texts: How to calculate initial concentration of first-order reaction in CSTR?

texts:
(This question comes from a Chemical Engineering background, but basic Math and Programming knowledge is also required. I hope it still falls in the scope of engineering.stackexchange.com  If not, please move.)

Let's assume a (slow hydrolysis) first-order reaction of a component D in a CSTR, which is described by the well-known ODE:

$$\frac{d[D]}{dt} = \frac{\dot{V}_{in}}{V_{liq}}([D]_{in} - [D]) - k_1 [D]$$

where $[D]$ is concentration of D, $\dot{V}_{in} = q_{in}$ is input volumetric flow, $V_{liq}$ is the reactor volume, and $k_1$ is the first order rate constant. The reactant is dissolved in water and converted to two gaseous components whose solubility is practically 0. Thus, the formation rate is proportional to the reaction rate of D, $k_1[D]$.

I have put this in a small Matlab/Octave (main) script:

% Define basic parameters
V_liq   = 2500;     % m^3
k_1     = 0.320;    % 1/d
D_in    = 180;      % kg/m^3
q_in    = 40;       % m^3/d
Y_M     = 420;      % m^3/t [D]
Y_N     = 389;      % m^3/t [D]
%% Part 1: Steady-state calculation
D_steady    = (D_in*q_in/V_liq)/(q_in/V_liq + k_1);       % kg/m^3
q_gas_M     = V_liq*Y_M*k_1*D_steady*1e-3;  % m^3/d
q_gas_N     = V_liq*Y_N*k_1*D_steady*1e-3;  % m^3/d

[D_steady, q_gas_M/24, q_gas_N/24] % Second element should = 120 (m^3/h)

  ans =

  8.5714   120.0000   111.1429

Now, I am trying to validate my dynamic simulation by passing a constant feed vector. The feed occurs every hour, with the fresh liquid replacing the same amount of reaction liquid, thus maintaining $V_{liq}$ constant. (Strictly speaking, this is not a CSTR anymore, rather a semi- or quasi-CSTR.)

I have put the model equations in separate function (using a for-loop for the feed):

function resultsArray = reactorModel1(D_feed, initialValue, parameters, D_in)
    % Simulate gas production per hour with algebraic reactor model
    % Feed is solved via a for-loop

    hoursTotal  = length(D_feed);
    k_1         = parameters(1);
    Y_M         = parameters(2);
    Y_N         = parameters(3);
    V_liq       = parameters(4);
    resultsArray = zeros(hoursTotal, 3);
    t           = 1/24;

    liquid_feed = D_feed/(D_in*1e-3);

    initialValue4Model0 = (initialValue*(V_liq - liquid_feed(1))*1e-3 ...
        + D_feed(1))*1e3/V_liq; % kg/m^3
    resultsArray(1, 1) = initialValue4Model0*exp(-k_1*t);
    % Simple for-loop with feed as vector per hour
    for pHour = 2:hoursTotal
        initialValue4Model = (resultsArray(pHour-1, 1)*(V_liq - liquid_feed(pHour))*1e-3 ...
            + D_feed(pHour))*1e3/V_liq; % kg/m^3
        resultsArray(pHour, 1) = initialValue4Model*exp(-k_1*t);
    end
    resultsArray(:, 2) = V_liq*Y_M*k_1*resultsArray(:, 1)*1e-3; % m^3/d
    resultsArray(:, 3) = V_liq*Y_N*k_1*resultsArray(:, 1)*1e-3; % m^3/d
end

Which is called in the second part of my main script, where I (wrongfully?) assume $[D](t=0) = [D]_{steady}$:

%% Part 2: Dynamic calculation with constant feeding
parameters  = [k_1, Y_M, Y_N, V_liq];
t_max       = 168; % hours
D_feed      = q_in*D_in/24*1e-3*ones(t_max, 1);
initialValue = D_steady;
resultsArray = reactorModel1(D_feed, initialValue, parameters, D_in);
[resultsArray(end, 1), resultsArray(end, 2:3)/24]

  ans =

  8.5223   119.3119   110.5056

As you can see, all three components at $t_{max}$ are lower than in steady-state. If you take a look at the progression of D (figure; plot(resultsArray(:, 1))), you see it slightly decreasing over time. However, all parameters (liquid volume, kinetic constant, flowrate of feed, concentration of D in water) are the same between steady-state and dynamic simulation!

So my question is: Is there a way to **analytically determine $[D](t=0)$ ** so that $[D](t)$ becomes constant? (As stated above in the comment, I need q_gas_M = 120, since only gaseous flows are continuously measured.)


texts: In Nastran, how to ignore fatal error due to failed convergence and move on to next subcase?

texts:
At the moment the whole analysis stops when 1 subcase fails to converge. How can I keep the analysis going such that all subcases are are run, even if they all might produce an error?

I'm pretty sure there is a command for this to write in the case control section.

All help would be appreciated, thanks!


texts: How does a diesel internal combustion engine start even though there are no spark plugs?

texts: I was just wondering how a diesel engine starts, given that there are no spark plugs. How does it build up 'momentum' for that first explosion in the cylinder? Does it have something to do with the starter motor?


texts: How to compute the size of a polygon moving along non-circular guide rails

texts:
I am trying to compute the optimal (a non-optimal solution would also work) size of carts that can move along guiding rails. Each cart is connected to the rails at two points. Each cart is also connected to the cart in front of it and the one behind it. It is a closed system. The carts can be connected directly as in picture (a) or there can be some arbitrary but constant size connector between them. In the first step I am just looking for a solution that works mechanically. It would also be great to know what is the best arrangement that allows the least force.

In picture (a) I can find many solutions. However, my guiding rails have to have a shape as in (c). I can change the rails a little bit but they will have to have inside angles (red) and outside angles (yellow) as depicted.

I tried experimentally to find a working solution through simulation, but is there an analytic way to compute which size of carts could move along these rails?

I don't have a kinematics background and don't know what it is that I am looking for. Any pointer towards keywords/ papers where I can start my research would be very much appreciated. So far I am stuck at "Polygon Effect".


texts: Does P&ID have cross-reference same as electrical drawing?

texts: In electrical i usually use cross-references to identify their symbols locations, I am still yet a lot to discover P&ID. So my question is, does P&ID have this such of thing?


texts: What is the purpose of building multistage rockets, rather then packing more fuel into a single stage?

texts: Reading an article about multistage rockets (not educated at all on the topic), and from the get go it seems to assume they are used/need to be used.


texts: Why don't massive industrial shredders shred themselves?

texts:
With the huge metal shredders that can shred an entire car or a bus, they can shred parts like the axle and engine which are large solid chunks of metal, just like the massive spinning shredder blades.

So why does the car get shredded and not the shredder? Are the blades made from harder/stronger metal, or is there something about their shape that makes them stronger (they just look like large plates with notches on)?


texts: How to calculate the velocity of gas in a pipe?

texts:
I was wondering how I can calculate the velocity of gas through a pipe.

The gas, assuming ideal behavior, in a pipe (cylinder) of volume of 222.4 L has a pressure of 1.95 atmospheres and a density of 2.25 kg/m$^3$. Knowing that there will be turbulent flow, the equation,

$$V\ =\ \sqrt\frac{2\Delta P}{{\rho (4f\frac{\Delta x}{D}\ -\ 1)}}$$

can be used. However, because this is a pipe with no change in volume, the pressure should remain even, so can I plug in 2.25 kg/m$^3$ for pressure and find the velocity? The pipe length is 10 ft and diameter is 1 ft.

Also, to find density of the gas the ideal gas equation was used, relating pressure and temperature. For this gas, the temperature was 298 K.


texts: Why does 3D source potential flow only satisfy Laplace's equation in spherical coordinates and not cylindrical coordinates?

texts:
3D source potential flow is given by:
$\phi = \frac{-\lambda}{4\pi r}$.

Laplace's equation in cylindrical coordinates is:

$\frac{1}{r}\frac{\partial }{\partial r}\left(r \frac{\partial \phi}{\partial r}\right) + f(\theta,z) = 0$

where $f(\theta,z) = 0$ since $\phi$ is independent of $\theta$ and $z$.

$\frac{1}{r}\frac{\partial }{\partial r}(r \frac{\partial \phi}{\partial r}) = \frac{1}{r}\frac{\partial }{\partial r} \left(\frac{\lambda}{4\pi r}\right) =
     \left(\frac{-\lambda}{4\pi r^3}\right) \neq 0$

Thus, the 3D potential flow is not a solution to Laplace's equation in cylindrical coordinates.

Now, Laplace's equation in spherical coordinates is:

$\frac{1}{r^2sin(\theta)}\left[\frac{\partial }{\partial r}\left(r^2sin(\theta)\frac{\partial \phi}{\partial r}\right) + f(\theta,\Phi)\right] = 0$

Where $f(\theta,\Phi) = 0$ since $\phi$ is independent of $\theta$ and $\Phi$.

$\frac{1}{r^2sin(\theta)}\frac{\partial }{\partial r}
(r^2sin(\theta)\frac{\partial \phi}{\partial r}) =
\frac{1}{r^2sin(\theta)}\frac{\partial }{\partial r}
(r^2sin(\theta)\frac{\lambda}{4\pi r^2})=\frac{1}{r^2sin(\theta)}\frac{\partial }{\partial r}(f(\theta))=0$

Therefore, source potential flow is a solution to Laplace's equation in spherical coordinates. As I understand it, a solution to Laplace's equation should be independent of coordinate system, so what is going on here?

All equations for this question have come from John D. Anderson Jr., Fundamentals of Aerodynamics Fifth Edition.


texts: how to automatically add non-specified dimensions to a design table

texts: I would like to create a boss using a spline with many points, then scale it using a design table.  The catch is that I don't want to manually set dimensions (in x,y, and z) for each of the points of the spline, for adding to the table.  I would just like -all- the dimensions of all the sketches to be automatically added, if I so desire.  does solidworks have  this functionality?  I can understand that this  might result in a night-mare, but then again, it might not be so hard to group the dimensions by x, y, and z for each point on the spline..


texts: Why are tunnel boring machines not using cone-shaped drills?

texts:
The surface area of the head of a tunnel boring machine is usually flat. A cone-shaped head would increase the surface area. The question is if it could speed up the boring process.

I know that with current machines the boring process is also limited by other factors. But that is not part of the question.


texts:
I am designing an enclosure that holds a lens (clearance fit) and a photodiode on a PCB. The alignment of the photodiode to the lens must be pretty tight, thus I am using a boss on the enclosure (also a clearance fit) to position the PCB so that the photodiode is directly underneath the lens. (see first image).

How do you address clearance fit gaps when doing tolerance loops? Is it good practice to shift everything to its worst case position when doing loops like so?:


texts: Unbalance voltage mesurements from 63 kV power transformer

texts:
After testing a power transformer(pt) and closing its wiring terminals I've encountered that phase S 63 kV correct voltage and phases R and T shows incorrect voltage 32 kV.

Can any body tell why?


texts: How to raise a pole with a handcrank and have it lock in place?

texts:
Background:
I'm going to build a homemade wind turbine. It will be all fancy and rotational so that it's always pointing to the wind, so it will be mounted on a frame etc.
This will be mounted on a pole that fits vertically through the roof of a barn.

However, the place I'm going to build it for quite often experiences high wind speeds that would probably cause the wind turbine to break or get damaged.

So, I would like the turbine to be retractable/extendable. My current best idea is to have a gear system and a handcrank, with some sort of worm-gear-esque arrangement at the pole end that will use the rotational force of the gear system to raise or lower the turbine.

Questions:

How best can I translate the energy from the gear system into raising/lowering force?
Is there any way to lock the system so that the pole doesn't simply fall when I stop cranking, and can be raised/lowered safely by handcrank?
Is this idea feasible to make by hand for an amateur with no background in engineering?


texts: How do I calculate the reactions in this truss?I would usually cut in the joint where beams 5,6,7 and 8 are and calculate reactions in the two trusses that are created.How do I do that when there is a force acting on the joint?


texts: Is it possible to narrow down a portion of shaft to its 1/5 of its diameter?

texts:
I designed this shaft for my center gripper. However the slot requires to be very deep, as you can see. I want to know if it's possible to produce
this part.
The main diameter is 30 mm and the small diameter is about 5 mm.
I chose turning as the process and the material is steel.


texts: How do gapless rails deal with thermal expansion?

texts: Gapless railroads have their joints welded together to reduce noise. The lack of a gap between rail sections also reduces wear on both the track and the wheels. However, because the weld essentially produces one very long track, the individual sections have no room to expand as they get warm on hot days. What prevents the track from warping beyond usability? (Yes, I have heard of tracks warping beyond safety margins on extremely hot days, but I'm wondering about just normal expansion between normal weather extremes.)


texts: how to implement autofocus for video projector

texts:
I have a modified pico video projector that I need to add an autofocus to.
The focusing ring already has a fast stepper motor added to it.

If the focus had to be done on the middle of the projection frame I suppose I could just put a laser distance sensor in the optical path of the projection by having a 45 degree IR reflect, visible spectrum pass dichro attached after and maybe before the final focusing and zooming lens. But I want the ability to focus to any point in the frame. This requires the sensor to be able to be rotated, or if it goes through lenses, tilted in two axis. I could do that with a small gantry system with stepper motors and the distance sensor attached to it, or galvonometer mirrors that would reflect the distance sensor beam to a given point/angle, but there may be a better way or a better sensor for this I am not aware of which wouldn't require so many parts.

Requirements are ability to measure distance up to 4 meters, accuracy about at least +-5cm up to 1 meter, +-10cm after that, which I believe is not much to ask from a sensor and acceptable accuracy for a video projection focus. Measuring on shiny or reflective surfaces don't need to be supported as projectors don't project properly on those.

Having a camera and software which focuses until software finds the sharpest result would work if it was fast enough (200 ms). As I understand with this method the lens is focused until the sharpest image is detected which is slow.


texts: Calculate max deceleration without front wheel slipping (bicycle)

texts:
I am trying to calculate the maximum braking force/deceleration for a bicycle.
Note: the question assumes only the front brake is used

Free body diagram:

For dry tarmac where I know there is enough grip to get the rear wheel to lift I managed to calculate the max deceleration (result=6.8m/s^2). (this is the deceleration where all weight is transferred onto the front wheel (rear wheel will start lifting up at higher deceleration)).

From the moment equilibrium equation (using the front tire contact patch as the origin) I got the following equation for maximum deceleration before the rear tire starts lifting off (assuming there is enough grip):

I used this to calculate max deceleration in dry conditions

However I am now trying to calculate the max deceleration in wet weather (lower coefficient of friction) where the front wheel slipping should be considered as an option.

I tried expressing Nf (normal force on front wheel contact patch) in terms of a (deceleration) and got the following result:

Which when simplified results in:

With this formula I can calculate Nf

Assuming that there won't be enough grip (in the wet) to make the rear wheel lift up.. I can then use Nf to determine Fbr (braking force).
To determine maximum deceleration (assuming wheel slip occurs before rear lift up) I can use the equilibrium of forces in x-direction:

  ΣFx=0=Fa-Fbr =ma-μNf --> a=μ*Nf/m

My questions:
- Are my assumptions/calculations correct? If so: is there a better/faster way of doing this?
To check if the rear wheel lifts up or if the tire slips first I will compare the max deceleration for slipping tire scenario and max deceleration for lifting rear wheel scenario and see which deceleration has a lower deceleration value to see which scenario will happen first

When braking some weight is transferred from the rear to the front wheel, but if the deceleration is too high the front wheel will slip.
Gently increasing brake pressure will lessen the chance of front wheel slipping...

How should I go about determining max deceleration without the front wheel slipping, given a certain friction coefficient μ ?
I can calculate the max braking force without slipping for a given Normal force on the front wheel but as soon as you start braking this normal force changes due to weight redistribution and I don't know how to account for this.

Thank you very much for any input! It is greatly appreciated


texts: Efficient Gearing to Climb a Rope Vertically

texts:
I am trying to design a gearbox of sorts that would climb a rope from turning a gear (motor, handcrank, etc). The largest issue is that, while both the top and the bottom of the rope will be attached to something, I cannot predict how taut the rope will be.

I was thinking about just wrapping the rope around a large worm gear and hoping that the weight of the device itself would generate enough friction to stop the rope from slipping off, but it doesn't seem like the best solution. I also thought about using a few helical gears radially around the rope, turning them with an internal gear ring that wraps around them, but this seems like an overly engineered solution that might not even work.

Any and all input is greatly appreciated.

-Lauren


texts: Which type of sensors to analyze polluting gas from vehicle emissions

texts:
I am thinking to develop a remote-sensing applications for vehicle pollutions. In such cases generally expensive optical IR and UV devices are used because more precise. These devices are generally ready-to-use and have also a graphical interfaces and other commands plus all the algorithms already implemented while I am interested only in the sensor part of such devices.

On the contrary electrochemical gas sensors are cheaper but much less precise. Generally these sensors have a response time from 20 to 60 seconds.

Suppose I can use a less precise estimate: can environmental polluting gas (electrochemical) sensors detect emissions of a low speed passing vehicle in a semi-closed environment such as a garage to have an approximate estimation?

My biggest fear is that these sensors are too slow to detect anything, even for a low-speed vehicle in load conditions.

Alternatively do you now any optical IR/UV open-path emitter/receiver sensor to analyze polluting gases from vehicle emissions and whose (electrical) output can be analyzed by embedded devices such as microcontrollers or micro-computers?

EDIT: The pollution gases due to road vehicles are typically CO, NO, NO2 but also CO2 should be monitored. These are the gases maybe with more concern but also SO2 might be important.
The goal is to have an estimate on how much each vehicle is polluting: this estimate is not precise but it becomes important having large enough data to see for example which brand is most polluting.
This is an example of device but it is used for industrial applications.

EDIT2 Let me reply to Bart's answer because it seems to me that the topic is not really clear here.

This has already being done (from late 80s-early 90s) using NDIR and UV. You do not measure the concentration directly but rather the ratio between a pollutant and CO2 because it is assumed to remain constant with the gases dispersion (so the wind effect should be minimized).

The idea is not to get a single precise costly and time-requiring measurement but to get many cheap less precise fast measurements. In this way it is possible to guess for example which brand or model is more polluting, and also to guess if a vehicle is polluting too much. With on-board expensive tests you confirm or reject those results.

From the analysis of emissions using extra data such as model/brand, category diesel or not you can provide also other estimations.


texts: Why does reducing the amount of emissions control improve the fuel economy of a car?

texts:
In addition to power and performance, one of the reasons VW cheated their emissions results was to improve the fuel economy of their cars. Why exactly does this happen?

I'm familiar with cars and how cars work so feel free to get technical.

And a follow-up question: Where is the "sweet spot" between burning more gas per mile but having that burned gas release fewer emissions, and burning less gas per mile but releasing more emissions per gallon burned?


texts: Three switches executing the same program for SCN5 Actuator

texts:
As indicated in How to reconfigure a control box unit for an SCN5 actuator  question I want have 4 actuation programs as described below

home, 100mm travel, home
home, 75mm travel, home
home, 50mm travel, home
home, 25mm travel, home

Controlled by 4 independent switches
I want only one switch to be closed at one time, so connected signals PC1, PC4, and PC8 as follows:

Switch 1 wire to PC1
Switch 2 wire to PC4
Switch 3 wire to PC8
Switch 4 wire to PC4 and PC8

I used 2 Position  toggle switches part number 7343k713 from McMaster-carr
The programs are as follows
Switch 1
Position 1 => 0mm, program next
Position 2 => 100mm, program next
Position 3 => 0mm
Switch 2
Position 4 => 0mm, program next
Position 5 => 75mm, program next
Position 6 => 0mm
Switch 3
Position 8 => 0mm, program next
Position 9 => 50mm, program next
Position 10 => 0mm
Switch 4
Position 12 => 0mm, program next
Position 13 => 25mm, program next
Position 14 => 0mm

Question:
Switch 2, 3 and 4 all execute the program 4 (Switch 4). PC2, PC4, and PC8 are connected together. How do I separate PC4 and PC8 connecting the SW4?


texts: Need help with interpreting units of kinetics data in a scientific paper

texts:
I need help with interpreting the kinetics of a scientific paper: https://www.researchgate.net/publication/284014208_Kinetic_modelling_of_methanol_conversion_to_light_olefins_process_over_Silicoaluminophosphate_SAPO-34_Catalyst

I am trying to reproduce the reactions in table 1 using a pfr in hysys. However, I am at a loss how to interpret the kinetics data given in table 3. The units given are in (mol gCatalyst−1 atm−1 h−1) which do not make much sense to me. I thought a 2nd order rate constant should have units of atm-1 h-1. Hence, I am unsure how to input the rate kinetics data.

Any help would be greatly appreciated.

Thank you!


texts:
I'm designing a circular shaft that's going to carry a spread radial load of about 200kg and also transmit a 160Nm torque. I'm not very familiar with materials but what I'm guessing I'll be able to get at a reasonable price locally is some lower grade steel.

Replacing the spread load with a single force in the middle of the shaft I guess will look something like this

Both points A and B are symmetrical so I'm taking in consideration only half of the shaft and calculating for that.

$$T = F\ell = 200 \cdot 0.5 = 100\text{ kNm}$$

Where $T$ is the torque at point $A$ created by the force $F$.

The tensile stress on the shaft will then equal

$$t = \dfrac{T}{W}$$

Where $t$ is tensile stress and $W$ is section modulus.

For a solid circular face the section modulus equals

$$W = \dfrac{\pi d^3}{32}$$

Now I have to assume either $t$ or $d$ in order to solve. I looked it up in this table and it looks like the tensile yield strength of steel is 350 kPa so I'm taking a conservative estimate of 300 kPa for $t$.

$$\begin{align}
d^3 &= \dfrac{32(T / t)}{\pi} \\
&= \dfrac{32 \cdot (100e3 / 300e6}{\pi} \\
&= 0.003397028 \\
\therefore d &= 0.150\text{ m}
\end{align}$$

Obviously there is something wrong either in my logic or calculations because I'm getting unrealistic results.

I went ahead and calculated the torsion stress as well with this formula. I found that shear stress for steel is about 200-300 kPa so I'm again taking a conservative 200.

$$\begin{align}
d &= 1.72 \cdot \left(\dfrac{M}{\tau_{max}}\right)^{1/3} \\
&= 1.72 \cdot \left(\dfrac{160}{200e6}\right)^{1/3} \\
&= 0.0159 ~ 16mm
\end{align}$$

which seems about right.

I was thinking of getting a 20 mm diameter profile but I would rather play it safe and ask for some help instead of just assume it's going to hold.


texts: Should the temperature of a heated metal cone decrease in a plastic enclosure?

texts:
Summary

A steel cone is heated by a nichrome ribbon to 45–50 °C. I placed a Type K thermocouple over the surface of the metal to measure the heat transferred over the metal surface. The thermocouple reads about 45 to 50 °C, which is expected. The issue is when I put a plastic cap (enclosure) over the metal cone, the temperature drastically decreases.

Procedure

There is a metal cone made of mild steel.

A nichrome ribbon wire of 0.09 mm thickness is glued as a vertical strip from the tip to bottom on the metal surface of cone.

On the opposite side of the metal surface a beaded thermocouple wire of 40 awg (0.08 mm) is glued from the tip to bottom.

Both of them are placed on the metal using a superglue.

A plastic cap that has a similar cone shape is put to the metal. The air gap between the metal and the plastic structure is 0.1 mm. In this gap the Nichrome wire and a Type K thermocouple are placed.

The structure is:

plastic cap ->Thermocouple(or Nichrome wire)->glue(Superglue or Loctite)->Metal surface.

Observations

Without the plastic cap, the thermocouple measures about 45 °C after 4 to 5 minutes of heating.
When the plastic cap is added, the temperature increases up to 40 °C and struggles to reach 45 °C. The approximate time it takes to reach 45 °C is 10 to 12 minutes.

Questions

How is it possible to ensure that the thermocouple is measuring the temperature of the metal and not of the plastic?
We do not want the temperature measurement to change when the plastic cap is inserted. Is there any quick way of heating the plastic side and also getting the right temperature measurement?

I am open to any suggestions to improve this topology.


texts: Unknown metal-piece connected to the case of an iPod Nano 2

texts:
I disassembled an iPod Nano 2 yesterday and was surprised to find a round brass-coloured plate glued to the back. I didn't find any mention of it at the teardown over at ifixit.com, as they didn't cut the case in half. The back of the logic board has two contacts pressed against this plate.
Since it just seems to be a piece of metal connected to the case and is quite discoloured, I'm reminded of galvanic anodes attached to chips to protect them from corroding. Does anyone know why this plate is there?
I'm a physics teacher and this seems like an opportunity to teach my students something.


texts: How can one calculate the change in heat energy when the specific heat varies with temperature?

texts: Many materials have a specific heat which varies with temperature, especially as the temperature change grows large.  How does one calculate the heat energy that an object receives in this case?  Can we simply use the specific heat capacity at the beginning temperature or the end temperature?


texts: I have several hundred .dxf files that are all pretty simple rectangles with MText inside. I am looking for a way to, in bulk, convert the MText to Polylines (TXTEXP) without having to open each file individually. Is this possible? What are the scripting capabilities of AutoCad? I am open to any technique or software.


texts: Glue plastic to glass with chance for easy removal later

texts: I have a 3d printed (ABS or PLA) case which houses small single board computer. I want to glue it to glass (car's windshield from the inside) so that it sticks nicely and does not vibrate. However, there should be a chance to remove the case from the glass later if wanted without damaging the glass in any way. Will someone recommend suitable adhesive and removal method (heat etc.)?


texts: Brake pad materials for use against an aluminium surface

texts:
For a project that I am a part of, we are in need of a brake pad material for use against an aluminum surface without causing any damage to it. So far through my research, the only safe alternative that I have found is 100% graphitized carbon brake pads.

What type of material composition should I be looking at which provides a reasonable coefficient of friction against aluminum while also limiting the wear to the pads and not the aluminum surface? Where would I find the physical properties of such a material?


texts: Is a Transatlantic tunnel technically possible today? How feasible would it be?

texts:
The question has been surfacing periodically in the media and books over the past 100 years or so. I realize we're talking about a lot of material and work hours to begin with; the subsequent maintenance would be a nightmare. There are no power stations, nor radio towers between the continents; there is no viable way (or is there?) to build in vents along the way; the bottom of the ocean is uneven, and there's a mountain ridge in the middle; and who knows what problems would be encountered if the engineers decided to actually drill under the ocean floor all the way.

Pumping the air out might turn out to be extremely expensive. Leaving the air in might create problems for the trains: that's a lot of air in a tight space to push through.

How feasible is it? Or is it even technically possible to have a tunnel under the Atlantic?


texts: What type of resin should be used to injection mold an instrument mouthpiece?

texts: I'm designing an electronic musical instrument and need to injection mold the mouthpiece.  This is my project: Multiwind.  The mouthpiece needs to be safe to go in the mouth, opaque (preferably black), durable enough not to wear excessively if the user rests their top teeth on it while playing, and maintain good dimensional tolerances in molding.  Other manufacturers such as Yamaha and Roland make mouthpieces that appear to have these properties.  What resin should I specify for the molding?


texts: Huge gap between ceiling and floor above

texts:
I guess this question would belong on an architecture page if Stack had one.
There is a 5 story building I was in recently that had fairly low ceilings (maybe about 8 feet) and a huge gap between floors (around 6 feet). Any specific reason for this design? All the pipes and electric cables could fit into a much smaller area, so it seems like either a waste of resources on making the building so tall, or they could have added more floors.


texts: FEA: Newton-Raphson algorithm for Dirichlet BC non-linear static analysis

texts:
I have a standard non-linear static problem to solve with FEA. I am applying displacement boundary conditions only, no external force. The equation to solve  look like these:

$K(u)u=R(u)$  Eq(1)

The terms $K, R$ are the stiffness matrix and residual vector(in this case internal force vector), in any standard FEA formulation, $u$ is the field variable(displacement). The relationship between $K, R $ can be given as per standard FEM definitions, $\partial F/ \partial U=R$(obtained from Taylor series expansion).  Due to the non-linear nature, the equations cannot be solved directly, an incremental iterative approach is needed.

I am confused on how to set up the NR algorithm. All examples I see are breaking up the external load into steps, and run iterations in each step to check for the convergence $Residual=External Force-Internal Force= 0$. But I don't have an external force vector, then how should I proceed with the incremental steps? Moreover, in this case, $External Force=0$ so how should the convergence be checked in each iteration step?


texts: How are the structural properties of intentionally frozen soil determined?

texts:
Soil freezes naturally all of the time. It is at this point that dirt work usually stops.

Occasionally soil is intentionally frozen to improve its structural properties. This process has been used notably in Boston's Big Dig and the Fukushima Daiichi nuclear plant.

When soil is intentionally frozen so that tunnels or vertical shafts can be excavated, the structural properties of the frozen soil are important. It would seem logical that the frozen water would help to stiffen the soil, but how are the actual structural properties of the soil determined?

Do all frozen soils end up with the same properties? i.e. the presence of ice controls the properties.
Are the frozen soil properties related to the unfrozen soil properties in any way?


texts: What is the difference between tolerance and uncertainty in measurement?

texts: Please explain with theoretical concepts and a brief example.


texts:
I've got an elastomer, NinjaFlex, that I have been tensile testing.

I 3D printed the tensile test specimens. I made some specimens with 100% fill and no voids and some specimens with an 80% infill (with intentional voids).
When I put a side crack in both specimens, the 80% infill specimens failed later than the 100% fill specimens.

I was hoping anyone could point me in the right direction of some theory which may explain why this is happening? My initial thoughts are the crack growth dissipates into the voids for the 80% whereas the 100% has no stopping mechanism and continues straight through the specimen.

Best regards!


texts: Direction of rotation of turbulent eddies in channel flow

texts:
Suppose we have a isotropic homogeneous turbulent channel flow. We know that this flow is associated with many swirling eddies of different length and time scales. I need to know the direction of rotation of eddies.
More specifically, I need to know if most of the eddies are co-rotating, counter-rotating or there is no definite answer (randomly rotating)?

Also, does your answer change if I remove the constraint of isotropy and homogeneity?

Thanks in advance


texts: What type of material can I use to make a model used for medical ultrasound practice?

texts: I’m attempting to make a model for medical professionals to practice ultrasound guided procedures. What substances or materials would be adequate to project a picture similar to human tissue? I have a few ideas but want to pick your brains. Thank you


texts: How would I go about designing a logic circuit that multiplies two 2-bit numbers?

texts: I'm just starting to dive into digital logic and I'm stuck on making a circuit that multiplies two 2-bit numbers. I partially understand that you need to use adders but I just cant fully wrap my head around the concept. I have made my truth table and then proceeded with the K-maps, but that's where I'm stuck. Any help would be much appreciated!


texts: What makes W1 (C80U) a tool steel compared to 1080 (C80) steel?

texts: I don't know why W1 is considered tool steel, if it's a carbon steel that has the same amount of carbon as 1080 steel. ISO calls it C80U, and 1080 C80, so they are very similar. So what makes C80U so special?


texts:
The concrete slab (?) supporting the swimming pool (≈ 10 x 10m x 1m) of my building has clearly a 'belly':

I'm not sure whether this was built this way or evolved over time, however, my best guess is that after 25 years the heavy load of the swimming pool deformed the structure and even the pipes that goes right under it.

Questions

What is the technical term for this?
Is this a problem or not? Why?
Any action should be taken in order to prevent an accident?


texts: Why is "regular" gasoline standard instead of something more knock-resistant?

texts:
The standard light petroleum distillate for vehicle engines, "regular gasoline," is (or is equivalent to) some mix of heptane (C7) and octane (C8).  Higher proportions of C8 are more knock-resistant, which allow for higher compression ratios and thus more efficient energy utilization in internal combustion engines.

Don't modern refineries produce pretty much any hydrocarbon mix they want through combinations of distillation, cracking, and alkylation?

If so, then why is "regular" gasoline produced in such quantities, and why is a premium charged for more knock-resistant ("higher octane") blends?  For example, if a refinery had to produce only one light fuel distillate, couldn't it just as easily and cheaply produce a "100 octane" blend as the current "87 octane"?

Or is it actually cheaper to produce "lower octane" petrol?

Note that "100 octane" doesn't mean 100% octane, as the "octane" number of a hydrocarbon depends on its isomers, with more highly-branched isomers having more knock resistance.  So 100 octane fuel can be produced with many blends of C7, C8, and even include lighter and heavier hydrocarbons.

A characterization of the isomeric constituents of crude oil might answer this question.  For example, if crude feedstock tends to have more linear isomers, then energy would have to be put into isomerization to produce more knock-resistant distillates.


texts: How to measure the power output of a stirling engine

texts:
I'm doing a project for thermodynamics where I have to measure the power (work over time) of a Stirling engine for varying temperature differences. I don't necessarily need an exact answer (as in: ... Watt), but a "relative" measurement would also work (i.e. when the temperature difference between the hot end and the cold end is doubled, the work increases by a factor of ...).

I've thought of filming the engine run in slow-mo, and then using the RPM of the Stirling engine to calculate power, but I could not quite work out how to do this.

Any suggestions?
Thanks in advance!


texts: Nonlinear system with time-optimal control

texts:
Given nonlinear system:
\begin{cases} \dot{x_1}=x_3+u \\ \dot{x_2}=-x_2+\dot{f} \\ \dot{x_3}=-x_3+x_2 \cdot \alpha \sin(\omega t) \\ \dot{x_4}=-x_4+x_2 \cdot (\frac{16}{\alpha^2}(\sin(\omega t)-\frac{1}{2})) \end{cases}
where, $x_1...x_4$ - variables;
$f=-(x_1+\alpha \sin(\omega t))^2$;
$\alpha, \omega >0$ - constants.
Problem: make variable $x_4$ negative in minimal time
How to formulate the criterion for the optimal time?
I would be grateful for advice and help.
EDIT
There is my code, where i try to used FeedbackLinearize
Clear["Derivative"]
ClearAll["Global`*"]

Needs["Parallel`Developer`"]

S[t] = \[Alpha] Sin[\[Omega] t];
M[t] = 16/\[Alpha]^2 (( Sin[\[Omega] t])^2 - 1/2);

f = -(x1[t] + S[t] - xe)^2

Parallelize[
 asys = AffineStateSpaceModel[{x1'[t] == x3[t] + u[t],
     x2'[t] + x2[t] == D[f, t] + x3[t], x3'[t] + x3[t] == x2[t] S[t],
     x4'[t] + x4[t] == x2[t] M[t]}, {{x1[t], xs}, {x2[t], 0}, {x3[t],
      0}}, {u[t]}, {(x4[t])}, t] // Simplify]

\[ScriptCapitalF] =
  FeedbackLinearize[
   asys, {{Subscript[z, 1], Subscript[z, 2], Subscript[z, 3],
     Subscript[z, 4]}, v}];

\[ScriptCapitalF]["ResidualSystem"] // Simplify

pars = {xs = -1, xe = 1, \[Alpha] = 0.35, \[Omega] = 2 Pi*1/2, k = 100}

OutputResponse[{asys, {xs, 0, 0, 0}}, 0, {t, 0, 100}]
Plot[%, {t, 0, 100}, PlotRange -> All]

\[ScriptCapitalF]["LinearSystem"] // Simplify

\[Kappa] =
 StateFeedbackGains[\[ScriptCapitalF]["LinearSystem"], {-1, -1}]

csys = \[ScriptCapitalF][{"ClosedLoopSystem", \[Kappa]}]

sr = StateResponse[{csys, {xs, 0, 0, 0}}, {0}, {t, 0, 250}];
Plot[#, {t, 0, 250}, PlotRange -> All] & /@ %[[{1, 4}]]

I didn't succeed, a system with such an arrangement of inputs contains a singular ResidualDynamic.


texts: Is there such thing as a check valve that takes no energy from water for water to pass through? What is the name of this/these check valve type/s? I barely know anything about engineering, just have this question.


texts:
There are numerous steel alloys, containing mostly iron, carbon, and some other metals. Generally speaking, we can think of them as if they were some type of steel.

My question is: do "non-ferrous steels" exist? I am thinking of pure, non-iron metals, containing a little carbon, just as is added to iron to turn it into steel.  Or asked another way, are there other metals besides iron that are doped with carbon in order to form an alloy like steel?

In general, how does the addition of carbon affect the properties of these metals?


texts: Break loose torque calculation of lock nut against rotating/acceleating bolts?

texts: I have a Scenario where my lock nut is tightend using a prevailing torque of 14 Nm (as mentioned by the manufacturer) on to the rotor placed between bearings (But the tightening direction and the rotor rotating direction is same unfortunately). The lock nut is loosened after particular life cycle of usage as the rotor rotates with a acceleration of 1230 rad/sec and every time it starts, the sudden acceleration loosens the lock nut. Is there a simple approch to calculate a appropriate prevailing torque for this Situation so that the lock nut does not loosen up when the rotor starts accelerating towards it's max RPM of 9400 in 1 second?


texts: doubling the existent two brackets - will it help with my grape press?

texts:
Here is how the top of my grape press twists as I pull the car jack downwards (marked blue). I was wondering if adding another bracket (marked purple) on each side would solve the twist issue. Thanks!

edit

I have attempted putting such plates but made of just 1" plywood. Here they are in the image below. It made little to no difference.I think those steel plates, four of them, nicely bolted like such, could solve this problem. But where do I get the solid steel, who is going to cut and drill it for me... It might be a bit of a challenge, or maybe i can find something pre-made at the hardware store.


texts: Shouldn't brittle materials be the ones failing under shear deformations?

texts:
It is known that brittle materials tend to fail under normal stresses, that is, tensile or compressive stresses. Brittle materials often are bound together into crystals by ionic bonds between atoms, with alternating positive and negative charged atoms.

I remember also that brittle materials fail when ionic bonds between layers are broken and the layers shift, causing like-charges to move close and therefore repel each other. The above picture I found illustrates this.

But wouldn't this situation happen more likely in shear, instead of compression or tension? If we had a cube of brittle material, wouldn't a shearing stress effectively shift those atomic layers in opposite directions, bringing like charges together, just like in the above picture? But apparently brittle materials fail more likely in tension or compression, and that's why maximum principal stress failure theory is used for brittle materials. This seems contradicting to me. Wouldn't a compressive stress, for example, simply squeeze the sample of material together instead of moving its layers?


texts: How to implement wifi for a headless IOT device?

texts:
Recently I purchased a TP-Link HS100 smart plug which I configured using an app and all is working well. Now I am trying to understand the underlying software and hardware architecture for such implementation. Based on simple google searches following is my understanding.

The headless smart plug makes a peer to peer connection to a device such as a mobile phone or computer. Using a device with a UI, network configurations are entered into the IOT device. The IOT device then connects to access point to make some type of authentication with a cloud service, and establishes a connection. The mobile app communicates the commands the cloud service which relays the command to the smart plug. This is pretty straight forward.

I like to understand a little bit deeper in both software and hardware architecture for this type of design. It is fair say that there is some type of wifi device like CC3100 or similar. There is some type of microcontroller like an ARM Cortex. It could be an integrated wifi controller such as a CC3200.

What is the underlying software and hardware architecture to implement similar microcontroller based design to setup and establish a secure communication link? What type of minimum security needs to implement to secure the device? I am hoping someone in this forum has experience in such an adaptation (2.4 GHz) and is willing to share their experience.


texts: Fabrication strategy to build larger version of our ESP

texts:
Our setup https://www.youtube.com/watch?v=uKuzshqjkYA
The diesel generator exhaust is routed via our test setup. (notice the difference between ON/OFF states). Generator in test is similar spec as a 20kVA https://www.americasgenerators.com/20-kVA-Perkins-Diesel-Generator-Non-EPA.aspx

This is a project i've been pursuing for the past few months. This is to capture fumes from particle laden gas sources. (A lot of generators in developing countries aren't maintained properly, and their soot traps don't work too well).

This allows nanoparticles/pm 2.5 to be captured and segregated much more efficiently, without using any mechanical obstruction. We've also put in a self cleaning mechanical assembly inside to clean the collected particulate matter continually.

This is a lab scale build. Would like to understand how to go about building larger versions of this setup that can work on generators much larger which are a major source of urban pollution such as https://www.hindustantimes.com/gurugram/gurugram-will-get-new-air-quality-monitoring-station-to-keep-eye-on-pollution/story-xWgfUGHgLRLWjJD1FmLatJ.html

What to keep in mind while scaling our mini setup?
Should we attempt it ourselves, our rather talk to companies who might be interested in something like this and already comfortable with large fabrications.

We want to make 4-5 such setups and install it for a small pilot in Southern India where generators are used heavily.


texts: How is the slip calculated in Abaqus small-sliding interaction?

texts:
I’m doing research on the sliding of 2 fracture surfaces.

To do that, I’m trying to understand the Small-sliding deformable interaction in the Abaqus (2018), and I use the Node-to-surface discretisation method.

Specifically, I’m interested in how exactly the ‘slip’ amount is calculated and imposed to the Abaqus.

I understood the derivation, that is presented in the Abaqus Theory Manual (6.11),  where the calculation of an ‘overclosure’ and a ‘slip’ is shown:

To check how ‘slip’ is calculated I created in Abaqus a very simple example with the slip upwards of the LHS body and downwards of the RHS body:

However, the problem I have is the slip in Abaqus is quite different from the one I understand. If we analyse the lower contacting cells with nodes 13 and 168 (see picture above), then using the logic in the derivation we can decompose it to this schematics:

As in the derivation, we have slave node13 penetrating RHS body which becomes node Xnplus1. Then we draw the anchor node ‘xo’ that coincides with the normal direction from the surface of RHS body to node13. Consequently, xi node is drawn to the normal from the Xnplus1 to the face.
Also, unplus1 = xnplus1 as in (5.1.1-4) as in the manual. I understand that the slip is then the distance from xi to xo in the vertical ‘y’ direction, i.e. slip_y = 0.352.

However, Abaqus gives me slip 0.28 all various configurations e.g. small or finite sliding, instantaneous load variation, fixed 1 increment size, surface-to-surface, and all other options are similar.

I’d be glad if you please could help me to understand this.

Sincerely,
AMAN


texts: Could magnets at the RHIC be damaged like the ones at the LHC were in 2008?

texts:
In 2008, an electrical fault led to a freaky magnetic quench at the Large Hadron Collider, which in turn released a lot of helium, damaging dozens of superconducting magnets in the process and setting the LHC back a full year. Magnetic quenches happen often in particle accelerators, and helium is often released in the process, but the accident at the LHC was spectacular in scale.

A cousin of the LHC is the Relativistic Heavy Ion Collider at Brookhaven National Laboratory. Both are hadron accelerators and, of course, use superconducting magnets. The colliders are similar enough that I think they warrant a close comparison. I'm not familiar with the ins and outs of the magnets themselves, though.

Are the magnets at the RHIC as susceptible to damage as the magnets at the LHC?


texts: Basic Drilling/Production/Reservoir Engineering Terms

texts:
I am trained as a seismic geophysicist but really enjoy getting to translate what I know into what other people can understand and use for their applications, if necessary.

For those with working in and/or retain practical knowledge of Oil/Gas E&P in terms of the engineering side, what is a usable or comprehensive list of terms to know in order to read (and understand) data from my engineer colleagues? For example, I know terms such as Water Cut, GOR, etc. I want to learn more and expand this list.


texts: Measuring the level of inflation of an airbag

texts:
I want to make an inflatable seat that is electronically controlled. I am specifically looking to be able to estimate the level of inflation of an airbag using small electronic sensors. The airbag is to be filled using a DC pump, and a solenoid will be used to control exhaust.

I have used the term "level of inflation" because I am using and airbag that somebody is sitting on, so the air will be getting compressed by the persons weight and movement. This will obviously cause variations in pressure and volume. In addition, I would like to use this measurement/information to inflate the airbags to the same levels at a later date. However, I won't necessarily be starting with a completely deflated bag every time I inflate the bag to this measured level.

I hope this makes some sense - apologies if it's too convoluted. I'm happy to answer further questions.


texts: How does one define 'safe' in engineering?

texts:
What is safe and what is acceptable in the context of Engineering.

Specifically speaking we are in the process of designing a test rig which will pump water. What is a maximum safe temperature for the water to achieve without infringing employee safety. ie water at ${90}$ $^oC$ will burn so clearly that's not safe.

Q: How can I calculate/find in order to justify the value of the maximum safe water temperature to operate the test rig.


texts: Surprisingly Low Efficiency of Compound Machine [Project Help]

texts:
I'm working on a school project that requires us to build a compound machine with a mechanical advantage of 9. It should be able to lift a 10oz soup can three or more inches by using the weight of fifteen pennies. My machine consists of an inclined plane with a mechanical advantage of 3.16 (base is 12 in, height is 4 in), a travelling pulley system with a mechanical advantage of 2, and a wheel and axle system with a mechanical advantage ~3.

Here is my machine:

The total mechanical advantage should be 19, but when I put the weights on the system, it turns out that I need 45 pennies to lift the can, which means my mechanical advantage is 3. I checked for sources of friction, but I couldn't find any of note. I could add a second pulley to increase the MA, but I'd prefer to fix the problem instead of implementing a patch-up solution. Any help would be greatly appreciated.


texts: I have a cold body of constant temperature A and a hot surface several times it's area. What is the best way I can absorb the heat from that surface using A. Will sheets of metal like alluminium or copper help?


texts:
Can you offer a solution to my question/problem?
I want to extend the the length of the tongue on my trailer, for two reasons:

Allow far more clearance for turning when backing the trailer, and allow backing to be to less sensitive to turning inputs in general.
But primarily to reduce the existing tongue weight of the trailer, which is excessive.

Given that I know (physically measured with gauge) the current tongue weight of my trailer, is there a way I can calculate the percentage (%) reduction of the tongue weight per 12" (1 ft.) increase in the length of the tongue?


texts: Why is the stress distribution on concrete approximated like this?

texts:
I'm reading here on reinforced concrete. It is explained there that in calculations, the actual stress distribution is replaced by a constant stress distribution over some limited distance from the top of the beam with the value of 85% of the compressive yield stress.
But why is this approximation chosen? Why 85% of the yield stress?


texts:
I'm not a mechanical engineer and am not used to looking at mechanical drawings. I'm trying to understand what these tolerance features mean.

There is a positional tolerance feature, which references datum A. But, what exactly is it specifying? That the middle point of the flat must be within 0.1 mm of the rotational axis? Or the thickness of the disc?


texts: Estimating Potential Flow through a pipe, from tanks to outlet

texts:
I am working on a project for an amazing hot springs project in CA. As part of this project, the county is requiring that we provide our own fire suppression water. We have 3 tanks of 40,000gal each. These tanks will equally feed into a 6" PVC pipe. From the tanks, the 6" pipe will drop 172' of elevation, and run approx. 1400'  with several bends and a few 90degree turns, terminating at a fire hydrant. The county has given us certain flow requirements which will be physically tested once the system is in place. I need to estimate the flow at that hydrant before we install this expensive pipe. If the estimate is considerably over our requirements, then I feel confident enough to begin the installation. If the estimate is close or below....then I have a problem.
I understand the equations for determining flow, BUT they always need numbers that I don't have- specifically velocity! I know my pipe diameter (6"), but how can I estimate velocity? To find velocity I need flow, lol. And so on.
Any help would be immensely appreciated!

Tanks- 3 tanks x 40,000gal = 120,000gal

Tank height to top= 20'

Pipe Interior Diameter= 6"

Elevation from Tanks outlet to Hydrant= 172'

Pipe length= 1400' (including approx. 5 x 45deg turns, 2 x 90deg turns)


texts: What is the preferred composition for modern concrete bridges?

texts:
It seems that most bridge are composed of concrete, e.g in Latvia

However, concrete encompases a lot of bridge types:

  Most concretes used are lime-based concretes such as Portland cement
  concrete or concretes made with other hydraulic cements, such as
  ciment fondu. However, asphalt concrete, which is frequently used for
  road surfaces, is also a type of concrete, where the cement material
  is bitumen, and polymer concretes are sometimes used where the
  cementing material is a polymer.

Which concrete material do modern civil engineers prefer when designing  bridges over motrways less than 30 meters above the underpass?


texts: Why is desert sand not processed to make it suitable for concrete?

texts:
The shape of the sand grains from our planet's deserts is too round to be used in concrete (1, 2, 3). This is why we are drawing the last sand resources from natural beaches for making concrete for the ever-increasing human demands.

Would it not make sense to crush the round desert sand grains in a mill to produce the sand required for concrete? If we break each sphere into two fragments, the resulting grains are sharp-edged and asymmetric, with "grip".

Is it a matter of cost?


texts: How to calculate Power of motor when used as a generator?

texts:
How can you calculate how much power can be generated by a motor when used as a generator (like a motor used in a wind turbine)?

Does the power depend on how fast the magnet is rotated? If so, is there a equation that lets you know given the rpm, how much power should be generated?

Also, how can I account for limiting factors such as the strength of the magnet (moving a coil around a stronger magnet should give more power than moving coil around a weaker magnet)?


texts: How to determine the region in a state plane where the equilibrium state is asymptotically stable

texts:
I have a non-linear system shown:-

$$\dot{x}_1 = x_2$$

$$\dot{x}_2 = -(1-\vert x_1\vert)x_2 - x_1$$

How do I determine the region in the state plane where the equilibrium state at the origin is asymptotically stable?


texts: How to deal with time derivative of speed toward time in staggered grid in CFD?

texts:
In my control equation, there is a term
$$
\frac{\partial \rho u}{\partial t}+\frac{\partial \rho u^2}{\partial x}+\cdots=\frac{\partial p}{\partial x}
$$

How to discretize it in staggered grid?

For convenience, I include a picture of a staggered grid:

If u is replaced by a scalar variable like $p$, we can simply integrate it in the scalar CV and write $p_P-p_P^o$ in which superscript $o$ means old time value. However in staggered grid, we store speed at cell face $w,e,n,s$ of a scalar CV then how can we write it in discrete form?

Basically I don't know how should we integrate this equation because there are two types of variables involved.


texts: What makes crosshead bearings hard to lubricate?

texts:
Regarding crosshead bearing failure, I have read that at slow speed it is difficult to establish a lubricating film because there is an imbalance between forces due to combustion and forces due to inertia. This information is from a maker of big low speed two stroke engines used for the propulsion of ships.

I don't quite understand the explanation. How are these forces imbalanced and how does this contribute to eventual failure of the bearing?


texts: How do they get more signals simultaneously inside a node of a neural network?

texts:
Why the circuit does not freeze/lock when the signals SUM ? But the electrical signals are SUM together in what sense?
This question is about neural network circuits because I don't understand what exactly at hardware level node is it
Is a line ?
I have a wrong image in my head about node concept because I translate like point:

  if 10 machines meet at the same point or node occurs the incident, then how is adjusting the time within a neural network?

What happens inside a 'node' in artificial neural network ? Can you show me an example of hardware electronic circuit implementation about a neural network?
a neural network?

Another suggest me this image to understand but I don't see circuit

  a circuit with input terminals 10 to 10 independent signals.

But this is a line not a 'node'

I try to find a circuit for what you call 'node' about an artificial neural network. i don't understand how is implemented a 'node' with an electronic circuit


texts: Superimposing a Vector Field onto a Toroid in Matlab

texts:
I am a systems and control PhD student in Aerospace Engineering.  Currently, I am trying to create a wind shear model of a toroidal thermal "bubble" in Matlab similar to the one in this paper (shown on the last page): https://arc.aiaa.org/doi/abs/10.2514/6.2009-6112

I have figured out how to model just the toroid in Matlab thanks to this helpful bit of code:
https://www.mathworks.com/matlabcentral/fileexchange/46444-visualizing-a-toroidal-surface-torus-in-matlab

For reference, the parameters I used were r = 200, R = 201, and I multiplied the z values by 1.5 to achieve the height I wanted.

But what I want to do now is sort of superimpose a wind shear model to the toroid in such a way that it resembles the figure at the very end of the paper.  I would like to frame it in such a way that I can visualize it with a quiver3 plot so I know the field is flowing properly.  I'm just not sure how to do this, since fluid mechanics and topology aren't really my areas of expertise.

The peak airspeed inside this thermal bubble, in the center of the toroid, should be 3 m/s.  The winds in the rest of the toroid should then weaken accordingly, as in the paper.  I greatly appreciate any help I might receive on this matter.


texts:
I am currently working on a problem where I have to design a column. The structure I am currently designing currently takes the following form,

When designing the column, I know that I have to calculate what the maximum axial and bending stresses acting on the column are due to the horizontal beam.
However, one thing I am unsure of is how do I calculate the bucking load/stress for the column? I'm not sure if I can treat the column as axially loaded due to the bending moment that is applied to it by the horizontal beam. Should I treat the load due to the beam as an eccentric load to account for the moment it applies on the column?

Also, when designing the column, other than than calculating the axial stress, bending stress and the buckling stress, are there any other parameters that I should calculate?

Thank you!


texts: Meaning of SNR in Instrument Specifications

texts:
I am evaluating the specifications of an FTIR instrument (Bruker Vertex) and came across the following statements/items:

  Signal-to-Noise 5 sec sample, 5 sec reference: >10,000:1 (<4.34 x 10-5
  AU noise) peak-to-peak @ 2,000 cm-1, 4 cm-1 spectral resolution and
  standard optical components

  Signal-to-Noise, typical 5 sec: 16,000:1 (2.71 x 10-5 AU noise)
  peak-to-peak 1 min: 60,000:1 (7.2 x 10-6 AU noise) peak-to-peak Note:
  Achieved typical Signal-to-Noise peak-to peak values are statistical
  numbers which depend on the applied measurement parameters and
  laboratory working conditions.

I was wondering how this should be understood. I would assume, that in order to specify the SNR you have to state how much input the system gets.
(Sth alike: For  X mW/cm-1 coupled into the system, at frequency Y,  at resolution Z the SNR is ...  )

To me, here it appears as if this was an "absolute" value (apparently depending on integration time). Is 10'000:1 this the ratio between saturation signal level and noise i.e. dynamic range? (This would only be of limited use...) And what could the

  5 sec reference

mean?

UPDATE: I may have been misguided by what I am trying to measure (emission of light source, without reference to the reference lamp in the system). Could it be, that 10'0000:1 refers to the signal level of the reference lamp vs. the noise level? Can anyone confirm?

Regards


texts: Effect of magnetic field on electronic components

texts: Are electronic components like diodes,transistors, micro-controllers, microprocessors, wireless transceivers etc are damaged by strong static or dynamic magnetic fields? If yes, at what strength the field becomes dangerous? Also, what are the ways to protect the components against such fields?


texts: How can you maximize air flow through a sound maze in a HVAC transfer grille?

texts:
My house has several transfer grilles like this:

Except they have no baffles inside them, so light and sound come through into our bedrooms quite easily. I'd like to put in a sound maze like this to block light and sound:

My concern is that I will be restricting air flow enough to impact the HVAC system's effect on these rooms when the door is closed. Is that a valid concern, and if so, what considerations should one make to maximize air flow through a sound maze like this?


texts: How do I create a 3D helical sine wave in Solidworks?

texts:
I'm trying to place this blue helical sine wave around the helix (which I already thickened) that is wrapped around an ellipsoid but I just can't make it work. What I'm trying to create is that body which I have created first but with wavy grooves along the outer edges of the helix.
I created the helix using the helix command with a variable pitch (pitch & revolution). Then I created the helical sine wave using equation driven curve command. All I've done so far is change the parametric equations randomly because I'm bad at calculus. Also, I have to follow an equation but it is explicit and not parametric but this plot of the parametric equation almost looks exactly what it should be.
I have just started using Solidworks last week so I'm not that familiar yet with most of the commands and features. I hope someone can give me an idea on how to solve this problem. Thanks in advance.


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It seems like pitch angle could be computed from just gyro data, which uses 2 gyros.

However, isn't pitch computed from acceleration rather than gyro data?

pitch = 180 * arctan (accelerationX/sqrt(accelerationY*accelerationY + accelerationZ*accelerationZ))/PI

where no gyro data is needed. So how could a copter be balanced with just gyro data?


texts: Hydraulic linear actuators as CNC axis instead of screws

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Lately I've been watching some videos on machining and hydraulics as it always interested me.

I was toying with the idea of building a budget CNC mill with threaded rod for the axes, but the issue of backlash was bugging me.

Then I thought about using hydraulic pistons instead. If used in conjunction with a  positive displacement pump and using a large hydraulic transmission ratio the issue of precision could be sorted out, and the incompressibility of the fluid would help to keep backlash to a minimum.

I searched but found little info on hydraulic actuators for precision positioning, so I believe there's something I must be missing


texts: Thai Cave Rescue-Using trace gas detection to locate chimney entrances

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One of the potential ideas that was suggested for rescuing the Thai soccer team trapped in the cave is to locate a "chimney" or secondary entrance to the chamber where the team is trapped.  However, crews searching for this have not been able to find one that is suitable.

Suppose diver crews were to bring a rare chemical or isotope into the cave that is easy to detect in minute concentrations, and let it diffuse through the cave network.  Then, searchers on the surface could be supplied with equipment or animals that can detect this gas, and would have a way of knowing how close they are to entrances that are connected to the main cave.

For example, 2,4-dithiapentane is found in truffles, which pigs can sniff out.  So the surface team could be supplied with already-trained pigs.  However, its high mass density might make it unsuitable for diffusing through the cave network in a reasonable amount of time.

Could this be a reasonable approach to locating entrances?  What chemicals or detection methods would be suitable? Please cite a specific chemical/isotope and detection method with your answer.


texts: Is gravity included in "static pressure"?

texts: In the context of Bernoulli, does "static pressure" typically refer to $p$, or to $p + \rho gz$?


texts: Household TV remote control use Infrared rays. Infrared rays have frequency from 300 GHz to 430 THz. What is the range of frequency used in TV remote?


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What are typical forging loads for various metals and configurations? I know that the typical test for a metal is to upset a 0.750" high x 0.500" diameter cylinder to a height of 0.5", but could not find any actual tables of what kind of load it takes to do this for various metals. In theory, I guess it would actually be plot of load x temperature for each metal.

I'm mainly concerned with upsetting loads and  backward extrusion loads.


texts: Air velocity through a tunnel 5,000 feet long and 30 feet in diameter?

texts: I am an architect in need  help with an aerodynamics problem for a design that I am developing. I need  to know the  the potential velocity of air moving from one end of a pipe to the other if any with a constant  20° difference in temperature. The temperature at one end of the pipe would be uniformly 20°F colder than the temperature at the opposite end.  I'm assuming the temperature difference would cause warm air to move to the cold end. The pipe /tunnel would be 30 feet in diameter and 5000 feet in length. I am interested in using any potential work or force from this volume of air, moving due to temperature difference. Thank you for any help that you can provide.


texts: Bedload discharge for canals of triangular cross-section

texts: All the methods I know of for calculating bedload discharge are for canals of rectangular cross-section (constant depth of flow). The bedload is first computed for a unit of width (using the constant water depth) and then multiplied by the width. However, I have an almost triangular cross-section, where the depth is not constant. How can I calculate bedload discharge in this case?


texts: synchronous generator power factor calculation with missing information

texts: I am given the rated apparent power, frequency, rated speed, and rated voltage of a 3-phase wye-connected synchronous generator. Also, I know that the generator delivers the rated apparent power at leading power factor. Given the armature resistance Ra, Xd, and Xq, and the power angle, how can I solve for the power factor? Note that I am not given the real power.


texts:
Typically the word "journal" refers to a collection of written records, experiences, or transactions. However, there is a common type of bearing known as a sleeve bearing, radial bearing, or journal bearing.

The terms "sleeve" or "radial" are self-explanatory, but I'm interested in knowing more about the use of the term "journal" for this type of bearing. What is the historical (or mechanical) reason for this naming convention?


texts: Velocity and Acceleration Polygons for Mechanism

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I need to determine the velocity and acceleration of point H using vector equations and drawing a polygon. Given data is shown. $\omega$2 is 5.8 rad/s and $\phi$2 is 120 degrees

I know how I can draw both velocities and acceleration vectors on a polygon but I am clueless to how to continue after the point I reached. I found the velocity of point B by multiplying $\phi$2 and the distance of the link 2.
Since VC= VB+VBC and VC=VE+VEC, I found the velocity of point C and added it to the polygon. With that at hand, I found the angular velocity of link 6 and link 3. Since point D is also on link 6, I found the velocity vector of it and placed it on the polygon. After this point, I am clueless regarding how to obtain Velocity of point H using polygons. Any help would be greatly appreciated.


texts: Hypocycloid degenerates to straight line

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Can someone please explain if the hypocycloid described below would degenerate to a line. If possible, can someone provide an actual plot of the entire question?

The scenario is as follows:

A circle starts rolling on a flat surface. After it completes one revolution, the path starts curving up in the arc of a circle till it becomes vertical and then the path becomes vertical. During the curved part of the path, the circle performs exactly half a revolution and then completes the other half of the revolution on the vertical path. Plot the locus of the point which was initially in contact the ground.

EDIT:
The problem is 2-D. Everything happens in a plane (I've copied the question exactly, except the original asks you to plot on paper). By vertical, it actually means upwards, parallel to the vertical edge of the paper and similarly for horizontal.


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Background
I am working on a project that involves heating air inside a small box, then measuring the temperature over time.  The purpose of the box is to be a basic test chamber for PID experiments.

Initial Test
I made a 10 cm * 10 cm * 10 cm box from 3 mm plywood. I then placed a small ~1 W heater inside with a temperature probe and observed the temperature rise... very slowly.

Proposed New Prototype
I am going to construct a new prototype once I decide how to calculate the approximate time to warm the air inside the box to a set-point.  Some specifications and assumptions are laid out below:

The ~1 W heater consists of 4 parallel 100 ohm resistors and a 5 V power supply (there is also a 330 ohm resistor and an LED for visual indication).  I don't want to change this heater design, as the intention is that this is easy to replicate and uses readily accessible 5 V power sources and electronic components.
Currently no fan has been used but I have a small 20 mm, 5 V fan on order, so will integrate this into the design at some point.
The box will be used at room temperature between 21–23 °C
Ideally a temperature rise up to 30 °C (or more) would be possible over a 5-10 minute time interval
The new proposed box size is 5 cm * 5 cm * 5 cm, 8 times smaller than the previous prototype.  This is open to change depending on the previous 2 requirements of maximum temperature rise and time taken to achieve that change.

I am not after exact timings - I am aware that losses through the box will have an effect. But if this effect is minimal, then a simplified approximate solution is preferable as some design parameters may change slightly.  I am looking for any guidance and calculations that will save me time instead of having to make different boxes and learn by trial and error.


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Question:

what i thought; see below.

we do not know density if i where to use that formula on the image file .

and i a m wondering why i was given the Reynolds number .

need help.


texts: Decreasing the circumference of a generator shaft

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I know that torque is proportional to RPM and vice versa, but id like to know why we cant just decrease the circumference of a generator shaft in order to compensate for increases in torque.

In other words, if the power input is held constant, will decreasing the circumference of a generator shaft increase RPM without decreasing torque? If not, why not and what happens? Im looking for reasons other than the laws of thermodynamics.


texts:
In the textbook : Electric Power Principles, in Chapter 1

on the working of a pv cell :

  The source current Is is the result of absorption of photons in
  sunlight that cause separation of valence electrons from their atoms.
  The resulting hole/electron pairs fall across the high field gradients
  present at the diode junction.  Because any voltage resulting from
  this current tends to forward bias the actual junction, the voltage
  available is limited

I don't understand the train of thought leading to a limited voltage, and I'd appreaciate a better explaination or a reading recomendation.


texts:
I have questions about a well pump application I am working on. It consists of a well that with a submersible pump that fills a reservoir tank. As far as I know, the tank is not pressurized. Here are some values associated with the system.

Static well level = 39 ft
Tank Discharge level = 28 ft
Well drawdown = 67 ft

A couple of questions I have are listed below.

Am I correct in assuming that the static head requirement for the system curve is 67 ft?

Drawdown is  a function of flow, so it's considered dynamic head. I keep on getting tripped up on the difference in suction vessel and discharge vessel pressure, though. The well is open to the atmosphere so there is no suction "vessel" pressure, but the tank is closed and so I keep on thinking there might be discharge vessel pressure, but if the water is releasing into open space and then dropping to fill the tank, wouldn't this also be atmospheric pressure, unless the tank is pressurized? Appreciate the assistance.


texts: Definition of stiffness for structural dynamics: How would you find the stiffness of an unusual beam directly?

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I have a structure which is essentially a curved beam (not an arch or anything simple) which I have modeled in microstran/spacegass. It looks something like this:

Or for something more simple, imagine I have a beam like this:

The definition of stiffness as I know it is: k = F/d

ie the stiffness of a structure in a direction is proportional to the Force applied to the location divided by the deflection of the structure at that location due to that force.

However in the case of these structures, the stiffness will vary depending on the direction I apply the load.

I have applied a downward load of 1 N to the center of each of the 'arches' and they deflect accordingly. However, they obviously deflect differently (in magnitude) when I apply an upward load at the same location. Note: I am doing a non-linear analysis.

So which is the correct deflection that I need to use in my calculation of k = F/d?

I am using this stiffness for structural dynamics purposes, I am trying to find the natural frequency at that location. The structure will therefore vibrate in both the upward and downward direction.

My initial thought was to apply a load of 0.5N in both directions and add the deflections. Would this be correct?


texts:
I was reading some documents that said
25 wt. %, 500 mlL-1
as well as
20 gL-1

I think 25 wt. %, 500 mlL-1 is referencing 25% weight of 500 ml of water so that would be 125 ml of water

20 g*L-1 would be 20 g per liter but since the reference is 500 ml then I should reduce this formula to 10 g to fit the 500 ml.

Is that correct?

$$\text{NiSO}_4\cdot6\text{H}_2\text{O}\quad\left(20\ \text{g}\cdot\text{L}^{-1}\right)$$
$$\text{NH}_3\quad\left(25\ wt.\%,\ 500\ \text{ml}\cdot\text{L}^{-1}\right)$$


texts: Timing belt transmission with lateral pulley movement

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What is the correct way to allow for lateral movement of a timing pulley in a transmission system?

For example, there are four pulleys, one of which has to move up and down.

Is there standard practice for this sort of arrangement?  Or an alternative that would allow the the large central pulley to move up or down.


texts: Matching up cam lock or cam and groove coupling

texts: I am trying to select new hose cam locks to connect to cam locks on an existing pipe system. There seem to be a lot of different types of cam locks as I've searched for them, so I am unsure how I distinguish between them. Are there different swages, groove radii, or other variables that I need to measure so I can match up new cam locks, or are cam locks all the same and only vary by diameter? If there are measurable variables, is there a chart available that lists these variables (e.g. like the charts for measuring steel C-channel weights)?


texts: Finding the right worm gear for a wormscrew that didn't come with technical specs

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I bought a CNC linear rail guide slide from ebay(seen here). I'm trying to find a proper worm gear to mate with the wormscrew. There is no technical specification that came with the kit however on the wormscrew. I've manually measured the pitch of the wormscrew to be 2mm(12.7 threads per inch).

I'm looking at this site's catalog, but I'm just not sure what minimum measurements of the wormscrew I need in order to find a proper gear that fits. I just need to keep track of the number of turns the gear makes. I don't think I really care about the gear's quality class, gear ratio, bore/hub config. I just need it to fit the worm. Am I correct to assume the module(pitch) of the gear also needs to be 2mm? Do the pressure angle, lead angle, and number of teeth affect the fitting of the gear onto the worm?

I've seen suggestions online that I should just take the kit to grainger or mcmaster and ask for a proper gear that fits, but I'm not near either of those places.


texts: Natural age hardening of aluminium 6082-t6

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I've been looking at using Aluminium 6082-T6 structures in impact energy absorption mechanisms. I planned to do some material testing, made specimens for testing then was distracted with another project for about a year. When I finally tested these specimens they broke in a surprisingly brittle manner with a much higher than expected proof stress.

I'm wondering whether 6082-T6 is an alloy that age hardens at room temperature as one of the technicians suggested this as the cause. If so, does anyone know of any studies into this phenomenon?

This is would be rather important for impact energy absorption as increasing proof stress can result in higher risk of fatality.


texts:
Given an adiabat turbine with state 1 fluid data as:
$$h_1 = a$$
$$p_1 = b$$
$$t_1 = c$$
and state 2 data fluid data as:
$$h_2 = unknown$$
$$p_2 = e << b$$
$$t_2 = f < c$$
$$h_2' = g$$
$$h_2'' = h$$
With kinetic and potential energy small enough to be ignored, a steam content of $x_2 = 0.965$
What is the technical work $w_{t,12}$
With the equation:
$$h_2 = h_2' + x_2(h_2''-h_2')$$
The specific enthalpy of $h_2$ can be easily solved. Now taking the first Thermo D. law, and using an energy balance, the technical work can be solved via:
$$W_{t,12} = \dot{m_{in}}(h_1 + \frac{c_{in}^2}{2}) - \dot{m_{out}}(h_2 + \frac{c_{out}^2}{2})$$
Whereby $\dot{m_{in}} =  \dot{m_{out}} = \dot{m}$
Atleast, this is what I had thought though I am missing $c_{in} \text{ and } c_{out}$, when checking the solution, it is suggest the specific work is solved "simply"
$$w_{t,12} = h_1 - h_2$$
Whereby the mass velocity and fluid velocity are unneeded.
My assumption in this solution, is that the author assumes $c_{in} \text{ and } c_{out}$ are equivalent thus equal zero in the equation, but I fail to see how $W_{t,12}$ can be divided by the mass velocity $\dot{m}$.
What am I missing compared to my assumed solution and the authors, where should I have understood that $\dot{m}$ is not required.


texts: What's more energy efficient: fewer air conditioners working at max capacity or more working at part capacity?

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The central heat and air in the house I'm renting is unable to keep the house below 80 °F during the hot summer here (100 °F days).  We've had 3 HVAC techs out to look at it and they all say there's "nothing wrong with the system" and that it's "sized appropriately."  The latest said perhaps it's just a combination of small factors (old house, leaky windows, etc.).

The property owner is going to provide me with two window units to use - one in the bedroom and one in the living room.  Would it be more efficient (in electricity cost) to turn off the central AC entirely and rely on the window units, or better to run all three systems?


texts: Simple steel column buckling calc - where am I going wrong? (Eurocode)

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I'm trying to follow an example of this, but I get a wildly different answer than expected and I can't see where I'm going wrong.

The example I've got, is for a 2.8 m steel column (RHS 150 x 100 x 5mm) fixed both ends with a simple static vertical central load. Couldn't be easier for a beginner. My calculation is:

Relevant properties (section properties taken from [here][1]) normalising length to metres:

Steel section: RHS 150 x 100 x 5mm. (unspecified hot or cold)
L: Free length = 2.8 m
E: 205 x 109 = 2.05 x 1011
I (table): Least 2nd moment of area = 3.923 x 106 mm4 = 3.923 x 10-6 m4
A (table): Area = 2373 mm2 = 2.373 x 10-3 m2
r (table): Least radius of gyration (as double check): 40.7mm = 0.0407 m
K: Effective length factor = 1 (fixed-fixed)
s: Slenderness = L/r = 2.8/0.0407 = 68.8 (intermediate)

EUler buckling force, calculated using I,K,L:

π2 x (E.I) / (KL)2= (3.1422 x (2.05 x 1011) x (3.923 x 10-6) / (1 x 2.8)2= 1.012 MN

Euler buckling force, calculated using A,s (as double check):

π2 x (E.A) / (s2)= π2 x (2.05 x 1011) x (2.373 x 10-3) / (68.8)2= 1.014 MN

So the two calculations agree within the limits of the data table figures.

The problem is, the correct answer is apparently Pc (compressive strength) = 124 N/mm2 = 294 kN.

The answer does confirm that slenderness is 68.8, and that the least radius of gyration is 40.7 mm, so I know I'm on the right track.

But there's no actual full calculation, and the error isn't an obvious factor that might suggest the problem, so I don't actually understand where Ive gone wrong.

(The actual question is part of a longer worked example, so if I get stuck anywhere else I might need to update this. But for now, that's the point I'm stuck at... )


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basically I am trying to build an oven that we are going to use to cure prepreg carbon fiber. I found a company that can make it but they are requesting the termal load in order to continue.

This is the information I already have:
Dimensions of the oven: 23.7in x 59in x 59in (height, width, depth)
Desired temperatures: max 284F, min 158F

I have found the formula to calculate this, but honestly, I don't know how to begin:

q = -k A dt/dx
q = heat transfer rate, Btu/hr
k = thermal conductivity, Btu/(hr-ft-F)
A = area normal to heat flow, ft^2
dt/dx = temperature gradient, F/ft


texts: What exactly makes reaction turbines work?

texts:
I was reading about reaction turbines on Wikipedia, it says: "Reaction turbines develop torque by reacting to the gas or fluid's pressure or mass. The pressure of the gas or fluid changes as it passes through the turbine rotor blades."

I understand the working of impulse turbine by utilisation of kinetic energy, but this confuses me. Can anybody explain?


texts:
Consider an electronic device, say wifi dongle. it is inside a wooden box. It may be a) powered up or b) without any power supply.

Is it possible to damage it to render it dysfunctional without damaging the box?

I believe this can be done using 1)Electromagnetic waves, 2) Static electric field and 3) Oscillating electric field.

Let us consider these options one by one. 1) Powerful em waves will induce large electric fields in the antenna and conductors. This may damage the subsequent electronics. What power and frequency is enough for the purpose? 2) Static electric field should induce voltage ascross conductors, resulting in damage. Is this correct? What field stregth is enough? 4) Oscillating electric field should be more effective than static one. What field strength and frequency are enough?


texts: What is the linear strain for given lateral strain?

texts:
So, I am trying to calculate the linear strain of a shaft which is under plastic deformation in yielding region.
The diameter is changing from 2d to 1.5d
I'm assuming that the volumetric strain is zero.$(\epsilon_v=0)$ or in other words $\mu = 0.5$
Now, I've tried the following two methods and I'm getting two different answers:
Method 1
$$\epsilon_v = 0 \\ \Rightarrow \epsilon_l + 2\epsilon_d = 0 \\ \Rightarrow \epsilon_l = -2(\frac{1.5d - 2d}{2d}) \\ \Rightarrow \epsilon_l = 0.5$$
Method 2
$$V_i = V_f\\ \Rightarrow \frac{\pi}{4}d_i^2l_i = \frac{\pi}{4}d_f^2l_f\\ \Rightarrow \epsilon_l = \frac{\Delta l}{l_i} = \frac{7}{9}$$
Where $\epsilon_l$ is longitudinal strain, $\epsilon_d$ is lateral strain($\bot$ to longitudinal direction), subscripts $i, f$ refer to initial and final conditions respectively.
All the strains are engineering strains only.
Now ideally, both the methods should give same solution.
Where am I going wrong?


texts:
I am designing a gearbox and wanted to know whether the key on the shaft and gear must fit exactly with the bore in the gear and keyway in the shaft.
Ex. If there is a key that is 3x3 mm, and does the shaft have to have a 1.5mm keyway and must the bore in the gear be 1.5mm? This is with respect to the key face not length, but also should the length be spec'd so that the measurements for the key and key way are the same?


texts: Designing the pivot point for a swingarm

texts:
I came up with the following design for a single wheel trailer:

The shock absorber is missing in this drawing.

What is the best way to mount the swingarm to the horizontal plate? It needs to pivot.

I was thinking about pillow blocks, but I'm not sure if they are suitable for this application. Design should be as simple as possible and easy to fabricate.


texts: What mechanism can make a wheel turn in discrete steps?

texts:
I want to make a wheel that behaves pretty much like a mouse wheel does — when you rotate it with your finger and release, it rotates back or forward by itself to match a nearest discrete position.

What are the common ways to do so?


texts: Why Silicon can be used in many engineering materials like oil (Silicone oil), grease, caulk, rubber(PDMS), resin? What property of Silicon allows so?


texts: What is the convention for the origin coordinates of a CAD drawing?

texts: Is there a convention to use (0, 0, 0) as the center of a CAD drawing? If so, why? Wouldn't it be easier to use (0, 0, 0) as the bottom left corner and start drawing on the positive coordinates?


texts:
If I already have a small DC axial 2m3/h fan blowing air at something, what will happen if I add a larger more powerful 6m3/h DC axial fan blowing from behind that one (i.e. its the larger fan first, then then smaller, then the object to blow air at)? Will the smaller one just hinder the airflow from the first, or are their outputs cumulative?

Many thanks!


texts: How can we control the output temperature of a multi-input single-output pipe air-flow system?

texts:
I am trying to optimize the heat control of a test bench at our facility. The test bench is basically a pipe with an air flow that can be heated up to desired temperature. To heat the air flow up, three heat zones are available as shown in the sketch below. Measurements of the temperature are available for $T_1, T_2, T_3$ and $T_4$. The three zones are each equipped with there own PID controller, so it is possible to set target temperatures for each zone. However the single temperature states obviously affect the values of each other, especially in the direction of the flow, but also slightly in upstream direction via conduction in the pipe material.

The ultimate goal is to set a target temperature for $T_4$ and control the three heat zones accordingly.
Right now, basically, only the PID controller of the second heating zone is used for the temperature control. Ideally I would like to use all three heating zones. The PID controllers of the heating zones could either be used to do so or just set to a static gain and building a control on top of this.

What is the general strategy to get such a MISO control set up?


texts: How do I compute the force required to pierce HDPE?

texts:
I have a $2\text{ mm}$ sheet of HDPE at $280-320^{\circ}\text{ F}$. I want to pierce the skin of this sheet with a $2\text{ mm}$-high pin with a surface area of $3.33\text{ mm}^2$. The pin is also made of HDPE and has cooled completely. With the Young's modulus of HDPE being $0.8\text{ GPa}$, how much force do I need to apply to have the cooled HDPE pin reach the molten layer of the HDPE sheet at $280-320\text{ F}$?

UPDATE: I've been told that the pin is supposed completely weld to the layer of HDPE.  Based on the melt temp of the HDPE and the starting temp of the pin, I just don't think its possible in the 2 minutes before the material is quenched.  I've attempted to figure out the rate of heat transfer, but can't find the thermal contact conductance coefficient, or the thermal contact resistance.  Searching online turned up a tool "CoCoE.exe" but was having trouble running the program on my computer.


texts: use of grinding wheel cutter instead of cold saw cutter

texts: We have a 3" pipe mill, in which ERW pipes are cut with the help of 18" cold saw cutter to cut thin section pipes. Can we use grinding wheel cutter instead of cold saw cutter? cold saw cutter are vary costly. pls suggest some substitute for cold saw cutter if any.


texts: Quicker way to weld hexagonal nuts in honeycomb pattern

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I am currently designed a structure that require hexagonal nuts to be placed side by side in honeycomb pattern, welded upon sheet. Other than doing it in old-fashioned way, is there any way/technique/machine/tools i might have missed to achieve the goal quickly?
Thank you in advance for your input, really appreciate any


texts:
I am having issues building a recreation of Focaults Pendulum (basic, inexpensive, undergrad project). At this point, I am going to purchase aircraft cable or suspension cable unless someone can recommend a slightly flexible rod.

I am going to use a 32oz plumb bob because I can't find a symmetrical spherical bob unless someone has suggestions. Last, if anyone has any recomendations on a frictionless or low friction pivot (360 degrees and pendulus) that would be amazing.


texts:
I am working on a project and I am defining the torque specs. I used the initial torque spec as a baseline and then went out on the floor and tested it using multiple torque wrenches.

The components I am testing are thyristor/diode modules.

It calls for 45 in.lb to heatsink and 26 in.lb to terminals. Even backing off with the the 15% allowable tolerance, I am below the low end of 38 in.lb to the sink and it feels like its about to shear. I am encountering this with all the components I am testing.

Question

Are the torque values I found through empirical testing sufficient? Should I be confident in applying them to a standard?

Also, I am assuming the quality of screw, type of material the sink is made out of, all effect how much torque should be applied?


texts: How good are graphene layers at shielding against ionizing radiation?

texts: I assume every materials laboratory has ways to test properties of new materials. Has anyone ever tested graphene's properties at shielding ionizing radiations? I guess It could be a good candidate due to tight packing of atoms


texts: How do I find the impact pressure of cavitation due to implosion of a super critical fluid bubble?

texts:
I have solved the Rayleigh-Plesset equation for a time varying bubble of a super critical fluid. I am trying to find if the impact pressure caused by SCF bubbles is lesser as compared to that caused by water bubbles. Here is the equation I arrived at:
$$
 x x'' + \frac{3}{2}(x')^2 + A\frac{x'}{x} = W
$$

Here $A$ and $W$ are constants that depend on the viscosity, temperature and specific heat of the fluid continuum. I have used Weierstrass' elliptic function to find an analytical solution for this second order, nonlinear equation. I have used the Chapman-Enskog theory for finding the viscosity of the SCF and its distribution.This is the equation I arrived at:
$$
  \boxed{
    R \ddot{R} + \frac{3}{2} (\dot{R})^2 + \frac{4\mu_0}{\rho_L}\left[1 + b_0 \rho_L \left(\frac{1}{y} + 0.8 + 0.7614\right)\right]\frac{\dot{R}}{R} = W
  }
$$
where
$$
  W = \frac{\exp(\gamma)\left(\frac{p_2}{4} - 1\right) + \frac{p_2}{4} + \frac{p_c}{2}}{\rho_L} \,.
$$
My question is how do I go about finding the impact pressure of such a system? And how do I model their distribution by a mathematical distribution?

Impact pressure in general would be $$\frac{P_{t}}{P}=\left(1+M^{2}\frac{\gamma-1}{2}\right)^{\frac{\gamma}{\gamma-1}}$$, for isentropic flow. $P_{t}$ is the total pressure and $P$ is the static pressure; the impact pressure is $$P_{I}=P_{t}-P$$. M is the Mach number and in this case it would be <0.8 as the bursting of a bubble in a fluid would be subsonic.$\gamma$ is the ratio of the specific heats.


texts: One of the criteria for getting an engineering license is working under a licensed engineer for a period of time. This seems like a chicken-and-egg problem. How were the first engineering licenses issued?


texts: How to Derive the Differential Form of the Contintuity Equation

texts:
The book "Gas Turbine Engineering Handbook" by Boyce, on p.  117 states, the continuity equation,
$ \dot m = \rho A V $,
has as its differential form,
$ 0 = \frac{d\rho}{\rho} + \frac{dA}{A} + \frac{dV}{V}$.
How did the second equation get derived from the first?


texts: Help me build a mechanical gizmo involving a pulley (I think)

texts:
Electrical engineer here. I'm looking to build an incredibly simple mechanism that in my mind involves kind of a pulley. Below is a diagram.

So it's essentially like a mechanical servo. I would like to be able to pull something, and cause another body (attached to an arm) to rotate. However, I don't know what kind of mechanism or part I need.

I want to build this. And I'm talking real simple here - like household items (popsicle sticks!) or hardware store (though I do have access to a 3d printer).

Any ideas would be thoroughly appreciated!


texts: What are the solutions to water problems in a retaining wall

texts:
What are the construction procedures that allow the mitigation of potential problems due to water in a retaining wall?

To be more specific: I'm talking about reinforced concrete walls.

The cases of water are: if I'm studying a reinforced concrete wall such that the soil is not saturated, and it rains so that the soil is saturated or if the water table level rises.

What are possible solutions? I'm looking for general solutions.


texts: This is a clevis made for linking the tie-rods to the steering rack. This part is under dynamic loading and is getting loosened. We tried using jam nuts but it did not work well. Due to loosening the thread came out of the rack and the part fractured maybe due to bending fatigue.


texts: Advice on Literature pertaining to transient pipe flow with heat transfer and friction

texts:
For a project I am working on I need to model the flow of argon in a long pipe. The flow is transient in nature since the tanks and regulator from which it enters cause the mass flow to change. Moreover, it reaches low temperatures due to the Joule-Thomson effect. Hence convective heat transfer from the pipe to the gas occurs.

Any recommended literature would be much appreciated.


texts: Keeping resonant oscillation of a pushchair to soothe a baby

texts:
I just came back from a walk with my 4-month-old. He's sleeping in his pushchair. I am sitting next to the push-chair and slightly pulling the pushchair's side so it gently rocks from side to side in it's resonant frequency. This motion is what keeps my son asleep. I estimate that I am keeping about 2.5 Hz oscillation with amplitude around 10 mm, my finger is pulling with force around 2 N each cycle. The oscillation is damped a lot.
So I am sitting there, keeping the oscillation going, thinking... How to automate this? What device could be pulling the pushchair so I can make myself a cup of tea?
As a fun challenge, will you help me find/design a device to do this?
Constraints:

Electro-mechanical, may have a micro-controller
Has to be easy to tune the frequency. Or even better find it itself.
As a bonus it could adjust to a range of amplitudes
It has to be safe = not produce massive G-forces
Preferably it should be pulling a string or rope that I will fix to a wall.
A prototype has to be pulled off by me:

off-the shelf parts, Lego Technic, re-purposing something ...
some experience with similar crazy one-of-a-kind builds :)
basic soldering and electrical-engineering skills
software engineer, programming a microcontroller is not a problem
some woodworking skills
can order a 3d print

under 50 USD in material

So far I am imagining a servo pulling a rope that will be controlled by a microcontroller. I am thinking if it would be possible to attach an accelerometer to the push-chair to find the resonant frequency.


texts:
One of the advantages of fluid bed drying especially in the pharma industry is the “Turbulence in the bed causes mild attrition to particles thus producing more spherical free flowing product.”

This is from the textbook and I don’t understand the meaning behind it. Can anyone explain?