• Title, Summary, Keyword: Unstructured Tetrahedral Mesh

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Fully Unstructured Mesh based Computation of Viscous Flow around Marine Propellers (비정렬격자를 이용한 프로펠러 성능 및 주위 유동해석)

  • Kim, Min-Geon;Ahn, Hyung Taek;Lee, Jin-Tae;Lee, Hong-Gi
    • Journal of the Society of Naval Architects of Korea
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    • v.51 no.2
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    • pp.162-170
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    • 2014
  • A CFD(Computational Fluid Dynamics) analysis is presented to predict hydrodynamic characteristics of a marine propeller. A commercial RANS(Reynolds Averaged Navier-Stokes equation) solver, namely FLUENT, is utilized in conjunction with fully unstructured meshes around rotating propeller. Mesh generation process is greatly accelerated by using fully unstructured meshes composed of both isotropic and anisotropic tetrahedral elements. The anisotropic tetrahedral elements were used in the flow domain near the blade and shaft, where the viscous effect is important, having complex shape yet resolving the thin boundary layers. For other regions, isotropic tetrahedral elements are utilized. Two different approaches simulating rotational effect of the propeller are employed, namely Moving reference frame technique for steady simulation, and Sliding mesh technique for unsteady simulation. Both approaches are applied to the propeller open water (POW) test simulation. The current results, which are thrust and torque coefficients, are compared with available experimental data.

TET2MCNP: A Conversion Program to Implement Tetrahedral-mesh Models in MCNP

  • Han, Min Cheol;Yeom, Yeon Soo;Nguyen, Thang Tat;Choi, Chansoo;Lee, Hyun Su;Kim, Chan Hyeong
    • Journal of Radiation Protection and Research
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    • v.41 no.4
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    • pp.389-394
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    • 2016
  • Background: Tetrahedral-mesh geometries can be used in the MCNP code, but the MCNP code accepts only the geometry in the Abaqus input file format; hence, the existing tetrahedral-mesh models first need to be converted to the Abacus input file format to be used in the MCNP code. In the present study, we developed a simple but useful computer program, TET2MCNP, for converting TetGen-generated tetrahedral-mesh models to the Abacus input file format. Materials and Methods: TET2MCNP is written in C++ and contains two components: one for converting a TetGen output file to the Abacus input file and the other for the reverse conversion process. The TET2MCP program also produces an MCNP input file. Further, the program provides some MCNP-specific functions: the maximum number of elements (i.e., tetrahedrons) per part can be limited, and the material density of each element can be transferred to the MCNP input file. Results and Discussion: To test the developed program, two tetrahedral-mesh models were generated using TetGen and converted to the Abaqus input file format using TET2MCNP. Subsequently, the converted files were used in the MCNP code to calculate the object- and organ-averaged absorbed dose in the sphere and phantom, respectively. The results show that the converted models provide, within statistical uncertainties, identical dose values to those obtained using the PHITS code, which uses the original tetrahedral-mesh models produced by the TetGen program. The results show that the developed program can successfully convert TetGen tetrahedral-mesh models to Abacus input files. Conclusion: In the present study, we have developed a computer program, TET2MCNP, which can be used to convert TetGen-generated tetrahedral-mesh models to the Abaqus input file format for use in the MCNP code. We believe this program will be used by many MCNP users for implementing complex tetrahedral-mesh models, including computational human phantoms, in the MCNP code.

Automatic Tetrahedral Mesh Generation Using Advancing Front Technique with Node Searching (절점 탐색이 적용된 전진경계법에 의한 사면체 요소망의 자동생성)

  • 전성재;채수원
    • Journal of the Korean Society for Precision Engineering
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    • v.21 no.3
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    • pp.91-99
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    • 2004
  • An unstructured tetrahedral mesh generation algorithm has been presented. In order to construct better meshes in interior region by using an advancing front technique, a connecting operator and a local finishing operator II have been developed in addition to the existing operators. Before applying digging operators that generate new nodes inside of a meshing region, a connecting operator is employed that uses existing nodes which satisfy certain conditions for producing well-conditioned elements. The local finishing operator II is introduced to terminate the meshing process more flexibly on remaining subregions. With these new operators, tetrahedral meshing process becomes more robust and good quality of meshes are constructed.

Boundary Layer Mesh Generation for Three-Dimensional Geometries with Thin Thickness (얇은 두께의 3차원 형상에 경계층 요소 생성)

  • Kwon Ki Youn;Chae Soo-Won;Lee Byung Chai
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.29 no.5
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    • pp.671-679
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    • 2005
  • A method of generation boundary layer mesh has been presented. This paper describes the generation of semi-unstructured prismatic/tetrahedral meshes for three-dimensional geometries with thin thickness. By of fretting of surface triangle elements prismatic/tetrahedral meshes are generated and using the node relocation method of this research intersected meshes can be efficiently improved. Finally tetrahedral meshes are automatically generated at the rest of the domain. Sample meshes are constructed to demonstrate the mesh generating capability of the proposed algorithm.

COMPUTATIONAL EFFICIENCY OF A MODIFIED SCATTERING KERNEL FOR FULL-COUPLED PHOTON-ELECTRON TRANSPORT PARALLEL COMPUTING WITH UNSTRUCTURED TETRAHEDRAL MESHES

  • Kim, Jong Woon;Hong, Ser Gi;Lee, Young-Ouk
    • Nuclear Engineering and Technology
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    • v.46 no.2
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    • pp.263-272
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    • 2014
  • Scattering source calculations using conventional spherical harmonic expansion may require lots of computation time to treat full-coupled three-dimensional photon-electron transport in a highly anisotropic scattering medium where their scattering cross sections should be expanded with very high order (e.g., $P_7$ or higher) Legendre expansions. In this paper, we introduce a modified scattering kernel approach to avoid the unnecessarily repeated calculations involved with the scattering source calculation, and used it with parallel computing to effectively reduce the computation time. Its computational efficiency was tested for three-dimensional full-coupled photon-electron transport problems using our computer program which solves the multi-group discrete ordinates transport equation by using the discontinuous finite element method with unstructured tetrahedral meshes for complicated geometrical problems. The numerical tests show that we can improve speed up to 17~42 times for the elapsed time per iteration using the modified scattering kernel, not only in the single CPU calculation but also in the parallel computing with several CPUs.

Automatic Tetrahedral Mesh Generation using Advancing Front Technique with Delaunay Node Searching (전진경계법에서 Delaunay 탐색조건을 이용한 사면체 요소망의 자동 생성)

  • 전성재;채수원
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • pp.1605-1608
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    • 2003
  • A unstructured tetrahedral mesh generation algorithm has been presented. To make better meshes in interior region using an advancing front technique, a connecting operator has been developed in addition to the existing operators. Before applying digging operators that generate new nodes inside of a meshing region, a connecting operator is employed that uses existing nodes which satisfy certain conditions for producing well-conditioned elements if possible. By introducing this new operator, tetrahedral meshing process becomes more robust and produces better quality of meshes.

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Diffusion synthetic acceleration with the fine mesh rebalance of the subcell balance method with tetrahedral meshes for SN transport calculations

  • Muhammad, Habib;Hong, Ser Gi
    • Nuclear Engineering and Technology
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    • v.52 no.3
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    • pp.485-498
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    • 2020
  • A diffusion synthetic acceleration (DSA) technique for the SN transport equation discretized with the linear discontinuous expansion method with subcell balance (LDEM-SCB) on unstructured tetrahedral meshes is presented. The LDEM-SCB scheme solves the transport equation with the discrete ordinates method by using the subcell balances and linear discontinuous expansion of the flux. Discretized DSA equations are derived by consistently discretizing the continuous diffusion equation with the LDEM-SCB method, however, the discretized diffusion equations are not fully consistent with the discretized transport equations. In addition, a fine mesh rebalance (FMR) method is devised to accelerate the discretized diffusion equation coupled with the preconditioned conjugate gradient (CG) method. The DSA method is applied to various test problems to show its effectiveness in speeding up the iterative convergence of the transport equation. The results show that the DSA method gives small spectral radii for the tetrahedral meshes having various minimum aspect ratios even in highly scattering dominant mediums for the homogeneous test problems. The numerical tests for the homogeneous and heterogeneous problems show that DSA with FMR (with preconditioned CG) gives significantly higher speedups and robustness than the one with the Gauss-Seidel-like iteration.

Assessment of Tip Shape Effect on Rotor Aerodynamic Performance in Hover

  • Hwang, Je Young;Kwon, Oh Joon
    • International Journal of Aeronautical and Space Sciences
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    • v.16 no.2
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    • pp.295-310
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    • 2015
  • In the present study, an unstructured mixed mesh flow solver was used to conduct a numerical prediction of the aerodynamic performance of the S-76 rotor in hover. For the present mixed mesh methodology, the near-body flow domain was modeled by using body-fitted prismatic/tetrahedral cells while Cartesian mesh cells were filled in the off-body region. A high-order accurate weighted essentially non-oscillatory (WENO) scheme was employed to better resolve the flow characteristics in the off-body flow region. An overset mesh technique was adopted to transfer the flow variables between the two different mesh regions, and computations were carried out for three different blade configurations including swept-taper, rectangular, and swept-taper-anhedral tip shapes. The results of the simulation were compared against experimental data, and the computations were also made to investigate the effect of the blade tip Mach number. The detailed flow characteristics were also examined, including the tip-vortex trajectory, vortex core size, and first-passing tip vortex position that depended on the tip shape.

Multi-dimensional Finite-Volume Flow Computation Using Unstructured Grid (비정렬격자 다차원 FVM유동계산)

  • Kim J. K.;Chang K.-S.
    • 한국전산유체공학회:학술대회논문집
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    • pp.182-187
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    • 1995
  • The present paper explains some advancement made by the authors for the compressible flow computation of the Euler equations based on the unstructured grid and vertex- centered finite volume method. Accurate solutions to the unsteady axisymmetric shock wave propagation problems and three-dimensional airplane flows have been obtained by a high-order upwind TVD and FCT schemes. Unstructured grid adaption is made for the unsteady shock wave problems by the dynamic h-refinement/unrefinement procedure and for the three-dimensional steady flows by the Delaunay point-insertion method to generate three-dimensional tetrahedral mesh enrichment. Some physics of the shock wave diffraction phenomena and three-dimensional airplane flow are discussed.

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