Dynamic similarity study of the truncated model test for submerged floating tunnels under wave actions

Abstract

Conducting experiments on full-span submerged floating tunnels (SFTs) is challenging due to their extensive length and limitations in experimental conditions. Truncated models offer an alternative for studying SFTs' dynamic response under wave actions. This study investigates the dynamic similarity between the truncated model and full-span structure in regular waves. Modal similarity is utilized in designing the truncated models, along with proposing constraint stiffness for the truncated boundary. A numerical model for simulating the dynamic response of SFTs under wave actions is established using Ansys and validated by physical model tests of the SFT segment with a free boundary. Comparisons of the natural frequencies, motion amplitudes, and mooring forces between the truncated models and full structures are conducted through numerical calculations. The horizontal, vertical, and rotational stiffness of the truncated boundaries are determined, with observed coupling effects between the horizontal and rotational constraints. The analysis of displacement amplitude for different truncation lengths indicates that as the truncation length increases, the displacement of the truncated model gradually approaches that of the full structure. It is also found that the sway amplitude at the truncated boundary is about 0.8 - 1.2 times of the full structure, while the way amplitude at mid-span is about 0.78 - 0.85 times of the full structure. The displacement distribution along the tube suggests that neglecting the rotation angle around the Z-axis at the truncated boundary leads to this discrepancy. The analysis results of this paper show that the proposed truncated model can effectively represent the dynamic response of the full structure. The dynamic similarity method for truncated model serves as a valuable reference for experimental design of SFTs.