Wave-induced motions of an air cushion structure in shallow water

Thiagarajan, Krish; Morris-Thomas, Michael

doi:10.1016/j.oceaneng.2005.05.015

Cited by 20 publications

(8 citation statements)

References 1 publication

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“…The wave height in the laboratory tests was fixed at 0.08 m. The model wave period was in the range 1.0-3.0 s, while the prototype wave period was 5.0-15.0 s, within the range of most wave periods for wind-generated waves. In ship dynamics, the magnification factor of oscillating motion of a ship in waves is not only related to the inherent characteristics of the structure and frequency of wave disturbing forces or moments, but also to the ratio of the wavelength (L) to the length of the ship [29][30][31]. In this study, the outermost distance from one bucket to the other, S, was selected to compare the test results.…”

Section: Methodsmentioning

confidence: 99%

Influencing Factors of Motion Responses for Large-Diameter Tripod Bucket Foundation

et al. 2019

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Large-diameter multi-bucket foundation is well suited for offshore wind turbines at deeper water than 20 m. Air floating transportation is one of the key technologies for the cost-effective development of bucket foundation. To predict the dynamic behavior of large-diameter tripod bucket foundation (LDTBF) supported by an air cushion and a water plug inside every bucket in waves, three 1/25-scale physical model tests with different bucket spacing were conducted in waves; detailed prototype foundation models were established using a hydrodynamic software MOSES with a draft of 4.0 m, 4.5 m, and 5.0 m and with a water depth of 10.0 m, 11.25 m, and 12.5 m. The numerical and experimental results are consistent for heaving motion, while exhibiting favorable agreement for pitching motion. The results show that the resonant periods for heaving motion increased with increasing draft and water depth. The maximum amplitude for heaving motion first decreased and then increased with the increase of water depth and spacing between the buckets. The maximum amplitude for pitching motion first decreased and then increased with increasing water depth but decreased with increasing spacing between the buckets. The wider the spacing between the bucket foundations, the larger the heave response amplitude operators (RAOs). Simply improving the pitch RAOs by increasing the spacing between bucket foundations is limited and negatively affects motion performance during the transportation of LDTBF.

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Section: Methodsmentioning

confidence: 99%

Influencing Factors of Motion Responses for Large-Diameter Tripod Bucket Foundation

et al. 2019

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“…Figure 3 shows an overview of the manufacture, transportation and installment of a jacket offshore wind turbine with suction-type foundation. The interactions between water waves and air-cushion supported structures have been widely studied in the past decades [12][13][14][15][16]. Generally speaking, the problem of floating structures with air cushions in waves involve not only hydrodynamics but also aerodynamics, which brings difficulties to the traditional hydrodynamic analysis approaches.…”

Section: Introductionmentioning

confidence: 99%

Numerical simulations of towing a jacket foundation with triple buckets

Tan

Liu

2023

IOP Conf. Ser.: Mater. Sci. Eng.

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Offshore wind energy is developing fast as a promising renewable energy resource that can be helpful in achieving the global net-zero emissions goal. In recent years, offshore wind turbine projects have gradually moved towards far-offshore sea areas, where massive jacket foundations with suction buckets are suitable options. To reduce transportation costs, the wet-towing method is usually favourable since the required buoyancy of the foundation can be provided by the air cushions in the suction buckets. This engineering background brings us a research topic that involves towing and air cushions in waves. This study considers the towing problem of a jacket foundation with triple suction buckets. First, numerical analysis in the frequency domain is conducted using WAMIT®. In particular, the NEWMODES subroutine is extended to consider three separate motion modes in the buckets. Numerical predictions of the natural period show satisfactory agreement with the available experimental data in the literature. Moreover, a time-domain numerical model is developed to simulate towing of the jacket foundation in regular waves based on the potential flow theory. The time-domain model numerically solves the towing force in regular waves, the body motions and the air pressures in the buckets. The simulation results generally agree well with the published experimental data. Besides, the present simulation results suggest that the transit towing force and the forward speed of towed triple-bucket jacket may be considerable in the initial towing stage.

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“…The ordinary floating body is equivalent to a structure with a foundation supported on a water-spring. On the other hand, the bucket foundation is equivalent to a structure with a flexible foundation supported on a series of springs coupled by the compressible air-spring and water-spring [10][11][12][13][14][15][16]. Therefore, to predict the air-floating performance of the bucket foundations accurately, it is inappropriate to use the same parameters and calculation methods that are used in predicting the hydrodynamic performance and response of traditional rigid-bottom platforms or ship structures.…”

Section: Introductionmentioning

confidence: 99%

Air-Floating Characteristics of Large-Diameter Multi-Bucket Foundation for Offshore Wind Turbines

et al. 2019

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In the present study, as a novel and alternative form of foundation for offshore wind turbines, the air-floating characteristics of a large-diameter multi-bucket foundation (LDMBF) in still water and regular waves are investigated. Following the theory of single degree of freedom (DOF)-damped vibration, the equations of oscillating motion for LDMBF are established. The spring or restoring coefficients in heaving, rolling and pitching motion are modified by a dimensionless parameter ϑ related to air compressibility in every bucket with the ideal air state equation. Combined with the 1/25 scale physical model tests and the numerically simulated prototype models by MOSES, the natural periods, added mass coefficients and damping characteristics of the LDMBF in free oscillations and the response amplitude operator (RAO) have been investigated. The results shown that the added mass coefficients between 1.2 and 1.6 is equal to or larger than the recommended values for ship dynamics. The coefficient 1.2 can be taken as the lower limit 1.2 for a large draft and 1.6 can be taken as the upper limit 1.6 for a small draft. The resonant period and maximum amplitudes for heaving and pitching motions decrease with increasing draft. The amplitudes of heaving and pitching movements decrease to a limited extent with decreasing water depth.

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Wave-induced motions of an air cushion structure in shallow water

Cited by 20 publications

References 1 publication

Influencing Factors of Motion Responses for Large-Diameter Tripod Bucket Foundation

Influencing Factors of Motion Responses for Large-Diameter Tripod Bucket Foundation

Numerical simulations of towing a jacket foundation with triple buckets

Air-Floating Characteristics of Large-Diameter Multi-Bucket Foundation for Offshore Wind Turbines

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