Modal & Operating Deflection Shape Analysis
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Modal Analysis and Operating Deflection Shape (ODS) testing are typically used to investigate natural frequencies of machinery and supporting structures. Modal analysis measures the natural frequencies, mode shapes and damping of structural natural frequencies. Where vibration analysis only measures the response of the machine or structure to unknown forces, modal analysis can be used to determine these dynamic forces.
A high percentage of machinery and structural vibration problems are caused by natural frequencies excited to resonate by rotating machinery. An analysis of a problem may include performing an ODS prior to a modal test.
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ODS Testing: Vibration data is measured at various points on the structure or machine in operation and the data mapped to a 3D computer model of the test structure. We use ME’scopeVES and the model can be animated at any of the frequencies at which the test structure was vibrating. The animation allows examination of how the structure or it components are vibrating or moving. This motion may include flexing, bending, twisting or relative motion across interfaces such as bolted or riveted joints. The data can also be animated in the time domain.
Modal Testing: A modal test involves measuring the test structure or machine’s response to a controlled input force. The force is typically applied with an instrumented hammer also called a modal hammer. The response of the test structure is measured with accelerometers at various points on the structure. For large tests, several accelerometers are used and moved to the many test points on the structure. After acquisition of the modal data, it is curve fit to develop a mathematical model which describes the dynamic properties of the test structure. Finite elements can then be used to calculate the effect of adding or removing mass, adding plate stiffeners, damping, tuned vibration absorbers, etc.
To view examples of Modal animation, please click on "Modal Gallery" on the menu above.