Nigel White

Wave loads and flexible fluid-structure interactions: current developments and future directions

The function of a Classification Society includes the setting of standards for the design, construction and maintenance of ship hulls to ensure adequate safety throughout their service life. Fundamental to this is the determination of the design loads to support the prescriptive Rule requirements and for application in direct calculations. The current design philosophy for the prediction of motions and wave-induced loads is driven by first-principles calculation procedures based on well-proven applications such as ship motion prediction programs. In recent years, the software and computer technology available to predict design loads has improved dramatically. With the stepwise increase in ship size and complexity it is necessary to utilise the latest technologies to assess the design loads on new ship designs. This paper discusses some of the recent experiences of Lloyds Register with regard to the current state of the art in the assessment of design loads and structural responses by reviewing recent work on the effects of flexible fluid-structure interaction for hull girder and also for sloshing applications. The paper also discusses the Lloyds Register strategic research programme on hydrodynamics, involving the use of state-of-the-art technologies for the solution of ship dynamic response problems.

Time Domain Analysis of Springing and Whipping Responses Acting on a Large Container Ship

As part of WILS II (Wave Induced Loads on Ships) Joint Industry Project organised by MOERI (Maritime and Ocean Engineering Research Institute, Korea), Lloyd’s Register has undertaken time domain springing and whipping analyses for a 10,000 TEU class container ship using computational tools developed in the Co-operative Research Ships (CRS) JIP [1]. For idealising the ship and handling the flexible modes of the structure, a boundary element method and a finite element method are employed for coupling fluid and structure domain problems respectively. The hydrodynamic module takes into account nonlinear effects of Froude-Krylov and restoring forces. This Fluid Structure Interaction (FSI) model is also coupled with slamming loads to predict wave loads due to whipping effects. Vibration modes and natural frequencies of the ship hull girder are calculated by idealising the ship structure as a Timoshenko beam. The results from springing and whipping analyses are compared with the results from linear and nonlinear time domain calculations for the rigid body. The results from the computational analyses in regular waves have been correlated with those from model tests undertaken by MOERI. Further the global effects of springing and whipping acting on large container ships are summarised and discussed.Copyright

Two- and three-dimensional springing analysis of a 16,000 TEU container ship in regular waves

In recent years, the increase in world trade has resulted in a large expansion of sea traffic. As a result, market demands are leading to the development of Ultra Large Container Ships (ULCSs), with lengths of up to 400 m and increased flexibility of operational requirements. The multicellular open-decked thin-walled structural design of these ships means that flexible hull girder dynamics become important for the prediction of wave loads. This paper investigates the importance of various hydroelastic modelling approaches on the global symmetric and anti-symmetric response of a 16,000 twenty-foot equivalent unit (TEU) ULCS design. Two- and three-dimensional linear and weakly non-linear flexible fluid–structure interaction models that respectively combine Vlasov beam and three-dimensional finite element analysis (FEA) structural dynamics with a B-spline Rankine panel and Greens function hydrodynamics are assessed and compared. Comparisons between rigid body and hydroelastic predictions demonstrate the importance of considering the effects of hull flexibility on the dynamic response and the suitability of different idealisations at preliminary or detailed design stages.