Type of Document Dissertation Author Xiao, Hong Author's Email Address email@example.com URN etd-07142009-130212 Title Numerical Simulation Of Dynamic Wave Force On Coastal Structures Under Extreme Storm Surge Conditions Degree Doctor of Philosophy Department Civil and Environmental Engineering, Department of Advisory Committee
Advisor Name Title Wenrui Huang Committee Chair Amy B. Chan Hilton Committee Member Tarek Abichou Committee Member Bill Hu Outside Committee Member Keywords
- Wave Overtopping
- Turbulence Models
- Wave Breaking
- Wave Run-up
- Wave Force
Date of Defense 2009-05-14 Availability unrestricted AbstractSea waves associated with storm surge is a key factor in the safety of coastal structures. Most of the damages on coastal structures during a storm event are caused by waves. Forces created by waves breaking against a vertical surface are often 10 or more times higher than the force created by high speed winds during a storm event. In hurricane season, a combination of storm surge and waves may cause overtopping of coastal protection structures such as breakwaters, dikes, seawalls, resulting in flooding and damaging of the areas behind these structures. When a wave crest is overtopping a coastal structure, complex vortices patterns are generated behind the structure. The vortices induced by wave result in the swash of the seabed, the stagnation of contamination, the settlement of mud and sand around the coastal structures, and the resonance of the structures. As matter of fact, wave force on structures is a very important issue in design, construction and management of offshore and coastal structures.
In this dissertation, a wave model based on Reynolds-Averaged-Navier-Stokes (RANS) equations is developed for estimating dynamic wave forces on coastal structures. Turbulent models are used for the closure of RANS equations. A generating-absorbing numerical wave paddle is used to generate waves, and an absorbing sponge layer for absorbing wave is adopted in front of the open boundary to absorb wave energy. In order to track the movement of the free surface, the Youngs’ version of Volume of Fluid (VOF) method is used to reconstruct the profile of the free surface at every time step.
The wave force model is validated against available experimental data and analytical results of wave force on coast structures. After validation, the model is applied to address several engineering problems in coastal engineering field:
1) Numerical modeling of wave run-up and forces on an idealized beachfront house
The wave model is applied to estimate the impact of a solitary wave on an idealized beachfront house located at different elevations on a plane beach. The model is satisfactorily tested against the experimental data of wave run-up, and the analytical solution of wave forces on vertical walls. The time histories of wave profiles, forces, and overturning moments on the idealized house are demonstrated and analyzed. The variations of wave forces and overturning moments with the elevation of the idealized beachfront house are also investigated.
2) Numerical modeling of dynamic wave force acting on Escambia bay bridge deck during Hurricane Ivan
Bridge decks in Escambia Bay were damaged during the storm surge of Hurricane Ivan in 2004. The wave model is used to investigate dynamic wave forces exerted on the bridge deck. The model was satisfactorily tested against experimental data of uplift wave forces on horizontal plates. The validated model was applied to investigate wave forces acting on the bridge deck in Escambia Bay in the case of Hurricane Ivan. The time history of wave profiles, turbulent velocity fields, and dynamic uplift and horizontal forces acting on the full-scale bridge deck were simulated and analyzed. Results indicate that, during the storm surge event of Hurricane Ivan, the maximum uplifting wave forces were larger than the weight of the simply supported bridge deck, causing direct damage to the bridge deck. Wave forces on three different deck elevations are discussed.
3) Effects of submersion depth on wave uplift force acting on bridge decks during Hurricane Katrina
A large portion of the Biloxi Bay Bridge was submerged and destroyed by surface waves and storm surge associated with Hurricane Katrina in 2005. The time history of wave forces exerted on the Biloxi Bay Bridge during Hurricane Katrina was investigated by the wave model. In order to evaluate the maximum uplift wave force, five different bridge deck elevations submerged at different water depths were investigated. The wave profiles, velocity field in the vicinity of the bridge, and dynamic wave forces on the decks were analyzed. Results indicate that the uplift force on the submerged bridge deck span exceeded its own weight under the extreme wave and storm surge conditions during Hurricane Katrina. Moreover, the numerical simulations suggest that the maximum uplift wave force occurred when the storm surge water level reached the top of the bridge deck.
4) Numerical modeling of levee overtopping during Hurricane Katrina
The wave model applied to estimate the impact of overtopping on levee during storm surge. The model was satisfactorily tested against empirical equation of overflow discharge at a vertical seawall, and experimental data of overtopping discharge at a sloping seawall. The validated model was used to simulate wave overtopping of the levee system during storm surge of Hurricane Katrina. The time history of wave profiles and velocity magnitude field in the vicinity of the levee are demonstrated and analyzed. It is concluded that the failure of parts of the levee system was caused by erosion during wave overtopping.
5) Numerical modeling of interactions of solitary wave and current in the vicinity of a horizontal cylinder
The numerical model is applied to study the interaction of solitary wave and uniform current and their impacts on a horizontal cylinder near the free surface. The model is satisfactorily tested against both the experimental data of forces on a circular cylinder, and the analytical solution of solitary waves. The validated model was applied to simulate solitary wave, uniform current, and their interaction with coastal structures. The hydrodynamic features of velocity field and vortex contours are demonstrated and analyzed.
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