S.E. Hirdaris

Hydroelasticity of ships: Recent advances and future trends:

Investigations into hydroelasticity of ships commenced in the 1970s. Since then the theory has been employed to predict the responses of a wide range of marine structures, such as mono- and multihulled ships, offshore structures, and VLFS. In recent years, with increasing market demands for new buildings of slender ocean going carriers and the continuously updated high-speed and unconventional multihulled designs, the maritime industry began to notice the advantage of assessing the usefulness and applicability of hydroelasticity in ship design. At first instance, the aim of this paper is to illustrate some of the applications of hydroelasticity theory to ships, with particular reference to recent and ongoing developments focusing on ship design applications and the effects of non-linearities and viscous flows. The paper also discusses the longer term potential use of weakly and fully non-linear fluid—structure interaction, as well as Navier—Stokes based fluid dynamic methods, for the improved modelling of ship dynamic response problems.

Risk analysis of damaged ships – a data-driven Bayesian approach

An accident occurring at sea, though a rare event, has a huge impact both on the economy and the environment. A better and safer shipping practice always demands new ways to improve marine traffic and this essentially requires learning from past experience/faults. In this regard, probabilistic analysis of accidents and associated consequences can play a very important role in making a better and safer maritime transport system. Bayesian networks represent a class of probabilistic models based on statistics, decision theory and graph theory. This paper introduces the use of data-driven Bayesian modelling in risk analysis and makes a comparison with the different data-driven Bayesian methods available. The data for this study are based on the Lloyds database of accidents from 1997 to 2009. Important influential variables from this database are grouped and a Bayesian network that shows the relationship between the corresponding variables is constructed which in turn provides an insight into probabilistic dependencies existing among the variables in the database and the underlying reasons for these accidents.

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.

Loads on ships and offshore structures

The 7th International Conference on Thin Walled Structures, ICTWS 2014, was held in Busan, South Korea, between 28 September and 2 October 2014. The conference was organised by the Lloyd’s Register Foundation (LRF) Professor Jeom Kee Paik, the LRF Research Centre of Excellence at Pusan National University and the Korea Ship and Offshore Research Institute, following successful events held at Glasgow (UK) in 1996, Singapore in 1998, Krakow (Poland) in 2001, Loughborough (UK) in 2004, Brisbane (Australia) in 2008 and Timisoara (Romania) in 2011. The highly successful ICTWS series are regarded today as a major forum for discussion and dissemination of knowledge and for mutual exchange of ideas in all areas of research, development, design and innovation pertaining to thin-walled structures including ocean engineering topics. Historically, the ICTWS community benefited from paper contributions in the research area of “Loads on Ships and Offshore Structures” and ICTWS 2014 contributors, inspired by the high relevance of this topic to the host country’s leadership in the maritime and offshore engineering fields, exceeded expectations. As a special issue was considered appropriate to underline the importance of the subject, I feel honoured that I was given the opportunity to write this Editorial note. The papers presented in this issue of Ships and Offshore Structures outline recent developments in the area of “Loads on Ships and Offshore Structures” from 54 authors representing five continents and 13 countries with active participation in the Maritime and Offshore Engineering communities. In summary, the topics presented discuss recent developments in the area of “Loads on Ships and Offshore Structures” emerging from studies on:

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.