Session: 06-05-01 Marine Hydrodynamics

Submission Number: 155157

Shape Optimization of Floating Bridge Pontoons With Mooring Constraints Under Wave Actions 

Deep-water floating bridges are typically supported by a system of discrete pontoon-type floating boxes. The hydrodynamic parameters of these pontoons are closely linked to the geometry of their submerged sections. A well-optimized structural shape can significantly enhance the dynamic performance of the floating foundation and, by extension, the entire bridge. This study optimizes the shape of mooring pontoons for deep-water floating bridges to reduce motion amplitude under wave action. The geometric shape of the pontoons is represented using a Fourier series expansion in spherical coordinates, with the Fourier coefficient matrix serving as the design variable. Surge and pitch motions of the floating body are taken as objective variables, and the gradient of the objective function with respect to the design variables is derived using the discrete adjoint method.

The results show that the optimized shape reduced surge and pitch motion amplitudes by a maximum of 77.84% and 89.73%, respectively, under different wave numbers. The optimized pontoon exhibits an elongated longitudinal dimension and a deeper draft depth, with the shape optimization effectively lowering the free surface wave heights around the structure. The influence of truncation orders 𝑁 and 𝑀 of the Fourier coefficients on the optimization results is then discussed. As truncation order 𝑁 increases, the shape at the still waterline becomes more complex and diverse, while increasing 𝑀 leads to greater complexity along the z-axis, resulting in a shallower draft depth.

Moreover, key cross-sections of this optimized shape are extracted to create an equivalent cross-sectional pontoon, whose surge and pitch motion amplitudes were 78.96% and 46.01% lower than those of the equivalent cylinder with the same still waterline cross-section, and 79.54% and 97.64% lower than those of the equivalent cylinder with the same draft depth. Comparative analysis demonstrates that when wave number 𝑘𝑅 < 1.89, the equivalent optimized pontoon exhibits the smallest surge and pitch motions. Overall, this study provides a foundation for the shape design of deep-water floating foundations.

Presenting Author: Chenyu Lu Harbin Institute of Technology

Presenting Author Biography: The Presenting author is a Pd.D student of Harbin Institute of Technology.