Abstract
Computational Fluid Dynamics (CFD) simulations, based on Reynolds-Averaged Navier–Stokes (RANS) models, are a useful tool for a wide range of coastal and offshore applications, providing a high fidelity representation of the underlying hydrodynamic processes. Generating input waves in the CFD simulation is performed by a Numerical Wavemaker (NWM), with a variety of different NWM methods existing for this task. While NWMs, based on impulse source methods, have been widely applied for wave generation in depth averaged, shallow water models, they have not seen the same level of adoption in the more general RANS-based CFD simulations, due to difficulties in relating the required impulse source function to the resulting free surface elevation for non-shallow water cases. This paper presents an implementation of an impulse source wavemaker, which is able to self-calibrate the impulse source function to produce a desired wave series in deep or shallow water at a specific point in time and space. Example applications are presented, for a Numerical Wave Tank (NWT), based on the open-source CFD software OpenFOAM, for wave packets in deep and shallow water, highlighting the correct calibration of phase and amplitude. Furthermore, the suitability for cases requiring very low reflection from NWT boundaries is demonstrated. Possible issues in the use of the method are discussed, and guidance for accurate application is given.
Highlights
While Computational Fluid Dynamics (CFD) enables the simulation of complex flow phenomena, such as two-phase flows and gravity waves, setting up a simulation of coastal or marine engineering processes, with correct wave creation and minimum reflection, can be a challenge
The first iteration was initialised with random input of small amplitude, and the resulting surface elevation was almost zero, while the Mean-Squared Error (MSE) of 3 × 10−5 was large
In combination with a calibration procedure, complex irregular wave patterns can be recreated in conditions ranging from deep to shallow water using a simple impulse source term acting in the horizontal direction
Summary
While CFD enables the simulation of complex flow phenomena, such as two-phase flows and gravity waves, setting up a simulation of coastal or marine engineering processes, with correct wave creation and minimum reflection, can be a challenge. The first category of wave generation methods directly simulates the wavemaker by a moving wall, requiring mesh motion/deformation in the CFD domain [1], which can be a complex and computationally-expensive task. Because these methods replicate the real processes in a physical laboratory tank, they incur the well-known drawbacks of physical wavemakers encountered in an experimental facility, such as evanescent waves, imperfect wave absorption and the required implementation of a wavemaker control system. Another drawback of conventional wave pistons is that they are typically limited to low order waves (first or second order)
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