Explore the vast range of titles available.

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.

The nonlinear stability of two horizontal interfaces of three-layered stratified non-Newtonian fluids plays a pivotal role in advanced engineering applications. This phenomenon encompasses temperature management systems, microfluidic devices, and precise coating technologies. In an existing study, a multilayer system is considered wherein a central Casson liquid (CL) layer is bounded above and below by Powell–Eyring liquids (PELs). The impact of a uniform tangential electric field (EF) and surface tension is explored within a porous medium. To avoid the mathematical complexity, the viscous potential flow (VPF) is used to simplify the governing hydrodynamic formulations. The model involves Navier–Stokes and Maxwell equations under the quasi-static assumption. To obtain a nonlinear formulation, the linearized regulator equations are derived subject to appropriate nonlinear boundary conditions. The plan interfaces are presumed to propagate horizontally. To handle the nonlinear ordinary differential equations (ODEs) arising from the analysis, He’s frequency formula (HFF) is applied, transforming the problem into linear forms suitable for a non-perturbative approach (NPA). A non-dimensional analysis introduces key dimensionless collections, which help to characterize underlying fluid behavior and reduce system intricacy. A brief methodological summary of NPA is included to support reproducibility and clarity. The numerical calculations indicate that the stability can be evidently improved by the orientation of the tangential EF in relation to the horizontal wavenumber. PolarPlots are employed to imagine the influence of varying parameters, offering valuable insights into the mechanisms of the governing interfacial stability.

This research modifies the existing fully nonlinear potential-flow model to investigate the motion and load responses of a weathervaning floating production storage and offloading (FPSO) vessel subjected to wind, waves, and currents. This study employs the mixed Eulerian-Lagrangian approach to track the instantaneous fully nonlinear free surface and the auxiliary function method to solve the time derivative of the velocity potential. This model develops the free-surface rotation technique and locally updated strategy to simulate the intense interaction between the structure and oblique waves. In the meantime, the slender rod model is applied to account for the coupled effect between the floating body and attached mooring lines, and the wind and current loads are computed by interpolating the coefficient matrix. The results of predictions under different sea conditions are compared with those of the industry standard software ANSYS AQWA and the measurements in a model test, and they are found to be in good agreement. Using this code, the weather-vaning behavior and resonance in the surge and sway motion of a turret-moored FPSO are successfully modeled. The proposed approach also accurately catches the nonlinear wave-structure interaction, such as wave run-up, bow slamming, and asymmetric sectional loads. The water pressure frequency spectra demonstrate that this technique can apply more accurate environmental loads to structure analysis and has the potential to enhance the durability of offshore structures.

Purpose The purpose of this paper is to apply the Peridynamic differential operator (PDDO) to incompressible inviscid fluid flow with moving boundaries. Based on the potential flow theory, a Lagrangian formulation is used to cope with non-linear free-surface waves of sloshing water in 2D and 3D rectangular and square tanks. Design/methodology/approach In fact, PDDO recasts the local differentiation operator through a nonlocal integration scheme. This makes the method capable of determining the derivatives of a field variable, more precisely than direct differentiation, when jump discontinuities or gradient singularities come into the picture. The issue of gradient singularity can be found in tanks containing vertical/horizontal baffles. Findings The application of PDDO helps to obtain the velocity field with a high accuracy at each time step that leads to a suitable geometry updating for the procedure. Domain/boundary nodes are updated by using a second-order finite difference time algorithm. The method is applied to the solution of different examples including tanks with baffles. The accuracy of the method is scrutinized by comparing the numerical results with analytical, numerical and experimental results available in the literature. Originality/value Based on the investigations, PDDO can be considered a reliable and suitable approach to cope with sloshing problems in tanks. The paper paves the way to apply the method for a wider range of problems such as compressible fluid flow.

The present paper reports the comparison of the ship motions and added resistance assessment using high fidelity RANSE simulations in virtual towing tank LincoSim, using 2D strip theory as implemented in ShipX v4.4.0 and 3D BEM potential flow software Hydrostar v8.2.1. All calculations are performed for a medium-sized RoPax ferry of Levante Ferries fleet, which operates daily routes in the Ionian Sea. Calculations by ShipX are performed in frequency domain (using strip-theory and direct pressure integration) and in time domain. The high-fidelity RANSE seakeeping modeling is based on the open-source CFD code OpenFOAM v12 using a standardized framework, tailored to take advantage of HPC facilities and based on a forcing zone formulation. The CFD simulations are performed for six wave periods in head and beam seas at the constant wave height of 3 m. Comparison of the obtained results shows that potential-flow methods are very efficient and reliable tools, suitable for the massive calculations in the first stages of the project. High-fidelity RANSE modeling seems to be more suited for selected cases such as analysis of roll and added resistance in beam waves.

Flowing and stagnant zones coexist in central discharging flat-bottomed packed beds. Continuum based approach has been widely used to predict the flow characteristics. In particular, potential flow (PF) model was often used due to its simplicity but has a difficulty in predicting the stagnant zone. In our previous work, a novel PF model was proposed to overcome the difficulty. However, due to the assumption of constant flow resistance coefficient, the local velocity effect and typical non-linear flow mechanism have not been addressed. In this work, the concepts of linear resistance (LR) and constant resistance (CR) flows were proposed first based on the effects of discharging velocity. Then, the local velocity effect on the flow resistance was obtained by connecting the resistances of LR and CR flows in parallel. Further, the effects of LR and CR flows were discussed and validated by recorded data in 2D central discharging packed beds. The improved PF model enables to capture the funnel flow variations under different conditions and develop further understanding of granular flow in the flowing and stagnant zones.Graphic abstract

This paper presents the mathematical modeling, fluid dynamic analysis, and experimental analysis of a spiral case without guide vanes. Using a specific case of the Archimedes spiral, the model eliminates the need for fixed or moving blades to simplify the design, manufacturing, and maintenance process of the turbomachine by reducing the number of system components while preserving the fluid dynamic performance of a turbomachine operating in turbine mode. The potential flow theory is used as a mathematical basis for developing a computational code that allows the automatic generation of the curves that define the geometry of the spiral chamber, simplifying the CAD modeling process. Finally, the process is validated numerically and experimentally under different operating conditions, reaching an average error percentage between numerical and experimental analysis of 5.893% of speed and 11.089% of pressure, guaranteeing the accuracy of the model.

The deployment of floating offshore wind turbines (FOWTs) in deep, typhoon-prone waters like the South China Sea requires platforms with exceptional stability. However, the performance validation of novel Tension Leg Platform (TLP) concepts under such extreme metocean conditions remains a significant research gap. This study addresses this by numerically evaluating a novel TLP design, including a regular hexagonal topology, a unique bracing structure and heave plates, and an increased ballast-tank height. A coupled numerical framework, integrating potential-flow theory and blade element momentum (BEM) theory within ANSYS-AQWA (2023), was established to simulate the TLP’s dynamic response to combined irregular wave, current, and turbulent wind loads. The resulting time-series data were analyzed using the Continuous Wavelet Transform (CWT) to investigate non-stationary dynamics and capture transient peak loads critical for fatigue sizing, which demonstrated the platform’s superior stability. Under a significant wave height of 11.4 m, the platform’s maximum heave was limited to 0.86 m and its maximum pitch did not exceed 0.3 degrees. Crucially, the maximum tension in the tendons remained below 22% of their minimum breaking load. The primary contribution of this work is the quantitative validation of a novel TLP design’s resilience in an understudied, harsh deep-water environment, confirming the feasibility of the concept and presenting a viable pathway for FOWT deployment in challenging offshore regions.

Rigid wingsails are increasingly adopted for wind-assisted ship propulsion, with Symmetrically Cambered (SC) profiles identified as highly efficient for thrust generation. This study investigates installation layouts for multiple SC wingsails, focusing on aerodynamic interference that limits their performance. A fast 2D potential-flow panel method is employed and benchmarked against wind tunnel and 3D IDDES data. Two representative layouts are analyzed: triple-in-line (TL) and quad-in-parallel (QP). Layout optimization is performed using a genetic algorithm with distances between sails as design variables, constrained by the total installation span, at apparent wind angles (AWAs) of 60°, 90°, and 120°. Results show that thrust generation decreases progressively from upstream to downstream sails due to interference effects, with penalties of about 4–6% in the TL and up to 28% in the QP layout. The optimization improves performance only for the TL layout at 60°, while the QP layout shows negligible gains. Analysis of pressure distributions confirms that downstream sails suffer from reduced suction on the leading edge caused by upstream wakes. Overall, the TL layout demonstrates significantly higher aerodynamic reliability than the QP layout. These findings provide new insights into multi-sail configurations and highlight the importance of layout optimization in maximizing thrust efficiency.

The stability of deep-sea aquaculture equipment under extreme sea conditions such as typhoons directly affects the safety and operational reliability of the aquaculture platform, which in turn affects the economic benefits of fish farming. Therefore, it is particularly important to systematically analyze the hydrodynamic response of aquaculture facilities using numerical methods. This paper employs the hydrodynamic analysis software AQWA, integrating the boundary element method of three-dimensional potential flow theory with the Morison equation, to conduct hydrodynamic research on a flip-type aquaculture platform. The calculations include the platform’s amplitude response operators (RAOs), added mass, as well as motion responses and mooring line tensions under extreme sea conditions. The results indicate that the platform’s sway, surge, and heave motions are highly sensitive to wave frequency in the low-frequency range, with a significant resonance phenomenon occurring at a wave frequency of 0.84 Hz. The main wind and wave responses of the platform manifest as surge and roll motions. To address this issue, it is recommended to add additional anchor chains on the short sides of the platform to effectively reduce the amplitude of surge and roll motions. Furthermore, under extreme sea conditions when the platform faces the windward waves on the short side, its motion response frequency is lower than when facing the windward waves on the long side, but the difference in response amplitude between the two conditions is small.