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ASSESSMENT OF PROPERTY INTERPOLATION METHODS IN LEVEL SET METHOD
J.K. Park(박준권),J.M. Oh(오정민),K.H. Kang(강관형) 한국전산유체공학회 2009 한국전산유체공학회 학술대회논문집 Vol.2009 No.4
In level set method, material properties are made to change smoothly across an interface of two materials with different properties by introducing an interpolation or smoothing scheme. So far, the weighted arithmetic mean (WAM) method has been exclusively adopted in level set method, without complete assessment for its validity. We showed here that the weighted harmonic mean (WHM) method for rate constants of various rate processes, including viscosity, thermal conductivity, electrical conductivity, and permittivity, gives much more accurate results than the WAM method. The selection of interpolation scheme is particularly important in multi-phase electrohydrodynamic problems in which driving force for fluid flow is electrical force exerted on the phase interface. Our analysis also showed that WHM method for both electrical conductivity and permittivity gives not only more accurate, but also more physically realistic distribution of electrical force at the interface. Our arguments are confirmed by numerical simulations of drop deformation under DC electric field.
초음파 가공용 터닝센터의 스핀들 열해석에 관한 기초 연구
박준구(J. K. Park),신성우(S. W. Shin),이인재(I. J. Lee),황예한(Y. H. Hwang),이영식(Y. S. Lee),이춘만(C.-M. Lee) Korean Society for Precision Engineering 2021 한국정밀공학회 학술발표대회 논문집 Vol.2021 No.11월
최근 금속가공분야에서는 우주항공, 자동차 부품 등의 고부가가치 제품에 쓰이는 난삭재의 가공방법에 대한 수요가 많아지고 있다. 이에 따라 난삭재의 효율적인 가공을 위하여 기존 절삭가공에 부가 장치를 부착하여 가공하는 하이브리드 가공방법에 대한 연구가 활발히 진행되고 있다. 그 중 초음파 가공은 초음파 진동(Ultrasonic Vibration)을 공구에 작용시켜 공구와 공작물 간의 접촉 시에 발생하는 초음파 진동을 통해 절삭 과 칩의 배출이 용이하도록 하는 원리를 이용한 가공기술이기 때문에 난삭재 가공에 효과적이다. 국내에서는 초음파를 이용하는 공작기계는 대부분 머시닝센터에 초음파 헤드를 공구 교환식으로 장착하는 방식으로 연구개발 중이며, 터닝센터형 초음파 장비의 연구개발 사례가 거의 없어 복합 가공이 가능한 가변주파수 초음파 터닝 센터의 개발이 필요한 실정이다. 하지만 스핀들의 구조 안정성이 확보되지 않으면 공작물의 가공정밀도에 영향을 미칠 수 있기 때문에 개발 전 열해석을 통한 스핀들의 구조 안정성 분석이 선행되어야 한다. 따라서 본 연구에서는 가공 진행 시 베어링 및 모터의 발열량을 열원으로 계산하였고, 냉각 자켓의 냉각 효과를 고려하여 열해석을 수행하였다. 또한 터닝 센터에 장착된 스핀들의 최대온도 및 온도 분포를 통하여 안정성 분석을 수행하였다.
박준권(J.K. Park),강관형(K.H. Kang) 한국전산유체공학회 2010 한국전산유체공학회지 Vol.15 No.3
Recently, several open source codes for computational fluid dynamics (CFD) have been introduced and are spreading fast. Our group has chosen the OpenFOAM as a platform to develop our own in-house code. In this brief review, we would like to share the information on the codes and what we have experienced so for. We introduce several features of OpenFOAM, which include the performance compared with commercial packages, estimation for current user population, and our own prospect for future improvement in performance and growth in user population. In addition, we briefly introduce our experience gained in embedding the level set method into the OpenFOAM.
레벨셋 기법을 이용한 전기습윤 현상의 동적 거동에 대한 해석 및 물성 보간 방법에 대한 고찰
박준권(J.K. Park),강관형(K.H. Kang) 한국전산유체공학회 2010 한국전산유체공학회 학술대회논문집 Vol.2010 No.5
Electrowetting is a versatile tool to handle tiny droplets and forms a backbone of digital microfluidics. Numerical analysis is necessary to fully understand the dynamics of electrowetting, especially in designing electrowetting-based devices, such as liquid lenses and reflective displays. We developed a numerical method to analyze the general contact-line problems, incorporating dynamic contact angle models. The method is based on the conservative level set method to capture the interface of two fluids without loss of mass. We applied the method to the analysis of spreading process of a sessile droplet for step input voltages and oscillation of the droplet for alternating input voltages in electrowetting. The result was compared with experimental data. It is shown that contact line friction significantly affects the contact line motion and the oscillation amplitude. The pinning process of contact line was well represented by including the hysteresis effect in the contact angle models. In level set method, in the mean time, material properties are made to change smoothly across an interface of two materials with different properties by introducing an interpolation or smoothing scheme. So far, the weighted arithmetic mean (WAM) method has been exclusively adopted in level set method, without complete assessment for its validity. We showed here that the weighted harmonic mean (WHM) method for rate constants of various rate processes, including viscosity, thermal conductivity, electrical conductivity, and permittivity, can be an alternative. I.e., the WHM gives more accurate results than the WAM method in certain circumstances. The interpolation scheme should be selected considering various characteristics including type of property, ratio of property of two fluids, geometry of interface, and so on.
박준권(J.K. Park),강관형(K.H. Kang) 한국전산유체공학회 2010 한국전산유체공학회 학술대회논문집 Vol.2010 No.5
Recently, several open source codes for computational fluid dynamics (CFD) have been emerged and are spreading fast. Our group has chosen OpenFOAM as a platform to develop our own in-house code. In this paper, we would like to share the information on the codes and what we have experienced so far. We introduce several features of OpenFOAM, which include the performance compared with commercial packages, estimation for current user population, and our own prospect for future improvement in performance and growth in user population. In addition, we briefly introduce our experience gained in embedding the level set method into the OpenFOAM.
레벨셋 기법을 이용한 전기습윤 현상의 동적 거동에 대한 해석
박준권(J.K. Park),홍지우(J.W. Hong),강관형(K.H. Kang) 한국전산유체공학회 2009 한국전산유체공학회 학술대회논문집 Vol.2009 No.11
Electrowetting is a versatile tool to handle tiny droplets and forms a backbone of digital microfluidics. Numerical analysis is necessary to fully understand the dynamics of electro wetting, especially in designing electro wetting-based devices, such as liquid lenses and reflective displays. We developed a numerical method to analyze the general contact-line problems, incorporating dynamic contact angle models. The method is based on the conservative level set method to capture the interface of two fluids without loss of mass. We applied the method to the analysis of spreading process of a sessile droplet for step input voltages and oscillation of the droplet for alternating input voltages in electro wetting. The result was compared with experimental data. It is shown that contact line fiction significantly affects the contact line motion and the oscillation amplitude. The pinning process of contact line was well represented by including the hysteresis effect in the contact angle models.