Structural dynamics is a type of structural analysis which finds out the behavior of a physical structure when it is subjected to dynamic loading. It can be divided into two catalogues depending on the results: Operating Deflection Shape (ODS) analysis and Modal analysis.
ODS analysis shows the actual deflection patterns of a structure at different frequencies or time instances, under certain operating conditions. The operating conditions can be rotating speed of the machine, load, temperature, pressure, etc. If the operating conditions change, then new testing needs to be done, and the results will change too. In contrast, with modal analysis, the expected results are modal parameters: natural frequency, damping ratio, and mode shape. The results describe the inherent dynamic properties of the structure, and are independent of excitations
Unlike in modal analysis, where a linear mathematical model is assumed, no mathematical model is created in ODS, and thus it’s not possible to predict the structural behavior under other conditions. But the advantage of not having a mathematical model is that ODS can work with any type of signals, and it’s especially suitable for structures with high non-linearity.
ODS allows user to visualize the behavior of a structure with actual operating forces and under real boundary conditions, and it is often used as the first investigating tool.