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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2015-10-02T08:49:10.083 | <p>How can I choose between Implicit or Explicit Analysis in ABAQUS for a simple rectangular composite structure with 2 layers of unidirectional lamina? I am trying to do a linear-static analysis to capture the tensile strain for the specimen. </p>
| |finite-element-method|abaqus| | <p>Further to existing answers: in a dynamic problem, an explicit method computes time-derivatives for use in updating through a timestep, by inserting into the dynamical equations the values of the fields and their spatial derivatives at the start of the time-step; an implicit method computes time-derivatives for use ... | 5627 | What is the difference between implicit and explicit analysis in ABAQUS? |
2015-10-02T09:54:56.790 | <p>From time to time I am tasked with additions or alterations to old buildings or structures. I would need to establish the "as built" structure and from that analysis see how the amended/new structure suits the existing structural components.</p>
<p>The challenge lies in the assumptions one is forced to make. Over t... | |materials|civil-engineering|structural-engineering| | <p>When it comes to concrete and steel, there were few standards for materials and design prior to about 1920, and you may not find any prior to 1905, at least that is my experience. Reinforced concrete technology was largely proprietary prior to about 1910 - as such the first multi-story reinforced concrete building ... | 5629 | Determining the properties of members of historic structures |
2015-10-02T15:13:41.620 | <p>In the context of Bernoulli, does "static pressure" typically refer to $p$, or to $p + \rho gz$?</p>
| |fluid-mechanics| | <p>I think there is no unique technical term to define pressures in different situations.
As a reference states <a href="http://hyperphysics.phy-astr.gsu.edu/hbase/pflu.html" rel="nofollow noreferrer">here</a>: <span class="math-container">$p_\text{static}=\rho g h$</span></p>
<p>If we consider the data computed from ... | 5635 | Is gravity included in "static pressure"? |
2015-10-02T17:30:03.270 | <p>I'm designing a crucible / extruder, and right now it has a .6mm hole to extrude from. Will this work? A chart with various metals listed would be nice.</p>
<p>Pictures:<br>
<sub><em>Click to expand</em></sub> </p>
<p><a href="https://i.stack.imgur.com/UPzKX.png" rel="nofollow noreferrer"><img src="https://i.stac... | |mechanical-engineering|thermodynamics|metallurgy|metals|experimental-physics| | <p>Making a nozzle with that long and thin of a hole is not feasible, but you could make a larger hole behind it and just have the last 3mm be 0.6mm in diameter. This would be feasible in a ceramic, but due to cost, I might make the nozzle into an insert that goes into a larger piece made of cheaper material.</p>
<p>T... | 5640 | How small can you get a stream of molten steel to be at low pressure? |
2015-10-05T01:49:44.163 | <p>I've heard the <a href="https://en.wikipedia.org/wiki/Mark_48_torpedo" rel="nofollow">Mk. 48 torpedo</a> is wire-guided, why not make it wire powered? The range would only be limited by the length of the wire. I'm wondering why this is not used and what problems it would have.</p>
| |mechanical-engineering|electrical-engineering| | <p>The main reason is that the power requirement for running the torpedo is vastly larger than that for merely sending control signals to it. This means <i>much</i> thicker wire would be needed to actually power the torpedo over the wire. Even if cost is not a consideration, a usefully long spool of such thick wire w... | 5663 | Is it possible to power a torpedo via a wire? |
2015-10-05T10:57:10.960 | <p>I am having trouble to calculate the differential equations of a simplified loading bridge.</p>
<p>The system is build as shown in the picture below (just a sketch):</p>
<p><a href="https://i.stack.imgur.com/YEj4q.png" rel="noreferrer"><img src="https://i.stack.imgur.com/YEj4q.png" alt="enter image description her... | |mechanical-engineering|control-engineering|modeling|mathematics| | <h2>Kinematics and dynamics</h2>
<p><a href="https://i.stack.imgur.com/94sUM.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/94sUM.png" alt="enter image description here"></a></p>
<p>Those are the steps to solve problems of this nature.</p>
<ol>
<li>Analize the kinematics of the system.</li>
</ol>... | 5665 | Differential equations of a (simplified) loading bridge |
2015-10-05T13:26:22.700 | <p>I understand the difference between the two in terms of how they function; one will release all of it's energy in small pulses with the other creates a constant stream of radiation.</p>
<p>My question is for materials processing such as marking or cutting. Why would I use one over the other?</p>
| |materials|optics|machining|lasers|cutting| | <p>Pulsed lasers release their energy in very short pulses which can have incredibly high <strong>peak</strong> powers. A run-of-the-mill nanosecond laser will have a peak power in the multi-kilowatt range while a femtosecond laser can easily reach into the megawatt range. In contrast, CW lasers generally do not reac... | 5667 | Difference between continuous wave laser and a pulsed laser |
2015-10-07T22:32:50.567 | <p>The Reynolds Number is defined as $Re = \frac{\rho v L}{\mu}$, where $\rho$ is the density, $v$ is the fluid velocity, $L$ is the characteristic length, and $\mu$ is the dynamic viscosity. By definition, inviscid flow implies that $\mu=0$. By this formula, this would make the reynolds number infinite and thus turb... | |fluid-mechanics|turbulence| | <p>No, inviscid flows are not necessarily turbulent. If there is nothing to "trip" the turbulence, then the flow will remain laminar. Features which could trip the turbulence include vibration, small temperature fluctuations, any geometric imperfections, velocity field imperfections, and other similar things.</p>
<p>F... | 5685 | Is inviscid flow necessarily turbulent? |
2015-10-08T00:25:27.780 | <p>I am going to machine something out of a small 40mm long x 8mm diam tungsten rod. The majority will be hollowed out using a larger bit, but at the very tip, I need a small hole, the smaller the better between .05mm and .6mm. I understand an L/D for that small hole should be less than 60%? Did I get that right?</p... | |machining|microfluidics| | <p><strong>Reposting my comment for clarity:</strong></p>
<p>"Before we get into making this: have you confirmed that a wall thickness of ~0.3mm around the hole is going to be thick/strong enough to resist the pressure required to push the molten steel through your nozzle/hole in the first place? That's very thin.... ... | 5686 | What's the smallest pin-like hole I can machine into a piece of tungsten using a metal lathe and common carbide tools? |
2015-10-08T03:46:57.153 | <p>They've printed jet engines with it that work after polishing. So how is the accuracy measured and how accurate is the DMLS process? I can't find the required info anywhere. </p>
| |machining|manufacturing-engineering|lasers| | <p>Accuracy will vary a lot depending on what you are interested in.</p>
<p>At the simplest level you are limited by the layer thickness, which is in the $20-100~\mu m$ range. This places a limit on the accuracy of the dimensions that can be achieved in the z direction. Theoretically you can achieve very high accuracy... | 5689 | What is the accuracy of direct metal laser sintering (DMLS)? |
2015-10-08T23:38:25.087 | <p>I have a 10 mm depth x 5 cm length 99% Tungsten rod. How can I machine the described hole so that instead of having a bevel from the tip of the main drill-hole bit, it has a perfect 90 degree corner all around as if the tip of the drill bit were like a flat router bit?</p>
<p>If this is not feasible, I can think a... | |mechanical-engineering|machining|metals| | <p>Wow, tungsten, huh? Whenever I see exotic materials, usually a design mistake is being made. The other answer by starrise is wrong for various reasons. Counterbores are normally only used for making sockets, not boring blind holes.</p>
<p>If you actually want to do this, the right strategy would be to set up the wo... | 5701 | How can I finish a round hole so it has 90 degree corners (flat bottom)? |
2015-10-09T14:10:41.717 | <p>A question asked about the <strong>necessary curing pressures for a composite resin in the autoclave</strong>. Looking through the corresponding <a href="http://hexcel.com/Resources/DataSheets/Prepreg-Data-Sheets/F155_us.pdf" rel="nofollow">datasheet</a> (HexPly F155), I'm confused:</p>
<blockquote>
<p><strong>Cu... | |composite|composite-resin| | <blockquote>
<p><strong>Cure Procedure</strong></p>
<ol>
<li>Apply vacuum of 22 inches (74 kPa) Hg minimum.</li>
<li>Apply 85 + 15 – 0 psig (586 + 103 – 0 kPa) pressure for laminates.</li>
<li>Apply 45 + 15 – 0 psig (310 + 103 – 0 kPa) pressure for sandwich.</li>
</ol>
</blockquote>
<p>I believe Steps #2 and #3 are pro... | 5706 | How do I interpret the curing pressure of a composite from this data sheet? |
2015-10-09T18:12:35.390 | <p>I'm trying to figure out the theoretical calculations for a Stirling Engine system so I can determine optimal piston size, optimal piston displacement and number of pistons. I want to calculate which configuration has the most amount to torque to turn something else, and the highest amount of RPM's.</p>
<p>What I h... | |automotive-engineering|experimental-physics|pistons| | <p>To "optimize" requires a desired outcome. Sterling engines, like most mechanical/thermodynamic systems are highly complex. You could optimize for efficiency, cost, power-to-weight, and many others. For learning the theory before you get to that stage I would recommend the wiki article, then do web searches based on ... | 5709 | Find optimal configuration for Stirling Engine |
2015-10-10T00:39:46.823 | <p>I have a 15 pound weight that I use to crush 8.4 oz red bull cans. A metal barbell with a handle and 2 ends. Not 100% flat ends, but close to flat. About 12 inches from end to end.</p>
<p>I hold the barbell by one end and lower it to crush a standing redbull can. sometimes the can crushes completely, other times it... | |mechanical-engineering| | <p>There was a very slight wobble of the weight as it went from "standing" to "dropping". The standing position had no wobble, but it created a wobble when released. The solution was hold the weight freely and to control the wobble, so when allowed to drop by gravity, no additional forces occur in transition. Can crush... | 5715 | Crushing drink cans |
2015-10-10T05:58:34.710 | <p><a href="https://i.stack.imgur.com/s9LVf.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/s9LVf.png" alt="enter image description here"></a></p>
<p>Hi, I'm having some problems with this truss question that I have in my homework. So far this is my solutions.</p>
<p>I worked out my solutions to th... | |civil-engineering|structures|statics| | <p>It may be worth reconsidering your deduced zero force members. But for this question it is not really necessary to determine which are zero force members in advance as this will come out in the analysis.</p>
<p>It is not important if the truss is determinate or not in order to get the member forces your are interes... | 5719 | Loaded Truss problem |
2015-10-10T06:47:34.927 | <p><a href="https://i.stack.imgur.com/SkVHG.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/SkVHG.png" alt="enter image description here"></a></p>
<p>I'm supposed to be finding the reaction forces first but from the FBD of the entire truss where am I supposed to start. If I take the moment at A then... | |civil-engineering|structural-engineering|statics| | <p>You seem to be treating all the connections between members as fully fixed but rather they are all hinges with the exception of joint E. The contact at E can be treated like a roller, thus there's a force normal to member DE as shown below which I have called $F_E$:</p>
<p><a href="https://i.stack.imgur.com/O0yFc.p... | 5720 | Frame/truss problem with sliding joint |
2015-10-10T14:00:46.633 | <p>I have an application (a tube with parts in it) which needs a certain static pressure in it in order to contain a sustainable air flow. Unfortunately the fan I wanted to use in a push-configuration is not able to create this pressure. Thus I thought that I could install another fan with a higher cfm at the end of th... | |fluid-mechanics| | <p>In order to get the air through the pipe, the pressure rise of the first fan has to be so high, that the pressure-loss within the tube is compensated.</p>
<p>Since your first fan (F1) is not powerful enough you can add a second fan (F2) to rise the pressure at the end of the pipe to ambient pressure, or use a more ... | 5723 | Increase static pressure |
2015-10-11T02:26:05.770 | <p>Assume I put an RF antenna in front of an object (typically the face of someone sitting in a chair, so able to move about +/- 10cm in all directions) at a typical distance of 1m. If I consider the system antenna/face as a resonant cavity, I'd get a fundamental resonant frequency of about 150MHz.</p>
<p>I have a gen... | |electrical-engineering|rf-electronics|distance-measurement| | <p>I do not believe this will be an effective scheme. The <a href="https://en.wikipedia.org/wiki/Q_factor" rel="nofollow">$Q$ of a resonator</a>, a number which describes the strength of the resonant peak, <a href="https://www.rp-photonics.com/q_factor.html" rel="nofollow">is given by</a>
$$
Q=\frac{f_0}{\delta f}\a... | 5728 | Measuring the distance to an object with RF resonance |
2015-10-08T05:21:18.700 | <p>I'm thinking about using the <a href="https://www.bopla.de/en/enclosure-technology/product/ultramas/ultramas-um-309-l-enclosures/um-32009.html" rel="nofollow">Bopla UM 32009 housing</a> for my product. It has little standoffs for attaching PCBs. These standoffs are made of plastic, and seem to be drilled (or molded?... | |plastic|fasteners| | <p>Typing "screws" in the search field of the Bopla website finds <a href="https://www.bopla.de/en/service/technical-information/plastic/general-information-on-plastic-enclosures/screws-and-attachments-for-plastic-enclosures.html" rel="nofollow">this link</a>.</p>
<p>It looks like the screw you need is has a shank dia... | 5735 | What screw for 2.0 mm plastic hole in housing |
2015-10-12T15:48:11.197 | <p>I live in Melbourne, Australia and a lot of the creeks here have been diverted through underground storm water pipes. I guessed that this is because land is highly sought after for development, and a lot of these creeks have been built over, however there are also a lot of cases where there is nothing built over the... | |civil-engineering|water-resources| | <p><strong>What's the reason for going to the cost and effort of doing this?</strong></p>
<p>In many places, placing a stream into a culvert can be cheaper in the long run. Streams (particularly fast flowing ones) erode the land and may require erosion protection added in the future. </p>
<p>An advantage is reduced l... | 5749 | Why are creeks sometimes piped underground in urban areas? |
2015-10-12T19:08:39.697 | <p>I'm running a simple tensile test simulation for a single element. Under Results I made a Chart object with Stress vs Strain, which can be manually exported to a csv file by right clicking on the table. The trouble arises from the parametrization. I've parametrized temperature in Workbench so that the same simulatio... | |mechanical-engineering|simulation|ansys|finite-element-method| | <p>There are several options for doing this:</p>
<ol>
<li>If there are only a few values to be saved per design point, you could use 'output parameters'. </li>
<li>If there is a lot of data to be saved, the report generator may be useful. Some information can be found here: <a href="https://www.sharcnet.ca/Software/A... | 5750 | ANSYS Workbench/Mechanical: Automatically export chart? |
2015-10-12T23:46:41.957 | <p>This is a basic control theory question, since Control Theory is a part of applied mathematics but also of engineering I was unsure whether to ask this here. </p>
<p>The question says:</p>
<p>Given the transfer function of a system is $G(s)=1/(s^2+3s+2)$, consider the design of a PI closed loop control system with... | |control-engineering|control-theory|transfer-function| | <p>There is a mistake in your expressions. The coefficient of $s$ is $2+k_p$. </p>
<p>The conditions are: $$\frac{1}{3} \left(3 \left(k_p+2\right)-k_i\right)>0$$ $$k_i>0$$ $$k_p>0$$</p>
<p>This simplifies to: $$k_p>0$$ $$0<k_i<3 k_p+6$$</p>
<p><strong>Update:</strong></p>
<p>If the transfer functi... | 5753 | Determine the range of values for a PI controller |
2015-10-12T00:18:41.260 | <p>I'm wondering what the technical name is for this kind of stepper-motorized arrangement (a positioning system? an XY table?)?</p>
<p><a href="https://i.stack.imgur.com/JLtsL.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/JLtsL.png" alt="enter image description here"></a></p>
<p>What is it typic... | |mechanical-engineering|stepper-motor| | <p>cartesian 2 axis robot</p>
<p>2 axis robot</p>
<p>cartesian coordinate robot</p>
<p>xz axis robot</p>
<p>xz gantry</p>
<p>For your purposes, compare the required precision, the load weight, and the control board and display, pc link, if it uses GCode or some other control. </p>
<p>Note that this kind of cartes... | 5755 | What is this kind of X-Y motorized system? |
2015-10-13T14:32:24.623 | <p>I have raw data obtained from EMED barefoot scan containing a matrix of pressure sensors over about 70 frames. This totals 70 matrices that record a snapshot of the pressure over the duration of a person's natural walk over the pressure plate. </p>
<p>I wanted to ask if anyone knows the algorithm that is typically ... | |biomechanics| | <p>Actually, scipy has a function that does exactly this. I used it on each of the 70 arrays that make up the time series, and points generate a smooth line.</p>
<p><a href="https://docs.scipy.org/doc/scipy-0.16.1/reference/generated/scipy.ndimage.measurements.center_of_mass.html" rel="nofollow">https://docs.scipy.org... | 5763 | Center of Pressure Line from Barefoot Scan (EMED) |
2015-10-14T02:35:34.203 | <p>I'm having problems understanding the worked answer for this problem: </p>
<p><a href="https://i.stack.imgur.com/29pZi.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/29pZi.png" alt="Problem definition"></a></p>
<p>Here's part of the worked answer:
<a href="https://i.stack.imgur.com/Rxy6q.png" r... | |mechanical-engineering|civil-engineering| | <p>Between ABC there is a single member. Hence the angle between AB and BC is always 90 degrees. Hence if AB rotates by theta, then BC also rotates by theta. As the length AB is 90mm, and the length AC is 40mm, then (by similar triangles):</p>
<p>$\delta_C = \dfrac{40}{90} \delta_A$</p>
| 5771 | Virtual Work - Determining Relationships in deflections |
2015-10-14T18:34:18.793 | <p>Turbulent flow involves extremely small scale fluctuations which are usually too small to resolve by using the Navier-Stokes equations directly. To overcome this, we model each transient variable $\Phi$ (e.g. velocity, pressure, etc...) as the sum of a time average quantity $\bar{\Phi}$ and some small fluctuation. ... | |fluid-mechanics|turbulence| | <p>Disclaimer: As you requested <em>general guidelines</em> here they are. After having a converged solution, you need to investigate it thoroughly and look for clues that the choice of the turbulence model altered the flow in an un-physical way.</p>
<p><strong>My Rules of Thumb for Turbulence Models</strong></p>
<ol... | 5778 | How do I select an appropriate turbulence model? |
2015-10-15T01:53:19.380 | <p>Weathering steel is supposed to form a protective patina when exposed to wetting and drying cycles. This protective patina prevents more corrosion from occurring. This is what differentiates it from regular (carbon) steel.</p>
<p><strong>In a situation where the environment does not allow the patina to form, does w... | |steel|corrosion| | <blockquote>
<p>In a situation where the environment does not allow the patina to form, does weathering steel perform any differently than carbon steel?</p>
</blockquote>
<p>Weathering steel is specifically designed to form a protective coating (i.e., patina) of rust that prevents the material underneath from corroding... | 5782 | Does weathering steel corrode the same as carbon steel when it doesn't develop a protective patina? |
2015-10-16T08:26:13.677 | <p>What is the difference between <em>Transport Phenomena</em> first edition (1979) and second edition (2002)?<br>
Which one do you recommend to be bought, taking into account that I am a student and that the first one is cheaper?</p>
| |fluid-mechanics|heat-transfer|chemical-engineering| | <p>Taken from the <a href="http://eu.wiley.com/WileyCDA/WileyTitle/productCd-0470115394.html" rel="nofollow">Wiley</a> page:</p>
<blockquote>
<p>About the Revised 2nd Edition: Since the appearance of the second
edition in 2002, the authors and numerous readers have found a number
of errors--some major and some m... | 5804 | "Transport Phenomena" (Bird, Stewart, Lightfoot) difference between edition 1 and 2 |
2015-10-16T19:28:13.597 | <p>In Rankine cycle there's the boiler where water gets boiled into overheated steam. On input there's a pump that delivers more water, and on output there's a turbine that picks up the energy of the compressed steam.</p>
<p><a href="https://i.stack.imgur.com/bhQ5I.png" rel="noreferrer"><img src="https://i.stack.imgur... | |thermodynamics|steam| | <p>The main reason is that it takes much less energy to compress a liquid than a gas by the same pressure difference. The pump takes a little bit of energy to compress the water, but a huge amount of energy is released when the steam expands in the turbine. This is why a phase change is used in the Rankine and related... | 5813 | How in Rankine cycle the turbine generates more power than the pump takes? |
2015-10-17T13:06:39.367 | <p>Just something I was wondering about when I've seen <a href="https://i.stack.imgur.com/xVr4T.jpg" rel="noreferrer">this</a> on reddit today. Unlike in firearms where the pressure propels the projectile, in a railgun, wouldn't the pressure ahead/behind of the projectile slow it down instead? If so, would it be by a s... | |mechanical-engineering|pressure|firearms| | <p>For both conventional guns and rail guns, the resistance from pressure ahead of the projectile is usually negligible. Venting probably won't help much either if the projectile gets near the speed of sound because the air ahead of the projectile won't have time to move out of the way. You could fire in an evacuated c... | 5818 | Does negative pressure inside the barrel affect low-powered railguns? |
2015-10-18T23:23:20.613 | <p>What does trip angle mean in the context of <a href="http://www.pqcontrols.com/m410.php" rel="nofollow">slope / level sensors / inclinometers</a>?</p>
| |sensors|terminology| | <p>From the link that you provided, it would seem that trip angle is a preset angle at which the sensor will "trip" or "switch on". The results of this can depend on purpose of the tilt meter. It can be wired to sound an alarm, turn on a light, etc.</p>
<p>From this <a href="http://www.spectronsensors.com/appsheets/SA... | 5832 | What is the meaning of a "trip angle" in a level sensor? |
2015-10-19T12:54:08.443 | <p>I'm making a remote starter for a car using a Raspberry Pi. The problem is that the car has a manual transmission. The driver needs to remember to place the gear shift in neutral when parking, otherwise all kinds of bad stuff could happen when the car is started in-gear. </p>
<p>What possible solutions do I have... | |electrical-engineering|automotive-engineering| | <p>They already have remote starters for cars with manual transmission. I know as i used to own one. The way a remote starter in a manual tramission works, or at least the one I owned, relied on the operator essentially arming the remote starter before leaving the car.</p>
<ol>
<li>having the engine running.</li>
<li... | 5838 | Remote start on a car with manual transmission |
2015-10-19T14:59:08.427 | <p>What's the mechanism behind disposable syringes jamming? How do you prevent this from happening or reverse the effect? They are a lot cheaper.</p>
<p>The problem is that once the syringe is pressed all the way in, the plunger sticks and can not be pulled back out.</p>
| |mechanical-engineering|medical-devices| | <p>There's a story on them <a href="http://www.pbs.org/newshour/rundown/self-destructing-syringes-force-safer-injection-practices/" rel="noreferrer">at PBS</a>. From the article:</p>
<blockquote>
<p>A nurse injects a patient with a syringe of antibiotics, reloads and moves on to the next patient in line. The syringe is... | 5840 | What is the purpose and cause of disposable syringes being single use only? |
2015-10-20T21:03:42.257 | <p>Here's my situation: </p>
<p><a href="https://i.stack.imgur.com/dMIvO.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/dMIvO.png" alt="enter image description here"></a></p>
<p>I'm trying to drop a payload via parachute with some accuracy. I'm worried that in the above setup, the line will inter... | |mechanical-engineering|aerodynamics| | <p>The chute should probably be shaped to pull itself away from the line like a kite.</p>
<p>It may be simpler however to use the line itself as the brake instead of using a parachute.</p>
| 5860 | Guiding a parachute via anchor: Possible? |
2015-10-22T12:34:54.370 | <p>I have a small vessel with a rectangular cross-section which needs to be ventilated at a relatively slow rate, ~$3\ \tfrac{\text{L}}{\text{hr}}$. The connections to the vessel will be tubes with an approximately 0.5" diameter, but the cross-section of the vessel is 4" x 1". The diagram below gives a rough idea of ... | |fluid-mechanics|airflow| | <p>Quick and dirty CFD simulation of your problem using ANSYS Fluent 14.5: I used a 2D duct, 8" x 4" with a 45-degree angle going from the inlet pipes to the main chamber. Assuming 3 liters per hour flow through a half-inch diameter pipe gave me an inlet velocity of 6.6 mm/s. Air enters from the left and exits throu... | 5878 | How can I create uniform laminar flow in a short duct? |
2015-10-22T20:53:36.683 | <p>Let's say I have a bar attached to the rim of a rotating wheel, <a href="https://i.stack.imgur.com/Zdg7G.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Zdg7G.png" alt="sketch"></a>, and it's in a vacuum so we can ignore drag. </p>
<p>If the wheel is rotated, does the bar experience a lateral for... | |mechanical-engineering| | <p>In a vacuum acceleration is all towards the centre of rotation. Acceleration and force are vectors in the same direction, hence with no lateral acceleration there is no lateral force.</p>
<p>In the real world it's not in a vacuum and hence there is an additional force acting on the bar, caused by drag. This drag is... | 5880 | Does a rotating bar experience lateral force? |
2015-10-22T20:57:29.887 | <p>More specifically, I'd like to know if unmanned rockets need to be specially designed to withstand the heat generated from air friction and shock waves during launch. I found the diagram below on the NASA website which shows some fairly high stagnation temperatures, but the problem is that I don't know how fast a t... | |aerospace-engineering| | <p>Surprisingly not as hot as expected. At standard temp of 25°C at sea leval launch. Will peak at 400°C, then begin to dissipate. As rocket nose cones designed to dissipate thermal energy by piercing air away from them.</p>
<p><a href="https://i.stack.imgur.com/sv0cV.jpg" rel="nofollow noreferrer"><img src="https://i.... | 5881 | How hot does a rocket nose cone get during launch? |
2015-10-22T23:42:29.920 | <p>Please note, this is not a shopping question; this is a <em>what type of component</em> works best for this scenario question. </p>
<hr>
<p>I have an induction heater circuit and a 5A max. / 24V wall wart, and I'd like to switch off / on the output of the wall wart so that I can control the power output of the in... | |electrical-engineering|power-electronics|consumer-electronics| | <p>If you want to use an SSR, you'll need to get one designed for switching DC. Like <a href="http://www.aliexpress.com/item/solid-state-relay-SSR-25DD-25A-actually-3-32V-DC-TO-5-110V-DC-SSR-25DD/1154754963.html?spm=2114.031010208.3.41.qum1ti&ws_ab_test=searchweb201556_2_71_72_73_74_75,searchweb201527_4,searchweb20... | 5883 | Identifying affordable alternatives for low-frequency high-current DC-DC solid state relays |
2015-10-23T01:59:50.227 | <p>I am in a first-year engineering design group where we are in the process of designing a cooling vest for motorcyclists for use in the city (1-2h length). Water will circulate through the vest, absorbing body heat, and then that heat will be dumped into a heat sink.</p>
<p>We initially decided on using Peltier chip... | |heat-transfer|design|cooling| | <p>What you first need to establish is your temperatures. Body temp min and max; ambient min and max. Select the worst case. Then take some guesses as to how much heat you have to pump. Is the vest insulated on the outside or does it have to cool the ambient as well? I would blind guess that you will need about 200 wat... | 5885 | What are heat sink options for a circulating-water cooling vest? |
2015-10-24T18:17:12.103 | <p>We are given a standard diagram of a rotating cylinder with the parabolic shape in the rotation.</p>
<p>Given:</p>
<ul>
<li>the distance between the vertex of parabola to the top of the parabola.</li>
<li>the original height of the water. </li>
</ul>
<p>I have a really general question regarding this problem. Fro... | |fluid-mechanics| | <p>I would like to add to Carltons answer and go a little more in depth on how to approach problems like that in general.</p>
<p><strong>Hydrostatics or Hydrodynamics</strong></p>
<p>There are two possible solutions to the problem. You can either choose a reference frame that rotates with the fluids or that stays sti... | 5905 | Force exerted on wall of a rotating cylinder filled with fluid |
2015-10-25T09:08:25.237 | <p>Sorry if this is the wrong forum, I'm not an engineer but I'd need a pro to answer my question.</p>
<p><strong>Short version:</strong>
Are there any tests or studies, if a carpet in an apartement can reduce noise from the apartment below. I'm searching for numbers rather than oppinions. The noise comes in all frequ... | |architecture| | <p>I have a background in acoustics, noise control and vibrations. I haven't done much in the way of residential applications though. </p>
<p>Honestly, your best bet is to lay down heavy carpet with an underlayment designed to maximize sound absorption, like <a href="http://www.soundisolationcompany.com/solutions-prod... | 5909 | Carpet for noise reduction (tests / studies) |
2015-10-25T22:37:41.507 | <p>In the buckling of columns we know that:</p>
<p>$$P = \dfrac{n^2\pi^2EI}{L^2}$$</p>
<p>The smallest value of P occurs when $n=1$ which gives a simple buckling shape (one wave):</p>
<p>$$P_{cr} = \dfrac{\pi^2EI}{L^2}$$</p>
<p>However for $n > 1$, as shown below the buckling shape is more complex and has many w... | |structural-engineering|beam|columns|buckling| | <p>Whether or not buckling modes with $n>1$ exists depends on how you look at the structure.</p>
<p>As @hazzey notes in his answer, columns with bracing may display buckling modes with $n>1$. These buckling modes, however, are simply equivalent to the $n=1$ modes of the individual segments that compose the colum... | 5910 | Buckling: Do buckling mode shapes of n > 1 occur in reality? |
2015-10-26T15:57:06.453 | <p>I'm trying to determine a level of vibration testing I should perform on my product. I understand electrical stress/life testing and I'm looking for a mechanical equivalent.</p>
<p>I have a DC motor running in my application that generates a certain level of vibration. I'm planning to do some environmental testing ... | |mechanical-engineering|vibration|product-testing| | <p>Q- The aim of this research study is mainly based on the comparison of measured frequency response function results for the threshold with and without damage, and comparing them with the theoretical model to update the modal parameters.
The study will be performed on isotropic beam, to study the vibration characteri... | 5923 | What level of vibration testing should I perform on my product? |
2015-10-26T16:38:07.030 | <p>I'm not sure how to calculate force $P$ when the moment is a given with the force $P$ at an angle. </p>
<p>I'm also having trouble breaking the moment into the $x$ and $y$ components.</p>
<p><a href="https://i.stack.imgur.com/SXy9z.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/SXy9z.jpg" alt="... | |mechanical-engineering|torque| | <p>$$
\tau = 500 \mbox{Nm} \\
$$</p>
<p>$$
\tau = r \times F \\
\tau = |r| |F| \sin{(\theta)} \\
$$</p>
<p>If the lower left angle is $43^{\circ}$, then the top angle from the bar $r$ to vertical is then $180 - 90 - 43 = \boxed{47^{\circ}}$. This means that $\theta$, the angle between the bar $r$ and the force $P$ is... | 5927 | Calculate the force when given the moment |
2015-10-28T10:23:35.860 | <p>I want to know if the sensor nodes in any cluster in a wireless sensor network may detect events in a different ratio i.e.some nodes could detect events more others in the same cluster, so is power consumption in these nodes will be higher than other nodes?
i want to know if there is an application in which this as... | |telecommunication| | <p>The function of a node and how it interacts on the mesh network (assuming a mesh-connected node) are two different things.</p>
<p>Such nodes almost certainly will have a microcontroller in them that performs the node function, like measuring temperature periodically or whatever. This micro then also usually decide... | 5940 | Could a one sensor node in a cluster sense a data more the others? |
2015-10-29T18:18:57.320 | <p>Hooke's Law defines a linear-elastic relationship between stress and strain. </p>
<p>$$ \sigma = E\epsilon $$</p>
<p>Steel behaves very much like a linear-elastic material, following Hooke's Law closely. It does, however, display non-elastic behaviors such as relaxation. Relaxation is the behavior wherein a member... | |materials|steel| | <p>In short, yes, relaxation should probably be considered plastic deformation, as plastic strain is defined as <strong>non-recoverable deformation</strong> when applied stresses are removed.</p>
<h1>Definitional Explanation</h1>
<p>Assume you have a sample of some material, in this case steel, and want to apply a lo... | 5962 | Is steel relaxation plastic? |
2015-10-30T01:00:59.637 | <p>By definition, prestressing is a self-balanced load. This is because it is in fact merely an applied state of internal stresses. </p>
<p>This can also be demonstrated mathematically (in this case for a simple parabolic cable) via Lin's load-balancing method. </p>
<p>For a cable which follows the layout given by
$$... | |civil-engineering|structural-engineering|concrete|prestressed-concrete| | <p>Comments by @Mr.P nudged me to realize that there is a redistribution of equivalent loads due to losses which cannot be trivially encompassed by Lin's method.</p>
<p>To demonstrate this, take the following simply-supported beam (ignore all concepts of units or scale here, this is a thought exercise).</p>
<p><a hre... | 5967 | How is prestressing with losses self-balanced? |
2015-10-30T07:16:32.320 | <p>for example :</p>
<p><strong>Sender:</strong> A cellular signal tower(Base Station(BS)) sends data(voice, GPRS, VOIP) to the cellphone. The sender will obviously have the carrier frequency and more power(voltage+current) to generate the carrier signal.</p>
<p><strong>Receiver:</strong> A cell phone which receives ... | |electrical-engineering|telecommunication| | <p>When a cell phone is sending, it generates its own carrier. The power for doing this comes from the cell phone's battery.</p>
<p>Batteries in a cell phone may last 12 hours, but that is not while transmitting. Depending on how "off" the cell phone is, it is only occasionally listening to the cell tower, and even ... | 5973 | How does a carrier signal work from a receiver's perspective? |
2015-10-30T22:36:52.547 | <p>I'm in school for electronics engineering. Would someone lay out the high level steps in becoming a professional engineer (PE) in the state of California?</p>
| |electrical-engineering|licensure| | <p>California has a few notable exceptions - they try to favor graduates from the in-state schools, but are very picky on structural engineers. Here they are, in no particular order:</p>
<ul>
<li>You do not need to have 4 years of experience if you are a resident and graduated from a California School. 2 years is ac... | 5982 | What is the sequence of exams to become a Professional Engineer in California? |
2015-10-31T02:53:00.950 | <p>How do I know when to use an upward or a downward curve when I'm drawing a bending moment diagram for a uniformly-distributed load (UDL) and what's the most reliable way of identifying the maximum bending moment?</p>
| |statics| | <p>The direction a bending moment diagram is drawn depends on the sign convention being used. The most common sign convention is:</p>
<p><a href="https://i.stack.imgur.com/ag9He.gif" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ag9He.gif" alt="PositiveSignConvention"></a></p>
<p>It is good practice t... | 5983 | Drawing Bending Moment Diagrams |
2015-10-31T06:35:28.450 | <p>In addition to power and performance, one of the reasons VW cheated their emissions results was to improve the fuel economy of their cars. Why exactly does this happen?</p>
<p>I'm familiar with cars and how cars work so feel free to get technical.</p>
<p>And a follow-up question: Where is the "sweet spot" between ... | |mechanical-engineering|automotive-engineering|environmental-engineering| | <p>Because most controls reduce efficiency, since they are aimed at protecting the catalyst - not reducing pollution. An air/fuel ratio of 14.7/1 keeps the catalyst happy. Engines can and do run cleaner and better without the catalyst, but the EPA is not only decades behind chemistry - it is not concerned with the envi... | 5984 | Why does reducing the amount of emissions control improve the fuel economy of a car? |
2015-10-31T15:49:06.700 | <p><strong>Regarding micro inverters for solar power systems:</strong></p>
<p>Is there technically a difference between an inverter classified as a "micro inverter" and and inverter classified as a "pure sine wave" inverter? Or is it simply a matter of using extra jargon to describe the size of the inverter?</p>
<p>... | |electrical-engineering| | <p>Stop.</p>
<p>You can't just attach <em>any</em> inverter on a PV panel or array, even if it does have the right power rating.</p>
<p>Your inverter needs to be a PV inverter specificaly. It has to be designed to do max-power-point tracking. That's because the panel doesn't have any specific potential difference: th... | 5988 | "Micro Inverters" vs "Pure Sine Wave" for Solar Systems |
2015-11-01T11:30:45.920 | <p>I have the same problem as described in this question:<br>
<a href="https://engineering.stackexchange.com/q/5535/2844">How to calculate the resulting temperature for a stream of air through a hot tube?</a>, but I want to increase the transferred heat by adding fins onto the inner side of the tube, parallel to the fl... | |heat-transfer| | <p>Internally finned tubes are not that common because of the high cost of manufacture. There aren't many sources for this kind of heat transfer. </p>
<p><a href="https://www.ruor.uottawa.ca/bitstream/10393/10870/1/EC52380.PDF" rel="nofollow noreferrer">This</a> paper provides a detailed description of numerical metho... | 5995 | Calculate thermal flow for air flowing through a tube, with fins |
2015-10-31T22:20:01.323 | <p><strong>TL;DR: how can I calculate the disturbance at each joint due to coupling forces in a two-link planar robot manipulator actuated by two independent DC motors?</strong></p>
<hr>
<p>I'm studying control theory and trying to work through a simple example using a two-link planar robot manipulator:</p>
<p><a hr... | |control-engineering|control-theory|dynamics|kinematics| | <p><strong>Non-Linear Control Approach</strong></p>
<p>Your approach is correct! I just want to point it out some tips.</p>
<p>$1^{st}$: Try to get the canonical form for the generalized coordinates:</p>
<p>$M(q) \ddot{q}$ + $C(q,\dot{q}) \dot{q}$ + $g(q)$ = $u$ </p>
<p>Were $M(q)$ is the inertia matrix, $C(q,\dot{... | 6006 | Feedback control of two-link planar manipulator |
2015-11-02T09:45:26.133 | <p>For a project using rotating voice coils motor in order to balance a system I need to determine the damping coefficient of these voice coils in order to insert it in a ADAMS model and analyse its performances.</p>
<p>Starting with the oscillation data obtained during a physical test on a mock-up, I used the Matlab ... | |mechanical-engineering|vibration| | <p>You need to find the effective mass of a rotating rod at the point where the damping force is applied. This equals $$m_{eff} = \frac{I_{pivot}}{\ell^2} $$ where $I_{pivot}$ is the MMOI about the pivot, and $\ell$ is the distance where the force is applied to the pivot.</p>
| 6012 | How to determine the damping coefficient? |
2015-11-02T11:46:32.560 | <p>Most/all nuclear fission reactors require cooling. Due to radioactive decay heat, this is true even when the reactor is switched off. Hence, there are requirements for nuclear plants to have power at all times: for example, in the United States, they must have backup battery power for 4–8 hours (<a href="http://w... | |safety|nuclear-technology|nuclear-engineering| | <p>I just thought that I would clarify something that Fred said. In an emergency shutting down the nuclear chain reaction is the easy part. The main issue is the decay heat. The decay heat comes from the residual radioactive components in the core.</p>
<p>This decay heat starts off at approximately 7% of the total rea... | 6013 | When backup cooling fails in reactors without passive safety, what is the risk of radioactive contamination? |
2015-11-02T20:45:50.640 | <p>I know that the neutral axis occurs where the sum of stresses (bending + axial) is equal to 0. I have found the stresses and drawn a diagram to represent forces. How do I determine the neutral axis?</p>
<p><a href="https://i.stack.imgur.com/wwGxq.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ww... | |mechanical-engineering|structural-engineering|structures|applied-mechanics| | <p>In order to calculate the neutral axis under this definition (see my comment under the OP), you need to figure out the stress distribution for each of the applied loads and then superpose them.</p>
<p>So, for this we need to calculate the properties:
$$\begin{align}
A &= 80\cdot80 - 60\cdot60 = 2800 \\
I &=... | 6016 | Finding Neutral Axis of a simple shape undergoing axial load |
2015-11-02T23:07:32.820 | <p>I can't find anything on this. Every source I can find on UV cured polymers describe the process and how they're cured using UV radiation but nothing on what the resistance to UV is once it has cured.</p>
<p>Specifically I'm looking at the Stratasys PolyJet (<a href="http://www.stratasys.com/materials/material-safe... | |materials| | <p>I can provide an anecdotal answer. We use UV cured adhesives to bond pieces inside of our UV lasers. These lasers produce intense UV light, some of which is scattered around inside of the laser head. The exposure to those specific UV wavelengths is much more intense than the exposure of a piece of material laying... | 6017 | UV resistance of UV cured photopolymers |
2015-11-03T02:57:00.033 | <p>Surprisingly this hasn't been asked before, so I must be missing something simple. </p>
<p>We use engineering stress and engineering strain in this eq. Stress = (Young's modulus) × (strain). This eq. is used in analysis of bending beams, twisting shafts and in buckling. So the final equation of bending $(\frac{M}{I... | |materials|structural-engineering|stresses| | <p>Adding to @starrise's answer:</p>
<p>With regards to your dismissal of reasons 1 and 2, you are forgetting to consider the cost-benefit analysis regarding them. As @starrise showed in their answer, the difference is usually not substantial (though other materials will usually have larger differences).</p>
<p>On th... | 6020 | Why do we even use engineering stress? |
2015-11-03T23:03:22.640 | <p>Magnetic locks seem to be fairly common on the doors of modern buildings, but I question their reliability when compared to a traditional, mechanical lock. I realize that the strength that it would take to actually pry a door away from a good electromagnetic lock would certainly be enough to damage the door or frame... | |mechanical-engineering|electrical-engineering|magnets| | <p>A lot of the responses here are very interesting but the inverse relation of magnetic fields and magnetic strength must be considered. if two attracting magnets are a certain distance apart (say 1 inch) their attraction is for example 2lb. if the two magnets are 1/2 inch apart their attractive force is 4lbs and a qu... | 6031 | Can a magnetic lock be negated or overcome by a stronger electromagnet? |
2015-11-04T14:16:09.203 | <p>I look at PID controler and do not understand derivatve term. I know it's used in order to not let the signal to overshoot the set value. BUT when the sigal is arising, its derivative is positive. So when we add the positive derivative term, the signal gets even higher, so its derivative becomes even higher!
I think... | |control-engineering|control-theory| | <p><span class="math-container">$$ e = r - y$$</span> </p>
<ul>
<li><span class="math-container">$e \rightarrow$</span> error</li>
<li><span class="math-container">$r \rightarrow$</span> reference input</li>
<li><span class="math-container">$y \rightarrow$</span> actual output of the plant</li>
</ul>
<p>If <span clas... | 6035 | How does the DERIVATIVE term slow down the signal? |
2015-11-04T22:44:48.653 | <p>I'm trying to solve the question attached below (please note the handwritten values are ones that I calculated/not part of question) I am assuming that to find the load $q$ I need to get the bending stress (which from my calculation was $45\text{ N/mm}^2$) and substitute into equation of Bending stress $= \dfrac{My}... | |mechanical-engineering|structural-engineering|structures|stresses| | <p>As always, the first thing you need to do is calculate your properties.
\begin{align}
A_A &= 150\cdot10 + 6\cdot(200-10) = 2640\text{ mm}^2 \\
\overline{y}_A &= \dfrac{150\cdot10\cdot195 + 6\cdot190\cdot95}{2640} = 151.8\text{ mm} \\
I_A &= \dfrac{150\cdot10^3}{12}+150\cdot10\cdot(151.8-195)^2+\dfrac{6\c... | 6041 | Calculating stresses of section with varying depth |
2015-11-05T09:04:40.973 | <p>What is the difference between an automatic transmission (AT) and an automated manual transmission (AMT)?</p>
| |mechanical-engineering|automotive-engineering|power-engineering| | <p>In answering this question I'm assuming you already know the difference between an Automatic Transmission (AT) and a Manual Transmission (MT).</p>
<hr>
<h2>Conventional Automatic Transmission (AT)</h2>
<ul>
<li>Minimal to no power interruption</li>
<li>Automatic moving-off</li>
<li>Various gear ratios</li>
<li>Ef... | 6047 | What is the difference between an automatic transmission and an automated manual transmission? |
2015-11-05T09:20:01.100 | <p>Figure 2 in <a href="http://uk.mathworks.com/help/simulink/examples/modeling-an-automatic-transmission-controller.html" rel="nofollow noreferrer">this tutorial</a> represents the shift map/schedule of an automatic transmission. How is this map constructed? I want to know how to design a shift map myself for another ... | |mechanical-engineering|automotive-engineering|power-engineering| | <p>The crucial piece of information is the torque curve of the engine ie. the function which relates torque to engine speed. </p>
<p>Any gearbox, manual or automatic, has two primary concerns the first is to allow access to the desired level of torque at any given road speed, for example changing down to give extra to... | 6048 | How is the shift map of an automatic transmission constructed? |
2015-11-05T21:51:20.493 | <p>I saw a <a href="http://www.cnn.com/2015/11/05/travel/macau-studio-city-wheel/index.html" rel="nofollow">story on CNN today</a> about a figure-eight ferris wheel being built in Macau.</p>
<p>I'm curious what path the cabins take, and how this occurs. Do they actually follow a figure eight pattern? Do they move from... | |mechanical-engineering| | <p>It looks like the cars don't actually move in a figure eight, though it is designed to look like they do from afar. In the image below you can see that the cars travel around an hourglass-shaped (or gourd-shaped) track which is behind the outer yellow steel structure that looks like a figure eight. </p>
<p><a href... | 6056 | How does the figure eight ferris wheel work? |
2015-11-07T16:31:29.847 | <p>I would like to know what mechanical parts can be used to convert a rotation movement from an axis to another.</p>
<p>For example: You have the shaft of a motor rotating vertically, but you need to rotate a part horizontally.</p>
<p>I already found the worm drive assembly but I would like to know if an "exhaustive... | |mechanical-engineering|gears| | <p>The go-to solution is <a href="https://en.wikipedia.org/wiki/Bevel_gear">bevel gears</a>. They are used when the shafts would intersect and allow the same ratios as normal gears.</p>
<p>You can also make one of the gears a <a href="https://en.wikipedia.org/wiki/Crown_gear">crown gear</a> so the other gear can be a ... | 6069 | Transform/change/convert rotation axis |
2015-11-10T08:04:23.520 | <p>I'm trying to find a material suitable to be printed and with the properties of whiteboard, easy to clean and reusable. I'm having difficulties to find alternative materials, or providers.</p>
<p>As far as I know <a href="http://www.magicwhiteboard.co.uk/" rel="nofollow">magic whiteboard</a> is an alternative but i... | |materials| | <p>I use polycarbonate film which is used for binding manuals. Polyvinyl chloride sheets are equally good but when using whiteboard markets you must encaustic they are stressed within 24 hours to avoid nasty stains</p>
| 6089 | Printable and reusable whiteboard material |
2015-11-10T17:55:19.880 | <p>If we have a simple adiabatic cylinder with a piston on top and we heat the gas from the inside, the gas starts to expand and move the piston up. This process is isobaric; but if the pressure on the piston doesn't change, how does it move up?</p>
| |thermodynamics| | <p>In reality, such a process is not <em>truly</em> isobaric; a small rise in temperature will cause the gas to build up an infinitesimally small amount of pressure, which moves the piston up an infinitesimally small distance, which restores the pressure to its original value. If you assume that the piston can react q... | 6097 | How does expanding gas in isobaric process move a piston? |
2015-11-11T09:35:06.280 | <p>I have a school case study to prepare a (business) plan for office building construction with at least one level of underground parking. I have it pretty much done, but I still need to clarify one thing (teacher is not available):</p>
<p>(1) What is implied by "Underground water level varies from 5-6m" for the cons... | |building-design| | <blockquote>
<p>(1) What is implied by "Underground water level varies from 5-6m" for the construction?</p>
</blockquote>
<p>Typically this means that the groundwater table starts between 5m and 6m below grade. In other words, if you dig over 5m into the soil, you will likely hit the water table and have water in y... | 6103 | Office Complex Foundations/Base Depth and Undeground Water |
2015-11-12T00:17:49.883 | <p>For example i have an exhaust pipe with very hot air from burning biofuel, and i have a turbine at the end of the exhaust that rotates and generates electricity.</p>
<p>Why is it more efficient to use the heat to boil water then use the steam produced to rotate the turbines? As in why is more electricity generated ... | |electrical-engineering|turbines|steam| | <p>A two phase chemistry that makes pressure using heat is necessary. </p>
<p>A pressure cooker with only air makes a lot less pressure than with a liter of water. </p>
<p>The water is in effect potential pressure stored in a cold state.</p>
<p>Supercritical fluids are actually more efficient than steam but require ... | 6108 | Why is using steam to rotate a turbine more efficient? |
2015-11-12T20:31:05.983 | <p>If biofuel is burnt, for example wood, and the stove I am building is made of metal, what is the most appropriate metal material I should use to avoid excessive corrosion in the exhaust pipe of the stove?</p>
| |materials|combustion|corrosion| | <p>Just to add some unique engineering solutions that are used, depending upon applications:</p>
<ol>
<li>Brick works wonders - it resists the acid in the smoke well and can withstand the heat. Not metal, but well worth it if the application is right.</li>
<li>For power plants, typical material use is acid brick line... | 6121 | What metal material to use for stove exhaust pipe? |
2015-11-13T15:52:31.983 | <p>Lavoisier's principle of mass conservation states that the mass of a system must remain constant over time. But, as far as I know, there's no similar principle for density.</p>
<p>So, is it possible to develop an alloy as dense as gold but made of constituents less dense than gold?</p>
| |materials|alloys| | <p>Unfortunately, your best bet is abusing the existence of isotopes of tungsten to produce "heavy" tungsten. A potential, but unexplored, alternative is to alloy tungsten with an interstitial atom other than carbon.</p>
<p>There is no way to make tungsten look or behave like gold beyond superficially, i.e. spraypaint... | 6128 | Alloys with same density as gold |
2015-11-14T04:49:34.043 | <p>The question has been surfacing periodically in the media and books over the past 100 years or so. I realize we're talking about a lot of material and work hours to begin with; the subsequent maintenance would be a nightmare. There are no power stations, nor radio towers between the continents; there is no viable wa... | |civil-engineering|tunnels| | <p>I'm assuming you are asking about a tunnel between North America and Europe.</p>
<p>There are two types of tunnel that "might" be possible: excavating a tunnel through the rock beneath the sea bed or sinking prefabricated sections of tunnel to the sea floor, joining them up and sealing them against water i... | 6134 | Is a Transatlantic tunnel technically possible today? How feasible would it be? |
2015-11-14T17:42:32.860 | <p>I'm trying to understand and identify the equations to use in defining the relationship between wind velocity, turbine rotor diameter, and power output for a wind turbine.</p>
<p>To simplify my question, let's use the following assumptions:</p>
<ul>
<li>Average wind speed of 8 m/s. </li>
<li>Rotor length of 40m f... | |energy|renewable-energy|power|wind-power| | <p>The power generated depends on the product of two factors:</p>
<ol>
<li>the windmill (wind turbine) power curve</li>
<li>the windspeed curve or histogram, % at each windspeed.</li>
</ol>
<p>Here's a plot of 2 wind turbine types <span class="math-container">$\times$</span> 3 synthetic (Weibull-distributed)
windspeed ... | 6144 | Relationship between wind velocity, turbine rotor diameter, and power output |
2015-11-14T22:39:47.933 | <p>I've recently designed what is essentially an aluminium box. I've done the entire design process of CAD software SolidWorks and then done some simulations of loading of the box.</p>
<p>Through iterations I've figured out the minimum thickness of the aluminium (AL6061 T6) box material to be quite small - 0.25 mm. Th... | |design|computer-aided-design|aluminum| | <blockquote>
<p>The Wikipedia page puts tin foil thickness at between 0.2 mm and 0.006 mm. That means that the upper end of the tin foil is easily comparable with the thickness of my box.</p>
</blockquote>
<p>Ooook. Let's look at this, from an engineering perspective.</p>
<p>First, scales. The smallest measurement ... | 6148 | Intuition vs software results |
2015-11-15T00:42:01.457 | <p>I need a small air compressor for a robotics application. I currently have one of those 12V tire inflators (200 psi, 1 CFM or so) that is sized well for this purpose (sample image below).</p>
<p>However, in the future I would like to replace this with a lighter compressor with similar specifications (for weight sav... | |mechanical-engineering|compressors| | <blockquote>
<p>If so, why can't I find such devices anywhere?</p>
</blockquote>
<p>In a word - <strong><em>Cost</em></strong>. </p>
<p>Running some quick searches for 300W DC motors, the brushless motors were typically 3x - 5x more expensive than their brushed counterparts. And as you pointed out, brushless moto... | 6150 | Lightweight Air Compressor |
2015-11-15T01:56:27.710 | <p>Do we have the technology to illuminate a small region on the dark side of the Earth with an artificial satellite in orbit around the Earth? By illuminate I mean bright enough to light objects for regular humans nearby to see better than they could have otherwise. Assume low Earth orbit and no moon to make it easier... | |aerospace-engineering| | <p>Sure. Even a cubesat could do this (if only for a few seconds). </p>
<p>Put a relatively powerful laser (maybe 100W?) on a satellite, focus and aim it at a square meter or so of ground, and light it up. 100 km (LEO) is short enough that a good laser can focus down to a pretty small land area, meaning a smallish las... | 6152 | Illuminate the Earth with an artificial satellite? |
2015-11-15T12:16:15.840 | <p>Is there any emitter/receiver (passive or active) systems that allow distance estimation in the range of 1~2 meters with an accuracy of few centimetres and don't need to have a direct line of sight as optical systems mostly do?</p>
<p>I was thinking about using such sensors as nodes to put on a suit that a human ca... | |electrical-engineering|sensors|distance-measurement| | <p>Ultrasonic sensing is can be used for distance measurement. Ultrasonic proximity sensing technology is commonly used in automotive as part of <a href="https://en.wikipedia.org/wiki/Advanced_driver_assistance_systems" rel="nofollow noreferrer">Advanced Driver Assistance Systems</a>. The basic theory behind this techn... | 6157 | Short range distance estimation systems |
2015-11-15T12:25:42.243 | <p>I know definition but how would you explain to complete layik ( as me ) what is MEMS and how it is used. </p>
<p>Examples: Silicon nanopore membranes (SNM) have been prototyped from silicon substrates by an innovative process based on MEMS technology.</p>
<ul>
<li><a href="http://whatis.techtarget.com/definition/... | |mechanical-engineering|applied-mechanics|power-electronics|systems-engineering| | <p>One way to think of MEMS is regular mechanical systems, but at a very small scale. Often these tiny systems are fabricated using technology developed for making silicon electronic chips, like nanometer-scale photolithography and etching.</p>
<p>However, describing MEMS as just downscaled regular mechanical systems... | 6158 | What is micro-electromechanical systems (MEMS)? |
2015-11-15T15:11:56.637 | <p>I am studying embedded systems and microcontrollers and now I have to face the interrupts. I understood the main concepts around them and how to implement them inside a C code, but I want to know how they work at hardware level. </p>
<p>I found this scheme on the internet:</p>
<p><a href="https://i.stack.imgur.com... | |electrical-engineering|embedded-systems| | <p>A interrupt is when the processor goes and executes some pre-determined code based on some event. This is done so that, with the cooperation of the specially executed code, the processor can return to executing the original code in such a way that its operation is not affected other than some additional time taken.... | 6162 | Hardware behind interrupts |
2015-11-16T02:37:53.643 | <p>I want to convert rotary motion (the orange propeller) onto a square path (the dark gray path). Is this a valid way to go about it? Would it be possible to use a square peg instead of a round one (the red circle) in order to keep the peg level as it travels? If not how could I keep it level? I'm a noob.</p>
<p><a h... | |mechanical-engineering| | <p>The reuleaux triangle is a great solution but I would prefer something that has fewer parts and is more compact...</p>
<p>Here's another option. The idea is to sandwich a bent peg between offset tracks. So the sandwich goes like this: Bottom Track, peg, Propeller, Top Track (Transparent). And Yes, I would round out... | 6170 | Is this Square Track Cam valid? |
2015-11-16T12:10:04.283 | <p>I need to design the roof structure for a sports facility. I have no information with regard to HVAC design at this stage. Also, the HVAC may change in future. Thus I don't know what load to apply to the structure. I intend to give the HVAC and electrical engineers a weight envelope in which they can operate.</p>
<... | |structural-engineering|hvac| | <p>I don't think what you are looking for really exists, in terms of a standardized list of HVAC/services loadings. Building codes don't usually specify dead loads, probably because they are, in principal, known. Typically only imposed (live) loads are specified. From the buildings I have worked on the services loading... | 6174 | Dead Load / Self Weight for ceilings & HVAC |
2015-11-17T04:19:21.503 | <p>Does the speed of the water flowing radially outwards from a water jet impacting a sink depend on how far the tap is opened?</p>
<p>At the moment, I understand that the maximum velocity of the water in the vertical jet is constant regardless of how far the tap is open (as it is accelerated by gravity, and disregard... | |fluid-mechanics| | <p>The speed at which water leaves the tap is not constant, as it has a finite area, which remains roughly constant, so increased flow does indeed increase the velocity. ($\dot m= \rho\, VA$)</p>
<p>However, we can still ask the question of how the flow profile of water flowing outward from a jet is dependant on flow ... | 6190 | Does opening a tap in a sink affect the radial speed of the water around the jet? |
2015-11-17T19:11:38.180 | <p>I want to know why ceramic or disk capacitors are not rated directly like electrolyte ones? Is it just a convention or some other reason is behind this? Like, the ceramic ones are rated as 762k. then the value of the capacitance is 7600pF. (7-1st significant digit, 6-2nd significant digit and 2=multiplying factor(10... | |electrical-engineering| | <p>There is not enough space.</p>
<p>But they do manage to find enough space on the bigger ceramic components though.</p>
| 6196 | Why Ceramic Capacitors Are Not Rated Directly Like Electrolytic Ones? |
2015-11-18T04:19:27.050 | <p>I was a doing a placement at a company, and they were designing a new heat pump. I was told the more compact you can make a heat-pump, the better it is for efficiency, and they mentioned something about this was because the power density was increased.</p>
<p>I get there are benefits from using less material and ma... | |mechanical-engineering|thermodynamics|heat-transfer| | <p>As far as I know the COP of a heat pump doesnt vary greatly with the size of the unit only with the technology used, quality of components, and the correspondingly price. As a general engineering rule, its easier to make something cheaper/more effective when you have less constraints. So having no footprint constrai... | 6203 | Are smaller heat-pumps more efficient? |
2015-11-18T13:38:15.003 | <p>I'm an undergraduate student of Electrical Power Engineering currently in 3rd semester, one of the courses we study is Digital Logic Design(dld) and I have found much interest in it but I am unclear whether the subject would have application in our field i.e. power engineering or not....Could anyone guide me that h... | |electrical-engineering| | <p>Having studied electronic and electrical engineering, I covered both the power/analogue and the digital part. There were certain power designs where using a digital microcontroller (to generate a square wave of a certain time period and duty ratio) helped.</p>
<p>There are methods of obtaining oscillators using dis... | 6212 | Relation of Digital Logic Design to Electrical Power Engineering? |
2015-11-18T20:28:32.723 | <p>I have a problem in understanding of gears (spur gears). I designed some spur gears but I don't understand how the modulus works. I saw that this modulus is some standard thing and it's calculated by diametral pitch. Do I need to make this diametral pitch from standards, or could I make whatever I want? How does thi... | |gears| | <p>Whenever you choose to design standard gears, you typically have two main parameters: the number of teeth $N$ and the module, or modulus $m$. The module can generally be interpreted as the distance between the gear teeth. In fact, the module is defined as the circular pitch $p$ (the circumferential distance between ... | 6215 | Spur gears design |
2015-11-19T01:07:00.053 | <p>Are there any established solutions for truning a gear (or wheel) half-circle in one direction, back in the opposite direction, and repeating? Mechanism must be driven by a motor and continuous rotary motion. Compact and simple mechanisms preferred. Below are two possible solutions I dreamed up. Which one is better ... | |mechanical-engineering| | <p>Selection of a mechanism highly depends on the end application. Here are some ways to evaluate a mechanism vs your application:</p>
<ol>
<li>Input (360 deg rotation in this case)</li>
<li>Output (180 deg rotation motion in this case)</li>
<li>Relationship between input and output (mechanical advantage, velocity, an... | 6221 | Rotary Motion to 180 Degrees Reciprocating Mechanism |
2015-11-19T10:51:00.163 | <p>I'm well aware that there are many different factors to be considered, such as ease of installation/maintenance, conversion from AC to DC, environment, distance, speed, frequency of turns, and so forth.</p>
<p>Setting all of those aside for now, suppose we build a 10-mile long demonstration track with some hills an... | |electrical-engineering|energy-efficiency|power| | <p>Your "Bonus question" holds the answer here. Assuming that the two trains are perfectly identical, and that the power consumption is identical (which, if you have the same weight, motor, and size, it will be), you are down to transmission loss.</p>
<p>The resistance of a conductor is R=L*Rho/A.
L=length
Rho=resist... | 6223 | Third Rail vs Overhead Cable: which is more efficient in terms of electricity consumption? |
2015-11-19T19:15:26.153 | <p>I need to spin a threaded rod to raise a picture on a frame. The weight of the picture + the parts that it hangs on will be around 6 pounds. Two motors are going to be used to lift it via threaded rods (like in 3d printer platforms) but I need them to lift about 8" in less than 4 seconds.</p>
<p>I am unfamiliar wit... | |mechanical-engineering|motors|stepper-motor| | <p>Direct answers to question:</p>
<ul>
<li><p>Whether a motor could overrun depends on motor power, momentum of the load, and resistance of the system. This could be a problem even with switches, but can be overcome with careful design.</p></li>
<li><p>Steppers are overkill if you need to move between two points with... | 6228 | High RPM - Stepper vs Brushless Motor |
2015-11-19T23:41:08.030 | <p>A wifi user is in a different room than the router. The computer is having a hard time connecting and receiving the wifi signal.</p>
<p>Can the wifi signal from the router to the computer be improved by opening a door to the room where the computer is?</p>
| |signal|wifi| | <p>I live in a big old 1920s built house. The bedroom is one floor above the router, and one room adjacent. The floors in my house are wooden, the walls are stone, the cielings are high and the doors are solid wood. If I try to stream video on Chromecast in my bedroom with the bedroom door closed, it intermittently ... | 6230 | Can wifi signal reception be improved by opening a door? |
2015-11-20T15:14:08.613 | <p>I have a rotary pump and want to gain knowledge about its characteristics. I have an uncalibrated flow meter. At best I want to get a flowrate/pressure-diagram. </p>
<p>I understand, I need to analyse the flow sensor in advance.</p>
<p>Things I have:</p>
<ul>
<li>Voltage and current measurement equipment</li>
<li... | |mechanical-engineering|pumps| | <p>I am working under the assumption that we are talking about a small pump with a flow rate appropriate to measure using a graduated cylender. It's a bit tricky with the tools described but I would make a vertical column using your vast set of tubing as a home made pressure sensor. Also you can use a stop watch and ... | 6238 | Method for determining pump characteristics |
2015-11-20T16:27:47.437 | <p>My father-in-law would like to install a hinged stair system in his garage that allows him comfortable access to his attic space.</p>
<p>He wants the stairs to swing up flush with the ceiling when not in use, and then to easily swing down when he needs it, and plans on using a set of pulley and weights as a counter... | |applied-mechanics|statics| | <p>The answer for this will depend on the location of where you attach your counterweight rope, but the generic solution is as follows:</p>
<p>Suppose you have a staircase of weight $W$. It can be assumed that this weight is centered at the midpoint of the staircase, or $\frac{L}{2}$.</p>
<p>Additionally, suppose yo... | 6239 | Calculate effort to raise hinged lever with distributed load |
2015-11-23T01:15:17.043 | <p>I've see the same lids every day but I never really thought about their construction. There is an indent in a "Solo Travel Lid" for coffee cups that is just above the hole that you drink the coffee from.</p>
<p><a href="https://i.stack.imgur.com/cHn26.png" rel="noreferrer"><img src="https://i.stack.imgur.c... | |design|applied-mechanics| | <p>From the "Solo Traveler" <a href="http://www.google.com/patents/US4589569" rel="nofollow noreferrer">patent</a>:</p>
<blockquote>
<p>A more specific object of the present invention is to provide a lid having an opening formed therethrough to enable drinking, and having a recess formed in the lid adjacent the open... | 6257 | From an engineering standpoint, what is the purpose of the indent in a coffee lid? |
2015-11-23T18:07:37.427 | <p>When you compress a bicycle pump and seal the opening, the pump will automatically return to it's initial position when you release it. I suppose this is how air suspension works as well?</p>
<p><a href="https://i.stack.imgur.com/durma.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/durma.png" al... | |pressure|energy|compressed-air| | <p>There is another reason for this in multi-cylinder engines. While one cylinder is compressing the air, another is decompressing it. The net result is that the torque as a function of position gets smoother as the number of cylinders is increased.</p>
| 6268 | Turning an engine over with engine compression |
2015-11-25T00:16:19.183 | <p>I am trying to bore out a red brass pipe from 3/8" to 10mm using my drill press and a standard twist HSS bit. Running the drill at 600rpm I can't get more than half an inch in before the drill starts binding. I tried running first with cutting oil, and then, thinking maybe the oil wasn't sticky/viscous enough, tri... | |mechanical-engineering|machining|drilling|brass| | <p>Reamers mentioned in an ericnutsch's answer are good solution (remember that these reamers are designed to increase diameter of existing aperture up to 0,5mm), but may be the better solution is to use senker.
But seems your problem is not in using wrong reamer type.
I would suggest you to check the straightness of y... | 6284 | How to drill larger bore in pipe? |
2015-11-25T21:15:02.287 | <p>My goal is to have an array of LEDs arranged in such a way that I can light the view of my action cam. My action cam has a horizontal field of view of 175°.</p>
<p>My first idea was to determine the angle of light emission of a given LED and stack them next to each other, each time being rotated by their angle of l... | |mechanical-engineering|electrical-engineering|design| | <p>Instead of generating a perfect set of lights, which may be expensive, it should be possible to correct some uneven illumination via software post-processing.</p>
<p>One solution is to generate a static, white-field exposure of the space you wish to image. Essentially, drape the area you wish to image with somethin... | 6304 | Equal illumination of an actioncam's field of view |
2015-11-27T06:01:27.993 | <p>I posted this question on <a href="https://electronics.stackexchange.com/questions/202839/three-heaters-on-single-pcb">electronics SE</a>, but was suggested that I post it here.</p>
<p>I basically having three heaters (serpentine pattern) on a PCB (fiberglass board), as the following image shows:<a href="https://i.... | |electrical-engineering|materials|heat-transfer|temperature|power| | <p>Well, air has <a href="https://en.wikipedia.org/wiki/List_of_thermal_conductivities" rel="nofollow">worse thermal conductivity than practically any solid</a>, so chances are that a hole will decrease the heat transmission. There are however solids with thermal conductivity very close to that of air, so if that board... | 6323 | Having three heaters on single PCB |
2015-11-27T13:28:46.553 | <p>This might be a stupid question, but I'm new to mechanics, so please bear with me. Suppose I have a compound gearing system defined in the image below (not to scale). </p>
<p><a href="https://i.stack.imgur.com/ZAqiM.jpg" rel="noreferrer"><img src="https://i.stack.imgur.com/ZAqiM.jpg" alt="compound gear system"></a>... | |mechanical-engineering|gears|applied-mechanics|torque| | <p>I think that the most useful answer to your question is that, in practice we are most concerned about the relative torque between two linked shafts. </p>
<p>To put it another way the forces on gears are only of interest to people who design gears and if you are designing a gearbox it's the ration of torque/RPM whic... | 6326 | Compound gear system ratio |
2015-11-28T23:05:42.363 | <p>Since all it really is is a heating element, what happens if I use a 240v/50Hz clothes iron with a 110v/60Hz supply?</p>
| |electrical-engineering| | <p>In general, anything with a heating element will produce only 1/4 the heat on 1/2 the voltage, since power is proportional to voltage squared.</p>
<p>In other words, you'll probably be disappointed with the results.</p>
| 6343 | What happens if I use a 240v clothes iron in USA? |
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