FEMtools RBPE (Rigid Body Property Extractor)

Extract the Rigid Body Properties of a Structure from Measured FRFs

The FEMtools Rigid Body Properties Extractor (Ft-RBPE) is a FEMtools add-on tool for extracting the rigid body properties of a structure from a set of measured Frequency Response Functions (FRFs). The following properties are obtained from the low-frequency portion of measured accelerances:

  • Mass (M)
  • Center of gravity locations (CoG)
  • Mass moments of inertia (MoI)
  • The rigid body properties can be used to validate a finite element model, for substructuring or motion analysis.

The Ft-RBPE is installed and used as an add-on to the FEMtools Framework or any other FEMtools configuration.


The rigid body properties are obtained by dedicated experimental testing (FRFs) and can be used as reference values for validating a finite element models. Other applications include:

  • Automated model updating using rigid body properties as reference target.
  • Reduce components to lumped masses for model substructuring in structural dynamics simulations or motion analysis.
  • Generation of rigid body modes for modal-based synthesis.


  • Easy to Use – A single control window is used for all settings, data visualization and table with results.
  • Cost Effective – Using the same equipment for experimental modal analysis, FRFs are inexpensive to obtain compared to traditional experimental methods that use dedicate machinery to identify CoG and MoI.
  • Robust Solutions – Rigid body properties are obtained from a (redundant) set of FRFs using curve fitting and straightforward equation solving. Assess the uncertainty of the results using error estimators.