ANALYSIS OF THE FLEXURAL MODE RESPONSE OF A NOVEL TRIMARAN BY SEGMENTED MODEL TEST

Abstract

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A NOVEL SHIP CONCEPT DESIGN IS SIGNIFICANTLY AN “AD HOC” PROCESS. IN THE PRELIMINARY DESIGN STAGE OF NOVEL VESSELS, IT IS VERY IMPORTANT TO BE ABLE TO DEVELOP AN INITIAL ESTIMATE OF THE EFFECTS OF STIFFNESS AND MASS DISTRIBUTION ON THE LONGITUDINAL FLEXURAL NATURAL FREQUENCIES DUE TO DIFFERENT GENERAL ARRANGEMENTS IN STILL WATER AT ZERO SPEED TO SATISFY DESIGN SPECIFICATIONS. FOR NEW EMERGING DESIGNS, THIS ESTIMATE HAS TO BE MADE BASED ON A MODEL TEST. THE EXPERIMENTS SHOULD ALSO BE PLANNED SO THAT SCALES EFFECTS AND OTHER FEATURES THAT ARE NOT PRESENT IN FULL SCALE CASE, ARE MINIMIZED. A MODEL WITH A LENGTH OF 1.5 METER HAS BEEN SELECTED. THE MODEL WAS CUT INTO FOUR SEGMENTS LONGITUDINALLY AND CONNECTED BY A BACKBONE BEAM WITH THREE ELASTIC HINGES JOINING THE FOUR SEGMENTS. WET VIBRATION TESTS WERE CONDUCTED ON THE MODEL, SHOWED SIGNIFICANT INFLUENCES ON THE FLEXURAL NATURAL FREQUENCIES THROUGH VARIATIONS IN STIFFNESS AND DIFFERENT MASS DISTRIBUTIONS. THE WHIPPING FREQUENCY WAS CALCULATED WITH A FOUR DEGREES OF FREEDOM THEORETICAL MODEL TO COMPARE WITH THE EXPERIMENTAL RESULTS. THE THEORETICAL MODEL SHOWS A GOOD AGREEMENT WITH THE EXPERIMENTAL RESULTS.