Session: 06-03-01 Fluid-Structure, Multi-body and Wave-body Interaction I

Paper Number: 123916

123916 - Wave Force Identification on a Four-Cylinder Array Using Visual Technology 

Cylindrical foundations are widely used as the support components for offshore wind turbines, offshore platforms and sea-crossing bridges. In extreme ocean environments, wave load is one of the crucial indexes in the foundation safety design. Using the wave parameters collected from field measurement, engineers and researchers can determine the wave load on the foundations by theoretical, numerical or experimental methods. In the mentioned methods, the regular or irregular waves with selected wave parameters are conventionally used without considering the randomness of waves in time and space in the actual marine environment. However, a practical problem is how to monitor or identify the wave load on cylindrical foundations after their construction is completed. The difficult of it is the ocean waves are much more complex than the waves used in the abovementioned methods. It is also important to realize that accurately using a potential function to represent the wave field under a storm condition is impossible.

When the size of the cylindrical foundation is large (the ratio of the characteristic length of the structure to the wavelength is larger than 0.2), the diffraction waves from the cylinder cannot be neglected, and using the Morrison equation is no more accurate in wave force identification. Fortunately, the wave force on the large-scale vertical cylinder can be identified from the waterline around the cylinder without determining the potential function of the wave field. Comparison with the experimental data illustrates that the wave force can be accurately identified, especially in force phase, which allows the researchers to further develop the higher-order wave force identification method to reduce the identification errors at the force crests and troughs. The identification method is easy for application with high computational efficiency after the waterline around the cylinder is determined. Most importantly, it provides the possibility for identifying the wave force by using the visual technique.

This study utilizes computer vision technology to identify wave forces on a four-cylinder array in a square configuration, under both unobstructed scenarios with full waterline information and obstructed conditions with partial waterline data. Based on the two proposed methods, experiments were conducted in a wave flume to validate the wave forces in the x and y-directions under both regular and irregular wave conditions. Four cameras facilitated the synchronized capture of photos, with the Canny operator enabling dynamic extraction of the waterline around the four-cylinder system. In unobstructed conditions, the identification method is formulated based on potential theory, employing the Recursive Least Squares (RLS) method to identify wave forces comprising linear, second-order, and certain higher-order components. For obstructed conditions, the method relies on linear wave theory to identify the predominant linear components in wave forces. Both proposed methods demonstrate promising potential for measuring wave forces on cylindrical structures.

Presenting Author: Jiabin Liu Harbin Institute of Technology

Presenting Author Biography: Dr. Liu obtained his doctor’s degree at Harbin Institute of Technology in 2019. In the same year, he entered the post-doctoral station of mechanics of Harbin University of Technology and was promoted to Associate Professor in 2022. His main research focuses on hydrodynamic problems in bridge engineering and ocean engineering.

Authors:

Jiabin Liu Harbin Institute of Technology
Anxin Guo Harbin Institute of Technology