The Efficient Application of an Impulse Source Wavemaker to CFD Simulations

Abstract

Computational Fluid Dynamics (CFD) simulations, based on Reynolds-AveragedNavier–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 inputwaves in the CFD simulation is performed by a Numerical Wavemaker (NWM), with a variety ofdifferent NWM methods existing for this task. While NWMs, based on impulse source methods, havebeen widely applied for wave generation in depth averaged, shallow water models, they have notseen the same level of adoption in the more general RANS-based CFD simulations, due to difficultiesin relating the required impulse source function to the resulting free surface elevation for non-shallowwater cases. This paper presents an implementation of an impulse source wavemaker, which is ableto self-calibrate the impulse source function to produce a desired wave series in deep or shallowwater at a specific point in time and space. Example applications are presented, for a NumericalWave Tank (NWT), based on the open-source CFD software OpenFOAM, for wave packets in deepand shallow water, highlighting the correct calibration of phase and amplitude. Furthermore, thesuitability for cases requiring very low reflection from NWT boundaries is demonstrated. Possibleissues in the use of the method are discussed, and guidance for accurate application is given.

On the Assessment of Numerical Wave Makers in CFD Simulations

“…For wave generation, five different methods are well known: the Relaxation Zone Method (RZM) [34,40,41], Static (SBM) and Dynamic Boundary Method (DBM) [9,42], Mass Source Method (MSM) [43,44] and Impulse Source Method (ISM) [45][46][47][48]. For numerical wave absorption, six different methods are available, i.e., the RZM, SBM, DBM, Numerical Beach (NB) implementations [2,49], geometrically sloped beaches [50][51][52] and the cell stretching method [53].…”

“…The location of the wave maker zone is defined by r(x) = 1, with r(x) = 0 everywhere else in the domain. a wm (x, t) is the acceleration input to the wave maker, which can be determined analytically for shallow water waves [45] or via an iterative calibration method for waves in any water depth [48]. Again, wave absorption can only be achieved through an additional beach.…”

“…To absorb waves in the numerical domain, various methods, termed as NBs or sponge layers, were developed. Examples can be found in references [37,48,[58][59][60]. In the following, the implementation by Schmitt et al [48] and Schmitt and Elsaesser [37] is discussed.…”

“…Examples can be found in references [37,48,[58][59][60]. In the following, the implementation by Schmitt et al [48] and Schmitt and Elsaesser [37] is discussed. Introducing the additional term, S(x)ρU(x, t), to the RANS momentum Equation (2), yields:…”

“…In the employed version of the DBM, such a pre-processing tool is not readily provided for pSSs. For the ISM, the calibration method proposed by Schmitt et al [48] is not yet able to calibrate the impulse source input based on a PSD distribution.…”