• Journal of Ocean Engineering and Technology
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• v.35 no.1
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• pp.38-49
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• 2021

Slug flow is the most common multi-phase flow encountered in oil and gas industry. In this study, the hydrodynamic features of flow in pipes investigated numerically using computational fluid dynamic (CFD) simulations for the effect of slug flow on the vertical and bent pipeline. The compressible Reynold averaged Navier-Stokes (RANS) equation was used as the governing equation, with the volume of fluid (VOF) method to capture the outline of the bubble in a pipeline. The simulations were tested for the grid and time step convergence, and validated with the experimental and theoretical results for the main hydrodynamic characteristics of the Taylor bubble, i.e., bubble shape, terminal velocity of bubble, and the liquid film velocity. The slug flow was simulated with various air and water injection velocities in the pipeline. The simulations revealed the effect of slug flow as the pressure occurring in the wall of the pipeline. The peak pressure and pressure oscillations were observed, and those magnitudes and trends were compared with the change in air and water injection velocities. The mechanism of the peak pressures was studied in relation with the change in bubble length, and the maximum peak pressures were investigated for the different positions and velocities of the air and water in the pipeline. The pressure oscillations were investigated in comparison with the bubble length in the pipe and the oscillation was provided with the application of damping. The pressures were compared with the case of a bent pipe, and a 1.5 times higher pressures was observed due to the compression of the bubbles at the corner of the bent. These findings can be used as a basic data for further studies and designs on pipeline systems with multi-phase flow.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.18 no.7
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• pp.1036-1043
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• 1993

GaAs/AIGaAs resonant tunneling structures have been grown by atmospheric pressure MOCVD. Resonant tunneling diodes fabricated with the structure grown at 650t showed a high peak-to-valley (P/V) current ratio of 2.35 at room temperature. P/V current ratio increased to 15.3 at 77K. Numerically calculated peak current agrees well with the experimental result. Resonant tunneling diodes with AIGaAs as a barrier and InGaAs as a quantum well and a spacer layer yielded a high P/V current ratio of 4.0 and a peak current density of 8.6KA/c# at room temperature because of increased carrier supply.

• International Journal of High-Rise Buildings
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• v.2 no.3
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• pp.229-244
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• 2013

Twenty six pressure models of high rise buildings with various cross-sections including twisted models were tested in a boundary layer wind tunnel. The cross-sections were triangular, square, pentagon, hexagon, octagon, dodecagon, circular, and clover. This study investigates variations in peak pressures, and effects of various cross-sections and twist angles on peak pressures. To study the effects of various configurations and twist angles on peak pressures in detail, maximum positive and minimum negative peak pressures at each measurement point of the building for all wind directions are presented and discussed. The results show that peak pressures greatly depend on building cross-section and twist angle.

• 한국연소학회:학술대회논문집
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• 2012.11a
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• pp.61-62
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• 2012

The present study has numerically investigated the effects of fuel-side dilution and pressure on flame structure and extinction scalar dissipation rate of turbulent syngas nonpremixedd flames. Numerical results indicate that for highly diluted case, peak temperature is decreased and stoichiometric mixture fraction is increased. By decreasing the pressure and the nitrgen dilution levelcreased, the extinction scalar dissipation rate is increased.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.9
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• pp.911-917
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• 2015

The objective of this work focuses on the analysis of injection rate and macroscopic spray behavior characteristics with injection pressures as well as combustion and exhaust emission characteristics with injection timing and injection pressure by using a common rail single-cylinder diesel engine. The injection rate was measured by applying the Bosch method, and macroscopic spray behavior characteristics were analyzed with a constant-volume vessel and a high-speed camera. In addition, combustion and emission characteristics were analyzed in a common-rail single-cylinder diesel engine with precise control of fuel injection timing and pressure. For injection pressures of 30MPa and 50MPa, the injection rate was higher at 50 MPa, and the spray development (penetration) was also higher in the same elapsed time. The peak in-cylinder pressure and rate of heat release showed a tendency to decline as injection timing was delayed, and the peak in-cylinder pressure and rate of heat release were slightly higher for higher injection pressures. Higher injection pressures also reduced the mean effective pressure, while the indicated mean effective pressure and torque increased as injection timing was delayed to TDC. Nitrogen oxides had a peak level at injection timings of $BTDC20^{\circ}$(30MPa) and $BTDC15^{\circ}$(50MPa); carbon monoxide emissions were reduced by delaying injection timing from $BTDC30^{\circ}$.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.3
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• pp.1-7
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• 2002

An experimental study was conducted to investigate the effects of leading edge extension(LEX) on the surface prssure distribution over a delta wing in a subsonic wind tunnel. Freestream velocity was 40m/sec and Reynolds number per meter was 1.7x$10^6$ with total pressure of 101Pa and total temperature of 278K. LEX changed the surface pressure distribution on the wing dramatically. Comparing with the results without LEX, the peak of pressure distribution decreased on the front chordwise location but it turned to increase on the rear chordwise location with increase of the angle of attaci. The spanwise gradient of the pressure distribution also increased in the rear chordwise location. Without LEX, the peak of pressure distribution increased and decreased irregularly with increase of the angle of attack at each chordwise location, but LEX made it increased almost linearly with increase of the angle of attack at all of the chordwise locations.

• Journal of Energy Engineering
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• v.20 no.3
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• pp.178-184
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• 2011

Compressed Air Energy Storage (CAES) is a combination of energy storage and generation by storing compressed air using off-peak power for generation at times of peak demand. In general, both charging and discharging of high-pressure vessel are unsteady processes, where the pressure is varying. These varying conditions result in low efficiencies of compression and expansion. In this paper, a new constant-pressure CAES system to overcome the current problem is proposed. An energy analysis of the system based on the concept of exergy was performed to evaluate the energy density and efficiency of the system in comparison with the conventional CAES system. The new constant-pressure CAES system combined with pumped hydro storage requires the smaller cavern with only half of the storage volume for variable-pressure CAES and has a higher efficiency of system.

• Journal of Korean Association for Spatial Structures
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• v.9 no.4
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• pp.81-88
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• 2009

Damage on low?rise buildings caused by typhoons and storms is increasing every year. Thus, this study examined the distribution of wind pressure coefficient at each position according to the height of monosloped roof, and measured wind pressure coefficient according to tributary area and compared it with the current wind load standard. We analyzed six areas in order to analyze characteristics at each position of a half span roof, and found that the wind pressure coefficient was around 25% higher at the high comer (HC) than at the low corner (LC). The distribution pattern of peak pressure coefficient at each position was the same as the AIK load standard, but in the results of our experiment, wind pressure was around 40% lower than the load standard at HC and around 37% higher than the load standard at LC.

• Genomics & Informatics
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• v.8 no.3
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• pp.103-107
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• 2010

The imputation of untyped SNPs enables researchers to validate association findings across SNP arrays and also enables them to test a large number of SNPs to reveal the fine structure of the association peak, facilitating interpretation of the results and the location of causal polymorphisms. In this study, we applied the imputation method to a genomewide association study and recapitulated the previously associated gene loci of blood pressure traits in Korean cohorts. A total of 1,827,004 SNPs were imputed by the IMPUTE program, and we conducted a genomewide association study for systolic and diastolic blood pressure. While no SNPs passed the Bonferroni correction p-value (p=$2.74{\times}10^{-8}$ for 1,827,004 SNPs), 12 novel loci for systolic blood pressure and 16 novel loci for diastolic blood pressure were detected by imputed SNPs, with $10^{-5}$ < p-value < $10^{-4}$. Moreover, 7 regions (ATP2B1, 10p15.1, ARHGEF12, ALX4, LIPC, 7q31.1, and TCF7L2) out of 14 genetic loci that were previously reported revealed that the imputed SNPs had lower p-values than those of genotyped SNPs. Moreover, a nonsynonymous SNP in the CSMD1 gene, one of the 14 genes, was found to be associated with systolic blood pressure (p<0.05). These results suggest that the imputation method can facilitate the discovery of novel SNPs as well as enhance the fine structure of the association peak in the loci.

• Journal of The Korean Society of Agricultural Engineers
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• v.61 no.2
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• pp.13-23
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• 2019

In this study, an overtopping model experiments and three dimensional seepage characteristics at the deteriorated homogeneous reservoirs were performed to investigate the behavior of failure for embankment and spillway transitional zone due to overtopping. The failure pattern, pore water pressure, earth pressure and settlement by overtopping were compared and analyzed. The pattern of the failure by overtopping was gradually enlarged towards reservoirs crest from the spillway transition zone at initial stage. In the rapid stage and peak stage, the width and depth of failure gradually increased, and the pattern of the failure appeared irregular and several direction of the erosion. In the early stage, the pore water pressure at spillway transitional zone was more affected as its variation and failure width increased. In the peak stage, the pore water pressure was significantly increased in all locations due to the influence of seepage. The earth pressure increased gradually according to overtopping stage. The pore pressure by the numerical analysis was larger than the experimental value, and the analysis was more likely to increase steadily without any apparent variation. The horizontal and vertical displacements were the largest at the toe of slope and at the top of the dam crest, respectively. The results of this displacement distribution can be applied as a basis for determining the position of reinforcement at the downstream slope and the crest. The collapse in the overtopping stage began with erosion of the most vulnerable parts of the dam crest, and the embankment was completely collapsed as the overtopping stage increased.