查看更多>>摘要：In the present paper,the unsteady cavitating turbulent flow over the twisted NACA66 hydrofoil is investigated based on an modified shear stress transfer k-ω partially averaged Navier-Stokes(MSST PANS)model,i.e.,new MSST PANS(NMSST PANS)model,where the production term of kinetic energy in the turbulence model is modified with helicity.Compared with the experimental data,cavitation evolution and its characteristic frequency are satisfactorily predicted by the proposed NMSST PANS model.It is revealed that the interaction among the main flow,the reentrant jets,and sheet cavitation causes the formation of the primary shedding cavity near the mid-span and the secondary shedding cavity at each side of the twisted hydrofoil,and further induces the remarkable pressure gradient around shedding cavities.Along with the development of the primary and the secondary shedding cavities,the great pressure gradient associated with large cavity volume variation promotes the vortical flow generation and the spatial deformation of vortex structure during cavitation evolution,and results in the primary and the secondary U-type vortices.Further,dynamic mode decomposition(DMD)analysis is utilized to confirm the interaction among the main flow,the main reentrant jet and two side reentrant jets,and cavitation.These results indicate that the proposed NMSST PANS model is suitable to simulate the complicated cavitating turbulent flow for various engineering applications.
查看更多>>摘要：This paper investigates the sloshing phenomena in a spherical liquid tank using the moving particle semi-implicit(MPS)method,a crucial study in fluid dynamics.Distinct from previous research focused on rectangular or LNG tanks,this work explores the unique motion patterns inherent to spherical geometries.The accuracy of our in-house MPS solver MLParticle-SJTU is validated against experimental data and finite volume method(FVM).And the MPS method reveals a closer alignment with experimental outcomes,which suggests that MPS method is particularly effective for modeling complex,non-linear fluid behaviors.Then the fluid's response to excitation at its natural frequency is simulated,showcasing vigorous sloshing and rotational motion.Detailed analyses of the fluid motion are conducted by drawing streamline diagrams,velocity vector diagrams,and vorticity maps.The fluid's motion response is explored using both time-domain and frequency-domain curves of the fluid centroid,as well as the sloshing force.
查看更多>>摘要：This paper presents an adaptive grid deformation technique for optimizing ship hull forms using computational fluid dynamics(CFD).The proposed method enables accurate and smooth updates of the hull surface and 3-D CFD grids in response to design variables.This technique incorporates a two-level point-transformation approach to move the grid points by a few design points.Initially,generic B-splines are utilized to transform grid points according to the displacements of the control points within a defined control box.This ensures surface modification accuracy and smoothness,similar to those provided by non-uniform rational B-splines.Subsequently,radial basis functions are used to interpolate the movements of the control points with a limited set of design points.The developed method effectively maintains the mesh quality and simulation efficiency.By applying this method to surface and grid adaptation,a regression model is proposed in the form of a second-order polynomial to represent the relationship between the geometric parameters and design variables.This polynomial is then used to introduce geometric constraints.Furthermore,a radial basis function surrogate model for the calm-water resistance is constructed to approximate the objective function.An enhanced optimization framework is proposed for CFD-based hull optimization and applied to KVLCC2 to validate its feasibility and efficiency.
查看更多>>摘要：Water entry problems represent complex multiphase flows involving air,water,and structure interaction,occurring rapidly in rough seas,and potentially effecting structural integrity of floating structures.This paper experimentally investigates asymmetric slamming loads acting on a 3-D elastic wedge section.The specimen,featuring two different bottom plates(stiffened and unstiffened),each 4 mm thick,aims to assess the effect of structural stiffness on dynamic loads.The experiments are conducted at different drop heights of 25 cm and 50 cm and varying heel angles from 5° to 25°.The paper describes the experimental conditions,including wedge geometry,material properties,and the test plan.The study explores the influence of heel angle on impact acceleration,revealing an increase in peak acceleration with a higher inclination angle,particularly in the vertical direction.Additionally,the hydrodynamic pressure resulting from asymmetric slamming is presented.The pressure results analyzed and compared at different locations along the length of the wedge.The experimental findings indicate that,despite the leeward side(stiffened)experiencing a smaller hydrodynamic load,the heel angle significantly affects pressure results on the windward side(unstiffened),leading to a more pronounced dynamic response.The time history of pressure results emphasizes the effect of elastic vibrations,particularly noticeable on the unstiffened bottom plate.This study contributes to a deeper understanding of asymmetric slamming on aluminum structures,facilitating the enhancement of mathematical models and the validation of numerical simulations.
查看更多>>摘要：The impulse response method is a frequently used method to calculate ship seakeeping behavior.In this paper,the restoring and Froude-Krylov calculation is conducted with constant evaluation of panel pressures as well as Gauss quadrature and an analytical integration.The applied panel grid is coarsened by an adaptive algorithm which is based on a normal vector condition.The comparison of methods is based on grid convergence studies which are followed by a verification of forces with computational fluid dynamics(CFD)results on the fixed duisburg test case in waves.Validations with experimental results in head,oblique and following waves show that all integration methods are accurate.The exact integration is numerically sensitive in some cases.Gauss quadrature is highly accurate,however,the additional effort is not beneficial since the geometrical accuracy has stronger influence on the force amplitudes than the integration method.Adaptive grid coarsening reduces the simulation time and is accurate up to a level,where the panel length comes close the wavelength.The added resistance at the investigated Froude number of 0.05 shows higher uncertainty levels,this applies to the results of both the numerical methods and model tests.
查看更多>>摘要：A Reynolds averaged Navier-Stokes(RANS)computational fluid dynamics(CFD)model is built to investigate the hydrodynamic response of a circular ice floe under the influence of a passing ship in calm waters.The ship,mirroring the KRISO Container Ship's hull design,progresses near an ice floe whose diameter is 30％of the ship's length and its thickness is 3 m.The ship advances at a constant speed,which is handled by using the overset mesh technique.This study focuses on the ice floe's motions and the hydrodynamic forces induced by three speeds and three transverse distances of the passing ship.Findings reveal that ship-generated wakes notably influence the ice floe's motions,with a greater influence on sway than surge.Additionally,the ship's speed and proximity distinctly affect the ice floe's motions.
查看更多>>摘要：Suspended vegetation in rivers,lakes,reservoirs and canals can change flow structure,which will in turn affect the sediment transport and cause the variation of water ecological environment.In order to study the characteristics of bend flow through suspended vegetation,three-dimensional numerical simulations are carried out by using the multi-relaxation-time lattice Boltzmann method(MRT-LBM).The drag force induced by vegetation is added in the velocity correction in the equilibrium distribution and a hybrid format combined bounce and specular reflection scheme is applied in the solid-fluid boundaries.After the validation of this model,six cases are designed to conduct the numerical simulations according to the root depth and the arrangement of vegetation.The simulated results show that the suspended vegetation can redistribute the flow structure in curved open channels.After the arrangement of suspended vegetation,the main flow moves to the side without vegetation,and the distribution of velocity tends to be balanced when vegetation is arranged on the entire cross section,the range of circulating current is reduced from the whole cross section to the local position without vegetation,however,the circulating current can still exist in the curve where the suspended vegetation enters less than half of the water depth.In addition,it can also be concluded that the suspended vegetation can affect the lateral gradient of flow velocity,and the bed shear stress in the curved channel.
查看更多>>摘要：Numerical investigations of floating platforms with different outer column inclined angles under two operating conditions of regular wave and irregular wave are presented in this paper.A coupled aero-hydrodynamic computational fluid dynamics in-house solver FOWT-UALM-SJTU is applied for the calculation.First,the validation for wave and wind generation are conducted to determine mesh distribution strategy.Based on these,the hydrodynamic motion response,aerodynamic performance and wake flow are analyzed to explore the impact of inclined angle.Conduct spectral analysis on the motion response under wave action,discuss the aerodynamic attack angle and inflow wind velocity along the blade spanwise direction in detail,reveal different trends in wake development and recovery.The results show that for the regular wave condition with the increase of inclined angles,the equilibrium position of surge motion is constantly rising,while pitch is decreasing.The maximum root mean square(rms)value occurs at angle=30°,compared with the original OC4 FOWT,the rms in power and thrust increase 0.35％,0.71％.And there are two low regions of attack angle and high regions of axial inflow velocity,corresponding to aerodynamic loads.The spectral analysis indicates that the natural frequency of pitch motion will increase with inclined angle.Besides,from the middle to far region of wake flow,the velocity recovery of FOWT with inclined angle will become faster,which is beneficial for downstream turbines to enhance more wind energy.
查看更多>>摘要：Aquatic vegetation is a vital component of natural river ecosystems,playing a crucial role in maintaining ecological balance,providing habitat and improving water quality.However,the presence of vegetation results in increased resistance in vegetated channels compared with non-vegetated channels,rendering traditional sediment movement predictions inadequate for the latter.Consequently,the concept of a vegetation influence factor,denoted by CDah,has been proposed by previous researchers to represent the effect of vegetation on sediment movement in watercourses.In this study,we focus on exploring the vegetation resistance coefficient(CD)among the vegetation influence factors,evaluating two different calculation methods for vegetation resistance coefficient,and presenting two expressions through genetic algorithm analysis to predict the incipient flow velocity of sediment in vegetated watercourses.The predicted values from the new formulae show excellent agreement with measured data,highlighting the high accuracy of the proposed methods in predicting the incipient flow velocity of sediment.Our results provide a solid theoretical basis for understanding the influence of aquatic vegetation on sediment particle movement.
查看更多>>摘要：This study aimed to investigate the previously unexplored effects of ice cover and submerged vegetation on flow structure.Experiments were undertaken under both open channel and ice-covered flow conditions.The bed material consisted of three non-uniform sands.The findings revealed that when vegetation patches were present on the bed and an ice cover was present,the velocity profiles exhibited a distinctive pattern with two peak values.Turbulent kinetic energy(TKE)also exhibited two peaks,one above the vegetation bending height and another at the sheath section,with a decreasing trend towards the ice cover.Furthermore,quadrant analysis showed that when the flow surface is covered by an ice cover,the contributions of inward and outward events increased compared with those observed in an open channel flow.In most cases,these contributions surpassed the sweep and ejection events.The findings enhance our understanding of vegetation's response to diverse surface conditions and have practical implications for river management and environmental engineering.
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