| The main task of Preliminary Design for Semi-Submersible Platform in company is to determine the principle dimension and estimate the cost. The general practice is to refer to determine the key equipment according to the function requirements first; then modify the he selected model vessel according to the experience and calculate the hydrostatic stability performance. If stability performance is not satisfied, the principle dimension has to be further modified to get satisfied design. Further modification usually required to considering the cost performance. In this preliminary design process, there are two shortages. The first, the motion response character is not analyzed. This may have a significant impact on the comfort, the work efficiency of the key equipment, the strength of the overall structure, the fatigue life and the positioning capability. The second,there is not rapid optimization method to find out the Preliminary Design with advantage of cost performance.The object of this paper is to improve the Preliminary Design process to solve the shortages described above. The research will be carried out around the three aspects of Principle Dimension of the semi-submersible platform, the Motion Response Characteristic and the rapid Optimization Method.In this paper, one Semi-Submersible Platform delivered by CIMC Raffles Offshore Ltd. is selected as model vessel to carry out the research. Firstly, study the relationship between the Principle Dimension and the Weight Control, Hydrostatic Stability and Motion Response Character via comparison of 6 different designs with single varied dimension of the model vessel,such as the number of column, the space between columns, the size of column section, the space between pontoons, the length of pontoon and so on. This comparison is carried out base on the principle of orthogonal test. Secondly, derive the mathematical formula of motion response according to the three-dimensional potential flow theory and the use the professional software of AQWA to calculate the motion response for these varied designs. Based on the comparison of motion response amplitude operator (RAO) and the Additional Mass due to motion with the model vessel., a simplified algorithm is proposed to be applied during the preliminary design to control the motion response character; Finally, the hybrid genetic algorithm based on the conjugate gradient method is used to optimize the model vessel to get a preliminary design with object of light weight of 25000 metric tons, and the other performance characters still at same level of the model vessel. The AQWA software also used to check the accuracy of the Preliminary Design obtained by the hybrid Generic Algorithm.In this paper, the research of solution pointed to the existing shortages of the company's preliminary design method is carried out. The relationship between the principle dimension,weight control, hydrostatic stability and hydrodynamic motion response is clarified. The proposal to analyze the motion response performance during preliminary design stage is reasonable, and the simplified calculation method proposed in this paper will be helpful practice to extend the preliminary design. In general,the research of this paper has achieved the goal of improving the preliminary design method of semi-submersible platform, and has the value of engineering application... |
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