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Highly accurate and precise heave decay tests on a sphere with a diameter of 300 mm were completed in a meticulously designed test setup in the wave basin in the Ocean and Coastal Engineering Laboratory at Aalborg University, Denmark. The tests were dedicated to providing a rigorous benchmark dataset for numerical model validation. The sphere was ballasted to half submergence, thereby floating with the waterline at the equator when at rest in calm water. Heave decay tests were conducted, wherein the sphere was held stationary and dropped from three drop heights: a small drop height, which can be considered a linear case, a moderately nonlinear case, and a highly nonlinear case with a drop height from a position where the whole sphere was initially abovethe water. The precision of the heave decay time series was calculated from random and systematic standard uncertainties. At a 95% confidence level, uncertainties were found to be very low — on average only about 0.3% of the respective drop heights. Physical parameters of the test setup and associated uncertainties were quantified. A test case was formulated that closely represents the physical tests, enabling the reader to do his/her own numerical tests. The paper includes a comparison of the physical test results to the results from several independent numerical models based on linear potential flow, fully nonlinear potential flow, and the Reynolds-averaged Navier–Stokes (RANS) equations. A high correlation between physical and numerical test results is shown. The physical test results are very suitable for numerical model validation and are public as a benchmark dataset. Highly accurate and precise heave decay tests on a sphere with a diameter of 300 mm were completed in a meticulously designed test setup in the wave basin in the Ocean and Coastal Engineering Laboratory at Aalborg University, Denmark. The tests were dedicated to providing a rigorous benchmark dataset for numerical model validation. The sphere was ballasted to half submergence, thereby floating with the waterline at the equator when at rest in calm water. Heave decay tests were conducted, wherein the sphere was held stationary and dropped from three drop heights: a small drop height, which can be considered a linear case, a moderately nonlinear case, and a highly nonlinear case with a drop height from a position where the whole sphere was initially above the water. The precision of the heave decay time series was calculated from random and systematic standard uncertainties. At a 95% confidence level, uncertainties were found to be very low—on average only about 0.3% of the respective drop heights. Physical parameters of the test setup and associated uncertainties were quantified. A test case was formulated that closely represents the physical tests, enabling the reader to do his/her own numerical tests. The paper includes a comparison of the physical test results to the results from several independent numerical models based on linear potential flow, fully nonlinear potential flow, and the Reynolds-averaged Navier–Stokes (RANS) equations. A high correlation between physical and numerical test results is shown. The physical test results are very suitable for numerical model validation and are public as a benchmark dataset.

This paper presents a benchmark study on the slamming responses of offshore structures’ flat-stiffened plates. The objective was to compare the fluid-structure interaction (FSI) simulation methodologies, modeling techniques, and established researchers' experiences in predicting slamming pressure. Three research groups employing the most common commercial software packages for numerical FSI simulations (i.e. LS-Dyna ALE, LS-Dyna ICFD, ANSYS CFX, and Star-CCM+/ABAQUS) participated in this study. Wet drop test data on flat-stiffened aluminum plates of light-ship-like bottom structures available in the open literature was utilized for validation of the FSI modeling. A summary of the experimental conditions including the geometry model and material properties, was distributed to the participants prior to their simulations. A parametric study on flat-stiffened steel plates having actual scantlings used in marine installations was performed to investigate the effect of impact velocity and plate rigidity on slamming response. The FE simulation results for the total vertical forces acting on the stiffened plates and their structural responses to those forces, as obtained from the participants, were analyzed and compared. The reliable and accurate predictions of slamming loads using the aforementioned commercial FSI software packages were evaluated. Additionally, equivalent static slamming pressures resulting in the same permanent deflections, as observed from the FSI simulations, were reported and compared with analytical models proposed by the Classification Standards DNV and existing experimental data for calculation of the slamming pressure. The study results showed that the equivalent load model depends on the water impact velocity and plate rigidity; that is, the equivalent static pressure coefficient decreases with an increase in impact velocity, and increases when impacting structures become stiffer.

The International Energy Agency Technology Collaboration Programme for Ocean Energy Systems (OES) initiated the OES Wave Energy Conversion Modelling Task, which focused on the verification and validation of numerical models for simulating wave energy converters (WECs). The long-term goal is to assess the accuracy of and establish confidence in the use of numerical models used in design as well as power performance assessment of WECs. To establish this confidence, the authors used different existing computational modelling tools to simulate given tasks to identify uncertainties related to simulation methodologies: (i) linear potential flow methods; (ii) weakly nonlinear Froude–Krylov methods; and (iii) fully nonlinear methods (fully nonlinear potential flow and Navier–Stokes models). This article summarizes the code-to-code task and code-to-experiment task that have been performed so far in this project, with a focus on investigating the impact of different levels of nonlinearities in the numerical models. Two different WECs were studied and simulated. The first was a heaving semi-submerged sphere, where free-decay tests and both regular and irregular wave cases were investigated in a code-to-code comparison. The second case was a heaving float corresponding to a physical model tested in a wave tank. We considered radiation, diffraction, and regular wave cases and compared quantities, such as the WEC motion, power output and hydrodynamic loading. The Danish partners acknowledge the support from the Danish Energy Agency through project 374 64017-05197. The Swedish partners were supported by the Swedish Energy Agency under Grants P44423-1 and 375 P44432-1. J.V.R. and G.G. acknowledge the support by Science Foundation Ireland under Grant 13/IA/1886. This research was made possible by support from U.S. the Department of Energy’s EERE Water Power Technologies Office. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. This work was authored (in part) by the National Renewable Energy Laboratory, operated by Alliance for Sustainable Energy, LLC, for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. Funding was provided by the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy Wind Energy Technologies Office. The views expressed in this article do not necessarily represent the views of the DOE or the U.S. Government. The U.S. Government retains and the publisher, by accepting the article for publication, acknowledge that the U.S. Government retains a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for U.S. Government purposes.

In this paper, a fully nonlinear unsteady potential flow method is used to predict added resistance, heave and pitch for the KVLCC2 hull in regular head waves at design speed. The method presents a nonlinear decomposition of the velocity potential and the wave field and an adaptive grid refinement. A formulation for the acceleration potential is used to obtain the pressure. To improve computational efficiency, a Barnes-Hut algorithm is introduced. A grid dependency study and a study on the impact of different time steps on the solution are performed. Numerical results have been compared with experimental data for the design speed. A general good agreement is found for added resistance, especially for longer waves. Heave and pitch are properly computed for all wave lengths in the range λ / L p p = 0.4 to 1.4.

Optimization of modern hulls when moving in a seaway puts new demands on the computational methods used. Nonlinear effects become important for wave loads and added resistance in waves in presence of large motions. The purpose of this paper is to present a method which aims to fill the gap between RANSE methods and partly nonlinear panel methods. The method solves the fully nonlinear free surface time-domain potential flow problem including a hull undergoing rigid body motions. Nonlinearities under the hypothesis of potential flow are taken into account, i.e. higher and lower frequency components, hull shape above calm water line and interaction between incoming, radiated, diffracted, reflected and ship generated waves. The potential flow method alone cannot handle roll motion since roll is dominated by viscous effects. Two methods to include roll damping within the potential flow code are used: the first one obtains roll damping coefficients through inertial and geometric characteristics of the ship. The second one uses model test results. Numerical results using both methods are compared. The code has already been tested in head seas. In this paper, numerical simulations of roll decay and roll motion in beam sea are compared to model test results.

A grid sensitivity study for a conventional propeller in open-water condition uses three grids and compares with experimental data. Thrust and torque are rather insensitive to the grid resolution, but local quantities such as pressure coefficient and velocity are grid sensitive. An uncertainty analysis method reveals that the data are not in the asymptotic range which might be partly due to the complexity of the propeller flow.

Three-dimensional steady RANS computations simulate the flow around a conventional propeller operating in open water conditions. Turbulence is modeled by the shear stress transport SST k-ω model. The influence of the turbulence model is investigated using the realizable k-e model in combination with enhanced-wall treatment as an alternative. Computed forces and velocity distributions downstream the propeller are compared with the experimental data obtained from open water tests and PIV measurements for the design advance number J. The thrust and torque coefficients arc compared for several advance numbers. The SST k-ω model performs well in predicting the performance of the propeller and the main characteristics of the propeller flow.

The distribution of hydrodynamic and hydrostatic pressure resistance on a ship hull is investigated for four variants of the Dyne tanker and for the Series 60 hull. A grid dependence study is carried out for a double-model of the tanker to investigate the discretization error from the fore and aft bodies. The hydrodynamic influence between the fore and aft bodies is investigated by a length variation of the midship part of the tanker. The distribution of hydrodynamic and hydrostatic pressure resistance is discussed for linear and non-linear computations. The study shows that it is important to investigate the discretization error from the fore and aft bodies separately, and that the fore and aft bodies may act as independent hydrodynamic systems at low Froude numbers.

Four different techniques that use wave cut analysis to predict the wave pattern resistance coeffcient of a ship hull are compared. Two of the techniques are based on longitudinal wave cuts and two are based on transverse wave cuts. The results are compared with values from pressure integration and with towing tank measurements of the residuary resistance. Three hulls were used for the comparison: the Dyne Tanker, the Series 60 and the SSPA Ro-Ro Ship model 2062 having four different fore bodies. The wave cuts were obtained from linear and non-linear solutions of the free surface waves. A technique to predict free-surface deformation at any distance downstream of a vessel quickly based on the information computed in one of the transverse wave cut methods is presented.

This paper presents a method for computation of far-field wash waves in deep water. The method combines a non-linear Rankine source method in an inner domain with a Kelvin source method for the far-field waves in an outer domain. Kelvin sources are distributed on a vertical matching wall, positioned at the outer edge of the inner domain. These sources are used to specify a boundary condition for the disturbance velocity potential on the matching wall. The boundary condition is used in the Rankine source solution of the inner domain. The size of the inner domain can be reduced in the transverse direction compared to a method using Rankine sources only, as the wave reflections at the edge of the inner domain are eliminated. Further, the far-field waves can be computed using the solution on the matching wall together with the the Kelvin source distribution. The verification of the present method includes a comparison for a single Kelvin point source and a comparison to a Rankine source method at intermediate distances for the Wigley hull and for a catamaran. A grid dependence study for the position, size and panel density on the matching wall is included for the Wigley hull. Computed and measured longitudinal wave cuts are compared for a catamaran both in the inner and the outer domain. Good agreement is obtained.

A potential-flow panel method is used to compute the waves and the lift force from surface-piercing and submerged bodies. In particular the interaction between the waves and the lift produced close to the free surface is studied. Both linear and non-linear free-surface boundary conditions are considered. The potential-flow method is of Rankine-source type using raised source panels on the free surface and a four-point upwind operator to compute the velocity derivatives and to enforce the radiation condition. The lift force is introduced as a dipole distribution on the lifting surfaces and on the trailing wake, together with a flow tangency condition at the trailing edge of the lifting surface. Different approximations for the spanwise circulation distribution at the free surface were tested for a surface-piercing wing and it was concluded that a double-model approximation should be used for low speeds while a single-model, which allows for a vortex at the free surface, was preferred at higher speeds. The lift force and waves from three surface-piercing wings, a hydrofoil and a sailing yacht were computed and compared with measurements and good agreement was obtained.

Low speed transportation is more energy efficient than high speed transportation in general. Ships with lower design speeds provide possibilities for using auxiliary wind propulsion devices to further reduce energy consumption. The kite is one type of auxiliary wind propulsion device that can be used for this purpose. The aim of this study is to investigate the influence of auxiliary kite propulsion on the performance of a panamax tanker, specifically on engine power reduction, course-keeping ability in different headings and on pitch and roll motion of the ship. The study is carried out by computer based simulations. Scenario combinations are established for various ship speeds, headings and weather conditions. For the purpose of simulation, a simplified auxiliary kite propulsion model is built and verified against full scale data. The SSPA in-house time domain maneuvering and seakeeping software – SEAMAN II is used for the study. The kite model is created as a subroutine to the SEAMAN software. The kite flies on the spherical surface along a predefined track. It performs span-wise rotation to achieve an optimum angle of attack. A NACA 4415 wing profile is adopted as the cross section of the kite. Aerodynamic forces are calculated based on the effective relative wind velocity and the optimum angle of attack. The radial component of the aerodynamic forces provides a traction force in the connection line. The traction force contributes to forces and moments acting on the simulated tanker. The numerical kite model was verified against full scale data. The deviations of traction force and thrust force between simulation and full scale could be controlled within 7%. Throughout the simulations, forces, moments, and motions of the tanker are recorded, as well as rudder angle and propeller efficiency. These output variables are plotted and analyzed to describe the influence of the auxiliary kite propulsion to ship performance. The result shows that auxiliary kite propulsion plays a significant role in reducing engine power in beam and following sea conditions. According to the SEAMAN simulations, a reduction of at least 40% could be obtained in many cases. The course keeping ability of the simulated panamax tanker is not affected by using the kite. The present study is a first step towards a fully dynamic kite model, where a control mechanism will be introduced to find the most favorable flying trajectory.

Following an interdisciplinary calculation procedure, the chain of events of ship collision, flooding, and loss of stability within given time have been investigated. The method established in the current work concerns the interaction between structural and damage stability computations and has been used to study the influence of various parameters, for example, significant wave height and size of damage opening on a RoPax ferry damaged in a collision with a ship of similar size.

This is the first joint reference paper for the Ocean Energy Systems (OES) Task 10 Wave Energy Converter modeling verification and validation group. The group is established under the OES Energy Technology Network program under the International Energy Agency. OES was founded in 2001 and Task 10 was proposed by Bob Thresher (National Renewable Energy Laboratory) in 2015 and approved by the OES Executive Committee EXCO in 2016. The kickoff workshop took place in September 2016, wherein the initial baseline task was defined. Experience from similar offshore wind validation/verification projects (OC3-OC5 conducted within the International Energy Agency Wind Task 30) [1], [2] showed that a simple test case would help the initial cooperation to present results in a comparable way. A heaving sphere was chosen as the first test case. The team of project participants simulated different numerical experiments, such as heave decay tests and regular and irregular wave cases. The simulation results are presented and discussed in this paper.