|
|
 |
|
Informal Seminar by Adam Przekop |
|
Date: September 7, 2005
Time: 12:00pm
Location: NIA, Rm 137
Sonic Fatigue Analysis by a Reduced Order Method
Adam Przekop, NIA
Sonic fatigue is an on-going concern for high-speed aircraft and spacecraft structures. Fast closed-form solutions for geometrically nonlinear plate and shell dynamics are available only for very simple configurations, and often are offered with insufficient modal expansion. On the other extreme, numerical simulation via the finite element method (FEM) in physical degrees-of-freedom (DoFs) is accurate, yet computationally intensive. The only practical alternative for the design of fatigue tolerant thin-walled structures, which exhibit nonlinear response characteristics, is a FEM-based reduced order approach.
In order to preserve versatility, the presented reduced order scheme is incorporated into a commercial FEM packages (MSC.NASTRAN and ABAQUS).
Within those codes, standard modules are used whenever possible, including pre-processing, eigenanalysis to extract basis functions, nonlinear static solutions to determine the nonlinear modal stiffness via indirect procedure, and stress recovery. The presented implementation offers different levels of fidelity, as they may be dictated by a particular application and time-precision trade-offs. Once the reduced order system equation of motion is formed, it can be solved using an equivalent linearization or time numerical simulation method. Upon completion of a modal solution, an inverse transformation produces displacement results from which the total stress can be directly recovered. A linear cumulative damage theory is subsequently applied and fatigue estimates produced. The fatigue module utilizes the MATLAB toolbox WAFO, and permits time and frequency domain estimation.
|
|
|
Home