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Item type:Publication, Access status: with files , Regularized machine learning for system identification of ship free-running manoeuvres from CFD-based synthetic data: a comparative studyThis study investigates supervised machine learning techniques for identifying ship hydrodynamic coefficients from CFD-generated data from free-running simulations. Specifically, ordinary least squares and regularized regression methods are applied to Abkowitz-type manoeuvring models. Training and validation datasets are derived from URANS simulations of zig-zag and turning circle manoeuvres, which are validated against experimental benchmark data. The analysis evaluates the effects of coefficient set size, minimum training length required for predictive model training, and manoeuvre combinations on model performance. Results demonstrate the suitability of large-angle zig-zag manoeuvres for hydrodynamic system identification, provided that multicollinearity is addressed through appropriate coefficient selection, regression models, or input data variability. Larger coefficient sets offer greater model flexibility for variable conditions but are more prone to multicollinearity. Regularized regression techniques effectively mitigate multicollinearity and notably enhance prediction accuracy, as does incorporating more diverse manoeuvring data. Among tested models, Ridge regression provided the best compromise between computational efficiency and prediction accuracy.Publicationtype: Journal Article31 13 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , An efficient approach to CFD simulations with small ships maneuvering in the wave field of larger ships via optimized forcing zones(Springer, 2026-06-05); ; ; ; The maneuvering of small ships within the wave field of larger ships is a common application in practical ship hydrodynamics. Examples include optimization of launch and recovery operations regarding ship motions, interaction between a tugboat and a cargo ship, or the safe approach of a patrol boat to a larger vessel. Due to the pronounced scale disparity between vessels, such operations are difficult to realize in wave-tank experiments. Computational fluid dynamics (CFD) simulations of such operations are challenging due to the comparatively large computational effort: The larger ship requires a comparatively large domain, while the smaller ship may require finer mesh resolution and time steps. The present work proposes an efficient approach to perform CFD simulations for such applications. By using forcing zones with optimized coefficients, the size of the computational domain can be reduced to the vicinity of the small ship, and the flow near the domain boundaries is forced towards the wave field solution of the larger ship. This corresponds to a one-way coupling approach, in which the larger ship is not affected by the small ship. The flow fields near the large ship are extracted from a CFD simulation. In the present study, the large ship is moving with constant speed in calm water, and the converged wave field solution is stored and used to define the boundary conditions for the CFD simulation with the small ship. An overtaking maneuver of the small ship is investigated. The resulting ship motions match closely with those of a simulation conducted for the two vessels in a single simulation domain. The proposed approach reduces computational cost by up to 87%. Therefore, the approach is particularly suitable when studying the effects of different ship maneuvers in the same wave fields, as in the aforementioned applications.Publicationtype: Journal Article70 8 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Influence of wave-generation approach and structure position relative to extreme-wave event on wave dynamics and wave-induced loadsThree different approaches to generate long-crested extreme waves near the onset of breaking are investigated: Stokes 5th-order wave theory, linear focusing based on the NewWave theory and nonlinear focusing via Peregrine-breather-type rogue waves. The aims of this work are to compare the extreme-wave dynamics and to investigate the influence of structure placement on the maximum horizontal forces. An efficient simulation approach based on the finite-volume method was proposed for these investigations. Fixed vertical cylinders with diameters of 5% to 20% of the wavelength were subjected to the waves. The present results show that extreme-wave dynamics varied considerably. Wave breaking started at ca. 60% (linear focusing) and ca. 72% (rogue wave) of theoretical maximum steepness for a regular wave. For same wave height and steepness, linear focusing or rogue wave had up to ca. 14% larger maximum crest height H<inf>c,max</inf> compared with the Stokes waves. For similar wave steepness, the Stokes wave gave the smallest horizontal forces, whereas whether linear focusing or rogue wave would give the largest forces depended on the severity of wave breaking. The main finding of this work is that the maximum horizontal force did not occur when the structure was positioned at the location of maximum wave elevation, but instead for placements up to 0.6 wavelengths before and up to nearly 0.18 wavelengths after the location of maximum wave elevation. Changing the structure’s position relative to the extreme-wave event changes the maximum horizontal forces by up to ca. 50% (linear focusing) and 22.7% (rogue wave). The variation reduced with increasing structure dimensions, to still ca. 13.8% (linear focusing) and 11.4% (rogue wave) for the fixed vertical cylinder with diameter of 0.2 wavelengths. The results of this study show that, to correctly determine maximum wave-induced loads, investigations must be repeated for different structure placements relative to the extreme-wave event. The work provides recommendations for performing such investigations and outlines related topics for future research.Publicationtype: Journal Article22 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Improved Simulation of Flows with Free-Surface Waves by Optimizing the Angle Factor in the HRIC Interface-Sharpening SchemeIn finite-volume-based simulations with free-surface waves, it is usually desired to obtain a sharp interface between both fluid phases. A widely used approach for interface-capturing and sharpening is the combination of the volume-of-fluid method with the HRIC scheme. The HRIC scheme contains a user-defined parameter, the angle factor, which influences the magnitude of the interface-sharpening. The present work demonstrates that the optimum value for the angle factor is case dependent: too small values can cause substantial flow disturbances, such as vorticity production within the wave and the occurrence of parasitic wave components, whereas too large values can cause excessive dissipation of wave energy. The optimum value for the angle factor was found to depend on the wave steepness, the aspect ratio of the grid cells, on the cell size and to a lesser degree on the time step size. Results from an extensive parameter study are presented, which can provide guidance for optimizing the angle factor for flow simulations of free-surface wave propagation. Further, two methods are presented which can be used to determine the optimum value of the angle factor. The magnitude of errors that can occur due to improper choices of the angle factor are discussed and recommendations are given to increase the accuracy of flow simulations with free-surface waves.Publicationtype: Journal Article217