texts: How to strengthen the floor to support a 120gallon fish tank

texts: My house was built around 1920, and has field stone foundation. The joists seem to be all 2"x8". I want to put a 120 gallon(as measured in the United States) fish tank in my home office, which will be roughly 1000lbs, plus a stand, which would be maybe another 100lbs, and the footprint of this  tank is 48"x24"x24". I  want to reinforce the floor under the tank  in the basement. I plan to place the tank along the exterior wall, about 12" away from the wall, over the first joist. To strengthen the floor, I want to use bridging to connect the joists. I will do this at every third of the  joist, for about  3-4 joists below the tank. I also plan to use two  4"x4"s, that are beneath the joists laying perpendicular to them, and are supported each by a jack post which will sit on the basement slab. I plan to use one jackpost at each third of the tank. Should this be a safe way to support the tank?


texts: Calculate deflection of a beam with an arbitrary shape

texts:
I have a beam with rectangular cross section, but rather an strange shape in the length wise direction as seen below:

So I have taken out the symmetry part of it:

And it actually has some nice radius's due to metal forming:

the beam is fixed at 0 and symmetric about 5. The Beam sees a Distributed load at s4. The distributed load is actually a gasket so when my beam deflect I actually need to iterate to make sure I reach a steady condition.

The reason why I would like analytic solution is for understanding of whats going on. The problem is a coupled problem, below the beam is a fluid flowing and also the beam has electric current flowing through it, so its all coupled and I would like to experiment with different materials.

So I made a function that represent my beam in Mathcad:

I have tried calculating the moment along the curve by saying that the axial force can be neglected and that the fixed(welded end) can rotate, it might not be 100% accurate but I assumed this will be close enough to the real world:

and the moment seems to make sense:

this also fits with FEM

The problem is that I can not figure out how to calculate the deflection:

Can you not simply take the derivative of the moment or something to get the deflection?

I have tried to solve this but it gives me  completely wrong answer and not a nice symmetric deflection curve, I also need to guess the slope at the beginning of the beam and make sure it's the same as the end (6.03225deg). So I have the curve of the beam (inside/outside i.e outside -inside= thickness) as well as the moment and the Young's modulus and inertia of the cross section, so I should be able to calculate the deflection right?


texts:
I have a sensor whose datasheet mentions that it should be connected to 5V Vcc.
A green LED glows on the sensor when it is powered from the source at 5V.
However, even if I power it with 3.3V, still the green LED glows.
Does this affect the working of the sensor in any way?
If somebody could please let me know about this, I would be very much thankful.


texts: Could boiling water inside a semi-enclosed pipe be a low-cost method for a silent marine propulsion system? (redesigned)

texts:
I am wondering if boiling water that is trapped inside of a semi-enclosed pipe would be a low-cost method of creating an underwater thruster that would function as a silent marine propulsion system.

Please reference the following conceptual drawing:

This drawing is showing a cross-sectional side view of a conceptual underwater thruster. There would be a copper pipe that would be partially positioned within a metal cylinder and within this metal cylinder there would be an AC induction heating element that would partially surround the closed end of the copper pipe. The other end of the copper pipe would be located outside of the metal cylinder and it would be open-ended. This heating element should create a rising water temperature gradient within the closed end of the copper pipe.

The AC induction heating element would be turned on and would remain on so that it would continually boil the water. This will cause the water pressure (psi) inside the pipe to be higher that the ambient water pressure outside of the pipe/thruster and this imbalance should cause the thruster to move forward as indicated on the drawing. This thruster could be mounted externally to a ship or submarine's hull or it could be installed internally in the stern area of either vessel.

The main premise of this idea is that the boiling water will not be able to exit the copper pipe so there should be continual high water pressure inside the pipe and thus continual thrust. Also, there should always be water inside of the pipe because there should be a continual circulating flow of warm water exiting the copper pipe while colder outside water enters it.

Could boiling water inside a semi-enclosed pipe be a low-cost method for a silent marine propulsion system?

EDIT

Based on the answers and comments I have received to original design above, I have redesigned this 'Boiling Water Thruster', shown in the new drawing below:

I believe this new underwater thruster design should provide silent propulsion for the ship/submarine, although the thrust would be low compared to propeller driven craft.


texts: Is it possible to modify a home gutter to absorb sufficient solar energy to melt ice?

texts:
This is related to the question Will dark gutters stay ice free better than light colored gutters? The current consensus seems to be that the mass of the gutters and limited light may make simply painting them black insufficient.

In my particular application the two major gutter runs are facing East and West so get decent amount of sun light. Physical location is Pittsburgh PA.

From an engineering perspective, these are some of the questions that would need to be addressed:

How much would I need to raise the temperature of the gutters to prevent ice build-up?
How can I calculate the energy required to raise the temperature of the gutters?
How much energy can I theoretically obtain from sunlight throughout the day for a given area during the winter at my latitude?
How would the analysis change if I also wanted to melt ice that had built up during the night?
What other factors should one consider when designing such a system?


texts: How to calculate the velocity of a piston-like linkage?

texts:
I ve tried to solve this problem in so many ways but still didn't manage to do it...

What would be the correct way to solve it please?

This arm of this mechanism has a length of 0,2m. The piston has an angular velocity of 2000 tours/min. What would be the velocity of point D for an angle theta of 60 degrees?

I think that what I am missing is the angle formed by the arm and the line, which is 50mm long. Example like here (different
exercise):

I am trying to look for this angle beta which could help me solve the problem

expected answer:2,88m/s


texts:
If we wanted to open gate with maximum force that man can apply at distance of 1m from pivoted joint.
So I want torque to determine motor and gearbox that can be used to automate gate.


texts: How do I find the vertical reaction forces?

texts: The horizontal Force $A_x$ is easy but how did they get the vertical forces $A_y$ & $B_y$? I tried using similar triangles for the Force and length of the sides, somehow I can't manage to solve it. I wonder where I am making a mistake.


texts: What meaning does the following sine wave have when it comes to amplitude?

texts: So I am getting into engineering and was curious what it means when a sine wave isn't even in a sense, at 0, from my understanding, the waveform has  peak to peak amplitude of 4, while having a positive peak of 3 and negative peak of 1, does it mean anything in specific when it isn't even at a positive peak of 2 and negative peak of 2?


texts: On the proof of the Principle of Virtual Work

texts:
I'm having some trouble understanding the proof of the Principle of Virtual Work for deformable bodies. I'll give below the proof that I've read, and, next, I'll remark what I'm not understanding.

The first thing to remember before going through the proof is that the virtual work done by a system of virtual forces in equilibrium as a rigid body undergoes a small, compatible displacement is zero.

PROOF:

Suppose that a deformable body is in static equilibrium under the external loads of a virtual $Q$-force system.

Since the body as a whole is in equilibrium, any particular particle can be isolated and will be in equilibrium under the internal virtual $Q$ stresses developed by the external virtual $Q$ forces.

Now suppose that the body is subjected to a small change in shape caused by some other source than the virtual $Q$-force system. Owing to this change in shape, any particle might be deformed as well as translated and rotated as a rigid particle. Hence, the boundaries of such a particle would move and hence do virtual work. Let the virtual work done by the $Q$ stresses on the boundaries of the differential particle be designated by $\text{d}W_s$. Part of this virtual work will be done because of the movements of the boundaries of the particle caused by the deformation of the particle itself; this part will be called $\text{d}W_d$. The remaining part of $\text{d}W_s$ will be the virtual work done by the $Q$ stresses during the remaining part of the displacement of the boundaries and will be equal to $\text{d}W_s-\text{d}W_d$. However, this remaining is caused by the translation and rotation of the particle as a rigid body, and, as reminded above, the virtual work done in such a case is equal to zero. Hence

$$\text{d}W_s=\text{d}W_d$$

If the virtual work done by the $Q$ stresses on all particles of the body is now added, this equation becomes

$$W_s=W_d$$

To evaluate first $W_s$, we recognize that this term represents the total virtual work done by the virtual $Q$ stresses on all the boundaries of all the particles. However, for every internal boundary of a particle there is an adjoining particle whose adjacent boundary is actual the same line on the body as whole, and therefore these adjacent boundaries are displaced exactly the same amount. Since the forces acting on the two adjacent internal boundaries are numerically equal but opposite in direction, the total virtual work done on the pair of adjoining internal boundaries is zero. Hence, since all internal boundaries occur in pairs, there is no net virtual work done by the forces on all the internal boundaries. $W_s$ therefore consists only of the work done by the external $Q$ forces on the external boundaries.

$W_d$, on the other hand, was obtained by integrating the virtual work associated with deformation of the element. This work includes the effects of all forces on the element, both stress resultants and external forces. However, when an element deforms, only the stress resultants perform any work. Thus, Wd represents the virtual work done by the stress resultants alone.

END OF PROOF

I understood the part concerning $W_s$.

However, I don't understand why "when an element deforms, only the stress resultants perform any work".

Next, it is said that "$W_d$ represents the virtual work done by the stress resultants alone". But, according to the paragraph pertaining to $W_s$, this work should be zero, since all particle's internal boundaries occur in pairs and that one side of an internal boundary of a particle undergoes the same displacement as the common side of a neighboring particle and such two sides are subjected to equal and opposite stresses, respectively.

If we were to apply this principle according to my (flawed) conclusion, all points of the deformable body would undergo no displacement at all: a complete nonsense.

Where's the flaw in my reasoning?


texts: How does the friction on the front and rear wheels of a car vary?

texts:
Consider a Rear-Wheel Driven car. The questions refer to friction between the wheels and the road.

1.Direction of friction on the front and rear wheels when car accelerates? Is it static or kinetic?

2.Direction of friction on the front and rear wheels when car is at constant speed? Is it static or kinetic?

Direction of friction on the front and rear wheels when car is decelerating? Is it static or kinetic?

Also, if friction at the car’s wheels is what causes the car to accelerate, how does it resist the car’s motion at the same time?


texts: What are the names of these connection mechanisms?

texts: I've tried to search for the name of the connecting mechanisms on these clips but I can't find it. I'm trying to build something where two parts are connected on one axis (diameter less than 5 mm) but each moves independently. So I need a connecting mechanism which doesn't let them come apart but which is also small enough to fit in that hole. What are some mechanisms that would allow this?


texts:
So I have to analyze this circuit, with inputs C0, A0, B0, A1, B1, A2 and B2, and outputs S0, S1, S2 and C3. It's been suggested I don't use a truth table to figure it out. I need to find out what the circuit does by deriving expressions for the outputs.

So far I've identified the XOR gate, and the AND gate sections for the A,B pairs, are adders. I am yet to figure out what the logic block is. By putting in values A=101, B=111, C0=0, I have found out that this whole system is an adder. But I don't know what the logic block section is. That's what I've done so far.


texts: Gate width calculation for Passenger car design vehicle

texts:
I am trying to figure out the minimum gate width required for parking a car inside the house which has a 15 feet road in front of it. Please refer to the image below:

Plot is 20 feet wide. I have assumed 6 inch wall and 2 feet X 2 feet columns. These are just rough figures. I am yet to do proper calculation to come up with technically correct figures. Vehicle under consideration is 17 feet X 6 feet as shown.

I have referred to AASHTO - Geometric design of Highways and Streets document to come up some calculation. Here is the turning path for a passenger class design vehicle:

Road is in pink for good visibility of dimensions. Plot is on the right side of the road where the curved path leads to. I mentioned the vehicle to be of dimensions 17 feet X 6 feet but according to the code, P class design vehicle has a size of 19 feet X 7 feet and I am using it directly. I have kept the gate columns right next to the road so as to get maximum area inside house boundary. Right now, they are 19.5 feet apart but ultimately they will be kept at 20 feet. To keep things on a safer side, I assumed the arcs to be circular and took the inner radius as 14 feet (instead of 14.4 feet) and outer as 26 feet (instead of 25.5 feet) and drawn this figure:

I am doing this for the first time and hence want it to be verified by you guys. By this design, I am getting a gate width of almost 16 feet. Are these calculations correct?

Is there any way I can reduce the gate width? Assuming that driver doesn't need to go into the house in one swing. He can make a partial turn, then reverse a bit and then align the vehicle properly to get it inside the gate. One thing that comes to mind is that vehicle under consideration is smaller than P class design vehicle (17'x6' as compared to 19'x7') but I don't know how to carry out the complete calculations for a given vehicle dimension. Also I am not sure whether reducing the dimensions of design vehicle will be a good idea.

EDIT:

1) This house is located in a very less crowded street (very few vehicles passing by) and one can always use full road width when trying to park the vehicle inside.

2) Moving the gate away from property line can be one way of reducing the gate width but property owner will be losing a good chunk of land which doesn't seem like a great idea. Also, the gate columns will have to be moved 11 feet inside to get a gate width of 13 feet - not a good idea at all.


texts: Why are some public benches made with arm rests that waste so much space?

texts:
While watching a YouTube video today, I noticed this public/park bench somewhere in the USA:
It looks strange to me the way the arm rests on each side are so far into the bench, wasting a rather large combined space if you count both sides.
Why aren't the arm rests located in the very ends? Usually when I notice something weird like this, it has some kind of logical explanation. I hope this is the case this time as well, and that it's not just somebody's misguided idea of "design" at the expense of utility.


texts: Question regarding the extreme wind velocity distribution in Eurocode

texts:
Above is the definition of the probability factor from Eurocode 1-4. It is used in context of calculating the extreme wind load on a building. Ignoring some other factors, it is used as follows:
$$v_b = v_{b,0} * c_{prob}$$
where $v_{b,0}$ is the extreme wind velocity with less than 0.02 probability of being exceeded. The factor $c_{prob}$ is used to reduce the extreme wind velocity in cases when considering time periods shorter than the 50 year-return period (0.02 probability).
I assume the formula comes from Gumbel distribution:
$$p = e^{-e^{-\frac{v-\mu}{\beta}}}$$
which can be solved for $v$:
$$v = \mu-\beta \ln(-\ln(p))$$
where $p$ is the probability of encountering extreme wind $v$.
Taking the ratio $\frac{v}{v_{b,0}}$ and considering that $v_{b,0}$ is defined to have to probability of being exceeded of 0.02, we get:
$$\frac{v}{v_{b,0}}=\frac{\mu-\beta \ln(-\ln(1-p))}{\mu-\beta \ln(-\ln(0.98))}$$
Defining $K = \frac{\beta}{\mu}$, we get:
$$\frac{v}{v_{b,0}} = c_{prob} = \frac{1-K \ln(-\ln(1-p))}{1-K \ln(-\ln(0.98))}$$
Finally to my question: Where does the exponent n come from in the Eurocode formula? As I have derived to formula in the picture, there is no need for the exponent. Is my derivation flawed? Is there something I don't know?
EDIT: Only reason I assumed Gumbel distribution was that I was able to get a similar formula using it. There seems to be nothing in Eurocodes that goes into detail as to what distribution is actually used.


texts: Determine compressive modulus from compressive strength data in spec sheet?

texts:
Is it possible to determine the compressive modulus of a polyethylene foam using the following spec sheet?

Minicel Type M Foam

It doesn’t contain any information regarding the compressive modulus, but does have compression strength in terms of a compressive stress at 25% and 50% compression. Could I just determine the strain at 25% compression (delta L/L) and then simply divide the stress at 25% by that?

Thanks


texts: How does bell housing guarantee the concentricity of the shafts?

texts:
I'm talking about IEC motors-gearbox alignement. Here are an example:

I found the drawing in cross hydraulic website, so it's quite reliable.
What i don't understand, is, how this design makes sure the perfect alignement of gearbox coupling and the motor?


texts:
The Maximum induced bending stress within the beam.

Given that:

$$\frac{My}{I}$$

The beam depth is 300mm, the width is 150mm. The beam is an I section beam with a 5mm wall thickness.

My calculations:

$$\begin{align}
I_{total} &= ( I_1 + A_1 \cdot d_1^2) + ( I_2 + A_2 \cdot d_2^2) + ( I_3 + A_3 \cdot d_3^2) \\
I_3 = I_1 &= \frac{1}{12}bh^3 = \frac{1}{12} \cdot 150 \cdot 5^3 = 1.562 \cdot10^3 \\
I_2 &= \frac{1}{12}bh^3 = 150 \cdot 290^3 = 1.016 \cdot 10^7 \\
A_3 &= A_1 = bh = 150 \cdot 5 = 750\text{ mm}^2 \\
A2 &= bh = 5 \cdot 290 = 1,450\text{ mm}^2 \\
I_{total} &= (1.562 \cdot 10^3 + 750^2 \cdot 150) \\
&+ (1.016 \cdot 10^7 + 1,450^2 \cdot 0) \\
&+ (1.562\cdot10^3 + 750^2 \cdot 150) \\
&= 42.797.499\text{ mm}^4 \\
&= 4.28\cdot10^{7}\text{ mm}^4 \\
\sigma_{bend,max} &= \frac{Mc}{I} \\
M &= 48\text{ kNm} = 48\cdot 10^6\text{ Nm} \\
c &= 150\text{ mm} = 0.150\text{ m} \\
I &= 4.28\cdot 10^{7}\text{ mm}^4 = 4.28 \cdot 10^4\text{ m}^4 \\
\therefore \sigma_{bend,max} &= \frac{48,000 \cdot 0.1475}{4.28 \cdot 10^4} \\
&= 168.23\text{ MPa}
\end{align}$$

The maximum induced bending stress within the beam is 168.23;MPa

These are my calculations. Are these correct?

I am not sure on the 147.5. As seen different ways to calculate.

Also not sure if i have done the calculations correct.


texts:
I work with left ventricular assist devices in patients with heart failure. These devices operate by maintaining a fixed speed of a centrifugal or axial rotor. The native heart continues to contract creating pressure differences between the pump inflow (heart) and outflow (aorta).
The device and the heart are in parallel by my reckoning. Volume A enters the heart. Volume B exits the aortic valve. Volume C exits the pump. Flow in the body is A= B+C. If the pump is off, flow in the body is A=B. If the aortic valve is sewn shut, the flow in the body is A=C.  It is considered dogma that when flow through the device increases, device power consumption increases. The heart and the pump share the pulsatility of the heart and are subject to the same afterload in most situations.
I want to understand why power increases when pressure across the pump decreases. I understand that there will be more mass-flow through the pump with a lower delta-P across the pump. What I don't understand is why this mass-flow slows the pump, ostensibly requiring more power to overcome apparent resistance. It seems more logical that increased flow decreases energy of rotor rotation as the reduction in pressure difference would seem to have the action of imparting energy to the rotor.
Why is more power required to turn the rotor with a lower delta P across the pump and what principles/equations explain this effect?


texts: What is the problem with combining two non-identical transformers in series?

texts: I have heard multiple people say that when wiring transformers together, it is important that they are identical, with the same voltage rating, wire gauge, number of turns, and core size, but I have not been able to find an explanation as to why this is. I have found answers for why you can't combine non-identical transformers in parallel but I can't seem to find an answer for why you can't combine them in series. Specifically, if you wired two transformers in series with identical primaries but different numbers of secondary windings (same wire gauge, different sized cores). What would the ramifications be? Is there any possible way to address these problems so as to make it feasible?


texts: What are the reasons that engine efficiency drops in low loads?

texts: It seems that in low loads the engine efficiency is very low, while in heavier loads the engine efficiency or fuel efficiency/economy is much better. What are the reasons for this?


texts: How Scalable is the Wave Disk Generator Engine

texts: How scalable is the wave disk generator engine?  Are there fundamental limits to how large or small the engine can be and if so, what are they?  I'm not looking for answers addressing microscale issues, but rather, I want to know if the fluid dynamics inside the engine require a certain size range in order for the combustion to work properly.


texts: Creating an isolate bed environment for sleeping (to reduce mechanical vibration from floor)

texts:
Having a serious issue with mechanical vibration in my home (I call it "mechanical" because its nature is not from sound, but rather from some sort of a device - for clear image whats happening, please refer this question - tried almost all ways as suggested there, with no obvious effect). And I need to sleep ASAP...
In other words - I need to create a very isolate bed environment. Rebuilding floor is not an option. Need something what I can add up to the current state of the apartment. Probably most radical way (construction wise) could possible be to create a second floor (for bed area only), attaching it to the walls (by making holes in walls).
But the actual idea I am looking for - is hanging bed. The question here - would it work? Could someone do some calculations whatsoever, to get a better picture of what result that could bring? F.ex. I imagine, for some level of vibration, some vibration force could endup making bed to swing (what sounds as a less damaging effect to me, while at sleep). Also, maybe there is a chance for vibration to exhaust while traveling via that construction?
Could someone please give some advice?

EDIT:

Now thought of maybe a better design. See image below. Idea - to place next to walls (to the right and to the left of the bed) some solid material (like very solid wood, metal etc.) which then is jointed via the ceiling. And attaching ropes to hang a bed. In this design, I really think vibration would not travel to the bed.
Anyone could please comment this? You help is needed so much, people...


texts: What lead screw to use for specific torque and speed requirements?

texts: The setup: I'm trying to mount a leadscrew powered by this motor Tetrix Max Torquendado Motor on a 40ish pound robot, in order to lift it 4" off the ground. I already have the linear motion, latching mechanism, etc. I'd like it to go as fast as possible, but for now, let's just say that it can take 4 seconds to lift the robot. There will be 40ish pounds of tension acting on the screw when the robot is hanging, and minimal compression. Also, resolution is unimportant. It seems like there's a simple way to calculate the pitch/diameter leadscrew needed based on the torque, motor, and time requirements. What leadscrew should be used, and generally how could I calculate this sort of thing?


texts:
I want to use a compressor to create a jet of air. At discharge from compressor how much CFM (Cubic Feet per Minute) are enough to create a force that can turn a heavy object (say 40 kg) at 3 rev per sec placed in front of air jet.

Just looking for a relationship between CFM and Jet Force.

Thanks.


texts: Adhesive to connect metal with a coating to plastic that resists mineral oil

texts:
I have a peristaltic pump that was having some leaks because of connections between the tubing so I decided to replace it all with a single piece of tubing. Upon doing this though, I observed that the tubing on the outlet side of the pump was being forced upwards.
My peristaltic pump comes with a base that is made out of plastic. I want to glue something to the outlet side of the pump that will create some friction on the outside of the tubing keeping it from moving. I have some M20 nuts that are just large enough to fit around tubing and might offer the proper resistance if I can adhere them to the plastic.
However, the metal has a black coating on it that might cause some issues, and I am pumping mineral oil so I need to use some glue that will resist that for prolonged use while the pump is on. I'm fine with the nuts being permanently affixed to the plastic. I was wondering if anyone on this forum has some ideas for glues I can use to do this.
Update
Here is a picture of the pump from Amazon. Looks like I got the last one. Anyway, the plastic is the black frame around the cylindrical motor.


texts: Why do forward osmosis membranes face less scaling?

texts:
Forward osmosis (FO) is an osmotic process that, like reverse osmosis (RO), uses a semi-permeable membrane to effect separation of water from dissolved solutes. The driving force for this separation is an osmotic pressure gradient, such that a "draw" solution of high concentration (relative to that of the feed solution), is used to induce a net flow of water through the membrane into the draw solution, thus effectively separating the feed water from its solutes.

In a second step, the diluted draw solution is pumped through RO membranes, leading to desalinated water and a thickened draw solution to be recycled. The stated benefit is that the FO membrane faces far less scaling than in an RO process.

Image source

Now the electrolyte used as draw solution can be optimized so that no scaling on the RO membranes occurs. Since the manufactuers of these plants don't publish the composition of the draw solutions, a lot of research went into that direction.

However, I have conceptual question on why FO is advantageuos at all: when water diffues through a membrane, the concentration of the solutes is higher near the membrane and this ultimately leads to scaling if hardness builders etc. are present. It is stated that this occurs far less when the diffusion is driven by osmotic pressure instead of pressure from a pump. Why is that so?


texts: what actually cause quench cracking ? non-uniform cooling or rapid cooling?

texts:
It’s well known that quenching most alloyed steels starting from AISI 4140 to high speed steels in water, brine , or sometimes oil will cause cracking and distortions.

in industry oil quenching sometimes replaced by molten salt, which considered better than oil in decreasing crack probability and this advantage attributed to uniform cooling provided by salt bath compared to other quenching mediums.

cracks and distortions caused by water or brine quenching usually attributed to rapid cooling , but sometimes they attributed to non-uniform cooling caused by vapor blanket. that’s so confusing!!

it is expected to obtain uniform cooling by quenching steel in high concentration salt solution "nearly saturated solution" thanks to large amounts of ion particles which disturb vapor blanket, but these type of solutions will also have high cooling rate compared to oil. such rapid cooling usually attributed to be the of quench cracks in water quenching !

O1 steel can’t fully hardened in parts larger than 1 inch!

so my problem if it is safe to quench thick parts of such low hardenability steels in very high concentration salt solution which are expected to combining uniform cooling with relatively high speed cooling to fully harden thick parts of such low hardenability steel ?


texts: I know military uses laser designators and they can be visible by their bombs or missiles from really long range. My question is how could I do such laser point tracking device? Lets say I point laser at wall and I want to detect its position. Should I use flir camera? Or is there specific laser detectors/scanners for such thing? I'm talking about hobby-level prices.


texts: How to uninstall SIMATIC STEP 7-Micro/WIN V4.0.8.06?

texts:
I recently installed SIMATIC STEP 7-Micro/WIN V4.0.8.06 but cancelled the installation after some steps.

But the program appears in the control panel and when I try to uninstall it, the error:- "Did not find Shared Comm client list in registry at:....." appears and the unistallation process terminates.

I also tried to uninstall the registry entries by opening  "HKEY_LOCAL_MACHINE > SOFTWARE" directory.
Still it won't uninstall.

Please help!!


texts: Pin support, why is there no horizontal reaction force?

texts:
I am trying to understand this problem:

If we break down the 10T, they behave like this:

The right end of the beam can move as much as it wants, but the left end is pinned.

Why is there no horizontal reaction at A, if there is a horizontal part of the forces being applied on the beam axis?

I imagine, the force will push one section, and each section will push the next one, until the end, where it will create a reaction, just like the vertical forces are doing?

Thank you a lot.


texts: Given the same diameter and height, which is stronger? A vertical standing cylinder or a vertical standing rectangular?

texts: I am interested in two cases. Case 1: Both are solid. Case 2: Both are hollow with the same wall thickness.


texts: Is the diameter before knurling assumed to be the same as diameter after knurling?

texts: If the diameter before knurling is 80. Is the knurled diameter also 80?


texts: Could adding extra engines to AMELIA disrupt airflow from the other engines?

texts:
AMELIA is the product of a partnership between NASA and the California Polytechnic State University. One of its innovations is circulation control. An engine is mounted over each wing, and high pressure air is redirected from the exhaust over the wing and through tiny slots, adding lift.

AMELIA is still in wind tunnel testing, but if it makes it to the prototype stage, it would have a carrying capacity of about 100 passengers. A good commercial comparison might be a low-seating version of the Boeing 737, although it's old. A newer (and perhaps better) comparison is with the Airbus A318. Its cousin, the A319, is a similar aircraft that has been more popular.

Anyway, assuming that a prototype/production version of AMELIA is manufactured, it might be pretty similar in size to these aircraft. They're all twinjets; AMELIA, though, has its engines on top of its wings. In theory, one could modify AMELIA to have more engines. This version would be different, just as the 747 is a completely different craft that the 737, or how the A318 can't compare to the A380. Scaling it up, though, could be possible.

Would the addition of two more engines1 interfere in any way with the airflow from the original engines and the subsequent lift produced? I doubt it, because engines on four-engine aircraft (e.g. the 747 and A380) don't seem to present any interference issues that impact performance. But the setup for AMELIA is pretty unique. Could adding an additional engine on either side interfere with airflow?

Image credit: NASA.

1For spacing considerations, imagine spacing like that on the A380. This gives some basic specifications, while this gives some drawings outright.


texts: I have thin, variable diameter PVC wires that run along a metal housing. Problem being, they can get pulled on and disconnect. I want to bond them down to the metal housing as a sort of strain relief but have not had success. There are holes in the metal so a glue would have to be pretty viscous. Taping over (tried VHB, teflon) still allows them to move around under the tape and instant adhesives (tried hot melt, acrylic) peel. Accepting all suggestions, and thanks in advance!


texts: How to span a 28' gap, preferably with wood

texts:
I am building a temporary structure in a windy area (this is for Burning Man).  We are essentially using 4x4s that are embedded into the ground (hard clay floor) that are spaced apart by 2x6 rafters.  The purpose of this structure is to hold some shade sails which will effectively catch a reasonable amount of wind (though we try to take them down if the wind gets too strong), and otherwise the structure is not load bearing.

Here's a sketch of the structure:

The problem is that this year we want the long rafters to reach about 27'.  Previous years were 24' long, a lumber length that is reasonably easy to find.  Furthermore, we previously only had rafters across the angular spans, there were no horizontal beams for support, and the shade structure was more than able to handle the wind load (to give an idea of what forces we are dealing with).

We can't find 28' 2x6 lumber in our area (or order it in time to get here), so I am considering my options, and so far I've come up with:

Using I-Joists (most expensive)
Sistering 2x8s together and figuring out a hanger solution
Sistering 2x6s together and hoping for the best (least expensive).

By "sistering" I mean to sandwich two 2x6s or 2x8s together (in offset lengths) to reach the full 27' using wood glue and then heavy duty screws on both sides (or perhaps bolting them together in a number of places if we wanted easier storage).

I have a feeling that #3 is enough, considering we'd also be adding the horizontal beams on the outside rafters and collar ties (or maybe a "half collar tie?) on the inner rafters.

Any thoughts on whether this would be good enough, considering what has worked for us before?


texts: How do I set skewness correction in fluent?

texts:
I am simulating a turbine that has curves. Mesh is structure completely. But there is high skewness in tip clearance and some parts of around of the blade:

When I use SIMPLEC Method, one factor (Skewness correction) appear under the SIMPLEC method in ANSYS Fluents method.

How I must adjust this factor? I dont know which number must be set? 1< or 1 , 2, 3?

I used K-e turbulence model and when I set Skewness correction to 5 or 20, the following error is appeared:

  "Error: Divergence detected in AMG solver: k

  Error: Divergence detected in AMG solver: k Error Object: #f"

Why does this happen?

Please suggest a way to reduce the skewness in ansys fluent and how can I check Skewness in Fluent?


texts:
I am learning how to use Proteus and I have come across the charging and discharging of a capacitor problem. My main problem is on how to use the graph feature of Proteus to simulate how the voltage against time looks like. I have tried to implement this problem on Circuit Wizard and it shows exactly what I want and now I would like to do the same on Proteus but I keep getting a straight line instead. Can someone please guide me through? I have attached the images of my attempt using Proteus and what I expect the graph to look like using Circuit Wizard.
My attempt using Proteus

Using Circuit Wizard


texts:
You might see in this short, 2-minute video that billionaire Manoj Bhargava talks about creating cables from graphene to conduct heat from the underground sections of the earth to the surface.

But as per the properties of graphene, it is only a good conductor if the number of layers is one or very few. Once you start stacking it up, it is just normal graphite and it's conductivity gets reduced.

What's proposed in the video is a cable made from graphene. My question is how is it possible to make a graphene rope without stacking up graphene layers (and thus ending up with graphite) or without converting it into nanotubes?

I would also like to know why stacking up graphene reduces it's conductivity? Why don't the layers behave independent of each other?


texts: Area of Heat Transfer and Carnot Efficiency

texts:
Question:

a) What is the area of the steel plate interface (in $m^2$) with the fluid conduit if the heat enters the steel plate at a temperature (T1) of 980K? Assume rest of the conduit surface (besides the steel plate interface) is well insulated.

b) What is the Carnot efficiency of the heat engine (in %) based on the heat entering the engine at T2 if the same amount heat is input to the heat engine?

Attempt
I'm a bit confused as to how to approach both (a) and (b). Since this is a heat engine, the $\Delta U = 0$ so $Q_{in} - Q_{out} = W$. So is the correct way of approaching (a) is to conclude that $Q_{in}$ at $T_2$ is $500kW$ and then utilizing the fact that $500kW = h(A)(1000K - 980K)$ to solve for $A$?

With that reasoning, the Carnot efficiency for (b) would be 20%.


texts: Decission between several position switches and one continuos position signal for controling rotating conveyor

texts:
We plan a conveyor that will dump something into containers. A level gauge on the tip of the container will measure the heap below. The conveyor is placed on a turntable and will e rotated horizontally a piece when the heap below is at a certain height, to make use of more of the container.

The system will look something like this but only drop of to one side:

Image source: DB Technologies BV

I need to decide between either a continuos signal for the position of the turntable, or discrete signals at every point the conveyor will be. we are talking about 6-7 position signals in that case (3 per container plus maybe one so the conveyor is out of the way when both containers are moved). From the mechanical or process standpoint, I don't see a need for a continuos signal, 3 positions per container are fine enough.

I assume that this amount of signalers is even easier to implement than a continous sensor. Is this assumption correct?

Is there an argument from the control and measurement system side of things for a continous signal?


texts:
I am making a tea nitrogen laser based off the rimstarorg youtube channel. I have a perfect setup as seen below

I use 11, 1kv diodes to convert my 7,500 volt lug on my neon sign transformer to DC. My dielectric, well, i tried everything from transparency paper, to mylar, to acrylic and i tried multiple layers for each one.

Yeah thats what happened. So I eventually just tried setting up a piece of aluminum foil on the bottom, my dielectric, and then one aluminum sheet with my spark gap, and for some reasonthe spark jumps between the bottom of my 2 angle pieces before it jumps between the TWO CLOSEST POINTS AKA THE SCREW THATS 1mm AWAY!!

I should also mention when i used just one piece of transparency paper this happened:

Please help me on where to even go from here, i don't even know what I'm doing wrong at this point


texts: Liquifying nitrogen using Joule–Thomson effect

texts:
I need equations to calculate these cryogenic problems:

Generally how much energy (joules) is required to convert room temperature (21 °C) nitrogen gas into 1 liter LN2 using Joule–Thomson effect ?
Is there a more energy-efficient way to do that ?
How much will cost to convert 1 liter vaporized nitrogen into liquid again in it's very low temperature right after vaporization above −195.79 °C ?


texts: Virtual work method for a disk with axisymmetric distributed and concentrated loads

texts:
I'm trying to determine all forces/reactions on a disk with a hole in the center.

The disk is loaded with a (known) uniform distributed load from A to C (all around the disk), a concentrated (known) load at D (all around the disk), is either simply supported (only force reactions, $M_W = 0$) at A and B or simply supported at A and rigidly supported (force and moment reactions) at B.

Bellow is a depiction of the problem:

I'm trying to determine the reactions $F_N$, $F_W$ and $M_W$ (if fixed and not simply supported at B).

I know how to do that for line problems with a sum of forces and moments.

In this axisymmetric case however, the dum of moments does not see easy to obtain. How could I do this?

I'm trying to get the reaction by the virtual work method. The sum of the product of force and virtual displacements needs to equal zero:

$\sum F \cdot \delta = 0$

I'm getting however strange results with this method, and I'm probably doing some erros in the derivation of the equations.

What would the virtual work equation look for this axisymmetric case?

Is there any resource were a similar problem is solved by this method?


texts: Conceiving a wind turbine as a thermodynamic machine

texts:
Traditionally, and continuing till the present day, wind turbines are conceived/presented as power plants which harvest the (macroscopic) kinetic energy carried by an externally available airflow, with corresponding upper bounds on how much can be harvested. Implicitly, this amounts on or relies on an assumption that it would be generally impossible to harvest the internal energy in the flowing gas by allowing it to exert expansion work onto our system (in contrast to this being possible in steam turbines). Naive calculations, with airflow-parameters (speed, temperature, pressure) typical for our terrestrial atmosphere, suggest that one should be able able to harvest much more energy in this way than merely a fraction of the airflow's kinetic energy.

Q: What, if anything, prevents us from building wind-turbines that significantly exploit "expansion work"?


texts: How accurate should Rayleigh-Ritz approximation be?

texts:
For a simply supported beam with a UDL, with boundary conditions of X=0, V=0 & X=L, V=0. Using a cubic trial function.

$$V=a+bx+cx^2+dx^3$$

The following curve is obtained (Red Line). It is shown in comparison to the simple beam theory curve (Blue line).

Is this the level of accuracy to be expected from a Rayleigh-Ritz method for this scenario using these conditions? I don't have an intuitive sense of how accurate the approximation should be so am unsure if I have made a mistake in my calculations or if this is an expected result.


texts: product to tackle problem of senior citizens of our society who forget to take pills due to Memory Loss

texts:
For a lot of senior citizens of our society, taking medications is a necessity.
Although necessary,it can be tedious sometimes. More often, these
patients forget to take pills due to Memory Loss. Is there any product to tackle this
problem or any such product can be designed?, Please suggest your valuable suggestion, Thanks


texts: Milling aramid composites produces unwanted fuzz at surface

texts:
I use standard end mills for cutting carbon fibre sheets. Generally the cutters are 2 to 3 mm diameter, with a flute length of about 8 mm. I use 3- and 4-flute end mills. These work quite well if they are surfaced (TiN) or solid carbide. Uncoated or HSS tooling becomes dull very quickly.

Now I need to work with an aramid composite, where the core is carbon fibre and the outer layers are Kevlar. Overall thickness is 2.5 to 5.0 mm.

The surface layers are not cutting cleanly - leaving a fine fuzz that is a pain to remove.

The cutter is cooled by airjet, spindle speed is at the maximum setting of 10,000 RPM. I have tried feed rates from 5 mm/sec to 25 mm/sec at various cutting depths without any significant improvement.

How could I improve the quality of the cut? I would like to try alternative types of cutters or machining strategies.


texts: Operation of radial blower without compensators in gas pipeline - What problems to expect and how to mitigate?

texts:
The situation is this: At a current project, there's a pair of (parallel, redundant) radial blowers to raise the gas pressure for the downstream consumers (CHP, gas burner). All vibrating machinery should be isolated from the pipeline by compensators.

Now, the installed compensators leak. New, better (stainless steel vs. thin rubber) ones have been reordered but will take a few weeks. We need to commission other machinery that depends on the blowers. So the contractor suggested the following interim workaround: Weld pieces of pipe so that the blowers are connected without compensators, install the compensators in a few weeks when they arrive.

The problem is, everybody knows that machinery needs compensators, but nobody I've asked so far has seen a blower operate without. So no one knows for sure what the problems are, and how grave.

Here's my thoughts on possible risks:

The vibrations could damage welds
The vibrations could damage gaskets

I think both are unlikely. Nevertheless, here's the mitigation so far:

The blowers are equipped with variable frequency drives, ramp up will be done slowly to avoid startup-shakiness
If there's massive vibration with the blowers running, we'll reconsider
After the provisional pipeworks are done, and again after the compensators are installed, there will be a pressure test
Further down the road, 10% of the welds will be X-rayed. I will make sure that many of those checks will cluster near the blowers
I'm thinking about having someone check the gaskets of the flanged connections near the blowers with leak detection spray after every or every few operation days

My question is: Did I miss a risk that's not covered by the mitigation mentioned above?

Here's some more facts and considerations:

pipeline upstream and downstream is stainless steel with welded and flanged connections
upstream and downstream, there's an arch after the compensator
downstream, the pipe can move a few cm (not mounted to the wall or anything for 2m)
upstream, the pipe is bolted to the floor shortly before the blowers
We are talking relatively small radial blowers - 120Nm3/h @ 20mbar $\Delta P$ maximum
Max. pressure in the pipeline will be 40-50mbar over pressure
The room this is happening in is Ex-Zone 1 or 2, all equipment (including the blowers) is Atex rated and there's a gas warning installed


texts:
I'm an electrical engineer, so please bear with me :). I came across this situation and I tried to find some equations to solve it, but all I could find was some Finite Element Theory, and I was wondering, if there is an easier way to solve the following situation:

A thin shell is supported in the middle and a force is applied on the four corners (by a screw or a bolt for instance), or (I believe it is equivalent) a thin shell is supported in one corner and a force acts on the other corner. I am interested in finding the resulting bending (assuming a linear material) or finding the necessary strength of the material to avoid breaking. Can someone point me to a textbook with a (perhaps simplified) solution, or is it necessary to use a Finite Element software?

Thanks in advance!


texts:
I have a half cylinder shape, and another half cylinder sketch perpendicular to that first cylinder. I wish to create a "half-dome" between these two surfaces (picture what should look like almost a pill sliced in half, but hollow). Here is my current design:

I want to create the dome between the sketch pictured and the top face of the half-cylinder. I've tried using dome and loft, but am having trouble doing so. I tried using revolve, but I cannot seem to pick a good axis so that it does what I want.

I am new to using Solidworks, but I've used Inventor in a class before and a lot of the features seem fairly similar. Any help would be appreciated. Thanks!

Edit:

I tried adding a center axis to the cylinder and then revolving 180$^\circ$:

Clearly something isn't right; the error says the axis cannot intersect the drawing, but the shape of the revolve seems to be in the right spot. I created an axis on the back of the half-cylinder so it didn't intersect, and the revolve command called it a not acceptable axis.


texts: Best way to send a signal in a very low frequency (250Hz)?

texts:
I am a programmer facing an electronic question, so I thought here is the place to ask!

I have a magnetic field sensor which provides me with magnetic field values (XYZ axis) 250 times a second.
An electronic circuit with a programmable microprocessor controls a coil, which can change the magnetic field close enough to this sensor. Yet, the two devices are not strictly positioned, so I cannot relay on positioning measurement.
I wish to send 2 different types of signals from the circuit to the sensor, which can withstand strong noises on the magnetic field, and be shorter than half a second (Yes, seconds - we are in 250 Hz !)

Current solution is to transmit a 17Hz square wave, then 12Hz, then 17Hz for signal A, reversing the order for signal B. But in order to detect these signals it is needed to send long enough waves, which brings the signals to length around 1.5 seconds.

So, my question here is: Is there a way, let's say a pattern, like musical pattern that can be used to signal faster, and still be reliable?


texts: Benefit of removing the center "engine hub" inside a fan

texts:
Most fans (small and large) have inner hubs (see image left).
Would there be a gain in efficiency by removing that center hub, thus creating more blade space?
You could fix the blades to an outer ring (see image right - yes awesome paint.net skills) and put the components necessary for rotation in the outer frame.
Are there fans that work this way?
Would they work at least comparably?
Are there reasons beyond airflow efficiency that this wouldn't work like the engine design being not worth it, using more electricity, etc.?


texts:
I have a project where I need to cut a typical 5 point star shape (i.e. ★) out of brass sheet. The stars are small (~8mm across) and in high quantities. I was thinking of making a punch and die of the appropriate size but have stumbled on the best way to do this.

I'm stuck on how would I mill the sharp corners of the punch and dies - I was thinking possibly a gear cutter but the angle may be wrong? Would there be a better way to approach this entirely?


texts: Will the airflow inside a vacuum hose keep a sphere centered inside of it?

texts:
Suppose you were to fasten a string to a ping pong ball, then fasten the string to a stationary object, and then use a vacuum cleaner with a strong vacuum to suck the ball partially into the vacuum hose. Due to the strong vacuum's pull on the ball, the string should be very taut and the ball should also be centered inside the vacuum hose.

Based on this setup and referring to the two drawings below, if you were to then push down on the string with your finger at the point indicated by the arrow in Figure A, would the tautness of the string move the ball from a centered position in the hose down until it comes to rest on the bottom of the vacuum hose?

Or, would pushing down on the string at that point cause a bend in the string, as shown in Figure B, with the result being that the ball would be pulled back towards the opening of the vacuum hose with the ball remaining centered inside the hose due to the strong airflow flowing around it?

The reason I'm asking this question is because I have been unsuccessful with keeping the string fastened to the ping pong ball, even with super glue, so I am unable to see what the ball will do.


texts: Quickly stopping a phone from attaching to a network

texts:
I struggled for a while to find which group I might ask this question in.  Figured engineering minds would be the best.
Some time ago I discovered a good friend was in an abusive relationship. This discovery was made in dramatic fashion as I witnessed an escalation and was able to quickly remove said friend (we'll call her Sara) from a dangerous situation. On the drive to my home she frantically turned her iPhone off, telling me her abuser was able to find her if it was turned on.
After an evening of discussion with my wife it was decided she would spend the night in our guest room and seek help the next day. She felt safe at our home because she knew her location was a secret.  She slept 12 hours that night.
The next morning I was cooking breakfast as Sara was washing up. I am an Android guy, my wife is an iPhone lady so we have a few lightning cords. I hadn't had my coffee yet and when I saw Sara's iPhone sitting on my counter I thought "I should charge her up so she has a full battery for what will be a tough day ahead."
I plugged her iPhone in and to my horror, it started booting.
First, I'd like to curse whoever decided that plugging in an iOS device meant it should immediately turn on. My Android phones have never done this! In their wisdom Google figured "if they wanna turn it on they will press the power button" which objectively makes a lot of sense.
I stared, panicked, as it turned on. I pressed and held the power button - that did nothing. There was no way, in that moment, to prevent it from reaching the point at which a cell tower negotiated with it and within 3 seconds a message "your iphone has been located" popped up.  The phone immediately began ringing.  HUNDREDS of texts came streaming in. Dozens of new voicemail notifications.
Suffice it to say, the other party knew Sara's exact location. We took immediate action and got her the help she needed but I am "the one that caused her to leave" so I've had to take some measures I wish I didn't have to take in order to bolster my home's defenses (namely ipcams and firearms).
In hindsight, I'm wondering what, if anything, I could have done once I realized the iPhone was beginning to start up. I tried everything I could to interrupt that process and was moments away from destroying the phone. What ideas do you have? I have phenomenal reception in my home, always full-bars thanks to a large cell tower a couple hundred feet away. Would quickly wrapping it in tin foil have made a difference? Throwing it in the microwave and closing the door? They're waterproof now right - throw it in a pot of water?
Thanks for any ideas!


texts: After I knit the surface some blue sketch lines presist

texts:
Knit command on SW 2017 results blue sketch lines even with all surfaces selected
I was following the steps in a tutorial and I am sure i got them all 100% correct up to that point.
what could be the reason?


texts:
So recently I went to Supercomputing 17 conference and picked this from a booth.

I would like to know as to what this device is? What's its name? Where to find its documentations?

Thanks


texts: What is the physical meaning of pulse rate and blood pressure, from a turbo machinery point of view?

texts:
Our hearts are peristaltic pumps, which has a periodic compression and expansion. The head developed can be taken as blood pressure.

There are situation when the blood pressure is normal while the pulse rate is high. What is the physical meaning of this?

Does it mean?

Low flow rate per contraction?
more pressure loss(an indication of blood vessel blockage)?
contraction rate of heart muscle is low?


texts: In P&ID, what is the difference in terms of information between pipe and signal line In the diagram?

texts: I got a question. In the P&ID, the pipe will have information such as size, spec, service, insulation size/type and etc. For signal line, is it necessary to have these kind of information? or they just a graphic representation with no information?


texts: Can you help me with a flow rate question?

texts: How many gallons of water (70 degrees F) can flow thru a pipe diameter (I.D. 0.475") at 50 psi over a 30 foot length in a 24 hour time frame?


texts: Increasing power output of microwave oven

texts: Microwave oven uses magnetron to generate hugh power em waves. How the power output of a microwave can be increased? It uses a 1-2 KVAC capacitor. Will doubling the voltage of capacitor double the power output?


texts: Should we use exhaust fans during wildfire smoke?

texts: We have exhaust fans in our baths, kitchen and master closets. There are wildfires with a lot of smoke. Our house has HVAC and was recently remodeled. Should we use exhaust fans?


texts: How can you convert 180 rotation into two separate motions?

texts:
I have a small servo that can rotate 180 degrees. I would like to get two different connected parts to move at different times, one part moving while the servo is between 0-90 degrees, the other part moving between 90-180 degrees, similar to the diagram. Due to space concerns I can't extend mechanisms above or below the pivots. Another constraint is that it can't rely on gravity, since the mechanisms might be in any orientation when used or idle. It's fine if there's a small range where both parts move.
My current thoughts have been to try and design a pin-slot track system, but I haven't been able to think of a way to  get both parts on the track and I feel like that's overcomplicating it.
Any help pointing me in the right direction would be greatly appreciated.


texts: What is the white fiber in the copper wire of headphones?

texts:
I got a pair of in-ear headphones, broke the left earphone, bought another set, broke the right earphone, and joined the leftovers of both. I found white, grey, or beige fibers near the copper of the newer one, the white set, from June 2019, and not on the grey set from January 2019.

I imagine that these fibers give the wire strength or insulate the Joule effect. At worst, I worry that they are asbestos. For reference, the headphones are Sony MDR-AS210 Sports In-Ear Splashproof Headphones.
What are these fibers and what is their purpose?


texts:
I'm looking for search terms, I'd like to find something like an electric hose clamp - a high-force, low-power, low-speed, motorized constricting mechanism.

I already googled some terms various combinations of constricting constrictor mechanism mechanical actuator squeezing -snake, have not been fruitful. Is there a term I am missing?


texts: How to determine impact load factor on small beams

texts:
For small beams, the following equation explodes to high values, which seems unreasonable:

$n = 1 + \sqrt{1+\frac{2h}{\delta}}$, where $n = \dfrac{F}{W}$, with $F$ the maximum force on the beam and $W$ a suddenly applied weight.

If it helps, I'm evaluating the following case: for a given work in height, the worker will be anchored to a structure. In order for him to be protected from a fall, I'm designing eyebolts for him to anchor himself with his lanyard.

In this case, the height of the structure is much higher than the length of the eyebolt.

The problem is that if I consider the eyebolt as a fixed-free beam, then its displacement $\delta = \dfrac{PL^3}{3EI}$ will lead to a very small number, which, as I mentioned before, will lead to a high value of n.

I suppose the equation for suddenly applied load doesn't apply here, right? If so, any tips for how to work around my problem?

For reference, see the "eyebolt" dimensions below:

Consider it a plate of 1/4". I don't think those are called eyebolts, though, and I'm unsure what's the correct translation.


texts: controllability matrix of a state space system - determinant

texts:
For state space systems, there is a test for 'controllability' involving finding the determinant of a 'controllability' matrix. The instructions for the test is typically to see if the determinant is equal to zero. If that determinant is zero, then the system is said to be NOT controllable.
My question I'd like to ask is about the condition of the determinant being 'zero'. We know that 'zero' means zero obviously. But what about a relatively small value like 1E-10? And what about 0.001?
Would a determinant having a value of 1E-10 mean that the system is controllable ----- because the value is not zero?


texts:
I am currently working on designing a teeterboard for the circus (a seesaw that people jump up and down on the ends), and need some advice on my methodology for wood selection. The primary wood will be Vic ash (a.k.a Tasmanian Oak), with a possible second layer of pine underneath. Currently i plan to do 3 point bend tests on each wood standalone, and with various thicknessses as a double or triple layer (ash/pine, pine/ash, ash/pine/ash, pine/ash/pine etc). This will be used to get material data.

My primary concerns are with scalability, i.e can the results stress values obtained be applied to the full size modeldue to the somewhat unpredictable and irregular nature of wood. My other concern is incorporating the glue into analysis. I do not know how to get a reasonable theoretical calculation for the multi-layer board, unlike the single board for which the calculations are extremely simple.


texts: Deformation of two perpendicular beams with parabolic properties

texts:
I want to calculate the deformation of the following structure:

I have numbered the vertical beam 1 and the horzontal beam 2. The hight of beam 2 is given by:
$h(x)=h\sqrt{1-x/L_2}$

So I thought I could solve this with Castigliano's method. Where beam 1 undergoes an axial load $F$ and a constant bending moment of $Fa$. Beam 2 undergoes a bending moment of $0$ on the left and $Fa$ on the right. The energy is given by: $U=\int_0^L\frac{F(x)^2}{2AE}dx+\int_0^L\frac{M(x)^2}{2EI}dx$
So for beam 1 and 2 the energy would be:

$$ U_1 = \int_0^{L_1}\frac{F^2}{2bhE}dx+\int_0^{L_1}\frac{F^2a^2}{2E\frac{1}{12}bh^3}dx = \frac{F^2L_1}{2bhE} + \frac{F^2a^2L_1}{2E\frac{1}{12}bh^3} $$

$$U_2 = \int_0^a\frac{F^2x^2}{2E\frac{1}{12}b(h\sqrt{1-x/L_2})^3}dx =
\frac{4F^2L_2^2}{Ebh^3}\left(\frac{\sqrt{1-a/L_2}(a^2+4aL_2-8L_2^2)}{a-L_2}-8L_2\right) $$

Where $b$ is the thickness of the part

Then I applied Castigliano's method, which gives the deformation of the shape in the same direction as $F$:

$$\delta=\frac{\partial U}{\partial F}= \frac{F}{E}\left(\frac{L_1}{bh} + \frac{a^2L_1}{\frac{1}{12}bh^3} + \frac{8L_2^2}{bh^3}\left(\frac{\sqrt{1-a/L_2}(a^2+4aL_2-8L_2^2)}{a-L_2}-8L_2\right)\right) $$

But this equation gives me wrong results. For instance, with $F=1500, E=113.76*10^9, b=0.005, h=0.007, L_1=0.05, L_2=0.04$ and $a=0.032$
I get a deformation of 9.8 mm, where as a FEA simulation (Nastran In-Cad) gives a deformation of 6.2 mm (in the same direction as the force).

I tried this without the parabolic property and this does generate correct results. That equation is:

$$\frac{F}{E}\left(\frac{L_1}{A_1}+\frac{L_2^2L_1}{I_1}+\frac{L_2^3}{3I_3}\right)$$

So I think there something wrong with my parabolic equation, but I can't figure out what it is.

Edit: did some trial and error, and if I fill in $h(h/2)$ for $h$ in the last term I get pretty accurate results. To clarify, the height used (in this situation) in the last therm ($\frac{8L_2^2}{bh^3}$) is the hight of beam 2 where beam 1 ends, on the left. But I still have know idea why this is and if this works for every situation


texts: Changing the quality of the transient process in a nonlinear system (in Mathematica)

texts:
I urgently need advice and help.
I have a system of differential equations like this:
$\begin{cases} \frac{dx}{dt} = y[t] \cdot \alpha \cdot sin(\omega t) + \frac{d}{dt}(\alpha \cdot sin(\omega t))
   \\ \frac{dy}{dt} + h \cdot y(t) = \frac{d}{dt}(e^{-(x[t] - 2)^2}) \end{cases}$
Parameters: $\alpha = 0.3, h = 1, \omega = 2 \pi 0.5, x(0)=1/4, y(0)=0$
It corresponds to the following structural scheme:

The code that simulates such a system is shown below:
 ClearAll["Global`*"]

pars = {\[Alpha]1 = 0.3, h1 = 1, \[Omega]1 = 2 Pi 0.5}

extr = Exp[-(x[t] - 2)^2]

sys =
 NDSolve[{x'[t] ==
    y[t] \[Alpha]1 Sin[\[Omega]1 t] +
     D[\[Alpha]1 Sin[\[Omega]1 t], t],
   y'[t] + h1 y[t] == D[extr, t], x[0] == 1/4, y[0] == 0},
  x, {t, 0, 500}]

The numerical solution is presented below:
Plot[{Evaluate[x[t] /. sys]}, {t, 0, 150}, PlotRange -> Full,
 PlotPoints -> 50]

It can be seen that the transition process is a transition from the initial point to the final one with a certain character.
I need to change this character i.e. make the transition from one point to another exponentially.
Like this:

What are the ways to solve this problem? What to do, add a regulator or manipulate the system of differential equations?
Please help me!


texts: Why is Flaring done in industries? Why can't the same gases be used for production of energy (Thermal energy)? Or why can't the excess gas be recycled in the previous stream from which it came?


texts:
I have a linear solenoid with a tapped M3 hole at the end of the plunger, like this:

I need to connect this plunger to a lever, so I want to add a mount which has a connection something like this:

Does anyone have any suggestions as to where I could find an M3 mount like this which I could attach to my solenoid?


texts: What is the minimum current required to charge a smartphone battery?

texts: I am planning to make a portable charger for my smartphone. My input current is 300 milliamps and I am not sure if that will be enough to charge my phone's battery. What is the minimum current required to charge a typical smartphone battery?


texts: Increasing suction air flow with multiple pumps

texts:
I'm trying to build a small pick and place system using a suction cup and a 12V vacuum pump. The problem I'm having is that I'm not getting a good enough seal between the cup and the object, and I read that it could be improved by increasing airflow. I've also read that placing pumps in parallel can increase airflow, but is there a limit to the number of pumps that can be placed in parallel? Would the pumps overheat as a result of using too many pumps in parallel? The pump I'm using has a datasheet vacuum pressure of -0.08Mpa and an airflow of 16L/min. The pump itself is composed of 2 pumps in parallel.

Any advice appreciated.


texts: Why is there a row of circular holes in this concrete beam?

texts:
The reinforced concrete beam (approximate dimensions 36" x 18") shown in the image below has a row of circular holes at 3/5ths of the height of the cross-section at approximately 300 mm centres.

My question is why does this concrete beam have these holes?

My first thought is that these holes were due to the tie bars providing lateral support to the formwork vertical walls. However, they appear to be too frequent for that to be true.


texts: How to design a cooling chimney for a computer server?

texts:
I'm building a server type computer consisting of integrated motherboard, CPU, RAM and hard disk.  There will also be a standard power supply unit.  This is to be a Steam Punked computer, so...

I want to know the feasibility of passively cooling the server using only a chimney effect.  So the electronics would be enclosed, with a chimney at the top and air intake(s) at the bottom.  All the components will be custom mounted so there is no typical computer case and therefore no particular size constraint.  How would I begin to evaluate /design this?  I believe that there are relationships between chimney proportions, temperatures and exhaust velocities.  Perhaps like this...

Mini computers (ARM /Celeron) exist that have no fans, so perhaps it isn't really a big deal and anything at all will work?


texts: Calibrating and measuring pressure in Megapascals using a pressure transducer

texts:
I have two columns of water at different (but constant) temperatures. If I calibrate a pressure transducer using the first column at differing heights, when I measure the second column how do I account for the change in temperature (and water density)?

I want to measure pressure in megapascals (MPa) so for the calibration I currently plot pressure transducer mV output at different column heights against the calculated megapascal for the corresponding height and temperature of water using the equation:

pressure = height (m) x water density (kg/m3) x gravitational constant (m/s2)

But the density of the second column is different so this value needs to be adjusted.


texts: Plastic hinge locations in pushover analysis

texts:
In pushover analysis, why do we force the plastic hinge locations, such as indicating in our model instead of waiting for them to occur naturally?
Also, do we usually need to show the spread of plasticity on a member in our model or it is too much academic?


texts: seeking help for decoding a call log / PCHR trace files (Call logs)of Huawei V900 R015 machine(.log files)

texts:
I have PCHR trace files of the above mentioned server . But unfortunately I couldn’t find an appropriate decoding software to read those files. I tried manual through a c program but it didn’t work well.
files are of the format .log for example

BSC0007_[PCHR]02Log20150928102948_20150928103252.log

the header of this HEX files contains this when it decoded to UNICODE

.........................
.........................
.........................
.........................
....TT__TOOLMBSC.........
.V900R015....C00SPH588...
..4........Ü_.ß..MBSC CHR
.........................

CHR: (Call History Record) Detailed info for the abnormal call.

PCHR: (Performance CHR) Limited info for all calls.

can anyone help me with these


texts: How to select the distance between two starwheeels holding a bottle?

texts:
If you have some experience in th field of packing and filling can you tell me which two areas should i choose to support the bottle with two starwheels ?

I think the red area should be supported as it has a straight line and the upper area
But I'm afraid if i didn't support the bottom area the bottle would flip because the movement of the conveyor?


texts: How to use MERRA data in Pavement ME Version 2.6 for rigid design?

texts:
We are testing out Pavement ME, Version 2.6 on our server, and we can't figure out how to import the MERRA Climate Data for rigid pavement designs.  We have followed the steps outlined in the help menu within the program, but it still is not working for us.  Any suggestions are greatly appreciated!
Thank you.


texts: If gold is a worse electrical conductor than silver and copper, why are gold plated contacts considered "better" by the market?

texts: I've always wondered if this is just a marketing thing, but all across the electronic supply spectrum I see "gold plated" listed as the best conductors for various contacts and connectors. However, silver is considered the most conductive element (6.2×107 S/m), followed by copper (5.9×107 S/m), with gold (4.5×107 S/m) being third. I get that any of those are better conductors than the most common (tin and steel) but I would think silver, being less expensive, more abundant, and a better conductor, would be preferred over gold. What am I missing here?


texts: Designing a hypoid gear set for 3D printing

texts:
I want to design a hypoid gear set with a ratio 2:1 for 3D printing with an ofset of 8 mm but I do not know where to start.
Otvinta.com has a calculator and a tutorial to go with it but the gears do not mesh at the end using my own inputs.
I believe there is no standard way to do it like involute spur or helical gears and that several companies like Gleason made their own standards and machines to manufacture them.


texts: Model-based Ziegler-Nichols tuning of a hover PID controller

texts:
Doing a fun project to reconnect with my engineering training: I would like to design a control scheme for hovering in-place at a set altitude with a vertically-oriented propeller, rocket, etc. Right now I'm not even worried about lateral motion, just the vertical component. My plan is to use PID control and tune with the Ziegler-Nichols method for no-overshoot. The system is so simple I can write down a model of the P-only controlled system rather than tune experimentally. Just using Newton's 2nd law and ignoring aerodynamic effects:

$$
\begin{align}
m x^{\prime\prime} & = g m + T \\
x^{\prime\prime} & = g + \frac{K(x - x_{target})}{m}
\end{align}
$$

Where $g$ is gravity, $m$ is mass, $x$ is height, and $T = K(x-x_{target})$ because my thrust is proportional to the error times the gain $K$. Using $sin(\omega t)$ as a trial solution I get:

$$
\begin{align}
\omega & = \textstyle\sqrt{\frac{K}{m}} \\
T_u & = 2\pi\textstyle\sqrt{\frac{m}{K}}
\end{align}
$$

However it seems like I get free choice of the ultimate gain $K$, since any choice of $K$ causes the system to oscillate, as far as I can tell. What am I missing?


texts:
When I start the car, why do I hear the engine working when I'm not pressing the gas pedal?
How exactly does the torque and power of the gears work?

Torque = Radius * Force

Power = Torque * Speed

Do the different gears have different torque? They should, because they have difference radiuses, right? I'm a bit confused on how torque and power relates to the torque and what happens when we switch gears.
How automatic transmission cars detect what torque to put into the wheels and how do they put it?
How electric cars detect what torque to put into the wheels and how do they put it?


texts:
What is the NORMAL STRESS in a thin walled pressure vessel?

I am aware of only 2 types of stresses in thin walled pressure vessels: Longitudinal & Tangential.

Is any one of these 2 is considered as the NORMAL STRESS? If yes, which one and why?


texts: Any effect of fire in structural design of buildings?

texts:
Do we consider possible effects of fire, when we do structural design for reinforced concrete buildings?
But for steel buildings we do?

Also for reinforced concrete buildings, the thermal expansion difference will not be issue because thermal expansion coefficient of concrete and reinforced steel is very close to each other?


texts: Minimum number of tetra elements required, to represent a cube?

texts: What is the minimum number of TET elements you need, in order to fully fill a cube(HEX element)?


texts: If I have multiple different DC voltage inputs, how do I get a stabilized output at an intermediate voltage?

texts:
Let's say I have $3$ DC lines input as $10 V (x A), 24 V (y A), 6 V (z A)$. Now I want to convert the output to say $16$ VDC at $k A$.

What kind of converter can I use?


texts: How is linear motion achieved in this automatic blackboard eraser?

texts:
In the animation shown below what can be the mechanism used for this purpose? I know it can be achieved by using rack and pnion gear arrangement. But how are this set up arranged in classroom environment, I have no little idea. Please help me about this mechanism.
And what can be best suitable material for this wiping action Thanks
Video link: https://youtu.be/VB3FGRPSqsI


texts: How to get version from an abaqus output database file?

texts:
I want to read some data from an .odb file, but when I open it using the C++ API I always get this error message:

file.odb is from a more recent release of Abaqus.
The current Abaqus installation must be upgraded before this output database can be opened.

I also tried a newer version of Abaqus, but I got the same error. Is there a way to get the version from an odb file so that I don't have to try all Abaqus versions?
My Abaqus version is 6.14-1.


texts: Why does paper under pressure become brittle?

texts:
In this popular YouTube video, a man attempts to fold a piece of paper more than seven times using a hydraulic press.

After the seventh fold was applied pressure from the press, the man shows the audience that the paper became brittle, and breaks apart almost how styrofoam does.

Paper isn't usually brittle, so what exactly took place such that the material properties of the piece of paper wildly changed?


texts: How can I calculate final gear ratio when the drive train contains multiple gears with some reductions on the same shaft?

texts:
I am trying to calculate some rather long and complex drive trains, this is a project that I have worked up to, but its the first  problem of its kind I have come across, to try and explain the position I am in please follow my example of how I am trying to calculate the final ratios and if I am going wrong, please can you point out where I have gone wrong and if you have the time, why.

Example:
In the image below is a simple drive train, it consists of three shafts with four gears turning.( I know it doesn't look it, but please assume all teeth are of the correct size and mesh with no problems)

Shaft 1

Input Gear 1 (Purple) has 24 teeth

Shaft 2

Driven 2 (Red) has 12 teeth

Driven 3 (Blue) has 15 teeth

Shaft 3

Output Gear(Green) has 10 teeth.

So the power travels through Purple,Red, Blue Green.

Now for my Math.

though a 2:1 is connected to a 3:2 I have been calculating  the ratio like this, but I am sometimes getting different answers with long (up 12 gears) trains in my project.

I would calculate the final ratio like this:

(12/24)x(15/12)x(10/15) = 0.416(RECUR.)

This is where I am going wrong
Is the Final ratio 100:416 (1:0.416)
or is it
 1/0.416 = 1.666 = ~16:10  or is it something else?

Any help is greatly appreciated, im stuck at the moment and need to get on!


texts: Recommended models for mineral liberation in crushers

texts:
I'm investigating comminution processes at work, and from my studies I know that there are different breakage models for different modes (Compression, attrition, fracture etc).

So far I have only seen population models for ball mills in use. These models use time, size fraction and axial distance in the mill to specify the mass fraction of material at any given location in time.

I am wondering if similar models exist for other comminution devices (Gyratory or Jaw crushers) and if so  what do they look like?


texts: what is expansion joint(compensating tube) in pressure vessels?

texts: I've seen it in the drawing,the expansion joint holds the nozzle.so why the expansion joint looks like this picture.what is the necessity of shaping the tube like this.in this picture the nozzle passes through the expansion joint has a diameter 57 mm.


texts:
Please bear with me - I'm not an engineer, I'm a software developer so lack the language / knowledge to describe what I want precisely.

I'm controlling a servo to rotate /pan a platform to hold a camera (think pan/tilt). This is fine.

However, I'd like to house the servo/electronics in a waterproof box, and have a platform on top of the box that Pans.

How can I transfer the rotation through a waterproof enclosure? Is there such a thing as a waterproof bearing, that the servo can rotate one side within the enclosure, and have the rotation exposed on the outside, so I can attach the Panning platform to it?

Does such a thing exist? If so, what is it called?

If not, surely this is a problems that has already been solved
 Can anyone direct me to a solution for this?

Thank you!


texts: Is there any practical way to partially absorb the heat from a refrigeration condenser

texts:
I have currently been experimenting with a phase change material to absorb the heat given off by the condenser in a small refrigeration system (about 1/5 hp compressor) and while it does absorb a substantial amount, it often requires a huge volume of the phase change material (many many kilograms of the stuff) which is not practical due to the heat.

Is there any other alternatives that can absorb heat without a huge increase in weight?


texts: How do I calculate the compressive strength of a wall?

texts: I literally just have a thin steel wall that stands vertically with a load on top. The thin edges of the wall are oriented vertically with the load applied on top of the top thin edge, with the large planar faces of the wall facing horizontally to the sides. I thought there would be an easy calculation based on height, length, thickness (width) and a material parameter for the steel I’m using, but internet searches have yielded me no useful information as to the specific scenario I’m looking for. Is it not that simple to calculate wall strength based on a top loaded compressive force oriented vertically downward onto the height of the wall? Someone please help!


texts: How monolitic is concrete when falsework is being crafted for parts of future structure only?

texts:
Suppose we craft a reinforced concrete pylon for a cable-stayed bridge. It's very tall and rather thin. No one builds falsework for the entire pylon - it'd be very impractical. Instead, a part of falsework is built for the lowest part of the pylon, filled with concrete, then some time later that falsework is removed and the next part is built for the higher part of the pylon.

So the pylon in not really a single piece of concrete, it a combination of pieces seamlessly united together because the concrete surface of the earlier part is kept clean until falsework is moved up and so new portion of concrete just sticks to it pretty well.

How "monolitic" is such monolitic concrete? How much does it differ from concrete put into falsework size of the entire structure?


texts: Is there a more active passive technique for removing humidity from the air besides salt blocks?

texts:
We can get really humid days sometimes. Recently I was digging around in boxes and found some old mineral specimens, and I set out a few of the salt crystal rocks. I soon found that they had pools of water accumulating underneath them, which required some cleaning and attention.

After putting them on drinkable trays, I found that the surface tension was pulling the water off the bottom of the block and causing it to collect.  This got me thinking about passing the air in coming to this space through a baffle of salt blocks.

The good thing about salt blocks is that the absorbed moisture can be 'wicked' away. Whatever the solution, this needs to be a cycle that is ongoing using the material(s) installed. I am fine to imagining the installation of a plumbed drain or collection reservoir.

Is there another material or better technique for removing moisture from the air in this passive manner?

*Passive meaning 'without an energized / motorized compressor to dehumidify'.  Mostly, the mechanism needs to be designed to leverage ambient energy or mechanics, and minimize maintenance cycles and materials handling.


texts: Does this exist? -Sliding Fluid Restrictor -Solenoid Valve -Ball Valve

texts:
I am trying to come up with a way to restrict beer flow using a valve that does not cause foam. I have found that a solenoid valve causes a change in the direction the beer must flow and this sharp change through a different size opening creates foam quickly. I have thought about a ball valve or pinch valve but I need it to be electric, work very quickly and have a small form factor.

Does anyone know if anything like what I created in this video exist? https://youtu.be/iE6qe7045Ck

The idea would be electromagnets that cause the metal pieces to slide in one direction or the other opening and closing the flow of beer. The idea is keeping the opening in the valve the same diameter as the inner diameter of the tubing I would be using (3/8"). It would need to handle at most 14 psi and at least 12 psi. (Average beer lines are 9-10psi)


texts:
I'm using Aspen Custom Modeler to create a model to be used in Aspen Plus and Aspen Plus Dynamics, and I'm having trouble figuring out how to code the mass balance, energy balance, etc. I'm essentially coding up a pump, but a pump which takes both flow and inlet pressure as arguments to determine the outlet pressure. My model code is as follows.

Model XePump

  In1 as input MainPort;
  Out1 as output MainPort;

  // Internal
  Pdiff             as press_diff               (description:"Pressure difference");
  Svar              as fraction                 (1.0,fixed,description:"Operating speed parameter");

  Pdiff = 1.0 * In1.P * (0.16169605386 - In1.F) * Svar;
  Out1.P = In1.P + Pdiff;
  Out1.F = In1.F;

End

The errors I'm getting are in Aspen Plus, the model doesn't have any outlet flow rate, despite explicitly setting it to be equal to the inlet flow rate. Any tips?


texts: 3D Printing Models exported to DWG from STL using 3DS Max have missing surfaces

texts:
I want to edit some STL projects with Inventor. According Autodesk documentation, since Inventor is not able to edit mesh models, the most practical way without installing other software in my situation, seems opening the STL with a program able to export to DWG, then importing the DWG in Inventor.

I have tried to open the STL model with 3DS Max but using the export to DWG function the resulting DWG seems a skeleton of the model rather than the DWG version of the original model.

Example

Original STL model

Exported DWG model

How could I avoid this problem?


texts: Center of Gravity of Precast Concrete Steps

texts:
The precast concrete stairs at the home I recently purchased do not have a footing.  Lack of a footing coupled with drainage issues has caused them to sink over time.   I'm going to raise them and get them properly supported underneath.

To do that I want to clamp them near their center of gravity (along the length), so that I can jack them up back to where they belong and minimize the risk of breaking the concrete (I'll continuously add temporary support underneath them as I slowly jack them up).

I have dug out the bottom of the steps and determined that they are monolithically poured and solid.

What is the measurement along the length of the steps where the center of gravity will be?

Edit:  This is not homework.  Here are the stairs in question:

You can see how they are pulling away from the foundation and have rotated forward and dropped.  The sidewalk slab in front of it has also sunk and needs to be raised, so it is worse than it seems in this photo.

I attempted to solve this by hand because it seems trivial.   I'm glad I asked, because the solution I came up with was wrong.  I assumed I could reduce it to working with the ratio of cross sections which are simply three rectangles (since they all have the same width).

If I take the area of each step individually I get:

$$\begin{align}
17.5 \times 18 &= 315 \\
14 \times 11   &= 154 \\
47.5 \times 3  &= 142.5
\end{align}$$

I noticed that if I add the bottom two steps together, they are a smaller combined area (and thus volume) than the large step [pretty sure this is where I went wrong ... when you multiply by width this is no longer the case].  So it appeared to me at the time that the COG would be somewhere in the large step.  I'll denote the COG as $c$.

So I then used this to give me $c$:

$$18 \times c = 18 \times (17.5 - c) + 154 + 142.5$$

That worked out to 16.98 (17 inches for all practical purposes).

However, after seeing @Chris Johns solution, I realize that what I had in my brain is not correct, and anybody with sinking stairs should ignore everything above.


texts: Calculating force exerted on plate by link

texts:
I am currently involved with a project using a mechanism similar to that seen in 'table tilters' and we are struggling to work out how to begin resolving the forces.

The image shows the state we are considering in equilibrium to resolve the forces. The plate (blue) is in a horizontal position and is 350mm in length

The linkages (red) are 270mm long and are at an angle of 20 degrees to the horizontal at this position.

The green component is restricted to motion in the vertical direction and is being pulled downwards with a force of 3000N.

We want to work out the downward force the linkages exert on the plate.

I started to try and break the system down into free body diagrams (below), but am struggling to make a start resolving the forces. Any advice would be greatly appreciated.


texts: How to build a steel flat bar rotating mechanism using an axle hollow shaft?

texts: I aim to build a system of a steel flat bar rotating around a pivot point with the help of a couple of dc motors mounted on the edges of the bar. After doing some search I decided to build it using a steel punched bar, a steel axle hollow shaft as the rotational axis and a couple of rotating gears to mount a potentiometer in order to take measurements. My issue is how to connect the flat bar with the hollow shaft in order to enable the bar to rotate around this point. What component should I consider ? I suppose that the hollow shaft should go through this component and then this component should be connected to the flat bar using some screws perhaps.


texts: Why aren't artificial gills used together with oxygen tanks for diving?

texts:
Artificial gills aren't used for diving, not because they can't extract oxygen out of water, but because they won't provide enough oxygen for someone to breathe (only arround 1% oxygen in water instead of 20% in air). So they stick with oxygen tanks.

But why don't they use them both at the same time? The gills will on give a little bit of oxygen, true, but over time it will allow the diver to stay underwater longer with the same oxygen tank. If you add a rebreather to that, so only arround 5% of your air goes away every breathe, it will be even longer.


texts: Can Dynamic Base shear be greater than Static Base shear?

texts:
I just modeled a High-rise building of 43 stories with an area of 700 square meter, Using ETABS as a software to model the building I got the Static and Dynamic Base Shear as the image below, my Question is the following:

Is it Reasonable that the dynamic base shear (Specx and Specy) is bigger than the static base shear (Ex and Ey) ? How can i know if this result is logical or not ?
If the result is Correct i don't need to scale the dynamic base shear ?


texts:
When driving piles, the resistance from the soil is constantly measured.
What happens when the expected resistance values from the soil are not obtained?
For a single pile or for multiple piles?
What do we do in that case?


texts: Cutting lego "+" cross-axle holes, lego knobs?

texts:
In short, I'm looking for ways to reasonably precisely machine a "+"-axle hole, Lego compatible sockets, Lego compatible knobs, Lego compatible round peg/axle holes, and other cutouts for Lego-compatible parts on a small/hobby scale. Preferably by removing material from existing slightly over-size knobs / slightly under-size holes.

I've been really enjoying making lego-compatible parts, which I mostly make with a 3D printer then modify by hand to achieve the desired fit. This is cumbersome and it's very hard to get good results.

My FDM 3D printer isn't proving precise enough to produce a good fit for parts straight off the print bed. While I'm working on improving that, I'm looking for ways I can more easily "finish" or refine prints to produce a better fit for real Lego.

"+"-axle hole: Most importantly I'm looking for a way to cut a Lego-compatible "+"-shaped axle hole, or trim/expand an existing hole to improve fit. I just can't figure out a sensible way to cut this in a sufficiently uniform, reliable manner. Filing it out is just not an option. Tips for making helpful jigs or custom tools would be more than welcome.
Lego knob: Knobs to go into Lego sockets are close to 4.9mm in diameter. I can not for the life of me figure out a good way to cut a nice accurate and smooth sided/topped 4.9mm knob from a slightly over-size knob printed in plastic.

For ideal results the knob should actually be slightly non-round (by a something like 100μm) so it deforms slightly into place, but I can't see that being practical to do at home. A nice round smooth fit would be a good start.
socket to accept a Lego knob: I haven't found any sensible way to do this. The knob diameter is 4.9mm. Most places that accept knobs aren't a round socket, they're usually 4 pegs, but round sockets a bit over 4.9mm are also used. A 5mm metric drill bit is too large and produces a loose, sloppy fit.
smooth bore round axle hole: A 3/16 inch imperial drill bit (4.76 mm) seems to be about perfect for a Lego round axle/peg shaft. So that much is working well, I can just print slightly undersized with thick walls, then drill it out and get a great result.

Note that there's a disturbingly thorough workup on Lego dimensions available here.


texts: Reduce high pitched noise from idle stepper motor

texts:
I have the following setup:
Stepper motor: Bipolar, 200 Steps/Rev, 42×38mm, 2.8V, 1.7 A/Phase - https://www.pololu.com/product/2267
Diver: DRV8825, with current limiter VREF = 0.85v - https://www.pololu.com/product/2133
Power Supply: 12v 2a DC
When the steppers are hooked up to the power supply they make a very annoying high pitched noise while the steppers are idle. I am fine with a bit of noise while the stepper is moving, but would like them to be silent while stationary. I cannot figure out what is causing the noise. Here is what I have tried to reduce the idle noise:

Reducing the current until the noise is gone (resulted in complete loss of torque when the current was low enough to remove the noise)
Used a 5v 3a DC power supply (motor did not power on at all with this supply, I am still confused why it is rated for 2.8v but won't work with 5v but will work with 12v)
Engage the sleep pin while the motor is not moving (removed the noise while idle, but when it disengages sleep pin to move again its jolts slightly and causes the step count to be off and over time the motor is no longer accurate)

These are not the only stepper motors that I have that have this noise issue, the only motors I have that do not have this noise issue are smaller 350mA neema17's and I think that is just because it has a lower amperage.
I have not been able to find a way to fix this issue. Are my configurations incorrect? What power supply should I be using? Is there anything else I can do to fix this high pitched noise while the stepper is idle. Any help will be greatly appreciated!


texts: Using one electrical pump for multiple hoses

texts:
I'm currently trying to figure out a cheap way to build a cocktail machine.
For now the machine should have about 20-30 possible input liquids. These liquids should remain in their original bottle and should electrically be pumped up when needed. (I know I could use gravity instead of pumps, but the bottles should be stored in a cabinet under the machine itself.)

At first I was looking for a good type of pump to use for this project and I think peristaltic pumps would be ideal because then I could be sure that the liquids haven't come in contact with anything but the hose.

Then I tried to find the cheapest pumps of this type available, but unfortunately the cheap ones are still about 5€ and they would only do 150ml/min. I think 500ml/min would be the absolute minimum required.

But now I'm thinking that maybe there is a cheaper way and I just don't know the components.

So my idea would be that maybe I could just buy one big pump (maybe something like this) and then connect all 20-30 hoses to it using a bunch of adapters (maybe a bunch of these).
Then I would just need cheap way to electrically close all but one hose at a time. So I was wondering if there if some sort of electric valve that is very cheap (maybe 1-2€) and doesn't come into direct contact with the liquid. I was thinking maybe some sort of electromagnet that squishes the hose or a DC motor that uses some sort of screw mechanism to bend the hose until nothing can pass through anymore.
I should also mention that I'm going to use something like an ESP8266 or maybe an Arduino to control the whole machine.

Is there any such component?

Edit:
As suggested in the comments it might be a better idea to simply pump air into the bottles to get the liquid out. This way I can run completely separated hoses avoiding the problem that liquids may flow back into the wrong bottle (which would especially suck for milk and cream etc.).
I found really cheap air valves that I could use for this purpose.
I could power/control them using a relay board like this which I'd attach to an Arduino. Then I'd then just connect a compressor or CO2 container at a reasonable pressure to the valve input.
Sounds like this could work to me. But what if these valves aren't perfectly clean? I should probably have some sort of air filter behind each of these, right? Any ideas how I could accomplish that in a cheap way?

I have intention of using this machine commercially btw.

Edit2:
Another problem with the air idea is that I'd have to buy a compressor for that. And they are loud and expensive form what I can tell and besides that they are completely overkill. I doubt I'd even need a 1 bar of pressure.
Is there maybe some sort of cheap low power (but therefore very quiet) compressor that I could use?

Edit3:
Could I build an air filter like this one but instead of using a PVC tube, simply use the hoses that go into the bottles?

Edit4:
Bottles that are carbonated in the first place could be another challenge because they would just push out liquid automatically over time unless I build a mechanism that detaches the compressor and then opens all valves that that no bottle can build up pressure while the machine is idling.

Edit5:
Maybe a quiet fish tank air pump could be used instead of a compressor.
I found some that are rated:
throughput: 192 liters / hour
power: 2 watts
pressure (MPa): >0.012
noise: < 40 db

I think 0.012 MPa would be 0.12 bars or 1.74 psi. But I have no understanding of how much that actually is and if it would be enough.


texts: AutoCAD 2019: How do I Find the Perfect Angles to Match Line Endpoints

texts:
I'm trying to match up two lines on a drawing I am doing, without changing the length of either line.  There is a perfect set of angles to do so- I just don't know what it each.  Is there a built in functionality to do this?

This is what it currently looks like:

Thanks!


texts: I have the following structure, in which I am failing to calculate the two reactions: Cz (apparently vertical) and Dz, in the roller support of the beam. The beam length is 7.5 m, the reactions Az, Cx, and the momentum in C are calculated correctly. The distributed load replaced with concentrated on the first beam. Thank you in advance for advice and help.