texts:
We develop a test station where we might have H2 leakage.

To prevent explosion we are considering intertisation using N2 gas (primary explosion protection).

However we also want to detect leakage events.

We are searching for a sensor, which (ideally) has the following characteristics:

Reliable H2 readings in Air and N2/Air mixtures
Temperature range -55 °C  .. 80 °C
Range, 0 .. LEL (4% vol-N2)
t90 smaller 15s
ATEX certified
PL according to EN ISO 13849-1
less than 5000 USD
combination of sensors also possible
First point is mandatory. In the otherpoints compromises are possible.

Sensors on the catalytic of electrochemical type seem to rely on O2. I have found sensors based on thermal conductivity, but these seem to have a bigger range and cost.

Any idea, what to use?


texts: Why was a coil chosen over a straight for this overbridge?

texts: I saw this meme on Facebook showing a coiled railway overbridge and an alternative plan. I replied that straightening that overbridge will force it to start at the other side of the road, and you need to build a u-turn and there is a valuable building off the frame. Is the coil rational, and why?


texts: Modeling heat and mass transfer modes inside rapidly rotating cylinder

texts:
My question is about simultaneous heat and mass transfer in rotating cylinder system. System can be detailed as:

A rotating cylinder contains wet porous substance in a lump shape.
Air stream enters the cylinder axially and can exit it by perforations on back surface of cylinder or radially by perforations on its curved surface.
Entering air flow is slightly higher temperature than porous medium and carries moisture from surface of porous medium.
RPM of cylinder is about +/- 25 for most of 1 hrs' run time. But for 5 minutes in middle of runtime gets as high as 1400 RPM.

In low RPM period, I have modeled the system's heat and mass transfer w.r.t. NTU analogy. Equations are roughly as follows:

$Re = \frac{ \dot{m_{air}} D_{drum}}{\mu m_{porous}}  $,
$Pr = \frac{Cp_{air} \mu}{k_{air}}$

$j = a Re^{-b}$,
$ NTU = \frac{j}{Pr^{\frac{2}{3}}} $

$h_{porous \, air} A_{cylinder} = (NTU)\times \dot{m_{air}} Cp_{air}  $

$Q_{air\, to\, porous } = h_{porous \, air} A_{cylinder} \times (T_{air} - T_{porous})$

Mass transfer is characterized based on NTU too. Driving force is partial pressure difference.

Main source of heat transfer is temperature difference b/w inflowing air and porous substance, $ T_{air} = T_{porous} + 45$ at start. For mass transfer $(X_{saturation at porous surface} - X_air)$, mole-fraction difference between input air water content and saturated layer at porous substance's surface.

I want to know, how would heat transfer conditions change under very high RPM. It will be a completely mixed system with more resistance to axial flow than before. So would NTU analogy still be used under such conditions? If not, how can I modify or replace it?

Simple figures for system:-

Any suggestions are welcome.


texts: What is the inuition behind the radiation view factor reciprocity?

texts:
I have known that the view factor reciprosity is that

Ai x Fij = Aj x Fji

But i can't intuitively explain the logic behind this, i do know that the view factor Fij is the portion of the radiation emitted by surface i that is recieved by surface j

I have looked up for the proof but that doesn't seem to help much

Thank you


texts:
I'm looking for any tips on a simple and cheap means of generating a regular spark for ignition of propane in air, could be electrical or other but needs to be simple and fairly reliable.

Criteria are :

needs to remotely ignite/re-ignite a propane jet through a 6 mm OD copper pipe, will be burning in open air (not an enclosed furnace etc)
it is a prototype so doesn't need to be packaged as a consumer product and will be closely monitored so needs not be completely foolproof but equally shouldn't be inherently unsafe.
Can have bulky remote elements via wires etc but the working end needs to be reasonably compact.

This is the prototype

https://youtu.be/zagkIKq17x0


texts: How to calculate the density of foam required to cushion impacts?

texts:
I have a treadmill desk and my downstairs neighbour is complaining about the noise. Specifically the noise made by the impacts of my walking. Unfortunately the floor of my flat is not concrete but made of wooden beams topped with a laminate floor: not a lot of mass to absorb the impacts and not much dampening either.
So, I have to do that myself. Ideally I'd have a big slab of marble and a length of open/closed cell foam of just the right density and dimension and would sandwich that underneath the treadmill. I don't have and couldn't carry a big slab of marble, so as a stand-in I'm going with a large wooden board as thick as they come (or can be glued together). Say a kitchen countertop. What I can't figure out is: How dense does the foam need to be?
Given

a treadmill with a weight $m_t = 26\mathrm{kg}$ that occupies an area $a = 8555\mathrm{cm^2}$ ($59\mathrm{cm} \times 145\mathrm{cm}$)
a human with a weight $m_h = 70\mathrm{kg}$ walking at a steady speed $v = 3 \mathrm{km/h}$ with decent shoes for runners
a wooden board with the dimensions of the treadmill used to evenly distribute the impacts across the foam
open or closed cell foam occupying the same area as the board / treadmill

Arrangement

Human
Treadmill
Board
Foam
Floor

Unknowns
I don't know the force of my impacts caused by the walking nor how much the shoes mitigate.
Resources
Reducing 3D Printer Noise


texts: Convert 2D projections to 3D View in AutoCAD

texts:
Suppose I have three 2D drawings prepared in AutoCAD LT.

That 2D drawings are supposed to represent top, left and front projections of the 3D solid body.

How can I view that 3D solid body?


texts: Alternative materials for reflectors in solar concentrating systems

texts: Other than the usual silvered mirrors, that are expensive to form into parabolas, what can be used as an effective reflector in parabolic troughs/dishes. I saw a few people tried using Mylar and Al-foil, but I am curious about its service life and durability. I need it to be economical and easy to fabricate.


texts:
The above is my daughter's tricycle that I plan to make run off some spare Lithium-ion 18650s. I was just thinking of mounting a small DC motor to where I am pointing, and it will use a small tyre to make contact with the wheel, and rotate it.

I have a few questions / concerns:
1) How do I calculate the Power (Watt) and/or Torque required from the motor, given the total weight of the tri-cycle, motor, and my daughter... in order to make it go at 5Kmph on a flat surface?

2) Both the rear wheels are free rotating independent of each other. So, if I rotate only one of them using the motor, will that push the cycle straight and forward, or in circles/curved path?

3) If she pedals instead of using the electric mode, I am guessing it will charge the battery, although I doubt she'd pedal fast and enough to overcharge it. Would I need to do something to prevent this?

4) Is there anything else that I haven't considered?

Considering the tricycle will not be used for more than an hour in a day, I can make a relatively small battery pack with less mAh capacity.


texts: How would I convert a GPS system on a drawing to something like Google Maps?

texts:
I'll link an image to this question so it'll hopefully make a bit more sense. For some background, I'm sort of a "Jack-of-all-trades" tech guy for my family company. Problems often get tossed onto my desk that I actually have no experience with, and the manager expects me to figure it out one way or another. So, here we are.
We recently won a job for a construction project, but there's one issue: There aren't any specific property pins out there where we can get a baseline to actually know where to start construction. As such, the engineer for the drawings gave me a map of the property pins with GPS coordinates so that we'd have a good survey on where to start. The only problem is this:

So, based on the image, I'm seeing a lot of coordinates that I can't really just look up. I'm seeing N - 749179.87, E-1319180.70 and a bunch of actual GPS coordinates that land me in the Greenland sea when I look them up. I'm sure this really isn't a difficult problem for anyone basically versed in reading drawings, but I am not one of those people. My question is two parted:

What is this system? Is it traditional GPS that I'm just using wrong, or is it some sort of Engineering GPS system stuff that I don't know about?

how do I read and/or convert these so that I can use them in an everyday application, such as Google Earth?

Thanks!


texts: Intuitive interpretation of the U-shaped Jakes Spectrum

texts: I was wondering if there is an intuitive interpretation for the Jakes spectrum? If I look at it in the time domain, which is basically the Bessel function zeroth order, it gives me a reading, how long the channel impulse response stays coherent i.e. phase and amplitude don't vary significantly. Or how long it takes, till the channel is decorrelated however if I look at the Jakes spectrum, the only thing which I can 'see' is how large the Doppler spread is but I can't get my head around, how should I interpret the amplitude (the y-axis). Does it mean, that the frequency components which are closer to the maximum shift are more prominent? And if so, is it just because of the Fourier transformation and there is no way to intuitively understand it?


texts: How to find the nearest locations around a given latitude and longitude point?

texts: I have a database of locations. Each location is a latitude and longitude pair. Now for each query, I want to get top "X" nearest locations around a given latitude longitude point. How do I actually calculate the distance between two lat long points and is there any efficient algorithm to do this instead of a simple for loop?


texts: What is the purpose of these diversions in a natural gas line?

texts:
The campus where I work has a long covered walkway (~.5 mile) which has several labeled pipes running under the roof (chilled water, fuel oil, air...). All of the pipes run dead straight except for the natural gas lines, which have little loops spaced about every 250ft, as seen in the attached image (the lowermost, yellow line. There's another natural gas line hidden above all the others, which also does the same thing.)

The line isn't branching at these points, and there doesn't seem to be any need to divert the pipe in order to support it.  I've looked at some building codes to see if I could find a reason (or even a requirement) to insert these.

Any ideas as to what these are? It's driving me batty!


texts: Writing a User Defined Function for Ansys Fluent

texts: Is it only possible to write a User Defined Function for Ansys Fluent in C? All of the tutorials I could access online do so. I was wondering if this could be done using Java, or any other language for that matter?


texts: Limiting the integral to a time window in PID controller

texts:
Would it make sense to integrate e(t) from t - c to t instead of 0 to t for the integral part of the PID controller?
What are the most common deviation from classic PID controller definition?


texts:
I just noticed "mirror" was actually created by applying thin layer of metal on top of glass. In fact, the polished metal is exactly how mirror gets its properties - while glass itself is just for structure.
From Wikipedia

The most common structural material for mirrors is glass, due to its
transparency, ease of fabrication, rigidity, hardness, and ability to
take a smooth finish.

A plate of transparent plastic may be used instead of glass, for
lighter weight or impact resistance. Alternatively, a flexible
transparent plastic film may be bonded to the front and/or back
surface of the mirror, to prevent injuries in case the mirror is
broken

So why then this "structure" necessary? Was that because of the metal layer being too thin to stand by itself?
And if that so, then it is possible to create detachable mirror, right? Where metal layer can be detached from it's glass structure
I mean, post-consumer wise, commercial mirror today isn't that easy to recycle.
And its just because of this manufacturing configuration? Or do i missed something?


texts:
I'm thinking about a system that would replace water in a swimming pool with clean water from an Artesian well.

The water in the well is about 1C and the swimming pool is around 20C. Reheating the whole pool is obviously very costly, so I'm looking to use a counter-current heat exchanger. What kind of efficiency can I expect from it?

This is just a concept idea for now, just looking at possible angles.


texts: Designing Block Diagrams For Control Systems

texts:
I'm looking for good software to design control systems, and more specifically to neatly design "block diagrams" for control systems.

Is there something like that?


texts:
I am working with a piece of equipment that has a vacuum sealed chamber.
The outer wall (ring) of the chamber is shown in the image below.
This ring is bolted to a bottom plate and a top plate is raised up and down using pneumatics.
When the chamber is sealed the differential pressure between the inside and outside is nominally maintained at 10 psid.
The system also has a laminar flow meter and once vacuum is pulled and the chamber is for the most part isolated, we can read about 1.5cc/min flow (leakage) in the chamber.
Maximum flow readings for all other system components other than the chamber seal is below 0.0.03 cc/min, so I am convinced the issue is with the sealing of the chamber.

In the image can be seen a gland for an o-ring.  This is an existing design, not of our own, so only minimal alterations to the design may be allowed.
We will be looking at the flatness and finish on the top plate, but there has always been some variability on leakage from cycle to cycle.

So, this is my question...
What is the likelyhood that adding a second o-ring in series with the first, with a minimal gap between them, may reduce the total leakage rate of the chamber?


texts: How are water-tight transmissions made, like the kind you see on inboard boats, pumps or food blenders?

texts:
I want to replicate the kind of interface you see on inboard boats, pumps, or food blenders. Basically, I want put a motor in a sealed vessel, and have it turn a prop outside the vessel, in water.

Is this usually done just with a layer of grease over a bearing? Are there any alternatives?


texts: When designing scissors, how do you design the blade geometry to ensure good cutting capabilities?

texts:
I have been looking online and found there should be two points of contact, one in the blades and one in the pin. In order to achieve this, I assume there's a slight angle of the blades into the opposite blade.

However, I couldn't find any information about specific numbers. How would I go about designing scissors that ensure the aforementioned contact while not being too hard to actuate?

Thanks!


texts: Designing a joint with bearing, how much do I need to protrude for the bearing to stand? With pictures

texts:
Hello all I'm designing a joint that needs a bearing to fit central but I'm wondering whether I have to protrude a bit on both parts so there will be some gaps between the bearing and the parts which allowing both components rotate freely.

I don't know how to describe this exactly or accurately so I attached some pictures for explanation The first picture is without protruding the second one is with protrude and the final picture is the location where I want to put the bearing(represented as red rectangle)

So if I am right how much should I protrude? The bearing is 6mm outer diameter 3mm inner hole.

Thank you very much


texts: How can I prevent twine from wrecking spindle bearings in a mower?

texts:
I have a grasshopper 725D mower.  This is a 3 blade ztr mower.
Blades are mounted on 1"shaft that passes through a pair of 1" x 2" x 1/2" bearings.  Bearings rest on a step in the spindle case, and also have a sleave that supports the centres.  The spindle housing is about 2.5" in diameter.
The blade is bolted with a 3/8" NCF bolt to the shaft.  There is a metal washer between bolt and blade about 2" in diameter, and a fiber washer between blade and bearing.
In operation if you hit any plastic bailing twine it wraps tightly between the blade and spindle housing, then melts and moves into the space between the fiber washer and the bearing.  There it destroys the bearing seal.  Net result is a $200 repair about once a season.
I'm looking for ways to prevent the plastic from melting and getting into the bearing space.
One thought I had was to fabricate a metal cup that went between the blade and the fiber washer that covered the spindle housing.  This would spin with the blade.  However the top edge of this would have to have some clearance, and I anticipate that it would collect dust, mud, shattered dry grass.  Not sure if this would be a win or not.  I also worry about water collected there, as I frequently have to mow wet grass.
This must be a frequent problem in mechanical engineering -- running bearings in a hostile environment.
Pointers to any standard ways to deal with this.


texts: Why ductile materials fail in shear when subjected to torsion?

texts:
I was reading the book Mechanics of Materials by Beer and Johnston.The author points out in torsion chapter that ductile materials generally fail in shear.And brittle materials materials are weaker in tension than in shear.From this they concluded that when subjected to torsion a circular shaft made of ductile material breaks along a plane perpendicular to it's longitudinal axis and the brittle material break along surfaces forming angle 45° with the longitudinal axis.

I couldn't get how they come to the fact that ductile material fail in shear and brittle material fail in tension.Any ideas?Thanks.


texts: What Specs are Important in Choosing a Similar Stepper Motor?

texts:
I am building a simple DIWire Bender.  Included in their Google Code Site materials list is the OrientalMotor 2 Phase Stepper Motor, which will be responsible for feeding and bending the wire.  Each motor is priced around $200, and in total they exceed my budget.  I am searching for similar but less expensive solutions below 100 bucks.

Which variables in this spec list would be critical in choosing a similar motor?

  Motor Type :  2-Phase

  Holding Torque : 368 oz-in

  Shaft/Gear Type   : Spur Gear

  Gear Ratio (X:1) : 10 :1

  Shaft : Single

  Type : Geared

  Output Step Angle : 0.18 °

  Connection Type   : Bipolar (Series) / Unipolar

  Current per Phase (A/phase)   : 1.4 [Bipolar (Series)] / 2 [Unipolar]

  Voltage (VDC) : 3.9 [Bipolar (Series)] /2.8 [Unipolar]

  Resistance (Ω/phase) : 2.8 [Bipolar (Series)] / 1.4 [Unipolar]

  Shaft Runout      0.05 mm (0.002 in.) T.I.R.

  Concentricity     0.075 mm (0.003 in.) T.I.R.

  Perpendicularity      0.075 mm (0.003 in.) T.I.R.

  Radial Play       0.025 mm (0.001 in.) maximum of 5 N (1.12 lb.)

  Axial Play        0.075 mm (0.003 in.) maximum of 10 N (2.2 lb.)


texts:
I'd like to know if I can use a gear train to drive a pinion, and thereby increase the torque of the rack. If so, how does the gear ratio of the gear train affect the torque of the rack relative to the gear ratio of the rack and pinion on its own?

Also, and this should perhaps be another question but I'll go ahead and ask it: If I have two separate racks separated by a distance of X, connected so that when one rack moves the other moves also, and use a pinion to drive only one rack, should I expect a decrease in the torque of the secondary rack, and if so to what degree?

In order to help ensure I get an answer to my specific question, I'd like to state upfront that I'm aware that the gear ratio of the rack is determined by the distance the rack travels relative to each rotation of the pinion.

So my question relates to whether or not the mechanical advantage created by a gear train is entirely lost if the gear train is used to drive a pinion which drives a rack, and how the torque of the rack scales when using a gear train to turn the pinion relative to the gear ratio of the rack and pinion themselves.


texts: Metallic flow behavior under eccentric loading conditions

texts:
So, I did a quick search around and didn't seem to find anything regarding this, so I thought perhaps I should just ask a question.

Metals are malleable and will generally flow/deform if you roll it repeatedly. Localized concentrated loads will thus change the shape of a piece of metal bit-by-bit if exposed to repeated loading of the same/similar orientations (kind of like molding a piece of playdoh, with each repeated load only displacing a very minor amount of material). Presumably, flow should be the same in all directions of the contact point non-isotropically for a homogeneous material.

But if there is eccentricity within the load, will that still hold true? If it does not, where is that critical limit for for X:B within the figure below that will produce some degree of eccentricity with the amount of metallic flow? Or am I thinking about this in a completely wrong way? See below example for what X and B refers to, and an example of what I am trying to figure out. Thanks!

Edit: I know flow will happen. What I am trying to understand is if load is eccentric, how will that affect flow behavior? Will it cause one side to flow more than the other IN THE ABSENCE of surface shear type loads? The below example will have all vertical loads (up/down) with assumed 0 lateral loads (left/right), and if you are just rolling it back and forth, will it flow more on the side closer to the edge just because it is closer to the edge? I don't think there are any formal theories but I can see it happening that way because flow ultimately is a localized plastic deformation that is constrained by surrounding material structure. If the surrounding material structure weakens, it somewhat makes sense that it will tend to have more plastic deformation in that direction. But is there some limit as to how far X has to be from the edge for it to be negligible? It's kind of like us saying eccentric loading on a concrete shallow foundation footing is okay if it is within the middle third. Hope that makes more sense what I am asking.


texts: What to do to increase the hp of a gx-160 engine?

texts: I saw a youtube video of an ultralight airplane with a 5.5hp engine that has been modified to produce 30hp. So how do I modify a 5.5hp engine to make 15hp+ of output?


texts: Equivalent Lengths of Pipe for Laminar Flows

texts:
I have a pipe network with laminar flow (peak output from the pump gives a Reynolds number around 1100).

I have some test data for the network and the results are really odd to me; I cannot explain the flow distribution using standard theory for K values or assigning equivalent lengths to pipe fittings. The results look like this:

Branches A and B are pipes of the same diameter (0.5cm), and are fed, via a T-junction by a pipe with double their diameter (1cm). The branches are the same length, the only difference between them is one has 2 holes in it (of 2mm diameter at the tip, and 1mm diameter at slightly downstream of midspan), the other only has 1 hole (of 1mm diameter, at the tip).

This minor geometrical difference causes 19 times more flow to go down branch B, according to my test results. But the theory I have for equivalent lengths of pipe suggests this shouldn't happen.

I suspect it's because the data only applies to turbulent flows. I also am doubting the accuracy of the test data (I did not conduct the test) given that large discrepancy between the two branches.

Does any body know a source of equivalent lengths of pipe/k factors that are valid for slow moving (laminar) flows? (below 2000 Re)


texts: How to import a CATIA assembly into SimMechanics

texts: I need to import an assembly from CATIA into SimMechanics but in CATIA, the .stl file format is available only for part files and not for assembly files. How can I do this? Is it possible to convert between the .CATProduct and .stl file formats?


texts: Simple, open source aerodynamics simulation software that can import Blender or Sketchup models?

texts: What are some basic, open source aerodynamics or CFD simulation software that can import Blender or Sketchup models? I am looking for software that is easy-to-use, free, and suitable for educational purposes.


texts: What is the output of a signal in time domain that passed through a High Pass Filter with simple transfer function

texts: If a signal function $ U(t) =  25 – (5 – t)^2$ is passed through a high pass filter with transfer function $\frac{s}{s + ω}$. what is the output signal Y(t). I know that the transfer function $H(s) = \frac{Y(s)}{U(s)}$. If I understand the basic concept, I can solve my own problems. I will also appreciate it if someone can reference a textbook.


texts:
I will try to translate it as best as I can
T = temperature
Pi = P initial
Vf = V final
Monoatomic  gas
The T doubles isobarically (process 1-2), absorbing heat Q12=250 J.
The gas is then cooled isocorically (process 2-3) until the T is equal to the initial T.
Calculate:
Q31, Delta U31, W31, if the system is brought to the initial state through an isothermal process. (process 3-1)
I calculated the values for the 12 and 23 processes:
Q12 = 250J
W12 = 100J
Delta U12 = 150J
Q23 = -150J
W23 = 0J
Delta U23 = -150J
Here's what I calculated to try and get closer to the answer:
Delta U = n Cv Delta T => Delta U = n Cv Tinitial = 150J
Using Delta U = n Cv Tinitial = 150J, I calculated:
n Cv Tinitial = 150J
n 3/2R Ti = 150J
nRTi 3/2 = 150J
nRTi = 100 J
So then I tried to use it for the isothermal formula for Q.
Using these two formulas:
Q31 = nRTi ln(Vf/Vi) (isothermal)
Q31 = 100 ln(1/2)
Q31 = -69,314.
But the book says that Q31 = -115J. I don't understand how they got that answer.
Here's the graph I came up with:


texts: Converting rotary motion to linear motion (door for sliding trash can)

texts:
I have one of these slide-out trash cans:

I want the trash can to slide out with the door being opened and slide in with the door being closed.

I'm thinking of a method to convert the door opening motion (rotational?) into the linear motion of the trash can. Now I have tried searching multiple ways for solutions on converting rotational to linear motion, but came up empty for this seemingly simple problem. The door motion of course isn't purely rotational as we're not talking about converting the hinge-motion, but the motion of the door.

A method that works is just attaching a string to the side of the door and onto the trash can. That works for pulling out the trash can, but pushing in obviously doesn't work with a flexible string.

I'm lacking to tools to properly model this problem, right now I am stuck to fiddling around - I'm assuming there are better ways to solve this.


texts:
Recently I encountered a problem of oil leakage from different driving systems SERVO gearboxes.
The transmitted mechanical power ranges from 2 to 8 kW, while the motor speed (the gearbox input speed) varies from 1440 to 3000 RPM.
Most of the units are 1 stage planetary gearboxes although some of theme are helical-bevel gears.
Despite the gearbox manufacturers (several European companies) are well-known and having significant heritage in this field, these gearboxes all begin to leak from their input seal before reaching 3000 hours of operation.
Replacing the oil to grease improves the amount of leakage, but the phenomena still exists.
Adding breathers / pressure relief valves, hardening the gearbox input shaft (which acts against the input seal), and replacing the seal material to viton - all made just a small improvement.
Furthermore, the same happens even in our air-conditioned lab - so the problem doesn't seem to be related to harsh environmental conditions.

I suspect the root cause is the continuous operation profile (the system runs for 24/7) - which kills the seal many hours before the units operation life.

Inspecting the seal and the shaft of a leaking gearbox did not show strong indications of wear. As suggested here, it may also be a vibration problem, probably coming from the motor.

Any ideas how to improve it?
Are there instances out there for SERVO gearboxes running continuously for more than 3000 hours before leakage?


texts: What kind of spring exerts a constant force but is also adjustable?

texts:
I'm trying to make a lifting mechanism that will support variable weights, similar to this product: http://www.humanscale.com/products/product.cfm?group=quickstand

On the quickstand there is a screw that adjusts the spring force between 4 and 11 pounds, which appears to be constant throughout its 17 inch stroke.

What kind of spring are they using? I've searched for a long time but there doesn't seem to be any off-the-shelf solution to accomplish this effect. There are adjustable gas springs, but that's done with gas bleeding which is obviously a one time adjustment.


texts: Connector for sliding plate to rotating rod

texts:
I want to couple a plate, which cannot rotate but only slide along a track, with a threaded rotating shaft. This is for a grip setup, where rotating the rod presses the plate forwards to apply pressure.

I don't know of a type of connector for this coupling, and have searched the internet but McMaster and other sites do not seem to have one. Does anyone else know of such a connection?


texts: Natural ways for passively cooling/heating a home?

texts:
I always think about how there surely must be natural ways to cool/heat a house, rather than using electricity, like solar panels, heaters, and AC. Does anyone have any good examples of houses/buildings that were engineered to be really effective at cooling and heating themselves, like with lots of ventilation through the ceiling or lots of glass at certain spots to concentrate sunlight?
I have tried looking this up but most results I find use solar panels. I'm looking for more radical examples that really don't rely on technology and electricity.
I'm looking for someone who has gone down this train of thought and has interesting examples to share! Thank you!


texts:
Let me just get this out of the way: this is a total newbie question.  But I appreciate any advice I can get!
I'm rebuilding / retrofitting a wood-and-steel trailer, and trying to identify affordable fasteners that won't turn into solid lumps of rust.  I live in a relatively dry area, but if there's any moisture at all, it's going to sprayed onto the underside of a trailer, along with road grime, salt, etc.
From everything I've found, the (readily available) materials that are most corrosion-resistant in their own right are stainless steel and hot dipped galvanized steel.  However, I'm bolting onto/through a bunch of mild steel, and stainless is appreciably more anodic and than mild steel, while zinc (plating) is significantly more cathodic. Is this a problem?  Is the zinc plating just meant to be sacrificial and shouldn't worry about it?  Am I looking at the whole question wrong?
I'm guessing I'm far from the first person to run into this question, but an hour communing with Google hasn't gotten me very far.  Any suggestions?


texts: cycle efficiency for (otto -diesel -dual) at constant Pr & Temp

texts:
It's written that at constant pressure & temperature for Otto & Diesel cycles
the efficiency of diesel is more than efficiency of Otto.
Efficiency = Work / Heat added = 1- (Heat rejected / Heat added )
from fig :
-(4->1)  Heat rejected is same
-(2'->3) Heat added for diesel is greater than (2->3) )heat added for Otto
so for diesel the term (Heat rejected / Heat added ) is less
so efficiency of diesel is more.
What make it not clear for me is that
work ( Cv(T4-T3) ) (3->4)  is same for both & heat added for diesel is more than that of Otto.
So if we use  eff= Work/(heat added)
Eff of otto will be more since less heat will be added and same work is done,
What makes it wrong?

source : http://slideplayer.com/slide/10748942/  slide 30


texts: Limitations of the cut-off ratio in real-world diesel engines

texts:
In an ideal diesel cycle, the cut-off ratio is set by the maximum gas temperature after combustion. That's all fine and good, but in a real-world engine what controls the cut-off ratio, and what are the limits to its flexibility? I feel like it must be the valve timing, but perhaps it is controlled by the fuel injection? Perhaps both.

Is it common to have variable cut-off ratios based on ambient temperature to achieve higher power ratings at lower temperatures? Or is this not possible in a real diesel cycle?

An example: If an engine runs both during the summer (35 °C) and the winter (-10 °C) in the Midwest can its cut-off ratio be adjusted such that the final post-combustion gas temperature is the same in both cases leading to much more power in the winter than in the summer?


texts:
Is this equation valid for a given mechanical system

The Inertia of the motor is $J_m$,there is no loss in the system.then conservation of energy can be used.

the motor is revolving with speed $\omega$.and the gears ratio are equal.
$v $ is the velocity of the weight $w$

I am asking that the can the total InertIa can be expressed as  $$\frac{1}{2}J'_m\omega^2=\frac{1}{2}J_m\omega^2+\frac{1}{2}mv^2$$.

equivalent moment of inertia referred to the motor shaft is $J'_m$.

This was told by my teacher I think there is something wrong here.
I am skeptical about this because we can't talk about adding the both terms and referring them to as total inertia referred to motor shaft.BOOK SOLUTION

What you might be saying is


texts: Using pressure drop to correlate mass flow

texts:
I am looking for a way to double check readings I am getting through a mass flow meter that appear to be reading lower than expected.

Once flow starts in the system, the pressure regulator at the supply tank drops in pressure readout. This drop should be due to the dynamic pressure of the flow of gas through the regulator so I was thinking it may be possible to correlate the mass flow meter's readings with the calculated mass flow resulting in the drop in pressure at the regulator. I started by using the ideal gas law (low enough pressures) to calculate the density of the gas at the static pressure  read by the regulator.

$$\rho=\frac{PM}{RT}$$

Then I took the pressure difference read from the tank regulator between the static no-flow to flowing as the dynamic pressure.

$$P_d=\frac{1}{2}\rho v^2$$

Using the above equation I calculated the velocity of the fluid flow, and then just used the cross sectional area to calculate the mass flow.

$$\dot{m}=\rho A_c v$$

When calculating the density I am getting an unreasonable value for fluid velocity so I was wondering if this procedure makes sense?


texts: Is there a moment at a point between two connected sliders, when one is subjected to a force? (schematic shown)

texts:
Background: I'm designing a machine that uses an actuator to push an object. The connecting component may not take certain bending forces, therefore I'm trying to evaluate the system with a free body diagram.

The moving system is support by preloaded linear rails. The red component is a load cell that may only take limited bending forces (it is however rated to handle the 50N in tension or compression)

Both sliders are preloaded and can be assumed perfectly parallel

My intuition tells me that there will be some bending forces, but I'm not able to be clear about this!


texts: Amount of thrust needed to Hover on the moon?

texts:
I am interested in knowing how many newton's of force is needed to keep 1 kg of mass hovering above the moon's surface.

And whether the current most powerful ion thrusters would be up to the task? I believe ESA tested an ion thruster recently which achieved 100 kilo newton's. (I massively mis-remembered this part. I was thinking of the X3 thruster, and the figure is 5.4 Newtons.)

Thank you in advance!


texts: Find the point where locus crosses the damping ratio line?

texts:
Given a transfer function, find the point where locus crosses the damping ratio of 0.5?
$$G(s)= \dfrac{K(s-2)(s-4)}{s^2+6s+25}$$
The textbook only shows this solved by Matlab or program, I would like to know how to do it by hand calculations?


texts: What is an engineering term for this type of arm

texts: I'm trying to describe a part -  it's an arm that holds an axle sleeve (which ultimately holds a wheel). I'm stuck right now describing it simply as a "wheel arm", but was wondering if there was some better, more engineering-appropriate term.   I'd appreciate any feedback. Thanks]1


texts: Effective radius of a tire and rolling resistance based on information on velocity and tire pressure

texts:
I need to make an nonlinear observer of a system and need to know how the charactaristics of a tire are to get the final conclusion.

I really need some good articles about how the effective radius of a tire will vary depending on velocity and pressure.
I would appreciate any articles about rolling resistance too.

I would appreciate if someone could give me a hint.


texts: How to measure resistivity of a given sheet of material?

texts: Suppose you have a thin sheet of a material of size say (1mtr X 2mtr X 1mm). You do not know what material it is. How to find its resistivity? One way I can think of is to measure resistance across smallest cross section i.e. 1mtr X 1mm, and then using $\rho = R\frac{A}{l}$, one can calculate the resistivity. However, in case of metal alloys, resistivity can be very low resulting in very low values of resistance which may not be picked by general multimeter and one may have to use micro ohm meter. Will this method work given the unusual shape of the conductor? Is there any other way to calculate the resistivity?


texts: Is it possible to send ESC/POS commands to EPSON TM-T88IV Printer through Windows command line?

texts: I am interested in learning more about ESC/POS commands. I have an EPSON TM-T88IV printer connected to my PC via parallel cable at port LPT1. Connected to this printer is an APG Cash Drawer. The PC is running Windows 7 Professional. I would like to know if it is possible to send ESC/POS commands to this printer through the Windows command line. If not, I would like to know what steps to take to be able to set up some sort of test environment.


texts: How to calculate the required airflow to dry a batch of sawdust?

texts:
Sawdust has to be dried while in storage waiting to be processed.

The time window for the drying is 12 to 36 hours.

The storage room is 20m x 20m x7m (L x W x H).

The sawdust is stored on 300m2 of the 400m2 available. It is placed on tent vented steel sheets at 0.5m above ground.

This gives a sawdust volume of 100m3 and an aproximate weight of 21000kg. Sawdust humidity 50%. I would like to take it as low as possible in the available time window. Let's say 30% would be acceptable. 20% would be great.

What airflow has to be provided from under the vented steel sheets in terms of volume, temperature and humidity?

I was thinking to use tubes to distribute the air under the steel sheet. The air in will be matched with roof fans taking the air out. I would like to have a rough idea so I know with what equipment to start.


texts: What does (a) the input of the activation function mean?

texts:
I am not very good at understanding the ANN theory, but please if anyone can explain me about what does (a) as input of the activation function mean?
and how to get this value?

Thank you


texts: Determining pressures of a compressible gas

texts:
A friend and I wrote a paper for a fluids class discussing the details (as they relate to fluid dynamics) of constructing a cannon that could shoot a steak fast enough to cook it.

We quickly discovered (but not quickly enough to change our topic) that our paper was a bit too ambitious for two twenty year old undergrads taking an introductory course in fluid mechanics. Nonetheless, we still busted out a ballistics simulator, a cookbook, and a compressive heating calculator and did our best.

One of the issues that stumped us was compressing the gas we used to launch the steak. We chose Helium because it was the least dense gas that probably won't burst into flames (like Hydrogen).

Using a compressive heating calculator, we found the velocity we needed to shoot the steak, and were using Bernoulli's equation to find the pressure we needed to launch at our chosen velocity.

The issue we ran into was density is dependent on pressure, but we needed the density to calculate the pressure needed.

How does one determine the pressure given the issue above? Is it simply several rounds of iteration until an acceptable answer is found?


texts: How can I define third type boundary condition in ANSYS Mechanical APDL?

texts:
I'm currently working on the thermal analysis of a pipe, but i do not know how to define a third type boundary condition on the inner surface.

finish
/out
/CLEAR,ALL

/PNUM,KP,1
/PNUM,LINE,1
/PNUM,AREA,1

/PREP7
!Constants used in the simulation
a=0.05
b=0.2
!third type boundary condition is used on the inner surface
Tb=30
qb=260
p0=3.1e5
!second type boundary condtion on the outer surface
hk=120
Tk=15
qk=490
hb=10
rho=7600
E=210e9
nu=0.3
alpha=1.2e-5
k=45
Tinf=20
!!!!!!!!!!!!!!!!!!!!
ET,1,PLANE77
!Material props
TOFFST,273
MPTEMP,1,Tinf
MP,EX,1,E
MP,REFT,1,Tinf
MP,PRXY,1,nu
MP,KXX,1,k

!!!!!!
K,1,0,0
K,2,a,0
K,3,b,0
K,4,0,a
K,5,0,b
LARC,2,4,1,a
LARC,3,5,1,b
L,4,5
L,2,3
AL,1,2,3,4

Lsel,s,LINE,,1,2
LESIZE,ALL,,,50
LSEL,inve
LESIZE,ALL,,,30
mshkey,1
AMesh,all
/solu
lsel,all
SFL,3,HFLUX,0
SFL,4,HFLUX,0
SFL,2,HFLUX,490

The problem is that i do not know how to apply convection boundary condition on the inner surface, where the inner radius is a and the temperature of the fluid is Tb.
Thanks for your help in advance.
yours sincerly,
David


texts: Removing beam deflection through axial force

texts:
It's been a while since I've done any comprehensive work with structural dynamics, so let me know if I get anything wrong here.

I have a horizontal beam that is clamped on one end and free on the other. It has the following parameters:

length $L$
elastic modulus $E$
moment of inertia $I$
mass $M$

There are no loads on this beam except for its own gravity, which can be modeled by a uniformly distributed load:

$$\psi = \frac{Mg}{L}$$

Using standard beam theory, we can calculate the deflection at points $x$ along the beam, as well as the maximum deflection $\delta_{max}$

$$\delta = \frac{\psi x^2}{24EI}(x^2 + 6L^2 - 4Lx)$$
$$\delta_{max} = \frac{\psi L^4}{8EI}$$

I have a physical constraint that $\delta_{max}$ can be no more than $\epsilon$, so I propose the following:

Spin the beam about the wall it's attached to at angular velocity $\omega$, which creates an axial centrifugal force. This should lower the value of $\delta_{max}$, and for all $\epsilon > 0$, I should be able to find $\omega$ meeting this constraint.

What I'm looking to derive is some function $\delta_{max}(\omega; \psi, L, E, I)$

My question is how can I incorporate the axial force? Each slice of beam $dm$ has centrifugal force equal to $\omega^2 x dm$ where $x$ is the distance from the clamp. I don't immediately see where to proceed from here.

Any help is super appreciated! ^^


texts: Phrase for describing a cable without a connector at the end

texts:
I've been translating a truck scale description in a business offer letter, and the specification table there, listing the five parts comprising the prospective order, says on line five:

  Cable for connecting the load cell to the weighing terminal, bare end. Length: 30m.

In the Russian original, the phrase "открытый конец" (literally "open end") most likely means that the cable has no connector attached to it. It probably comes out of the load cell, and then is cut at this length, 30m. The Buyer can attach the necessary connector.

What would be a naturally-looking phrase for describing the same "bare end" in a similar English document?

(Also asked on ELL SE)


texts: Which part of an aircraft can most benefit from a structural health monitoring (SHM) system?

texts:
In order to reduce operational cost and improve the safety and reliability of aircraft's the aerospace industry and government is increasingly evaluating new ideas such structural heath monitoring systems for aircraft's. Such a system will enable continuous monitoring, inspection and detection of damage to the aircraft with minimal human involvement. This will also help the airline industry to improve aircraft maintenance scheduling process.

Figure: Early Diagnosis for Microcracks in Aircraft

Currently Delta airlines and an aircraft manufacture has teamed up with Sandia Laboratory to install sensors in aircraft to help understand flaw detection. Research also indicates that ultrasonic sensors are most widely used sensing element.

Question:
Which part of an aircraft can most benefit from structural health monitoring (SHM) system? Is it the fuselage, wings, landing gear, flaps, rudder, elevator, vertical stabilizer or another component? Why is this component the prime candidate?

References:

In-flight sensor tests a step toward Structural Health Monitoring for safer flights
Structural health monitoring: Composites get smart
Early Diagnosis for Microcracks in Aircraft
Air Asia QZ8501: Pilot response to equipment malfunction caused crash


texts: Surface in the sun vs. surface in the shade

texts:
What is the difference in temperature between a  surface in the sun as supposed to one in the shade and how is it calculated?

For instance:
What will the  temperature be if a metal sheet lies in the sun and then what will its temperature be if the same sheet lies in a shaded area?


texts: What would be the best mechanism to rotate a plate from 0 to 15 degrees?

texts:
I'm designing a machine in a small university project that change position of a two-state gate. The two states shown in the Figure below are 0 and 17 degrees of elevation, correspondingly. The dimensions of the gate are L= 300 mm. and thickness=3 mm.. Also, the gate's material is Aluminium 6061. Other component's materials are steel stainless 304.The gate is not going to suppor any weight neither other forces, just their own weight.

I was thinking on a servomotor directly connected to the axis of the gate, but I'm concerned if a servomotor can work with the following operational characteristics:

Change the state in less than 1 second. Work, a petition but for 6 hours. (Is not going to change each 1 second, 2 in average). So, we can say that is going to change state 10k times in 6 hours, approximately.
Change from 0 to 15 degrees and vice versa.
There's no electrical restrictions.
There's no limit of motor dimensions.

Also, one frind suggest me to change the pivot place and use mechanism like the Figure below.

I'm looking for suggestions and recommendations for this design. I'll really appreaciate all your ideas and learn from the feedback!


texts:
If an I-shaped section is loaded in two directions (in both weak and strong axes), how can I find the maximum load-carrying capacity of them beam?

There is an interaction equation in AISC 360-10, but it's for beams which are also loaded axially. Can that interaction equation be used for only flexure in two directions, taking the axial force to be 0?


texts: How to remove heat from an IP66 enclosure?

texts:
I have a small IP66 polycarbonate enclosure with a Zirconia-based oxygen sensor which produces significant amounts of heat (the internal sense element runs at 450C using a 1.5W heating element, sensor surface reaches 85C). The enclosure also contains sensitive analog electronics to read the sensor. The residual heat from the sensor is driving the ambient temperature in the enclosure up past 40C (measured on the outside of the enclosure front panel). The oxygen sensor and another gas sensor are only rated for ambient temperatures of 50C maximum, so I'm worried about keeping those in spec. I'm also concerned about needing temperature compensation for the analog circuits.

How can I remove the excess ambient heat from the enclosure while still maintaining an IP66 rating?


texts: What's the purpose of these small closet-like-rooms-without-a-door?

texts:
I was recently on the UCLA campus (University of California Los Angeles) and I saw the Bunche Hall. I love the design and the architecture of the building. However I saw a little (what I would call) a closet with no door on the side but it was just three walls with a roof, extremely small, underneath the stairs, outdoors, a bit below the floor level. There is a small alley and then you take two stairs down and the closets face a fall.

I don't even know what to call it. My question is, from architectural/structural engineering point of view, what is this building device? Why is it there? What is its purpose? What is it even called? The two closets reminded of telephone booths but there was nothing but dirt, cobwebs, and leaves in there. Were they once used for something? I am posting the pictures below.


texts: How to measure a bearing temperature in a pump?

texts:
I found that Resistance Temperature Detectors (RTD) are mostly used for bearings, but it's not easy to drill the casing and we need to take a signal out to PLC and LabVIEW.

Is there a sensor that can measure bearing temperature through the casing?

Can I use an IR gun temperature and take a signal from it?


texts: Designing a submersible cooling system for rapid flow hot nitrogen gas

texts:
I'm trying to design a cooling system for cooling nitrogen at 300°C. My original design (which is very open to modifications) is an aluminum ring block with exterior fins and vertical holes through the block connected end to end to form a continuously undulating gas line. An amazing engineer proposed flowing the gas through multiple holes simultaneously to address the pressure drop problem along the original single gas line, but any better approach is encouraged.
My design operates by submerging the block into a water the size an Olympic swimming pool at 20°C. 468 g of nitrogen driven out of a vessel originally pressurized to ~5000 psi goes through the cooling system in roughly 10 seconds. The aim is to be able to cool the nitrogen down to 25°C as it exits the cooling system at that staggering flow rate.

What mass, geometry, and feature of the aluminum block, and/or modifications to the original design is required to achieve the stated aim.


texts: What casued periodic waviness in the sidewalls of this tunnel?

texts:
It looks like the digging of this ISIL tunnel introduced periodic waviness in the sidewalls of the tunnel. Similar (related?) waviness can sometimes be observed on dirt roads. What is the origin of that periodic waviness?

(source)


texts: What is the dollar value of "qualifying experience" in an entry-level US engineering job?

texts:
Motivation
Imagine that you are a recent graduate of an ABET-accredited engineering program in the United States. You have taken and passed the Fundamentals of Engineering exam and you are hunting for your first job as an engineer. You send out applications, sit for interviews and have the good fortune to receive two offers of employment. Both positions are interesting and offer reasonable compensation, benefits and responsibilities at established companies; however, only one of the two positions represents qualifying experience for the purpose of becoming a licensed Professional Engineer (PE).
Problem:
What is the dollar value of that qualifying experience?
In other words, how can the applicant calculate the value of progress toward PE licensure as part of the "total compensation" the job offers, as is commonly done for benefits such as employer-subsidized health insurance, relocation assistance or gym memberships, so as to make a more informed decision about which offer to accept?
Discussion
For a position to represent "qualifying engineering experience," The National Society of Professional Engineers specifies that it must involve:

A major branch of engineering
Supervision by one or more qualified engineers
The development of "technical skill and initiative in the application of engineering principles and sound judgment in reviewing such applications by others"
A reasonably well-rounded experience in that branch of engineering
Work of increasing complexity and responsibility

I myself interviewed for two positions at the same organization, with the same title, shortly after finishing my undergraduate degree. One of the positions was supervised directly by a PE and the other was not, nor did it involve work that would be reviewed at some point by a PE—it was made very clear during the interviews whether or not each job represented qualifying experience toward a PE.
In other cases, a recent graduate may entertain offers from both traditional engineering firms and companies that operate in related, but not strictly engineering, fields. For example, Accenture recruits engineering graduates at my alma mater for non-engineering positions. Some engineering graduates have a background that qualifies them for software development positions. Others may have the option of pursuing positions in R&D or pure research.
The best answers will thoroughly justify their analysis and cite references for any statistics used. I wouldn't discount a novel "back of the napkin" approach, though.


texts: How to calculate the volume of water flowing out of a tank?

texts:
How can I calculate the volume (cubic meter per second) of water flowing out a tank? (or the velocity in meter per second)

A horizontal pipe with a diameter of 1 meter is mounted (within the tank) 10 meters below the surface (that is 10 meter for the center line of the pipe).
What's the formula to calculate the water volume flowing out the tank?

Is the volume of the tank important?
Let's say one tank with a diameter of 5 meter and another with a diameter of 20 meter, the volume of the water flowing out at the beginning is the same I guess? Off course for the first tank volume will decrease quicker than for the second tank.

Is there a difference if the pipe is mounted within or outside the tank?


texts: Possibility of buckling in non-slender member?

texts: The above diagram is misleading. In reality, both the length and thickness are equal to 8mm.  As this is from a past paper (one notorious for awkward questions), I'm not sure if it's a typo (an 8m length would be much more straightforward).  Is there any possible outcome/plane in which this pipe would indeed buckle?


texts: What are the basic mechanism, components or parts to generate relative movements?

texts:
I'm an engineer in industrial design and despite that I studied mechanics, kinematics and dynamics, I got difficulties when I try to label or find components which could enable my designs have relative movements, i.e. one part rotates inside other.

I know I can design most of them but I guess that some must be already created and would like to know how to search them, instead designing new ones or asking for help in each specific project.

What are the basics relative movements and components that generates them?

EDIT

I'm trying to find a "movements library", to be able to find what are the most common movements and what mechanisms or components are used to achieve them. For example, materials libraries are pretty common in many countries, in them you can find a huge list of materials, with their properties, application and providers.


texts: Energy required to raise temperature of water flowing through a heater

texts:
I am trying to work out how much energy (ideally electrical heating) I need to put into a heater to raise the temperature of water from say 10 degrees C to 40 degrees C, if the water is flowing at 10 litres per hour.

Assume that the heater is 80% efficient.

I know that the specific heat of water comes into this at 4.18 J/g degree C but how do I work in the flow rate?


texts: Double interpolation for a large set of data in Excel

texts:
How do you do double interpolation for a large set of data in Excel?

The user is required to input an x value and y value then the program has to find the points and do interpolation if necessary. For example, if the x is 3.5 and y value is 4.5  then I'll have 2 x value and 2 y values so I need to do the double interpolation then final interpolation between the remaining values.

I have used a vlookup function and forecast function  but it doesn't seem to be working out. I have attached a picture of the data set.


texts: How do I calculate hourly LAeq sound pressure level using 1-mint LAeq values?

texts: I have continuous A-weighted sound pressure level (SPL) values at 1 minute time resolution (LAeq,1min). I would like to calculate LAeq SPL at half-hourly and hourly resolutions using these values. Can someone suggest on how this could be achieved?


texts: Can Rotary Friction Welding be used to join metals and ceramics?

texts:
Is Rotary Friction Welding a good method to join cylinders of a metal (such as Ti alloy) and a ceramic (such as SiC).
I know that Diffusion bonding can be used in such cases. However, it has its own disadvantages - particularly its time-consuming nature.
In this context has the use of rotary friction welding (or some other friction welding process) suitable?
It is clearly suitable for shape. But are the materials themselves amenable to this? Since friction welding relies on softening the materials by heating; the dissimilar ductility and thermal properties (SiC is particularly high melting) may pose  problem.
I found this which suggests that this is possible but cautions that material selection is important for determining suitablity.

Full Disclosure:
This problem was inspired by a problem on one of my engineering exams. At the time of asking, the exam had already ended a day ago, so asking this question does not (in my understanding) pose any ethical issues.


texts: Deriving relationship between LVDT and mass spring damper

texts:
I have this system below.

It is the schematic of a linear accelerometer moving horizontally, where $m$ is the total mass of the slide, $b$ denotes the viscous damping, and $k$ represents the spring constant. The relative position between the moving mass and the case is measured by a linear variable differential transformer (LVDT).

How do I derive the dynamic equation describing the relationship between $V$, the voltage output of the LVDT, and $x_1$ , the external position, and show that $V$ indeed can be used to measure the external acceleration? I'm supposed to also state any assumptions made and any possible problems and remedies.

I know that the mass spring damper system has the equation $mx_1'' + bx_1' + kx = 0$, and the moving core that is pulled by the mass spring damper system will induce a voltage in the LVDT. If I was given a transfer function for the LVDT, $G$, then I have $V = Gx_1$. But I don't know how to link the 2 concepts together to derive the relationship.

As for the assumptions, I would say the damping force is constant, i.e. the case is smooth. I'm wondering how the mass hitting the stopper will affect the system. Should it be made of rubber to absorb the impact and to minimize the shock wave?


texts: FOC current ripples with angle dependencies

texts: I implemented the FOC (Field Oriented Control) algorithm to control a BLDC motor at low speed. A phenomena I observed is, that at different electrical angles, the torque producing current breaks down and the field producing current increases (mostly around +-90°). I use a simple PI controller and no cross coupling compensation. If I keep this angle, the field producing current stays then constant at a nonzero value. Does anyone know, what could producing this phenomena? Maybe someone of you already implemented a FOC algorithm for a BLDC motor and also noticed this problem.


texts: Postion of overturning moment for retaining wall

texts:
I sometimes design my retaining walls with longer toes and heels, this is because in my FEA program, when I pull my footing under my wall towards the toe, I get lower pressures on my soil (springs) that when I pull it towards the heel (even with the added benefit of the earth on top). This tends to happen when I don't have too much counter balancing soil on my heel. Anyone else get these results? I've never seen any long toe retaining walls in the literature.
When calulating over turning moment by hand, all of the literature I've seen takes the point of rotation at the toe of the wall. If I look at my FEA design, the wall seems to be rotating much more around the heel. Is it justifiable to calculate the overturning moment at the toe? This seems to be the point that's most favorable for design, but is it realistic?


texts: How would the axial force in a rod of a doubly-built in structure be determined?

texts:
Assume the horizontal member can be treated as a beam and assuming the diagonal member may be treated as a rod, what is its axial force as a function of the applied loading $P$ and length parameters $L_i$. Assume that the connection between the beam and the rod may be treated as as socket joint.

Firstly, I have defined the vertical, horizontal and moment reactions at the top and bottom built-in ends as $V_1, H_1, M_1, V_2, H_2,$ and $M_2$ respectively. I have also defined the axial force (assumed tensile) in the diagonal member as $T$.

Vertical equilibrium of the beam:

$P + V_1 - Tsin(\phi) = 0$

Horizontal equilibrium of the beam:

$H_1 - T cos(\phi) = 0$

Moment equilibrium of the beam:

$M_1 + P(L_1 + L_2) - T sin(\phi) L_1 = 0$

Vertical equilibrium of the rod:

$T \sin{\phi} + V_2 = 0$

Horizontal equilibrium of the rod:

$T cos(\phi) + H_2 = 0$

Moment equilibrium of the rod:

$M_2 = 0$

Global vertical equilibrium:

$P + V_1 + V_2 =0$

Global horizontal equilibrium:

$H_1 + H_2 = 0$

When I attempt to solve the simultaneous equation, I get an indeterminate problem and can not solve for the value of $T$.


texts: When should anti-bursting reinforcement be used?

texts: When designing a bearing plinth, should anti-bursting reinforcement be provided? Under BS 5400, it was only mentioned in the section for end block anchorages of tendons. How should the code be interpreted?


texts:
I'm designing a movable cover on rails under a spring and with added friction to dampen the movement. The model that describes it's movement the best is Coulomb damping model. The cover is moved from it's equillibrium position to one side and realeased. I want to calculate the time it's needs to get back to equillibrium position.
The paper on the link bellow defines the equations.
https://www.studocu.com/en-us/document/university-of-toledo/mechanical-vibration/lecture-notes/ln-6-coulomb-friction/3247643/view
The initial preload distance $x_0$ needs to be large enough so that the spring force is larger than the static friction.
My problem is that when I put the values in the equation and try to calculate the time mentioned above I get the error from the acos() part of the function, as the value in the acos() brackets is smaller than -1 even though that the force in the spring is larger than the friction. If I make the spring stiffness larger, then the equation works, when the part in the acos() brackets is larger than -1. The equation I'm using is on the picture in the link bellow.

$$x(t) = \left(x_0- \frac{\mu m g }{k}\right) \cos\left(\omega_n t \right) + \frac{\mu m g}{k}$$
I really do not understand what this limitation means?


texts: As we know, if the damping model only depends on the instantaneous velocity, it can be called viscous damping, for which the damping force $f = Cv$. However, if $C$ depends on the deformation as $C(u),$ is this still named viscous damping? And if the damping force is modeled as $f=C g(v),$ where $g$ is a function of $v$, do we call this nonlinear viscous damping? Thank you!


texts: Do nylon and rubber bushes usually come in sizes between steel pipe sizes?

texts:
I'm in Cambodia where I don't speak the lingo and I'm hoping to do a little DIY project.

If I were to buy two different off the shelf steel tubes am I right in thinking that the most common nylon and rubber bush sizes are always between these common tube sizes and I should have no problem finding say top hat bushes?

Also, is there more common lengths that these bushes come in, and if one can't find the right length is there generally long lengths of nylon bushing that they can cut down for you?

Thanks


texts: Is it possible to protect electronics on a cubesat from 100-1000g of acceleration

texts: I am currently researching the feasibility of setting up a coilgun that launches Cubesats for a paper.


texts: What do the zeros of the transfer function tell you about a system?

texts:
I come from a mathematics background and I'm familiar with laplace transforms in-as-far-as they provide an algebraic method to solve ordinary differential equations.

So, when I read about transfer functions, I can clearly see the one-to-one correspondence between the poles of a transfer function and the eigenvalues used to solve the homogeneous ODE.  But I'm rather confused as to why the zeros of the transfer function are of particular interest to control engineers.  If we're ultimately interested in stability of the system, why even bother with the zeros of the transfer function?  The poles seem to tell you everything you really need to know.  Does the location of a transfer function's zero with respect to its poles matter in some way?  More importantly, how does their existence (or lack there of) affect how we design a suitable controller?


texts: Is there any way to see mass of a part in autodyn?

texts: I'm trying to model a blast in autodyn using axysimmetric wedge formulation in order to remap a 3d problem later. But I don't know how to calculate the radius of the explosive to match the given mass, or how to see the mass of constituent of multibody Euler part. Does anyone have any suggestions on this account?


texts: Heat storage mass vs. AIR in an ICF house

texts:
If we would want to build a family house (ICF) regarding operational costs, should we leave the insulation on the inside, or should we remove it from the inside?

If we would remove it, the walls would provide a great thermal mass.

But if we would leave it as it, as a normal ICF, then we would only need to heat/cool the AIR inside and not the walls.

Q: which solution would have less operational cost?

House is a very energy efficient one, almost passive house. Big windows facing south (in summer, outside shaders against the sun)


texts: Question in finding the direction of forces in a truss

texts:
This question primarily involves finding the direction of forces in a truss.
Let's give a scenario in Method of Joints
One source I found says that in finding the direction of the source, it would be beneficial to assume everything is tension, if one attains a negative value, the force would simply be in compression.
However, wouldn't this be inaccurate in resolving forces using equilibrium equations (summation of forces along x =0 ; summation of forces along y=0) as they are sign-sensitive?
For example, a truss with several members are given. For the first member, it is assumed that everything is tension; however, it is found that one internal force is compression. With Newton's third law, the adjacent joint will also experience an internal force that is in compression, should I change its direction? Would that not affect summation of forces along x=0 and summation of forces y=0 as mentioned?
Please enlighten me, thank you


texts: How can I connect a silicon hose with 2mm inner diameter to a smaller 1,9mm port

texts:
The biggest diameter of my pressure sensor input port has a size of 1.93 mm. The silicon hose which I want to connect with the sensor's port has an inner diameter size of 2.0 mm.

My honeywell pressure sensor:

My silicon hose:

As you can imagine - it does not fit. The port is to small or the inner diameter of the silicon hose to large.

What is the best way to bring both together? Are there adapters availabe? What is the name therefore? What is a good way in engineering to fix such an issue?

Thanks in advance for your help!


texts: Why does higher concentration of electonic components decrease the airflow requirement for cooling a PC system?

texts:
This source describes in detail a formula used to calculate the airflow requirement in order to cool a computer system.

$$Q = \dfrac{P_{loss}}{c_p \cdot \rho \cdot \Delta T}\cdot k$$

Clearly, the higher the packing density (k) the higher the airflow requirement.

From the same source:

  The k constant describing the packing density (concentration) of the components that prevent
  the free flow of air (k=80-95 rare placement, k=60 dense components)

k = 60 for high component density (ultra small pc)

k = 85 for low component density (spacious full tower)

Meaning a small crammed PC case full of high-end components needs less airflow to be cooled than a spacious tower with the same high-end components.
At this point, things make no sense. It should be like this:

k = 60 for low component density (spacious full tower)

k = 85 for high component density (ultra small pc)

60 = low, 85 = high

Do you think it's a typo?

EDIT

In this chart from the same source the airflow is lower with higher density components:


texts: How safe is this assumption for turbulence modelling in porous media?

texts:
I am studying the performance of volumetric solar receivers (specifically ceramic foams) versus the change of many parameters: solar flux, surface temperature, porosity, pore diameter, flow pressure and flow velocity. I have seen two ways in the literature to model porous media:

Drawing a complex 3D structure that is analogous to the porous zone.

While this might be a very-problem-specific solution, but turbulence modelling in that case is not a problem.

Averaging the governing partial differential equations to account for the nature of porous media and introducing new terms to the equations (porosity $\epsilon$ and superficial velocity).

And this is the approach I am taking which is used in porous models in many CFD solvers.

However, while reading about the treatment of turbulence in porous media in the FLUENT user guide I found that turbulence is not exactly modelled:

  turbulence in the medium is treated as though the solid medium has no effect on the turbulence generation or dissipation rates. This assumption may be reasonable if the medium's permeability is quite large and the geometric scale of the medium does not interact with the scale of the turbulent eddies. In other instances, however, you may want to suppress the effect of turbulence in the medium.

I find "medium's permeability is quite large" quite ambiguous (What values are considered large?) and don't know whether my model will be badly affected by this treatment or not and to what extent?

So has anyone came through this before? or am I overcomplicating things for a parametric study?


texts: For water steam cycle in a "combined cycle power plant" containing 3 boiler drums and dosing of 5% ammonia solution in the condenser. How can I calculate the pH of the boiler water in each of the drums? (LP- 4.6 bar, IP- 36 bar, HP- 162 bar)


texts: What is a good method of creating a pivot point between flat metal bars?

texts:
I could use a hand choosing the mechanism for joining the ends of 2 flat metal bars (each around 3/4" wide and 1/8" thick) so that they pivot freely but without play.

What I'm currently planning is to drill a 1/8" hole in one and a 1/4" hole in the other, put a 1/8" diameter rivet through the bar with the 1/8" hole, then a thin plastic (Teflon maybe) washer, put a Teflon plain sleeve bearing (looks like a tiny 1/8" long pipe with a .126" I.D. and a 1/4" O.D.) into the 1/4" hole, pass the rivet through that, then through another thin plastic washer, a thin metal washer, and then close the rivet.

I think it's important to avoid metal-on-metal contact, but I'm not certain about that.  Is there a simpler design that I could use?


texts: Efficient 3D mesh topology for CFD simulation of turbine blade

texts:
I´m developing a tool to generate an openFoam wind tunnel case of a wind turbine.  I already have the blade geometry constructed, but I'm really new to CFD and parametric meshing.  I found some articles where they mention a C topology to mesh the airfoil and also some software (bladedesigner) that mentions a topology named O10H, but none of these has a reference about how to implement these topologies and if there are others.  They also do not specify what the best use cases for each one.

Can someone help me to get started making an efficient mesh for my tool?

EDIT: At the end I want to have a domain like the picture below, with other blade orientation, but first I need to define the mesh topology around the blade.

My example Blade:

Some of the mesh topologies that I found:

Bladedesigner O10H topology

Various C topologies


texts: How would you build a road system that respected nature?

texts:
How would build a road system or transportation system that respected nature with the following constraints:

No paved roads or less than 10% paved roads
can’t use gasoline (oil)
allow nature to thrive and migrant with little to no impact
food and resources can be bussed in or grown locally to reduce transportation
it can involve new technology or possible new technology

Why?
I visited somewhere that has 8 lane highways in suburban areas. Eight lanes.... Where I grew up there were two lane or one lane roads. Even then you’d see roadkill daily. Some parts of the city where completely transformed from their natural state that wild life depended on for survival.
I think in the future we will have forest garden type cities or villages with less travel or less harmful travel with respect to nature and plant and animal life.
I’ve seen examples of this in many retro future artworks. But in some of those they still have roads that interrupt nature or flying cars.
What engineering answer would you give if this was your issue to solve?
For example, it doesn't have to be broad. It can be I'd build "mag lev roads for bikes and small vehicles and larger roads outside of cities".


texts: What motors to use to guide tape with high speed

texts:
My field isn't dealing with motors and such at all, however, I now need to build something that controls two motors.

So I have two guiding reels with tape between them, similar to old tape recorders. Now the important thing I want to control is the speed that the tape moves and the tension. Another important factor is that I want to be able to switch direction relatively fast.

So I went on the journey of figuring out what type of motors I need and it's quite overwhelming, there are so many types and when I read stuff online it's always "it depends".

What I am looking at now is buy two brushless dc motors with sensors that can sense the position, an Arduino and two motor drivers like the L6234 (https://www.st.com/en/motor-drivers/l6234.html). Then use the Arduino to control both motors.

I cannot find online if it is possible to change the tension in this way. My idea would be to use one motor to give a virtual load on the other motor to increase tension.

Is this possible using brushless dc motors and would my general setup up? Or do I need something completely different?


texts: How can I build a micrometer diameter laser beam from a common laser diode?

texts:
In order to build a lighting system for a microscope (with a digital camera) I want to make a very small diameter laser beam (parallel, rather than convergent). If possible around 1 um diameter.

How could I build such a laser using a common diode laser?


texts: Design of transverse reinforcement in a wide beam

texts: Besides satisfying nominal bar provision in the code, is there any special requirement in the provision of transverse reinforcement to ensure that the longitudinal reinforcement is fully effective in a wide beam design? That is, can I use the full reinforcement area (all bottom bars) to calculate the bending moment capacity of a wide RC beam, provided that all detailing and curtailment requirement is satisfied? Do I have to calculate the transverse reinforcement necessary to confine the longitudinal bars and make them fully effective? Or do I have to consider a reduction using some spread angle from edge of support? For example, in the design of a pile cap with wide pile spacing, using Eurocode or British standard.


texts:
I would like to fold thin metal sheets to a particular angle.

For example: fold a 0.1mm thick steel strip of width 20mm and length 150mm to an angle of 45° along its length (10mm panels on each side of the fold).

I would like to keep the radius of the fold as small as possible, ideally on the order of the thickness or smaller. I would also like to do this on a bench top. I plan to use a range of thicknesses, up to 1mm thickness. But I am flexible on this constraint (but need to use thicknesses <1mm).

Are there any tools/machines which can do this in a repeatable way (ideally with 1-2° variation or less)? Are there any standards for this type of forming?


texts: I want to get this out there. What is a typical and common  range of a small hole gauge?


texts: Whistle Design - Optimizing sound initiation pressure and volume

texts: Assume you can use any whistle type, is there a way to choose the pressure point at which a whistle makes noise? For example I have a whistle that starts making noise at 2 psi but I would like to lower that to 1 psi. Would I change the area of the inlet, outlet? what feature would you change to accomplish this?


texts: Material that holds shape when stretched

texts:
I'm looking for a lightweight material that will hold its shape when stretched out. Something like a rubber band that doesn't snap back. So it starts out small, but once it's stretched it stays large. (Apologies if there's a name for such a property that I don't know.)

Thanks!


texts: Should the corbel angle always be estimated as 60 degrees in masonry construction, or is there a formula to use instead?

texts:
In educational construction material as well as engineering publications, the corbel angle for significant excess loads, and also for substantial openings, in an ordinary brick wall is usually stipulated as being taken as 60 degrees to the horizontal.

For example:

In the first illustration, the reduced load is spread out, in the second a distributed load is spread out, and in the third, a point load is spread out. There are no buttresses or other "out-of-plane" support. The wall can be imagined as an indefinite length ordinary 100mm thick brick wall.

I've tried to find the source of that 60 degree value, to check when it's applicable and how it's calculated, but I can find nothing whatsoever on the topic. The few mentions online of "corbel angle" are all of a form that just state/assume 60 degrees (with no reasoning). I can't find anything else.

Related to this, when dealing with an opening, which of these is the correct way to use the corbel angle, and why? They can't both be correct, as they contradict, but there doesn't seem to be an obvious reason why the answer should be one rather than the other.

In the first diagram, the reduced weight is treated as causing a reduced load in nearby masonry at 60 degrees outward; in the second the heavier surrounding weight is treated as causing an increased load at 60 degrees inward.

How does the corbel angle actually work in these typical situations, where there is an excess loads + openings at some point in an ordinary brick wall, and how universally appropriate is it to always assume it's 60 degrees in ordinary brick or concrete construction?


texts:
I've been asked to modify an existing zimmer/walking frame for a tall person. Bashing the bits of metal is the easy bit, just use tube to make longer legs to replace the original short removable adjustable ones, using tube that's actually thicker wall than the original.

The tricky bit is now they've asked me for a new weight rating, given that the frame is larger. The original frame was rated for use by people up to 180kg. It would be quite easy to say that as the new height is $x$, we should derate the weight by $x$, or by $x^2$, or by $x^3$, but justifying a PIDOOMA for the exponent or the weight is more difficult.

What are the expected failure modes of the frame? Here's a picture of it after fitting with the extended legs, the lowest 500mm.

I'm assuming two failure types are relevant, prompt failure resulting in the user ending up on the ground, and increased wear meaning a weakening after several years' use.

For prompt failure, if I assume that all joints are hinges, then the weakest appear to be on the cross member holding the two side frames together, which is why I guess there are corner braces there.

The moment on those hinges, should the user slump sideways on the frame, will be increased slightly by the longer legs, but will still be dominated by the width of the frame, so not even by a factor of $x$. By my reckoning, it's the smallest height of the triangle formed by the width and height of the walker, and a diagonal from one handle to the floor contact on the other side.

As the new legs are stronger than the original, and use the original spring pins into the same size holes, there should be no reason at all to expect any reduction in simple vertical strength.

The fretting moment at the area of tube overlap where the adjustable legs couple to the frame, held in place by spring pins, will increase directly in proportion to the adjustable leg length. However, the overlap region has been increased in length, more than proportionately, to reduce the contact force caused by this moment. So it may be no worse.

A colleague has suggested a simple reduction to a nice round 100kg, which would certainly be conservative. My concern is that I wouldn't be able to justify it, and that it may exclude other potential users for no good reason.

Are there industry standard tests for this sort of thing? How would the original manufacturer have rated it for 180kg users?


texts: How is the sliding velocity between two spiral gears derived?

texts:
How is the component of the velocity along the tooth equal to Vsinα for both the meshing gears?

Making the relative sliding velocity Vs = V1sinα +  V1sinα


texts: Will standard M5 T-slot nuts fit these different 2020 aluminium extrusions?

texts:
I am trying to source the parts for a Wilson II 3D printer, and the recommended struts are made from 2020 aluminium extrusions, like so:

However, in Bangkok, I can only find this type:

Note that the profile/shape of the slot is markedly different from the image above.
Whilst looking about on the web, I have also found other types, like these:

Again, the profile of the slot varies considerably.
My question is whether standard full size

and half size T nuts

will still fit all of these different types? Or are there different T-nuts for the different types of extruded 2020 aluminium, depending on the profile/shape of the slot.
Also, why are there the different designs, does each type have an advantage for particular applications (with respect to strength, weight, etc.)?

Update
For completeness and accuracy, the 2020 extrusion, that I obtained in Bangkok, actually has this profile:

and here is a more in-focus photo, of four, in a 2 x 2 configuration:

As ericnutsch states, in his answer, only regular hexagonal M5 nuts will fit.


texts: Which software to get started with 3d Modeling

texts:
I'm a software engineer by trade, but I have an idea I'd like to turn into a prototype. for starters its going to be a rectangular project box with some buttons and displays, nothing too complex. I'd like to use this as an opportunity to learn 3d modeling. I've done 2d cad before and it was nice to be able to print the design, tape it to plastic or wood or whatever and drill holes and have them close to perfect.
I'd like to try 3d modeling, if it's possible to show that 2d plane that would be great too. I'm unsure which software to pick. Sketchup seems targeted towards a simpler interface, but I dont like the online only. I have an autodesk student liscence so currently leaning toward Fusion 360.
Are there any suggestions of where to start or what SW to use? THank You


texts: Why do the lights dim when I turn on a mitre saw?

texts: The other day I was sawing some wood on my mitre saw. I have a single light bulb in that room and it was on. The moment I press the button for the saw to turn on, the lights dim a little and go back to full brightness while the saw is running. The saw was connected to the same room. Why does this happen only when the saw is started? The saw has supposedly slightly  less than 2 kW power and uses a universal electric motor.


texts: Sky scrapers are often found in dense urban environments. Is there a known method to controllably demolish a sky scraper with minimal collateral damage?


texts: Raised plywood false floor for heavy equipment usages

texts:
I have a electronics assembly company, and we run two assembly lines. They consist of several machines, with the heaviest being around 4000lbs, on 6 metal casters. We currently have the line on a concrete slab, inside a large converted warehouse.

The concrete slab is badly spalled, and apparently didn't have a vapor barrier when originally poured. If we leave anything heavy on the floor (cardboard box), it will be dripping with water the next day. We maintain a humidity level of 45%, which probably brings more water up also. We are located in Florida, so have a high water table.

The landlord is willing to work with us to fix this issue, and a contractor recommended we do a vapor barrier on the slab, then a grid of 2x4's, then tongue and groove plywood. On the plywood we would install ESD safe vinyl tiles. They said this is common in gyms and dance studio's. They use rubber strips under the 2x4's to help dampen noise and vibration.

It's hard to find information on this method, is this suitable for this amount of weight, in an industrial environment? I really don't see of many other options if this isn't acceptable to do. I would assume we would do the 2x4's either 6" or 12" on center.


texts: What is the purpose of end plates when connecting beams together?

texts:
Quite often this kind of arrangement can be seen when beams are connected together. A rectangular plate is welded into a beam, and the plate is bolted to the other beam. I suppose one purpose would be simply that bolting is easier to do in some cases at the site rather than welding the beams together directly at construction site, but is there any other purpose?
I remember once hearing this kind of plate refered to as a moment plate, but I couldn't really find much information on such a thing. Is there some kind of moment-related purpose for this plate or am I just remembering wrong?


texts: How effectively will this evaporation setup cool down the water?

texts:
I devised a setup, and I show it in the diagram below. Suppose I have these specifications:

Water in the bottle is 5 liters and it's initial temperature is 28°C.
The bottle capacity is 6 liters.
The tank water is at an initial temperature of 35°C.
The air inlet fan AND the vapor exhaust have a CFM of 1000 (one is in negative I guess). The circular vent cross-sectional radius is 1ft.
The cloth surface area inside the enclosed space is $1m^2$ (I don't know if this is realistic considering the bottle size. If not, just use a suitable one in calculations.)
Ambient temperature outside enclosed space is 35°C.
Enclosed space volume is $5.8m^3$
(Don't ask about humidity inside enclosed space, as it is supposed to be constant since one fan will cause vapor, the other takes it out. For calculations, use a random, suitable, humidity %).

To bring the water temperature down to 3°C, how long will I have to run the inlet and exhaust fans? Please don't close this outright. It took a lot of energy to make that diagram, so if anything is missing, just comment and I'll update.


texts: How can flow in a centrifugal compressor at fixed conditions vary?

texts: Consider a centrifugal compressor. The compressor map usually plots the adiabatic head vs volumetric inlet flow for rated conditions of pressure, molecular weight and temperature at a given speed. But when pressure, temperature, molecular weight and speed are fixed, how can the inlet flow be made to vary ? Is it accomplished through the use of inlet vanes ?


texts: Hand-pressed metal stamping - fishing spinner blades

texts:
I want to stamp my own fishing spinner blades.

They look like this:

http://lurepartsonline.com/Online-Store/Colorado-Blades/Premium-Finish-Colorado-Blades.html

Specs are usually 1mm thick, 3x2" oval curved oval. Ideally, I would want to be able to adjust the size and shape, or apply grooves/patterns to the blade. I assume I can buy bulk sheet metal from a hardware store.

I'm thinking I could possibly get 3d-printed casts for different designs, or possibly prebuilt shapes?

I'm mostly a programmer, not a mechanic, so I'm just looking for a general idea of what is possible.

Is this feasible, and how much should I expect to pay in machinery?

I've seen some hydraulic presses go for under $1000, but it's a private hobby of mine and I could probably pay well over that if necessary.

I want to stress that this is an at home hobby and I don't want to rent machinery or order custom designs from a factory.

I realize cutting the metal won't necessarily give a perfect shine, so any addition points on finishing/painting would be appreciated.

This is a video of how these things are generally produced commercially:

https://www.youtube.com/watch?v=zjovDNw1GcY


texts: What is the engineering term for the gear style articulated arm

texts:
You loosen a screw (knob) and then move to the angle you want and tighten.

I need to know what the engineering term for this part is.

Thank you in advance


texts:
I thought the term sample period referred to the time interval between one measurement and another. But I've come across this article which says

About every tenth of a second, a dataset, $S(i)$, of the form:
...
is recorded (of course, the time between taking two datasets must be a multiple of the sample period, i.e., $\Delta t \mid (t_{i+1}- t_i), \forall i$).

Now, the way I interpret this is that $t_{i+1}- t_i$ is the time interval between a recording of a data set and the successive. So, if that's correct and $\Delta t$ (i.e. the sample period) is the time interval between one measurement and another, then $\Delta t = t_{i+1}- t_i$, but clearly some definitions must be wrong, otherwise the original author of that article would not have introduced two terms to identify the same thing, and would not have said that $t_{i+1}- t_i$ must be a multiple of $\Delta t$?
What exactly is the sample period $\Delta t$?  How is it different from the interval between one measurement and the other (i.e. $t_{i+1}- t_i$)? What exactly does it mean that $t_{i+1}- t_i$ must be a multiple of $\Delta t$ (I guess this will be answered once I know what's exactly the sample period)?


texts: Does Finite Element Method use direct stiffness method? Or it is another mathematical method? We definitely use direct stiffness method to solve frames. FEM is based on entirely this or depending on he mesh, it is something else? Direct Stiffness method is for when we have simple lines and nodes, but when we have a complex mesh we use another method in FEM?


texts:
I have been attempting this question for a while now. Could anyone give me a hand?

The question and the work I have done so far is below. My final "answer" is
P (force required to keep the gate closed) = 109,100.1526w + 346.84 (where w is the width of the gate). Since i cannot rearrange my answer in the form "P/w", I am assuming I have made a mistake somewhere, but I cannot identify my mistake.


texts: From the viewpoint of a civil engineer, what was the purpose of this bridge?

texts:
I have been searching for historical structures in the province of Van, Turkey, by examining the publicly available satellite imagery like Bing Maps. There is a historic bridge near Kaçit, Çatak. Its name is Zeril Bridge. I tried to figure out the places which are connected by the bridge. The two sides of the stream seem to be very steep and it seems to me that the bridge is situated in a strange location.

From the viewpoint of civil engineering, if you build this bridge today, what would your purpose for locating the bridge at that point be?

Coordinates of the Zeril Bridge: 37.915422 , 42.984053


texts: How to calculate % volume change due to wire drawing

texts:
I am currently doing some lab work involving wire drawing and trying to calculate the % volume change of the wire after wire drawing. I am using the geometrical data (length and diameter) of the wires before and after the drawing process for these calculations. From various sources online I have learned that the volume doesn't change for the wire drawing process.

However, my calculations don't seem to show this feature. I have calculated the volume of the wire (before and after the wire drawing process) using the formula:

Volume = $\small\sf\pi {(radius^2)(length)}$.

In my calculations the volume of the wire after each draw gradually decreased.

Can some tell me if this is correct or if there is another method to conduct this calculation. Any form of help would be greatly appreciated.


texts:
With a normal spring, you compress it using a linear force to store energy and then it decompresses and releases the energy, again in a form of linear force. Is there a mechanical mechanism that stores energy by rotating force and releases energy by rotating force?  It doesn't have to be spring operated, but I think it's the only way to work, with springs.

I want it to work for many many rotations (to store energy) and to produce many many rotations! what's the best mechanism for this?


texts: How to add radial protrusions to a disc in Autodesk Inventor

texts:
First post here, trying to get a little help with Autodesk Inventor.

I am trying to make a part that is basically a wheel with little nubs on the end (think of a lego with tabs on the outer circumference).

What I tried so far is making a rod and using the Constraint function to make the parts one piece. Is there a more direct way to do this? I can't seem to find a way to just add the tabs/nubs on the edge of the circle.


texts:
Im working on a headrest for a car that will electrically adjust up and down and have drawn up my plans. it now comes to the important questions, such as what motor to use. Ive been looking at motor sizing online but not found anything particularly helpful as im left with gaps and questions. i want a motor with a gear to raise and lower the arm of the headrest.
lets say:
m=1kg,
r of gear=0.03m,
t to max height=5s,
max height=1m,
gravity=9.81
(not my planned figures but random as id like to run the calculations myself)
What should my motor speed, load torque, inertia, stall torque, no load speed, armature inductance ect.?
if anyone knows the correct steps to go about this and can use my example values to explain or knows of a good link i would be grateful


texts:
This is actually only tangent to engineering, and mostly related to Quality Management Systems, so this could be off topic.
For a document which has a specific Document Naming System in a Document Control format such as:
[Project Name]-[Document Type]-[Sequential]

Such as:
10001-LTR-00028 - The 28th Letter (LTR)
10001-DWG-00054 - The 54th Drawing (DWG)

How should the records derived from these documents be named?, for example:
The 28th Letter Template
The 28th Letter Signed
The 54th Drawing Approved by Client

And how should the records at specific dates be named? for example:
The 28th Letter Scanned the 2021-05-16
The 54th Drawing Scanned the 2021-05-16

Thanks in advance.


texts: Why are many compliant mechanisms only flexible in the joints?

texts:
I've been playing around with 3D printing some compliant mechanisms, mostly to get precise linear motion, and I've noticed that many commercial compliant mechanisms are often designed like this:

Where the flexible parts are only thin by their joints. Is there any benefit to this over simply keeping it thin across the whole flexible part? All my designs use flexible parts which are thin all the way, granted I'm mostly working in PLA so I need the parts to be long and thin to handle the stresses without breaking, but what is the reason behind keeping those parts thick in the middle?


texts: What really is the difference between allowable stress design and ultimate limit state design?

texts:
I'm trying to understand this difference. From what I've read, ASD basically deals with making sure the stress in a structure does not exceed a certain limit, the yield stress of the material. It ensures that structures remain in their elastic region while subject to designed structural loads.
Limit state design on the other hand defines a set of ultimate limit states against which the structure has to be checked. These states can be static equilibrium of the structure (EQU), the strength of a structure (STR) and fatigue damage of the structure (FAT).
But don't these two design philosophies in the end boil down to the same thing, making sure the structure (steel structure for example) does not reach a stress too high? For example, we might check a steel beam against loads by calculating the expected characteristic loads such as wind and dead load, combine these according to different defined ultimate states and then check that the stress resulting from these does not exceed the yield stress of the beam. But isn't this in the end what allowable stress design does? What is the practical difference between the two?
EDIT: Making further research, I noticed that limit state codes do sometimes allow yield to occur. For example, in Eurocode 3, part 1-1, 6.2.5, it is stated that the resistance of a cross section against bending is determined using the plastic section modulus.
In this Youtube video, the differences are given:

Here the difference is given to be that in ASD, we use service loads which are the expected loads without any safety factors applied. Aren't these what are known as characteristic loads in limit state design? In contrast, it is stated that limit state design uses factored loads. So why is it that in ASD we use loads without any factors? Aren't safety factors there to take uncertainties in things like material properties and modeling theories into account? Why don't they exist in ASD?


texts:
In addition to the machine parts we manufacture in our foundry we also produce high quality steel abrasive including low carbon round corn, cut wire, steel grit amongst others. We will be happy to advise you of the best abrasive solution for your requirements.

Here what does "corn" imply? Is it powder?