Algorithm of step-by-stage optimization of ship structures according to the criteria of reliability and economy

Abstract

The issues of rational design of structures and reducing their material consumption with an optimal margin of reliability have never lost their relevance. In the conditions of real design of construction, ship, and aircraft structures, the designer most often has to reckon with not one, but several usually contradictory criteria and pursue several extreme goals. In such cases, the problem of optimal design is a problem of multicriteria optimization. The optimal design of ship structures is a technical and economic problem for which the minimum weight (or cost) is not the only sign of optimality. In this work, the task of designing a structure of minimum weight (or cost) with an optimal margin of reliability, which corresponds to the minimum total costs for manufacturing and operation during the established service life, is set. As optimization criteria, the minimum average expected total costs are considered, taking into account the possible damage from destruction and the minimum weight of the structure, while observing the restrictions on stress, stiffness, as well as the limitations of structural and technological parameters. The algorithm for the step-by-step optimization of ship structures is presented on the example of the optimization of the load-bearing structures of the twin deck hatch cover of a dry cargo ship, which revealed low reliability during operation. To determine the optimal design parameters, a random search algorithm was used in combination with the finite element method (FEM). The design of the main stiffener of the hatch cover obtained as a result of solving the optimization problem, despite a slight increase in mass, nevertheless fully meets the requirements of optimal reliability and economy. With the help of the proposed algorithm, the task of designing a structure of minimum weight with an optimal level of reliability, which corresponds to the minimum total costs for manufacturing and operation, is fundamentally solved. The technical and economic approach can be practically implemented in the design and modernization of ship structures, provided that statistical information is collected and systematized about the load, materials, costs of manufacture and repair, as well as the economic consequences of structural failures.