texts: Is there a way to reduce leaks and infrastructure damage when turning water on and off at the scale of city?

texts:
Cape Town, South Africa is experiencing an extremely serious drought, with estimates putting April 21, 2018 as the day that the city will be forced to shut off all municipal water supplies and begin water rationing, except to essential services such as hospitals.

One possible solution is to delay this date by turning the supply off and on for scheduled periods of time over the next few months. However, experts have said that this is not a solution that can be implemented, because the pipes aren't supposed to deal with this variation of pressure and leaks and other infrastructure damage will occur.

Is there a way that a city could implement a water rationing system where water is shut on and off periodically, while minimizing leaks and damage to infrastructure?


texts: Why is it called "Model predictive control"?

texts:
This will sound like a super silly question, but:

Why is it called "Model Predictive Control"?
I mean : the other types of control also compute the control input based on prediction of what is going to happen based on the "Model", no?


texts: Steam cycle for a boiler / radiator system vs Rankine cycle

texts:
Everything I've read on the Rankine cycle indicates that the feedwater pump is necessary for the cycle to work. However the steam cycle used in traditional household boiler / radiator systems seems to challenge this.

The cycle for the household boiler seems to be a closed loop cycle with just a heat source (boiler) and cold source (radiators). But those two pieces are sufficient to have steam flow through the radiators, condense, and then return to the boiler.

Is my understanding of the boiler / radiator cycle correct?
If so, and if the system was fitted with a turbine, could it produce any amount of power?
If it produced any amount of power, how inefficient would it be compared to a Rankine cycle?
Is there a name for the type of cycle in a boiler / radiator system?


texts: Find amount of sliding between 2 surfaces

texts:
in my project I am required to find how much two surfaces slide against each other (to see how much it'll will rub against skin). Does anyone know how I can find these results?

Thanks


texts: What are these rotary to linear movements called?

texts:
I’d like to know what the below movement mechanisms are called so I can better research them and incorporate them into my own designs.

They are both quite similar, they are from rotary electrical isolator switches found on vehicles and industrial switch gear.

Type 1:

A pin on the internal shaft or key follows the path of the cut out therefore forcing it in.

Type 2:

A linearly fixed T shaped shaft rotates and the internal plunger has a curved ramp. The plunger is sprung against the shaft. As the shaft rotates the T shaped runs up the ramp forcing the plunger down.

What are the two types of mechanism called?

I’ve tried searching for various terms but can only find basic cams etc. If there isn’t a specific terminology maybe someone could provide some search terms or some references


texts:
I have checked the definition of tonal masking on Wikipedia and google but I saw the definition of sound masking and auditory masking.

Auditory masking
Sound masking

But I want to know what exactly is tonal masking?


texts: What is the course content difference between conventional engineering and engineering technology programs?

texts:
I have seen institutions giving two different degrees to almost same courses. Some institutions give Bachelor/Master in engineering and some give Bachelor/master in Technology. So is their any underlying difference between Engineering and  Technology?  I am a student pursuing B-tech course. And in my semester subjects,  there is a subject humanities where we have to learn what's engineering and what's technology both!  But I didn't understand the difference as there is no such clear definition.

I have checked the Wikipedia articles and read the ABET definition of Engineering which says: The profession in which a knowledge of the mathematical and natural sciences gained by study, experiences and practices are applied with judgement to develop ways to utilize economically the materials and forces for the benefit of mankind. (Accreditation Board For Engineering And Technology, 2002)

But a Technologist also do the same thing. In what way are they different?  I have also checked the post for which it was informed as a duplicate post, and there the aspect on which they talked about is different from my question. I am not interested, being a technologist/engineer where will I get job. My question is specific to this point,  on what basis an engineer and technologist are defined?  what are the extra things that an engineer do or technologist don't and the vice versa.
I also checked the answers of that supposed original post,  the highest voted up answer has some basic faults. One thing I will like to mention technicians and technologist are not the same It was first defined in french and for completely different meaning. So I am looking for the particular differences an engineer and engineering has with technologist and technology.


texts: How to model subcritical open channel flow?

texts:
I'm trying to model subcritical flow in an open channel with a side weir of certain small length at the middle of the main channel, so a certain amount of fluid discharges through the weir. I need to match the two parameters - Froude number and flow depth just at the beginning of the side weir with experimentally measured values.
I tried modelling with upstream depth of water and velocity corresponding to required Froude number upstream of weir, at the inlet, which was kept at about 10m from the weir. However the flow depth reduces significantly by the time it reaches the weir.

How do I accurately model to obtain the required values of flow depth and Froude number upstream near the side weir?


texts: Is there correlation between friction of boundary layer and values of inlet and outlet pressure?

texts: Is there correlation between friction of boundary layer(or inertia and viscous forces in boundary layer) and values of inlet and outlet pressure in an axial turbine? For example, when friction of boundary layer decrease or boundary layer is not captured well, how to change values of inlet and outlet pressure in a turbine?


texts: Why do we use the strain-controlled test for the compressive strength of concrete?

texts:
As you all now, a typical stress-strain curve for concrete under compression can be seen in any reinforced concrete design textbook. The decreasing part of the curve (post-peak) can be obtained by testing the specimen with displacement controlled test machines.

My question is why do we prefer the strain controlled compression test instead of the stress controlled test?

We use the stress-strain curve to calculate ultimate strength capacity of the section. The reinforced concrete member which is designed according to the stress-strain curve is subjected to load such as dead loads, earthquake loads etc during its lifetime. I think that the strain controlled tests are not appropriate to model dead loads because they are constant. The stress controlled stress strain curves might be more appropriate for the dead loads and earthquake.


texts: How to calculate stress in a cylindrical-uniaxial-loaded bar with sudden changes in its diameter

texts: How can I calculate the von Mises stress in the cross-section of a bar like this that is axially loaded?


texts: Calculating the temperature of the lagging around an insulated pipe

texts:
I am solving the following problem:

  A Pipe 200 mm outside diameter and 20 m length is covered with a layer
  of 70 mm thick insulation having thermal conductivity of 0.05 W/m·K
  and a thermal conductance of 10 W/m2·K at the outer surface. If the
  temperature of the pipe is 350 °C and the ambient temperature is 15
  °C, calculate the external surface temperature of the lagging.

I have calculated the thermal resistances as:

$${ R_{pipe} = \frac{1}{A \times h_o} = \frac{1}{ (\pi \times 200^2 \times (1/10^3)^2 \times ()} = 3.183098862  }$$

$${ R_{insulation} = \frac{1}{2\pi KL} = \frac{1}{ (2\pi \times 0.05 \times 20)}   = 0.04776312933 }$$

The heat transfer is supposed to be:

$${ Q = \frac{\triangle T}{ R_{total}} }$$

What does it mean by "temperature of the lagging"? The change in temperature from the outside and inside already given.


texts:
What type of bearing should I use to allow a ring to rotate around a fixed axle. Axle is horizontal.

The rings inner diameter can be flush with the stationary rod or have a gap as needed. What type of bearing (or other device) would I use to allow the ring to spin freely?

I know I can get a basic bearing and maybe solder the ring onto the bearing but I want something more professional and elegant. Does there exist a two piece bearing set that you insert from either side of the rings inner diameter and connects together, and then can be slid onto the axle?


texts: Tan Tan Radius in AutoCAD doesn't put circle on right side

texts:
I've been struggling to this for some time now and can't really find the answer on the web, but: sometimes when I want to set circle inside of an angle, it just throws it out on the wrong side. Like on the photo below: I wanted to insert circle between two lines and trim it (so it would look like red arc at the end), where I choose 2 lines (TTR command) where the green stars are, but the circle got dropped on the other side.

What's going wrong here, what's the matter?
I had my mouse (while entering radius) on the right side of the vertical line.


texts: How can I get a stepper motor to engage with a freely spinning wheel?

texts:
I'm working on a project that uses a strong stepper motor to power a wheel that needs to be able to "coast" freely at times. The motor is too stiff when not engaged, and along with my gearing ratio, makes it impossible to get the free-spinning coast** that I want from the wheel when the motor is not powered.  I only need the wheel to turn in a single direction, so I've been playing around with a design (see image) where the  motor slides just a bit to engage via a small set of gear tracks to pull itself into the other gear.   I was thinking that I would simply just reverse direction when I wanted to pull the motor away to enable free-spinning. Unfortunately, it doesn't work so well. The gear does engage, but the little bit of play it has when it slides causes it to make contact with the very last tooth of the tracks at the same time. This causes it to make a grinding noise, and certainly isn't efficient.

Does anyone know how I could get this to do what I want? I've been searching online, but haven't found anything and I am not sure of how to technically describe what I'm trying to do in a few search terms.  So, I'd be grateful for any links to similar designs as well.

** Sorry, I forgot to add an important detail that will explain why I need to find a way to disengage the motor... The motor will turn the wheel forward, but when disengaged, the wheel needs to be able to turn freely in either direction.

So, it's two days later, and this is what I'm going to try next:

It consists of:

A drive gear (in red) that turns counterclockwise, with a one-way clutch bearing mounted to it. The clutch bearing turns freely clockwise.

There is an arm with an intermediate gear that will make contact with the large gear when engaged.

There is a spring attached to the arm. The spring pulls the arm down, to engage the gear. The important thing is that the spring is NOT strong enough to overcome the resistance of the idle stepper motor. So the  arm will not move unless assisted by the stepper motor.

So here's how I hope this will work, assuming we start with it not engaged:

The stepper motor turns on, counterclockwise. The movement, in addition to the spring, engages the intermediate gear. The clutch bearing prevents the arm from dis-engaging the intermediate gear, yet allows the stepper motor to turn the gears freely.

To disengage, we simply reverse direction of the stepper motor just a few degrees. The clutch bearing will lock, pulling the arm away.

I have yet to prototype this, as my 3D printer is down for a few days. But I would be interested in feedback and whether anyone thinks this will work.


texts: Is there anything in BS 8888 regarding the scale of a section view?

texts:
If a section view isn't sufficient enough to show all details required, can it be at a larger scale than its parent view? Is there anything in BS 8888 regarding recommended scales in section views?
Thanks!


texts: Passive Infrared Sensors (PIR) spectrum and reflections

texts:
I have a common PIR occupancy sensor (Lutron MS-OPS5M-WH). I am trying to get the sensor to cover an irregular-shaped room.
I could expand the field-of-view of the sensor to cover the whole room by installing a mirror so that the PIR sensor could "see" around a small corner. However, I need to know what material to make the mirror out of. I think standard soda-lime glass would reflect long-wave infrared, whether or not it's silvered, but it depends on the spectrum of light that these PIR sensor use.
Is this concept of using a mirror surface to let a PIR sensor see around corners a valid idea? And if so, what material does the mirror need to be made of?


texts:
When creating a detention pond I have only came across examples where the pond is created by digging. Is it possible that a pond is created by creating retaining walls / embankments? and if it is can you please provide examples.

Please note! this is a detention pond not decorative pond.


texts: Are "interference fit" equations appropriate for calculating barrel stress?

texts:
I am curious about calculating stress at various points along a barrel as a bullet is being fired through it. The interference fit (press/friction fit) equations immediately come to mind, but I am wondering if these equations are appropriate to use because of:

(i) The non-linear pressure curve of the gas behind a fired bullet

(ii) The bullet is moving through the barrel (dynamic system)

Here is a link to some interfernce fit equations I'm refering to,
http://www.engineersedge.com/calculators/machine-design/press-fit/press-fit-equations.htm

Any pointers?


texts: Pully size, imagine 2 systems A,B both transmitting power, both 1:1 but if OD of pulley is 50mm on A and 100mm on B, How do we choose optimal size?

texts: All searches resulted in ratio calculations, which makes sense, my question relates to creating a servo driven spindle with 1:1 ratio with timing belt. Is increased belt surface engagement important since its a toothed belt? Also system A and B are examples only.


texts:
What is meant by thermodynamic efficiency of an engine?
and what are the factors that affect the thermodynamic efficiency of a diesel engine?


texts: Why does a lead-compensator type system decrease to a step response

texts:
For example, the step response of $\frac{s+1}{s+2}$ is decreasing although its gain is +1, and this system has higher gain at high frequencies than low frequencies based on its Bode plot. But if I make the transfer function strictly proper, no matter how transient the pole I added is, such as $\frac{s+1}{(s+2)(s+1000000000000)}$, the system tends to respond "nicely" like those responses shown in textbooks and professor's examples.

Mathematically, $\frac{s+1}{s+2}=1-\frac{1}{s+2}$, so its response  to a step input is an exponential decay, is there a more physical/intuitive way to explain this?
Why systems with higher gain at high frequencies have decreasing response to step inputs?
Is there a reason that we prefer increasing(nice) step response (or do we prefer it at all)?

By nice, I mean something like this

By not nice, I mean something like this


texts: What's the concrete core for in a building?

texts:
I'm watching the progress of a new office building being built over the road (essentially a manual timelapse).

The way the building progressed was by the pouring of a concrete core in the centre of the building to the full height (~8 storeys), before a steel beam frame was constructed around it to the full width/length of the building, obviously making a frame for the outer walls and floors.

Although the core is substantial (not just a pillar or something), it wouldn't seem to have any structural effect on the outer parts of the floors of the building (near the outer walls).

My lay-person's guess on the purpose of the core is as a kind of protected fire space (dry-risers? wet-risers?) containing the stairs and lifts/elevators, but if I knew the answer I wouldn't be asking here.


texts: Equilibrium of forces in 2d plane, find angle alpha and w

texts:
If the force in member OA is 0.25F and inclined at $\alpha$ degree from the horizontal. Calculate the angle $\beta$ to keep the system in equilibrium and calculate the angle $\omega$. $\alpha$ = 20°. F = 100 N.

Attempt:

By alternate interior angles:

$\beta - \alpha$ is the angle between OB line and horizontal axis x.

Sum of forces in X direction should be equal to 0:

$$\sum F_{x} = -0.25F \cdot \cos(\alpha) -F_{OB} \cdot \cos(\beta - \alpha) + 100N$$

$$\sum F_{y} = 0.25F \cdot \sin(\alpha) - F_{OB} \cdot \sin(\beta - \alpha)= 0 $$

is this correct? I'm not sure what $F_{OB}$, it's not given. So I have two equations, and two unknowns: $F_{OB}$ and $\beta$. I tried to solve via wolframalpha but it didn't find any solutions. What do?


texts: Easily compute a good approximation of heat conductivity of cooled semi-vacuum (water vapor + air)

texts:
I am preparing a classroom demonstration about heat, including a demo of how a satellite loses heat only radiatively, since it's flying through a vacuum. I'd like to make the vacuum-production apparatus very simple and cheap.

The kind of pump used to semi-evacuate wine bottles to help preserve the flavor (supposedly) is the right kind of item in terms of cost (as cheap as $6); a slight modification of one of these improved the seal on its plunger dramatically, though I still doubt the pressure in the vacuum chamber gets much below 1/4th bar.

To enhance the vacuum, I'm venting steam from a kettle into the vacuum chamber (a cheap plastic jar with the wine-pump check valve attached through a hole in the lid), screwing the lid back on, pumping out as much of the hot water vapor as possible, then cooling the jar in the freezer.

I'm wondering if this really reduces the heat conductivity of the remaining gases (mainly, water vapor) very significantly. Reducing the density of a gas doesn't really reduce the heat conductivity very dramatically, and without such a reduction, the point of the exercise (simulating vacuum) is lost. I can measure the temperature easily enough, and I will get a vacuum gauge to measure the pressure, but it would be good to work from an approximate formula based on those two measures to determine the heat conductivity. I assume there will be little but water vapor in the jar when I put on the lid. I can find tables for water vapor heat conductivity above freezing, but at the temperatures and pressures where H2O only sublimates, I've found nothing so far.

What's a good approximate formula to use? Bear in mind that I'd also like to use not only regular water ice but also dry ice (packed around the jar) as the background for the satellite-simulating heat sensor to radiate against, so it would be best if the formula is a good approximation at dry-ice temperatures too. (Cosmic background is obviously not achievable cheaply, but the effect of even greater radiative cooling can reasonably be extrapolated from various other cooling approaches, such as burying the jar with water ice and dry ice.)


texts: Why is the Stress vs strain diagram preferable to the Load vs displacement diagram?

texts:
I’m really unsure what is the difference between stress vs. strain and load vs displacement graphs and why stress-strain is better.
I know that the units are different:

stress is in MPa and the load is Force N
and strain is no units and displacement/extension is units of length mm.

Can someone please me understand the differences and explain which one is better?


texts: What exactly is Hooke's law defined for?

texts:
I used to think that Hooke's law was a relationship between how much a bar under uniaxial loading deformed and the internal force (per unit area) that developed within that bar. But this clearly isn't the case as I have recently seen that Hooke's law is used in analyzing the stress in pure bending of beams. So it seems that Hooke's law is a lot more general than I had thought.
If Hooke's law isn't specifically defined for a bar under uniaxial loading, what physical object is it exactly defined for? What system/object is Hooke's law trying to describe?
My guess is that Hooke's law is defined for an infinitesimal cubic element which feels a normal stress on its sides from neighboring elements (picture below). That is, Hooke's law relates the normal stress and normal strain on an infinitesimal cubic element. This might make Hooke's law general enough so that it could be applied to many loading situations since we can think of any object as being made of many of these infinitesimal elements and the total strain of the object is the sum of the strains of all of the elements. Is this correct? I'd appreciate it if someone could clear this up for me.


texts: Can a electromagnet find a tube underground?

texts:
I was seeing how an electromagnet could attract a car when it's destroyed, and I was wondering, because I have to find the water tubes in my house (20/40 cm depeer), if I can put a wire inside the tubes and move the magnet until I find the force of the attraction of the two elements.
Unknown evaluation: any electromagnet/wire is good enough?

Expected result: the electromagnet will stick to the wire path.


texts: What diameter of particles will result in a blocked borehole?

texts:
My mine is looking to install a 600 mm open borehole to drop particles up to 150 mm through.  It's a 320m shaft to drop ballast down to save time compared to using the drift.

When it gets blocked they typically take a water truck out and that works.  They have used explosives to clear a blockage before but that was a decade ago.

Some of the seniors have rough rule of thumbs on the borehole diameter required to drop particles without causing a blockage but I'm unable to find any references. And it is based on experience and what they've always done. I'm unaware of any design work for this beyond "this should be large enough", but believe there should be more behind it than that.

Is there a formula available to determine the borehole diameter required to safety drop in the particles?


texts: Clothoid Curve / Euler Spiral Energy Transfer

texts:
I've seen in an advertisement that Clothoid curves–also known as Euler Spirals–"transfer maximum energy" to a ball bearing that is rolled down it. Firstly, I was wondering if that might be true based on the information I've provided; second, if it is true, what is the intuition / mathematics behind it?
Thanks for your help!


texts: What optics and display are used in Microsoft HoloLens?

texts:
How does Microsoft project an image so close to the eye yet understandable by the brain?

How is the display transparent?

This link has good information but is speculative.
https://www.reddit.com/r/HoloLens/comments/2v0nac/hololens_display_tech_and_what_to_expect_from_it/

What materials are used?

For a list of patents see this: http://vrwiki.wikispaces.com/Microsoft+HoloLens


texts: What method should i use in order to remove moisture from air of a container completely? Should i flush it with N2 or argon (its air-tight) or is there a device that i could use to remove moisture from the container? The container is prone to condensation due to extremely low temperatures. I need that water out :D


texts: How can I measure the impact of noise on a FFT?

texts:
Please, I have to solve a problem and I really need some help.

I have to give an efficient method to consider a maximum amplitude as a starting point to consider as noise the whole spectrum below itself. Like on the example of the FFT below. Let's consider only on X axis, the red plot, the maxium peak is at a magnitude of 0.4, between 7 and 8 Hz. The next peak is at a magnitude of ~0.3, and the next after that is at ~0.25, and so on (in a decreasing order).

How can I give a consistent method to find the threshold between noise and real signal in terms of magnitude.

The perfect answer would be transforming it in a closed-loop control where I could go adding transfer functions with natural frequencies corresponding to those peaks until the response are no longer affected (for a unitary step). But for that, I would have to tell the system what is the magnitude of each peak. That's where I lose myself...

Thank you very much in advance.


texts: What impact does reduction internal stress cause?

texts: I have noted that recovery primarily reduces the internal stresses of the material.What is particularly confusing is why would that work out.A slightly detailed answer to this is most recommended.Also I have seen somewhere people are referring this to as a phenomenon related with dislocation density.How are dislocation density and internal stresses related with each other


texts: How to derive fixed-end moment of a beam?

texts: Here is my attempt but I am not getting the right answer. Can someone tell me what I am doing wrong?


texts: How can I create uniform laminar flow in a short duct?

texts:
I have a small vessel with a rectangular cross-section which needs to be ventilated at a relatively slow rate, ~$3\ \tfrac{\text{L}}{\text{hr}}$.  The connections to the vessel will be tubes with an approximately 0.5" diameter, but the cross-section of the vessel is 4" x 1".  The diagram below gives a rough idea of the cross-section (viewed from above) with the height of the chamber being about 1".  The part circled in orange is the topic of this question. The flow will be forced in from the left and will exit passively from the right (or vice versa).

How can I couple the 0.5" tube to the chamber such that the flow in the chamber is uniform across the entire cross-section for the entire length of the duct?  In addition, how can I couple the two in the smallest amount of space possible?


texts: Does the turbo-compressor increase the efficiency of car engine?

texts:
Once the turbo is on, more air can participate to the combustion, which also requires more fuel. Then, it's clear that the turbo can give more power (at the price of more consumption).

Question 1: Can this be used as well to improves economy ? (i.e. less fuel for same  RPM than without turbo)

Question 2:  How does the gain behave with RPM, passed the initial threshold ? Does it make the total efficiency curve of the engine more flat, or less flat ?


texts: Difference between maximum shear stress and absolute shear stress

texts: What is the difference between maximum and absolute shear stress in multi axial stress system?


texts: What is the best way to build this parametrically in solidworks?

texts:
I want to make a structure like the following

where:

L is the total length and its fixed
$\lambda$ is the distance between each arc
n: is the number of repeated structures in the center

I have tried several ways to do that. The best two so far are both using a sweep along a line. One is using a Equation driven line and the other one is using arcs and a linear pattern, however in both cases I am missing something.
In general my specs are -ideally- the following. I want to :

manage all parameters as global variables from the "Manage Equations"
center the non straight structure
define different $\lambda$, $n$
have a fixed length L
(if at all possible) not be limited to arcs but also more generic shapes, eg. triangles or squares.


texts: Difference Between minimum steel required in Slabs and Shear Walls

texts:
My question is very simple, I need to know why the minimum reinforcement for slabs is less than the minimum reinforcement required in Shear walls?

What are the criteria and reasons to set minimum steel reinforcement in the two structural elements. (if a code reference is needed plz refer to ACI and EC)


texts: How much torque will I need to pull a 2250Kg load?

texts: I need to use this to find a motor that will be able to pull at most 2250 kg at a 1.5 m/s pace. At peak acceleration, I would like this to accelerate at 0.5 m/s2. The area that the load will be pulled is a concrete sidewalk with, at its most extreme, a 20° incline.


texts: What do these sigma subscripts represent?

texts:
Axial strength for balsa wood at different densities

What I don't understand are the subscripts under the sigmas (strenghths.)
How do I know where the compression (crushing) and tensile strengths are? I'd like to know what represents what. Thank you!


texts: Basic difference between "compress" and "pressurise"

texts:
We call air which is pressurised as "compressed air". But we don't call pressurised liquid as compressed. I know that liquids are incompressible.

So,

why particular word "compressed" is the created, we could call pressurised air instead of compressed air?
Is there any significant difference between them (aside from the words), if yes then explain?


texts: RHS column profile able to replace 3m UC 152x23 column?

texts:
I'm having some work done in the UK (Eurocode) which involves a steel column to support a beam at 1st floor (US: 2nd floor?) level. The column bears a very-close-to-vertical total load of 47.3kN  (including any relevant safety factors I guess, as that's the final figure in his calcs).

The engineer has specified a 152x152 23kg UC to be used for the column, with suitable end+base plates and fixings.

My issue is that the engineer has offered a low rate as its for a "charity job" (house belongs to an elderly frail relative). I've gone back to him with a set of 3 queries and got replies that are professional but curt and I don't want to go back again to ask if anything else is possible, unless I'm already privately very sure it is and can back it with calcs, as I don't want to lose his goodwill.

The only time he's said yes to any change, was when I also attached calcs to justify why I thought it should be OK. Unhelpful and not my job, I know!

In this case, I really need a slimmer column, to run flush with the 100mm partition wall.  Unfortunately I don't understand column slenderness calculations well enough to check if there's scope to replace the 3m 152x152 23kg UC by, say, a 100x100x10 25kg RHS, or even a 100x180x5 21kg RHS.  My tentative figures suggest that because of the RHS vs UC profile, both of these would be stiffer in any direction, than the UC and they'd fit nicely flush to the wall, so maybe they'd work.

I don't need an absolute calculation ("Does this profile work for that length and load"), but only a relative one ("Would this profile be at least as satisfactory as the one he's already said is good enough")?

What calculations are needed, to confirm if a more slender (in one dimension at least!) RHS profile would be at least as satisfactory/rigid in performance as a column, compared to the currently-proposed UC?


texts: Buying Liquid Oxygen in Small Quantities

texts: I am trying to work out costs and order parts for a small liquid fuelled rocket I have designed. My oxidiser is liquid oxygen but I can’t seem to find anywhere to purchase it on the internet. Does anyone know where to buy liquid oxygen?


texts: Do variables dimensions matter in PID simulation + I want the PID output to be volts?

texts:
I have a self balancing robot control loop that uses the PID controller. I feed the robot's angle (rad) to sum block that generates the error between the set point and the angle.

The error then goes to the PID and goes to DC motor block that needs the input to be in volts and generate an output in N.m.  Then the signal goes to the self balancing robot block that need the input to be in N.m and outputs a rad angle.

As you see I don't know how to make the PID output a voltage (V). How i can do that?


texts: How to remove a 'mesh edit' item in ANSYS Workbench?

texts: I accidentally inserted a mesh edit item and tried moving a node, but now can't remove it. The context menu doesn't have any helpful options and I don't see any relating tools in toolbars. How to remove it?


texts: What makes a pulley that is rated for horizontal pulling different from a pulley rated for lifting?

texts:
I have a home project that involves lifting a platform with a cable that runs through a series of pulleys to redirect the cable.
I'm selecting pulleys for the job and I see that some pulleys are rated for horizontal pulling while others are rated for lifting. This would make sense to me if they were fixed pulleys since it might imply the direction of force that the pulleys are suitable for, but that doesn't seem to be the case since I see free hanging pulleys that are marketed for horizontal pulling and lifting separately.
E.g.

For Vertical Pulling (https://www.mcmaster.com/3099T14)
For Horizontal pulling (https://www.mcmaster.com/3170T27)
Full catalog with more examples (https://www.mcmaster.com/catalog/126/1614)

What makes a pulley appropriate for horizontal pulling versus lifting?


texts: How to estimate the physical parameters of 40% Cu + 60% Mo alloy?

texts:
I need to know, or estimate the physical characteristics of the alloy which consists 40% copper and 60% molybdenum. I know only:

Density: $9.62 \frac{g}{cm^3}$
Thermal conductivity: $223 \frac{W}{m·K}$
Coefficient of thermal expansion $9.3 \cdot 10^{-6} \frac{1}{°C}$

How to calculate, or at least, estimate its boiling point, clectrical resistivity, Young's modulus, and Vickers hardness? Also partial answers are okay.


texts: How to measure water output over time - any better solutions than tipping bucket gauge?

texts:
I'm trying to figure out how to get an automated measurement of a trickle of water over time. (Application is measuring the water output by a dehumidifier; overall output would be a few pints of water per hour.)
Most automated tools for measuring water quantities are for full pipes and/or MUCH higher flow rates. For this type of super-low flow, it looks to my eyes like a tipping bucket sensor would be suited to the job. But the tipping bucket sensor isn't quite ideal for my needs. Specifically, the tipping bucket just dumps out the water after the measurement. I can't just allow the exiting water to dump anywhere because that would encourage mold, so that means I'd need to enclose the tipping bucket in a canister which routes the post-measurement water to a drain.
Currently this dehumidifier output is routed through a nice 1/2" PVC pipe to get the condensate to its proper drain. So, hook up a big canister, which has a tipping bucket inside of it, then routes the spilled water to an internal drain and back to the 1/2" PVC seems like a really clumsy solution. Is there a more elegant way to make this measurement in an automated fashion?

EDIT A few other requirements I should have thought to state up front:

Reasonable cost (willing to spend up to USD$100 or so on this)
Was hoping to find a prefabricated solution (for example something like a "picohydrometer"... but that's just a word I made up) rather than inventing something, if at all possible. But that's looking doubtful.


texts:
None of my fellow commuters know what this white panel with, what appears to be a red slider attached, is called and what it is for.

This particular one is on a platform edge which happens to be over a bridge (Maidenhead in Berkshire).

Does anyone know? The track is a straight section at this point. So I don't think it's any indication of cant.


texts: Do submersible water pumps need to be submersed in water to function properly?

texts:
I'm looking to build myself a cheap water fountain that filters out gunk for my cat. Here is how it will work (I think)...

Anyway just wondering if the pump has to be submerged in water in order for it work properly. I was hoping not because the bowl is fairly small and doesn't need to be huge.

So do submersible water pumps need to be submersed in water to function properly?


texts:
My North American facility is looking at a major shut down this fall.  In the area, three other large facilities are also doing either shutdowns or expansions in the fall.

A last minute project that I have been assigned requires a couple of weeks of machining custom components.  This is an issue as none of the local machine shops are likely to be able to fit the work within their schedule in the required time frame.

At this point I think my only option is to start looking beyond the local shops.  What should one look for when trying to source non-local machining?  Are there any red flags to look for when talking to a shop?


texts: How to query stress and strain values in a specific element in Abaqus?

texts:
I am trying to find easier way to get stress and strain values in a specific element in Abaqus.
Does anyone know how to do it? Is it possible to do with Query?

Thanks


texts:
this is a steel frame , top beams sitting on top of column with steel plate cantilever at both sides (one side longer than the other) , so there will be hogging moment at the center support. However, the top steel beam is one whole piece, does the connection between the steel beam and column need to take the moment ? Or the hogging moment will be taken by the steel beam itself ? Connection need not design to take the moment ??
If the connection need to take moment , then which moment value shall I use to design the connection between the steel plate and the steel beam ?


texts: Cost Value of Changing appliances that run on 240 down to 120

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I have lived overseas for many years and purchased your standard appliances.  Anyway moving back to the US, I had to purchase transformers to bring the voltage down from 240V to 120V.  I know that there also issues with cycles (50cycles verse 60) but that not an issue yet.

So my question is I am trying to figure out the electrical cost of running these appliances so I can make a decision of when the return on investment is right to replace these appliances with ones that run off 120V.

i.e. I have a 3000W transformer that runs an appliance - which uses 900W for two heaters and 600W for a pump.  I am paying about \$0.06 per kW-hour.  A new appliance is about \$325.

I have about 6 240V various appliances so it could drop my electrical bill.

thanks


texts: What is the fouling effect (in rate, foulant thickness) of sand inside tube side of a shell and tube heat exchanger?

texts:
I am working with RO reject which has high turbidity (mainly insoluble salts and also sand now). This is also my process stream and needs to go through a heat exchanger at 50-60C and flowing at 0.25m/s. Can I find a model to predict fouling rate at the current state (temp, TSS, Re etc.). Also I understand that chemical fouling arises because of the salts in the solution is this true? As you can see I am trying to make a comparison between particulate fouling and chemical fouling. So any inputs on foulant thickness and fouling rate or even direction of research will be helpfull.
PS the sand has to be eliminated


texts: how derivative gain in PD controller influences tracking error

texts:
List item

For a proportional and derivative feedback control, the the response and tracking error in frequency domain can be represented as
$Y(s)=\frac{KG+K_dSG}{1+KG+K_dSG}S_p \\
e(s)=\frac{1}{1+KG+K_dSG}S_p$
where $K$, $K_d$ are propotional gain and derivative gain. $S$ is Lpalce variable. $S_p$ represents set point. $G$ is the plant. What I am interested in is the error behavior in time domain with respect to derivative gain $K_d$. Firstly for simplicity I assume my plant is perfect: $G=1$, so that
$e(s)=\frac{1}{1+K+K_dS}S_p$
By sinusoidal and periodic $Sp$, the error in time domain at steady status seems to be
$e(t)=A\vert|\frac{1}{1+K+K_dwj} \vert|\sin{\left(wt+\angle\frac{1}{1+K+K_dwj} \right)}$
where $A$ and $w$ are amplitude and frequency of the set point. In this expression both $K$ and $K_d$ have clear influence on the magnitude of the error. However when I tried simulation(on Simulink), the error influenced by $K_d$ barely nothing. I would expect the error behavior in time approaches to zero as $K_d$ increases or goes to $\infty$ per the exression of $e(t)$. However it is not. Is there any misktake in my derivation for $e(t)$?


texts: Regarding design of a compressed air delivery system based on a screw air compressor

texts:
I want to select a screw compressor for my application wherein I need a pressure of about 18 psig, and 300 cfm at the aforementioned pressure. The compressors I'm finding suitable for the system have their pressure ranges listed in the catalogues starting at 116 psi. So, I'd need to design a system (duct with changing area) to decrease the pressure first. What's confusing me is that the catalogues specify the flow rate as Free Air Delivery, whereas, in my system, since I have a duct, it would incorporate an impediment, and thus change the flow rate of the compressor. Also, the change in pressure through the ducting (due to changing area) is going to alter the flow rate due to density changes as well, I suppose.

My question is this:

How do I find out which compressor would fulfill my volume flow rate requirements based on Free Air Delivery as the only volume flow rate given in the catalogue?
What would be the best system to change the pressure of the compressor (116 psi) to the required pressure (18 psig). How can I control the pressure while achieving the required flow rate in the system. (Is the varying cross sectional duct with pressure regulation valves the best option)?


texts: What is the purpose of the ink delivery disks found in most rollerball pens

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See picture.
In most rollerball pens there are those peculiar looking disks near the nib, the purpose of which I have not yet figured out, apart from being some kind of ink reservoir/flow control.

Non-uniform separation between the disks:
The further away from the tip, the smaller the separation. My guess would be that towards the top end of the "plates column"/bottom of the cartridge where the ink pressure is the highest, the liquid ink has more tendency to gush out, the denser plates serve as an "impedance" to avoid this from happening, and that a smaller "impedance" is required in the lower end to help the ink flowing when exiting the column

Flat edges:
Not all disks are circular with some that have asymmetrical flat edges on them, I'm not sure why this is apart from preventing the ink from jamming on the top?....
My reasoning seems very inadequate so I'd like some explanation as to why having such a specific design?

Two flat disks, which clearly serve a purpose. Also, notice that there are rings of ink being formed around the disks.

See Pilot V5/V7, Uniball Rollerpens, Sakura etc for reference, this is a common feature found in a lot of Japanese pens.

Please reconsider before closing my question. I admit that there may not be any truly essential physical principles attached to it, but I believe it's worth thinking about, given that the design has been used so widely. (Plus, this is going to be part of my undergrad summer project(!)). There is already a paper devoted to the study of rollerball pens, but not so much on the disks system. https://www.researchgate.net/publication/265598521_Modeling_and_Simulation_of_a_Rollerball_Microfluidic_Device


texts:
I want to feed USB data through a glovebox, using binding posts seen in the first picture. My thinking was that, in theory, the USB cord is just made of four wires (one for power, 1 ground, two for data). I tried cutting the cable, and soldering the four wires to banana plugs as seen in the first picture. These plugs can be plugged into the binding posts to make contact with the other side of the post and connect to the usb.

So, when I plug my cable into my computer, it gives me USB malfunction. Although this may be a stupid question, what is potentially the issue causing this malfunction?

Other than my lack of knowledge about how a USB actually works, two obvious issues include using different banana plugs on each wire, and horrendous soldering skills.

I realize that this isnt the best picture. When I plug this cord in, I have used electrical tape to isolate the wires from one another.


texts: Why large industrial units combine induction and synchronous motors?

texts:
We usually use induction motors to turn electrical energy to mechanical, however synchronous motors are the machines on the other side of the grid (generation).

A week ago we had a student visit to the hydroelectric and ... centrals and afterward we paid a visit to a steel company. I noticed that they use the combination of the synchronous and induction motors to do the exact same job, so the output power of the motors were exactly the same so the task and the hours of operation.

Why just not using induction motors ?


texts: I'm studying the Hilbert transform and its properties. I found out that Hilbert transform can be considered as a linear time-invariant system. How can I show this?  I guess this should be trivial as my book does not show it.


texts:
I have this water rower (Sunny Health & Fitness Water Rowing Machine w/LCD Monitor) :

I am going to make a monitor for it (to calculate time/500m and watts). I am going to attach a magnet to the tip of one of the blades and a sensor on the inside of the tank. I was wondering what the physic equations to calculate the minutes/500m were. Please ask any clarifying questions.

Further information :

The monitor provided with the machine is very inaccurate and cheap.

The handle is attached to a fabric cord. The cord goes into the machine and goes around a pulley (it is now parallel with the cord coming from the handle). It then goes around a circle and is wrapped around many times. When the handle is pulled, the circle moves, which it attached to a shaft.

Also attached to that pole/shaft is the fan. The fan has three blades at the end of three poles. The blades are a couple inches wide and are about 1/4 in water. There is also a bungie cord wrapped around the pole to bring the handle back. I don't think that the bungie cord changes the equation.

Here are some images:

Note : there are several images of better quality on the Amazon website linked in the 1st paragraph.


texts: Help with linear rod drill press like design/materials

texts:
I am putting together a basic machine for “pad printing” extremely small and precise parts. The design is very much the same as most homemade drill presses and consists of linear rods, flanged bearings and compression springs, but in place of a drill bit is a 30mm conical silicone rubber pad/stamp. The object being stamped will be positioned underneath on a precision XYR stage. A basic hand lever will be used to press the the rails/block downwards, applying minimal pressure. Scale will be approximately 10-15” tall. The blocks will be made of aluminium at this point and will be mounted to a very large solid base. Screws will he used to fix each component together. My goal, once set up, is for the pad to land in the exact same spot every time and with absolutely no movement or variation. It needs to be very rigid and with no slop.

I would like to know what diameter linear rods I should use, and if it makes much difference. I was originally looking at 40mm but this seems large?

Should I use standard steel rods? I have also considered introducing a ball spline shaft to prevent rotation.

I am not sure what size or type screws would be best suited for holding this thing together.

Are there any other factors I am overlooking that will help out?

I have come up with a few different layouts and I may be overthinking it. Do any of them make a difference to the overall result and accuracy of the press? Is there any particular direction I should be taking?

Thank you


texts: How to calculate flow rate of pump and velocity if only given length of pipe and volume of tanks?


texts:
Some background: I am working for an ed-tech startup and we are hoping to release our first product soon but have been hitting a lot of hurdles with our current manufacturing strategy. We want to produce 100-200 products to test our market before taking on more risk and going into injection molding, but we are running challenges with finding an economical method for producing the first 200 parts.
Every machining shop that we have visited have given us a quote of 25+ dollars for each set of pieces. It's hard to justify making that investment since there is a possibility that we would want to adapt our design to better fit market needs as we bring it out.
The solution that we have thought of has been to invest in a DIY machining kit to try and produce our product to meet demand and possible iterate on our product. Images on the parts that we want to create are listed below:

If anyone has shared a similar experience and has a background in manufacturing/machining and can answer the following questions it would be very appreciated:
What is the best material that we should use for these pieces?
Criteria: We are mainly looking for a material that won't crack under a lot of pressure and feels and looks nice. Options from manufacturers we have spoken with: Delrin, Aluminum, High Density Polyetheline, plywood.
Some challenges that we have been facing have been to find an affordable way of finding the actual material. Most machining places say that the material would cost 1$ a set. However, online, it is super expensive for a pretty small sheet: https://www.interstateplastics.com/Delrin-Plastic-Black-Sheet-ACEBE5~SH.php?thickness=0.250&dim2=12&dim3=12&src=adwordspla&thisisforcallrail=1&campaignid=225228743&adgroupid=37851262274&creative=153445283219&matchtype=&network=g&device=c&keyword=sheets-ACEBE5SH-0.25-12.00-12.00&gclid=CjwKCAiA4o79BRBvEiwAjteoYFOOMRTpCPiFcAvXJTgjU4Hdt35RKLWdvqlCamLzXVEZEi2BTNjJzhoCWBAQAvD_BwE&
Followup: Where would be a good source to find a cheap material to work with?
Are there any recommendations for DIY machine kits and what is the price range that we should spend for a machine?
Criteria: Our quoted price for 100 product is 4,000 dollars and budget for the machining kit is Ideally less than 1,000 dollars. Would it be possible to work with plastics or aluminum with a kit in this price range and still maintain good quality products?
How hard is it to learn how to machine for these products?
Context: I know that the process involves actually coding the trajectory and path that the mill is going to take to produce the product. How difficult is it to learn the necessary coding for path planning and how hard is it to learn how to choose the right drill bit for each task? Would we, as beginners, be able to create each piece with either aluminum or plastics and make it good quality?
Is there another manufacturing service that would be ideal for what we trying to accomplish? We have also investigated laser cutting and water jetting. However, It would be impossible to buy any of these machines.
Thank you so much,
Ryan


texts: Determining the first moment of area (Q) when calculating the shear flow of a built up member

texts:
Consider the two scenarios in this picture:

On the left, calculating Q=A'y[bar]' is easy. A is the area of the top board since the cross sectional area of that board corresponds to the area on the opposite side of the shear plane to the centroid of the member.

I am confused about how to choose Q on the right hand side scenario. The two shear planes are perpendicular to the plane that separates A' from the rest of the member, meaning the definition I used for the first case on the left simply doesn't apply. Based on other sources I have consulted, the area I should choose is the area of the board in the center of the two upright members. I have no good justification for this choice.

Edit: More information: Before I was introduced to the concept of shear flow, I was taught how to make shear stress calculations at any given height above or below the centroid of a beam cross section. To calculate this shear stress, a first moment of area (Q) needed to be calculated. This Q value was explained to me to be the area of the cross section of the beam on the opposite side of the desired horizontal shear plane.

Take the example above. In that diagram, the shear plane is a plane running along the longitudinal axis of the beam at a height $y$ above the neutral axis. The $Q$ value = [Area of the hatched region (which is all of the area on the opposite side of the shear plane from the neutral axis)]$\times$[$\bar{y}'$(height of the centroid of this area above the neutral axis)].

That is how I understand Q. Now let's apply this understanding of Q to figure b in the first picture. The two shear planes are vertical planes that run along the longitudinal axis of the beam. Thus, a horizontal plane cannot be defined co-planer to the 2 vertical shear planes to denote that I want to calculate the shear flow along this horizontal plane. In short, my definition of Q has broken down spectacularly. How is Q defined for case (b)?


texts:
Here are screenshots of the data-sheets of two separate products for a reference. They both are nickel plated, used for coupling nuts. The former is shielded, the latter is not, I wonder if this is the main reason to chose one over the other.
GD-Zn coupling nut:

CuZn coupling nut:

I believe GD stands for Gadolinium (Gd), but I might be wrong. I could not find much on the internet, apart from the following:

Alloying Gd with Zn significantly reduces melting temperature of the alloys (the eutectic alloy melts at ∼860°C) compared to that of pure Gd (1313°C) and also improves the ductility over the GdZn intermetallide.

This information however is about comparing Gadolinium Zinc alloy with pure Gadolinium, not pure Zinc. It hints us about the manufacturing process of such an alloy, and I suspect it has more to do with itch electro-magnetic properties, which are unclear to me.
What is the purpose of GD-Zn alloy? What advantages they provide over CuZn (Brass) alloy?


texts: Using a Copper Waterblock or Aluminum Heatsink to Cool Water via Thermo Electric Cooler

texts:
I am attempting to create a ThermoElectric Cooler to Chill Water. I have thought of two options as to how I can cool the water:

Some limitations of the design:

The water is still, not moving. No "PVC water pipes" can be used.

1) Running the still water through a copper water block, as shown below.

I would have the Peltier cool the waterblock, which would then take water from the top and cool. Nothing would be pumped in, water would freely exit and enter the holes from the top and exit without any assistance. (design limitations).

2) Having the water touch an aluminum heatsink

I would have the Petier cool the aluminum heatsink and simply have the water run through the grills of the cooled heatsink .

Question:

Given the above designs, which would be more efficient at cooling water? Having water seep into the waterblock, or have water run along the grills of the aluminum heatsink? This is given the water is still, no pipes to funnel in water to the waterblock just gravity.


texts: Electrical Resistance of molten aluminium oxide

texts:
I would like to calculate or find the electrical resistance (in ohms) of aluminium oxide at or past its melting point, for the purposes of using it as an electrolyte in a molten state.

My apologies for the broadness I just can't seem to find anything specific to this. Even if you don't have an answer due to the nature, any direction for a conclusion to this question would be greatly appreciated.


texts: What happens when the surface ends at the laminar zone of the boundary layer?

texts:
When a body travels through any fluid(like aircrafts and cars), due to viscosity of the fluid a boundary layer is formed around the surface of the body which separates the velocity of the fluid inside the boundary layer(near the surface of object) to velocity of the fluid.The boundary layer consists of three zones laminar, transient and turbulent zones respectively.

Is it compulsory for all the three zones to exist in a boundary layer? If we consider a small smooth surface, is it possible that the surface ends at the laminar zone of the boundary layer and there is no turbulent zone in boundary layer over the surface? And if it is possible will there be a low pressure zone at the end of the surface or something?


texts: In this problem(attached as a picture), the authors have chosen the horizontal element to calculate the shear and I understand the solution. But, the thing I don't understand is: Why  don't they take the vertical element (shaded by me, in the blue color) if we take the horizontal element we find a smaller value for shear, which is in our interest cause we are looking for the smallest shear.


texts: How do wastewater sludge degassing systems work?

texts:
There are high-rate anaerobic digestion systems where you remove substrate from the digester, let it settle in a tank, and pump back the settled sludge (possibly not all of it) to ensure a higher sludge retention time.

One problem with settling of sludge is that the forming of gas bubbles prevents settling. So before the settling tank, there's a degassing system. This is a basic PFD of such a process:

Image source

How do these degasifiers work? What are their operating principles?


texts: How to calculate force required to open a door on a horizontal hinge

texts: I have a door that will hang on a vertical hinge.  The door will be 20 feet wide and 10 feet tall, there will be one hinge at each end of the door and the hinges will be 11.75 inches from the top of the door, and will have an amount of counterweight above the hinge.  The counterweight will be a series of weights along the 20' width of the door.  The goal will be to open the door by creating torque at the hinge in the counterclockwise direction at either end, so I am trying to create an equation to determine the torque necessary so that I can play with the weight of the door (this is my first post, please let me know if there is any more information that you need):


texts:
this is my first project that i am working on. I want to make a IR sensor mount using stepper motors.

I seen this on youtube and would like to make a similar design.

I plan on using aluminium mounting hubs to transmit the torque from the shafts to the aluminium frame as shown above. My question is how is the torque transmitted from the motors to this camera mount? Is there a bearing and if so, what kind?


texts: System identification on a system with constraints

texts:
I am trying to estimate a transfer function for a pan - tilt unit which is not as easy as I hoped.

Its input parameter is a velocity, but it is constrained to move from 0°  - 359° and the other way around. Saying in another way, it is not capable of continuously pannning 360°. When it hits 359° it will not move in same direction, but has to move in the other direction. Pan can be moved with max velocity $\approx \frac{\pi}{2}$ rad/s and for the tilt is the max velocity $\approx$ 0.3 rad/s.

The same goes for the tilt, it is just limited to move within a more narrow field.  Both the pan and tilt part is driven by stepper motors.

What kind of test can be performed to identify the system? I know its position and the velocity it moves with at all time.  My idea was to change input direction when the position reaches a limit, but it would just mess up my sine sweep.

The system ID has to be used to apply a proper controller by using pole placement, and make the system act as i want it.  The system has to be able to track  a face.

The input to the system is a Pixel displacement which by using some simple math can be converted into angular displacements => the input is the angular displacement..  The PTU has to center itself such that the camera mounted at the top keeps the face at the center at all time.


texts: Given a material point that goes on a circular trajectory, of radius R, in the z=0 plane, write the intrinsic components for the velocity

texts:
So, I know it's a long shot but my Mechanics exam is coming up in less than a week and my course is really vague and poorly structured. Also, it has all these exercises with no example at all, so I'm kinda stuck.

Would anyone guide me through this problem please? The following ones are similar in structure, and I'm sure that if I understand this one, I'll be able to do the other ones alone.


texts: Could we use NE 555 Timer for industrial magnetic proximity switching circuit?

texts:
I actually need a magnetic proximity switching circuit such that
In the case of water in fuel sensor, whenever the water level in water in fuel sensor increases the magnetic float shall move and come in forward in the proximity of hall sensor which in turn switches the magnetic reed position and the output has to given to the ECU is this concept correct. Can we do this with a timer circuit? Will timer circuit do the purpose? Does timer circuit need any extra protection circuit when used in industrial applications?


texts: What is proper name of shaped shaft ends for ensuring their mutual position?

texts:
Maybe this is topic for English board, but it's terminus technicus

I'm seeking a name for the shape which secures two parts in a defined mutual position. The literal translation from my language is "lock".

For example: I want to make two shafts concentric, so I make ??? on their ends. On the first shaft, I reduce its outer diameter from 100 mm to 80 mm for last 10 mm of its length. On the second shaft, I made the negative shape. So these parts fit in.

What word can replace ???


texts:
im monitoring an overhung pump 19kw . and it shows a high peak at 7x rpm . on Thrust Vertical DE of pump.

what does it mean ?


texts: How to calculate the required torque for an azimuth/elevation antenna rotator?

texts:
I want to build an antenna rotator for a 1M dish. How do I calculate the required torque for the motor of the elevation axis?

Here's a sketch of the problem:

If the "bottom" of the dish is the pivot point, what would be the required torque to rotate the dish around this pivot point? Obviously the motor will have a series of reductions to reach the required torque and speed. The last stage a worm gear with a turn ratio enough to prevent rotation from the antenna weight when no power is being applied.


texts: I have a table flat surface made from aluminum, and the table legs are made from medium carbon steel. What are 3 welding processes that could be used to weld the legs to the flat surface.


texts: When can the effect of self-weight be neglected?

texts:
When studying the strength of materials at the introductory level, we often make five simplifying assumptions.

Material is homogeneous and isotropic.
Material obeys Hooke's law
Body is assumed to be prismatic
Effect of self-weight is neglected
Load is assumed as static load.

Under what circumstances is assumption 4 valid?  When can the effect of self-weight be neglected and when must it be included?


texts: Given a known relation between the saturation pressure and temperature of an unspecified metal, how can we determine the following properties?

texts:
This problem contains multiple parts, and I will write my initial attempts at solving the problem under it's corresponding section

If we're given that the vapor pressures (described in Atm) of both the liquid and solid phases are as follows:

ln(p_sat) = A - B/T + Dln(T)

We are also given a table of coefficients for the two cases of the Solid-Gas and the Liquid-Gas transition:

[Situation, A, B(K), D;

Solid-Gas, 19.25, 15773, -0.755;

Liquid-Gas, 21.79, 15246, -1.255]

(There are no units given, just those numbers)

And we are expected to determine:

a.) The normal boiling point

My initial thought was to work with the given equation and solve it for T, assuming p_sat to be 1atm (the normal boiling point) but ran into obvious algebraic difficulty in isolating T, and without introducing the Lambert W function (which I feel is beyond the scope of an introductory thermodynamics course) I'm not entirely sure what the best method to proceed is.

b.) The triple point temperature

In this case, my initial thought is to find the temperature at which the equation as written for both of the situations. That is, if there is no particular affinity for either the Solid-Gas or the Liquid-Gas transition it makes sense to me that the corresponding temperature would be the triple point.

c.) The difference between the heat capacities of the liquid and the solid

d.) The heat of fusion at the triple point

f.) The slope of the liquid-solid boundary line at the triple point given densities of liquid and solid phases to be 5.66 and 7.14g/cm^3 respectively and if the atomic weight of the metal is 65.4.

Any assistance would be very much appreciated. Even just pointers towards other equations I might be able to bring in.

Best,
-Richard


texts: Why are the support reactions of the two pin-connected members different?

texts:
Can someone please explain why the support at C does not have a vertical reaction force while the support at E has?
Doesn't the support at C have the same kind of pin connection as the support at E?


texts: Stepper motor - optimal voltage when using a chopper driver

texts:
When running stepper motors with a chopper driver, the motor voltage applied is much higher than what the motor is rated for, because the chopper is a current source.
The question however is, what voltage to use in order to get the maximum performance out of the motor (for example, to get the holding torque the motor claims to have)?

I came across the following formula in some forum (without explanation provided)

Vmax = SQRT(inductance) * 32

So that would mean that if I'm using some stepstick stepper drivers that support a maximum of 36V I should look for stepper motors with inductance below (36/32)^2=1.26mH, otherwise I won't be able to run them at their rated performance (of course they also should be rated for current less than the maximum RMS current of the stepper).

1. Is this correct?
2. Where does this formula come from? Why 32?


texts: Connector drawing - please help find C abbreviation/symbol meaning

texts: Please help me to identify what C5 stands for in this picture. Full drawing is available here.


texts: Are there impulse turbines operating on hot exhaust gas?

texts:
Are there impulse turbines that operate efficiently on hot exhaust gases rather than water as the working fluid?

Im thinking about something analogous to a water wheel, since it seems that bucket/blade design in such a turbine would be much easier to do for an amateur since it wouldn't depend so closely on the intended operating conditions as for turbines that rotate in a perpendicular plane to the flow


texts:
I am developing a toy for 2-6-year old children with parts in acrylic ( Poly(methyl methacrylate)). I searched Toy Safety Directive 2009/48/EC and Regulation 1907/2006 REACH for mentions of perspex or acrylic and found nothing.

Is acrylic OK for children's toys under EU regulations?


texts: Gear acceleration and maintaining torque

texts: If trying to achieve a 1:4 gear ratio, will a planetary gear system help reduce the loss of torque? Or is it essentially no different than the loss of torque when using a large drive gear to rotate a small driven gear?


texts:
I'm not sure I'm in the right place for this, if not, Apologies.

In my education material under Construction Steel, in its application it lists Masking Details.

Under Tool Steel it list an application as Maskin Parts.

But nowhere I look or ask have I been able to find an answer as to the difference in meaning between Part and Detail has here.
And from my other education material the word 'detail' is used for (as far as I can confirm) anything on a schematic and I've never encountered the word 'part' in such connotation. On the other hand in the workshop I hear the word 'detail' used to refer to anything made.

Oh, and the language I'm taking the education in is Swedish, so I've translated the terms.


texts: Quantifying the reaction force on fixed tubing connected to a peristaltic pump

texts:
I am not sure how I should consider the forces due to hydrostatic pressure when calculating the reaction force due to a fluid being pumped through fixed tubing with a peristaltic pump that I am using in my experiment. Below is a rough schematic of my setup, the pump is pulling the fluid up from the same reservoir as it is pumping it back out into. It's not to scale, but it reflects the general setup where the tubing diameter is fixed and the relative heights.
The green 'box' represents the fluid where the tubing is submerged, and the circle is the pump that is outside of the fluid. For simplicity, I am assuming that inside the control-volume (CV) 1) the flow is steady, 2) frictional effects are negligible, 3) the weight of the tubing and fluid are negligible, and 4) that the flow is laminar. This let's me use the equation from (Cengel, and Cimbala) $\sum\vec{F}=\sum_{out}\beta\dot{m}\vec{V}-\sum_{in}\beta\dot{m}\vec{V}$ where $\beta=4/3$, and $\dot{m}$ is the mass flow rate. The red arrows are the velocities inside the tubing ($V_1$), and exiting the tubing ($V_2$), the blue arrows are the reaction forces ($F_x$, and $F_z$) to hold the tubing in place. For now I am treating the bend angle as a variable $\theta$.
The flow just after the pump is unsteady, and there are frictional losses in the pump but they have dissipated upon reaching the outlet, this means that there will be a pressure difference between the inlet (not shown) and the outlet of the pump that eventually feeds into CV. I guess this can probably be estimated with a Bernoulli or energy equation, but I'm not sure the best way to approximate the pressure at point 1 ($P_1$) without measuring it directly considering that the tubing is submerged. The pressure at point 2 ($P_2$) is obviously just hydrostatic pressure.
Sorry this is so long, but basically I'm just not sure how to approximate $P_1$.


texts: Need some advice, control system animation. Appreciate some help!

texts:
I would like to have a 3d simulation of a helicopter landing on a ship.

I thought about using matlab for this, as a far as I know you can connect models from Simulink to virtual worlds using blocks, which is the main feature of the Simulink 3D Animation toolkit (https://es.mathworks.com/products/3d-animation/features.html). You can even edit 3D objects, or you can import it from CAD packages. My main question is the following, where do I define the dynamics equations of the helicopter? I haven't really worked with CAD software neither animation, so I don't know how to do this. I'm not even sure if this is the right way to do it but it should look like this.

The model of the helicopter is simple. The controller is feed (SENSORS) by the position and velocities of the center of mass of the helicopter. The controller outputs (ACTUATORS) are the main thrust, the tail thrust and the tilt angles. These four are the inputs to the helicopter. The reference is the vector position 0 which is the landing point.

As I said my main problem is the animation. If it wasn't for this, I could just create a model of the helicopter in simulink blocks and another model of the controller in simulink, connect them together, play it and see the plots of the desired tracking variables. But I want to do a 3D animation of the tracking of the reference.

I attach a photo of the helicopter dynamics to make myself clear.


texts: Materials science and materials engineering

texts:
Good day,
I would like to enquirer the followings:

What is the difference between studying materials science and materials engineering?
Are there any jobs exclusive to those who have studied materials science/ materials engineering


texts: Design for CNC -cut sheet+bolt connection

texts:
I'm making a corner shelf for spare toilet paper from a thin plywood sheet, say 5mm.

I want to connect the plywood to the corner walls with a bolt/nut joint like this:

My question is -- how do I calculate the size of a cutout for such a joint so that a wrench would fit?


texts:
What is the method to compute the effective bending stiffness "EI" of a composite structure, in this case a shaft (as seen below).
The shaft is hollow with outer radius $r_{o}$, inner radius $r_{i}$, and modulus of elasticity $E_{1}$. Four rods are inserted into the shaft's thickness. They are placed at an equal angular separation. They have a radius of $r_{m}$ and are at a distance $r_{c}$ from the shaft's center. They are all made of the same material with modulus of elasticity $E_2$.
Is the effective bending stiffness simply the sum of all bending stiffnesses $\sum_{}^{}E_{i}\int{}\int{r^2dA}$?

Thanks!
Regards,
Omar


texts: I have a project which involving several mating parts and also shaft guided through bearings, my issue here is that I don't have much experience with tolerances and manufacturing processes and I cannot determine the perfect balance between cost and accuracy. I am using Aluminium 6061 for raw material. For example I have some guidance "shafts" which are "made" by removing a large material from the part, I made some research and I saw that a +- 0.025 mm is a typical tolerance for a decent CNC machine. My question is, could I go down with that value, in terms of cost or is already a tight tolerance ?


texts:
I have an issue with simulink, basically it's to do with a second order system, well two first order systems in series. As I understand it as you increase the damping factor (above 1), the system should respond slower and be more sluggish. The damping factor = (tau1+tau2)/(2root(tau1*tau2)). So, looking at this system with damping factor 1(with it's response):

and this system with damping factor 1.19 and it's response:

What gives?! The system with the damping factor 1 hasn't even reached steady state by 250 secs while the system with damping factor 1.19 has had a faster response, why is this happening?

Thanks for reading.


texts: Use Fiber microscope to view micron sized particles

texts:
Can I use Fiber microscope to see micron sized particles?
That's mean, can Fiber microscope be used as a typical optical microscope?
Generic Handheld 400x Fiber Optical Microscope Inspection


texts: Which mode does get excited under action of dynamic loading?

texts: I am working on the vibration of the continuous system, I have seen lots of books on vibrations which talks about the natural frequency and mode shapes of the continuous system. I am interested in finding when particular time varying load is applied on continuous system how do we know which modes of the systems are excited and why?


texts:
I have a few questions regarding the physical interpretation of the information presented on a Bode plot. I believe it is one of those cases where I "don't know what I don't know", so please bear with me if I meander.

1) The magnitude plot of a Bode diagram represents the ratio of a system's output and input amplitudes, in dB. Given any system, is there a threshold dB which represents "too much", or is it a system-by-system assessment which must be made by the designer? (Note: I believe I know the answer to be the latter, but want to be sure). Could you provide a contrasting example, such as a filter design vs. something with vastly different technical requirements?

2) What is the physical interpretation of a magnitude plot having infinite gain at $0$ rad/s (for example, the bode plot of a pure integrator)? When an undamped second order system hits resonance, you get a theoretically infinite-dB magnitude response, which is obviously bad. So why does this logic not apply to very low frequencies? Is the infinite gain of a pure integrator simply a mathematical construct?

3) In controller design, what is the physical interpretation of phase margin and gain margin? I understand the underlying mathematics which brings about those particular properties, but not what they represent. For example, the gain margin is the amount of gain which can be added to the system prior to it going unstable, but why would you want more gain? Is it simply that more controller gain allows it to better track the input signal?

4) How does the gain of the system as represented by the magnitude bode plot relate to the gains of the controller? I feel as though much of my confusion stems from this distinction, where large bode plot magnitudes are not necessarily desirable but large controller gains always seem to be so.

Thank you very much in advance.


texts: System for aligning/truing objects to each other in a plane for CNC machine

texts:
I apologize for the vague title. I know my problem, but I am having problems describing it in concise words, which is making it difficult for me to google.

I am building a CNC machine that is similar to a pick and place machine. I used extruded aluminum for the rails, and I am certain that everything is squared up. I had a local machine shop create a plate that has a grid of holes, so that I can attach "parts" that can be used by the CNC machine. However, this grid of holes is not machined at the tolerance that I need (budget constraints). I need a system for making sure that the "parts" are square to the cnc frame. One of my ideas was to use leveling springs similar to how you adjust a the bed on a 3D printer to be square with the frame. However, I am unsure if this is the best idea, and I would like a second opinion.

It is important that the machine has a resolution of 200um (if you were to move in a straight line across the machine ~500mm all parts that should be on that line should not be more than 200um above or below it). I know that some solutions maybe more expensive than having the plate machined to lower tolerance, but if I were to mass produce this machine I would like a way to adjust the alignment of parts.

Thank you for taking the time to read and/or answer my question!


texts: Why are there so many types of screw head drives? Why aren't some strictly better than others?

texts:
When I look at the types of screw drives, I see... a lot.

History probably explains why so many existed, but I fail to understand why some still exist today.

For example, compare Double Hex  with Spline .
It seems obviously clear to me that the Double Hex has a higher chance of wearing out or slipping, and it seems to have no advantage whatsoever.

Or for example, compare the usual Hex Socket  with the Robertson .
Again, the Hex Socket appears to have a far higher chance of eventually wearing out or slipping, and again, no apparent advantage.

So why do these keep being used? Do they really all have at least one physical advantage over the others? Or is it a cost thing, or is it something else?


texts: How to calculate the viscous damping coefficient given drag force

texts:
Force due to drag at low velocities, is equal to some constant times negative velocity

$$F_{d}=-c_{1}V$$

The viscous damping coefficient equals decay constant divided by 2 times mass

$$\gamma = \frac{c_{2}}{2m}$$

So, is $c_{1}$ the same as $c_{2}$?

How is the drag force related to the viscous damping coefficient, what equation is there to relate them?
I think the relationship is linear but I'm not certain.

For context, this is for a mass-spring system inside a beaker of water being damped by the friction of the water.


texts: What is a slotted open ring with a thread called (like on bicycle brake levers)?

texts:
I'm looking for a small ring that allows a thin cable to pass through but can also lock to close that opening, like on bicycle brake lever screws (shown below). However, I'm having trouble finding the part because I don't know what it's called.

Do they have an official/technical name?


texts: Help with finding support reactions of a truss

texts: Can you please help me find the answer to the above question, I am unsure how to work with F2 as I can't find the distance from Moment A or Moment J to this. Thank you


texts: FOC algorithm for BLDC motor and rotor position estimation via IMU

texts:
I would like to implement the Field Oriented Control (FOC) algorithm on my STM32 board for controlling a 3 phases sensorless BLDC motor.

By googling I found a very interesting Application Note from Texas Instruments which explains very clearly how to apply the FOC algorithm for driving a sensorless 3 phase BLDC.

On page 10 of the application note, there is a block diagram of the algorithm and there is a block called Sliding-Mode
Based
Rotor
Position Estimator.

Since in my application I have an IMU (Inertial Measurment Unit) fixed on the shaft of the BLDC motor, I can get both rate and acceleration data.

Once combined the data into my Kalman Filter (outputs a quaternion), I have both speed and position information of the rotor.

Can I use IMU's data for the rotor position, instead of estimating as shown?
Is it correct considering the rotor angle got from the IMU for closing the loop?


texts: How do you implement a pattern over a bent plate in Autodesk Inventor?

texts:
I am attaching the model part as an Image below for your reference:-

I need the pattern like this on the above model.

I have the model shown above, and want to put embossed lines 0.2 mm thick with 0.2 mm spacing in between on the top, sides, and the bends. The feature should be parallel to the horizontal section. I tried using emboss but I don't know how to emboss all three sides.


texts: Why does the 1kg mass move towards inclined plane here?

texts:
Assumption :All frictionless surfaces.
EDIT: In the book , it doesn’t say friction has to be present but as PeteW has mentioned , i think it should be necessary too. So , in that case let me take two cases. One when friction is present between 5Kg and 1kg block and other when it is not. So , depending upon it. Check it.
The triangle wedge (white color) is always fixed. The blue color wedge of 5kg moves down and so does 1kg is given in Q.
So , the main question to find the time when 1kg block touches the inclined plane. Assume in one case a inertial frame and in another , any non inertial frame of your own choice.
My main confusion is that how do we know if the 1kg block will move towards right direction. It can be left or no direction also.
If I draw the FBD for 1kg block , it has N from 5kg which cancels out due to its mg=1g. So , there is no external force to make it move right.


texts:
Today, I was thinking about seat belts.

On that note, why do the ones in cars and planes differ? Planes have only belts on the waist, but cars have waist and diagonal. Is there a reason that this is so, or are the difference just... [Insert suitable word]?


texts: What is the best configuration to install Solar Panel? Should I give space between the adjacent panel?

texts:
![Solar cell array installation, the adjacent cell has space between them
]2

I would like to install solar panel/cell in my flat office's roof top. Should not difficult to install. Just to install it 2x4, 2x4, 2x4 (total 24 cells, 120cmx80cm wide each cell). Mean, in between 2x4 array with another array, there will be space for maintenance service isle). But between the panel in the array, will be no space (picture 1). It was on my mind. But then there comment saying that there should be space between panel in the array (picture 2), probably just 2-5cm, not so big.  In my opinion, the first option is the best while the panel will keep all the energy comes from the solar. But however, I don't know what is the justification for this opinion. Then my question is, what is the best configuration between the two array (option 1 or option 2)?


texts: Is it possible to build an efficient Electric Vehicle engine with minimal to no computing control systems?

texts:
First of all, I am neither an electronic nor a mechanical engineer, so if some of what I say sounds ignorant, that's most likely because it is.
I have been thinking about this for a while now. I love EVs and the fact that they are one of the best ways to cut down carbon emissions. On the other hand, I hate the fact that more and more modern vehicles are coming with a large amount of control being handed over to Electronic Control Systems. Would it be possible to have an EV that has little or no Electronic Control Systems in it? Is it possible to mechanically control features such as ABS, power-steering, etc without electronics?I mean, how much AI do you actually need in these vehicles? Are we just including it because we can, or because it is absolutely necessary? Essentially, is it possible to build an EV that would survive an EMP bomb?
Thanks.


texts: How to create an airtight connection between Stainless Steel and PTFE?

texts:
I have these two parts shown below, the bottom cylindrical part is stainless steel, the rectangular upper piece is PTFE (Teflon). The SS prongs from the lower part need to insert into the holes of the PTFE part.

I'd like to create an airtight connection between the two; but I'm unsure of how to go about it.

I'd like to avoid adhesives all together as this will undergo high temps.


texts: Weight Sensing Problem: Need to detect 10kg load down to milligram accuracy

texts:
So I need to build some type of scale where one can place four 600mL beakers on it and measure out its weight down to a milligram level of accuracy. I'm doing this so I can dose a very small amount of liquid (2 microliters) into the beakers at a time. The problem is that load cells and essentially all resistance based force sensors are only accurate down to ~.03 - .05% of their fullscale load (at best). I've looked into piezoelectric sensor solutions but it seems that they are ill suited for detecting static loads.

I'm completely open to having 4 seperate scales but the problem of having an accurate enough load cell will still exist.

Is there any way to detect changes in weight to this level of accuracy? Any suggestions?


texts: Will an electric water pump has slower flow if it must pump through a longer tube?

texts:
I am planning a series of ponds, where the first pond (near the source of electricity) has the highest water level, the water flows to the second, lower pond, via a small water fall, and to a third, lowest pond, again via a small water fall. The pump, located in the first pond, has a fountain that sprays into the first pond, but I plan to place an underground pipe to pull water from the third, final pond.
Bird's eye view:
                 ________________________
 __________     /  2nd pond              \
/ 1st pond \    |                        |
|          |    |                        |
|    >o<  <--fountain (pump's output)    |
|     .    |    |                        |
|     .    |    |                        |
|     .    ~~~~~~                        |
|     .    ~~~~~~ <-- waterfall down to  |
|     .    ~~~~~~      2nd pond          |
|     .    ~~~~~~                        |
|     .    |    |                        |
|     .    |    |                        |
\_____.____/    \__________!!!!!!!!!_____/
      .                    !!!!!!!!! <--waterfall down to 3rd
      .          __________!!!!!!!!!____________
      .         /   3rd pond                    \
      .         |                               |
      .         |                               |
      . <--underground PVC pipe                 |
       .        |                               |
        .       |                               |
         .      |                               |
          .     |                               |
            . . . . . . . . . . <--water flows into pump here
                |                               |
                |                               |
                |                               |
                |                               |
                \_______________________________/

The pump is like this:

Water is pumped in through the "Flat Box Filter", then sprays out the fountain at the top. If I were to lengthen the bendy pipe, replacing it with 10-20' of underground PVC to pull water from the third pond, assuming the same width pipe as the bendy tube, would that reduce the power of the pump? Or because it is all submerged anyway and water pressure will equalize, would the pump impellers not have any additional strain?


texts: how to find the tension matrix knowing the extensions

texts:
At a point $ P $ on the surface of a body, the rosette of 45 gauges indicated in the Figure is glued, whose readings are $\varepsilon_1 = 2 \times 10^{-6}$ , $\varepsilon_2 = 1 \times 10^{-6}$ e $\varepsilon_3 = -4 \times 10^{-6}$, respectively in elements 1, 2 and 3. Calculate, using the Mohr circle, the principal stresses and directions main points at point $ P $, knowing that the material of the body presents the following
features: $ E = 200 $ GPa and $\nu$ = 0.3. (note: assume a flat state of tension applied to the body).

I use
\begin{equation}
\begin{cases}
\varepsilon_\mathrm{1} \equiv \varepsilon (\alpha=0^\circ) & =
\varepsilon_{xx}\cos^2\alpha_1 + \varepsilon_{yy}\sin^2\alpha_1 +
\gamma_{xy}\sin\alpha_1\cos\alpha_1 \\
\varepsilon_\mathrm{2} \equiv \varepsilon (\alpha=+45^\circ) & =
\varepsilon_{xx}\cos^2\alpha_2 + \varepsilon_{yy}\sin^2\alpha_2 +
\gamma_{xy}\sin\alpha_2\cos\alpha_2 \\
\varepsilon_\mathrm{3} \equiv \varepsilon (\alpha=90^\circ) & =
\varepsilon_{xx}\cos^2\alpha_3 + \varepsilon_{yy}\sin^2\alpha_3 +
\gamma_{xy}\sin\alpha_3\cos\alpha_3
\end{cases}
\end{equation}
and after some calculations i arrive to the deformation matrix at $P$ point:
\begin{equation}
\underline{\underline{D}} \equiv [D] \equiv D_{ij} =
\begin{bmatrix}
\varepsilon_{xx} & \varepsilon_{xy} & \varepsilon_{xz} \\
\varepsilon_{yx} & \varepsilon_{yy} & \varepsilon_{yz} \\
\varepsilon_{zx} & \varepsilon_{zy} & \varepsilon_{zz} \\
\end{bmatrix} =
\begin{bmatrix}
\varepsilon_{xx} & \gamma_{xy}/2 & \gamma_{xz}/2 \\
\gamma_{yx}/2 & \varepsilon_{yy} & \gamma_{yz}/2 \\
\gamma_{zx}/2 & \gamma_{zy}/2 & \varepsilon_{zz} \\
\end{bmatrix} =
\begin{bmatrix}
2 & 2 & 0 \\
2 & -4 & 0 \\
0 & 0 & 0
\end{bmatrix} \times 10^{-6}
\end{equation}
i've done $|\epsilon_{ij}-\delta_{ij}\epsilon|=0$ and got the values $\epsilon_{I}=-1+\sqrt{13}$,
$\epsilon_{II}=0$, and $\epsilon_{III}=-1-\sqrt{13}$,
and i use hookes law and got
$\sigma_{I}=\frac{E}{(1+v)(1-2v)}((1-v)\epsilon_{I}+v\epsilon_{II}+v\epsilon_{III})=1.70\times 10^{5}$
However the solutions say that the tension matrix is
\begin{equation}
\underline{\underline{\sigma}} = [\sigma] = \sigma_{ij} =
\begin{bmatrix}
0.175824 & 0.307692 & 0 \\
0.307692 & -0.747252 & 0 \\
0 & 0 & 0
\end{bmatrix}~\mbox{[MPa]}
\end{equation}
But i don't understand how can i arrive to the tension matrix. I thought is through hookes law but i guess i'm making a mistake somewhere....Could someone explain me how to i get the tension matrix?
In the solutions the deformation matrix is
\begin{equation}
D  =
\begin{bmatrix}
2 & 2 & 0 \\
2 & -4 & 0 \\
0 & 0 & \varepsilon_{zz}
\end{bmatrix} \times 10^{-6}
\end{equation}
which is different from mine but i also dont understand why $\varepsilon_{zz}$ is not 0


texts: Can you suggest a 0 to 10 Volts mesuring unit with an easy .NET (C#) API?

texts:
I am looking for a voltage input module that measures a voltage input in the range of 0 to 10 Volts (slowly changing during a 5 seconds period). It should be connected to a local Windows computer that has a preexisting .NET (C#) software program (with its source code available) for plotting the input. I am completely inexperienced in this area of device acquisition, so I find it difficult to select the device model that would fit the purpose, and, confirm the existence of the accompanying .NET API.
For example, if I select a USB voltage input module from Lucid Control company, they offer these two downloads (scroll below to see the API + .Net examples) that do not seem to function. The supplied .dll file cannot be added to the project. The documentation is lacking.
https://www.lucid-control.com/downloads/
That shows that a solid device recommendation is needed to accommodate an easy update of the program code using the provided API.
Thanks.


texts:
I am writing a physics paper for school and I'm trying understand if this model is correct? Can anyone confirm/deny?
$$
V = \frac{4}{3} \pi R^3_1 \\
R_1 = \left( \frac{3V}{4\pi} \right)^\frac{1}{3} \\
\sigma = \frac{pR_1}{2t} \\
\epsilon = \frac{R_1 - R_0}{R_0} \\
E = \frac{\sigma}{\epsilon}
  = \frac{pR_0R_1}{2t(R_1-R_0)}
  = \frac{pR_0}{2t\left(1-\dfrac{R_0}{\left(\frac{3V}{4\pi}\right)^\frac{1}{3}}\right)} \\
$$
is this correct?
$$
E \propto \frac{p}{V^\frac{1}{3}}
$$


texts: Steel surface welding with high-frequency current

texts:
High-frequency currents induce skin-effect resistance that is used on some applications to weld metals.

Assume you have two steel rectangles of dimension $h_0, w, l$ and $h_1, w, l$ placed together along the $h$ axis. I'm wondering if placing a strong enough current through appropriate probes in the transverse faces of the rectangle, will generate enough heat to weld the touching faces uniformly, with no sticks or rods involved


texts: Designing electronic enclosures for manufacturing

texts:
I am trying to design a simple plastic electronic enclosure for a PCB and I wanted to learn how to get the enclosure as ready as possible for manufacturing. I basically wanted to understand the process that a mechanical engineer would go through to make sure the design of the enclosure is good enough for manufacturing.

So far I have read about stress/strain and wanted to find out what other things I should know when designing plastic enclosures.

For example, a lot of enclosures such as the one below, seem to have added extrusions on the internal sides, I would like to understand the functionality behind these - are these to do with stress and strain making the product more resistant?

Any ideas of the processes involved by a mechanical engineer to make a manufacture ready plastic enclosure would be great


texts: Coupling two double shafted stepper motors in series

texts: Coupling two identical double shafted stepper motors in series using two identical drivers will that double the torque?


texts:
Im in the process of building an espresso machine from readily available parts. I have a solenoid pump that supplies pressurized hot water to the coffee grounds. I want to be able to tune the pressure and flow of the system.

I can tune the max line pressure using an over-pressure valve, but I'm less sure about how I can reduce the flow-rate and maintain whatever pressure I set at the OP valve.


texts: I have a staggered 2x4 wall on a 2x6 sill plate as illustrated below (16" on center on each side = 8" on center each stud). The wall is loaded from both sides by floor joists, so I would consider it to be loaded in the center of the axis of the "5.5" inch wall. My problem is that this causes an eccentricity of 1 inch with regards to the 2x4 studs centre line. Should I consider this to be equivalent to a 2x4 wall with studs @ 8" on center with a 1" eccentricity? Can the studs buckle in opposite directions?


texts: How can I measure the amount of voltage stored in a sealed lead-acid battery?

texts:
I know that the simple way to measure the voltage stored in a lead-acid battery is to simply measure the positive and negative using a voltmeter.

In my case, I think that my battery has a builtin charge controller and it is sealed like the picture below. How can I effectively measure it without opening?

If there is no way to measure it, how do I open this thing? I tried to open it using flat screwdriver and it leaves a dented mark.


texts: Main Beam Cut and Settled at Some Point What Are The Options?

texts:
It looks like someone cut the main beam and there was settling at some point in the past. There is a noticeable dip and cupping in the floor near the main beam in the floors above. Why might someone have done this and what are the trade offs between the various remedies?
As I understand it the range of solutions are

Put in permanent steel columns with a 2' x 2' cement footer
Replace the main beam
Put in a new cement footer across the foundation to prevent further settling.
Some other solution

Some extra context; The main beam runs most the length of the house which is 46' in length and 26' in width. It looks like it has been cut about 4' from the end of the house. The house is two stories and the main beam supports a load bearing wall that divides the house approximately in half; the floor plan/load bearing wall is in the same position on each floor. The contractors that have taken a look at did not seem to understand what caused the settling nor did the structural engineer; they just pointed out that it was a problem and did not give any advice or context beyond saying that we should put in permanent columns.
Main beam with temporary columns

Cut main beam; the main beam ends next to the black tar paper

Support for the cut beam?


texts: Have there been successful attempts at using a computer's heat to warm something up?

texts:
Computers get hot.  So usually we try to make them less hot.  But what if instead of trying to cool down a computer we used that heat for something else?  Not necessarily any thing big like a whole room; maybe just something like a pet's cage.

Is funneling the heat generated by a computer (any kind; desktop, server rack, etc.) a practical thing to do?  Are there any reliable stories of it being done successfully?


texts:
I have rope on a spool that is on a cart that is powered and moving at a constant velocity of 0.5 m/s. The end of the rope is passed thru a break and fixed to the wall. one break has a compression spring with an unknown force to create friction to maintain a constant tension on the rope. The spool has a friction of .1 and is .5 m in diameter.

I want to calculate the force the spring needs to put on to maintain a constant tension as a result of the movement of the cart but do not know where to start


texts: What is a transparent material that insulates well?

texts: I need to create a transparent box that can stay warm inside while in cold temperatures, below 0 degrees, for as long as possible. Glass and plastic are transparent but afaik they don't insulate that well. Is there something else that I could use?


texts: can submersible pumps be used for leachate from landfill that may have some solid particles of size 15-20mm?

texts: I would like to know if submersible pumps can be used to extract leachate from leachate wells. The leachate is likely to contain solids of size 15-20mm. Further the pump should have diameter less than 200mm. The head required is 65-70m and a min flow of 500 L/hour. If not then please suggest an alternative.


texts: Why do you need helicoil if you can just use a tap?

texts: I'm new to thread repairs and I was just wondering when using a helicoil, why does the helicoil need to be inserted if you have already tapped the new threads into a hole? Can't you just put a bolt in once you've tapped new threads?