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FEA Project Outline

FEA Project Outline. START. Finite Element Analysis. 1. 2. 3. 4a. Consider the physics of the situation. Devise a mathematical model. Obtain approximate results for subsequent comparison with FEA. Plan a finite element discretization of the mathematical model. Preprocess:

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FEA Project Outline

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  1. FEA Project Outline START Finite Element Analysis 1 2 3 4a Consider the physics of the situation. Devise a mathematical model. Obtain approximate results for subsequent comparison with FEA. Plan a finite element discretization of the mathematical model. Preprocess: Build the finite element model in the computer. D2 D1 4b Physics FEA H Revise the finite element discretization Are error estimates small? Does mesh revision do little to alter the FEA results? Solution: Generate and solve equations of the finite element model. No What is at fault, Inadequate physical basis for the model or a poor finite element model? Yes STOP 4c No 5 Postprocess: Output/display computed results for examination. Yes Are the FEA results free of obvious errors, such as disagreement with the intended boundary conditions? Are FEA results physically reasonable? Do FEA results agree reasonably well with predictions and approximations obtained by other means? Adapted from RD Cook et al., Concepts and Applications of Finite Element Analysis, 4th ed., John Wiley & Sons, 2002

  2. FEA Project Outline - overview • What you may consider conducting a finite element analysis (green dashed box) is only part of a finite element analysis project • In this class we will use commercial FEA software as part of a series of FEA projects • A project involves both high-level and detail decisions • High-level decisions – what is the proper physical basis for the model? • Detail decisions – is the finite element representation adequate? • Each decision level involves different methods of evaluation • High-level decisions require reasonable approximate solutions • Detail decisions require critical evaluation of FEA software output

  3. Initial Sequence START Finite Element Analysis • Steps 1 – 5 are a linear sequence of defined steps, but • The analysis project is not complete after step 5! • You cannot complete a FEA project without doing at least two finite element analyses! 1 2 3 4a Consider the physics of the situation. Devise a mathematical model. Obtain approximate results for subsequent comparison with FEA. Plan a finite element discretization of the mathematical model. Preprocess: Build the finite element model in the computer. D2 D1 4b Physics FEA H Revise the finite element discretization Are error estimates small? Does mesh revision do little to alter the FEA results? Solution: Generate and solve equations of the finite element model. No What is at fault, Inadequate physical basis for the model or a poor finite element model? Yes STOP 4c No 5 Postprocess: Output/display computed results for examination. Yes Are the FEA results free of obvious errors, such as disagreement with the intended boundary conditions? Are FEA results physically reasonable? Do FEA results agree reasonably well with predictions and approximations obtained by other means? Adapted from RD Cook et al., Concepts and Applications of Finite Element Analysis, 4th ed., John Wiley & Sons, 2002

  4. Evaluation Blocks START Finite Element Analysis • Note the evaluation blocks in the middle of the flowchart • Even if the solution looks OK in general, you do not have the detailed information required to answer YES at block D1 (Detail Step 1) 1 2 3 4a Consider the physics of the situation. Devise a mathematical model. Obtain approximate results for subsequent comparison with FEA. Plan a finite element discretization of the mathematical model. Preprocess: Build the finite element model in the computer. D2 D1 4b Physics FEA H Revise the finite element discretization Are error estimates small? Does mesh revision do little to alter the FEA results? Solution: Generate and solve equations of the finite element model. No What is at fault, Inadequate physical basis for the model or a poor finite element model? Yes STOP 4c No 5 Postprocess: Output/display computed results for examination. Yes • Mesh Revision – make elements smaller, re-run the analysis, compare (mesh convergence evaluation) • Error Estimates – differences in postprocessing treatments Are the FEA results free of obvious errors, such as disagreement with the intended boundary conditions? Are FEA results physically reasonable? Do FEA results agree reasonably well with predictions and approximations obtained by other means? Adapted from RD Cook et al., Concepts and Applications of Finite Element Analysis, 4th ed., John Wiley & Sons, 2002

  5. Finite Element Analysis block START Finite Element Analysis • We will use commercial software for the FEA portion • FEA involves three distinct steps: • Preprocess – Establish problem geometry, define material and component properties, apply boundary conditions (constraints and loads), discretize (create nodes and elements), specify solution parameters • Solution – Find element stiffness matrices, assemble global problem matrix, introduce boundary conditions, solve (typically for nodal displacements) • Postprocess – Calculate secondary quantities (such as strain and stress), condition results as requested, create graphical displays (contour plots, vector plots, etc.), create portable numerical output files • An interesting point: The Pre- and Post-processing steps are generic to essentially all FEA software packages 1 2 3 4a Consider the physics of the situation. Devise a mathematical model. Obtain approximate results for subsequent comparison with FEA. Plan a finite element discretization of the mathematical model. Preprocess: Build the finite element model in the computer. D2 D1 4b Physics FEA H Revise the finite element discretization Are error estimates small? Does mesh revision do little to alter the FEA results? Solution: Generate and solve equations of the finite element model. No What is at fault, Inadequate physical basis for the model or a poor finite element model? Yes STOP 4c No 5 Postprocess: Output/display computed results for examination. Yes Are the FEA results free of obvious errors, such as disagreement with the intended boundary conditions? Are FEA results physically reasonable? Do FEA results agree reasonably well with predictions and approximations obtained by other means? Adapted from RD Cook et al., Concepts and Applications of Finite Element Analysis, 4th ed., John Wiley & Sons, 2002

  6. Software Options • Many FEA codes are available: • ANSYS, ABAQUS, COSMOL, Nastran, Dytran, LS-DYNA, Marc, etc. • Why so many? • Some are special purpose – e.g. HyperSizer for composite material analysis • Some are general purpose – those listed above, with a variety of structural (and perhaps thermal and fluid-flow) capabilities • Even the general purpose codes have specialty areas • ABAQUS has a strength in constitutive (material property) capabilities • LS-DYNA has strengths in transient and dynamic problems • Most FEA programs began development before computers had GUI’s • I complained once to a professor about the lack of power in the campus computers. He reminded me that the first FEA he conducted was on a computer with 32k (not M or G, that’s a k), no hard drive, and of course software he had to write himself …

  7. Our Software • MSC.Patran + Marc • Patran is a pre/post processor code • It supports all the major general purpose FEA codes • It also supports customized, user-defined input and is very useful for post-processing full-field experimental data

  8. The Process • How it all works • The first step is to tell Patran which analysis code you will use • Then it configures options to reflect capabilities of that code • You create a FEA model using a consistent user interface • “Analyze” invokes a translator that creates an input file for the analysis code and starts the run • The analysis code creates an output file • “Read Results” invokes a translator that associates the analysis code output with the finite element model • Postprocessing is now done with a consistent user interface

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