scholarly journals Computational Estimation And RANS Simulation of Free Surface Flow Around A Ship Hull

2012 ◽  
pp. 118-121
Author(s):  
Katuri Samarpana
Keyword(s):  
Free Surface ◽  
Complex Geometry ◽  
Computational Prediction ◽  
Breaking Waves ◽  
Surface Flow ◽  
Ship Hull ◽  
Operating Conditions ◽  
Surface Phenomenon ◽  
Hydrodynamic Behaviour ◽  
Different Shapes

Ship hydrodynamics present many unique challenges due to complex geometry, environment, and operating conditions, which results in many complex physics and modelling issues. This is commonly studied through experiments in a towing tank and experiments in a sea keeping and manoeuvring basin. Recently hydrodynamicists have begun to venture into computational prediction of hydrodynamic behaviour of surface ships. Free surface phenomenon around a ship hull plays an important role in its resistance. Wave making resistance comes from the very presence of free surface. Therefore its accurate prediction is very essential for ship design. The flow problem to be simulated is rich in complexity and poses many modelling challenges because of the existence of breaking waves around the ship hull involving two-phase flow, and because of the resolution of thin turbulent boundary layer. The paper aims to computationally estimate the effect of free surface for a moving ship. Commercial software is used for grid generation and flow solution. 1. Solution of a Rudder of a ship in submerged condition. Few different shapes of the rudders are examined. 2. Solution of flow- around a complete ship with free surface. In the present work, flow through the ship hull is computed using a finite volume commercial code, ANSYS 12.1. The ship geometry is modelled using solid modelling software, CATIA V5R9. A three-dimensional structured hexahedral grid is generated using grid generating code, ICEM-CFD V10.0 .Turbulence is modelled with Reynolds Stress model. The resistance of the ship is predicted, and compared against the experimental values. The rudder of the ship is also analyzed. Two different shapes, one wedge shaped and a standard NACA0012 foil, for which experimental results are available in literature, are analyzed. The lift coefficients and flow separation are predicted for different angles of attack using various turbulence models.Computational results are in good agreement with the experimental ones.

Nonlinear Sloshing in Fixed and Vertically Excited Containers

2002 ◽  
Author(s):  
Jannette B. Frandsen ◽  
Alistair G. L. Borthwick
Keyword(s):  
Perturbation Theory ◽  
Free Surface ◽  
Small Perturbation ◽  
Numerical Solutions ◽  
Vertical Direction ◽  
Nonlinear Effects ◽  
Breaking Waves ◽  
Surface Flow ◽  
Nonlinear Behaviour ◽  
Computational Domain

Nonlinear effects of standing wave motions in fixed and vertically excited tanks are numerically investigated. The present fully nonlinear model analyses two-dimensional waves in stable and unstable regions of the free-surface flow. Numerical solutions of the governing nonlinear potential flow equations are obtained using a finite-difference time-stepping scheme on adaptively mapped grids. A σ-transformation in the vertical direction that stretches directly between the free-surface and bed boundary is applied to map the moving free surface physical domain onto a fixed computational domain. A horizontal linear mapping is also applied, so that the resulting computational domain is rectangular, and consists of unit square cells. The small-amplitude free-surface predictions in the fixed and vertically excited tanks compare well with 2nd order small perturbation theory. For stable steep waves in the vertically excited tank, the free-surface exhibits nonlinear behaviour. Parametric resonance is evident in the instability zones, as the amplitudes grow exponentially, even for small forcing amplitudes. For steep initial amplitudes the predictions differ considerably from the small perturbation theory solution, demonstrating the importance of nonlinear effects. The present numerical model provides a simple way of simulating steep non-breaking waves. It is computationally quick and accurate, and there is no need for free surface smoothing because of the σ-transformation.

scholarly journals Influence of the hydrofoil inclination angle at free surface flow around junctions

2020 ◽  
Vol 43 ◽  
pp. 103-108
Author(s):  
Costel Ungureanu ◽  
Costel Iulian Mocanu
Keyword(s):  
Boundary Layer ◽  
Free Surface ◽  
Bluff Body ◽  
Three Dimensional ◽  
Free Surface Flow ◽  
Breaking Waves ◽  
Surface Flow ◽  
Vortex Structures ◽  
The Body ◽  
Flow Topology

"Free surface flow is a hydrodynamic problem with a seemingly simple geometric configuration but with a flow topology complicated by the pressure gradient due to the presence of the obstacle, the interaction between the boundary layer and the free surface, turbulence, breaking waves, surface tension effects between water and air. As the ship appendages become more and more used and larger in size, the general understanding of the flow field around the appendages and the junction between them and the hull is a topical issue for naval hydrodynamics. When flowing with a boundary layer, when the streamlines meet a bluff body mounted on a solid flat or curved surface, detachments appear in front of it due to the blocking effect. As a result, vortex structures develop in the fluid, also called horseshoe vortices, the current being one with a completely three-dimensional character, complicated by the interactions between the boundary layer and the vortex structures thus generated. Despite the importance of the topic, the literature records the lack of coherent methods for investigating free surface flow around junctions, the lack of consistent studies on the influence of the inclination of the profile mounted on the body. As a result, this paper aims to systematically study the influence of profile inclination in respect to the support plate."

scholarly journals Grid Type Impact on the Results of the Volume of Fluid Method in the Free Surface Flow Calculations Around Ship Hull

2018 ◽  
Vol 1 (1) ◽  
pp. 151-157
Author(s):  
Karol Sugalski ◽  
Tomáš Skrúcaný
Keyword(s):  
Free Surface ◽  
Fluid Dynamic ◽  
Free Surface Flow ◽  
Triangular Mesh ◽  
Surface Flow ◽  
Ship Hull ◽  
Hexahedral Mesh ◽  
Two Phase ◽  
Advantages And Disadvantages ◽  
Hexahedral Meshes

Abstract This article presents results of the free surface flow around ship hull on two different types of computational grid. Each type of mentioned grid has its own advantages and disadvantages in particular cases, mostly in one phase simulation. Omitting cases with capitation, there is no free surface involved in one phase simulation. Multiphase simulations are crucial in the ship design process and optimization. Recreating free surface on the triangular mesh causes difficulties, in contrast to the hexahedral meshes, where calculated surface is more aligned to the physical border of the fluids. In this paper, results from the triangular mesh were compared to results from hexahedral mesh. Conclusions about triangular meshes in two phase simulation are presented. The computational fluid dynamic toolbox OpenFOAM is used to perform calculations of the total resistance of work boat in calm water.

Free Surface Effects on Hydrodynamic Analysis of Flapping Foil Thruster in Waves

2013 ◽  
Author(s):  
E. S. Filippas ◽  
K. A. Belibassakis
Keyword(s):  
Free Surface ◽  
Breaking Waves ◽  
Numerical Results ◽  
Operating Conditions ◽  
Oscillatory Motion ◽  
Ship Motions ◽  
Sea Waves ◽  
Thrust Coefficient ◽  
Hydrodynamic Analysis ◽  
Stage Of Development

The analysis of an oscillating wing located beneath the ship’s hull is investigated as an unsteady thruster, augmenting the overall propulsion of the ship and offering dynamic stabilization. The unsteady thruster undergoes a combined oscillatory motion in the presence of waves. For the system in horizontal arrangement the vertical heaving motion is induced by the motion of the ship in waves, essentially ship heave and pitch, while the rotational pitching motion of the flapping propulsor about its pivot axis is set by an active control mechanism. Our method is based on coupling the seakeeping operators associated with the longitudinal and transverse ship motions with the hydrodynamic forces and moments produced by the flapping lifting surfaces, using simplified unsteady lifting line theory. First numerical results presented in Belibassakis & Politis [1],[2] indicate that high levels of efficiency are obtained in sea conditions of moderate and higher severity, under optimal control settings. For the detailed investigation of the effects of the free surface in the present paper a potential-based panel method has been developed for the hydrodynamic analysis of 2D hydrofoil operating beneath the free surface, undergoing heaving and pitching oscillations while moving with constant forward speed. The instantaneous angle of attack is influenced by the foil oscillatory motion and by the incident waves. At a first stage of development we consider moderate submergence and relatively low speeds permitting us to approximately neglect effects due to breaking waves and cavitation. Numerical results are presented concerning the numerical performance of the developed BEM. Also results concerning the thrust coefficient and the efficiency of the system over a range of motion parameters, including reduced frequency, Strouhal number, feathering parameter and compared against other methods. Our analysis indicates that significant efficiency can be obtained under optimal operating conditions. Thus, the present method can serve as a useful tool for assessment and the preliminary design and control of such systems extracting energy from sea waves for marine propulsion.

Investigation of a Heavy Liquid Metal Free Surface Target Experiment

2012 ◽  
Author(s):  
Karsten Litfin ◽  
Frank Fellmoser ◽  
Abdalla Batta ◽  
Andreas G. Class ◽  
Thomas Wetzel
Keyword(s):  
Heavy Metal ◽  
Free Surface ◽  
High Speed ◽  
Fluid Velocity ◽  
Heat Removal ◽  
Surface Flow ◽  
Operating Conditions ◽  
Scale Model ◽  
Stable Surface ◽  
Wide Range

Several distinct reactor strategies are proposed within the context of the IP Eurotrans framework programme for the transmutation of nuclear waste. A pool type reactor filled with liquid heavy metal and containing a subcritical core is one of the promising designs. Additional neutrons required for the nuclear reaction are generated by a spallation reaction inside the core. A high power proton beam is guided through a vacuum tube from an accelerator into the liquid heavy metal pool i.e. into the reactor core. At the point where the beam hits the metal surface special construction effort is indispensable to handle the high heat production. A specific target design is used to ensure a high fluid velocity and a stable surface at the beam entry. This design employs a concentric vertical feeder establishing a free conical surface with velocity up to 2.5 m/s ensuring stable surface flow and appropriate heat removal. The proposed target geometry has been constructed using underlying rules developed by the MYRRHA design group for the free surface target in the MYRRHA research reactor. A full scale model of this design using lead bismuth eutectic (LBE) has been set up and experimentally investigated at the of the Karlsruhe Institute of Technology (KIT). Measurements taken by high speed digital imaging visualize both conical inner and outer jet free surface. They show a stable surface in a wide range of operating conditions starting from 35% of the nominal flow rate and agree well with numerical investigations using commercial CFD code Star-CD and Star-CCM+. Previous concerns related to splashing or cavitation during the start-up or shut-down procedure proofed unjustified.

3D Viscous Free-Surface Flow around a Combatant Ship Hull

2009 ◽  
Author(s):  
Florin Pacuraru ◽  
Adrian Lungu ◽  
Viorel Maria ◽  
Theodore E. Simos ◽  
George Psihoyios ◽  
...  
Keyword(s):  
Free Surface ◽  
Free Surface Flow ◽  
Surface Flow ◽  
Ship Hull

scholarly journals Numerical solution of a free surface flow problem over an obstacle

2019 ◽  
Vol 106 (120) ◽  
pp. 135-148
Author(s):  
Samira Beyoud ◽  
Dahbia Boukari-Hernane
Keyword(s):  
Free Surface ◽  
Flow Problem ◽  
Vries Equation ◽  
Free Surface Flow ◽  
Surface Flow ◽  
Inviscid Fluid ◽  
Subcritical Case ◽  
Runge Kutta Method ◽  
Different Shapes ◽  
Gravity Acceleration

We consider a free surface flow problem of an incompressible and inviscid fluid, perturbed by a topography placed on the bottom of a channel. We suppose that the flow is steady, bidimensional and irrotational. We neglect the effects of the superficial tension but we take into account the gravity acceleration g. The main unknown of our problem is the equilibrium free surface of the flow; its determination is based on the Bernoulli equation which is transformed as the forced Korteweg-de Vries equation. The problem is solved numerically via the fourth-order Runge-Kutta method for the subcritical case, and the finite difference method for the supercritical case. The results obtained are illustrated by several figures, where the height h of the obstacle, and the value of the Froude number F of the flow, are varied. Note that different shapes of the obstacle have been considered.

scholarly journals FREE SURFACE FLOW SIMULATION AROUND AN APPENDED SHIP HULL

Brodogradnja ◽  
2018 ◽  
Vol 69 (3) ◽  
pp. 25-41
Author(s):  
Yavuz Hakan Ozdemir ◽  
◽  
Baris Barlas ◽  
Keyword(s):  
Free Surface ◽  
Flow Simulation ◽  
Free Surface Flow ◽  
Surface Flow ◽  
Ship Hull
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