20. Modal Test Results of a Ship Under Operational Conditions

Sea vessels are exposed to a complex vibration environment, influenced by the sea as well as by operational conditions. Particularly, the hydrodynamic load effects are difficult to estimate analytically. Experimental results are therefore important to verify the analytical models. In the present paper preliminary results from a full-scale modal test of a Ro-Lo vessel carried out for three different operating conditions are presented. Since little full-scale modal testing seems to have been conducted on vessels in operation, the experimental setup together with preliminary modal parameters extracted from the measurements are presented. This preliminary study is focusing on investigating the data with respect to operational conditions and shows a significant variation of the modal damping of the vessel in operation, with approximately 400 %, 200 % and 400 % difference in the first three global vertical bending modes, respectively.