Optimization Of Ship Structures Research Articles

Reliability-based design optimization of river-sea-going ship based on agent model technology

The common ship structural optimization design is a deterministic method without considering uncertain factors, whereas the Reliability-Based Design Optimization (RBDO) can compensate for this deficiency. The RBDO of ship structure is a multi-parameter, high-dimensional, and high-nonlinear optimization solver. There exists a difficulty in guaranteeing accuracy and efficiency due to massive computation. In this study, the high-precision agent model for the limit state of ship hold structure is established based on agent model technology, including BP neural network, Radial Basis Function neural network, and Support Vector Machine combined with SMOTE oversampling algorithm. Furthermore, the reliability computation program is developed using Monte Carlo Simulation Method. A river-sea-going ship is considered the research object. The definition of rules, structural direct calculation result, and reliability requirement within all life cycles are considered boundary conditions. The RBDO system is constructed by the simulated annealing algorithm to investigate the lightweight structure. The established system can improve the efficiency and accuracy of the RBDO, which is significant for the ship's structural optimization design.

Комплексный подход к топологической и параметрической оптимизации судовых конструкций

Комплексный подход к топологической и параметрической оптимизации судовых конструкций

Ship structural safety optimization: an integrated artificial intelligence and multi-criteria decision-making method

ABSTRACTMajority of the world cargoes is transported through the sea, and failure of the ship structure is a major concern and thus needs to be avoided due to its catastrophic nature in terms of system loss. In view of this, ship structural safety is assessed regularly so as to prevent their failures and implement cost-effective improvement measures that ensure optimal operations, especially in the realm of uncertainty. In this research, a methodology for safety assessment and optimization of ship structures using discrete fuzzy set theory as an artificial intelligence method and Technique for Order Preference by Similarity to the Ideal Solution as a multi-criteria decision-making method is developed. The two algorithms are integrated in a logical manner to achieve ship structural safety optimization under uncertainty.

Differential Equations of Stiffened Panels of Ship Structures and Fourier Series Expansions

The article presents the theory used in the LBR-5 software for ship structural optimization. Fourier series expansions are applied to solve the governing differential equations. Structures are modeled as cylindrical stiffened shells as the general case, with flat plates as a special instance.

Discrete Optimization of Ship Structures from the Viewpoint of Practical Design

In practical design of ship structures, it is obvious that some structural elements, for instance, longitudinals, must be chosen from a given set of standard discrete values being available commercially. Furthermore, some integer parameters such as the number of transverse web frames in the midship segment should be considered as the design variables to be optimized. In view of those facts, we investigate especially how to deal with the above kinds of discrete design variables in this paper. A cargo ship with large hatch opening is taken as the numerical example. The structural construction cost of hold length between two transverse bulkheads is chosen as the objective function to be minimized by genetic algorithms. Besides the conventional variable design parameters, some particular parameters such as the serial number of standard shaped steel for longitudinals and for transverse frames, the number of longitudinals in a given length, the number of transverse web frames in the midship segment, etc., are also selected as the design variables from the viewpoint of practical design. For each design variable, we describe it by a specific length binary string with a corresponding relationship to its available discrete values. Through the numerical analyses, it shows that the present method is a simple yet efficient method to deal with the discrete optimization of ship structures. The search efficiency of some genetic strategies such as the elitist preserving selection, the multi-point crossover and the uniform crossover is also investigated in this paper.

Discrete Optimization of Ship Structures with Genetic Algorithms

A discrete optimization method using genetic algorithms is developed for the optimization of ship structures. In this method, the constrained minimization problem is first transformed into an unconstrained one by a penalty term depending on the degree of constraint violation. Since the search procedure of the genetic algorithm is done based on the evaluation of fitness function, the unconstrained minimization problem is further converted into a maximization of the fitness function. The discrete design variables are coded into a binary string of finite length. The search procedure from generation to generation is carried out by a simple genetic algorithm with the genetic operators of reproduction, crossover and mutation. A cargo ship with large hatch opening is taken as the numerical example for the illustration purpose. The influences of penalty coefficient, population size, crossover probability and mutation probability on the optimum design are investigated. The comparison between the genetic algorithm and the multiplier method is also made. It demonstrates that the present method can handle the optimization of ship structures with discrete design variables well.

Optimization of Ship Structural Design by Genetic Algorithm

In general, ship basic design is based on design-spiral approach where variable design parameters are defined through repetition of trial and error. This kind of approach is a process of satisfying a lot of complicated design criteria empirically, rather than optimizing some object function. However, in order to realize optimum or rational design for a new type of structural concept with complicated design criteria, it is necessary to model the design problem as strictly as possible and accomplish more highly numerical optimization.As for ship structural optimization, the object function (hull steel weight or total cost including material, fabrication and paint cost) is closely related to principal dimensions and general arrangement. Therefore, in order to obtain better design in the optimization process, it is desirable to search broader design space with many design variables such as principal dimensions, arrangement, frame spaces, stiffener spaces, scantlings and material.This type of optimization is considered as a combinatorial optimization problem, and such optimization method that is robust and quickly converging to global optimum is required. In this paper the authors apply the genetic algorithm which simulates the law of the survival of the fittest to structural optimization problems.At first, the authors apply the genetic algorithm to minimum weight problem of a hatch cover with 6 independent variables, and compare several approaches to the genetic algorithm through numerical experiments. As a result of the examination the authors propose the genetic algorithm which attaches importance to vicinity search as the method appropriate for structural optimization problems.Then, the authors apply the genetic algorithm to the optimum design problem of a double hull tanker with 40 independent variables. It is shown that the proposed method is effective for the optimization with a variety of independent variables of different types. Using this method it is possible to obtain more accurate optimum design of ship structure by enhancing the accuracy of the estimation of object functions and many appropriate constraints.

Optimization of Ship Structures Based on Plastic Design

In this paper a procedure for the optimization of ship structures is developed based on plastic design of ship structures consisting of the transverse and longitudinal members using the Sequential Unconstrained Minimization Technique (SUMT). Using the developed method, the optimization of a segregated ballast tanker is carried out considering the weight of one hold length as the objective function. Midship section scantlings are chosen as the design variables. Constraints are considered with respect to plastic collapse of hull girder under longitudinal bending, of structural members subjected to axial force, shear force and bending moment, and of platings subjected to lateral pressure. Constraints are also set in buckling strength of platings under inplane load and in design variables such as minimum plate thickness. The variations of maximum bending moments and shear forces due to changes in design variables are calculated based on Taylor series expansion method so as to reduce the computation time of iterative calculation for function minimization in the SUMT procedure. The tanker structure got optimized and the results show that the proposed method based on plastic design is an effective tool in the optimization of ship structures. A comparison of the proposed method with the optimization based on elastic design is also made and the results are presented.

On fuzzy optimization of ship structures

Introduction de la theorie des ensembles flous dans le domaine de la conception structurale des navires. On donne une formule pour les problemes d'optimisation des structures

Studies on optimization of ship structures (The 4 th report)

When a large-sized framed structure is designed with consideration of optimization, some difficulties on the points of computer time and convergence will arise. To overcome these difficulties, some suboptimization techniques applied to partitioned substructures have already been discussed. In these procedures, however, only boundary conditions of forces on substructures are considered, hence obtained solutions do not satisfy the displacement compatibility in the total structure. Furthermore major optimization is necessary. The procedure proposed herein is to combine the major optimum and suboptimum under nearly satisfaction of force balance and displacement compatibility. To compare it with usual procedure, calculations of two examples are presented.

Studies on Optimization of Ship Structures (The 3rd report)

In regard to oil tankers of apploximately 130250 thousand ton deadweight, optimum design of longitudinal strength members is undertaken. Ship size, main proportion, transverse web space and so forth are varied. Rule requirement specified by the ship classification society of Japan is adopted as standard for design. A kind of nonlinear programming techniques, SUMT is used for numerical search. By some numerical results obtained, trends of optimum longitudinal frame space, frame area and plate thickness are examined. Furthermore the influence of using high tensile steel combined with mild steel and that of taking account of fabrication cost are studied.Main conclusions are as follows : I In comparison with actual design, optimum longitudinal frame space, frame area and bottom plate thickness are larger, hence steel weight of midship section decreases by 13%.II As ship size increases, both longitudinal member size and steel weight of midship section increases, however steel weight per cargo space decreases.III When 50 kg/mm2 high tensile steel is used combined with mild steel, steel weight decreases by about 12%, while steel cost remains almost unchanged.

Studies on Optimization of Ship Structures (The 2nd report)

As one approach towards the optimization of ship structures, such stiffened structures as bulk-heads, side and bottom shells are considered. Stiffened structures are transposed into flat grillages composed of straight orthogonal beams laterally loaded and their optimum design analyses are conducted by using framed structure analysis and nonlinear programming. The relationships between loaded area, beam number and optimum arrangements of beam sections in both simplified grillages and the bottom grillages of oil tankers are discussed. Conclusions obtained are as follows :I. The combination of matrix force method for framed structure analysis and nonlinear programming (here, SUMT method in corporating DFP method is used) can be successfully applied to the optimum design of grillages.II. In design of grillages, as the number of beams increases, the weight of grillages increases.Furthermore, the weight in case of grillages is larger than that in case of single beam structure.III. Optimum arrangements of beam sections in simplified grillages are such that shorter beams with large sectional area hang longer beams with small sectional area, still more in case where total load is applied only shorter beams, longer beams are not necessary.IV. Optimum arrangements in the bottom grillages of a center tank of oil tankers are a little different from in case of simplified grillages because of bottom platings working as a part of longitudinal and transverse girders and of difference in allowable stress between longitudinal and transverse girders.

Studies on Optimization of Ship Structures (The 1 st report)

Studies on Optimization of Ship Structures (The 1 st report)