Modeling VOF Waves
The VOF Waves model is used to simulate surface gravity waves on the interface between a light fluid and a heavy fluid. This model is typically used with the 6-DOF Motion model for marine applications.
The concept of a steadily-progressing periodic wave train is a convenient model that is used in coastal and ocean engineering applications to give fluid velocities, pressures, and surface elevations caused by waves. Assuming that the waves are propagating steadily without change (the steady wave problem), the wave train can be uniquely specified and solved in terms of three physical length scales: water depth, wave length, and wave height.
The main theories that have been used for the steady wave problem are:
- Stokes theory
An explicit theory that is based on an assumption that the waves are not very steep. This theory is best suited to modeling waves in deeper water.
- Cnoidal theory
An explicit theory for modeling waves in shallower water, where the wavelength is long compared to the water depth.
Simcenter STAR-CCM+ provides the following VOF wave models:
- Flat Wave
A flat wave represents a calm plane of water.
- First Order Wave
A first order wave is modeled with a first order approximation to the Stokes theory of waves. This approximation generates waves that have a regular periodic sinusoidal profile.
- Fifth Order Wave
A fifth order wave is modeled with a fifth order approximation to the Stokes theory of waves. This wave more closely resembles a real wave than one generated by the first order method. The wave profile and the wave phase velocity depend on the water depth, wave height, and current.
- Superposition Wave
A superposition wave is a linear superposition of different partial first order waves. It can be used to simulate more complex wave phenomena, such as a cross sea or spectral waves. A cross sea is a sea state with two wave systems traveling at oblique angles. This state can occur when water waves from one weather system continue despite a shift in wind.
- Cnoidal Wave
A cnoidal wave is used for shallow water applications, where the wavelength is long compared to the water depth (that is, the wavelength is greater than ten times the water depth). The Stokes theory that models first order and fifth order waves is not suitable for these applications.
- Irregular Wave
An irregular wave can be used to describe a short-term sea state by a wave spectrum, that is, the power spectral density function of the vertical sea surface displacement.
- Linked Wave
The linked wave model uses any other pre-defined VOF wave model as a reference. The linked methodology uses a proxy wave specification approach, where field functions for initial conditions, boundary conditions, and forcing parameters are defined only once for the VOF wave that is being referenced. The linked VOF wave field functions are then assigned to regions/boundaries only once, and repeated entries are avoided. This process speeds up simulation preparation as it enables a quick switch between different VOF waves.
VOF waves can be forced to a specific solution at a boundary. Typically, the solution of the 3D Navier-Stokes equations is forced towards a solution that is based on a simplified theory. The forcing source terms adapt the solution to the simplified solution that is imposed at the reduced domain boundary. A VOF wave can also be damped in the vicinity of selected boundaries to reduce wave oscillation near those boundaries.