Date of Award

8-2002

Level of Access

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil Engineering

Advisor

Vijay G. Panchang

Second Committee Member

Bryan Pearce

Third Committee Member

Huijie Xue

Additional Committee Members

Kewal K Puri

Zeki Demirbilek

Abstract

Methods to incorporate the effect of ambient currents in the prediction of nearshore wave transformation are developed. This is accomplished through the construction of a finite-element coastal/harbor wave model based on the extended mild-slope wave-current equation. Improved boundary conditions are developed to overcome the existing problems associated with the ignorance of exterior bathyrnetric variations and the oversimplified absorbing boundary conditions. Tests indicate that in many coastal applications the effect of exterior bathymetric variation can be approximately simulated satisfactorily by a one dimensional (ID) model using two representative 1D depth profiles. With the 1D-2D boundary interfacing technique, more realistic incident wave conditions can be specified along the open boundary. For outgoing waves, spurious reflections can almost be completely eliminated while using the newly derived generalized absorbing boundary condition that accounts for boundary reflectivity, incident angle, and depth variations across/around the boundary. Multiple nonlinear mechanisms for wave-current interaction, wave breaking, and the wave-direction -dependent boundary conditions, are handled successfully and efficiently with iterative techniques. Model validation for wave-current interaction is carried out using three wave-current problems of common interest and varying complexities. Comparison against results from other types of models based on parabolic approximations or Boussinesq equations indicate generally good agreement. Finally, the model is applied to a harbor engineering problem pertaining to waves approaching an inlet with a jettied entrance, where wave-current interaction can create a complex wave pattern that adversely affects small craft navigation and cause scouring. The role of ebb and flood currents on wave transformation and on breaking in the vicinity of the inlet is investigated using the model in conjunction with hydraulic laboratory data. It is found that although the ebb currents cause larger waves outside the inlet, much of the wave energy is soon dissipated due to breaking, while during the flood tide more wave energy can penetrate into the inlet throat.

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