texts: Why viscosity ratio should be greater then 1 for longer bearing life?

texts:
When selecting bearings, engineers should be concerned also about specifying the lubricants that will provide an optimal performance. In order to do that, the viscosity ratio is the parameter to defined in order to select the lubricant. Viscosity ratio is defined as:

$$ \kappa = \frac{\nu}{\nu_{1}} $$

Where

$ \nu $ is the operating viscosity of the lubricant [$mm^2/s$]
$\nu_{1}$ is the rated viscosity depending on the bearing mean diameter and rotational speed [$mm^2/s$]

From literature, it is said that a viscosity ratio greater than one can extend the bearing's life. If $ 0.4 \lt \kappa \lt 1$ it is recommended to use additives. While if $ \kappa \lt 0.4$ it is compulsory to use them.

What are the reasons behind this?


texts: How to determine fixed end moment in beam?

texts:
Why the Fixed End Moment (FEM) for  BC is 3PL / 16?
It's clear in the first figure that  that when one end is fixed, while the another end is pinned, then the fixed end moment is 3PL /16 ... But for the span BC, we could see that B is the roller and C is the pinned connection, there's no fixed support in the span BC


texts: Are Rolling-Element Bearings Practical for Light Loads?

texts:
I have a 5" x 4" x 3/8" plastic panel (wall thickness of 1/8", ribbed). I need to slide the panel over a 12" plastic track that is U-shaped (like a skateboard ramp). This motion could be repeated 2 million+ times.

The panel is rigid and maintains 2 contact edges when traversing the curved surfaces.

My question: Should I be worried about wearing-out the plastic components at this scale?  What options are there to protect this mechanism?

I'm considering:

plain plastic on plastic rails / tracks / sliding pegs
mini ball bearings

Any thoughts on using cheap bearings for this?


texts: Would creep have been a major problem for pykrete designs?

texts: During world war two the British had plans for an aircraft carrier made of pykrete (a mixture of 14% sawdust or wood pulp and 86% ice.) the idea was to have a refrigeration system to stop the ice from melting however I can't help but think that since the temperature would still be very near to the melting temperature of ice that creep would have been a problem. does anyone have any knowledge about the properties of ice regarding creep?


texts: What kind of material is "hot-cure resin"?

texts:
What is "hot-cure resin"? Is it the resin that has been once melted and solidified again?

It is used talking about the big glassy boxes shown in this image. Here is the context:

  Working with neuroscientists Steve Smith and Mark Lythgoe, Cattrell
  captured fMRI digital data relayed while subjects were caught in the
  act of looking and listening, and then used RP to transform these
  isolated processes into computerised virtual models. Out of these she
  made waxy resin sculptures, embedding them in solid square
  ‘brain-boxes’ made of transparent hot-cure resin.


texts: How much clearance does a car need when turning a corner?

texts:
I am contemplating buying a new car. However, the approach to the underground garage in my apartment has a 90 degree frustrating turn. Given the dimensions of the approach and car, what is the max turn circle for the car to fit the garage and turn?

given Ackerman steering and the overhanging front part of the car I believe you can use Pythagoreas' theorem to get R min and R max. delta R should be less than the shortest path in the pathway, ie 2.5m. unfortunately the result does not seem plausible. feedback would be greatly appreciated.


texts: Minimum required rolling friction between pulley and the rope

texts:
The 40 kg weight accelerates and runs on a rope from 0 to 50 km/h in 10 seconds.

I want to calculate the minimum required rolling friction that I need (acceleration without slipping) to achieve acceleration in a time of 10 seconds from 0-50km / h.

Friction adjustment (later for different speeds and accelerations) I would change by increasing /decreasing the angle between the drive pulley and the pulley 2 as shown in the figure. Currently, the angle is 15 '.

My question is:
How to calculate the minimum required rolling friction (or better say, minimum required angle which is 15' now) between the drive pulley and the rope of 40kg of weight moving along the rope, as shown in the drawing?

All pulleys are covered with rubber, and the rope is synthetic, Dyneema. What aditional information do I have to apply for the correct calculation?


texts: Why does the synchromesh in manual transmissions act on the output shaft?

texts:
Wikipedia has a good animation of a manual transmission, but something irks me.

If I understood correctly, in the animation, the input shaft is in green, and the output shaft is in cyan. The dog clutches (synchromesh in modern cars) are therefore between the free gears and the output shaft. This forces both the engine and the gear assembly to change speed in a gear shift. If the synchromesh were between the input shaft and the free gears, only the input shaft (therefore the engine) would need to change speed during a gear change. I don't see anything after a quick Google that suggests things are different in many other gearboxes.

What is the reason for this that I'm apparently missing? Acting as a flywheel is the only that crosses my mind.


texts:
In the figure attached for reference, it is given that if $R_1$ is the resistance element of valve 1 and τ ∝ $R_1$, but I am not able to understand it intuitively.
If $R_1$ is high, output flow through that valve must be less, this means it is easier to store the liquid in the tank. Hence, τ ∝ $\frac{1}{R_1}$.
Please tell where I am wrong in my logic. TIA.


texts: Why are turbo compound engines not more widely used?

texts: Turbo compound engines extract some exhaust energy by using it to power a turbine connected to the driveshaft.  Why are these engines not more widely used?


texts: How much does the elasticity (Young's Modulus) of concrete and asphalt change with ambient temperature?

texts:
I'm assuming here that all materials will have a change in elasticity due to thermal expansion/contraction and a resultant reduction/increase in the strength of the bonds of the atoms leading to a varying young's modulus. But how significant is it (at normal non-extreme ambient temperatures -  maybe from -10°C to 50°C)?

If anyone know's of any research into this. Or even a table of values like the following, that would be very useful: http://www.engineeringtoolbox.com/young-modulus-d_773.html

The reason I am asking is I am interested in Structural Health Monitoring, and I've read a lot of researchers claim that temperature has a major impact upon structural stiffness due to changes in material stiffness. I'm yet to find substantial evidence of this.


texts: How significant is a 8,500 lb concentrated load in a large (25+ floors) residential high-rise?

texts:
I'm thinking of installing a rather large aquarium on the 4th floor of a residential high-rise which has a total of 27 floors. I plan to place it directly against a concrete column with a diameter of around 4 feet.

I think the main issues are:

Overloading the slab such that it falls through the slab.
Not overloading the floor to the extent that it falls through the floor but overloading the column.

Who do I need to talk to in order to find out if this is feasible before the project actually starts? The building manager, a civil engineer, or....?

The load is spread over about 8.5 ft². Are high-rise buildings designed to support live loads of this type and magnitude?


texts:
I am doing research on the impact of vehicles on roadways, specifically garbage trucks. In my research I am finding largely different "answers."

For example "Using American Association of State Highway and transportation Officials (AASHTO) vehicle load factors (VLF), a full, residential garbage truck is equivalent to 11,700 passenger cars." http://files.dep.state.pa.us/waste/Recycling/RecyclingPortalFiles/Doylestown_Township_504.pdf

However, when calculating based on EASL the number is 1,279 https://www.lrrb.org/PDF/201432.pdf

What is the difference and why are the answers so different?


texts: How 2 lasers interacting causes a dot of light

texts:
Take a loom at this diagram

You have probably heard of this before but im just curious what laser they are using to do this. They do t appear to be ionizing air. It seems the one laser is just for color on the particle but what is the other? I would like to try this at home and make a dot for fun but i dont quite understand whats going on here. Any ideas?


texts:
I am making a testing facility for pumps. This facility has to be able to handle 500 m3/h with at little turbulence as possible. The basin itself is 5 meters long, 2,5 meters wide and 2 meters tall. The water level in the basin is kept at 1,9 meters.

The basin is designed in two sections: the first is where the discharge flow comes into the basin (pipe ends about 1 meters in from the bottom). In that area the water flows freely.

After that it has to flow over the retaining wall (1.7m high), which should create a somewhat uniform flow.

Are there better solutions to do this?

One other idea I have is a retaining wall somewhat like this:

This makes for three plates with cutout stripes.

The idea behind this is to have a more uniform flow across the entire basin instead of a overflow, making it create a small bit of turbulence there.


texts: Comparing the performance of glass and granite in a heat storage application

texts:
Background
I am working with a small team on a university project to build a greenhouse heat sink. This will pass warm air at the top of the greenhouse down through a chamber underground filled with a material to absorb and store the warm air. We have two prototype greenhouses; one will act as a control for baseline measurements and the other will have the heat sink.
Set-up
I have built several temperature sensors and loggers for the final prototype, but some preliminary tests are being made on various materials:

Granite chips between 15-25mm, irregular shape
Tempered glass fractured into small pieces 7-15mm approx., atleast 2 sides are flat
Concrete fragments 30-80mm, irregular shape - test not completed

These were placed in a 5 L box. The box has a small fan and piping at the bottom to blow air into the chamber and release the air through a number of 6 mm holes in the pipe at the base of the box.  The top of the box is sealed except for a vent which has the same diameter as the tube with the fan.  A PT1000 temperature sensor is also inserted into the centre of each material to capture measurements every second.  Here is an image of the test box:

Procedure
The free air space was calculated on a smaller sample of both materials to give a rough figure of 42% for the granite and 43% for the glass. Two tests were then performed on the granite and then the glass:

Both cooled outside for a several hours to about 5.5 °C, then brought into the room and left for 1 hour with the fan on. The temperature was recorded as the material warmed up to room temperature.
After the first test the materials were then placed in a freezer and cooled down to -20 °C, the temperature was recorded again.

Results
As can be seen below, the glass exhibits a lag in both data sets, warming up and cooling down, after which the temperature change becomes more linear. Whereas the granite shows a more linear change in temperature throughout.
Glass Warming (x-axis seconds, y-axis temperature)

Glass Cooling (x-axis seconds, y-axis temperature)

Granite Warming (x-axis seconds, y-axis temperature)

Granite Cooling (x-axis seconds, y-axis temperature)

Questions
We are discussing the results at the moment and I am interested in expert opinions of the data we collected. The data is interesting and we are interpreting it correctly. Specifically:

The shape of the glass fragments allows for a more interlocking shape, which could restrict airflow more, but wouldn't this still have a more linear temperature change?
Could the glass data be due to minor thermal expansion changes in the material?
The glass has a lower thermal conductivity rating than the granite, is this the reason for the lag?


texts: How can I calculate how much weight can lift my stepper motor?

texts:
I have this stepper motor: Stepper Motor, Nema 17 Stepper Motor 4-lead 1.8 Deg 40N.cm Holding Torque 1.7A 42 Motor with Motor Mounting Bracket and Screws for 3D Printer/CNC

I want to know how can I calculate how much weight it motor can lift in this situation:


texts:
In a robot or spacecraft attitude representation, using quaternion is relevant.
The kinematic equation is as below
$$
\begin{bmatrix}
\dot{q}_0 \\ \dot{q}
\end{bmatrix} =
\frac{1}{2}
\begin{bmatrix}
-q^\top \\ q_0\,I_3 + q^\times
\end{bmatrix} \omega.
$$
In this equation quaternions derivative are calculated based on angular velocity $\omega$. I want to calculate $\omega$ based on quaternions derivatives. So I should inverse the matrix multiplied to $\omega$ in above equation. Is there any straight forward way to inverse it analytically?


texts: Viability of creating a wireless LAN bridge between mobiles and PCs using a portable router?

texts:
I am creating a network to share files between a mobile device and multiple PCs directly through a LAN. The purpose of which is to use smart phones to capture files from remote devices which are outside the range of the internet.

The current plan is to use a portable router that could be brought on site and act as a bridge between the mobile client and the PCs to allow for the passing of the desired files.

I am new to LAN and router network and have had issues when trying to use the router as a bridge as so I was wondering if it would be better to create the network with the device in router, repeater and bridge modes? What would be the reasons for this? Or is there a better way to create a network?

NOTE: for this application the mobile device needs to be able to talk to multiple PCs at one time so WiFi direct is not a valid option. And there is nowhere on site to leave a permanent router which is why a portable router is a suggested option.


texts: Is there a term for this kind of eccentrically threaded fastener or washer that has wrench flats and curved faces

texts: Is there a standard term for this fastener or for the kind of problem it is intended to address?


texts:
I have an application that is drawing fluid from a reservoir via a standard dip tube. This application has a special requirement that once the fluid is depleted from the reservoir, the pump pulling liquid from the reservoir needs to shut off before drawing air into the system.

The function of this type of valve would be more or less the opposite of a floating shutoff valve used in toilet tanks where the floating mechanism closes the valve once the tank is filled. My application would do the opposite, where the float closes a valve on the dip tube or shuts of the pump once the tank is empty (or close to it).

Does anyone know if this type of valve exists on the market, or is it something I need to design on my own? Thanks!


texts: How are the modern hydraulic cylinders very precisely controlled?

texts:
My guess is that they use brushless Motors that in turn powers the hydraulic pump.
But there must be some kind of valve that could help in the process. Still the burning question is just by adjusting the flow and pressure will it actually control precision required hydraulic equipment? Since there are lots of valves, which combination of valves can work?

I know there are many easy ways to control an electric actuator with feedback, using Arduino or simple "pwm" etc.


texts: Is there a way to auto-reverse cassette tape with gears only?

texts:
From what I read, tape decks auto-reverse by having a sensor keep track of an encoder. When the take up pulley stops turning, the logic board reverses the direction of the motor (and does some other stuff to pickup different tracks on the tape).

In my art project the rotating reels are the only necesseary parts, and the exact speed of the tape doesn't matter. All I want to do, is rotate one reel and then move the input gear to the other reel when the tape has run out on one side. It just needs to rotate forever.

I assume it would be somewhat similar to this mechanism:

I would like to use as few parts as possible, and no electronics (except for the small motor that drives the mechanism). Is this at all possible?

UPDATE

I have not yet seen the perfect solution, but I did find this cassette tape adapter:

From the Wiki page on this type of adapter:

  To simulate tape movement, a system of gears or a drive belt connects the tape player's drive motor (via the take-up spindle) to a wheel inside the adapter. This wheel rides against the detection wheel to simulate tape movement. Because the wheel never stops spinning, the deck never senses an end-of-tape and never tries to reverse the tape.

I think my solution would look similar to the inside of that adapter, but then stuck to the back of a normal cassette. It will provide the drive motor, also rotate the spindles that the reels are on.

What I'm looking for is a gear mechanism that will 'walk' to the reverse gear when the first gear stops turning (like in the image above). Does that make sense to anyone?


texts: How to find the stability margin of a transfer function?

texts:
In the control there are two kinds of margin

Phase Margin
Gain Margin

There are plenty of examples available to find about it.

Now here is my doubt.

What is stability margin? I was studying this pdf. On page-13, just before the Ziegler-Nichols' Tuning Methods topic, there is a paragraph which contains the stability margin values. But it does not explain how to find these stability margin values. Can anyone explain the steps to find the stability margin?

Thanks in advance :-)


texts: Half Sine Impulse in a modal Transient Analysis

texts:
I have a MDOF FEM model in which I perform a modal transient analysis based on the modal eigenfrequencies extracted in a prior step.
I wish to excite only the first natural frequency of the system via a half sine impulse of 10G. I do not want to see contributions from other modes.

Is this possible? I'm not sure how to define the time abscissa value which correlates to the first natural mode. Any suggestions will be appreciated.

Best Regards


texts: Extracting load info on Abaqus with Python

texts:
I have a model on Abaqus that I've managed to run some 85 jobs on manually. Between jobs, only the loads vary, and I select these loads by resuming what I need and suppressing what I don't with my mouse (essentially, choosing k out of n pre-defined loads every time).

I'm new to scripting on Abaqus with Python, but I have been digging a fair amount through the official scripting guide, with no help. The task I'm working on requires me to extract, FOR EACH JOB, all active loads with their component magnitudes, and elements that they act on.

Query 1:

Logically, one should be able to find job-specific loads from the corresponding odb file. But I'm unable to find forces by probing into it
(odb.rootAssembly->steps->...?).
Going into the mdb (mdb.model->steps->loadStates), however, simply lists
down all the n pre-defined loads, which isn't very unhelpful. I need the k choices I make for each simulation.

Where do I find this information?

Query 2:

In general, how do I get for any element or node set, the elements or nodes in that set? (I believe nodes and elements are numbered in Abaqus)

I'll appreciate any help whatsoever. Thanks.


texts: how to get more number variance compared as the csv output file of two model stl files in Cloudcompare

texts:
we are using the CloudCompare for comparing two mouth STL model for Final doctoral theses, like works done in this paper(pdf) shown blow:

and the instruction said here:

so i have tried to insert the STL file and use this align method :

so the output are only 256 numbers by this columns names:

so asked how to increase the result number of compared output result in CSV file and is this methods is right for accessing to the compared this two models?

also what is the means of the csv colums means whis are like this:

i have uploaded the two STL files here, for more information.

http://s7.picofile.com/file/8387291350/stl_files.zip.html

Thanks for your attention.


texts:
Let’s say I have a circular rod that has an outside lip with a larger diameter and certain height. The rod moves axially, and the intent of the lip is to mechanically stop the rod at a maximum axial displacement. How would I calculate the maximum static axial force I could apply to the rod before the lip shears off of the rod?

I have a pretty good understanding of how to apply this problem in a simple cantilevered beam with a load orthogonal to the beam surface that provides a shear stress, however I can’t seem to wrap my head around this kind of problem, especially regarding second moment of area with a cross section that is radial instead of on a constant plane. As far as I can tell, the process is:

Draw a FBD to find resultant forces on the shaft.
Determine the resultant normal and shear stresses due to axial, shear, torsion, and bending forces.
Use Mohr’s circle to determine sigma max, sigma min, and tau max.
Apply one of the failure criteria for brittle/ductile materials.

Can anyone provide some guidance or direction?


texts: What's the name of position-setting spring clips used in plumbing?

texts: Could someone tell me if there's a general name for the kind of spring clips that slide onto a rod and set a position for some other attached element. I've seen them on sinks and toilet tanks -- here are pictures:


texts: Detailed dimensions of an aircraft engine compressor blade

texts:
I am working on rub-induced vibrations in compressor stages of aircraft engines. The work is carried out in partnership with a company, therefore there is a limited amount of it that could be published openly.

Is it feasible to release open source compressor or turbine blade designs (e.g., NACA airfoil profiles for wings), as is commonly done in the software industry? By which I mean, detailed dimensions—in particular for the cross-section profiles and stacking laws—and the associated material properties.

If this has already been done, I'm not aware of it. Are there specific obstacles preventing the open source movement from spreading from the programming world into the engineering world? If so, are they technical or non-technical obstacles and how could they be overcome?

Not only would these specific designs be very useful for my own work, displaying relevant characteristics and realistic behaviors from an engineering perspective, while sharing all geometry and material property details, would allow other researchers to reproduce published results.


texts: I have seen a number of products made of brass with a silver-looking coating covering the brass on the outside. These products are all quite cheap (for example a small watering can or clothes hooks). What is the cheapest silver-looking material to coat brass with and what process would be used to perform the coating operation for mass production (500,000+ per year) of these products? I'd imagine chrome plating or electro plating would be too costly for these sorts of products so I wonder how things like these are made.


texts: Attached image is from a very high water table and high salinity area. What is the type of pavement defect and how to address the issue?


texts:
Consider the rigid bar $ ABC $ linked to two bars, $ AD $ and $ BF $, as shown in the figure.
All bars are made of mild steel which is admitted to be an elastoplastic material ($ E $ = 210 GPa,
$ \sigma_Y $ = 250 MPa) but the bar $ AD $ has a uniform and rectangular cross section of 20 mm $ \times $ 6 mm while the $ BF $ bar consists of two sections, $ BE $ and $ EF $, with section area respectively equal to $ A_ {BE} = 1200 $ mm $ ^ 2 $ and $ A_ {EF} = 2400 $ mm $ ^ 2 $. The strength of the $ P $ force
applied in $ C $ is gradually increased until the displacement of the $ C $ point reaches 2.5 mm.
Calculate the residual stresses in the bars and the residual displacement of the $ C $ point when the $ P $ force is removed.

The resolution says:
Now consider the extreme case where the $ C $ point offset is increased to 2.5 mm.
What will happen to the displacements and forces at the other points of interest on the rigid bar $ ABC $?
Since the maximum force $ P $ does not change during the path $ \delta_C in [1.206 \ , ~ 2.5] $ mm the forces on the bars $ AD $ and $ BF $ do not change:
\begin{equation}
\begin{cases}
F_{BF} &= P + F_{AD} = \left(\displaystyle\frac{L_{BC}}{L_{AB}} + 1\right) P \\
F_{AD} &= \left(\displaystyle\frac{L_{BC}}{L_{AB}}\right) P
\end{cases}
\end{equation}
In this case, the displacement of the point $ B $ remains fixed ($ F_ {BF} $ constant) and the geometric rotation of the mechanism occurs
around $ B $. At constant force, there will be a continuous increment of variation in the length of the bar $ AD $ being the
total displacement value in $ \delta_A ^ t $ (for $ \delta_ {C_p} = $ 2.5 mm) given by:
\begin{equation}
\begin{aligned}
\frac{\delta_A^t+\delta_B}{L_{AB}} =
\frac{\delta_A^t+\delta_{C_p}}{L_{AC}}
\end{aligned}
\quad\Leftrightarrow\quad
\begin{aligned}
\delta_A^t = \frac{\delta_{C_p}L_{AB} - \delta_BL_{AC} }{L_{AC}-L_{AB}}
\end{aligned}
\end{equation}
deltaA tot =  1.6983  mm
I can't understand how they calculated deltaA tot ?
I also tried to use the relationship $\frac{\delta}{L}$ but i'm not getting it.
Could someone explain it to me?


texts: Extreme temperature quick disconnect terminals

texts: I am doing R&D work and am in need of terminals that can withstand 1,000 degrees Celsius, but cannot seem to find anything anywhere.  The highest temperature ratings I have found are around 600 degrees Celsius.  The terminals will be used in a furnace like enclosure.  Any guidance would be appreciated.


texts: Detailing Fixed Cotton Duck Bridge Bearings

texts:
I'm looking for a justification for the use of cotton duck bearing pads without a sole plate. I'm specifically considering their use with precast I-girders.

Say I have a two span bridge, simply supported for dead load, with expansion bearings at the abutments and fixed bearings at the piers.

The configuration for the expansion bearings that I'm familiar with is:

(bearing plate embedded in girder - welded to sole plate - which is attached to stainless steel sliding plate - that rests on a PTFE sheet - which is attached to the cotton duck pad)

The configuration that the Nebraska Department of Roads specifies for a "fixed" bearing is:

(bearing plate embedded in girder - sitting on cotton duck pad)

How can this be justified as a fixed girder? Are there studies that support the reliability of counting on friction between the bearing and a steel plate?
If it's not truly a fixed girder, do I have a "floating" bridge? What design considerations/concerns does this raise? If you've encountered this consideration what is your design approach?


texts:
The calculations for a design I am doing are making me go round in circles.  I have simulated the design but I cannot seem to resolve this mathematically and it is really bugging me!

Below is an image of the design - two levers with different moments connected to each other by a hinge at their ends.  Each lever's pivots can slide from left to right.  The system equilibrium is maintained by an actuator between the two levers exerting a static force.  This force is what I am trying to calculate.

I believe I need to work out the moment on each lever (easy enough) and resolve for a torque around the hinge point where the two levers are connected. From here I can calculate the force on the actuator using a free body diagram.  Calculating the moment around the hinge point however is proving tricky as it is not as simple as just adding the two moments together (so my simulations tell me).

Note. Currently I am only interested in the static force to keep system in equilibrium.

I would appreciate the help.

Cheers


texts:
I've been looking into EV AC chargers for businesses (basically, any and all AC chargers up to 2 x 22kW). One thing I've noticed is that quite a few chargers look alike, sometimes to the point of just having different stickers.

This raised two questions:

Which companies actually design and manufacture EV AC chargers?

Do other companies add something to existing designs? Or do they put the chargers in a different jacket and then resell them?

Sorry if this is not the right place to ask this question. I wasn't quite sure where else to go to.


texts:
To save on material, I am requested to design a continuously supported beam with a maximum bending capacity that is half of its maximum bending moment and to strengthen the beam at certain intervals where its capacity is exceeded. What is a feasible strengthening scheme without changing the beam's overall dimensions significantly.

This beam is going to be used as a waling where stiffeners will be added at strut-waling connection. This is also the location where moment capacity will be exceeded.


texts:
On a datasheet, sensitivity temperature drift (TCs) is specified in %/K.

I read this as "the percent change per kelvin".

Is this is simple as this sounds, or is there a reason for using kelvin over celsius?

I.e if TCs=0.01 and the temperature changes from 20C to 30C, or from 293K to 303K, then the total percentage change is 0.1%?


texts: How to increase temperature of the condenser part in a refrigeration cycle?

texts:
I have made a refrigeration system at my home. I am using r134a as the refrigerant.

I want to achieve a temperature of about 70-degree Celcius in the condenser part and 0-degree Celcius in the evaporator part.
(Currently, I think I am able to achieve 30-degree Celcius in the condenser part and about -10 degree Celcius in the evaporator part.)
In order to achieve so, I was thinking to decrease the length of the condenser coil and increase the evaporator coil length.
Is it possible to achieve such temperature as mentioned above?


texts: In heat transfer, we come across Stanton number which is the ratio of heat transferred into a fluid to the thermal capacity of the fluid. But what does this physically mean and its importance in engineering applications?


texts: Orthographic (engineering) drawing with same top and front view?

texts:
I came across this while reading on third angle orthographic projections.

The object has the exact same front and top view - both views are trapeziums of exact shape and size (As shown in the image). Also there is a hidden circle center line right thorough the middle of both of them.

I am unable to complete the projection as I cannot visualize this object - so I can't work out the right and left views.

The single image represents both the front and top views - I can't work out the left and right views.


texts: How would I drop something directly in the middle of a vertical pipe?

texts:
Not sure if this is the right place to ask, but it is for a physics experiment.
I'm trying to find out how the internal diameter of a copper pipe affects the time it takes for a magnet to drop through. Dropping the magnet in the centre would allow me to ensure consistency for each drop.


texts:
I am looking at Phase Change Materials as a building fabric option and from reading up on the topic theres something I don’t understand. Hopefully somebody can help explain.

I read that when a substance melts it stores latent energy, otherwise charging the material. When the material freezes again it releases this ‘stored’ energy and this is what is utilised for heating or cooling. However, I’ve also read that some substances can store energy during the freezing process and this is where it loses me...

Am I misunderstanding the process or is this specific to certain materials?

Thanks in advance

Kind Regards

L


texts: How to focus the flashlight of a smartphone?

texts: How would I go about collimating the light from a smartphone's flashlight into a more focused beam? I'm working on a project where I need a focused beam of light to act as a light source so I can take pictures of the retina of a human patient using a smartphone. I'd rather use the built-in flash of the camera than build my own light source, but the light from the flash is very diffuse.


texts:
Hi I use this circuit to detect phase loose, so if one of the phase lost , the phase loss signal will be high, the problem in this circuit are.
1-if the input voltage less at 50% it give phase loss , i did try to increase the resistors (R99,R100 and R102) this make work but it cause another problem
is when i have phase loss and if input voltage more than 380Vac , the circuit does not detect phase loss becuase all optocoupler are on.
So how can i make this circuit work right like if i loss one phase , the phase loss signal be high and is not turn off at high input voltage and also how can avoid getting phase loss when the voltage at less than 50%


texts: Axial deformation of variable cross-section member

texts:
I've been given a problem which I've attempted to solve, and hope some fellow engineers could possibly see if my approach is correct.

We are asked to calculate a column's axial deformation due to an applied load of F = 25 kN and the force due to the column's own weight. We are also given that ρ = 7800 kg/m3, E = 200 GPa and g = 9.81 m/s. It's vertical length is L = 1 m and its radius varies vertically as r = (0.03)/(1+y).

This is the approach that I took where I first found the force due to the column's weight as a function of y:

$$F(y)=\int_0^y \rho g A(y) \, dy$$
$$F(y)=\int_0^y \rho g \pi \left (\frac{0.03}{1+y}  \right )^2\, dy$$
$$F(y)=(0.03)^2 \rho g \pi \int_0^y \frac{dy}{(1+y)^2}$$
$$F(y)=(0.03)^2 \rho g \pi \left (\frac{y}{1+y}  \right )$$

I then put this into the axial deformation equation and integrated to get the following:

$$\delta_{w}=\int_0^L \frac{F(y)dy}{A(y)E}$$
$$\delta_{w}=\int_0^1 \frac{(0.03)^2 \pi \rho g \left (\frac{y}{1+y}  \right )dy}{\pi \left (\frac{0.03}{1+y}  \right )^2 E}$$
$$\delta_{w}=\int_0^1 \frac{(0.03)^2 \pi \rho g y(1+y)^2dy}{(0.03)^2 \pi E (1+y)}$$
$$\delta_{w}=\frac{\rho g}{E}\int_0^1 y(1+y)dy$$
$$\delta_{w}=\frac{5 \rho g}{6 E}$$
$$\delta_{w}=\frac{5 (7800)(9.81)}{6 (200)(10^9)}$$
$$\delta_{w}=3.18825(10^{-7})$$

For the applied load I did:

$$\delta_{F}=\int_0^L \frac{Fdy}{A(y)E}$$
$$\delta_{F}=\frac{F}{E}\int_0^L \frac{dy}{\pi \left (\frac{0.03}{1+y}  \right )^2}$$
$$\delta_{F}=\frac{F}{(0.03)^2 \pi E}\int_0^L (1+y)^2 dy$$
$$\delta_{F}=\frac{7 F}{3 \pi (0.03)^2 E}$$
$$\delta_{F}=\frac{7 (25)(10^3)}{3 \pi (0.03)^2 (200)(10^9)}$$
$$\delta_{F}=1.03156(10^{-4})$$

And finally, adding the two deformations I got:

$$\delta_{total}=\delta_{w}+\delta_{F}$$
$$\delta_{total}=-1.0347(10^{-4})$$

Where the negative sign is due to the fact that the forces are compressive. Is this result for the deformation of the beam accurate? My main point of concern is whether I calculated $F(y)$ correctly.


texts: Does power braking increases acceleration?

texts:
Power braking (increasing power while brake applied) at start help to start car at higher speed, but on other hand we lose traction due to tire slippage.

Does this increase acceleration (as shown in movies)? If yes, then why don't F1 racers do it?


texts: Why we don't use fillets while making buildings?

texts:
Why don't we use fillets when making buildings and houses (i.e why do we leave the edges sharp?)? Does stress concentration factor not matter in making structures?

I am talking about the building like this-->

I know this edge is not highly stress concentrated(only the atmospheric pressure is acted on these edges, which is easily bearable by this building.) but assume the time of any natural disaster, at that time these type of edges would be more likely to fail.And making the edges round doesn't affect the cost much.I think.

NOW ANOTHER EXAMPLE.

This is also stress concentrated.As we climb the stairs there will definitely some forces will act.


texts: How to quickly design and simulate crank based mechanisms?

texts: I'm doing a project on Theo Jansen's Mechanism, where I have to modify the mechanism. What is the most efficient way to design these mechanisms? Is there any good software where I can just draw the links and input crank and test out the mechanism? I have used GeoGebra, but it doesn't simulate the mechanism physically, and while using Creo I found that the pin joints often get stuck - like they suddenly fold up and do not move. Also, creating the links one by one takes quite a lot of time.


texts: How to avoid oxidation of Si using a sub nanometer layer

texts: Which material can be used to protect a Si layer from Oxidation by a sub nanometer layer?


texts:
Consider the following problem from Hibbeler's Engineering Mechanics, Statics. (13th edition)

and the associated free body diagram and equilibrium equations

The problem is solved by equating $N_B$ to zero. Let's say I was asked to determine all support reactions and the force in cable CD (as in the picture, not requiring the ramp to just start being lifted) It seems that 3 equilibrium equations are not sufficient, as there are 4 unknowns $F\, ,N_B\,,A_x\,and\, A_y $

What renders this statics problem unsolvable, is it statically indeterminate?


texts: I'm using two stepper motors (datasheet below) to pan and tilt a platform. The bottom motor spins fine without the breadboard glued to the top platform. However, it behaves unpredictably and skips steps when the breadboard is glued in place (shown below). My question is why does this happen? Is it related to rotor inertia?


texts: Memory management in for multiple cores of a processor

texts:
I come across a question-'How big an address space should I allocate for each ARM A53 core in a mobile processor?' What is the answer for this?
Does it refer to memory management in SoC?


texts: How do I set the default coordinate system for the line tool in Autocad?

texts: On my laptop, I set a variable that makes it so the line tool defaults to Cartesian coordinates. On my desktop, I can't seem to find the variable name. I have been searching for hours.


texts:
Sorry, it seems like the answer to this question is just a quick google search away; but I have not found a page defining what the axis is.

My guess was that the axis of a piple is the imaginary line running down through the middle of the pipe. However, this doesn't make sense based on a question I am looking at in a calculus book. The question is "write the vector field describing the flow if the axis of the pipe is the unit circle in the $xy$ plane." This makes me think that the axis of a pipe is cross section of a pipe, but that doesn't really  make sense either because usually an axis is a line, not a circle.


texts: Calculating the torque requirements of the motor for a specific case

texts:
I want to use a DC 12/24V motor to rotate an assembly of glass tubes(image attached) through a hollow shaft of 25mm OD and 22mm ID, the shaft is supported on bearings on both the sides(assume minimum friction), two 3mm thick circular plates hold the four tubes together at both the end. The shaft is attached to the center of the disk.

Data:

Glass tube: 58 mm OD, 45 mm ID 1.8 m long
Disk: 180 mm OD, 3 mm thick attached at 25 mm from both the edges of the glass tube.

Even a general procedure/idea of calculating torque requirement is appreciated


texts: How to provide concentricity tolerance in assembly?

texts:
I have a part(let's name it as supporting plate) which is gonna be welded on two parallel sides of a rectangular channel.
The supporting plate has holes drilled at its end, the two supporting plates holes must be concentric within some dimension so as that the pin can be assembled without any problem.

How can I provide/represent such concentricity tolerance in assembly?

I have attached a picture for your easier understanding.

Advanced thanks for your help and support

Thanks & Regards
Charles A


texts:
I need a 8 m x 4 m x 0.6 m RC plinth (mechanical requirement) which needs to be built onto loose gravel. Obviously I am going to over excavate, back fill with selected material and bed my plinth on that.

The plinth accommodates 2 x 65 m3 water tanks, placed symmetrically.  The tanks are $\phi$3 m, 9 m high and weigh 796 kN when full. The wind load on each creates a 206 kNm moment and horizontal force of 38 kN.

I need to design the plinth for bending and check the soil for shear failure. I assume the max. bearing capacity of the soil to be 150 kPa.

I want to simulate this using FEM. How do I address the support conditions. I understand that I should use springs as supports, but how would I get the equivalent spring constants if my spring is soil?


texts:
I have an absolute value encoder with 14-bit resolution and want to implement a speed controller. For high speeds, the offset between the old and the new position value is large and so the accuracy of the estimation for velocity is high. If I target a low speed, then the accuracy of my estimation shrinks, since I have only a little difference between two steps of the encoder.

I see two solutions to increase the resolution. First, the time between two measurements can be increased, but then the speed controller begins to fail for very large speeds.

Trajectories for the position controller could be calculated to come up with a velocity controller.

What do you think is the best solution for speed control to achieve a large dynamic of speed and how is this done normally for industrial applications?


texts: What is the name of the part that allows a steam wand to have a moveable joint?

texts: On espresso machines, there is some kind of pipe joint which allows the steam wand to move while maintaining its seal. What is this component called?


texts: Tangential forces on the boundary in Abaqus

texts:
In Abaqus I print the problem's geometry of a plate 2D with a crack at the edge, bound on the left side in the x-direction and subjected to uniform effort in y-direction (uniform pressure - perpendicular to the two opposing edges) as shown in the figure:

How can I apply the tangential forces on the boundary as shown in the figure:

Thank you.


texts: Can I use a PIR sensor on a home made sonar?

texts:
I'm currently building a sonar running off an arduino. My radar includes an ultrasonic sensor that will detect the distance an object is sitting at, and a servo motor that the sensor will sit on top of. I was wondering if it was at all practical to use a PIR sensor with this setup so that the radar will be able to detect people instead of just inanimate objects. I'm worried that while rotating, the sensor might just constantly stay high if it sees any moving person.

I have no prior PIR sensor experience and that is why I was hoping someone with some experience could let me know if this is worth pursuing or if will be too much of a problem.

The range of this sonar isn't too important. Although I would like it if it could scan several meters, under 1 meter would still be fine.


texts: Method for comparing efficiency of heater block designs?

texts:
How would I go about comparing the efficiency of different heater block shapes for the outlined system?

So, in the attached diagram there is a cylindrical heater cartridge (A) that is used to transfer heat to the cylindrical polymer (B) through the heater block(C).

(A): Heater Cartridge

(B): Polymer liquid flow, carrying heat out

(C): Heater block, aluminium

(D): Temperature Sensor

This setup is for the heater block of a 3D printer. The aim being to provide constant heat to the polymer (B) that flows through the system. The aluminium block acts as a thermal storage to reduce temperature fluctuation in the polymer filament as the flow rate changes. The temperature sensor (D) reacts to changes and controls the heater cartridge in order to try and maintain constant temperature.

I wish to redesign this heater block to find the most efficient shape for this function.

So, my question is how would I calculate the efficiency of different shapes for this purpose? Losses to the surrounding air will have to be taken into account as the surface area will change with different shapes. Different shapes having different surface area to volume ratios.

I must admit I don't know where to start with this problem, it has been quite some time since I've had any formal thermodynamics education. Any answers, pointers or links to resources are greatly appreciated. Thank you!


texts:
I am trying to build a worm gear based on a single axis solar tracker for a worm gear box. I need some guidance choosing a worm gear & drive motor for the application. These are the steps I have explored so far - if I am wrong could someone please give links to material which gives a good explanation so I can learn and understand it better.

Motor planning to choose; Worm gear selection

General equations for worm gear & motor:

1) $Efficiency = \frac{\text{output Power of worm gear}}{\text{input Power of worm gear}} = \frac{P_o}{P_\text{Input}}$

2) $\text{Output power} = P_o = 2*\pi*\text{Output speed} * \text{Output torque}/60$

Output power in kW
Output speed in rev/min
Output torque in Nm

3) $\text{Input power} = P_\text{Input} = 2*\pi*\text{Input speed} * \text{Input torque}/60$

4) $\text{Net Torque}= T_\text{output} + T_\text{Input} + T_\text{holding} = 0$

In order to drive a 250 kW plant I have assumed 15 kW per row, this gives me 16 rows with 1 column.

The worm gear has to drive 16 rows with coupling with single column item.

Each panel weighs 20 kg and there are 60 panel per row which gives 1200 kg.
Each row has a structural weight around 700 kg.

This gives a net weight of 1900 kg per row.

So, the load on the worm gear would be 1900*16 = 30400 kg.

Based on my calculations above, how can I calculate the exact motor & drive motor required. I need some specific relation here.


texts: Why do color TVs make black and white snow?

texts:
If you let a color TV display something from an unplugged display port, it displays snow, right? Randomly varying black or white pixels on the whole screen.

My guess was that the television was decoding the noise from the unplugged wires as a video signal.

Assuming this, it makes sense that B&W TVs make B&W snow (they would decode the noise as being a B&W video signal). But then color TVs should make colored snow, right? Shouldn't they decode the noise as being a color video signal?


texts: Buckingham Pi Theorem doesnt work for this case?

texts:
Question from my Fluid Dynamics book (White 7e - 5.15)

The thrust F of a propeller is generally thought to be a function of its diameter D and angular velocity Ω, the forward speed V, and the density ρ and visocity μ of the fluid. Rewrite this relationship as a dimensionless function.

I want to solve this question using the Buckingham Pi Theorem. The solutions provided by my professor only use the Ipsen's method.

But I don't understand what repeating variables to choose.

According to the Buckingham Pi theorem each pi must contain the repeating variables. But in this example that is not possible??


texts: What is the theoretical maximum energy efficiency of hydro turbines?

texts: From what I've read it seems that hydro turbines can theoretically achieve 100% energy conversion from kinetic to electrical energy. However, I just wanted to double check if this was true.


texts: explaining ohmic loss and understanding inverter efficiency curve

texts:
I'm trying to understand an efficiency curve from PVsyst, using this documentation
However, I'm not sure what this sentence means:

This production is penalized by an ohmic loss$^1$ of the internal components (transformer and transistors), which increases quadratically$^2$ with power  (like R · I²)$^3$. *

What is meant by ohmic loss in this instance?
When it mentions that it increases quadratically, does it mean in quadratic form (equation) i.e. $ax^2 + bx + c = 0$ and how does this relate to the efficiency curve of an inverter, relative to power loss?
What does the equation represent, and what does it suggest when either parameter $R$ or $I^2$ is greater than the other?


texts: Determining the microstructure of steel after welding in modern computer software

texts:
How can the microstructure of steel after welding be determined in modern computer software?

I am aware that there are 'classic' methods of predicting microstructures like Schaeffler, DeLong or WRC constitutional diagrams. What I am wondering about is:  which algorithms are used in programs based on finite element method (FEM) computing (i.e. ESI Group software, particularly SYSWELD)

What I want to find out in particular:

1. How does a FEM model made of austenite differ from the one that is made of ferrite?

2. Is a FEM model enough to determine the microstructure of a material, that is represented by that model? If not, what else do you need to examine transformations of microstructure during the welding process?


texts: Ansys Fluent: how to change the temperature digit precision in writing to file XY-plot?

texts:
I want to write to file data from XY-Plot with temperature depending on the location. In Axis menu I set a max precision (9) for X and Y. However, Fluent writes data like this

293.094 0.000364067
293.094 0.000361604
293.094 0.000359141
293.095 0.000356678
293.095 0.000354215
293.096 0.000351752
293.096 0.000349289
293.096 0.000346826
...

I need a data about temperature as precise as possible (cause I want to use it in another program) but Fluent writes to xy-file only 3 digits after the decimal point despite my settings (for example, 293.194 instead of 293.093621..). I set precision this way for a many times for another physical quantities (velocity, heat flux at walls etc.), and there was always good precision exporting to in xy-files. But not for temperature.

I tried to google this problem but didn't find any special information for Fluent about this case.

Thanks a lot for any help!


texts: What is the name of this piece in the image attached?

texts: What is the shiny metal piece around the tube in the picture called?


texts:
My strength of materials book provides the following equation to determine the x-component of the normal stress acting on all possible planes of a two dimensional element.

$$
\sigma_{x^{\prime}} = \frac{1}{2}(\sigma_x + \sigma_y ) + \frac{1}{2}(\sigma_x - \sigma_y
)\cos(2\theta) + \tau_{xy}\sin(2\theta)$$

My question is -- in what orientation are the non-primed variables assumed? My instinct is that the initial orientation that the non-primed quantities are given in is irrelevant, only the numerical value of the components matter and the angle from which you measure the new components (primed quantities).

For example, if you are given a 2-D element that is initially inclined at 60 degrees and you have the values of $\sigma_x$, $\sigma_y$, and $\tau_{xy}$ in that orientation and you want to find $\sigma_{x^{\prime}}$ at the 0 degree orientation you would compute the equation above using a value of $\theta = -60$ because you have to measure relative to where you "start".

Is that correct or do I have this completely confused?


texts: a small noiseless motor with accurate RPM control?

texts:
What kind of motor is suitable for the below requirements?

2700 rpm, needs to be accurate, not +- few rpms. I think the best approach is to use a hall effect sensor and adjust current/voltage on the fly? Or a better idea?
Be as noiseless as possible. The noise 12V square fan motors make is perfect.
Torque is not much of an issue as even though it is rotating a 100g load on top of it the load is supported by 4 bearings.

What motor am I looking for?


texts: What kind of electric motors are used to build industrial robot arms?

texts:
I'm fascinated by how robot arm nowadays can combine precision with operating speed (e.g. KIRA by Motorized Precision).

I can imagine building a robot arm with stepper motors would be pretty precise but (from my experiences with stepper motors) wouldn't be able to deliver the speed.

Servo motors (from my experience using them in combination with a raspberry pi) would be a bit faster but not fast enough.

DC Brushed motors are lack position awareness.

I don't have experience with brushless motors but I've mainly seen them being used for drones which is quite a different use case.

So I want to know what kind of motor might in those kinds of industrial robot arms that are able to do the split between speed and precision.


texts: When can the thermal and mechanical energies of a fluid control volume be considered separately?

texts:
For a fixed control volume of a fluid, the conservation of energy equation is typically written as something like
$$\dot{Q} - \dot{W} = \frac{\text{d}}{\text{d}t}\iiint_{CV} \left( \hat{u} + \frac12 V^2 + gz \right) \rho \,\text{d}V + \iint_{CS} \left( \hat{h} + \frac12 V^2 + gz \right) \rho \, \mathbf{V}\cdot\hat{\mathbf{n}} \, \text{d}A.$$
Is there any criteria for which we can reasonably decouple this into separate conservation equations for thermal and mechanical energy? That is, into the form
$$\begin{cases} \dot{Q} = \frac{\text{d}}{\text{d}t}\iiint_{CV} \hat{u} \rho \,\text{d}V + \iint_{CS} \hat{h} \rho \, \mathbf{V}\cdot\hat{\mathbf{n}} \, \text{d}A, \\ -\dot{W} = \frac{\text{d}}{\text{d}t}\iiint_{CV} \left( \frac12 V^2 + gz \right) \rho \,\text{d}V + \iint_{CS} \left( \frac12 V^2 + gz \right) \rho \, \mathbf{V}\cdot\hat{\mathbf{n}} \, \text{d}A. \end{cases}$$
I know that for some common types of analysis the mechanical terms are negligible compared to the thermal and ignored entirely. Does this imply that a separate mechanical energy conservation equation can be posed?
I suspect this depends on the relative magnitude of the viscous dissipation function. Is there some dimensionless number that quantifies this?


texts:
I have a simple wall mount I want to analyze using hand calculations (pure beam bending if possible) that looks like this:

I want to be able to model it as if it was in a state of pure bending with a point load at the very end of the single bar section. The two bar section is fixed to the wall. However, I'm a bit confused with how to treat the "pin" (for lack of a better word) that connects the two sections together. Obviously, it's purpose is to transfer load to the two bars mounted to the wall, but I'm not sure if it would be a poor assumption to assume 50% of the load is transferred to each bar, and that the only force transferred through the pin is a straight downwards force and a moment.

I know it's probably a pretty basic/simple problem, but I was hoping someone could provide some insight on how I could deal with the pin and the two bars using hand calculation. Thanks!


texts:
I have acquired an old loading dock built in 1930 that has toe-bearing rafters in addition to undersized purlins.  As you can imagine, many of the rafters have sagged.  Also, because of the toe-bearing design of the rafter, the building has no eaves.

There are many articles about avoiding toe-bearing design.   But there aren't many articles about remedying the situation in retrospect.   Here is a drawing of the existing situation.   The small white block in the middle of the rafter is a purlin.

So here are some questions and thoughts:

Inexpensive Fix - The articles state that you could use some type of joist hanger to possibly fix the problem, but it's not clear to me at all what type of joist hanger would help me.  This would be a low cost way to fix the issue. I could:

Jack up the sagging rafters
Sister up a new rafter, and
Use a joist hanger to help prevent cracks in the re-entrant corner.

Is there a Simpson Strong-tie (or some other brand) hanger that would help solve this issue?

Medium cost Fix - I would really like eaves, so I was thinking another much more involved approach might be to:

Support the existing rafter with a false wall,
Lower the wall by half a block, and then
Sister up a new rafter that has a proper birdsmouth cut that will allow the rafter to sit on the heel.

The sistered rafter could now extend beyond the wall, giving me an eave.  Here's a picture of what I am thinking about:

Edit:  Ugh, it's not clear from the angle I posted, but the sistered rafter is sitting on it's heel on the lowered block/sill plate.   It's not hanging in the air.

A properly engineered sistered rafter can take the load from the purlin on down, can't it?

Edit:  Based on a comment, here are more details:  The existing rafters are 2x6, 24" centers.   The pitch is 4/12.   Just from visual inspection, the re-entrant corner on the birdsmouth appears to be right around half the thickness of the 2x6, so it seems like it's effectively a 2x3.  I believe the purlin is about 9' from the birdsmouth, but I would need to remeasure that, if it's critical.

Most expensive fix - Replace the entire roof with prefabbed trusses.  Seems like overkill, but that sort of depends on the answers to the questions above.
Better/cheaper/easier ideas?


texts: A way to calculate the magnitude of the moment

texts:
In my engineering textbook, I didnt understand the example given to explain the magnitude of the moment. It asks to calculate the magnitude of the moment about the base point O of the 600-N force in five different ways. Now, I dont understand the third way it calculated the moment. What I don't understand is why d(1) = 4 + 2 tan(40) and so the moment is 460(d(1)).

It used the principle of transmissibliity to move the vector force to point B and so we dont need one of the component as it is parallel with the distance. And to calculate the distance we have 4 + 2 tan(40). I understand upto 4 but I dont understand why we add 2tan(40). How is 2 vectored with tan(40)?

Use picture I have uploaded.


texts: How land clearing would be done in this theoretical situation?

texts:
Given the following fictious scenario:

A construction project requires that a big swampy landscape has to be cleared. This swamp landscape has various trees (also trees with a big diameter), a wet region that is a swamp, a lake and some rocks. A construction company has to clear all that things to build a theme park with big coasters and roads on this. Now I am interested in how this company would do this in a cost-saving and also fast way. How costs can be minimized without being too slow?

My idea:

Tree felling with chainsaw and then stump removal with excavator or pure removal of trees with excavators and/or bulldozers. The second version (version without felling trees before) is faster, but may require stronger machines (more costs?)
Rocks can be removed by excavators if rocks are small. Larger rocks must be blasted.
Excavators begin to dig holes around the swamp and the lake.
Now water can be removed from the lake and the swamp by a pipe inserted between the wet region and the holes.
The land must be made flat by bulldozers.

Is this procedure plausible in this fictious (it is not real) scenario?


texts: How to calculate the resulting temperature for a stream of air through a hot tube?

texts:
Given the temperature $T_1$ and volume flow rate $\dot{V}$ at the start of the tube, which has a temperature of $T_0$ and an inner surface of $A_0$, what is the resulting temperature of the stream going out of the tube? ($T_2$).

I assumed that the temperature $T_0$ is fixed, and the material is aluminium and the flow is laminar. Maybe i have to assume more?

I think it boils down to finding the heat transfer coefficient between the copper and the air stream - but this depends on the temperature difference, which changes as the air is heated up.

Here a small sketch of my problem:


texts: Can air-powered diaphragm pumps pump out the effluent at a higher pressure than inputed?

texts: I am working on an acid filtration system and I need to be able to pressurize the effluent from the diaphragm pump such that the acid can be forced through a filter. I am not quite sure if a diaphragm pump can pressurize the influent and also be able to adjust the pressure. Can they do this? Or is there another pump that I should look for?


texts: I have been doing research on renewable energy systems and I must admit that I am a newbie in this specific area. I have noticed that stand-alone systems have their own specific monitoring system available on the market. I just wonder what functionalities and/or features would be added to these separate monitoring systems if I decided to build my own hybrid system. It's going to be like a common off-grid wind-solar system with a battery bank as backup power source.


texts: How to calculate the mid-span lifting capability of a single-beam wooden gantry crane?

texts: The explanations already submitted (ex: "How to calculate deflection of a simple beam with a load in the center") didn't help me much. I'm building a single beam gantry crane out of Doug Fir and need to know how to calculate the needed dimensions for the beam itself; not just the answer. I see all kinds of wood beam calculators on line but they all ask about the beam spacing of the floor joists, or the rafters or the roof trusses which is irrelevant in my case. I must not be using any of these calculators correctly because I can't get these to show a single-beam calculation. Anyone know how to calculate this long-hand or is there a table available somewhere? I know it can be done because I've lifted many a diesel truck engine block with a quality straight-grained 4 x 10 x 8 foot long Doug Fir beam using block and tackle with nary a problem. The application for what I'd like to calculate and eventually build "Norm Abrams" style is 3000 lbs with perhaps a 10% safety factor. Again I just want to know HOW to calculate the mid-span single-beam lifting capacity based on Wood species, cross dimension, and beam-span. I gotta believe this is much easier than I'm trying to make it. Your thoughts?


texts: This may be a silly question, but I'm not a mechanical engineering. What's the best way to calculate the energy required to reduce the pressure of a gas stream below atmospheric pressure? Obviously you could work out the energy for isentropic expansion and apply an efficiency factor, but this seems like it may be inaccurate. I know my stream's mass flow rate, temperature and desired final pressure.


texts: Air flowrate required for testing a pneumatic cylinder?

texts:
First time designing with pneumatics here. I want to build a continuous use device (with ~30 back and forth actuation per minute)  but do not currently have access to a large compressor.

Is there a way to manually test my device as I build it, and then use a real compressor later?   I calculated that my device (a simple cylinder that lifts a 500g mass) will use 5 cubic feet of air per minute (cfm).  I will need a compressor capable of 15 cfm and cannot afford this cost at the moment (need to invest it on other things).

I am guessing the pressures I will be working with are around 90 psi, but maybe up to 120 or 180 depending on the cylinder I use.

Is there a way I can rig something up with say a bicycle pump?  Surely someone has been in this situation of wanting to engineer/prototype without a big compressor available. There's math and calculations of course, but I am more of a hands-on engineer.

Thanks for suggestions.


texts: Should we protect our AC's outdoor unit from sunlight?Does it increases the durability of an AC and its refrigerant if it is well shaded?

texts:
My AC outdoor unit gets direct sunlight (no shading whatsoever) from morning to noon. Temperature normally soars up to 40 degree Celsius (I am from India). I have two questions:

Is this bad for the AC's refrigerant, does it lose efficiency over time?
Does an AC compressor located in full sun work harder than one located in the shade?


texts:
Hi Guys wanted some help for breaking down a block diagram which can be seen below. I know that typically with feedback systems be it negative or positive you would employ using the following:-
Close Loop = $C.L.T = \frac{open loop} {closed loop}$
However the signal $q_{i-1}$ is confusing me typically without it, the closed loop would be
$\frac{q_i}{d_r,i} = \frac{PDG_i(s)}{1-PDG_{i}(s)}$ as a result of positive feedback I'm not sure how to treat that $q_{i-1}$ signal in the system can anyone help help derive the transfer function.


texts: Designing a Chilled Process Water System for Small Plant

texts:
I am designing a new, closed loop,chilled water system for our small injection molding outfit and can use some help where to begin. Here are some of my knowns:

Northeast NJ, USA, no air conditioning.

4 hydraulic machines( 2x250ton, 1x310ton, 1x400 ton), total HP, 210hp

4 molds, ~1 ton per mold

material is HDPE

I have 2 existing, relatively new, air cooled chillers, a 4 ton unit, and a variable speed 10 ton unit.

The 4 machines are located in a square, total piping for a loop to all would be ~ 250',  25' up in the air, would need 3 machine "drops"

My oil heat exchangers will have water savers @ ~ 105*F
My molds should be ~ 55-65*F

I would like a central system, say a 500 gal. tank or so, cooled with my existing chillers and pumped through the loop to each machine, returned to my tank. Capability of adding say 2 more machines @ another 10hp + another 2 molds @ 1 ton each would be nice so lets say, 40 ton in an non-central setup.

I do not want a cooling tower

How should I go about calculating my circulating pipe/pump sizes? My 2 chillers have their own pumps
In a non-central setup, I don't have enough chiller for my requirements ( 14 tons < 25 tons) Will 14 tons be enough in a central setup with 500 gal of water? If not, how do I calculate how much of a chiller i'd still need?
My TO PROCESS goal for water temp. is ~60*F

Any guidance in any direction is appreciated


texts: What is the difference between FEA and CFD?

texts: Many of us think FEA is used for structural problems and CFD is used for fluid dynamics problems. But I have read that the above statement is wrong. So please explain the exact usage of those two.Also please give the basic difference  between them.


texts: Is this Proportional Electro-pneumatic valve a direct replacement for other valves listed?

texts:
In the midst of trying to redesign the pneumatic subsystem of a combined system, I'm at the point of validating a new valve would serve as a direct replacement. The reason for the redesign is an inconsistency of operation over many cycles. The delay between the shifting of the solenoid and the pressurization of the Retract side of the Cylinder is inconsistent, causing errors throughout the rest of the system. The goal with the redesign is to return the system to a closer approximation of the original configuration (shorting piping), while using modern valve technology to retain remote control.

Current Pneumatic Circuit:
The system pressure is 90-110 psi, then Filter, Regulated to 60-80 psi, and Lubricated.

An interest in operator safety moved flow control valves outside of machine guarding at a midpoint in the life of the machine, though there isn't documentation available demonstrating that artificial volume increase in the cylinder. This added roughly 236 inches of 3/4 piping to the system.

For pneumatic reasons, the flow controls have been installed to allow free flow to the cylinder from the source, but metered flow from the cylinder to the exhaust.

The Flow coefficient of the flow control valve is 8.3.
The Proportional Electro-pneumatic valve supports pressure control of the (A) port, aligned to the retract side of the pneumatic cylinder. The maximum effective area of the valve is 52 mm^2, with a flow coefficient of 2.9

Issues investigated beyond the valves:
Lubrication is regularly checked throughout operation.
The cylinder is new and properly configured
Header pressure doesn't vary
regulated pressure doesn't vary.
The solenoid is in good working order.
There isn't an issue with the electronic control circuitry.


texts:
First of all, excuse my little knowledge, I'm a computer programmer by trade and unfortunately have very little knowledge of physics, engineering, DSP but I'm willing to learn.

I would like to measure the quality of a road surface when riding on it on a skateboard. Basically I'd be interested in the smoothness of the road. For "smoother" roads, there should be little vibration, for less smooth roads there should be more.

Ideas I had so far is strapping the TI SensorTag 2 (CC2650) to the skateboard and recording the accelerometer graph during a ride and then taking those frequencies (fourier transform). Unfortunately, the maximum sampling frequency I can get from the SensorTag seems to be 10 Hz which seems way too little. My uninformed back of the envelope calculation is that I kind of need to detect 1cm large "potholes" and that I'm going about 10 km/h. So the frequency I need detect needs to be at least 277 Hz (10 km/h / 1 cm). Also I believe to derive the "degree of vibration" from that I need the velocity that I'm traveling. The question is where I'd get that from... Sure, I could integrate the acceleration data but that seems like it'd be quite imprecise. Also I could use the GPS on my phone for that but that seems rather imprecise too.

A friend of mine proposed a potentially simpler approach of recording the sounds the wheels create while riding. And then derive the degree of vibration from that. But I'd also need the travel velocity for that, right?

Does this make any sense? And if yes, what could be a good approach?

Many thanks!


texts:
A common practice in naval research is to construct brass models of ships to study the reflectivity of a vessel. This can (supposedly) be used to understand the way it reacts to radar and the way antennas on the ship might be affected by the ship.

This seems strange to me though because the wavelength of radar usually has an intimate relationship with the dimensions of the object being sensed. For example, if you have a radar with a 2 foot wavelength, it will not even see a 1 foot model model at all. So, how could a brass model possibly be of use? It would not seem to scale.


texts: What is the opposite of flaring a tube (pinching?) and is there a tool to do this with aluminum?

texts:
I'd like to make my own structure that will hold roughly 50-100lbs of equipment. Since I need this to be portable, I feel like aluminum tubing would be the most practical.

My structure will basically be a 2.5'-10' cube. I want to get 2.5' tube sections that I can connect very sleekly (word?) and make a cube that is 2.5' at its smallerst and 10' at its largest.

Taking a cue from a photography backdrop, they have 1" diameter tubing that sort of fits into itself. The tube is not flared, but it's pinched so it's the same size as the inner diameter.

Is there a name for this "pinch" I'm talking about? And if so, is there a tool I can buy to do this?


texts: Auxiliary engines on cargo vessels, what types are used for what purpose?

texts:
On large cargo ships (dry bulk carriers, or tankers) there are main and auxiliary engines.  Auxiliary engines can be internal or external combustion (generators vs boilers) and generate electricity to power the ship's equipment (cargo pumps, cargo cranes and all other machinery).

I have read that tankers can have pumps that are powered by the main engine.

I have a number of questions about the engine usage related to powering equipment:

Generally do ships have either boiler(s) or generator(s) as auxiliary engines, or could they have both for different purposes?
Do newer ships more commonly use generators instead of boilers?
Are larger equipment (cranes or cargo pumps) powered by the auxiliary engines or is it common to have these powered by the main engine?


texts: Choosing the best type of portable cord for a consumer electronics product

texts:
Consumer-level electrical portable cords come in a variety of types (and gauge, but that's not the subject here) and each must have its rationale, considering the cost constraint (performance/price sweet spot) and environmental use cases (exposure to water/oil/others liquids, abrasion, visibility, temperature...).

I have a hard time finding out a good reference (the most appropriate wikipedia page is poor on pointers) on how these standard cord types came to be, and how a product designer would choose a particular cable type over another.

Typical examples:

SVT/SJT cables are used for computer power cords;
HPN cables are used in North America on kettles and toasters;
I've seen electric irons with cotton-braided cables, I'd expect them to have  constraints as kettle cables, plus mobility;
lawn mower cords are typically SJTW with flashy colors (not green...);
extreme temperature car block heater cables are STOW, it seems that rubber starts to go hard at -40°C
household vacuum cleaner cords are often SV (and often at the gauge limit but are pretty long and tend to be used for a few minutes only...) while garage vacuums are using SJTW (also with bigger gauge in my experience);
SJOOW seem to be used in construction


texts: What is the purpose of a vacuum cleaner's bypass valve?

texts:
I took apart a cheap domestic vacuum cleaner because I am making a small vacuum-forming system, and I only need the motor/fan assembly, so I repackaged it to save space.

Inside the vacuum cleaner is a valve, which I gather is called a bypass valve and is present on most/all vacuum cleaners.  In this case it's just a circular plate held against a gasket by a spring:

Based on my measurements, this valve will open and let air through if the pressure difference across the opening is greater than about 10 or 11 kPa.  It sits inside the machine where the user can't get to it, between the fan intake and the outside atmosphere.  In my hacked mini-vacuum, the gasket is on the outside of the box, where I can block it if I want to.

My question is, what is the point of this valve?  For my purposes, the more vacuum I can get, the better.  But I don't want to block the valve if it would permanently damage / set fire to the motor.

(it's a 700W 240V AC motor, and for vacuum forming I will be running it for 1 or 2 minutes at a time).


texts:
Lavoisier's principle of mass conservation states that the mass of a system must remain constant over time. But, as far as I know, there's no similar principle for density.

So, is it possible to develop an alloy as dense as gold but made of constituents less dense than gold?


texts: Designing a PID Controller for Satellite Control

texts:
As an Aerospace Engineering Student, I have been trying to make a project of a PID Controller to control the attitude response of a satellite using the parameters from a project called Kufasat.

The parameters are described below (moments of inertia, mass, initial angular velocity, etc):

Attitude Kinematics equations are also below:

The idea is to design a PID controller to stabilize the angular motion of the satellite, reducing it to zero values. I have been trying to create some models in Matlab to insert the PID parameters, but all I got is divergences only. I feel like my model is unstable, or that I have been missing something here.

I have also tried to use the Aerospace Toolbox, but got no success at all. I also do not know if this toolbox would help me with this problem.
Furthermore, I have been thinking of State Space Formulation, but I have no idea of how I would organize all these variables in order to formulate the four matrices (A, B C and D), to make me able to apply a PID Control technique.

It is clear that I am lost, and I am even willing to pay someone to help me, as my advisor professor do not have enough time to help me build this.

Please, someone help me. I am desperate and need to finish this by the end of July.

Thank you so much.

Edit1:

Also, I have written a code in Matlab with all the calculations:

clear all

omega = [0.06 0.03 0.09];
I = [0.0547 0.0519 0.0574];
Kp = 0.008;
Kd = 0.08;
Ki = 10^-6;
phi_EAngle = [70; 40; 50]

Theta(1) = phi_EAngle(1)
Theta(2) = phi_EAngle(2)
Theta(3) = phi_EAngle(3)

R1 = [1 0 0; 0 cosd(Theta(1)) sind(Theta(1));0 -sind(Theta(1)) cosd(Theta(1))];
R2 = [cosd(Theta(2)) 0 -sind(Theta(2));0 1 0;sind(Theta(2)) 0 cosd(Theta(2))];
R3 = [cosd(Theta(3)) sind(Theta(3)) 0; -sind(Theta(3)) cosd(Theta(3)) 0;0 0 1];

R = R3*R2*R1

phi = acos((1/2)*(trace(R)-1))
a_x = (1/(2*sin(phi)))*(R'-R)

a(1) = a_x(3,2);
a(2) = a_x(1,3);
a(3) = a_x(2,1);
a = a'

q = a*sin(phi/2);
q_x = q'*q
q(4) = cos(phi/2)

phi_p = a'*omega';
a_p = 1/2*(a_x-cot((phi/2)*a_x*a_x))*omega'


texts: How much weight can a cardboard of size $n \times m$ hold?

texts:
I am interested in knowing how much weight a piece of cardboard can hold in proportion to it's size.
Suppose we have independent variables $x$ and $y$ corresponding to length and width and that these two vectors are in $\mathbb{R}^2$. Then I think (could be wrong) the formula would be
$$f(x,y) = \lambda_1 x + \lambda_2 y $$ where $\lambda_1 = \lambda_2$ if the piece of cardboard has square dimension.
However I am kind of stuck from here because I don't know how to get the $\lambda$ scalars to complete the formula. I tried looking online and there doesn't appear to be a general formula (surprised because cardboard is so common in our lives). Does anyone have any insight into figuring out this problem?
edit: the weight is assumed to be evenly distributed


texts: Normalizing the compressive stress to a cylinder

texts:
I'm not an engineer but a neuroscientist.

I do research in spinal cord injury whereby a clip is used to clamp the spinal cord to induce a bilateral compression injury model.

My research looks at the differences in the injuries to the neck and lower back spinal cord. The key problem here is that the neck spinal cord is wider in diameter than the lower back cord.

Our clip is 1 mm in width. So my question is, if a 35 gram clip is used to clamp a cord of a smaller diameter, and we wanted to hold the distribution of force equal in a larger cord, would the force increase or decrease?

My logic says that the force must be increased, but when we do a 35 gram injury to the neck cord, all of the animals die so it may be difficult to use force normalization in our particular case.

Thanks!


texts: How to calculate the maximum starting traction force for a train with multiple carriages?

texts:
Suppose I have a convoy composed of the following elements:

A locomotive with 4 driven wheelsets (2 wheels per wheelset and therefore 8 wheels).

$n$ carriages with 2 wheelsets each.

Assuming the weight is uniformly distributed on the wheels, from my understanding the maximum force that can be applied by the locomotive avoiding wheels slipping is given by:

$$F_{max} = m_{locomotive} g \mu$$

Where $\mu$ is the adhesion coefficient.

The point is that I'm not sure if I should consider also the passenger carriers and if not, then why. I think I should not consider them since the force that prevents the locomotive's wheels from slipping is just its own weight.

Furthermore, what if the locomotive had only 6 driven wheels out of the 8? Would that change anything?

In that case I think I should multiply the $F_{max}$ obtained by 6/8 am I correct?


texts: I have set of random points in the workspace as shown in the figure. I want to automatically dimension those points (Linear dimension only) in the best possible way by using any programming language as shown in the right image (for example). Is there any better algorithm for doing it?


texts: How deep do you have to check for problems underneath a building site?

texts:
When you're putting up a new building, you have to check the soil underneath for stability. How deep do you typically have to check? What's the extent of your "due diligence" when ensuring that a building won't collapse because of unstable ground? I imagine there might be different rules in different jurisdictions, but is there a typical, ballpark depth?

(Relatedly: Has a building ever collapsed because of unstable conditions below the checked area?)

I'm a total newbie, and I apologize for the many flaws you will be able to spot in this question.


texts:
Considering how bad rubber tires is for environment (Microplastic on tyre - NatGeo),

Today tires consist of about 19 percent natural rubber and 24 percent synthetic rubber, which is a plastic polymer. The rest is made up of metal and other compounds. Producing tires still has monumental environmental impacts, ranging from continued deforestation to the climate-harming fossil fuels used to make synthetic rubbers to the assembly process. Modern car tires require about 7 gallons of oil to make, while truck tires take 22 gallons
A 2013 report by Tire Steward Manitoba, in Canada, found that
passenger light truck tires lost nearly 2.5 pounds of rubber during
their service life (average of 6.33 years). The Kohl study found that
Americans produce the most tire wear per capita and estimates that,
overall, tires in the U.S. alone produce about 1.8 million tons of
microplastics each year.
Exactly how much of that waste ends up in waterways depends on many
factors, says Sousa, ranging from where the road is located to the
weather; rain, for example, can cause more particles to flow into the
environment. Research into the topic is relatively new, he notes, so
estimates will improve as more work is done. But with millions of
vehicles traveling the streets every day, he says, “you start to have
a grim idea about the amount of tire (particles) released.”

How far have we developed eco-friendly tyres alternatives?
Would metal mesh like what NASA have on their rover (nitinol tyre) would be answer to this?

Considering it's airless, strong, and lightweight characteristic, while still fully recycleable in a closed loop
The only downside is the cost. But might could be replaced with steel-variant mesh
Not sure about comfortability & high speed noise & vibration though
What do you think?


texts: Quantifying the amount of structural/hysteretic vibrational damping that occurs in proportion to deformation? (ie. Based on how "bent" something is?)

texts:
Three different conceptual types of vibrational damping forces are described here:

Viscous: $f(t) = -c \cdot v$
Coulomb: $f(t) = -c \cdot \text{sgn}(v)$
Structural: $f(t) = -c \cdot |x| \cdot \text{sgn}(v)$

$c$ is a damping coefficient, $v$ is velocity, and $x$ is a measure of the deformity of the object studied.
In other words, viscous damping force is proportional to velocity. Coulomb force represents friction, modeled as being velocity independent once motion is initiated. Structural represents greater damping at greater amounts of deformity.
The authors use the following passage to describe the nature of structural damping:

Structural damping may be viewed as a sliding friction mechanism between molecular layers in a material, in which the friction force is proportional to the deformation or displacement from some quiescent or rest position. Imagine a  rod made of a bundle of axial fibers. The sliding friction force between each fiber and its neighbor will increase as the rod is bent and the fibers are pinched together. This pinching phenomenon occurs in most materials as the various molecular layers slide past one another. The result is a damping force that is proportional to the displacement from the undisturbed position. This mechanism was verified for a wide range of materials by Kimball and Lovell in 1927.

If you were looking at the internal damping applied to a point on a vibrating string, the degree of point structural deformity could be determined by some derivative of the transverse displacement ($y$) with respect to length ($x$). Eg. $y_{xx}$ or perhaps a higher derivative like $y_{xxxx}$.
I believe one would likely expect the structural damping to increase considerably the more the deformation increases (eg. as $y_{xx}$ increases). I don't think there would be a linear relationship between bend and structural damping but rather a nonlinear one.
The article I linked was from 1975.
Are there any theories or concepts that would describe further the relationship between deformation and damping force in this scenario or quantify the relationship between them?
Thanks.


texts: how to obtain solution of this bessel equation using Frobenius method

texts:
Given this equation:
$$
\frac{1}{r}\frac{d}{dr}\bigg(r \frac{dT}{dr} \bigg) - \bigg(\frac{2h}{bk} \bigg)(T-T_a) = 0
$$
I can let $x=r\sqrt{(2h/bk)}$ and $z=T-T_a$ to obtain the bessel equation using the appropriate substitutions
$$
x^2 \frac{d^2z}{dx^2} + x \frac{dz}{dx} - x^2z = 0
$$
To express the solution for $z$, I read that one technique is to use the Frobenius method, but I am not sure how to apply this to be Bessel function above... Any help ?


texts:
What kind of positioning holding Hinges do Laptops & Notebook Computers use?

Is there a set of Mech/ Engineering terms for hinges similar to these and are there a category of them that I can study/ look into?


texts: For arc-length method in nastran, how to analyse post-buckling behaviour with load decrease

texts:
I am currently trying to model the buckling behaviour of a cylinder using sol 400 nonlinear static analysis using Nastran. I am using the arc-length (modified Riks) method as apparently it can increment load and displacement in both positive and negative directions, as opposed to Newtons method which only increases the load or displacement increment. However, my problem is that the analysis always stops after a certain load due to convergence problems.

I have tried changing many of the parameters such as MINALR/MAXALR ( min/max arc-length ratio between increments) and MXINC(max increments), however I still don't get any good results.

I feel like I am missing a parameter that enables the load to decrease after a maximum load has been reached.

I am aware that load control and displacement control is possible, but my understanding is that arc-length method uses neither of these, and is sort of a combination of the two. My model has a force applied without any enforced displacement. Is this maybe the problem?

Any other ideas which might help me?

Thanks in advance.


texts:
Given:

A pump system is defined with dynamic head of 46 feet.
The height between the static pressure gauge and the surface of the water is 9
feet.

Assumptions:

Friction losses between the tank and pump are approximately 0.

Hint:

The pressure gauge is capable of sensing static head, but not velocity head.

Find:

The velocity of the water through the pipe.

Work:
Use Bernoulli's equation, solve for V2.
$\dfrac{P_1 * g_c}{\rho g} + \dfrac{v_1^2}{2 g} + Z_1 = \dfrac{P_2 * g_c}{\rho g} + \dfrac{v_2^2}{2 g} + Z_2 + H_A$
Rearrange to solve for V2.
$v_2 = [(\dfrac{(P1 - P2)g_c}{\rho g} + Z_1 - Z_2 - H_A)2 g]^{1/2}$
Point 1 is defined at surface of water...
$ v_1(@P_1) = 0 ft/sec, Z_1(@P_1) = 9 ft, P_1(@P_1) = 0 PSIG.$
Point 2 is defined at static pressure gauge...
$ P_2(@P_2) = 23 PSIG, Z_2(@P_2) = 0 ft.$
$v_2 = [(\dfrac{(P1 - P2)g_c}{\rho g} + Z_1 - H_A)2 g]^{1/2}$
Should the dynamic head $H_A$ be added or subtracted here?


texts: Why aren't nuclear reactors designed to handle the loss of the heat sink?

texts: I always wonder why nuclear power plants aren't designed to handle a loss of the heat sink. At the point at which hydrogen is being made from the water, can't you just remove the water and catch the molten corium into a concrete container until it cools off?


texts: How does a microfluidic lipid nanoprecipitate mixer for mRNA vaccine production look like and operate?

texts:
Apparently, in the production of mRNA vaccines the microfluidic components play a major part in encapsulating the mRNA in a stable lipid coat (the technical term is likely not 'coat'). This step is also apparently a bottleneck in vaccine production (FWIW I still think patents should be waved to ease global vaccine production, though other things are needed as well). I wanted to ask how microfluidic devices used here are built, but with a short google I didnt even find out how one looks like - So I ask about that:
How does the device look like? How is the basic function? How large or small is the mixer in a n industrial application? I've seen picutres where reaction chambers, mostly stainless steel blocks with the chamber milled inside, where assembled lego-like on a board and fitted together with a vise or similar - this appears to be appropriate for lab work, but maybe the same systems are used for production?
So, I hope that someone here has either better google foo than me or works in the industry and can share some knowledge - there's a huge area between trade secrets and the trivially googleable, usually hidden in trade press and catalogs, that is available to someone with experience in the relevant industry.


texts: What's the point of draft in sand casting

texts:
I know what pattern draft is and it's usefulness in removing castings from rigid moulds. That's the definition you can find anywhere.

My problem is when you sand cast. Sand casting is the most common amateur metal casting technique, with lots of YouTube examples. Yet all the decent examples have a draft incorporated. Since you destroy the sand mould when extracting the casting, I can't see any benefit from a draft. It just adds an unnecessary level of complexity when designing and making the pattern. Any shape could be successfully removed, so what's the point of pattern draft in sand casting?


texts:
I'm trying to measure the rotational speed of a turbocharger, but the laser tachometer I have can only measure up to 99,999 RPM and it isn't enough (display starts to output letters) and devices that can measure higher than that are quite expensive. I have seen Arduino based tachometers that use a photodiode coupled with a laser but it seems to require the beam to be broken, something that can't be done with the turbocharger. Is there any other option to measure its rotational speed, even it is less accurate?

It's for a small project so buying a $200 tachometer isn't justifiable.


texts: Measure stress of gas acting on a spherical container

texts:
How can I measure stress in a thin- walled sphere containing a gas? Is there a way to predict what the stress will be without actually needing to fill a sphere with gas? I am talking about hoop stress/longitudinal stress.

The thickness of the walls of the container is unknown at this point; I know the radius and the material (EVOH); the internal pressure will be 10 atm. The question then is how will I know how much stress is too much for the material to handle? Would it be the material's yield stress value? Once that is found, how will I know how much of a safety factor is acceptable?


texts: How to calculate frequency response of the system? and find missing values

texts:
I can convert the H(s) into the frequency response which is:
() = (/(1+ ))
and the output in the steady state is:
() = |(2)|sin(2 + ⟨(2))
The phase: ⟨(2), has to equal /4, but how do I find  and ?


texts:
Background:
The CS bolts are available with Black Oxide coating. I have read that the coating is applied using hot dipping and cold dipping methods. Also that hot dipped coating is more durable than cold dipped one.
Problem:
How to check if a given bolt is hot dipped or cold dipped. I am looking for a crude method that  does not involve any lab test, but for on spot check.


texts:
Apologies if this is the wrong place to pose this question, or if it is poorly formulated, I would appreciate any help, even if that is pointing me to a place where I can learn more about solving problems like this.
I'm trying to work out what is going on in the following assembly of magnets (neodymium) and magnetic materials (probably steel) / non magnetic materials (probably plastic).

The assembly contains three rows, which are free to move horizontally,  but constrained on the other axes. And, each row can move independently of the others.
What I would like to do is make a computer model of this system, and just play around with the parameters to get a feel for what happens with different numbers of magnets, different arrangements of the steel pieces, etc.
So my question is how would I compute the net magneto motive force acting on each component in this assembly?


texts: Can mercury escape undectectably from a CFL bulb? or does it have to shatter for the mercury to be liberated?

texts:
I read that the mercury vapour inside a fluorescent lamp is pressurized at 0.2% of atmospheric pressure.

Can mercury escape undectably through a small crack in the glass yet still light up? Or will the pressure difference cause it to explode and/or stop working?


texts:
My problem is a bridge with a horizontal cord of span 12 m between two piers of arbitrary height. It is required to use a pin-connected truss, consisting of steel members bolted together to steel gusset plates. Assume the end supports at the piers to be a pin and a roller.

A vertical loading of a concentrated force $F$ [19.5 kN] acting 4 m from the left-hand support, and linearly distributed load $q$ [1250 N/m] acting on the central 6 m of the span. This load can be applied in part to several joints on the top cord within the given region.

The force of the wind and the weight of all members are to be neglected.

Assume the maximum tensile force in each member cannot exceed 4.25 kN, and the maximum compressive force cannot exceed 3.5 kN regardless of the length of the member.

I knew that I can reduce the concentrated force by adding a pin on that force and join the pin to multiple members, but doing that leaves me with too much unknowns.

And also, am I able to reduce the 19.5k N load by replacing the single pin, where the load acts and adding two pins between the load so the load will be 9.75 kN in each pin? This approach is used

There is no restriction about how the bridge should look like, but I designed mine so to have in each member tension not more then 4.25KN and compression less than 3.5 KN.


texts: How to calculate residual strength of a corroded structure from their stress values?

texts:
Currently, I have an actual entire corroded bridge model in the FEM analysis in Abaqus
I want to estimate the residual strength of this bridge due to corrosion
from the output results in the Abaqus, I can have stress and strain values

but I was wondering how to calculate the residual strength of this corroded bridge,? is there any possibility to derive an equation to estimate the residual strength of this bridge using the results from Abaqus model?

thank you very much in advance


texts: Is it a problem to have two heat sources controlled for different temperatures on the same heating circuit?

texts:
This is the situation - I have three heat sources, called CHP, burner 1 and burner 2 on the same circuit. All three feed to the same heating manifold, with various heat demands.

Preferably I want to heat with the CHP; if that is not sufficient, additionally with burner 1; and only use burner 2 if that is still insufficient. The CHP is always running and not controlled for temperature.

The reason for this scheme is that the CHP burns (free) sewage gas and earns money (electricity), burner 1 burns sewage gas and burner 2 uses (expensive) natural gas. Burner 2 is installed in case all other heat providers fail or the sewage gas runs out.

Here's my idea for a control scheme, where the actual temperatures are more examples than set in stone:

In normal operation, the return flow is 75 °C or higher
If return temp. < 73 °C, burner 1 is activated and heat controlled to 73 °C return
If return temp. < 71 °C, burner 2 is activated and heat controlled to 71 °C return

In the last case, burner 1 should run at nominal power and burner 2 at enough power to raise return temp. to 71 °C.

Will I run into problems with two burners on the same circuit controlling for different temperatures?


texts: Acoustic transmission through houseboat hulls

texts:
The short version is: should I be worried about bass transmission through water into my neighbors' hulls?

I am renovating a small houseboat (12x30 ft) to live on. It is one large room, and I plan on putting my reasonably large hifi system into it (260W/channel at 8Ω). One side of the boat is glass windows, the other is a plywood wall with an ~8" cavity with studs. The floor is a plywood floor, and the hull is a fiberglass shell with marine ply inside.

I am familiar with audio transmission/reflectance/resonance in, say, an apartment context, which can be roughly modeled as adjacent resonant cavities. How will transmission differ through water? Will I have higher transmission at bass frequencies? The houseboats adjacent to mine have thick concrete hulls (say, 6-12"), so maybe the point is moot and I should be only worried about transmission over the surface of the water, which I know is highly reflective.

tl;dr am I going to pwn my neighbors with bass through the water or should I be more worried about the glass wall and transmission through the 12 ft of air separating the boats? What other factors may contribute that I may be missing?

Thank you for your help.


texts:
I’m trying to learn creep analysis in Ansys, and am currently working on deriving creep constants, specifically C1, C2, and C3 for the Norton Power Law.
I understand that the equation is usually shown in 2 ways:
$$\dot\epsilon = A \sigma^n t^m$$
or
$$\dot\epsilon = A \sigma^n \exp\left(-\dfrac{Q}{RT}\right)$$
Which form does Ansys use? I can’t seem to find an answer in any of the manuals or anywhere online.
For example, I know solid works uses the first form, where $C_1 = A$, $C_2 = n$, and $C_3 = m$.


texts:
I work frequently with materials sensitive to oxygen and moisture, within a glove box. However, there are frequently times I want to move these samples from the glove box to a scanning electron microscope (SEM) or other device without exposing them to air. I can easily use some small module (eg tupperware) which can be sealed manually in the glove box to allow me to safety transfer my samples to another glove box. But, if I want to see it in a SEM or another device, I must have another way to transfer it without exposure. These samples can be very very small, 1 inch in size or less.

I could easily build a small box or module for transferring my samples, and seal that box by hand in the glove box. However, I need a mechanism I can use to unseal the module once it has been placed inside of another device, where it is inaccessible by hand. If I could find a small valve that could be opened automatically, that would be suitable for example.

Can anyone suggest such a mechanism for breaking a sealed environment automatically?