A precise prediction of the dynamic behaviour of ship structures is important to avoid resonances and high vibration levels under operation conditions. For model correlation purposes and forced vibration calculations experimentally determined natural frequencies, corresponding mode shapes and damping values are necessary. To identify modal parameters using classical modal analysis, much effort is required to achieve an adequate excitation of these big structures. Good results were obtained using a big excitation mass (600 kg) in combination with sensitive seismic accelerometers. For several reasons this classical modal approach with its artificial excitation is restricted to the use at a ship yard only. To obtain modal parameters of ship structures under real draft, ballast, loading and surrounding water conditions, a suitable testing technique is needed. To evaluate the suitability of operational modal approach both, classical and operational modal analysis were applied under ship yard conditions as well as operational modal analysis during several test trails. Under ship yard conditions both testing techniques have shown adequate results. For the identification of the lowest elastic modes of the ship structure operational modal analysis is the preferable tool. Applying operational modal analysis under test trail conditions, harmonic vibrations, induced mainly by main engine and propeller blade excitation, pollute the recorded Power Spectral Densities and reduce the frequency ranges for modal parameter estimation.
Parameter identification of ship structures using classical and operational modal analysis
Parameteridentifikation von Schiffsstrukturen mittels klassischer und operationeller Modalanalyse
2006
15 Seiten, 25 Bilder, 2 Tabellen, 10 Quellen
Conference paper
Storage medium
English
Schiffbau , Mechanik , Strukturdynamik , Modalanalyse , dynamisches Verhalten , Frequenzbereich , Schwingungsanalyse , Schwingungsanregung , Übertragungsfunktion , Schwingungsmessung , Messung mechanischer Größen , Sensorik , Beschleunigungsmesser , Analog-Digital-Umsetzer , Korrelation , mathematisches Modell , Finite-Elemente-Methode , numerische Simulation , Resonanz
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