texts: How to properly use the lift-curve slope for divergence calculations?

texts:
I was reading Wright and Cooper's writings on static aeroelasticity and I think I'm missing something.
To calculate the acting lift, the equation $L = q S a_1 \theta_0$ is used, where $q$ is the dynamic pressure, $S$ is the wing area, $a_1$ is the lift-curve slope ($\frac{\delta C_L}{\delta \alpha}$) and $\theta_0$ is the initial incidence angle.
However, the way I see it, that only equals to the traditional $L = qS C_L$ when/if I have a curve where both $C_L$ and $\alpha$ are zero at the same time, since the slope indicates the rate of my $C_L$ variation but not the starting point.
So the question is: is the Wright and Cooper's formula only supposed to calculate the increase in lift generated or am I reading it wrong?

I'll try and show a few examples of where that is used, so it may clarify.
In divergence studies, to calculate the total lift:
$L_{total} = L_{rigid} + L_{elastic} = q S \frac{\delta C_L}{\delta \alpha} (\alpha_0 + \theta)$
Where $\alpha_0$ is the original angle of attack and $\theta$ is the twist angle due to aerodynamic loading. The way I see it, this should be equal to $\large L_{total} = qS C_{L_{\alpha+\theta}}$, but it isn't. I'm not sure if it's not supposed to, or if I'm seeing it wrong.
In Wright and Cooper's book, to calculate the pitching moment on an airfoil.

Here again, they calculate lift as $L = q c a_1 \theta_0$, and that is not equal to $L = qc  C_L$, because the admitted $C_L$ values will be lower.
I hope I made myself sufficiently clear, thank you in advance.
Edit: added figure 8.1 and tried to clarify a bit.


texts: Relation between channel and path loss exponent

texts:
I am referring a paper "Outage Analysis of Ambient Backscatter
Communication Systems" wherein i came across the equation $y_r(n) = \frac{\tilde{h_{sr}}}{\sqrt{d_{sr}^{\alpha}}}+\frac{\tilde{h_{tr}}}{\sqrt{d_{tr}^{\alpha}}} + w(n) $------(1), where $\tilde{h_{sr}}$ and $\tilde{h_{tr}}$ are Gaussian channels between source to reader and tag to reader respectively, $\alpha$ is path loss exponent, $d_{sr}$, $d_{tr}$ is the distance between source to reader and tag to reader respectively.
My query is can we write the equation (1) if we consider other channels such as Nakagami-m, Rayleigh etc.
Any help in this regard is highly appreciated.


texts: I2C (QUIIC/STEMMA) power source from microcontroller output pin

texts:
I2C buses are frequently exposed via a 4-pin connector that carries ground, power, SDA, and SCL.  The power is generally supposed to be 3.3V, but exceptions exist.   Pinout examples include QUIIC, STEMMA, and PMOD.
I assume that I2C masters (typically development boards containing a microcontroller) will supply the power pin. The simple peripherals may choose to utilize that power, provided sufficient current is available.    My question is, are there any standards for the minimum current a master can supply?
Would it be reasonable to create a low-power SoC board that can source only 25mA of 3.3V directly from one of its pins (without an external regulator) and route that to the power pin?  Is that enough available power to support an interesting set of low-power (or self-powered) peripherals?
The PSoC 5LP I'm planning on using has a built-in boost regulator so it can run off a wide range of battery voltages.
Example low-power peripheral: Sparkfun CCS811/BME280 (Qwiic) Environmental Combo Breakout Board.   The CSS811 has a peak current draw of 56 mA, but the average over a measurement cycle is only 0.7 mA.  Can a capacitor in the power line carry the peak load if I can only supply 25mA?
The board's schematic shows a 1uF cap and 0.1uF cap for decoupling.   Interestingly it contains a notation saying someone estimated the average draw at 17 mA (without justification).    The BME280 is very low power, less than 1mA in any mode.   Is the 1uF cap sufficient to cover the current deficit at a 1Hz sample period?   Would I need to augment the capacitors?
I guess I could add a small 3.3 regulator, or even a voltage follower so the uC can vary the I2C bus VCC voltage.  Just trying to understand what options are reasonable to keep size & battery consumption low.


texts: How to calculate area of cross section needed to sustain a point load on a beam?

texts:
Consider a beam that is simply supported at both ends by fixed supports and a point load is applied directly in the middle. The force (F), length of beam (L), Young's Modulus (E) and tensile and crushing strength (σ). The amount of deflection is not known.

Let's say 1,000,000kN was applied to the beam, how would I calculate how large the cross-section would need to be in order for it to not fail and break?


texts: Why do we prefer resistance over conductivity in describing Ohm's law?

texts:
In my mechanical engineering training , I've noticed that many constitutive relations (e.g. fourier law, poiseuille law, hooke's law) involve a flux which increases as the material parameter increases.  In heat transfer and fluid flow, this is called a "conductivity".  In solid mechanics, the stress increases as some elastic moduli increase.

Given this trend, I found it perplexing that in electrical engineering the preference is to use resistance rather than conductance, with current increasing as resistance decreases in ohm's law.  Is there an advantage to using resistance instead of conductivity in electrical engineering in general?  Or is it just traditional notation handed down the great minds who came (and published) before us?


texts: Any Idea of This China's "Transparent Concrete"?

texts:
I am currently make an attempt to make miniaturized version of this China's solar highway on my garage
https://www.youtube.com/watch?v=zK8FvzI3yDA
Just so i can re-evaluate the performance
However, I am curious with the top-most layer. In various online media source it keeps saying "transparent concrete" (which obviously 100% transparent) while i found none information on the web how to create one (not even scientific paper)
What i got so far is the "translucent" version, using fiber optics. But it's not that "transparent" as you can see in video above..

My best guess its not concrete at all (although many well-known media source said so), possibly kind of plastic (polycarbonate or sort)...
What do you think? Is it possible to make concrete of that kind?


texts: ft-lbs to ft-lbs3 or newtons as well as strength of metal

texts:
I am trying to figure out how much torque this piece of metal that I have can deal with before breaking.

Are there any tools online that can help me calculate these items?

The hardness of this iron is 167-229Ha
tensile strength is >=58kg/mm2
elasticity is >= 45%
density is 0.785

Currently the pipe is a hexagaon that's 55mm in diameter, then the ends are cylinders that are 40mm in diameter.

Since this is early in the design phase I'd like to be able to adjust torque and the size of the metal pipe so that it wouldn't break.

Currently I have 1200RPM 15HP motor that I have reduced down to 85RPM which if I calculated correctly should be around 926 ft-lbs of torque.

Are there any tools that will help me convert from ft-lbs to lbs-ft3 or calculate these values?
one such online calculator.


texts: Equation for temperature of gas at Joule-Thompson Inversion State

texts:
Assume that a gas obeys the following equation of state:

$\nu = {\frac{RT}{P}}-{\frac{a}{T}} + b$

Where $a , b $ are constant.

Derive an equation for the temperature at the Joule-Thompson inversion state.

My professor gave us the following hint:

$ T = {\frac{\mu_{JT}c_p + \nu}{\frac{\partial \nu}{\partial T}}} $

Where ${\frac{\partial \nu}{\partial T}} $ is held constant at P

My attempt at the solution starts here:

When I differentiate the equation of state wrt T, I get

$ {\frac{\partial \nu}{\partial T}} = {\frac{RT}{P}} + {\frac{a}{T^2}}  $

Plugging this back into the equation for T leads to:

$ T = {\frac{\mu_{JT}c_p + \nu}{\frac{RT}{P}+{\frac{a}{T^2}}}} $

Is this the correct approach to take to solve for the temperature at the Joule - Thompson inversion state? It seems I have need to take a cubic root for the temperature so I was not sure if this is what the intended answer is.


texts: How can I damp oscillating behaviour caused by quantization in a digital control system?

texts:
After introducing a quantization block in the simulink model, the output of the controlled system starts to oscillate around the zero fixpoint.
I am using a lqr controller to regulate the system, which was designed based on the continuous system.
Can I tune the parameters of the lqr design to fix this problem ? Which method is recommended here ?


texts: An elderly friend of mind whose eyesight is fading  recently asked me if there was a way to illuminate her new induction stove top so that the "burner rings" would be easier to see, to her it just looks like a big black non descript surface. I was thinking maybe a blacklight would illuminate the little square marks embedded in the glass that define the pan rings or locations. I suppose I could just buy one and try it but to save time and money I thought I would ask the experts here to see if anyone had any experience with black light being used to make these kinds of markings pop out visually.


texts:
"We use 230V – 3 phase with each phase at 16A (so 11kW charging power)"
"...the total loss is only about 3.5%, with 1.0% being lost in the transport of electricity through the cables, Tesla charger, and charging cable. The remaining 2.5% is lost in the Tesla when converting from alternating current (AC) to direct current (DC), plus during storage in the battery cells. "
https://tm3een.home.blog/2020/12/29/efficiency-when-home-charging-at-11kw/
Will the losses be the same using single-phase 120 Volt charging?
Is there some other combination of Voltage, Amperes, or Phasing where the losses would be even less?


texts: How to calculate the maximum spacing between Hemholtz coils?

texts:
I would like to design a long, uniform magnetic field using Hemholtz coils but am not sure how far I can separate them before the field lines diverge and become two loops that go around each coil rather than one which goes through both.

I have formulae for finding the magnetic flux at different points but I am not sure how to use them to determine this distance I am trying to calculate.

Does anyone have experience in this area who could offer some advice?


texts: Component-based simulation versus block-based simulation

texts:
Modelica touts as one of its advantages over Simulink that it is "component-based" whereas Simulink is "block based".

What exactly does this mean?


texts:
I did a couple of quick calcs to better understand the phenomenon of biaxial bending. One thing that is currently tripping me up is the sign convention. For example, if we have a rectangular beam as follows

with $b = 15''$ and $h = 30''$ and a coordinate system established as show with origin at exactly the middle. $I_x = 33750\text{ in}^2$ and $I_y = 8437.5\text{ in}^2$. Furthermore we have a moment $M_x = 100\text{ lb.in}$ occuring about the +x axis and a moment $M_y = 100\text{ lb.in}$ occuring about the +y axis. Intuitively, we can tell $M_x$ is causing compression at the bottom and tension at the top of this section. Likewise we can also say $M_y$ is causing compression at the right and tension at the left of the section. However, when we run the numbers:

$$\begin{alignat}{2}
\sigma_{top} &= \frac{M_xy}{I_x} = \frac{(100\text{ lb.in})*(15\text{ in})}{33750\text{ in}^4} &&= 0.044\text{ psi} \\
\sigma_{bot} &= \frac{M_xy}{I_x} = \frac{(100\text{ lb.in})*(-15\text{ in})}{33750\text{ in}^4} &&= -0.044\text{ psi} \\
\sigma_{right} &= \frac{M_yx}{I_y} = \frac{(100\text{ lb.in})*(7.5\text{ in})}{8437.5\text{ in}^4} &&= 0.088\text{ psi} \\
\sigma_{left} &= \frac{M_yx}{I_y} = \frac{(100\text{ lb.in})*(-7.5\text{ in})}{8437.5\text{ in}^4} &&= -0.088\text{ psi} \\
\end{alignat}$$

It is highly confusing to me that $\sigma_{bot}$ and $\sigma_{right}$, which are both in compression, have opposing signs. Equally confusing is the fact that $\sigma_{top}$ and $\sigma_{left}$, which are both in tension, have opposing signs. Can anyone bring light to this basic mechanics of materials issue?


texts: Is it possible to design a bus that doesn't rock?

texts:
Trivially you can prevent rocking with many vehicle by eliminating the suspension. But is it possible to allow a floaty suspension that glides over potholes, without also having to rock back and forth, with some kind of stabilization? I know that it's possible in buildings, but having a fixed platform really helps.

I ask because the rocking motion is one of the primary sources of carsickness, and a bus trip this evening left me feeling rather queasy. This seems like something that could be improved, especially in such expensive vehicles.


texts: "Set redefined" Error When Running a Restart Job in Abaqus 6.12-1

texts:
Using Abaqus 6.12-1, I am trying to submit a restart job with an added step. I've followed exactly the instructions in section 19.6.5 of Abaqus 6.12-1 CAE user's manual, but receive this error:

  A node set with the same name "ASSEMBLY_SEM-2D-PART-1_Fixed Nodes" defined in the original analysis has been redefined in the current analysis. Existing sets cannot be modified in a restart analysis.

Looking at the input file for job-2, I see that this is in fact true, Two Nsets used for BCs have been redefined. One is used for a displacement and the other for an encastre. I did not modify these sets in any way. I also checked the .rpy file and it didn't report any changes to sets.

I intend to modify the value for the displacement in the added step. However, to isolate the problem, I have tried the following, none of which have worked.:

Not modifying the value for the displacement (propagating it).
Deactivating the displacement in the added step.
Adding a deactivated step in the original model and activating it upon restart.

Why does this happen?

Also, my end goal is to do this in a Python script. Modifying an input file (manually or programmatically) is not an option.

I can work around the problem as per agentp's comment and many helpful comments on this LinkedIn page. The problem, however, remains unsolved. I'll leave the question open for anyone with the same problem or with a solution to see.


texts: What's the most practical way to measure angular velocity for small rotations?

texts:
I'm looking to measure the angular velocity of an arm as it moves. It seems to be a difficult thing to research, since the term 'angular velocity/frequency' is usually reserved for other areas of circuit analysis.

I imagine something like a tachometer or a generator is most practical, but I can't find anything dealing with an incomplete rotation (i.e. about 90-120 degrees). Any help or push in the right direction would be greatly appreciated.


texts: How can we find it with the current technologies? Can it done without touching the haystack? Any cool stuffs like X-ray or some penetrating technologies ?


texts: What is the diffusion process that takes place in a diffuser/stator?

texts: I understand mass diffusion. But what is the meaning of 'diffusion' which converts the kinetic energy to rise in pressure in a stator/diffuser?


texts: Is it useful to stuff my glasses with newspaper to protect them?

texts:
(I'm not sure if this question belongs to this stack exchange, but it seems appropriate to me)

I have a very practical situation and our knowledge is lacking to be able to solve our debate.

The situation

In our country, and I'm guessing everywhere in the world, people seem to always fill their drinking glasses with about one or even half a page of newspaper. I'm talking about regular 20 or 30 cl drinking glasses or mugs.

When asked why they do this, it is to "protect the glass". The most scienty of them told me "the pressure given by the paper inside the glass helps hold its integrity in case the glass undergoing opposite pressure from the outside (which it most likely is considering it's packed in the same box with many other glasses).

My argument is that the glass being a solid and pretty much not flexible at all, you'd have to put a huge amount of paper in each glass to actually make a difference.

Ideally, not adding too much pressure from the inside to not break it that way, but filling it so that there is as little air as possible seems to me that this is the safest option. But that is by far the worst in terms of using paper and time consumption.

What I told them to do is focus on the outside of the glass when packing. Adding a few layers of very scrunched paper to act as some kind of "spring" all outside the glass, therefore spreading the pressure coming from the outside into the paper, instead of helping the glass sustain said pressure by adding pressure from the inside.

The questions :

What solution works best to protect the glass ?
What solution is actually viable, not costing 20 minutes per glass and thousands of pages of newspapers.
Is there anything else to this?

Note that I am not a native english speaker and there might be false friends between our languages.

By "pressure" I mean the act of applying a force onto a surface.

"Scrunched" was google translated, it should mean "the extreme opposite of flat, like when you make a ball with paper and then expand it again"

Thanks for reading and for your time :)


texts: Do car power windows have limit switches?

texts: As part of an ongoing Raspberry Pi project, I want to automatically open and close my car windows depending on the interior temperature and whether or not it's raining.  Currently, when I manually hold the window switch down after the window is completely raised or lowered, the lights (headlights, interior lights) dim slightly, which indicates to me that current is still flowing to the window motor.  I'm worried about overloading the motors with my automated system, since I was just planning to blindly apply current to the motor for a fixed period of time.  So, my question really is, does the motor rely on the user releasing the switch after the window opens/closes, is it just designed to handle small periods of deadlock, or is there some more elegant protection going on in there?


texts: Distribution of shear stress in beam bending

texts:
Beer, Johnston, and DeWolf's Mechanics of Materials includes the following image of the distribution of shear stresses in a bending beam: (Axes and load vector carried forward from Fig 6.1 in the text by me for clarity in this question) This image represents the bottom part of a beam below a slice in an offset xy plane so the analysis of the shear stresses is being conducted in the top shown surface. The beam is being bent by the load V.

The text mentions that the shear stress along $D_1'-D_2'$ are a parabolic function of x. However, they never mention why. So my question is, why? I don't understand where this would pop out of the math or why this should be the case intuitively.

Consider this example. I have a book in front of me so that I'm looking at the cover. I fix the bound edge and push the opposite edge with a force perpendicular to the cover. The book will bend in a uniform profile at any slice parallel to the ground. This would seem to be to demonstrate that the stresses are independent of the height of the slice. Why is this wrong?


texts: Does outgassing, of adhesives, stop when the cure time is reached

texts: The reason for my question is I'm planning to use DAP Rapid Fuse general purpose (Ethyl Cyanoacrylate) adhesive on a few microscope components and do not want the outgassing to effect the glass optics. So knowing the outgassing characteristics of Ethyl Cyanoacrylate would be very helpful. Thanks


texts: Find clutch for parallel hybrid sailboat

texts:
I am replacing my dead diesel engine in my sailboat.

I wish to replace it with a new diesel and an electric motor in parallel hybrid.

Hybrid vehicle drivetrain

This would allow me to:

Run the propeller using the diesel engine only.
Run the propeller using the electric motor.
Generate power by running the diesel and motor as a generator with a disengaged propeller.

In order to to do this I need a clutch so that I can disengage the propeller, please see the attached drawing.

It would look kinda like this.

Clutch requirements:

Bi-directional - must be able to go forward and reverse.
Ability to engage/disengage remotely, electrically or mechanically.
Stay engaged with springs. A power would need to be applied to disengage the clutch.
Torque >= 600Nm.
Does not need to be able to engage/disengage with differential shaft speeds, although it wouldn't hurt.

9.5488 x Power (W) / Speed (RPM) = Torque (N.m) =>

9.5488 x 50 000 (W) / 800 (RPM) = 596 Nm

I know that I won't get full 50 kW from the Diesel engine at 800 rpm shaft speed but I am using it as a worst case scenario, especially since the electric motor can generate a lot of torque during acceleration and develop much more than 20 kW for short periods of time.

My question is, do you have any suggestions regarding what clutch I could use?

I have spent days now searching the internet and I am simple out of my league.
Please help with links to products, ebay or anything else that would help me find a clutch that would work.

I would love to be able to use something that is readily available such as the clutch that is between the engine and the gearbox.

I appreciate your help, thank you.


texts: What is this kind of X-Y motorized system?

texts:
I'm wondering what the technical name is for this kind of stepper-motorized arrangement (a positioning system? an XY table?)?

What is it typically used for?

It appears to have two steppers as opposed to generic DC motors, so it's presumably for precision work, and I'm trying to see if it would be appropriate for my (experimental biology-related) application.

The unstable kind of two-axis arrangement I suppose would make it too wobbly for something like CNC-machining, but perhaps might work well for scientific experiments.


texts: In ansys workbench, unable to apply bearing load

texts:
I'm using Ansys workbench 15 and new to it. I want to perform ball bearing stress analysis but I'm unable to apply bearing load to it. The problem is when I select faces and click on apply, it again shows no selection.

Can any body tell me what is the problem and how to perform ball bearing analysis.

Boundary conditions:

No separation type contact between grooves and bearings ball (grooves of both inner and outer races.)
Fixed support to outer race.

Fig. is attached showing contacts.

Part 1 indicates groove of inner race and part 10 indicate grooves of outer race.

contact body - grooves

target body - balls

I want to apply radial load on bearing using bearing load at the center of inner race. My load is nearly 3000 N with rotational speed of 30 rad/sec.
I used Solidworks software to create my 3D model and then save it as .igs file and import it into Ansys.


texts:
The power went out in my block just now, so I got in my car and drove around and found a utility truck next to a pole that is at the junction between the block circuit and an adjoining circuit (which was on). At that area are two large buildings which used to be industrial buildings fed by three phase power, but the buildings were recently converted to be residential. The pole looked fine. It had some stuff running down the side of it.

The guy was in his cherry picker basket, but only about 10 feet up the pole, well below the wires. He was messing with something for a minute or two, then he made a motion with his hand and there was a blue flash and the whole neighborhood came back on, street lights, houses, everything.

I think he must have caused the outage because I got there in my car in only 2 or 3 minutes after the lights went out, so either it was the fastest power company response time in history, or he deliberately cut off the whole neighborhood for some reason.

What could he have been doing?


texts: Cheap and accurate angle measurement for PID feedback control

texts:
I'm working on a PID-controlled barn door tracker mount for astrophotography in an isosceles configuration:

For those not familiar, the purpose of the barn door tracker is to compensate for the rotation of the earth during astrophotography. The axis of rotation of the tracker is aligned with Polaris, and the upper arm of the tracker rotates about that axis once in a sidereal day (approximately once per 24 hours). So the movement is very slow, but not unnoticeable.

A lot of people use a curved bolt configuration to make it so you can simply set the motor at a constant rate of rotation and get a constant angular rate, but I don't like the inability to address sources of error with that configuration. Instead, I would like to use PID control.

My motivation is both for a fun project, but also to create something that is more accurate than a curved-bolt configuration and cheaper than entry-level equatorial mounts. Ignoring the cost of microcontrollers, I'm aiming to have the entire setup cost less than $120. If I can't make it for that cheap, then I might as well get a professionally-made mount.

I've been looking at different methods of getting angular feedback, and I'm most interested in two: encoder and accelerometer. An encoder would be fairly easy to implement in code and resolution could be influenced by hardware. However, a quadrature encoder would use up almost half of my budget, and I'm skeptical of using just an incremental encoder, in case my PID tuning is off. Not to mention I would have to implement an additional way to home the tracker.

After playing around with an app that lets me see the sensor outputs on my smartphone, I wondered whether an accelerometer might be a cheap alternative. There are plenty of sensors that are USB or Arduino-compatible out of the box. My biggest concern, however, is that of accuracy. The angular change is only about half a degree per minute, but in the isosceles configuration, the rate of the motor must change accurately to maintain a constant angular speed. I need something that will be able to capture that slow of a change accurately.

I'm not a controls or robotics guy, so for all I know I'm completely missing some other component that might fit the bill. Any thoughts on the advantages or disadvantages of the sensors I've mentioned? Or places I might look for more affordable types of sensors?


texts:
Can a worm gear be used for linear motion as well as for rotation?

To be more specific. Suppose I want the worm gear to rotate as well as move forward, is it possible to achieve that ?


texts: Is a filter burst possible under fuel line pressure?

texts:
I have read a few ISO standards for performing the so-called 'burst pressure' test in which a filter or an element of one is tested to failure. I am curious whether such a failure can occur under normal fuel line pressures (e.g. after filter clogging). To break down:

What is a typical fuel line pressure?
Can a blocked/clogged filter 'burst' under such pressure?
If not, what is the worst that could happen?


texts: Cheapest way to produce 200-1000 pieces of 0.2 mm copper plates

texts:
I want to build a strong electro magnet. I came to the conclusion that the smartest arrangement would be something like hundreds of thin sheets of 0.2 mm copper with PTFE isolation. This reduces resistance (diameter) and allows maximally compact stacking.

I struggle a little bit, because actually no one seems to produce something like this. Instead industry prefers wires, even if they are not compact enough to get a good performance.

Question is: What is the smartest, cheapest and easiest way to get sheets like in the image below? Diameter would be around 4 to 8 cm.


texts: What injectors are typically used for mixing sewage sludge?

texts:
One typical way to heat sewage sludge digesters is to pump the sludge through heat exchangers, raw sludge is injected before or after the HX. What kind of injectors are typically used for this?

I'm not loking to brainstorm ideas what could be used, I'm looking for solutions that are common and proven in the field.


texts: Crooked floor, but ceiling with no incline - could it possibly be a screed?

texts:
This question is related to the situation in an apartment in a reinforced concrete building that is approximately 30 years old.

The ceiling is almost perfectly straight and level.

However, the floor from which the existing screed was allegedly removed is lop-sided or crooked at many places, having differences between spots in the same room that go to 4 cm.

Is it possible that there were multiple layers of screed and only one was removed? Is there any way to determine if what I'm looking at is the reinforced concrete slab itself or another screed?


texts:
I have connected a 200 bar helium tank and a manometer to a pressure regulator. The end of the manometer's tube connected to the regulator is leaking. It's attached with anaerobic thread sealant, so I can't remove it.

Here is the video of the connection

It leaks between rotating and non rotating parts

I tried using bath sealant, but it doesn't sustain 200 bar. I also attempted sealing it with melted soldering wire, but it doesn't stick, no matter how much flux I use. I need some kind of sealant, that is tough enough, but aerobic

The tube is guaranteed to sustain up to 300 bar, but apparently it doesn't.

How do I fix the leakage?


texts: GD&T for Multiple Surfaces as Single Feature

texts:
I'm looking to get some collective agreement on a question that I have come across a few times now.  When referring to features that are technically independent, what is the general consensus on dimensioning them?  Take, for example, the part below:

The 8.5" and 7" diameters are technically independent.  And when being inspected, would typically be reported back as individual diameters. A metrologist would provide me with measurements of the two different  8.5" diameters and the four different 7" diameters. These measurements would be calculated off of each of the individual arcs.

Engineering drawing practice (as far as I've always learned) is to call out the number of places where that feature exists.  However, often it makes much more sense to have the feature reported back based on multiple surfaces.  For example, the 8.5" diameter would be much more practical (and likely more inclusive of design intent) if it were based on the combination of the top and bottom (as shown) surfaces - essentially a single diameter.  Similarly, the 7" diameters would be based on two surfaces on each side of the part.

Now I cannot find any guidance in any of the ASME Y14 standards that clearly indicate how to dimension this.  Is there a recognized difference between saying "2X" vs "2 SURFACES" as shown here:

This scenario comes up quite often especially when considering features like crush ribs, or splines, and as I am often reviewing engineering drawings, I've been looking for a specific reference to point to when explaining the differences to other engineers.

I was taught that stating "2 SURFACES" informs manufacturing/metrology that the feature is based on the combination of both (or multiple) surfaces, where 2X implies that they are unique.

I know that the ASME Y14.5-2009 standard introduces a concept called "Continuous Feature" which MIGHT be a solution to this situation, but the examples and definition are still somewhat unclear and a little ambiguous in my opinion.

Does anyone have different thoughts?


texts:
I suppose this is a logical extension of my earlier question here - in fact, this is probably what I was meaning to ask in the first place. I posted as "centrifugal pump", although the same concept can be observed in other (radial or axial) pumps.

Getting to it, pretty much any photo of a high-efficiency impeller you can find shows that the blade "twists", or has three-dimensional curvatures that are much more complex than taking a flat blade profile and simply extruding it, i.e. this Francis turbine runner:

First part of this question being, is this for the same reason that an airplane propeller twists - (forgive me, rather generalizing here) due to flow field conditions and the radial velocity effects? Are the same principles at work here?

Second part being, how does one go about constructing structures like this? There must be some math behind it that isn't completely CFD-based, as you can see the same ideas in the Rocketdyne F-1 turbopumps constructed in the '60s. However, no matter how many pump design sources I try to find, I can't find any that treat the impeller vanes as anything other than a two-dimensional chord on the impeller back shroud (see below image).

So, in essence, how would I start to go from a basic pump design (inlet/outlet velocity triangles, simple impeller) to a more "advanced" or "efficient" design like an impeller of the above nature?


texts: Is there an inward (radial) force acting on a magnet inside a magnet?

texts: With a magnet inside another hollow magnet, for example an iron rod in a hollow cylinder, the iron bar placed inside the cylinder with poles attracted to opposite poles of cylinder (likes repel opposites attract), is there also a force along the radius of the cylinder? Per the closed loop rule, the magnetic flux along the sides of the iron rod flows in opposite direction to that of the cylinder. It would seem like the magnetic flux on the inside of the cylinder "squeezes" its way past opposite flux from the iron rod (the iron rod being fixed in place along the longitudinal axis by attraction at poles), compressing it from all directions at once, repelling the iron rod with a vector towards the centre of the radial axis.


texts: Would pumping down (below 0 psi) on a gas cylinder regulator cause it to break?

texts:
Would pumping down on a gas cylinder regulator cause the needle of the valve to break since it’s trying to go below zero? Would this also cause a problem with the regulator itself?
I’ve included the actual picture of the regulator.

Thanks for your time!


texts: Practices used for making a material light weight and giving it more strength

texts:
What are common practices used in making a material light weight and giving it more strength.
By practice I mean:

Making holes in the material to reduce weight

Reduce thickness to the bare minimum to keep it light

Create air pockets to occupy a larger volume with the same mass.

Which one is the best practice for giving light weight and exceptional strength


texts: What is the first moment area of a rounded rectangle?

texts: I need to calculate the plastic section modulus of a rectangular section with rounded corners. First I need to know the formula for first moment area of a quadrant. I can't find it anywhere on the internet. Does anyone know?


texts: What shape does a rod bend into when you push the ends together?

texts:
If I have a uniform rod --

And then I push on each end toward the center >--<

So it bends >^<

What shape does it make? Is it a parabola, a catenary, or something else?

Assume constant stiffness along the rod. I'm using the rod to draw an aerodynamic shape, and I'd like to know what shape I'm drawing. I've read about parabolas and catenaries, but I don't know the answer to this question.

Cheers!


texts: How to design a reinforced concrete ship keel?

texts:
I am building a small ship (or very large sailboat) that will have a concrete ballast at the base of the keel. I am looking to increase the weight of the concrete (lb/ft3), but I also want to maximize the impact resistance of the concrete to resist cracking/shattering should the boat hit a rock hard vertically due to waves.

The simplified dimensions of the concrete portion of the keel will be 11.5" W x 18" D x 40' L. This will essentially be bolted on to the bottom of a laminated wood (fir) keel which is 11.5" W x 12" D x 40' L (simplified dimensions).

How can I determine the best concrete recipe and reinforcement scheme for this particular usage?

I need to determine:

optimal size of rebar to use;
optimal size(s) of aggregate;
how many parts of cement, sand, and aggregate to mix;
and the optimal amount of rebar to include.

In general heavier is better; I am not looking to lighten the concrete. I know concrete recipes are a topic all on their own; what I need is a recipe to start with that will produce a strong and heavy concrete that resists cracking from a heavy impact. The boat will displace 100 gross tones of water and may be subjected to waves with crest-to-trough wave height of about 6' in areas where there is an unlikely yet possible danger of striking underwater obstructions. It doesn't need to support being continuously jackhammered, but support get hit perhaps say 5 times over it's expected lifetime of say 20 years (just to give you an idea of infrequency). I am not planning to strike bottom, but it can and does happen despite all cautions taken.


texts:
I want to be able to precisely rotate a item. For this I have positioned the item on top of a very large gear. It is driven by a smaller gear. When the item is in the correct position, I will lock the smaller gear and the item is fixed in the correct position.

How can I achieve a more precise system without making the large gear larger and the small one smaller(without using motors)?


texts: Are the points of inflection and contraflexure the same?

texts:
In theory of bending of beams, often these terms are used. There are no clear definition present. Most of them contradicting. Which of the property(bending moment and shear force) is zero in which case?

The definition of contraflexure is defined as the point of zero bending moment. Then why have another term, i.e inflection point?

NOTE:The wikipedia link has no references.


texts:
Consider the following circuit:

Let both capacitors be charged to equal voltage. The circuit acts as LC oscillator circuit with resonance at $f= \frac{1}{2\pi\sqrt(LC)}$, where C is the resultant capacitance of C1 and C2. What frequency of oscillation will be experienced by both the individual capacitors? Will it be same as f, or different?


texts:
Let’s say we have a thin band (made out of PLA, 3D printing material) with a rectangular cross section. In drawing, it would look something like this:

Let’s say a force of 15 N is to be applied from the top down to the band, how am I supposed to figure out the minimum thickness (and or height) that could endure the force and do not undergo deformation or failure?


texts:
I understand plane strain/stress relations are typically utilized for 2D materials. I was wondering if we consider a 2D material acting in a 2D space, would we have a stiffness matrix such as
\begin{equation*}
\left[
\begin{array}{ccc}
C_{1111} & C_{1122} & C_{1112} \\
& C_{2222} & C_{2212} \\
& & C_{1212}
\end{array}
\right]
\end{equation*}
rather than just plane strain/stress relations imposed on the classical stiffness tensor in 3D. Are there any situations where such a formulation would be appropriate in the real world? Thanks for the insight!


texts: Rack and Pinion: Increasing Linear Movement of Rack

texts: I would like to know if there's a way to increase the linear travel of a rack relative to the rotation of the driven shaft, either through a gearing system or some other means?


texts: Calculating R-value from temperature differential

texts:
A home windows installation rep gave me a quote today and conducted the following temperature differential demonstration.

Alice pointed a heat gun (with a surface temperature of 165F) at the interior surface of a window.
Bob measured the exterior surface of the window (with a no-contact laser thermometer) to be 45F.

Is there any way to calculate R-value (or any other standard thermal insulation reference) given the temperature differentials resulting from the above setup and procedure? Can the setup or procedure be improved in order to get an R-value or any other standard and useful benchmark or metric? If so, how?

Fig. 1. Test Setup

Edit: Per one of the answers, let's make the simplifying assumption the temperature of the window's interior surface is equal to the temperature of the heat gun.


texts:
I know the meaning of (instantaneous) “center of rotation” and “center of zero acceleration” for a rigid body. I know that they do not coincide (in general) and that their positions change with the motion of the rigid body.

Then I know that for each point of the body we can define an instantaneous “center of curvature” related to the trajectory. My question is, how are these centers of curvature related to the “center of rotation” and “center of zero acceleration” of the whole rigid body? Is there any relation among them, in the most general case?


texts:
Are there any recommended clamps for holding samples of a viscoelastic material in place? My goal is to have the clamps hold the rectangular samples along lines drawn parallel to edges of the samples for elastic testing.

Hand screw clamps appear to be completely inappropriate as the material just squishes out of position. But, I think most clamps would suffer this weakness.


texts: Finding characteristic time required to reach steady state in the pump equation

texts:
Consider the pump equation
$$\rho \frac{\partial w}{\partial t} = K' + \frac{\mu}{r} \frac{\partial }{\partial r} \left(r \frac{\partial w}{\partial r} \right)$$
Subject to $w(r=R,t)=0$, $w(r=0,t)$ is finite, $w(r,t=0) = \frac{K}{4\mu}(R^2 - r^2)$.
Solving this equation by finding the steady state solution, and using $w = \bar{w} + w_{ss}$, I managed to find the solution for the above equation.
It looks like
$$w(r,t) = \sum_{n=1}^{\infty} a_n J_0(j_{0,n} r/R) e^{-\frac{\lambda _n}{ \rho} t} + \frac{K'}{4\mu} (R^2-r^2)$$
where $j_{0,n}$ are the zeros of the Bessel $J_0$, and $\lambda _n = \frac{\mu}{R^2} j_{0,n} ^2$.
I have been asked to examine the centerline velocity $r=0$ and to determine the approximate time $\tau _s$ it would take to achieve the new steady state.
What does this mean? What is $\tau _s$? When I plug in $r=0$, the $J_0$ terms in the summation just go to $1$, so the expression for $w(0,t)$ is
$$w(r,t) = \sum_{n=1}^{\infty} a_n  e^{-\frac{\lambda _n}{ \rho} t} + \frac{K'}{4\mu} (R^2-r^2)$$
How do I go about figuring out $\tau _s$? Any advice would be appreciated.


texts: Can a PID controller have a simple on/off output?

texts:
The crux of  a PID controller is:-

output = Kp * error + Ki * integral + Kd * derivative

So typically there is proportionality and a continuously varying (analogue) output.  In the case of a simple process like a domestic gas boiler, the boiler is either fully on or fully off.  Or, say a cooling fan that can only be switched on or off to keep something cold.

In these cases, can a PID controller be used at all? There is still an error term.  Or would an alternative form of control be necessary?


texts: How can I accurately measure the actuation force of small buttons (<1cm diameter) using home equipment?

texts:
I'm trying to measure the actuation force of buttons on the Playstation Vita, in preparation of building an external device that presses these buttons automatically. Specifically, I'm trying to measure the force required to push the buttons on the D-Pad on the left, and the action buttons on the right.

Googling "how to measure actuation force" will give you pages of results of mechanical keyboard enthusiast forums, and they often mention measuring the actuation force by stacking pennies / whatever coins you have until the key is depressed and the computer recognises the keypress. I can't do that normally here, since the buttons are really small (<1cm for the action buttons) and even the smallest coin my currency has cannot be stacked onto it without toppling over.

In an attempt to mitigate the problem, I made the following setup. It still uses coins as weights to push down the button, but I rested the coins on the ruler that in turn rests on another object of somewhat equal height/thickness to the game console, in this photo, the remote control seen in the background. I conducted the experiment by continuously adding coins with a game running on the console until it registers a keypress, and then summing up the weights of the coins.

However, the results are rather inconsistent and questionable. I repeated my experiments several times (by knocking down the coin tower and stacking it up again) as standard practice, and I got values ranging from 100g to 180g, which feels extremely high for buttons on a handheld game console, and that large spread seems to be telling me that my experimental technique is just plain wrong.

Some possible causes of inconsistencies from the setup:

The coins are not the same - I'm stacking 5 different coins at once
The coins are not stacked in the same order each time I redo the experiment
The center of the coin tower is not aligned with the center of the button on the game console - I don't know how to do this without the coin tower making contact with the neighboring buttons or it toppling over

Some steps I have taken to possibly improve accuracy:

The ruler used is a stiff metal ruler and does not bend significantly
The ruler is kept horizontal
The only points of contact of the ruler are the remote control seen in the background and a single button on the D-Pad.

TL;DR: How can I improve the accuracy of my setup, or other better ways to measure actuation force of such small buttons?

Update & Final Results I used the weighing scale method, and the results are 80g for the D-Pad and about 120g for the action buttons on the right. Thanks everyone!


texts: How is forward motion initiated in this case?

texts:
Source:byjus.com

Do these forces cancel out each other? If yes, how is forward motion initiated?

Also, in this situation, since friction between the road and the wheels is enabling motion, which force is opposing the motion?


texts: Solidworks - Projected Curve is incomplete

texts:
-- This issue might be due to a bug in SolidWorks 2014 SP2 --

I'm trying to route a water hose from one location to another without passing through a keepout area (the red box shown).

I am simply sweeping a circle (red sketch) along a Projected Curve defined by two orthogonal sketches, one on TOP (green curve) and one on FRONT (blue curve).

It's very nearly working, apart from that I cannot seem to persuade Solidworks to complete the Projected Curve.  It always seems to stop short of the final location.

Each of the two control curves begin and end with straight line segments that are tangent to the spline that governs the path.  I need these to get a nice, straight controlled entry/exit from the flat surfaces.

The control points begin and end at the same locations in space (projected onto their respective planes).

What am I doing wrong, that is preventing this curve from being completed?


texts: Why not build container ships from plastic?

texts:
This may sound crazy but bear with me. I was thinking about why cargo ships are built from such heavy material as steel, while smaller boats are often made of plastics. I know cargo ships carry a lot of weight and the sea can be rough. Those ships of course need to maintain structural integrity and such.

But wouldn't it be possible to build a structure from steel, supported by the strength of the containers that fill the ship. And then build a thick hull around it made from a combination of plastics and compartments of some kind of foam (polyurethaan?).

The advantages are that plastics are flexible (a bump doesn't result in damage as easily), easy to work with, easy to repair, cheap, and really light compared to steel.

The idea is kinda like how tall buildings are built from a strong structure, but have an outside "hull" of glass (see image below).

I didn't do any calculations on it (I'm a software engineer, unfortunately not a hardware engineer).

Does anybody know the reasons why big (cargo) ships are not made from plastics?


texts:
Could an air compressor be used to compress steam? What would be practical problems if any?

Say I have saturated steam at 1 barg and I need to compress it to 2 barg. In theory could I just pipe to the inlet of a conventional air compressor (reciprocating type).

Sounds dicey to me but when someone came up with this idea during brainstorming for a DIY project I couldn't come up with cogent reasons why this would be a bad idea.


texts:
Rio de Janeiro, Brazil is currently stunned by the fact that yesterday a span of a brand new (innaugurated in January) bicycle bridge along the coast collapsed when struck by a wave, killing some people that were on it at the time.

A few videos have surfaced:

This one is of the moment it collapsed, but the man behind the camera didn't notice what happened until a few moments later, so you don't can't clearly see the wave impacting the structure, but you can see how the waves are redirected and slam against the structure almost vertically.
This one is from after the collapse, but clearly shows the aftermath. At 2:15 you can see an example of another wave running up the rocks, spraying up higher than the road. At 2:30 you can see the columns (including their topping, where the beam was supported are in perfect condition and don't seem to present any damage.
This article shows a video representation of what is believed to have happened: the waves lifted the beam off the pillars and caused a rigid-body rotation around its own axis. This, along with the mint condition of the tops of the columns implies that the project probably did not adopt a beam-column connection which could resist tension, which would therefore have impeded the beam's "liftoff".

Now, my actual question is: how does one calculate a structure to resist such a load? I've done some searching and have found some articles ([A] [B] [C] [D]) regarding wave action on bridges, but they all consider the more common case of a wave moving in a horizontal direction striking the side of a bridge. Now, how should one translate this to this case, with the wave being thrust (and possibly sped up) vertically?

Are there any codes which consider such cases? Also, more generally, are there any codes which define even standard wave action? International codes are fine. (I'm leaning a bit on Rick Teachey's position on the "recommendations/finding stuff" meta post for this part).


texts: Solving 1D Unsteady Homentropic Flow using Method of Characteristics

texts:
I am looking to solve the 1D Unsteady Homentropic Flow equations using the Method of Characteristics (MOC). I am using Zucrow and Hoffman's Gas Dynamics Volume 1 as a reference and I am currently stuck.

In chapter 13, the authors begin describing the use of MOC to solve the 1D unsteady flow equations. I understand their methodology till  I get to the step that states to substitute equation (13.16) back to equation (13.15).

For this example:
$$
u = u(x,t)
$$

and
$$
p = p(x,t)
$$

For homentropic flow, $$ \rho = \rho(p) $$

Equation (13.15) is the following:

$$
(\rho u \sigma_1 + \rho a^2 \sigma_2) ( u_x + \frac{\rho \sigma_1}{\rho u \sigma_1 + \rho a^2 \sigma_2}u_t) + (\sigma_1 + u\sigma_2 )(p_x + \frac{\sigma_2}{\sigma_1 + u\sigma_2} p_t) = 0
$$

Equation (13.16) is the following:
$$
\frac{du}{dx} = u_x + \lambda u_t
$$

$$
\frac{dp}{dx} = p_x + \lambda p_t
$$

The resulting equation (13.18) when you substitute (13.16) into (13.15) is:

$$
(\rho u \sigma_1 + \rho a^2 \sigma_2) du + (\sigma_1 + u\sigma_2 ) dp = 0
$$

I understand that
$$
\lambda = \frac{\sigma_1}{u\sigma_1 + a^2\sigma_2} = \frac{\sigma_2}{\sigma_1+u\sigma_2}
$$

However, I have not been able to get (13.18) from back-substituting (13.16) into (13.15).

Does anyone have any suggestions for me to consider, look into, etc.?

Thank you!


texts: How to shape sheet metal like Willys hood latch?

texts:
I am want to produce Willys' hood latches like links below
Hood latch link 1
Hood latch link 2
Hood latch link 3
What kind of metal shaping process is this?
Even I could not figure the mold out.


texts: Question about flow temperature and storage temperature in a cogeneration plant

texts:
Let's assume I have a cogeneration plant that produces heat with a nominal output. The heat is given into a heat storage tank, which is filled from above. The maximum flow temperature of the cogeneration plant is 85 °C, if this occurs an emergency shutdown takes place. The maximum water temperature in the heat storage tank is 95 °C.

Is it theoretically possible in this case to reach a water temperature of over 85 °C only with the cogeneration plant?


texts: What methods exist to measure the modulus of Elasticity of Soil?

texts:
I would like to know what test can be done to quickly measure the modulus of elasticity of soil with varying parameters (density, moisture content etc).

One method I know is using the oedometer test. By varying the vertical stress and measuring the variation of strain, we can measure the modulus of elasticity.

However, the oedometer test can take a lot of time. (48 hours). Is there a way that is quicker?


texts:
How quadrilateral elements represented in most FEA solvers for structural mechanics problems?
I know that Nastran-95 represent quadrilaterals for membrane and bending elements as a set of triangles:

At the same time there are a lot of literature where stiffness matrix for quadrilaterals is computed using ξ-η coordinates:
The question is which one of both methods is used in modern FEA packages?


texts: How to communicate to keep original dimensions of a part in a technical drawing?

texts:
Example: let's say that I have a rectangular part that I would like machined. I'd like to cut it to change the length, but the width and thickness are fine as is. The width and thickness are not nice round numbers. Is there any convention on how to communicate this through a technical drawing? Something like "AS IS"?

Related to Do I need to mention every dimension on a to-scale drawing?


texts: Why doesn't axial turbomachinery blades block fluid from flowing?

texts: I know this is a silly question, but shouldn't the high speed rotating blades (in case of an axial air compressor or an axial air fan for example) block the air from flowing? What makes air flow between blades?


texts: Selection of Aluminum (or steel) tubing dimension based on uniform load on supported beam

texts:
I am installing shades on a section of deck. The shade will be made of sections of fabric (which will let some wind through), but I assume a solid section.
Dimensions are 3.5ft*4ft = 14ft^2 = 1.3m^2

I will put the shades on and off, but I want to make sure it won't break if there is a sudden gust of wind. Suppose a 60 mph wind gust = 26.8 m/s and 1.2kg/m^3 air density. This leads to 561.4N of force. (I know the 4X4 red cedar post will hold. I know the fabric will hold. The seam may break, but that's an easy fix.)

The shades will be supported by 2 tubes (beams), one on top, one at bottom. So, I assume an even load. I also assume the load is even on the whole length on the tube. So, 1 tube of 1.066 meter should support roughly 281 N.

I was able to find how to compute the maximum moment of 37.43 Nm.

This is where I can't finish my calculations. Will a (generic) 1in aluminum tube (1/16in thickness) I find at the store enough?
I found the tensile strength of aluminum is between 33000 to 76000. So I assume the generic tube I find at the store will be the lowest one at 33000.


texts: When is it necessary to consider digial control rather than directly coding in the gain matrix?

texts:
I designed a LQR controller and want to implement it on a microcontroller. I don't know about digital control and don't know when to apply it.

After a brief research, I found out that I need to apply the z-Transform, instead of Laplace-Transform. However the gain matrix is derived from time-domain.

The microcontroller I use is a OpenCR1.0.


texts: Thin or thick wall for expanding rubber pressure cylinder

texts:
If I want to expand a rubber cylinder by a certain internal volume - with all else held constant (type of material, length and radius (without constraining it), etc.) will a thinner or thicker walled cylinder cope with greater volumetric expansion before rupture?

(The thick and thin versions have the same ID, it is the OD which changes in each case.)


texts: What should be the angle of the motor to the base?

texts:
I have a boat that uses a propeler above the water. The propeler blows the wind to the back of the boat and it makes the boat go straight.

There is one problem with this approach: I am using a big propeller and I need to move the motor high so the propeller does not touch the water. As high as I move the motor there is an undesirable increase in the torque generated by the motor related to it's base. I mean, if I move the motor higher, it makes the boat sink the front part of it, if I move the motor down it eases the sink of the front of the boat.

I said it all to ask this question: can you see the red lines and the right angle (in red) at my image? If I make that angle (instead of 90) to become 130 will it reduce the force that makes the front of the boat sink? Or making the angle 40, will ease this force?

You need to remember one thing: when we increase/decrease the angle (from 90) the height of the force becomes lower and lower, so it should reduce the torque but it also creates another force (vertical component) that can make the bottom of the boat "fly" or sink.

I thought a lot about this and I have no idea if I should increase or decrease the angle (red) in order to prevent the front of my boat to sink cause when I increase a lot the power of my motor my boat gets very fast but the front of it eventually gets inside the water and the bloat flips, which is terrible.

edit

I made some experiments today and I tried an angle of 70 degree, in that case, when speed is low the back of the boat sinks but when I go fast the tip (front) sinks. When I tried and angle of about 110 degree and the speed is low the tip (front) of the boat almost sinks with low speed but for some reason when it goes fast the front does not sink much more. What's going on?


texts:
This is my first question on this forum,
In the case of a project I use the beaglebone black (BBB) as motherboard and a LoRa Nemeus XM001 module, this last one integrates the Nemeus MM002 module. The module and the motherboard are connected via an UART (Rx/Tx) link and I use minicom as a terminal to communicate AT commands between the BBB and the XM001 module.
My problem appears when booting the module, the following line of code appears in the minicom:
"+DEBUG: START,nemeus-mm002-master16W18_08-modem"
The appearance of this line of code is in theory normal, it is part of the boot procedure.
MM002-xx-EU AT Commands
However the module seems to be stuck after the appearance of this line as if it was executing a command that never finishes ...
Have you ever encountered this problem ?
Thank you in advance for your answers,


texts: Why do we consider the normal component of velocity in a flux and not the original direction of velocity?

texts:
Below is the equation of convective flux of an arbitrary property that is carried by particles. When particles move they carry their property along with them. Given a fixed surface in space, in order to calculate the amount of property crossing a surface S we just use the formula.  Note that $\Psi$ is the amount of the property per unit mass, $\rho$ is the density of particles,  $v$ is the velocity and $n$ is the normal vector of the surface.
$$\Phi =\int \rho\ \Psi\ v.n\ dS\  $$
Derivation of the formula is taken from
I don't understand why do we have to include the normal component of the velocity vector of the particles ($v.n$).  I understand that the particles are crossing the surface, but why can't they just cross the surface while keeping their original direction?
By the way, the surface is not meant to be real, it is just virtual... that's why the particles are able to cross it after all.


texts: Calculation of critical internal thread according to VDI 2230 Part 1

texts:
I’m doing a “Systematic calculation of highly stressed bolted joints – Joints with cylindrical bolt“ according to VDI 2230 Part 1. In step of calculation R11 “minimum length of engagement”, when my internal thread is critical, I have to calculate the ratio of $s/d$.

In my specific application I’m using a tapped thread joint (TTJ) and I’m connecting some kind of tube (internal thread) with a threated bolt. And because my tube is thin-gauged I get a small $s$ and therefore my ratio $s/d$ is smaller than $1.4$.

VDI 2230 only considers ratios greater than $1.4$ and here my questions arise:

What is the effect on my calculation when I’m out of the mentioned ratio-borders?
Is it possible to compensate the effect?
What’s the amount of error I’m introducing?
...

Okay, I could reconstruct my connection – but that’s not the topic of my question.

Thanks in advance for your help.


texts: What is the optical Lagrange invariant of an afocal system?

texts:
I am solving an optics exercise that requires to design a Keplerian telescope with a given magnification M (negative), a certain object size L and the restriction of not having lenses faster than F/1 (wavelength of the signal and resolution are also given, but they are used for solve successive questions). In particular, the exercise requires to retrieve the NA of the objective lens from the optical invariant of the system.

Given these information, I would say that, using the fastest lenses possible, I would need a first lens with radius R1=L and a focal length of F1=2L (so that the F/1 requirement is satisfied), while the second lens should have a focal length of F2=|M|F1, a distance from the first of d=F1+F2 and a radius of R2=|M|L. However, I am not sure how to retrieve the Lagrange invariant  from this theoretical design: for once, since the system is afocal, the object should be at infinity, thus how can the marginal ray be defined? Moreover, in this case both the first and the second lens limit the marginal rays of the system, and being the object at infinity I am not sure how should it be tilted (shouldn't it be parallel to the optical axis? But then wouldn't it coincide with the chief ray?).


texts: What is the unit of measurement of fatigue damage in a structure?

texts: I looking the specific meaning of fatigue damage in structures. I have one structure and which is subjected to repeated loading cycles. I want to see is this design is safe from fatigue point of view.


texts: What is the strongest and lightest material?

texts:
I have heard titanium is the strongest and the lightest material. It is used for my glasses frame. Is it true that it is the strongest and the lightest as well?

Strongest, the biggest forces can it bear without damage or breaking $\frac{Newton}{m^2}$.

Lightest, the least weight of a certain volume of material $\frac{kg}{m^3}$.

i.e.: a material is quite strong to bear some load, but also heavy at the same time. Another material is light enough, but can not bear any load. So, what I am asking is what is the strongest material but lightest as well.


texts: How Single Link Flexible Manipulator Controller controls the vibration of the link tip?

texts:
I'm control engineering student.

As seen on the video link below, how the controller controls the tip vibration and the link movement at the same time? Please explain using the block diagram of the system, since i am quite confused.

I already know about simple feedback controllers. For instance if i have a simple dc motor position control. How it works is if the now position of the motor is less than the setpoint, the controller add a little bit power to the motor so the motor turns. Otherwise, if the now position is more than the setpoint, controller trying to reduce power or inverse the polarity of the power given to match by the setpoint.

But for the flexible manipulator i have no idea about how the control system works. Since the controller must regulate the motor speed and direction of rotation to somehow reduce the tip vibration.

Single Link Flexible Manipulator Controller


texts: Why did steam locomotives not transfer power by cogwheels?

texts:
Modern cars use cogwheel to transfer power from the engine to the wheels.
Steam locomotives used some kind of bars (sorry, I'm not a native speaker) to transfer the power to the wheels.

Why did the engineers not use cogwheels?
Would steam locomotives had been faster if they had used cogwheels?


texts: How to measure time taken to run SCPI commands?

texts:
We all know that every program takes time to run. Normally in Python, the time built-in Python library would be sufficient to measure time-taken to run code. How may I determine how long a SCPI (Standard Commands for Programmable Instruments) command takes to run?
The computer hardware platform is Microsoft Windows. The measurement instrument is Agilent 34401a DMM. The serial communication protocol is RS232.


texts: Nuclear wastegate thermal dissipation systems?

texts: How do shoreline nuclear facilities lower the temperature of wastewater generated by their cooling systems before it enters the ocean?


texts: Why are aircraft carriers so expensive to build?

texts: The aircraft carrier USS Nimitz cost \$4.5bn. The cruise ship Allure of the Seas cost \$1.2bn. Why is the difference so huge?


texts: estimating the surface area of a steam coil immersed in a tank

texts:
I've been tasked to design a steam coil that will be immersed into a tank in order to maintain the fluid temperature above 25C (but not to exceed 40C), and I need to calculate its surface area & length. The fluid is a highly viscous oil additive and it's not agitated.

My approach was the calculate the total energy needed to heat the coil, using $Q = m.c_p\Delta T$. where m is the mass of fluid in the tank, $c_p$ is the specific heat capacity of the fluid, and $\Delta T$ is the difference between the initial temperature of fluid (25C) and what it should be maintained at (~35-40C).

Then I equated this energy to $UA\Delta T_m$, the energy delivered by the steam, where $U$ is the overall heat coefficient for steam, $A$ is the outer surface area of the coil and $\Delta T_m$ is the log mean temperature difference.

I am assuming this approach is correct, but I'm doubting my calculations because

It doesn't match with Immersion Coil Surface Area Calculator For Heating with Steam
It seems quite large

Apart from the temperatures I've mentioned above, these are the only parameters I've been provided with from the company:

inner diameter of the tank = $3.35\,m$
outer diameter of the tank = $3.6\,m$
height of tank = $6.5\,m$
density of the fluid = $850\,kg/m^3$
viscosity of the fluid = $30, 000\,Cst$
pressure at which steam enters the pipe = $150\,psi$
Heat time of $2\,hours\,(7200s)$
pipe diameter of $2'' (0.0508\,m)$

So here's the calculation I did:

$M_{fluid} = V * \rho = \frac{PI * 3.35^2 * 6.5}{4} * 850 = 49000\,kg$

Assuming the $C_p$ to be $1800\,J/kg.K$,

$Q = 49000 * 1800 * (40 - 25) = 1.323\,GJ$

I estimated $\Delta Tm$ to be $86$ using:

$\frac{(ΔT_1 - ΔT_2)}{ln(ΔT_1/ΔT_2)}$

With $T_1$ being the inlet steam - the final temperature of the fluid = 145 C.
With $T_2$ being the outlet 'steam' - initial temperature of the fluid = 45 C (I estimated the outlet 'steam' to be around 100.

Taking the $U factor$ to be 100 (estimated from this site),

A = 1.323 GJ / (100 * 86 * 7200) = $21m^2$.

And the corresponding length would be $\pi DL = A$ and $L = 131m$. Clearly something (or a few things) are wrong here since I don't think the tank can be that big so help would be appreciated on where I went wrong.


texts: Mesh Wifi Router Network for a Small Village

texts:
I was wondering if its possible to create mesh network of WiFi for relatively large area? I am talking about the size of small village (~20km2). The idea is to use centralized connectivity with enough bandwith, then distribute them using mesh wifi router (like Google WiFi) for every X radius
Is this a pipe dream? What would likely be the obstacles?
Mesh-type should be used to maintain just single SSID over a whole network

Google Wifi: We recommend a maximum of five Wifi points in a single
mesh set up

Edit: I am just not aware if there's any limit for this case to happen, and why Google Wifi even have that 5 limit value while theoretically to my knowledge, as long as it's placed nearby to each other, wouldn't it could be used to expand the signal unlimited time? I just couldn't find answer elsewhere. Any input is highly appreciated


texts:
I'm looking at designing a small gadget (think something like a Fitbit in size) where the case has a couple of buttons on it.  For various reasons the buttons have to be around the narrow side (edge) of the case.  I am fairly lost as to what the standard button mechanical design for this type of application would be.  I mean, I know about (much bigger) buttons with a cantilever or a linear spring or spring and pivot, or rubber dome switches, but here... the whole thing it tiny!  The largest buttons that can fit are roughly 12x5mm, and the "mechanism" has to fit in a few mm of thickness.

The prototype has oval plastic buttons which are ~12x5mm and 4mm deep, and C&K PTS840 tactile switches on a PCB behind them.  These switches have a tiny little plunger 1.7x1mm with 0.2mm of travel that the buttons can hit.  In general the buttons can push the plunger just fine.  However there isn't really anything keeping the buttons in place or restricting them to move in a straight line, they kinda rattle around in holes in the case and can both tilt / jam at an angle and fall out.

I think this is probably a solved problem for cell phones / smartwatches / whatever, but I don't know what the standard solutions are.  Could you please let me know what the major different of approaches are and what their pros and cons are?

P.S. This would be designed for injection molding in the future; PC/ABS material.  Wall thickness is around 1.2-1.4mm.

UPDATE  I took apart some sports watches; they all have buttons with a metal spring loaded plunger that goes through a O-ring seal and hits a tactile switch.  The total height of the mechanism is about 5mm (from the outside surface of the button to the switch on the PCB).  That's a good mechanism (and waterproof) but I don't have room to fit something like that; and it probably can't be easily made out of just plastic parts.  I'm still looking for a good solution.


texts: Circuit analysis, voltage in and voltage out

texts:
I want to solve $V_o$ in terms of $V_i$ from  the following circuit.

$R_1=95.7  \Omega, R_2=9.1  k\Omega, R_3=1.0  M\Omega$

So the solution is form $V_o=kV_i$ and I want the factor k.

I know that:

$R_{123}=R_1+R_{23}$

and $R_{23}= 9017.94$ so the $R_{123}=9113.64\Omega$

But how do I get the factor k?


texts:
I am designing a printed piece that will deflect air from an exhaust fan on a computer 90 degrees. My question is, what would be most efficient, a circular radius, parabolic radius, or hyperbolic radius in the ducting to change the flow of the air 90 degrees upward. I'm trying to minimize the resistance of the ducting to maximize my exhaust air flow.

I know very little in this domain, so please forgive me for not knowing even the terms to search for.


texts: How much graphene is required to coat a 5 inch (diameter) sphere if the graphene layer must be 35 nanometers thick?


texts:
I have laminar flow in a tube. Consider the tube to be 0.2 m long and with an average velocity of 0.05 m/s. The analytical expression for my transfer function is: $E(t)= \frac{\tau^2}{2*t^3}$ for $t$>=$\frac{\tau }{2}$ and $E(t)=0$ for $t < \frac {\tau }{2}$.  $\tau$ is the mean residence time. In this case: $\tau$=0.2m/0.05m/s=4 s. I want to convolute this with an exponential equation: $E_2=(1-exp(\frac{-t}{2.55}))$. This equation descripes the magnetization of a particle in a static magnetic field.

I want to get the average magnetization of the particles at the outlet of the tube. So I thought I would do the following: $E_{out}(t)=E(t)*E2(t)$. I would then take the value at t=4s. I have the results from CFD which gives the following: CFD result, the red line is the magnetic field and the green line is $E_{out}(t)$. I'm interested in the value at x=0,2m which is 0.7942.

My results of the convolution are totally different:Convolution result

What am I doing wrong? I'm a little bit confused. Has anyone an idea of how to approach this problem.

Best regards,

Gesetzt


texts:
I'm building a scale model for a proposed construction project.

Is it possible to simulate foundations operating in soil in a scale model?  What do people typically use?


texts: thermal resistance and thermal time constant with ambient temperature

texts:
If water at the same temperature is heated with the same heat power source in two different ambient temperatures (one ambient is low and the other ambient is high) then which water sample will reach the equilibrium state of temperature more quickly, or both will take same time?

This question is related, if we just change the ambient temp. and start heating the object then how will it affect to thermal resistance and thermal time constant?


texts: Learning about composite resins, should the resin be able to adhere to the selected filler?

texts:
I'm learning about composite resins, and the various filler additives, but I wondered about the relation between the two. For example....
An epoxy resin has poor adherence to a material such as polyethylene, but it has strong adherence to a material such as polyamide 66.  If you have an epoxy resin with powdered polyethylene, vs polyamide 66, beyond the characteristics of the powdered material itself, what impact does the resins ability to adhere to the powered filler have?


texts: solution of system of coupled partial differential equations

texts:
I have following system of coupled Partial differential equations.
How can I solve the system by Maple?
\begin{align}   m_1\frac{\partial^2 u_1}{\partial t^2}+A_1\frac{\partial ^4u_1(x,t)}{\partial x^4}+k(u_1-u_2)=F_1(t) \delta(x-x_1),  \end{align}
\begin{align}    m_2\frac{\partial^2 u_2}{\partial t^2}-A_2\frac{\partial ^2u_2(x,t)}{\partial x^2}+k(u_2-u_1)=F_2(t)\delta(x-x_2).  \end{align}

In here,  $A_i, m_i, x_i$ and $k$ are constants where $i=1,2$ and $\delta$ is Dirac Delta function.
Boundary conditions:

$u_1(0,t)=\frac{\partial^2 u_1}{\partial x^2}(0,t)=u_1(l,t)=\frac{\partial^2 u_1}{\partial x^2}(l,t)=0$,

$u_2(0,t)=u_2(l,t)=0$

Initial conditions:

$u_i(x,0)=w_{i0}(x),$

$\frac{\partial u_i}{\partial x}(x,0)=y_{i0}(x)$ for $i=1,2.$

Since $F_1(t)$ and $F_2(t)$ are unspecified (ungiven) functions, solutions $u_1,u_2$ which we seek will be depended on  $F_1(t)$ and $F_2(t)$.

Maple Code:

PDE1:=m1*diff(u1(x,t),t$2)+A1*diff(u1(x,t),x$4)+k*(u1(x,t)-u2(x,t))=F1(t)*delta(x-x1);
PDE2:=m2*diff(u2(x,t),t$2)-A2*diff(u2(x,t),x$2)+k*(u2(x,t)-u1(x,t))=F2(t)*delta(x-x2);


texts: Sealing a rotating shaft in a 3D-printed part

texts:
I need to seal a rotating shaft that protrudes through a wall in a 3D-printed enclosure I am designing for a school project. The enclosure is for what will be a small generator that will be used in all weather conditions, so I'd like to make the shaft waterproof. To clarify, it is not the motor shaft that needs to be sealed, it's just a 1/4" diameter metal shaft which connects to some gears in the enclosure. Do I need anything more than a waterproof bearing (which I will be buying, not 3D printing) press fit in the enclosure wall? Such as, do I need some type of rotary seal as well? Is a press fit setting for the bearing enough to prevent water intrusion between the bearing's outer diameter and the enclosure wall? And how should I design the enclosure wall to hold the bearing (i.e. Is all I have to do make the wall the same thickness as the bearing? Does it need some sort of lip to hold the bearing?)?

I have searched for a long time online about how to do this, but nothing I've found is very helpful or is too confusing for me to understand. Any help is greatly appreciated!


texts: What is the bending moment formula for continuously supported beam of equal span?

texts: Is there a standard chart in Eurocode for the maximum and minimum bending moment in uniformly loaded beam for indeterminate structures where we can use directly? Many textbooks give different coefficient values for the moment for continuous beam, some wl2/10, some 0.046wl2. I know that hogging and sagging moment are different. Is there an authoritative reference for this?


texts:
Typical acoustic speakers come mounted in boxes. The shape of the boxes is important because the speaker throws pressure both forwards and backwards, so the back pressure goes into the box and resonates, thus the shape and material of the box has a noticeable effect on the sound quality. A constraint on speaker manufacturers is the size of this box.

In a home, however, if a speaker is mounted in a wall or other special enclosure, it may be possible to build a large or unconventional sound box for the speaker. Has there been any research done on the design and characteristics of such custom enclosures?


texts: I have an application in which speed of the shaft is 0.54 rpm. The input speed of the motor (induction 4 pole AC motor) is 1400 rpm. So the gear reduction is enormous. I had two helical redactors coupled together and I read that in this situation  when you have such big reduction (2 stage reduction) and super low speed you have to limit the input torque. I don’t understand this – why is this necessary? The start up torque of AC motor is 2-4 times higher than the nominal torque, how to start this application? Can someone tell me why in big reduction systems it is necessary to limit input torque?


texts:
I'm not sure this is the right stack exchange community to be asking this, but I have a little issue. There's a great microscope-camera from Carl Zeiss (AxioCam HRc) which I got for free and would like to use. It originally came with a PCI interface board and a driver CD; the PCI interface board is built into a computer which runs Windows NT and the driver CD is missing. To make matters worse, Zeiss doesn't support this model anymore.
So I wanted to know if it's possible to just remove the PCI interface board and attach it to my Windows 10 computer, and also to somehow take the driver from Windows NT and install it on Windows 10? I know that Windows has always been big on backwards-compatibility, but I'm way out of my depth when it comes to drivers, interfaces, etc. and so I don't even know if and how I can do this. Any help would be highly appreciated!


texts: How can I apply a fixed and adjustable force to my flexible sample?

texts:
I major in microelectronics. I just want to apply a fixed and adjustable force to my flexible sample.

'Fixed' means that the force could be hold for given time without change.
'Adjustable' means that the force would be changed after my setting or its value could be changed with time and rule.

It would be better if the force was horizontal.

My sample can endure the force with value about 10 N. And I hope the force could be adjustable between 0 and 10 N.

I think a stepper motor with load cell may be the solution but I don't know how to realize it exactly. The only thing I can think of is to hang different balance weight to one side of my sample. I know some kind of universal testing machines could also get this done but they are too expensive.


texts: How to model a UDL over a plate for bending?

texts:
If I have a square plate of height h supported along one side (an L-bracket, modeled as fixed support), and there is an evenly distributed force acting over the face of the plate. From load analysis I am able to determine the resulting force (acting in the centre of the plate) to be P, thus the distributed load over the plate is P/A = P/(L^2)

My question is if we are considering the bending of the plate, can we model this as a cantilever beam with UDL of P/L or will it be something else? I am leaning to the former, and my calculations with such an assumption seems to yeild a reasonable result, but I wanted to double check.

Cheers


texts: Why do trains not have a high-friction emergency braking system?

texts:
Looking at the capacity of train networks, systems like CBTC help increase capacity, but the spacing of trains is ultimately limited by poor braking performance.  In my understanding, safe distances are calculated by assuming a worst case situation ahead, such as a derailment or collision.  The train behind must have adequate stopping distance plus a safety margin behind the train in front.  Since trains have such poor braking performance, this required spacing is very large, especially for heavy and/or higher speed trains.  Why aren't trains, especially in, for example, very dense subway systems, equipped with some auxiliary braking system, such as additional rubber shoes that could contact the track, or even maybe extreme things like plows off to the side of the track, that could stop the train very quickly in a rare emergency, such as the train ahead derailing?

--edit--

Let me add a bit more detail about the thinking behind this question: Commuter trains in my area can brake at about 0.05g, so they stop in about 1/2 mile.  Once you multiply out all of the various safety factors, they wind up requiring 10 minute spacing.  By comparison, a bus driving down the highway maintains a following distance of less than 10s.  Since the spacing for trains is based on a worst case scenario of an instantaneous derailment ahead, and braking distance is proportional to the square of deceleration, even a 40% increase in emergency braking deceleration is good for nearly a 2x increase in capacity on a track. 0.1g is unlikely to cause injury to passengers, and this is only applicable in the worst case catastrophic derailment ahead.  Since this scenario almost never happens, even a single use brake that completely destroys the train and damages the track is acceptable as long as the passengers aren't injured.

Another example in my area is BART.  BART's bottleneck is in the transbay tube, with one track in each direction.  There's been talk about building a second tube, perhaps at a roughly 10 billion dollar cost.  This would be necessary because BART says it can't maintain a headway of less than 2.5 minutes safely.  If a bus can maintain a 10s headway safely, the only thing keeping the capacity of BART from being 15x better is braking performance in an emergency.


texts: What is a non-equilibrium boundary layer?

texts: I studied a manual of Ansys CFX about turbulence models and I came across the term  "non equilibrium boundary layer".  What does this term mean?


texts:
Let us assume that the an object collides into me in one of two scenarios, either I’m standing on shore, or else we’re submerged underwater. The object doesn’t change it shape, and possesses the same velocity prior to the collision. Would the consequences be the same? more severe? less severe?

Points to take into account:

The "wet" weight is larger than "dry" weight, thus the hitting body has more momentum prior to collision. This is true especially if for instance the hitting body has some cavity which may be filled with water thus giving it larger effective mass during collision.
My another concern is the effect of the medium. Since water are incompressible, I should start "feeling" the body "pushing" water towards me earlier (prior to impact), thus the effective duration of the collision is longer, which should imply smaller forces.
Aside from that, since the collision in water cannot be thought of as sudden, how should I acount for drag forces during the process.


texts:
For this problem , why we dont have to consider the max shear occur under the concentrated load just like the case in max shear act on point ?
In the previous question , the author 'move the load' so that the the center of the beam is between the FR (resultant force ) and the load ...
Why in this case , we just need to consider 2 supports only ? Or the question is wrong ?


texts: How do I calculate the bite force of a mechanical gripper jaw? Which software can be used to simulate the same?

texts: I plan to mount a gripper mechanism on a drone to grip a payload. How do I calculate the force generated by the gripper to hold a given weight. What simulation software can be used to simulate the bite of this jaw and get the force


texts: What is the composition of Arizona Ice Tea 1gal plastic bottles stamped #7 OTHER and PP COMPATIBLE?

texts:
I wished to know the composition of Arizona 1gal plastic jugs that I have.
The bottom is stamped PP COMPATIBLE and has a #7 OTHER RIC code.
I understand PP recyclable would be #5 triangle.  #7 means it doesn't fit in the plastic recyclable categories 1-6.
They're great bottles and would be nice to reuse for water storage and so forth.  Therefore the inner layer composition, safety and leaching become my concern.
It feels and looks like PP, so my guess is it's #7 because of the (polystyrene?) label that is glued right on.
On 1/13/2020, I wrote to hello@drinkarizona.com, which was the inquiry address given at their Contact Us webpage.  Below is the letter

Hi,
Can you tell me the composition of your #7 bottle such as the gallon
ice tea comes in? Your FAQ page seems to imply it's a special grade of
PP, at least in part..
https://www.drinkarizona.com/faqs
I am most concerned what is the inner layer, what is its composition, and
whether there are added plasticizers such as BPA and BPS.
Thank you,
X

As of 2/10/2020 I have received no reply.
I do not have a photo of the Arizona bottom handy, but here is a pic of another bottle,
this one a 6oz. juice bottle, which is also #7 OTHER and has the same "G" in rectangle logo that appears on the Arizona bottle.  Searching this emblem and major bottle manufacturers I was unable to identify the maker and inquire that way.

Update: Here are pics of an Arizona 1g jug:

What are Arizona plastic gallon jugs made of?


texts: How to calculate the max torque due to angular momentum of a beam given motor specs

texts:
I have non-rigid beam attached to a gearbox and motor assembly. The gearbox outputs $1000 N \cdot m$ at the shaft. The beam is rotated at $3000 RPM$ around it's center. If the motor is switched off immediately and acts as a brake, is it possible that the torque generated from the momentum of the beam could be greater than the $1000N \cdot m$ that the motor originally produced, and if so how?

I am trying to work out the max torque a beam could create at the gearbox mount when the power is cut suddenly, however we don't know any of the beam characteristics such as where the point loads are, how long it takes to stop etc. All I have is the gearbox and motor specifications.

Edit: This question is different from a similar one I asked here. In the other question I mentioned that the beam was uniformly distributed, however in this example I have no beam information. All I have to go off is the motor and gearbox specifications.


texts: Clutch for high-speed operation (>40 000 rpm)

texts:
I'm currently working on a setup where at some operations my motor has to drive a shaft up to the motor's maximum operating speed (12,000rpm) and a torque of ~0.14Nm but at other conditions this shaft can drive the motor up to 40,000 rpm. However, since this is outside the motor's operating range, and the shaft doesn't transmit any power (i.e. the torque on this shaft is zero), I want to decouple the motor from the shaft.

I have been looking for electromagnetic clutches but so fare I only found clutches with a maximum operating speed of 20,000rpm. Do you know if such clutches, of other mechanisms, exist with maximum speeds of 40,000rpm and higher?

Thank you advance!


texts: What is the difference between washer and O-ring? what is their advantages over the other?

texts:
I am designing a hydrophone, from the piezo buzzer. To hold the circular piezo plate, I have designed a mechanical fixture. I need to use washer/o-ring to make it leak-proof. I am confused about which one to use.

Can you please explain the difference between washer and o-ring. What is the difference between them?


texts: Given the tensile strength of a rod, how do you calculate the max weight that can be hung from it?

texts: Given a 3.25" long, 0.125" diameter rubber rod with tensile strength 1200 psi supported on both ends, how much weight can you hung from the middle of it without breaking it? (This is not homework I am trying to design a PC case and I have no idea what I am doing.) How does this change if we use a 0.25" diameter rod instead?


texts: Are these "parts pickers"? "JLF" and "Little Joey"

texts:
I'm reading company training materials and I don't understand a few terms.  I'm hoping that some of you might be able to decode.  The company receives product and delivers it to work sites.  I believe these are forklifts or ?order pickers?.  An excerpt from the slides:

  "if your branch has a personal man up device like the Little Joey or JLF"...

Can you help me to understand the terms used in that excerpt?  I assume Little Joey is referring to https://bigjoeforklifts.com/pages/products  but I couldn't find "JLF"; perhaps a trade name.


texts: 1 Ton Wooden Gantry Crane - Structural Advice

texts:
Here is the model (yellow line is 1ft) of the gantry crane I used to build the real-life model:

It is a little wobbly now that I've built it. I haven't put the wheels on the ends yet. Can you think of any way to make it more stable and strong? I'm afraid of traversing a drop off with a load like this:

Pretend there are wheels and a chain hoist. For the moment, I've put some screws through with the intention of later drilling holes for some long bolts at yet-to-be-determined locations. Any ideas?


texts: How much pressure would I need to push water out of tank?

texts: How much pressure would I need or, better yet, how do I compute for the pressure required to push water out of a submerged tank? Do I use 1 meter as head or 7 meters? (Please just bear with the drawing :) )


texts: Inert gas use during HVAC line installation

texts:
When brazing HVAC linesets, the correct method is to flow an inert gas through the line in order to prevent interior oxidation of the copper and brazing products.  However, as a specifier, I can say that this needs to be done until I'm blue in the face, but contractors (in my experience) are notorious for skipping this step.  It adds cost, time, and a system where this is not done will not fail immediately, but it will contribute to the premature failure of the system.  In the long term, this simply looks like a system that ran it's course, rather than the product of poor installation practices.
Is there a way to tell by inspection after installation that this practice was followed, or are you at the mercy of the contractor if someone is not watching?


texts: What are some practical applications of nonlinear control and multivariable control in the industry?

texts:
All the books I've used in my control systems class give a definition multiple-input, multiple-output systems and nonlinear systems, but all the techniques covered in the folloing chapters apply only to single variable LTI systems. The only occasions in which nonlinear systems are analyzed they are linearized from the very start in order to apply said techniques.

What are some examples of real life situations in which one cannot use LTI systems, but rather a nonlinear or multivariable model?
What sort of techniques are used to analyze these systems, and what sort of math is required to understand them?


texts: I am trying to model a hovercraft and I need to obtain an air inlet flow ratio in (kg / s) of a propeller based on its dimensions (it can be the radius) and speed, is there an equation like that? Where could I find it?


texts: Why do corrugations give strength to pipes?

texts:
I have read that corrugations give strength to pipes and the same strength can be achieved with thinner wall when compared to plain pipe.

But I don't understand why (how) the corrugations gave strength to the pipe. How do they work?


texts:
In FEM is symmetry technically a boundary condition?

For example using the FEM on a symmetrically loaded and supported beam. The FEM can be simplified by using symmetry.

However, is this symmetry just implemented as a boundary condition or is it technically one? Because it's not actually constraining the movement given that the result is the same with or without it.

So my own impression is it's not a boundary condition?


texts: Gear profiles (involute and root) generated by power skiving

texts:
@Involutius contributed an article on the equations that describe the root profile of gears which are cut by a trapezoidal-profiled hobbing tool. From that article, I was able to do a slightly different derivation to get accurate curves for the involute as well as the trochoidal root curve, for both normal and profile-shifted gears. Thanks so much, Involutius!

But I have another question regarding gear tooth profiles. The entire discussion of the root curve profile is based on a conventional (and, for that matter, a flat trapezoidal) hobbing gear cutter. I'm interested in somewhat more exotic gear applications, and I wonder if the newer power skiving machines can cut, say, negatively profile-shifted spur pinion without the severe impact to tooth strength.

Simply put, my question is, "Does power skiving have a dramatically different result for root gear profiles than conventional hobbing?"


texts: How to calculate indeterminacy of pin-jointed frame?

texts:
I understand that to calculate the indeterminacy of a pin-jointed frame, the unknowns have to be considered i.e. the number of elements corresponding to the number of internal forces, plus the number of reaction forces.

The equations that can be written to solve for these unknowns are vertical and horizontal equilibrium at each node i.e. 2 equations per node.

So, the number of unknowns minus the number of equations results in the indeterminacy of the pin-jointed frame.

However, why do we not include the possibility of being able to write moment equilibrium as one of our equations? For the analysis of beams, the moment equilibrium equation is considered for calculating the indeterminacy of the beam.


texts: How long do external hard drives and the data they contain last?

texts: How long do external hard drives and the data they contain last in case of lack of any use after downloading the data and the condition of storage having a room temperature, average humidity of 60-70% and low to none physical pressure?


texts: Proper metal for turning/milling a ball-peen hammer

texts:
I've got a simple question here.

What material should hammer's head be made of? We're talking about medium sized ball-peen hammer, used for riveting brass, copper, aluminum and steel rivets. I have acess to lathe and miling machine.

I was thinking about using material CK-45 (AISI 1045; Mat. number 1.1191), is it proper to use?

Thanks for all the help!


texts: Can two different modeling programs be used to confirm the results of each other?

texts:
Computer Models

Computer modeling is used in various engineering fields. I am specifically considering structural analysis or finite element analysis (FEA). Sometimes models are used to speed up repetitive calculations that could be done by hand. Sometimes models are used to perform calculations that are not easy or even possible to do by hand.

Checking

There are a few standard methods for checking the results of computer models.

Run verification models and confirm that the results match a previously calculated answer.
Run simple models that can be checked by hand calculations.
Test physical models.

The problem with the first two checking methods above is that they either only check specific situations or they only check the simple parts of the program.

The physical model method can be expensive for full size models and scale models may not always give the same results as the full size.

This leaves a gap in what results can be checked. For any complicated model, there is no easy way to check that the results from the program are correct. The engineer must trust that the software produced correct results from the model.

Comparison Check

The model could be input into two different programs (made by different companies). The assumption is that if the results of the two models are similar enough, then the results should be correct for the model used. This would not catch any errors in creating the original model, but it would catch errors in the software implementation.

Could two separate programs be used to check the "correctness" of the results from the model?
Would using this method of comparing a model in two separate programs provide the same level of assurance in the results as any of the other checking methods?
What could be the disadvantages of using this procedure?


texts: Polyurethane tube simulation in Solidworks

texts:
I am doing polyurethane tube simulation in Solidworks Simulation. I am using material PUR for polyurethane already defined in Solidworks. I have a question about the model type to be selected for material? As polyurethane is plastic, should I choose Non-Linear elastic or plastic or hyperelastic? Any help would be greatly appreciated.

Thanks a lot.


texts: How to determine ideal flow path length for specified pressure drop

texts: I have designed a flow resistance element and I would like to be able to keep the total pressure drop across the element to < 5.0 inches of water (from 5cc/min to 5,000 cc/min). I have run some bench tests on the current design and the pressure drops are a bit too high. I would like to avoid changing the diameter of the bore and would prefer to shorten the length of the flow path. What would be the best way to calculate the ideal flow path length to achieve the pressure drops I am looking for?


texts:
I've been working on a design that requires a plastic snap feature. I've assumed up to this point that the material will be injection molded ABS, with material properties I pulled off of matweb.

After several dozen iterations on the design, I've pushed the geometry of the snap as far as possible give the geometric conditions of the feature and I'm right on the edge of acceptable (Factor of safety of ~1.1). If my loading conditions end up being too conservative or any features of my part come out slightly out of spec I could easily have parts that fail. I'd be much more comfortable with an FOS up above 1.8.

Ideally I'd like to lower the Youngs modulus of my material and I'm wondering if ABS can have its material properties 'toyed' with by using a different formulation of the plastic. Also, how consistent are material properties of injection parts?