Vortex Induced Vibration in Submerged Floating Tunnels: DVL a Distributed Vortex Layer Model

The paper deals with the simulation of the dynamic nonlinear behaviour of seabed anchored submerged floating tunnels (SFTs) under environmental excitation, by addressing the problem of vortex induced excitation. A model based on the ‘fluid oscillator’ approach is proposed, tailored to be coupled to a geometrically non linear FE developed, for the anchor bars, in a previous work. The approach allows for representing the entire anchoring bar, thus reducing the computational effort required for global modelling of the SFT. In this light, mainly based on a lumped fluid oscillator model, a computationally more efficient approach is here sought in the form of a continuous model (Distributed Vortex Layer - DVL). This consists of a distributed ‘aerodynamic’ mass which is connected to the structural element and to a fixed reference system by distributed non linear spring-dashpot elements. Governing equations of motion are obtained substituting Galerkin-type decomposition of both the structure and the aerodynamic mass displacements; global equations of motion are integrated by a step-by-step procedure based on the Newmark method. Validations of the numerical model are finally given, regarding experimental results obtained for two basic structures: an elastically suspended rigid cylinder and a long slender cylinder.