texts: How can I determine how many cycles to average for when taking a measurement using Lock-in Amp if I know sensor spectral noise density?

texts:
I am taking a phase sensitive measurement of an AC magnetic field using an SR830 Lock-In Amplifier and a magnetic sensor. I know I have to average over a number of measurement cycles to get an accurate reading. The amount of time I should average is determined by the measurement frequency, the time constant on the lock-in amplifier, the filter slope, the noise measured by the sensor and the required accuracy. See the following diagram I have pulled out of the SR830 manual (T = time constant, ENBW (Equiv. noise bandwidth). Wait time = min. time that should be allowed before averaging starts):

I have measured the spectral noise density of my sensor using the lock-in too:

Now say I want to take a measurement that would have an expected output of 1μV at 10~Hz with an accuracy of 1%. How many cycles/how long would I have to average? Could you help to explain how you figured this out?

I will expand if the question is unclear.


texts: Is there a way to convert a short throw in one direction into a long throw in two directions

texts:
I have a motor that I have created a simple adapter for; this lets us attach any parts we might design to solve the final problem:

I would like to convert the motors motion to oscillating motion in two directions from one.

The classic "woodcutter" solution to this is:

However that does not give me the throw I would like for the final motion in either direction.  Ideally this mechanism will sit on the floor - which SORELY limits the available "height" during rotation of any such "arm"

This motor has very high torque so it may be possible to move other structures while at a mechanical disadvantage in oblique (aka not smashing through the floor) planes?

In a nutshell after a couple of days thinking it idly over haven't managed a better solution yet.

Considered some sort of scissor motion? but couldn't firm up the details.

Is there a classic - obvious - solution to this problem?

Full disclosure: I have no formal training whatsoever in engineering.

Appreciate any assist.

EDIT: I should add that I did think about some sort of reversing screw mechanism?
but didn't manage to make that work yet in practice. perhaps That could be part of the solution but it doesn't solve the problem of throw either, well not without being really long and actually working.  I might figure something out with this I guess?

This would result in motion in the other direction - which would be okay but if there is a more reliable or "better" way to get this motion would love to hear  of it. Struggling with the screw solution.


texts:
How can I calculate field strength of a Neodymium Ring magnet at an angle?
I have a Neodymium Ring magnet, and I rotate the magnet around an axis perpendicular to the poles. (Not continuous rotation). For a given distance from the surface, and or for a given angle away from the center of the field, how can I calculate the field strength?

I have looked at some methods to calculate field strength, but they refer to electro-magnets, and current. Where this is a rare earth magnet, I am unsure how to perform such calculations.

The application is a device that exerts a magnetic field into a device, where either a weak, or non-existent field is not already present.


texts: Are standard structural bolts acceptable for all cold climates?

texts:
The specifications for standard (ASTM A 325) bolts do not list minimum service temperatures. I am thinking of outdoor applications like Alaska or Canada (lows of -60F) and wondering if the cold temperatures would have an effect on the bolts.

There is a type of bolt (ASTM A 320) that has a grade that specifies testing at low temperatures (-150F). Those bolts seem to be for cryogenic facilities. It seems that this is over-kill for most outdoor locations where the coldest ever recorded temperature on earth is about -128F in Antarctica.

Is the cold a concern for standard structural bolts? Are there European standards that might apply?


texts: Dynamics of Mass in Epitrochoidal Motion via Ringless Planetary Gear System

texts:
I'm trying to model the planar dynamics of a mass travelling about an epitrochoidal path due to being rigidly attached to a planet gear that rotates about a sun gear. Assume the gears to be circles that rotate about each other with no slip for reasons of simplicity.
Both the sun and the planet can rotate. The input to the system is a torque on the planet carrier, pushing the planet parallel to its path about the sun. The output is the torque of the sun.
As i have very little experience with modelling dynamics, i don't know where to start. I was thinking that separating the problem into a fixed and inertial frame may be best, but i'm not sure.
How should i go about showing the output torque as a function of the input torque and the system constants (e.g. planet mass, sun diametre, etc.)?
I drew a quick diagram of the system as a simple model with circles for reference.
Cheers :)
EDIT:
To clarify, i've already solved the kinematics of the problem and have equations governing position, velocity, and acceleration for the mass according to the rotation, rotational velocity, and rotational velocity acceleration of the planet and Sun. What I want to find out is the dynamics. Specifically how torque on the planet carrier will affect torque on the sun.


texts: When designing a carburetor, is the air to fuel ratio calculated or just experimentally adjusted?

texts: Does anyone actually calculate carburetors air to fuel ratio when designing one in practice? You would have to calculate the flowrate of air, the pressure drop, the rate of flow due to pressure difference etc. Do engineers just adjust them empirically until it's right?


texts: What generates more friction? Spur gears or a timing belt?

texts:
In my project a knob (usually rotated by hand) can be turned also by a stepper motor. On the other hand, when the motor is not energized, the knob can be rotated manually as normally.
To transmit the motion from the motor I would like to use three spur gears made in acetal (low friction material).
My fear: when the motor is off will the operator receive a bad feeling if turning the knob manually? I mean: the teeth of the gears will not generate too much friction (and a "clunky" feedback) when compared to a timing belt? (See attached image.)
My intuition says that adopting a belt I should obtain a more smooth movement and low friction. Is my intuition right? Anybody has a direct experience in this kind of problems?
P.S.
No high rotation speed here. The knob will be turned by the motor for max 180° at a speed comparable by a normal human wrist.


texts: Calculating Forces using equations of equilibrium

texts:
The homogeneous bar shown in Fig. P-106 is supported by a smooth pin at C and a cable that runs from A to B around the smooth peg at D. Find the stress in the cable if its diameter is 0.6 inch and the bar weighs 6000 lb.

When using the equilibrium of moment equation at point C, The Tension in the string is found to be 2957.13 lb.

6000(5) = 5(T) + 10(T)*(3/(34)^(1/2))

I tried to use the equation of equilibrium for Vertical Forces.

  6000 = T + T(3/(34)^(1/2))

  T = 3961.714 lb

Is there any mistake in applying the equilibrium vertical condition? I'm having trouble finding any faults. The diagram for forces is given below


texts: Fasten adjustable perpendicular cylinders rotating on axis

texts: What part(s) make it simple to secure two perpendicular cylinders together when one of the cylinders is rotating on its axis?  In the drawing below, C(3) rotates with a simple motor.  C(1) and C(2) rotate with C(3) because C(3) is rotating on its axis.  All three cylinders are about an inch in diameter because they are just plastic right now.  I'd like to use metal later on to fasten them together, but I'm trying to make them fit together nicely.  The axle C(3) will eventually be a lot smaller in diameter than one inch.  And C(1) and C(2) need to be able to easily slide but still be secure on C(3).  The goal is to make it easy to assemble and disassemble the cylinders.  I thought of using a lock pin seen in the second picture below.  The issue is that lock pins only allow a rotation of 180 degrees before impeding and this needs to rotate almost a full rotation.  Are there any mechanical parts that would function like a lock pin but still make this rotate more than 180 degrees?


texts:
This is a problem from the book Engineering Mechanics Statics vol-1 by Meriam Kraige

The rectangular steel yoke is used to prevent slippage between the two boards under tensile loads $P$ .If the coefficients of static friction between the yoke and the board surfaces and between the boards are all $0.30$ the question is to determine the maximum value of $h$ for which there is no slipping and to find out the corresponding normal force $N$ between the two boards for $P=800N$ if impending motion occurs at all surfaces.

Here is what I tried

For the first part if $\theta$ denotes the angle between the top part of yoke and horizontal then $\cos \theta = \frac{200}{210}=\frac{150}{h}$ which gives $h=157.5 mm$

For the second part I tried to draw the FBD of the top block.

From FBD $$P=f_1+f_2+f_3+f_4$$ and $$mg=N_3-N_1$$ Also by taking moments about COM I got $P=f_3-f_1$.However I am not able to proceed after this.Any help shall be highly appreciated.Thanks


texts: Interference fit advice for permanent assembly

texts:
Many bicycle cranks have permanently assembled spindles on one side, as shown in the picture. This is a steel spindle inside an aluminum crank arm. I am not sure how these are manufactured. But I sometimes build custom cranks and I want to duplicate this because it might be easier to press together a joint than to machine a spline on both sides for a joint that technically never needs to be disassembled.
Given the moderate forces involved, do you think this can be done just with a tight press fit? Can you suggest tolerances for the hole and spindle?
If a press fit wouldn't hold, what if I use a retaining compound like loctite 680?


texts: What is the plastic blister chemical compound that stores plastic toys?

texts:
I have observed that plastic toys that are stored in the plastic blisters, which is transparent, tends to stay the same over a long time. There are no chemical reaction taking place even after decades of storage.

I am specifically asking about the plastic toys like Hot Wheels and Matchbox. I would like to know what is the chemical compound used for such stable use.

Thank you for reading my question.


texts: Can plasticizer leach out of cured concrete?

texts:
About 6 months ago I have poured concrete in a plastic mould. The mould was plastic plinth for sun umbrella. It is usually filled with water but it cracked so I filled it with concrete. Before pouring I glued the cracks with generic cyanoacrylate glue..
I prepared concrete mix with coarse and fine sand, cement and PP fibers. I was aiming for 0.3 water to cement ratio. I added a superplasticizer based on 2-octyl-2H-isothiasol-3-on. The plasticizer was dark purple fluid with distinct smell.I used quite a lot of it, somewhere near the max of recommended dose.
The concrete stayed soft for quite a while and I thought it would not harden at all. After a week it became warm and solidified. The surface at the opening where I poured it in (the top) was soft to the touch for a few weeks. You could scratch it with a fingernail. But now is rock hard.
What I have noticed after a few weeks was dark purple excretion under the glued cracks. And I think it even softened the glue. It looked purple like plasticizer, smelled like plasticizer and had a stingy taste. The concrete itself is of normal color.
Now, even after a few months a purple excretion leaches out of cracks in plastic.
Is this really plasticizer leaching out? Is this normal?

Things to consider:
Final w/c somewhere around 0.3.
Max recommended dosage of plasticer.
On top of the mold is an empty cavity which I left filled with water to keep the concrete moist during curing. The surface of concrete underneath is hard.


texts: How different is using styrofoam rather than empty cans when pouring concrete?

texts:
In the recent 6.4 earthquake that hit Taiwan, it was seen in a newswire photograph of rubble that metal cans were embedded in the concrete.

The quote from an official regarding this practice:

  For such purposes in construction, it was not illegal prior to September 1999, but since then styrofoam and formwork boards have been used instead

I suspect that the reason to use it is that the cans and the associated empty space is cheaper than actually having solid concrete (and may be partly necessary to reduce the weight of the concrete and thus associated stresses with it).

However, the 'Styrofoam and formwork boards' being the acceptable standard now makes me wonder how different that actually is from empty cans.


texts: Research of transients in nonlinear systems with linear dynamic links

texts:
I am having difficulties of this nature. There is a nonlinear system of the following type:

I need to analyze analytically the transient process in such a system. The analytical study of the transient process is understood as the solution of the differential equation for such system and its analysis, i.e.:
1. Estimation of the time of the transient process by analyzing the properties of the solution components.
2. Assessment of the presence / absence of oscillatory components.
3. Estimation of the amplitude of the oscillatory components.
The situation is complicated by the following circumstances:
1. The presence of linear dynamic links in the system, which implies the use of LTI techniques. At the same time, the presence of a quadratic nonlinear link makes this impossible.
2. The presence of a nonlinear quadratic link forces us to consider the option of drawing up the corresponding differential equation in the system. At the same time, the presence of linear dynamic links in the system determines the presence of convolution operators in the differential equation, which turns the differential equation into an integro-differential equation with a complex structure, the methods for solving which in general form do not exist.
Problem:
It is necessary to choose the path of analytical calculation of transient processes in a nonlinear system with linear dynamic links.
I ask for help and advice from specialists, which path and method to choose. Numerical methods are not considered.


texts: Large scale nonsymmetric standard and generalized eigenvalue problems in engineering

texts:
I apologize if this is not the right forum for my question, but I cannot think of better place to reach a large number of engineers within a short time span.
Question: I am a mathematician working in the field of high performance scientific computing. My goal is to determine the need for solving large scale nonsymmetric dense standard and generalized eigenvalue problems in industry. I would like to

see examples of large scale nonsymmetric eigenvalue problems that you have had to solve in the past and
learn about the performance of the software that you would like to have in the future.

Background: I am one of the authors of a new software library called StarNEig for solving dense nonsymmetric standard and generalized eigenvalue problem. StarNEig can compute all eigenvalues/eigenvectors of a dense nonsymmetric matrix $A$ and all the generalized eigenvalue/eigenvectors of a dense nonsymmetric matrix pencils $A - \lambda B$. StarNEig is currently limited to real matrices and real matrices pencils with real and complex eigenvalues and eigenvectors. StarNEig can be substantially faster than either LAPACK with parallel BLAS and ScaLAPACK, the de facto standard libraries in field of dense numerical linear algebra. StarNEig is freely available from GitHub and some performance figures can be found on our front page, see link above.
Motivation: At this point we request input from potential users of the StarNEig library. This will help us guide the future development of the library. If I can argue that the existing software is outdated and insufficient to fulfill the future needs of industry, then this will dramatically improve our chances to obtain additional funding and provided the community with better software in the long run.
Some possibilities: I expect that the quadratic eigenvalue problem $$(\lambda^2 M + \lambda C + K)x=0$$ will be a rich source of nonsymmetric problems. The quadratic eigenvalue problem is equivalent with the generalized eigenvalue problem $$Ay=\lambda By$$ where $$A = \begin{bmatrix} 0 & K \\ K & C \end{bmatrix}, \quad B = \begin{bmatrix} K & 0 \\ 0 & - M \end{bmatrix}, \quad y = \begin{bmatrix} x \\ \lambda x \end{bmatrix}. $$ We see that $A$ and $B$ symmetric when the mass matrix $M$, the stiffness matrix $K$ and the dampning matrix $C$ are all symmetric. However, I understand that there are many systems where this is not case. In particularly, I gather that there are gyroscopic systems where damping matrix is either skew-symmetric $(C = -C^T)$ or a general nonsymmetric matrix. I imagine that such problems can be found in the design and analysis of rotating mechanical systems such as turbines and engines. I am told that the presence of non-conservative forces produces stiffness matrices that are not symmetric.
I expect the analysis of transients in electrical circuit to be a rich source of nonsymmetric eigenvalue problems. Certainly, I can build small toy examples that lead to nonsymmetric matrices, but I do not know enough to determine what relevant systems look like. I have access to nonsymmetric eigenvalue problems describing power networks.
What would the ideal answer look like? A short list of real applications with a clear need to solve large nonsymmetric eigenvalue problems with references to specific books or papers. A wish list describing the software that you would like to have in the future.
What is a large problem? There is no precise definition. However, a problem is certainly large if you need a multi-node multi-core parallel computer to solve the problem in the time you have available.


texts: Are there high torque stepper motors with rear and front mount availabe on the market

texts: I'm looking for a high torque stepper motor which has a mount wholes on both sides (rear and front). A double shafted model would be great.


texts: Is the current on the terminals of an opened circuit is zero?

texts:
Say we got this circuit:

Initially we had the X resistance, but then I opened the circuit in the terminals of resistance X, and I moved the resistance X to the equivalent circuit (my teacher says this is a shortcut of how doing it). My doubt is about calculating the equivalent resistance: it is obvious that R1 is in series with R3, and then they are in parallel with R2.
But, since I opened the circuit, the current that are going to those terminals is going to be zero, so there are no nodes, because the current doesn't divide. So, why couldn't I say that R1 and R2 and R3 are in series, or R1 and R2 are in series and these are in parallel with R3.

What's missing me? Doesn't the current in terminals is zero?


texts: What is the purpose of these “partially filled in” locomotive wheels?

texts:
I recently visited a railway museum with a lot of Soviet-era locomotives. The picture below shows the wheels on a locomotive from the 1930s or 1940s. Some of the wheels are thicker on one side (as it it were a partially filled cup). What is the purpose of that?

(Now that I am looking at the picture again I wonder if they are balancing the weight of the coupling rods in some way.)


texts: Get 2KV AC 15AMP draw from 2 lines of 220

texts: How would I go by getting around 2KV ac rms able to support an average current of 15amp and max of 20amp out of 2 lines of 220? And what kind of relay could take that? Looking for a winding ratio.


texts:
I've recently designed what is essentially an aluminium box. I've done the entire design process of CAD software SolidWorks and then done some simulations of loading of the box.

Through iterations I've figured out the minimum thickness of the aluminium (AL6061 T6) box material to be quite small - 0.25 mm. This seemed almost too small to me so I looked up kitchen 'tin' foil for comparison. The Wikipedia page puts tin foil thickness at between 0.2 mm and 0.006 mm. That means that the upper end of the tin foil is easily comparable with the thickness of my box.

I'm aware that tin foil is probably not AL6061 and it's probably not tempered at all but this has thrown me into quite a bit of confusion as to whether or not I can trust my simulation results (I've not given any specific details of my simulation since I don't want to turn this into a homework style question - but I'm happy to share if it helps).

So my question is; can I trust the results at AL6061 T6 is significantly stronger than aluminium foil (it would help if I can find what aluminium the foil is made of)?


texts:
I want to add a mid-drive e-bike motor to a pull wagon. I have to carry a heavy load up ramps frequently and adding an ebike motor to my wagon would make the job a lot easier. I already decided to put the motor on the "back wheel" (non-directional) and use the cart in "reverse" while on electric power, so the directional wheels would be at the back, with me. The issue I have is how to transfer the torque to the wheel? I can attach a sprocket to one wheel and use a bicycle chain, but that would give me a single wheel drive. Would that work? would that make the wagon really hard to control?
Other ideas I got was installing a shaft and then powering both wheels, but then they would have the same speed which is bad for turning. My last idea was to add a 5th wheel in the center and power through that wheel.
We are talking about a speed of "walking" speed, with loads of 350-500 lbs on a cart design to take ~1200 lbs wheels of 7 inches (total diameter).
Any ideas?
Wagon


texts: Creating strongest possible sectional aluminum round tube

texts:
I want to attach a mast and sail to a dinghy. The mast length would be 10.5 feet tall to accommodate a 20-22 sq ft sail, but for transportation purpose would need to be collapsible into at least two pieces.
I have to decide between a tapered mast or one single diameter. If tapered, I would insert 0.75" OD aluminum into the 0.875 which will have a 0.875 - 2 x(0.058 wall) = 0.759 ID (maybe too tight of a fit and difficult to (dis)assemble?
Using 6061 aluminum, I have a few options:

a two-piece tapered mast with 0.875 OD and 0.75 OD tubes (wall=0.058" for both)
a two-piece, non-tapered mast 0.875 OD, 0.058 wall using a 0.75 OD ferrule/connector tube that I would secure on one side with pop rivet.
a 3 piece, mast using the same method as above
or 4 sections?

Which mast construction would offer the best strength without causing a permanent bend? How long do the overlaps need to be when using connector tube? Would 0.058 wall thickness be strong enough?
***NOTE: I tried to calculate wind pressure on the sail using F= A x P x Cd and P=0.00256 x v^2
F (in lbs), A (sail area in sq/ft), Cd (Drag coefficient: I used 0.8 and 1.2)
F=22 x 0.36864 x 0.8 = 6.5 lbs (for 12 mph wind)
F=22 x 0.576 x 1.2 = 15.2 lbs (for 15 mph wind)
These numbers seemed low, but then again, the sail is small.


texts: How are small triacs able to "switch" or control high power AC loads

texts:
I am currently looking ways to control or siwtch a max 220v 35A load. Simple magnetic relay rated for such load would work, but i am exploring the other alternatives too.

here i stumbled into triacs, in which solid state relays are made of. I stumbled into this ic

https://www.st.com/resource/en/datasheet/t16t.pdf

and i could not get the grasp on how a small triac such as this one.

is able to switch a high load of 220v 16amps

Thank you!


texts: Piping construction, flanged connection - Difference between Collar and Flat collar

texts:
Consider a collar (V-Bördel) and a flat collar (glatter Bund) for a flanged connection, in conjunction with a loose flange.

What are reasons to use one over the other? I want to know because a tender specified a flat collar but it seems (I'm not on site, just helping with clerical work an spotting the discrepancy) the constructor installed collars. Most likely they simply got a better deal on the one type. Is there an important functional difference?


texts: Why doesn't the flow of current through the conductors in the rotor of a fan affect it?

texts:
The rotor of fan is shown as a series of circles arranged in a circular manner. From youtube videos, I came to know that this is sort of a top view and the circles actually represent conductors through which current 'can' flow into the screen or come out of the screen (towards the viewers).
I wonder as to what happens to the current that arises in these conductors (due to the induction of EMF).

Where do the electrons flow to ? There has got to be some path, which makes that path a conductor, and hence susceptible to be affected by lorentz force.

So why isn't that shown ?
(Diagrams would be highly helpful)


texts: How do pilots of Deep Sea Vehicles operate the control surfaces and thrusters from inside a pressure hull?

texts:
A Deep Sea Vehicle (DSV) like Trieste or Limiting Factor or now Fundouzhe have control thrusters, ballast that has to be dumped, and other equipment to operate the DSVs.
But the pressure hull is a solid sphere minus the porthole windows and a hatch?
How does the pilot control these systems? Is there some conduits cut through the pressure hull? Optical penetrators could be used but how does this not compromise the integrity of the pressure hull? How else might it be done?


texts:
Am I correct in saying that the residual stress of a component, that has undergone plastic deformation and then unloaded, is determined fully by the elastic component of the residual strain? And if so, is this because the plastic component is permanently deformed and hence is in a state of equilibrium unlike the elastic strain which is held out if equilibrium by the plastic deformation?

This makes sense in my head but the notes I am using don't strictly state this but instead say: "the residual stress is related to the residual elastic strain".

Thanks for your help!


texts: Narrowing down injection moulding material selection

texts:
How do I narrow down specific values when selecting a plastic for injection moulding?
My part is uniform in wall thickness and thins out where a hinge a present.
Properties:

Will not go under many cycles in its lifetime, however, needs to be rated for thousands of cycles
The entire part is about as long as a finger and the hinge will displace minor distances (2-3 mm)
Will have to operate in temperatures from -20 to 60 Celsius
Applied forces are minor and not sudden

I have designed the hinge as follows:

I have the model in CAD and have run FEA to figure out stresses (ie. Von Mises). I have also 3D printed it in ABS, and it has passed vibration testing and performs as designed.
The criteria I have narrowed down based on matweb is:

I need the hinge to bend easily, so it does not affect the entire product- a low flexural modulus
As the plastic part is supported in one area, I need it to be able to withstand vibration testing. Therefore, sorting by the lowest density so that it does not collapse underneath its own weight
Shore Hardness D of around 60 to 80, as I need the part to not be flimsy yet not too rigid
Despite the hinge being able to bent easily, I need it to also return to its original form when it is not stressed- a high resilience

How do I go about determining specific values for the criteria? Are there other mechanical values I am neglecting?


texts: Suggestions for low friction surface materials for a "beltless static treadmill"

texts:
I'm currently developing a treadmill for clinic gait research. If I were to build a flat treadmill with no moving surfaces what materials or coatings would be worth exploring as walking surface. Ideally, the surface would be durable, safe to touch with bare skin, capable of supporting a healthy adult, and low cost. The user would most likely use the treadmill wearing socks, made of either cotton, wool, spandex, or nylon. Delrin has been explored but is not adequate and produces a residual friction load on the user, producing artifacts in gait.

If you don't necessarily have a suggestion for a material, please suggest a way of calculating the equivalent friction coefficient between a surface and a fabric. This method could be experimental or based on theoretical methods using a materials database.


texts: What is the meaning of dew point -20 or -40 or -70 deg.C? Since below zero centigrade, water cannot dew (already freeze)?

texts: I saw these specifications listed for a compressed air dryer (desiccant type). I also wonder, can we extract moisture without make it liquid (dew) first when in it is in a vapor state? How would we do this?


texts: Heat Exchanger water to air temperatures

texts:
I have been having a debate with a coworker  regarding heat exchanger fluid temperatures and while I thought I firmly grasped the principles, I was not arguing my point very well.

I am looking at an air to water coil for an air handler. I was selecting the coil based on a leaving air temp of ~60F (it's an industrial space with a lot of ventilation). I am using condensing boilers so I sized for 180 leaving water temperature with 140 return on the coldest day which gives a 40 degree temperature delta.
On the air side, I am bringing in 5 degree air (EAT) at a rate of 16000 CFM on one of the air handlers. My coworker wants to lower the temperature to 140 supply and 100 degree return, his reason being that it would still be a 40 degree temperature delta on the water side so the thermal output would be the same. I believe the hotter supply temperature will result in more rapid heat transfer but I didn't really have any good argument against his logic. He was simply relating the two rules of thumb equations for air and water: [Btu/hr]=1.08*CFM*deltaT and [Btu/hr]=500*gpm*deltaT to prove his point.
My argument was that this does not account for the heat transfer taking place from one side of the coil to the other, but I was not able to adequately illustrate my side to the point that he would agree.

First of all, am I even right about operating the system at 180 degrees being a more efficient solution, and, if so, how do I fit the heat exchanger heat transfer into the system of equations?


texts: Calculate forces/ torques on a parallel spring array

texts:
I am stuck on the calculation of forces on a certain system involving parallel springs.
The schematic of the system is as follows:

The lower plane is fixed and the upper plane movable. There is a symmetric 2x2 matrix of springs between the upper and lower plane. All springs (same size and spring constant) are rigidly attached to the respective planes. The upper plane has a rigid extension (not shown in the image) where forces can be applied such that the upper plane moves/rotates.
In a parallel setup of springs with a symmetric force acting in -z direction I know that I can just add up the spring constants. However what if the force is not parallel to the springs? In  case of a single spring I would model the bending of the spring as beam, but what about a spring array?

Is there a way to compute the forces/ torques acting on the upper plane when I know the relative position (rotation and translation) of the upper plane to the lower plane?

Thank you in advance!


texts:
I'm thinking of making a RC tank that should be simple as possible. But I'm not sure how to make proper steering for the tank. I googled about tank steering and found (for me) complex solutions as dual differential steering.
Now, my question is - Is it possible to steere the tank with momentum?
Idea for project is - Left motor will power left Wheele(tracks are too complicated to design), right motor will power right Wheele. Powered Wheele are at the back. So if I want to steere the tank to the left side, right motor will be on, left will be off. Does this method Works? Should right motor go forward but left go backward?

Here is the sketch. This is sketch for rotating/steering from place.
I guess it will work fine, but what if tank moves forward/backward and wants to steere?


texts: Is it possible to have open loop with same input term as the output?

texts:
For example, i have this differential equation:

$$\dot{y} =  1.8 + 0.58u \sqrt{y}$$

Is it possible to model this system in open loop?? My understanding is that since the term $y$ is in the output as well as one of the input terms, then it is only possible to model with a feedback loop.


texts: Help sizing of lug attachment flange/plate?

texts:
Apologies for the crude drawing attached, but here goes. Given Fx, Fy, and Fz loads applied at the lug hole, I've distributed the loading into each of the 6 fasteners to size them. I've also sized the lug itself using the airforce lug sizing method.
But now I'm trying to size the portion of the lug fitting that I've labeled as "lug flange" and am kind of hitting a wall. I could throw this into FEM for sizing, but I'm thinking to size it by hand, I could separately determine the bending moments/torsion created in the x, y, and z directions about the bolt group center. But I’m lost as to what the next step would be. I’m mainly interested in sizing the thickness of the plate.

Any thoughts are greatly appreciated. Thanks


texts: How to calculate the lateral bending capacity of a laced strut?

texts:
The vertical bending capacity of a twin UB laced strut can be calculated by $M_c = p_y \cdot 2Z_x$. Where $Z_x$ is the section modulus of a single UB section about its major axis.

For lateral bending capacity, can we calculate this by using $I_c = 2I_y + 2As^2/4$, where $s$ is the separation distance between centroid of the two UBs, and $Z_c = I_c/e$, where $e$ is the distance from centre of laced strut to extreme fibre?

Would the built-up member have a lower bending capacity due to the two beams being laced together at fixed intervals instead of being joined continuously together via welding?

In summary, can we design laced strut for significant lateral bending instead of mainly axial compression?


texts: My dogbone bamboo sample's grips keep breaking

texts: I used an Instron 5581 Tensile Testing machine to test the tension of several bamboo samples that were sanded into dogbone shapes. They kept breaking at the grips and I am not sure why?


texts: How to tune a PID for a pure integrator system?

texts: Given a plant with a transfer function of K/s, how can I tune a PID to control it? I found articles explaining how to tune an integrator with time delay, but not for just a pure integrator system.


texts: Torque Required to rotate a horizontal drum/cylinder with material inside

texts:
I need to find the torque that will rotate a stainless steel drum that is filled with small steel balls. The total volume of this drum is 210 cubic feet, and there will be 38 cubic feet of material inside at any given point in time. It is a horizontal cylinder that will rotate through its central axis. What is the torque required to start turning the drum.

Mass of Drum: 13,500 lb
Mass of Material inside: 13,700 lb
Diameter of Drum: 38"
Length of Drum: 297"

Drum to Rotate at 10 rpm

Friction in the bearings and the drive is negligible.

I know I have to consider that the material will move up the side of the drum as it rotates, but I'm not sure how to go about doing this.


texts: Do companies recover CO2 and water from the purification step of cryogenic air separation, and how?

texts:
In the 3rd step of cryogenic air separation, filtered air is purified to remove water, CO2, and hydrocarbons from the N2-O2-Ar stream. Im interested in knowing what happens with that CO2 and water. Can both resources be recovered in a useful form? Can the CO2 be purified/ are Praxair or others currently doing this?

Context: Im doing research on a theoretical industrial process which uses pure CO2, water, and N2. I want to know if all these inputs can be obtained from a standard air separation facility (of course N2 can). Im particularly interested in CO2 recovery.

Please note I'm not interested in buying gases. I'm working on a publication about a theoretical system to produce protein from air and solar power.
In your answer it would be helpful to provide links to papers or websites which give descriptions of the recovery process (energy costs etc).

Thank you


texts: Why is it generally assumed that the evaporator works isothermally?

texts: Since an evaporator also a heat exchanger, how can the inlet and outlet temperatures of the HEX accepted as the same, i.e. isothermal? In this case, cold stream (inlet and outlet of the evaporator in the refrigeration cycle) does not incur any change in temperature, which requires an infinite size of the heat exchanger.


texts: Is pin column-beam joint always have less moment, more deflection compared to fixed joint?

texts:
I am referring to the answer here:

It seems that on a simple structure

(The diagrams on the left the images below have fully-fixed connections, while on the right the columns are pinned connections to the beams.)

A: The deflection on beam is bigger in pinned model, but the deflection on beam/column joint is bigger in fixed model

B: The moment on column in pinned model is 0

C: The axial load on column in pinned model is bigger, because the moment is being transformed into axial load (?? is this reasoning true??)

My questions are:

These conclusions are true for this particular simple model, but are these three conclusions always true on any general model?
And why? Can it be explained in terms of loading flow and statics? Or this is just FEM behavior that we can't explain more intuitively?


texts: Can any Air rotameter be used for refrigerant gas by using equation conversion?

texts:
Currently, I am trying to find rotameter calibrated for R134A gas flow. However, most companies only sell rotameter or variable area flowmeter for water/Air/Nitrogen flow. Is it possible to use any air rotameter for R134A and convert the scale reading to corresponding refrigerant flow through the use of rotameter conversion equation(shown below) ? Will the converted mass flow rate be accurate?

Qs = Qi * sqrt((TsPa)/(TaPs))
Where Qs = true SCFM
Qi = indicated flowrate ('SCFM')
Ts = calibration temp (R)
Ta = actual temp (R)
Pa = actual pressure (psia)
Ps = calibration pressure (psia)
Thank you!


texts: I'm studying communication systems and I have a question about Double Sideband Amplitude Modulation as to why the transmission bandwidth is twice the message bandwidth. Is it necessary the message signal is symmetric about the origin. Why is it that only one half of the spectrum of positive frequencies deemed useful.


texts: Response of a system to a step function (Heaviside function)

texts:
I'd like to compute the response to a step function of a electrical/thermal system. Generally I can "easily" compute the transfer function $H$:

$$H(\omega) = \frac{V_{out}(\omega)}{V_{in}(\omega)}$$

Since the Fourier transform ($\mathcal{F}$) of the Heaviside function is (computed with WA):

$$\mathcal{F}(\theta(t)) = V_{in}(\omega) = \sqrt{\frac{\pi}{2}}\delta(\omega)+\frac{i}{\sqrt{2\pi}\omega}$$

Hence, noting $\mathcal{IF}$ the Inverse Fourier transform:

$$V_{out}(t) = \mathcal{IF} \left\{ \left( \sqrt{\frac{\pi}{2}}\delta(\omega)+\frac{i}{\sqrt{2\pi}\omega} \right) H(\omega) \right\}$$

To check my math I tried to compute the response for a simple RC system:

I should get the well known charge of the capacitor. The transfer function:

$$H(\omega) = \frac{1}{1+i\omega R C}$$

Computing the Inverse Fourier transform ($\mathcal{IF}$) with WA ($R=C=1$) I get:

This would be correct if we were going backward in time :/. So the question is... What am I doing wrong?

I did the same using Laplace Transforms and everything works fine... But I don't understand why.

P.S. I don't want another method, I just want to understand what's wrong in my approach.

P.S. the reason why I am using WA is that for my more complicated system I need to compute the Fourier transforms using WA.


texts:
I have a 12v 300 watt power supply.  I replaced 13 20watt halogen bulbs with 13 3watt LED bulbs. Questions:

should I downgrade power supply since I'm now drawing 39 watts as opposed to the 260watts I was pulling with the old halogen bulbs?
Am I correct in assuming that power usage is based on the total wattage of the lights and not the rated wattage of the power supply? If true, then my power consumption has dropped from a rough equivalent of 3 100watt light bulbs to approximately a single 40watt bulb, correct?


texts: Why is it desirable to have high g value for sensing applications, while high d value is desirable for actuation in piezoelectricity?

texts:
In piezoelectric materials, two parameters are defined to construct relations between electrical and mechanical energy conversions. These parameters are the charge constant d and the charge constant g. In literature, it is always stated that  high g value is desirable for sensing applications, while high d value is desirable for actuation. This is proved as follows:

d is defined in two ways :
d= strain developed/ applied electric field
Based on this definition, large d constants relate to large mechanical displacements which are usually sought in actuators.
also d is defined as :
d= induced charge density/ applied stress
Based on this definition, however, I can conclude that high d value is also desirable for sensing applications, as more charge is induced per applied unit stress.

Regarding g constant, it is also defined in two ways
g= induced electric field/ applied stress
Output voltage is obtained by multiplying the calculated electric field by the thickness of ceramic between electrodes. High g constants favor large voltage output, and are sought after for sensors.
The second definition is

g= strain developed/ applied charge density.
Based on this definition, however, I can conclude that high g value is also desirable for actuating applications, as more strain is developed per applied unit charge density.
So I got confused of what is stated in the literature. Am I wrong ?

Also, Based on the definitions of d and g :
d= induced charge density/ applied stress
g= induced electric field/ applied stress
I can say that g = epsilon* d ; (epsilon is the electric permittivity)
electric field  is equal to the charge density divided by the permittivity.
So what is the importance of defining 2 parameters?I think that defining one of them is adequate.


texts: Adding a black plastic layer to increase retained heat in compost

texts:
I have some invasive climbing weeds to break down into compost. I don't want to discard the biomass, but I do want to thoroughly kill all the weeds and ideally the seeds over a period of months.

The bags I have are made of recycled wool packs. Typically weed bags are made of black plastic, but mine are a light tan colour. Assuming a position where the bag is exposed to some sunlight and some shade during the day, and also exposed to wind/breeze blowing across its surface, in theory would a layer of black plastic over the top significantly increase the retained heat in the centre of the weeds inside the bag?

It may be worth mentioning that as they decay, most composting materials produce heat as a consequence of bacterial activity, though not massive quantities in a slow compost.

(Redirected from Physics, where they pointed out this was an Engineering question. I understand the potential for a redirect to Gardening, but the question is really about heat transfer and retention, not the plants!)


texts: ANSYS Workbench/Mechanical: Automatically export chart?

texts:
I'm running a simple tensile test simulation for a single element. Under Results I made a Chart object with Stress vs Strain, which can be manually exported to a csv file by right clicking on the table. The trouble arises from the parametrization. I've parametrized temperature in Workbench so that the same simulation is run once for each temperature. However, the results are not saved for each substep for each design point, and it would be tedious to have to open Mechanical, re-solve, and export the Chart as many times as I have temperatures.

Ideally there would be a macro that runs every time the simulation is solved in Mechanical, exporting the Chart's table to a csv (appending it if possible so that the data for all temperatures is in the same file).

Is there any way to do this? I would imagine it could be achieved with JavaScript in Mechanical (for which I cannot find any documentation).


texts: Is it safe to slightly cut the edge of RCC column for passage of pipe in bathroom?

texts: The RCC column was cut in my absence due to passage of pipe for bathroom fittings. The thickness is about 1.5 in. Will it hamper the stability of structure?


texts:
On the image below there is a regular prism which is angled by $\alpha$.

The (black) mass m1 applies a torque $M_k$. The mass m2, which is the rest of the Body applies the torque $M_s$ In the opposite direction. The black dot on the bottom right corner is the pivot point.
So i wanted to calculate the normal force distribution on the bottom surface which is completely touching the ground.
Because the force F1 has to be smaller than F2 right?
My final Goal is to calculate the friction of the prism.
So my question was: Does it matter if i calculate the normal Force by $ F_N = m * g$. Or do i have to integrate $M$ over the whole bottom surface and thus derive the mean of the normal force.

Another problem is: If the prism is accelerated by a another torque $M_a$ is applied. So you definitely cannot calculate the normal force by $m*g$ anymore.


texts: Inexpensive and moderately accurate (field) method of measuring THC (Total Hydrocarbon Content) in water

texts:
I am working in a construction company which is building hydropower plants in Northern Norway. We are monitoring the Total Hydrocarbon Content (THC) of our process waste water. This particularly important during tunneling as the machines are likely to leak.

At the moment we are sending waste water samples to an analysis company and there are some disadvantages of that, including the price, the delay in information, and the risk of volatile hydrocarbons evaporating during transportation.

I would like to take weekly samples in the field and do the analysis myself. I am an environmental engineer with some background in the laboratory from my time as a student, but I have never tried to find THC before.

I have been trying to find a simple and inexpensive way of measuring the THC in the water, but most of the instruments I have seen on various company websites are very sensitive (measuring in the ppm range) and meant to measure the THC continuously on some industrial flow (like this).

The measuring range should be something like 1-100 mg/L, and I simply cannot find any method or instrument that suits those needs. Do you know of any kind of instrument that can perform this analysis, or a manual method? I am looking for an inexpensive, portable, and simple solution.


texts: Why stagnation temperature doesn't change in stator

texts:
I was going through a review of rotary compressor and i understood that the stagnation pressure and stagnation temperature both change in the rotor stage (as energy is being added).I also read that in the stator stage the stagnation temperature remains a constant but there is loss of stagnation pressure. If there is a loss in stagnation pressure shouldn't the stagnation temperature increase (I am guessing here that the loss is converted into heat)? (I am guessing this has to do something with expansion but I am not sure)

additional info: https://physics.stackexchange.com/questions/292589/why-does-a-diffuser-increase-pressure


texts: Designing clamp band - coaxial force in screws, zeroing torque in structure - Calculation problems I can't simplify my mindset (help)

texts:
At first I want to apologize while English is not my first language.
I am a student, and I have to design such configuration:

I already have designed the "fork" (the part on the right side).
Now I am at the point of calculating for the clamp band which is one part with a steel rib ($a$ dimension).
My problem is that I do know that there is a torque caused by force F and the torque caused by friction forces between the clamp and the shaft neck (where $R$ dimension is), I have to find force values that causes that torques zero in the assembly and then I have to transform those Friction torque to find a suitable screw that will stand the coaxial force caused by clamping, but I am probably overthinking this problem because I am thinking like this:
When the structure is clamped there is a coaxial force in the screw that is causing radial forces to form and is causing the change of radius that is different in infinite points on the inner circle. Now the radial forces wont be the same in whole area that is holding the shaft neck because half of the band won't deflect, so apportionment of the forces (their value to be precise) will change with the deflection of the band - so the force is linked to Δr.
Because of the above the resultant of the radial forces on each of the quarters of the band wont be located on the inner circle with the tilt of 45° and -45°. So, because of that for now I have such variables:
X- coaxial strength in screw,
Δr - change of the radius when the band is clamped - different in all areas where band is flexible.
y - variable that depicts the level of tightening the screw in mm
Fr - radial forces linked to X,y and Δr.
$\alpha$, $\beta-$ degrees that are depicting in what points on the inner circle resultant Fr is hooked
T - friction force caused by Fr
So this picture, pretty accurately depicts what I have in mind:

I know that this is complicated and probably impossible to calculate with my level of knowledge, so I am asking for help because I can't figure out what I can do here to actually calculate it.
I was trying to find some examples how to handle this but there is nothing helpful on the internet and it's unfortunate since it is quite easy for me to get "things" when I see examples.


texts: What is the difference between sommerfield number and bearing characteristic number in bearing design?

texts:
After reading a few texts on the topic of sliding contact bearings I am confused between the bearing characteristic number and the sommerfield number.

As per J.E shigley's text both bearing characteristic number and sommerfield number are same and is given as

But as per V.B bhandari,R.S khurmi texts the bearing characteristic number and sommerfield number are different and is given as

then again in Wikipedia I have seen that they too followed the shigley's text definition with an additional number called Hersey number given as


texts: Pump with high pressure, low delta pressure

texts:
I'm looking for a circulation pump in a very high pressure loop and having trouble finding one. I'm hoping I just don't know the correct search term and someone can point me to it.

The absolute pressure (what the housing needs to be rated to) is 100 bar / 1500 psi, but the pressure rise created by the pump is less than 1 bar /  15 psi.

I think a centrifugal pump would be appropriate, it would just need an extra beefy housing and appropriate seals. Is there a common name for this type of pump?


texts: Electrical flowchart in Microsoft Visio : issues

texts:
I am trying to recreate in Microsoft Visio a diagram of a photovoltaic power plant that would look like the one below.

But I have some issues for doing so, in particular :

I don't know how to create a "grid" symbol like the one that is at the bottom right of this picture
I don't know how to make an "abbreviated line" with tildes like the ones you can see Inside the PV modules at the extreme left of the picture.

Can someone give me some help with this?


texts: Value of Mechanical Constants in Real-World Applications

texts:
I've recently been reading through introductory texts on the mechanical properties of materials such as this. Most start with a description of various material constants such as Young's modulus, Poisson's ratio and a zoo of other properties, and try to determine these properties through a study of dislocations and interatomic interactions.

However, when I read about the very specific test conditions for these kinds of properties, it's not immediately obvious how well these kinds of coefficients and measurements translate to the real world.

For example, I can find coefficients describing hardness, toughness, etc. from laboratory experiments under specific experimental conditions, but it's not obvious that these coefficients can give a more than qualitative description description of how well my nail can hold together a desk, how well my steel truss can hold up a roof, etc., which are ultimately the questions I might be interested in. These coefficients seem to describe very specific geometries, and it seems that I can only get answers about more general geometries using FEA, leaving these kinds of measurements as useful for 1) qualitative descriptions and 2) feeding parameters into FEA.

I think some of the confusion stems from the seemingly arbitrary nature of all these parameters. It appears that someone designed a test and came up with a new parameter every time they were interested in a behavior under different conditions, and there's no minimal degrees-of-freedom type argument that prevents me from coming up with my own test and modulus.

Put another way, what is the argument that the mechanical properties covered by the usual texts (Young's, Poisson's, hardness, toughness, etc.) can give me a complete mechanical description of a system under arbitrary geometries and loads?

Thinking about the parameter space more abstractly, each test can be represented as a material-dependent function that accepts a given material geometry and load geometry and maps it onto strain (throwing out hysteresis and time dependent phenomena for simplification). If we represent our inputs in R^n and our outputs in, say, R^m, what is the minimum number of moduli and constants needed to define this function? What's the argument I won't open up a textbook and find that it defines a new and non-redundant mechanical parameter.

And, if such a well defined relationship exists, where might I find out more about how to go from the parameters derived from well defined experiments (stretching a cylinder, squeezing a flat plate, etc.) and more general material and stress geometries?


texts: Finding the pull-through capacity of a nutted bolt and washer in ASA plastic

texts:
I have a uniform load applied to the underside of a plastic sheet which is to be resisted by the combination of a bolt, washer, and nut as depicted below (the other end of the bolt is secured and will not budge).

The thickness of the Luran S 777k ASA (Acrylonitrile Styrene Acrylate) plastic is currently unknown, but to get the ball rolling let's just say it is 1/8" thick (EDIT: confirmed). The plastic will bear directly on the square washer.

For modeling purposes, I have decided to assume the plastic is totally fixed/rigid and that the load is being applied to the bolt. In this model, it is the washer that is bearing on the fixed plastic.

I expect that the limiting factor of this system is going to be the pull-through capacity of the plastic as (I assume) the washer will tear it apart way before the washer or the bolt fail. How can I determine the pull-through capacity of this system? Is my assumption that the pull-through capacity of the plastic is the limiting factor valid?

My idea is to simply obtain the shear resistance of the plastic material online somewhere, and calculate the pull-through capacity like so:

Shear strength of the material is $\tau_{\text{ASA}}=??$
Load-resisting cross-sectional area: $$A=4s_{\text{washer}}\cdot t_{\text{plastic}}$$
Therefore the pull-through capacity of washer bearing on plastic is: $$P_t=\tau_{\text{ASA}}\cdot 4s_{\text{washer}}\cdot t_{\text{plastic}}$$

However, I'm concerned there may be other considerations at work here that I need to take into account. Is it really this simple?

Thanks to hazzy for the simple but reassuring answer, and the points he made.

It turns out that the limiting consideration for this particular problem seems to be fatigue/cyclic bending of the plastic around the washer, since in actuality the load is being applied at either end of the plastic section (instead of uniformly as I proposed in the model above).


texts: How were multiple vacuum pumps used to raise water over 10m (e.g. by a steam engine)?

texts:
I can imagine a steam engine driving multiple regular old vacuum pumps, which each raise water ~10m.  I would think that someone would combine the multiple pumps into a single piece of machinery for raising water >10m without high pressure.

Was such a thing in use before the Newcomen steam engine (driven by horses or something)?  How was it designed?  Was the same pumping system used with the Newcomen steam engine?


texts: Regarding Question On Control System Engineering

texts:
Transfer function= 400/(s^2 + 12s + 396)
Calculate rise time, settling time, peak time, overshoot, undershoot


texts: why do centrifugal compressors have curved blades?

texts: Why are centrifugal air compressors built with backward curving blades?


texts: Estimating whether the flow through a valve or nozzle cavitates

texts:
My understanding is that cavitation occurs in the flow of a liquid when the static pressure drops below the vapor pressure, even intermittently. So even if the time-averaged static pressure (what you might measure) is above the vapor pressure, the pressure fluctuations from turbulence or other unsteadiness could be large enough to cause cavitation locally. So comparing the time-averaged static pressure against the vapor pressure isn't enough; you need to add some extra cushion to account for the pressure fluctuations. (This is my interpretation, not having read too deeply into this.)

So, in various books, websites, and journal articles I have seen two different types of dimensionless numbers for estimating whether the flow through a valve or nozzle cavitates. They are generally called the cavitation index or cavitation number. They take one of two forms:

$$\sigma = \frac{p_\text{in} - p_\text{vapor}}{p_\text{in} - p_\text{out}}$$

or

$$\sigma = \frac{p_\text{in} - p_\text{vapor}}{\tfrac{1}{2} \rho V^2}$$

where $p_\text{in}$ is the inlet pressure, $p_\text{out}$ is the outlet pressure, $p_\text{vapor}$ is the vapor pressure, $\rho$ is the liquid density, and $V$ is some characteristic velocity of the flow (say, in the nozzle case, the velocity at the outlet). Some forms of this number are inversions of the numbers above, but these aren't that different.

What is the difference between these parameters? Based on energy conservation you can relate the pressure drop to the flow rate, but typically there is an empirical coefficient added in to account for non-idealities. Is there something else I am missing?

Is one form preferred over the other? Best I can tell whether to use one or the other depends on what sort of data you have (so, for flow over a turbine blade, the velocity form is preferred), but I've seen both even for nozzles.

Where can I get accurate data to predict cavitation based on these numbers? I've tried using some data on atomizer nozzles from various journal articles but generally they use different forms of the cavitation number. Some of the data suggests the flow through the nozzle will cavitate at the pressures I want, but other data for similar nozzles suggests it won't. I'm not sure what the source of the inconsistency is. My understanding could be faulty, the cavitation number model could be too simplistic, the data could be inaccurate, etc.


texts: I am working with a normalized ball-screw drive where the nut has holes for screws to screw onto the moving part. The catalogue says these holes have diameter 13.5 mm. What is the appropriate screw size (metric) to use on such a part?


texts: Why do high pressure multistage air compressor have different piston diameter sizes?

texts:
I meant like this kind of compressor https://www.bauer-kompressoren.de/fileadmin/_processed_/csm_compressor-block-junior2_b92a76a02e.jpg
also would the compressor reach high pressure if the diameter of all the piston have same sizes


texts: What is the difference between a state observer and a Kalman filter? Having implemented various types of Kalman filters, I'm still a bit confused, mainly because state observers require the selection of poles similar to a control system setup, whereas Kalman filters don't. Any clarification on the two and their differences would be great.


texts: Maneuverability calculation of a catamaran ship with azimuth thruster?

texts: In a competition about ship prototype performance, my team decided to make a small catamaran ship with azimuth thrusters. This competition was originally about speed contest but due to COVID-19 it was replaced with report, video, and presentation contest. the competition required us to report maneuverability test using the IMO criteria, but it seems there is no criteria for catamaran with azimuth thrusters. I would like to know how should we calculate the maneuverability of our ship.


texts: What domestic water valve is least likely to jam over time?

texts:
I'm doing some work on a domestic water system, mostly 15 or 22mm copper pipe with compression fittings.

The work includes replacing various stop-cocks and drain valves some of which are probably 30 or more years old. Some are jammed solid, some turn easily and some turn eventually after squirting with oil and waggling back and forwards for a while.

Most of them rely on brass to brass contact, maybe with a fiber washer, and some gland packing to maintain a seal around the shaft.

I need to replace all these items, if my main criteria is working life expectancy, what should I replace these with? More or less the same thing? Or new ball valves with polished steel ball in a nylon housing? Bearing in mind that whatever I use is only likely to be turned on average, once every few years?


texts: Why would 12L14 material be a "feature" of a work-holding flange nut?

texts:
Anyone who's spent much time in a machine shop will be familiar with the hardware commonly used for work-holding and fixtures on a machine tool. In particular, the flange nut is a common item used with strap clamps and other work-holding devices. TeCo is a well-known manufacturer of these items.

I just happened to be shopping for some of these flange nuts for a fixture and noticed that some of these are specified as being made from 12L14 (leaded steel). This detail is not buried in the data sheet, but appears where I would interpret it as a feature, meaning a purchaser might have reasons for choosing one in this material, as opposed to one in a stronger steel for example.

My question is why 12L14 might be a preferred material in this application. I've understood leaded steels to be free-machining, which would make manufacturing easier (although making the part non-weldable), but I can't imagine that would be a driving factor in high-volume parts like this and in any case wouldn't rise to the level of a feature to be advertised if that were all it was.

I have two theories:

The lead in 12L14 somehow increases the lubricity of the fastener, making it less likely to bind (or perhaps gall) in a frequently used fastener like one in a manufacturing fixture.
Lower tensile strength (although not that much lower) is a plus, because if over-tensioned, it's better for the fastener to give than the t-slots machined into an expensive machine table.

Can anyone enlighten me?


texts: How can I calculate the maximum possible deviation from equilibrium, that can still be compensated, given a limitation on the control input?

texts: For example we have an inverted pendulum attached to a cart, with the cart having a speed limitation. Having derived the linearized model, how can I calculate the maximum possible deviation on the angle, and angular rate from the linearized model and the speed limitation ?


texts: Cold worked Fe-Ni rod is very brittle and not suitable for drawing. What would be the best heat treatment parameters for increasing the ductility of a Fe-Ni Alloy? Does increase in the Co content make it brittle? Thanks in advance.


texts:
For an experiment I need to use an electric motor, unfortunately I'm not an expert of electric machines. The electric motor I need has to comply with some requests:

It must be brushless.
It has always to turn at low speed, from 0 to max 6 rad/s.
Its width can't exceed 2cm and its diameter can't exceed 11cm.
It is energized by a battery.
It has to develop a quite intense torque.

So I'd like to know which type of electric motor meets these requests (if any).


texts: Resistance spot welding multiple metal thinknesses

texts:
I have a question for all experienced in manufacturing of steel products;

Is it possible, and or workable to resistance spot weld dissimilar metal thicknesses together? for example, 1.5-2mm thick steel to 3mm thick steel.

And please elaborate on the limits... such as the minimum thickness to the maximum thickness that is able to be welded reliably and quickly in a manufacturing environment.

Thanks in advance for your help :).

Thomas


texts: How can I build and maintain an accurate pressure on a fuel line without using a fuel pump?

texts:
Background

I am building an engine from scratch for the sole purpose of becoming a better mechanical engineer--I'm currently a second year undergrad. The engine I'm designing is a single piston 4-stroke gasoline engine. I have no intention of using it on anything yet and only want to make it run reliably.

Problem

I'm using fuel injection and I've heard I need to control the pressure on the line fairly accurately. I'd like to avoid using a fuel pump in favor of something I can actuate with a microcontroller. One of the harder things I've found in mechanical engineering is that it is difficult to find what parts exist that can solve your problem. So my question is, what are some ways that I can do this if I don't use a fuel pump? I really want to become a good engineer so any insight is greatly appreciated.


texts: Why is there a delta for locally stable in the sense of lyapunov?

texts:
Why does this definition (screenshotted above) for locally stable i.s.L. require a $\delta$ term? Why not just say, something is locally stable i.s.L. if "for any ball of size $\epsilon$ around the fixed point, all trajectories initialized within the $\epsilon$ ball stay inside the $\epsilon$ ball"?

Can someone provide an example where introducing this $\delta$ ball is significant?


texts: Effective Throat of Flare-Bevel Weld with Reinforcing Fillet

texts:
Occasionally I have to design T-connections between rectangular tube steel (HSS) members where I have a flare-bevel weld between the corner of the tube and the connecting flat member.  If the weld stress is high enough, a reinforcing fillet may be required.

Per AWS D1.1-2010, Section 2.4.2.7,

The effective throat is illustrated by Figure 3.3 and Annex A (pasted below)

Thus far, I have been unable to easily calculate the minimum effective throat of a flare-bevel with reinforcing fillet due to the complex geometry of the weld throat.  The best method I have found so far is to draw it in AutoCAD to scale and figure it out from there, but this is relatively time-consuming.  It is not immediately evident to me which plane of the weld is the minimum throat since the contour of the weld changes along its width.

Has anyone seen a formulaic (i.e., programmable) methodology for determining the effective throat of a flare-bevel with reinforcing fillet?  I mostly work my calculations in Mathcad, so having something I can program into steps would be highly beneficial to my workflow.


texts:
I want to control the flow of chemical proportionate to the forward speed of the vehicle( if the speed is more discharge is more vice-versa). Need to integrate vehicle speed with encoder and control the solenoid valve.
Is it possible to change duty cycle of PWM with respect to vehicle forward speed?


texts: How to know the maximum offset distance in solidworks that doesn't result a defromed shape

texts:
using the offset tool on surfaces can result a shape different from the one offset from, as in broken lines or edges instead of curves like this:

is there a way to know the maximum distance i can offset to without resulting such deformation other than trial and error especially if i dont have designe constrains?


texts: Could a bolt this size actually be used on a project?

texts: could there ever be a structure that would require something like this?


texts: What is the smallest capacitor in size, which has been engineered and how much is it's capacitance? I presume it must be something etched on chip.


texts: Using seismic base isolators in light, flexible buildings

texts: Using seismic base isolators dissipate a great deal of energy that would enter to a structure, but at the same time they increase the natural period of vibration of the structure. Now, if we had a light and flexible building, does using seismic base isolators create a negative effect from this point of view, since a flexible building's period is already high and base isolator makes it even more causing it to shake much longer?


texts: At which temperature and humidity should outside air be drawn inside?

texts:
I have a greenhouse that get’s mold in the winter because it’s to humid.
I have now installed a heater and a ventilation system drawing outside air into the greenhouse. I wish to start the vent based on weather conditions however I cannot figure out which settings to use. I know the temperature and relative humidity inside and outside, and I want to know when to draw outside air in, only when then outside air is drier than the inside air. Any ideas?


texts: Plot variation in heave v/s speed v/s change in mass in one graph?

texts:
So I am trying to plot variation in Heave (Z-direction) of three ships with a change in its Speed (which is in Froude number i.e. non-dimensionalized) and change in its Draft (mass).

What's the best way to visualized this in one graph/plot? This is for my research work.

Thank you for your time.


texts: Baffle vs Bottom Temperature Measurement/Control

texts:
In an industrial jacketed reactor, we have two temperature probes:

one on a baffle the extends down about to the 50% fill line
one built into reactor, very close to the bottom valve.

When is it more reliable and practical to use one location over the other when monitoring and controlling the temperature in a chemical process? Please ignore  obvious situations, such as the liquid level is too low for the baffle so the bottom must be used.

I've heard some reasons for each location. For example, baffle temperature is best when reacting at a constant temperature, or when a slurry presents possible solids buildup on the bottom probe.

Are there any solid industry best practices relating to this?


texts: Beams in Bending: Bending stress / strain distrution

texts:
first post so bear with me please!

Studying Mech Eng and in all notes provided and I have come across online the stress/strain distribution is shown as I have sketched belo (see pic). Surely this is only a representation of the right hand side of the beam (for hogging as shown) as the left would be as I have sketched below.

Am I correct in assuming this? Why do they always just show the first distribution? Why only show the 2 triangles and not the full square? What is the distribution in the middle of the beam (assuming that is where a single point load is applied)?

Hope this is clear enough to understand!

Thanks for you help!

EDIT: Additionally, I feel this is where my confusion orginated from:

I now understand the stress distribution is constant throughout the length of the beam (although unsure as to why it's shown in that particular direction). But can someone please explain why the above image then makes sense. Is this only valid on the right hand side?


texts: Why don't we use hot water instead of steam to drive the turbines?

texts:
I guess if we do this then, the size of the turbines could become smaller.
The condensor's size also might be reduced.
But the catch over here is the energy density of hot water is less then that of steam. This could be overcome by increasing the amount of water sent in.


texts: What will happen if I install a 46 watt fluorescent bulb on a 15 watt light fixture?

texts:
I bought a germicidal UVC florescent lamp online and i would like to put it in a an 20 inch box for sanitation uses. After going to the hardware store I couldn't find any light that is compatible with the T8 light bulb other then this 15 Watt fixture:

http://www.homedepot.com/p/Lithonia-Lighting-1-Light-Flush-Mount-White-Ceiling-Fluorescent-Closet-Light-CUC8-15-120-LP-S1-M4/202193137

The maximum current it can support is 0.27A. The UVC bulb function at 0.6 A.
Here is the link for the bulb:

https://www.1000bulbs.com/product/7342/GERM-3000008.html

So the the questions are:

Would their be too much current drawn that the heat my damage the lamp if I install it this way? (even though I would be using it for 15 min. maximum each time)
If get a new lamp that has compatible power with the closet light above, would the lamp give the specific light wavelength required to get ultra-violet radiation (250nm)? Because I know that different ballasts would give different light temperatures.


texts: What does a stalled hydraulic pump mean?

texts: What does it mean when a pump stalls? I could not find a useful explanation with the search terms pump stalling and hydraulic pump stalling. I'm trying to understand what Elon's tweet means. Maybe an animation could help but checking the videos section with these search term also didn't help me.


texts: Determining the load on a pump vibration isolator

texts:
It seems to me that pump vibration isolators need to support:

The weight of the pump
The weight of the water in the pump
The weight of the water (only) in the drop to the pump

The supplier of vibration isolators on my project does not seem to share this view.

I understand that pump manufactures want none of the pipe weight to bear on their connections. The pipe hangers can be adjusted to prevent that.

A braided flex connector can prevent the thrust force due to pressure in the pipe from being an issue at the vibration isolators.

But the water weight in the drop to the pump seems to have no support other than what is provided by bearing on the bottom of the pump’s volute. This weight is transferred to the vibration isolators.

In the diagram below (considering only on the discharge side of the pump to explore the concept), the vibration isolators need to support 8 feet of water in the 14” diameter drop.

The water weight is 59.75 lb/ft in the chart here:
Pipe weights per foot

So the water weight (due to only the discharge pipe) on the vibration isolators seems to be:

(59.75 lb/ft) * (8 feet) = 478 lbs

Is this correct? Or are the vibration isolators not subjected to the water-weight in the drop for some reason?


texts: Smoothing caps/other methods to increase lifetime of incandescent segment displays (Looking for advice)

texts:
A while ago I salvaged a few incandescent seven segment from an old avionics module. This is the closest thing I could find online (I don't think its this exact model but same brand, pin number and such).
I plan to make a clock using an atmega328 using these as the display. They run off 5v DC so I was planning on driving them directly off the pins. Because of pin limitations I was going to multiplex them using the method described here.
Because I don't have many of these and online they go for about $70, preserving them and extending the lifetime would be ideal. I read online that keeping them on will extend the lifetime, and am wondering if switching them on and off would be damaging in anyway and if so would it be beneficial to use some caps to smooth out the power?


texts: Why does my heat pump condenser outlet make a single pass through the evaporator before the expansion valve?

texts:
I'm hoping to modify a hot water heat pump to capture both the hot and cold side. I'd work with an HVAC shop to make the modification but want to understand the circuit. It's not the simplest of units in that it includes an economizer circuit, but the standard building blocks are there: compressor, condenser (a shell-and-tube heat exchanger for the hot-water), expansion valve, and evaporator fan coil.
What's strange to me is that the refrigerant path from the condenser output flows through a tiny portion of the evaporator - a single pass of the bottom-most tubes (1 set out of about 40 or so) - before continuing to the filter-drier and then the main flow is on through the economizer heat exchanger, the main expansion valve, and finally the main portion of the evaporator (the other ~39 sets of tubes) (a portion is diverted after the filter-drier for economizer / vapor injector operation).
I'm curious why this might have been done - seems like it's just a waste of heat. The pipe leading there is even insulated until it reaches the fan-coil - and later again as it reaches the economizer heat exchanger.
Other details which probably aren't relevant, but just in case: the refrigerant is 134a, the max water temp is ~80C, and the unit has a reversing valve so it should be usable as a chiller (haven't tried) but the filter-drier is unidirectional mounted for water heating.
Thanks for any ideas.


texts: Deciding on number of tubes to construct a heat exchanger

texts:
I’m a chemical engineering student and I’m learning about heat exchangers,I came across this question and had a doubt ,

Cold water is heated from 20 degree C to 85 degree C while hot process stream is cooled from 130 to 55. Overall heat transfer coefficient is $348 W/m^2 . DegreesC$ .

Surface area of each tube is 0.092$m^2$ , how many tubes would be required to construct this heat exchanger ?

Rate of heat transfer = 165800W

I calculated LMTD = 39.79

And I calculated the area , which is about 11.97$m^2$

Number of tubes = $11.97/0.092 = 130.4$ tubes.

In this case, I need 130.4 tubes . Do I round up to 131 or round down to 130? and why ?


texts: Glass bottle with a prolonged neck that continues into the inner space

texts:
Is it possible to create following two shapes from glass using currently known glass mass production techniques?
Shape #1: bottle with a prolonged neck that continues into the inner space, like this (cross section):
     | |
     | |
    /| |\
   / | | \
  /       \
 /         \
|           |
|           |
|           |
|           |
|___________|

Shape #2: same as shape #1 but with some circle holes in the the bottom, like this (cross section):
     | |
     | |
    /| |\
   / | | \
  /       \
 /         \
|           |
|           |
|           |
|           |
|   _  _____|

I'm not a mechanical engineer, but intuitively it feels like extra holes might make the production easier/possible...

If such shapes can be produced using current glass mass production approaches - how much more expensive (in %) such a bottle would be compared to the same sized bottle with regular bottle neck? Is it merely the extra cost of extra glass?

If it is impossible to create such shapes in one step - can it be made in two steps? E.g.:

2.1 create two halves of the shape (cut in the middle as on the above picture) and press them together into one shape as long as they are still hot;
2.2 create the bottle (without bottleneck) and the bottleneck separately and then press them together into one shape as long as they are still hot.
I first thought it were impossible, but then I saw this:
http://www.sygmall.com/en/5021000-kitchenware/14284-creative-double-bottleneck-oil-bottle.html
which seems to be a more complex shape and that made me doubt...


texts: How do I mechanically convert 200 steps into 360 discreet degrees?

texts:
I have a Nema 17 stepper motor that does 200 steps per revolution, or 400 800 and 1600 micro-steps if in micro-stepping mode for convenience sake I would like to somehow translate the 200 steps into 360 steps. What gear ratio / micro stepper configuration do I need to convert 200 steps to 360 steps.

Update

If anyone wants an easy way to create an involute spur gear, I found this page, converted the to DXF in illustrator then extruded in Rhino!
http://geargenerator.com/


texts:
I'm planning to build a mini backpack gravity kart. Uphill by foot bringing kart in back, downhill driving offroad that kart.
So, it must be small, light, "flat" (similar to a skateboard).
I'm thinking about steer. My two choiches are:
- normal front wheel steering, driven by lateral lever instead of steering wheel
- fixed wheel, steering made by braking left or right brake

I prefer the second solution because of simplicity, the kart could be very minimal.
but I never seen kart like that, what are the cons of that steering system?


texts: What is the equivalent of a capacitor in pneumatics?

texts:
I am building a desoldering gun. While the pump I am using provides decent suction, I would like a quick powerful vacuum burst to prevent the solder from solidifying in the nozzle rather than in the chamber.

I figure there must be the equivalent of a capacitor where a vacuum is held in reserve and released when needed. Does such a device exist? If so what is it called. Finally, are they available in small sizes, say the size of a tennis ball?


texts: What is the top limit for torque per diameter ratio for electrical rotation mechanism working in a tube?

texts:
Use case: industrial stop valve placed in an another pipe welded perpendicularly making a T-shape.

To make the question more specific let's consider 50mm inner diameter pipe for the linear actuator inside with electric motor and some gear drive (most probably needed).
The achieved torque should be continuously sustainable through the life-time of 20,000 hours. Rotation speed and power are of secondary importance while length should be reasonable, let's say: 1000mm.

I considered planetary, cycloidal, harmonic drives, magnetic gears and various direct drive motors with an option to stack them on the same shaft. The top value I found is achievable with electric motor and planetary gearbox: ~40Nm.

Can it be significantly higher, say 100Nm and what is the limit?


texts: Why is it unwise to choose cylindrical horizontal beam

texts: I heard that it is unwise to choose cylindrical horizontal beam. My question is why?


texts: Calculating the bending moment ($M$) of a beam as it relates to stress ($σ$) and strain ($ε$)?

texts:
I am trying to learn how to work out the bending moment for progressively complex systems to model a beam. I am assuming only one axis of motion (transverse = $y$).
For the basic equations of motion, $σ$ represents stress and $ε$ represents strain in terms of longitudinal stretch of each segment of the beam resulting from transverse ($y$) displacement.
(1) Simple Spring
If you model the beam as a simple spring for which $E$ (Young's Modulus) is the spring constant and $I$ is the cross-sectional moment of inertia, according to this reference, you get an equation of motion and bending moment of:
$σ = Eε$
$M = EIy_{xx}$
According to Wikipedia though, it's the following, so I'm not sure about signs:
$M = -EIy_{xx}$
(2) Damped Spring

If you add a damper to the bar simulation, according to this reference, you get the following:
$σ= Eϵ-ηε_t$
$M=-EIy_{xx}-Iηy_{xxt}$
Question
I am having trouble understanding how to extrapolate these principles to increasingly complex beam models.
Three Element System:
For example, in a three element model you can have:

$σ + \frac{η}{E_2}\dot{σ} = E_1ε + \frac{η(E_1+E_2)}{E_2}\dot{ε}$
Four Element System:
Or in a four element model you might have:

$σ + (\frac{η_1}{E_1} + \frac{η_2}{E_2})\dot{σ} + \frac{η_1η_2}{E_1E_2}\ddot{σ} = (η_1+η_2)\dot{ε} + \frac{η_1η_2(E_1+E_2)}{E_1E_2}\ddot{ε}$
How would you similarly go about expressing the bending moment with these types of more complex models?
My Guess
From looking at the two known equations above, except for the signs which I don't know how to anticipate, it looks like the equation for the bending moment can be defined somewhat as follows.
Two Element System:
$σ= Eε-η\dot{ε}$
$M=-EIy_{xx}-Iηy_{xxt}$
$M = -I(σ_{bend})$ (which roughly matches this ref)
$σ_{bend}= Eε_{bend}-η\dot{ε}_{bend}$
$ϵ_{bend} = y_{xx}$
Three Element System:
If so then for the three element system we might have:
$σ_{bend} + \frac{η}{E_2}\dot{σ_{bend}} = E_1ε_{bend} + \frac{η(E_1+E_2)}{E_2}\dot{ε_{bend}}$
$M = E_1Iy_{xx} + I\frac{η(E_1+E_2)}{E_2}y_{xxt} - \frac{η}{E_2}\dot{M}$
Is this the right idea? What do you do with signs here? It seems like the signs don't match to the equations of motion in the two given examples so I'm not sure if there's something more to be done with them.
Thanks for any help.


texts: Can a car's Electronic Stability Control (ESC) operate using electromagnetic braking?

texts:
The Wikipedia article for ESC describes the process as using hydraulic anti-lock brakes.

However, is it possible for electromagnetic braking to be used instead, with an electic motor/generator in each wheel?

I would expect this configuration to reduce the components needed for ESC (especially for electic cars), as well as enabling ESC for smaller vehicles (where I've heard it's hard to fit), while lowering response time.

So can ESC be implemented using electromagnetic braking from motors? If not, why? If it can, than why isn't it commonly used? Has it ever been attempted?


texts: How do locks for shoe lockers in Sentōs work?

texts:
(Please move this question to the appropriate exchange site if it is not this one; I originally posted this here, and a comment suggested that I move it here.)

In Danganronpa it appears that the lock at 9:27 in this video has a weird shape, and I cannot figure out how it might work.  Using Google, it appears that these are locks for shoe lockers in Sentōs, but I haven't been able to find a picture showing how they work.

A comment on the original place I put this question pointed me to this website, which says "The wooden key was interesting as it had grooves in it. If the pattern of the grooves match the pins in the lock then the key will go all the way down and trip the catch on the lock."  However, this seems a little suspicious because then it looks like you could open any lock by using a small stick.

After some more googling I found this auction which has pictures of inside of the lock (and also pictures of the key, which are different from those in the game; I am now guessing that the key shape in the game probably does not exist, but only because I cannot come up with a lock mechanism for it).  It does not explain how it works, though, and I am still interested in this.

How do they work?  More specifically,

Is the picture of the lock in the video realistic?
Is the description from that website accurate, and if not then how does it work?


texts: How EnB will inform to UE about incoming call in RRC connected state in LTE?

texts:
Generally if UE is in RRC Idle state, ENB will inform to UE via paging message about CS domain i.e incoming call.

My doubt is in LTE, when UE is in RRC Connected State, how Network(EnB) will notify to UE about incoming MT call ? In which Information element(IE) or message ?

Any help will be appreciated !!


texts: Tower crane with a cabin on ground level

texts:
Pardon me for kind of a stupid question, but I keep wondering. Traditionally, tower cranes' cabins are located at the top of the tower. I can understand why it have been necessary up to ~1990s, when it was the only way for a human to get reliable real-time visuals of what's going on. But today, with the advent of camera and monitor technologies (when cameras and LCD monitors are dirt-cheap), what is the exact problem with moving the crane operator's cabin to the ground level and make all visuals using a system of cameras?

Searching the Internet for the answer, I've encountered quite a few of companies that produce camera systems for cranes, but it looks like that majority of them propose to use cameras as additional viewing aids (i.e. "view from the hook", "view from the pulley", etc), but not replacing the sky cabin.

From kind of delitant point of view, having a cabin up high actually poses a bunch of problems, i.e.:

safety: fallen crane = very real chance of death or major injuries
comfort: it's very hard to maintain proper air conditioning and temperatures up high
time consumption: a way up to the work place takes 20 minutes for an operator, and takes lots of physical endurance to do so

Is it really feasible in modern world to continue using sky cabins on the tower cranes? Am I missing something obvious, or is it just very persistent tradition that nobody dares to break?


texts:
I am curious as to how pump salad spinners work: not in terms of how they spin and use centripetal forces to get rid of water.

I mean in terms of how the pump itself works. How does the 2D motion of pushing the pump get converted into the rotation and spinning of the salad spinner itself? Are there gears involved? I would like to know the underlying mechanism of it.


texts: Can my total dynamic head (TDH) be more than the "Rated Head" on the pump?

texts:
I have just received a recommendation to use a pump with a "Rated Flow" of 1cu.m/h and a "Rated Head" of 91m. I am realizing I am actually not familiar with these two terms (Rated Flow and Head).

My total dynamic head is a little more than the "Rated Head" (It's 110m), and I intend to pump at a flow rate a little less that the "Rated Flow" (I intend to pump at 0.5cu.m). Both these values--though not very efficient--fall well-within the constraints of the pumping curve. Should I be worried by the "Rated" labels? What exactly do they signify?


texts:
In the picture above we have the expression of stretch with respect to strain tensor, but in case of infinitesimal strain theory, we take stretch equal to 1+T.E.T
I don't understand why by taking Taylor series expansion, the answer would be 1+ x, with x= T.E.T, with my calculation, the first derivative is 1/radical(1+2x) not x


texts:
I need to design a water to air heat exchanger with a blower for a small greenhouse as an engineering project. There aren't much design specifications - only that it must maintain a temperature of between 15 and 25 degrees celsius during winter nights (-4 degrees celsius approx) the material of the box it will be placed in is polycarbonate with dimensions 1x1x1,5m.

I am looking for a good source or a textbook to work from for the design of the heat exchanger as well as  determining all the variables. it is a semester project and have just started with the design, if somebody could guide me in a direction I would appreciate the help.


texts: Relations/Equations to do with light diffusing materials

texts:
I recently started as designer at a making custom signage (small signs viewed up close, so there are lots of sizing limitations) and none of the other designers have any solid rules to rely on for building these signs when they are light through light diffusing acrylic. Often signs will look patchy, with individual LED's being distinguishable through the acrylic, due to the variation in lighting, but not the consistency of the acrylic.

Are there any established equations/relationships between the light diffusing properties of a material and the resulting scattering and intensity of the light? How can I measure or estimate the light diffusing properties?
The variables I can currently estimate or measure are: light intensity of the LED's, their spacing, thickness of material its shining through and the resulting light intensity, as well as, grading the resulting light pattern.

One of the issues we face is that our supplier does not send a consistent opacity of light diffusing acrylic, so a thickness that would normally look fine, will now either not let enough light through, or it will look patchy (because of point source LED's.) To be clear, the variation is batch to batch, not on the same sheet.

  Ideally, these relations/equations would help me understand the
  difference in thicknesses required. Any starting point would be helpful.


texts: I was looking at laminar flow filters to aid in my mycology work I'm doing. Most filters use an aluminum extrusion with fins. I figured the options out there are pretty expensive for what you get and figured I could just 3d print my own straightener. Question is what shape do I use? I have seen honeycomb used and would be an easy option, but it really got me thinking about what shape would be optimal for this. We all know that when streamlining a positive body that a teardrop is close to optimal, but putting teardrops in a grid would yield a weird negative shape in the pattern. Any thoughts or ideas on this would be greatly appreciated, I plan on open sourcing the final design. Thanks


texts:
I would like to build a clock where the face rotates. Imagine a standard clock, but instead of hands pointing to the hour, there would be a rotating face plate with a small window, as it were. The face plate would obscure everything except the current hour, which would be visible through the window. If it makes any difference, I need it to be a 24-hour, not a 12-hour, clock.

I have considered buying a 24-hour high-torque clock movement (because I'm not interested in building the actual gears, etc.), but I get the impression that it would be hard to attach anything to it other than standardized clock hands. I could try to glue the face plate onto the hour hand, but I don't know if that would hold effectively.

Any ideas?

Thank you. (Also, if this isn't the right forum, please send me in the right direction.)


texts:
I am looking for a away I can convert the horizontal rotation into vertical, typically we use bevel gear for such thing.
But I am using a SG90 servo motor for which I am struggling to get the correct gears to achieve my requirement.

I am not sure is there is any other way I can do this using the SG90 servo motor. I am looking for something which I can 3D print if nothing is readily available.


texts:
In historical or modern buildings, flat ceilings are typically made of concrete, wood, metal, solid bedrock (for carved tunnels), or generally a material that can withstand pushing forces (pressure) and pulling forces (tension).

A ceiling made from bricks / masonry would typically be vault-shaped, because otherwise it would crash. This is what we find in a lot of historic buildings.

I can so far only remember flat brick ceilings from imaginary buildings e.g. in a roleplaying context or in video games. But I wonder if there are cases where such a thing can be realistic.

In theory, I can imagine two ways to achieve a flat ceiling with masonry:

By using very good cement, so the entire thing would behave like one solid piece of rock or concrete.
By imitating a vault, in a way similar to how a Fresnel lens imitates a regular concave lens:
Use slightly V-shaped bricks, and stack them like this, more or less: `\\\|||///``.

My question is:

Can this ever work?
Does this technique have a name?
How far can you go with this, what are the limitations?
Are there historical examples?


texts:
Complete amateur here with a product idea and a need to find out whether it can work in theory.

I need to push a lever vertically down through 90 degrees and have a lateral arm swing horizontally through 180 degrees (and with greater speed than lever one going down).

Is this possible and how should I describe it/specify it for to a prototyping company?

Any advice gratefully received!

PS: Apologies, gentlemen. Here's a sort of diagram.


texts:
I'm trying to bond semiconductor samples (Si and Ge) area ~1-2cm^2 to
fiberglass printed circuit board (PCB)
We use West system marine epoxy for other things. 105 resin 209 hardener (long cure time.)
So that's what I used. (mixed at standard ratio)

I wanted a controlled thickness for electrical isolation.
So I also tried adding some fillers to the epoxy.
Glass beads (9.8 mil .. kinda thick IMO, sprinkled on surface.)
Alumina oxide, 240 grit. (~1 part Al2O3 to 2 parts epoxy, by weight.)
All samples (but one Ge) were from an old piece of Si wafer.
Samples and pcb were cleaned in acetone,
and scrubbed with cotton tipped applicator.
Epoxy mixed. applied and samples pushed into place.

And allowed to cure for 24 hours.

They where then dunked into liquid nitrogen (LN2).
After a few dunks, warming in room air,
the samples glued with Al2O3 filler had fallen off.

After more dunking the samples held with raw epoxy and beads fell off.
A few more tortures that also included warming more rapidly
with a heat gun.  And I'd lost everything but the Ge sample.

As a final abuse the Ge sample was taken from LN2 and placed into
a cup of warm water, several times.  It remained attached.

All the bonds failed at the Si interface, and the epoxy remained attached
to the PCB  (except for the glass beads, that failed everywhere.)

So what's wrong?

My first thought was about the coefficients of thermal expansion (CTE) Here's a link to some values, Si is very low.
The pcb is ~ 12-14 ppm.

I then thought about cleaning.  The old Si samples may have all sorts of hand grease.

The final difference is that the Si samples are polished on both sides,
while the Ge was only onthe top... the bottom was rough.

wow, that was a long question, (sorry)
I made up a new batch of samples today to try and answer those questions.  They will cure over the weekend.

I also wonder if I need a different epoxy?  The West 105 stays somewhat pliable.
I don't know if that's a good or bad thing.