Research On Hull Form Optimization Of Inland 7500t Bulk Carrier With Twin-Skeg Under Multiple Loading Cases Based On CFD

China has vast waters and numerous rivers,especially the Yangtze river,known as the golden waterway.However,there are many kinds of ships sailing in the Yangtze River,and their performance and quality are uneven,which greatly limit the waterway transportation capacity.Therefore,it is necessary to develop a ship type that can adapt to the characteristics of inland waterway and have excellent performance to develop the shipping potential of the Yangtze River waterway.At the same time,with the launch of the Energy Efficiency Design Index（EEDI）by the International Maritime Organization and the launch of the Green Ship Code by the China Classification Society,these relevant regulations and specifications have higher requirements for the Energy consumption level of newly built ships.All these have greatly promoted the research on energy-saving ship forms and the development of energy-saving technology.As a ship with excellent performance,twin-skeg ship type has long been widely studied and constructed^[1].It has the characteristics of excellent resistance performance,high propulsion efficiency,good maneuverability,small tail subsidence and small hull vibration,and is very suitable for restricted waterway like inland river.In this paper,a7500t Yangtze Twin-skeg bulk carrier is taken as the key research object,and full parametric modeling software CAESES and related optimization methods are used to carry out sensitivity analysis of the ship’s shape parameters and shape line optimization research under various operating conditions,and verified.The main work of this paper is as follows:1)In this paper,full parametric modeling of the mother ship using CAESES is carried out.The basic principles and processes of CAESES modeling are introduced,and the characteristic curves and parameters used in the modeling process are introduced and analyzed.Finally,the accuracy of the mother ship is verified.2)CFD software STAR-CCM+was used to simulate the mother ship and the sample ship selected in the following process,so as to obtain their total resistance values and the axial velocity distribution of the flow field at the stern plate.At the same time,the model resistance test of the mother ship is carried out,and the resistance errors are all within 2%after comparison,which proves the reliability of CFD numerical simulation.3)In this paper,120 sample points were selected in the design space for each working condition by uniform design sampling,and CFD numerical simulation was carried out on the sample points to obtain the total resistance of each sample point and calculate the uniformity index of the stern flow field.On the basis of these data,kriging method was used to construct an approximate model,and after the completion of modeling,the accuracy of the approximate model was verified by a variety of different accuracy verification methods.The accuracy and reliability of the approximate model are proved.4)Based on the approximate model,the sensitivity analysis of optimization parameters was carried out by using the improved SOBOL method,and the influence of each parameter on the total resistance and the uniformity index of the stern flow field was quantified into the main effect and the total effect and analyzed.5)Finally,using the optimization module of CAESES software,the approximate model is combined with NSGA-Ⅱalgorithm,and the ship shape parameters are optimized by direct eight-objective optimization and artificially adding weight coefficients into two-objective optimization problem.Finally,four optimization schemes are selected and compared.The work of this paper provides a reference for the full parametric multi-condition optimization design of double-stern ship in inland river.