Research On Hull Form Design Optimization Based On SBD Technique

With the rapid development of computer technology and the continuous improvement ofoptimization theory, optimization techniques have been introduced into the field of ship design.Optimization algorithms and advanced CFD techniques are successfully integrated together intowhat is known as Simulation-Based Design (SBD) techniques, which opens a new situation forhull-form optimization design and configuration innovation. A worldwide attention has beenconcentrated since the SBD techniques was presented. In this paper, numerous internationalresearches are summarized and reviewed. And fundamental elements of the SBD techniques aredescribed and crucial components are analyzed profoundly. Foucus is on breaking through keytechnologies as hull geometry modification and reconstruction, global optimization algorithms,and codes integration. Combined with high-fidelity CFD codes (on RANS), an automatichull-form design optimization platform is established, and the hull-form reverse design pattern isdeveloped. Based on that, the application of the platform in the hull-form optimization design isillustrated by three practical examples in detail.First, the global particle swarm optimization algorithm (PSO) is studied, and itsinitialization method and the inertia weight factor are improved, which provides effective andefficient scientific methods for solving the hull-form optimization design problem. Based on that,supported by series model test database and combined with potential theory and empiricalformula, a multi-objective global optimization system with high reliability and fast response forship hydrodynamic performance is established at the initial design stage. In the procedure, thehull geometry is modified automatically by Lackenby method. Three objective functions,admiralty coefficient, percentage of time and non-dimensional turning diameter, are chosen ascriteria for evaluating the ship performance on powering, seakeeping and maneuveringrespectively. Specially, some valuable empirical formulae derived from extensive model testsdata of parent ships, strip theory and empirical formula are used to calculate the objectivefunctions.Furthermore, two geometry modeling methods to modify the hull surface are developedduring optimization cycles, which are Bezier Patch method and Free-Form Deformation methodto represent a complex geometry and to satisfy different design requirements. The high-fidelityCFD solvers based on RANS, complex grid automatical regeneration method and approximationstrategy are integrated into the hull-form design optimization software platform with independentintellectual property.Next, an example of the optimization platform application for a surface combatant hulloptimization is illustrated. In the procedure, the improved PSO algorithm is adopted forexploring the design space. The objective function, namely, the total resistance, is assessed byRANS solvers. The results verify the feasibility of the platform by showing that the decrease ofthe total resistance for the optimal design is very significant. Subsequently, the multi-objectiveoptimization design for the bulb of DTMB5415is carried out; the resistance of three different speeds are selected as the three objective functions. In order to reduce the computational cost, theapproximation strategy based on experimental design and response surface model is adopted.The results show that the reduction of the total resistance is about6%for the optimized hullformat the design speed (Fn=0.28),while the numerical noise are clearly smaller than this value. Itmay be of interest to look at off-design conditions too: in the entire speed range, a maximumreduction of about6.73%is obtained at Fn=0.21. The given combatant design optimizationexample demonstrates the practicability and superiority of the proposed SBD technique for themid-high speed ship.Finally, selecting the total resistance and the quality of propeller disk wake field asobjective functions, two bulk carriers are optimized by optimization platform. The6600DWTbulk carrier's optimization results present an obvious reduction of resistance for the optimalsolution. This is a promising result for the bulk carrier design, which will be very difficult to getby traditional design approaches guided only by the experience of the designers. The44600DWTbulk carrier's optimization results show that the decrease of the total resistance is significant inthe entire speed range, with a reduction of about5%, taking into account gains of propulsionefficiency produced by the improvement of wake field, and the comprehensive energy-savingeffect will be further expanded. This is very large improvement in the resistance performance oftwo bulk carriers, considering the small modifications allowed and the good initial performancesof the original hull. And it indicates that the SBD techniques are very attractive for low carbonshipping design.