Optimization and search design of floating dock hull structures based on strength and stability requirements under overall longitudinal bending state

BACKGROUND: Today, automation of hull structure design is of great interest in the shipbuilding industry. The development and advancement of Russian automated hull design systems for transport vessels, military ships, floating structures, including floating docks, are the most promising and priority tasks. Optimization and search design of hull structures allows formalizing the problem of automated decision-making and ensures the specified structural parameters, including low weight, labor intensity of manufacture or cost depending on the problem formulation.

AIM: This works aims to formulate and solve the problem of designing floating dock hull structures based on requirements to strength and stability under overall longitudinal bending state. Based on the automated parametric design method for ship structures developed by the Department of Ship Design and Maintenance of St. Petersburg State Marine Technical University and adopted as a basis for the development of automated design systems for ship and other engineering structures, the problem under consideration is designated as the high-level problem of designing the floating dock structures.

METHODS: It is assumed that the previous lower-level stages have implemented structure design processes based on requirements to the lowest thicknesses, local strength, strength, and stability of pontoon structures during its overall bending. The Rules of the Russian Maritime Register of Shipping (RMRS) are used as a technical standard providing the requirements to overall strength and stability. The structure of the Rules in relation to the floating dock hull design is such that it is required to apply iterative search methods to solve the problem under consideration. To solve the problem, it is proposed to use mathematic programming tools.

RESULTS: In this problem, the mathematical relationship of the cross-sectional area of the girder and the variable parameters is taken as the objective function. The trajectory of variables determines the required initial thicknesses allowance of the plate structures that have the most influence on the overall strength of the dock hull. Yield strength of such plate structures may also be included in the variable parameters. The constraints of this problem are determined based on design considerations and the RMRS Rules. Equality constraints allow to solve the problem for some fixed value of the selected variable. Equality constraints may include restrictions that allow automatic adjustment of the specified plate thickness of structures adjacent to structures of girder stays or the condition determining the yield strength. Inequality constraints are determined by the relevant overall strength and stability as specified in the RMRS Rules.

CONCLUSION: The described problem is tested by examples of structural designs of a cast-in-place dock with a carrying capacity of 12,000 tons and a pontoon dock with a carrying capacity of 29,300 tons. The study shows that the proposed method can adequately solve the problem and MS Excel’s Solver tool may be used to solve it.