The wavemaking resistance of a rigid ship in steady rectilinear motion at the free surface of a previously calm ocean is evaluated by means of a linearized three-dimensional potential-flow formulation. Solutions to the disturbance potential of the steady perturbed flow about the moving ship are obtained by means of a Kelvin wave source distribution method. Particular emphasis is placed on computational aspects and accurate and efficient algorithms for the evaluation of the fundamental Kelvin wave source potential function are discussed. To illustrate the proposed method, experimental and theoretical predictions are compared for a variety of ship forms. In general, this approach shows the correct behaviour of the variation of the wavemaking resistance with forward speed in both a qualitative and quantitative manner.

This paper discusses the numerical evaluation of the characteristic Kelvin wavelike disturbance trailing downstream from a translating submerged source. Mathematically the function describing the wavelike disturbance is expressed as a single integral with infinite integration limits and a rapidly oscillatory integrand. Numerical integration of such integrals is both cumbersome and time-consuming. Attention is therefore focused on two complementary Neumann-series expansions which were originally derived by Bessho [1].2 Numerically stable algorithms are presented for the accurate and efficient evaluation of the two series representations. When used in combination with the Chebyshev expansions for the nonoscillatory near-field component which were recently obtained by Newman [2], the present algorithms provide an effective solution to the numerical difficulties associated with the evaluation of the Kelvin wave source potential.

The extreme responses of a turret moored tanker are sensitive to non-aligned wind, wave and current conditions. Such conditions commonly occur in the Gulf of Mexico during the passage of the eye of a hurricane. Conventional design practice often relies on a collinear or, at best, a "guessed" non-collinear combination of 100-year environmental return period wind, wave and current conditions. Hence there is a need to derive response-based design criteria, i.e. that particular combination of wind, waves and current which most likely yields the 100-year return period response. The long term response characteristics of a turret moored tanker in deep water Gulf of Mexico conditions are investigated through the use of a comprehensive hurricane hindcast database. The effects of turret location and wave spreading are considered. The 100-year long term responses are compared against the short-term 100-year design responses derived from a 100-year hurricane design analysis. Response-based design criteria are then derived. Introduction Turret moored tanker based FPSO systems are widely used in many deepwater areas. Conventional design of such systems often relies on the assumption of a design storm event comprised of a collinear (or at best a guessed non-collinear) combination of 100-year environmental return period wind, waves and current. However, it is well known that the extreme responses of a turret moored tanker are sensitive to non-collinear wind, waves and current (Refs. 6-8). With few exceptions, the effect of non-collinear wind, waves and current has received little attention. Such events commonly occur in the deepwater Gulf of Mexico during the passage of the eye of a hurricane. The resulting effects on the motions and mooring line tensions may be significant as such systems have a natural tendency to weathervane, i.e. align themselves against the prevailing direction of wind, waves and current. This then poses the question of how well the "conventional" design recipe really works for these systems in significantly non-collinear environments. In order to address this problem the actual long-term response characteristics need to be investigated and the 100-year return period responses need to be derived. Response-based design criteria may then be stipulated to capture specific response characteristics, e.g. the 100-year maximum offset storm is that particular combination of wind, waves and current that most likely yield the 100-year return period offset. Notice that the associated wave height, wind speed and current speed for such a non-collinear design event may well be lower than those normally referred to as 100-year return period environmental criteria. Also, the 100-year return period offset storm, say, is merely intended to estimate the 100-year offset while other responses (e.g. roll or mooring line tension) should be ignored. Theory The long term Gulf of Mexico environment is described by means of a hurricane hindcast database of 35 storms over an 85 year period since 1900 (Ref. 3). The original database contains some 240,000 records with the hourly values of wind, waves and current parameters.

Present day offshore lift operations feature the lifting of substantial loads horn a transport barge by means of large capacity semi submersible crane vessels with stem mounted dual cranes. During such operations the transport barge is moored perpendicular to the stem of the crane vessel. The motional behaviour of the crane vessel and transport barge are affected by hydro-mechanical coupling effects arising either from the hydrodynamic interaction between the two nearby vessels, or from mechanical coupling via the cranes, hoisting tie and slings. In order to investigate the hydrodynamic interaction effects a two-body diffraction analysis has been performed for a crane vessel and a nearby transport barge. The coupled equations of motion have been solved to establish the absolute and relative importance of the hydro-mechanical coupling between the two vessels. Whilst the crane vessel responses are hardly affected by hydrodynamic interaction, the transport barge motions may be significantly altered. It is demonstrated, however, that the hydrodynamic interaction effects are an order of magnitude smaller than the mechanical coupling effects and may be ignored for practical purposes. INTRODUCTION Nowadays it is generally accepted that the application of large capacity crane vessels may result in significant cost savings in offshore installation work, e.g. by adopting integrated topsides or lift able jackets 1. Recent years have seen the advent of two giant Semi Submersible Crane Vessels (SSCV?S) with twin revolving cranes mounted at the stem, the SSCV "DB102" (2×6,000 t maximum capacity) and the SSCV "M7000" (2×7,000 t). Large scale offshore lift installations feature the lifting of loads of up to 10,000 t from a transport barge by means of an SSCV. The loaded transport barge is usually moored perpendicular to the stem of the SSCV at a separation distance of only a few meters. During such operations the crane vessel and transport barge are subjected to wave induced motions, while their motional behaviour is also influenced by mechanical coupling via the cranes, hoisting wires and slings. The resulting complex dynamic behaviour of the hydro-mechanically coupled crane vessel and transport barge has been the subject of several investigations 2 which have culminated, amongst others, in the development of the LIFSIM time simulation program 3. As part of this effort a study has been performed into the hydro-mechanically coupled motions of a crane vessel and a transport barge. Common engineering practice in computational lift dynamics is to ignore hydrodynamic interaction effects. It is rc3CO@Sd, however, that the hydrodynamic interaction effects between two nearby vessels can only be analysed properly by means of a complicated two-body diffraction analysis, a major and expensive task 4. However, evidence from model tests suggests that the hydrodynamic interaction effects are at least an order of magnitude smaller than the mechanical coupling effects via the cranes, hoisting wires and slings, indicating that, for most practical applications, the hydrodynamic interaction effects can be ignored.

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