texts: Does passenger car traffic actually damage roads?

texts:
Pavement Design

In roadway pavement design, the (US) controlling design load is usually the Equivalent Single Axle Load (ESAL). This number attempts to quantify how much bending stress a given vehicle causes in the pavement. Trucks have a much higher ESAL load than cars. In this case "truck" means "semi, big rig, freight carrier" and not a family pickup truck.

Typical values are:

Car Axle = 0.0002 or 0.0003 ESAL
Legal Truck Axle = ~2 ESAL (wide range based on weight)

By this measure, a typical car or pickup truck doesn't place any appreciable stress on the road pavement.

Pavement Life

Two sections of road that are designed and built exactly the same and a certain period of time.  This period of time could be 5 year, 10 years, 20 years, etc.

Road driven on only by typical family or commuter vehicles. Basically only passenger vehicles (not busses) and not hauling goods or construction materials.
Road with no vehicle traffic, but experiences the same weather conditions as (1). This would also include salt application in areas where that it common.

Questions

Would you be able to tell which section of pavement was driven on?

Would light weight vehicles cause so little additional damage to the pavement that it would be indistinguishable from natural weathering?

The corollary is that trucks cause all of the pavement damage.

Just to be clear, I am not concerned with visual things that you would be able to use to differentiate, e.g. oil stains, rubber marks, etc.


texts: Calculating kWh two-phase alternating network 3 wires

texts:
I want to do a project to measure electrical consumption but I have the following question:
How to calculate kWh consumed in a 3-wire biphasic network?  Example: I have the following chains on the wires:
Phase 1 (127V): 2A
Phase 2 (127V): 3A
Neutral: 0.5A
How do I calculate how many kW will be consumed in 1 hour?


texts: Autocad "Aligned" Constraint - distance between two parallel lines

texts:
I am creating the 3d Design in Autodesk Autocad 2017. I need to specify distance between two parallel lines, I could successfully defined the parallel constraint but not able to add constraint that would restrict the distance between them. As per documentation here we can use "Aligned" constraint to restrict the distance between point-point/point-line/line-line.

  Aligned Constrains the length of a line or the distance between two
  lines, a point on an object and a line, or two points on different
  objects.

  Point & Line Selects a point and a line object. The aligned constraint
  controls the distance between a point and the closest point on a line.

But when I try this constraint I am not able to select the line but the closest point on line gets auto selected. Now these parallel lines end at different points on sketch and in turn results in Constraint which just defines the distance between line end points which is not desirable.

I need perpendicular distance between two parallel lines to be constrained. How can I achieve this?


texts: is bending moment on roller supports at beams zero?

texts:
isn't the bending moment supposed to be zero on roller supports at beams?
then why isn't it zero here in this picture at x=2?


texts: ElectroMagnetic Pulling Force fdropoff with distance

texts:
I am looking make a quick and dirty test ring using an off the shelf electromagnet. My force needs are small, less than a pound but I need to do so in a non contact manner. I know these magnets are strong but I was looking for a back of envelope formula to estimate holding force at various distances. I am thinking 1cm away from the surface of magnet. The hope is to get a 100+ lbs holding force magnets and still have a 1 or 2 lbs of hold a bit of distance away from the surface.

Thanks in advance.


texts: What's the difference between structural pop rivets, and non structural?

texts:
It may be a simple or obvious question, but I'm confused what's changed between those.

That would be an example of a non structural rivet, does the bottom half of the mandrel steam inside the hollow rivet fall out, unlike structural where it stays, thus strengthening the rivet due to it not being hollow?

Bit confused between both.


texts: How to determine how much energy recovered from regenerative braking

texts: I am considering a regenerative braking system implemented with a AC permeant magnet motor with an efficiently of ~96%. It is easy to determine via energy equations the kinetic energy of the car and therefore how much energy is possible at max efficiently but regenerative systems also rely on the brakes of the car to slow it down to a stop. Is there a particular rule or reference to how much conventional braking is required for a given scenario? I wonder if it is possible to determine how much the motor would actually decelerate the car and then work out energies from there. Could anyone offer some advice?


texts: Do internal / external stresses affect modal frequency?

texts:
Imagine a cantilevered beam, fixed on one end and with a tension line connecting the other end to ground (e.g. perpendicular to the length of the beam).

If I increase the tension, does the modal frequencies of the beam change?

On the one hand, tension affects the frequency of a string.  So, would pulling on the beam (in tension) cause it to have a higher frequency?
On the other hand, the bending stiffness of a beam is not affected by a lateral force.  So, if the stiffness is not affected, then neither should the frequency.

What can help me reconcile these two comments?

Bonus aspects of the question:

If the stress is high enough to affect the slope of the stress-strain curve, then the stiffness changes because the modulus changes.
In Nastran, you cannot apply a load while performing an eigenmode / eigenvalue normal modes analysis.  Does that mean it is not a linear phenomena?


texts: What is the actual difference between a control function with Securtiy Integritiy Level (SIL) II and one without?

texts:
Consider a simple example:

there's a vessel with water and a continuos level sensor (4-20 mW signal)
there's a water line with a magnetic valve, feeding the vessel
When the water level is below a certain treshold, the valve opens - this is realized via a PLC unit somewhere

Now, consider the same scenario, the water level is critical for human safety so the whole refilling function needs to be SIL II. Now I - not an electrical or control systems engineer - need to understand how much more complications, cost, etc. will arise due to the SIL II requirement.

p.s. To give you an idea how much or little I know: My understanding is that I either need a safety PLC or a SIL II certified measurement amplifier with an additional potential free contact set to the correct level, hardwired to the relais controlling the valve.

Since SIL are describesd in an international IEC norm, I assume the answer will not be highly dependent on local codes.


texts: Transfer of moments in beams with internal hinges

texts:
We have a beam with 1 internal hinge just like the picture. We know the internal hinge can not transfer moments between AB and BD. We know the 30 kN force makes some moments on BD & AB. If B (internal hinge) can not transfer moments between the two elements, then why does the 30 kN (which is applied on BD) cause moments in AB?

I don't know if i'm clear enough but the 30 kN force makes some moments on AB while we know that no moments can transfer between AB & BD.


texts:
I'm looking for a power source that is able to deliver 12V at 15-30A (yes, amps). I was looking at high capacity batteries, but looking at the specs, they either say they have a lower discharge voltage than 12V, or they don't say anything at all.

Do such power sources exist?

I'm hoping to use this in a hydraulic system. The pumps I've seen require 12V/24V and consume around 10-15A minimum. I've been looking at Hydraulic Power Units (HPUs), and their specs say that power consumption is really high.

Reading around, it seems most, if not all, hydraulic systems are powered by small diesel engines. I would really like to avoid that, if it is possible.

If such high capacity power sources do not exist, what would be my alternative?

Apologies for the above sounding like a "find things for me" question. This was not the intention. Maybe I haven't actually understood fully how hydraulic systems actually are designed. Also, I'm not very good with words.

I am new to hydraulic systems, and I am in the process of designing a portable hydraulic system, similar to ones used in vehicles, like construction vehicles. However, my hydraulic system will not be part of a vehicle. I realise vehicles use their engines and some form of petrol/diesel to electricity generator to obtain the power required, but I cannot see a way of obtaining that same power without using a vehicle's engine.

How would I go about getting that same power without the use of a vehicle? Ideally, the system can be moved around without it being attached to AC wall electricity, but that can be left until a later date.

Details/Background of my project:

I would like to build a hydraulic exoskeleton that uses as little electrical components as possible. I have gone for hydraulic over pneumatic as hydraulic packs a lot more punch than pneumatic. Most of the sites online sell the valves, pumps, pistons etc, but I have previously found it difficult to find a way of powering these pumps, up until I asked on here a while back, where I was introduced to HPUs. From what I have understood (do correct me if I'm wrong), I need a way of powering these HPUs to generate the necessary RPM and flow rates.

I have found the pistons I would like to use, the hydraulic fluid, how much to use, the reservoir tanks, the filtering system, etc, but I am stuck on the power source. I just have no idea how to harness the power I need for this. This is where I started looking at ultra-high capacity batteries.

To be honest, I don't even know which would be best, a DC- or AC-input motor. My thought was that the constant forward drive of the motor required a DC source, hence the batteries. The link I provided in the comments below points to AC motors.

I'll keep adding details if and when they are required. As I said, I'm not good with words and I'm new to hydraulics.


texts: Choosing appropriate response type in experimental design (DOE)

texts:
I am designing an experiment to minimize the number of failures in wood-based materials arising from the application of wood screws. The first part is screening for significant factors and 2-way interactions. I am using a single material type and cross-section (1x1 LVL rails with the screws inserted on a specific face, with the same torque and speed) so my experimental factors are:

Length of the rail (continuous)
Distance of the screw from the end of the rail (x position, continuous)
Distance of the screw from the edge of the rail (y position, continuous)
Screw diameter (4 standard sizes, discrete)
Screw length (3 standard lengths, discrete)

As I see it I have to basic options for response variable:

Failed/Pass (meaning that the screw cracked the piece or not, categorical)
Failure rate (I test the same treatment 10-20 times and input the % of failures)

I am using SAS JMP to aid with the DOE and it provides a 24 treatment table with no repetitions. My question is:
Can I simply run each individual treatment 10 times and calculate the ratio of failed components (0%-100%) and call this my response result? Or does this introduce any bias or statistical errors as the original design contemplates no repetitions and the original response would be simply Fail/Pass?
In the end I would like to provide a predictive model to keep failed parts to a minimum.


texts: How are protective sheets attached to plastics?

texts:
When you buy plastic sheets such as acrylics, polycarbonate sheets etc, they come with a paper/plastic protective film. Like in this image :

Protective Film for Acrylic Sheet PMMA Panel

You notice that there is no adhesive (at least not something tacky) that is present on the sheets, and there is no residue when the sheet is peeled off, I was wondering if anyone can shed some light on how these protective films are applied ?


texts: Material for car mounted fire extinguisher bracket

texts:
Don't try this at home. I am taking personal responsibility for what happens in my car.

Hi all,
I recently purchased a fire extinguisher for my car (it weighs 1.5 lbs or 0.68 kg). I browsed the internet for a decent bracket to mount it inside my car, under the front passenger seat. Everything was fairly expensive which made me want to make a DIY version that would be cheaper.

I have been trying to find what sort of materials I can/should use. The last thing I want is the bracket to break and have a 1.5 lbs metallic projectile flying inside the car in the event of a crash.

The bracket should be 16" or ~40 cm wide so that I can use the bolts on which the passenger seat is mounted to attach the bracket. (See picture below)

Obviously I could use some thick steel and be safe but I don't really have easy access to tools to cut metals so I would like to try something else.

My requirement for the bracket is that it should be able to hold on to the fire extinguisher in the event of a frontal collision on the freeway. Which would be an impact of, if my memory serves me right, of
65 mph + 65 mph = 130 mph or ~210 kmh
If my math is correct this would be equal to
210000 * 0.68 = 3966 N

After that I'm not sure where to go...
If I was considering using a PVC pipe, would I be able to relate those Newtons to the tensile strength of the pipe to figure out if it would hold up?

I had also thought about 3D printing the bracket but a friend pointed out that it's hard to make measurements with PLA because the printer layers the material so the "resistance" or "strength" is different in different directions.

I am also open to other material suggestions!
Thank you.


texts: How to I design a planetary gear with a gear ratio of 2:1 ( doubling the torque)

texts: Trying to design a 2:1 gear ratio planetary gear, and I'm not sure how to begin. In the past I've had luck using this site to create an illustrator file that I can extrude in Rhino. This does not generate planetary gears, and I'm also unclear as to how design a planetary gear with a 2:1 ratio.


texts:
I'm trying to calculate the energy per unit length the vacuum pumps require to vacuum a cylinder with a diameter D. Which formulas should I use?

I used a typical formula for compressors and the result I got was that the air exited at 12,000 K at the end of the process! Also 500 kWh/km to vacuum a 3.3 m diameter cylinder (the initial pressure is 101,325 Pa and the end pressure is 99 Pa).


texts: How fast can a VEX robotics light sensor operate?

texts:
In my engineering class we must make a machine that can sort 15 marbles with 3 different types in less than 2 minutes. I plan on having one marble go over/under a light sensor with a flashlight on the opposite side so it can read its reflection, then have a gear with three cups spin according to what the light sensor value is.

Do you think that the light sensor will be able to read the value and spin in less than 1 second? Or should I put something to stop the marble while it is being read?


texts: How can I calculate the rate of power consumption of a solar car along a known route with changes in elevation?

texts:
I am working on designing and creating a solar powered car for the Solar Car Challenge. The car will have to race from Dallas, TX to Minneapolis, MN in 5 days (~5 hours of driving a day) along back roads. My team is still in the planning/concept generation phase and I'm in charge of designing the solar array. To begin designing, I need to first know how much power the car will consume per hour.

My textbook gives the power consumption of a car as $$ P_{w} = F_{foward}v = (F_{roll}+F_{air})v  $$ where $F_{roll} = \mu_{r}mg$ and $F_{air} = (1/2) C_{d}A\rho v^2 $. I'm assuming a rolling resistance coefficient of 0.017, a drag coefficient of 42, and the estimated mass and frontal area of the car are 275 kg and 2.45 m$^2$, respectively. I thought a good way to estimate the minimum required speed $v$ would be to get the elevation of the route (Google Maps with "avoid highways and toll roads" selected) at various points and plug it into the formula above.

Using this elevation finder, I was able to get the elevation at a certain distance for ~27,000 points and export the data into Excel. If I understand correctly, $V(t)$ would be given by $$ V(t) = \frac{\left(\sum _{n=1}^{27298}\sqrt{dx^2+dy^2}\:\right)}{dt} $$

Where $dx$ is a change in horizontal distance, $dy$ is a change in elevation, and $dt$ is change in time. I have the data and I have the equation, but I'm not sure how to convert this into something that Excel can use to get my speed.

Here is the spreadsheet of all the data points.


texts: How to use mesh as a reference object in Solidworks?

texts:
Suppose I want to design some device against a scanned 3D model like eyeglasses. I have imported STL model and drew a reference plane by three points of it.
I can sketch on this plane, but I can't see where plane intersects with an object. How to compute this?
Or I can only draw extra planes and lines?
In the following picture an intersection is visible, but it is only visible during plane definition stage. Once defined, plane becomes 100% transparent.


texts: Are spring constant and rate constant the same thing?

texts: I am shopping for a spring on McMaster and there is a quantity listed as "rate constant".  Is this the same thing as spring constant?  If so, what are the units of this value? (lbs/in, lbs/ft, other)?


texts:
I was wondering where the negative sign comes from in the following simplification for diffusion in 1 dimension.  The initial equation is given as follows:

$$\frac{\partial C_i}{\partial t} A \Delta x= (N_{ix}|_{x} - N_{ix}|_{x+\Delta x}A + R_iA \Delta x )$$

Which simplifies to:

$$ \frac{\partial C_i}{\partial t} = -\frac{\partial N_{ix}}{\partial x} + R_i$$


texts: How to calculate the external work of plastic deformation due to wire drawing (the work done by the wire drawing machine)?

texts:
I am currently trying to process some data from a wire drawing (cold drawing) test. I would like to know how I can calculate the external work of plastic deformation due to wire drawing, which is basically the work done by the wire drawing machine.

The data that I have are the length and diameter of the brass wire before and after each wire drawing operation (brass was drawn 3 times) as well as the time and force data for the wire drawing operations.

Any form of help would be appreciated. Thanks in advance.


texts:
Hello to all of you with more expertise about engineering than me...and anyone else that is curious.
I like to fantasize about projects, so this may be more of a thought experiment, but I'll throw it out there.
If I were to have a camper trailer, the camper is made primarily of fiberglass, and the supporting trailer is steel, How would I go about connecting the two?  If I just bolt it on there, I expect the camper part would get ripped apart because the the elasticity of the two materials is so different.  Flexing in the steel frame would just rip the fiberglass apart...no?
I assume when the trailer experiences forces from bumps in the road, the steel will flex, but the fiberglass wont, or at least will flex in a totally different way.


texts: Whats the purpose of a main metering system in a carburetor?

texts:
I'm confused on how to differentiate mixture control from the main metering system, and why we even need one at all. Let's say we had a large resovior, and a needle type mixture control system. The differential pressure would push/pull fuel from the discharge nozzle at our set mixture ratio? Then where does the need for the main metering system come in?

Float-type carburetor

Any help is appreciated, thank you!


texts: How do the springs really work in my design?

texts:
I'm designing a machine to test a static object (I'll refer to it as A)'s resistance to deflection due to impact force.

This design uses a pneumatic(probably wont be using hydraulic) cylinder to apply the impact force to the surface of A. (However, if I were to use the pneumatic cylinder alone to apply the force, I would have to position the surface right at the end of the piston stroke. If I allowed the piston stroke to be slightly more than the distance between the two to completely apply the force on the surface(overexerting the cylinder), I will damage the cylinder over time and reduce its lifespan.)

Hence, I added an extended head to the piston end with the use of springs and linear guides(shafts) within it. In my head, I picture it as the head exerting the impact force(F) first at a pretty high speed and then when the head stops at the surface of A the springs absorb the remaining of the piston stroke.

However, I have some concerns too so I'm hoping some of you more experienced and knowledgable people out there can help.

Since the speed is moving at a pretty fast speed(completes the stroke(completely extends) in 1 second), would the head be able to totally transfer the force F from the cylinder piston to the surface of A or would the springs somewhat absorb the force and lower the resultant output force? How should I select springs for this purpose?
To determine the force of the cylinder, use Force = mass * acceleration. The thing is, I have the equivalent load mass(60kg) but I don't have the acceleration. I only have the distance(stroke length = 300mm) and maximum piston velocity(300mm/s). Since the velocity is pretty fast and stroke length is not that long, how should I calculate the acceleration? Can I assume that the acceleration will be constant since the piston will extend completely pretty fast?
The cylinder applies a force equivalent to a 60kg load. How should I be calculating the output? In terms of force, F=ma or kinetic energy, 1/2*m(v^2)? Since there will be spring energy in play as well(?)


texts: Can I remove one or both of these support posts in my basement?

texts:
Below is a picture of two supporting posts in my basement. The posts are directly underneath the kitchen/dining room.  Would it be feasible to remove one or both of the posts? What would the cost roughly be to make this change?

Note: I know that I should have a structural engineer take a look before actually making any changes. Also, I live in the mid-west.


texts: Stabilization of telescope on gimbal using data from encoders and gyroscope

texts:
I'm designing a control system for a balloon-borne telescope experiment. As the balloon is constantly moving and the gondola is rotating, I want to stabilize the telescope which can be controlled in 3 axis of rotation. I have encoders for each axis motors and gyroscope located on the electronics box around 20cm apart from the telescope's center of rotation.

Is there a possibility of performing a sensor fusion, like Kalman filter, for these two groups of sensors?

I have a prepared model of the control loop, but have then realized that the sensors are in different places and while gyroscopes measure gondola movement, the encoders measure the telescope rotation.


texts: How to choose correct motor for my application?

texts:
I'm looking to play around with making a massage pad that I can lie down on and has massage nubs that are motor driven. There will be a motor that rotates the nub (the part that does the actual massaging) and motors that translate the nub in 3D "space".
I'm wondering if there's a good way to choose which motors are appropriate for my application. I understand the difference between motor types but don't know how to calculate torque required in this scenario. Perhaps there are other motor specs to consider too.
Thanks so much for any guidance you can offer!


texts:
In this problem, why did the author use ${(30×10^3)} {/s} =  {VQ} /{ I} $ only?
Shouldn't it be $4(30×10^3) /s = VQ / I$?

I said so because the board at the centered is connected by 4 bolts , 2 on the left and 2 on the right . The faces on the right also resisted by the same arrangement of nails , right ?


texts: Does electricity go through non-metal materials or not?

texts:
Ever since I was a little boy, I've always had this idea that electricity can only go through metal materials. For example, if I put a 100% metal screwdriver into the socket in the wall, I'm going to get electrocuted. Logical. Or if I take a long wire of copper (or even gold) and hold it with my hands and then stick the far end into a powered-on toaster, I'm going to get zapped.
Also ever since I was a child, I've had this screwdriver which (of course) has a metal "main part" (for the actual screwing), but whose "hand part" is made of what looks like glass or plastic. It's transparent. And there's some kind of little "spring thingie" inside it near the top. This has always confused me. I think at some point, an adult told me that it's a special screwdriver which is safe to use when there's live power. But is it?
Why is that "spring thingie" necessary at all? Isn't simply the glass/plastic cover around the metal enough to insulate my hands from the electricity that only travels through metal? I don't understand why there would be a need for some "special" kind of screwdriver with a spring inside it to protect me from electricity when it doesn't travel through non-metal materials anyway.
And even if this is such a special screwdriver, how can I know that it actually still works after all these years? How could I trust it even if it were brand new? What is it about that spring that somehow makes it safe to use it on live power?
I vaguely remember that classic story about the famous scientist who went out with a kite in a thunderstorm and got zapped by lightning hitting the kite, then traveling through the non-metal string to his hands. But did that really happen? Or is that a major misunderstanding on my part? Or did he somehow use some kind of metal wire (unlikely)? This story seems to go completely against my understanding of electricity, in that it apparently does travel through non-metal materials.


texts: Is it possible to power an AC motor, using alternating positive and negative DC current?  I would assume toggling between each at 60hz would work.


texts: How does infill material affects the capacity of a tubular section with H-section inside?

texts:
How does one consider the moment capacity of a combined pipe plus H-section if the infill material is:

Sand, friction angle 30 degree
Grout, C20
Concrete, C45

Eurocode has a section on composite design, which requires use of shear connectors. Where shear connectors are not feasible due to lack of space, can bearing of infill material be relied on for moment transfer? For example, what would be the moment capacities of a 600mm outer diameter pipe section with 10mm thick wall containing a 300x300mm H-section with 25mm thick flange and 16mm thick web, both grade S355 steel, based on each of the three infill materials?


texts: Reducing air flow speed without much backpressure

texts:
I am setting up a test-bed for an experiment. Here's what I have.

A circular car exhaust like this
Image
The gas comes out of the exhaust at a velocity, x.
We need to lower the gas velocity to X/3

Conditions

The 'reducer' should exert very less backpressure on the flow

What possible directions should I look into, if you know any pre-filters, baffles, geometries that can help me reduce the flow rate in minimum size, that'd be awesome.


texts: Refute my assumption: Bearings Don't Improve Efficiency

texts:
If two surfaces rub together with a normal force between them, friction is generated.  You could add lubrication between those two surfaces and reduce that friction.

Bearings essentially consist of two surfaces rubbing together and, as before, under load, friction will occur.  As before, you could lubricate the bearings and reduce that friction.

So absent a better understanding, I can't see how bearings add much of anything to efficiency.  This must be wrong or all of industry would be spending money frivolously on unnecessary parts.

So my question is, in what way is my argument wrong?


texts: How to calculate failure stress on a hollow pin loaded in shear

texts:
Calculating limit stress on a solid pin loaded in shear is straightforward, and there are several handy calculators which will do single shear and even double shear. However, everything I have found assumes that the pin is solid.

For weight savings reasons, one might want to replace a solid pin with a hollow pin. However, stress flow in a hollow object is different from in a solid object, so it seems dangerous to assume that the peak stress is purely inversely proportional to area without consideration of the nature of the cross-section.
How to take into account the cross-section when calculating failure stress in single-shear and double-shear loading for a pin with arbitrary ID? Is it sane/safe to use the existing shear eqn. above with the hollow cross-section area and then bump the required safety factor by, say, 2x?
UPDATE: The best answer includes design tables and/or guidelines. Pure theoretical approaches are interesting but ultimately unsatisfactory, as 1) they can be easily simulated with FEA as well and 2) they might not include real-world experience.


texts: Can self-discharge cause a Li-ion battery to swell?

texts:
Suppose a Li-ion battery, with a polymer electrolyte, is left unused for a few years with no load connected. Can self-discharge alone during this time cause any gassing in the the battery?
If yes, can this make the battery physically swollen?


texts: Precision measurement of liquid level in a tank which is continuously opened and closed

texts: I need to measure the level of the liquid in a tank. The tank is opened and closed frequently. Measurements are made in milliseconds. I tried to measure the level of the liquid by using an ultrasonic sensor, but the measurement was not accurate enough. I need to measure accurate to one milliliter. Measurements are made from the top of the tank. Can anyone suggest some sensor that will accurately measure the liquid level?


texts: What organization specifies unit of measure conversions?

texts:
A recent work project involved a number of unit conversions between various systems of measurements.  Due to the scale and critical nature of the project, we wanted to ascertain that our conversion factors were as accurate as possible.

While only tangentially related, what I couldn't determine was who held final authority in declaring what the "one true" conversion factors should be.

For example, NIST provides a set of conversions and does not make explicit reference to other standards organizations.  This article on International Bureau of Weights and Measures (BIPM) implies that the BIPM is responsible for declaring those conversion factors.

Is there a single organization responsible for declaring and verifying the accuracy and precision of conversions?


texts:
Kinematic pairs are the connection between 2 links that can have relative motion between them.
But In six bar chain as shown below:

There are five pairs for them to be a kinematic chain. But if I consider links between ((1,4),(3,4),(3,2),(2,1),(2,6),(6,5),(5,1)).I get 7 kinematic pairs. I have the resources suggesting that this chain has only 5 kinematic pairs. How?
EDIT:


texts: Implications of concatenating EEG signals

texts:
I am wondering about the mathematical implications of concatenating very small windows from different trials.  All of the trials are the same size, and are for the same period of time after a stimuli.

In other words, let's say my data has 3 channels, 6 trials, and 10 data points per trial ( size of data [3x10x6]).  What I want to build is a new data set with the same 3 channels, but with concatenating the windows of 2 datapoints for all of the trials, and then repeating this for the all of the possible number of windows.  In this example it would be 5 windows (size of new data [3x12x5]).

I assume that any frequency analysis will be pointless due to dramatic changes in the signal, but what other implications to the data should I be concerned about? Would it still be reasonable to remove trending or denormalize this new data?


texts:
I think I understand how heat pipes work, and thus the following one has me flummoxed:-

It's from a typical bulk order Chinese web site, but I've seem many similarly contorted arrangements.  They are very common in the over clocking /modding community.  There is never discussion as to which way the heat sink must be oriented for efficient operation.
My example seems ridiculous.  With an U bend in the middle, I don't see how heat sinks like this can evaporate at the hot end and condense at the cold end.  Surely the condensate will just pool in the U bend?  Even with condensate wicking, it must be easier to wick downwards with gravity than upwards fighting gravity.
Are these types of heat sinks just a con?  Overclocking /modding heat sinks are never spec'd with a deg. C /W rating or recommended orientation.  This would not do in the engineering world.  Can it work equally effectively in any orientation?


texts:
I'm looking for a formula to arrive at a pump curve for a centrifugal pump: $H(Q, n)$ - total head delivered as a function of flow and speed (rpm), and of course some pump specific parameters. I find no formula I can transform into this. For actual pump selection I would of course use the pump curves from the supplier, but a formula like this would be interesting for simulation purposes of pumping systems where VFD is used.

As both head and flow are mostly a function of speed, impeller size and shape  I think a non purely empirical fomrlua for a pump curve should exist.

p.s. Alternativly, I considered using a simple polynomial or similar curve and fitting it numerically to an existing pump curve. Pump simulators, is this an actually useful approach lacking an analytically correct curve?


texts:
In Euler's bending theory, it's stated that the critical stress of a beam is always larger than the yield stress of the beam. I don't really undertstand the difference between them. Critical stress is defined as the stress that the maximum stress applied before the beam starts to buckle.

Does the yield stress here mean the stress which the beam start to deform plastically? Why shouldn't the yield stress be smaller than the critical stress?

When the object is subjected to stress, the beam will deform plastically before it starts to bend and break.  So I think that yield stress is smaller than the critical stress.


texts: Boundary conditions at interface for1D transient heat conduction problem in cylindrical coordinates

texts:
The problem I am currently working on involves rapidly cooling liquid aluminum in a cylindrical graphite crucible and getting the radial temperature distribution over time, possibly using finite difference methods.
This is a 1D transient problem in only the radial direction using the following equation and I am only concerned about the liquid portion of aluminum (no source term and constant thermal properties).
$$\frac{1}{a}\frac{dT}{dt} = \frac{1}{r}\frac{d}{dr}\left(r\frac{dT}{dr}\right)$$
The main problem I am having is determining the boundary conditions, especially at the interface between the graphite inner wall with the liquid aluminum (as graphite and liquid aluminum have different thermal diffusivities). The boundary condition at the outer graphite wall involves convection and the BC at the centerline of the cylinder should have no heat flux for symmetry but I am not sure how to get a boundary condition at the interface (I am thinking of equating heat flux of graphite to aluminum).
I was wondering if anyone here has any idea on how to get the boundary condition at the interface or have any credible sources that I can look at. Thank you.


texts: How to calculate mass flowrate of gas from vacuum pump curve?

texts:
Let's assume we have a liquid ring vacuum pump. The pump curve for this pump is plotted as "suction capacity" in m3/hr vs suction pressure in mbar(a).
How does one calculate mass flowrate of the gas from this curve?
I guess the more specific question is: "Is the plotted volumetric flow of the gas refer to the flow measured at the suction of the pump (at the corresponding pressure) or at the outlet of the pump, where the pressure is atmospheric"?


texts: Is there a theoretical bound to how tall a structure can be built?

texts:
Assuming that there are no constraints on cost, land to develop, or supply of materials, is there a theoretical limit on how tall a structure can be built?  What are the main physical constraints that limit the tallness of structures?

I emphasize structure because i don't want to limit the discussion to skyscrapers or other structures that would also have biological (human) occupancy constraints.

Update:

Based on the comments, I want to further impose the constraint that the structure must support its own weight.  I realize that this question is a bit theoretical in scope and that real engineers always have to work with cost/material/land constraints in practice.  I'm just wondering, if we eliminated those particular constraints, is the tallness of a self-supporting structure infinitely unbounded, theoretically?


texts: Are mechanical pocket watches inherently water-proof and last "forever"?

texts:
Recently, I bought a cheap (~$53) but elegant mechanical "retro pocket watch", newly made. That is, not an antique made in the 18th century or anything.
So far, it's worked flawlessly and feels very solid. But who knows what it will be like in 10 years? Or 20? Or 50? Or... 100?
Can I expect this thing to work for at least the rest of my life? Is it likely as good durability-wise as the fully hand-made ones of days past? Or maybe even better?
I also wonder if it's waterproof. I'm not going to go swimming with it anytime soon, but I may well pick it up to check the time when it's raining cats and dogs. Or I could accidentally drop it in a pool of water, etc.
Since it's fully mechanical, shouldn't it in theory work under water just as well? No batteries, no electronics? Even if water pours inside the glass covers on both sides, shouldn't it keep ticking? And aren't all metal parts stainless these days, so there would be no long-term damage?


texts: Moment of Inertia of a Rectangular Cross Section

texts:
I have a question that is annoying me for a long time. I know that I can calculate the moment of inertia of a rectangular cross section around a given axis located on its centroid by the following formulas:

I also know that more generically, the moment of inertia is given by the integer of an area times the square of the distance from its centroid to the axis.

So lets say I have a rectangular section with a height of 200 mm and a width of 20 mm.

If I use the formulas of the first method, in relation to an x axis parallel to the width:

$$I_x=\frac{bh^3}{12}=\frac{20\cdot200^3}{12}=1333.33\text{ cm}^4$$

Using the second method, why do I get different results when calculating twice the area of half a section, multiplied by the square of the distance from its centroid to the x axis.

$$I_x= 2A_{half\ section}d^2 = 2\cdot(200/2\cdot20)*(200/4)^2= 1000\text{ cm}^4$$


texts: Which thermodynamic property does the PdV for a free expansion define if work is zero? Considering there is a finite change in PdV.


texts:
I know that you can have metallic and ceramic composite brakes.
My question is can you have disc brakes for a car that consists of polymetric materials or would this be impossible due to its low melt temperature ?


texts: For train track, why does the ballast need "good drainage"?

texts:
Why does the ballast of train track need good drainage?

I read something about preventing "fouling" of the ballast, but don't know what that means or why it would be structurally bad.

Could foundational support play a role, where soggy ground would give way under the track?

I'm also trying to understand why ballastless track apparently doesn't need good drainage. That continuous slab of concrete surely is not permeable to water.


texts:
I have a sphere in AutoCad that I want to slice into a semi-sphere. With the SLICE command, I press o to slice as an object.
Now the prompt shows:

Select a circle, ellipse, arc, 2D-spline, 2D-polyline, to define the slicing plane.

How to select a circle?


texts: Why do bluetooth headsets get interference (choppy sound quality) outdoors?

texts:
This is more of a general physics question to help me understand how to choose sports headsets in the future, however it is too specific to a certain use case (bluetooth headset) to belong in the Physics StackExchange.

Problem:

3 of my 4 sports bluetooth headsets suffer from choppy sound quality (signal interference?) the minute I step outside. It seems to be especially bad under a clear sky no matter the time of day.

The 4th and the most expensive headset does not suffer from this, but it has a different (more compact) design. The worst performance was by the cheapest sports headset (from ebay) and it was unusable outdoors.

Observations:

In all cases my phone is located in my trouser pocket, but moving it closer to my head (the headset) seems to lessen signal interference, but not remedy the issue completely.
In all tests the headsets have been fully charged.
The speed of movement also seems to play a factor, but I am not able to reproduce that affect every time.
I can say that clothes are not a factor, as the same clothing indoors produces no interference.

Theories:

background EM radiation coming from outer space?
EM radiation coming from our sun? Although I have not observed if the moon reflecting the EM from the Sun plays a part or not.


texts: Model Reduction - Export matrices from ANSYS to MATLAB

texts:
I am trying to reduce my model in ANSYS using Craig-Bampton Method.

My ultimate goal is to read system matrices, stiffness, damping and mass matrix with MATLAB.

The size of stiffness matrix that I export from ANSYS is more than 10 GB.

My aim is to simulate my structure as a flexible body in Simscape Multibody using finite-elemente import method - superposition of ridig body and deformation models. Deformation model is described in space-state using system matrices.

Should I build my flexible body with deformation model for each part (say it is a table, should I describe every leg of my table and the plate using rigid body and deformation model)?

Concerning model reduction I am really not sure what to do

Should I use Component Mode Synthesis Method - Fixed-Interface Method (CB Method)?

Should I generate superelements for every part selecting master degrees of freedom on the interfaces conecting to the other parts of the structure? If yes, what is the next step?


texts: "Sliding door" - is top weight bearing more efficient?

texts:
I'm an artist building a project which one could think of as a "sliding door" – a very narrow panel running on grooved wheels riding in tracks at top and bottom. It will be motorized and driven by a stepper motor, timing belt and pulleys. I will probably end up driving it from top and bottom too so it doesn't rack.

This is the gist of it:

My question: does it matter if the load is on the top set of wheels or the bottom set?

I realize this is a dead simple "more efficient to push or to pull" type question but the answer is not obvious to me.


texts: How does non-electrical ATEX apply to springs?

texts:
This question relates to the ATEX directive, which is the European regulation governing the design of products to be used in explosive atmospheres. In particular, I am asking about the part relating to non-electrical (i.e. mechanical) devices.

Does anyone have experience in applying non-electrical ATEX to products containing springs? If so, do you know of any good guidelines as to how to conduct the assessment?

I'm thinking that the main potential ignition source would be a mechanical spark, which could conceivably be generated if the spring was to fail. So, the question boils down to: how to assess whether this is a genuine concern or not?

One possible option would be to assume as a worst-case that all the stored energy in the spring is converted into heat in the spark, and compare that to the minimum energy needed to ignite the explosive mixture; however, my gut feeling is that would be very conservative.


texts: Estimate the grain size after grain growth

texts:
An uncold-worked brass specimen of average grain size 0.009 mm is heated to 600 degrees Celsius for 1000s, what is the average grain size based on this graph?

How to tackle this problem? I don't know if I am using the graph correctly.
My approach was:

1000s is 16.67 min, $\log(16.67) = 1.22$

So $\frac{22}{100}$ between 10 and 102. Which is about 0.67 cm to the right of 10 on x-axis.

Now lets estimate this corresponds to 10-1.333 on the y-axis of the 600 degrees celcius graph line. So 0.046 mm.

But this does not seem correct, because I did not incorporate the 0.009 mm starting position. Which corresponds to heat treatment time of about 1 min at 600 degrees so should I add 1 min to the 1000s? And thus look look at the point on the graph at 17,76 min?

The answer in book seems way off, they talk about average grain size 0.2 mm. To me that seems like they looked at the graph of 700 degrees Celsius.


texts:
Firstly, I am sorry that the title of this question isn't helpful. I have bought these motors for a project:

5V 7mm 2 Phase 4 Wire Stepper Motor

I assumed that the 1.7mm diameter threaded shaft would take an M1.7 nut, but it does not. Standard thread gauges haven't given me a good fit and I am thinking that this thread is probably some industry standard. The motors are designed to adjust the lenses in digital cameras, so does anyone know were I might find standards relating to this?

Alternativley, is there some list of common threads that I can just try all the 1.7mm diameter nuts to find a good fit? I have time and money but don't know where to look.


texts: How can I increase my ultrasonic sensor accuracy?

texts:
I am using a long ranged ultrasonic sensor to measure milk height in milk silos. Milk is stirring.

Milk Silos Design: Shows two type of silos both are stirred in different direction


texts: How will using desert sand instead of concrete sand affect my concrete recipe?

texts: I've read that desert sand is too round for concrete mixes. But, I'm not building a dam, I'm building a 3 foot landscaping wall. I'm interested in using desert sand for the color, so this is an aesthetic choice. How will using desert sand affect the strength of my mix? Are there ways to counteract the effect? I've been reading everything. Is desert sand ok to use, just uneconomical for large projects?


texts: Will a sacrificial anode protect any length of metal that it is connected to?

texts:
When using a sacrificial zinc anode, is there a limit to the distance that its protection will extend?

The protection works based on electrical conductivity, so distance would seem to affect the performance of the anode based on resistance. On the other hand, there doesn't seem to be a large current induced, so the any voltage drop would be very small.

The Wikipedia article only mentions that the total number of anodes is usually equally spaced. Does this mean that one large anode in one place protects an entire structure the same as ten smaller anodes equally spaced?


texts: Difference between ACI Code and Eurocode in Stiffness modifiers?

texts:
According to the ACI Code stiffness modifiers (modifiers used to reduce the moment of inertia) are used for each structural elements for example 0.7 for columns and 0.35 for beams...

For those who do seismic and/or wind design according to Eurocode where are these modifiers used and if they are not clearly available like in the ACI Code how does the code apply these modifiers ? does eurocode use a coefficient to reduce the compressive strength of the concrete instead of using these coefficient?

Thank you in Advance.


texts: Heat Resistance of Melamine Particle Board

texts: I want to make a cheap thermoforming fixture out of melamine particle board so I can form some PETG plastic sheets. The forming temperature ( hence oven temp) for thermoforming PETG is around 300 deg. F. So the melamine particle board will be exposed to this temp for about 3 minutes. Are there any dangers to doing this? Thank you!


texts: Is the concept IC Engine a viable concept?

texts:
The Concept IC engine is a reciprocating engine that opens the exhaust valves soon after combustion begins.  The inventors claim that the exhaust acts similarly to a recoilless gun so that the piston is still pushed while the exhaust has more energy than a conventional engine, allowing more energy to be extracted by a turbo.

Is this a viable concept?


texts: Calculating mass flow rate of a scramjet engine?

texts:
First post here.

I'm an undergraduate ME interested in fluid mechanics. I came across scramjets and I was interested about the engine. I want to calculate the mass flow rate of the engine and I made an attempt because it doesn't seem right and I can't find any resource explaining how to calculate the mass flow rate of a scramjet.

I arrived at this using standard definitions: $ \dot m = (\frac {P}{RT}AM\sqrt{\gamma RT})  $

where $P$ is the absolute pressure of free stream (air, in this case)

$R$ is the gas constant for air

$A$ is cross sectional area

$M$ is the Mach number

$T$ is absolute temperature

$\gamma$ is ratio of specific heats

I'll be honest, I have no strong intuition about this since I'm only a junior undergrad who only has taken Thermo and Fluids (no heat transfer yet, compressible flow not in curriculum) but if you guys can steer me in the right direction I would be very happy. I sense that it should be more geometry dependent, maybe angle of attack should be considered as well?

Thank you everyone!


texts:
I downloaded FreeCAD 0.18 from the Ubuntu Software (snap).
I don't know where are the libraries, so i can do
import FreeCAD

and run standalone Python programs with FreeCAD utilities.
Another version of FreeCAD had libs in the /usr/libs/freecad-python3 directory.
Now there is nothing there.
The installed program exists in /snap/freecad, but there are so many folders and files there.
Does anyone know which one should i include, in order to import Draft, FreeCAD etc?


texts:
Are there any satellite thrusters that mimic the "thrust reversal" feature of airplanes i.e. (A320...).
I already know of procedures to decelerate a satellite such as using two separate thrusters firing in opposite directions however a single  thruster would be far more economical -encorporating the thrust reversal.


texts: Carefully attaching Pt-wire to mild/carbon steel surface

texts:
Problem:

I have a near 100% Pt wire (25 AWG / D ≈ 0.45mm) that I would like to attatch to a cold rolled steel (E235 / EN 1.0308) surface. Assume this surface is flat.

Goal:

Keep wire attached to the surface for ~3 minutes while temperature
sinks from 800C to 500C. The wire is not carrying any load except its
own (max 20 cm).

While:

Minimizing added heat capacity / mass
Avoiding gases up to 1000C (so no
tape)
Thermal conductivity
Minimizing steel tempering (solidus
~1420C)

Thoughts:

I have considered soldering/brazing with a silver alloy (mechanically weak, but strong enough?). I soldered an iron wire onto the same surface with 60/40 Sn-Pb soldering wire in 20 seconds and achieved a solder strong enough to lift the entire test object (over one kilo) and bounce it around. Looking briefly at the metallic and atomic properties of Pb/Sn and Ag, I'm hoping silver will bond even stronger with the steel surface. I assume I should also be trying to dissolve/reduce the oxidation layer on my steel before and during the soldering.

I've also been thinking an Al-Mn alloy can be easily made with a perfect melting temperature, achieve a BCC crystal structure (like my steel), and hopefully create a stronger bond to the steel. Is this a realistic approach? I have no experience with obtaining this, its price and the overall doability. I'm also unsure of whether corrosion makes an aluminum alloy unsuitable for this brazing technique.

I have previously considered welding the platinum straight onto the steel, but I assumed this would have a major impact on the mechanical strength of my steel.

Question:

Does anyone have a good way to solve this that is preferably swift, simple, repeatable and does not require expensive machinery (2000 USD+). I already have soldering, brazing and TIG/MIG/stick welding capabilities.


texts: Is there any cost effective static stress simulation for rapid prototyping (FDM / 3D-printing)?

texts:
I've been using the static stress simulation (computed locally) which, until recently, has been free with the Personal licence of Fusion 360. Is there a reasonable alternative?
The cost that Autodesk charges for cloud credits works out to be much greater than is generally the cost to print a part and perform a real world test. I'd rather not landfill the PETG/PLA; but I'm willing to if that's what it takes to avoid the hundred's of dollars cost to simulate. The cost to add locally computed simulation back to Fusion 360 is prohibitive even if it was a one-time-cost; but, worse, it's a subscription.
Is there any free for personal use static stress simulation software? Is there some way to restore locally computed simulation to fusion 360? Is there some other viable solution?


texts: What should be the density of a compressed gas while measuring the flow rate using Rotameter?

texts:
Say we have a required mass flow rate, in order to have equivalent volume flow rate, we need to consider density of the operating fluid (compressible fluid).

To measure the  volume flow rate in LPM, I'm using a rotameter. I'm controlling the flow using a needle valve upstream of the rotameter. The regulated pressure upstream of the needle valve is 20 bar and the pressure downstream the rotameter is ambient (1 atm).

Should I consider the density of the operating fluid (say oxygen) relating to the upstream pressure (20 bar) or the downstream (1 bar ambient)


texts: How do renewable energy sources deal with reactive loads?

texts: If a power grid were to fully switch to renewable power generation methods how would they deal with reactive loads?


texts: How large of an area of the earth's surface would we need to cover in mirrors to negate global warming?

texts:
How large of an area of the earth's surface would we need to cover in mirrors to negate current levels of global warming?

Let's assume that the reflective component of the mirror is made of aluminium foil and that it is kept clean.

And let's also forget about ocean acidification. I'm only really interested in negating the retained heat component of atmospheric carbon.

This question was initially asked here on physics.stackexchange but was rejected because it "was an engineering question".


texts: What colour of tarp will let in the least amount of heat?

texts:
Source: Low Tunnel Construction: How to Build a Mini Hoop House

I have a small greenhouse that I want to keep as cold as possible in the spring. I plan to cover the greenhouse with a polyethylene tarp to shield it's contents from the sun.

However, I'm not sure what colour of tarp would be the most effective at shielding heat.

I suspect that light coloured tarps would allow for solar gain. And I wonder if a black tarp might also retain warmth by absorbing heat from the sun.

Question:

Are there specific colours of material that are known to let in the least amount of heat?


texts:
The process of punching a soft material uses a hallow punch with beveled and sharpened edges that is driven into the material. The backing material is usually a soft metal or wood.

I am working on such a process and have a few questions for the community.
I am punching 3 mm discs of thickness 0.2 mm from a elastomer material with tensile modulus of 220 MPa and a max tensile strength of 35 MPa. The disc remains within the hallow punch and is extracted afterwards.

I have measured the force required to punch using a force gauge and found that 140 N was required to punch and retain the disk.

The end process will use a pneumatic cylinder to drive the punch.

1) Is the punch force calculation the following - "Punch Force = perimeter x thickness x shear stress"? Can the shear stress be equated to the materials tensile strength? Using the above, I get a punch force of 66 N. This is well below what is measured using the gauge. Why?

2) What is the effect of a blunt or dull blade on the punch force? Hows does the blades increase in contact area influence the punch force (shear)?

3) In the above example, what is the relationship between the normal force/pressure to the punch force?

4) How would you select a backing material? Softer than the punch's material (HSS Steel), but not too soft as to deform when struck by the punch?

Thanks.


texts: Estimating fan CFM from RPM, HP, and diameter

texts:
I am trying to determine the approximate CFM of several axial flow fans being used in agricultural storage in the developing world. The only information the storers have is the power, RPM, and diameter of their fans.

I would like to estimate the CFM at various levels of Static Pressure, and within a range of likely blade pitches.

Is there a way to to do this? I've looked at the fan laws, but it seems like these are meant to calculate changes in variables, not the absolute values of the variables themselves.

Thanks.


texts: Guidelines to develop quality engineering training content and select a trainer

texts:
Our organization has recognized the need to improve quality of both incoming material and outgoing products. Our products are primarily electrical/electronic but mechanical components are an integral part of the end product.  As result of sharing insight gained from this question and other public articles in process improvement, I was able to get management's attention concerning the possible need for additional training for team members in quality engineering.  So management asked me to provide a high level proposal for a quality engineering training program with a focus on six-sigma principles. This leads me to ask two questions which I believe are related:

What are the most commonly used statistical tools in quality
engineering?
What should be the focus when looking for a six sigma
consultant to train a manufacturing engineering organization?


texts:
Sinkholes have been known to occur in the middle of cities or other locations where they affect buildings:

Some areas are more prone to sinkholes than other areas because of the presence of old mines or limestone bedrock. Even in these areas where sinkholes are more common, humans continue to build buildings and even airports.

How do engineers prevent or mitigate sinkholes? Is it as low-tech as dumping in rock until no more fits?


texts: what is the commercial name of active power filters?

texts:
I've been studying for a while now topics related to power quality issues, such as harmonics caused by non-linear loads and power converters, and I've been working on Active Power Filters, but since I live in developing country sadly all we have is theoretical knowledge, So I appreciate if you add any professional knowledge to those conversation.

What is the commercial name of an active power filter (if I write
that under electronics in Amazon, it doesn't give me any result)
Same question goes to Unified Power Quality Controller ? (I can't
find those in Amazon too)
What are the main manufacturers of those devices in the world?
Could you recommend any good readings about this topic to have an
idea about the industrial and marketing field


texts: How is electrical building code defined and applied to new constructions?

texts:
A new home (completed in early 2020) in San Jose California does not have GFCI outlets in all the bathrooms. I thought this was a requirement (according to https://www.redwoodcity.org/home/showdocument?id=15416). There are also some kitchen outlets that don't seem to follow this code. I'm not sure whether the builder has overlooked this or there is some loophole to the rule (such as when the builder got approval for the plans).
In general, I'd like a better understanding of how building code is defined and enforced. E.g. what level is it defined (municipal/state/federal) and how it is applied to buildings. Ultimately I'd like to know if the builder made a mistake or if I'm uninformed.


texts: Why is buckling said to be independent of material strength?

texts:
In many sources, such as here, it is said that buckling failure is independent of the material's strength.

But in many building codes, yield stress of the material is a factor that changes the allowed buckling load. The Perry-Robertson formula for example, which is the basis for buckling curves in Eurocode has yield stress as a parameter. The formula is derived by assuming initial curvature on a beam and solving for the allowed load so that yield stress is not reached in the cross section of the beam. So clearly yield stress affects the magnitude of allowed load against buckling. So why is it correct to say that buckling has nothing to do with yielding?


texts: I've seen the terms "SCADA boxes", "SCADA out-of-the-box", "SCADA turnkey systems" used in various articles but without a definition. I'd like to know whether the terms are synonymous and if not what is the "generally accepted" concept of a "SCADA box"?


texts:
I'm having trouble with this problem:

G and a are given, and we are asked to calculate A, B and C.

What I've Done:
The first thing I tried was a free body diagram cutting through A and C to create one body and C and B to create another.

From here I calculated $A_y$ and $C_y$ as being equal to $-G\frac{\sqrt{2}}{4}$
Then I moved onto the second body:

Here I ran into problems immediately. If I placed the moment at either B or C then it follows that the x component of the other must be zero, which it isn't (I have a numerical solution). So I've either made a mistake with my free body diagram or I'm doing something wrong with the second moment.

Here are my equalibrium calculations:
Body 1:
$$\Sigma M^{A}=C_y\cdot 2a+G\frac{\sqrt{2}}{2}=0 \\
\Sigma F_x=A_x-C_x+G\frac{\sqrt{2}}{2}=0 \\
\Sigma F_y=A_y+C_y+G\frac{\sqrt{2}}{2}=0$$

Body 2:
$$\Sigma M^{B}=3a\cdot C_x=0 \\
\Sigma F_x=C_x+B_x=0 \\
\Sigma F_y=B_y-C_y=0$$

My results obviously make no sense. What am I doing wrong? I have also tried to calculate for the whole structure but there were too many unknows which I couldn't get rid of.


texts: Steering wheel torque when car is turning

texts:
How can I calculate the torque that is needed to keep the steering wheel at the same steering angle during turning at given speed?

Example case:

A car with Ackermann steering geometry weights 1000 kg. It is going though a curve - the steering angle is constant 5 degrees. Car's velocity is 10 m/s. Steering ratio is 15:1 (15 degrees on steering wheel means 1 degree of actual steering angle). What torque do I need to apply to the steering wheel to hold those constant 5 degrees on steering?

Reasons:

I need to know the torque because I want to robotize steering of a passenger vehicle and since torque will be applied by human driver's hands I need to supply such torque by an electric motor (probably a stepper with a required "holding torque" specification).

I know the torque could probably somehow measured on the steering wheel (with a torque wrench) with power steering off but it would be nice to be able to at least roughly calculate it. I actually need to know all torques for all car's normal operation scenarios (turning when standing still, when turning in speed, when going through a curve etc.).

EDIT:

I may have forgotten few parameters for the example. Say car's width is 1.5m (tire to tire) and distance between front and read axle is 2m.


texts: Are super-batteries theoretically possible?

texts:
Is it theoretically possible and/or economically viable to construct batteries capable of supplying an entire city with electricity for a day or two?

One of the big problems with power plants of any kind is waste motion. The turbines keep churning, the head of steam continues to form, during the off-hours. If we could somehow store all that energy for later use, we would need a lot fewer power plants, and would be able to spare a lot of resources.

Is anyone working on this, or is it just not worth it? Would batteries of this kind do more harm than good?


texts:
I need a vacuum pump to provide at least 21" Hg of vacuum. Looking at the cheap rotary pumps on ebay, this one seems to be way more than fit for the job.

Is there a way though I can regulate it though to provide lets say around 15-20" Hg? This isn't a vacuum chamber or something and I don't want to have a crazy amount of vacuum.


texts: Minimum distance between long curtains and radiator for good air flow?

texts:
It's a known fact that you cannot place a curtain near a radiator because it will trap hot air behind the curtain and also block cold air from going through the radiator from bellow.

But obviously there must be a minimum distance you can place a curtain that goes from ceiling to floor in front of the radiator that would allow it to do its normal work. What is this distance in centimeters(hopefully) ?


texts: How to calculate the heading of an aircraft given coordinates from the ground

texts:
I'm trying to figure out how to calculate the heading and flight path of an aircraft when it's measured from the ground. I literally have no idea where to start.
The coordinates from the ground are (-5.60, -20.91, 24.14) and the aircraft's speed is 374.16 n mi/hr
I'm really just looking for a formula or directions to a good resource, not looking for the problem to be solved.


texts:
If I pour a sample of aggregate into a container full of water and measure the displacement of the water due to the sample, does this give me Bulk Volume or Solid Volume?

And what is the difference?


texts: Is there any method to recycle air-pollution into fertilizer?

texts:
Vehicles and Factories produce air-pollution like Nitrogen Dioxide(NO2) and Sulfur Dioxide(SO2).

Plants use Fertilizer with those same compounds (NO2 & SO2)

So, by what method can air-pollution be captured, and recycled as fertilizer ?


texts: How to detect milk spillage or milk boil?

texts:
In my country we generally boil milk before we drink. Often the milk heats up and spills from the pot. I want to detect milk boil before it spills off.I am thinking of a thermal camera solution that reads the temperature of liquid, but again it should be small enough to fit beside the gas stove. I have knowledge of python and arduino.

Please give me some ideas which works without physically touching the milk.


texts:
I have a motor coupled over a synchronous belt (AT5) to a bigger tooth wheel (1:4), and the problem comes up that the belt is moving up or down (depending on the rotation direction) until it reaches the edge of the motor pulley (with flanged wheel). This leads to a noisy belt and the belt will probably be damaged over time.
The alignment of the motor axis with the other transmission axis is as good as possible and I also tried a different test stand, but I always see the same problem. So this seems to come from how the endless belts are manufactured.
I may use a phase, but I'm unsure if this is normally used and if the belt gets damaged from the phase?
So my questions is, how can I prevent the belt from walking up and down on the synchrounous pulley?


texts: How they put heavy cranes on top of the building?

texts: I saw crane on very tall building. How do they put such heavy item on such high building?


texts:
Is there generally any cheaper way to get a bunch of gear wheels. I've been to some local companies who specialize in gear production and the price is always somewhere in the range 100-150 USD for a single gear. This is well beyond what I'm willing to pay.

As a side question, why are the prices so high? I understand that the machine has to be set such that it must cut my desired dimensions but $100 is 3 days wage in my area and surely it wont take 3 days to set it up, nor does it consume anything?


texts: Why there are grooves at inner side of plastic nasal spray cap?

texts: My suggestion was that they are for Tamper-evident band, but there isn't one beneath the cap.


texts: Does weathering steel corrode the same as carbon steel when it doesn't develop a protective patina?

texts:
Weathering steel is supposed to form a protective patina when exposed to wetting and drying cycles. This protective patina prevents more corrosion from occurring. This is what differentiates it from regular (carbon) steel.

In a situation where the environment does not allow the patina to form, does weathering steel perform any differently than carbon steel?

I am thinking that there might be situations where weathering steel without a patina might actually corrode faster (perform worse) than carbon steel. The alloy differences may cause the change.

My situation is a steel deck with a layer of aggregate on top. The aggregate will likely keep the top of the deck from ever completely drying or at least greatly slow the process. This will keep a patina from forming. Various people that I have talked with at the client have said that they would rather have carbon steel instead of weathering steel. They seem to think that it will perform better.

I know that the real answer is to provide a layer of protection (waterproofing, paint, etc.) over the steel, but this is not an option. I wanted to provide my exact situation in case someone requests specifics.


texts: Why do small gears used to turn big gears allow more force with less effort?

texts:
If I have a small gear that I am turning a large gear with, from what I know that gives me the ability to move heavier things.  Like a winch of sorts.  Why does turning that little gear allow that mechanical advantage.  I saw a video that said gears were really lots of levers. I can’t visualize the lever.

In a car, for example, why is first gear more powerful that fifth for initial movement?  I don't know how to visualize it.  In order for me to lift a car with a lever, I need a fulcrum close to the car and an effort arm fairly long (I guess).  So where's the fulcrum and effort arm in the gear moving the car here?

Is my question worded correctly for what I ask in the body?

edit:  Am I correct that gears in a car transmission are mostly for ratio aspect of things?  if I look at two gears together, I can see the ratio and one turning twice as much as another.  But what is missing is the longer arm that eased the effort.  Is that "effort arm" replaced with a strong source of power (an engine) to make up for the missing long effort arm?

edit:  This is the video I saw that made me think about it, https://youtu.be/odpsm3ybPsA?t=3m5s  I started it at the point I'm asking about.  It's pretty quick for the part I'm talking about, maybe 2 minutes.  You see that guy turning the crank to move that little gear?  See the long crank, the "effort arm"?  That looks like a lever to me.

Then I saw images somewhere, that had similar ideas and it was showing the crank, like on a well crank, being the "circle" or wheel moving the axle which turns the small gear.

In a car though you don't have that big wheel to turn first.  You have the small drive shaft.  Is there a bigger wheel or gear I am missing?  One that is rotating before the first small gear that turns the big one?  edit:  Is this the flywheel?


texts: Designing a good downscaled compaction test

texts:
When storing a large amount of polymer material, afterwards we are experiencing bad flow properties during processing. We expect it is due to storing the material for long periods of time at high temperature and humidity in our warehouse.

I want to do some small scale test to reproduce the conditions and test a number of additives to enhance the flow properties of the material. We want to have a relatively small amount ($3\,\mathrm{kg}$) of material in a box and add weights to simulate the weight of the $500\,\mathrm{kg}$ box.

Are there any standardized test for these types of compaction test?
How do I determine the weights needed to simulate the weight of a $500\,\mathrm{kg}$?

An attempt at answering question 2 was made by assuming we want the same pressure on the large box as on the test scale. In the large box, assuming the material a hydrostatic fluid, it experiences a pressure at the bottom of the box:

$$ P = \rho_b g h \approx 10\,\mathrm{kPa} $$

where I have assumed a bulk material density $\rho_b=500\,\mathrm{kg/m^3}$, gravitational acceleration $g\approx10\,\mathrm{m/s^2}$ and a material height $h=2\,\mathrm{m}$. At the test scale we then need to provide the same pressure by applying a force:
$$ F=m_tg=PA_t \rightarrow m_t={{PA_t}\over{g}}=\rho_bA_th=50\,\mathrm{kg}$$

for test box with area $A_t=0.1\,\mathrm{m^2}$.

The polymer is a TPE (SEBS) with about 10% oil by weight, Shore 60 hardness but flexible when compounded.


texts: Can Sheet Metal Be Formed With Bends At Weld Joints?

texts:
I understand that a weld, if done properly, is stronger than the base metal. Does this mean that if you have a part that needs to be formed, the bend can be made along the weld? Or is the weld filler more brittle or have some other material property that would prevent this?
As an example, I have the part in the image below. It is to be formed with bend lines at the green dashed lines. Due to manufacturing limitations, I cannot form the entire part at once, so I have to split it, form it and re-weld it. I can split it anywhere along the length of the part. But, out of curiosity, I'm wondering if I can make a vertical cut on one of the green dashed lines (indicating a bend line), form the parts separately, weld them back together, and make the final bend along the weld joint.
The welding process is TIG. The base metal is 1100 Al, which is welded on both sides with 1100 Al filler.


texts: What happens if current provided to mono phase motor is less than rated power

texts:
I have a 0.5 kW single-phase AC motor. What happens if the supply is 220 V but can't supply the full current needed? Will the motor torque be lower? Or will it be slower?

Will it be any different if this motor is a water pump motor?


texts: Commercial electric motor with integrated torque sensor and torque control

texts:
Are there any commercial solutions for electric rotary motors with integrated torque sensor and torque control?

I'm only aware of www.sensodrive.de which are essentially the drives used in the DLR/Kuka Light Weight Robot. But those use harmonic drives (gear ratio of 1/100, < 10 RPM). I need something with much higher RPM and lower torque range (less than 0.01 Nm resolution would be good). Up to 300-1000 RPM but no more than 5 Nm torque is required. So something with a small gear ratio or no gear at all.


texts: Can Siphoned water travel a distance of 2500 ft with a height difference of 10 ft?

texts:
I have access to lake water.  My land is situated in the back of this lake. In summer, water in the lake shrinks to a distance of about 2000 to 2350 ft away from my land. My land is 10 feet above the water surface level. So I want to draw this water through a siphon. Can this work, if I dug up 10 ft depth near the land as the distance is 2000 to 2500 ft? The depth of water from the surface level of the water is around 15 ft.
ETA:
"350 lpm is sufficient for my 15.5 Acres of lands."  "I would like to use 2.5-inch pipe [ID or OD not specified by the OP]"


texts: Help with a simple calculation of the required mass for a counter-weight for a horizontal hatch

texts:
Hello fellow engineers,

A friend is part-way building an outside storage chest. For whatever reason, the materials and size of storage that he is going for means that the door is heavy to lift and not very practical. I've suggested that he manufacture a counterweight system to aid in opening the door.

I've made an attempt to calculate the required weight by modelling using simple moments and balancing forces, but I'm not happy with the result as I'm pretty sure I'm missing things from my model.

Please see this sketch and my 2 calculation sets. (I've modeled this as a simple statics pulley sort of problem.)

Since I've modeled this as a statics problem, my issue becomes how to account for the force applied by the person lifting the door, which I have assumed would be applied at the eyelet.

Assuming my equations are correct, as theta increases, T1 should decrease since M2 is obviously constant. But isn't tension constant?

I think I'm nearly there but perhaps need a push in the right direction... It's been a while since I've done something like this!

Thanks.


texts:
Chapter 4, Part 3 of the MEPDG (Mechanistic Empirical Pavement Design Guide) states

  "The 'effective' dynamic k-value represents the compressibility of all pavement layers beneath the PCC slab and base course".

However, the Manual of Practice for the MEPDG states

  "The effective k-value, therefore, essentially represents the compressibility of underlying layers (i.e. unbound base, subbase, and subgrade layers) upon which the upper bound layers and existing HMA or PCC layers are constructed."

I find these two definitions contradictory in regards of the inclusion or not of the base layer in the k-value estimation.

I have two questions:

1)  Does the k-value represents all layers beneath the PCC slab or only all layers beneath the PCC slab and base?

2) Is the static backcalculated k-value from the FWD data the value I should enter directly as input in the Rigid Pavement Rehabilitation analysis in Pavement ME Design?


texts: Can I charge 18650 Li-ion cell from 5 V USB?

texts:
I've got a flashlight with a 3.7 V 18650 cell that charges with a 3.5 mm barrel plug.  They provided adapter that says 4.2 V +/- 0.5.  Can I use a 5 V USB to barrel plug adapter to charge it?

UPDATE
So the adapter clearly says +- .5 v.  Is this an obvious misprint. It must be .05 right?


texts: How do you determine the L/D ratio of F-117 Nighthawk?

texts:
I was trying to look for an L/D ratio published everywhere on the web and I can't seem to find it (for a project). Since I couldn't find it, I wanted to try calculating myself. Can't seem to find $C_l$ or $C_d$ though without some sort of paywall on research papers.

The equations are:

L = $\frac{1}{2} C_{l} \cdot \rho v^2 A$

D = $\frac{1}{2} C_{d} \cdot \rho v^2 A$

So L/D would just be:

$\frac{L}{D} = \frac{C_l}{C_d}$

or would the effective area be different for L and D, where L is the area of the top/bottom view of the plane, and D is the area of the front/back view?

The only quantities I have are:

v = Mach 0.92 = 315.62 $\frac{m}{s}$..............................top speed

$\rho$ = 0.003996 $\frac{kg}{m^3}$....................density of air at 40,000 ft (assuming it's flying at its maximum altitude)

I couldn't really find any area of the plane; only wingspan and vertical length, but that would give an inaccurate area of the plane. How would I determine this? If $\frac{L}{D}$ is just $\frac{C_l}{C_d}$ does anyone happen to know $C_l$ and $C_d$? Thank you in advance.


texts:
In framing the question, I can't be more specific as I have no idea (though a suspicion) about what this came from.

I have a number of them that are several different diameters from 125mm to about 300mm.
They are very thin steel (< 1mm) and each size came in a tight stack, as though laminated.  They don't seem to have been glued together as they come apart easily.  We have had them for about 20 years.  Note the notch at 7 o'clock possibly to align or secure a stack.
I suspect they are part of some sort of electrical winding, but I would have thought they would have "teeth" on the outside.
Any ideas what they came from?
Nowadays they are part of an art project.


texts: Estimating rate of drying by comparing identical process with different ambient humidity

texts:
We have a drying process where we take a thin bread product and cool it in a room at 11 C and 90% relative humidity. The product comes in at 80 C and comes out at 22 C. There is air blowing across the product. Because of the design of the room (nearly a sealed box) it is hard to estimate the water gain of the air before and after passing the product.

I would like to size a dehumidifier to keep the cooling room at 60% relative humidity - however I need to estimate how much water I need to removing from the air. We would adjust the temperature to ensure that the product is 22 C at the end of the cooling process.

I can estimate how much evaporation is occurring at 90% relative humidity by doing a simple mass balance - however this will be higher at 60% relative humidity.

I was wondering what the best approach is to take data from the 90% relative humidity condition and make a back of the envelope estimate of an evaporation rate at 60% relative humidity?

At the moment I'm thinking of assuming the rate limiting step is mass diffusion between the air at the surface of the wrap (100% relative humidity) and the ambient humidity. If I do that then maybe the rate is merely proportional to the water kg of the air at the ambient humidity vs 100%?

Thanks in advance


texts: Reverse-engineering spur gears - do I have enough data to make a gear that will mesh correctly?

texts:
I'm trying to reverse engineer a set of spur gears that I have on a model RC car, but they are tiny, so there's a limit to what I can measure with my calipers.  My plan is to create a new gear design with a few important changes that will mesh with these existing gears, then have it professionally 3d printed in nylon.

I've used this image as a reference for what data I might want to obtain:

And here's an image of the gears in question:

So far I have these measurements for each gear:

Gear 1:

Teeth:  10
Pitch Diameter: 5mm
Outside Diameter: 6mm
Root Diameter: 4mm

Gear 2:

Teeth: 22
Pitch Diameter: 11mm
Outside Diameter: 12mm
Root Diameter: 9.5mm

Note:  I don't know how to obtain the base diameter, only the root diameter, since the base diameter doesn't seem to be directly measurable.  Also, the pitch diameters are a guess, but I'm assuming for simplicity the people who designed them probably picked 5mm and 11mm to go with 10 and 22 teeth respectively.  It's the sort of thing I'd probably do.  Also it matches with the centre-to-centre measurement of the meshed gears being 8mm, which is the same as (5mm + 11mm)/2.

I'm thinking of using this OpenSCAD script to replicate the gear designs:

https://github.com/openscad/MCAD/blob/dev/gears/involute_gears.scad

Do I have enough data to make a replica of these gears using that script?  If not, what else do I need?  The script's comments seem to indicate that I need to know the pressure angle, but looking at the diagram I linked, I can only figure that out if I have the base diameters.


texts: Does solidworks store license and user information inside files?

texts:
For patent and security issues I want to know if SolidWorks (relevant versions are 2012, 2015 and 2016) stores user, license and further metadata inside .sldprt, .sldasm and .slddrw files.

If so:
Are there measures of evaluating the metadata and/or tampering it?

Is there a way to circumvent the delivery of metadata by e.g. exporting as STEP?


texts:
I am looking for feedback on my camera rig design. I am going to run a track along the ceiling of my studio to move my camera back in forth. I also want the camera to be able to pan, so I want to incorporate one of my spare nema 17 stepper motors. Below is a rough sketch of my proposed design.

A couple concerns I have:
1. Is this too much axial load on the stepper motor shaft? The camera weighs about 2.5 lbs including the housing that will attach to the flange.
2. The flange is attached to the stepper motor by a set screw. I do not want the safety of my camera to rely on a set screw as this is mounted from the ceiling.

Any design suggestions would be very helpful. Thank you!


texts: Lengths of Connectors in Steering Linkage

texts: Below is a picture 4-wheel vehicle steering linkage. I figured that in order to steer correctly $(W+D)tan\theta_1=Dtan\theta_2$ where $\theta_1$ is the angle of the outside front wheel, $\theta_2$ is the angle of the inside front wheel, $W$ is the distance between the two front wheels, and $D$ is the radius of curvature of the arc the rear inside wheel follows. The front wheels are the ones at the bottom of the picture. How can I figure out what lengths of the segments of the linkage will satisfy the equation for all values of $\theta_1$, $\theta_2$, and $D$?


texts: How many power strokes per rotation in a 3 cylinder engine?

texts: How many power strokes occur for every complete rotation in a regular 3-cylinder engine? Or in other words, every how many degrees does a new power stroke takes place? Does anyone know please?


texts: Convective fix for air conditioning dilemma?

texts:
I live in a part of Mexico that can get really hot in the summer. I've got an un-airconditioned bedroom on the other side of a wall from a room cooled by a powerful Mirage mini-split AC.

The problem is that the only communication between the two rooms currently is the bedroom doorway which opens from a shared hallway.  This is insufficient because of the dead air volume above the doorway (the ceiling is inclined similarly to that over the AC unit). Please see pictures for reference.

My idea is to bore two holes 8-10 inches in diameter through the wall as shown in the detail shot. The purpose would be to establish a convection loop, where the hot air from top of the bedroom would flow out into the area of the AC unit (and be entrained in the cool air flow from it). To compensate for the reduction in pressure, cold air would replace the ventilated hot air by flowing in through the hallway and into the bedroom doorway. I understand that this scheme, if it works, will probably put an additional load on the AC. That's acceptable.

I haven't done any math on this idea (indeed, I'm not sure what math to do), but am just guessing at the size of the holes. Intuitively, it seems feasible.

Any thoughts on whether this would be effective before I get out my chisel and hammer?

Overview shot to demonstrate problem:

Detail shot, with proposed holes:

Update:

First, many thanks to all who responded, and particularly for the exhaustive analysis provided by Olin. The hole is being cut now, and the design has changed due to some unforeseen realities in the masonry. It will now be a rectangular opening about 12" x 20", with the top corner about 6" from the ceiling and wall. I'll report back on the outcome, and whether a fan is necessary.

Thanks again!


texts: Determine abs pressure in a tank where the atm and vac pressures are given

texts:
Given:

A problem in my thermodynamics text reads as follows...

A vacuum gauge connected to a tank reads $5.4\cdot psi$ at a location where the barometric reading $P_{Hg}= 28.5\cdot in$. Determine the absolute pressure in the tank. Take $\rho_{Hg} = 848.4\frac{lbm}{ft^3}$.

My Solution:

The formula for a vacuum gauge is as follows...

$$P_{vac}=P_{atm}-P_{abs}$$

Rewrite as...

$$P_{abs}=P_{atm}-P_{vac}$$

Determine atmospheric pressure but first convert $ft$ units to $in$ since that is how we traditionally define pressures in English units...

$$P_{atm}=\rho g h$$

$$\rho=848.4\cdot\frac{lbm}{ft^3}\times\frac{ft^3}{(12in)^3}=.4910\cdot\frac{lbm}{in^3}$$

$$g=32.174\cdot\frac{ft}{s^2}\times\frac{12in}{ft}=386.0\cdot\frac{in}{s^2}$$

$$P_{atm}=.4910\cdot\frac{lbm}{in^3}\times386.0\cdot\frac{in}{s^2}\times28.5\cdot in=5402\cdot\frac{lbm}{in\cdot s^2}$$

Question:

The atmospheric pressure obtained cannot be right because the scalar value $5402$ is no where near $14.7$ and the units obtained ($\frac{lbm}{in\cdot s^2}$) look completely wrong. Shouldn't they be $\frac{lbf}{in^2}$? Where did I go wrong? After this is solved I know how to obtain the absolute pressure in the tank so I shall stop here.


texts:
Currently I am powering a worm to drive a worm gear that is pinned together on the same shaft to a spur gear to drive another spur gear.

I would like to simplify the process.

Is there a way to power a worm that drives a worm gear to mesh with another worm gear as spur gears mesh together?


texts: How to properly fit almuminum glass window without leakage?

texts:
I got a brick-wall house.  The wall is 25cm thick.  I want to add windows.  There are 2 ways of adding a window:

Adding the window on the inside side of the wall, so that if the aluminium frame of the window is 5cm deep, it means that there will be a 20cm of the wall exposed as "outside of house area".
Another option is to install the window on the outside side, so that the 20cm of the wall will be inside of the house, where I can make better use of it.

I like option (2), but the problem is that I heard rumours that (2) causes water leakage and that I better follow (1).

I am really doubtful of this rumour, and I think the real issue might be that the installation is not done properly.

My questions:

Is the rumour correct?  And why?
Any special installations procedures for (2) to avoid water leakage?
If I adopt (2), should I leave some small wall-lip on the outside?  E.g. instead of making the window flush against the outer wall, I pull it inwards by, say, 2cm, so that the after installing the 5cm-thick aluminum frame, 18cm is inside the house, 2cm outside the house?


texts: How different are dc motor designs from dc generator designs?

texts:
Some dc motors can be used as generators as well by applying mechanical torque to the output shaft to induce a current.  However, even if a dc motor can do this, I imagine they were not designed for this purpose and thus perform less efficiently when used as a generator rather than as a motor.

In my admittedly naive understanding, dc generators and dc motors are essentially the same machinery, but with inputs and outputs reversed.   This leads me to believe that some other design considerations are used to make one direction more efficient than the other.

How differently are dc generators and dc motors designed to make one direction of input/output more efficient than the other?  What can one do electrically or mechanically to improve the efficiency in either direction?

In particular, I'm interested in converting a dc motor into a generator and want to know how I can improve its efficiency in converting mechanical energy into electrical energy.


texts: Is it possible to create a sub-surface pond?

texts:
Has anyone designed a pond that extends beyond its surface perimeter?

Example cross section:

brown - existing surface (or brought to grade)
black - designed pond
blue - capacity


texts: Method for permanent adjustment of pitch and roll of a mounting plate

texts:
I have a 2D lidar mounted to a plate on a robot. I am looking for a method to adjust the pitch and roll of the plate so the plane of the laser is parallel to the ground.

Currently, I am using thin metal shims, but I want to find an easier method that will last. I was thinking about using set screws, but I've been told that it's a bad idea because they will inevitably come loose due to vibrations.

What other methods exist for adjusting the roll and pitch of a mounting plate? Are there any specially engineered solutions for this?

For reference, I'm using a Hokuyo 20Lx lidar.


texts:
I have general problem of understanding how forces are transfered from 3d members problem to plane problem.

For example what would be 2D representation of forces F1 and F2 acting on horizontal A beam, and what will be effect of beam A,B,C,D and column 1 and 2 on horizontal A beam.

How can I represent horizontal beam A in 2D so I can do calculations of bending moment, shear forces etc.

All joints can be considered as welded.

EDIT  (After Mr. Wasabis answer)

I can replace influence of force F1 with reactions of beam B

so reactions are influencing horizontal A (beam C and F2 are igonred for simplicity). Is this OK - With moment Ms1 in plane perpendicular to horizontal A causing torsion of horizonta A.


texts: Calcultate speed from accelerometer for runner

texts:
I hope you are well.

I am writing to you because I am working on a sports project and I have a little trouble interpreting my results.

we placed the accelerometer on the legof a runner and we have the acceleration data of the player according to the 3 axes (x,y,z) according to the points of measurement (1 point = 2.6ms).

I have for the moment considered that the acceleration (m/ms) in y and I get this for 200 points:

I subtract 9.81 from my data and then I calculate the integral of this function by the method of the strangles on the left and i get this :

I have several questions to ask you: - Knowing that the accelerometer is placed on one leg of the runner, How can I determine the speed of the runner according to the result of my integral? what conversion do I have to do? - Finally, should I also consider the speed in x and z?

Thanks a lot for your help.


texts:
About all those oil tankers off the coast of California … | Grist

  The giant ships burn fuel to keep lights on, power equipment, and heat the large volumes of crude oil resting in their tanks.

I'm assuming that crude oil can't be heated in steel frac tanks, places other than salt caverns, and salt caverns.

  While underground caverns may not seem like the best place to store an emergency oil supply, they're actually very secure. For one thing, since they're 2,000 to 4,000 feet (610 to 1,219 meters) underground, the extreme pressure prevents cracks from forming and leading to leaks [source: DOE]. Also, the natural temperature difference between the top and bottom of each cavern encourages the oil to circulate, which maintains its quality.


texts: What is "water surface elevation" and "headwater"?

texts:
I want to understand the meaning of headwater, and I stumble across this page, and this diagram:

This is where it got me. Headwater is defined as

  measured from the flow line (invert) of the culvert inlet, to the
  water surface elevation

But I have no idea what does water surface elevation mean. Is it the actual water surface ( doesn't look like it as there is another normal water surface elevation)?

And if it's not, what it is, and how it is being defined?


texts: Why would the flexural modulus be different than the elastic modulus?

texts:
I'm reading the Wikipedia page on flexural modulus. It is said:

  Ideally, flexural or bending modulus of elasticity is equivalent to the tensile modulus (Young's modulus) or compressive modulus of elasticity. In reality, these values may be different, especially for polymers.

But how can they be different? Young's/elastic modulus is measured in the tensile test, by pulling a sample of the material and measuring the stress/strain response. In the bending test we bend the sample instead, but the fibers at the bottom (as seen in the picture) are in tension. Thus, if we inspect as small sample at the bottom of the beam, it is subject to tensile forces only and it should therefore behave in the same way as if the sample was being subjected to the tensile test. How does the sample know it is part of a beam being bent instead of being a part of a beam being pulled? How can the two moduli be different? The article mentions polymers specifically, but do the moduli differ for metals as well?


texts: Calculating the Braking Energy of a vehicle

texts:
you might find my question stupid. I am unfortunately not an engineer and didn't find the answer on google.
I want to calculate the braking energy of a vehicle decelerating from v2 to v1 (km/h). Given are the Wheel inertia mass moment "I" and the wheel diameter "d" as well as the vehicle mass "M".

Could you give me the equation needed for that?

Thank you !


texts: What are heat sink options for a circulating-water cooling vest?

texts:
I am in a first-year engineering design group where we are in the process of designing a cooling vest for motorcyclists for use in the city (1-2h length). Water will circulate through the vest, absorbing body heat, and then that heat will be dumped into a heat sink.

We initially decided on using Peltier chips for our heat sink, but when we brought this up with our instructor he was unenthusiastic (they are highly inefficient apparently). Then we decided to look into short-acting (1-2h) endothermic chemical reactions, but here ran into information overload.

What kind of practical options are there for such a heat sink?


texts:
The question given is

A uniform rod, of mass $m$ and length $2a$ smoothly hinged to a vertical wall is connected to a point on the wall above the hinge by a light inelastic string. Find the magnitude and direction of the force on the rod from the hinge.

The diagram given is

I have constructed the forces on to the freebody diagram as such

Using the vertical component of net force:
$$F_x=T \sin(20)-mg+R_V=0$$
$$\implies T\sin(20)=mg-R_V$$
Using the horizontal component of net force:
$$F_y=T \cos(20)-R_H=0$$
$$\implies T\cos(20)=R_H$$
$$\implies T=\frac{R_H}{\cos(20)}$$
Finding the moment around the hinge A:
$$\tau=T\sin(20)*2a\sin(50)-mg*a\sin(50)=0$$
$$\implies T\sin(20)=\frac{mg}{2}$$
$$\implies T=\frac{mg}{2\sin(20)}$$
Then, equating the two equations for $T\sin(20)$ I get:
$$\frac{mg}{2}=mg-R_V$$
$$\implies 2R_V=mg$$
Finally equating both equations for $T$:
$$\frac{mg}{2\sin(20)}=\frac{R_H}{\cos(20)}$$
$$\implies \frac{2R_V}{2\sin(20)}=\frac{R_H}{\cos(20)}$$
$$\implies \frac{R_V}{R_H}=\frac{\sin(20)}{\cos(20)}$$
And since $R_V,R_H$ are the vertical and horizontal components of the same force respectively, the $tan^{-1}$ of this ratio is equal to the angle between the resultant and the horizontal hence:
$$\tan^{-1}(\frac{\sin(20)}{\cos(20)})=20°$$
Which is wrong as the answer given in the book is that the angle is $82.7°$ and the reaction force is $0.474mg$, I am aware that this entire method is a hackjob but I have no clue on how to tackle this question properly, are the reaction forces I drew the problem or is it my working onwards?
How would I tackle this problem properly?


texts: Why do some pipelines have regular 90 degree deviations?

texts:
On this satellite image, there are pipelines extending from a terminal at sea to an LNG (Liquid Natural Gas) storage facility.  Why do the pipelines, at regular intervals, deviated from a straight line?

Is it a simple way to prevent / dampen shock waves from passing through the liquids from one end to the other and damaging equipment on the other end?  Could you use baffles in the pipes instead?  Would baffles significantly increase drag whilst these deviations increase resistance only slightly (due to longer pipe and forcing fluid to change direction multiple times)?

https://www.google.com/maps/@51.4402401,0.6996781,959m/data=!3m1!1e3