texts: When are Single Point Urban Interchanges used?

texts:
There is a topic discussing the pros and cons of roundabouts. A less common intersection is the Single Point Urban Interchange (SPUI).

This is an intersection that seems to be mostly used on overpasses. What makes this intersection unique is that all of the different exits, on ramps, and crossing road lanes go through the same location, i.e. the "single point".

When might a SPUI be beneficial, and when might other intersections be better?


texts: What is this drawing style that faces the x-y plane but stylisticly pulls the z axis down and to the left?

texts:
Notice that x and y are proportionally equal and perpendicular to your line of sight, but z is not. It's not 30-90-30 isometric. Also z should actually be pointing right at you rather than down and to the left if this was true 3D rendering. Hence this is a style. Does it have a name?
Note: z is free to scale any way you like so this style can be made into a kind of isometric. That is x, y and z can all have the same scale. But regardless of that does this have a name that wont be confused with 30-90-30 isometric?


texts: Would a sacraficial anode be used to protect large boat (aircraft carrier) or is there something different?

texts:
I did the calculation for the surface area to anode ratio (zinc) for a project recently.  It was my first time going through this exercise, and I ended up with a 7.2% number for surface area ratio (which was later confirmed externally by computer modelling through a different group).  This brought me to think about aircraft carriers and large cruise ships, where this value is rather large.
If a ball-park number of 7% is correct for general applications, how are sacrificial anodes addressed on these large vessels?


texts: FFT output for noise sensor shifts after some time

texts:
I am using a noise sensor (ADMP401) along with Arduino Mega. I use FFT to convert the noise sensor analog output to frequency domain, then remove the first 30 bins (to remove some board noise), then calculate the rms value of the remaining bins. So, during a period of 10 seconds (which is my polling period), I have a set of 12 rms values from which I take the median value to get the ambient noise equivalent.

Its working fine and I can see the output value responding to noises. I usually get an output of around 7 to 10 for silent conditions. The problem is, for some units, this base value of 7 to 10 shifts to around 2 to 3 after running for some time and then will remain at that lower level. Still the sensor will respond to noises. But since this shifting is happening, I am unable to correlate the output to dB levels.

I am using openmusiclabs FFT algorithm for arduino. Has anyone experienced this kind of behavior while working with noise sensors and FFT?


texts: How to solve LMIs with equality constraints using MATLAB?

texts:
I would like to find n by n matrices P and Q that minimize

J = norm(P) + w*norm(Q), where w is a given weight,
subject to
P>=0, Q>=0, and f(P,Q)=0, where f(P,Q)=0 is a given function of P and R.

I tried to solve this problem using the lmi solver of MATLAB, but have no idea how to deal with the equality constraint: f(P,Q)=0.

f(P,Q)=0 is equivalent to f(P,Q)>=0 and f(P,Q)<=0, but MATLAB only solves strictly feasible constraints.

But the above problem contains not strictly feasible constraints.

Is there any good solution to handle this kind of problem using MATLAB?

Thank you.


texts: Why don't hydroelectric plants use cascades of turbines instead of single turbines?

texts:
In a gas turbine engine there're multiple sets of blades - one set after another and combustion products pass all the sets and each set of blades gets some of the power. This increases utilization of power from burning gas.

Meanwhile hydroelectric plants use turbines with a single set of blades and the typical usecase is where there's a channel for feeding water from an elevated reservoir and the turbine is at the bottom and water runs through the turbine and then just flows down the river. I assume there's still some mechanical power left unextracted when water flows out of the turbine.

Why are water turbines not "chained" so that water exiting the first turbine drives the second turbine using the residual mechanical power?


texts: Today I came across this question and I can't sleep thinking about how to solve it. How do I find the principal values and sketch a shear force and bending please see my attempt as I'm not sure if this is correct. diagram on the below picture?


texts: I have a 1/2-20 stud that I need to step up to a 3/4-16 stud. I searched around for 1/2-20 female to 3/4-16 male thread adapters, but was only able to find such a product on McMaster for sizes 1/2 and smaller. Are there "thread adapters" (assuming that's what they're called) for larger sizes? If so, does anyone know where I can buy them?


texts: multiple wall, pressurized gas pressure vessel

texts:
I was thinking about interesting powder metallurgy method, hot isostatic pressing. Often thick steel walled vessel is required increasing costs and decreasing the prevalence of this technology.

This led me to consider say several metal spherical concentric tanks. I wonder if the inner most tank is at very high pressure more so than the metal wall could handle but was counter acted mostly by a second concentric tank pressurized nearly to the same pressure but slightly less, and so on so forth until finally the outer most tank was low enough pressure to be contained.

I'm not really sure of the net forces? Would there just be large compression forces on the tanks? Would there be a large net force inwards or outwards? I ask because it would be interesting if say I had two balloons and everything worked out such that say I had a 99% chance of rupturing balloon A at pressure P_1 but it balloon B had less than 1% chance of rupturing at pressure P_2 and I found both had low chance of rupturing at respective pressures with balloon A contained inside balloon B. Maybe this help to understand the idea I wonder about, perhaps it is a fallacy I'm not sure.


texts: How do I connect multiple water-filled syringes?

texts: I'm trying to connect 4 separate syringes containing water and we need water-tight tubing to prevent water from leaking out of the system. The water would theoretically need to be pushed out of one syringe and into another syringe. We were wondering if there was anything relatively cheap that could do the job? I've included an image as reference.


texts: Fluid head loss coefficient for drilled hole cross profiles

texts:
I am attempting to solve the flow rate for a fixture and need to calculate the losses in the fixture that consist of ported holes. Please see picture below. Blue arrow signify air flow and red arrows signify capped holes.

From my mechanical engineering schooling I figured this would be similar to flow in a pipe, however when calculating loses how should I account for the cross profiles for the porting (red arrows)? Essentially, I am trying to figure out the Kl, loss coefficient, variable in Hloss = Kl*(V^2)/2g. For pipes it is normally a corner component and thus I have a table of loss coefficients.

I attempted to research prior to posting this, but I am not 100% sure what this corner profile is even called.

Thanks in advance.


texts: VFD or soft start to minimize power consumption on starting a motor?

texts:
I want to use the smallest generator possible to run a standard three-phase AC well pump. According to this website and others, it is advisable to use a generator capable of 3x the running kVA if the pump is started directly, and 2x the running kVA if the pump is stepped up using a star-delta starter. So for all but the first few seconds of use, the generator will be running at between 33% and 50% of its rated load. This seems wasteful:

Bigger generators costlier, bigger, and heavier
Diesel generators, which are typically the only economical choice over 10 kVA, decline steadily in fuel efficiency as the load falls below about 85%, and below about 60% there is a risk of cylinder glazing
The application of dummy loads, as the linked website above suggests, will indeed prevent glazing, but at the cost of significant useful efficiency.

So I am thinking of installing either a soft starter (which gradually increases voltage) or a variable frequency drive (which gradually increases frequency, and hence power demand) in front of the well pump.
Soft Starters
I guess you can think of a star-delta as a coarse, step function-like soft starter. In the initial Y-connected phase, voltage is comparatively lower, then when the motor is switched to Δ-connected, voltage increases by a factor of $ \sqrt{3} \approx 1.73 $. The website linked above says that with a star-delta starter, the generator should be rated for at least 2x the running kVA. The soft start I've been looking at, however, can ramp up from 30% of running voltage to 100% in as long as 30 seconds. My thinking is that $\frac{30\%}{1/\sqrt{3}} = 0.5196\ldots\approx\frac{1}{2}$, so the soft starter should need about half the kVA of the star-delta. So I should be able to start a pump that wants 5 running kVA with a 5 kVA generator, right?
Variable Frequency Drives
My understanding is that VFDs can be used to soft start a motor by gradually increasing frequency (and possibly voltage with it). I understand that VFDs provide many advantages over soft starts. But do they use any less peak power on startup?


texts: What is the cost of heating of a 60k sqm building to 27 degrees celsius vs 20 degrees celsius?

texts:
How can I calculate the cost of heating a building such as http://group.canarywharf.com/estate-building/5_north_colonnade/ ?

Its size: 59,142 sq m / 636,600 sq ft

The temperature is in many places more than 27 degrees celsius. I would like to show, that an investment in better heating control would pay off quickly, if the temperature was reduced to 20 degrees celsius.


texts: What is the principle behind controlling thermoacoustic combustion instability with a speaker?

texts:
From "ThermoAcoustics and the Rijke Tube: Experiments, Identification, and Modeling", thermoacoustic instability can be subsided using an amplifier and a speaker.

It says in page 4,

  The microphone signal (AC coupled) is fed via the DAQ board to
  Simulink, where it is recorded and multiplied with the variable gain.

Isn’t it merely increasing the amplitude of the audio input? How is it possible to reduce thermoacoustic combustion instability?


texts: Linear actuator on a scissor lifting table

texts:
I am designing a scissor lifting table and I have an issue with the linear actuator.  This table should be lifting 100 kg. I studied the problem in two ways : a static study and a power study. My table is a 3-level table. Here is a schema of a one level table :  (1) and (4) are V-rails that guide wheels on points A and F. (5) is the linear actuator. (2) and (3) are scissors, and all the mechanical connections between the different parts are pivots (revolute).

In this static study, I found (page 3) that the two linear actuators have to lift a load of minimum 2158.2 N. So each linear actuator has to be lifting 1079.1N.

In this power study, I found (page 2) that the two linear actuators have to lift 12988 N (6494 N without the safety factor). So each linear actuator has to be lifting 6494 N (3247 N without the safety factor).

Between the two results, I have a ratio of 3. I guess the second study is false, but I'm struggling finding why, and I still have no solution...

I hope you can help me, and I thank you for your time :)

Muthu


texts: How does reaction rate depends on concentrations in irreversible reactions?

texts:
Consider the following consecutive, second order, irreversible reactions are carried out in a batch reactor:

A + S Yield(k1) X

X + S yield (k2) Y

One mole of A and two moles of S are initially charged to the batch reactor. Find the mole fraction of X remaining in solution after 75% of A is consumed. Assume k2=2k1.

I know some differential equations are needed but I'm not sure how to set this up.


texts: Can I use polymer clay to make a mold and then melt HDPE plastic in it in the oven? My goal is to be able to dig a fairly uncomplicated shape in a polymer clay block and then fill that mold with small HDPE plastic filaments. I'm hoping that the melted plastic would fill the mold with the help of gravity pushing it down or I can get it out to apply pressure a few times. Will the polymer clay melt? Do I have to bake it beforehand? If clay doesn't work, what other easily found and cheap substitute exists? Thank you.


texts:
I have watched a property tour around an apartment in the Steinway Tower (NY) on YouTube and I noticed one detail that bugs me, namely gas stoves.
In Poland it is very uncommon for new blocks of flats to have gas installation, because safety law requires all pipes to be visible and accessible (they cannot even be obscured). Also if a building has more then X floors (I don't remember how many) it is strictly forbidden to construct gas installations.
I am curious how it is done and what steps are taken to provide fire hazard safety in tall buildings and how does US law regulate such designs?


texts: Nusselt number definition for a constant wall temperature

texts:
We know that for constant heat flux $\dot{q}$ Nusselt number can be written as

$Nu = \frac{hL}{k}$ with $\dot{q}=h(T_f-T_s)$, therefore $Nu =\frac{\dot{q}L}{k(T_f-T_s)}$

However, I'm a little bit stuck on writing a definition for a constant wall temperature, lets say in a duct with $T_s=const.=500K$ where $\dot{q}$ is not a known constant from boundary conditions.

How can one derive $Nu$ in this case?


texts:
Problem

I have two USRP antennas close to each other. I know that signal strength on the receiving end has to be at least -80 dBm. Both antennas have 2 dBi of gain. I want to compute what is maximum propagation loss so that this system still works. Signal is being transmitted with power of 10 mW.

Attempt to solve

Since i want to know the maximum amount of power loss during transmission to one antenna to another. I can form equation as. $p_0=$ power of transmitted signal, $p_{m}=$ minimum acceptable signal strength, $x=$ maximum amount of signal loss during transmission.
$$ p_0 \cdot x = p_{\text{ml}} $$
$$ x = \frac{p_0}{p_{ml}} $$

My solution is ratio of powers so I can use dB units, by converting them with base-10 logarithm.

$$ x_{dB}=10\cdot \log_{10}\left(\frac{p_0}{p_{ml}}\right)$$

i need to change -80 dBm to millliWatts with $-80\text{ dBm}=10^{-80/10}\text{ mW}$. After this I can sum antenna gain to my answer since we are using logarithms.

$$ x_{dB}=10\log_{10}\left(\frac{10^{-80/10}\text{ mW}}{10\text{ mW}}\right)+2\text{ dBi} +2\text{ dBi}$$

$$ x_{dB}=-86\text{ dB} $$

However my answer seems to be incorrect ?


texts: My customer wants to use my products to do something unsafe. What is my ethical obligation?

texts:
We sell products that attach to a motor drive's DC bus. We also formerly sold diode kits that let you hook one product up to multiple drives. We stopped selling those diode kits because they were unreliable with modern hardware, and we had better solutions. My customer tells me he wants to keep using the old diode kits, because he can have his repair techs disconnect power to one drive and have it replaced, while the others are still powered on.

I maintain that this is an unsafe practice, because diodes are not safety-rated devices. (See question here.) But my customer is rather insistent. What is my ethical obligation in this case?


texts: Is my procedure applicable to make a room soundproof?

texts:
Recently I found it essential to make my room soundproof and for this I have worked out the following way:

The walls of my room are made of cement. I want to add two glass layers (of different thickness) inside them. To make it clear, think of my room for the time being a hollow cement cube. Now I want to add one hollow glass cube inside this cement cube (whose dimensions are intentionally kept less than the cement cube) and then do the same for the second glass cube (whose dimensions are also intentionally kept less than the first glass cube). Now what I want to do is to suck out the air between two consecutive layers by a stopcock.

My questions are

Will this procedure make my room soundproof?
Will my room be durable?


texts:
I'll be the first to admit that I have always been somewhat confused by best-practice dimensioning standards surrounding pipe threads. While there is a decent amount of literature available online, (such as this) I still find the implementation to be a bit vague -- specifically regarding thread depth.

ASME B1.20.1 (AKA the NPT bible) makes me think that one should callout thread-features such that they run to the "vanishing point" or L4. However, L2 is designated as the "maximum thread engagement distance".

In my experience, the engagement depth on NPT fittings can vary wildly (depending on quality of machining, amount of teflon tape used, and the person wielding the wrench, etc etc). This inconsistency can cause other issues when it comes to actually assembling -- but that's another topic in itself.

To summarize, my questions are...

Which 'L-value' should I be using for thread depth when designing NPT fittings (i.e. in my cad model)?
If that value is L4, do machine shops know that I'm referring to vanishing point on my drawing and not max engagement depth?
Bonus: Are there any other 'best practices' surrounding this topic which may be useful?


texts:
"1 TR is equivalent to the rate of heat transfer needed to produce 1 U.S. ton (2000 lbs) of ice at 32F from water at 32F in one day, i.e., 24 hours."

While defining 1 Ton of Refrigeration (TR), why doesn't some specific value of pressure come into definition?

Isn't freezing water (to ice) related to pressure?
-->If yes then why do we go away with it while defining 1TR ?


texts: Two 3/4HP / 500W motors to run in opposite directions, at precisely the same RPM, controllable from zero to 5000 RPM?

texts: I am designing a machine where I need two 3/4HP / 500W motors powered from 110VAC to run in opposite directions, at precisely (+/- 0.3% perhaps) the same RPM, controllable from zero to 5000 RPM by a dial or pedal or other control.  The loads are the same, and gears are probably not practical at the form factor (6" wheels 3" apart) and RPM.  I don't need computer control, positioning, or major telemetry, I do need a way to know what RPM they are running.  What is a good way to handle this economically?


texts: Finding the torque required for telescopic cable mechanism

texts: I am designing a linear telescopic system that gets elevated with a step motor, but to find the compatible motor, I need to work out the torque that is required for the elevation. I have uploaded my CAD model to this thread with how cables are connected. Could someone please teach me how do I go about calculating the torque that is required? it is even more difficult with a pulley that is also moving up in the system. Thank you in advance...


texts: Transistor and diode on induction cookware

texts: Will a 1 kW induction cook top damage a transistor which is kept on its surface? If yes,  what is the mechanism? Is it electromagnetic induction?


texts: What types of oil reservoirs are applicable to radio/microwave heating and advantageous to SAGD?

texts: I am doing a project looking into the advantages of radio/microwave heating of oil reservoirs. I've seen research indicating that RF/Microwave heating can be used for environments such as shallow, tight, high permeability, fractured, etc zones. What are the disadvantages of applying techniques such as SAGD in these zones?


texts: What is the difference between plastic and compact cross sections?

texts:
I'm studying beam cross section classifications here.
It is explained that the difference between plastic and compact cross sections is that while both do develop their plastic moments, only plastic cross sections have sufficient rotation capacity to form a collapse mechanism.
I don't quite understand what happens when a compact cross section undergoes local buckling. In the text there is an example of a rigidly supported beam. When enough moment is applied, the ends develop plastic hinges and from there on the beam acts as a simply supported beam with moments on the ends. With more rotation, the middle also develops a hinge and the structure collapses.
So let's consider this scenario with both a plastic and a compact cross section. Plastic cross section develops the plastic hinge, and has enough rotation capacity to form the collapse mechanism. But what happens with the compact cross section? By definition it also forms the plastic hinge, but this one doesn't have the required rotation capability to form the collapse mechanism, so what happens with this one?
So how does the compact cross section form a plastic hinge and not a complete collapse mechanism?


texts: Is a mechanism similar to a bendy-straw ever used to change the direction of a rotation in engineering?

texts:
I had a typical bending drinking straw and when I twisted the outside tip, I expected the straw to rotate in an L-shape, so that the other end of the straw would be rotating sideways. Instead, I found that the straw remained perfectly in place, and the other end twisted in place regardless of the bent angle.

So I was just curious: Do they ever use this particular mechanism in engineering, rather than, say, gears?


texts: Specific energy vs Specific power in batteries

texts:
When looking at the Wikipedia page for Lithium-ion batteries, one can see that there are some technical details such as Specific Energy and Specific Power, but I don't know how to connect them.

For example, one can see this:

  Specific Energy: 100–265 Wh/kg

and

  Specific Power: 250 - 340 W/kg

According to the theory, power equals energy divided by time; i.e. 1 W = 1 Wh/t. So can guess that t is the discharge time. Li-ion batteries usually have a discharge rate of 1 C, which means that the battery would be discharged in around one hour. Looking at those numbers, it doesn't look like my logic is correct, therefore I would like to know if this is the case or if those numbers don't really match?


texts: Verifying MERV Integrity for Specified Material

texts: This is a question related to materials science. Essentially I want to purchase MERV 16 material from a manufacturer and I want to verify that it's true MERV 16 material when I receive the order. Would anyone know an experimental setup idea or test I could set up to verify their product?


texts: Understanding the torque of a motor/gearbox combo

texts:
Imagine a typical DC motor / planetary gear combos.

Is my thinking correct:

Say you have a 100 kg mass on a frictionless surface.  The gearbox output shaft has a 0.10m arm with which you push the mass. (ie, linearly a few inches).  You want to accelerate the mass at 0.1 m/s2.

Does that mean, it would take a force of 10 N (ie 100 x 0.1), and hence a torque of 1 Nm  (10 x 0.1)?

If that's correct, and say after the gearbox the spindle indeed delivers 1 N.  It's a 6000 rpm motor and a 100:1 gearbox.

In fact, would that mean the motor itself indeed delivers "$1 \text{Nm}$" .. it "doesn't matter" about the gearbox?

Or, if the output spindle is indeed delivering "$1 \text{Nm}$", would that mean the motor itself to purchase would be rated 1/100 = $10 \text{mNm}$ ?

{ie, 10 milliNewton-meter ... 0.01 Newton-meter!}

The figure seems way too low, but I'm likely mistaken.


texts: Relative improvement in flow from diameter change with sub-milliimeter tubing

texts:
I want to calculate the improvement in flow rate that can be achieved with changing the tubing size when the tubing is sub-millimeter size.

I originally approached this using a simplification of Poiseuille's law which says $\Delta Q=\Delta r^4$

However, lets say I'm changing from 0.5 to 1.5 millimeter tubing.  That gives $\Delta r=0.050$, which when raised to the 4th power is a tiny number (6.25E-05). This seems wrong intuitively, based on the relative increase in size (i.e. new tube is 300% of the original tube)

If I convert to micrometers first, the result jumps to 6.25E06, which seems really really large.

What am I missing here, because this doesn't seem like the right approach.

Thanks!


texts:
If we multiply the identity matrix by any vector or a matrix, then the result is the vector or the matrix themselves (like a mirror).
Tensors represent physical quantities, so if it wasn't a physical quantity then it is not a tensor. Right?
What about identity matrix, is it considered to be a tensor? Maybe not because it is an operation not a physical quantity. But there is a tensor that represents it which is the Kronecker delta.
Is the information that I wrote true? I'm trying to understand more about tensors.


texts: What is the logic behind using a wall tap/piezometer to measure the static pressure. Is it that near the walls, the fluid velocity is zero, because of the no slip condition and hence the pressure measurement near the wall would only be static pressure. There is this point in the book that i am consulting, it says "there is no pressure variation normal to straight streamlines, this fact makes it possible to measure static pressure in a flowing fluid using a wall pressure tap". Does this point mean that because there is non-variance of pressure in normal direction to the straight streamlines, thus giving a single value for static pressure, whereas in regions of curved streamlines, we would have progressively increasing values as we go away from the center of curvature of the family of curved streamlines. Also, why do we require a separate static pressure measuring instrument alongside a pitot tube (for fluids passing through a pipe) in order to measure velocity through the Bernoulli eq. Why can't we calculate velocity directly as is done, for free streams of fluids, such as river water.


texts:
I am trying to compelte this question, however when i run the simulation there is no voltage atall on the output votlage, and cahnging the capacitor value as requested in the question does not chane the output at all.
Here is my version, the only thing i can see that is different is that the example circuit does not have AC listed in the parameters. however i cant find a votlage source like that one without the AC parameter.

If anyone could help me to get this working i would be extremely grateful.


texts: What's the difference between aircon modes Auto, Sun, Snowflake?

texts:
Most air conditioners have three modes: Auto, Sun, Snowflake

What is the difference it terms how it works?


texts: Finding all the pressure acting on base of cylidner

texts:
Water is filled in a flask up to a height of 20 cm. The bottom of the flask is circular with radius 10 cm. If the atmospheric pressure is $1.013 \times 10^5$ Pa,find  total force exerted on the bottom of flask. Take g = 10 ms-2 and density of water = 1000 kgm-3. P0 is atmospheric pressure here.
Now, here if I draw the FBD of the base of flask. Then, there are three pressures acting on the base. Atmospheric pressure acting from top and below because fluids exerts pressure in all directions. Then is the hpg pressure.
Total pressure on the bottom of flask is $P_0 -P_0 + hpg$. Is this correct if it asked total pressure acting on the base?


texts: What is the "allowable number of axle-load to failure equation" used in Pavement ME Design?

texts: How is the allowable number of axle-load to failure equation actually used in the software? Is there any documentation regarding the calculation of the tensile strains?


texts: how to calculate the time for retransmission in slotted Aloha

texts: I need to configure my code to make retransmission in slotted Aloha in case of collision, how to choose the timer ?


texts: Why don't we make mainsprings out of Kevlar?

texts:
The most important factor for mainspring is, as far as I understand the matter, is their yield point.

In this regard, Kevlar beats steel by at least factor of two. So why aren't we using it instead of steel in watches, well their mainsprings specifically.

I could understand the costs factor, but even premium watches seem to avoid it.
As a matter of fact, finding any non-steel mainspring is pretty rare.

Is there any reason for that?


texts: How to size a refrigeration compressor based on an evaporator size?

texts:
I purchased an evaporator holding the following specifications:
Cooling Capacity = 2 kW
Size = 66 X 53 X 43
What I need to know is how to choose a compressor just to gain this full cooling capacity?


texts: Why diesel engines are considered steady torque engines?

texts:
Diesel engines are considered "steady torque", which means that torque is same no matter the revolutions whereas torque depends on revolutions for an engine that runs on Otto cycle.

What is the reason for this?


texts:
What is "Bearing stress" and Is it different from Crushing stress?
If yes explain How?
and
When does an element come under Bearing Stress?

This question came to my mind while studying knuckle joint from a book of machine design in my current semester(IV) and something similar that I've studied earlier in my last semester in mechanics of materials:

I.) By GERE mechanics of materials TOPIC:Tension, Compression, and Shear

II.) By V.B. BHANDARI elements of machine design TOPIC: DESIGN AGAINST STATIC LOAD

See the two cases and try to observe the acting area and force being applied they seem to be the same...

VB BHANDARI

GERE MOM


texts: Mounting methods for thin wall cast aluminum

texts:
Having a cast aluminium enclosure with the 3mm wall thickness. now I need to mount this to a mounting plate which fixed in vertical walls. can I have some idea on how should I choose the appropriate fastener?

Cast aluminium enclosure
mounting plate
for now, I have placed a 5M countersink bolt

Thanks in advance


texts: How to design a hemispheric flexible pressure vessel?

texts:
Consider a balloon, it is a flexible, expanding pressure vessel made of synthetic rubber. I am trying to design a system that will use hemispheric pockets of neoprene to grip an object, much like the one found in this journal:

  H.  Choi and M.  Koç, 'Design and feasibility tests of a flexible gripper based on inflatable rubber pockets', International Journal of Machine Tools and Manufacture, vol. 46, no. 12-13, pp. 1350-1361, 2006. (Behind a paywall, abstract available here)

Although I am not entirely certain where to start, I am dealing with a high pressure (8 bar) and need to work on a small scale (max radius of 40mm).

Values I have recieved from equations found online suggests thickness values in meters and radius expansion reaching the hundrends of meters.

What equations do I need to calculate a solution?

Are neoprene, latex and chloroprene viable materials to use or should I find alternatives?

Is a hemisphere that best pocket shape I can use?

Additionally, how can I calculate the amount of expansion?


texts: What affects the spring constant or spring life spans?

texts:
What factors would degrade a spring's life span other than stress applied?

Will high cycles (e.g. 100k load-unload continuous cycles) and high speed (100 ms/cycle), affect the spring constant (k)? What does it means if the spring constant decreases or increases after 1 million cycles (does it means the spring has reached its lifespan, or degrade, or...)?

Consider the spring is under applied appropriate force.


texts: Calculating max weight capacity of brushless motor

texts:
I am having trouble determining the maximum weight capacity a motor can handle. I provided the specs below. The calculations are for the top row or the 580KV model.

So to start off,I'm only taking maximum values, I took the Watts and converted it to HP. About 10.06HP. Then I took this and converted it to Newtons. Around 7480N and my weight of about 725N + the vehicle at 88N so 813N. So would this motor be able to move 813N from a stand still on 27in tires? Assuming it's flat ground and no wind. If not would it be able to if already traveling at 10mph?

On a side not how fast would it be traveling if the wheel diameter is 27in, the rpm is 30,000, it's producing 7500W of power, with 82Kg of weight onboard, and the gear ratio is 1.25:1? Also acceleration? thanks


texts: Can polycarbonate dance pole support the torque of a dancer?

texts:
I'm creating a light up dancing pole. This requires a translucent material that is strong enough to support the weight and force of a human being, even when it's hollowed out to so LEDs can go inside. The material must also be reasonably affordable, so something like diamond is out of the question.  I figured that polycarbonate was my best bet.

I did some searching and found a polycarbonate tube with the right dimensions (8ft length, ~45mm outer diameter).  Here are the exact specs:

Length: 8 ft
Outer Diameter: 1.750 in.
Inner Diameter: 1.500 in.
Wall Thickness: 0.125 in
Weight: 0.332 lb/ft

My question is whether this pole can support the torque of an average-strength 150lb human dancer.  Not someone who is using all their bodily strength to destroy the thing, but apply force at different angles and forces.

It will be secured to the ground by bolting it to a weighted platform.  My concern is whether the pole could potentially break.


texts: How to estimate cooling time of pipe due to inner flow (instationary heat transfer)

texts:
I have to determine the cooling time of a pipe from its initial temperature $\vartheta_{\text{wall,}1}=500 \text{ °C}$ to the temperature $\vartheta_{\text{wall,}2}=150 \text{ °C}$. The cooling happens due to an air flow through the pipe with the temperature $\vartheta_{\text{inlet}} = 30{\text{ °C}}$ and due to contact to the air in the environment $\vartheta_{0} = 20{\text{ °C}}$ at the outer surface of the pipe. Is there a quick way to estimate it? I thought about using Newton's Law of cooling but the problem is the heat transfer coefficient.

Data for inlet:

Inlet temperature: $\vartheta_{\text{inlet}} = 30{\text{ °C}}$
$p_{\text{inlet}} = 4 \text{ bar}$
$u_{\text{in}} = 5 \text{ m/s}$

Geometric/matrerial data of pipe:

Initial wall temperature (assumed to be constant) $\vartheta_{\text{Wall},1}=500 \text{ °C}$
Outer diameter $D_\text{o}=0.0210 \text{ m}$
Wall thikness $t = 0.0005 \text{ m}$
Length $L = 0.2000 \text{ m}$
Material not sure about it lets assume is some steel material


texts:
is it possible to calculate the flow of water out of a pipe where gravity is the only force acting upon the water and therefore generating the flow. The pipe diameter is X and there is minimal fall (say 6 inches?).

The real life scenario here is that I am trying to calculate the flow of water out of a washing machine waste when the filter plug is removed at the bottom?


texts: Type of electric actuator for a music box?

texts:
I'm currently thinking about creating a small piano-like (but of course nowhere as big or complicated) music box which can be digitally controlled with a microcontroller. Therefore I need to know which kind of electronic component has the ability of creating a rapid movement throwing up a kind of "hammer" against a string.

It should be able to have a maximum speed of 0.2 m/s with a maximum force of ~45N. Minimal speed should be approximately 0.05 m/s with a force of only 5N.

Is there a component which fits these requirements? (Or do you have any other suggestions how I could solve this?)

[I initially wanted to post this on the electronics-forum, but I assume the one for engineering fits my question better, if I'm incorrect, I apologize]


texts: How does one plot an Abbott Firestone curve

texts: I have a Mitutoyo Sj-210, that plots automatically a Firestone curve. I have another device that gives me the SRM values and ect but no curve. I have no idea how the Sj-210 does it despite being useful. How would i plot a Firestone curve manually. What would I have to do on Excel to take the values I have and plot them.


texts: Problem finding value of the gain such that the closed loop is stable

texts:
I have the following transfer function:

$G(s)=\frac{-s^3 +s}{s^4+3s^3+2s^2}$

and this is a transfer function of a plant with two poles in the origin. So I want to desing a controller with two poles in the origin in order to have zero steady state error. So the controller I want to desing is of the type:

$C(s)=\frac{k}{s^2}$

now, I want to find the k such that the closed loop is stable, but I am having some problems in doing so. I am using the Routh criterion, and I have that the closed loop is:

$\frac{-k(s-1)}{s^4+2s^3-ks+k}$

and the table for the Routh criterion:

$1$|$0$|$k$

$2$|$-k$|

$\frac{k}{2}$|$k$

$\frac{-k^{2}-2k}{\frac{k}{2}}$

$k$

and where I have omitted terms it means that there is a zero and the bar $|$ has been used to say that these numers are in different columns.

By doing this I obtain that the closed loop is stable if $k>0$ and $k<-4$, but if I use these values I have that the closed loop is unstable.

And also I would like to ask if there is a simpler way to find the value of $k$ instead of using the Routh Criterion, for example using Matlab.

What am I doing wrong?


texts: Initial shallow gradient in measured stress strain curve

texts:
What's causing the initial shallow gradient of the stress strain curve of ceramic in this graph?
The rest of the curve is a straight line alright until the yield point.
Edit: the material being tested is alumina ceramic.


texts: Why are tri-axle trailers with single wheels more stable than double wheels?

texts:
I'm revising for the UK LGV theory test. One of the questions goes something like this:

  Which axle configuration is most effective at preventing petrol tankers from rolling over?

  A. Tandem axles with double wheels
  B. Tandem axles with air suspension
  C. Tri-axles with single wheels
  D. Tri-axles with double wheels

The correct answer is apparently C, with the following explanation:

  The type of suspension fitted to a vehicle will influence its resistance to ‘roll-over’. Modern tri-axle semi-trailers fitted with single wheels on each side extend the tracking width available, making this the most stable configuration.

I have the following questions:

Why are single wheels better than double wheels?
Is this specific to a tri-axle setup, or does it also apply to twin-axles or single-axles?
Is this specific to trailers, or does this apply to rigid vehicles as well?
If single wheels are better, why do so many vehicles have double-wheels?


texts: How to determine energy dissipated from work applied on a load cell

texts:
I am using a load cell to see how much force people can apply on it, to help determine their health.
I am integrating the force applied on the bracket in Newtons in relationship to time, giving me the area under the curve as an impulse in Newton*second
I was wondering if I could transform these results in kinetic energy somehow.
Since no velocity is generated from the exercise (the load cell is bending by a few micrometers), this would mean that I would have zero energy generated, but this doesnt make sense, of course energy must be dissipated from pushing on the load cell.
What is the relationship of the inpulse I measure in regards to energy?
Thanks!


texts: Buckling: Do buckling mode shapes of n > 1 occur in reality?

texts:
In the buckling of columns we know that:

$$P = \dfrac{n^2\pi^2EI}{L^2}$$

The smallest value of P occurs when $n=1$ which gives a simple buckling shape (one wave):

$$P_{cr} = \dfrac{\pi^2EI}{L^2}$$

However for $n > 1$, as shown below the buckling shape is more complex and has many waves:

My question is do the buckling mode shapes for $n > 1$ ever occur in reality? If the column begins to buckle as per the shape for $n = 1$ then wouldn't it just continue to buckle like this until failure? How would the other buckling modes ever occur?


texts: RC Bandpass Filter on pspice :unity gain frequency

texts: I am simulating a pspice bandpass RC filter by cascading 2 opamps one HP and one LP. I am getting this bode plot at the end. Is the unity gain frequency the 2 frequencies at 0 dB?


texts: How is the area moment of inertia calculated for angle iron?

texts:
The formula for the area moment of inertia for a rectangular cross-section is b * h^3 / 12.  But it looks like when computing the value for angle-iron in this table:

http://www.engineersedge.com/standard_material/Steel_angle_properties.htm

... they have assumed that the piece is bent into a flat plate, so that both sides are aligned to resist the bending force.  Of course, this is completely unrealistic.   Only one face is typically resisting the bending force (the vertical face in most applications) and the other face simple keeps the vertical face from buckling.   As I missing something here ?


texts: What is a mechanism with teeth like this called?

texts: I'm trying to describe a part that I'm designing that has a disc with incremental teeth, like what is pictured here; which mates with a similar part. What is this type mechanism called? And what are the "teeth" called (for some reason I thought they were called detents, but found that not to be the case)?  Thanks.


texts:
I think that some of you know what is rolling resistance. It is force that works in opposite direction to roll and is caused due to deformation of tire. It also affects car wheels.
There is one problem with it. I have found 2 equations around:

$F_\mathrm{roll} = -V_\mathrm{car} * C_\mathrm{rr}$
$F_\mathrm{roll} = W_\mathrm{load} * \sin\alpha * C_\mathrm{rr}$

However, none of them seems to be right one. First one seems to be incomplete, inaccurate, but second one doesn't depend on speed making car shake when being in standstill.
I need to know what is accurate(but still game-compatible, not too heavy) equation for rolling resistance.


texts: Stability of a closed loop control system

texts: I have a question regarding control theory. Say I have a closed loop feedback system and I have found the closed loop transfer function, how would I then assess the stability of my closed loop system ? I have heard about the terms "poles and zeros". How would one find these and use them to comment on the stability ? Could I use software such as matlab for this analysis?


texts: Understanding metalwork manufacture -- How are Purchase Quotations prepared?

texts:
I have been involved with a number of metalwork design projects lately and I'm increasingly finding myself asking for quotations for small prototype runs (often one-off jobs) to verify the validity of a design.

The kind of items I'm talking about are small items like electronic product enclosures, mounting plates for screwing PCBs onto etc.  Items that would probably fit into a shoebox and are made of machined or folded plastic, aluminium, mild steel.  Not heavy engineering, so no welding etc.

Question: How would a large custom metalwork manufacturing company (1000+ employees let's say) interpret my design files and what steps would they be likely to take in order to estimate costs for a small run of prototype units?

If I give them a 3D STEP file (output from Solidworks for instance), how would they evaluate the complexity of the design and convert that to a list of costs such as tooling charges, material costs and setup-time costs etc?

What I think might happen:

They load the STEP file, find the smallest stock material size that fits the design - this gives the materials cost.
An engineer analyses the features in the design and does the CAM toolpath generation and other operations at this level.  This becomes NRE tooling costs and production line job-change costs.
Shipping costs are estimated based on the final object's size, shape and weight.

But this sounds like it would take a long time to organise and would be expensive in terms of man-hours, which they would want to avoid since I haven't given them any money yet.  Quite often the quote comes back to me within a couple of days, which suggests that they might simply be "eyeballing" the project, guessing the price and adding a wavy-hand percentage to cover the guesswork.

How does this kind of thing work in this industry?  I have asked one of our smaller manufacturers but they seemed reluctant to answer this sort of question as if it was some kind of closely guarded secret.  I want to stay on their good side so I stopped asking :)

I'd like to hear details from those with experience in custom machining, sheet metal fabrication (stamping, folding etc) and other related activities.


texts: Physics motion simulator for flying object

texts:
I want to see how different combination/position of fan on airplane affect stability of airplane.

I need simulator to test one of the idea which involves specific position for propeller on the plane. Before moving on to 3d print and test the model I need to see how aerodynamic affect my flying machine and if any kind of stabilization required at least in normal weather condition with uniform airflow.

I tried using the Ansys but it only shows the statistics with respect to lift, air flow directions, it does not actually simulate object flying. I need to see if idea even work, is there any good simulator for that? Or someone can give me reference in Ansys software that can allow me to achieve my purpose.


texts: Heat load calculations with heated air changes

texts:
I am working on a building project that requires a high ventilation rate for fire safety: 6 air changes per hour (ACH).  The winter design temperature is -14, so moving that much air through the system will obviously impact the total building heat load significantly with a 200,000 ft3area.

When I run the analysis with the Revit loads tool before setting the ACH, it returns a heat load of 103,000 Btu/hr.  If I set the zone ventilation to 6 ACH, it returns a heat load of 1,662,000 Btu/hr.
From a simple heat transfer standpoint, it would make sense that the heating load would skyrocket when you are pumping that much cold air into the building.  However, during the winter, part of that makeup air will be infiltrating the building through a heater, so the delta T will not be the difference between the -14 degrees F, and the 50 degree F setpoint, but, rather the heater output temperature and the setpoint.

Does anybody know of a way to account for this within Revit?


texts: Optimization with GA (genetic algorithm)

texts:
I want to optimize the below function with GA(genetic algorithm):
$$
\min_{l_{x_1},l_{x_2},l_d}||S_QS(z)||_2
$$
$S_Q$ and S(z)  are defined as:
$$
S_Q=\Biggm[\matrix{6.6549 &-0.806&6.883\cr
-0.806 &12.146 &6.818\cr
6.883 &6.818 &29.071}\Biggm]
$$
$$
S(z)=\Biggm[\matrix{z-1-l{x_1}&-0.05&-1 \cr
-l{x_2}&z-1&-1\cr
-l_d &0 &z-1}\Biggm]^{-1}
$$
where z is the z-transform variable
I write below code and using optimization toolbox in MATLAB
function z=objective_function(o)
lx1=o(1);
lx2=o(2);
ld=o(3);
Sq=[6.6549,-0.806,6.883;
    -0.806,12.146,6.818;
    6.883, 6.818,29.071]
z=tf('z')
s=[z-lx1-1,-0.05,-1;-lx2,z-1,-1;-ld,0,z-1]
z=norm(Sq*inv(s));
end

but do not work and give me that error (The "norm" command cannot compute the H2 norm of improper discrete-time models)


texts:
I noticed that when a group of people enter in an hydraulic lift/elevator often when the last person steps in the lift/elevator has a small but noticeable recoil: the lift goes down a few mm then it compensates.
This creates a recoil.

It seems that regardless of the number of persons on the lift/elevator this effect triggers when several people enter the cabin in succession and always happens when the last one steps in.

My hypothesis is that a sensor perceives the increased pressure but does nothing while the pressure is building,  instead when the pressure is stabilised because no more person enters it gives a bit of extra oil to the piston and we experience the recoil.

Is my idea correct? Or is there a better explanation?


texts:
I am currently reading “Fundamentals Of Vehicle Dynamics” by Thomas D. Gillespie.

The author mentions how the asymmetric pressure distribution across the length of the contact patch of a tire while rolling results in Rolling resistance. This, then inevitably creates a moment about the axis of the wheel which resists its movement.

The author states, however, that this asymmetric pressure distribution only occurs when a tire is rolling. There isn’t any asymmetry when it’s in a dead-stop position.

What I want to know now is the reason for this asymmetric pressure distribution. What causes it? How does Rolling generate asymmetry?


texts: If I use clay tempering, can I take a thin piece of steel and make it hard as a very thick piece?

texts: If I use the forging process of clay tempering, can I take a thinner piece of steel and and make it as strong as a very thick piece of steel? Getting the same strength, without the extra weight?


texts:
I am conducting few trials for checking the placement of a thermocouple on a valve for measuring the temperature of the valve and the material is an X45 alloy. You can see the slot taken on the valve and the thermocouple is inserted in the slot (picture is attached).
Procedure:

Turned on the muffle furnace with a set point of 300 deg C

After the furnace temperature is stable at 300 deg C, kept the valve inside the furnace.

Kept the valve inside the furnace and let it attain an equilibrium.

Took the valve outside after set amount of time and measured the temperature using a microcontroller (arduino + MAX6675). IT took about 10 seconds to measure the temperature and I could not run the wires inside the furnace as I did not have access to high temperature withstanding cables for the thermocouple. Also, as the valve is taken out for measuring the temperature,  there will be some heat loss due to atmospheric exposure.

After 2 hours of this trial, I found the temperature of the material to be around 250 deg C.
Due to the huge difference between setpoint and the material temperature, I wanted to raise a question.

NOTE: The thermocouple and the furnace are calibrated.
My question is, if a material is placed in a furnace with a setpoint temperature, would the temperature of the material be same as the setpoint after a certain amount of time? My guess is there will be some temperature difference but since I am not a mechanical engineer, I want to clarify this in this wonderful forum.
Thank you!
Vish


texts: My RAM truck has a feature that intrigues me and I want to know how it works.  In auto-dimmer mode, the truck will automatically put on low beams headlights when there is on-coming traffic at night, as well as when it is behind another vehicle moving in the same direction at night.  However, it is smart enough to not go to low beams when my truck's headlights are reflecting back light off of signs.  My guess is that my headlights are putting out a unique digital signature, so when the sensor registers that digital signature from a reflection, it knows not to dim.  When the light is coming from another vehicle, it knows that that light is not its own, because that light does not have the digital signature.  Does anyone know?


texts: What is this strange nut and what to do with it

texts:
I bought a cheap version of this machine, because all decent ones had costs of hundreds of dollars of transport to my region. The machine seems to be made of solid parts, but is really badly assembled. I hope to reassemble it into a working state. This is how it should look like:

And it is the photo of the worst part of what I bought. My question is about the brass (?) nut:

What is the role of the nut? Why it has something which looks like a small ball inside? Should it be put in the position, in which it is in every other photo of this machine?


texts:
A wooden police baton has to be hung on the back of an officer and released only when s/he wants it to be released. I thought about "push to stow, push to release". This is a thought experiment, I am not a manufacturer...

The baton is smooth without grooves so alternative solution of releasing by rotation (like BNC plugs, or push/push pen) won't work.

Where can I find a simple design of such contraption or what terms would I use to describe this?

This is a rough model of a four bar (ABCFD) which push point E toward the object to hold (LMNOQ)

The object, represent here as rectangle LMNOQ, moves on a fixed bar (HL).
When pushed up (represented by piston A1 expanding), point E moves towards the edge NQ. The angle FDB (in the locked position) is > 180 , so it should be locked, as with locking pliers.

In the open position, LMNOQ is lower, and point E is far from it.
(this model is only for showing the idea. I am sure it should be modified to work in the real world)

HOW can a SECOND push unlock point D?

[]
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texts: Percent (%) error between calculated gain and measured gain of FET amplifiers

texts:
I've recently been learning about FET amplifier circuits and I'm looking for some information that can help explain why the calculated and simulated Gain Values can differ by up to 15% in some cases.

this image is an example of the first FET amp.
 http://www.electronics-tutorials.ws/amplifier/amp14.gif
which gives the following values
calculated Gain = -11.8
simulated Gain = -13.4
difference = 12.698%
any help explaining this difference will be greatly appreciated.


texts: Typical power consumption of large compressor

texts:
This one should be easy to answer by looking at the thermodynamics, but I find it not to be. Say we have a natural gas stream, ~700 N∙m3/h, that we want to compress from 16 bar to 250 bar. What will the power consumption of the compressor be?

The thing that stymies me is that the power uptake is not path independent, but mostly depends on how many cooling steps you have in between. Or so it seems to me. You don't need to do the math for me, I just provided the numbers as an example. I would appreciate a detailed explanation of how to arrive at an approximate real world value.


texts: Viscosity of select species at atmospheric pressure for very large temperatures?

texts:
I'm dealing with hot combustion products flowing through heat exchangers and I'd like to perform some calculations regarding the flow properties (velocity, temperature, pressure and density) as it passes trough the heat exchanger.

I've a 1D model already built and I'd like to test it and validate it, but I'm lacking some critical information.

Is there any place where I can find the absolute viscosity [Pa*s] as a function of temperature (for pressures of 1atm, or close to it) for some select gases?

I need to know the viscosity between 300K and 2500K for gaseous CO2, H2O, N2 and O2. In polynomial form (something similar to the NASA/JANAF polynomials) would be nice, but in table would also be good.

I've already tried NIST, but it doesn't have that information for the temperature range I'm interested in.

Is it possible to run a macro for FLUENT, Star ccm+ or OpenFOAM and get those values from those programs? I have legal access to all of them.


texts: at what point is increasing pressure ratio diminishing in returns?

texts:
piston engines of ww2 planes had pressure ratio of at least 10, while jet engines were still vastly superior with a pressure ratio of only 3.
Certainly pressure ratio of 1 would bring 0% fuel efficiency, while you don't gain as much going from 3 to 6,so there must be asymptotic behaviour here.
Is there a formula or some empirical rule i could use to predict what will be the relationship between fuel efficiency and pressure ratio?


texts: Flat Head Machine Screws with Undersized Threads

texts:
I am in search of a flat head machine screws with an 82 degree countersink that have 1/4-20 UNC thread, but have a countersunk head that is characteristic of a 5/16-18 standard screw. That is, I want a standard machine screw with an oversized head.

I have been trying to search for these, but no search term I've tried works. If such a fastener existed, what would it be called? Can anyone confirm that they do or do not exist commercially?

(I know of course that I could fabricate them, but for a number of reasons, that's not desirable.)


texts:
I'm a software engineer that works on custom embedded devices. I program these devices through a typical RJ-45 ethernet cable. In most cases, I can connect my computer to these devices through a typical network switch and update multiple devices at the same time.

However, some devices are not compatible with others, and will cause issues if connected. For example:

I cannot have traffic from Device A reach Device B, or vice versa. Typically, I only need to be connected to one at once, so my current solution is just moving an ethernet cable that is connected to my computer to Device A or Device B, but I'd like to improve that.

I'm looking to either build or buy a togglable network switch, where the system can be in one of two states: Computer to Device A (and vice versa) or Computer to Device B (and vice versa). Basically, I minimally need to toggle ports on a network switch on and off.

I haven't been able to find something like this online, so I was wondering if I can rig a switch up by splicing some network cables and toggling them in some way, but I'm worried about interference and potential byte corruption.

Any initial suggestions?


texts: Deflection Of Beam In Structural Rigid Jointed Frame

texts:
This is a recommended follow on to one of my previous questions. It was stated that I could find the deflections of a beam by idealising it as a simply supported beam and then calculating accordingly. The loads laterally on the beam would cause a deflection perpendicular to the axis of the beam whereas the side-sway loads would cause deflections perpendicular to the column and thus the beam as well.

The main question is: how do I find the magnitude of the deflection on a particular beam within a rigid jointed multi-storey, multi-bay frame like the one shown below:

How would I find the lateral deflection of each column and beam using traditional structural analysis methods? I can find the moments and all forces using moment distribution (Hardy Cross) method but I need the deflections in order to use serviceability limit states in design. I've also thought about the slope-deflection equation, however, I can only find the slopes at each end of the beams.

Also, how conservative are these results?


texts: Which types of steel would be most appropriate for blunt cutting weaponry on a combat robot?

texts:
I'm getting more serious about a combat robot design I've been contemplating for several years now (BattleBots, Robot Wars, etc) and find myself overwhelmed by the sheer variegation of ASTM and AISI grades and alloys.  I hope that by detailing the application, those familiar with the nomenclature can steer me in the right direction.

The overall design is a full-body spinner - somewhere around 0.75m in diameter, at least 2500 RPM.  (Approximately 205 MPH weapon speed, though this is a minimum target.)  The circumference is lined with five or six solid-mount blades approximating the size and shape of forestry mauls, though slightly thinner - while primarily relying upon inertia and brute force, I would like to retain some degree of sharpness/cutting.

Structural integrity is the key attribute, remaining intact (if deformed to some degree) in spite of high-speed impacts with fixed hazards, opponents, and/or similar spinning weaponry.  Any significant separation would be of serious concern owing to the high-speed rotation.

The blades will be mounted to the outside of the body with high-strength bolts, anchoring roughly half the length and 60% the mass of each individual blade.  (I have no intention of ever welding these pieces as even a fractured blade would be swiftly replaced.)

Withstanding impacts and remaining affixed with minimal distortion is highly desirable.  Retaining a sharp edge would be nice, but this is mostly wishful thinking - for the sake of other traits, some sacrifice must be made.

What little I understand of this sort of metallurgy has me looking at ASTM-S1, which seems to be recommended for high-speed impacts and sudden shock-loading.  (Also assuming those terms mean what I think they do.)

Any guidance/recommendations in this department would be greatly appreciated.


texts:
How is "16.7 million colors" in a display calculated?

Also, is it a software or a hardware thing (the 16.7 million colors)?


texts: When calculating a force, why do I get different result when I try to calculate via torque vs via sum of forces at an axis?

texts:
If I just do it by writing that the sum on y axis is 0 I get

$100+x=200$

$x=100$

If I try torque around the top:

$x*800=200*500$

$x=125$

So what am I doing wrong?


texts: How come counterweight is needed to stabilise camera?

texts:
With gravity camera stabilisers like below, how come counterweights are needed to stabilise the load (camera)?

Is it to ensure that the handle joins at the centre of gravity? If so, why does it have to be at the centre of gravity?


texts: What is the effect of different ways to adding liquid materials into a mixing tank?

texts:
I am working with body wash products and there is a problem happening with the mixing process.
I use a 5000-liter tank to mix all the liquid materials including water, surfactant and preservatives. When I use a vacuum pump to add liquid materials from the bottom of tank, the content of preservative is A (g/100g). However, when I add them throug hthe top of tank, the content of preservative decreases.
I am really confused because everything (amount of materials, equipment, machines) used in 2 ways is the same. And I have no idea why the content decreases.
Please share your opinion. Thank you.


texts: What relationship is there between mass of water vapour produced in combustion and the energy lost through producing this water?

texts:
I am performing a number of simple heat transfer experiments with the application of a magnetic field around the fuel line to evaluate the effects.  To attempt to quantify some of the heat losses in the system I have worked out how many moles of water will be produced by combustion of a butane-propane gas mixture in air. I am hoping to find a relationship between that mass of water and the energy lost from the system by producing that water.

I know the relationship between the HHV and LHV but that seems to only deal with water vapour that has been condensed into a liquid so I'm unsure if that is any use.


texts: What is the effect of ageing on preconsolidation pressure?

texts:
Preconsolidation pressure is the maximum effective vertical overburden stress that a particular soil sample has sustained in the past.

How far in the past does the soil remember its loading/the pressure it sustained?

In other words, suppose that at a certain time the Preconsolidation pressure of a soil is $p_0$ due to certain load it had bore in the past. Then does the Preconsolidation pressure $p_0$ changes as the time passes given that the soil is left undistrubed?


texts: Why is the derrivative of a displacement at the end of a rod equal to 0?

texts: I'm studying a book on finite elements method and well, simply, I don't understand how they get this boundary condition.


texts: How to attach lycra / leather to Polyurethane foam?

texts:
What would be the best solution for attaching polyurethane foam to a lycra sheet of material. I was thinking a chain or pad stitch or possibly glue, but not sure if sewing would be  the best alternative or another approach might work better to secure firmly these two types of materials together?

Or alternative, how to bond polyurethane foam with a leather sheet?


texts: Calculating time to heat up water at flow rate of 150 ℓ/min. @ 1100 bar

texts:
The dimensions of the container for the water is 6.06m by 2.44m the depth of water is at 1m equating to 14.786m^3 or 14,786 ℓ of water.

The sytems is a closed system with a pump circulating the water 150 ℓ/min @ 1100 bar. How long would it take for the water to heat up from 20*C to 30*C?

How would the time change if the depth of water increase to 2m (ie. 29.572 ℓ).

Q: What formula(s) do I need to use to find the time required for the water heat up from 20*C to 30*C. Also what other variable is required for me to calculate this time?

Any pointers will be highly appreciated.


texts: Why shouldn't we put high voltage cables physically underground?

texts:
sorry for the odd title. We're working on a project to find a cheaper and safer way to install high voltage power lines in the Scottish highlands. One of my group mates had a really cool idea to instead of actually digging underground, you could just lay the cables and cover them with dirt/some other material which we haven't thought about at the moment.

I am asking because I assume the industry would currently be using the best available technology to them, and they don't use this method; they lay them underground. I'm trying to figure out the potential drawbacks to this proposed method.

1) Initially i thought it could be regulations, i.e. minimum depths etc, however, as far as I can tell from official documentation, there are only guidelines. In general, cables are laid between 0.45m -1m below ground, but not always. For example from a cable map I found, there was an 11kV line just 35mm undeground in Edinburgh. Official documentation seems to imply depths are situational, and as long as a risk assessment is performed, shallower or deeper depths can be allowed.

2) In terms of cost, digging through the rocky terrain of the Scottish highlands would pose significant challenge and cost. Getting heavy vehicles out onto that sort of terrain isn't easy. Using some sort of packing material, such as dirt, would surely be a cheaper option? There would of course be costs incurred due to rough terrain for transport trucks etc, but I don't see how it could cost more than digging through the terrain.

Potential drawbacks I can think of:

1) Using a mound structure would pose issues such as erosion. However, maintenance (which must be carried out on cables anyway) shouldn't be too difficult, especially since faults in the structure would be easy to spot since it is overground. It may require more regular maintenance due to weathering, but that would be offset by the fact that each maintenance trip wouldn't involve unearthing the ground?

2) Potential damage to cables. I don't even know if this is a real drawback (in comparison to the existing system since cable damage isn't very uncommon). I read some case studies from one of the regulatory bodies, and it seems damage came mostly when projects were undertaken without consulting the relevant authorities for cable maps. I assume the mound layout would be very similar, and probably wouldn't encounter a greater frequency of damage to the cables, but this is pure conjecture.

3) It would be an easier target for malicious activity since it would be easier to get to without the need for heavy machinery. However, cable maps aren't very difficult to get, and someone could just as easily target shallow cables using the current system.

Ultimately, does anyone have any criticisms of the potential solution? Or does anyone know of this idea having been implemented but not worked, or was determined to not be feasible? Thank you very much!


texts: Why don't we make bricks out of coffee grounds?

texts:
Okay, so I've noticed that a lot of people grind coffee, and a lot of companies grind it on an industrial scale.

Having produced some of the drink we called coffee, a huge proportion of the mass of the beans is simply thrown away, discarded. It's biodegradable, at least, but it's still waste.

Could coffee grounds, dried out and compressed, be used as a building material?

If it can, it would have these benefits:

A building material from a wasted resource
The source material is plentiful, it's everywhere.
No additional mining or agriculture would be required to produce it.
Like wooden housing, it would bio-degrade if left abandoned. So it's a low environmental impact.

Questions on this topic:

Can it be done?
What challenges would it present?
What practical issues are keeping this from happening?
What would it be like living in a coffee house?


texts:
We all know the typical streamline shape which looks like a tear. But what is the optimum shape (for speeds 0-200 km/h)?

Is the front a half sphere or is it an ovoid? How are the sides and the end formed? Can it be described in a formula or in a bezier curve? What is the drag coefficient compared to standard tear drops? Image with explanations how the shape must be built to minimize the drag are perfect.

And no, I don't accept flat plates and perfectly laminar airflow :). The shape must be built around a pipe with diameter R and must not be longer than 10R.


texts: What is a tolerable amount of elongation in steel?

texts:
I was looking at the elongation of various steel alloys, and the numbers were in the 10-20% range.  Is this the amount of elongation at the point of failure?  If so, what is the percentage of elongation that we would observe before reaching plasticity?  Did I use the term plasticity correctly?  I mean the point at which the material will no longer return to its original state.
I would assume there are probably two numbers here.  The elongation just before yield stress, and then the recommended maximum elongation that would actually be safe to use in practice.
Thanks.


texts: Would a structurally sound pressure cooker be able to withstand an internal vacuum?

texts:
Would the body of a normal round pot shaped pressure cooker (built to cook foods at 15 psi) be able to withstand being evacuated down to high-vacuum pressures?

Apparently it has been done before: i.e. this instructable but was this person just lucky it didn't implode?


texts: How to solve an overconstrained static free body diagram?

texts:
How does Force Effect https://forceeffect.autodesk.com do it?  Given a 10m long bar angled as the hypotenuse of a 3, 4, 5 triangle with an xy pin constraint a (0,0), another xy constraint at (4,3), and a vertical force of 100N applied down at (10,6) Force Effect calculates the x and y reaction forces below at C and A. I am not as interested in this particular answer in how to get to it by a codeable algorithm.

So the equations are:

Sum Moments about C = 0 =>  Y$_{ca}$(R$_{ax}$)  + X$_{ca}$(R$_{ay}$) +  X$_{cb}$(F$_{1}$) = 0 =>  3 R$_{ax}$ - 4 R$_{ay}$ = -4(-100)

Sum Moments about A = 0 => Y$_{ac}$(R$_{cx}$) + X$_{ac}$(R$_{cy}$) + X$_{ab}$(F$_{1}$) = 0 =>  - 3 R$_{cx}$ + 4 R$_{cy}$ = -8(-100)

Sum Forces Y = 0 => R$_{ay}$ + R$_{cy}$ + F$_{1}$ = 0 => R$_{ay}$ + R$_{cy}$ = -(-100)

Sum Forces X = 0 => R$_{ax}$ + R$_{cx}$ = 0

Which could translate to a 4x4 matrix:  Ax = b

|  3.   -4.    0.    0. |   | Rax |  =  | 400 |
|  0.    0.   -3.    4. |   | Ray |  =  | 800 |
|  0.    1.    0.    1. |   | Rcx |  =  | 100 |
|  1.    0.    1.    0. |   | Rcy |  =  |   0 |

And attempting to solve for x = inv(A)* b gives the following error in SciLab (or MatLab)
-->inv(A)
       !--error 19
Problem is singular.

So the matrix is not invertible- whatever that means!

I’d be open to some sort of substitution method to solve it if that is any easier.

This is not homework.  This is a simplified version of a real-world problem of a large free body being held in place by two fixed pins.  It is not dynamic – nothing is moving.


texts: How do engineers really use numerical simulation?

texts:
Disclaimer
I'm an applied mathematician by training, not an engineer.  My work research primarily focuses on creating new "methods" to solve different PDE's related to solid deformation (elasticity) and fluid mechanics.  In this sense, i know how to solve a pde problem computationally.  From my perspective, engineers use my work as "tools" to accomplish their work.

However, due to my lack of education/experience in engineering, i admit i'm actually rather clueless on how numerical solutions to pde's are really used in an engineers actual practice.  The primary source of my confusion is the following:

I've been told that engineers never (or should never) conduct numerical simulations (e.g. finite element analysis, CFD, etc...) without knowing or having a good idea ahead of time what the simulation "should" look like.  This helps engineers discriminate realistic results from questionable ones.

However, i argue that  if the engineer already knows what is supposed to happen in the simulation, then what's the point of simulation in the first place??? I've always assumed that simulations are needed for predictive purposes, which assumes ignorance of what is to come.  That is, I think of a simulation as a stand-alone tool to predict the future when you don't know what to expect.

What i'm looking for is a broader perspective into how/when/why engineers use numerical simulations like CFD and Finite Element Analysis, especially if good engineering practice dictates that you should already know what to expect when you're simulating?


texts: Atmel's ATtiny20 is 1.55x1.4x0.53mm in size. It is one of the smallest microcontrollers. What is the actual chip size inside it (i.e. without the packaging),like what is described here?


texts: Bolted joint junker test with finite element method

texts: Anybody knows a tutorial to make a finite element analysis for bolted joints like junker test(fastener vibration) in Solidworks or Ansys?


texts: How does the change in temperature of water in a tube depend on the angle that the tube makes with the gravitational field/the horizontal?

texts:
Let's imagine a tube that is open at one end and is filled with water. A constant source of heat is applied to a specific spot somewhere at the middle of the tube, for a example a preheated soldering iron of constant temperature. Let's say you measure the temperature of water at the upper end of the tube over a specific amount of time when the tube is parallel to the gravitational force, or 90 degrees to the horizontal. If you keep all the conditions constant, including the amount of time for heating, but change the angle so that it is 80 degrees to the horizontal, then 70, 60 and so on... You will find that the increase in the temperature becomes less as the angle decreases. But what would the graph of the increase in temperature vs sine of the angle look like? And what is the theory behind it? I undertstand that there are convection currents of natural convection caused by a buoyant force, which is caused by the difference in density and which will be counteracted by a normal force of reaction as the the tube becomes tilted. However, I would like to understand more of the physics involved in order to model the phenomenon.
The following graphs are based on primary data (collected by me). The tube used was a burette, the mark of 17 ml was in between the mark of 1 ml and the source of heat, which was at the mark of 25 ml. I realized that the wire of the thermometer at the mark of 17 ml could pose a confounding variable as it was curved, so it was not used in the fourth measurement session.


texts: Why is the wet/dry boundary of ground not dangerous for foundations?

texts:
A building, such as a house, rests on a foundation. Beneath it is natural earth.

When it rains, the ground around the foundation becomes wet. But the ground underneath the foundation does not. There is a wet/dry boundary somewhere near the edges of the foundation.

My question is, how is this stable and safe in the long-term? Shouldn't this wet/dry boundary cause some sort of movement or instability? Shouldn't the ground start sagging?

Note, I'm not asking about sinkholes. That's a different phenomenon caused by holes developing in carbonate rocks. I'm asking about the properties of soil---soil that is permeated, or not, with water.


texts: How do we specify among a shim, spacer, and washer?

texts:
Our small radio-control model cars have shims, spacers and washers. I am tasked with clarifying the manual and getting parts naming consistent.

We have these items from less than .5mm thin up to 1/8" thick. I'm thinking of calling everything under .5mm a shim, and everything .5mm and thicker that is available off the shelf a washer. And spacers will be anything .5mm and thicker that we have manufactured ourselves for specific needs on the car.

How do engineers define the difference between these terms?


texts: How can the vendor be approved/disapproved based on validation test data?

texts:
The power requirement for a sub system is 5V +/- 10% @ 1A of current. A RFQ was issued and a prospect vendor was selected. A first article of inspection (FAIR) has been submitted which includes 15 power supply samples. The samples have been tested with and without a 5 ohm resistor load using two separate calibrated DMM’s . Without the resistor the output voltage is 5V with little variation. Under a 5 ohm load the numbers are not too great. Below are the measurements (V):

4.56, 4.71, 4.95, 5.12, 4.61, 4.83, 4.65, 4.69, 4.79, 4.81, 4.67, 4.74, 4.63, 4.74, 4.81

Should the vendor be approved as a supplier?


texts: Is a differential gear setup equivalent to a voltage divider?

texts:
I was wondering if a differential gear setup works equivalently to a voltage divider in the electric domain. As far as I understand, voltage is analogous to torque in mechanical engineering and resistance would be analogous to rotational resistance.
So, in a voltage divider, depending on both the internal resistances $R_1$ and $R_2$ used for the divider but also the two loads $R_{L1}$ parallel to $R_1$ and $R_{L2}$ parallel to $R_2$, we get different values for how the voltage is divided between the two branches. The internal resistances need to be low compared to the loads for the voltage divider to actually divide the voltage the way it's intended with
$$
V_1 \approx V_0 \frac{R_1}{R_1 + R_2}, \qquad
V_2 \approx V_0 \frac{R_2}{R_1 + R_2}
$$
but in practice, the load would affect the divider and the true voltages we see should be calculated as follows
$$
V_1 = V_0 \frac{R_1 || R_{L1}}{(R_1 ||R_{L1}) + (R_2 ||R_{L2})}, \qquad
V_2 = V_0 \frac{R_2 || R_{L2}}{(R_1 ||R_{L1}) + (R_2 ||R_{L2})}
$$
where $R_1 ||R_{L1}$ is the total resistance of the two resistances in parallel.
I wonder if this is equivalent to how the torque is divided between the two outputs of a differential. Lets say the differential also has two internal rotational resistances $R_1$, $R_2$ so that when one internal resistance is higher, the torque is mostly redirected to the output with the lower internal resistance. And when they are both equal, in theory the torque is distributed equally. However, when considering the loads $R_{L1}$, $R_{L2}$ on both ends, would that affect the torque distribution the same way as with the voltage divider? My intuition is that the torque at the first output is somewhat proportional to the ratio between rotational resistance on output 1 and the sum of rotational resistances on both outputs. So with input torque $T_0$, and outputs $T_1$, $T_2$, I would assume we get
$$
T_1 = T_0 \frac{(R_1 + R_{L1})}{(R_1 + R_{L1}) + (R_2 + R_{L2})}, \qquad
T_2 = T_0 \frac{(R_2 + R_{L2})}{(R_1 + R_{L1}) + (R_2 + R_{L2})}
$$
Notably, while I think in the voltage example, the internal and load resistance are parallel, in the mechanical example I assume both are in series. So I'm almost certain that this assumption of mine is wrong.


texts: precision positional control needed for shifting position of lenses

texts:
Looking for a way to shift a 30mm lens in two axis perpendicular to another lens. The lens is for shifting a video projection up, down, left, right. Basically what you will find in tilt-shift camera lenses or video projectors with motorized lens-shift feature.

The travel distance is very short, 1/4th of the 30mm lens diameter, but precision has to be at least 1024 steps across that 30mm/4 length.

Would love any ideas how to implement this. Can only think of a gantry based system but can’t find small enough motors. Speed is also a concern, needs to go from one edge to the next in 1/3 seconds.

Haven’t been able to teardown tilt-shift camera lenses or motorized video projectors to see how it is implemented there.


texts: what's the best shape for inducing condensation?

texts:
What would be the best ceiling shape for inducing condensation?

I'm guessing it would a curve ︶ or V shape, but those are just guesses.
(I don't have any background on thermal physics)


texts: Could future fusion energy exist without the input of any petroleum or natural gas products?

texts:
Given a successful deuterium-tritium fusion reactor such as that conceived by ITER, could the world's energy needs theoretically be met without the input of any petroleum or natural gas products?

Deuterium is currently typically produced by the girdler sulfide process from seawater which requires a natural gas input, although methods involving electrolysis or distillation are known.

Lithium is currently mined, although there are methods known of extracting it from seawater.

Could the extractions of these elements be powered exclusively from the energy produced by fusion reactors in the future? This would leave seawater and the reserve of lithium from the earth's crust as the only fuel sources (or just seawater, if we are extracting the lithium from it).


texts:
I have tried to learn about "hysteresis" from different engineering knowledge sources and what i am able to understand that in simple words or nutshell, it is delay between output and input
Is there anything wrong with my understanding?


texts: Do I need to worry about galvanic corrosion when inserting a steel bar through aluminium?

texts:
My design uses a round steel bar inserted through a hole in an aluminium component with a tight fit (no movement). The operating environment is dry, 20-40°C.

Do I need to worry about galvanic corrosion, and if so how long will this last before starting to corrode? Also, what storage conditions should I avoid that would accelerate the corrosion?


texts:
Hi, I'm having some problems with this truss question that I have in my homework. So far this is my solutions.

I worked out my solutions to the reaction forces but don't know if they're correct.

The next step is the find the internal forces ZB
YB
SU
SV
TV
RT
RS
QS
JL
JK
NP
MP
HO
HM
IO
MO

Is there an easier way to find all these? e.g. are some of them the same?. Wouldn't using either method of joints or sections be too tedious here?.
 Thanks.

[![enter image description here][2]][2]


texts: adding fillet between parts in an assembly

texts:
How would you add a fillet between two parts in a Solidworks assembly, and propagating the fillet body to one of the parts?
In the example below I have two parts, yellow and gray, and when adding an assembly fillet feature, Solidworks adds it to the gray part. I'd like to treat the grey cylinder as if it were part of the yellow part for the purposes of creating a fillet between them, and then propagate that fillet to the gray part. The second image shows what I'd like to achieve, but between two assembly parts instead of two part features.

I found an example of a convoluted way of getting something like this to work, but I was hoping things have improved since the video was published in 2013.
https://www.youtube.com/watch?v=6IAGTlvgBgU


texts: Slow integration of system ODE under specific conditions in adsorption problem

texts:
I am trying to solve the system of ODEs below. I am applying the finite differences to z, so I get a system of ODE that I can solve with a solver like ode45.

The problem is that under the conditions that interest me integration is too slow (time step is very small) and I get no result. I would like to know what is the underlying problem and if there is any way to solve it. I have tried:

using different solvers (tried all of them)
using dimensionless variables
using the pdepe function of Matlab to solve the PDE system directly without applying finite differences myself. Same problem occurs.

Full code (using the parameters that do not work)

function transport_model()
global parameter L Di epsb Q Cfeed K tfinal npz npt F ui h

parameter = [0.044511*432.75 432.75];    % isotherm parameters
L = 0.4;            % m, column length
epsb = 0.367;       % column bulk porosity
ui = 4e4;        % m/s, velocity
Cfeed = 200;     % feed concentration
K = 0.0782          % s-1, mass transfer coefficient
tfinal = 400;      % min, final time for calculation
npz = 50;           % number of discretization points in z
npt = 20;

F = (1-epsb)/epsb;
tspan = 0:tfinal/(npt-1):tfinal;
y0 = zeros(2*npz,1);
h = L/(npz-1);

sol = ode15s(@sedo, tspan, y0);
t = sol.x;
C1 = sol.y(1:npz,:);
q1 = sol.y((npz+1):end,:);

plot(t, C1(end,:))
xlim([0 tfinal])
ylim([0 Cfeed])

function DyDt = sedo(t,y)
global Cfeed K  npz F ui h

N = npz;
y(1) = Cfeed;
DyDt = zeros(2*N,1);

% Forward finite differences
DyDt(1) = -ui * 1/(2*h)*(-y(3)+4*y(2)-3*y(1)) - F * K * (y(1) - ilangmuir(y(N+1)));
DyDt(N+1) = K * (y(1) - ilangmuir(y(N+1)));

% Central finite differences
for i=2:N-1
    DyDt(i) = -ui * 1/(2*h)*(y(i+1)-y(i-1)) - F * K * (y(i) - ilangmuir(y(N+i)));
    DyDt(N+i) = K * (y(i) - ilangmuir(y(N+i)));
end

% Backward finite differences
DyDt(N) = -ui * 1/(2*h)*(3*y(N)-4*y(N-1)+y(N-2)) - F * K * (y(N) - ilangmuir(y(N+N)));
DyDt(2*N) = K * (y(N) - ilangmuir(y(N+N)));

function c = ilangmuir(q)
% langmuir solved for c
global parameter

a = parameter(1);
b = parameter(2);

c = q /(a - b * q);

However, if I try to model a different case (different conditions) I get the correct response. So I am assuming this is a numerical problem caused by the conditions I am trying to model and not an error in the model. For instance, if I use the conditions below I get the correct response.

parameter = [0.044511*432.75 432.75];    % isotherm parameters
L = 0.4;            % m, column length
epsb = 0.367;       % column bulk porosity
ui = 0.0056;        % m/s, velocity
Cfeed = 0.0025;     % feed concentration
K = 0.0782          % s-1, mass transfer coefficient
tfinal = 4000;      % min, final time for calculation
npz = 50;           % number of discretization points in z
npt = 20;


texts: Solenoid with 3mm stroke and ~1ms response time possible?

texts:
I need to extend and retract a needle as fast as possible with dwell time while retracted, while one option I really like would be to use Scotch Yoke with dwell. However that would mean the stroke and dwell times are a fixed ratio where as ideally they would be independent leading me to look at linear actuators.
My question as stated above is if a solenoid could be made to respond in the 1ms range? The few solenoid data sheets I have viewed that bother with reaction times are ball parked around 10ms - though I presume these times could be shaved to some degree by preloading to counteract the return spring and reversing current to speed up desaturation of core (anyone got any information on how much this could save?) or do I need something more advanced such as voice coil, or ???
[I am looking to put around 1N of force behind the needle.]


texts: What screw for 2.0 mm plastic hole in housing

texts:
I'm thinking about using the Bopla UM 32009 housing for my product. It has little standoffs for attaching PCBs. These standoffs are made of plastic, and seem to be drilled (or molded?) to a diameter of 2.0 mm.

My questions: What type of screw would be appropriate for this hole diameter? A regular M2 machine screw won't work well. An M2.5 might work, but would probably deform the standoff.

An M2.2 self tapping screw might work I suppose, but I think the hole is a bit large for this (recommended is something like 1.8 mm).

Is there some kind of imperial screw that fits well into a 2.0 mm plastic hole?


texts: I am building a tree house in my backyard and it is going to be relatively simple. There are no parts that require drilling into the tree. The whole house is propped up by four 4x4 wood supports. I'm wondering if quikrete is the way to best support the whole structure or if there are better alternatives.


texts: What is the "quick bleeder valve" in this tool changer pneumatic schematic (and other questions)?

texts:
I'm building a CNC router around a HSD ES330 spindle motor that has pneumatic tool-changing ability. The manual recommends the following pneumatic circuit:

I'm not sure I understand the purpose of the "quick bleeder valve" (circuit element #5 in the diagram). Searching for "quick bleeder valve" doesn't turn up anything with that symbol, or a part I'm confident buying on McMaster-Carr. I know the one-way flow restrictor (element #4) is supposed to slow the tool ejection speed; I guess during tool unlocking, air returns via #2, but I'm not sure if that exhaust air escapes through the bleeder valve, or the 5-2 valve #6.

I do have a one-way flow restrictor (although I'm not entirely sure how to adjust it).

What is the "quick bleeder valve?"
Do I really need it?
Where is this air exhausted?


texts: How to mount skateboard wheels to an t-slotted framing

texts:
What is the best way to attach skateboard wheels to an t-slotted framing?
Also, is there a more economical way?
Bonus: How to design shock absorber for it?


texts: How does virtual work method relate to matrix method or FEM in structural analysis?

texts:
I understand the relationship of force method and displacement method and how we use them in matrices in FEM.
How about virtual work? Is it used in matrices and FEM too?


texts:
I recently read in an online article, that researchers have found the recipe of concrete used by imperial Roman architects. The cited article however uses a recipe described by Vitruvius, which is 2,000 years old. So how exactly is this finding the recipe?

Nevertheless, I actually want to ask if one can extract a detailed recipe from the article, understandable by a layman. Even though I read the article, I am not even close to an engineer and thus it is hard for me to judge if the article adds something new to the ancient recipe given by Vitruvius. In the end, I am looking for a step-by-step instruction approach, much like this article, maybe even more detailed (for example, in the article, the process to create the quicklime is not described with much detail, temperature missing, etc). I basically want to know, which is the most accurate formulation of the production process of ancient Roman concrete backed by science.


texts: I’m following Anderson’s Fundamentals Of Aerodynamics. However, the proof for the above theorem is not provided. Every time I try it, things get really lengthy and cumbersome. Is there some nice and short method to getting around to prove the time rate of change of circulation over a chose closed loop 0 in an inviscid, incompressible flow ?


texts: What are equations related to the compaction of composite metal powders?

texts:
Say I am trying to create a metal composite and have a mixture of 3 different metal powders each with varying weight %'s. I'm going to compact them into the shape of a ring by applying a force P. The inner and outer radius of the ring are given and I am asked to determine the thickness of this ring after compaction.

My first question is, each of these metals have a true density (ie. 8900 kg/m3 for Al). Looking at this powder alone, if density is reached, can it be further compressed or does adding any more force P do nothing because it physically cannot obtain a greater density (due to atoms themselves etc.).

Second question, assuming you cannot compress more than the true density, is there a formula to determine how much force corresponds to the density achieved?

Thanks in advance


texts: Why is deviatoric stress the one causing distortions?

texts:
I'm reading this text on stress.

It is mentioned that the Cauchy stress tensor can be split into a sum of two other tensors: hydrostatic pressure $\pi$ and deviatoric stress. Hydrostatic pressure is defined as the mean of the normal stresses. Deviatoric stress tensor is what we get when we subtract a tensor with the pressure on diagonal from the original Cauchy stress tensor.

$$\begin{align} \ \,\\ \left[{\begin{matrix} s_{11} & s_{12} & s_{13} \\ s_{21} & s_{22} & s_{23} \\ s_{31} & s_{32} & s_{33} \end{matrix}}\right] &=\left[{\begin{matrix} \sigma_{11} & \sigma_{12} & \sigma_{13} \\ \sigma_{21} & \sigma_{22} & \sigma_{23} \\ \sigma_{31} & \sigma_{32} & \sigma_{33} \end{matrix}}\right]-\left[{\begin{matrix} \pi & 0 & 0 \\ 0 & \pi & 0 \\ 0 & 0 & \pi \end{matrix}}\right] \\ &=\left[{\begin{matrix} \sigma_{11}-\pi & \sigma_{12} & \sigma_{13} \\ \sigma_{21} & \sigma_{22}-\pi & \sigma_{23} \\ \sigma_{31} & \sigma_{32} & \sigma_{33}-\pi \end{matrix}}\right]. \end{align}$$

where

$$\pi=\frac{\sigma_{11}+\sigma_{22}+\sigma_{33}}{3}$$

It is then said:

  The second component is the Deviatoric stress and is what actually causes distortion of the body.

My question is: Why do the diagonal stresses in the deviatoric stress tensor cause distortions, considering they are still normal stresses?

I've been taught that normal stresses cause only volumetric changes, and don't cause distortions, that is, don't change the shape of the element. It is the shear stresses, which lay off-diagonal, that cause shape changes to the element.

The shear stresses are present unchanged on the deviator tensor, but the normal stresses are now differences between the normal stresses on the element and their average. But they are still normal stresses, so why are they present in the deviator tensor, if the purpose of the deviator tensor is to include only stresses that cause distortions?


texts: Is there a bellows geometry that allows for torsional motion?

texts:
A typical folded bellows allows for axial expansion/compression, lateral offset, and angular deflection. Is there a bellows fold pattern that can accommodate a relatively large torsional rotation about the longitudinal axis?

Motivation

I'm looking to prototype a waterproof (IPX67 or IPX68) flexible housing for DSLR cameras with large zoom lenses. A picture is worth a thousand words:

Dan Carr testing the RainCoat Pro 2 on a grizzly bear photo trip in British Columbia. From shuttermuse.com Photo: Rowan Thornton

The photographer in the kayak is using a rain coat, which merely protects from rain. But the thought of my kayak turtling with $10k worth of camera and lens exposed makes me pucker. So I'd like to begin prototyping a flexible watertight bellows to surround the lens and mate with a flexible "bag" covering the camera body.

Of course, a regular bellows (like a bellows plunger) will allow for a zoom lens to accommodate changes in length. The problem is accommodating control of the zoom ring on the lens, which is torsional rotation of the outside of the bellows. I anticipate the maximum rotation is about 135° (+/- 65° or so from mid-zoom).

Is there a fold pattern to allow a cylindrical surface to be torsionally deformed like I'm describing?


texts: Hydraulic siphon spillway entry and exit velocity magnitude and profiles

texts:
I am working on the hydraulic seawater flow though a siphon spillway. My task is to determine at a location in front of the spillway the flow velocity and profile when

The flow enters the spillway
The flow exits the spillway

See attached a drawing of the problem.

Now the basic formula for calculating the flow  through the siphon is

$$
\Delta H = \xi \frac{v^2}{2g}
$$
where:

$\Delta H$ = pressure head

$\xi$ = total friction losses

v =flow velocity

g = gravitational acceleration

Question is: what is the flow profile and velocity at the location in front of the spillway (see drawing) for a given pressure head, geometry and friction loss factor?

Please note that I am not looking for a full fledged CFD analysis at this stage.

Any help on how to tackle this problem is appreciated.

.


texts:
I am finding different opinion, but I can not find a mathematical demonstration about this topic.
for example here is described as non homokinetic:
Oldham coupling vs Universal joint

here is homokinetic:
Book


texts: Calculating horizontal force exerted on a wall by a panel

texts:
I need to mount a heavy panel against a wall.  The panel will be first mounted on two legs which go from the top of the panel to the floor.  These legs will transfer most of the panel's weight to the floor, and will also be bolted to the wall to prevent the panel falling forward.  Since there are only two legs (behind the panel), there will be some force exerted on the bolts and thus on the wall as the panel tries to fall forward.

How do I calculate this horizontal force exerted on the wall?

Thanks!

Here's a drawing:


texts:
My house is heated by a condensing natural gas furnace that is rated as 92% efficient. It has the option to draw combustion air directly from outside. I know the main advantage of this is avoiding negative pressure within the house to reduce drafts. However, I thought of a few questions:

Outside air is colder. Does this decrease the maximum temperature of the flames?
As the outside air is colder, it is also denser. Does the furnace's performance increase due to increased oxygen content?
The furnace's exhaust temperature exiting outside is about 43 degrees Celsius, so there is still some heat in the exhaust that is not going towards heating the house. What could be done to utilize more of that heat?


texts:
Looking through texts such as Shigley's Mechanical Engineering Design, you come across tables of the stress concentration factor (defined as $K=\sigma_{max}/\sigma_{avg}$) such as the following:

This plot is sourced from Pilkey's Peterson's Stress Concentration Factors, which, unfortunately, I do not have access to (and even less so now, since interlibrary loans are on hold), so I do not know what underlies this plot.  However, the line seems to be related to Kirsch's elastic stress distribution since the value of the stress concentration factor approaches 3 when the ratio r/d approaches zero.

That exact item, though, is what gets me.  In the limit of radius going to zero, the bar no longer has a hole in it, and according to Saint-Venant's principle, the stress a a point in the middle of a long bar should be equal to the average stress on that cross section.  Hence:

Why does the stress concentration factor go to 3 instead of 1 as r approaches 0?


texts: Is it possible to spot weld three rather than two plates?

texts: I have a situation where ideally, I would like to resistance spot weld three rather than the usual two plates together (individual plate thickness approximately 0.7mm). Is this at all possible? If not, why not? Are there any precautions one should take?


texts: How Gas Springs or Gas Struts are pressurized with nitrogen gas and then sealed?

texts: Prior to testing and probably painting, the last stage of manufacturing a gas spring or gas strut is pressurizing with Nitrogen. I was wondering how this step is done. I think it is filled with gas from the rod side and the rod seal works as an one way path, meaning, nitrogen gas is injected into the cylinder with certain amount of pressure, and then when the injection is stopped, the pressurized nitrogen in the cylinder pushes the seal back and seals the gas strut, but I’m not sure.