Wave-current interaction effects may significantly influence the mean wave drift forces on a structure as well as the motion responses and wave elevation around the structure. Additionally, the drift force may be used to estimate the wave drift damping of a moored structure. A new numerical potential theory code for industry applications (MULDIF) has been recently developed, where the hydrodynamic interaction between waves and current of arbitrary direction with large volume structures is consistently included. The code also handles multiple bodies and finite water depth including wave-current interaction effects. The aim has been to create a robust and easy-to-use practical tool. Initial validation studies against model tests have been conducted. The numerical results show a strong heave-pitch coupling due to the presence of the current. Preliminary results for a semi-submersible show good agreement for the motions provided that the mooring used in the model tests are accounted for. The free surface elevation around the semi-submersible is presented in contour plots.

A recently developed numerical design method for analysis of green sea events and resulting impact loads on deck structures of FPSO’s, is validated against model test data. Steep irregular wave conditions are considered, and numerical time series reconstructions are made using the measured wave as input. A second-order numerical random wave description is combined with standard 3D wave diffraction and related vessel motions to predict the relative wave kinematics. A modified shallow water formulation is applied for the prediction of the propagation on deck, and resulting local pressures on the deck-house are estimated by a similarity solution. From this an analysis of the structural integrity can be made. Comparisons to the experiments are made for the relative wave amplitudes, water propagation on deck, and the resulting deck-house loads. A reasonably good agreement is observed for the reconstructions, in a statistical sense, but also for individual events. Thus selected green sea events are investigated in detail, and characteristics identified. The agreement with the model tests is promising especially on the background of the simplified approach used, as well as the expected statistical scatter.

This paper presents a new unified seakeeping-maneuvering simulation model valid for surface ships and underwater vessels. If the total ship motions are derived from the traditional formulations for the hydrodynamic and maneuvering models, considering them as two separate problems, the results will be inconsistent. It has therefore been necessary to develop a unified formulation which calculates the total ship motions including both the maneuvering aspects and the wave induced motions. Focus in this study has been on submarines. Examples of application of the developed time domain simulation code are given. These are simulations of the response and corresponding control plane forces of a submarine in straight line motions in regular waves at given headings. The developed code can also be used to e.g. simulate turning circles. This has been conducted for the same submarine, and the results are compared to experimental results. Additionally, simulations of the response of a surface vessel (Wigley hull) with forward speed in regular waves at given headings are presented. In this case only the potential forces are considered. The results from the simulations are used to establish motion transfer functions, which are compared to other numerical and experimental results. There are some limitations in the developed method which affects the application area of the numerical code. This refers particularly to underwater vessels. This will be addressed, and further possible development of the method will be discussed.

The main purpose of this paper is to present experimental results from model tests of a semisubmersib-Ie platform at large angles of list. Very little work has previously been done in this problem area, and hardly any of it has been published. Therefore, we entered our test programme for the following two reasons: To provide insight into the problem of a large list angle, and to see how far linear hydrodynamic theory could be used to predict the forces and motions of the platform. Both items are discussed in the paper.

The influence from a current on the relative motions and wave drift forces for moored floater can be quite significant. In this paper, a benchmark study is carried out for three programs, MULDIF, WADAM and WASIM, with the focus on their capability on handling the wave-current interaction problem. A semi-submersible model Troll B and a tanker model KVLCC2 are used for this study. The motions, free surface elevation at specified off-body points and mean drift forces are calculated by the programs in different current or forward speed conditions. Analysis results are compared and discussed, with the aim to evaluate the numerical performance of each programs and their validity range in terms of current speed.