texts: Regarding the ITTC Guidelines for Ship CFD applications

texts:
I was reading through the  ITTC – Recommended
Procedures and Guidelines - Practical Guidelines for Ship CFD Applications (https://ittc.info/media/4196/75-03-02-03.pdf) document and this little thing kept me thinking. In page 9 the distance y of the first point from the wall can be computed is said to be computed as $y = \frac { y ^ { + } L } { \operatorname { Re } _ { L } \sqrt { \frac { C _ { f } } { 2 } } }$. And right below $C _ { f } = \frac { 1.328 } { \sqrt { R e _ { L } } }$.

Now let's try to deduce the formula for $y$.
 \begin{cases}
   \tau  _ {  w  } = \frac { 1 } { 2 }  \rho   U  _ { e } ^ { 2 }  C  _ {  f  } \\
 u ^ { * } = \sqrt { \frac { \tau _ { w } } { \rho } }
\end{cases} $\Rightarrow u ^ { * } = \sqrt { \frac { \frac { 1 } { 2 }  \rho   U  _ { e } ^ { 2 }  C  _ {  f  } } { \rho } } \Rightarrow u ^ { * } = U_e\sqrt{\frac{C_f}{2}}$

$\begin{cases}
 y ^ { + } = \frac { yu ^ { * } } { \nu } \Rightarrow y=y ^ { + }\frac{\nu}{u^{*}}= y^{+}\frac{\nu}{U_e\sqrt{\frac{C_f}{2}}}\\ Re_L= \frac{U_e L}{\nu} \Rightarrow \frac{Re_L}{L} = \frac{U_e}{\nu} \Rightarrow \frac{\nu}{U_e}=\frac{L}{Re_L}
 \end{cases}$

$\Rightarrow \boxed{y =\frac{y ^ { + }L}{Re_L\sqrt{\frac{C_f}{2}}} }$

So in the deduction $C_f$ is the local friction coefficient, but in the guidelines, $C_f$ is obtained using a formula for an average friction coefficient. So in my opinion $C _ { f }$ should be calculated by $\frac { 0.6642 } { \sqrt { Re _ { x } } }$.

What do you think?


texts: Resistance measurement for electrically conductive textile sheet

texts:
I have some rolls of coated textile I want to characterize, including some measure of how well the material conducts electricity in the plane of the textile so I can judge which type is least likely to produce electrostatic sparks.

I've found two methods used for measuring surface resistivity or resistance in high-resistance materials.  The first is using a flat plate at either edge of a square sample, where sample size is irrelevant as long as it's square.  This gives resistivity in ohms per square.  This would require me to cut samples and would prohibit in-situ testing of the end-product that this textile is going to be used for.

The second method used a set of needle-point probes to pick random points on a sheet.  First a measurement was taken with 1cm between the probes, and then a second measurement was taken with a 10cm distance between the probes.  The results were not the same, but no explanation was given as to why two measurements were taken or what this technique is useful for.  This technique would be much easier to implement, but I'm not sure if the results are useful or how they should be interpreted.

What's the appropriate measurement method for my application?  Are there any standard procedures for performing the second method I described above?


texts: Are there any materials that can not be drilled or sawed?

texts:
Are there any materials, such as a type of tempered glass, that can not be drilled or penetrated by any means (steel drills, diamond drills, saws, lasers, ablation with focused ion beam machines, etc) without some sort of dramatic evidence of such drilling (cracks throughout the entire piece, or a dramatic change of color of an area covering several square centimeters, etc)?

If not, are there materials that can not accept holes over a certain size, but that will accept smaller holes?  For instance, maybe there is a material that can accept 50 micron holes but not 1mm holes.

The machinist may or may not have access to a full-fledged laboratory with million-dollar equipment, including things like focused-ion beam machines.
If there is a material that resists attacks using inexpensive machines (under $100,000) but not things like focused ion beam machines, that would still be interesting to me.

Additional info:

My goal is to build a tamper-evident container about the size of a brick, perhaps 120mm x 120mm x 180mm.  That rules out some materials, such as nitrogen triiodide, which can not be used to make containers.

I'm aware that there are existing ways of building these containers using electronic sensors connected to something, such as a random arrangement of printed wires encased in epoxy, or some sort of mechanical trigger.  I seek to develop a more sensitive scheme that is harder to bypass by having the container itself be made out of a material that amplifies the effect of an intrusion attempt.

I'm pretty familiar with tamper-evident seals, and find they all are either pretty easily defeatable (i.e. in a lab setting; perhaps they are good enough for particular field applications), or require detailed non-automated inspection to determine tampering (such as requiring the detailed comparison of before & after photos, as I hear is done using random solder and wire-brush marks on some nuclear program auditing seals).  I am also familiar with some micro-level tamper-evident schemes, such as putting an additional patterned metal layer on a chip, with capacitive sensors on the layer below to sense tampering.

I realize these sorts of clever electronic or mechanical schemes can provide some degree of tamper evidence.  Lately I've become curious if these traditional approaches can be improved upon by deploying a special material that is inherently tamper evident.


texts: Accurate distance sensor via soft materials

texts:
I'm trying to find a sensor that can measure distance between sensor and some sort of detectable material (metal or small wireless chip) size of no more than a penny.
It should be able to measure through fabric as thick as (~40cm) with max distance of 2 meters and accuracy 0.3%.
What are my option if any?


texts: How to grind smooth hard rock to create a road surface

texts:
I have a situation where I have a rough granite roadway about 15 feet wide and 50 feet long. The granite is solid granite. The surface variability is on the order of a maximum of about 4 inches. In other words at no place on the surface is one segment of the granite more than 4 inches higher than the granite adjacent.

I need to smooth this into a crown. A crown is a gentle slope that allows water to shed off to the side of the road.

Is there any kind of mechanized equipment that can do this kind of work?


texts: Concept design for an extension to a blanket raft slab

texts:
A blanket raft is a type of solid slab raft consisting of deeper ‘toe’ sections running around the edge of the foundation as well as a central deeper ‘beam-like’ section which offer rigidity to the slab. The blanket raft in question is 250 mm deep with top and bottom A393 reinforcing mesh supported by 400 mm deep 600 mm wide toes with 4 no. top and 4 no. bottom 20 mm diameter bar reinforcement and 16 mm diameter shear links (see below).

This blanket raft is to be extended to accommodate additional plant, however, the average loading per square metre is to be less. Consequently, the same depth of 250 mm and reinforcement detail can be used with two layers of A393 mesh top and bottom. The primary difficult depends on where to place the deepened ‘beam-like’ sections and how to achieve fixity between the existing foundation and its extension. The proposed method to achieve this is to scabble back the edge of the existing slab (to achieve good bond with the existing concrete) and to drill and dowel the new rebar into existing slab. By way of a concept design, I have proposed the location of the deepened 400 mm deep by 600 mm wide sections of the slab extension.

Is this a good layout for the deepened sections of the extension to the blanket raft?

Is it necessary to put a deepened toe on the extension immediately adjacent to the deepened toe of the existing slab?

Should the dowels be epoxied in or greased in (do they only need to function in shear)?

Can you suggest what are the primary considerations during the concept design stage?


texts:
Hi there I found my self with a broken pair of headphones for which I am designing a spare part in Inventor right now. (Using Inventor Professional 2020).

I have the problem that I have a set of extrusions to move since they are interfering with other parts of the model and because the model itself is not in the right dimensions yet (I went with modelling the part to coarsely resemble the proportions and shape and bother with the dimensions last which is usually a straightforward enough thing to do). Now how can I move the extrusions shown in the below picture? I have tried moving the axis on which I have placed the extrusions but that leaves me with the end of the extrusion hanging in the air which is obviously not to be desired. Moving the layer on which the 2D Shape to be extruded is drawn after moving the axis is not possible since this results in an infinite loop of dependencies (why actually?)

Since I just realized that other than in some other SE(-ish) sites it is not posible to post attachments you find the 3D model of my part here: https://drive.google.com/open?id=1Kg2T7q0JwWIVn6-k4mO3M5ZtNvWAFk4N
so you can tinker around with it as needed. If someone sports an older version of Inventor I can provide a version saved in an older format on demand.

Obviously answers like "remodel it completely" are not the type of advice I want to hear. If it is really not possible without going beyond reasonable labour ok then be it that way else not.

EDIT: As pointed out by Optical Resonator it is not clear that I tried to go with an extrusion that is always orthogonal on the bent surface but this is what I tried to archive...


texts: Where do the tributary angles/ratios for tributary areas come from?

texts:
When preparing load calculations for a slab, the quick method is to define the tributary areas of a slab for the beams/columns below. These are generally taken as lines at mid-span of the slab panels and, depending on the support conditions, at the edges at angles of 30 & 60 or 45 & 45 degrees.

Where do the 60/30 and 45/45 angle ratios come from? Example distributions are shown in the image below.

I know that in reality the ratios depend on the stiffness and end conditions of the various structural members, I also take it that the tributary areas are somewhat affected by the load they are carrying. Would excessive loading on one panel, compared to the adjacent panel affect the areas?


texts: How do I convert coefficient values from 1/3 octave band to 1/1 octave band?

texts: I have some coefficient values i.e. 74.9, 81.3, and 80.5 at frequency centers 63, 160 and 400 Hz. The values are 1/3 octave band values. I would like to convert them to the 1/1 octave band values. Can someone suggest how to do that?


texts: Name of the ball screw nut used in pistons?

texts:
I have seen several products on the internet marketed as 'ball screws' that have both the screw itself and the special ball bearing nut. They are intended to have a motor mounted on one end of the screw to rotates it, causing the nut to be moved.

However, I'm looking for the particular kind of ball screw where the nut is part of a gear, and mounted via axial bearings, so that as it is rotated it remains stationary and the screw is extended.

Are these things sold in complete units without any machining necessary? What are they called/where can I find one?


texts:
What is the minimum value of $R_2$ (in $R_1$) to minimize loading effect?

Please explain the concept.


texts: Incompressible flow field and Solenoidal flow field

texts: In case of incompressible flow, divergence of velocity field is zero so we can say that the velocity field is solenoidal. However, given that a flow field is solenoidal, is it necessarily incompressible?


texts: Is it better to heat a heat pump evaporator or the load directly?

texts:
I have a heat pump which moves heat from outside to inside. I also have a solar heating array that collects radiant heat from the sun. Given that my goal is to heat the inside (with minimal energy consumption from the heat pump), my question is: Is it better to heat the air inside with the solar array or to heat the heat pump's evaporator outside?

Breaking this down, it's a question of whether it's better to use these sources in parallel or in series. In parallel, the solar array heats the inside directly and the heat pump heats the inside directly. In series, the solar array heats the evaporator and the heat pump heats the inside directly.

Some other relevant details, the evaporator exchanges heat by convection and is limited to a minimum temperature of 0°C. This is because any colder and you risk freezing the convector, thus stopping convection. The environment can get as low as 3°C at night, meaning heat is exchanged across a minimum of a 3°C difference.

Assumptions for this, the heat pump can move 5kW of heat across a 12.8°C difference (8.3-21.1°C), consuming 2kW. The indoor heat loss is (let's say) 5kW for a 15°C temperature difference (5-20°C). The solar array acts as a heat reservoir with 10kWh stored at 40°C (5°C to 40°C). Finally, let's assume the heating time is 10 hours.


texts: What size feet for this wind-protection panel?

texts:
I need to create a series of free-standing perspex panels to add height to an existing fence for wind-proofing purposes.
My idea is that each panel would be fixed to two supporting poles that are mounted on flat horizontal 'feet'. In this diagram, the wind would be directly onto the unprotected side of the fence, so the new panels are on the 'inside' of the fence:

Dimensions:

Height of existing fence: 1 m
Height from ground to base of perspex
panel: 1 m
Height from ground to top of perspex panel: 2.75 m
Width of each panel: 1.4 m

-> Surface area of each panel: 2.45 $m^2$
Feet:

Made of iron (7.86 $g/m^3$) with cross-section 10 mm x 100 mm

-> Mass of each foot (per meter length): 1000 g/m
How long / heavy do those feet have to be to make the panels stable in a wind of (say) 6 m/s?


texts:
I am in the process of designing an off road vehicle and require a form of articulation between the front and back half and cannot find relevant information on the types of joints available.
I'm looking for movement similar to the vehicle in the video posted
https://www.youtube.com/watch?v=WT73uOhKSAY


texts: Should I discard part of the data (steel traction test)

texts:
(please excuse my bad English. I don't speak English)

I have to deal with an old hydraulic machine, recovered from a deposit. I have no knowledge on mechanical engineering. Only civil engineering.

The machine is for doing traction tests on steel bars (for example ribbed bars). The machine is old, from the 70’s or 80’s I guess.

It has a system for plotting the stress-strain/deformation chart on paper, but also has digital instrumentation added, which is being read by an old PC still running Windows XP, and it only provides the raw data from the instruments (as a text file).

The digital system seems to be added, I guess, in the 90’s, and comes with a handbook with some instructions (as for example, how to calibrate the machine), but no explanation on the internal workings.

I need to algorithmically process the raw data produced by the tests, to extract various parameters.

As I had been taught theoretically, the type of chart I should get, must look like this:

But off course, this is a real world physical test, so I get this kind of chart

I had been told that it starts with an accommodation phase which I should ignore, and I need to extract various information from the rest of the chart.

Now, here is a zoom of the “elastic phase”

I have no knowledge on why it behaves that way, but I conjecture (guess) that the traction force is increased in discrete steps, and between each force increase, the machine waits some amount of time for the steel bar slowly elongating until it reaches a stress-strain/deformation static equilibrium.

If that conjecture is correct, then I should isolate only the “static equilibrium” points to do calculations, and discard the other, because the other points are transient states, and the theoretical applications of the test are only for static behaviors (civil engineering applications).
If the conjecture is correct, I should discard the transient states and retain only the static data for purposes of static mechanic applications of the traction test, which are the only theoretical applications of the test in civil engineering.

But off course, I have no knowledge on dynamic mechanics, and I may be making some huge mistake. I’m not a mechanical engineer.

So, the question is:
Is the conjecture correct?
Should I make some additional considerations?

[Edit] I would welcome if you can give me a book title, for reference, on the dynamical behavior of this type of machine.


texts: What are the 'poles' off the side off this aircraft carrier's flight deck?

texts:
Looking at a model of the HMS Ark Royal I found myself intrigued by the prominent 'poles' lining the flight deck. Some investigation on Google reveals that they can apparently be lowered to lay horizontally, presumably to keep them out of the way of any aircraft landing or taking off.

(Source: https://www.hydro-international.com/content/article/discovering-h-m-s-ark-royal)

The only hint of a purpose that I found was an old Google Group where someone mentions they are radio antenna. Unfortunately, I could not find a more authorative source.

So my question remains, what are these?


texts: If a fire-extinguishing bomb of sorts could be engineered or if a huge fire cover could be used, would they work better than the dumping of water?

texts:
In several regions of the world, fires rage through hundreds and even thousands of acres, and there is effectively little response that stops the fire, especially coupled with bad winds and extreme temperatures, not to mention dryness. We can dig ditches, fly over the fire with charter planes and other aircraft so as to try to put the fire out by dumping water. Short of this however, little has been devised to stop fires.
In theory, would it be possible to build some kind of bomb that carries a massive amount of some kind of compressed agent that puts out fire upon explosion? Perhaps on a molecular level there are agents that have been engineered to repel fire, and that can be built on so as to do so even more efficiently. If they were built into a big enough bomb, the explosion over a vast area of forest might seriously reduce an otherwise totally uncontrollable fire.
Perhaps otherwise, helicopters could carry some kind of really, really big fire blanket that they drop over patches of forest for say 20 minutes before lifting them back up again. Or, simply lower and detach until the fire is out. That might seriously reduce the infernos some areas experience, where other planes could come in afterwards with water that would much more effectively put out the remains.
I ask this only because it seems like since I was a kid, big forest fires have always been handled in the same way: People evacuate, helicopters and planes come in and dump water and voila. While this does help, mostly the region just remains totally helpless to the overall natural catastrophe. However, surely something could be engineered to combat these terrible tragedies, since there are so many different possible approaches. Smothering, water, human-engineered liquids, etc. With the devastation of our climate, it seems more pertinent than ever.


texts: Bending moment diagram from shear force diagram

texts:
In this question my bending moment diagram (BMD) doesnt return to 0, what's wrong with it?

To get the bending stress $\sigma = My / I$ , so i have to get the M (maximum moment) first.

To get the maximum bending moment, I have to get it from the graph of bending moment. To get bending moment, i have to get the shear force from the shear force diagram (SFD).


texts:
What are the advantages and disadvantages (technical, financial etc.) of having battery swapping system over charging stations for electric cars? As per my reading, battery swapping seems feasible for electric buses and 2-wheelers but not for cars. Is that really the case?

Also, is it possible for the battery to be housed under the bonnet instead of having it under the floor of the car so as to do away with underground swapping (like the one showcased by Tesla)? I know that the battery is placed there so as to lower the center of gravity. However, if there aren't any other significant benefits, can the aforementioned be done and battery swapping be made easier?


texts: How to interpret this BS 5950:2000 clause for splices in compression members?

texts:
A bolted end plate splice in a strut is designed to transmit compression by direct bearing of connecting cross-sections. If, after accounting for the bending moment due to strut action and additional moment due to moment amplification effects, the bolts themselves still experience no tension due to the large compressive force, is it possible to design the bolts to take only vertical shear?

How would the size of bolts affect the intended stiffness (underlined clause in red below) in the strut, assuming I provide the bare minimum to counter shear due to self-weight?

If you are answering with an example, you may use a 25m laced strut comprising of two numbers of UB914x305x287kg/m, taking a compression load of say 6000kN being spliced at a quarter span from each end support with 4 numbers of M20 bolts.


texts: How to convert a DC motor into a servo motor using a rotary encoder and a microcontroller?

texts:
Operating/ Rated Voltage: 24V
No load Speed: 350 rpm
No load Current: 150mA (max)
Max efficiency: 1.4 Kg-cm/300 rpm/ 14.2W/ 0.87A
Max power: 4.5 Kg-cm/180 rpm/28.2W/1.4A
Stall Current: 2.9 A (max)
Stall/ max Torque: 8 Kg-cm
Gear Ratio: 1:34
1496 pulses per revolution of output shaft and 44 pulses per revolution of motor shaft
coil resistance : 30 ohms.
How can I use these data to make a model of the dc motor? How can I use that model to make this motor into a servo motor using microcontroller like the arduino.
What are the topics I need to study.
Things I have done so far -
Read about transfer function of electro mechanical systems and tried to formulate a transfer function. But there are some things I couldn't figure out- like the inductance of the armature and the exact number of gear teeth in the gear, the inertia of the armature and some other stuff as well.
Things I plan to do -
I found out about MATLAB's system identification toolbox and black box modeling, Which doesn't require complete model of the system.
So I plan to use that toolbox to estimate transfer function of the dc motor. In order to collect data I will be using an arduino with pyserial to log voltage and current input to the motor, motor shaft position and time.
Later I intend to use Z transform to convert the inverse of the transfer function into discrete time domain from continuous time domain.
For the next step I am planning to make a controller which will combine a feedforward (Using the inverse transfer function) and a Feedback (PID based) controller together.
Is there any guide/example/tutorials available on this topic?
Am I heading in the right direction? or am I missing something.
TIA.


texts: How to select the correct grinding wheel type for precision grinding of tool steels?

texts:
I am planning to move from conventional grinding wheels to super-abrasive grinding wheels. I am unable to decide the right type of super-abrasive wheel for my manufacturing operations (I am into knife manufacturing).

How do I select a the correct grinding wheel type for precision grinding of tool grade steels such as those used in knife manufacturing?

Specifically I would like to know what the differences are between resin bonded and vitrified CBN grinding wheel. I would also like to know which wheel can be used for precise and fine grinding applications.

Thankyou.


texts: Low friction application: Ball joints or Universal joints?

texts:
I'm trying to find the right joint for a small but sensitive application. The joint should be around 10mm-20mm long with a diameter/height of <10mm. Because of the high sensitivity (thus a need for a low friction joint), do ball joints or universal joints typically have lower friction?

I see that camera stabilisers tend to use universal joints - do universal joints tend to have lower friction then?


texts:
QUESTION: Air at 35°C enters a 10 m long section of a rectangular duct of cross section 25 cm by 15 cm made of
commercial steel at an average velocity of 10 m/s.

*Take density of air and dynamic viscosity as 1.145 kg/m^3 and 1.895 x 10^-5 kg/m.s respectively.

Determine:
(a) Reynolds number

see my working here below,

i take the cross section 25cm * 15 cm as my area. I need help finding the diameter of pipe and please do confirm my workings cause i feel like its somewhat off since from my calculation above my Reynolds number is quite big.


texts: Determining frequency of an ultrasonic transducer

texts: Ultrasonic transducers emit sound at a frequency greater that 20 KHz. What are the ways the frequency of sound emitted by such a transducer can be verified?


texts: Conceptual problem: how to define pressure boundary conditions for stratified fluid in units of pressure/density?

texts:
This may be a trivial problem, but I'm having a tough time with conceptualization.

I'm using a code for modeling flow out of a tank.  I'm not experienced in fluid dynamics; I'm more experienced with chemical aspects of the problem.  I want to use pressure boundary conditions (a constant pressure at the bottom of the tank and atmospheric pressure at the tank outlet).  The code is for incompressible flow and I must input the pressure values in terms of pressure/density (units of m2 s-2).

The problem is I don't understand which densities to use for each boundary condition.  At the bottom of the tank, I'm guessing that I should use the tank fluid density (or some weighted average if there is more than one kind of fluid layer in the tank).  But what should I use at the top (where the boundary condition is the pressure of the atmosphere)?  When I divide atmospheric pressure by the density of air, I get a value that is higher than the bottom boundary of the tank and flow goes the wrong way (down, not up to the outlet).  When I divide atmospheric pressure by the same density that I use for the bottom boundary (the density of the fluid in the tank), my output shows pressure values that are lower than atmospheric.  It seems like I should get this, but I don't.  Any help would be appreciated, but unfortunately, I'm not allowed to post the code.


texts: number of electric vehicles that can be charged with specific amount of energy

texts:
I used minutely sampled wind speed data for one year to calculate the yield power from specific wind turbines to be used in electric vehicles charging station.

I am supposed to calculate the number of electric vehicles that can be charged within each day given the total constant energy from wind turbine.

My question is:

How many batteries can I charge using a 100 kW supercharger if I have energy of 45 MWh for one day? Battery capacity is 50 kWh, it takes 21 min to fully charged (or up to 80% for example) using 100 kW supercharger.


texts: What mechanism is available to rotate a metal piece on another metal piece?

texts:
I am trying to find some type of mechanism where I can have a smooth but not too stiff rotation between two metal pieces. I was thinking of putting a shoulder screw through the pieces (the pieces will be side by side) and a nut at the end.

A real world example I can think of is how when you're unfolding a ladder, the part that unfolds has a joint where rotation occurs. It's smooth and stiff enough that you can let go midway and the ladder wouldn't collapse inward, but not too stiff that you have to apply so much force to unfold the ladder. What do they use to do that?


texts: The distinction between lateral mass participation and vertical mass participation

texts:
Refer to the chapter 14 of the Wilson book "Dynamic Analysis of structures": calculation of stiffness and mass orthogonal vectors.

The table 14.6 shows the lateral mass participation and vertical mass participation for a frame structure.

I don't understand how can one tell whether an eigen mode contributes to lateral mass or vertical mass. From my understanding, mass participation for each mode is determined by the general mass and the eigenvector of the mode, and eigenvector of the mode usually consists of contribution from all the $x$, $y$ and $z$ direction, so how can one tell whether the mode is contributed to lateral or vertical direction?


texts: Does heat treating steel change its Thermal Expansion Coefficient?

texts: Given two identical samples of heat treatable steel in both composition and geometry, if one of the pieces is annealed or hardened would there be a measurable difference in their thermal expansion coefficient?


texts: I have a system involving a tank of nitrogen gas inflating a balloon, the tank pressure drops from about 4500 psi to 120 psi, inflating the balloon to 20 psi. How can I calculate the average flow rate (both mass and volumetric), and the time it takes the balloon to reach 20 psi. From my amateur standpoint, Bernoulli's equation seem to involve the pressure drop rather than the driving pressure relative to flow velocity. Can anyone help with that?


texts: Industry standard factor of safety for ballast design

texts:
What design standards exist for the design of ballast against uplift forces, and what factor of safety against uplift do these design standards promulgate? I am familiar with a typical FS of roughly 1.5 against sliding forces due to active soil pressure for the design of many types of structures (including cantilevered retaining walls and gravity dams), but I am not aware of any such standard FS against uplift.

It is possible- perhaps likely- that the safety factor can vary depending on the nature of the loading. Specifically I have in mind uplift due to wind. But other forms of applied uplift may include: buoyant forces, dynamic/static pressure applied by some other fluid (e.g., water, etc.), and load transference forces (perhaps in a machine where ballast is used to counteract forces applied to some arm/member).

The way I have done this in the past is to use standard load combination equations in design codes. For example, the ASCE 7 2010 load combinations for design of the limit state considering wind uplift* are as follows**:

ASD: $~~~~~~~~~~~~~~~~0.6D+1.0W_{working~stress/service~state}^{***}$
Strength design: $0.9D+1.67W_{working~stress/service~state}^{***}$

However, the problem with this approach is twofold.

First, using these load combinations directly leads two different, inconsistent effective factors of safety:

$Effective~FS_{ASD~Method} = 1.0/0.6 = 1.67$
$Effective~FS_{Strength~Method} = 1.67/0.9 = 1.85$

Secondly, the intention of a design code such as ASCE 7 is to provide guidance for the load side of the design equation. The resistance side of the design equation is usually left to the various engineering groups/societies who publish standards for different materials used to resist loads, e.g. the American Concrete Institute (ACI), or the American Institute of Steel Construction (AISC). These groups provide standard factors of safety (ASD design) and resistance factors (LRFD design). However as far as I am aware, there is no American Institute of Ballast.

Also note that for this question I am not considering uplift due to seismic forces, because seismic events occur in the form of a spectral acceleration which results in a force, and that force gets higher as the mass of the ballast increases. Therefore ballast is not effective on its own in preventing uplift due to seismic acceleration (though in some cases it may be effective in restraining lateral seismic acceleration via friction).

* Note that in ASCE 7 2010/IBC 2012 forward, wind loads are factored loads (factored up by 1.6); prior to 2010, wind loads were working stress and the ASD load factor was 1.0 (LRFD load factor of 1.6).

**The actual ASCE 7 load combinations utilize the ASCE 7 2010, factored wind uplift load, i.e.:

$~~~~$7. ASD: $~~~~~~~~~~~~~~~~0.6D+0.6W_{ASCE~7~2010}$

$~~~~$6. Strength design: $0.9D+1.0W_{ASCE~7~2010}$

*** Due to the above notes, $W_{working~stress/service~state}=0.6W_{ASCE~7~2010}$.


texts:
I'm creating a simulation in abaqus of a endmill removing material from and aluminium plate. The simulation is almost working, but only the surface level element are being removed from the plate. The interior elements are not interacting with the end mill.

Any ideas on how I can solve this?

Phil


texts: EMC filter selection and installation while there is power line filter leakage current

texts:
I am working in telecom company which is willing to install EMC telephone line filters and EMC power line filters on single facility that has all the equipment. I have been reading about filters issue from last two to three weeks. I have seen that all the manufacturers that are building these type of filters are providing leakage current data for EMC power line filters for single phase and three phase power line filters but no such specs for telephone line and data line filters.
My query is:

Can power line filter, telephone line filter and data line filter be install on same single facility even though power line filters have leakage current?
How I can separate the power line filters from other filters on single facility so that telephone line does not get noise from leakage current of power line filter due to the ground loop?
Will separate ground/earth for each filer will eliminate the noise problem or not?
Is there any other solution that I can use to keep telephone lines secure from noise of leakage current of power line filters.


texts: Looking for best material for a cryogenic ball mill cup and balls

texts:
I am working with a set of alloys that must first be ground up in a ball mill at cryogenic temperatures. It is important that no contamination makes it into the material and careful steps are taken to ensure this end.

Unfortunately when we ran a set of samples through our RBS lab and then again through PIXE we saw that we had Fe and Cr contamination. At first it was thought that it came from the cutting tools used to prepare the samples so we ran another sample that was cut using EDM. The results were the same. The only other contact the material has with a stainless steel is from the ball milling step.

We have been using a 440C for the cup and balls but it would seem a 316L may be a better fit for this application. I know 440C does not typically do well at cryo-temps but that is what other labs have been using so we didn't expect for there to be problems of this type.

Some things to consider for the new cup and ball material are machinability, cost, availability, cryogenic properties, vibration and fatigue resistance, and ability to be sealed (cups are filled in an inert Ar atmosphere). Another possibility is a heat treatment of the current 440C materials, however I am unsure what the best approach would be in that regard.


texts: Optimal tightening torque for a SS screw on an aluminium threaded hole

texts: As in the title, I need some indication about the optimal tightening torque to choose when screwing in a SS screw (A2-70, say) into an aluminium threaded hole. In particular, I am concerned with metrical dimensions (M8, M10 and M12).


texts: Energizing of armature as function of position in electric motor

texts:
How is the armature in an electric motor energized (i.e. main conditions on signal as function of position)? Let's consider the following parameters:

$n_a$,$n_f$ the number of armature and field pole pairs, respectively
$\gamma_{a,k}={\pi k\over n_a}$, $\gamma_{f,k}={\pi k\over n_f}$ the position of armature and field pole $k$ ($k\in \{1,\ldots,2n\}$)
$\gamma$, the angular position of the shaft
$I(\gamma)$, the current in armature as a function of position ($\forall\:\theta\in\mathbf{R}\::\:I(\theta+\pi)=-I(\theta)$)
$I_k(\gamma)=I(n_f×(\gamma-\gamma_k))$, the current in armature pole $k$.

The most important question is: should $I_k(\gamma_k)=0$ (i.e. should the current commutate whenever a field pole passes an armature pole)?

I created the gif below to illustrate. The vectors represent the magnetic moments: blue is armature, yellow is field.


texts: Deflection of a cantilever beam composed of separate (not bonded) planks

texts:
In the case of a simple cantilever beam having a uniform shape and being loaded at its end - the calculation of the deflection at any point along the beam is well known.
What happens if we split it along its longitudinal axis?

I realize we are eliminating the shear forces along that axis between the beam segments, and this allows each segment to slide relatively to its neighbors. However, I'm not sure how this phenomena affects the beam deflection. How can I calculate it?


texts:
In the notes , the author stated that when the force is applied through the centorid of cross section , the channel will bend and twist.
but , on the second page , the author stated that the shear center lies on an axis of symmetry of member's cross sectional area...
So, i am confused whether the member will twist or not when the force P is applied thru the centroid or shear center ....

Why the shear center is located at O , which is located outside of the C channel ?

Is there anything wrong with the notes ?


texts: replace support in qualitative influence line analysis

texts:
In i ) I was told that for the pinned support , we can assume to replace it with a roller , while for the cantilever , we can assume it to be supported by double roller .

For the cantilever , why we cant replace it with roller instead of double roller ? What 's the difference between double and single roller ?

In iv ) I was told that we can use roller guide , so from the figure , it's single roller , right ? So , IMO , the ii) was wrong , for the cantilever , we should always use single roller


texts: How is the Outlet flow rate in a water system controlled?

texts: The Hardy Cross method for analysis of fluid systems assumes that in inlet flows and outlet flows for the system are known. However, when one constructs such a system in real life, how do we ensure that the flow entering and exiting the system will be exactly equal to the parameters set initially? e.g. if the system is connected to a water tank for input, and has a loop with 3 outlets, and we assume that the input water flow is 300 l/s and the outlet flows are 100 l/s each. We decide all lengths and diameters as part of stating the initial condition to apply the Hardy Cross equation, and the method tells us what the flow rates will be based on the analysis. How do I know that the system will obey these parameters, and that the flow rates will match the initial assumptions I made.


texts: Derivation of the stiffness of a uniformly loaded cantilever beam

texts:
The stiffness of a uniformly loaded cantilever beam is given as follows:

I am trying to derive the stiffness, but I am facing a problem. I would be glad, if someone could help me out.

What I have done so far:

From my understanding, the stiffness $k$ is defined as:
$$k = \frac{F}{\delta}$$
where $F$ is the force that moves the beam at a certain point by $delta$

Hence, I calculate the tip deflection and the equivalent point load at the tip and use those two values to get the stiffness.

I know that the deflection curve is:

$$y(x) = \frac{p}{24EI}(6L^2x^2-4Lx^3+x^4)$$

The tip deflection becomes: $$\delta_{tip} = y(L) = \frac{p}{24EI}(6L^4-4L^4+L^4) = \frac{pL^4}{8EI}$$

For the equivalent force at the tip, I do the following:

I calculate the equivalent point load
Then I calculate the equivalent tip load from the point load (moment = 0 around fixed end)

But then I end up with the following stiffness:

$$k=\frac{\frac{1}{2}pL}{\frac{pL^4}{8EI}} = \frac{4EI}{L^3}$$

which is wrong...


texts: Is it wrong to consider that these velocities are the same?

texts: I have this simple problem and I am wondering if it's wrong to consider v1= v2 =v3 = v/3. "A" is the area. The fluid is air, I am not considering head loss. Thank you.


texts: Efficiency loss for a cooling element for cooling parts smaller than the cold plate

texts:
I would like to cool a small device, with a size of 45x45 mm² and a thermal load of ~40 W. Currently, I have a cooling system available, capable of cooling a thermal load of 52 W, and a cold plate with the dimensions of 60x80 mm². Due to the size difference I expect a small drop in the efficiency.

Is there a way to calculate that drop, and to estimate if I still can use that cooling device? As a naive approximation I would take the difference in the area size ($80\cdot60-45^2=2775$), which is approximately 60 % of the original cold plate. Can I therefore expect a loss of 60 % of the original cooling capacity, i.e. I only can cool a thermal load of 30 W for the given dimensions, or is that approach wrong?


texts: mass calculation from transfer function or bodeplot

texts:
I have a double mass rotary model. The two masses are connected by an axis which together acts as a spring damper system of the fourth order. The system is actuated by a motor and the angle of rotation is measured by rotary encoders at each end of the mass. The input to the motor is milli-volts which then converts into corresponding torques. The output measured is angle of rotation of the mass. The actuation and the measurement is on the same side.
The system looks similiar to this

The transfer function from output to input of the system is,

$Plant = \large
{\frac{(4700 s^2 + 4393 s + 3.245 (10)^8)}{(s^4 + 7.574 s^3 + 1.202(10)^5 s^2)}}$

Is it possible to determine the mass of the system from the transfer function or bodeplot? How can I relate the voltage, torque, mass and angle of rotation?


texts: Cooling system design of a heavy duty truck

texts:
I'm looking for information pertaining to the design of an engine cooling system in a heavy duty truck -- one that's used for long haul shipping. I've found some resources that provide details on the main components -- radiator, fan, pump, reservoir, thermostat, etc. -- but, I've found little in terms of the specific design features -- pipe diameter(s), flow rates, etc. Some design information on the cooling system in a popular truck model, such as a Volo VNL series with a D13, D13TC or Cummins X15 engine would be appreciated.
My ultimate goal is to try to construct the cooling system, removed from the engine. Specifically, I'd like to know the exact parts that go into the cooling system of one of these trucks. I know the pump is driven from the timing belt of the engine, I'm assuming this means the rpm of the pump is equal to the rpm of the crankshaft, and therefore varies depending on the vehicle demand. I understand the mechanism for the fan might be slightly more complicated, as its necessity is only imperative for when the vehicle is stationary. I'd also appreciate some recommended resources for learning about some of these design components. I'd really appreciate some guidance and any useful information. Please let me know fi you have any questions.
Regards,
Lucas W.


texts: How to Wire a Brushless Motor with 8 stators?

texts: I am currently for the past few years creating a Brushless Motor on and off. The stator I have built has 8 Stators and I cannot seem to find out how to wire this. I see most Brushless Motors with 9 Stators. Is this possible and if so how would I be able to get this working? If you do know how to wire this can you please provide a small diagram on wiring this? Thanks!


texts: What is the thickness criteria to consider a beam with changing thickness Continuous?

texts: I have a beam as shown below that have a span having 60 cm in thickness and the other spans 30 cm do I consider this beam as continuous or does the changing in thickness affect that ? if there is anything like an article about these criteria (especially in ACI code)


texts: How is fuel mixed with air in a jet engine?

texts: I am working on an idea that involves a jet engine, but I don't quite know how the fuel system works. In a combustion engine like that in a car, you have nozzles that spray the fuel into the piston chambers (I think, correct me if I am mistaken), and then it's ignited when the piston compresses the chamber (sometimes using a spark plug, sometimes it doesn't). How is fuel mixed with air and ignited inside a jet engine? I know that compressed air comes from the intake system (the fan blades pull in and compress air and direct it into the part where it mixes with fuel), but how does fuel get mixed in?


texts: Normative Document for 'Grade 520' Steel

texts:
I am specifying a product made in Australia, which is made of "Grade 520 Steel." The manufacturer of the product lists a minimum yield stress of 520 N/mm² (75,400 psi) and a minimum ultimate stress of 650 N/mm² (94,300 psi) with a minimum elongation of 20% and Young's modulus of 205 kN/mm² (29,700 ksi.) They describe the steel as "A fine grain micro alloyed carbon steel which is fully weldable." The raw steel form should be solid round bar.

My problem is that the plan checker wants a reference to a normative documents (ISO, EN, ASTM spec, etc.) for the material grade. I cannot find who (if anyone) defines  this grade of steel. What is the standard organization and standard number that would govern this material?

I have, of course contacted the manufacturer, but what's above is all that they've been able to tell me so far. The only material specification '520' I've been able to find is a withdrawn ASTM tube spec. This component is significantly over-designed, so I'm not concerned with the actual properties, just finding the appropriate document. There are other products available made with ASTM materials, but for visual reasons we'd prefer the Australian product.


texts: How to make datum planes on a cone in Creo?

texts:
I am trying to make this

I was able to make the base feature but I am facing problems with the secondary features. So could anyone shed some light on how to make the datum planes on cones.

I made one feature using this
as was instructed from where I am learning.
However, I am unable to make the plane for the other feature.

So far I have made this

Thanks in advance


texts:
I have an 4 stroke spark ignition engine simulator which takes user inputs and outputs performance data.

I need rpm, torque and brake specific fuel consumption (bsfc) to plot the bsfc map. I am able to plot torque and bsfc against rpm respectively without any problems.

Since a contour plot requires x(rpm), y(torque) and z(bsfc) where z is a function of x and y, how can I express bsfc in terms of rpm and torque or can I take advantage of the simulator to produce raw data required to plot the map saving me trouble in deriving the equation. If its the latter, how can I obtain bsfc data? What parameters should I change or keep constant?


texts:
Background Information:

My design team is trying to create a small RC car that can climb a 30 degrees incline that is 6inches high. We have two motors on a 3 wheels vehicle with the motors powering the 2 back wheels. The wheels are about 20cm length and 18cm width (15cm without) with the tires. The tires we currently have are made of plastic. The track is painted on wood so is pretty slippery. 4 double A batteries for each wheel.

Our vehicle is unable to make it up the incline.

What are some ways to make the vehicle go up the incline?


texts: Bend allowances when making a C-shape plate

texts:
I am trying to find the formulas for making bends in sheet metal. I understand there are formulas for bend allowances. My issue is how do I determine where to bend if I want the inside dimension to be an exact number and if I want the outside to be an exact number. For both of the below questions the material is 6061 aluminum .080 thick with a .1 inside bend radius and 90 degree bends.

For example for the picture I included. If I wanted the piece to be 7" on the inside and the sides to be .5" I would do 7 + .5 + .5 + (2 x bend allowances) to get the total length of the plate I think? but how do I know where to put the bend lines to get 7" exactly on the inside?

Also on a totally separate plate how would I go about getting the total length of the unbent plate plus how would I know where to place the bends for an outside measurement of 7"

This seems like it might be so trivial but I just can't seem to grasp what is going on.

To clarify it would be 7" between verticals for the first one and 7" on the outside of the verticals for the second one.

This is not an exact part I need. It is an exercise in how to determine the lengths needed for what I am asking for. This information seems to be harder to find than gold.

Edit: I have read How do I size metal plates to get the correct dimensions after folding?
and still don't understand. How does bend allowance and bend deduction help me. I am confused as ever and also extremely new at this.

I have done a little bending on my brake and seem to have something so please clarify if you can.

On a piece where I need the inside verticals to be exactly 7" I drew a centerline and measured 3.5 + .05( half of radius) from center and drew a bend line. Did same on opposite side. It seemed like I got 7" but it could be just luck.

Also on a piece where I need exactly 7" on the outside of the verticals I drew a centerline and did 3.5 + .05 - .080(thickness of the sheet metal) from center and seem to have gotten 7" on the exterior verticals.

Are these two formulas even remotely correct?


texts: Epoxy/Adhesive to bond solid wood and acrylic

texts:
I am trying to bond solid wood with with clear acrylic, with requirement to able to withstand shearing force, not more than 6kg over an area of 100 sq.cm.

Have tried to bond with result of the Acrylic side getting shear off. Has anyone used better epoxy for the job? Thank you in advance!


texts: Clarifications on the calibration of a magnetometer?

texts:
I've been reading up on magnetometer calibration (sensor fusion in general) recently and got confused about some things.
To my understanding, hard iron effects (e.g. inductors and magnets) which are constant in the coordinate system of the sensor (i.e. moving together with the sensor) cause a translation of the measurements while soft iron effects cause rotation and scaling of the measurements along certain axes. When both are combined, the theoretically spherical measurements which should be obtained when measuring the magnetic field at a certain point in space along arbitrary axes of the magnetometer will be observed as an arbitrary ellipsoid.
This is mathematically expressed as an affine transformation (rotation and scaling) of the unit sphere such that the original orthonormal axes are transformed into the semi-principal axes of a translated ellipsoid. The calibration is the inverse operation.
My problem is that this method assumes the semi-principal axes of the ellipsoid correspond with the three axes of the sensor. Why is this assumption made? Shouldn't you need to know the direction of the magnetic field beforehand in order to align it with one of the magnetometer axes and then check the rotation? Could we not just stretch the semi-principal axes of the ellipsoid to obtain a sphere without rotation? Also, this calibration technique does not take the true magnitude of the magnetic field into account (i.e. the magnitude of measurements after calibration will only be relative to the magnitude during calibration)?


texts: What is the most corrosion resistant 55HRC stainless steel?

texts:
55 HRC is a very high hardness, even for steels.

Ideally the corrosion resistance of the steel would have to match AISI 316L or be even better.

Qenched stainless steel can go to 55HRC. Even to 65 HRC. But this is at the price of a high Carbone content. Carbone react with free Chromium and makes it unavailable for corrosion resistance. So that qenched stainless steel often have a poor corrosion resistance.

The most basic option is AISI 420. It has the minimum amount of Carbone needed and show a relatively good corrosion resistance. It is available at a very good price.

In the other hand we have the Cronidur30/Bohler N360. It is basically like if the 420 had been highly alloyed with everything available. It has 15% Chromium,  1% Molybdenium, 0,4% Nitrogen and some Vanadium. This gives it a really higher corrosion resistance but it actually only poorly match AISI 304, the most basic Austenitic Stainless Steel. It cost something like $30 per Kg. That's 6 time the price of the 420.

Precipitation Hardening stainless steel like 13-8 Mo PH would only reach 45 HRC. That's already high. I'm wondering if there is specific versions that can do better. This type of steel has a better corrosion resistance than quenched steels. I know that Myodo produce a steel called H1 but it is only available in Japan.

There is also some maraging stainless steels that can reach 55HRC. I have no idea of the price and actual corrosion resistance.

Highly strained by cold working classical stainless steel like 301 or Springflex can reach very high hardness. I don't know for what plate thickness 55 HRC could be reached. The other point is that cold working produce Martensite and reduce corrosion resistance. I don't know how good is final corrosion resistance.

I thought about high temperature Nitrocarburation. However this process reduce corrosion resistance. I don't know by what amount.

Another solution is to use a surface treatment like chemical Nickel. However I'm not totally confident in this type of solution because the corrosion resistance is reduced to 0 locally where the coating is breached.

If you have any idea. I would be greatly interested.

Thanks

Edit : to make it short

I'm looking for a steel that :

is as corrosion resistant as 316L or better
reach a hardness of 55 HRC

The steel will be used in a sort of bearing that is in contact with salty and a bit of citric acidic mixture in an industrial environment.


texts: FE Exam practice: "How many years until you're a millionaire?"

texts:
One of the early questions in the NCEES FE Industrial/Systems Exam studyguide has a solution that I can't decipher.
The question is as follows:

Bob wants to be a millionaire. To achieve this goal, at the end of the year he invests $5000 each year into an account that pays 10% interest, compounded yearly. How many years will it take Bob to reach this goal?

The part I need help with is the solution to this problem, it's in the image below within the red box. I have no idea how it gets from (5000)((1+0.1)^n - 1)/0.1) to 21 = 1.1^n. Can anyone provide an alternate solution or some explanation? Thank you!


texts:
I want to do something like this:

but I have 3 questions that need to be answered:

Is it possible to make this kind of lens?
If it is possible, what are the equations/measurements needed to make it?
Are there another alternative to make cylindrical image flat?

Additional note: Please no "image processing" or programming to flatten the image because I need to take a very high and precise image of the surface and I want to prevent any kind of blur from the camera input.

Thanks in advance!


texts:
I'm in the design process for a cooling system. There is the need for some valves to control the flow of cooling fluid. In most machine states there's a constant fluid flow through either of two branches of the circuitry.

Initially I was working with 2/2 directional control valves with direct acting solenoid. Having low system pressure I'm forced to use direct acting valves. A power consumption of 4 W seems to be the lower boundary for a valve with ND 2mm. This is a waste of energy, since most of the time the valves stay in a constant state.

I then changed to 3/2 valves, so that only one state will consume energy. But 3/2 direct acting valves are exceptionally expensive and are available with small diameters only. I thought about ball valves, but those in turn are manufactured with diameters starting from 1/2" and have big gearboxes making them expensive as well.

So finally: Is there a possiblilty to switch a liquid between two brances of a circuit which I didn't think/know of?
Tubing has mostly 8mm inner diameter, fluid is water/glycol mixture with temperatures between 10 and 90 degrees. Voltage available for controlling valves is 12V.
Perhaps I'm just missing the affordable ball valve manufacturer or some tricky workaround?


texts: How to allow only one mode of resonance in a cantilever beam

texts:
So I am designing a MEMS structure consisting of cantilever arrays.
For my problem, I want the cantilevers to vibrate only at their 1st mode of resonance and reject all the other modes of resonance passively.
Is there anyway I can achieve this mechanically, that is by modulating the cantilever structure?


texts: Do the tubes of an automotive radiator flow in parallel or series?

texts:
The radiator in my car is damaged. One tube has a severe gash in it. I need to drive the car about 100 km before I can get a replacement radiator installed and coolant drains too fast to reasonably refill the cooling system every so often (with water of course, I'm not going to be leaking antifreeze all the way!)
Can I, e.g.

rip out some of the cooling fins around the damaged tube and crimp it shut on both sides of the gash or
fill the gash completely with a high-temperature sealant

in order to (hopefully) dramatically impede the loss of coolant?
Will doing one or both of these things only cause the radiator to lose efficiency due to no flow going through a single tube, or will completely blocking the flow of one tube stop all coolant from flowing through the system?
I.e. are the tubes of a radiator run in series:

or parallel:

?
I imagine they are run in parallel and these are safe temporary fixes.


texts: What is the engineering standard for filenames with fractions and inches?

texts:
I need to save some engineering files that need the thicknesses in the filename. Windows hates "/" or "\", so I can't use a simple fraction. Symbols like this...

⅓, ⅔, ⅕, ⅖, ⅗, ⅘, ⅙, ⅚, ⅛, ⅜, ⅝, ⅞

...are nice, but don't cover the full gamitt of dimensions (ie. 1/16").

In addition, Windows hates " in the filename, so I assume in is used instead?


texts: A device to provide real-time proportional resistance to variable force

texts:
I'm considering a potential product but I'm not sure about the core technology I'd need.

The fundamental idea is that there would be a cable (or something similar) that would be pulled.  But as it was pulled with X force, the device (mechanically and/or electronically) would provide equal (but slightly less) resistance.

So if it's pulled with 10 pounds, it would respond with (for example) 9 pounds of resistance (so the net result would the cable moving at 1 pound pressure).

But it would also need to react in real-time (more or less instantly), as the pull force would be constantly changing.

Is there already some kind of device that does that  I'm not an engineer, more on an entrepreneur, so I'm a bit out of my depth here.  Thanks!


texts: Can't solve the 2nd order differential equation of a stepper motor single step position

texts:
I want to assess how much time it takes for a single step of a stepper motor to settle.
Starting from

$$\tau=J\frac{d²\theta}{dt²}$$
Taking
$$\tau=K_m cos(\theta)\approx K_m \theta$$
Yields
$$K_m \theta -J\frac{d²\theta}{dt²}=0$$
Or in Laplace domain
$$K_m\theta(s)-J(s²\theta(s)-s\theta(t=0)-\dot{\theta}(t=0))=0$$
However the initial conditions are:
$$\theta(t=0)=0$$
$$\dot{\theta}(t=0)=0$$
Therefore
$$\theta(s)(K_m-Js²)=0$$
Now what :( ?

I do have the control systems toolbox of matlab, for the following steps, but honestly I don't know what they are.


texts:
Not sure if I'm applying the formula correctly. I'm trying to find the deflection in a cantilever beam that is loaded by a uniformly-distributed load. The formula is:

$$v=- \frac{wx^2}{24EI}(x^2+6L^2-4Lx) $$

where:

$$v = \text{Deflection} \\
x= \text{Distance from wall} \\
w=3\ \text{kN/m} \\
E=200\ \text{GPa} \\
I=986e6\ \text{mm}^4\\
L=10.5\ \text{m}$$

So for $x=10.5\ \text{m}$ I'm getting:
$$v=- \frac{3000(10.5)^2}{24*200e9*986e6}(10.5^2+6*10.5^2-4*10.5*10.5) \\
v=-2.31e-14$$


texts:
I have a typical, classical (but modern-made) Western porcelain toilet.
Just a couple of years ago, they redid the entire bathroom (unasked for, forced "upgraded"). I've noticed many times when I'm about to get up from the toilet that it "wobbles", as if it's not "sealed" to the floor. In fact, it clearly isn't. It seems like I could just lift it straight up. It's not "fixated" to the bathroom floor, but merely standing there.
Is this a mistake? Lazy and incompetent workers? Or is it on purpose? Is this the "new thing" that they do for some reason?
I should clarify that nothing visually indicates that it's "broken" when you look at it, but when you sit on it, it's possible (and often happens by accident) that it "leans" a bit to the side if you aren't careful.
I truly cannot tell if this is intentional or a mistake, and what the purpose would be for not "sealing" it properly to the floor.
I should further clarify that it doesn't "rattle around" just like that. You need to "lean" with your body to one side for it to leave the floor on the other side. I haven't dared to make any further "experiments" since I'm scared that I'll break it.


texts:
My in-view sketch toolbar has disappeared recently -

How can you make this reappear? So confused, don't even know what it's name is!


texts: Why does combustion happen at constant pressure in jet engines?

texts: Why does combustion happen at constant pressure in gas turbines but at constant volume in pulsejets? I need to ensure my design adds heat at constant volume. Is it because combustion starts from essentialy the escape point in pulsejets with the flame front acting like a wall?


texts: What approaches are there for demolishing a structure and how is an approach chosen?

texts:
From my office on the 21st floor of a building in Vancouver, BC two parking garages in the process of being demolished are visible. A third is just out of view a few more blocks away.

One of these structures is being taken down by a team consisting of an excavator with a jackhammer, an excavator with a claw and a man holding a hose. The jackhammer punches holes in the cement, and the claw breaks it up and allows it to fall to the floor below.

A couple of blocks away a different approach has been taken where it seems they are cutting the concrete into chunks and then lowering it down with a crane.

We've all seen the news clips and YouTube videos of demolition via pyrotechnics.

Are there other approaches?

Presumably, demolition by explosion requires a large amount of upfront time, effort and engineering skill as detailed in this answer. All of this culminates in one significant event, the detonation, and then substantial cleanup.

The jackhammer and claw approach seems like it is at the opposite end of the spectrum and requires relatively little skill and lots of labor to proceed at an excruciatingly slow and noisy pace.

Cutting and lowering seems to be in the middle with more expensive machinery to cut and skilled operators required. It also seems to move very slowly but anecdotally seems to have none of the noise associated with jackhammering.

What does the decision tree/matrix look like for picking an approach? Surely cost plays heavily into it but watching these sites move forward day by day I'm curious as to how two very similar sites in the same city (so permitting is presumably similar) chose different approaches and neither chose to use explosives.


texts: how to twist a sweep around a spiral in solidworks

texts:
.

I create two helixes, identical except for two different diameters of wind.  connecting their ends, I create a spiral slide as a surface.  I then create an hour-glass like revolved surface, then use the intersection of these two surfaces to create a helix that starts out with larger diameter, gets smaller, then gets large again.  I then create a sketch at the end of this and use the two sketches to define a spiraling sweep.  the problem is, the sweep doesn't twist properly as it follows the helix.  I would like it to twist such that if a surface of the sweep was tangent to the original hour-glass like revolved surface, it stays that way all the way along.  I think this must be possible, but as you can see in the image, that is not what it's doing.


texts: Calculation for cantilever retaining wall, with small/no heel

texts:
I'm trying to work out a "rough and ready" calculation for the simple retaining wall below (about 1.00m high).
The structural engineer has designed a cantilever with a large heel, as usual, but on checking, it's hard to excavate under the retained bank to put a "heel" in.  On the other hand, it already has a very large "toe" in the design, because there's a path going in front of the wall, so making the "toe" more substantial or adding a "key" beneath it to stop sliding would be much easier.
I'd like to get an idea about load calcs for replacing the usual "T" shaped cantilever with an "L" shaped cantilever as I've seen elsewhere, like this:

The physical dimensions we have so far (all in mm) are W1=200, H1 = 950-1050 varying along the length of the wall, W2 = 900, H2 = 300. The soil is London Clay (in London, UK), and the base is embedded below ground level which may be all that's needed to prevent sliding. I'm happy to do worst case assumptions and over-engineer for simplicity and durability, which would be fully saturated soil, active soil parameters, "worst case" clay, and poured foundation grade RC35 or similar concrete. Minor soil settlement isn't an issue, as it isn't being built on. The excavator can't quite reach to dig at the end of the toe, so if a key (if any) can be near the stem, that would be easier by far.
The current design is for a base slab about 800-900 front-to-back and 300 high, a uniform stem 200 wide, and 2 x A393 welded grid in each of the base and the stem with right-angle 10mm rebar connecting them, so I've taken those values and would keep the same reinforcement (they might be the best or not, I can't tell, but they seem reasonable?).
I'm hoping to find out what might be possible, and how to calculate any better options.


texts: Torsion and Bending stress calculated from deflection

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I need help to check a calculation I did. I want to know if it is possible to use this method or if I am using an assumption which is wrong. Let me explain the problem, a beam with length $l$ is fastened in one end. A force $F$ an a moment $M_v$ is applied at the end of the beam, see figure below. The beam has a circular cross-section. Due to the force, the end of the beam will deform a length $\delta$. Only the deflection is known and the geometric parameters, such as the length and diameter.
Using Euler-Bernoulli beam theory the deflection can be expressed as:
$$\delta = \frac{Fl^3}{6EI} \tag{1}$$
Where $E$ is the Young's Modulus of the material and $I$ the inertia, which is $I=\frac{\pi d^4}{64}$ for a circular scross section. Here $d$ is the diameter of the beam.
Inserting the inertia in (1) and rearranging it as an expression of $F$ gives:
$$F = \frac{3 \delta \pi d^4 E}{32l^3} \tag{2}$$
This can be inserted in the general formula for maximum bending stress in a cross-section
$$\sigma_{max}= \frac{Fl}{\frac{\pi d^3}{32}} = \frac{32Fl}{\pi d^3} \tag{3}$$
Here the bending resistance for a circular-cross section has allready been inserted in the formula and the bending moment has been replaced for the maximum moment which is $Fl$.
This is the part which I am not so sure on, I use the force from (2) and insert it in (3) to get the maximum stress. Please let me know if this is possible or if I am making an error.
Furthermore, the shear stress can be calculated from $\tau = \dfrac{M_v}{W_v}$ where $W_v = \dfrac{\pi d^3}{16}$, which is the torsion resistance in the material. I then proceed to use the von Mises yield criterion to get an estimate of the maximum stress in the material.
$$\sigma_{von\ Mises} = \sqrt{\sigma^2+3\tau^2}$$
As I asked before, I am mainly interested if this is a possible way to proceed with solving this problem or if I am using some methods/assumptions which are wrong.


texts: Streamlines at the boundary of rotating and stationary domains are malformed

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I am simulating a turbine and have divided the mesh into domains: the piping before and after the blade and the turbine blades. The domain containing the blades rotates at 2000 rpm while the other domains are stationary.

The mesh is structure and the mesh (between the domains) is conformal.

The turbine I am simulating is an axial-flow Wells turbine. The solution is steady state. This turbine has 8 blades (360 / 8 = 45° angle between blades). Due to the circumferential symmetry, only one-eighth of the annulus has been computed, imposing periodic boundary conditions in the tangential direction. In my model, the computational domain has been restricted in the axial direction to four chord lengths upstream and eight chord lengths downstream of the blade. Blades are symmetry (Naca00XX).

The computational domain is as follows:

According the following figures,

I want to obtain streamlines as in the following image from Insight analysis of biplane Wells turbine performance (Fig. 7):

Shaaban, S., & Hafiz, A. A. (2012). Effect of duct geometry on Wells turbine performance. Energy Conversion and Management, 61, 51-58.


texts: Why does my trimmer feels heavier when it is operating and its fully charged?

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I have a Philips trimmer which when fully charged feels much heavier than when it is not charged. Also , the blades move much faster when it is fully charged I.e it’s weight , speed of blades kind of light increases as it more  charged. What is it that can contribute to make it feel more heavy ?
Also , please let me know if you have any confusion in my Q or need more info.


texts: Can anyone help me with the concept of bearing stresses in steel reinforcement in Reinforced Concrete?

texts: When there is tension reinforcement(steel) embedded in concrete, does it not also undergo bearing stresses on account of the weight of the concrete and other forces which are acting above the steel? Does bearing stress have no impact on the yielding of the said reinforcement. Why is it that we only discuss bending stresses as a the only cause of yielding in steel and ignore the effects of bearing stresses?


texts: How can I calculate the maximum load of a steel box section frame?

texts: Is it possible to calculate the maximum load of the steel structure shown in the image using its dimensions?


texts: Process disturbance in PI controller help

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This is the project i'm working on and i'm struggling to understand one sentence which is stopping me from progressing the project.

I'm struggling to understand what it means when it says to add +/- 80% step changes in Qh to represent process disturbances.


texts:
This question appeared in my midterms.

A pipe transports water from a storage tank A to storage tank B. Storage tank A is at an elevation of 20 m above B, the pipe length is 6.4 km.
The present discharge rate is 75% of the required discharge rate.
A new design is proposed which would lay a new 2.4 km pipe segment (alongside the older one) running from point D to B.

(Consider the two pipes from DB to be in parallel,  nothing complex)
Diameter of original pipe is 200mm.
Calculate the diameter for this new pipe that would allow the required discharge rate to occur.
Assume friction factor 0.02 (fanning friction factor) for all pipes.
(Assume no minor losses due to bends and other stuff. Flow friction only).

Here's how I went about the solution.

First I found the flow from the original design using:

$$H=\frac{fl Q^2}{3d^5}$$

$$ Q= 0.0122  m^3/s  $$

Next

$$ Q = \frac {3}{4} Q_r$$

$$ Q_r = 0.01633 m^3/s $$

Now I go to the new design and take head loss equation in the first segment of original pipe running from AB-1.

$$ H = \frac {fl_1Q_1^2}{3d^5} + \frac  {fl_2Q_2^2}{3d^5}$$

Since they're part of the same original pipe, everything is same except length and discharge, so:

$$ H =\frac {f}{3d^5} (4000Q_1^2 +2400Q_2^2) $$

$$ 20 =\frac {0.02}{3(0.2)^5} (4000Q_1^2 +2400Q_2^2) $$

$$ \frac {24}{25} = 4000Q_1^2 + 2400Q_2^2 $$

$$ \frac {24}{25} - 40000 (0.01633)^2 = 2400 Q_2^2$$

And here is where I hit a little snag:

$$ 0.96 - 1.0667 = 2400 Q_2^2$$

$$ -0.1066 = 2400 Q_2^2$$

Negative. The square of the flow is negative.

How do I even proceed from here? The only thing that comes to mind is possibly calling the flow imaginary. But that makes no sense.

Is my solution correct? What did I do wrong?
What does one do if this happens somewhere?
Can you please look over my solution to see if I made a mistake anywhere?


texts: How is the reaction progress variable $c$ coupled with Temperature equation while solving the SIMPLE algorithm in CFD?

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While solving the Navier-Stokes equation using SIMPLE algorithm, we solve the transport equation for additional scalar at the last step according to the SIMPLE's procedure.

We need to add a new scalar, reaction progress variable $c \ \epsilon \ [0,1] $, to model the extent of burning in case of diffusion flames, but I am not able to understand how is this variable coupled with the temperature equation?How do we recalculate the temperature once we have solved for $c$ ?

If we proceed according to cycle below, can someone please expand upon the transport equation part (STEP 4)--

Do we solve for Energy (Enthalpy) equation first and then find out $h$ and then, $c$ or is it something else? Because as far as I understand, I know that $c$ is used to calculate Temperature of the cell.

Please correct me if I am wrong.

EDIT: $c$ is the reaction progress variable denoting the extent or fraction of reaction, $h$ is enthalpy, $u$ is speed, and the $2nd$ and $3rd$ term on RHS below denote source terms independent of $c$.

$$ \frac{\partial (\rho c)}{\partial t}  + \frac{\partial(\rho u c)}{\partial x} = \frac{\partial(\rho D_{eff} \frac{\partial(c)}{\partial x})}{\partial x} + \omega_{deflagration} + \omega_{detonation} $$


texts: Mechanical Engineering: How To Amplify Kinetic Energy In Axial Rotational Gear Machinery?

texts:
When I originally posted this question 2021-04-08, I was inspired by pulley physics, especially after viewing these videos at this link and this link and this link. It is not necessary to go to these links. Just to bear in mind the concept that inspired my question which is that less kinetic force on one end is needed through a series of simple machinery to lift more weight at the other end. I began to wonder if there is an equivalent method in physics to do something similarly in axial gear machinery so that the force applied on one end of the axle is amplified to move more weight, cause more torque, and increase the rotational speed on the other end of the axle.

I began to conceptualize something along the lines of the above planetary gear set (epicyclic gear train), where input force/energy on one end of the axial is amplified through a series of transmission gears so that the output side has more speed and torque. The machine I envision is a simple compact machine that converts in line axial rotational motion into mechanical advantage so that the same work can be done with less applied force.
The question then becomes this: How can rotational kinetic energy be amplified, and does anything already exist that accomplishes this?
Conceptually, what I am after is the mechanical analog of what the electrical transformer/inverter does when input electrical energy goes into the system. However, in this present question, it is not electrical energy, but kinetic energy that is being transformed/inverted/amplified. So a related physics question would be: how can kinetic energy be amplified in rotational machinery and applied to the simple compact machine described in this present post?
These are my questions which I will be most grateful to know. Any suggestions or insights would be most helpful.


texts: Deciding between Electric or Hydraulic Actuators for a Dynamic Load of around 4 kN to 6 kN

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This is a project regarding linear actuators for a 4 Wheeled Robot, with spider like hinged legs. The first question on my mind was to figure out is if a hydraulic system has any weight to Force(strength) advantage on this load category of max 6 kN to an electric-mechanical system with a brush-less motor. Since its a mobile unit and has to be water and dirt resistant.

Also most important question is what Force class does the hydraulics start to outshine the feather weight electric actuators?
Spider Robot needs to operate within the parameter:

dynamic load of max 6 kN
operated with 12 V battery pack.
quick actuation speeds at least 6 mm/s
brush-less DC motor 1000 W (with Feedback) preferred in electric or hydraulic systems for efficiency.

Thank you for any advice or for sharing your experiences.


texts:
The soil in my area has a very thick clay content (apparently left behind by glaciers, damn ice age). Because of this drainage in my yard is horrible. I've put in some underground drainage (french drain) that empties into a ditch. But unfortunately the french drain is below the drain pipe, which mean the french drain system when really flooded just sits there full of water instead of draining.

I really want to stay away from sump pumps, or anything powered. I looked at creating a bell siphon, but that doesn't seem like it could pump above itself.

Could I somehow use a holding tank above ground to provide the necessary "push"of the water. I was thinking something similar to how a toilet works, that I would just have to "flush" when I wanted it to drain.


texts:
First time asking question here.

I'm not a mechanical engineer!

I have a simple question that I can't explain the answer to it.
I have a double gear (2 concentric gears with different radius) and I don't understand why the torque is the same for both.
I found in the internet that the torque should be the same because they are cocentric, but don't understand why.

Thanks!

Gear Example:


texts: Derive a Transfer Function from first principles (PID, system identification, statics)

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I want to derive a transfer function of my system so I can plug it into MATLAB and use the PID tuner tool.

My system is a balancing beam with a motor on each end of the beam.

My first principles calculations for this system:

Taking only the clockwise moment (at 0 degrees, equilibrium):

So the clockwise moment goes from being $\text{Thrust Left} + Mg$ to $\text{Thrust Left} + Mg\cos\theta$ where $\theta$ is the tilt of the beam.

So the overall moment is decreased. In order to hold the beam at equilibrium (at any value of tilt), the ThrustLeft needs to be multiplied by $\dfrac{1}{\cos\theta}$.

Because thrust is proportional to the square of motor speed, the motor speed needs to be multiplied by:

$$RPM_{\text{left thrust}} = k \dfrac{1}{\sqrt{\cos \theta \ }}$$

Subsequently, the force required by ThrustLeft to maintain equilibrium at any angle is given by:

So the thrust required increases at an increasing rate as the angle of tilt increases.

If you're still with me, thanks very much. Subsequently, the tilt against time is the same as the graph above (albeit on a slightly different scale). The angle of tilt increases at an increasing rate over time.

I need to represent this as a transfer function! But my theory is poor.

I'm assuming it would be something like

$$f(t) = k \dfrac{1}{\sqrt{\cos t}}$$

where $f(t)$ is a function of tilt with respect to time.


texts: Plastic Multiplier for Perfectly Plastic Materials

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I'm trying to apply the associated flow rule to elastic-perfectly plastic material,
i.e.,$$d\epsilon_{ij}^p=\lambda\dfrac{\partial f}{\partial \sigma_{ij}}$$,
where $f$ is a yield function with no hardening variable, $\lambda$ is a plastic multiplier. I understand that $\lambda$ can be found through consistency condition ($df=0$), which gives $$\lambda=\dfrac{\dfrac{\partial f}{\partial \sigma_{ij}}C_{ijkl}d\epsilon_{kl}}{\dfrac{\partial f}{\partial \sigma_{ij}}C_{ijkl}\dfrac{\partial f}{\partial \sigma_{kl}}}$$
This seems confusing to me since after yielding is activated for perfectly plastic deformation $d\bf\sigma=0$ and $d\bf\epsilon^e=0$ when $d\bf\epsilon^p>0$. Therefore $d\epsilon_{kl}=d\epsilon^p_{kl}$, substituting this into $\lambda$'s expression renders $\lambda$ indeterminate.
Maybe there's something I understand wrong, but if this is the case, how would the plastic deformation be predicted for such the material? Thanks!


texts:
So, streamlines are a family of curves which, for every instant in time, are the velocity field envelops.
And in general, envelopes of a vector field are the curves whose tangent vector at each point coincides (in direction and sense but not necessarily in magnitude) with the corresponding vector of the vector field.
For reference, I got these definitions from a YouTube video.
What is the use of streamlines in Fluid Mechanics when velocity fields seem sufficient?


texts: What are the disadvantages of free-flow intersections?

texts:
I've recently learned about free-flow intersections. In particular, the DCMI, and the Stack interchanges.

What are the disadvantages of using them, compared to the "normal" signaled intersections? do they cost significantly more?


texts:
I'm trying to understand the concept of mechanical resonance.
https://en.wikipedia.org/wiki/Mechanical_resonance

I cannot find much references about how exactly is the phenomenon known. I.e. how was it discovered and how is it measured in contemporary engineering applications?


texts: How to drive variable power (up to 1500w) to a grill heating element

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I have a heating element like the following:

which is rated to 1500W. I need to be able to drive up to 1500W of power to it, but potentially less. I will be plugging it into a 120V wall outlet.
I am wondering what kind of components I need to make this happen at the lowest possible price point. :)
Thank you for your opinion


texts: How far can I drive an electric bicycle with a 250 watt engine using three serial connected 12 V motorbike batteries?

texts:
How far can I drive an (average sized) electric bicycle with a 250 watt engine using three serial connected 12 V motorbike batteries?

Trying to research the feasibility of this. I would like to serial connect three 12 V motorbike batteries and use them to run an electric bicycle. Maybe batteries similar to DYNAVOLT Motorcycle GEL Upgrade Mg5-3b Battery

So how far would I be able to go with this solution? A rough estimate would be good too. Would it work in practice? I have seen a YouTube video with a guy powering his electric bicycle with one single 12 V battery so it should at least work to some extent.


texts: Sizing plate washers for through-bolting to concrete

texts:
We are working on some equipment that is going to be attached to existing, 3,000 psi reinforced concrete floor slabs. In some locations, the best way to do this is to through-bolt and 'sandwich' the slab with a piece of threaded rod (5/8" rod in our case.) On the top side of the slab, our equipment has a large steel bearing surface. On the bottom side, we expect we'll need steel plate washers. We were thinking of using square washers cut from 1/2" A36 steel. What I don't know is how big of a square would be 'standard.'

Is there a chart or standard practice for what size plate washer to use on what size fastener? I couldn't find one in AISC, but may have missed it, or maybe it's in an ACI standard? If there's no prescriptive chart, what checks would typically be done to size it by calculation?


texts: Why does epoxy resin become opaque after long exposure to water and LED lamps?

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I want to put LED lamps in water. Up until now I used epoxy glass for its isolation, but after one year it starts to become opaque and lose its clearness.

What causes the epoxy glass to cloud and become opaque? How can I avoid this problem while keeping the lamps isolated from the water?


texts: Magic Formula: Calculating of lateral forces

texts:
To obtain lateral force according to slip angles, I use Pacejka Magic Formula, but my graph's style is not similar with picture which i added. I cannot find where the mistake is.
clear all
clc
a1y=-22.1;
a2y=1011;
a3y=1078;
a4y=1.82;
a5y=0.208;
a6y=0.00;
a7y=-0.354;
a8y=0.707;
Fz=2;
Sh=-0.28;
Sv=-118;
Cy=1.5;
Dy=a1y*Fz^2+a2y*Fz;
BCDy=a3y*sind(a4y*atand(a5y*Fz));
By=BCDy/(Cy*Dy);
Ey=a6y*Fz^2+a7y*Fz+a8y;
alpha_r=-10:0.01:10;
PCKy=(Dy*sind(Cy*atand(By*rad2deg(alpha_r+Sh) - Ey*(By*rad2deg(alpha_r+Sh) - atand(By*rad2deg(alpha_r+Sh))))))+Sv;
plot(alpha_r,PCKy)


texts: DC Inverter motor AC utilization category

texts:
I am looking at specs of an air conditioner unit. It uses DC inverter technology and maximum current listed as 21.5A

So are DC inverter motors considered resistive or inductive? What utilization category this device is in? AC-21, 22 or 23?

Because I am looking for an isolating/safety switch and it is rated for AC-21 as 40A but 25A for AC-22 and 20A for AC-23
https://www.katko.com/fi/tuote/kum-116u/
So it is difficult to decide if this switch is underrated for the air conditioning unit or not.

So the question is what current rating should the isolating/safety switch should be for use with 21.5A DC inverter motor system? Obviously the answer also depends on the utilization category that the spec is based on...

Thanks!


texts:
I have looked for a way to make a cyclorotor mechanism which allows the blades to rock/rotate (in the picture below, its rocking I believe) to no avail. I am not able to find the required length of the green link or that green circle (refer picture). Any idea on how to find out the required length? also, how to determine the eccentricity?

The picture drawn using paint was the idea I was working on. Here the blade is supposed to spin by 180 degrees when the whole system completes one rotation with intermediate positions as shown in the figure. I am not able to determine the length of the remaining links to connect the system. I was thinking on the lines of 4 (or is it 5?) bar mechanisms as in two of the links have been given in each quadrant but cant find any logical way to find the remaining links.

please help !


texts: Where does the light in the ceiling of the British house of commons chamber come from?

texts:
I am sorry if this is a strange question. Sometimes I like to visit parliaments from around the world and compare their buildings.

After looking at the British house of commons chamber, I noticed that there was sun light coming out of ceiling of the chamber. At first I thought that the ceiling was made of glass and it was just sun light. However after checking the building from outside there seems to be at least another floor on top of the chamber. So it can't be sun light. Then I thought that it must be just some electric light.

However, after checking some old images of the chamber(before electricity was used) there is still light coming from ceiling.

Does anyone know how this happens?


texts: Creating a "pinhole" small enough to allow only one molecule to pass through

texts:
Consider a "cartridge" of sorts. Is it possible to construct a "pinhole" in the cartridge such that only one molecule will pass through at a time? If so, what sort of equipment would I need to construct such a pinhole, or what sort of company would I need to contact? (The cheaper the method, the better.)

For reference, the molecules in question are deoxribonucleotides, which are about 13 angstroms or 1.3 nanometers in diameter. The molecules would I believe be in the state of a gas.


texts: Are there tools to select the best material based on their functions?

texts:
I'm working on a small engineer project and I need to know which materials are candidate depending on their functions. For example, I needed a material for a part of the machine that need to be transparent but not easy-break as a crystal glass. I found the site called MakeItFrom, that allow to compare materials based on their mechanical, electric, optical and more properties. But the comparison between two or more materials will take their time. Is there any way or tool to select easier and confiable the material based on their functions?
Image below is an example of the comparison based on material's properties


texts: Is there any aspect of an Explosion resulting from a nuclear weapon test that cannot be simulated using super computers?

texts:
This Washington Post news article states that with the advent of computer simulation of nuclear tests, live tests are no longer needed.
Generally speaking there are 3 aspects of an Explosion resulting from a nuclear weapon test that are tested:
(a) effectiveness, (b) yield, and (c) explosive capability.
Russia  carried out its last nuclear test in 1990, UK in 1991,the US in 1992,  France and China in 1996, India & Pakistan in 1998.
List Of Nuclear Weapon Tests
Therefore, does this mean that all aspects of a Nuclear Explosion can be simulated using Super computers or is there any aspect of a Nuclear Explosion that cannot be simulated by Super Computers?


texts: Why are home geothermal systems usable anywhere in the U.S. but industrial geothermal plants limited in geographical use?

texts:
Geothermal systems are used in regions across the U.S. for home use, but industrial geothermal plants are only used in areas where subteranian temperatures are very high. Why is this?

https://en.wikipedia.org/wiki/Geothermal_energy_in_the_United_States

https://www.energy.gov/eere/geothermal/geothermal-maps


texts:
I am building a stair from aluminium to go to my basement, the stair sides-plates are made from 10mm thick aluminium AWS 5454.

I am planning to tap M10 thread into this plate. To avoid the step slipping against the stair sides a tension of 715N is required. The bolt material is A2-70.

But will this aluminium thread be able to hold this load? How do you calculate this?


texts: Nylon brittleness as function of moisture content

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Can someone explain the how/why Nylons brittleness is to some degree a function of it's moisture content. I don't understand HOW the water content changes the elongation at break of the material.

Water doesn't bond or change the chemistry of the nylon when absorbed, my understanding is that it just fills some of the voids within the nylon. so then how is this changing the slope of the stress/strain curve?


texts: CFM needed to ventilate a Ethereum mining rig?

texts:
I am planning to deploy two Ethereum mining rig in my store room. Both rigs will have a total of 14 RX 570 GPU's and rest of usual suspects. The GPUs and PSU will be running at full usage while other items nearly at idle.

I don't have any ventilation in store at the moment so I will be installing a few 120mm fans (maybe 6 or 9) as intake on one side (in the wall) and exhaust on the other.

Can someone give me an estimate (very rough one) of how much CFM I should intake/exhause in order to sufficiently cool these 2 rig?

EDIT: Apologies for the delay but my query was to install fans in the walls on the store room and not on either side of case. The case will have its own fans but I wanted to know how much CFM air to bring in the store room from one wall to exhaust it at another.


texts: Uniform values from different MEMS 3-axis accelerometers

texts:
I have to find a solution to uniform values on 3-axis accelerometers on different android devices. I mean, a device with a specific accelerometer, under the same acceleration, give me values for 3 axis that are different from the values of another device with different accelerometer. I need some kind of normalization.

I tried to calculate sensitivity for different accelerometers (reading values with smartphone under +1g and -1g and calculating half of the difference for each axis) and I thought calculate the difference of sensitivity between two accelerometers (supposing to take one of these as the target for my normalization) and sum or subtract it to each output value of each other accelerometer. Is it the right way??

What can I do otherwise? Is possible to solve my problem?


texts: How to Measure Air Flow in a Large Tunnel at Various Different Points?

texts:
I am a student who is interning at a company this summer, and I've been put in charge of its first R&D project which will require me to collect a lot of data.  The machine with which I am working is called a Tunnel Finisher.  It is essentially a long tunnel through which clothes are pulled in order to dry them and remove wrinkles after a wash cycle.  Hot air is blown down on the clothes through louvers from a shaft above the tunnel which leads from a fan that maintains the flow of air.  What I would like to do is measure air flow, above the clothes, at the level of the clothes, and below the clothes, at multiple points in the tunnel.  Because the air in the tunnel is hot and clothes move through it, this measurement cannot be done manually; I need sensors that can be placed in the tunnel, preferably stuck to the walls, that will provide data while the machine is operating normally.  The goal of this endeavor is to reveal dead spots of significantly less air flow in the machine.

I've looked at some different kinds of sensors, but I don't really know what I'm looking for, and I assume what I end up using shouldn't be too expensive.  I was hoping someone here could provide some insight as to which air flow sensors, or other type of sensor, I should be looking at for this purpose.


texts: Why diametral pitch is not used in S.I units

texts: Here in this book of Theory of machines by S.S. Rattan it is written that diametral pitch is not used in S I units. Why is that so?


texts: What are these "water fountains" in the middle of a river in North Korea? (Probably also found elsewhere.)

texts:
While watching a video of somebody flying an airplane over North Korea, I noticed in a river these two "water fountains":

I vaguely recall seeing this previously, probably in the US, as well. My question is: What are they for? Just ornamental? Or do they have some kind of practical purpose?


texts: How to machine a metal shaft that cannot be turned on a lathe

texts: On a lawn mower there is a non-removeable metal shaft on which a pulley stack sits. The problem is that worn out bushings caused the shaft to wear in two places and this is causing the drive belt for the blades to be out of alignment and thus throw the belts. My question is, how can I engineer a solution to either shim up or machine the shaft on the deck when turning it on a lathe is not an option?


texts: FRF based material constant optimization

texts:
I need advice on how to optimize a finite element model of a transversely isotropic material. I have modeled the material with 5 nominal moduli in Abaqus and performed an eigenvalue extraction. Additionally I have done a modal analysis of the modeled part, have a full set of eigenvalues and have separated bending, torsional and in-plane modes. So far so good.

The initial moduli are just a starting point as the measurement is done on coupons and the material itself is sensitive to the measurement method. What I would like to do is use my initial eigenvalue extraction in conjunction with my FRF results to calibrate the material characteristics in the model input.

I have done some searching and it appears as though a DOE approach and creating a response surface may be an option. I am concerned about the time required(FEA jobs) for a full factorial DOE with 5 factors however. Additionally, I have investigated the Matlab optimization toolbox and read about using sequential quadratic programming for this correlation. I am comfortable with Matlab but have never used that toolbox and do not know how to create a transfer function between the inputs and outputs. Finally, I know about iSight but must find an alternative.


texts: How does a union joint with two male threads work?

texts: How does union joint with two male threaded ends work? Does one male end rotate 360 degrees around it axis? How is the inside of the union constructed? Can I connect two pipes with female threads using a union joint and assemble/disassemble it without too much pain? Specifically, I am looking at a stainless steel union joint.


texts: Can an enclosure be water tight and NOT air tight?

texts:
I am trying to create an air tight cable exit system for a fuel tank.

Basically, an instrument is to placed in the tank, with its cable exiting through the top of the tank. This exit point needs to be air tight.

However, most of the cable glands i see on the market are specified as being water tight.

Can i assume this to mean it is air tight as well ??


texts:
I have no engineering background at all, but when I bumped my small electric heater and it started whining and creating a burning smell, (since it's labor day with no stores open to buy a new one) I unplugged it and took it apart. Once I got down to the electric motor housing, I could spin the fan with a finger and hear the same whine, and noticed the axle (or whatever you call a rod that rotates a fan) attached to the fan was slightly crooked where it was housed within this piece.
Further inspection revealed that the brass-colored bearing (if that's the correct term) isn't securely seated within the star-shaped housing, but rather just held down by the thin tin flaps, and beyond that pressure moves freely, allowing it to seemingly cause the friction / disturbance creating the whine.
Is there a reason for the bearing to be held in place by this flimsy star chamber rather than a solid seating?
I tried to straighten it out and it appeared straight, but once I put it back together, the whine had only been reduced marginally, and the burning smell still occurred.


texts: The Horizontal Force of Water as it turns 180 degrees

texts:
For a National Board Exam Review:

  A uniform area jet travels to $600 \frac{ft}{s}$ and a
  $100\frac{ft^3}{s}$. What is the horizontal force acts on the water jet
  if it undergoes a $180^\circ$ turn?

I would normally provide an answer but even review instructor cannot answer question...

So I try:

$${ F_x = \frac{ \gamma Q }{ g } \left(\nu_2 \cos(\theta) - \nu_1\right)}$$
$${ F_x = \frac{ 62.4 \frac{lb_m}{ft^3} ( 100 \frac{ft^3}{s} ) }{ 32.2 \frac{ft}{s^2} } \left(600 \frac{ft}{s^2} \cos(180^\circ)- 0\right) = -116273.2919\,lb_f }$$
Is the negative sign logical? All choices are from the range of ${1.35*10^5}$ to ${ 5.32*10^5 }$ lbf