texts:
What are the advantages and disadvantages (technical, financial etc.) of having battery swapping system over charging stations for electric cars? As per my reading, battery swapping seems feasible for electric buses and 2-wheelers but not for cars. Is that really the case?

Also, is it possible for the battery to be housed under the bonnet instead of having it under the floor of the car so as to do away with underground swapping (like the one showcased by Tesla)? I know that the battery is placed there so as to lower the center of gravity. However, if there aren't any other significant benefits, can the aforementioned be done and battery swapping be made easier?


texts: Why does a proportional controller have to have a steady state (offset) error?

texts:
Been brushing up on my control systems knowledge and I keep seeing that a P controller WILL NOT have 0 error and that doesn't make sense to me.

Imagine a tank problem, the setpoint is 50 cm, you open the drain valve and the level goes down to 49. Controller output goes up and you start putting water into the tank. Controller output does not go to 0 until the level is back to 50. So while this may take a while if your Kp is low, it will get there.

I understand that steady-state error is not measured at infinite time but the idea that a P controller will not reach the SP is odd to me.


texts: Is this corner window correctly structured?

texts: Is this L-type corner window correctly structured? We used 18 rebars in total, 6 for each window. This building will soon have an RCC lintel.


texts:
Why Bode plots are on jw axis when determining gain and phase margin?
Usually it is explained as 1+G(s)H(s) should not be zero and margins represent how far away from this we are. But for showing this ("distance" to G(s)H(s) = -1, i.e. 0dB, -180 degree phase combination) we use bode plot which are GH values on jw axis. I would rather expect it to be on the whole s plane.


texts:
I asked this question at physics but i think this suits it more. I'd like to know few things about how does one design a Thermal Power Plant? There is something fundamentally lacking in my knowledge as I think there are a lot of parameters that I’m having trouble defining or estimating. I suppose this comes from difference between classroom studying and practical knowledge. So, let's talk about a small thermal plant of 1MW capacity. I have tried my best to be as clear as possible, but if some sentence is not making sense, I apologize in advance.

Starting with the steam turbine, I'm really struggling to find any specifications of that small size, while I know for sure that 1MW thermal power plants exists. And even when I do find the specifications, they mention only Temperature at which steam is to be fed and its Pressure. (Example: https://www.siemens.com/global/en/home/products/energy/power-generation/steam-turbines/d-r-steam-turbines.html) While these two are important and are the only parameters needed to find the enthalpy (h1), shouldn’t mass flow rate be included too? And what about the steam that will come out of turbine, only with that I’ll know what’s enthalpy at end (h2) and will be able to find its efficiency. Sometimes in specification they mention exhaust pressure without the temperature. How does that help? By multiplying the difference in enthalpies with mass flow rate ’ll get the power that I’m pumping in Turbine in form of steam. (correct me if I’m wrong here).

Once I understand the above, I’d like to know how the 1MW generation reacts to variable mass flow rate of constant temperature and pressure. As for the other components, I believe knowing the state of exhaust steam will help in deciding them. So, I may talk about them later.

If there are any free source books or videos available discussing the above then I’d be happy to go through it.


texts: How does Alloy 20 compare with Ti 6-4, C-276 and 316 stainless for corrosive service?

texts:
While I've designed tons of plastics for corrosive service, the fasteners to hold the plastics together are inevitably metallic.  There have been a lot of ways to protect them from rusting (due to exposure to things like 33% HCl, 50% H2SO4, 50% NaOH, and 15% NaOCl, for example) that I've seen, but here is a new one I haven't heard of until today - Alloy 20.  It's a nickel alloy apparently and seems to hold up pretty well.

One of my concerns about Alloy 20 is whether the parts are easy to obtain and available across the world? How does it compare with Grade 5 Titanium, Hastelloy C-276, and 316 SST as a fastener in plastics?


texts: Calculate effort to raise hinged lever with distributed load

texts:
My father-in-law would like to install a hinged stair system in his garage that allows him comfortable access to his attic space.

He wants the stairs to swing up flush with the ceiling when not in use, and then to easily swing down when he needs it, and plans on using a set of pulley and weights as a counterbalance to make raising and lowering the stairs easy.

I am thinking of the stairs as a "lever", where the lever itself is the "load" (i.e. the load is distributed).  If he places the ropes in the middle of the stair system, then obviously the "effort" is in the middle, while the fulcrum will always be at an extreme end.

My confusion is, since the load is distributed evenly, is this a second class lever or a third class lever?   Really I don't care what class it is, but it would be nice to understand how to roughly calculate the weight required to lift the stair system.  :)

Obviously we can just install it and keep adding weight to see what works in order to solve the problem, but I'd like to rough out some calculations first to see if there are any gotchas.

I found this link to a related Question, but this situation is just different enough that I can't tell if it solves my problem?

Any hints on what the equation(s) would look like to calculate the required weight (in pounds) to lift the stair system that weighs, say, $L$ pounds, and the ropes are $d$ distance from the hinge?


texts: "Transport Phenomena" (Bird, Stewart, Lightfoot) difference between edition 1 and 2

texts:
What is the difference between Transport Phenomena first edition (1979) and second edition (2002)?
Which one do you recommend to be bought, taking into account that I am a student and that the first one is cheaper?


texts: Numeric quadrature vs summation of running costs in model predictive control

texts:
Usually, an MPC consists of discretizing the optimal control problem in time using some numerical quadrature scheme. So the infinite-dimensional OCP reads
$$\begin{aligned}J(\vec{u}) &= \varphi\left(\vec{x}(t_i+t_{hor})\right) + \int_{t_i}^{t_i+t_ {hor}}l(\vec{x},\vec{u})\text{d}t \\
\text{s.t.}\\
\dot{\vec{x}}&=\vec{f}(\vec{x},\vec{u}), \quad \vec{x}(t_i)=\hat{\vec{x}}_i\end{aligned}$$
which can be transcribed to a static nonlinear program using, e.g., the trapezoidal rule for the integral and some other (or does it have to be the same?) integration scheme, e.g., the explicit Euler for the ODE, i.e.
$$\begin{aligned}
c(\vec w) &= \varphi\left(\vec{x}_N\right)+\frac{t_{hor}}{N}\sum_{k=0}^{N-1}\frac{l(\vec{x}_k,\vec{u}_k)+l(\vec{x}_{k+1},\vec{u}_{k+1})}{2}\\
\text{s.t.}\\
\vec{x}_{k+1}&=\vec{x}_{k}+\frac{t_{hor}}{N}\vec{f}(\vec{x}_k,\vec{u}_k), \qquad k=0,...,N-1\\
\vec{x}_0&=\vec{\hat{x}}_i
\end{aligned}$$
where $\vec{w}=[\vec{x}_0^T\ ... \ \vec{x}_N^T \ \vec{u}_0^T\ ... \ \vec{u}_N^T ]^T$ are the decision variables, $t_{hor}$ is the MPC horizon, and $N$ is the number of discretization steps.
But often it can be observed that instead of the above sum, the cost function simply reads
$$c(\vec w) = \varphi\left(\vec{x}_N\right)+ \sum_{k=0}^{N}l(\vec{x}_k,\vec{u}_k).$$
My question is, under what conditions is this possible? Can I always do this? I guess that it depends on whether the actual value of the integral matters or not but this implies that the integration does not change the optimal decision variables $\vec w^\ast$ since it involves just a scaling of the cost function? I could also imagine that it has to do with the function $l(\cdot)$ itself. Maybe this only works if $l(\cdot)$ is at most quadratic in the decision variables? Although I have seen this notation in nonlinear MPC.
EDIT 1: added ODE equality constraint and final costs
EDIT 2: Adding the final cost, I can see that one might need to have both discretizations to be the same or non at all for the continuous integral? Since in the discretized version, $\varphi\left(\vec{x}_N\right)$ depends on the final state which is the result of the ODE integration which, in this example, was done using the explicit Euler while the continuous integral has been approximated using the trapezoidal rule leading to different accuracies in the solution when they should probably be of the same order of accuracy? Therefore, just using the second sum leads to just adding up the values of the running cost term evaluated at the discretized steps which, in turn, depend on the ODE discretization. So this seems to make more sense to me than having two different integration schemes.


texts: Can drawing views in Solidworks be scaled without keeping aspect ratio?

texts:
I'm making weldment drawings that involve a long W-Beam with a number of flanges welded to the web. The problem is that because the weldment is so large, lines become difficult distinguish from each other when the weldment is scaled to fit the page.

What I want to be able to do is scale the X- and Y-axes of the view independently so lines become clear while still fitting everything on the page, like SDS/2 does. Solidworks does not appear to have this feature.


texts: How to get all forces and displacements values in abaqus and export it to excel?

texts:
I have made bridge model in Abaqus,
I also have done experimental study and I have the load-displacement data from my experiment,

I am now going to compare the results from Abaqus and the results from experiment

From this step, I want to compare the load-displacement curves between experiment and analysis in Abaqus.

how to get this information from abaqus to excel, please help me resolve this problem, I really appreciate it

Thanks


texts: How to reduce resonance from livingroom table

texts:
Odd ting, the table surface echo/resonance sound when speaking, especially lower lower frequencies. It helped putting on a cloth, but it did not completely remove resonance. Putting a rug beneath did not affect. Wonder whether box for roof lights may act as sound box or if it is just room size and large surfaces that are the cause? Also, would putting sound absorbing mat on wall or roof help?
Greatful for all answers.


texts: What's inside a peak expiratory flow meter, and what's the difference with an anemometer?

texts:
The peak expiratory flow meter is usually used to manage asthma. I wonder what's inside it and how can it measure peak flow?

What's the difference between this and an anemometer? Can an anemometer be used to do this work? Or is there something can be used to DIY one (like small computer fan)?


texts: Bending equation and max deflection of UDL and multiple point loads

texts:
I have a beam, simply supported with 2 points loads and 2 UDLs. The loads are symmetric about the centre of the beam.

I've tried to derive an expression for the moment along the beam and then via 2 integrations obtained expressions for slope and deflection respectively.

Could someone please let me know whether I'm close with what I have or help me to create an overall moment equation, which i can plot in MathCAD preferably, and also help me with finding the maximum deflection of the beam? Attached is the FBD for the problem.

Below is my attempt at a solution for deflection (In the case where x = L).

Any help is much appreciated.


texts: I'm trying to mesh a model of a morphing wing in Abaqus and have been running into issues. It was recommended that I partition the model into smaller parts, but it seems that the more I try to partition, the longer it takes. After partitioning into about 5 or more (small) pieces, it takes about 5 minutes or longer for each additional part. Is there a better way to go about this? I've posted a screenshot of my model so far.


texts:
How can I "tie" pressure change due to a mass leakage from the flow?
In a "closed" system I'd use $pV=nRT$ but this is an "open" system...

My open system is an horizontal (no gravity issue) pipe (constant sections) in which flows a gas. We may think pipe walls as permeable walls. Hence we have one incoming flow to the pipe inlet, and two outgoing flows: one from the pipe outlet and the other from the pipe wall

Assume the simplest case: Mach<0.30 and density is almost constant. To be complete, leakage is a known variable and I need to find outlet pressure


texts: Can Flowmaster be used to model an entire pipe run?

texts:
I just started using the Flowmaster program (ver 08.11.01.03 if relevant) to model a series of stormwater pipes which are almost certainly in a pressure flow situation based on a first round analysis using open channel flow which failed due to insufficient pipe capacity.

I completed my model yesterday by modeling each pipe between structures and noted that the hydraulic grade line easily exceeds the grate elevation for a lot of my structures and is thus overflowing. In these situations, I sort of brute forced the program to model the next pipe section by assuming the downstream hydraulic head was equal to the height of the water column at the downstream structure.

This isn't ideal as it doesn't account for losses due to pipe bends, structures, and other elements that can cause additional losses. I have previously created an Excel spreadsheet to model these sorts of losses, but it was a very complex spreadsheet created for another company that I no longer have access to.

Given that I previously made something like this with just Excel, it seems like Flowmaster should be capable of doing the same. Is it possible to use the program to model everything in the run in a single go so that losses are properly accounted for?


texts:
I am curious to know if a Jacob's Ladder would produce enough hot air to keep a hot air balloon afloat, or in other words, that it could be a substitute for a standard gas burner used for hot air balloons which carry humans. I am not actually planning to build one and use one for a real hot air balloon, it's just a scientific curiosity that I've had for a long time that I would now like to get an answer to from the Engineering community.

I am thinking that one could use several car batteries connected in series as the power source and a cable from these batteries would be connected to a high voltage transformer which would provide the high voltage for the Jacob's Ladder.

Not being an engineer, I have no idea how large the Jacob's Ladder would have to be in proportion to the hot air balloon, nor do I have any idea as far as how long the two rods would have be or what their thickness would have to be to handle the high voltage spark and heat from the plasma.

Also, I understand that the Jacob's Ladder could not inflate a hot air balloon by itself, one would still have to use a standard hot air balloon inflater/fan for doing that, yet once it's inflated, the Jacob's Ladder would then be turned on and would produce the hot air needed to make the balloon rise and keep it afloat.

Could a Jacob's Ladder produce enough hot air for a hot air balloon?

EDIT

Based on the comments and answer I've received about this idea, I am now thinking that instead of using car batteries, one could bring on board a small gas-powered electric generator and connect that to the high voltage transformer. A small, lightweight model like the one shown below may be an ideal model to use:


texts: Determining the headloss according to Darcy-Weisbach with pipes in parallel and series

texts:
Given the following situation:

Pipe A and B have a known and identical length and diameter, and are in parallel. I'm assuming the flow trough pipes A and B are also identical, as is the roughness of the pipes.
Pipe C also has a known length and diameter (which is different from the diameter of pipe A/B).

I'm interested in the total head loss at the end of Pipe C. I am aware of the following Darcy-Weisbach equations that are relevant in this case (parallel and series):

Here the total headloss is the sum of the headloss per pipe, placed in series.

Here the total headloss over set of 2 parallel pipes is equal to the headloss of one of them.

But, how do I combine these two equations to retrieve the total headloss over pipes A, B and C?


texts: I have a huge model for which I am performing modal analysis. Abaqus fails to solve with Lanczos solver and hence I use AMS solver, which successfully computes the solution. But since AMS solver always does mass normalisation and I need modal masses, is there a way to extract modal (generalised) mass from abaqus in this case?


texts: Open loop versus closed loop Model Predictive Control

texts:
I hear a lot about open loop and closed loop Model Predictive Control (MPC).

What is the difference between an open loop MPC and a closed loop MPC?

Any block diagram demonstrating the difference is also appreciated.


texts: Why is electrical energy most commonly stored in metal acid batteries?

texts:
Why is electrical energy most commonly stored in relatively expensive metal acid batteries, which have a short life, rather than hydrogen gas accumulated through electrolysis?

Hydrogen is a versatile energy source itself and with low cost technology is a cheap, clean and reliable fuel.


texts: How could I get the coordinates of the circumscribed circle giving the 3 points coords?

texts:
I have the coordinates of 3 points thrgouh which, a circle should pass . Having the coordinates of the points in 3D, how could I have the coordinates of the center of circumscribed circle ?
also : if one of the points has some deviations and causes a circumscribed circle couldn't pass through the 3 points, is there a way to determine the required coordinates of the third point in a way that the circle could be constructed to find the deviation in space ?


texts: How do I calculate the member forces of a truss when external force acts on the member (not joint)?

texts:
Given a three member truss structure shown here:

How do I find the vertical and horizontal displacements at M?
Assume all members are elastic and E,A, I and constant.

I start with finding the reaction forces with
$F_x=2P-H_B=0, H_B=2P$ (rightwards) and
$M_B=2l*V_A-2Pl=0, V_A=P$ (upwards)

Hence $N_{AB}=2P$ and here is where I get stuck. I cannot find the forces that put joint A into equilibrium.

Edit: Additionally, show all member forces


texts: Optimization of ash stockpile height to minimize haul truck fuel costs

texts:
How would I find out the optimum height of an ash stockpile in order to minimize diesel haulage costs, for a CAT haul truck?

My stockpile height is required to be between 25m to 50m.

I have worked out the fuel consumption and time taken from the start point to the haulage area, based on required speeds obtained from the rimpull-speed-gradeability curves for that particular CAT truck. But I'm not sure how to relate this to the calculating the optimum stockpile height?


texts: 'Length measure' vs. 'length measurement'

texts: I have to write a scientific paper where I refer to a CAD drawing. Now, I'm a bit confused, because I have to refer to the length "parameters" on that drawing (as opposed to the angle "parameters"), e.g. the segment lengths l1, l2, ... Should I refer to these length parameters as "length measurements" or as "length measures"? I used both as a synonym so far, but I'm not sure if that is accurate.


texts: Determination of Warping Function for Thin-walled Multi-cellular Beams

texts: I am trying to find warping function $\mathcal{T}$ for a thin-walled multi-cellular beam. There are four rectangular cells. The governing differential equation for $\mathcal{T}$ is Eq. 8.98 as shown in attached figure. But I don't know the boundary condition.


texts:
The question reads

  Design a horizontal pressure vessel with hemispherical head supported by saddle support and fitted with 2 nozzles welded to the head. It's used for storing and delivering fuel oil with API gravity 70. Internal pressure is 140/150 Psi and internal temperature 190-200 deg C.

I can't figure out where to start.There seems no way to find out the thickness or radii. How do I approach this problem?


texts:
I am building a very simple turbine that runs on steam. I want to make it as simple as possible, thus avoiding impulse and reaction turbines.

I want to design the turbine to fit in an exhaust pipe (about 15cm diameter) so that steam would rotate it, and generate electricity.

How many blades must the turbine have? I know wind turbines are most efficient with 3 blades, does this also apply to simple steam turbines?


texts: Is there a relationship between temperature and pressure of a refrigerant?

texts:
When searching for a pressure temperature relation for a refrigerant a chart appears.
But I was wondering are these charts made by experimenting on the refrigerant or is there a relationship which can be applied for every refrigerant in order to determine the temperature of the refrigerant at that specific temperature


texts: Simple way to duct a PVC pipe through a stainless steel sheet cover

texts:
I need to duct a PVC pipe (DN80) through a stainless steel sheet metal covering. The hole thing needs to be tight against stormwater. There's tons of products to duct pipes through thick walls, but I'm at loss on how to do that here. The cover is horizontal, upside checkered. Ideas I've considered:

Welding a short stainless steel pipe stub onto the sheet and use a ring seal
Hole with ID of pipe in steel sheet, flange the pipe through the sheet

Both of these appear overblown to me.


texts: What is the amount of force that will cause failure?

texts:
What is the amount of force required to cause the beam to deflect, shear or otherwise fail?
The force would be generated by a hydraulic piston. Let's
call those units PSI.  The piston will be mounted to the flange by the brackets at each end. They will be L4" x 6" x 5/8" that is 4" long. A piece of 5/8" plate will be welded to the center of the angle. 4 holes will mount the base plate of the piston to the bracket with 7/16" bolts. The brackets will be back gouged and welded to the flange of the W12x14# 6" from the end of the beam
The beam will be 4' long and the hydraulic piston will move along a 12" span. It will clamp onto and press varying thicknesses from 0" thick up to 12" thick. The piston itself will be 18" long and can be mounted from either end of the beam. A 6" die will be mounted to the opposing end as the piston.
The beam and brackets are both A36 steel. All welds will be mig.
Let's say failure = deflection so great the beam will not return to its original shape. Or where the beam fractures / tears etc.
I would assume there would be a point where the force generated would simply bend the beam, without generating additional increase in psi. That would be failure as well.
I made a dwg. File but can't figure out how to upload it the jpg quality isn't great. Hm.
Please let me know if there's anything else I can add to make this more clear / solvable. Thanks!


texts: Why does my engine accelerate so slowly in rev at neutral?

texts:
Mustang EcoBoost - Turbo 4cyl - 2.3L
310hp 350ftlb
4.7 sec 0-60mph on 3600lbs car
When revving in neutral at WOT it takes like 0.9 seconds to go from 1200rpm to 5000rpm
The physics don't seem right. So I'm thinking it's electronically limited by software to not go all out in neutral.
Since I feel like if it can take a 3600lbs car from 0-60mph in 4.7 seconds it should be able to rev itself by 3800rpm in like 0.1 seconds, not 0.9 seconds.
My question is how many times faster could cars rev if they weren't electronically limited like this? I didn't do the kinetic energy calculations to see how quick in theory it could be based on 0-60 of the car since I feel there would be less efficiency due to lower load when revving.
What could it do?


texts: Refill evacuated water reservoir from elevated tank, without valves?

texts:
Is there a way to refill an evacuated water supply reservoir from an elevated water supply tank, without using any valves, but only the power of gravity?

I already know that a siphon is needed to start the flow from the elevated supply tank, but I do not know how to push the air out of the lower reservoir, send water into it, and then retain the water without admitting air through the water fill tube or air communication tubes.

Also, where would be a place to look for possible solutions to these questions? I have researched the technology of intermittent dosing siphons for sewer flush systems from the 1880's before electricity was widespread, and I know that air communication tubes can be extremely complex and dynamic in operation, but there is apparently no formal way to describe it.


texts: Calculate surface area and outward normal of each face(non-planar) for a irregular hexahedron.

texts: I am using the vector cross product to calculate each surface area and thus the outward normal. However, this approach fails when the surfaces are non-planar. So what is the best approach to calculate surface area and normal for a non-planar face of a hexahedron?


texts:
I need design a trolley with four casters, the four casters are installed on the four corners of a 460mmX405mm metal plane. And the load will be a cubic 380mmX225mmX350mm (Height is 350mm), weight about 150Kg, site at the center of the metal plane.

The dimensions of the casters is as below:

You see the support point of the caster and the wheel are not on a vertical line, so I'm afraid when all four wheels in the same direction, the trolley will not be stable. So I go here for some suggestions(or some formulas are better), if the trolley can works stable? Or I must change my design, such as enlarge the metal plane?


texts: What is the difference between tau = VQ/It and tau = V/A?

texts:
What is the difference between the formulas $\tau = VQ/It$ and $\tau = V/A$ for finding shear stress due to transverse loading? I understand that the use of first moment of area, is the only reason for the more complex formula to account for shape?

For a square cross section the maximum shear stress used for failure analysis is simply 4V/3A, which relates to tau = V/A except it has a multiplication factor of 1.33. What is the point of this safety factor, since the rectangle is such a simple shape, and which formula should I use? The factory of safety ends up being very different due to the extra 1/3.


texts: Exploiting fluid dynamics for the optimal design for gas mixing in a furnace

texts:
Background

This is the standard design for a thermal furnace used in the Clauss process, which converts H2S to SO2.  The main problem with the furnace is that gas mixing is rather poor and results in only a 60% conversion rate.  This in turn increases downstream equipment costs to handle the impurities.  A design improving the mixing of the gases is highly sought after.

H2S and O2 is fed separately into the reactor.  The combustion reaction starts and increases temperature to about 1400 °C.  The choke point in the centre of the reactor is there to force the gases to better mix on either side of it.

  What I have done thus far

I have a design modification on the injectors that allowed much greater mixing, with inspiration taken from fuel injectors in motor vehicles.

I did not include the choke point in this drawing.  It was merely done to test the validity of the concept.

The twice-angled injectors provide horizontal as well as radial velocity to the inlet gases.  This causes a swirling effect on the fluid, improving mixing by about 60%.  Mixing is here defined as the homogeneity of the outlet product distribution.

The advantages are two fold: The gas particles need to travel further due to the swirling, increasing the time they stay in the reactor.  Thus, a larger conversion is also achieved, or viewed from a different perspective, a smaller reactor is needed to achieve the same conversion as the standard unit, dramatically reducing costs.

  The question

I wish to exploit certain fluid dynamics phenomena to improve upon the mixing.  Eddy formation, for example, is used in the choking section. What else can be done to improve mixing?  What features can be added/removed?

PS: Explain your proposed design in words, no need for actual modelling.
Of course, it would help me to see the idea, but it is not necessary.

I have access to Fluent in which I simulate these designs and compare them to the standard unit.

I am still eager to see what you can come up with.


texts: What does "a" mean at the end of a refrigerant's designation (R-134a)?

texts:
I was studying the designation of names to refrigerants.

The following is the basic formula:

R - (m - 1) ( n + 1) ( o )

where:
m = number of carbon atoms in the refrigerant
n = number of hydrogen atoms in the refrigerant
o = number of fluorine atoms in the refrigerant

So R-134a has:

1 + 1 = 2 carbon atoms
3 - 1 = 2 hydrogen atoms
4 fluorine atoms

What does the 'a' at the end mean?


texts: How do I add magnets to the mechanism of my exercise bike?

texts:
I have an exercise bike that works by a (I'm assuming solid iron) flywheel and a 'horseshoe' of magnets that are moved in and out to set the difficulty.

I have attached an image of the same design found on Google Images so you can see what I have:

What I want to do is make the bike harder to pedal. For this, I have bought a bunch of neodymium magnets online, after reading that they were the strongest magnets you can easily get.

I bought a bunch of circular ones and smaller flat ones. I've routed an 'arm' out of MDF to screw them onto - so far I've only done the circular ones but I would have gone on to try the flat ones as well. I've illustrated what I'm doing here:

So I'm using the MDF arm as a lever to move the magnets in and out in the same way as the horseshoe would. The idea is to test the concept before I go messing around with the real horseshoe.

And I'm glad I tested it because so far, nothing is working as I would intuitively expect. The magnets have no effect at all on the flywheel!

What's going on?


texts: How to achieve pulsation damping in pneumatic rather than hydraulic system?

texts: My background is in electrical engineering so I am something of a novice when it comes to pneumatic systems, but I have been tasked with designing a sampling system that draws an extremely low flow at low pressure with a diaphragm pump (0.25 lpm) which is then read by a flow meter (0..1 lpm) before passing through an oxygen sensor. The trouble is that the pressure pulsations from the pump cause a very inaccurate reading at the flow meter. We have since discovered that implementing a makeshift latex reservoir between the pump and flow meter almost eliminates the problem completely, however this is not a very industrial solution. After further research I found that a similar solution in hydraulic systems is known as a hydraulic accumulator, but I can't seem to find an equivalent product for pneumatic systems. Is there some obvious solution that I am missing or does no such product exist?


texts: why do 15kV 60mA transformers have to be so big?

texts: I need a high voltage power supply for the homemade CO2 laser I am building. I understand that a 15kV 60mA transformer is a thing, but its very big and heavy and its out of phase meaning each lug is only 7,500V and the difference is 15,000V. This would work for most applications but not one where i need 15kV positive and GROUND. I have seen simple arc lighter things that generate a supposed 15kV from a small battery, but the amps must be low? How can i design a simple 15kV high amperage transformer that can be smaller than a neon sign transformer?


texts:
I don't know where to turn to get an answer to this and I hope this is not the wrong setting to ask for this.
I am looking for this Song Chuan relay ( and I prefer not to order it clear from China.  How do I go about to match this unless no other manufacturer makes it.  If I need any relay how do I type it online instead of having to deal with all kinds of things I have to shuffle through and still nothing.  I think this is a pretty complicated business.
If the manufacturer's name is worn out on a relay, one could be in for an interesting obstacle course to match it online.  It appears that only by knowing the manufacturer's name one can zero in for a particular relay.
What am I missing?
How would you match this relay and buy it here in the U.S. somewhere?
Thank you very much in advance.


texts: How can we derived the equivalent Lumped Mass Model for irregular building and how to calculate the errors?

texts:
Intuitively, building can be represented as a lumped mass model ( the taller the merrier!):

Assuming a building is a lumped mass cantilever column also makes the global stability checks easier because building codes often assume building structure as a cantilever column.

But if my building structure is discretized and response analyzed in terms of FEM ( with column/beam as line element, and slab/wall as area element), then is it possible that, from the stiffness matrix and everything I have in FEM, I can still approximate the structure as a lumped mass model? If yes, how to do it? How to calculate the errors involved?

A practical application of doing this is in this question. But for the purpose of this question, let's assume that I do it for academic purpose and don't really want to care about the application.


texts: Classifying motor imagery using EEG data

texts:
I am an undergraduate student who is trying to classify motor imagery from EEG data!

I have no experience working with EEG or any neuroscience background, I only have a very basic knowledge of how EEG, ERD/ERS and frequency domain work from the papers I've tried to read but don't understand and the basic idea of what they are doing. I also have a reasonably basic knowledge of supervised Machine Learning.

I plan to use ERD/ERS to classify Left foot, Right hand and rest to classify motor imagery in real time!

What is the easiest way to do this?

So far I have bandpassed the data between 7-30 Hz for Mu and Beta wavelengths as they are the ones related to the motor imagery as well as removing the baseline and just plotted the Power Spectral Density. I passed this data through a basic SVM; linear and gaussian, optimised parameters with poor results (60% accuracy on average)

I have no idea how to do feature extraction, where to start, how to properly classify EEG data. and how to do this in real time.

If someone could guide me and provide the steps on how to proceed I would extremely grateful!

I want to work in the field of Brain Computer Interfaces as I find it fascinating, this is my first step :)

Here is the link to the dataset and its details BCI competition: IVc


texts: What is the practical limit on the number of storeys in residential buildings built with monolithic reinforced concrete?

texts:
I have recently bought a flat in a 25-storey building. I wonder what is the practical limit for the number of storeys in a mass-produced residential buildings built from monolithic reinforced concrete?

Can we expect the number of storeys in typical buildings of this type to rise in the forthcoming years or this is the reasonable limit of the technology? In all references I saw so far it was claimed that this technology has no limits on the height of the buildings. But I doubt this because all skyscrapers I know were built from steel.

If monolithic reinforced concrete has no limitations, why have very tall buildings not been built with this technology?


texts: A statics problem containing a distributed triangular load and a linear load

texts:
I have came across this problem and I couldn't figure it out

I have used the following equation

$$\begin{align}
y &= 6 - \dfrac{2}{3}x \\
V &= 26 - \dfrac{2}{3}x^2 \\
M_x &= 26x-\dfrac{2}{9}x^3
\end{align}$$

for the triangular part of it but the answers provided with the question are not matching mine


texts: Longtitudinal Centre of Gravity for Ship Cargo

texts:
I did a Civil Engineering course some years ago and this question from my textbook, I have found what seems impossible to get the correct answer of 46.2 m for. By putting this question up I am hoping that I will be able to come to a conclusion on how this should be solved.

A ship displaces 10,000 metric tonnes and area of its plane of flotation is 1,480 m^2. The centre of mass is 49 m and centre of area of plane of flotation is 55 m from the stern.

The metacentric height for pitching motion about transverse principal axis is 91.5 m. The ship is loaded in sea water with 300 metric tonnes of cargo. Find minimum allowable distance of mass centre of this extra load from the stern if, when ship passes from sea water into a fresh water canal, the stern draft must not increase by more than 0.3 m ?

Assume metacentric height and area of plane of flotation are not altered by the change in draft, density of sea water is 1,025 kg/m^3 and density of fresh water is 1,000 kg/m^3.

Just looking for some help on this from someone who understands ship stability well.

Here is my attempt at finding a Solution to this Question

The first step:

We will put the 300 Tonne Cargo Load at the ships centre of gravity of 49 m, so we don't have to correct ourselves.

Firstly we will treat this as if the cargo has a weight shift from centre of flotation to centre of gravity to calculate the aft added draft from the cargo.

We need to run the Change of Trim Formula

by using COT = (100 * LBP * w * d) / (W * GML) with d = 6 m because you want to have initial LCG AT 49m

COT = (100*LBP*300*6) / (10,300*91.5)

Aft Added Draft = (LCF / LBP) * COT = (55 / LBP) * [(100*LBP*300*6) / (10,300*91.5)]

and LBP cancels out,

so Aft Added Draft = (55*100*300*6) / (10,300*91.5) = 10.5 cm at original 49 m CG

The Second Step:

Now we need to take into account sinkage change due to density, for 10,000 Tonne Ship + 300 Tonne Cargo all at 49m CG

Tonnes per centimetre (TPC) = Density of Sea Water * Area of Waterplane * 1/100

TPC = 1.025 * 1,480 * 1/100

TPC = 15.17 Tonnes per cm

Parallel Sinkage in Fresh Water = 10,300 / 15.17 = 678.97 cm

And because the Density Changes

at 49 m CG the Sinkage Change = [(1.025 - 1) / (1)] * (10,300 / 15.17) * (49/55) = 15.12 cm

The Third and Final Step:

The cargo will shift from the ships centre of gravity of 49m, to where it should be.

For this part we will firstly have to calculate the remainder draft.

The remainder draft = 30 - 10.5 - 15.12 = 4.38 cm

Like before we need to use Aft added draft formula, but this time we need to find d (distance moved)

So now find d in following formula:

Change in Draft Aft (from shifted load) = LCF [(100 * w * d) / (W * GML)] = 4.38 cm

Now solve for d

4.38 cm = 55 [(100 * 300 * d) / (10,300 * 91.5)] = 55 [30,000 d / 942450]

so d = 2.5m

and this gives my answer so far of 46.5 m from stern for Longtitudinal centre of gravity of cargo.

This is 0.3 m off the answer,
so this is what I mean by it seems impossible to get the correct answer of 46.2 m. By putting my answer up along with the question, I am hoping that I will get feedback from someone who knows how this works and can point me in the right direction.


texts: Peclet Number and first principle for open system

texts:
The Peclet number express the ratio between the heat transferred by advection and by conduction (diffusion). If it is sufficiently high the heat transferred by conduction can be neglected with respect to the other term. In a book I've found that the first principle of thermodynamic applied to a tube, under the assumption of high Pe, is the well known formula:

$$Q=mC_p(T_{in}-T_{out})$$

How should this be modified if the previous assumption is not fulfilled?

$$\frac{dE}{dt}=\sum m(h+z+v^2/2)+Q-L$$


texts: How does this AGV rotate without rotating the payload?

texts: How does the AGV carrying payloads of huge heights as compared to it's size turn without turning the payload? Even if the body is attached to a center bearing, the bearing is very smooth then how come these bots are able to rotate so precisely?


texts:
Im currently writing a model for a guidance law named Maintaining Guidance law.

The law looks as following: $$ a_{M} = [K_1,K_2]*[\dot{\lambda_T} ,\dot{\lambda_D}]'$$

Since im using a linear model I use the following calculations:

$$ \ddot{y} = \ddot{y_T}-\ddot{y_M}=a_T-a_M$$
$$ \dot{y} = \dot{y_T}-\dot{y_M}$$
$$ y = y_T-y_M$$

Where: $$\dot{\lambda} = \frac{y+\dot{y}*t_{go}}{V_{c}*t_{go}^2}$$

And K1 and K2 are vectors calculated before.

The engagement looks as following:

I tried to transform it into X-Y axis however I got stuck in few things I couldnt figure out as:

1) In this model, $\dot{\lambda}$ depands of $t_{go}$ which becomes small close to the end and makes $\dot{\lambda}$ huge ---> $a_M$ is huge ---> $V_M$ is not constant as taken in linearized models.

2) The same problems occurs when I use $v_{c}$. In all the linear model $V_c=V_{M}+V_T$ where the velocities are constant. How to use it then in my model since its not constant/almost constant.

Is there any tips of how to transform it to X-Y graph but still keep it linear?

Thank you!


texts: I realise that "bomb" can refer to all sorts explosives, but I am mainly interested in air-dropped bombs. Ever since reading about the USS Forrestal fire, I wondered about the safety of bombs when stored or transported in general- but in plain English: suppose I were able to hold a bomb in my hands- say, the B61 Nuclear bomb or the GBU-10 Paveway II- would it be okay to drop it on the ground? How often could I drop it before it damages the bomb? Is there a minimum speed/impact required that could be reached without using an aircraft?


texts: Valve that opens at low pressure closes high pressure

texts: My fluid handling system requires a valve that will open at low pressures (2-6 PSI) and close at high pressures (8 PSI). Is there any commercially available valve that is suitable for this application?


texts: Suggestions on how to keep electronics cool in high ambient temperature location?

texts:
What are the best materials and methods to keep the internal temperature of a device lower then the ambient temperature outside of the device? Based on the following information:

Starting temp of device is 20°C
Ambient temperature around the device is 200°C
The time in this environment would be one hour (1hr), after which it would be removed
The electronics in the device would be very low powered
The size of the device would be 2" square
The device would be re-usable
The device is in an oven, hot air surrounding it
Inside the device is also air
It is a simple sensor outputting readings to a bluetooth module

The goal would be to keep the internal components below 125°C

Any suggestions on how to achieve this would be helpful.


texts: Find the load applied to each wheel by the anti-roll bar

texts:
Wikipedia says that an anti-roll bar is a device that balances the weight of car between the wheels, preventing it from rolling. I want to simulate this in a game, but I don't know the equations behind it. I need to know how much weight the anti-roll bar transfers to each wheel. That means that I need to obtain a value that I can add to the load of wheel to manage it.

$W_{load} = W_{static} + W_{transfer} + W_{anti-roll}$

The static load is dependant on weight distribution. I do it like so:

$W_{static} = L_{0} / L * m * g / 2$

Where $L_0$ is the longitudinal distance from the opposite (e.g., if checking the rear wheel, than this is the front wheel's distance) wheel joint axle to the centre of gravity, $L$ is wheelbase and $m$ is mass of the car.

The $W_{transfer}$ is acceleration-dependent.

How can I obtain the $W_{anti-roll}$ value?


texts: What is the etymology of "bridge cam gauge"?

texts:
On the pictures below is a tool called "bridge cam gauge", mentioned in this answer. I wonder why the words "bridge" and "cam" are used in its name.

I found a definition of "cam" that might be relevant:

  A curved wedge, movable about an axis, used for forcing or clamping two pieces together.

As I understand, the 'cam' here is the flat roundish beaky plate that you can rotate about its hinge.

But what about "bridge"? Wiktionary offers a variety of senses, which makes it hard for a non-native speaker of English.

Also asked on ELU SE.

P.S. It is also called "cam type weld gauge"


texts: How can I stop carbon fibre mat from fraying?

texts:
I want to use a woven carbon fiber tube in cloth form to act as an acoustic absorber in a 40 mm internal diameter pipe. The bad news is that it has to carry a variety of solvent/air mixtures at temperatures up to 80 °C.

When it is cut to length the ends fray horrendously. Now, an obvious way to stop this would be to put some tape around the end. Unfortunately I cannot find a tape that can withstand alcohols, ketones, hydrocarbons and chlorinated hydrocarbons. The solvents are why I am using carbon fiber in the first place. I could move to glass fiber but I expect I would encounter a similar problem.

How can I stop the cut ends of the mat from fraying?


texts: How to hermetically seal a circuit in a visual & bluetooth transparent solid cube ~2-3"?

texts:
I want to encase a circuit in a ~2-3" cube of some kind of visually and Bluetooth transparent material.  What material will do this?

Something like:
1. half fill a cube shaped mold with liquid or jelly material
2. add circuit
3. fill up mold so that circuit is 'floating' in the middle and sealed.
4. wait for material to dry
5. circuit is now sealed within sold, transparent cube, and can be controlled via Bluetooth from iPhone app.

I want to demonstrate that the circuit with battery and Bluetooth communication can be controlled wirelessly from iPhone management app.


texts: can anybody tell me what subject in Mechanical engineering deals with the making of External cases for electronic gadgets? I know I need to use CAD/CAM but I am asking this question because I want to know about the materials - How to determine what to use, where and why. Suppose I want to design an IP 67 casing for an electronic gadget, How would I go about it, where do I start?


texts: Number of layers required for composite mold

texts: I am new to manufacturing and especially to composites. I have a cylinder to be made out of carbon fiber (only the outer shell) and I know the weight I want from this structure after manufacturing. Is there a way to calculate the number of layers required for this process assuming a 1 to 1 ratio between the resin and the reinforcement. Really sorry if this question doesn’t make sense or not clear enough


texts: Transition frequency of power transistor

texts: Why transition frequency of power transistor is typically below 30 mhz?  Detailed search on internet doesn't reveal any power transistor which can handle 5 Amp or more and has transition frequency of more than 30 mhz.  While signals transistors have frequency up to 300 ghz.


texts: Measure distance between a circle and an ellipse center in autocad/inventor

texts:
I am working on a robotics project, I got a SolidWorks sldprt/step model of the robot(cca. 40 solids). However, I have only Autocad/and Inventor available.

I need to measure a distance from n ellipse center (endpoint) and a circle center - joint axis.

Unfortunately, the ellipse and the circle lay in different z levels, are hollow and belong to different solids. No matter what I try, I can get neither the inventor nor the autocad to measure the distance using annotate or measure.

Thanks for the help.


texts: I'm using existing architectural designs and some mechanical designs too, all CAD files in formats *.dwg, *.dgn and the drawings have smart solid geometries including voids. Using CAD software what is a void space and why is it important to create voids as an object?


texts: What plastic material blocks the most amount of light?

texts: If I have a grid array of LED's surrounded by roughly 0.7mm thickness plastic walls. What material at this thickness would prevent light bleed side to side so that individual LED's can light up but not light up their neighbor?


texts: Force required to rotate an object on a plane - moment of inertia?

texts:
I have a rectangular shape with uniform mass, approx 6m x 1m. It rotates around an axis in the centre of its width but 1m from one end. The axis has some friction but this is not known.

What I need to work out is how much force is required to start rotating this object from different positions from the axis.

I fear I may be plunged out of my depth but if anyone could point me in the right direction it would be really appreciated!


texts:
In Eulerian description of fluid flow, we observe how the properties of the fluid are changing at a point. Since a point has zero dimension hence a zero area, how can we make sense of the 'finite pressure at the point' phrase?

Since fluids are discrete in nature, a collection of molecules, the way I think about it is that Imagine that we are measuring the pressure with a measurement device [assume] which is cylindrical in shape having diameter enough so that Knudsen number is quite low [continuum hypothesis is valid]. At the molecular scale, Pressure is collisions of the fluid molecules with the measurement device. We position the device in the fluid with direction of fluid flow in such a way that diameter is the characteristic length. Let's say we keep on decreasing the diameter of the device hence the Knudsen number will keep on increasing and it will reach a point when the continuum hypothesis is not a good approximation anymore.

Shouldn't it be that the diameter should approach a finite threshold value [no matter how small it is] rather than zero for continuum hypothesis to hold true?

[On the same note, when a pitot tube measures local velocity, it does not measure velocity at a point 'strictly' because it has a finite area of opening for the fluid to enter and I guess surface tension effects will also come in to play if we decrease the area of the opening. There is only so much area we can decrease theoretically for the continuum hypothesis to hold true.]

Hence the way I visualize a point in Eulerian description of fluid flow is that it is a collection of the minimum number of molecules for which the continuum hypothesis must hold true. Since molecules occupy space hence the point in this context does not have a zero area but a finite positive area [no matter how small it is].

Please tell me if this interpretation is correct or not and flaw in reasoning.


texts: How does one build a waterproof basement?

texts:
I have been doing a bunch of research online into how to build a basement that is below the water table.  The common wisdom is to "not waste the money doing that" but as someone who doesn't like to be told no and always likes to fully understand their options, I am curious how I could go about building a basement that is below the water table.

I know it is possible to build a waterproof basement because submarines exist, marinas often build underwater sections of buildings, pools are a thing, etc.  The ideal would be to have the primary structure for the basement be poured concrete with no windows or other holes in the walls (plumbing/electricity/air would come in through the ceiling from the higher floors).

For simplicity, lets assume that I don't need sewer out of the basement (perhaps by using an up-flush system to pump sewage/water out). Lets also imagine that the basement is on a flood plain so I can build it while it is dry, but it will be completely submersed in water later in the year.

Finally, again for simplicity lets assume that I am building in a location that has no building codes I need to abide by (so any option is on the table), but I do care about the structure being sound for a long time (e.g., 100 years).

What are the techniques I could use to water PROOF the basement so that it can be fully submerged under water for extended periods of time without leaking?


texts: How can I extract transfer function an unknown nonlinear system?

texts: I am trying to do PID control for my servo electronic motor system. This system uses SSI encoder output for feedback mechanism. I will calculate PID parameters according to ziegler nichols tuning methods. However I must know transfer function of this system while determining PID parameters. So how can I extract transfer function of my system? Is there any way by using MATLAB/SIMULINK or Labview? I think I need a methodology for this? I do not know how can I do. Can anyone explain clearly.


texts: convert rotational movement to linear in opposing directions using worm gear

texts:
I'd like to use a worm drive to achieve the same results as pinion gear with a rack on either side. namely that the rotation of the worm gear would cause one rack to move left and the other to move right.
is it possible to have one thread on the worm gear and create right hand thread on one rack and left hand thread on the other rack?


texts: What should I take Live Load and Sustained Dead Load for Parking and Technical Floors?

texts:
I have a residential Tower (36 story) and i want to find the design loads (Live Loads and Sustained Dead Loads in t/m2) for Technical and Parking floors.

I am currently using the ASCE (Table 4-1 Minimum Uniformly Distributed Live Loads, Lo, and Minimum Concentrated Live Loads) as a reference to find the loads for the typical floors but it doesn't refer to either technical Floors nor Parking.

If anyone know any reference that I could use to find these loads I would appreciate it.


texts: Why manufacturers prefer Brass over Copper in electrical conductors?

texts:
I am working on product where we need pogo pins, as copper is better conductor of electricity I was searching for the copper pogo pins. After about a month of searching, it is come to my notice that most of the manufacturers are dealing with pogo pins not of copper but of brass.

Even when I inquired about the pogo pin that suited voltage specification of 250V 15A. The manufacturers insisted on using Brass than copper.

Apart from this I also seen many smart watches which were using pogo pins were using Brass instead of copper?

Is there any basic issue with using copper? What are the scenarios when we should chose Brass over the copper while building electrical connectors?


texts: How to pre-process paint residue prior to an RO system?

texts:
I am planning to install a reverse osmosis (RO) waste system that will purify waste before putting it into a drain.
However there are certain substances like fibrous matter, fats, grease and specifically paint residue that could clog the RO system. So, I need to pre-filter the the waste somehow to remove those contaminants before putting it into the RO system. How can I do this?


texts:
I'm confused about the Lagrangian of a piezoelectric material. I've seen multiple sources which seem to contradict each other.
The way I personally approach the problem is the following ($\underline{note}$: I'm ignoring the work done by external forces and charges for now, since they are not relevant to the discussion):

$L = K - U $

where $K$ is the kinetic energy, and $U$ is the potential energy which consists of mechanical strain energy $U_m$ + electrical energy $U_e$.

$K = \int\frac{1}{2}\rho \dot u_i \dot u_i dV$

$U_m = \int\frac{1}{2}S_{i}T_{i} dV$

$U_e = \int\frac{1}{2}E_{i}D_{i} dV$

where $\rho$ is the density, $\dot u_i$ is the velocity, $S_i$ is the strain tensor (Voigt notation), $T_i$ is the stress tensor (Voigt notation), $E_i$ is the electric field, $D_i$ is the electric displacement field. This results in the Lagrangian:

$  L = \frac{1}{2}\int(\rho \dot u_i \dot u_i - S_{i}T_{i} - E_{i}D_{i}) dV$

The problem is that most references write the Lagrangian as:

$  L = \frac{1}{2}\int(\rho \dot u_i \dot u_i - S_{i}T_{i} + E_{i}D_{i}) dV$

with the sign in front of the electrical energy reversed. Examples:

Example 1: if you go to page 56, you'll see they derive the Lagrangian from the electrical enthalpy, and I don't get why it gives a different result (in the form of a + sign in front of the electrical energy).

Example 2: same result, with the constitutive relations substituted in the Lagrangian.

So my question is twofold:

(1) Where is the error in my approach in that it yields the wrong sign in front of the electrical energy?

(2) In the main book I'm studying, which is Engineering Analysis of Smart Material Systems. Donald J. Leo, 2007, if you go to page 218, equation 5.47, the author gives the potential energy of a piezoelectric material (static case, no kinetic energy so $L=-U$):

$  U = \int(\frac{1}{2}S_{i}c_{ij}^D S_{j} - S_ih_{ij}D_j + \frac{1}{2}D_{i}\beta_{ij}^SD_{j}) dV$
which is actually derivable from my Lagrangian approach rather than the one given in the two previous reference examples when you substitute the constitutive relations into the Lagrangian:

$ T_i = c_{ij}^DS_j - h_{ij}D_j $

$ E_i = - h_{ji}S_j + \beta_{ij}^S D_j $

How do we reconcile the contradictory references?


texts: Optimizing flue gas temp for maple syrup evaporator

texts:
I have a simple maple syrup evaporator. Fuel is burned in a firebox located under 1mm stainless steel pans containing maple sap--which becomes syrup once enough water is evaporated. After passing under the pans, exhaust gasses flow up through a chimney. (Some evaporators use flue gasses to preheat sap, but that is not the case for this evaporator.)

A high fuel consumption rate will cause evaporation to be faster, but a greater amount of heat will escape the system in the flue gas, causing energy efficiency to be lower. A lower fuel consumption rate will cause energy efficiency to be higher (lower flue gas temperatures), but the evaporation process will be slower.
If I know the cost of energy =X/kcal and I know the cost of one hour of evaporation in terms of labor, overhead, etc =Y/hour, it seems like it would be possible to calculate the optimal flue gas temperature--which we could then use to control our rate of fuel consumption.
For simplicity, I think we can assume that heat loss through means other than steam production and flue gasses are minimal enough to be ignored.
My intuition tells me that it's possible to calculate the optimal flue gas temperature for this scenario based on the cost of energy and time, but I'm not quite sure how to get there. Any help you can provide is much appreciated!


texts: Normal Shockwaves occurrence at cone tip with Angle Theta

texts: I have a question regarding shockwaves. So as far as my knowledge, a flow moving at Ma= 1 will create a normal shockwave ($arcsin(1/Ma)$) , and a flow moving faster will cause an oblique shockwave. So can a  normal shockwave occur if the flow is diverged with angle Beta, if it was close to speed of sound?


texts: Calculating heat transfer in a cooling loop

texts:
Imagine a closed pipe like below, filled with a liquid. The pipe is copper.  Then imagine a small point heat source of X watts applied to the outside of the pipe in the position shown.  Heat warms the pipe, then the liquid, and circulation develops.  As there's only heat applied on one side of the loop, the liquid naturally cools in the other half.  There'll be convection and radiation there.

Is there any way I could begin to model this so that I could establish a temperature rise at the heat source?  So for example, X watts input would lead to a Y degree temperature rise in the pipe at the point of application.

For context, I'm looking at a heat source of say 10W, and a maximum rise of 20 degrees.  So the design element here is the size of the loop and the diameter of the pipe.  I would like to nominally target ⌀22mm for the pipe.

I don't have access to finite elements. A back of the envelope, on a toilet wall or a fag packet calculation would be appreciated.  Is it even possible or does this have to be determined empirically?


texts: How do you clean/restore corroded battery terminals?

texts:
I'm sure everybody has come across a case like the following:

My experience is that this corrosion must act as an insulator(/or shortcircuit). I have managed -in some cases- to clean by scrubbing and using alcohol based cleaners. However that is not always the case.
Could someone suggest the best way to restore an adapter (if its possible).
If possible, it would be nice - along with or instead  of commercial products that maybe available in only certain parts of the world-  to  have a solution/substance that is appropriate.  If the requirement is just, scrub harder then that's also ok.


texts: Can using different types of alcohol in a cloud chamber produce different particle tracks?

texts:
The design for a cloud chamber is rather simple, and many factors can be changed without producing different results. There is one curious point that I've stumbled upon, though: The type of alcohol vapor used. I've read about methanol, ethyl alcohol, and isospropyl alcohol.

Will any of these choices produce different particle tracks? The factors I'm considering include the length of time the track exists for before it fades and the clarity of the track (i.e. opacity/transparency relative to the rest of the vapor).


texts: ABAQUS: How to connect a shell edge with a shell face?

texts:
I'm performing a buckling analysis of a stiffened aluminium panel. The panel and flatbar stiffener(2) is created as one 3D shell extrusion. The T-stiffener (1) is another 3D shell extrusion.

How do I connect the two parts? I have tried the "create interaction"-button, but have no clue how to do it. I guess the load transfer might not work as intended if I connect them wrongly as I'm not very used to shell elements either. Can I connect the shell edge of the T directly to the face of the panel? I'm using Abaqus btw.

The partitions of the panel and T-profile are there to simulate HAZ-effects. Are there other options to specify heat affected zones and potentially residual stresses?

All help is highly appreciated!


texts: Can a switched mode power supply for a neon sign be used for making lichtenberg figures?

texts: I am trying to find a cheap power supply that will produce the high voltage needed to create lichtenberg figures on wood.  I ruled against using a microwave oven transformer due to the high current, so only the neon sign power source sold on ebay for ~$10 would be in my price range.  Wikipedia's article on neon sign transformers suggests just those with an iron core are used by hobbyists to make lichtenberg figures, and that manufacturers are now producing switch mode power supplies to power the neon signs.  I can't be certain of the specs of the ebay transformers since they are generic units produced in China, but assuming that they are switch mode power supplies, will they be able to fit my needs for a power supply?


texts: will a force with same frequency as natural frequency make system resonance (in multi-dof)?

texts:
assume we have a multi-dof system and a force is applied with same frequency as one of the natural frequencies. will this system be resonant in any circumstances?
(system is undamped).


texts: How to calculate the diameter of a transmission shaft from RPM & Torque

texts:
If I know the torque and rpm that the shaft need to operate at, can I calculate the diameter of the shaft?

A motor operating at 60 rpm applying 1,000 Nm of force on a shaft that has a modulus of rigidity of 50 GPa and is 10 cm in length.

Can I calculate the diameter of the shaft so that it would not fail?

The tensile strength is:

Tensile Strength, Ultimate  686 MPa
Tensile Strength, Yield     490 MPa

This will be a horizontal shaft, the length isn't final yet but I am estimating that it will be 2,000 mm long and supported at 200 mm from each end.

There shouldn't be any unforseen shocks being applied to the shaft. It will be transmitting the power from a 15 HP motor that's connected via a coupling on one end.


texts: Control System; Finding resonant frequency of 3rd order

texts:
We've been requested to find the resonant frequencies of a 3rd order plant in class and were presented to the following method to do so:

My question is, when using the $\ \omega_r $ formula, to find both of the resonant freq's do I need to place $\ \omega_{n1} $ with $\ ζ_{1} $ to get $\ \omega_{r1} $ (and $\ -\omega_{n2} $ with $\ ζ_{2} $ to get $\ \omega_{r2} $),
or I am supposed to use the same $\ ζ_{2} $ (of the Pole) for both, like this:

$$ \omega_{r1} = f(\omega_{n1}, ζ_{2}) $$

$$ \omega_{r2} = f(\omega_{n2}, ζ_2) $$

I hope the question is clear enough, thanks!


texts: WW2 technology - How was this on-screen frame counter added to old film-media footage?

texts:
Please refer to the following youtube video (pause it as soon as it starts)...

"USS William D Porter, the Unluckiest Ship in the Navy" by The History Guy
https://youtu.be/f9Gb4PakFTU?t=162

There is a running clock super-imposed over the film which gives a HH:MM:SS:FF (where FF is the number of frames elapsed this second, 0-29).

How did 1940's technology achieve this?

I suppose I must concede that this counter may have been added years or even decades later, but the clocks on display here (there are several clips within this video that feature different styles of clocks) seem to "blend in" with the old footage which leads me to believe that they were added (perhaps in post-processing) during the war period.

Given the astonishing ingenuity of wartime engineers I think this would be a relatively trivial task for them, but I would like to know how it was done.


texts: How to size a fan for open air application?

texts:
Assume that you have an axial fan placed in open air with no duct. How can I go about calculating the air speed at a distance x from the fan?

The fan is about 1 m above the ground in an open space. I want to use the fan to generate power from a wind turbine, so I need to know what the air speed will be at the turbine.


texts: In Raymer diagram “Take off parameter- Take off distance”, what is the difference among “balanced field length”, “over 50 ft”, “ground roll”?

texts:
Raymer in his book Suggests a method to find Wing Loading W/S (for example we consider jet with 2 engines) (starting from specific thrust T/W, CLto, density/reference density etc.). In step 1: he suggests to use graphichs "Fig. 5.4 Takeoff distance estimation": you enter takeoff distance (in ordinate), so .. in abscissa you can determine Takeoff Parameter ("TOP") Step 2: From "TOP" you can find (W/S)=(TOP)sigmaCLto*(t/W) The questions are : in figure 5.4 you can find many diagrams: takeoff distance for a) "Balanced field Length" b) "over 50 ft" c) "ground roll". Which one I have to use? What is the difference among them? Which curve you have to use, in order to calculate "take off parameter"?

Source: Daniel P. Raymer, Aircraft design: a conceptual approach. Chapter 5 Thrust-to-weight ratio and wing loading, paragraph 5.3 Wing Loading, sub-paragraph Takeoff Distance, page 88-89 and "Fig. 5.4 Takeoff distance estimation".


texts: How to determine reinforcement design strip widths and locations

texts:
When designing reinforced concrete slabs it is common to divide the slab into 'design strips', which are then used to rationalise the reinforcement design along (typically orthogonal) lengths of the slab (also known as the Hilleborg Strip Method).

I have mostly seen this approach used in design software (for example, SAFE), however they offer little to no advice as to how and where these design strips should be located/sized.

What rules and considerations do engineers apply when locating/sizing design strips?


texts: How can I use a p-iris/autoiris lens on a camera without a connection port?

texts: My team owns a Point Grey camera that we need to attach a wide angle lens to. The wide angle lens we have has a cable allowing for autoiris and p-iris control, but the camera doesn't have the autoiris/p-iris port. Is there another way to connect the iris controller? Can we get away with not using it at all?


texts: Does electrolysis of warm water differ from electrolysis of room temperature water?

texts:
Typical energy efficiency of water electrolysis is about 75%.
Will this change with the temperature of water?


texts: Optimizing support board placement on work table wing

texts:
I'm currently building a work table that will have "wings" on each side that are fixed to the mid section of the table via a hinge.  These wings, in turn, have hinges that fix a support board to them which will rest against the mid section of the table.  I'm currently in the process of deciding where to place the support and am wondering if anyone has any engineering input as to an optimal placement.

Because of how the rest of the table in constructed, I am limited as follows:

$14'' \leq A \leq 19''$
$B + C \leq 38''$

Then there's also obviously the fact that:

$A^2 + B^2 = C^2$

I'm not sure what the optimal setup is here.  The only scenario I've solved for is trying to make $A = B$ so that the angle $\theta$ between $A$ and $C$ is 45 degrees.
This implies $\sin(\theta) = B / C = 1 / \sqrt{2}$.  Plugging this into the equations I have above, I found that:

$A = B$ implies that $14'' \leq A = B <= \frac{38}{1 + \sqrt{2}} \approxeq 15.3$

Are there any other more sophisticated approaches to this problem than the "make $\theta=$ 45 degrees" approach?

p.s. - I studied Physics in college, so have a math / physics background, but know very little about applied engineering like this.  Also, let me know if you require / would like any additional information.


texts: what impact does drop height have on powder segregation?

texts: In the pharmaceutical environment, the drop height from the hopper to the area where it collects must be minimized. Tubes can be used to minimise the height. I know that it affects powder segregation. But do not understand the mechanism of it. How does it affect powder segregation ? As long as the flow is optimal (eg. no bridging), then why will powder still segregate if drop height is not minimal ?


texts: MSC Nastran CQUAD8 on a pipe - excessive pivot ratio

texts:
I'm modelling a pipe in Patran with CQUAD8 elements, but I get this error, like the structure is not costrained. I do have costrains on both ends of the pipe. What can the problem be?

If I use automatic costrains it works, but I don't know why and where these constrains are put. I don't have any control over the solution. I'd like to know the actual problem here. With CQUAD4 works fine.

Thanks for helping me out.


texts: Why does hydrogen fuel produce less horsepower than gasoline in internal combustion engines?

texts:
I was looking at hydrogen as alternative fuel and came across an article stating that although $\textrm{H}_2$ produces more energy than conventional fuel, it produces less horsepower in internal combustion engines.

I thought that more energy ($143\ \textrm{MJ/kg}$ for $\textrm{H}_2$ vs $46.4\ \textrm{MJ/kg}$ for gasoline) would mean more heat, more temperature, more pressure and thus more force and horsepower. Why, then, does $\textrm{H}_2$ produce less horsepower than gasoline in internal combustion engines?


texts: Third Rail vs Overhead Cable: which is more efficient in terms of electricity consumption?

texts:
I'm well aware that there are many different factors to be considered, such as ease of installation/maintenance, conversion from AC to DC, environment, distance, speed, frequency of turns, and so forth.

Setting all of those aside for now, suppose we build a 10-mile long demonstration track with some hills and turns along the way and featuring both a third rail and an overhead cable. Suppose further that we have two trains (one equipped with a pantograph, the other with contact shoes). They have the exact same weight and are programmed to accelerate and decelerate at the same rate, and run at the same speed.

Which one will have consumed more electricity at the end of the ten-mile run?

Bonus Question: A third rail is a lot wider and thicker than an overhead wire. Is more electricity wasted that way?


texts: how to solve internal hinge problem with loading given on hinge


texts: How does Milkor MGL Granade Launcher's trigger and cylinder mechanism work

texts:
I want to know how does Milkor MGL's trigger and cylinder work. In particular, I am interested in how exactly the trigger action switches the cylinder among the cartridge chambers. As far as i know, the trigger itself works in a basic double action principle, but, I simply, cannot figure by myself how it does manage to rotate the drum forward, it doesn't work like regular pistol revolver but in a rather different manner. The following video demonstrates the basic drum cycle.

https://www.youtube.com/watch?v=KMzeIyqHW4Y

I will greatly appreciate if you can give me some sort of diagram or schematic to make things clear.

Thanks in advance


texts:
I want to prototype a wah-wah guitar pedal using an arduino, a potentiometer, and some meccano I have lying around.
I thought of two ways to do this :

the first one is to put a pinion on the pot, and connect a rack to the pedal itself; however I can already see that it can't be as simple as that, because the rack to pinion angle will change as the pedal gets pushed more.

the second one is to use several gears, the first one on the axle of the pedal, the last one on the potentiometer, so that the full motion of the pedal results in a full potentiometer rotation; I don't like that one much, as I don't think I have the requisite gear ratios.

Having absolutely no background in mechanics, that's it for me; I don't even know the name of the concepts I might be needing. Can Stackexchange Engineering provide some pointers for making this at home, with no complex tools beyond a sander, a dremel, and such?

Thanks for your attention.


texts: Can a chain of nested thermal heat pumps be used to to gain thermal energy out of the environment?

texts:
Assume the following setup:

Input -> First    ----------> Second    ----------> etc.
Air      heatpump   hot air   heatpump    hot air
T_0        |        T_h1>T_0     |        T_h2>T_h1
           v                     v
        cold air              cold air
        T_c0<T_0              T_c1<T_h1

or

Ts are temperatures; the darker the red, the warmer. The barriers between the areas are isolating materials. The throughput is smaller for nested pumps so that the most inner, hottest area is quite small and heated up slowly in comparison to the out ones. The heat pumps would operate with different fluids suited for the temperature differences. The output temperature (after etc.) is limited by the availability of the right fluid and the construction of a pump which can withstand the heat.

The only question to decide whether such a machine could operate efficiently, i.e. provide more energy than the pumps consume, is how much do the heat pumps consume? I'm searching for figures to estimate the consumption of thermal heat pumps (let's assume they're electric).

I'm pretty sure that it's not a perpetuum mobile of the second kind because the system is fed with the energy taken out of the cold air which leaves the first (left) heat pump.

The figures for the energy consumption would show whether such a machine can be constructed and provide (heat) energy rather than consume more than it provides. Example use cases would be geo-/climate-engineering and production of electricity or heat for heavy engineering.


texts:
I'm having some trouble using a motor driver board. I'm pretty sure its being driven properly since there is ~3V @ the output v.s. none when its off. However it should be supplying ~2A (rectifier bottleneck) of current, rather than topping out at 120mA. I've tried both outputs, both give the same results.

I'm using this motor driver: http://www.amazon.com/gp/product/B00CAG6GX2/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

I have both output enable jumpers in place, and have tried with and without the 5V enable jumper in. I tie one logic input to 5V and the other to GND. The driver is powered through a 5V DC-DC converter (~2A verified). Am I doing something silly, or is it likely a dead H-bridge?

UPDATE (moved from self-answer):
I'm sorry for not being more specific. It turns out that for the 3v motors I was attempting to drive the L298 is not the best solution since it has a few volts drop at high currents, leaving the motors with almost nothing across them if using a rectified 3V power source.

Note: The following is based upon using the L298 on its own, NOT with the original board. I've tried increasing the voltage supply to 6V, and this seems to be working. I intend to increase to a higher voltage, as well as using pwm across a smoothing capacitor in parallel with the motor in order to give a proper output voltage while using a large enough source to account for the drop across the internal transistors in the L298.


texts: What methods are there to test the flexural, tensile and compressive strength of concrete?

texts: The only one I know is the three point bending test for flexural strength.


texts: Feasibility of a motorized 3-axis gimbal for visualization

texts:
Recently some friends and I conceived of a method for visualizing in real-time the pitch/yaw/roll of an aircraft where a model aircraft is mounted inside a gimbal; then, the controller for the gimbal would receive telemetry from a flight simulator and update the position of the aircraft to show you how steep the aircraft is climbing or what compass direction it is heading. (see this diagram for an idea of what we are talking about.) Not free-floating, but with a motor at each axle to keep the position correct.

We began our search for this by scouring the internet but haven't found any examples of a motorized gimbal like this. There are several difficulties we have encountered in designing our own, also.

What is a safe and effective way to translate control signals and power through an axle so that the inner gimbal ring motors will receive enough power to turn a balance 3D model on all axes? We considered wireless communication for the motors and using batteries but the batteries would add a lot of weight to each ring which would need to be balanced out.

Also, has this idea already been proposed and dismissed for being impractical? I don't want to reinvent the wheel (no pun intended) but also don't know the correct search terms to find a product like this.

Thanks in advance for any help you can give me,


texts: How to Calculate Mean Radius of Irregular Contact Face (Torque Transmission)

texts:
In a simple situation, one simply takes the average of outer diameter and inner diameter to gain the mean radius for calculating torque transmission through a contact face, such as a clutch.

But how would you work this out if there was no simple ID and OD to work with, say for example if the ID was broken by an array of holes as shown below:


texts:
I have the following differential equation:

$$\ddot{\psi_t} + \omega^2 \psi_t = \omega R_s i_f - \omega u_f + \dot{u}_t - R_s \dot{i}_t$$

where $w$ is the electrical speed of the motor.

I have considered R.H.S. as $\Delta\omega$ and would be feed-forwarded, so I obtain the following transfer function:

$$\frac{\psi_t}{\Delta\omega} = \frac{1}{s^2 + \omega^2}$$

Any tips for controlling the above undamped second order system? Can I use PI controller for this?


texts: When are Nyloc nuts indicated instead of cap nuts?

texts:
Are there any applications in which a Nyloc nut is preferred to a proper cap nut?

As best I can tell: a Nyloc nut is just a specialized cap nut that will fail under lower torque and temperatures than a metal cap nut.


texts:
I’m trying to analyze the bending of an I beam using the Timoshenko beam equation and I can’t seem to find the value for the shear coefficient anywhere.
Surely someone must’ve done the work (given how common I-beams are in structural engineering) and has a value or table of values. Or are there any algebraic (empirical) equations I can solve to get the values ?
Thanks !


texts:
I'm relatively new to solidworks and i would like to know if there is a way to mate a bearing in solidworks such that it acts as a one way bearing. In the rack and pinion setup in the figure, the rack is the driver and reciprocates, i want the shaft to turn only clockwise and freewheel in the other direction.
I havent been able to find any way to perform this mate and motion study dosent help either. Ive also searched for cad files on it but its also a dead end.
I use SW2016


texts: Pattern of zero stress in regular truss structure

texts:
I'm reading David Hutton's Finite Element Analysis, and recently programmed the truss analysis from scratch (in java). The figure shows the screenshot of a regular truss, with two ends fixed and a load at center. The hue and the stroke width indicate the axial stress, while the red-blue figure distinguish tension from compression.
I find the zero stress (marked with red circles) in the case of N=5, 9 (and 13, 17, etc.) interesting but confusing. Is there explanation for such pattern? or has my program mistakes?


texts: What is a gearbox with switchable outputs called?

texts:
I need a mechanism with which one motor can drive one of two outputs. So only one output should be active at a time, but the mechanism should be able to switch between the outputs.
What is a mechanism like that called?


texts: How can the shear capacity of a concrete slab be determined for effective depths under 200mm? [Eurocodes]

texts:
All,

I'm designing a minor slab to Eurocode 2. It's purpose is more for show than any real structural purpose however I need to justify it's ability to resist it's own self weight and possibly the accidental loading of a person climbing upon it.

The slab itself is 680mm wide, 160mm deep (100mm effective depth to rebar) and has a maximum span of 1200mm, so there is little room for shear reinforcement. Ideally, this slab should be kept as small and simple as possible.

This is a small slab and acts as a cope for a sheepile wall and so spans between the 'zig-zag' of the piles.

Eurocode 2 states the following:

As can be seen, for slabs with an effective depth (d) of less than 200mm, the equations do not hold up as the inequality K <= 2.0 must be satisfied.

There is very little explanatory text around these clauses and I am looking for guidance. Does this mean that a solution is impossible using these equations? If so, what other guidance can I refer too?

If not, what significance does the k value have? Does a k value > 2.0 give me a conservative result that I can continue to use?

Ultimately; How can the shear capacity of a concrete slab be determined for effective depths under 200mm within Eurocode 2?


texts: How is MRI SNR affected by the frequencies that are included?

texts: So for MRI imaging, if an image is taken, and portions of the Fourier transform image are removed so that some portion of the higher frequencies are not included, would this reduce the SNR?  I assume that it would because you'd be removing a portion of the signal data.  Sorry if I'm off on this but this is what intuitively seems to make sense when thinking about it.


texts: Is it possible that a considerably thicker portion of slab would decrease the moment capacity of a raft slab

texts: If I Design this slab as a flat 1500mm thick slab throughout ignoring the step will the design be conservative. I'm worried the extra stiffness created by the step, will attract the moment into the step as it is acting like a beam and therefore my model may not be conservative and there could be possible failure.


texts: Using the „Singularity elemination factor“ in SOLIDWORKS Simulation

texts:
I’m new to the nonlinear static simulation in SOLIDWORKS… and therefore I’m trying to understand the advanced options in SOLIDWORKS Simulation. And here the “singularity elimination factor” is mentioned.

I found this link - https://www.javelin-tech.com/blog/2014/04/singularity-elimination-factor/ - with a short explanation about the SEF. But still there are some general questions for me to clarify and I hope you can help me.

Questions:

The proposed modification of the value SEF enables the simulation to terminate. Values closer to 0 are more effective. But how is this adjustment of SEF affecting the results? Is there anything to be aware of?
This article mentions four points (stiffness singularities, incremental strain being too large, incremental rotations being too large, contact iterations non-converging) which may cause the simulation fail. How can I relate which of the four points is responsible for the simulation fail?

Thanks in advance for your help.


texts: Block and Tackle with Ramp - stopping rope drag

texts: I am designing a block and tackle system to haul wood up a ramp onto my porch. The issue I am having is that the rope seems like it will rub against the top of the ramp and cause it to fray. How can I prevent this from happening?


texts:
I want to be able to hold a 1/2" diameter shank boring bar on my existing lathe tool post but don't know how to buy the correct one.

The post we have is a Phase II 250-111: https://www.mscdirect.com/product/details/09044017?item=09044017

The boring bars we have a 1/2" shank diameter. I'm hoping to get a different brand for the tool holder because it is cheaper. Which of the options below would fit? I'm confused by the OXA or AXA as I don't see that specified in the post description from Phase II.
https://www.mscdirect.com/product/details/30579627
https://www.mscdirect.com/product/details/30574867

or even
https://www.amazon.com/Quick-Change-Boring-Holder-250-004/dp/B07THWWQQD

or an even cheaper option:
https://www.amazon.com/Boring-Bar-Holder-1-2/dp/B077V5HKNR


texts: Can a casio fx series do this operation?

texts:
"Calculators stackexchange" doesn't exist, so I guessed this would be the right place to ask. Can a calculator solve $-0.2 \cdot e^{-0.06-4.2i}$?

Or any $e$ to a complex for that matter. I've been solving this with Wolfram Alpha or Matlab when in a project, but I'd like yo know if is there anyway to get it done in a calculator.


texts: For a given surface area of sunshine are the latest solar panels more or less efficient than a Stirling engine?

texts: I was wondering if the efficiency of current solar panels are better or worse than the current state of the art Stirling engines. I understand the former isn't a static variable and solar panels are improving constantly.


texts: What are these metal cylinders often found in the streets of London?

texts:
I often find these metal cylinders in the streets of London: a silver-colored tube with a round tapering at one end and a hole with no thread at the other.

What are they?


texts: Energy/Efficiency Calculations for Large Multi-stage Package HVAC

texts:
I frequently use the Equivalent Full Load Hour (EFLH) estimation method to calculate the expected energy usage for commercial HVAC equipment.  While not ideal, it works well enough to given an order of magnitude for the energy savings that we can expect if and when equipment is replaced.  The EFLH can usually be approximated well enough form available tables for different building types in various locations, and the efficiency, usually in the form of SEER or EER, is typically right in the product data.

While working on a large manufacturing plant, I came across a slew of 50-ton Trane Voyager rooftop package units. The high efficiency versions of these units have 5 stages, but do not provide any indication of traditional efficiencies that I am used to seeing throughout their literature.
https://www.trane.com/content/dam/Trane/Commercial/global/products-systems/equipment/unitary/rooftop-systems/voyager-commercial-27-1-2-to-50-tons/RT-PRC033L-EN_05112019.pdf

Is there a straightforward way to go about calculating energy usage for equipment like this?


texts: How can I get the horizon or vertical length of the uneven object?

texts:
Just like the picture shown I want to have the length from the front end to the windshield in horizon, and want to have the length from the lowest point to the highest point of the hood in vertical.

Would like to know what tools I need to measure stuff like this, its mostly with in 1-2 feet in dimension

Thank you very much.

PS: If this is in wrong site please help to relocate thank you


texts:
I am trying to do this question and I have everything but one.

Solving for $A_x$, $x$ force at $A$.

$$\begin{gather}
F_x = 6\cdot20 + A_x \\
A_x= -120\text{ kN}
\end{gather}$$

Is this correct?

Sign normally doesn't matter, if you're consistent, but it's causing an error in my working out the moment.

Evaluating it, I get -1852.5 which is incorrect. The answer is 1132.5.

If I change the sign of $6\cdot20$ to $-6\cdot20$, I get the ‘correct’ answer, -1132.5.

$$\begin{gather}
F_x = 20\cdot6 + A_x = 0 \\
A_x = -120 \\
M_D = -30\cdot7\cdot3.5+2\cdot E_y = 0 \\
E_y = 367.5 \\
F_y = D_y + E_y - 30\cdot7 = 0 \\
D_y = -157.5 \\
F_y = -D_y - 60 + A_y = 0 \\
A_y = 60-157.5 = -97.5 \\
\sum M_A = M_A + 6\cdot20\cdot3-60\cdot4-D_y\cdot11=0
\end{gather}$$


texts: Difference between Linear Force and Force about an Axis

texts:
I am confused between How forces work when applied in singular linear direction vs Force Applied to a continuous mass about an axis(example to rotate it).
Example 1:
Consider an object of mass $m$ which is lying on a table with friction coefficient $k$, so the minimum force $F$ required to move the object will be $F = Mgk$
Example 2:
Consider a similar example with a slight change.
Imagine the object of mass $M$ is for example a door, held straight with hinges. The Hinges also have a friction coefficient $k$, will the minimum force required to swing the door open be equal to the force we found in Example 1?
Also, I cannot understand how to calculate and what to consider to find the minimum force required to move an object along its axis or to move it in one direction and set it in ideal motion.
Imagine the object has same dimensions and properties in both examples.


texts: What is the difference between the Polar Moment of Inertia, $ I_P $ and the torsional constant, $ J_T $ of a cross section?

texts:
This question is so fundamentally basic that I am almost embarrassed to ask but it came up at work the other day and and nearly no one in the office could give me a good answer. I was calculating the shear stress in a member using the equation, $\frac{Tr}{J_T}$ and noticed, that for a shaft with a circular cross section, $J_T = I_P$.

Both $I_P$ and $J_T$ are used to describe an object's ability to resist torsion. $I_P$ is defined as, $ \int_{A} \rho^2 dA $ where $\rho$ = the radial distance to the axis about which $I_P$ is being calculated. But $J_T$ has no exact analytical equations and is calculated largely with approximate equations that no reference I looked at really elaborated on.

So my question is, what is the difference between the Polar Moment of Inertia, $ I_P $, and the torsional constant, $ J_T $? Not only mathematically, but practically. What physical or geometric property is each a representation of? Why is $J_T$ so hard to calculate?


texts: If you look at any launch it appears as though rockets do not take the shortest path. Their trajectory bends. Why do rockets not fly straight up after launching; wouldn’t that be less atmosphere to traverse?


texts: I am looking for the term used to describe a situation I've encountered. I'll use a standard hydraulic cartridge that you'd use to keep a door shut as an example, except this one can be locked out with a rotary valve. How would you refer to the valve being pushed open by pressure or load? If under pressure, the valve is unable to close until pressure is relieved. Is there a term for this? I thought it may have been "Jetting", but that doesn't exactly describe this situation.


texts: Why prefer plain pipes over corrugated pipes for storm sewage and culverts?

texts:
Recently I observed installing new storm sewage along a city street. Pipes have plain surface (not corrugated) and are made of some plastic looking like HDPE (polyethylene) and their diameter is around 0,5 meters and the walls are around 40 millimeters thick. That's a lot of material. I assume the same structural strength could be achieved if the pipes were made corrugated and with much thinner walls. I saw corrugated plastic pipes for storm sewage once and so they surely exist.

Why would plain surface pipes be preferred over corrugated pipes for this scenario?


texts: How to generate NACA 5 digit airfoil coordinates?

texts:
I want to generate NACA 63824 airfoil coordinates to use them in my bachelor thesis.
I tried airfoil tools and java foil. But I can't generate 638xx series.

Can you recommend me a program or a code that generates these airfoil coordinates?


texts: How does the number of braces in a balsa wood tower affect the load capacity?

texts:
I am deciding between two design ideas for a project in which I have to build a balsa wood tower that can maximize load weight and minimize structural weight (maximize efficiency). I've included a picture with the two designs I am deciding between.

I am wondering which design would be able to hold greater weight, whether increasing the number of braces changes the load capacity, and in which way it changes (linear correlation, exponential correlation, etc.).

More specifically, I'm considering a load weight of 145 N, and I am looking for the values of the internal member forces, especially those before buckling (assuming a static system).

My understanding of this subject only extends to truss calculations, considering diagonal bracing (e.g. Howe Truss), which is why I am posting on this forum. Further, if you'd be willing to give a brief explanation of these diagrams from Bracing for Stability, I'd really appreciate it.


texts: Computer "Ports", port scans and daemons

texts:
If I do a port scan from the internet, do I hit a bundle of wires that are physical ports into the motherboard (like a PCE port)?

Or do I actually go into the operating system and interact with the virtual or 'logical' ports of the OS?

I am trying to understand what the difference is between these ports, and why, if they are logical, I would be able to scan any of them from the internet, because it implies my bytes are passing over hardware to reach these 'logical' ports inside the CPU and cache, rather than on the peripheral hardware (before they are rejected)… This feels wrong...

But if they are actually physical, then where are they? And, if I have a daemon listen on a port that is "opened", does this mean that the program is listening to bytes that pass over a physical component on the motherboard, exterior to the cache-ram-cpu area?


texts: Solid-liquid separation of a crystal slurry

texts:
Let me preface my question by saying I am a recent chemical engineering graduate and apologize if my inexperience shows.

I have designed a batch process which results in a water slurry stream containing an insoluble precipitate (biurea) with impurities such as chloride, complex salts and DOC which leaves the reactor at high temperature.

I would like to separate the precipitate, remove impurities and produce a dry product (with no particular size distribution requirements).

To achieve this I plan to use a plate filter press to produce an output stream of about 50-70 wt% solids. Is this a good choice? it seems to have low capital and operating costs (higher labour intensity) than a centrifuge and more suited to a batch process compared to a belt filter press.

I am unsure how cleaning is typically implemented in an industrial process. I would like to wash the precipitate thoroughly to remove as much chloride, salt, DOC etc. impurities as possible.Is washing supposed to be performed INSIDE the plate filter press? or is the solids washed in a separate tank to be recycled to the filter press until the desired level of washing is achieved? Should I heat the washing liquid to improve solubility?

For drying I would like to use a simple tray vacuum dryer but read that this does not scale well - I need to produce about 600kg/day dry product.

Thank you and please let me know if I should clarify.

EDIT:
stream leaving the reactor is at 120 degC before entering the filter press and contains 5-15 wt% solids of precipitate. I am designing that the stream leaving the filter via conveyor is about 50-70% solids


texts:
Is there any pump available which can suck the water just like solenoid pump ( which means i can just put the input pipe in water and it will suck the water and get it out unlike DC motor pump which have to be submurged in water, which is not feasible for my project) but the good pressure is also needed.
I am thinking about piston pump but i am not being able to understand if it's going to work with my project or not.

In my project,i have a jug of water from which i want to get the water and send it to other but I can't submerge the motor in water all the time.


texts: Place a greenhouse: how to orient it for the best effect?

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I'm looking for the best orientation (North-East-South-West) of a greenhouse (simplifiable as a rectangular solid).
My question is more specifically about the sun position effects (over the times of the day and over the days of the year).
With sun effect I mean both solar exposure for plants and temperature increase within the greenhouse. Anyway I think both aspects go hand-in-hand.

Thus, how can I calculate the position of the greenhouse?

PS: if can help to better focus my question, the question could also be re-arranged e.g. for house's rooms: which is the coldest/hottest room in my house?

EDIT: solar exposure's issue was solved. Now it remains how to deal with temperature gain. In short: with maximum solar exposure I will get automatically the higher temperature inside the greenhouse?


texts: position of feed stream discharge in the fractionating column

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In the book 'Chemical Engineering' by Coulson and Richardson (Volume 2, 5th edition), in the section 'Fractionating Column')(page-560), it's said that,'The feed stream is introduced on
some intermediate tray where the liquid has approximately the same composition as the
feed.' This gives no definite position of the feed discharge.

Our professor explained that the feed is discharged somewhere below the sieve plate, which is a plate situated in the middle of the column.

My question is, is there a particular reason for the feed stream being discharged here?

Can the feed stream be discharged anywhere in the stripping section above the liquid?'