266 research outputs found
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Experimental study on inertial hydrodynamic behaviors of a complex remotely operated vehicle
This paper presents an experimental study on inertial hydrodynamic behaviors of an open-frame remotely operated vehicle (ROV) that has a complex open-frame hull but a large capacity to hold more instruments on board than those of other ROVs. A 1:4 scaled model was tested by a vertical planar motion mechanism in a circulating water channel of Harbin Engineering University. The inertial coefficients, which can be used for the simulation of motions and therefore for the maneuverability of the ROV, were calculated. Particular attention was paid to discuss the properties of the cross-inertial coefficients, which are related to the inertial forces/moments induced by the motion in other directions
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Investigations on the feature of turbulent viscosity associated with vortex shedding
The main purpose of this paper is to investigate the turbulent viscosity, particular its spatial distribution, in the flow around a fixed or moving cylinder. For this purpose, two-dimensional numerical simulations of turbulent flow is performed using the OpenFOAM, in which the Reynolds-averaged Navier-Stokes (RANS) equation, with either k-É or k-Ï SST turbulent model, is solved using the finite volume method. The numerical model is validated by using both experimental and numerical results in terms of the mean drag coefficients and the Strouhal number. Turbulent viscosity is significant only in a confined area around the vortex shedding (critical area), and the width of the critical area is considerably affected by the Reynolds numbers (Re) and the motion of the cylinder
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Numerical simulation of fully nonlinear interaction between steep waves and 2D floating bodies using the QALE-FEM method
This paper extends the QALE-FEM (quasi arbitrary LagrangianâEulerian finite element method) based on a fully nonlinear potential theory, which was recently developed by the authors [Q.W. Ma, S. Yan, Quasi ALE finite element method for nonlinear water waves, J. Comput. Phys, 212 (2006) 52â72; S. Yan, Q.W. Ma, Application of QALE-FEM to the interaction between nonlinear water waves and periodic bars on the bottom, in: 20th International Workshop on Water Waves and Floating Bodies, Norway, 2005], to deal with the fully nonlinear interaction between steep waves and 2D floating bodies. In the QALE-FEM method, complex unstructured mesh is generated only once at the beginning of calculation and is moved to conform to the motion of boundaries at other time steps, avoiding the necessity of high cost remeshing. In order to tackle challenges associated with floating bodies, several new numerical techniques are developed in this paper. These include the technique for moving mesh near and on body surfaces, the scheme for estimating the velocities and accelerations of bodies as well as the forces on them, the method for evaluating the fluid velocity on the surface of bodies and the technique for shortening the transient period. Using the developed techniques and methods, various cases associated with the nonlinear interaction between waves and floating bodies are numerically simulated. For some cases, the numerical results are compared with experimental data available in the public domain and good agreement is achieved
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Improved model for air pressure due to wind on 2D freak waves in finite depth
This paper presents an improved model for evaluating air pressure acting on 2D freak waves in a finite depth due to the presence of winds. This pressure model is developed by analysing the pressure distribution over freak waves using the QALE-FEM/StarCD approach, which combines the quasi arbitrary Lagrangian-Eulerian finite element method (QALE-FEM) with the commercial software package StarCD and has been proven to be sufficiently accurate for such cases according to our previous publication Yan and Ma (2010) [8]. In this model for air pressure, the pressure is decomposed into the components related to the local wave profiles and others. By coupling with the QALE-FEM, the accuracy of the pressure model is tested using various cases. The results show that the pressure distribution estimated using this model is close to that computed by using the QALE-FEM/StarCD approach when there is no significant vortex shedding and wave breaking. The accuracy investigation in predicting the freak wave heights and elevations demonstrates that this pressure model is much better than others in the literature so far used for modelling wind effects on freak waves in finite depth
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Quasi ALE finite element method for nonlinear water waves
This paper presents a newly developed quasi arbitrary Lagrangian-Eulerian finite element method (QALE-FEM) for simulating water waves based on fully nonlinear potential theory. The main difference of this method from the conventional finite element method developed by one of authors of this paper and others (see, e.g., [11] and [22]) is that the complex mesh is generated only once at the beginning and is moved at all other time steps in order to conform to the motion of the free surface and structures. This feature allows one to use an unstructured mesh with any degree of complexity without the need of regenerating it every time step, which is generally inevitable and very costly. Due to this feature, the QALE-FEM has high potential in enhancing computational efficiency when applied to problems associated with the complex interaction between large steep waves and structures since the use of an unstructured mesh in such a case is likely to be necessary. To achieve overall high efficiency, the numerical techniques involved in the QALE-FEM are developed, including the method to move interior nodes, technique to re-distribute the nodes on the free surface, scheme to calculate velocities and so on. The model is validated by water waves generated by a wavemaker in a tank and the interaction between water waves and periodic bars on the bed of tank. Satisfactory agreement is achieved with analytical solutions, experimental data and numerical results from other methods
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Improved MLPG_R method for simulating 2D interaction between violent waves and elastic structures
Interaction between violent water waves and structures is of a major concern and one of the important issues that has not been well understood in marine engineering. This paper will present first attempt to extend the Meshless Local Petrov Galerkin method with Rankine source solution (MLPG_R) for studying such interaction, which solves the Navier-stokes equations for water waves and the elastic vibration mequations for structures under wave impact. The MLPG_R method has been applied successfully to modeling various violent water waves and their interaction with rigid structures in our previous publications. To make the method robust for modeling wave elastic-structure interaction
(hydroelasticity) problems concerned here, a near-strongly coupled and partitioned procedure is proposed to deal with coupling between violent waves and dynamics of structures. In addition, a novel approach is adopted to estimate pressure gradient when updating velocities and positions of fluid particles, leading to a relatively smoother pressure time history that is crucial for success in simulating problems about wavestructure interaction. The developed method is used to model several cases, covering a range from small wave to violent waves. Numerical results for them are compared with those obtained from other methods and from experiments in literature. Reasonable good agreement between them is achieved
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A hybrid method for modelling two dimensional non-breaking and breaking waves
This is the first paper to present a hybrid method coupling a Improved Meshless Local Petrov Galerkin method with Rankine source solution (IMLPG_R) based on the Navier Stokes (NS) equations, with a finite element method (FEM) based on the fully nonlinear potential flow theory (FNPT) in order to efficiently simulate the violent waves and their interaction with marine structures. The two models are strongly coupled in space and time domains using a moving overlapping zone, wherein the information from both the solvers is exchanged. In the time domain, the Runge-Kutta 2nd order method is nested with a predictor-corrector scheme. In the space domain, numerical techniques including âFeeding Particlesâ and two-layer particle interpolation with relaxation coefficients are introduced to achieve the robust coupling of the two models. The properties and behaviours of the new hybrid model are tested by modelling a regular wave, solitary wave and Cnoidal wave including breaking and overtopping. It is validated by comparing the results of the method with analytical solutions, results from other methods and experimental data. The paper demonstrates that the method can produce satisfactory results but uses much less computational time compared with a method based on the full NS model
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Incompressible SPH method based on Rankine source solution for violent water wave simulation
With wide applications, the smoothed particle hydrodynamics method (abbreviated as SPH) has become an important numerical tool for solving complex flows, in particular those with a rapidly moving free surface. For such problems, the incompressible Smoothed Particle Hydrodynamics (ISPH) has been shown to yield better and more stable pressure time histories than the traditional SPH by many papers in literature. However, the existing ISPH method directly approximates the second order derivatives of the functions to be solved by using the Poisson equation. The order of accuracy of the method becomes low, especially when particles are distributed in a disorderly manner, which generally happens for modelling violent water waves. This paper introduces a new formulation using the Rankine source solution. In the new approach to the ISPH, the Poisson equation is first transformed into another form that does not include any derivative of the functions to be solved, and as a result, does not need to numerically approximate derivatives. The advantage of the new approach without need of numerical approximation of derivatives is obvious, potentially leading to a more robust numerical method. The newly formulated method is tested by simulating various water waves, and its convergent behaviours are numerically studied in this paper. Its results are compared with experimental data in some cases and reasonably good agreement is achieved. More importantly, numerical results clearly show that the newly developed method does need less number of particles and so less computational costs to achieve the similar level of accuracy, or to produce more accurate results with the same number of particles compared with the traditional SPH and existing ISPH when it is applied to modelling water waves
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A hybrid model for simulating rogue waves in random seas on a large temporal and spatial scale
A hybrid model for simulating rogue waves in random seas on a large temporal and spatial scale is proposed in this paper. It is formed by combining the derived fifth order Enhanced Nonlinear Schrödinger Equation based on Fourier transform, the Enhanced Spectral Boundary Integral (ESBI) method and its simplified version. The numerical techniques and algorithm for coupling three models on time scale are suggested. Using the algorithm, the switch between the three models during the computation is triggered automatically according to wave nonlinearities. Numerical tests are carried out and the results indicate that this hybrid model could simulate rogue waves both accurately and efficiently. In some cases discussed, the hybrid model is more than 10 times faster than just using the ESBI method, and it is also much faster than other methods reported in the literature
Ï production in pâPb collisions at âsNN=8.16 TeV
Ï production in pâPb interactions is studied at the centre-of-mass energy per nucleonânucleon collision âsNN = 8.16 TeV with the ALICE detector at the CERN LHC. The measurement is performed reconstructing bottomonium resonances via their dimuon decay channel, in the centre-of-mass rapidity intervals 2.03 < ycms < 3.53 and â4.46 < ycms < â2.96, down to zero transverse momentum. In this work, results on the Ï(1S) production cross section as a function of rapidity and transverse momentum are presented. The corresponding nuclear modification factor shows a suppression of the Ï(1S) yields with respect to pp collisions, both at forward and backward rapidity. This suppression is stronger in the low transverse momentum region and shows no significant dependence on the centrality of the interactions. Furthermore, the Ï(2S) nuclear modification factor is evaluated, suggesting a suppression similar to that of the Ï(1S). A first measurement of the Ï(3S) has also been performed. Finally, results are compared with previous ALICE measurements in pâPb collisions at âsNN = 5.02 TeV and with theoretical calculations.publishedVersio
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