Dynamics_70_M6_Spectrum.ppt

Spectrum Analysis Module 6 Module 6Spectrum Analysis A. Define a spectrum analysis and its purpose. B. Understand the underlying concepts and terminology. C. Learn how to do a response spectrum analysis. D. Guidelines for spectrum analysis. E. Random Vibration Analysis Spectrum AnalysisA. Definition Purpose What is spectrum analysis? A technique to compute a structure’s response to transient excitations that contain many frequencies. Excitations could be from sources such as earthquakes, aircraft noise/ flight history, missile launches. A spectrum is a representation of a load’s time history in the frequency domain. This is also referred to as response spectrum. Spectrum Analysis… Definition Purpose El Centro Earthquake ( 1940 ) Spectrum Analysis… Definition Purpose Spectrum analysis follows a modal analysis. Computes the maximum response of the structure to a given spectrum at each natural frequency. This maximum response is computed as scale factor*mode shape. These maximum responses are then combined to give a total response of the structure. Spectrum Analysis… Definition Purpose An alternative is to perform a transient analysis. Transient analysis is generally more time consuming, especially when a number of components and load conditions have to be considered. However, transient analysis is more accurate. In spectrum analysis the focus is to get the maximum response quickly, and some information is lost (phase). Spectrum Analysis… Definition Purpose Used in the design of: Nuclear power plants (buildings and components) Airborne Electronic equipment (aircraft / missile) Spacecraft components Aircraft components Any structure or component that is subjected to seismic or other erratic loads Building frames and bridges Spectrum Analysis… Definition Purpose ANSYS allows four types of spectrum analysis: Single-point response spectrum** A single response spectrum excites all specified points in the model. Multi-point response spectrum ** Different