 compression ratio, firing order 1-3-4-2) operating at 2000 rpm with 30% throttle open. Ambient conditions are 1000 millibars of pressure at 12 degrees C (285 degrees K).

When cylinder 1 is on its compression stroke (increasing pressure), cylinder 2 is on its power/expansion stroke (decreasing pressure).

Obviously, for most of the period in question, the pressure in cylinder 2 is higher than that in cylinder 1, but there is a cross-over point at which the pressures in both cylinders are the same. My question is, at what crank angle should I expect to find this equality?

If necessary, and for simplicity, assume that 100% of the petrol/gasoline has fully combusted into CO2 & H2O, but if you'd like to assume more realistic figures please do so. I doubt that it would affect the equality point too much though.

Because the equal point is obviously fairly late in cylinder 1's compression stroke, inlet valve timing is probably irrelevant. The exhaust valve timing though might be relevant, so please assume that it (they) open after the equal pressure point.


texts: What are some examples of laser-based additive manufacturing techniques?

texts: I'm trying to research additive (or 'bottom-up') fabrication techniques that rely on lasers or other advanced photonic systems. So far, the most prevalent technique I've come across is two-photon polymerisation, but I'm struggling to find any others. Any further examples would be much appreciated.


texts: What happens when throttling in an isothermal process

texts:
Consider an isothermal expansion of an ideal gas (always at ambient temperature $T_0$), from some initial pressure $p_i$ to the ambient pressure $p_0$, such that the maximum work available is:

$W = mRT_0\ln(\frac{p_i}{p_0}) = p_iV_i\ln(\frac{p_i}{p_0})$. (1)

If the pressure is throttled to some intermediate pressure, $p_1<p_i$, then presumably the expansion work can be be split into two phases, one with constant pressure $p_1$ and one with variable pressure, i.e. $p<p_1$. the maximum work available should then be the sum of these two phases, i.e.

$p_1V_1\ln(\frac{p_1}{p_0})$ (variable) + $V_i(P_i-P_1)$ (constant) (2)

For an ideal gas, the exergy is then just $mRT\ln(p_i/p_0)$, so without the throttling the exergy efficiency is 100%.

My question is, firstly, is this correct? Secondly, is the exergy destruction in the valve (1)-(2)? Thirdly, can you throttle (regulate pressure) without destroying a significant amount of exergy?

Furthermore, how do you draw ideal gas throttling on a PV diagram?


texts: What are the benefits of a digitally controlled TIG welder?

texts:
There are "analog" TIG welders where the parameters are directly controlled by rotary knobs and buttons. For example this one. Then there are "digital" ones where parameters are controlled by one rotary encoder and several buttons. Link this one.

Besides the actual difference in the user interface, does a digitally controlled welder have any general benefits over an analog one when it comes to welding performance? (Or perhaps vice-versa?)


texts: Electric motor power needed to move an scissor jack?

texts:
I'm trying to build a device that, on receiving a signal, lifts the mattress from one side (in a "slowly kick you out of bed" manner). Since linear actuators are generally expensive and i'm on a tight budget, I though of using a cheap scissor jack (like this one ), and move it with a simple electric motor, or most likely a gear reducer motor, but i'm no engineer (well technically a software engineer but that doesn't help here) so i don't know where to even begin to do the calculus. ¿Could anyone give me some pointers? I can do the math but i'm lost on the physics part.

PD: This is also my first time building any device, so if i'm missing some painfully obvious solution to this problem please tell.


texts: Can Fast Fourier Transform be used to monitor for fault vibrations in a hard disk?

texts:
We want to monitor hard disks for present problems or pending failure.

Can the Fast Fourier Transform (FFT) of a given hard disk in question, then, be compared with a reference FFT for a perfectly working one, and then conclude hard disk may be faulty or about to fail if its FFT differs significantly from the reference?

FFT would be used to detect unexpected frequencies, or harmonics, that do not normally occur in a 'healthy' hard disk.  FFT would input vibrations from hard disk, and output the collection of vibration's constituent frequencies.  This would be compared to the frequency domain function of 'healthy' hard disk.


texts: Transmission of rotational power across a waterproof boundary

texts:
Considering the situation where:

A non-waterproof motor is used inside a waterproof box
Something must be rotated by that motor in a wet environment outside the box

What is the correct way to transmit the rotational power from the motor to the exterior environment?

Notes :

Rotation speed 1-10 rpm
Exterior environment has constant low power water spray
Low cost is a priority

NB : Apologies for using incorrect engineering language. I do not have an engineering background. I invite anyone to correct my words as appropriate.

Thank you
Elliot


texts: i designed a gearbox with 3 shafts.i wanted to do sth so shafts only have rotating movement and not any other type of movement.i cant find any type of mate that can do that,any suggestions?


texts: What manufacturing process is suited for production of the elastomer strip?

texts: What manufacturing process should be adopted to manufacture a LEGO® compatible strip made by material which is rubber like?


texts: Why do modern MRI scanners use an axial static field?

texts:
Last night I was reading some fascinating history of the first full-body MRI scanner and noticed that it's fundamentally different from modern scanners in one particular way: the static B field is vertical, while all the modern machines I've seen pictures of strongly suggest a static B field parallel to the patient's axis.

Is there a reason why most modern machines orient their static field along the patient's axis and not through their frontal plane - was that first scanner's vertical field a non-fatal "mistake"?

Are there implications for image quality depending on which slice is selected, or is there a limitation on which slices can be selected? Are axial slices (which I imagine to be what modern machines optimize for) perhaps more commonly useful than frontal slices?

Edit: I don't know why this was migrated without conferring with me. This question is about the application of these scanners, i.e. what medical diagnostic reasons are there to prefer one slice orientation over another. Clearly engineering issues impose constraints on what medical professionals can do, and I'm interested in those too, but I want this to be primarily about what these machines do (specifically with humans in the B field) rather than about how they achieve that.


texts: How do you call a map that shows the characteristics of a train tunnel (3D) in paper (2D)?

texts:
I have googled for a while and I can't seem to find the correct term to refer to this.

Imagine you have a tunnel in where trains, cars, or anything goes through.

This tunnel might elements along its extension, such as cracks, fissures, weak spots, etc. To visualize this in paper, a 3D figure must be "projected" into 2D.

I'm looking for the word to refer to this kind of map.

The closest I've come to is calling it "A projection map" but is there a more suitable term for this?

In japanese it can be called a "展開図(てんかいず) Tenkaizu", but a dictionary translation, or a google translation don't fit since that term is also used to describe the diagrams of how to fold paper to build something. (like a cube)

I tried in the "English" site, but I was referred to this site instead.

What do you call a 2D map that shows the characteristics of a 3D
train tunnel?


texts:
The usual woodworker/house builder rule of thumb is to place the top hinge 6" (150 mm) from the top of the door, and the bottom one 9" (228 mm) from the bottom - the common reason for this is illusion of "foreshortening" and this results in a visual balance of the hinges on the door. If a 3rd hinge is used, it is placed halfway between the top and bottom hinges.
In modern office buildings it is common to see a hinge spacing that doesn't follow the usual rule.
What is the reason for this arrangement of hinges?


texts: Steel tube wall thickness for moving a machine

texts:
I need to move a machine, approx weight of 900Kg
I will put 3 tubes under the machine and roll the machine on the tubes
Holidays season, all industrial suppliers are closed around me and only have access to 2 kinds of tubes:
20mm diameter and wall thickness 1.5mm
or
25mm diameter and wall thickness 1.5mm

Is the thickness enough to support the weight?
Material is construction steel (we call it S235 here but I don't know the international name)
i would be interested in the formula to make the calcultion also

Thank you


texts: Can we have plinth beam below ground level for small homes?

texts:
For a small 30 square meter home (8 x 3.75) is it feasible to have plinth beam 2 feet below ground? Technically, is it better than or worse off than standard procedure of plinth beam at ground level?
Also, please consider the fact that it is an earthquake prone zone.


texts: How to verify results from a manometer/venturimeter?

texts:
I'm designing a system to determine pressure drops across thin samples while simultaneously measuring velocity (and through multiplying by area, volumetric flowrate). I need a way of determining how accurate my setup is. The big catch is that what drives the flow is a pressure regulator, so flowrate is entirely dependent on what pressure loss I experience. If I had anything more than my phone this second I would generate and attach more professional pictures.

Moving down the line is the following. First, a pressure regulator downsizes the pressure from the source to whatever value of pressure I want. Then it goes through my clamped sample (in my case I'm dealing with feathers most of the time but it's fairly versatile). Following the test section the cross sectional area of the pipe diverges to double the diameter and then extends for a few inches.

There are three static ports. The first is before the test section. The second is after the test section. The third is after the pipe diverges. My manometer will test between 1 and 2 as well as 2 and 3. 1 and 2 will indicate the pressure loss across the feather/sample. 2 and 3 indicate the static pressure decrease due to the divergence which will allow me to approximate velocity through the Bernoulli equation.

So in essence: how do I validate my manometer readings between both cases? I want to be able to say with confidence that my setup works.


texts:
I live somewhere where it's relatively warm the entire year (around 10ºC is the coldest you'll get in some days during a normal winter).

I am dreaming of a house design that I intend to build in the near to mid-term future.

I have dogs and I want to build a room dedicated for them outside, where they'll sleep, have a shade and be protected from the rain and wind, that they can go in and out whenever they want. This room will have it's entrance from the garden only.

The point of this question is: Is there any kind of wall design I can use that will give them a clear entrance but at the same time won't allow (at least most of) the wind rage through?

My sketch is a design roughly like this, but I am not sure if this would really stop the wind from going in or not:

I am asking it here because I am sincerely interested in the physics of such design and how it could control the flow of the wind.


texts: How to install a doorway through a stone wall where a barrel ceiling is on one side

texts: We have an old stone built cottage.  We have a garage we are converting to a bathroom.  The garage roof is a barrel brick ceiling.  We need to break through from the house to the garage but need to know how to approach putting a lintel in where the roof is barrelled as to get the door height we would need to remove some bricks from the barrel   any advice or links to articles/you tube videos would be appreciated. Thank you.


texts: why does the body have an no angular acceleration if the applied force passes the center of mass?

texts:
While I was looking for the definition of the center of mass , I found this text :
 "If a single force acts on a    body and the line of action of the force passes through the centre of mass, the body will have linear    acceleration but possess no angular acceleration."

why does the body have an no angular acceleration if the applied force passes the center of mass ?


texts: Are there any materials known to be sound-insulating but thermally-conductive?

texts:
Are there any materials known to be sound-insulating as well as thermally-conductive?

Cost is not an overriding concern, but preferably costing "reasonable amounts" and much less than national defense spending levels.

This is a thought experiment that I'm pondering regarding the idea of a computer case which conducts heat while isolating or dampening all of the sound inside.

There's multiple holes in the idea when fully formed regarding financially reasonable, allowing air-flow, etc, but to keep this question narrow I want to just dismiss all of those concerns for the thought experiment.

I recognize conducting one type of energy while insulating against another is not a straight-forward thing.  The closest material that comes to mind is water, but that's not completely accurate because it does conduct kinetic energy (i.e. hydraulics).  It is better described as acting as a sort of low-pass filter.

So if no materials come to mind, I'd be interested in hearing of something that could filter sound very effectively while conducting heat as well.

I'd like to put the qualifier that the material is a solid, but I'd be interested really in any material with these properties just because I believe (perhaps wrongly?) that there are likely a very small number of them. Again, don't think in terms of the goal concept I mentioned regarding a computer case, this is just one step towards that thought experiment (which is likely not reasonable, or else products would be on the market right now that provide such).


texts:
Can we build a building that could last thousands of years, if it was abandoned, in a humid continental climate?

Is this even possible with present knowledge?  How would such a structure be built? What foundation can actually withstand seasonal temperature changes, and precipitation, without requiring repairs after a couple decades at most?

It doesn't need to be very large, assume the size of a simple home, so 1500 square feet.


texts:
I'm not sure if this is the right place to ask this, however:

I would like to know if it's possible to make videocam Eyewear. What I mean:

Take simple glasses without lens
Instead of lens, use screens on which video from camera will be displayed
I build two cameras, one on the left, one on the right,which will capture video to left and right screen.

Can this be done? How can it be done? What is needed to create this?

P. S. Is it also possible to add a zoom in and out feature through an exterior control?


texts: How do I calculate how many newtons a hollow rod can carry without buckling?

texts:
how can I calculate how many newtons a 600[mm] long rod with a known yield strength (300 [MPa]), young modulus (190 [GPa]) and hollow (outer diameter = 16[mm], inner diameter = 10[mm]) will carry without buckling?
Thanks.
Edit: My main question is "How do I use the yield strength in the Euler buckling formula? What does it do and how do I determine "Factor Counting for End Conditions" for suspension pushrods?


texts: Any idea on how to prove this formula of tension?

texts:
The formula is:
$$T= \dfrac{\left(\sum (\text{coefficient of tension})_i\right) \cdot g_{effective}}{\sum \frac{(\text{coefficient of tension})_i^2}{m_i}}$$
I tried to prove this formula but not getting it. An example for this formula is below:

Explaining the Q:
1g + 2g means correction of tension is 1 for 4kg block and 2 for 2kg block. In the end, g is always the same. Then, in the denominator it is the addition of $\text{coefficient of }T^2 / \text{mass}$.
About $g$ effective on top, in case of inclined plane.its value would be $g \sin \theta$ if it is like this:


texts: Behavior of materials on application of tension

texts: Does a test body subjected to a strain that causes plastic deformation still have elastic recovery?


texts: How the patterns or widths will be given to numbers while encoding data to barcodes like for 1 it will be 2221 and for 2 it is 2122. I didn't understand how these widths are given


texts: Why if the truss is statically determinate, both bars are free to lengthen or shorten?

texts:
source

Because the truss is statically determinate, both bars are free to
lengthen or shorten, resulting in a displacement of joint B.

Why is being statically determinates related to being free to lengthen or shorten?


texts: Device (electronic valve?) for controlling O2/Nitrogen levels in sealed chamber

texts:
I'm designing an environmentally sealed chamber which will need to have its oxygen level controlled.

The chamber has a volume of roughly 1.5 liters. I don't expect pressure to vary too much ... maybe .8 to 1.2 bar. I'm not sure about flow rates, but we would want fairly fine control over the O2 concentration, so maybe a maximum of around .1 L/s?

To that end, our intent is to have a supply of nitrogen (or other inert gas) and a supply of oxygen. I've never worked with gas canisters of any sort before, but I need to be able to feed controlled amounts of nitrogen and oxygen into the chamber as well as control a relief valve of some sort, all electronically. What sort of valves/controls would I need to allow a controlled amount of gasses in/out of the chamber?


texts:
I am working on a small waste treatment  project where there is a small mixing vessel (about 5 liters - more or less 20cm diameter). The mixing process produces methane gas which shouldn't escape the confines of the mixing vessel (odor and flammability).
Some other salient parameters (as I perceive them):

The shaft diameter is small (about 16mm).
the shaft rotates really slow (about 10-30 rpm).
the pressure of the gas is low (just over 1Atm ).

I was wondering whether what type of seal would be most appropriate for this type of application. My first instinct was  a lip sea with a garter spring. I know there are other types of seals (e.g. packing, mechanical seals, tandem, cartridge), but I have little to no experience with most of them.
The cost would be a primary driver in this application, so any indication about the *cost effectiveness * would be welcome. For example, I have seen some of gas seals used in the petroleum industry but the cost is prohibitive.


texts: Can a hypoid bevel gear set have a 1:1 ratio?

texts: [![enter image description here][1]][1]Is it possible for a hypoid bevel gear like the one pictured below to have a 1:1 ratio? If 1:1 isn’t possible, any idea what the smallest ratio could be in order to output the least amount of gear reduction?


texts: Using complementary filter in rotation matrix

texts:
I am using accelerometer and gyroscope and try to compensate earth gravity.
I figured out use of complementary filter, that calculates pitch and roll angle.
On account of compensating gravity I am transforming the local acceleration in global world frame by rotation matrix.
Therefore I am using angles of gyroscope.
Problem: Angles of gyroscope are affected to drift over time.
Now I want to combine absolute angle of accelerometer and relative angle of gyroscope in rotation matrix, preferably in use of complementary filter.
Does someone now, how to fuse measuered angles of both sensors in rotation matrix?
That is what complementary filter of accelerometer and gyroscope looks like for calculating roll angle:
Roll_angle = 0.98(Roll_angle(-1)+Gyro_roll_angle*dt)+0.02*Accelerometer_roll_angle

I want to use the complementary filter in rotation matrix (R).
I can’t imagine that formula is correct:
R = 0.98(R(-1) * R_gyro)+0.02 * R_acc

Does someone know how to compute rotation matrix in terms of using angles of gyroscope and accelerometer?


texts: Find the acceleration of a block relative to incline plane in non and inertial frames?

texts:
A block can slide on a smooth inclined plane of inclination $\theta$ kept on the floor of a lift. When the lift is descending with retardation i.e. $ a \; m/s^2 $. Find the acceleration of the block relative to the in inclined plane.
How I solved till now:

Above is the FBD I drew.
I have written some points and want to confirm them:

From an inertial frame. The acceleration of the block should be
mg+ma?
Since it asks for acceleration of $m$ relative to the incline, I can
take a non inertial frame which is sitting on the inclined plane at
the top. So, I have marked a person there. For that person, the lift
will be at rest. So, then the acceleration of the block would be $mg
sin \ \theta$. Since, I view it from NIF. Then, I add a pseudo force
which will be $-ma$ (a is acceleration of lift).  I have assumed
that the person also has an acceleration $a m/s^2$ as given in Q
(then only the person sees the lift at rest). Then, the pseudo force
is always negative. So, it acts in the direction towards the NIF on
the mass $m$. So, we get:

$mg sin\ \theta$ - $ma sin \ theta$ = m*(relative acc of block wrt inclined plane).
Therefore, answer is $(g-a)sin \ \theta$.
I have solved this much. But my answer is wrong. The correct answer is $g+a= sin \ \theta$
Also, if there is a way to solve it in inertial frame, it would be great to know, since most answers solve it with non inertial. Is there a way to solve with inertial frame also?
EDIT:
I solved it this way now. (Different way).It is a photo. So , I hope it is clear to just read. Only thing I got wrong is that when I added a pseudo force.
My equation becomes :
N(normal by the wedge in the lift)-$m(g+a)$sin $\theta$ - ma = $m*(velocity of block wrt inclined plane = $a_v$).
$m(g+a) =N.$
$m(g+a) $- $m(g+a)$sin $\theta$ - $ma$= $m* a_0. $
This is what I got.
So , if I don’t include the N and -ma. Then , my answer comes to be right.


texts: Is there a standard percentage to increase structural steel weight to account for bolts?

texts:
Weight of Structural Steel
When calculating the weight of a steel structure, I usually calculate the weight of all of the various members and plates first. I then add an additional percentage to account for the weight of nuts and bolts. This percentage is usually between 2% and 5% of the total weight.
It makes sense that bolts will add additional weight beyond just the weight of the members. It is also complicated and time consuming to do it the "proper" way, e.g. deduct the weight of the hole and add the weight of the correct length and size of bolt. This is done with a spreadsheet or by hand and without the aid of specialized steel detailing software. Another complication is that furnished bolt lengths are partially determined by the fabricator.
The Problem
My company has always done this. The one time that a third party reviewer asked why the steel weight was ~5% higher, we were unable to cite a code reference where this was called for.
How is the weight of fasteners typically included in steel weight calculations? This can either be for a bid weight or a design dead load weight.
As additional information, in all welded construction, the weight of bolts might be so minor that it is negligible. Some of my projects use completely bolted connections including built-up members.


texts: Why can't proportional gain alone, reduce the error to zero?

texts: I was told that the proportional gain alone cannot the drive the error signal to zero in a feedback loop. Why is that? If there is a tiny error, there will be a tiny or larger (depending on the number of proportional gain) correction, so why won't the error signal reach zero? When the error tends to zero, the correction will tend to zero as well. But just before error becomes zero, there WILL BE corrective action, so why it cannot achieve the desired output?


texts: How much (uniformly distributed) weight can this L beam support without bending?

texts:
As you can see in the picture, the L beam is 1in x 1/2in x 1/8in thick x 72in long and is made of ASTM A36 steel. It's bolted onto a vertical upright on both ends.

What is the maximum uniformly distributed load that this L beam can support without bending?

What you see in the picture will serve as the front end of a shelf, with a wooden plank (and supports) resting on it.

Here's the link to the A36 steel properties: https://www.metalsdepot.com/steel-products/steel-angle

Could you please also share how you arrived at your answer, so I can calculate for different L beam lengths and loads?


texts:
What is the name of the angle if I have larger wheels on the rear axles compared to the front, this would make the cars body and chassis not parralel to the road, unlike if the wheels were the same size.

In other words the body and chassis would be at an angle.

Does this angle have a certain technical name?


texts: What is the purpose of building foundations?

texts:
According to many sources, one of the purposes of building's foundations is "To distribute the weight of the structure over large area so as to avoid over-loading of the soil beneath." (Wikipedia)

On the Wikipedia page on foundations, there is the following picture:

So the foundation seems to consist of some type of "legs", with a larger surface area on the bottom. But if the point is to distribute the weight of the building over an area, why not put the bottom of the building in contact with ground? Isn't the bottom of the building itself a much larger contact area than the area the foundation can provide? In the picture, the bottom of the building does seem to rest at ground, so why do we require the foundation to have these large surface area rectangles at the bottom if the whole weight of the building is already resting on ground?

Here is another picture from the same page:

This seems to be some sort of lodge or a cabin, with stones used as foundation. Here it is evident that the building itself is raised above ground with the stones used as a contact to ground. But now the small stones suffer all the weight of the structure. Wouldn't they be under quite a heavy load over small contact area and possibly sink into the ground? Why not simply have the building's floor, a much larger contact area, rest on the ground?


texts: What is a safe soil load to avoid settlement?

texts:
For residential design, looking at IBC 2012 Table 1806.2 it seems a safe soil load to design for is 1500 psf if you want to save time and cost isn't yet an issue.  (assuming you're not building on a swamp)

Aside from the problems of swelling and shrinking clay with the weather, for the types of soil listed in the IBC, is there a factor to use to safeguard against settlement to a certain small amount, or is this already 'built in' to the tables?

Does anyone know what the IBC limits its settlement to with the 'presumptive load bearing' table?


texts:
My original theoretical consideration was using the electric motor's rotor as drive shaft in a car. It led me to this question: "What will happen if we place a couple of separate, small stators around a long rotor instead of 1 large stator around a short rotor?"

I am a biology teacher. A motor design like this seems useful to me when I consider the structure of skeletal muscles. A skeletal muscle is constituted of a lot of long cells/fibers. Our body controls the force produced by the muscle by controlling the number of contracting fibers at a time. When we want to pick up a pen on the table, a few fibers are recruited; but when we want to pick up the table all fibers are recruited to generate enough force.

I guess that via changing the number of the active stators, a motor like this can be more efficient.

Is there any electric motor design like this? Or, is it possible and if it is, does it make sense from the points of efficiency and weight?

Edit:


texts: Calculating diesel volume in a horizontally-cylindrical tank

texts:
This is about several diesel tanks that need to be monitored in terms of diesel volume.
I want to measure and monitor the volume of Diesel liquid inside horizontally cylindrical tanks with standard dimensions, however the safety rules are strict, where no electrical devices or wires has to exist in the tank zone, which limits the solution to few methods or devices.
What i want to achieve is to measure the diesel volume inside the tank without having to use an ultrasonic sensor, as it will require some modification to the tank, not mentioning the wires connecting from the transducer to the display unit. the question here is whether we can use a sensor that can be attached to the output pipe of the tank and calculate the diesel volume. a sensor to measure pressure or flow, will it work for such requirements ? If yes, how do I calculate the volume based on those values ? and is there's any device in the market that can provide the volume of liquid inside the tank straight forward without the need to make any further calculations using the outlet pipe ?
The tank is similar to the one in the picture below.

Thank you.


texts:
Regarding the similarities, I know that the complete similarity is not always possible because all geometric, kinematic, dynamic similarity can not be met simultaneously.

Is it because both geometric and dynamic similarity can not be achieved at the same time?

What's the reasons? Please give some examples and explanations.


texts:
Weight lifters will use the term "one rep maximum" in order to refer to the maximum amount of weight that they can lift one time.  The one rep max is often used as a proxy for how strong someone is (or isn't).

Recreational lifters, other types of athletes, and the general population rarely bother with testing themselves in order to determine their maximum strength.

From a human factors and usability point of view, it can be useful to know what the average maximum strength of a population is so that design can take those limitations into account.  Please see the footnotes 1,2,3 for some practical applications of this question.

My question is if it's possible to estimate a person's maximum strength for a given activity by seeing how many repetitions they can complete at a lower weight.  For example, if someone can bench-press 100 lbs 10 times in a row, can that be used to estimate the maximum amount they could bench-press once?

If so, does that estimation model:

hold consistently across activity types?
hold consistently across increasing amounts of weight?
hold consistently across age and gender distributions?

1An entertaining example: amusement park / carnival attractions can be designed differently in order to accommodate the various distributions of strength.
2A mobility example: aids for the disabled can be enhanced if it's found that their maximum strength is below the threshold for a device.
3A diagnostics example: restraints can be designed just to the maximum of a particular demographic's abilities in order to provide a more comforting or friendly appearance.  This provides a humanizing touch while maintaining the accuracy of the diagnostic test.


texts:
I am currently taking a course titled "Electric machinery and drives". We have started with the very basics, i.e with the following equation:

$\tau_{motor} = \tau_{load} + \frac{\partial (J\omega_m)}{\partial t}$

where, $\tau$ is the notation for torque and $J$ is the notation for "polar moment of inertia, $\omega_m$ being the angular velocity of the motor shaft.

My question is: what is the source of the load torque $\tau_{load}$?, i.e is there some external agency that tries to rotate the shaft in the opposite direction?

On a side note, please also explain what the equation simplifies to if the load is just simply a massive flywheel


texts: Practical Application of Adiabatic processes

texts: The concept of Adiabatic is basically the isolation of a system in a realm where energy doesn't flow either way. Adiabatic compression and expansion is a common phenomenon harnessed in equipments and machines to heat or otherwise cool. The practical application of adiabatic can vary in design and technique, hence my question. If I have a tank of nitrogen gas at 300°C and 4500 psi and I want to cool the gas to 25°C and fill the nitrogen into a large balloon to a pressure of 20 psi, how can I harness adiabatics (especially adiabatic expansion) to cool the gas to my desired temperature between the tank and balloon.


texts: How to indicate bolt direction on a drawing?

texts:
Consider the following steelwork drawing:

The location of the 6 no. M12 bolts are indicated with a circle and cross.
However, it is not clear whether the shank of the bolts should point into or out of the page. Without explicitly drawing the nut and bolt, what is a shorthand way to indicate the direction of the bolt shank and location of the nut?
EDIT: I've done some digging and it seems there is no short hand for this. It is dealt with via an explicit drawing of the washer/nut and the use of drawing notes. I'll keep the question open in the hopes someone knows a shorthand way to notate which side the nut is to go on


texts: Can a threaded fastener stretch so much it can be miss-read as a different pitch?

texts:
Can a threaded stud of mild steel, size 5/8"-11 over a threaded portion of 1.25" stretch so much over time that it reads 5/8"-13?
Unthreaded portion of the stud reads .625-630" in diameter, threaded area is in the .610-.605" range, there is visible thread blunting/wear, more progressive the closer you get to the end of the stud.
I know the M16 x 2.00 is sometimes miss-read as 5/8-13, but my M16 x 2.00 die does not chase over the stud, and my tap does not work through the stud's accompanying nut.
I know the machine it comes from is old, and though I've never seen it, I've heard of proprietary threads, so before I go crazy looking for/trying to make a weird sized tool, I figured I'd ask.
So has anyone ever seen a thread stretched so far it reads a different pitch, yet visibly, it doesn't look so deformed?


texts: Output matrix for system with accelerometer

texts:
Consider a generic second order state space SISO system

\begin{equation}
\left[ \begin{array}{c}{\dot{\tilde{x}}_{1}} \\ {\dot{x}_{2}}\end{array}\right]=A \left[ \begin{array}{c}{\tilde{x}_{1}} \\ {\tilde{x}_{2}}\end{array}\right]+B \tilde{u}
\end{equation}

\begin{equation}
\mathbf{\tilde{y}}=C \left[ \begin{array}{c}{\tilde{x}_{1}} \\ {\tilde{x}_{2}}\end{array}\right]
\end{equation}

We can interpret $\tilde{x}_1$ as the position, $\tilde{x}_2$ as the velocity, and $\dot{\tilde{x}}_2$ as the acceleration. If I were to measure the state of my system using an accelerometer, how would I include it in this model? Is there a way of choosing matrix $C$ such that $\tilde{y}=\dot{\tilde{x}}_2$?

My first intuition would be to copy the equation for $\dot{\tilde{x}}_2$

\begin{equation}
\mathbf{\tilde{y}}=a_{21}\tilde{x}_{1} + a_{22}\tilde{x}_{2} + b_{2}\tilde{u}
\end{equation}

though I am not sure about that. Having a direct input-to-output term would mean that the system had infinite bandwidth (and therefore an instantaneous response).


texts: Series or parallel overloads in control circuits controlling several motors?

texts:
I think that putting the OLs of all the motors in series { figure (1) } provides better protection such that if any one of the motors is overloaded the circuits trips preventing the rest of the motors from working during the fault condition. But then, connecting them in parallel { figure (2) } provides better selectivity such that when a fault occurs, it's much quicker to determine the point.

Which is better? Which is conventionally used?


texts: Is a heavier car better than a lighter one?

texts: I am planning to build my own sports car when I am older and am very eco-friendly. I was wondering if a lighter car with everything else the same would be better than a heavier car. I am not expecting it to go up to 120 mph or something really fast, I just want it to have a really high mpg. I was thinking the lighter car would be better than a heavier car at stopping, and a heavier car would be better at accelerating, but not too heavy because it wouldn't be able to accelerate as well. So I was thinking a car with weight in the middle would be best.


texts: Constant crosshead speed or constant strain rate for comparing samples of differing thickness?

texts: Say I have two different specimens of a material, one is 10mm thick and the other is 1mm thick.  Assume that this material has properties which vary depending on the rate of deformation (I would call this behavior non-Newtonian in a fluid, I'm not sure if this has a different name in solids).  I want to test their mechanical properties under compression (e.g. modulus, plastic deformation, etc).  Should I run the compression tests for these materials using a constant crosshead speed (e.g. 5mm/min, which would be 50%/min for the thick sample and 500%/min for the thin sample), or using a constant strain rate (e.g. 50%/min, which would be 5mm/min for the thick sample and 0.5mm/min for the thin sample)?  If both samples are made from identical materials, which control method will show them as having identical material properties?


texts: ESD from human affects electronics. Why it does not affect the pacemaker? Is it beacuse it is much below the surface?


texts: Calculating the amount of teeth on ring gear in planetary gear system

texts:
I need to make a planetary gear system such as the following:

The sun and planet gears will be stationary (so that they can only rotate around their centers, not around the sun gear). My goal is to make it so that whenever the sun gear rotates $90^{\circ}$, each planet gear will rotate $-180^{\circ}$ and the ring gear will rotate $-90^{\circ}$. I am fairly certain from my own simulations that a $2:1$ ratio for the sun-to-planet gear system will produce the $90^{\circ}:-180^{\circ}$ rotation I need.

Therefore I have two questions:

Will a $2:1$ ratio make the sun and planet gears rotate in a $90^{\circ}:-180^{\circ}$ ratio?
How many teeth are needed on the ring gear (or what is the gear ratio) to make the gears rotate in a $90^{\circ}:-180^{\circ}:-90^{\circ}$ fashion?


texts: Audio frequency sweep spectrogram artifacts... hints?

texts:
I'm wondering how to interpret artifacts on spectrograms like the following which shows the recording of a linear frequency sweep.

In this case:

The recording is done with a cheap microphone and cheap sound card, and playback was done using an off-the-shelf system, which could have its own issues.
There are obviously harmonics which can be seen at the beginning of the chirp, but I can't remember where these can come from, then also those "X" patterns that are catching my attention.
There are some fixed-frequency perturbations, some constant, some pulsed and periodic

I'm looking for hints, ideas to perform root cause analysis, pointers to common and less common phenomena causing unwanted artifacts.

Collected hints so far:

Playback issue: speaker saturation or sound clipping, which can cause harmonics, and can be witnessed using another recording device.
Playback issue: clock desynchronization can cause waveform skips which cause very short pulses (of one sample).
Short pulses (not on the attached spectrogram, they're short vertical lines) can be caused by power line transient perturbations.
Missing anti-aliasing filter can cause capture of aliases of non-audible signals.
Out-of-band noise caused by sigma-delta ADCs (ref) which can also be filtered by low-pass filter.
Audion noise caused by capacitors in power circuits, eg. in LCD panel amplifiers.


texts: Problem reading control effort frequency response plot

texts:
I am trying to plot the frequency response control effort of a control scheme in Matlab, and in particular I want to do this for different values of tau, which is a constant used to add a pole at high frequency.

The plot that i get is:

in particular, this is the control sensitivity function of a 2 dof control scheme:

and the code for obtaining the plot above is:

s = tf('s');
P = 1/[(1+s)*(1+0.05*s)^2];
C = (s+1)/s;

%2 DOF

tau_1 = 0.1;
CF_1 = [(1+s)*(1+0.05*s)^2]/((1+tau_1*s)^3);

tau_2 = 0.01;
CF_2 = [(1+s)*(1+0.05*s)^2]/((1+tau_2*s)^3);

tau_3 = 0.001;
CF_3 = [(1+s)*(1+0.05*s)^2]/((1+tau_3*s)^3);

Q1 = (C+CF_1)/(1+P*C);
Q2 = (C+CF_2)/(1+P*C);
Q3 = (C+CF_3)/(1+P*C);

figure;
bodemag(Q1,'r',Q2,'b',Q3,'g'),grid
legend('tau = 0.1','tau = 0.01','tau = 0.001')

my doubt is given by the fact that the control sensitivity function starts at zero for all the three cases. Shouldn't it start at an high value and then decrease?

In this case it does the opposite, so it starts at zero and grows until a value and stays constant there.

How do I read this plot? Or it is complitely wrong?

If I plot the step response I obtain:

from it I zoomed to show better all the coloured lines.

Can somebody help me clarify my doubts? Thanks in advance.


texts: How to perform SLS check with strut-and-tie method?

texts: I am using strut-and-tie method to design a corbel. I noticed that Eurocode mentions strut-and-tie only in section 6, which is ultimate limit state design. How do I perform serviceability limit state design for the corbel using strut-and-tie method?


texts: Calculate force that can be exerted by a bending actuator

texts:
I have a model of a cantilever (fixed on one end, and free on all other boundaries) that bends in response to an internal stress field.

How can I calculate the amount of force this cantilever can exert on an external object?

The experimental analogue, as far as I know, is the blocking force--if you start with the cantilever in a flat state and physically obstruct the bending of the cantilever, how much force must you exert in order to keep the cantilever flattened out?

Additional Info

The model I'm using is a PDE that describes a non-linear, hyperelastic solid. For a given state of deformation, I can calculate the stress tensor and potential energy density throughout the cantilever.

So far, I have been using the finite element method to find the state of deformation in static equilibrium.


texts: Determine the parameters for this given nyquist plot

texts:
I have seen quite many of this type of question and I want to find how to solve them but I haven't cracked it yet. For example this is one:

My thoughts so far:
Replace $$s \rightarrow j\omega$$, $$G(j\omega) = \frac{k(a-j\omega)^2(1-j\omega)^n}{(a^2+\omega^2)(1+\omega^2)^n}$$
For $$\omega \rightarrow \infty$$ it is: $$G(j\infty)=\frac{k\omega^2*(-1)^n\omega^n}{\omega^{4+2n}}$$ $$=\frac{k(-1)^n}{\omega^{2+n}}$$ which is zero for $$n \geq -2$$ and infinite otherwise. But we can see that there is no point at which the plot approaches infty, so it has to be $$G(j\infty)=0$$
We also can see that $$Re(G(j0.5) ) = 0  $$
My problem is that with that not know parameter n , I cannot split the transfer function into Real and Imaginary part so there must be some hint to find the parameter n, before anything else. Is there a way to identify how many poles there are by just looking at the plot?


texts:
Does structural metal tubing (e.g., either as HSS, or in space frames, or even motorcycle/bicycle frames) ever come with any small metal rods or columns inside of the tubing itself?

While it might add some weight (and/or manufacturing complexity), could it also significantly improve the rigidity and load-bearing ability of the tubing?

*Edit: a more "biological" visualization of this could be similar to that of a bird bone's hollow structure (see this image), but with possibly far fewer crossbeams (to save on weight), perhaps just one or two small "spokes" or crossbeams every now and then?


texts: Is using a radiator to warm water inefficient and if so why

texts:
I'm currently designing a Hottub for my scouting. This isn't the first time we are doing this. In the past, we build a wood stove around a radiator as shown above. Now I'm wondering if this is efficient. I've read that a radiator uses convection where warm air goes up and warm water cools down. We use the radiator to warm up water my applying warm air.

Any great thoughts about this system are more than welcome.


texts: Tangential nozzle on vessel - weld preparation

texts:
What is the proper and recommended weld preparation for true tangential nozzle on pressure vessel.

Where can something about this thematic be found.

EDIT


texts: If the turbine drives the compressor, then what limits the engine speed?

texts:
My understanding of a typical jet engine is that when running, the turbine extracts energy from the hot exhaust gases. This drives the turbine, which is coupled to the compressor at the front of the engine. As a result, when the turbine accelerates, the compressor accelerates. This increases the mass flow rate of air into the engine, which in turn increases the mass flow rate out of the engine, producing more thrust. It also means more energy is extracted by the turbine, which drives the compressor even faster.

It seems as though it is a cycle that should continue to increase without limit. Therefore, my question is what stops the engine spin speed from increasing to infinity (ignoring material limits)? Why does the spin speed of the engine stabilise if the compressor and the turbine are continually driving each other at increasing rates?


texts: What are some common ways that I can vaporize Metals into a vacuum chamber? How can I keep these Metals in a gaseous state?


texts:
I did a Civil Engineering course some years ago and from my textbook I had a question on boundary layer thickness.
So far I have been able to calculate the transition distance, but I am not sure how to calculate the boundary layer thickness from there.
The purpose of this question is to work out how to calculate the boundary layer thickness from what I have said.


texts: How to limit axial movement for a key joint?

texts:
I need to design a simple gearbox for homework. I figured out to locate 2 sliding spur gears on the input shaft and 2 fixed spur gears on the output shaft. I prefer to use key joints, as they are the simplest possible.

How can the sliding gears be constrained? Will a long key do?
How can the fixed gears be fixed into place? Will another design of key joint work?


texts: Determining the direction of internal forces in a truss

texts:
I am learning the method of joints, but there's no explanation on how to figure out the direction of internal forces in my course.

How do you know that BA is tension and BC is compression?


texts: Can someone please give me a hint on how to draw velocity triangles for this specific inward flow reaction turbine problem?

texts:
I'm trying to calculate the hydraulic efficiency for this turbine by using the formula:
E(hyd) = (VwU)/gH
where  Vw= Velocity of whirl at inlet, U=velocity of runner at inlet, H=Given Head, and g=acceleration due to gravity.

But every time I get the efficiency more than 1 (which of course isn't possible).

I have tried this multiple but everytime it is more than 1. So I'd really appreciate if someone would properly guide me on how to make velocity triangles for this specific problem. Thanks.


texts:
I've come across two forms of the Darcy-Weisbach Equation, and each one seems to yield a different result when I am solving for $Q$ (flow).

$$h_{f}=\frac{\lambda Lv^{2}}{2gD}$$

$$h_{f}=\frac{f LQ^{2}}{3D^{5}}$$

How do these equations differ, and what (if any) is the relationship between $f$ and  $\lambda$ ?


texts: Control joint and contraction joint in concrete

texts: What is the difference between a control joint and a contraction joint in concrete? I mean, a control joint is to control the cracks in concrete due to temperature or shrinkage etc... I understand it. But then what is a contraction joint? I saw this term when I was reading about dams, when they pour large concrete masses and make contraction joint to account for shrinkage. Why don't they also call it a control joint?


texts: Undesired vibration of a beam under foot traffic

texts:
The other day I was in the waiting room of a doctor's office in a new building as part of UCLA medical complex. A new construction as part of multi million dollar extension of existing medical complex in west Los Angeles.

I felt a small tremor and because of California's proximity to San Andreas fault immediately suspected an earth-quake! When the tremor did not go on as I expected and died out I realized it must have been caused by the impact of steps of another patient. I paid more attention and noticed the vibrations are very noticeable specially when the stride of the person resonates with natural frequency of the floor.

Here is my question re. undesired vibration of beams and floors under foot traffic.

Consider we have a beam of steel WF 12x120 with 20 feet  span with I(xx) = 1070 inch^4.

What is the deflection under the foot of a man weighing 180 lbs.
Lets assume he is wearing work-boots with negligible flexibility and when he lands on his foot he exert equivalent momentum as if he fell down 2 inches?
And what is the vibration of this beam if we assume 5% damping?

As a comparison static deflection of this beam under same load is.
0.001614 inch = $Wl^3/48EI$


texts:
I have an HMI (Siemens MP 377) to print collected data on a LAN connected printer.
Now I would like that the data that are being sent to the printer is also received at a computer through Ethernet LAN. The HMI however has a single LAN port.
I have done some research on the internet already. Now the problem is that whether I should use LAN switch or HUB to copy the data so that both printer and computer receives the same data? Following, how would I visually see what is coming to the computer (or printer, because they both are receiving the same data)?


texts: Is constant force a useful parameter for correct drilling operation?

texts:
I'm trying to figure out a correlation between correct feed rating and the feed force.

Can a specific feed force be declared to create the correct feed rate per material per tool speed?


texts: Temperature when steam expands into a vacuum

texts:
Moran and Shapiro  Fundamentals of Engineering Thermodynamics (p147) has a worked example:

  Steam at a pressure of $15$ bars and a temperature of $320^{\circ}C$ is contained in a large tank. Connected to the tank through a valve is a turbine followed by a small initially evacuated vessel with a volume of $0.6m^3$. The valve is opened and the vessel; fills with steam until the pressure is $15$ bars and the temperature $400^{\circ}C$. The valve is then closed. The filling process takes place adiabatically and kinetc and potential energy effects are negligible. Determine the amount of work developed by the turbine in kJ ...

The solution is then given but in a comment at the end they add:

  If the turbine were removed and steam allowed to flow adiabatically into the smaller vessel without doing work, the final steam temperature in the vessel would be $477^{\circ}C$, as may be verified

How do you find the temperature without the turbine?

They start by observing that with their assumptions the energy rate balance reduces to:

$$\frac{dU_{cv}}{dt} = -\dot{W} + \dot{m_i}h_i$$

and integrating this and re-arranging they have:

$$ W_{cv} = h_i\Delta m_{cv} - \Delta U_{cv}$$

Because the smaller vessel is initially evacuated the changes are just the final values which they indicate with the subscript 2:

\begin{eqnarray*}
W_{cv}&=&  h_i\Delta m_{cv} - \Delta U_{cv}\\
  &=& h_i m_2 - m_2 u_2\\
  &=& m_2(h_i - u_2)\\
  &=& 386.6 kJ
\end{eqnarray*}

They have:

steamtables(400C, 15bar, v) = $0.203\,m^3/kg$  (use for mass)
  steamtables(400C, 15bar, $u_2$) = $2951.3\,kJ/kg$
  steamtables(320C, 15bar, $h_i$) = $3081.9\,kJ/kg$

What is the temperature of the steam in the second question


texts: Seals that form around a moving (linear) rectangular object

texts:
I am looking to find a seal like the one in the image that seals around the outside of a rectangular object and allows it to move, but when I search "square seal" I just get round o-rings that have a square cross section. Can anyone tell me what I need to search for to find such a seal as the one in the picture?

It is to be used so that the glass in the picture below can be moved forward and back through the container holding a liquid.


texts: How to extract a building's heat isolation and thermal inertia based on temperature curves?

texts:
So imagine we have a house with some isolation and some thermal inertia. This house also has a heating system that turns on (starts heating) when the observed temperature curve goes below some predefined temperature threshold.

I figured that in the scenario where the heating system is off (the observed temperature is above the threshold the temperature decrease will give us information on the thermal isolation and inertia. We need of course to take in to account the external temperature, the wind, and the sun irradiation.

I was wondering if there was a way to dissociate the information of the thermal isolation and the information of the thermal inertia. Clearly, if we had information about the thermal power loss it would give an indication but unfortunately we don't.

The data I have :  Observed inside temperature and desired inside temperature, outside temperature, wind, humidity from a weather station in the same city (so I guess only the external temperature can be used)

Objective: Determine the conductivity and thermal mass of the house for sales purposes (sell more isolation, help them master energy efficient behavior  etc)


texts: Prototyping disposable protective tong sleeves - materials?

texts:
I am interested in, perhaps, going in the direction of bio-plastics. However there might be some other options I haven't yet thought of, so that's the reason I'm opening this dialogue.

Before securing a manufacturer, I want to know what limitations, or options, I may have with regard to food safety, durability of product, look and feel of said materials, and implementation. Some compostable materials might not meet certain food-safety needs, perhaps exposure to acids or heat might result in types of unwanted degradation.

I am, basically, asking to collectively weigh the pros and cons of each material (e.g. Bio polyethylene, corn plastics) against the elements.
Which would be the absolute best material to use? Not only for functionality, but for the sake of being eco friendly also.


texts: How to find the center of gravity(Cg) of machine?

texts:
Consider, while building a new machine which has different elements in it. For instance, a machine having a driving assembly, main body, chassis, crucible etc.
Then, how would I calculate the center of gravity and how would I know the calculated value is an exact value or Cg value gives a balanced system?

Should I calculate a center of gravity of each element or the whole system?

Suppose I need to calculate the center of gravity of each element, how would I calculate? What are the factors to be considered other than weight and distance from the reference plane?

Any suggestions would be appreciated.

Thank you in advance


texts: How can I hold an adjustable angle between two load-bearing plates?

texts:
I have two wooden plates with the same dimensions (5 cm thick, 50 cm long and 35 cm wide).

The distance between plates must be at least 10 cm. Plate P1 is fixed but P2 rotates about the y-axis. Angle alpha can go from 0 degrees (when the plates are parallel) to at least 90 degrees.

How can I realize this design in practice? Which mechanical elements should I use? It must be strong, there will be load of max. 30 kg hanging on plate P2. There must be some mechanism that will connect these two plates and enable P2 to rotate but when one sets a desired angle between plates, the mechanism must hold the angle constant.


texts: Coil winding magnetic tensioner: How does it Work?

texts:
I ordered this model:

https://www.ebay.com/itm/coil-winding-mechanical-tensioner-MT-01-wire-diameter-0-04-0-12-tension-device/181965432380?hash=item2a5dfc263c:g:KFIAAOSw~4NZt4lY

I downloaded this diagram to get a better idea of the parts(This from a different model but they share a majority of components):

I'm just curious about the 1-10 knob on the back that puts a metal pad either closer or farther away from the device. I assume this varies the magnetic resistance

I'm also curious about the back-tension button. I see that when you tighten the screw the tension arm takes more pressure to pull down.

All-in-all, I just want to know how the knob on the back works in conjunction with the back-tension

Also, If you've used a Coil winding magnetic tensioner before, any info on its functions I would love to learn about.

I'm reaching out because there is basically nothing online about how these things work and all the labels on my tensioner are in Chinese so I'm clueless


texts: Effect of frequency resolution on the frequency spectrum of impulse force delivered by an electromagnetic shaker

texts:
this is a part of my parameter study for the experiment (a vibration analysis with a force impulse input). This specific part studies the frequency resolution effect on the spectrum. The input (i.e.: impulse force)

My main question is: why increasing frequency resolution (or frequency bin) would lead to the disappearances of sudden peaks at 50 and 150 Hz?
Note that the original input signal is the same, the only thing changed is the number of FFT lines (also known as spectral lines) and via that the frequency resolution.
Edit: Upload for measurement set-up

Edit 2: Sampled point format

Sampled point format, from 0 to 170 Hz (zoom in)


texts: Applying modern control systems to real mechanical engineering problems

texts:
My aim was to damp the vibration of a stepper motor ( Nema 8 ) using only spring systems. I have taken modern control course and I wanted to apply it here.

So I first analyzed my open loop system and found it to be highly unstable. I then used Ackermans formula to find State feedback $K$ after checking it to be controllable and observable, and I found $K$. I plugged my $K$ in Matlab and the solution becomes perfect.

THE PROBLEM:

Now what is this magical number (matrix) $K$ I need to insert in my system to make this work? What is the value of $K$ in real life? What does $K$ represent?


texts: Feasability of melting through ice crust with radiocative heater

texts:
I'm pretty interested in space exploration. Here I'm interested in a moon of Jupiter (Encealadus) which is covered by a thick ice crust, but apparently has at some depth a liquid water ocean which contains interesting molecules/salts/etc. Therefore has been some talks about how/if a probe could be sent there to investigate whether there might be life in that ocean. The most obvious way would seem to melt your way through the ice crust.

So I've decided to try to make a napkin calculation about the feasibility of this idea, from an energy perspective. I'd be curious to know if you see wholes in that reasoning, if some constants are wrong, etc. It's a napkin calculation - I just wrote it down & calculated mentally. So obviously not meant to be an accurate answer, most about a ballpark estimate. It's rounded to whatever integer makes calculations easier to do with just pencil/paper.

Energy needed to melt the ice

We assume @ stp (probably not right), use common values for water (there are salts in it so probably not right)
To estimate that, we must know the mass of ice to be melted.
To get the mass of ice, we need the volume of ice our probe would displace

Volume & mass of ice

Assuming a radius of 1m for our probe for 1km of ice crust. This is essentially a huge cylinder, so V = d*(2pi*r²), where d = thickness of crust (1km) and r = radius of our probe (1m). You get:
 - V = pi*10⁴ m³
 - density of ice = 10³kg/m³

With that, we can get the mass of ice to melt:
 - pi*10^7 kg of ice to melt through

Consider specific heat for ice of ~2kJ/kg, it seems we would need:

~10^8 kJ to melt all that ice.

Energy available from radioactive source

For P-239, I found ~200 meV as value for energy of a fission event.
Molar mass = 239*10⁻² kg/moles or ~50 moles/kg
Avocadro number ~6*10²³ atomes/mole

Let's say we bring 1kg. P-239 has as half-life of ~24 000 years or 600*10³ months. We'll use the half-life to calculate a rate of energy emitted per month, which we can then compare to the energy needed to melt the ice to see if have any chances of melting through it in a reasonable amount of time.

So, taking avocadro's number with the molar mass & considering 1kg of P239 we have ~4*10¹¹kJ of energy. Since we're using the half-life to get a rate of emission, we need to divide that by two (e.g. only half the Pu decays during the half-life).

We find that we emit ~10⁶kJ/month/kg of Pu we bring.

Conclusion

It seems we would need quite a few months to melt through just 1km of ice.

Questions

What might be wrong about that calculations, implicit assumptions that may not be right, etc.
What other considerations we omitted that may have significant impact? E.g. our probe might be much smaller, will also have things other than Pu (affects heat dissipations?), etc.


texts: Pavement stage construction; reduction of Structual Properties

texts:
Which properties of flexible pavement layers are reduced (discounted) in a stage construction design with an overlayed layer?

Thickness of stage 1 Layers?
Structural Number ?
Modulus of Resilience ?
layer coefficient ?
Other properties?

Additionally, do all layers get effected by the reduction?


texts:
I made a pallet lift table out of 1/4" SS304 and now have about 5x the deflection that beam calculations predict. I noticed that the machine was shipped supporting a 500lb pallet.
I thinking a few things:
1. Either shock loading from the 500lb pallet when the truck was going over bumps exceeding yield.
2. Creep from the pallet being supported for about a week now. Computer stress was about 6000psi, so pretty far from yield.

The table had two edges bent up on a press brake. One end of the table needs to be open to roll pallet lifts onto the table. I'm thing of going from 1/4" SS304 with edges bent on a press brake to welded 3/8" T1 A514. The yield of T1 is about 90kpsi, about 2x more than SS304.

Does anyone know the creep / cold flow SS304 vs A514/T1? Is there calculations to compute? I'm also open to comments/suggestions.


texts: Why hydroelectricity needs to flood so much land surface if only the height difference matters (hydrostatic pressure is not affected)?

texts:
Taking into account the fact that what matters in hydroelectric power generation is the potential energy of water, one would be led to the conclusion that we do not need the rest of the reservoir on the picture below, i.e. everything what is to the left of the picture.

Why one has to flood big areas of land if even a reservoir with small surface gives us what we need, i.e. equal pressure at the turbine (given by the height of the water column above it, the hydrostatic pressure is not affected by the area of the dam) and the same flow rate of water, given by river's flow rate?

If one wouldn't be restricted by the need to regulate the flow rate to the turbine, one could in principle build a power plant at a waterfall's edge, e.g. by digging a hole in the rock from the of the waterfall to its foot and putting a turbine there. Much smaller cost, no land flooded. Correct, or are there any other restrictions?

[https://en.wikipedia.org/wiki/File:Hydroelectric_dam.svg]


texts: Indicate continuous background process in flowchart

texts:
I'm trying to create a flowchart of the operational process for a widget that I'm designing. What would be a good way to indicate a "background" process that occurs but can be affected by other steps in the flowchart?

For example, I want to indicate that a vehicle will drive continuously and scan for obstacles continuously. If an obstacle is detected, the vehicle will then stop driving, change direction, and then continue driving and scanning again.

How can I most effectively indicate this in a flowchart?


texts:
I'm having some difficulty with the following problem:

The fan operating parameters are adjusted to reduce the constant negative pressure at the inlet ($p_\infty-\Delta p$) within a certain range of fans speed u. Calculate the thrust and drive power. $u$ and $\Delta p $ are given values. Picture below.

I'm wondering wether there are enough given parameters to solve the problem. Thrust is simply $\Delta p \cdot S$. I've tried using Bernoulli so as to calculate the relative speed v the observer moving with the fan would feel. ($u^2 + \cfrac{2\cdot\Delta p}{\rho} = v^2$). To determine $S$ it seems I'd need at least volumetric expenditure which wasn't given. Any hints are appreciated.


texts: Need to route air, like a solenoid does, but with many output directions

texts: There might be a proper term for what I'm looking for, but forgive me, I'm not a professional engineer.  I have a small cylinder with compressed air that connects using push-to-connect's (like these).  I am looking for a device that, like a solenoid, takes the pressurized air as an input and then can switch which port the air comes out of.  The difference is that I want to have more than two output ports.  Something in the range of 4-8 would be nice.  I will be controlling this with an Arduino.  Does such a device exist?  If so, what's it called?


texts: how to automatically create an assembly from a part

texts:
something really funky happened recently, trying to track down what actually happened.  I created a sweep on a 3d-sketched path, then mirrored it accross a plane so that the initial sweep and  the mirrored sweep share some of the same volume.  Then I tried to circular pattern the two of them around a central axis.  ordinarily when I try to do this I get the error "only merging features can be patterned".  however, one time doing this, I was researching how to do it, then, on giving up, I clicked something and bada-boom the whole thing worked.  with a catch.  it seemed like solidworks had automatically created an assembly with the same name, imported the part into it, and carried out the operation that I wanted it to do, but in the assembly, not the part.  I swear I didn't do all these  things myself.  now, I'm trying to figure out how it  happened, because, obviously, super useful!

For the record, I've found a work-around. creating a solid surface with which to connect all the sweeps, then sketching the end profile of the sweep on the solid surface fixes the problem, and no assembly is necessary.  so  you could say that this is a superior solution anyway because it avoids the extra file getting generated, but I'm still super curious about the other thing that happened.

Second edit:  I tried to reproduce the error for a commentator.. and.. failed.  it worked!  exactly the way I wanted it to!  Right in the part!  So.. we still have  a mystery, but it isn't clear if it's worth trying to solve..


texts: Is it safe to hold up a large heavy mirror with copper wire?

texts:
I have a very large antique mirror with some dense heavy wood framing it.  I've stripped out some home electrical wire to use the copper ground wire as the cable that ties to the back of the mirror frame and holds it up on the wall.  My question is how can I tell if the copper wire is strong enough to rely on and is it possible it will snap given time?

If I search the internet for load bearing on copper wire it refers to the wrong kind of load i.e. electrical which is not what I want to know.


texts: I have been involved in wire drawing for some years now. But only recently, I noticed that the wire surface was uneven and had burrs when inspected under a microscope (see photos). The wire is a Ni-Fe alloy which is cold worked by swaging/hammering before it is cold drawn to the final diameter. What can be the cause of these burrs? I would highly appreciate any valuable input. I will gladly provide more information when needed.


texts: How fast could a Mini Cooper go in a vacuum?

texts:
Lord Evulz just stole the Earth's atmosphere. Our hero must race his trusty old Mini - which he had already prepared to be airtight, to ensure the tires do not explode, with pre-packaged oxygen to supply his fuel with, etcetera... - to the last escape rocket before his air supply runs out.

Assume regular Earth highway conditions - (with no traffic because everybody asphyxiated to death) - with the only difference that there is no air resistance. What are the limiting factors on the car's top speed? And what velocity might be attained?

If the specific model matters much, take the 1977 British Leyland Mini 1000 - because it is Mr Bean's car and I fully expect him to find a way to drive it into orbit.


texts: Heat treatment processes in Nickel-Based Superalloys?

texts:
What is the difference in heat treatment process between Wrought
Ni-Based superalloys &cast Ni-Based
superalloys


texts: Control: control action of a PID controller with feedback

texts:
I'm programming the controller for a drone and I've got a question that may be basic, but I need to understand this perfectly to continue with the most interesting part of the project.

The sensors of my drone give me the position (x,y,z) and orientation (quaternion: x,y,z,w) of the drone, and I need to control the altitude of the drone, so I need to control the velocity in the z coordinate because that velocity is send to a topic of my drone (for those who use ROS, to the cmd_vel topic) and changing the velocity I can control the altitude.

So, basically the input of the controller is the desired position of the drone, then I have a PID controller and the plant (unknown model, so I have to "guess" the parameters of the PID), and the feedback is the current position.

Which would be the output of the controller (I mean, the $u_k$, with the discrete model of the PID that is the input of the plant)? Is it a position or a velocity? If it is a position, then I can do something like: (position_current - position_before)/timestep. But I don't know what is theoretically correct, because maybe I can find some $k_p$, $k_i$ and $k_d$ to have the desired velocity as the output.

Thanks :D

Edit: this is basically the model I'm using


texts:
Why can I not tow 50,000 lbs (40,000 cargo and 10,000 Trailer bed) using multiple pickup truck each individually capable of towing 30,000 lbs?

I was told that the towing capacity does not "Add up" where if one SUV can tow 30,000 lbs. Two SUVs can only Tow 30,000 lbs (maybe a little more).
Is that true?


texts:
I am trying to calculate the effect of insulation and weather conditions on a cottage. The cottage is made from a timber frame while the panels are of 4mm plywood. The weather conditions vary throughout the year between 0 and 30 Celsius. Cottage is around 25 m2 with 2.2 m height, consider as single room.

Question 1: What is the indoor temperature range if the insulation material used has an R-2.0?
Question 2: If we are to install a timber furnace, how much timber do we need to maintain the room at optimal conditions during the winter ? How long will it take to reach the optimal temperature ? (assume optimal is 25 Celsius)


texts: Guidelines for motor shaft length and pulley engagement

texts:
Searched, but didn't find this discussed here previously. I'm upgrading a hobby-level CNC router (a Shapeoko 3) to have wider belts (it came w/ 6 mm GT2 (2 mm)), I'm going up to 9 mm (otherwise same specs).

I ordered new pulleys and belting from SDP/SI, but when I went to install them was concerned that the end of the motor shaft (6.35 mm diameter NEMA23) is inset from the end of the pulley by almost 5 mm (4.88 mm). With the previous pulleys, they were flush with the motor end (but probably should have been slightly off to allow the belt to run true).

Is that too great a distance? What would be the maximum distance that the pulley could be off the shaft? What guidelines are there for this? How is it determined? (I've tried searching but haven't been able to find anything – am I not using the correct terminology?)

What is more important, that the belt run true or the pulley be on the shaft? There's only a couple of inches between the idlers (pairs of flanged bearings on M6 bolts) and a great deal of engagement.

The pulley in question is SDP/SI part # A 6A51-020DF0908.


texts:
How are all LTI systems also dynamical systems?
I understand that LTI systems are linear and time invariant and that dynamical systems describe how one state develops into another, but how would this make all LTI systems dynamical systems?


texts: Are these oscillations normal in a boiler?

texts:
I recently helped upgrade an old (±20years) 4ton boiler (heavy fuel oil) with some monitoring instrumentation. I decided to have a look at the data and I'm not sure if these kind of oscillations are normal for an older boiler? I haven't really worked with boilers before.
Ignore the sudden drop (a topic for a different question), I'm referring to the oscillating behavior in the steady region. It seems to be rather...excessive? but follows a relatively consistent profile which leads me to believe its just a really barebones control system.


texts: Part to pierce the valve on a 16g CO2 cartridge and connect to a Solenoid valve

texts:
The specific part that I’m after is something that can connect to a solenoid valve and a CO2 cartridge that will break the seal on the end of the CO2 cartridge.
The solenoid valve connection is roughly 1/2”/12mm (female, threaded)
which is just about the same as for the CO2 cartridge as shown below 3/8"/9mm (male, threaded).
I want to be able to control the flow of CO2 using an electric current. Does anyone know the name of the part that I would need and where to get one? Thanks in advance :)


texts: Pressure design thickness and how relates to hoop stress

texts:
Stress = Force / Area

Lets see with static force... what happens to stress output when decrease the area.

# Stress = Force / Area
F = 50000
A = [15.0,10.0,5.0]

S = zero(A) # Initialize the output
for i in 1:length(A)
    S[i] = F / A[i]
end

m = DataFrame(hcat(A,S))
names = ["area","stress"]
names!(m, Symbol.(names))
print(m)

3×2 DataFrame
│ Row │ area    │ stress  │
│     │ Float64 │ Float64 │
├─────┼─────────┼─────────┤
│ 1   │ 15.0    │ 3333.33 │
│ 2   │ 10.0    │ 5000.0  │
│ 3   │ 5.0     │ 10000.0 │

With decreasing area we increase the stress.

So in thinking about hoop stress then how the minimum required thickness is obtained. Using the ASME B31.3 pressure tmin to find t

304.1.2 Straight Pipe Under Internal Pressure
t = PD / 2(SEW + PY)

The numerator has P * D so anything in the denominator will dilute the numerator...

So to see how P and D affect the t output we can iterate through a range of static pressure and changing Diameter... so lets see what this looks like:

# Define numerator inputs
P = 200 # static P
D = collect(1.0:1.0:24.0) # varying D

# define the denominator static inputs
S = 20000
E = 1.0
W = 1.0
Y = 0.4 # temp coefficient

# initialize output
out = zero(D)
for i in 1:length(D)
    out[i] = P * D[i] / (2*(S*E*W) + (P*Y))
end

# plot the output
plot(D,out,seriestype = :bar, title="t = static P in relation to Diameter")

So a big factor in the minimum required thickness for pressure containment is the P vs diameter.. at say static P increase the D and we need a thicker wall for pressure containment.

So in thinking about S = F / A

How does this relate to the pressure design thickness calculation.... S in the tmin calculation is in the denominator and S is static in this equation governed by the 3:1 ASME safety factor in relation to materials tensile stress.

Intuitively i can see how at a static F over varying Area - how the stress INCREASES... (as we saw top of the post) because there is less area to distribute the stress over... so stress would increase pounds per sq inch...

But doesn't that mean for smaller D in a pipe, we have less A so that the stress would increase... but running pressure design thickness calculation.. at smaller D we need a thinner wall for pressure containment.

For sure im missing something here! (then again i see no area in the pressure tmin calculation)

Anyone can help me connect the dots?

Thanks


texts:
I have been trying to figure out how to calculate the required dimensions for liquid phase gas through a solenoid valve. Many companies (Swagelok, Bürkert, Asco) provide "Flow coefficient calculators" where you can enter values for the inlet pressure, outlet pressure and pick the medium flowing through the valve. There is no option to choose whether the gas flowing through the valve is in liquid phase or not though.

How would one go about finding the required size of a valve, if you know the pressure drop, required mass flow / volume flow and the medium flowing through it? Would you assume the flow to be just any incompressible fluid (i.e. water) and use

$$Flow \ coefficient = Volume \ flow \ \times \sqrt \frac{specific \ gravity}{dP} $$

Also, when would you have to be concerned about cavitation?


texts: What type of fountain nozzle ejects water in an oval shape?

texts:
I have seen one video about fountains, and there are some kind of nozzles.  What type of nozzle is used in the fountain shown below?

As can be seen in the photo, the fountain nozzle causes an oval shape to form from the water cascading back down.


texts: Where can I find efficiency metrics for diesel engines?

texts: I am doing long term planning for a small fleet of tugboats. A lot of the engines (propulsion, generators, hydraulics) are Detroit Diesels of various sizes (e.g., 4-71, 6-71, 12V-71). Newer engines are more efficient, but it is not clear to me how this can be quantified. I am trying to make decisions about repowering vessels and would like to see some metrics that I can use to calculate fuel consumption for a given workload. Is there a place or places where I can get information on fuel consumption for work done for individual engine models?


texts: Why aren't detent clutches used in car transmissions?

texts: In automatic transmissions some parts need to be moving with the engine in one moment and in the other they need to be stopped. Why don't transmisisons then use detent clutches to accomplish this?


texts: Why are trams always electrified with DC, while trains can be electrified either with AC or DC?

texts:
Trains can be electrified either with DC voltage or with AC voltage. Various networks across various countries uses various standards.
My question is however for trams, which are basically a lighter version of a train who is able to criculate on streets. (I am fully aware some networks are in between trams and trains). All of them seems to be electrified with low-voltage DC, with the exeption of T4 in Paris and the T11-express in Paris which are more like a light-metro than a tram.
Why are trams never electrified with AC ?


texts: How can I increase the CFM of my ceiling fan?

texts:
Since I am unable to change the pitch of the blades on my ceiling fan, I am considering buying a larger one. The current one is certainly efficient enough as that is why I bought it in the first place (CFM/watt); however, I need more airflow.

Altering the pitch would have been ideal but that is not an option.  This ceiling fan has hidden blade connections.  How can I modify the fan blades to increase the airflow produced by the fan?

For example, does the idea of winglets have merit? What would be the effect of winglets on a ceiling fan vs an airfoil?  Or, would notching the trailing edge as suggested in this answer help increase airflow?


texts:
How does the Michelson interferometer measure the self-coherence function of coherent light in an incoherent background? Detection of coherent light in an incoherent background (Coutinho et al., 1999) is still the best analysis and implementation of this concept despite considerable progress in semiconductor fabrication and photonics since its publication.

The reason I ask this question is because airplane pilots need to see the landing strip, ground landmarks and the horizon while at the same time harmful visible light laser rays are filtered.


texts: How do I change the text alignment in a radius annotation with AutoCAD?

texts:
I have two files open in AutoCAD. One uses horizontal text in radius annotation (see the first picture). The second uses a straight line in radius annotation (see the second picture). I cannot find any difference in the settings of the two files. How do I get the second file's annotation like the first?

Picture 1:

Picture 2:


texts: Why does my model of a wind turbine show high RPM with low power output?

texts:
I am designing a wind turbine to generate 1300 W.

I modeled the output voltage of an AC generator using the following specifics:

Number coil turns = 300.
Copper wire gauge = 1.02 mm.
Knowing the density of copper, I calculated the weight of the coil to be 4.39 kg.
Magnetic field strength = 1.24 T. (here are the specs for the magnet)
Area = 1 m2.
Rotational speed = 45 RPM.

I plugged these numbers into the output voltage equation:

$$\epsilon = NBA\omega\sin(\omega t)$$

to get a value of 1753 V. I am assuming that my generator will generate at least the 0.74 A to output a power of 1300 W.

Then, I modeled my turbine. I used the equation:

$$P_T = \frac{1}{2}\rho A v^3 C_p$$

to calculate rotor power. I assumed:

My turbine would be 30% efficient.
The wind velocity would be 10 m/s.
The area swept by blades would be 2.63 m2.
The density of air would be 1.25.

After plugging these values in, I get a power yield of 493 W. However, I find that the rotor speed is well above 45 RPM. This equation gives the tip speed ratio of the turbine:

$$\lambda = \frac{wr}{v}$$

Knowing that the optimum tip speed ratio of a three-blade turbine is 4.2, radius of the rotor blade is 0.915 m, and velocity of air is 10 m/s, that angular velocity would be 45.9 rad/s or 440 RPM.

How can I get 1300 W from this turbine when the theoretical yield from power of the rotor is only 493 W, even though my rotor should turn at the correct RPM for the generator to produce 1300 W?


texts: Interference fit in acrylic/plexiglass (PMMA)

texts: I'm trying to fit a shaft into a hole in an acrylic piece that is 5mm thick to cause an interference fit. The shaft has a max. diameter of ⌀5mm and a min. diameter of ⌀4.988mm. I have access to a laser cutter with a precision of 0.2mm. This basically means that i have to cut the hole in the acrylic to a diameter of less than ⌀4.788mm, to ensure an interference fit right? Lets say I cut the hole in the acrylic, using a diameter of ⌀4.788mm, the diameter could be as low as ⌀4.588mm. Would the shaft of ⌀5mm even fit in this hole? Given the material and uncertainty in the laser cutter, what diameter do you think is suitable? Thanks


texts: number of total reactions in a structure

texts:
In the example A , Why the author stated the total reactions = 9 only ? How to determine the total reactions for this type of questions ?

we can see that there is a total of 3 reactions (vertical , horizontal and moment) at the cut of the 4 parts , right (circled part) , and 3 reactions below . So , the total reactions is 4x3 + 3 = 15.


texts: Design decisions for variable speed motor switch settings (vs., say, rheostats)

texts:
Why do some variable speed motor switches have the highest speed setting next to the off setting instead of the lowest speed setting next to the off setting?

For example, most 3-speed household air-circulating / cooling fans will have 3 speeds with 3 being the highest. And the sequence will be: Off > 3 > 2 > 1. Why isn't it Off > 1 > 2 > 3? What design considerations are taken into account?

By contrast, most rheostat settings (e.g., light dimmer knobs/switches) have the dimmest setting closest to the off position.


texts: How to make wheel rotate slower in one direction than the other?

texts:
For one axle with one wheel, can the following rules be met and if so, what would be the most simplistic implementation?

Rule #1. Axle rotates clockwise: Wheel rotates at a 1:1 ratio with the axle. The direction of the wheel compared to the axle does not matter.

Rule #2. Axle rotates counter clockwise: Wheel rotates, but at less than a 1:1 ratio with the axle. The direction of the wheel compared to the axle does not matter.

If this already exists as a part manufacturers produce, what is it called?

How far have I gotten with this concept? Not very. Having a ratcheting mechanism sounds like it'd be a necessity or possibly some kind of planetary gear train.. but I'm coming up empty for actual solutions.

The purpose of this would be to have a single motor drive a small toy car/robot forward/right when the motor rotates one way and forward/left when the motor rotates the other way. The motor would be attached to a bevel/mitre gearbox similar to the image below. The bottom is where the motor would go and the mechanism I'm describing should go on both the right and left sides along with the wheels. At least, this is what I'd envision so far to accomplish my goal.

PS: I'm really just doing this for the novelty of it. I'm just getting into electronics and this was a challenge for myself (which I need help with it would seem, lol).


texts: Method of Hydraulic Resistances (Crane TP 410), how accurate is it really?

texts:
A bit vague but a question for you working engineers out there.

For a couple of years now I've been designing fluid systems, mostly using Crane's TP 410 as the guiding resource for pressure drop calculation and flow rate calculations. One thing that has bothered me is that I've never really gotten to validate my models against real life systems.

My question is, in the field how well does this method hold up ? Are the modeled results fairly accurate? Anecdotal evidence is welcome as well as something more concrete like a trade study.

I understand this isn't a traditional question you'd get on this site, so if this is the wrong forum just let me know and I'll take down my question.


texts: Is there a generator that uses night and day this way?

texts:
Is there a liquid or compounds that can change from gas then to liquid and back in a vacuum or with air?

In the picture below the hour glass looking devise liquid comes in contact with light or heat it vaporizes passes the neck turning a electric turbine. At the absence of heat or light it would drain back into the lower half. Water is not the only liquid that could be used. Can this work?

In a vacuum water cannot be a liquid but under enough pressure like on the lowest picture, the weight would be measured allow enough pressure for water to be in a liquid state when it is out of the sun. A balance between a super cooled liquid, gas state and heat/or light.
Black dye could be added to increase performance.


texts: What is the physical meaning behind the concept of shear lag in fibre reinforced composite structures or the concept in general for any structure?


texts: Mathematical transformation of a heading angle to a roll angle

texts:
I'm trying to understand a function in a SIMULINK example of a path following UAV simulation. The gist is that, the UAV Waypoint Follower block provides a required heading from a list of waypoints and this heading is converted, by the heading control block, into a Target Roll that is used by the autopilot.
The heading control block is the following function:

This function in the absence of wind evaluates to:

$$
\phi = \text{atan2}(p(\psi_d - \psi)V,g)
$$
meaning,

where, $\phi$ is the target roll, $V$ is the current speed, $\psi$ is current heading, $\psi_d$ is the desired heading and $p$ is the proportional gain "PHeadingAngle".

I'm struggling to understand how that equation works mathematically, and how it transforms a heading to a roll angle.

If possible, I'd also like an explanation for how the function deals with wind. I know that it transforms the heading angle and the speed using the wind speeds but am unsure how that transformation works.


texts: Illuminate the Earth with an artificial satellite?

texts: Do we have the technology to illuminate a small region on the dark side of the Earth with an artificial satellite in orbit around the Earth? By illuminate I mean bright enough to light objects for regular humans nearby to see better than they could have otherwise. Assume low Earth orbit and no moon to make it easier.


texts: thickness and other specifications PC + ABS for allowing light through?

texts:
So we are developing a plastic case, where we want light to be diffused through the case. The light is kept 2-3 mm away from the inside wall.
I wanted to know what thicknesses allow passage of light,
and also what colors allow better diffusion.
I have seen a couple of products which are in White.
But otherwise there is usually a light pipe for the diffusion.

Update:

Material most likely will be ABS+PC or just ABS.
presently design is 1mm. we are thinking that particular area reduce thickness a bit and keep a provision for a cylinder to block light from diffusing to other areas.
Any idea on what mix would be the best?
or if color will also affect the diffusion.  I cant recollect any black abs part which diffuses light. Only white I have seen.


texts:
Is there a standardized file format for parametrised solid modelling? I am familiar with STEP and IGES file formats for saving solid models, but AFAIK they don’t store information regarding parameters, so that the another person (not the one who created the file) can modify some parameter.

I know that every proprietary file formate (Solidworks, Inventor and so on) stores the parameters, but I am interested in a non proprietary file.

Many thanks in advance!


texts:
From Krulikowski (1997), the callout for several coplanar surfaces using the Profile symbol is done by using two surfaces to establish datum plane A-B and then tolerancing the remaining coplanar surfaces in reference to A-B.
Can other non-coplanar features reference this datum plane A-B as I would a normal datum? See below for example.

In the O-ring groove above (2.5 x 1.6), the callout on the left is for coplanarity. The callout on the right is for location and form, NOT coplanarity. I guess it would be obvious that it is not coplanar, but something about it looks off.
Is referencing datum A-B for non-coplanar features legal, illegal, or just plain bad notation? Or is it just a matter of preference?