The effect of structural discontinuity on antisymmetric response of a container ship

Recent trends in capacity, hence size, growth in container ships have increased the importance of torsion, particularly how it is influenced by the large deck openings and structural discontinuities present in such ships. This paper investigates the consequences of these effects on the ‘dry’ antisymmetric modal characteristics and consequent wave-induced loads. A beam model with more accurate representation of warping and structural discontinuities is applied to a box beam to assess these influences and compare predictions of natural frequencies and mode shapes with previous calculations and finite element (FE) predictions. The analysis is subsequently applied to a feeder containership travelling in regular oblique waves and resultant loads are compared with predictions obtained from previous two (2D) - and three-dimensional (3D) hydroelasticity analyses

The influence of nonlinearities on the symmetric hydrodynamic response of a 10,000 TEU Container ship

The prediction of wave-induced motions and loads is of great importance for the design of marine structures. Linear potential flow hydrodynamic models are already used in different parts of the ship design development and appraisal process. However, the industry demands for design innovation and the possibilities offered by modern technology imply the need to also understand the modelling assumptions and associated influences of nonlinear hydrodynamic actions on ship response. At first instance, this paper presents the taxonomy of different Fluid Structure Interaction (FSI) methods that may be used for the assessment of ship motions and loads. Consequently, it documents in a practical way the effects of weakly nonlinear hydrodynamics on the symmetric wave-induced responses for a 10,000TEU Container ship. It is shown that the weakly nonlinear FSI models may be useful for the prediction of symmetric wave-induced loads and responses of such ship not only in way of amidships but also at the extremities of the hull. It is concluded that validation of hydrodynamic radiation and diffraction forces and their respective influence on ship response should be especially considered for those cases where the variations of the hull wetted surface in time may be noticeable

Hydroelastic modelling for the prediction of wave induced loads on bulk carriers

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The influence of structural modelling on the dynamic behaviour of a bulker in waves

Modelling assumptions when idealising the structure of mono-hulled vessels may have an effect on the predicted wave-induced loads, when using fluid-flexible structure interaction (FFSI) models. The aim of this paper is to demonstrate the influence of structural modelling on the dynamic behaviour of a bulker in waves, a ship structure with large deck openings. Three idealisations are used, namely the original bulker with all relevant deck openings, and the open and closed ship configurations where the deck structure between deck openings is ignored and plated over, respectively. Two- and three-dimensional hydroelasticity analyses are applied for each configuration and model. Dry hull natural frequencies, mode shapes and steady state wave-induced loads, such as vertical and horizontal bending moments and twisting moment, in regular waves are presented and discussed for all configurations. It is shown that the major influence of the structural modelling occurs in the antisymmetric dynamic behaviour of this vessel

Feasibility study for the estimation of service factors of a Great Lakes bulk carrier incorporating the effects of springing and whipping

This paper presents a summary of an investigation into the effects of hull flexibility when deriving an equivalent service factor for a GLBC. The long term wave induced bending moment predicted using traditional 3D rigid body hydrodynamic methods is increased for the effects of springing and whipping, based on 2D hydroelasticity predictions. The analysis results were correlated with full scale measurements that are available for this ship

Use of hydroelasticity analysis in design

Application of hydroelasticity analysis in various stages of the design process can provide improved predictions of global wave-induced loads, such as torsional moments for mono-hulled vessels and splitting and torsional moments for multi-hulled vessels, by modelling the physical problem more accurately. The complexities involved in generating the data for the fluid-flexible structure interaction (FFSI), on the other hand, can be considered as a disincentive to its extensive use by designers. This particular issue led to the work described in this paper on the application of 3D hydroelasticity analysis tool for the dynamic behaviour of ships in waves through the use of the G-Hydroflex portal. This web-enabled application allows users to solve FFSI problems by utilising large Grid based computer resources. The portal also allows geographically dispersed designers to work together with ease and security. Following the description of the portal architecture, applications to a range of mono- and multi-hulled vessels are illustrated and further improvements discussed

Evaluation of rogue wave induced loads using 2D hydroelasticity analysis

Evaluation of wave-induced motions, accelerations and loads are important for predicting the performance of ships in waves and assessing their strength. Rogue waves are a phenomenon that has become an important issue recently due to a number of key incidents and/or loss of life. Two-dimensional (2D) hydroelasticity analysis has been extensively applied to predict wave-induced motions and loads in regular and long-crested irregular waves, including severe weather conditions. This paper focuses on the evaluation of symmetric motions (i.e. motions and distortions in the vertical plane) and global wave-induced loads for a Leander class frigate in head irregular and rogue waves using a 2D hydroelasticity analysis. Predicted motions are compared with test measurements from a rigid model in head irregular and rogue waves. Two options for generating rogue waves, namely optimizsation and NewWave approaches, are investigated. Comparisons are made between irregular and rogue waves. The effects of forward speed and slamming are discussed

The influence of forward speed and non-linearities on the dynamic behaviour of a container ship in regular waves

The aim of this paper is to compare the heave and pitch motions for the S175 containership, travelling in head regular waves, obtained from the frequency domain linear and time domain partly nonlinear potential flow analyses. The frequency domain methods comprise the pulsating and the translating, pulsating Green's function methods, with the relevant source distribution over the mean wetted surface of the hull. The time domain method uses the radiation and diffraction potentials related to the mean wetted surface, implemented using Impulse Response Functions (IRF), whilst the incident wave and restoring actions are evaluated on the instantaneous wetted surface. The calculations are carried out for a range of Froude numbers, and in the case of the partly nonlinear method for different wave steepness values. Comparisons are made with available experimental measurements. The discussion focuses on the necessity for a nonlinear approach for predicting the radiation potential and the possible numerical methods for its formulation