Overall Vibration Performance Research On Low Ballast Oil Tanker

This dissertation is aimed at the study of low ballast tanker’s overall vibration. The selected parent ship is a300,000crude oil tanker. Traditional VLCC ship is60m wide. A new type of low ballast water VLCC ship is developing which breadth is68m in order to meet the Ballast Water Convention. The performance of the ship has many changes as the change of breadth. The paper aims to study the impact of the overall vibration characteristics. The presence of vibration is the source of many accidents, which can also lead to the fatigue failure of structure and discourage the exertion of machinery and equipments. What’s more, the noise caused by vibration can do harm to people who work on the ship and affect the comfort of the ship. Therefore, it is of great necessity to study the overall vibration characteristics of the large vessels.In this dissertation, the target tanker is a new one which is gained after a series of similarity transformation based on the parent tanker. All the transforms is for the purpose of decreasing the ballast water and thus lowering the pollution caused by it. This dissertation is organized as follows.First of all, this article describes the background and significance of the thesis as well as domestic and foreign research status on the ship vibration problems briefly.Secondly, the paper describes the theoretical knowledge of ship’s global vibration, including the influence caused by ship hull’s outboard water to vibration, empirical formula used for estimating the global vibration and detailed calculation methods.Thirdly, the paper establishes the finite element model of both parent ship and target ship. And research the inherent characteristics of the two by using ANSYS finite element software and then analyze the result.Finally, research the overall vibration response of the target ship and parent ship.The results show that the vertical natural frequency of the target ship is lower than parent ship which is closer to the encounter frequency and has greater probability of having wave-induced vibration. Although vertical vibration response acceleration value caused by host excitation is increased, the response acceleration value caused by propeller excitation decreases and can alleviate the effects of host vertical excitation.