Nonlinear Dynamics of Anchoring Elements for Submerged Floating Tunnels subject to Hydrodynamic Loads

Seabed-anchored Submerged Floating Tunnels (SFTs) are interesting modular structures which are deemed
to be a valuable option for crossing deep and long waterways, such as sea straits, fjords, bays and alpine
lakes. Due to their inherent flexibility, SFTs are prone to the effect of dynamic loadings, such as earthquakes,
waves, currents and traffic. Among all of them, hydrodynamic loadings are deemed to be the most critical
for serviceability and fatigue life assessments of the whole SFT, because of their consistent and cyclic nature.
While the global hydrodynamic response of the SFT can be studied by resorting to several modeling strategies,
the local dynamic response of the anchoring elements is inherently hard to capture with standard finite element
models, because their natural frequencies are well-separated from those of the global vibration modes.
The present work briefly reviews the main findings of the research activity recently carried out by the authors
on this topic [1, 2]. A reduced-order cross-sectional model of the SFT is formulated and the coupled system of
equations governing its dynamic response is derived. Different loading conditions are then identified as critical
and studied one at time. The multiple time-scales perturbation method is applied to derive approximate closed-
form solutions of the steady-state vibration amplitude of the anchoring elements. As an application example, a
parametric analysis in the drag coefficient of the anchor is carried out, providing useful considerations aimed at
supporting the preliminary (conceptual) design phase of SFTs.