Ship response estimation in early design stage

Abstract: A practical way to estimate the ship response in early design stage is investigated in this thesis. Focus has been put on the ship vertical bending moment and shear force in operation area. ISSC spectrum is used to indicate the sea state. Napa strip method is employed to derive the transfer function. The ship response is thus generated in frequency domain. The vertical bending moment and shear force along the ship are then calculated according to the critical wave case indicated from the response function. Based on the results, the validation of DNV-GL rule and IACS rule is discussed. In this case, the overestimation is discovered for the still water vertical bending moment and shear force. On the other hand, there is underestimation in wave vertical bending moment and shear force. The total vertical bending moment and shear force is reasonable. Since only static loads and total loads are required in the rules, the rules are judged as valid in the early design stage. The feasibility of Napa strip method has been commented and the Napa strip method is judged practical according to its accuracy and time consumption. For ship design, the wavelength and the wave steepness are the main parameters affecting the loads on hull. The block coefficient is crucial for the nonlinearity in hogging and sagging condition. More models, especially other types of ships are expected to be analysed for this topic in future study. Other methods, such as panel method could take into use in the future work. The probability of operation can be further developed based on this study.