• Journal of computational fluids engineering
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• v.12 no.4
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• pp.74-84
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• 2007

The flowfield characteristics in a straight rectangular channel have been investigated through a numerical model to analyze the regenerative cooling system that is used in rocket engine cooling. The supercritical hydrogen coolant introduces strong property variations that have a major influence on the developing flow and heat transfer characteristics. Of particular interest is the improved understanding of the physical characteristics of such flows through parametric studies. The approach used is a numerical solution of the full Navier-Stokes equations in the three dimensional form including the arbitrary equation of state and property variations. The present study compares constant and variable property solutions for both laminar and turbulent flow. For laminar flow, the variation of aspect ratio is examined, while for turbulent flow, the effects of variation of channel length and Reynolds number are discussed.

• Journal of the Korean Society of Propulsion Engineers
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• v.6 no.2
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• pp.9-17
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• 2002

For turbulent spray combustion flows a coupled numerical procedure was developed, This method was discretized by using generalized curvilinear coordinates to handle complex geometries. The preconditioning and eigenvalue rescaling techniques were employed to provide efficient convergences over a wide range of subsonic Mach numbers. The accuracy was validated by simulating the laminar cavity flow. The film cooling effect of a liquid rocket engine (KSR-III) were investigated by a spray combustion analysis. The film cooling showed a negative effect on the combustion efficiency. In the combustion chamber wall, the film cooling effect was revealed to be promoted by the production of fuel rich zone.

• International Journal of Naval Architecture and Ocean Engineering
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• v.4 no.3
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• pp.256-266
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• 2012

Cavitating flow simulation is of practical importance for many engineering systems, such as marine propellers, pump impellers, nozzles, torpedoes, etc. The present work has developed the base code to solve the cavitating flows past the axisymmetric bodies with several forebody shapes. The governing equation is the Navier-Stokes equation based on homogeneous mixture model. The momentum is in the mixture phase while the continuity equation is solved in liquid and vapor phase, separately. The solver employs an implicit preconditioning algorithm in curvilinear coordinates. The computations have been carried out for the cylinders with hemispherical, 1-caliber, and 0-caliber forebody and, then, compared with experiments and other numerical results. Fairly good agreements with experiments and numerical results have been achieved. It has been concluded that the present numerical code has successfully accounted for the cavitating flows past axisymmetric bodies. The present code has also shown the capability to simulate ventilated cavitation.

• The Journal of the Korean dental association
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• v.53 no.3
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• pp.178-186
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• 2015

Dental polymer-based luting materials are classified into esthetic resin cement, adhesive resin cement and self-adhesive resin cement. Due to the different component of each type of resin cement, the preconditioning method of tooth surface and the steps are different from each type of resin cement. The pre-treatment of adherend (ceramic, resin and metal) surface also varies with the type of resin cement and the manufacturer. In this study, the characteristics of each type of resin cement, mechanical properties, indication and advantages were investigated. Through these, clinical tips on using resin cements were suggested.

• Proceedings of the KIEE Conference
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• 1996.07b
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• pp.734-736
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• 1996

This paper presents a method of calculating a selective number of eigenvalues in power systems, which are rightmost, or are largest modulus. The modified Arnoldi method in conjunction with implicit shift OR-algorithm is used to calculate the rightmost eigenvalues. Algorithm requires neither a prior knowledge of the specified shifts nor the calculation of inverse matrix. The key advantage of the algorithm is its ability to converge to the wanted eigenvalues at once. The method is compared with the modified Arnoldi method combined with S-matrix transformation, where the eigenvalues having the largest modulus are to be determined. The two methods are applied to the reduced Kansai system. Convergence characteristics and performances are compared. Results show that both methods are robust and has good convergence properties. However, the implicit shift OR method is seen to be faster than the S-matrix method under the same condition.

• Journal of Energy Engineering
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• v.4 no.1
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• pp.126-139
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• 1995

저속의 압축성 유동장에서의 원형 실린더 주위의 유동 및 열전달특성을 해석하였다. 비압축성 유동장에서의 실린더 주위의 유동 및 열전달현상에 대하여는 실험과 수치해석을 포함한 광범위한 연구가 진행되어 왔으며 매우 잘 알려져 있다. 실린더 벽면과 주위 유동장의 온도차가 큰 경우, 밀도의 변화가 커지므로 유동장은 압축성 유체가 되나 지배 방정식의 복잡함과 적절한 수치해석 방법의 부족으로 실린더 주위의 유동장을 압축성유체로 해석한 경우는 매우 드물다. 현재 압축성유동 해석에 널리 사용되는 time marching algorithm은 저속의 유동장 해석시 지배방정식에 나타나는 eigenvalue들의 괴리에 의하여 수렴속도가 현저히 떨어지게 된다. 본 연구에서는 이와 같은 난점을 극복할 수 있는 time-derivative preconditioning 방법을 사용하여 온도차가 큰 유동장에서의 강제 및 혼합대류에 대한 계산을 수행하였고 이들의 열전달특성을 비교하였다. 강제대류의 경우 실린더 벽면 온도의 증가에 따른 밀도 감소의 영향은 유동장의 Re수를 감소시켜 확산의 영향을 증가시키면서, 혼합대류의 경우 부력의 영향은 가열되는 유동장의 범위와 재순환 영역을 강제대류에 비해 현저히 감소시킨다.

• Nuclear Engineering and Technology
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• v.49 no.6
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• pp.1114-1124
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• 2017

Acceleration/preconditioning strategies available in the SCEPTRE radiation transport code are described. A flexible transport synthetic acceleration (TSA) algorithm that uses a low-order discrete-ordinates ($S_N$) or spherical-harmonics ($P_N$) solve to accelerate convergence of a high-order $S_N$ source-iteration (SI) solve is described. Convergence of the low-order solves can be further accelerated by applying off-the-shelf incomplete-factorization or algebraic-multigrid methods. Also available is an algorithm that uses a generalized minimum residual (GMRES) iterative method rather than SI for convergence, using a parallel sweep-based solver to build up a Krylov subspace. TSA has been applied as a preconditioner to accelerate the convergence of the GMRES iterations. The methods are applied to several problems involving electron transport and problems with artificial cross sections with large scattering ratios. These methods were compared and evaluated by considering material discontinuities and scattering anisotropy. Observed accelerations obtained are highly problem dependent, but speedup factors around 10 have been observed in typical applications.

• Bulletin of the Korean Mathematical Society
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• v.53 no.2
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• pp.423-440
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• 2016

The bubble stabilization technique of Chebyshev-Legendre high-order element methods for one dimensional advection-diffusion equation is analyzed for the proposed scheme by Canuto and Puppo in [8]. We also analyze the finite element lower-order preconditioner for the proposed stabilized linear system. Further, the numerical results are provided to support the developed theories for the convergence and preconditioning.

• Journal of Korean Neurosurgical Society
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• v.39 no.4
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• pp.314-316
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• 2006

Intradural lumbar disc herniation[ILDH] is a rare pathology. The pathogenesis of ILDH is not known with certainty. Adhesions between the ventral wall of the dura and the posterior longitudinal ligament[PLL] could act as a preconditioning factor. Diagnosis of ILDH is difficult and seldom suspected preoperatively. Prompt surgery is necessary because the neurologic prognosis appears to be closely related to preoperative duration of neurologic symptoms. Despite preoperatively significant neurological deficits, the prognosis following surgery is relatively good. We report on case of ILDH at L3/4 with differential diagnoses, and the possible pathogenic factors are discussed.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.666-670
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• 2008

The low-speed preconditioning technique is applied to solve the compressible Reynolds averaged Navier-Stokes equations for low-speed flows. The space discretization is based on Roe's flux-difference splitting with third-order-accurate MUSCL extrapolation. Time integration is performed employing a diagonal approximate factorization algorithm. The dual-time stepping has been incorporated to solve the unsteady flows. Full multigrid method is implemented to accelerate the convergence rate. To verify the algorithms several cases have been tested. Demonstrated the improvement on convergence and quality of the solution.