Copyright © 2009 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. Practical FEM Analysis  What do you need to run a FEM analysis?  (Likely) error sources?

Copyright © 2009 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved.  CAD import  Geometry cleanup / repair Geometry cleanup / repair  Prepare geometry according to mesh requirements  Meshing, mesh quality checks Meshing, mesh quality checks  Material, properties (i.e. thickness) Material, properties (i.e. thickness)  Loads, constraints (boundary conditions) Loads, constraints (boundary conditions)  Export of FE solver deck  Analysis  Postprocessing  Loadstep(s) What do you need to run a FEM analysis? improvements / recommendations

Copyright © 2009 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. 2.5 mm Exercise: target element size: 3 mm What do you need to run a FEM analysis?  CAD import  Geometry cleanup / repair Geometry cleanup / repair  Prepare geometry according to mesh requirements

Copyright © 2009 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved mm What do you need to run a FEM analysis?  CAD import  Geometry cleanup / repair Geometry cleanup / repair  Prepare geometry according to mesh requirements

Copyright © 2009 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. What do you need to run a FEM analysis?  CAD import  Geometry cleanup / repair Geometry cleanup / repair  Prepare geometry according to mesh requirements

Copyright © 2009 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. requested element size: 10 mm What do you need to run a FEM analysis?  CAD import  Geometry cleanup / repair Geometry cleanup / repair  Prepare geometry according to mesh requirements

Copyright © 2009 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved suppress edges requested element size: 20 mm What do you need to run a FEM analysis?  CAD import  Geometry cleanup / repair Geometry cleanup / repair  Prepare geometry according to mesh requirements

Copyright © 2009 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. What do you need to run a FEM analysis? Summary of likey error sources (I)

Copyright © 2009 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. Stopp, … something seems wrong. Gary Larson What do you need to run a FEM analysis?  Meshing, mesh quality checks Meshing, mesh quality checks

Copyright © 2009 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. Meshing: the element configurations What do you need to run a FEM analysis?

Copyright © 2009 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. Meshing: the element configurations What do you need to run a FEM analysis?

Copyright © 2009 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. Boundary between 2 different materials must be represented by a clear boundary between the elements What do you need to run a FEM analysis? Meshing

Copyright © 2009 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. Symmetrical boundary Condition requires symmetrie wrt. loads and geometry Reduce model to ¼ of geometry Meshing What do you need to run a FEM analysis?

Copyright © 2009 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. Meshing: Element Quality Checks Always perform quality checks on the meshes you create. Check with “local experts” regarding the appropriate values for each element type required by your element checking computer programs. Be aware that, in these situations, “correct” answers can vary a great deal as illustrated in the following table where the range between “OK” and “very poor” is quiet wide. What do you need to run a FEM analysis?

Copyright © 2009 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. Quatation: C.A. Felippa Meshing What do you need to run a FEM analysis?

Copyright © 2009 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. What do you need to run a FEM analysis? Summary of likey error sources (II)

Copyright © 2009 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. Prof. D. W. Dehmel Attention: Be consistent with your units!!! What do you need to run a FEM analysis? Material

Copyright © 2009 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. What do you need to run a FEM analysis? Summary of likey error sources (III)

Copyright © 2009 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. What do you need to run a FEM analysis?  Loads, constraints (boundary conditions) Loads, constraints (boundary conditions)  Loadstep(s)

Copyright © 2009 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. What do you need to run a FEM analysis?

Copyright © 2009 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. accident CER 2008 accident Dakar 2005 What do you need to run a FEM analysis? Load identification …

Copyright © 2009 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. What do you need to run a FEM analysis? Summary of likey error sources (IV)

Copyright © 2009 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. 1 a. Determine project goals e.g. max. deflections, peak stress, vibration characteristics, thermal stresses, stifness, fatigue, optimization, … General modeling aspects  Planning the solution Form a consensus with all involved to establish objectives; Customers may be unable to clearly define goals 1 b. Examine the component under investigation Note the strength and weaknesses of past performance Examine the components in their working environment Study reports written on similar studies Discuss the problem with the authors of related reports What do you need to run a FEM analysis?

Copyright © 2009 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. 1 c. Know the timetable for conducting the analysis. -This information will help to determine whether or not compromises in accuracy and confidence need to be made to deliver timely results 1 d. Consider Boundaries and Surrounding Systems Determine the amount of the surrounding structure that should be included in the model to obtain an accurate representation of the operating environment / actual BCs Reading reports, Discussing similar projects with design engineers, Visiting test labs, Physically inspecting the components in their operating environment, Study layout and detail drawings General modeling aspects  Planning the solution What do you need to run a FEM analysis?

Copyright © 2009 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. 1 e. Linear Assumption. Deflections are small relative to the size of the structure, e.g. for thin structures, a deflection that is less than the thickness; the deflection between two supports should be only a small percentage of the distance between supports Small rotations. Any angle measured in radians should be small enough that the tangent is approx. equal to the angle; a ten degree angle introduces an error of approx. one percent in all related calculations; a thirty degree angle results in approx. a ten procent error General modeling aspects  Planning the solution What do you need to run a FEM analysis?

Copyright © 2009 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. 1 f. Consistent Units. It is the responsibility of the user to create the model using a consistent set of units. Be particularly careful when using someone else’s work. They may have used a conversion factor but failed to clearly document it. General modeling aspects  Planning the solution What do you need to run a FEM analysis?

Copyright © 2009 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. Quotation: C.A. Felippa 1 g. General modeling aspects  Planning the solution What do you need to run a FEM analysis?

Copyright © 2009 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. 1 h. Review the Plan „See the end before you begin“: -What results will be most useful -What do you expect to happen -What things can go wrong -What questions will be asked when you present your results -How, and in what form will you present your results General modeling aspects  Planning the solution What do you need to run a FEM analysis?