CGWAVE

Wave prediction is a vital ingredient in harbor design and boat operations. Spatial variations in wave heights and directions for various input conditions must be estimated for existing and modified harbor layouts, such as breakwater alignment and sediment movement. Energy amplification in standing waves and the associated horizontal and vertical motions can cause damage to small boats and lead to downtime in ship loading and unloading operations. CGWAVE is one of the most comprehensive harbor wave prediction models available. To validate the model’s accuracy, a rigorous comparison of the wave model is performed against field data for three harbors in Hawaii and California to identify weaknesses and strengths of the model. This research will be used to help develop more accurate wave prediction models for use in harbor design for coastal communities.

» Overview

Features

The formulation of this model makes it capable of solving problems which normally require vast amounts of computer resources. The model has been rigorously validated against all known controlled test cases for which sufficient data are available. This section demonstrates the validation of non-linear dispersion relation, wave breaking, bottom friction, spectral input and modified boundary conditions used in this model. Comparisons made between model estimates and measurements from laboratory and field data are presented. The effects of grid resolution on model estimates are also presented.

Examples

Examples The model in Figure 1 is based on the complete solution of the elliptic refraction-diffraction-reflection-dissipation (breaking + friction) equation, with no limits on angular scattering. As such, completely arbitrarily shaped domains with breakwaters, jetties, and shorelines with any reflectivities can be accommodated. This is unlike other models which require a rectangular water domain and dominant wave propagation direction along one axis everywhere inside the domain. Entire spectrum (long to short waves) are acceptable. SMS is used to discretize into wavelength dependent finite elements. Monochromatic or spectral simulations (for significant wave heights) can be readily performed. Results (wave heights/phases) can be viewed with SMS, wave velocities, direction of max velocity, pressures also can be provided. An example of long wave propagation/reflection in Los-Angeles Long Beach harbor complex (with various jetties, breakwaters, etc.) is shown below in Figure 1.

Figure 1: Wave penetration in Los Angeles/ Long Beach Harbors Modeled Phase Diagram. Boundary Reflectivity set to zero; 30 s. long wave resonance study. Waves incident from bottom right



Figure 2: Simulation of short waves on plane sloping beach. Phase diagram. Expected bending of wave rays is observed. Incident wave angle is 60 degrees from normal at 3 km offshore. Incident wave period is 6 seconds. Length of the coastline is 6

km.


Figure 3: Simulation of waves in Barber's Point Harbor, Hawaii. Phase diagram. Previous models contained spurious reflections from inappropriate open boundary treatment. Incident wave angle is 60 degrees from normal at 6 km offshore. Incident wave period is 50 seconds. Coastline length is approximately 6 km.



Figure 4: Amplification factors vs frequency (resonance curve), model vs data for two locations in Barber’s Point Harbor.





Figure 5: Simulation of wave breaking, Battjes & Jansen (1978) lab study of wave shoaling, reflection, & breaking.




Figure 6: Ponce de Leon inlet, Florida. Model results and data shown for a longshore transect.




Figure 7: Simulation of waves in Ponce Inlet. Phase diagram. Normal incident wave angle, 15 second wave period. Coastline length is approximately 4.8 km.



Figure 7: Simulated wave heights due to reflection, shoaling, refraction, diffraction, and breaking near a shore-connected breakwater on a sloping beach. Results compare very well against lab study of Watanabe et al





Figure 9: Simulated wave heights due to reflection, shoaling, refraction, diffraction, and breaking near a detached breakwater on a sloping beach. Results compare very well against lab study of Watanabe et al.





Figure 10: Simulation of waves in Kahului Harbor, Hawaii. Phase diagram. Normal incident wave angle, 15 second wave period. Coastline length is approximately 4.8 km.





Figure 11: Wave height comparison at a number of gage locations in Los-Angeles/Long Beach Harbor.





Figure 12: Simulation of wave reflection, shoaling, and breaking off North Sea coast. Data from Massel (1992)