Engineering Analysis on Vibration Characteristics of Merchant Vessels with Theoretical and Onboard Test Approaches
Abstract:Recent development of ship design, such as flexible hull structures with somewhat light ship weight in terms of larger/longer/wider principal particulars and long-stroke diesel engine of high brake horsepower, has been demonstrated dramatically. Nevertheless, this kind of ship design concept harmfully degrades system stability of electronic instrumentation and operating performance of human beings in sea service. Therefore practical prediction on structural vibration behavior of designed vessels is of primary concern and has to be taken into account at the preliminary design stage. Two theoretical approaches, preliminary prediction by empirical formula and numerical solutions by finite-element technique (matrix analysis methodology), are briefly reviewed. An onboard test system for structural vibration measurement is developed and comprehensively described. In fact, a standard procedure of data acquisition and analysis system for structural vibration measurement is already set up to deal with several kinds of vibration research work in practical engineering fields. Natural frequencies of vibration behavior for a 1200 TEU container vessel are checked out by preliminary prediction of empirical formula and measurement data from onboard tests. Moreover, a comparison study by finite-element analysis and full-scale measurement is also performed on vibration characteristics of hull structures. The amplitude of vibration acceleration induced by unbalanced moment of the main engine is calculated for any point of hull at the resonance condition and the installation of an electrical balancer onboard is taken into account for vibration countermeasures also. All approximate predictions, compared with onboard test results, are found to meet with an acceptable level of engineering accuracy. The practical package of approximate approaches in both theoretical and onboard test aspects to investigate vibration characteristics of structures, for instance, hull, machinery, piping, and shafting system, in universal service is quite reliable and easily performed on portable computers for extensive engineering applications.
Document Type: Research Article
Publication date: 2001-10-01
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