Abstract
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.
Highlights
The submerged floating tunnel (SFT) is an innovative solution used to cross deep waterways [1,2].The SFT consists mainly of a tunnel for vehicle transportation and mooring lines for station-keeping.The tunnel is usually positioned at a certain submergence depth, typically greater than 20 m, with positive net buoyancy that is balanced by mooring lines anchored in the seabed [3,4].Considering that wave/current/wind effects are greatly reduced, the cost is almost constant along the length [5], and ship passage is not obstructed by the structure, the SFT has been regarded as a competitive alternative to floating bridges and immersed tunnels
Because static displacements of the tunnel are only affected by weight, buoyancy, and and stiffness components of tunnel and mooring lines, direct comparison can be made after initial stiffness components of tunnel and mooring lines, direct comparison can be made after initial modeling of the entire SFT system
Regular and irregular seismic excitations are utilized for SFT dynamic analysis
Summary
The submerged floating tunnel (SFT) is an innovative solution used to cross deep waterways [1,2]. Along this line, numerous researches have been carried out to verify structural safety in wave and seismic excitations on the SFT. The initial studies of hydro-elastic responses of a long SFT with many mooring lines by random waves and seabed earthquakes were conducted by Jin and Kim [28] and Jin et al [29] by using commercial software, OrcaFlex. To add the capability of hydro-elastic analyses of a long SFT with many mooring lines in the in-house coupled dynamic-analysis program, a new approach called ‘dummy-connection-mass method’ is developed. The effect of seismic-induced acoustic pressure is not considered since the resulting frequency range is much higher [30], and it is of little importance for the mooring design
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