texts: Calculation of unit mass of beam shell by using patran or nastran

texts:
I would like to know how to calculate unit mass of beam having uniform cross section, made by shell, by using Patran or Nastran, not by manual.

Would there be any functions to calculate mass or unit mass?


texts: Finding transformation of forces and moments

texts:
I have two sets of forces and moments, measured by two 6 DOF force/torque sensors at position A and B on a robot arm (B at end effector). My goal is to use this measurements to relate the forces/moments at position A to those at position B, i.e. find a transformation of  $F_A, M_A$ to $F_B, M_B$. The transformation is static and no other external forces apply.
The related formulas for that are:
$$
F_B \approx RF_A \\
M_B \approx RM_A+t\times F_B
$$
Is that correct (it's addaped from this)?
My goal is now to find an optimal (in a least squares way) matrix R and vector t. How would I do this? Is the Kabsch algorithm suitable for this?

Update:
Below a small sketch of the setup. It is some sort of handle on the robot arm. A force is applied (and measured) at Sensor A, the goal is to use the measured force at sensor B to find the transformation.


texts:
I am analyzing a built-up C-channel for bending purposes (2 point loads of 1200 N each @ 30 cm symmetrically from the CL). The flanges are made of a different material than the web, they are also of a different thickness. The two materials have very different elastic and strength properties. Assume a perfect bond between the flanges and web.

So far i have used the "equivalent section" trick to convert the flanges' dimensions as if they were made of material 2 and to find the stresses in both the web and flanges, after this i ran an FEA on the beam and the stresses are very close to what the theory predicts.

The next and hardest step in the analysis is to figure out the deflection of the beam due to the bending load. While the "equivalent section" trick is helpful to find the maximum stresses, i'm not sure it can be used to find the actual deflection. Additionally, i need to figure out the shear center of the section and all formulas i have seen so far assume a uniform thickness in the web and flanges which is not my case.
Furthermore, since the shear center will be located somewhere to the left of the section, there will be a resultant torque on the section which will induce a shear stress in both the flanges and web. While Roark's formulas for stress and strain provide guidance on how to calculate torsional shear stresses in C-channels, it generally assumes uniform material properties which is not the case of this channel. The materials are a ton weaker in shear than they are tension/compression so this is actually my main concern.

Can anybody recommend any resources, tools or tricks to solve this problem? I have access to my college's mechanics of materials books and even in the advanced edition i could't find anything that might help me. In theory i could simply use FEA software for this section but i will have nothing to verify the results against and I always like to at least have an analytical ballpark number to double check.

Any help would be greatly appreciated. Thank you fellas.


texts: Speed Control of Quadcopter along with Position Control Using PID with Simulink

texts:
Within MATLAB Community, I found an example of a simple quadcopter model control built with Simulik and SimMechanics, The controllers handle position and orientation control. I want to extend this controller and add a speed controller (Quadcopter Vx,Vy,Vz), and keep the position control as well. What should be my starting point? I believe I can't use two PID controllers for the same input since they'll interfere with each other, thus one PID will oscillate. The current controller is given below:

What would you suggest I should start with? I intend to use MATLAB/Simulink. Thanks for the information in advance.
Note: I have every sensor I need on the model to measure errors.


texts: im importing my 2D sketch from AutoCAD and trying to extrude base in Solidworks. I realized that when I tried to extrude a shape, it's connected to another shape, and it's extruding together with it which I don't want. How to solve this issue. I have attached a picture of two shapes which extruding together.


texts: Design of Compound Elliptical Concentrator and Compound Parabolic Concentrator

texts:
What is the process in design a Compound Elliptical Concentrator and Compound Parabolic Concentrator if I wanted to achieve 100% optimal concentration ? Let's assume random numbers of: A light source being 14 meters wide, the aperture is 4 meters wide and the distance between them being 12 meters.

I was doing random searches on solar energy and came across solar concentrators which I've never heard of before, but saw you can design them based on knowing information above. I can't find anything easy enough to understand so a newbie like me can follow clearly.

For example, for the CPC. The equation is for the maximum concentration: $$C=\frac{1}{sin^2(\theta)}$$

If I wanted a 100% concenctration would have a 1 (100%) in place of the C then solve for the theta to get the half acceptance angle ? Would I go backwards from this and adjust the base of the concetrator to have an aperture of 4 meters and a base of whatever gives me an angle of theta?

Here is an image of what I meant (found randomly online with no explanation):


texts: Can an AC rated temperture switch be used in a DC control circuit?

texts:
Looking to add a "high oil temp" warning on a machine tool by adding a temperature switch into the hydraulic circuit, right after the radiator before returning to tank. I know monitoring from the tank would be better, but tapping into the tank is not possible.

The switch I would like to use....

https://www.mcmaster.com/7079k95

....is rated for 120/240 AC.

I would like to use the switch to trigger an input on my PLC. The switch is normally open and would close at over temperature, allowing a +24vDC to connect to the PLC input(PNP).

Can this switch, as only rated for AC, be used to carry the low-amperage +24vDC signal?


texts: What are the factors that made narrow-gauge railways cheaper in the early 1900s, and are they still applicable today?

texts:
Back when railways were being massively build, in the 1900-1910 decade for example, most new lines were made with narrow gauge, instead of the standard gauge which is 1435mm for most of the world.

For instance, in Switzerland, most new train lines built between 1890 and 1914 used a gauge of 1m. Urban tramways used 1m gauge too.

The reason for this is that this was much less expensive. I wonder however what factors lead to the construction of such smaller railways to be less expensive. Understandably the earthworks are lighter, but not so much as the width of the vehicles dictates this and not the width of the tracks.

Quotes as for where I learned that narrow gauge was supposedly cheaper : From Wikipedia page on narrow gauge railways.

  Since narrow-gauge railways are usually built with smaller radius curves, smaller structure gauges and lighter rails, they can be less-costly to build, equip and operate than standard- or broad-gauge railways (particularly in mountainous or difficult terrain).

Also quoting the page for the railways line between Glovelier and La Chaux de Fonds, Switzerland

  La voie normale permet de mettre en service des trains directs depuis
  Bâle jusqu'à Saignelégier pour les jours de Marché-concours. Mais la
  construction a coûté cher. La compagnie est rapidement en difficultés
  financières et n'a plus d'autres choix que demander de l'aide à sa
  rivale. Les deux compagnies font direction commune dès 1906.

  (My translation (emphasis mine) )
  The normal gauge allowed to have trains directly from Basel to Saignelégier on
  days of Market. But the construction costs were prohibitive. The
  company was quickly in financial difficulties and had no other choice
  than asking the rival company [translation note:The narrow gauge
  railwy Saignelégier-La Chaux de Fonds] for help. Both companies had
  common leadership since 1906

If a new line were to be built today, now that massive industrial construction machinery is available, would it still be significantly less expensive to make it narrow gauge ?


texts: What engineering discipline deals with ensuring that a manufacturing and testing process is clearly defined and followed?

texts: I work for a small engineering and manufacturing company. To date our production process for each product has been defined in each critical aspect by the design engineer, then handed to the production department and rarely looked at again by engineering. Many noncritical aspects are undefined and left to the variable judgement of the assembly workers. I'm considering assigning an engineer to the task of analyzing and documenting the entire production chain of a product for consistency and quality purposes, and to look for cost saving improvements. What discipline of engineering would this be considered, if any?


texts:
A neighbor has a Nokia RM 1187 with erratic behavior: sometimes it was fine, then pressing one key triggers another, and now the on/off key is not working and the phone does not turn on. All contacts from A to I are missing from the SIM card; in switching SIM cards to another phone and back to this one, it's possible that this erratic phone transferred those contacts to the phone memory. I opened the case and the phone looked spotless with no signs of water damage, galvanic or salt corrosion. The phone has one large chip that seems to take care of most of the phone's functionality, the horizontal one visible from the back without the battery:

I have now created two backups of the current contacts, so those are safe.
I would still like to recover the previous ones in case they are on the phone. I need the phone to turn on to create a backup of contacts to a microSD card. When I charge the phone, it shows NOKIA and an animated charging sign. When I connect it to the computer, the same thing happens and it does not show as an external disk. I tried pressing each key for 4 seconds and it did not turn on.

How can I turn on this phone with a failing on/off button, or how can I access the phone memory to look for contacts?


texts:
A vacuum evaporation system works keeping warm water inside a sealed vessel, which is evacuated with a reversed compressor (or vacuum pump) to keep an inside pressure lower than atmospheric pressure, with the objective of lowering evaporation temperature and increase overall process efficiency. Next picture shows a highly optimized vacuum evaporator system schematic (for the subject of this question we can ignore all heat recovery subsystems):

I am interested in an ambient temperature vacuum evaporator (i.e. 25 ºC). Vapor pressure of water at this temperature is 3.17 kPa, so we need an inside pressure lower than or equal to this value.

There are two main sources of energy expenses. First is enthalpy of evaporation, which at this conditions is 2440 kJ/kg, so we need to add this amount of energy to maintain water temperature at 25 ºC during process. Second is compressor work to keep process pressure inside vacuum vessel. We can approximate it as a reversible adiabatic thermodynamic process (i.e. isentropic process).

Entropy of saturated water vapor at 25 ºC and 3.17 kPa (the one that compressor evacuates because liquid water stays in the bottom of the tank) is  8.56 kJ/kg. Internal energy at same conditions is 2410 kJ/kg. Because process is isentropic, entropy of discharge steam is the same, so its thermodynamic state is 400 ºC 101 kPa and internal energy is 2970 kJ/kg. Because process is adiabatic, compressor work is equal as change in internal energy: 2970 - 2410 = 560 kJ/kg.

Energy needed to run an idealized system as the one described will be the sum of the enthalpy of evaporation and the compressor work: 2440 + 560 = 3000 kJ/kg.

Is this estimation correct?

400 ºC compressor discharge steam looks quite hot to me. This can explain why most common industrial vacuum evaporation systems work at higher water temperatures and lower vacuum levels. It is right?


texts: Is there a difference between piezo ceramic disc transducer and a piezo ceramic bender

texts:
I really do apologise if this is a stupid question but I for the life of me can't find an answer. I need to do a project where I measure the liquid of water in a tank using ultrasound and am planning on doing it with Texas Instruments TDC1000.

The problem I'm having is that I can't find the ultrasonic transducers that they use in their examples in my country and was thinking I could maybe just use one similar to it. However I can only find ceramic benders. I would just like to know if they are the same and if not what is the difference.

Thanks


texts: Suggestions needed: Automatically recognising key elements of object in 2D image for technical drawing reconstruction

texts:
Disclaimer: I am aware that this is a vague  question, I am merely looking for suggestions on where to start. If you find that this question is better asked elsewhere, suggestions are more than welcome.

Problem: From a 2D image displaying an object (displayed as either lines or filled areas), I need to recognise and pinpoint the location of key elements such as sharp corners, rounded corners (fillets), holes, etc. in order to create a technical CAD drawing of the object.

Current knowledge: I am capable of automatically creating drawings (measurements, lines) in CAD software such as CATIA. It is the classification and location of these key features I am after.

Question(s): Simply put: where do I start? Is computer vision my answer?
I am aware of OpenCV's contour and hough circle methods, and have tried these with a certain amount of success. This enable me to find rounded corners and sharp, 90° angles. Is OpenCV the best way to go, could you suggest different libraries, or should I ignore computer vision altogether and focus on training a convolutional neural network to classify parts of the image and go from there?

Again, apologies for the vagueness of this question from a first-timer.


texts:
Goal

I am creating a project where I will need to move small beans around in turbulent air flow. I will have a heat source to which I do not want the heat to leave easily (I want the beans to be allowed to heat up).

I initially tried to purchase a fan that simply had high CFM (about 400 cfm or so) but that seemed to be a poor choice as it just sucks all of my heat away and does not move my beans very effectively.  This fan was simply a 120mm computer case fan. I believe my problem was that it pushes air with high velocity but with little momentum behind it.

My thought process

So I feel that this article gives a pretty great definition of the different types of fans and motors. I am not product searching but rather just trying to pick the appropriate blower / fan type that would best help my application.

I think that I want low CFM and high static pressure if I am understanding correctly? Based on this I think that the squirrel cage type blowers may be good enough. Please do correct me if someone has more experience with this though.

Follow up

Once a type is established, what is the best method to actually size up the right sized blower?


texts: Which drawer design can hold more weight?

texts:
I want to build drawers for my kitchen. On Youtube I found this Channel, where a guy does woodworking. In a video about making kitchen drawers, he says that the bottom surface of the drawer will be stronger if the joint connecting the bottom to the sides is positioned lower. https://youtu.be/wLMQ_6Y29pY?t=5m15s (5:15 to 6:03).

To me, it should make pretty much no difference. Am I wrong?


texts: Equation used to obtain the adjustment angle of a pivoting lid support mechanism?

texts:
The following image shows a CAD model in its folded and unfolded form.

I was able to successfully give it the ability for it to be adjusted between a 25 and 45 degree form, at 5 degree increments; but would still like to know a mathematical equation, for future projects.
The following images displays the arms at various angles:

This is the pivot bracket that moves to hold the arm at each adjusted angle, it is rotated at the center of the small sky-blue circle; please note the green circle has a triangle within it as well:

One end of the pivot bracket slides along 5mm deep notch/track/mortice, that is sloped at 2.5 degree angle:

This the approximate distance of each holes:

I’ve gone ahead and measured each internal angles and the distance between the arm & pivot bracket at each adjusted angle; they each add up to 180 degrees:

I’m interested in the mathematical formula that would be used to obtain the values: 29.1, 17.0, 15.0, 14.1


texts:
For weeks I have been searching internet , but still unable to find answer , so here it goes:
I have to calculate pressure losses in heating circuit , and am stuck at calculating losses in T fittings. Here are some crude drawings of problem

I know:

diameters of each pipe leading to fitting (Da,Db,Dc)
flow rates through these pipes (Qa , Qb , Qc)

What I need to know is Pressure drops:

∆Pc-a=Pc-Pa=?
∆Pb-a=Pb-Pa=?

I know of minor loss formula , but don't understand how to use if fitting has more than 2 ports.


texts: How can I couple two small parallel shafts offset a short distance from each other?

texts:
I have two parallel shafts, 3 millimetres in diameter and offset by 8 millimetres, both anchored in surrounding housing by ball bearings. When one shaft is rotated (via gear), I want the other shaft to rotate with it. I have less than a cubic centimetre of space between the shafts in which to place the coupling mechanism.

So far I have been using a stiff orthodontic elastic looped around high-friction rollers fixed onto the shafts. However, this introduces backlash, resistance, and unpredictability.

A timing belt would work well but the pitch length would have to be no greater than 1.07", which is smaller than any timing belt I can find on the market.

Any suggestions for coupling these shafts precisely in a space- and preferably cost-efficient way?

Edit: I believe the offset is too large for Oldham coupling. Here's an image of the shafts without surrounding housing:


texts: reducing rotational speed from gearmotor to below 1rpm

texts:
I need to produce a very slow rotational speed for a disk -- 0.25rpm, or 1 rotation in every 4 minutes.  The disk is nominally 12" in diameter.  It will be driven by a DC gearmotor, through a worm and gear with a 1:20 drive ratio.

The slowest gearmotor that I can find (within my budget and space parameters) is the Servo City 12rpm motor here: https://www.servocity.com/motors-actuators/gear-motors/heavy-duty-gear-motors/premium-planetary-gear-motors

But even at that slowest speed, and with the 1:20 worm gear, that still only gets me down to 0.6rpm, more than twice as "fast" as I need.

The options that I can think of would be an additional pair of gears being driven by the worm gear, or a planetary gear reduction unit between the gearmotor and the worm gear.

A few more parameters:

All of the components I'm already using for the mechanism are based upon .25" dia. driveshafts (most are from Servo City)
I need to go with off-the-shelf components; nothing fabricated (modified is OK)
It must be long-wearing and precise (no plastic or cheap alloys)
There's limited space between the worm gear and the disk
My budget for whatever solution to reduce the speed is =/< $50

I had been considering some of the gearboxes from AndyMark ( https://www.andymark.com/Gearboxes-s/55.htm ) but frankly, I'm put off by the fact that they don't even list the shaft diameters for their gearboxes; most of them seem to be proprietary sizes intended for use only within specific systems.

Any ideas would be appreciated!


texts: I have 3D model ready in Autocad. I would like to color it and extract a 2D png file from it to use

texts:
I am new to the AutoDesk AutoCAD drawing software. I would be really appreciated it if someone could help me out. I will attach the image of the content.

I found 3D drawing from the internet, which is STP file extension. I imported the 3D content into AutoCAD. It is a Cessna plane drawing actually. But, the problem is the plane is not colored. How can I color it since it has multiple layers on the drawing?

Finally, after the coloring process, I wish to get png files from some specific angles to be able to use it in my 2D drawing. How can I manage to do that?

Thank you for your help.


texts:
How can I build a v shaped pathway for drones? It would be a sort of racing path and there would be multiple drones flying over the pathway at the same time.

The race would be a relay race. So there are multiple path breakpoints and each drone would have to carry a small item passed onto it while racing over the path. We have to protect the item at all cost and also be really fast at the same time in order to win the race.

The shape of the path is "V" because I would like to build a v shaped inflatable structure which would protect the drones if they fall off onto the path while racing.

1 more point: since a drone racing envrionment would take quite a lot of space, all of this would be built in a small hilly area where it would be quite windy.

So what material can I use to make the drone racing pathway? What material to use for the inflatable v shape pathway? What to use so that it resists wind?

Any other mechanism can be suggested for the pathway keeping in mind 2 important factors

Protection of the item
Speed

Thanks


texts: Stiffness of highly compressible materials

texts:
A foam which I have performed compression tests on shows results similar to the following hysteresis cycle:

(Note that the first bend in the graph is not the yield point; the hysteresis cycle returns to the origin.)

I would like to characterize the compressibility of the material using a commonly used statistic.

The Young's modulus is an obvious candidate (see dotted line), but it doesn't really capture the characteristics of the material when you compress it further.

Instead I had the idea of using the dashed line: the minimal value of stress divided by strain over all values along the curve of the compression. However, I don't know whether that is a commonly used statistic to describe compression of foams.

What commonly used statistic best describes the compression behavior of a foam at higher strain values?


texts: Mechanism that moves two parts linear to each other

texts:
I'm designing a machine that will seal plastic tubes. The idea is to clamp the tube with two beams. These two beams have to move away to let a piece of the tube through, then those beams should move to each other so that the plastic tube gets folded and hold between the two beams. One beam moves exactly the same as the other, only in the reverse direction.
Currently, the design uses timing belts to accomplish this, but I'm searching for other ways to accomplish this type of movement, but I'm having a hard time finding mechanisms like this on the internet because I don't know how to call it. Is there a name for this kind of mechanism/movement? Or do you know any other ways to accomplish this movement?

Some illustrations that might clarify my explanation:

Another way I came up with is using a ball screw mechanism where one half of the axle has it's screw tapped the other way around, but that part is probably expansive to built. An rack and pinion system with two racks would also work. Other alternatives I came up with all use two motors.


texts: How to make an arduino pick an individual plant seed?

texts:
I am trying to build a robot which would plant seeds instead of humans doing it (lettuce, radish and so on). The only problem i have so far is picking an individual seed.
How could i do it? I've seen some discs designed especially for such appliances, but those are really expensive and i think that there has to be an alternative.


texts: Relation between airespeed and pushing force

texts:
I'd like to know how can I estimate the maximum speed that can be achieved by a
"portion of wind" accelerated upward from rest on the surface of
a place by pushing forces.

So far I've thinking in the relation between lift and speed (for an object such as an air plane),

$Lift=\frac{1}{2}ρv^2 × C_l × area$

But not sure if I can use this expression for "a portion of air", for air moving specifically.


texts: Beam with constant load distribution on three supports - force distribution to supports

texts:
I have following example (the question is at the bottom):

The load distribution $q$ is constant.  I add condition of zero bend in center of the beam, $w_B = 0$, and the assumption $F_{RA} = F_{RC}$.  So I have:

$$F_{RA} + F_{RB} + F_{RC} = q\cdot 2 L$$
$$F_{RB} = 2 q L-2 F_{RA}$$

Divide beam to two sections (from left)

I. $x_1\in\{ 0;L\}$

$$M(x_1) = F_{RA} \cdot x_1 - q \frac{x_1^2}{2}$$
$$\frac{\partial M(x_1)}{\partial F_{RB}}=0$$

II. $x_2 \in\{0;L\}$

$$M(x_2) = F_{RA} (L + x_2) + F_{RB}\cdot x_2 - q \frac{(L + x_2)^2}{2}$$
$$\frac{\partial M(x_2)}{\partial F_{RB}}=x_2$$

Use condition $w_B = 0$
$$w_b = 0 = \frac{1}{E\cdot I_z} \left ( \int_0^L M(x1) \cdot \frac{\partial M(x_1)}{\partial F_{RB}} dx_1  + \int_0^L M(x2) \cdot \frac{\partial M(x_2)}{\partial F_{RB}} dx_2 \right )$$

$$0 = \int_0^L M(x2) \cdot \frac{\partial M(x_2)}{\partial F_{RB}} dx_2 = \\ \int_0^L \left ( F_{RA} (l + x_2) + F_{RB}\cdot x_2 - q \frac{(l + x_2)^2}{2} \right ) \cdot x_2 dx_2 $$

Substitute for $F_{RB}$

$$\int_0^L \left ( F_{RA} (l + x_2) + (2 q L-2 F_{RA})\cdot x_2 - q \frac{(l + x_2)^2}{2} \right ) \cdot x_2 dx_2 $$

Solve for $F_{RA}$

$$F_{RA} = \frac{1}{4} q l$$

It's this result correct? It seems suspicious to me. I supposed $F_{RB}\geq F_{RA}.$


texts: Are "Imperial Eastman" compression connections sized the same as regular imperial connections?

texts:
I have some high pressure and vacuum lines off of a tool from the 1980s and they are labeled as, for example, "3/8 imperial - eastman," which seems to be different from how normal compression connections are labeled.

Is this the same as regular imperial units, or is there some difference I need to be aware of? Where can I find these parts?


texts: Sizing crumple zone for multi-vehicle collisions

texts:
I need to size bumper beams for the crumple zone of a very lightweight vehicle.  Together with the driver, the vehicle will weigh 300kg.

Sizing the beams for a single-vehicle collision against a fixed object is simple.  To prevent brain injury, I need to keep the average deceleration under 50 G, so the average crushing force must be no more than ~ 150 kN.  Dividing the kinetic energy by the force gives me the needed crush distance.

However, if the vehicle is in a collision with another (heavier) vehicle, I am unclear about when and how the two crumple zones will collapse.  Looking at NHTSA crash test data, it seems the crumple zones in most passenger cars are designed for a deceleration of about 15 G against a rigid barrier.  For a 1,700-kg car, this would mean an average crushing force of 255 kN.

If my vehicle with beams designed for a crushing force of 150 kN crashes into a vehicle designed with a crushing force of 255 kN, what happens?

a) Assuming my crush zone can absorb all the excess kinetic energy in the collision, what will the deceleration of my vehicle be?

b) Can I rely on the crush zone of the other vehicle absorbing some of the energy before the force on my vehicle over a significant period of time rises above 150 kN?  If so, how much?


texts: What is the meaning of a "trip angle" in a level sensor?

texts: What does trip angle mean in the context of slope  / level sensors / inclinometers?


texts: How many support beams/rods needed for a firewood storage cabinet

texts:
I am building a firewood storage cabinet which should support around 100-150 kg of firewood.
The cabinet is made out of wooden boards (20 mm thick for all sides). The length is 550 mm and depth is 400 mm. The wooden logs are 300 mm in length.
150 kg for a wooded shelf of 20 mm in thickness is too much (I want to use 20 mm wood for all sides) and I want to make sure it will not bent. My idea is to reinforce the shelf with hollow steel rods under it. Round rods, because those can be easily drilled into the walls of the cabinet. I know square rods are stronger, but square holes are tricky to make.
The problem is that if the rod is thicker than D=10 mm and the distance from the front is is more than x=50 mm, the rod will be visible under the shelf from a distance (the shelf start at 340 mm  from the ground). So I would like to keep the first rod around x=100 mm from the front and use rods of D=10 mm for the aesthetics of it.
I am not sure though if a rod of D=10mm / d=2mm is strong enough for this. Or how many rods will be enough (n).
My question is, what size steel round ronds (D / d) can I use and how many of them (n) will be enough? Another option would be to only use the thinner rod front rod and thicker rods after. But I am also very curious how this can be calculated.
Below is the schematics with sizes and some variables which I used:
       rod length = 550 mm
total wood weight = 150 kg
                D = round rod diameter
                d = rod wall thickness
                n = number of rods needed to support the weight


texts: Methods for determining Work of Diesel Engine's Isentropic Process

texts:
Air in the cylinder of a Diesel Engine is at $30^o\ $$C$ and $138\text{ kPa}$ in compression. If it is further compressed to 1/18th of its original volume. Which of the following most nearly equals the work done in compression of the displacement volume of the cylinder is $14.2$ Liters

Answer is $11\ \text{kJ}$

$$T_1 = 30^o\ C + 273.15 = 303.15\ K$$
$$P_1 = 138\ kPa$$
$$V_d = 14.2\ L*(1\ m^3/1000L) = 0.0142\ m^3$$

Attempt 1: Using isentropic relation

$$r_k = 18 = V_1/V_2$$
$$V_1 = \frac{mRT}{P_2} = \frac{1*0.287*303.15}{138} = 0.63046\ m^3$$
$$V2 = 0.03502578502\ m^3$$
$$P2 = \frac{mRT}{V2}=\frac{287*303.15}{0.0350257} = 2484\ Pa$$
for air:
$$k = 1.4$$
$$W = \frac{(P_2V_2 - P_1V_1)}{k - 1} = \text{(A very very small value)}$$

Attempt 2: Using $r_k$ and displacement volume:

$$r_k = \frac{(V_d + V_c)}{V_c}$$
$$V_d = 14.2L = 0.0142\ m^3$$
$$V_c = 8.3529411*10^{-4} = V_2$$
$$V_1 = V_c + V_d = 0.01583529\ m^3$$
$$P_1V_1^k = P_2V_2^k $$
$$\frac{138*0.01583529^{1.4}}{(8.3529411*10^{-4})^{1.4}} = P2 = 8487.512\ kPa$$

Plug in everything into the work function
$$W = \frac{P_2V_2 - P_1V_1}{k-1} = 12.1 \ kJ$$

Ok, I'm getting close but I don't know what I'm doing wrong... Any hints? And why doesnt' method 1 work?


texts: Actuate a tilting platform from a single point

texts:
I would like to be able to tilt a platform (the green cuboid below, pivoting around the red point) from a single solenoid (one of the blue cylinders below). The solenoid cannot move (other than the shaft) and can only push (or pull).

I need something that will connect the solenoid to the platform so that one pulse of the solenoid will tilt the platform one way and an identical pulse would tilt the platform the other way. The platform can also be manually moved, so the solenoid must be able to cope with the platform being in a different position than expected.

Any ideas would be really well received! If I can clarify in any way, please let me know.


texts: I want a shockproof table for a model train. That is, protection from physical jolts, not electrical volts

texts: I have an N-scale model train (N-scale is about half the size of HO scale). It's so small I could set up an entire layout on something the size of a coffee table. Put a glass top over it and I could use it as a coffee table. Problem is that people bump into coffee tables and whenever they do, the train will jump off the track, and I'll have to take the lid back off in order to put the train back on the track. So I'm wondering if I could make a shockproof mounting for this small model train layout.


texts: In Solidworks Hole Toolbox, what is Thread Minor Diameter according to DIN 13-1

texts:
Dear StackExchange Community,
I recently discovered how to use the Toolbox customization to specify new threads in Solidworks 2021 SP2.0, such as ISO fine metric threads (DIN 13-3- ... -9). However, when I started populating the Thread Data of my thread (M10x0.75), I was faced with the problem of matching the columns of the Thread Data with the ISO norm values. I could get that the Thread Minor Diameter Inside is equivalent to D1 in DIN 13-1 based on the values entered for already defined threads, such as M2x0.4.

However, I don't understand what the Thread Minor Diameter is. Initially, I thought it would be d3 in DIN 13-1, but for M2x0.4, d3 = 1.509, and Thread Minor Diameter for M2x0.4 in Solidworks is marked as 1.548.

Nobody in his right mind would check those values, that anyway do not appear in the drawings, but as an OCD person, this has been bugging me for too long, and I would appreciate if someone can explain this Thread Minor Diameter value in light of the DIN 13-1 norm to me.
Thank you for your help, and take care,
David


texts:
I was reading a text talking about Joule's experiment(mechanical equivalent of heat)
The mechanical equivalent of heat was a concept that had an important part in the development and acceptance of the conservation of energy and the establishment of the science of thermodynamics.. The apparatus used in the experiment is shown below:

I have noticed that there is a spring balance in that apparatus. Why is there a spring balance in the mechanical equivalent of heat apparatus?  What will happen if it is removed?


texts: Would a double helix spring be more or less effective than two springs?

texts: Say I have a spring in the shape of the backbone of DNA. If I unwind the two parts which would have more potential energy when pushed all the way down, the double helical or both of the individual springs combined?


texts: Is there an optical technology able to measure the temperature of dry air?

texts:
Optical IR sensors are able to measure the surface temperature of solids. But is there a range of the EM spectrum that can accomplish the same for measuring the temperature of nitrox (dry nitrogen, oxygen mixtures)?

If so what are the constraints?


texts:
I'm building a catapult and I asked a question and got this response. Is there an equivalent for the wave spring but for angular motion like a torsion spring? Or any improved design on the torsion spring.

Edit: An improved design by my opinion would be an increased spring constant in a decreased length


texts: Practical method of calculating coefficient of contraction?

texts:
I had a look at this link.

The problem is the orifice is located on the bottom of the tub, instead of the side. The water jet will project downwards, instead of with an X and Y component (as mentioned in the article).

Are there any other methods of calculating the coefficient of contraction of a orifice where the orifice is located on the bottom of the container or do I just have to estimate ~0.62 etc.

See here to see my experiment.


texts: What is the condition of real eigen values other than symmetric matrix?

texts:
I have some difficulty to solve this question:

What is the condition for real eigen values other than symmetric matrix?


texts: Can changing the colour of roofs change the average temperature in a suburb?

texts:
I want to be able to determine if changing the colour of the roofs in a suburb will change the average temperature of the suburbs.
E.g. if the roofs in a suburb were changed from black to white would that reduce the average temperature and by how much.
Is there a way to calculate this has it been worked out


texts:
I would greatly appreciate any insight into this.
I'd like to place a ducted fan inside of a box with the bottom cut out. The fan is attached to the sides of the box by support rods. The ducted fan pulls in air from the top of the box and accelerates it towards the opening at the bottom, as shown in the attached picture.
My question is, how big should the dimensions of the box be in order to match the thrust of an unenclosed fan? is there a simulation approach I can take to better understand how the box's size and the placement of the fan affect thrust, without going full-blown with CFD?


texts: What options are available to create a vacuum with hydraulics?

texts:
What options are available to create a vacuum using hydraulics?  I am working on constructing a small planter which needs a vacuum to operate.

Planters operate best at a pressure of 10 PSI.  I think flow is around 30-50 gallon per minute range per row unit. This design has 2 row units.


texts: MSC Adams: “angular kinetic energy” vs “angular momentum about a center of mass”: which is the most relevant measure of the flywheel's storage?

texts:
MSC Adams produces several different measures of a rotating body. In a flywheel, what is the difference between 'angular kinetic energy' (in newton-mm) vs 'angular momentum about the center of mass' (in newton-mm-sec), and which is the most relevant measure of the flywheel's storage, which is usually measured in Kinetic Energy (in Joules) as in http://www.calculatoredge.com/mech/flywheel.htm?
Bonus points: how would one compare results from MSC Adams and of the usual calculation (in the link above) to cross-verify each other?


texts: Pressure distribution on an inclined plate

texts:
I'm attempting a fluid mechanics questions that requires me to sketch a pressure distribution along the surface of the plate and explain why it shaped the way it is. I'm struggling to comprehend how to sketch this distribution.

Does it vary linearly/non-linearly? Is it continuous or constant along the plate?

My general thoughts are that it would be it triangular shaped and would decrease linearly as you went further away from where the water jet strikes the plate.


texts: What are the consequencies of intermittently charging a smartphone battery?

texts:
I would like to build a little water mill to place under the sink of the kitchen to produce electricity. Considering that the mill will work when the user opens the tap to wash a dish, using a dynamo and a little electric circuit (bridge rectifier and a low pass filter), I would be able to generate a continuous electric signal of about 6 V, 0.1 A for a couple of minutes. The idea is to charge a battery, typically an external one used to charge a smartphone, i.e. a battery with a capacity of 2500 mAh.

I am wondering if the repeated short sessions of charges will affect the battery in any way. Obviously, the battery will need a couple of dish-washing sessions to be fully charged, but will these short sessions affect its efficiency, or even alter the charging time ?


texts: I was designing a whit-worth quick return mechanism, I have provided the contact sets but they fail when I try to animate. The contact set is defined for the crank and slotted link.


texts: How would I model a load bearing brick wall supported on a beam in FEM

texts:
I have a continuous beam supported on columns. I need the brickwork above to act as load bearing wall for the next floor above. How would I model this in a FEM suite like SUMO (Prokon) ?

In SUMO I can insert concrete shear walls, but no brick walls. Since brick walls offer no tensile restraint, I can't use concrete shear walls.


texts: Is it possible to define a finite element that isn't planar? For example the shell element shown in the picture below...


texts: Force limits for gear rack and pinion gear

texts:
I am accessing the feasibility of using a gear rack and pinion gear to move a moderately heavy object. I have never used gear track for a larger project so I don't have an intuitive basis for judging the fitness of gear rack for this application. To set aside the factors of velocity and acceleration let me ask the question this way :

What approximate size gear rack and pinion gear would be needed to vertically suspend a 2000 pound weight?

Alternatively, how much weight could be reliably suspended with a 1" wide 6 tooth per inch gear rack?


texts: Using a controller for a simple heating system

texts:
I am new to control modeling. Given the following problem: I want to control the heating of a house. Therefore, a top unit should be switched on (nominal load, no ramp up) as soon as the production of the main unit is above a certain level. How would you do this? Is it possible to set the output of a p-controller to a fixed value?

if main_unit < level:
  top_unit = 0
else:
  top_unit = nominal_load

Thank you very much for your help


texts: Determine if car is moving forward or backward

texts:
I would like to know if there is someway i can figure out if the car wheel is rotating in clockwise or anticlock wise direction.
Im working on a project which determines if car rolled back on a hill before the user accelerates forward.
I tried this using gps co=ordinates to determine if there is roll back. As this roll back could be in cms before user moves forward, im not getting reliable results.
The only way i can think of now is to depend on wheel rotation. if the wheel rotates backward on slope i would know that it did roll back a little. So is there a way for me to determine if wheel rotated in clock wise or anti-clock wise direction through CAN bus interface or something.
Any help here would be greatly appreciated.


texts: Static load analysis for four-bar linkage?

texts: I am facing a difficult question and can't find answers anywhere else. What on the left is a hydraulic ram, it's pushing the box in the centre to move upward, while the four-bar linkage attached on box C is designed to regulate the centre box's motion and make sure it moves on a desired path. Assume all parts are rigid bodies except the hydraulic ram. O1, O2, B and G's location are known. At this instant, the ram provides an upward force which counterbalances the weight of the box, and it also gives a force pointing rightward, which is 1500N. The question is asking for the forces on each bar of the four-bar linkage, ignore the forces due to acceleration. Looks simple right? Just static load analysis. But my question is, where does the 1500N apply to? Does it apply to point G and B at the same time at 1500N? Or it only apply to G at 1500N? Any help is appreciated. I am not asking for the solution of the question, just where the 1500N applies to. Thanks. Diagram is here


texts: compare l/min output of CO2 pressure reducer to bar (compressed air)

texts: I have a pressure reducer calibrated for Argon and CO$_2$ output. If I connected it to a gas tank with compressed air, how can I convert the output information "liters of Argon / CO$_2$ per minute" to "pressure of compressed air in bar"?


texts: Why a zero too close to the imaginary axis gives bad berformances?

texts:
I am studying control systems, and I have found that if I consider I control scheme where I filter the reference , if the zero of the pre-filter is too close to the imaginary axis, we have a degradation of the performances. For example, I have plotted this in Matlab:

in which I moved towards the imaginary axis by increasing a constant value tau_num. The closest zero to the imaginary axis is relative to tau_num = 0.7, which infact has the worst performances, since it is present a resonance peack.

Thus, so far I have demonstarted this to be true just with Matlab, but I don't understand the reason for which this happens. I have found just that it is present a limit from the physical components, for which the zero cannot be too close to the dominant pole, but I haven't found anything else.

Can somebody please help me? Thanks in advance.

[EDIT] I am working with the following scheme:

in which I have a prefilter $C_r(s)$, and the transfer functions I am using are the following:

P = 1/[(1+s)*(1+0.05*s)^2];
C = 10*(s+1)/s;

and for the pre-filter I am considering different values, which are shown in the plot above, which are:

tau_d1 = 0.9;
tau_num1 = 0.1;

tau_d2 = 0.9;
tau_num2 = 0.4;

tau_d3 = 0.9;
tau_num3 = 0.7;

C_r_1 = (1+tau_num1*s)/(1+tau_d1*s);
C_r_2 = (1+tau_num2*s)/(1+tau_d2*s);
C_r_3 = (1+tau_num3*s)/(1+tau_d3*s);

and the closed loop transfer functions are:

T1 =  C_r_1*C*P/(1+C*P);
T2 =  C_r_2*C*P/(1+C*P);
T3 =  C_r_3*C*P/(1+C*P);

which I plot in this way:

figure;
bodemag(T1,'b',T2,'r',T3,'g'),grid
legend('tau_num = 0.1','tau_num = 0.4','tau_num = 0.7');
title('amplitude of frequency response as zero gets slower')


texts: In structural analysis, does inelastic analyis mean the same thing as non linear analysis?

texts:
In structural analysis, does inelastic analyis mean EXACTLY the same thing as non linear analysis?

If not what is the difference?


texts: I  want to use sensor for stretchable or bendable movements on knees, on fabric. But I am confused that which sensor is better to use and why?


texts:
In the following kinematic chain, I would like to get equation to go from
$F_{in}$ to $T_{out}$.
(excuse the poor drawing, nodes 3,4,5 are always aligned)

Here's my attempt :
The torque at $1$ is : $C_1 = F_{in} \times a$
So $F_2 = \frac{C_1}{b}$ ( opposite direction of $F_{in}$)
But $F_3 = F_2 \times \cos{(\alpha_1)}$.
Here's where I'm suspecting to go wrong :
$F_5 = F_3 \times \cos{(\beta_1)}$.
$T_{out} = (F_5  \times \cos{(\theta_1)}) \times f$.
TL;DR; Can I chain force transmission property along a kinematic chain ?


texts: I have a long-duration EMG signal (~4 hours long) with a sampling frequency of 1 kHz. If I want to filter the data with a low-pass filter in 10 Hz in MATLAB, should I filter the signal with moving window? I am using Butterworth (4th order) IIR filter.


texts:
I am using an LED as a point source for a school project. I have two questions in regards to the LED(s).

I know that light follows the inverse square law when measuring perceived brightness, but all sources I can find show examples of a round bulb light. Is there an altered version of the formula for LED’s that incorporates factors such as the fan angles?

Also, I will most likely be adding more LED’s to my project to increase the total lumens/lux. I’ve seen many people ask the question whether lumens will add in such a scenario. In theory they would but it wouldn’t be perceived that way. My question is; is there a formula/equation/calculation that can help me predict the lumens perceived by x number of LED’s, d inches apart from one another, measured at y feet away, with regard to joining and isolated parts of the fan angles of each LED.


texts: Abaqus vcct fatigue consistently underpredicts disbond growth rate

texts:
I'm modelling a fatigue disbond using abaqus. I've understood the disbond growth rate is equal to:
$$\dfrac{\partial a}{\partial N} = c_3 \Delta G^{c_4}$$
I've set up an analysis with MMB specimen. I've set $c_3 = 5.59\times 10^{-20}$ and $c_4 = 4.33$. The strain energy release rate is shown below:

Doing the math myself, I find:
da_dn_expected = c3 * energy_release ^ c4 = 5.59e-20 * 635 ^ 4.33 = 7.645e-8 [m/cycle]

Comparing that to the simulated results:
da_dn_found = element_width / cycles_to_next_node_release = 0.001 / 13713 = 7.29e-8 [m/cycle]

Which is a 5% difference with what I expected to find.
I've run a number of simulations with different mesh sizes as well as different settings and I've found the same difference amoung all of these results for all different crack lengths. I've added a figure below to illustrate:

Does anybody know what is causing this offset?


texts:
so for my project im designing a Tesla turbine and have calculated that the torque it will output is 38Nm. I would like to know what more information I would need that i could calculate theoretically to calculate how much power it would output from this.

Thanks.


texts: Formula for converting linear to rotational motion

texts:
I am trying to design something that rotates 90 degrees based on a small (10mm or so) linear motion, using this basic setup as an example.

There are a lot of questions about how long the arms need to be, how far they need to anchor from the point of rotation, etc. that i need to know. I am assuming there is some formula that governs the relationship that someone can point me to?


texts: Fluid dynamics' equivalent to current smoothing

texts: Is there an arrangement of components the takes a source of gas with oscillating pressure and outputs a steady near constant pressure stream?


texts: What is causing a pulsating, low-frequency vibration in an induction motor?

texts: I have this old squirrel cage induction motor (nameplate below) that I just replaced the bearings on. When it runs, there is a rattling noise that gradually gets louder and then softer, repeating every ~5 seconds. Here's a video of it in action. I don't think the motor made this noise before replacing the bearings, but I'm not sure. (I just bought it and the only time I ran it was briefly at the seller's house.) Does anybody know what might be the source of this rattle? I've put pictures of the motor and the rotor below, as well. Thanks!


texts: What is the criteria for bubble entrapment in a closed headspace tank set to drain?

texts:
Suppose a closed tank does not have any pressure relief system and is set to drain from the bottom. It is said that because the headspace pressure drops as the liquid level goes down, the tank will not properly drain.

However, in real situations, I would guess air bubbles start to form in the bottom hole and rise to equilibrate pressure and allow the liquid to drain. I think this ends up depending on the rate of formation and motion of the bubbles which are affected by the geometry and fluid and so on. Is there a systematic way of looking at this? How do you work it out on paper?


texts: How to calculate kinetic energy of gas flow in pipe given tempearture, pressure, pipe diameter and velocity

texts:
Ive been given a question and asked to calculate the kinetic energy of a gas given the temperature, pressure, diameter of pipe and velocity. I've been looking and have been unable to find any equations that can use this information. The only hint Ive been given is "STP conditions" but am unsure how that is relevant to solving the question. I cannot figure out how to solve this question. Below is the question given.

Air at 300 °C and 130 kPa flows through a horizontal 7-cm ID pipe at a velocity of 42.0 m/s.
a) Calculate the kinetic energy (in J/s), assuming ideal gas behaviour.

Any formulas or advice about how to approach this question would be greatly appreciated.


texts: Does unloading beyond yield point also affect tensile strength?

texts:
I know that with strain-hardening you increase the yield and tensile strength. So if you unload at point D, then you also have cold worked it a bit right?
So the stress-strain curve will look different after point D and have a higher tensile point?


texts: How does pressure energy convert to thermal in incompressible flow?

texts:
I am thinking of a straight thermally isolated pipe, and incompressible flow through it.
Due to friction, pressure energy drop of fluid, (increase of internal energy), can be calculated via the Darcy–Weisbach equation.
If I look at the internal energy of fluid as the average velocity of molecular  movement, and pressure energy as impact of molecules on the pipe:
how come that one of these energies can raise and another drop, in the incompressible flow?
Because in an other situation where we start to apply external heat to a pipe, we expect both pressure and internal energy of the fluid to rise?

Edit 1:

As pressure energy I am referring to $\frac{p}{\rho}$, and as thermal (internal) energy to $c_v T$. All for a mass of 1 kg.
By using the Kinetic Molecular Theory principles, I thought that I can visualise the process of flow as I mentioned: temperature increase - molecule speed increase, which leads to a higher pressure exerted on walls of pipe.
But in reality, as the pressure drops, the temperature increases which messes my approach.
Can I take in consideration that the density of any fluid (for example water), isn't constant (with drop of pressure and temperature rise, density lowers at some decimal), and therefore the pressure drops, even with temperature rise, which fits my visualising process, or is this all too much of trying to simplify the situation?
Any answer appreciated.


texts: How to create a logic circuit that multiplies two 4 bit numbers, using only 16 2-input AND gates and 3 4-bit adders?

texts:
"Sketch a combinational circuit which takes as input, two 4-bit binary numbers,
A3A2A1A0 and B3B2B1B0, and which outputs the 8-bit product P7P6P5P4P3P2P1P0.
Assume that you have available sixteen 2-input AND gates and three 4-bit adders.
Please explain the reasoning behind your design."

After a bit of fiddling I got close to the final circuit but I found that three 4-bit adders wouldn't be enough. To save time (and my complete lack of being able to explain anything) I found this, which is almost exactly what I need except it used two 4-bit adders and one 6-bit adder. I want to know if it's even possible to construct a circuit that can multiply two 4-bit numbers using the gates specified above, and if so, how can you do it?

Thanks in advance.


texts: If a fluid is incompressible,is it correct to say that the flow may or may not be incompressible?

texts: From my understanding,when there is  no change in volume due to pressure applied on a fluid,the fluid can be called as incompressible.As there can be still be change in volume due to other properties,can I say that flow may be compressible?


texts: Capacity of plain concrete foundation on grade [Civil UK]

texts: A client has asked whether a container can be placed on an existing unreinforced concrete foundation of depth 100 mm. The grade of the concrete is unknown. How can the capacity (in kPa) of this plane concrete foundation be evaluated?


texts: Why automakers are/should be making medical ventilators?

texts:
I am not very familiar with the mechanics of neither a car nor a medical ventilator. Considering global coronavirus pandemic and shortage of medical ventilators in many countries, I saw some news suggesting that automakers are starting to manufacture medical ventilators, or the leaders of countries are requesting them to do so (e.g. here or here). So I was wondering if there is some overlap or similarity in production engineering of a car and a medical ventilator that makes automakers as the best candidate for making medical ventilators.

In other words, from an engineering viewpoint, what makes automakers suitable for engineering and manufacturing medical ventilators at this moment?


texts: Gyroscope/Powerball gearing system for bikes?

texts:
There is an interesting and potentially useful property to do with the procession of Gyroscopes, as well as devices like the "Powerball" toy.

When the gyroscope is rotating (Ws) and then force is applied to increase the procession (Wp) the Ws rotation increases.

Experiments with the Powerball show that a small increase in Wp results in a very large increase in both Ws and the resistance to an increase of rotational velocity in Wp.

More intuitively, imagine the dynamics here as being like a variable gear that increases in gear ratio at an accelerating rate as the speed of the input increases.

Would it be practical to design a vehicle such as a human powered bike or a motorised car that used this property of a gyroscope instead of a conventional gearing system.


texts: Second order system with additional pole

texts:
Why is it that a second order system with an additional pole or zero can be approximated into the general second order system for analysis?

This was asked during our lecture and I am still looking for the answer.

In my reading I've only learned that when an additional pole or zero is added to the system, the step response of this system starts to resemble the step response of the original system. I am not sure if this is the answer to the question.


texts:
I have a pump [m^3/(sV)], a tank [no units], a valve [m^2/s] and a level sensor [m/V]. The units are for the gains in the respective transfer functions. How should i connect my control block? Where should the takeoff point to the level sensor be?  I'm supposed to be using the pump to control the water height as measured by the level sensor.
Here's what i've come up with. The numerators of the transfer functions have gains with units displayed below the transfer functions.

These are the transfer functions for better understanding

How should i know where to put what? I've tried using unit analysis but it doesn't make any sense? I don't even know what the outputs of the controller should be, so i cant really do the analysis well enough.


texts: What is the difference between to Eurocode design equations (6.10a and 6.10b)?

texts:
In Eurocode, two equations for loads are given for STR limit state:
$$1.15K_{FI}G_{kj,sup}+0.9G_{kj,inf}+1.5K_{FI}Q_{k,1}+1.5K_{FI}\sum_{i>1}\psi_{0,i}Q_{k,i}$$
$$1.35K_{FI}G_{kj,sup}+0.9G_{kj,inf}$$
Designer is required to calculate using both, and the design value of the load comes from the equation that gives the least favourable result. But what is the actual difference of these equations, why do we need two? I can see that the bottom equation (6.10a) only takes into account permanent (dead) loads (letter $G$) and the one above considers temporary (live) loads as well (letter $Q$).
Why don't we need to consider the live loads in one of the equations? My lecture material says that the lower equation is rarely the deciding one, but it must always be checked. I've read my lecture materials and the Eurocode section on this, but I can't really get any good explanation of this. If somebody could explain the difference between the two equations and why we need them both I would be very grateful!


texts: Do gears on the same axle share both speed and torque? So if a large gear and a small gear were in the same axle the small gear would have the torque of the large gear?


texts:
I would like to calculate the deflection of the following geometry with a 3D load in Y direction:

Do you know of any textbook, website etc. which discusses how to do that analytically ? I cannot find any suitable reference.


texts: Which course to take? Optimal control? Nonlinear control?

texts: I have tried to compare two courses, and there seems to be some overlap, but not as much. Which method is better when controlling a nonlinear system? Also, what is the main difference between the two?


texts:
When can I design a boundary element of a shear wall as a column?
Is there a link to a solved example?
Help please.


texts:
I am using a psychophysical model to calculate the probability (P) of detecting an electrical stimulus to the skin (amplitude = x) over time (t):

\begin{equation}
P(x;\alpha(t),\beta) = \dfrac{1}{1+e^{\beta(\alpha(t)-x)}}, \text{ } {\small \alpha \text{= threshold & } \beta \text{ = slope}}
\end{equation}

To find the model parameters I would like to use a logistic regression function:

\begin{equation}
logit(\pi) = b_0 +b_1X +b_2T
\end{equation}

Does anyone know how to implement this logistic regression function in LabVIEW? As inputs I have a timevector, an amplitude vector and a response (0 or 1) vector.


texts: Is there any need to consider loading sequence in construction stage for structure analysis?

texts:
Load sequence in phases can be considered applying the self-weight load only to the story added in the appropriate phase.

Assuming that the material will not go into yield stage ( will always be at the elastic stage), is there any need to consider load sequence in construction stage for structural analysis?

I think there is no need, because no matter what, the final finished structure should always have the maximum loads at each floor/element, whereas during the construction, each floor/element loading is only partial. So if we consider the final structure analysis, we already consider everything adequate for design. No?

But why code of practice still recommend it?


texts: Find the instance when discrete time model has a specific value

texts:
I have the following model:
$$ x[k+1] = Ax[k] + Bu[k]$$
$$ y[k]   = x[k] $$
where $x \in \mathbb{R} $ is the state, $A \in \mathbb{R}$, $u \in \mathbb{R}^4$ are the inputs and $B \in \mathbb{R}^4$ and $y[k]$ is the output.

From theory this can be solved using:
$$ y[k] = A^k x[0] + \sum_{i=0}^{k-1} A^{k-1-i}Bu[i]$$

How can I find the time instance $k$ when $y[k]$ has a specific value?


texts: Voltage controlled linear actuator with spring back

texts:
I have a machine/robot that has a manual joystick to control forward and reverse. The joystick is connected to a mechanical linkage system that goes forward/backward, which than controls a hydraulic pump. I want to be able to "hack" the joystick to control the forward/backward motion through software. I have a few design criteria that I am trying to work around, hoping to get some input/help:

1) I need a failsafe. If I cut the power while the machine is moving and then turn it back on, I would like the machine to start in neutral, not where (forward/backward) it last was.

2) Its not a binary forward/backward so some voltage control would be nice  to make it smoother.

3) Able to control manually and through software. I would like to send X voltage to it through software (arduino + hardware) but not lose functionality if someone wants to take physical control.

Any advice on what kind of set up I would need to do this?


texts: What is the inclination angle in an Orthogonal rake system?

texts: In a single point cutting tool (right cut) what is the inclination angle ( lambda) in an Orthogonal rake system? I'm having difficulty in visualizing it. Please explain it in terms of ASA system.


texts:
I wanted to derive the formulae for active, reactive and apparent power.
While I understand the concept of phasors, I think I would find an analytical proof that doesn't involve phasors, more intuitive. I recently came across an article that explained how active power is basically the time average of the product of instantaneous voltage and current through the load. I could make sense of it.
I was wondering if there are similar derivations for reactive and apparent powers as well, that do not employ phasors.
What I thought of:
The derivation of active power led me to think that I could perhaps derive the other formulae too, using integrals.
I had the following equations with me:
$$\begin{align}
I(t) &= I_m \sin(\omega t + \phi) \\
V(t) &= V_m \sin(\omega t)
\end{align}$$
When I decomposed $I(t)$ in terms of $\sin(\omega t)$ and $\cos(\omega t)$, I immediately saw that while finding the average of $V(t)I(t)$ over a time period, the term with $\cos(\omega t)$ would not contribute.
So, the term $I_m \sin(\phi)\cos(\omega t)$ would have something to do with the reactive power. However, I still am unable to logically arrive at the pre-established formula for reactive power: $\dfrac{V_m I_m \sin(\phi)}{2}$.
I was unable to make a headway with the derivation of apparent power, either.
Any help or pointers would be greatly appreciated.


texts: Dead weight pressure tester for very low positive pressures

texts:
Does the dead weight tester technology provide capability for an accurate, low pressure calibration standard in the range of zero to 150 cm H2O, and if so is there a manufacturer that provides such an instrument?

If not, what is the best primary standard for that range of pressure in terms of accuracy?

I suspect for dead weight testers there might be a lower limitation due to the balance of gravitational force and frictional force. I am looking to measure gauge pressure.


texts: Should I expect fluid velocity within a pipe to increase beyond the inlet velocity?

texts:
I'm using commercial software to simulate unsteady incompressible flow of air through a 1m long rectangular pipe with cross section 0.2mx1m.  I have a velocity inlet condition (u=100m/s, $\nabla p=0$) and a pressure outlet condition (p=0, $\nabla u=0$).  For simplicity, I'm running the simulation in 2D on the x-y plane, with the pipe oriented horizontally and with wall boundary conditions on the bottom of the pipe (along y=0) and a symmetry condition at the top of the pipe (at y=0.1).  I used a symmetry condition so as to reduce the number of cells in my mesh and thus speed up computation time.  I also made sure to bias my mesh toward the wall boundary to ensure proper capturing of the boundary layers.

When I run the simulation to a steady state, I observe that the maximum velocity within the pipe is slightly larger than the inlet velocity ($|u_{max}|\approx 101$).  This is counter-intuitive to me.  I expect the velocity to be bounded by the inlet velocity.  It doesn't make sense to me that the fluid velocity should accelerate at all.  Therefore, I ask:

Would the same thing happen in real life?  If fluid enters a rectangular pipe of similar dimensions and length at a particular inlet velocity, should I expect a velocity profile within some cross-section of the pipe to exceed the inlet velocity?  If so, what causes the fluid velocity to increase within the pipe (from a physics/mechanical engineering perspective)?

Or is there a problem with the way I setup the problem (i.e. a numerical issue that I should be aware of for this problem)?


texts: LQR control effort / control bandwidth relationship

texts:
I'm working with a linear system, having given matrices A and B
$$A = \left[\begin{array}{cc} 0 & 1 \\ -0.9 & 0 \end{array}\right]$$
$$B = \left[\begin{array}{c} 0  \\ 2 \end{array}\right]$$
assume we have full state and no feedtrough matrix $D$ so
$$C = \left[\begin{array}{cc} 1 & 0 \\ 0 & 1 \end{array}\right]$$
$$D = \left[\begin{array}{c} 0  \\ 0 \end{array}\right]$$
I want to design an LQR feedback controller for this system: the LQR theory states that by increasing the elements on the diagonal of $Q$ I will make the corresponding state errors smaller and by increasing the scalar $R$ I will change the control effort, and this tradeoff will be reflected in the $K$ matrix
$$K = lqr(A,B,Q,R)$$
However, my question is the following: is it possible to increase the bandwidth without increasing the control effort? I'd like a more reactive system, but I have saturation limits to be taken into account.
Note: I know that MPC would be probably better but it's more to understand the control efforts / control bandwidth relationship in LQR controllers.


texts: I was wondering what is the smallest possible rocket to get to LEO. I know that rocket fuel accounts for 90% the total mass of the rocket. Lets say I have 500g of payload and my rocket is made from an aluminium shell. How much fuel would I need to get to LEO and how tall and wide would the rocket need to be?


texts:
I'm trying to get my bearings (a somewhat heavy-handed expression) on pump design and I'm finding in the various books I've procured on the subject that there is very little consideration given to the output pressure developed by a pump.

If there isn't much detail to this question, I apologize; I'm still in the far-below-basic level of understanding. Obviously, head is a key parameter of pump design, but my concerns are with output pressure. The reason being, I'm considering for example rocket engine design where the key parameters of pump requirements are chamber pressure and flow rate. I understand that flow rate varies with head by the characteristic Q-H curves.

So, how does pump head vary with or affect the output pressure developed by a pump? Are the two concepts related, or are they independent of one another? If they are related, how would I go about figuring out the required head parameters from the pressure and flow requirements?


texts:
I see that most worm gears are self-locking but I'm looking to make my own non-self-locking POM worm gear. It'll only be of module 1. Does anyone know what needs to be changed in order to make a self-locking worm gear non-locking? Is it just the angle of the threads?

EDIT

Many motorised locks tend to have a worm gear on the motor shaft though - like this one. The lock is designed to be manually turned as well. Does that mean the friction caused by manual turning will be high?


texts: Visualising why divergence of vorticity is 0

texts:
I'm new to fluid mechanics and preparing myself for university next year and I'm reading up on vorticity and circulation at the moment.

I understand the maths behind why the divergence of vorticity is 0, however, I cannot visualise why. I find it quite easy to visualise the divergence of magnetic fields, and that there is no net flow of magnetic field across a closed surface.

On another thread, an answer explains that the magnetic field lines always come back in a loop and therefore there is no divergence.

Could anyone shed some light on this and possibly help me understand this a little bit more, please?

Thanks :)


texts: What is this small rotating part from a cell phone?

texts: What is this tiny rotating piece of hardware that I found inside my Samsung GE1202? It has E9C written in blue on it.


texts: Negative Eigenvalues in Ritz Solution of First-Order Shear Deformation Theory

texts:
I am trying to write a MATLAb code for determining the natural frequencies of a first-order shear deformation plate using Ritz method. I am using Legendre polynomials as trial functions in Ritz method, and my code works well for static analysis of plate. I have solved few structural problems with my code and compared the results with MSC NASTRAN. The results are accurate with maximum error of 5%.

However, when I try to find eigenvalues, at least one eigenvalue comes out to be negative. Also, the eigenvalues do not match with eigenvalues obtained from MSC NASTRAN (Modal Analysis).

Is it possible for a plate to have negative eigenvalues?


texts: Is there a motor design where a rotor gradually moves into a stator?

texts: I was wondering if there is a motor/generator design where the rotor moves gradually in and out of the stator along the axis of rotation, or the stator moves over the rotor.  If so, I'd like some resource(s) to read more about it.  The application I have in mind is for a wildly variable load like a wind turbine. If this is a bad design, please briefly explain why.  Thanks in advance.


texts: Evaluating drag and convection for a flower heat budget model

texts:
I am currently in the process of creating a heat budget model to compute stigma surface temperature. Stigmas are part of the reproductive organ of a flower (which in my case are flowers of orchards). I've attached a picture to show how it looks like. The stigmas are the white shaped bits that are popping out of the flower center. (picture not taken by me, https://thumbs.dreamstime.com/z/white-fruit-flowers-spring-beautiful-cherry-petals-anthers-stigma-branch-orchard-early-sunny-day-ready-109463924.jpg).

These things are hyper small, like in the fractions of the mms. Still, I've decided to simply consider the entire organ as if it only had 1 stigma and compute a budget for that one specifically. I consider this stigma as a cylinder and perform the necessary calculations there. My question is hence the following: would neglecting the other stigmas and only considering one would have a significant impact on the evaluation of drag and convection resistance? I am asking this because for objects of such small size, the turbulence they must generate must be so small, that I feel like the turbulence created by one stigma would not effect the others, but I'd like to know the thoughts of other people who have more knowledge than me on this matter.

I am a meteorologist by formation so I still have lots to learn in terms of understanding the mechanics of turbulence, but I have a fundamental grasp at it .

Thank you!


texts: Can you assume that the forces in the vertical direction are evenly distributed for an off level rigging problem?

texts: This is an off-level rigging problem. When solving for the tension forces in the red slings (lifting from point A), can the assumption be made that the y force vector at points B and C are each half of the weight of the object? Or must one calculate the force vectors at point A? In which case the y vectors are not symmetrical.


texts: With ebikes, is there friction from the motor when riding with the electronics turned off?

texts:
One may want to ride an electric bike with the electronics turned off. There are many reasons to do this, i.e. flat battery, fitness (who would have thought)
When riding an ebike conventionally, is there a resistive friction caused by the DC motor?
If so, do e-bikes have a way to 'disengage' the motor from the wheel? Potentially, a clutch


texts: How to get the maximum power point from I-V curve for Organic Photovoltaics (OPV)?

texts:
I am taking organic solar cell course on Coursera, and I have a question about I-V curve for a certain solar cell. The question asks for the solar cell characteristics such $V_{oc}$, $P_{max}$ and $FF$. I get the $V_{oc}$ correctly but I couldn't calculate the other two correctly as they provide me with an excel sheet of the current and voltage.

I plotted the voltage on the x-axis and current,power on y-axis below. I need to get the correct $I_{max}$ and $V_{max}$ from the graph with (I-V) in blue and (P-V) in orange.

Here is the question from Coursera:

  Download this dataset DataSheet (, decimal mark: dataset) and
  calculate the maximum power point (Pmax). Give answer in either W or
  mW, a valid form of answer would be '94' or '0.094'.

  Hint: You may need to do an interpolation to get the correct answer,
  if the value you are looking for does not exist.


texts: How to duplicate measurements from one piece of material to another?

texts:
I am not sure if this is the right place to ask this but. I have an offroad skateboard from MBS. I bought their brake system which comes with a circular piece of aluminum. Pictures attached.

You can see that on the circular aluminum brake part (don't know the proper name), it has 5 holes drilled. I called the company and they said they have CAD files and it is done in mass. I don't have those CAD files and I am not a CAD expert, nor do I have a machine to cut it.

I want to know the best way to measure (with basic relatively inexpensive tools, if needed I'll buy more), and replicate those holes with high precision on the sprocket. As you can tell, this is going to spin, so any measurement that is a little bit off is going to make the sprocket wobble.

The sprocket is not the same exact size as the aluminum brake part.

I am not looking for measurements. I am looking for how to measure. Not the fish itself, but I want to learn how to fish.


texts: Why do we pave roads instead of making them from removable parts?

texts:
If roads were made of removable parts, we'd probably have fiber cable internet everywhere by now I'd say.
It'd be so much easier to install e.g. new electricity and water infrastructure and to maintain them if roads where made like that. We'd be able to redefine the whole architecture of a neighborhood if necessary, without the need to take existing roads into account. We could even make an urban area a landscape again with ease if e.g. a city wanted more green areas somewhere. We could make machines that piled road parts on top of each other making maintenance as easy as pie.
So why do we still pave roads? There's probably some aspect of civil engineering I'm not taking into account..


texts: Rubber band Powered Free Flight Helicopter

texts:
I am building a free flight helicopter for a Science Olympiad competition, and the general rules are as such: https://www.soinc.org/sites/default/files/uploaded_files/Helicopters_2017_Diagram.pdf

This leaves a lot of opportunity for math that is well beyond my ability, so my questions are as such:

You get scored based on how long the craft stays in the air, but you can get 25% added (up to 75% total) for each single bladed rotor, is a single bladed rotor a worthwhile investment?
I have tried using an airfoil shaped wing at the regional competition, and it failed because of how heavy it was, but people have been suggesting a helical blade shape, what are the mathematical advantages of this over a flat rotor.
The central shaft has no given dimensional restriction, what is the optimum length of the core?

Thanks in advance.


texts: Is it possible to reuse or the oil recovered from a spill?

texts:
I don´t know if this is the rifght place to ask this question, but I would like to know if after the remediation of a soil contaminated with hydrocarbon you can reuse or even sell the oil recovered. And if it's possible, do you know any companie that can do that?

Thanks for your help and sorry for my bad english.


texts: Translations from "Oil" Flow Rate - Pressure drop to "Air" Flow Rate to Pressure Drop charts

texts: I keep getting check-Valve companies that have their product data sheets registered in Pressure Drop-Flow Rate for oil(Hydraulic oil) and I need it for Air.  Is there a translation between oil and air in fluid mechanics that can make this translation?


texts:
By flexible endoscope I mean colonoscope, gastroscope, etc.

From this video I can see that an endoscope can swivel its tip while in place, kind of like a periscope.

But while moving axially, i.e. "telescoping" (is that the right word?) or "snaking its way in," or in other words, while being inserted, how does an endoscope turn?

Does it have to hit something (e.g. the interior wall of the colon), and only due to the resistance of hitting that something is it able to turn?

Or is it designed in such a way that it can turn in midair, without having to come into contact with anything, while maintaining the turning point at the same point in space as it snakes further in, à-la the classic computer game snake?


texts: Check valve in compressed air pipe network?

texts:
I am working on a building that would like to used compressed air for some pneumatic actuators.  They would like to bring the air in from an adjacent building that has more than enough capacity, but the air quality coming over is not sufficient and I need to add a dryer and filters to bring it to the correct quality.

Depending on the usage in the other building, I could feasibly see air that has run through the dryer and filters in the new building being effectively siphoned back to the other building.  Is there a reason that I could/should not install an inline check valve where the piping comes into the new building right before the filters and dryer?
Check valves are used extensively on the compressors and receivers, but a brief look online didn't turn up anywhere where people were using them as I propose.


texts: What should a road's traffic volume to justify the number of lanes?

texts: Is there a standard that transportation engineers use for the number of vehicles a road should carry daily  for it to be widened to four, six, eight lanes, etc? Curious because I've noticed that some states seem to be unnecessarily widening their interstates to six lanes in rural areas, and others refusing to do so in places that need it.


texts: Efficiency in a gas turbine or aircraft engine

texts:
Most modern aircraft engines, such as the one depicted below taken from Wikipedia, are composed of several compressor stages which are driven by a turbine (or several), and a combustion chamber in-between, in order to increase the temperature of the flow.

In general, manufacturers and designers focus on increasing compression ratios as well as combustion temperatures for efficiency enhancement.

My question is, under simplifying assumptions such as perfect gas, no energy losses or friction, and constant inlet temperature and velocity: How is the efficiency of this thermodynamic cycle evaluated? How can one quantify the efficiency gain from a pressure or temperature increase?


texts: Isolating vibrations originating from my machine

texts: I'm developing a machine with a reciprocating motion (mass: 50-100 kg, period: 1.35 s, accelerations: 1 g). This machine is part of a process line, and I don't want the resulting "shaking" to interfere with other machines. How do I go about doing this? A very stiff frame is an option, but a more elegant solution is preferable. Basically I'm building a frame around the reciprocating motion, and I have to connect that frame to the process line.


texts:
Consider the state of tension indicated in the Figure. Determine the range of τxz values for which the maximum tangential stress is less than or equal to 60 MPa.

I did σ(med)=(60+0)/2 = 30
To find the radius I did σ(max) = σ(I) = σ(med)+r <=> 100=30+r <=> r=70
But in the solution is

My question is: why is my radius wrong?


texts: Why shooting precision improves using two hands in opposing directions?

texts:
I wonder if someone knows a control theory model that explains the reason why using our two hands (typically in opposing directions) improves gun shooting precision. A similar situation seems to happen when be hold pencil between two fingers, or when we try to position a small object, or when you try to position some object with the two hands instead of just one.
Is there some general principle going on? Can someone model the situation mathematically?
Some pictures below:


texts: What is the exact definition of renewable energy

texts:
I was wondering, in laymen terms, what is the exact definition of renewable energy and what are its various forms, which ones are better and in what situations can they / can they not be used.

How do you weigh the cost of setting up this technology with its payoff, and how do you set these benefits apart from those derived by investing in other areas such add healthcare, research, and development in other areas such add food and disease fighting?

Sends like there are manpower-based investments and research based investments.

I realize this is a very broad question, but tried Wikipedia and could not find a laymen answer to my broad question.

NOTE: If my question is to broad, then please just pinpoint this very basic question: how do you define renewable energy?


texts: Calculating energy loss from laser when shining through a material

texts:
When attempting to trap a particle in a laser beam i was able to achieve the effect.

Pretty cool but now when i put of piece of plexiglass that is 1/8” thick i can no longer achieve the effect. The beam hits a focal lens when its diameter is around 6mm and focuses 50mm away. I put the piece if plexiglass 15mm after the focal lens. Now it is obvious that my 25mW laser will lose power but i wonder how, where, and how much? I imagine reflection and scattering accounts for most of it but there is more that plays a part. I want to know if theres a equation that takes a material, thickness, laser wavelength and power and will maybe give me my power on the other side of the material.


texts: Why do a swamp cooler and dehumidifier effectively cool a room when paired together in an enclosed space?

texts:
I've read in more than one place (e.g., here and here) that a swamp cooler (a.k.a., evaporative cooler) can be effectively paired with a dehumidifier to cool an enclosed space, but this makes no sense to me. It seems like the evaporative cooling would be cancelled out by the heat resulting from condensing the water vapor. No energy is leaving the system as a result of these processes, and waste heat is generated by each device, so it seems the only effect would be to make the room hotter.
The only exception I can imagine is if the water resulting from dehumidification holds the bulk of the heat from that process and is quickly drained, while the evaporative cooler has its supply replenished with cooler tap water. But the articles don't specify that.


texts: Is battery-charge-stop-at-XX-percent circuitry not cheap?

texts:
I'm curious why IBM/Lenovo ThinkPad line is basically the only manufacturer/brand of mobility devices that includes circuitry and software that allows one to vastly prolong battery life of laptops used as stationary workstations by making sure to never charge the battery prior to it being discharged to below 96%, and having options to start charging only when the battery goes, say, below 46%, and stop charging at, say, 50% or 80%, vastly improving long-term battery health (compared to when the battery is always kept at 100%, and always topped up to 100% all the time, for months at a time, and somehow never happens to reach its advertised cycle count).

Why the other laptops and mobile phones never seem to have any such functionality?  Is the circuitry behind such feature somehow intrinsically expensive and not worth it?  (Or is it just the case that stationary usage is not accounted for in the design of such other devices?)


texts: How to accurately calculate the rpm from a gear train

texts:
I'm trying to build a self-regenerating door lock as a side project in college and i'm having some difficulty accurately calculating the gear trains output (in rpm), the purpose of this gearing system is to operate a AC generator. Any help at all would be much appreciated!

I've estimated that a torque of about 1.12 Nm will be used to turn the door handle down 50 degrees. This torque will be transmitted through the shaft which is attached internally to a one way gear. The one way gear is attached to both a fly wheel and the gear train.

My goal is to get an output of about 100 rpm to operate the generator. My question is what factors must i include in the calculation? do i need to include things such as the weight of the gear train and how do i factor in the fly wheel? Thanks!


texts: Dense, non-conductive UHV compatible material?

texts:
I'm not sure if this sort of question is appropriate here or not so please let me know if not!

I am designing a UHV vacuum system with a few interesting requirements. Inside of the vacuum chamber will be a multi-stage vibration isolation system consisting of masses sitting on springs (likely viton or other UHV compatible elastomer material). In addition, I will be using electromagnetic coils to create magnetic fields inside of the vacuum chamber.

The magnetic fields will be changing in times. This means that in general eddy currents can be induced in conductors. These Eddy currents create their own magnetic fields which can be problematic for my application and thus they are to be avoided. One way to avoid Eddy currents is to avoid conductive materials in the chamber.

The vibration isolation system will operate better if its natural frequencies are low. This can be accomplished by using larger masses.

If I wasn't worried too much about the Eddy currents/magnetic fields I would likely make the vibration isolation out of 316 Stainless Steel ($8 \frac{g}{cm^3}$).

However, I am curious if there is any non-conductive material which could be machined or formed into the appropriate shapes for my vibration isolation stage which also has a high density. For example, some ceramics I find have a density of $~3 \frac{g}{cm^3}$.

Does any one have a recommendation for a material which could suit my needs?

Other requirements:

UHV compatible down to $10^{-11}$ torr
Non-magnetic. In addition to not supporting Eddy currents the material should not become magnetized by the changing magnetic fields which are induced (magnitude of ~300 Gauss maximum)


texts: What are the advantages of parallel pushrod configuration?

texts:
A topic that came up in a recent discussion was pushrod engines (specifically V2 configuration in a motorcycle) with four cams. After some googling, I was able to find an example in the Harley-Davidson Evolution engine (used in the Sportster models).
Four distinct camshafts add a lot of complexity, because they need to be driven by separate gears. From what I've been able to find, the main reason to do that is in the different tappet construction, which requires the tappet to be directly "over" the camshaft:

Now it appears Harley may have decided to adopt roller-tipped sliding square or cylindrical tappets of the kind being used in large numbers by makers of radial aircraft engines—notably the Wright-Lawrance J-series engines, one of which would in 1927 power Charles Lindbergh’s solo flight across the Atlantic. Because these had to be located directly above the cam lobe, the simplest way to have the distinctive parallel pushrods that the A, B, and C-model Harley singles employ was to have a separate camshaft under each.
How the Harley-Davidson Sportster Came to Have Four Cams

I don't really understand this explanation. Why does putting the tappet at an angle like dual- or single-cam engine do prevent using the aircraft engine technology? As far as I can imagine, those are also directly "over" the camshaft (meaning radially), they just reside at an angle that enables driving two rocker arms in the head.
In fact, I was able to find numerous examples of HD engines with roller-tipped tappets that used only one camshaft. So if that's technically possible, what specifically was gained by the parallel tappet layout?


texts: Why does this magnetic charger cause short circuit when it sticks to the metal leg of my table?

texts:
Recently, I have bought this product. It is basically a USB cable, with a magnetic end, and a tiny attachment that goes into the mobile device.

I plugged it into my laptop cooling stand (which has USB hub), and then plugged the tiny "adapter" into my phone. The magnetic end of the cable was free, and it stuck onto the metal leg of my work table.

It caused short circuit and burnt the fan. I only realized this after I plugged it into my laptop, and the same thing caused the laptop to restart immediately.

Here is a photo of the gadget.

What is the reason behind this? The leg of my table is not connected to my computer, obviously. So, how come this USB cable was able to burn my fan, and restart my laptop?


texts: Does the air cushion on which the original hyperloop will sit require energy constantly or not

texts: Does the air cushion on which the original hyperloop idea envisioned by Elon Musk  require energy constantly to keep afloat, as the hovercraft does or would it be designed as the modern air suspension where energy requirement is once off, air is let into the  suspension cylinder, vehicle is floating in air then valves and seals take over.


texts: Increasing Yield Strength with Plastic Deformation

texts:
I'm trying to tackle a mechanics problem to be solved using a finite-element analysis, but I'm stuck on one particular bit of theory first.

I've done analysis using a linear-eleastic model, and elasto-plasticity with constant yield stress.

Now I've got to do elasto-plasticity with increasing yield stress. I've been given a table of values to use with this:

plastic strain ￼       0.00  0.01  0.02  0.03  0.04  0.05  0.06
yield stress  (MPa) ￼  200   210   220   225   230   235   240

I don't understand the concept of an 'increasing yield stress', I've only ever come across a material with a single yield point - where it yields...

If anyone can shed some enlightenment that would be great. Happy to provide more info if needed.


texts:
I have question-related to industrial management, actually, it is a problem on arrow on activity network diagram. I tried to solve the question my self, below are the images. If I did any mistake kindly let me know.
Question:


texts: A device like this, submerged in water, would it rotate?

texts: The paddles are pulled counter-clockwise, using a muscle-like mechanism that attaches between the distal part of the paddle, and the inner part of the paddle next to it, similar to the arrow in the image below, and the hypothesis is that it would cause the device to rotate in a clockwise direction. What are some thoughts on the hypothesis?


texts: Calculating needed motor to spin a disk at low RPM

texts:
I'm designing a machine that I need to spin a horizontal disk at low RPM using a motor and gearbox. I'm not good at physics so I need help to find a motor/gearbox to fulfill my needs.

It's a horizontal disk, a shaft is connected at the middle of the disk, connected to the gearbox on top of disk.

There are wheels under the disk to lower the friction and handle weight.

On top of the disk, there are meats.

On the disk there is a blade. When the disk spins, cutted meats comes out of disk from bellow.

Disk and shaft's weight is 5kg, meat is 25kg (max), motor and gearbox are secured to the machine, Disk's friction to the machine is negligible.

Required gearbox speed is 30 RPM.

How should I decide which motor/gearbox is good for this project? I know the speed (30 RMP), how to calculate the needed Torque?

Thank you.


texts: How to make smoke for a small wind tunnel?

texts:
I am making a small (desktop) wind tunnel for educational purposes, I want to have 10 fairly thick smoke-streams about 3cm apart. I have experimented with incense but the stream is not thick enough and barely visible.

I was thinking of using a pipe with holes drilled in it to get the 10 smoke-streams, the low pressure of the airflow drawing the smoke out through the pipe from a container with the burning substance.

What can I burn that will produce a nice thick white smoke and is non-toxic?

Is there a different/better way to get non-toxic 'smoke' without burning anything?

Is the pipe a good way to distribute the smoke or are there any other/better techniques to getting the multiple streams?


texts: What is the axis of rotation of a turning car?

texts:
I was wondering while parking my car, what is the axis of rotation/pivot of a turning car? Does it differ when it is turning frontwards of backwards?

Is it different for a 4x4?


texts: Import from DWG creates duplicate contours that cause sketch errors

texts:
I have an Illustrator file that I exported as DWG through Illustrator, and I'm using this as a wireframe for a sketch insert for an engraving. I imported the DWG file in, everything looked okay, but when trying to extrude, there was an error. Using Repair Sketch, I found the issue to be that there are just 2 layers of paths stacked on top of each other, and this is what caused the duplicate contours. There aren't any duplicate paths in Illustrator, and SolidWorks doesn't seem to identify these contours as "duplicate paths". This is what happens when one of the contours is deleted:

Is there any way to either bulk remove these contours or prevent them from doubling up to begin with? Any help would be appreciated. Thanks!
EDIT: Just as a clarification I used 0 stroke in Illustrator, but this still created the separate layer as shown.


texts: How do I properly compute mean time to failure?

texts:
I have a product of which we have shipped something like 500 units over the last five years. This product is not intended to be user serviceable; a failure of any component results in the unit being replaced. The majority of these units have never seen problems and are still working fine. Some have been damaged and come back for repairs.

How would I go about computing mean time to failure (MTTF)? Would I include only the units that have failed? Or would I also figure in all units that are currently operating? What about the fact that I only have the date of sale, not the date of installation? And that I don't know what fraction of the installed time the unit is running? Should I just make reasonable assumptions?


texts: Making sheet metal parts in Autodesk Fusion 360

texts:
I'm trying to do some sheet metal work in Autodesk Fusion 360 and it has proved frustrating in the extreme.  Maneuvering sketches and bodies to where I want them has proved extremely difficult.  I understand that Autodesk Inventor has far better support for sheet metal parts, which is great if I could afford Inventor.

What is a workflow for making sheet metal parts in Fusion 360?


texts: How do I connect pneumatic components with metal tubing?

texts:
I'm building a small pneumatic control cabinet with a couple filters, regulators, valves, and flow restrictors. I had started by using 8 mm push-to-connect fittings and nylon tube, but it seems I can make things more compact by using metal tubing.

Thing is, I'm having a hard time finding any kind of basics tutorial for how one does this. I've seen a few photos, and found a couple pipe-bending tutorials, but I don't know what kind of fittings to use.

It seems I can use flared fittings, is that what's usually done?

Unfortunately, I can't find metric sizes on McMaster-Carr, so I'm going with 5/16". But while they have aluminum tubing and bending tools for 5/16" OD tubing, they don't have fittings. They do have 1/4" and 3/8" fittings.

Can I under- or over-size the fitting and the pipe like that?
Are there any good resources for learning how to fabricate a control system using metal tubing?
The thing I'm controlling is the tool changer on a nice spindle motor. It has 8 mm OD push-to-connect fittings, 6 mm ID tubing. 3/8" metal tubing has a 1" bend radius, while 5/16" tubing has an 11/16" bend radius, allowing for slightly more compact layout.


texts: Measurement of girth of abdomen (automatic) using body impedance measurement

texts:
The task I got is to measure the girth of the abdomen continuously for a 24 hour period using a suitable method. I have thought to measure the impedance between two points in the abdomen and use the formula.

Roh=Resistance X (Area / Length)

Is this practically feasible?  Are there any better methods to achieve my task?

This is my Previous question. I have gone down the impedance route for now. What I am envisioning is a belt worn around the waist to do the task.


texts: What does the D stand for in the steel grade 16MND5

texts:
I would like to know what does the "D" means in steel grade 16MND5.

According to the standard EN 10027:

16 means 0.16 % C
MN 5 means 1.25 % Mn (5 must be divided by 4 to get the Mn mass fraction)

But nothing is specified for D.