texts: How does loading and unloading work in an air compressor?

texts: I am looking at an ammonia refrigeration unit and trying to understand how loading and unloading solenoid valves work? and also how to modulate the compressor motor over a period of time.


texts: Influence of shear force on pressed part with steep walls

texts:
I'm working on a project that involves pressing a softened thermoplastic sheet in a two-part mold to form a part 0.090" thick. None of us at our small company are experts in matched molds, and we've come up against a question that must be answered before we put more financial resources into the project.

The shape that we are working with can be approximated as an arc, with the open side up. That makes a female mold with a cupping shape and a male mold with a rounded shape. Our question resides in the pressures that we can achieve along the side walls that approach vertical. In my mind, this is a simple statics problem. Assuming there are no other significant effects besides the normal force between the mold faces, then if $F$ is the pressing force and $\theta$ is the angle of the sidewall, measured from horizontal, the sidewall normal force $N$ will simply be $N=F\sin(\theta)$.

If my assumptions are good and shear doesn't play a significant effect on the final geometry, then $N$ is reduced to below 20% of $F$ when $\theta=10^{\circ}$. That has potential to heavily influence the quality of part in those regions. My question is, as someone with no prior molding experience, is the normal force the only significant player when it comes to pressing a part at steep angles?


texts: Calculating moment of inertia for a hollow discontinuous circle?

texts:
This is a pretty simple problem, but I'm just not sure how to go about it. I want to find the moment of inertia of a discontinuous hollow circle. But since the shape is so irregular, I'm not sure how to go about solving for it. I've posted the shape in mind, so hopefully that'll clear up any confusion.

Would an equivalence be needed to calculate the moment of inertia? For example, would I assume that the "new" diameter to calculate with for the outer circle is (0.625 - 0.375)?

Note: All these numbers have inches as units.


texts:
I have always used the term "invert level" as the "floor level" of pressure and gravity pipelines alike. A long section for pressure pipe from another engineer came across my desk where his "invert level" indicates the bottom of the trench  as the level below the pipeline (includes bedding)

I have gone through various handbooks at the office and did an online search, I can not find a distinction between pressure vs gravity pipes, but the reference often refer to gravity pipelines or channels.

Is the term "invert level" applicable as the "floor" of a pressure pipe or the bottom of the trench?


texts: Cutting a larger circle on center of a smaller circle

texts: At work, we cut a 6" hole in the wall for a duct. Later we decided we now want a 10 inch duct in the same place. what tricks are there to center the larger hole over the center of the smaller hole if it is already cut? I'm using a hand saw to cut into dry wall.


texts:
all is this sturcture stable ? or structural determinate ?

Let the top support as A , bottom support as B ,
By taking moment about A, i managed to get 10(4*4)/2 -HA(2) = 0 , HA = 40kN,
HA = HB  = 40kN ,
By taking moment about C , i managed to get -10(4*4/2) + 4(VB + VA) -40(2) = 0
VA + VB = 40kN , however , i still not able to get the exact value of VA and VB, where did i miss out ?


texts: Why don't most consumer vehicles use kinetic energy recovery systems?

texts:
I know that Formula One and some sports cars have KERS systems to recover kinetic energy, but is there an expense/practicality barrier to installing them in consumer vehicles? As the technology clearly serves efficiency purposes beyond just providing extra horsepower, and as KERS can capture energy electrically or mechanically, it seems that it would be a useful step towards increased consumer vehicle efficiency.

Note: I recognize that there's a significant cost associated with thermoelectric capture, and that this suggested duplicate raises the concern of how it's impractical to slow heat dissipation. However, if we limit the energy capture to brakes (typically cooled by natural convection and therefore not subject to any air/liquid cooling), could we see a more practical energy capture solution than trying to capture kinetic energy straight from an internal combustion engine?


texts: Torsional Constant of Thin-Walled Multi-Cell Structures

texts:
I'm asked to analytically calculate the composite torsional constant of the following structure.

No other information is given, such as the applied torque.

I know how to calculate the torsional constant for each component (an equilateral triangle and a semicircle), but I don't think I can just add them weighted to the areas.

Is there anything else I can try?


texts: Determine coefficients of friction based on the torque required to rotate a part on a shaft

texts:
I'm trying to model a part that rotates on a shaft. I measured empirically that it has a static torque of around 500 N·mm and a dynamic torque of around 400 N·mm. I want to simulate it in CAD but my software only takes static/dynamic friction as inputs.

How can I convert the torque values to static/dynamic friction values for the part-shaft contact surface?


texts: I have a CAD file in SketchUp that I would like to edit using code (ie: its dimensions, properties, etc.) What is the best way to do this? If I export the file as an STL, is there a program where I can edit the STL using code? Thanks.


texts: Replacing a straight rigid link by a curved rigid link

texts: Suppose we have a horizontal rigid bar hinged at one end to the wall. An inclined straight link hinged at one end to the same wall, is pinned to the rigid bar at its center. A load P is acting at the free end of the horizontal link. For static analysis we draw the free body diagrams for both the bodies and equate the net force and moment to zero. How will the static force analysis change if we replace the inclined straight link with a curved link? Will it depend on the nature of the curve?


texts: What makes the material travel through Archimedes' Screw?

texts:
...or in other words, why doesn't the material just stick to the screw, rotating in place, without progressing along its length?

In the simplest case, the answer is obvious: gravity. If it's a granular or liquid material and the screw is tilted to a side, it will just roll/slide/flow along the blade, to remain on the bottom side of the tube.

But then, Wikipedia says:

  A variant of the Archimedes' screw can also be found in some injection molding machines, die casting machines and extrusion of plastics, which employ a screw of decreasing pitch to compress and melt the material. Finally, it is also used in a specific type of positive displacement air compressor: the rotary-screw air compressor. On a much larger scale, Archimedes' screws of decreasing pitch are used for the compaction of waste material.

In such case the forces - pressure, shearing, viscosity, adhesion, all would outweigh gravity, and probably in some cases friction against the tube walls. For example, in injection molding, what is there to keep the half-molten plastic from forming a clumping mass, sticking to the screw and keeping rotating in place without any progress? When the pressure increases, which force prevents the material from backing up into area of lower pressure?


texts: What resolution (pixels/mm) should I use in SVGs for CNC

texts:
I am planning a mechanical 40% keyboard build and are coincidentally on the home stretch of a homemade CNC project.

The only thing the CNC needs to do for the keyboard project is to drill 7*48 holes. So what I need to do now is layout those holes in SVG. Therein lyes the question. What resolution should I use for the SVG. I want to space the center of the keyboard switches 19mm apart. An online pixel to mm converter suggested that 72 pixels is exactly 19.05mm (which actually is what Cherry MX says should be their spacing).

Now, I do understand that this really doesn't matter, but I am curious as I am new on CNCs and was suspecting that there is a number that will "just work".

Thanks.


texts:
A mechanism popped up in my mind when I was studying kinematics, see picture below
$J1,\ J2,\ J3$ are rotational joints and there are two translational joints $J4$ and $J5$ between two sliders and the cross hatched rail. Sliders are free to move horizontally towards or away from one another. Now when I imagine a motion in which a force is applied vertically at $J1$, pushing or pulling on the said joint, thus sliders move away or come closer, I think it is a one degree of freedom mechanism. However the famous formula $3n-2j-3$ where $n$ is the number of links and $j$ is the number of lower pair joints, gives two degrees of freedom. Considering the rail as a ground link, with two sliders and two arms ($J1J2$ and $J1J3$) we have $n=5$ and we have $j=5$
$3*5-2*5-3=2$
So, what is with that?


texts: Why do earth cuts sometimes have steps on their walls

texts:
A neat image from Wikipedia:

There're clearly visible steps on the cut wall. This makes the cut wider at the top and so requires more work so those steps have some serious reason behind them.

What's the purpose of these steps?


texts:
I have an Aluminium square cross sectional rod of $20mm$ X $20mm$. Length 700mm.
At the end of this rod there is a mass of $660$ $g$ attached.
My question is what torque do i need to lift this mass up assuming my pivot point is at the other extreme of the rod? And how do i consider the mass of the rod in the calculations!


texts: Why do thicker turbine blades delay flow separation?

texts:
I studied about the effect of turbine blade thickness on flow separation in following. The blade section is Naca 00 XX in this turbine.

The paper states that if blade thickness increases, separation on the blade delays. Why does this happen?

The paper also states that if the blade thickness increases, there is higher pressure on the suction surface and hence this gives a delayed separation. Why does this happen? Why is there high pressure on the suction surface?

The paper also states: Blade (A) has lower torque than blade (E). Why?


texts: Can lithium ion batteries solve the world's energy storage problem?

texts:
This questions boils down to the following important questions:

Do we physically have enough materials in the earth's crust to make enough lithium ion batteries to support global storage demand?
Can we produce lithium ion batteries at a cost/kWh to make it economically feasible? Many speak of the supposed $100/kWh barrier, but at what cost per kWh do we need to compete with existing non-renewable energy sources?

Lithium ion batteries have been the most talked about means of storage for renewables, but can they solve the world's energy storage problem to support a transition to renewable energy?


texts: Which materials can be used to make permanent casting molds for cast iron?

texts: I am interested in comparing the different materials that can be used to make castings of cast irons, and therefore was wondering which material is commonly used/which materials can be used to make permanent casting molds (to be used specifically for cast iron). Thank you.


texts: Are there standards or guidance for the placement and location of rest areas on newly constructed or designated U.S. Interstates?

texts:
As the highway engineers here may already know, U.S. highway 71 through most of Missouri was recently redesignated as a section of Interstate 49 after the completion of grade separation work at several locations.  However, having been on the road recently, I noticed one thing that is missing from it that most rural Interstates have: rest areas.  While private facilities are available at most exits from that stretch of road, the lack of rest areas on an over 100 mile stretch of road when most Interstates have them at roughly 50 mile intervals strikes me as an oversight by MoDOT, and left me wondering if it was a substandard highway for that reason alone.  Furthermore, I reviewed the 2017-2021 Transportation Improvement Plan for the MoDOT Southwest District, and there were no projects in there to add rest areas to I-49.

So, are there any standards or guidance materials for the placement/location of rest areas (with or without services) on newly constructed or designated rural Interstates?  Or can a highway be built or upgraded to "Interstate standard" without such provisions without drawing a peep from standards or guidance material?


texts: Extracting other mineral from salt in evaporated seawater

texts:
I recently stumbled upon this news,

seawater contains 47 minerals and metals. Starting with the most
abundant and proceeding to the least abundant, these are chloride,
with a concentration of 18 980 parts per million (ppm) in seawater,
sodium (10 561 ppm), magnesium (1 272 ppm), sulfur (884 ppm), calcium
(400 ppm), potassium (380 ppm), bromine (65 ppm), inorganic carbon (28
ppm) and strontium (13 ppm). Then follow boron (4.6 ppm), silicon (4
ppm), organic carbon (3 ppm), aluminum (1.9 ppm), fluorine (1.4 ppm),
nitrogen in the form of nitrate (0.7 ppm), organic nitrogen (0.2 ppm),
rubidium (0.2 ppm), lithium (0.1 ppm), phosphorous in the form of
phosphate (0.1 ppm), copper (0.09 ppm), barium (0.05 ppm), iodine
(also 0.05 ppm), nitrogen in the form of nitrite (also 0.05 ppm) and
nitrogen in the form of ammonia (once more 0.05 ppm). Thereafter, we
have arsenic (0.024 ppm), iron (0.02 ppm), organic phosphorous (0.016
ppm), zinc (0.014 ppm), manganese (0.01 ppm), lead (0.005 ppm),
selenium (0.004 ppm), tin (0.003 ppm), caesium (0.002 ppm), molybdenum
(also 0.002 ppm) and uranium (0.0016 ppm). Then come gallium (0.0005
ppm), nickel (also 0.0005 ppm), thorium (also 0.0005 ppm), cerium
(0.0004 ppm), vanadium (0.0003 ppm), lanthanum (also 0.0003 ppm),
yttrium (also 0.0003 ppm), mercury (once more 0.0003 ppm), silver
(also 0.0003 ppm), bismuth (0.0002 ppm), cobalt (0.0001 ppm) and,
finally, gold (0.000008 ppm). Altogether, there are some 50
quadrillion tons (that is, 50 000 000 000 000 000 t) of minerals and
metals dissolved in all the world’s seas and oceans.

Which is quite surprising for me (thought those white crystal was only NaCl).
Assuming I already have TONS of general salts (mixed) from simple seawater evaporation, is there any way to separate each mineral? Let's say by pouring the salts in magnet (for material that is having magnetic properties), etc.

(lithium salt pond, which seen exactly same as NaCl pond)
Apologize for shallow understanding of the topic. Any suggestion is highly appreciated since I can't find the answer elsewhere
P.S: This question have been posted earlier in Physics


texts:
In this solution Helicoptor Fire Control System

CMA is used. For motion analysis we use computer vision and image processing. But what is special about CMA.


texts: Why does my VFD and pump configuration stop pumping?

texts: I recently installed a VFD to reduce the speed of my pump, however, occasionally the configuration will stop pumping liquid through the system. The pump is a three phase 60 Hz and this issue has happened when running the system at 13 Hz and 40 Hz. Any thoughts?


texts: Most efficient/low power consumption way to pump water

texts:
I am working on a small project where I, from a relatively confined space in a well that has a diameter of 30 cm, will need to transport the water upwards about 2 meters.

I have been looking at ram pumps but cant really see a way to utilise that as i dont have a "higher" water source. I have also been looking at electric pumps on Alibaba and it seems that i'll land at around 2W, which seems like a lot for an iot device - i really dont want to have to recharge the device every week, esp. since there is little energy to harvest nearby.

The requirements are:

Ability to pump water upwards 2 meters
Flow of around 12 liters per hour would be enough
Ideally 12V or lower

What are the best options? :) I know that product recommendations are not allowed, but what techniques should I look at overall? Is there a resource somewhere that compares the efficiency of different pumping methods?

[EDIT] RE comments: In terms of effeciency, I mean as low wattage as possible. I wont have easy access to recharging (solar and wind are out, but potentially the energy of the water flowing down into the well could produce a minor charge for the battery). If we can get to a point where the battery only needs to be changed once a month, that would be perfect.


texts: BER peroformance of MPSK and MQAM in Rayleigh fading channel

texts:
I have a question regarding bit error rate (BER) performance over the Rayleigh channel. I observed BER performance over the AWGN channel using Simulink in MATLAB. I used to change the "SNR" parameter in the AWGN block to get the BER.

What if I want to edit the block to get the BER but in Rayleigh fading channel (I want for every SNR, to get the BER). There is a Rayleigh fading channel block but I don't know how to use it.

I want to observe the BER performance of MPSK and MQAM over Rayleigh fading channel.

The figure below shows my blocks for observing BER in fading channel, the parameters in the fading block and my result.

In AWGN I generated binary bits, then modulated them by using the BPSK. After that I added the noise and then I demodulated it and finally I got the BER for every SNR.

However, I tried to edit it so I added the Multipath Rayleigh fading channel block to observe the BER in fading channel.

Here is the figure:

Regarding the Doppler spectrum type, there are several types: Jakes, Flat, Gaussian, Rounded, Restricted Jakes, Asymmetric Jakes, Bi-Gaussian, Bell and "specify as dialog parameter".

In the "Result" figure, the simulated one is the blue one (wrong) and the theoretical one (red) I got by using the "berfading" command, which is the correct one.

As you can see, my result in not correct. Are my blocks correct? Are there any parameters I should change, especially in the fading block, to get the correct result?


texts: Is it possible to power a torpedo via a wire?

texts: I've heard the Mk. 48 torpedo is wire-guided, why not make it wire powered? The range would only be limited by the length of the wire. I'm wondering why this is not used and what problems it would have.


texts:
Are there theories that assert about the ideal shape (i.e., ignoring structural constraints) of a propeller?

Just looking at the shapes that emerge in practice, it appears that both the fluid speed relative to the propeller and the fluid's viscosity are factors that radically affect the optimal shape.  Are there any laws that relate these factors?

From what I have observed in practice, I would conclude that a ducted fan with blade angles matched to the desired Mach number, and diameter matched to the desired power, is a maximally efficient propeller, meaning that it converts rotational energy into the maximum possible mass flow to its rear.  Is this (or some statement like it) correct?

And if so, does it apply across the full range of viscosity and flow speeds – from hypersonic air flight to trawling under water at just a few knots?


texts:
Help out a college student.
How do you derive the deflection equation y(x) of the shown stepped cantilever beam in the figure? Each segment has a unique Young's modulus and moment of inertia. The thickness of segment 1 is larger than segment 2. I will be needing the deflection equation to derive the resonant frequency of the beam using Rayleigh method shown:
$$
\omega^2 = \frac{\int_{0}^{L} EI \left( \frac{d^2y(x)}{dx^2} \right)^2 \,dx}{\int_{0}^{L} \rho A (y(x))^2 \,dx}
$$
where L = L1 + L2
https://www.researchgate.net/publication/274736623_Experimental_and_Numerical_Study_of_Crack_Effect_on_Frequency_of_Simply_Supported_Beam
I have tried using the deflection equation of a uniform cantilever beam with concentrated load F at the free end $y(x) = \frac{Fx^2}{6EI}(3L-x)$, but when I substitute this equation to Rayleigh equation and compare the resonant frequency values to COMSOL (FEA) simulation results, it does not follow the trend of resonant frequencies obtained when I try to vary the length of segment 1. However, it does follow trend of resonant frequencies when the width and thickness of segment 1 is varied.
I hope you can give me some advice. Thanks!


texts: What is the splice length for two reinforcement bars in tension of different diameter?

texts:
For reinforcing in concrete, anchorage / lap lengths are determined by the multiplying the diameter of the rebar with a factor. Generally a factor of 40-45 is accepted as the de-facto standard. According to EC2, the factor falls within the range from 34 and 66, depending on concrete quality, etc.

It is my understanding that the factor is in linked to the amount of shear resistance required to act against a force pulling out a rebar at its ultimate tensile stress. The factor is thus the height of the shear cone created.

When lapping a bar of larger diameter with a smaller one, my explanation above would be used to argue the case that the smaller diameter is taken to determine lap length.

I have found various sources where people have said the smaller bar should be used. I can find no code references defining it though. I would assume that one goes for the larger diameter to be safe, but the extra steel obviously increases cost.

Any advice would be greatly appreciated.


texts: Structural engineering: Would I need a beam for this?

texts: If I was designing a simple gabled house with a 21 ft vaulted ceiling as the peak of the roof, and the house was about 32 ft x 40 ft with no load bearing walls (other than the 4 exterior walls)...  would I need a beam across the entire peak of the house? If so would it have to be steel cause of the 40 ft span?


texts: Standard bicycle monorail design considerations

texts:
I have been thinking of a design for a standard bicycle monorail. I don't have the resources to prototype it right now so I would like to bounce the design off the community.

Basically thinking of a half cylinder track that is larger diameter than a bicycle wheel. For a prototype I was considering ripping 2 inch pvc in half for the straight sections. In application people could ride a standard department store quality bike on to the track at an enterance and off at an exit without any modifications or reconfigurations to their bicycle.

My biggest concern is balance stability on the track (even on a straight section not considering corners). On a normal path the operator corrects from a disturbance by gyroscopic precession (and resultant turning) of the front wheel. The track will limit this but will provide an elevation change toward the outside of the track that may assist. Thoughts? Any prior art you know of? Thanks!

I don't want to debate the usefulness of the idea, but just so everyone is in the know, there are three potential benefits:

Lower cost for longer distance bicycle path infastructure.
Lower rolling resistance than a normal flat path.
Lower cost for snow removal and maintenance.


texts: How to calculate the ideal and realistic estimate of thermal efficiency of absorption chiller?

texts:
How Can I calculate the ideal and a realistic estimate of the thermal efficiency of the system (thermal, electrical and water) per 1 kWh chilling energy (removed from the chilled water)?
What is the difference between ideal and realistic thermal efficiency in absorption chillers?


texts: I've tried to find some rules of thumb about this without any luck. I'm designing a part with a blind cartridge bearing bore. It's a 624 bearing (13x4x5) and the fit size guides point me to a tolerance of 13.0-13.026mm for the bore for my application, so slip fit on the housing. FWIW the shaft is the rotating part of the design and will be pressed into the inner race. Do I need to create some kind of lip or shelf inside the bore so that the inner race doesn't come into contact with the housing and create friction? It seems like this would obviously be a concern if both the inner race and outer race are the same thickness.


texts: Calculate the radius of iridium atom, given that Ir has an FFC crystal structure, a density of 22.4 g/cm3 and atomic weight of 192.2g/mol

texts:
Calculate the radius of iridium atom, given that Ir has an FFC crystal
  structure, a density of $22.4\text{g/cm}^3$. and atomic weight of
  $192.2\text{g/mol}$.

Everyone whom I asked this question is giving different answers. By the way, I was going to ask something about this. Why are they finding that the atomic radius of iridium atom is $1.34\text{pm}, 1.35\text{pm}, \text{1.36pm}$? According to textbook solution, it seems $1.36\text{pm}$. However, they said that all answers correct. Thereupon, I wanted to check their answer from wikipedia, that gives anohter answer too. What would you say? Are all answers correct?

Kindest Regards!


texts:
I'm trying to design a mobile robot which has to climb over flat 60° inclined wet glass surfaces.

I was thinking to use a large vacuum system composed by a large fan connected to a brushless motor. By looking on google, I found this photo:

As it is possible to see, they use a brushless motor with a fan to generete some kind of vacuum to keep the robot on the wall. This system is very similar to the RC wall car toys which are able to vertically move on flat walls.

My idea is to create a vacuum chamber and to make it connect to the surface by using a soft rubber gasket (to avoid leakage), but I do not know how to design the vacuum generator.

How many RPMs do I need?
What shape should the fan have?

The robot has a weight of about 30-35Kg and its size is 1000x800 mm.
The surface which can be used for the vacuum generator is the space between the tracks and it is about 800x600 mm.

I hope you can help me!

Thank you a lot!

EDIT 2
Information after @ericnutsch answer.

This is my ideal design.

I would like to use a cylider as case for the fan/impeller, use a rubber gasket for the cylider borders in order to avoid leakages (when possible). The cylinder/case will be suspended by springs in order to make it touch the surface by using the weight of the chassis. I do not know if the drawing is clear, but this is what I would like to acquire.
The dimensions showed in the figures are realistic and the weight of the robot is about 30-35kg.

EDIT 3

on #Mark answer:

I've found this impeller which can be customized and can have a diameter of 550 mm. It comes with some specifications:

EDIT1:
This is what I tried so far:

During last months, I did several tests with different solutions:

Using rubber tracks with Linatex which offers a great grip over flat surfaces
Multiple suction cups with a vacuum generator

The Linatex works very great up to 60° if the surface is not wet, if it is wet, they works fine up to 18°.

The 4 suction cups works fine only if the robot moves very very slowly (0.1 m/s) otherwise they lose the vacuum.


texts:
In structural engineering we have to accept the fact that you can never be exactly sure how much load a structural member can resist, that the load carrying capability of an element is not one exact value but distributed with some probability distribution function (quality of laid concrete, for example, is quite dependent on many conditions on the worksite, such as the workers skill, etc.). The same goes for structural loads. Therefore we cannot say with absolute certainty whether some structural is stable, we can only calculate certain probabilities.
In the image below, the left curve represents the probability density of the possible loads, and the one of the right represents the probability density of the load carrying capacity of some structural element. The y-axis is the probability density, and the x-axis is the structural load. The red area where the curves overlap is a range of loads where structural failure is possible; before that range there is "zero" possibility of capacity being that low, therefore the capacity must be higher than any possible load (failure is defined as a scenario where the load is greater than the capacity). Beyond this range the load has "zero" possibility of being higher than the capacity therefore no chance of failure.

The actual probability of failure can be calculated as follows, according to Wikipedia:
$${\displaystyle P_{f}=\int _{0}^{\infty }F_{R}(s)f_{s}(s)\,ds\qquad \mathrm {} }$$
where $F_R(s)$ is the probability the cumulative distribution function of resistance/capacity (R) and $f_s(s)$ is the probability density of load (S).
I have hard time understanding why the above formula gives the probability of failure. This is supposed to give the probability of the load being higher than the capacity/resistance, but I just can't wrap my head around how that works. Could somebody explain this to me in more detail? I am familiar with probability distribution functions and cumulative distribution functions, but I don't understand what's happening here. Why do you take the cumulative function of the load resistance but the probability density function of the load?


texts:
Consider the collision of two soliton pulses propagating with identical amplitude, equal velocity
in two opposite directions on a nerve. Assume that the collision is head, reversible and adiabatic. Consider the presence of viscous friction in the system. Then the pulses pass through each other almost undisturbed with the generation of some small amplitude noise.
Now, How can I prove this mathematically or in any other way?
Forgive me if this is not the right place to ask this question. If it is not, please tell me where to ask this question.


texts:
Something simple is tripping me up in a design, and the problem can be reduced to a simple 'seesaw' setup: a rigid beam with pin joint and a weight hanging from each end. I have attached an image with dimensions and values of interest:

.

The pin joint is not centered in the beam so that one end is further from the joint than the other. The beam has been rotated to an angle, and the length of each side's projection onto the horizontal is known. My question is this: In analyzing this problem I end up showing that the torque induced by each weight is equal but the reaction induced at $F_2$ by $F_1$ does not equal $F_2$, and vice versa. Have I made a mistake in my analysis, and if so where?

Known: $A=30\ deg;\ R_1=10\ inch;\ R_2=5\ inch$

Given: $F_1=10\ lbs;\ F_2=20\ lbs$

Determine the vertical reaction force $F_{1,2}$ induced at $F_2$ by $F_1$:

1) $F_{1,tangent}=F_1\cos(A)$

2) $L_1=R_1/\cos(A)$

3) $\tau_1=F_{1,tangent}L_1=F_1R_1=100\ in.lbs$

4) $L_2=R_2/\cos(A)$

5) $F_{1,2,tangent}=\tau_1/L_2=100\cos(A)/R_2$

6) $F_{1,2}=F_{1,2,tangent}\cos(A)=15\ lbs$

Using this result of $F_{1,2}=15$ and going backwards yields $\tau_2=75\ in.lbs\neq\tau_1$. So it seems like I made an error, but I can't find it.

To look at it another way, wouldn't this result suggest $F_2$ cannot be greater than $15\ lbs$ without breaking equilibrium. Yet when $F_2=20$ the torque induced is $\tau_2=100=\tau_1$.

And so I keep going in circles. I could really use some help! Thank you for your time.


texts: What is the best way to fasten securely a load onto a hollow brick?

texts:
Due to the ongoing COVID pandemic, I decided to put a basketball hoop on one of our outside walls, so that me and my son can stretch a bit. The problem is that the wall I plan to put the basketball is built with hollow bricks, (see below).

The thickness of the brick is close to 10cm.
Additionnal specs :

the wall is getting its fair share or rain during autumn and winter and its facing the wind, so I want to make sure that no moisture will find its way in.

there may be some dunking (we are on average 100 kg each) involved so I need to make this as robust as possible.

I considered but I find them lacking :

screw plastic wall plugs

screw anchors

Toggle Bolts

expansion anchors

hollow wall anchors

In most of the cases my main worry is that because the brick is hollow the won't find enough support. So, I wonder what is the best practice for this type of brick.
I would greatly appreciate any guidance on the matter.


texts: Stability of 3D-printed mask after sterilisation

texts:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6797553/
https://www.hatchbox3d.com/collections/pla

We are 3D printing masks that need to be used by medical staff treating COVID19 patients.

The first link is an overview of the material we are using for masks in general.

The second is the specific product we are making masks out of.

Quesions:

1- To sterilize; can we safely do 120C for 30 minutes without the mask losing shape? What about 70C for 30 minutes? Will it affect integrity and water/air proof "ness"

2 - Should we sterilize in humid air? dry air? again to maintain shape and impermeability

3 - will this be stable with exposure to 1) Vapor H2O2 @ >480 ppm for 30 minutes? 2) 1:9 bleach:water immersion? 3) household disinfectants (google Lysol)

We are making masks from this material and would be happy to recieve insights from people in the field.


texts: What is the minor diameter of a thread in terms of its nominal diameter and pitch?

texts:
I'm trying to find the formula for calculating the tensile stress area of a bolt. According to page 1528 of The Machinery's Handbook (29th Ed.), that formula is given as

$$
A_S=\frac{\pi}{4}\left(\frac{d_m+d_p}{2}\right)^2
$$

Where the pitch diameter is $d_p=d-0.649519\times P$, and the minor diameter is $d_m=d-1.299038\times P$.

I was trying to understand where the definitions of $d_p$ and $d_m$ come from. The Wikipedia page for the Unified Thread Standard (link) was very helpful for understanding that. However, it is not clear where the equation for $d_m$ comes from. The value 1.299038 is equivalent to $\frac{3\sqrt{3}}{4}$. Translating this to be in terms of $H$ instead of $P$ results in $d_m=d-2\cdot\frac{3}{4}\cdot H$. In other words, it would appear that the boxed dimension in the drawing below (versions of which appear on pages 1807, 1912, and 1973 of the handbook mentioned above) should be $.75H$ instead of $.625H$.

I'm assuming I must be missing something obvious here because I'm seeing variations of the formula for $A_S$ listed above everywhere. The best I can figure is that the equation for $A_S$ assumes that the outermost 1/8th of the V is included in the nominal diameter of the bolt. However, I can't find any justification for this. If someone could explain it to me, I would greatly appreciate it.


texts:
I'm not an engineer, but I build custom audio equipment and systems as a hobby. My question to you is: from a computer power supply (PSU) which converts AC power into DC of various voltages (12 V-5 V) would it be possible to power a Bluetooth receiver which uses 5 V 1 A power from a wall plug USB socket, directly from the PSU?
I've tried using the red (5 V) wire with the ground to a female USB cable which I plug into the Bluetooth receiver, but to no avail. The part I don't know about is the 1 A. What is the relevance of this?


texts: I want to run an AC sweep from 1 Hz - 10 MHz and calculate the output of the circuit (the voltage on RL), however spice shows that my voltage is 0 in a lot of parts that it shouldn't. I believe the circuit to be correct since it is copied from a book. I must have misunderstood something because I run into similar problems using the sine source (transient sweep not ac).


texts: Injection nozzles and static mixers for LSR - How do i prevent an uncleanable blockage between runs?

texts:
I'm trying to implement a new material in our processes, and that's a 2 part, highly viscous (500-1000 Pa s) liquid silicone rubber. I will also be adding a pigment, so that's 3 components that need to be mixed before entering the mold.

I have very little experience with injection molding, and this part has me stuck in my thought process.

These will be low volume production. Maybe 5-10 runs per shot. Sometimes even 1 shot. Each shot in the range of 10-20cc

Once the three parts enter the static mixer, the ticker starts. at room temperature this has a pot life for about a day, but at temperatures around 100C, the cure time is in the range of 5 minutes.

How do I go about clearing out the injection nozzle and static mixer of the messy, thick, sticky, virtually insoluble in anything LSR so that the parts are not jammed unusable for my next use (which could be in a week)

The entire process and set up is still in the concept stage, I'm open for a radical rethinking, but the material choice remains fixed.


texts:
I am trying to interpret the hole specifications in the attached diagram. What does each component mean? I understand what 'Thru All' means, does 4x mean 4 holes? What is the diameter of the hole? is it 5mm or M6 = 6mm? What is 6H?

Thanks in advance


texts: At what cold ambient air temperature will power lines fail?

texts:
I'm wondering just how cold it would have to be before electric power can no longer flow through overhead power lines. I know power lines generate a certain amount of heat just as a side effect from electric current, but I don't know if sucking off this heat will make them fail, or if very cold air will make them fail for some other reason. I'm looking for the reason and the approximate air temperature where failure will occur.

There are also transformers and metal pylons to worry about. Presumably wooden telephone poles would be fine, but the big metal pylons in long-distance lines might suffer too much thermal contraction.

I'm interested in overhead power lines only, which are exposed directly to air. Transformers and the metal pylons count too. I'm not interested in underground lines. I'm not interested in power plants themselves, which of course have their own vulnerabilities. Just the transmission infrastructure.

Also, I'm not interested in stormy weather either. I don't care about snow or ice accumulating on the cables, or rain short-circuiting something or wind blowing something down. All I care about is the cold ambient air affecting power transmission.

So how cold does it have to be before overhead power lines fail?

EDIT: For all I know there is no lower limit. Very low temperatures might actually be a benefit if they safeguard against overheating.


texts:
I found an ingenious design of a spring ball launcher on grabcad and I'm interested in adapting it to accelerate a $43.7 \mathrm{~mm}$ diameter, $45 \mathrm{~g}$ golf ball enough to reach $65.5 \mathrm{~cm}$. My calculations are shown below together with my questions.

First, my project puts a limit on using max $1 \frac{N}{m m} $ springs, so I started by calculating the energy necessary to compress the spring:
(1) $
\begin{array}{l}
h_{\max }= 65.5 \mathrm{~cm}\\
E_{h}=m \cdot g \cdot h \\
E_{h_{\max }}=0.289 J \\
\end{array}
$
That means I need to compress a $0.99 \frac{N}{m m} $ spring about $24 \mathrm{~mm}$ by applying a force of $24 \mathrm{~N}$. This brings my first question: Is that too much for thin PLA/ABS 3D printed parts to handle?
(2) $
\begin{array}{l}
k_{s} =0.99 \frac{N}{m m} \\
E_{s} =\frac{1}{2} k \cdot x^{2}\\
x_{s} =\sqrt{\frac{2}{k_{s}}\cdot E_{h_{\max }} }= 24.165 \mathrm{~mm}\\
F_{s} =\ k \cdot x \\
F_{s} = 23.923 \mathrm{~N} \\
\end{array}
$
The best spring I could find was this one, and its small diameter might force me to change the initial design of the launcher.
Does anyone think I can find something better or will this do the job?

Then, I started thinking about electric power and the rack and pinion system. I didn't know exactly where to begin so I assumed that moving the red rack $24 \mathrm{~mm}$ in $3 \mathrm{~s}$ was a reasonable estimate for a DC motor. Is that correct? From where should I start this kind of analysis?

I arbitrarily decided that the rack would slide the $24 \mathrm{~mm}$ with 3/4 of the gear full rotation. That brought me to a $10 \mathrm{~mm}$ pitch diameter gear with ten $1 \mathrm{~mm}$ gear module. Is that reasonable? How should I decide these values based on the initial $24 \mathrm{~N}$ estimate?
My previous choices brought me an angular velocity of about  $15 \mathrm{~rpm}$ (or $1.571 \frac{\text { rad }}{s}$). Together with the initial required energy of $0.289 J$ and another requirement of using at most $12 V$, I found a current consumption of $38 mAV$.
(3)  $
\theta =\frac{3}{4} 2 \cdot \pi \cdot \text { rad } \quad w =\frac{\theta}{3}=1.571 \frac{\text { rad }}{s}
\\
$
Here I assumed the torque on the gear to be the same as the work done by compressing the spring. Then I set this to be the electrical power necessary to produce this torque.
(4) $E \cdot w=0.454 W$
$ V=12 V \quad I =\frac{(E \cdot w)}{V}=37.837 \mathrm{~mA}$
Are these last equations correct? If so, how do I go about looking for an adequate DC motor that fits my needs?
Any corrections, comments and/or suggestions are welcome!


texts: Connecting gypsum plaster pieces without space between them

texts:
I would like to know more about how to connect pieces of gypsum plaster effectively, without space between them. I have a few pieces of gypsum plaster (around 10 mm thickness, 20 cm width, 30 cm height) and would to connect them and form a simple box. I was thinking about some kind of steel clamps which could effectively connect the pieces, but I am not sure.

I am interested in connecting gypsum plaster board pieces without using screws e.g. without destroying the material in any way. It is about a model, which could be disassembled and reassembled again. That is why I first though about some steel clamps or some steel frames in which the parts could be inserted and removed.

Any ideas or where to look?


texts: Should Engineers Understand Equations without Relying on Derivations?

texts:
As I've progress through my undergraduate engineering program, I've noticed a shift away from physical intuition - understanding why certain phenomena or equations make sense because of basic patterns we are already familiar with - to mathematical intuition - showing why equations and their phenomena should occur by mathematical derivation.

An example of this I came across today in aerodynamics:

For Isentropic Flow: $\frac{p_0}{p} = (1 + \frac{\gamma-1}{2}M^2)^{\gamma/(\gamma-1)}$

I can usually follow the derivation of the equation, identify the variables in it, and apply it to appropriate cases. But, I cannot describe why this equation is justified by simply looking at it - I must follow the mathematical derivation. There is no way I'd be able to describe this equation to a layperson in a way that could satisfy them. I can't come up with an explanation that satisfies myself; I want to know why $1+$ is there, why $\gamma- 1$ should be divided by $2$, and why the Mach number should be squared, without solely relying on the mathematical derivation. I have this problem with many  formulas I have learned.

I know a fundamental part of engineering is understanding the equations and phenomena we use to to describe physical systems. Now, it seems like I should just trust the equations and make sure I'm not using them improperly.

Should I, as an engineer-in-training hoping to complete research, focus on trying to understand equations to my satisfaction, or should I instead just become well acquainted the equations, their use cases, and their general behavior?

Note: I acknowledge questions on this site should have answers and not just be discussed. I hope this question has an answer that has some consensus among experienced engineers.


texts: Why have they stopped having curbs on streets?

texts:
Growing up, roads always used to have a clearly separated sidewalk with a height difference.
All new streets I see have no such curbs/height differences. Instead, it's just one "blur" of road/sidewalk.
What is the point of this? Or rather, why did they not always do this? Surely it's easier to just make it one big slab of asphalt?
Why did they go out of their way to make a "curb"/height obstacle before, but no longer?


texts:
I would like to know if a lifting force will be created by the Coanda effect from high velocity air that is directed underneath a half-toroid shaped saucer by a centrifugal impeller.
I am seeking an answer to this question to make sure that I fully understand how the Coanda effect creates a lifting force so I do not waste time and materials building a prototype of it.
To illustrate how such a saucer and a centrifugal impeller could be put together to generate a lifting force via the Coanda effect, I created a 3D CAD drawing of it and I have displayed this drawing below in three different viewing perspectives.
The first drawing shows a cross-sectional view with its main components labeled, the second drawing shows a top side perspective view, and the third drawing shows a bottom side perspective view.

I want to point out that this saucer is not a true half-toroid shape because one side of this toroid goes up at a 45 degree angle and the other side slopes downward in an arc. The reason for this 45 degree angle is to have the airflow go across a flat surface which should minimize the Coanda effect across this particular surface area of the saucer.
If I understand the Coanda effect correctly, the high velocity air exiting the centrifugal impeller should be pushed up into the half-toroid area of the saucer by ambient air pressure. Some of the kinetic energy of the high velocity air molecules pushing against the bottom surface of the saucer's toroid area should be transferred into the saucer which should cause the saucer to move in an upward direction.
There is a circular cutout in the center of the saucer to allow air to flow into the centrifugal impeller. (Air going down into its inlet should create a vortex above the top surface of the saucer which should create an additional lifting force, although this is secondary to the answer that I am seeking.)
Will high velocity air directed underneath a half-toroid shaped Coanda saucer by a centrifugal impeller create a lifting force?
EDIT
I think an improvement to this design would be to add a bell-shaped air inlet to the top of this Coanda saucer. The spinning vortex inside of the air inlet piece should create low static air pressure inside of it and the ambient air pressure pushing against the exterior surface of the air inlet should create an upward lifting force upon the air inlet.


texts: second order linear filter and coefficients sign

texts:
Courses on automatics define usually the second order transfer function as

$$
H(s) = \frac{1}{\frac{s^2}{w_n^2} + \frac{2z}{w_n} s + 1}
$$
(sse here for instance).

However, it assumes that the coefficents $a,c$ of the corresponding second order differential equation
$$
a\ddot x(t) + b \dot x(t) + c x(t)= u(t)
$$
have the same sign.

Why is that ? If I consider the inverted pendulum linearized at the unstable equilibrium, then these coefficients won't have the same sign since the dynamics of the angle is:
$$
m\ddot \theta(t) - mg\theta(t) = u(t)
$$


texts: Cad align with point vs auto fit at Cloudcompare via GEOMAGIC Control

texts:
I need to compare two STL (Dental model Scanned) files and find the deviation between their points, SO this two STL files have different boundary, so i already used the GEOMAGIC Control software for comparing STL files.

I found these two like:

Are there any open source alternatives for geomagic?

How to compare/quantify (populate) two .stl models having shape difference to see result as color stl file and bar telling plus and minus changes?

useful for finding free alternative software for Geomagic, So i installed the Cloudcompare in my Linux OS, and aligned two stl file  and used the compute cloud/mesh distance icon and get this output picture of stl which shown geomagic output above:

So in Cloudcompare the Auto fit Aligning method don't work correctly and based of the user advises said which almost don't working correctly;

  Sadly it's still very buggy and not well documented so you're likely
  to lose more time by using this method (even if it's 'automatic') than
  directly using one of the above. Maybe in the future if someone dares
  to dig in the code and fix it...

So i must Align the two model by selecting at least for point in reference model and the target model, so i want dose by using this mechanism (manually give some reference point to align process) give the output acceptable in compare with Geomagic control best Auto fit mechanism for aligning?

It would be very useful to have more knowledge about this kind of aligning (manual selecting some reference point) with Auto fit aligning method because this works are for one academical research. for example i show the parameters for the manual aligning parameter in Cloudcompare Software  and using finally using Cloud registration:

as you can see the model finally has been setting aligned. in the cloud compare site about Cloud Registration method said:

  Automatic registration Fine registration with ICP For now, the only
  automatic method to very finely register two entities is the
  well-known Iterative Closest Point (ICP) algorithm. See the Fine
  registration (ICP) section.

So i have already used the Geomagic Control for finding variance result vs couldcompare here:

So dose this photo confirm the acceptable sameness of this two methods used for aligning used for variance Calculations?

Update:

Based of Dear Daniel suggestion i updated the result by calibrating the color of the result and the output shown below:

So does it means here we have some color changed in the deviation determined calculated by using CloudCompare Software with using Cloud Registration option with suggested Final Overlap 80% instead of 100%, but i think i must go through the those data outputs comparing with each others,am i right?

As some additional request,If  possible, could you possibly explain the the Excel column meaning of the output data of this deviation result made by Cloudcompare, Shown below?

Thanks a lot.


texts:
Need help with this.

Part of a sea defense consists of a section of a concrete wall 4 meters high, and 6 meters wide.

a) Calculate the resultant thrust on the section when the sea reaches a height of 3 metres relative to the     base of the section.

b) Calculate the overturning moment experienced by the section about point A.

This is my answer. Have i done this correctly? I am not sure if i am on the right track with this or not. Especially the overturning moment.

a) Thrust

$Density of water = 1000kg/m^3$

Width = 6m

Height of fluid = 3m

$f = pg \frac{h} {2} A$

Ft = 1000 x 9.81 x 1.5 x (6x3)

Ft = 264,870 N

b) Overturning Moment

$M = Ft \frac{h} {3}$

$M = 264.870 x \frac{3} {3} = 264.870 Nm$


texts: Approximately how many types of stress are there?

texts: Approximately how many types of stress are known/defined? Ex. Piola stress,  Cauchy stress ...


texts: Principal on gaining more height based on nested poles?

texts:
How do people design height gaining based on nested poles ?

Consider this picture (I made them) :

If I want to achieve height based on these 3 poles, how they should behave?

Is this how the behave?

I had been searching over the internet I haven't found the related material, and it's kinda hard what to type. I'm doing some tasks on designing a simple machine (no foundation knowledge but with will) and my English is sort of limited, especially to technical stuff but I hope you understand it .

*Imagine like there's somehow an auto increasing portable stair to get over the tree, the poles(both sides) are consisted of  poles fragment on each of them, how the fragments behave in this case.


texts: How can I filter out a signal while extracting only the desired one?

texts:
I know that my input signal contains a main sinusoidal signal, and I know its frequency but not its amplitude.

Until now, I have been successfully using the least-squares method to generate a sinusoidal signal with the least difference from my input.

However, this method breaks down when faced with slightly more complicated input signals, where the noise is big enough to disturb the list square. As a consequence, it's not efficient anymore.

What are some other ways I can accomplish this filtering that don't have the same issue?


texts:
I"m working on a design and having difficulty calculating possible misalignment.

I have a shaft (diameter D, tolerance t) that is running through two bushings. The two bushings are separated by a distance L. The two bushings are of width W1 and W2 (measured along the axis parallel to the shaft), with internal diameter of D1 and D2 with tolerances of T1 and T2. (see image below)

How do I go about calculating the potential misalignment of the shaft? When I started this I though it was going to be a quick 5 minute challenge but the more I work on it the more difficult it's seeming.


texts: Book(s) for Machining Characteristics of Materials

texts:
Peace be upon you all,
Is there a book or handbook which describes the machining characteristics of various engineering materials. For example where I could find data similar to following:

Material Name: Aluminum
Hardness Range: X-Y
Force/ Power Required to machine: A hp

etc.
It is apparent that such data is hard to come by in combined form but still I am hoping for some guidance in this regard.
Regards


texts: What is the difference between pressure and stress?

texts: Since the units are the same ($\frac{N}{m^2}$), what's the difference between pressure and stress?


texts: What is the (thermodynamic) explanation for heat/temperature reduction due to wind?

texts:
Here is my fan in my office. Sometimes I used it if my air conditioner (AC) has problems, or I my self have problems with my health due to the freon. What I observed is that the heat (or probably temperature) will be reduced if I turn on the fan (I mean, there will be wind blow there) even if the room is remain segregated from outside (no air interchanged with outside).

Then my question, what is the explanation for heat reduction due to wind blowing?


texts: 18' header beam installation for single story room addition

texts:
Im expanding my 28' wide single story composite shingle  home.  I want to come out perpendicular off 1 plane of the roof to expand master bedroom, and then remove
the wall.  The foundation is crawl space with peer and beam foundation. Im installing an 18' 14x3.5 psl beam above the wall being removed that will have the 2x6 rafters and 2x6 ceiling joists nailed to the face.  Im in sf bay area with no snow load. The beam will rest on two opposite 90 degree corners of the foundation peer.  My question is do i need to reinforce the peer foundation at those corners to accomodate the load created at the peer and beam foundation corners as a result of removing the wall under beam.  I believe there may be 6' concrete columns under the concrete beam at the corners.


texts: Has the kangaroo's jumping ever been copied in human engineering?

texts: The kangaroo has incredible jumping abiltiies. Its Gastrocnemius muscle is a major part of generating its jumping force. Has any engineer based a design, probably a vehicle, upon the kangaroo's locomotion system?


texts:
I know it's possible for a PVC pipe to develop a staic charge due to fluids flowing through them. This is a twist on that idea.

Can a sealed length of pvc (say 3.5 feet in length) - tethered below the surface in a flow of water (river or stream), develop an ESD charge on the inside of the PVC pipe surface? Would the conductivity of the water disipate any potential charge? Can the inside surface develop a different potential than the outside surface?


texts: What do you call the difference between the on and off temperatures in a simple thermostat?

texts:
A simple thermostat will turn on at one temperature and off at a higher temperature. This keeps the thermostat from cycling on and off too quickly. The difference between these values is sometimes called dead band and sometimes called hysteresis. Both words apply to more complex processes like hydraulic valves and PID controllers, but what I am curious about is which one is better used to describe a simple thermostat.

What term(s) do you use in this context? Please cite sources if you can.

For some background, this question came up as a result of this Engineering SE question


texts: How to scale up a gear's diameter, increasing number of teeth and keeping teeth size constant?

texts:
I'm trying to use a gear system to run a rotating circuit board which will be attached to the larger of two gears.
I have a set smaller gear for the rotation which has 0.350" diameter gear with 15 teeth and
Pitch Diameter of   0.312". Obviously I need to keep the teeth and gaps the same.
My gear which will have a circuit board seated onto it has an outer diameter of 2.7"
What I have been doing has resulted in the tooth thickness being too large, or the width of space being too large, resulting in gear slap or gear slippage. Suggestions?


texts: How can the alloying materials of recycled steels be separated?

texts:
As I know, a very considerable part of the currently processed steels (around half of it) is coming from recycling.

But during the steels coming into the recycling process are coming normally from various sources, and thus they are containing very different alloying materials.

But the output of the reprocessed steel must be steel containing alloys exactly in the specified ratios.

Do some type of "separation", or "removal" of the previous alloys of the recycled steel happen? And if yes, how does it work?


texts: Is ductile iron a good material for a support column cap?

texts:
I am planning on having some column caps made (for Lally columns) and it seems to me the best approach would be to have them cast from ductile iron. The picture below shows the basic design:

Of course steel is an alternative, but I don't trust welds and I doubt the same strength can be achieved by welding. Note that those are 1/2" ribs, so it would be expensive to have steel cut and welded for the fabrication.

Is there any counter-argument to using ductile iron?


texts: How to dump moist air without heat backflow in evaporative cooling system?

texts:
I'm looking to design or purchase an evaporative cooling system for a small 70ft^2 California dorm room without air conditioning. This room has a single window and door to a large common space with a freezer. The common space and room currentl reach temperatures of 80+, while outside the room reaches temperatures of 90+.

An evaporative cooling system cools air by using heat to vaporize water. This can only go so far, as a closed room will eventually become too humid and water will cease to evaporate. For this to work in steady-state, then, moisture or moist air must continuously be sucked away from the room. Practically, I can only think of doing this by having the moist air leave the room. Mass balance implies that new (unfortunately hot) air must enter the room.

So our system is now dry hot air entering through one window, passing through a fan and over a basin of water to cool it, and leaving through my door towards warm common space.

My questions:

1) Would simply having an ultrasonic humidifier blow water into a continuously flowing air stream be sufficient to cool the air, or otherwise be more efficient than just running the air over a water bucket? If the heat is truly just going into enthalpy of vaporization, this seems like it'd be more efficient.

2) This design relies on the air cooling process being sufficiently "fast" relative to the air's flow rate. Otherwise the hot air will enter but only be slightly cooled by the system before leaving our cooling system, entering the main room and discomforting the occupants. Everyday experience suggests that opening a window, even with an ice bucket in front of the window, won't absorb heat quickly enough when it's 90 degrees outside and 80 inside. At the same time, evaporative coolers have found commercial success, so is this simply not true?

3) How can I effectively have moist air "leave" a room? Is simply opening a door enough such that the cool, moist air will diffuse out on its own? If I leave the door closed and turn on a fan and ice water in front of an open window, can I expect warm dry air to come in through the bottom of the window and by mass balance necessarily leave as cool, moist air (unintuitively) through the top?

4) I'm hoping that my moisture sink will be the common space outside my door, but given that this is almost, if not just-as warm as my room, it seems that would let heat back in from that end as well. Does this backflow doom our system?

I understand that, in more industrial contexts, these kinds of questions require simulation tools to answer. I just wonder if there's back-of-the-hand heuristics (e.g., convection is faster than conduction) that I can use to do this without needing to break out Ansys or fuss around too much with system configurations.

If cooling my room like this is, indeed, hopeless, how does a $40 evaporative cooling system manage to circumvent these problems from a heat/ mass balance perspective? Where does it dump the moisture, and how does it prevent heat backflow? Is there a better system design I'm missing?


texts: clockwork motor output in joules formula

texts:
I'm trying to understand the output of clockwork coils in joules or watts for different coils. You know the pullback car or windup pocket watch mechanism. I have heard it also called power in the barrel.

I found this below image as is the best approximation of the power output, but I don't know the coil size, or how to determine the size of a coil barrel for a particular out requirements.

Question, how to determine output of a clockwork motor of given sizes?


texts: How do gears engage and mesh in a sliding mesh gearbox?

texts:
In this video, the counter shaft is not rotating while a gear slides into place. But if the counter shaft was rotating, wouldn't the gear sliding over have a difficult time engaging with a gear on the counter shaft?

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


texts: Need advice: Estimating the compressive yield strength of abdominal tissues from the data of its rigidity or stiffness constant

texts:
I am doing research on biomedical device development, and focusing on devices that work on grasping tissues in the abdominal area. I need some help with applying the concepts of material strength to human tissues.

In simple language, let's assume that the stiffness constant (or the spring constant, K) of a given tissue is known, and we assume that it is a constant and hence the compression of the tissue is linearly proportional to the compressive force applied on it.

Given that we know K, is there a way to figure out the upper limit of the Force or the upper limit of the compression I can allow, before the tissue gets damaged? i.e. can we estimate the compressive yield strength of the tissue given that we know its K?

Another small confusion: If we are talking about the point at which tissue damages, is that the point of yield strength or ultimate strength?

I'm familiar with basic solid mechanics and strength of materials on a very beginner level and I'm getting stuck in applying those concepts in the context of biomechanics. Any help in this direction would be really helpful.

PS: This is not Homework help, I work as an RA and I'm stuck at this issue in my research :)


texts: How to regulate torque/RPM on an IWD vehicle

texts:
Generally, I'm interested in simple (DIY) electric vehicle design problems. I saw some photos of electric vehicles as in the following pic:

or also you could check this youtube video.

The vehicle is using an independent wheel drive, so it has 4 bicycle hub motors - one for each wheel. How is possible to regulate/sync the motor's RPM/torque in the turns? In the classic one-motor design this is solved by using a differential but how it is solved in an independent wheel drive scenario?

I am also wondering what happens when one wheel temporarily leaves the ground (e.g. in some off-road scenario). Wouldn't it start spinning very fast in the air, without contact with a surface?

As a programmer, I could imagine some Arduino-based "software differential" for the front wheels, which will regulate the RPM on the wheels based on the "steering wheel" angle, but I don't know how to do the same on the rear wheels.

Also, using an Arduino in such projects doesn't sound very "bullet-proof" but a car, especially such an important thing as engine RPM/torque regulation, needs to be "bulletproof" even as a DIY project, so I am not convinced that this would be a reasonable solution.

How it is possible to solve the independent wheel drive problems in the simple DIY world?


texts: horizontal angle of view based on distance from window

texts: I am looking for an equation to provide me the angle of view based on a distance from a window. I'm only interested in the horizontal not the vertical.


texts: Control theory: Closed loop zeros, Root locus and its dynamic response

texts:
Why the closed loop dominant poles of the root locus can show the response of the system? Wont it neglect the effect of the closed loop zeros?

As I read on the books, root locus method deal with the closed loop poles. It sketch the locus of the close-loop poles under an increase of one open loop gain(K) and if the root of that characteristic equation falls on the RHP. It means the close loop pole fall into RHP and make system unstable. But the exercises and examples also treat Root locus as a method of designing compensation or gain to fulfill the system requirement like damping factor and setting time. Isn't the root locus method for stability only?

I thought the system response should include the closeloop zero. Did I miss something?

Also, can Nyquist plot also used to show the system response and to design the system? As I thought its some how same as Root locus, with frequency being the varying K(gain).


texts:
I would like to know if there is any theory behind designing the fixation for any part. To optimise the number of mounting holes and fasteners.

If so what is it called and where can I get it?
 Please help me.


texts: Specific heat at constant volume used in non constant volume processes

texts:
I have commonly seen that the work for an isentropic compression is written as:
$$
W_{in} = c_{v}(T_1 - T_2)
$$
What confuses me is that since it is a compression (volume is changing) why do we use the constant volume specific heat?
Thank you kindly for your time and help.


texts:
When calculating the factor of safety for a fillet weld that is loaded in shear what should be the maximum allowable stress?

Some books suggest using the distortion energy (Ssy = 0.577Sy for the maximum allowable stress) while others use maximum shear stress theory (Ssy = 0.3Sut for the maximum).

Are both of these ways correct? Which one is used more in the field?


texts:
I have a question on my work which I cannot figure out. I have three chains which support a beam. On the beam acts a distributed load. I want to calculate how much load will go to each chain.

I know the sum of each force/moment is equal to zero. The magnitude of the distributed load ($w$ Newton/meter). The length of the beam $L$ (Meter) and the sub-distances ($x_a$, $x_b$, $x_c$, $x_d$ Meter). $F_{vt}$ (newton) represents the concentrated force of the distributed load ($F_v = w*l*0.5$)
and $F_{av}$ is the concentrated load in section $x_a$.

So if you go through all the point you get four formulas. The first one for point $a$ is:

$$\begin{gather}
\sum M_a = 0\\
F_b(x_b) * F_c(x_b+x_c) - (w *L)* \dfrac{L}{2} = 0
\end{gather}$$

But in $x_a$ section forces are also action, which should a moment around point $a$. But how can I calculate the resultant force ($F_{av}$) for section $x_a$?

I have tried the following but I get a net force in this section of 0 N ($F_{av} = w\cdot\dfrac{0}{L} = 0$). So there is no force acting in section $x_a$?

Can somebody help me out with this part?


texts:
I want to know how is exactly modulated a LTE subcarrier.

Since I'm working on Synchronization Signals (P-SS, S-SS) the subcarriers I'm talking about are centered around DC.

I have coded the algorithms that output diverse information (Zadoff-Chu sequences, m-sequences...) that will be carried by the specific 62 subcarriers (1.4MHz BW) corresponding to both PSCH and SSCH.

I'm now willing to modulate the information on the subcarriers.

My guess is that this formula is some kind of sinusoidal signal, i.e. for PSS:
s(t) = sin(2πkFe/f + φ) factor the data I want to map on.

I've found what seems to be the general equation of the subcarrier, s(t)=A(t)exp(|wt + phi(t)|) giving a classic s(t)=A(t)cos(wt + Phi(t))

But I haven't found anything precise until now on OFDM documentation about the complete modulation.


texts: How to design and make thermal inkjet print head / nozzles

texts:
I'm recently interested in print-heads, especially thermal inkjet print heads.
I would like to design a simple print head with nozzles in a row with no chambers, but only a straight linear pipe-like structure, and the heating resistors stuck on the side.

I'm quite lost here. I don't know what kind of material I should use, or what should be the diameter of the nozzle, and etc.

I want to look at the earliest version of thermal inkjet print heads but all that I can get in google patent is the latest, and high tech version of print heads that I can barely understand.

Can anyone tell me what to do, or where to look at?


texts: Derivation for the Formulas of the Approximate Ultimate Analysis of Coal

texts:
I've been given the following to memorize; But my head is so crammed with many others that I need to find another way; Are these formulas Empirical? I was hoping that if I derive it from a much more primitive form; I maybe able to remember it.

$${ (\frac{A}{F})_t = W_{ta} = \frac{Q_h \frac{kJ}{kg} }{3117} \frac{kg_{air}}{kg_{fuel}} }$$

$${ (\frac{A}{F})_t = W_{ta} = \frac{Q_h \frac{kCal}{kg} }{745} \frac{kg_{air}}{kg_{fuel}} }$$

$${ (\frac{A}{F})_t = W_{ta} = \frac{Q_h \frac{Btu}{lb_m} }{1340} \frac{kg_{air}}{kg_{fuel}} }$$

I know if I'm provided the answer to one of these; I can easily derive the others because I've memorized the conversions. What I don't get is how ${\frac{kJ}{kg}}$ got to ${ \frac{kg_{air}}{kg_{fuel}} }$. I cant figure out where the 3117 came from.

${Q_h}$ is Higher Heating Value, ${ \frac{A}{F}}$ is Air to Fuel ratio


texts: Is Hamilton Jacobi Bellman optimization used in engineering control?

texts: Is solving stochastic HJB a practical method for stochastic optimal control in engineering field or it is just a method used in finance?


texts: I have a simulation software which shows energy consumption at 30 minutes timestep. If a system consumes 0.06 kWh at 6am, and 0.09 kWh at 630am, how to calculate the energy consumption between 6-7am? Can I assume it is the average of both timestep? Does finer timestep, eg. 10 minutes interval returns a different result?


texts: Why not design a Wind Turbine like an Anemometer?

texts:
Anemometer measures wind speed. It's shaped with little cups---hollow half-spheres. That looks very logical as the cups grab the wind and the other side is rather streamligned to cut through the air as it spins.

So why are there no wind turbines designed like this? (At least, I've never seen them.)

You could go further and make the cups ellipsoidal (more pointy). You could even add a inner shield, maybe like half a torus, around the inside to further streamlign the cups and help them grab wind.

This would be a vertical axis wind turbine (VAWT). Been looking around at VAWTs on Youtube for a while and found a lot of interesting designs, but never seen one with cups. Why not? I know I've seen anemometers spinning around very rapidly in good winds, so its seems logical.


texts: Wall temperature of pressure cylinder - Boundary condition

texts:
I have a thick-walled pressure cylinder, that transports fluid and experiences only internal pressure.  During the process, the outer wall temperature is measured.  And I have no clue about the inner wall temperature.  The only fact, that I know is, the temperature on the outer wall is due to inner wall temperature that is conducted outside.  So, the inner wall temperature should be always greater than that of outer wall.

Now I would like to reproduce the same situation in a simulation software by providing the outer wall temperature as input and read out the inner wall temperature data on the corresponding nodes.  To do this, I am applying surface loads on the outer wall, which is the measured value as the boundary condition.  But with this I see the inner wall temperature are always lesser than the outer wall temperature.

When I tried to give the internal pressure as boundary condition for the inner wall, the software says, pressure data for the given nodes are not required.  Any idea about, where am i going wrong, or what am i missing? thanks in advance


texts: Do fine and coarse screws have different diameters?

texts: I wonder, do fine and course screws have different diameter if they are the same standard size? For example, what is the outer diameter for 5/16″-18 and 5/16″-24 if I measure them with a caliper? Is it possible that a 5/16″-24 has a diameter of 0.3015inch diameter (which I measured)?


texts: What is the difference between a blade and a vane in a turbine? When constructing velocity triangles, there are two angles at inlet and outlet (α & θ, β & φ), respectively. My textbook defines α & β as blade angles and θ & φ as vane angles. What is the difference between them?


texts: Increasing convergence rate using Optimal Control and Pontryagin Maximum Principle

texts:
My question is in addition to Tuning the optimal control synthesized according to the Pontryagin maximum/minimum principle and choosing the cost function, but requires help from the mathematical side of view.
Given system of ODE:
$F=\begin{cases} \dot{x}=g \\ \dot{g}=-k_g \cdot g+k_g \cdot\frac{df}{dx}+u \\ \dot{h}=-k_h \cdot h+k_h \cdot\frac{d^2f}{d^2x} \end{cases}$
where:
$\boldsymbol{X}=(x,g,h)$ - vector of variables, which is moving towards some final state $\boldsymbol{X}_f$;
$f=e^{-(x-c)^2}$;
$c$ - unknown constant;
$k_g,k_h$ - parameters, can be selected from the range $3>k_g,k_h>1$;
$u$ - control input;
Feature: this system go to a state in which $g=0$ and $sign(h)=-1$.
Algorithm:
To ensure usual convergence, I chose the cost function in the form:
$J= \int_{0}^{\infty} (g+u^2) dt$

Hamiltonian:  $H=-(g+u^2)+\boldsymbol{\lambda} \cdot F$
where $\boldsymbol{\lambda}=(\lambda_1,\lambda_2,\lambda_3)$

Co-state equation: $\dot{\lambda}=\frac{dH}{d\boldsymbol{X}}$
where $\boldsymbol{X}=(x,g,h)$

Solve equation for control input $u$: $\frac{dH}{du}=0$

4.Write resulting system of equation:$\begin{cases} F=... \\ \dot{\boldsymbol{\lambda}}=... \end{cases}$

Solve numerically.

Problem: in what ways can the cost function be written to maximize convergence rate to the final state $\boldsymbol{X}_f$ for given parameters $k_g,k_h$.
$J= \int_{0}^{\infty} (???)dt$
I would be glad and grateful for any help.


texts: What what software tools do engineers use to programatically generate and parameterize 2D CAD designs

texts:
For many years I've been writing scripts to generate SVG graphics, first in stand-alone python scripts, then in Inkscape extensions, and then in various JS frameworks.
I'm considering creating a web-based analog to the Inkscape extensions framework (with no document inputs, output-only e.g. this) so that graphic/industrial designers can create their own adjustable graphical widgets or products and host them online. I'm trying to assess whether or not that would be useful to designers or engineers.
Are there ways in UI-based CAD software to specify e.g. circle B is 1/3 radius of circle A and circle C is 2x the radius of circle B, so that when circle A changes radius, all the circles change size?
I am currently working on a project that is just a single "widget" (see demo video) and I want to abstract out the parts that could be used to make other widgets.  I'm a programmer and not an engineer so I would really appreciate insights from the discipline.


texts: For improving the gear strength, which one is better based on manufacture and economy? Increasing module or increasing N? With the same surface strength.


texts: Guiding a parachute via anchor: Possible?

texts:
Here's my situation:

I'm trying to drop a payload via parachute with some accuracy.  I'm worried that in the above setup, the line will interfere with parachute deployment or - if not deployment - operation during flight (imagine wind pushing the chute into the line).

I haven't tested this yet but plan to.  Does anyone know how the payload to anchor connection might be engineered to ensure full deployment throughout the descent?


texts: Can you shape a magnet and how would it effect its field

texts: Long story short im playing with mental designs of an electric motor and I'm not sure on some things regarding magmets/magnrtic materials and my designs are in flux do to these variables. I'm wondering one if you can put a "blade" along an auger that holds a current to act as an electromagnet basically build a case to hold the blades n wires or if youd have to shape a magnetic material into the full auger. This idea is kind of like the wind towers that spin like a cyclone instead of the air making the rack spin I'm wondrring if you can force rotation with a coil around it. My idea is basically put the auger in a coil launcher set up so that when a current goes through the coil it spins the auger.


texts: Looking for something to reflect ultraviolet light at extremely low wavelengths

texts: I have been working on a product that involves the reflection of low wavelengths of UV light (200-250nm). However, I have not come across many materials that are able to do so and the high-reflectivity mirrors I come across are extremely expensive. What mirrors would be able to reflect UV light at such wavelengths at around a 50-75% reflectivity rate?


texts:
I am in the process of helping my son design a sort of model of the Bloodhound SSC car for his school project, using balsa wood, model aircraft wheels, etc... It doesn't have to a like of like, but vaguely resemblant so that you can tell what it is just by looking at it. It would also be nice if the car could move and I was thinking of using on this small CO2 gas canisters as a means of propulsion:

You can get some which are threaded, as above, or some which are just plain. What I haven't been able to find is a way to quickly release the pressure from the canister to propel the car. Are there any small on/off manual valves that would fit this type of gas canister? I haven't been able to find any, the only ones apparently in existence are for fitting onto bike tyres to (re)inflate them.

The only method I have come across is people using some sort of puncturing device (e.g. with a nail) that is generally sprung-loaded to pierce the gas canister when launching the model car. This puncturing device can be made part of the car, but more generally tends to be part of the "launching pad" as it adds weight and unnecessary complexity to the car. I would like to avoid this if I can.


texts: What Rubber is Best for Laser Cut McKibbens PAMs?

texts: I'm a layman engineer who's decided to take another step forward in my research and work with McKibbens Pneumatic Artificial Muscles. I’m new to creating custom rubber components and laser cutting, so please bear with me. My intent is to be able to order sheets of rubber, which can then be cut in a laser cutter into strips. I would then like to melt the long edges of the strip and fold the rubber strip onto itself, connecting the edges to form a rubber tube. The melting part is for fusing the two sides together. I was wondering what types of rubber would be best suited for this? I was thinking natural or silicone rubber, but again I’m new to making my own rubber components.


texts: Polyurethane with microbial resistance properties

texts: I'm looking for a polyurethane with microbial resistance. Doing some research I found two commercial types: DESMOPAN 9392A and DESMOPAN 2792A. Both are manufactured under GMP conditions and limited suitability for use with food contact, but only one of them has microbial resistance. So, I need to know what is the chemical process that gives it the anti-microbial quality.


texts:
I'm looking for an explicit numerical example of a parametric surface (u, v) |-> (x(u, v), y(u, v), z(u, v)) that models a fan blade like that in the attached picture.

Googling results in NURBS/PDE approaches but with no numerical explicit data.

I would like to find a more simple model to be used in a engineering class for upper high school students.

Thanks, Humberto.


texts: Calculating features of a 3 phase power timeseries

texts:
I have data from a number of high frequency data capture devices connected to generators on an electricity grid.  These meters collect data in ~1 second "bursts" at ~1.25ms frequency, ie. fast enough to actually see the waveform.
The meters are collecting voltage and current from each of the 3 phases. An example of the data (plot and tabular) is shown below, with one phase shown in each colour.
I want to roll this waveform data up to some summary statistics at a lower frequency (20ms). Specifically, I am looking to calculate:

Active power, reactive power and power factor
The grid frequency as it changes over time

Apologies but I'm a mechanical engineer and this is not my strong suit! All of the references I can find refer to idealised situations, where the phase angles etc are pre defined. I could fit idealised sin curves to each of the timeseries, but I feel there is a better solution. Are there any simple techniques to calculate the above directly from the timeseries?

Here's a "toy" data set of the first few waves of one voltage phase as a pandas Series for those who are interested:
import pandas as pd, datetime as dt
import pandas as pd, datetime as dt
ds_waveform = pd.Series(
index = pd.date_range('2020-08-23 12:35:37.017625', '2020-08-23 12:35:37.142212890', periods=100),
data = [  -9982., -110097., -113600.,  -91812.,  -48691.,  -17532.,
         24452.,   75533.,  103644.,  110967.,  114652.,   92864.,
         49697.,   18402.,  -23309.,  -74481., -103047., -110461.,
       -113964.,  -92130.,  -49373.,  -18351.,   24042.,   75033.,
        103644.,  111286.,  115061.,   81628.,   61614.,   19039.,
        -34408.,  -62428., -103002., -110734., -114237.,  -92858.,
        -49919.,  -19124.,   23542.,   74987.,  103644.,  111877.,
        115379.,   82720.,   62251.,   19949.,  -33953.,  -62382.,
       -102820., -111053., -114555.,  -81941.,  -62564.,  -19579.,
         34459.,   62706.,  103325.,  111877.,  115698.,   83084.,
         62888.,   20949.,  -33362.,  -61791., -102547., -111053.,
       -114919.,  -82805.,  -62882.,  -20261.,   33777.,   62479.,
        103189.,  112195.,  116380.,   83630.,   63843.,   21586.,
        -32543.,  -61427., -102410., -111553., -115374.,  -83442.,
        -63565.,  -21217.,   33276.,   62024.,  103007.,  112468.,
        116471.,   84631.,   64707.,   22405.,  -31952.,  -61108.,
       -101955., -111780., -115647.,  -84261.])


texts: How do you check a weld for applied moment?

texts:
I have a single angle connected to a double angle via a 3/16" weld

I know there is a factored, applied moment at that connection. I would like to ask how I can go about checking the capacity of this connection for moment? There is a lot of stuff in AISC for welds in Chapter J, partially and fully restrained moment connections but I am not sure where to start. What chapter/section of AISC codifies this kind of problem?


texts: How are maximum speed limits determined for banked curves?

texts:
I was once told that the speed limits on banked highway curves (specifically off-ramps) were determined by assuming zero friction between the car and the road, such that as long as you stayed on the correct path of travel, the banking of the curve would prevent a vehicle from sliding outwards. That is, the angle of the banking would mean that the portion of your gravity vector normal to the road surface provides enough centripetal force without counting on your wheels to provide any 'sideways' friction.

I am not a civil engineer and have no familiarity with the relevant codes, but I was wondering if this is true, or a myth. If it's not true, is there a simple formula used to set these speed limits, or is it a much more complicated procedure/judgment?


texts: "The monofilament wire has a tensile strength of 18 kg" What does this mean?

texts:
I am used to strength being measured in units of stress, such as pounds per square inch, or Pascals.

I am assuming what the author is trying to say is, "this filament will break when holding 18 kg," is that correct?


texts:
I am bit confused in considering the methods to apply for designing.

Consider a machine, which as several parts mounted on the frame (frame is of any sectional shape for exampe: ´I´ section).  Let the length and width of the frame is 2m and 0.6m respectively. Here the Distribution of the masses of the different components on the frame are eccentric in nature. And the machine supports at the four cornes which is similar to the support of the chair.

My question is, how do I calculate the deflection, bending moment, shear stress etc of the Frame or whole machine due to the Forces acting on it.

Since the Forces acting here are eccentric and not exactly on the beam, I think it is not possible to solve it by using Beam theory.

So, could anyone suggest me how to carry out this problem to solve it analytically. Or any advices on the study of any related topics are appreciated.

Thank you


texts: What is the maximum frequency of an AC current?

texts: I saw that the rpm of a synchronous motor is proportional to the frequency of current alteration and I was wondering if there is a theoretical maximum frequency (regardless of magnet strength)? Also could changing the frequency be used to control the speed of a synchronous motor?


texts: what do we mean by lightest? I mean, 10 g of aluminum is just as light 10 g of steel. So what's the point?


texts: What part is this and how do I create it in Fusion 360?

texts:
I am new to Fusion 360 and I am trying to create a plastic part that snaps onto a plastic tube (torus in Fusion 360).
Unfortunately, I am not sure what the name of the plastic part is, and I have been trying to Google something for the past half hour, with no luck.
Below is my best drawing attempt. The curved snap-fit part is the one I want to create. The longer tube is just there to show the other part being attached to it.
Can someone please identify the part (the keywords I should search for on Google) and direct me to some resources on how to create it in Fusion 360? Thank you.

Here is the closest picture I could find:
Its description on Google was "Durable Aluminum Alloy Golf Shaft Adapter Sleeve Accessory F9 Casing Scheduler, Connector", but I am not sure which keywords are relevant to my use case here.


texts: Is stroboscope a substitution for accelerometer testing?

texts: given that handy stroboscope can also check translational vibration of parts, is it a substitute for a test that can be done by accelerometer for stationary vibrating equipment?


texts:
I have a plate of aluminum 5 mm thick to which I would like to attach a hook. The plate runs roughly vertically, but only spans around 18 cm from anchor point to anchor point. The hook should be able to withstand upwards of 1000 kg.

I've drilled a 12 mm hole through the plate and my strategy is to insert the hook bolt in it and tighten it using a nut on each side.

However, in order to keep the aluminum from deforming, I'm going to need one or two steel washers.

My question is, whether it is necessary to use a washer on both sides or whether one side is sufficient?

If one is enough, does it make any difference, which side it rests on?

My reasoning goes like this: The job of the washer is to keep the hook from bending the aluminum by spreading the force over a large area. As long as a single washer is taut against the aluminum – held there by the nut – the hook won't be able to bend either way.


texts: What are the common failure points of waterproof cases?

texts:
I am making a waterproof case for my Galaxy S5 and/or my Raspberry Pi. I plan to make the main body from (or at least decorate it with) wood, though I can use other, stronger materials where needed.

I am thinking of using some controller (as opposed to the touch screen) while underwater if that would make it easier to avoid common points of failure. My question is, where do normal waterproof cases usually fail (leak)?

My design criteria are, from most important to least important:

Durability / Maximum Depth
Usability Underwater (mostly using the camera)
Cost
Aesthetics

If I took my phone scuba diving and dove to the maximum depth of about 33 meters, there would be about 43 psi acting on the case. Would the failure point then become the case itself cracking under pressure?


texts: Permanent uneven deformation of asphalt car park under portable cabins

texts:
Cabins have just been installed on an asphalt car park. The portable cabins weigh 4000 kg with 4 no. 300 mm square spreaders under each foot.

The car park is constructed from:
1" thick rolled asphalt
2" thick bitumen macadam
6" thick granular subbase
well compacted ground

The effective pressure on the asphalt is:
4000 kg = 40 kN / (4 × 0.3²) = 111 kN/m²

The question is whether this load is likely to cause permanent deformation of the asphalt leading to problems with ponding of water in the future.

I know this is a complicated question depending on the semi-solid nature of the asphalt and its rheological characteristics. The temperature for the duration of the portable cabins is not expected to exceed 30°C. The cabins are expected to be in place for approximately a month.

Any guidance, rules of thumb or a point in the right direction would be appreciated.


texts: Time duration for a mechanical wind up mechanism?

texts:
Is there a specific way to figure out the gear ratio I would need for a wind up mechanism that could last around one year? Would I start out with a really high tooth and step down too a small enough ratio for a complete cycle to last a year?

Do I need to devise a polynomial function, then use calculus to solve for the gear ratios, number of teeth, and time?


texts:
In the notes , i noticed that the shear stress on the top plane and the front plane will 'meet together' at the edge . I dont understand it why the direction is like that .

Is it possible for both the shear stress to become like this (opposite direction ) ?


texts: Questions about making stainless steel boiler

texts:
I am currently working on a project (or actually returning to a project) and need to have a heat exchanger boiler made. The hx boiler will be relatively small, a 10" long cylinder around 4" in diameter. One end can be capped, but the other should have a flange so I can work inside the unit. Inside, I will have a coil of copper tubing (heat exchange) and various other sensors/ports. I don't have access to a full machine shop to fabricate such a boiler myself so I am contacting a number of companies. My question really is in regards to the thickness of the steel required for the boiler. The boiler, at max pressure, will only be at 2.5 bar. Additionally, the material must be food-safe; the main boiler will contain water that will be used in food preparation. Given these working parameters, of what type and how thick should the stainless steel be? I will attach various rough sketches of the system for extra information.
Thanks in advance for the help!


texts: Non-toxic material for deformable wire/rod without work hardening

texts:
I am looking for a non-toxic material for a wire/rod that allows room temperature deformations without work hardening.

Example uses are semi-rigid cables that one can bend and that hold their shape afterwards or snake-like cellphone holders like the one in the image below.

I looked at a very old one I had lying around and found it was simply a lead rod. (Or at least is looked and felt like a lead rod.) To me using lead did make sense since its recristallisation temperature is lower than room temperature - hence no/very little work hardening.

Are there any alternatives that are at the very least non-toxic or even better bio-compatible? I looked at electronics solder since their melting point is fairly low but found they do exhibit work hardening at room temperature and break after multiple deformations.


texts: How to size a motor for a lifting mechanism?

texts:
I am building a machine that has to lift a load of approx 80 kg including the material and lifting mechanism's weight. The velocity requirement is quite low (around 4.5 cm/s or 0.045 m/s). The whole lifting assembly will run in a guiding channel and will have rolling contact with the guide. The beam shown in blue will be the one to be lifted. Also attached to it will be another assembly. The lifting approach i have chosen for this purpose is telescope lift (also called continuous lift), both assemblies will be lifted using a pulley system and steel wires being pulled by a motor sitting at the base frame. Also during the uplift,there will be a continuous decrease in pulling force due to outflow of material (about 25 kg). I don't want to use a speed control circuit. A friend of mine has suggested to use a very high torque output and over powered motor to cater for variation in load.

My question is that what type of motor is most suited for this job.


texts: Indeterminate beam with a guide at each end

texts:
I've been battling with a statics question (as attached) and can't for the life of me figure it out.

I've attempted removing the left side guide joint so then there are only 3 reactions and it should be statically determined.

However, I don't know how to reapply the loading conditions for the removed guide as it is axial not transverse to which the boundary condition applies. (X direction in Cartesian coordinates).

Can someone point me in the right direction on this matter?


texts: How can I calculate the buoyant force on an object without knowing in advance the amount of water displaced?

texts:
Suppose I know the mass and volume of an object, as well as its exact shape and density distribution as a function of space (x,y,z).  Without submerging it to determine the amount of water displaced, how can I determine the buoyant force?  Is there a way to determine the amount of displaced water based on knowing the density of the object as well as its shape?

Ultimately, I'd like to use this information to predict whether a particular design I have made will sink or float, but I need to know the buoyant force in order to do this.  How can I predict this force a priori without experimentation?


texts: In a nonlinear static two-step subcase, why does the load step decrease after the first step?

texts:
I am using MSC Nastran for nonlinear static analysis (sol 400).

Step 1 contains a small perturbation load laterally on a thin-walled cylinder.
Step 2 contains a very large compressive load.

Usually when I do this, the Load Step increments from 0 to 1 for the first step. Then for the second step, the load increments from 1 to a number under 2 (basically until it stops because the structure fails.) So in this second step, if the indicated load step is 1.3, then the actual compressive load in that load step is 0.3*applied load. (0.3 because take away 1.0 as that is from the previous step.)

The problem is now I am in a situation where the load step starts decreasing the moment the second step starts (right after LOAD STEP = 1.0).

I am using the arc-length method, so the load can decrease, but it shouldn't decrease this early. I want at least some compressive load until it starts decreasing. Because my understanding is that the compressive load in the second step is negative, and is therefore actually causing tension instead of compression.

So does anyone know what might be wrong and how to solve this problem?
I would appreciate any kind of help, thank you!


texts: What does "bedding-in" mean in casting technology?

texts: I've heard this term used a lot in literature but I don't understand what the technique is they are referring to. Please help me out here.


texts: How are reinforced soil retaining walls replaced when they wear out?

texts:
A reinforced soil retaining wall is a system where a thin retaining wall is anchored into the ground it holds using plastic meshes. The wall surface is typically assembled of small concrete blocks (about 0.3 meters thick and similar length and height) and once every several rows of blocks are assembled ground is being put behind the blocks, leveled and compressed and plastic mesh is being put onto ground and onto blocks exposed horizontal surface, then the same is repeated until the entire wall height is built. The wall is either vertical or very steep.

What happens when the concrete wall wears out? If we disassemble it then the mass of the ground should erode quickly and collapse. How is the wall replaced once it wears out?


texts: Modifying a fixed camera lens for close focus

texts:
I found this article on hacking macro lenses. The author used a lens extension tube to allow closer focusing. IE The lens's Minimum Object Distance (MOD) was significantly reduced.

I cannot find an affordable lens that suits my requirements, so I would also like to extend or shorten an existing lens to achieve my goals. Basically I am trying to hack a close-focus machine vision industrial camera from an S-Mount Raspberry Pi camera. The problem I'm running into is that compatible lenses have too high MODs. Given the constraints below, how do I solve the variables?

The Constants:

Object Size: 4" x 5"
Object Distance: 4.5" (Object to Lens)
Camera Sensor: 0.25"
The Object should be in focus and snug to the edges of the captured image
Avoid fish-eye or wide angle lenses, if possible

The Variables:

Focal Length (Lens to principal focus)
Image Distance / Back Focal Length (Lens to sensor)

I found this article which discusses Optics and the Lens Equation. I could simply solve the lens equation as follows: 1/115 mm + 1/x = 1/6 mm. In this case, the image distance would be 6.3303 mm. Is it really that simple though?

I can use any standard lens (3 mm, 4 mm, 6 mm, 8 mm, etc). My concern is that extension rings result in image magnificaion which would cut-off the image. I could plug my numbers into the magnification equation. and then extend my object size to include a 20% buffer, for example. But making that adjustment changes the figures for the lens equation. The two equations are intrinsically linked and I'm not sure how to solve them inclusively.