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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2016-03-11T11:22:28.093 | <p>I'm working on a flood defence scheme in which a section of RC flood wall becomes sheet piles. The reasons for this aren't important, but the solution isn't to simply make all walls one or the other. </p>
<p><strong>My issue is how to connect these two very different types of wall in a way that provides an expansio... | |civil-engineering|geotechnical-engineering|reinforced-concrete|retaining-wall| | <p>We used a simple rubber between two concrete walls. I don't see any reason you can't use the same for a concrete steel wall connection. As these sorts of walls don't settle much you should be ok just coupling these two together without worrying about one settling and dragging the other. Just weld a flat sheet (possi... | 7879 | Connections between RC retaining walls and sheet pile retaining walls |
2016-03-11T13:53:04.200 | <p>A cascaded PID controller is depicted in following image (courtesy of <a href="http://www.controlglobal.com/assets/Media/0512/article_547_fig3.jpg" rel="nofollow noreferrer">controlglobal.com</a>):
<a href="https://i.stack.imgur.com/fCyjy.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/fCyjy.png" ... | |control-engineering|control-theory|pid-control| | <p>In general, poor performance of PID2 will cause poor performance in PID1, in both disturbance rejection and setpoint tracking.</p>
<p>There are some special instances where poor performance of PID2 in the form of high frequency oscillation is attenuated by G1, so the performance of PID1 is not significantly affecte... | 7885 | Is it important to have a good behaviour inside internal loops of a cascaded PID controller? |
2016-03-11T21:15:29.307 | <p>I have been trying to model a custom gear to fit on to another physical gear. I having been using <a href="http://www.rushgears.com/tech-tools/part-search/build-custom-gears" rel="nofollow">this 3d model gear generator</a>. What I know about my <a href="https://www.servocity.com/html/32_pitch_hitec_servo_gears.html#... | |gears| | <p>Gears will only mesh together when they both share the same Diametral Pitch. There are many online descriptions for this term, that is what you want to learn about. Here is an example of one: <a href="https://www.bostongear.com/pdf/gearology/chapter02.pdf" rel="nofollow">https://www.bostongear.com/pdf/gearology/chap... | 7896 | 3d model gear to fit another gear |
2016-03-11T21:35:03.963 | <p>I've heard that both of these coupling types introduce a degree of kinematic error in the driven shaft. What does it actually mean in practice? Is it that the driven shaft doesn't turn uniformly even when the input shaft does? But is this error arbitrary or the same amount of error is experienced for every revolutio... | |mechanical-engineering| | <p>The short answer is that universal joints are tolerant of angular misalignment while Oldham couplings are intended for use where the shafts are misaligned but parallel.</p>
| 7898 | Oldham coupling vs Universal joint |
2016-03-11T23:18:31.990 | <p>I love ejection seats and the flying contraptions they usually reside in. In fact, I like them so much that I want to make my own, despite my profound lack of training and inexperience with mechanical engineering in general. After doing a little research into the materials for my ejection seat, I found a large coll... | |aluminum|welding|alloys|rivets| | <p>As an aside, if you want to bend and play with it. Here's a tip. Get a pot of soap, a gas blow torch and sit by a bath. Smear the part with soap. Heat with the blow torch until the soap turns black, then drop it in the cold bath. </p>
<p>Depending on your air temperature you've now got a few hours to bend it to you... | 7901 | Aluminum for an Ejection Seat Replica |
2016-03-13T19:42:53.723 | <p>The diagram is for three materials with different thermal conductivities. I think number 1 is the material with higher thermal conductivity because it transfers the heat faster so it gets to the steady temperature sooner than the other two. Am I right? If not or if my reasoning isn't correct, I appreciate your help.... | |thermodynamics|heat-transfer|thermal-conduction| | <p>$\dot{Q} = k A \frac{\Delta T}{l}$</p>
<p>$l$ thickness </p>
<p>$A$ surface area</p>
<p>From this follows that besides other factors the rate of heatflow is proportional to the thermal conductivity $k$.</p>
<p>$\dot{Q} \propto k$ </p>
<p>Therefore a high thermal conductivity allows for a fast heat transfer, hen... | 7915 | Relationship between thermal conductivity and reaching the steady temperature? |
2016-03-14T04:46:00.937 | <p>I'm running a simulation in a CAD on a rather simple assembly with several parts in which a motor effectively rotates a part. If the motor is set to constant 10RPM, the part rotates fine and the max. motor torque is around 500N-mm. However, if it's set to 5RPM, it gets stuck and the motor torque reaches 8000N-mm.</p... | |mechanical-engineering| | <p>Simulating a process is a big task which includes various preprocessing steps. We try to model the real world yet are not able to do it 100%. So sometimes it’s hard to find errors in your model. Please check for the following errors:</p>
<ul>
<li>Cad Modeling Error</li>
<li>Material Properties Error</li>
<li>Discr... | 7921 | Why does a motor lockup at low RPM in my simulation? |
2016-03-14T09:29:52.880 | <p>I'm trying to model a part that rotates on a shaft. I measured empirically that it has a static torque of around 500 N·mm and a dynamic torque of around 400 N·mm. I want to simulate it in CAD but my software only takes static/dynamic friction as inputs.</p>
<p>How can I convert the torque values to static/dynamic f... | |mechanical-engineering|torque|friction| | <p>It is difficult to model with friction coefficients in this case, because the normal force is dependent on very small changes in dimensions and material strengths that your software may or may not support. Friction is by no means as easy as it is in the text books. The basic idea is find the force normal to the fric... | 7924 | Determine coefficients of friction based on the torque required to rotate a part on a shaft |
2016-03-14T15:39:05.923 | <p>I have a circular puck of stainless steel that is 9.5 mm in diameter. In the center, there is already a 5 um pinhole. My objective is to basically cut the steel along the dotted line, approximately 0.5 mm from the pinhole. <strong>Can you advise on what techniques to can make this cut precisely?</strong></p>
<p>... | |steel|cutting| | <p>CNC Milling should be precise enough (0.01 millimeter accuracy).</p>
| 7934 | How can I cut a thin (1mm) sheet of stainless steel with high precision? |
2016-03-15T04:32:55.640 | <p>I've been looking at solutions to compress gases and getting stunned by the cost and maintenance requirements of existing systems to fill cylinders (whether for SCBA or chemical storage) to 2000-4000psi: The cost of entry is over 4 figures, with commercial systems like those used in fire stations and SCUBA shops ru... | |hydraulics|compressors|compressed-gases| | <p>The elephant in the room is that while gasses are compressible, hydraulic oil is only negligibly so. </p>
<p>This difference has two major effects:</p>
<p>Firstly, the output volume flow is limited by the intake volumetric flow divided by the compression ratio. Let's say we have a hypothetical compressor that pull... | 7947 | Why no hydraulic piston gas compressors? |
2016-03-15T13:52:51.870 | <p>I am currently looking at a set of truss layouts produced by our truss manufacturing partner for a residential building project. I have reason to believe these layouts are generated using Alpine (Intelliview?) software. In any case, the design summary contains abbreviations which I cannot understand since I do not h... | |structural-engineering|structures|structural-analysis| | <p>NCBCLL is IBC Code for Non Concurrent Bottom Chord Live Load, used for uninhabitable/inhabitable attic space live loads @ 10/20 PSF through Alpine ITW</p>
| 7955 | Truss manufacturer drawings unclear |
2016-03-16T01:23:30.243 | <p>Al<sub>2</sub>O<sub>3</sub> is a hard, white material used for making firebricks and numerous molded ceramic parts.</p>
<p>Say I had a firebrick, took a core out of it using a thick-walled diamond hole saw and a drill press.</p>
<p>What lathe insert material would I then use to machine the outside of the Al<sub>2<... | |materials|machining|ceramics|lathe| | <p>In industrial applications probably the closest approximation is in dressing bonded abrasive wheels. These use abrasive particles including aluminum oxide but a different bonding medium which makes them a bit tougher than standard fire bricks. With this is mind a diamond tipped dressing tool would probably be a good... | 7964 | What's the most cost-effective cutter bit material that can be used to machine aluminum oxide? |
2016-03-16T14:46:13.220 | <p>Folks,</p>
<p>so today in the Lab I came up with this problem (see picture). It shows a cross section of a cutting machine. There's a blade moving with a constant speed $\frac{dx}{dt}$ towards the center of the roll made up of wood. This roll is turning with a adjustable speed $w$. Let's assume we keep $w$ also con... | |mechanical-engineering|materials| | <p>Your rotation speed $w$ is an <a href="https://en.wikipedia.org/wiki/Angular_frequency" rel="nofollow">angular frequency</a> (usually denoted with a small greek omega $\omega$, by the way). And its just what its name says: the change of angle of your roll in a certain amount of time. What is probably confusing is th... | 7975 | What is the analytical approach for a fiber cutting machine? |
2016-03-16T18:15:13.300 | <p>I'm trying to do some sheet metal work in Autodesk Fusion 360 and it has proved frustrating in the extreme. Maneuvering sketches and bodies to where I want them has proved extremely difficult. I understand that Autodesk Inventor has far better support for sheet metal parts, which is great if I could afford Invento... | |cad|autodesk-inventor| | <p>This video about <a href="https://knowledge.autodesk.com/community/screencast/af415e28-f8ee-4b0d-b83b-b6076c2a941d" rel="nofollow">Faux Sheet Metal</a> parts was incredibly helpful.</p>
<ol>
<li>Start with a set of sketches that describe your sheet metal project.</li>
<li>Create patches based on those sketches. Ea... | 7987 | Making sheet metal parts in Autodesk Fusion 360 |
2016-03-16T18:37:33.820 | <p>Shear areas have been obtained for a few different cross-sections. I-sections usually define their shear areas as equal to the product of the height of the section and the thickness of the web (assuming they fall under the thin-walled category).</p>
<p>However, what would the shear area for these sections be (assum... | |modeling| | <p>You can calculate the shear stiffness directly and then get an effective area after the fact if you'd like.</p>
<p>$$A_{shear}=\frac{V}{\gamma_{ave}\,G}$$</p>
<p>You can calculate average shear by averaging over the height (not area):</p>
<p>$$\gamma_{ave}=\frac1h \int \gamma\;dz$$</p>
<p>You can calculate shear... | 7989 | Shear area of atypical section |
2016-03-16T22:57:03.320 | <p>I'm building a catapult and I asked a question and got <a href="https://engineering.stackexchange.com/a/7873/5412">this</a> response. Is there an equivalent for the wave spring but for angular motion like a torsion spring? Or any improved design on the torsion spring.</p>
<p><strong>Edit:</strong> An improved desig... | |springs|projectiles| | <p>The main advantage of wave springs compared to coil springs is that you can have the same stiffness and travel for less uncompressed length. This stems from the fact that a compression type coil spring needs to have an open helix to provide room for the spring to compress. </p>
<p>In comparison the various types of... | 7991 | Wave torsion spring? |
2016-03-17T04:39:32.493 | <p>I am trying to recreate the following model of a wooden roof truss provided to me by a truss manufacturer:
<a href="https://i.stack.imgur.com/ObODF.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ObODF.jpg" alt="enter image description here"></a></p>
<p>My question is twofold:</p>
<ol>
<li><p>Wh... | |civil-engineering|structural-engineering|modeling| | <p>The most common way to model this structure is as follows (ignore the fact that the proportions are a bit off):</p>
<p><a href="https://i.stack.imgur.com/CHPnw.png" rel="noreferrer"><img src="https://i.stack.imgur.com/CHPnw.png" alt="enter image description here"></a></p>
<p>So, all of the diagonals are pinned-pin... | 7998 | How do you model a real-life truss in structural analysis software? |
2016-03-17T07:45:42.193 | <p>I have thin weir, really just a sheet of metal with a smooth and straight upper edge. I want to know how much water will flow over this weir, when the water level on the higher side is a few cm above the edge.<br>
I'm interested in the special case when the water on the lower side i below the level of the weir:<br>
... | |fluid-mechanics| | <p>Carlton is mistaken. Look at the exponent carefully. It should be 3/2, and not 2/3, this will obviously make a huge difference.</p>
<p>In <a href="https://engineering.stackexchange.com/a/22873/1832">another answer</a>, I give an explanation for why this equation is the case:</p>
<blockquote>
<p>At each locatio... | 8001 | Formula to describe flow over thin weir |
2016-03-17T12:32:46.257 | <p>Display screens connected to cameras are significantly different from windows or mirrors. Looking through a window or mirror, we can focus on infinity, and we can move our vantage point to see a little different. With a display screen showing live camera footage, we see the field of view from a single point (the c... | |materials|optics| | <p>Transmitting each individual <em>photon</em> is infeasible, given the amount of computation that would be required, but technology for capturing some information about incoming light direction already exists and is used in the <a href="https://illum.lytro.com/illum" rel="nofollow">Lytro</a> "light field" camera.</p>... | 8007 | Can cameras+display screens with window/mirror-like optical behaviour exist? |
2016-03-17T14:37:55.613 | <p>This question originates from <a href="https://engineering.stackexchange.com/questions/7955/truss-manufacturer-drawings-unclear">this</a> and <a href="https://engineering.stackexchange.com/questions/7998/real-life-truss-modelling">that</a> question. I have realized the concerns boil down to the following figure.</p>... | |structural-engineering|structures|structural-analysis| | <p>As mentioned in the comments to the question, since you are using a 3D analysis tool, you need to fix rotations around the X and Y axes. If you had been using a 2D analysis tool, simple pinned and roller supports would be suficient since rotations are only allowed around the Z axis, but since this is a 3D model, rot... | 8014 | How Do You Determine Truss Stability in a Modeling Program? |
2016-03-17T14:41:26.263 | <p>What are the best materials and methods to keep the internal temperature of a device lower then the ambient temperature outside of the device? Based on the following information:</p>
<ul>
<li>Starting temp of device is 20°C</li>
<li>Ambient temperature around the device is 200°C</li>
<li>The time in this environmen... | |electrical-engineering|thermal-insulation| | <p>There are drawer sized data safes available that are fire rated for 30 - 60 minutes. Perhaps you could inspect one of these for ideas on insulation /thermal mass. I think that they utilise some sort of cheap ceramic like concrete. Although 200 degrees isn't that much. I would have thought that some form of fire ... | 8016 | Suggestions on how to keep electronics cool in high ambient temperature location? |
2016-03-17T18:03:53.943 | <p>I want to know the heat conduction coefficient of a cup in order to investigate why tea cools at different rates in different containers. I know the cup is mostly plastic and paper. How do I determine the heat conduction? Do I use a known value?</p>
| |thermodynamics|heat-transfer|thermal-conduction| | <p>If you are interested in knowing why your tea is cooling in different times, you already answered the question yourself. It is due to the different thermal conductivities of the different items you use it to store.</p>
<p>$\dot{Q} = A U \Delta T \tag{1}$</p>
<p>is the heat flux you want to know. This gives you a r... | 8024 | How can I determine the thermal conductivity of an open container? |
2016-03-18T06:54:59.630 | <p>I've seen two methods to describe porosity of porous media (specifically metal foams):</p>
<ol>
<li>Porosity $\epsilon$ which is a ratio between volume of voids and total volume of the medium.</li>
<li>PPI (Pores Per Inch) which is the number of pores in one linear inch.</li>
</ol>
<p>Unfortunately while reading s... | |mechanical-engineering|heat-transfer|porous-medium| | <p>The answer is system specific. That is, unless you know something else about the structure of your porous material, there is no clear relation between pore density and pore size. A simplified 2D example may look like this (where the circles are pores):</p>
<p><a href="https://i.stack.imgur.com/IGpUB.png" rel="nofol... | 8035 | Is there a relation between porosity and PPI density in porous media? |
2016-03-18T16:29:27.933 | <p>Consider a concrete column is under compression from top loading and also carries some shear stresses.</p>
<p>If take a plane 2d element in the column with these stresses and rotate it to the point it gives out the it maximum normal stress then rotate it to give out maximum shear stress which both values should be ... | |mechanical-engineering|civil-engineering|structural-engineering| | <p>The short answer is because it is too complicated/impossible to do so.</p>
<p>Here is a diagram of the principal stress trajectories for an <em>uncracked</em> concrete beam under both flexure and compression:</p>
<p><a href="https://i.stack.imgur.com/8g7N8.gif" rel="noreferrer"><img src="https://i.stack.imgur.com/... | 8043 | Why don't we use principal maximum stresses when designing a structural element? |
2016-03-18T17:35:16.133 | <p><a href="https://i.stack.imgur.com/aj7XI.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/aj7XI.jpg" alt="Increase yield strength"></a></p>
<p>I know that with strain-hardening you increase the yield and tensile strength. So if you unload at point D, then you also have cold worked it a bit right?
... | |materials|metallurgy| | <p><strong>Summary: If you are loading and unloading the same sample, the stress-strain curve will not change and the tensile strength will be the same, because stress and strain are calculated from the initial geometry. If you are comparing two otherwise-identical samples with different levels of cold work or strain h... | 8045 | Does unloading beyond yield point also affect tensile strength? |
2016-03-18T20:33:18.630 | <p>Using DePriester Chart and Given one of mole fractions ($z$), pressure and temperature we can acquire K-values for that properties and bubble and dew properties.</p>
<p>Now there are sometimes that we get some K's and using the summation of $y/k$ we get some quantities that are not 1, like 0.9 or 1.2. My question i... | |thermodynamics| | <p>You can represent K as $K_i = \frac{p_i^{sat}}{p}$ for an ideal mixture using Raoult's law. </p>
<p>This equation directly yields the correspondance of $K$ and $p$. If the pressure is below the dew point pressure $K_i$ will be larger. Hence $\frac{z_i}{K_i}$ will be smaller and subsequently the sum over it.</p>
<p... | 8047 | Physical meaning of some earned values using DePriester Chart |
2016-03-18T21:38:23.820 | <p>I have a situation where a 5mm steel rod needs to be in contact and rolls over segments of a 80mm steel pipe's inner face. Would it be a good idea to loosely slip a Teflon bushing over the rod and use it as a roller? I haven't seen loose fitted bushings, so I'm not sure if it'd be right to let a bushing rotate like ... | |mechanical-engineering|bearings| | <p>This is fine in principal, there are a few applications where a similar arrangement is used, in fact it is common for nylon wheeled castors to just have a plain bore. </p>
<p>In this situation the bushing will tend to travel along the rod as it rotates unless it is constrained so you will need something to locate i... | 8048 | Using a Teflon bushing as a roller |
2016-03-18T22:52:11.110 | <p>I'm curious about whether a typical liquid CPU cooler (like, e.g., this <a href="http://rads.stackoverflow.com/amzn/click/B00A0HZMGA" rel="nofollow">Corsair H60</a>) would be able to effectively cool a square sheet of aluminum with 15" sides and a thickness of 1/8".</p>
<p>I'm not even sure how to properly formulat... | |mechanical-engineering|cooling| | <p>Your best bet may be to make a hole in the aluminium sheet and mount the fan to either blow or suck the air from between the laptop base and the aluminium sheet ie using the 1/8" gap...</p>
| 8049 | How effectively would a typical liquid CPU cooler cool a 15"x15"x1/8" sheet of aluminum? |
2016-03-19T08:23:35.063 | <p>I found this strange looking bit in a bit set of uncommon bits, including Security Torx, hexalobular, tri-wing, spanner head, 12-point flange, Torq-set and others. It's the only one that I could not identify, what is it for? </p>
<p><a href="https://i.stack.imgur.com/6A1Be.jpg" rel="nofollow noreferrer"><img src="... | |mechanical-engineering|fasteners| | <p>There is one sold on Amazon.com, an "Eazypower 80935 1/4 inch Y-Shape Cup Hook Installer and Remover". <a href="https://rads.stackoverflow.com/amzn/click/com/B000PSABL0" rel="nofollow noreferrer" rel="nofollow noreferrer">https://www.amazon.com/Eazypower-80935-4inch-Installer-Remover/dp/B000PSABL0</a></p>
... | 8054 | What is this Y-shaped screwdriver bit, and what is its purpose? |
2016-03-19T15:52:00.510 | <p>This question is so fundamentally basic that I am almost embarrassed to ask but it came up at work the other day and and nearly no one in the office could give me a good answer. I was calculating the shear stress in a member using the equation, $\frac{Tr}{J_T}$ and noticed, that for a shaft with a circular cross sec... | |mechanical-engineering|structural-engineering|applied-mechanics|stresses| | <p>This is almost a coincidence, and it is only true for solid or hollow circular cross sections. Of course shafts carrying torsion often <em>are</em> circular, for reasons that are independent of the question! </p>
<p>The torsion of a circular shaft is physically simple because of the symmetry of the circular shape. ... | 8064 | What is the difference between the Polar Moment of Inertia, $ I_P $ and the torsional constant, $ J_T $ of a cross section? |
2016-03-20T04:18:43.430 | <p>I'm trying to use a 1500 RPM-rated electric motor to accelerate a (light, 25kg) shaft up to 50 000 RPM. At these speeds I figure using a belt system or roller chains is out of the question due to wear and friction; are these kinds of speeds possible to achieve reliably with a mechanical transmission or do I need to ... | |gears|energy| | <p>It sounds like you need something like a <a href="http://www.cutawaycreations.com/cutaways.php?project=pratt-whitney-pt6-turboprop-engine#/IMAGES/pratt-whitney-pt6-turboprop-engine/images/image4.jpg" rel="nofollow noreferrer">turboprop transmission</a> operating in reverse. These are generally planetary gearboxes fo... | 8074 | Getting high RPM out of a low RPM motor |
2016-03-20T16:18:43.787 | <p>I have an outer pipe and an inner pipe a lot smaller than the inside of the the outer pipe, and the head of the (mini) turbine will be connected to a metal rod. There will be wires connected to the head and it will be turning to the wind. How should I set up the wires?</p>
| |design| | <p>A <a href="https://en.wikipedia.org/wiki/Slip_ring" rel="nofollow">slip ring</a> connector is the usual way to solve this problem. The electrical contact is made by fixed brushes which make sliding contact with a rotating ring. </p>
<p>The key point is to ensure that you maintain a good and consistent electrical co... | 8080 | How to make a wire turn with a turbine head |
2016-03-21T04:43:23.813 | <p>First a little background, I've been working in Michigan as an engineer since getting my BSME in 1998 (I graduated with my MSME in 2010). I've worked for a number of companies in a variety of industries as an engineer, but never under the direct supervision of a licensed PE since all of the work I've done has been c... | |licensure| | <blockquote>
<p>How can I verify my engineering work experience without having worked under a PE?</p>
</blockquote>
<p>Many states offer the ability to substitute sufficient / substantial work experience for directly supervised work experience. The key difference here is that the obligation is upon the applicant to de... | 8090 | How can I verify my engineering work experience without having worked under a PE? |
2016-03-21T17:47:11.380 | <p>I have 8" thick reinforced concrete walls and I would like to anchor my horizontal corner reinforcement with only 1 hook (I have only 1 layer of reinforcement in both walls). The problem is CSA A23.3 (same for ACI if I'm not mistaken) restricts minimum hook length to 6" or $8d_b$ = 120mm = 5" in my case. </p>
<p>If... | |reinforced-concrete| | <p>I'd agree, you cannot fit a <em>horizontally oriented</em> 5" 90° bar bend in an 8" thick wall if you want your rebar curtain to be located at the center-line of the wall. However, there is no reason that the bent bars will not fit if you orient the bend vertically. The bars can be placed such that the 5" 90° bar be... | 8098 | Basic Hook development length using CSA A23.3 provisions |
2016-03-22T11:45:11.853 | <p>How can the microstructure of steel after welding be determined in modern computer software?</p>
<p>I am aware that there are 'classic' methods of predicting microstructures like Schaeffler, DeLong or WRC constitutional diagrams. What I am wondering about is: which algorithms are used in programs based on finite e... | |metallurgy|finite-element-method|structural-analysis|software|welds| | <p><strong>Summary:</strong></p>
<p><strong>1) The answer to this question is difficult. You would need to know how austenite and ferrite behave in relation to what you are doing to them. You would also need to know their compositions, temperature field, etc. The results here could vary significantly depending on the ... | 8111 | Determining the microstructure of steel after welding in modern computer software |
2016-03-22T15:36:35.213 | <p>I'm constructing 2.2 meters span, 1 m wide shelf. Want to make it cheap but thin.
I'm planning to use 18mm thick OSB board and reinforce it with a layer of stronger material stuck to it's bottom.</p>
<p>My first idea for reinforcement is 2 strips of 60*4 mm steel.
I'm not very familiar with the subject. I found OSB... | |materials|structural-analysis|composite| | <p>Hi to the next person to read this,</p>
<p>The preceding appears to be all correct, however, it appears to be for a solid composite beam. If you are using a USB board as a core, you must rather do composite beam calculations.</p>
<p>I landed on this post because I wanted to refresh my memory to calculate composite... | 8118 | How do I calculate the structural properties of a fiberglass laminated wood panel? |
2016-03-22T16:09:16.050 | <p>I have modeled a beam as fixed-fixed. The reaction forces are -1494 lb.ft and 761 lb (vertical). There is no horizontal reaction.</p>
<p><a href="https://i.stack.imgur.com/drvLH.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/drvLH.jpg" alt="enter image description here"></a></p>
<p>Now I know t... | |structural-engineering|structures|structural-analysis| | <blockquote>
<p>Should I invert the directions of the reactions or should I preserve the same directions?</p>
</blockquote>
<p>As long as you keep your directions consistent while solving for the weld forces, it won't matter whether you have them positive or negative. Referring to my answer to your <a href="https:/... | 8119 | How to transfer reaction forces of beam to a weld? |
2016-03-22T20:38:47.533 | <p>I have a vehicle with 4 wheels. Say I replace the wheels with large helical gears (pinions). If I set the vehicle on linear helical racks, it should be able to travel in one dimension. Say I replace the racks with a similarly toothed ground surface, could the vehicle travel in 2 dimensions (without rotating the body... | |mechanical-engineering|gears| | <p>Is this theoretical. If so I will bow out, but if not, Airtrax Sidewinder Forklift already does this. See the video. <a href="https://www.youtube.com/watch?v=vAiwLRGsNrE" rel="nofollow">https://www.youtube.com/watch?v=vAiwLRGsNrE</a></p>
<p>techtooler</p>
| 8127 | Multi-Directional Rack and Pinion Drive - Vehicle Motion Using Helical Wheels |
2016-03-22T21:56:13.437 | <p>I am trying to solve a fairly simple question but I'm kind of stuck on the technicalities:</p>
<blockquote>
<p>Imagine that water is evaporating into initially dry air in the closed
vessel shown schematically in Fig. 8.1-1(a). The vessel is isothermal
at 25 °C, so the water’s vapor pressure is 3.2 kPa. This v... | |thermodynamics|pressure|chemical-engineering|process-engineering|vapor-pressure| | <p>$\frac{1}{22.4}\frac{\mathrm{mol}}{\mathrm{L}}$ is only valid for standard conditions. Use the ideal gas law to calculate the concentration for your conditions.</p>
<p>$s \equiv$ standard conditions</p>
<p>$2 \equiv$ your conditions</p>
<p>$p_s V_s = n_s R T_s$</p>
<p>$\frac{p_s V_s}{n_s T_s} = R = const = \frac... | 8132 | How do temperature and pressure influence the rate of evaporation of water in a closed vessel? |
2016-03-22T22:08:47.683 | <p>With linear bearings, could they be used to join one rod with another to form a cross-junction and rotate with around a 0.3N-mm torque? Suppose the rods are fairly thin, eg, 5mm in diameter. That is, could linear bearings bear a radial load? Would the bearings deform? </p>
<p><strong>UPDATE</strong> Here's a diagra... | |mechanical-engineering|bearings| | <p>The bearing should have figures on the moment loads it can take. Failing that, use two bearings and allow them enough movement so effectively each is just supporting a purely radial load.</p>
| 8133 | Could linear bearings bear axial load? |
2016-03-22T23:05:55.630 | <p>In the problem statement below, the question states to find the maximum load $\vec{P}$ that the truss can support. My method of approach was:</p>
<ol>
<li>Draw a FBD for the entire structure.</li>
<li>Generally I would identify all external forces, however for this problem I felt it was unnecessary because I felt t... | |structures|statics| | <p>The reason is that <strong>you assumed that the elements around node <span class="math-container">$\text{D}$</span> will be the first to fail</strong>. That is not the case. Indeed, it is the elements under compression (<span class="math-container">$\text{AB}$</span> and <span class="math-container">$\text{BC}$</spa... | 8134 | Where did I go wrong conceptually when attempting to calculate the maximum force on a truss at a given joint? |
2016-03-23T07:54:50.540 | <p>I got a position error measured by a linear encoder like in the picture below.</p>
<p><a href="https://i.stack.imgur.com/wcExZ.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/wcExZ.jpg" alt="Position error graph"></a></p>
<p>Could anyone explain some possible reasons for this kind of shape to oc... | |control-engineering|control-theory|pid-control| | <p>Your system is not reaching the target value. Possibly this is due to static friction in the actuator mechanism, which causes it not to move until the force exceeds some threshold.</p>
<p>Assuming you are using a PID controller, the residual error will cause the I error term to accumulate slowly. This will cause th... | 8139 | Square shaped position error |
2016-03-23T18:48:08.183 | <p>Can a vertical round tube safely support a cantilevered arm mounted near the top of the tube?</p>
<p>ROUND VERTICAL TUBE:</p>
<ul>
<li>6061 Aluminum</li>
<li>2 inch Outside diameter</li>
<li>0.25 inch wall thickness </li>
<li>3 feet height</li>
</ul>
<p>ROUND VERTICAL TUBE / CANTILEVERED ARM INTERFACE:</p>
<ul>
... | |structural-engineering|beam|aluminum|mechanical-failure| | <p>I'm going to run with this assuming the arm looks like the following diagram (I'm ignoring the 11.4 pounds of the bar for now to make the concepts easier to explain - that can be added later by assuming all 11.4 pounds run through the center of the bar.):</p>
<p><a href="https://i.stack.imgur.com/xLAkg.png" rel="no... | 8144 | Strength of a Vertical Round Aluminum Tube with load cantilevered off it? |
2016-03-24T07:50:00.190 | <p>What are the criteria for choosing repeating variables in Buckingham's Pi theorem in dimensional analysis? In many problems, it's solved by taking D,V,H (Diameter, Velocity, Height) as repeating variables. Why do they take the above variables as repeating variables, when the problem also contains the following varia... | |fluid-mechanics| | <p>The repeating variables are any set of variables which, by themselves, cannot form a dimensionless group. Diameter, velocity, and height cannot be arranged in any way such that their dimensions would cancel, so they form a set of repeating variables.</p>
<p>For example, let's assume that we suspect that a fluid we... | 8146 | Choosing of repeating variables in Buckingham's Pi theorem |
2016-03-24T12:54:47.907 | <p>I think there is an error in this questions solution and I want someone to check:</p>
<blockquote>
<p>Example 8.1-4:Mass transfer from an oxygen bubble A bubble of oxygen originally 0.1 cm
in diameter is injected into excess stirred water, as shown schematically in Fig. 8.1-1(d).
After 7 min, the bubble is 0.... | |thermodynamics|chemical-engineering|process-engineering|vapor-pressure| | <p>Your approach is wrong because the left hand side represents the derivative of the composition of two time dependent functions. You completely ignored that fact and started cancelling terms. I try to give a simpler example:</p>
<p>$\frac{d 4x^3}{dx} = kx^2
\Leftrightarrow 12x^2=kx^2
\Leftrightarrow 12=k$</p>
<p>... | 8148 | Mass Transfer from an Oxygen Bubble |
2016-03-24T13:53:53.253 | <blockquote>
<p>A steam power plant employs two adiabatic turbines in series. Steam
enters the first turbine at 650 C and 7000 kPa and discharges from the
second turbine at 20 kPa. The system is designed for equal power
outputs from the two turbines, based on a turbine efficienct of 78%
for each turbine. Dete... | |mechanical-engineering|thermodynamics| | <p>The answer in the solution manual simply assumes a set of four values of intermediate pressure (that somehow magically the actual intermediate pressure lies within!):
$$P_2 = \begin{pmatrix}725\\750\\775\\800\end{pmatrix} \text{kPa}$$</p>
<p>And for each pressure in the set, the one that results in an equal power ... | 8149 | Determining intermediate pressure between two turbines |
2016-03-26T17:10:25.213 | <p>Suppose the fit for a rod and a hole in a gear is supposed to be free running and the fit is 3mm H9/d9. For the specification of the hole for the manufacturing of the gear, is "3mm H9" already adequate since d9 only refers to the shaft tolerance which may not be pertinent to the manufacturing of the gear? Sometimes ... | |design|tolerance| | <p>Your clearance range is the minimum hole diameter minus max shaft diameter to max hole diameter minus minimum shaft diameter. </p>
<p>Answer: Yes. Your math seems correct. </p>
<p>This is a useful tool: <a href="http://www.amesweb.info/FitTolerance/FitTolerance.aspx" rel="nofollow">http://www.amesweb.info/FitToler... | 8173 | Specification of hole design tolerance |
2016-03-27T17:15:19.463 | <p>I am working on a project and I have some questions about setting up a passive heating system (thermosiphon) with a heat exchanger.
I will have a main boiler with a coil of copper tubing inside. This coil will be my heat exchanger. It will then continue to pass through an object which is the target of the passive he... | |heat-transfer|heat-exchanger| | <p>In the broad sense your question is asked I'd say yes, this will work either way. </p>
<p>Two things to consider that could be an indicator for you to go with #1 or #2:</p>
<p>Depending on the actual design, the isolation of the copper coil in between the heater and the item to be heated you might try and keep the... | 8179 | Thermosiphon System |
2016-03-28T12:33:59.117 | <p>Consider a fixed steam engine, such as in a Lancashire cotton mill or pumping in a Cornish mine. Then consider a fixed diesel engine such as a large generator or ship's engine. </p>
<p>Why does the steam engine have one or two large cylinders with long stokes, but the diesel has many cylinders with relatively shor... | |steam|diesel| | <p>The difference of few large cylinders or many small cylinders has less to do with running on steam or diesel, but more with the era in which the engines were built. Early engines (both steam and diesel) had few, large cylinders, probably because that is how engineers tried to make more powerful engines: make everyth... | 8193 | Why do steam and diesel engines have differing cylinder configurations? |
2016-03-28T13:30:42.413 | <p>I'm using AutoCAD 2015, and I run into this all the time. I'm given a group of DWG drawings, and I want to plot them into one monochrome PDF, but they do not have monochrome.ctb selected as the plot style. Is there any way in Batch Plot to publish to PDF using monochrome without editing the individual DWG files? ... | |autocad| | <p>After playing around with it for a while, this seems to work:</p>
<ol>
<li>In the Batch Plot dialog, add all the drawings/sheets you want to include:</li>
</ol>
<p><a href="https://i.stack.imgur.com/y57FU.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/y57FU.png" alt="Batch Plot dialog"></a></p>... | 8195 | How do I batch plot drawings in monochrome without editing DWG? |
2016-03-28T13:30:59.527 | <p>I am currently working on a project (or actually returning to a project) and need to have a heat exchanger boiler made. The hx boiler will be relatively small, a 10" long cylinder around 4" in diameter. One end can be capped, but the other should have a flange so I can work inside the unit. Inside, I will have a coi... | |materials|boilers| | <p>In addition to the excellent answers on pressure vessels already posed a steam boiler has the additional complication that, as you are dealing with a change in phase under pressure there is a particular hazard with steam that you can get very rapid pressure spikes under certain conditions so the safety regulations f... | 8196 | Questions about making stainless steel boiler |
2016-03-29T06:12:02.857 | <p>I am designing a wind turbine to generate 1300 W.</p>
<p>I modeled the output voltage of an AC generator using the following specifics:</p>
<ul>
<li>Number coil turns = 300.</li>
<li>Copper wire gauge = 1.02 mm.</li>
<li>Knowing the density of copper, I calculated the weight of the coil to be 4.39 kg.</li>
<li>Mag... | |mechanical-engineering|turbines|wind-power| | <p>I don't think you really designed a 1300 W wind turbine. You <em>assumed</em> your generator would be able to produce the necessary current but to be able to produce 1300 W you have to build a wind turbine big enough, given its efficiency. </p>
<p>At $C_p=0.3$ and $v=10\ \mathrm{m/s}$, you simply need an area of:
$... | 8207 | Why does my model of a wind turbine show high RPM with low power output? |
2016-03-30T12:06:20.637 | <p>I am making a testing facility for pumps. This facility has to be able to handle 500 m<sup>3</sup>/h with at little turbulence as possible. The basin itself is 5 meters long, 2,5 meters wide and 2 meters tall. The water level in the basin is kept at 1,9 meters.</p>
<p>The basin is designed in two sections: the firs... | |water-resources|turbulence|flow-control| | <p>Assuming you are wanting to minimize turbulence in the region of the pump, you would probably need to use flow straighteners somewhere upstream of the pump. You would have to study the optimal diameter and length of the straighteners. MIT simply used <a href="https://en.wikipedia.org/wiki/Flow_straightener#A_low-c... | 8221 | Best way to get rid of turbulent flows? |
2016-03-30T13:44:17.563 | <p>I have the situation from the following drawing:</p>
<p><a href="https://i.stack.imgur.com/gHSf2.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/gHSf2.png" alt="enter image description here"></a></p>
<p>It represents a model for measuring the torque of a generator.
There is an arm connected to ... | |mechanical-engineering|torque| | <p>You need to apply <a href="https://en.wikipedia.org/wiki/Newton%27s_laws_of_motion" rel="nofollow">Newton's second law</a> that states:</p>
<blockquote>
<p><strong>Second law</strong>: The vector sum of the forces F on an object is equal to
the mass m of that object multiplied by the acceleration vector a of
... | 8222 | motion equation of rotor and stator |
2016-03-30T16:35:47.030 | <p>We have obtained an old mercury-vapor <a href="https://en.wikipedia.org/wiki/Diffusion_pump">diffusion pump</a> for high vacuum. However, we do not want to operate it with mercury in our lab due to health concerns (which is presumably the reason it was scrapped by the original owner). </p>
<p>Instead, we plan to fi... | |pumps|safety|vacuum|vacuum-pumps| | <p>I did some internet searching and did not find anyone that had done a direct swap out. Granted, probably the majority of these replacements occurred before the existence of the internet ;-). As I am sure you are already aware (but to be thorough), modern diffusion pump designs do use <a href="http://www.vpcinc.ca/Pr... | 8224 | Replace mercury with silicone oil in diffusion pump |
2016-03-31T07:55:06.040 | <p><strong>Important note</strong>: I am writing a structural FEM software from scratch, so I won't able to use existing commercial FEM package. I would need to know how all the important quantities are calculated from the first principles.</p>
<p>I would need to determine the <strong>accidental torsional effect</stro... | |structural-engineering|structural-analysis|seismic| | <p>There is a paper on how to account for <a href="https://wiki.csiamerica.com/download/attachments/9536133/Fahjan%2C%20Accidental%20eccentricity.pdf?version=1&modificationDate=1338950028768&api=v2" rel="nofollow">accidental eccentricity in dynamic modal analysis of buildings</a>:</p>
<blockquote>
<p>The met... | 8234 | Accidental Torsion and Equivalent Static Load for an irregular structure |
2016-04-01T00:56:08.217 | <p>I have a 10 mm diameter rod of 99.5% pure tungsten that I want to drill a 0.1 mm hole in using my Grizzly G0768 lathe. The hole only needs to be between 0.1 mm and 1 mm deep and is for a 3D printer hot nozzle. I don't know if this will break the bit yet, but I will try it when the drill chuck comes in the mail. If t... | |machining|drilling|lathe| | <p>Call local machine shops, and ask them, if they have a sonic mill. It uses special bits with coolant and ocelats to make the cuts. It can cut accurately through 1/2 inch in about 45 minutes. It shouldn't be too expensive, basically it vibrates the the material.</p>
| 8246 | How can I cheaply drill a 0.1 mm hole in a small piece of tungsten? |
2016-04-01T09:14:06.017 | <p>I am working on a project to bring light into a bunker. The bunker is 3-4 meters below the ground.</p>
<p>I am looking into bringing natural light into the space, instead of using electricity. The space is difficult to access and light must therefore be transported by flexible cable for about 20 meters from the sur... | |fiber-optics| | <p>You can send your light via internal total reflection. You need to research a flexible material that's hollow inside (to fill with liquid) and the material's index of refraction match the formula for total internal reflection.</p>
| 8250 | Create a DIY light tube |
2016-04-02T18:34:07.813 | <p>Here is some background to the problem (in a stirred tank):</p>
<p>"With yield stress non-Newtonian (viscoplastic) fluids, it is possible to generate an agitated volume around the impeller, defined as a cavern, surrounded by a stagnant region where the shear stress is insufficient to overcome the apparent yield str... | |mechanical-engineering|fluid-mechanics|chemical-engineering|process-engineering| | <p>For your curved surfaces, the lever arm for the calculation of torque is a constant $D/2$. That is not true in the case of the cavern's faces. In that case the lever arm is a variable ($r$). To calculate the torque you would need to integrate the stress over the area times the lever arm. It should look something lik... | 8267 | Working Out Shaft Torque in a Stirred Tank with a Cylindrical Cavern Formation (using a non Newtonian fluid) |
2016-04-03T17:43:38.397 | <p>How does union joint with two male threaded ends work? Does one male end rotate 360 degrees around it axis? How is the inside of the union constructed? Can I connect two pipes with female threads using a union joint and assemble/disassemble it without too much pain? Specifically, I am looking at a stainless steel un... | |piping|pipelines|joining| | <p>Typically, most threads on pipes (in the USA at least) are male <a href="https://en.wikipedia.org/wiki/National_pipe_thread" rel="nofollow noreferrer">NPT</a> and all the couplings or fittings are female NPT.</p>
<p><a href="https://i.stack.imgur.com/hZoVe.jpg" rel="nofollow noreferrer"><img src="https://i.stack.im... | 8272 | How does a union joint with two male threads work? |
2016-04-04T22:05:14.957 | <p>I'm trying to understand the derivation of the turbulent kinetic energy equation, as described in this link: <a href="http://www.diva-portal.org/smash/get/diva2:379743/FULLTEXT01.pdf" rel="nofollow">Evaluation of RANS turbulence models for flow problems with significant impact of boundary layers</a>.</p>
<p>I'm abl... | |fluid-mechanics|turbulence| | <p>The two terms are equal due to the product rule and continuity equation. The use of the continuity equation might not be obvious, however.</p>
<p>In their notation, the Reynolds decomposition is $u_i = \overline{u}_i + u^\prime_i$. Taking the continuity equation and averaging leads to:</p>
<p>$$\frac{\partial \ove... | 8285 | Deriving the turbulent kinetic energy equation |
2016-04-05T08:42:50.100 | <p>In Autocad 2015 for Mac, I have created a cylinder with a torus wrapped around it. The torus is 2 mm thick, with 1 mm embedded inside the cylinder and 1 mm outside. I want to subtract the torus from the cylinder, so I will be left with a semicircular groove around the cylinder. I have already done this once, but I h... | |design|autocad| | <p>To be honest this came entirely from chance and I still have NO idea what caused the problem. The answer by @ChrisJohns will probably be a more likely cause of the issue, as for me I'm simply going to put it down to a bug, because this is how I fixed it:</p>
<p>Turn it off and on again. Make your torus/etc and put ... | 8292 | How to subtract a region where two solids intersect? |
2016-04-05T12:12:48.140 | <p>Can anyone tell me how to go about this problem? </p>
<p>There is a square shaped laminate (polyethylene fiber and epoxy resin composite) that is constrained on one side. A gun is fired and the bullet hits the laminate. What kind of stresses result in the laminate? How should I go about their calculation? When I sa... | |composite| | <p>An additional complication is the behaviour of the bullet itself on impact, which is not only difficult to model but can vary a lot according to the construction of the bullet, it's geometry and mass, and the angle and energy of impact. </p>
<p>For example a low-velocity, unjacketed lead bullet might squash against... | 8293 | Impact load of a bullet on a laminate |
2016-04-05T18:25:28.110 | <p>How do people design height gaining based on nested poles ?</p>
<p>Consider this picture (I made them) :
<a href="https://i.stack.imgur.com/JQUC2.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/JQUC2.png" alt="enter image description here"></a></p>
<p>If I want to achieve height based on these 3... | |mechanical-engineering| | <p><em>Telescoping</em> is the English term for this and a search for <a href="https://www.google.com/search?q=telescoping%20mechanisms&source=lnms&tbm=isch&sa=X&gws_rd=cr#q=telescoping%20mechanisms&tbm=isch&pws=0&gws_rd=cr" rel="nofollow">telescoping mechanisms</a> will give lots of info on... | 8302 | Principal on gaining more height based on nested poles? |
2016-04-06T05:07:05.793 | <p>Is there a big difference between salt water and normal tap water in terms of thermal properties (heat capacity, for example)? </p>
<p>If so, can anyone give me a table of thermal and thermodynamic properties of salt water? </p>
| |fluid-mechanics|thermodynamics|heat-transfer| | <p>MIT provide a table of water properties at a range of salinity and temperature values: <a href="http://web.mit.edu/seawater/" rel="nofollow">http://web.mit.edu/seawater/</a></p>
<p>There is also excel/matlab correlations as well.</p>
| 8311 | Thermal properties of salt water |
2016-04-06T10:41:47.753 | <p>Suppose there is a cubic material with an internal heat source ($\Delta q / \Delta t =$ Constant), and is immersed in a sufficiently large amount of water. Now I would like to use finite difference method to simulate the steady state temperature distribution.</p>
<p>I think a natural convection boundary condition w... | |thermodynamics|heat-transfer|chemical-engineering|thermal-conduction|convection| | <p>Your approach is absolutely acceptable so long as you realize its limits. The reason you are not seeing a method like this in a text book is because it is a mix of numerical methods and conventional empirical methods that is not particularly common. </p>
<p>The reason it is not common to approach a problem this way... | 8315 | Convective heat transfer coefficient in finite difference method boundary conditions |
2016-04-06T13:07:24.357 | <p>I have about 12 bottles of water. If I want to minimize the energy consumption of my refrigerator, should I put these bottles in the fridge or leave them out?</p>
| |thermodynamics|energy-efficiency|refrigeration| | <p>Many factors play in this scenario:<br>
1- the shape of the bottles and their material thermal insulation index.<br>
2-how you place the bottles on the shelves: do they promote air current or impede it.<br>
3- the frequency of opening the fridge door.<br>
As many have mentioned there is an initial load when room tem... | 8316 | Difference in energy consumption between empty fridge and fridge filled with bottles of water |
2016-04-06T23:33:31.797 | <p>I'm trying to calculate the clamping force resulting from torquing a nut and bolt to a particular level.</p>
<p>I have found this formula in various forms in a lot of places.</p>
<p>$$T = KDP$$</p>
<ul>
<li>$T$ = Torque (in-lb) </li>
<li>$K$ = Constant to account for friction (0.15 - 0.2 for these units)</li>
<li... | |mechanical-engineering|applied-mechanics|torque| | <p>The correct answer is 100 N-m (force) not 100 KG (mass).</p>
<p>The error was in failing to keep all the units consistent throughout.</p>
<p>Off the top of my head 1 N force is about the force exerted by gravity for one "standard apple." That equates to about 0.25 pounds.</p>
| 8324 | Calculation of Clamping force from bolt torque |
2016-04-07T12:20:47.343 | <p>I am measuring the rotational speed of a shaft using a disk with 60 cuts and an optical fork. The signal from the optical fork is sent to a frequency to voltage converter and after that to a data acquisition system.</p>
<p>What is the working principle of this frequency to voltage converter? Is it counting pulses?<... | |measurements| | <p>There are a number of ways.</p>
<p>As Russell described, one way is to make a fixed size pulse each period, then low pass filter the result.</p>
<p>Another is to make a frequency-dependent filter. Feed in a signal with fixed amplitude and varying frequency. The filter varies the amplitude as a function of freque... | 8333 | How does a frequency to voltage converter work? |
2016-04-08T17:48:51.833 | <p>I'm finding myself using control charts and I'm unclear on a very basic point. I've read page after page of texts, but they all focus on how to make the initial chart rather than walking you through how to update it.</p>
<p>To make things easier, I'll set the situation:
I'm making an Individual Control Chart. Every... | |statistics|quality-engineering| | <p>Out of desperation, I got in contact with some very nice statisticians at NIST. They walked me through the answer to my question, which boils down to: control charts are an empirically derived chart with strong statistical backing. However, because of this by its very nature, there is no one right answer. It depends... | 8349 | How do I update an individual control chart? |
2016-04-08T21:15:48.993 | <p>Does anyone know how to determine the moment of inertia of the filled circular sector shown below?</p>
<p><a href="https://i.stack.imgur.com/sqZ9I.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/sqZ9I.jpg" alt="enter image description here"></a></p>
<p>Apparently I have to use $dA=r\ d\theta\ dr... | |statics|mathematics|moments| | <p>Consider an infinitesimal element of area $r d\theta dr$ which is at a distance $r \sin (\theta)$ from the $x$ axis. </p>
<p><a href="https://i.stack.imgur.com/d9NGX.jpg"><img src="https://i.stack.imgur.com/d9NGX.jpg" alt="enter image description here"></a></p>
<p>Its moment of inertia is $r d\theta dr (r \sin (... | 8355 | Determine the moment of inertia of a filled circular sector |
2016-04-09T18:30:49.700 | <p>What is the physical meaning of using negative frequencies while making Nyquist plots?</p>
<p>I know that we do a mapping from $s-$ plane to $f(s)$ plane, and we move along a contour. What I don't get is that Is the Nyquist plot purely a mathematical construct? Is there no relation between the frequency on plot and... | |control-theory| | <p>The negative frequencies are not physical, neither do they convey any new information. The value at the negative frequency is the complex conjugate, and hence the plot is symmetric about the real axis. If you know one you can get the other as a conjugate.</p>
<p>The value in plotting the negative values (or going a... | 8363 | Why are negative frequencies included in the nyquist plot? |
2016-04-10T07:54:08.047 | <p>I'm an engineering enthusiast but I don't yet have a formal education in engineering and I'm hoping you guys can tell me about the implications of using a metal road design in terms of durability and cost. </p>
<p>My (vague) idea is (for 2 lanes of road) a set of 3 rails laid down as a vertical layout for a length ... | |civil-engineering|highway-engineering|roadway| | <p>Asphalt, which is essentially crushed aggregate bound with bitumen has a lot of advantages for road building. </p>
<ul>
<li>It is porous and so can drain by allowing water to pass through it as well as running off the surface. </li>
<li>Because it is made up of particles of crushed masonry it has good friction char... | 8367 | What would be the implications of a metal highway design? |
2016-04-12T01:49:34.647 | <p>Why does the AISC handbook only list one figure for Section Modulus for shapes such as Angle(L) steel? Shouldn't there be two? The steel is asymmetric. Is the figure given just the Delta to the bottom or something; figuring a design only needs to be concerned with Tension?</p>
| |steel|geometry| | <p>To quote <a href="https://en.wikipedia.org/wiki/Section_modulus" rel="nofollow">Wikipedia</a>:</p>
<blockquote>
<p>The elastic section modulus is defined as $S = \dfrac{I}{y}$, where $I$ is the second moment of area (or moment of inertia) and $y$ is the distance from the neutral axis to any given fibre. <strong>I... | 8391 | AISC Section Modulus numbers |
2016-04-12T15:34:23.993 | <p>The two terms seem interchangeable and I can't find a strict definition for both, so what's the difference between them if there is any?</p>
| |mechanical-engineering|pumps|turbomachinery| | <p>A centrifugal pump consists of two main components</p>
<ol>
<li><p><strong>Electric motor</strong><br />
It is usually an induction motor. All electrical engineering courses would cover this in the lower year.<br />
An electric motor has two components</p>
<ul>
<li><strong>Stator</strong> - It is the stationary part... | 8398 | What's the difference between impeller and rotor in centrifugal pump? |
2016-04-13T11:58:42.207 | <p>I am trying to solve the problem:</p>
<blockquote>
<p>The critical resolved shear stress for iron is 27 MPa. Determine the
maximum possible yield strength for a single crystal of Fe pulled in
tension.</p>
</blockquote>
<p>I think that this is related to the equation $\sigma_{yield} = \dfrac{\tau_{crit}}{\cos... | |mechanical-engineering|materials| | <p><strong>The book should probably have said "minimum possible yield strength" or "maximum possible resolved shear stress." Note that the maximum yield strength of any real single crystal does not depend on one slip system and thus can not be infinite despite what <a href="https://en.wikipedia.org/wiki/Schmid's_La... | 8407 | Determine the maximum possible yield strength for a single crystal of Fe pulled in tension |
2016-04-13T12:32:50.223 | <p>I know that an hydraulic jump can occur only when the Froude number is higher than 1 (supercritical flow), and I am familiar with the Bélanger equation. However, I feel like I have a fundamental misunderstanding about hydraulic jumps: if a jump can occur when Froude number is larger then 1, what prevents the flow in... | |fluid-mechanics|hydraulics|open-channel-flow| | <p>First a hydraulic jump is where fluid will transition from supercritical (having a Froude Number greater than one, to subcritical (having a Froude Number less than one). When the Froude number is near one, the jump is very weak and somewhat gradual such that you might not even be able to tell it is "jumping".</p>
<... | 8408 | Where exactly will a hydraulic jump occur? |
2016-04-13T12:34:26.537 | <p>I have trasfer functions of a plant and a controller in laplace domain. I checked for the closed loop response by applying a step response. The system is found to be stable. </p>
<p>I checked the response of the system for the same step reference in discrete domain. I can see that the closed loop response of the di... | |control-engineering|transfer-function|matlab|feedback-loop| | <p>The plant and controller:
$$\text{sys}=\frac{4700 s^2+4393 s+3.245\times 10^8}{s^4+7.574 s^3+120200. s^2}$$</p>
<p>$$pid=0.287\, +0.008 s+\frac{0.5}{s}$$</p>
<p>The closed-loop system obtained as $\frac{pid*sys}{1+pid*sys}$:</p>
<p>$$csys=\frac{37.6 s^4+1384.04 s^3+2.59961\times 10^6 s^2+9.31337\times 10^7 s+1.62... | 8409 | Closed loop response of a discrete system |
2016-04-14T15:17:09.750 | <p>Given a nonlinear system, such as:</p>
<p>$$\begin{align}
x_1' &= x_2 \\
x_2' &= −x_1^3 + u \\
y &= x_2
\end{align}$$</p>
<p>How can I check the <strong>zero-state observability</strong> of the system?</p>
| |control-engineering|control-theory| | <p>I've found the answer.</p>
<p>To check if a system is <strong>zero state observable</strong>, put $u=0$ and check whether $x=0$ when $y=0$. If yes, it is <strong>zero-state observable</strong>. Otherwise not!</p>
<p>For the given system, by putting $u=0$ and $y=0$, we see that $x_2=0$, therefore $x'_2=0$ and thus ... | 8423 | How can I check whether a nonlinear system is zero-state observable? |
2016-04-15T06:20:07.400 | <p>I am trying to perform simple 2D CFD analysis on Fluent having 3 adjacent zones(inlet, porous and outlet).
<a href="https://i.stack.imgur.com/YawGb.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/YawGb.png" alt="Zones figure" /></a></p>
<p>The problem I have is whenever I select non-equilibrium th... | |cfd|porous-medium|fluent| | <p>I found the issue addressed in Fluent user guide:</p>
<blockquote>
<p>Parts are groups or collections of bodies. Parts can include multiple
bodies and are then referred to as multibody parts. <em><strong>If your
geometry contains multiple parts then each part will be meshed with
separate meshes with no connection be... | 8432 | How to force creating a conformal mesh interface between zones in Fluent? |
2016-04-15T16:09:16.783 | <p>As from the derivation we are able to see that the implicit density based solver (such as BTCS) is unconditionally stable for any courant number. So what is it, which limits the upper boundary of CFL while using it in practical applications?</p>
<p>I need this for simulations in ANSYS Fluent.
I have been told that ... | |cfd|ansys| | <p>Analytical stability results for backward-time, centered space (BTCS) discretizations only apply to the first order (linear) hyperbolic partial differential equation. The only reason why they are applicable to the navier stokes equation is because navier stokes tends to exhibit behaviors similar to this first order... | 8439 | What limits my Courant number in Implicit Density based Solver? |
2016-04-16T17:24:27.867 | <p>I am curious to know the difference between a lead compensator (lead filter) and a PD controller with a low pass filter. From the theory I can see that the transfer function of both these controllers are same. By choosing appropriate gains and placing zeros and poles at right frequencies, we can obtain same bodeplot... | |control-engineering|transfer-function|feedback-loop|pid-control| | <p>A lead filter implies that the zero has a lower frequency than the pole. While a PD controller with a low-pass-filter does not necessarily imply that order. Also a lead filter (usually) does not have the zero and pole to far apart from each other, meaning that the bode diagram does not get very close to the asymptot... | 8448 | Is lead filter same as PD combined with a low pass filter? |
2016-04-16T20:09:47.670 | <p>I was very surprised when i found out that Newton's solution to the problem of solid of minimal resistance was a body with somewhat strange nose cone - the end of the nose cone is a plane perpendicular to the body's axis. So my question is, was Newton's calculation confirmed and used somehow by space programs?</p>
| |fluid-mechanics| | <p><strong>TL;DR</strong></p>
<p>Newton got some things spectacularly right, and other things spectacularly wrong. In this case, he didn't remotely understand the <em>real</em> physics of the problem - and neither did anybody else until a few hundred years after his death. </p>
<p>You shouldn't believe everything in ... | 8450 | Was Isaac Newton's solution to the problem of solid of least resistance comfirmed in space programs? |
2016-04-18T03:04:12.720 | <p>I very much ruined 3 $10 diamond hole saws making this ceramic insulator out of a firebrick and Ryobi drill press. Drilling out the large core took 1-2 hours and a lot of arm strength.</p>
<p>Therefore, I will turn to custom ceramic shops or my own castable refractory molds. I am concerned that the custom ceramic ... | |metallurgy|casting|ceramics| | <p>There are a number of approaches to this, depending on exactly what you want to achieve. </p>
<p>There are <a href="http://www.castreekilns.co.uk/dense-castable-189-c.asp" rel="nofollow">dense castable refractories</a> which will operate up to 1800C. For small quantities the best source is likely to be a ceramic ki... | 8462 | What is the highest-temp castable refractory cement available? |
2016-04-18T17:02:57.040 | <p>I have some questions in the basics of machinery terminology </p>
<ol>
<li><p>Can a spring ever be a link? Most books (eg. Ham et al. 58, Shigley pg. 5) consider links to be rigid. However, I have come across articles using springs as links.</p></li>
<li><p>Are joints always the same thing as kinematic pairs, or do... | |mechanical-engineering|terminology|kinematics| | <p>@katipra I am adding this as another answer since it was too long for the comment section. But it's a reply to your aforementioned comment.</p>
<p>Good news. Based on the actual definitions of Merriam-Webster of machine vs. machinery:</p>
<p>"Machine: 1) an assemblage of parts that transmit forces, motion, and ene... | 8473 | Questions on machinery terminology |
2016-04-19T01:02:51.577 | <p>What kinds of sensors can be used to monitor the condition of a hard disk?</p>
<p>We want to be able to detect when a hard disk is not operating correctly.</p>
<p>Unexpected vibrations may be caused by spindle problems (probably low frequency), or by head crashing (high frequency).</p>
| |mechanical-engineering|electrical-engineering|motors|sensors| | <p>There are two types of sensors commonly used in hard disks to detect vibration and head crashing. They are:</p>
<ol>
<li><strong>Accelerometer</strong>: Accelerometers are used to detect sudden vibrations. </li>
<li><strong>Sudden Motion Sensors:</strong> These are mostly used in Apple Notebooks to detect a sudden ... | 8477 | What sensors should be used to analyze vibration of a hard disk? |
2016-04-19T18:56:22.023 | <p>In a tensile test the peak load was 69kN, but the point of failure load was 60kN. Why is it lower?</p>
| |mechanical-engineering|structural-engineering|civil-engineering|stresses| | <p>That is due to <a href="https://en.wikipedia.org/wiki/Necking_(engineering)">necking</a>.</p>
<p>When a bar is under tension, two opposing mechanisms take place:</p>
<ul>
<li>The bar loses cross-sectional area since it attempts to retain its volume while being stretched (see <a href="https://en.wikipedia.org/wiki/... | 8488 | Why is the point of failure load lower than the peak load? |
2016-04-19T19:44:19.940 | <p>I have a tube, at the bottom of the tube is burning wood and an air inlet. How can i increase the speed of the exhaust gas coming out of the tube? I thought about "bottle-necking" the exhaust pipe to make it go faster (Bernoulli's principle) but is there any other way?</p>
| |fluid-mechanics|thermodynamics|combustion| | <p>i am not sure about bottelnecking what does it means but the only natural way to increase the exhaust velocities is to place a <strong>NOZZLE</strong> at the outlet as it converts the pressure energy into kinetic energy(<strong>From Steady Flow Energy Equation)</strong> and to have more kinetic energy you should hav... | 8489 | How to increase the speed of exhaust gas? |
2016-04-20T15:02:14.247 | <p>I am analyzing an industrial ventilation system that at some point operates two industrial size blowers in parallel. They often show oscillating behaviour: one blower briefly draws more power / generates more flow, and the other performs less. Then the roles reverse. The only practical, known way to reduce the oscil... | |mechanical-engineering|fluid-mechanics|pumps| | <p>The reason is due to slight instability of the fans, and bad fan stability selection. To begin with, all backwards inclined fans have, to some extent, an unstable range. All fans are designed to operate at an RPM using an RPM chart. This includes the stable and unstable ranges of the fan:</p>
<p><a href="https:/... | 8505 | Why do parallel fans/blowers show an oscillatory behavior? |
2016-04-20T15:59:05.797 | <p>We want to monitor hard disks for present problems or pending failure.</p>
<p>Can the Fast Fourier Transform (FFT) of a given hard disk in question, then, be compared with a reference FFT for a perfectly working one, and then conclude hard disk may be faulty or about to fail if its FFT differs significantly from th... | |mechanical-engineering|electrical-engineering|motors|sensors| | <p>Im pretty confident in that you can see some changes in the fourier analysis if you have a sensitive enough sensor in the right place and the failure is mechanical. Similar methods are used to measure the health of bearings with success.</p>
<p>However, you do not know what you are looking for. Unless your a very s... | 8508 | Can Fast Fourier Transform be used to monitor for fault vibrations in a hard disk? |
2016-04-22T10:23:38.033 | <p>I'm trying to figure out what kind of pump I should use to boil water at low temperature. Here is my idea of the setup:</p>
<p><a href="https://i.stack.imgur.com/cQb6C.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/cQb6C.png" alt="enter image description here"></a></p>
<p>The dark blue water co... | |mechanical-engineering|fluid-mechanics|thermodynamics| | <p>You can use a water pump to evaporate water. But you shouldn't.</p>
<p>The evaporation chamber needs to be closed, except for the suction pipe. Otherwise when you lower pressure water (or air) will flow in, raising pressure again. So you can create small batches of vapor. </p>
<p>The water will evaporate where pre... | 8534 | Can I use a water-pump to lower pressure and boil water? |
2016-04-22T14:25:04.783 | <p><a href="https://i.stack.imgur.com/PTClt.png" rel="noreferrer"><img src="https://i.stack.imgur.com/PTClt.png" alt="enter image description here"></a></p>
<p>Hello, I've been asked to show that:
$$d\Gamma=\tau 2\pi r^2 dr$$</p>
<p>Where $\Gamma$ is the torque applied to the shaft and $\tau$ is the shear stress of t... | |mechanical-engineering|fluid-mechanics|applied-mechanics| | <p>Your Average MechEng's answer is fantastic and it is often how I explained the area of a thin circular shell to my students. But the mathematical derivation of such formula might be of interest to some. Using the above answer's diagram:</p>
<p><a href="https://i.stack.imgur.com/X3XXO.jpg" rel="nofollow noreferrer">... | 8541 | Force Balance Question |
2016-04-22T18:47:45.563 | <p>An uncold-worked brass specimen of average grain size 0.009 mm is heated to 600 degrees Celsius for 1000s, what is the average grain size based on this graph?</p>
<p><a href="https://i.stack.imgur.com/pRS7L.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/pRS7L.png" alt="enter image description he... | |materials|metallurgy| | <p>Grain growth is the movement of grain boundaries by diffusion to reduce the grain boundary area. This graph tells that at 600 degrees, a treatment of one minute shall give the y coordinate of the 600 degrees graph. So treating a sample for 1000s shall mean heating the sample at 600 from time t=0.0. The starting poin... | 8547 | Estimate the grain size after grain growth |
2016-04-23T13:21:24.327 | <p>With gravity camera stabilisers like below, how come counterweights are needed to stabilise the load (camera)?</p>
<p><a href="https://i.stack.imgur.com/CGmS7.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/CGmS7.jpg" alt="enter image description here"></a></p>
<p>Is it to ensure that the handle... | |mechanical-engineering| | <p>A camera system is more sensitive to rotational shake than any translation. That is because translation causes a shift proportional to the noise but rotation causes an error proportional to the distance to the target.</p>
<p><img src="https://i.stack.imgur.com/GqjQ2.png" alt="Camnoise"></p>
<p><strong>Image 1</str... | 8550 | How come counterweight is needed to stabilise camera? |
2016-04-23T16:34:08.953 | <p><a href="https://i.stack.imgur.com/dzdEC.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/dzdEC.png" alt="enter image description here"></a></p>
<p>The flux in the gas can be written as:</p>
<p>$$N_{1}=k_{p}(p_{1}-p_{1i})$$</p>
<p>And the flux in the liquid can be written as:
$$N_{1}=k_{x}(x_{1i... | |heat-transfer|chemical-engineering|process-engineering|diffusion| | <p>Convert both the pressure and concentration terms as mole fractions.
Now you have y for gas phase mole fraction and x for liquid phase mole fraction.
Henry's law is taken as am equilibrium relation in your question, so the equilibrium diagram(y vs x) is just a straight line through the origin with slope H'.
Taking t... | 8552 | Derivation of Overall Mass Transfer Coefficient |
2016-04-24T15:09:23.040 | <p>I read in a documentation to some adhezive: <em>the tensile strength is 13 N/mm<sup>2</sup></em>. How many kilograms can the 10x10mm bonding hold?</p>
<p>I tried to calculate it by the following:</p>
<p>$$\begin{align}
F &= m/g \\
\therefore m &= Fg
\end{align}$$</p>
<p>the strength is in N/mm<sup>2</sup>... | |structural-engineering|stresses| | <p>Pay attention to your unit analysis. You multiplied by the acceleration due to gravity, rather than dividing by it. Unit analysis would have shown this to be nonsense.</p>
<p>$$13 \frac{N}{mm^2} \cdot 100 mm^2 = 1300 N = 1300 \frac{kg \cdot m}{s^2}$$</p>
<p>Therefore, to get kg, you need to divide by an accelerati... | 8560 | Tensile strength to weight conversion |
2016-04-24T19:21:57.257 | <p>The precast concrete stairs at the home I recently purchased do not have a footing. Lack of a footing coupled with drainage issues has caused them to sink over time. I'm going to raise them and get them properly supported underneath.</p>
<p>To do that I want to clamp them near their center of gravity (along the ... | |mechanical-engineering|structural-engineering| | <p>The equation to find the center of gravity of an object which can be subdivided into smaller parts is the following:</p>
<p>$$\text{CG} = \dfrac{\sum \overline{y}_iA_i\rho_i}{\sum A_i\rho_i}$$</p>
<p>where $\overline{y}_i$, $A_i$ and $\rho_i$ are the <a href="https://en.wikipedia.org/wiki/Centroid">centroid</a>, a... | 8564 | Center of Gravity of Precast Concrete Steps |
2016-04-27T06:04:40.573 | <p>How is the position of a train modeled in a computer control system?</p>
<p>I can think of two basic approaches but I am not sure which (if any) are used in the real world.</p>
<h1>Lat, Long</h1>
<p>Ex: (-42, 23) </p>
<p>The position of the train is modeled by its real world position. The only issue I could se... | |civil-engineering|software|rail|transportation| | <p>Speaking personally (as someone who deals with this sort of thing for a US Class I on a regular basis) -- operational and maintenance personnel find railroad locations the same way you and I find highway locations -- milepost + track name, and named locations called "stations" in US railroad parlance.</p>
<p>The fo... | 8610 | How to notate the position of a train? |
2016-04-27T13:56:56.740 | <p>I have acquired an old loading dock built in 1930 that has toe-bearing rafters in addition to undersized purlins. As you can imagine, many of the rafters have sagged. Also, because of the toe-bearing design of the rafter, the building has no eaves.</p>
<p>There are many articles about avoiding toe-bearing design.... | |structural-engineering| | <p>OK, so after having a couple more roofing gurus come out, I just had one with an "ahha moment" that seems so obvious now looking back on it. So far this seems to be the best solution to my particular problem, and may help somebody else in the future with a toe-bearing rafter situation.</p>
<p>The idea is simply bu... | 8613 | Fixing a Roof with Toe-bearing Rafters |
2016-04-27T18:13:24.710 | <p>I have assembled a small DIY drip-irrigation system for my terrace garden. Please have a look at the attached image. I switch on a small pump to start the drip-irrigation system and then switch it off. But even after that, the water keeps flowing through the system and stops only when I physically lift the pump out ... | |fluid-mechanics|siphon| | <p>I had this problem and solved it by looping the outlet pipe above the tank water level, cutting and fitting female hose connectors, and fitting them to a three-way male connector. On the third outlet I fitted a very short piece of hose with a standard connector, and at the other end of the pipe I used a Gardena 'wa... | 8619 | How to stop water flow in a siphon? |
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