• Journal of the Korea Computer Graphics Society
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• v.25 no.4
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• pp.1-8
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• 2019

In this paper, we propose a new framework that can express the detailed movement of liquid sprayed from wet hair or fur. In wet hair, not only the friction and adhesion of the hair but also the movement of the liquid has a distinctive motion compared to the dry hair. However, the recently proposed techniques only considered the contact force and friction of the hair and did not improve the movement of the liquid dispersed in the wet hair. This problem is detrimental to the quality of the result because it does not capture the detailed features expressed in the interaction of hair and liquid. The main point of this paper is to alleviate this problem and improve the quality of the result. As a result, we propose a combining framework that can efficiently express FLIP (Fluid-implicit particle) based fluid simulation and interaction of hair particles. The proposed method expresses the movement of the liquid sprayed in a curved shape which was not expressed in previous studies.

• Journal of the Korea Computer Graphics Society
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• v.26 no.5
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• pp.1-13
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• 2020

In this paper, we propose a new method to stable simulation the directional ice shape by coupling of freezing solver and viscous water flow. The proposed ice modeling framework considers viscous fluid flow in the direction of ice growth, which is important in freezing simulation. The water simulation solution uses the method of applying a new viscous technique to the IISPH(Implicit incompressible SPH) simulation, and the ice direction and the glaze effect use the proposed anisotropic freezing solution. The condition in which water particles change state to ice particles is calculated as a function of humidity and new energy with water flow. Humidity approximates a virtual water film on the surface of the object, and fluid flow is incorporated into our anisotropic freezing solution to guide the growth direction of ice. As a result, the results of the glaze and directional freezing simulations are shown stably according to the flow direction of viscous water.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.27 no.1
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• pp.9-16
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• 2014

Using a level set method and topological derivatives, a topological shape optimization method that is independent of an initial design is developed for linearly elastic structures. In the level set method, the initial domain is kept fixed and its boundary is represented by an implicit moving boundary embedded in the level set function, which facilitates to handle complicated topological shape changes. The "Hamilton-Jacobi(H-J)" equation and computationally robust numerical technique of "up-wind scheme" lead the initial implicit boundary to an optimal one according to the normal velocity field while minimizing the objective function of compliance and satisfying the constraint of allowable volume. Based on the asymptotic regularization concept, the topological derivative is considered as the limit of shape derivative as the radius of hole approaches to zero. The required velocity field to update the H-J equation is determined from the descent direction of Lagrangian derived from optimality conditions. It turns out that the initial holes are not required to get the optimal result since the developed method can create holes whenever and wherever necessary using indicators obtained from the topological derivatives. It is demonstrated that the proper choice of control parameters for nucleation is crucial for efficient optimization process.

• 한국전산유체공학회:학술대회논문집
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• 2001.05a
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• pp.93-98
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• 2001

An adaptive Cartesian grid method having the best elements of structured, unstructured, and Cartesian grids is developed to solve the steady two-dimensional Euler equations. The solver is based on a cell-centered finite-volume method with Roe's flux-difference splitting and implicit point Gauss-seidel time integration method. Calculations of several compressible flows are carried out to show the efficiency of the developed computer code. The results were generally in good agreements with existing data in the literature and the developed code has the good ability to capture important feature of the flows.

• Proceedings of the Korea Water Resources Association Conference
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• 1993.07a
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• pp.535-543
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• 1993

이 논문의 목적은 기존의 상수도 관망을 개선하는데 있어 어느 관을 교체 또는 재생할 것인가와 펌프용량을 얼마나 늘릴 것인가를 결정함으로써 관망내 각 급수지점에서의 요구유량및 수압을 만족시킴은 물론 그에 드는 비용을 최소화시키는 모델을 개발하는데 있다. 이 논문은 관교체 비용, 세관 및 재생 비용, 관보수 비용, 펌핑 비용, 펌프시설 확충비용 등의 다섯가지 비용들을 비교 검토함으로써 의사결정을 하게 된다. 제약조건식으로는 급수 조건식, 에너지 방정식, 수리학적 방정식, 결정 조건식, 한계 조건식, 정수 조건식 등이 있다. 이 모델을 수식화하면 정수혼합 비선형계획법 (mixed-integer nonlinear programming, MINLP) 문제가 된다. 이 문제를 풀기 위해 비선형해법의 GRG (generalized reduced gradient) 방법과 분기와 한계 (banch and bound) 기법을 통한 implicit enumeration 기법을 접목시키는 방법을 제안하였다.

• 한국전산유체공학회:학술대회논문집
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• 2002.10a
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• pp.95-102
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• 2002

Studies of the numerical characteristics of implicit upwind schemes, such as upwind ADI, Line Gauss-Seidel(LGS) and Point Gauss-Seidel(LU) algorithms, for preconditioned Navier-Stokes equations ate performed. All the algorithms are expressed in approximate factorization form and Von Neumann stability analysis and convergence studies are made. Preconditioning is applied for efficient convergence at low Mach numbers and low Reynolds numbers. For high aspect ratio computations, the ADI and LGS algorithms show efficient and uniform convergence up to moderate aspect ratio if we adopt viscous preconditioning based on min- CFL/max- VNN time-step definition. The LU algorithm, on the other hand, shows serious deterioration in convergence rate as the grid aspect ratio increases. Computations for practical applications also verify these results.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.8
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• pp.1-11
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• 2004

A comprehensive study has been made for the investigation of the convergence and stability characteristics of the LU scheme for solving the Navier-Stokes equations on unstructured meshes. For this purpose the characteristics of the LU scheme was initially studied for a scalar model equation. Then the analysis was extended to the Navier-Stokes equations. It was shown that the LU scheme has an inherent stiffness in the streamwise direction. This stiffness increases when the grid aspect ratio becomes high and the cell Reynolds number becomes small. It was also shown that the stiffness related to the grid aspect ratio can be effectively eliminated by performing proper subiteration. The results were validated for a flat-plate turbulent flow.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.9
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• pp.1-11
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• 2004

A comprehensive study has been made for the investigation of the convergence and stability characteristics of the LU scheme for solving the Euler equations on unstructured meshes. The von Neumann stability analysis technique was initially applied to a scalar model equation, and then the analysis was extended to the Euler equations. The results indicated that the convergence rate is governed by a specific combination of flow parameters. Based on this insight, it was shown that the LU scheme does not suffer any convergence deterioration at all grid aspect ratios, as long as the local time step is defined using an appropriate parameter combination.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.15 no.2
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• pp.108-115
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• 2003

Two types of one-dimensional dispersion-correction scheme are developed to take into account the dispersion effects for the simulation of tsunami propagation using ADCIRC finite element model based on shallow-water equations The first is an implicit scheme, and the dispersion-correction is accomplished by controlling the weighting factor assigned to each spatial derivative term of different time levels. The other scheme is explicit and the dispersion is considered by adjusting the element size. The validity of the dispersion-correction scheme proposed in this study is confirmed through the comparison of numerical solutions calculated using the new schemes with analytical ones considering dispersion effect of waves.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.17 no.1
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• pp.3-10
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• 2007

In this paper, we show that the status certificate-based encryption(SCBE) scheme proposed at ICISC 2004 and the certificateless signature(CLS) scheme proposed at EUC workshops 2006 are insecure. Both schemes are claimed that an adversary has no advantage if it controls only one of two participants making a cryptographic key such as a decryption key in SCBE or a signing key in CLS. But we will show that an adversary considered in the security model of each scheme can generate a valid cryptographic key by replacing the public key of a user.