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<p>The submerged floating tunnel (SFT) is an ultra-long underwater structure and its vortex-induced vibration (VIV) characteristics closely relate to the stiffnesses of the supporting system. This paper establishes the relationship between the VIV behaviors of the tether-type SFT and the supporting stiffnesses from both the intermediate tethers and boundary connections with seabed. A theoretical VIV model that can simultaneously considers the effects of these two types of stiffnesses is built by the isolating/assembling technique, where the effects of both intermediate tethers and boundaries are equivalent to elastic constraints and the wake-oscillator model (WOM) is used to account for the fluid-structure interaction. The stiffnesses of the intermediate tethers are ascertained based on the principle that the tether force equals the net buoyant within its support range at static equilibrium. Also, the boundary stiffnesses are determined by equilibrating the seabed soil stiffness in the buried area and the joint constraints with the rock tunnel segments. Effects of the tethers/boundary stiffnesses directly display in the frequencies/modes obtained from the characteristic equation with the matching/boundary conditions between adjacent tube-segments, and next reflect in the VIV response obtained by the mode expansion and the Galerkin truncation. Based on the various combinations of the two types of stiffnesses from the actual engineering conditions, the VIV characteristics and the nonlinearities in lock-in region for the three typical categories of tether’s stiffnesses (i.e., lower, medium and larger) are systematically discussed, and the unsafe parameter combination and unstable lock-in region are ascertained. The results indicate that increasing stiffnesses can enhance the natural frequency and suppress the excitation of higher-order modes. When the adjacent natural frequencies differ greatly, outside/within the transition region the responses is/isn’t dominated by a single mode. In the case of low tether stiffness with close adjacent natural frequencies, in the coupling region the responses of symmetric positions about the mid-point are different and exhibit irregular fluctuations. Nonlinear phenomena of modal competition, energy transferring, beat, and vibratory frequency jump are observed. The modelling technique provides reference for similar slender structure with various supporting stiffnesses, and the results supply design recommendations for SFT.</p>

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Establishing relations between the vortex-induced vibratory behaviors of tether-type submerged floating tunnel and its multiple intermediate/boundary supporting stiffnesses

  • 期刊论文

  • 发表日期：

    2026年4月30日

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  • Yujie Li,
  • Zhuangpeng Yi,
  • Shenao Wang,
  • Donghuang Yan,
  • Quan Pan

摘要

The submerged floating tunnel (SFT) is an ultra-long underwater structure and its vortex-induced vibration (VIV) characteristics closely relate to the stiffnesses of the supporting system. This paper establishes the relationship between the VIV behaviors of the tether-type SFT and the supporting stiffnesses from both the intermediate tethers and boundary connections with seabed. A theoretical VIV model that can simultaneously considers the effects of these two types of stiffnesses is built by the isolating/assembling technique, where the effects of both intermediate tethers and boundaries are equivalent to elastic constraints and the wake-oscillator model (WOM) is used to account for the fluid-structure interaction. The stiffnesses of the intermediate tethers are ascertained based on the principle that the tether force equals the net buoyant within its support range at static equilibrium. Also, the boundary stiffnesses are determined by equilibrating the seabed soil stiffness in the buried area and the joint constraints with the rock tunnel segments. Effects of the tethers/boundary stiffnesses directly display in the frequencies/modes obtained from the characteristic equation with the matching/boundary conditions between adjacent tube-segments, and next reflect in the VIV response obtained by the mode expansion and the Galerkin truncation. Based on the various combinations of the two types of stiffnesses from the actual engineering conditions, the VIV characteristics and the nonlinearities in lock-in region for the three typical categories of tether’s stiffnesses (i.e., lower, medium and larger) are systematically discussed, and the unsafe parameter combination and unstable lock-in region are ascertained. The results indicate that increasing stiffnesses can enhance the natural frequency and suppress the excitation of higher-order modes. When the adjacent natural frequencies differ greatly, outside/within the transition region the responses is/isn’t dominated by a single mode. In the case of low tether stiffness with close adjacent natural frequencies, in the coupling region the responses of symmetric positions about the mid-point are different and exhibit irregular fluctuations. Nonlinear phenomena of modal competition, energy transferring, beat, and vibratory frequency jump are observed. The modelling technique provides reference for similar slender structure with various supporting stiffnesses, and the results supply design recommendations for SFT.