To identify and resolve vibration problems, it is important to analyze the dynamic behavior of a structure.
Modal analysis is the first step for a thorough characterization of the structure’s dynamic behavior. Natural frequencies and corresponding mode shapes of the entire structure are calculated and checked for potential resonance with the excitation frequencies of the main sources of vibration (propeller and machinery).
Significance of each mode is indicated by parameters as Mass Participation Factor and Effective Mass, measures of the sensitivity of the mode to excitation from any particular direction.
To ensure that the dynamic response of the structure will be captured, the cumulative effective mass of the calculated modes will have to amount to at least 90% of the total structure mass.
Modal analysis paves the road for more complex dynamic analyses, as Modal Frequency Analysis, Response Spectrum Analysis and Power Spectrum Density Analysis. Direct Frequency Response analysis is another technique to obtain the structural response at discrete harmonic excitation frequencies.
