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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2015-07-29T10:38:09.310 | <p>PSOC4 provides a quadrature decoder functionality but I was unable to find specifics on its performance in the datasheets. Sure I know I need to read and utilize the count until the 16 bits of its counter overflow, but that's some 32k per iteration of the main loop of my program. If a precise encoder is attached to ... | |electrical-engineering|embedded-systems| | <h2>Quadrature decoder</h2>
<p>Looking at the <a href="http://www.cypress.com/file/131666/download">PSoC 4 TCPWM datasheet</a> the maximum operating frequency of the counter block is 48MHz, with a counter resolution of 21ns.</p>
<p>Assuming that you have a high resolution <a href="https://en.wikipedia.org/wiki/Rotary... | 3967 | How fast movement (cycles/s) can I reliably read with PSoC4 quadrature decoder? |
2015-07-28T22:52:34.127 | <p>For example, if there is many floating point operations, it could "rewire" the area of some of its integer units to handle floating point instructions, and vice versa. Or if there isn't too many calculations, but there is many I/O need, it could parallelize its IO better.</p>
<p>As I know, the FPGAs load their HDL ... | |electrical-engineering|embedded-systems| | <p>It seems that such (Xilinx) FPGAs already exist.
<a href="https://en.wikipedia.org/wiki/Reconfigurable_computing#Partial_re-configuration">https://en.wikipedia.org/wiki/Reconfigurable_computing#Partial_re-configuration</a></p>
<p>In partial reconfiguration, one part of the FPGA continues to run while another part i... | 3973 | Is there an FPGA which could "re-wire" itself on the need? |
2015-07-30T16:40:59.113 | <p>Atmel's ASF (Atmel Software Framework) is periodically updated by Atmel. When an update is available, Atmel Studio notifies you and asks if you want to download the update. If I install the update, this does not update any code in my existing projects.</p>
<p>I want to determine what code changes have been made i... | |embedded-systems| | <p>I think what you're looking for is the <a href="http://www.atmel.com/webdoc/asf/asf.VersionConversionWizard.html" rel="nofollow noreferrer">ASF Conversion Wizard</a>. According to the linked page, this wizard is supposed to be launched whenever the ASF version changes. If is not launching for you, you can open the A... | 3978 | How can I determine the code changes in an Atmel ASF update? |
2015-07-31T13:43:05.453 | <p>In the Linux kernel's dtsi file (am335x-bone-common.dtsi) for the AM335x processor, there is the am33xx_pinmux tree, with values like this:</p>
<pre><code> i2c0_pins: pinmux_i2c0_pins {
pinctrl-single,pins = <
0x188 (PIN_INPUT_PULLUP | MUX_MODE0) /* i2c0_sda.i2c0_sda */
0x18... | |electrical-engineering|embedded-systems| | <p>To update your .dts file (that includes the file am335x-bone-common.dtsi) for a pinmux assignment, consult the datasheet to determine which pin(s) are assigned to a function. This is in section 4.3 (broken into subsections per module). Clicking on the hyperlink for a pin (check your package type, ZCE BALL or ZCZ B... | 3980 | In a device tree for AM335x, how do I know what pinctrl values to use? |
2015-08-03T14:48:51.097 | <p>I'm considering using the i.MX 7 processor for a new design. The overall architecture appears to be similar to the i.MX 6, at least from comparing the block diagrams.</p>
<p>What mechanisms exist for communication between the Cortex-M4 core and the Cortex-A7 core(s)? Does the stock Linux kernel provide any such m... | |design|embedded-systems| | <p>The generic term for multi-core systems that run different kernels (or bare metal code) on different cores is Asymmetric multi-processing (<strong>AMP</strong>). Other related terms are <a href="https://en.wikipedia.org/wiki/Heterogeneous_computing" rel="nofollow noreferrer"><strong>Heterogeneous Computing</strong>... | 3982 | What IPC mechanisms exist for the i.MX 7 (or i.MX 6) multi-core processors? |
2015-07-29T14:56:20.197 | <p>I have discovered a problem when using the SPI peripheral in slave mode on an Atmel SAM4S. Occasionally words can become bit-shifted. I can force this condition by enabling the peripheral some number of clocks after <code>NSS</code> goes active. I do this by waiting for NSSR, then using a delay loop to wait a spe... | |electrical-engineering|embedded-systems| | <p>This is due to the design of their SPI peripheral. In slave mode, the shift register is shifted each <code>SPCK</code> (assuming <code>NSS</code> is low and <code>SPIENS</code> is set). There is an internal counter (not shown in the block diagram) for the shift register, and when it reaches the word size, the cont... | 3984 | Why are words bit-shifted for an Atmel SAM4S SPI slave? |
2015-07-28T18:26:32.947 | <p>For an embedded Linux system, if I have two or more network interfaces, how do I ensure that they always get the same interface names every boot</p>
<p>In other words, I want, for example, eth0 to always map to one physical Ethernet port, eth1 to the next, etc.</p>
<p>My Linux "distribution" is home-grown, and I u... | |embedded-systems| | <p>You mentioned that you do not <strong>need</strong> udev but if you are not opposed to installing it then you may want to consider using <a href="http://linux.dell.com/biosdevname/" rel="nofollow">biosdevname</a>. There is a great <a href="http://www.freedesktop.org/wiki/Software/systemd/PredictableNetworkInterfaceN... | 3986 | How do you ensure physical network interfaces always get the same interface name across reboots on an embedded Linux system? |
2015-07-31T16:08:51.560 | <p>I have an Atmel SAM4S MCU with a 12-bit internal ADC. I would like to achieve 16-bit resolution at a sample rate of 500 Hz. The input to the ADC is fairly low-frequency (about 20 Hz max frequency content), and low noise (less than one 12-bit lsb RMS).</p>
<p>How can I achieve 16-bit resolution with this processor... | |electrical-engineering|embedded-systems|adc| | <p>You can increase the effective resolution by intentionally oversampling the input signal. Here is brief summary of the idea from an application note on the topic provided by Atmel:</p>
<blockquote>
<p>The theory behind ‘Oversampling and decimation’ is rather complex, but using the method is fairly easy. The techn... | 3989 | How can I increase my processor's ADC resolution? |
2015-08-04T13:38:27.773 | <p>If I have a 10 MHz digital signal, how fast do I need to sample with a logic analyzer to avoid any bit errors? Does the minimum sample rate increase if I want to attach a protocol decoder (e.g. SPI)?</p>
<p>I am aware of the <a href="https://en.wikipedia.org/wiki/Nyquist%E2%80%93Shannon_sampling_theorem">Nyquist-S... | |electrical-engineering|embedded-systems| | <p>The least you can do is given by <a href="https://en.wikipedia.org/wiki/Nyquist%E2%80%93Shannon_sampling_theorem">Shannon-Nyquist theorem</a>: to be able to read a signal, you shall sample at least twice its frequency. Here, you can sample at 20MS/s (Mega sample per second). Nevertheless, 2 points for one period is ... | 3991 | How fast should I sample with a logic analyzer? |
2015-07-28T23:14:09.687 | <p>I am thinking on analog circuits, whose circuit design could be read (or, at least, significantly altered) from software. Do they already exist?</p>
| |electrical-engineering|embedded-systems| | <p>Yes, it's called Field-programmable Analog Array (FPAA):</p>
<p><a href="https://en.wikipedia.org/wiki/Field-programmable_analog_array">https://en.wikipedia.org/wiki/Field-programmable_analog_array</a></p>
<p>They are exactly the analog version of the FPGAs. There are many different subtypes (current or voltage dr... | 3993 | Do "analog FPGAs" exist? |
2015-08-07T00:45:24.977 | <p>I am currently working on project where the commands for a PC to the MSP430 will be communicated via UART. These commands need to be converted to binary to be able to written to the SPI bus. </p>
<p>For example 'a' from PC is translated to 0x61 on the microcontroller. What is really needed is hex 'a' Thus<br>
ASCII... | |electrical-engineering|embedded-systems| | <p>The input from the PC is a character, i.e. an ASCII-value. To understand how this is saved, have a look at the <a href="http://www.asciitable.com/" rel="noreferrer">ASCII-table</a>. The numbers '0' to '9' are represented by the ASCII-codes <code>0x30</code> to <code>0x39</code>. The capital letters 'A' to 'Z' are re... | 4007 | How to convert ASCII to binary to facilitate a UART to SPI bridge for an MSP430? |
2015-08-07T23:31:06.100 | <p>I am currently working on develop an IOT architecture. The sensing devices are to be integrated with microcontroller. The microcontroller will be integrated to some type of RF communication device. As the community is well aware RF communication protocols that will fit the bill. Once in consideration are Bluetooth... | |electrical-engineering|embedded-systems|iot| | <p>The present technology is all about IOT i. e with millions of devices connected over internet. Zigbee and BLE are two types of wireless communication which is used for interacting between two or more things or devices. Both have their own protocol and both have their merits and demerits.</p>
<p>BLE(Bluetooth low en... | 4009 | What are the pros and cons of using Zibgee over BLE or vice versa for IOT application? |
2015-08-03T23:35:45.480 | <p>I need to configure the clock systems for a MSP430F5528 microcontroller. The current development board has a 24MHZ crystal attach to XT2 pins (XT2IN/XT2OUT). The current design will need to support the follow peripherals.</p>
<ul>
<li>UART</li>
<li>ADC</li>
<li>SPI</li>
<li>Timers</li>
</ul>
<p>Few GPIO's will be ... | |electrical-engineering|embedded-systems|power| | <p>It depends a bit on the quality you expect from some of the peripherals and what their qualities are at given clock speeds.</p>
<p>Will you want a very high speed SPI interface and can this specific chip support that on the Fast Auxiliary Clock? Or are you going to do 1MHz SPI at most? So also for all the other dev... | 4011 | What needs to be considered when configuring the clock system for a MSP430F5xxx micro-controller? |
2015-08-01T13:39:10.427 | <p>I have been working on and off on small embedded systems project on and off. Some of these projects used an ARM Cortex-M4 base processor. In the project folder there is a <strong>startup.s</strong> file. Inside that file I noted the following two command lines.</p>
<pre><code>;**************************************... | |electrical-engineering|embedded-systems| | <p>In addition to the other answers, I'd like to add that when carving up RAM between stack and heap space, that you also need to consider the space for static non-constant data (e.g. file globals, function statics, and program-wide globals from a C perspective, and probably others for C++).</p>
<h2>How stack/heap all... | 4013 | Defining the heap and stack size for an ARM Cortex-M4 microcontroller? |
2015-07-31T15:28:14.623 | <p>A colleague mentioned that Thumb instructions were significantly slower than ARM instructions (this was for an AT91SAM7S32 processor). Is this true? What are the performance benefits of one instruction set over another?</p>
| |embedded-systems|computer-engineering| | <h2>In General</h2>
<p>THUMB instructions aren't to my knowledge intrinsically slower than ARM instructions, but rather are more limited in capability. If your code only needs the functionality of THUMB instructions, it will occupy less space than ARM, but would be the same number of instructions and, other things bei... | 4019 | How do Thumb instructions compare to ARM instructions for performance? |
2015-08-16T10:44:26.503 | <p>I notice that quite a number of deep excavation projects adopt double I-section walers to form a box beam since standard rectangular hollow sections don't come with such large sizes. The I-sections are usually factory butt-welded together at the flanges.</p>
<p><a href="https://i.stack.imgur.com/Thkkd.jpg" rel="nof... | |structural-engineering|steel|geotechnical-engineering| | <h3>Bolts</h3>
<p>Flanges can be added to the members as Wasabi mentioned in his answer. Another option would be to cut a small hole in the web of the members to allow for an iron worker to insert his hand to insert a bolt or hold a wrench. The reduction in strength from the access holes is minimal. This type of access... | 4043 | How can double I-section walers be spliced to ensure effective moment transfer? |
2015-08-16T15:19:12.180 | <p>I am trying to calculate the loads in the suspension components of a typical car double wishbone setup. I have found <a href="http://www.fsae.com/forums/showthread.php?11179-analysis-of-wishbones" rel="nofollow">a thread on the www.fsae.com forum</a>, which seems to be exactly the kind of thing I am looking for. It... | |mechanical-engineering|automotive-engineering|structures|statics|mathematics| | <p>Initially after reading your question I thought that it was using the <a href="https://en.wikipedia.org/wiki/Direct_stiffness_method" rel="nofollow">stiffness method</a> but after seeing the image on page 7 of that forum post I don't think that's what it is. This is because the stiffness method relates forces to dis... | 4046 | Calculating automotive suspension wishbone loads by considering the structure as a 3D Truss |
2015-08-17T12:21:36.487 | <p>I live and work in the UK, a country known for relentless roadworks. </p>
<p>Last week I drove through roadworks on the M1 that lasted for 18 miles, necessitating road users driving at 50 mph. Of course, almost all of this impressive stretch was simply coned off, with active work only present on one or two small si... | |civil-engineering|highway-engineering|construction-management| | <p>There is some merit in the argument that one mile on one mile off construction would be dangerous. Works vehicles would have to enter and exit every mile from live traffic. They'd go from 50mph to some stupid speed like 2mph and back every mile go get along the works.</p>
<p>I would seriously question though whet... | 4053 | What is the justification for working on such large stretches of road? |
2015-08-17T18:21:48.513 | <p>The AISC 360-10 <em>Specification for Structural Steel Buildings</em> gives provisions for calculating the maximum unbraced length of a compression flange that separates yielding moment from lateral torsional buckling (LTB). This formula is (AISC 360-10, Eqn. F2-5):</p>
<p>$$ L_p = 1.76r_y\sqrt{\frac{E}{F_y}} $$</... | |structural-engineering|steel|beam| | <p>As discussed in the earlier answer, if we look at the curve of moment capacity versus unbraced length we see three regions of behavior -- yielding, inelastic LTB, and elastic LTB (see Fig. C-F1.1 in the AISC <em>Steel Construction Manual</em>). It is important to note that we only have inelastic LTB due to residual ... | 4058 | Unbraced Length for Lateral Torsional Buckling vs. Yield Strength |
2015-08-18T13:24:24.987 | <p>The <strong>Darcy-Weisbach equation</strong> is used to calculate the frictional pressure losses in pipes transporting incompressible fluids. This equation uses a dimensionless <strong>Darcy friction factor</strong>, also known as the Moody factor, to account for the relative roughness of the pipe surface.</p>
<p>T... | |fluid-mechanics|chemical-engineering|pipelines| | <p>As an engineer, sometimes you need an answer, and it might not be the best answer, but you've got to get one.</p>
<p>In this case, there are two ways to handle this. The first would be to <strong>extrapolate</strong> the turbulent flow backwards to the end of the laminar flow. Since the turbulent flow is always h... | 4063 | Estimating Darcy Friction Factors for Critical Flow |
2015-08-18T14:10:51.443 | <p>I would like to build a <em>little water mill to place under the sink of the kitchen to produce electricity</em>. Considering that the mill will work when the user opens the tap to wash a dish, using a dynamo and a little electric circuit (bridge rectifier and a low pass filter), I would be able to generate a contin... | |electrical-engineering|battery| | <p>The slower you charge a Lithium battery the better. They are not keen on very fast charge/discharge fluctuations.</p>
<ul>
<li><p>One reason is that faster charging also results in higher temperatures which stresses a battery and therefore reduces battery life.</p></li>
<li><p>Another reason is that lithium plating... | 4064 | What are the consequencies of intermittently charging a smartphone battery? |
2015-08-19T14:20:49.930 | <p>Does a standard formula exist for calculating the (maximal) deflection of a constrained rectangular plate that is loaded with a evenly distributed pressure?</p>
<p>I found this <a href="http://www.roymech.co.uk/Useful_Tables/Mechanics/Plates.html" rel="nofollow noreferrer">Useful tables of mechanics</a>, however I'... | |mechanical-engineering|deformation| | <blockquote>
<p>deflection of a constrained rectangular plate</p>
</blockquote>
<p>By this I assume you mean that all edges are fixed.</p>
<p>My general go-to for these types of formulations is <em>Roark's Formulas for Stress and Strain</em>, 7th Edition. These formulations assume a flat plate with straight bounda... | 4077 | Deflection of constrained rectangular plate |
2015-08-19T16:40:53.750 | <p>I am designing a pattern for a sand casting. It has only one critical dimension which is a 4" inner diameter cylinder. If I use a 4" core, will the casting shrink away from the core? In other words will the inner diameter of the cylinder end up being 4.1" or something like that? What kind of shrinkage can I expect f... | |manufacturing-engineering|casting| | <p>Ductile iron is actually likely to expand during the casting process, as shown in the table found on the <a href="https://en.wikipedia.org/wiki/Casting_(metalworking)#Solidification_shrinkage">Casting Wikipeda page</a>, which is in part cited from <a href="https://books.google.com/books?id=JVTJi30phCwC&pg=PA66&a... | 4081 | How do the dimensions of a ductile iron casting change as it cools? |
2015-08-21T14:19:19.387 | <p>For a National Board Exam Review:</p>
<blockquote>
<p>To what height will a barometer column rise if the atmospheric
conditions are 13.9psia and 68F and the barometer fluid is mercury?</p>
</blockquote>
<p>Answer 28.3in</p>
<p>I have encountered questions with irrelevant variables; I assume temperature is irr... | |fluid-mechanics| | <p>You were using the wrong unit for density. It must be in slugs/ft<sup>3</sup>, not in lbm/ft<sup>3</sup>. By the way, 32.2 lbm = 1 slug.</p>
| 4090 | Barometer Column with Mercury |
2015-08-21T16:07:18.440 | <p>I have an (AC) power grid topology with generators, consumers, power lines, tranformers, etc. I also have a "snapshot" of the system's state, i.e., I know how much real power the generators feed, how much real power is used by the consumers, I know the reactive power values, and voltages. I also know the parameters ... | |electrical-engineering|power| | <p>you can use this free software <a href="http://www.interpss.org/" rel="nofollow">Internet technology based Power System Simulator (InterPSS)</a> also there are a lot of better Commercial software.</p>
| 4091 | How to apply power flow analysis? |
2015-08-21T16:19:21.160 | <p>From my understanding, there are two uses of a gearing system: to change the speed of output rotation (trading it with torque), and to change the axis of rotation. Now, in a car, for example, it is necessary to have multiple available gear ratios, to allow for high torque and high acceleration when the car begins to... | |mechanical-engineering|motors|gears|torque| | <p>A given mass of copper and iron can only produce so much torque : increasing torque further would require more current which means (a) the increased magnetic flux saturates the iron and (b) the I^2R losses in the copper overheat the motor. So more torque requires more iron and copper; i.e. a bigger, heavier, more ex... | 4093 | What is the use of gears in a device with a fixed gear ratio? |
2015-08-21T17:33:55.650 | <p>I have always thought that lateral load is horizontal and not vertical in direction. For example, from this <a href="http://web.mit.edu/course/4/4.441/1_lectures/1_lecture18/1_lecture18.html" rel="nofollow noreferrer">MIT notes</a> and many others:</p>
<blockquote>
<p>The lateral load resisting systems for earthq... | |structural-engineering| | <p>In the general case, you need to resolve the transverse load into <em>two</em> components, in the planes of the two principal axes of the beam cross-section. Of course when beginning a study of combined loads, one of the two transverse components would probably be zero, which is apparently the case in the quote from... | 4097 | Standard specification for direction of lateral load for beams |
2015-08-22T02:42:44.827 | <p>For a National Board Exam Review:</p>
<blockquote>
<p>Calculate the Reynold's Number, $Re$ for water at 20 °C flowing in an open
channel. The water flowing at a volumetric rate of 200 gal/sec. The
channel has a height of 4 ft and a width of 8 ft. At this temperature,
water has a kinetic viscosity of 1.104*1... | |fluid-mechanics|open-channel-flow| | <p>Reynold Number can be calculated using
Re=VD/Vk
Since the Volumetric flow rate is given Q=200 gal/sec and the area (4x8)ft² we can get the Velocity V
Q=AV</p>
<p>Convert 200 gal/sec to ft³/sec
200 gal/sec x 1 ft³/7.48 gal= 23.74 ft³/s</p>
<p>Q=AV
26.74=(4x8)(V)
V=0.8356 ft/sec.</p>
<p>Sing the channel is a rectangle... | 4111 | Reynolds Number for a Rectangular Duct |
2015-08-22T04:38:51.010 | <p>The <a href="https://drive.google.com/file/d/0BwUq8KuaDLbTU2Z3YVd1cGo5YUY3WHlybUpISS0tU3pYNlEw/view?usp=sharing" rel="nofollow">Peng Robinson</a> Equation of State gives a better approximation of the critical compressibility factor $Z_c$, where experimental data ranges between $0.24$ and $0.28$ (<a href="http://book... | |thermodynamics|chemical-engineering| | <p>It is important to understand that the critical point of a pure substance is characterized by certain properties. For example, the first and second partial derivative of the pressure with respect to the molar volume at constant temperature vanish. Secondly, it is important to understand that the critical point given... | 4113 | Discrepancy of calculated critical compressibility factor in Peng Robinson EoS |
2015-08-22T12:58:26.757 | <p>Recently there has been road construction around on the main road leading into my office building. I observed the construction crew removing asphalt in the form of a trench as showed in pictures below. Later on they filled up with aggregate and poured a layer of black tar and filled with something. The trench has be... | |civil-engineering| | <p>Given the very little detail you've provided, it's not possible to be sure.</p>
<p>But I don't think it's any more complicated than a simple resurfacing. The top layer has been planed off, and a new top layer laid.</p>
<p>Planing is done when the underlying structure is fine, but there are superficial problems: a ... | 4117 | What is the purpose of digging up trench and then filling with something similar to asphalt crack filler? |
2015-08-22T15:52:33.933 | <p>I'm trying to understand the concept of mechanical resonance.<br>
<a href="https://en.wikipedia.org/wiki/Mechanical_resonance" rel="nofollow">https://en.wikipedia.org/wiki/Mechanical_resonance</a></p>
<p>I cannot find much references about how exactly is the phenomenon known. I.e. how was it discovered and how is i... | |mechanical-engineering| | <p>I don't think you could point to any one person or group and say, "They discovered mechanical resonance." It's something that's always been around and people have used it to their advantage for centuries, if not millennia.</p>
<p>I've done more than a few vibration tests looking for the kind of resonances where the... | 4118 | How is Mechanical Resonance detected? |
2015-08-22T23:52:56.703 | <p>I am just posting here to verify that I am properly using a tool that is new to me, a micrometer. Here is what the precision label specifies, basically that it can measure up to an inch and down to 1/1000" (a notch on the round scale).</p>
<p><a href="https://i.stack.imgur.com/qKpGi.jpg" rel="nofollow noreferrer"><... | |measurements|tools| | <p>These kind of micrometers have two scales, a coarse and a fine. You add them together to get the final reading.</p>
<p>The fine scale is etched around the part that turns. With nothing in the microcometer and it closed all the way, the 0 on this scale should line up with the horizontal line on the fixed part to t... | 4124 | How to read micrometer? |
2015-08-23T01:59:35.437 | <p>For a National Board Exam Review:</p>
<blockquote>
<p>A floating cylinder 8cm in diameter and weighing 950 grams is placed in
a cylindrical container 20cm in diameter and partially full of water.
The increase in the depth of water in the container due to placing the
float in it is:</p>
</blockquote>
<p>Ans... | |fluid-mechanics| | <p>The first part of your maths is OK.</p>
<p>$P_1$ = $296.649$ $Pa$</p>
<p>Now, pressure at the base of a fluid is:</p>
<p>$P$ $=$ $\rho gh$</p>
<p>Rearrange the equation & $h$ $=$ $P/\rho g$</p>
<p>Using your numbers & the fact that the density of water is $1$ $g/cm^3$ or $1000$ $kg/m^3$,</p>
<p>$h$ $=$... | 4129 | Height Increase by a Floating Cylinder Over a Larger Cylinder |
2015-08-23T08:47:52.650 | <p>I am trying to understand what the dynamic factor $K_v$ describes. I know that a low $K_v$ factor results in quieter and smoother work of the gear but what exactly does $K_v$ tell me?</p>
| |mechanical-engineering|gears|dynamics| | <p>A <a href="https://www.google.com/search?q=dynamic%20factor%20gear%20agma" rel="nofollow">google search</a> for this actually returns pretty good information.</p>
<ul>
<li><p>"The dynamic factor $K_v$ accounts for internally generated gear tooth loads which are induced by non-uniform meshing action (transmission er... | 4133 | Gears - dynamic factor $K_v$ |
2015-08-24T04:37:34.770 | <p>I made a test in Ansys but the result doesn't seem to be the final steady state. The two bodies didn't touch each other. How can I get the right result?</p>
<p><a href="https://i.stack.imgur.com/e809N.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/e809Nm.jpg" alt="manual contact"></a>
<a href="h... | |applied-mechanics|simulation|ansys| | <p>Okay so I ended up having a play in ANSYS Mechanical Workbench. I did a mock up of your problem. Here's how I've been able to successfully model it. Note that a lot of my decisions are based on the <a href="http://www.ansys.com/staticassets/ANSYS/staticassets/resourcelibrary/presentation/2014-sd-mechanical-contact-b... | 4140 | How to simulate the contact between two distant parts in Ansys workbench？ |
2015-08-24T13:00:57.333 | <p>The UK is about to start trials of <a href="http://www.thetimes.co.uk/tto/life/motoring/article4524398.ece" rel="nofollow">wireless charging for moving cars</a>.</p>
<p>What kind of power transfer efficiency is likely to be achievable in such a system, compared to just plugging in the car directly?</p>
| |power-engineering|inductive-charging| | <p>This is not exactly a comprehensive answer, but I found an interesting article on <a href="http://eandt.theiet.org/news/2014/apr/onroad-charging.cfm" rel="nofollow">The Institution of Engineering and Technology</a>'s website. It is fairly interesting, if not incredibly technically detailed, and I encourage you to ch... | 4141 | Efficiency of wireless charging for moving cars |
2015-08-24T21:36:03.453 | <p><a href="http://co.routt.co.us/building/handouts/notching.pdf" rel="nofollow">IBC 2308.8.2</a> states a rule of not notching more than 1/6 the depth of a wooden joist (emphasis added):</p>
<blockquote>
<p><strong>Framing details.</strong> Joists shall be supported laterally at the ends and at each support by soli... | |structural-engineering|beam| | <p><strong>The 1/6th rule</strong></p>
<p>IRC allows a notch 1/6th of the depth of a wooden joist (but not within the middle third) on the basis that the joist is sized sufficiently for the stress at midspan, and a 5/6th depth beam in the end thirds is hence sufficient for the lower stress experienced there. Hence a 1... | 4149 | Is it acceptable, with reinforcement, to notch a floor joist more than 1/6 of the depth? |
2015-08-24T22:47:30.640 | <p>I have seen this somewhere in the wild, perhaps a space-efficient storage system in lieu of two shelving units. I'm trying to reproduce, and failing.</p>
<p>Imagine two stacks of trays which hold things that must not fall out, so the trays must remain horizontal. The trays are all connected to the same track, which... | |mechanical-engineering| | <p>Image in my mind: The track is on a wall, with the trays being perpendicular from the wall. The track is rectangular (with rounded corners obviously). </p>
<p><strong>Solution 1:</strong><br>
If the things that the trays are holding are relatively light (to the tray/shelf), or if its feasible to perfectly balance t... | 4151 | How to keep a tray horizontal when moving around a closed, vertical track? |
2015-08-24T23:58:14.887 | <p>For a National Board Exam Review: </p>
<blockquote>
<p>A 29.53" * 39.37" pressure vessel contains ammonia with f = 0.041. Compute the minimum required discharge capacity of the relief device in $\mathrm{\frac{kg}{hr}}$.</p>
</blockquote>
<p>The solution is shown as:</p>
<p>$$C = fDL = 0.041(\frac{29.53}{39.37})... | |fluid-mechanics|refrigeration|pressure-vessel| | <p>By dividing the diameter and length dimensions, which are in inches, by 39.37 you are converting them to metres. The problem you are trying to solve has inputs that are in both English and metric units, but the answer needs to be in metric/SI, so you need to convert everything to SI units prior/during calculation.</... | 4153 | Why divide the dimensions of a pressure vessel by 39.37 when calculating discharge capacity? |
2015-08-25T08:03:14.777 | <p>What are the advantages and disadvantages of bevel gears?</p>
<p>This is what I've already found:</p>
<p><strong>Advantages:</strong></p>
<ul>
<li>possibility to change operation angle</li>
</ul>
<p><strong>Disadvantages:</strong></p>
<ul>
<li><p>must be precisely mounted</p></li>
<li><p>shafts' bearings will b... | |mechanical-engineering|gears| | <p>Another advantage is to counter mechanical thrust which is why the bearings are usually conical</p>
| 4159 | Advantages and disadvantages of bevel gears |
2015-08-25T20:58:12.193 | <p>Is there a method to test for thermal oxide on a painted steel part after the paint has cured? I'd rather the method be nondestructive but it only being destructive in the presence of thermal oxide is also acceptable.</p>
<p>I am specifically looking for laser oxide under 3mils of polyurethane, if that helps.</p>
| |manufacturing-engineering|product-testing| | <p><a href="http://www.materialsviews.com/no-escape-for-rust-non-destructive-detecting-of-corrosion-under-coatings/" rel="nofollow">This article</a> written on May 02 2012 states that no non-destructive methods exist currently, other than a scanning Kelvin probe (which requires long measurement times).</p>
<p>Howeve... | 4172 | What is a method to detect thermal oxide layer after steel is painted? |
2015-08-26T17:21:01.837 | <p>For a given laminate made of composite material (composed of fibers oriented in a carefully designed sequence coated and embedded in a matrix material), where can I begin estimating the stiffness and/or strength of the material? How can I know (within a beginning estimate tolerance) how to design a part out of comp... | |mechanical-engineering|materials|composite| | <p>There are quite a few ways to find out the stiffness and/or strength of a composite material, with a good understanding of the materials that make up the composite material.</p>
<p><strong>1. Pre-engineered composite materials</strong></p>
<p>Several materials, prevalent mainly in the aerospace industry, are pre-e... | 4182 | How do I calculate an estimate for the properties of a composite material? |
2015-08-26T18:19:54.513 | <p>I am trying to figure out if a motor I have is capable of spinning a wheel. Here is all of the information I have:</p>
<p>MOTOR: 190 g.cm min.</p>
<p>WHEEL: 26 cm diameter, weighs about 59 grams</p>
<p>I imagine that I would have to calculate the linear speed of the wheel in order to convert it to the same units ... | |mechanical-engineering|torque| | <p>Check out <a href="https://robotics.stackexchange.com/questions/7796/calculating-required-torque/7799#7799">my answer to a similar question at the Robotics SE</a>. You are asking only about a motor and a <strong>wheel</strong>, and you do not give the weight of the vehicle (assuming there is one), so I cannot commen... | 4186 | How to calculate if a motor is capable for a load? |
2015-08-27T23:10:45.337 | <p>I just started mechanics of materials, and it seems that my knowledge from statics has gotten rusty over the summer. But there was a new concept introduced in the first example problem today.</p>
<p>There was a horizontal bar connected to a wall (fixed support). I understand that with a fixed support, there are ho... | |mechanical-engineering|beam|statics|torque| | <p>It's useful to be clear about the fact that the 'cut' is an imaginary one. Since the portion of the beam no longer attached to the wall (because of our imaginary cut) is not falling or rotating, it must be subjected to the same type of forces/torques as if it were attached directly to its own 'wall'. The 'wall' in... | 4197 | Why is there a moment at the cross section end when you cut a body? |
2015-08-28T01:19:03.463 | <p>I've been given the following to memorize; But my head is so crammed with many others that I need to find another way; Are these formulas Empirical? I was hoping that if I derive it from a much more primitive form; I maybe able to remember it.</p>
<p>$${ (\frac{A}{F})_t = W_{ta} = \frac{Q_h \frac{kJ}{kg} }{3117} \f... | |combustion| | <blockquote>
<p>Are these formulas Empirical? I was hoping that if I derive it from a much more primitive form</p>
</blockquote>
<p>This is <strong><em>probably an approximation</em></strong>, let's try to calculate stoichiometric air to fuel ratio and heat of combustion for liquid octane as an example:</p>
<p>$$ C... | 4200 | Derivation for the Formulas of the Approximate Ultimate Analysis of Coal |
2015-08-28T20:52:38.440 | <p>Why do we design cars to turn by turning the front wheel?</p>
<p>Wouldn't it better to keep all wheels straight and turn by rotating the wheels on one side of a car more then the wheels on the opposite side of the car, like tank tracks do? That way you can turn even if you are standing still. Why don't cars do this... | |automotive-engineering|wheels| | <p>Meet the skid-steer loader:</p>
<p><a href="https://i.stack.imgur.com/m6M4o.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/m6M4o.png" alt="Skid-steer"></a></p>
<p>It's a versatile beast of a machine, packing lots of power, multiple attachments and (most relevantly to the topic at hand) great ma... | 4209 | Why do cars turn by turning the front wheel? |
2015-08-30T06:12:53.267 | <p>For a National Board Exam Review:</p>
<blockquote>
<p>A uniform area jet travels to $600 \frac{ft}{s}$ and a
$100\frac{ft^3}{s}$. What is the horizontal force acts on the water jet
if it undergoes a $180^\circ$ turn?</p>
</blockquote>
<p>I would normally provide an answer but even review instructor cannot an... | |fluid-mechanics| | <p>Try considering the force required to stop the jet, then the same force again to accelerate the jet back to the same velocity, but in the opposite direction.</p>
| 4225 | The Horizontal Force of Water as it turns 180 degrees |
2015-08-30T11:19:18.820 | <p>I want to mount a heat source onto several heat pipes. The heat will be forwarded to coolers (four heat pipes, 200 mm) which are able to distribute up to 120 W without increasing the temperature of the device which should be cooled. The device itself will generate up to 100 W heat. Now I was wondering what would hap... | |heat-transfer| | <p>Well, how much the clamp heats up is determined by a great number of factors, chiefly (off the top of my head):</p>
<ul>
<li>The properties of the pipe (material properties: density, material
type, size of contact area etc)</li>
<li>How the clamp interfaces with the pipe (e.g. metal on metal, thermal
interface mate... | 4227 | Mounting heat source onto heat pipes |
2015-08-30T17:31:08.970 | <p>I'm an engineer in industrial design and despite that I studied mechanics, kinematics and dynamics, I got difficulties when I try to label or find components which could enable my designs have relative movements, i.e. one part rotates inside other.</p>
<p>I know I can design most of them but I guess that some must ... | |mechanical-engineering|design|kinematics|biomechanics| | <p>There is a fascinating historical collection of mechanisms compiled in the late 19th century here: <a href="http://507movements.com/about.html" rel="nofollow">Mechanical Movements</a> and somebody is working through the task of making animations of them for the website.</p>
<p>Manufacturing technology has progresse... | 4232 | What are the basic mechanism, components or parts to generate relative movements? |
2015-08-31T13:11:53.067 | <p>To pick a specific example, a flyover that goes over a ground-level road/rail need only be as tall so that the tallest vehicle travelling in the outermost lane can clear it.</p>
<p>Or another, an elevated road/metro rail that runs along a ground-level road need to be as tall as the tallest vehicle.</p>
<p>But why ... | |civil-engineering|transportation| | <p>Looking at the the street view provided by the OP I would say that vertical profile constraints are at play here. The ramp needs a certain vertical clearance near its start and near its end. Rather then have the road return to ground level, the designers may have opted to use one vertical curve over the entire ramp... | 4238 | Why are flyovers/metro rail tracks much higher than traffic? |
2015-09-01T20:43:17.637 | <p>I'm encasing the abutment ends of prestressed concrete bridge girders in concrete before the deck pour. (For lateral stability and to prevent the soil from spilling through.)</p>
<p>Discussion of intermediate diaphragms for prestressed girders abounds, but I haven't found information on structural behavior of end d... | |bridges|prestressed-concrete|deflection| | <p>I have no resources to point to in regards to this, but I'm fairly certain your gut-feeling is correct. In fact, end diaphragms exist in bridges primarily to hold the soil on the approach. They can also be useful for temporary lateral stability of the beams, but if that were the only reason, temporary metallic braci... | 4251 | What is the effect of end diaphragms on prestressed girder forces/deflections? |
2015-09-02T10:33:09.343 | <p>I am taking organic solar cell course on Coursera, and I have a question about I-V curve for a certain solar cell. The question asks for the solar cell characteristics such $V_{oc}$, $P_{max}$ and $FF$. I get the $V_{oc}$ correctly but I couldn't calculate the other two correctly as they provide me with an excel she... | |chemical-engineering|renewable-energy|photovoltaics| | <p>As you have the power-voltage curve, finding the maximum power point is easy: it's the turning point on the power-voltage curve.</p>
<p>The problem is that the absolute values in your graph look completely wrong. If the graph is flipped upside down, and based at zero power, zero current and zero voltage, then the b... | 4254 | How to get the maximum power point from I-V curve for Organic Photovoltaics (OPV)? |
2015-09-02T19:13:50.997 | <p>Two questions.</p>
<p><strong>Has anyone had experience in retrofitting consumer (locally-available) square aluminum tube as telescoping structural support?</strong> Ergo; with 0.125" wall thickness square tube at an outside dimension (OD) of 1.5", would minor superficial sanding and end beveling of an inner squar... | |mechanical-engineering|materials|tolerance| | <p>Aluminium rubbing on aluminum generally will wear very rapidly. You generally want some sort of plastic bushing to reduce friction and wear. (Like with luggage handles there's just a little piece of plastic between the tubes) you should also have a bushing for the other end of the joint (the one inside that's not vi... | 4263 | Assist for vertically telescoping support? |
2015-09-02T19:31:02.100 | <p>I am designing a block and tackle system to haul wood up a ramp onto my porch. The issue I am having is that the rope seems like it will rub against the top of the ramp and cause it to fray. How can I prevent this from happening?</p>
<p><a href="https://i.stack.imgur.com/PkHNo.jpg" rel="nofollow noreferrer"><img sr... | |applied-mechanics| | <p>Here is how I would solve this in true bodge-job fashion:</p>
<h3>Materials:</h3>
<ul>
<li>2x bricks, the type with holes in</li>
<li>1x short section of broom-handle</li>
<li>1x short plastic pipe, or toilet-roll tube (bigger than broom handle)</li>
<li>2x pencils, or bits of string, or something</li>
</ul>
<h3>... | 4265 | Block and Tackle with Ramp - stopping rope drag |
2015-09-03T07:33:44.673 | <p>"Sketch a combinational circuit which takes as input, two 4-bit binary numbers,
A3A2A1A0 and B3B2B1B0, and which outputs the 8-bit product P7P6P5P4P3P2P1P0.
Assume that you have available sixteen 2-input AND gates and three 4-bit adders.
Please explain the reasoning behind your design." </p>
<p>After a bit of fidd... | |electrical-engineering|computer-engineering| | <p>The first step is ANDing all the combinations of inputs which takes all the 16 AND gates available.</p>
<p>Lets call those results $S_{00}$ $S_{01}$ $S_{02}$ $S_{03}$ $S_{10}$ etc.</p>
<p>Is we arrange them in how we need to add them we get:</p>
<p>$$
\begin{matrix}
& & & S_{03}&S_{02}& S_{01}... | 4270 | How to create a logic circuit that multiplies two 4 bit numbers, using only 16 2-input AND gates and 3 4-bit adders? |
2015-09-03T09:56:25.713 | <p>I'm studying "signals and systems". We can indentify two kinds of signals: power signal and energy signal.</p>
<p>The definitions are:</p>
<p>Energy of a time-continous signal
$$ E_x = \int_{-\infty}^{+\infty}{|x(t)|}^2dt $$</p>
<p>Power of a time-continous signal
$$ P_x = \lim_{Z\rightarrow+\infty}{\frac{1}{2Z}\... | |telecommunication|power|energy|signal|systems-engineering| | <p>First point is that signum is not continuous with the jump at $t=0$. </p>
<p>Second because of the absolute value in the integral it has the same $E$ and $P$ as a constant signal $1$.</p>
<p>This means that $E_{sgn}=+\infty$ and $P_{sgn}=1$</p>
| 4271 | What kind of signal is the signum function? A power signal or an energy signal? |
2015-09-03T11:09:09.517 | <p>An input device sends a 20ms positive signal to perform an action. The signal is captured using an interrupt triggered on the rising edge of the positive signal. It appears that there might be some electrical noise on the signal line. I suspect this because the interrupt is getting trigger inadvertently. I currently... | |electrical-engineering|embedded-systems| | <p>With a 20 ms pulse width you really should not be using interrupts directly.</p>
<p>The usual thing is to have some timer generating periodic interrupts at maybe 250Hz or so, then if on two consecutive timer events you read the input as active you can be reasonably sure you have a pulse lasting at least 1/Timer fre... | 4275 | How can electrical noise be isolated in an Embedded System? |
2015-09-04T12:45:05.283 | <p>I am trying to identify the section designation so I can determine it's properties.</p>
<p><a href="https://i.stack.imgur.com/W5znc.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/W5znc.png" alt="enter image description here"></a></p>
<p>I have looked under "C 150 x 100 x 40" but I can't find it... | |civil-engineering|beam|standards| | <p>In the Southern African context this would be defined as a </p>
<p>"cold formed lipped channel" section. I am not sure if it the same across the world though.</p>
<p>Here is one <a href="http://www.macsteel.co.za/products/cold-formed-sections?b=55" rel="nofollow">supplier's link</a></p>
| 5294 | What is the name of this section? |
2015-09-04T15:21:11.230 | <p>Every morning when I get up, I use <a href="http://www.mrcoffee.com/specialty/grinders/automatic-burr-mill-grinder-stainless-steel/BVMC-BMH23.html" rel="nofollow noreferrer">this coffee grinder</a> to grind beans for my morning coffee.
<a href="https://i.stack.imgur.com/bX9v7.png" rel="nofollow noreferrer"><img src... | |process-engineering|product-engineering|grinding| | <p>Without getting into the why of static and grinding, I think the problem always lies with these plastic bins that the grinds end up in. Glass would be much better.</p>
<p>The simple solution which nobody has mentioned here,
is to quickly dip a spoon in water and briefly stir the beans adding a few drops right befor... | 5297 | How to prevent static buildup in an electric burr mill coffee grinder? |
2015-09-04T18:19:43.767 | <p><strong>Question:</strong> How is shelf deflection determined? More specifically, how is the deflection determined when one or more edges of the plate have reinforcing edging applied to them?</p>
<p>I have been able to find <a href="http://www.roymech.co.uk/Useful_Tables/Mechanics/Plates.html" rel="nofollow norefer... | |mechanical-engineering|beam|deflection| | <p>To add to Wasabi's answer - especially dealing with wood's anisotropy, here are a few things to consider:</p>
<p>1.) IF wood is end grain, plywood, oriented strand board, etc then for all design purposes, it is isotropic - as the grain is going in the "up" direction - where no real bending occurs. As a result, you... | 5299 | How is shelf deflection determined? |
2015-09-05T00:53:52.910 | <p>In the rankine cycle, water is first pressurized and then heated to produce steam before it is used to turn a turbine. As far as i know, this is what is considered the best way to extract mechanical work on the turbine, but i want to understand why this is so. How is it that we can extract more work on a turbine f... | |thermodynamics| | <p>A good way to understand why the phase change is so important is by looking at the Pressure vs. Volume diagram for the Rankine cycle (path 1-2-3-4-1):</p>
<p><a href="https://i.stack.imgur.com/Jhxl0.png" rel="noreferrer"><img src="https://i.stack.imgur.com/Jhxl0.png" alt="enter image description here"></a></p>
<p>... | 5307 | Why use steam in the rankine cycle? |
2015-09-05T01:11:32.173 | <p>In my admittedly naive understanding of the rankine cycle, steam is condensed back into water after passing through the turbine. Why not reuse the steam instead? It would seem to require less effort to reuse heated steam than to intentionally condense the water only to reheat it once again.</p>
<p>I'm sure i'm mi... | |thermodynamics| | <p>It's for almost the same reason as my answer to <a href="https://engineering.stackexchange.com/questions/5307/why-use-steam-in-the-rankine-cycle">your other question</a> on the Rankine cycle: The work output of the cycle increases as the integral (area) of the P-V diagram (or T-S) diagram is increased. Condensing ... | 5308 | Why do we need to condense steam in the rankine cycle? |
2015-09-06T09:01:27.770 | <p>When a rectangular piece of plastic (say a credit card) experiences an increasing compression force, the plastic eventually buckles. Is it possible to find the equation of the plastic's cross section once it has buckled elastically? </p>
<p>What I have in mind is two fingers squeezing a plastic card. The fingers ar... | |statics| | <p>The axial compression of the member should be negligible compared to the sideways deflection. This means that it doesn't depend on the cross section of the card. This is <em>exactly</em> Euler buckling.</p>
<p>The equations for buckling are usually used to determine the load at which buckling will occur. This is wh... | 5322 | The Equation of a buckled card |
2015-09-06T13:50:21.160 | <p>Something hit me during my last flight: our ears feel that the pressure around us changes quickly during liftoff and landing, they hurt more and more until we make them pop. However, the cabin must maintain a level of oxygen higher than outside the aircraft because it isn't dense enough at ~10km to breathe normally.... | |pressure|aircraft-design| | <p>There's a difference between being pressurized to an absolute value and being pressurized to a relative value. </p>
<p>For instance, if the cabin immediately pressurized to the same atmospheric pressure as your departure terminal, then your ears would not pop on ascent, but they would have to pop at some point on t... | 5325 | If aircraft are pressurised, why do our ears pop during liftoff and landing? |
2015-09-07T07:13:54.313 | <p>I often see specifications for refurbishing works on gas pipelines calling for blanking spades, to separate the area worked on from the rest of the gas system. This is in addition to closing valves.</p>
<p>Googling showed me some pictures of how blanking spades look like, but I don't yet understand the process of i... | |pipelines|safety| | <p>You are correct, blanks are installed at a pipe flange where two runs connect. Typically you break the joint and pry the flange apart to install the blank, but this can cause problems if/when the prying action torques the next joint in the piping system and damages the gasket. I've heard of a person replacing every ... | 5334 | How are blanking spades entered into gas pipelines? |
2015-09-08T03:39:59.077 | <p>I'm currently working on problems for my mechanics of material course, and I just learned how to calculate the shear stress on a bolt holding stacked plates. That whether it be a single or double shear, I have to account for every shear plane. However, what happens for the bearing stress? I know that it depends on t... | |stresses| | <p>I think answer to the question <em>would the bearing stress differ</em> is ==></p>
<p><strong>YES!</strong> </p>
<p>bearing stress <em>would</em> vary along the bolt in different sections in plates...</p>
<p>and you <strong>cannot</strong> look at the entire bolt at once to calculate the bearing stress </p>
<... | 5344 | Does the bearing stress vary along the bolt? |
2015-09-08T06:48:31.593 | <p>I have a system with a motor, some masses, damping and springs. One of the masses is loaded with an unknown external force F. I want to estimate the force F using data of the motor (mainly current). There are some unknown disturbances, like temperature and friction in the system. Can this be done or are there better... | |mechanical-engineering|control-engineering|sensors|kalman-filters| | <p>First, start with a precise mathematical description of your system. Second, analyze it observability. If the system is observable, of course you can estimate the (augmented) state vector (along with the load as an unknown parameter). In practice, there are always some factors that are often a subject to experimenta... | 5345 | Can a load be estimated using a Kalman filter? |
2015-09-09T02:34:25.843 | <p>I know lasers can cut or create holes on some hard materials such as diamond and metals. Is there any similar concept in tunnel engineering?</p>
<p>If not, what are the difficulties?</p>
| |materials|lasers|tunnels| | <p>Barring other difficulties, it is unclear what advantages laser cutting would have in such an application. Lasers are <a href="https://engineering.stackexchange.com/questions/2991/why-are-lasers-used-for-concentrated-light-applications-instead-of-incoherent-li">useful in drilling/cutting of materials</a> because of... | 5355 | Is it possible to use lasers to build tunnels instead of mechanical digging machines? |
2015-09-09T08:08:40.533 | <h2>Short form: How would one calculate the perfect shape of a range hood?</h2>
<p>See drawing below. Will the curve of the profile of the range hood be exponential? Quadratic? What if the range is enclosed from three sides that create a box open only from the front - what curve should one choose? Sigmoid? Cubic? Some... | |fluid-mechanics|hvac|airflow| | <p>Making a duct that flares along an exponential curve to 2 feet (60cm) in diameter would create a larger duct that won't solve your problem.</p>
<p>It would be an expensive duct to make (think <a href="http://www.all-brass-instruments.com/uploads/brass/20/200400529718-7.jpg" rel="nofollow">tuba bell</a>), and if you... | 5357 | Perfectly aerodynamic kitchen range hood |
2015-09-09T08:09:39.283 | <p>I am trying to manipulate some data that were obtained from a three point load experiment on a porcine tibia.</p>
<p>I would like to obtain a stress-strain curve for the various specimens; however, the only data that was given from the Instron three-point loading set up was Load (N) vs Deformation/Extension (mm).</... | |mechanical-engineering|materials|stresses|biomedical-engineering|biomechanics| | <p>It's fairly complicated. I found an article in The Bone Journal <a href="http://www.thebonejournal.com/article/S8756-3282(98)00076-3/fulltext?refuid=S8756-3282(10)01400-6&refissn=8756-3282">Comparison of three-point bending test and peripheral quantitative computed tomography analysis in the evaluation of the st... | 5358 | Convert Load Deformation (Extension) Data to Stress-Strain Curve |
2015-09-10T09:37:59.240 | <p>How can I compute the Frequency Response Function (FRF) if I use two three-axis MEMS accelerometer to measure the input excitation and output response?</p>
<p>I have read from some books that the FRF can be computed as the ratio of response to excitation, e.g., $ H(s) = x(s)/F(s)$, where $s$ is the Laplace variable... | |civil-engineering|structural-engineering|vibration|modal-analysis| | <p>The body of your question (the title is somewhat different) asks about computing the frequency response function (FRF) between a multi-input, multi-output (MIMO) system. First off, the numerical transfer function/FRF between two time domain signals is usually calculated by calculating the cross power spectrum betwe... | 5365 | How do I conduct an experimental modal analysis with a three-axis accelerometer? |
2015-09-13T14:35:18.607 | <p>Let us assume you have a large forging press or drophammer, and drawings for a set of smaller parts that all need to be forged from the same material. Would it be feasible to construct a forging die so that all the parts could be forged from a single billet and then separated as a machining step? Or is this more e... | |manufacturing-engineering|forging| | <p>I've previously worked in the forging industry and you can certainly forge multiple parts in a single stroke of a large press but there are problems. The obvious ones are the size of the available press and the economics of the operation. However, even from a metallurgical point of view, forging a complex part l... | 5396 | Is it feasible to forge multiple, smaller parts in the same forging operation? |
2015-09-14T18:46:12.063 | <p>Just a short question: Is there any usefulness in doing block diagram reduction piecewise?</p>
<p>The reason I am asking is that I find it much (!) easier to just find the final $\frac{output}{input}$ transfer function using mathematics (the brute force method), but my professor does it stepwise. </p>
<p>If I am t... | |control-engineering|control-theory| | <p>When you are solving a problem in the real world, there are 2 main important requirements</p>
<ol>
<li>Get the correct answer. </li>
<li>Solve it using sound methods. </li>
</ol>
<p>There might be a half-dozen different ways to solve a given problem, so long as you arrive at the correct answer and don't pick a met... | 5408 | Block Diagram Reduction: Is it necessary to do it stepwise? |
2015-09-14T21:09:45.450 | <p>I want to simulate a turbine in Fluent. For this reason, I studied some papers. In these papers, Turbulence is modeled using the realizable k–e model and Non-equilibrium wall functions are used in the near wall flow modeling. There are the following sentences in these papers:</p>
<ul>
<li><p>The Boussinesq approach... | |mechanical-engineering|fluid-mechanics|turbines|cfd| | <p>The <strong>basic assumption</strong> of the RANS approach (see the answer by @Algo) is that there is an overall steady solution to the problem. This overall steady solution features small scale oscillations <em>around</em> the mean value. </p>
<ul>
<li>In a first step the Navier Stokes equations (NS) are rewritten... | 5410 | What is the Boussinesq approach? |
2015-09-14T21:37:19.430 | <p>While studying some papers, I didn't understand the following sentences:</p>
<blockquote>
<p><code>deltP</code> the pressure drop across the turbine, evaluated using the mass average values at the inlet and outlet sections of the computational domain, respectively.</p>
</blockquote>
<p>What is the exact meaning... | |mechanical-engineering|pressure|cfd| | <p>Averaging is a tricky business (see <a href="https://www.researchgate.net/publication/245354712_Averaging_Nonuniform_Flow_for_a_Purpose" rel="nofollow">Cumsty 2006</a> for an introduction). Basically the problem is, that our thermodynamics usually talk about <strong>a</strong> pressure and <strong>a</strong> tempera... | 5411 | Understanding pressure drop and mass average values |
2015-09-15T11:50:55.000 | <p>I have gas pipeline with biogas, low pressure - approx 40mbar over atmosphere. I want to remove a small amount of condensate, inside a building, without creating an <a href="http://www.engineeringtoolbox.com/hazardous-areas-classification-d_395.html" rel="nofollow">ex-zone</a>. Small amount: I honestly don't know bu... | |mechanical-engineering|pipelines|safety|valves| | <p>There are <a href="http://mankenberg.de/en/20/prgb:7/product:kondensatableiter-schwimmergesteuert/produkte.html" rel="nofollow">swimmer operated condensate traps</a> (link contains cut view). The operating principle seems fairly simple, a swimmer in the pot opens a valve when enough condensate has accumulated and cl... | 5422 | Device to remove condensate, without creating a hazard (EX) zone |
2015-09-15T16:06:10.750 | <p>Consider a centrifugal compressor. The compressor map usually plots the adiabatic head vs volumetric inlet flow for rated conditions of pressure, molecular weight and temperature at a given speed. But when pressure, temperature, molecular weight and speed are fixed, how can the inlet flow be made to vary ? Is it acc... | |mechanical-engineering|compressors| | <p>In general every compressor (axial and radial) will deliver a certain flow rate depending on the back-pressure down stream of the compressor. So by changing the pressure difference over the compressor: for example closing a throttle upstream or downstream of the compressor the flow rate will change accordingly. This... | 5431 | How can flow in a centrifugal compressor at fixed conditions vary? |
2015-09-16T22:53:40.500 | <p>A motor gives its strength in N-cm or oz-in, but how do you know how much you require? I know you can just calculate the minimum torque you need to move the load, but is there a typical amount over that minimum that is standard? Like 20% or reaching a certain acceleration?</p>
<p>What I'm using a motor for is my e... | |electrical-engineering|stepper-motor| | <p>Without more details about your design, the dynamics of your mechanism, or your calculations, its virtually impossible to address your question with any certainty. </p>
<p>However, i offer some advice that may prove useful to you:</p>
<p>If affordable, I would use double the minimum holding torque needed for the ... | 5451 | How much stronger than the bare minimum should a motor be? |
2015-09-17T21:22:49.660 | <p>I'm working on analysis of a bridge wall-pier for dead and live loads. When modeling the pier in finite element software (LARSA), I'm running up against several modeling questions:</p>
<ol>
<li>Is it valid to model the wall as a single column element? (Going to a plate mesh seems like overkill for a run-of-the-mill... | |structural-engineering|bridges|finite-element-method| | <p>I'll go through your questions one by one:</p>
<ol>
<li><p>A simple model like you have shown is fine to get model loads. Once you get those loads, you can then use a more specific technique to design the pier. (strut and tie).</p></li>
<li><p>Rigid links are ok. Just make sure that you are capturing the various in... | 5462 | Simple Finite Element Modeling of Wall Piers |
2015-09-18T15:35:39.757 | <p>I am currently tinkering with typewriters and two things striked me when I started to read about their maintenance:</p>
<ol>
<li>They are supposed to run almost completely dry, except for a very tiny amount of lubricant at very specific points;</li>
<li>Gummy or sticky gunk buildup - usually due to over-oiling + du... | |mechanical-engineering|tribology| | <p>The best option would probably be "clock oil" which is intended to be long lasting, non-acidic, and (importantly) non-spreading. If you apply it in small enough quantities, it will stay where you put it, and not move around through capillary action.</p>
<p>Sewing machine oil is probably a reasonable alternative, bu... | 5467 | Which lubricant (oil or not) to use if I want to prevent sticky/gummy buildup? |
2015-09-20T09:37:06.603 | <p>For rectification I am given the following information</p>
<p>$x_e$ = 0.95</p>
<p>$x_f$ = 0.50</p>
<p>$x_b$ = 0.15</p>
<p>$v$ = 8</p>
<p>$q$ = 1.17</p>
<pre><code>**VLE Data**
x y
0.00 0.00
0.10 0.17
0.20 0.31
0.30 0.44
0.40 0.55
0.50 0.645
0.60 0.73
0.70 0.81
0.80 0.88
0.9... | |thermodynamics| | <p>Well a stage is an equilibrium stage ie. given some feed composition z, temperature and pressure, vapour of composition y goes up and liquid composition x goes down. </p>
<p>Whether you are calculating actual or theoretical stages, you will hardly ever get a whole number. If you look at the graph, last stage (where... | 5480 | McCabe Thiele - number of stages |
2015-09-21T11:22:14.297 | <p>A journal I am reading about circular hydraulic jumps provides the equation and I quote:</p>
<blockquote>
<p><span class="math-container">$H$</span> Depth after hydraulic jump, <span class="math-container">$h$</span> depth before hydraulic jump, <span class="math-container">$V$</span> velocity after hydraulic jump, ... | |mechanical-engineering|fluid-mechanics|mathematics| | <p>$F=\frac{dp}{dt}$ is, in some sense, a more fundamental expression of Newton's law than $F=ma$ because $F=ma$ doesn't allow for situations with changing mass. You can easily derive the second from from the former by using $p=mv$ which gives $F=m\frac{dv}{dt}=ma$. </p>
<p>Your question seems to be more about how t... | 5490 | Equating $\frac{dp}{dt}$ and $F$ at a hydraulic jump? |
2015-09-22T12:05:07.420 | <p>The following scenario:</p>
<p>I am tasked to design a 6.6m high reinforced concrete wall in an industrial building. We have a 10 ton Telehandler (telescopic loader) with 7m maximum reach, loading 1500kg loose material in a scoop.</p>
<p>I need to cater for a "runaway vehicle collision" where:</p>
<p>the vehicle ... | |civil-engineering|reinforced-concrete| | <p>In a situation like this you will need to resort to energy methods. Depending on how complicated you wanted to get you could do a dynamic calculation also.</p>
<p>I would recommend looking at the guidance in Eurocode 1991-1-7 (Accidental Actions). In particular look at Annex C which describes dynamic design for imp... | 5507 | Telehandler wall collision forces |
2015-09-23T03:59:12.370 | <p>I have a very basic understanding of how gears work, and while trying to learn more, I've run into a small point of confusion.</p>
<p>If a 2:1 gear ratio is achieved by having twice as many teeth on one gear than the other, then how are 250:1 ratios achieved? Certainly there aren't gears with 2500 teeth on one gear... | |mechanical-engineering|gears| | <p>Planetary Gear Sets can provide a high reduction in a small space. Also, they can be connected in a similar fashion to gear train to further increase the reduction. Also, one benefit is the output shaft is co-axial with the input shaft.</p>
| 5514 | How are high gear ratios achieved in a small space? |
2015-09-23T12:04:21.123 | <p>What would the ideal thickness of the dump trailer bed be, so it can withstand loading rock from a height of 1 meter?</p>
<p>The spacing of ribs is yet to be decided.</p>
<p>The goal is that the trailer be as light as possible, whilst being strong enough to withstand hauling rock every once in a while.</p>
| |mechanical-engineering|metals| | <p>See <a href="https://engineering.stackexchange.com/questions/5494/steel-selection-for-building-a-trailer">this similar-ish question</a>. The ideal thickness will be the thickness >= the thickness required to keep stresses below the yield strength of "the metal." </p>
<ol>
<li>Pick a metal, find its yield strength. ... | 5518 | What is the ideal metal sheet thickness used in a 1 tonne atv/tractor dump trailer? |
2015-09-23T13:11:17.030 | <p>I'm currently designing a small reinforced concrete bridge on private property. The project is in Scotland. </p>
<p>It's very small scale, a single lane, with a span of around 4.5m. Service life is taken as 120 years.</p>
<p>Using Eurocode design for standard road bridges seems far too over-the-top (there will no... | |civil-engineering|structural-engineering| | <p>I'm going to take a slightly unconventional approach, and suggest you design to an <em>assessment</em> standard; namely BD21/01<a href="http://www.standardsforhighways.co.uk/ha/standards/dmrb/vol3/section4/bd2101.pdf"> [pdf link]</a>.</p>
<p>My reasons are:</p>
<ol>
<li>It's a UK standard, and you're in the UK</li... | 5523 | Looking for a loading code for use in the design of a small scale private bridge? (4.5m span, one lane) |
2015-09-23T17:32:43.037 | <p>According to <a href="http://rads.stackoverflow.com/amzn/click/0962373109">Hoffman</a>, the standard $k-\epsilon$ turbulence model incorporates a two-layer approach (inner region and outer region formulations to reperesent mixing length) when it comes to regions adjacent to wall surface $(y^+ \approx 30 - 50)$. </p>... | |mechanical-engineering|fluid-mechanics|cfd|turbulence| | <p>There are two ways of "<em>wall treatment</em>" both feature two layers but at different $y^+$. The general idea is that the velocity gradients in the <a href="https://en.wikipedia.org/wiki/Boundary_layer" rel="nofollow noreferrer">boundary layer</a> are so high that one would need a very high number of grid cells i... | 5528 | Why does the standard $k-\epsilon$ model use zero equation models? |
2015-09-23T21:22:32.013 | <p>I would like to fold thin metal sheets to a particular angle. </p>
<p>For example: fold a 0.1mm thick steel strip of width 20mm and length 150mm to an angle of 45° along its length (10mm panels on each side of the fold).</p>
<p>I would like to keep the radius of the fold as small as possible, ideally on the order ... | |mechanical-engineering|metal-folding| | <blockquote>
<p>I would like to fold thin metal sheets to a particular angle. </p>
</blockquote>
<p>It sounds like you're looking for a <a href="https://www.northerntool.com/shop/tools/product_7825_7825" rel="nofollow noreferrer">sheet metal brake</a>.</p>
<p><a href="https://i.stack.imgur.com/B2zem.png" rel="nofol... | 5531 | Folding of thin gauge metal sheets |
2015-09-24T15:10:36.517 | <p>I am intending to construct a small pressure vessel. It needs to be around 7 centimeters in length and width and around 1-2 centimeters in depth. It must be capable of being pressurised to 300 psi with sufficient space to contain a small amount of liquid (say 5cc) </p>
<p><strong>Constraints</strong></p>
<ul>
<li>... | |mechanical-engineering|pressure|pressure-vessel| | <p>Sure. <a href="http://rads.stackoverflow.com/amzn/click/B0015V45F4" rel="nofollow">CO2 cartridges</a> are made of <a href="https://www.reddit.com/r/Blacksmith/comments/119rd7/co2_cartridges_as_a_metal_source/" rel="nofollow">steel</a> and hold <a href="https://www.physicsforums.com/threads/12g-co2-cartridge-energy-i... | 5539 | Is this pressure vessel feasible? |
2015-09-25T14:34:11.360 | <p>We have some metal parts in our machines, which are anodised aluminium. Those machines are due to be shipped to the customer in the near future, but I have noticed some pitting or slight rust developing on some of the anodised aluminium surfaces. I have tried cleaning it with 70% IMS, but to no avail (the surface is... | |materials|chemical-engineering|surface-preparation| | <p>Chuck is right that there could be some galvanic action contributing to your issue. One other possibility is that your aluminum has been contaminated with steel particles at some point. Your second picture does seem to clearly show rust, which wouldn't be happening if the metal was all aluminum. It's less clear what... | 5553 | Cleaning anodised aluminium |
2015-09-26T22:26:33.333 | <p>Say, in a firearm, after giving off a shot, if the barrel were to be closed off, does there exist a way to store some of it in an external pressure vessel, without requiring a mainly-external source of power and complex machinery?</p>
<p>Forgive the possibly stupid question, I'm a bit of a layman as far as engineer... | |pressure|combustion| | <p>Absolutely. There is a device called a bore evacuator which has been in service for a long time on large caliber guns. Its purpose is to draw combustion gas out through the muzzle after the shot cycle is over, so that said gas (which is usually toxic) doesn't flow backwards out the breech and into the crew compart... | 5560 | Is it possible to store leftover pressure from burning a propellant in a pressure vessel? |
2015-09-28T08:10:40.533 | <p>I've learned in school that pressure in water changes like</p>
<p>$$p(h) = \rho g h$$</p>
<p>where $h$ is depth in meters, $\rho$ is density (e.g. 1000 $\frac{\text{kg}}{\text{m}^3}$ for water) and $g$ is gravitation acceleration ($\approx 9.81 \frac{\text{m}}{\text{s}^2}$) and $p$ is the pressure in Pascal.</p>
... | |civil-engineering|pressure| | <p>In simple terms earth pressure is both very similar and very different. </p>
<p>The vertical earth pressure is given by:
Density x height x gravity.
Here the density depends on the material, which varies with type of soil.</p>
<p>The horizontal earth pressure is where it diverges from the simple water model. The p... | 5566 | How does pressure change with depth in earth? |
2015-09-28T13:58:53.050 | <p>The recent <a href="http://www.nature.com/news/the-science-behind-the-volkswagen-emissions-scandal-1.18426?WT.mc_id=SFB_NNEWS_1508_RHBox">Volkswagen pollution test cheating scandal</a> has shocked many people with its widespread extent as well as how it was hidden for so many years. </p>
<blockquote>
<p>Last year... | |automotive-engineering|product-testing|air-quality|emissions| | <p>Details have emerged in the German press that indicate this was known about in 2007 (<a href="http://blog.caranddriver.com/report-bosch-warned-vw-about-diesel-emissions-cheating-in-2007/" rel="nofollow">from German newspaper Bild am Sonntag, as translated by Automotive News</a>):</p>
<blockquote>
<p>According to ... | 5570 | How was Volkswagen able to trick the lab pollution test? |
2015-09-28T19:33:40.583 | <p>Take a hollow aluminium cylinder with outer radius $r$ and length $h$, capped with two circular endcaps. How thick does the aluminium have to be, that is what is the inner diameter of the cylinder, to withstand 1 atm on the outside and 0 mbar on the inside, without crumpling?</p>
| |materials|metals|geometry|vacuum|buckling| | <p>I found this formula <a href="http://www.eng-tips.com/viewthread.cfm?qid=91966" rel="nofollow">here</a>:</p>
<p>$$p_{crit}=\frac{2\,E\,t}{D}\left(\frac1{(n^2-1)\left(1+\left(\frac{2\,n\,L}{\pi\,D}\right)^2\right)^2}+\frac{t^2}{3(1-\nu^2)D^2}\left(n^2-1+\frac{2\,n^2-1-\nu}{\left(\frac{2\,n\,L}{\pi\,D}\right)^2-1}\ri... | 5576 | How thick does an aluminium vacuum cylinder have to be? |
2015-09-29T03:05:37.480 | <p>I´m developing a tool to generate an <a href="http://www.openfoam.com/" rel="nofollow noreferrer">openFoam</a> wind tunnel case of a wind turbine. I already have the blade geometry constructed, but I'm really new to CFD and parametric meshing. I found some articles where they mention a C topology to mesh the airfo... | |airflow|cfd|wind-power|meshing|wind-tunnels| | <p>I would recommend using third party software for meshing like gmsh, gambit or fluent where you can import your geometry, edit it, define the topology and get the mesh.
Gmesh is free while the rest are not.
You might be able to find many tutorials on meshing in these softwares on youtube</p>
| 5583 | Efficient 3D mesh topology for CFD simulation of turbine blade |
2015-09-29T13:25:58.347 | <p>My understanding so far is that a jump occurs when the Froude Number $\left(Fr=\frac{v}{\sqrt{2gh}}\right)$ of the radial flow falls with a decreasing velocity due to friction and viscosity; and the jump occurs at the critical point where $Fr=1$. However, I also learnt that the height of the jump is dependant on th... | |mechanical-engineering|fluid-mechanics|hydraulics| | <p>I am researching on this topic actually. Hydraulic jump is not an easy matter as it seems to be. the location of the jump also depends on the thickness after the jump. if you increase the height after the jump(for example, put a bump). the location of the jump will move upstream. it depends on a lot of parameters, s... | 5591 | What causes circular hydraulic jumps in kitchen sinks? |
2015-09-30T02:11:15.903 | <p>I am printing a wheel with a 2.5mm hole in the middle to accept a shaft of a motor with a set screw. The problem I am having is that the wheel is always wobbly when spinning (sometimes more, sometimes less without changing any parameters). Is there anything I can do to make this print as perfect as possible and prev... | |mechanical-engineering|3d-printing|prototyping| | <p>Also, the plastics used in most hobbyist printers are really not well suited to carrying any load and are usually too soft and flexible to machine properly. </p>
<p>However if you can find a piece of tube, either metal or rigid plastic, to fit the axle accurately, design the wheel bore so that the tube can be pres... | 5601 | How do you make a 3D print with an accurately aligned bore hole? |
2015-09-30T10:04:35.117 | <p>Instead of using an alternator to charge the battery, and a starter to start the engine, why not just put one electric motor which is always connected with the engine? When we want to start the motor, we supply electricity to it; and when the engine is started, it spins the motor to generate electricity and charge ... | |mechanical-engineering|electrical-engineering|electric-vehicles| | <p>One problem with generating electrical energy from a car engine is that the RPMs are constantly changing, and consequently the power output of an electrical generator would vary with engine speed. An alternator is very good at responding to these variations; the current in the rotor can be quickly adjusted to chang... | 5603 | Why not use just one electric motor in a car? |
2015-10-01T11:48:03.677 | <p>I am in the process of helping my son design a sort of model of the <a href="http://www.bloodhoundssc.com/project/car" rel="nofollow noreferrer">Bloodhound SSC car</a> for his school project, using balsa wood, model aircraft wheels, etc... It doesn't have to a like of like, but vaguely resemblant so that you can tel... | |valves|propulsion|compressed-gases| | <p>In the end, I decided to use an <a href="http://www.estesrockets.com/rockets/engines/mini/1502-1-4a3-3t" rel="nofollow noreferrer">Estes 1/4A3-3T rocket engine</a> (the smallest one they do):</p>
<p><a href="https://i.stack.imgur.com/Xoy8X.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Xoy8X.jpg... | 5621 | Valve for mini CO2 gas canister? |
2015-10-01T23:21:58.187 | <p>So, I must do the following conversion from my engineering textbook: </p>
<p>$0.155 \frac{m^2 * ^{\circ} C}{W}$ to $\frac{^{\circ}F * ft^2 * hr}{Btu}$</p>
<p>I can get as far as: </p>
<p>$0.155 \frac{m^2 * ^{\circ} C}{W} * (\frac{1 ft}{0.3048 m})^{2} * \frac{1 W}{3.4123 \frac{Btu}{h}} = .39108 \frac{ft^2 * ^{\ci... | |heat-transfer| | <p>I suspect you're converting a value of <a href="https://en.wikipedia.org/wiki/R-value_(insulation)" rel="nofollow">thermal resistance</a>, which means that the temperature units represent a temperature <em>difference</em>, rather than specific values of temperature. In this case, the constant 32 drops out of the co... | 5625 | Convert 1 one compound unit to another involving temperature |
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