texts: What kind of mechanisms are there to give an object free rotation?

texts: I am doing a project where there is a plate with a hole on it where one ring will be mounted. The ring and plate need to be attached somehow. However, the ring must be able to rotate around the roll axis. I already have some ideas, but there are too complicated. (with bearing, etc) My questions is: what are some similar mechanisms that I can inspire? (The picture shown below is the basic demonstration of the project. The ring which is needed to be able to rotate is shown with the red color)


texts: Linear Motion Stage with Offset Loading Problem

texts:
I'm currently developing a linear motion system which will have to withstand a large offset load (see image below). There will be two rails, each with a carriage on, which will be connected by a beam/stage (see yellow beam); and a 1,000 kg load will hang 1 m away from the front carriage.

I'm trying to calculate the rolling moment that the carriages will experience due to the offset load. After doing a free body diagram of the system I believe the front carriage will experience a moment of:
M = 1 m * 1,000 kg * 9.81 m/s^2 = 9,810 Nm
And the back carriage will experience 0 Nm moment.
Therefore, I believe I will need some carriages which can withstand a rolling moment of at least 9,810 Nm.
However, I spoke to a linear motion supplier and their engineer stated that they didn't believe the front carriage would experience any moment loading at all, and so they quoted me for a carriage which could handle 1,000 kg of compressive load, but fell really short on it's moment roll load capacity; which was about 600 Nm. The only explanation they have given so far is that the back rail would highly reduce the moment experienced by the front carriage... but I disagree.
How much moment do you think the front and back carriages will experience and why?
Thanks in advance,
James


texts: How do I calculate the density of a lined pipe?

texts:
I'm having some trouble figuring out how to calculate the density of a lined pipe given the diameter measurements and the specific gravity of the materials.

The Problem

Calculate the density of an empty rubber lined steel pipe with an inside diameter of 0.075 m, and an outside diameter of 0.079 m. The rubber lining reduces the pipe inner diameter of the pipe to 0.069 m. Assume that the SG of steel is 7.9 and the SG of the rubber is 1.52.

My Attempt

I multiplied the ratio of the cross-sectional area of the steel part to the cross-sectional area of the whole pipe with the density of steel. I did the same for the rubber lining and then added the two values together.

$$\begin{align}
\rho_{substance} &= SG * \rho_{water} \\
\rho_{steel} &= 7.9 * 1000 kg/m^3 = 7900\text{ kg/m}^3 \\
\rho_{rubber} &= 1.52 * 1000 kg/m^3 = 1520\text{ kg/m}^3 \\
r &= \dfrac{\phi}{2} \\
r_{outer} &= \dfrac{0.079}{2} = 0.0395\text{ m} \\
r_{inner} &= \dfrac{0.075}{2} = 0.0375\text{ m} \\
r_{lining} &= \dfrac{0.069}{2} = 0.0345\text{ m} \\
A_{pipe} &= \pi(0.03952^2 - 0.0345^2) = 0.00116\text{ m}^2 \\
A_{steel} &= \pi(0.0395^2 - 0.0375^2) = 0.000484\text{ m}^2 \\
A_{lining} &= \pi(0.0375^2 - 0.0345^2) = 0.000679\text{ m}^2 \\
\text{steel:pipe} &= \dfrac{0.000484}{0.0011} = 0.417 \\
\text{lining:pipe} &= \dfrac{0.000679}{0.00116} = 0.585 \\
\rho_{pipe} &= \text{steel:pipe} * \rho_{steel} + \text{rubber:pipe} * \rho_{rubber} \\
&= 0.417 \cdot 7900 + 0.585 \cdot 1520 = 4184\text{ kg/m}^3
\end{align}$$

Correct Answer

According to the key, the answer is supposed to be 990 kg/m3 (neglecting the air in the tube).

Is my entire approach wrong? I know how to find the composite density of, say, a slurry stream (water + solids) but how do I find the composite density of a lined pipe?


texts: Observability using the Discrete Extended Kalman Filter (EKF)

texts:
I have built (several) discrete Extended Kalman Filters (EKF). The system model I am building has 9 states, and 10 observations. I see that most of the states converge except one. All except 1-2 of the EKF state estimate appears to drift. Since the EKF is dependent on all the states being convergent, the rest of the states are very erroneous after the divergence.

How do I check the observability of the EKF? Do I simply check the rank of the measurement Jacobian and see if it's less than the maximum rank of the measurement Jacobian?

After adding more measurements in my simulation, I was able to get things to converge. However, my question about observability still remains!

Issue:

Ground truth and EKF estimate graphs can be found here or see below.

Notes:

The model is quite non-linear between time steps 400-600 hence some divergence of some of the states
Figure/State 6 is the one that seems to be diverging
Please ignore the "sensor readings" plots for Figures 8/9

Things I have tried:

I know for linear state space systems you can use the Cayley Hamilton Theorem to check observability.
I have tried to check the Innovation/measurement residual e and all innovations converge to 0
I've also tested different inputs and they don't seem to affect the convergence of the diverging state(s)
I've tuned the EKF without any sign of convergence for the diverging state(s)
Graphs for another input signal: or see below
After talking to a colleague, he suggested that I investigate another issue that could be that there is an observation that is linearly dependent on 2 states, e.g. y = x1 + x2. There is an infinite number of values that could satisfy the same y, but shouldn't observability capture this issue as well?

Please let me know if there's anything else I can provide.

Ground truth & EKF estimate graphs:
Click on image for larger view

Additional input signal:
Click on image for larger view


texts: Pneumatic-based, paddle wheel-type lifting apparatus for aircrafts

texts:
I am wondering if a pneumatic-based, paddle wheel-type lifting apparatus would have any practical application within the aeronautical or aerospace fields.

Please reference the conceptual drawing below.

It is showing radial bladed impellers ('paddle wheels') embedded halfway within an enclosure. The impellers are rotated by electric motors (although they can be any kind of motor). This enclosure has lower ambient pressure within it due to the suction of the intake pipe of the attached centrifugal blower. The centrifugal blower is being rotated by its own electric motor.

Since the impeller blades that are outside of the enclosure encounter higher air resistance/drag as compared to the blades within the enclosure, the paddle wheels should generate a net force in the direction indicated by the arrows on the impellers.

Although I do not believe that this lifting apparatus would be a replacement for aircraft propellers, I believe that it may have a practical application somewhere within the aeronautical/aerospace field, yet at this time I don't know what that would be. Perhaps one application would be that this lifting apparatus could be used on a STOL/VTOL aircraft or a drone to provide vertical lift/hovering capabilities.

Would this pneumatic-based, paddle wheel-type lifting apparatus have any practical application within the aeronautical or aerospace fields?

EDIT

Edited the Title text and made wording edits to the Body text. Also, revised the original drawing and reposted it.


texts:
I've been studying gimbal lock and am puzzled by something in regards to the Apollo 11 mission mentioned on Wikipedia.

They preferred an alternate solution using an indicator that would be triggered when near to 85 degrees pitch.
"Near that point, in a closed stabilization loop, the torque motors could theoretically be commanded to flip the gimbal 180 degrees instantaneously. Instead, in the LM, the computer flashed a 'gimbal lock' warning at 70 degrees and froze the IMU at 85 degrees"
— Paul Fjeld, Apollo Lunar Surface Journal

What I don't understand is this instantaneous flip of a gimbal by 180 degrees to prevent a gimbal lock. Which gimbal? And how would that change anything? I'm struggling to conceptualize how it would prevent the lock.


texts:
If a member is very slender then its length will be large compared to its cross-sectional area. I've heard and read that slender members can potentially cause the stiffness matrix of a beam/frame element to become ill-conditioned in FEM.

Question: How/why can a slender member cause the stiffness matrix to become ill-conditioned?

Here are my own thoughts regarding this question, which may or may not be correct - I'd like some confirmation. A long slender member will have larger axial stiffness than flexural stiffness. In the stiffness matrix, the axial stiffness term has the length of the member ($L$) in the denominator. However, the flexural stiffness terms typically have $L^2$ and $L^3$ in their denominators. Therefore, given constant cross-sectional properties ($A$ and $I$), as $L$ grows the flexural stiffness terms approach zero much quicker than axial stiffness. Is this the reason for the potential for ill-conditioning? Or is there something I'm missing?


texts: Windmills in empty fields. Why no trees?

texts:
I have noticed that windmills are generally built in empty fields with no trees around, and I've been wondering why...

A windmill is generally way taller than trees and I can imagine that trees don't actually affect the flow (see picture).

But is this the reason why there is nothing around or is there something else that makes them waste so much space around? And is the velocity profile from the first figure a realistic one?

If I search for the theory of external convection, the velocity profile looks like this for flow over a plateau:

In the second case, wouldn't the velocity be higher if there is an obstacle? Or is it because the obstacle is a porous medium that damps the flow? And lastly, is the velocity profile at earth level looking like that? Is there really an origin to it, or is it fully turbulent all the way?


texts:
What I am after is the center line of this wave, which is 0. How can I calculate that value though?

For example, run the code below for a simple example in Matlab. This will plot a simple sine wave with a couple of periods.

x = linspace(0,7.5*pi,100); y = sin(x); plot(x,y); mean(y)

The result (and the problem) is that mean(y) is 0.0368, and not 0.
But I am plotting a sine wave oscillating around 0 of course.

How can I calculate these kind of averages correctly (without me having to plot and actually examine each signal manually to get the periods right)?


texts: Are there ever job openings that say "Only M.S. degrees apply", and if so, will an M.Eng. still cut it?

texts: If these exist, then I would imagine they are in research. Is an M.Eng. looked as favorably upon as an M.S.?


texts: Engineering Drawing-Projection of intersection curve of two standing cones

texts: I have this projection of two intersecting cones, and I am asked to draw the intersection curve of the two cones on the projection. What is the right way to do it?


texts: Variational Problem of slow steady flow of viscuous fluid in 2D

texts:
I have a Problem with a transformation.

The energy function is the following:

$$I(u_1,u_2,P)=\int_R [\frac{\mu}{2}(u_{i,j} + u_{j,i}) u_{i,j}-Pu_{i,i} dx_1 dx_2 - \int_R f_i u_i dx_1dx_2 +\int _S t_iu_idS$$

where

$u_{i,j}=\frac{du_i}{dx_j}$ and Einstein's summation convention is applied (sum over repeating indices).

The task is to compute the variation $\delta I=0$

In the result sheet they do following transformation, which I do not understand:

$$\begin{align}
\tag{1}I(u_1,u_2,P)&=\int_R [\frac{\mu}{2}[(\delta u_{i,j} + \delta u_{j,i})u_{i,j}+(u_{i,j} + u_{j,i}) \delta  u_{i,j}] dx_1 dx_2 +[...]\\
\tag{2}I(u_1,u_2,P)&=\int_R [\mu(u_{i,j} + u_{j,i})\delta u_{i,j}dx_1 dx_2 +[...]
\end{align}$$


texts: Suppliers who write dynamical specification inside their data sheet?

texts:
I am a beginner in control system for hydraulic servo systems. The reason why I haven't started yet to do simulations of hydraulic servo system is because I have no information about the components I want to use.

For exampe. To do a simulation of a hydraulic system, you need to know the dynamical characteristics of the components you are using.

If you look at this document, you sure know what I'm talking about.

Let's a assume that you are building a system like that and you want to simulate it in MATLAB.

Well, OK. First you need to know what components you want to have. That's easy, just follow the picture. Then when you have found all the components you need, you also need to know the dynamics such as gain factors, damping, leackage etc.

The problem that all suppliers I have visit, don't show their specification inside the data sheet of the products they are selling.

Example, if you want to do a transfer function of a hydraulic pump and you go to Bosch Rexroth to buy a hydraulic pump. All they going to give you are static equations e.g formulas.

So that led me to the question: If I want to have dynamical information of hydraulic pump, hydraulic cylinders, electrical motors. What supplier should I visit then?


texts: What is the advantage of successive linearization?

texts:
In this link, two methods have been referred for linearization.

1- offline linearization

2- online linearization

However, I do not understand what is the role of "successive linearization" in the online method. What is the difference between successive and typical linearization?


texts: Understanding required torque for a motor lifting a weight

texts:
This is a continuation of me trying to understand torque and stepper motors in my other question.  I'm trying to understand the torque a motor would be required to generate to lift a small weight, and the formulas involved.

The first part of my question is to verify if I am calculating this correctly:
Let's say I have a 450 g mass (roughly half a pound) then the force of gravity pulling it down is:
$\begin{align}
F &= ma \\
&= 0.450 \:\mathrm{kg} * 9.8 \:\mathrm{m}/\mathrm{s}^2 \\
&= 4.41 \:\mathrm{N} \\
\end{align}$
If I have a stepper motor with a spindle for my string that pulls up my motor with a radius of 5 cm.  I think my torque needed would be:
$\begin{align}
T &= Fr \\
&= F * 0.005 \\
&= 0.022 \:\mathrm{Nm} \\
\end{align}$
So now if I want to move that mass I need to find a stepper motor that can output more than 0.022 Nm of torque, right?

The follow-on to my question is that if I want to see how fast I can move it then I need to look at a Torque speed curve, right?
My confusion is this: do I have to ensure that I'm moving slow enough to get the torque I need, or does that curve say if you need this torque you won't be able to go above this speed because the motor won't let you?


texts: Seperating two glass pieces with a circuit board inside

texts:
I want to repair an outdoor lamp (see images below) however I can't get the glass container open. The methods I found on the internet are based on glue removers or based on heat but I'm not sure this will damage the print inside, as this is what I try to repair. Note that I think it is glued, however if this is not the case please let me know.

What I tried so far:

Wringing it with a screwdriver (the image on the side shows a clear 'edge' on top, however I can't get really deep
Applying moderate heat

Goals:

No damage the the circuit board inside
No damage to the glass container (if unavoidable I prefer breaking the bottom part which does not contain LED's)
Usage of common house tools or tools that are fairly cheap to get (and safe for me to use on a kitchen table)

Images:

Bottom view

Top view

Side view

Related:
Loosening glass that is vacuum


texts: What surface temperature (rise) is required to (dis)qualify a combustion appliance from obtaining a "zero clearance to combustibles" rating?

texts:
How far must the surface temperature of a UL-listed combustion appliance rise to prohibit the manufacturer from specifying it for a zero clearance to combustibles installation?

(I looked in UL 127 but was unable to find a straightforward answer there.)


texts: What is homogeneous temperature in thermodynamics? Can homogeneous temperature assumption derive no heat transfer? If yes, why?


texts: Measuring fracturability / airborne fuzziness of carbon fiber tow vs stainless steel tow

texts:
My friend uses carbon fiber tow in creating a component for automobile machines. However the carbon fiber is actually much tougher than it needs to be. As a risk manager in software I am concerned that his carbon fiber tow poses an unnecessary health risk for his workers working with this material, due to the high airborne asbestos-like risk that may present itself in the manufacturing process.  Of course he educates his workers on this risk and they all use proper protective gear.

Basically, carbon fiber tow is prone to breaking and producing airborne particles when handled by hand, and I'd like to know whether stainless steel tow is less prone to breakages. But I am not sure what quantitative measurement to examine.

For his application, stainless steel tow is a perfect mechanical substitute. Thank you for not questioning whether it is a perfect substitute for his automobile part, because it is. The question here is whether stainless steel tow is more or less prone to breakage than carbon fiber tow.

There are two metrics that I began trying to learn more about that could be valid here. The first is "Fracture toughness" and the other is "tensile toughness". I am really just trying to get data on which is better, or how I could scientifically prove the stainless steel tow is less prone to breakages.

We can assume that the diameter of each fiber within the tow is about 5-15 micrometers. What's the best data we can gather on the subject?


texts: How to control the current while using "DC-DC XL6009 Adjustable Boost Step-up Power Converter Module Replace LM2577" in a circuit?

texts:
I want to power my WiFi modem with my powerbank and the modem's requirements is DC 12V-1A. But my Powerbank has DC 5V-2A that is why I will use a step up converter but how about the Amperes, how can I decrease it to 1A?
We have a terrible electric company and I want to make this so I can still use the internet while there is a power interruption and it takes 6 to 12 hours. Online classes are going on that is why I want to make this.
[DC-DC XL6009 Adjustable Boost Step-up Power Converter Module Replace LM2577]
specs: https://shopee.ph/product/201062777/6508449595


texts: Empirical correlation for low reynolds convective heat transfer coefficient

texts:
I am looking for a heat transfer coefficient for a shape (rectangular cross section preferred, could estimate with flow over flat plates) in 2 m/s cross flow.
I have found a few empirical correlations from which I can find the Nusselt number and then estimate the heat transfer coefficient, but they are only valid for Reynolds as low as 5000.  I've combed through Incropera's Fundamentals of Heat and Mass transfer, as well as a few other textbooks - they all seem to report the same correlations. The Reynolds number for this estimation is ~100, since it is operating in air at near vacuum (~800 Pa) and only at speeds of 1-2m/s.
Any suggestions?


texts: Is there any software for testing cad model waterproofing and isolation?

texts: I have a cad model of a plastic box that is made of two parts. Two parts are connected with resin isolation. I want to test if my part is at least in theory ip86 water-resistant. So is there any software for testing cad model waterproofing and isolation?


texts: Why is hardening and brittle nature so related?What is work hardening or strain hardening as far as true stress strain diagram is concerned?


texts: How to track parts through high-temperature oven and abrasive treatments?

texts:
I have been thinking of a problem and I would like to brainstorm about it with the community.

Scenario:
Machined parts going through termal treatment in an oven and further abrasive treatments. Temperatures of 900 celsius in the oven. Minimal space for marking. Laser do not work. RFID neither. 10mm marking space possible.

How can one track these parts? Any kind of paint? High temperature magnetic memory?


texts: Solving heat loss equation associated with solar trough concentrators

texts:
My project is about finding the efficiency of solar trough (cylindrical parabola) concentrator  that will boil water in a pipe located at the focus (check picture please). In the process of doing so (of course I made many assumptions, but I think they are irrelevant to my question now) I am trying to solve for heat loss from the pipe referred to as Q_loss (please always refer to my picture). I started by assuming Tco in equation3, and knowing T_ambient, T_sky I could find h_w and Q_loss. Using those result in eq2 I could find Tci(internal temperature of the glass envelope cover around the pipe). Now I want to substituting Tci in eq1 to find Q_loss which I will compare against the Q_loss I got from eq3 to see if my assumption about Tco was right, but the problem is that I don't have Tr(temperature on the pipe's surface which i assumed constant). How I would go about finding Tr please? I read many papers, but none of them pointed how to find it. They assume it is known or something!
I have being thinking about this issue for days now. Please advise. Appreciate any guidance]1


texts: Spades used in pressure testing PE Pipe lines

texts: As we all know the industry is heading into PE pipelines in the gathering fields fast. Some applications use DN560-DN1000, and the spades is very heavy and in awkward positions. Is there PE spades/blanks in the market to ease the manual handling?


texts: Basic Hook development length using CSA A23.3 provisions

texts:
I have 8" thick reinforced concrete walls and I would like to anchor my horizontal corner reinforcement with only 1 hook (I have only 1 layer of reinforcement in both walls). The problem is CSA A23.3 (same for ACI if I'm not mistaken) restricts minimum hook length to 6" or $8d_b$ = 120mm = 5" in my case.

If I want to put my reinforcement in the middle of my wall, there is no way for me to get that 6 inches. Can I simply assume that the bar is held by my vertical reinforcement (see picture)?


texts:
Why does the Ultimaker 3D Printer has a Heater + Heater transfer plate (aluminium) + Glass?

I wonder why a glass plate, and if is possible to remove the glass and print directly in the aluminium plate adjusting the heating.

Link to the ultimaker.

Pictures:


texts: How should the welded corner of this bracket be detailed?

texts:
Consider the design of the bracket shown in the figure below (it is assumed that the anchors are sufficient and are not considered below).

My question concerns the detailing of the welded connection detail and the overall strength of the bracket. The design principle is that the welded connection shall have a capacity equal to atleast the moment capacity of the plate. Note that the bracket behaves as a cantilever so the point of maximum moment is the connection itself.

Steel partial factor $= 1.15$

Permissible stress in steel $= \frac{275 \text{ N/mm}^2}{1.15} = 239 \text{ N/mm}^2$

Elastic modulus $= \frac{bd^2}{6} = \frac{100 \times 10^2}{6} = 1666 \text{ mm}^3$

Moment capacity $ = 239 \times 1666 = 398174 \text{ Nmm} = 398 \text{ Nm}$

Load $F$ partial factor $= 1.6$

Maximum load $F_\text{max} = \frac{398 \text{ Nm}}{1.6 \times 0.5 \text{ m}} = 122.5 \text{ N} = 12.5 \text{ kg}$

The connection is then designed so that it is atleast as strong as the plate it is joining. There are three options shown in the picture below:

closed corner (3 passes with a 6mm leg length E42 electrode)
open corner (3 passes with a 6mm leg length E42 electrode)
semi-open corner (2 passes with a 6mm leg length E42 electrode)

My first question is which of the three corner details is preferred for this design? Will all three details provide at least the moment capacity of the plate? Could you recommend an even better detail?

My secondary (bonus) question is whether my maths above is correct and that the bracket should conservatively be capable of supporting 12.5 kg (assuming a suitable anchoring detail)?


texts: How did the RBMK control rod design cause an increase in reactivity when moved downwards?

texts:
I have been trying to understand a particular aspect of the Chernobyl accident - the role of the graphite displacers on the end of the control rods. The basic story is that the graphite displacers caused the reactivity of the core to increase when the rods moved down, a non-intuitive effect that the operators were not expecting/sufficiently aware of.

All literature I can find tells basically the same story, but I shall refer here to this PDF.

On page 17 of that PDF it describes the graphite displacers and shows a schematic of a control rod in the raised position and in the "initial insertion" position.

The text indicates that:

  On moving down of absorbers into the core, their displacers displace water columns from the lower part of the core. Thus, inserting of absorbers from their extreme top position introduces a positive reactivity into the core because graphite absorbs neutrons much less than water

The graphic shows a control rod "extreme top" and "initial insertion" positions. In the second case the graphite has moved in the channel, displacing water there and increasing reactivity in the lower part of the core. The image has a "+" symbol showing this.

Also, there is reduced reactivity above the displacer as a result of water replacing the graphite in that position, and reduced reactivity at the very top of the core due to the presence of the boron control rod. There are "-" symbols showing these effects.

My question is, if the graphite displacer was already in the water column, how could moving it downwards change the overall reactivity of the core?

Obviously the reactivity distribution changes, but it seems to me looking at the diagram that the (+) and (-) from the graphite movement would cancel out overall, leaving the (-) from the boron rod: an overall reduction in reactivity.

Clearly I'm misunderstanding something.


texts: Stability Check of Masonry or Brick Vault (or arch)

texts:
I need Some help in Checking the stability of a masonry vault (Voute in french) or even an arch.

Hand Calculation:

If anyone know any article or reference that can help me to check the stability of this model.

Software:

Does anyone know any software where this type of structure (compression only elements since the masonry wall and arch does not take any flexure)I tried to model it in robot but their was no method to make the panels or bars take only compression and the results were not correct (although if anyone knows a way to do it in robot is very much welcome to correct me).

Any further information can be provided.


texts: Calculate force to lift piston from a given closing pressure

texts:
I am trying to calculate the force required to close the valve on an annular blow-out preventer. A rubber ring (called a packing unit) closes around the pipe when a force is applied from underneath, as shown here:

The actual valve has the hydraulic fluid coming into a chamber that goes the around the outside of the main body, which then lifts a piston which applies the force to the packing unit, as shown here:

(source: geologie.vsb.cz)

In the documentation for the bop it says that the hydraulic pressure required to close or open the valve is 3000 PSI.

From this, how do I calculate the force to close the valve?

I assume you just multiply 3000 by the area the pressure is acting on:

$$3000*6894.7*(\pi R_o^2 - \pi R_i^2)$$

Where $R_i$ and $R_o$ are the inner and outer radius of the ring, shown in the picture in the second link. Units of these are meters. $6894.7$ is to convert from PSI to N/m2.

But this gives a HUGE force. Am I doing something wrong in the maths? Or am I interpreting the documentation wrong. Does a 3000 PSI closing pressure not mean that you have to apply 3000 PSI of pressure to the hydraulic fluid acting on the  outer ring of the piston? Maybe it means that 3000 PSI is needed to squish the packing unit so it closes? In this case what information do I need and how do I calculate the force required to close the valve?


texts: Do solid rivets fully fill the holes when installed properly?

texts:
Suppose I have two parts with holes aligned and I have to install a solid rivet into the "combined" hole.

Clearly the rivet diameter must be slightly smaller than the hole diameter, otherwise it simply won't fit. So I heat this slightly smaller rivet, insert it into the hole and then deform its tail so that the rivet now has two heads and sit properly in place.

Assume I follow all the procedures and best practices.

Does the deformation only affect the tail or does it also make the middle of the rivet expand and fill the gap between the hole walls and the rivet?

In other words, if I wait till the rivet cools down and then grind the rivet head off - will it leave its place easily or will I have to force it out?


texts: Air flow bench connected with a manometer. Atmospheric pressure of the manometer changes each time the bench is restarted. Why?

texts:
I was doing the air flow in a 90 degree bend experiment.

On the first run, I connected the manometer to the tappings on the outer wall, then I turned off the bench and changed the connections to the inner wall. Then, I turned on the air flow again.

Each time I done this I got a different reading on the manometer for the airbox pressure and the atmospheric pressure.

The air flow settings weren't changed and no change in room temperature or nothing. It was like 10 minutes difference between each run.

Why is this?


texts: Multiple varying cross section beam with uniform loads

texts:
I have the following cantilever beam problem where I need to find the deflection of the tip at P.

I tried to compute the deflection of the beam using Castignliano' s theorem as described in this similar thread.
Where my moment is defined as
$$
M(x) = w_1 \cdot x \cdot (L_1 - \frac{x}{2}) + w_2 \cdot x \cdot (L_1 + L_2 -\frac{x}{2}) + w_3\cdot x \cdot (L_1+L_2+L_3 - \frac{x}{2}) + P \cdot (L_1+L_2+L_3-x)
$$
Then I defined:
$$
EI(x) = EI_1 \cdot H(L_1-x) + EI_2 \cdot H(x-L_1) \cdot H(L_1-L_2 - x) + EI_3 \cdot H(x-L_1 -L_2)
$$
Next I calculate the deflection using Castignliano's theorem:
$$
\delta_j = \int_0^L \frac{M(x)}{EI(x)} \frac{\partial M(x)}{\partial P_j}dx
$$
However, when I apply this method the integral I obtain increases and then it starts to decrease, which it should not. If my formula is indeed correct (which I am ot sure of) I think the probem has to do with the integral bounds I use.
Should I use
$$
\delta_{P} = \int_0^{L_1+L_2+L_3} \frac{M(x)}{EI(x)} \frac{\partial M(x)}{\partial P}dx
$$
Or should I split the integral up?


texts:
Has anyone tried to do this?

I have two GPS receivers, and when they are near each other, they calculate different positions.
The difference is about 5-10 meters, but in reality it is several centimeters.

So, I'm trying to do this, connect two receivers to one antenna. And again I get different positions. The difference is about 1-2 meters.
The receivers are the same model and on the same boards.
The other receivers work well.

So, has anyone dealt with something similar?

As I think, if they are connected to the same antenna, the calculated position should be the same.

May be somebody has two GPS receivers that are the same and can test this...?


texts: What are safe locations for openings in reinforced concrete beams?

texts:
I had an argument with a friend about the safe location for openings in reinforced concrete beams. I've chosen position 1, a little above reinforcement steel, as at this location, the beam is subjected to tension in the lower fibers which is resisted by reinforcement steel and, assuming failure case, the concrete at lower fibers is cracked.

Any other opinions?


texts: How to model a planetary gear system with transformation matrices?

texts:
I need to model the planetary gear-train with transformation matrices of  1 sun and 2 planets system, with no ring and an "arm" or carrier holding the gears ,like in the second picture. I already have a dynamical model of the simple system derived analytically, but I need to model it dimensionally to be able to specify the spatial relationships—the relative positions and orientations of the epicyclic geartrain to simulate it.
I only have experience deriving homogeneous transformation matrices of robot joints but I don't know where to star for a gear train system or what method to use.
I'm not sure about which frames of reference to use and how to set up the coordinate system between the gears correctly, for example; what would be the difference between considering a fixed frame of reference for the sun vs a rotating frame of reference? Also, I don't know which and how to include variables like mass, stiffness and damping, like shown in the first picture (for example).


texts: Pacejka "Magic Formula" tire models origin of the name

texts:
It might be a little off topic but I'm trying to find source for why is that model called magic formula? I read that it's a simple function of commonplace functions, a data fitting. Is it simply an empirical model with an unusual name?

The model (or rather series of models) I'm referring to:
https://en.wikipedia.org/wiki/Hans_B._Pacejka

So far only this lecture mentions the history of the name:
http://textofvideo.nptel.ac.in/107106080/lec15.pdf


texts: How is motor torque related to capstan equation?

texts:
I know that capstan equation relates $T_{in}$ and $T_{out}$ as $T_{out} = T_{in}e^{u \cdot F_c}$, where $u$ is friction coefficient and $F_c$ is wrap (slip) angle. In my situation, the capstan is driven by a motor. Input and output ends of the wrapped material are free (under tension but not supported). Both motor torque and the angular velocity of the wrapped material are positive (clockwise). The wrapped material is elongating and moving at the same time.

What I don't understand is the role of motor torque in the scenario. The equation does not take motor torque into consideration and I couldn't grasp how it has no effect at all.


texts:
Given a system describing a 2-vehicles platoons that can be described as such :

$v_k$ the speed of each vehicle
$s$ the gap between the vehicles.

We can describe the state of the system as :

$\dot{s} = v_0 - v_1$
$\dot{v_k} = u_k$

Hence, writing the state of the system as $x = (v_0, s, v_1)^T$ yields the following state equation :
$$\dot{x} = Ax + Bu$$
with :
$A = \begin{pmatrix}
0 & 0 & 0 \\
1 & 0 & -1 \\
0 & 0 & 0
\end{pmatrix}$, $B = \mathbb{1}$.

The eigenvalues of $A$ are all $0$, so the system should be marginally stable.

However, it seems to me that taking any $v_1 \neq v_0$ as initial conditions gives $s \to \infty$ so $x$ isn't bounded, so it isn't marginally stable.

Where am I wrong ?


texts: How do we know that deformations occur in a uniform fashion throughout the length of shaft?

texts: When equal and opposite torque act on  the two ends of a circular shaft,how do we know that deformations occur in a uniform fashion throughout the length of  shaft?Is it because that all cross section of shaft have same torque acting on them and hence the stress distribution on the cross section is same which further results in same strain throughout the cross section?If not,then how?


texts: $\lambda_1$ factor in context of buckling

texts:
I'm studying this text about buckling.
There a factor called $\lambda_1$ is defined:
$$\lambda_1=\pi \sqrt{\frac{E}{f_y}}=93.9\sqrt{\frac{235}{f_y}}$$
But how was that last step made? Where did that factor of 93.9 come from? Usually we take the elastic modulus of structural steel as around 200GPa, so how is there 235 under the square root? I feel like there is some step missing.


texts: How can one determine the LTE base station providing service to a mobile device?

texts:
In order to have continuous service a mobile devices switches to base station with higher signal strength.

Question: Is it possible using the mobile device (Android or iPhone) to determine to LTE base station to which the device has established a connection?

Note: I am interested only for LTE service/devices


texts: How to calculate external pressure resistance in spheres and cylinders?

texts:
Although I have seen a lot of literature online about how internal pressure resistance is calculated (i.e the pressure in a gas tank) I haven't found anything about the opposite scenario (i.e the pressures on a deep sea submarine).

How would one calculate the thickness of material needed and stresses involved at high pressures externally? Please assume a very basic level of physics knowledge (I have GCSE knowledge for sure and can probably work out and search up some of the more basic stuff, but I'm certainly no engineer).


texts: Why do plate exchangers typically serve lower pressure fluids than shell and tube heat exchanger?

texts:
According to Wikipedia http://en.wikipedia.org/wiki/Heat_exchanger, plate exchangers typically serves lower pressure fluids than shell and tube heat exchanger, why?

Tubes in plate exchangers are simpler and have larger diameter, seems to be more robust to hold higher pressure fluids.


texts: Why does "Google self-driving car"'s roof camera rotate?

texts: I'm intrigued by this video in which the roof camera rotates continuously. One reason could be to capture 360 degrees around, but then again two cameras or more could do the same job capturing different parts of the landscape. It seems to me a waste of energy in making the camera rotate, and also having mobile parts make it more vulnerable to breaking. I don't see why not using a system of many static cameras.


texts: How do electric companies supply electricity to homes in countries where energy is privatized?

texts:
Before I start, sorry if this doesn't make sense English is not my first language.

In my country electricity is nationalized so there is only one energy company and one grid. When you build new house you just connect your house cables to the gird.

My question is in country/region where there are multiple companies providing energy, does each company have its own grid/cables/wires reaching homes?

And what happens if there is a new company, does it have to build it is own grid?

Are there multiple transmission lines for each company?


texts: What are boundary conditions and initial conditions with respect to differential equation? Do they mean the same for partial differential equation? How to BC and IC vary for different types of PDE?


texts: Why does the Compressor Fan for an Air Conditioner need a Starter Capacitor?

texts:
Our house air conditioner went out last Saturday afternoon on a +100 F day. Was able to diagnose the problem itself as a problem with the starting circuit of the big compressor fan of the outside compressor unit. If I gave the fan a strong push with a stick to start it rotating, then the fan motor would start up and the air conditioning would work fine. An AC technician later determined that the compressor fan needed a new start-up capacitor, and now the AC works fine.

My question is this: Why are large 2-ton house air conditioners designed so that their compressor fans require start-up capacitors to turn on? The diameter of the compressor fan on our house AC appears to be roughly the same as that of an inexpensive box fan that I can get at Walmart, and the ac motors on those simple box fans don't require a start-up capacitor to turn on, do they? You just plug them in and they smoothly start revving up to speed all by themselves. So why do house air conditioners use compressor fans that need these trouble prone start-up capacitors, and why can't a simple self-starting ac motor like that of a box fan be used instead for the compressor fan?


texts: What's wrong with transporting a refrigerator on its side?

texts:
I tried to deliver a refrigerator and the customer saw that the refrigerator was lying down in the truck instead of standing up. He refused to accept it, claiming that the compressor would be damaged by having it on its side.  I tried to explain that that made no sense, but his friend came to me and also said the same thing.

Is transporting a refrigerator on its side a problem? If so, why?


texts: How can I *more accurately* measure the weight of a hanging bottle?

texts:
I have a project where I need to be able to measure the volume of remaining liquid in a bottle based on weight. The idea is to use a Force Sensing Resistor:

(model FSR402-Short Tail: http://www.interlinkelectronics.com/FSR402short.php)

(source: interlinkelectronics.com)

My issue is that I can't seem to get an accurate consistent reading on the pressure exerted on the device when any kind of shifting (such as replacing / refilling the bottle, moving the device location, etc) would create a huge variance in the data points. It can vary from 20-150 points easily... which is too large of a margin since 150 points could equate to about 500ml of liquid.

The idea was to loosely hang the bottle & connector to the pressure plate (see second image) using two centrally located screws. the pressure plate would have a set of two rubber feet perpendicular to the screw placements to allow the pressure to be focused on the rubber footing with the FSR.

This produced two main issues that I did not foresee with the CAD design:

over-tightening/under-tightening of the screws
inaccurate or inconsistent readings of the pressure from very minor shifts or bumps.

What can I do to improve my design, shown below?

1) Top perspective view of pivot mechanism.

2) Side perspective view, translucent with descriptions.


texts: Estimating Static Pressure @ Target Airflow (boost fans)

texts:
How do I estimate a pressure/flow curve for a filter of specified area, efficiency rating, MERV and MPR?(Duct work is negligible)

I am trying to pick an appropriately rated fan/fans to maintain a target cfm:

I'm trying to add a filter to a wall-mounted AC unit. If I can't do this I will need to replace the whole system. I'm trying to calculate the resulting static pressure assuming I can boost flow to maintain cfm. I have chosen a filter and I know my target cfm; How do I find static pressure so I can choose the right fan to boost the unit.

constraints are as follows:

the unit is rated for approx. 400 c.f.m. on a 240V circuit
inbuilt blower motor: 8P DC280-340V 30W
filter area is ~$3ft^2$
filter efficiency is 93%
filter MERV rating 12
filter MPR rating  1900
I don't have any more information

How do I figure this out? I've looked at the Affinity laws:

$ \frac{Q_{1}}{Q_{2}} = \frac{N_{1}}{N_{2}} $

$ \frac{H_{1}}{H_{2}} = (\frac{N_{1}}{N_{2}})^2 = (\frac{Q_{1}}{Q_{2}})^2 $

$ \frac{P_{1}}{P_{2}} = (\frac{N_{1}}{N_{2}})^3 = (\frac{Q_{1}}{Q_{2}})^3 = (\frac{H_{1}}{H_{2}})^\frac{3}{2} $

Also perhaps important:

Flow coefficient: $ C_{v} = Q \sqrt{\frac{SG}{\Delta P}} $ (can i estimate $C_{v}$ of my filter?)
Darcy's law?
Dynamic pressure?
Bernoulli's principle?

I don't really have any test equipment. I was hoping to estimate all necessary values based on product specs and labels. I'd like to know how to calculate my estimated pressure and flow, although perhaps I might up-vote a ballpark answer if it helps me pick a fan:

I have ~2.5" gap space behind my baffle to install my boost fan/fans. I was thinking of installing some 120mm, 110V, 100cfm muffin fans in this space. What total CFM should I aim for? Are muffin fans the right choice?


texts: How can I fit a DN16 flange to a DN10 flanged pipe?

texts:
One of the valves on my 3 bar line just failed. Without it, our production has ground to a stop and we can't operate until we get a replacement (which we have already ordered). In order to make a deadline, I am trying to find a way to use a (properly rated for pressure) DN 16 flanged valve to fit with the existing DN 10 piping.

Is there any way to (safely) connect these two flanges together temporarily?


texts: What is the power and max flow rate required to rotate a 300 W wind turbine?

texts: I have purchased a wind turbine with a power of 300 W, the start up wind speed is 2.5 m/s, rated wind speed is 11 m/s, and the survival wind speed is 45 m/s, and what I'm going to do is to make an educational modeling for how to generate electrical power using a wind turbine, I mean that I will provide the wind using an axial fan, My question is, how can I predict the power of the fan and its max flow rate required to make the turbine rotate at its maximum power?


texts:
I would like to create an interface that increases the frequency out of the wall, 60 hz, to 24khz. I have chosen 24khz as the operating frequency of an induction heater I am planning on building and I would like some advice as to how I should go about doing that. Here is a block diagram of what I am attempting to construct.

I want the power ratio to remain as near to unity as possible through each block so I must also take into account the impedance and heat loss through each step as I design them. If anyone can assist me on how I should design the frequency multiplier circuit, I would be very grateful.


texts:
What's the best way to precisely measure intricate mechanical parts?

For example, notice the tiny differences between the pitch in these two threads, and the tiny variations in external width of the cylinder:

I've been using a micrometer and a vernier caliper.

The micrometer is capable of more precise measurements, but it's no good at getting into tight spots. The jaws of the verniers have a sharp, bevelled edge that can fit into some tight spots, but it's less accurate, and hard to know if the jaws are making firm contact to the desired surface, or catching an edge or another surface (like the outer diameter of a thread, for instance).


texts: Why Stirling engine not used as primary source to operate generator in thermal power plants?

texts:
I did some research and found out that in order to generate that amount of electricity( consider about 100MW) the size of the Stirling engine will be very big as compared to that of a steam turbine.
But then some articles said that upon using helium in the Stirling engine the size will become much smaller. This will also increase the power density of the engine.
If this is the case then why is Stirling engine not used, is this due to lack of research since steam turbines became popular.


texts: Dumping microwave oven energy on electronic device

texts:
Microwave oven generate around 1 KW of power. If this energy is dumped on a electronic device, say wifi router, gsm phone or fm receiver etc, what will happen? Will the devices be damaged?
By dumping I mean the magnetron at a distance of 1m or less from the electronic device and assume body cage absent.


texts: What is the field on engineering that combines chemistry and electronics together?

texts: I am looking for a career advice as I am interested in chemistry and electronics at the same time but the universities somehow have the two as different major. Is there any branch of engineering that combines the two?


texts:
The exact question

Assuming you have outsourced a FEA of a structural design (steel tubes and sheet metal, bolts and welds design):

What would you look for in the report to have confidence in the outsourced work findings

What questions would you ask them about it.

Is there anything that would set off a red flag that the outsourced work did a poor job or you would simply not trust their findings?


texts: How does a power hacksaw lift on the forward stroke?

texts:
Hacksaw blades cut on the pull stroke (back into the machine) and are supposed to lift on the push stroke, all the DIY setups I have seen cut on both the pull and push stroke, i.e.

What type of setup would allow you lift ever so slightly on the push stroke? Alternatively, are power hacksaw blades bi-directional? All help appreciated.


texts: Is there a term for a circular dependency in system design and engineering

texts: Is there a term used in systems engineering that describes a situation in which the design of one subsystem (call it "A") affects the the requirements for another subsystem (call it "B") while at the same time the design of B affects the requirements for A?


texts: I am using concentrated NaCl(10%) to elute Cobalt (II) ions from a cationic exchange column. How would I determine the volumetric flowrate of regenerant needed to completely elute the cobalt ions from the resin?


texts: Can we see a nanowire, whose dia is say 1 nm but length is 10mm, with naked eye? To see an object does at least two out of three dimensions must be greater than the minimum size one's eye can see?


texts: Are stress concentrations a concern when replacing rivets with high strength bolts?

texts:
A common method of repairing old riveted structures is to replace any damaged rivets with new high strength bolts.

When this is done, the new bolts are typically installed like they would be on a new structure which results in a bolt pretension. My concern is that the one bolt location might be effectively slip-critical while the rest of the existing rivets are something less than slip-critical. This may concentrate stresses on the one bolt.

When new high strength bolts are installed within an array of existing rivets, is there a concern with stress concentrations resulting from the increased clamping force from the bolt?


texts: Boundary conditions for a cantilevered Timoshenko Beam

texts:
I am trying to find out the boundary conditions for above given Timoshenko beam. The boundary conditions that I have derived are

$x_1 = 0$
$$ \overline{u}_2^L = 0 $$

$$ \phi_3^L = 0 $$

$x_1 = \alpha L$

$$ \overline{u}_2^L = \overline{u}_2^R $$
$$ \phi_3^L = \phi_3^L $$
$$ -K_{22} \left( \dfrac{d\overline{u}_2^L}{d x_1} - \phi_3^L \right)  + P + K_{22} \left( \dfrac{d\overline{u}_2^R}{d x_1} - \phi_3^R \right) = 0 $$
$$ -H_{33}^c \dfrac{d \phi_3^L}{d x_1} + H_{33}^c \dfrac{d \phi_3^R}{d x_1} = 0$$

$x_1 = L$

$$ K_{22} \left( \dfrac{d\overline{u}_2^R}{d x_1} - \phi_3^R \right) = 0 $$
$$ H_{33}^c \dfrac{d \phi_3^R}{d x_1} = 0 $$
where,
$x_i$: coordinate along $i$-th direction
$\overline{u}_2^L$: transverse displacement of left portion of beam
$\overline{u}_2^R$: transverse displacement of right portion of beam
$\phi_3^L$: sectional rotation of left portion of beam
$\phi_3^R$: sectional rotation of right portion of beam
$K_{22}$: Sectional shear stiffness, equal to $\dfrac{5}{6}GA$ for rectangular cross-sections
However, in the book ``Structural Analysis with Applications to Aerospace Structures'' by Bauchau and Craig, the boundary conditions at $x = \alpha L$ are
$$ \overline{u}_2^L = \overline{u}_2^R $$
$$ \phi_3^L = \phi_3^L $$
$$ -K_{22} \left( \dfrac{d\overline{u}_2^L}{d x_1} - \phi_3^L \right)  + P = 0 $$
$$ H_{33}^c \dfrac{d \phi_3^L}{d x_1} = 0$$
Why are shear force and bending moment equations at $x = \alpha L$ are different than mine?
Thank you.


texts: Why can soda bottles withstand so much pressure?

texts: Is it due to the PET material that it is made of or is it more the shape and structure of the bottle? If it is due to the shape/structure of the container, is it possible to achieve such pressure resistance using another plastic?


texts: What is the name and purpose of this Instrumentation / Mechanical fitting

texts: The component I am interested in is the blue "head" in the attached image. I call it the sensor head but will like to know if it has a specific industry name


texts:
My friend and I are currently working on a cloud chamber cooled by the compressor of a deep-freezer. We have built an isolated box that contains the cold pipes of the compressor. The pipes cool down to a whopping -40C. On the top of our box lies an aluminium plate, and on top of that a well isolated chamber. With the aluminium plate 5 or 6 cm away from the compressor pipes, the plate just gets -15C. Connecting the tubes and the plate with a folded fin heatsink gives us -20C. Moving the plate down onto the tubes results in a much better -35C, however this is not a very favorable option as this makes the plate harder to look at. Unfortunately, bending the pipes is not an option either.

We think the air in the box is simply not thermally conductive enough. The heatsink was not doing a very good job either, presumably because the fins where too thin and were in contact with a lot of air.

Our question is: What would be the best way to transport the "coolness" of the pipes towards the plate. Would it be better to fill the box with some sort of liquid that would transport heat more efficient then air?

We are using a computer fan to circulate the air in the box. The fan is pointed upward, so the airflow flows via the pipes onto the plate.

Images:


texts: How can I calculate overcurrent from over voltage for the AP9101C IC

texts:
I designed a battery charging, protection, and boost circuit for a project I am working on. However, I made a complete noob mistake and forgot to find the overcurrent value for the battery protection IC I am using, and it turns out the overcurrent value is too low.

The manufacturer makes multiple protection ICs in the same package size, so I can likely just swap it out with a new IC with a higher overcurrent value. However, overcurrent is specified as overcurrent voltage, and I am not sure how to convert this into an actual current draw.

I need the protection IC to allow charging current of at least 1A (no more than 2A), and a discharge current of at least ~1.5A (and no more than 2A). The battery is a 2200mAh li-po cell so this should be perfectly within spec.

This is the datasheet for the IC (I am using the AP9101CAK6-ANTRG1 variant):
https://www.diodes.com/assets/Datasheets/AP9101C.pdf?src-supplier=Digi-Key

Here is what I have tried:

I changed the value of R2 (from the example circuit, R5 in my circuits) to 1k from 2.7k . I noticed no difference in the allowed current draw.
I shorted P- to Battery - to bypass the MOSFETS, this allowed for higher current draw, which confirmed that it is a problem with the protection IC and not the boost converter.

I also am having trouble with getting the battery to charge, I tried connecting the battery directly to the charge IC and charging worked normally, so again there is a problem with the protection circuit.

If it helps at all, I have attached my circuit schematics below

Any help would be greatly appreciated as I have struggled with this for several hours, but I think I lack the background knowledge to figure this out.


texts: can we run rotary compressor of Air conditioner with different frequency level?

texts: I am working on split type AC compressor. I actually want to know, if i changed the frequency of the compressor to run on different power level, will it affect the life of the compressor. My actual work to run the Compressor with different power level. I will use VFD ( variable frequency drive) to change the frequency of compressor and it will take different power with respect to the frequency. can you tell me that all rotary compressor is designed for a specific frequency. ?


texts:
I was originally planning to as this on Physics Stack exchange, but found this question while searching, which directed the asker to here.

While my question is not a duplicate of that, it still falls in the same classification, so I believe it's on topic here.

That said, I recently had a Fluorescein angiography and the following thought occurred to me about it.

Assume there's a piece of graph paper in front of me, the job of the lens in my eye is to project a sharp image of the paper on my retina.  I have astigmatism, in both eyes as it happens, making glasses with a cylindrical correction necessary to read anything.

So, during the angiogram, the exact process is reversed.  The camera involved projects a sharp image of my retina on a photographic sensor.  Except I don't have my glasses on, so I would expect the astigmatism would lead to an imperfect image on the sensor.

How then is the camera able to get a sharp image?  When reviewing the results afterwards with the doctor, I was quite impressed with the detail and clarity of the images.


texts: How is high static water pressure avoided in municipal water systems?

texts:
Most cities get their water supply from local sources (springs, rivers, lakes) so the pressure in the system is never more than what is produced by the pumps.
But some cities get their water from elsewhere, typically from a much higher elevation.
Portland Oregon for instance gets its water from Bull Run Watershed, which is more than a kilometre higher than the city.
Portland's Water System | The City of Portland, Oregon
With that elevation difference, if there is no significant flow, the static water pressure in the city pipes would be over 100 atmospheres, which clearly isn't possible.
How is water pressure prevented from becoming catastrophically high?


texts: Is it possible to determine plastic hinge location of a frame in SkyCiv? Is it also possible determine moment -curvature relationship curve in SkyCiv? If yes, how?


texts: Activating lights using a motion sensor?

texts: I was wondering how I would configure some sort of setup to get lights like this turn on a timer once activated by a motion sensor. I want them to turn on for about 15 seconds and then turn off once tripped by a motion sensor but I have no engineering experience and I don't know where to start. One of my friends told me I would need to configure an Arduino board setup causing it to shut off power to the lamps after 15s but after extensive research, I'm not even sure that's possible. Is there any way to pull this task off?


texts: Are boxy edges normal in SolidWorks when working with a drawing?

texts: I'm giving SolidWorks a try and am following one of their tutorials on creating a part. When I create circles they are looking a bit "boxy" to me. My graphics card has 512MB of ram and I have checked the rendering settings that I found and everything seems to be OK - but I would have expected something more "circular" and less rough looking, but I'm new to working with CAD - is this normal?


texts: Most efficient airflow pattern to cool a recessed shelf

texts:
I have a recessed shelf which holds three components that each generate heat:

A projector
A computer
An audio power amp

The shelf is located at the top of the wall and open at the front but closed on the 5 other sides.  Because of this, the airflow created by the component fans is simply not enough to cool the space and things are beginning to overheat.

I'd like to install a fan to cool the space but not sure what the best placement and airflow direction would be to cool the space.  One consideration is the direction of the existing projector fans which create a bit of an airflow pattern on their own.  I'd also like to keep the heat inside the house since it's beneficial in the winter.

My question is basically, what is the optimal direction and placement of a single fan in order to exchange the air and cool the space?

EDIT: To clarify, I intend to cut a hole in one of the existing surfaces and install the fan to move air between rooms, and not just to blow air around inside the shelf.


texts: Generating random samples for some concrete structural characteristics

texts:
I want to test a program that performs FRP concrete structural strengthening calculations according to a particular design code.

As inputs for these calculation, there is

existing concrete cross section
concrete compressive strength
existing steel cross section
initial live and dead loads
future dead and live loads after strengthening

I am looking for the best models that describe these random variables. Could you advise on this matter ?


texts: Repairing blind in bathroom: How do spiral springs with 3 revolving drums work?

texts:
I am trying to repair a plissee blind, that does only fold up until half, then stops, no matter how high you push it.
It has a metal-thing holding three metal spirals that can be connected to the plastic drum in the middle. The middle plastic drum has two square-shaped holes where the metal spirals can be connected (see pictures, it's hard to describe).
It also has a kind of shuttle that is connected to the two strings pulling the blind.
The shuttle is connected to the metal-thing via another string. The metal thing should strongly pull the shuttle to the right, so the blind will be kept up (this is the problem).
If you pull the blind down, the shuttle should move left and should be kept left by the weight of the blind.
So far I understand it. But now I have no clue how I can make the metal-thing have that strong pull to the right.
I can pretty much guess how the left and the right metal spiral should be connected to the middle plastic drum, because I could see some dirty marks on the metal thing, caused by the metal spirals moving around.
But I have no clue what to do with the middle metal spiral. Even theoretically, I have no clue about its function, because however I put it, it seems to "do nothing".
Is there anybody out there with a better technical understanding to imagine that spiral spring in practise? I am thankful for every hint or resource, as I could find absolutely nothing online (at least in German; I am missing the right research words in English, as these seem to be kind of special terms).

Edit:


texts: If an airfoil underwent horizontal loading, would it stiffen the airfoil?

texts:
I am designing a wing for a Vertical Takeoff and Landing aircraft. I am trying to choose a wingtip winglet for my aircraft. One of the option is a aft-swept wingtip winglet. However, this structure would cause the horizontal loading of my wing to increase, according to my lecture notes. I am wondering whether this effect could strengthen my wing?
Here is a picture of my aircraft, the red crossed component is a rotation mechanism for my wings


texts: Rayleigh damping in structural mechanics

texts:
In structural mechanics, we often approximate a partial differential equation by a system of ordinary differential equations in matrix form

$$\boldsymbol{M}\ddot{\boldsymbol{q}}(t)+\boldsymbol{B}\dot{\boldsymbol{q}}(t)+\boldsymbol{K}{\boldsymbol{q}}(t)=\boldsymbol{f}(t),$$

in which $\boldsymbol{M}$ is the mass matrix, $\boldsymbol{B}$ is the damping matrix and $\boldsymbol{K}$ is the stiffness matrix. The vector $\boldsymbol{q}(t)$ is the displacement vector which contains the displacements at specific positions and the force vector $\boldsymbol{f}(t)$ does specify the forces applied at the same positions at which the displacements are specified.

It is possible to deduce the mass matrix $\boldsymbol{M}$ and the stiffness matrix $\boldsymbol{K}$ by introducing finite elements. The damping matrix $\boldsymbol{B}$ is not as easy to determine.

A possible model is Rayleigh’s damping model. It is given by

$$\boldsymbol{B}=\alpha \boldsymbol{M} +\beta \boldsymbol{K}.$$

Now what I do not understand is the problem of choosing $\alpha$ and $\beta$. Are they obtained by system identification, while testing measured data with simulated data?


texts: How are common free body diagrams and similar illustrations made?

texts: Over my education I've come across tons of engineering illustrations, most commonly free body diagrams and similar. I still do not know what software(s) is used to generate these. So many look very similar, and I haven't been able to find out how they're made. Does anyone know the common software(s) used for these? I've included some examples


texts:
I'm working with an Arduino Due's two DAC pins.
I want to output to a single 4W 5.7Ohm speaker to test my code, with the intent of eventually outputting to a set of speakers (woofer, mid-range, and tweeter) for better quality for frequencies between 87.31Hz to 3520Hz+.
I'm using the DAC pins in 12 bit mode, with output between .55 - 2.75V @ 3mA according to the linked sources (I know forums aren't definitive sources, but I've cross checked and many forum posts and sites are around this range. 3mA comes from total for all I/O pins of 130mA divided by 42 I/O pins total, not counting the 12 PWMs)
I understand that I need a circuit like the following:

DAC output to "reconstruction filter" to smooth the quantized output.
anti-aliasing filter, possibly the same as above, to remove noise (Nyquist Frequency stuff)
Use an audio-tapered potentiometer for volume control by reducing amplitude of signal.
Removal of both the DC offset and centering the signal on 0v using a capacitor/filter.
Use an OpAmp to as a voltage follower to buffer the Arduino Due from the load of the speakers.
Use an OpAmp (possibly the same one as above) to increase the power of the signal (via an external power source probably, because the Due cant drive much) to a range suitable for the speaker.
A high pass filter to remove unwanted noise from the output.

I will be playing a sample at 16kHz, which I assume means I will have a variable duty cycle and therefore cannot use anything sensitive to this to function properly.
My questions are the following:

Is this overkill for this kind of circuit, or way under the bar for a proper setup?
How do I know where my high pass filter cutoff frequency should be, as my sample is of an acoustic instrument with natural overtones, meaning knowing just the frequency of the root note is not enough.
Without a power source providing positive and negative voltage, is it enough to offset with a capacitor to get a balance on 0v, and is this lost over the OpAmp if it does not have a negative voltage going in? Can I just balance it at the end with a capacitor then?
Is the OpAmp buffer/voltage follower enough to stop my Arduino from dying?

Thanks for the help. I'm new to audio circuits, my experience is in DC and programming the Arduino.


texts:
I´m designing an access control device and I need to place it in a plastic case so it can be easily installed on a wall, for example.
Also, the PCB will have a special coating for humidity protection.
Regarding IP code grading for dust and water protection I would like to know:

If the device is on the outside without protection (roof or similar), would an IP54 plastic case be enough?

If the device is on the outside but it is protected with a roof or similar, would an IP54 plastic case be enough?

If this is not correct, what would be a right IP code grading for the case?


texts: What diameter hole will a twist drill bit of a given size actually make in a piece of metal?

texts:
I have a piston of diameter 0.7 mm exactly and a 0.7 mm drill bit.  Let's call the diameter of the piston $r_1$, the diameter of a hole at the end of a tube $r_0$, and the final-actual diameter of the tube hole $r$.  Then with fluid being pushed by the piston through the hole at the end ($r_0$) I calculate that I need:

$$
\pi (r^2 - r_1^2) \lt \pi r_0^2 \\
\iff r^2 \lt r_1^2 + r_0^2 \\
\iff r \lt \sqrt{r_1^2 + r_0^2}
$$
in order to prevent back-flow in the negative direction of the piston movement.  I'm ignoring gravity.  With $r_0 = $0.05mm, $r_1 = $0.35mm, I come up with:
$r \lt \sqrt{(0.05)^2 + (0.35)^2} \approx 0.3536$.  So can I get a hole that's between 0.7 and 0.7072 mm (preferably closer to 0.7 mm) using a 0.7 mm bit?

It's okay if the tolerance is so tight that the piston gets stuck at room temp, because the piston is a rod of continually fed material that will be melted in the tube.


texts: Why can’t one see for 2nd order system that it is at its stability limit neither in the Nyquist plot nor Bode plot?

texts:
Consider $$\hat{G}(s) = \frac{1}{s^2+s}$$
than the Nyquist plot is

and the Bode plot is

In both plots it seems that the closed-loop system is stable even when the eigenvalues are {0, -1}. For a higher order closed-loop system one can see that a system like

$$\hat{G}(s) = \frac{1}{s^3+s^2+s}$$

is at its stability limit since ne Nquist plots hits the real axis at -1 and in the Bode plot there is no phase reserve when magnitude hits 0. Why dose the Nyquist and the Bode plot fail for a closed-loop system of 2nd order?


texts:
I need to specify a stepper motor to drive a system of gears that isn't yet produced. I have almost no information about the system except that it will involve a stack of planetary gear sets with a common 3/8" shaft, with a total weight of about 100lbs (mixed metal and plastic). It will need to rotate very slowly, about 1 rpm, and occasionally reverse.

I'll be able to get hold of one planetary gear set soon. What would anyone recommend to get a handle on the needed motor? I figured I'd wrap a wire around the shaft and pull it with a fish scale to see how many ounces it takes to move it, then multiply that by the number of sets. Given that value, how could I convert that to a motor spec? I'm assuming that most of the requirement will be in overcoming the initial inertia & friction.


texts: The blade efficiency of a turbine is defined as the ratio of the power extracted from the fluid by the rotor to the power available at the inlet of the rotor. The power available at the inlet of the rotor is given by the sum of the power extracted from the fluid by the rotor and The power available at the outlet of the rotor. In calculating the blade efficiency of a franscis turbine, the power available at the outlet is taken as the kinetic energy outflow rate. why is the effect of vaccum or negative pressure at the outlet of the rotor ignored? Is it neglected??


texts:
What is the meaning of sentence "Measured Data has 30 PPM accuracy"?
I want to know what is the meaning of PPM accuracy.


texts: What is the benefit of additional planetary gears?

texts:
A planetary gear is a gear that rotates not around an axle but around another gear known as a sun gear, or star gear. I have designed prototype systems in the past that used a single planetary gear rotating around a rotating gear. However since then almost every system I've seen using planetary gears have used multiple gears, most commonly in sets of 3, 4, 5 and 6.

What is the mechanical advantages and disadvantages of using multiple planetary gears and what is the optimum number of gears?


texts:
Suppose that we were to install bicycle pedals into a passenger car, say a civic coupe, in such a way that pedaling is as mechanically efficient as riding an ordinary bike.  Further suppose that we have a transmission with whatever the appropriate gearing would be for actually moving the beast under pedal-power.

What would be the maximum speed of such a vehicle for an ordinary operator who puts out about 200W?

The following variables reduce the ambiguity of the problem... Please comment if more info is necessary:

Human power output 200W
Sea level
2019 Honda Civic Coupe
Power lost to friction on gears and whatnot: 0%
Power lost to road friction and air resistance: 100% at peak velocity

UPDATE: To be clear, I am not asking an open-ended "what if" type question.  Specifically, I am not open to arbitrary answers about possible things resulting from a pedal-powered car.  I am specifically interested in its speed limitations, which is a well-grounded physics problem.  This is a "practical, answerable question" in the sense that the force input via human pedal-power and the force applied to the car via friction and air resistance are measurable and reasonably well-known quantities.  Therefore, the maximum speed for a given car propelled by an average human operator should have a well-defined and unambiguous value.  In other words, there is one and only one numerical answer to this question, and it is therefore not open-ended.


texts: How can I build an anti proximity alarm?

texts:
I am trying to build an alarm that works in an opposite way to a security alarm in a shop. In shops RF tags on items set off an alarm as you walk through a detector. I wanted to build alarm that sounded as you move out of range of a detector, rather than into range.

The tags on high value items seem to be simple coils of wire encased in a thin plastic sleeve, they don't appear to have a power source.  I presume they emit a small signal that is enough to trigger the walk through loop.

Basically my gran keeps leaving her keys on the table and walking out the front door and getting locked out. I figured if she had a tag on her key fob that would trigger an alarm on her wrist or bag when she was more than 2 or 3 metres from her keys might solve the problem and save her a fortune in locksmiths!


texts: On the website https://www.ansys.com/academic/students/ansys-student a number of different free softwares are available to be downloaded, but they are all the latest 2021 versions and do not include Ansys 2020 or 2021 R2, only Ansys 2021 R1. Is there a way to download earlier versions or download Ansys 2020 or 2021 R2? I am grateful for any suggestions.


texts: I need a heated surface for a project and was thinking of using one of these  PCB heater beds. But I'd need to drill a few holes in it - can I do this without stopping it working? Thanks


texts: What's the name of a device to simulate an object jumping in the air?

texts:
I want to make a film of a puppet jumping in the air into the water of a lagoon. I am looking for a pad with a spring release timer that I can bury in the sand so it's out of sight from the camera, wait 10 seconds for example, and the spring or coil releases and throws the puppet in the air, making it look like the puppet jumping with its legs. The mechanism is similar to "jack-in-the-box" and all I can find is the fast-food restaurant. I have also found no relevant results with "spring with delay", "spring release with pad", and "spring release with timer".
What is the name of such a device?
Update: Here's a drawing for what I want to achieve:

I am looking for the name of the complete mechanism, including the pad for launching and the release timer.


texts:
Im new to rotary solenoids and I had like to understand the definition of stroke.

For example, some rotary solenoid has in its technical information a parameter called stroke options and it says 25-45 degrees.

Here is a link to some example - link

Does it mean that the solenoid has a maximum rotation of 25 or 45 degrees but I can also use limits of +-10 for example it will have to be +- 25/45 degrees?

Thank you.


texts: I was trying to model experimentally the interdiffusion of two miscible liquids. Is there an optical method to find out the extent of diffusion; the addition of fluorescing agent into any of the two fluids would work, but will it not influence the diffusion process by changing the chemistry of the fluid itself?


texts: Is there a way to quantify the amount of radiofrequency interference? Do any units exist that quantifies how much radiofrequency interference is there?


texts: What type to mechanical joint to achive Slide then Rotation motion

texts:
I have two parts (Green and red fixed) i want to connect them with a joint (Blue) that permit the green one to slide outwards then rotate.
Side View (Right part)

a simple pivot point doesn't work since the  two piece will collide with each other.
I thought about using 4-bars linkage, but couldn't figure out the right combination to give the path of motion I'm looking for


texts: What function does this device perform better than a flat, horizontal bench?

texts: I am curious to understand the engineering and design principles behind this device, which I will refer to as the half-assed rest, because it seems to be an inferior design of a normal chair or bench. It seems to be designed explicitly to be hostile to the homeless by being designed this way, but perhaps I’m wrong in my assumptions about its intended function.


texts:
I'm working on developing a speed controller for a motor that is geared to rotate a mass. Currently, the motor in question has a step voltage applied to it and moves the mass at a relatively slow speed. As it has been explained to me, applying a step voltage to a motor would create a large inductive load due to a high value of dv/dt, but as a novice in motors, I have been unable to find any constitutive relationship defining this rule.

Additionally, if I am attempting to ramp from a slow wind-up speed, to a high operating speed, and finally to a slow wind-down speed - what are some things I should take into consideration when designing the controller for this device.

I am definitely a novice in the field of controller design and am just beginning to learn all of this. I will be using labview.

Thanks!


texts: Why is the tv playing if the carrier frequencies in our RF project appear unsupported?

texts:
My group made an RCA video/audio to RF modulator for a school project. The video is a NTSC composite video signal. Here is a clip of our tv receiving the output of the project on NTSC channel 2:

https://drive.google.com/open?id=1-1xRHI8razjYvvptTsPsPBHt8T0z-yi5

In the video, we use an usb-to-hdmi adapter from Raycue, a hdmi-to-composite video/audio adaptor from Ozvavzk, and a tv from Thomson Consumer Electronics (model 19GT241).

I made measurements of our audio and carrier signals using a Siglent SDS 1202X-E Oscilloscope and a $12 active probe (which is listed on eBay as "RF Active Probe 0.1-1500 MHz").

I measured the audio carrier signal to be 55.2 MHz and I measured the video carrier signal to be 59.2 MHz. I did a FFT of the two signals - the audio's bandwidth looks narrow like a dirac-delta function and the video's bandwidth is about 500 KHz wide.

According to the "Pan-American television frequencies" article on Wikipedia, if we are to transmit on channel 2, then our audio and video carrier signals should be tuned to 59.75 MHz and 55.25 MHz, respectively. I can't find information that supports the carrier frequencies of our project are alternative ones for channel 2. Why is our tv playing audio and video if the carrier frequencies in our RF project are not tuned according to the article?


texts:
I was wondering, what are the factors to consider or how to find the required technical specifications for the new machine?

For example, if we consider a design of horizontal centrifugal casting machine with orbitary dimensions, Let suppose I do not know the dimensions of the machine. How do I calculate

centrifugal force required?
Torque of the Motor?
Power required to rotate the rotating tube?

To calculate the Centrifugal force, $F_c=mv^2 / r$ or $F_c=M\omega^2r$.
where, angular velocity, $\omega=2\pi N/60$.

Hence, in order to calculate the centrifugal force we need to have the Speed ($N$) of the rotating tube. But, how do we know that whether the assumed Speed is enough for the casting process? Using this $F_c$, torque and power can be calculated, $T=F_c*r$ and $P=2\pi NT/60$.

Assuming $N=200\text{ rpm}$, I have carried out some calculations which are as follows, $\omega=2\pi N/60=20.94\text{ rad/s} = 3.33\text{ rps}$.

Let, part to be cast is Aluminium and has $\phi_{out}=20\text{ cm}$, $\phi_{in}=10\text{ cm}$ and $L=50\text{ cm}$. Then, $V=3750\pi\text{ cm}^3$ and $m=31.83\text{ kg}$. Hence, from $F_c=M\omega^2r=173.13\text{ N}$ (considering inner radius of the cast part as the Minimum distance need to achieve which 5 cm).

Dimensions of rotating tube is assumed as $\phi_{out}=30\text{ cm}$ and $\phi_{in}=20\text{ cm}$ and $L=50\text{ cm}$. Torque required $T=173.13\cdot0.15=25.96\text{ Nm}$ (considering radius as the outer radius of the rotating tube that is 15 cm).

Power, $P=543.70\text{ W}$.

Are the steps I have performed are correct? If so, How do I know that assumed $N$ is the suitable value for the present machine or what is the usual Speed of the rotating tube in horizontal casting machine considered?

If not, how do I approach when there are several unknowns or dependencies present in the system, for example centrifugal force depends on angular velocity which in turn depended on speed of the rotating tube.


texts: Plastic Vacuum Cleaner Part -- Why did they design it this way?

texts:
I've designed a whole lot of different parts and products in my time: Plastic, metal, lighting products, electrical products and automotive parts.  I generally can look at a product and figure out why did they do that.  Here's one that has me baffled.

Its the bottom of a consumer grade vacuum cleaner.  Molded in the plastic is a slot (which I'd generally refer to as a bayonet mount).  I can see that the mount definitely is out of normal die draw (large undercut) and requires a slide (and that tooling is definitely not cheap...)  I can't figure out what that mount is for.  It doesn't seem to match the cord or any of the accessories that I can see.

Any ideas on what that 'bayonet mount' is for?  Why would the manufacturer spend real investment dollars for tooling something so obtuse?

Possible

Something they use in their manufacturing process?
Something to ensure the part control during the molding ejection process from the die? Note: I've seen molded parts get stuck in the wrong half of the tool and that can be quite ugly...  The other side of the part is heavily engineered, with lots of ribs and other details.
Could it be for planting a sales/marketing sign when the product is sitting in a sales display?

Any ideas?


texts: Are abandoned nuclear smoke stacks strong enough to be filled with water (for pumped storage)?

texts:
I noticed that there are a growing number of abandoned stacks of this type:

Image source.

I wonder if they are physically strong enough to hold water, for use in pumped storage:


texts: How to increase maximum rotational speed limit of a reduction gearbox?

texts:
Reduction gearboxes made of machine steel gear have a maximum limit to prevent changing their physical properties (softening). They change their properties as a result of the temperature increase which is subject of many variables: friction between gear teeth, ambient temperature, quality of bearings are among the main dependencies. The most typical engineering solutions are such as making gear of different stronger materials which withstands higher temperatures, oil bath or liquid cooling.

I want to know what are possible ways to increase the durability of the same gear in a given gearbox. I can heat the gear pieces to a high temperature using torch that makes it "tempered" or "annealed" making it stronger. Which one of those known processes intended specifically for this purpose and how do I find the procedure (heating, followed by cooling or not...) and temperatures needed to alter the structure of the steel?

Also are there other ways to increase the rotational speed limit beside gear tempering and gearbox cooling? Assume for this topic that bearings do not limit the speed.


texts: In the Principle of Virtual Work, what's the meaning of virtual?

texts:
I'll talk here of the principal of virtual work in the context of virtual forces.

The idea of virtual work may seem strange at first. But it's one of the most fascinating I've encountered.

The problem I had at first with the idea of a set of virtual forces was the "definition" given in most textbooks. Usually, it goes something like this: "In this statement, the term virtual means the forces are not related to the deformations of the body."

But, as far as I know, the forces applied to a body are always related to the deformations. This relationship may be more or less complicated, but it's a relationship that exists. This made me think that virtual forces are forces that are virtual or imaginary in a litteral sense. We imagine them to be there, but they're actually not there. So, whenever you find a "definition" such as the one you find above, all you'll be reading is something like: "a virtual force is a force that is virtual".

It's a childish idea (in the best sense of the word childish), but many applications show it to be a very powerfull one: amazingly, it works.

Would you agree with meaning of virtual force such as I wrote it?


texts: I was just wondering for this question if you can see anything wrong with it. The answer in the textbook is 220MPa but i get 193MPa


texts: column bending stress under vertical earthquake load

texts:
In
Fema national US&R response system - Structrual collapse technicican training manual

It says:

"There are also vertical loads generated in a structure by earthquake shaking, but as mentioned previously, these forces rarely overload the vertical load resisting system. Earthquake induced vertical forces have caused damage to heavy concrete structures with high dead load compared to design live load. These vertical forces also increase the chance of collapse in concrete frame buildings due to either increased or decreased compression forces in the columns. (Increased compression that overloads columns or decreased compression that reduces column bending strength.)"

I didn't understand the second part of last sentence in paranthesis, where it says "....or decreases compression that reduces column bending strength".... what does this mean and why?


texts: How to support height extender on a rail?

texts:
I've got an 1/8" thick steel rail with 1.5" diameter and 15' in length sitting on two 5/32" thick steel rails with 2.5" diameter and 100" in length 14' apart:

I want to add a diagonal support for a rope that is supported with 3/32" thick wires. I started into the initial design, and stopped here because I don't feel I'm heading in the right direction:

  How can I structurally strengthen a support to a rail with wires to allow 164" of vertical clearance from the rail to the extended end of said support? Giving a total of ~264" of ground-to-end rope length.

If it's not clear, the rope will hang down to the ground from the end of the extending support rail. Also, if it's of any relevance, the three rails in the first image are schematics from the actual existing physical structure that is already welded together and cemented into the ground (18" deep).

This is where I am now:

Imagining, here, that the two lower triangular shaped supports are rails to be welded and shaped to the curvature of the rails they attach to. The area below and between the main rails are used for gymnastic rings, some hanging ab straps, and a lowered hanging pull up bar. I mention this because the design, as it stands, seems to clutter up the "work area," if you will.


texts:
I'm having a difficult time identifying a resistor's value as I can't find the golden / silver tolerance line.

The problem is that I can't see a silver or gold line here! They're both brown on both sides


texts: Get results of output for each one value of the input - MATLAB ODE

texts:
I am simulating a mass - damper - system in Matlab and I have the following vector (1x100) as input to my system:

ut = linspace(0, 10);
u = 5 * sin(2 * ut) + 10.5; % input of our system - external force

Now, I want to take the value of the output for each value of the input vector using this differential equation:

function dx = odefun_4(t,x)
    m = 15;
    b = 0.2;
    k = 2;
    dx = [x(2); u/m - (b/m)*x(2) - (k/m)*x(1)];
end

which is called from my main .m file like this:

[t,X] = ode45(@odefun_4, [0 10], [0;0])

I tried to pass the u vector by making it global variable but I get an error stating: Dimensions of arrays being concatenated not consistent.
I also tried to set the Refine parameter using odeset and the options argument of ode45 solver but still don't get the desired results. I could really use some help.


texts: I have some plungers made of 38CrNiMoAlA. Their required hardness to be achieved via quenching/tempering is 51 HRC. I've scoured our technical order for heat treatment of steel alloys but the material is not there. I even checked the internet, it doesn't seem to exist at all. The closest I could get was 38CrMoAlA. Please help if you know this material or something close to it.


texts: Does this PID-like algorithm make any sense for a solar inverter?

texts:
The application

I want to implement the control of a photovoltaic inverter. The goal would be to keep the consumption of a microgrid (the power absorbed from the grid) to a constant value.

Notes:

I can only measure the grid load and the PV inverter setpoint. I cannot measure the PV production.
My measuring frequency is about 1s

Some numbers: let's say that I have a load varying (quite fast) between 500 and 1000W and a 500W solar panel, and I want to keep the power absorbed from the grid at ~500W (this is my target). Thus, if the measured grid load is at 769W, the PV inverter should provide 769-500=269W (inverter setpoint).

This would seem trivial, in the sense that I can control the inverter and tell it to provide exactly 269W. However, due to several delays (communication latency, inverter command reception time and the time it takes to adjust to the new inverter setpoint), it might take several seconds for the new command to actually take place: by the time the 269W setpoint is reached, the new requested value will probably be different (as the measured load varies).

The algorithm

I tried implementing a PID-like algorithm to fix this, and it seems to work more or less fine. However, compared to normal PIDs, there is a key difference. In my algorithm, I measure the grid load (PV = Process Variable) and calculate the correction that needs to be applied to the inverter setpoint (SP) based on how far the PV is from the target (T):

$E = PV - T$

$C_P = k_P \times E$

$C_I = k_I \times \int_{0}^{now} E(t) \, dt
 $

$C_D = k_D \times \frac{\partial E}{\partial t}$

$newSP = SP - (C_P + C_I + C_D) $,

where $k_P$, $k_I$ and $k_D$ are tuning constants and $newSP$ is my new setpoint (control signal) for the PV inverter. This is different from the usual PID process, since I calculate a correction to apply to the current setpoint, and not the setpoint directly. I can do this since the PV and the SP refer to the same physical quantity, and it seems to make more sense this way. This also actually reduces or eliminates the need for an integral component, since by design we have no steady-state error that needs to be compensated for.

However, I do not have any PID training, nor I have tried producing a first-order plus deadtime model of this system. I might be completely wrong.

Testing

I've been testing this setup and it works well for this application, better than I could make a normal PID work (but to be fair I have zero experience on tuning a PID). As expected, I found that in this algorithm the integral component is mostly harmful, as it only leads to oscillations: the P and I components do not need to balance each other anymore like on a normal PID, since the P correction goes to 0 once we reach the desired target, and the setpoint becomes stable. Thus, I have found myself using mostly a PD control.

Questions

Does this PID-like algorithm make any sense in this case? In particular, the choice to act on the correction value instead of the PV value itself?
Is this a standard control method? I would like to find some base-level theory on this.
Is this application more suited to some other control mechanism?


texts:
I have an O-shaped aluminum (7075) profile WxDxH - 40mm x 200mm x 25mm
The inner channel is 20 mm wide and 10 mm deep - runs through the entire length of the bar.

Inside, I have a 20 mm x 10 mm bar (also Al 7075). As you can see from the attached picture, on the opposite face there's a hole in which a flat screw is used to fasten the two pieces in position.

This telescopic mechanism needs to withstand large loads >50 kg (>110 lbs) on both ends and I'm worried that using only a screw would mean that there will be slippage.

Is there a better way to design a secure clamp for such a telescoping mechanism? I need to be able to do fine positioning and have the confidence that it won't move.

Thanks in advance for your help.


texts: What happens if one pumps from municipal water supply during power outage?

texts:
During the 2003 Northeast blackout I had the misfortune of being in Manhattan.  After about 12 hours municipal water pressure was gone – I assume because the pressure is supplied from water towers or reservoirs that are fed by electric pumps.

In such a condition, what would happen if someone determined to get water from a tap connected a (perhaps gas-powered) pump to a municipal water supply line?

I know that older municipal systems may often lack functional backflow check valves everywhere.  In such an event, it seems likely that the pump would suck air into the system through any other consumer taps that were left open.  So it would get whatever water is between it and the closest open taps, and then it would pull get air.

Therefore, for purpose of this question let's assume that all outlets are either closed or else protected with working backflow valves.  Will the pump be able to pull water all the way from the raw water supply, through whatever treatment facilities and supply pumps normally feed the mains, and finally out the service tap to which it is connected?

I suspect not, but I have no idea of where it would stop.  (For example, if municipal water is always fed by gravity from a reservoir of treated water, then presumably when the reservoir runs dry the utility would lock it to prevent air from entering the supply system.  But I have no idea what facilities or mechanisms are upstream in a major water utility system.)


texts: What is a good sensing element to monitor corrosion in a bridge structural health monitoring system?

texts:
The question relating to measuring structural integrity of bridges brought awareness to six categories of structural health monitoring of bridges. They are

Bridge foundations
Concrete superstructures
Movable bridges
Steel fatigue
Structural dynamics
Corrosion protection

Question:

What is a good sensing element to measure bridge corrosion? What characteristics in this sensing element make it a good candidate for corrosion monitoring? Is an ultrasonic transducer a good candidate?


texts: What are the challenges in building a 'sports car' frame and body?

texts:
Clearly if it were easy to produce attractive looking cars for cheap, there would be a lot more 'modern' and good looking cars on the road.  While beauty certainly is in the eye of the beholder in many respects, I would rather have a car that looks more like a Porsche than a Prius.

So why don't most automotive companies manufacture cars that look as good as a sports car?  Specifically what is the major cost driver for the production of a sports car's body?


texts: Technical obstacles in making a noiseless thermic motor?

texts:
There seems to be no noiseless thermic motor for cars or motorcycles on the market.

Is there a technical obstacle at making such a product ?

Is there a way to isolate/eliminate noises from the explosion process and from the moving parts ?


texts: gain margin and phase margin - significance

texts:
While gain margin(s) and phase margin(s) in Bode Plots of open loop transfer functions are defined at particular frequencies (when they exist) --- such as phase margin is defined at frequencies where the dB gain cuts through 0 dB ------ may I ask if these particular frequencies (ie. gain margin frequencies and phase margin frequencies) are points of interest only because we can conveniently define them at these frequencies?

I was thinking that, if we choose a particular frequency in a Bode Plot where the dB gain curve does not cut through 0 dB, and where the phase curve does not cut through -180 degrees, then there would simply be TWO degrees of freedom, such that a particular combination of additional gain and additional phase would push the system to an unstable condition (or onset of instability).

Do gain margins and phase margins also (in some way) cover other regions of the Bode Plot - aside from the very specific frequencies where the gain margin(s) and phase margin(s) are defined?

Thanks all!


texts: IC engine where the piston is the spark plug

texts:
I recently had an idea about the design of an internal combustion engine. Normally, the spark must be timed using some kind of circuit, but if there was a "spike" on the piston:

then would there be no need for a specialized ignition system?

Of course, there would have to be some kind of insulation between the spike and the casing, and between the spike and the piston.


texts:
In the figure below we have that the gear $A$ is has an fixed axis and has the radius of $R_a = 0,1m$ and, in the instant represented in the figure spins clock-wise with angular velocity $\omega_a = 4\text{rad}/s$. The gear $C$  has radius $R_c = 0,1m$ and gear $D$ has radius $R_d =0,2m$ and they has been firmly weld each other. An arm of length $0,2m$ connects the rotation axis of $A$ and $C$ and $D$. The $B$ gear spins around $A$ but without any connection with $A$ and has radius $R_b = 0,4m$. In the instant presented by the figure $B$ spins in the counter clock-wise and has angular velocity of $\omega_b = 1\text{rad}/s$.

The question I have is

  What is the velocity of the center of gears $C$ and $D$ expressed in $m/s$?

My attempt: I've tried to derive the velocity of the point $v_P$ where $P$ is the point of connection between $A$ and $C$ and I've tried to encounter the angular velocity of $C$ and $D$ using that for a point $Q$ of $B$ must have the velocity equal

$$v_q = \omega_a(L/2) = 0,4m/s$$

Witch leads us to the angular velocity

$$\omega_c = \omega_d = v_q/L$$

But still I couldn't find the velocity using that. Someone have a hint?


texts: Why do heat pumps take more time to heat up a space than resistive heaters?

texts:
I was wondering why do heat pumps heat a place so slowly as compared to the resistive heaters?
(This thought just came to my mind when upon ironing my shirt the iron became hot quickly which is a resistive heater while the back of my refrigerator takes time to heat up which is a heat pump example)


texts: Flowcharts in PLCs, garage door design problem

texts:
In Automating Manufacturing systems by Hugh Jack, Chapter 11: Flowchart based design, 11.6: practice problems, question number 3. I've attached a photo of the book's solution (link 1) and an other one of my own solution (link 2). My problem with the book's solution is that after the start block, assuming the door is already closed, then the user would have to press the button twice according to the flowchart for the door to open.

The question is:

"Design a garage door controller using a flowchart. The behavior of the garage door controller is as follows, - there is a single button in the garage, and a single button remote control. - when the button is pushed the door will move up or down. - if the button is pushed once while moving, the door will stop, a second push will start motion again in the opposite direction. - there are top/bottom limit switches to stop the motion of the door. - there is a light beam across the bottom of the door. If the beam is cut while the door is closing the door will stop and reverse. - there is a garage light that will be on for 5 minutes after the door opens or closes."

Link 1:http://www.4shared.com/photo/YPA5d2kYce/image.html
Link 2:http://www.4shared.com/photo/9yyZRsj8ba/image.html

Am I right? Or what am I missing? Do I have to assume a certain position of the object whenever faced with such type of questions?