Study On Wind Load Characteristics And Energy Efficiency Optimization Method Based On Added Resistance And Seakeeping Performances

Topics of the energy conservation,emissions reduction,performances optimization and navigation safety are general appeals of the industry,as well as the necessary requirements for international regulation adaption.The ship energy efficiency optimization technique considering performances in real sea states is a key segment for ship design that embodies the future development tendency.Wind load is an important part of the environmental load assessment.For container ships,the container stacking configuration has relatively significant influences on the wind load characteristics.In order to quantitatively study the forms and principles of wind load acting on ships,a systematic series of wind tunnel tests with multiple wind speeds under full wind angle range are carried out for 10,000 TEU large container ship model with the same container loading quantity but different stacking configurations.CFD calculation and empirical formula are applied for cross validation.It is concluded that the geometric shape parameters for longitudinal and lateral projected area exposed to the wind,especially the area and the centroid position,are of significant impact on wind load characteristics.Conventional stacking configurations with streamlined or stepped layouts have better wind load characteristics in general.Special stacking configurations with multiple vacancies on the deck occupy certain advantages in such aspects as yaw moment performances.Meanwhile,although CFD calculation and empirical formula are capable of predicting the wind load characteristics and improving the computing efficiency to a certain extent,shortcomings are still demonstrated in engineering practice,which requires constant researches and improvements.Subsequently,the paper proposed a simplified correction method for speed loss coefficient calculation,which is applied to the correction calculation of the Attained EEDI value for each sea area along the given route.It is concluded that the wind resistance has significant impacts on the ship energy efficiency measurement level.For the statistical calibration of wind and wave data characterizing averaged sea conditions,wind resistance increases the risk for violating the EEDI-related mandatory guidelines for newly built ships.For the statistical calibration of wind and wave data characterizing extreme sea conditions,wind resistance causes significant deterioration on ship resistance and energy efficiency,which even might threaten the navigation safety.Considering the increasing practical demand for resistance and seakeeping performances for ship navigating in real sea states,the paper conducted a systematic hull form optimization for ITTC-A2 high speed purse seine.Based on NSGA-II algorithm as the control algorithm,the paper established an optimization system involving resistance and seakeeping parameter indexes.Radial basis function method is applied for parameter modeling and hull form transformation.According to the general mathematical structure of multi-objective optimization problems,the paper modeled a systematic optimization procedure including objective functions,design variables,control variables,and monitoring variables through the engineering assistant software iSight,which realized research closed-loops of Calculation and Analysis – Model Updating – Hull Form Optimization and Reconstruction-Calculation and Analysis.In addition,the paper proposed the Convex Hull method in selecting representative iteration points that reflect the optimization iteration tendency.Series of optimization quality verification are conducted for those selected iteration points based on calm water resistance and surf-riding/broaching indexes.Results suggest that the optimization procedures are practical and effective in hull form optimization considering resistance and seakeeping performances under real sea states.The paper also proposed that the computing efficiency can be greatly improved through the applications of surrogate models,while due to certain defects,surrogate models can not completely replace the high precision numerical calculation.Finally,the paper conducted comprehensive consideration towards the multi-objective ship hull form optimization for the submerged segment and the optimum design of the container stacking configuration for the exposed segment,and then conducted an integrated energy efficiency optimization design.Results demonstrate that the multi-objective ship hull form optimization for the submerged segment improved the EEDI calculation baseline value without speed loss and the speed loss coefficient at the same time through hull form rearrangement.Also,the optimum design of the container stacking configuration for the exposed segment carries out further improvements towards the speed loss coefficient by minimizing the longitudinal wind load.The combination of them makes it possible that the optimization range of ship energy efficiency can reach 4%-6%.Among the overall optimization range,the multi-objective ship hull form optimization for the submerged segment occupies the major part,yet the influence of the wind load is still significant,which is not allowed to be neglected.The work of this paper provides valuable references to wind load assessment and related energy efficiency assessment,ship hull form optimization based on resistance and seakeeping performance,as well as the integrated energy efficiency optimization design.