engleski

Beam structural modelling in hydroelastic analysis of ultra large container ships

Increase in global ship transport induces building of Ultra Large Container Ships (ULCS), which have a capacity up to 14000 TEU with length up to 400 m, without changes of the operational requirements (speed around 27 knots). It is not fully clear how the present Classification Rules cover some dynamic phenomena typical for ULCS as for example springing and whipping, so these ships have to be submitted to direct strength calculations. Hydroelastic analysis seems to be the most appropriate method for rational design of ULCS, where free vibration analysis represents one of the most important steps. It can be done using either 1D or 3D FEM model of ship structure. Beam model is usually used in preliminary design stage, while full 3D FEM model is more appropriate for final strength check. This chapter presents a sophisticated beam model for ship vibration analysis which includes shear influence on torsion as an extension of shear influence on bending. First, the methodology of hydroelastic analysis is presented, and then the complete differential equations of beam coupled horizontal and torsional vibrations are derived. Finite element formulation for application to ship-like structures is given. Contribution of transverse bulkheads and relatively short engine room to the hull stiffness is elaborated, and it is followed by description of numerical method for vibration analysis and procedure for cross-section parameters determination. Theoretical contributions are illustrated with numerical examples which include free vibration analysis of a large container ship, and the results of its complete hydroelastic analysis, as well as torsional analysis of ship-like pontoon. In addition, also frequency dependent and independent formulation of finite element properties are given.

Hydroelasticity, Springing, Container ship, Beam model, FEM

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