Modal Vibration Testing & Frequency Analysis

Experimental modal analysis is a vibration testing technique for determining the natural frequencies, mode shapes and damping ratios of a structure.



Curve Fitting & Excitation Techniques

During modal testing, an instrumented hammer, electromagnetic shaker, or piezoelectric actuator is used to excite vibration of the test article.

The vibration amplitude and phase in response to the excitation is measured at multiple locations using sensors including accelerometers and laser vibrometers. Frequency response functions are calculated with a dynamic signal analyzer.

Curve fitting techniques are used to extract the natural frequencies, mode shapes and damping ratios of a structure.



Versatility of Modal Testing

These modal parameters may be used for finite element analysis (FEA) model validation (correlation) and refinement, failure investigation, vibration troubleshooting and diagnostics, and quality assurance.

Due to the versatility of modal testing it can go by several names such as resonance test, natural frequency measurement, frequency response test (FRF), modal survey, or modal vibration test to name a few.










Modal Testing Services Include:

  • Natural frequencies, mode shapes and damping ratios
  • Hammer, shaker and piezoelectric excitation
  • Laboratory and field (on-site) testing available
  • Finite Element Model Validation
  • Modal Assurance Criterion (MAC)
  • Generator vibration testing






Experimental Modal Analysis






Modal Testing Applications

Recent modal test applications include flight qualification of helicopter modifications, mixed flow impellers, gas turbine blades and an optical table.

The modal assurance criterion (MAC) is a technique for quantifying the comparison of mode shapes from two sources. A MAC value greater than 90% generally indicates highly correlated modes. SimuTech engineers often use MAC to compare the mode shapes from two test articles or to correlate the results from a modal test with those from a corresponding finite element analysis.

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Related Mechanical Testing Services Offered


Generator Vibration

Performing vibration tests on utility scale electric power generators in fossil and nuclear plants.

Ground Vibration Testing

Measure the dynamic response characteristics of an airframe with MIMO signal processing and analysis.

Campbell Testing

Measuring the natural frequencies and mode shapes of rotating turbine blade (bucket) rows.