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A PRACTICAL APPLICATION OF THE INCOMPLETE CHOLESKEYDECOMPOSITION CONJUGATE GRADIENT METHOD TO LARGE EDDY SIMULATION INNERBOUNDARY PROBLEMSSae Yul Lee AbstraktThe objective of this study is to investigate a time and memory saving solution algorithm for inner boundary fluid flow problems, such as flow within the steam generator tube bundle region. In most algorithms for the numerical solution of the NavierStokes equations, a pressure correction equation (a Poisson equation) must be solved to ensure mass conservation. The pressure correction coefficient matrix is sparse and usually quite large; most of calculational effort is spent solving the matrix equations. The Choleskey decomposition method, which is one of the most effective direct solvers, showed difficulties in computational time and storage for the calculation of practical bundle problems. To avoid the problems inherent in direct solvers, the Incomplete Choleskeydecomposition Conjugate Gradient (ICCG) method was adopted as the Poisson equation solver. There are several efficient techniques for solving large sparse matrices, but the advantages of these techniques disappear when applied to inner boundary problems. The pressure coefficient matrix of inner boundary problems has an irregular pattern of nonzero elements. A preconditioning technique must be developed in order to apply the ICCG method to flow problems with varied boundary conditions. In this study, the coefficient matrix is scanned columnwise. 