RESEARCH IN THE MODAL LABORATORY AT UMASS LOWELL

Extensive development has been done in the general area of modal analysis and has drawn much industry interest. Here at the University, there has been several major contributions in new ideas in this area. Some of the past work as well as current and future work is described below.

• Model Reduction Techniques - Work in this area has been extremely important to all of the modelling techniques and interfacing of analytical and experimental modal data. Techniques such as System Equivalent Reduction Expansion Process (SEREP) and the Improved Reduced System (IRS) have played an important role in all general modal analysis research areas. These model reduction techniques have been widely accepted and implemented into commercially available software packages such as DDS FEMTools, SDRC/CORDS, LMS/LINK, DYNAVIEW, and MSC/NASTRAN for advanced model correlation studies.

• Modal Vector Correlation - Work in this area has concentrated on the development of appropriate techniques such as the Pseudo Orthogonality Check (POC) and Coordinate Orthogonality Check (CORTHOG) for correlation of analytical and experiemntal modal vector sets.

• Structural Dynamic Modification - A tremendous amount of effort has been devoted in this area and major contributions to the field have been made here at the University. In particular, work was done on the local eigenvalue modification procedure in the area of complex modes and generalized beam modifications. Some research continues in the area of structural dynamic modification with emphasis on sensitivity studies.

• System Optimization & Localization of Model Changes - Research on analytical model improvement using experimental modal data has been continuing. Work has concentrated on mass and stiffness matrix optimization using generalized inverse techniques. Recent work in this area has been directed into localization of model changes to identify where discrepancies between analytical and experimental data exists. Investigation into new techniques will continue in this area.
  
  
• Estimation of Rotary Degrees of Freedom - New techniques have been developed to expand experimental modal data to include rotary degrees of freedom in order to support structural dynamic modification with generalized beam elements as well as system modeling studies. Additional techniques for estimation of rotary degrees of freedom will continue.
  
  
• Nonlinear Response - Research is continuing in this area to investigate the use of linear modal components for nonlinear applications; several new approaches are currently being explored with promising success.
  
  
• Advanced Manipulation of Experimental Data – A variety of different applications all require some manipulation of measured data.  These include all types of applications.  In many cases singular value decomposition and other linear algebra techniques are used to support these efforts.  These range from operating data, pretest considerations, advanced reduction of experimental parameters, etc.
  
  
• Design Optimization by Inverting Targets – This general approach extends beyond model optimization approaches and considers the disassembly of system models to obtain component information to be used for design optimization of components used in system models with prescribed characteristics.

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