Application of a low frequency moment shaker for vibration testing

Martin Wesley Trethewey, Leonard L. Koss, Jeremy S. Trethewey

Research output: Contribution to journalConference articlepeer-review


A novel device know as a Frequency Shifting Shaker (FSS) has been previously proposed by Koss for low frequency (less that 1 Hz) vibration excitation. The system consists of oscillating an eccentric mass shaker along an axis (i.e., y-axis) perpendicular to an imbalance forcing function axis (i.e., z-axis). The system produces a dynamic excitation moment, instead of a point force, at the operational sideband frequencies. The inherent operation of the device produces a `modal shaker' in that it only excites a mode when the sum or difference frequency coincides with a natural frequency. The device produces a controllable high amplitude excitation at a very low frequency (i.e., 0.5 Hz) making the technique well suited for vibration testing of large structures. Previous work has demonstrated the fundamental feasibility with a laboratory model. The objective of this paper is to report on experiences gained with a full scale prototype FSS system with a large test structure (inertial vibration isolation test bed). The results from two tests are compared; 1) a traditional modal analysis using an impact test and; 2) an Operating Deflection Shape (ODS) analysis using the FSS as the excitation. The comparison was excellent provided the FSS was capable of sufficiently exciting the mode.

Original languageEnglish (US)
JournalProceedings of SPIE - The International Society for Optical Engineering
StatePublished - Jan 1 2000
EventIMAC-XVIII: A Conference on Structural Dynamics 'Computational Challenges in Structural Dynamics' - San Antonio, TX, USA
Duration: Feb 7 2000Feb 10 2000

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


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