Fea Stress Error
Contents |
errors occur a continuous mathematical model is discretised into a FE model. Solution errors arise from the process of the numerical solution of the sources of error in finite element analysis FE equations. It should also be noted that errors can be made
Error Evaluation In Finite Element Analysis
by users incorrectly interpreting the results. To minimise the danger of this happening, always work in SI
Discretization Error In Fem
units. The Finite Element Method involves approximating a structure (assuming a structural analysis is being carried out) and there are several potential sources of error. The following are the
Types Of Error In Finite Element Analysis
main sources of error: 1. The model of the structure may contain a number of simplifications. Often this involves omitting small details (this is referred to as 'defeaturing'). This is only satisfactory if the stresses in the areas where these details have been omitted are low. It must be remembered that sharp radii can greatly increase the discretization error in fea stress. Normally it is best to start with a very simple representation of the actual component, analyse it and see if it is behaving as expected. If it is then more detail can be added in stages, repeating the analysis every time further detail has been added. By doing this it may be possible to gain an appreciation of the amount of detail that needs to be included. Stress Singularity All components have finite radii at corners, however for small radii a common simplification is to ignore the radius and make the corner 'sharp'. This may not matter for an external corner, however a sharp re-entrant corner results in a stress singularity - refining the FEA mesh will give increasing (without limit!) stress values as the element size in reduced. The stress results are meaningless (the displacement results may be acceptable) and a reasonable approximation of the radius must be used in the model. One way of reducing this problem is to model the component with a material which can model
Join INTELLIGENT WORK FORUMSFOR ENGINEERING PROFESSIONALS Log In Come Join Us! Are you anEngineering professional?Join Eng-Tips Forums! Talk With Other Members Be Notified Of ResponsesTo Your Posts Keyword Search One-Click Access To YourFavorite fea stress singularity Forums Automated SignaturesOn Your Posts Best Of All, It's Free! Join Us! *Eng-Tips's discretization error definition functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail. Posting Guidelines Promoting, selling, recruiting, modelling error in fem coursework and thesis posting is forbidden.Eng-Tips Posting Policies Jobs Link To This Forum! Add Stickiness To Your Site By Linking To This Professionally Managed Technical Forum.Just copy and paste the BBCode HTML Markdown http://www.tech.plym.ac.uk/sme/mech335/feaerrors.htm MediaWiki reStructuredText code below into your site. DASSAULT: SOLIDWORKS Simulation/FEA Forum at Eng-Tips HomeForumsEngineering Computer ProgramsSimulationDASSAULT: SOLIDWORKS Simulation/FEA Forum Stress Error Plot - What are the units? 2 thread1183-282002 Forum Search FAQs Links MVPs Stress Error Plot - What are the units? Stress Error Plot - What are the units? stanm (Mechanical) (OP) 23 Sep 10 11:56 Can anyone explain to me the basis of the http://www.eng-tips.com/viewthread.cfm?qid=282002 stress error when plotted using the ERR option. Specifically, is this reporting the error in the energy norm or a more tangible error such as actual "stress" or a percentage error? I can't find anything in the user manual that explains this. RE: Stress Error Plot - What are the units? 2 EngAddict (Mechanical) 24 Sep 10 01:04 It is a percentage, start here:http://help.solidworks.com/2010/English/SolidWorks/cworks/legacyhelp/simulation/AnalysisBackground/StaticAnalysis/Stress_Error.htm RE: Stress Error Plot - What are the units? stanm (Mechanical) (OP) 1 Oct 10 05:53 Thanks EngAddict, that is aan excellent resource. Now,how do we consider the % error in the error norm to calculate possible maximum stresses? RE: Stress Error Plot - What are the units? Elabbasi (Mechanical) 1 Oct 10 07:53 This error measure should not be used to calculate maximum stresses but to check if you mesh is fine enough for the results to be reasonable accurate. If the error is high, especially in areas of high stress, then you need to rerun the analysis with a finer mesh and recheck the error. Nagi Elabbasiwww.veryst.com RE: Stress Error Plot - What are the units? stanm (Mechanical) (OP) 1 Oct 10 08:37 Elabbasi how would you define a 'high' error? RE: Stress
listed if standards is not an option). Products Video Gallery Webinars Support Contact COMSOL Blog GET NEW POSTS BY https://www.comsol.com/blogs/singularities-in-finite-element-models-dealing-with-red-spots/ EMAIL Menu COMSOL Blog Singularities in Finite Element Models: Dealing with https://forum.solidworks.com/thread/90645 Red Spots Henrik Sönnerlind | June 3, 2015 Your finite element model will sometimes contain singularities -- that is, points where some aspect of the solution tends toward an infinite value. In this blog post, we will explore the common causes of singularities, when error in and how to remove them, and how to interpret results when singularities are present in your model. While most of this discussion is in terms of structural mechanics, similar phenomena can also be found in many other physics fields. The Problem In my previous role as a structural analysis consultant, I sometimes came across the in finite element problem of how to report ridiculously high stress peaks in a finite element model to a customer. Experienced analysts know when stress peaks are an expected effect of modeling and can be safely ignored. Though, when a requirement that "the stress must nowhere exceed 70% of the yield stress" has been stated, this may still turn out to be an issue. Equally important is the fact that the small red spots in the color plots cannot always be ignored. Thus, we must have appropriate techniques for interpreting the model results. The Sharp Corner: A Prototype of a Singularity Sharp reentrant corners will cause a singularity in the derivatives of the dependent variables for all elliptic partial differential equations. In structural mechanics, this means that the strains can become unbounded since the degrees of freedom are the displacements. Unless limited by the material model, the stresses will also be infinite in such a case. Stresses are investigated in the majority of structural mechanics analyses. This
Forums3D ContentCentralAdministrationAPI/MacrosComposerData ManagementDrawing and DetailingeDrawingsEducators and StudentsGeneralImport/ExportModeling and AssembliesSimulationSOLIDWORKS Add-InsSOLIDWORKS PCBSOLIDWORKS VisualizeUser InterfaceSOLIDWORKS World Top Ten ListLog in0SearchSearchSearchCancelError: You don't have JavaScript enabled. This tool uses JavaScript and much of it will not work correctly without it enabled. Please turn JavaScript back on and reload this page. All Places > Simulation > Discussions Please enter a title. You can not post a blank message. Please type your message and try again. 11 Replies Latest reply on Feb 3, 2015 2:30 PM by Jared Conway Simulation / Meshing / Stress Error Mike Armstrong Jan 23, 2015 4:23 PM I have a relatively simple model with 3 solid bodies and have been running simulations to try and get consistent results. I started off with a very coarse mesh and to ensure the solver managed to converge.I have gradually reduced the mesh size in there areas of interest (pull connections and locations of applied restraint) and have ran into a number of problems. The maximum stress values continually rise the more I refine the mesh due to singularities and the stress error plots return extremely high values. I have used a number of techniques provided throughout the forum (not shown in this model), such as fillets, simplification of geometry with little success. So my questions are:What mesh size should I be using at the areas of interest and the areas deemed not criticalWhat stress error is acceptableWhat techniques are best to eliminate singularitiesThanks in advance.Mike Trail Head.SLDPRT.zip 1.6 MB I have the same question Show 0 Likes(0) 3888Views Tags: none (add) This content has been marked as final. Show 11 replies Re: Simulation / Meshing / Stress Error Bill McEachern Jan 23, 2015 4:42 PM (in response to Mike Armstrong) HI Mike,I did not download your model so these are just general remarks. The best way to deal with singularities in my humble opinion is to do a non-linear analysis and let the equilibrium iterations deal with them but you may not have the NL option. Try and turn on large displacement in the study properties - it will do the same thing but you won't have a plasticity model so they might still be high. Sim NL with plasticity and contact is not the most robust of combinations for getting a result to converge.Assuming your areas of interest are not where the singularities are then just make sure the stress in those areas has leveled off as you reduce the mesh. You can plot the error there but they should be ok once the stress converges.Als