Study On Harbor Resonance Induced By Different Dynamic Causes

The study of harbor resonance is a very important subject of coastal hydrodynamics, and larger oscillations were observed in many harbors. A series of recent harbor resonance accidents are addressed and the wave dynamic characteristics of harbor resonance are summarized in this thesis. Then, the previous study in this field is reviewed, and the following problems are further studied:(1) Assuming that the open sea has a horizontal seafloor and that the harbor is rectangular but with a planar bathymetry, the analytic solution of longitudinal oscillations is obtained based on the linear shallow water approximation. The shallow water equations are extended to a linear, weakly dispersive, Boussinesq-type equation by modifying the longshore velocity component, which is then used to achieve the analytic solution of possible existing transverse oscillations.(2) A Boussinesq model which can simulate wave generation and propagation is developed to simulate oscillations induced by seafloor movements inside a harbor of constant slope, and the numerical results are used to examine the analytic solutions. Small-scale seafloor movement usually induces evident larger transverse oscillations, but large-scale seafloor movements induce evident longitudinal oscillations. These oscillation modes (both transverse and longitudinal oscillations) are sensitive to the location of the moveable seafloor, and the amplitude of each mode changes with the seafloor's velocity and the seafloor maximum displacement. The numerical result of each eigenfrequency agrees well with the theoretical solution; in addition the spatial structure of each mode is also well-captured.(3) An edge-wave numerical model is developed based on extended Boussinesq equations with the internal wave-generation method. The numerical model is then used to investigate the nonlinear properties of standing edge waves, to examine the performance of the offshore breakwater in reducing the intensity of edge wave action and to simulate harbor resonance induced by edge waves.(4) Long-period oscillations inside the harbor with constant depth induced by different wave groups are simulated by the Boussinesq model. The simulations show that short waves with low frequencies can excite more obvious long-period oscillations than those with higher frequencies. Temporary features of wave-wave interactions in different states are investigated by the wavelet-based bispectrum. Furthermore, the response time and the damp time are estimated by a simple method. (5) To compare the oscillations induced by steady and transient waves, the physical experiments were conducted to reproduce the impact wave generation, propagation and inducing oscillations. These landslide-generated impact waves can be viewed as a superposition of wave components with solitary and dispersive wave characteristics. The waves with solitary characteristics are considered to play an important role in harbor resonance, and the components with dispersive characteristics do not induce evident oscillations. To further verify these conclusions, the Boussinesq model is used to simulate oscillations induced by a solitary wave and a packet of dispersive waves.