• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.3
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• pp.834-845
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• 1995

An experimental study is made in a nearly two-dimensional 90.deg. curved duct to investigate the effects of interaction between streamline curvature and mean strain on turbulence. The initial shear at the entrance to the curved duct is varied by an upstream shear generator to produce five different shear conditions ; a uniform flow (UF), a positive weak shear (PW), a positive strong shear(PS), a negative weak shear (NW) and a negative strong shear(NS). With the mean field data of the case UF, variations of the momentum thickness, the shape factor and the skin friction over the convex(inner) surface and the concave (outer) surface are scrutinized quantitatively in-depth. It is found that, while the pressure loss due to curvature is insensitive to the inlet shear rates, the distributions of wall static pressure along both convex and concave surfaces are much influenced by the inlet shear rates.

• Journal of Mechanical Science and Technology
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• v.15 no.1
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• pp.117-124
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• 2001

This paper presents turbulent characteristics of an impinging F-O-O-F type injector in which fuel ad oxidizer impinge on each other to atomize under the different momentum ratio. Water was used as an inert simulant liquid instead of fuel and oxidizer. The droplet size and velocity in the impinging spray flow field were measured using a PDPA. The gradient of the spray half-width(b$_2$) along the long-axis direction declined throughout the entire spray flow field with increasing the momentum ratio from 1.19 to 6.48. However, the gradient of the half-width(b$_1$) along the short-axis direction decreased with increasing the momentum ratio. The turbulence intensity and turbulent kinetic energy were converged into the center of the center of the initial region with increasing the momentum ratio. As the momentum ratio increased from MR=1.19 to MR=6.48, the turbulent shear stress decreased. The results of this study can be used for the design of an impinging type injector for liquid rackets.

• 한국전산유체공학회:학술대회논문집
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• 2002.10a
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• pp.133-138
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• 2002

A 3-D axisymmetric computer program is developed to predict the NO behavior in SNCR system for the stoker incinerator with the waste treatment capacity, 200ton/day. To this end a turbulent reacting flow field calculation is made using proper assumption and empiricism. The stoker bed is assumed to be a homogeneous waste-volatilized gaseous state. The initial composition or reactants are assumed based on the data of the ultimate analysis. Turbulent is resolved by k-e model and turbulent reaction is handled by eddy-breakup model harmonized with empirical chemistry data for gaseous combustion, NO and urea reaction. The liquid droplet is traced by Lagrangian method incorporated by aerodynamic drag, Coriolis and crntrifugal forces. Radiation is treated by sensible heat loss model. Calculation results are in good agreement with experimental data at the outlet of post combustion chamber in Daejon 4th industrial complex. The flue gas shows the temperature range of $900\sim1000^{\circ}C$, velocity of 5m/s and NO concentration of 140ppm at the exit while the measured temperature, flue gas velocity and NO concentration are $967^{\circ}C$, $3\sim4m/s$ and $100\sim200ppm$respectively. Using the developed computer program a parametric study has been made with the variation of heat content of waste, castable length and SNCR variables for the determination of proper injector location. In general, the calculated results are consistent and physically acceptable.

• Geomechanics and Engineering
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• v.29 no.4
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• pp.391-405
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• 2022

A newly proposed grouting simulation method, the sequential diffusion solidification method was introduced into the numerical simulation of combined bi-borehole grouting. The traditional, critical and difficult numerical problem for the temporal and spatial variation simulation of the slurry is solved. Thus, numerical simulation of grouting and blocking of flowing water in karst conduits is realized and the mechanism understanding of the combined bi-borehole technology is promoted. The sensitivity analysis of the influence factors of combined bi-borehole grouting was investigated. Through orthogonal experiment, the influences of proximal and distal slurry properties, the initial flow velocity of the conduit and the proximal and distal slurry injection rate on the blocking efficiency are compared. The velocity variation, pressure variation and slurry deposition phenomenon were monitored, and the flow field characteristics and slurry outflow behavior were analyzed. The interaction mechanism between the proximal and distal slurries in the combined bi-borehole grouting is revealed. The results show that, under the orthogonal experiment conditions, the slurry injection rate has the greatest impact on blocking. With a constant slurry injection rate, the blocking efficiency can be increased by more than 30% when using slurry with weak time-dependent viscosity behavior in the distal borehole and slurry with strong time-dependent viscosity behavior in the proximal borehole respectively. According to the results of numerical simulation, the grouting scheme of "intercept the flow from the proximal borehole by quick-setting slurry, and grout cement slurry from the distal borehole" is put forward and successfully applied to the water inflow treatment project of China Resources Cement (Pingnan) Limestone Mine.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.1C
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• pp.1-5
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• 2010

The river maintenance processing has revealed that the river beds in Korea have been significantly polluted in various ways for the last two decades. Thus, the dredging, transportation and landfilling of these contaminated materials are attracting public attention these days. In this study, electrokinetic method was applied in order to accelerate the settling processes of clay particles in suspension and evaluate the factors affecting the settling behaviour. It has been found from the testing results that the settling velocity under the influence of electrokinetics was much faster than the gravitational one, and the water content of slurry soil reduced significantly after the electrokinetic processing. The initial water content of slurry soil should be one of the important factors affecting the settling behaviour as well as variation of water content, and hence the electrokinetic processing would be the cost-effective method for the field application.

• Journal of Korean Tunnelling and Underground Space Association
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• v.11 no.4
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• pp.411-417
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• 2009

The thermo-flow field in road tunnel is influenced by some facts such as piston effect of vehicle's move, operation of ventilation facilities, natural wind and buoyancy effect of fire plume. Among those, piston effect is one of primary causes for formation of air flow in road tunnel and has an effect on initial direction of smoke flow in tunnel fire. In this study to analyze the unsteady flow in the tunnel caused by the run of vehicle, the experimental study of vehicle-induced unsteady flow on a reduced-scale model tunnel is presented. While the three types of vehicle shape such as basic type of rectangular shape, diamond-head type and stair-tail type are changed, the pressure and air velocity variations with time are measured. The rising ratio of pressure and velocity are in order of "basic type of rectangular shape > stair-tail type > diamond-head type". The experimental results would be good data for development of a numerical method on the vehicle-induced unsteady tunnel flow.

• Journal of Astronomy and Space Sciences
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• v.34 no.2
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• pp.127-138
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• 2017

The current study designs the mission orbit of the lunar CubeSat spacecraft to measure the lunar local magnetic anomaly. To perform this mission, the CubeSat will impact the lunar surface over the Reiner Gamma swirl on the Moon. Orbit analyses are conducted comprising ${\Delta}V$ and error propagation analysis for the CubeSat mission orbit. First, three possible orbit scenarios are presented in terms of the CubeSat's impacting trajectories. For each scenario, it is important to achieve mission objectives with a minimum ${\Delta}V$ since the CubeSat is limited in size and cost. Therefore, the ${\Delta}V$ needed for the CubeSat to maneuver from the initial orbit toward the impacting trajectory is analyzed for each orbit scenario. In addition, error propagation analysis is performed for each scenario to evaluate how initial errors, such as position error, velocity error, and maneuver error, that occur when the CubeSat is separated from the lunar orbiter, eventually affect the final impact position. As a result, the current study adopts a CubeSat release from the circular orbit at 100 km altitude and an impact slope of $15^{\circ}$, among the possible impacting scenarios. For this scenario, the required ${\Delta}V$ is calculated as the result of the ${\Delta}V$ analysis. It can be used to practically make an estimate of this specific mission's fuel budget. In addition, the current study suggests error constraints for ${\Delta}V$ for the mission.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.66 no.2
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• pp.69-75
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• 2017

The gas turbine static starter rotates the stationary synchronous machine by the interaction of the rotor and the stator. The detection from the initial position of the rotor has been an important issue to drive with optimum torque. Previously, the gas turbine starter was used by attaching the encoder to the synchronous machine, but the position and velocity of the rotor have been estimated by sensor-less method until recently due to the difficulty in attaching and detaching and damage caused by the shaft voltage noise. In this paper, Rotor initial(stationary state) position estimation, forced commutation control(speed less than 10%), and natural commutation control(speed more than 10%) method using magnetic flux with integrated terminal voltage were presented and the sensor-less speed control performance was verified. As a result of making and evaluating the 29 kVA synchronous machine and the starting device, the performance of each control mode was satisfactory. Furthermore, the applied technology is expected to be used for the development of the gas turbine starter of tens of MW class and the field application.

• Journal of Institute of Control, Robotics and Systems
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• v.19 no.8
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• pp.702-708
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• 2013

Underwater TRN (Underwater Terrain Referenced Navigation) estimates an underwater vehicle state by measuring a distance between the vehicle and undersea terrain, and comparing it with the known terrain database. TRN belongs to absolute navigation methods, which are used to compensate a drift error of dead reckoning measurements such as IMU (Inertial Measurement Unit) or DVL (Doppler Velocity Log). However, underwater TRN is different to other absolute methods such as USBL (Ultra-Short Baseline) and LBL (Long Baseline), because TRN is independent of the external environment. As a magnetic-field-based navigation, TRN is a kind of geophysical navigation. This paper develops an EKF (Extended Kalman Filter) formulation for underwater TRN. A filter propagation part is composed by an inertial navigation system, and a filter update is executed with echo-sounder measurement. For large-initial-error cases, an adaptive EKF approach is also presented, to keep the filter be stable. At the end, simulation studies are given to verify the performance of the proposed TRN filter. With simplified sensor and terrain database models, the simulation results show that the underwater TRN could support conventional underwater navigation methods.

• Journal of Advanced Marine Engineering and Technology
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• v.32 no.8
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• pp.1221-1230
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• 2008

Inflatable rubber dams are used for controlling flood, impounding water for recreations, preventing beach erosions, diverting water for irrigations, and generating hydropower. They are long, flexible, inflated with air, cylindrical structures on a rigid horizontal foundation such as concrete. The dam is modeled as an elastic shell inflated with air. The mechanical behaviors of the inflated dam model were investigated by using the finite element method. The analysis process such as One Way Coupling Fluid-Structure Interaction consists of two steps. First, the influences of the fluid side were investigated, viz, the shape changes of the inflated rubber dam due to the fluid motions was captured when the height of the dam was 30cm with air pressure 0.01MPa, at which the pressure distributions over the surface of the dam were calculated. And next, the structural deformations were calculated using the pressure distributions. The initial inlet velocity for flow field was set to 0.1m/s. The structural deformation behaviors were investigated. The final research goal is to develop a Korean Inflatable Rubber Dam to be used for generating small hydropower.