Equivalent Linearization Analysis Of Geometrically Nonlinear Random Vibrations Using Commercial Finite Element Codes

Two new equivalent linearization implementations for geometrically nonlinear random vibrations are presented. Both implementations are based upon a novel approach for evaluating the nonlinear stiffness within commercial finite element codes and are suitable for use with any finite element code having geometrically nonlinear static analysis capabilities. The formulation includes a traditional force-error minimization approach and a relatively new version of a potential energy-error minimization approach, which has been generalized for multiple degree-of-freedom systems. Results for a simply supported plate under random acoustic excitation are presented and comparisons of the displacement root-mean-square values and power spectral densities are made with results from a nonlinear time domain numerical simulation.Rizzi, Stephen A. and Muravyov, Alexander A.Langley Research CenterLINEARIZATION; ACOUSTIC EXCITATION; FINITE ELEMENT METHOD; RANDOM VIBRATION; OPTIMIZATION; MATHEMATICAL MODELS; POTENTIAL ENERGY; COMPUTERIZED SIMULATION; LOAD DISTRIBUTION (FORCES); SPECTRAL BANDS; ROOT-MEAN-SQUARE ERRORS; ACOUSTIC FATIGUE; DEGREES OF FREEDOM

This report documents two new implementations of equivalent linearization for solving geometrically nonlinear random vibration problems of complicated structures. The implementations are given the acronym ELSTEP, for "Equivalent Linearization using a STiffness Evaluation Procedure." Both implementations of ELSTEP are fundamentally the same in that they use a novel nonlinear stiffness evaluation procedure to numerically compute otherwise inaccessible nonlinear stiffness terms from commercial finite element programs. The commercial finite element program MSC/NASTRAN (NASTRAN) was chosen as the core of ELSTEP. The FORTRAN implementation calculates the nonlinear stiffness terms and performs the equivalent linearization analysis outside of NASTRAN. The Direct Matrix Abstraction Program (DMAP) implementation performs these operations within NASTRAN. Both provide nearly identical results. Within each implementation, two error minimization approaches for the equivalent linearization procedure are available - force and strain energy error minimization. Sample results for a simply supported rectangular plate are included to illustrate the analysis procedure.Rizzi, Stephen A. and Muravyov, Alexander A.Langley Research CenterLINEARIZATION; RANDOM VIBRATION; APPLICATIONS PROGRAMS (COMPUTERS); STIFFNESS; STRUCTURAL ANALYSIS; FORTRAN; NASTRAN; RECTANGULAR PLATES; FINITE ELEMENT METHOD

This report documents two new implementations of equivalent linearization for solving geometrically nonlinear random vibration problems of complicated structures. The implementations are given the acronym ELSTEP, for "Equivalent Linearization using a Stiffness Evaluation Procedure." Both implementations of ELSTEP are fundamentally the same in that they use a novel nonlinear stiffness evaluation procedure to numerically compute otherwise inaccessible nonlinear stiffness terms from commercial finite element programs. The commercial finite element program MSC/NASTRAN (NASTRAN) was chosen as the core of ELSTEP. The FORTRAN implementation calculates the nonlinear stiffness terms and performs the equivalent linearization analysis outside of NASTRAN.

This report documents two new implementations of equivalent linearization for solving geometrically nonlinear random vibration problems of complicated structures. The implementations are given the acronym ELSTEP, for "Equivalent Linearization using a Stiffness Evaluation Procedure." Both implementations of ELSTEP are fundamentally the same in that they use a novel nonlinear stiffness evaluation procedure to numerically compute otherwise inaccessible nonlinear stiffness terms from commercial finite element programs. The commercial finite element program MSC/NASTRAN (NASTRAN) was chosen as the core of ELSTEP. The FORTRAN implementation calculates the nonlinear stiffness terms and performs the equivalent linearization analysis outside of NASTRAN.

Annotation This text synthesizes a wealth of useful information for analyzing random vibrations and structures into one coherent body of knowledge. It takes a practical yet progressive look at two major fields related to random analysis: linear and geometrically nonlinear structures, and the behavior of random structures under random loads. System harmonics and oscillations, random functions, and the theory of random vibration are covered extensively throughout the text, which includes innovative methods for calculating the probability of failure for dynamic systems. Simplified examples demonstrate applications for daily use and present new approaches to failure analysis. The author evaluates the use of random process methods for the stochastic analysis of crack growth in detail, providing a better description of failures resulting from crack propagation. For young engineers, the book touches on finite element programs such as ANSYS and the probabilistic analysis program PROBAN, facilitating solutions to more complex problems. It also illustrates how to write a FORTRAN program to build a numerical procedure suitable for the design needs.