texts: What would happen if we tried to run a motor in space when it is not attached to anything to provide support to it?

texts:
I know that when a motor runs it generates torque and that torque can be used to do useful work. On the other hand, the motor needs strong support that absorbs the reaction torque. In our case let us assume that that support is provided by a workshop floor on which the motor is firmly attached (the workshop floor is essentially the Earth).  The Earth receives the reaction torque and being the massive object it is, it doesn't move.

Now let us imagine that we took our motor into space where there is no gravitational field.  What would happen if we tried to run the motor?  Assuming the motor is powered by a battery pack. The battery pack and its control electronics are neatly packed around the stator.

Would the motor rotate at all?  Would the rotor and the stator rotate in opposite directions? Would there be a transfer of energy from the batteries to rotational mechanical energy?


texts: Identifying coefficients to determine cutting speed for PA6 plastic

texts:
As part of a study at work, I have to calculate the cutting speed and feed rates for cutting plastic.

I have found a formula for cutting speed calculation:

$$v={{C_V*K}\over{T^m+t^{x_v}+s^{y_v}}}$$

where:

$C_V$ is a coefficient that is dependent on processing conditions;
$m$ is the specific retention figure;
$x_v,\ y_v$ are coefficients relative to the cutting depth and feed;
$K$ is a correction coefficient;
$T$ is sharpness resistance; and
$s$ is the feed rate.

variable descriptions may not be completely correct as they were translated from Russian

For cutting metal there are lots of tables and sources for finding the coefficients but I can't find any for cutting plastic.

How can I calculate the cutting speed for plastic? Is there a different formula that doesn't involve these coefficients, or another method I can use to identify the coefficients?


texts: Can I make a fishing line going through a small hole waterproof?

texts:
Here's the setup, going through those four valves will be some fluid, probably water, but I need some fishing line going through this cylinder to be sealed.  The line is anchored at two points, the top and bottom, and will be used to draw two points together.  This apparatus is to heat and cool wound up fishing line, as that can be used as a muscle fiber.  When hot water is applied, it contracts, when cool water is applied, it expands.  This does mean that the line will be moving some percentage of the length, which may also mean that the diameter will change slightly.

Fishing Line Makes for Superhuman Artificial Muscles


texts: At what volume would air bubbles become static in a fluid with viscosity of 7000cps

texts:
I would appreciate any help with this as its been a few years since my fluid dynamics courses at University!
Basically I am trying to determine the cause of voids that we are seeing in a set resin.
There are a multitude of other influences at play including venting and the geometry of the cavity that is being filled, but this made me curious about the movement of air through this resin during application and if under normal atmospheric application (not under vacuum) if this would always be inherent to the process.
As stated, the cps value of the resin is 7000, would someone be able to point me in the direction of a formula which I can use in excel to specify the volume of the air bubbles to predict their velocity in this fluid?
Thanks


texts:
Define "production tooling"?
What are its advantages?
And why production tooling is essential for manufacturing?


texts: how does this z-axis micro-adjust lead-screw design work

texts:
The picture (which I found on the web without any accompanying explanatory text) shows a home-made z-axis micro-adjust lead-screw add-on to the vertical milling attachment of a vintage hobbyist lathe.

The greenish motor-and-spindle-mount casting rides up and down on the black post, sandwiched between two plates, which ride up and down on two smaller posts.

I can't quite make out whether there is a threaded bushing of some kind where the arrows are pointing. How would that aspect of the design typically be engineered?

I'm thinking that if those plates were simply threaded, without some kind of insert, you could have a somewhat loose and sloppy sandwich.


texts: What IPC mechanisms exist for the i.MX 7 (or i.MX 6) multi-core processors?

texts:
I'm considering using the i.MX 7 processor for a new design.  The overall architecture appears to be similar to the i.MX 6, at least from comparing the block diagrams.

What mechanisms exist for communication between the Cortex-M4 core and the Cortex-A7 core(s)?  Does the stock Linux kernel provide any such mechanisms (which likely would assume a specific RTOS or firmware running on the M4), or is this custom firmware for both processors in Freescale's offerings?  The processors appear to share pretty much everything, so I would imagine you could implement a shared memory buffer with an atomic semaphore, or something along those lines.

Ideally, I would like to have the M4 firmware "take over" some peripherals while the A7 processor is in a low-power mode (i.e. manage periodic communication transfers or some data analysis until something "interesting" happens that requires the A7 to do something).  From the block diagrams and the i.MX 6 SoloX reference manual, it appears the hardware doesn't preclude this.


texts:
I'm having trouble welding the inner corners of my material. Welding material is sometimes deposited on either one side or both sides, but never really connecting the two parts.

Side/flat welds work fine:

But those pesky inner corners don't:

The material I'm using is 1mm thick 16x16mm square steel tubing.
Welding settings are 20 Amps DC electrode positive and welding electrode is 1.6mm steel.

Am I doing something wrong? Is there a trick to this I'm missing?


texts:
I have created a simple serial robot with some servos and CAD.

Each joint has 180 degrees of freedom, where they all have 180 degrees of freedom.
I haven't specified where the 180 degrees of freedom actually is practically because that range is adjustable to what is sensible, which I am not sure about.

I really want to be able to control the end effector with two joysticks, one for x & y axis and one for z axis. Because right now (like all other youtube videos) I can only control one servo at a time...
So I understand I'll need to use some rotation matrices and stuff to make this work but I don't know where to start!

The textbooks I have are quite dense mathematically and too much for just a small part of the overall project, can someone please let me know what is the easiest way to achieve this or point me in the right direction?
More than happy to have a chat outside of stack exchange if someone is willing to somewhat walk me through it.
Cheers!


texts: Calculating Load Inertia in a Leadscrew System

texts:
Three common terms used in leadscrews are lead, # of starts, pitch. There definitions are usually as follows:

Lead usually refers to the amount of linear travel when the leadscrew
turns one revolution.
# of Starts refers to the number of independent threads along the length of the leadscrew.
Pitch refers to the distance between threads. In leadscrew with one start, pitch = lead. With multiple starts pitch = lead / # starts.

In many leadscrew catalogues, the equation listed for translating a load's linear mass into angular inertia is:

$ J_{load} = m\times({\frac{1}{2\pi p}})^2$

where:

$m$ is the mass of the load.

$p$ is the pitch in threads per inch.

My main issue here is that the units are threads per unit length instead of length per thread. The mix in nomenclature here is very confusing. In a leadscrew with one start, I can easily do $\frac{1}{lead}$ and plug that as $p$ into the equation. But what about when there are multiple starts? Do I still use $\frac{1}{lead}$, or $\frac{1}{\#ofstarts\times lead}$? What is the derivation of this equation?


texts: Failure of MOSFET-Based Capacitor Dump Circuit After 168 Joules...Why? Parasitics? Thermal-Transient-Land? Jupiter?

texts:
In both simulation and reality, I'm simply unable to get this circuit to oscillate in a way that creates extra power dissipation. The only direction I can get it to go, is less power dissipation due to I think two things: 1). The good high-frequency gain of the 2N7000 and 2). The severe restriction on available current to charge Q1's gate (~340uA @ Vbuss = 340VDC). My biggest concern are transients that could be coupled onto Q1's gate via its C_gd (Miller) capacitance so in LTspice, I've inserted PCB and external-wiring inductances around Q1 and Q2, and modified these inductances in many different ways while pushing transients into the system. My hope was that something goes awry, but the current, under the shamefully few conditions that I know of to consider, seems to me to be truly clamped to around 700mA maximum, thus placing a hard limit on Q1's power dissipation at about 250W or less.
As soon as my microcontroller hits the "DUMP" button (turning off the PC817 optocoupler, hence allowing Q1's gate charge up) Q1 fails catastrophically. The three-ohm resistor makes an alright fuse, keeping the 0.6 kilojoules mostly in the capacitors unless a flying piece of this resistor-fuse gets across the buss terminals, in which case the threshold-of-hearing in my left ear went up a little last night.
280VDC remained on the buss after failure, so it took (starting_energy_578J - end_energy_392J) 186 joules to kill it.
Why is this too much to ask from a Minibloc? Either transient thermal parameters are coming into play here that I've missed, or there's sustained oscillation that I've missed.
Tj starting temp = heatsink starting temp = 30 degrees C.
Heatsink: 1/4" thick anodized Aluminium, 4" x 5", 1.5" fins.
Looking forward to your response; thanks.


texts: Unbraced Length for Lateral Torsional Buckling vs. Yield Strength

texts:
The AISC 360-10 Specification for Structural Steel Buildings gives provisions for calculating the maximum unbraced length of a compression flange that separates yielding moment from lateral torsional buckling (LTB).  This formula is (AISC 360-10, Eqn. F2-5):

$$ L_p = 1.76r_y\sqrt{\frac{E}{F_y}} $$

where

$L_p =$ limiting length that separates full yield moment and LTB
$r_y =$ radius of gyration about the $y$-axis
$E =$ Young's modulus
$F_y =$ yield strength of material

Assuming that one is using regular structural steel, the Young's modulus of the material is assumed to be the same regardless of steel grade.

This equation works out such that a steel with a lower yield strength may actually be braced at a lesser interval than one with a higher yield strength.  In other words, given the same beam size, the material with the higher yield strength buckles first.

I have also found this to be applicable to design using the ASME Boiler & Pressure Vessel code, specifically Division III, Subsection NF for supports.  With temperature effects on yield strength and Young's modulus taken into account, it's possible that a member at an elevated temperature may buckle at a longer length than one at room temperature.

This seems counter-intuitive to me.  Why would a weaker material exhibit less LTB action with the same given length?


texts: Convergent-Divergent Nozzle Design from Exhaust Velocity

texts:
I'm working on designing a Cold Spray system that uses a convergent-divergent nozzle to achieve a 800 m/s exhaust velocity.  I'm assuming 400 psi nitrogen at room temperature is provided at the inlet of the nozzle.  The throat area is 0.0859 square inches (tiny, I know).

$$
\begin{align}
  \dot{m} &= \rho\ v\ A \\
  \rho &= 31.920\ \frac{\text{kg}}{\text{m}^3} \text{(N}_2\text{ at 400 psi)},\\
  v &= 353.575\ \frac{\text{m}}{\text{s}} \text{(speed of sound at 400 psi)},\\
  A &= 5.54*10^{-5}\ \text{m}^2,\\
  \Rightarrow\qquad\dot{m}&=0.625\ \frac{\text{kg}}{\text{s}}
\end{align}
$$

assuming $M = 1$ in the throat.

This figure seems absurdly large.  Can someone shed some light on the situation?


texts: Stress Tensor decomposition into Compression & Tensile forces

texts:
I'm working on a project that does a finite element simulation of a mesh. I can output the stress tensor at each node, but I'm not so sure how to implement failure criteria.

If my material is brittle, say concrete, what's the best way to identify failure?

My current approach is to compute the von mises stress and compare against the compressive yield strength of the material, however this is completely ignoring the possibility that some portions of the mesh might be under tensile stresses for which the yield strength might be much lower.

Is it possible to resolve the stress tensor into tensile and compressive components?

Thanks!
Clayton


texts: Why is a cart with swiveling casters in front stable, but not if the swiveling casters are in back?

texts:
Consider a four-wheeled cart that has swiveling casters for the two front wheels, and has wheels that don't swivel in back.  For example, a common shopping cart, or trolley if you prefer.  If such a cart is pushed and let go, it will continue to roll in the same general direction, and so I'll call it stable.

On the other hand, if the same cart is turned around, pushed, and let go, then the cart won't continue in the same direction for long; it has a tendency to spin around, so I'll call it unstable.

Why is a cart with swiveling casters in front stable, but is unstable when the same cart is turned around?


texts: Is it possible to calculate Young's Modulus of Clay from load-controlled tests?

texts:
I'm trying to get the compressive strength (and Young's modulus) of a clay sample.

The method I found is called 'Unconfined Compressive Strength of Cohesive Soil'. According to ASTM D2166M, I have to set the loading rate to 0.5-2%/min (axial strain).

The machine I have though, is stress-controlled. It measures the load in Pa/s.

Since concrete samples can be tested through a similar method; is there a method that I can use to measure the elastic modulus and/or compressive strength of the clay using something with a rate of Pa/s?

For example, if I set the loading to something very low (e.g 1Pa/s) will I get acceptable results?
(Note: for concrete it is acceptable to use 0.15MPa/s)


texts: Defining the heap and stack size for an ARM Cortex-M4 microcontroller?

texts:
I have been working on and off on small embedded systems project on and off. Some of these projects used an ARM Cortex-M4 base processor. In the project folder there is a startup.s file. Inside that file I noted the following two command lines.

;******************************************************************************
;
; <o> Stack Size (in Bytes) <0x0-0xFFFFFFFF:8>
;
;******************************************************************************
Stack   EQU     0x00000400

;******************************************************************************
;
; <o> Heap Size (in Bytes) <0x0-0xFFFFFFFF:8>
;
;******************************************************************************
Heap    EQU     0x00000000

How does one define the size of the heap and stack for a microcontroller? Is there any specific information in the datasheet to guide to arrive at the correct value? If so, what should one look for in the datasheet?

References:

Decoding the Startup file for ARM Cortex M4
Default stack/heap sizes


texts: The design of precast concrete-- are they the same with cast-in situ design?

texts:
I am curious as to how different is precast concrete design than conventional cast-in situ reinforced concrete design as far as structural engineering is concerned.

To my mind, they should be the same, because precast is essentially using the same materials as cast-in situ, with the same material characteristics. The only difference between them is just one is casted in batch in a factory, and another is casted on site.

Am I right? What does Euro Code or ACI say about it?


texts: I have developed a second order transfer function model for a permanent magnet dc motor in terms of speed and voltage. I had performed open loop no load experiments on the dc motor and derived the parameters. When I experimentally apply a 12 V to the dc motor the speed that I get does not match with the simulation results obtained from the developed model. How do one validate the open loop transfer function model? Should I use the loaded condition values of voltage and speed for validation


texts: polar moment of inertia for compound shape

texts:
I have a shape that I'd like to calculate the polar moment of inertia for:

the diameter is 600mm; the hexagon in the middle sides are 70mm each; the holes around the hexagon are 130mm from the center of the disk and they are 16mm.

$$ \frac{\pi D^4}{32} - \frac{5\sqrt3}{8}s^4$$

How can I remove the 5 holes from the calculation? Is that even something that's done?

[EDIT]
The disk is 30mm thickness.
The mass of the disk is  66.5Kg

The mass of the small holes is total 0.3Kg

The hexagon mass is 3Kg

weight without holes is 66Kg

mass with the circular cutouts is 66.5-0.3 = 66.2kg
mass with the hexagon cutout is 66.5-3 = 63.5Kg
mass with all the cutouts is 63.3Kg

Which percent change in weight would help calculate the polar moment of inertia for this shape?


texts: Determine the reactions on supports A and C and write the functions of the internal forces for the beam sections AB

texts:
The figure shows a metallic structure composed of two beams $AB$ and $BC$ connected to each other by a pin in $B$, the structure being supported in A and C through fixed supports. In the AB beam, a constant distributed load $ w= 300 N /m$ and a torque counterclockwise $M_D = 600 Nm$ are applied. Disregard the proper weight of the structure
Determine the reactions on supports $A$ and $C$ and write the functions of the internal forces for the beam sections $AB$

I've done this free body diagramm

Then i got $R(Ax)=0$ and $R(Ay)=0 $and $R(Cy)=800N$, $R(Ay)=1000N$,$ F=-800N$
But in the solutions they said that $R(Ax)=-1920N $and that$ R(Cx)=1920 N$
How to i get to this results?
For the writing the internal forces for the beam i've calculated correctly for $0<x<3$ but for $3<x<6$ i am not getting the correct result (the correct result $V(x) = -300 x+ 1000$ ; $M(x) = -150 x^2 +1000 x -600$)
However i got

and i know that this is wrong because $d/dx M(x)$ is not igual to $V(x)$
Could someone help me?
Edit: i notice that i forget to draw a Force in X for B

UPDATE: i already understand why my body diagramm for 3<x<6 and why my expression for V(x) and M(x) are wrong (i forgot to draw the moment and i should't have drawn the 800 force and the (x-3) is also incorrect)


texts: Best way to maintain flow of fluid under head?

texts:
I have a crucible with molten metal flowing under its own head. As per torricelli's law the velocity of the fluid would be $\sqrt{2gh}$.

Is there any mechanism with which I can maintain a constant flow rate of my choice?


texts:
Current State
Currently I have designed a coffee roaster that mostly uses the stainless steel tri clamps / tubes that many brewers use. The system can get up to 450 degrees F (232°C) even with moving air.
Question
I was wondering if someone has come across a cheaper material or system than the tri clamp one?  The requirements are to withstand 450 degrees F (232°C) or more, and to be food safe.  Current material is stainless steel which works for food safe but the pipes with all the clamps are up to $300 or so which is more than the rest of the project.
What I have investigated so far
I looked at many plastics available and while some can handle higher heats, those are generally more expensive. I also looked at using HVAC ducting but learned that galvanized steel can let off gasses when heated up.  So are the stainless steel tri clamps the best solution for the money or is there something cheaper out there that I am not thinking of?


texts: gas regulator exhaust gas during diaphragm adjustment?

texts: On my air tool compressor or scuba gear you can see or hear a diaphragm regulator sloughing off a tiny amount of gas to the atmosphere when you adjust the regulator down.  Does a natural gas regulator do the same if there is variation in the supply line pressure?


texts: I would like to know what kind of glass is used in biometric attendance machines over which we press our thumb? Is there something special about these glasses or their manufacturing?


texts:
Still in the long term purpose of understanding the various factors of consumption of my car, I recently discovered that I have about 15-20% difference between the liter/km (and indeed, liters) given by the car computer vs the value I obtain by filling the tank quite to the same max level each time divided by km done since the last filling.

-> Where is the problem ?

On a few measures on more than 40l,  I see about 7l of difference between liters used according to the computer vs the gas pump. So I don't think imprecision of my "filling at same level" could explain. Idem for evaporation (plus it's in the wrong order, since the computer see more liters consumed than what I do have to refill).

-> On which kind of sensors is based the consumption evaluation? tank level, or some accumulated flux at injection? Or more indirect? Are some values empirically estimated rather than measured, or accumulated with bad precision? Are my sensors faulty, or is it quite a common imprecision?


texts: Why do hydraulic systems use special fluid - what's wrong with water?

texts: As a hydraulics layman thinking about hydraulic systems, it seems that the important factor is to have a liquid that doesn't compress much or at all. Doesn't water meet this requirement, and what other properties should the liquid have (if any) that water doesn't?


texts: I don't understand a simulation result of frequency vibration analysis of ultrasonic tranducer

texts:
I am building a ultrasonic transducer like this (with double-exponential (75%-25%) match and 2 ring PZT8 50x20x6.5 (for the moment I do not take account of pre-stress on bolt) :

When I simulate the 2 piezo ring I got 33kHz resonant frequency. So in my mind, to get a maximum of z-displacement on the matching of the transducer, I thought it was a good idea to tweak the length of the matching to get 33khz resonant frequency for the transducer (solid - without piezo effect being simulated). After doing this, I make a simulation with solid + piezo effect and I get no 33kHz resonant frequency :

I done some other simulation for other length and get same thing :

So it seems that if solid & piezo ring are both at 33kHz, I got effectively a maximum z-displacement but not at 33 kHz...
Here is how I polarized thr rings :

So my question is : Why I don't get a 33kHz resonant frequency with piezo effect when solid + piezzo ring are both at 33 kHz resonant frequency?
Here are some other simulated result for displacement & stress :

Is there something wrong with it or can someone explain me what happen?


texts:
How can I find left and right directions associated with each zero for a MIMO transfer function?

Intia

First it can be expressed in Smith-McMillan form and can find poles and zeros. Then how to find the "left and right directions associated with each zero" ?
In above image poles & zeros are found for the first transfer function.


texts: how to release specific degree of freedom in ANSYS Workbench?

texts: I'm designing a truss which has 9 elements in ANSYS Workbench. since it is a truss, all of the elements are truss elements and can not tolerate momentum. I used LINK 188 element type for them. now, all I want is to define 2 of those elements as beams so that momentum can be transmitted between them(so we want 8 truss members and 2 beam members). but the important point is that only momentum about y axis must be transmitted, not momentum about z axis. I used BEAM 188 element type for these 2 members but it constraints all DOFs. any suggestion?!


texts:
Please indicate if this question would be better asked on other fora, I'm not an engineer but computer scientist, and have very little experience with FPGA's / ASICs.

As far as I understand from what I have read online, FPGA's can take up the role of compiled C/C++ and even OpenCL programs and simulate output of a GPU.

My question is if it would be possible to connect a normal desktop PC GPU (NVidia) to an FPGA such as from Xilinx / Lattice Crosslink such that the video signal can be re-processed afterwards? Would this be possible with a DisplayPort or HDMI connection?

Alternatively, if the processinig is entirely moved to the FPGA, is it common to have high bandwith connections (order of > 10Gbps) into an FPGA?


texts: What is the maximum degrees per step of a stepper motor for a 3D printer?

texts: I am making a reprap rostock (delta style printer) and I am trying to use as many parts I already have as possible. The stepper I have are 7.2 degrees per step. Even with microstepping, would this resolution get me high quality prints?


texts:
I'm interested in bringing in a GHT thread compatible product, but my sample's diameter was slightly smaller. GHT has a large (pitch to pitch) diameter of 1.0625 inch. The sample I received has a diameter of 1.0415 inch on the male side, and it doesn't leak and screws in perfectly.

Is this diameter difference meaningful for the long term reliability of my product?


texts: Remote start on a car with manual transmission

texts:
I'm making a remote starter for a car using a Raspberry Pi.  The problem is that the car has a manual transmission.  The driver needs to remember to place the gear shift in neutral when parking, otherwise all kinds of bad stuff could happen when the car is started in-gear.

What possible solutions do I have for making an interlock that prevents the car from starting in gear?  It's a 2001 Honda Accord, if that helps.  I have seen transmissions with sensors (switches) on every gear, but this transmission does not have those.  I thought of monitoring the speedometer sensor, but I think that info would come too late.  I'm thinking I might have to put one or more switches on the shift lever to detect its position, but this sounds like a lot of work.


texts:
My (highly limited) engineering intuition says: Dual railing is good - for balance, for switching of tracks, for lightening load and making sure it is applied in basically the same direction always, and perhaps other reasons I haven't thought of.

So, why ever have monorails? I mean, ok, if you want to fit into some super-narrow crevice then maybe I can see the motivation, but other than that - what are the benefits?

Note: I'm interested in non-magnetic monorails, although if you want to provide an answer for maglev's as an interesting side-note that's also fine.


texts:
I have a second order system and I need to control it using a PI controller. I need to tune the gains of the controller in order for the system to satisfy the below specifications:

$$ OS\% < 10\% \rightarrow Overshoot $$
$$ t_r < 1.2 \ seconds \rightarrow Rise \ Time $$

I have derived the third order transfer function of the closed loop system with the controller and I am not able to understand which characteristic polynomial I have to use in order to achieve the specified requirements.

EDIT:

Transfer function of the plant is:

$$ G(s) = \frac{10}{(s+1)(s+9)} $$

Transfer function of PI controller is:

$$ C(s)=\frac{K_p(s+c)}{s} $$ where $\ c = \frac{K_i}{K_p} $

The closed loop transfer function (linear unity feedback) is:

$$ T(s) = \frac{10K_p(s+c)}{s(s+1)(s+9) + 10K_p(s+c)} $$

So now how should I proceed in order to compute the gains $\ K_p $ and $\ K_i $ of the controller in order to satisfy the given specifications ?


texts: Calculating the change in flow rate with a change in pipe diameter

texts:
At datum height I have a pipe A (ID = 25mm) that discharges water at a volumetric flow rate of 10l/min, and unknown pressure.  When this pipe is connected to a polyethylene pipe B (ID = 12mm), 50m long running to a height of 6m, then the end of this pipe B discharges water at 3l/min
Do I have enough information to calculate what the change in discharge rate at the end of pipe B would be if pipe B was of diameter 25mm instead of 12mm, and if so how could I?  The equations I'm seeing seem to require a pressure measurement.
I've seen this answer, but it appears to ignore friction losses.
I'm guessing minor losses from the transition at the join of unlike pipe sizes can probably be ignored for an approximate answer.


texts:
I'm doing my first machine design for a project and I have a Honda GX160 combustion motor which has the following specs for power and speed:

I'd like to use 0.24 HP at 2000 rpm. Is this possible? Or I can just get 2000 rpm at 2.1 HP as the NET POWER curve shows?

I'm using this motor because it's the only one I have available for this project.

(It would also work for me at 1300 rpm if it has at least 0.24 HP, but I don't think its recommended)

Thank you!


texts: Do you need to be a chartered engineer to submit structural calculations to building control in the UK?

texts:
I’m a graduate structural engineer with 4 years experience, working in the UK. A family friend is planning on doing a house extension which will require some structural calculations for steel beams. My question is:
What will building control in England stipulate in terms of the structural engineer’s qualifications, liability insurance etc?
Do you need to be a chartered engineer with insurance to undertake structural calculations in England?
I think my experience is sufficient for what is a relatively simple calculation pack but I’m not sure what the legal stance is on this in England.


texts: Working out pressure drop from leak rate

texts:
I am trying to work out the acceptable pressure drop/increase on a leak test rig for a given leak rate. A simplified version of the test rig looks like this:

The gas (air) supply is at 1 bar above atmospheric pressure, and the inlet & outlet control valves + pressure sensor are part of the test rig and can be assumed to be leak-free. I am also working on the assumption that the process is isothermal.

Test 1

The first test is to open the inlet control valve, with the outlet control valve closed and the valve of the thing under test also closed, and look for a pressure increase on the pressure sensor. At the start of the test, the pressure sensor is at atmospheric pressure.

Here's my attempt, using $PV=nRT$:

Moles of gas gained downstream of the valve under test due to leakage past the valve:

$n_2 = n_1 + \frac{LR * \Delta t * P_1}{RT}$ (1)

where $P_1$, $V_1$ and $n_1$ are the initial conditions ($P_1 = P_{atm}$), $LR$ is the leak rate past the valve under test and $\Delta t$ is the duration of the test.

The final pressure can then be worked out as:

$P_2 V_2 = n_2 RT = (n_1 + \frac{LR * \Delta t * P_1}{RT}) RT$

with $V_2 = V_1$ (the volume hasn't changed), we get:

$P_2 = \frac{P_1 V_1 + LR * \Delta t * P_1}{V_1}$

and then obviously:

$\Delta P = P_2 - P_1 = \frac{LR * \Delta t * P_1}{V_1}$

Question

Is that the right approach? Should I use $P_1 + 1 \text{bar}$ instead of $P_1$ in equation (1)?

Test 2

Now the whole thing is pressurised to 1 bar by opening the inlet control valve, the valve under test and closing the outlet control valve, before closing the inlet control valve, which is when the test starts. This is to look at leakage out of the "thing" through pneumatic fittings, etc... We are now looking at a pressure drop from 1 bar, instead of a pressure increase as in test 1.

I am using essentially the same approach, except that we're now looking at a number of moles of air lost in equation (1), which becomes:

$n_2 = n_1 - \frac{LR * \Delta t * P_1}{RT}$ (1a)

The rest follows as per test 1, so that:

$\Delta P = P_2 - P_1 = -\frac{LR * \Delta t * P_1}{V_1}$

of course, this time $P_1 = P_{atm} + 1 \text{bar}$ and $LR$ is the leak rate out of the "thing" rather than past the valve.

Question

Again, is that the right approach?


texts: Projected area in hoop's stress structural mechanics

texts: While calculating hoop's stress we consider projected area. Infact in bearing stress from pins in a truss something similar is applicable.Can you explain why we are taking something like this instead of the curved area?


texts: How do I include statistical significant index in bar chart in excel?

texts: I want to have a star dot above each bar chart. I don't know how to present that index. Please anyone help me to resolve this problem,


texts:
I need a 3D CAD software that permits to create parts and assembly.
Right now, I try FreeCad, Salome and BRL-CAD.
The first one can create only single parts, not assembly.
Salome have the same problem.
BRL-CAD can create parts and assembly, but it's use is not intuitive and the graphical module right now is not mature.
Any other?


texts:
I'm trying to re-remember how to resolve forces in pin joint frames. I seem to have gotten stuck rather quickly and the examples I've been through don't replicate the same issue.

Here is my truss I'm working on (terrible image, sorry)

When trying to calculate the reaction force at B1, B2 and B3 I get different answers depending on where I take moments about from.

Example:

Moment about B1,

F(B2) = 2 x F(B3)

6 x F(B3) + 3 x F(B2) = -10 x 3

Therefore:

F(B3) = +2.5kN

F(B2) = +5kN

or

Take Moment about B2,
F(B1) = F(B3)

3 x F(B3) + 3 x F(B1) = -10 x 3

Therefore

F(B1) = +5kN

F(B3) = +5kN

or

Moment about B3,

F(B2) = 2 x F(B1)

6 x F(B1) + 3 x F(B2) = -10 x 3

Therefore:

F(B1) = +2.5kN

F(B2) = +5kN

Different answers for the each restraints.
Can someone please advise where I am going wrong?
Thanks
Rich


texts:
From the "meep meep" of the smallest scooter to the "BLLLAAAAAGGGGGHHH" of the largest seagoing container vessel, vehicles seem to have horn sounds that, in an auditory way, seem to indicate their mass. Of course, nothing prevents a designer from putting a "large" sounding semi truck horn into a mini automobile, it seems one would only do this for a joke and indeed, I can imagine it would make people laugh because of the unexpected mismatch between the vehicle and its warning sound.

Are there actual engineering guidelines that drive such design decisions? Presumably, from a psychological acceptability standpoint or from safety or general human-machine interface principles?

Note to audience: I tried my best to find the most appropriate SE mini-site. We have "Sound Design" which seems to relate to music; and "User Experience" which doesn't say so but seems 100% related to software design.

Note to site moderators: A tag for usability engineering or human machine interface design would be helpful.


texts: Phase Change Materials Charge and Discharge

texts:
Is there a way to approximate the charge and discharge time of a PCM. I understand that this is a transient process as a material melts from the outside in, but I was wondering it there a means of estimating this time in order to determine the charge and discharge cycles. I am looking for a good source that shows different melting times, steady state calcs or published data.

I have been looking at different vendors of these materials but their tech sheets rarely include this info. I am particularly interested in Eutectic salts if anyone has a good source on this sort of info.

Thanks in advance,

Regards

P


texts: What are a few low-cost options for building linkages?

texts:
I'm working on a project trying to combine a pantograph linkage with a four-bar linkage. I'd like to build it out of relatively at-hand materials (AKA, nothing requiring a machine shop), and I'd like to do some educational projects in the future involving students building linkages, too, so low-cost would be great. Relatively stiff and able to run unattended as a display are also desirable.

I'm thinking that bolts and nuts are going to be problematic after it runs for too long. Is there a particular type of bearing that would be easy to use/acquire? ...a good material for the rods? I have a Carvey CNC machine, so HDPE and wood are easy to machine for me. It's mostly the pivots/bearings that I'm having trouble with.


texts: Increase in internal energy and temperature

texts: A banquet hall (150 m3) is to be used for a formal dinner for 20 persons. Each person occupies 0.075 m3 of space and has an average heat transfer rate of 500 kJ/hr. If the AC system fails, determine the increase in the internal energy and temperature of air in the hall during the first 15 minutes of failure. Take the hall to be well insulated from outside. If the hall and all its contents are considered as system how much will be the increase in the internal energy of the system.


texts: What type of acturator with motor to choice for measurement with step = 0,25 μm?

texts:
I need to select some linear acturator or build it. I see it as:

On green platform there is pink device. This device must be measured. For this purpose we need to choose linear acturator with carriage (dark blue on picture). Carriage must go along one direction. This carriage must to carry some electrical equipment. Mass of this equipment = 400 g (0,88 lb).

Specification:

Carriage (other moving element) must have range of motion = 50 mm (2 inch). Minimum motion (step) must equal 0,25 μm (or less). Allowable error of measurement = 7%. We plan to measure 100 points along and only ahead because repeatedly of measurements don't care.

Question

What types of acturators may be appropriate for this task? What variant is better?

Additional explanation:

I have considered two options:

Linear acturator on base ball screw rail with carriage and stepper motor. This solution does not satisfy this problem because has low precision.
Piezo acturator - useless too, because it has limitation on range of motion (max. 30 mm, when need 50 mm). Moreover piezo acturator very sensitive to
payload (if that's devices can move 100 g - it's already good).

Note.

It's acceptable for my objective if linear acturator will be move platform (green on picture) with electrical equipment. Blue stand with measurement equipment can fixed. In that case payload to platform = 2 kg. And step same = 0,25  μm.


texts: What is the difference in CFM, at a given static pressure, between a CPU fan and a Squirrel Cage Blower fan when moving air through ductwork?

texts:
I have a Delta ASB0912L DC Brushless fan.  PDF here.

In the datasheet it says,

RPM 3800
CFM 67.80
IN H2O 0.302

On the blower, squirrel cage fan, Dayton from Grainger, found here (Rectangular Permanent Split Capacitor OEM Specialty Blower, Flange: Yes, Wheel Dia: 3", 115VAC)

It says,

RPM 3010
CFM @ 0.200-In. SP78
CFM @ 0.300-In. SP74

I want to exhaust fumes from a spray booth.  I know there are many articles and plans online.  I am trying to understand the math here.

It seems intuitive to me the Grainger fan is more powerful and will remove more air than the CPU fan.  But the math makes no sense to me.

On the CPU fan it has .302 for Static Pressure and .3 for the Grainger and the CFM is pretty close.

I am moving air through 6' of ductwork, 4" in diameter, and neither tell me what CFM means in this context.

Given a 2'Lx2'Wx2'H spray box.  Again, I'm not asking for plans.  I can get that already.  I only want to understand what these numbers mean and the spray box application gives the question context.

Why doesn't the CPU fan move almost as much as the Blower based on the specifications?  Also, is the Delta IN H20 given static pressure or is that something else?


texts: Do high speed trains use ventilation and filtration systems similar to aircraft?

texts:
This article discusses the ventilation and filtration in aircraft:

  Ventilation rates provide a total change of air 20 to 30 times per
  hour. Most modern aircraft have recirculation systems, which recycle
  up to 50% of cabin air. The recirculated air is usually passed through
  HEPA (high-efficiency particulate air) filters, of the type used in
  hospital operating theatres and intensive care units, which trap dust
  particles, bacteria, fungi and viruses.

Does ventilation and filtration in high speed trains typically work the same way, including with similar air renewal intervals, recycling rates, filtration quality?


texts: What is the function of this device in the middle of the man-made lake?

texts: Can anyone identify what the blue and orange floating item with paddles is in this picture of what appears to be a Chinese fish or turtle farm?


texts:
I enjoy creating mechanical designs but I am not a trained mechanical engineer.

I have a technical issue with a joint design that needs to be permanently retained using a press (snap) fit. Any idea on the size and tolerances for these two 304 SS parts to be pressed together using an arbour press without permanent deformation of either part? I will use a little lithium grease to help with the press fitting which will also serve as general lubrication for the shock absorber joint.


texts: Is there a good reason for long and fixed-length serial numbers?

texts:
I am involved in an upcoming product launch and we recently had a discussion about serial numbers. We will of course use variant-specific model identifiers and revision numbers, but couldn't see any good reason to include any leading zeros in serial numbers, or otherwise make them fixed-length with padding numbers, prefixes, characters, etc. But this seems to be a common practice.

Is there anything wrong with 1, 2, ... 10, 11, 12, ... 100, 101, 102, ... ? What possible advantages are lost by just starting at 1 and counting up?


texts: How can I add roof-mounted solar panels to a van without making it unstable at highway speeds?

texts:
We have an extended Chevy express with a 24" high-top, on which we intend to install roof-mounted PV.

I'm really concerned with how to properly install the panels. We've selected six 100 W Renogy panels and a 400 Ah LiFePO4 battery pack, but it might be too much for our roof. I'm worried that if we are going 80 mph up I-5 and hit a 40 mph cross-breeze we could tear the roof off the van, rip the panels off the roof, destabilizing and roll the vehicle, etc. How can I avoid or minimize these risks?

I was initially thinking of laying three panels long-ways on each side of the van, with a ~20" section down the middle I can walk down and hang out or service the panels, and where the roof vent will go. Each section then would only be 22" wide (140" long) with space on both sides for air to dissipate to either side.

My plan is to build my own rack with bent heavy conduit and bolts. The rack should be pretty strong. But could unwieldy pressures blow out the panels? I don't know what thresholds they should withstand. The product shows 2400 Pa high winds and 5400 snow, but what does that correlate to in driving down the road?

You'll notice that with the current layout, the panels must go over each side by 4.5 inches. To me, this means they can be more affected by wind. If the roof was just flat instead of the bubble top, mounting might be much easier.


texts: What determines the cost of the wind turbines?

texts:
If there is an 11kW wind turbine, and a 15kW wind turbine. Why is the 15 kw wind turbine more expensive?

I know it seems like a basic question, but what exactly makes it more expensive? Is it only the generator? Or is there something less obvious that causes it to drive the turbine price higher, with higher power?

I am hypothesizing that the weight of the turbine might be the major factor that determines the price of the turbine, and not its generator capacity.

Any additional thoughts are welcome.


texts: How to convert permeation units to molecules/second?

texts:
How do I convert $\dfrac{\text{cm}^3\cdot\text{mm}}{\text{m}^2 \cdot \text{day} \cdot \text{atm}}$ for permeation of gas through EVOH to molecules of gas permeating per second as a function of thickness of EVOH?

In other words, I am trying to use the permeation units to determine how much a container will be emptied of gas via permeation after a given amount of time.


texts:
Can anyone help me to identify this electrical connector set?

Hint: One male plug style connector has some text saying "HC 0617 CANNON"


texts: How to increase kg per hr capacity of screw press to achieve the same applied pressure per unit volume of raw material?

texts:
The current capacity of screw press is only 100 kg/hr. Motor is 22kw, shaft RPM is 16, applied torque is 13,120 Nm, theoretical volume is 0.000967 cu m.

Am I correct to say the press is going = 13,120 Nm divided by 0.000967 cu m will get the pressure Nm/cu m?
If it is ok how can I increase the capacity to meet the same applied pressure equal to above answer?

Regards,

Romy


texts: Why servomotor has such low torque compared with stepper motors?

texts:
It is easy to found stepper motors with torque over 2NM for a few coins, however, only expensive industrial servomotors achieve this torque.

Examples:

Stepper motor: 10usd for 1.3nm with 2.8V at 3.5A rpm 0.6kg
Servo AC motor: 278usd for 2.39nm with 220V~ at 3A 3000rpm 6kg
Servo DC motor: 67usd for about 0.4nm 24V at 7.8A 3000rpm 1Kg

Torque is not power, and closed loop has many benefits, but I am still confused:I believe many industrial purpose require quite high torque (CNCs, robotic, etc.) and it would be preferable (to my understanding) a lower rpm with higher torque. Additionally, it seem to me that any purpose for a servomotor require more than a few 0.4nm

Why is this torque that different?

What is the benefit / purpose of those non-hybrid servo-motors?

What am I missing?


texts:
How do I quantify how much kinetic energy would be released from popping a balloon?

I believe that any additional kinetic energy that results from the balloon will come from it being pressurized, but how is that calculated?


texts: Is there any reason for Abaqus to give this error message "Illegal memory reference (signal11)" whenever the number of statev is greater than 15?

texts:
I work with Abaqus CAE/Standard a lot!

Whenever I have tried to put the number below the *Depvar keyword to be greater than 15 (and there can be any subroutines (UMAT or USDFLD) with no coding in it, just the basic input parameters as provided by Abaqus User Subroutine Guide), the job always, without fail, aborts right away and gives me the error: "Illegal memory reference (signal 11)".

Keep in mind, there is no actual code anywhere in the user subroutine where there could be any mistake; I have tried this just as a curiosity, and just as expected, as soon as the number of dependent variable is higher than 15, it aborts right away!!!

What's the cause of this?


texts: Help an electrical engineering student with a beam deflection question

texts:
The theoretical formula for my beam deflection is:

$  v(x) =
\begin{cases}
-\frac{Px}{48EI}(3L^2-4x^2),  & 0\le x \le {L\over2}\\
-\frac{P(x-L)}{48EI}(L^2-8Lx+4x^2), & {L\over2}\lt x \le L
\end{cases}$

I need to derive the formulae for the slope $v'$, curvature $v''$ and $v'''$

Is this just a simply case of taking the first, second, and third derivative of the original equation? I know absolutely nothing about structural beams...


texts:
I am looking for ideas for the following. I want to design a flexible plate where I can control the bending of the plate. In particular, a 5”x2”  plate will be used which can be bent  with some attached mechanisms.  The plate will be dragged in water so it should  not buckle under water pressure itself, rather its buckling should be controllable. I know there are certain shape memory alloys which can do that when powered (may be some piezoelectric actuator can do this also, I am not sure).

Can it be designed with some actuating mechanism like this below:

I would appreciate your comments and suggestion. Thanks


texts: Reason of Using exactly 5 Wheel Studs per Wheel

texts:
So today when I was taking a taxi and looked at the vehicles, I observed that the majority of the light vehicles (i.e. 16-person minibus/ 4-6 person cars) use 5 (or less frequently, 6) wheels studs for each wheel.

Intuitively, 6 evenly distributed components are more stable as it has 3 axes of symmetry, as compared to 5.

Is there any mechanical reason for that?


texts: Where can I find (cite-able sources) properties (such as specific heat at constant volume, thermal conductivity, viscosity etc...) of air at different temperatures (Range of 200K to 2000 K)?


texts: Strechable object that can transfer current

texts:
Does some material/metal exist that can be stretched and still transfer current?

For example:
Say I have a rectangular item made of some metal or material(unknown to me at the time). On both ends, I have two small sensors attached. These sensors do nothing but want to establish communication between each other. For the purpose of this question, let's refer to them as sensor A and sensor B. Sensor A sends a message to Sensor B. Since the metal is not very stretched, it manages to transfer the message in electrical current to Sensor B in an elapsed time of .1 second.

Now, imagine that we stretch the metal a bit more, where its width is lowered and its length is increased. Since the message now has to travel further, I would expect the delivery to be greater than .1 second.

Note: Numbers used are just an example.

What sort of material or metal can I use to pass current, that when stretched, would alter the total distance a current would have to travel?

Ideally, the two sensors will at the minimum be separated by 3-4 inches, and the metal/material would only stretch up to 1 inch.


texts: Will this work for single output twin engine

texts:
I’m wondering if anybody can help me by critiquing my project idea of having a failsafe power train 4x4 for remote touring.

Instead of having one big engine, I’m toying with the idea of running two small engines, parallel to each other, which would turn a mitre gearbox (90* bevel gears), which would both then have output shafts entering a differential to mate them into a single output.

I would run a differential lock so that I could disconnect a blown motor and drive turn the differential off a single engine (instead of just having the opposite side of the differential spin in reverse).

The only major hurdle I have thought of so far, is that the shafts would be spinning in opposite directions as they enter the diff which would be relatively ineffective and make me ever so slightly sad.

I’m thinking to overcome this I’ll need a 180* bevel bear to reverse the drive rotate of one of the shafts.

What say you?


texts: Deformation gradient, strain tensor from cylindrical coordinates

texts:
I do not have any engineering background but I am studying some mathematics to try and understand and solve this problem. I have a mesh (M1) in cylindrical coordinates and this deforms into a mesh (M2) (again in cylindrical coordinates). I need to compute strain in radial, longitudinal and circumferential directions.

Basically I have done the following computations on each point of the mesh. The deformation gradient F is computed:
$$F = x·X^T·(X·X^T)^{-1}$$
where:

$x$: the deformed cylindrical coordinates (3x1 matrix)
$X$: the undeformed cylindrical reference coordinates (3x1 matrix)
$X^T$: transpose of $X$
$X^{-T}$ : inverse of transpose of $X$

The Langrangian finite strain tensor $E$ is then computed:
$$E = \dfrac{1}{2}(F^T·F-I)$$

where:

$F^T$ : transpose of $F$
$I$ : identity matrix (3x3)

I then take the diagonal of $E$ and this gives me the principal strains in the orthogonal cylindrical coordinates.

Questions:
Am I doing it right?
Do I need to do some further computations on the diagonal of $E$ to get the principal strains at each point of this mesh that is deforming?


texts: What causes the pressure change in a horizontal pipe with no energy input. Is it the head loss? If so, how?


texts: Can I use more than 2 linear guides to support a linear stage?

texts:
I am designing a home CNC mill for machining nonferrous metals.  I plan to use linear guides to support either a Y-axis table or the 2 legs of a Y-axis moving gantry.

Linear guides are used to provide low friction linear motion along one axis while resisting forces in other directions (both rotational and translational).  They come in many sizes as shown below, and must be mounted to very flat surfaces and adjusted for parallelism with respect to a "reference" guide.

I have a number of identical linear guides at my disposal that are 12mm in width which is on the smaller end of the spectrum (although they are lower in height profile). I am curious if using more than 2 linear guides (3 or 4 all in parallel) is beneficial (provided that I mount them all in parallel).  Are there any drawbacks I should think about when considering using more than 2 linear guides to guide something?

The reason I ask is (1) I don't want to waste a linear guide if this is a "weakest link" situation, and (2) using 2 linear guides is by far the most common I've seen in commercial designs for linear stages.

Someone might ask "if you're worried about rigidity why dont you go buy some bigger stronger linear rails"?  I guess that's also part of my same question - could using multiple smaller linear guides additively achieve the same effect as a bigger stronger linear guide (while at the same time maybe  being lower profile which I think should decrease the moment arm for the roll axis)?

Here are some diagrams from newports website if they help for reference: https://www.newport.com/t/manual-positioning-basics

straightness deviation:

tilt rigidity:

load capacity:


texts: Mouth-style whistles, i.e. whistles using flexible materials

texts:
I'm wondering if there is much literature around whistling, i.e. human-mouth style whistling.  Either using your lips or your fingers.
To make my query less vague: say I wanted to create a rubber football with a tube through the axis of rotation (i.e. the axis refers to when the football is thrown in a spiral).  How should one shape the tube, and how fast would one need to throw the football, to make it whistle comparably to a human?  Do we know roughly how much additional drag the whistle will put on the football, when compared to a traditional football shape?  I imagine the material properties of the rubber will matter.  The rubber I will be using will be about the consistency of a rubber o-ring.
I've done a little searching on this topic but I am not certain what keywords are relevant, as there is an enormous literature on whistles, mostly not of the type I am asking about here.


texts: How to test the component material properties after casting?

texts:
We have conducted tensile testing after casting(using test specimen from casted parts), but results are not met the required value. (Due to highest wall thickness / material accumulation)
How to check the material property in this case?
what type of practice will be used for material testing after casted parts in tensile testing?


texts: I'm a bit confused with the wording of the question. What does it mean by expressing the bending moment and the deflected shape of BC as a function of z? Thank you]1


texts:
I want to model an ideal truss in ANSYS 16.1 and by ideal I mean all of the joints are pinned joints and so the momentum can not be transferred at joints(like attached image). The problem is that I don't know how to model the pin joints for the truss structure. I would be appreciated if some body can help me by providing solutions or ideas.
Cheers


texts: Engineering economics - Factors P/A question

texts:
The Autocar E3 refuse truck has an energy recovery system developed by Parker Hannifin LLC that is expected to reduce fuel consumption by 50%. Pressurized fluid flows from carbon fiber-reinforced accumulator tanks to two hydrostatic motors that propel the vehicle forward. (The truck recharges the accumulators when it brakes.) The fuel cost for a regular refuse truck is $900 per month. How much can a private waste-hauling company afford to spend now on the recovery system, if it wants to recover its investment in 3 years plus a return of 14% per year, compounded semiannually? Assume no inter period compounding

İt is not a homework question.

I tried to solve it using factors, as the new system will save us half the cost of fuel per month, we can afford 450 USD per month on the new system. İt will be our annuity. I am not sure if I should use (P/A, %7,6) or find the effective interest rate first for a year than use it like (P/A,%14,xxx,3)

The answer for both formulas are different however this logic can be used for P/F,F/P so I don't understand.


texts: How to build a paper ramp for a small car?

texts:
I have been assigned to build a ramp for a small car. I have only one A2 sheet of paper, scissors and a stapler. What would be the best slope profile, in order to move the car as far as possible after leaving the ramp, using only gravity? Any other ideas on construction?

The car is 1:43 size. The weight is 100 g. The car must stay on the track and there is no initial push.


texts:
for shear flow at D , the Q = Ay , i tried another method , i gt 30000 , instead of 29750, why the ans is different from 29750? why cant i use this method( i break the shaded area into 3 parts
 ( as shown in figure) my working is Q = Ay = (60x10x35) + (2x30x10x150) = 30000

Is my working not acceptable ?


texts: What's the setpoint of the temperature on the primary side of a heat exchanger?

texts:
I have a heat exchanger with known flows on priamry and secondary sides - $\dot m_p$, $\dot m_s$, known temperature in $t_{si}$  and a desired temperature out on the secondary side $t_{so}$. How to find the required $t_{pi}$ analytically? So far I've always done these calculations numerically with the excel solver.
This is where I get stuck in solving analytically - from the energy balance we find:
$$ t_{pi}=t_{po} - \frac{\dot m_s c_s}{\dot m_p c_p} * (t_{so} - t_{si})$$
but we need  $t_{po}$, when I try this (from the heat transfer equation) I think I'm stuck:
$$ t_{po} = \frac{kA \Delta T_m}{\dot m_p c_p} + t_{pi} $$
because to solve I'd need to extract my temperatures from the $ln$ in the denominator of $\Delta T_m$ and that's where I'd rather look in a textbook than do the math myself. Except my textbook (Perry) doesnt have that detail. $A$ is known and $k$ can be estiamted, so is known for the purpose of this questions.
So, for given mass flows, and desired outlet temperature on the secondary side, what is the required inlet temperature on the primary side?
The ultimate problem I want to solve is that I want to ask a question about HX control and I feel it would help to have this equation.


texts: How are loads transferred to bearing piles in a wall pier?

texts:
I've been working on the design of a reinforced concrete wall pier for a three-span bridge. I roughed out the design based on a number of example plan sets and now that I'm taking a crack at the actual design calculations, I'm questioning the logic of the example plans. (Plus, I just dislike "designing" on the basis of "Well, we've been doing it this way and nothing's fallen down yet!")

The design is thus:

My questions are:

Why would the piles be stopped short of the cap?
With the piles stopped short of the cap, what is the load path from the girders to the piles for vertical and lateral loads?

I'm also confounded by the fact that I'm typically seeing US #6 bars for the (a) bars (which seems large given that the cap will not see much flexure) and US #5 bars for the (c) bars (which seems small given that it looks like these bars would be necessary to transfer lateral loads from the cap into the wall).


texts: What is the practical use of Assur Groups and structural analysis?

texts:
In Mechanisms and Machines Theory we were introduced to Assur groups and structural analysis where a mechanism is subdivised into elementary Assur groups of different classes.
But what is really the practical use of it?


texts: Question about color filters for a liquid crystal display

texts:
I'm not sure if 'engineering' is the right place to post this question. I'm studying how color filters for a liquid crystal display are fabricated. I found a table on the web which compares pros and cons of each pattern (Please take a look at the attached image).

Questions:

Why are the mosaic and delta patterns difficult to fabricate?
Why is the driving circuit of the mosaic pattern complex?


texts: Phase response of a continuous transfer function

texts:
Let $\omega_0 \in \mathbb{R}$ and $\omega_0 > 0$. Be $G(s)$ a transfer function defined as:

$$G(s)=\frac{1-\frac{s}{\omega_0}}{1+\frac{s}{\omega_0}}$$

We're interested into evaluating its phase response in a continuous LTI system. First, we split $G(j\omega)$ into its real and imaginary parts (assuming $\tau=\frac{\omega}{\omega_0}$):

$$G(j\omega) = \frac{1}{1+\tau^2}\left[1-\tau^2+j\left(-2\tau\right)\right]$$

Then using the definition of phase of a transfer function we have:

$$\angle G(j\omega)=\arctan\left(\frac{\mathbb{Im}\{G(j\omega)\}}
{\mathbb{Re}\{G(j\omega)\}}\right)=\arctan\left(\frac{-2\tau}{1-\tau^2}\right)$$

So, for any $\tau \gg 1$ (which implies that $\omega \gg 1$) then the following should hold for Taylor's series:

$$\angle G(j\omega) \simeq \arctan\left(\frac{2}{\tau}\right) \simeq \frac{2}{\tau}$$
which approaches $0$ as $\omega$ gets bigger.

Here comes the discrepancy. Let $\omega_0 = 1$ (for plotting reasons), why does Wolfram Alpha give me the following Bode plot?

Also, I expected one discontinuity point at $\omega = \omega_0 = 1$ (and another one for $\omega = -\omega_0$ not shown in the plot), but I guess I messed up something since the beginning.

2018-12-12 (in response to Sam F.) Here's how I've separated the real from the imaginary part of $G(j\omega)$.

$$
\begin{align}
G(j\omega)
&=\frac{1-j\frac{\omega}{\omega_0}}{1+j\frac{\omega}{\omega_0}} \\
&=\frac{1-j\tau}{1+j\tau} \\
&=\frac{1-j\tau}{1+j\tau}\cdot\frac{1-j\tau}{1-j\tau} \\
&=\frac{(1-j\tau)^2}{1^2-(j\tau)^2} \\
&=\frac{1^2+(j\tau)^2-2\cdot 1 \cdot j\tau }{1+\tau^2} \\
&=\frac{1- \tau^2+j(-2\tau)}{1+\tau^2} \\
\end{align}
$$


texts: Warehouse Expansion: Is a new fire pump and tank required

texts:
For an existing Warehouse, with sprinkler system already installed:
We are adding 3 mezzanine floors, with around 27000 Sq. ft for each floor. While designing sprinkler system, is it necessary to add new Fire tanks, Fire pumps for sprinkler system once again or can we connect the sprinkler riser to the existing system. We are also adding around 12 Fire house box(3 per floor) which will be connected to the ring main. Is it okay?


texts: How to estimate wind generation using power curve?

texts:
I am trying to verify windfarmer generation estimates manually. To do so I am trying to manually calculate the estimated energy production (kWh) of a wind turbine. The information I have available is the

Hourly weather data (wind speed, direction & air density at Hub Height,
and temperature)
Power Curve of wind Turbine
Thrust Coefficient of wind turbine
Temperature de-ration curve of wind turbine
Turbine specifications (blade radius, swept area, cut in & cut out speeds, Cp, Rated Power, etc)

How would I use this data to estimate the potential annual generation?

I tried multiplying hourly wind speeds * the specific value in the power curve, then de-rating the result based on the given temperature, However it seems to significantly overestimate the answer.

Unfortunately I cannot share the data, but all I am looking for is a formula or calculation methodology. Any help be greatly appreciated!


texts: How to purify/treat air smell produced by a kitchen?

texts:
Ignore the ugly look.

Sometimes I cooked food with very strong smell. That smell sometimes is not expected by many neighbors, they protested. Rather than to use exhaust fan, I considered to install funnel on top of the stove, then I will pipe it to the roof. I expected it will send the air-smell high enough. But, learned from another neighbor, that way is still not solve the problem. The air-smell sometimes is still there, especially when wind blows, the smell went anywhere. It considered become pollutant. Then, I was thinking how to solve. What is the best way to treat that air-smell?

Is any method how to treat that smell so it become neutral (or "clean") before it "delivered" the the free air? Just consider like water-waste treatment of any industry, it must treated before released to the nature/river. I expected that there is one device which such the smell, and proceed until it clean, and then deliver to the air.


texts: What is the purpose of the steel plate in this coupler?

texts:
I've found a shaft coupler that has a steel plate in between, but it's not clear what its function is:

If it is to add strength to the coupler, isn't the coupler as strong as the weakest link, i.e. the aluminium ends? Does anyone know what the purpose of the steel plate is?
EDIT: Here's another similar design:


texts: Is it possible to "boost" a WiFi signal using an aluminum soda can?

texts:
I recently discovered that one of my roommates had attempted to boost the WiFi signal by cutting up a soda can and placing it near the router, like this:

My roommate was probably following an internet guide like this one, which advises shaping the modified can "like a radar dish" and placing it around the external antenna of the router. However, our router has no external antenna.

Will either configuration actually boost the router's reception? I don't know too much about antennae, but I suspect that the second configuration works more like a shield.


texts: Looking for elegant ways to divert airflow

texts:
I am working on capturing air pollution particulate matter from Diesel Generators. Consider the following scenario.

A 15KVA generator that outlets smoke from the exhaust
The smoke goes into our capture setup.
After every 30-40 mins of operation we need to electro-mechanically clean the capture setup. The cleaner assembly takes approx. 60 seconds.
For that duration we need to re-direct the flow of the exhaust to another outlet with some kind of timing/logic

i.e.  The best example is a ‘Y’ configuration attached to the exhaust, where the flue gas will flow only in one exhaust at a time.

For the better understanding I am enlisting the design parameters as follows:

Flue gas velocity: 15 m/s
Diameter of the pipe at inlet: 4 inches
Diameter of the pipe at outlet: 4 inches
Operational temperature: 450°C - 500°C

I am looking at a lowcost/robust way to solve this problem :) as we're building this prototype on a budget, hence we want to examine all the options/suggestions that might be suitable in achieving our above goal/purpose.

PS: I've already looked at the standard diverter valves- but they seem to be an overkill/very expensive(like 2500$)/not designed for our application where temp. is high.


texts: The finite step response of a system pole at the origin is unbounded, how is this critically stable?

texts:
This is a question one of my students brought up in class and I thought it was worth posting.

When considering the stability of a linear time-invariant system it is often useful to look at the pole positions on the pole-zero map. Usually one of the first things that is taught in an undergraduate systems engineering course is that poles located on the LHS s-plane are stable, while poles located on the RHS s-plane are unstable. Furthermore, poles located on the imaginary axis are considered "critically stable".

An example of such critically stable systems would be:
$$G_1 = \frac{Y_1}{U_1} = \frac{1}{s^2+\omega_n^2} $$
$$G_2 = \frac{Y_2}{U_2} = \frac{1}{s}$$
The exact value of $\omega_n$ is not important for this question. The poles of $G_1$ and $G_2$ are plotted on the pole-zero map below.

So lets take a look at the behaviour of these critically stable poles. If subjected to a finite step input, $G_1$ will produce a bounded oscillation with constant amplitude:

If subjected to a finite step input, $G_2$ will produce an unbounded response (linear response approaching infinity as time approaches infinity):

I thought that only unstable systems had unbounded finite step responses.

If the finite step response of a LTI system with a pole at the origin is unbounded, why do we say that the system is critically stable?


texts: For a flow driven by a pump between 2 parallel, stationary plates, why is the shear force vertical and is there positive and negative shear force?

texts: Why is the shear force vertical when the flow is horizontal? Also, why is the shear force at the top surface of the control volume negative and the bottom is positive when they are both in the same direction?


texts: what is the range of the measurable relative elasticity with a commonly used strain gauge

texts:
I'm looking for a data that what is the typical application range for a common uni directional strain gauge like used in weight scales?
I've read about around 200 ppm in a research gate article, can I measure 40 ppm with a cheap setup (arduino nano plc, industrial grade op amp, soldered connections)?


texts: Is it significantly less challenging to build an ORC piston or turbine than the same for a water steam engine?

texts:
An organic rankine cycle engine is a steam engine that uses, instead of water, a fluid with a higher vapor pressure. This allows a rankine cycle type process at lower temepratures, like the waste heat of a motor or geothermal energy.

I would expect the mechanical part of the ORC engine to be significantly easier to build, and thus cheaper, because the temperatures are lower and so thermal expansion is less of an issue. However, I don't know enough about constructing pistons or turbines to be sure. Can someone shed light on this?


texts: Is there a difference between a "brushless motor" and a "motor without brushes"?

texts:
On the Dyson website they promote their new motor by saying:

Dyson Hyperdymium™ motors work very differently to conventional
brushed motors. We replaced the brush with digital pulse technology,
added neodymium magnets and built a ceramic shaft that's three times
stronger than steel. This makes our motors durable and powerful, yet
smaller, lighter and cleaner than ever before.

I find it odd that they are referring to their motor as a brushed motor, having replaced the brushes - as opposed to simply calling it a brushless motor.
To my knowledge, the main difference between brushed and brushless motors is that on a brushed motor the coils are on the rotor and the magnet on the stator, and with a brushless motor, this is the other way around.
I am having trouble finding any in-depth information about Dyson's motor, but from these two images on their website:

it looks like the coils could be on the rotor - which would explain why they are referring to it as a brushed motor, but without brushes.
Is this the case? Is there a semantic difference between a "brushless motor" and a "motor without brushes", or are Dyson trying to be sneaky and imply that they invented the brushless motor...?


texts: Required power to spin fan at certain RPM

texts:
I have a flat piece of wood shaped like this:
And it is turning around axle.
What i would like to know is, if it is rotated e.g. at 1000 RPM, how much power would that take?

I know that drag force should be equal to this:
$$
F_D=\frac{1}{2}C_D\rho_{air}Av^2
$$
And power:

P = Fd
⋅
v

I am using P air = 1.2 and Cd = 1.1 (i don't know if this is correct) .

First i calculated speed based on outer radius(27cm), but because of V^2 that was a big mistake, now i have split horizontally (or vertically if you are watching the picture) in parts of 0.5cm, and then calculated power for each part individually and then add them together, but i am getting what i think is lower value than what it should be (in range of 150-200W), i am getting ~87W at 660RPM. I am guessing i have a wrong approach to this problem.

EDIT 1:
Here is python code how i calculated power with my way and also with Yaniv way.

RPM = 500
RPS = RPM / 60
def estimatedPower(RPS):  # RPS = revolution per second
    finalPower = 0
    forceSmallPiece = 0
    forceBiggerPiece = 0
    for i in range(0, 54):
        radius = i/2
        if radius > 11:
            A = 0.0008
            V = radius/100*2*3.1415 * RPS
            F = (1.1*1.2*A*V*V)/2
            forceBiggerPiece += F
        else:
            A = 0.000375
            V = radius/100*2*3.1415 * RPS
            F = (1.1*1.2*A*V*V)/2
            forceSmallPiece += F
        P = F * V
        finalPower += P*2    # *2 is because there are 2 blades
    print("power: ",finalPower)
    return finalPower, forceSmallPiece, forceBiggerPiece

finalPower, forceSmallPiece, forceBiggerPiece = estimatedPower(RPS)

AngularSpeed = RPM * 2 * 3.1415/60

Fd = forceBiggerPiece
Fd1 = forceSmallPiece

torque1 = Fd * 0.19
torque2 = Fd1 * 0.055

torque = (torque1 + torque2) * 2    # *2 because there are 2 fan blades
p = torque * AngularSpeed

print("Power with torque: ",p)


texts:
I'm making sort of a desk cycle. What are the ways to make silent circular motion with resistance ? (I don't need to adjust resistance and resistance should be just light.)

If I didn't need resistance, I could use a bearing. Or maybe there are regular bearings that have some specific resistance ?
I see there are also magnetic bearings but I had really difficulties to find their prices and those ones that I found costs in hundreds. Are there some cheap ones, ideally ~ 15 or less bucks ?
Or do you have an idea how to achieve silent circular motion with resistance ? I was thinking of something like winding/unwinding - continual never ending loop against some weight but that would require changing of the motion from wind to unwind to make it never ending and honestly it seems it isn't very simple to design.

Many thanks


texts: What must the ideal sampling rate be, to sample an input in regards to PLC's?

texts:
I'm trying to understand what the ideal sampling time for an input change represented in the form of a timing diagram should look like, for a PLC.

I understand the relationship between the sampling rate and input change to an extent. The sampling rate must be faster (at a higher frequency) than the rate of the input changes.

If I consider an example of an input that stays on for 25ms then switches off (when the input changes to a high), what is the ideal sampling rate to always measure this change and why?


texts: Design of a Four-Bar Infinity Coupler Linkage

texts:
How can I control a Four-Bar Infinity Coupler such that it does not accidentally become a Paralellogram Linkage? It seems to me that, when the bars are all horizontal, gravity could change the movement of the green driven linkage.

https://www.youtube.com/watch?v=NZZtXUcRZVs


texts: Can solar panels absorb heat for energy?

texts: Solar panels can absorb sunlight and use it for energy, but can they absorb the heat that is generated from their use and use the heat for energy?


texts:
Just a quick question for you. Well hopefully.

A contractor has installed a retaining wall with colorbond fence on top. In the contract he stipulated that he would use 65mm x 65mm x 1.6mm powder coated steel posts.

He has, by mistake, installed, 76mm x 38mm x 1.6mm powder coated steel posts.

The whole fence is now leaning over and has failed. Now given that these posts are cemented into the sandy soiled ground, which of the posts would be stronger?

The posts have been installed standing up. I.E. the 76mm has the fence attached to it and the 38mm is facing each of the gardens.

Any help gratefully received.

Thanks


texts: How do tractors with a highly placed carriage power their wheels?

texts:
I see tractors with really high wheels and with the carriage placed really high. Similar to this one:

How are the wheels powered? Is there is an electric motor for every wheel powered from diesel generator somewhere in tractor?


texts:
We need to position skips to within a few (~10?) cm on level ground. I've seen positioning systems for roll on/off containers, these were horizontal guide rails on the ground and presumably the container is pushed between them.

Skips are lowered onto the ground from above:

Source: Loacker

At first glance, a few bars jutting from the ground at an angle (to form a funnel) could do the trick. From looking at videos the skips swing when beeing set down. The bars would need a coating with PE or a similar soft(er than metal) and tough material.

I don't want to invent something as I'm sure this is a solved problem. So far my googling hasn't brought me to a solution. What to do when your skip needs exact placements?


texts: Heat Exchanger Design - finding necessary variables

texts:
I'm working on a project to design a shell and tube heat exchanger. There's a mixture of 68.4% C,3H6 and 31.4% C3H8 being cooled from 135 $^\circ$F and 321 psia to 100 $^\circ$F and 285 psig. The volumetric flow rate of the hydrocarbon stream is 200 GPM. The cooling water on the outside is initially at 85 F and 60 psig and exit pressure of 50 psi.

I'm not sure if my process is correct, but I found the average of the inlet and outlet pressure and temperature in the hydrocarbon stream and then used those values in the ideal gas equation to find the densities of each hydrocarbon, I then took the average of the two densities and multiplied by the volumetric flow rate to find the mass flow rate of the hydrocarbon stream. I was then going to use the equation
$$Q =m^o C_{p1} (T_2-T_1)(0.684) + m^oC_{p2}(T_2-T_1)(0.314)$$ to find the heat transfer of the hydrocarbon stream and then balance it with the water stream. I'm not exactly sure how to find the specific heats of the hydrocarbons. I checked perry's handbook but couldn't find anything at the average temperature. I'm just looking for any advice on whether or not this would be a correct procedure and if so, where could I find the specific heats of the hydrocarbons.


texts: Material requirement for excavator bucket, brushes and pins

texts: I would like to know what properties would be necessary in a metal material used to construct an mining excavator bucket the brushes and pins for mining coal. I think that hardness and toughness would be necessary for the bucket however the brushes may need to be made of a softer material to save the pins and bucket from wear.


texts: Boundary Conditions fro Static Structural Analysis of a Turbine Rotor Using FEM

texts: I am trying to perform static structural analysis of a turbine rotor which is rotating at a given angular speed, say 1000 rad/s. I also know the pressure distribution from CFD analysis. What are the boundary conditions for static structural analysis? I can use angular velocity as inertial load, pressure distribution from CFD as applied load. Do I have to restrain the  translation/rotation of surface 1, shown in figure? If yes, why?


texts:
I am a high school physics student and I've been trying to simulate the acceleration of a car as it fully accelerates from rest, but I'm finding it's much harder than I thought. Here was my first attempt (without including air resistance):

I used the horsepower to calculate the kinetic energy of the car since power = $\frac{\Delta E}{\Delta t}$ and in this case $E$ is the kinetic energy of the car. I substituted this into $KE = \frac{1}{2}mv^2$ and after manipulating the equation I ended up with:

$$v(t)=\sqrt\frac{2\dot{}hp\dot{}t}{m}$$

After taking air resistance into account, I substituted actual hp and mass of a Ferrari and took the limit as $t\rightarrow \infty $. My simulated top speed was very close to its actual top speed, but something wasn't right. The acceleration curve is decaying and at $t=0$ acceleration is infinite.

One source tested the acceleration of a few super cars from 0 to 60 and the acc vs time curve looks like this: After more research, I figured I must take into account torque, gear ratios, and RPM, but it only confused me more. Does anyone have any insight to make a realistic simulation, what equations to use, or which properties of the car are relevant? One car I would like to use for the simulation would be the Koenigsegg Regera because it has one fixed gear, which I thought could make calculations more simple. Thanks for any help or advice.

(Update)

Thanks to previous answers, I have found out that I can use a torque curve to relate the engine's RPM to torque, and thus solve for acceleration. The only problem that remains is how to find the rate of change of engine rpm. Consider a car at rest is running at 1000 rpm. If the driver then completely floors the throttle, how would I figure out how fast the rpm increases and approaches redline? To my current understanding, I need this information to find the torque at any given moment.


texts: Meaning of $\lambda_1$ factor in Eurocodes

texts:
I'm reading here on buckling resistance of members according to Eurocode.
Non-dimensional slenderness is defined as:
$$\bar{\lambda}=\frac{\lambda}{\lambda_1}$$
where
$$\lambda_1=\pi \sqrt{\frac{E}{f_y}}$$
$$\lambda = \frac{L_{cr}}{i}$$
The plain $\lambda$ is by definition the slenderness of the column, the ratio of its effective length to its radius of gyration. But what is the meaning of $\lambda_1$? No explanation besides its definition is given in the text. It is some factor by which we can divide the plain lambda or slenderness to make it "non-dimensional", but why does it take the form it does? What meaning does the square root of the ratio of elastic modulus to yield stress multiplied by pi have?


texts: Displacement of Gaussian point after structure simulation

texts:
When we did the simulation, we would get deformation and got each nodes displacement.

In physics, it shows the trajectory of a system of particles of the objects.

Is it the same as the displacement of the Gaussian point? Does displacement of the Gaussian point (obtained from the Subtraction from two phases gaussian point) also mean the trajectory of a system of particles of the objects?

Thank you very much.


texts: Which frame is optimal for children's bicycle trailers? tubular or rectangular frame and why?

texts:
I need to construct a 3D wooden bicycle trailer for Kids. The weight of bicycle trailers must also be light!
The Frame should be made of wood.
what criteria should I use to construct a Frame,Children's weights?

Thank you


texts: I am working on ANSYS Mechanical. As i was reading the user's guide i saw a section about contact behavior. Symmetric and asymmetric. Can someone explain me on this? How to use these contacts?


texts: How to size a heat exchanger for a shear thinning fluid?

texts:
To size a heat exchanger, I need to know (among other things) the Reynolds number (Re) as an indication of the flow conditions. The Re number depends on the viscosity. In a shear thinning fluid, I can't assume a constant viscosity, instead it will depend on the shear rate that is not constant throughout the pipe. I've asked on Physics SE about the shear rate in turbulent shear thinning fluid flow in a pipe, but received no helpful answer.

Here at Engineering.SE, I am not looking for an in-depth examination of the beauty of the Navier-Stokes equation, but for a practical approach to sizing a heat exchange for such a fluid. How to go about it?


texts:
I am going to try and ask this question again.

In this formula to calculate shear stress in a solid shaft:
τ = T r / J

If I want to solve for the radius; I should use the modulus of rigidity from the material sheet in the formula for τ ?

example, knowing
T = 1000Nm
J = pi * R^2 / 2
τ = modulus of rigidity from material sheet

If I want to design for a solid shaft with a known material and known torque then I can use the formula: τ = T r / J
replacing

[EDIT]

Density     2.6989 g/cc 0.097504 lb/in³
Mechanical Properties   Metric  English Comments
Hardness, Vickers   15  15  Annealed
Modulus of Elasticity   68.0 GPa    9860 ksi
Poissons Ratio  0.36    0.36    calculated
Shear Modulus

I added the above material property. Let's say that I am making a solid shaft that will be under torsional stress, the shaft will be spinning but at a low RPM so there's no shocks to them.

To keep things simple forget about about factor of safety.

τ = modulus of rigidity from the material property sheet, is that correct? If it's not correct; how would I calculate the diameter of the shaft based on the info that I have which are;
maximum torque
the polar moment of inertia
the mechanical property sheet


texts: Which glue is good for transparent ABS plastic and easy removal?

texts:
Hello all I need to glue some ABS plastic parts together some of them are transparent.

I used AA glue before but it will make my transparent parts foggy and after sticking them together its nearly impossible to disassembly.

So is there a better option than the AA 502 glue for easier removal and not fog my transparent parts?
Thank you


texts: What is the significance of a processors bit capacity?

texts: I'm learning about how processors send an address to ram through the address bus, and receive and send data from ram through the data bus. In the videos I have watched, the processor was an 8 bit processor that had 8 wires coming out for the data bus, and 8 wires coming out for the address bus, where each wire carried one bit of information, either off or on. That got me wondering. Does a 32 bit processor basically work the same way, but it can send more bits through the address/data bus at one time. What about a 64 bit processor. I haven't learned about registers yet, but I'm getting there. Does it have something to do with the size of the registry? I understand the parts of a processor, but I don't understand what people mean when they classify a processor by its bit capacity.


texts: How widely used are ethylene receptor inhibitors in fruit packaging & shipping?

texts:
Ethylene works as a gaseous "aging" hormone for many fruits.

There are lots of papers on ethylene receptor inhibitors (e.g. 1-MCP) to delay this process. I also found out that 1-MCP has been EPA-approved in 2002:

  In 2002, 1-MCP was approved by the Environmental Protection Agency for use in the U.S. as a tool for delaying ripening. The molecule has since been approved in 27 countries, including some in the European Union, for fruits as diverse as apples, kiwis, avocados, and persimmons. [...] Fruits are treated in an enclosed room for several hours, and the treatment blocks the receptor for up to 12 days. [...] The molecule has also been particularly successful in apples—in 2006, it received two gold medals from French apple industry trade groups. In bananas, however, this molecule's impact can sometimes be misleading [...]. 1-MCP may prevent banana skin from undergoing ripening-induced yellowing, but it doesn't always stop ripening of the fruit inside, possibly because it can't pass beyond the skin.

What I can't find out is how widespread such ethylene-inhibiting products are used in practice in the industry (of fruit packaging & shipping). Are there any statistics on this, even on small sub-sectors?


texts: What equations can be used to determine the height of Bernoulli ball levitation?

texts:
I need to design a controllable Bernoulli ball airflow levitation setup.

For context, the ball will be about 80 mm in diameter, and I need to be able to operate the height in range from zero to one meter from the air outlet.

What equations can be used to compute height vs airflow and outlet geometry?


texts: Different Color Intenensities from simple ON/OFF RGB subpixels

texts:
I recently got interested in an electronic paper.
One design that I liked was the one from Mirasol, Interferometric modulator display.

However, what I don't understand, is the following:
Their subpixels are either ON (color) or OFF (black).
Therefore, I am wondering how they can produce lighter and darker colors?

By lighter and darker colors, I mean that the color intensity is tuned. For instance for red:


texts:
Hey guys I need some help with a fluid mechanics problem.

I have a capillary with the given dimensions $d=0,15 mm$ and $L=5 cm$ and the operating conditions  $p_{1}=4\cdot10^{5} Pa$,  $p_{2}=0.25\cdot10^{5} Pa$
I want to calculate the velocity of oxygen flowing from 1 to 2. So I start with the formula for pressure drop with laminar flow
$\Delta p=\zeta \frac{L}{d}\frac{\rho u^{2}}{2}$ with $\zeta =\frac{64}{Re}$

which gets me $u=261 \frac{m}{s}$
After calculating Reynoldsnumber to check wether laminar assumption was right, I see that flow is turbulent ($Re=10175$)  So instead I have to take $\zeta =\frac{0.3164}{\sqrt[4]{Re}}$ (Blasius)
But with a little help of wolfram alpha

  solve p=(0.3164/((udrho)/eta)^(1/4))l/d(rho*u^2)/2 for u

I get a velocity of $u=142.9 \frac{m}{s}$.

Does this make any sense? I'm really not sure if I can calulate the velocity like this.


texts: Alternative substrate for nanomolding synthetic "gecko tape"

texts:
I have been interested in the prospect of leveraging Van der Waals force in an adhesive material for several years now.  The most notable example I have seen thus far is the highly publicized GeckSkin product resulting from biomimicry of Gecko locomotion.

Some key features of Nano-hair structure include:

  anisotropic attachment
  high pulloff to preload ratio
  low detachment force
  material independence / van der Waals adhesion
  self-cleaning
  anti-self matting
  non-sticky default state.

There is obvious far reaching impacts of such materials in everything from robotics to home decor and without a supply (I have already contacted the team involved with little feedback on estimated time to market) I have been investigating the prospect of good old fashioned DIY.

In my pursuit I have come across a simple method of NanoMolding synthetic gecko tape.  The key ingredient of which is the Millipore Isopore Polycarbonate Filter Membrane (Product# TMTP04700) which conveniently enough is sold on Amazon.

More information with respect to robotics can be found here.

Theoretically one could use the membrane to create a negative mold from which a more permanent reusable mold (possibly a Resin?) could then be used for future casts.  I figure resolution may be somewhat of an issue in this case, however, so this leads me to my question.

TL;DR
I would like to know if there are other materials with similar surface properties that may be good candidates to replace the membrane.  Something more readily available, reusable, lower cost, natural or man made.

Bonus  I am also open to suggestion on alternative methods for creating the synthetic setae.

 I had a hard time finding a place for this question as it is applicable to so many fields and there currently is not a dedicated Material Science StackExchange community.


texts: Ion exchange membrane that is dimensionally stable in organic solvents

texts:
For an electrochemical flow cell stack employed in electrosynthesis, I require an proton exchange membrane (PEM) in order to enable "divided cell" electrolysis mode.

The Nafion proton exchange membrane that is currently used exhibits massive dimensional changes due to swelling upon contact with organic solvents, for example a length increase of close to 100% in Methanol, or 50% in Acetonitrile. These solvents are crucial for many experiments and thus cannot be avoided.

This dimensional change lead to failing seals between the gaskets and the membrane and thus to crossover of material between the anodic and cathodic compartments.

I'm thus looking for alternatives to Nafion, the requirements are as follows:

-swelling in the mentioned solvents <20%

-high conductivity

-commercially available (or otherwise sourceable)


texts:
I need to calculate the required motor for a mobility scooter with the following user requirements.

The mass of the scooter with passenger = 120kg

Max Speed of scooter                   = 9Km/h

Time from standstill to max speed      = 10s

diameter of wheel is 0.203m

The scooter can hande a slope of   5 degrees

This is my working but it doesn's seem right.

Force

F = ma +mg sin (5)

F = (120 x 0.25) + 2 x 9.8 sin (5)

F = 30 +1.7

F = 31.7 N

Circumference of wheel

2 x PI x radius

= 0.63774 m

RPM

RPM = Distance per hour travelled / circumference x60

RPM = 9000 / 38.28 = 235.11 RPM

Convert RPM to Rads

235 x 2x PI/ 60

= 24.61 rads

Torque

Torque = radius x force

T = 0.105 x 31.7

T = 3.32 Nm

Power  (mechanical)
= T x 24.61

P(mech) = 79.2W

= 0.079 kW

An 80 W motor seems a bit low for a 120kG mobilty scooter to reach a top speed of 2.5 m/s with accleration of 0.25 m/s^2.

Would somebody be able to verify if this motor size is correct or if not where the mistake is in the calculations.


texts: I need something similar to a 3" to 5" curtain tension rod to fix my popping air ducts

texts:
The air ducts in my house have a couple of places where they make popping sounds as they expand while heating, one of the loudest ones is annoyingly in my bedroom.
I know by pressing around where I need to add compression against the wall in order to secure it in place to stop the popping. But I can't get a drill/screw in there since the hole is too small. My thought is if I can find something like a curtain tension rod I can put it inside the duct and push the walls apart which would give it no option to shift around in that area.
Problem is I absolutely can't find a tension rod short enough online. Is there a similar tool I can use that can range between 3" - 5" in length and acts like a tension rod?


texts: Chemical engineering calculations - basis

texts:
You have a gas of the following compositions : 40% N2, 30% CO2, 30%,CH4 in a tank . What is the Average Molecular Weight of the gas if your compositions is based on molar ?

I found that the AMR with basis set at $100$kg-Mol = $29.2$kg/kg-mol

As Im still learning , I tried to give a basis of $100$kg ... but I don't get the same AMR.

Why is this the case ?


texts: What is the difference between Ordinary reinforced concrete shear walls and special reinforced concrete shear walls?

texts: In ASCE 7-10 Table 12.2-1 two types of shear walls can be used ordinary reinforced concrete shear walls and special reinforced concrete shear walls what is it the difference between these walls ? (Reinforcement, Shape, Usage) and when do i use each type ?


texts: Can I use a single stator coil to actuate/rotate two rotors inside and outside of the stator

texts: I want to design a motor system where a single stator coil is responsible for two rotors of neodymium magnets on its outside and inside, will this work, and what are the downsides I should be expecting? Any advice on perfecting the design will be very helpful.


texts: Software correction of CAD or Gcode based on machine measurements

texts:
I own a CNC machine (Shapeoko 3 XXL) which I use to make projects that require good 90° angles, and I have been through several steps of improvement/calibration of the machine that are described in the documentation. However the rails of the machine's frame are nearly impossible to "square" below a deviation of about 1mm/meter or 2mm/meter. Besides that, the rails may be slightly different and some unknown factors can play a role an reduce precision of the machine. I suppose however that repeatability is far better than actual precision.
So I have though of something: why not measure the difference between the CAD and the result on several points on the xy plane of the machine and apply a correction to recalculate the CAD model, or even better, just the Gcode?
It makes so much sense that I thought I would easily find a computer program that already has been designed to apply such corrections on the Gcode, but I didn't fin any result on any search engine. Have you ever heard of such a project?


texts: Solidworks - How to safely clone a large multi-assembly project?

texts:
I have a top level project directory with about 40 Assembly files and several hundred SLDPRT files and they are all highly dependent on each other.

The original version of this works fine and has no errors that we know of.  Now I wish to safely clone this entire set of design files to form the basis of the next iteration of our design.

(The originals are of course backed up off-site and are entirely safe from any accidental corruption by stray references in the new cloned version.)

The question is, given the complexity of the project and the huge number of cross-references in the design, how can I make a cloned copy that has absolutely no residual links to the old design files, so that I can be 100% confident that the new cloned directory is going to be self-contained and free from broken reference errors?

For a single assembly or part it would be a simple case of using the "Pack and Go" feature of solidworks, but how can I reliably do this for multiple assemblies that are themselves cross-linked?  I'm worried that I might make a mistake somewhere and not realise it until a year later by which time it would be almost impossible to fix.


texts:
I'm attempting to design a system that consists of 4 secondary(ABCW), 1 primary(Film) tank, and a pump. The idea being to Transfer the contents of each secondary tank to the primary one, then back to the source tank before repeating the process for each of the remaining secondary tanks.

The simplest way to do this would be with a 2 way pump, but they seem to be very expensive.

So I've been trying to design around a uni-directional pump, but the simplest layout I've come up with requires 3-4 solenoid valves to route the flow back in the reverse direction.

(Dark squares represent solenoids, large box is the pump)

Not knowing the first thing about hydraulics, I'm hoping this isn't the optimal design. Could anyone point me in the right direction? Or show me an affordable ≥5L/min bi-directional DC pump?

Edit: the volume of the tanks is ~1L
Edit 2: Affordable = Ideally under $100, not over 200


texts: Motor, a gearbox and a drum with a cable lifting a mass

texts:
A lifting device consists of an electric motor, a gearbox and a drum with a cable for lifting a mass.

The speed after the initial acceleration is $v=0.5\,\text{m/s}$.

The gear efficiency $\eta=0.7$

Maximum motor torque is $T=15 \, \text{Nm}$

Motor inertia $J_m=0.005 \, \text{kgm}^2$

Drum diameter $d = 0.5 \, \text{m}$

Motor rotating speed after initial acceleration $n=2600\, \text{rpm}$

The inertia of the drum $J_L$ is considered small and thus neglected.

I want to Calculate how much time it takes for the motor to accelerate the mass $m=510 \,\text{kg}$ from standstill upwards to the given speed. Assume constant acceleration.

I know applying Newton's second law that:

$$F-mg=ma$$ and then we get the acceleration

$$a=\frac{F-mg}{m}$$ and the speed v

$$v=at$$ so $$t=\frac{mv}{F-mg}$$

The motor rotates the geared system $\omega_M$ and the geared system rotates the drum $\omega_L$.

The mass $m$ causes the torque $T_L=mgr$ on the rope drum. So the power of the load is $P_L=T_L\omega_L$. And therefore $\eta P_m=P_L$ and there I get the $\omega_L$ when $$\omega_L=\frac{\eta\, T_m\, \omega_m}{T_L}$$

But how do I get force $F$ so I can calculate the time or is there better way to do this?

Or can I calculate the acceleration $a = \frac{T}{J_{motor}}$