• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2005.11a
• /
• pp.64-71
• /
• 2005

To achieve efficient supersonic combustion within a manageable length, a successful fuel injection scheme must provide rapid mixing between fuel and airstream. In former days, various injection concepts have been investigated. Cavity flow is the open type, that is, length-to-depth ratio L/D=4.8, aft ramp angle is $22.5^{\circ}$. An experimental study on a transverse cross jet injection into a Mach 1.92 supersonic main stream which flows over a cavity was carried out to investigate the effect of the momentum flux ratio(J), the jet interaction characteristics, and the pressure distribution in the combustor and using the primary diagnostics : schlieren visualization and wall static pressure measurements. Fuel penetration height and jet interaction characteristics depend strongly on the momentum flux ratio.

• The Bulletin of The Korean Astronomical Society
• /
• v.42 no.1
• /
• pp.42.1-42.1
• /
• 2017

We investigate the evolutionary properties of red supergiant stars (RSGs), using stellar evolution model of Modules for Experiments in Stellar Astrophysics (MESA). In this study, we calculate models with mass range of 9-39M_sun and several different convection parameters (e.g. mixing length, overshooting, and semiconvection) at SMC, LMC, Milky Way, and M31 metallicities. We compare the calculated evolutionary tracks with observed RSGs in SMC, LMC, Milky Way and M31, and discuss appropriate input physical parameters in model calculation. We find that a larger mixing length parameter is necessary for M31 metallicity to fit the positions of RSGs in H-R diagram, compared to lower metallicity environments. Theoretically predicted numbers of yellow supergiant stars (YSGs) are also compared with the observed population. We find that Ledoux models with semiconvection can better explain the number of YSGs. Finally, we investigate the final radius, final star mass, and final hydrogen envelope mass of RSGs and discussed the their properties as type II-P supernova progenitors.

• Journal of the Korean Geotechnical Society
• /
• v.19 no.4
• /
• pp.75-81
• /
• 2003

To investigate the reinforcing effect of subsurface layers of marine dredged clay(DMC) mixed with the micro-fiber(MF), a series of laboratory tests were performed on the DMC specimens with and without MF through uniaxial and triaxial compression tests. For the test programme, the elapsed time after dredging of marine clay, mixing rate and length of MF, and curing time of the composite were chosen as the important factors affecting the strength behaviour. The strength of the DMC mixed with MF and waste lime(WL) used for the admixture was found to be enhanced with the increasing content and length of MF, and with decreasing water content of DMC. MF and WL were applied as materials for trafficability improvement of the very soft reclaimed ground by DMC.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
• /
• 2003.11a
• /
• pp.56-63
• /
• 2003

Micro/nano adhesion and friction properties of mixed self-assembled monolayer (SAM) with different chain length for MEMS application were experimentally studied. Many kinds of SAM having different spacer chains(C6, C10 and C18) and their mixtures (1:1) were deposited onto Si-wafer, where the deposited SAM resulted in the hydrophobic nature. The adhesion and friction properties between tip and SAM surfaces under nano scale applied load were measured using an atomic force microscope (AFM) and micro scale applied load were measured using ball-on-flat type micro-tribotester. Surface roughness and water wetting angles were measured with SPM (scanning probe microscope) and contact anglemeter. Results showed that wetting angles of mixed SAMs showed the similar value of pure SAMs. The coating surface morphology was increased as mixing of SAM. Nano adhesion and nano friction decreased as increasing of the spacer chain length and mixing of SAM. Micro friction was decreased as increasing of the spacer chain, but micro friction of mixed SAM showed the value between pure SAMs. Nano adhesion and friction mechanism of mixed SAM was proposed in a view of stiffness of spacer chain modified chemically and topographically.

• Magazine of the Korean Society of Agricultural Engineers
• /
• v.34 no.2
• /
• pp.49-59
• /
• 1992

In our researches we made mix-design, with the mixing ratio and pre-cracked ratio of steel fibrous different from each other, building the steel fibrous concrete beam which had pre-cracks. To obtain the fracture characteristics of steel fibrous reinforced concrete, series of experiment were conducted on pre-cracked beam subjected to 3-point bending. Thus, we carried out experiments on the destructive characteristics of its pre-crack and post-crack and the result is as follows. 1. The compressive strength of steel fibrous concrete beam increased more slightly than plane beam, and the tensile strength increased 37%, 59%, 94% and 121% respectively when the amount of fibrous was 0.5%, 0.1% 1.5%, and 1.75% respectively. 2. As the amount of steel fibrous mixing increased ant the steel fibrous inhibited the crack growth, the crack condition of steel fibrous concrete beam was retarded irregularly, and this increased fracture load. 3. The defiance of destruction was reduced in the ratio of 1.35 times and 1.22 times respectively when the length of pre-crack was each 2cm and 4cm in comparison with the case of being without the length, and was similar to that of plane beam when the amount of steel fibrous mixing was below 1.0%, and increased linearly when it as above 1.0%. 4. The experimental formula seeking fracture energy was follows and thus we found that the value of fracture energy depended upon tensile strength and the size of speciment. $G_f=K\;{\cdot}\;f_f^'{\cdot}$da/Ec 5. We observed that in the load-strain curve of steel fibrous concrete beam the progress of the crack became slow, compared with plane beam because the crack condition became long to the extent of about 10 times. Concrete was faultiest brittleness fracture through the study, it was known ductile.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2001.11a
• /
• pp.853-858
• /
• 2001

The PSC bridge being built by ILM may have greater bending moment during its construction rather than after completion. When it occurs, Engineer should suggest to reduce stress-resultants than to make bigger cross-section with considering stability ,economics, and proper span-to-depth ratio. The used method is to install extruded nose at the end of girder. It substitutes the weighted segment for the light. From the reference, the stiffness of extruded nose, is 1/10 of the main girder, and the length is 60 to 70% of the length of the span, with little justification. In this study, the proper length and stiffness of the nose element is determined by the parametric study and idealizing procedure. The results about the extruded nose through the mixing of the parameter of its stiffness and length, the proper length of extruded nose is 80% of the longest span and the proper stiffenss is 13% of the bending stiffness of the superstructure and the proper length of extruded nose is 70% of the longest span and the proper stiffness is 9.5% of the bending stiffness of the superstructure.

• Journal of Korean Society for Atmospheric Environment
• /
• v.23 no.4
• /
• pp.430-439
• /
• 2007

The objective of this work is the air quality modeling according to the practical roughness length using the building information as surface boundary conditions. As accurate wind and temperature field are required to produce realistic urban air quality modeling, comparative simulations by various roughness length are discussed. The prognostic meteorological fields and air quality field over complex areas of Seoul, Korea are generated by the PSU/NCAR mesoscale model (MM5) and the Third Generation Community Multi-scale Air Quality Modeling System (Models-3/CMAQ), respectively. The simulated $O_3$ concentration on complex terrain and their interactions with the weak synoptic flow had relatively strong effects by the roughness length. A comparison of the three meteorological fields of respective roughness length reveals substantial localized differences in surface temperature and wind folds. Under these conditions, the ascended mixing height and weakened wind speed at night which induced the stable boundary stronger, and the difference of simulated $O_3$ concentration is $2{\sim}6\;ppb$.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.7 no.2
• /
• pp.62-69
• /
• 2003

Swirl injectors have the advantage of stable combustion, high efficiency, and insensibility to variable O/F ratio. Recess length is the length from outer orifice tip to inner orifice tip. It is the very important variable of performance of swirl type injector Recess length have influence on collision, mixing, spray, and combustion of propellants. This study investigated on the engine performance with the change of recess length through CFD, cold flow test, and combustion test. In result, we could confirm the change of engine performance with the change of recess length. And we found that performance forecast process through CFD, cold flow test is the right process through combustion test.

• Horticultural Science & Technology
• /
• v.35 no.3
• /
• pp.289-299
• /
• 2017

The objective of this study was to determine the effect of replacing perlite (PL) with pellets processed with poultry feather fiber as an inert material to prepare growing medium. The growth and flowering of Salvia splendens 'Vista Red' grown in individual growing medium $Biosangto^{(R)}$, peat moss (PM), PL, and two pellets (P45-1 and P45-2) were evaluated. Peat moss was mixed with PL, P45-1, or P45-2 at various ratios (1:0 to 1:3 or 3:1 by volume) to investigate the feasibility of replacing PL with pellets. Nutrient composition of the growing medium and leaf tissues was analyzed. The number of florets, inflorescence length, plant height, and fresh weight of plants grown in media containing P45-1 or P45-2 were reduced compared to those grown in individual growing medium PM or PL. As the mixing ratio of P45-1 or P45-2 to PM was higher, the growth of salvia, such as inflorescence length, plant height, number of leaves, and fresh weight was inhibited. Our results indicate that mixing three parts PM with one part of P45-1 (PM/P45-1/3:1) or P45-2 (PM/P45-2/3:1) accelerated flowering and increased the number of florets and leaves compared to other mixing ratios of PM and pellets media. The concentrations of phosphorus (P), calcium (Ca), boron (B), iron (Fe), and copper (Cu) in individual growing medium PL, P45-1, and P45-2 were significantly lower than those in PM. The concentration of N was the highest in leaves of plants grown in P45-1 or P45-2 amended media, and the concentrations of P, Ca, and zinc (Zn) in leaves were lower in individual growing medium P45-1 or P45-2 than in PM and PL. The pH of PM/P45-1/3:1 or PM/P45-2/3:1 media was maintained at optimal level (5.8-5.9) and the concentrations of macro- and micro-elements in the media and leaves were considered to be optimal levels. Therefore, mixing three parts PM with one part P45-1(PM:P45-1/3:1) or P45-2 (PM:P45-2/3:1) is recommended for improved growth and flowering in salvia. This suggests that P45-1 or P45-2 can replace PL as an inert material to prepare growing medium.

• 한국연소학회:학술대회논문집
• /
• 2003.12a
• /
• pp.131-136
• /
• 2003

Experimental study on combustion characteristics of double swirl coaxial injectors has been conducted for the assessment of critical design parameters of injectors. A subscale thrust chamber has been fabricated with a water-cooled copper nozzle, which allows a chamber to be reused without replacing parts. Two different designs of injectors have been tested for the understanding of the effects of recess length on combustion. Clearly, the recess length drastically affects the combustion efficiency and hydraulic characteristics of the injector. Internal mixing of propellants in the injector with the recess number of two increases a combustion efficiency and reveals sound combustion although a pressure drop required for the similar amount of mass flow rates increases compared with the injector of the recess number of one.