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8





           Fluid Coupling in the

           Combined Finite-Discrete

           Element Method








           8.1 INTRODUCTION


           Many engineering problems of discontinuous media involving fracture and fragmentation
           also involve interaction between solid discrete elements and fluid. There are two types of
           such problems:
           • The Computational Fluid Dynamics (CFD) problem with combined finite-discrete ele-
             ment coupling. In this type of problem, the discrete elements are submerged inside
             a fluid.
           • The combined finite-discrete element problem with Computational Fluid Dynamics
             coupling. In this type of problem, most of the volume is filled by solid discrete elements,
             while the fluid fills the gaps and voids between discrete elements.



           8.1.1   CFD with solid coupling

           A typical problem of the first type is, for instance, deposition of solid blocks into water in
           coastal defence construction operations. In this problems, interaction with fluid influences
           the way the solid particle move through fluid, and therefore the transient behaviour of
           the solid system and the final state of rest is greatly influenced by interaction with water.
           Problems of this type are best considered as problems of Computational Fluid Dynamics
           with deformability, kinematics and dynamics of individual particles being resolved using
           the combined finite-discrete element method. Standard CFD models for both compressible
           and incompressible flow, together with various turbulence models, are readily available
           in the form of either finite difference based techniques or finite volume based techniques.
           Both finite volume and finite difference techniques use discretisation of the spatial domain
           to approximately satisfy the governing equations in integral form. Finite difference and
           finite volume based CFD techniques are based on Eulerian formulation. The essence of
           this formulation is that the grid is fixed in space and does not move with particles of fluid.


           The Combined Finite-Discrete Element Method  A. Munjiza
            2004 John Wiley & Sons, Ltd ISBN: 0-470-84199-0
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