• Korean Chemical Engineering Research
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• 제59권4호
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• pp.626-631
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• 2021

전기투석장치, 전기화학 전지, 미세유체역학 분석 장치 등에서 사용하는 이온 교환 막 근처의 대표적인 비선형 전기동역학 현상은 전기와류 불안정성이다. 전기투석 장치에서 전기와류 불안정성은 물질 전달 속도 증폭을 통해 물질 전달에 대한 이점을 제공한다. 그러나 전기화학 전지나 미세유체역학 장치에서 발생하는 불안정성은 원치 않는 물질 전달 기작을 유발시킨다. 본 연구에서는 전기와류 불안정성의 제어하기 위해, 인가 전압과 공간 제약 효과의 전기와류 불안정성에 대한 영향을 연구하였다. 그 결과, 인가 전압과 공간 제약의 정도에 따라 불안정성의 동역학이 안정 영역 - 고정 영역 - 혼돈 영역 순으로 전이됨을 밝혀내었다. 더불어, 동역학 전이에 대한 안정성 곡선을 수치적으로 결정하였다. 결론적으로, 공간 제약 효과는 전기동역학적 혼돈을 제어할 수 있는 효과적인 기작으로 활용 가능할 것이다.

• 한국연소학회지
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• 제7권1호
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• pp.23-30
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• 2002

Instability of oblique detonation waves (ODW) at off-attaching condition was investigated through a series of numerical simulations. Two-dimensional wedge of finite length was considered in $H_2/O_2/N_2$ mixtures at superdetonative condition. Numerical simulation was carried out with a compressible fluid dynamics code and a detailed hydrogen-oxygen combustion mechanism. Present result reveals that there is a chemical kinetic limit of the ODW detachment, in addition to the theoretical limit predicted by Rankine-Hugoniot theory with equilibrium chemistry. Result also presents that ODW still attaches at a wedge as an oblique shock-induced flame showing periodically unstable motion, if the Rankine-Hugoniot limit of detachment is satisfied but the chemical kinetic limit is not. Mechanism of the periodic instability is considered as interactions of shock and reaction waves coupled with chemical kinetic effects. From the investigation of characteristic chemical time, condition of the periodic instability is identified as follows; at the detaching condition of the Rankine-Hugoniot theory, (1) flow residence time is smaller than the chemical characteristic time, behind the detached shock wave with heat addition, (2) flow residence time should be greater than the chemical characteristic time, behind an oblique shock wave without heat addition.

• Journal of Mechanical Science and Technology
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• 제19권9호
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• pp.1821-1832
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• 2005

This study realizes the conceptual method to predict combustion instability in actual full-scale combustion chamber of rocket engines by experimental tests with model (sub-scale) chamber. The model chamber was designed based on the methodologies proposed in the previous work regarding geometrical dimensions and operating conditions, and hot-fire test procedures were followed to obtain stability boundaries. From the experimental tests, two instability regions are presented by the parameters of combustion-chamber pressure and mixture (oxidizer/fuel) ratio, which are customary for combustor designers. It is found that instability characteristics in the chamber with the adopted jet injectors can be explained by the correlation between the characteristic burning or mixing time and the characteristic acoustic time: In each instability region, dynamic behaviors of flames are investigated to verify the hydrodynamically-derived characteristic lengths of the jet injectors. Large-amplitude pressure oscillation observed in upper instability region is found to be generated by lifted-off flames.

• Bulletin of the Korean Chemical Society
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• 제20권4호
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• pp.411-416
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• 1999

A new kind of differential flow induced chemical wave is introduced by theoretical calculation. A differential flow between the counter acting species of a dynamical activator-inhibitor system may destabilize its homogeneous reference state and cause the medium to self-organize into a pattern of travelling waves through the differential flow instability (DIFI). In a chemical system, also, the differential bulk flow may change the dynamics of the system, thus it has been refered to as the differential flow induced chemical instability (DIFICI). For DlFICI experiments, one directional flow has been commonly employed, resulting in periodic wave patterns generally. In this study, we considered two directional flow for the DIFICI wave by exchanging artificially the flow direction at some period.

• Korean Chemical Engineering Research
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• 제58권2호
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• pp.319-324
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• 2020

전기와류 불안정성은 전기투석 장치, 갈바니 전지, 전해 전지 등의 이온-선택성 이동 현상계에서 발견되는 비선형 이동 현상이다. 이 불안정성은 이온-선택성 표면 근처 공간 전하층의 요동에 의해 발생하며, 불안정성의 발현은 물질 전달 속도를 증가시켜 준다. 따라서 전기와류 불안정성은 물질 전달 측면에서 중요한 의미를 가진다. 최근의 실험적 기법들이 불안정성의 직접적 가시화를 가능하게 해주었으나, 실험적 한계점에 의해 불안정성의 원론적 연구는 제한된 영역에서만 이루어지고 있다. 본 연구에서는 일정 전위 모드에서의 전기와류 불안정성에 대한 수치 해석을 진행하여 전류-시간 곡선과 불안정성의 거동 간의 상관관계를 밝히고자 하였다. 시간-분해 해석을 통하여, 불안정성의 발달 거동을 SCL 형성 - 전기와류 불안정성의 성장 - 정상 상태 도달로 구분 지었다. 더불어, 인가 전위에 따른 전이 시간들의 크기 법칙 또한 수치적으로 유도하였다.

• Bulletin of the Korean Chemical Society
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• 제8권3호
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• pp.196-200
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• 1987

A nonlinear theory presented previously is applied to the Oregonator, which is a model for the Belousov-Zhabotinskii reaction, to study instability near the critical point driven by diffusions. The result shows that the theory may be applied to an actual system.

• Journal of applied mathematics & informatics
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• 제25권1_2호
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• pp.51-66
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• 2007

A layer of compressible, rotating, elastica-viscous fluid heated & soluted from below is considered in the presence of vertical magnetic field to include the effect of Hall currents. Dispersion relation governing the effect of viscoelasticity, salinity gradient, rotation, magnetic field and Hall currents is derived. For the case of stationary convection, the Rivlin-Erickson fluid behaves like an ordinary Newtonian fluid. The compressibility, stable solute gradient, rotation and magnetic field postpone the onset of thermosolutal instability whereas Hall currents are found to hasten the onset of thermosolutal instability in the absence of rotation. In the presence of rotation, Hall currents postpone/hasten the onset of instability depending upon the value of wavenumbers. Again, the dispersion relation is analyzed numerically & the results depicted graphically. The stable solute gradient and magnetic field (and corresponding Hall currents) introduce oscillatory modes in the system which were non-existent in their absence. The case of overstability is discussed & sufficient conditions for non-existence of overstability are derived.

• Korean Chemical Engineering Research
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• 제57권5호
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• pp.735-742
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• 2019

이온 선택성 표면이 가지는 파상구조와 전기와류 불안정성 간의 전기동역학적 상호작용을 수치해석을 통하여 연구하였다. 유한요소법을 이용하여 전기장-이온 이동현상-유동장을 완전결합 해석을 하였다. 이를 통해 파상구조가 제공하는 전기와류 생성 기작인 Dukhin's mode의 유효성 및 역할을 제시하였다. Runinstein's mode와 경쟁관계에 놓이는 Dukhin's mode는 (i) 과한계 영역으로의 전이 전압을 낮춰주고 (ii) 혼돈계인 과한계 영역에서 전류를 비선형적으로 증가시켜준다. 또한, (iii) 전기와류 불안정성에서 발생하는 비효율적 혼합의 원인인 고주파수 Fourier 성분을 배제하여 전기와류의 혼합 효율을 상승시켜 준다. 결론적으로, 본 연구에서 제시한 기작은 전기투석, 화학전지 등의 이온 선택성 이동현상 시스템에 대한 에너지 효율적인 기작으로 활용 가능할 것이다.

• 한국연소학회지
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• 제8권1호
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• pp.46-56
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• 2003

The present paper is concerned with the development of the computational biology in the past half century and its relationship with combustion. The modem computational biology is considered to be initiated by the work of Alan Turing on the morphogenesis in 1952. This paper first touches the life and scientific achievement of Alan Turing and his theory on the morphogenesis based on the reactive-diffusive instability, called the Turing instability. The theory of Turing instability was later extended to the nonlinear realm of the reactive-diffusive systems, which is discussed in the framework of the excitable media by using the Oregonator model. Then, combustion analogies of the Turing instability and excitable media are discussed for the cellular instability, pattern forming combustion phenomena and flame edge. Finally, the recent efforts on numerical simulations of biological systems, employing the detailed bio-chemical knietic mechanism is discussed along with the possibility of applying the numerical combustion techniques to the computational cell biology.

• 대한수의학회지
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• 제46권1호
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• pp.67-70
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• 2006

An 8-month-old 3.15 kg female Cocker-spaniel with history of ataxia referred to the Veterianary Medical Teaching Hospital, Chungnam National University. There were no abnormalities in CBC and serum chemical analysis. Agenesis of dens was found on dorsoventral view in cervical radiography. Compressed cervical spinal cord and enlarged cerebral ventricle were observed in magnetic resonance imaging. It was diagnosed as atlantoaxial instability with hydrocephalus. For conservative therapy, neck brace was applied and diuretics and prednisolone were administered. The dog's ataxia became better gradually.