Dynamic Response of Ship Hull due to Slamming

Abstract

In this thesis full-fledged Finite Element Analysis is done for Free vibration analysis and Dynamic Forced Response Analysis of ship hull due to the slam induced load in sea way. This topic is of concern for ships and offshore structures in terms of safety, serviceability assessment including habitability. The aim is to investigate the validation available of dynamic response prediction methods. Three-dimensional Finite Element model is developed according to the ship (135m dry cargo vessel) particulars provided by the ISSC committee II.2 Dynamic Response. Preliminary model was developed in SESAM/GeniE and later this model is used for Hydrodynamic Analysis in SESAM/HydroD and Finite Element Analysis in ABAQUS/CAE. Mass data and Bottom pressure time traces were also provided by the committee which was used for further model development and input for slamming load respectively. Committee was also provided the estimated characteristics sea state. Added mass matrices and Total damping matrices has been calculated in HydroD which was introduced in ABAQUS for Wet mode models. Low frequency natural hull girder frequencies with associated vibration modes for Dry-mode and Wet-mode models (Lightship condition, Ballast condition, Fully Loaded condition) were determined. The validity of the frequency analysis results were verified through the further investigations involving study of Classification society and ISO rules and regulations. Implicit dynamic analysis was done for the Acceleration and Strain time traces in the specified location of the ship due to the impulse load. Calculated response data will be compared to the measured data on the actual ship while at sea. The result from free vibration analysis and forced dynamic response analysis were in agreement with the accepted knowledge. A number of approximations made in the phase of model development and calculations of hydrodynamic parameter were done assuming zero forward speed which has influence on the results. In order to realize the true potential value of this work it would be necessary to compare actual ship response data to calculated data and sorting out the possible disagreements. This work is a possible source to demonstrate the adequacy of hull structural analysis tool which can potentially leading to future design improvements.