Superelement, Component Mode Synthesis, and Automated Multilevel Substructuring for Rapid Vehicle Development 2008-01-0287

This paper presents the new techniques/methods being used for the rapid vehicle development and system level performance assessment. It consists of two parts: the first part presents the automated multilevel substructuring (AMLS) technique, which greatly reduces the computational demands of larger finite element models with millions of degrees of freedom(DOF) and extends the capabilities to higher frequencies and higher level of accuracy; the second part is on the superelement in conjunction with the Component Mode Synthesis (CMS) and also Automated Component Mode Synthesis (ACMS) techniques. In superelement, a full vehicle model is divided into components such as Body-in-white, Front cradle/chassis, Rear cradle/chassis, Exhaust, Engine, Transmission, Driveline, Front suspension, Rear suspension, Brake, Seats, Instrument panel, Steering system, tires, etc. with each piece represented by reduced stiffness, mass, and damping matrices. Super-element has the advantage that matrices can be passed from one organization to another without revealing proprietary details or concern. This virtual technique is very efficient, economical and versatile for the automotive and aerospace applications. The component mode synthesis is a form of superelement dynamic reduction wherein matrices are defined in terms of modal co-ordinates (corresponding to the superelement modes) and physical co-ordinates(corresponding to grids on the superelement boundaries). In the AMLS method, the structure is recursively divided into thousands of superelements/substructures and eigenvectors associated with these subdomains are used to represent the structure's response rather than the traditional global eigenvectors. Reduction of the finite element discretization is based on many small, local, inexpensive eigenvalue problems. The mobility at various interfaces between body and other components, and acoustic sensitivity response at driver's ear are presented for a five million DOF and 4.8 million DOF vehicles. A comparative study of CPU time and Elapsed(wall-clock) time for different methods and number of CPUs are presented. It is concluded that the methods such as AMLS/ACMS, and acoustic superelement in conjunction with CMS are very cost effective and 4 to 6 times faster than the use of conventional techniques.