texts: No increase in temperature during bending?

texts:
Good day, I am a mechanical engineering student, we conducted three-point bending test for a metal specimen and I am wondering why the temperature of the specimen did not increase as the UTM certainly did work on the specimen, therefore some thermal energy increase should be present.

This is in comparison when we conducted tensile test to another specimen in which we realized that the metal became appreciably hot.

I think it was because bending involved tension and compression, reasoning that because they are opposite of the other, while tension releases thermal energy because of the pulling away (rupture) of interatomic bonds, compression accepts thermal energy because it needs for the compression of the bonds? Therefore no (or minimal) thermal energy increase could be observed after bending.

I can't research anything related to this phenomena on the internet. (Also we had never conducted yet a compressive test, so I don't know if compressing the metal reduces its temperature). I also know the physics of thermal expansion (metal expands with increase in temperature), I am not just sure if it applies the other way around.

I just want to know if you think my hypothesis is correct, or if not could you provide a link or explanation? Thank You


texts:
In my aerospace company we have repetitive discussions regarding the stacking of low tolerance fasteners with non-countersunk washers. For example a fastner NAS6703-X (size 10) has a max. base radius of .02". A non-countersunk washer NAS1149 size 10 would clash with the base radius if modelled.
Having done a fit check, there is no clash but to avoid issues we have used bigger sized washers on some occasions. I find it odd to use different sized bolt/washer combinations.
Are you aware of any guidance material regarding this, respectively has anyone else met this topic?
Thank you!


texts: Using a pattern of features as datum BOTH individually and as a group, for different FCFs

texts:
The quick:

I've come up with a handful of possible options for how to structure the Datum Reference Frames (DRFs) and Feature Control Frames (FCFs) for this part.  I've narrowed it down to the two shown below, but I don't know which is better, or if there is maybe another way of doing this I'm overlooking. I believe both are compliant to ASME Y14.5-2009, and I'm leaning towards option 1, but I wanted to get another set of eyes here  to make sure the intent is understandable and clearly communicated. ASME Y14.5-2009 is a drafting standard, used in the U.S. and other countries to ensure prints are created and interpreted the same way across geographic and cultural divides.

The dirty:

This is a cast part.  It is cast to near net shape and then machined to final specifications.  I need to check both the relationship of the machined features to each other and some of the machined features to the casting.

In checking the machined features to each other, I want to check the position of one group of features (hole pattern) to another group of features (different hole pattern).  For this, I've simply declared the first set as a datum feature, and created a compound true position FCF for the other set using the first set as the secondary datum.

Now, for checking the first set to the casting, I need to check each machined feature individually to it's cast member.  I'm struggling with how to apply a datum using the "INDIVIDUALLY" requirement (as defined in section 7.4.8, and figures 7-26 and 7-37 of ASME Y14.5-2009) to these holes for this FCF, while also maintaining the group datum for the other FCF.


texts: Lowest temperature at which a spring powered mechanical wrist or pocket watch will stop operating

texts:
In the Wired article 9 Russian Adventurers Mysteriously Froze to Death. A New Theory Explains Why, it is stated that:

Without body heat to keep it warm, in such cold weather—estimated to be –13 degrees F (-25 degrees C), based on readings from the closest weather stations—a person’s watch stops ticking about an hour after their death.

How cold must it be for a mechanical spring powered wrist or pocket watch, circa 1950s, to stop operating?


texts: Find optimal configuration for Stirling Engine

texts:
I'm trying to figure out the theoretical calculations for a Stirling Engine system so I can determine optimal piston size, optimal piston displacement and number of pistons. I want to calculate which configuration has the most amount to torque to turn something else, and the highest amount of RPM's.

What I have managed to achieve:

(1) Internal energy = Thermal difference + Work

$$ΔU = Q + W$$

(2) Work = Rotational Kinetic Energy

$$W = \dfrac{1}{2}Iw^2$$
(3) Assuming that Inertia is standard wheel

$$I = \dfrac{1}{2}Mr^2$$

(4) Equation I have so far

$$\dfrac{1}{4}Mr^2w^2 = ΔU - Q$$

I am unsure on how I can relate the equation to the pistons. According to HyperPhysics

  Internal energy is defined as the energy associated with the random,
  disordered motion of molecules.

That sounds like pressure to me, and I know that:

  Pressure = Force / Area

But I think I need a better way to express the physics of pistons.

The Q component of internal energy is also difficult for me to find, because a heat source (like a candle flame), will be creating a heat differential on the piston. This heat differential in Joules, will be a little difficult to find as well.


texts: Approximating volume flow based on valve opening

texts:
I want to approximate the volume flow going through heating/cooling units, but all I have are valve openings (unit=%). Since the valve does not have a linear relationship between its opening and its volume flow, I will have to approximate it based on standard values.
The datasheet specifies "Equal percentage flow control is ensured by the special design of the ball."
I do have the maximum volume flow powered by the pump (at 100% valve opening). Since, to my understanding, valves are designed that way to create linear relationships between valve opening and heat transfer of the downstream heat transfer unit, I assume that there are "standardised" valve characteristics and approximating the volume flow based on the valve opening is possible. But how?


texts: Determining the magnitude and coordinate angles of a resultant couple

texts:
Here is the exercise that I just can't seem to figure out. The answer should be 71.9 Nm with coordinate angles 44.2, 131 and 103.

I know that the couple moments caused by the forces $F_1$, $F_2$, and $F_3$ are -20j and 24i and -16k respectively.

But I can't seem to figure out the moment caused by the two $F_4$ forces. First I thought it only caused a moment around x-axis, but this is wrong. Then I tried $M = r \cdot F$. But I just can't express $r$ (from tip of $-F_4$ to tip of $F_4$) in a vector.
So can anyone help me with finding the coordinates of the ends of the bar where the forces $F_4$ work on, so that I can make a position vector out of it?


texts: Pump Terminology: Suction Piping vs Suction Waterway

texts:
Karassik and McGuire state in their 2012 book, [1] p. 415,

The available energy that can be utilized to get the liquid through the suction piping and suction waterway of the pump into the impeller is thus the total suction head less the vapor pressure of the liquid at the pumping temperature

My question is: what is the suction piping and the suction waterway and what is the difference between the two?
References
[1] McGuire, J. T., Karassik, I. (2012). Centrifugal Pumps. United States: Springer US.
https://www.google.com/books/edition/Centrifugal_Pumps/KEzjBwAAQBAJ?hl=en&gbpv=1&dq=%22suction+waterway%22+pump&pg=PA415&printsec=frontcover


texts: Is it possible to design automatic transmission without torque converter?

texts: So the reason why torque converter is needed is because it disconnects engine from transmission. It has also extra benefit of multiplying torque but that is not 100% necessary. From what I have seen all automatics have some sort of constant input which is always connected to the shaft. Would it be possible to design an automatic transmission which wouldn't have constant input and therefore wouldn't need torque converter?


texts: Searching for Anterior Cruciate Ligament MRI Images for Finite Element Model.

texts:
I'm searching for 3D MRI images for generating an mesh to be used in a Finite Element Modeling project. My group has access to a low-resolution CT scan and cadaver knees, but we don't have any good MRI scans. I'm hoping that there might be a public repository of MRI anatomical images somewhere. Any pointers?

If not, how acceptable is it to ask to loan out CT time. This is an unfunded graduate project, so the scan would have to be pro-bono.


texts:
Creating a drawing for a part that will be CNC milled.
Should all of my dimensions come from a baseline on the part, like an edge or is it ok to use Centerlines?

See yellow highlighted dimensions below for example.  1.775 is from the centerline of the part.  Would it be better to dimension it from the edge of the material as shown with the red arrow?  Same for the other yellow highlight, 0.100 X 4.

Thanks for any advice.


texts: What equation are we using to describe forces in FEA?

texts:
Engineers often use Finite Element Analysis software to solve for stresses inside complicated structures to generate pictures like the one above.

I am familiar with FEA as a method to solve differential equations. So what (differential) equation are we using to describe forces/stresses inside objects?

When it comes to analyzing forces, I know only Newton's laws. But how can we use the laws in here, when the internal stresses are dependent on the geometry of the object?


texts: Shell vs. solid elements for a fatigue analysis using FEM

texts: What are the advantages and disadvantages of using quads (shells) vs using hexas (solid) in my mesh for a fatigue analysis using a finite element software. Thanks.


texts: Structure other than a wall to reduce wind?

texts: I own a small farm which apparently lands in the middle of 2 small mountains therefore is a big wind tunnel.  The wind gets pretty insane here.  Wondering if there is a structure I can put around my yard that would reduce the wind but be more cost effective than building a 10ft brick wall around my entire property.


texts: Is conversion from EMC (*.ngc) to heidenhain (*.h) CNC code possible?

texts:
I have some gcode created with dmap2gcode. This and Meshcam are the only software I could find that could would take a large image and create the necessary gcode.

Now I would like to try cutting this on a different machine. This machine however is only connected to a SolidCam PC and cant be messed with. I know that it can produce Heidenhain gcode files which seem to be the closest format to what is used in the .ngc file.

Is there software which could translate the EMC gcode to Heidenhain gcode?

Sample .ngc

( Code generated by dmap2gcode-0.07.py widget )
( by Scorch - 2014 )
(Settings used in dmap2gcode when this file was created)
(=========================================================)
(dmap2gcode_set show_axis  1 )
(dmap2gcode_set invert     0 )
(dmap2gcode_set normalize  0 )
(dmap2gcode_set cuttop     1 )
(dmap2gcode_set cutperim     1 )
(dmap2gcode_set disable_arcs 0 )
(dmap2gcode_set yscale     127 )
(dmap2gcode_set toptol     -0.127 )
(dmap2gcode_set vangle     45 )
(dmap2gcode_set stepover   1.02 )
(dmap2gcode_set plFEED     254 )
(dmap2gcode_set z_safe      6.35 )
(dmap2gcode_set z_cut       -12.7 )
(dmap2gcode_set diatool    6.35 )
(dmap2gcode_set origin     Default )
(dmap2gcode_set tool       Ball )
(dmap2gcode_set units      mm )
(dmap2gcode_set plunge     simple )
(dmap2gcode_set feed       381 )
(dmap2gcode_set lace       None )
(dmap2gcode_set cangle     45.0 )
(dmap2gcode_set tolerance  0.0254 )
(dmap2gcode_set splitstep  0 )
(dmap2gcode_set gpre       "G17 G90 G64 P0.001 M3 S3000" )
(dmap2gcode_set gpost      "M5|M2" )
(dmap2gcode_set scanpat    "Rows" )
(dmap2gcode_set scandir    "Alternating" )
(dmap2gcode_set imagefile  x )
(dmap2gcode_set ROUGH_TOOL     Ball )
(dmap2gcode_set ROUGH_DIA      6.35 )
(dmap2gcode_set ROUGH_V_ANGLE  45 )
(dmap2gcode_set ROUGH_R_FEED   381 )
(dmap2gcode_set ROUGH_P_FEED   254 )
(dmap2gcode_set ROUGH_STEPOVER 1.02 )
(dmap2gcode_set ROUGH_DEPTH_PP 2.54 )
(dmap2gcode_set ROUGH_OFFSET   0.508 )
(dmap2gcode_set ROUGH_SCANPAT  "Rows" )
(dmap2gcode_set ROUGH_SCANDIR  "Alternating" )
(=========================================================)
G17 G90 G64 P0.001 M3 S3000
G21
G91.1
G0 Z6.3500
F381.0000
G18
F254.0000
G0 X254.0000 Y127.0000
F381.0000
G1 Z-11.7156
 X248.1755 Z-11.7342
G2 X247.6719 Y127.0000 Z-11.7835 I0.0438 K-3.0451
G1 X245.5041 Z-11.7844
 X244.5407 Z-11.8400
 X242.7233 Z-11.8420
G2 X242.2197 Y127.0000 Z-11.7970 I-0.5310 K-3.1026
G1 X233.1107 Z-11.7978
 X231.2495 Z-11.7528
G2 X230.7240 Y127.0000 Z-11.7038 I-0.5473 K-3.0262
G1 X222.0310 Z-11.7541
 X220.6734 Z-11.7722
 X218.9655 Z-11.9030
 X218.1772 Z-11.9114
G2 X217.5860 Y127.0000 Z-11.9992 I0.2959 K-4.0213
G1 X215.1993 Z-12.1024

a sample from the .H file:

0 BEGIN PGM PLATTENP1 MM
1 BLK FORM 0.1 Z X+0.000 Y-500.000 Z-42.000
2 BLK FORM 0.2 X+500.000 Y+0.000 Z+0.000
3 ; TEIL-NAME    : PVC_UNTEN - KOPIE
4 ; PROGRAMM-NR. : 1
5 ; DATUM - ZEIT : 30-OCT-2015 - 11:13:10
6 ; ERSTELLT MIT SOLIDCAM
7 ; PP-STAND 2.0 VOM 28.10.2015
8 * VERWENDETE WERKZEUGE:
9 ; T19 SCHAFTFRÄSER D19.746
10 ; T12 SCHAFTFRÄSER D5.968
11 * WERKZEUGE/JOBS:
12 TOOL CALL 19 Z S7000
13 *     HSR-R-CONT-FERTIGMODELL
14 CYCL DEF 32.0 TOLERANZ
15 CYCL DEF 32.1 T0.05
16 CYCL DEF 32.2 HSC-MODE:0 TA3
17 L X+142.093 Y-142.093 R0 FMAX M3
18 L Z+16.000 FMAX
19 L Z+0.490 FMAX
20 CC X+140.696 Y-140.696
21 CP IPA+45.000 IZ-0.044 DR+ F3000
22 CC X+140.696 Y-140.696
23 CP IPA+90.000 IZ-0.087 DR+
24 CC X+140.696 Y-140.696


texts: I used a 2N3055 powerTrans with a collector transformer (6-220v)load with an audio input base bias from a  audio source , I am getting 160vAC from 6v DC , i want 220 v AC out , Can anyone suggest a solution


texts: Faster car drifting (motorsport) when using limited slip vs welded differential

texts:
I have been drifting RWD (rear wheel drive) cars for some years now. I tend to think about every engineering solution that other drivers use and how does it work before applying it to my car.

What has been baffling me from some time now is: Why using LSD (limited slip differential) results in bigger speeds when drifting?

Food for thought:

Welded differentials (100% lock) are very common in this motorsport since you are dealing with kinetic friction on rear tires anyway - which is constant regardless of their rotation speed (unless you match tire speed to ground and grip using static friction).
Open differentials (0% lock) on the other hand practically make drifting (powersliding) unusable as almost all of the engine torque is routed to unloaded wheel resulting in slowing down.
Slow motion drifting video: https://www.youtube.com/watch?v=OG0cyjqDJCw


texts: What's a professional way of tracking design history in plant engineering?

texts:
If you look at the design documentation in our projects (Biogas and waste-to-energy plants), you find out what we plan to build but not what other options were considered and why they were discarded. This information rests only in the engineers head. Occasionally, a plant will be in a conceptual stage for years, sometimes switching between engineers. So I find myself revisiting an option that a coworker considered and ultimataly discarded last year.

What is a good way to track design decisions, the 'whys' and 'why-nots'? I'd strongly prefer an approach that's tried, tested and used elsewhere in industry.

Additional information: My company will be pursuing ISO 9001 certification, an approach that fits with this QA regime would be prefered.


texts: Chemical engineering equivalancy to the spring-mass-damper/RLC circuit

texts:
I understand the equivalency between the MSD and RLC circuits.  Mass ~ resistance, spring ~ inductor, damper ~ capacitor.

With the equations of the form
MSD:

$$ m\ddot{x} + c\dot{x}+ kx = F    $$

RLC:

$$ L\ddot{i}  + R\dot{i} + \frac{1}{C}i = V    $$

I was thinking a bit about what the chemical engineering equivalent would be for a "plant circuit".  For a capacitor, I thought it could be equated to a tank with a inlet at the top and the outlet at the opposite end (also at the top).  It would fill without outputting anything until it is full.  However, if the inlet stops, the outflow stops and thus doesnt work as a capacitor.

For resistance/mass, i thought the tank size might be the best representation.

I have no idea for an inductor/damper.

After some more thinking, it became clear that a single tank cannot possible approximate such a system, and it has to be a dual tank system.  However, this complicates the ODE to such a point where a equivalency is not intuitive at all!

Would be awesome if someone could shed some light on this for me.  I might be missing something somewhere.


texts: Could a knife blade & shaft be made of 100% diamond?

texts:
I am reading a novel set in the future. A planet has been found where there are extensive deposits of diamond. Presumably diamond is mined much like marble is here on earth (there is not a lot of detail on this).

A character has a knife where the blade/shaft is a single piece of diamond. In 2015 here on Earth you can purchase diamond blade knives, but they seem to be all steel (no diamonds per comment by @mart). There are some saw blades that have pieces of diamond attached to a steel blade.

Assuming large quantities of reasonably priced materials, would it be possible to design and manufacture a functional knife made from a single section of diamond (all but the handle)?


texts: How to write a Cost engineering support plan?

texts:
How would I write a Cost Engineering support plan which reflects the Project Control Cycle?

A wine company is wondering if they should invest in another factory. Only this time it will be in the USA. This will be their first factory in the USA and they are wondering what the cost will be and what kind of steps you could take to support the business case through the different project phases.

What are the steps that need to be taken to successfully support a business case decision?

The problem is I haven't done anything like that before and I don't know what the structure of the report should be and to which things I should focus on. Any help would be greatly appreciated!


texts: Controller design with pole placement method with given damping and settling time

texts:
I was given the following equations and asked to design a controller for $u=-Kx$ using a pole placement method with the closed loop system having the damping and settling time $T_s$ given.

Am I supposed to use the $\dot x_1$ and $\dot x_2$ equations or are they totally unrelevant?

Also, which pole placement method is easier for the case, root locus or Bode and Nyquist plots?

$$\begin{gather}
\dot x_1 = x_2 \\
\dot x_2 = -x_1 +\dfrac{1}{6}x_1^5-x_2+u \\
u = -Kx \quad \zeta=1.02 \quad T_s = 0.40
\end{gather}$$


texts: Way to keep object on linear rail in the position you leave it in despite smaller external forces?

texts:
Problem:
I have a rod on a linear rail system. This rod can be pushed forward or backwards. There is air blowing out of the front of the rod (~2 lbf) causing it to move to the back position by default. I am wondering if a mechanism exists that will allow the rod to be moved, but when the rod is let go of, remains where it is despite the force from the air. Something similar to a cordless blind system.
Does a device like this exist that can be bought as an individual mechanism?
Possible solutions:

The most feasible solution (that I am not fond of) is a friction brake. Just a rubber collar that will go around the rods near the bearings. It would work, but I am worried about long term wear, operator fatigue, and possible joltyness when breaking static friction.

An overly complicated "solution" could be to have a constant force spring powered motor assembly to be continuously pulling the rod forward with 2 lbf. The problem with this is that once the air is turned off, the rod will fly forward (not acceptable). I could set it up  so that to turn off the air, the spring motor assembly must be braked in some way. That just gets complicated though and interferes with emergency shut off.

My third solution would be to replace the linear rail system that the rod slides on with threaded rods. The air rod could then be moved by spinning a hand wheel that would in-turn spin the threaded rods. I see some friction problems here and would not like the speed restraint of this system, but it could possibly work.

Closing Statement:
If you have any other possible solutions, alternative designs, or comments about my solutions, I would appreciate the input. Thank you.


texts:
Should standard SI units be used in this formula or are other units supposed to be used for the formula for stress in a thin-walled spherical pressure vessel?

$$\sigma_{yield}=\frac{P_g r_i}{2t}$$

where $\sigma_{yield}$ is the yield strength of the material, $P_g$ is the gauge pressure, $r_i$ is the inner radius of the sphere, and $t$ is the thickness of the sphere wall.


texts: How to work out the damping or deflection curve from deflection angles?

texts: I have a crane boom that is rotating and when it is stopped suddenly, the boom flexes back and fourth several times. I have measured the angles between each deflection and have $3.16 ^\circ$, $2.42 ^\circ$, $1.77 ^\circ$ and $1.31 ^\circ$, which if plotted in Excel forms a logarithmic curve equal to $$y = -1.33ln(x) + 3.2221$$ The goal now is to find how to plot this as a sin curve with the period of 3.5 seconds so that it it looks like a deflection vs time chart (or damping curve), similar to the one in red below. Can someone please explain how I can do this?


texts: What is a reference that i can use to find the interpretation of a symbol in a gas line schematic?

texts:
I have a schematic for some gas lines in a wafer processing unit.  One of the symbols which occurs is a circle with an x in it that has the left and right quarters filled in to form two black triangles.  (I've attached a drawing.)

From context, i can tell that these represent valves to allow or block flowing of the gas.  However i would like to find this symbol in some guide to give a more exact interpretation of the meaning, and just to have an authority that i can cite to.

I have not found the symbol in the context of a gas line schematic in any online reference.

Where, and how, can i look?


texts:
I'm currently designing scissors, and I have to describe the tolerance and fits of the parts. What kind of tolerance must be used for the pin holding the two blades together, though allowing for rotations? (i.e. clearance, transition, or interference).

Thank you very much for your insights!


texts: Does anyone know how to calculate the width of the support (x) required for 6x10 lumber spanning 5’ supporting 2700 lb of uniform load and a load perpendicular to grain of 2000lb/ft2?


texts: I have a 50 HP screw compressor that has just began to load and unload within 10 seconds when previously would take between 40 and 60 seconds. Nothing has been added or removed from the system. Any idea why this is happening?


texts: What does TIR stand for in Window Pane Fenestration?

texts:
When looking at glazings within various public databases I see the fields "tir" shown often. E.g as seen below:
"glazing_data": {
        ...
        "tir_front": 0.0,
        "tir_back": null,
        ...
    }

What does this field stand for?


texts:
I'm having trouble reading several dimensions on this technical drawing.
First, I don't know how big is the diameter of the marked cylinder.
M24 is a threaded hole in my opinion and that cannot say anything about the cylinder.

And what is the diameter of the rotor ? Is it 40 ? if yes then why they didn't put any diamater mark next to the number 40 ?
And I cannot find out the angle of the central key relative to slots?


texts: How high will a flywheel catapult launch a payload?

texts:
First off, this is not a homework question or anything like that. I'm trying to build a catapult to launch a payload using a flywheel as an energy device!
It goes like this:

The flywheel spins up to maximum speed. All other components are at rest.
The catapult lever (in resting position, with a payload at the end of it) engages a tooth.
The flywheel tooth (always extended) connects with the catapult lever tooth and rotates it over a certain angle. During this time the flywheel is slowed down a certain amount and the lever gains a great amount of speed.
At the end of the interaction between the flywheel and the lever tooth (after some degree of rotation) the lever gets to the end of its stroke and abruptly stops, the payload continues flying upward and the remaining energy of the flywheel makes it continue to spin (it can freely "slip" past the lever tooth at the end of the movement).

I've attached a couple pictures which describe the two states, T0 and T1 (basically step 3 and 4 respectively).

My question is, how do I determine the final energy of the flywheel after this interaction given the following parameters: Moment of Inertia and initial Kinetic Energy of the flywheel, mass of payload, and the basic geometry between them. Assume the weight and inertia of the catapult lever are negligible and there is no friction between the interaction of the two moving parts.
I originally thought this problem would be as easy as assuming all the kinetic energy of the flywheel just went into the upward motion of the mass (the flywheel would come to a complete stop). However, after thinking about it for a while I realized it is probably not that simple at all...I smell some differential equations which scare me and has been a while since I've done any of that which is why I am asking for some help. Maybe it's not that complicated after all, but I am at a dead end. Anything would be appreciated.
Thanks in advance.


texts: What are the Principle directions? Are they unit normals of three planes perpendicular to each of the principle stresses?


texts: Why do we remove (or reduce stiffness of) anti-roll bars from the front side to prevent under-steering?

texts:
Under-steering is caused when, at a corner, the front wheels lose traction and as a result the car does not take the corner as quick as it should. So basically what we should do is try and get both the tyres to have a better grip on a corner.

Now what an anti-roll bar does is it allows both tyres to remain on ground during  a turn so that we get maximised traction.

So why don't we increase the stiffness of the anti-roll bar when faced with the problem of under-steering?


texts: I have a need for a pump that can suck a vapor from a 0.1 atm environment, and flow into a 1 atm environment. I know that there are electrical pumps that can do this. But are there any pumps like this that can be operated manually? (powered by hand or body weight)


texts: How can I draw an angled wall with constant thickness per slice along an axis?

texts:
This questions is hard for me to formulate, so here is the problem:
During these Covid-19 times, my dad (a mechanics manufacturing teacher) made two articles (1, 2) on how to design and model custom-fit respiratory masks in SolidWorks in order to 3D print them (let’s not talk about the masks efficiency here, these were mostly made for fun, but are also probably better than nothing).

While 3D printing the 3 masks he designed, I noticed that the movements were sometimes a bit weirds and shaky on the main part (on the right in the Cura screenshot below), that is because even though the walls thickness is 0.8 mm (which corresponds to 2 times the nozzle diameter, so that it would just make two continuous perimeters per layer), because the walls aren’t straight but are at an angle, that means the layer slice is thicker the more the walls are angled.

With a little bit of very simple maths (here with Pythagore), you can determine the thickness of the wall on one layer, here on the next picture with a 45° slope (the printed thickness of the wall is x, in red):

Now, that is all good and logical, my question is: how can you design that kind of shape (made with splines and smoothing function) in a CAD software so that it has a constant thickness on each layer or slice of the model, here on the vertical axis? This would make the model much more 3D printing friendly.

I hope I am understandable, as I had a bit of trouble translating some names to French (CAD functions for example). Thanks!


texts:
We were learning about superpositions of potential flows.
so,
$$\Psi_{doublet}  = \Psi_{source} + \Psi_{sink}$$
where: $\Psi_{source} = \frac{Q'}{2\pi}\theta_1$, and $\Psi_{sink} = \frac{-Q'}{2\pi}\theta_2$
I then expect:  $\Psi_{doublet} = \frac{Q'}{2\pi}(\theta_1 - \theta_2)$
but final form we were given was, $$\Psi_{doublet} = \frac{-Q'}{2\pi}(\theta_1 - \theta_2)$$
I have no clue as to where that extra minus sign is coming from.
Thank you guys kindly for your time and help.


texts: Compact way to regulate 3000psi (200bar) down to 30psi (2bar)?

texts:
This was originally posted on the Lego page, and closed because it's not actually about Lego itself.  I thought I'd give them a chance first, in case someone had done this already and had some application-specific knowledge.  But it looks like not.

Anyway, I have a Lego Pneumatic Engine (LPE) set up as a "steam" locomotive, and I want to power it with a HPA, paintball, auxiliary SCUBA, or whatever-someone-decides-to-call-it tank:

I think a 6.1cm diameter, 0.22L or 0.35L tank will fit nicely in place of the 0.5L plastic water bottle.  I can redesign things and move some structure around if I have to, but the overall size is pretty well fixed.

The air inlet is a sports inflator needle pushed into the black rubber hose at the front, with a bicycle pump currently attached to it.  The maximum pressure there is about 35psi (~2.3bar).
I can use a longer hose there if needed too, but that's about as short as it can be.  The straight section with a slight kink is the inflator needle.

So, is there a compact way to regulate the HPA tank from 3000psi (200bar) down to 30psi (2bar) with a schrader-valve type connection at the end?

I see that a fair number of HPA tanks (but not all) come with a factory-attached pre-regulator, that can apparently be adjusted by taking it apart and changing the spring.  But it seems like a stretch to me, to take something that is designed for 3000psi in / 800psi out, and get it all the way down to 30psi out instead.  Maybe it's possible, and if so, that's great!  But it seems like a bit much to me.

It seems more likely to me, to just barely get into the range that a shop air regulator can handle, and use that for the final delivery as well as a complete shutoff.  But there are still adapters to be found, and perhaps some creative folding to make it all fit in the available space.

I also found this, which says it takes 4000psi in and is fully adjustable from 4000psi out to 0psi out.  It looks a bit cumbersome at first glance, compared to the space that it would go in, but no real size reference except for the gauges.  Also, with such a wide range of adjustment, it might be difficult to have it "barely on" and stable at my required 30psi.  Not to mention a rube-goldberg chain of adapters, probably on both the inlet and the outlet sides of it.

Is there an elegant way to get the required 100x drop in pressure, with decent regulation (there's a throttle valve after the final regulator), in the space shown, and with the right connector at the end?  (imitation schrader valve)


texts: Is the PCV valve open during high engine load

texts:
I was learning about PCV valve, when one of the online resources pointed out that the PCV valve will be closed during  high engine load to prevent the lean-mixture (blow-by) in the crank case from entering the combustion chamber, as a lean mixture is not desirable during high engine load.
But my basic automobile engineering textbook (local author) points out that during higher engine load, the blow-by increases and causes the crank case pressure to rise thereby increasing the opening of the PCV valve and letting more blow-by enter the combustion chamber.

Now I'm confused wether the valve actually closes or opens during high engine load.


texts: How to design spray nozzle (like in pulverizer) for 3d print?

texts: How do spray nozzles work? How do they convert liquid to aerosol? Is it possible to print tiny spray nozzles from metal powder?


texts: Difference between gas combustion engine and gas turbine?

texts: I am a non-engineer and I am using a gas power plant data base. Some plants listed are of the type "combustion engine", some of the type "gas turbine", some "steam turbine" and some "combined cycle". I believe to understand that combined cycle is a combination of combustion engine and steam turbine. But what is the difference between combustion engine and gas turbine then? Or does it mean the same?


texts: Shell Breathing Modes and Base Excitation

texts:
I have been reviewing "Vibration of Continuous System" by S. Rao as part of self-studying to help with work. I started reviewing the chapter regarding shells and noticed that shells have beam and breathing modes (see picture below).
I was wondering, for a shell structure that is experiencing translational base excitation is there "an easy" method to show that the forced shell vibration does not have a significant contribution by the shell breathing modes?
Intuitively, I believe that the first shell mode (similar to a beam mode) would be the major contribution to the forced response. However, I'm not sure how to quantify this assumption.
Thank you!


texts: What specific characteristic of proportional solenoid valves makes the flow to current behavior quadratic?

texts:
If experimental data is obtained from a proportional solenoid valve, specifically flow vs current (assuming inlet pressure is constant), the fit is nearly quadratic in nature.

Andersen's Analysis and Design of Pneumatic Systems predict that the flow area of an orifice is linearly proportional to the flow rate for constant inlet pressure. But for a valve, the magnetic characteristics must also contribute a relationship between applied current and displacement of the valve poppet which changes flow area of the orifice.

Is the electromagnetic element the main factor leading to the quadratic flow vs current relation, or are other factors involved?


texts: What is the correct term for long cuts in a floor joist?

texts:
I would like to identify the correct term for a long, lateral cut within a floor joist.

Based upon this guide and several other sources that I have come across, a notch is a cut that is allowed to have a width up to $\frac{1}{3}$rd of the depth of the floor joist.  In other words, a 9" joist can have a notch cut in it up to 3" wide.

In my particular case, I would like to make a cut several feet long in order to increase the available head room.  I would like to know the correct term so I can research joist reinforcement requirements.

Bonus points for providing additional references regarding US building codes related to this type of a modification.


texts: What's the name for a kind of gear that slips tightly over the top of another gear and can drive the gear it's surrounding?

texts:
What's the name for a kind of gear that slips over the top of another gear and can drive/turn the gear it's surrounding?
I'm making a handcranked flashlight with my 7 year old. We're thinking of using a stepper motor with a gear on the end from an old printer, something like the one pictured. I've seen this kind of crank flashlight made with just a 'female' gear embedded in the crank handle, that slots right over the 'male' gear (as pictured here). That's the best way I can describe it. What's the name of this kind of gear? One that would slot right over the top of the gear in the picture below and be able to drive it?  I can't seem to find what I am looking for anywhere, any ideas? If I knew it's name then I could search for it. Thank you!

Edit** What I looking for is kind of like this internal spur gear (the image below), but with that outer ring FITTING REALLY TIGHT around the inner spur gear, with the number of cogs matching exactly (not like this picture, where the outer ring is really big compared to the inner gear).


texts: Can I use a water-based ultrasound-cleaner with oil?

texts:
I'd like to clean my bicycle chain with as little effort as possible, so I thought an ultra-sound cleaner would be best. Professional oil-based ultrasound cleaners are way too expensive for a hobbyist, but water-based ultrasound cleaners are pretty cheap.
Could this work or is it doomed to fail because you need different kinds of transducers (or something like that)?
I understand that the risk is all mine, so I won't sue any of you for damages. I'd just like a more qualified opinion than my own. I'm assuming here that the worst that could happen is that it doesn't work and I end up with an oil-smeared device that I need to properly dispose of. Oil is less conductive than water, so I see no risk of shorting the device.


texts:
In the picture below, the stepper motors are fixed to stay in place. They have small pulleys that rotate the bigger pulleys. If building such a system, how should the bigger pulley be attached?

Looking at the image it seems the smaller U-shaped piece where the camera is mounted is fixed to the bigger pulley. This is simple with some screws but how is the pulley connected to the frame? Does the same method apply to the other side?


texts: Are dynamic frequency transmitters common? What's the terminology to use when searching for one?

texts:
Newbie question, moderately educated on RF but only the signal, not at all about the hardware. Looking to start experimenting on a concept that would require a dynamic shift over time from one frequency to another between the transmitter and receiver. When a part is listed as, for example, a 443Mhz transmitter, is that typically the only frequency it can output at? If so, what key word would I search for on a part site to find a dynamic frequency transmitter?

I tried searching "dynamic frequency transmitter" on distributor sites such as Mouser Electronics with no apparent luck in the results.


texts: Aircraft force in g's experienced by pilot

texts:
Given:

The acceleration of high-speed aircraft is sometimes expressed in g’s (in multiples of the standard acceleration of gravity). Determine the upward force, in $N$, that a $70\cdot kg$ man would experience in an aircraft whose acceleration is $6\cdot g’s$.

My Solution:

I account for the normal acceleration due to gravity by subtracting $1\cdot g$ from the upward acceleration of the aircraft. This is what we would see if we had drawn a free body diagram (not shown)...

$$F=ma=m\times(6g-1g)=70\cdot kg\times5\times9.81\frac{m}{s^2}=3433.5\cdot N$$

Solution in Text:

However the solution in the text does not do this...

$$F=ma=m\times6g=70\cdot kg\times6\times9.81\frac{m}{s^2}=4120.2\cdot N$$

Question

Why is the net upward acceleration not $5\cdot g's$?.


texts: Defining fresh air rates for sizing heating coils

texts:
dear StackExchange colleagues;

If I want to find the fresh air rate in kg/s and the supply rate in kg/s during winter and summer for the case below:

DATA:

Indoor condition all year        =       22oC dB temperature, 50% saturation.
Outdoor condition summer         =  28oC dB temperature, 80% saturation.
Outdoor condition winter          =     -3oC dB temperature, 80% saturation.
Maximum occupancy                  =   1000 people.
ADP of the cooling coil                    =       8oC
Fresh air requirement                  = 12 l/s/person
Supply air rate                         =      8 air changes per hour.

Fresh Air Flow Rate

Fresh air rate = 12 l/s/p x 1000 people =         12,000 l/s =         12.0 m3/s

The specific volume at the outside condition may be determined from a psychrometric chart.

It is approximately 0.88 m3/kg.

Mass flow rate = Volume flow rate / specific volume

Mass flow rate     (Fresh Air)   = 12.0 / 0.88      =       13.64 kg/s.

Supply Air Flow Rate

The ventilation supply air rate is taken from table B2.3 and is given as 8 air changes per hour; the mass flow rate can be calculated.

Volume flow rate (m3/h)         =       Volume of room (m3) x air change rate (ac/h)

Volume of room (m3)             =       40 x 20 x 8          =       6400 m3

Volume flow rate (m3/h)         =       6400 (m3) x 8 (ac/h)

Volume flow rate (m3/h)         =       51,200 m3/h

Volume flow rate (m3/s)         =       51,200 / 3600               =       14.22 m3/s.

Mass flow rate = Volume flow rate / specific volume

The specific volume at the supply condition may be approximated at this stage from a psychrometric chart. It can be taken as 0.834 m3/kg.

Mass flow rate (Supply Air) = 14.22 / 0.834                =       17.05 kg/s.

right this procedure is for the air flows during summer, I did all the calculations for winter and found:

Fresh Air Flow Rate: 12/0.77 [0.77 from the chart with -3oC and 80%]
Supply air Flow Rate: 14.22/0.88 [ from chart with room temp conditions plus 8, 30oC and 50%]

I have this example that is very close to my doubt:
http://www.arca53.dsl.pipex.com/index_files/psy21.htm

it contradicts my thinking, he uses the same flow for winter and summer, can I do that?

thanks a lot


texts: Limits of Injection Molding Regarding Overhung Edges

texts:
I'm looking to redesign a seal my company currently uses. The original task was to re-source it from a lower cost supplier with the same design as is in current production. However, the supplier doesn't work with the type of material the seal is currently made of (rubber) so in the change of material, we may look at potential design changes. In the interest of cost savings, I'm looking to remove a thread feature from the seal and the mating part, and replace it with a snap fit feature. However, I'm concerned about the ability of the injection molding process to create the current design I'm considering. I'd normally go the supplier, but it's been two weeks since the last (unrelated) item I've sent to them and I haven't heard back, so I'm turning to Engineering.SE for a quicker turnaround time.
A rough sketch of the design is below. The right edge is where the part is currently threaded, and that lip would interface with a similarly sized slot in the mating part, locating the seal properly and preventing it from pulling away (the part inside the smaller diameter lip must translate relative to the seal).

Potentially further complicating this is the fact that the outer diameter is currently reinforced with a steel ring that is fully enclosed in the rubber (plastic in the redesign.) Our customer will probably be looking to keep the strength and rigidity added by this.
What I'm ultimately asking is whether it'll be possible to injection mold this part, particularly whether it's possible to construct a mold that can be removed from this part without destroying it. As a follow-up, if injection molding is entirely impossible, are there other plastic forming processes that could be used to bond and form around a steel ring and create such a part? Extrusion clearly won't work and I can't see vacuum forming working either, and the volume is too high for rapid prototyping to be feasible, but beyond that I don't know enough about the various options as far as plastic forming. (I haven't settled on a replacement material yet, but I'm guessing it'll be some sort of polyurethane.


texts: From advanced prototype to low-volume production

texts: So to the point. In our project (Robotics project) we mostly use sheet metal and PLA printed parts to build. But we want to level up and be ready for an advanced run and even low-volume production of the product. Right now we're in the last days of an advanced prototype (Phase II) . My question is, what do you guys recommend to level up the design and start to be ready for low-volume production (15 - 20 pieces)? What are the tips and tricks when designing a more finished product? For example, The two things we're considering to change are CNC machining the plastic parts that have high loads on them, and for other 3D printed parts we are considering using different technology than FDM printing. Right now plastic injection molding is not an option, we are not in mass production. Carbon composites are not an option too. I will be glad to hear from you about more ways of bringing the product closer to an industrial one and start thinking about low-volume production. Any article/guide will be great!


texts: What materials can I use for the roller and band of a DIY Van de Graaff generator?

texts:
I have made a VDG generator with a rubber band as the belt and a glass roller. It doesn't seem to work. I think the rubber band may be conductive.

I was thinking of using other materials for the band and the roller, such as:

+------------+--------------------------+
| Roller     | Band                     |
+------------+--------------------------+
| Glass      | Rubber from a balloon    |
| Glass      | Strip from a plastic bag |
| Human Hair | Rubber from a balloon    |
| Glass      | Silk                     |
| Glass      | Felt                     |
+------------+--------------------------+

Which of these pairs would work, and why?


texts: Differences between 2D hydrological modelling programs eg. HECRAS 5.0 (2D), TUFLOW, MIKE Flood

texts: Just wondering what the difference is between 2D flood modelling programs. I am primarily considering whether HECRAS 5.0 (2D - currently in Beta) would be an acceptable alternative for simple 2D flood depth and velocity studies when compared to TUFLOW and MIKE Flood?


texts: Importing a time-temperature list into Ansys Fluent for simulation

texts:
I am using Ansys Fluent for my simulation.

I have a series of connected U pipes surrounded by a hot block (343K) with an inflow of cold water (298K) which is discharging the block.

I would like to simulate only one U pipe with the block around and run the simulation for 720 seconds. Then use the output temperatures as inlet for the simulation using UDF to simulate the second block and U pipe.

The outputs from the first section are a table of temperature with respect to time. It is an Excel file with two columns. I would like to use the exact values from the table (not an approximated function). How can I import these values into Ansys?


texts: How to calculate the amount an object can take from PSI

texts:
I'm pretty sure this is a very straight forward question. But here goes.
So 6061 Aluminum has a yield point of 37,600 PSI. Which is Lbs force per square inch. How do I determine the yield point if I have .25" x .25" piece of 6061 Aluminum?


texts: How would I go about charging titanium dioxide for e-paper technology project?

texts:
I'm experimenting with rubbing a balloon on a silk (to get the electrons) and then touching the balloon to two small aluminium foil balls to see if they'll repel but they don't (if I do it with aluminium foil sheets, they stick to the balloon for some reason, and again, they don't repel). What's happening here?

My final goal is to charge titanium dioxide powder by rubbing a charged balloon in the powder. (I don't know if that will work though)
Is that cheapest way to go about doing this?


texts: Often beeswax is used to seal small air leaks on some musical instruments. One of the disadvantages of beeswax is that it has a melting point of around 140 degrees Fahrenheit and can therefore flow to other parts of instruments with deleterious effects. Do you know of a nontoxic substitute for beeswax with a higher melting point?


texts:
I'm studying how industrial plastic film pallet wrappers work. The wrappers apply a certain amount of pre-stretch to the plastic film (by means of different rolls) before applying it to the object that has to be wrapped.

If the object to be wrapped isn't spherical, i.e. it has edges, then the plastic film is pulled more when it reaches an edge, and so there is an variation in how much the plastic stretches.  I believe that this variation in stretching leads to the plastic film breaking when the pallet is rotating very quickly and subsequently has high pull on the film.

Are there techniques that make it possible to even out these variations and to make the tension the film is under during application more uniform?


texts: Effect of high frequency welding near by the electronic things

texts: I have high frequency welding machine. During the welding time, I can see a wave in my lap and computer and also that time stuck my computer.Can you please help to solve this problem?


texts: Retain information memory on MSP430 in mass erase operation?

texts: MSP430F2619 has 256 bytes of information flash memory. This memory is again segmented in 4, 64 bytes segments. Segment A of this memory can't be erased during mass erase and production programming. I want to store device specific configuration data which is more than 105 bytes long. This I will store in Segment A and B. But how do I make sure that part in segment will remain even after mass erase or production programming.


texts: Problem in the inverse kinematic model of a car like vehicle?

texts:
I'm a electrical engineering student and i am building a simulation of a car like vehicle .
As I understand it:

The input for the forward kinematic model are the control
variables and the output is the position of the vehicle
The input for the inverse kinematic model is the position of the
vehicle and the output are the appropriate controls that will make
that position.

Am I wrong? Please give me a source or a document that contains the correct inverse kinematic model of a car like vehicle


texts: Using modes from linear buckling analysis as imperfections

texts:
I'm reading this article on buckling.

It first introduces us to linear buckling analysis, and then mentions that linear analysis can be unrealistic as it doesn't take imperfections into account. Then it is said:

  One good strategy is to first perform a linearized buckling analysis and then use the computed mode shape as imperfection. The idea is that the structure will be most sensitive to this shape.

So if I understand correcty, the article suggests that to get a more realistic analysis we first compute the linear buckling modes, use this as initial imperfections and then do a non-linear analysis.

But I don't exactly understand why the structure is most sensitive to the buckling modes computed from linear analysis. What does this statement mean exactly?


texts:
For rectification I am given the following information

$x_e$ = 0.95

$x_f$ = 0.50

$x_b$ = 0.15

$v$ = 8

$q$ = 1.17

**VLE Data**
x       y
0.00    0.00
0.10    0.17
0.20    0.31
0.30    0.44
0.40    0.55
0.50    0.645
0.60    0.73
0.70    0.81
0.80    0.88
0.90    0.94
0.95    0.97
1.00    1.00

The VLE data is derived from a given diagram. There may be some inaccuracies there. However drawing with pen and paper in the diagramm gives me the same error I'll explain later on.

With all this data I developed the McCabe Thiele Diagramm for this problem.

Putting everything together in Excel

The grey dotted line indicates my $x_b$ and in orange I drew the theoretical stages. My Problem is: Usually you would come up with a whole number of stages, in this case I would get $9\frac{5}{7}$.

There is also an $E_k = 0.7$ given.

$$n=\frac{n_{th}}{E_k} = 13.87$$

My question is: Why do I not get whole numbers? I am under the impression that there always have to be whole numbers. However in Absorption we where supposed to give answers like $n = 1.2$.

I thought maybe the given mole fractions took $E_k$ into account and therefore I would get a whole number after dividing $n_{th}$ by 0.7.

Is this just an error in my VLE Data and actually I would end up with n = 14? 13+1 to be accurate. It's hard to use the given diagramm since it's very small and I couldn't draw accurate enough in it. Also on what stage is the feed? I wouldn't get a whole number the either.


texts: Why do we assume the moment is zero when analyzing a simply supported beam?

texts: When calculating the reactions of a simply supported beam under any type of loading we assume that the moment about the reaction points is zero. What if our assumption is wrong and in actual practice there is a rotational effect about that point? Why do we make such inappropriate assumption?


texts: Why adding alloy elements in a steel for increasing tempering temperature while keeping the same hardnes and ductility?

texts:
What is the advantage of adding alloy elements in a steel in order to increase the tempering temperature while keeping hardness and ductility the same as before?
If I wasn't clear enough, I want to know what difference makes a higher tempering temperature, if hardness and ductility will be the same.


texts: What would be a reasonable estimate for the amount of petroleum needed to find, produce and deliver one barrel of petroleum?

texts: A basic "balance sheet" might allocate fuel needed for exploration, well development, production, crude oil transportation, refining, further product transportation and delivery to a customer. (This would vary, of course, depending on source and market.) It would seem quite important to know if we are approaching the point where producing more oil actually reduces the supply.  Comparison with biofuel costs might also be interesting, but that's another question.


texts: what to learn to design mechatronics device that move

texts:
I want to design an artificial leg for disabled people. The idea is design of a Device for patients with problems on one side of the leg from the knee down. This device first detects intent to move through movement of the hip.  The knee flexes when it detect force in the ankle foot. Then it decides the type of motion needed for the foot by using force sensors placed on the sole of the healthy foot. These force sensors are placed on three different regions; heel, metatarsal and toe. Using the human gait pattern in relation to force and time. This device can segment the pattern of the person’s gait and analyze the required gait of the disabled ankle-foot so it may assist the patient to move appropriately. This device also assists in telerehabilitation as it records the patients gait data and sends it to a medical professional for efficient follow up and prevention of further injury or fall.

I have little knowledge on where to start and I want to take courses. I know I need mechanical and electrical engineering lessons. However, I don't know which courses to take and where to take them. Any recommendations?


texts: Why aren't there moments in truss bridges?

texts:
One of the assumptions we make when analyzing truss structures (method of joints for example) is that all the components are assumed to experience only compressive and tensile forces, not bending moments. But why can we make this assumption? This is not made clear in any texts that I've read on the subject. I would assume that if we put a load on what is essentially a set of beams positioned over a gap, the beams would experience bending as well (for example the horizontal beams in Warren truss).

I read some answers on another topic on Quora: Why truss bridges use a non-fixed support?

One of the answers was that if we used fixed supports on both ends, then the truss bridge would experience bending moments and the whole purpose of using a truss network would be lost. Could somebody shed some light on this? Why is this fact true?


texts: Issue with collapsed element in LISA Finite Element Analysis

texts:
I'm new to the FEA world and trying to learn the ropes through resources available online. I've imported a model into LISA FEA that I would like to analyze, however, when I press solve to conduct my analysis I'm getting an error message that states the following:

  Error: Element 1 is collapsed. More than one local node share the same local node.
  Warning: Elements 395, 400, ... overlap each other.
  Failed

Being so new to this, I do not have any idea as to how to interpret this. M question is: how can I tweak my model to get rid of these error messages. Namely, how do I "uncollapse" an element? How do I stop elements from overlapping?

Although this is a LISA specific question, and I would appreciate advice as to how to overcome this directly through LISA, I am also open to general advice applicable to other types of FEA. If anyone could give me a few pointers as to how this issue is dealt with in FEA software, I would be greatly appreciative.


texts: Why is it impossible to create an observer for this not fully observable system?

texts:
Consider a 1D point-mass moving along an axis. A force $u$ is applied as control. There is no gravity or other forces involved. The system can be described in state space equations as:

$$\begin{align}
A &= \begin{bmatrix} 0 & 1 & 0 \\
                     0 & 0 & 1 \\
                     0 & 0 & 0 \end{bmatrix} \\
B &= \begin{bmatrix} 0 \\
                     0 \\
                     \dfrac{1}{M} \end{bmatrix} \\
C &= \begin{bmatrix} 0 & 0 & 1 \end{bmatrix} \\
D &= [0]
\end{align}$$

The shown system is controllable, but not observable. Not even structurally observable and most certainly not fully observable. Thus, it should be impossible to construct an observer for this system.

However, if I know the initial state of the system, I can compute the full state at every time, i.e. by integrating the system's output. How does this fall in line with the concept of observability? How would I incorporate the initial state into the equations?

I can't find the error in my train of thought, but I am certain there is one. Do I misunderstand observability?


texts: How to determine the compressor power in a refrigeration system?

texts:
The picture below represents a refrigeration unit

In order to calculate the power produced by the motor, two quantities must be measured

Angular speed of the motor. This parameter can be observed from the tachometer, which indicates the rotational speed of the the compressor. The belt pulley ratio is used to find the rotational speed of the motor.
The torque produced by the motor. In my lab's manual, it is written that the spring balance reading times the troque arm is equal to the torque produced by the motor. Can you help me understand how does this spring balance reading indicates the torque produced by the motor? (I know that the the torque is equal to Fxd, but I can't understand how does the spring balance reading represent the force produced by the motor)

Also, it is written in the manual
"Assume typical compressor friction force =5N"

Does this value represent the friction between the belt and the motor? If not, then What does this value represent?

And I think that since there is friction, then power dissipation will occur due to friction and thus Power delivered to the compressor = Power produced by the motor minus power dissipated by friction"

Please, if there is something wrong, correct me


texts: How does thermonuclear warhead yield scale with size?

texts: The Tsar Bomba packed a yield of 50 megatons into a package 2.1m in diameter by 8m long.  Assuming that the lead tamper modification was not used (which boosts the yield of the Tsar Bomba design to 100 megatons), how much would the yield scale as a multiple-stage thermonuclear warhead (assume that extra stages are added as-needed) was scaled up, say to 3.5m diameter and 20m length?


texts: Does this soil get compacted by occasional heavy vehicle traffic?

texts:
Soil compaction can occur through heavy vehicle traffic. I attached a picture (see below). There are three samples approx. to 5m distance to each side of a paved road. Vehicle traffic is sprodically (few times in a year, e.g. at harvest).

Do you think at the sampling points in the soil (0-30-cm depth) compaction could have occurred through vehicle traffic? The blue area is untilled, i.e. more aggregate stability. The grey part is tilled, i.e. soil aggregate structure is loose.*

*The thing is, I noticed very high accumulation of soil organic matter under the blue area which also had lots of vegetation one yr prior to sampling -- unlike the grey area which has been cropland for long time. It is said that compaction can suppress mineralization of soil organic matter because of lower aeration in soil which inhibits decomposer communities.


texts: Selecting a water pump for low flow and 1 Bar pressure

texts:
I am designing a small automatic drip irrigation system. There will be about 10-15 drippers. Flow through the system will be about 1 l/minute, but this may change if expanding or reducing the system. The entire dripping irrigation system expects a pressure of around 1 Bar (precision is not needed). I only have a water reservoir and I planned to use a submersible pump (ideally a quiet one) to pressurize the fluid system.
This seems to be harder than I expected because all the pumps I see are designed for completely different conditions - especially much large flow - e.g. 15 l/minute. If there is one with a lower throughput, then it also has a smaller pressure than I need. It looks like moving a small amount of water at a higher pressure is harder than a larger amount.
Some ideas:

Can a water pump e.g. 12V, 1.5 Bar, 15 l/minute be used with a lower voltage to achieve 1.5 bar and 1/l minute? Could this be combined with pressure sensor and PID regulator?
What about some water returning back to the reservoir to keep the water flow at 15 l/minute. Could a pressure valve returning water back to the reservoir be used for this?


texts: How/where can I find the bending and shear strength of certain materials?

texts: I'm working on a design project and I need to know the bending/fluxural strength and the shear strength of some materials so I can determine if my design will fail. However the wikipedia page (for aluminum 6061, for example) only lists the tensile strength. Is there a way to calculate the fluxural and shear strength or are these values in a database somewhere?


texts: Can I increase pressure on the output side of a backstop/security valve?

texts:
I'm working on a system with non-deterministic pressure (because it's based on bio mass fermentation) where CO2 is generated and input into the system at maximal pressure x (e.g. 2 bar). If additional CO2 is produced it ought to be stored in a container with pressure > x and released back into the system through a pressure regulator if the pressure in the system falls < x.

I assume that the input side of the container/storage has to be a backstop valve in order to keep the pressure in the storage. Based on technical terms (which I only know superficially) it has to be a security valve, because it has the function of releasing pressure > x. Usually security valves do that into a space with less pressure (in my use case the pressure will be higher at the second occurance of over-production of CO2). Is there a backstop-security value which allows to redirect all pressure y with y > x into a container with pressure > y?

The container/storage has to contain a (different) security valve which releases pressure into the room if it exceed the maximum of the container.


texts: Natural gas boiler Vs. Electric Heater efficiency

texts:
If a facility buys natural gas at 8 dollars/Mcf to provide heating from an 85% efficient natural gas boiler, what is the equivalent cost of electricity ($/kWh) for a 95% efficient electric heater?

I'm not sure how to relate these.  What equations can I use?  Where do I begin?


texts: Low cost feedthrough for an acrylic vacuum chamber

texts:
I am currently building myself a "hobby" vacuum chamber from 1 inch tickness acrylic sheets (I am very aware that acrylic is not the proper material). Inner dimensions of the the chamber is 40x40x40mm. After a few simulations in Solidworks, safety factor and displacements seemed okay.

What I need is to feed 8 cables through the sheets. After a research, I couldn't find any airtight cable gland or any low cost vacuum feedthrough. What is your suggestion for a low cost feedthough?


texts: How can steno's law of superposition be relevant in construction?

texts: Steno's law of stratigraphic superposition states that younger layers of rock sit atop older layers. Meaning that the youngest stratum in a sedimentary sequence will be at the top and the oldest at the bottom. I'm trying to understand how this phenomenon would affect the construction of a civil structure like a building or a bridge for example.


texts: Why do centrifugal compressors have a higher compression ratio per stage than axial compressors?

texts: It is common for centrifugal compressors to have a pressure ratio of one stage of 3, while axial compressors often have compression ratio per stage of around 1.25. What is the source of that difference in performance? Is it because the air nearer the axis of rotation in an axial compressor is slower, while in a centrifugal compressor all of the air has to pass through the high speed tips of the vanes?


texts:
Ive been wondering about how small of a cooler you can build.

Although this probably is just really low-level engineering, i have a rather particular question.

For my idea, the cooler has to be as small as possible, rather efficient and not use a chemical compound or reaction that is not locally reversible. It has to be an fully working circle that, theoretically, keeps working, solely relying on electricity for power.

While I understand how certain cooling systems work, I could not find a satisfying example, since mobile phones, tablets and other handheld devices rely on, if any, air cooling.

However, what I'm searching for woul'd be a small cooler that can reach slightly lower temperatures than the surrounding area, lets say about 5 °C, maybe less or even more, if it just gets below average surrounding temperatures (room-temperatures).

Would this be achievable in a watch-like size?
And how efficient woul'd that be, running on electrical reloading only?

EDIT:
The heat would, as far as i understand thermodynamics, not be a big problem.
A short-range "relocation" (idk the term) about a few centimeters to a small vent would be enough.


texts: Where exactly will a hydraulic jump occur?

texts:
I know that an hydraulic jump can occur only when the Froude number is higher than 1 (supercritical flow), and I am familiar with the Bélanger equation. However, I feel like I have a fundamental misunderstanding about hydraulic jumps: if a jump can occur when Froude number is larger then 1, what prevents the flow in rivers from "jumping" immediately whenever its Froude number becomes slightly more than 1?

I mean how can a fluid develop a very high Froude number without making a hydraulic jump? According to what I read, in industrial applications such jumps are specially induced on the fluid to dissipate its energy. So I want to understand how it's done.


texts: Lubricant fluid and Rubber compatibility

texts:
I have a portable band saw, which I plan to add lubricant fluid to (this is getting ahead of myself, as I haven't even constructed a portable band saw stand). The main problem with this and the reason why manufacturers do not advise using lubricant fluid is because the band saw blade might slip off the tires.

So that got me wondering what rubber and cutting fluid pairings would be compatible. I don't mean just chemical compatibility in which the rubber would NOT BE degraded by the fluid, but fluid that will not cause rubber to slip.

Also, I've been wondering... Why do portable band saws use a tire wheel (grips) rather than a train wheel (with ridges) type of wheel?


texts: Do DC generators require more maintenance than AC generators?

texts:
Whilst researching, I found several sites that suggested DC generators required much more maintenance than AC generators. From what I can tell these sites seem to have assumed that the AC generator was brushless while the DC generator had brushes. So it would make sense that the DC generator would require more servicing in this scenario.
However, I'm still wondering if there is any truth to this, is there some other factor that results in DC generators having a shorter lifespan than AC generators?
The sites in question:

site 1
site 2
site 3


texts:
From wikipedia:

  Before opening either door, the air pressure of the airlock—the space between the doors—is equalized with that of the environment beyond the next door to open

Anyone knows how this work? What the mechanism make possible "equalize" the air pressure between the doors? For example, in the ISS (International Space Station).


texts:
I need help with a question regarding diffraction gratings. It goes something like this:

Assume that you have a diffraction grating. When you shine light of different wavelength through this grating it will give different amounts of maxima. Let's say the grating has to satisfy the following: If we shine light of wavelength $\lambda_1$ we get $3$ maxima and if we shine light with wavelength $\lambda_2$ we get $5$ maxima. What values of the grating constant are possible given the criteria stated above?

I have tried to solve this using the grating equation, $d\sin a = k\lambda$ where I set $k = 1$ for 3 maxims and $k = 2$ for $5$ maxima and then look at what different values for the angle $a$ give. With $90^{\circ}$ as the maximum angle. However, using this method I find that $d > \lambda_1$ for $3$ maxima, and $d > 2\lambda_2$ for $5$ maxima which seems wrong to me. Is this answer wrong?

I would really appreciate all help!!


texts: Belt is to thick for my snowblower, how to thin or leave?

texts:
So I got a new belt, and it was the right length but the wrong thickness. I needed a 3/8 belt but it was a 1/2. I did go to get it but the guy looked it up and told me I needed this one. So I got it. But when I installed, as I figured, there was a small issue.

So the belt is running up on the "brake" as I call it. It is along the idler and when not engaged this flat metal holds it in place, so the belt does not run when I do not want it to I guess. But the belt is so thick that it is rubbing against this metal when engaged, when the metal is far from the pulley (I think it is called). So it has been burning the belt from friction.

So this is my thought to solving...

Let it burn. I am sure it wouldn't take time to burn down to the right thickness. My only problem is that the 'strings' could show. If this is a good idea in general.
Cut that metal off. All I see it doing is keeping the belt from spinning when not engaged. But the belt would be loose were I do not think that would be a problem to begin with. So unless it does have another purpose than to just keep the belt from moving. Couldn't I just cut that off? Then it would not contact the belt and problem solved. Thing I do not like on this is when I do get the proper belt will it be needed then. Side thought: Does this keep the belt from falling off?

2nd Update: Another thought is, since the belt is too thick, how could I thin it while it is running? I would have to remove a whole 1/8 inch.

I do not want to return the belt, it was only $7 anyway. So I hope this was understandable and there is a answer to this.

Note: I again, am not sure were to ask a question like this so I wold hope this is fine.


texts: Positions of Max Load a human would exert on horizontal rods of such a system by positioning leverage & bodyweight?

texts:
My mechanical & civil engineering usage is gone as the last time I did that was in Freshman year & my major went in another direction, but I've tried to be as thorough as possible using a prior question.
PS: If this has to go to Physics SE, please let me know or move it.

Based on this question I posted on DIY:
What kind of Extruded Aluminum sections to replace main wooden frame on this DIY project?,

I received a very detailed & interesting answer here from Ben Welborn pointing out various factors around angles, lengths loads, torque, Center of Gravity/ Mass etc.
I still have to completely digest the math/ calculations, which I'll have to do with my uncle.

That question was centered around the vertical sections, whereas he did help with determining some of the detailed loading parameters.

Here, I am curious to find "In what position would a human be exerting Max Load on the horizontal rods, and what would that load be?"

Constraints:
Human body weight: 200 lbs for simplicity. No added plates, dumbbells, barbells etc.
Rods are 36-40" wide and 1-2" in Diameter if that helps.

Position types:

No aerials & similar momentum; i.e. Handclap pull-ups.
Static positions as shown or what you guys can think of,
Dynamic positions/ movements; Hanging V-up, i.e. Straight vertical Hang and full leg sit up from the waist, but in steady control (I guess the 90 degree L-position would be max leverage), NO Crossfit style momentum.
No purposefully destructive positions/ movements as suggested in one comment;

The worst case scenario I believe would be to have Žydrūnas Savickas at the top of your structure (or at the midspan between two supports), resting his feet on the wall, grabbing one of the rungs and then trying to do a 524kg deadlift.

Please do not constrain yourself to only the given examples of what people are able to do, but I'm sharing examples to kick start things. Positions vary in being 1 or 2 handed/ legged, both on same or different horizontal rods.

Which of these or other positions/ leverage you might think of would be position of Max Load?


texts:
I'm not an engineer, just a novice hobbyist, so I'm not sure my terminology "compression clamp" is correct, but I'm attaching a drawing showing what I'm trying to accomplish.

This plate will be placed over two rods and then "screwed (partly) shut" so that the plate will "squeeze" the rods and not budge under normal operational stresses.  The machine screw is inserted into the hole the pink arrow points at and threads into the hole the yellow arrow points at.

My question: It seems to me that the threads will align properly if the gap between those two sections is cut in advance of the threading operation. Is that right? Or should the pink-arrow hole be left smooth-walled and only the yellow-arrow hole be threaded?


texts:
Sorry if this is the wrong site for the question.

How can I power this household lamp off the cigarette lighter in my car?

JANSJÖ LED wall/clamp spotlight, white

It comes with an AC adapter:

Intertek
4005088
kmv-070-030-na-2
Input 100-120V ~ 50/60Hz 0.09A
Output 7V = 0.43A 3W

In this picture the bottom has the standard 2 AC wall outlet prongs. They are difficult to see, but are there. The top has the two female sockets for the detachable cord that runs to the LED lamp.

Is the output DC?

I suppose I could just plug it into an inverter, but was thinking there might be a DC adapter to go from the vehicle's 12-15V to the required 7V for the LED.


texts: Materials to use for a low friction cable-pull

texts:
I'm posting this question on this stack-exchange site, because it appeared to be the one made for this kind of questions. If this happens to not be the case, I'm sorry, I didn't know better. Also forgive me any issues with terminology (or point them out to me), I'm not an engineer.

I want to build a music instrument (I won't go into details here, because I think it's not necessary). In this instrument there will be keys (in the picture I drew, the keys are the blue boxes, as seen from above. The Black arrows indicate the directions in which the keys are movable). If a key is pressed (which means "moved up" in the picture), I want a little string to be pulled.
The rope is drawn with black color, and one can see the way it is attached to the keys. The red circles are supposed to be the bars that will press the string out of its equilibrium position.

In the picture, the middle key is pressed, and the string is elongated because of this.

My question is: What materials should I use for the string AND the bars, to make the string glide on the bar as friction-less as possible?

Some additional information:
There will be 20 keys, and the distance they move, if they are pressed, is 5 millimeters. The string can't be thicker than a thick guitar string.

My initial thoughts were to use fishing line, and make the bars out of brass. But maybe there are better options to use.

Edit

The string isn't vibrating, and it won't be the thing to be responsible for the sound. Maybe I should have written "rope" instead of string. The purpose of the strings seen is to activate a little switch, when the key is pressed. To accomplish this, as the keys are pressed (and move), the string will be elongated, as it slides over the red bars. The ellongated string then pulls a little switch.

It is to say that there is some tension on the string (the switch effectively raises one of the vibrating strings, so the force acting on the non-vibrating strings is roughly the same force it takes to pull a guitar string out of its equilibrium position).


texts: Finding phase velocity for froude number scaling

texts:
So I am calculating phase velocity of a wave for Froude number scaling for model testing of a boat. I got data from Lloyd's Rules saying for the specific sea area I did $H_s=3.6\text{ m}$ and $T_z=6.8\text{ s}$.

Assuming a regular, progressive wave (this is where I might be wrong) and using the deep water relationship of $\lambda = \dfrac{gT^3}{2\pi}=712.5\text{ m}$.

Wave celerity $v=\dfrac{\lambda}{T}=\dfrac{712.5}{6.8}=104.7\text{  m/s} = 377\text{ km/s}$? Am I doing this right? Are ocean waves supposed to be that fast?


texts: Kfactor for laminated steel plates rolling

texts:
I need to make a flat pattern for a cylinder made from a steel plate 44mm thick laminated with explosion cladding stainless steel plate of 8mm total plate thickness is 52mm.

How I usually work is take the mean diameter of the cylinder (Inside diameter + thickness ) * PI. To get the developed length of the cylinder. resulting in use of Kfactor 0.5

But now there are materials bonded to each other I fear the Kfactor of 0.5 might not be correct.

Additional the laminated plate 8mm is on the inside diameter side.

The plate will be rolled into shape.

What Kfactor should I use in this case or is 0.5 a good Kfactor?


texts:
From my understanding, the Euler Bernoulli Beam theory is mostly used for small angle displacements, and an implication of this assumption is that the length of the beam is subject to distortion and stretching, meaning that when the beam is bent, its length is greater than when relaxed, due to the fact that the end of the rod always remains in line with the end of the rod at equilibrium. The theory thus fails for larger displacements when the change in length of the beam actually affects the result.

Does Timoshenko beam theory suffer from this issue as well? Do beams in Timoshenko theory have consistent length? Are there simple ways of conserving the length of the beam in these theories? Or is the only way to use Geometrically Exact Beam theory and do finite element methods?


texts: How to calculate the speed and force of the piston in a vacuum syringe?

texts:
Suppose i have 4 empty syringes. And by empty i mean they were having the air sucked out of them, and they "contain vacuum". Assume the head of the syringe is blocked so vacuum can be formed.

I want to understand how to choose between this 4 different syringes.

My goal is to have the piston reach the highest speed possible. I don't know how to calculate what is better.. should i increase the diameter? - should i keep the diameter the same but make the syringe longer.. what is better?

When i release the piston - the atmospheric pressure will make the piston move pretty fast - and blow up the head of the syringe.

This is not a real world example. Just something for me to learn. I don't know what the piston friction with the walls is - but is the same for all 4 syringes so does not matter when comparing them.

Also i don't know the mass of the piston either.. i mean we can use a gut number like 0.25 kg. And the bigger piston is 1kg.

Now how to calculate all this?

Also i'm interested in forming an intuition of what to expect given changes to the design of this syringes rather then exact numbers. What happens if i increase the diameter 3 times.. is it better or worse .. that kind of thing.

Does it matter how long the syringe is? Can it happen that if i make it too long then the piston is actually slowed down? Is this piston constantly accelerating while is in the syringe and there is still vacuum in front of it .. or not actually? Can air to air turbulence slow things down? Where is the highest acceleration at? Maybe in the middle of the syringe ?

I say this because if we go down to 1 mm tube, then capillarity is so high that you need to push on it like crazy to make things move. I'm thinking about what force is needed to squeeze that fluid in a medical equipment (needle + tube). So when it comes to tubes like this, maybe having a higher diameter is better?! Maybe this applies to air also?

I can put the numbers in a calculator and get the result, but i'm interested more on how to think about this, not just the formula. How do you break it down in your mind - and not be wrong?

But i do want to lean how calculate the exact numbers as well. Thanks :)


texts: How to reduce oscillations (rapid changes of control signal) when controlling a real system, which occur due to noise in measurement from sensors?

texts:
I have a real mechanical system (ball & beam) which I want to control. The system is approximated by the second order transfer function:

$$ T(s) = \frac{b_0}{s^2+a_1s+a_2} $$

and in state-space form:

$$ \dot{x_1} = x_2 $$
$$ \dot{x_2} = -a_1x_2-a_2x_2+b_0u $$

where the parameters $\ b_0,a_1,a_2 $ have been identified, so they are known. I have designed two controllers. The first one is a full state feedback controller described by the equation:

$$ u = -Kx+k_rr $$

where the term $\ k_rr $ is because I want input reference $\ (r) $ tracking. The other controller is a dynamic state feedback controller desctibed by the equations:

$$ u = -Kx-k_iz $$
$$ \dot{z} = x_1-r $$

Both controllers are doing well but the only problem I have is when the ball reaches the reference point there is a bit of oscillation of the system (the beam oscillates) in order to keep the ball at the desired point. I have found out that the oscillations occur due to the measurement of the ball's position and not because of the gains of the controllers because this happens even if I make these gains smaller. The sensor used to measure the ball's position on the beam is a linear potentiometer and it appears that the measurements include some unwanted noise which results to rapid changes of the control signal which leads to the oscillations. I have tried to reduce the noise by using a low pass filter with the below transfer function:

$$ F(s) = \frac{15}{s+15} $$

The block diagram of the control loop is:

The oscillations have been reduced but not achieved a satisfactory level. Is there any way to modify these controllers in a way to affect these oscillations and reduce them ? Would a PID-controller perform better due to the existence of the derivative of the error ? Or should I design a better filter for the noise reduction which should also be fast (because the system is functioning in real time) enough ?

I place some plots for two different cases (PD-controller gains) where the actual position (output) is shown compared to the reference and the control signal. Note that the sudden changes to the real system's output are due to external disturbances I apply in order to check if the system goes back to the reference.

First Case ($\ K_p = 3.9352 $ & $\ K_d = 2.248 $):

Second Case ($\ K_p = 2.3536 $ & $\ K_d = 1.6423 $):


texts: Calculate thickness of a 1 square meter window made of acrylic in a submarine to endure 100meters

texts:
This question would have two parts:
1 - How to calculate thickness of a 1 square meter window made of acrylic in a submarine to endure 100meters of deepness in salt water?
I don't remember the procedure to calculate this, even If I have done it in the past during mechanical structure classes. So any help with the calculus, or from where to get the formulas, is appreciated.
2 - Roughly speaking, this is the same strength required for the material to endure the weight of a column of 100m tall and 1 square meter base of water? So, 100 Tons?


texts: Is there an easier way to calculate rocket engine Isp?

texts: I am trying to calculate the $I_{sp}$ of a rocket with a thrust of 500 kN. I know that you can calculate $I_{sp}$ with $I_{sp} = \dfrac{v_e}{g_0}$. However, to calculate $v_e$, you need the $I_{sp}$: $v_e = g_0 \cdot I_{sp}$. How do I calculate both without having to set one value (Other than $g_0$)?


texts: Calculation of the stored energy for a heat storage tank

texts:
There is a heat storage tank that is directly loaded from the top and the heat is also taken from the top.
The colder water from the heating circuit return flow enters the heat storage tank at the bottom. This creates a layered water temperature in the heat storage tank.

There are three temperature sensors inside the heat storage tank.

Is it possible to calculate the stored energy via these three temperature sensors?

Edit - Calculation Attempt according to Solar Mike:

$V_{storage} = 1000\ l = 1\ m^3$

$t_{top} = 82\ ^\circ C$, $t_{middle} = 70\ ^\circ C$, $t_{bottom} = 55\ ^\circ C$

$t_{average} = \frac{82+70+55}{3} = 69\ ^\circ C$

$Q = M \cdot c_{H_2O} \cdot \Delta T = V_{H_2O} \cdot p_{H_2O} \cdot c_{H_2O} \cdot \Delta T $

$\ \ \ = 1\ m^3 \cdot 1.163\ \frac{kWh}{m^3K} \cdot (69\ ^\circ C - 20\ ^\circ C) = 56.987\ kWh$

Does this calculation give me a fairly correct value for the stored energy?


texts: How does a nuclear reactor initiate nuclear fission?

texts: How do we start a nuclear chain reaction? For example, if we wanted to do it this weekend, what would we need, and what are the basic steps? I'm not looking for a text book response or highly detailed information. I'm only curious about the most basic components. For example, we need to take A and B and submerge it into C? That's all I'm asking. If you had a daughter, and she asked, "What happens in a nuclear power plant?", what would you tell her?


texts: Is hall sensor also used in PMSM drive scheme as like used in BLDC motor?

texts:
I am little bit curious about, is hall sensor also used in PMSM motor drive? Since in PMSM motor the voltage applied is sinusoidal, all 3 phase are active, so a rotating flux is introduced, which is not in BLDC motor. In BLDC motor only two phase are active at any instant. So it is necessary in switching in BLDC motor. But due to rotating flux in PMSM there is no any requirement of position sensor. Is my view correct or not?
Please help me.


texts: How to calculate the flow rate of a gas through a pipe?

texts:
I am trying to calculate the flow rate of Nitrogen through a cylindrical pipe.

I only need a ballpark value, and the only information I have is the inlet pressure as 15 psig (assuming the same pressure throughout the pipe, so there is no pressure drop), the pipe diameter as 6" and material which is stainless steel.

I tried applying Bernoulli and Poiseuille's equations but I since there is no pressure drop and I do not have a pipe length I am unsure how to use these equations.


texts: How to read the block diagram for the 2nd order integrator feedback system?

texts: This is a prework for a lab, I haven't seen things in the picture before and have no idea on how to transfer this to an equation.


texts: Would it be possible to put an anti-condensation coating on, say, an ice bag such that it will not get wet in use?

texts:
I have seen anti-condensation coatings for glass, but as far as I know they're designed to cause any moisture that does form on them to sheet rather than bead. They do not, however, actually prevent condensation, and I don't see how any product could (other than extreme insulation, of course). The formation of condensation is an issue of physics; warm moist air meets cold surface and since cold air holds less moisture than warm, the moisture forms on the cold surface. On the other hand, engineers are pretty clever, so if there's a way to prevent this, it may be possible, even if I can't figure out how.

This question is actually prompted by some reviews of some ice packs I recently purchased from Amazon, in which reviewers complained about condensation, which seems like a nonsense complaint.

Sorry about the tag, but I tried "condensation," "dew," "moisture," "water," and maybe a couple of others and got no match.


texts: How to consider shear forces in CEB/fib 2010 three-layer model for concrete slab design?

texts:
I have a question about design of concrete shells with three-layer method described in p.7.3.2.2 fib Model Code for concrete structures.
The main idea of method is that we divide shell on three layers. The outer layers provide resistance to the in-plane effects of both the bending and the in-plane axial loading, while core provides a shear transfer between the outer layers.

The action effects of applied loads are expressed as eight components, three moments per unit width($m_x,m_y,m_{xy}$), three axial forces per unit width ($n_x,n_y,n_{xy}$) and two shear forces per unit width ($v_x,v_y$) in directions parallel to the orthogonal reinforcement.
(there is positive directions of forces on picture)

Then we use some formula to find forces in the outer layers.

$$\begin{alignat}{1}
n_{x,inf,sup} &= \frac{n_x}{2} &&\pm \frac{m_x}{z} &&+ \frac{v_x^2}{2v_0}\cot(\theta) \tag{7.3-1}\\
n_{y,inf,sup} &= \frac{n_y}{2} &&\pm \frac{m_y}{z} &&+ \frac{v_y^2}{2v_0}\cot(\theta) \tag{7.3-2}\\
n_{xy,inf,sup} &= \frac{n_{xy}}{2} &&\pm \frac{m_{xy}}{z} &&+ \frac{v_x v_y}{2v_0}\cot(\theta) \tag{7.3-3}
\end{alignat}$$

where:
The subscript notation inf and sup refer to the interior and superior faces on the element. The interior face is the tensile face for an element in positive bending.

$$v_0=\sqrt{v_x^2+v_y^2}$$

$\theta$ is the inclination of compression stresses in the core layer

Here we have the picture for the equations:

And here is my question(s):
Why is plus sign in equations (7.3-1 - 7.3-3) in front of

$$\begin{gather}
\frac{v_x^2}{2v_0}\cot(\theta) \\
\frac{v_y^2}{2v_0}\cot(\theta) \\
\frac{v_x v_y}{2v_0}\cot(\theta)
\end{gather}$$

Why $v_0\cot(\theta)/2$ direction in sup part of shell is the same as inf part?

I don't understand how we got this part in equation.
Does anybody have any information about the three-layer model? Can you explain me this part?
Do you know any articles explained this?


texts:
I am a chemical engineering student learning about material balance, so the problem below will not be a ‘real’ one , but just an exercise for me to understand better.

This system below is not a reaction.

My question is: can I say that the overall material balance for this system is:

$$F1 + F2 + F3 = P1 + P2 + P3$$

I have this doubt because Feed 3 comes in after Product 1 and Product 2 have been removed. Does this matter at all?


texts: Circular keyways - advantages / disadvantages?

texts:
What are the advantages and disadvantages of using circular section ("Scotch") keys, keyseats and keyways?  I am not referring to Woodruff style, I am only interested in the type where the key itself if a full cylindrical piece and the shear force is diametric.  For instance...

Woodruff style and straight cut style seem overwhelmingly more common than circular section types.  What is the reason for this?

It seems to me that it would be very convenient to be able to simply drill a keyway/keyseat into a parts before turning the ID/OD to it's final diameter.

In addition I would think that a circular feature such as this would eliminate stress concentrations that would be present on broached and milled square section cuts.  Key joint cutting is in any case a precision operation so I doubt there's any major loss in tolerance quality over other types of keys.

I don't have any particular application in mind for this, I'm merely curious.  However I would like to know some situations where circular keys are advantageous or not.

Edit: Further thoughts: Wouldn't a circular key actually experience more of a compression force than a shear force, especially under high torque applications?  Given the many non-parallel shear forces all converging at the centre of the key, this would manifest as compression would it not?


texts:
Is $p\cdot V^γ= \mathrm{const.}$ valid for only adiabatic reversible process and not for adiabatic irreversible process if not why?
Today I was doing an objective question as mentioned above and chose option "any adiabatic process" but the ans was "only reversible adiabatic process" but i couldn't understand why. All i know is that path followed by both process will be different but how will it affect the adiabatic equation i.e $p\cdot V^γ= \mathrm{const}$.


texts: Switching speed of PN diode is limited by reverse recovery time. Can Schotkky diodes rectify signals of GHz frequency? If yes, which ones?


texts: Interpretation of the testing data of my vehicle

texts: This is a plot of Yaw moment vs Lateral acceleration of my vehicle. I know that it can give me the analysis of trimmed conditions during cornering, yet unable to properly quantify it. What all can I achieve out of this plot. Thanks


texts: What is an unstructured mathematical model?

texts: I want to model a chemical process. I was searching in the literature to find similar works. In some of papers they say that "we proposed an unstructured model". What does it mean? What is the difference between a structured model and an unstructured model?


texts: Theoretical strength of pure and perfect crystals are way higher than the strength of crystals with dislocation?

texts:
Apperently in the beginning of material science they theoretically calculated the strength of perfect crystals, which was way higher than the experimental strength. The difference was later ascribed to the presence of dislocations.

How is this possible?
To strengthen a material you can strain-harden it by plastically deforming it and thus impose more dislocations into it. So the more dislocations the higher the strength will be; how then is a crystal with no dislocations stronger than one with dislocations?


texts:
In my project I've been using galvo scanners for rotating small mirrors but they seem like an overkill at this point for several reasons:

1) Even though I use the slowest and smallest scanners out there, they are still over 100 grams each, in a device where every gram matters,

on top of that, their drivers are rather large (8cm x 6cm) and need special dual rail +-12V power supplies and +-5V DAC circuits to run. These all require space of their own and I need everything take up as much little space as possible.

2) While they can achieve the rotation speeds I need they seem to exceed it. The cons of using galvos which is space for all the electronics seems to outweight the pro of the high speeds which aren't used to the fullest anyway.

Since steppers just need one 3.3, 5 or 12V PSU and one stepper driver I thought I'd give them a try.

The smallest steppers I am aware of which are readily available are NEMA 14, which is huge for this.

The requirements are simple:

1) torque is extremely low as a small 10x10mm 1mm thick mirror is rotated which is glued onto it.

2) acceleration and rotation speeds are important and demanding though: 500 degree/second

I've found a stepper but the rotation speed is abysmal for this. The 28BYJ-48

My question is this:

1) Can small enough steppers meet this criteria (low torque but high speed requirement) at all?
Bigger motors seem to achieve the desired result https://youtu.be/KgPyR0Rg3FQ?t=1m17s
2) If yes, what stepper(s) should I check.
3) can they not make those loud sqeaky noises like in CNCs and 3d printers?

https://youtu.be/pyFZKc356eQ?t=2m1s


texts: the angle of water surface in a moving car

texts:
in this picture, there is a container of water and it is moving on the slope.
we want the acceleration of the container while the angle of water surface is parallel to the slope.
so the book says the answer is that we let container move by its own weight so $\color{red}{a_x=g\,sin\alpha}$.
but what i'm asking is that let us think the slop doesn't exist. so the accelerations would be like this:

and the formula of the angle of surface in fluid mechanics is: $$\color{green}{tan\,\theta= {\Sigma a_x\over \Sigma a_y}}$$
so in this case $tan \theta $ would be:
$$tan \theta={gsin\alpha\over gcos \alpha}=tan\alpha$$
so $$\theta=\alpha$$
and this means:

and this is wrong because we know if we let the container move by its own weight, the $\theta$ would be $0$
i don't know what am i missing here.


texts: How do I determine overcurrent protection for a transformer?

texts: What is the required: an overcurrent protection for a 3phase, 150kVA, 277/480V-120/208V transformer. With an expected load of 20a mps (3 phase 208v).


texts: Should sum of all joint reactions be zero when nodal displacement is applied?

texts:
I created a structural model of a laced strut using plate elements. To study second order effects of bow imperfection, I applied a joint displacement of 20 mm in a SAP 2000 v18 model. When the analysis was completed, I double checked the results and found a large joint reaction in the range of 300,000 kN at the joint with applied displacement. Elsewhere, joint reactions do not exceed 1,000 kN.

The model ran with no warnings or errors. I expected the sum of all forces to be zero for equilibrium, but that seems not to be the case. The global displacement looks fine with the laced strut bending to the specified displacement.

Should all joint reactions sum to zero, if nodal displacement is applied?
Should the joint reaction at the node with specified displacement be disregarded?


texts: i have problem with cartesian coordinates pendulum EOM in matlab

texts:
I made my code like this,

function DK = pendulum_cartesian(t,K)
g = 9.8; l = sqrt(K(1)^2 + K(2)^2);
DK = zeros(4,1);
DK(1) = K(3);
DK(2) = K(4);
DK(3) = ( (-K(1)*K(3)^2) - (K(1)*K(4)^2) + K(1)*K(2)*g )/(l^2);
DK(4) = ( (-K(2)*K(3)^2) - (K(2)*K(4)^2) - (K(1)^2)*g )/(l^2);

theta = atan(K(2)/K(1));

plot(t,theta);

end

and i typed,

[t,K] = ode45(@pendulum_cartesian, [0,10], [0.1,0.00017,0.1,0])

but there is no value in theta, and plots nothing.

where is a problem?