22 Dynamics_01_Intro[1]

22 Dynamics_01_Intro[1] - Introduction to Dynamics 1-2 D Y...

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Unformatted text preview: Introduction to Dynamics 1-2 D Y N A M I C S D Y N A M I C S D Y N A M I C S D Y N A M I C S Introduction to Dynamics A. Define dynamic analysis and its purpose. B. Discuss different types of dynamic analysis. C. Cover some basic concepts and terminology. D. Introduce the Variable Viewer in the Time-History Postprocessor. 1-3 D Y N A M I C S D Y N A M I C S D Y N A M I C S D Y N A M I C S Dynamics A. Definition & Purpose What is dynamic analysis? • A technique used to determine the dynamic behavior of a structure or component, where the structure’s inertia (mass effects) and damping play an important role. • “Dynamic behavior” may be one or more of the following: – Vibration characteristics - how the structure vibrates and at what frequencies. – Effect of time varying loads (on the structure’s displacements and stresses, for example). – Effect of periodic (a.k.a. oscillating or random) loads. 1-4 D Y N A M I C S D Y N A M I C S D Y N A M I C S D Y N A M I C S Dynamics … Definition & Purpose • A static analysis might ensure that the design will withstand steady- state loading conditions, but it may not be sufficient, especially if the load varies with time. • The famous Tacoma Narrows bridge ( Galloping Gertie ) collapsed under steady wind loads during a 42-mph wind storm on November 7, 1940, just four months after construction. 1-5 D Y N A M I C S D Y N A M I C S D Y N A M I C S D Y N A M I C S Dynamics … Definition & Purpose • A dynamic analysis usually takes into account one or more of the following: – Vibrations - due to rotating machinery, for example. – Impact - car crash, hammer blow. – Alternating forces - crank shafts, other rotating machinery. – Seismic loads - earthquake, blast. – Random vibrations - rocket launch, road transport. • Each situation is handled by a specific type of dynamic analysis. 1-6 D Y N A M I C S D Y N A M I C S D Y N A M I C S D Y N A M I C S Dynamics B. Types of Dynamic Analysis Consider the following examples: – An automobile tailpipe assembly could shake apart if its natural frequency matched that of the engine. How can you avoid this? – A turbine blade under stress (centrifugal forces) shows different dynamic behavior. How can you account for it? Answer - do a modal analysis to determine a structure’s vibration characteristics. 1-7 D Y N A M I C S D Y N A M I C S D Y N A M I C S D Y N A M I C S Dynamics … Types of Dynamic Analysis – An automobile fender should be able to withstand low-speed impact, but deform under higher-speed impact. – A tennis racket frame should be designed to resist the impact of a tennis ball and yet flex somewhat....
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22 Dynamics_01_Intro[1] - Introduction to Dynamics 1-2 D Y...

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