This paper discusses the potential of deterministic wave prediction as one basic module for decision support of offshore operations. Therefore, methods of different complexity—the linear wave solution, the non-linear Schrödinger equation (NLSE) of two different orders and the high-order spectral method (HOSM)—are presented in terms of applicability and limitations of use. For this purpose, irregular sea states with varying parameters are addressed by numerical simulations as well as model tests in the controlled environment of a seakeeping basin. The irregular sea state investigations focuses on JONSWAP spectra with varying wave steepness and enhancement factor. In addition, the influence of the propagation distance as well as the forecast horizon is discussed. For the evaluation of the accuracy of the prediction, the surface similarity parameter is used, allowing an exact, quantitative validation of the results. Based on the results, the pros and cons of the different deterministic wave prediction methods are discussed. In conclusion, this paper shows that the classical NLSE is not applicable for deterministic wave prediction of arbitrary irregular sea states compared to the linear solution. However, the application of the exact linear dispersion operator within the linear dispersive part of the NLSE increased the accuracy of the prediction for small wave steepness significantly. In addition, it is shown that non-linear deterministic wave prediction based on second-order NLSE as well as HOSM leads to a substantial improvement of the prediction quality for moderate and steep irregular wave trains in terms of individual waves and prediction distance, with the HOSM providing a high accuracy over a wider range of applications.

To ensure survival of floating structures in rough seas, a precise knowledge of global and local loads is an inevitable integral part for safe design. One of the key parameters is the vertical bending moment. Not only vertical forces but — as previous investigations revealed — also longitudinal forces significantly contribute to the vertical wave bending moment. Three segmented ships, equipped with force transducers, are investigated systematically in high and steep regular waves and in harsh wave environments at several cruising speeds to identify the structural loads. The model tests are carried out in the seakeeping basin of the Technical University Berlin at a scale of 1:70. To cover possible influences of the bow geometry, three different types of vessels are chosen, a bulk carrier with a full bow, a Ro/Ro vessel and a container vessel with a V-shaped frame design. For identifying the influence of the wave height and steepness on the vertical bending moment, model tests in regular waves with different crest/trough asymmetries are performed with the Ro/Ro vessel and the bulk carrier. The program can be subdivided into three parts, each characterized by the same wave lengths with varying wave steepness. The first test series includes regular waves with small amplitudes, thus linear wave theory can be applied. In the second part the same (regular) wave lengths have been generated with increased wave heights, i.e. increasing crest/trough asymmetries and wave profiles within Stokes II domain. During the last part of the experimental program the wave heights are further increased to reach wave profiles within Stokes III domain. For the evaluation of the test results in regular waves — in particular in high steep waves — the results are compared to the respective Response Amplitude Operator determined by the transient wave package technique. Here the focus lies on the asymmetry of the hogging and sagging loads with respect to the wave steepness and the bow geometry of the investigated ship models. Furthermore, the influence of the freeboard height on the vertical bending moment is analysed. For this purpose a container vessel is investigated with two different freeboard configurations in a harsh wave environment.

This paper addresses the Higher Order Spectral (HOS) method as very fast and accurate non-linear method for deterministic wave forecast. The focus of the paper lies on wave propagation, with the objective to draw conclusions on the applicability of the HOS method for deterministic wave forecast. Systematic numerical and experimental investigations are conducted. The investigations comprise exact solutions of the nonlinear Schrödinger equation (NLS) as special non-linear wave groups, which are used as initial conditions for the subsequent simulations. Different parameters such as relative water depth, wave steepness and propagation distance are varied to evaluate the applicability of the HOS method. The results obtained are validated by experiments as well as fully non-linear simulations. It is shown that the HOS method is capable for non-linear wave forecast due to high accuracy and fast calculation time at once.

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The current demand of liquefied natural gas (LNG) from remote marine locations pushes the design of floating LNG (FLNG) liquefaction or regasification facilities, where LNG is transferred between shuttle carrier (LNGC) and terminal. Even if the tandem configuration is the primary choice for LNG transfer at rough offshore locations, side-by-side configurations would be the preferred option because of existing midship coupling manifolds on the present carrier fleet (no need for manifold modifications) as well as standard mooring systems and transfer-process-chains similar to oil-transfer. Therefore, the operation conditions at rough seas have to be improved to allow side-by-side LNG-transfer and to reduce offloading downtime. Within the SOTLL-project, side-by-side LNG transfer up to HS = 3 m is reached as a transfer limit using a new flexible pipe design, the advantages of sheltered areas at the leeside of the terminal barge and an optimized ship transfer position due to a flexible longitudinal offloading position. In addition to the evaluation of the hydrodynamic characteristics of this multibody system, one key aspect is the analysis of the exciting forces and motions due to wave amplification between the ships. In the gap between the hulls, the incoming wave field is amplified and changes dramatically. Depending on gap width, longitudinal offset, wave heading and length, large wave amplifications, standing waves and other resonance phenomena are observed which may result in high relative motions and increased forces of the entire mooring system. In this paper, the gap effects are investigated in detail with numerical approaches in frequency domain, validated by model tests at TU Berlin. A typical offloading scenario with barge and carrier is investigated for different gap sizes to identify suitable transfer configurations and ensure safe LNG offshore transfer up to HS = 3 m.