Regular waves onto a truncated circular column: A comparison of experiments and simulations

Abstract

Accurate prediction of hydrodynamic forces on offshore structures is critical for safe and cost effective design of fixed and floating offshore structures exposed to a harsh environment. In the present paper, nonlinear interactions between regular waves and a single surface-piercing truncated circular column have been investigated using a frequency domain potential flow solver (DIFFRACT) and a full CFD solver in OpenFOAM for direct comparisons. Both the predicted free surface elevation around the column and the total force acting on the column have been analysed and compared with experimental data from MOERI. The degree of non-linearity and the contribution of each harmonic to the free surface run-up and wave forces have been examined, and evaluations of the accuracy and computational efficiency of the potential flow solver and the full CFD solver are provided and compared in the paper. Also of note are the local forms of the scattered waves around the column in numerical simulations, which are consistent with the Type-1 and Type-2 patterns identified in physical experiments at Imperial College.

An experimental decomposition of nonlinear forces on a surface-piercing column: Stokes-type expansions of the force harmonics

“…The cylinder was also located midway up a 1 : 20 plane slope with the same local water depth as the flat bed tests to investigate the effect of the sloping bed on the nature of the incident waves and the loading on the cylinder. It is our aim that the well-documented experimental data should reveal the important physics and also provide a useful dataset for validating existing numerical methods such as computational fluid dynamic codes (CFD) based on the Navier-Stokes equations (Chen et al 2014), potential-flow solvers both to second order in the frequency domain (Sun et al 2016) and fully nonlinear in the time domain (Fitzgerald et al 2014). This paper is organized as follows.…”

Study on the Optimal Wave Energy Absorption Power of a Float in Waves

“…The systematic verification of the grid spacing in x-direction, ∆x, and in z-direction, ∆z, at the water free surface was carried out. The parameters of incident wave were set the same as that in Sun et al [33], which are shown in Table 1. In Table 1, H is wave height, L is wave length, k is wave number, A is wave amplitude.…”

“…The time-step convergence is verified in this section. The same wave conditions as Sun et al [33] were studied. Mesh B with L (85) and H (17) was used, and then the time steps were set to ∆t = T/175, T/350 and T/700.…”

“…The RAOs (Response Amplitude Operator) of the wave-surface elevation around the truncated column under an incident wave of k 0 r = 0.657 (k 0 r is the dimensionless wave number, where k 0 = 2π/L and L is wave length, r is the radius of column) was studied and compared with Sun et al [33]. An average value of free-surface elevations at wave probes in 10 stable wave periods were obtained and plotted in Figure 7.…”

“…Firstly, a three-dimensional numerical wave tank was established by STAR-CCM+, then convergence studies with respect to mesh and time step were verified. The problem of a truncated column in regular waves was simulated and compared with a potential flow solver DIFFRACT and a CFD tool OpenFOAM [33] and available experimental data from MOERI [34]. Secondly, the resonance condition of a particular float was solved not only by numerical method but also by analytical method.…”