• International Journal of Fuzzy Logic and Intelligent Systems
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• 제10권4호
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• pp.263-268
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• 2010

The premature convergence of genetic algorithms (GAs) is the most major factor of slow evolution of GAs. In this paper we propose a novel method to solve this problem through competition of multiple offspring of in dividuals. Unlike existing methods, each parents in our method generates multiple offspring and then generated multiple offspring compete each other, finally winner offspring become to real offspring. From this multiple offspring competition, our GA rarel falls into the premature convergence and easily gets out of the local optimum areas without negative effects. This makes our GA fast evolve to the global optimum. Experimental results with four function optimization problems showed that our method was superior to the original GA and had similar performances to the best ones of queen-bee GA with best parameters.

• Advances in Energy Research
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• 제1권1호
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• pp.53-78
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• 2013

Methane carbon dioxide reforming (MCDR) is a promising way of utilizing greenhouse gas for hydrogen-rich fuel production. Compared with other types of reactors, Compact Reformers (CRs) are efficient for fuel processing. In a CR, a thin solid plate is placed between two porous catalyst layers to enable efficient heat transfer between the two catalyst layers. In this study, the physical and chemical processes of MCDR in a CR are studied numerically with a 2D numerical model. The model considers the multi-component gas transport and heat transfer in the fuel channel and the porous catalyst layer, and the MCDR reaction kinetics in the catalyst layer. The finite volume method (FVM) is used for discretizing the governing equations. The SIMPLEC algorithm is used to couple the pressure and the velocity. Parametrical simulations are conducted to analyze in detail the effects of various operating/structural parameters on the fuel processing behavior.

• 한국자동차공학회논문집
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• 제8권5호
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• pp.86-95
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• 2000

A modified spray impingement model has been developed, which is assessed against experiments for the impinging sprays on the small combustion chamber at various gas pressures. To investigate spray behaviors in the diesel combustion chamber, a transparent constant-volume chamber is made which is similar to the combustion chamber of the real diesel engine. The chamber is pressurized by N2 gas from 0 bar to 20 bar to find the effects of ambient pressures. The behaviors of spray injected into this chamber and dispersed after impingement on the cylinder wall is measured two-dimensionally using laser sheet Mie scattering method. The physical submodels have been properly modified to improve the prediction capability of original KIVA code to describe the spray behaviors after impingement on the curved cylinder wall. In terms of spray dynamics and evolution. numerical results give qualitatively good agreements with experimental data.

• 한국추진공학회지
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• 제2권3호
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• pp.90-98
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• 1998

본 연구에서 개발한 고압증발 모델을 이용하여 고압 연소장에서의 액체연료추진제의 증발 과정을 수치적으로 해석하였다. 고압상태에서 액적의 증발 특성에 중요한 영향을 미치는 실제 기체의 거동, 온도 및 압력에 따른 가변물성치의 영향, 주위기체의 용해현상을 고려하였고 일반적인 상평형 관계식을 이용하였다. 실험치와 비교하여 고압증발모델의 예측능력을 체계적으로 검증하였고 로켓엔진의 고온 고압 연소실조건에서 LOX 액적의 증발 특성을 상세하게 논의하였다.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2015년도 제51회 KOSCO SYMPOSIUM 초록집
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• pp.127-130
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• 2015

The objective of this study is to investigate the real flame shape and characteristic of annular combustor. To identify the effects of combustor length ratio and equivalence ratio on the flame shape in annular combustion configuration, the employed parameters are combustor length ratio 0.6-1.0, equivalence ratio 0.7-1.1. The flame shape is visualized using DSLR camera and precision optic mirror. The flame intensity is analyzed by $OH^{*}$ chemiluminescence images with ICCD camera. CO and NOx emission performance is also examined using an exhaust gas analyzer. From the visualized images, it is confirmed that the different tendency appeared in combustor length ratio 0.6-0.7 and 0.8-1.0. The results of $OH^{*}$ chemiluminescence show that the flame intensity is the most uniform for equivalence ratio 0.9. The smaller equivalence ratio is, the less emission of CO and NOx will be in this investigation range.

• Asian-Australasian Journal of Animal Sciences
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• 제27권12호
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• pp.1721-1725
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• 2014

The objective of this study was to evaluate the in vitro effects of coconut materials on ruminal methanogenesis and fermentation characteristics, in particular their effectiveness for mitigating ruminal methanogenesis. Fistulated Holstein cows were used as the donor of rumen fluid. Coconut materials were added to an in vitro fermentation incubated with rumen fluid-buffer mixture and timothy substrate for 24 h incubation. Total gas production, gas profiles, total volatile fatty acids (tVFAs) and the ruminal methanogens diversity were measured. Although gas profiles in added coconut oil and coconut powder were not significantly different, in vitro ruminal methane production was decreased with the level of reduction between 15% and 19% as compared to control, respectively. Coconut oil and coconut powder also inhibited gas production. The tVFAs concentration was increased by coconut materials, but was not affected significantly as compared to control. Acetate concentration was significantly lower (p<0.05), while propionate was significantly higher (p<0.05) by addition of the coconut materials than that of the control. The acetate:propionate ratio was significantly lowered with addition of coconut oil and coconut powder (p<0.05). The methanogens and ciliate-associated methanogens in all added coconut materials were shown to decrease as compared with control. This study showed that ciliate-associated methanogens diversity was reduced by more than 50% in both coconut oil and coconut powder treatments. In conclusion, these results indicate that coconut powder is a potential agent for decreasing in vitro ruminal methane production and as effective as coconut oil.

• 한국가스학회지
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• 제12권2호
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• pp.92-98
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• 2008

가스배관 열화부재의 실시간 역학물성 측정기술로 계장화 압입과 압입흔적 입체측정의 융합이 시도되었다. 압입하중-변위곡선을 계장화 압입시험으로 획득한 후 반사식 레이저 스캔너를 이용하여 압입흔적을 3차원으로 관찰하였다. 압흔 단면프로파일로부터 소성역 크기와 실제 접촉경계를 분석할 수 있었고, 두 값을 이용하여 소재의 항복강도와 경도를 계산하였다. 항복강도는 단축 인장시험에서 얻어진 값과 유사한 경향을 나타내었고, 경도는 재료쌓임 영향으로 압입곡선에서 계산된 값에 비해 $20{\sim}30%$ 낮은 값을 나타내었으나 최대 인장강도와 정량적인 관련성이 있음을 확인할 수 있었다. 덧붙여 압입하중 인가부의 형태를 수정하여 압입시험과 동시에 압흔주변 형상변화를 측정하기 위한 시스템도 고안되었다.

• 한국분무공학회지
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• 제9권4호
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• pp.83-89
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• 2004

Vaporization characteristics of a liquid heptane droplet in high-pressure and temperature flow field are numerically studied. Variable thermodynamic and transport properties and high-pressure effects are taken into account in order to consider real gas effects. Droplet Vaporization in convective environments was investigated on the basis of droplet vaporization in quiescent and convective environment. In quiescent environments, droplet lifetime is directly proportional to pressure at the subcritical temperature range but it is inversely proportional to pressure at the supercritical temperature range. In convective environment, droplet deformation becomes stronger by increasing Reynolds number due to increase of velocity while droplet deformation is relatively weak at a higher pressure for the same Reynolds number cases.

• 유기물자원화
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• 제26권4호
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• pp.5-10
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• 2018

본 연구에서는 압력, 전해질, 유기물 등 가스하이드레이트 부존 지역의 물리화학적 인자가 치환반응에 미치는 영향을 실험적으로 규명하였다. 가스 주입 시 초기 압력이 높을수록 초반 반응속도는 향상되었으나 시간이 지남에 따라 치환효율이 일정한 값으로 수렴하였다. 전해질과 유기물 등의 경우 가스하이드레이트 해리 후 재생성 과정에서 일부 영향을 미치는 것으로 밝혀졌다. 향후 실제 유기성 메탄 하이드레이트가 부존된 퇴적토를 활용한 추가 연구를 통해 국내 해저 지질특성에 적용 가능한 기술 개발이 가능할 것으로 기대된다. 궁극적으로 향후 동해 울릉 분지의 가스하이드레이트 매장 지역 현장 적용을 통해서 유기성 자원인 메탄을 회수하고 활용할 수 있을 것으로 예상된다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.802-806
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• 2004

For the protection of the local air quality and the global atmosphere, the emissions of trace species including nitric oxides (NO and NO$_2$) from gas turbines are regulated by local governments and by the International Civil Aviation Organization. In-situ measurements of such species are needed not only for the development of advanced low-emission combustion concepts but also for providing emissions data required for the sound assessment of the effects of the emissions on environment. We have been developing a laser absorption system that has a capability of simultaneous determination of NO and NO$_2$concentrations in the exhaust jets from aero gas turbines. A diode laser operating near 1.8 micrometer is used for the detection of NO while a separated visible tunable diode laser operating near 676 nanometers is used for NO$_2$. The sensitivities at elevated temperature conditions were determined for simulated gas mixtures heated up to 500K in a heated cell of a straight 0.5 m optical path. Sensitivity limits estimated as were 30 ppmv-m and 3.7 ppmv-m for NO and NO$_2$, respectively, at a typical exhaust gas temperature of 800K. Experiments using the simulated exhaust flows have proven that $CO_2$ and $H_2O$ vapor - both major combustion products - do not show any interference in the NO or NO$_2$ measurements. The measurement system has been applied to the NO/NO$_2$ measurements in NO and NO$_2$ doped real combustion gas jets issuing from a rectangular nozzle having 0.4 m optical path. The lower detection limits of the system were considerably decreased by using a multipass optical cell. A pair of off-axis parabola mirrors successfully suppressed the beam steering in the combustion gas jets by centralizing the fluctuating beam in sensor area of the detectors.