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Item type:Publication, Access status: with files , Prediction of waves in tanks excited by ship motion and moving walls with a three-dimensional fully linear finite difference approachMitigation of waves in shipboard swimming pools excited by ship motions is a topic of current interest that has not yet been extensively investigated. Various damping mechanisms have been applied to mitigate waves excited in tanks, such as porous baffles or different types of internal baffles. However, most of these devices are installed in LNG tanks to prevent serious sloshing effects. Furthermore, these are passive devices and, hence, unable to control wave-induced excitations. Our focus was on the validation and verification of the three-dimensional (3D) fully linear Finite Difference Method (FDM) based on the previously developed method of Qi et al. (2024) for predicting waves in a transversely placed swimming pool excited by ship motions and piston-type actuators. We validated our FDM approach against comparative Computational Fluid Dynamics (CFD) simulations as well as experimental model test measurements. The CFD tools solved the Reynolds-averaged Navier-Stokes (RANS) equations, relied on an appropriate turbulence model and the Volume of Fluid (VOF) method to capture the free surface of the liquid in the model tank, and employed the overset technique to specify the motions of the active actuators. Our FDM considered ship-induced roll excitations as well as simultaneous roll and sway excitations, albeit only at frequencies outside the range of the pool's resonance frequency. For these periods, our approach accurately predicted not only the mitigated waves in the pool, but also the optimum amplitude of the actuators needed to mitigate such waves. Our FDM can be applied to obtain a preview of excited waves under various conditions, leveraging its principal advantage of extreme computational efficiency.Publicationtype: Journal Article18 89 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , A three-dimensional fully linear finite difference approach to predict waves in tanks excited by ship motions(Elsevier, 2024-06-15); ; ; ; We developed a three-dimensional (3D) linear frequency domain approach using the finite difference method (FDM) to predict shallow water waves in a partially filled tank or a swimming pool excited by ship motions. This approach assumed that the exciting tank motions are so small that the water motions in the tank are proportional to the exciting tank motions. The dependence of fluid motions (relative to the tank) on the vertical coordinate was assumed as known; hence, calculations could be reduced from three to two spatial dimensions, reducing the computational complexity of this approach. Also, non-rectangular tank shapes can be modeled. Moving side walls (piston-type actuators), which may be installed to dampen or to excite waves in the pool, are taken into account by specific boundary conditions. The bottom friction is accounted for by a non-dimensional parameter which is determined empirically. To validate the FDM approach for a model tank without moving sidewalls, we consider harmonic and irregular tank motions, comparing results of the FDM with results of commercial Computational Fluid Dynamics (CFD) software and of model tests. By solving the unsteady Reynolds-averaged Navier-Stokes (URANS) equations combined with the volume of fluid (VOF) technique, our CFD simulations are carried out over a broad frequency range including sloshing eigenfrequencies of the model tank. Thus, we demonstrate that the FDM approach yields predictions of acceptable accuracy efficiently except near resonance. Based on the comparative CFD simulations, the limits of our FDM for tanks without moving sidewalls are also discussed.Publicationtype: Journal Article31 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Numerical study on steady wave drift forces of an obliquely moving ship(2019-09); This paper considers numerical computation of the steady wave drift forces acting on an obliquely moving ship. The traditional forward speed seakeeping problem was extended to consider the ship with a drift angle. A computer code was developed based on a time domain Rankine panel method. Once the velocity potential around the hull was determined, the first order wave induced motions were calculated and then the second order wave drift forces were evaluated using a near field method. Based on the developed code, the longitudinal and transverse steady wave drift force, as well as the steady yaw moment were computed for a container ship in head and beam waves. The effects of the drift angle on the steady wave drift forces were included and discussed. The numerical results were compared with the published experimental measurements, which shows fairly good agreement.Publicationtype: Conference Paper122 233 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Experimental investigation of vortex-induced vibrations using 3D-accelerometry and digital image correlation(2019-09); ; ; Tower structures of wind turbines are often installed in various configurations at the port before being transported by ships. Vortex-induced vibrations may occur when the natural frequency of the structure is close to flow vortex shedding frequency. This leads to a considerable reduction of their fatigue life. The phenomenon is well-known for risers in the oil and gas industry. Here, we present an experimental study of vortex-induced vibrations (VIV) of a fully and partially submerged hollow cylinder in water. A circulating water channel generated the flow towards the test bodies. Two hollow cylinders with a length-to-diameter ratio (l/d) of 28.13 and 18.5 and an outer diameter of 32 mm were used. Each cylinder was equipped with three-dimensional accelerometers. From the acceleration data, a two-fold integration delivered the motion amplitudes of the cylinders at the location of the accelerometer. In addition, a speckle pattern was applied to the cylinders and captured with two high-speed cameras, arranged in different orientations to the cylinder. Three-dimensional Digital Image Correlation (DIC) was used to measure the motion trajectories for the areas of the cylinder, covered by a speckle pattern. First, decay tests for the test bodies were performed in air and water. From the motion trajectories, the natural frequencies and damping coefficients were evaluated. Second, tests in uniform flow were conducted under fully and partially submerged conditions for different flow velocities. Flow effects such as reduced velocity on vibration were assessed in terms of motion amplitudes and frequencies in longitudinal and transverse direction. The results from DIC and accelerometer measurements were compared and the suitability of DIC for VIV investigations was discussed.Publicationtype: Conference Paper145 166 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Wave-Induced Motions of Moored and Coupled Multi-Body Offshore Structures(2019-09); In the recent past, very large floating structures (VLFS) are used to realize a variety of large marine facilities like floating piers, bridges or logistical hubs, substituting the traditional bottom mounted structures. In most cases VLFSs consist of a number of individual modules that are assembled with connectors and hold in place by mooring systems. To ensure proper working and safety conditions, their hydrodynamic response in different sea states needs to be investigated. Previous investigations relied mainly on potential flow solvers which do not account for viscous and other nonlinear effects. However, flow properties under severe conditions are highly nonlinear. To capture the physics of such phenomena field methods are the preferred choice. The present work aims to investigate the hydrodynamic response of such a moored and coupled multi-body VLFS in waves using a flow code that computes multiphase unsteady incompressible flow simulations using the Navier Stokes equations coupled with a six-degrees-of-freedom (6 DOF) multi-body solver and mooring model. A total number of 14 simulations have been conducted for single and multiple cuboid set-ups. The set-ups are based on the model tests performed at TU Delft. The hydrodynamic responses were assessed and show a favourable comparison for most cases between the computed and measured results.Publicationtype: Conference Paper165 280 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Squat computations for container ships in restricted waterways(Curran Associates, Inc., 2011); ; ; ; The paper presents results of dynamic squat computations in restricted waterways with two potential flow solution methods and a solver of Reynolds-averaged Navier-Stokes equations (RANSE). Computational results are compared with model tests and full-scale measurements for two large post-panamax class container carriers. Ways of computational time reduction are discussed.Publicationtype: Conference Paper41