Forced Vibrations.pptxbbbbbbbbbbbbbbbbbb

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1. Forced Vibrations:

2. Harmonic Force: A dynamic system, such as one that can vibrate, is often subjected to external forces or excitations, known as the 'forcing' or 'exciting' function. This excitation is typically time-dependent and can be harmonic (varying regularly like a sine wave), periodic (varying in a more complex but repeating manner), or random in nature. The following analysis focuses on harmonic excitation, as it is the most common type, often arising from engine vibrations or other sources of imbalance. The diagram above depicts a spring-mass system subjected to harmonic excitation. This takes the form of a fluctuating force with a maximum value 'F' applied directly to the mass, such as an unbalanced engine inertia force.

3. Harmonic Forces continued: The equations can be used to calculate the spring force or harmonic force, by separating the force from F=ma into two separate components.

4. Equation is used to calculate the max amplitude ratio, as variable speed devices will normally aim for the peak value. If the maximum amplitude ratio is not being sought after, and just behaviour at a specific speed, then a different equation can be used.