• 한국전산유체공학회:학술대회논문집
• /
• 2008.03b
• /
• pp.547-550
• /
• 2008

A solid rocket motor has quite complex physical condition such exothermal chemical reaction in subsonic area and supersonic ex pansion in a converging-diverging nozzle. To introduce a simulation tool for compressible flow in supersonic range as well as incompressible chemical reaction zone in a whole rocket nozzle is a essential demand. Since the flow vary subsonic to super sonic, the convergence in computation becomes very low and unstable in a whole domain of rocket motor. This paper reports the 2-D Axisymmetric and simple 3-D solid propellant combustion and flow of gases in rocket motor by using a precondi tioning, shear stress turbulence modeling, AUSM(p). To simulate the simplified combustion process, Double base solid propellant is used to calculate reaction of solid propellant.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.14 no.4
• /
• pp.297-301
• /
• 2008

On-site measurement of ship wave has been carried out in the vicinity of Mokpo inner harbour. The wave data were collected and logged 5Hz by the ultrasonic instrument for 12hour on May 17, 2006. The number of data was 216,000 and the maximum wave height was 81.41cm in normal weather condition. It was found that the wave conditions in this water area are predominantly affected by the ship-generated waved under normal condition. By comparing with the wind-generated waves in the open region which were irregular but with dominant directional characteristics, the existing harbor wave field was much more complex.

• Journal of Korean Society of Rural Planning
• /
• v.25 no.1
• /
• pp.39-50
• /
• 2019

The purpose of this study is to figure out the current condition of local governments (Si or Gun) to implement rural development policy in the face of the central government's drive for increasing devolution. Since late 1990s or early 2000s when scope of rural policy began to expand quantitatively, there has been considerable increase in rural residents' participation into community projects as a whole. Nevertheless, there exists regional differentiation in local governments' efforts to systematically support rural development projects (CRDP: Comprehensive Rural Development Programme) and community activities by setting up intermediary organizations or hiring rural development professionals in a public office. According to this survey on local government officials, regions that have made such efforts to support rural policy at a local level, show more advanced level of institutional capacity than other regions in local decision making process for CRDP, role of strategic rural developmental plans, vitality of community actors, etc. In the era of increasing devolution, these differences can be expected to result in diverging performances of each area in regionalized rural policy. The central government needs to introduce EU's LEADER-type rural development programmes to support community acitivities by various local actors and at the same time promote local governance building for rural policy, adopting institutional rewarding system such as rural planning contract.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.28 no.6
• /
• pp.688-696
• /
• 2004

Nonlinear dynamic behavior of diffusive-thermal instability in diluted CH$_4$/O$_2$ diffusion flames is numerically investigated by adopting detailed chemistry and transport. Counterflow diffusion flame is adopted as a model flamelet. Particular attention is focused on the pulsating-instability regime, which arises for Lewis numbers greater than unity, and the instability occurs at high strain rate near extinction condition in this flame configuration. Once a steady flame structure is obtained for a prescribed value of initial strain rate, transient solution of the flame is calculated after a finite amount of strain-rate perturbation is imposed on the steady flame. Transient evolution of the flame depends on the initial strain rate and the amount of perturbed strain rate. Basically, the dynamic behaviors can be classified into two types, namely non-oscillatory decaying solution and diverging solution leading to extinction. The peculiar oscillatory solution, which has been found in the previous study adopting one-step chemistry and constant Lewis numbers, is net observed in this study, which is attributed to both convective flow and preferential diffusion effects.

• 한국연소학회:학술대회논문집
• /
• 2004.06a
• /
• pp.95-101
• /
• 2004

Dynamic behavior of diffusive-thermal instability in diluted $CH_4/O_2$ diffusion flames is numerically investigated by adopting detailed chemistry and transport. Counterflow diffusion flame is adopted as a model flamelet. Particular attention is focused on the pulsating-instability regime, which arises for Lewis numbers greater than unity, and the instability occurs at high strain rate near extinction condition in this flame configuration. Once a steady flame structure is obtained for a prescribed value of initial strain rate. transient solution of the flame is calculated after a finite amount of strain-rate perturbation is imposed Oil the steady flame. Transient evolution of the flame depends on the initial strain rate and the amount of perturbed strain rate. Basically, the dynamic behaviors can be classified into two types, namely non-oscillatory decaying solution and diverging solution leading to extinction. The peculiar oscillatory solution. which has been found in the previous study adopting one-step chemistry and constant Lewis numbers, is not observed in this study, which is attributed to both convective flow and preferential diffusion effects.

• Progress in Medical Physics
• /
• v.13 no.1
• /
• pp.37-43
• /
• 2002

Effect of scatter media materials and thickness, located between radioactivity and small gamma camera, on imaging characteristics was evaluated. The small gamma camera developed for breast imaging was consisted of collimator, NaI(T1) crystal(60$\times$60$\times$6 ㎣), PSPMT(position sensitive photomultimplier tube), NIMs and personal computer. Monte Carlo simulation was performed to evaluate the system sensitivity with different scatter media thickness(0~8 cm) and materials(air and acrylic) with parallel hole collimator and diverging collimator. The sensitivity and spatial resolution was measured using the small gamma camera with the same condition applied to the simulation. Counts was decreased by 10%(air) and 54%(acryl) with the parallel hole collimator and by 35%(air) and 63%(acryl) with the diverging collimator. Spatial resolution was decreased as increasing the thickness of scatter media. This study substantiate the importance of a gamma camera positioning and the minimization of the distance between detector and target lesion in the clinical application of a gamma camera.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.30 no.1
• /
• pp.47-53
• /
• 2017

A boundary layer integral combined with a 1-D isentropic core flow model has been successfully used to determine heat transfer rate on the surface of a supersonic nozzle. However its accuracy is affected by the core flow condition which is used as a boundary condition for the integral calculation. Because flow behavior near a nozzle throat deviates from 1-D isentropic condition due to 2-D flow turning and interaction between core flow and boundary layer, accuracy of heat transfer calculation decreases at a nozzle throat. Therefore, CFD is adopted to deduce improved core flow condition and increase accuracy of boundary layer integral at nozzle throat in this research. Euler model and SST $k-{\omega}$ model is solved by CFD code and used as a boundary condition for boundary layer integral. Developed code is tested in the supersonic nozzle from the previous research and improvement in accuracy is observed, especially at nozzle throat and diverging section of the nozzle. Error between experimental result and calculation result reduced by 16% when a calculation is made based on the SST $k-{\omega}$ model. Method developed in this research is expected to be used in thermal design of the rocket nozzle.

• Journal of Korea Water Resources Association
• /
• v.33 no.2
• /
• pp.195-205
• /
• 2000

Many types of factors were devised to calculate time of concentration. Singh(976) derived time of concentration of overland flow using kinematic wave theory for plane, converging, and diverging geometric configurations. The present paper investigated the time of concentration for particularly plane geometric configuration. A theoretical equation of time of concentration is derived based on the assumption of impervious overland flow as in the open channel flow. The study characterized the overland flow by many types of characteristic flow such as rough turbulent flow, smooth turbulent flow, laminar flow, and then suggested a theoretical equation on each flow condition. The present paper further considered the rainfall intensity as a main factor and devised an approximate composite equation reflecting the effect of rainfall intensity given at various return periods.

• Journal of the Korean Society of Environmental Restoration Technology
• /
• v.19 no.6
• /
• pp.19-30
• /
• 2016

The projection of climate-related range shift is critical information for conservation planning of Korean fir (Abies koreana E. H. Wilson). We first modeled the distribution of Korean fir under current climate condition using five single-model species distribution models (SDMs) and the pre-evaluation weighted ensemble method and then predicted the distributions under future climate conditions projected with HadGEM2-AO under four $CO_2$ emission scenarios, the Representative Concentration Pathways (RCP) 2.6, 4.5, 6.0 and 8.5. We also investigated the predictive uncertainty stemming from five individual algorithms and four $CO_2$ emission scenarios for better interpretation of SDM projections. Five individual algorithms were Generalized linear model (GLM), Generalized additive model (GAM), Multivariate adaptive regression splines (MARS), Generalized boosted model (GBM) and Random forest (RF). The results showed high variations of model performances among individual SDMs and the wide range of diverging predictions of future distributions of Korean fir in response to RCPs. The ensemble model presented the highest predictive accuracy (TSS = 0.97, AUC = 0.99) and predicted that the climate habitat suitability of Korean fir would increase under climate changes. Accordingly, the fir distribution could expand under future climate conditions. Increasing precipitation may account for increases in the distribution of Korean fir. Increasing precipitation compensates the negative effects of increasing temperature. However, the future distribution of Korean fir is also affected by other ecological processes, such as interactions with co-existing species, adaptation and dispersal limitation, and other environmental factors, such as extreme weather events and land-use changes. Therefore, we need further ecological research and to develop mechanistic and process-based distribution models for improving the predictive accuracy.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2009.11a
• /
• pp.627-630
• /
• 2009

Ejector system can induce the secondary flow or affect the secondary chamber pressure by both shear stress and pressure drop which are generated in the primary jet boundary. Ejectors are widely used in a range of applications such as a turbine-based combined-cycle propulsion system and a high altitude test facility for rocket engine, pressure recovery system, desalination plant and ejector ramjet etc. The primary interest of this study is to set up an configuration and operating conditions for an ejector in the condition of sonic and subsonic. Experimental and theoretical investigation on the sonic and subsonic ejectors with a converging-diverging diffuser was carried out. Numerical simulation was adopted for an optimal geometry design and satisfying the required performance. Also, some ejectors with a various of nozzle throat and mixing chamber diameter were manufactured precisely and tested for the comparison with the calculation results.