When modeling intricate structures, subassemblies, or mechanism dynamics, the subassembly rigid body characteristics might be too complex or inaccurate to calculate. With the LMS Test.Lab Rigid Body Properties Calculator, LMS offers well-known FRF measurement techniques to extract essential parameters such as center of gravity, moments and principal axes of inertia.
Frequency response functions (FRFs) are measured in the same way as in experimental modal analysis. The structure is suspended in free-free condition using a soft suspension. FRFs are measured with standard modal testing equipment: an impact hammer or a shaker, force cells and accelerometers. For the precision of the rigid body properties, 6 different excitation locations and 8 output points (measured in 3 directions) are required. The rigid body properties calculator uses the mass line characteristics of the measured FRFs and the known geometrical coordinates of the measurement points to calculate the rigid body properties. There is no need to first identify 6 rigid body modes with the classical modal parameter identification, since it is usually not possible to perform this task accurately. The calculator is able to compensate for the residual effect of the first flexible modes on the mass line.
Three mass line methods can be defined, using either measured FRFs, corrected FRFs of which the flexible modes have been subtracted, or lower residual terms from a standard modal analysis. These three mass line methods guarantee optimum accuracy and compensation of flexible modes. Optimized data selection capabilities make FRF selection easy and visualization possible and assist users in selecting the frequency band with double cursor on either selected FRFs or sum of all FRFs. The LMS Test.Lab Rigid Body Properties Calculator supports the creation and visualization of geometries, center of gravity and principal axes and the immediate animation of rigid body modes.
