texts: Proof load for screwing into aluminium plate

texts:
I have a required clamping force for fastening two pieces of metal together, and am trying to work out if an m4 bolt will be sufficient. The pieces will be fastened without a nut, just a hole through one piece and a threaded hole in the aluminium block it needs clamping to.
The clamping force that the fastener must be able to withstand is 3400N, so I have found that an m4 bolt should be suitable at grade 8.8 or higher (with an allowance for 75% of proof strength) https://www.engineeringtoolbox.com/metric-bolts-minimum-ultimate-tensile-proof-loads-d_2026.html.
However, how can I verify that the thread in the aluminium plate will be able to withstand this force, or does the size of the hole not effect this (eg. if it can withstand it for an m6 bolt it will be fine with an m4)?
Diagram to show hole placement and depth in aluminium.


texts: Is torque produced at the crank of an engine lower than at the wheels?

texts:
Im specifically referring to motorcycle engines, but for arguments sake a car engine wouldn't matter either

Say 100Nm was measured at the wheel using a rolling dyno, then based on the reduction ratios(say 5) from wheel to sprocket to gearbox to the clutch, would the torque produced at the crankshaft be less? 100/5 = 20Nm

Assuming no losses, the power produced at the engine would be the same at the wheel but since there are multiple gear ratios, the torque is increased whilst the angular speed has reduced.  So if the crankshaft was turning at 10000 rpm... with an overall gear ratio of 5. The wheels are turning at 2000rpm?


texts: Will a mobile phone (UE) in an LTE network not originate a call if signal strength is below a threshold (RSRP, RSRQ etc)?

texts:
What is the behaviour of a mobile phone (UE) in an LTE network if the measured signal strength of reference signals are low (RSRP, RSRQ) before call origination?

Will the mobile attempt the call or not?
Do the 3GPP specs indicate what the requisite thresholds are?


texts: What is this locking pin for a hinge called?

texts: The following is a picture of a locking pin for a tubular hinge which specifies Maritime use. I assume it has something to do with railings but I'm thinking of fabricating my own similar hinges. "Locking pin" seems awfully vague. I know I've seen this before; the little nub at the end is spring loaded and presses into the pin


texts: I'm designing a lifting device powered by a motor, i would like to know if the forces exerted by the load on pulley 1 and 2 are equal when the motor star running , or if in pulley 1 is exerted more force because the location of the load at the end of the lifting platform. The lifting platform only moves vertically, restricted by rails. What I want to know if the load will exert a perpendicular force that could create friction on the rails


texts: Best plastic composite alternative to wood

texts:
I am planning to replace the material that is used for Cricket Stumps.  Cricket is a game similar to baseball.  One difference is the presence of 3 successive stumps between the hitter and catcher.  The ball will hit the stumps if the hitter misses it.  The combined weight of the stumps is 7 lbs.  Each stump is a 28 inch long wooden cylindrical stump of 1.5 inch radius weight 2.3 lbs.
The stump can be hollow inside.  As of now the regular stumps are made of solid wood.

I am in search of a lightweight alternative for the wooden stump.  The material should be able to withstand the force of the ball which typically travels at 80 mph.

Is there any cheap and lightweight plastic material that can drastically reduce the weight of the stump and still withstand the forces mentioned above?


texts: Determining the final surface temperature and final gas temperature flow through a tube in a room

texts:
I am trying to calculate the final temperatures as stated above. There is hot gas flowing through a tube that is insulated and inside of a room (no wind). I will try to walk you through my thought process in doing so while typing out the formulas I'm using.
I'm starting with a visual resistor method (shown below). The main issues I believe I'm having is with both convective forces (inside the tube and outside, assuming there is convection inside).  The formula for hrad (shown below) is one I found online but I'm not sure if that is correct.
NOTE: I'm not using the Nusselt equations shown as I did find one for a cylinder in cross flow that I'm using.
I am using the Rayleigh number for the external convection while also trying to use radiation as a factor.  The problem arises when I try to run the system without insulation the outer surface temperature is MUCH lower than it should be (900F inside, 100F outside , its showing 550F surface temp).  I know that this should be near the 900F mark as metal is a terrible insulator.  I'm losing most of my heat transfer from my convection internally so I'm assuming that I'm doing something wrong there but can't figure it out.
Working on this today and when I completely remove the convection from the inside flow the temperatures seem to be a lot better.  Another question that now arises is do the k-values for steel change with temperature? I'm assuming this is a definite yes but now am looking for a correlation between the temp and k values.  This may be digging too deep now and basically need a full experiment to do but maybe its something that's already done?  Thank you!
I've been trying to create an excel document that will be able to calculate these variables for any inputs for the system.
I was hoping that someone who knows more than me about this can look over what I'm using and hopefully tell me whether I'm using the correct equations/values.
If anyone could explain my wrong assumptions/thinking that would help immensely.


texts: Why and how are resonance frequencies of a system dependent upon the shape, mass and the way it is constrained?

texts:
I was reading a general overview on the frequencies before conducting a modal analysis for my structure using ANSYS, in hopes of obtaining the natural frequencies for my structure. I read in some article that if you change the geometrical shape of your structure, change its overall mass, and even change the locations of the supports on it while conducting the modal analysis, it is very probable you will see a different set of modal frequencies.
My question is why and how?
Moreover, I also want to ask that after getting the natural frequencies for my structure, does this mean that ALL the structure must be excited by an external frequency equal to natural frequency, to expect some dangerous and catistropic failure? Or even if I excite certain parts of my structure, for example some specific locations on my structure where it is connected to another part (which is essentially causing my structure to vibrate at these connecting locations) should also be dangerous?


texts: How to calculate effective section modulus of a slender section?

texts: Hi how to calculate the effective section modulus of a class 4 section using Eurocode 1993? Can someone show me an example? I tried searching online but cannot find anything useful. My main problem is to determine the stress at both ends of the web plate. Is the stress ratio always -1 since the code mention pure bending? But if so, then the web is always fully effective.


texts:
I am having some difficulty determining the constants $a, b, k$ in the open circuit voltage transfer function $T(s) = v_{0}/v_{i}(s)$, which is given by $T(s) = \dfrac{k [s + a]}{[s + b]}$

I know that the constants must be in terms of the elements $\{C_{1}, C_{2}, gm1, gm2, GL[=1/RL]\}$ positive. I also know that the $gm$ can be negative when switching the input terminal.

Any help is much appreciated.


texts: Running 220V single phase motor on 240V, and did I burn it?

texts:
I have a motor thats rated for 220V single phase. My house has 240V single phase. Im trying to run this motor but it doesn't budge and I don't even hear a hum. I know power is getting to it from checking with a multimeter. Could it possibly have burned from too high of voltage?

Secondly, if wired improperly, say, ground was accidentally switched with one of the hot wires running to the motor, could this somehow burn the motor?

Not sure whats going on with this thing, and I don't see any reset buttons either or fuses either.

Thanks.


texts: What's a simple machine to lift and drop a 100 lbs weight repeatedly using an electric motor?

texts: Essentially I have a 100 lbs. pile driver with an eyelet for lifting it on top. (It's on rails) I want to set up and automated machine to lift and drop the driver at a variable pace. Preferably I would like to use a cheap electric motor. I can use pulleys, and/or a block and tackle system to reduce the amount of work the motor needs to do. I can route/3D print materials if need be. I have looked at mechanical systems and setups all over the internet, but have yet to find a simple effective solution for what I am trying to do.


texts: Predictive object tracking with 2 IMUs and a stereo camera

texts:
I am quite new to this so please forgive me for any mistakes.
I am working on a simulation project and have very little clue as to what to do and I hope someone can point me to the right direction.

Here is the summary of my problem. (Please keep in mind that this is a simulation, no real equipment or IMU is involved)

I have an object O and a stereo camera C. Both have an 9dof IMU attached and are moving freely in space. O and C are 3m in range. O's IMU broadcast acceleratometer info periodically. C is equipped with software to extract the 3D position of O. Find the best way to fuse the data and predict O's position in C's reference in the very near future.

My thought on solving the problem is as follows: (please point out any mistakes I have because I am honestly super new at this...)

Initialize the distance between O and C with an error distribution
Every time I receive O's imu data, I need to calculate where it is
approximately with an error distribution
then use a nonlinear Kalman filter to fuse the 2 distributions
together and find where O might be.

My question is this

How do I calculate where O is given approximate initial pos, and
9dof IMU data?
How do I combine C's IMU and O's IMU so that the measurement is done in C's reference frame?

If anyone can point me towards the right direction I will be very very grateful. Thank you so much!!


texts:
I'm trying to drive an aluminium plate using a motor via a 20mm-wide 2mm-thick stainless steel tube. The tube is driven by a 6mm motor shaft via a pulley and the torque will be around 5Nm at most. Is it a good idea to attach the plate to the tube with a split collar like this?

However it's not clear what the rated torque and axial force are. If this isn't a good way, what might be an alternative without welding or adhesive?


texts:
How can the DOM MILD Steel ASTM A513 Type 5 Tube be improved for corrosion resistance.

it has a low but good welding and machinery ability but if we want to improved the material for corrosion resistance what element will we apply to it?

can we reduce carbon added to make it excellent welding ability and add more magnesium to make more corrosion resistance.?

or we can use Application of zinc coating – steel galvanization it’s a process which creates a coating of zinc over metals surface.

need more formal answer on this subject.


texts: How to Solve this error message on Abaqus 'time increment required is less than specified' and 'too many attempts made for this increment'?

texts:
I am currently working on my dissertation project using abaqus, my model is an arch bridge consisting of a shell and solid elements, there are concrete and steel materials also, I have checked all of the constraints, and I found that there are some constraints giving the error messages 'time increment required is less than specified' and 'too many attempts made for this increment', specifically, those constraints happened in shell-solid tie constraints. the other constraints between solid to solid were fine.

Can anybody help me resolve these problems?


texts: What determines when a road should be widened?

texts: I know this depends on a variety of factors including overall traffic volumes, peak traffic volumes, types of vehicles, and type of road, but how exactly do traffic engineers determine how many lanes a section of road should contain and when the number of lanes should be increased?


texts: Electron micrographs, is it showing electrical charges?

texts: Are electron photographs showing electrical charges? Do electrically charged parts show up more (darker in the photo) ?


texts:
From the 5 options, which one shows the worse wind effect? Is it (b) because wind speeds accelerate through a gap? But how about in comparison to (c)? Or (d) due to the height and sharp corners?
If it's (b), does building shape matter? Meaning, what if it's two square/rectangular building with a connecting bridge (without the splay or funneling of wind)?
Thanks!


texts: what is the difference between jblade, qblade, and xflr5 softwares?

texts:
I am working on a propeller design, and I've came through Jblade which helped me in the airfoil design, yet as I can remember, xflr5 can also do this...
doing some internet search, i found that Jblade is based on qblade and xflr5/xfoil... so does this mean the jblade is more accurate? or everyone of these 3 softwares has a specific field of application?
thanks


texts: Why don't engineers build highways with corners such those on NASCAR speedways?


texts:
Could someone please clarify the difference between flux and normal derivatives?

I am studying PDE's and I came across Neumann Boundary condition (In this condition, the value of the normal derivative is given).  I then came across the following: For a steady state thermal process, the Neumann condition describes a prescribed heat flux.


texts: How much pipe would I need in the ground to cool an outbuilding?

texts:
I want to experiment with geothermal cooling, and have an r-10 insulated workshop which I'd like to cool during the worst of the summer heat this year. The workshop is about 400 square feet (37 m2), and 11' (3.3 m) ceilings, with a concrete floor.

To keep costs down, I'm not interested in investing in a heat pump.  I'd like to try laying long horizontal loops of pipe in the nearby ground 4–6' down (1.2–1.8 m), run water through them, and then through a radiator in the shop I can blow air through.

The ground around here is the typical 55 °F (13 °C) average temperature, and in this area is mostly heavy dense clay.  The water table will be many feet below the loops in the area I plan to lay them.

While I could do this experimentally, lay an arbitrary amount of pipe, and take measurements (inflow/outflow temp difference and flow rate), I'm wondering what equations and engineering knowledge I should be looking at to give me rough back-of-the-napkin numbers on how much pipe I'm looking at to produce a certain temperature differential in the shop.


texts: What is the cheapest way to build a fireproof box?

texts:
I'm breaking my brain for a two weeks trying to find a way to build a fireproof box 100 cm × 100 cm × 100 cm with 1 door at the cheapest price.

The immediate candidate is sheet metal, which needs to be at least 1.5 mm thick in order to be welded, but metal sheet is expensive (at least locally, $600 for the box).
Rockwool is going to be extremely heavy for this size
Polycarbonate is not fireproof, and also costly
drywall not fireproof, costly

I'm looking for an idea.


texts: How to establish good ohmic contacts between Gold electrodes and Germanium Hall bar?

texts:
I am trying to get good ohmic contacts at low temperatures (4K) for a SiGe/Ge/SiGe quantum well Hall bar and so far this has been very challenging to me.
The electrodes are made with Gold and these are connected to the arms of the Hall bar with Aluminium. The Aluminium is used because Ge oxidizes fairly easily so I anneal the device at 300C for 1 hour. This breaks the GeO2 native oxide from the Ge surface and oxidizes the Aluminium. The Aluminium oxide is then absorbed into the bulk of the Al, clearing the interface. A similar technique is used for Si at higher temperatures, but since temperatures higher than 300C would, as I was warned by the person who grew my heterostructure, upset the Ge strain, I shouldn't employ higher temperatures. That is why my annealing time is longer than the 10 minutes usually used for Al/Si contacts.
The theory and technique sound ok but in practice, this did not work. So I created two Au electrodes and connected them with an Al contact to test if the problem was in the metal-metal part of the contact. This produced a higher resistance then I was expecting (10kΩ) and in a few cases no ohmic behaviour at all.
I learned then about Gold-Aluminium intermetalics (white and purple plague)
https://en.wikipedia.org/wiki/Gold%E2%80%93aluminium_intermetallic
which apparently can produce high resistance in the contact between Au and Al. It is a problem in wire bonding, by what the article says, but I imagine if it could be a problem for contacts deposited by evaporation as well (?)
Is there a way to prevent these problems? I believe high temperature facilitates the white and purple plagues so the annealing is not a very good thing, but on the other hand, if I do not do it I will have trouble with the Al/Ge side of the contact.
I have been thinking about substituting the Al for AuGe alloy. Is there a downside to this idea I am not seeing? Does it require annealing?
Thank you very much


texts: At What height do we splice vertical bars in Columns and Shear walls?

texts: At what height do we splice the vertical bars in columns and shear walls is it at the middle of the element or at the bottom ( Slab level) and why ?


texts:
In designing mechanical parts in an assembly, sometimes the mating surfaces are raised faces. I've been told it's to provide a better seal. However, for piping (flanges), it seems to be the consensus that a raised face flange does not provide any extra seal functionality, but has more to do with the manufacturing method (forged vs cast).

My question doesn't necessarily apply just to piping flanges, but to designing parts in general. Is it desirable to use a raised face on mating parts, and when (always, sometimes, etc)?


texts: Ignore the thread in Collision Detection in Solidworks

texts: How can I ignore the thread in standard parts in Solidworks (for Example nut with thread) in the collision simulation without deactivating the component? I can disable all the 180 nuts in the list of components, but there has to be a way to solve this problem more elegantly. On the other hand, the collision detection notifies me about a possible collision with components (those that include thread) even before the movement simulation.


texts: What is the difference between 250W band heater and a 200W one? Can they reach the same temperature?


texts: Calculation for lowering temperature in a room… room-fridge with water mist?

texts:
I was looking at how the water cools my body when it evaporates off it. Then I thought the specific heat capacity could be used to calculate how much energy (i.e heat) would be taken out of a room when water that absorbed its heat is transferred out of the room.

I tried and researched all I could, but as I am not an physicist, I can't really get calculations together.

I have a setup with one mister, which is simply a device that atomizes water to small drops (I have no clue how small), and a large fan (it draws air) on the ceiling to "suck" up the vapour and transfer it to the open.

Room size = 2m x 2m x 3m

Mister sprays 1L of water per minute (16.67ml per second), as tiny drops.

I am getting confused, as some water would probably vaporise and some would remain water. I think that the small drops have a large surface area, so absorb energy fast, and thus turn into gas (steam?). I can't understand how to calculate the heat energy transfer from the room to the water and steam, how to use ratios. All this is getting messed up the more I think of it.

Can someone direct me what I must calculate, as I'm really dumbfounded as of now.


texts: What is the name of this kind of through-hole fastener?

texts:
I've seen these before but I don't know what they're called. It's a two piece insert that creates a through-hole between them.
I drew a picture to help identity it!


texts: Heat equation for solar radiation on a wall

texts:
I'm trying to model the effects of solar radiation on a (thick) concrete wall. My assumptions are followings:

The wall behaves as an half continuum with parameters $k = 0.8 W/Km$, $\rho=2500 kg/m^3$, $c_p=880J/kg K$
Solar radiation is simulated as an heat flux on the wall surface $\dot{q}(0,t) = 650 W/m^2$
There is an exchange of heat between wall and surrounding air,  modeled using an heat transfer coefficient $h=15W/m^2K$ and considering air temperature as constant with $\vartheta_\text{air}$

Now I should solve the heat equation
$$ u_{,t} -\alpha u_{,xx}=0$$

Under following IC and BC:
$$\begin{cases} u(x,0) = \vartheta_0 \\ 650+ h(\vartheta_\text{air}-u(0,t))= -k u_{,x}(0,t) \end{cases}$$

I tried to solve this PDE using Mathematica, but gave me a nonsensical result. Taking $h=0$ however leads to good results. So I'm quite sure the error lies in the consideration of the flux between wall and air (boundary condition), but don't see it.

EDIT: Here is the code I used in mathematica.

k=0.8; c=880;  rho=1950; a=k/(c*rho); h=15; theta_air=0;

heqn=D[u[x,t],t] == a*D[u[x,t],{x,2}];
ic1=u[x,0] == 0;
bc1 = h*(theta_air-u[0,t])+650 == -k*Derivative[1,0][u][0,t]
theta_0 = 20;

sol=DSolveValue[{heqn,ic1,bc1},u[x,t],{x,t}][[1,1,1]]

f[x_,t_]=sol;
theta_0+f[0.,7200]
theta_0+f[0.1,7200]

which gives:

15.3649+0.i
2.6153+0.i

Again, this PDE gives the correct result assuming $h=0$ (no heat exchange between wall and air). This result was checked with the solution of an exercise found on a book.


texts: Why is a mold required in isostatic pressing after performing Sintering

texts:
After an a object is formed through direct laser sintering, as a post-processing procedure the object is sent for hot-isostatic pressing, In hot isostatic pressing the sintered object is placed in a mold and then pressure and heat are applied.
I was wondering what would go wrong if the bare object without the mold  was made to undergo pressing? Remember the sintered object already has a shape acquired during sintering so it may need a mold to get a specific shape during pressing.   My assumption- In hot isostatic pressing the object might get softened and hence deformed due to heat and thus the requirement of a mold to keep the object firm. Is this assumption true??
And apart from deformation are there any other undesirable effects caused to the un-molded object during hot isostatic pressing?


texts: Is it possible to "expand" air flow area in a duct over a short distance?

texts:
Is it possible to increase an air column's diameter over a short distance? Let me explain:

Imagine a small 10 cm electric computer cooling fan that's pushing air into a cone-shaped duct 20 cm long. If the exit side of the cone-shaped duct has a diameter of 5 cm, I would think the diameter of the air "column" at the exit of the duct will be halved, and the pressure to be double of what it is at the beginning of the duct.

Now, if the diameter of the cone-shaped duct is instead increased to 20 cm on the exit side, will the air column have double the diameter and half the air pressure than at the beginning of the cone-shaped duct?


texts: Are there ways to measure modulus of elasticity with an experimental apparatus?

texts:
It seems that measuring the modulus of elasticity of a material always involves the strength of materials or linear elasticity approach, where they make some experimental measurements for variables such as applied force, strain, deflection/deformation, etc... and then use some linear elasticity solver to back out the strain value.
Are there any experimental devices that actually measure the modulus directly?
Edit 1:
I'm mostly interested in orthotropic materials. It's not very intuitive to me how Young's modulus is measured in orthotropic materials.


texts: How to split mercury with a magnetic force?

texts:
Do you think, one could split a mercury drop into two drops with the magnetic force? Mercury is a liquid metal, hence if I put a current through it, it will become a electromagnet (a wire with a current induces a magnetic field).

If I then place two magnets on each side, but sufficiently separated, I thought that the fluid "electromagnet" will split and both sides will travel to the magnets.


texts: Can we make significant energy from human waste?

texts: I am trying to find if making energy from human waste (excrement, sewage) is profitable? Lets say I live in a city of 16 million people which does not put waste into use. What could be the profitability?


texts:
Consider this hypothetical ideal scenario:

If I have a test coupon in a tensile test that has a constant cross-sectional area throughout its length (i.e. along the tensile loading direction) and there are no flaws or imperfections at all, where does necking occur?

In this case stress is uniform throughout the volume of the coupon (no stress concentrations).

Thanks.


texts: Mat foundation Reinforcement with 3 layers

texts:
I have a mat foundation that is 3 m thick (44 story building), I know how to design the upper layer and bottom layer but since at the top layer the reinforcement is too dense I want to make a third layer of reinforcement but my problem is I don't know how to design the third layer.

If for example in total in the top layer I need 55.8 cm2/m so I place T25@15 cm (32.8 cm2/m)in the top layer, for the remaining reinforcement area need I want to place them in a different layer just below the top layer bearing in mind that the effective depth will change so I can't just say 55.8-32.8 = 23 cm2/m and place them.

How can I calculate the remaining reinforcement needed ?


texts: How do you convert "kps" to Pounds per Square Foot (psf)?

texts:
I'm looking at a soil bearing capacity report, which has a column labeled "kips" and the values are followed by "kps".

A "kip" is 1000 pounds, but I'm not sure how to convert from "kps" to psf.

The data has values in the 17 to 45 kps range. If I assume that there are 1000 psf in one kps, then the soil bearing capacity would be 17,000 pounds per square foot to 45,000 pounds per square foot. This seems wrong to me, as I would expect the values to be in the 1,700 to 4,500 range.

What does the abbreviation "kps" actually mean?
How do I convert kps to psf?
If a "kip" is 1000 pounds, why does a "kps" seem to be only 100 psf?


texts: Designing and fabricating custom gears and sprockets

texts:
I need to get a motor from an electric motorbike to drive a single-speed BMX Bike chain, and I haven't worked with bikes/sprockets before so I don't know where to start (I was only supposed to be doing the throttle and electronics, not sure how I ended up with the chain drive).

I know I need a sprocket with as few teeth as possible (~10-14 or less) and can be mounted onto a 9.5mm shaft double flattened to 8.4mm, and 4.5mm long, and have the teeth fit a standard single-speed BMX bike chain.(measurements are from a set of calipers, motor doesn't have any specs :P) I have a sprocket from the motor, but it isn't the correct tooth size/spacing for a bike chain.

Is this something that exists or can be made on a part-by-part basis, or do I need to weld something up?


texts: Is it possible to make your own Q-Thruster?

texts: Is it possible to make a homemade Q-Thruster assuming you cover all the safety requirements? I know the one made by (http://cannae.com/) uses a magnetron and resonate cavity to bounce the microwaves, and honestly seems easy to build. All I would need is to get the magnetron from a microwave and build a resonate cavity chamber to bounce the microwaves.


texts: Transferring energy generated by photovoltaic methods

texts: One of the many challenges facing PV power generation is how to store surplus energy for night time demand. My question is this: since the sun is always shining somewhere on the planet, would it be possible to design an international smart energy grid that can transmit DC current for long distances? Is any research related to this question being conducted?


texts: I need a roller setting where I input a 1 feet fabric and need it to be reduced and compressed about 9 inches and released back as 1 feet fabric

texts:
I have a requirement where I need to input 1 ft wide flexible 5mm thick fabric into a roller setting where my width is reduced to 9 inches and compressed and released back as 1 ft. I thought of using special rollers (which I call Zigzag rollers) for this purpose but the problem I assume is that this setting will tear the fabric. Please help me design it.
The fabric is essentially a loop of 2 ft length.
The Idea is to wet the fabric, clean an object and compress the fabric to collect all the wet dirt and and continue the same process. But since the mechanism has to be on the sides of the rollers I need the width be reduced due to space constraint.


texts: shock-resistant electromechanical linear actuator?

texts:
I was wondering, if there is a shock load resistant electromechanical actuator that can withstand powerful impacts?
Is there an electromechanical counterpart for pneumatic cylinders that is as shockresistant as hydraulic or pneumatic actuators?

And if not, is there some kind of way to make them withstand impacts via external parts?


texts: Mathematical modelling of the crank in a two-stroke (diesel) engine

texts:
I need to use a mathematical model of the crank in a two-stroke (diesel) engine. Since a real two-stroke engine endures anharmonic motion, I need to implement higher order harmonics - preferably into a second order ODE, e.g.:

$$ \ddot x +2\zeta\omega_n\dot x+\omega_n^2x=\mu r\omega^2\cos (\omega t+\phi)+\Gamma\omega_n^2\cos(\omega t)$$

How do one model the anharmonics that a two-stroke diesel engine suffers from by using higher order harmonics? Is it adequate to implement e.g.:

$$ \sum _{i=1}^m\kappa_i\omega_{n,m}^2\cos(i\omega t+\phi_i)$$


texts: How to control suction strength on a breast pump?

texts:
Most of the breast pumps I've examined utilize a very similar mechanical design; that is, they use lead-screw motors to produce linear actuation of a piston-like device inside a cavity.

However, some breast pumps also offer electrical controls for both speed and suction strength.  From the lead-screw design, I can easily understand how to control the speed of suction.  But I'm not quite sure how suction strength is controlled.  How is this typically done in lead-screw actuated piston-like air pumps?


texts: How much should I adjust torque specs for lubricated threads?

texts:
The factory manuals for motor vehicles give torque specs for most nuts & bolts. My (possibly incorrect) assumption is that these are for dry threads as would be used in a factory where no oils or grease are present at the assembly site, or where proper protection from these lubricants are provided.
As a home mechanic (or even a pro, working in a shop), it's often the case that threaded holes will have some sort of lubrication in them due to leaks during running or drips/slop during reassembly. It's also possible/likely that nuts or bolts will get some sort of lubricant on them as they're being installed to hold a lubricated part in place.
Since lubrication on the threads will allow the bolt to spin more easily into the hole, it's possible that torquing to the factory spec will actually over torque the bolt, possibly leading to catastrophic failure while in use. Is there some sort of standard amount by which a torque spec for a particular nut/bolt should be adjusted (reduced) to account for the lubricated threads? Would the adjustment be based on materials in use? (cast iron vs steel vs aluminum vs other)


texts: using a coil for an electrochemical reaction

texts:
I wish to calculate the amount of energy required for electrolysis through induction, instead of electrodes. If there is a crucible metal core
with solution inside and the coil wrapped around it. Can there be the required voltage for the electrolysis reaction and enough current to transport the ions?
If I have the resistance of the solution inside the crucible (derived from its resistivity of an area) and the voltage produced from the inductor will this tell me how much current is flowing through the solution and then inturn allow me to calculate Faradays laws?
Not really asking for a solution more the correct steps to get there.
Thank you for taking the time to read the question.


texts: How to design a kalman filter with different sampling rates?

texts:
This question is related to https://stackoverflow.com/questions/22598107/kalman-filter-with-redundant-state-measurements.
How would one design a Kalman Filter (or EKF) when two measurements of the same state variable have different refresh rates ?
For example, one sensor may be precise and high-frequency but have long-term drift while the other is less precise but has lower refresh rate and doesn’t drift of the long term.


texts: In the context of a known disturbance $d(t)$ in a control loop, what is the $\Delta t$ at which the control loop has to be executed?

texts:
As an example, consider a P-T1-system with a PID-controller. First look only at the P-T1 system, set a $y_r$ and wait a long time - then we take a look on its output $x$ and see that it has still a disturbance $d$ which variates with time (see the plot, system output $= x$). In this model, the system output is, after you wait a long time, a constant plus $d(t)$.

The next step is to introduce a PID-controller:

For this loop alone we could just use some experience-based technique like the Ziegler and Nichols procedure to adjust its parameters $K_p$, $K_i$ and $K_d$ optimally. If we switch to discrete control loop, because the controller is digital,  we will have one additional parameter: The $\Delta t$ at which the controller operates.

What $\Delta t$ is required for the control loop to diminish the effects of $d$ on the system output? The trend will of course be the smaller $\Delta t$ the better, but is there a general rule for the maximum $\Delta t$?


texts: Implementing logic expression and the truth table of logic function

texts:
(a)Z=(B+C')A+B(C+D')+BD

Z=AB+AC'+BC+BD'+BD

Z=AB+A'C+B

Z=B+AC'

(b) A B C|Z

0 0 0|0
0 0 1|0
0 1 0|1
0 1 1|1
1 0 0|1
1 0 1|0
1 1 0|1
1 1 1|1

(c)       BC  00 01 11 10

 A 0   |0  |1 |1 |1|

   1   |1  |0 |1 |1|

I was able to complete the 1st 3 Q's i.e.(a),(b),(c).But i didn't understand the last 2 Q's i.e. (d),(e).Can someone give me a hint or push me in the right direction? Thanks in advance


texts: Why does net positive suction head (NSPH) include velocity head?

texts: When the absolute pressure dips below the vapour pressure, cavitation occurs. Why would dynamic pressure be taken into account in this case?


texts:
I am looking at the specifications for thread lockers, and henkel/loctite specify "Torque break" and "Torque prevail" in in./lb. as shown in the link below:

http://www.na.henkel-adhesives.com/industrial/product-search-1554.htm?nodeid=8797951950849&msdsLanguage=EN_US&selectedTab=technical

I had expected to see the torque required to break the "lock", and to continue turning in in.⋅lb. (or N⋅m) as described on wikipedia:

https://en.wikipedia.org/wiki/Thread-locking_fluid

What does this "Torque break" value mean, and how is it calculated?


texts: How are eigenvalues of a cell in the finite volume discretization calculated? (for euler fluid equations)

texts:
I am building a program to numerically solve the euler fluid equations based on finite volume discretization and am having trouble on a step where the eigenvalues of a cell need to be calculated according to the picture below. The eigenvalues for each cell are calculated by dotting the velocity vector with the normal of the face and adding C, the speed of sound.

Dotting the velocity vector with the normal of the face of the cell make sense. Therefore, to my understanding, you must have 4 eigenvalues, one for each face, for each cell. I am confused by the next part, which says to calculate the average of the neighboring cells at each face. The notation used does not differentiate between the left or right face, making it seem like there is only one eigenvalue for each computational direction (for each cell). I am having trouble understanding the exact representation of this term and its meaning.


texts: What is the highest repetition rate achieved for pulsed Terawatt and Petawatt-order lasers?


texts: Strain gauge - Non-uniform strain distribution

texts: If the strain gauge is placed in the area of non-uniform strain/stress distribution, will the gauge average the strains along its lenght? The gauge will not be able to capture local maximum strains, but would such use of strain gauges impact the gauge negatively? Would that measurement be eqiuvalent to the (deformation in point A - deformation in point B)/length?


texts: Does angular velocity of a body rotating on top of another rotating body add up or multiply?

texts: I want to mount a small engine on a shaft of a large engine and rotate them both in the same direction, will the RPMs be a sum of the their RPMs or will the resulting number be a multiplication?


texts: Pressure difference/drop(or loss?) in a Laminar pipe flow

texts:
Consider a "pressure-driven" flow ( inlet $P_1$ and outlet $P_2$  pressures "imposed" by an engineer) in a pipe of some length.

Under a steady-flow, fully developed region :

My understanding:

For "this" pressure difference or drop or gradient $\left(\dfrac{P_1 - P_2}{L} = \dfrac{\Delta P}{L}\right)$, there will exist a flow rate, $Q$.

Further, if there exists a "frictional LOSS", we cannot achieve the same flow rate for the imposed pressure difference, $P_1 - P_2$.

Now, to calculate the frictional loss, I cannot understand why textbooks use the same nomenclature/notation/ variable of pressure difference/drop, as $\dfrac{\Delta P}{L}$ is an externally imposed parameter and not a result of flow happening.

All the textbooks use the same notation $\left(\dfrac{\Delta P}{L}\right)$ for the pressure difference/drop that "drives the flow"  AND equate the same as frictional loss and write an expression (with density $\rho$)

I am missing the lead somewhere. Help me out!


texts: How to pump same amount of paste every time?

texts:
I am not sure if I am on the right site for this, but here it goes.
I have a friend who makes a hot sauce for a company he runs. It is very pasty (made of pepper flakes in an oil).

The problem is, when he makes a batch, he's got to continually stir up the batch while trying to pour an equal (and evenly distributed) amount of the paste into the bottles.

He wants system that makes it easy and predictable to do this faster. Ideally, he would make the paste, put it in something that keeps it stirred, and from there fill each bottle with the same amount of paste.

What kind of contraption would do this?


texts: Changing fields from mathematics to control engineering

texts:
I did my undergraduate in maths and physics and will be working in control theory for my future job. Not to my surprise, my engineering background is rather lacking. I have taken a look at materials on modern control theory (state-space, optimal control, dynamical systems) and with my mathematical background, do not foresee big difficulties learning these topics. Classical control theory (PID controller, block diagrams etc.) which seems to still be used in many implementations, on the other hand, is deeply rooted in electrical engineering and many concepts/tools are foreign to me. (E.g. I am familiar with laplace transforms and how to use them to solve DEs, but not the language of block diagrams and transfer functions)

1) Could I have a rough roadmap for the topics that I need to catch up on? As of now it seems that I need to learn what is usually called 'signals and systems' and  'feedback control'. What are some other essential topics that must be learnt to be an effective engineer?

2) There is a huge array of textbooks for control/electrical engineering out there. What are some good/classic/standard references that lead up to control, or are particularly suited for someone of my background. (We see lots of books titled 'mathematics for electrical engineers'. Is there somehow a book along the lines of 'electrical engineering for mathematicians'?)


texts:
I've got what is basically a hammock frame design, made from tubing, that I'm trying to make as light as possible, while meeting a necessary strength safety factor.

I've hired a few different mechanical engineers to tell me if the design is feasible and, if so, what the best combination of aluminum/steel and diameter/wall thickness would be optimal.

Before hiring anyone, I went through a few iterations of a physical prototype and have been able to see some of the problems when a load is applied.

The problem is that some of those problems aren't showing up on the FEAs, and, additionally, there seems to be a lack of familiarity with the different aluminums and steels (comparative strengths, weldability, etc.).

Is this more of a job for a structural engineer, or am I just not hiring good enough mechanical engineers?


texts: Transmission for constant-speed, variable-torque output from variable-speed, variable-torque input?

texts:
I'm interested in designing a transmission to achieve a constant-speed, variable-torque output from variable-speed, variable-torque input -- something like a CVT, but applied backward. Is such a thing possible? Do any examples of a transmission like this exist commonly?

I'm happy to answer any clarifying questions, as I'm imagining this doesn't include all the needed information. Thank you in advance for your patience!

EDIT: I should mention that the specific effect that I'm looking for is that when the input speed increases, the output speed remains constant, but the output torque increases proportionally.


texts: How do the columns in the 'magic mountains' sculpture stay up?

texts:
I am reading this story on artist Ugo Rondinone's sculpture in the Nevada desert (Building an Artist’s ‘Magic Mountains’ to Draw Visitors to the Desert) and simply wondering (as an artist myself): how did they make those columns stay up?

I didn't see any information on dimensions but from the photo with the artist below, one might guess that these columns are abut 25 feet high?

Assuming there is a solid concrete footing for the columns to stand on and some preparation of the "joints" between the stones:

Is the weight of the stones enough to keep them stacked and resistant to wind and weather (as such weather as there might be in the desert)?
Is it likely that the stones are drilled to incorporate some steel armature?

I understand that the stones could just be balanced, but given that this is a funded and likely insured project, I find that hard to believe likely.


texts: Equivalent moment of inertia in a crank-rocker mechanism

texts:
I'm attempting to model a crank-rocker mechanism (see picture). A motor is connected to the crank side and is driving the mechanism with a torque $\tau_{motor}$. A load is attached to the rocker side which applies a torque $\tau_{load}$. The moment of inertia on the motor side is $J_\theta$ and the moment of inertia on the load side is $J_\varphi$. I want to find the equivalent moment of inertia $J_{eq}$ that the motor experiences from $J_\varphi$ and $J_\theta$ combined.

I have used Freudenstein's equation to find the relationships $\varphi(\theta)$ and $\frac{\partial \varphi}{\partial \theta}(\theta)$.

For a gearbox (with constant gear ratio) the solution would be $J_{eq} = (\frac{N1}{N2})^2 J_\varphi + J_{\theta}$ (see https://electronics.stackexchange.com/questions/325607/dc-motor-differential-equation?noredirect=1&lq=1).

What is $J_{eq}(\theta)$ in my case? My intuition is that the relationship should become something like $J_{eq}(\theta) = ( \frac{\partial \varphi}{\partial \theta}(\theta))^2 J_\varphi + J_{\theta}$. However, I have not been able to prove this.


texts: Why does the minimum force have to be parallel to the incline?

texts:
If we have an object on a frictionless inclined bench, why does the minimum force applied to keep it steady have to be parallel to the incline (or perpendicular to the reaction force)?

In other words, why does the angle θ in the image have to be 0 in order for the force to be minimum?

Consider we know the weight of the object and the reaction of the incline.


texts: how to pattern a cut-loft around a helix

texts:
I'm trying something fancier..  hopefully it will be clear from the screen-shot.. linear and circular patterns work.  now, however, I'd like to spiral the cuts.  first try isn't working..  it gave me an error at one point, but I didn't comprehend it, and it hasn't shown up again.

here is a second screen-capture presenting the problem.  I try to select the outside of the cylinder as the surface that the pattern should be normal to, and it doesn't work..

partial solution:  I tried the following (somewhat lame, it gave me no sound?) tutorial and this time it worked:  https://www.youtube.com/watch?v=X9xSMBdqcr4 .  two things I've learned:  the first one.. is rather trivial but irks me for some reason.  a helix can't be created from an existing sketch,  you have to create a fresh sketch just for it.  this seems.. wasteful of time and effort, particularly considering the second thing I've learned:  in order for the curve driven pattern to work, the helical path -must- be on the surface to which the object to be patterned is to be  normal...  so the question would become, why is solidworks built this way.  is  there a reason for it, or is  it just an oversight? :-)


texts: How do I best model a torque applied over a non-radial line?

texts:
I am looking to use FEA (specifically, Creo Simulate) to re-create the results of a static strength test on a part my company will be testing in our lab. Because the lab results are the ones we will be using to determine the utility and capability of the part, I'm doing this mostly as an exercise, to strengthen my FEA skills and to see how close to reality I can get the results of the analysis to be.

For a couple different reasons (write access to model files, investigation of the bolt functionality of Creo, more realistic application of load) I am attempting to model part of the test stand in addition to the part of interest. The part itself has a flange with a bolt pattern as part of its design, and we are using that bolt pattern to attach it to an adapter. The adapter will attach to the output of the motor, with the torque being applied through a key that sits between the adapter and the motor output.

Below I have a picture of the keyway in the adapter for clarity. The part of interest is attached to the back side of this adapter, the key fits along the entire length of the keyway, and the adapter connects to the test stand output using the four larger bolt holes (these don't transmit any significant torque, they simply keep the assembly together.)

My issue is determining how best to model the applied load on the walls of the keyway. My intuition tells me that the load will vary along the length of the keyway, as what we're really applying is a torque that gets distributed throughout the key.

Given that $T=r \times F$, I'd expect there to be an inverse relationship between the force I should apply and the position along the keyway at which I apply it. Does the fact that this line of action is not radial complicate things?
In addition, I have two coordinate systems defined, the standard Cartesian, and a cylindrical one with the z-axis going through the center hole of the adapter as you might expect. Will applying the load in one coordinate system or the other significantly alter the result, and is one preferable? Will the distributed force equation be easier to define in one coordinate system?


texts: Optimizing return temperature in a brazed plate heat exchanger

texts:
I have a brazed plate heat exchanger similar to these. I can regulate flow and temperature of water on the primary side of the exchanger to achieve the desired temperature of water on secondary side. The desired temperature and flow on the secondary side are not under my control.

How do I optimize the flow and temperature on the primary side so that I get the lowest possible temperature for water exiting the heat exchanger, while still achieving the desired temperature on the secondary side?

Note: The transfer medium is chemically treated water, the maximum temperature is around 100 °C at 4 bar.

If I increase the flow to some maximum value I will also increase the heat loss through the pipe walls. However, increasing the flow rate would allow me to lower the supply temperature, which decreases the heat loss. How would I calculate the best flow rate and supply temperature combination to minimize heat loss through the pipe walls?


texts: Pre-Defined Numbers to be used in Sizing Mechanical Parts

texts: I recall there was a set of "engineering numbers" that were to be used when deciding how big to make something. So that if, for example, you wanted your screw to be 1.36mm you'd instead round up or down to the nearest of these prescribed numbers, perhaps to 1.2 or 1.5. This way everyone's things were more likely to be the same size because instead of randomly selecting sizes that were particular to a specific situation, we'd all be using the same set of pre-selected numbers instead. Does anybody know what this concept was called? Thanks!


texts: How energy intensive is creating artificial islands in the IJsselmeer?

texts:
The City of Amsterdam is building a series of artificial islands for new housing. One of them is Centrumeiland. Its size is 13 ha. (130,000 m2). Its creation requires 800,000 m3 of sand (Source), i.e. approx. 6 m3 per m2.
The method of construction is the “pancake method” (Source):

When an island is built-up this way, porous screens are placed in the
water to hold the island’s shape and sand is sprayed into the screens
to form a layer of batter-like sludge. As this layer settles and
drains through the fine mesh, it hardens and another layer of sand is
sprayed on top. Pancake by pancake, the island rises until it is two
meters above the water level.

The sand comes from the bed of the IJsselmeer in which the islands are located (Source), so probably some 20-50 km away.
I wondered how energy intensive this practice is.
Could it be done with renewable energy (windmills powering pumps)?


texts: How in Rankine cycle the turbine generates more power than the pump takes?

texts:
In Rankine cycle there's the boiler where water gets boiled into overheated steam. On input there's a pump that delivers more water, and on output there's a turbine that picks up the energy of the compressed steam.

The steam pressure is roughly identical against the turbine and the pump; the pressure of the boiler section.

What makes the steam power the turbine instead of backing up and forcing the pump to turn backwards? - well, this one is simple, power delivered to the pump. But then how comes the turbine produces more power than the pump takes? The pump, after all, must overcome the same pressure that propels the turbine and deliver the same amount of water that is being ejected as steam. I'm missing some significant element of the device. What is it?


texts: I am being asked to compare a fan which is going obsolete with its proposed replacement. From a mechanical and electrical point of view, they are almost completely identical so I have no concerns from that point of view. However, when I look at their respective performance curves, they are somewhat different, especially in the low air flow region. This is outside of my area of competence, and although I have done some reading about it, I am not sure what to make of it. Can somebody explain to me which one is best and why (I have purposefully not put any legend)?


texts: Sliding mode surface derivative using numerical method

texts:
In the article Controller Design using Bifurcation Map for Aircraft Spin Recovery, the sliding surface derivative is obtained using a numerical method.

The steady space system is defined by the following equations:

$$\dot{\underline{x}}=A(\underline{x},t)+B(\underline{x},t)\underline{U}, \\
\underline{x}=[V,\alpha,\beta,p,q,r,\phi,\theta], \\
s=\left[\begin{array}{c}
\dfrac{d}{dt}(\phi-\phi_d)+\lambda_1(\phi-\phi_d) \\
\dfrac{d}{dt}(\alpha-\alpha_d)+\lambda_2(\alpha-\alpha_d) \\
\dfrac{d}{dt}(\beta-\beta_d)+\lambda_3(\beta-\beta_d) \\
\end{array}\right]$$

where $\lambda_1$, $\lambda_2$ and $\lambda_3$ are positive real numbers.

The article states:

  The control law from reaching law in Eq. (6) can be derived
  as:
  $$\dot{s}=\dfrac{\partial{s}}{\partial{x}}\dot{x}=\dfrac{\partial{s}}{\partial{x}}(A+Bu)=-Qsgn(s)+Kf(s).\tag{8}$$

  By solving the above equation (8) for u (3 x 1), one gets expressions
  for u as:

  $$u=-\left(\dfrac{\partial{s}}{\partial{x}}B\right)^{-1}\left[\dfrac{\partial{s}}{\partial{x}}A+Qsgn(S)+Kf(s)\right].\tag{9}$$

  The matrix $\frac{\partial{s}}{\partial{x}}$ is computed numerically.
  The control inputs computed are subject to position and rate
  constraints on control surface deflections as listed in the Table 1.

Which numerical method is used to compute $\dfrac{\partial s}{\partial x}$ in $u$?And also how would be the exact form of matrix of $\dfrac{\partial s}{\partial x}$ (element of $\dfrac{\partial s}{\partial x}$ in columns and raws)?


texts: Recommended books for process engineering?

texts:
I made a career change from machine design to CNG processing. What I’m looking for are some good books/handbooks that cover the following topics. Something similar to Machinery’s Handbook.

Piping, flanges and welding (for gas). E.g. pipe dimensions, pressure ratings, losses, metallurgy etc.
Heat exchangers (tube & shell)
Boilers
PLC controls

Thanks!


texts: best refractory cement for embedded heating element furnace

texts:
first post

I designed a 2000 watts 1000 degrees Celsius furnace with following chamber size: 11 cm length, 12 cm width and 15 cm depth. The refractory that I use is 1880 C high temp tabular alumina refractory with 94 percent al2o3, 5 percent sio2, 0.2 percent fe2o3 and 0.6 percent cao. The heating element is 1.2mm in diameter with 2000 watts and is planted inside the refractory material with 3mm offset from inside of the chamber.

everything is OK so far but something is confusing me, here are the questions:

1- The furnace heat-rate is so slow (about 10 degrees in minutes). Is this problem is related to refractory?

2- What kind of refractory should I use for best performance and longer life cycle?

any kind of help would be very useful.


texts: Would a plane lift from ground if in a free treadmill?

texts:
I was wondering if the force generated from the engines of a jet plane would lift it up from the ground if in a free treadmill.

Would it take off?


texts:
A cursory search indicates that drills size in round decimals of an inch (e.g. 0.3, 0.4, 0.15 inch) are not common, but are they a production item or would they only be available as some sort of custom or special purpose tooling?
What about for other "round hole" tools like mills and reamers? Looking up the second, they seem to be sized in terms of decimal inches, but the list I found didn't seem to have uniform increments so I suspect the choice of values came from something else.


texts: How to choose linear shaft diameter for a lifting system?

texts:
I'm working on a lifting system that uses a ball screw and linear shaft as guide and I would like to determine which shaft diameter would be enough for my application.

So here is a sketch of the system that uses 3 linear shafts and 3 linear bearings. The grey transparent huge block weighs 40 kg and its dimensions (which I guess are important to determine radial loads?) are 90 cm (width) x 70 cm (depth). How can I determine (approximately) the diameter required for the 3 shafts and also determine whether 2 shafts would be enough?

After reading this guide:  http://www.nookindustries.com/LinearLibraryItem/Linear_Components_Design_Considerations I found that using a diameter of 1/2" with a length of 35 cm for the shaft would create a deflection that produces a misalignement angle around 0.25° (which is acceptable if I refer to what is written on that guide).

But I am really not convinced that a single shaft with such a small diameter could support that 40kg load.


texts: Locations of max stresses in a circular beam?

texts: If a torque and axial force is applied to a beam with a circular cross section, where along the cross section of the circular beam is the location of the max shear stress, max bending moment, max torque, and max axial stress? Correct me if I am wrong, but from class, I learned that max bending moments occur away at the neutral axis at the top and bottom of the beam (i.e. 90 and 270 degrees). Secondly, I think that the max shear stress occurs at the neutral axis (i.e. 0 and 180 degrees) since that is the apex of the parabolic shear profile but I am unconfident in that answer because I read that fracture points due to shear occur at 45 degrees. Lastly, I am not sure where along the beam the maximum torque and axial stress would occur. Thank you.


texts: Controlling the flow of powder from a container

texts:
I was wondering how you would control the flow of powder from a container (with a small cylindrical dispenser at the bottom).

The container is filled with powder. As the container drains, less pressure will be exerted on the bottom most powder, affecting the flow rate (at least, I think).

Say I select 32.5 grams and hit a button. What process would you use to deliver this measurement of powder from the nozzle?

Would a lasar work?
Would there have to be a measurement of the current mass?
Would you need to know density?

I also posted this on Quora and got a very nice introductory answer but something more specific could help me.  Also, I was given a link to the Weisbach equation, but the contents of the container will be a powder. Probably varying in their size and density as some powders will be finer than others. But in general, how would you solve this?

I know the pharmaceutical industry uses expensive equipment to achieve this, but I am not thinking industrial. They are filling tiny little pill capsules with exact proportions. The focus here is household use, with maybe 15–40 g servings

What I am looking to do is input varying size of serving. 20 g, 22.5 g, 35.5 g serving. Optimally, the system will have an electronic motor component, CPU and a valve that opens/closes with use of the motor...

One of my part time jobs is at McDonalds. We have this cream/milk dispensing machine. You input double-double, and out comes 2 creams for the corresponding cup size. I wonder how those work? The paramount different in systems being those dispense liquids, and we're looking to dispense powder solids.


texts:
I am studying about wind turbine and turbine.

I have some questions, but first, I explain some cases as follow:

Low velocity air over an airfoil at a zero-incidence angle does not initiate flow separation. If the air velocity slowly increases, the flow separation starts from the blade trailing edge (TE). If the velocity or the incidence angle increases further, the separation point or stall point moves towards the blade leading edge (LE). If the stall point can be pushed towards the TE, the airfoil performance or the turbine blade performance increases as the attached flow transfers more energy to the blade.

Now, I want to know that how I can claim that efficiency of turbine increase up to given angle of attack?

The efficiency increase with increasing angle of attack while flow separation also increase with increasing angle of attack. I don't understand this case!

With regards to above explanations, if angle of attack increases; separation point or stall point moves towards the blade LE and the turbine blade performance decreases as there is low attached flow. I know that when angle of attack increases, tangential force also increases and for this reason, the efficiency of turbine increases but I want to know about increasing efficiency from the point of flow separation!

How can these two things (increasing efficiency and increasing separation) be linked together?

I am grateful to all who guide me about these cases and if it is possible, please place useful links and papers related to these cases.

In fact, I am studying more about the Ws turbine. In my investigations, the air velocity(inlet velocity or axial  velocity) is constant and rotational velocity(r $\omega$) is changed and in other words, rotational speed is decreased in my calculations. this method is performed in the following paper. In this paper, There is the used equation for efficiency.

A comparison of computational...

$\eta = \frac{T \cdot \omega}{\Delta p_\mathrm{t}\cdot Q}$

$T =$ shaft torque

$\omega =$ angular speed

$U = r \cdot  \omega =$ rotational speed

$\Delta p_\mathrm{t} =$ total pressure drop across the turbine

$Q = V_\mathrm{inlet} \cdot A$

$A = \pi\left(R_\mathrm{casing}^2-R_\mathrm{hub}^2\right) =$ through flow area

$\frac{V_\mathrm{inlet}}{U} =$ flow coefficient

Also, please see the following figure:

In fact, The  various  values  of  the  flow coefficient  were  achieved by  varying  the  rotational  speed  of  the rotor  at  a  constant  value  of  the  axial  velocity,  which  are  similar with  those  performed  by  Kim  et  al.  [1,2],  Takao  et  al.  3  and  Zahari et  al.  [4].

1  Kim  TH,  Setoguchi  T,  Kinoue  Y,  Kaneko  K.  Effects  of  blade  geometry  on  performance  of  Wells  turbine  for  wave  power  conversion.  Journal  of  Thermal  Science
2001;10(4):293–300.

2  Kim  TH,  Setoguchi  T,  Kaneko  K,  Raghunathan  S.  Numerical  investigation  on  the
effect  of  blade  sweep  on  the  performance  of  Wells  turbine.  Renewable  Energy
2002;25:235–48.

3  Takao  M,  Setoguchi  T,  Kinoue  Y,  Kaneko  K.  Wells  turbine  with  end  plates  for wave  energy  conversion.  Ocean  Engineering  2007;34:1790–5.

[4]  Zahari  Taha,  Sugiyono,  Sawada  T.  A  comparison  of  computational  and  experimental  results  of  Wells  turbine  performance  for  wave  energy  conversion. Applied  Ocean  Research  2010;32:83–90.

Now, I am grateful that guide me about these cases and discuss together about these cases.


texts:
I have an (AC) power grid topology with generators, consumers, power lines, tranformers, etc. I also have a "snapshot" of the system's state, i.e., I know how much real power the generators feed, how much real power is used by the consumers, I know the reactive power values, and voltages. I also know the parameters of the power grid's infrastructure such as the maximum power of the transformers or the impedance of the power lines.

The problem I am facing now is this: Suppose one generator feeds more real power, and one consumer uses more real power. How can I calculate what the load of the power grid's nodes is? I want to ascertain that, e.g., no transformer or power line is loaded beyond its limit.

I basically know that there is something called "power flow analysis," which I've been reading up. The matrices, Newton-Raphson approach to solving the equations, etc., is not the problem: What I do not know is how to apply the matrices to arrive at an answer to my question. I basically need help to formulate the equations: What are my input variables, what are my results?


texts: How to solve this linear motion problem?

texts:
Context:
I have a lead screw rod, nut and a pulley aligned vertically. The nut is attached on top of the pulley so their respective bores are aligned and the rod is arranged so that it is threaded through the nut but its diameter is smaller than the pulley bore so no contact is made between rod and pulley.

When the pulley spines the nut turns, because the pulley and nut are in a fixed position the rod moves up and down via the spinning nut and through the pulley bore. Essentially a linear actuator.

Problem:
My problem is how to support the rod from lateral load. Please could you comment on the validity of my proposed solutions and propose your own if you have something more effective

Potential Solutions: A: The most obvious to me would be to have a linear guide rail with a linear bearing in parallel and a secondary nut on the threaded rod that is not fixed like the first nut so that as the rod moves up and down the secondary nut provides support via the guide rail.  The issue with this is it predetermines the height of the mechanism as it will be has high as the linear guide rail, I would like the height to be as small as possible.

B: Put a linear bearing through the rod and fix it's position to the wall of the actuator so that as the rod moves up and down it moves through the linear bearing which provides support via the wall. The issue with this is I think linear bearings are designed for smooth rods and the gaps in the threaded rod could allow the ball bearings to flick out under load, is this a correct assumption ?

C: Have 3-4 roller bearings arranged around the outside of the rod, so that the rod moves between the bearings. The issue is I don't know if there is enough contact area to be effective.

Diagrams:

I appreciate what I am essentially looking for is a spline shaft, but that is not something I have access to so I am trying to mimic the linear aspect using a regular lead screw

All help appreciated.


texts: How do external irreversibilities decrease the efficiency of thermodynamic cycles?

texts:
In gas power cycles, one mentioned that:

  The Carnot cycle is both externally and internally reversible.
  Therefore making the Carnot cycles more efficient than other practical
  cycles.

Question:

How do external and internal irreversibilities affect the efficiency of a Thermodynamic cycle?


texts: Faraday cage to reduce EMI in audio amplifier

texts:
western United States.

Problem / Question

The bad power in my house is somehow producing EMI in my audio equipment. Will a simple Faraday cage help? (Using an aluminum metal screen)
If not that, then what would be the best, most practical, cost-effective solution to blocking this interference.

As is usual on S.E., if you think I'm wrong about something, please tell me why.
I'm not inexperienced with engineering / physics, although not a professional. Technical explanations are welcome but not required.

Story

I recently moved into a new rental house. It has old wiring (pre-60s) which is mostly un-grounded and quite degraded. The landlord offered to ground a few of the outlets, but not replace all the wiring. For now, I'm going to have to live with the wiring as-is.

Why I think this is EMI

Using an amp with a cord as an antenna, the noise behaves exactly like radio wave reception in a TV or a radio. It changes depending on angle, and dissipating somewhat when I block it with my body.
I'm using a new power conditioner with ground noise eliminating circutry.
There was no noise at all, even without the power conditioner, at my last place.
Several other non-audio electrical appliances around the house hum, and sound quite a bit like the noise I hear in the amps.
The produced audio frequencies from the noise are all above 500hz or so. It's my understanding that ground loops are usually low-frequency.
Using other outlets, grounded or not, all have the same issue.

Things I already tried that didn't work

Plugging in to the grounded outlets around the house using an extension cord.
Turning off as many things as possible to find the source of the noise.
Using different circuit breakers, turning off as many as possible.
Using different combination of audio equipment to reduce noise. Using shielded, balanced audio cables greatly reduces the hum. However, that's not possible with everything I own.
Standing in such a way as to reduce the noise. This works somewhat, but is untenable. (this lead me to the Faraday cage idea).


texts: Heat transfer Calculation, for Cooling for an aluminium box

texts:
To go into more detail, I basically have a controller and its housing is basically an aluminium box that I need to add heat sinks to. But first I need to calculate how much heat is being dissipated by the controller towards the environment around it so that I can choose an appropriate heat sink that is rated for that specific heat. There isn't enough space for a big heat sink so the maximum I can cool is around 10W of heat dissipation, which is why I need to calculate the heat that is being given out by the controller in all directions. Since a box has 6 sides, how do I go about summing up all the heat flow rates for all sides? What other things should I be thinking about in terms of the cooling sink to be chosen? Should I also account for the heat across time?
Some clarifications

Heat is coming from the resistors inside the controller. And no there aren't any airflows inside and air flow outside is going to be inside the engine bay of a car, so I don't know if that is negligible or not.

The box dimensions are 17cm x 8cm x 22cm with wall thickness of 3mm but the floor of the box is 5mm.

The box isn't moving and is made of aluminium.

85 degrees Celsius is the maximum allowed temperature but I am aiming for an operating temperature of 80 degrees Celsius.


texts: How to calculate effective strain in plane stress?

texts:
What is the correct formula to calculate the effective strain under plane stress conditions?

In plane stress it is assumed that the out of plane stresses are zero. The out of plane strains are not zero but these tend to be ignored. Wikipedia gives the equation for equivalent strain as:

$\epsilon_{eq} = \sqrt{\frac{2}{3}{\epsilon}^{dev}_{ij}:{\epsilon}^{dev}_{ij}}$

But from the 2/3 in the equation above it is clear that this was derived from the full strain tensor. How is the effective strain calculated if the out of plain strains are not calculated in the plane stress approximation? Do these have to be calculated to then calculate the effective stress or is it common practice to just neglect these in the formula above?

(I am using the terms effective and equivalent here interchangeably, please correct me if this is wrong as I can't seem to clear up what the difference is if plasticity is not involved).

UPDATE

This is my current thinking. If stresses are calculated from strains using a plane stress simplification then in vector notation (from wiki):

$
\begin{bmatrix}
   \sigma_{11} & \sigma_{12} \\
   \sigma_{12} & \sigma_{22}
\end{bmatrix}
=\frac{E}{1-v^2}\left((1-v)
\begin{bmatrix}
   \epsilon_{11} & \epsilon_{12} \\
   \epsilon_{12} & \epsilon_{22}
\end{bmatrix}
+v\mathbf{I}(\epsilon_{11}+\epsilon_{22})\right)
$

And $\epsilon_{33}$ can be calculated from $\frac{-v}{E}(\sigma_{11}+\sigma_{22})$. Considering that all of the strain components have now been calculated it is possible to then calculate the deviatoric strain using the conventional 3D formulas for the hydrostatic and deviatoric components. Does this seem correct?


texts: How many states need to be measured for a reduced order observer?

texts:
I have a DC motor system with three states.
The states are:

$x_1$ = position (degrees),
$x_2$ = velocity (degrees per second)
$x_3$ = current (Amps).

My plant input $u(t)$ is measured in volts.

The dynamics are such that:

$$\begin{gather}
\frac{dX}{dt} = AX + Bu(t) \\
Y = CX + Du(t)
\end{gather}$$
And:
$$\begin{align}
A &= \left[\begin{matrix}
0 & 1                 & 0     \\
0 & -\dfrac{b_m}{J_m} & \dfrac{K_m}{J_m} \\
0 & -\dfrac{K_m}{L}   & -\dfrac{R}{L}
\end{matrix}\right] \\
B &= \left[\begin{matrix}
0 \\
0 \\
\dfrac{1}{L}
\end{matrix}\right] \\
C &= \left[\begin{matrix}
1 & 0 & 0
\end{matrix}\right] \\
D &= [0]
\end{align}$$

Where $J_m$ is the rotor inertia, $b_m$ is the viscous damping, $R$ is the armature resistance, $k_m$ is the motor constant, and $L$ is the inductance.

My objective is to control the position of my DC motor.

The rank of my observability matrix is equal to the number of states in my system, so the system is fully observable.

$$Q = \text{rank}
\left(\left[\begin{matrix}
C \\
CA \\
CA^2
\end{matrix}\right]\right)$$

I am measuring the position using an encoder and hope to employ a reduced order observer to do this.

Partitioning the A matrix into quadrants yields the measured and observed dynamics:

$$A = \left[\begin{matrix}
A_{11} & A_{12} \\
A_{21} & A_{22}
\end{matrix}\right]$$

In my case:
$$\begin{align}
A11 &= [0] \\
A12 &= \left[\begin{matrix}
1 & 0
\end{matrix}\right] \\
A21 &= \left[\begin{matrix}
0 \\
0
\end{matrix}\right] \\
A22 &= \left[\begin{matrix}
-\dfrac{b_m}{J_m} & \dfrac{K_m}{J_m} \\
-\dfrac{K_m}{L}   & -\dfrac{R}{L}
\end{matrix}\right]
\end{align}$$

Now the Observability of my reduced state observer partition is:

$$Q_{Obs} = \text{rank}
\left(\left[\begin{matrix}
A_{12} \\
A_{12}A_{22}
\end{matrix}\right]\right)$$

The rank of this is 2 (full rank).

I've seen in other projects that the following condition must be satisfied:

$$\begin{align}
Q_{Obs} &\approx Q-(\text{number of states}-\text{number of measured states}) \\
2 &\approx 3-(3-1) \\
2 &\approx 1
\end{align}$$

How many states need to be measured in a reduced order observer?
Why is it that my system is fully observable, but I cannot measure all the states of my system?
If I measure both position and velocity it seems that $Q_{Obs}=1$. Making the equation:

$$Q_{Obs} \approx Q-(\text{number of states}-\text{number of measured states})$$

simplify to:

$$\begin{align}
1 &\approx 3-(3-2) \\
1 &\approx 2
\end{align}$$

Does this mean the system is not observable without measuring all three states?

4. If I assume the mechanical time constant is much slower than the electrical time constant (poles are closer to 0 in the real axis):

Can I measure only position and estimate velocity while neglecting the electrical dynamics?
Will this provide a robust estimator when implemented?


texts: Why laser cutting speed suddenly decrease when cutting sheets from 1 to 3mm thickness then stabilize?

texts:
Please to understand what I mean, see the picture below :

I don't understand why it is not a linear curve (or almost), because at first sight it should be no ?
If you need 10 sec to cut a length of 1mm thickness, why not 20 sec for a 2mm and 30sec for 3mm... I can't figure this out !
If you have an answer, please don't hesitate to share your experience with me !


texts:
The Sommerfeld number can be written as

$$ S = \frac{6 \ \mu \ U \ b}{p \ c^2} $$

where

U: Velocity
b: Width
p: Pressure
c: Minimal Clearing
$\mu$: Absolute Viscosity

As far as I'm aware, it may be used for both thrust and journal bearings. It is also known as the Dimensionless Bearing Number
or dimensionless surface pressure.

What I don't understand or differently stated, I couldn't find any resources on the significance of that dimensionless number.

For instance the Reynolds number is the ratio of the inertia and viscous forces. Depending on the situation, any value, approximately, above 1000 or 3000 is considered to be turbulent flow.

What is the ballpark for the Sommerfeld number?

When is it too small or too large to disrupt operation or damage the bearing?

Do several "zones" of values exist that exhibit similar behaviour? (such as between 1 and 3 it behaves as ....?)

In case there are huge differences between journal and thrust bearings in regard to the Sommerfeld number, I would be more interested in the thrust bearing case.


texts: What can be the reason of the constant 50 Hz sound in my home?

texts:
I am suffering from a strange hum in my home. I have just bought my home and living in 3 months. A month ago I've started to hear a humming noise. Then, I recorded the sound and looked at its frequency response. The peak was at 50 Hz. After a while, I started to use an application named "SignalScopeX" for iPhone. It gave me the same results, in this app you can see the response in real time and there is a peak at exactly 49 Hz. I measured several times (in night and day) and the sound exists every time. Is there a possibility that in pure silent mics response 50 Hz, or is it real sound? I hear it but still I want to be sure about that. I suspected an electrical machine vibrating my walls (I am living in Turkey, main electricity is 50 Hz). Me (living in 6th floor) and my neighbours (living in 5th and 7th floors) cut of our home electricity but still, the sound is exists. What can be the reason of the sound?

Some of my thoughts are:

There may be a constant working motor like an aquarium on the 10th floor. Is it possible?
There is a general electricity line of building in one of my room. If there is any leakage may it cause the sound? How can I measure it? Are there any more possibilities?


texts: Why does sulfur concrete require no cement?

texts: Sulfur concrete only uses sulfur as a binding agent then an aggregate. Why does it not use cement?


texts: Which sort of equipment is specifically designed for flowing/pumping low density solids (powders) e.g. for loading from a drum to a receiver?


texts: Sieve trays used in Liquid liquid extraction tower instead of bubble cap and valve trays?

texts: In an LLE operation pilot plant, i saw that sieve trays are used instead of bubble cap and valve trays... In LLE operation, they require good mixing, so i was shocked why bubble cap and valve trays are not in used. I heard that sieve trays is commonly used in LLE plate tower too. Why is the benefit of using sieve trays in LLE operation other than the fact that it is easy to clean ?


texts: Steel thickness required to mount cantilevered arm

texts:
Consider an arm of length $D$ supporting $W$ weight. The arm is welded to the plate with bolts $d$ inches apart. How do I determine the thickness of the steel plate 6 in wide by a length supported every $D_1$ inches that the arm is bolted to?

$W$ is nominally 300 lbs.


texts: Determination of Young's Modulus for use in Analysis

texts: I am writing a finite element code for my final year project of BS Mechanical Engineering. The geometry is an integration of several parts composed of different materials. I don't have exact values of material properties. However, I do have ranges of them. For example, for Steel1020, Young's modulus varies from 205-215 GPa. Should I use lower limit of Young's modulus or higher limit of Young's modulus, or average (geometric / arithematic)?


texts: How to use a specific list of components in a stream in ASPEN-HYSYS?

texts:
In HYSYS it is possible to create multiple lists of components using their proper fluid package to better calculate the properties of very different molecules.

Here I defined two lists:

List 1

List 2

I also defined the fluid packages I need and when I go to simulation and create a stream, I can only specify the composition for the first list of components as shown after. How should I do if I want to use the second list of components?


texts: Simulation of First Order System (Matlab & Simulink)

texts:
Yesterday, I tried to find constants $k_1$ and $k_2$ for the following system:

$$\frac{\mathrm d RH}{\mathrm dt}=k_1+k_2(RH_{ext}-RH).$$

Now, I have some first computations for $k_1$ and $k_2$ and would like to test how good a simulation with these parameters works. I think I could also write this as state space model:

$$\dot{x}=-k_2x+\left[\begin{matrix} k_1 & k_2\end{matrix}\right]\left[ \begin{matrix} u_1 \\ u_2\end{matrix} \right],$$

$$y = x,$$

where $x = RH$, $u_1=1$ ($const.$) and $u_2=RH_{ext}$. I have measurement data for $RH_{ext}$ in Matlab (vector), a time vector $t$ with the same length and would like to do a simulation for $RH$.

Any suggestions how I could proceed? Simulink is possible, but just a script-based solution would be even better.


texts:
I was not sure on which site to ask this question, but I guess Engineering might do well from the aspect of matter.

I am wondering, what is the shelf life of a HEPA filter, can I just buy a few of them for my air cleaner and let them sit in my drawer?


texts: How should a bridge deck closure pour be positioned?

texts:
The Question:

Where should a closure pour be located relative to centerline of girder and how should the closure pour width be detailed/designed?

And now, a little background:

When designing a steel girder bridge using phased construction with dead load deflections exceeding 2", my state (Nebraska, USA) requires a closure pour. No guidance is provided on how to locate or design the closure pour. As a point of reference, I'm dealing with a 100 ft span and a 44" deep girder.

I've done moderately extensive Googling and found varied suggestions. Align the edge of the pour with centerline of girder. Don't align the edge of pour with centerline of girder. 2' minimum width. 3' minimum width. And an interesting suggestion from Nevada DOT (p. 16-10) that:

  The required width can be estimated by considering the
  closure pour to be a fixed-fixed beam and by limiting the stresses in the concrete to the
  cracking stress.

Which sounds quite promising, though I haven't fully digested the particulars of execution.

Where my noggin really starts to hurt is when I start thinking about how my girder deflections will be affected by phasing and a closure pour. Say my girder has a tributary deck width of 96" in the finished condition. But during phased construction, only the left 2/3 of this deck will be poured. Do people execute a series of analysis runs looking at all the intermediate conditions and the progressive deflections/stresses?


texts: I have a motor which its output shaft has a key, and it will be connected to a wheel/tyre. I'm wondering how can I lock the hub axially, so there is no way it can move freely along the axis, which could mean that eventually the wheel-tyre could go off. I'm not sure if a split coupling with a keyway a could work, but I doubt it's designed to press the key and restrict axial movement. Any ideas/suggestions, thanks :)


texts: Firing a bullet on wooden block and then finding the average resistive force by block?

texts:
For a Q in which we are firing a bullet of 0.04kg onto a wooden block which is stopped after a distance of 60cm after penetrating inside it. It’s u=90m/s.
For this Q , we can find a=-6750m/s^2. Using$ v^2 = u^2 +2as$
Now, this a can also be compared with a body moving with$ -6750 m/s^2 $.Not necessarily a wooden block needs to be there.
Then , second point. My book provides average resistive force by the block on bullet = $0.04*6750=270N.$
Now , I am confused since the mass of block is not given . How can find the average resistive force exerted by it.
One way I though of is this but I am not sure if it correct or wrong.
So , using Newton’s third law here.

Force by the bullet on block = -( Force by block on bullet). OR Force by bullet on block = -(force by bullet on block ). Both are not similar here, why is that?

$0.04*(-6750) $= -(mass of wooden block * -6750). So , in the end we force has to be equal. Therefore , we considered F=270N since finding force by bullet on block is not what Q asked. It asked is the average resistive force by block on bullet.

Is writing average here really necessary ?


texts: Why to avoid low and high fluid velocities in hydraulic systems

texts:
I know that different geometries of piping, orifices etc... have different critical Reynolds values. If the value is exceeded laminar stream will turn to a turbulent form which causes a variety of problems. But why shouldn´t the value be too low?

I.e. for pressure piping up to around 300 bars I assume that I have to be inbetween of 3 to 12 m/s.

Do too low velocities cause problems like cavitation? What are the reasons?

FYI: To have a practical example. I am asking because I want to design a hydraulic system but I only have a NG25 valve available but NG6 is probably already enough.


texts: Running a hydraulic pump below minimum RPM

texts:
If I had a pressure compensated, hydraulic piston pump, how might the performance look in terms of pressure if I were only looking in the regime of 0 RPM and the minimum ratedRPM?
I.E If a pump was rated for 500 RPM minimum, and I accelerated the shaft's RPM from rest, would the pressure grow exponentially, linearly, or something to the preset pressure value?


texts:
I want to find the moments around points A and B in the following figure.
Suppose the structure is fixed at the point where $F_{ax}$ and $F_{ay}$ are located.
I consider A and B to be hinges so that the rigid links can rotate.
Is it plausible to calculate the external moment at points A and B with respect to the external forces, such that the structure remains in equilibrium?
I know that the moments in hinges are 0, but would external moments keep the structure in equilibrium?


texts: What is the capacity of a WWII Submarine battery in kWh?

texts:
After reading about submarines in World War II, I was curious about their battery capacity, specifically in comparison to modern Battery Electric Vehicles (ie Tesla, Bolt, Leaf, i3, etc).

I haven't been able to find a source that either answers the question in kWh or gives me enough information to calculate it myself.

My current guess is about 30 kWh, based on a figure of 12000 Ah in a 120 cell system, and a voltage of 2.75 V - 1.05 V

I would accept an answer for any class of submarine in WWII, but I was looking at the US Balao class.


texts: corrosion in electrical parts and wiring

texts:
I work in a pharmaceutical plant where saline solution is produced and bottled. The environment has to be clean (by pharma standards), which rules out many greases and other protective coatings.
As expected from a saline environment (from my experience it can be as agressive as a marine one), the corrosion over all parts in the room is heavy.

I have mostly controlled the corrosion of structures (all of them have to be made of stainless steel: 316L for those parts in contact with the product, 316 for some others and some structural parts of the equipment are made of 304 SS) by carefully selecting materials, specially material pairs (when I have to), introducing electrical discontinuities in structural joints (if I have a bronze piece, for example, in contact with a SS one, I introduce teflon washers/separators to reduce galvanic corrosion), and at least in one case by using a sacrifice anode.

But the corrosion of electrical components and wiring is something I haven't been able to control, to the point that I've had to replace all the wiring in one of the machines in as little as 5 months. Wires (not only power lines, but also control ones, such as termocouple wiring) get rusted not only in the terminals (where it's evident), but also under their plastic sleeves. In the case of control wiring, this causes noisy signals that result in machine stoppages and downtime (my most recent case is a termocouple that sent a correct signal of 180°C but showed (unreal) peaks of up to 270°C that, of course, triggered an alarm in the PLC).

I can only blame it on corrosion, as the problem goes away by replacing all the wiring and terminals. The wires I took off show corroded under the sleeves, and some of them were brittle. (If you think it's not corrosion, I'd like to hear your opinion).

I can't hide all the wiring from the product (in particular some of the termocouples my get some product spray) and my electrical boxes are as separated from product and tigth as possible (even they don't hold to any IP standard).

So my questions are:

Is there anything I can do to prevent this sort of corrossion in electrical components and wiring?
Is there anything akin to a sacrifice anode that I can use in electrical parts / wiring?


texts: What will remain constant during the circulation of working substance in a refrigerating machine?

texts: For Example, the pressure of evaporator can be changed, also the pressure of condenser and many more parameters. What is that parameter which remain constant while others keep changing ?


texts:
Surprisingly this hasn't been asked before, so I must be missing something simple.

We use engineering stress and engineering strain in this eq. Stress = (Young's modulus) × (strain). This eq. is used in analysis of bending beams, twisting shafts and in buckling. So the final equation of bending $(\frac{M}{I} = \frac{\sigma}{y})$ and torsion $(\frac{T}{I} = \frac{\tau}{r})$ will give us value of engineering stress but not the value of stress.

Why are we considering engineering stress instead of true stress while we know it will not give correct value of stress?

Some things I read are:

Difficult to measure.
Not that much of a difference and we can just apply a Factor of Safety.
"We don't consider materials to change their cross-sectional area after loading, since we design to have no plastic deformation the elastic region is most important, therefore what happens after the proportional limit is not important"

Firstly, 1 and 2 are not real reasons for me. Number 3 seems plausible since we always design in the elastic region, but is this it? Does engineering strain even give valid information after the proportional limit?


texts: Is there a mode of failure criterion for a valid unconfined uniaxial compressive strength test for intact rock core specimens?

texts:
I have read the latest revision of the ASTM D7012 standard, which includes the test procedure for determining the unconfined uniaxial compressive strength of intact rock core specimens. There, I do not see any discussion on what makes the test valid or invalid based on the mode of failure.
From textbook, “Fundamentals of rock mechanics” 4th ed., by Jaeger, Cook, Zimmerman, the authors state that,

Under unconfined compression, a rock tends to deform elastically,
until failure occurs abruptly. This failure is accompanied by somewhat
irregular longitudinal splitting. With a moderate amount of confining
pressure, longitudinal fracturing is suppressed, and failure occurs
along a clearly defined plane of fracture. This plane is typically
included at an angle less than 45 degrees from the axial direction
(direction of compression). This plane is characterized by shearing
displacement along its surface, and is referred to as a shear
fracture.

As emphasized, there can be two modes of failure for when one conducts a compressive strength test: irregular longitudinal fracturing for unconfined testing, and shear fracturing for a "moderate amount" of confining pressure.
The above is relevant because when reading the textbook, "Core Analysis: A Best Practice Guide" by McPhee, Reed, and Zubizarreta, the authors seem to imply that shear failure should occur for a valid UCS test. The authors preface their section on unconfined compressive strength testing with the following two points:

"Unless otherwise specified, UCS tests are normally performed on vertical (bedding plane perpendicular) samples..."
"In some applications, the 'unconfined' tests are performed at nominal confining stress (150 or 300 psi). Often referred to as quasi-UCS (q-UCS) test, effectively this is a triaxial test but strength test data measured at nominal confinement are much less influenced by plug irregularities and discontinuities."

The quasi-UCS test sounds quite similar to the "moderate amount" of confining pressure test described in Jaeger et al. that produces shear fracturing.
So the ASTM D7102 standard does not address bedding plane orientation with respect to the rock core/plug, nor does it address the mode of failure and if there is a particular mode of failure that needs to occur for the unconfined compressive strength result to be valid.
My question surrounds these points of note. I am looking for an answer that addresses issues surrounding bedding orientation, mode of failure, and if the "quasi-UCS" test is still considered an unconfined compressive strength test.


texts:
It's true that most bridges are "two directional."

But three way bridges are pretty rare, globally. I can understand why there wouldn't be many for rivers, but if bridges are designed based on the lie of the surrounding ground, why wouldn't there be a large number of non-river sites that would support such bridges.

On the other hand, three out of the world's bridges exist in Michigan (and only ten or so elsewhere in the United States). What is it about the land, topography, or other features of Michigan that cause it to have a disproportionate number of the country's and world's three way bridges.


texts: Why did they build a sarcophagus over Chernobyl instead of pouring concrete over the building?

texts: Wouldn't it be easier to just pump concrete over the reactor until it's all covered up with a solid concrete instead of hurting so many workers and putting so much effort and costs building a structure over it and cleaning up the area?


texts: I need clarification on how pressure is measured

texts: I have a vessel that has a pressure measuring device. The value it shows as the pressure inside the vessel is 6 inches of water column. Is inches of water column meant to always be used as gauge pressure, or does one have to specify gauge vs atmospheric?


texts: What is theoretical (physical) limit a MicroSD card's capacity?

texts:
There was time (a decade ago) when I got 8 MB (yes, 8 MB, not 8 GB) SD card for my Nokia cellphone ( At that moment, the maximum storage on the market was 32 MB, marketed as the "breakthrough in high-capacity" cards).

However, as everything, those achievements left in history and then achieved 1GB...100GB... now 1000GB for the same sized MicroSD. I am interested:

On what does this increase depends? transistor development or? why they didnt produce 100 GB cards 10 years ago?
Is there any maximum capacity limit of what technology can achieve within a single MicroSD card?


texts: The physics behind the condensation in tents?

texts:
When you compare single wall tent to double wall tent usually you will hear short summary "double wall tent prevents condensation from building up".

So in most fair comparison it should work like this -- I have imaginary single wall tent (i.e. tent with only one layer, the rainfly) and using it will cause condensation to build up. OK.

So now let's add to this tent inner tent (mesh layer) and this prevents condensation.

Hmm... I don't see it. I mean, condensation occurs when the warm air is cooled down to the point it no longer can hold steam. I guess the mesh barrier can slow down the process (i.e. you would have warm space inside, middle space between layers, and the cold air outside), the warm air from inside not so soon reaches the outer layer. But eventually it will reach it.

Second guess would be that inner mesh gets a little wet, and by this it helps the air to hold the rest of the amount of steam. But this effect I would say is a condensation anyway, just not visible because of the nature of the mesh.

So is there any other effect that contributes to the notion "inner tent prevents condensation"?


texts:
How are dangerous to build things studied?

Such as, nuclear reactors, jet engines, sawing machines.

How do engineers discover, how they ought to be built, while avoiding getting or getting others hurt?

Is there perhaps a component of "anticipating to avoid risk based on earlier experience"? But how does this allow designing potentially dangerous things?


texts: Z-axis of Downham (Elliot) Mini Borer is jammed. How to recover?

texts:
I have a Downham Mini Borer (similar/identical to an Elliot) that has no mechanical stop on how far the Z-axis can be wound in the upward direction. This means it's possible to wind it up against some internal, physical limit. That's the situation mine is now in and it doesn't want to wind back the other way.

I imagine the hand-wheel has a worm gear, which turns a wheel around a nut on the vertical threaded bar in the pic below. At the hidden end of the threaded bar, that thread must end, either as an abrupt stop, or as a gradual transition back to the full diameter of the round bar, and it's that that the nut is jammed against. I've tried getting at that nut by removing the automatic feed selector, but the casting that accepts the drive doesn't want to separate from the main head.

Does anybody have any experience of this phenomena on this or a similar borer/mill?


texts: Curve-linear vs. Cartesian coordinate systems: linear-elastic & isotropic elasticity tensor

texts:
For shell elements, is the elasticity tensor for linear-elastic & isotropic materials the same in a local curve-linear (convected) system vs. a local Cartesian system?

I wonder because intuitively, for a shell element & linear-elastic isotropic material, the only direction that matters (material-property wise) is the z direction. And in this case, the local z axis is aligned with the curve-linear coordinate system. But how do we mathematically show it?


texts: How to calculate the required energy to heat water at high pressure?

texts: I am trying to calculate the amount of energy required to heat 12,300 kg of water from 70 °C at 25 MPa to 120 °C at 40 MPa. I have thought of using Q = mcT but I know that the specific heat capacity of water varies slightly with pressure. How can I calculate the energy required since c varies?


texts: In the rankine cycle, water is first pressurized and then heated to produce steam before it is used to turn a turbine.  As far as i know, this is what is considered the best way to extract mechanical work on the turbine, but i want to understand why this is so.  How is it that we can extract more work on a turbine from steam than from regular unheated, un pressurized water?


texts: Is a Home's Temperature Affected by Solar Gain Through Windows on Cloudy Days?

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Do homes increase in temperature due to solar gain with curtains open if it's overcast?

In other words, Does having curtains closed reduce the temperature of the home on an overcast day?

In other words, Does an overcast day prevent the warming effect of the sun hitting a homes window and raising it's temperature?

In other words, Closing the curtains on a sunny clearly keeps a room cooler. Does closing the curtains on an overcast day have the same effect? Why?

Thank you for your time.