• 한국연소학회:학술대회논문집
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• 한국연소학회 2000년도 제21회 KOSCO SYMPOSIUM 논문집
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• pp.24-32
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• 2000

A brief introduction is given on the conditional moment closure model for turbulent nonpremixed combustion. It is based on the transport equations derived through a rigorous mathematical procedure for the conditionally averaged quantities and appropriate modeling forms for conditional scalar dissipation rate, conditional mean velocity and reaction rate. Examples are given for prediction of NO and OH in bluffbody flames, soot distribution in jet flames and autoignition of a methane/ethane jet to predict the ignition delay with respect to initial temperature, pressure and fuel composition. Conditional averaging may also be a powerful modeling concept in other approaches involved in turbulent combustion problems in various different regimes.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제20권4호
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• pp.309-332
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• 2016

Finite element method has been applied to solve the fundamental governing equations of natural convective, electrically conducting, incompressible fluid flow past an infinite vertical plate surrounded by porous medium in presence of thermal radiation, viscous dissipation, Soret and Dufour effects. In this research work, the results of coupled partial differential equations are found numerically by applying finite element technique. The sway of significant parameters such as Soret number, Dufour number, Grashof number for heat and mass transfer, Magnetic field parameter, Thermal radiation parameter, Permeability parameter on velocity, temperature and concentration evaluations in the boundary layer region are examined in detail and the results are shown in graphically. Furthermore, the effect of these parameters on local skin friction coefficient, local Nusselt number and Sherwood numbers is also investigated. A very good agreement is noticed between the present results and previous published works in some limiting cases.

• Nuclear Engineering and Technology
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• 제49권8호
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• pp.1680-1688
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• 2017

In this study, analysis is performed on entropy generation during cilia transport of water based titanium dioxide nanoparticles in the presence of viscous dissipation. Moreover, thermal heat flux is considered at the surface of a channel with ciliated walls. Mathematical formulation is constructed in the form of nonlinear partial differential equations. Making use of suitable variables, the set of partial differential equations is reduced to coupled nonlinear ordinary differential equations. Closed form exact solutions are obtained for velocity, temperature, and pressure gradient. Graphical illustrations for emerging flow parameters, such as Hartmann number (Ha), Brinkmann number (Br), radiation parameter (Rn), and flow rate, have been prepared in order to capture the physical behavior of these parameters. The main goal (i.e., the minimizing of entropy generation) of the second law of thermodynamics can be achieved by decreasing the magnitude of Br, Ha and ${\Lambda}$ parameters.

• Nuclear Engineering and Technology
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• 제49권8호
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• pp.1654-1659
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• 2017

The boundary layer of a two-dimensional forced convective flow along a persistent moving horizontal needle in an electrically conducting magnetohydrodynamic dissipative nanofluid was numerically investigated. The energy equation was constructed with Joule heating, viscous dissipation, uneven heat source/sink, and thermal radiation effects. We analyzed the boundary layer behavior of a continuously moving needle in Blasius (moving fluid) and Sakiadis (quiescent fluid) flows. We considered Cu nanoparticles embedded in methanol. The reduced system of governing Partial differential equations (PDEs) was solved by employing the Runge-Kutta-based shooting process. Computational outcomes of the rate of heat transfer and friction factors were tabulated and discussed. Velocity and temperature descriptions were examined with the assistance of graphical illustrations. Increasing the needle size did not have a significant influence on the Blasius flow. The heat transfer rate in the Sakiadis flow was high compared with that in the Blasius flow.

• 한국연소학회지
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• 제5권2호
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• pp.9-17
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• 2000

A brief introduction is given on the conditional moment closure model for turbulent nonpremixed combustion. It is based on the transport equations derived through a rigorous mathematical procedure for the conditionally averaged quantities and appropriate modeling forms for conditional scalar dissipation rate, conditional mean velocity and reaction rate. Examples are given for prediction of NO and OR in bluffbody flames, soot distribution in jet flames and autoignition of a methane/ethane jet to predict the ignition delay with respect to initial temperature, pressure and fuel composition. Conditional averaging may also be a powerful modeling concept in other approaches involved in turbulent combustion problems in various different regimes.

• Journal of Advanced Marine Engineering and Technology
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• 제23권2호
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• pp.216-225
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• 1999

Four turbulent $k-{varepsilon}$models(i.e standard model modified models with streamline curvature modification and/or preferential dissipation modification) are applied in order to analyze the tur-bulent flow of wall-attaching offset jet. The upwind numerical scheme was adopted in the present analyses. The streamline curvature modification results in slightly better prediction while the preferential dissipation modification does not. The obtained analytic results will be used as refer-ences for further study regarding Reynolds stress model. In addition this paper introduced a method of increasing nozzle outlet velocity gradually for numercal convergence. Even though the method was simple it was efficient in view of convergent speed CPU running time computer memory storage programming etc.

• 한국운동역학회지
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• 제22권3호
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• pp.315-324
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• 2012

The purpose of current study was to investigate the effects of the heights on the lower extremities, torso and neck segments for energy dissipation during single-leg drop landing from different heights. Twenty eight young healthy male subjects(age: $23.21{\pm}1.66yr$, height: $176.03{\pm}4.22cm$, weight: $68.93{\pm}5.36kg$) were participated in this study. The subjects performed the single-leg drop landing from the various height(30, 45 & 60 cm). Force plates and motion-capture system were used to capture ground reaction force and kinematics data, respectively. The results were as follows. First, the ROM at the ankle, knee, hip and trunk was increased with the increased heights but the ROM at the neck was increased in the 60cm. Second, the angular velocity, moment and eccentric work at the ankle, knee, hip, trunk, and neck was increased with the increased heights. Third, the contribution to total work at the knee joint was not significantly different, while the ankle joint rate was decreased and hip and neck rate was increased in the 60cm, and trunk rate was increased with the increased heights. Lastly, the increase in landing height was able to augment the level of energy dissipation not only at the lower extremities but also at the trunk and neck. The findings showed that drop landing affect trunk and neck with lower extremity joints. Therefore, we need to consider that trunk and neck strengthening including stability should be added to reduce sports injury during prevention training.

• Geomechanics and Engineering
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• 제29권2호
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• pp.99-111
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• 2022

Instability of bolted rock mass has been a major hazard in the underground coal mining industry for decades. Developing effective support guidelines requires understanding of complex bolted rock mass failure mechanisms. In this study, the dynamic failure behavior, mechanical behavior, and energy evolution of a laboratory-scale bolted specimens is studied by conducting laboratory static-dynamic coupled loading tests. The results showed that: (1) Under static-dynamic coupled loading, the stress-strain curve of the bolted rock mass has a significant impact velocity (strain rate) correlation, and the stress-strain curve shows rebound characteristics after the peak; (2) There is a critical strain rate in a rock mass under static-dynamic coupled loading, and it decreases exponentially with increasing pre-static load level. Bolting can significantly improve the critical strain rate of a rock mass; (3) Compared with a no-bolt rock mass, the dissipation energy ratio of the bolted rock mass decreases exponentially with increasing pre-static load level, the ultimate dynamic impact energy and dissipation energy of the bolted rock mass increase significantly, and the increasing index of the ratio of dissipation energy increases linearly with the pre-static load; (4) Based on laboratory testing and on-site microseismic and stress monitoring, a design method is proposed for a roadway bolt support against dynamic load disturbance, which provides guidance for the design of deep underground roadway anchorage supports. The research results provide new ideas for explaining the failure behavior of anchorage supports and adopting reasonable design and construction practices.

• 한국해양학회지:바다
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• 제12권4호
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• pp.390-399
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• 2007

하계 동중국해 북부 대륙붕 해역에서 해수 혼합을 연구하기 위하여 2005년 8월과 2006년 8월에 한국해양연구원 연구선 이어도호를 이용하여 해수 물성 및 난류 관측을 수행하였다. 유속 변형으로부터 산출한 난류운동에너지 소산율은 표층에서 $10^{-7}{\sim}10^{-4}$, 저층에서 $10^{-7}{\sim}10^{-6}$와 수온약층에서 $10^{-7}$ W/kg의 높은 값이 나타났다. 관측 자료는 표층의 경우 바람에 의해 지속적으로 혼합이 이루어짐을 보여주었다. 수온약층 하부에서의 높은 소산율은 내부파의 영향으로 판단된다. 저층의 높은 소산율은 저층의 탁도 분포의 경향과 일치하여 조류에 의한 해저면층 교란의 결과임을 시사해주었다. 바닥에서의 연직확산계수는 낮은 안정도와 높은 난류상태의 복합적인 영향으로 $10^{-3}{\sim}10^{-2}m^2/s$로 높은 값이 나타났다.

• 대한토목학회논문집
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• 제28권6C호
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• pp.339-347
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• 2008

현장 관입 실험은 프로브 관입에 따라 주변 지반을 의도적으로 파괴시켜 지반특성을 파악할 수 있다. 본 논문의 목적은 현장 점토지반에 서로 다른 크기의 프로브 관입으로 인한 간극 수압 소산 특성을 이용하여 파괴에 따른 교란 효과를 분석하는 것이다. 현장 실험을 수행하기 위해 콘관입 시험(CPT), 딜라토미터 시험(DMT) 그리고 현장 속도 프로브 장비(FVP: Field Velocity Probe)가 사용되었다. 샌드 매트(sand mat), PBD 그리고 사석을 이용한 지반 개량 중인 부산 북컨테이너 현장에서 실험이 진행 되었으며, 샌드 매트(sand mat)공법 이후 실내 실험을 수행하기 위해 시료가 채취 되었다. 실내에서는 물성치 실험 및 압밀 실험을 수행하여 지반 특성과 수평압밀계수 값을 도출하였다. 현장 실험은 지반 개량 후 압밀도 90% 시점에서 사석 제거 후 케이싱을 통해 CPT, DMT 그리고 FVP 순서대로 실험이 수행 되었다. 관입에 따른 영향 범위를 최소화 시키기 위해 각각의 실험은 3m 간격을 유지 하였으며, 매 심도 24m에서 관입을 멈추고 시간에 따른 간극 수압 변화 양상을 측정하였다. 실내 압밀 실험을 통해 수평 압밀 계수$(C_h)$를 산정하였으며, 현장 실험을 통해 각 프로브에 따른 $t_{50}$ 값을 계산 하였다. $t_{50}$값을 이용하여 산정된 등가 유효 반경은 FVP가 가장 작게 그리고 DMT가 가장 크게 산정되었다.