This study experimentally validated the reliability of the lab-scale rock drill apparatus and investigated the effect of bit design factors on the performance of drilling. To test drilling efficiency of a drill bit, a testing system was designed and manufactured. Using the testing system, the drilling rates and specific energy of a conventional drill bit and newly proposed drill bit with different button arrangement were compared. The newly proposed model was tested to be superior in drilling performance than that of the conventional model. The testing system developed in this study could be used to predict and test the performance of newly developed drill bit models. Also, the system has to be improved further for measuring more accurate and quantitative data for future drill bit developments.

The purpose of this study was to collect the basic data on establishing the conservation plan for the domestic wetland through flora and life form analysis at Junam wetland. The vascular plants were recorded as 222 taxa; 58 families, 167 genera, 200 species, 3 subspecies, 1 forma and 18 varieties. Among 8 life forms, Therophytes (Th), Hemicryptophytes (H) and Hydrophytes (HH) showed high percentage, and these species comprised 71.1% of the whole flora at Junam wetland. One taxa (Euryale ferox) rare plants designated by Korea Forest Service were observed. The naturalized plants were 38 taxa including Fallopia dumetora, Oenothera odorata, Ambrosia artemisiifolia var. elatior and so forth, and naturalized ratio was 17.1%. The naturalized made up about 45 percent of the species composition. The specific plants by floristic region were 13 taxa including Euryale ferox., Hydrocharis dubia, Prunus davidiana and so forth.

A new circuit structure and control method for a high power interleaved dual-buck inverter are proposed. The proposed inverter consists of six switches, four diodes and two inductors, uses a dual-buck structure to eliminate zero-cross distortion, and operates in an interleaved mode to reduce the current stress of switch. To reduce the total harmonic distortion at low output power, the inverter is controlled using discontinuous-current-mode control combined with continuous-current-mode control. The experimental inverter had a power-conversion efficiency of 98.5% at output power = 1300 W and 98.3% at output power = 2 kW, when the inverter was operated at an input voltage of 400 VDC, output voltage of 220 VAC/60 Hz, and switching frequency of 20 kHz. The total harmonic distortion was < 0.66%, which demonstrates that the inverter is suitable for high-power dc-ac power conversion.

Coal fly ash waste from thermal power plants has recently been considered as a fill material for abandoned coal mine voids in Korea. A volume of fluid method, used in computational fluid dynamics, was adopted to simulate the process of coal ash injection into mine cavities. The difference in the filling efficiency of coal ash versus water using both upper and lower injection points was also investigated. Results show that use of a lower injection point more stably packed the cavity and provided a higher density of fill than use of an upper injection point. Thus, it would be better to place the nozzle of the injection pipe near the bottom of the mine cavity, below the groundwater level. NOMENCLATUREC ε 1 , C ε 2 , C ε 3 , C ε 4 = Coefficients of turbulent dissipation rate E i = Total energy f i = Body force vector (F int ) i = Internal forces (such as solid pressure force between particles) g = Gravity acceleration H i = Total enthalpy h i (T ij ) = Phase i enthalpy evaluated at the interface temperature T ij k = Turbulence kinetic energy k eff,i = Effective thermal conductivity M i = Interphase momentum transfer per unit volume m ij = Mass transfer rate from phase j to phase i (m ij ≥ 0) m ji = Mass transfer rate from phase i to phase j (m ji ≥ 0) p = Pressure, assumed to be equal in both phases Q ij = Interphase heat transfer rate from phase j to phase i Q i ij = Heat transfer rate from phase pair interface (ij) to phase i S u,i = Energy source S i α = Phase mass source term S i v = Phase momentum source term T i = Viscous stress tensor T i = Temperature of phase i u i = Fluctuant fluid velocity of i (i = x) u j = Fluctuant fluid velocity of j (j = y) v i = Velocity of phase i v g = Grid velocityGreek letters α i = Volume fraction of phase i ε = Turbulence dissipation rate µ t = Turbulence viscosity ρ i = Density of phase i ρ a = Density of air ρ w = Density of water ρ c = Density of coal ash σ k = Prandlt number of turbulence kinetic energy σ ε = Prandlt number of turbulence dissipation rate τ i and τ i t = Molecular and turbulent stresses, respectively