Non-Hydrostatic Computations of Nearshore Hydrodynamics

Non-Hydrostatic Computations of Nearshore Hydrodynamics

Jacobs, R.P.M.

Stelling, G.S. (mentor)

Civil Engineering and Geosciences

Hydraulic Engineering

Environmental Fluid Dynamics

2010-06-16

The nearshore zone is an active zone that can be quite inhospitable to humans due to violent wave breaking and strong rip currents. Rip currents are shore normal jet-like currents that typically extend from near the shoreline out past the line of breaking waves. Observations have concluded that a rip current system generally consists of 4 parts. Part 1 is the shoreward mass transport due to the waves carrying water through the breaker zone in the direction of wave propagation. Part 2 is the movement of this water mass parallel to the coast known as a longshore current. Part 3 is the rip current itself, a seaward flow of water through a narrow rip channel. And part 4 is an alongshore movement outside the breaker zone of the expanding rip head. With the use of the numerical model XBeach, in which a non-hydrostatic model based upon the numerical scheme as developed by Stelling and Zijlema (2003)was implemented, the fluid motions in the nearshore zone are simulated. The method of Stelling and Zijlema utilizes an edge based compact difference scheme for the approximation of the vertical gradient of the non-hydrostatic pressure. This ensures accurate wave breaking and dispersion characteristics, which is important for an accurate simulation of the nearshore hydrodynamics. Two test cases are used to verify the model for replication of the hydrodynamics in the nearshore zone. The first case consists of irregular wave breaking in a laboratory barred surf zone. The second case is a wave induced and bathymetry driven rip current in a directional wave basin. The numerical model is further developed with the addition of an eddy viscosity model and a non-reflecting boundary condition. With these additions the depth averaged model gave very satisfactorily results for both cases. The XBeach model is an accurate and efficient simulation package for the dynamics in the nearshore zone. This study shows that application to real world situations should give realistic and accurate results. Therefore the model could be applied in coastal engineering applications and in the research for energy extraction methods from wave induced currents.

Non-hydrostatic pressure
Rip currents
Breaking waves
Surf zone

http://resolver.tudelft.nl/uuid:8c863037-a490-4cf5-8253-11eef4d8892d

Student theses

master thesis

(c) 2010 Jacobs, R.P.M.