Focused wave impact with a fixed FPSO (CCP-WSI Blind Test Series 1)

The incident waves were generated in the COAST Laboratory Ocean Basin (Figure 1) using the EDL paddle control software. The software is designed to reproduce the desired free-surface elevation by applying various corrections to account for the change in water depth in front of the wave paddles and the nonlinear propagation of the wave fronts. In this case, each wave was create using linear superposition of 244 wave fronts with frequencies evenly spaced between 0.101563Hz and 2Hz and a theoretical focus location, x0, 13.886m from the wave paddles. Each wave front is then transformed back to the position of the wave paddles by the control software. The amplitudes of the frequency components were derived by applying the NewWave theory to a JONSWAP spectrum with the parameters in the Table 1 where Alpha is the angle of propagation relative to the centre-line of the basin and Phi is the phase of the components at the focus location. All waves in this Blind Test Series have a Phi of π (trough focused).

3.1. Wave parameters - Part 1

In Part 1, the 3 waves have all been generated at 0° incident wave angle. The waves are based on the NewWave theory formed from spectra with T_p = 1.456s or 1.362s and significant wave height, H_s = 0.103 or 0.077, i.e. two wave cases (FW2 & FW3) differ by H_s and are essentially steeper versions of one another with the same relative frequency contributions; FW2 and FW6 differ only by peak frequency and are essentially steeper versions of one another with the same H_s (Table 1).

3.2. Wave parameters - Part 2

In Part 2, all 3 waves have the same steepness (kA = 0.17). The waves differ only by incident angle (Table 2).

The CCP-WSI Blind Test Workshop - Series 1 was a ‘blind’ validation of numerical WSI codes (The CCP-WSI Blind Test Series 1 is now closed). Consequently the only physical measurement data released at the time of participation was the surface elevation data from the wave gauges in the empty tank tests (see Figures 3 & 5 for the wave gauge positions). This data should be sufficient to reproduce the incident waves in each of the cases which are identical to those used in the cases with the structure in place. The surface elevation data from the empty tank tests are supplied in the supporting set of text documents (one for each wave case), e.g. 11BT1.txt corresponds to the empty tank tests for the 11BT1 wave case.

A set of criteria have been selected to ascertain the validity of codes and these correspond to the submission data requested for participation in the CCP-WSI Blind Test Workshop – Series 1. The Validity assessment criteria are as follows:

PART 1:

• Time series of the surface elevation (run-up) at WG 16, 18, 17, 24 and 7 (Figure 3)

• Time series of pressure at P1, 2, 3, 4, 5, 6 (Figure 2).

PART 2:

• Time series of the surface elevation (run-up) at WG 15, 16, 17, 24 and 7 (Figure 6)

• Time series of pressure at P1, 2, 3, 4, 6, 8 (Figure 4).

The CCP-WSI Blind Test Series 1 is now closed. The individual participants results, the final report and the experimental data for the test cases (with the structure included) will be released shortly. Please join the combined CCP-WSI & SIG-WSI community mailing list on the 'Contact Us' page for updates.

The CCP-WSI Blind Test Series 1 is now closed. The experimental data for the test cases (with the structure included) is now available and can be found here. The data is arranged as follows:

• For each of the test cases (e.g. 11BT1) there are two text files, one for the surface elevation measurements (11BT1_surfaceElevation.txt) and one for the pressure measurements (11BT1_pressure.txt).
• The surface elevation measurements are unfiltered measurements; the first row contains the column headers and begins with a '#' for post-processing purposes; the first column is the time in seconds and the proceeding columns are surface elevation in metres at each of the probes corresponding to the validation assessment criteria defined above.
• The pressure data has been filtered and treated for thermal shock (as documented in Ransley et al. 2019); the first row contains the column headers and begins with a '#' for post-processing purposes; the first column is the time in seconds and the proceeding columns are pressure measurements in Pascals at each of the probes corresponding to the validation assessment criteria defined above.

NOTE: When using this data please state that 'the physical data is from the CCP-WSI Test Case 3 (originally the CCP-WSI Blind Test Series 1)' and be sure to cite Ransley et al. 2019 as the source of this data (see full citation in the 'Relevant References' section below).

Ransley, E., Yan, S., Brown, S., Mai, T., Graham, D., Ma, Q., Musiedlak, P.-H., Engsig-Karup, A. P., Eskilsson, C., Li, Q., Wang, J., Xie, Z., Sriram, V., Stoesser, T., Zhuang, Y., Li, Q., Wan, D., Chen, G., Chen, H., Qian, L., Ma, Z., Mingham, C., Causon, D., Gatin, I., Jasak, H., Vukčević, V., Downie, S., Higuera, P., Buldakov, E., Stagonas, D., Chen, Q., Zang, J., Greaves, D., A blind comparative study of focused wave interactions with a fixed FPSO-like structure (CCP-WSI Blind Test Series 1), International Journal of Offshore and Polar Engineering, 29(2) (2019): 1-15, https://doi.org/10.17736/ijope.2019.jc748

Ransley, E. J., Survivability of Wave Energy Converter and Mooring Coupled System using CFD, Ph.D. Thesis, University of Plymouth (2015), http://dx.doi.org/10.24382/1289

Hu, Z., Mai, T. Greaves, D. and Raby, A., A Numerical and Experimental Study of a Simplified FPSO in Extreme Free Surface Waves, in Proceedings of the 26th International Ocean and Polar Engineering Conference, 26 June - 2 July 2016, Rhodes (Rodos), Greece.

Mai, T., Greaves, D., Raby, A. and Taylor, P.H., Physical Modelling of Wave Scattering Around Fixed FPSO-Shaped Bodies, Applied Ocean Research, Vol. 61 (2016), pp. 115-129.

Ma, Q., Yan, S., Greaves, D., Mai, T., Raby, A., Numerical and Experimental Studies of Interaction between FPSO and Focusing Waves, in Proceedings of 25th ISOPE conference, 21-26 June 2015: Hawaii, USA, Vol.3: 655-662.

Accompanying documents: