Optimization of tuned mass damper for seismic control of submerged floating tunnel

Abstract This study presents the optimization process of a tuned mass damper (TMD) to mitigate the lateral motions and mooring tensions of a submerged floating tunnel (SFT) under seismic excitations. A time-domain hydro-elastic-simulation model is established to solve the coupled dynamics among the tunnel, TMD, and mooring lines. The wet hydro-elastic natural frequencies of the SFT with mooring are estimated. The spring and damping coefficients of TMD are optimized by using metaheuristic optimization algorithms, i.e., harmony search (HS), genetic algorithm (GA), and particle swarm optimization (PSO). HS is coupled with the time-domain dynamic-simulation model to perform the iterative process of updating the coefficients by HS, running the simulation with updated coefficients, returning the results back to HS. The optimized coefficients obtained by HS are also cross-checked by using GA and PSO with the pre-established objective function, which shows consistent results. Subsequently, the effectiveness of TMD with the optimized parameters is tested for a variety of seismic conditions that can cover the most seismic magnitudes. The time histories, spectra, and statistics of SFT dynamic responses and mooring tensions are systematically analyzed and discussed. As intended, the optimized TMD effectively attenuates the resonant hydro-elastic transient motions of the SFT at its lowest lateral natural frequency. The mooring tensions are also significantly reduced by adopting the optimized TMD, especially in large earthquakes.