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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2015-06-27T13:31:11.017 | <p>Normally, in investment casting, the mould is preheated before pouring the liquid metal in to reduce thermal shock from rapid cooling. </p>
<p>In a vacuum, the heat transfer due to gas convection is reduced to zero, which will also reduce the thermal shock. Does that mean that, if performing investment casting in a... | |metallurgy|metals| | <h3>Convection, Conduction, Radiation</h3>
<p>Of the three modes of heat transfer, only one is affected by the vacuum. As you noted in your question, gaseous convection should be eliminated. That being said, the thermal shock is present as soon as the hot material hits the mold. As soon as the two materials come into c... | 3353 | Is it necessary to preheat an investment casting mould when working in a vacuum? |
2015-06-27T23:22:44.917 | <p>I'm trying to understand the importance of protective coatings on steel structures like the Golden Gate Bridge. For example, if we stopped maintenance on the Golden Gate Bridge today and left it packed with empty cars, what would be its expected lifetime (until a car falls into the water) and the variance of that li... | |civil-engineering|bridges|corrosion| | <p>If you are really considering catastrophic failure, what you are asking actually has several parts. The first is the coatings aspect, the second is the metal structure, the third is the connections, the fourth is the cables, the fifth would be the substructure and the sixth is the foundation. A failure of any one ... | 3356 | How do protective coatings affect the lifetime of bridges? |
2015-06-28T02:57:28.337 | <p>I recently discovered that one of my roommates had attempted to boost the WiFi signal by cutting up a soda can and placing it near the router, like this:</p>
<p><img src="https://i.stack.imgur.com/Xisb7.png" alt="Airport router with carved up soda can"></p>
<p>My roommate was probably following an internet guide l... | |electrical-engineering|signal|wifi| | <p>It is too small a surface area to be an effective microwave reflector. The shape is wrong too, it must be parabolic with respect to the transmitting fractal antenna of the router. Yours is perpendicular to it.<br>
<a href="http://www.instructables.com/id/Easy-to-Build-WIFI-24GHz-Yagi-Antenna/" rel="nofollow norefe... | 3358 | Is it possible to "boost" a WiFi signal using an aluminum soda can? |
2015-06-28T21:49:59.043 | <p>I'm interested in metalworking as a hobby, to make small parts for my numerous other hobbies. I'm looking at those cheap, typically Chinese import mini-lathes and mini-mills. I've read about their limitations as compared to larger machines; this question is not about that.</p>
<p>My question is, <strong>what are ... | |mechanical-engineering|machining| | <p>If the cost and workspace are not the problems, you should take 2 separate machines. Otherwise, a combo machine will save the money and workspace</p>
| 3367 | What is the difference between using separate lathe and mill or a combination machine? |
2015-06-29T14:03:34.793 | <p>There is a room on the south side of the building, which doesn't have any ventilation vents, but does have a window.</p>
<p>Opening a window doesn't cause good air circulation (by which I mean that the air in the room is still hot, and the air on the street is still cold).</p>
<p>How does one create good air circu... | |fluid-mechanics|hvac|airflow| | <p>The fundamental problem is that hot air must leave the room and cold air must enter it, both at the same time through the same single opening. The conflicting forces will mostly cancel each other out, resulting in very little actual exchange of air.</p>
<p>What you really need is old technology.</p>
<p><em>Double... | 3374 | How does one create a draft in a room (with a single window)? |
2015-06-29T14:06:55.073 | <p>What type of a mechanical device can I use and program to apply a controllable force within the range of what a human can to an area about the size of a fingertip? It is desirable for the applied force to be precise and known.</p>
| |mechanical-engineering| | <p>I agree the compressed air is the way to go. There are many vendors that sell small cylinders and even have bumpers available for the end of the actuator rod that could approximate a fingertip.</p>
<p>For control, you don't mention any requirements, but if they're simply manually controlled on/off application of fo... | 3375 | Applying an adjustable force to a small area |
2015-06-29T15:28:41.657 | <p>I am interested in finding a way to calculate the force necessary to do a backwards extrusion. Typically these would be for forgings 0.5 to 3" in diameter (or square) of different kinds of steel. The diagram below shows a typical type of forging I might want to do:</p>
<p><img src="https://i.stack.imgur.com/FCVagm.... | |mechanical-engineering|forging| | <p>You can find formulas for Backward extrusion in <a href="https://books.google.com.tr/books?id=_ZVqPgAACAAJ&printsec=frontcover&dq=editions:ISBN0470505923&hl=tr" rel="nofollow">Groover's Principles of Modern Manufacturing 4th edition</a> section 17.5.2. I summarized required formula but if you need more i... | 3381 | How can I calculate backward extrusion force |
2015-06-30T06:09:49.630 | <p>If I have a vehicle (V1) with one 100 kW engine and an identical vehicle (V2) with 2 of these 100 kW engines, will this mean that V2 will have double the torque of V1 and double the top speed of V1?</p>
<hr>
<h3>Suspected Answer</h3>
<p>It's not like in a series circuit in which, when you have two identical batte... | |mechanical-engineering|automotive-engineering| | <p>There is no simple answer. What is the top speed limiting factor? For a truck, it's mostly handling so no amount of power can increase that. For a sports car, it's mostly aerodynamic resistance. While the aerodynamic resistance (more precisely it's called <a href="https://en.wikipedia.org/wiki/Drag_%28physics%29" re... | 3392 | Does having 2 engines together increase anything? |
2015-06-30T13:02:46.953 | <p>In a Vacuum Metallurgy (Casting), a mold needs to be heated (500 to 700 degrees) to reduce thermal shock on the metal surface. Normally, a gas fired oven is employed for such job, but in a vacuum environment how do you achieve the same?</p>
| |metallurgy|metals| | <p>A second idea for added control, if needed:</p>
<p>If your molders can accomplish it, you could also bury a <a href="https://en.wikipedia.org/wiki/Heating_element" rel="nofollow">heating coil</a> in the mold before you harden it. The heating cable would need to be able to withstand the liquid metal temperatures, s... | 3394 | Heating Sand/Ceramic/Refractory Material under vacuum |
2015-06-30T15:21:46.420 | <p>I am looking to complete a materials science/engineering-based Master's degree in the UK. Those which I have been looking at, particularly Leeds and Manchester, do not seem to be accredited by the <a href="http://www.iom3.org/" rel="nofollow">IOM3</a> or other institutions.</p>
<p>I am interested in becoming charte... | |materials|education|licensure| | <p>Try asking the <a href="http://www.iom3.org/" rel="nofollow">IOM3</a> & other accrediting institutions why the courses you are interested in are not accredited and if there is a possibility that they could be accredited in the near future.</p>
<p>The courses may not cover material that such institutions conside... | 3396 | What are the career implications of choosing a non-accredited postgraduate degree? |
2015-06-30T18:20:20.170 | <p>The rubber casing for my iPhone cable has frayed and split near the phone port, and I would like to seal it somehow to stop the split from spreading further. Would Krazy Glue be an effective sealant? I've heard that superglue can eat away at some materials.</p>
| |materials|adhesive| | <p>Where a cable enters a connector is a point strain, point strains are remarkably prone to failure. I would not use glue at all particularly a rigid glue like super glue. I would use dental floss or string, and caulk or a curable plastic putty.</p>
<p>To begin take a length of string about two foot long and fold it ... | 3397 | Can Krazy Glue be used as a sealant? |
2015-06-30T20:29:08.570 | <p>How can I "tie" pressure change due to a mass leakage from the flow?
In a "closed" system I'd use $pV=nRT$ but this is an "open" system...</p>
<p>My open system is an horizontal (no gravity issue) pipe (constant sections) in which flows a gas. We may think pipe walls as permeable walls. Hence we have one incoming f... | |fluid-mechanics|gas| | <p>You can't use the <a href="https://en.wikipedia.org/wiki/Ideal_gas_law" rel="nofollow">ideal gas law</a> in an open system, but you can use <a href="https://en.wikipedia.org/wiki/Bernoulli's_principle" rel="nofollow">Bernoulli's equation</a>. </p>
<p>Starting with the conservation of energy: </p>
<p>$$ E_{in}... | 3402 | Pressure drop due to mass loss |
2015-07-01T05:09:35.830 | <p>I've had trouble with leaky pipe flanges, since my flanges are made of plastic. The problem comes down to the fact that sealing a flange is based on torque. Torque relies on bolt friction, which can change even between different bolt diameters. Therefore, it's a terrible indicator of the clamping force. </p>
<p>Is ... | |mechanical-engineering|piping|bolting|threads| | <p>I'm sure there are specific strategies relating to pipe flanges, but for the broader issue of controlling that all of your bolts are tight enough, here is some background information.</p>
<p>When tightening bolts in any clamping application, what's really important is the total clamping force. In any simple joint, ... | 3409 | Measuring pipe bolt torque without a torque wrench |
2015-06-23T18:04:15.747 | <p>I have a small issue that is causing a lot of problems. I'm on a <a href="https://en.wikipedia.org/wiki/Formula_SAE" rel="nofollow noreferrer">Formula SAE</a> team and our battery is consistently shorting between our positive terminal and our chassis. Our chassis is the grounding point. </p>
<p>Our battery is under... | |electrical-engineering|automotive-engineering|battery| | <p>A piece of thick plastic or timber will make a lid that will solve this or use a gel battery and lay it on its side</p>
| 3415 | How to prevent shorts between exposed battery terminals and racing vehicle chassis |
2015-07-02T02:12:59.257 | <p><em>The question</em>: Consider $1\ kg$ of air at $32\ C$ that is expanded by a reversible polytropic process with $n=1.25$ until the pressure is halved. Determine the heat transfer.<br>
Specific heat constant volume for air is $0.1786\ kJ/kg.K$</p>
<p>The correct answer is: $17.02\ kJ$ heat added</p>
<hr>
<p>M... | |mechanical-engineering|heat-transfer| | <p>You can't use the specific heat constant of constant volume - a polytropic process isn't constant volume or constant pressure.</p>
<p>Instead, what is derived is the specific heat of polytopic expansion:</p>
<p>$$c_n = c_v\frac{n-k}{n-1}$$</p>
<p>Where k is the <a href="https://en.wikipedia.org/wiki/Heat_capacity... | 3420 | The Heat Added in a Reversible Polytropic Process |
2015-07-02T06:01:49.487 | <p>I major in microelectronics. I just want to apply a fixed and adjustable force to my flexible sample.</p>
<ul>
<li>'Fixed' means that the force could be hold for given time without change.</li>
<li>'Adjustable' means that the force would be changed after my setting or its value could be changed with time and rule.<... | |mechanical-engineering|mechanical-failure| | <p>The poor man's solution would be to simply stack weights onto your sample.</p>
<p>While that seems low tech, you need surprisingly little different weights, which you can usually buy in sets, to get a massive range of forces.</p>
<p>The applied force is guaranteed to be independent of deflection, and this solution... | 3423 | How can I apply a fixed and adjustable force to my flexible sample? |
2015-07-02T12:19:03.220 | <p>The Bond number is a dimensionless number typically used to analyze cases where two fluids of different densities are in contact and subject to gravity only. I'm analyzing a system where gas and liquid are entrained in a pipe (think garden hose with trapped air pockets), and both are subject to high accelerations, ... | |fluid-mechanics| | <p>After some more thought on this, I'm realizing that the Bond number is more of a measure of the ratio of <em>body</em> forces to surface tension. Since I am looking at acceleration by way of <em>surface</em> forces, I'm not sure the traditional Bond number is applicable here. </p>
<p>@Mark's answer regarding dime... | 3431 | Bond number for accelerating flow |
2015-07-02T12:43:50.503 | <p>So one of the proposed suspension systems that will be used on the <a href="https://en.wikipedia.org/wiki/Hyperloop" rel="nofollow">hyperloop</a> include the externally pressurized air cushions. These cushions lift (or at least help lift) the capsule and reduce drag when the capsule is in motion. Also, the tube itse... | |fluid-mechanics|transportation|drag| | <p>The air used for the air cushions will come from the air still in the tube pressurized by the pod itself.</p>
<p>Thus the system remains closed (all air that is released is sucked out of the environment).</p>
| 3432 | How does the pressurized suspension of the Hyperloop not affect the tube pressure? |
2015-07-02T15:26:59.073 | <p>Due to the fact that pipe flanges rely on bolts, and bolts rely on friction, it seems obvious to me, as a manufacturer of piping, to recommend that bolt torques need to be checked every so often, to ensure piping doesn't leak. I've got a few questions about this, but here is the first one:</p>
<p>How often do you ... | |mechanical-engineering|piping|bolting|maintenance| | <p>There is no answer because there are too many variables, amount of vibration and thread geometry being just two of them. A joint could last for 10,000 years or work loose tomorrow. There is no way to know.</p>
| 3441 | How often do you need to check torques on bolted flanges? |
2015-07-02T18:31:29.740 | <p>I have been reading about embedded systems, and particularly the reset modes. As I understand a microcontroller can have several reset modes. </p>
<p>What is brownout reset (BOR) and power on reset (POR)? What is the difference between BOR and POR?</p>
| |electrical-engineering|embedded-systems| | <p>When the V<sub>dd</sub> drops below a brown out threshold voltage, BOR will hold the microcontroller in reset state. Not all devices have BOR detection, but most do, and some have multiple voltage thresholds to select from.<br>
Between a BOR and Power On Reset the whole range of startup voltages can be covered to pr... | 3443 | What is the difference between BOR and POR micro-controller reset modes? |
2015-07-02T20:42:34.323 | <p>I have seen a number of structures within rivers, which resemble steps, and which allow the water to cascade down them instead of flowing naturally down the course of the river. </p>
<p>Example 1: River Avon in Bath</p>
<p><a href="https://i.stack.imgur.com/rPrQj.jpg" rel="noreferrer"><img src="https://i.stack.img... | |civil-engineering|hydrology|flow-control| | <p>The two photos in the post show the same structure: <strong>Pulteney Weir</strong>, downstream of <a href="https://en.wikipedia.org/wiki/Pulteney_Bridge" rel="noreferrer">Pulteney Bridge</a> on the River Avon in Bath. The shot of the "Seine" in <em>Les Miserables</em> was <a href="http://www.imdb.com/title/tt1707386... | 3450 | What is the purpose of these "steps" in rivers? |
2015-07-03T02:07:55.673 | <p>I am answering this question:</p>
<blockquote>
<p>Steam enters the superheaters of a boiler at a pressure of 25 bar and
dryness of 0.98% and leaves at the same pressure at a temperature of
370 °C. Calculate the heat energy supplied by the superheaters.</p>
</blockquote>
<p>The answer is supposed to be 405.51... | |thermodynamics|steam| | <p>You just got the math wrong</p>
<p>$$h_1 = 962.11 + (0.98*1841.01) = 2766.2998 \ \mathrm{kJ/kg}$$
$$q = (h_2-h_1) = 3171.8 - 2766.2998 = 405.5 \ \mathrm{kJ/kg}$$</p>
<p>(I omitted your $m$ in final equation since we are calculating per kg.)</p>
| 3455 | Calculating the heat energy supplied by a superheater |
2015-07-04T05:40:35.293 | <p>I am trying to solve the problem:</p>
<blockquote>
<p>What is the lifting force of in kN for a 10 m diameter spherical balloon with helium inside at 101 kPa and 320 K surrounded by air at 101 kPa and 298.15 K?</p>
</blockquote>
<p>The given answer is 5.28 kN.</p>
<p>I start from the Buoyancy Formula:</p>
<p><span cl... | |fluid-mechanics| | <p>Just for additional information, incase you didn't know how to get the specific gas constant of He.</p>
<p>The general formula is Universal gas constant over the molecular weight of the specific gas is equal to the specific gas constant:</p>
<p><strong>Ru/MW = Rgas</strong></p>
<p><strong>8.314/4.002 = 2.077 KJ/Kg .... | 3468 | What is the lifting force of a helium balloon in air? |
2015-07-05T10:09:05.673 | <p>I am solving the problem:</p>
<blockquote>
<p>A gas bubble rising from the ocean floor is 1 inch in diameter at a depth of 50 feet. Given that specific gravity of seawater is 1.03, the buoyant force in lbs being exerted on the bubble at this instant is nearest to:</p>
</blockquote>
<p>The given answer is 0.020 l... | |fluid-mechanics|thermodynamics| | <p>the difference in densities is essential. A bubble of air will have much more of a buoyant force than a bubble of oil in the water.</p>
| 3473 | Calculating the buoyant force of a rising bubble |
2015-07-05T11:12:49.380 | <p>I am solving the following problem:</p>
<blockquote>
<p>Air having an initial pressure of 6516 kPa and an initial volume of 0.113 m<sup>3</sup> is compressed adiabatically to a final volume of 0.057 m<sup>3</sup>. Calculate the work done by the gas as it compresses to a final pressure of 17237 kPa.</p>
</blockquo... | |thermodynamics| | <blockquote>
<p>Is my relation correct?</p>
</blockquote>
<p>Yes, it's correct. And here is the derivation:</p>
<p>mechanical work is defined as:
$$W = \int_{V_i}^{V_f}P\,dV$$</p>
<p>multiplying by $\frac{V^{k}}{V^{k}}$:
$$W = \int_{V_i}^{V_f}\frac{PV^{k}}{V^{k}}\,dV$$</p>
<p>Since $PV^{k}$ is constant, we can sa... | 3475 | Why do I get negative work done for adiabatic compression of air? |
2015-07-05T13:50:10.037 | <p>In fluid kinematics I can't understand the meaning of these terms : vorticity and circulation.<br>
Can somebody give me a description of these terms so that a lay person can understand them easily?</p>
| |fluid-mechanics| | <p>There are fundamental types of motion (or deformation) for a fluid element: translation, rotation, linear strain and shear strain. Usually all these types of motion occur concurrently which makes the analysis of fluid dynamics somehow difficult.</p>
<p>One can express the rate of translation vector mathematically by... | 3478 | What is the meaning of vorticity and circulation? |
2015-07-06T00:26:33.297 | <p>I am trying to find the enthalphy of Helium if its internal energy is 200 kJ/kg. The answer is given as 333.42 kJ/kg, but I keep getting the wrong answer.</p>
<p>I've tried the following:</p>
<p>$\begin {align}
H &= U + PV \\
H &= U + mRT \\
\end {align}$</p>
<p>Universal Gas Constant, $R_u = 8.314 \:\mat... | |thermodynamics| | <p>Following your method: You can't assume that temperature of Helium at that particular state is $273.15\ K$, but we can calculate it as follows:</p>
<p>$$u = C_{v}\Delta T$$
$$\Delta T = \frac{u}{C_v} = \frac{200}{3} = 66.66667\ K$$
$$h = C_{p}\Delta T = 5*66.66667 = 333.3 \ kJ/kg$$</p>
<p>As John said, Values from... | 3484 | Finding the enthalphy of Helium given internal energy |
2015-07-06T15:40:46.590 | <p>While deciding what tool (library) to use for a simulation of a hybrid gas turbine plant, I found that different libraries/tools of thermodynamic properties yield different values than the other.</p>
<p>I made a simple test to calculate $c_p$ of air at $300\ K$(same goes for enthalpy by the way) only for simplifica... | |mechanical-engineering|thermodynamics|simulation|numerical-methods| | <p><strong>What do you think is the reason for the difference in values?</strong></p>
<p>It's likely that they have calculated the coefficients of whatever model they are using from different data sets (or sub-sets). It's also possible that they are using different models.</p>
<p><strong>is this level of accuracy suf... | 3492 | Different calculations for values of thermodynamic properties |
2015-07-07T15:56:36.713 | <p>My Lego model has a winch on the front. It's a simple spindle with a reel on it with a rubberised cog for winding at one end and two cogs at the other (as shown below).</p>
<p>Is there a technical name for the cog/gear on the blue spindle that stops the cog on the grey spindle spinning freely? Is this a common mech... | |gears|pulleys| | <p>I would say that you have a <a href="https://en.wikipedia.org/wiki/Ratchet_(device)" rel="nofollow">ratchet</a>. Ratchets do fail. The <a href="https://en.wikipedia.org/wiki/Brownian_ratchet" rel="nofollow">Brownian Ratchet</a> is a simple thought experiment done by thermodynamic physicists that shows that ratchet... | 3506 | Gear that prevents another gear spinning freely |
2015-07-08T13:31:04.777 | <p>Does anyone have a feel for the flatness of Portland Cement when poured in a standard/typical way? Say, for example, that I wanted to pour a cement "cube" (20"x 18"x 19.25") in a mold. How flat would the top surface be without any special procedures? </p>
<p>Background:
I am going to mount a forceplate on top of th... | |concrete|tolerance| | <p>If you live in a country that uses ACI standards, you might consider specifying flatness using an F<sub>L</sub> or F<sub>F</sub> number. ACI 117, Commentary Table R4.8.4 has this information, with flatness ranging from "Conventional" to "Super Flat." For the dimensions you have listed, specifying anything beyond "... | 3517 | Typical flatness of Portland cement |
2015-07-08T20:47:36.880 | <p>I've been shopping around for gears, pulleys and other transmission components for building a milling machine over the past few weeks. Many of these parts are so rudimentary and ubiquitous, yet the prices are very high. A ribbed pulley, for instance, about 3 inches in diameter often sells for over $30 online. Many o... | |mechanical-engineering|linkage| | <p>In such cases you don't pay for the rubber, but for the administrative and storing costs. Manufacture a such rubber and then try to sell it on the ebay. With taxes, all of the law regulations, with post costs, etc.</p>
<p>For example, if you only want a rare screw to repair a device, you can easily pay even tens of... | 3524 | What factors into the high cost of transmission components? |
2015-07-09T21:26:55.567 | <p>Over in <a href="http://chat.stackexchange.com/transcript/message/22676589#22676589">Programmers chat</a> we were discussing whether a gold skeleton would be feasible. That got me thinking:</p>
<p>If I were to build a Terminator (T-800) using pure gold as the endoskeleton, would the skeleton be able to support the ... | |materials|stresses|metals| | <p>The following table gives some of the material properties of four metals: gold, aluminium, titanium and iron. </p>
<pre><code>Metal Tensile Shear Bulk Young's Brinell Density
Strength Modulus Modulus Modulus Hardness
MPa GPa GPa GPa GPa g/cm^3
Gold... | 3534 | Would a T-800 with a gold skeleton deform under stress? |
2015-07-10T07:04:24.203 | <p>Would the body of a normal round pot shaped pressure cooker (built to cook foods at 15 psi) be able to withstand being evacuated down to high-vacuum pressures?</p>
<p>Apparently it has been done before: <a href="http://www.instructables.com/id/Pressure-Cooker-Vacuum-Chamber/" rel="nofollow">i.e. this instructable</... | |mechanical-engineering|structural-engineering|pressure| | <p>Round profiled vessels fail at vacuum collapse pressures far below those designed for internal pressures. If more vacuum resistance is required, corrugated designs are preferred. Thin bellows survive upto 30% of external pressure as vacuum.</p>
| 3538 | Would a structurally sound pressure cooker be able to withstand an internal vacuum? |
2015-07-10T16:30:23.910 | <p>I have a strip of stainless steel encastree'd at one end to which is applied a constant pressure on one side, and I need to know what the deflection equation y = f(x) is at equilibrium.
If the deflection was small I would be able to use one of the very well known deflection formulas which assume vertical loads, but... | |mechanical-engineering|beam| | <p>For large deformation, there are changes to the strain-displacement relation and vertical equilibrium, but horizontal equilibrium remains unchanged.</p>
<p>Let N be the axial force and M the bending moment, for finite rotations, these are defined as:
$$
N=EA\epsilon^o
\\
M=EI\kappa
$$ where
$$\epsilon^o = \frac{du... | 3541 | Large deflection of a cantilever beam with distributed normal load |
2015-07-10T16:32:20.300 | <p>I am answering the following question:</p>
<blockquote>
<p>Gas initially at a pressure of 101.325 kPa and temperature of 60 °C
undergoes the following cycle:</p>
<ul>
<li>1-2: Adiabatic Compression through compression ratio of 4.5:1</li>
<li>2-3: Heating at constant volume through a pressure ratio of ... | |mechanical-engineering|thermodynamics| | <blockquote>
<p>What am I doing wrong? Is it not an Otto cycle?</p>
</blockquote>
<p>No, it's not an Otto cycle. It would be if it wasn't for the last process, heat rejection (cooling) in Otto cycle is performed at constant volume not constant pressure.</p>
<p>This should be the <span class="math-container">$P-v$</span... | 3542 | Thermal efficiency of a given complete cycle |
2015-07-11T02:12:58.180 | <p>I am solving the following problem:</p>
<blockquote>
<p>The tank of an air compressor has a volume of 3 cubic feet and is
filled with air at a temperature of 40 °F. If a gauge on the tank
reads 150 psig, what is the mass of the air in the tank?</p>
</blockquote>
<p>The given answer is 1.78 lbs.</p>
<p>This ... | |mechanical-engineering|compressors| | <p>You forgot to divide by 1.5 at the bottom of your equation.
Try it and see, but I suggest you use exact values to start good habits.</p>
| 3544 | Finding the mass in the tank of an air compressor from gage pressure |
2015-07-11T16:18:46.103 | <p>I am contemplating buying a new car. However, the approach to the underground garage in my apartment has a 90 degree frustrating turn. Given the dimensions of the approach and car, what is the max turn circle for the car to fit the garage and turn?</p>
<p><img src="https://i.stack.imgur.com/A7A8w.jpg" alt="garage a... | |automotive-engineering| | <p>Something important to consider is that if the corridor taking you down to the underground is narrower then the width of the way turning in, then there are certain sizes of cars that are able to go in but are unable to go out from the underground garage. So these cars can only go out in reverse.</p>
| 3547 | How much clearance does a car need when turning a corner? |
2015-07-12T03:57:26.417 | <p>Air in the cylinder of a Diesel Engine is at $30^o\ $$C$ and $138\text{ kPa}$ in compression. If it is further compressed to 1/18th of its original volume. Which of the following most nearly equals the work done in compression of the displacement volume of the cylinder is $14.2$ Liters</p>
<p>Answer is $11\ \text{k... | |mechanical-engineering|thermodynamics|engines| | <p>Your second attempt is correct, you just had two mistakes: </p>
<ol>
<li><p>If you re-calculated $V_1$ you'll find that it equals $0.01503$ not
$0.0158$ $m^3$.</p></li>
<li><p>same issue with $P_2$.
$$P_2 = \frac{138*10^{3}*0.01503^{1.4}}{(8.3529411*10^{-4})^{1.4}}= 7.889*10^6\ Pa$$</p></li>
</ol>
<p>Substituting ... | 3550 | Methods for determining Work of Diesel Engine's Isentropic Process |
2015-07-13T16:43:00.907 | <p>Almost all of the new Snapdragon CPU series (610, 810) have an overheating problem. This overheating problem may occur in the first few hours of using mobile phones that are equipped with the CPU, as we can see from the various reviews from around the web on Xiaomi mi4i, LG G4, Sony Xperia Z3+, etc.</p>
<p>I assume... | |quality-engineering|computer-engineering| | <p>There is no good reason to think that Qualcomm's QC people did not detect the problem. It's what you do about it that is the problem.<br>
That there is or ever was a problem is denied by Qualcomm, some users and some independent testers. But at least one reasonably well documented test set indicates that when runnin... | 3554 | How do products like the overheating Snapdragon CPU make it through quality control? |
2015-07-14T12:29:28.053 | <p>I am designing an NFC device but am still a little unsure about the principles behind NFC/RFID. From what I understand:</p>
<ol>
<li><p>A primary coil constantly emits a 'carrier frequency' magnetic
field.</p></li>
<li><p>This field induces an e.m.f. on a passive secondary coil which is in
a secondary circuit.</p><... | |electrical-engineering|wireless-communication| | <p>The transmitter to receiver coupling is similar to how a transformer works. for a ideal transformer, whatever impedance is connected to the secondary appears as the impedance of the primary divided by the square of the turns ratio.</p>
<p>For example, imagine a 7 V AC source and a 1:2 stepup transformer. If you c... | 3566 | How do NFC/RFID devices transmit data? |
2015-07-14T17:41:09.513 | <p>The common description for a continous PID-controller is written like this:
$$y(t)=K_p⋅e(t)+K_i\int_0^t e(τ)dτ+K_d\dfrac{de(t)}{dt}$$
The best value of the constants $K_p$, $K_i$ and $K_d$ for a given controlled system will depend on its time constant(s), be it a $\text{PT}_1$ system, or $\text{PT}_2$ system, etc. .... | |control-engineering|control-theory| | <p>One way would be to implement some form of adaptive control. If your range of time constants is small and known, you could use something called <a href="http://www.controleng.com/search/search-single-display/back-to-basics-how-gain-scheduling-works/52cd5aac6a456dfb6b1352494e4dd169.html" rel="nofollow">"gain scheduli... | 3571 | How do you set up a PID-Control if the time constants of the controlled system are variable? |
2015-07-15T01:58:10.700 | <p>I am solving the following problem:</p>
<blockquote>
<p>A Pipe 200 mm outside diameter and 20 m length is covered with a layer
of 70 mm thick insulation having thermal conductivity of 0.05 W/m·K
and a thermal conductance of 10 W/m<sup>2</sup>·K at the outer surface. If the
temperature of the pipe is 350 °C ... | |thermodynamics|heat-transfer| | <blockquote>
<p>What does it mean by "temperature of the lagging" ?
</p>
</blockquote>
<p>Air's comment:</p>
<blockquote>
<p>The lagging is not really the insulation layer itself but the cladding around the insulation layer. The insulation has no real structural properties to speak of; lagging not only holds t... | 3574 | Calculating the temperature of the lagging around an insulated pipe |
2015-07-15T17:42:40.840 | <p><a href="https://i.stack.imgur.com/mOgz0.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/mOgz0m.jpg" alt="enter image description here"></a></p>
<p>$\rho, p_o, \alpha, F_g, h, b$ are given. $F_T$ is wanted. There is a plate that can rotate around $A$. The plate measures b perpendicularly to the s... | |mechanical-engineering|fluid-mechanics| | <p>It looks like, from your math, you attempt to find the total normal force due to the pressure on the incline $F_p$, and then try to find a distance $l_a$ from point A such that if $F_p$ was applied there the torque would be equivalent to the torque caused by the pressure.</p>
<p>I'm not sure what you would use $l_a... | 3582 | Calculating pressure force on inclined area |
2015-07-16T02:41:15.393 | <p>Given the question:</p>
<blockquote>
<p>Calculate the energy transfer rate across a 6 in wall of firebrick with a temperature difference across the wall of 50 °C. The thermal conductivity of the firebrick is $0.65\ \frac{\text{Btu}}{\text{hr ft }^\circ\text{F}}$ at the temperature of interest.</p>
</blockquot... | |thermodynamics|heat-transfer| | <p>L=6 inches(2.54cm/(1 inch))=15.24cm</p>
<p>∆T=50℃</p>
<p>k= 0.65 Btu/hr-ft℉((1W/cm℃)/(57.79Btu/hr-ft℉))= 65/5779 W/cm℃</p>
<p>q_k/A=k/L ∆T</p>
<p>q_k/A= ( 65/5779 W/cm℃)/15.24cm × 50℃</p>
<p>q_k/A=0.0369 W/〖cm〗^2 = 369 W/m^2</p>
| 3585 | Problem with Energy Transfer Rate Conversion |
2015-07-16T06:25:14.473 | <p>For an assignment, I was given:</p>
<blockquote>
<p>Calculate the heat loss per linear ft from $2$ $in$ nominal pipe. ($2.375$ $in$ outside diameter covered with $1$ $in$ of an insulating material having an average thermal conductivity of $0.0375$ $Btu/hrft^oF$. Assume that the inner and outer surface temperature... | |heat-transfer|pipelines| | <p>I get 115.706...<br />
= 116
ie their answer.</p>
<p>What you are doing wrong (in this problem and your other recent one) is going too fast and not visualising how the data given translates into the real world situation. You are applying formulae correctly and seem to have a good understanding of what is involved t... | 3588 | Heat Loss per Linear Ft |
2015-07-16T09:24:31.383 | <p><a href="https://engineering.stackexchange.com/questions/370/how-do-i-calculate-the-forces-on-a-desk-and-its-legs">This question about calculating loads on parts of a desk</a> made me finally ask my first question on SE.</p>
<p>What generally applicable standards are there for office furniture (desks, let's say), t... | |mechanical-engineering|standards| | <p>In the United States at least, the design of mass-produced furniture if covered under ANSI/BIFMA (Business and Institutional Furniture Manufacturer's Association) <a href="https://www.bifma.org/store/ViewProduct.aspx?id=1375047">X5.5</a>. I don't have a copy of the standard to give you specific values, but in broad ... | 3591 | What loads are office desks required to withstand? |
2015-07-17T21:56:42.583 | <p>If I have a flat span of steel material, 3.0m x 150mm wide and 5mm thick, and apply an increasing downward force to the middle, at some point it will fail.</p>
<p>But if the profile of that piece of steel was T shaped instead of a flat span, it is much stronger. </p>
<p>Is the Safe Working Load (SWL) for differe... | |mechanical-engineering|materials|structures| | <p>There are better ways of <em>uniformly</em> stiffening a plate e.g., by the <em>Sandwich</em> principle. A somewhat compromised version is the <em>Isogrid</em>, these are the distributed I-beams.</p>
<p>In both methods, effective bending rigidity is increased by making plate central parts hollow and so lighter in w... | 3605 | How much strength does adding a T piece add? |
2015-07-18T00:11:36.530 | <p>I am solving the following problem:</p>
<blockquote>
<p>A liquid-to-liquid counterflow heat exchanger is used to heat a cold fluid from 120 °F to 310 °F. Assuming that the hot fluid enters at 500 °F and leaves at 400 °F, calculate the log mean temperature difference for the heat exchanger.</p>
</blockquote>
<p>T... | |heat-transfer|heat-exchanger| | <p>$\triangle max$ and $\triangle min$ are not defined as maximum and minimum temperature differences in a heat exchanger. Quoting from Wikipedia:</p>
<blockquote>
<p>The LMTD is a logarithmic average of the <strong><em>temperature difference between the hot and cold feeds at each end</em></strong> of the double pip... | 3606 | Log Mean Temperature Difference of a Counterflow Heat Exchanger |
2015-07-18T14:44:59.970 | <p>Pressure drop across a porous medium can be described by the Forchheimer extension to Darcy’s law:
$$-\frac{dp}{dx} = \frac{\mu}{K_1}\cdot v + \frac{\rho}{K_2}\cdot v^2$$</p>
<p>where $K_1$ and $K_2$ are permeability coefficients that depends on medium geometry (Pitz-Paal
et al., 1996).</p>
<p>I just came across t... | |mechanical-engineering|fluid-mechanics|porous-medium| | <p>Expanding Dan's answer (after some research), The main reasons for the so-called instability in porous media that is subjected to a heat flux (e.g. Solar irradiance) with air as a working medium are the behavior of dynamic viscosity of air with temperature (Viscosity increases as temperature increases) and the bell-... | 3609 | What is "flow instability" in porous media? |
2015-07-18T18:23:49.867 | <p>I work for a small engineering and manufacturing company. To date our production process for each product has been defined in each critical aspect by the design engineer, then handed to the production department and rarely looked at again by engineering. Many noncritical aspects are undefined and left to the variabl... | |documentation|procedure| | <p>Most engineering discipline are capable of defining manufacturing and test process. It is the management function to ensure the processes are followed. Generally depending on the size and structure of the organization most defining manufacturing and testing process are mostly handled by manufacturing test and proc... | 3612 | What engineering discipline deals with ensuring that a manufacturing and testing process is clearly defined and followed? |
2015-07-19T11:51:35.880 | <p>I have some tomato plants on my balcony (4th floor in a 7 story building). The balcony is a recessed one.</p>
<p><img src="https://i.stack.imgur.com/Qamnt.jpg" alt="Photo of recessed balkonies"></p>
<p>The building has lightning protection on top.</p>
<p>To support them, I put a 2 m long aluminum rod into each po... | |electrical-engineering|building-design|safety| | <p><a href="https://what-if.xkcd.com/16/" rel="nofollow noreferrer">xkcd</a> has a fantastic description of how lightning works. <a href="https://www.youtube.com/watch?v=6MUYsIjTKvk" rel="nofollow noreferrer">This video</a> is also quite good (especially as of 0:56, but the rest is worth watching as well) since it show... | 3617 | Will lightning strike an aluminum rod in a pot on my balcony? |
2015-07-19T07:33:37.257 | <p>Is it possible to use an IR sensor to differentiate accurately between carbon fiber and a human hand kept on the carbon fiber surface?</p>
<p>I would like to move the sensor from one end of the carbon fiber object (a rectangular surface) to the other and be able to detect a significant difference in reflected inten... | |materials|sensors| | <p>Some IR sensors just receive. In this case they distinguish only by difference in infrared emission from the environment. These sensors could not see a hand if it was inside an oven mitt for example or if the hand was the same temperature as the surface, but in most cases it would work.</p>
<p>In a photo gate setup... | 3623 | IR sensor with carbon fibre |
2015-07-19T20:37:25.677 | <p>Referring to von Guiricke's early experiment to hold vacuum using <a href="https://en.wikipedia.org/wiki/Magdeburg_hemispheres" rel="nofollow">Magdeburg hemispheres</a>, what is the best known shape to hold say 10 atmosphere vacuum (external pressure) using <em>any material or material combination</em> without buckl... | |mechanical-engineering| | <p>When I design pressure vessels to hold vacuum, here are the preferences I usually give to customers:</p>
<ol>
<li>Spherical is always the best in terms of minimizing the thickness, but not the most economical in therms of amount it can hold or for being friendly to the manufacturer</li>
<li>Ellipsoidal (2:1) heads ... | 3624 | What is the most lightweight geometry for a vacuum holding vessel? |
2015-07-20T04:43:09.243 | <p>Making extremely accurate machines seems like a chicken and egg problem. How do you make one if you don't already have one?</p>
<p>For example, how was the first <a href="https://en.wikipedia.org/wiki/Indexing_head">indexing head</a> made without an indexing head to make the indexing plate? How was the first lath... | |mechanical-engineering|engineering-history| | <p>For plenty of detail on building accurate machine tools from scratch, read the excellent and detailed "Foundations of Mechanical Accuracy"
By Wayne R. Moore. It's an old book and there are plenty of copies around if you use your favourite web search engine.</p>
<p>The basic principles for increasing accuracy are la... | 3627 | How are increasingly accurate machines made? |
2015-07-21T01:47:14.253 | <p>I am doing B.E. in Mechatronics Engineering. I am due to take a subject called 'Sensors and instrumentation'. So far I only have the syllabus for the course. I decided to do some reading in advance of the course starting.</p>
<p>The syllabus refers to "low pass sensors" and "band pass sensors".<br>
When I web searc... | |electrical-engineering|sensors|power-electronics| | <p>You are combining two concepts. </p>
<ol>
<li><p><strong>A sensor</strong> is any device that responds to a desired signal in some manner to produce an output that is used to detect the presence of the desired signal or to allow some desired attribute of the signal to be measured - such as its amplitude, frequency... | 3639 | What is meant by the terms "low pass sensor" and "band pass sensor" in a course syllabus? |
2015-07-21T09:48:56.713 | <p>What is this tiny rotating piece of hardware that I found inside my Samsung GE1202? It has E9C written in blue on it.</p>
<p><a href="https://i.stack.imgur.com/H4kSJm.png" rel="noreferrer"><img src="https://i.stack.imgur.com/H4kSJm.png" alt=""></a></p>
| |electrical-engineering|motors|consumer-electronics| | <p>That is a micro vibrating motor to produce the "buzz" effect from your phone.
I used much <a href="http://www.chicagovibrator.com/Store/tabid/84/c/truck-vibrators/Default.aspx">much larger vibrating motors</a>, air driven, on the bottom of my Class 7 dump truck. Mounted under the bed, they would vibrate the bed, lo... | 3644 | What is this small rotating part from a cell phone? |
2015-07-21T14:43:24.177 | <p>Would it be possible to power a small LED light using the headset jack of a regular smartphone, and if so, how would you connect the LED light with an audio jack. How would such an implement look like. I'm not very versed in electrical terminology so simplified explanations are appreciated. </p>
| |electrical-engineering|audio-engineering| | <p>Another option to consider is that many phones have a high intensity LED built in near the camera lens which works as a flash. It may be possible to use mirrors or a light pipe to make use of this. </p>
| 3648 | Powering LED light using smartphone headset jack |
2015-07-21T15:41:57.677 | <p>I need to design an automatic shifting system, for a <a href="http://students.sae.org/cds/formulaseries/about.htm" rel="nofollow">FSAE car</a>. Clutch and shifts are electronically engaged and disengaged using a <a href="http://pi-innovo.com/" rel="nofollow">Pi Innovo</a> engine control unit (ECU). </p>
<p>The issu... | |electrical-engineering|automotive-engineering|control-engineering| | <p><strong>Overview:</strong><br>
I wouldn't be worrying about clutch life. From my experience with FSAE events they're not long enough to actually wear down a clutch. </p>
<p><strong>However(!!):</strong><br>
One of the main reason racers actually blip the throttle/rev match is to avoid <strong>compression lockup</st... | 3649 | Automatic Shifting without Electronic throttle |
2015-07-22T18:10:00.393 | <p>Searched, but didn't find this discussed here previously. I'm upgrading a hobby-level CNC router (a Shapeoko 3) to have wider belts (it came w/ 6 mm GT2 (2 mm)), I'm going up to 9 mm (otherwise same specs).</p>
<p>I ordered new pulleys and belting from SDP/SI, but when I went to install them was concerned that the ... | |mechanical-engineering|pulleys| | <p>If I understand you correctly, you're worried about the radial load on the motor shaft due to belt tension when the pulley is located axially 5mm further from the motor. </p>
<p>Whether or not the loading scenario you've described is OK depends on many factors; the shaft dia, material properties of the shaft, the m... | 3657 | Guidelines for motor shaft length and pulley engagement |
2015-07-23T13:47:44.550 | <p>Recently, tube steel manufacturers in the US have begun using the new ASTM A1085 specification for forming tube steel (a.k.a. hollow structural section or HSS) shapes, as opposed to the existing A500 specification.</p>
<p>From what I've read (<a href="https://www.aisc.org/WorkArea/showcontent.aspx?id=33730">here</a... | |structural-engineering|steel|specifications|columns|hss| | <p>AISC's magazine, Modern Steel Construction periodically publishes a guide to specifying grades of steel to help engineers stay aware of developments in the market. Their latest <a href="http://msc.aisc.org/globalassets/modern-steel/steelwise/2015/steelwise.pdf" rel="nofollow">edition</a>, from this February mentions... | 3661 | Tube Steel - ASTM A1085 vs. A500 |
2015-07-23T14:21:05.247 | <p>I'm running an FEA on a vessel that has a "splashing water" effect with vibrations. The problem I'm really coming up against is <em>what kind of Young's Modulus and Poisson's ratio to use for the fluids?</em> - air and water. I have been successful in using the bulk Modulus, and treat it as uncompressible - i.e. P... | |mechanical-engineering|modeling|vibration|finite-element-method| | <p>Section 2.1.14 of the Abaqus Example Problems Manual is 'Water sloshing in a baffled tank', which might be useful (even if you don't use Abaqus at your own institution, the manuals are hosted by many institutions that allow public access). The Abaqus water model uses an equation of state (EOS). If you download t... | 3664 | Modelling splashing water in FEA |
2015-07-23T19:02:23.740 | <p>Is there a calculation / rule of thumb that can determine a containers rough maximum negative pressure (vacuum) from it's rated internal pressure (assuming a single layer construction so there is no additional bracing preventing expansion).</p>
<p>As an example for a 50 litre stainless steel keg (cylindrical with c... | |structural-engineering|pressure|stresses|mechanical-failure|pressure-vessel| | <p>Failure of cylindrical shells under external pressure depends on length in addition to all the factors for internal pressure. If you can get your hands on a copy of the ASME boiler and pressure vessel code Section VIII division 1, and section II part D, you can calculate it yourself using the formulae in UG-28. Alte... | 3668 | Calculating maximum internal pressure from maximum rated external pressure? |
2015-07-24T14:55:40.963 | <p>I know that when a motor runs it generates torque and that torque can be used to do useful work. On the other hand, the motor needs strong support that absorbs the reaction torque. In our case let us assume that that support is provided by a workshop floor on which the motor is firmly attached (the workshop floor is... | |electrical-engineering|motors|torque| | <p>The stator and the rotor would rotate relative to each other in the same way as if one end were attached to the Earth. If your frame of reference was attached to either the stator or the rotor, you would see the things attached to the other part rotating in the same way as if you were standing on Earth. The only d... | 3674 | What would happen if we tried to run a motor in space when it is not attached to anything to provide support to it? |
2015-07-24T15:35:05.160 | <p>This is a schematic for a plastic piece that has an oval hole on it. I understand that the Ø12 part of the measurement is for a diameter, but I do not understand what the <strong>"X25L"</strong> at the end is indicating nor do I understand the <strong>"2-"</strong> at the beginning. What is the meaning of those numb... | |mechanical-engineering|drafting| | <p>The "2-" refers to the fact there are two of these holes somewhere on the print. Rather than making that same note every time the hole appears, you can say "2-" or "6-" and leave it to be assumed that all similar holes are identical to the dimensioned one. (At my company, we use "2x" or "6x", but this person may not... | 3677 | How does a dimension like "2-Ø12X25L" describe an oval hole? |
2015-07-25T23:03:44.690 | <p>I need to select a solid body in ANSYS Design Modeler, with script, in a design with multiples bodies. With the following command I select all the solid bodies, but this is not what I need.</p>
<pre><code>ag.bodyPick;
ag.gui.SelectAll();
</code></pre>
<p>I'm creating a script to model two spur gears engaged, first... | |mechanical-engineering|design|computer-aided-design|ansys| | <p>You can select a single body by this code:</p>
<pre><code>agb.AddSelect(agc.TypeBody, bodyname);
</code></pre>
<p>Here is the script:</p>
<p>(Key ideas: First, assign name "GEAR" to the gear body <code>ag.fm.Body(2).Name = "GEAR";</code>. Second, creat gear object by <code>gear = selectNode("GEAR");</code> where ... | 3685 | What is the script function to select Solid Body in ANSYS Design Modeler? |
2015-07-27T14:34:30.440 | <p>How can I calculate the propulsive force produced by ejection of a gas? I suppose it depends on the gas, the velocity with which it ejects, the amount of gas, and some other parameters, like the geometry of the nozzle for example. I would like a calculator to play with the gas density, the gas velocity etc, and see ... | |aerospace-engineering|gas|propulsion| | <p>It's pretty basic conservation of momentum kind of problem. A converging diverging nozzle is used to accelerate the gas such that it's supersonic leaving the nozzle. These problems are pretty well-defined. There are lots of calculators out there that let you monkey around with varying different parameters without ge... | 3703 | How to calculate propulsive force of gas ejection |
2015-07-28T11:41:34.847 | <p>I wish to investigate an active vehicle braking method for use in extreme situations. Very high accelerations are acceptable in situations where this would prevent the much worse accelerations present in a collision. </p>
<p>I was thinking of a system that will use ejected gas/liquid to reposition the position of a... | |automotive-engineering|projectiles| | <p>15 g might seem like a lot, and it is, if the 15g is sustained as it would be in something like an aircraft's aerobatic maneuver. 15g isn't unreasonable as a limit to what humans can take in a short duration event like a crash, Indy car drivers have sustained horizontal impact forces many times that without signific... | 3713 | Vehicle emergency high-deceleration braking and steering system |
2015-07-29T14:47:09.493 | <p>I'm designing a compact mechanism for the deployment of a mast. The idea is that the linear actuator for the deployment is on the other side of the pivot, and a slider increases the lever arm to enable the actuator to deploy the mast. </p>
<p>I ran through the maths (shown in details below), and wrote the code for ... | |mechanical-engineering|modeling|mathematics| | <p>If you plot the x values of OP and HP, they cross zero, which seems unphysical.</p>
<p>Looking more closely, you are doing your rotations backwards, i.e. you are doing our rotations in +theta whereas you want to go in -theta.</p>
<p>This is something I often do too. To fix, just replace theta with -theta in M.</p>... | 3729 | Discontinuity in mechanism simulation: is the mechanism jammed or is my analysis wrong? |
2015-07-29T19:27:19.243 | <p>I am an engineering student and I took my second dedicated controls class last semester. It was cool math and whatnot, but after all was said and done: I still have no idea how to make an actual working control system. </p>
<p>In other words, there was no tie-in to reality at all; it was all Laplace-domain mathemat... | |control-engineering|control-theory| | <p>If you are in the unlikely position to have/know the transfer function of your plant/equipment then nothing beats a good predictor.</p>
| 3734 | How can I approach the application of control theory to real control systems? |
2015-07-29T22:55:47.283 | <p>Is there a term used in systems engineering that describes a situation in which the design of one subsystem (call it "A") affects the the requirements for another subsystem (call it "B") <em>while <strong>at the same time</strong> the design of B affects the requirements for A</em>? </p>
| |terminology|systems-engineering|systems-design| | <p>Another term that would be applicable is <strong><em>mutually reliant</em></strong>.</p>
| 3737 | Is there a term for a circular dependency in system design and engineering |
2015-07-30T16:14:07.703 | <p>Occasionally I have to design T-connections between rectangular tube steel (HSS) members where I have a flare-bevel weld between the corner of the tube and the connecting flat member. If the weld stress is high enough, a reinforcing fillet may be required.</p>
<p>Per AWS D1.1-2010, Section 2.4.2.7, </p>
<p><a hre... | |structural-engineering|welds|hss| | <p>I've spent some time working out the geometry for this configuration and believe I've developed a set of cases that will work to determine the total effective throat of this connection.</p>
<p>The solution is divided into three cases.</p>
<h2>Case 1 - Undersized Fillet Weld $(L_2 < RO)$</h2>
<p>For this case, ... | 3745 | Effective Throat of Flare-Bevel Weld with Reinforcing Fillet |
2015-07-31T08:31:21.547 | <p>I'm looking for a material with a Young's modulus of less than 100 Pa. I've looked at elastomers, but I haven't had any luck.</p>
| |stresses|biomechanics|elastic-modulus| | <p>You are asking for an unrealistic material. If you peruse the <a href="http://www.engineeringtoolbox.com/young-modulus-d_417.html" rel="nofollow">engineering toolbox</a> you'll find that the Young's modulus of typical materials is measured in 10<sup>9</sup> Pa so the value you are asking for is 7 orders of magnitud... | 3752 | Material with very small Young's modulus |
2015-07-31T14:14:40.423 | <p>I have a wheel I CNC milled <a href="http://www.lowes.com/pd_304090-210-304090.0___?productId=3122447&pl=1&Ntt=foam" rel="nofollow">out of foam</a> and I need to mount a motor to it. I designed and printed a part that would attach the motor to the foam, but I anticipated that the wheels would be wood back th... | |mechanical-engineering|materials|motors| | <p>I would design a hub with a flange to fit against the side of the wheel and use an adhesive that's chemically compatible with the foam and has good bonding strength to metal. 3M has some solutions that we've used for bonding foam sheets. You'll want to take advantage of the fact that adhesives are strongest in shear... | 3755 | How do you mount a polystyrene foam wheel to a motor? |
2015-07-31T15:14:27.970 | <p>Temporary structures are usually constructed in a less precise manner than permanent structures. This is more so in a braced deep excavation where the walls are in constant motion as the excavation progresses downwards. During the assembly of walers and struts, there could be a small gap between the strut-waler conn... | |structural-engineering|welds| | <blockquote>
<p>How does one decide whether the fillet weld connecting the strut to the waler need to be designed against compression <strong>due to possibility of such a small gap?</strong></p>
</blockquote>
<p>In our office, we generally design welds to take compression load due to the exact reason you're specifyi... | 3757 | Should a welded connection between strut and waler be designed to take compression load? |
2015-08-02T07:23:43.680 | <p>For a Board Exam Review: </p>
<blockquote>
<p>A triple thread worm has a diameter of 3 inches. The wheel has 25
teeth and a pitch diameter of 5 inches. Material for both the worm and
the wheel is of phosphor Bronze. Compute the Helix Angle</p>
</blockquote>
<p>Answer is 0.2</p>
<p>Helix Angle can be obtaine... | |design|gears| | <p>If I get your descriptions right you have everything you need given. You can use the pitch diameter.</p>
<p>$$tan(H) = \frac{\pi \cdot d_p}{N_t \cdot P_a}$$</p>
<p>$$tan(H) = \frac{\pi \cdot 5\:\mathrm{in}}{25 \cdot 3\:\mathrm{in}}$$</p>
<p>$$tan(H) = \frac{5\pi}{75}$$</p>
<p>$$tan(H) = \frac{\pi}{15}$$</p>
<p>... | 3777 | Finding the diameter of a Triple Thread Worm Gear |
2015-08-03T05:27:15.603 | <p>Reviewing for a National Board Exam: </p>
<blockquote>
<p>How many 5/16 inch holes can be punched in one motion in a steel plate
made of SAE 1010 Steel 7/16 inch thick using a force of 55 tons. The
ultimate strength for shear is 50 ksi and use 2 Factor of Safety</p>
</blockquote>
<p>Answer is 5.</p>
<p>This... | |steel|stresses| | <p>The shear force required should depend upon the shear area:
$$N \pi \biggl(\frac{5}{16}''\biggr) \biggl(\frac{7}{16}''\biggr)$$
or number times circumference times height, since the side-walls of $N$ cylinders are resisting.</p>
<p>That would drop your answer by almost exactly the right amount. Short tons could t... | 3780 | Number of Holes punched through a Plate of SAE 1010 Steel |
2015-08-03T05:49:38.307 | <p>We know that demand for electricity is not constant. Power plants are not operated under full load conditions. What if power plants were operated under full load condition and excess electricity was stored in capacitors? I have read that capacitors of 10 kF capacitance are available. Could the use of such capacitors... | |energy-storage|power-engineering| | <p>Capacitors are currently "rather too costly" for this purpose.<br>
I've revised my estimated cost after some more research but you appear to be in the 'well over one hundred thousand dollars" range! </p>
<p>The dear way: If you were to assemble a 10kF 150 volt capacitor from available smaller capacitors now it wou... | 3781 | Can large capacitors allow power plants to run at full load and store excess electricity? |
2015-08-03T14:54:44.720 | <p>I have seen several products on the internet marketed as 'ball screws' that have both the screw itself and the special ball bearing nut. They are intended to have a motor mounted on one end of the screw to rotates it, causing the nut to be moved.</p>
<p>However, I'm looking for the particular kind of ball screw whe... | |mechanical-engineering| | <p>Festo makes complete assemblies that fit your description. You can also buy the individual components from them, or from a company like McMaster Carr.</p>
<p>www.festo.com</p>
<p>www.mcmaster.com</p>
| 3785 | Name of the ball screw nut used in pistons? |
2015-08-05T08:58:25.907 | <p>Steel seems to be a very complex material, not least because of the different phases and microstructures. At the moment, I'm especially interested in the bainite formation that happens when austenitic steel is cooled rapidly (but not rapidly enough to drive the martensite formation). </p>
<p>My question: What is th... | |materials|steel|metallurgy| | <p>There is a lot more going on in this question than appears at first glance. Density of austenite is fairly straightforward: it is approximately the atom-weighted sum of the face-centered cubic densities of the substitutional constituents as the microstructure consists of a single phase. In other words, Fe, Mo, V, et... | 3803 | Densities of different phases of steel (austenite, bainite) |
2015-08-05T10:41:00.317 | <p>I want to algorithmically process <strong>energy meter data</strong>. The energy meter measures a heat or power producer or a heat or power consumer (but not both, so the measured energy will always have a positive sign). No additional information is known about the energy system (like maximum load) neither about th... | |measurements|energy|metrology| | <p>There are two ways to do it.</p>
<h3>The old way</h3>
<p>The traditional way is to develop a set of somewhat arbitrary rules based on the errors you manually classify. You filter out non-monotonicity (easy), identify resets (easy), and try to spot other bad values (trickier). That gives you a set of values to mark a... | 3807 | How to automatically process energy meter data considering outliers and meter reset? |
2015-08-05T17:02:16.623 | <p>My drafting program outputs a .dwf format file. In it, arcs are encoded as </p>
<pre><code>(Circle 602331619,844923003 537072960 32715,65588)
</code></pre>
<p>where my so-far affirmed interpretation is <code>(Circle, X-center,Y-center Angle Unknown1,Unknown2)</code>.</p>
<p>The image for the arc is shown below (h... | |civil-engineering|drafting|autocad| | <p>The file format for *.dwf files is defined. A reference for the various drawing commands can be found <a href="http://paulbourke.net/dataformats/whip/" rel="nofollow noreferrer">here</a>. Specifically, the definition of the <code>Draw Circle/Circular Arc/Circular Wedge function</code> is <a href="http://paulbourke.n... | 3815 | AutoCAD .DWF Circle Output Meaning |
2015-08-06T06:07:46.417 | <p>In an air-conditioned house equipped with an air extractor that removes for instance wet, smelly, etc. air from the bathrooms and kitchen, what are sensible cost-effective systems to prevent:</p>
<ul>
<li>Heat loss during the winter by bringing in cold air and extracting hot air from inside the house</li>
<li>Heat ... | |heat-transfer|hvac|airflow| | <p>What you want is called a <i>heat exchanger</i>. Imagine two long air tubes with a thin wall between them. The air exiting the house travels in one tube, and entering air in the other, but in opposite directions. Over the length of the tubes, heat transfers thru the thin wall. Ideally, by the time the house air ... | 3824 | How to minimize heat loss in an air extractor? |
2015-08-07T13:05:36.557 | <p>I am a beginner in Electronics. I am trying to make a small robot controlled by an Arduino. The problem is that I do not know how to calculate the power required to rotate a structure with a servo motor placed on its axis (see picture below).</p>
<p>My servo motor is a Dynamixel MX-28 T with an average stall torque... | |mechanical-engineering|electrical-engineering|stepper-motor|robotics| | <p>With the structure (and masses) being distributed perfectly even on both sides of the servo, the servo will not require any additional force to rotate the structure since the mass on one side is always balanced out or negated by the mass on the other side.</p>
<p>You will still have to overcome friction forces and ... | 3834 | The couple of my servo motor is it powerful enough? |
2015-08-07T22:25:28.387 | <p>In a sensor project I'm involved with, we have a requirement to bypass the airflow from one sensor while it does some further measurements. To do this, I implemented a flap driven by a <a href="https://www.pololu.com/product/1053" rel="nofollow noreferrer">standard servo</a> which rotates the flap through approximat... | |mechanical-engineering|design|airflow| | <p>Are you bound to the shape/configuration of part you constructed in your question? If not, a simple 3-way <strong>pneumatic solenoid valve</strong> would make this very simple and leak proof(relatively speaking). They are inexpensive too.(eBay) You would have an input and the valve will allow flow through one outlet... | 3842 | Airflow selection mechanism |
2015-08-08T02:39:39.027 | <p>Power cords for laptop computers have a transformer built into them. The power supply has a transformer that steps down mains level power to a lower voltage and rectifier that converts the current from AC at the mains to DC.</p>
<p>Power surges con occur for a variety of reasons, such as a nearby lightning strike.... | |power-electronics| | <p>An occupational hazard of mine is working with a lot of people who own laptop computers. I also happen to live in the central plains of the United States, and we get our fair share of thunderstorms. They're not as pretty as the lightning storms of Phoenix, AZ, but they're generally a lot more powerful.</p>
<p>Ane... | 3846 | Evaluating the probability of damage to a laptop computer from power surges |
2015-08-08T13:50:08.957 | <p>Given a successful deuterium-tritium fusion reactor such as that conceived by ITER, could the world's energy needs theoretically be met without the input of any petroleum or natural gas products?</p>
<p>Deuterium is currently typically produced by the girdler sulfide process from seawater which requires a natural g... | |renewable-energy| | <p>The energy cost of obtaining Deuterium and Lithium is minimal compared to the energy released by the fusion process. There are many references that provide relevant information but a sensible one to refer to is the official ITER site "Fusion for energy". <a href="http://fusionforenergy.europa.eu/understand... | 3850 | Could future fusion energy exist without the input of any petroleum or natural gas products? |
2015-08-09T04:21:47.880 | <p>It does make sense centrifugal compressors exist, because gases can compress.</p>
<p>We all know that liquids don't compress like gas. Then why do centrifugal or reciprocating pumps exists? </p>
<p>See even a the Wikipedia article on <a href="https://en.wikipedia.org/wiki/Centrifugal_pump" rel="nofollow">Centrifug... | |fluid-mechanics|pumps| | <p>All real materials are compressible. If you look at thermodynamics tables, even small change in pressure causes density change in fluid. But as an engineer, when working on pumps you can omit small and effectless changes in density of fluids. So pumps, compressors, and fans all do the same thing: they compress mate... | 3854 | Why do pumps really exists? |
2015-08-10T01:58:17.750 | <p>Current gear manufacturing methods for gears usually depend on power tools, or computerised machines, or something like that.</p>
<p>However, watchmakers and clockmakers at one point in history needed to make gears by hand. So what tools did they use? How did they make gears (especially really tiny ones)?</p>
| |gears|engineering-history|manufacturing-engineering| | <p>Have look at these two:-</p>
<p><a href="https://i.stack.imgur.com/YcCuf.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/YcCuf.jpg" alt="clock1"></a></p>
<p><a href="https://i.stack.imgur.com/Sk6Ez.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Sk6Ez.jpg" alt="clock2"></a></p... | 3863 | How were gears manufactured before power tools, CNC, etc |
2015-08-10T12:25:25.637 | <h1>The Tibetan Bridge Type</h1>
<p>I have a question regarding the bridge type called "Tibetan Bridge".
Recently close by my home town a new tourist attraction was built, the <a href="http://www.highline179.com/en/guinness-world-record-for-the-highline179/" rel="nofollow noreferrer">Highline 179</a> bridge.
<a href=... | |civil-engineering|bridges|architecture| | <p><a href="https://en.wikipedia.org/wiki/Suspension_bridge#Precursor" rel="nofollow">The section on the precursor to modern suspension bridges, in the wikipedia article that you mentioned</a>, talks about bridges of the "Tibetan saint and bridge-builder Thangtong Gyalpo" and points out that they "did not include a sus... | 3865 | What is a Tibetan Style Bridge? |
2015-08-11T13:24:00.290 | <p>When an ideal gas with constant specific heat is throttled adiabatically, with negligible changes in kinetic and potential energies: </p>
<ul>
<li>(a): ∆h = 0, ∆T = 0 </li>
<li>(b): ∆h =0, ∆S > 0 </li>
</ul>
<p>The answer is supposed to be (b). </p>
<p>Please explain why answer (a) is wrong and (b) is correct.... | |mechanical-engineering|thermodynamics| | <p>You answer this by applying first and second laws of thermodynamics.</p>
<p>First Law
$$Q - W = \triangle E_{sys}$$
since throttling process is adiabatic and there is no mechanical work applied on or extracted from the system then $Q$ and $W$ = 0.</p>
<p>that leaves us with $\triangle E_{sys} = 0$, and for steady ... | 3881 | Adiabatic throttling of ideal gas |
2015-08-12T16:45:16.400 | <p>Is this how it works?</p>
<p>The fingers generate moment.<br>
The load generates moment.<br>
Finger moment > load moment, so the load is cut.</p>
<p>How do I use an equation to identify the most vulnerable point of the product?</p>
<p>More questions on this topic:</p>
<p>What is the typical accelaration of sciss... | |mechanical-engineering|statics| | <p>Your general idea is correct. Your fingers apply a force which can be translated to a moment at the rotation axis. The reaction forces applied by the object to be cut must generate an equal moment at the axis. If the necessary reaction forces are greater than the object's shear resistance forces, then the object is... | 3906 | How to analyze the free body diagram of a pair of scissors? |
2015-08-12T18:52:57.830 | <p>Looking for some hints on how to create a <strong>rough estimate</strong> for the following problem.</p>
<p>Given two steel gates with the same dimensions, same material - e.g. everything is the same. The only difference is that the middle parts have different structures.</p>
<p>When applying some force to the to... | |structural-engineering|beam|stresses|reinforcement| | <p>As grfrazee said, you won't know for sure until you do a finite element analysis. I was intrigued by this question as a colleague and I got into a discussion about this. While we both agreed the diagonal bracing would be better at resisting deflection, we wondered by what factor it would be better.</p>
<p>We were r... | 3909 | Strength of a welded steel gate with vertical bars vs. crossed diagonal bars |
2015-08-13T13:21:31.570 | <p>I'm trying to crimp some pins onto 20 AWG wire. </p>
<p>I can either use a tool like this:</p>
<p><a href="https://i.stack.imgur.com/ihyNm.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ihyNmt.jpg" alt="specialty crimper"></a></p>
<p>Or I can just use pliers, which are obviously cheaper and mo... | |tools| | <p>The proper crimper will indent the cylindrical body of the contact, leaving the outside diameter unchanged. </p>
<p>Pliers will simply squash the contact, making it oval, and larger than the original diameter in one direction. This may prevent the contact from seating correctly (or at all) in the connector housin... | 3926 | What is the advantage of using a four-sided crimper vs. pliers? |
2015-08-13T14:37:52.000 | <p>In my lab we use a number of materials which are <a href="https://en.wikipedia.org/wiki/Hygroscopy" rel="noreferrer">hygroscopic</a> and must therefore be stored in a dry environment. For that purpose we have numerous dry cabinets very similar to the one shown below (<a href="http://rads.stackoverflow.com/amzn/click... | |hvac|dehumidification| | <p>I believe warmer air has more capacity to hold vapour so instead of condensing onto the items inside the cabinet, the moisture stays in the air. I have 2 cabinets and neither have any outlet so the water vapour can't go anywhere. Also they are relatively cheap to buy as have a simple design.</p>
<p>They seem pretty... | 3928 | How do dry storage cabinets work? |
2015-08-13T16:13:38.813 | <p>We regularly bolt an angle iron against an existing building element (flange down), and use the flange as support for a new concrete slab. Is there any design approach to assist with the sizing / spacing of the chemical anchors as well as confirming the suitability of the angled section? Epoxy anchors are one form ... | |structural-engineering| | <blockquote>
<p>...and use the flange as support for a new concrete slab</p>
</blockquote>
<p>By this, I assume you mean a shelf angle (or a connection angle) to support a concrete floor. The image below is an example from the <em>PCI Design Handbook</em>, 7th Edition.</p>
<p><a href="https://i.stack.imgur.com/fXP... | 3931 | Angle Iron Cleat at Slab-Slab connection |
2015-08-14T07:53:00.993 | <p>I'm hoping to rebuild a joystick (sidewinder strategic commander), though the parts inside it are a bit too wobbly because they have been worn beyond tolerances. Due to this wobbling on one (rotation) axis, the sliding action is rough on the x/y plane.</p>
<p>Any recommendation on how and what to use, if there is a... | |plastic|tolerance| | <blockquote>
<p>Any recommendation on how and what to use, if there is a compound I can apply to make up for what was lost through friction?</p>
</blockquote>
<p>At first thought, I'm thinking that you scuff the surface of the plastic parts and try to rebuild the missing area with <a href="http://www.jbweld.com/coll... | 3945 | How to rebuild and lubricate worn plastic parts? |
2015-08-14T14:03:25.020 | <p>I'm using a OnePlusOne and while using my sunglasses I can see the phone screen in portrait mode, however if I rotate the screen to landscape I can't see anything at all.</p>
<p>My sunglasses are polarized.</p>
<p>What is the reason for this?</p>
| |electrical-engineering| | <p>The screen of your phone uses a polarizing screens as well. When you hold you phone in portrait mode, the screens are oriented in the same direction so you can see the image. When you rotate it 90deg, the screens are not aligned and light cannot pass. </p>
| 3949 | Why can't I see my phone screen in landscape with sunglasses? |
2015-08-04T21:20:15.227 | <p>The TI MSP430F20XX series has a 12-bit internal ADC output, which is right-justified.</p>
<p>What is the difference between a left-justified output and a right-justified output? What are their pros and cons?</p>
| |electrical-engineering|embedded-systems| | <p>On this processor, the register that holds the conversion result is 16 bits wide. </p>
<p>A right-justified result means that bits [(<em>N</em>-1):0] (where <em>N</em> is the number of bits of precision) of the register contain the ADC value and the most-significant bits of the register are set to zero.</p>
<p>A l... | 3959 | What are left justified and right justified ADC results? |
2015-08-05T18:12:00.707 | <p>I am writing a driver for the <code>Samsung K9WAG08U1D NAND flash</code> chip. The specification of the memory chip mentions it has a page size of 2048 bytes (2kB). I am using a <code>TI MSP430F2619</code> which has 4096 Bytes (4kB) of RAM. This means I need to allocate a 2k memory buffer just to write to flash. My ... | |electrical-engineering|embedded-systems| | <p>You don't need to fill the page register all in one go.</p>
<p>You begin a page write (i.e. the "Page Program" operation) by writing the Serial Data Input command (<code>0x80</code>), the column address, and the row address. Then you transfer the data to the page register (up to 2112 bytes). This transfer can be ... | 3961 | Saving RAM Memory when writing to 2K page size NAND flash |
2015-07-30T10:33:42.867 | <p>The development board for the touchscreen chip we got is too good ;)</p>
<p>The chip provides the readouts over I2C, passes it to FPGA (I could provide the model if I find a magnifying glass... but I'd prefer a more generic answer anyway) and the FPGA passes the data over RS232 to an FDDI which connects over USB to... | |electrical-engineering|embedded-systems| | <p>It does, unfortunately depend a little on the FPGA itself.</p>
<p>But most cases that will probably not work, unfortunately. In many logic chips with programmable I/O type pins, the final stage looks a bit like this:</p>
<p><img src="https://i.stack.imgur.com/x1GT6.png" alt="schematic"></p>
<p>This is both a ... | 3965 | What is the behavior of unpowered FPGA pins on I2C bus? |
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