The aim of this study is to develop a viscous numerical wave tank using a coupled solver between the wave generation and absorption toolbox waves2Foam, developed by Jacobsen et al. [1] and the overset method built in the open source CFD software OpenFOAM © . This wave tank can be used to analyze the behavior of Floating Offshore Wind Turbine (FOWT) in nonlinear waves. A mesh convergence analysis is presented on a simple 2D case in order to validate the CFD model. The results are compared to experimental data from the literature and show good agreement. The response of a floater developed for a FOWT is analyzed. The free surface elevation, heave and pitch motions are compared to experimental results from the literature. Comparisons between experimental data and numerical results are discussed.

The horizontal wave drift force acting on a vertical floating column, without then with a heave plate, is considered. Computations are performed with a diffraction-radiation code and through the Morison and Rainey equations. Focus is on wave frequencies around the heave resonance where the drift force may be significant, even though the scattered wave-field being weak. It is found that the Morison equation overpredicts the drift force while Rainey equations perform rather well.

Tuned Liquid Dampers (TLDs) have proved their efficiency to mitigate the vibratory response of slender buildings under wind or earthquake excitation. Simple semi-analytical models are proposed here to derive the hydrodynamic coefficients (added mass and damping) of axisymmetric TLDs fitted with circular or radial perforated screens. Comparisons are made with experimental values obtained with an Hexapode test bench. Good agreement is observed.

The maximum displacement of turret moored floating production and storage units (FPSO, FLNG) has been steadily increasing over the past decades and is likely to increase even further in the future. Furthermore, some of these turret moored units are designed to keep position in even the harshest of environments (e.g. 10,000-year storms) and very deep water (e.g. more than 2000m depth). As a consequence, the demands on the capacity of mooring systems are also increasing and larger turret sizes with relatively smaller chaintable openings result. The turret cylinder is neither completely open (due to strength considerations) nor completely closed (due to installation and inspection requirements). Therefore, the mass of water inside the turret will to a degree be forced to move with the turret, but also to a degree be able to enter and exit the turret. As a result, a combination of inertial, hydrostatic, and piston mode effects similar to those found in open moonpools can occur. An additional complicating factor is that the turret is surrounded by an open annular space which influences the flow of water around the turret bottom. Both piston mode and inertia of water inside the turret will impose additional loads on the turret and its support system. It is therefore imperative that these loads be taken into account in the design phase. A number of tools, both experimental and computational may be used to obtain estimates of loads. However, whichever method is chosen, a necessary step is to identify the natural periods of the piston mode taking place in the turret. Investigations, whether numerical or experimental, must obviously focus on these periods. In this paper, analytical, computational (CFD) and experimental methods to obtain natural piston mode periods of turret moonpools are described. The methods are applied to simplified, yet realistic, turret models. Results from these different methods are compared. Respective figures of merit are discussed.

Bundle arrangements are currently used in the design of underwater riser towers or oil export lines. A bundle is made of several parallel pipes linked together at intervals. Even if individual pipes are of circular section, the global external cross-section seen by the fluid is non-circular. When placed in a current, a bundle may be therefore prone to plunge instability [6], also know as “galloping”. When designing such bundle’s section, it is important to be able to predict its susceptibility to galloping and what are the implications on the whole structure. Galloping is taking place in a low frequency range compared to VIV but with larger amplitude, up to several diameters. Instability can also occur in torsion through a coupling effect with transverse oscillations. Riser Vortex Induced Vibrations have been studied for decades, and numerous experiments have been performed both in-situ and in model test facilities to understand and predict the instability of a slender cylindrical structure in current. The main motivation is the consequences of VIV on riser fatigue life. If galloping and related instabilities are well known in aerodynamics [9], no large specific experiment or study exists for hydrodynamic flows [1], [7]. Therefore no guidelines exist to help prevent or predict galloping while designing cross-sections and pipe arrangements. Until recently, only the Blevins criteria [1] were available to predict the risk of instability. Based on recent examples of riser tower, experimental and numerical investigations are carried out within the “Gallopan” project in the frame of CITEPH (Concertation pour l’Innovation Technologique dans l’Exploration Production des Hydrocarbures) [11]. The main objective is to propose guidelines to avoid or reduce the risk of galloping in bundle cross section design. Two cross section shapes are investigated, a square cross section for which results are available in the literature [1], [10], and a bundle cross section specifically designed to be unstable. Model tests are performed in two steps: • Captive tests and transverse forced oscillation tests in steady current to derive hydrodynamic coefficients; • Free oscillations tests in steady current to identify the range of reduced velocity where instability occurs as well as the response amplitudes. A specific experimental arrangement, based on a vertical pendulum system is used. Numerical investigations are focused on the use of a standard riser analysis tool. Hydrodynamic coefficients issued from experiments are introduced. Model test set-up is reproduced for comparison purpose.

Galloping may take place for non-circular cross sections, such as an ice-coated electric power line or a riser bundle, under current action. This type of instabilities occurs at lower frequency than Vortex Induced Vibrations but with unbounded amplitude, and might be detrimental for riser integrity. In a recent joint industry project, the CITEPH “Gallopan” project, galloping instabilities were investigated for two types of cylinders: an academic square cylinder and a generic riser tower cross section. Model tests and numerical computations were performed to assess the propensity of both cylinders to gallop. Experiments on the square cylinder are reported here. Three types of tests were performed in steady flow: loads measurement on fixed cylinder, at various headings; loads measurement on the cylinder with over imposed cross-flow harmonic oscillations; free transverse oscillations. By using analytical calculations, the ability to predict galloping instability occurrence and amplitude, of each of the three above methods, was compared. Compared to typical results found in literature, these experiments were conducted at a larger scale, and thus with Reynolds number closer to on-site values, i.e. over 10 5 .

This paper presents a state-of-the-art methodology to build a numerical hydro-mechanical model of a floating LNG Terminal with a LNG carrier moored alongside, complying with the physical mechanical behavior and hydrodynamic phenomenology involved in such a complex system. The required numerical functions are available for intensive engineering applications in the PRINCIPIA’s software DIODORE™ dedicated to sea-keeping and mooring analysis. The methodology has been validated by comparison with non-captive model tests in IFREMER basin in the frame of the SALT 2 JIP led by PRINCIPIA. The paper describes first the academic side-by-side case that has been tested in basin, associated with the comparison between the experimental results and the numerical application using DIODORE™. In a second step, the main physical parameters of the simulation are analyzed and some gained insights are exposed.

Deepwater field developments are usually associated with large submarine packages to be installed such as suction anchors, manifolds and other subsea equipment. Key data for the lowering operation engineering are the added mass and drag coefficients of the package, which is usually a complex structure made of plates (mudmat, drop object protection…), piping and miscellaneous equipment. To extract these hydrodynamics coefficients, it is usual industry practice to consider the package overall volume or to sum the individual components coefficients which may lead to very different results. Experimental investigations on generic complex structures have been conducted within the CITEPH project “Offshore installation of heavy package – phase II”, with the aim of better understanding the hydrodynamics coefficients to be used for the design. This paper presents the work that has been performed during this joint industry project, in 2010/2011, with the support of TOTAL, TECHNIP, SAIPEM and DORIS Engineering, on shielding effect. In particular, model tests set-up and main results are discussed. The trends that have been found and the empirical laws that have been established as functions of dimensionless numbers are also presented.

An experimental campaign is reported on the slow-drift motion of a rectangular barge moored in irregular beam seas. The 24 m long false bottom of the basin is raised and inclined at a slope of 5%, from 1.05 m below the free surface to 0.15 m above. The barge is moored successively at 4 different locations, in water-depths ranging from 54 to 21 cm. The measured slow-drift component of the sway motion is compared with state-of-the-art calculations based on Newman approximation. At 54 cm depth good agreement is obtained between calculations and measurements. At 21 cm depth the Newman calculation exceeds the measured value. When the flat bottom setdown contribution is added up, the calculated value is 2 to 3 times larger than the measured one. A second-order model is proposed to account for the shoaling of a bichromatic sea-state propagating in decreasing water-depth. Application of this numerical model to the scale-model tests shows that in shoaling conditions the setdown contribution to the slow-drift excitation can counteract and not necessarily add up to the Newman component.

An experimental campaign is reported on the wave response of a rectangular barge supporting two rectangular tanks partly filled with water. Flat and chamfered tank roofs are successively tested, at varying heights above the free surfaces inside the tanks. The tests are carried out in irregular wave systems coming from abeam. The measured barge roll and sloshing motions in the tanks are compared with numerical results from a linearized potential flow model. Good agreement is reported in mild seastates. Nonlinear effects, associated with large amplitude sloshing motion and/or roof impacts, are investigated.