texts: How to model this real-world system to define transfer function for stability?

texts:
The system shown is an off-axis drive system that rotates the platform to 60° via a substantially-sized NEMA 34 stepper motor. The axial force required by the stepper/ballscrew assembly has already been determined. The maximum axial load on the ballscrew occurs at 40° and is approximately 150lb-force or ≈ 670N. The linear rail is a dual-rail quad-bearing carriage system capable of supporting over 5x the load weight. The stepper motor also will never reach a rotational velocity of more than 2.4 rev/sec and will be operated at full step to maximize torque. (200 ppr or 1.8° per step) The maximum motor torque required at the greatest load point is 1.7Nm. The stepper we have chosen provides 5.6Nm. Long story short, the system is not lacking in power or structural integrity in any way.
However, the system will be operated at specified degree points at low-stepping speeds. For example, it will be stopped at 40°, and then "stepped" in slow increments of 1.8°. I am controlling this via LabVIEW and can rotate the stepper at any number of 1.8° steps per second I choose. This positioning control is 100% open loop and determined by the operator. I am trying to determine the mechanical stability of the system as it is given this "step" input under a load. I'm not sure where to begin with deriving a transfer function or how to model it. As you can see, there are gas springs that assist the operation. Maybe it should be modeled as a spring-dampener system? I am not sure. I have Simulink and would like to be able to model they system in there...I'm just not sure where to start. Thank you.


texts: Beginners material science for handling a load

texts:
I’ve got a reasonably strong grasp of Newtonian mechanics, but as far as material science goes I don’t know which of the many material properties I need to use to solve my problem:
I’m trying to mount a heavy object at the end of a lever arm. I’ve got a 1 cm (0.4 in) diameter steel rod, and I’m planning to embed half of it in a concrete wall to hold it in place, and the other half will extend 2 m (6.6 ft) parallel to the ground with a rope holding 50 kg (120 lbs) sitting in a notch at the end. I’d like to buy a thinner rod if possible, but picturing this in my head it seems with about 980 Newton-meters (eh, 1330 ft-lbs?) of torque I’m likely to bend the rod.
Which material science properties do I use to figure out how to minimize elastic deformation and avoid plastic deformation entirely?
Note: This question was originally posted to Physics SE, and was moved here on request from @Gert :)


texts: A unsolicited lighting installer went up on my roof and told me that I had had a lightning strike and that the cable along the roof line (going from one rod to another) was crystallized and that I needed to have all cables replaced. I sensed a scam and sent him away. Was I right? Can these cables 'crystallize'?


texts: How to find the angle of deformation in Ansys APDL?

texts: After solving my problem in APDL, and started doing some post-processing, I want to find how much the deformed shape has rotated (i.e. the maximum angle the furthest node has made comparing with the original unreformed shape), I'm doing 2D analysis, is this exactly what is shown as, z-component of rotation, or there is other thing I need to know?  and in which units, deg or rad?


texts: How to find the speed of a boat needed to become airborne on a wave

texts:
I am doing a small dynamic project that needs to predict the boat's (boat with propeller) movements in a wavy sea condition as shown below:

as the boat is at the peak of the wave, how to determine how much would be the boat's speed for it to fly away from the water? (how will it move...)
the known information are:
1 wave's speed in x and y direction at the peak point is 0.5 m/s and 0.4 m/s respectively, boat's hp is 100.
2 boat's velocity (3 m/s - 5 m/s ), weight (250kg) , size (cross sectional area immersed in water is 0.081 m^2 , volume immersed in water is 0.244 m^3, height of boat is 2m, length 3m and width 1m)
3 wave's height 0.3m, length 3m.
4 drag coefficient is 0.09.
5 viscosity of water is  8.90 × 10−4Pa·s
6 boat's buoyancy
7 water's drag force (needs to be used)
(the air friction can be neglected, use pure water density)
calculation:
in y direction: I calculated the buoyancy force and found it to be 2452.5 N same as the weight in calm water. when the wave hits and rises the boat which formula should I use to calculate the force being applied to the boat in the y direction?
in x direction : I calculated drag force using this formula:

and found it to be 4478.985N , but I am not very sure how to find the the force of the boat, so that I can compare it with the drag force, if the value is larger , then will the boat would fly away from the boat?
please help me with the concept of how to solve this problem....
if any information is missing, please inform me... I will update....
Thanks...


texts: Is a circle the strongest 2D shape for containing internal pressure?

texts: I understand how a circle (or sphere if you want 3D) is the best shape for holding a vacuum inside a container, but what if you wanted to have a large positive pressure inside of the container instead of outside? Would a circle/sphere still be the best shape as far as material required to hold X amount of pressure?


texts: Hack a kitchen freezer for lower temperature

texts:
Common home freezers usually have the lowest temperatures of about -24 degrees Celsius. Freezers that go lower exist but these are much more expensive (times much). I wonder whether a common kitchen freezer (standalone without fridge) could be easily hacked to achieve lower temperatures than those -24C (like -40 or -60/-80).
I guess the task is either to hack the thermostat for lower temperature or to disable the termostat at all and supply custom thermo-regulation-circuitry (attach thermometer and then switch the whole freezer on/off as needed to regulate the temperature).
Any ideas how to do this? I guess the structure of the freezer should probably be able to withstand a bit lower temperatures that what it is designed for.


texts:
Capacitive touchscreens do not rely on touch as the name suggests but rather measure the distortion of the electrostatic field. To my understanding a touchscreen might be able depending on the build to detect touches from a distance of a couple of tenths of a millimeter above the surface.

Is there a way to influence the electric field of the touchscreen from a greater distance such as a centimeter above the screen?

What I am thinking is that creating an electrostatic charge might perhaps help, for example similar to the way an ionizer works. Unfortunately I lack the electrical knowledge to understand the implications of 'the other half of the capacitor' which is needed to excite the touchscreen.

The goal is to create a 'hover stylus' similar to the wacom digitizer (which of course works differently based on electromagnetic resonance).


texts: How do I calculate the weight needed on a press board to deliver a certain amount of pressure?

texts: I'm building a press for cider. I'm going to be using a 24" x 24" press board. I'm looking to deliver 40 psi to the cider. How can I determine the amount of weight required, in tons? What sort of equation would I use?


texts:
I have developed a design for a river cleaning machine which can cut and collect weeds. The problem which is facing is how to rotate the circular blade which is attached in front of the machine. I mean first is to directly attach on a dc motor's shaft but there are less to zero options available for waterproof dc motor. Next is to shift the motor to another place and add a chain connection between the motor and the blade.

I am not a mechanical engineer. Can anyone help to figure out what should be the best way to solve this as I have to use nonwaterproof motors.

The black circular spiky thing is the blade which is attached in front of the body.


texts: Why do most BMS systems for li-ions and li-pos stop discharging at 2.5V? Are there better systems or is this the standard

texts:
From what i've read online, 3.0V is the absolute maximum li-ion and li-po batteries should be discharged and around 3.2-3.4 is preferable for preserving battery life.

if that is the case, then why is it nearly every single 4s BMS I find stops discharging at 2.5V-3V!

https://www.amazon.com/s?k=4s+bms&ref=nb_sb_noss

Edit: I can see the potential reason to want to maximize use in a cycle as an emergency option, but I don't imagine people wanting to buy systems where this is the default and unalterable! Is there a BMS system or standard for a way for managing batteries that both manages to balance batteries and not kill them pre-maturely at the same time?


texts: How does a compressor know to lower condensing pressure in chiller?

texts:
I am working on an indirect ammonia chiller that is used to cool the ice in an arena. The system consists of 3 reciprocating compressors, an evaporative condenser with a vfd on the fan, a float throttling valve and a plate heat exchanger acting as the evaporator.

With one compressor operating, the condensing pressure of the ammonia ranges from 140 psi to 180 psi depending on the speed of the fan. When the condensing pressure is higher, the compressor is doing more work. When the fan speeds up, the head pressure lowers which corresponds to  a drop in compressor work.

I know that lowering the condensing pressure reduces compressor work and am familiar with the pressure-enthalpy chart that is used to describe the refrigeration cycle. My question is, how does increasing the fan speed cause a drop in compressor work? The fan kicks on and rejects more heat from the gas, but what is the process or mechanism that occurs as you follow the refrigeration cycle that results in the compressor lowering the condensing pressure?


texts: 8W Solar panel high amperage low voltage

texts:
I have to put together a small solar system for a college project.

I have solar cells with an output of 3.65A and 0.6V. Now if I paralel two groups of two cells connected in series I will double the amps and volts. And the output power will be like 8W.

The question is, do a 1.2V panel really work? Can I charge a 12V battery? I mean the panel will be 8W and high amperage low voltage.

Do I need to have a minimum 12V panel to charge battery? This means I will have to put in series 20 cells to obtain 12V.

Are there high voltage low amperage solar cells so I don't need to put together so many cells?


texts: Does opening a tap in a sink affect the radial speed of the water around the jet?

texts:
Does the speed of the water flowing radially outwards from a water jet impacting a sink depend on how far the tap is opened?

At the moment, I understand that the maximum velocity of the water in the vertical jet is constant regardless of how far the tap is open (as it is accelerated by gravity, and disregarding air-resistance), but the volume flow rate is greater the further the tap is opened.

I'm thinking that a higher volume flow rate results in a greater depth around the bottom of the jet which reduces the effect of friction between the water and the sink as the contact surface of the water has reduced, which would decelerate the water at a lower rate than if it were shallower, but am not sure.

Could someone explain precisely how opening a tap affects the radial speed of the water around the bottom of the jet?

EDIT

I should have clarified that, for my question, the area is variable.
What I had in mind was more like a variably sized circular hole beneath a constant-height water tank.  I used the word "tap" for simplicity, but I realise now this is a bad substitute, and has caused more confusion than intended.


texts: What type of glue is best used to glue stainless steel bolt (not screw) used as self tapping to a hole (no thread) in a 3d printed nylon (polyamide) part? It will be an M2 metric bolt.


texts: Can you postcure epoxy composites outside the mold?

texts:
Say I make a fiberglass/epoxy part on a plastic mold, and it cures at room temperature. The epoxy system calls for a postcure at 250F, but the mold cannot withstand 250F.

If I take off the part and postcure it separately, am I likely to see dimensional changes in the cured part? Is there any way to postcure the part off-the-mold without losing accuracy?


texts: How do I set Reciprocating and Rotation motion in Fluent or CFX?

texts:
I want to model the following case(Attached picture)

This case have reciprocating and rotation motion. Is it possible that this case models in Fluent or CFX  without writing Code?

How i set this reciprocation motion in CFX? Is it possible that give me related paper and useful links and tutorials about this case? I found documentations about this case but don't found tutorial about this case.


texts: How do I update an individual control chart?

texts:
I'm finding myself using control charts and I'm unclear on a very basic point. I've read page after page of texts, but they all focus on how to make the initial chart rather than walking you through how to update it.

To make things easier, I'll set the situation:
I'm making an Individual Control Chart. Every thirty points, the chart is updated. In January, I put points 1-30 on the chart. February, I put points 31-45 on, and March points 45-60. So, the chart needs to be updated now. Where do I go from here?

Assuming none of the data points were out of control, here's what I think happens:
I think points 1-30 are removed from the chart. I think the chart has the average and control limits calculated using data points 31-60.  I think that future points (61-90) are plotted on the newly updated chart until data point 90 is reached, at which point the chart is updated, points 31-60 dropped, and the average and limits recalculated using points 61-90.

I am aware that the limits for updated versions of the chart should be calculated using xbarr +/- 3s/c4.

Edit:

So, using the power of randbetween, I've made some sample charts and sample data. The first is for the month of January, where data was taken every day, giving 31 data points, and at the end of the month, the chart that follows.

Date    Value   Average        SD         UCL           LCL
1/1/2016    9   6.161290323 2.887868582 14.82489607 -2.502315423

And a bunch of values for the dates stretching out over the next few months (I can post all 60 rows if really desired).

Okay, so I've plotted the first 30 datapoints. So far so good. In February, only 15 samples are sampled for data. The datapoints are added to the chart for a total of 45 datapoints on the chart:

In March, another 15 samples are sampled and this brings the total number of datapoints up to 60:

Now at this point, I know that the chart must be updated. But there are a few ways I can do it. One of which is to remove the January data (the first 30 datapoints) both from the chart and from the calculations and only plot datapoints 31-60, with datapoints 61-90 being plotted on this as well (at which time, we would go through the process again):

Or I could calculate the average, SD, and the upper and lower limits based on datapoints 31-60, but plot datapoints 1-60:

Or I could re-calculate the average, SD, and upper and lower limits on datapoints 1-60 AND plot datapoints 1-60:

All of these give different limits, different charts, and all of them seem equally valid because nowhere does it seem to discuss what you do to actually update the chart once it has been made.


texts:
What is meant by "designing analytically" ?
Especially in control systems design
Does it mean theoretically design?


texts: How to calculate the bending resistance of a square metal bar?

texts:
I have an old bend/twisted wooden door. It has some character to it so I want to keep it and add square metal bars to straighten it. I have provided a sample drawing of the door and where it is twisted. I have drilled a hole in the upper most open part and if I pull with a scale I am able to straighten it with about 20kg (I haven't used a scale yet, but I will)

I intend to put square metal bars on the bent sides (maybe even inside and out) and straighten the wood.

My question is what is the formula that I can use to calculate the size of the metal bar? For example I see there is a square profile bar 40x40x3mm that I will be able to buy and attach. So, is this going to be enough for the long side 2m and for the short side 1m?
I can also order this square profile bar to be slightly bent and attach it so the two bends - the one of the wood and the one of the metal counter each other. But I am not really willing to go that way. I think its way too complicated.

Thank you in advance.

Edit:

I think a visible rectangle bar on one or both faces will be stronger and more simple to attach, so I will go with that.
No bend is acceptable - I want it straight.
So the next question following the comment is how much of a bend do I need for what type of bar for each of the sides - short(1m) and long (2m)?


texts: I am an M.Tech student from Manipal Institute of Technology, Manipal. I want to deduce the mathematical relationship between Forward Voltage and Forward Current of an LED from the characteristics given in the datasheet. How to derive equation from the graph?


texts: What is the definition of rate $(−ra)=−\frac{dCa}{dt}$ or $(−ra)=−1/V\frac{dNa}{dt}$ ? I think the general one is the second one and first one is for constant volume reaction system. Is the above written rate equation only valid to batch reactor? If not can we use this in a PFR or MFR? In PFR we know the rate comes out to be $(−ra)=−\frac{dFa}{dV}$ ,can we equate $−1/V\frac{dNa}{dt}=−\frac{dFa}{dV}$? If not then why? Is the rate equation not valid everywhere? Can we equate with CSTR as well ? eg $-\frac{dCa}{dt}=\frac{Fa_o-Fa}{V}$ (considering it a constant volume reaction system CSTR)


texts: Ensuring even flow in liquid pumping in distribution circuit under suction

texts:
I have a liquid circuit which looks a bit like that:

The system is under suction, and the flow rate through each unit should be about 10ml/min. However, we noticed that unit n and the ones the furthest away from the pump and bottle were not getting enough flow. Any suggestions on how to make sure each unit gets about the same amount of flow? My initial thought was to add a second pump at the end of the line to help the liquid (water) go round the circuit. Another possibility is to separate the load of n units into 2 circuits in parallel, 1 to n/2 and n/2 + 1 to n at the bottle/pump location so that both circuits will have a better chance of seeing the same amount of liquid.

Some precisions:

there is a restrictor on the return path of each unit to restrict the flow and create a pressure differential to allow the liquid to go round
the length from unit #1 to unit #n is about 3m, the pump and bottle are located between unit #4 and #5.
the tubing diameter along that length is 4.8mm ID, and each teed off line in each unit is 1.6mm ID, with the restrictor 0.38mm ID (~60mm length)
the pump is a diaphragm liquid pump
there is a vent port with a filter on the bottle lid to allow for the pressure to vent out.


texts: Can you help interpret hand-drawn technical drawing?

texts: I can't seem to figure out the proper left view for the following image, and the full and half sectional cutout for the left and front projection.


texts: Statically indeterminate fixed-pinned beam problem

texts: F=32KN; Mf1=60KN-m; Mf2=-58KN-m; g=30KN/m I need to solve this using Force method. Find the reaction at the pinned end.


texts: Can photolithography be used on a 3D object?

texts: So normally, photolithography would be used to etch on a flat plane. I have a 3D object that I would like to have wires etched onto on 4 sides. Is there an adaptation of photolithography that allows for this?


texts: Should we split a building containing a factory and a storage according to (NFPA 13) code?

texts:
I asking for a building that contains a desalination plant and a storage of water bottles (in carton boxes).
Should we split the factory and the storage or not (according to NFPA 13)?
And which section in the code that deals with this matter?


texts: What are the pros and cons of between Zigbee and Z-Wave communication protocols used in IoT device space?

texts: Recently, both Zigbee and Z-wave tend to be the most commonly used protocol to communicate between Internet of Things (IoT) devices. Most of these IoT devices tend to have a combination of mechanical or optical related transducer or actuator device component coupled with a micro-controller and respective software stack. What are the major differences between Zigbee 3.0 and Z-Wave in relation to communication between IoT devices?


texts: Is there a submarine that uses fewer than 4 rudders?

texts:
This question is restricted to post-WWII submarines designed to have a greater speed while submerged and to cruise underwater (unlike WWII U-boats).

As highlighted in this question, there is no need to have 2 rudders (one on the upper side, the other on the lower one) and 2 fins for pitch control (stern plane?) (one on the left and one on the right side). As I don't know the exact vocabulary, for the rest of the question I'll name all those fins "rudder", whatever axis they control.

As highlighted by the Zeppelin NT, 3 independent rudders offset at an angle of 120 degrees are enough to control rotation along all axis on a vehicle based on equality between buoyancy and weight. (Note that with 2 independent fins, you can have a 2-axis control (e.g. roll and pitch)*)

I see several possible advantages of using fewer rudders:

fewer links between rudders and the hull, easing stealth (less hydrodynamic interaction, smoother shape)
shallower draft (even shallower than X-shaped discussed in that question) **
maintenance costs (fewer moving parts)

Of course, rudders' dimensions should be adapted to provide enough authority.

As I failed to find submarines with fewer than 4 rudders, I would like to know if it has already existed.

* I think some ship uses 2 fins for roll control
** some submarines already uses smaller bottom rudder, I suppose for this purpose.


texts: Is it possible to move gear on a shaft in one moment and in the other allow it to rotate freely?

texts:
Before I describe the problem I would just like to say that I'm no engineer this is my hobby, all I know is from google or if someone told me or from books. Something obvious to you may not be obvious to me. Thanks

I want to move a gear with the shaft like they were one in one moment and in the other I want to stop the gear using clutch brake while continuing to rotate the shaft.

One way to achieve this is using air bearings which would be the perfect solution if they weren't so impractical because of the required compressor and other parts.

Second solution would be to use two clutches. One to connect the gear to shaft and another clutch to brake the gear when the first one is not connected but I don't want to use more than one clutch pack because they are expensive.

Third solution is to use sync cone but that is much slower than clutch and that is why I don't want to use it.

Fourth solution which I found is using a shaft mounted brake to lock the gear with the shaft but I'm not sure if this would count as a clutch brake and if it would lower the efficiency of the system as whole.

So my question would be is there a way to achieve the problem described without using more breaks or clutches (if shaft mounted brake wouldn't count as a break then that is also OK)? The perfect solution would be a bearing which I could "turn off" and let it rotate with the shaft but I'm not sure if something like that exists.


texts: Ripple tank simulation for simulating light waves?

texts: Can anyone help shedding some light on how ripple tanks are programmed? example I'm looking to simulate light waves, to perform theoretical calculations, as opposed to for just visual effect. The ones I've found lack the ability to set a specific wavelength and place objects (e.g slits, walls) at specific locations.


texts:
To preface this question, almost all of my FEA experience has come from SolidWorks, so I haven't had to deal with these types of problems.

I'm designing a truss structure in PATRAN composed of 1D line elements.

At some point, I have to do the following two things:

Mesh each individual line to create nodes
Apply properties (material, cross-section, stiffness) to curves

Sometimes I apply the properties first, but when I attempt to mesh PATRAN tells me "Curve is in property xyz which does not support Bar2."

Sometimes I mesh first, but when I analyze the truss my results file is sometimes empty. I can't tell what distinguishes when it works and when it doesn't.

In which order should I do these?


texts: Problem finding temperature gain of air through heated glass tube

texts:
I have a 20 cm long glass tube of outer diameter 6.4 mm and inner diameter 4.3 mm. Air at Ti = 20 °C is pushed through the glass tube at 2 litres per minute. The glass tube has a wire wound resistance heater on it which we can assume is perfectly thermally insulated from the ambient air.
My aim is to find out the power needed to heat the air flowing through the tube to Te=650 °C at the tube exit.

After doing the calculation using

Where  is the power supplied by the heater (W),

 is the mass flow rate (kg/s),

 is the density of the air kg/m^3 at the bulk temperature   ,

I get the power required as being 12.5 W. This seems to me to be too low. Unfortunately I do not know where I am going wrong. Does anybody have any idea where I am making a mistake in my calculation?


texts:
in short, I want to implement a PID controller that takes in distance and returns velocity.
Details: I am simulating robots following each other. I wish to maintain a constant distance, d between these robots. I can obtain the distance between the robots at any time and then I can adjust the velocity of the following robot accordingly. My problem is the formulation that achieves the transformation of the information provided by the PID to velocity so as to achieve this constant distance. My current attempt is to use the error provided by the PID as the velocity for the following robot, that is;
v2 = e(t)
where v2 is the velocity of the second/following robot and e(t) is the error yielded by the PID at time t.
The problem with this approach is that it vehicle velocity is only as big as the error, so that way velocity only increases if the error increases, so if the constant distance I want is relatively small. I can never achieve this.
I also tried using the error as the acceleration, with the idea that the velocity should only grow as error grows and decrease in a similar fashion according to:
v2 = v2 + e(t) * dt
where 'dt' is the change in time.
But then when I get negative errors. I wish to avoid reversing or backward motion. So we can call it a stop-go implementation if possible. But ideally when the error in the desired distance reduces ultimately both velocities will be moving with the same velocity. Any approaches and suggestions will be highly appreciated. Thanks very much. I am doing all implementation tests in python. If more clarification is needed please let me know.


texts:
I'm looking to electroplate brass rings with gems glued on top of them (though I believe this is then considered electroforming as the copper builds on the glue or epoxy and around the ring and gem?).

What I'd like to know is:

What amp and volt size rectifier would be best? Some say 3amp is enough for small scale Jewelry others insist on going up to 25 to 30amp. I can get a 30amp 20volt online for relatively cheap - http://m.aliexpress.com/item/1919812106.html

(They have other smaller rectifiers, all have US plugs but do not state the plug outlet voltage. I live in Australia and need to be sure I can use an adaptor (not a converter) to plug into a 220v outlet).

If I use brass rings do I need to paint them first with a copper conductive paint? What if I want to eventually do silver plating? Would brass be okay to silver plate? I know I would need a different bath for that though, I'm just thinking of possibilities for the future.
Instead of using a copper conductive paint could I instead make my bath with copper sulphate, sulphuric acid and distiled water mixed together?
This is the copper sulphate I am currently using for the bath: http://www.bunnings.com.au/manutec-500g-copper-sulphate-soluble_p2961523
Is this pure enough? For my anode can I use a 99% pure copper sheet to will only 100% suffice?
Lastly, do I need to agitate the bath continually? I wouldn't mind a slightly organic look and have read that without agitation this will happen but I do not know to what extent.

I have experimented with copper plating a silver plated ring but the copper did not build up and part of the ring was eaten way at. I used the copper sulphate and boiling water for the bath, a copper pipe for the anode, and hooked the leads up to a 6 volt battery which attached to the anode and my cathode was a copper wire which wrapped around the ring. Not sure where I went wrong if it was the wrong type of copper sulphate, if I need conductive paint, a rectifier instead of a battery or what. Any assistance anyone could provide would be so very greatly appreciated. I've done so much research but am still at a bit of a loss as to what I need to improve upon to make the process work. I'm very keen to start plating my own jewelry.


texts: Where should I study contact mechanics (for introductory level)

texts: I am MAthematics and MEchanical Engineering student and this is my senior year. For reserch and personal interest, I need to learn about contact mechanics. From where I should start and what is the prerequisites for this subject.


texts: Reduce line weight of border in Solidworks sheet format

texts: Is it possible to reduce line-weight (thickness) of border in Solidworks sheet format. I want to reduce the thickness of the lines shown below as I find it too much thick.


texts: Racing cars have spring with constant rate whereas Off road vehicles have variable spring rate

texts:
In the term of machine design and mechanical engineering.

If same spring is to be used in both smooth and rough road what will be the effect in suspension of the vehicle and if instead of using same spring for smooth and rough road how about using spring with variable spring rate.

I am new to this and sorry for my bad English.
But i am stocked in finding the comparative answer of this question.
Can anyone help me out here????
Please....


texts: What's the best type of steam Trap for Superheated Steam?

texts:
Process Engineering Newbie here.
What kind of Steam Traps are best suited for condensate removal in super-heated steam line or manifold?

The super-heated steam is to be supplied to a process reactor and will be at a temperature of around 390 to 420 degree Celsius.
Also the system is supposed to run at different pressures ranging from 1 to 19 barg. I understand that this is not an optimal system. This is a research project and we are developing a proof-of-concept Prototype and is not for deployment in the industry. Hence, the wide range of pressure and high temperature.

I hope experienced engineers in the forum can guide me on how to select a suitable type of steam-trap.

Thanks in Advance!


texts: What does Leonardo da Vinci mean in his statement on arches?

texts:
I was recently reading some of Leonardo da Vinci's notes on architecture. One passage on arches states:

  An Experiment to show that a weight placed on an arch does not
  discharge itself entirely on its columns; on the contrary the greater
  the weight placed on the arches, the less the arch transmits the
  weight to the columns. The experiment is the following. Let a man be
  placed on a steel yard in the middle of the shaft of a well, then let
  him spread out his hands and feet between the walls of the well, and
  you will see him weigh much less on the steel yard; give him a weight
  on the shoulders, you will see by experiment, that the greater the
  weight you give him the greater effort he will make in spreading his
  arms and legs, and in pressing against the wall and the less weight
  will be thrown on the steel yard.

There are two parts to my question:

What are the physical principals behind Leonardo's statements on the distribution of an arch's load to its columns?
How does his experiment demonstrate these principals?

On 1, I interpret his scenario as in the below diagram. There is some arch which is supported at is ends by two columns $C_1$ and $C_2$. There are additionally two abutments $A_1$ and $A_2$ to the sides of the arch to counter the arch's horizontal thrust. A downward force $F$ is applied to the apex, which is directed through internal compression forces to the arch's ends, where we see $F_1$ being applied to $A_1$ and $C_1$ (and analogously for the other side). My understanding is that no matter how large $F$ is, the vertical components of $F_1$ and $F_2$ must both be $F/2$ in order to satisfy the static equilibrium constraints.

Then, how do I reconcile this analysis with Leonardo's claim "the greater the weight placed on the arches, the less the arch transmits the weight to the columns"? Is Leonardo assuming a different setup than I have? Or is one of us wrong?


texts:
As I heard, the life expectancy of photovoltaic cells is normally some decades, as so. This is very long, regarding their high cost, it has significant (negative) effect on the total costs.

Why do they age? I can see the only possibility which could damage their atomic structure, and this is the very high energetic ultraviolet (or even soft röntgen) photon spectrum of the sun (which is only a small part of its power).

And, I think, these photons could be maybe easily filtered out by a transparent plastic layer over the silicon.

Thus, why do the solar cells age, and what happens in them on the atomic level?


texts: Increase in target emission rate (TER) when using a air source heat pump (ASHP) in standard assessment procedure (SAP) calculation

texts:
I am running a SAP calculation on a proposed building which will be utilising a 8.5 kW ASHP for space and water heating. I am also running a comparative analysis against a mains gas boiler to show the reduction in dwelling emission rate (DER).

I have noticed that when specing the heat pump in my model the TER shoots up from 14.49 kgCO2/yr/m2 (in the gas powered model) to 21.5 kgCO2/yr/m2. This is having a pretty massive impact on the percentage improvement of DER over TER between models.

Can any one explain why this happens? I cannot find an explanation elsewhere and I would hate to overstate the potential improvement the heat pump brings.

Cheers


texts: Does a Faraday cage effectively act as a notch filter?

texts:
In reading about Faraday cages, I have found that most "real world" designs incorporate multiple layers of mesh.  For example, this article from the National High Magnetic Field Lab discusses several different shielded rooms built of varying layers.

  In the MagLab's High B/T Facility at the University of Florida's Microkelvin Laboratory in Gainesville, for example, all electromagnetic waves must be excluded. The magnet there is in a "tempest" quality shielded room, featuring walls made of layers of copper and welded steel that absorb the entire spectrum of EM radiation.

My presumption is that each layer is tuned to or built for a particular range of frequencies. It's not clear to me if the tuning is due to thickness requirements for the layer and therefore a cost factor, or if there are other factors driving the design of each layer.

My question then, is can (or should) a Faraday cage be treated as a notch filter as opposed to a high-pass filter?  If so, how do you determine the lower end of the notch?


texts: How should I calculate the centroid of a hollow structure when analyzing a wind load?

texts:
I am trying to solve the following problem:

  A masonry chimney having the shape of a conical frustrum is 25 m high.
  The external diameter at the top and internal diameter at the bottom
  is 2 m. The chimney is 0.5 m thick at its base. If the weight of the
  chimney is 1800 kN, find the uniform horizontal wind pressure that may
  act on the chimney per unit projected area of the chimney in order for
  tension at the base to be just avoided.

I am using the equation:

$$\mathrm{Centroid} (\bar{y}) = \dfrac {A_{1}y_{1} + A_2y_{2}} {A_{1} + A_{2}}$$

where $A1$ and $A2$ are the shaded areas in the figure below. Observe that the object is a chimney, so it is hollow in the centre portion; we are not adding up the area of that.

The centroid becomes:

$$ \bar{y} = \dfrac{ (\dfrac{1}2  *0.5 *25) * \dfrac{25}3   + (\dfrac{1}2  *0.5 *25) * \dfrac{25}3}{(\dfrac{1}2  *0.5 *25) +(\dfrac{1}2  *0.5 *25) }$$

$$\bar{y} = 8.333$$

However, I created a 3D model of the solid chimney in CAD and found the centroid to be 8.035, which does not match my calculated centroid. It is close to 8.333 but not exactly the same as my $\bar{y}$.

When I calculate the total wind pressure, which centroid should I use? The one I calculated by hand from the 2D cross-section, or the one I generated in CAD from the 3D model?

The CAD generated centroid is for a 3D solid and $\bar{y}$ calculated is for that central section.


texts: Mechanical vibrations: kinetics of kinematics?

texts:
In books of dynamics, I normally see topics in kinematics and then in kinetics, and finally a last chapter on mechanical vibrations dealing with SDOF and MDOF systems. But I do not see any book mentioning how the topic of vibration fits in dyynamics? It feels natural to say to mechanical vibrations would be an extension of kinetics.

What is the correct classification of mechanical vibrations?


texts: When is DC power generation superior over AC power generation?

texts: If the goal is to transmit power over a large distance, I can see the advantage of an alternator over a generator:  more power, less loss.  If the target DC load is small and very close by, would an alternator still be more advantageous in terms of power production?  Is there any case where DC power generation is more advantageous to AC power generation?


texts: What is a tesla turbine and how is it different from other turbines(like pelton or francis turbine)?

texts: I came accross this word tesla turbine while reading about the applications of boundary layer flow but couldn't find much details of such turbine anywhere.


texts: I cannot properly understand the "pressure" referred to in Bernoulli's Principle despite my efforts

texts:
I get that with Bernoulli's Principle an increase in area = a decrease in velocity = an increase in pressure. I also understand the concept of pressure being force per unit area.
My difficulty is with understanding what is meant by pressure in this context. Is it the pressure exerted on the fluid from the pipe's walls (with an equal pressure exerted by the fluid on the walls)? Is it something else?
If it is the pressure exerted on the fluid by the walls of the pipe, why does it decrease when cross-sectional area decreases? I can see why from a mathematical perspective, that it occurs from how the formulae can be rearranged, but to me that just doesn't intuitively make sense. I just can't viscerally understand it, and a lot of how I understand things comes from visualising it, which YouTube videos unfortunately have not helped me with (as they explain how the formulae work, and I can see the decreasing area which in my head means pressure should increase [even though I can recognise it does not]).


texts: Do we need to use cracked section in Fundamental period calculation for a building?

texts:
When using modal analysis to determine the building period do we need to use the stiffness modifiers (or in another word use the cracked section) to calculate the building period ?
Can Anyone refer to any article or ACI reference that indicate anything related to this topic ?


texts: How do I determine plate thickness and anchor size for a 10-ton span supported by synthetic rope?

texts:
I am supporting 25,448 pounds over a series of cables, spaced 20' apart, over a span of approximately 424', left to right.  The load is mostly in an area of the middle 10' of the span.  I am using synthetic rope/cable with 68,500# capacity.

I want to design a plate to secure the cable on both sides.  The plate will be attached to a curbing that is concrete roughly 24" thick.  How can I determine how thick my plate should be and what anchors I should use? I am planning to use 24" x 24" plates with an anchor in each corner.


texts:
Background
When I took my first class in controls (2006-ish as taught by an aerospace professor for a mix of ME and EE students) it was basically all done in Laplace-transform, transfer functions etc.
More recently (2012) I took a graduate level controls class at a different school and it was almost all state-space. Really it was a bunch of abstract linear algebra proofs that happened to relate to observability and controllability. I chalked up the difference to the fact that it was for grad students who would be working on a more theoretical class of problems (almost no mention was made to relate this to any real system).
Now, from talking to undergrads at the same school, I'm given to understand that state-space is the way that control theory is currently taught. Laplace methods are briefly covered but quickly dismissed as out-dated.
I work in combustion and have no real idea what's going on.
Questions

Is this an accurate indication of the way that controls is being taught these days?
Either way, does that match with the state/foreseeable future of controls?

I'm also interested to know the merits of one method over the other.


texts: How many decimal places of GPS should be stored to be accurate within a few feet?

texts:
I'm building a software application that uses GPS for a purpose related to roads.

I'd like to know how many decimal places of GPS data should be stored to provide measurements that are accurate to within a few feet?


texts: Applications of simple spring harmonic oscillator

texts:
For pedagogic reasons I am looking for applications in engineering for the simple spring harmonic oscillator, i.e. something like this ("harmonic" implies in particular "without damping"): .

The angle to the horizontal my be between 0 and 90 degree and one spring may be missing.


texts:
I would like to clarify if the equations that I got from this figure are correct.

$$-T_{CD}sin(30) + T_{DE}cos(0) = F_x = 0$$
$$T_{CD}cos(30) - \frac{W}{2} = F_y = 0$$
and
$$-T_{ED}cos(0) + T_{EG}sin(10) = F_x = 0$$
$$T_{EG}cos(10) - \frac{W}{2} = F_y = 0$$


texts: Heating Sand/Ceramic/Refractory Material under vacuum

texts: In a Vacuum Metallurgy (Casting), a mold needs to be heated (500 to 700 degrees) to reduce thermal shock on the metal surface. Normally, a gas fired oven is employed for such job, but in a vacuum environment how do you achieve the same?


texts: Relation of Digital Logic Design to Electrical Power Engineering?

texts: I'm an undergraduate student of Electrical Power Engineering currently in 3rd semester, one of the courses we  study is Digital Logic Design(dld) and I have found much interest in it but I am unclear whether the subject would have application in our field i.e. power engineering or not....Could anyone guide me that how should I study dld with what things in mind related to future perspective?


texts: Do 36 inch diameter fans exist that push 25,000 CFM?

texts:
I own a warehouse that needs to push 25,000 CFM.  I currently have an old warehouse exhaust fan that doesn't push anywhere close to this.  The diameter of the fan blade is about 36 inches, but the frame in which the fan sits is 41 x 41 inches.  I've done a bit of looking and can't seem to find a fan that is 41 inches or less in diameter that pushes 25,000 or more CFM.  So, I really have two questions:

Does a fan exist that would push 25,000 CFM which that could fit into the 41 x 41 opening (probably means close to a 36 in diameter fan blade); and
Is there a mathematical function that relates RPMs of a fan, the number of blades, and size of the blades to CFM (or a similar function such that when you plug in the size and speed of the fan, you can find the CFM)?

Thanks.


texts:
I have a set of kitchen knives which I've owned for 18 years. These knives were sold as "never need sharpening". I assumed that to be complete nonsense at the time BUT it has proved to be true! These knives have never once been sharpened in 18 years and are used every day.

How is this possible - and given that it is possible, why are most knives still made to be sharpened regularly? They were not at all expensive so that can't be the reason.

EDIT: I've just found the claim from the original packaging: "These Fusion Infinity knives are fused with tungsten carbide giving them an extremely hard edge. There is no need to sharpen these knives."

So, the question becomes resolves down to "Why doesn't everyone do this?" None of the answers have tried to address this angle yet.


texts: Is there a technical name for a sound dampening suspended cylinder in loud indoor environments?

texts: Several years ago, I was visiting the Advanced Photon Source at Argonne National Laboratory, and I remember that in one of the working areas there were some large cylinders suspended in the air above the electronics racks by wire.  Our tour guide had mentioned that the researcher had been an acoustic engineer and put them up himself to dampen the constant loud drone of the facility.  I was skeptical before I walked under it and, despite the area being quite open and unshielded acoustically to the machinery, the cylinders had done a near perfect job of dampening the sound.  Now that I've been working in facilities with similar noise issues, I'm wondering if this is a common solution or if there is a name for these simple noise dampening devices?


texts:
Can a screw such as the one below be used as an air engine in pressure range between 700 kPa and 2500 kPa
on other words Can I reverse compression process with a screw to work as air engine


texts: Do stators in axial flow compressors have airfoil geometry?

texts: In axial flow compressors the role of a stator is to gradually change the direction of flow to exchange some of the kinetic energy of the flow into pressure. Therefore it stands to reason that they do not require an airfoil shape, since they're not accelerating the air, unlike the rotor blade. So, are stator blades just curved plates without camber?


texts:
I'm want to make a 2 meters wide sphere that should be circular enough as a giant hamster ball! I could make it of some sort of strong plastic or steel. It should have a hatch on top that can be opened or closed so that anyone can enter.

EDIT: what I'm asking for is the topology of the sphere and how can I build it in a way that makes it completely rounded when assembled. I'm asking about the parts and assembling it


texts:
Three problems:

Internal friction due to stuffing materials. - Why does it not matter? If it does then there must be some limits like rpm etc.

Not entirely leak proof. - Why are we supposed to keep it leaking (installation)

Have o-rings eliminated stuffing boxes?

Edit: Stuffing box is a dynamic sealing mechanism --like o rings (static and dynamic sealing). They are used as seals in rotating, translating mechanisms.
To better understand here are 2 examples.

Steam engines: if there was no stuffing box, all the steam would leak out of the piston rod side-- not creating pressure. In petrol/diesel engines, SB is replaced by piston rings.  From SB in Steam Engine

Boats: if there was no SB, water will start filling the boat from the hole -used for the propeller shaft.  From Stuffing Box:


texts: How can a Wi-Fi access point be visible from one device but not from another?

texts:
We have a strange issue while trying to configure small router for bridging between available access point and ethernet network. While this AP is perfectly visible from desktops and mobile devices, it is not visible form the bridging router.

I wonder how can it be? Visible WiFI it is just radio signal. Are there any advertised properties which can be filtered on?


texts:
I have a question that maybe will be very easy for you.
I am working on a district heating model using Dymola, and now I have to incorporate a boiler into my model, such as this one.

I was asked to present my results in the form of "energy curve consumption of the boiler" but I do not know how to get it, I have been reading about, but the concept isn't fully in my mind, can anyone help a little here?


texts: Please Help me Read this Engineering Drawing

texts:
I am trying to CAD up a drawing for a plate for this motor to mount to. I figured it would be easy since they provided an mechanical drawing, but I have never seen one like this before. Can you please help me read this? It is from China and I don't even have any idea what units it is in. I have read these before but I am completely stuck on this one. I am trying to figure out the spacing of the mounting holes on the front of the motor. Here is the drawing

,

and here is a picture of the actual motor if that helps at all.

From what I can tell the mounting holes are on the bottom (or left if you rotate it). Any help is GREATLY appreciated. I can't continue my project until I get this figured out.


texts: Does a transformer use power when output isn't under load?

texts:
I was reading about how AC to DC converters work with a step-down transformer and then a diode bridge to convert the lower, stepped down AC voltage into DC. What I don't understand is since the input AC appears to be connected to the primary coil of the transformer, how does the DC load affect the power used from the AC supply?

Does the DC load somehow feedback and lower the resistance of the primary coil so that more power can be drawn?

When there is no load on the DC side, does power still flow through the AC primary coil, and if so, why doesn't it just melt?


texts:
Apologies if this is not the correct SE for this sort of question. But, this is the only place I've seen an appreciable number of CAD questions. If this isn't appropriate for engineering.se, a pointer to a more appropriate site would be greatly appreciated.

I have this spline model of a car fender in 3DSMAX:

I am trying to figure out how to turn this into something I can use in a CAM package like Fusion 360 or Inventor. I'd considered just building the model in Fusion, but there are a number of compound curves that are difficult to describe parametrically. (Also, my MAX skills are a lot better than my Fusion skills.)


texts: How the amount of bolt's preload in a single lap joint can change the natural frequencies?

texts:
Few days ago someone told me that the amount of bolt's preload in a single lap joint can influence the natural frequency of the beam. So to test that out I modeled a 3D single lap joint in ABAQUS and defined bolt load for it. I realized that the difference between the natural frequencies related to preload of 1 N.m and 13 N.m is in the order of 0.01. Did I model it wrongly or the amount of preload can’t change the natural frequencies?
the screenshot of abaqus model:


texts:
I am new to SolidWorks and am designing an enclosure. My model looks like this -

I want to add a projection onto the sides of the surface with the slotted hole, so that the front view vaguely looks like this (just for representation,I have omitted the slotted rectangle) -Front View

How can I do this?


texts: Gearhead & 'teeth-track' to drive rotation of ringed encasement?

texts:
I am not an engineer, so apologies if this one is a bit of an ill-thought out...

Can anyone show me an example of something like the following scenario:

A small stepping motor driving rotation of a ringed encasement, via a gearhead on the rotation shaft interlocking with a 'teethed track' which is inlayed on the wall of the encasement (I know, see the diagram).

If not, why is this a stupid idea? The stepping motor has to be small to fit in the encasement (for a 'wearable') - are the forces involved here unreasonable?

The ringed encasement is supposed to rotate to a precise position - I imagine that in these situations, rotation would continue after the power to the stepping motor was killed, necessitating some kind of braking mechanism?

I appreciate your help]1


texts: Why is Carnot Factor defined as 1 - (T(cold) / T(hot))

texts:
This is the proof I've found for the Carnot Factor:
$$S = \frac{Q}{T} \qquad \qquad (1)$$
$$S_{in} = S_{out}\qquad \qquad (2)$$
Because entropy stays the same when using an ideal engine:
$$  (1) \& (2) \Rightarrow \frac{Q_{in}}{T_{in}} = \frac{Q_{out}}{T_{out}} \qquad \qquad (3)$$
$$  (1) \& (2) \Rightarrow Q_{out}= Q_{in}\frac{T_{out}}{T_{in}} \qquad \qquad (3)$$
From the energy conservation law
$$ W = Q_{in} - Q_{out}\qquad \qquad  (4) $$
Then from (5) (3) & (4), the Carnot factor $\eta $ is calculated as:
$$ W = Q_{in} - Q_{in}\frac{T_{out}}{T_{in}}$$
$$ W = Q_{in}\left(1  - \frac{T_{out}}{T_{in}}\right) $$
$$ \eta = \frac{W}{Q _{in}} = \left(1  - \frac{T_{out}}{T_{in}}\right) $$
I don't see, why $T_{out}$ must be smaller than $T_{in}$.
There are no restrictions that says $T_{in} > T_{out}$. It's just necessary, that $S_{in} = S_{out}$. Maybe my book simplifies certain aspects?


texts: How do I calculate the structural properties of a fiberglass laminated wood panel?

texts:
I'm constructing 2.2 meters span, 1 m wide shelf. Want to make it cheap but thin.
I'm planning to use 18mm thick OSB board and reinforce it with a layer of stronger material stuck to it's bottom.

My first idea for reinforcement is 2 strips of 60*4 mm steel.
I'm not very familiar with the subject. I found OSB modulus of elasticity here , transformed width of the OSB board to it's steel equivalent, that gave me 38mm. Then I ran it through L-beam moment of inertia online calculator, and beam calculator assured me that the sag would be much less than my acceptable 1cm. (The load is under 100kg)

My second idea is to use glass fabric instead of steel. Glass itself is just 3 times less strong than steel, so that makes this option at least worth evaluating.

Hence comes the question:
Where do I find properties of the layer I'll get when I put fiber glass and pour epoxy on it? The only thing that's stated for the "structural fiberglass fabric" available on the market is it's ultimate tensile strength.

I'm talking about the glass fabric, not the plastic sheet reinforced with it:


texts: Nyquist plot - what is the meaning of circles with dB values on complex plane

texts:
Let's start with arbitrary transfer function as an example, such as:

obj = tf([1 2],[1 0 2 5]);
nyquist(obj);
grid on;
axis([-2 2 -2 2]); axis equal

As far as I do understand what is gain (expressed in dB), I am unable to figure out, nor find any information about circles that appear after we use grid. For some reason there is vertical line at Re=-0.5 associated with 0 dB value. On the left and right of this line we see non coincident circles in the shape of peacock's eye with decreasing or increasing values. Circles converge to points [-1,0] and [0,0].

We can see that system's curve starts at point [-0.4,0] which corresponds to -7.9588 dB gain, crosses -10 dB circle twice, where on both occurrences system's gain doesn't match -10 dB value.

Moreover, just from the fact that that we have infinite line denoted with 0 dB value, one can infer that it has absolutely nothing to do with actual gain, which on Nyquist plot should be circular around point [0,0]. In this case my question is simple: what does those dB values  and circles mean?


texts:
The problem : I need to create a mechanism with 2 parallel shafts, at some distance apart, rotating in the same direction, either clock- or anticlock-wise.

The distance (> 1m) makes it impractical to set a chain of gears between the shafts, so my approach is to have a third shaft at 90 degrees with bevel gears; the driving motor could attach to this third shaft. It has been pointed out to me that a pulley-belt approach could also be used, but the distance between the parallel shafts makes me prefer the 90-degree shaft approach.

Not being a mechanical engineer, I tried to understand a bit more about bevel gears, and found out there are straight, spiral and other types. The 3D library I'm currently using for generating the gears creates angled teeth.

So here's the 1st question : for any type of bevel gear except the straight ones, does the geometry of the teeth have any impact on the direction of rotation ?

Since I don't want different rotation speeds on the parallel shafts, and there is no constraint on the rotation speed of the third, 90-degree shaft, so far my plan is to create gears with identical sizes (number of teeth).

And here comes the 2nd question : Should I use larger or smaller gears ? What's the impact of the number of teeth on the gear operation for the bevel gears ?

As a side note, I plan to 3d-print these gears for the prototype, so any comment that can factor this in is highly appreciated.

Thank you all in advance.


texts: Can Fortran 90 be used with Aspen Plus, or only Fortran 77?

texts: I am attempting to write a user model in Fortran that can be connected to the Aspen Plus process simulator. Can Fortran 90 be used, or does Aspen only work with the older Fortran 77? I have checked the Aspen Plus documentation, but can find nothing about which versions of Fortran it is compatible with.


texts: How to get corrugated plastic roofing strips to span 3m for rainwater exclusion experiment without building additional ground supports?

texts:
I'm trying to build structures to exclude some percentage of rainwater on experimental plots. I have three 20ft beam supports across the plot, spaced 3m apart and held in place by 4x4 posts that were stepped down in height by a total of 1ft across the three of them-creating a slope.

However I realized that the polycarbonate roofing can't span the 3m gap between supports without sagging. In the specs they suggest support every 3ft, so I am looking for a way to achieve this support with my existing materials- roofing panels (6" wide by 12ft) and pvc irrigation piping (depicted on the right below).

Here are the material specs: Suntuf specs

One thought I had was creating rafters with the pvc, or creating additional support beams of pvc between the wood posts to shorten the span to 1.5m. I'd like to find a solution that uses minimal additional materials and has the potential to last for several years at least. I'm really trying to avoid any pooling or spilling of water, as it would kill the point of the experiment.

Any clever engineering solutions on how I can help the polycarbonate sheet span this 3m gap?


texts: Direct Optimisation - How to Create Time Efficient Study

texts:
I made a simulation of this cylinder that is being suspended mid air and held up by 8 rods, 4 on top and 4 on the bottom. The entire model is cooled to 15K

I managed to find the forces required for 6 of the rods to have a safety factor of above 1 as pictured below (green being above 1):

The two rods in red have a safety factor of less than 1. All rods have a parametrised force so I would like to know how to create a design study to get all of the rods to be above 1 or at least all have the same safety factor under 1. Basically, I am only interested in changing the forces that are applied to the rods.

I've tried an Adaptive Multiple Objective with the goals of all rods having a safety factor above 1 but it didn't produce any meaningful results.


texts: Can I seal the inside of a water well to use it as water reservoir when the well is dry?

texts:
We've had unusually dry weather and our well has run so low that we had to call in a water hauling company to refill it a few days ago.

The water man told me that even though he dumped in ~ 1000 gallons, a great part of it will seep out of the well to the surrounding (drier) aquifer, the same way groundwater makes its way inside the well in normal conditions. Now a few days later, the water is low again.

I'm thinking some kind of drinking-water-safe plastic poly sheet sown or welded together at the seam would create a long and flexible tubing that could be progressively immersed inside of the well (with weight at the end) to effectively waterproof it on the inside.

The well could then be refilled to the top and hold all the water that it's containing, instead of slowly seeping it out. Under normal conditions, the sleeve can be removed.

The well is 2 feet wide, 15 feet deep. 2 ft diameter, 3 ft long concrete pipe sections stacked on top of each other.

There's also another well on the site (very low water as well) that's 4 feet wide, 15 feet deep - a much better candidate for the concept as it could hold twice as much water.

Does this sound doable? What are the problems I might face?


texts: Why is gas pressure specified instead of mass flow?

texts:
Clarification: This question is all about the gas supply to the water heater. It has nothing to do with the water supply.

My hot water heater specifies 5.5-10.5 W.C. (water column inches) of pressure. I measured the pressure to be 7 W.C. Within spec. The problem is, this pressure reading measures the same (7wc) whether the main gas valve is (a) wide-open  (b) half-open or (c) fully closed.1

But this makes sense. Because let's assume the system pressure at the gas source is 7wc (plus a nominal pressure drop). If there is any flow at all through the pipes (and no gas is exiting through the pipe walls) then we would expect the pressure (at steady-state) at any point inside the pipe to equal the system pressure. If it were any less, then gas would flow from the source of high pressure to the point of lower pressure at the measuring point until the two pressures reach equilibrium.

So why did the engineers specify pressure? It seems like they should, at the very least, specify a mass flow rate of gas. For example, if any obstruction were inside the pipe and impeding flow or the valve were not completely open, this would result in a malfunctioning heating system. But that problem would not necessarily cause a low pressure sensor reading. But it would create an unacceptably low mass flow rate.

So what gives? Is this just an oversight? Or is there some reason  I can't see why pressure and not mass flow is specified?

1 My valve is old and it leaks. So, when it's fully shut off, its mass flow rate through the chamber is, let's say, 1% of that when it's "wide open."


texts:
I am in the process of designing a chiller test rig, of which a very simplified diagram would be (the quick coupling might just be replaced by a non-return valve):

I am struggling to find the type of valve I need where the "??" is. The purpose of this valve is to create some load on the chiller and simulate having a real system connected to it. In other words, I (think I) want some resistance (flow restriction/increased pressure?) at that point in the circuit. Can you advise what kind of valve I would need for this (something manual ideally, not electrically actuated).

The fluid is a mix of ethylene glycol and water at 0°C. The chiller is set up to run at ~25psi at the outlet and the liquid flow rate is ~6 l/min.


texts: Signals and systems convolution problem?

texts:
hey guys I'm having trouble with a convolution problem here

A continuous-time linear system has the input/output relationship

$$\int_{-\infty}^t (t-\lambda-2)  x(\lambda) d{\lambda}$$

For $1 ≤ t ≤ 2$, determine the output y(t) arising from the input $x(t) = u(t)−2u(t−1)$

So the graph is going to be something like this right

(probably ignore the axis labels it's wrong I know; I'm just providing a sketch for the $x(\lambda)$ function)

I'm really confused about how to proceed


texts: I have designed a product and I found that there is a patent on that specific product. There also seems to be many patents and for the smallest or most obvious use of items. I am wondering if anyone has had experience creating a product and finding there are patents on it and then how do you counter with that? How can you be sure you 100% violate it?


texts: Choosing a pump to inject liquid into a pressurised water pipe

texts:
I'm interested in using a pump to inject liquid into a mains water pipe (3-6 bar pressure)

I don't know what pump to use as they all seem too big for the task they are carrying out. I want to use a variable speed 12V/24V pump that only needs to inject a max of 2L per hour but is this going to be too small to deal with injecting into a pressurised pipe?

Could somebody show me an example of the smallest pump you could use for this?


texts:
Mold for Injection Molding is very expensive and is justified for mass production.

However, at Prototype stage, how we make the same part with less expensive method. I know 3D Printing is a way but it doesn't have Isotropic properties as its a layered structure.

3D Printing is usually meant for visualization purposes and doesn't fulfill needs of Prototype testing. What are methods can be used to produce one-off injection mold type items during prototype development?


texts: How does one become a control systems engineer?

texts:
From what I understand, a control systems engineering job is almost always a senior level position. What kind of entry level jobs do most engineers have before they are qualified to actually design control systems? Is a PE license necessary for this kind of work?

I am currently working on a masters degree in electrical and computer engineering. I am mostly interested in control theory and that is the subject of my thesis.


texts: How are circular dependencies dealt with inside MBSE?

texts:
How are circular dependencies (best) managed inside of MBSE environments? Let's say I have two properties that are linked to each other / they are linked to properties that affect each other.
How is this managed both from an abstract "best-practices" point of view?
How does MBSE/simulation software deal with this?


texts: Why can we ignore transverse shear stress in thin beams?

texts:
In a text I'm reading on Euler-Bernoulli beam theory it is said that as the beam is assumed to be thin, the effect of transverse shear stress is ignored. If the beam is thick, we need to use Timoshenko beam theory which accounts for transverse shear.

Let's consider a simple loading case:

For the same load F, if the beam is thin, the normal stress distribution inside the cross section of the beam is bigger since the smaller cross sectional area has to be in higher state of stress to counter the moment caused by the load. If the beam is thicker, the same moment is spread across a larger area and the stresses across the cross section are smaller.

But these same normal forces also cause the transverse shear:

Transverse shear is caused by the fact that since the moment felt by the beam is higher when we move to the left, the normal forces inside the beam when considering a small box inside the  beam (as in the above picture) are at imbalance and thus a transverse shear has to be present to maintain equilibrium. But if the beam is thick and the normal forces are smaller, why does the transverse shear now become relevant? Shouldn't the situation be the other way around: Thicker the beam, smaller the transverse shear?


texts: How to calculate flowrate of water through a crosssection of pipe?

texts:
Assume we have a pipe with  a diameter of 10mm. Water is flowing through that pipe and we know that the water pressure at the 'open' end of the pipe is 2 atm. How would one go about calculating the flowrate of water? Reasonable assumptions are allowed.

I at first thought of using Poiseuille's equation, but that requires you to have a container length. Right now I have found no way to calculate flow in my situation.


texts: Correct terminology for a zero turn stator winding on a BLDC?

texts:
I'm designing a BLDC motor with some unique geometry constraints (~250mm long, ~45mm diameter with a ~35mm bore down the center) and am considering using straight copper bars carrying high current instead of multiple turns around a core for the stater windings (motor needs to provide high torque at or close to stall for extended periods).

Are there existing motor designs that are similar that I could read up on? What would be the correct terminology to describe such a design so I can search for prior art on the subject?


texts: How to convey the image of a 14 mm object through a thiner (8 mm) pipe?

texts:
My setup and constraints are the following (see figure below):

A rectangular pipe (~50 mm long, section 8 mm).
The pipe has an apperture at one of its end, which is larger than 14 mm.
A 2D object (a sign) that can be represented as a segment of length 14 mm.
The pipe can embed any number of optical element, as long as all of it fits into the 8 mm.
At the other end of the pipe, there can be several complementary optical elements to restore the image, without any size constraints.
A camera sensor (the size of the sensor does not matters here).

What I want to do is be able to convey the image of the object through the pipe, and obtain at the other end of the pipe an image that is not distorted (e.g. a change of apparent size is ok, but a tilted image is not.) and that can be retrieved on a camera sensor.
A simple mirror with a 45° angle (to reflect without distorsion), would be too close to the object to be able obtain the entire image of the object.

So far I have tried to use a tilted mirror, with a small angle which reflect rays coming from the object parallel to the pipe into a lens and then into the sensor, but then the image is tilted and cannot be focused entirely (the image plane is not perpendicular to the guide).
I have also tried to add a second mirror parallel to the first to correct the image plane, to no avail.
I was also thinking of a system of lenses at the entrance of the guide, to "compress" the image before reflecting the image into the pipe with a 45° angle so that there is no distorsion, but my intuition is that the optical system will be too big to fit the 8 mm constraint.
Has anybody an idea as to whether this is possible at all ?


texts:
"... a multiview projection is a technique of illustration by which a standardized series of orthographic two-dimensional pictures is constructed to represent the form of a three-dimensional object. Up to six pictures of an object are produced (called primary views), ..." (Source: Wikipedia, Multiview projection). While the resulting six views of orthographic projection are the same, a difference in arrangement of these views around the viewing box, lead to two different projection schemes: first-angle and third-angle projections, with the chance to mix things up (to say the least) when drawings are transferred from one convention to another.

To mitigate this issue, the projection angle is denoted by a projection symbol on engineering drawings. This international symbol shows the projection (top and front view) of a truncated cone, that defines and identifies either first-angle or third-angle projection.

Other than that national and supra-national standardization tries to minimize confusion by the two concflicting systems. From Wikipedia, Multiview projection we learn that first-angle projection is standard throughout Europe and Asia (excluding Japan). Whereas third-angle is standard in the USA, Japan, Canada, and Australia. The UK or at least some British companies, so the article claims, switched from first-angle to third-angle during World War II.

Which are the default multiview projection schemes for countries in Central and South America as well as Africa? Preferably backed by national regulations or standards, if applicable.


texts: Rubber Band for Belt in Belt Drive system

texts: Looking to drive a series of belts for lateral translation using a series of pallet bands (92" rubber bands about 1" wide). Approximately 16 bands would be driven by a singular band as illustrated (roughly) below. I am hoping to use a geared up stepper motor with planetary gearbox that will respond to sound levels to effect the speed of translation. I am wondering if anyone has any advice about using rubber bands as belts in a pulley driven system, ideal arrangements for transfer of power, pulley types etc.


texts: Why would a "delayed loudspeaker" be so expensive in the 1970s?

texts:
Recently, I read about some major musical concert held somewhere in the USA to a record-large audience.
Since there were so many people, not all could see or even hear the music from the main loudspeakers.
Therefore, they put additional loudspeakers far away from the scene, connected with cables from the main equipment at the stage (presumably).
Since sound travels slower in the air than electrical signals inside cables, the music coming out from the far-away loudspeakers would have been out of sync with the actual sound waves, unless they did this "clever trick".
The clever trick apparently consisted of them spending a huge amount of money ("the cost of a new car per loudspeaker") on then-cutting edge electronics which delayed the signal exactly so that it would match the sound waves, and thus not cause disharmony.
While this made me think of how clever that sounds, I don't understand why exactly this would be so costly, even if it was in the early 1970s. In fact, I don't understand why it had to be so technical at all. It seems like this could've been accomplished in some analogue manner, very cheaply. The cost of a new car, many times over? Really?
What made it cost so much money? And had nobody ever held a big enough concert before this relatively late date, which would warrant a similar solution?
Did they have concerts for many years which sounded bad for the people far away, because the real audio waves were mixed (unsynced) with the local loudspeakers?
And if they barely heard the music so far anyway, did it really matter at all? Or was this more of a way to sell tickets by claiming a "perfect hi-fi-quality experience for every single participant"?
(Sorry I can't remember the name of the concert; I thought I had it bookmarked.)


texts: High Voltage, High Current, Bipolar (4 Wires) Stepper Motor Control

texts:
I am new here, and I'm new to Arduino. I am making an attempt to control a high voltage (~48V), high current (~6A), bipolar (4 Wires) stepper motor.

I understand how to drive a stepper motor, and I have found the bipolar schematics on the Arduino library, but none of the solutions handle a motor this big.  Most drivers use the SN754410 or L293 from what I've seen.  I have also noticed stacking of the SN754410 chips for higher current ratings, but I suppose I would need 6 of them, and they still will not handle 48V.

Would I have to build my own dual h-bridge from NPN Transistors or MOSFETS?  Does anyone have an example circuit that has some protective features, such as the back current diodes.  Would this be enough protection to avoid damage to the Arduino?  I would also like to keep this relatively cost efficient.

Thanks in advance!  I hope I made everything clear.


texts: Is it feasible to forge multiple, smaller parts in the same forging operation?

texts:
Let us assume you have a large forging press or drophammer, and drawings for a set of smaller parts that all need to be forged from the same material.  Would it be feasible to construct a forging die so that all the parts could be forged from a single billet and then separated as a machining step?  Or is this more expensive than making a forging die for each part and forging them separately from individual, smaller billets?

For the purposes of this question, you can assume that the parts all have a linear geometry -- say, if you wanted to forge a crankshaft and camshaft set for an engine in a single operation.


texts: How much Ni-chrome wire is used in your average home electric heater?

texts: I'm working on an AI Home Temperature controller for my computer science project, and I would like to know how much Ni-chrome wire (in terms of length and diameter) is used in an typical home electric heater?


texts: Determination of blower mass flow from limited information

texts: For a variable speed centrifugal blower, can a rough measure of mass flow be obtained from only motor speed and power when the outlet restriction is variable?


texts: How to design a method to estimate vx=speed in direction of swimming

texts:
We have a body that goes underwater (let's say a whale) with magnetometer and accelerometer data. I also have GPS, date, depth, pressure and temperature data.
I want to know if there is any simple way (Matlab code most preferably) to combine data from magnetometer and accelerometer to find a way to estimate speed of the body (whale).

I have thought of 2 ways to perform this but I don't know how to proceed:

Differentiate depth to determine speed of descend
Use acceleration and magnetic data to determine pitch, roll, yaw (I prefer this method).

Please feel free to provide a link if there is an already-existing matlab code for all of this.

Feel free to ask question so I can further explain. No gyroscope data


texts:
I have purchased these copper heat-pipes; however, I am wondering how to bend them without kinking them or cutting them open due to pressure on weak points/bends.

These are flat copper heat pipes, so I can't use a pipe bender; however, these are sold specifically to be bent, according to descriptions, so I was wondering if anyone here has any experience or tips for bending these flat copper heat pipes.

To be a little more specific, I want to make a 90 degree bend in the middle of the copper heat pipe, without making kinks (which degrade performance).

Furthermore, would wrapping copper foil around the heat pipes allow for greater thermal dissipation? Apparently some computer modders have seen success; however, I thought it would be appropriate to ask opinions here as I will try to wrap copper foil set in place by thermal paste to the heat pipes.


texts:
Is it possible to have a helical gear and a worm gear with the teeth angled the same amount, so that the helical gear can drive the worm gear, unlike a spur gear.
Can the helical gear also move the worm gear along the axle like a gear rack. until the worm gear is stopped and then it resumes driving the worm gear normally.
This is to make an OR gate, I can show an example using Lego Technic gears here:


texts:
Is the maximum tensile strength a property of a material ? If it is so then suppose I am given the maximum tensile strength of two flat spiral springs to be $30MN/m^2$ and I have to find the dimensions (length per unit thickness $l/t$) of the spring I need to have to make some spring controlled system in an indicating instrument.

Do I need to divide the maximum tensile strength by two, multiply it by two or leave it as it is ?

I know I can calculate the dimensions of the spring by
$$f_{max} = \frac{Et\theta}{2l}$$
where

$E$ is the modulus of elasticity (given to me)

$\theta $ is the maximum angle of deflection $\pi/2$


texts: Is there a reliable online reference for head losses of PEX tubing at various nominal sizes and flow rates?


texts: How this adapter inside the bearing is called? How to find/make a replacement?

texts:
This is an ABEC7 bearing with a 12 mm hole and a 19 mm external diameter:

It has a tightly mounted adapter (the black part), which in turn has a 6mm hole and two external diameters: 12 mm (partially hidden in the bearing, partially visible) and 15.5 mm (fully visible). The adapter is required for a common 5 mm axle of two bearings. The wider parts are on the outside. The narrower parts are fixed into a common wheel.
Unfortunately, the adapter is made of aluminium and I would want one which is made of steel. Thus the questions:

What is the proper technical name of the adapter?
Can it be bought "off the shelf"?
If not, can it be easily ordered from a typical metal workshop?

EDIT: I was asked for a precise drawing and so I attach it. As seen, I need two versions, both with an increased internal diameter. I could adapt, however, an off-the-shelf part into any of these versions with a drill, apart from the 16/18 mm outer diameter, which is better but not necessary.


texts: Looking for dropping servo mechanism idea

texts:
My friend and I have an idea to make prototype of vending machine.
We need suggestions for making strong dropping mechanism.
The idea is:

The user orders X item. Let's take a can of cola for example.
Then the cola can drops in container.
Then you place your hand below the container and the item drops in your hand.

The problems we have to solve are point 2 and 3.
How to make the dropping mechanism, strong and gentle?
We have 3d printer.
Sample drawing:


texts:
I have a swim platform on the back of my boat that extends 24” from the transom. It is supported by 5- 1” diameter stainless steel arms that are attached To the transom 13” below the platform and at 2” from the rear of the platform.
I would like to change the platform out for one that is 48” but would like to reuse the stock transom mounting points for the support arms. The new longer arms would therefore go from 13” below the platform back approx. 42” wher they would attach to the new platform.
Is there a way to calculate the new support arm angle and to determine if it will be enough support at the new reduced angle?
The width of the platform is 128” side to side and the support arms are evenly distributed across the width from about 6” in per side.
I’m here because I’m not an engineer or mathematician so bear with me if I left some crucial data out.
And if I do need to find a local engineer to call this, would it be a structural?
Thanks


texts:
I am currently looking at a set of truss layouts produced by our truss manufacturing partner for a residential building project. I have reason to believe these layouts are generated using Alpine (Intelliview?) software. In any case, the design summary contains abbreviations which I cannot understand since I do not have a copy of the software. Please see below:

According to this document R, U and W stand for reaction due to design load, uplift due to wind load and bearing width, respectively. TCLL, TCDL, BCLL and BCDL stand for top chord live load, Top chord dead load, Bottom chord live load and bottom chord dead load. However I cannot for the life of me determine what Rw, Rh, RL  and NCBCLL stand for. Any ideas?


texts: How does this transformation actually happen?

texts:
I cant exactly give you the  complete relevant details of the variables but assume the following (bold means vector):

B(x) ~ $\frac{1}{8\pi}*(\nabla\frac{1}{r})\times\int \mathbf X'\times \mathbf \Omega' dV(\mathbf X')$

where r=|X-X'|, prime denotes evaluation at point X' and dV is the volume throughout the domain and it holds as $r \rightarrow \infty$

Let this integral be evaluated for a large value of r (say R). My question is why is the following possible if the above integral holds on a spherical surface,

$8\pi R^2(\mathbf n \times \mathbf B)_{r=R} = \int \mathbf x \times \mathbf \Omega dV - \mathbf n \mathbf n. \int \mathbf x \times \mathbf \Omega dV$

For exact reference see pg 519 of the book in the link Fluid Dynamics by G.K.Batchelor. What I am asking about is the derivation between equation 7.2.3 and 7.2.4. Though this book is considered a classic, but damn its hard to keep up with these technicalities.


texts: How to automatically process energy meter data considering outliers and meter reset?

texts:
I want to algorithmically process energy meter data. The energy meter measures a heat or power producer or a heat or power consumer (but not both, so the measured energy will always have a positive sign). No additional information is known about the energy system (like maximum load) neither about the type of energy meter - only data stored in a database can be accessed. Processing will be done by an algorithm looking at data for a given time interval (no live processing).

Usually, data are weakly monotonic of the form

2015-04-01 00:00 20.78 kWh

2015-04-01 00:05 30.80 kWh

2015-04-01 00:10 73.99 kWh

2015-04-01 00:20 82.30 kWh

2015-04-01 00:25 82.30 kWh

2015-04-01 00:30 83.44 kWh

...

The energy produced or consumed for a given period is simply the difference of the energy meter counts. So far, so good. However, the algorithm has to deal with the following three problems:

1. Outliers "above" have to be detected as invalid data.

2015-04-01 00:00 20.78 kWh

2015-04-01 00:05 30.80 kWh

2015-04-01 00:10 500 kWh

2015-04-01 00:20 82.30 kWh

2015-04-01 00:25 82.30 kWh

2015-04-01 00:30 83.44 kWh

....

2. Outliers "below" have to be detected as invalid data.

2015-04-01 00:00 20.78 kWh

2015-04-01 00:05 30.80 kWh

2015-04-01 00:10 20 kWh

2015-04-01 00:20 82.30 kWh

2015-04-01 00:25 82.30 kWh

2015-04-01 00:30 83.44 kWh

....

In unlikely cases, there might be several consecutive outliers above or below or a combination of both.

3. A reset of the energy meter has to be detected automatically.

2015-04-01 00:00 20.78 kWh

2015-04-01 00:05 30.80 kWh

2015-04-01 00:10 3.99 kWh

2015-04-01 00:20 12.30 kWh

2015-04-01 00:25 12.30 kWh

2015-04-01 00:30 13.44 kWh

...

After a reset, counting starts a again from another level (a reset is simply a level shift). The level the counting starts from after the reset is often zero, but can also be any other positive number. A reset can occur at an arbitrary point in time (usually not too often).

To my eyes, problems 1. - 3.  seem ubiquitous in measurement engineering and must have been already addressed. Nevertheless, I couldn't find any literature on this topic. Does anybody know about existing solutions to this problem? All help will be highly appreciated.


texts:
I'm looking for products that can be used as non-toxic PVC plasticizers.
I've used ATBC as a product that I can add to, for example, the inside of a pool toy, which with time absorbs it and becomes softer.
The problem I want to solve is to find readily available products that are made of ATBC or other non-toxic plasticizer, and that can be absorbed in the same manner.
The only one I've found and used is Sculpey Clay Softener which is composed by 100% ATBC, but this is very expensive: https://www.amazon.com/-/pt/dp/B0047V7A56/ref=sr_1_13?__mk_pt_BR=ÅMÅŽÕÑ&dchild=1&keywords=sculpey+clay+softener&qid=1608119391&sr=8-13
Are there any other, more common and readily available, items that are composed by ATBC or other product that performs the same task?
An alternative plasticizer that is of higher quality, i.e. leaks out at a smaller rate or doesn't compromise the strength of the PVC, would be even better. My main objective is to make the item softer, but without making it a lot more susceptible to popping and avoiding products that might be toxic/damaging when absorbed by skin.


texts: Live load contribution in total energy of elastic plate

texts:
I study a model for plate bending due to tangential live load applied to its upper surface $x_3=h$. After deformation the load remains tangential to the deformed upper surface. What would then be the contribution of the load to the plate energy? My guess is
$$
\int_{\Gamma_h}\boldsymbol\sigma_h:\nabla{\bf r}_hd\boldsymbol x,
$$
but not sure.

Any guess, reference or hint?


texts: How to find out what a material is made of specifically?

texts: Let's say I buy a barbecue grill, is there a material testing kit that I can buy that'll allow me to find out what metal the grill is made from and if it were galvanized or cured in a particular substance?


texts:
I've been using 3d printers for prototyping for a long time, and I'll admit it's incredibly convenient to be able to throw together a CAD model, send it to the printer, and have it ready to assemble in a few hours. But that's just it, anything complicated with many moving parts often requires many prints and subsequent assembly which burns a huge amount of my prototyping time.

I was watching the first Iron Man movie the other day and noticed Jarvis say the line "commencing automated assembly," which got me thinking, for something as complex as, say, a motorcycle, what's the current state of the art as far as general purpose automated assembly?

Note that by "general purpose" I mean able to construct essentially arbitrary parts using a mixture of printed components of a given material (say sintered metal) and standard parts (servos, wires, gears, PCBs, etc.). Feel free to ignore the difficulty in entirely automated PCB reflow.


texts: Why prefer any other pipes over plastic pipes for drainage and culverts?

texts:
Plastic pipes look superior - no corrosion, lightweight, easy to install, a bit flexible. Yet there're lots of cases when culverts and drainage pipes are made of steel (corrosive) and reinforced concrete (very heavy).

What can other pipe materials do that plastic cannot in drainage and culverts?


texts: Why do the poles and zeroes of a transfer function cause a slope change in frequency response?

texts:
Why is it that as the frequency approaches a pole or zero of a system, the slope of the magnitude of the transfer function changes by 20dB/decade?
Whenever I see this stated when reading about transfer functions, it's never explained. What causes this property of transfer functions?


texts: Mechanical device that creates friction when rotating?

texts:
I am designing a  mock-up aircraft throttle, like one of these:

In an airplane, it it slides forward and backward to control the thrust of the engines. The problem is, I am not sure how to go about adding more friction to the sliding motion. If I were to just design a sliding handle, If you let go of it, it wouldn't be held in place, and it would slide back down. I need something sort of "reverse bearing" that will add friction to the rotation of the handle, so that when you let go of the handle, it wont slide around-- it will just stay in the same position until it is moved again.


texts: Do all airfoils have a lift curve slope of $2\pi$?

texts:
I know that according to the thin airfoil theory all airfoils (symmetric or not) have lift curve slope of $2\pi$. I also know that finite wings should have less inclined lift curve because of the downwash. Then I saw this formula used for finite elliptic wings which is fine.
$$
\frac{dC_L}{d\alpha}=a=\frac{a_0}{1+a_0/\pi AR}
$$
The problem is $a_0$ is not $2\pi$ in examples that above formula is used. I am thinking that since non of the downwash effects are present for airfoils (infinite wings) $a_0$ should always be $2\pi$. What am I missing? Is it because not all airfoils are thin?


texts: Increasing speed and efficiency of ac induction motor

texts:
If you wanted highest efficientcy and speed from an AC motor what would you do?
Could the rate of alternation of current be optimizes?
More windings?
Materials?
More lamination?
Other factors I haven't thought of?


texts:
I would like to work on a science project which I will measure people how much pressure I have to put on a pressure point to start to hurt somebody. Is there a device which I can measure the pressure that I apply onto the person's skin?
Thank you!


texts: Equivalent sheet metal thickness of different alloys

texts:
I want to replace steel plates that are being used as trim tabs on a boat with 90-10 cupronickel. The main design parameter is to make sure the plate has no less flex than the part being replaced. In other words if we were to take strips of both materials, fix them at one end and put a weight on the other, the replacement material should not bend down any more than the original material.
The steel I assume probably has a tensile strength of around 50,000 PSI and the cupronickel I guess is maybe half that. So, in that case do I just make the cupronickel sheet double the thickness of the steel, or is it more complicated than that? What is the relevant formula or calculation?


texts: What materials or techniques can I use to reduce this electrical effect when building spotwelding tables?

texts:
I have been experimenting with building various support tables around press-type spot-welders.  These are relatively simple fixures; think of a tabletop with legs under it and devices like sliding gibs, pins, clamps, rollers, etc mounted to the table top to guide a specific set of parts.

My problem is what material to use to build these tables.  Being in a metal-working shop, I usually reach for things like angle iron, sheet metal, and Unistrut.  This is fine for building most parts of the tables, but due to a phenomenon inherent in spot-welding, it is not smart to build steel pieces bridging over the copper electrodes and shunts.  I cannot think of the name of the effect right now, but basically if you have a steel member passing through the magnetic field that surrounds the shunts and other parts that come off the secondaries of the transformer, it will reduce the effective current delivered at the ends of the electrodes.  I think the current drop is proportional to the mass of the steel (and presumably the distance), but I am having trouble finding reliable information on this effect.  If I knew its name, that would help.

I am exploring two solutions for building these tables.  One would be if I had a formula modeling the mass and distance of the steel relative to the current, I could (maybe) fit the steel structural members in a position where I will not get (much) interference.

Another solution would be to keep steel members out of it and to build those parts out of another material.  I considered aluminum angle, but I really do not know if this would behave like the steel in the induced magnetic field.  My gut tells me it would not, but I really do not know.  Another choice could be plastic bar and sheet although I am not eager to go there since that would cause more fasteners, countersinking, thicker material and/or more supports to get comparable strength.

Do any of you know of a useful formula or rule of thumb that could guide me as to steel placement?  Do you know if aluminum would not have side-effects in this situation?  Do you have other ideas for materials that are easy to work with? Another idea: Is there a shielding that would help in this situation?


texts:
They didn’t give me the radius of the wheel where external force F is acting .

How can I calculate the reactions at A,B .

When they didn’t give me the radius .

Is this question “ Wrong “ ?

Note the force F in the right down wheel

Can someone confirm that $ A_y = 0 , B_y = F $


texts: Which turbulence models are suitable for CFD analysis on a streamlined vehicle body?

texts:
Many commercial and open-source CFD codes implement several closure methods for the non-linear convective acceleration term of the Reynolds-averaged Navier-Stokes (RANS) equations. Common methods (also known as turbulence models) include

Spalart–Allmaras (S–A)
k–ε (k–epsilon)
k–ω (k–omega)
SST (Menter’s Shear Stress Transport)
Reynolds stress equation model

Which of these are suitable for CFD simulation of a streamlined vehicle body? The purpose of the simulations is to guide the refinement of the body shape to minimize aerodynamic drag forces. An exemplary answer would briefly outline the advantages and disadvantages of each method for this simulation application.

Potentially useful details:

The vehicle  is a small one-person vehicle with approximate dimensions

L = 2.5 m,
W = 0.7 m, and
H = 0.5 m.

It will be travelling at speeds ranging from 0 m/s to approximately 12 m/s. All three wheels are enclosed by the body envelope, and the vehicle has an approximate ground clearance of 15 cm except near the wheels, where the body shell extends down to within 1 cm of the road surface.

Normally aerodynamic forces at these speeds are very nearly negligible, but assume that this vehicle is being designed to compete in a "Super Mileage" competition on a smooth track, is very light-weight, and uses low friction drivetrain components throughout, so the aerodynamic forces have a significant effect on the achievable fuel consumption.


texts: Precision of a steeper motor and gears vs multiple motors

texts:
We are a student team trying to design a low cost CNC plasma cutting machine.
The CNC will be a table with two rails and a bridge moving on them in which the head of the plasma torch will be.
Now we have to decide on the configuration of the steeper motors to move the bridge. It has to be pushed from each end of it, we have tought about:

Two motors, one on each end of the bridge.
One bigger motor in one end (or the middle) and a mechanical transmission (a shaft and a couple of gears) to push from the other end.

Given that the small motors cost about $15 each and assuming the big one is double the price, mass, torque, etc, what option would give the most precision with an acceptable cost?
Shaft would be a metal rod, but I dont know how much money could be precise enough gears.
EDIT 1:
We finally went for double motors.
As the project is aimed at managing the project itself and setting up a production chain, and not at designing a good product, we didn't think much about the pros and cons, and thought that just doing two of the same was less work than designing the mechanical transmission and its production and assembly process.


texts:
Recently I've been scratching my head over an assignment, and I have trouble understanding a couple of the parts.

The issue I have is with the overall calculations, since we've just started on mechanical issues and I have no experience except easy transmissions. Therefor, I am wondering how I calculate the ratio of the compound gear between A and B, and how many turns the worm gear have to turn to make the C spur gear travel a specified distance of 100mm.

The question goes as follows;

  How many revolutions does the worm gear have to complete, for the
  spring to compress entirely?

The C gear is connected to a rack that then compresses a spring, that'll have to travel 100mm.

Thanks!


texts: Root Locus and Routh–Hurwitz stability criterion

texts:
A satellite launcher has a unit feedback system, whose TF global open loop is given by:

$$G_c(s)G(s) = \frac{K(s^2-4s+18)(s+2)}{(s^2-2)(s+12)} $$

a) Draw the root locus for this function

b) Determine the range values of $K$ that make this system stable.

I don't know where start to evaluate a), because the TF has the same number of zeros and poles so, in this case, there's no branches and asymptotes?

In the item b), I achieve the following expression to evaluate the Routh–Hurwitz criterion:

$$s^3(1+K)+s^2(12-2K)+s(-2+10K) -24 + 36K = 0$$

However, when I finished the Routh–Hurwitz table and evaluated the inequalities, don't seems correct with the root locus provided by MATLAB.


texts: Control systems, Nyquist plot and root locus

texts:
I need help in understanding the connection between Nyquist plot and root locus plot.

Let's say I have a Nyquist plot, what can I infer about the root locus plot? and vise versa.

Given the root locus plot, can I draw the Nyquist plot?