texts: Why don't public transport networks have more routes to each terminal?

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When using public transport, we often need to change routes in the middle of the journey. These changes have costs – I can think of the following, but there may be more.

If we're reading, working, etc. on board, we need to take a break, losing flow.
We spend time moving from one route to the next.
We spend time waiting for the next departure.
There are lots of passengers moving between routes. They take up space and cause queues when on- and off-boarding. This also increases the risk of accidents.

As far as I can understand, we could decrease the necessity of route changes by having multiple routes to the terminals (final stations).

I've reviewed the subway maps of London, New York and Oslo, finding that none of them do this to any significant degree – the terminals usually have just one route.

As an example, let's look at the simplest of the three – Oslo:

Imagine that you're travelling from Østerås (orange, left) to Ellingsrudåsen (orange, right). No changes required – route 2 takes you all the way.

But if you're travelling from Østerås to Mortensrud (purple, bottom right), you would have to change trains from route 2 to route 3 at some point.

Let's imagine that we use some of the capacity used for routes 2 and 3 to serve routes 6 and 7. Route 6 (gray) serves Østerås-Mortensrud, and route 7 (brown) serves Kolsås-Ellingsrudåsen:

With this design, some route changes can be avoided. If we added enough routes, many more route changes could be avoided. Granted, we would have to wait longer for a route that went exactly to the station we want to go, but we would always have the option of taking the first train and then changing like before.

So, I've been asking myself, why don't public transport authorities do this? These are the reasons I can think of:

Simplicity for passengers: When only one route serves a particular station, you don't have to think about which route you'll board. Also, the maps would be more chaotic.
Simplicity for transport providers: More routes would mean more difficult (and therefore costly) planning and management.

From my (admittedly ignorant) perspective, the above reasons don't seem sufficient to outweigh the advantages of fewer changes. Have I overlooked some problems with adding more routes? Or am I underestimating the costs and/or overestimating the benefits of more routes?


texts: Calculating water content of a tank given humidity?

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I have a 4700 gallon tank and am looking to create a table of the water content by mass in the tank given relative humidity %. The tank is held at 70 degC and 18 psig, and the only thing inside the tank is normal air at varying humidity %.

I believe this has something to do with partial pressures and steam tables.


texts:
My task is to create a 3D Sketch of a trombone like the one below

My professor recommended defining the points 1-4 and putting a spline through them. I did that, but my resulting design looks weird. It curves inward between points 1 and 2 before curving out towards the rest of the points. I'm not sure what I'm doing wrong, and I don't know if I have enough given constraints to curve it outward manually myself by editing the spline


texts: First of all, I would like to know about the service life of a flashback arrestor. In my laboratory, I got three flashback arrestors {WITTgas RF53N(1/4”NPT-F), Brass} from the ex-students who used those items in 2012 and already finished their graduation. I joined the laboratory in 2015. In this circumstance, I want to know if there is any possible way to check those flashback arrestor. All the flashback arrestors they used are for the premixed combustion in a Constant Volume Combustion Chamber. My purpose is also same. But I want to know first whether those flashback arrestors are dead or alive.


texts: What does "Percent Trucks in Design Lane" input represent?

texts: In the AASHTO Pavement ME program version 2.6, for the traffic input "Percent Trucks in Design Lane" is the default value of 95% based on the maximum percent of trucks that can occur in the design lane or the average percent of trucks that ride in the design lane?


texts: Other working fluids in Rankine cycle power plants

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Why do power plants that use the Rankine cycle use the working fluids:

sodium
mercury
serine
benzene
potassium

Can such plants use other fluids?


texts:
I'm trying to wrap my head around the question: "what is the optimal slip ratio and how do I go about controlling it?". I'm working on a control strategy for an electrical vehicle. The issue I'm facing is that of maximizing traction. The way I can measure slip ratio is by measuring difference between wheel velocity and vehicle velocity (both of which let's assume are measured separately).

Now, what I need to do (I think) is to figure out a way to maximize traction by always keeping the slip ratio at some specific value. But what value? Also it seems wrong to always try to keep wheel speeds at an offset from vehicle speed. I suppose I only should be doing this during acceleration/deceleration? How can I do this in a generic way without having to implement different strategies for accel/decel?


texts: Combining solar water heating with pellet stove water heater

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I am looking to combine a pellet stove water heater with a solar water heater.
First of all I wold like to apologise for the ugly drawing, though I think it represents my idea well enough.
The whole thing will be a closed loop cycle or two cycles rather.
What we are looking to do is use whatever energy we can collect from the solar panels in the winter time and use it to aid the heating of the boiler/buffer vessel. The main source of energy will be the pellet stove.
My question is what can we do in order to use the solar energy first so we don`t end up stealing energy from the boiler.
P.S. The drawing is just the direction of my thoughts.
Please feel free to butcher it :)


texts: Where can i get the aerodynamic data of aircrafts for controller design and testing?

texts:
I have some research papers on aircraft controller design that i want to simulate, but no system data is given in the research paper itself. I am also unable to find the aerodynamic data for any commercial/fighter aircraft anywhere.
So i want to know where do the academic researchers get their data sets from? And is there some way for me to get trimmed or untrimmed aerodynamic data for my simulation?


texts: How to make stick change angle after pressure is added?

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I am currently trying to create a small product with my 3D printer.

The product consists of a flat wide stick first, which then is connected to a 45 degrees angled stick. What I now want to achieve is that the 45 degree angled plate gets to the same level as the flat plate when pressure gets added. So it goes from 45 degrees to 0 looking something like this:

I have been doing a bit of googling and came across something called a torsion spring which I assume could work pretty well looking like this:

However, I do not currently own a torsion spring at home and I assume torsion springs cannot be made using a 3D printer. I was wondering if there is an optional solution for this task?


texts:
I am very much confused finding the time constant and DC gain for the below step response. The idea is to find PI gains for speed control and I am following this tutorial online Tutorial Link

Motor specifications

Below is the open loop step response when a 10 V is applied across the DC motor. The battery is of 26 V, which means that a PWM duty cycle of 38% or 0.38 (10/26). The X-axis is time(seconds) and the y-axis is Gear box output shaft RPM. Initially it stayed at 100 RPM and then it fell down to 50RPM.

As explained in the tutorial link provided above,I am trying to find a first order transfer function between PWM Duty cycle and the output shaft angular velocity. What should be my DC gain ? Currently i am applying only 0.38(38%) duty does the time constant change if applied 1 (100 %) duty cycle ?

I am new to this topic let me know if any further information is needed.

Thanks


texts: How does indoor temperature factor in when determining ideal relative humidity in a home?

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I am having trouble understanding how indoor temperature plays into what a healthy indoor relative humidity level should be.  Most sources I have come across searching the topic online provide a range based on the outdoor temperature.  For example, according to Therma-Stor, "The ideal relative humidity for health and comfort is about 40–50%. In the winter months, it may have to be lower than 40% RH to avoid condensation on the windows."  I understand this is important for preventing condensation that can lead to mold and other problems, but I have not seen condensation forming on any windows and I think the air may be too dry in my case.

I live in a home that was built in 1938.  It is not well-insulated and there have been several additions in its history.  It is currently winter in my location, so the furnace is running.  I do not feel any drafts coming from outside, so I believe most of the heat escapes due to the poor insulation -- the closer I am to exterior walls, the colder it feels.  The thermostat in my home is set to 64 degrees Fahrenheit (17.8  $^oC$).  Increasing the temperature beyond that has a minimal effect on the downstairs temperature, while the upstairs temperature increases drastically.  I have looked at the air ducts, but I cannot find any place where I am able to adjust the airflow.

The outdoor temperature ranged from 19-49 degrees Fahrenheit (-7 to 9.4 $^oC$) today, with a current outdoor temperature of 21 degrees Fahrenheit (-6 $^oC$) and humidity of 79%.  I just measured the temperature and humidity in my bedroom, which is downstairs, and it is 57 degrees Fahrenheit (13.9 $^oC$) with a humidity of 37%.  In the office, which is upstairs, the temperature is 64 degrees Fahrenheit (17.8 $^OC$) with a humidity of 35%.  I placed the thermometer/hygrometer in the center of each room.

Considering the temperature of my bedroom is quite low, I am assuming that the 37% humidity level is pretty dry -- the thermometer/hygrometer also provides a reading of "Low" next to the humidity level.  It seems that most sources I have found assume a more reasonable indoor temperature in the range of 68-72 degrees Fahrenheit (20 to 22 $^oC$).  I do have a portable humidifier I could run in my room, and I am wondering what would be an appropriate humidity level under these outdoor and indoor conditions? Is there some sort of an equation I could use, maybe something similar to how the thermometer/hygrometer determines when to display a reading of "Low," "OK," or "High?"


texts: best way to reinforce existing structural header?

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House remodeling.   I need to enlarge (from 7 to 10-12 ft) and shift (about 5ft sideways) an existing header where one passes between rooms.  On one side, the header has 2x8 ceiling joists nailed to its face; cathedral ceiling 2x12 rafters, on the other side, are nailed to the top of it.  The existing header is a flitch beam, steel sandwiched between two 2x10s. I have computed (pretty conservatively) the load on the new header at about 900 pounds per linear foot (total) and about 575 plf of live load.  There are several ways to proceed, and I can't decide among:

Sister a 2x10 piece of LVL (engineered wood) to the exposed face (the cathedral side) of the existing header.  Unfortunately, the original carpentry was a little sloppy, and the existing header isn't directly on top of the girder which supports the floor which supports the wall with the header).  Unfortunately, it's off to the side of the face where I'd add the LVL, so it'd be unacceptably off center after I did that.
Rip out the existing header and replace it with a 2-ply LVL beam (3.5" x 9.5").  This is "best" in the sense it's very strong (so can make the opening 12ft wide instead of 10ft).  But a gigantic PITA: have to build temporary supporting walls on both sides of existing header, sawzall the thing out of there, etc.  Oh, did I mention that almost every piece of Romex in the house runs right along the edge of this header ?   At least I can do my own electrical work ...
Like #2, except after all the sheetrock is off, try to remove the flitch plate from the existing header, and the 1/2" plywood from the part that wasn't formerly over the opening, and then insert a new fitch plate of the proper length.  Probably a non-starter too, especially if they used glue when they built the original flitch beam.
Put some sort of piece of structural steel under the existing header.  I'm currently favoring this option.   Not sure what to use - angle, square tube, channel ?   Strength shouldn't be an issue.   Deflection definitely is - there's no framing or door, but there is sheetrock; I've been told up to 1/2" might be ok.  That means I need a section with a moment of inertia of about 10 in^4 (if I'm computing correctly).

Thoughts on what I should do?


texts: Center of Pressure Line from Barefoot Scan (EMED)

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I have raw data obtained from EMED barefoot scan containing a matrix of pressure sensors over about 70 frames. This totals 70 matrices that record a snapshot of the pressure over the duration of a person's natural walk over the pressure plate.

I wanted to ask if anyone knows the algorithm that is typically used to determine the Center of Pressure Line (indicated by the path on the heatmap below). One thing I have tried is to consider each row as an array and find the index of the maximum pressure across the row, and create a line by matching up all the points that correspond to these indices. My approach fails to produce a smoothed line (even when using Gaussian smoothing).


texts: Specifying GD&T feature when not expecting the fabricator to measure it

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For context: I work designing one-off science exhibits. Generally we design around pretty sloppy tolerances when we can, so things can be cheaper to make, with less precise tools, and at more facilities. We sometimes make everything in house.
Question: Occasionally, we'll call out a GD&T feature for a vendor, on a welded frame for instance. Parallelism, lets say. I generally don't expect the vendor to actually check this parallelism directly, but use it as a way to indicate design intent: what's important, and what's not. Should the one-off part come back significantly off, we will escalate to actually measuring the feature. We can then use this feature spec deviation to talk the vendor about a replacement.
Is this an appropriate use of GD+T? Is this CYA (Cover Your Ass)  type usage relatively common? How often are GD+T features called out but not measured by the fabricator, or our QA until a problem arises?
Certainly our usage case is not the most common one, and of course for aerospace and etc, the answers will (potentially) be different.
Just wanting some outside voices of what the correct approach is.


texts:
In this NASA document, it is mentioned on page 221 (239 of the pdf) that a "23 tol gear box" was used. What does that mean?

A google search for "23 tol gear box" (with quotes) comes up completely empty, and "tol gear box" shows only irrelevant results. A search for just tol doesn't come up with any convincing results either. I can't rule out that it is a typo of some sort.

From the context I presume it to mean that the gearbox output runs 23 times as fast as the powered side, but I have to be certain.


texts: How to derive phase equillibrium criteria for more than 2 phases mathematically?

texts: I know the derivation of phase equilibrium criteria derivation for 2 phases. I am not getting how to extend the derivation to more than 2 phases. Please help me out on that. Thank you


texts: How to check if bending moment diagram is correctly drawn

texts:
EDIT: I will state my test problem description and then my solution. But before that, I would like to apprise you of the absence of the actual description given during test (which happened in Zoom and there I was provided with the link leading to tasks).
Problem 1. I was given a beam (that you may see below added as a picture from my textbook) and assigned to draw diagrams of internal forces ($Q$, $N$, $M$) which are shear force, axial (normal) force and bending moment. My question is how you know immediately that these diagrams are drawn incorrectly if all subconditions such as "differential identities" and "all equilibrium equations" hold true. Otherwise, I miss something and do not realise about this.

Here you might see a beam whose endings are A and B. At them, there are supports (at A it is non moving, so there arises two reactions, and at B it is moving, so leaving me with one reaction). The data is as follows: $q = 12 \frac{kN}{m} $, $M = 8 kNm$, $F_1 = 5 kN$, $F_2 = 14 kN$, $l_1 = 2.6 m$ and $l_2 = 1.2$, so $l = l_1 + l_2 = 3.8 m$.
First step is to solve reactions, for which I must compose equations of equilibrium:
$$ \sum_n F_n ^x = 0 \Rightarrow X_A - F_2 = 0 \Rightarrow
X_A = 14 kN $$
$$\sum_n M_y ^A (F_n) = 0 \Rightarrow M + F_1 \cdot l_1 + l \cdot Z_B - q \cdot l \cdot \frac{l}{2} = 0 \Rightarrow Z_B \approx 17.27$$
$$\sum_n M_y ^B (F_n) = 0 \Rightarrow M - F_1 \cdot l_2 + q \cdot l \cdot \frac{l}{2} - Z_A \cdot l = 0 \Rightarrow Z_A \approx 23.33 kN$$
Notice that:
$$\sum_n F_n ^z = 0 \Rightarrow ql - Z_A - Z_B - F_1 \equiv 0$$
So, these reactions are correctly found and the equilibrium is maintained. Next, we are going to draw diagrams of internal forces. Here I am not going to be idle and show you my actions, so you would help me:

Idea is shown above on the pictures. Let us begin. The cut comes to the point C or to the part of the beam at C. Thus, we must consider two parts of the beams.
The part AC where $0 \le x \le l_1$. Internal forces are determined with equilibrium equations, so
$$\sum_n F_n ^z = 0 \Rightarrow Q_z + ql - Z_A - Z_B - F_1 = 0 \Rightarrow Q_z = 23.33 - 12x$$
Note that $l = x$ along the segment according to method of cut, sections. Next,
$$\sum_n M_y ^C (F_n) = 0 \Rightarrow M_y + M - Z_A \cdot x + q \cdot x \cdot \frac{x}{2} = 0 \Rightarrow M_y = 23.33x - 6x^2 - 8$$
$$\sum_n F_n ^x = 0 \Rightarrow X_A + N_x = 0 \Rightarrow N_x = - 14 kN$$
Note that the following equations are true:
$$\frac{\partial M_y}{\partial x} = Q_z, \\ \frac{\partial Q_z}{\partial x} = - q$$
Thus, internal forces are found correctly and the equilibrium at the cut is maintained. Let us compute the internal forces' values at endings of the cut:
$$M_y (0) = - 8 kNm, \ M_y (2.6) = 12.098 kNm \\ Q_z (0) = 23.33 kN, \ Q_z (2.6) = - 7.87 kN$$
The second part is CB where $ 2.6 \le x \le 3.8$. Internal forces:
$$\sum_n M_y ^B (F_n) = 0 \Rightarrow M_y + M - Z_A \cdot (x + 2.6)- F_1 \cdot x + q \cdot (x + 2.6) \cdot \frac{x + 2.6}{2} = 0 \Rightarrow M_y = - 6x^2 - 2.87x + 20.098$$
Hence,
$$Q_z = \frac{\partial M_y}{\partial x} = - 12x - 2.87$$
The axial force is the same because on the cut there is no force $F_2$, because it is cut off. Again we compute values of internal forces and draw our diagrams:

The second problem was much harder. I had to do the same things but in that time, I was to determine the distribution load $q$, which they denoted by $p$. I had to draw diagrams of internal forces. In addition to that, I was provided with I-beam whose dimensions were given. I guess that this I-beam was given to make me compute the polar moment of the figure and use some formulae from strength materials theory to find such values of $q$ for which the beam is stable. That is the point. Technically, I drew incorrect diagram. But numbers are correct, so I drew incorrectly and compute correctly :)


texts: Gear coupling and clearance between pitch surfaces

texts:
I have a couple of spur gears (0.4 mm module, ISO8/AGMA9 precision, 24 and 120 teeth). I want to make their backlash as small as possible. But also I don't want them to jam. Where can I get the normal clearance between their pitch surfaces (and the tolerance of the clearance)?

Maybe there is some handbook to use?


texts: Cleaning tape for automatic part cleaning during manufacturing

texts: Is there something like a consumable cleaning tape for automatically cleaning parts during manufacturing? Some parts need to be cleaned before automatic assembly, e.g. magnets before adhesive being applied to one of their surfaces. Tape may be soaked in cleaning agent like isopropyl alcohol. I'm looking for something ready to use, before trying to make it on my own.


texts: Bending moment when there are no constraints

texts:
I faced this problem in an old book (Hall Allen S., Theory and Problems of Machine Design; 1961)
The answer according to the book is 592 [in.lb], but I think the bending moment should be 0 because there are no constraints.
Could anybody help me to understand this?


texts:
Over years of flying small airplanes I have seen fatigue cracks and frayed brackets and connections.
I wonder if there is an easy way to search the propagation of stress wave in machinery and connection brackets and parts. I am not concerned here with vibrations so much.

Let's say we have a bracket holding the block of an engine to another part and at short intervals of time it undergoes huge stresses of impact of rotation of the engine cylinders, shafts, etc.

This stress wave propagates inside the bracket and reflects and interfere with its refractions and echo until it dies out by dispensing its energy into friction or transferring to other parts!
I know there is a large volume of empirical tests involved but I am concerned with a mathematical modeling scheme. Thank you!


texts: Could a water stream be used as a fiber optic sensor and detect when the stream is broken?

texts:
I have a small idea/project I am working on in which I want to use a water fiber optic sensor that can detect whether the water stream is broken and if so shut off the water.

Having looked into fiber optic sensor systems in general, all I have managed to work out is I would need an intrinsic sensing region system.  I do not know what type of Optical Modulation mechanism I would need so have hit a wall.

Any guidance into which of these systems, Intensity modulated, Phase modulated, Wavelength modulated or Polarization modulated, could be useful would be massively appreciated as I'd love to be able to look into this further.


texts: Why is hydro-electric power still scarce in some places?

texts:
70% of the Earth's surface is covered in water, why can't a hydroelectric power plant be set up on each and every river? Is it that its too expensive?

Why is electricity still a problem in countries that have abundant number of rivers? Why can't each and every river be associated with a hydro power plant through dams? What makes a river unsuitable?

My basic question is that Earth has got abundant amount of water. Then why is (hydro) electricity still scarce in some places? Is it that its too expensive?

My research shows that it might be expensive to set up but it is quite cheap in the long run compared to other power plants besides itself being low-maintenance.


texts: Why would bathrooms have two layers of doors?

texts:
I work in a university building designed in the 1930s, located in western New York State (not in NYC). To enter classrooms, offices or labs one passes through a single door. However, the restrooms ALL have two layers of door with a closet-sized compartment in between. This poses issues for people with mobility impairments. All the inner doors have transoms, with a ventilation grating above each transom. Both the men's and women's restrooms have these two-layer doors.

The two door system is awkward and wastes space. Surely there are better ways to prevent hallway users from peeping in. And the bathrooms are not noisy; I've been in classrooms that share a wall with a restroom and have never heard any water-related noise. Finally, the grating between the restroom and the compartment eliminates the argument that the reason is odor control. I suspect the reason relates to the building codes in force when the building was designed - but why would a building code require two layers of door on a restroom?

Thanks for any insights!


texts: What does time temperature specifically give us?

texts: What is a Time Temperature curve basically? I have come across this a couple of times while dealing with heat treatment in my industry. A detailed reply to this is most welcome.


texts: Plate rolling - Hot or Cold rolled plate stainless steel

texts:
What is preferred material for plate rolling (roll bending) when talking about stainless steel - hot rolled stainless steel plate or cold rolled stainless steel plate.

Final product would be for example shell of pressure vessel.

I would prefer to use hot rolled stainless steel plate ( for example 6 mm thick), which will ensure that less deforming of material occurs when rolling.


texts:
I am trying to calculate critical force $P$, if two rods (same diameter and length - rigid fiberglass sandwiched on two  steel plates) are parallel to each other.
$$
P = \frac{\pi^2 EI}{(KL)^2}
$$

I believe the configuration of both rods pinned would be $K=1$ (as shown in figure below - B). I am a bit confused if this configuration would behave as springs in this scenario? How would you calculate the the critical force besides using FEA?


texts: In equilibrium is engine torque zero? Vehicle dynamics

texts:
Consider following equations for a driving wheel in a car.

$$ J\dot{\omega} = T - F_x R - F_r R \\
m\dot{v} = F_x + F_r $$
where $J$, $\omega$, $T$, $F_x$, $R$, $F_r$, $m$, and $v$ are wheel inertia, angular velocity, torque input, traction force, tire radius, rolling resistance, mass and translation velocity respectively. Now assume that the vehicle (or the wheel) is in equilibrium state then both derivative should be zero. As it turns out you will get:
$$ 0 = T $$
because:
$$ 0 = F_x + F_r$$

Does that mean that if the vehicle is in equilibrium, even though you may press the pedal gas you torque is still zero? Imagine that you are riding your car on a slippery surface and you still press the pedal, it will of course transfer torque to the wheel. But the translation velocity will remain constant. Then the second diff equation is zero but not necessarily the first one. And you can have same reasoning on the first diff equation. So despite the fact that "equilibrium is when no changes are happening" what does equilibrium mean in this context? Does equilibrium in first equation mean that $T = 0$? That if you don't press gas pedal it leads to equilibrium state?


texts:
I'm attaching a metal pipe to a metal tube as shown in the below diagram. The bolt is threaded through one wall of the pipe and does not pass through the opposite wall of the pipe, but is tightened to the point of bottoming out against it. The bolt passes through unthreaded holes in the tube. It needs to support a load in the direction of the red arrow. I need a bit of a gap between the pipe and tube, so I'll be relying on the ability of the bolt to resist bending under this force. Assuming that nothing else will give out first, what metric would I use to estimate how much weight it can support before flexing the bolts? Is it "bending stiffness" rather than "shear strength"? Bolts don't typically advertise bending stiffness, so how would I estimate that? I know distance between tube and pipe is a factor because it increases the leverage the force has to bend the bolt.

I'd think that filling the void between tube and pipe with nuts/washers would strengthen this arrangement when two flat surfaces are being attached, but since the pipe is round, is there any point? I don't expect a precise answer I just need a way to get a ballpark estimate without bending the bolts before selecting them. Hardware stores don't care for that.

It's for an improvised rail if anyone's wondering. I need upwards of 80% of the circumference of the pipe for the slider to grip it, which is why I'm attaching it in such a dumb way.

Something like this (not my image) will be rolling along it.

I haven't found a way to manufacture a proper cradle for the pipe. (EDIT, a U channel would probably work if I can find one the right size) I know that it would be much stronger if done vertically, but this has some advantages given my situation.


texts: Why is North considered the reference direction in Surveying?

texts:
While Surveying, the North is always considered the reference direction, for the purposes of mapping. I have specifically the following issues:

The magnetic compass, has a least count of 30 minutes, and it deeply affected by local disturbances.
The pole star, which denotes the astronomical north, is not visible during the day time, while it is the best time to conduct the surveying process.
The sun, definitely cannot be taken as the reference object, as it is not fixed during the day, and also suffers from the sun moving from the north to south and backwards during various parts of the year.

Therefore, I would like to know, as to why the North was chosen as the reference direction for Surveying and Mapping.


texts: calculating flow rate in a given water tank and Water Head in hydropower

texts:
I'm calculating feasibility of using grey water in high rise buildings to generate hydroelectricity.
let's assume a given water volume of 100 cubic meters a day and a water head of 100 meter.
what should be the diameter of the pipe and thus what should be the flow rate in order to maximise the total power generated through the turbine?
lets assume emptying the tank will be done once ( or more ) a day.


texts: How to take the engineering FFT of Signal in Matlab?

texts:
All,
The FFT function in matlab gives a theoretical mathematical FFT of the signal, and is not scaled to units and is real imaginary and not amplitude-frequency
is there an alternative way of FFT to do this ? and is  this link correct?


texts: Why are Whitworth threads angled at 55°?

texts:
You're probably thinking, "Well..  Why not? It's gotta be something.." Right?

But 55° is kind of an odd angle if you think about it.. and it does seem like a pretty specific choice  considering a perfect equilateral/equiangular triangle consists of 60° angles. Wouldn't 60° be the default/simple/obvious choice for a triangular profile? Wouldn't it have been easier to manufacture? It seems like 60° would at least be the most logical starting point (like starting at zero) during the design phase. Or any other common, suitable, trigonometric angle; i.e. 30°, 45°, even 90°.

 Also, Whitworth strikes me as a pretty meticulous, character; detail oriented, with a careful consideration for all aspects of his designs. Plus, when it comes to mechanical engineering, he has a history of favouring experimental & unorthodox geometry.


texts:
See below for an extract from a general arrangement drawing from the 1980s. It makes reference to a '9" rocker slab' which appears to be a slab supported by steel beams.

Does anyone have any more information on the construction details of a rocker slab?


texts:
I have recently bought myself a Flux Beamo laser cutter and am now in the process of setting up fume extraction for it to vent outside. The laser unit has a built in fan of which I haven’t been able to find the specs but it’s fairly powerful. It also comes with a 2 meter length of 100mm diameter ducting which attaches to the laser via a hose clamp. My plan is to use about 400mm of that ducting to go from the laser cutter that is sitting on a table to a section of 100mm PVC pipe about 1 meter long, which will sit again the wall and go up to a 90° bend and then though the wall to the outside. I now have a couple of questions. The first is that I’ve seen small fans on AliExpress that are designed to fit into 100mm pipe: https://a.aliexpress.com/_mMqOjk9
They claim to be 12 watt and I thought that I could add one in between the ducting and PVC pipe to increase extraction, but by doing this am I actually increasing air flow even if it is less powerful than the laser fan before it? I don’t want to restrict the flow of the existing fan. My second question is that I will need to put some type of cover over the hole on the outside to stop rain coming in, however I’m not sure wether to use one with angled slats that are always open or one the has tilting slats that only open when the fan is pushing? I feel like the second one has more resistance but I’m not sure to what degree.


texts: What's the function of those coils there?

texts:
What do they do?

The aux contacts are normally open and the device is MR PQM 500 reactive power compensation system.


texts: How to design a fan that can be used to convert concentrated air to power

texts:
I am trying to design mechanism that is sort of like a wind turbine (uses wind as "fuel") but has a fan size that is in a pelton turbine. I was wondering if there is any math/equation that I can use to know how much power can be generated or how many rpms can the fan produce when attached to a generator. The equation of the wind turbine is not that applicable because the wind coming in will be going through a pipe (like in a peloton turbine, which has water), and the fan size is too small.

Is there an equation relating air velocity in a pipe and how much power that can generate?


texts: Thermal efficiency of a given complete cycle

texts:
I am answering the following question:

  Gas initially at a pressure of 101.325 kPa and temperature of 60 °C
  undergoes the following cycle:

  1-2: Adiabatic Compression  through compression ratio of 4.5:1
  2-3: Heating at constant volume through a pressure ratio of 1.35:1
  3-4: Constant entropy expansion to initial pressure
  4-1: Constant pressure cooling to initial volume

  If $Cp = 1\ \mathrm{\frac{kJ}{kg\ K}}$ and $Cv = 0.678\
> \mathrm{\frac{kJ}{kg\ K}}$ for the gas, determine the thermal
  efficiency for the cycle.

The given answer is 41.41%.

Since it sounds pretty much like the Otto cycle, I try using the formula with compression ratio $r_k = 4.5$:

$$k = Cp/Cv = 1.47$$

$$e = 1-(1/(r_k^{k-1})) = 50.68\% $$

What am I doing wrong? Is it not an Otto cycle?


texts:
I’m reading “Theory of Machines and Mechanisms” by Joseph Shigley.

Page No. 118 - The author states that   A mechanism has as many instant centres as there are ways of pairing the link numbers. Thus, for an n-link Mechanism there are N = n(n-1)/2  instantaneous centres.

Now consider the following image having 3 links (one of them being the fixed reference frame), two of them being connected by a revolute joint.

The way I see it, there should be 2 instantaneous centres. One, point A itself about which each link can rotate. Second, some instantaneous centre in the plane about which this linkage system, as a whole, describes rotational motion at any given instant.
But by the formula the no. Should be 3.

So, where am I going wrong ?


texts: How do engineers work with extremely small objects?

texts:
Please excuse me if my question is not well-worded. My background is pure mathematics and I am not familiar with engineering, but sometimes I feel fascinated by the things engineers have achieved.

Anyway, when I read about neuroscience or nano-engineering, I read things like engineers have been able to arrange atoms on an extremely small metal (like the IBM movie) or neuroscientists can measure voltage changes of an ion-channel inside the membrane which is extremely small.

When I was a child, I learned that levers enable us to move extremely heavy objects but we were never told how engineers work with extremely small objects. For example, how is it possible for neuroscientists to insert an electrode under the membrane of a single neuron to measure voltage changes? Or how is it possible for scientists at IBM to arrange atoms in an IBM shape? Or if I want to build a robotic arm that it can move with a precision under 1mm, how can that be done?

I know how microscopes and scanners work, I don't understand how moving things in very small regions work. In short, what I am looking for is a short list of methods or tools that engineers use to tackle engineering challenges at extremely small scales.


texts:
I have an arduino powered CNC machine with the Protoneer v3.00 shield. I have a probe setup for auto levelling which works correctly, I get a depth map for the board.

But the issue is that this depth map is created to the point at which the bit touches the board, but the board has some flex in it such that it is raised above the table in the centre. This therefore means that when it comes to milling, any flex in the board gets pushed down by the bit before any milling occurs and so the depth map is not correct as it has not taken account of this.

I realise therefore I need to ensure the board is firmly clamped to the table at all points and so I think a vacuum table is the best option. I have found one which is 210mm x 120mm and has a 10mm x 10mm grid for the vacuum holes (vacuumtablesuk SEAL2 VT2012).

I will be needing to clamp standard FR4 fibreglass PCB board, and I am wondering what vacuum pump would be suitable? I am lost as to how to choose a vacuum pump so any advice and links to suitable pumps would be greatly appreciated!


texts: How does plant evapotranspiration reduce the required size of a chiller used to control the climate of an indoor farm?

texts: When HVAC companies estimate the required size of a chiller unit for a greenhouse or an indoor farm, they reduce the estimated load by plant "transpiration cooling." I understand how transpiration converts sensible heat to latent heat, however I don't understand how that would reduce the required size of a chiller unit.  If an artificial light is adding 4000 BTUs of energy into a grow room, the HVAC system still needs to remove that heat, regardless of the state it is in.  Transpiration does not remove heat from a room, it just transforms it.


texts: Control effort in mixed sensitivity design

texts:
I am dealing with mixed sensitivity controller design in SISO systems and I am comparing this approch with the classic approch. In particular, I have placed a weight for the sensitivity function in order to reach specific desired performances. After doing this, I have plotted the frequency responce of the control effort, and I have found this:

so, what I have found is that the control effort when using the weight is higher the when we don't use any weight.

I haven' t found anything about why the control effort should be higher, but my opinion is that this happens because with a weight the controller has to do more work to force the system to have specific specifications.

But this is just my opinion, because I haven't found any reference about this.

Can someone explain why the control effort is higher? Thanks in advance.

[EDIT] To clarify what I am doing is the following:

so I am placing a limitation on the bandwidth, on the resonance peak and on the low frequency, and this limitation is given by the red line, which is my weight, which I tuned with the desired specifications.

And the plant is not non-minimum phase.

[EDIT 2] I can also plot the step response of the control effort:

and also from here is evident that the control effort is higher.

But also I can see that both start from zero, and in particular, the blu line, so the one which identifies the mixed sensitiviy approch remains at a constant value in the step response.

Why this happens? Thanks.


texts:
Given two pumps that are similar :
$H_1=70-1.41x10^{-3}Q_1^2$
$H_2=100-1.1x10^{-3}Q_2^2$
Find the geometric scale :
$\frac{D1}{D2}= ?$
I am also given maximum efficiency = 1.
I tried solving but I got stuck I don’t know which pi terms should I use for instance:
I tried
$ \pi_{gh},\pi_Q,\pi_{\nu} $
and got stuck with hard complicated algebra.
Here is the result in the denominator it should be $Q_2^{2}$.
Left side of the lower (2nd) equation.


texts: Mechanically, is an arc stronger than a rectangle?

texts:
I was wondering, what is the strongest : a rectangle or an arc (same width/height) ?

you have to imagine the screenshot in 3D : you have 4 walls and a paved layer (the rectangle) or a dome

Reason why the rectangle would be stronger : same size as the dome but more raw materials

Reason why the dome would be stronger : the vertical pressure is directed to the walls -> Keystone

Assumptions :

the 4 "walls" are infinitely strong
the dome / rectangle has a weight negligible relatively to the force applied
The dome / rectangle is not infinitely strong, it can bend / break given the vertical pressure

EDIT

I am making a plastic box and people will walk on it (box size is size of a foot). for some reasons walls must be thin and the box must be pretty thin too and we wondered what shape is stronger / is less likely to bend in its center


texts: What is a common polarizing 50/50 beam splitter cube coating

texts:
I am having problems locating references of the typical thickness and material of the coating along the hypotenuse side of 50/50 polarizing beam splitter cube.

Does anyone know what these coatings usually are? Have references or published paper references? etc.

Thanks.


texts: Construction Entity and Construction Complex

texts:
I attend to engineering design of a new irrigation system, comprising 4 pump stations and 3 lengthy water mains between them.

Definitions by ISO 12006-2:

Construction Entity is an independent construction result of significant scale serving at least one user activity or function.

Construction Complex means two or more adjacent construction entities collectively serving one or more user activity or function.

In my case, the irrigation system must be identified as a construction complex, comprising 4 pump stations + 3 pipe mains = 7 'construction entities'.

How can I collectively and separately name the mentioned parts of the project? (In my native language those all are 'objects', however, definition for 'construction object' by ISO is something different).

Please advise, can I use the term 'entity' in English-written documents (e.g. 'list of newly built entities', 'entity # 1'), or it is better to use such terms as works, structure, facility, unit, site, plant? So that it be understandable for English-speakers in construction environment. (Note that the words used do not need to conform to ISO 12006-2; I have just used it as a reference.)

What terms have you really met and used for such cases?


texts: On modifying imported STL files in Solidworks

texts:
Some weeks ago I downloaded a  couple of 3d models from Thingieverse in STL format and I wanted to make some minor modifications before printing. The modification were:

I wanted to split a multi part STL files into separate models (I had trouble with printing all of them together)
I wanted to move a few millimeters a feature to improve (IMHO) the load carrying capacity of the model.

However, upon importing in in Solidworks I realized that I was unable to edit by applying new features based on the existing STL. (From what I recall I was not even able to remove some of the parts with a cut extrude feature). I did a little search and realised that generally STL files are not editable. (In the end, I used blender to edit the part, and I made the other part from scratch).
So my (main) question is:

Is there a procedure I can follow so that I can convert an STL file to a native sldprt file (FeatureWorks has a similar functionality but I couldn't apply it)

Additionally, I have the following bonus questions ( I can create separate post if you feel the question needs more focus) :

Is the non editability of the STL a feature meant to protect intellectual property (similar to a PDF)?
What is the concept of STL in layman's terms? Does it store, vertices/edges/faces/volumes? (I got the impression that the STL build the model by creating basic tetrahedra)


texts:
As a follow-up to How does the pressurized suspension of the Hyperloop not affect the tube pressure?, I believe (though I can't find where I read it now) that the Virgin Hyperloop One implementation will use magnetic levitation rather than air pressure. While the FAQ there has a "Speed, Propulsion/Levitation, Energy" category, it doesn't seem to address levitation explicitly.

Question: Does the Hyperloop One indeed use magnetic levitation, and does the primary levitation force require constant flow of electrical current (vs permanent magnets on both sides), and if so, would that be through copper, or through superconducting windings?

edit 1: to the first part of the question; yes it does indeed use magnetic levitation, see the YouTube video also shown here.

edit 2: You've earned the "Tumbleweed" badge (Asked a question with zero score, no answers, no comments, and low views for a week) for "Does the Hyperloop One suspension require constant current through copper windings?"


texts:
In a PE (polyethylene) foam factory there have been some incidents with static electricity that have created minor fires. Fire is a concern in such a factory, as PE is highly flammable, and even more as PE foam uses propane or butane gas in its manufacturing process (that's what creates the bubbles in the foam).

The issues we've been having are mostly related to the thinnest of the foams we produce, which is 1 mm thick. It's formed by extrusion into a flat fabric of about 1m width and we form rolls of 350 linear meters. The machine's speed is about 78 meters / minute.

The foam is rolled over cardboard cores in a torque machine (the shaft is chrome-coated steel). The plant is located in a very dry, cold place (humidity is often around 40-60% and temp ranges between 10-28°C).

I've gathered the following observations while analysing this problem:

While the roll is below 45cm in diameter, the static electricity is negligible (I don't have an instrument to measure it, I just get my arm near the roll and see if the hair is drawn towards the foam).
Once the diameter gets beyond the 45cm diameter the static is noticeable, to the point of firing little sparks (when it reaches the max diameter).
The static builds up first near the sides of the roll, even though it can be felt in the center too. All of the incidents result from a spark igniting the roll in any of the sides, never in the center.
The foam goes through a series of rolls (puller, thkcness measurment) before being formed into a roll. Most of those rolls are metallic (steel) and in direct contact with both the fabric and the chasis of the machine (grounded). I can't notice static in the fabric as it leaves this series of puller rolls.
There's static buildup no matter if the foam is in contact with the shaft or not (sometimes it moves sideways, leaving the cardboard core and "touching" the shaft).
I suspect some slipping between each layer of foam while the roll is formed (due to the shaft rotating slightly faster than the foam is fed), but I can't confirm (the mechanism is synchronized by a PLC).

My hypothesis is that the static buildup is being caused by friction of the foam with the surrounding air, at a rate that is faster than its ability to release it through the shaft (its only contact with ground).

Questions:

Shall I discard the idea that the static buildup is being caused by friction between layers of the foam in the roll (as they're the same material, theoretically they're not apart in the triboelectric series)?
Other than spraying the area (or even the foam) with any watery solution to increase the conductivity of the air, what would you suggest to keep the sparks from jolting and causing fires?

2A. If a watery solution spray is the best solution there is, what makes a good mixture?

2B. Would a metallic side plate in contact with the shaft and the side of the roll be a good, safe solution? If so, what material would you use?

How could I measure the static electricity built up into the roll to ascertain a "safe limit"?


texts: Is there a 6th equilibrium equation for a static beam?

texts: For a scholarship exam I'm taking, it takes simple enough ideas and then messes with them in crazy ways. In this question four of the equilibrium equations I'd use to solve this are linearly dependent. Is there a 6th equation I can use to get a definition answer? Is it something to do with the fact the forces are exerted by springs?


texts: Do I need to worry about increase in temperature/pressure in ultrasound cleaner?

texts: I'm building an ultrasound cleaner. The main chamber is filled with water and it is heated. The chamber is completely sealed so the pressure inside increases with the temperature. An ultrasound emitter will be added to the bottom to increase cleaning effectiveness. Do I have to worry about the temperature/pressure increasing considerably inside the chamber because of the added ultrasound energy? Are the cavitation bubble's effects localized do the bubble itself or should I expect a considerable increase in pressure/temperature inside the chamber?


texts: I found these symbols in a electronic datasheet.. Are these all logic gates? or another?


texts: What's the best way to get an ultrasonic sensor that can vary its operating frequency

texts:
Long story short I'm looking to build an ultrasonic sensor that can also be used to communicate with a seperate sensor. (So it must be able to send out a pitch around ~42kHz, but also alter the pitch so that a second sensor could listen to the output and determine an FSK signal, so I could change the output signal to 43kHz if I wanted). Optimally it'd have an operating range of around 10kHz or more (so 38kHz to 48kHz), but I'm not especially set on an particular range.

At first I was thinking I'd just buy a piezo electric speaker such as this one, but I'm unable to find a microphone that can listen to a 42kHz signal.

Next I was thinking I could just buy a prebuilt ultrasonic sensor, but the only ones I can find don't allow you to modulate the output frequency.

I know things like this already exist as the ones on cars can modulate the output frequency, however I'm unsure what the best route for me would be. (I haven't had tremendous success finding an OEM sensor that I could modulate from a car but I'm open to that possibility).

Thanks in advance!


texts: What height is needed to drop a 72 kg mass to impart a 5000g shock onto a test piece

texts:
I am trying to design a simple drop / shock testing machine.

We want to rate our products to be shock rated to 5000g.

In order to test our products to 5000g I plan on dropping a weight onto the product imparting a shock. (See drawing)

My question is; How high would I need to drop my 72 kg
weight from the test piece in order to rate by product to survive a 5000g shock.

I understand that the impulse time and distance is quite critical in the final numbers regarding the calucations. Lets say for calucation sake, that both materials were to be steel.


texts: What's the difference between Creep and Dynamic Viscous Damping?

texts:
What's the mechanism behind each phenomenon and what's the difference between them?

Why is Creep considered in the Constitutive Equation (taken as an inelastic strain) while damping is considered in the Equilibrium Equation?

I'm particularly interested in concrete structures.


texts: is it possible to achieve 1000C temperature in a cabin?

texts:
is it possible that if i have a cabin which is insulated from outside but is built with some sort of material like copper and there is a heating element of sort which is providing 100C constantly but because room is totally insulated and shut can the temperature goes upto 1000C or not ?
if it is what kind of material can be used other can copper ?


texts: Which kind of thermal oil is used in solar thermal power plants and how are they produced?

texts:
I'm currently researching some mechanisms for a simulation game, which also covers several electrical power plant options. As part of this, I'm currently looking at a solar thermal power plant, which in the first phase is meant to use thermal oil for heat transfer and storage.
Unfortunately I cannot find details on which exact thermal oils are usable in such a plant and how they are produced. I found that there are several options:

Mineral oil based
Synthetic silicon based
Biological

I checked several power plant pages, but they never go into that detail.
So I'm looking for the kind of thermal oil that can be used in this context, the chemical composition and where/how it can be produced, so I can model a rough production chain. Also it would be nice to know if that oil has to be exchanged frequently or if it can stay inside the closed cycle for a long time.
Thanks in advance


texts: How to convert 7.62cm linear motion to 150-180° rotary motion

texts:
I need to convert 7.62cm/3in linear motion from an actuator to 150-180° (150 is minimum) rotary motion. I am aware of the existence of gears, but would probe here to see if there is some simpler method. I could use rods mounted in some way. It has to be compact and rugged, however. I'd also be interested in formulas for this type of conversion. Thanks!

Edit:
I found this contraption  for microlinear precision, whilst googling for scotch yoke. Is this a scotch yoke? If not, what is it? I can probably awfulhack one of these with a file, some aluminium rods and strips. But it would be prettier if I bought one.


texts:
There exist devices (e.g. Bosch PTD 1) which measure the temperature and humidity/moisture of the room and remotely (without contact) of a wall they are pointed at.

I understand that you can measure temperature remotely using basically an infrared camera and Stefan–Boltzmann law (and making assumptions about the emissivity). I also understand that you can measure moisture in a wall by placing electrodes on it and measuring the conductance or dielectric constant.

I was wondering how moisture is measured by these devices remotely when they are typically about one metre from the wall? The device in question includes a laser, but this might just be an aid to show the area being measured.


texts: not sure how to use a signal from a sensor to make a lightbulb turn on or off

texts: I am a very new student of engineering. I am in high school. The problem is my grandpa has an obsession with checking to see if the garage door is closed. So my dad is trying to get me to develop a solution. So far I have the idea of using photoelectric tripwire sensor to sense if the door is closed. But, I have no idea how to get the signal out of the sensor and to the lightbulb, or how to get the lightbulb to receive the signal.


texts: How does the figure eight ferris wheel work?

texts:
I saw a story on CNN today about a figure-eight ferris wheel being built in Macau.

I'm curious what path the cabins take, and how this occurs. Do they actually follow a figure eight pattern? Do they move from one wheel to the other somehow?

The story has a picture with the caption

  The cabins don't actually cross in the middle. They follow a gourd-shaped track. Each ride takes around 15 minutes.

I don't understand what that means. A "gourd-shaped" track?


texts: How does the pressurized suspension of the Hyperloop not affect the tube pressure?

texts: So one of the proposed suspension systems that will be used on the hyperloop include the externally pressurized air cushions. These cushions lift (or at least help lift) the capsule and reduce drag when the capsule is in motion. Also, the tube itself is supposed to have a very low pressure. But won't 100s of capsules moving in the tube releasing significant amounts of compressed air pressurize the tube and thereby significantly increase drag? I suppose this could be solved by perpetually depressurizing the tube, but I did not see any information on it. Does anyone know how this problem was addressed or am I just missing something here?


texts: How to couple two pistons to a rotating shaft so that the piston heads move like this?

texts:
Assume two vertical pistons with their flat head facing upward.

Is it possible to couple them to one rotating shaft in a way that the position vs. time diagram gets like this? (This is one complete cycle)

Each color being representing a piston.

The equations are:

Red: $$2 \left|\cos(\pi t)\right| - \frac12$$

Blue: $$2 \left|\sin(\pi t)\right| - \frac12$$ (The first with a phase difference of $\pi \over 2$)

I think because of the Absolute values, this can not be a simple crankshaft.

Can anyone help?

EDIT:

Actually I want to get as close as possible to this diagram of motion, which is the ideal theoretical case. Maybe this can help you for a better approximation.


texts: Why only the spectrum range of radio waves can be reflected from atmospheric layers while higher ranges (Infrared-Visible Light-Ultraviolet) can't?

texts: From communication prospective why can't higher frequency ranges be reflected from atmospheric layers and what is the effect of parameters (like temperature, pressure, etc) of the atmospheric layer on reflection of waves for sky wave and space wave propagation.


texts: Can the signal reflections from seismographic surveys be intercepted and interpreted to produce valid results

texts:
I am watching the news about Turkey conducting seismographic surveys in the Eastern Mediterranean and from day 1 I have been wandering if a "listener" can record the sound produced by the survey vessel using a hydrophone array and, knowing the position of the sound source, be able to produce meaningful results? Furthermore, could the origin of the sound be worked out as well as the mapping data?
From what I understand, these vessels drag an array of hydraulic "hammers" that produce a loud sound and an array of hydrophones to record how the sound waves are reflected/absorbed from the surrounding environment. My best guess is that the sound emitted has a rich spectrum so that we can observe the level of attenuation on each frequency band (bin) in order to distinguish different materials, as well as the timing of the reflections to map the environment in 3D by measuring the delay and triangulating.
Does the location of the listener matter in the quality of the analysis? If so, to what degree?
I know that the speed of sound is a lot faster in water than it is in air wouldn't this make the area where the survey is audible from larger? And does distance from source matter more, or the amount of surrounding noise?


texts: Most non-sound-conductive materials, especially when abutting conductive material

texts: I was wondering what the most non-sound-conductive materials are, especially where those materials are abutting materials that are sound conductive.  For example, imagine a long bar or block, and sound is being conducted through one half, but the sound needs to be killed so that it doesn't flow through the other half.  What materials would be best for the latter?


texts: How can we calculate torque required to rotate the wheel (mass unknown)

texts: Is it possible to calculate torque required to rotate wheel but weight of wheel is unknown?


texts: Formula to calculate the total failure rate of a system composed by parallel components whose failure rate is described by Weibull distributions?

texts:
As per title, I would like the equation to calculate the effective failure rate of a system or branch of parallel/redundant components whose failure rates follow a Weibull distribution. I found what I need for components whose failure rate is described by an exponential distribution at pag. 394 (table 6.2.1-3, equation 1) of the book "system reliability toolkit" that can be found here.
I would like to find the analogous for Weibull distribution.


texts: When settlement criteria of a foundation is satisfied, bearing criteria is also automatically satisfied?

texts: We design the foundations to settlement criteria than bearing correct? Because settlement criteria is stricter? I mean, can there be an example where the settlement criteria is satisfied but bearing is not? Can you think of such example? If not, then checking bearing would be redundant?


texts: Finding the Shear Center for a Beam with 1 Axis of Symmetry

texts:
I am trying to solve this problem of finding the shear center for the given beam and I have found that e = 35.94 mm, however the solution that was shared with me, had the answer of 39.17 mm.
My method is to integrate the segment for each force from 0 to l, which is the length of the segment, however in the solution that was shared with me the integration for the segment is from 80 to 120 mm, which does not make sense as the the integration of q dl, is for the segment's length.
Now obviously I integrate from 0 to 40, for a total of 40 mm length but the other solution integrates from 80 to 120 mm which is also 40 mm but there integration will definitely lead to different answer and so there is ambiguity as to which method should be followed.
Any guidance would be highly appreciated.


texts: I have this aggregate gradation curve in hand, how can I say whether its gap, well or uniformly graded?


texts:
A two-stroke engine equipped with a single cylinder having a bore of 12 cm and a stroke of 50 cm operates on an Otto cycle. At the beginning of the compression stroke air is at 100 kPa, 25 ℃. The maximum temperature in the cycle is 1100 ℃ . Use the PG model.

What would the efficiency be if the clearance volume were 1200 cc?

Using the Eqn: $$1-\frac{1}{r^{0.4}}$$  I keep getting 50.2%, but Mastering Engineering is telling me I'm wrong.  Does anyone see an error with this?  I'm lost.

I have V1=6854.84 which gives me a compression ratio of 5.71239 because V2 is 1200.  I must not have the right compression ratio because from there it should just be plug and chug but I can't see what I'm doing wrong.


texts: Doubt regarding meta-stable and labile region of a supersaturated solution

texts:
I have read in a paper that the for formation of new crystals in a solution the energy released due to formation of solid from solution should be more than the energy needed to overcome solid-liquid interactions. As in the meta-stable this is not favorable, no new crystals form in the meta-stable region i.e. low supersaturation state. My doubt is, if it is thermodynamically unfavorable to form new crystals in meta-stable region then why does crystals grow in meta-stable region. In a way, it is also the formation of new crystals.

The exact lines from the text is: "The formation of stable nuclei only happens if the increase in interfacial energy resulting from the formation of a solid{liquid interface is offset by a decrease in energy released by the formation of a (thermodynamically favored) solid. At low supersaturations, the energy required to form a solid{liquid interface is bigger than the energy released upon formation of a cluster which are consequently unstable resulting in a very low nucleation rate. Only when the supersaturation is high enough, i.e. when we enter the labile region, stable solid particles will form."


texts:
I have a mini-lathe with a 500W 3/4 HP variable speed motor, that is run by a controller at two different gearings. However, even at the LOW gearing I find the torque to be a little inadequate.

Is it possible to upgrade this motor to brushless and get more torque/HP?


texts: Breaking strength of stainless steel bar

texts:
I'm considering attaching a stainless steel bar on a sailboat masthead.

My initial thought was to use a bar with a cross section of 3/8x2" and 1/4x2".  The bar will be supported for 3" of its 5" length.

What is the breaking strength if a load is applied 1" past the support?
What kind of safety margin would I have if the downward load is 2500 lbs?

Or would I be better off using rectangular channel 1" x 2" with a 1/8" or 1/4" wall thickness?


texts: LED controller to control individual RGB diodes remotely?

texts:
I'm working on a project which utilizes an iPad to change colors of individual lights in array of ~200 RGB LEDs. I have little knowledge of large-scale LED configurations and could use some direction. All lights will be on, it's only a matter of programmability to  assign a color to a certain LED in the array.

I need a controller that:

Can handle connections for iPad use over WiFi (Raspberry Pi-esque... Python is ideal)
Facilitates color-changing of individual LEDs in the array.

A design question based on the above requirements: I assume there are no LED strips where diodes on the strip may be individually controlled; am I wrong in assuming this? If not, what is the optimal wiring option?

I had a look at the Pixelpusher by Heroic Robotics, but that board seems overkill for what I'm trying to accomplish.

I'm well-versed in using the Raspberry Pi for the situation of remotely-controlling a few LEDs, but I don't think it has enough power to handle the 200 diodes I need. If I'm missing some configuration details that would make this possible, please let me know.

Thanks.


texts: Why isn't there yet such a thing as a "Minimum Life Module" standard and concept deployed?

texts:
Why are large companies not producing, selling and maintaining the concept of "Minimum Life Modules"? What I mean is a standardized "module" hosting exactly one human being, with the exterior dimensions of a normal container used in shipping and with standardized outlets for power, Internet, water input and sewer output on the outside as connectors?
Inside, it would feature standardized locations for the toilet/shower area, as well as a table for a computer and some sort of bed. Naturally, they could sell various "themes" depending on what kind of person will be living there. Somebody who never needs or uses a desktop computer could use that space for something else, etc. The important part is the form factor and standardized interfaces, allowing them to be stacked in gigantic and ultra-space-efficient warehouses indefinitely or just briefly.
Traveling would be done entirely inside of your own house. You'd be shipped with existing facilities right to the new location. You wouldn't even need to care that you're being moved, going on as usual until you reach the destination. Where you have all your stuff with you.
The doors for entering and exiting would again be standardized and very secure. They would be opened through some unique identifier on you, so you could even go to an unsafe location and still relax inside your module.
In the large areas housing these things for permanent residency, an annoying/loud neighbour can be easily avoided by simply requesting a new location. Or it could even automatically re-arrange the modules without any action needed, based on previously entered desires and preferences. Of course, they would be quite well sound-proofed either way, so it would not be a big issue.
Met somebody and want to meet?
Joe has requested to pair his module with yours. Do you accept? y

Sue and Joe, living in different areas of the country, both move toward each other without having to arrange any kind of traveling, and soon enough, their modules are synced, docked next to each other. They don't need to think about how they got there or where they currently are. They both open their doors and now they have a two-roomer house. They decide to make it permanent, so now their combined modules are moving as one.
If there is ever "trouble in paradise", they can easily go back to their own modules for a while, until they miss each other again.
In order to not feel claustrophobic, there are large "windows" in the form of flat screens which display a live view from the outside camera of the module that is the furthest away from the stack, or a selection of different live feeds or even made-up 3D world scenes such as an enchanted cartoon forest or a view of space.
It would be so much cheaper and more convenient than a normal house or apartment. I seriously lie in bed and wonder why this is not a thing yet, and when it's coming.
And please don't think I'm talking about some dystopian scenario where they have cameras and mics and spying on all their "customers". These modules wouldn't be just handed out, but had to be purchased. Still, I suppose there would be companies and maybe governments offering them for free in exchange for "telemetry".
If done correctly, however unlikely, this seems like a fantastic yet doable thing to me. And for me personally, it would solve many really serious problems at once.
Why is this not a thing?


texts: Why channel 1, 6 and 11 are best for Wifi communication 802.11n?

texts:
In 802.11n 2.4Ghz, the spectrum is varied from 2400Mhz to 2500Mhz and consists of 13 (or 14) channels, each channel having 20Mhz band width.
When I search google for best channel, all websites say 1,6 and 11 are the best channels since they won't overlap. But from my study, i found the following.

channel 1 : 3 [2, 3, 4]
channel 2 : 4 [1, 3, 4, 5]
channel 3 : 5 [1, 2, 4, 5, 6]
channel 4 : 6 [1, 2, 3, 5, 6, 7]
channel 5 : 6 [2, 3, 4, 6, 7, 8]
channel 6 : 6 [3, 4, 5, 7, 8, 9]
channel 7 : 6 [4, 5, 6, 8, 9, 10]
channel 8 : 6 [5, 6, 7, 9, 10, 11]
channel 9 : 6 [6, 7, 8, 10, 11, 12]
channel 10 : 6 [7, 8, 9, 11, 12, 13]
channel 11 : 5 [8, 9, 10, 12, 13]
channel 12 : 4 [9, 10, 11, 13]
channel 13 : 3 [10, 11, 12]

Channel 1 overlaps with 3 channels, Channel 6 overlaps with 6 channels and finally channel 11 overlaps with 5 channels.

So from my study, I conclude that channel 1,2,3,11,12,13 have less overlap interference.

Am I correct?


texts: Can boundary layer theory be applied in finite element methods as it is applied in finite volume method? i.e The flow away from the boundary is considered inviscid and solved first, then the flow inside the boundary layer is solved?


texts: I am learning about Variable Reluctance ( VR ) Stepper Motors.  As stated in my reference, they "have no detent torque."  What does this mean?


texts: Dead Load / Self Weight for ceilings & HVAC

texts:
I need to design the roof structure for a sports facility. I have no information with regard to HVAC design at this stage. Also, the HVAC may change in future. Thus I don't know what load to apply to the structure. I intend to give the HVAC and electrical engineers a weight envelope in which they can operate.

Is there a standardised list available which would give an indication of what loads I can assume for this?


texts: Dynamic Cone Penetrometer (DCP) results and correlation

texts:
I have been reading about DCP and watched a video of how it is done (the video is not in English). But there are some things that are still unclear and I would greatly appreciate some help and clarification. I have these questions:

Is there a standard number of times that the hammer must be dropped?
What is recorded after an $x$ number of hammer drops?

Lat/long coordinates of where test occurred?
How far the metal head penetrated the ground (in cm)?

What happens to that data? What does it correlate with to give us the strength of the ground? What is that strength measured in?


texts:
I have some homework question that i require some help understanding.

1) For the first question highlighted in red (referring to diagram viii), I know for sure that reactions at the supports is dependent on the length a because it determines the magnitude of moment it creates about the support and that it is not dependent on H because it is in the direction of the force(weight P) itself.

However, what I am uncertain about is the cable CE. Is this considered a two-force member in which tension at both ends will cancel each other out, hence varying the length L will not cause the reaction forces at A and B to change?

2) For internal loadings, I am guessing that it will depend on the length L, because for internal loading, we are viewing the forces at the particular point and hence varying the angle of elevation will change the Rx and Ry component of the forces that the point and that it does not cancel out.

And also, is it true that for a two-force member that is in equilibirum, the net translational forces and rotational moment will be 0 throughout the entire segment?

Thanks in advance.


texts: Is there such a material that is resistant to torque while easily stretching when under torsion?

texts:
I need a shaft that can be stretched along its length while also being resistant to torque enough to be a functional shaft (see pictures). I have a rotating sphere within another rotating sphere, hence the use of universal joints. But due to the universal joints I can't use a shaft that is long enough to slide up and down. You can see in my images where there's a shaft missing. I don't know of the existence of any rubber that is sturdy enough to withstand the torque applied while also being stretchy enough to span that gap. Perhaps there's other ways to achieve what I am trying to achieve without the use of universal joints (I am open to suggestions).

Edit:

Perhaps I could 3D print a sort of origami shaft that unfolds?

This is getting to be a bit ridiculous lol what I'm trying to make shouldn't be rocket science


texts:
I have a question please that I need help on.
Consider the chain that is draped over the sprocket with mass moment of inertia of 0.005kgm^2 about central axis. If 4kg block is released from rest from H=1, by using energy approach what is angular velocity of sprocket at H=2? Radius of sprocket is 100mm. Where H is from sprocket to mass.
Help please
I tried using WyG=1/2Igw^2+ 1/2mv^2 and got 41.76rad/s. Though, I spoke to my teacher and he said it is slightly off? But I don’t see what I did wrong?
I posted another questions as the other one is closed


texts: Can air suction be increased by consecutive pc fans in small air tunnel?

texts:
I want to make a small air filter using standard axial pc fans in order to suck smoke like that have been produced in soldering process.

But I assume filtering will make it difficult. Am i wrong? The air have to be forced through the granulated carbon filter.

I researched about radial fans which produced spesifically for this job(suction), but they have disadvantages like price, vibration and noise. They are at least 60dba. May not suitable to be used in room.

My main purpose is increasing suction of air, not the air flow. I can go with minor flow. (if my expression is not true please correct)

The question is, can a group of fan in same direction, increase the suction of air? Can it force the air to pass through carbon filter about 1-2cm thickness?


texts: Can I use household vacuum cleaner with AquaFilter as construction/industrial one

texts: I'm going to buy Thomas vacuum cleaner with Aqua filter and use it to sand walls a bit with grinder. And after finishing the decoration, use it as an ordinary cleaner. May construction plaster, putty sanding harm it? Or it is OK to use the household vacuum for small amount of grinding?


texts:
This question, in short, is: Can a gas be compressed with high pressure liquid?

As a scenario, imagine a tank full of atmospheric gas at STP. Could something like a pressure washer pump (in this case water, but generally any) liquid into the tank thereby compressing the gas inside the tank? Pressure washers often reach pressures that are quite high (easily 2000+ psi depending.) This seems like a cheap (if inefficient) way to get high pressure gas.

I haven't been able to find any material on this idea, and I find it highly unlikely that I am the first person to think this. What this indicates to me is that this is NOT a good idea but the reason is not obvious to me.

If the reason happens to do with the choice of gas/liquid, would this be solved with different materials? For instance, if the water is a problem for some reason could something like ln2 be used to compress nitrogen gas in some sort of specialized pump that could handle those type of temperatures?


texts: Force and Headloss Calculations for Three Stage Condenser

texts:
I am looking for some guidance on calculations for a natural condenser project. I am a Computer Engineering student, so this stuff is out of my range.

The fundamental question I am trying to answer is: what fan speed is required to push air through the following system to overcome head loss?

A basic mockup of the system is shown below. Some additional details of the design:

This will be installed in a greenhouse to reduce humidity and ideally collect some water for reuse.
The long, narrow rectangles represent PVC pipes of diameter 20cm (0.2m). Both pipes are identical, aside from length.
The storage tank on the bottom will collect any condensed water.

Functional procedure of the design:

Humid air (90% relative humidity, 30 deg C) will enter the pipe at stage 1. A fan will be installed to move air down.
The air will travel 2m down into the ground (denoted by the rectangle) to a storage tank at (12.7 deg C). The humid air will condense into liquid in the cooler temperature and collect in the storage tank.
The air will travel 2.5m up and return into the greenhouse (unknown humidity and temperature).

In our small-scale testing, we were able to achieve condensation using a computer fan and 1.5" diameter PVC pipe. However, we'd like to calculate the required fan speed for the full scale prototype.

We attempted to calculate head loss using equations in MATLAB, but weren't sure what the pressures would be at each stage. I understand this is a lot of info, but any guidance would be much appreciated!


texts: Heatseeker when locked on target(say a jet), follows the target until the it is hit, what happens when target is moving and changing it's direction.how does the heatseeker it's changes direction at such high speeds?


texts: Oval aeration tanks - what are they called, what are the key differences in operation to circular tanks?

texts:
Consider this overview picture of a WWTP:

In the back, you see two oval tanks with bridges and walls, separating an inner from an outer area. These are aeration tanks.

Is there a specific reason to build them like this, instead of circular, or is there a specific process that calls for this shape? I'm aware of aeration tanks with an aerated zone and an anoxic zone, built concentrically with circular tanks.


texts:
Is there any difference between resonance and flutter. Both of them are related to overlap of external excitation frequency and Natural frequency then increase in amplitude even inifite amplitude theorytically.

What is the difference between them?


texts: Can you use a flex (spider) coupler as a dog clutch in a motorbike/atv/go kart/lawn mower like setting?

texts:
My question is simple: I want to make a dog clutch system for a wakeboarding cable system and was wondering if a flex (spider) coupler could used?  The power, velocity, torque is similar to a go kart / lawn mower, atv etc.

Dog clutch:

Flex Spider Coupler (the one with a nylon/plastic insert)

Background: I am working on a unique wakeboarding cable system design which goes forward and backwards at the same speed.  The idea is to build a hybrid winch/cable 2.0 system which uses a 6.5 HP 3600 RPM engine to pull a 200 pound person 30 km/h (spool is 0.3 m radius). Ideally a system would have a neutral, forward and reverse, but forward and reverse alone would also be acceptable (with a skilled operator).

I can easily gear down to get the required speed/torque but I currently can not find a transmission/gear box which offers reverse at the same or similar speed ratioto forward.  The two options I found are a:

1/ TAV (Torque-A-Verter) Style Reverse Gearbox which has a 1:1.3 forward, 1:2.6 reverse and a neutral

2/ Planetary reverse gearbox which has a 1:1 forward, 1:1.5 reverse and no neutral.

If this is not possible, I would also be interested in alternative solutions.


texts:
I was looking for some shear strength properties of common polymers/plastics.... I have not found any usefull information yet. I know polymers aren't that linear elastic, but I expected to find some range of shear properties. I would like to use it for a stress evalution of a general cross section at shear.

Can someone help me with some numbers or tell me why it is impossible to give such figures?


texts: Is it practical to make a solar furnace for small scale metal production?

texts:
Solar furnaces using mirrors to concentrate sunlight on a small area do not produce much power - perhaps 1kW per square metre of mirror - but can reach very high temperatures. From the earliest metalworking through to the beginnings of the industrial revolution, metal refining and working was limited by the difficulty of supplying enough heat to the furnace. For a small scale operation - the sort of activity carried out before the industrial revolution - could a solar furnace have been used instead of one using a fuel (usually charcoal) and air mixture?

I'm imagining a sunny hillside with perhaps 10 to 100 polished metal mirrors, perhaps a square metre apiece, aligned by humans running about, all pointing at a small crucible or forge inside as much insulation as could be wrapped around it.

Would it be possible to use that for refining or forging?

I want to ask, over on history stack exchange, whether such an arrangement was ever used, but I thought I'd make a fool of myself asking a question over here before I make a fool of myself asking one over there. Thanks!

Edit: I did find these:

Fresnel solar forge
Woodward solar forge

I'm guessing it would have been hard to make a large Fresnel lens until relatively recently. Mirrors are much easier, they have lovely shiny steel armour in many museums, and child labour to polish the metal and align the mirrors would have been cheap in the past. The Woodward forge looks good but the blog says that it hasn't been used for metalwork. Has anyone made this work on a small scale with mirrors?


texts: How to find out experimentally without electronic or electrical instrument to measure the vibrational frequency of some type of spring

texts:
How to find out experimentally to measure the vibrational frequency of some type of spring without electronic or electrical instrument?

I am just wondering about the advance stage of the discovery of the theory of vibrations it became in the 19th century


texts: Calculating area moment of inertia for a beam with underslung plate?

texts:
In a number of designs, a beam will have an underslung welded plate attached, as shown below:

In this sketch, a symmetrical standard steel beam/column of dimensions H1 x B1, with web and flange thickness w and t, has a wider plate welded under it of dimensions H2 x B2 (with B2 >> H2, ratio around 10:1 ~ 30:1).

For simplicity, I'm only considering stiffness in the vertical plane, not torsion/eccentric/lateral loads.

An example might be, if symmetrical static vertical point loads/UDLs were applied on the plate of such a beam, at both sides, at various points along the beam's length, and one wanted to evaluate the beam's bending moments or deflection along its length, or something like that. The usual methods for loads on a simple beam would be used, but you'd need to know its area moment of inertia first.

I'm assuming one doesn't just add the area M.o.I. (or 2nd moment of inertia - same thing) of the two together, as the value of the composite depends on the positions of the two.

What's the easiest way to calculate the value for this setup?


texts: Are there any turborotonde / turboplein designs with more than four exits?

texts:
For an at-grade intersection of multi-lane roads, the "Turborotonde" (Dutch language Wikipedia article) or "Turboplein" (Dutch language wegenwiki article) is an alternative to the multi-lane roundabout:

Source: Juerd, Wikimedia Commons, CC-BY-SA 4.0

Or the larger turboplein:

Source: Rijkswaterstaat / Joop van Houdt, via wegenwiki

Both examples have exactly four exits.  In principle, I can imagine that such a design can be extended to more than four exits.  Are there any examples of a turborotonde or turboplein design with more than four exits?  What would it look like?

See also: For an at-grade intersection of multi-lane roads, what are the (dis)advantages of a "turborotonde" or "turboplein" compared to a classical roundabout?


texts:
Does the quality of a microphone affect the frequency and intensity(dB) of the sound it can pick up?

Do all microphones pick up sound as it is in real life?


texts: If I have a beam with the left end being "A" and it is fixed at that end and the right end being "B" with a roller support, would KAB=3EI/L??


texts:
I'm trying to find the best way to move a heavy weight around. Probably the best way is to put it on wheels but I don't know which physics concepts it involves so I can make a better research.

I have found about rolling force and initial force but it's still unclear for me what can I do to decrease the force needed. What I found but not sure:

Increase diameter of the wheels
Wheels/floor made of low rolling resistance coefficient
Decrease the weight (can't be done)
Good bearings

Is this correct? What about the number of wheels, moment of inertia? Am I missing something else?


texts: Determine the sign of torques for a planetary gear system

texts:
I am trying to calculate the power distribution of a planetary gear system, specifically a Wolfrom system like this one:

In order to find the output power, I need to find the torque for the rings 5 and 6. Torque and angular velocity of the sun 1 is known. Also I have all the other angular velocities. I am trying to figure out a methodology to design the free body diagram of this system.

If the positive sign is clockwise, how can I add the torque T5 and T6 to this free body diagram?


texts: Implementing a linearized differential equation in a simulink control loop

texts:
I have the following differential equation.

$$\ddot{x} = \frac{q}{m}\cdot I^2 - k_s (x+l)$$

I want to linearize it around an (unknown) point $x_0$. I know I can calculate $I_0$ by inputting $x_0$ (and $\ddot{x}=0$) into my differential equation.

$$ 0=\frac{q}{m}\cdot I_0^2 - k_s(x_0+l) \Rightarrow I_0=\sqrt{\frac{k_s\cdot m}{q}(x_0+l)} $$

I then take the partial derivative.

$$\Delta \ddot{x} = \frac{2*q}{m} I_0  \Delta I -k_s \Delta x = 2\sqrt{\frac{k_sq}{m}(x_0+l)}\Delta I -k_s \Delta x $$
$$ \Rightarrow  \Delta \ddot{x} +k_s \Delta x  = 2\sqrt{\frac{k_sq}{m}(x_0+l)}\Delta I$$

I now have a differential equation describing my equation of motion in terms of differences around my working point. This working point is not set though, and changes depending on the x value my system currently has.

My initial approach to this problem was to use a sensor that reads my x value and then simply plug it into my control loop.

(For simplicity I've set $x=p_{is}$.)

However, this does not feel like it's the correct way to do things.

This is for $x_0=0.001\text{m}$.

How would I actually go about implementing this linearized transfer function into my loop? Are there even ways to let Simulink linearize my system directly, without me having to manually linearize around a working point?


texts: How to make a panel of LEDs appear to be a single source infinitely far away

texts:
I have a square panel of 100 LEDs (a series of LED strips).  I would like to use some sort of optics setup to make this panel emit light that looks like it's from a single source at infinity.

Is this possible with a diffuser / fresnel lens type setup?


texts: Is evaporative cooling for a pool effective?

texts: Hot humid east TX; Large subdivision pool is warm ,92F. A plan is being make to cool it with evaportive spray . One data point is : dry bulb= 82.0 , wet bulb = 79.7 F. This is likely typical average of 24 hours. The cost of pump and spray may be $ 3000 ( to purchase). How much cooling could be expected ? My thought is at this high humidity it will not be cost effective but I can't put numbers to it.  My bad: by "large subdivision pool ", I mean 10,000 sq ft / 450,000 gal.


texts:
I have noob question,I dont understand why are parts made from woven carbon fiber composite stiff.

I understand that carbon fibers are strong and have high Young modulus,its stiff and strong when the applied force is tensile type parallel to the direction of the fibre,basically its strong and doesnt stretch when we use it as rope and hang some weight from it,but otherwise,its very flexible yarn.

The woven twill cloth without resin is not much stiffer when it comes to holding complex 3D shape,like car mirror for example,than t shirt or woven shopping bag.Its still massively strong and stiff under tensile load in the direction of fibre,but if force is applied in any other direction,its extremly weak and soft.

Even when epoxy resin is applied,and its cured properly,I dont understand how the carbon fiber can improve strenght or stiffness over the values provided by the epoxy which have lower tensile strenght and Young modulus than carbon fiber,but is isotropic so  its strong and stiff more equaly in all directions.

For example when making car mirror,there is not much tensile load,I dont understand how could carbon fiber improve it,why not just make it from epoxy resin only and skip the CF.When car goes fast it blows air on the mirror,its pressure/compressive force perpendicular to the woven carbon fiber surface,when it comes to perpendicular compressive force,as when crushing in hand carbon fiber cloth in 3D shape,its about as strong and stiff as pajamas.

I dont understand how this carbon fiber twill cloth that is soft and weak in every possible direction except when trying to stretch it becomes super stiff once resin was cured.I cant imagine reason why it would be any stiffer in ability to hold complex 3D shape than the stiffness of the epoxy resin alone,since when force is applied perpendicular to fibers,the fibers have practicly zero strenght and stiffness,so they cant contribute to the stiffness of the part.

Maybe car mirror is vague and unclear example,sphere is better.If I imagine carbon fiber composite sphere,I dont see how it will be stiffer against crushing force than cured resin alone without CF.Even if you tried to stretch it by grabbing left and right side of sphere,the carbon fiber will not begin to be loaded in tensile kind of way until the sphere collapsed into pancake disk shape.

Is there some "mechanism",some fundamental factor that I dont understand, that helps the cured resin to "translate" the high tensile stiffness of carbon fiber to other directions,so the cured part,such as mirror,sphere or car wheel are stiff and hold their shape against crushing,twisting forces?


texts: Is there any material that blocks a static magnetic field? So that if I put it between a magnet and a piece of metal, they won't interact with each other?


texts: Evaluating the probability of damage to a laptop computer from power surges

texts:
Power cords for laptop computers have a transformer built into them.  The power supply has a transformer that steps down mains level power to a lower voltage and rectifier that converts the current from AC at the mains to DC.

Power surges con occur for a variety of reasons, such as a nearby lightning strike.  If a damaging power surge were to occur, would the power supply prevent the power surge from damaging the laptop computer?


texts: How thick do I need to make the insulation in my homemade furnace?

texts:
(This is probably a simple question, but I've been staring at it so long I'm not sure I know how to do it any more. I have an Excel spreadsheet with like 3 different ways to calculate this, and they all give different results, so I know I've screwed up somewhere.)

I would like to build a do-it-yourself 1700-degree-Celsius (though will settle for 3000F) electric muffle furnace because I like electricity and playing with fire. I am trying to get an idea of the cost, which means I need to know how thick the insulation need to be.

Unfortunately, materials rated for those kinds of temperatures tend to both be expensive and have relatively high thermal conductivity values, so I plan to use enough high-temperature insulation to reduce the chamber temperature to about 1300C/2400F, surrounded by cheaper, lower-conductivity insulation to bring the exterior temperature down to the target. I want the inside of the furnace as large as I can affordably make it, so instead of a rule of thumb I'd like some real equations I can play with the parameters of.

The furnace will be of a front-loading box design.
The furnace will run on 120V AC, with a target power dissipation of 1200W.
For convection calculations, I am assuming a 10 W/m^2K heat transfer coefficient as this will be free-standing. I also assume room temperature is 21C and I'd like to target a maximum of 43C on the exterior surface.
My current calculations use a 12" x 12" x 8" furnace chamber, though I'll probably settle for whatever it turns out I can afford.

I am considering the following refractory materials as insulation:

Kast-O-Lite 30 LI Insulating Castable: Max 3000F/1650C, max ~0.75 W/mK
Alumina Fiberboard: Max 3100F/1700C, max ~0.45 W/mK
NC-28 Insulating Fire Brick: Max 2800F/1540C, max ~0.44 W/mK
NC-26 Insulating Fire Brick: Max 2600F/1430C, max ~0.32 W/mK
NC-23 Insulating Fire Brick: Max 2300F/1260C, max ~0.27 W/mK
8# Ceramic Fiber Wool: Max 2000F/1100C, max ~0.3 W/mK

(I'm thinking about using Satanite, ITC-100HT, and ITC-296A as coating materials, but I can't find data about how much that would improve the conductivity ratings.)

I'm also pretty new to this, so any advice at all is appreciated. (Hell, maybe I'm overthinking this, the ratings mean nothing, and I should just put "a bunch" of insulation in an see what happens.) I plan to use MoSi2 elements and a nitrogen atmosphere, and will be sintering various powdered metals, including steel. I'll be slapping a PID controller on it for controlled ramp-soak phases.


texts: Closure Pours having Differenial Elevation in Bridge Construction

texts:
Differential elevation at time of closure pours is considered a short
term concern. What are the recommended remediation techniques available to address the concern during phase construction of bridges.


texts: How to obtain strain and stress values by editing abaqus input file?

texts:
I am currently working on abaqus modeling, I am trying to find a quick way to get the strain and stress values shown in the output file.

What do I need to put in the .inp file? Does anyone know how to resolve this?


texts: Calculating the heat energy supplied by a superheater

texts:
I am answering this question:

  Steam enters the superheaters of a boiler at a pressure of 25 bar and
  dryness of 0.98% and leaves at the same pressure at a temperature of
  370 °C. Calculate the heat energy supplied by the superheaters.

The answer is supposed to be 405.51 J.

The Properties of Steam are:

At 25 bar and 370 °C: $h=3171.8\ \mathrm{kJ/kg}$

$h_{f}=962.11\ \mathrm{kJ/kg}$, $h_{fg}=1841.01\ \mathrm{kJ/kg}$

$h=h_f+xh_{fg}$

$h=962.11+0.98*1841.01=4070.474\ \mathrm{kJ/kg}$

$Q=m(h_2-h_1)=4070.474-3171.8=898.674$

What am I doing wrong?


texts: allan-variance noise terms of MEMS accelerometer

texts:
Specific noise terms are given in datasheets of MEMS sensors.
In example the specification of accelerometer contains information about random walk and in some cases the bias instability.

Both quantities are determined by computing the allan varianz and allan deviation.
The result of the allan deviation consists out of more noise terms than random walk and bias stability.

Why are only random walk and bias instability mentioned in datasheets?
Are those the terms that cause most noise?
If yes why?

One more thing:
Different noise errors are represented by different slopes of allan deviation.

Is it like a characteristic of allan deviation that different slopes occur after calculating a specific amount of overlapping clusters (groups of samples)?

Reference:

Allan Variance: Noise Analysis for Gyroscopes


texts:
I'm building a motorized standing desk and am looking into what to use for the linear actuators. I'm targeting a stroke of 450mm and a lifting force of 100kg. I found some Linear Actuator on ebay that would work but I was wondering if I could go cheaper.

If I'm using this calculator right then a for lead screw with 2mm pitch and 8mm diameter to lift 100kg I need a torque of ~114 N*cm.

I think this lead screw and a Nema 23 should work. Together that's half the price of the linear actuator.

Is that right? I don't have much experience and could easily be missing something obvious.


texts: Why choose approximation over interpolation to implement digital lofting?

texts:
Before widespread use of digital computers lofting was done using a thin flexible strip, called spline, held in place by a series of weights. This technique is a type of interpolation (curve exactly passes over sample points) using a physical analog model (minimal potential energy of a thin flexible beam).

With the advent of digital computers and CAD tools, engineers developed a digital version of lofting splines, but instead of using a similar interpolation technique they chose an approximation technique by means of distant control points called NURBS.

With an approximation approach you need to perform an iterative process to manually fit a curve to the desired path. In the field of graphic design this may not be a drawback, but in the field of engineering, where accuracy is a maximum, an interpolating approach is much more useful because you can easily interpolate smooth surfaces from a few sample points (analogous to use a lofting spline or a set of French curves). Why was this decision made?

EDIT

I clarify that this is not a question about a particular software, but on the history of the development of CAD tools.


texts: Drawing best practice and datum self-referencing

texts:
I'm in a bit of a pickle with one of the quality techns that works for us (the company) over a profile of surface tolerance. I initially submitted something resembling figure 1 (top capture) and quality came back to me saying figure 2 (bottom capture) would be better.

I've never seen ''auto-referencing'' of datum and I don't see the point because it doesn't add anything to the GD&T. I've never seen anything like this in any book, reference or drawing I stumbled upon over my (short) carreer. Are there any arguments to which practice would be best? I'm open to any source saying one way should be the preferred one.

Thanks!


texts: An electrical engineer here. Using a stepper motor for a robotic arm. A stepper motor at the base of the arm has a max holding torque of 6kgcm. The arm is around 30cm in length from this base motor meaning that the max weight that can be supported at the end of the arm is 200 grams. There are other motors along this length that the base motor has to support too. How can i mechanically increase the torque of the motor so it can support 800g to 1kg ? The max torque (6kgcm) is provided at the highest rated voltage on the electric side of things, Is there any mechanical methods to improve torque of a stepper motor without wrecking its precision/step accuracy? I've heard gearboxes increase torque but I want to know all options and find the best one.


texts: P&ID Symbol identification, unknown meaning

texts:
I'm aware that answers may vary and it really does depend on the company/country where the PID was drawn but I have checked back for the last 30 years and found no drawing legend that describes what this symbol is and was hoping someone could point me in the correct direction.

The symbol being "GOS±"