tag:blogger.com,1999:blog-2676899947385060142024-02-20T20:40:59.543-08:00Engineering SimulationWe plan to cover a wide variety of topics on engineering simulation, mainly divided into physics based (FEA/CFD) and Software based (ANSYS products). We hope our experiences can help you "Engineer, Simulate and Innovate".SIMUTECH-NYhttp://www.blogger.com/profile/09561308028653715021noreply@blogger.comBlogger14125tag:blogger.com,1999:blog-267689994738506014.post-19326192213369960522011-09-05T20:06:00.000-07:002011-09-05T20:06:54.776-07:00Cloud this.. Cloud that... What about Cloud Simulations? Cloud FEA/CFD?Firstly, sorry for the long silence and no recent posts in a while. Too many things happened...with the latest being me under the surgeon's needle. I had a cervical disc hernia and it was so bad that no simulation could help ;) I needed to undergo surgery. I am slowly recovering now... but need your help on a question that has been on my mind lately:<br />
<br />
Do you think Cloud FEA/CFD will actually see the daylight? I have created a poll on this recently and already have seen some great comments and interest on this topic. I would love to hear from you! Here you go:<br />
Poll: <a href="http://linkd.in/qwh6pu">Cloud Computing for FEA/CFD? Do you like it?</a><br />
<br />
Once I have this poll completed (in 28 days from today), I plan to update this post (or publish a new post) with a final report and analysis of what the simulation community thinks. <br />
<br />
I am really interested in hearing what you have to say!Rob Atchutunihttp://www.blogger.com/profile/11384621959808576485noreply@blogger.com1tag:blogger.com,1999:blog-267689994738506014.post-15627994167437883402010-10-26T10:24:00.000-07:002010-11-05T06:40:49.631-07:00The dreaded question: Is the solution converged?<!--[if gte mso 9]><xml> <o:officedocumentsettings> <o:relyonvml/> <o:allowpng/> </o:OfficeDocumentSettings> </xml><![endif]--><!--[if gte mso 9]><xml> <w:worddocument> <w:view>Normal</w:View> <w:zoom>0</w:Zoom> <w:trackmoves/> <w:trackformatting/> <w:punctuationkerning/> <w:validateagainstschemas/> <w:saveifxmlinvalid>false</w:SaveIfXMLInvalid> <w:ignoremixedcontent>false</w:IgnoreMixedContent> <w:alwaysshowplaceholdertext>false</w:AlwaysShowPlaceholderText> <w:donotpromoteqf/> <w:lidthemeother>EN-US</w:LidThemeOther> <w:lidthemeasian>X-NONE</w:LidThemeAsian> <w:lidthemecomplexscript>X-NONE</w:LidThemeComplexScript> <w:compatibility> <w:breakwrappedtables/> 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name="Bibliography"> <w:lsdexception locked="false" priority="39" qformat="true" name="TOC Heading"> </w:LatentStyles> </xml><![endif]--><!--[if gte mso 10]> <style> /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin-top:0in; mso-para-margin-right:0in; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0in; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin;} </style> <![endif]--> <p class="MsoNormal">This is perhaps the most asked and important, yet dreaded, question in CFD analysis.<span style=""> </span>Some people will say “yes, the residuals were XXXX” just to dismiss the question.<span style=""> </span>But is the answer that simple?<span style=""> </span>Unfortunately it is not. <span style=""> </span>That is just one measure we should use in determining whether a solution is converged.<span style=""> </span>The definition of convergence is, in a mathematical sense, the approach towards a definite point.<span style=""> </span>Basically we are trying to get our numerical solution sufficiently close (accurate) to a definite point (exact solution). <span style=""> </span>To help understand what convergence is in practice, we must step back and look at what we are trying to accomplish in modeling.</p> <h2>Overview</h2> <p class="MsoNormal">The goal of CFD modeling is to obtain virtual flow field which represents the physical situation.<span style=""> </span>In traditional CFD modeling, the first step in this process is to create a grid that represents the physical domain.<span style=""> </span>Once the mesh has been created, the boundary conditions and other physics models are applied to complete the computational model.<span style=""> </span>The computational model is then solved.<span style=""> </span>As analysts we must think of the convergence ramifications when executing both the meshing and solving steps.</p> <h3>Meshing Convergence</h3> <p class="MsoNormal">Typically when people speak of meshing in regards to convergence they are considering refining the mesh in certain areas to reduce the residuals in this area.<span style=""> </span>This is a technique that is commonly used, but is not what we will be discussing here.</p> <p class="MsoNormal">However when you consider what we are representing the continuous flow field by using discrete approximations, we must ensure that our grid is sufficient fine—that it approximates, to sufficient accuracy, the physical flow field.<span style=""> </span>Typically this is done by investigating successively finer and finer meshes to show that the solution converges to a fixed limit.<span style=""> </span>Many people refer to this as “grid independence,” but in reality is it is convergence of the discrete computational model to the continuous physical system.</p> <h3>Solver Convergence</h3> <p class="MsoNormal">When monitoring a solver run, people generally just examine the residuals.<span style=""> </span>Residuals are a measure of change of the solution between iterations at it tends towards the discretitized solution.<span style=""> </span>Different solvers specify different levels at which the residuals must meet to be a “converged” solution.<span style=""> </span>However these are just a general rule-of-thumb.<span style=""> </span>In general the residuals can reduce to a certain level but the flow field may not have reached an iteration independent solution.<span style=""> </span>Conversely the residuals <i style="">could</i> converge to a level higher than the specified tolerance yet could reach a fixed solution for the quantities of interest (although it we would still have to check the mesh convergence of this solution).<span style=""> </span>Because of this it is typically recommended to monitor several relevant quantities during the solution phase to make sure these converge in addition to the residuals.</p> <p class="MsoNormal">Of course the question that naturally arises is: <i>What are the variables we should monitor?<span> </span></i>This is where our years of schooling and experience come into play.<span style=""> </span>In general we want to monitor variables that are relevant for the problem we are solving.<span style=""> </span>For instance for many problems we are concerned with the pressure drop through the domain so we should monitor this quantity as the solution progresses.<span style=""> </span>If we were investigating the flow over an airplane it would be useful to monitor the lift and drag.<span style=""> </span>If we were to model a heat exchanger, it would be useful to monitor the temperatures leaving the domain and the heat flux through the various surfaces. <span style=""> </span>So there is no single monitor that that is sufficient to determine convergence for all problems.<span style=""> </span>We must use our engineering judgment to determine the most useful quantities to monitor.</p> <h2>Summary</h2> <p class="MsoNormal">In summary, answering whether a solution is a converged solution is a complex answer.<span style=""> </span>It is a question that, as a modeler, we must always have in the back of our mind.<span style=""> </span>When we are developing a concept for the model in our mind we should be thinking about the variables we should monitor.<span style=""> </span>When developing a mesh we should be thinking about developing another to test mesh convergence (grid independence).<span style=""> </span>When crunching the numbers, we want to monitor both the residuals and the monitor points we have created.<span style=""> 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mso-para-margin-top:0in; mso-para-margin-right:0in; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0in; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin;} </style> <![endif]--> </p><p class="MsoNormal">This discussion is not meant to be an end-all be-all in regards to convergence.<span style=""> </span>In fact entire books have been written about the subject, so I will not claim to have described in completely in this blog.<span style=""> </span>I just wanted to present some questions that we, as modelers, should always be considering when <b style=""><i style="">developing and solving</i></b> our models.<span style=""> </span>We should understand the true nature of convergence, feel confident when asked whether our 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mso-para-margin-bottom:10.0pt; mso-para-margin-left:0in; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin;} </style> <![endif]-->Nicholas Lynnhttp://www.blogger.com/profile/00807917230282580239noreply@blogger.com0tag:blogger.com,1999:blog-267689994738506014.post-26086364648981778432010-08-12T11:50:00.001-07:002010-11-05T06:43:48.763-07:00Get started with Entry-Level HPC and ANSYS<p>Ansys Mechanical has supported and been tightly integrated in the <a href="http://www.ansys.com/products/hpc/features.asp">High Performance Computing (HPC) </a>arena for many years and many versions. However, I've seen a quite some hesitation from users and companies to introduce HPC into their engineering simulation environment. Reasons generally come down to cost and complexity.</p><p>True, setting up a central cluster with many nodes is costly. The complexity of configuring it, optimizing it (for Ansys and the other array of applications that will share it), and maintaining it can be daunting.<br />However, I've worked with a large number of customers recently getting into "entry level HPC". Even though our primary workstations are getting more powerful (6-core processors are here, 12-core processors are coming soon) and we're able to run larger jobs on them, there's still a need to offload the job to an HPC environment. Let's face it - we've all closed our emails, web browsers, and office apps during those painfully slow solves to try a free up just a few more Mb's of ram, hoping the run won't crash.</p><p>What I consider "entry-level" is to have at minimum a 2nd workstation (or server), can be high or low end, expensive with lots of CPU/RAM/disk space, or inexpensive (assembled from all those spare components laying around). The idea here is to try HPC - a simple setup to send a solve over to a 2nd computer. If you have the compute power in your 2nd computer for high-end analysis, great! If not, get something set up to at least introduce yourself to the concepts and see how it works.</p><p>I recently worked with a customer who purchased a very high-end single-node compute server. Why just one? Simple answer... cost constraints. We were able to set it up, get the Ansys users up and running and accustomed to HPC (and adopting its advantages) and then when the budget allowed, the customer added additional compute nodes to the existing cluster.</p><p>Off-loading the solve can be done a number of ways, including Remote Solve Manager (RSM), batch scripts, Distributed Ansys, even simply using Remote Desktop. (Great discussion points for future topics!) This simple "entry level HPC" setup can free up your primary workstation during those intensive solves. It is amazingly convenient to build a model on my laptop, hit "Solve", shut down my laptop, go home, and come in the next morning with a fully solved model!</p><div>I love to hear your thoughts!</div><div><br /></div>Jason.<div></div>Jason Zbickhttp://www.blogger.com/profile/06162718813708532112noreply@blogger.com4tag:blogger.com,1999:blog-267689994738506014.post-6857980970267932472010-08-10T07:13:00.000-07:002010-11-05T06:44:16.269-07:00When NOT to use comparative Charts for CFD softwareRecently there was an article in <a href="http://www.deskeng.com/">Desktop Engineering</a> where it compared several commercial CFD products in the marketplace today. I am all for this! Sure! What shocked most in the industry who read this article was how terribly inaccurate this was and how biased it was towards one single product. I wish it was featured in a "marketing section" vs. an engineering magazine such as Desktop Engineering. In this rebuttal article from Mentor Graphics (Dr. J), the author claims to even have received an apology from Desktop Engineering: "<span class="Apple-style-span" style="font-family:Arial, 'Lucida Grande', 'Lucida Sans Unicode', Verdana, sans-serif;"><span class="Apple-style-span" style="font-size:small;">To their credit, when we notified them, Desktop Engineering apologised to us, sent out an apology to all of its readership and promised that such a chart would not go out again."</span></span><div><br /></div><div>Here is a direct link to the rebuttal article: "<a href="http://www.mentor.com/products/mechanical/blog/post/lies-damned-lies-and-cfd-comparison-charts-part-i-5e5ab4d8-530a-4c48-bdce-446eb20ec249">Lies, Damned Lies, and "CFD Comparison Charts" - Part I</a>" You can also see the original "comparative charts" here as reference.</div><div><br /></div><div>In this article, Dr. J aptly points out the one-sided take by CF Design. Though he mainly talks about improper comparison of <a href="http://www.mentor.com/">Mentor Graphics</a>' FloEFD, there are several inaccuracies on this comparative chart when it comes to <a href="http://www.ansys.com/">ANSYS</a> CFD products (FLUENT, CFX) as well. Any current FLUENT and CFX user can testify to these inaccuracies! Dr. J, the count on "misleading statements" in the DE article are well beyond 27 if we include the ANSYS CFD products. I still don't believe this article ever got published! It begs more research and accurate information.</div><div><br /></div><div>Having been in the simulation industry (FEA, CFD) for close to a decade, this false comparative chart regarding CFD products is really appalling, especially coming from a magazine such as DE. Negative marketing campaigns are not a good idea. If you do them, please know the facts about competition first! And then do not do it as a "guide" to helping engineers decide on what CFD code to chose!</div><div><br /></div><div>Update: Folks from Blue Ridge Numerics have responded on LinkedIN forums on this and seems like they are working on it. Good to know:) You can follow their comments here: <span class="Apple-style-span" style="font-family: arial, sans-serif; font-size: small; color: rgb(14, 119, 74); line-height: 15px; ">www.<b>linkedin</b>.com/<b>group</b>s?home=&gid=66032</span></div><div><br /></div><div>I look forward to your feedback.</div>Rob Atchutunihttp://www.blogger.com/profile/11384621959808576485noreply@blogger.com0tag:blogger.com,1999:blog-267689994738506014.post-81272800431352863522010-07-19T10:18:00.000-07:002010-07-21T11:10:23.128-07:00Fracture Mechanics in Turbine Blade Analysis<div style="text-align: left;">I would like to take some time to start a discussion on fracture mechanics.<span style="mso-spacerun:yes"> </span>The calculations for a basic fracture mechanics analysis are fairly simple, but they can play a very important role in failure analyses.<span style="mso-spacerun:yes"> </span>This topic comes up quite frequently in turbine blade work.</div> <p class="MsoNormal"><o:p> </o:p></p> <p class="MsoNormal">So what is fracture mechanics?<span style="mso-spacerun:yes"> </span>In short it’s a method of determining the time it takes a crack in a part to grow to failure under a specific loading condition.<span style="mso-spacerun:yes"> </span>The crack growth stage of fatigue can make up a significant portion of a products life.<span style="mso-spacerun:yes"> </span>This happens in products ranging from bicycles, to airplanes, to steam turbine blades.<span style="mso-spacerun:yes"> </span></p> <p class="MsoNormal"><o:p> </o:p></p> <p class="MsoNormal">At the heart of fracture mechanics is the stress intensity factor K defined as:</p><p class="MsoNormal"><span class="Apple-style-span" style="color: rgb(0, 0, 238); -webkit-text-decorations-in-effect: underline; "><img src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj3ocuPhyphenhyphenO6emnsRDlbUG2GExmHSvn67llD_R0oJBawYcPH4GnqmdAgWSrX4Vm4mJFz-8qL57l9btt7r-V_reqQ_j2B2cl3bIhWcvsB9UEh07GaXGTGweHMt5zU8tn062nBvxKjL0S1O4I/s320/FM1.jpg" border="0" alt="" id="BLOGGER_PHOTO_ID_5495669947999819458" style="display: block; margin-top: 0px; margin-right: auto; margin-bottom: 10px; margin-left: auto; text-align: center; cursor: pointer; width: 255px; height: 80px; " /></span></p> <p class="MsoNormal">Where:</p> <p class="MsoNormal"><o:p> </o:p></p> <p class="MsoNormal">f(g) is a correction factor based on crack geometry.<span style="mso-spacerun:yes"> </span>This value tends to be between 1 and 1.4.<span style="mso-spacerun:yes"> </span></p> <p class="MsoNormal">a is the crack length</p> <p class="MsoNormal"><span style="font-family:Symbol;">s</span> is the remote stress</p> <p class="MsoNormal"><o:p> </o:p></p> <p class="MsoNormal">Fatigue crack growth is divided into 3 regions as shown in the figure below.<span style="mso-spacerun:yes"> </span>In this figure, crack growth rate (da/dN) is plotted on the vertical axis in log scale and <st1:place st="on"><st1:placename st="on">Stress</st1:placename> <st1:placename st="on">Intensity</st1:placename> <st1:placetype st="on">Range</st1:placetype></st1:place> (<span style="font-family:Symbol;">D</span>K=K<sub>max</sub>-K<sub>min</sub>) is plotted on the horizontal axis in log scale.<span style="mso-spacerun:yes"> </span>Region I is associated with crack threshold effects (the area where a crack first begins to grow), Region II is an area of linear growth (<st1:city st="on"><st1:place st="on">Paris</st1:place></st1:city> region), and Region III exhibts extremely high/unstable crack growth. </p> <p class="MsoNormal"><o:p> </o:p></p> <p class="MsoNormal" align="center" style="text-align:center"><span class="Apple-style-span" style="color: rgb(0, 0, 238); -webkit-text-decorations-in-effect: underline; "><img src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhRkXnMjXsKj2_GhE34EJgVtjlLJll4vaF5v_zXQEygPZ_uOQMUwxHFtitvf7BEotUx2Axa57CeWAjOJHHkAvKTvcQ9FwwOgax_MbPU-rZSeV3a-FSfIH8XXiaesg-7nvZRfWLPFchA614/s320/DaDn.jpg" border="0" alt="" id="BLOGGER_PHOTO_ID_5495679743891303970" style="display: block; margin-top: 0px; margin-right: auto; margin-bottom: 10px; margin-left: auto; text-align: center; cursor: pointer; width: 320px; height: 242px; " /></span></p> <p class="MsoNormal" align="center" style="text-align:center"><o:p> </o:p></p> <p class="MsoNormal">For design purposes the focus is on Regions I and II. Crack growth is so fast in Region III that it does not have a significant effect on the total crack propagation life.<span style="mso-spacerun:yes"> </span>Noted on the graph is <span style="font-family:Symbol;">D</span>K<sub>th</sub>, the threshold stress intensity which is determined through testing.<span style="mso-spacerun:yes"> </span>This value marks the beginning of crack growth.<span style="mso-spacerun:yes"> </span>K<sub>c</sub> is the critical stress intensity and values higher than this predict fracture.</p> <p class="MsoNormal"><o:p> </o:p></p> <p class="MsoNormal">When performing a turbine blade analysis we often want to determine if a dynamic stress condition is severe enough to grow a crack (Refer to previous posts on blade analysis).<span style="mso-spacerun:yes"> </span>To determine that, we run a fracture mechanics analysis for Region I of the above graph.<span style="mso-spacerun:yes"> </span>If the stress condition and initial flaw size is not capable of growing a crack then we need not be concerned with removing the near resonant condition.</p> <p class="MsoNormal"><o:p> </o:p></p> <p class="MsoNormal">This analysis starts with calculating the stress intensity factor range:</p> <p class="MsoNormal"><o:p> </o:p></p> <p class="MsoNormal" align="center" style="text-align:center"><span class="Apple-style-span" style="color: rgb(0, 0, 238); -webkit-text-decorations-in-effect: underline; "><img src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEijpmQYe7RoBnQ-PqifZRFc3fYopq-MMSy5A6oMdgwvrkoVoDgpX9iO0wuArtdAgRBck7XQ3DdtiOyL631rN02xhzsNLZlKqggLxDPquche-dLNQDgYvSho0fr5N7ePEsW76sWzOdZHFz4/s320/FM2.jpg" border="0" alt="" id="BLOGGER_PHOTO_ID_5495680065759016162" style="display: block; margin-top: 0px; margin-right: auto; margin-bottom: 10px; margin-left: auto; text-align: center; cursor: pointer; width: 320px; height: 42px; " /></span></p> <p class="MsoNormal"><span style="mso-spacerun:yes"> </span></p> <p class="MsoNormal">In the case of an edge crack on a turbine blade airfoil the a correction factor f(g)=1.12 is typically used. <span style="font-family:Symbol;">Ds</span> is the stress range, or dynamic stress for turbine blades (again refer to my last post on dynamic stress analysis).<span style="mso-spacerun:yes"> </span>If <span style="font-family:Symbol;">D</span>K is greater than <span style="font-family:Symbol;">D</span>K<sub>th</sub>, then a crack will propagate under the given loading condition.</p> <p class="MsoNormal"><o:p> </o:p></p> <p class="MsoNormal">One other thing to consider is the R ratio.<span style="mso-spacerun:yes"> </span>Test results for <span style="font-family:Symbol;">D</span>K<sub>th</sub> values are very dependant on the conditions which they were tested at.<span style="mso-spacerun:yes"> </span>A particular <span style="font-family:Symbol;">D</span>K<sub>th</sub> value will only apply to a loading condition that has the same R ratio as the test.<span style="mso-spacerun:yes"> </span>The R ratio calculation is shown below:</p> <p class="MsoNormal"><o:p> </o:p></p> <p class="MsoNormal" align="center" style="text-align:center"><span class="Apple-style-span" style="color: rgb(0, 0, 238); -webkit-text-decorations-in-effect: underline; "><img src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh8GoxF207gWXFBsHTynznakyZyWeFO5o3TUeehR3L2kj9s4FADNTQZf8xRku708XyoljXn-1Rdi4abTIAOXxo1YCFprsjNgTSfX_QKnsUpKb2ojW97aQanIe0gux76TcJdageZ2t66hGo/s320/FM3.jpg" border="0" alt="" id="BLOGGER_PHOTO_ID_5495680393871185842" style="display: block; margin-top: 0px; margin-right: auto; margin-bottom: 10px; margin-left: auto; text-align: center; cursor: pointer; width: 200px; height: 114px; " /></span></p> <p class="MsoNormal"><o:p> </o:p></p> <p class="MsoNormal">Where <span style="font-family:Symbol;">s</span><sub>m</sub> is the mean steady stress and <span style="font-family:Symbol;">s</span><sub>d</sub> is the alternating or dynamic stress.<span style="mso-spacerun:yes"> </span>If the R ratio for the <span style="font-family:Symbol;">D</span>K<sub>th</sub> test is different than calculated above, the <a name="OLE_LINK2"></a><a name="OLE_LINK1"><span style="mso-bookmark:OLE_LINK2"><span style="font-family:Symbol;">D</span>K<sub>th</sub></span></a> will need to be adjusted to account for the difference.<span style="mso-spacerun:yes"> </span>One common method for the compensation of <span style="font-family:Symbol;">D</span>K<sub>th </sub>is <st1:city st="on"><st1:place st="on">Walker</st1:place></st1:city>’s Equation:</p> <p class="MsoNormal"><o:p> </o:p></p> <p class="MsoNormal" align="center" style="text-align:center"><span class="Apple-style-span" style="color: rgb(0, 0, 238); -webkit-text-decorations-in-effect: underline; "><img src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgEXfWVrIK8X6Ljy8SyxZrhtyNBu1RioclaonZItEWUuMRr3dA-f6-y-6K6pbB_6WCEKo-qG1OWyXA0cxITpGdKu_nt7KRzPUeql1xGaNIw_EYNAoen0hhBQk-2Yj8tGAxm4qDbQBbwwbw/s320/FM4.png" border="0" alt="" id="BLOGGER_PHOTO_ID_5495682145169733826" style="display: block; margin-top: 0px; margin-right: auto; margin-bottom: 10px; margin-left: auto; text-align: center; cursor: pointer; width: 227px; height: 100px; " /></span></p> <p class="MsoNormal"><o:p> </o:p></p> <p class="MsoNormal">Where <a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj9_w7ARThhdfT0uv7pAcu7y40eDEWMazMJFYMnTDGXFUJWxuQiT0f1XsokCRFtIMi-Cc3tCcExIgUyzihlCQUqvKYVRvfCcc50MAKCzYBzFFyR6t21lIcHyGxCApQzEepP0TTLtFBc8AU/s1600/FM5.png"><img src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj9_w7ARThhdfT0uv7pAcu7y40eDEWMazMJFYMnTDGXFUJWxuQiT0f1XsokCRFtIMi-Cc3tCcExIgUyzihlCQUqvKYVRvfCcc50MAKCzYBzFFyR6t21lIcHyGxCApQzEepP0TTLtFBc8AU/s320/FM5.png" border="0" alt="" id="BLOGGER_PHOTO_ID_5495682686549191490" style="cursor: pointer; width: 47px; height: 38px; " /></a> is the value at R=0, <span style="font-family:Symbol;">g</span> is a material constant and is typically between 0.3 and 1.<span style="mso-spacerun:yes"> </span>Steels are typically around 0.5.<span style="mso-spacerun:yes"> </span>Using this relationship, and assuming that <a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj9_w7ARThhdfT0uv7pAcu7y40eDEWMazMJFYMnTDGXFUJWxuQiT0f1XsokCRFtIMi-Cc3tCcExIgUyzihlCQUqvKYVRvfCcc50MAKCzYBzFFyR6t21lIcHyGxCApQzEepP0TTLtFBc8AU/s1600/FM5.png"><img src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj9_w7ARThhdfT0uv7pAcu7y40eDEWMazMJFYMnTDGXFUJWxuQiT0f1XsokCRFtIMi-Cc3tCcExIgUyzihlCQUqvKYVRvfCcc50MAKCzYBzFFyR6t21lIcHyGxCApQzEepP0TTLtFBc8AU/s320/FM5.png" border="0" alt="" id="BLOGGER_PHOTO_ID_5495682686549191490" style="cursor: pointer; width: 47px; height: 38px; " /></a> is a constant, you can calculate the <span style="font-family:Symbol;">D</span>K<sub>th</sub> value for any R ratio.</p> <p class="MsoNormal"><o:p> </o:p></p> <p class="MsoNormal">Thanks for reading, <span style="mso-spacerun:yes"> </span></p><p></p>MIKESOBOLhttp://www.blogger.com/profile/02272786154679200185noreply@blogger.com1tag:blogger.com,1999:blog-267689994738506014.post-11944145704532533362010-06-15T20:18:00.000-07:002010-06-15T21:26:12.475-07:00Do we really need training if the software is so easy?<div>Firstly, I want to say sorry for the long absence from this blog. I was finishing up my MBA from <a href="http://www.simon.rochester.edu/index.aspx">Simon School of Business, University of Rochester</a>. Thank you for all those who supported me during the past 2 years. A big thank you!<br /><div><br /></div><div>Recently I had a very interesting phone discussion on "Training" for simulation software (ANSYS, Moldflow etc.). The question this young gentleman asked me was "<i>All the simulation software firms claim that their software is really easy to use. But then they suggest 2-5 days of training! Why this mismatch?</i>"</div><br /><div><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjBaEW3SLhx16kJM-MMdEZhDLS5amDW40jJlW1FLhSvTgAqos16bhsVuLn3cRmLPa7ax_iZ3NTLGuv6Cmy6iQ97QvNBATGeDpaAhr5aaCbPo1LGdZqwasdRgEoGG3_7U_WexkT38_Zs_PbN/s1600/ansys_training.gif"><img style="MARGIN: 0px 0px 10px 10px; WIDTH: 200px; FLOAT: right; HEIGHT: 88px; CURSOR: hand" id="BLOGGER_PHOTO_ID_5483222179102399858" border="0" alt="" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjBaEW3SLhx16kJM-MMdEZhDLS5amDW40jJlW1FLhSvTgAqos16bhsVuLn3cRmLPa7ax_iZ3NTLGuv6Cmy6iQ97QvNBATGeDpaAhr5aaCbPo1LGdZqwasdRgEoGG3_7U_WexkT38_Zs_PbN/s200/ansys_training.gif" /></a></div><div>This question really intrigued me and I have heard several versions of this question in the past 9 years of my sales career. So, I thought I would put out my thoughts on this topic and also get some feedback from you guys on this. Let us see some concepts leading to such a question on training:</div><div><br /></div><div><b>1. "Yes! The software is easy": </b>Most of the software today is far more easier to use than it ever was before. <a href="http://www.simutechgroup.com/Simulation_Software/ansys-software/ansys-product-overview.html">ANSYS Workbench</a> has changed the paradigm on the once clumsier and "specialists only" fea software. But has the ease of use of software really eliminated the need for training? The ease of use has certainly helped analysts do more analyses and more efficiently and also lowered the "barriers to entry" to some extent. Students right out of school now are getting employed as full-time analysts. Some pundits may claim that "easier" software still do not have all the bells and whistles needed and I may give it some merit. But for most analysts, a easy to use simulation user interface such as ANSYS Workbench is just fine! But that still mean one doesn't need <a href="http://www.simutechgroup.com/ansys-training.html">ANSYS training</a> atall?</div><br /><div><b>2. "I can learn it on my own":</b> I have heard this several times as well and this is true to some extent as well. Most of the simulation software today is at a point where one can install it and start using it right away with very little effort. And the in-built tutorials will probably be just enough to get you there. But then why a formal training?</div><br /><div><b>3. "In-house experts are my gurus":</b> Several larger firms have already established in-house experts who are probably well suited to teach most of the fea courses out there today using the software of their choice. And the newbie analyst can probably use the aide of some perseverance and in-house guru expert can probably get there too....<br /></div><div><br /></div><div>So, that being said, then why pay for formal training?<br /></div><div><b><br /></b></div><div><b>1. Makes you an efficient user</b> (I did not say flawless user):</div><div>While it is true that the software is easy today, a formal training will give you a good understanding of most of the quirks and enhance your familiarity with the product in a systematic way. Within 2 days or so, you will know where most of the buttons are, how the product works, what is behind all that math and matrices, what solver to use and when to use (and also when not to use) and most importantly gives you direct hands-on exposure under experts guidance. By the time you are back at work ready to use the software, you will be able to "hit the ground" running with the software. You will know atleast how to set-up your own models, mesh them and solve it (doesn't guarantee you will do it right though, that is where your 2 yrs/4yrs etc. of education or years of experience comes handy).</div><br /><div><b>2. It gives you a jump-start:</b></div><div>You sure can learn it on your own. And believe me, most of what you learn about the software, it actually will be learnt on your own (over years). The training only gives you a jump-start to get you there quicker.</div><br /><div><b>3. Makes your co-workers more efficient:</b></div><div>Training makes life for your "in-house gurus" much better. Now instead of asking "What is this button?", you will now ask "Does an axi-symmetric model make more sense for this? Can I use a submodel for this?" to "Shall I use Anand's model or Neo-Hookean?" You will make your guru's time much more efficient!</div><br /><div><b>4. Improves your ROI on simulation software itself!</b></div><div>Formal training surely enhances your chances of getting a better Return on your Investment on your software expenditure! Yep, you will now be able to use the software better, run more analyses and hopefully save millions for your firm (for which they bought the software in the first place).</div><div><br /></div><div>I have also heard some other benefits over years such as "Great to know the teachers and now I have an outside resource available", "I wouldn't have been this diligent to do this in just 2 days or even few months", "I needed it for <a href="http://www.sti-tech.com/sti/nys_pe_credit.html">NY PE Credits</a>" and "I just needed to get away from work!"</div><div><br /></div><div>However, now that you may be a little more convinced on the value of training, end of the day, personal motivation and dedication goes a lot farther. Training is just a drop in the ocean!</div><div><br /></div><div>I am eager to hear your feedback (even if you agree or disagree, I want to hear it). </div><div><br /></div><div>Rob.</div><br /><div></div></div>Rob Atchutunihttp://www.blogger.com/profile/11384621959808576485noreply@blogger.com10tag:blogger.com,1999:blog-267689994738506014.post-989255933492515842010-04-29T12:36:00.000-07:002010-05-03T10:44:22.204-07:00Turbine Blade Dynamic Stress Analysis<div style="text-align: left;"><span class="Apple-style-span" style="font-family:inherit;">Here is the second installment on our turbine blade analysis discussion. (Part one is here: <a href="http://simutechny.blogspot.com/2010/02/turbine-blade-modal-analysis.html">T<span id="goog_1372078367"></span>urbine Blade Modal Analysis</a>)</span><br /><span class="Apple-style-span" style="font-family:inherit;">This time I will focus on a dynamic stress analysis. Once you have created the interference diagram that was discussed in my last post, you will be able to identify conditions where resonance may occur. Typically I find any case where the resonant condition is less than 3% different from the forcing frequency (impulse line on interference diagram). I then run a dynamic stress analysis on each of those conditions using </span><a href="http://www.sti-tech.com/sti/bladest.html"><span class="Apple-style-span" style="font-family:inherit;">BLADE</span></a><span class="Apple-style-span" style="font-family:inherit;">.</span><br /><br />Resonant conditions were covered in my last post, but I think it is important enough to summarize it here. The dynamic amplitude and stress response of a structure depends on the following factors:</div><div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in; margin-left: .3in; margin-right: 0in; margin-top: 0in; mso-list: l0 level1 lfo1; tab-stops: list .3in; text-indent: -.3in;"><span class="Apple-style-span" style="font-family:inherit;">1.</span><span style="font: normal normal normal 7pt/normal 'Times New Roman';"><span class="Apple-style-span" style="font-family:inherit;"> </span></span><span class="Apple-style-span" style="font-family:inherit;">The natural frequencies of the system<o:p></o:p></span></div><div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in; margin-left: .3in; margin-right: 0in; margin-top: 0in; mso-list: l0 level1 lfo1; tab-stops: list .3in; text-indent: -.3in;"><span class="Apple-style-span" style="font-family:inherit;">2.</span><span style="font: normal normal normal 7pt/normal 'Times New Roman';"><span class="Apple-style-span" style="font-family:inherit;"> </span></span><span class="Apple-style-span" style="font-family:inherit;">The damping properties<o:p></o:p></span></div><div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in; margin-left: .3in; margin-right: 0in; margin-top: 0in; mso-list: l0 level1 lfo1; tab-stops: list .3in; text-indent: -.3in;"><span class="Apple-style-span" style="font-family:inherit;">3.</span><span style="font: normal normal normal 7pt/normal 'Times New Roman';"><span class="Apple-style-span" style="font-family:inherit;"> </span></span><span class="Apple-style-span" style="font-family:inherit;">The forcing amplitudes or stimulus ratio, defined as the ratio of the dynamic forces to the static steam loads on the blade<o:p></o:p></span></div><div class="MsoNormal" style="margin-left: .3in; mso-list: l0 level1 lfo1; tab-stops: list .3in; text-indent: -.3in;"><span class="Apple-style-span" style="font-family:inherit;">4.</span><span style="font: normal normal normal 7pt/normal 'Times New Roman';"><span class="Apple-style-span" style="font-family:inherit;"> </span></span><span class="Apple-style-span" style="font-family:inherit;">The phase angles, defined by the harmonic content (nodal diameter) of the modes.<o:p></o:p></span><br /><span class="Apple-style-span" style="font-family:inherit;"><br /></span> </div><div class="MsoNormal" style="text-align: justify;"><span class="Apple-style-span" style="font-family:inherit;">The steam flow field is non-uniform due to nozzle asymmetry and irregular spacing geometry within the steam flow path. Other factors may include geometry variations of wakes, leakage flows and disturbances in the turbine structure such as joints and steam extractions. Since so many variables are involved and some of the fluid phenomena are still unknown, it is extremely difficult to estimate accurately the dynamic forces and consequently the stimulus ratio.<o:p></o:p></span><br /><span class="Apple-style-span" style="font-family:inherit;"><br /></span> </div><div class="MsoNormal" style="text-align: justify;"><span class="Apple-style-span" style="font-family:inherit;">When calculating the alternating stresses using </span><a href="http://www.sti-tech.com/sti/bladest.html"><span class="Apple-style-span" style="font-family:inherit;">BLADE</span></a><span class="Apple-style-span" style="font-family:inherit;">, I typically assume a 1% stimulus ratio so that results can be easily scaled. In practice the stimulus ratio varies for different machines and for different blade rows. When </span><a href="http://www.sti-tech.com/sti/bladest.html"><span class="Apple-style-span" style="font-family:inherit;">BLADE</span></a><span class="Apple-style-span" style="font-family:inherit;"> calculates these stresses it assumes that the system is at a resonant condition. Therefore, the resonant stresses that are output by </span><a href="http://www.sti-tech.com/sti/bladest.html"><span class="Apple-style-span" style="font-family:inherit;">BLADE</span></a><span class="Apple-style-span" style="font-family:inherit;"> need to be detuned (i.e. reduced) if the particular stimulus is not precisely at resonant frequency. For example let’s say the conditions that were selected to run a dynamic analysis on were within 1% of resonance and this occurs at 3500 Hz. This could lead to a significant detuning since the forcing frequency would be 35 Hz away from resonance.</span><br /><span class="Apple-style-span" style="font-family:inherit;"><br /></span> </div><div class="MsoNormal" style="text-align: justify;"><span class="Apple-style-span" style="font-family:inherit;">The detuning of these resonant stresses is accomplished through the transmissibility function or sometimes referred to as the magnification factor. A derivation of the transmissibility function can be found in a mechanical vibrations text typically in the harmonic vibration chapter. For convenience here is the final result:<o:p></o:p></span></div><div class="MsoNormal" style="text-align: justify;"><span class="Apple-style-span" style="font-family:inherit;"><br /></span> </div><div class="MsoNormal" style="text-align: justify;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg5VCMnXL2NCaPnNycP3VbWbeyz49aA0M2FMQZMNkcyhbnO2CMOJn9oTFRVj9GqkHOyd5C-rgZeWIs9LRlgBybR0H8FqzGztRXWaLsH3uZ7hAxkKyYjvNSDKYoUp1n1Y4UiC2JCW1HknXM/s1600/transfunc.jpg"><img alt="" border="0" id="BLOGGER_PHOTO_ID_5465646771470715954" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg5VCMnXL2NCaPnNycP3VbWbeyz49aA0M2FMQZMNkcyhbnO2CMOJn9oTFRVj9GqkHOyd5C-rgZeWIs9LRlgBybR0H8FqzGztRXWaLsH3uZ7hAxkKyYjvNSDKYoUp1n1Y4UiC2JCW1HknXM/s320/transfunc.jpg" style="cursor: pointer; display: block; height: 99px; margin-bottom: 10px; margin-left: auto; margin-right: auto; margin-top: 0px; text-align: center; width: 320px;" /></a></div><div class="MsoNormal" style="text-align: justify;"><span class="Apple-style-span" style="font-family:inherit;">Where:<o:p></o:p></span></div><div class="MsoNormal" style="text-align: justify;"><p class="MsoNormal" style="text-align:justify"><span style="font-family:Symbol; mso-bidi-font-family:Arial">s</span><sub><span style="mso-bidi-font-size:11.0pt; line-height:130%;mso-bidi-font-family:Arial">d</span></sub><span style="mso-bidi-font-family:Arial">= Dynamic Stress<o:p></o:p></span></p> <p class="MsoNormal" style="text-align:justify"><span style="font-family:Symbol; mso-bidi-font-family:Arial">s</span><sub><span style="mso-bidi-font-family: Arial">r</span></sub><span style="mso-bidi-font-family:Arial">= Resonant Stress<o:p></o:p></span></p> <p class="MsoNormal" style="text-align:justify"><span style="font-family:Symbol; mso-bidi-font-family:Arial">h</span><span style="mso-bidi-font-family:Arial">=Frequency Ratio (excitation frequency/natural frequency)<o:p></o:p></span></p> <p class="MsoNormal" style="text-align:justify"><span style="font-family:Symbol; mso-bidi-font-family:Arial">z</span><span style="mso-bidi-font-family:Arial"> =Critical damping ratio<o:p></o:p></span></p></div><span class="Apple-style-span" style="font-family:inherit;"><br /></span><br /><div style="text-align: justify;"><span class="Apple-style-span" style="font-family:inherit;">Once the stress values are detuned you will now know the frequency and nodal diameter for each possible resonant condition and the dynamic stresses that occur there. With this you will be able to judge if this near resonant condition is significant and if a design needs to be modified to reduce the stresses or shift the frequencies to detune the resonant condition.</span></div><div style="text-align: justify;"><span class="Apple-style-span" style="font-family:inherit;"><br /></span> </div><div style="text-align: justify;"><span class="Apple-style-span" style="font-family:inherit;">Thanks for reading and welcome your comments and suggestions.</span></div>MIKESOBOLhttp://www.blogger.com/profile/02272786154679200185noreply@blogger.com2tag:blogger.com,1999:blog-267689994738506014.post-60086298099375213372010-03-17T16:26:00.000-07:002010-05-01T21:16:20.052-07:00CAE Sales Engineer<b>Update May 1, 2010: This position is no longer available. Our sincere thanks to all the applicants. We greatly appreciate your response and wish you all success in your future endeavors. - Rob.</b><br />
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CAE Sales Engineer - Rochester, NY<br />
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi6RuLFmIKlN-X5yfKSK1dVMuFc7tbzYHgDaIPPXIONxoWM-6Gec31y9-EwTqLYbxgVf7cdAI7DxOnWn2UltCKUPEMFq_vMhBLMNWl8DX2eMdJb3cGelvsAfPMxoDQD3dtZpke_pZ-_l_SX/s1600-h/simutechlogo_col.jpg" onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"><img alt="" border="0" id="BLOGGER_PHOTO_ID_5449767293500746578" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi6RuLFmIKlN-X5yfKSK1dVMuFc7tbzYHgDaIPPXIONxoWM-6Gec31y9-EwTqLYbxgVf7cdAI7DxOnWn2UltCKUPEMFq_vMhBLMNWl8DX2eMdJb3cGelvsAfPMxoDQD3dtZpke_pZ-_l_SX/s200/simutechlogo_col.jpg" style="float: right; height: 108px; margin-bottom: 10px; margin-left: 10px; margin-right: 0pt; margin-top: 0pt; width: 159px;" /></a><br />
<a href="http://www.simutechgroup.com/">SimuTech Group</a>, Inc., is a leading mechanical engineering firm specializing in offering high-end engineering simulation services and products to our customers. SimuTech is the largest reseller of <a href="http://www.ansys.com/">ANSYS</a> engineering simulation software across North America. To complement the sales and support of this technology, the company provides training, mentoring, consulting and testing services. We are also resellers of other leading simulation software such as <a href="http://www.moldflow.com/">Autodesk Moldflow</a>, <a href="http://www.simutechgroup.com/Simulation_Software/fe-safe.html">fe-safe</a>, <a href="http://www.simutechgroup.com/Simulation_Software/tosca/tosca-structure.html">TOSCA</a> and <a href="http://www.simutechgroup.com/Simulation_Software/civilfem/civilfem-ansys.html">CivilFEM</a>.<br />
<br />
At SimuTech, we pride in our employees and their dedication towards providing excellence in engineering simulation. We hire and retain the top engineering simulation experts in the industry. We offer industry leading compensation and benefits package. We have an immediate opening for a passionate and top performing Sales Engineer to grow our upstate NY (East) territory for all ANSYS products.<br />
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In this position, the individual is responsible for locating and developing new accounts and maintaining existing ANSYS customer relationships. Below are key qualifications and job requirements:<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjNRrj7anKl6Qj12q66CHhyphenhypheni7kjLaGkwxOZYj9s_xoKfsPIaWZqMW0X9uCGczF66LcEfNGkyio3i9W5WESpWOKdFRb51ZTiZ85UuAf_xY1Mc0PD-E_fO17Fek77UZ6psvYdzzqjN5MoAR8E/s1600-h/ANSYS-logo.gif" onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}"><img alt="" border="0" id="BLOGGER_PHOTO_ID_5449766923199103810" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjNRrj7anKl6Qj12q66CHhyphenhypheni7kjLaGkwxOZYj9s_xoKfsPIaWZqMW0X9uCGczF66LcEfNGkyio3i9W5WESpWOKdFRb51ZTiZ85UuAf_xY1Mc0PD-E_fO17Fek77UZ6psvYdzzqjN5MoAR8E/s320/ANSYS-logo.gif" style="cursor: pointer; float: right; height: 47px; margin: 0pt 0pt 10px 10px; width: 166px;" /></a><br />
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<span style="font-style: italic;">Preferred qualifications</span>:<br />
2+ years min. of proven direct sales experience<br />
Bachelors degree in engineering (preferably mechanical engineering)<br />
Excellent prospecting, qualification, presentation and selling skills<br />
A team player attitude, customer service oriented with strong work ethic and hunter attitude.<br />
Experience in selling engineering simulation is not required but knowledge is preferred.<br />
Experience selling to C-level and major accounts is a plus.<br />
Valid driver's license with a clean driving record is required.<br />
<div>Travel about 25% of time is expected.<span class="Apple-style-span" style="color: #333333; font-family: Verdana;"><span class="Apple-style-span" style="line-height: 24px;"><br />
</span></span><br />
If you are a top performer, have a drive to succeed and a passion for sales, please forward your resume to roba@simutechgroup.com <span class="Apple-style-span" style="border-collapse: separate; color: black; font-family: 'Times New Roman'; font-size: medium; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px;"><span class="Apple-style-span" style="font-family: Verdana, sans-serif; font-size: 13px; text-align: left;"></span></span></div>Rob Atchutunihttp://www.blogger.com/profile/11384621959808576485noreply@blogger.com4tag:blogger.com,1999:blog-267689994738506014.post-10196098192773432032010-03-02T09:58:00.000-08:002010-09-24T12:57:59.411-07:00Creating a Model with a Moving Wall in ANSYS CFX<div>Ever see those cool CFD animations of a model with a moving boundary? Ever wondered how much of a headache those are to set-up? Well it turns out it is not bad at all. I have run through a generic example below to show you how quickly you can do it in CFX.<br />
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<i>Problem Description:</i><br />
In this problem we are going to be modeling a moving wall on a tank. The assumption that the wall motion is know will be made and supplied to the CFX in a comma separated value (csv) format. The model will be general so that you can apply the method to similar problems.<br />
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<i>Set-up:</i><br />
The geometry was generated with two bodies combined in one part. The one domain, hereafter called the port, is the domain where the mesh is going to be deformed because of the moving wall. The other domain is the tank to which the fluid is being ejected. The mesh in this region will not be deformed.<br />
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So we move along to opening the mesh file in CFX and we begin by changing it over to a transient run. The next step would be to opening the Default Domain and in the panel change the Mesh Deformation option to Regions of Motion Specified. The next step is to create a sub-domain for the port region under the Default Domain. In the sub-domain panel, select the port region for the location and move over to the Mesh Motion tab.<br />
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We are going to use a specified mesh motion using ccl. In the current case the motion is in the z-direction so I specify a name of the cel expression MeshMotion which we will define next. A key point we are going to use is that we want to compress the mesh in the entire domain evenly to maintain the best quality mesh we can.<br />
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<i>Defining a temporal functions from csv file</i><br />
Since we are assuming we know the movement of the wall, we are going to read it in using a csv file. We first must make sure that it has the proper header. The header of the csv file should follow: <br />
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[Name] <br />
SpecifiedMotion <br />
[Spatial Fields] <br />
X <br />
<br />
[Data] <br />
X [m], displacement []<br />
…<br />
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Now the data should be a function of time. But we import it as a spatial variable. We will change it over when we define our cel expressions. To bring this file into CFX, we choose Tools -> Initialize Profile Data from the pull-down menu. After selecting the data file we notice the function is consistent with our header.<br />
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The next step is to change the spatial function into a temporal one. We will do this by creating an expression called MeshDeformation. We will then define this as SpecifiedMotion.displacement(t * 1[m] / 1 [s] ) * StrokeDistance. Note we will define StrokeDistance later.<br />
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<i>Interpolation Functions and Other Expressions</i><br />
First we will generate a function that will be used to make sure we compress the entire sub-domain evenly. We do this by generating a user-function we will call InterpolationLocation. We put unit of [m] in the Argument Units and [] for the Resulting Units. For the one-dimensional function we will supply the data pairs 0, 0 and 4, 1. We do this because the port mesh at 0 [m] will not be deformed and the port mesh at 4 [m] will deform the full amount we will specify (my port is 4 [m] long).<br />
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Next we must create our MeshMotion expression. For this we define it at MeshDeformation*InterpolationLocation(z-Total Mesh Displacement Z). Note the InterpolationLocation is the function we just defined and Total Mesh Displacement Z is the predefined expression that outputs the total mesh displacement in the z-direction relative to the initial mesh. We defined the MeshDeformation expression earlier.<br />
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The final expression we need to define is the StrokeDistance. We simply define this through a cel expression to be -4 [m]. The negative sign indicates that displacement will be in the –Z direction.<br />
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That is all there is to it. That wasn’t so bad was it? Now there are just the smaller things to add into the model such as transient result files and initial conditions. These are straightforward as in your other models. Hope you found it useful. Obviously more complexity can be built into the model, but this shows the basics of the moving mesh portion.<br />
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Per requests, I have included some images to help you follow along. The first image is shows how to set-up the CSV file. Note you can do this in a text editor like notepad, or you can use Excel to develop the data and save the data as a CSV file. Either way the ASCII data should look like:<br />
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<div class="separator" style="clear: both; text-align: center;"></div><div class="separator" style="clear: both; text-align: center;"></div><table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><img border="0" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjQms6-IiwV-XZaz0vTw-TKViRDaUFp1qcrBCKg5bLmDSGi3QshL-4fwuAqku1Bo_esEzULGcrXAe3hRwv4V_ems1ygcMQdaKdVzH7604898TYYneGlgQTQMX82vvqQx0-82QBwtJeuJa09/s320/CVS.JPG" style="margin-left: auto; margin-right: auto;" width="270" /></td></tr>
<tr><td class="tr-caption" style="text-align: center;">How the CSV file should be spaced.</td><td class="tr-caption" style="text-align: center;"><br />
</td><td class="tr-caption" style="text-align: center;"><br />
</td></tr>
</tbody></table><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjQms6-IiwV-XZaz0vTw-TKViRDaUFp1qcrBCKg5bLmDSGi3QshL-4fwuAqku1Bo_esEzULGcrXAe3hRwv4V_ems1ygcMQdaKdVzH7604898TYYneGlgQTQMX82vvqQx0-82QBwtJeuJa09/s1600/CVS.JPG" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"></a></div>The next step after we generate our CSV file is to import this into CFX. This is done by selecting from the pull-down menu Tools -> Initialize Profile Data. Point to the location of your CSV and select OK. If you now look under User Functions in the tree, you will see SpecifiedMotion. Double-click this and the image below would appear.<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><img border="0" height="523" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjgcgtV6MIarJ5zG-9I1-8Za9BO9CdCDjBeICv4WP1ioSbA3XOHBjF7NdYomnpH7mmWB40b18Xn-pDkbceKy-qWyv08kpkpvWo3NbMJTzj96hqoSOL1htg4U1sxREHn-Fys6Dqt2CtoGBax/s640/FunctionSM.JPG" style="margin-left: auto; margin-right: auto;" width="640" /></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Function from CSV File</td></tr>
</tbody></table><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjgcgtV6MIarJ5zG-9I1-8Za9BO9CdCDjBeICv4WP1ioSbA3XOHBjF7NdYomnpH7mmWB40b18Xn-pDkbceKy-qWyv08kpkpvWo3NbMJTzj96hqoSOL1htg4U1sxREHn-Fys6Dqt2CtoGBax/s1600/FunctionSM.JPG" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"></a></div>Now that we have this we can generate our CEL expressions. These expressions are given above and shown in the image below.<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><img border="0" height="209" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjsQbJkQulYje3-w7HmGmriYrjVADkCYIygKe55uR-0yIq1TotezKMIv-u80l-T69aqcBeO5JmBdOOQIdDKoz2cmBIFusOqUxIdyajbCIzO6w4FTYFwEyGiq6s_-SR9yWP5qEVfd3UV6IAK/s640/Expressions.JPG" style="margin-left: auto; margin-right: auto;" width="640" /></td></tr>
<tr><td class="tr-caption" style="text-align: center;">CEL for the above Example</td></tr>
</tbody></table><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjsQbJkQulYje3-w7HmGmriYrjVADkCYIygKe55uR-0yIq1TotezKMIv-u80l-T69aqcBeO5JmBdOOQIdDKoz2cmBIFusOqUxIdyajbCIzO6w4FTYFwEyGiq6s_-SR9yWP5qEVfd3UV6IAK/s1600/Expressions.JPG" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"></a></div>The file piece of the puzzle is to add the InterpolationLocation user-function. The final syntax of this user-function is shown below. Note that the 4 is length of the chamber we wish to compress.<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><img border="0" height="580" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiqttukJ5EzTvF_coqGoCJ3pYl3IntA4OFW8Z-jwVHhHwcACrj_33Cdq22qNdX-zc4TEKE64WZq3RQjDzTZSbIOfLDoIk94cu-_EkUJ78HWayxANqu7T2RjZkC1in1MEPadpT4bQn5HSE90/s640/FunctionIL.JPG" style="margin-left: auto; margin-right: auto;" width="640" /></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Using a CFX user function for interpolation</td></tr>
</tbody></table> I hope you found the original demo interesting and new images helpful in generating these types of models. Cheers!!!<br />
</div>SIMUTECH-NYhttp://www.blogger.com/profile/09561308028653715021noreply@blogger.com21tag:blogger.com,1999:blog-267689994738506014.post-85498690113226578632010-02-26T13:41:00.000-08:002010-03-01T13:54:35.414-08:00Load incrementation of initially weak structuresI just worked on an FEA model which was essentially a flat, very thin plate of plastic with a pressure applied. Initially, I always use small displacement and linear contact (bonded) for debugging a model just to make sure that loads and boundary conditions are correct. This saves time because large deformation effects can introduce much longer solve times. The linear model solved fine.<br />
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When I turned on the large displacement option (nlgeom), the model failed to converge even after several cutbacks (bisections). I certainly did not expect to solve the model in one substep, but I thought the default bisection algorithm would find a converged solution. I was using automatic timestep control. I reduced the initial substep until I eventually obtained a solution, but by this point the subsequent substeps were so small that it would take many, many substeps to complete the load step.<br />
<br />
I noticed that after the first substep converged, convergence for later substeps required only a few iterations. Therefore, I broke the load step into 2 separate steps. In the first step, the load was reduced to the value that converged earlier, about 1/1000th. In the second step, I specified the full load with a reasonably sized initial substep. The model had no trouble converging, even though the load had dramatically increased between steps. The reason is that the initial stiffness of the plate is bending only, because it was flat. Since it was a very thin plastic component, the bending stiffness is very low. The first step established some membrane stiffness as the plate tries to assume a more spherical shape. Once the load generates some membrane stress and there is membrane stiffness, subsequent predictions of displacement are more accurate.<br />
<br />
I have also used this 2 step load strategy for preloading of bolts. Sometimes, not always, the contact resisting the preload has trouble converging with the full preload. Before contact is established, there is no stiffness resisting the preload. Then, the contact overcloses so much that the solver cannot resolve the overclosure efficiently.Jeff Heckmanhttp://www.blogger.com/profile/00727515400876564003noreply@blogger.com1tag:blogger.com,1999:blog-267689994738506014.post-86010679070539163652010-02-21T11:31:00.000-08:002010-02-21T14:21:29.186-08:00Engineering Simulation at Olympics<a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh4auH2s0NogFSYujJbgZIfxqXziIf9JsWjRjWfm0WUPXL7jIBnXEYfSUyJFmBVJSjNDHwatHE1GDKTrpEkOtYatspxiJEjLtC8KI3bi9YYMlnCLhJPYXbEDb1Q88kagU9SlMa-HcEZFZ6B/s1600-h/Skeleton_Slider_CFD.jpg"><img style="margin: 0pt 10px 10px 0pt; float: left; cursor: pointer; width: 320px; height: 221px;" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh4auH2s0NogFSYujJbgZIfxqXziIf9JsWjRjWfm0WUPXL7jIBnXEYfSUyJFmBVJSjNDHwatHE1GDKTrpEkOtYatspxiJEjLtC8KI3bi9YYMlnCLhJPYXbEDb1Q88kagU9SlMa-HcEZFZ6B/s320/Skeleton_Slider_CFD.jpg" alt="" id="BLOGGER_PHOTO_ID_5440803328992996978" border="0" /></a>I have been watching Vancouver Winter Olympics 2010 with great deal of attention. My loyalties lie with US but cheer any genuinely great sporting achievement. What fascinates me is the true grit and determination of these athletes to overcome great odds to attain perfection! And knowing our passion "engineering simulation" has helped them along towards these levels of perfection really brings a huge smile on my face.<br /><br /><span style="font-size:78%;">Images Courtesy: www.fluent.com </span><br /><br />I wanted to bring light to some of the engineering simulation such as FEA, CFD etc., that goes on in preparation towards these levels of perfections.<br /><br />Above images show pressure contours on a simulated skeleton slider, with pathlines colored by velocity magnitude (<i>Postprocessed by Ensight</i>). The story behind the simulatio<a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi71spfIZhov-7HwMVPLpdxxA9S7TNLQESQW4StYo8_ktSsiGEzI3ZJp0euZpm6bisqUM9lc1ViplrXfoOLRBTkqNyZF5SJnMFUhbStwOYWZDjx8Tu5foN1maClWVdrSHwaUDpjQzL50Eu0/s1600-h/Skeleton_Slider.jpg"><img style="margin: 0pt 0pt 10px 10px; float: right; cursor: pointer; width: 194px; height: 256px;" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi71spfIZhov-7HwMVPLpdxxA9S7TNLQESQW4StYo8_ktSsiGEzI3ZJp0euZpm6bisqUM9lc1ViplrXfoOLRBTkqNyZF5SJnMFUhbStwOYWZDjx8Tu5foN1maClWVdrSHwaUDpjQzL50Eu0/s320/Skeleton_Slider.jpg" alt="" id="BLOGGER_PHOTO_ID_5440786275051887634" border="0" /></a>n is as interesting as the technology itself. You can read the complete story <a href="http://www.fluent.com/about/news/newsletters/05v14i3/pdfs/nl8.pdf">here</a>. The story in short goes something like this: In preparation for 2006 Winter Olympics at Turin, Italy, <a href="http://en.wikipedia.org/wiki/Kristan_Bromley">Kristan Bromley</a>, the top-ranked skeleton bobsled competitor in the UK, approached the Elite Sports CFD Unit - a part of the Sports Engineering Research Group (SERG) in Sheffield, UK - and asked them to provide CFD flow simulation support to increase his chances of success. Bromley's goal:<br />Minimize the overall aerodynamic drag by assessing small changes in surface texture of his skin-suit. Bromley ended up with a respectable <a href="http://en.wikipedia.org/wiki/Kristan_Bromley">5th ranking in Turin Winter Olym</a><a href="http://en.wikipedia.org/wiki/Kristan_Bromley">pics</a> and went on to bring home the first gold medal for Britain since 1965 at the <a href="http://en.wikipedia.org/wiki/Kristan_Bromley">2008 FIBT World Championships</a>. Bromley maintains philosophy of using advanced technology to enhance on-ice performance. Although, the CFD analysis may have been just a drop in the ocean in terms of the dedication, grit and determination for such olympic athletes, it is still atleast a drop!<br /><br />More information: http://www.bromley-aet.com/<br /><br />Below are a few more articles that show the role of engineering simulation that goes into such perfection!<br /><a href="http://www.ansys.com/magazine/issues/1-1-2007-sports-and-leisure/s06-giving-ski-racers-edge.pdf">ANSYS Article:</a> Giving Ski Racers an Edge<br /><a href="http://www.fluent.com/about/news/newsletters/05v14i3/a7.htm">FLUENT Article:</a> CFD for Bob Sled Team<br /><a href="http://www.ansys.com/magazine/issues/1-1-2007-sports-and-leisure/s08-ice-axe-impacts.pdf">ANSYS Article:</a> Finite Element Analysis on Mountain Climbing Ice Axe to study crack initiation on serrated blade.<br /><br />Hats off to all the fantastics athletes and the engineering simulation that is enhancing their performance on ice! :)Rob Atchutunihttp://www.blogger.com/profile/11384621959808576485noreply@blogger.com0tag:blogger.com,1999:blog-267689994738506014.post-18353048832069460872010-02-05T13:03:00.000-08:002010-11-05T06:44:52.283-07:00Turbine Blade Modal Analysis<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEifea2_lzJZbGQCMlo_AfqkJzTaTcWbD1RTFvwzzEu26-Bm_WkHjTT5kyIYDVObfYq3iYrAkmb_LloR-DAsFuxoQnU1u7uf2hUQplA2chF1qfTLpMmZ2SN__AglAcQ7w0yyO-ngRvrLwvs/s1600-h/InterferenceBlog.jpg" onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}"><span class="Apple-style-span" style="font-family: 'times new roman';"><img alt="" border="0" id="BLOGGER_PHOTO_ID_5434869182843060450" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEifea2_lzJZbGQCMlo_AfqkJzTaTcWbD1RTFvwzzEu26-Bm_WkHjTT5kyIYDVObfYq3iYrAkmb_LloR-DAsFuxoQnU1u7uf2hUQplA2chF1qfTLpMmZ2SN__AglAcQ7w0yyO-ngRvrLwvs/s320/InterferenceBlog.jpg" style="height: 219px; width: 320px;" /></span></a><span class="Apple-style-span" style="font-family: 'times new roman';"><br /></span><br /><div class="MsoNormal"><span class="Apple-style-span" style="font-family: Verdana, sans-serif;">I have recently had the opportunity to work on a few steam turbine blade failure investigations and have found a whole new world of engineering simulation that I had not been exposed to. Analysis of turbine blades is its own animal and even though steam turbines have been in use in power generation for a very long time, the physics of power generation is so complex there are many areas that are still not well understood. Being new to turbine analysis I thought my experiences as I lean steam turbine analysis may be useful to others. The first topic I would like to describe has been fundamental to all of the turbine projects that I have been involved with: Modal analysis of a bladed disk row. In each investigation, modal analysis was used to calculate the natural frequencies and mode shapes for a particular stage of blades. This is a valuable tool in determining if the blades are operating near a resonant condition that could be responsible for a failure. </span></div><div class="MsoNormal"><span class="Apple-style-span" style="font-family: Verdana, sans-serif;">As you can find in any vibrations textbook, modal analysis is an eigenvalue procedure in which the eigenvalues of the equation of motion are the square of the natural frequencies and the eigenvectors are the mode shapes. For blade analysis, </span><a href="http://www.simutechgroup.com/"><span class="Apple-style-span" style="font-family: Verdana, sans-serif;">SimuTech Group</span></a><span class="Apple-style-span" style="font-family: Verdana, sans-serif;"> uses an in-house developed code to run a modal Finite Element Analysis on turbine blades. This program is called </span><a href="http://www.sti-tech.com/sti/bladest.html"><span class="Apple-style-span" style="font-family: Verdana, sans-serif;">BLADE</span></a><span class="Apple-style-span" style="font-family: Verdana, sans-serif;">.</span></div><div class="MsoNormal"><span class="Apple-style-span" style="font-family: Verdana, sans-serif;">A portion of the bladed disk is modeled in </span><a href="http://www.sti-tech.com/sti/bladest.html"><span class="Apple-style-span" style="font-family: Verdana, sans-serif;">BLADE</span></a><span class="Apple-style-span" style="font-family: Verdana, sans-serif;"> which usually consists of a 360°/N sector, where N is the number of blades in the row. The mass and stiffness matrices for the bladed disk sector are then reduced to a superelement containing selected fewer degrees of freedom. These selected degrees of freedom are called master degrees of freedom. They are selected in such a way as to be able to represent and predict the dynamic behavior of the bladed disk. </span></div><div class="MsoNormal"><span class="Apple-style-span" style="font-family: Verdana, sans-serif;">At operating speed, the rotating system stiffens because of the centrifugal effects. This stress stiffening causes the natural frequencies to be higher than their corresponding values calculated at zero RPM. The effect of the stress stiffening is evaluated and incorporated in the analysis. </span></div><div class="MsoNormal"><span class="Apple-style-span" style="font-family: Verdana, sans-serif;">If a rotating bladed disk is excited by a forcing which is fixed spatially, there are 3 conditions that need to be satisfied in order to produce a resonant condition:</span></div><div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in; margin-left: .3in; margin-right: 0in; margin-top: 0in; mso-list: l0 level1 lfo1; tab-stops: list .3in; text-indent: -.3in;"><span class="Apple-style-span" style="font-family: Verdana, sans-serif;">1.</span><span style="font: normal normal normal 7pt/normal 'Times New Roman';"><span class="Apple-style-span" style="font-size: medium;"><span class="Apple-style-span" style="font-family: Verdana, sans-serif;"> </span></span></span><span class="Apple-style-span" style="font-family: Verdana, sans-serif;">The natural frequency of the blade row is equal to some per-rev forcing frequency</span></div><div class="MsoNormal" style="margin-bottom: .0001pt; margin-bottom: 0in; margin-left: .3in; margin-right: 0in; margin-top: 0in; mso-list: l0 level1 lfo1; tab-stops: list .3in; text-indent: -.3in;"><span class="Apple-style-span" style="font-family: Verdana, sans-serif;">2.</span><span style="font: normal normal normal 7pt/normal 'Times New Roman';"><span class="Apple-style-span" style="font-size: medium;"><span class="Apple-style-span" style="font-family: Verdana, sans-serif;"> </span></span></span><span class="Apple-style-span" style="font-family: Verdana, sans-serif;">The number of nodal diameter of the natural mode equals the forcing harmonic number.</span></div><div class="MsoNormal" style="margin-left: .3in; mso-list: l0 level1 lfo1; tab-stops: list .3in; text-indent: -.3in;"><span class="Apple-style-span" style="font-family: Verdana, sans-serif;">3.</span><span style="font: normal normal normal 7pt/normal 'Times New Roman';"><span class="Apple-style-span" style="font-size: medium;"><span class="Apple-style-span" style="font-family: Verdana, sans-serif;"> </span></span></span><span class="Apple-style-span" style="font-family: Verdana, sans-serif;">The excitation must be able to couple with the blade disk mode shape. For example, the forcing on the blade row must be in a direction that matches the mode shape deflection. If the forcing is along the axial direction of the turbine and the mode shape shows deflection only in the tangential direction, the mode can not be excited. Of course many modes contain components in both axial and tangential directions.</span></div><div class="MsoNormal"><span class="Apple-style-span" style="font-family: Verdana, sans-serif;">If all of the above conditions are met, resonance will occur. This natural frequency-forcing relationship is usually illustrated as an Interference diagram. In the Interference diagram, the natural frequency is plotted against the number of nodal diameters (harmonic content of a mode). An example of an interference diagram is shown above. The line through the origin is called the </span><i><b><span class="Apple-style-span" style="font-family: Verdana, sans-serif;">Impulse Line</span></b></i><span class="Apple-style-span" style="font-family: Verdana, sans-serif;"> which corresponds to the operating speed. Whenever the Impulse Line intersects the natural frequency curves, a resonant condition may exist. </span></div><div class="MsoNormal"><span class="Apple-style-span" style="font-family: Verdana, sans-serif;">The Interference diagram is used to locate frequencies of interest for a more detailed stress analysis. Resonant stresses are calculated for these conditions and detuned as necessary to estimate the true dynamic stress in each blade. The dynamic stress will also depend on the damping present in the system as well as the stimulus ratio (the ratio of dynamic forcing to the steam bending force in the blade). Dynamic stress analysis is a discussion on its own and will likely be a topic of future entries.</span></div><div class="MsoNormal"><span class="Apple-style-span" style="font-family: Verdana, sans-serif;">Thanks for reading.</span></div><div class="MsoNormal"><o:p> </o:p></div>MIKESOBOLhttp://www.blogger.com/profile/02272786154679200185noreply@blogger.com1tag:blogger.com,1999:blog-267689994738506014.post-63632536771114208492010-01-26T09:43:00.000-08:002010-05-05T19:39:03.236-07:00Limit load analysisI worked on a <a href="http://www.asme.org/Codes/International_Boiler_Pressure.cfm">2007 ASME B&PV Code, Section VIII, Div 2 analysis</a> of what was essentially an elbow casting with some additional detail. The more traditional approach would be to use stress linearization on an elastic analysis for stress categorization. However, since the elbow was thick-walled relative to the radius, stress linearization can be non-conservative because the stress distribution is non-linear. Think about the difference between a thick walled cylinder and. thin walled cylinder.<br /><br />I used the limit load analysis method instead. The limit load analysis has established itself as the preferred method, subject to its limitations, to assess primary sizing (Protection Against Plastic Collapse). The limit load analysis eliminates the need for stress categorization because it is a pass-fail criterion. The material definition is elastic-perfectly plastic. So, the limit load analysis is trying to predict when a plastic hinge forms in a plate an uncontrolled deformation with result with any additional applied load.<br /><br /><a href="http://www.amazon.com/Elastic-Inelastic-Analysis-Materials-Engineering/dp/1560326867?ie=UTF8&tag=engineesimula-20&link_code=bil&camp=213689&creative=392969" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;" target="_blank"><img alt="Elastic And Inelastic Stress Analysis (Materials Science & Engineering Series)" height="200" src="http://ws.amazon.com/widgets/q?MarketPlace=US&ServiceVersion=20070822&ID=AsinImage&WS=1&Format=_SL160_&ASIN=1560326867&tag=engineesimula-20" width="132" /></a>The basis for the limit load is straightforward. A value of 1.5 is applied to the desired load (i.e. design pressure+static head+dead weight). Recall that a plastic hinge is formed in a rectangular cross-section beam with an elastic-perfectly plastic material when the moment is 1.5 X the moment required for initial yield. You can find this discussion in a Continuum Mechanics textbook in a section on Beams. I have the book by Shames and Cozzarelli, "<a href="http://www.amazon.com/Elastic-Inelastic-Analysis-Materials-Engineering/dp/1560326867?ie=UTF8&tag=engineesimula-20&link_code=btl&camp=213689&creative=392969" target="_blank"></a><a href="http://www.amazon.com/Elastic-Inelastic-Analysis-Materials-Engineering/dp/1560326867?ie=UTF8&tag=engineesimula-20&link_code=btl&camp=213689&creative=392969" target="_blank">Elastic and Inelastic Stress Analysis</a><img alt="" border="0" height="1" src="http://www.assoc-amazon.com/e/ir?t=engineesimula-20&l=btl&camp=213689&creative=392969&o=1&a=1560326867" style="border: none !important; margin: 0px !important; padding: 0px !important;" width="1" />," which has a pretty good description of this derivation with lots of pictures. So, if you enter 1.5*S (in some cases 1.5S is equal to yield strength at temperature) as your FEA yield strength, and the model converges, you will not develop a plastic hinge in the component you are analyzing. There will likely be plastic strain, especially at structural discontinuities.<img alt="" border="0" height="1" src="http://www.assoc-amazon.com/e/ir?t=engineesimula-20&l=bil&camp=213689&creative=392969&o=1&a=1560326867" style="border: none !important; margin: 0px !important; padding: 0px !important;" width="1" /><br /><br /><strong>Bottom Line:</strong><br />Did the analysis model converge at the desired load (i.e.1.5*Design Pressure)? If yes, Section 5.2, Protection Against Plastic Collapse is satisfied. If not, Section 5.2, Protection Against Plastic Collapse is NOT satisfied.<br /><br />Advances in the capabilities of computers have enabled the method, since the limit load analysis will take longer to run than an elastic stress analysis. However, post-processing effort is reduced to near zero. Also, there is no question about whether or not the stress categorization line (stress cutline) is in the limiting location.<br /><br />JeffSIMUTECH-NYhttp://www.blogger.com/profile/09561308028653715021noreply@blogger.com6tag:blogger.com,1999:blog-267689994738506014.post-48003038042369717132010-01-17T20:44:00.000-08:002010-01-17T20:44:54.548-08:00Engineering Simulation blog... a beginning.First question we asked ourselves is why blog? Does this help our customers? The simulation community? Does it help us?<br />
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Being an engineering simulation consulting firm and working with a wide range of customers in various industries, we see several unique simulation requirements, from leading edge to bleeding edge! We have seen several times how what we learn in simulating for one industry can so easily be transferable to another industry; how simple tricks or having "been there, done that" would have saved us hours and hours of frustration (if not days!). We also have done some "cool" projects which we love to share with anyone over a cocktail discussion. We have a love-hate relationship with simulation... years of passion and also sometimes days of frustration!<br />
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So, that being said, we thought, blogging about our experiences, analyses and physics in general could be a great way to help the simulation community, our customers and also create our voice! So, we plan to post interesting analysis stories, tricks, tips, macros, glitches, software patches (or atleast direct to the right resource), FEA vs. Testing, our perspectives and more.... If our experience, macros, resources etc., can save a few hours for a fellow analyst, we will consider our blog a success!<br />
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Let us "Engineer, Simulate and Innovate" together.<br />
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This blog is maintained by our engineering analysis group out of Rochester, NY office. <br />
Our blogging team (The SimuSquad) includes:<br />
Jeff Heckman, Jason Zbick, Rolf Orsagh, Mike Sobol, Nick Lynn and Sriram "Rob" Atchutuni.SIMUTECH-NYhttp://www.blogger.com/profile/09561308028653715021noreply@blogger.com1