In order to explore the fishery, oil and gas, and tourism resources in the ocean, Very Large Floating Structures (VLFS) can be deployed near islands and reefs as a logistic base with various functions such as a floating harbor, accommodation, fishery processing, oil and gas exploration, environment surveillance, airplane landing and taking off, etc. However, in addition to the complicated hydroelastic coupling effects between the hydrodynamic loads and structural dynamic responses, when tackling the hydroelastic problems of floating structures deployed near islands and reefs, several other environmental effects and numerical techniques should be taken into account: 1) The influences of the non-uniform incident waves (multi-directions, different wave frequencies); 2) Complex seabed profile and its impact on the incident waves; 3) Nonlinear second order wave exciting forces in the complex mooring system, shallow water and coral reef geological conditions; 4) Parallel computing technology and fast solving methods for the large scale linear equations, accounting for the influence of dramatic increase of number of meshes to the computation efforts and efficiency. In the present paper the theoretical investigation on the hydroelastic responses of VLFS deployed near islands and reefs has been presented. In addition, based on the pulsating source Green function, the high performance parallel fast computing techniques and other numerical methods, in solving large scale linear equations, have been introduced in the three-dimensional hydroelastic analysis package THAFTS. The motions, wave loads, distortions and stresses can be calculated using the present theoretical model and the results can be used in the design and safety assessment of VLFS.
Abstract There are two types of breakwater including fixed and floating. The fixed breakwater is usually used in shallow water sea area, not adapted to deep water area. In deep water area, the floating breakwater is an important type of marine equipment which can improve the work environment conditions effectively. In the course of design for breakwater, the motion responses and wave absorbing performance should be focused importantly. Especially, wave absorbing ability is a key factor for evaluating the performance of breakwater. In this paper, taking the double cylindrical floating breakwater as the research object, the in-house three-dimensional hydroelasticity software THAFTS is used to calculate the motion responses and wave absorbing coefficients of floating breakwater with two different character length, and the effects of length have been analyzed. At the same time, the wave absorbing coefficients at the monitoring points same with model test under different wave period are calculated and compared with model test results. Through the comparison, the calculation results have a good agreement with the model test results, and the breakwater has a good wave absorbing performance when the wave period is less than 6s. The research here offer the reference for further optimization of floating breakwater. And the self-developed software THAFTS can play an important role in performance prediction.
Abstract In the past few decades, 3D hydroelastic theory, an important branch of ship mechanics, has been developing dramatically. It offers a fluid-structure interaction method calculating response of structure of ship or offshore platform directly, which plays an significant role in the evaluation of wave loads on maritime structures. For platform with multiple modules, it is not only referred to loads on modules themselves but also to connectors’ loads between modules for their performance prediction. Absolutely, the 3D hydroelastic method described here can solve this problem accurately and directly. In this paper, 3D hydroelastic software, named COMPASS-THAFTS, has been developed by CSSRC and CCS on the basis of 3D hydroelastic theory initially established by Wu (1984). This software is very proper for designers and researchers of offshore structures because of its convenient and fast processing function. The COMPASS-THAFTS software mainly contains two modules, frequency-domain module and time-domain module. In this paper, we will focus our attention on introduction of integrated framework and processing functions in frequency domain module of COMPASS-THAFTS. Taking a certain offshore platform as application object, the 3D hydroelastic responses are calculated and the results are processed, and finally, the internal rules of data are analyzed. In subsequent work, some new modules, such as mooring module, will be integrated into COMPASS-THAFTS.
Abstract Nowadays, more and more 20,000 twenty-foot equivalent unit (TEU) class ultra large container ships (ULCS) have been built in service across the worldwide. It is paramount that hydroelastic specialists become paying close attention to structural responses and loads predictions due to up to a 400m length of the ships. First of all, mesh convergence by finite element analysis is necessary to determine in the numerical calculation. In this paper, based on the three-dimension linear frequency domain hydroelasticity theory, the hydrodynamic meshes convergence is discussed when modelling the hull surface of the ULCS. Ascribe to the Sunway TaihuLight, rank 3 in the current TOP500 supercomputer list, the Message Passing Interface and the multi-level parallel programming model are used aimed to the wetted panels, the wave frequencies and so on. Several sets of different global grid density and grid distribution along the ship’s length for the containership are calculated to compare the hydrodynamic coefficients such as added mass, damping, wave exciting force, ship motions and exterior loads with several typical service speeds in the head regular wave. It has been concluded that sensitivity of numerical modelling converges to a stable state with increasing the panel numbers per ship. Therefore, one set of grid division optimised, and superposed elastic modes numbers are recommended in the hydroelastic analysis of numerical hydroelastic prediction of springing and whipping.
The rapid expansion of world population, the exhausting of inland resources and the requirement of sustainable development of world economy have strengthened the efforts of mankind to increase the capability of resource exploitation and space utilization in the ocean. Very Large Floating Structures (VLFS) are among those marine structures that have attracted long lasting attention in ocean utilization for several decades. The applications of different size VLFS as floating piers, floating airports, floating hotels, floating fuel facilities and even floating cities have triggered extensive researches. Several projects including the conceptual design and construction of VLFS have been launched, for instance, Mega-Float in Tokyo Bay, Floating oil storage bases in Kamigoto and Shirashima islands, Floating emergency rescue bases in Yokohoma, Floating performance stage in Singapore, Large floating bridge in Norway, Mobile offshore base (MOB) in USA and Multi-purpose floating base near islands in China. Due to much larger dimensions, relatively smaller global rigidities and lower natural frequencies than an ordinary ship, a VLFS has apparent flexible body responses rather than rigid body motions in waves. Hence hydroelastic analyses are of great importance in design and safety assessment of a VLFS. Extensive researches have been carried out during the past decades in the development of prediction methods of hydroelastic responses of VLFSs. However, most publications in this field were for VLFSs in open sea. If a VLFS is deployed near islands and reefs in complicated geographical environment, the wave conditions, wave loads and the hydroelastic responses of a VLFS will be quite different than in open sea. In this paper the three-dimensional hydroelasticity theories that have been widely used in the analysis of a VLFS in deep or shallow open sea with constant water depth are briefly introduced. Based on these theories the numerical approaches of hydroelastic analyses of a VLFS near island and reefs in shallow sea, developed recently by CSSRC, are described. Some important technical problems, including description of wave environment, design scheme, connectors between modules, hydroelastic responses, coupled responses with mooring system and safety analysis of a VLFS deployed near islands and reefs are also discussed.
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