Application Of Rough Set Theory In Hull Form Optimization

The International Maritime Organization has proposed ship Energy Efficiency Design Index(EEDI),which presents new challenges on the development of green ship.We must strengthen the study of energy-efficient hull form.With the development of computational fluid dynamics(CFD)and computer technology,CFD-based hull form optimization continues to progress,and has become an effective way of energy-saving.It integrates the technology of hull surface parametric modification,CFD numerical simulation and optimization,and ultimately achieves the hull form of optimal performance.However,hull form optimization is a typical complex engineering problems with a large number of numerical simulation and complex design and performance space,resulting in low efficiency and difficulty to obtain global optimal solution.The problems above are currently solved mainly in the following aspects.a)Development of efficient optimization algorithms;b)Development of approximation techniques;c)Development of high performance cluster computers,etc.Although the above technology has been used in hull form optimization,the efficiency and solution quality are still unable to meet the engineering requirements.In this context,this paper applies design space reduction technology to hull form optimization.Around the application of space reduction techniques in hull form optimization,this paper carries out the following work:a)A brief description of rough set theory(RST)and expression of optimization problems using the language of rough set theory.The basic flow of design space reduction using rough set theory is finally proposed through a function example.b)Key issues of design space reduction are analyzed.First,through comparative analysis of uniform design and optimal Latin hypercube sampling,uniform design is determined as experimental design method for sampling.Second,the decision threshold is determined according to the principles of statistical analysis.Finally,space reduction is applied to wave resistance optimization of KCS.c)Introduces the sequential space reduction method to the hull form optimization.First,the interval theory is used to calculate the intersections and unions of two sets of subspaces.Second,the recommended value of termination condition of sequential sampling method in engineering optimization is provided after the analysis of function examples.Finally,the wave resistance optimization of the standard model KCS is carried out with sequential design space reduction method.Through the above study,a hull form optimization method based on rough set theory is presented.The method can reduce the design space significantly,which will contribute to improving optimization efficiency and quality,thus accelerating the development of energy-saving ship.