During the near-seabed immersion stage, the submerged tunnel element suspended by immersion rigs and anchored to the seabed is at risk of possible bottom grounding and collision with the installed elements. Specifically, the wall effect would have an important role on the motion characteristics of the tunnel element when it approaches the seabed (The wall effect is the influencing behavior of one large planar surface approaching another large planar surface underwater). To investigate this effect, this research conducts 3D experiments using a 1:60 scale model of a combined tunnel element and immersion rig system. The six-DOF motions of the tunnel and immersion rig are measured simultaneously for various regular wave conditions. The collected measurements for different relative clearances are compared in both time and frequency domain. Nonlinear effects of the near-seabed interference are found to be particularly significant when the relative clearance ratio (clearance beneath tunnel / height of tunnel element) is smaller than 0.26, especially when the incident wave period is near the resonant roll period of the tunnel/rigs. To further explore the contributing factors of the seabed interference and to determine suitable operating conditions in practice, a fully coupled tunnel-rig numerical model is built based on the potential flow theory. Additional damping is also included in the coupled motion equations for the resonant roll scenarios and good agreement with experimental data is achieved for relative clearance ratio of δ/d ≥ 0.42. Overall, the experimental and numerical results demonstrate that besides the relative clearance, the near-wall effect of the seabed is also closely associated with the roll of the tunnel element and thereby has a strong dependence on the incident wave height, wave period and wave obliquity. The study is expected to be helpful for understanding the near-seabed effect on the responses of large-scale rectangular floater so that the installation and positioning can be performed accurately and effectively.

在近海床浸没阶段，由沉浸钻机悬挂并锚定到海底的淹没式隧道元件可能会发生底部接地并与已安装的元件发生碰撞的风险。具体地说，壁效应在隧道元件接近海床时将对隧道元件的运动特性起重要作用（壁效应是一个大平面接近水下另一个大平面的影响行为）。为了研究这种效果，本研究使用了1:60比例的隧道单元和沉浸钻机系统组合模型进行了3D实验。在各种规则波浪条件下，可同时测量隧道和沉浸装置的六自由度运动。在时域和频域都比较了收集的不同相对间隙的测量值。当相对间隙比（隧道下方的间隙/隧道单元的高度）小于0.26时，特别是当入射波周期接近隧道的共振侧倾周期/时，近海床干扰的非线性影响特别明显。钻机。为了进一步探讨海床干扰的影响因素并在实践中确定合适的运行条件，基于势流理论建立了完全耦合的隧道钻机数值模型。对于共振侧倾情况，耦合运动方程中还包括附加的阻尼，并且相对间隙比达到了与实验数据的良好一致性。δ/  d≥0.42。总体而言，实验和数值结果表明，除了相对间隙外，海床的近壁效应还与隧道单元的倾角密切相关，因此对入射波高，波周期和波倾角有很大的依赖性。 。该研究有望有助于了解近海床对大型矩形浮子响应的影响，从而可以准确有效地进行安装和定位。