texts: Does air pressure difference of intake exhaust contribute to jet thrust?

texts:
I know momentum of the airflow inside jet engine generates thrust, but what about the pressure difference in front of and at the back of the engine? The air sucking intake at the front has lower than atmospheric pressure and the exhaust has higher than atmospheric pressure, does this pressure differential contribute to the thrust generated by the engine in adition to the momentum thrust?

The high pressure zone push the engine from the back side and low pressure zone pulls it from the front.
For example, if the exhaust has 1 square meter surface area, and the exhaust pressure is 2 atmosphere, then there is pressure equal to 10000 kilograms pushing it from the back since 1 atmosphere is ten thousands kilograms per square meter.

Which of these two is true?


texts: Chamber Wall Thickness for Liquid Fuel Rocket

texts:
In, How to Design, Build, and Test Small Liquid-Fuel Rocket Engines, by Krzycki, page 18 has the following equation:

$$t_w = \dfrac{PD}{16000}$$

Assuming the following:
Pressure ($P$) in combustion chamber is 500 psi.
Mean Diameter of Combustion Chamber ($D$) is 2 inches.
Working Stress (as given in the book) 8,000 psi for the Copper.

Chamber Wall Temperature of 100°C (I know that's low, help me out here, I'm new).

Solve for Combustion Chamber wall thickness.
Working Stress is listed as about 8,000 psi in the book, is working stress the same as proportional limit?

While I am a mechanical engineering student, this question isn't homework. I'm a hobbyist with a passion for rocketry. I know this is my first post here, I don't want to get off on the wrong foot. Please substitute different values if that helps! I was hoping someone could walk me through this. Specifically what I don't understand, if I multiply a pressure variable (500 psi) by a diameter (2 inches), what unit of measure is the answer? Obviously $$500*2=1000$$ But 1000 what? $$1000/16000=0.0625$$ .... Is 0.0625 inches? That's 1.5mm and that doesn't seem thick enough at all....


texts:
Strain in the x and y directions are defined by the following equations:

$ε_x=\frac{du}{dx}+\frac{1}{2}[(\frac{du}{dx})^2 + (\frac{du}{dy})^2]$

$ε_y=\frac{dv}{dx}+\frac{1}{2}[(\frac{dv}{dx})^2 + (\frac{dv}{dy})^2]$

My question is when the strain is negative, the first term will be negative and the terms in the square brackets will always be positive.  However, this does not occur if the strain is positive, does this mean that the terms in the square brackets need to be directional?


texts: Determine surface area of arbitrary physical object

texts:
Assume a physical object with arbitrary shape whose dimensions are on the order of 1 meter. How would one measure the surface area of the object?

There may be many reasons for determining the surface area:

Plating or painting the object
Determining rate of sublimation
Determining how strongly it smells
Determining heat loss

If more detail is needed, then assume the object is a rock or stone.

This question is inspired by a similar controversial question on Physics.SE. In that thread it was clear that those with a mathematical background felt that the question was ill-defined, yet some creative answers were proposed. As this is really an engineering question, I feel that a generalized, better-defined version of the question would be on-topic here. See also the meta thread discussing the merits of asking this similar question on Engineering.SE.


texts: What type of spring is used in this antique receipt holder?

texts: Pictured is an antique McCaskey Register Co Receipt Holder. I have tried to find a modern equivalent, but I have not had much luck. I am considering building my own, is the spring used a readily available component? What should I be looking for?


texts: What is the best way to dry something that is quite thick?

texts:
I wonder what is the best way to dry something that is quite thick. The gravity will attract the water down, but the sun will "elevate" the water.

So I can choose to flip the object every 30 min so that each side gets the same amount of sun that will evaporate the water. But at the same time, the water that was slowly getting downward thanks to gravity will "travel" back to the other side because gravity is now attracting it to the other side. So, each time I turn the object the water inside the object will be kind of "stuck in the thickness".
Because of this gravity attraction, I can choose to only flip the object once every 2 hours or once every 6 hours.
Capillarity should also be taken in account.

I wonder which would be the best interval between 2 flips based on these conditions:

Let's the object is a latex mattress that was completely submerged in a swimming pool (20cm thick, 170 long and 110 wide)
Let's say it will dry in a garden (not in contact with the grass), under sunny condition (about 25°C), with a humidity of about 65%, and low wind (let say between 11.9 and 19.7 km/h ―or 7.4–12.2 mph― : Level 3 on the Beaufort scale)

I also wonder which of these 3 factors, evaporation, gravity or capillarity would be the major one first at the beginning of the drying and then toward the end?


texts: Solidworks static simulation having issues

texts: I've got everything set. Material is aluminum alloy 6061. I've set the component contacts to no penetration. I have a contact set where both blocks meet and keep getting the same error. The bottom part is fixed. The head coming out has a no penetration contact with the top block. The only thing that works is by making it globally binded but I'm pretty sure that they are meant to not be binded


texts: Quantifying Instrument Precision Using Multiple Measurements: Rounding

texts:
I'm working with a spectrometer that collects raw data as a 16-bit integer value, so the readout I get from a measurement always varies between 0 and 65,535.

I'm trying to avoid implementing data with false precision in subsequent analysis of the data. In order to quantify the level of instrument precision / repeatability, I took multiple measurements of the same target with consistent illumination.

The highest and lowest values measured for the consistent target varied by 1250 values.

How would one use these results to properly round the data collected by the spectrometer in order to avoid implementing false precision? Is there a set of 'best practices' for rounding measured values? Would I want to round my output to the nearest 1250 values? To the nearest 1000? The nearest 2000?

Let's say the output from the instrument for a measurement on a completely different target is 59279. Knowing the instrument is imprecise to 1250 values, what should the output be rounded to in order to avoid false precision?


texts: How to 'smooth/flatten' the surface of a disturbed liquid without contacting it?

texts:
I would like to essentially flatten or smooth the surface of a viscous liquid after dropping an object into it, without actually touching the liquid. For example, if I drop a rock into a tub of oil, I need the oil to move into the void and return to having a smooth surface as fast as possible.

It seems that I need to create some sort of force that acts against the liquid surface from above, or a force from the sides that acts as a kind of 'wiper' to smooth it out.

I have looked into using ferrofluids and electromagnets on the sides or bottom of the liquid vat/container, however many demonstrations I have seen result in a 'spiky' surfaces when magnets are brought near the liquid due to non-uniform field lines.

I have also looked into trying to suspend diamagnetic nanomaterials in the liquid which could be repelled by a magnetic field from above the vat, however I'm not sure about whether diamagnetic materials exist which would could be used like ferrofluids in the sense of staying suspended in the liquid.

My job depends on being able to do this, so if anyone has any ideas I'd really appreciate hearing them.


texts: How to determine gradient of load/extension graph?

texts:
Here's the excercise: A tensile test is carried out on a mild steel specimen of gauge length 40mm and cross-sectional area 100mm2. The results obtained for the specimen up to it's yield point are given below:

Load (kN)     | 0 |   8   |  19   |  29   |  36
Extension(mm) | 0 | 0.015 | 0.038 | 0.060 | 0.072

I need to determine the gradient of the load / extension graph.
When the data is plotted (in the book) on a graph it gives a straight line therefore the gradient should be any load (of the given values) divided by the
corresponding extension gradient = load/(extension/1000) except e.g. the first one (8kN) gives 533*106 while the third one (19kN) gives 500*106.

Why and which one do I use for the calculations?


texts:
I have essentially a hollow tube created from 3D splines that define the inner and outer surfaces.  How can I extrude a flange from the exterior surface?

I did not mention, this is Solidworks 2012.

This can be done by wrapping onto a cylinder, but my thinking is that a 3D extrude would be more appropriate that would extrude from one inner surface to an outer surface ... like a boundary extrude.

Wrapping onto a cylinder

This is a spline surface, and I can't figure out how to do it appropriately.  In my real world example, this is actually a tube, so I can't blind extrude, because it will also fill the inside void.


texts: Calculating the Fraction of Steam in a Mixture

texts:
I have a stream ($10,000$ $m^3/d$) of inert gas and steam. The temperature of the stream is $195$ $^oC$, and the absolute pressure is $1455$ $kPa$.

I am trying to find the amount of steam that can be present in the system. I can assume $100\%$ quality saturated steam.

Would I be correct in approximating the steam fraction to be:
$P_{sat@T}$ / $P_{stream}$

At $195$ $^oC$, the $P_{sat}$ of steam is $1398$ $kPa$. Therefore the fraction of steam is:
$1398/1455$ $=$ $96\%$.

I can then find the volume of steam: $0.96*10,000$ $=$ $9,600$ $m^3/d$.

Is my reasoning correct. Any other ways to calculate this question?


texts: Convert values of utilization category from AC7a / AC7b to AC5a / AC5b - Is it possible to estimate?

texts: I have a contactor which is rated at 440V and 25 A for utilization category AC7a and 8.5 A for AC7b. Is it possible to give an estimate about the maximum current and power usage for appliances of categories AC5a / AC5b?


texts: Will the water in a gold fish bowl signficantly abosorb Bluetooth or WiFi if transciever is at bottom of bowl?

texts:
Using WiFi or bluetooth frequencies 5.8GHz and 2.4-2.485GHz respectively, I want to place a hermetically sealed circuit at the bottom of a gold fish bowl, and want to know if the water will significantly attenuate WiFi or Bluetooth.

Gold fish bowl would be probably 6" to 1', or more.

So, I want to know rate of signal absorption per distance through intervening medium of water.


texts: Need Anchors for Pre-cast Concrete Panel with Insulation Inside

texts: I am looking for a solution for mounting a shelf that holds a pressure sprayer to precast Concrete panel with a Foam core insulation sandwiched in the middle.   total weight to support is 300 pounds, The shelf has 6 holes to mount with located in 2 rows of 3. The panel is  8 inch total (3 inches then 2-inch foam panel then 3 inches). ( diameter of holes in Shelf is 1/2 inch so I think 3/8 inch anchors are appropriate.  If anyone could send a link to a product that would be great.   Engineering data / Submittal type info would be very helpful as well.   I need to validate that the ANchors are appropriate for precast concrete.  Thanks in advance!


texts: Maximum height view-able in the box when looking through slit

texts:
The problem is illustrated in the picture below. A viewer looks through a slit and into a room. The problem is to find the maximum height of the wall in the room that the viewer can see if they are able to move 'right in front' of the slit and up to 166 cm away from the slit 'in the right'. (If it makes things harder or anything.. the slit is 3.5 cm wide)

In other words, what distance must the viewer be from the slit too see most of the wall which is 280 cm tall

This is just a problem for fun. I am not sure how one might go about finding this optimal distance from the slit. While it can be done by experimental trial and error, I have a guess that one can see more of the wall if the viewer is closer (right next) to the slit.


texts: Calculating Bending Force on a Fixed Metal Plate

texts:
At work we've had a steel pipe support break on us, and I can't for the life of me figure out what happened. Here's some background info:
A long (125m) steel heating pipe (ø51mm) is suspended, resting on 27 identical supports over its total length. The very last support fixes the pipe in place there (to prevent it from expanding through a wall), but it is free to move in all the other ones.
This 27th support is the one that broke, and my best guess is that it might have had something to do with the sum of the frictional forces of the 26 other supports being greater than the force required to bend/break the 27th support.
The pipe is heated (from 20 to 90 °C) and expands as a result. A quick google yielded me the following equation for thermal expansion of a steel pipe:
F = E * α * dt * A = 200 GPa * 0,012 * 70 * 7.1e-4 m2 ~ 117 MN

Assuming the pipe is fixed on one end, the force of thermal expansion would be 117 Mega Newtons, which to me pretty much just means there's absolutely no stopping the expansion.
Now comes the part I'm confused about. The pipe is supported by 26 equally spaced supports, through which it is 'free' to move. I say 'free', because I assume it needs to beat static friction first.
The formula for static friction I found was as follows:
f_s = μ * m * a

I found a value for the static friction coefficient μ being 0.75 for steel-on-steel, but this seemed to vary a lot depending on where I looked.
The mass of the pipe is approximately 4.57kg/m, so about 570kg in total.
The acceleration in this case is equal to g, so 9.81 m/s2.
Interestingly, friction is contact area independent.
Now, filling in the equation, I am left with 0.75x570x9.81 = 4194 kg.m.s^-2 so about 4200 N.
Am I correct in assuming this means the total friction force experienced by the pipe when heating up is 4200N? And that the fixed end of the pipe would have to be strong enough to resist that force in order for it to expand only in the other direction?

The next part of my question is, how can I calculate what the maximum amount of force on that 27th steel plate can be before it bends/breaks? I can calculate that the torque on the steel plate at the pipe's location is 4200N * 50mm = 210 Nm, but that doesn't really mean anything to me, nor do I know if that's even remotely close to the truth. All steel involved is s235 structural steel.
Either way, I don't think it broke because of the friction force, but rather because it was mistakenly also fixed somewhere else. The thermal expansion force is more than strong enough to break steel if it has to, so that seems more likely to me.
If anyone has any idea how to tackle this problem, help would be greatly appreciated!
Edit:
As a requested clarification, here's a simple isometric sketch of the situation.


texts: How to achieve successful Peltier cooling

texts:
I'm using a TEC12706 Peltier module for making a cooling setup. The hot side rejects heat to a Cooler Master Hyper 410R cooler and the cold side fin gets cold enough to form water condensate on itself.
I then tried to connect a small 12V CPU fan to the cold fin and measured the temperature of the air coming from the fan, the fan basically throws air onto the cooled fin and the air then escapes from the sides, but I'm only able to achieve a temperature drop of 0.2C in the air. I think it may be due to the less contact time of air with the fin, how can I increase the contact time of air with the cool surface or is there something else going on?
A similar setUp!


texts: Fun Force Problem - Basic Structure of Two beams supporting weight

texts:
I'm very new to engineering and thought I'd start with some basic problems and test them out with my own constructions! I've come up with this fun problem and would love some help solving it.
Say you have two beams of wood with a thickness of 10cm.
Say you then set up a series of 13 3m tarpaulin sheets that are attached to the beams via screwed-in hooks, with 10cm between them, and placed 300kg worth of soil in each one, with a max depth of 5cm in the lowest point of the tarp.
What opposing force, in the form of grounding wire, will be needed to stop the beams from toppling over?
I have not formally studied physics since high-school, but my thinking was that there would be a torque force that needs to be opposed, my thinking is as follows:
The torque force at each point would be represented by the formula τ=rF, as the hooks would be perpendicular to the ground so sin(θ) would be 1.
We can therefore work out total torque applied to each beam with the sigma:

The problem I now face is trying to calculate the force needed for H, as well as θ. I don't understand how the torque is distributed across the beam and how that impacts the force needed to counteract it.
Is the presence of a wire like H even necessary, or can the beams be grounded with foundation to support the weight?


texts: I want to build a proximity sensor that will detect if an object is within 100 cm of the sensor and then send a signal to a raspberry pi. What type of short range detection device should I use to build me sensor? I don't need to know the distance, just if the object is there or not. I have found many different types with a wide range in  prices. I want the parts to be low cost.I have been looking at the MuRata Proximity Sensor Pyro-Infrared Sensor, but the range doesn't appear to be enough. Any resources and/or part recommendations would also help.


texts: Determine force distribution from a bolt pattern

texts:
Need some help designing a bolt pattern for a pressure tight enclosure.

How do i determine the force applied at a distance from a bolt location so that  I meet the minimum force to compress the gasket along the entire length of the enclosure but while using the minimum number of bolts?

And if anyone know how to model this on solidworks that would be very useful as well!


texts: Need help identifying this three-layer diverging diamond-style interchange

texts:
I'm an avid fan of Cities: Skylines, and it has occurred to me that one of the types of interchanges that seems to fare very well with the simulated traffic is this three-layer diverging diamond (style) interchange. I realize this isn't a true DDI, because they require traffic lights in a staggered traffic flow on the same second level.

Is there a name for this specific type of interchange, and do they work as well in real life as they do in simulated life?

Source: https://steamcommunity.com/sharedfiles/filedetails/?id=636634176


texts: Has large scale mono fermentation of sugar beets been achieved?

texts:
Sugar beets are an interesting substrate for biogas production due to their high content of easily digested sugars and starches. However, they lack macronutrients to sustain the bacteria population. Reports of mono fermentation (no co-substrates) on a lab scale exist, the longest running experiment I'm aware of ran for 240 days using an SBR for solids/bacteria retention (which somewhat alleviates the need for macronutrients).

Is there any plant digesting only sugar beets on a large scale (>10 t/d), where it is confrmed that no co-substrates are used? I want to stress confirmed, because the fact that a reference sheet does not mention a co substrate does not mean it's not there.


texts: Maximizing radiator cooling while minimizing fan noise

texts:
I've got the following idea in mind. I have a water-cooled PC, I wish to minimize fan/pump noise by lowering their speeds, while maximizing the cooling that can be done.

There is the simple solution of setting a target water to air delta, (water temp taken from a reservoir, operating under the assumption that this will be the average water temperature) and allowing for (PID?) control to ramp up speeds until that delta is met.

But is there a better way? For example I can sample die temperatures of the CPU/GPU, the inlet and outlet temperature of each heat exchanger (to within +/- .2 degrees C), and obtain flow speed (+/- 2%) . Can I do something interesting with these data points in real time?

What equations should I be looking at to solve this? Am I over-engineering by attempting to calculate all of this? For example I know from test data that at most the delta across most radiators for this application will be approximately 1-3 degrees C


texts:
This comes from the composites store website:

These high performance carbon shapes are produced by packing a high volume of carbon fiber into epoxy resin under tension resulting in an unmatched tensile and compression stength.
These shapes are twice the stiffness of Aluminum.
Compared to a wet lay-up of Carbon Tow the shapes are:
350% Stronger in Tension
550% Stronger in Compression

Quote source
It doesn't explain why.  Carbon Tow are long continuous strands of carbon fiber.  So somehow putting it under tension first, then fixing it in position with the epoxy makes it stronger?  How?


texts: Optics for a triangulation laser distance sensor

texts:
I'm trying to build a laser distance sensor using triangulation (With this as my main inspiration, Webcam Based DIY Laser Rangefinder).

My plan is to use a linear CCD array as the imager, such as the Toshiba TCD132D, for detecting the absolute distance to an object. I'll basically try to make a higher resolution version of the Parallax TSL1401-DB.

Due to my limited knowledge of optics and lenses, i have a hard time figuring out what the optical setup should be. Note that the distance sensor should be able to measure distances from 20 cm to 5 m, with a precision of +/- 0.5 cm.

I assume that the object would cause the laser beam to have a diffuse reflection, and that some kind of convex lens should be used to focus the diffuse reflections on a few pixels in the linear array.

I would prefer an off the shelf board mounted lens, but since the linear array sensor is 1.4 cm wide, none of the lenses i have found would be a good fit. Does any of you have any suggesting regarding which optics to use, and preferably any literature or tutorials that would make me understand this topic a bit clearer?


texts: how can I improve my chain-drive lifting system?

texts:
I am, in actuality, a network engineer and not a trained mechanical engineer. It was kind of a hobby of mine until recently, when my boss gave me the opportunity to try my hand at mechanical engineering through CAD design (Autodesk Inventor) about two years ago and I took to it like a duck to water. I have been working in that subject since then.

My problem, however, is that I am unfamiliar with most of the best-practices of mechanical engineering and it has been a "trial by fire" sort of situation. Currently my main problem has to do with the alignment of a chain-drive system used for balancing a counterweight and lifting mechanism.

Details:

Horizontal alignment is great in my CAD design, however when I actually order and build out the products, I find it extremely difficult to get the alignments properly set and I end up spending hours fidgeting with the axle and chain sprocket alignment... I am currently using aluminum extrusions (via MISUMI) for the frame design.

In the images below, you will find an example (several components have been redacted due to proprietary design). The images show the main components for operating the lift mechanism. One side houses the sprockets for the Counterweight, the other for the forklift itself. It is controlled by an AC servo motor which attaches to a custom gearbox, and finally to one of the chain axles (the counterweight).

**The design must use these aluminum extrusions, however this makes it very difficult to properly align the bearing housings for the axles, often making everything off-center or skewed, Even when using an accurate measure and square.

Can anyone suggest some improvement points or alternative types of components for mounting the axle/sprockets?

Side Profile:

Perspective Profile:


texts: What does it mean if you've been told to design a compensator to ensure that the closed loop phase margin is at least 120 degrees? Isn't a compensator typically designed using the open loop transfer function? Using the matlab command allmargin() for both closed loop and open loop transfer functions of the same system yields different results!


texts: Shear Stress / Flexure Stress Formulas / Tables

texts:
Is there something similar to the Section Modulus in the Flexure Formula

$$\rho_{max} = \dfrac{M_{max}}{S}$$

where $S = \dfrac{I}{c}$ for shear stress formula?

So in

$$\tau_{max} = \dfrac{VQ}{IT}$$

then there should be a Shear Section Modulus published which would be $Q(\text{of centroid}) / IT$

So you can get $\tau_{max} = V * \text{Shear Section Modulus}$.


texts: Making my microcontroller transmit audio to any bluetooth headphones/speakers

texts:
I am creating a microcontroller on a custom PCB design for an MP3 player. I would like to consider integrating bluetooth into it. When I say integrating bluetooth into it, I specifically mean transmitting the chosen song on my custom MP3 player to any bluetooth speaker device that has been connected to it.

Most of what I see on the web specifically talks about receiving audio. AKA, audio from a cellphone would be provided to my system and music will be played. This is the opposite functionality of what I really want (although if the module supports both, that is fine).

I've taken a look at this module:

RN52 Bluetooth Audio Module
RN-52 Bluetooth Hookup Guide
SparkFun Audio Bluetooth Breakout - RN-52

It looks promising, but all of the projects I see in reference to it are still the receiving design. Whenever it talks about audio out, it also specifically mentions the MIC IN pins. Since my data coming in isn't technically through a MIC, I didn't know if this functioned the way I would expect. From what I gather, MIC IN tends to only support 8Khz, while MP3 files are up to 48KHz.

The other one I was looking at:

Microchips BM62/64 Bluetooth® 4.2 Stereo Audio Module

This one seems to have a lot of the buzz words I've found while researching this, such PCM formatting, but the pictures on the page labeled 5 once again only show receiving data from a Bluetooth device such as a cellphone.

All other projects that I see that involve transmitting to anything also involve having a second custom microcontroller and Bluetooth module on the receive end. Instead, I want the receive end to be any generic Bluetooth audio receiver; similar to how I can pair any Bluetooth device to my cellphone and output it from my cellphone to the headphones.

Any direction or confirmation of functionality would be great.


texts: How to integrate air duct into roof insulation & bituminous sheeting?

texts:
This is the situation: We have a flat concrete roof with (from bottom to top) bituminous sheet, insulation, bituminous sheet. There's a blower to be set onto the roof, blower has a stand with a broad flange (only one side drawn):

My question is, how to connect the upper sheet to the blower stand? Due to thermal expansion, there will be movement between the insulating layer and the blower, so simply glueing the sheet to the blower will tear soon.

How to do the connection?


texts: How to Determine Tensile Strength of PMMA Optical Fiber?

texts: I researched the properties of acrylic, or PMMA, and found different results on its mechanical properties. Tensile strength is a material property, but is it affected by shape or size? I’m working on a project that involves the use of PMMA optical fibers. I want to know how much tension different diameters of fiber can handle. Would diameter affect the tensile strength? If so, I would like to know how to calculate the tensile strength of fibers of several diameters ranging from 0.75mm to 2mm. I don’t think the fibers will be subject to much force to break them, but it would be helpful to know what they can handle. Thanks in advance for any helpful answers.


texts: Calculate mass flow rate of saturated fluid through pipe

texts:
Its very basic question. But there is no data all over internet about it.
Let's see how we calculate mass flow rate through pipe.
We take velocity of fluid and c/s area of pipe. Then we find volume flow rate using continuity equation. After that we multiply it by density So far so good.
$$\frac{mass}{sec} = density \times  area  \times  velocity$$
But which density?
The liquid is saturated (partly water and partly vapour with some dryness fraction)
Now if we see the density of water and water vapour at saturation point (100 celcius), there is a lot much difference.

for water its around 1000

for vapour its around 0.598

Both will give different answers.
This question is still haunting me even after my engineering is completed.
Over the years, I have seen numericals using them both without any reasonable explaination.
Help me understand this please!
Let's say dryness fraction is 0.6


texts: Designing a Safe and Crush-proof Pokemon playing card box using a 3D Super-Elipsoid

texts:
My friend has two young Pokemon-addicted sons who carry their 60-card playing decks with them everywhere, typically in a cargo pants pocket.  Unfortunately, they have either managed to destroy every card box they've tried, or been bruised by sharp corners/edges during other activities.
I thought I could design and print a better one.  I started with an inner rectangular box surrounded by a shell having curved edges and corners for safety, and with slightly bulging sides for strength.
Then I researched a bit on getting more crush resistance from the shape itself (rather than adding ever more infill) and found that catenaries are very crush-resistant, as are parabolas.
Then I stumbled into Squircles, the more general Super-Ellipses, and the 3D Super-Ellipsoid.  This seems to be exactly what I'm looking for!  A closed 3D surface with continuously varying curvature.
[the above edited for clarity by CGW; the next section added in the hopes it will focus answers]
Given that an ideal sphere, and even an idealized ellipsoid of revolution, won't fit nicely in a pants pocket, what general engineering guidelines should [the OP] follow in designing a card box?  Rounded corners and edges are a must, to protect fabric and flesh. Are internal ribs on near-flat surfaces a good option?
[end of added material]
The generic form of the 3D Super-Ellipsoid is:
(x/a)^n + (y/b)^n + (z/c)^n = 1
Where:
a, b and c are axis scale factors,
n is the exponent controlling the shape (2..8, typ. 5-6), and
x, y and z are bounded to +/-1
But the above isn't directly usable to create a point cloud.
The parametric form would iterate over three angles.  But the problem I'm having is with powers greater than two.
Anyone have some clues to share?
I promise to include a full write-up (including credits from this thread) when I post the final box on Thingiverse.  (Perhaps using OpenSCAD?)
BTW, after finding the Squircle I detoured to write a blog post about the characteristics of generalized equations of the form X^n + Y^n = 1


texts: Does this exist - Water flow control with energy recovery

texts:
Classically, if you have free flow (high level to low, no pump) between two vessels you want to control you use some restricting orifice, or flow over a variable height weir. Both dissipate energy.

Now you could have a turbine in the flow, attached to a generator. If you adjust the torque applied by the generator to the turbine, you can control the flow over some range and extract power. I think this is an old idea, I just don't know the corect term to properly google it.

There are many considerations why this may not be feasible or worth the trouble in a given instant (e.g. hydraulic efficency of turbine over the flow ranges required). The applications I'm thinking of would be wastewater treatment plants with flows 1-10m³/s and heads <1m - so single digit kW most likely. At these heads, Banki or axial flow type turbines would probably be used.

My question is about the possibility - Can you actually control flow by appying breaking torque to a turbine, what does this do to hydraulic efficiency?

Maybe I'll ask about the electrical side in a different question, while certainly not trivial it's out of scope for now.


texts: Why does stress act a point instead of on an entire area normal to the stress?

texts:
I've often heard stress acts at a point and not on an entire cross-sectional area to which the load is applied normally.
Im a little confused here, Let us consider an area of cross-section A and let a load P be applied normal to A resulting in stress s.
Does this mean-

s acts at a point on A and not on the entire A? If yes, why?
Is the value of s the same at all points on A?
Isn't A significant to s?


texts: I make solid curved wood furniture and frequently need something like a metal plate (1/8") with a (3/4" about) supporting pipe attached at 90 degrees. Welding is a little too cumbersome but I was wondering if you guys out there know about any connecting solutions similar to a concrete anchor setup?


texts: Does the strength of a servo motor depend on the motor or the power?

texts: I am making a life-size robotic dog, and i am having trouble with getting it to walk as it is too heavy for my 4 micro sg servos. Can i make the servos more powerful with more power? If not i can just see if i can make the dog lighter. Many thanks


texts: Finding the velocity of water flowing through a gravel filled pipe

texts:
I have a scenario where I have water flowing through a gravel filled pipe, and I need to find the velocity. The pipe is gravity fed (no pumps). My approach is to find the seepage velocity ($V_s$) which is the Velocity divided by the porosity. My understanding is that the seepage velocity is defined as the apparent velocity through the bulk of the porous medium. So that is what I need to find.

I found the velocity using the Darcy Weisbach equation and porosity of gravel from online research, however I am getting a very high value for the seepage velocity (about 56 m/s) even when using the highest porosity value.

Another method that was suggested to me would be to use $Q = KIA$ where $k$ = hydraulic conductivity of gravel, $I$ = hydraulic gradient and $A$ = cross sectional area. However, this condition is only for laminar flow conditions (very slow velocities - such as groundwater under an aquifer. So I don't think I can use this equation. This method gives me a very low velocity which also seems incorrect.

Both methods seem to give me odd values so could anyone assist me with this problem?


texts: What are the characteristics of a motor that will generate current and is powered by a 30 cc, 2-stroke small engine?

texts:
Problem: I am trying to hobby-build a generator using a (old, working, throw-away gas, yard blower) 30 cc, 2-stroke engine.  The 2-stroke engine will spin a motor and I want the motor to generate DC current.

My research:

Normal small-fan motor without magnets will NOT work; and if it does, it is extremely inefficient
Ideally, one should use a brushed, DC motor to generate the power
A DC motor used as a generator typically has permanent magnets
Brushed DC motor is preferred to brushless DC motor (not sure why)
Brushed motors may be spun/rotated in either direction (CW, CCW); however, one direction (CW) is preferred and slightly more efficient
One can generate AC current from a DC source using an inverter/converter
Ideal building blocks: (input) gas/oil mix --> run 2-stroke-engine --> spin brushed DC motor --> generate DC power --> charge a 12 volts car battery (12-volt 1ah; 12 DCV) --> 12 VDC to 120 VAC Inverter/Converter --> 120 AC current (output)

What I have tried:

I used a small-fan 120-volt AC motor (without a permanent magnet) and realized that it will not work; it generates very little power
I did google-searches and found some small cheap brushed DC motors on Amazon [e.g. 12/24V 30W High Speed CW/CCW Permanent Magnet DC Motor For DIY Generator (DC 12V 3000RPM)]. Interestingly, its comments/description on Amazon says “The stator windings of the motor are copper wire…” this confused me since I believed that in a DC motor with permanent magnets, the stator is the permanent magnets; i.e. it is not based on stator windings. Also, the motor’s physical dimensions are 1.97 x 1.18 x 1.97 inches.  It seems rather small (physically).  Is this unit good enough? Will it overheat?


texts: I am planning to design an autonomous bot that takes power from a chemical reaction.i was thinking if CO2 produced via some chemical reaction can drive small wheels so as to generate electricity which can be used to move the bot forward.Which chemical reaction for the production of CO2 would be best for that? Thanks.


texts: Prototype filters-- Frequency scaling, Typo on Wikipedia?

texts:
On prototype filters' wiki page:
$L \to \frac{\omega_c'}{\omega_c}\,L$,
should it be:
$L \to \frac{\omega_c}{\omega_c'}\,L  \,\,\,?$?


texts: How did the snifting valve in Newcomen's steam engine work?

texts: Its function was to expel the air that came inside the cylinder along with the steam to prevent the engine to become "wind logged". Since the valve was non-return, how did Newcomen stopped steam from leaving after pushing out the air?


texts: Help with two-port network parameters problem!

texts: Help me, please. I im studying circuit analysis and i couldn't solve this problem.


texts: How to compute core stress in honeycomb structure?

texts:
Assume I have a honecomb(sandwich) panel under distributed normal load. Each edge of this panel is simply supported(pinned) as on the picture below:

The problem is how to find the core stresses σ-z (not on sides of the panel) as on the picture below:

Also it will be very useful if you present some equations that describe σ-z in an ordinary (not honeycomb) panel. I'll be very pleased if you recommend some literature.


texts: Are there standard terms that correspond to the anatomical axes, planes, and directions?

texts:
The field of human anatomy seems to have standardized on a number of useful terms to unambiguously describe the human body.  For example the three planes and axes as well as various directions seem to be unambiguously defined and those definitions universally accepted.  Those terms also seem indispensable for clear verbal and written communication.

If I were using the anatomical terms, I'd be able to refer to the plane made by the side of a book case as a sagittal plane, and refer to a dimension measured from left to right as measured along the frontal axis.

Are there corresponding standardized terms in mechanical or structural engineering that refer to axes, planes, and directions?

If not, how are such axes, planes, and directions customarily communicated verbally and in writing?


texts: How would you calculate the force needed to rotate along the x axis vertical earth anchor in dirt?

texts:
I'm a high school student who hasn't had the pleasure of taking physics yet, so forgive me if the answer is obvious. The problem I have involves an earth anchor drilled vertically into the earth.

I am trying to figure out the equation that would give the highest amount of permissible force uniformly distributed on the exposed top part before the anchor would rotate. Just a force perpendicular to the vertical auger. What I mean by rotate is that it would pivot at a point halfway down the auger, like a lever with a fulcrum in the middle (x axis), and not unscrew itself from the earth (z axis). Of course this would be easy if it were in air, but I'm lost at how to calculate it in dirt. I came here from Physics Stack Exchange.
The auger would be 9 inches long and immersed in 1.52 g/cm consistently dry soil. Any help would be greatly appreciated.


texts: IP Rating Required to be Dishwasher Safe (Commercial and Residential)

texts:
The core question is "What Ingress Protection (IP) rating is required for an item to be dishwasher safe?"  Is the answer different for residential versus commercial dishwashers?  Is the practical residential answer different than the regulated answer (e.g., for food prep or medical settings).  Does the use of dishwashing detergent invalidate the rating in practice?

Note, IP ratings are not cumulative from IPX6 (jets) or less to IPX7 (immersion) or more, so an item might technically need a dual rating, but I've rarely seen that in my very limited research. Are both needed?

The difficulty of performing some tests appears to vary (e.g., 1 meter immersion is pretty simple compared to water jet set at a specific flow rate, angle, and turning rate).  Might this lead to some certifications not being sought?

My most immediate interest is shopping for a cooking thermometer, but it seems applicable to a variety of other equipment like small speakers (picnic disaster) and phones (baby vomit) and keyboards.  I know at least some hospital/medical keyboards are specified as IP66 or IP67 and also washable and dishwasher safe (and presumably "coffee-safe" and "Coke-safe").  Some flexible membrane keyboards are described similarly but are not rated.

Simple queries such as "What IP rating is dishwasher safe" or "Is IP66 dishwasher safe" were not directly fruitful.  Several manufactures describe some of their products as dishwasher safe that are rated variously at IP66 or IP67 or IP57 (but not other comparably rated products even from the same manufacturer).


texts:
I am going to store used li-ion batteries for some long time >1 year, and I have read that optimal storage conditions are:

cool ambient temperatures, like 2-5 degrees celsium
3.82V voltage per cell.

What I cannot find is what is correct operation sequence to prepare a used battery for cold storage (which is initially in random state)?

Should I charge it to 4.2V then discharge to 3.82V?
Should I discharge it to 3.6V then charge to 3.82V?


texts: Do smoke alarms become more sensitive as they get older?

texts:
From what I understand a smoke alarm works by emitting some sort of radioactive particle and then counting how many of these particles hit a receiver. When there is smoke in between, it blocks some of the particles and so the alarm goes off.

As it gets older the radioactive particles per minute that are being released will reduce, because some of it has already been emitted and so there's less of it to emit. (half life and such).

Does this mean that when it get's older and emits less particles that it becomes more sensitive?


texts: How does the diameter of a worm gear affect the amount of force needed to turn it

texts:
Can anyone help inform a discussion I'm having with fellow modellers on a model railway forum?
I have a locomotive powered by an electric motor turning a 20mm diameter worm gear meshing with a spur gear. The loco performs badly, it lacks power. I am planning to exchange the worm gear for one which is 6.5mm diameter as I'm convinced this will increase the amount of force the motor can exert on the spur gear.
Some on the forum say it will make no difference - one rotation of the worm will move the spur gear forward by one tooth and the effort needed is the same regardless of the diameter of the worm gear.
I've tried supporting my argument with rudimentary physics but I'm confused as to whether i use formulae associated with rotational inertia, torque or centrifugal force. None seems to be directly applicable.
Assuming all other factors are constant, how do I calculate the force needed to turn the two sizes of worm gear?


texts: Why does a thermodynamic cycle need a condenser?

texts:
Why do we have to condense the gas after a turbine or other heat engine, to feed it back to the heater?

Wouldn't it be more efficient to feed it to the heater as warm as it goes out of the thermal engine?


texts: How to make slider driven crank go in a certain direction when transmission angle is zero?

texts:
I am building a fatigue testing machine that includes the ability to induce stress from torsion, however I am stuck at how to convert the linear motion from the linear actuators we have chosen to torque efficiently. Because the cycles of the machine will be in the millions and involve high accelerations, a rack and pinion mechanism is not an option, so we have looked at a four bar linkage slider crank mechanism.

The problem with the slider crank is that we need to transmit the maximum torque at the extremes of the linear actuator position i.e. when the actuator is fully extended and fully retracted. The slider cranks transmit the most when the transmission angle is 90 degrees, so we have to try and create the motion in this video.

I understand most slider cranks that have the slider as the input and rely on inertia to keep going in a certain direction. Our setup needs to be able to go very slow and can't rely on inertia to keep the crank spinning. Does anyone know how we can achieve this type of motion?


texts:
I am working on a project where 1L of cold water (20C) has to be heated (80C) very quickly (30 seconds).

There were a few designs I was considering

Heater cartridge (similar to what you would find in a 3D printer) - I can get up to 800W
Peltier - 10 peltiers would add up to about 700W, but would require a power supply that could handle 60A, which would be difficult to find for a reasonable price
Nichrome wire - The challenge with nichrome is how to transfer the heat to water. I was thinking of getting insulated nichrome and rapping that around a metal container that would hold the water.
Blow torch or other flame - If this is the best method, I would need help calculating the 'wattage'.

I don't think any of these methods would work because the wattage is too low in any manner. I know water heating is typically measured in kW, but on 120V AC, the circuit would break at 3.6kW (30A circuit breaker).

So my question is what is the best method of heating the water with the given parameters (not limited to the ideas I had)?


texts: I am trying to model the shear failure of an annular ring with a uniformly distributed pressure, the ring is hashed out. I am not sure how the problem would be modelled as part of the ring is supported and under pressure and the other section is unsupported and under pressure. Any advice would be appreciated.


texts: Are the Beam elements created from a 3D polyline in Ansys SpaceClaim also 3D in their DOF?

texts:
I have created a 3D polyline and assigned a Beam profile to it. But I don't get the results from my Explicit analysis where this beam is in contact with a shell surface. I am afraid that the Beam has not enough DOFs as I would need.

since the Explicit solver in Ansys is AutoDyn, I can not check what element types I have. where can I check them ?


texts: solidworks mating gear with shaft problem

texts: I am trying to mate a gear with a shaft via a key.key coincident with gear and cocentericity of gear with shaft cannot both be made.


texts: Is there any way to conserve energy for the following scenario of lifting weight?

texts:
A pulley can be used to provide mechanical advantage while lifting weight.
Suppose a combination pulley is made such that in order to lift something four times heavier, one can use the same force but the rope needs to be pulled four times further. The rope needs to be pulled further in order to conserve energy.
But i was just curious if there is any system or arrangement which will follow the law of conservation of energy by which one could reduce the effort used to lift the load and on top of that will not have to pull the rope further.


texts: Smoothed Particle Hydrodynamics (SPH) Vs. Large Eddy Simulation (LES) for Gearboxes

texts:
In the not too distant future I will be looking to simulate lubricant oil flows in a gear box, with rotating gears located in a bath of oil. I will be looking at the distributions at various angles of incline. Generically, a model may look something like this:

Does anybody have experience with Smoothed Particle Hydrodynamics (SPH) CFD packages that can provide advice on its limitations? I am less interested in absolute values of density/velocity etc., primarily I need to see the distribution of the fluid.

I am new to this branch of CFD and all I can find is advertising guff from the people who make the software and are trying to sell it. As I understand it, pre-processing time will be considerably lower than LES CFD since SPH does not require a mesh, where as an LES simulation would require a complex mesh with multiple rotating frames. Since we aren't looking at discrete volumes with SPH, instead at particles, the convection term is done away with making computation easier.

The companies selling SPH seem to be targeting exactly my application, I'm guessing that's for a good reason...


texts: What device is this, and how does it work?

texts:
There is this device I saw when I was a child at a big music store, that makes me curious.

It was meant to listen some CDs to try them out before the purchase.
You stand under a bell-shape kind of "speaker" to hear the music, but as soon as you step out you aren't able to hear anything anymore.

I've been searching the net, but probably I haven't used the appropriate keywords because I didn't find anything.
What's this device called, and how is does it work?

I'm interested in particular about the sound and how it's possible to transmit it only in a very limited area, and being able to hear it well only inside that little "circle"


texts: Why are steel I-beams mostly symmetrical?

texts:
From what I understand most types of steel are strong both in tension and compression, yet they are still usually significantly stronger in tension. Suppose a common I-beam supported on both ends and with a load on top of it; the bottom flange experiences tension, while the top one compression, yet since steel is somewhat stronger in tension, why would the bottom flange be as thick as the top one? Is it not done because it's easier to manufacture symmetrical ones or is there some other reason?

Is it possible to use assymetrical I-beam to save weight and steel in that case or is my thinking completely off?


texts: How much can a double Peltier stack cool to -30 C?

texts:
I need a -30 C freezer. Inside volume 5-30 l. I've seen videos of double Peltier stacks reaching -50 C with one Peltier running at 12V and the other at 5 or 7 V.

How big a freezer could such a stack cool to -30 C? Either a cube with up to, say, 5 cm thick expanded/extruded polystyrene (EPS/XPS) walls, or a wide neck Dewar with EPS/XPS lid.

Hot side cooling is probably with a waterblock, pump and heat exchanger with fan. T-hot ... does 40 C at 30 C ambient sound realistic?

I'm thinking of something like standard TEC1-12709 or -06 modules (12 V, 6/9 A, 40x40 mm), if they do the job. Local ones are kinda expensive (20-30 EUR). Aliexpress has some for a few USD. Are they ok?

I found some math to calculate Peltiers (https://www.overclockers.com/peltier-stacking/), but I was a bit overwhelmed (or maybe just lazy ;). EPS/EPX seems to have about 0.035 W/(m·K) thermal conductivity. I haven't found (or researched) Dewar thermal conductivity.

The freezer should reach -30 C in a finite time, e.g. 30 min, so remove a bit more heat at -30 C as is flowing in.

So, if you have experience I'd appreciate estimates. Calculations would be cool, too.

Compressor coolers or Sterling cryocoolers are probably not an option.

Thanks!


texts: Relationship between Pressure and volume with Air

texts:
So the below question might sound like a homework question but in reality it is an oversimplified explanation of what I'm trying to measure.

Let's say we have a perfect machine that pushes out 600cfm into a box. On the other end of the box is another machine that only consumes 300cfm from the box.

What is the pressure in the box and how do I calculate that? I've looked into Boyle's Law and something just doesn't seem right about the results I'm getting so I'm trying to make sure that this is the right law I should be looking into.

If it's relevant, assume a volume of 360in3 and temperature of 310 K.


texts: Why there is no piston style pedal bicycle?

texts:
I have interested in walking bicycle. For the concept is just bicycle that you don't cycling pedal but stepping or striding to drive wheel

Which leads me to think that is it better if we use linear or ellipse motion of leg to transmit to bicycle

The closest mechanic I could think is piston crankshaft like a car. It convert linear motion to rotation

How disadvantage of the mechanic compare to cycling motion?


texts: How to evaluate the fuel consumption rate of an air conditioner in a vehicle?

texts:
Using two cases studies: I. When the windows are wound up and air conditioner is turned on. II. When the windows are wound down and air conditioner is turned off.

Case studies are evaluated for driving in city and highway but more importantly how can the fuel consumption rate of the AC be measured so as to suggest when it is more economical to use it and reduce the effects of drag on the vehicle?


texts: How thick of an oxide might form on a cast zinc part?

texts:
I'm looking into possible failures of a cast zinc part. I'm wondering if the Zinc-oxide that develops after a time would have a thickness great enough to cause dimensional tolerancing issues?

Tolerances on my parts are plus-minus 0.1 mm. Assuming the part is made within spec could an oxide (or other zinc corrosion) cause the part to fall out of spec?

Environmental conditions are standard air pressure, room temperature and normal air composition.


texts: How does the superposition principle relate to Bernoulli-Euler and Timoshenko beam theory?

texts:
I have a shaft with a bearing in each end, and a large eccentric mass covering the entire "free length" of the shaft.

The attachment of the eccentric mass is done using heat shrinking.

Without bearings:

Without bearings and eccentric masses:

I need to calculate deflection equations $y_{ab}$ ($x\in\{0,a\}$, from outmost left to left hand side of flywheel), $y_{BC}$ ($x\in\{a,b\}$, from left hand side of flywheels to right hand side of flywheels), and $y_{CD}$ ($x\in\{b,l\}$, from right hand side of flywheels to outmost right):

This is similar to Shigley's Mechanical Engineering Design problem 4-19, 10$^{th}$ ed.:

FBD:


texts: I am hoping to create an exercise bike with a 12v motor attached to a 12v battery that will get charged up when the bike wheel turns.  It's more complicated than this, there will be a media player too, but the tricky part is, I would like to have a relay that is also attached to the feed from the bike that only closes or passes voltage from the battery when the bike generates a certain amount of power. I also want to avoid it constantly going on and off as the bike fluctuates in voltage, some form of delay.  Some form of display of the voltage would be great or even a way to display with LED the voltage created by the bike as it generates (red to green kind of idea). I understand this may seem a bit much, but a voltage regulator that only passes power when it generates the correct amount is the bit I need help with.  many thanks. Scott


texts: How to find press fit/ slip fit for non standard size parts?

texts:
I am looking for calculator or chart for slip fit and press fit for non standard size parts.

For example, I have oversized dowel pin 10mm +0.03/+0.01 diameter. I need to create a slip fit hole for that oversize dowel pin. What the size and the tolerance of the hole should be?

Another example is I have an undersized plastic bushing which diameter is 20mm -0.05/-0.02 diameter. I need to create press fit hole for that bushing. What the size and the tolerance of the hole should be?


texts: What pressure is taken as the pressure of liquid

texts: I am learning pure substances in thermodynamics.I read a sentence "Consider a piston cylinder containing liquid at 20 degree celsius and 1 atm pressure."My question is that the pressure of liquid  inside the cylinder will increase as we will go downward .So,is 1 atm pressure at the top of the piston or the average pressure of liquid in the piston?


texts: Trying to simulate the bending of a right angled pipe in solidworks

texts:
I have created a bent right angled tube in solid works.

It has a constant inner diameter of 1" and thickness of 1/8".

The tube is comprised of a straight portion 1 ft in length, followed by a 90 deg bend with a 10 cm radius of curvature, then another straight portion 10 cm in length. I apologize for mixed units, I am just trying to make a proof of concept at this time so I will change the dimensions later.

I've fixed the first flat face of 1 ft section at the top, and I have set the material to natural rubber for now but I would probably want it to be neoprene or polyethylene in the finished product.

I want to deflect the second shorter straight portion by an angle of 45 deg in the plane and measure the deflection in the curved section. Is there a way that I can directly apply a deflection (angular preferably) to the end of the 10 cm length tube and measure the change of the arc in the curved section? I have had to apply a load, but I don't really have any idea of knowing what that should be to correspond to the desired deflection.

Below is an image using alloy steel because the simulation kept failing if I applied a load to rubber?


texts: What is the use of gears in a device with a fixed gear ratio?

texts:
From my understanding, there are two uses of a gearing system: to change the speed of output rotation (trading it with torque), and to change the axis of rotation. Now, in a car, for example, it is necessary to have multiple available gear ratios, to allow for high torque and high acceleration when the car begins to move from stationary, and also high speed when the car is already on the move.

However, I know that some systems still have gears when they only used a fixed gear ratio. For example, in my lab, we work with a robot arm, and my colleagues often talk about the gearing system in the arm. But the arm does not repeatedly change its gear ratio like in a car. So what are these gears actually doing?

If they are to change the speed / torque of the output of the motor, and this is a fixed gear ratio, then why was the arm not designed with a different motor entirely -- one which provides the desired speed / torque properties? My intuition is perhaps that it is easier to mass produce motors that have high speed and low torque, and so it is more economical to buy one of these generic motors and attach it to a gearing system, rather than design a bespoke motor that has very high torque at its output by default....is this correct?


texts: How to Calculate the Minimum Radius a Rod Can Can Be Bent Staying in the Elastic Range?

texts:
I am wondering if there is a formula (or how to derive one) for calculating the minimum radius a rod (with a given radius/diameter) can be bent around while staying in the elastic range.  Obviously, this will depend on the modulus of elasticity for the material.

I am searching for a general formula for this rather than a specific solution for a particular material.  With a general formula, I can evaluate trade offs using different materials (with different moduli), different rod radii, and different radii of bending.

Stated more simply, if I wanted to wind a rod of radius X made of a material with modulus of elasticity M around a spool, how would I calculate the minimum radius S of the spool?


texts: What Causes Asymmetrical Buckling in this structure?

texts:
I've been playing around with structural modelling on the SkyCiv platform and have created this structure, related to a project I am working on to educate myself.

It is 2m wide, 3m long and 1.5m high and is made from malabar ironwood, which has a young's modulus of about 13000, a density of about 1000kg/m3 and a poisson's ratio of about 0.27 (I think).
Every 10cm, there is a woven PE sheet of 2m x 3m x 0.4mm dimensions, there are 14 in total. Each sheet has 3kN force acting on it and therefore a pressure of 0.5kPa, which I'm assuming is distributed uniformly. It's quite hard to be sure, but I think the PE sheet has a young's modulus of 0.3, a density of 0.91, a poisson's ratio of 0.029 and an ultimate strength of 20MPa.
Whenever I solve these loads using linear static + buckling simulations, one side is buckling. What causes asymmetrical buckling? Is this a known phenomenon? I have triple-checked the model and it is symmetrical.


texts: How much larger must the ID of a cylinder be than the OD for a Slip Fit? Material: Delrin (Acetal)

texts:
I am prototyping a nested waveguide made of four cylindrical sections.  Each piece is turned on a lathe from Delrin (acetal) rod.  Each piece fits inside the next larger one.

There are no moving parts.  It is an antenna.

My question is:  how much larger must the ID of a cylinder be, than the OD of the one which fits inside it?

In my drawing, I have indicated that they be 10 thousandths of an inch larger, but I do not know if this is correct.

I would like to be able to disassemble the cylinders during experiment, to take measurements, and then put them back together.

Each cylinder is to be electroformed with nickel on the outside, so the thickness of the metal layer will also be taken into account.

Here is an updated drawing with tolerances added and revised diameters.


texts: Can DC motors be used for regenerative braking only?

texts:
I am an engineering student working on a machine to tension steel wire rope for maritime uses. The wire rope (max, ~2000m, diameter 44mm) sits (without tension) on a spool (diameter 2m) and has to be winded under tension (150 to 200kN) to a winch on a ship. This means I'll have to find a way to create an opposing torque on the wire rope drum while the wire is being unwinded from it.
One of the ideas I had (with the help of this forum) was to use a DC motor for regenerative braking on the drum, I, however, have very little knowledge about electrical systems and was wondering if this would even be possible in the first place (due to the high torque). And if so, how would I select a DC motor for this application, and what calculations would come in handy for this?


texts: What amplitude is used for a finite element modal analysis excitation?

texts:
In a typical finite elements analysis package, a modal analysis gives the N first natural modes, and it is possible to get the equivalent stress and total deformations for each of these frequencies.

But what amplitude did the solver use to get these results?

Why can't we obtain a gain instead, for displacements and stresses and for each frequency?


texts:
I have been trying to build a sliding keyboard phone attachment for a while now, but can't seem to get anywhere.
Basically, I want to combine my Moto Z Play with this cheap, generic bluetooth keyboard.
I tried double hinges, but they had too much slop. I tried a detachable fixed clamp, but that cannot be put into a pocket.
So now I am looking at making it a slider like the Motorola Droid 4 I used before.
I do have a 3D printer, so making clamps and cases/housings is no problem.
But printing a sliding mechanism will probably not result in anything remotely durable.
So my question is, what kind of sliding mechanism could I use for the sliding motion? The requirements are as follows:

It needs to be tiny. There is really not a lot of space to waste here.
It needs to be passably durable. As long as the parts are not too hard to get I don't mind having to repair it once a year or so.
It needs to cope well with dust, since I am planning on carrying that around in a trouser pocket like a normal phone.
Low sliding resistance is very optional. A higher resistance wouldn't be bad at all.

I looked at linear rails, but those are too large (especially the carriages). Also I fear that the ball bearings wouldn't like the dust.
I figured that just bent steel profiles could do the trick, but I couldn't find anyone who made Z profiles with that small of a middle section (I would need it to be like 3mm or so).
I am very much lacking the terminology to know what to search for.


texts: Focusing light from a laser shot into one point

texts:
I'm planning to build a laser shooting target. Something like this:

In the long term I want to build something advanced like a professional grade target, in which the user is able to tell exactly where was the shot, but for now I'd be happy with a basic one like in the image.

Basically whenever a laser shot hits the black area it counts as a shot inside.
I'm just unsure about how can I do it since I don't want it to easily confuse a shot with regular light, and if possible I would like to use optics side-effects to avoid cross-shooting (whenever one shoots someone else target, while misaligned with it).

To begin with, one has to be 10 meters away from the laser target, with a variation of a meter at most.  The targets are held at a meter and a half high.  The laser of a gun, in conformance with the regulations, has a ~3 mW peak during 15-20 ms of activity. The black area is about 7 cm in diameter.

I don't know the official specifications for a laser target in terms of light, but I found a brand with the specifications of one target (end of the page). It states "Sun resistance: 70k Lux." Does that mean that it is able to distinguish a laser shot from the ambient light at up to 70k lux ambient light? What is a simple way to understand the amount of light that represents?

My idea so far its having a photo sensitive transistor in a PCB bolted to the back of the target.  An aluminium sheet in the front with a circle in the middle of it, and a smoked acrylic sheet in its back (to fill the circle). And either a fresnel or a biconvex lens right next to the acrylic.

Both the biconvex lens and the acrylic converge the frontal light to a point (the point where the photo transistor stays), so that spot becomes mostly light coming exactly from the front of the target, and becomes sort of immune to most ambient light (since it will refract to the points around the transistor).

The problems I see so far are:

Which one (fresnel/biconvex) has the shortest light converging point?
(I would prefer the target as slim as possible)
If one shoots the edge of the valid area, it's not a straight shot. Assuming one is perfectly aligned with the target, and the weapon is at its height, it would already become a ~90.2° incision. Being a little misaligned (half meter) and being half a meter lower than the target while shooting the center would represent a ~90.4° incision. Being misaligned and shooting the edge opposed to the misalignment direction would be an even more tilted shot. Is that little tilt enough to make the lens focus out of the transistor? It seems like a really small deviation.
Is it worth it to get a sheet of red cellophane between the acrylic and the transistor? It would filter the non-red light, wouldn't it?
To avoid counting lights turning on or a cloud passing by as valid shots, can I can count 30 ms from the moment in which the light peak happens, and see if it has disappeared?

So basically the main question is:

Would either of these two lenses solve my problem, by converging the light coming from one direction into one point? Would it be practical? Are there better alternatives (like leaving the transistor alone without focusing; mirrors; etc.)?

EDIT:
Floris guess was probably right. The signal seems to be modulated. I managed to have a shot at the spec sheet of one of the guns:
Those graphs mean that with UIPM 2014 signal it pulses 10 times in 15.6 milisecs?
Should I get my target also recognising those pulses?
I bought a BH1750FVI light sensor module, can those kind of sensors recognise differences of light in fractions of miliseconds?
EDIT2:
Found the official regulations:

Together with what was already answered, it should be enough to help anyone with the same question.


texts:
I have had three houses with right angles in the layout, and in each one that configuration causes vortices to form that suck in leaves, snow, and any debris blowing by and keep it in the nook of the building.  Rough idea in the following sketch, with the prevailing wind from the left:

What passive methods or designs can be used to disrupt and prevent such vortices?


texts:
In plane stress state:

How can one comment about the state of stress for the given condition?
I am not sure but I guess that we can use the principle of superposition. Though I do not know how can I do that.


texts:
I’m trying to assemble a pistol pin into a piston using creo parametric 5.

When I select the surface of the pin and the inside hole of the pistol this works fine and say that it is partially contrained.

However, when I select the planes front on the pin and the piston it says invalid constraint.

The first part of the image works fine but not the second part.

Any ideas why this may be ?


texts: Fixing a blind bolt hole when the first 2-3 threads are ruined?

texts:
One of my suspension bolts came undone while I was mountain biking recently, sadly I didn't notice.  I landed a big drop with only 2-3 threads left engaged, and unsurprisingly it's ruined them.

The rest of the threads (another 20 or so) are fine.  It's a blind hole.

I have the right size tap to cut the thread, but I don't know if that's the right thing to do.  Don't I risk being "out of sync" with the 20 good threads and causing problems with them?

I feel there should be a tap that you insert deep into the bolt hole, and it then somehow expands into the known-good threads, before being able to be wound out.

If that does exist, please let me know what it's called and where I can get one.

If it doesn't, please give me advice on how best to fix this hole with the existing tap that I have is Frame Tap


texts: Best Fan position for maximum airflow in a Vent

texts:
I need to add a simple ventilation duct to my room.
The purpose is to draw stale air from the room to the outside.
Is it better to place the fan at the intake (position 1) or at the output end (position 2) for maximum air flow?  Does fan position make a difference?
I attach a sketch for clarity.
Thanks!


texts: Before the yield point, the deformation is elastic, and then it is plastic. But what happens to the elastic 'part' of strain after the load is removed? Is it retracted fully or partly, and how does this relate to the extent of plastic deformation?


texts: How would I most easily create a mechanical intervalometer for a digital camera?

texts:
i.e. a battery powered device which presses a digital cameras capture button at some constant interval of ~60 seconds.

Would it be an easy project for someone with little experience with electronics?

The camera will be in a water-tight housing (a large housing with space for somethings as big as the camera itself) a few meters underwater. Hence why i dont think a wireless remote control device will work.

There seems to be two devices I could just buy which would do the job, the MicroBot Push and the Tempus All  TEMPUS ALL Mechanical Intervalometer but I don't want to pay 150 dollars for something so simple.

Any advice appreciated!


texts: How can I determine the required thickness of these plate materials?

texts:
I am designing something with a sandwich construction that needs to squeeze the internal layer uniformly. The lower plate is to be made from cast iron and the upper plate needs to be made from copper. The squeezing will be done with four threaded rods, nuts and some spring washers.

The squeezing force I need to apply is 30720N, so I guess 7680N per nut (or is it not so simple?). And what I really don't know is, how do I determine a thickness of material required, given its properties and my design details? My requirements are

Plates will not deform like playdough between 20˚-150˚C
Plates will not buckle like a spring very much, so that the sandwich pressure is not applied unevenly.

kamran's answer describes the red line below as the lever distance in his model.

I have tried my best to read up on Young's Modulus and Shear Modulus, etc., but I do not grok how to correctly apply these to real life.

Question: Can someone kindly point me to a formula or a workflow so that I can calculate the answer myself?


texts:
I'm thinking about building another trailer. I've built lots of smaller trailers in the past, but this time I'd like to build myself a small tandem axle gooseneck rated for 7,500 lbs.

I am a certified welder, I have a Bachelor's degree in Physics, and I work as a software developer. I have the know how, but I would like some input on material selection.

Round Pipe
Angle Iron
I-Beam
Rectangular Tubing

I am currently leaning towards the Rectangular Tubing as the best for support, but I cannot seem to find anything online that confirms this.

After deciding on the best material for the trailer, where would I find good charts to tell me what size and thickness I should use? Obviously, I could go overkill, but I would like to build this one smarter rather than throwing as much iron at it that I have.

Does anyone have any input? Is there a better group to post this in? I was looking for something along the line if Industrial Engineering, but this is all that pulled up.

EDIT:
I was trying to keep this a generic question where someone could tell me something like, "Here is the formula we use, and this is how to use it..." It looks like I won't get that, though.

My heaviest load would be a tractor with a front end loader and a brush cutter on the back with a total weight of 5500 to 6500 lbs. A tandem axle trailer with two (2) 3500-lbs axles can support this load fine. I have selected axles from Southwest Wheel's torsion axle with brakes (the front axle will have brakes, but not the rear).

Trailer length will be 18-foot, and have a gooseneck configuration (it distributes the weight better and pulls smoother than a bumper trailer). For calculations, I'm going to use 7500-lb capacity.

I am looking at the structural data for square tubing using a spec sheet HERE (trying not to advertise another website, but that is where I see data). Page 21 shows data values for various sizes and thicknesses.

There is a line called Bending Factor. For an 18-foot trailer (18 x 12 = 216 inches), 3/8-inch thick 4x2 square tubing shows a Bending Factor of (x=1.03 , y=1.55).

I was using Rogue Fabrication's Calculator yesterday, where I entered the following values: Tube Shape=Square Tubing, Outside Diameter=4-in, Wall Thickness=0.1875-in, Material="Cheap seamed tube", Load=3800-lbs, Tube Length=216-in, and Hazard Factor=1, I got that my material is 1.22 times as strong as the loading conditions.

Next, I tried EasyCalculation's Beam Deflection Calculator, with values of Length=216, Width=2, Height=4, Wall Thickness=0.1875, Force=3750. It shows a deflection of about 100 inches for 2 lengths of rectangular tubing. If I use 4 lengths, that drops the force down to 7500/4=1875 per beam, and deflection down to 50 inches. Those deflection values seem really high. That is more iron than most trailers have.

The old tandem axle trailer I use now only has two (2) lengths of 4-inch angle iron (1/4-thick). It flexes a couple of inches, but not 50 inches. I must be missing something.

How do I calculate the amount of flex a 20-ft length of material would have?

If square tubing is not best, that's fine as long as you let me know what would be better and how you selected that configuration when you comment.


texts: What is the impact toughness for some common bicycle frame materials?

texts:
I've been trying to compare popular materials for bicycle frames in terms of their mechanical properties. One thing I noticed is that it's hardly possible to find a data sheet specifying the impact toughness of a material. I've only found it for some carbon-fibre composites and nothing else.

Why is impact toughness not a commonly listed material specification? Is it considered unimportant? Are the measurement and testing standards unclear? Are there any other reasons?

I'm specifically referring for aluminium 6061 and 7005, steel 4140 and 4130, Titanium 3Al-2.5V and some carbon fibre composites. I could find the data for carbon fibre, but none for any of the metal alloys.


texts: Does the characteristic polynomial contains all the poles of a closed-loop transfer function?

texts:
The Transfer Function of a Closed-Loop system is: $T(s)=\frac{Z(s)}{1+G(s)Z(s)}$.

The BIBO stability of $T(s)$ is guaranteed if all the poles of $T(s)$ have negative real value.

In many textbooks I've read, it's written without further explanation that the zeros of the characteristic polynomial $1+G(s)Z(s)=0$ are the poles of $T(s)$, without any conditions on $Z(s)$.

In one textbook, it was written that $Z(s)$ should be bounded. If $Z(s)$ is bounded, i.e. has no poles, it's obvious that the characteristic polynomial contains all the poles of a closed-loop transfer function.

But in many physical systems, $Z(s)$ has poles. I have a theoretical example in which $Z(s)$ has a pole at $s_0$, while $G(s)$ has a zero at $s_0$, such that their product is finite and different from 1 $Z(s_0)G(s_0)\rightarrow A_0 \neq -1$. Therefore, $T(s)$ will have a pole at $s_0$, while the characteristic polynomial will not have a root at $s_0$. Therefore, we found an example for characteristic polynomial that doesn't contains all the poles of a closed-loop transfer function.

Therefore, it seems as if a necessary condition for working only with the characteristic polynomial is that the $Z(s)$'s poles won't coincide with the $G(s)$'s zeros. But is there a necessary and sufficient condition?

Why is this question not addressed in control-theory textbooks? If it does, please refer me to those textbooks.


texts: Is there a maximum phase margin a PID controller can give?

texts:
I'm having trouble understanding the plot attached. The bode plot here shows the bode plot of a plant to be controlled with PID. So, if I want a phase margin of 30 degrees at the bandwidth frequency, then as shown on the picture, based on the formula (PM=180 + ...) my bandwidth after PID controller is applied is 30 hz, with a phase margin of 30 degrees at that bandwidth frequency (30 hz). Say now I want a phase margin of 50 degrees. From calculation this will then occur at the frequency corresponding to phase of -130 degrees, in the phase plot of the plant. But this is weird then; I will obtain the same frequency if I want, say, 60 degrees of phase margin (i.e. phase in plant of ~-110 degrees)! So the same frequency for different possible phase margins?

I'm confused.... Is it then the bandwidth that can give this phase margin is 0 i.e. not realisable? So there is a maximum phase margin that can be realised?


texts:
I have two alum plates (45cm x 20cm x 1mm) that are hinged on the long side with two 30 x 80 hinges (30 x 40 each tang) in the middle, and "L" bracket / 20mm brace at the ends secured with a M4 loc nut  and bolt. As you might imagine, however much you tighen the lock nut on the M4 mushroom bolt, it cannot keep the flap up due to the "mechanical advantage" of the plate weight. Or, if tighten to the nth degree to hold plate ... the latter cannot be repositioned!

I have looked at 'stays', but they will only 'lock' in the fully open state, (I need to hold the flap between -90 (closed) to +20 from horizontal)

My idea at present is to construct a stay using two flat alum bars constucted as a "V" with the outer points at around 4" on the unit and barn door, and the pivot at about 7" (ie pointing forwards) The pivot will have a fixed bolt / thumbwheel.

It's this latter part I seek advice on. Even though the surface area will be larger - and so I could use a M6 bolt - is there any action I can take to make the friction grip between the approx 1" diameter area on each bar stronger? (A fibre washer will reduce the contact area of metal, so that might not be an option)

In an ideal World, I'd opt for something like a plastic 'crown' gear fixed on each component. When loosened, you can turn the item to a new angle before re-engaging teeth again. (A system used on some cheap Chinese photo light fittings)


texts: How to model a sheet metal nut in SolidWorks?

texts:
I want to know how to model and how to use an injection nut in SolidWorks.

The problem starts with me not knowing the correct term in English for them thing I want to model (Einpressmutter).

I'm referring to a metric nut (with metric thread, if course) which exposes a circular, radial notch at one end. This end is to be forcefully inserted into sheet metal with a hole slightly smaller in diameter than the nut's end.

Penn Engineering nuts for sheet metal

There is no problem for me in modeling such a part. What I want to have, is like a combination of a part and a forming tool. I.e. I want to drag this part into a closed sheet metal area and the holes for the nut should be created automagically.

Google didn't reveal anything useful. I found only tutorials in creating regular nuts, yawn. The SW tutorials weren't helpful either. But this, again might be caused by using the wrong search term.

I'd appreciate  a link to  a tutorials as well as a better search term or a basic outline of the method.

further clarification

Yes, "press nut" was the word I'm searching for.
Yes the nuts I want to use need holes drilled/punched/lasered into the sheet before insertion.
I probably need different nuts of different sizes and threading, so I'm here for an abstract solution
I know the hole wizard. I know how to place a part into an assembly and to align it.

What I want is this behaviour:
Upon manually placing a press nut into an assembly and aligning it in its recommended position on a metal sheet, the necessary hole shall be generated automatically in the metal sheet.


texts: Considering all the variables are the same, how to rank these connections from highest to lowest bending moment?


texts: Getting an object to travel at 35 to 45 mph

texts:
I'm doing a project which simulates a car accident, with a cube block which has sensors on it crashing into a wall.
This object is on a 3 m track mounted on a linear bearing to reduce friction.

So this object needs to be travelling at a speed and it impacts a solid wall (with about 40 G of deceleration in that impact). This impact is what I am recording.

My question is, how can I get this object to travel at that speed? (which is about 35 to 45 mph, if my math isn't wrong that is)


texts: selecting correct stepper motor to lift 5kg for Arduino project - newbie questions

texts:
I am trying to figure out what stepper motor is best for my Arduino project.  I want to lift 5kg in steps, doesn't have to be fast, its more important to lift the weight.  I have done some calculations and come to the conclusion that I need a 3NM motor (rounding up for additional margin etc).

5kg x 9.8ms2 = 49N
49N x 0.05 = 2.45Nm

5kg x 0.1ms2 = 0.5N

49.5N = upwards force

49.5N x 0.05m = 2.475Nm
49.5N x 0.5m/s = 24.75 Nm/s = 24.75W (0.1m/s would also work bringing down the power requirement)

I've concluded that I can use this motor or this one.  Looks like I need a driver too so this motor and driver looks like it would do the job.

Are my conclusions correct?  If so is it simply a case of connecting the motor to the driver and the driver to the Arduino using a motor shield such as this one (for multiple motors).  Looks like I can't connect the motor to the shield directly because of power requirements.  I assume then when its all connected I can use this code to run it.  I think I used the stepper motor in that code example before (almost four years ago so I can't quite remember).  Also how exactly is the power supplied?  To connect two motors I'm thinking it would need 4 PSUs, one for the Arduino, one for the motor shield and one for each of the motor drivers.

Any advice to help me better understand this would be much appreciated.


texts: Mirror specification used in Solar Fresnel Collector systems

texts: Im designing a Linear Fresnel collector system, and wanted to know what type of mirrors would be suitable for use as the reflectors. Thickness, type, coating etc. I couldnt find a manufacturer of ''tempered mirrors'' where I live. I need it to be able to resist hail and the elements and have a life of 20-25 years. Can the experts help me out. Thanks.


texts:
I am definitely not the captain of the Evergreen what is currently stuck in the Suez Canal: https://www.google.com/search?q=Evergreen+Suez+Canal
But from an engineering point of view, what would be the best method to move this cargo ship, back to work when it is stuck in the sand.
ex.: highering the canals water level or pulling it with near other cargo ships?
Thanks.


texts: Ways to reduce turbulence in internal flows

texts:
Often it's desirable to reduce the turbulence level in an internal flow without changing the Reynolds number or fluid. This could be measured by the turbulence intensity, though other measures might be better in different circumstances. I haven't seen a good compilation of these techniques, and I believe such a compilation could be very useful to engineers.

Below are the ways I'm aware of:

Flow straighteners reduce turbulence and swirl, but have an associated pressure drop. You can also get similar effects with meshes, porous media, and fibers.
It's commonly believed that turbulence transition begins in pipe flows at a Reynold numbers of about $2300$ in general, but laminar flows at far higher Reynolds numbers can be obtained with better quality experimental setups as discussed in this review paper on turbulence transition in pipe flows:

  Experimental evidence suggests that the laminar state can be achieved in pipe flows over a wide range of $Re$ with the record standing at $Re = 100,000$ by Pfenniger (1961). Reynolds himself managed to achieve $Re
= 13,000$, and Ekman (1911) later improved on this to $∼50,000$ using Reynolds’ original apparatus. There have been many others (Barnes & Coker 1905, Draad et al. 1998, Gilbrech & Hale 1965, Goldstein 1965, Hof et al. 2003, Nishi et al. 2008, Paterson & Abernathy 1972, Schiller 1921, Wygnanski & Champagne 1973) who have achieved Hagen-Poiseuille flow over a wide range of $Re$ greater than 20,000, which is the upper value in Figure 2. Achieving laminar flows at high values of $Re$ is an indication of the quality of an experimental facility and gives some confidence that the observations will not be contaminated by extraneous background disturbances such as entrance flow effects, convection, and geometrical irregularities.

From what I understand, in addition to the effects listed above, surface roughness and vibration can also trigger turbulence, so you can delay the development of turbulence with smoother surfaces and/or vibration damping in some cases. The standard transition criteria appears to be correct, but for systems that don't take special precautions to eliminate disturbances.
Relaminarization is when a turbulent flow becomes laminar, and is a stricter version of what I'm after. I'm interested in reducing the turbulence level. The flow could still remain turbulent, just less so. Here are a few ways to do this discussed by this review article:

dissipation of turbulence (could happen from enlargement in a pipe)
curved or rotating flows (could introduce swirl, though)
acceleration (could happen from a contraction in a pipe)

There are a number of papers on suppression of turbulence via sound emission or vibration. I don't know much about this, but I'm aware that it exists. If anyone knows more about this, or knows a good place to learn more, I'm interested.

If you can change the fluid entirely, that could be a good option to reduce turbulence by reducing the Reynolds number. There also are a variety of additives (mainly for water?) which can suppress turbulence (polymers, fibers, viscous liquids, etc.), but that's an entire other subject.

What other methods exist?


texts:
Question:

See what I tried below and verify if I'm wrong. I need help here.


texts: Force required to open a door of volume lxbxh and weight w

texts: A door of volume l x b x h and weight w is hanging vertically on a horizontal hinge. How can I determine the force/torque to open or close this door?


texts:
My immediate thought was Rust-Oleum clear spray, but rustoleum, krylon, and any other alkyd-based paint will react with the zinc and flake off. Primers cover the patina and are therefore not useful. I have not been able to find any other clear paint that would work for this.
Context: This is a decorative application so I'm not sure if this is the right venue. I've added a black patina to galvanized steel pipe using a copper sulfate solution. I need to add a coating to protect the patina and prevent it from yellowing over time.
Any ideas?


texts:
I downloaded a 3D  model of a planetary gearbox from Rossi website, so the 3D model is reliable. As you can see, there is no keyway on the opening of the gearbox, thus i can't connect my shaft with traditional key designs.

And here is axial section view of the gearbox, the shaft sits inside the left side.

What woud be the best way to connect the shaft with gearbox ? should the shaft has exactly the form of inside gearbox i mean can the shaft come directly into the gearbox? or i should have consider a soort of coupling ?
Here is the suggested output side details:


texts: turbojet axial compressor: blades of HP compressor

texts:
I noticed that blades of HP compressor are shorter in axial dimension next to its LP counterpart.

Why?

I understand why it is smaller in radial dimension (this is because compressed air has smaller volume, and whole air passage is converging), but it seems to me that longer (again, in axial dimension) blades can transfer more energy to the air being compressed.

But it is obvious to be some good reason to make them small.

So why?


texts: How can I better structure documentation for a quality control process?

texts:
In my organization, every unit is built by hand, and every unit is tested. Every product has a written construction procedure and a written test procedure. We're in the process of updating and improving all those procedures. One potential problem we're trying to eliminate is when the checkout personnel skip a step during testing. If all you have is a list of fifty steps, and no step-by-step record of what you've already done, that's an easy thing to do.

One proposal is to require them to print a new copy of the procedure and check a box next to every step, every time a unit is checked. That's going to cost a lot of time and paper.

Another idea is to digitize the whole thing. Have a server running somewhere that the checkout tech logs into, which will show them the relevant procedure for the unit they're testing. They check the boxes as they go through the procedure, and it all gets stored electronically. This has a higher initial overhead, but should save a lot of resources in the long term.

The best proposal I've heard so far is to just roll our own checkout database and interface, but I feel like that must be reinventing the wheel. Is there software to support this sort of thing already in existence? Are there other, better ideas? Is there an accepted industry standard for solving this problem?


texts: What are rules of thumb for designing a gravity feed system for cylinders?

texts:
So, I just printed out this battery holder off Thingaverse.  Unfortunately, it doesn't work very well, so I'm interested in redesigning it.  There's a number of issues but the most annoying one is that the batteries keep getting stuck and not gravity feeding like they are supposed to, forcing you to shake the holder or reach up the output slot to bump the batteries until they feed out again.

The reason is obviously that the holder is just a box and that the cylindrical batteries jam up against each other at the bottom where the downward motion suddenly becomes horizontal.

A quick perusal of things like soda vending machines and ammo feed mechanisms shows that a v-shaped feed mechanism seems to be the standard way of doing this correctly.

However, I have no idea what sort of convergence angle and other considerations need to be made for designing such a device.  I could made a tall, slowly converging angle, but that makes the storage box a lot taller and lower capacity than is idea.  Too sharp of a convergence angle and I'll have the same jamming issues found in the existing design.

So, I assume that there is some sort of literature out there for designing feed systems for cylindrical objects.  Obviously, things like cylinder density, surface roughness and other factors will affect this, but I assume that there's at least some sort of rough rule of thumb out there for what the optimal shape should be - e.g.: 45 degree convergence angle + some factor * the cylinder W/L ratio, etc.

I know I can figure this out with Edisonian trial and error, but I really don't feel like burning up a bunch of PLA and time if there's a decent standard rule of thumb I can use as a starting point for experimentation.


texts: How to determine the torque and rpm of a Stirling engine?

texts:
I am actually working on making of a Stirling engine. I did some research work but most of the content on the internet is qualitative. So I am trying to build a small scale Stirling engine and trying to gather knowledge through trial and error way.
But since this is not my field of expertise so I thought to raise the question to the community first.
Suppose there is a Stirling engine whose Tcold is 0-degree Celsius and Thot is 200-degree Celsius.
The piston is 35mm in diameter and the stroke is 24mm.
The engine is made to run using air at a pressure of 2 bar.
Can anyone help me to determine the torque and rpm of this engine?


texts:
I have a conceptual design that I've been evaluating which can be summarized as a simple pendulum extended to 3D (i.e. swing not limited to x-z plane). If I want to actually build the conceptual design, is it possible to have a pivot point that does not permit rotation about the pendulum leg axis, but does allow for it to swing "freely" in 3D space?

An easier way to probably ask is, if the pendulum is hanging statically, can I constraint the motion such there is no rotation about the leg-axis (statically coherent with z-axis) and later, dynamically, allow for it to swing "freely" in 3D space?.

I should emphasis, I'm looking for a "product" idea that permits such motion. I thought a universal joint may work, but I think that in order to swing "freely" the joint must be able to rotate about the z-axis.

In the end, the more and more I think about it, I'm wondering if it's theoretically possible? Does this give rise the the "elastic pendulum" idea, where a spring must be involved?


texts: How do I convert this mechanical system into a mechanical network?

texts:
How do I convert this into a mechanical network? like a circuit network.

my attempted work is this:

is this schematic correct?


texts: How to predict shadows of a house (3D modeling + sunlight)?

texts:
Imagine a house/building, seen from outside, at sunrise. As the the sun moves in the horizon, a) the shadow of the house is displaced/deformed, and b) some faces of the house have more/less sunlight in the afternoon than in the morning.

I need to predict those changes along the day and along the year. Besides the external 3D shape of the house, this only depends on space & time. Space: the latitude, longitude and orientation of the house/building. Time: the hour, day, month of interest.

I have the exterior measurements of the house. At this point I treat the house as a solid object (ie I don't care about the light inside the house; I also don't care about cases where light which passes thorough the building eg two opposite windows).

I only need to predict two interrelated things (along the day/year) for planning and visualization purposes:

The shadow of the house
The faces of the house which will be receiving light

With (1) I can predict how the adjacent buildings/parks/spaces would be affected by sunlight decrease and with (2) I can plan to put more/less and/or smaller/larger windows in different places of each wall of the house.

I know that many years ago this was possible with a plugin for Google Sketchup, but for different reasons I would like not to use this option but a free application (if FOSS, even better). Given the recent surge of 3D modeling/design programs I thought maybe there are other programs which are capable of doing this.


texts: Amplitude RMS vs Amplitude in understanding vibration

texts:
I am reading this paper, which talks about dealing with mechanical noise.

When characterizing their existing noise, it says the following:

  The integrated RMS vibrations up to 1 kHz on the mixing chamber plate
  are approximately 2 μm in the vertical z direction and 6 μm in the
  lateral directions x and y.

It seems they integrated noise spectral density.

In implementing some of the mechanical noise isolation technique, what I care about is what the actual, physical size of the total vibration I will have, rather than the magnitude of individual components, which I believe Power Spectral Density represents.

So, I think the integrated RMS is what I am interested. (let me know if I am wrong on this point)  But does this figure actually equal the actual magnitude of oscillation?  For example, if I bolt an object onto a plate which has an integrated RMS vibrations of 2 μm in the vertical z direction, will it actually oscillate vertically by about 2μm?

What I am having a hard time understanding is their 1kHz integration bound.

Shouldn't one be interested in the integrated RMS vibrations up to the infinity? why stop at 1kHz?


texts: How is gas flow through (extremely long) pipelines monitored and controlled?

texts:
(This is closely linked with measuring the Mach number inside a nozzle but it is not regarding the supersonic flow)

Friction and heat transfer have effects on the Mach number of the compressible flow (Fanno and Rayleigh flow). As it is extremely important to have tight control over the flow properties, here are my questions:-

how does one know the Mach number of the flow inside long pipelines carrying some sort of gas (e.g. WEPP)?
What Mach number is maintained through these pipelines?
Considering the cyclic temperature changes and friction inside the pipes, how is the Mach number maintained constant / within a range?