Global dynamic analysis of a 700-m-long SFT section considered in the South Sea of Korea is carried out for survival random wave and seismic excitations. To solve the tunnel-mooring coupled hydro-elastic responses, in-house time-domain-simulation computer program is developed. The hydro-elastic equation of motion for the tunnel and mooring is based on rod-theory-based finite element formulation with Galerkin method with fully coupled full matrix. The dummy-connection-mass method is devised to conveniently connect objects and mooring lines with linear and rotational springs. Hydrodynamic forces on a submerged floating tunnel (SFT) are evaluated by the modified Morison equation for a moving object so that the hydrodynamic forces by wave or seismic excitations can be computed at its instantaneous positions at every time step. In the case of seabed earthquake, both the dynamic effect transferred through mooring lines and the seawater-fluctuation-induced seaquake effect are considered. For validation purposes, the hydro-elastic analysis results by the developed numerical simulation code is compared with those by a commercial program, OrcaFlex, which shows excellent agreement between them. For the given design condition, extreme storm waves cause higher hydro-elastic responses and mooring tensions than those of the severe seismic case.

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This paper investigates the response characteristics of a stow net under wave and current excitations, as well as the feasibility of its monitoring system to check net functionality and prevent loss of fishing gears. The stow-net model is based on one of existing types used in southwest coast of South Korea. The measured wave and current data there are acquired and inputted as environmental loads for numerical simulations. The Morison equation for a moving object with equivalent net model is utilized as the external-force estimator, which has been validated by many researchers regarding fish-cage studies. Since the modelling of all the net elements is inefficient in terms of computational time in time-domain simulations, cruder equivalent-drag net elements are devised with equivalent wet mass, projected area, and axial stiffness. The performance of stow net is highly influenced by current velocity. Stow nets submerge more in stronger currents, which results in less wave forces. The proposed monitoring system can provide useful information, such as net functionality and loss of stow net, using the minimum number of monitoring sensors.