IHFOAM includes two newly-developed boundary conditions.

Wave generation

Wave generation is critical in numerical coastal engineering simulations. Generating waves is always the beginning of the vast majority of the cases we are dealing with. An accurate wave generation process lays the foundations of realistic final results. If the starting point is not accurate, all the errors introduced in this initial step will propagate until the end.

This boundary condition has been coded from scratch to realistically generate three-dimensional waves at the boundaries according to a number of wave theories, including:

• Stokes I, II and V, cnoidal and streamfunction regular waves.
• Boussinesq solitary wave.
• Irregular (random) directional waves, first and second order.
• Piston-type wavemaker velocity profile replication.

The references  can be found in the following table:

Furthermore, wave generation has been linked with active wave absorption to work simultaneously on the same boundaries. This generates the target waves while absorbing the boundary  incident waves.

Active wave absorption

Active absorption of waves is one of the key features of physical and numerical experiments in coastal engineering. On the sea, reflected waves travel away from the study zone. However, in numerical experiments this is not the case, as the domains are constrained in dimensions due to computational restrictions. This situation causes inconvenient reflections that, if not handled adequately, can distort the results.

In this sense, active wave absorption is a great advance, as it allows waves to be absorbed on the boundaries without adding noticeable computational costs to the model. This feature contrasts with the already available relaxation zone absorption, which adds a large domain to the zone of interest (in the order of magnitude of 1.5-2 wave lengths) and is known to produce an increment in the mean water level due to  wave damping, as shown in Mendez et al. (2001).

IHFOAM includes 3 types of active wave absorption: 2D and Quasi-3D theories as presented in Schäffer and Klopman (2000) and enhanced for the model. Furthermore, IHFOAM features a newly developed full 3D theory for cases in which Quasi-3D is not applicable. Check the References for complete details regarding the theories, the implementation procedures and their performance. Furthermore Quasi-3D has been linked with the generation, allowing simultaneous wave generation and absorption on the boundaries, accounting even for for high amplitude incident waves.

All the theories are stable and have an adequate performance for all the relative water depths, presenting reflection coefficients typically below 10%.

The following images refer to a test in which a real 3D sea state (sea+swell with 45º mean propagation direction) is presented. The waves are generated on the closest boundary, and the rest are purely absorbent using the full 3D theory.

A comparison between the theoretical directional spectrum (top panel) and the measured one (bottom panel) is shown as follows: