Experimental and numerical investigation of a jacket structure subject to steep and breaking regular waves

• Published in: Marine structures Vol. 72; pp. 102744 - 17
• Main Authors: Wang, Shaofeng, Larsen, Torben Juul, Bredmose, Henrik
• Format: Journal Article
• Language: English
• Published: Barking Elsevier Ltd 01.07.2020; Elsevier BV
• Subjects: Accuracy; Breaking waves; Experiments; Exposure; Extreme waves; Hydrodynamics; Jacket structure; Kinematics; Loads (forces); Mathematical models; Nonlinear waves; Numerical and experimental investigation; Offshore; Offshore engineering; Offshore structures; Parameter uncertainty; Parameterization; Potential flow; Regular waves; Shallow water; Slamming; Slamming force; Steep and breaking waves; Structural damage; Turbine engines; Turbines; Wave breaking; Waves; Wind power; Wind turbines; Steep and breaking waves; Slamming force; Jacket structure; Numerical and experimental investigation
• ISSN: 0951-8339; 1873-4170
• DOI: 10.1016/j.marstruc.2020.102744

Jacket structures installed in shallow water less than 50 m for offshore wind turbines are frequently exposed to steep and even breaking waves, which may result in severe damage of the structure. However, the models for calculating wave loads were primarily developed for monopile structures, and may not be suitable for jacket structures. The aim of this paper is to improve the understanding of extreme wave loads on jacket structures exposed to steep and breaking waves, based on a combination of numerical modeling and large scale experiments. The experiments with a 1:8 scaled jacket structure exposed to controlled regular waves were conducted in the WaveSlam project. In this study, the measured wave surface elevations and water particle velocities from the experiments are reproduced using a fully nonlinear potential flow solver with a fairly good agreement. Furthermore, the validity of the Morison equation applied to jacket structures is investigated. A reasonably good agreement is achieved for the steep waves without occurrence of breaking. In terms of the breaking waves, the calculated hydrodynamic forcing is examined by subdividing it into a quasi-static and an impulsive slamming force component. The quasi-static force is well reproduced by the Morison equation given the fully nonlinear wave kinematics. Furthermore, eleven degrees of parameterization of the slamming force history are statistically analyzed for a better understanding of the slamming force characteristics. Significant variabilities are presented in these parameters, as a result of the inherent uncertainties in the wave breaking process. In the end, practical implications of the proposed slamming force description to load assessment of a realistic offshore wind jacket structure are discussed. •The large-scale experimental data with a jacket structure subject to steep and breaking waves is studied.•The steep and breaking wave kinematics are reproduced by a fully nonlinear potential flow solver OceanWave3D.•The Morison equation is proven to be a good approximation applied to jacket structures.•The slamming force time history caused by the breaking waves is parameterized into dimensionless parameters.•The application of the slamming force description for offshore wind turbine load assessment is discussed.