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2015-01-20T18:35:59.493 | <p>Is it possible to "pump" a powder the same way liquids can be pumped?</p>
<p>If so, what are the challenges? If not, what are some alternatives?</p>
| |pumps|liquid|fluid-mechanics| | <p>Yes you can pump powders using a diaphragm pump. The above comments all focus on alternate ways to transport powder they are not talking about pumping. Check out powder pumping with a diaphragm pump on youtube.</p>
| 1 | Is it possible to "pump" a powder? |
2015-01-20T18:41:51.527 | <p>What is the <a href="https://en.wikipedia.org/wiki/Barometric_formula" rel="nofollow noreferrer">barometric height formula</a> for a mixture of gases?</p>
<p>The main problem I can see, the curves describing the minimal energy (kinetic + gravitational/centrifugal) won't be any more a simple derivative, but a functi... | |pressure|gas|nuclear-technology| | <p>The barometric height formula is defined as:</p>
<p>$$ p(z) = p(0)\exp(-Mgz/(RT))$$</p>
<p>For a centrifuge the upper expression is transformed to:
$$ p(r) = p(0)\exp(M\omega^2r^2/(2RT))$$</p>
<p>As you see the $g$ is transformed to the radial acceleration $a = \omega^2 r$. The factor $2$ stems from the integrati... | 4 | Multi-gas barometric height formula in isotope separation devices? |
2015-01-20T19:49:53.683 | <p>The United States have different rules about exactly how one obtains an engineering license, but the general process is the FE exam, a few years of work, and the PE exam. Suppose one then wishes to practice engineering in Germany. What are the legal requirements for doing so?</p>
| |licensure|international| | <p>Take all this with a grain of salt. I work in Germany as an engineer and don't have any special license sides my degree, but I'm employed and your situation may be different.</p>
<p>Generally, engineer is a free profession in Germany. This means, if you are an engineer (have an engineering degree from a university ... | 6 | What is the process of transferring an engineering license from the United States to Germany? |
2015-01-20T22:03:47.020 | <p>I think, here is the main problem the difference between the internal and the external temperature.</p>
<p>For example, in Saudi Arabia, in 50 C, a passive house needed probably much sophisticated planning as in Paris.</p>
<p>Compared to the traditional cooling systems, in the second case is enough only to get a c... | |civil-engineering|architecture|cooling| | <p>In order to build a passive house you have to limit the final energy use for cooling to 15 kWh/m² per year and your primary energy use for HVAC and lighting has to be less than 90 kWh/m² per year minus the deduction for compactness, so let's say around 70 kWh/m².</p>
<p>I guess getting to 15 kWh/m² final energy use... | 14 | How are passive houses made in very hot regions (like Saudi Arabia)? |
2015-01-20T22:16:03.560 | <p>Liquid hydrogen cooling could be some intermediate solution between helium and liquid nitrogen based cooling. For example, some type of superconductors could be cooled by liquid H<sub>2</sub>, and this could be much cheaper than the liquid He.</p>
<p>What are their most characteristic applications in the industry?... | |superconduction|cryogenics| | <p>The combustion chamber and nozzle of the Space Shuttle main engine were cooled with liquid hydrogen. Liquid hydrogen was also the fuel. It was used as a coolant before it was burned (<a href="https://en.wikipedia.org/wiki/Regenerative_cooling_%28rocket%29" rel="nofollow noreferrer">regenerative cooling</a>).</p>
... | 16 | Do liquid hydrogen-based cooling devices exist and what are they used for? |
2015-01-20T22:41:57.420 | <p>I'm making a robot for the Sparkfun AVC. I was curious if I could use only the knowledge about</p>
<ol>
<li><p>How the car is being steered at every time interval,</p></li>
<li><p>How many times the wheels have rotated,</p></li>
</ol>
<p>to get a general sense of where the car is. I would use computer vision to av... | |control-engineering|robotics| | <p>The correct way to do this is by using what is known as a <a href="http://en.wikipedia.org/wiki/Particle_filter" rel="nofollow">particle filter</a>.</p>
<p>The maths for estimating your next position is quite simple and other answers have already provided that, but this is how you deal with the uncertainty. <a href... | 20 | Knowing how many times the rear wheels have rotated, and the angle of the front wheels at every time interval, how do I find the location of a car? |
2015-01-20T22:53:44.837 | <p>I recently had a project where I made an aluminum linkage (similar to a scissor lift) operated by linear actuators. Aluminum pieces were fabricated from 6061 "standard" aluminum stock, 6mm (0.25 inch) thick. The bars are at most 750x75mm (30x3"). The application was mostly cosmetic (for a special effect) rather than... | |bolting|aluminum|linkage| | <p>Steel and aluminum don't like each other! that's why you are getting the binding. Only use Stainless steel with aluminum. And of course never use aluminum fasteners for an application like this due to strength. And use all nylon washer if you can or between the SS washer and where is touches the moving part.</p>
| 22 | What method can I use to make a pivot point in an aluminum linkage? |
2015-01-20T23:14:48.790 | <p>As far I know, the depleted fuel cells are crushed, and solved in nitric acid.</p>
<p>What is coming after that? This nitric acid should probably contain a very wide spectrum of different salts (practically, all of the elements between 35-65, and yet a lot of transurans, and a lot of uranium (both of 235 ad 238), a... | |nuclear-technology|nuclear-reprocessing| | <p><strong>Fission Products Extraction</strong></p>
<p>The seperation of plutionium and uranium from the other fission products is done with the organic molecule <a href="http://en.wikipedia.org/wiki/Tributyl_phosphate" rel="noreferrer">tributyl phosphate</a> by <a href="http://en.wikipedia.org/wiki/Liquid%E2%80%93liq... | 26 | How does nuclear fuel reprocessing work? |
2015-01-20T23:41:29.103 | <p>I've found myself tapping and threading a lot lately, and doing so with hand taps and dies. What would be the next step up from using a drill-press to cut holes for tapping, and a lathe for turning parts to diameter for threading?</p>
<p>What are options for making this easier and more precise short of a 6-figure ... | |machining| | <p>For tapping threads, there are a few steps between free hand tapping and fully automatic machines. Which one is right for you will depend on the material you're tapping, the size of the threads you're tapping, and how large your production run is.</p>
<p>The first step would be to buy a guided tap wrench, which is ... | 32 | What machinery should I invest in for tapping and threading? |
2015-01-20T23:46:47.343 | <p>It's true that most bridges are "two directional."</p>
<p>But <a href="http://en.wikipedia.org/wiki/Three-way_bridge">three way bridges</a> are pretty rare, globally. I can understand why there wouldn't be many for rivers, but if bridges are designed based on the lie of the surrounding ground, why wouldn't there be... | |structures|design|civil-engineering| | <p>Multi-way bridges are rare for river crossings for the reasons you describe; however, they are seen as a component of highway interchanges, usually when left entrances/exits are present or access ramps have been "braided" into an existing system interchange, or where a SPUI has been built over an existing divided hi... | 33 | Why are three way bridges rare? |
2015-01-20T23:50:02.410 | <p>My design uses a round steel bar inserted through a hole in an aluminium component with a tight fit (no movement). The operating environment is dry, 20-40°C.</p>
<p>Do I need to worry about galvanic corrosion, and if so how long will this last before starting to corrode? Also, what storage conditions should I avoid... | |steel|corrosion|materials| | <p>Aluminum and steel are very near to each other in the <a href="http://en.wikipedia.org/wiki/Galvanic_series" rel="noreferrer">Galvanic Series</a> for seawater. So even if your apparatus is exposed to a corrosive environment along those lines, it should not corrode very quickly.</p>
<p>The aluminum will corrode firs... | 34 | Do I need to worry about galvanic corrosion when inserting a steel bar through aluminium? |
2015-01-20T23:51:19.933 | <p>If I have structural or tool steel that has been treated to some standard (ASTM, SAE, ISO -- e.g., for hardness) but I don't know the details of the treatment, is there a "safe" temperature below which I can work the steel without affecting its performance characteristics?</p>
| |steel|machining|metallurgy| | <p>There are three key temperature which may affect the properties of steel. As mentioned in the accepted answer the recrystallization temperature is the most significant as it can potentially affect any steel, especially ones which have been cold worked to improve their properties or have a high alloy content eg stain... | 35 | At what temperature do I risk altering the structure of steel? |
2015-01-20T23:59:10.837 | <p>I am starting to use steel in some of my designs, and while trying to learn more about this material and its properties I have realized that there is so much more to it than I thought.</p>
<p>How does the grading system used for steel work? For instance, what does "Grade 11SMn30" mean, and how does this affect the ... | |steel|materials| | <p>Based on it being an EN steel grade:</p>
<p>The first number is 100x the carbon content percentage (so 0.11%), the letters are added elements (sulphur and maganese), and the last number is the sulfur content (0.30%). <a href="http://www.steelnumber.com/en/steel_composition_eu.php?name_id=155">You can see the full ... | 37 | What does the steel grade "11SMn30" mean? |
2015-01-21T00:03:53.533 | <p>The LTE specification specifies SC-FDMA as the encoding scheme for the reverse link (mobile to base station) when the forward link uses OFDMA.</p>
<p>What is the reason for the difference?</p>
| |electrical-engineering|telecommunication|lte|modulation| | <p>SC-FDMA is encoded and transmitted from the handset where there are power tradeoffs. This encoding is better than OFDMA for the handset for the following related reasons:</p>
<ul>
<li>Reduces peak to average power ratio</li>
<li>Increases efficiency of the power amplifier</li>
<li>Increases battery life</li>
</ul>... | 38 | Why does the LTE Specification define SC-FDMA as the modulation scheme for the reverse link? |
2015-01-21T00:46:44.707 | <p>Recently, both Zigbee and Z-wave tend to be the most commonly used protocol to communicate between Internet of Things (IoT) devices. Most of these IoT devices tend to have a combination of mechanical or optical related transducer or actuator device component coupled with a micro-controller and respective software st... | |electrical-engineering|telecommunication|iot| | <p>I will leave the main part of the previous answer below, as it contains more information about the differences between several radio protocols.</p>
<p>As for the differences between Zigbee 3.0 and Z-Wave, let's do a side by side comparison:</p>
<ul>
<li>Frequency: Zigbee uses the 2.4GHz band, while Z-wave uses the... | 50 | What are the pros and cons of between Zigbee and Z-Wave communication protocols used in IoT device space? |
2015-01-21T01:19:55.740 | <p>I am thinking mainly in $\frac{kWh}{m^3}$ and $\frac{\$}{m^3}$.</p>
<p>In the past some decades a wide range of surprisingly efficient water desalination plants were built, mainly in desert regions (Middle East). These plants use reverse osmosis via a system of multiple pressered membranes. This solution seems to b... | |water-resources| | <p><strong>For reverse Osmosis</strong></p>
<p><a href="http://urila.tripod.com/desalination.htm" rel="nofollow noreferrer">This site gives the minimal required energy for sea water desalination by RO as 2.78 kJ/l (fresh water)</a>, this is if you consider only the reversible process. According to <a href="https://en.... | 54 | What development possibilities could yet exist in water desalination? |
2015-01-21T01:23:13.033 | <p>I have been investigating recapturing energy from house lighting using solar panels.</p>
<p>Are there solar panels specifically designed to capture indoor lighting with a higher efficiency?</p>
<p>If so, what are the differences between the outdoor and indoor solar panels designed for this purpose?</p>
<hr>
<p><... | |electrical-engineering|photovoltaics| | <p>I have this 150 Watt panel, 12 volt(said to be). In testing it with two 100 Watt (equal too regular 100 watt old kind) bulbs used for lighting the room. This one panel can light up two other LED bulbs from the two on the ceiling. WOW, I thought that was impossible. That you only get 10% from the panel. Not so...</p>... | 55 | Are there different solar panels for recapturing energy from household lighting? |
2015-01-21T02:29:22.187 | <p>I would like be able to measure LED brightness using a cost effective instrument.</p>
<p>What are the available instruments to measure LED brightness and respective cost effective techniques?</p>
<p>Background: I'm interested in converting what the customer thinks is acceptable brightness to actual LED brightness ... | |electrical-engineering|optics| | <p>There are two aspects that you need to consider here: One is physical measurement of luminance, luminous flux, or illuminance (I'll come on to the differences in a moment), and the other is the much less clear-cut issue of human perception.</p>
<p>Let's deal with the physics first. There are three concepts to expla... | 62 | How can I measure the brightness of a LED? |
2015-01-21T02:42:04.263 | <p>The debate of traffic circles (also called roundabouts or rotaries) versus traffic light intersections has been in progress for a while. Those in favor of traffic circles <a href="http://www.wsdot.wa.gov/Safety/roundabouts/benefits.htm" rel="noreferrer">say that</a>, among other things, that they are safer than traf... | |traffic-light|highway-engineering| | <p>Roundabouts let traffic flow more smoothly and there is also less reliance on technology that can malfunction due to a series of factors (i.e. power outage, etc).</p>
| 63 | What are the pros and cons of a traffic circle versus a traffic light intersection? |
2015-01-21T03:15:17.020 | <p>I have a 2 mm thick steel plate which is 300 mm long and 30 mm wide, supported at either end. It supports a weight-bearing wheel that can roll along the plate. It currently supports the maximum weight that I expect it to support when the wheel is in the middle, but it flexes a little bit too much. Would making it wi... | |mechanical-engineering|steel|stiffness| | <p>As mentioned in other answers, what controls the deflection is the second moment of area, and the easiest way to increase it is increase the thickness. Doubling the thickness would increase the 16 fold the second moment of area and it would increase the weight by 100%</p>
<p>However below I am outlining, another wa... | 68 | How does width and thickness affect the stiffness of steel plate? |
2015-01-21T04:05:04.740 | <p>One of the valves on my 3 bar line just failed. Without it, our production has ground to a stop and we can't operate until we get a replacement (which we have already ordered). In order to make a deadline, I am trying to find a way to use a (properly rated for pressure) DN 16 flanged valve to fit with the existing D... | |steam|piping| | <p>If you have access to a lathe you should be able to quickly machine a flanged reducer out of <a href="http://en.wikipedia.org/wiki/Nylon_6" rel="nofollow">Nylon 6</a>. Not sure what temperature you're operating at but make it a bit thick and it will easily be able to handle 3 bar.</p>
| 74 | How can I fit a DN16 flange to a DN10 flanged pipe? |
2015-01-21T09:16:09.513 | <p>For one-off, bespoke electronic products, or ventures on low budgets, what is the cheapest way of ensuring the product conforms to EMI/EMC requirements of CE marking? This can be at design time and / or throughout the manufacturing process.</p>
<p>Examples:</p>
<ul>
<li><p>A small-run, electronic microprocessor b... | |electrical-engineering|emc| | <p>First of all, the main documents you need to know:</p>
<ul>
<li>DIRECTIVE 2004/108/EC relating to electromagnetic compatibility:
<a href="http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2004:390:0024:0037:en:PDF" rel="nofollow">http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2004:390:0024:003... | 86 | CE Marking on low budgets: conforming to EMI / EMC requirements in ELV and mains circuits |
2015-01-21T10:09:38.163 | <p>There has recently been a series of <a href="http://www.theguardian.com/business/2015/jan/14/cheesegrater-leadenhall-building-bolt-city-london" rel="nofollow">high profile bolt failures</a> on <a href="https://en.wikipedia.org/wiki/122_Leadenhall_Street" rel="nofollow">'The Cheesegrater'</a> in London, which have be... | |mechanical-engineering|civil-engineering|structures|metallurgy| | <p>I know it's an old thread, but I'm putting my solution on here because I've just come across this issue.</p>
<p>Understanding the causes could help you deal better with hydrogen embrittlement.</p>
<p><strong>Overstressing:</strong>
Primarily, extra stress put on material results in the form of blisters, cracks, h... | 87 | How can we prevent/detect hydrogen embrittlement? |
2015-01-21T10:24:26.413 | <p>When designing a steel beam, the resistance to buckling is related to M<sub>cr</sub>; the elastic critical moment for lateral-torsional buckling.</p>
<p>However the Eurocodes give no advice about how to calculate this parameter.</p>
<p>How would you calculate it?</p>
| |civil-engineering|steel|beam|eurocodes| | <p>The answer by Frédéric Bourgeon is great. You may also find useful this <a href="https://www.eurocodeapplied.com/design/en1993/elastic-critical-moment" rel="nofollow noreferrer">free online calculation tool for elastic critical moment</a> in eurocodeapplied.com. It is based on the aforementioned NCCI but it is much ... | 88 | How do you calculate Mcr (critical buckling moment) |
2015-01-21T10:34:49.407 | <p>It is common to lift bridges to replace bearings, etc.</p>
<p>In an ideal world the lifting capacity required of the jacks would be the self-weight of the bridge divided by the number of jacks (+ allowances for wind/snow, etc.).</p>
<p>From my (limited) experience, however, bridges begin to 'stick' to their bearin... | |civil-engineering|structures|bridges|maintenance|friction| | <p>So there's an incorrect assumption underlying your question.</p>
<blockquote>
<p>In an ideal world the lifting capacity required of the jacks would be the self-weight of the bridge divided by the number of jacks (+ allowances for wind/snow, etc.).</p>
</blockquote>
<p>And the assumption there is that the lifting... | 89 | Additional jacking force to overcome stiction/dry friction |
2015-01-21T22:09:23.393 | <p>I've looked around for different types of <a href="http://en.wikipedia.org/wiki/Concrete_pump" rel="nofollow noreferrer">concrete pump</a>s and simply don't know if there are many different types, what their mechanisms are and which ones are the most predominant ones.</p>
<p>What I've found:</p>
<ul>
<li>This <a h... | |mechanical-engineering|pumps| | <p>I've found <a href="http://www.ritchiewiki.com/wiki/index.php/Concrete_Pump" rel="nofollow">a fairly comprehensive source</a>. There are five main types:</p>
<ul>
<li><strong>Mechanical pumps:</strong> A piston and a rotary valve are used the push the concrete through.</li>
<li><strong>Hydraulic pumps:</strong> Hyd... | 120 | What are the predominant types of concrete pumps and what are their working mechanisms? |
2015-01-21T22:18:05.123 | <p>How are spindle speeds calculated for a drill bit?</p>
<p>I've seen dozens of charts that highlight the rpm that should be used for specific drill bit types, bit diameter, and material. However, what if my chart doesn't have the particular type of material or bit that I am using? I'd also like to have some intuitio... | |machining|mechanical-engineering| | <p>Rotational speed is a by-product of the desired result and is generally a compromise to optimise other factors.</p>
<p>To give a simple example of why this is, consider that a twist drill cuts across its entire frontal surface. While the rotational speed of the bit is constant across the face, the linear speed varie... | 121 | Determining Drill Speed |
2015-01-21T23:55:26.270 | <p>What is an effective method to re-engineer a current product to reduce engineering bill of material (EBOM) cost?</p>
<p>This is a continues improvement project for a current product in electronics space. Attached is an example of a PCB board. The product consists of many similar boards. The BOM includes active and ... | |electrical-engineering|cost-engineering| | <p>In addition to the above,</p>
<ul>
<li>Consider arrayed components instead of discretes. i.e., a 4-unit 1k SMT 1206 for an IC's pull-ups instead of 4pcs 1k 0805. Saves board space and assembly time also.</li>
<li>Weigh the expense of going double-sided with any possible reduction in PCB footprint.</li>
<li>If out-s... | 126 | How to reduce Engineering Bill of Material Cost for electronics products? |
2015-01-22T10:12:39.987 | <p>Given a tolerance within which your workpiece should be manufactured, say some length should be $10\pm1$mm. If you determine that your uncertainty in measuring this length is $0.2$mm (at 95%). How should a measurement of $9.1$mm be treated?</p>
<p>Clearly there is a significant probability that this value will actu... | |tolerance|measurements|statistics| | <p>Measurement variations are very common and should be taken in to consideration when engineering systems. In most cases high precision equipment is available but might be cost prohibitive to justify purchasing for the project. Therefore, the goal of the engineer is to design the system to account for measurement vari... | 137 | How does measurement uncertainty combine with tolerances? |
2015-01-22T17:56:18.063 | <p>As I heard, the life expectancy of photovoltaic cells is normally some decades, as so. This is very long, regarding their high cost, it has significant (negative) effect on the total costs.</p>
<p>Why do they age? I can see the only possibility which could damage their atomic structure, and this is the very high en... | |photovoltaics| | <p>For a different angle, my experience with solar cells is space-based, rather than terrestrial. The biggest drivers for degradation of space based solar cells are particle radiation and orbital debris impacts. The particle radiation degrades by wearing down the junction, and the orbital debris degrades primarily by i... | 150 | Do solar cells age? Why, and how? |
2015-01-22T18:25:15.817 | <p>I think, it could be a reactor utilizing californium-242 (or, at least, weapon-grade U-235) cooled and moderated by heavy water.</p>
<p>Essentially, it were similar to an atomic bomb, but - of course - it would be optimized for stay around the equilibrial state.</p>
<p>The result were probably a very strong neutro... | |nuclear-technology| | <p>An almost-critical sphere of fissionable material would do. Add some neutron reflecting material that can be rotated to increase or decrease the neutron reflection. Or you could have two halves of a critical sphere that are moved closer together or further apart to control the reactivity. </p>
<p>A moderator is not... | 151 | Smallest possible controlled chain reaction-based nuclear fission reactor? |
2015-01-22T20:40:52.330 | <p>I punch metals before I start a bit in them, but with small-diameter bits I am finding that they wander inside the material. E.g., drilling a 1/8" hole in 1/2" of aluminum the (titanium-coated HSS) bit will come out the other end a measurable distance to a side (orthogonal to the drill feed direction) from where it... | |materials|machining| | <p>It's common to start with a shorter, stiffer tool such as a center drill or a spotting drill. In addition, using the shortest drill bit that drills the hole you need will increase stiffness. Because of the flutes in a drill, the stiffness goes down geometrically as the length increases. The other variable you have c... | 160 | How do I keep my bit from wandering on a drill press? |
2015-01-22T20:59:09.643 | <p>I want to design a small wind turbine that can be easily carried out of the classroom into the sports field in relatively low-wind conditions (5-15km/h) that can power a small ultra-bright 5V LED - just enough to show that it works.</p>
<p>How do I calculate the power I can get from different blade diameters in the... | |electrical-engineering|renewable-energy|power-engineering|wind-power| | <p>There is a useful calculator at <a href="https://rechneronline.de/wind-power/" rel="nofollow noreferrer">https://rechneronline.de/wind-power/</a></p>
| 162 | How to correctly size the blades for a small educational wind turbine? |
2015-01-22T23:16:05.397 | <p><a href="https://en.wikipedia.org/wiki/Pontoon_bridge">Pontoon bridges</a> differ from traditional bridges in that they are supported not by structures anchored to the floor of the body being spanned but by floating pontoons that are connected by a more rigid structure that supports a roadway. They're often used by ... | |civil-engineering|bridges| | <p>Yes, and they have been used successfully in some major applications. One of the example in your list is <a href="https://en.wikipedia.org/wiki/Evergreen_Point_Floating_Bridge">Evergreen Point Floating Bridge</a> "Its 2,310 meters (7,580 ft) floating section is the longest floating bridge in the world.". It carries... | 165 | Are pontoon bridges being considered to extend bridge span? |
2015-01-22T23:16:44.680 | <p>By "modern computers," I mean electronic programmable computers such as those that were developed about the middle of the 20th century.</p>
<p>My understanding is that early computers such as Charles Babbage's "calculating machines" worked mainly on mechanical principles, like a modern "abacus". Apparently later ma... | |computer|electrical-engineering|engineering-history| | <p>HDE 226868 already mentioned the transistor in detail, so I will add many, many technological advances and theoretical backgrounds for the evolution of the computer.</p>
<ul>
<li><p><strong>Metallurgy</strong><br>
For the mass-market you need cheap and reliable methods to produce the desired electronic elements. Fo... | 166 | What engineering advances paved the way for "modern" computers? |
2015-01-23T01:27:14.347 | <p>I understand that you can have a device with angular measurements for rotation and elevation, and use trigonometry to calculate the distances... but only if you have some distances to start with. How did they accurately measure the first straight-line distance over any distance significantly long enough to give usab... | |engineering-history|surveying| | <p>The device for taking horizontal and vertical angles that you mention is called a theodolite. Theodolites only started being phased out as the main surveying tool in the 1980s when total stations where introduced. Below is a Soviet theodolite from 1958, (ex Wikipedia).</p>
<p><img src="https://i.stack.imgur.com/V1K... | 170 | How was surveying for maps done before lasers? |
2015-01-23T13:38:05.777 | <p>The Eurocodes gives the following equation for estimating a "simply supported bridge subject to bending only"*:</p>
<p>$$n_0 = \frac{17.75}{\sqrt{\delta_0}}$$</p>
<p>Where</p>
<ul>
<li>$n_0$ is the natural frequency <em>in hertz</em></li>
<li>$\delta_0$ is the deflection at mid-span under permanent actions <em>in... | |bridges|dynamics|eurocodes| | <p>There is some more information on this in Ladislav Fryba's book "Dynamics of Railway Bridges" (1996). If you read chapter 4, you will see formula 4.53 on page 92:</p>
<p>$$f_1 = 17.753 v_{st}^{-1/2}$$</p>
<p>With $f_1$ being the first natural frequency in Hertz and $v_{st}$ the midspan deflection in mm. This is ex... | 179 | Derivation for bridge natural frequency estimate in Eurocodes |
2015-01-23T17:34:03.773 | <p>There are numerous steel alloys, containing mostly iron, carbon, and some other metals. Generally speaking, we can think of them as if they were some type of steel.</p>
<p>My question is: do "non-ferrous steels" exist? I am thinking of pure, non-iron metals, containing a little carbon, just as is added to iron to t... | |steel|alloys|metals| | <p><strong>Summary: The Fe-C system, and thus steel, is unique due to a eutectoid transformation from a high-solubility phase to a low solubility phase that allows for a wide variety of microstructures and properties which are highly and relatively easily tunable. Other first-row transition metals have different, and l... | 186 | Do "non-iron steels" exist? |
2015-01-23T18:03:09.120 | <p>As I know, a very considerable part of the currently processed steels (around half of it) is coming from recycling.</p>
<p>But during the steels coming into the recycling process are coming normally from various sources, and thus they are containing very different alloying materials.</p>
<p>But the output of the r... | |steel|metallurgy|alloys|recycling| | <p>First the scrap is separated at the source ; for example cast iron generally only contains Si and Mn. High vapor pressure elements boil off or collected in the flux/slag : eg, Zn, Pb, Sn, Bi, An ,,,,Aluminum oxidizes and goes into the slag. Steels do pick up Cr, Ni, Mo, and Cu residuals , generally these are advanta... | 191 | How can the alloying materials of recycled steels be separated? |
2015-01-23T18:05:35.530 | <p>Consider a large auditorium, a church, or some other very large, essentially one roomed building with a high ceiling. Suppose that the building has many entrances which enable cold air in/hot air out and traffic in and out of the building is unavoidably large. </p>
<p>I would imagine that any attempts to control ... | |civil-engineering|building-physics|energy|hvac| | <p>Another option to the radiant solution above would be under floor air distribution systems (UFAD) using displacement ventilation. These systems require a raised floor plenum which works well in theatre style auditoriums, where you often have this anyway. The plenum essentially becomes your supply duct.</p>
<p>The s... | 193 | What is the most efficient means of warming a building with a high ceiling? |
2015-01-23T20:21:06.483 | <p>For a <a href="http://en.wikipedia.org/wiki/Piston_pump" rel="nofollow noreferrer">piston pump</a> you can calculate/measure things like,</p>
<ul>
<li>Average Volume flow rate (m³/s)</li>
<li>Geometric Values (Surface)</li>
<li>Pressure over time</li>
<li>closing times of the valves</li>
<li>energy conversion effic... | |mechanical-engineering|pumps| | <p>• Piston pump has a wide range of pressure
• It can manage force without the moving flow rate.
• The Pressure and flow rate variations have a small effect on the pump performance.
• It has the capability to move high viscosity fluids such as abrasives and slurries with an excellent design.
• Low speed.
• The fluid d... | 200 | What are characteristic values for a piston pump? |
2015-01-24T05:36:09.180 | <p><strong><em>Disclaimer</em></strong>
I'm an applied mathematician by training, not an engineer. My work research primarily focuses on creating new "methods" to solve different PDE's related to solid deformation (elasticity) and fluid mechanics. In this sense, i know how to solve a pde problem computationally. Fro... | |modeling| | <p>There isn't much left to say but that knowing result before runing simulation isn't knowing exact numerical value but to have certain expectations regarding solution based on understanding the physics of the problem. Usually engineers set problem and choose general method and when we finally formulate problem as set... | 207 | How do engineers really use numerical simulation? |
2015-01-24T13:13:19.357 | <p>These days most of modern electronics use rechargeable batteries as a power source. Also, these days most modern rechargeable batteries are <strong>Lithium Ion</strong> or <strong>Lithium Polymer</strong> based. Like any other devices, over time these rechargeable batteries lose the ability to recharge, retain and d... | |energy|electrical-engineering|energy-storage|chemical-engineering|battery| | <p>One of the problems that plagued older rechargeable batteries (e.g. Nickel Cadmium ($\text{NiCad}$) and Nickel Metal Hydride ($\text{NiMH}$)) was the <a href="https://en.wikipedia.org/wiki/Memory_effect">memory effect</a>. The memory effect occurs when a rechargeable battery is not fully discharged. It then "forgets... | 211 | What causes rechargeable batteries to age? What can be done to extend life of these batteries? |
2015-01-24T15:27:54.717 | <p>EMI/EMC issues are common in most electronic designs. Electronic and Hardware Engineers use many different strategies to mitigate these issues: These include (But not limited too)</p>
<ul>
<li>Designing filter circuits </li>
<li>Strategic selection of micro-controller clocking frequency </li>
<li>PCB layout conside... | |mechanical-engineering|electrical-engineering|emc| | <p>Generally speaking meeting the EMC/EMI requirements is the EE job. The biggest part of radiated EM waves usually comes from a poor PCB, and of course there is little the ME can do about that. Providing more space, if possible, can relax some constraints for the EE that will have more space to properly route his/hers... | 212 | Can Mechanical Design help meet EMC/EMI requirements for electronic products? |
2015-01-24T16:22:45.257 | <p>Austenite is <strong>non magnetic</strong> while $\alpha$-ferrite and pearlite <strong>are magnetic</strong>. (<a href="http://www.sciencedirect.com/science/article/pii/030488539390454A">Magnetic properties of pearlite vary as a function of carbon content</a>) </p>
<p>If a strong magnetic field is applied in a part... | |steel|process-engineering|materials|metallurgy|magnets| | <p>This will at least depend on the:</p>
<ul>
<li>Rate of Cooling</li>
<li>Magnetic field strength</li>
<li>Exact composition</li>
</ul>
<p>The magnetic field will alter the microstructure as you can read in, for example,</p>
<ul>
<li>Yudong Zhang, Nathalie Gey, Changshu He, Xiang Zhao, Liang Zuo, Claude Esling, Hig... | 214 | Can we change steel properties by application of magnetic field while quenching? |
2015-01-24T16:41:54.090 | <p>Localities in the US have different road layout and setups.</p>
<p>For example the <a href="http://en.wikipedia.org/wiki/Michigan_left">Michigan Left</a>, <a href="http://en.wikipedia.org/wiki/Jughandle">Jersey Left/Jug Handle</a>, vs a standard 4 way stop with left turns at the intersection.</p>
<p>Have any of th... | |civil-engineering|highway-engineering| | <p>Yes.</p>
<p><strong>Michigan left</strong></p>
<p><a href="http://web.archive.org/web/20090510121808/http://www.tfhrc.gov/safety/pubs/04091/10.htm#1022">This page</a> (pdf <a href="http://web.archive.org/web/20090510122331/http://www.tfhrc.gov/safety/pubs/04091/04091.pdf">here</a>) is very informative, though you ... | 215 | Has a specific type of alternative intersection been shown to reduce congestion & accidents? |
2015-01-24T19:17:31.397 | <p>I was looking at high pressure pipes and their pressure ratings. I'd like to know how these pressure ratings are determined.</p>
<p>I assume that pipes are tested until failure, and the failure pressure is multiplied by some safety factor to determine its 'rated' pressure, but is there a formula to calculate what t... | |mechanical-engineering|pressure|mechanical-failure| | <p>In the world of plastic piping, the formula is different, because the material doesn't <a href="https://en.wikipedia.org/wiki/Yield_(engineering)" rel="nofollow">yield</a>. For <a href="https://en.wikipedia.org/wiki/Isotropy#Materials_science" rel="nofollow">isotropic</a> plastics, B31.3 shows piping as:</p>
<p>$$... | 218 | How to calculate the pressure a pipe can withstand? |
2015-01-24T20:39:22.510 | <p>Weight lifters will use the term "one rep maximum" in order to refer to the maximum amount of weight that they can lift one time. The one rep max is often used as a proxy for how strong someone is (or isn't).</p>
<p>Recreational lifters, other types of athletes, and the general population rarely bother with testin... | |statistics|biomechanics| | <p>This actually isn't as much of an engineering question as it is a physiology question. There are actually a number of widely used estimates to predict your one-rep maximum, aka "1RM", if you know how many repetitions you can do at a lower weight. <a href="http://www.weightrainer.net/training/coefficients.html" rel="... | 223 | Estimating maximum lift or strength |
2015-01-24T20:46:33.150 | <p><a href="https://www.refrigerationbasics.com/RBIII/controls1.htm" rel="nofollow">Cut-in, cut-out</a> <a href="http://en.wikipedia.org/wiki/Thermostat" rel="nofollow">thermostats</a> are commonly used with refrigeration devices in order to hold a consistent temperature range. </p>
<p>Their general operations is suc... | |electrical-engineering|circuit-design|refrigeration| | <p>A <a href="http://en.wikipedia.org/wiki/Bimetallic_strip" rel="nofollow noreferrer">bimetallic strip</a> is used. Two different metals like steel and copper expand at different rate and a strip of the two bound together as result bends with temperature changes. A contact placed at the end of the strip will close whe... | 224 | Thermostat design properties |
2015-01-24T21:51:11.753 | <p>Some dc motors can be used as generators as well by applying mechanical torque to the output shaft to induce a current. However, even if a dc motor <em>can</em> do this, I imagine they were not designed for this purpose and thus perform less efficiently when used as a generator rather than as a motor.</p>
<p>In my... | |mechanical-engineering|electrical-engineering| | <p>In Ye olden days DC generators were brushed commutated devices. They had a one or more stator windings and an armature winding. Field wound DC generators as well as motors were commonly connected in one of three methods: Series, Shunt and Compound. Without getting into details, each had its own set of strengths and ... | 226 | How different are dc motor designs from dc generator designs? |
2015-01-25T12:13:28.800 | <p>Since the units are the same ($\frac{N}{m^2}$), what's the difference between pressure and stress?</p>
| |pressure|stresses| | <p>Pressure is force applied per unit area. It arises due to external forces on the surface of an object.</p>
<p>When external forces are applied, in order to avoid deformation internal forces are generated which are called Stresses. Both pressure and stress have the same unit. </p>
| 229 | What is the difference between pressure and stress? |
2015-01-25T16:00:44.127 | <p>I want to do some very simplified drag calculations on a vessel. My hope was that calculating the skin-friction resistance would be enough to get a good estimate of the surge resistance.</p>
<p>Because wave-making resistance is very speed dependent, I assume you can neglect it when the vessel is below a certain spe... | |drag|marine-engineering| | <p>"Hull speed" is actually the ratio of speed to the square root of length.
To make things even more confusing, length is in feet, and speed is in
knots. That's how the constant 1.34 arises. (ProTip: Let's never speak of
it again!)</p>
<p>Wave resistance ($R_w$) begins its rapid rise at a Froude number (Fr) of
abou... | 231 | Below what Froude number can I neglect wave-making resistance on a vessel? |
2015-01-26T11:41:47.390 | <p>As a hydraulics layman thinking about hydraulic systems, it seems that the important factor is to have a liquid that doesn't compress much or at all. Doesn't water meet this requirement, and what other properties should the liquid have (if any) that water doesn't?</p>
| |mechanical-engineering|hydraulics| | <p>In addition to the other answers, water is commonly used as a primary working fluid in industrial hydraulic systems <em>with</em> additives to prevent the issues mentioned above. Typical applications include furnaces, foundries, plastic extrusion, etc. Anywhere that standard hydraulic oil represents a major fire or ... | 270 | Why do hydraulic systems use special fluid - what's wrong with water? |
2015-01-26T12:03:23.730 | <p>As this will depend on Pressure drop $\Delta p$, assume that it does not leave the range from 0 to 100 bar. The <a href="http://en.wikipedia.org/wiki/Hagen%E2%80%93Poiseuille_equation" rel="noreferrer">Hagen-Poiseuille equation</a> for an incompressible fluid is defined as:</p>
<p>$$ \dot{V} = \frac{\pi R^4 \Delta ... | |fluid-mechanics|microfluidics| | <p>Same answer as above, "Yes BUT..."</p>
<p>This is from a practical point of view:</p>
<p>Other than HPLC, nearly all "microfluidics" applications are far into the laminar region. Poiseuille's law works very well most of the time.</p>
<p>When going below 100<span class="math-container">$\mu$</span... | 271 | Can you use the Hagen-Poiseuille equation for a pipe which radius is in the sub-millimeter region? |
2015-01-26T17:56:37.703 | <p>For a project I had built a <a href="http://en.wikipedia.org/wiki/De_Laval_nozzle" rel="nofollow noreferrer">convergent divergent nozzle</a> designed for Mach number = 3. In that project, I could know the flow has gone supersonic by seeing the manometer fixed between the throat and the divergent section (drop in pre... | |fluid-mechanics|gas|pipelines|measurements| | <p>If you still looking for answer, </p>
<p>You could keep a well-designed wedge, with static holes on the wedge surface, eighther 1. the surface of the wedge is aligned with the flow axis or 2. aligned symmetric line with the flow axis. you will have pitot pressure from Raleigh pitot-tube.</p>
<p>Now you could measu... | 280 | How to know whether the flow is supersonic in a nozzle? |
2015-01-26T20:33:45.380 | <p>A friend and I wrote a paper for a fluids class discussing the details (as they relate to fluid dynamics) of constructing a cannon that could shoot a steak fast enough to cook it.</p>
<p>We quickly discovered (but not quickly enough to change our topic) that our paper was a bit too ambitious for two twenty year old... | |fluid-mechanics|gas| | <p>I know this is an old post, however there is a fairly simple way to determine the gas pressure required for launching things from a tube. </p>
<p>Assume isentropic expansion, so that the expression $\frac{p}{p_0}=\left(\frac{V_0}{V} \right)^\gamma$ holds. Here, $p_0$ and $V_0$ are the initial pressure and volume be... | 283 | Determining pressures of a compressible gas |
2015-01-27T14:31:24.163 | <p>This is inspired by a project I undertook for my Physics class last year; I'd like to apply it in the future.</p>
<p><strong>Background:</strong> For the project, I and a few classmates were required to build a small car powered by any of a number of sources; we opted for a mousetrap that turned two rear wheels on ... | |mechanical-engineering|friction|applied-mechanics| | <p>The friction you are talking about when referencing the cloth would more correctly be refered to as rolling resistance. In a true sense, you need to increase (the coeficient of) friction to increase traction or increase the force acting normal to the ground.</p>
<p>You can increase the coeficient of friction by cha... | 298 | How can I improve traction on a wheeled vehicle yet reduce friction? |
2015-01-27T15:52:56.227 | <p>It's been a long time since I went over heat exchangers and even then it was all theoretical. I'm looking for anyone with real world experience with different types of heat exchangers.</p>
<p>I'm looking at building a external wood burning stove. <a href="http://www.crownroyalstoves.com/Websites/crownroyalstoves/im... | |mechanical-engineering|thermodynamics|heat-exchanger| | <p>I can't speak from real (=hands on with my own hands) experience, but in industrial applications I see mostly <strong><a href="http://en.wikipedia.org/wiki/Shell_and_tube_heat_exchanger" rel="nofollow">shell and tube</a></strong> type HX. Exhaust is in the tubes, the shell has the water.</p>
<p>Pros:</p>
<ul>
<li>... | 302 | Most efficient heat exchanger for dirty air/water medium? |
2015-01-27T21:37:38.480 | <p>With the huge metal shredders that can shred an entire car or a bus, they can shred parts like the axle and engine which are large solid chunks of metal, just like the massive spinning shredder blades.</p>
<p>So why does the car get shredded and not the shredder? Are the blades made from harder/stronger metal, or i... | |crushing|shredding|waste-disposal| | <p>The blades are indeed made of, or tipped with a hard steel/carbide, but they also don't contact each other. The shredding action is created by the shear forces of the two corotating drums of "teeth", and this non-contact between the hard points, high shear strength, and gearing advantages allow it to power through w... | 309 | Why don't massive industrial shredders shred themselves? |
2015-01-27T22:28:43.523 | <p>I live in Louisiana these days, in an area that is known for its numerous antebellum plantation homes (circa early 1800s). While touring one of these homes it was clear that almost everything about the house was designed around keeping cool in the summer. Some examples:</p>
<ul>
<li>4-meter-high ceilings to allow ... | |civil-engineering|energy-efficiency|heat-exchange|cooling| | <p>In dry/arid areas a <a href="http://en.wikipedia.org/wiki/Windcatcher" rel="noreferrer">wind catcher</a> tower in conjunction with a <a href="http://en.wikipedia.org/wiki/Qanat" rel="noreferrer">qanat</a> is a great way to keep buildings cool. The underground water stays cool and cools the air passing over it that i... | 313 | How to design a house to be cooled passively? |
2015-01-28T08:12:50.767 | <p>To size a heat exchanger, I need to know (among other things) the Reynolds number (Re) as an indication of the flow conditions. The Re number depends on the viscosity. In a <a href="http://en.wikipedia.org/wiki/Shear_thinning" rel="nofollow noreferrer">shear thinning fluid</a>, I can't assume a constant viscosity, i... | |mechanical-engineering|heat-exchanger|fluid-dynamics| | <p>First, as Arthur notes, even the best Nusselt number correlations are often as much as 20% off, so don't expect any analytical method to give results that are much better than approximate.</p>
<p>With that said, there are ways to compute the Reynolds number for shear thinning fluids. <a href="http://www.sciencedir... | 329 | How to size a heat exchanger for a shear thinning fluid? |
2015-01-28T15:00:33.337 | <p>A <a href="http://en.wikipedia.org/wiki/Helicopter_rotor#Flybar_.28stabilizer_bar.29" rel="nofollow noreferrer">helicopter flybar</a> is a kind of gyroscopic stabilizer which acts in feedback to the pitch of the blades. The effect, in words, is that as the helicopter starts to pitch or roll in a particular directio... | |aerospace-engineering|feedback-loop| | <p>This angle is determined by the lift characteristics of the rotor and the rotational inertia of the whole helicopter. You are exactly correct that the angle changes the phase of the feedback.</p>
<p>For the purpose of discussion let's assume the helicopter has pitched forwards slightly and needs to be corrected bac... | 332 | What is the effect of changing the angle of a helicopter flybar? |
2015-01-28T19:27:50.297 | <p>Many commercial and open-source CFD codes implement several closure methods for the non-linear convective acceleration term of the Reynolds-averaged Navier-Stokes (RANS) equations. Common methods (also known as <em>turbulence models</em>) include</p>
<ul>
<li><a href="http://en.wikipedia.org/wiki/Spalart%E2%80%93Al... | |mechanical-engineering|fluid-mechanics|fluid-dynamics|simulation|modeling| | <p>In case you only have the resources to perform one simulation only I would agree with @Subodh and use $ k-\omega\:SST$.</p>
<p>In case you can afford multiple simulations I would use different models and compare. This way you can identify the influence of the turbulence model in your particular application.</p>
<p... | 336 | Which turbulence models are suitable for CFD analysis on a streamlined vehicle body? |
2015-01-28T22:00:19.550 | <p>The specific example I have in mind is a car tire with a small leak in it. As the pressure increases, does the outflow of air increase linearly, i.e. $v\propto P$, or does it have some more interesting behavior?</p>
| |fluid-mechanics|pressure|fluid-dynamics|valves| | <p>Yep, the answer is a bit more interesting.</p>
<p>The mass flow rate ($\dot m$) will vary as $C_d A \sqrt{2 \Delta P}$ (discharge coefficient, cross sectional area, and change in pressure across the valve). Barring compression of the fluid, velocity will behave the same way.</p>
<p>The devil of the thing is in $C_... | 337 | For a small valve in a fluid system, what is the relationship between pressure and flow rate? |
2015-01-29T08:59:38.777 | <p>Suppose I have a concrete tank, round, vertical, diameter in the range 16m-24m. One half the floor is filled with gravel or concrete to a height of maybe 2 meters. When the tank is empty, that will mean I have about 5 tons per m² more weight on this half, when the tank is full (with water or a slurry that's mostly w... | |civil-engineering|soil|geotechnical-engineering| | <p>Here's a really (and I mean really!) quick and dirty set of calculations that might give you an idea of the magnitudes of settlement you could be dealing with. </p>
<p>The settlement potential of the tank location can be determined a number of ways, but probably the best thing to do would be a plate load bearing te... | 346 | Settling of unevenly loaded storage tank |
2015-01-29T21:18:31.507 | <p>This is related to the question <a href="https://diy.stackexchange.com/questions/58612/will-dark-gutters-stay-ice-free-better-than-light-colored-gutters">Will dark gutters stay ice free better than light colored gutters?</a> The current consensus seems to be that the mass of the gutters and limited light may make si... | |solar-energy| | <p>And so, as promised, I'll do it.</p>
<p>First assumption:
Let's work with 1m long strips of gutter. It'll be easier to calculate everything starting from here.</p>
<p>Let's say the gutter is already full of ice. (We'll work on the ice filling problem later on)</p>
<p>The standard gutter size (according to <a href... | 356 | Is it possible to modify a home gutter to absorb sufficient solar energy to melt ice? |
2015-01-30T10:54:13.783 | <p>I recall learning about the bronze age in school. Why was bronze so important to the technological development of humans? Why not some other metal? </p>
| |materials|metallurgy|engineering-history| | <p>I'd like to add to what @Fred said.</p>
<p>Bronze wasn't the first. Before the Bronze Age, there was a comparatively brief <a href="http://en.wikipedia.org/wiki/Copper_Age" rel="nofollow">Copper Age</a> [also <a href="http://en.wikipedia.org/wiki/Metallurgy_during_the_Copper_Age_in_Europe" rel="nofollow">this</a>].... | 371 | What made bronze the first widely used (non-ornamental) metal in human civilization? |
2015-01-30T16:30:13.347 | <p><a href="http://en.wikipedia.org/wiki/Otto_Lilienthal">Otto Lilienthal</a>, sometimes hailed as the first aviator, became famous for his many gliders, which pioneered new experiments in aeronautics. However, powered aircraft didn't take off - pun intended - until the Wright brothers successfully flew their powered a... | |engineering-history|aerospace-engineering|aircraft-design| | <p>I'm going to answer my own question because just before posting it I found an answer.</p>
<p><a href="http://www.lilienthal-museum.de/olma/e213.htm" rel="nofollow noreferrer">The Otto Lilienthal Museum</a> has a comprehensive list of Lilienthal's designs. One is listed as the "small wing-flapping machine." It didn'... | 380 | Did Otto Lilienthal ever experiment with non-human-powered aircraft? |
2015-01-30T18:28:07.380 | <p>The cabin noise of vehicles is <a href="http://elevatingsound.com/the-top-30-quietest-cars-a-cabin-noise-test-by-auto-bild/" rel="nofollow">a large concern in the luxury market</a>. Why haven't any automakers used the same techniques as are employed in <a href="http://en.wikipedia.org/wiki/Noise-cancelling_headphone... | |electrical-engineering|feedback-loop|audio-engineering|automotive-engineering| | <p>Some reasons why noise reduction in vehicle cabins is not a standard feature, yet:</p>
<ul>
<li>As @Trevor Archibald states, safety is a very good reason. There is still a need to hear
some noises from outside the vehicle such as the sirens of emergency
vehicles: police, ambulance, fire fighters truck</li>
<li>Hear... | 382 | Is active noise cancellation useful in vehicles? |
2015-01-31T19:04:29.037 | <p><strong>Background:</strong><br>
In an automobile, only <sup>1</sup>/<sub>3</sub> of the potential energy in the fuel is converted into mechanical energy and significant portion of the energy is lost as heat. </p>
<p>There have been previous attempts to recuperate this lost energy. In the early 1990's, Porsche de... | |mechanical-engineering|electrical-engineering|thermodynamics| | <p>The use of any idea/technology is dependent on its cost effectiveness. Efficiency is just one part of the analysis. If the modules were free and never went bad, they would certainly be in use. However, high temperature modules are expensive for their power produced; making them currently not cost effective.</p>
<p>... | 389 | Thermoelectric Technology to Harvest Energy from Internal Combustions Engines |
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