MEK Institut for Mekanik, Energi og Konstruktion

1. Theoretical and experimental investigation of transient wave-induced vibrations (whipping) in large container ships MEKInstitut for Mekanik, Energi og Konstruktion Section of Coastal, Maritime and Structural EngineeringBld. 403 Content: Currently, a large number of large container ships are built to cope with the increasing demand for ship born transportation of goods from especially Asia to Europe and USA. The increasing size of the vessels requires a careful structural analysis taking due account of the wave-induced loads. A major point of concern today is the importance of wave-induced hull-girder vibrations both in the form of steady-state vibrations in relative low sea states (called springing) andtransient vibrations in severe sea states (named whipping). These phenomena are currently not included in the standard rules from the ship classification societies. The present project is concern only with whipping. Based on accurate theoretical investigations for a wedge entering a calm water surface, a formulation of the whipping vertical bending moment has been suggested. This formulation takes into account the hull girder flexibility, the stochastic properties of the waves and the relative submergence of the section of the ship responsible for the slamming impact leading to a transient whipping vibration. However, the formulation is based on a number of simplified assumptions and also contains the unknown average length of the section subjected to a slamming impact. Hence, experimental validation is required before such theory can be applied in actual design studies. Experimental data is available trough the SeaSence project, where an onboard measuring system both gives information of the wave-induced bending moment and the corresponding sea state. The aim of the project is to use this huge amount of data to verify/amend/disregard the current theoretical formulation. The project will include FFT analyses of time series, optimization of parameters related to slamming, importance analysis related to the pertinent local and global ship parameters and, finally, an evaluation of the importance of whipping on both the extreme loads and the fatigue damage of large container vessels. Supervisor:Jørgen Juncher Jensen, Phone: 45 25 13 84, e-mail: jjj@mek.dtu.dk Ulrik Dam Nielsen, Phone: 45 25 19 70, e-mail: udn@mek.dtu.dk Master project 06-11-2006