Modal Analysis

Modal Analysis is used to characterize the 3-dimensional response of a mechanical structure to arbitrary inputs. The response of any structure can be broken down in to one or more modes that each have a shape and frequency. Any input to the structure (such as a hammer hit or vibration) will excite these modes to varying degrees. If only one mode is excited, the structure will vibrate at one fixed frequency in one fixed shape. However, it is very rare that only one mode is excited for a given input, and the structural response is the summation of many modes, each vibrating at their own frequency and shape, all superimposed over each other.

The aim of Modal Analysis is to measure the shape and frequency of each of these modes. The measurements involve applying a known input to the structure at one or more points, and measuring the response at another point or points. Frequency Response Functions, for FRFs, are then calculated for each of these points. The result is a collection of FRFs for many points throughout the structure, which can be analyzed to get the mode shapes and mode frequencies.