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| Version 2013-2014 |
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| HULG0339-1 | CFD for marine structures
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| Duration : | 30h Th, 35h Pr |
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| Number of credits : |
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| Lecturer : | L. Gentaz, D. Le Touze |
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Language(s) of instruction :
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| English language |
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Course contents :
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| a) POTENTIAL FLOW NUMERICAL SIMULATION
- Potential flow model
- Usual hypothesis for the wave resistance problem in potential flow : steady flow, linearization of free surface boundary conditions
- Kelvin and Rankine Green function methods for the wave resistance problem
- Intruduction to panel methods
- Examples of computations with a linearized potential flow solver
b) VISCOUS FLOW NUMERICAL SIMULATION BY METHODS BASED ON NAVIER-STOKES EQUATIONS
- Navier-Stokes Equations, RANS (Reynolds-Averaged Navier-Stokes) Equations in cartesian coordinates
- Boundary conditions, Free surface conditions, compatibility with no-slip conditions
- Navier-Stokes Equations in curvilinear space, partial and total transformation, metrics
- Conservative formulation
- Case of unsteady computational space, deformation velocities, constraint on generalised metrics
- Mesh Modelling : Finite Element, Finite Difference, Finite Volume, comparison, consistency, stability
- Velocity-Pressure coupling, Checkerboard instabilities, unknowns localization strategies, Rhie and Chow interpolation
- Velocity-Pressure-Free Surface coupling, Large linear systems solving, preconditioning
- Tracking and Capturing method (VOF, Level Set) to compute free surface
- Functional decomposition of RANS Equation to include wave generation and propagation in RANS solvers : the SWENSE (Spectral Wave Explicit Navier-Stokes Equations) principle : advantages compared to usual way to compute wave influence.
c) SPH MESH FREE METHOD :
- General presentation of the SPH method
- Interpolation kernels
- Time marching schemes
- Boundary conditions
- Improvement of accuracy : renormalisation, smoothing, Riemann solver
- Extension to multi-physics simulations, example of fluid-structure modelling using SPH
- Parallelization aspects
d) PRATICAL TRAINING :
- Pratical work using a free surface Navier-Stokes solver developed at Centrale Nantes will be proposed to study and compute ship resistance and wave-body interactions cases.
- It includes the meshing of the fluid domain around the studied structure, study of computation convergence with meshing refinement, comparison of results with experments or coming from other numerical methods. Bow impact problems will be studied using a SPH meshless method.
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Learning outcomes of the course :
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- The goal of this class is to present an overview of the CFD methods for the simulation of free surface flows. Both potential and viscous flow models are studied. The lecture gives exhaustive information concerning the strategies for the discretisation of potential flow equations, Navier-Stokes equations and for the representation of the free surface, either by free surface tracking techniques or by free surface capturing techniques. The pros and cons of eauch strategy are discussed.
- In addition to well established field discretization methods, the SPH (Smooth Particles Hydrodynamics) method is presented. This method has been recently developed for hydrodynamics problems, and solves Navier-Stokes or Euler equations on the basis of a set of interpolating kernels moving with Lagrangian control points, thus not relyingg on any mesh structure. This method is especially efficient for the solution of certain problems of great interest faced by ship designers, such as bow or stern slamming, green water on deck, sloshing flows in LNG tanks, ect...
- Pratical projects are proposed to the students, based on the use of a potential flow solver for naval application, REVA or a finite difference Navier-Stokes solver especially developed for naval applications, ICARE, and on a SPH code dedicated to free surface flow problems, SPH-Flow. Both softwares are developed by Ecole Centrale de Nantes, with partners such as Hydrocean and Bassin d'Essais des Carènes, among others.
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Prerequisites and co-requisites/ Recommended optional programme components :
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Planned learning activities and teaching methods :
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Mode of delivery (face-to-face ; distance-learning) :
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Recommended or required readings :
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- "Computational methods for fluid dynamics" by J. H. Ferziger and M. Peric, Springer Ed.
- "Smoothed Particle Hydrodynamics, a meshless particle method" by G. R. Liu and M. B. Liu, World Scientific Ed.
- Proceedings of the ONR (Office on Naval Research) conferences.
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Assessment methods and criteria :
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| Written exams (2h) + reports of pratical training |
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Work placement(s) :
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Organizational remarks :
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Contacts :
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| L. Gentaz and D. Le Touze |
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