• 대한기계학회논문집B
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• 제24권10호
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• pp.1317-1325
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• 2000

A new efficient numerical method for computing three-dimensional, unsteady, incompressible flows is presented. To eliminate the restriction of CFL condition, a fully-implicit time advancement in which the Crank-Nicolson method is used for both the diffusion and convection terms, is adopted. Based on an approximate block LU decomposition method, the velocity -pressure decoupling is achieved. The additional decoupling of the intermediate velocity components in the convection term is made for the fully -implicit time advancement scheme. Since the iterative procedures for the momentum equations are not required, the velocity components decouplings bring forth the reduction of computational cost. The second-order accuracy in time of the present numerical algorithm is ascertained by computing decaying vortices. The present decoupling method is applied to minimal channel flow unit with DNS (Direct Numerical Simulation).

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1998년도 추계 학술대회논문집
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• pp.7-12
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• 1998

Optimized high-order compact(OHOC) schemes were proposed, which have high spatial order of truncation and resolution to simulate the aeroacoustic problems due to unsteady compressible flows. Generally, numerical schemes are categorized explicit or implicit by time-marching method. In this research, OHOC differences which were developed with explicit time-marching method is used to have implicit formulation and the implicit OHOC differences result in block hepta-diagonal matrix. This paper presents the comparisons between the explicit and implicit OHOC schemes with a second order accuracy of time in the 1-d linear wave convection problem, and between the explicit OHOC scheme of 4th-order accuracy in time and the implicit OHOC scheme of 1st-order accuracy in tine for the 1-d nonlinear wave convection problem. With these comparisons, the characteristics of implicit OHOC scheme are shown in the point of CFL number.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.1821-1826
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• 2003

In this study, we discuss CIP method, which can treat compressible/incompressible problem and multi-phase problem. We can apply this method to the general equations by using CCUP. In this paper, non-staggered grid arrangement and predictor-corrector method are used to enhance later development and the solution accuracy and convergence performance. To validate the numerical algorithm proposed in this paper, the two-dimensional unsteady flow in the driven cavity is simulated. The numerical results of this subject using the present algorithm are compared with other numerical results. As a result, it is prived that the present scheme gives stable and improved solutions, and the results even coarse grid are in good agreement with other result using a fine grid arrangement.

• 한국전산유체공학회지
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• 제12권2호
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• pp.14-20
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• 2007

We present an improved immersed boundary method for computing incompressible viscous flow around an arbitrarily moving body on a fixed computational grid. The main idea is to incorporate feedback forcing scheme of virtual boundary method with Peskin's regularized delta function approach in order to use large CFL number and transfer quantities between Eulerian and Lagrangian domain effectively. From the analysis of stability limits and effects of feedback forcing gains, optimum regions of the feedback forcing are suggested.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.225-228
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• 2002

Supersonic jet impingement on a flat plate has been investigated to show the flow physics for different jet heights and to demonstrate the adequacy of the characteristics-based flux-difference Wavier-Stokes code Current study also compares the steady-state solutions obtained with variable CFL number for different grid spacing with the time-accurate unsteady solutions using the inner iterations, displaying a good agreement between the two sets of numerical solutions. The unsteady nature of wall fluctuations due to bouncing of the plate shock is also uncovered for high pressure ratios. The methodology is then applied to a complex vertical launcher system where the jet plume hits the bottom wail, deflects into the plenum and eventually exits through the vertical uptake. Flow structures within vertical launcher system are captured and solutions are partially verified against the flight test data. Present jet impingement study thus shows the usefulness of CFD in designing a complex structure and predicting flow behavior within such a system.

• 충청수학회지
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• 제28권4호
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• pp.623-633
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• 2015

In this paper, a general Weighted Essentially Non-Oscillatory (WENO) interpolation is proposed and applied to a semi-Lagrangian method. The proposed method is based on the conservation law, and characteristic curves are used to complete the semi-Lagrangian method. Therefore, the proposed method satisfies conservation of mass and is free of the CFL condition which is a necessary condition for convergence. Using a several standard examples, the proposed method is compared with the third order Strong Stability Preserving (SSP) Runge-Kutta method to verify the high-order accuracy.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2007년도 춘계 학술대회논문집
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• pp.23-29
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• 2007

We present an improved immersed boundary method for computing incompressible viscous flow around an arbitrarily moving body on a fixed computational grid The main idea is to incorporate feedback forcing scheme of virtual boundary method with Peskin's regularized delta function approach in order to use large CFL number and transfer quantities between Eulerian and Lagrangian domain effectively. From the analysis of stability limits and effects of feedback forcing gains, optimum regions of the feedback forcing are suggested.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.704-708
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• 2000

A new efficient numerical method for computing unsteady, incompressible flows, DRANS (Decoupled Reynolds-Averaged Navier-Stokes), is presented. To eliminate the restriction of CFL condition, a fully-implicit time advancement in which the Crank-Nicolson method is used fer both the diffusion and convection terms. is adopted. Based on decomposition method, the velocity-turbulent quantity decoupling is achieved. The additional decoupling of the intermediate velocity components in the convection term is made for the fully-implicit time advancement scheme. Since the iterative procedures for the momentum, ${\kappa}\;and\;{\varepsilon}$ equations are not required, the components decouplings bring fourth the reduction of computational cost. The second-order accuracy in time of the present numerical algorithm is ascertained by computing decaying vortices. The present decoupling method is applied to turbulent boundary layer with local forcing.

• 한국치위생학회지
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• 제7권4호
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• pp.441-453
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• 2007

This study was conducted among 831 industrial workers in Gumi City in Gyung-Sang-Buk Do for the purpose of acquiring knowledge to improve quality of life though industrial workers' oral health promotion. Oral examination and questionnaire surveying were used to evaluate workers' oral health state and subjective health state and analyze their effect on quality of life. At the same time, the scales used in measuring the subjects' health state and quality of life-OHIP and WHOQOL-BREF-were validated for their constituent concepts and their relations were analyzed through structural modeling. The analysis results can be summarized as follows; The constituent concepts of OHIP and QOL factor structural models were validated since they were all in the range of appropriateness, as shown in the result of analysis using Indices of Fit-GFI, CFL, TLI and RMSEA. The result of analysis of constituent concepts to identitify the relations between OHIP and QOL confirmed that OHIP influences QOL.

• 대한방사선협회지
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• 제27권2호
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• pp.115-123
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• 2001

The two ligaments, the anterior talofibular ligament(ATFL) and the calcaneofibular ligament(CFL), arise from the anteroinferior aspect of the lateral malleolus, and therefore avulsion fragments are superimposed on the lateral malleolus on the srandard rad