FULLY STRESSED DESIGN in MSC.Nastran PowerPoint PPT Presentation

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AGENDA. Introduction Theory Requirements Implementation Examples Concluding Remarks. ACKNOWLEDGMENTS. The EA-3B Preliminary Design Model was provided by Mr. Kris Wadolkowski, Vice President, Aerostructures, Inc., San Diego, CA. Mr. Dan Barker and Mr. Michael Love of Lockheed-Martin Aeronautics provided important guidance during the development of the design requirements..

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1. FULLY STRESSED DESIGN in MSC.Nastran Presented by Erwin H. Johnson Project Manager MSC.Software 3rd MSC.Software Worldwide Aerospace Users Conference Toulouse, FRANCE April 8-10, 2002

3. ACKNOWLEDGMENTS The EA-3B Preliminary Design Model was provided by Mr. Kris Wadolkowski, Vice President, Aerostructures, Inc., San Diego, CA. Mr. Dan Barker and Mr. Michael Love of Lockheed-Martin Aeronautics provided important guidance during the development of the design requirements.

4. DESIGN SENSITIVITY & OPTIMIZATION ENHANCEMENTS IN THE 2001 RELEASE Discrete Variables Fully Stressed Design Enhanced text interface Support of FREQ3/4/5 Random Analysis Support Complex Eigenvalue Support External Response - DRESP3

5. DS&O RELATED ACTIVITES FOR THE MSC.Nastran 2002 RELEASE Performance Enhancements Eigenvector Sensitivity/Optimization Dynamic Response Enhancements Miscellaneous Enhancements Updated User’s Guide

6. INTRODUCTION Fully Stressed Design (FSD) has been implemented in the 2001 Release of MSC.Nastran Produces a design where each design variable is at its limit under at least one load case Provides a rapid means of performing initial sizing of aerospace vehicles Allows for the design of a virtually unlimited number of element sizes FSD is a well known design technique that has long been implemented in codes such as FASTOP, LAGRANGE and ASTROS

7. BACKGROUND for FSD in MSC.Nastran MSC.Software has been aware of FSD but has not previously implemented the technique because: MSC.Software has concentrated on more general Mathematical Programming (MP) methods FSD lacks a theoretical underpinning There are several motivations for implementing the technique FSD is fast FSD can handle many thousands of design variables, something our MP methods cannot do Numerous client requests


9. FSD REQUIREMENTS Applicable for Static and Static Aeroelastic Analyses Supports multiple load cases and multiple boundary conditions Supports composite materials Allowable limits on Stress and/or Strain Limits can be imposed on design variables and property values Design Properties - Areas of rods - Thicknesses of plates (PSHELL and PSHEAR) - Thicknesses of composite layers

10. FSD LIMITATIONS Bar and Beam Cross Sections cannot be designed Ply Orientation is not an available design variable If an element is constrained, but there are no design properties associated with the element, the constraint is ignored. If a property is designed, but there are no constraints associated with the associated elements, the property is held invariant. Shape design variables are not supported. Material and Connectivity Properties are not supported. None of these limitations apply for Math Programming design tasks.

11. FSD INPUT The text interface developed for Math Programming is used for FSD The DESSUB case control command identifies the constraints that are to be applied in each subcase DESVAR and DVPREL1 entries define the designed properties DRESP1 entries define the responses DCONSTR entries define the constraints Other Case Control Commands and Bulk Data entries are ignored Two new parameters control the FSD algorithm: FSDALP - The ? relaxation parameter of the resizing algorithm (default = 0.9) FSDMAX - Maximum number of FSD design cycles (default = 0)

12. FSD RELATIONSHIP to MATH PROGRAMMING FSD and Math Programming (MP) Design Cycles can be run sequentially There are up to FSDMAX FSD design cycles followed by up to DESMAX MP design cycles MP cycles can be skipped with DESMAX=0 The FSD result is often an excellent starting point for an MP design task All design model user inputs are honored in trailing MP design cycles Additional ANALYSIS types (e.g. FLUTTER) can be included DVGRID, DVPREL2, DVMRELi, DVCRELi, DRESP2 and DRESP3 entries are honored

16. DESIGN TASK FOR PRELIMINARY MODEL Problem Statistics - 339 GRIDs 219 CBARs 295 CQUAD4s - 235 CRODs 69 CSHEARs 77 PBARs - 43 PRODs 3 PSHEARs 25 PSHELLS 23 Static Load Cases - 23093 responses Two Design Strategies - 1st Strategy - Existing PSHEARs, PSHELLs and PRODs were designed - 71 Design Variables 2nd Strategy - Each CROD,CQUAD4 and CSHEAR Element was independently designed - 654 Design Variables

21. DESIGN TASK FOR CANTILEVERED MODEL Symmetry has been used analyze half of the actual structure which has the load applied at the center of the tip face 8000 PSHELL properties in the half-model Each property is a design variable Variables have an upper limit of 1.0 and a small lower limit Limit applied on the von Mises stress in each element Final design is a function of the allowable stress Smaller allowables require more structure Looking for a design concept, not a viable design

23. CONCLUDING REMARKS Fully Stressed Design is available in the 2001 Release of MSC.Nastran Enables rapid structural design of aerospace structures User Interface borrows from SOL 200 interface with two additional user parameters Possible future developments (with no current plans): A specialized user interface to create the design –model Extension to PBEAM, PBAR and/or PWELD properties User feedback is solicited

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