• 유변학
• /
• 제8권1호
• /
• pp.30-38
• /
• 1996

단축 압출 공정에서 혼합 증진 장치로 사용될수 있는 새로운 스크류가 본 연구를 통하여 개발되었다. 스크류의 체널을 따라가면서 정규유동에서 존재하는 폐쇄유선을 깨뜨리 기 위하여 배리어를 공간상에서 주기적으로 배치하여 카오스 혼합을 일으키는 것이 새로운 스크류 설계의 기본적인 아이디어이다. 본 논문에서는 단축 압축기상에서의 카오스 혼합에 관한 기본 역학 구조를 설명하였고 카오스 스크류를 사용하여 실험적으로 카오스 혼합을 관 찰하였다. 단축 압출기에서의 기존 스크류와 비교하여 카오스 스크류를 사용하였을 경우 혼 합성능이 월등하게 증진됨을 실험적으로 얻은 혼합형태로부터 알수 있었다. 또한 카오스 스 크류는 특허 출원된 다른 혼합장치들에 비하여 형상이 간단하여 제작비가 저렴하고 스크류 특성이 우수하며 수해석적 면에서 스크류특성, 체류시간, 변형척도등을 예측할수 있는 장점 이 가진다.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2000년도 추계학술대회논문집B
• /
• pp.609-614
• /
• 2000

This numerical study investigate resonance frequency of natural convection for steady state, periodic flow and chaotic flow in two-dimensional direct numerical simulations, differentially heated, vertical cavities having aspect ratios near unity. The enclosure cavity has isothermal and time dependent temperature side walls and adiabatic top/bottom walls. The aspect ratio is 1/3, 1/2, 1, 2, and 3 for the varying Rayleigh number. Resonance frequency for AR=1 has decrease as the aspect ratio and the Rayleigh number are increasing.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2006년도 추계 학술대회논문집
• /
• pp.159-162
• /
• 2006

In the microfluidics devices the most important thing is mixing efficiency of various fluids. In this study a newly designed mixer is proposed to enhance the mixing effect with the purpose to apply it to microchannel mixing in a short future. This design is composed of a channel with cross baffles periodically arranged on the both bottom and top surfaces of the channel. To obtain the flow patterns, the numerical computation was performed by using a commercial code, ANSYS CFX 10.0. To evaluate the mixing performance, we computed Lyapunov exponent and obtained Poincare sections.

• 한국가시화정보학회:학술대회논문집
• /
• 한국가시화정보학회 2007년도 추계학술대회
• /
• pp.63-65
• /
• 2007

The paper reports on a new type of combinatorial chaotic and serpentine micromixer. Such a new and novel micromixer is simple to fabricate and easy to use. The micromixer is characterized and visualized with the help of the Micro-LIF technique. The new micromixer will e further applied to lab-on-chip device. The mixing capabilities of this mixer is about 30-33%.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2003년도 The Fifth Asian Computational Fluid Dynamics Conference
• /
• pp.121-122
• /
• 2003

In this study a microchannel with various arrangement of blocks is newly proposed. This design comprises periodically arranged simple blocks. In this configuration, the stirring is greatly enhanced at a certain geometric parameter set. To characterize the flow field and the stirring effect both the numerical and experimental methods were employed. To obtain the velocity field, three-dimensional numerical computation to the Navier Stokes equations are performed by using a commercial code, FLUENT 6.0. The fluid-flow solutions are then cast into studying the characteristics of stirring with the aid of Lyapunov exponent. The numerical results show that the particles' trajectories in the microchannel heavily depend on the block arrangement. It was shown that the stirring is significantly enhanced at larger block-height and it reaches maximum when the height is 0.8 times the channel width. We also studied the effect of the block stagger angle, and it turns out that the stirring performance is the best at the block angel ${45^\circ}$.

• 대한기계학회논문집B
• /
• 제34권1호
• /
• pp.53-59
• /
• 2010

본 논문에서는, 자기유체역학(MHD)을 기반으로 마이크로 채널 내부에 다중 와류 유동을 발생시키는 새로운 형태의 카오스 마이크로 믹서를 제안한다. 제안된 마이크로 믹서의 마이크로 채널 내부에는 양측면과 바닥면에 전극들이 배치되어 있다. 배치된 전극들에 인가되는 전압 조건에 따라 다양한 형태로 로렌츠 힘이 유도되며, 이렇게 유도된 로렌츠 힘은 마이크로 채널 내부 유체의 추진 및 혼합을 야기할 수 있다. 제안된 MHD 마이크로 믹서의 혼합 양상을 평가하기 위해 3 차원 전산유체역학 시뮬레이션을 수행하였다. 이를 통해 다양한 유동 조건에 대해 MHD 마이크로 믹서의 혼합 성능을 평가하였다.

• Structural Engineering and Mechanics
• /
• 제28권1호
• /
• pp.107-127
• /
• 2008

Wind turbine blades are increasing in magnitude without a proportional increase of stiffness for which reason geometrical and inertial nonlinearities become increasingly important. Often these effects are analysed using a nonlinear truncated expansion in undamped fixed base mode shapes of a blade, modelling geometrical and inertial nonlinear couplings in the fundamental flap and edge direction. The purpose of this article is to examine the applicability of such a reduced-degree-of-freedom model in predicting the nonlinear response and stability of a blade by comparison to a full model based on a nonlinear co-rotating FE formulation. By use of the reduced-degree-of-freedom model it is shown that under strong resonance excitation of the fundamental flap or edge modes, significant energy is transferred to higher modes due to parametric or nonlinear coupling terms, which influence the response and stability conditions. It is demonstrated that the response predicted by such models in some cases becomes instable or chaotic. However, as a consequence of the energy flow the stability is increased and the tendency of chaotic vibrations is reduced as the number of modes are increased. The FE model representing the case of infinitely many included modes, is shown to predict stable and ordered response for all considered parameters. Further, the analysis shows that the reduced-degree-of-freedom model of relatively low order overestimates the response near resonance peaks, which is a consequence of the small number of included modes. The qualitative erratic response and stability prediction of the reduced order models take place at frequencies slightly above normal operation. However, for normal operation of the wind turbine without resonance excitation 4 modes in the reduced-degree-of-freedom model perform acceptable.

• 대한기계학회논문집B
• /
• 제21권7호
• /
• pp.919-927
• /
• 1997

The main purpose of this study is to determine bifurcation as the primary instability of a glass melting furnace. Steady-state and unsteady characteristics of natural convection in the partially open cavity as appeared in a glass melting furnace is investigated by using numerical analysis. Three types of convection, such as steady laminar, unsteady periodic or unsteady quasi-periodic convection may occur according to the temperature difference between upper two isothermal surfaces along the depth of cavity in a glass melting furnace. In the temperature difference of 150-900 K between batch and free surface, the larger the temperature difference, the weaker the convection strength and unsteadiness. Since the glass viscosity is increasing exponentially in the lower temperature, the batch freezes the thermofluidic field especially below the surface of it. If the depth of cavity is 0.5 m, the bifurcation to time-dependent natural convection may occur in the range of 60-650 K. If that is 1.0 m, it may occur in the whole range of temperature difference.

• 한국해양학회지:바다
• /
• 제28권4호
• /
• pp.133-142
• /
• 2023

이 논문에서는 RNN (Recurrent Neural Networks)-LSTM (Long Short-Term Memory) 을 적용하여 Lorenz 시스템을 예측하는 자료 기반 인공지능 모델을 구축하고, 이 모델이 미분방정식을 차분화하여 해를 구하는 역학 모델을 대체할 수 있는지 가능성을 진단하였다. 구축된 자료기반 모델이 초기 조건의 작은 교란이 근본적으로 다른 결과를 만들어내는 Lorenz 시스템의 카오스적인 특성을 반영한다는 것과, 시스템의 안정적인 두 개의 닻을 중심으로 운동하면서 전이 과정을 반복하는 특성, "결정론적 불규칙 흐름"의 특성, 분기 현상을 모사한다는 것을 확인하였다. 또한, 적분 시간 간격을 조절함으로써 전산자원을 절감할 수 있는 자료기반 모델의 장점을 보였다. 향후 자료기반 모델의 정교화와 자료기반 모델을 위한 자료동화 기법의 연구를 통해 자료기반 인공지능 모델의 활용성을 확대할 수 있을 것으로 기대한다.

• 한국전산유체공학회지
• /
• 제9권4호
• /
• pp.20-33
• /
• 2004

In this study a stretching-mapping method is proposed for calculating the materials' stretching exponents, which are to be used in quantification of the mixing effect. In this method, the mapping tensor associated with the deformation of each fluid material is first obtained. Then deformations of a lot of materials are obtained by applying the mapping tensor. The local stretching rates and their space-average values are next computed with the mapped deformations. Application to a simple time-periodic flow within a cavity shows that the method is indeed effective compared with the conventional method; i.e. the mapping method is fast and yields the same results as the conventional one.