CreationDate stringlengths 23 23 | Body stringlengths 57 10.9k | Tags stringlengths 5 114 | Answer stringlengths 39 16.3k | Id stringlengths 1 5 | Title stringlengths 15 149 |
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2015-03-18T14:52:43.163 | <ol>
<li>Honey dippers are often made of wood. Is there a property of honey that drives this?</li>
<li>Honey dippers are shaped like ovoids with lateral grooves. Is there something about the viscosity of honey that caused this decision? Is this design somehow superior to using a spoon?</li>
</ol>
<p><a href="http://... | |fluid-dynamics|design| | <p>Honey dippers work by using the viscosity of the liquid to raise a small amount of the liquid from a reservoir. Spoons work by trapping the small amount of liquid in a gravity well. Spoons therefore will work even when the liquid has low viscosity. The honey dipper method only works with appreciable amounts of li... | 2131 | What drives the honey dipper design? |
2015-03-18T19:18:08.730 | <p><strong><em>Scenario:</em></strong><br>
Suppose the emergency brake button in the cab of a train is not working. Would the emergency brake cords / buttons in the passenger cars still work?</p>
<p>This question is inspired by <a href="https://scifi.stackexchange.com/q/84144/23802">this question on the SciFi StackExc... | |mechanical-engineering|rail| | <p>I was trained to operate diesel electric locomotives for the Canadian Pacific Railway about 20 years ago. I'm not sure if the technology has been updated, likely not that much. The other posts about how the brakes work are correct. Air is pumped from the locomotives to fill reservoirs on each car to be able to relea... | 2133 | If the emergency brake in a train is broken, do the passenger car brakes still work? |
2015-03-19T18:21:05.420 | <p><a href="http://en.wikipedia.org/wiki/Jewel_bearing" rel="nofollow noreferrer">Jeweled bearings</a> use a metal spindle with a jewel lined pivot hole (pictured below). They have been important in the manufacture of mechanical timepieces since the early 1700's. Their importance lies in the fact that they can be mac... | |mechanical-engineering|friction|bearings| | <p>Compasses. </p>
<p>"The business part of a compass is out of sight. This is a set of tiny magnets glued under the compass card and surrounding the jeweled pivot that supports the center of the card." -The Annapolis Book of Seamanship, by John Rousmaniere</p>
| 2147 | Are jeweled bearings commonly used for applications other than mechanical timepieces? |
2015-03-20T02:28:52.070 | <p>I'm creating a light up dancing pole. This requires a translucent material that is strong enough to support the weight and force of a human being, even when it's hollowed out to so LEDs can go inside. The material must also be reasonably affordable, so something like diamond is out of the question. I figured that <... | |mechanical-engineering|materials| | <p>Given the variables involved and the relatively low cost of polycarbonate tubing, I'd be tempted to just buy a length and test it. Use a fairly chunky dancer to build in a factor of safety.</p>
<p>Polycarbonate isn't brittle and so catastrophic failure is unlikely. However, it scratches easily, which might degr... | 2149 | Can polycarbonate dance pole support the torque of a dancer? |
2015-03-20T14:51:32.553 | <p>One of the places I frequent recently had the curb and sidewalk rebuilt by the city. Previously, there was a roughly continuous transition from the street to the rest of the private drive next to the building. </p>
<p>After the rebuild, the sidewalk was leveled out which created two sloped areas coming from the s... | |civil-engineering|terminology|roadway| | <p><strong>Name</strong></p>
<p>I'm not sure that it has a specific name. It is just, "the way driveways are when there is a sidewalk." </p>
<p><strong>Geometry</strong></p>
<p>Like most things related to roadway design in the US:</p>
<ol>
<li>It has been studied. There is a well named report available called, <a h... | 2157 | Term for double slope from street |
2015-03-21T01:23:41.477 | <p>Magnetic bearings work by levitating a rotating shaft so that it is not in contact with its supports. This greatly reduces the friction of the system.</p>
<p>In all of the literature that I have seen on magnetic bearings, the bearings are described as "low friction" and not "no friction". </p>
<p><a href="https://... | |mechanical-engineering|friction|magnets|tribology| | <p>There are two types of losses in magnetic bearings, windage and electromagnetic losses. Windage or aerodynamic loss is the dissipation of rotational energy due to the viscosity of air or other gases trapped between the rotating and stationary portions of the system. These effects are more significant in high speed a... | 2162 | What causes friction in magnetic bearings? |
2015-03-23T03:59:28.190 | <p>In Ernest Cline's novel <a href="http://en.wikipedia.org/wiki/Ready_Player_One" rel="nofollow noreferrer"><em>Ready Player One</em></a>, the main character lives in the "stacks" - a dystopian vision of what a trailer park may look like in the future. The "stacks" are primarily composed of trailerhouses stacked</p>
... | |civil-engineering|structures| | <blockquote>
<p>Can a typical mobile home support that much weight?</p>
</blockquote>
<p>No, most mobile homes are just flimsy wooden constructions where emphasis is on weight saving. If you want to stack cheap housing blocks I suggest stacking steel old shipping containers. They also come preequipped with anchor po... | 2180 | How high can you stack mobile homes? |
2015-03-23T13:36:47.700 |
<p>It's a movie trope that snipers are spotted because someone catches a glimpse of a reflection of the scope. It seems to me that this is a serious design flaw.</p>
<p>I also know that a good number of scopes have "lids" to protect against dirt, etc., when not in use.</p>
<p>My thought is this: Why is the front-mo... | |optics| | <h3>The lenses which make up the scope will always reflect some light (~0.5%).</h3>
<p>All optical materials will reflect some amount of light. This is due to the fact that light travels slower inside of the medium than it does in the surrounding air. The slowing down of a wave always results in some reflection... | 2184 | Must rifle scopes have revealing reflections? |
2015-03-24T14:14:22.033 | <p>I was wondering, what is the strongest : a rectangle or an arc (same width/height) ? <img src="https://i.stack.imgur.com/4JPEA.png" alt="screenshot"></p>
<p>you have to imagine the screenshot in 3D : you have 4 walls and a paved layer (the rectangle) or a dome</p>
<p>Reason why the <em>rectangle</em> would be stro... | |structural-engineering| | <p>The answer to your question is very simple. </p>
<p>If the arch and the rectangle are made of the same material, and the rectangle height and width are equivalent to the arch rise and span, and they are loaded with the same load in the same place, and the weight of the material is neglected, the rectangle will alwa... | 2204 | Mechanically, is an arc stronger than a rectangle? |
2015-03-24T23:51:19.043 | <p>I am mounting solar panels on top of a recreational vehicle (RV). To reduce drag, I was planning on building a small ramp in front of the panels to deflect wind before it hits the flat panel and mounts. Here is a rough sketch (red is brackets, black is panel, purple is ramp):</p>
<p><img src="https://i.stack.imgur.... | |automotive-engineering|airflow|solar-panel|drag| | <p>The concept of what you're doing is sound, and as Russell McMahon notes the efficiency gains could be significant enough to justify the change.</p>
<p>I'd strongly suggest that you consider adding a ramp to the back edge as well. Drag force is very sensitive to the downstream (rear) end of a body as well You get so... | 2207 | How would adding a wind deflector in front of roof-mounted solar panels affect drag on an RV? |
2015-03-25T16:48:06.667 | <p>I have a PCB of approximately 4" x 4". It has a single long spiraling trace on it. The trace is 50 mil 4 oz copper, so nominally it's good for something like twenty amps before it overheats. But this board overheats much faster. My supposition is that the windings being so close to each other has a compounding effec... | |electrical-engineering|heat-transfer|temperature|power| | <p>Assumptions:</p>
<ul>
<li>The copper side with the traces is modeled as a sheet of copper rather than traces.</li>
<li>The body is thin enough that thermal conductivity within the body is unimportant, and the entire device is considered to be at a uniform temperature.</li>
<li>Only the two broad surfaces contribute... | 2217 | How can I calculate the temperature rise of a circuit board for a given power dissipation and area? |
2015-03-27T04:21:19.403 | <p>Why is it that a second order system with an additional pole or zero can be approximated into the general second order system for analysis?</p>
<p>This was asked during our lecture and I am still looking for the answer.</p>
<p>In my reading I've only learned that when an additional pole or zero is added to the sys... | |control-engineering|control-theory| | <p>I think there must be some other restrictions placed on your professor's comment. Adding a pole to a general second order system makes it a third order system and the dynamics can change dramatically. </p>
<p>One example I can think of in which adding a pole or zero does not change the system dynamics dramaticall... | 2228 | Second order system with additional pole |
2015-03-27T06:25:38.760 | <p>If you look at the design documentation in our projects (Biogas and waste-to-energy plants), you find out what we plan to build but not what other options were considered and why they were discarded. This information rests only in the engineers head. Occasionally, a plant will be in a conceptual stage for years, som... | |design|project-management| | <p>Others have made a lot of good comments about documentation in general, but I want to suggest a particular class of software that will help tremendously.</p>
<p>I find <a href="https://en.wikipedia.org/wiki/Revision_control" rel="nofollow">version control software</a> to be excellent for these sorts of issues. It's... | 2229 | What's a professional way of tracking design history in plant engineering? |
2015-03-29T18:19:15.250 | <p>In order to reduce operational cost and improve the safety and reliability of aircraft's the aerospace industry and government is increasingly evaluating new ideas such structural heath monitoring systems for aircraft's. Such a system will enable continuous monitoring, inspection and detection of damage to the aircr... | |electrical-engineering|aerospace-engineering|sensors| | <ul>
<li>First you need a part that <strong>exceeds its fatigue limit under expected stresses</strong> because you need slow coalescence of cracks occurring uniformly in the measured area, not a local defect which might occur outside the sensor placement and resistant to modelling based on measurements from other piece... | 2240 | Which part of an aircraft can most benefit from a structural health monitoring (SHM) system? |
2015-03-30T06:08:09.233 | <p>This one should be easy to answer by looking at the thermodynamics, but I find it not to be. Say we have a natural gas stream, ~700 Nβm<sup>3</sup>/h, that we want to compress from 16 bar to 250 bar. What will the power consumption of the compressor be?</p>
<p>The thing that stymies me is that the power uptake is n... | |mechanical-engineering|gas|compressors| | <p>Maybe I didn't get the problem it sounds a little bit simple, but as I see you would have to calculate using a PVT correlation (Peng-Robinson for exemple) the power your transformation requires in a ideal system (ΞS=0, the power required for this transformation is path independent) and then you can divide the value ... | 2244 | Typical power consumption of large compressor |
2015-03-31T11:24:20.767 | <p>I had a <a href="http://www.omegaeng.cz/ppt/pptsc_eng.asp?ref=PX26&Nav=preb02" rel="nofollow">PC Mountable Wet/Wet Differential Pressure Sensor</a>
I used it to measure a pressure difference , I don't know how to convert its output to pressure ! </p>
| |electrical-engineering|pressure|sensors| | <p>Well, it looks like your sensor is +/-5psid (based on the link you provided), so looking at the datasheet, we have (assuming a 10VDC excitation) 16.7mV at 1psi and 50mv at 5psi. Assuming the sensor is linear (the datasheet states that linearity is +/-0.25% of full scale), you have the following relationship:</p>
<p... | 2260 | Px26-015 pressure sensors output |
2015-03-31T20:08:01.130 | <p>...or what type of motor is used there?</p>
<p>I found this type of motor - usually powered with low-voltage AC (~12V), but at times with 230V, in several appliances that require very slow rotation and sometimes a fair momentum - a color-shifting lamp, the microwave plate, an ice cream mixer...</p>
<p>The funny pr... | |electrical-engineering| | <p>Had a similar problem with my electrolux microwave turntable rotating when door was opened and stopped when closed. Also while rotating you could force it into the opposite direction. After checking the 3 safety microswitches which were found ok. Have noticed that mains polarity, live and neutral swapped influences ... | 2265 | Why does the microwave plate start in a random direction? |
2015-03-31T20:39:13.563 | <p>What general specifications are there in building a storm shelter in the American Midwest? I believe the major considerations are tornados and severe thunderstorms, as well as flooding along river valleys. </p>
| |structural-engineering| | <p><a href="https://www.fema.gov/" rel="nofollow">FEMA (Federal Emergency Management Agency)</a> publishes some specifications for the design of safe rooms.</p>
<p>Per <a href="https://www.fema.gov/safe-rooms" rel="nofollow">their guidance</a>:</p>
<ul>
<li><a href="https://www.fema.gov/media-library/assets/documents... | 2266 | Building a storm shelter |
2015-04-01T20:22:55.213 | <p>I am trying to figure out what kind of device is being used to stop and start the flow of liquid inside this device. Below is a link to the device. It looks too small to be a solenoid or a pump. How else would they do it?</p>
<p>I heard somewhere it may be a Venturi system but how do you electronically control a Ve... | |electrical-engineering|valves|liquid|actuator| | <p>I'm going to cheat by referencing the patent. ;)</p>
<p>Automatic Bar Controls owns the Wunderbar site and has a patent on the product. The patent is <a href="https://www.google.com/patents/US8925769?dq=8925769&hl=en&sa=X&ei=GZUcVZjgFYGqNteEgdAE&ved=0CB4Q6AEwAA">US008925769</a>. The actual detail dr... | 2280 | What type of liquid flow control could this device use? |
2015-04-03T16:09:37.653 | <p>I know that the rubber on car and truck tires wear, and the road concrete wears out. I wondered:</p>
<p>While steel is hard and elastic, it still causes friction (interaction
between molecules) and therefore abrasion.</p>
<p>Let's say we have on average 20-30 wagons with four axles with a full load of 50-60 tons o... | |civil-engineering|materials|rail|transportation| | <p><em>This is an admittedly North American response.</em></p>
<p><strong>MGT</strong></p>
<p>In the US, how much traffic goes over a given track in a year is measured in Million Gross Tons (MGT) e.g. 1 MGT = 2 000 000 000 lbs [spaces instead of commas to be world-friendly]. This is a measure of the total weight of c... | 2295 | How many train passes can railway tracks endure? |
2015-04-03T17:39:29.163 | <p>A lot of research has been devoted to creating electrical devices that emulate biological sensors, including:</p>
<ul>
<li>Visual: Cameras, color/light intensity sensors</li>
<li>Auditory: Microphones, ultrasonic sensors</li>
<li>Tactile: Pressure sensors, temperature sensors</li>
<li>Balance: Gyroscopes, accele... | |electrical-engineering|sensors| | <p>Odor assessment is usually performed by human sensory analysis using <a href="http://en.wikipedia.org/wiki/Chemoreceptor" rel="nofollow">chemosensors</a>:</p>
<blockquote>
<p>A chemoreceptor, also known as chemosensor, is a sensory receptor that
transduces a chemical signal into an action potential.</p>
</block... | 2297 | Sensors / processing algorithms to emulate a human's sense of smell |
2015-04-03T21:31:26.793 | <p><strong>Given:</strong></p>
<p>My thermodynamics text reads as follows:</p>
<p>In SI units, the force unit is the newton ($N$), and it is defined as the force required to accelerate a mass of $1\cdot kg$ at a rate of $1\cdot\frac{m}{s^2}$. In the English system, the force unit is the pound-force ($lbf$) and is def... | |mechanical-engineering|thermodynamics|international| | <p>Here's how I like to think of it. lbf is the force acting upon the mass. This is what, for example, your bathroom scale is measuring. lbm is the actual mass of the object. So the F =m*a in English units, lbf = lbm * a (aka gravity 32.2 ft/s2).</p>
<p>That's at least how I've always looked at it.</p>
| 2300 | Pound-force (lbf) vs Pound-mass (lbm) |
2015-04-03T23:18:11.360 | <p><strong>Given:</strong></p>
<p>A problem in my thermodynamics text is stated as follows...</p>
<p>Determine the mass and the weight of the air contained in a room whose dimensions are $V=$ $15ft$ x $20ft$ x $20ft$. Assume the density of the air is $\rho=0.0724\cdot\frac{lbm}{ft^3}$.</p>
<p><strong>My Solution:</s... | |mechanical-engineering|thermodynamics|pressure| | <p>A pound force is defined as the force required to accelerate a slug at 1 ft/s^2.
The density of air is $\rho = 0.0724 \ lb_m/ft^3 = 0.0724/32.2 \ slugs/ft^3$</p>
<p>The weight of the air is
$\rho V g = 0.0724/32.2 \ slugs/ft^3 \cdot32.2 ft/s^2\cdot 6000 ft^3 = 0.0724\cdot 6000 \ slugs\ ft/s^2 = 434.4 lb_f$ </p>
| 2302 | Mass and weight of air in a room |
2015-04-03T23:56:48.727 | <p><strong>Given:</strong></p>
<p>The acceleration of high-speed aircraft is sometimes expressed in gβs (in multiples of the standard acceleration of gravity). Determine the upward force, in $N$, that a $70\cdot kg$ man would experience in an aircraft whose acceleration is $6\cdot gβs$.</p>
<p><strong>My Solution:</s... | |aerospace-engineering| | <p>Well, the concept of g force measurement goes by measuring the net acceleration considering all effects. That is assume an object in free fall it will have a 0g acceleration, meaning Force= M(g-a), where a is pseudo acceleration=g. Hence F = M*A = M(g-g), A=The acceleration in g. Therefore, A=0g, which is freefall a... | 2303 | Aircraft force in g's experienced by pilot |
2015-04-04T04:30:51.033 | <p><strong>Given:</strong></p>
<p>A problem in my thermodynamics text reads as follows...</p>
<p>A vacuum gauge connected to a tank reads $5.4\cdot psi$ at a location where the barometric reading $P_{Hg}= 28.5\cdot in$. Determine the absolute pressure in the tank. Take $\rho_{Hg} = 848.4\frac{lbm}{ft^3}$.</p>
<p><st... | |mechanical-engineering|thermodynamics|pressure| | <p>$ \rho = 26.3 \ slugs/ft^3 $</p>
<p>$\rho g = \gamma= 847\ lb_f/ft^3$ "specific weight"</p>
<p>$ ft^3 = (12 in)^3$</p>
<p>$ P = \rho g h = \frac{847 lb_f}{(12 in)^3}\cdot 25.8 in$</p>
<p>The issue is the difference between a lb mass and lb force.</p>
| 2306 | Determine abs pressure in a tank where the atm and vac pressures are given |
2015-04-04T07:24:34.600 | <p><strong>Given:</strong></p>
<p>A problem in my thermodynamics text reads as follows...</p>
<p>The barometer of a mountain hiker reads $13.8$ $psia$ at the beginning of a hiking trip and $12.6$ $psia$ at the end. Neglecting the effect of altitude on local gravitational acceleration, determine the vertical distance ... | |mechanical-engineering|thermodynamics|pressure| | <p>I'm glad we got rid of that obsolete system of obscure units decades ago. The metric system is so much easier.</p>
<p>From the definition of the <a href="https://en.wikipedia.org/wiki/Slug_%28mass%29">Slug</a>, </p>
<p>${1 Slug = 1 {lb}_f.{s}^2/ft}$.</p>
<p>Substituting that into the units you got, the ${slugs}$,... | 2311 | Determine elevation from the difference in air pressure |
2015-04-05T06:48:07.117 | <p>I was recently on the UCLA campus (University of California Los Angeles) and I saw the Bunche Hall. I love the design and the architecture of the building. However I saw a little (what I would call) a closet with no door on the side but it was just three walls with a roof, extremely small, underneath the stairs, out... | |civil-engineering|structural-engineering|building-physics|building-design|architecture| | <p>I do not know, I've never been there and I have no other information other than what is in your question. However, ...</p>
<p>I'd say that best guess, until somebody who knows more presents, is your suggestion of now-unused telephone booths. </p>
<p>On the wall are two plates. These are at the same height in each ... | 2319 | What's the purpose of these small closet-like-rooms-without-a-door? |
2015-04-05T09:58:48.483 | <p>I know that in case of wedge we have a 2D behavior which creates a discontinuity across the shock, but I am unable to understand why this discontinuity is not present in the case of a conical surface. I have a vague idea that the continuity equation ensures this as, due to increase in the flow area, the velocity mus... | |mechanical-engineering|fluid-dynamics|shock| | <p>The answer to this question is complicated since the flow is fundamentally different.</p>
<p>When supersonic flow hits a <strong>wedge</strong> it is abruptly turned by one <em>oblique shock</em>. After this all streamlines are parallel since in this 2D-flow-scenario the geometry/flow-area does not change anymore.</... | 2321 | Explanation of supersonic flow differences between a 2D wedge and a 3D cone |
2015-04-05T11:59:37.073 | <p>What are the construction procedures that allow the mitigation of potential problems due to water in a retaining wall?</p>
<p>To be more specific: I'm talking about reinforced concrete walls.</p>
<p>The cases of water are: if I'm studying a reinforced concrete wall such that the soil is not saturated, and it rains... | |civil-engineering|retaining-wall| | <p><strong>Design</strong></p>
<p>In design, the presence of water behind the wall can have two effects. It can cause additional force to be applied to the wall from hydrostatic pressure, or its presence can cause the soil characteristics to change. </p>
<p>Changing soil properties has the most effect on clayey soils... | 2322 | What are the solutions to water problems in a retaining wall |
2015-04-06T03:33:21.427 | <p>I am trying to come up with a way to restrict beer flow using a valve that does not cause foam. I have found that a solenoid valve causes a change in the direction the beer must flow and this sharp change through a different size opening creates foam quickly. I have thought about a ball valve or pinch valve but I ne... | |mechanical-engineering|electrical-engineering|fluid-mechanics|valves| | <p><a href="http://www.globalspec.com/learnmore/flow_control_flow_transfer/valves/pinch_valves_multiturn" rel="nofollow">Look at pinch valves</a>: A small piece of tubing that can be pinched shut pneumatically or mechanically (solenoid). When open, you have the full diameter of your tubing. The only part that touches t... | 2329 | Does this exist? -Sliding Fluid Restrictor -Solenoid Valve -Ball Valve |
2015-04-06T09:38:22.343 | <p>I'm currently looking around for a new bike and I've noticed lots of load-bearing carbon parts (frames, cranksets, forks etc.) with an interesting finish like this:</p>
<p><img src="https://i.stack.imgur.com/Cj8gy.jpg" alt="Carbon crankset"></p>
<p>and I was wondering <strong>what this type of carbon cloth is call... | |mechanical-engineering|materials| | <p>The forged composite material used by Lamborghini and Calloway (a.k.a. "forged carbon") has a higher modulus and tensile strength than other composite materials like glass fibers and even traditional carbon fiber composites made with twill or satin weaves. The "randomness" of the fiber orientation in the "forged car... | 2333 | Forged carbon fibre finish |
2015-04-06T21:45:19.850 | <p>The ISO 9223 standard indicates that there should be no corrosion at temperatures below 0 degrees celsius. Independent researchers have however proposed to lower the minimun temperature stated in the standard to lower values in order to account for the actual corrosion observed in Nordic climates. What is the explan... | |materials|corrosion| | <p>As Dan mentioned in the comments, the presence of salt (and other pollutants) can alter the freezing point of water. </p>
<p>The <a href="http://www.iso.org/iso/catalogue_detail.htm?csnumber=53499" rel="nofollow">ISO 9223 abstract</a> states:</p>
<blockquote>
<p>key factors in the atmospheric corrosion of metals... | 2339 | How does corrosion occur at a temperature below 0 degrees Celsius? |
2015-04-06T23:20:08.780 | <p>What are the recommended or relevant standards for US city planning with regards to depth ranges for various utilities such as water, natural gas, and power, as well as for subway or rail, etc...?</p>
<p>For example, water and gas lines should be buried well below the frost line to prevent damage from ground moveme... | |civil-engineering|design|standards| | <p>First, if you care about a certain city, look up the information. This should be information that is readily available. Big cities are usually go about publishing this information online.</p>
<p>Tunnels (subway or vehicle) are different enough that they don't have standard depths. They are designed to be far enough... | 2340 | How deep are utilities typically buried? |
2015-04-07T11:30:24.463 | <p><img src="https://i.stack.imgur.com/EYwcJ.png" alt="enter image description here"></p>
<p>From the previous examples I've seen, there is a connection rod, for example, between a and c and then another rod from c to one of the pins. However, in this case, the rod ac is directly connected to another pin? I assume the... | |mechanical-engineering|applied-mechanics| | <p><a href="https://i.stack.imgur.com/1I0VP.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/1I0VP.jpg" alt=""></a></p>
<p>I have had the same exercise in school, maybe it helps, you just know $B= 1/2 AC$, and you know C is in horizontal line from 0.</p>
<p>If you want the acceleration diagram let ... | 2343 | How to draw the velocity and acceleration diagrams if there is no connecting rod between the pins? |
2015-04-08T02:45:00.753 | <p>I want to build a small ice cannon that uses pressurized air (either through an air compressor or a CO<sub>2</sub> cartridge) to shoot small ice pellets at my coworkers. I plan to use a thermoelectric cooler to freeze the water but I don't understand how to spec it.</p>
<p>For example, what are the key parameters of... | |mechanical-engineering|thermodynamics|cooling| | <p>Calculate latent heat Q= ML , using amount of water you want to freeze . Divide by time you want to want the cannon to be made. You Get cooling capacity . Add losses to this.</p>
<p>Make trials of TEC from calculator below.
<a href="https://viveksilwal.wordpress.com/2015/04/15/28/" rel="nofollow">https://viveksilw... | 2355 | How do I spec out a thermoelectric cooler? |
2015-04-08T21:53:54.640 | <p>In some cars, I have noticed the rear wheels are located at the extreme rear of the vehicle. However, I have noticed that the rear wheels of buses are always located about 1/4th of the way forward from the rear. What is the reason for this?</p>
| |mechanical-engineering|automotive-engineering| | <p>Most busses in the U.S. use a rear engine/rear drive layout, with the engine located behind the rear axle for ease of maintenance. There is no drive shaft per se, because the engine/transmission/rear axle are integrated.</p>
| 2363 | Why are rear wheels not placed at the extreme rear of a bus? |
2015-04-09T17:45:20.373 | <p>Most people have had the experience of moving the tab of an <a href="https://en.wikipedia.org/wiki/Beverage_can#Stay-on-tab" rel="nofollow noreferrer">aluminum can</a> back and forth until it breaks off. It usually only takes a few complete back and forth motions before the tab breaks off.</p>
<p><img src="https://... | |mechanical-engineering|materials|mechanical-failure|fatigue| | <p>Almost everyone is partly right. You can fail the ring-pull by simple overload in one 'cycle' or you can accumulate plastic strain in three or four cycles. This wouldn't normally be considered even low-cycle fatigue but I don't know that there's a lower limit on how many cycles Paris' Law can be applied.</p>
| 2382 | Why do beverage can tabs break when bent? |
2015-04-09T17:46:10.807 | <p>I was thinking about this <a href="https://www.kickstarter.com/projects/voltera/voltera-your-circuit-board-prototyping-machine/description" rel="nofollow">kickstarter project</a> where they print circuit boards, and later they show it printing solder paste. I've seen other liquid or paste dispensing systems like th... | |mechanical-engineering|fluid-mechanics| | <p>I do this type of things quite a lot at work, and yes they are typically syringe-actuated device, where you either apply a pneumatic pressure inside the syringe barrel for a certain amount of time (such as this <a href="http://www.loctite.co.uk/loctite-4087.htm?nodeid=8802622210049">glue dispensing machine</a>) or m... | 2383 | controlled depositing of goo with a syringe |
2015-04-10T13:47:48.143 | <p>I've been studying the design of turbopumps and their impellers, all the design equations and what-not; this question concerns the contours of the impeller vanes. I'm going to attempt to enter aerospace engineering in the future, so I figured I might as well start getting exposure to the concepts now.</p>
<p>I'm cu... | |mechanical-engineering|fluid-dynamics| | <p>I should have a little more overview than I have of pumps but I don't. What you refer to seems to be called an <strong>entrance vane</strong> or an <strong>impeller guide vane</strong>. The purpose is to help the water gain the required rotational velocity:</p>
<blockquote>
<p>... in connection with a centrifugal... | 2398 | Contours of radial-flow impeller vane |
2015-04-11T16:55:05.160 | <p>I want to pull some weight horizontally and for that i have settled for a linear actuator.</p>
<p><img src="https://i.stack.imgur.com/Sao5w.gif" alt="enter image description here"></p>
<p>The actuator should pull some weight as it moves back and forth as the gif shows. </p>
<p>There are linear actuators i could f... | |mechanical-engineering|linear-motors| | <p>For a minimum of moving parts, you can get linear stepper motors. With the right kind of controller (microstepping), the motion can be very smooth and quiet.</p>
<p>For example, I have in the past worked with linear actuators from <a href="http://www.nipponpulse.com/" rel="nofollow">Nippon Pulse</a>, driven by a mo... | 2409 | How does a rodless electrical linear actuator work? |
2015-04-12T05:46:26.693 | <p>I understand how a circle (or sphere if you want 3D) is the best shape for holding a vacuum inside a container, but what if you wanted to have a large positive pressure <em>inside</em> of the container instead of outside? Would a circle/sphere still be the best shape as far as material required to hold X amount of p... | |mechanical-engineering|pressure|geometry| | <p>It's all about the fact that spherical shell would not experience bending if the load is evenly distributed over the surface (which is the case when pressure is the only load). The very idea of using shells is to create them of such shape that stresses due to bending would be low, and the load bearing capacity of th... | 2419 | Is a circle the strongest 2D shape for containing internal pressure? |
2015-04-12T05:59:16.773 | <p><strong>When we apply a vertical shear force Sy and the structure is symmetric about x axis, then why is it logical to have the position of shear center at the location of intersection of line of action of shear force and x axis?</strong></p>
<p>If we go by basic definition then the moment about the shear center du... | |mechanical-engineering|structural-engineering|aerospace-engineering|structures| | <blockquote>
<p>why is it logical to have the position of shear center at the location
of intersection of line of action of shear force and x axis?</p>
</blockquote>
<p>That statement isn't logical. I think you have misunderstood how the shear centre is defined. </p>
<p>The shear centre is the point such that an ... | 2420 | Logic behind location of shear centre |
2015-04-12T18:09:56.273 | <p>I have been searching for this answer for awhile. I've read numerous texts and even watched some lectures online, but often times this is never explained and just given. The viscous stress term in the Navier-Stokes equations looks like</p>
<p>\begin{equation}
\nabla \cdot \tau = \nabla \cdot \mu \left(\nabla\vec{u}... | |mechanical-engineering|fluid-dynamics|fluid-mechanics| | <p>I agree with @sturgman one should not look at individual parts but try to understand it in ints context.</p>
<p>Looking at the very basic version of the Navier-Stokes-Equation (using <a href="http://en.wikipedia.org/wiki/Einstein_notation" rel="nofollow">Einstein-Notation</a>):</p>
<p>$$\rho\frac{\mathrm{D}u_i}{\m... | 2423 | What is the physical interpretation of the second term in the viscous stress tensor in the Navier-Stokes equations? |
2015-04-13T02:50:23.227 | <p>Consider a balloon, it is a flexible, expanding pressure vessel made of synthetic rubber. I am trying to design a system that will use hemispheric pockets of neoprene to grip an object, much like the one found in this journal:</p>
<blockquote>
<p>H. Choi and M. Koç, 'Design and feasibility tests of a flexible g... | |pressure|thermodynamics|compressed-air| | <p>This is fully doable. This is the in the higher range as bicycle tires (although with the outer tire as well and not the inner tube alone).</p>
<p>Alright, here goes:</p>
<blockquote>
<p>What equations do I need to calculate a solution?</p>
</blockquote>
<p>The pressure in a tube can can be modelled by the foll... | 2427 | How to design a hemispheric flexible pressure vessel? |
2015-04-13T06:33:37.157 | <p>I am trying to find some information regarding the design of plastic hinges that can move freely but also hold a position in any degree, like in this little camera: <a href="https://www.kickstarter.com/projects/podolabs/podo-the-first-stick-and-shoot-camera">https://www.kickstarter.com/projects/podolabs/podo-the-fir... | |mechanical-engineering|plastic| | <p>Here is an idea for you if you can't find an off-the-shelf product that fits your need. There are plastic coolant hoses that can be bent and stay in any position desired to direct the coolant flow for machine tool applications. The hoses are built from articulated plastic ball and socket joints. The hoses have the d... | 2429 | Information regarding plastic hinges that can hold the position |
2015-04-13T13:19:19.540 | <p>I have to draw two custom pipes, 1 1/4" & 2", with on one end male tapered pipe thread and on the other end parallel pipe thread. The connections are Parallel female thread with a tapered male thread, with Teflon tape as sealant.</p>
<p>I'm familiar with the metric tread, but the British/ Whitworth thread syste... | |mechanical-engineering|threads| | <p>After some discussion with an experienced college and a continued search, I'am able to answer my own question.</p>
<p>DIN 3858 is valid for type C stud ends as in DIN 3852-2 and type Z tapped holes with parallel internal thread as in DIN 3852-2. Example Type C stud <a href="http://mdmetric.com/4100/Chapter%20D%20U... | 2433 | British tapered pipe thread; Wall thickness? & Thread designation tpd? |
2015-04-13T14:49:51.510 | <p>Are there any industry standards (<a href="http://en.wikipedia.org/wiki/Specification_(technical_standard)" rel="nofollow noreferrer">Engineering Specifications</a>) for the minimum / maximum space required for the electrical box that holds a regular AC wall plug?</p>
<p><img src="https://i.stack.imgur.com/dr0USs.j... | |electrical-engineering|standards|specifications| | <p>The normative reference for the design of wall boxes for electrical work in the US is NEMA OS-1 for metal boxes and NEMA OS-2 for nonmetallic boxes. This, in turn limits the size that components to go into these boxes (including outlets) may be.</p>
<p>If you don't want to buy the standard, you can find a good bit ... | 2435 | Industry standard for AC wall electrical box space |
2015-04-13T16:57:14.100 | <p>Many states require that a PE applicant have some number of years of "progressive engineering experience". Are there details as to what qualifies? For example, if an engineer is working in sales and not design, I would tend to think that would not count. But that's just my impression. Are there defined rules? Genera... | |licensure| | <p>The state of California has some specific guidance as to what is considered experience. (<a href="http://www.bpelsg.ca.gov/applicants/faq_eng.pdf" rel="nofollow noreferrer">California FAQ</a>)</p>
<blockquote>
<p>Qualifying engineering work experience is that experience in the appropriate branch of engineer... | 2437 | What constitutes progressive engineering experience? |
2015-04-13T16:27:56.593 | <p>Given the information on swords <a href="http://quantumchymist.blogspot.co.uk/2014/02/why-arent-more-blades-made-of-titanium.html?m=1" rel="nofollow">here</a>:</p>
<blockquote>
<p>When you need to place a great deal of strength into a thin blade, steel remains the best all around choice. Titanium blades will be s... | |materials|metals| | <p>As a HEMA practitioner and a physicist, I can tell you that different swords need different properties and it is unlikely one material will be the end-all for a sword material. Depending on the sword, you may actually want different parts of the blade to have different properties. <a href="https://www.google.com/sea... | 2440 | How do I use this " Low-Density, High-Hardness, High-entropy Alloy" to make a good shortsword? |
2015-04-13T21:21:38.260 | <p>Here is <a href="http://s.hswstatic.com/gif/gear-worm.jpg" rel="noreferrer">an image of a worm gear</a>. What is english word for mechanical element (two of them will be necessary for a worm gear) in which the worm shaft will "lie" and rotate?</p>
<p>Here is one photo of the element where it is part of a housing; I... | |mechanical-engineering|gears| | <p>Not only does the shaft have a "bearing" surface but the ends of the shaft also need something to "bear" against due to the "thrust" of the shaft in either direction. So I would add the term "thrust bearing" to the mix some where in there ... this can be as simple as adding a single steel ball for a bearing surface... | 2447 | What is the mechanical element that holds a worm gear shaft in place called? |
2015-04-15T13:33:17.973 | <p>Is there a method for plating steel with stainless steel? </p>
<p>If so, is it chemical, electrical, or electrochemical? </p>
<p>I did a quick search on the internet but was unable to find a service. I'm interested in applying a food safe finish to something that would otherwise be cost prohibitive to make out of ... | |materials|steel| | <p>Someone mentioned allclad plating with stainless steel. That is not quite correct. They take a pair of thin stainless steel pots, then position them to have a 1/8 inch gap, and pour aluminum into the void. Since the melting point of aluminum is so low compared to stainless steel, this works quite well, and the stain... | 2478 | Is stainless steel plating possible? |
2015-04-16T06:48:03.313 | <p>I have an aluminum square tube (diameter 1/2") that I would like to attach to a flat aluminum surface which has a circular hole of smaller diameter in it for water to flow through at low pressure. Would welding a flange to the square tube (with screw holes for going into the surface) be the best option, or are there... | |mechanical-engineering| | <p>If it needs to be removable, then yes, attaching a flange will be the best choice. If so, you'll need to put some sort of seal between the flange and the existing aluminum surface. The faying surfaces of aluminum will not, on their own, form a good seal. There are many types of seals, but an elastomeric gasket or O-... | 2494 | Best way to attach a square tube to a flat surface? |
2015-04-16T07:57:00.897 | <p>Recently I observed installing new storm sewage along a city street. Pipes have plain surface (not corrugated) and are made of some plastic looking like HDPE (polyethylene) and their diameter is around 0,5 meters and the walls are around 40 millimeters thick. That's a lot of material. I assume the same structural st... | |civil-engineering|piping| | <p>You are correct in your assumption that corrugations give pipes strength and hence such pipes can have thinner walls that smooth walled pipes made of the same material when used for the same application.</p>
<p>Pipelines are made to transport fluids or slurries. When it comes to the flow of fluids or slurries in a ... | 2496 | Why prefer plain pipes over corrugated pipes for storm sewage and culverts? |
2015-04-16T12:26:33.823 | <p>I have a 8-pole synchronous machine (as a generator), which is rated to produce 1000 kVA. Its synchronous reactance is 0.4 Ohms.
It is connected to a diesel engine with the grid frequency 60 Hz.
The load is resistive type, 500 kW, 480 V.
I need to calculate the speed, power factor and power angle.</p>
<p>I know th... | |mechanical-engineering|electrical-engineering| | <p>If the load is purely resistive, the power factor is 1 and the power angle is zero by definition.</p>
| 2500 | Synchronous machine power factor and angle |
2015-04-16T23:36:50.343 | <p><a href="http://en.wikipedia.org/wiki/Chemical_oxygen_generator">Chemical oxygen generation (COG)</a> is used in commercial airliners to supply emergency oxygen to passengers and crew if the plane is depressurized. Weight for weight it produces far more oxygen than compressed oxygen tanks.</p>
<p>I read the origina... | |aerospace-engineering|aircraft-design|chemical-engineering|compressed-gases| | <p>One advantage these chemical systems may have over compressed tanks is how well they are suited for intermittent use and long-term storage (as opposed to regular, continuous operation). The <a href="https://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/amt_airframe_handbook/" rel="nofollow">US FAA Avia... | 2507 | What are the advantages of chemical oxygen generation over compressed tank storage? |
2015-04-17T04:34:05.567 | <p>I am designing a system where a beam is acted on by a horizontal force. I intend to hold the beam in place with a set of screws, although I am uncertain how much force they will be able to withstand.</p>
<p>What method can I use to determine the holding force of screws?</p>
| |mechanical-engineering| | <p>Many cities have either their own code on allowable load for nails and bolts or have adopted a uniform building code. </p>
<p>In Los Angeles for example the building department has published these codes on their site, or give them to you as a hand out for free. </p>
<p>American Wood Council has many pages of gu... | 2510 | How to calculate screw pullout strength? |
2015-04-17T09:11:43.427 | <p>Electronic cigarette elements that heat the fluid are usually termed "atomizers." They are usually just some nichrome wire or similar wrapped around a wick that becomes saturated with the nicotine fluid. </p>
<p>What is the process that "vaporizes" the fluid? Does the element just heat the fluid until it evaporates... | |thermodynamics|vaporization| | <p>Vapor is something that forms over any liquid and does not require the liquid to be above its boiling temperature. The atmosphere is a great example; it contains about <a href="https://www.google.com/search?q=how+muych+water+vapor+in+the+atmoshpere&oq=how+muych+water+vapor+in+the+atmoshpere&aqs=chrome..69i5... | 2511 | Are electronic cigarette "atomizers" just evaporating the fluid? |
2015-04-17T15:08:22.973 | <p>The design of a retaining wall commonly involves determining the lateral earth pressure using either Rankine theory or Coulomb theory. Both theories involve mobilising the shear resistance of a triangular wedge of soil extending for a considerable distance away from the base of the wall.</p>
<p>In the case of a dou... | |civil-engineering|geotechnical-engineering|soil| | <p>From what I read, you are looking at the pressure the sand between the sheet piling exerts on them. In this case, I see two possibilities: (1) <strong>log-spiral analysis</strong> or (2) elastic analysis of <strong>Boussinesq</strong>.</p>
<p><strong>Log Spiral Analysis</strong></p>
<p>The log spiral analysis ass... | 2516 | How to determine the lateral earth pressure in a double-walled cofferdam? |
2015-04-17T18:14:56.800 | <p>In a typical finite elements analysis package, a modal analysis gives the N first natural modes, and it is possible to get the equivalent stress and total deformations for each of these frequencies. </p>
<p>But what amplitude did the solver use to get these results? </p>
<p>Why can't we obtain a gain instead, for ... | |mechanical-engineering|finite-element-method|simulation| | <p>The short answer is, there is no amplitude used. Even more important though, is the fact that <strong>the displacements and stresses shown in the results of a modal analysis cannot be used to say anything about the physical behavior of the part in absolute terms.</strong></p>
<p>The basic equation of motion is </p>... | 2520 | What amplitude is used for a finite element modal analysis excitation? |
2015-04-17T19:32:28.337 | <p>In my mechanical vibrations class we studied the method to orthonormalize a set of differential equations by the mass matrix (principle coordinates). This is where you take the matrix of eigenvectors from the un-damped system and normalize it by the mass matrix. </p>
<p>Multiplying the mass matrix by the modal matr... | |mechanical-engineering| | <p>The one-word answer is "maybe".</p>
<p>In real structures, damping is often nonlinear, and hard to model from first principles. Also, a physically realistic but "arbitrary" damping matrix does not have nice mathematical properties - for example the mode shapes will be complex (i.e. different parts of the structure ... | 2521 | Orthonormalization of Damping Matrix -- modal analysis |
2015-04-18T15:17:38.743 | <p>We sell products that attach to a motor drive's DC bus. We also formerly sold diode kits that let you hook one product up to multiple drives. We stopped selling those diode kits because they were unreliable with modern hardware, and we had better solutions. My customer tells me he wants to keep using the old diode k... | |electrical-engineering|ethics|sales|safety| | <p>Your absolute minimum responsibility is to inform your customer that you consider the intended usage to be unsafe and that you do not recommend or endorse using it in this way. This should be done in writing and be acknowledged by the customer. </p>
<p>The next level depends on context. It is not impossible that yo... | 2534 | My customer wants to use my products to do something unsafe. What is my ethical obligation? |
2015-04-19T05:49:23.140 | <p>This is the top part of a basic sit/stand base I'm making. It is a monitor platform and sliding keyboard tray.</p>
<p><a href="https://i.stack.imgur.com/NPFC4.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/NPFC4t.jpg" alt="enter image description here"></a></p>
<p>Instead of the large base wit... | |mechanical-engineering|power-electronics|hydraulics| | <p>Put the fixed point of the rail on the back on both the upper <em>and</em> lower rails in the video you linked they are on opposite sides leading to a side to lateral movement. </p>
| 2547 | Miniature electric or manual jacks? |
2015-04-19T16:52:08.270 | <p>How small/compact can a pump or other mechanism be, that would allow compressing gas (or liquid) to pressures of excess of 10GPa, continuously?</p>
<p>Throughput may be minuscule, of order of milligrams per hour; even lower is acceptable. Also, for "size of the device" let us count all the necessary infrastructure:... | |pressure|pumps|compressors| | <p>Such high pressures can be achieved via <a href="https://en.wikipedia.org/wiki/Diamond_anvil_cell" rel="nofollow">diamond anvil cells</a> (DAC). The heart of these cells are two diamonds mounted on tungsten seats symmetrically in front of each other which are separated by metallic plate. Metallic plate has an apertu... | 2551 | Gigapascal pressures in a small package |
2015-04-19T19:12:42.510 | <p>Is it possible to convert the energy you would normally lose when braking your bicycle to rotational energy by attaching an extra wheel which would start to rotate once you use your brakes? E.g., when facing a red light after riding down a hill.</p>
<p>If you could restore that energy, you could regain part of your... | |mechanical-engineering|bicycles|regenerative-braking|flywheels| | <p>There are a few fundamental difficulties. </p>
<p>The energy stored in a flywheel is a combination of its moment of inertia and its speed. To get a higher moment of inertia you either need more mass or a larger diameter. The problem being that bicycles tend to be very sensitive to both weight and space. This leaves... | 2557 | What are the technical obstacles for using flywheel-based regenerative braking on bicycles? |
2015-04-21T18:29:41.173 | <p>Is there a specific chemical that is used frequently in the production of liquid crystal displays? During my internet research so far, it seems as if the specific chemical composition of the liquid crystal does not matter very much. <a href="http://www.sigmaaldrich.com/materials-science/material-science-products.htm... | |chemical-engineering|optics|liquid| | <p>The article <a href="http://www.ijestr.org/IJESTR_Vol.%201,%20No.%207,%20July%202013/Liquid%20Crystal%20Display.pdf" rel="nofollow">Liquid Crystal Display: Environment & Technology</a> (2013) provides a detailed list of chemicals often used in LCDs. There are a myriad of chemicals that are used, each serving a s... | 2571 | What liquid crystals are used most frequently in displays? |
2015-04-21T19:11:45.827 | <p>Oblique cutting generates transverse cutting force which reduces tool life. Oblique cutting involves principal and auxiliary cutting edges in the cutting action which increases friction and advances wear in the cutting tool. </p>
<p>Orthogonal cutting doesn't have those complexities, but oblique cutting is found to... | |mechanical-engineering|materials|mechanical-failure| | <h1>Short answer</h1>
<p>Orthogonal cutting increases pressure and decreases tool life. Thus isn't used if aim isn't cutting. Lathe operation is a shaping operation, not a cutting operation most of the time. </p>
<h1>Long answer</h1>
<p>Orthogonal cutting isn't suitable because</p>
<ol>
<li>Cutting forces act on a ... | 2572 | Oblique cutting implemented in Industrial applications |
2015-04-22T06:36:20.740 | <p>I'm building a press for cider. I'm going to be using a 24" x 24" press board. I'm looking to deliver 40 psi to the cider. How can I determine the amount of weight required, in tons? What sort of equation would I use?</p>
| |mechanical-engineering|pressure|hydraulics| | <p>The obvious place to start is "what does psi mean?" It's an abbreviation for "pounds per square inch".</p>
<p>If we have a 24" x 24" board, then we have </p>
<p>$$24~in\times24~in=576~inΒ²$$</p>
<p>To get 40psi, i.e. 40 pounds for each square inch, we would need </p>
<p>$$40~\frac{lbs}{inΒ²}*576~inΒ² = 23040 ~lbs$$... | 2577 | How do I calculate the weight needed on a press board to deliver a certain amount of pressure? |
2015-04-22T15:04:50.520 | <p>I'm dealing with some hydrocarbons (diesel, gas oil, kerosene, ethanol) where I'm putting them in a chamber and shining light through them to hit a sensor on the other side in order to measure their colour. Unfortunately what I'm finding is that the lenses and reflective surfaces in the chamber that I'm using for th... | |materials|optics| | <p>A super-hydrophobic coating would work well for you because super-hydrophobic materials are self-cleaning. <a href="http://www.sandia.gov/" rel="nofollow">Sandia National Labs</a> has a nice report on super-hydrophobic coatings which can be found <a href="http://www.sandia.gov/research/research_development_100_awar... | 2583 | How to avoid dyed liquids staining reflective/transparent surfaces |
2015-04-23T09:56:08.000 | <p>I am designing a metal plate that will be laser-cut (or machine-cut) and then folded. I want to know how to size the pre-folded plate in order to get the right dimensions after folding.</p>
<p><img src="https://i.stack.imgur.com/Y5Pq3.png" alt="Diagram of a folded 2mm aluminium plate with holes and window"></p>
<p... | |machining|metal-folding| | <p>Yes use Aluminum 5052 H32 for sheet metal parts with bends. r =or> T.
I do it like this, get the lengths of the straight lines and set aside.
The t/T is a little more than .50, say .53 until you get the real number.
K= t/T, radius of the neutral line is inside r + t = r + .53T
For a 90 degree bend, length of the ben... | 2589 | How do I size metal plates to get the correct dimensions after folding? |
2015-04-23T21:00:11.883 | <p>I need to release pressure of around 50psi, after 3-4 seconds of initiating, from a vessel using a mechanical switch. I had considered a pneumatic solenoid, but I want to forgo the inconvenience of charging the device with electricity in addition to the air, as well as save the space that would be needed for the bul... | |mechanical-engineering|pressure|compressed-air| | <p>There are three possibilities here that come up offhand, between my own mind and ratchet freak's comment:</p>
<ul>
<li>The choke that ratchet freak mentioned -- this is the simplest approach if you are OK with a slow decay of pressure</li>
<li>The dampened piston that ratchet freak also mentioned, where the mechani... | 2594 | Are there any precedent designs for a mechanically-delayed pressure release valve? |
2015-04-24T06:16:10.763 | <p>A quote from my textbook :</p>
<blockquote>
<p>Turbomachinery flows are steady only in a time-averaged sense; that is, the flow is periodic,
with a period equal to the time taken for a blade to move a distance equal to the spacing
between adjacent blades. Despite the unsteadiness, in elementary analysis all v... | |mechanical-engineering|fluid-dynamics| | <p>The words <strong>unsteady</strong> and <strong>periodic</strong> have different meaning depending on the context they are used in. My answer is mainly with regards to axial or radial turbomachines.</p>
<p>Lets say our machine is running at a specific operating point. The rotation of the blades (the shaft) does not... | 2595 | What makes a flow periodic in Turbomachines? |
2015-04-24T19:27:27.740 | <p>I want to embed a wire inside a plastic and heat it to specific temperatures (80$^\circ$C 100$^\circ$C 130$^\circ$C 180$^\circ$C). I want to find a material that is resistive enough for resistive heating, but also I want the wire's resistivity to vary fairly strongly with temperature - this way I can know the actual... | |electrical-engineering|materials|heat-transfer| | <p>Just about anything you can find will exhibit a temperature dependence on its resistivity. The first hit looking up nichrome says it's temperature dependence is 0.004/°C.</p>
<p>A better model for resistivity is the Steinhardt-Hart(sp?) equation, but you probably don't need something that elaborate. Since you... | 2605 | Material which can be used for resistive heating and simultaneous temperature measurement |
2015-04-25T08:40:28.170 | <p>Why are tremors of an earthquake felt most on the upper floors of a building in comparison to lower floors? Does this have something to do with a third class lever?</p>
| |mechanical-engineering|civil-engineering|applied-mechanics|seismic| | <p>Harmonic coupling with the building's natural vibration frequencies, dissipation of energy in a massive building, and the variety of vibration modes that can experience coupling could result in more or less displacement and more or less velocity at lower floors or upper floors. There's no universal relationship bet... | 2609 | Why are tremors of an earthquake felt more on upper floors? |
2015-04-25T12:17:45.800 | <p>I am making a device for measurements. I would like to measure the distance within accuracy of 1 mm. Range could be 2 cm to 15 cm . I looked at <a href="https://www.sparkfun.com/datasheets/Sensors/Infrared/GP2D120XJ00F_SS.pdf" rel="noreferrer">Proximity Sensors</a> but the readings displayed by these sensors are not... | |mechanical-engineering|measurements|sensors|tolerance| | <p>Was looking for other distance solutions, and came across this question.</p>
<p>A sensor that I've found works well is the Sharp GP2Y0E02B (digital version) (newer version is the GP2Y0E03). Configuring it as an I2C sensor, using an Arduino, I've been able to get <em>sub-millimeter</em> resolution (0.156 mm - Range... | 2612 | Distance sensors with accuracy of 1 mm? |
2015-04-26T04:07:32.957 | <p>I have a simulation software which shows energy consumption at 30 minutes timestep. If a system consumes 0.06 kWh at 6am, and 0.09 kWh at 630am, how to calculate the energy consumption between 6-7am? Can I assume it is the average of both timestep? Does finer timestep, eg. 10 minutes interval returns a different res... | |mechanical-engineering|electrical-engineering|hvac| | <p>In SI units the measure of "amount" of electrical energy is the Joule.<br>
Energy is a measure of "work done".<br>
Energy can be (and often is) expressed in terms of 'rate of doing work'.<br>
The rate at which work is done or at which energy is supplied or utilised is also named "Power".<br>
Work done = 'rate of doi... | 2614 | Calculating kWh for different timestep |
2015-04-26T23:39:46.737 | <p>This may fall a little under chemistry processes but I felt it has enough pertaining to aerospace to put it here. Basically, I'm in the process of attempting to develop a way to derive $I_{sp}$ as pertaining to rocket engines rather than rely on charted information.</p>
<p>Since specific impulse is essentially the ... | |aerospace-engineering| | <p>There is no general formula for isp that would provide accurate values all the propellant combinations and nozzle expansion ratios one might use. The <a href="http://www.grc.nasa.gov/WWW/CEAWeb/ceaHome.htm" rel="nofollow">NASA Chemical Equilibrium (CEA) program</a> can provide the information you are looking for and... | 2622 | Calculating real or more accurate specific impulse |
2015-04-27T04:40:18.970 | <p>I have a structure like such:</p>
<p><img src="https://i.stack.imgur.com/CZvAm.png" alt="Structure"></p>
<p>Due to my lack of knowledge of ANSYS, I have made the singular distributed loading (GI) represented as two distributed loadings (GH and HI).
Would this be an accurate model?
<img src="https://i.stack.imgur.c... | |structural-engineering|structures|modeling|stresses| | <p>Adding just a slight notion:</p>
<p>Your experience would always expect the beam HE to buckle, because it is a Eulerian buckling beam (don't know if it's also called like this in English).
The numeric only sees an evenly distributed load, so there will be no buckling... Try to alter your forces to the left and righ... | 2623 | Is a distributed load in two parts equal to a full distributed load? |
2015-04-27T07:12:50.343 | <p>Some sources say that higher pressure in hydrocyclones implies better performance it leads to a finer filtration. But why?</p>
<p>Is it because water is almost incompressible and the particles can be pressured and their density increased? </p>
| |mechanical-engineering|fluid-dynamics|pressure|cyclones| | <p>The use of the word <strong>performance</strong> might be misleading since a connection to <em>pressure loss</em> is quite reasonable. However, in this context I guess <strong>performance</strong> is connected to the filtration. </p>
<p>Using higher pressure implies in deed a higher pressure loss but it also result... | 2626 | Hydrocyclone effectiveness vs. absolute pressure |
2015-04-27T18:16:46.357 | <p>If a permanent room or platform is suspended from a larger structure (say, on a cable that is attached to a hook on a track in a ceiling) and designed to be in constant but not necessarily repetitive motion, does the load that the room/platform places on the larger structure count as a dead load or a live load?</p>
... | |structural-engineering|structures| | <p>A moving load should always be classified as a live load even when its weight is known and remains the same. A dynamic body of mass has an extra degree of freedom. This positional uncertainty calls for a higher factor of safety. Your "permanent" room is not much different from a "permanent" mobile trailer in that bo... | 2633 | Is a permanent platform that is hanging and moving a dead load or a live load? |
2015-04-29T08:05:42.903 | <p>An idea that keeps popping up in my head, that I don't know enough structural/civil engineering to know if it's good from a technical point of view.</p>
<p>Take a piece of <a href="http://en.wikipedia.org/wiki/Polyethylene" rel="nofollow">polyethelene</a> (PE) piping, fill it with concrete, let the concrete bind. M... | |structural-engineering|columns| | <p>This approach has been used in many, many scientific studies, and is an active area of research in the materials engineering community, but with a different material. FRP (<a href="https://en.wikipedia.org/wiki/Fibre-reinforced_plastic" rel="nofollow noreferrer">Fiber Reinforced Plastic</a>) is used to wrap around ... | 2651 | Would a PE-pipe filled with concrete make a good pillar? |
2015-04-30T00:15:41.107 | <p>Here is the link to the current CA PE Exam application: </p>
<p><a href="http://www.bpelsg.ca.gov/pubs/forms/ceapp.pdf">http://www.bpelsg.ca.gov/pubs/forms/ceapp.pdf</a> </p>
<p>Page 2, which is the list of engagements/references, states: </p>
<blockquote>
<p>For each engagement claimed as qualifying experienc... | |licensure| | <p>As it turns out, I have been approved to sit for the Civil PE exam in California this fall even though none of my references were CA PEs. So I suppose that answers my question. </p>
| 2658 | Do references for the California PE application have to be California PE's? |
2015-04-30T06:57:52.027 | <p>Why is a Non-causal PD Controller:
$C(s) = K_ds + K_p$</p>
<p>When a causal PD Controller is:
$C(s) = (K_ds + K_p)/(\tau s + 1)$</p>
<p>The difference being the denominator. $\tau$ is the time constant and is "<em>sufficiently small and does not perturb the other poles substantially</em>".</p>
| |control-engineering|control-theory| | <p>Because with the form:</p>
<p>$C(s) = K_ds + K_p$</p>
<p>you have a non-proper transfer function. In process engineering, you always need to have <a href="http://en.wikipedia.org/wiki/Proper_transfer_function" rel="nofollow noreferrer">proper transfer functions</a>, where the degree of the numerator is less than o... | 2663 | Causal and Non-Causal PD Controller |
2015-04-30T10:44:18.687 | <p>I am currently doing a project which has led me to my first encounter with IR cameras, and I am therefore quite curious as to how they operate. Specifically, I would like to know the following</p>
<ol>
<li>How is heat converted to an electrical signal (current or voltage)?</li>
<li>How is the <em>spectral bandwidth... | |electrical-engineering|thermodynamics|heat-transfer|optics|temperature| | <p>There are a lot of questions in your question, and it should probably be broken up into multiple different questions. I don't want to wait until that happens though so I'll address the ones that I know the answers to. </p>
<blockquote>
<ol>
<li>How is heat converted to an electrical signal (current or voltage... | 2664 | How does a microbolometer (IR camera) work? |
2015-04-30T22:50:14.330 | <p>I'm trying to design a bioreactor to produce citric acid with whey and Aspergillus Niger. </p>
<p>The first step in the process would be to put whey into the reactor with some dextrose (approx. 10%). Then, this solution should be sterilized, and I was thinking of using batch steam sterilization by direct injection ... | |chemical-engineering|process-engineering|steam| | <p>It all depends on the sterilization level you want to achieve. As you say, you would need to know the death kinetics parameters, or equivalently the log-decimal reduction time (D) and how it changes with temperature (Z). As sterilization is a problem that takes place almost everywhere in food industry, a standard st... | 2673 | Steam sterilization of whey in a bioreactor |
2015-05-02T09:20:04.410 | <p>I'm trying to develop a thermoelectric (Peltier tile-based) beverage cooling system. Ideally, I'd also like a device to solve the warm beer problem if the thermodynamics give me any confidence.</p>
<p>First, I'll detail my thought flow in the theory sense and then I'll get to my specific setup that I had in mind.</... | |mechanical-engineering|thermodynamics|heat-transfer| | <p>There are two wattage ratings for a peltier plates. One is the power consumed, the other is the heat transported across the chip <strong>when there is a temperature difference of zero</strong>. An important note is that the amount of heat transported across the plate is dependent on the temperature difference across... | 2676 | Determining behavior of heat exchange system |
2015-05-02T10:03:48.727 | <p>I have 3-axis accelerometer and 3-axis gyroscope sensor data coming from my bike trip. Until now I have extracted only basic information like overspeeding, hard acceleration and sudden turns.</p>
<p>What additional motion characteristics can I infer from this data? I also have x, y coordinates.</p>
| |mechanical-engineering|electrical-engineering|sensors| | <p>This information you have, in theory, allows complete reconstruction of location and orientation of the bike along the entire path. This is basically what is referred to as <i>inertial navigation</i>.</p>
<p>However, the problem in real life is that there will be some error on all the signals. Since determining l... | 2677 | What kind of motion information can be extracted from 3-axis accelerometer and 3-axis gyroscope sensor data |
2015-05-02T13:48:56.413 | <p>I need to connect two flat bars of metal with some kind of bearing that doesn't increase the joint thickness by more than 2-3mm (the less the better), as shown here:</p>
<p><a href="https://i.stack.imgur.com/9nH2w.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/9nH2wm.png" alt="two bars of 50x5 m... | |mechanical-engineering|bearings| | <p>I recommend a sliding contact bearing. It's easy to manufacture and seems to do the job for a prototype, especially if it has to be cheap. Steel seems to be the better choice in this case.</p>
<p>Rather use two thinner bars for one of the links, so you get a double lap. This will reduce the moment on the bearing an... | 2680 | How to design a narrow bearing that supports shear direction load |
2015-05-04T04:18:36.493 | <p>I am rebuilding a mini soil compactor roller. </p>
<p>I replaced the old 8 hp Kubota diesel engine unit with a new Dongfeng unit. I want to weld the coupling shaft, which is built from 2" pipe with rubber damper at one end, to the hydraulic motor. </p>
<p>How can I ensure the shaft is balanced after we weld it to ... | |mechanical-engineering|flywheels| | <p>With some low friction bearings you can spin it on the shaft and wait for it to come to a rest and mark the low point, do this a few times and you may see them gathering at the bottom.</p>
<p>Then drill out a portion of the wheel where it is heaviest and repeat.</p>
| 2686 | Balancing flywheel and coupling shaft at home |
2015-05-05T05:09:47.133 | <p>I have been wondering about this question for quite some time. Assuming an ideal case, the energy from photons hitting solar cells is converted into electric energy as described by the equation:</p>
<p>$RI^2t=W\equiv E=\hbar\nu$</p>
<p>where $\nu$ is the frequency of photons. Using a lens won't increase the freque... | |electrical-engineering|optics|photovoltaics|solar-energy| | <p>A new way to convert solar power has been discovered at the University of Michigan. Please check out :
<a href="https://phys.org/news/2011-04-solar-power-cells-hidden-magnetic.html" rel="nofollow noreferrer">https://phys.org/news/2011-04-solar-power-cells-hidden-magnetic.html</a></p>
<p>It uses the magnetic compon... | 2690 | Will more electricity be generated by using a lens to focus sunlight onto solar cells? |
2015-05-05T18:31:05.723 | <p>I have made a Python program in which I have computed the deflection of a beam.</p>
<p>I am plotting the deflected beam and am now asked to show the length of the beam.</p>
<p>If the beam is not deflected, it is easy to show the length of the beam but when the beam is deflected, I guess the length of the beam is l... | |mechanical-engineering|structural-engineering|structures|beam|statics| | <p>A subtle bit of wording - the exact length does not change, as pointed out by Air above in his answer. However, the horizontal projection of the beam does change, as the shortest path between two points will always be a straight line. Thus, by curving, the tip of the beam will have to move backwards a bit in the x... | 2693 | Does the length of a beam change upon deflection? |
2015-05-05T20:20:10.200 | <p>If I use an ultrasonic sensor will it detect the water level? </p>
<p>I was thinking about a product to read water level on water boxes (common in Brazil). I researched about instrumentation for this measure, and I think that an ultrasonic sensor is the best option. Will the water correctly reflect ultrasound and ... | |electrical-engineering|measurements|sensors|control-engineering| | <p>Or you could just buy one. They are used in oil industry to measure liquid level in wells. They are necessary to turn the pump jacks off /on. </p>
| 2695 | Can I use a ultrasound sensor to measure water level? |
2015-05-06T02:29:30.643 | <h3>Weight of Structural Steel</h3>
<p>When calculating the weight of a steel structure, I usually calculate the weight of all of the various members and plates first. I then add an additional percentage to account for the weight of nuts and bolts. This percentage is usually between 2% and 5% of the total weight.</p>
<... | |structural-engineering|steel| | <p><a href="http://www.dot.ca.gov/hq/esc/techpubs/manual/bridgemanuals/bridge-design-aids/page/bda_11.pdf" rel="nofollow">Caltrans Bridge Design Aids, Section 11</a> adds 3% for welds and bolts:</p>
<blockquote>
<h3>Furnish Structural Steel (Bridge) and Erect Structural Steel (Bridge)</h3>
<ol>
<li>Segregate ... | 2699 | Is there a standard percentage to increase structural steel weight to account for bolts? |
2015-05-06T12:49:24.117 | <p>I'm looking for a power source that is able to deliver 12V at 15-30A (yes, amps). I was looking at high capacity batteries, but looking at the specs, they either say they have a lower discharge voltage than 12V, or they don't say anything at all. </p>
<p>Do such power sources exist?</p>
<p>I'm hoping to use this i... | |electrical-engineering|power-electronics|hydraulics| | <p>Pretty much all electric motors demand a lot more power for starting from a dead stop than for generating motion in a steady state. There are a whole lot of schemes for smoothing out this 'inrush current' demand, either from the electrical side or from the mechanical side (by decoupling the load and gradually re-con... | 2705 | Hydraulic power source |
2015-05-06T15:19:00.057 | <p>In <a href="http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20000036534.pdf">this NASA document</a>, it is mentioned on page 221 (239 of the pdf) that a "23 tol gear box" was used. What does that mean?</p>
<p>A google search for "23 tol gear box" (with quotes) comes up completely empty, and "tol gear box" show... | |mechanical-engineering|gears| | <p>Oh, I get it. The typo is a missing space. It's supposed to mean "23 to 1".</p>
| 2714 | What does "tol" mean in a gear box? |
2015-05-06T19:44:03.523 | <p>Note: This may be UK-specific, I'm not sure.</p>
<p>I overheard part of a conversation about 3-phase electricity, one guy was saying that mains generators use 3 coils (or something) and as it spins it produces 3 different waves of alternating current that are 120 degrees apart. That's why the power lines often have... | |electrical-engineering| | <p>In North America, you generally don't see 3 phase power being delivered to houses. The transformers (whether they're up in a pole, or in a green box on the ground) take apart the 3-phase 1100V power delivered to them and step it down to 110V. For 220V, two feeds are connected appropriately, and 220V is delivered t... | 2721 | Does a 3-phase electricity grid need to be synchronised and are the phases split between houses? |
2015-05-06T20:51:48.677 | <p>In order to make this a manageable question, let's add a few simplifications. </p>
<ol>
<li>The dust particles can be well described as uniform spheres of radius $R$ and density $\rho$. </li>
<li>The space is enclosed and there is no bulk flow, i.e the air is still in a macroscopic sense.</li>
<li>The air is at t... | |fluid-mechanics|air-quality| | <p>Solid particle settling time in air depends mainly on the size of the particle. Different forces become significant depending on what size range you're talking about, so it's hard to give an answer that's both concise and accurate.</p>
<p>I'll do my best to synthesize the important points rather than parrot a refere... | 2725 | How long does it take for dust to settle out of the air? |
2015-05-07T08:23:58.640 | <p><strong>Background</strong>
I am working on a project that involves heating air inside a small box, then measuring the temperature over time. The purpose of the box is to be a basic test chamber for PID experiments.</p>
<p><strong>Initial Test</strong>
I made a 10 cm * 10 cm * 10 cm box from 3 mm plywood. I then p... | |thermodynamics|heat-transfer|heat-exchange| | <p>A simple approach would be to just consider the heat added.</p>
<p>The specific heat equation gives the temperature change due to heating as</p>
<p>$$Q=mc\Delta T$$ where $Q$ is heat added, $m$ is mass. $c$ is the specific heat of the material in question (~1.005kJ/kgK for air at room temperature) and $\Delta T$ i... | 2734 | Heating the air in a small box |
2015-05-07T17:39:16.427 | <p>I understand the difference between a #3 finish on a piece of stainless steel compared to a #4 finish being that the surface roughness is different. Specifically, a #4 finish is classified as having an Ra value of less than 25 micro-inches where as a #3 finish has an Ra value of less than 40 micro-inches. </p>
<p... | |materials|steel| | <p>In addition to hazzey's answer I'd just like to add that <strong>passivation</strong> of stainless is very important to reduce the risk of corrosion, especially in welded products.</p>
<p>Typically the steel is cleaned then dipped into various chemical baths following welding. This allows the steel to restore its c... | 2742 | Will stainless steel with a #3 finish corrode faster than a #4 finish? |
2015-05-08T13:06:06.750 | <p>I am a high school student wondering if the pulley system described below will work, and if so, how to go about it.</p>
<p>Basically, I have a small system where as you pull back an object, it causes two lengths, labeled $d$ and $p$, to move forward. $d$ is dependent on many factors other than just the pulley syste... | |mechanical-engineering|pulleys| | <p>If I understand your question correctly, then you want to know if there is some mechanism which can convert a movement of distance $d$ to a movement of distance $p$, given that you want $p=\sqrt{A+Bd^2}-C$. If $d$ is caused by pulling on a rope, then the easiest way I can think to achieve your objective is a spring... | 2752 | How to design and build a pulley system for a given purpose? |
2015-05-10T07:34:37.737 | <p>I have a Fisher and Paykel Washing Machine (model number WL80T65C, well past warranty) which got rained on (a lot) and one of the capacitors blew up. I've done an amateur replacement of the capacitor which might work but when taking the circuit apart I forgot to take a photo until half way through. I've managed to p... | |electrical-engineering|circuits|embedded-systems| | <p>The sad faces are where the hand insert components go. If any sad faces are showing, the operator hasn't finished their job.</p>
| 2764 | What does a Sad Face on a circuit board mean? |
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