texts: Why is strain also normalized to the parameters of engineering strain?

texts:
I get that you normalize stress to engineering stress, so that it is independent of the cross sectional area. This means you can calculate (roughly) the stress needed to elongate the specimen to the degree you want. But why normalize the strain aswell?

I would have thought that the orginal length of the specimen does not matter. Lets say you want to make the specimen 2 mm bigger, then I would have thought that you would need the same engineering stress no matter how long the specimen is. Thus that elongation is only dependant on cross sectional area and load.

For example you have a specimen, with orginal length, of 60 mm and 100 mm and then you want (l-lo) to be 2 mm. I would have thought that it would take same amount of engineering stress. And that a 2% strain would lead to different stresses needed, since in one this means an elongation of 1.2 mm and with the other an elongation of 2 mm.

Does this mean that the length of a specimen also determines how 'easily' a specimen elongates?
That it more difficult to elongate a 100 mm to 102 mm than a 60 to 62 mm. Because the tensile stress-strain curve implies that to elongate a 60 mm specimen to 61.2 takes same amount of stress as elongating a specimen to 62 mm.

If the length of the specimen relates to how easily you can elongate it, does this then also explain why the gauge length should be specified when giving the percent elongation (%EL) when talking about ductility? Because most of the plastic deformation is at the neck, so not uniform and thus independant of the length of the specimen orginally.

So before necking the elongation is dependant of orginal length and engineering stress and after necking is independant of orginal length?


texts: What degree of open span/narrow support can rigid PIR thermal insulating foam sustain under the short term load of setting concrete?

texts:
I've found data related to the deformation and shear performance of typical PIR (polyisocyanurate) foams such as Celotex/Kingspan, but I'm not sure how to use these figures in my own situation.

I am refitting a solid floor building in the UK. The existing oversite slab is intact and uncracked, but never had insulation. So the plan is to lay appropriate DPM/VCL, about 100-120mm Celotex (or equivalent), lay A242 mesh, and pour about 120 - 130mm of either dense concrete or screed. It won't be bearing any load other than usual UK floors (~ 2kN/m^2), and the area is <= 4 x 6 m.

Unfortunately due to the way the original slab was laid and the topology of the immediate area, there is a slight chance that moisture could seep under these, above the original slab. Realistically it's unlikely/no evidence, but it is possible, so I'd like to rest the Celotex/DPM/VCL layers on some kind of front-to-back orientedbattening, and provide airbricks, to create a shallow ventilated void between the original oversite slab and the new flooring.

If this is done, the batten widths and spacing would be quite crucial - if the battens are too narrow, or too widely spaced, the Celotex will deform excessively or even shear in the ~< 24 hours that the concrete/screed is fluid. (After it's set, of course, there will be no deformation beyond the equilibrium it was at when it set.)

I can imagine that narrow battens might have a limit on safe spacing different from wider battens, as shear and deformation are different phenomena. So there might be a range of "safe limit" combinations.

But I can't find anywhere, the appropriate formulae and safety factors that should be used, to calculate the limits of batten width/spacing beyond which shear and deformation would become issues.


texts: Big Beam LVL or Glu Lam load capacity to support a gymnast

texts:
I need help knowing if I am selecting the correct wood beam.

The load will be all near the center and a 250 pound man will be doing pull ups on it. I would estimate a 1,000 pound dynamic load to be safe.

I am looking at a 3.5in x 12 in x 20ft Big Beam (LP makes it, it's an LVL). It will only be supported at the ends.

How can I calculate the correct beam size? Thanks.


texts: Most of the RF receivers have a clock for synchronization. Are there RF receivers which do not need clock? If yes,  how do they work?


texts: Meaning of "female eye" in a list of parts

texts:
A fellow translator is translating a list of parts into Russian, and can't understand the meaning of "female eye". Here's the table:

Maybe someone here could come up with some ideas about the possible meaning of this "female eye".


texts: System Identification Toolbox - How is the quality of the model output calculated?

texts: I'm searching for the calculation of the quality of the estimated model output compared to the measured data. I'm working with the System Identification Toolbox. You can see an example here http://de.mathworks.com/help/ident/ref/compare.html at the first graph. Is the percentage calculated with an integral or any other method?


texts: Is it feasible to mount a 40kg shelf on a rotating and sliding pole?

texts:
I want to build a shelf that can I can place near a wall and still be able to rotate it around 180 degrees. I therefore would want to mount the shelf on a rotating pole and to reduce the needed distance to the wall would have a sliding mechanism that lets me slide the shelf off-center to one side (see the following sketch).

I built the following prototype out or cardboard to verify the idea.

So given I can get the center pole to be stable enough (for example by attaching it to the wall) is it feasible to have such a sliding mechanism that can hold a weight of around 40kg in the off-center position and still slide? Am I missing any other critical problems here? Any hints for similar existing parts or mechanisms would be greatly appreciated.


texts: How to water seal a metal plate into the wall of a plastic water tank?

texts:
I have a 10 x 10cm square plate of metal I would like to insert into a hole in the wall of plastic water tank (cube shape), I'm planning on 3D printing the tank itself (only 1-2 litres).

What would be the best design to stop water from leaking between the plate and the plastic body?

So far all I can think of is to make the hole in the tank smaller (i.e. 8 x 8cm) than the metal sheet and perhaps using a sealant and affix it using screws possibly, but as there's live wiring around it I need to be sure it has the best possible seal. Any design ideas would be much appreciated


texts: Help me find a paper/textbook on axial compressor in turboshaft engine

texts: I'm trying to calculate the values of pressure, temp, speed and density of air going through an axial compressor (12-stage) a helicopter. I've read a few bachelors' thesis and papers but wasn't able to find anything particularly helpful for this task. Can anyone offer advice or, ideally, a paper/textbook with relevant information? Thanks in advance.


texts:
For a National Board Exam Review:

  Calculate the Reynold's Number, $Re$ for water at 20 °C flowing in an open
  channel. The water flowing at a volumetric rate of 200 gal/sec. The
  channel has a height of 4 ft and a width of 8 ft. At this temperature,
  water has a kinetic viscosity of 1.104*10^-5 ft^2/s

The given answer is 600,000. I have tried to solve the problem like this:

$${ D_{eq} = \frac{2*4*8}{4+8} = \frac{16}{3} }$$

$${ V = \frac{Q}{A} = \frac{200 \frac{gal}{sec} * \frac{1ft^3}{7.48gal}}{4.8 ft}  = 5.570409982 \frac{ft}{s}}$$

$${ Re = \frac{VD}{\mu_k} = \frac{ 5.570409982 \frac{ft}{s} \times \frac{16}{3} ft }{ 1.104\times 10^-5 \frac{ft^2}{sec} }  = 2691019.315 }$$

Am I using the wrong equivalent diameter? Why am I not getting the correct answer?


texts: Is there any way to improve the strength of simple at-home aluminum/copper/brass castings (sand-casting hammers)

texts:
I'm just getting-into melting-down cans to make aluminum-based slingshots, hammers and the like.  In my ignorance I didn't realize that copper/brass were also things that I could process which has left me hoping to learn:

should I be looking to make an alloy or using 1 metal and, if 1, which would be optimal?
are there any "additional treatments", such as quickly cooling the hot metal-product into a block of ice, or perhaps having the casting box on a vibrating-panel to further 'settle' things?  All I know to do for increased-strength is to make as-clean-as-possible a mix IE scoop as much slag/skim from the top of the molten metal as possible!
is there enough variance among aluminum (or non-alloy metal products) to make it worthwhile to source specific-types, IE maybe aluminum from a car-engine part will make a stronger/better ingot than one made from a heap of aluminum cans?

A hammer and a sling-shot are my 1st goals with this, so while I'm not the best at knowing 'strength-types' I don't think "tensile" strength will be as important as yield-strength or compressive-strength but not sure, if I've gotta choose between optimizing for the slingshot OR the hammer, the hammer is far more important (and I'm not interested in working with lead to do this!)

Thanks a ton for any insight on this am in the middle of diving-in, learning I could do this at-home was truly a christmas-present LOL :)


texts: Anomaly in viscous force - vs - velocity relationships

texts:
It is well known that the viscous force (or drag force) is directionally proportional to the square of the velocity in many cases. For example the torque on motors driving a fan-type load (pump) is proportional (approximately) to the square of the rotational speed. The air drag force on a car or a plane has a similar relation between linear drag force and straight line velocity.

However in a mass-spring-damper system common in mechanics and control theory, the viscous force F is proportional to the velocity itself, as in the relation is F = -Bv, where v is the velocity and B is the viscous damping constant.

What is the reason for such an anomaly? Are they for different conditions/situations? If so, how? Or am I missing something entirely here?


texts: Deflection and stress in a freely rotating beam

texts: How do I calculate the deflection and stress of a beam that is rotating freely (for example in space) when a moment is being applied to it, for example by rocket motors at the ends of the beam?


texts: Switching transient of a transformer on no load

texts: Is there any equation to calculate the switching transient of a power Transformer? How much it will be for a 30MVA transformer (33/11kV) at no load?


texts: Buckingham-Pi Dimensional Analysis when there is a non-dimensional parameter: How is it accounted for?

texts:
I am in the process of completing a design project for my fluids course in which Buckingham-Pi /Dimensional Analysis is needed to find the optimal parameters needed to achieve a rotational rate of 120 rpm.

So the question at hand is that the rotational rate of an anemometer is a function of density, viscosity, wind speed, rod length, sphere diameter, rod diameter, and number of spheres.

[Omega = f(rho,mu,Ds,Dr,Lr,N,U)] and from that we need to non-dimensionalize the parameters and get Pi groups in which we analyze and determine the optimal dimensions required to achieve a rotational rate of 120 rpm.*

I have met with the professor regarding the project and I was told that the dependent variable (group with the omega) is to be plotted on the y axis against all other groups (independent Pi groups on the x axis). He also mentioned that rho, and mu are parameters because the same results should occur regardless of the fluid used in testing.

**I have worked out the problem and have achieved the Pi Groups and even plotted them; but I do not know how to account for the the non-dimensional value N( # of spheres); or what needs to be done next. **

All work for Pi-Groups

Graphs/Excel Stuff

I chose random ranges that fit within the spec so is that even correct to get some data points to graph so can you do that?

(All pi groups which use rho and mu, are plugged in as  the values at the top since I'm not sure what range to use for them since it can be any fluid, so not sure if my approach is even remotely correct?).

NOTE : Pi (4) when plotted was taken to be the Reynolds's # which is the inverse of the computed Pi group (I mention this on excel spreadsheet).

*First graph is dependent pi group (5) against all other pi groups.

*Second is with the avg rotational rate of 120 rpm as the parameter for the dependent pi group (5).

*Third is just wind speed Pi group (4) against omega dependent pi group (5).

Have a look and let me know if I'm doing something wrong/right.

Any and all help is appreciated :)


texts: Does this exist - 'screwdriver gun' with cartridge to automatically load new screws?

texts:
I'm looking to do some really repetitive assembly that involves screw-driving a ton of M2 screws over and over again into threaded holes to put two plastic pieces together.

Because it's a high volume job, I want to find the right tool. I thought it would be so awesome if there was a one handed electric screwdriver of some sort that would dispense the M2 screw as I hold the button, then once it's in the threaded hole/fully dispensed a new one pops out of the gun, and I can move onto the next hole, etc.

Found some related stuff for nails obviously, which is good for woodworking but not exactly my application:

https://www.aliexpress.com/item/Woodworking-decoration-chain-with-screw-gun-professional-automatic-screw-driver-decorating-tools-220V-780W-1PC/32832683890.html

Could anyone confirm if what I'm looking for exists, and point me to some example products? Also down to modify similar existing tools to suit my application if need be. Thanks!


texts:
The storage coefficient (s) for artesian basin can be determined by the following equation (Theis equation):

$$s=\frac{Q}{4\pi T}\int_{\frac{r^2S}{4Tt}}^\infty\frac{e^{-u}}{u}du$$

Does this equation work for confined aquifers with an arbitrary t or there are some limits for time (t) to be used in this equation?


texts: Are front wheel drive vehicles inherently flawed?

texts:
Perhaps similar to reasons for having a better braking system at the front of a vehicle as when braking, the weight shifts to the front, creating a greater downward force on the front wheels that further increases the traction.

When accelerating, the converse seems to be true (?), the weight must shift to the rear, pushing down on the rear wheels. Surely this

reduces the traction in general for the front wheels when accelerating
Would get only worse the greater the acceleration. I imagine with a rear wheel drive car, the traction would increase with greater acceleration.

I personally haven't driven a rear wheel car yet. However, it feels very uneasy when moving off in a front wheel drive where the weight seems to offload from the front and seem to make the wheels more likely to slip.

Aside from historical reasons, what are some good reasons that FWD cars are widely used today?


texts: Building a custom indirect actuator, any thoughts?

texts:
I’m trying to create a custom indirect actuator, that is controlled by a microcontroller, for a custom robotics project.
I have selected motor and gears (according to Fd = W = T2*pi) so that the actuator should be able to push with around 46N of force (10N over what I require to make up for any losses or forces, such as friction, efficiencies of gears, etc).
I want to be able to tell the instantaneous stroke of the actuator and the force it is exerting at any time.
But the solution I'm hoping for should be cheap and easy to implement, as we are hoping to send our finished robotics design into mass production.
My initial approach: was to use a rudimentary potentiometer/voltage divider. Connecting the wiper to the microcontroller will allow me to see the position of the wiper with respect to the conductive strip. Could I use this potentiometer to also calculate dynamic force?
If I constantly poll the wiper while the actuator is active, I could get two position values and the time between them. This would give me an instantaneous velocity value. Doing the same thing again would give me a second value which I could use to find the instantaneous acceleration.
The problem with this is the mass. I have read that actuators have an “effective mass/weight” – a value that is usually incorporated somehow in the datasheet. However, my actuator would be a custom design therefore there is no datasheet accessible for this.
Can anyone please help me figure out the effective mass/weight of my actuator? Or if you have any other approach please do let me know.
Any thoughts would be much appreciated. Thank you for reading.


texts: What material should I use to store molten metal?

texts:
I'm performing an experiment based on slag corrosion behavior of the refractory material. I need to store molten metal at $\approx$ 1600-1700 K for that.

Specifically, I'm working on slag corrosion and penetration behaviour of refractory (MgO-MgAl2O4). I'm going to use immersion method, so in this method "Cylindrical or square pillar shaped samples are held in the corrosive liquid(slag) in a furnace. Immersion time, temperature and atmosphere can be varied" So, for storing slag+molten metal, I need to use a crucible.

Please suggest what would be the best choice of material for crucible.
What is a crucible material?


texts: How can I calculate the force required to bend a 10 mm thick plate in a rolling machine?

texts: We have a rolling machine with 3 rollers; the bottom has two rollers with diameters of 168 mm and one top roller with a diameter of 219 mm.  I want to calculate the required force to bend a 10 mm thick plate which is 2,500 mm wide.  The rolling machine is connected to a 10 HP motor with a gear box and the rollers have an rpm of 8.


texts: Window header sizing: total load on header

texts:
I have a flat roof (dead load = 20 psf, live load = 30 psf) spanning 11 feet with a 2 ft. overhang. I'm trying to calculate the total load in plf on the header marked as X.

Is this calculation correct:
TL = (DL + LL) × (11/2 + 2)
= (20 + 30) × 7.5
= 375 plf


texts:
Is it acceptable for fire-rated gypsum board to be stored outdoor (covered parking area) in a humid city?
Is it acceptable to be damaged at edges and sides?
Does it need spacers when stored flat on each others?


texts: Confusion in the Lagrangian description of Material Surface in Continuum Mechanics

texts:
In Lagrangian or Material description, the physical properties are
described in terms of the material coordinates and time. It focuses on
what is occurring at a fixed material point (or particle) labeled by
its material coordinates as time progresses.

My confusion:  But the material surface (defined below) is written in terms of material coordinates only in case of the reference configuration and there is no time parameter. I understand that in reference configuration it is logical to not be dependent on time, but in the definition of material description, time is supposed to be included.

In Eulerian or Spatial description, the physical properties are
described in terms of the spatial coordinates and time. It focuses at
a fixed point in space as time progresses.
A material surface is a mobile surface in the space constituted
always by the same particles.
In the reference configuration, the material surface is defined
in terms of the material coordinates as   f(X,Y,Z) = 0, where the set
of particles (material points) belonging to the surface are the same
at all   times.
In the spatial description, it is defined as f(x,y,z,t) = 0. The
set of spatial points belonging to the   surface depend on time, and
the material surface moves in space.


texts: How do I calculate the additional energy required to pump fluid through a restriction?

texts:
Let's say I have a pump pushing fluid through a 250 ft pipe, 1.5'' diameter, at a rate of 20 gallons per minute. I would like to calculate the delta in energy required to pump this fluid with and without a restriction at the end of the 250 ft line. The restriction results in 0.01 psi pressure drop.

What equation is needed to calculate this energy?

Update:

Based on comments below, I was able to figure this out. First, I need to convert my $\Delta P$ to pressure head using the following formula:

$\Delta P = \rho_{fluid} * g * h$

where

$g =\text{ acceleration due to gravity}$

$h =\text{ pressure head}$

This formula itself is a simplified form of what can be found here

$P_2 - P_1 = \gamma (h_2 - h_1)$

where

$\gamma = \rho_{fluid} * g$

This gives us all the ammunition we need with the help of the pump power equation found here

$P_{\text{pump_power}} = q * \rho_{fluid} * g * h$

where

$q =\text{ fluid flow, volume per time}$

If you plug in our $\Delta P$ formula from above (you have to rearrange to get the h on it's own), you get the following:

$P_{\text{pump_power}} = q*\rho_{fluid}*g*\frac{\Delta P}{\rho_{fluid} * g}$

which, with handy cancellations, leads to:

$P_{\text{pump_power}} = q * \Delta P$

Nice! Dimensionnally, if your flow is in gallon per minute (which it was for me) you'll want to convert to cubic inches per second - this way, if your $\Delta P$ is in psi (which again, mine was) some of your inches will cancel out. You'll then have to convert BACK to feet from inches, but then you can easily go from $\frac{\text{ft-lb}}{s}$ to horsepower or kilowatts or whatever you want.


texts:
Fluid with mdot = 0.025 kg/s and Tm,i = 25oC is flowing through a long metal
cylindrical tube where the diameter is 0.032 m and the length is 2 m. The surface of the tube is heated with a heat flux of 3000x^2 W/m2.


texts: Motorcycle Engine Vibration - Difference between left and right side

texts:
I measured the vibration (jerk) on the left and right side of different motorcycles. I tested different engine types: Boxer engine, 3 cylinder, and V4. I measured the vibration on the same route, while driving for approx 30 minutes. I take the average jerk for every measurement. For every measurement the jerk on the right side of the motorcycle is higher than on the left side. I switched my sensors, since I thought this would be due to my sensors, but the results are the same. The difference is about 5-10%.

I'd thought that the vibration would be more or less symmetrical, but it seems to be different.

Could you think of a reason why the vibration differs?

Edit

Due to comments and answers here is some additional information:

I ran the experiment with different participants on different motorcycles
It seems that the difference of jerk occurred while standing, as well as driving (I cannot measure new data right now - but evaluated my existing datasets)
This is the route I used
The motorcycles used in this experiment are regular ones you can buy at any retailer


texts: What would be the best way to calculate velocity of gas from a three phase separator? I know that operating temperature is 75F, pressure 1000 psia, pipe diameter 20 inch, and pipe length to the point where velocity needs to be known is 45 inch. I'm having some trouble determining pressure drop over such a small distance and was wondering if there is a better way I could work this out.


texts: What is the manufacturing method used to make aluminium C channel

texts: I don't know how this is made and I don't know the name of the method to search for it to learn more.


texts:
For a while, I was curious as to what the firing orders for inline 7 and inline 9 engines were. I was able to find them in datasheets like this one, which is a project planning guide for the MAN 35/44 four-stroke medium-speed Diesel engine. However, upon examining the sequences I was surprised to see that the inline 6, inline 8, and inline 10 versions of this engine fire all cylinders on one half, then all cylinders on the other. For example, the inline 8 version has a firing order of 1-3-2-5-8-6-7-4, as opposed to a more traditional 1-6-2-5-8-3-7-4 firing order, and the inline-10 version fires 2-3-4-1-5-9-8-7-10-6. Why is this? It seems counterintuitive because I initially thought that the combustion-induced vibration would generate a significant rocking moment.
Another interesting thing is that the inline 6 and inline 7 versions fire front-to-back. 1-2-4-6-5-3 (instead of 1-5-3-6-2-4) and 1-3-5-7-6-4-2, respectively (assuming right-hand rotation, i.e. CCW at the rear end). I'm also curious as to why they do this.


texts: Shear stress derivative in polar/cylindrical coordinates

texts:
I have an embarrassing question that I just can't seem to figure out. I have a fracture problem that is infinitely easier to solve in cylindrical coordinates. The boundary conditions, however, are expressed in cartesian coordinates Namely, at a particular surface:$$  \sigma_{xz}=0 $$

I just cannot figure out how to represent this in cylindrical coordinates. We were given a similar example in class notes where the boundary condition is: $$\sigma_{yz}=0$$and, we were just told that, in cylindrical coordinates, this is equivalent to $$\mu \frac{1}{r}  \frac{\partial u_3}{\partial \theta}|_{\theta = \pi}=0 $$ where $\mu$ is the shear modulus of the material.

Can anyone point me in the right direction to obtain a similar statement for $\sigma_{xz}$, or, similarly, show me how the statement for $\sigma_{yz}$ was obtained? I get that $$\sigma_{xz}=\frac{\partial u_3}{\partial x_1} + \frac{\partial u_1}{\partial x_3}$$. There's a step in the change of variables that I'm missing.


texts: Is it possible to power bio-chips with blood sugar?

texts: Suppose I want to implant a bio-chip that consumes a lot of power into my body, for example, a full-fledged CPU, and I don't want to lug around a heavy battery like the ones used in pacemakers, is it possible to be in Rome and do as the Romans do, i.e. draw and utilize the sugar inside my blood as fuel, like a huge living and breathing body cell or an organ like the liver? Let's assume I can put this device where there's a lot of blood flow, say the jugular vein.


texts: What happens when you over torque a joint comprising of two different materials ? Will the corresponding material wear make the joint leak proof ?


texts: What shear strengthening schemes are available for an I beam?

texts: I would like to double the shear capacity of an I beam by welding some steel plates. What strengthening schemes are available? How would you define the shear area for the strengthening scheme proposed?


texts: How does one calculate the principial component stresses in an ellipsoidal tank due to head pressure?

texts:
I have parameterized the following common bulkhead tank, which has cylindrical walls (easy enough) and ellipsoidal bulkheads. The upper tank is full of a fluid of density 800 kg/m^3 and the lower is full of a fluid of density 1141 kg/m^3. Dimensions are in m, internal tank pressure (in green) is in 10s of kPa. I assume the shared bulkhead is perfectly rigid & no pressure is transmitted between tanks.

I am trying to calculate the principal stress components in the ellipsoidal bulkheads so that I can obtain full-body radial and longitudinal stress profiles. I can't find any information on how to do this, or (better yet) a generalized approach to determining surface stresses from pressure in non-spherical or non-cylindrical situations. I'm not an engineer by training & I have trouble knowing where to start with this. Help?


texts:
I know the current should be higher than 0.67 mA, because I know phones use current in the order of 1A. Also the charger is able to support up to 1A, it doesn't make sense that the charger would have such a superior current than the phone will draw.

I connected the multi-meter in series with the phone charger. That was done by stripping the red wire then cutting it, and then I held the 2 rods of the multi meter at both ends. The phone indicated that it was charging.

Since the phone indicated that it was charging and the battery was not full, I would take out the possibility that the phone disconnected the charger automatically. Also, I'm not sure about the idle state of the phone. The phone was turned on, and it has about a 3 inch screen. The battery is 1800 mAh. It still doesn't make sense that even in "idle" state it will draw such a small current while charging. Please let me know if I need to provide any more information about the measuring method, I didn't elaborate much on it because I thought it was simple, but I totally understand the possibility of a small mistake.

Here's another picture of the way of measurement, the reading is 0.45mA (from a different phone).


texts: What is the torque required to rotate a 450 lb., 35' long cylindrical load 90 degrees?

texts:
I need to create a simple machine to assist in rotating a cylindrical load, akin to a roll of carpet, from a horizontal position to vertical. The load weighs 450 pounds, which is distributed evenly along a 35 foot length. The machine would use a geared motor to rotate the load from the bottom of the cylinder.

I need two questions answered: 1 how much torque would the motor need to rotate the load, and 2 how heavy would the machine need to be to keep it from tipping over?

The machine would be assisted by human power, but I'd like to begin with the values needed for the machine to do all the work, then work my way backwards from there. Thanks!


texts:
For a National Board Exam Review:

  To what height will a barometer column rise if the atmospheric
  conditions are 13.9psia and 68F and the barometer fluid is mercury?

Answer 28.3in

I have encountered questions with irrelevant variables; I assume temperature is irrelevant here; so I try;

$${ P = \rho gh }$$
$${ 13.9\frac{lb}{in^2} = (13.6)(62.4 \frac{lb}{ft^3})(\frac{1ft}{12in})^3 (32.2\frac{ft}{s^2})(\frac{12in}{ft})h }$$

Im getting h = 0.073...

Why isn't my solution with the right answer?


texts: What is the best practice for ensuring the best possible connection between a battery cable and a battery terminal

texts: I've seen a number of opinions on conductive gels to ensure the best conductivity between battery terminals and battery cables. I'm interested in knowing an expert's opinion on the matter. I'm particularly interested in products that work well in harsh marine environments.


texts: How do you calculate the shear force on the screws that connect a door to a jamb via hinges

texts:
I'm trying to calculate the shear forces on hinge screws or bolts.  Here is a schematic of the door with the relevant values:

First, I took a free body diagram of the door and its hinges.  The calculations to find the forces are also shown below.  The forces consist of direct shear which is just the total weight divided by the number of bolts (4) and shear from torsion about the centroid of the bolt group.

Next, I took the free body diagram of just the door and calculated the forces a similar way:

Where I get confused is when I take the free body diagram of just a single hinge and sum the moments about its center of mass, I get a non-zero moment, which doesn't make sense to me.

Can someone explain to me where my approach or thinking is incorrect?


texts: Reinforced mesh at different distance in a concrete slab?

texts:
Trying to determine some information regarding the reinforced concrete slabs (reinforced with mesh) in an apartment, by looking through the holes in the middle of the rooms for lights, I've come across the following situation:

mesh located at 40 mm from the bottom of the ceiling in the middle of the room (visible in a plastic tube used for the light cables) and mesh located at 17 mm from the bottom of the ceiling nearer the edges.

What I'm seeing might be a different level of reinforcement?

The reinforcement is in 2 directions, but this is the information I can get from what I can see in existing holes.

Details:

the slab height is 140 mm


texts: How much aluminum does a HV, MV or LV transmission line use?

texts:
I have accurate statistics about the total length of high-voltage (110-400 kV), medium-voltage (1-70 kV) and low-voltage (0-1 kV) transmission lines in my country, and they are:

High-voltage: 22 500 km
Medium-voltage: 140 000 km
Low-voltage: 240 000 km

I would like to obtain an accurate estimate of how much aluminum is used for the transmission lines, but so far have failed to find any. I assume all lines have approximately 3 conductors due to the 3-phase system (in some cases there may be a fourth one, but 3 is a good approximation). Thus, to calculate the amount of aluminum, I would need an accurate estimate of conductor radius for high, medium and low voltage networks. Obviously, I cannot climb to reach the transmission line and measure its size by a vernier caliper!

One source I found is http://large.stanford.edu/courses/2010/ph240/harting1/ where a figure says that optimal radius (one that minimizes total costs) for a 2.25 GW 3-phase 765 kV line is 4 centimeters.

Thus, for a total length of 402 500 km of transmission lines, there would be 402500000*pi*0.04^2 = 2023186 square meters of aluminum, or by weight 2023186 m3 * 2700 kg/m3 = 5462602200 kg of aluminum, per phase. Three phases would require 16.4 million metric tons of aluminum. Per capita, that would be approximately 3 metric tons, or 3000 kg.

I feel that estimate may be a bit on the high side, because I found a statistic that about 25 kg of aluminum is used per year per capita. Thus, it would require 120 years of production to manufacture 3 metric tons of aluminum per capita. I don't believe that all lines, including the low-voltage (and presumably low-current) lines would use 4 cm radius conductors.

So, how much aluminum does a kilometer of high voltage (HV), medium voltage (MV) or low voltage (LV) transmission line use?


texts: Peltier Element - Segregation of the Hot/Cold

texts:
Referring to this diagram:

How does the height of the P and N components affect heat or cold generated on this thermoelectric element?

The idea I keep having is that it seems like the hot and cold sides are too close to each other. Would increasing the distance, via lengthening the height of the P and N components help to segregate the differential more or would this decrease the differential produced?


texts: Calculate the minimum motor power required to lift a human?

texts: I'm working on a Home-Made Automatic Grappling Hook of sorts, as a project for university. I've designed a Blueprint accounting for everything but (embarrassingly) the motor, as I'm unsure how to calculate the minimum motor power required to lift me. Is there an equation/simple solution to work this out?


texts: Would this be a practical way to convert tidal energy into electrical energy?

texts: Imagine a structure that is held above the water by pylons that are grounded on the ocean floor. In between these pylons is a pontoon that, when tides are rising holds and lifts a heavy weight. When the tide is falling the weight is supported by the structure, which can gradually let the weight down, and in doing so create electricity. Would this be a practical or even viable way to create electricity? Why or why not?


texts: What is the most common control method in Underfloor heating?

texts:
I am trying to research the common methods on an underfloor heating system that are available in the market.
I know there are usually,

On/Off control to control the flow of water into the pipe
Outdoor reset control to control the supply water temperature.

I think the most common is ON/OFF control (simple PI controller), but not sure about it.


texts: What is the difference between being UL recognized and being UL listed?

texts: A product can be UL recognized or UL listed. I understand that there is some difference between these two things, but I have never had a full and clear explanation of the difference. What is, in fact, the difference?


texts: Why does a vehicle under crosswind need corrective steering?

texts: If we consider a stationary car, a moderate wind hitting it broadside might tilt it a bit, but not move it otherwise. Now, consider the car moving perpendicular to that wind (e.g., driving straight forward). If the car were a rolling rigid body, it would still move straight ahead so long as the wind is not strong enough to overcome the friction between the tires and the road. However, experience says that it can sometimes require a significant steering input into the wind to keep the car moving straight ahead. What about the dynamics and architecture of a vehicle make it tend to steer itself when subjected to a crosswind?


texts: Minimum thicknesses of an elliptical cylinder pressure vessel

texts:
For pressure vessels in the shape of circular cylinders, we can use $\sigma_{hoop}=\frac{pr}{t}$ to find the minimum skin thickness by setting the hoop stress the maximum allowed value, and then solving for t. But, what about (the more complicated) elliptical cylinders?

Since ellipses have a semi-major axis and a semi-minor axis (as opposed to circles with just a single radius), it stands to reason that an elliptically cylindrical pressure vessel would have two minimum thickness (instead of just one). Is this correct? If so, how does one go about finding them?


texts: How to calculate if a motor is capable for a load?

texts:
I am trying to figure out if a motor I have is capable of spinning a wheel. Here is all of the information I have:

MOTOR: 190 g.cm min.

WHEEL: 26 cm diameter, weighs about 59 grams

I imagine that I would have to calculate the linear speed of the wheel in order to convert it to the same units that the motor torque is listed in. However, I don't know if I am doing it correctly or what the next step would be to solve this.


texts: Determining brushed DC motor inertia for modeling a motor

texts:
I'm making an model of a DC motor, and following the guide for measuring motor parameters:

I am having trouble measuring the motor's inertia, as the guide for this section is vague. This is a graph of my RPM over time (in milliseconds):

I know the graph is noisy, but its the best I can capture at the moment.
What I can't figure out is, to find the acceleration, what section of this graph is the linear region the guide refers to? It states

  The acceleration is therefore
  the change in velocity for the linear part of the exponential curve divided by the time
  elapsed for the detected rate of change in velocity

Another document, states this when saying how to measure motor inertia:

  The rotor inertia can be estimated from measurements of the mechanical time constant, kt
  ,
  and R. Alternatively, a constant current could be applied to the motor and the motor’s position differentiated
  twice to get acceleration α. Then the inertia can be estimated using the relation J = T /α = ktI/α. Note
  that constant current/torque/acceleration is not possible for long periods of time.
  (from Mystery Motor Data Sheet)

This implies there is another way to measure inertia using kt and R (which I know both of), but doesn't seem to state it. I would love to know what it is.


texts: Which is more durable in sandy desert conditions: electric motors or hydraulic pistons?

texts:
If we have a tracking system placed in a tough desert environment with occasional sandstorms and temperatures that go as high as 50C, which actuator would be better: a hydraulic piston or an electric motor with a gearbox?
My main concern is performance and resistance to conditions


texts: Are there general-purpose acoustic FFT sensors for plant diagnostics?

texts:
For the purpose of detecting a defect or failure in a machine, it is often practical to physically listen to any abnormal noises that a machine might be making, and even use a simple stopwatch to determine the frequency of these noises. This practice often gives clues as to what part of a machine is having problems.

For the purposes of detecting failure in a large plant, filled with many machines that might not have many sensors, one can also often isolate a machine with a problem by listening to abnormal ambient noises, and tracing them back.

Is there any sort of practice in which a microphone is placed at a certain location to detect the "ambient sound signature," and then is used as a sort of sensor for problems in plants? I can imagine a baseline being made with this microphone and then used as a reference for abnormal ambient noises, then paired with a monitoring camera to detect whether there is any explanation for non-regular noises.


texts: Unable to multiply the part along the same axis as rotate in SolidWorks

texts:
I am trying to multiply part with Linera Pattern and have each instance rotated by 180 degrees. Unfortunately, I can't specify the same axis for both rotation and copying. It says
The selection is not parallel to `Direction 1`

But how it can be non-parallel, if it is the very same axis?


texts: Steel Worm/Steel Wheel vs Steel Worm/Bronze Wheel

texts:
I have a question regarding worm drives, specifically double-enveloping types:

Do steel worm/steel wheel combinations last longer than steel worm/bronze wheel or steel worm/brass wheel combinations? If one were to use hardened tool steel for both the worm and wheel?
Are they also stronger than steel/bronze or steel/brass drives?
How much stronger are they?

Note: I know little about the underlying science behind gear design, just curious.


texts: Can someone tell me what the type of connector is??


texts:
I'm trying to figure out what angle to turn the front tires of my small robotic car (about a foot in length) so that it moves in a circle (on level ground) of radius $r$ (will be accommodating circles of different radii). In addition to being able to set my car's speed, it is equipped with a sensor which includes a gyroscope, accelerometer, and a magnetometer.

I'm just looking for some kind of equation that relates the car's tire angle, the car's speed, the circle's radius, and maybe the angular velocity readings from the gyroscope.

It has a car-like configuration.


texts: Modelling a system with multiple hysteresis behaviours and mutual interference

texts:
I'm trying to model a non-linear, static SISO system with

input variable $u$
disturbance variable $z$ (can be controlled for identification purposes but not during actual operation)
output variable $x$
system behaviour $N\{x,u,z\}$ is hysteresis afflicted for both $u$ and $z$
$u$ and $z$ influence the hysteresis characteristics of each other

I'm searching for any literature that deals with this kind of problem.
It should contain approaches on how to model such a system and if possible a way to invert it, because ultimately I'm trying to linearize the overall behaviour $N^{-1}\{N\} = 1$.


texts: FEM: What's D in the equation for half band width

texts:
In the equation for half band width given below,

  B = (D + 1)f

my textbook states D to be the maximum difference between node numbers in an element and all the elements are considered for its determination.

I don't understand what the above statement means, can someone please explain what D means and how to find its value.


texts: Approaches to whether a projectile gets intercepted

texts:
Hi everyone,

How do I approach questions like part (ii)?

From what I understand now, I believe the shortest method is that as long as the ANGLE of the relative velocity of B with respect to velocity of A is = Angle of thetha which in this case is arctan(50/150)?

Is this correct?

Another method I tried was to find the time taken for projectile and intercepter to reach the same x coordinate and use this to obtain the time in terms of thetha. Then I equated the y coordinate using this time in terms of thetha but I ended up being unable to solve them with 10sin - 10/3cos sin + cos = sqrt(3) + 3

What other ways are possible as well?

Thank you


texts: How to unserstand Correct boundary condition at outlet for incompressible flow?

texts:
I am simulating flow around a model. This model have an inlet and an outlet. Flow is incompressible. I know that value of pressure at the outlet is very much different from ambient pressure(Operating pressure). But, I don't know real value of pressure at the outlet. Now, I applied value of zero gauge pressure at the outlet (Is this OK? Why?) and this means that pressure at the outlet is equal to operating pressure while this is not. How do i find correct boundary condition for outlet?

But some people say that when flow is incopressible and boundary condition at inlet is velocity, we can use pressure-outlet as a boundary condition at the outlet because flow is not dependent on outlet pressure (so, we can use zero gauge pressure at the outlet). Why?

Thank.


texts: Lifting a Mass with one or multiple motors

texts:
I’m working on a DIY project and need some assistance. I have a single motor that can lift a load of 500 pounds.

Is it possible to use 4 smaller motors to lift the same load as long as the 4 smaller motors equal the same torque as the single motor?

This isn’t a question about gearing or placing the 4 motors on a single shaft....each of the smaller motors would work independently to lift the load.

My thought is this... You have a 3’ lever on a fulcrum situated at a given distance (let’s say the fulcrum is exactly in the center of the 3’ lever. 100 foot pounds is placed on the lever, but the load does not lift. Is it possible to place another lever against the load with the exact same conditions as the 1st lever. Then, both levers are given 100 foot pounds....will the load lift with the added mechanism.

This is hypothetical of course.... I would love to understand this.


texts: Which is the best way to construct a trapeziun dome with a 76' diameter

texts: When building a trapezium dome, is it better to construct the dome row by row or by first making a vertical arch?  Is some form of bracing required?


texts: How does the glass layer transfer the touch to the touch sensitive layer on Galaxy phones?

texts:
I have a Galaxy Note2 with a front glass layer that is broken, while the screen itself is ok, as well as the touch panel.

If I understand properly, the front glass has only a protective function and is not the same as a "touch panel".

My question is, how technically does the glass transfer the touch actions to the touch panel? On the answer I will base the way of the glass replacement.


texts:
I am wondering how a helicopter manages to stay balanced and stay in one spot while it is in the air.
I understand that there is a second rotor that is used to counteract the angular momentum and also the use of swashplate to direct the helicopter forwards and backwards.
Assuming the angular momentum of the main rotor is not an issue,
Is there a sensor on the helicopter that can detect if it is not upright? Is the swashplate then adjusted to tilt the copter into an upright position?


texts:
I'm working on a solution to this problem and I would like some advice and help. A fixed-ring epicyclic gear train is required to have an overall ratio of 5.5:1.

If the sun gear is to have between 10 to 15 teeth, suggest the most appropriate numbers of teeth for each of the constituent gears.
How many planet wheels would you propose for this design?


texts: Appropriate finish type for a new lathe crossfeed?

texts:
I have a metal lathe with a broken part. The part is not available, so I have to machine one up from scratch.

As this part is the lower half of the crossfeed assembly on the turret cutter, it has to be accurate, which is no problem for straightness and tolerance.  However, as ways and gibs have to be able to hold lubricant (so the parts don't just slide on each other and wear out), there must be a standard for surface finish that's preferable for this type of assembly.

I can't seem to find a clear specification for what to use, so what would be an appropriate finish type for those conditions?


texts: Can someone explain my this sentence about feedback systems?

texts:
The sentence is

  In a closed loop system when the loop gain grows typically we have an instability


texts:
Hello, so I'm looking for some help with part (a) of the question below. I've never seen an example like it before and I'm not sure where to start. How do I work would which is the missing member for the truss below? Any help would be greatly appreciated.

Thank you!


texts: Production methods for AC mains power plug pins?

texts:
What are the production processes and steps involved in producing a mains powered device that plugs into a standard mains socket (like a smart plug for example). Mains plug pins are usually made of brass or steel, afaik. And for most countries, there is a plastic sleeve at the end of L&N pins to prevent fingers from reaching live pins as they are inserted / removed. This would require an insert to the injection mold.
Alternatively, since engineering is about lateral as well as brute force thinking, can you just buy brass plug socket parts of the shelf rather than manufacture them to order. How would this impact on the process?
Please elaborate with as much detail as possible!


texts: Is there any benefit to using triaxial weave pattern instead of common twill?


texts: Height limits of brick and mortar tower?

texts:
What are the factors limiting the height of a "tower" made of typical fired brick and mortar?

By "tower", I mean a structure whos point is to be tall, and can support a human standing on or near its top.  I'm interested in the self-supporting structural aspects, not limitations of construction techniques, or environmental factors like wind loading, possiblity of earthquakes, etc.  I want to understand what limits such a structure mostly from its own weight and properties of the material.

The point is to maximize height for any given land area the thing sits on.  I'm trying to leave reasonable latitude for land area to understand the constraints, but let's not get silly like wrapping around the earth or end up with a star made of diamond, as a similar questions mentioned in a comment devolved to.  If a maximum is required to avoid silly answers, let's say about the area of a typical Manhattan city block, with reasonable latitude on shape.

I understand this material can handle high compressive loads, practically no tension load, and has a high density as building materials go.  My gut feel (I'm a electrical engineer, not so fluent with structural engineering) is that the optimum (least material for highest result) shape would be a circular crossection, probably with exponentially decreasing diameter with height.  How well does that scale due to ground loading?  What if this is built on bedrock?  Wouldn't that be about the same properties, if not better, than the brick and mortar?  Would that allow scaling some shape aribtrarily, or do the proportions of the shape change with size?


texts: I want to know the water flow rate from a certain height knowing the flow rate at near the ground level

texts:
I used a bucket to find out that at 1 feet high (a garden faucet) the flow rate from an half inch pipe is 1 gallon in 26 seconds
At 3 feet high (face basin) the flow rate is 1 gallon in 30 seconds
at 11 feet high (upstairs face basin) the flow rate is 1 gallon in 1 minute
at 15 feet high (upstairs showerhead) the flow rate is 1 gallon in 2 minutes

Graphing the data I see that this flow won't make it to the 23 feet I need it to fill a rooftop water tank. Is there an equation I can use to estimate the water flow I would need, measurable from the one foot pipe (It changes daily from the water company these days, some days it is more than strong enough) to reach 23 feet? I want to know if i'll have to just save money for a pump after all, or a bigger tank. Keep in mind I'm not an engineer, tho I did try to solve myself this with a natural number e or ln in there somewhere lol. It's been much too long since college math.


texts:
I am designing an NFC device but am still a little unsure about the principles behind NFC/RFID. From what I understand:

A primary coil constantly emits a 'carrier frequency' magnetic
field.
This field induces an e.m.f. on a passive secondary coil which is in
a secondary circuit.
The secondary circuit comprises a system that converts data into a
modulation signal, which is realised by a modulating impedance in
the second circuit.
This impedance causes something in the primary circuit to change,
thus receiving data.

It is step 4. that I am most confused by. Sources I've read simply say the load impedance is "felt" by the primary coil, whatever that means.

Also, what is the function of having a separate transmit and receive antenna on NFC transceivers?

As a physicist I have very little prior exposure to electrical engineering or system design!


texts: Strain gauge placement to measure a twisting beam

texts:
Where is it best to place a strain gauge to measure the twist of a beam? And what type of gauge is best?

In my application, I have a small metal part which experiences a twisting and bending force. The beam part is 8mm wide, 9mm long, and 1.3mm thick. It is fixed at the two screw holes, and a force is applied to the little flat rectangular patch at the end of the cylinder.

As you can see in the image, most of the stress occurs around the root of the beam, but I'm not quite sure which areas on the surface are experiencing compression, and which are experiencing tension.


texts: Relationship between wind velocity, turbine rotor diameter, and power output

texts:
I'm trying to understand and identify the equations to use in defining the relationship between wind velocity, turbine rotor diameter, and power output for a wind turbine.

To simplify my question, let's use the following assumptions:

Average wind speed of 8 m/s.
Rotor length of 40m for an overall diameter of 80m.
Ideal conditions, so we can neglect direction of wind with respect to the positioning of the turbine.


texts: Carpet for noise reduction (tests / studies)

texts:
Sorry if this is the wrong forum, I'm not an engineer but I'd need a pro to answer my question.

Short version:
Are there any tests or studies, if a carpet in an apartement can reduce noise from the apartment below. I'm searching for numbers rather than oppinions. The noise comes in all frequencies and shapes, from trampling to yelling, machine noise etc.

If there aren't any tests, please give me your oppinion, if you're an experienced professional in this field.

Long version:
I need to find a way to reduce noise in my apartment. I'm living in the topmost floor, so only the noise from below is the problem. Apparently our landlord put laminate in all apartements, without any form of insulation. My neighbors aren't the type of people that seem to be (neither could be made) aware, that noise exists.

After browsing the web for months, trying out various earplugs for >300$, hanging thick curtains, rearanging my apartement etc. I'm just searching for something more. If it's 5% less noise - fine. If it doesn't help at all I don't want to spend time and money on it.
I know, that I propably should better find a new place to live or make my neighbors be more silent, but this is not a perfect world, things cannot be done in the best possible way.

Not sure why Mythbusters never tested this stuff.

EDIT:

RED = Insulation (Foam, ..., whatever)
White = Heavy wood
Blue = Inner shell, also heavy wood
What if I layed carpet and built something like this? I set up directional lamps for every wall and the ceiling. Sure, light is not sound, but it bounces too, right? Or will that totaly not work? Maybe I worsen it by that, like I build a trumpet..


texts: Entering frequency dependent elastomer properties in abaqus

texts:
I am trying to enter frequency dependent viscoelastic properties for an elastomer into abaqus.  I found where to enter the properties:

Edit Material->Mechanical->Elasticity->Viscoelastic

Domain: Frequency
Frequency: Tabular

The test data that I have to enter is G* (complex) in which the real component is the shear storage modulus and the imaginary component is the loss modulus.  Using this and the Poisson ratio I can compute the complex bulk modulus, K*.  However abaqus is looking for the following test data as a function of frequency:

Omega g* real
Omega g* imag
Omega k* real
Omega k* imag

Are these the values for shear and bulk modulus or are they the Fourier transform of these quantities?


texts:
Before I explain my problem I'd like to mention I'm still green and about 2 weeks into these topics. I learned most of it from youtube videos, wikipedia and other science sites, so I'll be explaining the smallest details in order to confirm I didn't mess anything up.

I have several questions regarding the P-N junction; the forming of a depletion region - the nature of ions created during the diffusion of carriers to be specific.

So here's what I've figured out so far (please correct any inaccuracies):

We dope the n region of the semiconductor with an element that has more electrons in it's valence shell than the semiconductor atoms. The added element "wants to behave" like the rest of the atoms in the crystal due to the rules of covalent bonds and gives away it's excess electrons. In doing so it becomes a positively charged ion, because it has less electrons than protons. Now there are a lot of free electrons in the conduction band of the n region which increases conductivity.
We dope the p region of the semiconductor with an element that has less electrons in it's valence shell. The rules are the same except this time it wants to accept missing electrons to fit in the structure, so it becomes a negatively charged ion. Now there are a lot of electrons missing in the valence band of the p region which increases it's conductivity.
a depletion region forms because the excess electrons in the n part are attracted to the holes in the p part. In doing so, the ions on both sides of the p-n border become neutral/complete again and they refuse to accept electrons at this point, so they create a barrier.

My questions are:

Am I right in thinking the depletion region forms because the dope ions have regained the balance between the amount of protons and electrons, so they repel electrons which are the only real charge carriers (By real I mean holes are just empty spaces for electrons, not some magical positive charge carriers that can move in a way that electrons do.) ?
How come the depletion region even exists, shouldn't the depletion region atoms still share their electrons/holes with the rest of the structure?
This one might be offtopic, but do atoms with 8 electrons in their valence shell accept or give away electrons? Is the octet rule a key concept to understand all of this fully, or maybe it has nothing to do with it?

Also, if you could recommend some good literature that can explain these topics thoroughly I'd be grateful.


texts: Stirrups are not shear bearing diagonals but just spacers?

texts:
Tension and compression re-bars in a concrete beam are connected by stirrups vertically tied together. If the space in between (this corresponds to web of an I-Beam)  carrying shear load predominantly why are stirrups not placed along $\pm 45^0$ principal stress direction for better material economy ?

Such a design practice could be in aerospace engineering for lightweight construction but not found in the originating civil/structural construction practice ?


texts: what is the chance of sustaining load if beam is 20 feet long?

texts:
what is the chance of sustaining load if beam is 20 feet long as center pillar of house is removed in first floor and added 20 feet long beam with 20 mm rods in RCC beam?

House details :: 30*40 sq feet, g+2 storied building.


texts: Got to pour outdoor concrete next week, but forecast is cold. What are my options?

texts:
I have to pour outdoor concrete next week. The pour is in two main parts - a 100 mm cover / 2nd pour over a 6 x 3 m area of existing concrete from a 1st rough pour, and the bottom stub part of a retaining concrete wall profile about 500 mm wide x 750 mm high x 4 m long.

Unfortunately the weather outlook is quite cold, getting up to 6-8°C (43-46°F) late next week daytime, but generally otherwise around 2-4°C (36-41°F) in daytime, which is below the 5°C minimum for concrete. The concrete can be poured in the morning so it'll have about 6 hours of daylight to start setting, but nights are forecast to be cold - close to zero (0 - 1°C / 32-34°F). Both are exposed outdoor pours, there isn't an issue with wind or rain, just temperature.

I can't really afford to put off the pour (previous pour date didn't happen for unrelated reasons) especially with no guarantee that the week after (or the one after that) will be any better,but I do have several days to prepare, if preparations are needed to ensure success.

If nothing else comes up, I might have the capability, as a last resort, of "tenting" the entire poured areas under a lightweight wood frame overlaid with heavy polythene (DPM) and running some air /space heaters under it for a couple of days before or after, if there isn't a better option. But that's only a layperson's guess.

What are my options for ensuring the concrete sets properly despite the forecast low temperatures?


texts: Modeling Water Flow Through Saturated Medium

texts:
I am working on a project that uses a variable-speed pump to achieve a desired pressure across a medium (coffee grounds). The system includes a pressure sensor in-line between the pump and the medium. I've been reading up on water flow through soils (as this seems somewhat analogous), but I am having difficulty extracting the important information.
Does there exist a reliable way to model pressure/flow of water through saturated soils and if so, might someone be able to highlight this discussion?

Cheers


texts: In what (free) software can I draw bodies in a 3D coordinate system?

texts: I'm looking for a software in which I can make images of this kind.


texts: Low-tech ways of assessing relative strength of a material (yield point)

texts:
I want to compare strength of a metal before and after heat treatment, to assess to effectiveness of that treatment. (See my previous question, Aluminium softened by brazing. How to harden?).

Specifically, I want to find the yield point (the strain a material can take without being deformed, ie the range where it remains elastic).

I have two ideas that use a similar setup. Shove a length of material (constant width, height, length, shape) in a vice. Apply a force to the end. Fasten a $1 digital luggage scale to the other end. Hang a container of water or sand, adding a little each time. Deflection could be measured as the distance from that end to some reference point with a digital caliper.

Then, either:

Apply an increasing force, until the force is no longer proportional to the deflection (since up till the yield point, materials bend according too hooke's law). Or,
Apply a force and release. Repeat with increasing forces until the material no longer returns to its original shape.

The problem is, to achieve any real accuracy, both 1 and 2 above would involve 10's of manual iterations per assessment.

Besides buying or hiring a rheometer, are there any practical alternatives?


texts: What's the difference between linear and nonlinear continuum mechanics?

texts:
I have been recommended to read a book about nonlinear continuum mechanics, but when I have taken a look at the table of contents, I found myself familiar with most of the concepts in the book since I have taken before a basic course in continuum mechanics.
So I can't find a big difference between linear and nonlinear continuum mechanics except for hyper elasticity concept (probably).
Could someone explain to me the major difference between them?


texts: Why didn't 3D printing become a standard commodity after around 2012?

texts:
Around 2012, you had big news coming out about 3D printing: Things like replacement body parts being produced for about 1% the cost, individuals being able to produce guns off the printer, etc.  You could go to Barnes & Noble and/or Books-a-Million and buy household models of 3D printers for very affordable costs.  It was said that it would go on to become the "next industrial revolution".
...What happened?  It's 2020 now, and it's been several years since I've heard of it on a regular basis.  It's still around, sure, but mainly in factories, specialized shops, a few hobbyists' homes, and that sort of thing.  In general, it's like the Internet was before the 90's.
It was such a versatile, powerful technology though, and it didn't cost that much to get just a very basic one.  So especially given both the hype and the legitimate results from around 2012 and 2013, why is 3D printing currently like the Internet before the 90's, instead of the Internet after the 90's?
I am a software person and will probably get lost on a lot of non-layman's speak regarding hardware.

To be clear, I'm not specifically referring to industrial-grade 3D printers.  I just mean ones that can at least work with soft plastic or wood that can at least create cheap, little stuff to set around the house or something.  These were being sold on store shelves around 2013.
Both \$150 household gadgets and \$250k industrial devices are included, the same as if this were talking about computers being a "standard commodity".


texts: What is the relation between frequency of piezo element and its shape?

texts:
I was reading about piezo elements and its frequency.

I found on the internet that : The composition of the ceramic material and the shape and volume of the element determine the resonance frequency -- generally, a thicker element has a lower resonance frequency than a thinner element of the same shape. Determining Resonance Frequency

I found also that : At ultrasonic frequencies large surface area parts draw considerable current and resistive heating of the electrodes becomes the limiting factor. Piezo Systems - Frequently Asked Questions

First question, does that mean that if the piezo element is circular has a different frequency as a rectangular piezo element plate when they have the same thickness?

I know that frequency = velocity/(2*thickness)

My second question, what is the relation between frequency of piezo element and its shape?


texts: Is there any side effect to soft start an AC motor?

texts:
I have a ground to water heat pump for my home heating/cooling (scroll compressor). The 3-phase 15kW-peak motor can be soft started but this option is off by default.
I'm aware of all the positive effects of a soft start but I cannot find any negative, are there any? In general or specifically for scroll compressors? Why would the option be off by default?


texts: How can the Saturated Liquid Line be two phases?

texts:
TLDR
Why do all of the resources I find say that any point along the saturated liquid line is 2 phases?
How can statement 1 and 2 both be correct?

Steam Quality @ p,v,t on sat liquid line= 0 =>(100% liquid)
number of phases present on saturated liquid line = 2

It has to be 1 phase the liquid phase. I say that because if I calculate the steam quality on the saturated liquid line it's 100% liquid.
Background
I was reviewing materials studying for PE...I hit this, and now feel like everyone else is wrong and I am right.  Since I know that is not reasonable, someone please help me understand what I am missing here. By intuition I solved it correctly but when i looked at the answer I felt like the gibbs phase just doesn't make sense, because I can't get over the fact that a saturated liquid line means 0% vapor.
The problem is as follows:


texts: Torque and Speed of a DC Motor with Pulleys and Wheels

texts:
I want to know how to calculate the speed of an electric skateboard

If i have that situation(from the picture below) i will need an acceleration=0.16m/s^2?

and a force F~=15N?

So i will need a power output Po=150W to move that skateboard with a velocity=10m/s ???

Can i calculate the torque that i need with this T=r*F ??

where r=radious of the wheel

and F i think that's the force that i need

if yes,i will need a torque of 0,036m*15=0.54Nm?

So,in that case,if i have a motor that has a torque=0.54Nm with a power output=150W will move the skate with a speed of 10m/s? With what i'm wrong??

I can calculate the torque of the motor with this

T = (I * V * E *60) / (rpm * 2pi)?

So in my case if i have a motor 270kv 1665W with Continuous current: 80A with 60%efficiency with a Lipo Battery 22.2V 10.4Ah 30C, I will get:

Power Input   =22.2*10.4  =230.88W

Power Output  =230.88*0.6=138.52W

RPM=270*22.2=5994RPM

Torque=(10Ah*22.2V*60%ef*60)/(5994RPM*2*3.14)=7.992/37.642,32=0.21Nm?

So what speed the board will have??

With what i'm wrong?Please explain

How the diameter of the wheel affect the speed and acceleration?

if i have 72mm wheels,so 0.22m circumference with 5994 rpm will have 0.22*5994=1.318m/min? so 21.96m/s?? if i'm not wrong,how the mass affect that speed? and the not enought torque?

How the diameter of the pulley A and B and the number of teeths and the distance between the teeths affect the torque and speed?

How can i calculate the output torque and speed of the pulley A ??

With what i'm wrong,how i can calculate what i need please be patient i never take physics/engineering class i just searched on internet don't be annoyed with my calculus

Update: if i have torque=rm(v/t) i will get v=(timetorque)/(rm),in my case v=(60*0.21)/(0.036*90)=3.88m/s?? It's that right? If i get more torque with the pulleys from the motor to the wheel i can get something like 7m/s?

Ok Update2: i have 2 gears ,one with 27T other with 14T ,i founded that the ratio is 27/14=1.92 so the torque is 0.21*1.92=0.4Nm? and the speed will be 5994/1.92=3121RPM?

If yes,i will have v=(timetorque)/(rm) V= 7.4m/s? i can't understand what i'm doing wrong..

Maybe if i think that i have enought torque to move the board,and if the wheel rotate with 3121rpm and 72mm diameter with 0.22m circumference,it will make 0.22m each rpm so 3121*0.22=686.62m/min=11.44m/s. What is the true ??#Please help !#

Update 3:
if i will use a 36T pulley with a 14T pulley on the motor with 138.52W power output,5994RPM,0.21Nm torque,70mm wheels

and i need a torque=0.54Nm

i will have 36/14=2.57 ratio ,so 0.21*2.57=0.54Nm torque and 5994/2.57=2332RPM

so each min i will make 0.22m(circumference of the wheel)*2332rpm=513m/min=8.55m/s??


texts: I am trying to model water gas shift reactor on Aspen using an Rgibbs reactor. Unfortunately whenever i pass the stream into the reactor(HTS) the amount of CO and H2 both are increasing and C in the system is not balanced. Aspen is not prompting an error regarding elemental balance not being intact. I am confused what should I do


texts: Which method is better to solve indeterminate trusses, force or displacement method?

texts:
For statically indeterminate trusses, which method is better? Force or displacement method? And why?
I read somewhere that displacement method is not suitable for trusses but I must verify.


texts: How to calculate inlet and exit area of a gas turbine engine compressor diffuser?

texts:
*Originally posted in Thermodynamics.. reposted here

Helloooo everyone! Self proclaimed jet engine designer here~ Don't worry I won't be designing airliner engines anytime soon.

I know when air passes through a diffuser or a duct of progressively larger cross section it gets slowed down, compressed with an increase in temperature. And when the passage is of progressively smaller cross section the opposite would happen.

Now.. a great many online publications for laymen explain the above fact clearly.. sometimes with nice illustrations but they don't go as far to detail the calculations. And I find specialized literature to be rather difficult to understand.

For example what would the outcome be if air is discharged out of a compressor (at 300K 300m/s 1.5 bar) and passes through a diffuser that has an exit area of twice that of inlet area? I don't think it will be so simple because all three properties I've mentioned must change simultaneously..

Could an expert thermodynamitician explain this please? Thanks in advance!


texts: Where does the energy stored in a capacitor come from?

texts:
My textbook reads, “the power supply does work on the electrons, so their potential energy increases. You recover this energy when you discharge the capacitor.”
I don’t get why this is the case... doesn’t the power supply increase the K.E. of the electrons?
Now where does the energy for the capacitor come from and what it ‘form’?


texts: I would like to run a smartphone using a primary battery instead of rechargeable for a project. What are the 4 contacts used for on the factory LiPo?

texts:
Most phone batteries will have a connector of some type with 4 contacts.  Of course two of those I'd expect to be +- Voltage, but the other two compose some sort of mystery input to the phone (thermistor? signal?  I don't know).  I was hoping to substitute a primary battery instead of the factory one for my project (I have a 3.6v primary battery), but my device always seems to have a problem with it, presumably due to the battery protection circuit.

I thought I might just leave the protection circuit in place and wire power to both input and output- that way whatever input the phone needs to see is still there, but even that approach seems not to work.

Please help me bypass this system so that I can use a custom battery in this device.

Above is a diagram with some measured resistance/voltage values.  If a value between points isn't shown, you can consider it an open circuit (although I didn't measure battery resistance)


texts: Interpretation of shear flow/shear center of L-profile

texts:
I have calculated the shear flows and center of an L shaped profile. I assume they are correctly calculated (I followed the same steps as during the lectures for an I shaped profile). However, I have some problems with the interpretation of the results. The results are shown in my simple sketch.
The height of the profile is 1.5 times the base (but this actually doesn't matter) and thickness is very small compared to other dimensions. Given this, I calculated that the shear center is about 0.49xH to the left of the center of gravity (c.g.) to counter act the torsion of the shear flow.

My confusion regarding the results:
The net result of the vertical shear flow is equal to the vertical force V. The net result of torsion of the shear flows is equal to the torsion moment of the vertical force (0.49xHxV).
But there is no horizontal force to counter act the horizontal shear flows. How is this possible?
I am confused because in the lectures we have only seen shear flows in symmetric profiles (like C an I).


texts: Difference between lead screw and worm screw?

texts:
I am confused whether a lead screw and a worm screw are the same exact thing. In my engineering workshop lab, they come up as separate things. For example, a worm screw is there in the indexing head of the milling machine (as part of the worm drive), while the lead screw is part of the feed mechanism in the milling machine and the lathe machine. They both look like the exact same thing. Can someone tell me what's the difference?
https://en.wikipedia.org/wiki/Leadscrew
https://en.wikipedia.org/wiki/Worm_drive


texts: Does the order of the states in a state vector matter?

texts: Say you have a state vector, 1, with states [position, velocity] and you have corresponding A1 and B1 2X2 matrices. Say also that you the same state vector,2, but in a different order [velocity, position] with corresponding A2 and B2 2X2 matrices. Are any calculations, say for a SS controller, you make yield different results or just the same results but in a different order?


texts: What determines the breakdown voltage of diodes?

texts: Some diodes have reverse breakdown voltage of 50v and some 1000v. What determines this difference?


texts:
I have data:
mass = 740 kg
wheel diameter = 670 mm
Rw = 0,335 m
power (max?) = 750 horsepower (551kW)

Now I would like to calculate car acceleration when throttle is max and speed in this moment = 100 km/h = 27,78 m/s
I calculate wheel RPM from this:
wheel speed(RPM) = v(km / h) * 25 / (3 * pi * r(m))

I get
WHEELrpm = 100 * 25 / (3 * 3,14 * 0,335) = 792

Next I calculate engine rpm:
RPMengine = RPMwheel * idifferential * igearbox * iclutch

where:
iidifferential  = 3,42
iclutch = 1
igearbox (gearbox ratio) = 2,55

RPMengine = 792 * 3,42 * 2,55 *1 = 6907

next I calculate torque from:
torque = (POWER * 5252) / rpm

I get
torque = (750 * 5252) / 6907 = 570

And now, apart from the resistance, I want to calculate drive force and acceleration.
I found this:
Fdrive = torque * gearboxRatio * iidifferential  * n / Rw
n - transmission efficiency (0,7?)

But I wonder if I can use it considering previous calculations. How to correctly calculate the acceleration now?
I try to base on this: https://engineering.stackexchange.com/a/22021
but I dont understand this formulas


texts: Why doesn't prestressed concrete crack at the top before the load is applied?

texts: In prestressed concrete, we add a tensioned steel cable at the bottom half of the beam to balance out the tensile forces resulting from the applied load. But before the load is added, doesn't the beam deflect upwards and cause tensile cracks now at the top of the beam (situation 5 in the above picture)? Let's say we tension the cable and cast the concrete and then release the cables into compressive stress. I don't see how in practice we can immediately apply the designed load to balance the situation before the beam bows upwards and cracks at the top.


texts: Mechanical vibration: 2 springs attached horizontally to a wheel at a vertical distance a above the center, find the natural frequency of the system

texts:
Context: introductory mechanical vibrations, 300-level engineering. ISBN13: 978-0-13-287169-3

See problem solution below

As seen in the "Potential Energy" section, the author writes that the distance the springs compress is $$s=(a+r)\theta$$When I derive  $s$ I get $\tan(\theta)=s/a$ , $s=atan(\theta)$ , and by small angle approximation $s=a\theta$. How is he getting $(a+r)$?


texts: Meaning of this sentence in lecture notes about buckling of nonlinear column

texts:
Above picture is from my lecture notes. It deals with a column subject to axial load, which follows Euler buckling theory. The material is nonlinear, approximated by two lines as seen in the stress-strain diagram. The two elastic moduli, $E_1$ and $E_2$ are calculated. Then the buckling stresses corresponding to both moduli are calculated.
It is then noted that neither of the buckling stresses are located in the range where the material follows the corresponding elastic modulus.
It is then stated:

Application of Euler's theory becomes problematic when the elastic modulus changes significantly. The buckling now happens when the material reaches the lower limit, which is also when its modulus changes.

Why does the bolded sentence hold true? Why is the buckling now assumed to happen at the limit of the first line? I cannot picture in my head what happens in the situation when neither of the buckling stresses are inside the ranges where their corresponding elastic moduli are defined. And if we are able to somehow conclude that the buckling happens at this lower limit (240MPa) why is the application of Euler's theory "problematic"? Didn't we just get an answer?
Another thing is said:

In design norms there are often limitations to the slenderness and deformations due to the theoretical variety of the buckling event.

What does this last sentence mean? What kind of limitations are there and what is meant by the "theoretical variety of the buckling event"? (please note that these lecture notes are not in English, but this is the closest translation that I could come up with)


texts:
1) Under Visualization in Abaqus, contours for displacements-U1 and U2 are available. How could I generate contours for displacements in x-y direction, that is Ux and Uy? Similarly how can I get contours for stresses Sigma_x, Sigma_y and Sigma_xy?

2) To find homogenized elastic constants of a representative volume element of a fiber reinforced composite (that means to get homogenized E1,E2,E3,G12,G23,G13,v12,v23,v13), I need to find elastic constants of each element. I also need to get volume of each element. How can I get this two information (elastic constants and volume) for each element?

3) In Abaqus, in the representative volume element of fiber reinforced composite, fiber is aligned parallel to z axis. How could I rotate the axis so that the fiber would be aligned parallel to x axis? Noteworthy that I am modeling 2D planar problem.

I would really appreciate your kind help. Thanks in advance!


texts: What type of batteries are used in smart wristband?

texts:
I'm making one project for my class, some kind of smart wristband, but not sure which type of battery should I use. I found a lot of good wristband online, I see that they usually have 60 - 100mAh batteries.

Can someone tell the type of batteries used in Smart wristbands?


texts:
I have a MIMO system with a 2x2 transfer matrix, for example consider:

$\begin{pmatrix}
\frac{2}{s+1} & \frac{1}{(s+1)(s+2)}\\
 \frac{1}{(s+1)(s+2)}&\frac{2}{s+2}
\end{pmatrix}$

I would like to know how to characterize the influence that each channel has on another channel using Matlab.

So I would like characterize the effect of the coupling between the channels.

I know that to see how much a channel influences another i could use RGA, but is there also a way to see this by looking at the step responses and the magnitudes of the frequency responses?

Thank's in advance.


texts: maximum capacity factors of combined cycle gas power plants

texts: What is the maximum annual capacity factor that can be expected of a CCGT plant? I see in US in 2015 the average was about 0.56, but can it be higher? I guess it needs some time for maintenance but I don't know how much. Any guidance on where I can get such information?


texts: Is there an instrument that can measure thickness of an object through strain?

texts: So basically, I am doing a project to design a measurement tool for measuring the different layers of the quartz crucible used in the semiconductor industry. Since the crucibles undergo some deformation through the fabrication process, I was thinking if there is any technology that makes use of the degree of strain to measure the crucible layers. Could UV rays be used for the measurement with a small fragment of the deformed crucible?


texts: Actual amount of reinforcement gained by adding gusset to welded steel tube construction

texts:
This question bothers me for quite a while and is about bicycle frame construction, specifically a BMX frame and even more specifically it's front triangle.
It is a heavy duty frame by definition, and most common point of frame failure in this area, is lowest point around area D - and may happen even if type1 gusset is present.
It's usually a crack along weld (which, if unnoticed, may result in tube C snapping off upon next considerable impact and is highly unwanted).

I am looking into building a frame with type2 gusset, which appears more reliable overall, but unfortunately lack knowledge to confirm this.

I tend to think additional heat stress from second weld during type1 gusset install does not do good and useful weld surface does not increase a lot.

With type2 gusset, however, useful weld surface increases considerably, also holding all three tubes together, which should relieve stress on area D as well.

However, few reputable people suggest type2 construction would still need type1 gusset between tubes B and C, but cannot back up their argument with real data.

To summarize - by what amount does type1 gusset does actually improve situation here, and would it be any use along with type2 gusset?
I would rather increase tube B wall thickness around weld area rather than add type1 gusset, if this proves an issue.

Additional info:

Frame tube material is 4130 chromoly steel, TIG welded.
Tubes A and B are usually around 35~38mm outer diameter and have 1.25mm thick wall.
Tube C wall is usually 2-3mm thick.

Frame experiences repeated cycles of 'sharp' dynamic loads (i.e. handling rider mass upon landing from height).


texts: How does the optimal-gear indicator work?

texts:
Some modern cars, including models by BMW, Ford and Audi, have a system on the panel that tells the driver the next gear to use while driving, for optimal fuel economy.

How does the vehicle decide which gear provides the best fuel economy? What data does it require to make that indication in real time?


texts:
I'd like to mock up a quick prototype of a chassis assembly for a type of cart, which, in production, would be composed of CNC bent aluminum extrusions (hollow, approximately 5/8" circular profile), and connected using plastic joints. I'm wondering if anyone could recommend methods for prototyping the tubular components.

I'm considering using PVC, but I would like to use something I could bend and shape angles into relatively easily.


texts:
I would like to determine the mechanical output torque and power of a small motor without using expensive strain guages and similar and have come up with the idea of determining the maximum mass that the motor shaft can lift.

With reference to the image, if I suspend a mass over a pulley and find the maximum mass that the output shaft can lift (and wind the string around its shaft in the process), can I calculate the torque as: T= mgr where m is the mass in Kg, g=9.8 m/s2 and r is the radius of the shaft in metres?

If this is correct then for the setup shown, and assuming the motor could lift no more than 25g, the value of T= 0.025x9.8x0.002= 0.00049 Nm. Then if the shaft is spinning at 1000 rpm, Power= 0.49W

Thanks


texts: Why does the fulcrum pin of a band brake experience "double" shear stress

texts:
My machine design textbook states that the fulcrum pin of a band brake during braking is subjected to a double shear. How do you say it is subjected to a double shear and not to a single one.
By double shear the textbook means:
  Double shear stress = 2 * shear stress


texts:
I think there is an error in this questions solution and I want someone to check:

  Example 8.1-4:Mass transfer from an oxygen bubble A bubble of oxygen originally 0.1 cm
  in diameter is injected into excess stirred water, as shown schematically in Fig. 8.1-1(d).
  After 7 min, the bubble is 0.054 cm in diameter. What is the mass transfer coefficient?

The solution goes on to state:

$$\frac{d}{dt}(c_1\frac{4}{3}\pi r^3)=AN_1=-4\pi r^2k[c_1(\text{sat})-0]$$
$$\frac{dr}{dt}=-k\frac{c_1(\text{sat})}{c_1}=-0.034k$$

Shouldn't it be:
$$\frac{dr}{dt}=-3k\frac{c_1(\text{sat})}{c_1}=-0.102k$$


texts: Calculate aperture size in plate where water falls on, at a certain water flow

texts:
I have a construction where water falls on/through a perforated plate via a waterfall (see image below). The plate needs to evenly distibute the water over the underlying structure. My question is how to calculate the hole sizes (or total hole area) in the plate, so the water distributes evenly and does not overflow? Flow rate coming from the waterfall is 30m3/h, some dimensions are in the image below.

Hopefully someone can help me, thanks.


texts: How can I model two attached rotating rings?

texts:
I am trying to model an object in which there are two rings who are attached to each other and can rotate independently along the Y axis (see attached image).

The object needs to be machined and not too costly to produce, and solid (the rings won't detach if pulled onto).

I have little knowledge in mechanical engineering but I'm working with an engineer and I want to give them the right pointers.


texts: Purpose of normalization of Jacobian in a parallel manipulator

texts:
I am currently studying a robotics paper, where a normalized frobenius norm of a matrix is calculated as part of determining the condition number of the corresponding linear system of equation:

$\mathbf{W}$ is defined as
$$\mathbf{W} = \frac{1}{n} \mathbf{I}$$ and inserting this definition into $\left|\left|\mathbf{J}\right|\right|$ results in
$$\left|\left|\mathbf{J}\right|\right| = \sqrt{\text{tr}\left(\mathbf{J}\mathbf{W}\mathbf{J}^{T}\right)} =\sqrt{\text{tr}\left(\mathbf{J}\frac{1}{n}\mathbf{I}\mathbf{J}^{T}\right)} = \sqrt{\frac{1}{n}\text{tr}\left(\mathbf{J}\mathbf{I}\mathbf{J}^{T}\right)} = \sqrt{\frac{1}{n}\text{tr}\left(\mathbf{J}\mathbf{J}^{T}\right)} .$$

The normalization factor is therefore independet of $\mathbf{J}$. Therefore, what is the purpose of scaling $\left|\left|\mathbf{J}\right|\right|$ down by a factor proportional to its dimension?

In terms using $\kappa(\mathbf{J})$ to optimize a mechanism, this would mean that the respective value of each iteration would simply be scaled down by constant factor, and therefore not influence the results. Am I missing something here?

Thanks in advance!


texts: What is the importance of pitch ratio? And why is the value different for different aircrafts?

texts: I tried looking online, but all I can find is what pitch ratio is, butI can't find anything related to the question above. Help will be appreciated.


texts: Why is the thread of the screw linear? Can it be wavy?

texts:
I noticed that the screw-on of my water tap often loosens itself up after I rotate the tap left and right enough times. Every time I rotate the tap left, it loosens the screw a bit, then if I rotate the tap right, the screw does not tighten itself to the same amount.

This, repeated enough times, loosens the screw enough so that the tap would leak.

I thought it might be solved if the screw would have a wavy thread. So, for example, instead of gently sloping downwards by 1 mm every revolution, it would slope up 1 mm for the first half, and down 2 mm for the second half. This way, the screw would lock itself in a local "peak" in the thread, and not loosen itself no matter if I rotate the tap left or right.

Is there such a kind of screw? If so, what are they used for? If not, is it because they have some kind of mechanical weakness?


texts: Linearisation of the Equations of Motion of an Inverted Double Pendulum

texts:
I am working to develop a deep reinforcement learning model for balancing an inverted double pendulum.
To do so, I needed to derive the equations of motion, via the Euler-Lagrange (EL) method and now need to linearise the EL equations to get the local stability near the equilibrium point, when:
$$\theta(t)=0\:\:\:\:\:\:\:\:\:\:\:\phi(t)=0$$
i.e., both pendulums are in the vertically upright position; vertically stable.
After reading several papers, the linearisation most commonly used, as described here is:
$$sin(\theta(t))\approx\theta(t)\:\:\:\:\:\:\:\:\:\:\:sin(\phi(t))\approx\phi(t)\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:(1)$$
Using these linearisations, the final acceleration equations each have a term that is multiplied by either $\theta(t)$ or $\phi(t)$, which does not even make sense.
For example, one of the terms in the $x$-acceleraion equation is:
$$-M^{2} g l^{2} 4I + 4 M l^{2} - M l \theta(t)+...$$
As seen, the last term $M l \theta(t)$ is a multiplication of the mass, length and angle. How can a value just be multiplied by an angle?
Instead, if using, $\theta(t)=0$ & $\phi(t)=0$, then:
$$sin(\theta(t))=sin(0)=0\:\:\:\:\:\:\:\:\:\:\:sin(\phi(t))=sin(0)=0\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:(2)$$
Using the above linearisations, there are no values in the final acceleration equations that are being multiplied with just an angle?!?
Can someone please explain why the papers have used the linearisations stated in $(1)$ instead of $(2)$, or provide some links to the relevant literature? Intuitively, the linearisations of $(2)$ correlate with the initial idea of vertically stabilising the pendulums?
Thank you.


texts: Calculating the output torque of a two-input epicyclic gear system

texts:
For a simple planetary gear system with a single input shaft of a known torque, the output torques of the other two shaft can be calculated using the equations below (for a steady state system).
<img src="https://i.stack.imgur.com/2X3xH.png" alt="Torque ratios of standard epicyclic gearing
" />
If I were to apply torques to two of the shafts how could I go about calculating the torque of the final shaft for a steady state system?
My intuition is that for a steady state system the sum of external torques (the shafts) must be 0. In this case the output torque will be the sum of the two inputs.
Edit: By the above comment I mean Tt + Tc + Ts = 0
Am I missing something?


texts: Increasing the stiffnes of a structure by adding stiffener, but at the same time reducing main surface thickness

texts:
Let's say I'm designing a table surface which has to be stiff, rigid, but at the same time, not too heavy. It is rectangular in shape and ratio of length:width is quite large. It is only supported on both ends of its length. If I use a 50 mm slab of gray cast iron for the surface of the table, during maximum loading the table will bend and the Z-axis displacement at the center would be 0.04 mm. This table will be used as a machining table, and the maximum tolerance of the workpiece will be 0.005 in (0.127 mm), so I think the 0.04 mm deflection of the table is already good because it will give room for tolerance from other component of the machine, such as cutting tools, spindle, etc.
Problem is, with 50 mm steel slab, the maximum weight criterion is exceeded. The whole table is designed to be able to tilt on A-axis (it's a trunnion table), driven by a motor. The heavier the table is, the bigger and exponentially more expensive the motor would be. I have to reduce the weight of this structure, but I have to keep the stiffness.

What if instead a simple flat 50 mm slab I make it like 20 mm slab with extra stiffener profile on its underside? Like honeycomb pattern, or any other stiffener configuration. which is possible because it's a cast iron anyway, just have to create the mould.. by doing that I could reduce the weight by almost 40kg

The question is: Is it theoretically possible? 50 mm slab gives 0.04 mm bending displacement, now I want to make it like 20 mm slab plus some stiffener to reduce weight, but I would like to keep same performance with 0.04 mm maximum displacement. The maximum load is 1200 N, concentrated in small area in the middle of the table.

EDIT: previously I wrote the requirement as 0.005 mm deflection, but it is actually 0.005 in (0.127 mm). However, this +- 0.127 mm figure is basically the machining tolerance of the workpiece that will be made on top of this table, so I guess the tolerance of table itself should be much lower than that, I don't know the exact number yet but it just won't go as low as 0.005 mm that's probably too extreme. I'm still in the early stage of the design so a lot of design requirements is still open to revision..


texts:
Currently I'm doing a personal project, but I've some doubts about the calculation process. Well, I've a platform (2.30m length x 0.32m width). This platform is supported by 4 wheels with a diameter equals 120mm. This platform loads a motorbike. The maximum mass (platform + motorbike) that it will move is about 400kg. The surfaces contact are rubber with concrete (coefficient of friction 0.45). Rolling coefficient I think is 0.02). I'm uncertain wether to put 2 driven wheels or 4. The platform must travel a distance of 7 m. For the process I propose a speed of 0.1 m / s.
Well, How can I calculate the required torque to move this platform with a motorbike?


texts: If aboard a train being driven along a track by centripetal force, would it feel like you were on a regular straight track?

texts:
Question: If aboard a train being driven along a track by centripetal force, would it feel the same as if you were on a regular straight track?
I hope this isn't subjective, I think there is a right or wrong answer here. Either it does feel similiar or it doesn't so hopefully this question isn't closed. I don't see it as an opinion based answer.
I recently did a little khan academy course because I  wanted to understand the physics of centripetal force. I was a little unsure of some things so I devised this thought experiment to help me clear things up in my own head. I was hoping you fine folks might be able to help clarify a few things for me.
The Scenario:
You board a train cart, sit down and make yourself comfortable inside your carriage. This train is special because it doesn't have an engine, the carriage is driven along a rail sitting on a rotating plane, your carriage starts close to the axis of rotation and is pushed towards the edge of the plane and away from the rotating center axis by centripetal forces. A lot like being inside a centrifuge!

Details:
Now I know as your radius changes the centripetal force changes, so the speed of our train changes as given by the formula: Centripetal force = mass x velocity^2 / radius. Constant acceleration/deceleration isn't good for passengers so for this scenario were going to presume the rpm of the plane is being altered to induce a generally constant speed like a normal train.
The track in  the picture is a little short so please use your imagination to extend it, it's just to get the general idea across.
What I don't understand:
What I'd like to know, is once the train is at it's correct speed and my body has caught up to that speed, could I hypothethically get up and walk around on the train like a person would in a normal train or passenger plane, drink a cup of tea or go to the bathroom. Because I'm moving forward I'm not dealing with the forces imposed by centripetal forces, that's an asuumption I'm making which I presume is correct but what I'm not sure about is because the angle of my velocity vector is changing constantly (The direction I would fly off in if  were to jump of the train.) does my body have to be for lack of a better word consistently updated by the carriage, pinning me against the train  window at a suffiently high rpm? I don't know if that force is there or not. So the real question can I have a cup of tea on board or not?


texts:
I was comparing the wheels of the Curiosity rover and the Perseverance rover and noticed that the latter had a very flat cylindrical design as compared to the former.

This got me thinking about which wheel profile was sturdier. That got me thinking about various things that might be different. Intuitively, I felt that the convex wheel would be better off because it would be able to transfer some of the applied force into normal components, which would keep the shear stresses lower (Aluminum 6061 has a shear strength of only 207 MPa, compared to the tensile yield strength of 276 MPa).

So I decided to test it on Ansys:

From these, I can visibly see that the regions of maximum stress are lower in the convex wheel. But I am starting to doubt if I'm misreading something. Could someone knowledgable help?

TL;DR

Among convex and flat profiles, which one is sturdier? (If you feel the word sturdy is ambiguous, please interpret it as "less metal fatigue", perhaps.)