Seminar on Ship Vibration

Since the first ship vibration seminar (Laivojen värähtelyt ja niiden torjunta, VTT seminaarisarja N:o 22, Espoo 1980) organized by VTT in 1979, considerable progress in this field has been made. The purpose of this second seminar is to present the current state of research activities. The ship vibration research in the VTT Ship Laboratory has been largely carried out within a joint project with COMECON countries. The first five year project was completed in 1980. The second project started in 1981 and is mainly dealing with superstructure and afterbody vibrations. The prediction methods for propeller excitation, treated in the first paper, now include the effect of cavitation, too. Experimental verification is made possible by the development of equipment for pressure measurements and cavitation photography.Propeller excitation from the point of view of a shipyard is discussed in paper no. 2. Development in the calculation methods are presented in papers no. 3 and 4. According to experiencies gained from three dimensional finite element models, it is possible to predict the vibration level with reasonable accuracy. New features, such as an easy modification of mass distribution and a realistic three dimensional fluidstructure interaction capability, can now be incorporated in the model. Modal synthesis techniques are currently being developed. The exciter test system now includes a hydraulic shaker, controlled by a desk top computer. The same computer also gathers and processes signals from the vibration transducers. This system, described more closely in paper no. 5, has been succesfully used in the prediction of vibration level of several ships during construction stage. Our guests from the famous Krylov Ship Research Institute, with whom we have had close and fruitful cooperation during many years, present their views and research activities in papers no. 6 and 7.