texts: Why are the facades of historic residential buildings in Paris tilted backwards?

texts:
In any major city that features an historical center, the list of attractions advertised by tourist guides seldom includes what, in my opinion, would constitute the destination's most important part: historical residential buildings.
Unlike cathedrals and palaces, these are hardly ever carefully designed, nor elegantly engineered.
In Paris, these buildings are from two to five stories high, and, from the second floor and up, their facades are tilted backwards from the street. This, I believe, is a unique Paris feature: you won't find anything like it in any other city: neither in France, nor anywhere else.
Sometimes, the facade of the ground floor is titled the other way, so that the building looks like a section of a pyramid placed on top of a section of an upended pyramid.
What's the idea?
I have heard a number of theories about this phenomenon, none of them backed by data from a reliable source.
The examples in the photos illustrate my point. Please note that the sketch of the Place de Greve, where the tilt is also clearly visible, dates back to 1750, which proves that the tilt is by no means a recent phenomenon.
So, what's the big idea? From the engineering point of view, what would be the advantage of tilting the facade backwards? Does it have anything to do with the building materials (limestone, I believe, rather than bricks and lime render)? Any ideas?


texts: How to we ping to check accessibility of a website or a server from different locations?

texts: Do we have an online utility which can be used to ping by selecting locations?


texts: Nitrogen purging via outdoor unit: Gas not going thru?

texts:
I'm installing a new Daikin 4MXL (36K BTU) outdoor compressor, with 24K and 9K indoor unit (I previously installed a smaller dual zone Daikin)
One of new indoor unit's lineset will be behind drywall, so I cut off flare joints and to solder on sleeves. So I need to nitrogen purge. I have a nitrogen tank and a purge valve on the regulator to get the flow 2-4 PSI when I'm ready.
But I can't get it to work in concept with higher pressure (around 100 PSI). Something doesn't seem to be flowing right.
Both indoor units are connected to the outdoor compressor with flares that wrench tightened but not too tight (e.g. not torqued down yet).
Same for flares on 24K indoor unit. The 9K indoor air handler's lineset is the I have sleeves on to join pipes with flux paste in them. They're ready to solder.
So it is now a complete closed lineset circuit between the indoor and outdoor units.
Here's the problem - I can't verify that nitrogen flows all the way through properly in order to start soldering.
INJECTING NITROGEN INTO LIQUID SERVICE PORT "blocked":
I tried about 100 PSI of nitrogen into liquid side service port. Seems to almost immediately get stopped in some short run of pipe by sound of it. I turn off the gas, unscrew the adapter and it and injected out quickly and briefly:
INJECTING NITROGEN INTO VACCUM SIDE SERVICE PORT "DISAPPEARS":
When I try flowing 100 PSI into vacuum side service port, I hear the gas flowing into the pipes, pressure keeps dropping in my nitrogen cylinder, I keep hearing gas go into the pipes (when doing it for a minute or two). Soap test on flared connections at unit don't bubble, yet I don't feel anything coming out the liquid side service port with a wet finger. Seems like 100 PSI would be more than enough to let some gas all the way through and enough to feel if I'm putting 100 PSI in, even if some flares are leaking slightly. It's likeleaking somewhere inside or getting misdirected. (note, new unit and I never powered up or toughed allen wrench valves to release refrigerant)


texts: Terzaghi's Equation with more than one column

texts:
I've been send to do a project about the construction of a building. Throughout the project I had a doubt I couldn't solve and wish you could help me with:

When we are working with foundations, we can apply Terzaghi's formulas to get the bearing capacity of the ground. However, in everything I've read they always use a single column. How can I apply the formulas having the weight of the building and a more than one column?


texts: How to interpret the phase plot from an accelerometer on vibrating machinery

texts:
Attached is a plot of amplitude vs frequency and on the inset phase vs frequency. I have constructed this phase plot via $\arctan\left(\frac{Im}{Re}\right)$
How can I interpret the phase plot or extract some meaningful info from it, particularly in the region of the almost vertical line? This line occurs at around 102Hz which is nowhere near the amplitude peaks.


texts:
Suppose I have a heat generator with a connected heat storage tank. If the heat generator remains the same and the heat storage tank is dimensioned larger, the running time of the heat generator increases due to the higher storage losses.
Why is this so?

Normally, the surface with exponent 2 and the volume increases with exponent 3 - should the heat storage tank not have fewer losses?


texts: Do magnetic fields applied to a fuel line have an effect on heat output?

texts:
I am doing my final year engineering project on Magnetic Field Assisted Combustion and was curious to see what people thought about it.

Companies sell rare earth magnetic arrangements to be attached to fuel lines of gas burners and they are said to improve combustion efficiency but why exactly?

I have performed a number of experiments using a standard butane/propane gas burner with some magnets manufactured by one of said companies and have had some contradicting results. With lower strength magnets, heat transfer unexpectedly slowed down but with a much stronger arrangement, heat transfer rate was increased.

Also, the burn out time of the same amount of gas took 8 minutes less with the magnets in place around the fuel line.

I have read a number of journals on similar subjects but even within these, the actual reason for the increase in heat output is still not known.

Any thoughts on the subject would be massively appreciated and possibly give me some other areas to investigate that I have not already thought of.


texts: CO2 probe measuring at temperatures up to 150 °C

texts:
I'm looking for a $CO_2$ measuring probe (analog current output, digital out: RS232/485 - probe will be connected and transferring real time data to the data logger) that would operate up to 150 °C (hot air sucked out from the heated column which is highly concentrated by $CO_2$). The probe will not measure $CO_2$ concentration continually but in cycles - every 20 or 30 minutes, the probe should operate for about 1 or 2 minutes.

Another $CO_2$ probe should measure (rather control) trace amount of $CO_2$ after it's separated from the exhaust gas (small scale experimental boiler burning coal) - operating temp. approx. 75 °C. This probe is expected to measure $CO_2$ concentration rather continually or at least in cycles being 60+ minutes long.

I have found tons of probes, but all of them can operate up to + 60/70 °C. Some of them can withstand high temperatures while not measuring $CO_2$.

Do you have any experiences with such probes?


texts: What type of plastic is a good clear, flexible plastic for prototyping? (~0.5mm - 1.5mm thick)

texts:
I'm prototyping a hardware that involves many thin walls to bend around curves and such, so it needs to be flexible, cheap, and also transparent. It may also be the same plastic used in a production version.

The only example I can think of is the plastic you find around the inside of a new dress shirt collar. (McMaster Carr doesn't seem to have anything like it, except polycarbonate, which seems expensive and overkill; surely I'm thinking of a much cheaper plastic. Maybe PP, but not finding enough info to confirm, or find out where to get some in that form.) I almost went with transparency rolls for transparency projectors, but it's too thin/flexible (5 mils).


texts: Engineering calculations in a tool that will handle units

texts:
I know Mathcad handles units along with numbers which makes it easier to avoid errors by tracking units the way we would by hand.
e.g. 250 kW + 500 W

I just wanted to compare tools before I switch to Mathcad. Are there  any other tools people are aware of which will handle units as well?
I am especially interested in free / open source alternative that could do this unit-tracking either natively or with a Plugin.
e.g. Python or Jupyter notebooks etc.
If I must go with a paid version then Mathcad (or Mathcad Express, its free cousin) works as well unless there's a paid competitor that had more features or ease of use.


texts:
Can somebody help me find the equation for the deformation of a simply supported beam under trapezoidal load (with intensity Q1 and Q2, at starting point X1 and end point X2)?

I am trying to find it myself using double integration, but without luck. I already have a numerical solution - but it's too slow (i'm doing thousands of calculations).


texts: Is there any way a portal frame with pin joints at the top of the columns can be stable? Are portal frames ever done with pin joints at the bases? (Aside from those with raft foundations/combined footings)?


texts:
I have customized a fan for our centrifuge. How may I design it? Can you recommend me some software / resources ?

These are the the specifications:

Type : Radial

Capacity : 5000 Nm3/h

Head : 100 millibar

Speed : 2925 RPM


texts: How to retrofit seed starting trays to prevent root circling

texts:
I grow plum trees from pits using seed starting trays:

Unfortunately, I have a problem where the roots of the seedlings grow in circles around the bottom of the cavities of the trays. The circling roots cause problems when the trees grow to maturity (they strangle each other out).

Instead of the roots growing in circles, I need to train them downwards towards the hole (where they will be air-pruned).

The problem is normally solved by using seed starting trays that have specialized vertical fins that prevent the root from growing in circles:

Question:

I would like to retrofit my existing trays (I have several dozen) so that they function like the anti-root circling trays. I think this might be achieved by adding some sort of vertical fin in each cavity that would act as a physical barrier/re-router to the roots (but I'm not sure how to do this).

How can I retrofit my existing trays to prevent root circling?


texts: Do references for the California PE application have to be California PE's?

texts:
Here is the link to the current CA PE Exam application:

http://www.bpelsg.ca.gov/pubs/forms/ceapp.pdf

Page 2, which is the list of engagements/references, states:

  For each engagement claimed as qualifying experience, list the name of the person who will serve as your reference. Individuals serving as references must be licensed as Professional Engineers in California in the discipline of licensure for which you are applying or legally exempt from licensure. Individuals serving as references must have been appropriately licensed, or exempt from licensure, during the period of the engagement. YOU MUST LIST A MINIMUM OF FOUR REFERENCES. At least one of the applicants licensed references must be from someone who is or was in a supervisory capacity over the applicant, for each engagement for which the applicant desires credit. References must be from individual legally authorized to practice civil engineering in the state or country where the projects are located.

This statement is very confusing. First it says:

  Individuals serving as references must be licensed as Professional Engineers in California in the discipline of licensure for which you are applying or legally exempt from licensure.

Then later on it says:

  References must be from individual legally authorized to practice civil engineering in the state or country where the projects are located.

So, which is it: do the references have to be CA PE's, or not? Can someone tell me for sure?


texts:
We have standby diesel generators that are only run a few times a year. How long can we reasonably keep the diesel stored on site before using or disposing of it?

It is accepted that there is a finite shelf life particularly after the UK has started using B5 (5% biodiesel) but I have been unable to find any guidance or papers indicating how long it is recommended to store it.

I know that it depends on how well it is stored (contaminants etc.) but any best practice guidance / documents / journal articles that anyone could point me to would be much appreciated!


texts: How do Test Indicator Flexible Holders hold rigidly when tightened?

texts:
If one were to search on Amazon for "Test Indicator Flexible Holders" you will turn up many items using this mechanism (please ignore the magnetic base; I'm not focusing on that part, just the red components and the knob):

You can watch this video to see how they work:

https://youtu.be/wVtT6xP_yjo

It is clear from that video that, indeed, that single knob tightens down both (ball?) joints, both the joint mounted to the top of the magnetic base, but also the joint closest to the holder that is intended to hold the oscilloscope probe.

My question is two-fold (primary/important question is first):

Exactly how does this entire mechanism act to clamp both arms rigidly, in space? From the video and the pictures, it is not readily apparently what clamping action is at play here. My only guess is that there is some clamping action acting upon both links, but how can the single big black knob act to clamp all (ball?) joints?
Does this entire mechanism have some "standard" name in the industry? I know about ball joints, but are these really just ball joints? I speculate that these aren't true ball joints, because of the single knob being sufficient to clamp them all rigidly, leading me to speculate that the combination of joints, linkage arms, and joints have some standard name.


texts:
I am trying to solve the problem:

  The critical resolved shear stress for iron is 27 MPa. Determine the
  maximum possible yield strength for a single crystal of Fe pulled in
  tension.

I think that this is related to the equation $\sigma_{yield} = \dfrac{\tau_{crit}}{\cos{\Phi}\cos{\gamma}}$.

The book says:

  The minimum stress necessary to introduce yielding occurs when a
  single crystal is oriented such that $\Phi=\gamma=45°$; under these
  conditions, $\sigma_{yield}= 2\tau_{crit}$.

When I tried check my answer, the solution manual said I should use $\sigma_{yield}= 2\tau_{crit}$:

  In order to determine the maximum possible yield strength for a single
  crystal of Fe pulled in tension, we simply employ Equation 7.5 as
  $\sigma_y=2\tau_{crss}=(2)(27\ \mathrm{MPa})=54\ \mathrm{MPa}$.

I don't get this. Doesn't this calculate the minimum yield strength, not the maximum? The solution manual is considering the possibility of the iron crystal being pulled in tension in a direction that is most favourable and makes one of the slip systems reach the critical value the quickest.

But to know the maximum possible yield strength shouldn't you calculate the situation in which tension is applied in a direction that makes $\cos\Phi\cos\gamma$ as small as possible? So, basically, in a direction in which the resolved shear stress is just a fraction of the applied tensile stress?

The solution manual gets the yield strength when you pull the single iron crystal in such a direction that the resolved shear stress is the largest fraction possible of the applied stress. But if you reorient the single crystal, couldn't it withstand a way larger applied tensile stress and thus have a higher yield strength?


texts:
How are automotive engine mounts tuned to behave differently for different frequencies, like they are soft for high frequency low amplitude vibrations and hard for low frequency high amplitude excitations..?

I am aware of active or hydraulic mounts, but want to know how a regular mount is tuned to behave in such a way..?


texts: Solidworks - Copy equation driven linear pattern sketch to other plane

texts:
I am trying to create a 3d sketch similar to this (that is equation driven)

(the image is a screenshot from a tutorial but the sketch in the tutorial is not equation driven unfortunately). image source: https://www.youtube.com/watch?v=GBNAnqolQ-I (at 12:46)

SW file: https://drive.google.com/open?id=1VuQUzYxyjPer2lX7t0EAsDkeTctPBQJj

I made a sketch of a few points using a linear sketch pattern (amount of instances and spacing are both equation driven). The points that can be seen in the images below in my sketch will be used as the 'corners' of the 3d sketch .

If my explanation is unclear/incomplete please let me know and I'll try and fix it.

I want to have the same sketch on another parallel plane, I tried copying the sketch over to another plane but unfortunately when I change the equation variables the original linear sketch pattern sketch (on the original plane) does change (amount of instances/spacing) but the copied sketch (on the parallel plane) does not.

I also tried using 'convert entities' but unfortunately I cannot (or I don't know how to) select an entire sketch instead of individual points/lines/shapes etc using 'convert entities'. If I'm not able to select the entire sketch using 'convert entities' I am quite sure that when the number of instances of my original sketch changes the sketch on the second plane created using 'convert entities' will not have these instances added.

I could manually redraw the sketch (using the same equations/variables for the amount of instances in the linear sketch pattern and for the spacing in the linear sketch pattern) but I think there should be a better/more efficient way of doing it.

What am I doing wrong? What could be a possible solution to this issue?
Should I not use a loft for creating this model? is this the right approach?

Some images:

First sketch drawn on original plane:

 (the sketch = the 36-ish points on the line on the left side of the left plane in the image)

Sketch copied over to second plane:

This looks as if it has worked, however as soon as I change the variables in my equations the following happens (the original sketch's linear sketch pattern changes (the amount of instances/the spacing change) as they should according to the corresponding equations) but the copied sketch does not change at all.. which is an issue since I need all of the copies to change whenever I change the original.

background: I am trying to model DC motor windings using loft feature (as explained in the following post How to model Motor Windings in Solidworks?). I am trying to create the points required for the 3d sketch that can be seen in 'step 1' of the post I linked above.

What I am trying to achieve: (original sketch (in the green circle) to be copied over to the 3 lines (in the red circles) and all copies to change (number of instances/spacing) when i change the original sketch (by changing my equation variables).

EDIT: I just thought of an issue with the approach explained above; if I were to change the variables in my equations which would result in more points per sketch, the 3d sketch which i would draw by hand wouldn't get extra segments added automatically so i don't think it's a good approach.

Alternative approach (current plan of attack):

1) Draw 1 'spiral' (4 points) using 3d sketch (dimensions driven by equations/variables)
2) use loft feature to create solid body out of this sketch
3) linear pattern the loft feature (amount of instances in pattern and pattern spacing once again determined by variables/equations)

This way the model should update properly whenever the variables are changed in my equations and I won't have to do any manual fixing (I think). Any thoughts/suggestions/criticism regarding this approach? If so please let me know.

Thank you!


texts: dimensions for electrical outlet faceplate cutout

texts:
What are the dimensions for the cutouts in an electrical outlet faceplate?

I need to add several outlets in a sheet metal covering but I cannot find the dimensions or a dxf to use for the shape.  The closest I've found is the following image from http://www.archtoolbox.com/materials-systems/electrical/electricalfaceplates.html

The only problem is that it gives rectangular dimensions without providing the corner radius and spacing between the two outlets.


texts: Are these horizontal timbers removable in an attic/loft?

texts:
There are 3 horizontal lengths of timber stretching across the centre-level of my attic/loft space and are attached at either end to the rafters with a single nail. I can wobble them by hand and they don't seem to be under any tension/compression.
The House is a bungalow in a T shape and in the picture attached, I am facing towards the top of the T from near the bottom of the T. The roof is a purlin roof and the supports under the purlins are on top of 2 central masonry walls (the hallway) and the house is a solid masonry structure.
From what I can tell, these horizontal members are either leftover temporary supports from the initial construction or are mid-level collar ties?
Could I remove these 3 timbers to open up the attic space for easier access & light storage? I would move them up higher, just under the ridge board, either way.
Any insight is appreciated as I'm not sure which way to go exactly and just looking for some guidance before I talk to an engineer.
Thanks,
Derek


texts: What happens when an LCD screen shuts off?

texts:
I read about how an LCD screen works here, and it made me wonder what actually happens when the screen shuts off. Based off of this, I can think of several possibilities:

Electricity is supplied to all the pixels/crystals, thus making them all appear dark. While this fits with the on/off explanations given in that article, it seems like a significant waste of energy to use extra energy when not in use.
Electricity is not supplied to all the pixels, which would light them all up, but the backlight shuts off, so the screen appears dark.
Electricity is maintained to the pixels that were receiving electricity when the screen was on, but the backlight shuts off so the screen appears dark.

I would be curious to know if different phases of the off screen are different (such as a off-screen-like screen saver versus a sleep mode or being shut off, etc.).


texts: Can channel bandwidth can transmit any VALUES of frequencies as long as they are within range

texts:
I know that channel bandwidth is the range of frequencies it can transmit . Let's say channel bandwidth is 100 Hz . Does that mean it can transmit any signal whose bandwidth is 100Hz regardless of actual values of those frequencies .
For example signal 1 has  frequencies 200Hz- 300Hz .
Signal 2 has frequencies 800Hz-900Hz.
Borh signals have badwidth 100Hz
Can the channel transmit both of these signals?


texts: Is there an equivalent to the 'equal' constraint from solidworks in fusion 360?

texts:
I used to use Solidworks a few years back and am now trying to learn Autodesk Fusion 360. So far I'm pretty impressed but one thing I've not found is something like the equal constraint that Solidworks offered.

My thoughts were that it would clutter a sketch less to make a load of lines constrained to be the same length and then specify the dimension once to lock those constraints down.

Is that possible or is there an equivalent?


texts: How do old wind turbine towers pickup magnetism overtime?

texts:
I was conducting some robotics tests on a old wind turbine today, and noticed strong magnetic fields around the steel tower. This magnetic field does not exist on other modern wind turbines at the same site. I am completely baffled by this, so I’m hoping I can find some answers here.

These turbines are located in San Gorgonio Path near Palm Springs, CA. They are Nordtank 65 wind turbines, decommissioned about a decade ago. The towers are steel, bare, without paint. Overall they have very little rust as the climate is very dry and hot. The turbines still contain their generators, which contain magnets. But I don’t think these magnets are very strong.

Using a decent mechanical compass, I can clearly see about 40 degrees of deflection as I walk towards the base of the tower from about 10 feet away. I tried this on all 6 decommissioned Nordtanks, all of them exhibited the same behavior. I tried on modern 0.5 MW turbines nearby while they are generating, but the max compass deflection I got was about 5 degrees at a distance about 5 inches away from the tower itself.

When I first observed the magnetic field, my theory was that the turbine tower was still heating up from the morning sun. Due to Seebeck effect, there could be current flowing in the material as the base is cooled by the foundation buried into the ground. However the deflection on the compass did not stop even though the temperature stabilized.

What could have caused this? I would love to find out!


texts: Difference between strong, weak and differential forms?

texts:
We recently covered fundamental laws in our Computational Continuum Mechanics course last term. There are many forms of these laws and I am confused which one to use and when.

For instance in mass continuity, we can write the integral version (I am not gonna write it here) as usual. Then we can use the Jacobian to write it like this
$$ \int_{V_0} \rho_0 - J \rho \ \ dV $$
which can be said to be the weak form. Then by localisation, we can have
$$ J(\pmb{x},t) = \frac{\rho_0(t)}{\rho(\pmb{y},t)} $$
where $\pmb{y}(\pmb{x},t)$ is the deformed configuration position and $\pmb{x}$ is the undeformed configuration position (if that make sense) which is now the strong form. So isn't this good enough already? Why don't we use this in our code, because this is also point-wise.

We can also derive the differential form of course which is
$$ \frac{\partial \rho}{\partial t} + \nabla \cdot (\rho \pmb{u})$$
where $u$ is velocity.

If I just wanted density with time, is it better to use the strong form? Would I just use the differential form if I want to include velocity or something? Also our lecturer mentioned that the Jacobian strong form is in Lagrangian form but differential is in Eulerian form. I know the meaning of both but I am not sure what it means in this context.


texts: Finite element method, question about the solver

texts:
So I am working with COMSOL Multiphysics and I have a very complex simulation. I have a boundary condition that evaluates to 1 if the value of a variable is 20 and 0 otherwise. I could implement my code just fine in COMSOL. However, I am facing a problem (see a draft that I made below please). Basically, for the first iterations whenever the variable reaches 20 it turns the boundary condition to 0, but as I have more iterations the limit slightly increases (thus reaching values above 20). After some time the limit comes back to 20 and the same problem as before occurs again. Any thoughts?
I have already tried to increase the solver tolerance but the some problem occurs
Thanks in advance


texts: How to design a house to be cooled passively?

texts:
I live in Louisiana these days, in an area that is known for its numerous antebellum plantation homes (circa early 1800s). While touring one of these homes it was clear that almost everything about the house was designed around keeping cool in the summer.  Some examples:

4-meter-high ceilings to allow hot air to rise to the ceiling.
Floor-to-ceiling windows to allow hot air at the top to escape and cool air to be drawn in at the bottom.
Porches on the sunny sides of the house to prevent sunlight from entering the windows.
Large central staircases to allow hot air to rise to the second floor, drawing cool air in on the bottom floor.
Some have a cupola, a central observation room at the top of the house, again to allow hot air to escape at the top of the house and draw air in from the bottom.

My question is: Given our modern understanding of thermodynamics, how could one design a home today to be cooled passively? Could we do any better than the plantation owners of the 1800s?

Let's define cooling as making the house more comfortable for humans. This means that it is not only important to reduce the temperature, but also to block sunlight and maintain airflow. Also, if possible, it would be very beneficial to extract moisture from the air.


texts: What fluid is generally used for laboratory testing of hydraulics?

texts: Which liquid is generally used or is it better to carry out hydraulic laboratory tests?


texts: Chain length increasing during rotation of chain sprocket pair?

texts:
I am writing a program to calculate chain lengths required for a particular sprocket pair when I noticed this
Consider a 9 teeth sprocket paired with an identical 9 teeth sprocket (image reference) the pitch circle is green and the initial position of the chain (used to calculate the chain length and number of links) is shown in BLUE. The total length is 285.75mm which comes out to be 18 link chain for 15.875mm chain pitch.

Now I rotated the pitch polygon by 10 degrees (0.25 of the angle enclosed by 1 link which is 360/9 = 40deg) this is shown in orange. Then I drew the taut chain again (orange lines). Now if I measure the chain length, it is lesser than the calculated length before (by about 0.3mm)!

Why is this happening? Am I doing something wrong? This also means that if I had adjusted my centre distance to make the chain links a whole number in the second configuration, then as it rotates to the first configuration, the chain length increases..but we assume that the chain is inextensible
Added another drawing for reference (pardon the messy nature). The green curves are the sprocket and chain in initial position, the magenta curves are the rotated configuration. As we can see, the pink line between the 2 sprockets cannot accommodate the 5 chain pitches and is interfering with the RH sprocket teeth. Practically, the chain slackness will take care of this change in length. My question is about the theoretical aspect. Is it impossible mathematically to wrap such a chain around sprockets without encountering any changes in link length during rotation??


texts: Why does positive phase and gain margins cause any system to be stable whereas negative phase and gain margins cause the system to be unstable ?


texts: How do the bubble oscillations in two-phase flows affect the dissipation rate of turbulent kinetic energy?

texts:
I am investigating the effects of bubble oscillations (calculated using the Rayleigh-Plesset equation for bubble dynamics) on the turbulence in two-phase flows. Since I am using cryogenic fluids, the thermal effects also play a role. I am trying to find out the connection between the oscillation frequencies and how they influence the turbulence dissipation rate.

I guess that, when the frequencies are high, i.e., when the liquid-vapour interface oscillates at high frequencies, the turbulent kinetic energy in the flow increases. So, will the dissipation rate also increase proportionally to the turbulent kinetic energy? (epsilon proportional to k^1.5)


texts: Shear force and bending diagram un-uniformly distributed load

texts:
I already got great help on this topic, but I'd like to make sure that I get it.

For example, take a beam of length 6 meters, left side fixed support and right side rolled support. There is a load of 30 kN-m that starts at 3 meters and ends at 6 meters with a magnitude of 60 kN-m.

The function of the load is easy, f(x)=10x. The centroid is given by
$$\frac{\int_3^6 10x² dx}{\int_3^6 10x dx} = 4.67m$$

And the force translated into a point load is
$$ \int_3^6 10x dx   = 135 kN $$

So the sum of forces as seen from a is 0, and can be used to calculate Mb
$$ \sum Ma =0 = 4.67*135 -6*Mb \Rightarrow Mb = 105 kN \Rightarrow Ma=35kN$$

Then to find the shear forces I integrate the equation from 3 to x taking into account Ma
$$ \int_3^x 10x dx -Ma   = 5x² -75 $$

And to find the Bending moments I just integrate again, this time for the whole equation

$$ \int_0^x (5x²-75 )dx = \frac{5x³}{3} -75x $$

Alas this does not give the complete answer, I have many uncertainties, for the shear forces I notice that it only gives the correct answer for x between 3 and 6; for x under 3 it becomes Ma, and I imagine if the length of the beam would be greater than the distributed load's length, it would be Mb for x>6. If I would add a point load of 3kN at l=2, do I need to replace Ma with Ma'- 3kN in the shear force equation? What would happen with a point load after 6 meters (eg lenght of beam = 9 meters, point load at 7m)?

As for the bending moments, I kinda get the right answer for x between 3 and 6, but it is 90 kN too much, which is the BM at the start of the distributed load. For x=2 for example I get completely wrong answers, and I need to revert to calculating BM by using trigonometry to calculate the actual area under the shear force curve.

I mean I can solve them, but I don't get the why - why can't I use the BM function to calculate all of x, considering the boundary condition should have been solved in the first integral (from 3 to 6 ). Why do I need to substract the BM at the beginning of the distributed load,...

I would greatly appreciate if someone would take the time to enlighten me - as it is I'm not really confident for the exam (I can't afford to fail)


texts:
This is an HVAC mechanical engineering question on a document from a manufacture where they convert units of electrical energy to therms of natural gas.

Carrier has writeups for building energy simulation modeling, and this link is a PDF for a writeup using the HAP software.

Question:
The example on page 2 as a high level feasibility they convert units of NG to kWh:

  In a certain locale the price for electricity is 0.0960 dollar per
  killowatt hour and the cost of natural gas is 0.937 dollar per therm.
  If we convert the gas price to use units of kWh, we get a gas price of
  0.0320 $/kWh. Therefore a kWh of electricity is three  times as expensive as a kWh of natural gas. If the average annual COP of the
  DHRC is more than three times that of the gas boiler, then heating
  cost will be reduced by using the DHRC. If the COP of the DHRC is less
  than three times that of the boiler, heating cost will increase. Note:
  This is a single example for illustration. Energy prices vary widely
  by location and over time. You should use your own local utility
  prices to assess heat recovery viability for your projects.

I know 1 therm = 29.3001 kWh or 1 kWh = 0.03413 therm.

But what’s the math behind coming up with “convert the gas price to use units of kWh, we get a gas price of 0.0320 $/kWh”?


texts: Protect equipment against electromagnetic radiation

texts:
They say that in the near future high cosmic radiation is possible. In addition, the Earth’s magnetic field is likely to weaken.
I want to create something like a camera that would protect against electromagnetic radiation. What will be effective for this? Useful articles, real examples? I want to protect equipment, for example, my phones, watches, if at least somehow.
Thanks in advance


texts: Maximum MPC prediction horizon for an unstable plant

texts:
In the following book,

Model Predictive Control ToolboxTM (User's Guide)

    Alberto Bemporad
    Manfred Morari
    N. Lawrence Ricker

At page 1-6, it has been mentioned that

  If the plant is open-loop unstable, the maximum possible p is the number of control intervals required for the plant’s open-loop step response to become infinite.

Here, p means the prediction horizon.

This claim does not look reasonable to me.
I have not understood the reason for this claim.
What will happen if I choose the prediction horizon longer?


texts:
I'm currently designing my own centrifugal fan for one of my projects, everything excluding the motor.

My design is similar to the above just that the outlet is much shorter.

The problem I'm facing is that my fan produces a high pitch noise. Assuming I keep the blades design and the power parameters the same, how can I reduce the high pitch frequency?

To my understanding, the volute casing has a tiny gap at the start of the volute tongue (indicated as Rc), could this be the cause of the high frequency noise?


texts: Gear/Mechanics problem: How to design to allow for 2 types of rotation

texts:
I am designing a new mowing system that can effectively mow around poles. The machine consists of an arm that is attached to the back of a tractor and runs off its PTO. At the end of the arm is a rotating - boomerang- shape head that when it comes into contact can turn 180 degrees around a pole before snapping back into place. There are three blades on the bottom of the head that is turned by pulleys and belts that receive power from a rotating shaft off of the mower arm. If the head was to remain stationary. This would be no issue, but the problem is that the head is supposed to be allowed to freely swivel around the pole and that will be affected by the belt system that receives power from the shaft we want to swivel around. -Ill add in drawings to be clear -

I am assuming that a gearbox will need to be added to the shaft off of the arm to allow for the two rotations and for the mower head to be able to swivel back to its original position via a torsion spring and keep the belt from slipping. I am just having some trouble visualizing what that configuration will look like. Some ideas I had would be some type of planetary gearbox or incorporating some kind of anti-reverse gear that will only attach when the head begins to swivel to change the speed of the belt to compensate.
Any help will be greatly appreciated.


texts: Increasing torsional-stress resistance of an Auger at its motor-shaft joint

texts:
An auger is used to move plastic balls and is rotated by a stepper motor. Due to the balls getting jammed sometimes, this induces stress on the auger at the motor-shaft junction and breaks. Images below describe the issue better.
Specification:

Auger - 3D printed PLA
Motor - Nema 17 (4.2kgcm torque)
Plastic Balls Weight - 3 grams
Auger RPM - 180rpm

Possible solutions that I've thought:

Adding epoxy at the fracture section to strengthen it
Increasing the fillet diameter at the fracture section

Are there other options to solve this?


texts:
I've been working on a flat pattern design to send to the machine shop and have run into a problem making the support piece. The problem I've been hitting is I can't figure out how to flange off of the sides in a triangle shape to meet the top. The best way to explain this is through the attached screenshots.

The triange support piece in between the bend is the problem child. I'm basically trying to make that piece but as a bend off of the side of the part. The reason I want to do this is so that the flat pattern will come out properly. If anyone can explain to me how to make this bend correctly or a better way of doing this it would be greatly appreciated. I'm going to attach one more screenshot of my attempt on the other side.

This is my first post so if anyone has any pointers on what else to include in the post please let me know. To anyone that replies thank you in advance.


texts:
I would like to measure the force with which the bolt (dark blue) pushes on the break pad (grey) to stop the wheel (light blue). I am thinking that I could put some component between the bolt and the break pad (red part). There is about 1 cm gap between the bolt and the brake pad, when the brake is in neutral.
I'm thinking I will use an arduino to read the value.
What kind of component can I use? A strain gauge on the side of the red component, or maybe a capacitor that is compressed?


texts: Boundary conditions for this beam deflection problem

texts:
consider the diagram above. I know that deflection is described by the equation
$$EI\frac{d^4y}{dx^4}=p(x)$$
where $L$  is the length of the beam, $E$ is the Young's module, $I$ is the moment of inertia, $p$ is the distribution of load and $M$ is the torque.

I have the boundary conditions

$y(0)=y'(0)=0$ which means that the left end of the beam is immovable.

$y(L)=0$  which mean that the right end of the beam is supported by something.

Then, what would be the condition for $y'(L)$ ??


texts: How do I dimension the natural frequency formula?

texts: with masses declared as grams and static stiffness as N/mm, how do I dimension them for Hz ?


texts: Chart that describes how full the pond is

texts: when designing a pond it is customary to produce a chart for the local council, specifying the height of the water for the volume stored. What is the name of this chart?


texts: Is there any defined mathematical parameter that can give me the average distance of a volume to a point?

texts:
I'm currently trying to design a bulk-handling system which minimizes the distance from the bulk material pile(s) where the material is loaded (the volume) to the unloading platform(s) (the point), but I have many possible combinations on the volume shape and the number of unloading point. I would ideally like to iterate through various designs in order to find the most feasible one, and a useful parameter to get from each design would be to get this average travel distance from the pile to the platform.

I have toyed around with the idea of using the centroid as the average distance to a point, but the problem is that the directional component of the centroid makes it such that it doesn't truly represent the average distance. For example, a disk with a radius of 10 meters might have the same centroid as a disk with a radius of 100 meters, but the average distance from the center would be different.

$$\int_{V}r\text{ d}V$$

A slightly better representation would be the moment of inertia, since the squared component better represents average distance (so that opposite directions don't cancel out).

$$\int_V r^2\text{ d}V$$

However, to truly get the average distance, I would need something that looks more like this:

$$\int_V \lvert r\rvert\text{ d}V$$

Is there any simple way of getting this value from a CAD software package, or is it derivable from any other existing mathematical definitions like the centroid or the moment of inertia? Similarly, if this average distance is obtained only relative to the centroid, how could I extrapolate it to another arbitrary point?


texts: I want to import initial state of a model using predefined fields in import analysis and change the general stiffness matrix and continue simulation. But by default model get the section(material) state of the job file specify in predefined fields. Is there any method to change general stiffness?


texts:
In Etabs, if I model a building with semi-rigid diaphragms assigned to the floors, the floors will now transfer gravity loads when default meshing is assigned (as compared to rigid diaphragms transferring only mass and lateral loads). If i'm working with a simple model with only walls and floors modeled (no columns), the weight distribution will be incorrect since all the weight from the entire floor is going to the walls. One way to correct that would be to model the columns. Can another way to correct it be to assign a weight modifier of 0.01 to the floors and use dummy beams on top of the walls with assigned gravity loads based on tributary area?

I'd appreciate some insight. Thank you.


texts: How do LED traffic light diffusion lenses work?

texts:
In my area traffic lights with bulbs are being gradually replaced with LED traffic lights. Sometimes these lights have no diffusion lens and the individual LEDs can be seen. Other times the lights have diffusion lenses which give a very smooth, consistent color.

How do these lenses work?

Traffic light in Brookline, MA, with no diffuser:


texts: Electric field inside a metal is zero , when it is placed in an external electric field. What about human body? If it is placed in an external electric field, will the field inside the body be zero? I am confused because human body is a conductor but not as good as metals.


texts: How can I determine pressure inside contained cylinder when heat is added?

texts:
I have a contained and thermally insulated cylinder of radius r. Inside this cylinder, there is water that reaches up to a certain height inside the cylinder (hw). There is a heater underwater that will supply thermal energy to the water at a certain wattage. The rest of the space is filled with air at atmospheric pressure (ha is the height the air occupies so that ha + hw = htotal).
I start supplying thermal energy at a given wattage to the water. My goal is to keep the water bubbling at a fixed rate for as long as I can control the pressure inside the vessel. I want to know:
How can I determine at what rate does the pressure increase? How do I determine the increase boiling point of water? How do I relate the input heat in wattage to bubbling rate? (evaporation rate?) I want to keep the water bubbling at a constant rate, how do I determine how the heater wattage should increase to match the increasing boiling point as the pressure builds up? Is there a reference for what a bubbling rate (evaporation rate?) looks like?


texts:
I am about to present my work on vibrations to a NVH specialist at work and he is supposed to help me.

I have calculated PSD's, now my question (subjective, I know) is how should I plot the data? I've been plotting $PSD \big[\frac{g^2}{Hz}\big]$ against frequency $\big[Hz\big]$, both in linear axes. I've been told the frequency axis should be in logarithmic scale, which makes sense, what about the PSD axis?


texts: How can I modify a pair of two-way switches so that the circuit can also be opened or closed remotely using a device?

texts:
I have a pair of two-way switches at different floors to control a light bulb. I wish to put an Android-phone-controllable external switch over either switch to flip it up or down. I am familiar with the programming and circuit side, but the problem is I couldn't find any mechanic part to do the external switch's job like mentioned above.

The reason why I'm not going wiring over the original switch is because my mother isn't familiar with smartphones, so I want to implement it without interfering with the basic usage.


texts: Most efficient turbine for harnessing energy from bidirectional air flow?

texts:
I am currently working on designing an oscillating water column as part of a project. In summary:

  OWC are devices with a semi-submerged chamber or hollow open to the
  sea below, keeping a trapped air pocket above a water column. Waves
  force the column to act like a piston, moving up and down, forcing the
  air out of the chamber and back into it. This continuous movement
  force a bidirectional stream of high-velocity air, which is channelled
  through a Power-Take-Off (PTO). The PTO system converts the airflow
  into energy.

https://en.wikipedia.org/wiki/Oscillating_water_column

In my case, the PTO system is a turbine, the rotation of which will power a rotary vane pump.

(Number 2 is the pump rotor)

The pump rotor and the turbine would be on the same axis and connected by a rod. In short, the rotation of the turbine would directly power the pump; electricity would not be produced in the process.

I've been searching to see what turbines would be the most efficient, but I haven't found any information. What would be the most efficient turbine for this situation? Is it a Wells Turbine? Something like a bidirectional impulse turbine

or something else?


texts: How to design electronics to mitigate tin whiskers?

texts:
Tin Whiskers are a major problem in the design of electronic circuits and the manufacturing of electronic hardware.

What are Tin Whiskers? How can electronic products be design to mitigate the issue of Tin Whiskers?

References:

David Gilbert and Tin Whiskers
Understanding and mitigating tin whiskers
Don’t Let Tin Whiskers Destroy Your Design
Mitigation Strategies for Tin Whiskers
Tin Whiskers Are Real and Complex


texts: Gearing for Multiple Forward / Reverse on Single Drive Shaft

texts:
This model illustrates my question:

Red is a motor
Green is the drive shaft
Orange are nylon straps
Blue are spools for the straps

I want to be able to drive multiple spools in multiple directions at the same time. They should be individually controllable and able to stay still, wind, or unwind. They may all move at the same speed.

My best guess is that this has something to do with idler gears, planetary gears, and servo-controlled clutches. But I don't really understand how to employ these, or know whether I'm on the right track.

I appreciate any help! I'm especially interested in solutions which are cost effective and robust.

This seems common enough that there must be a solution already?


texts: Determine the transfer function of a movement equation

texts:
The problem is the following. I have to control a spaceship (assuming no gravity, no mass, no friction / no external forces). In other words, the first equation in this question leads to $0 = 0$. My goal is to reach a position for a given acceleration (i.e. throttle).
The movement equation (assuming a constant acceleration) is the following: $x(t) = 0.5 * a * t^2 + v0 * t + x0$ where $v0$ is the initial velocity and $x0$ the initial position ($x0 = 0$). Finally, I get $a = (goal - t*V0) / t^2$ where $goal= target - traveled_distance$
I put this equation in my system. There is a sensor to measure the velocity. Each time the velocity is measure, I can send a new acceleration command.
I got the following plots (the first one is the acceleration, the second one the velocity, and the last one the trajectory)

On the last plot, we can clearly identify the response of a second order system. I also observed that increasing $t$ reduces the overshoot (so I guess that $t$ is acting like a proportional gain).
My question is what would be the corresponding transfer function? I tried to identify it with a second order differential equation but did not get any convincing results.


texts: Equivalent Force: Hydraulic rams in H frame machine press

texts:
A 100ton H frame machine press can use 1x100 ton ram to exert this amount of force.

Can 3x33 ton rams do the same job if they are applied to same area as the 100ton ram?

Also in relation to a H frame does the bed hanging rods/bolts take most of the ram force or do the legs disperse the force as well as support weight.

My apologies if this is a very basic question or if the basic understanding is wrong


texts: For a column, what does "rotation fixed and translation fixed" mean

texts:
So there's a permutation of rotation and translation each being either fixed or free for a column.  What do each mean?

If the column is toe nailed to a plywood / beam underneath which is it?

If it's in a steel bracket nailed to a column below what is it?

If it has a 2x6 plate of a wall on top nailed to it what is it?

Does bracing in the middle of the column for either affect it?

My case is a 8x8 wood post


texts:
I'm trying to simulate a compound action potential for calibrating research instruments. The image below is a small overview of the design.

I've already completed the data acquisition from a live animal, and processed the data in MATLAB to make a nice, noise-less signal, with 789 values in 12-bit format. I then cloned the repository to the Pi using Git. Below is the Python script I've written on the RPi. You can skip to def main in the script to see functionality.

#!/usr/bin/python

import spidev
from time import sleep
import RPi.GPIO as GPIO
import csv
import sys
import math

DEBUG = False
spi_max_speed = 20 * 1000000
V_Ref = 5000
Resolution = 2**12
CE = 0

spi = spidev.SpiDev()
spi.open(0,CE)
spi.max_speed_hz = spi_max_speed

LDAQ = 22
GPIO.setmode(GPIO.BOARD)
GPIO.setup(LDAQ, GPIO.OUT)
GPIO.output(LDAQ,GPIO.LOW)

def setOutput(val):
    lowByte = val & 0b11111111 #Make bytes using MCP4921 data sheet info
    highByte = ((val >> 8) & 0xff) | 0b0 << 7 | 0b0 << 6 | 0b1 << 5 | 0b1 << 4
    if DEBUG :
        print("Highbyte = {0:8b}".format(highByte))
        print("Lowbyte =  {0:8b}".format(lowByte))
    spi.xfer2([highByte, lowByte])

def main():
    with open('signal12bit.csv') as signal:
        signal_length = float(raw_input("Please input signal length in ms: "))
        delay = float(raw_input("Please input delay after signal in ms: "))
        amplitude = float(raw_input("Please input signal amplitude in mV: "))
        print "Starting Simulant with signal length %.1f ms, delay %.1f ms and amplitude %.1f mV." % (signal_length, delay, amplitude)
        if not DEBUG : print "Press ctrl+c to close."
        sleep (1) #Wait a sec before starting
        read = csv.reader(signal, delimiter=' ', quotechar='|')
        try:
            while(True):
                signal.seek(0)
                for row in read: #Loop csv file rows
                    if DEBUG : print ', '.join(row)
                    setOutput(int(row)/int((V_Ref/amplitude))) #Adjust amplitude, not super necessary to do in software
                    sleep (signal_length/(data_points*1000) #Divide by 1000 to make into ms, divide by length of data
                sleep (delay/1000)
        except (KeyboardInterrupt, Exception) as e:
            print(e)
            print "Closing SPI channel"
            setOutput(0)
            GPIO.cleanup()
            spi.close()

if __name__ == '__main__':
    main()

This script almost works as intended. Connecting the output pin of the MCP4921 to an oscilloscope shows that it reproduces the signal very well, and it outputs the subsequent delay correctly.

Unfortunately, the data points are seperated much further than I need them to be. The shortest time I can cram the signal into is about 79 ms. This is due to dividing by 789000 in the sleep function, which I know is too much to ask from Python and from the Pi, because reading the csv file takes time. However, if I try making an array manually, and putting those values out instead of reading the csv file, I can achieve a frequency over 6 kHz with no loss.

My question is this

How can I get this signal to appear at a frequency of 250 Hz, and decrease it reliably from the user's input? I've thought about manually writing the 789 values into an array in the script, and then changing the SPI speed to whatever value fits with 250 Hz. This would eliminate the slow csv reader function, but then you can't reduce the frequency from user input. In any case, eliminating the need for csv.read would help a lot. Thanks!


texts: Why don't escalators slow down when people get on?

texts:
My friend and I were discussing this earlier: why don't escalators slow down when people get on? We are not interested in any fancy schmancy computers that might adjust their speed for capacity/traffic flow, we were simply wondering about the most basic possible escalator.

So our thoughts were: If an escalator is running at a constant speed, and then a single person (or more people) stand on it, it is obviously doing more work to lift that mass. Should the speed of the escalator drop? If something is keeping the speed from changing, does that mean the torque of the motor changes? Or does it simply draw more power but keep the same torque? Are we missing something obvious?


texts: Determining thrust equations for a custom UAV

texts:
I have been tasked to mathematically model and simulate a 2 propeller, 2 motor UAV. But I am struggling with determining the thrust equations, of the propeller, for my design.

I know that:

Ft = Ct * rho * (w/(2*pi))^2 * D^4

Where rho is the density of air ;

D, the diameter in meters of the propeller;

Ct, the thrust coefficient;

And w is the angular velocity of the propeller.

However, I was not given Ct although it is necessary for this equation.

I have been told I can use something called the  "experimental propeller force-thrust constant" or Kf (units: N/V) to calculate Ct however, after multiplying Kf by the voltage of the motor driving the propeller, I am at a total loss as to how to do so.

I used dimensional analysis in an attempt to receive a clue to the equation:

Ct = Ft/(rho*(w/(2*pi))^2*D^4)

Therefore Ct's units are

N/((kg/(m^3))*(rev^2/sec^2)*m^4)

Which is equivalent to:

(N * sec^2)/(kg * rev^2*m)

Using the definition N = Kgm/s^2 the units of Ct are rev^-2.

Using the last two unit expressions I have arrived at this equation:

Ct = Kf * V / ((w/(2*pi))^2 * D * m)

Where V is voltage and m is mass.

The units work, but I know that doesn't mean its correct.

Can anyone kindly verify if this equation is actually correct? Otherwise can someone please explain how to achieve the equation for Ct using Kf?

Any constructive comments are much appreciated. Please forgive my visually unfriendly web math notation.


texts: Locking the shaft of a small fan-like setup

texts:
I have a fan-like setup where a 4 mm-thick rod is attached to a small motor-driven shaft (also 4 mm thick) such that the rod turns about its centre as the shaft turns:

It's a closing mechanism for a catflap. It normally can rotate in both directions, but when late at night, it should lock the outward direction but allow the inward direction.

The flap's right rail slides over the rod so when the rod rotates, the flap opens up. The flap's other rail slides over a similar rod, but is connected to a bearing instead. Here's a rough sketch:

How can I block the shaft from rotating further clockwise (or the rod, for that matter) regardless of the current position? I'm hoping to have the shaft/rod blocked (using another motor) so that it won't rotate by +5 degrees or so even under some 7 kg-cm torque.


texts: What is the entirety of breadth of road called?

texts: As roadway consists of a width of road on which a vehicle is not restricted by any physical barriers or separation to move laterally source, what is a similar term which encompasses the width of the entire road's infrastructure - barriers, drainage ditches, sound screens, generally the entirety of terrain allocated for construction as a road is built?


texts: What is a mesh topology? I have read this term being used in a lot of articles dealing with meshing the computational domain, but could not understand its intuitive meaning. And why is topology called a global property? Also, what does topology mean wrt CFD analysis anyways? Thank you.


texts: Why using Tyristor (SCR) for inverting the DC voltage in HVDC systems?

texts:
In High Voltage 3 PHASE  Transmission Systems the voltage needs to be rectified (from the AC generation source to DC), transmitted, and then inverted back (From DC to AC). For doing this, usually LCC (Line commutated converter) are used. LCC consists generally of SCR thyristor valves, and as we know, thyristor can be controlled with a firing angle  when the voltage between anode and cathode is positive. So it can be controlled only for the turning ON, while for turning off a reverse voltage neeed to be applied.
Now, everything is clear for the rectifing part (Thyristors rectify the voltage as a common diode when the AC half-wave is positive and then is turned OFF automatically).
But what happens for the inverting part, if we cannot control the turning off? I mean, how can we create a sine wave at the AC output if we have a DC voltage that is constantly applied to the thyristor (we have always the condition for turning on but not for turning off, since V_DC is always positive) ?


texts: Explanation of supersonic flow differences between a 2D wedge and a 3D cone

texts:
I know that in case of wedge we have a 2D behavior which creates a discontinuity across the shock, but I am unable to understand why this discontinuity is not present in the case of a conical surface. I have a vague idea that the continuity equation ensures this as, due to increase in the flow area, the velocity must increase.

But still it would be great help if I could get a proper explanation, I couldn't find one in books and net.

I would also like to know which 2D constraints are actually relieved which causes the 3D relaxation effect.

EDIT:- I think i need to reiterate the question, I wanted to ask why does the supersonic flow bend toward the surface in case of being obstructed by a cone unlike in case of wedge, and as per its reasoning i have also read that the flow is more free in case of cone, due to presence of 3 dimensions, commonly known as 3D relaxation, so it would be nice if someone could comment upon it too.


texts: Will the pressure inside a pressing mold will be constant if I'm working with a fluid inside?

texts: I'm pressing glass and I want to know if the pressure that the walls of my mold feel is the same through all the internal surfaces. I'm willing to assume that glass will behave purely as a fluid (very viscous) in the temperature range I'm working it.


texts: Do crank-sliders require some minimum amount of momentum to work in linear-to-rotary convertions?

texts:
I've been doing some reading into spinning wheels and old-fashioned sewing machines and so far as I can tell, they use a system similar to a piston in an engine. The main difference being, the oscillation is coming from a treadle. It got me wondering about something though. With the way the linkage works, rotation to oscillation should work fine at any speed. That being said, couldn't oscillation to rotation be messed up if the oscillations are happening too slowly?

If the connecting rod doesn't pass the middle point (where the rod is angled at 0°), another oscillation might cause the connection rod to push backwards, reversing the rotation. Also, if the rod is angled at 0° (almost exactly), the linkage might jam because the oscillation isn't being directed one way or another? If that is the case, the crank/wheel would need to have enough momentum to pass that spot when the next oscillation happens?


texts: Simulating a mass - spring - damper system

texts:
I have a mass - spring - damper system with external force and I am trying to simulate it using Matlab. I want to have a linearly parameterized form and use the least squares method to find the estimators. I have reached the stage where I have the form:

$$ y = \theta^T  z $$
$$\theta = [\theta_1 \ \ \theta_2 \ \ \theta_3]^T$$
$$z = [-s\frac{y}{Λ(s)} \ \ -\frac{y}{Λ(s)} \ \ \frac{u}{Λ(s)}]^T$$

where $\ Λ(s) $ is a stable filter $\ Λ(s) = s^2 + 3s + 2 $ and $\ y $ is the output of the system (the mass relocation) and $\ u $ is the input of the system (the external force).

I am trying to calculate the elements of $\ z $ vector and for $\ z_1 = -s\frac{y}{Λ(s)} $ for example I have done the following:

$$ z_1 = -s\frac{y}{Λ(s)} \Rightarrow \ddot{z_1}+3\dot{z_1}+2z_1 = -\dot{y}  $$

$$x_1 = z_1 \Rightarrow \dot{{x_1}} = x_2 - y$$

$$x_2 = \dot{z_1}+y \Rightarrow \dot{{x_2}} = -3x_2 - 2x_1 + 3y$$

From now on I want to use the ode45(...) function but I am not able to figure out how to finally calculate $\ z_1 $ and then put it in the $\ z $ vector.


texts:
I have been trying to build an electric go kart, and power requirements (as always) have been the problem. I have been going through some formulas to find out how big of a motor I would need from how much torque is required.

Formulas used:

$F=ma$
$M=Fr$

My specs:

Weight of vehicle (driver included): 200kg
Top speed: 20m/s (45mph) acc. (a)= 2m/s^2(10 sec to reach top speed) radius(r)=0.2 (variable tho, this is the problem)

From calculations, F=200kg*2m/s^2=400N, torque=400N*0.2m=80 Nm. If a smaller radius is used(say 0.1 m instead of 0.2 m), less torque is needed(400N*0.1=40Nm). Clearly, there is some misunderstanding, or we would all use smaller wheels if they resulted in less torque needed. What am I doing wrong? maybe I did not understand the formulas correctly? If I am correct, how would you explain using bigger wheel sizes?


texts: How to make water go into my house, from a lake without energy?

texts:
Basically, I'm thinking about a system, that filtrates, and makes a lake's water drinkable, drives water into my house's faucets without electricity, and all these should be able to work when it is -20 Celsius outside. The water heating is not a problem, it is going to happen with a good old wood consumer stove.

*I even thought about adding a microsystem, that makes energy, like this: https://youtu.be/rPdpnunr1k0

The ram pump I would like to build is something like this:

https://youtu.be/CG0laNqJWY0

https://youtu.be/nFZYD05I29s

I draw a basic thing I don't even dare to call a plan:

The lake water goes down, into a simple filtration system and makes the mentioned hydro energy tool work, then flows (underground) into the other filtrating tool (under the house), that makes drinkable water. The next stop is a huge container or a few smaller, then the ram pump makes the water go up about 3 meters into a cold water container, and from that to a heatable storage.

The ram pump makes "wastewater" but I could make that into a smaller pond or something.

I wish to know more about this topic so I appreciate every idea to make this notion better and make the pump, the hydropower tool and the whole system more efficient.

Thank you in advance.

Edit: The electricity made with the turbine is to store it in a battery or more batteries, so I could use it to make light or charge a laptop.

The problem I have is to make the system work in -20 Celsius and to use a turbine to make electricity efficiently.


texts: How to debunk this "Perpetual Motion Machine?"

texts:
Here is video of a purported "perpetual motion machine."

How do you explain its behavior?


texts: Will more electricity be generated by using a lens to focus sunlight onto solar cells?

texts:
I have been wondering about this question for quite some time. Assuming an ideal case, the energy from photons hitting solar cells is converted into electric energy as described by the equation:

$RI^2t=W\equiv E=\hbar\nu$

where $\nu$ is the frequency of photons. Using a lens won't increase the frequency of photons, thus no extra electricity is generated.

Am I correct in thinking that no extra electricity will be generated by solar cells when a lens is used to focus light onto them?


texts: Can strength be expressed in a single value? Can flexibility?

texts:
I'm trying to communicate information about the strength and flexibility of certain materials to laymen. Are there any recognised proxies for strength and flexibility?
I've tried:
$$\text{Strength Proxy} = \sqrt {\text{Tensile Strength} * \text{Flexural Strength)}}$$
and
$$\text{Flex Proxy} = \frac{1}{\sqrt{\text{Tensile Modulus} * \text{Flexural Modulus}}}$$
My plan was to normalise the distribution and give some value from 1-10 for each material but the above formulae gave some results that didn't make sense.
However this is defined it will be imperfect. Therefore I am just looking for a systematic way to make a first approximation.


texts: What is the order of execution in system models?

texts:
I'm learning SysML/MBSE right now. In what order is a model "executed", that is: in what order are dependencies between properties reconciled?
For instance, if I have one component/subsystem property that depends on another property lower or higher in the system structural hierarchy, how is that dealt with sequentially?


texts: Why do we need to take distance of center gravity of a distributed load to a point in order to calculate moment?

texts:
From the picture above, in order to calculate the moment of load acting on the beam we take moment $M=\frac{W}{L}×L×\frac{L}{2}$.

Why can't we calculate the moment as $M=\frac{W}{L}×L×L$?

Why do we need to take the distance from center of gravity to a point as the distance?


texts: Engineering formula to relate engine displacement and power

texts:
I am currently rating two motorcycles to decide which one to buy. The criteria which is most important to me is the power-to-weight ratio. Now, I want to calculate the power of the motorcycle by looking at its displacement. The engine displacement is the amount of air-fuel mix that an engine can burn at a time. Looking at google, I cannot find a concrete formula to convert the engine displacement (cubic centimeter) to power (horsepower).

Currently, I am looking at two models:

Suzuki Raider J 115 Fi (fuel injection)
Honda XRS 125 (Carburetor)

I know that the Honda model will provide more power but I want to look at the other model's fuel efficiency. I want to convert to see whether the power difference is not that significant. For the sake of comparison/formula, assume that you feed both with the same amount of fuel.

Can you please advise?


texts: Questions regarding CR-P2 battery specification

texts:
I am working with CR-P2 batteries. I have a few questions that I am trying to answer. I would appreciate if anyone kindly help me with these questions. Thanks in advance.

I have found in google two different types of CR-P2 batteries from different vendors. One group has 1500 mAh capacity and another group has 1400 mAh capacity. Most of them claims 10 years battery life. Why these two battery capacity numbers are significant? How significant is the capacity difference of 100 mAh?
When we draw large pulse current from the battery (let's say 3500 mA) it generates heat. I am assuming it is because of the resistor inside the battery that heats up. Is there any other reason? It causes battery faster degradation. Why does that happen?

Thanks again for your help.

Best,
Niloy


texts: How to calculate value of force required to move CNC rounter?

texts:
I want to design CNC rounter. I want to know how much force required to move router in to material.
How to consider this.
I guess there are many factor like

Material
Feed rate
Depth of cut
number of cutting tool's flute.

I don't want to try out and error for this please give me some clue.


texts: Given an equivalent stress vector(or Traction vector) in a plane stress state, how can one determine the 3 components of the 2*2 Tensor matrix, i.e. sigma_x, sigma_y and tau_xy?


texts: What are the engineering principles for a train to get electricity from the railway

texts:
How many general methods are there for transferring electricity from the railway to a train? I could see that some trains are connected by a pantograph and some have a third rail.

Are there any other methods? What is the general engineering principle behind each? What are the basic differences (pros and cons) of each method? I was looking for these questions but could not find a good review. If anyone has a reference or could answer them kindly do.

Also, is it possible to build a small model of such a system and scale it up? I am not talking about a commercial model train. I am aiming at self-designing the same engineering principals and demonstrating them on a scalable small model. If so, I would be happy to have a nice tutorial reference.

I am focusing on Electric multiple units (EMU).


texts: Mounting a timing pulley on a ball screw shaft

texts:
I have a pretty basic question.

I need to install a timing pulley on a ball screw shaft (6mm):
http://uk.rs-online.com/web/p/products/2816419/

The processed end (the pointy side) of the shaft is secured by a support mount, I need to place a timing pulley on the other side. I'm not sure how to go about this. E.g. this pulley: http://uk.rs-online.com/web/p/timing-belt-pulleys/0744508/

Would a mounting hub or a pulley with a holding screw work? Thanks.


texts: How do I calculate an estimate for the properties of a composite material?

texts: For a given laminate made of composite material (composed of fibers oriented in a carefully designed sequence coated and embedded in a matrix material), where can I begin estimating the stiffness and/or strength of the material?  How can I know (within a beginning estimate tolerance) how to design a part out of composite materials?


texts: Efficiency model for centrifugal pumps, using relations from Europump's Ecopump project

texts:
Context:

I'm trying to create a mathematical model for centrifugal pumps. This model should describes how the operational variables of centrifugal pumps $(Q, \Delta P, ...)$ related to it's design parameters $(Stages, Dimensions, ...)$ and it's use-case $(\rho, \mu, ....)$ .The intention behind this job is to develop an educational simulation environment. Anyway, after spending reasonable time reading+hacking various references I didn't find an idiomatic, integrated, already provided model to use. And I decided to assemble it using different parts from different sources.

Currently I think that:

One important part of the model is to write $f(\eta,Q,...)=0$ or finding relation between Efficiency, Flow + design parameters on allowable, preferred or at list rated flow range.

Proposal:

To overcome the above bulleted item of my modeling problem, I picked mandatory conditions of an acceptable Ecopump project's centrifugal pump. Reference: Assessing the Energy
Efficiency of Pumps and Pump Units By: Bernd Stoffel

  Ecopump is the name of the successful flagship project that Europump
  launched in 2004 to bring the pump industry’s commitment to energy
  savings to the fore.

Following equations from the referred handbook, describes minimum $Efficiency$ required at these three different flow rates: 1-$BEP$, 2-part-load$(PL)$ and 3-over-load$(OL)$ , in terms of design parameters:

$\eta_{BEP,min\, requ} = -11.48*(\log(n_s))^2-0.85*(\log(Q_{BEP}))^2-
0.38*\log(n_s)*\log(Q_{BEP})+88.59*\log(n_s)+13.46*\log(Q_{BEP})\qquad (7.4)$

$\eta_{PL,min\, requ} = 0.947*\eta_{BEP,min\, requ}\qquad (7.5)$

$\eta_{OL,min\, requ} = 0.985*\eta_{BEP,min\, requ}\qquad (7.6)$

$#Where:$

$Q_{PL} = 0.75*Q_{BEP}$

$Q_{OL} = 1.1*Q_{BEP}$

Although the above conditions are three inequality rule that define a floor for a real pump $\eta$ value, I make an important suggestion here about a conceptual minimum Ecopump which exactly overlays those minimum requirements so $\eta_{real}==\eta_{min}$ ,and using those three points for $\eta$ it is possible to interpolate a second order polynomial and find $\eta(Q)$ for that conceptual minimum Ecopump with specific design parameters.

I expect that this model along with its numerical results could help instructors to cover following topics in a classic pump course:

How efficiency of a pump is related to other parameters.
How much a pump efficiency should be, to fulfill mandatory items of standards.
How does $\eta$ change related to $Q$
How to deal with modern standards about pump efficiency

Questions:

Part One:
Am I on the right way? Or is(are) there any better way(s) to achieve the mentioned four goals.

Also:
The original $(7.4)$ equation have an additional $-C$ constant with the following description:

  The constant C(in [%]) depends on MEI and additionally on the type and nominal speed of the size.

Part Two:
From the handbook it is not clear for me how to calculate this constant, but for my approximate educational model I simply put it aside, Is this approximation acceptable? How much it affects my model? How to substitute more accurate value for $C$?

Any idiomatic points to create a better model are appreciated.


texts: Conductive Heat Transfer calculation over time

texts:
I am trying to heat the oil in a 1/2 inch thick rectangular steel box by using an Insulated heated blanket covered on all 6 faces of the box, the working conditions of the operation are at -50 Celsius, the temperature of the oil is required to be at 15 Celcius during the operation, so I need to determine how much heat/power is required by the blanket and how much time will it take for the temperature of the oil to change from -50 Celsius to 15 Celsius?

one face resistive diagram,
Rb = resistance by the blanket thickness of 1 inch,
Rw = rectangular steel box wall


texts: What's the best way to design a joint with two fasteners?

texts:
When you're trying to design a relatively long joint with only two fasteners, what's the best way to arrange them? Since fasteners effectively radiate a circle of clamping force around them, what's the best way to evenly distribute this force?
I originally thought of this question while thinking of the best positions for the binder clips holding my 3D printer's build plate on, but the core concept is surely applicable in larger applications too.
Some ideas off the top of my mind:

1 fastener at 25% and the other at 75%. This is flawed in my mind because the 50% mark will receive far less clamping force than the rest of the joint.
1 fastener at 33% and the other at 67%. This is also not great because the middle section of the joint is receiving a double dose of clamping force, which is obviously not very evenly distributed.

From these two examples, I can see that the ideal position is somewhere between 1/4 and 1/3 of the joint length for each fastener. What would this position exactly be?
What about a joint with more than two fasteners?


texts: Physical interpretation of the relative displacement tensor?

texts:
I've resolved a relative displacement tensor into a strain tensor and a rotation tensor, where

the strain tensor is:
$$
 \varepsilon_{i,j} =\begin{pmatrix} 0.2 & 0 & 0 \\ 0 & 0.8 &0.4\\0&0.4&0.4\end{pmatrix}
$$

and the rotation tensor is:
$$
\omega_{i,j} = \begin{pmatrix} 0 & 0 & 0 \\ 0 & 0 &-0.2\\0&0.2&0\end{pmatrix}
$$

How would these conditions physically change a small cube (with respect to the Cartesian cooridates (x,y,z) ?


texts: Is current suppose to pass through a capacitors dielectric? What happens if it does?

texts:
I have been building my first simple circuits with just resistors, LED's wire, and alkaline batteries.

Now I would like to add capacitors to my components box. Read a couple of articles online on the matter and it seems pretty deep, so to get the next step in the learning process going, I wanted to use the same technique I did with resistors and LED's, which is to plug a capacitor or two up and make some examinations.

but first, I wanted to straighten a vague point in my notes on the concept of capacitors:

Between the plates of a capacitor is the dielectric, is the built up charge between the two plates eventually suppose to traverse through the dielectric?


texts: Is is possible to use singularity function to expresse the horizontal forces ?

texts:
I know how to translate torques and vertical forces into singularity functions, but may i also express the horizontal forces with singular function? if yes then what would be that expression?

Here the green beam is fixed at point A, and a distributed load acts on the beam, and a horizontal force acts at the upper edge of the beam.


texts: When does window insulation have more impact than attic?

texts:
Is there any way to determine either empirically or by convention a rule-of-thumb when one should spend money on insulating windows rather than insulating the attic of a house or building to keep it warm in winter and cool in summer?

In other words, how do we determine where to place the next piece of insulation to maximize the increase in total building system insulation effective R-value?


texts: Could magnetic levitation transportation systems become a commonplace technology?

texts:
Magnetic levitation systems of transportation such as trains seem to be commonplace in early 2000's science fiction, and while some systems exist currently, they aren't exactly common.

It seems to me that this technology has grown unpopular (or at least has fallen into obscurity) in recent years and I'm curious as to why that may be.

Is it primarily technical factors or perhaps technology issues that prevent wider adoption of mag-lev transportation systems?  Or is there something else that's slowed the rate of installation?


texts: Why do some metals with bcc structure show ductile-brittle transition in charpy impact test?

texts: I was learning about the charpy impact test and came across the graph on this webiste that shows the impact energy for bcc and fcc structures as a function of temperature. I tried searching for an explanation as to why the graph differs for the two crystal systems but couldn't find any. Some places say it's because of the slip planes but I still didn't understand.


texts: Can I improve this exhaust gas probe to be immune to pressure changes?

texts:
I'm designing a probe to provide a stable and continuous stream of exhaust gas sample to an analyser. The probe has to be inserted into the exhaust for about 20–30 cm to keep outside air from entering the probe. The static pressure there is about 1000 Pa above atmosphere. The dynamic pressure is probably way higher. The material of the probe is brass.

The problem here is that the fluctations in the environment inside the exhaust may have significant influence on my sampling. The analyser precisely dilutes the exhaust gas to match the sensor's specs, and environmental changes may alter the dilution ratio, resulting in incorrect readings. The probe has to offer a sample at a pressure as constant as possible.

The pressure inside the exhaust will force exhaust gas into the probe, and with changing engine load, the temperature, static, and dynamic pressure will change, forcing a different amount of exhaust gas into the probe. I want to have that pressure as stable as possible, so that I can correct for it in my calculations.

I have studied the pitot tube and my design is now as illustrated below:

I have tried to eliminate the influence of dynamic pressure, but I'm not sure if this is the best way to create a sampling of constant pressure.

So tl;dr, consider image above, is there a better way to offer samples of constant pressure, in an environment that has fluctuating static and dynamic pressure, and temperature?


texts: Why are engineering programs so course intensive?

texts:
Most undergraduate majors require 10-12 courses in the major, and maybe up to three courses from other departments as "co-requisites." But most engineering majors require 15-18 courses in the department itself, plus 10 -15 courses in math, chemistry, physics and computer science as "co-requisites."

In one engineering program I looked at, a "minor" consisted of six engineering courses, plus 14 courses in "co-requisites." I "get" that much, particularly the co-requisites (basically enough for another minor). But the major consisted of 18 engineering courses, three times the "six" for the minor, whereas other majors, require twelve courses (double the six for the minor) as well as co-requisites.

That's 25-33 courses, that is two thirds to four fifths of the whole curriculum, versus about one-third for other majors. Why is that?


texts: Is there a way to derive a formula of modulus of rupture vs compressive strength?

texts:
Is there a way to derive a formula of modulus of rupture (flexural strength) vs compressive strength?

I want to know is there any mathematical reason for the $\sqrt{f_{c} ^{'}}$ placed somewhere in the formula?


texts: Reduction of a simple distributed loading (correct question)

texts:
I am not yet at the chapter of equations of equilibrium, plus it says the couple moment is not 0, so I assume it just about the loadings and not including the reactive forces and reactive moment.

So if I call the top one F1 and the bottom loading F2 I got:

$$F_1+F_2=0= -4b\dfrac{1}{2}+2.5(b+a)\dfrac{1}{2}$$

solving this i got $a=0.6b$

Moment around the free end of the bar (not $A$, but opposite side) due to the loadings is (counter clockwise positive):

$$M= -F_1\cdot\text{center of triangle} + F_2\cdot\text{center of triangle}$$

Because you can replace the loading with force $F_1$ and force $F_2$ and its line of action is through the center of the triangle area ($\dfrac{1}{3}\text{base}$):

$$M= -8= -4b\dfrac{1}{2}\cdot\dfrac{1}{3}b+2.5(b+a)\dfrac{1}{2}\cdot\dfrac{1}{3}(b+a)$$

So what am I doing wrong?
Because M can never be negative with me, plus the answer should be $b= 5.625$ and $a= 1.539$.
But this to me makes no sense, because then $F_1+F_2\neq0$.
And if I should take the reactive forces into account at $A$ then you can never have still a moment, because then it is not static anymore.


texts: Placement of supporting boiler in heating circuit

texts:
In my thesis, I deal with heating circuits, where several heat generators are present, e.g. a combined heat and power unit and a supporting boiler.
Usually, the boiler is placed in front of the heat storage tank, but I have also repeatedly seen heating circuits where the boiler is placed behind the heat storage tank.

For example, the structure of the heating circuit of an IEEE paper:

What are the advantages and disadvantages?

Do I understand correctly that if the boiler is in front of the heat storage tank, the water of the heat storage tank is heated and if it is behind it, it has its own reservoir of water which it heats?


texts: Are concrete screws suitable for repeated removal and reinstallation?

texts:
Is a concrete screw like the HILTI HUS3 removable?
I.e. can it be repeatedly unscrewed and reinstalled as required? Will this damage the fixing or the hole in the concrete?
We're thinking about using it for a bund that occasionally will need to be removed for access.


texts: Solidworks Flow Simulation the Rotation option missing

texts:
I am looking for assistance to understand why, with SolidWorks 2017, in the "Flow Simulation wizard - Analysis Type" I have no "Rotation" option?

What do I need to do in order to see it?.

The "Rotating Region" is not active, it is a gray icon in "Command Manager".

wizard - Analysis Type

Rotating Region" is not active


texts:
To experienced supercar owners/engineers:

What is the best fuel for a turbocharged 6 liter V8, 7.6 liter V10, or 9.2 liter V12 (Audi R8 or Lamborghini Aventador type cars) in terms of speed/horsepower efficiency and minimization of wear on the engine? Mileage efficiency can be discarded (it can do 4 gallons per mile... not a problem :) ).


texts:
I have a transformer for troubleshooting.
It is a 3 phase DELTA-WYE Step down (11KV/400V) transformer, the low side voltages (secondary) are
Line to line voltages:
RED-YELLOW    : 400 V
YELLOW - BLUE : 400V
BLUE- RED     : 400V
Line to Neutral Voltage:
RED-Neutral    : 400 V
YELLOW - Neutral : 400 V
BLUE- Neutral     : 05 V
What are the possible causes that might cause the issue? So far I have found that the transformer rating has not been impacted. I could not figure out if the transformer has grounded neutral or not.
What should be the list of causes?


texts: Use two gear racks to multiply linear motion

texts: I have an object (shown in green) that I want to pull out distance X and then I want another object (shown in red) to move 2X. What would be the best way to achieve this?  I thought that gear racks connected to each and then linked by a gear train might work, but I can't quite figure out the best way to lay that out (or if there is a simpler way to do this).


texts: Non-Clutch Vehicle Drivetrain - How Does it Work?

texts:
I am making a vehicle simulation, but just noticed a big issue - there are a lot of cars with no clutch in them, but I haven't driven a car with automatic/clutchless-manual gearbox, nor been even a passenger in such a car. Consequently, I have no idea how such vehicle drive or operate.

For a vehicle with a clutch, I know how it drives and I also know the physics behind it operation  - torque from engine gets transmitted through the clutch to the transmission, then to differential and then it reaches wheels, the wheels generate torque from ground friction which goes the other way around and slows down the engine. If the clutch is disengaged, then the engine won't transfer torque. If the clutch is partially engaged, then some of the engine torque will be transmitted and the rest of it will be lost in some form of heat during clutch slippage.

However, I have no idea how vehicles with an automatic gearbox or a semi-automatic gearbox (e.g. sequential) work. As far as I know, they don't have a clutch. However, I've seen that such vehicles can have their engine revving while not transmitting any torque to the differential.

Is it that they're directly connected to the transmission or is there something else there? What I am asking for is some sort of guidelines for me to figure out how to calculate their maths (plus, if possible, some equations would help).


texts: What is this weird upside down U shaped pipline for?

texts: There is this tall upside down shaped U pipe near a sugar refinery on Maui and I can't figure out what it's for ? I've also see these in other industrial areas near salt flats.


texts: Additional jacking force to overcome stiction/dry friction

texts:
It is common to lift bridges to replace bearings, etc.

In an ideal world the lifting capacity required of the jacks would be the self-weight of the bridge divided by the number of jacks (+ allowances for wind/snow, etc.).

From my (limited) experience, however, bridges begin to 'stick' to their bearings, and an additional allowance for over-coming this has to be provided.

Does anyone have any guidance about how to determine this figure?


texts: Is it illegal to use the hydrodynamic energy contained within the city water supply to generate electricity?

texts:
If someone were to invent a device that uses the hydrodynamic energy contained within the city water supply to generate enough electricity to reduce their monthly electric bill (however unlikely this would be), would it legal to do so?

In other words, are there any existing federal/state laws that specifically state that a home owner cannot use any device that generates electricity from the hydrodynamic energy contained within the city water supply?

I have an idea for such a device but I don't want to invest the time and money to construct it if say sometime in the future my local water company finds out about it and then sends one of their lawyers to my home informing me that I have to stop using it or face heavy fines.


texts: How can I measure the coefficients of friction of pulleys?

texts:
I have to study several industrial pulleys made for lifting heavy weights.

It is important to select one which has a low coefficient of friction because the system is based in a hoist and several corner angle transmissions under heavy load. So that there is lots of strength lost by friction. I also have many other constraints of course. I'm not searching for pulley brand but for a test mechanism I could use to check the already selected candidate pulleys' coefficient of friction.

I could test the static coefficient of friction quite easily using a weight at one side and a dynamometer at the other side.

However my application wile involve several lifts a day with up to 20 meters of rope running under heavy load (1~2 metric tons per pulley). The speed is relatively low. 1m/s in the rope would be the absolute maximum.

I don't know if the static coefficient of friction will be enough to make a relevant selection. What do you think about it ?

I had several ideas to build a testing machine. All seems to be quite complicated :

I firstly imagined 2 big hydraulic jacks with a dynamometer at each side. I'm not sure of the minimum length of the jacks but I had in the idea that 2m would be a minimum to get something representative.
I then imagined a relatively compact system with an endless rope running under load between a motor and pulley. I would measure the torque between the motor axis and the wheel actuator. I'm not sure of what I would exactly be measuring here but I could make some comparisons.
I also imagined a system with 2 opposite pulleys under tension. I would measure the strength needed to move the rope with a dynamometer. I'm quite sure I should not do it manually but with a constant speed or constant strength system. I'm afraid to build a labyrinthine system.

Do you have better ideas or insights on how to do it ?

Regards


texts: Appropriate bearing to spin a dove prism?

texts:
I want to spin a dove prism (image rotating prism) around it's long axis at a controlled rate (100 to 300 RPM). The purpose is to get a de-rotated image of a spinning object (by looking through the prism).
The prism is small and light - about 20x20x150 millimeters and maybe 0.1 kg.
My idea is to mount the prism inside a spinning bearing. I tried an inexpensive "pillow block bearing" ($20) and mounting the prism inside, but that didn't work well:
(a) The friction needed to turn the bearing was much higher than I wanted - I want it to spin freely (for example, if I give it a spin with my fingers, I'd like it to keep spinning for a while). I was driving the rotation with a small DC motor with a belt (controlling motor speed with a knob). The friction was a problem.
(b) The axis of rotation didn't seem to be as constrained as I'd like - I want it to really just spin in one single axis that doesn't move around, so the view through the prism stays centered on a fixed point (assuming the prism is properly aligned with the bearing - I'm going to 3D print a fixture to hold it in place).
Can I get a recommendation for the appropriate type of bearing for this? (Or, some other way to accomplish what I'm trying to do?) It would be nice if it's not expensive (< $100).


texts:
I have been doing a good bit of research lately into a new form of electric "jet engine" developed by researchers in Wuhan, China; in the article summarizing the technologies used to produce this remarkable device, they state that they used a compressor in conjunction with a cavity magnetron to produce a high-temperature plasma, that was then ignited by a spark plug and accelerated up a quartz tube to produce thrust.
During the two college chemistry classes I took, however, I learned that microwaves are not necessarily the most high-energy form of radiation on the spectrum, and are thus considered to be non-ionizing. My question is whether or not it is indeed possible to achieve air ionization solely by using microwave radiation.


texts: Turbocharger boost control using two valves with a vac and boost reference for wide boost control range

texts:
Can someone explain how the above boost control setup would work. The valve on the left uses a vac source applied to the top of the diaphram which would effectively help hold the spring closed at high boost levels providing high boost than a single valve setup would. I assume this would be used to give a large boost control range (similar to a CO2 boost controller). Is this correct?

I'm not sure what the D port on the actuator does though, I assume that D and E are both connected and would both work against the spring opening it?

What control circuit would be required to drive the two valves. Would you need a split range controller with two different duty curves, or could you run them from a single controller with a single curve, eg run the two valves from a single PWM output?


texts: High Pass Filter Design from Transfer Function

texts:
I need to design an active high pass filter circuit that implements the following transfer function:

$$G(s)= 4.15\times\dfrac{s+530}{s+2200}$$

where, $K = 4.15$, Pole @ 2200 rad/s and Zero @ 530 rad/s.

I have already designed the non-inverting amplifier component of this circuit, using two resistors of value 1k and 4.15k. The issue I have is the passive component of the circuit and trying to control the poles and zeros of the transfer function. This is all I have attempted, I am completely stuck.


texts: Simple and easy Open Source CAD tools for basic 2D and 3D designs

texts:
We are planning to start a basic course on Computer Aided Designs (2D and 2D) for high school kids.

The idea  is to help them shape their innovative ideas into something tangible.   We shall finally help them develop prototype using 3D printers or mass produce later on.

We would like to know what all open source  options are available for 2d and 3d designs. Most importantly we are looking for tools which are simple and easy enough so that high school students  can use it (we will be limiting to simple designs).

Any suggestions ?


texts:
How much mass can be attached at the end of aluminum square tubing (6063 T5, 1x1”, 1/16 thick 8’ long tubing supported for the length 1’, cantilever approximately 7’.
I want to run my dogs with atv and tie them to the tubing so they stay away from the all terrain vehicle (atv). They will pull, somewhat down. I like Aluminum since it is light, but you can recommend better material. Thanks.


texts: Choice of transfer function in a system where the controller adapts to give the intended behavior

texts:
Consider a negative feedback loop with input $r(t)$ and output $x(t)$. The difference

$$ e(t) = r(t) - x(t) $$

is the input to a controller $C(s)$ and the output is $u(t)$. Then, $u(t)$ is the input to $G(s)$ and the output is $x(t)$. The transfer function for this system is

$$ H(s) = \frac{G(s)C(s)}{1 + G(s)C(s)} $$

It is known that $H(s)$ has the behavior of a forced-damped system. Given a $G(s)$, $C(s)$ is chosen so that $H(s)$ will reflect a forced-damped system.

If $C(s)$ is always chosen to give the intended behavior for $H(s)$, is there any reason that one form of $G(s)$ may be better than another? For example, consider $G(s)$

$G_{LP}(s) = \frac{1}{s}$
$G_{HP}(s) = \frac{1}{M s^2}$

where $M$ is a constant. The corresponding $C(s)$ are

linear low-pass filter: $C_{LP}(s) = \frac{K}{p + s}$
linear high-pass filter: $C_{HP}(s) = \frac{Ks}{p + s}$

where $K$ and $p$ are constants. The quantities

$G_{LP}(s)C_{LP}(s) = \frac{K}{s(p + s)}$
$G_{HP}(s)C_{HP}(s) = \frac{K}{Ms(p + s)}$

only differ by a constant $M$, but $K$ can always be tuned for each choice of $C(s)$ so that the appearance of this extra constant $M$ does not matter.

To reiterate, would one choice of $G(s)$ be preferable from a physics/engineering perspective if the behavior of the overall system remains the same?


texts: I want to use a winch to raise and lower a load, but now I'm unsure, if the winch can handle the lowering? Normally, winches are only used to pull a load, right? When I now reverse the motor direction, the winch unrolls the rope and gets pulled in addition by the load. Where goes now the energy? A big part should go into the gearbox i think. The motor cannot act as a generator, since it is powered when unrolling the winch, because of the stand still brake. So I think the load will accelerate until the friction in the gearbox is high enough to balance the system. Am I right with this assumption?


texts: What are the materials most transparent to microwaves?

texts:
I need to build special equipment for a microwave oven ( 2.45 (GHz)).
But even glass and plastics do heat up in microwave ovens. Where can I find a list of the materials that are the most transparent to this frequency ?

Thanks


texts: How to know which modes are excited by a given input in modal analysis?

texts: Consider a simple structure such as a beam, plate, ... Assume that you know how to determine the different modes of vibration of the structure. You are given an external input, such as a force or moment at a certain location. How can you then determine which modes will be excited how much? (Just a general question, I am not considering a specific case.)