• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.23 no.2
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• pp.40-40
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• 1987

In order to examine the flow motion in a combustion chamber of a motored diesel engine, the variation of instantaneous are velocity at a fixed point in combustion chamber was measured by the constant temperature hot wire anemometer, varing engine speed, shroud shape and shroud position. The results are summerized as follows: 1. The variation of air velocity in a combustion chamber is closely related with the valve timing and piston velocity. 2. The air velocity in the cylinder at suction stroke is being increased and maximized at 60° ABDC in compression stroke and then decreased at the e.v.o. in expansion stroke. 3. The mean velocity using shroud valve was less than no shroud valve. However the turbulent intensity using shroud valve was larger than no shroud valve. 4. The turbulent intensity with 90°shroud valve was larger than that of 120°shroud valve, and 90°shroud valve at 180°shroud position had the largest turbulent intensity.

• The KSFM Journal of Fluid Machinery
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• v.4 no.1 s.10
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• pp.7-13
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• 2001

In developing a multistage compressor, the stage matching is one of the critical design issues. The mismatching can be often observed even if each stage has been proven good and then used as part of a compression system. A good matching among the stages can be achieved by changing various design parameters (i.e., passage cross sectional areas, blades angles, stagger angles, curvature, solidity, etc.). Therefore, designers need to find out what parameters must be changed and how much. In this study, a method to search the design parameters for optimum stage matching has been used based on an 1-D mathematical model of a compressor, which uses the data obtained from the preliminary test to identify the design parameters. This methodology is applied with a two-stage axial compressor, which was originally designed for a helicopter gas turbine engine. After identifying design parameters using preliminary test data, an optimization process has been employed to achieve the best matching between the stages (i.e., maximum efficiency of the compressor at its operation modes within a given range of the rotor speed under given restrictions for required stall margins and mass flow). 3-D flow calculations have been performed to confirm the usefulness of the corrections based on the 1-D mathematical model. Calculational results agree well with the experimental data in view of the performance characteristics. Some promising results were produced through the methodology proposed in this paper in conjunction with flow calculations.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.10
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• pp.1824-1832
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• 1992

This study investigated the compressive Young's modulus and the impactinduced damage of CFRP angle-ply laminate under same impact energy condition. The specimens of angle-ply laminate composites [0.deg.$_{6}$/ .theta..deg.$_{10}$/ 0.deg.$_{6}$] with .theta..deg. =30.deg., 45.deg., 60.deg. and 90.deg. were employed, and damaged by steel balls of diameter of 5mm and 10mm propelled by air gun type impact testing machine. The impact damaged zones were observed through a scanning acoustic microscope(SAM), and their cross-sections were observed through a scanning electron microscope(SEM). The compressive Young's moduli before and after impact were measured, and compared with the theoretical values calculated. The results obtained were as follows: (1) The damage areas on the interfacial boundaries showed more severe change on the back side interface than on the impact side interface with increasing ply-angle. (2) The damage areas on the interfacial boundaries became larger with increasing impact velocity or ply-angle. (3) The impact damaged zone showed the delamination on the interfacial boundaries and transverse cracks inside laminas. (4) The impact damaged zone was affected by the impactor size and speed or ply-angle under same impact energy condition. (5) Compressive Young's moduli before and after impact were lower than theoretical value, but showed a similar change according to ply-angle. (6) Compressive Young's moduli after impact were higher than those before impact, but there was no remarkable change in apparent compressive modulus after impact.t.act.

• Transactions of the Korean Society of Automotive Engineers
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• v.19 no.4
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• pp.78-83
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• 2011

Natural gas is one of the most promising alternatives to gasoline and diesel fuels because of its high thermal efficiency and lower harmful emissions, including $CO_2$. Although the high octane value of natural gas increases engine output and efficiency due to the high compression ratio, this fuel is prone to such difficulties as a narrow limit of inflammability and a slow combustion speed in the lean burn operation domain, leading to unstable combustion and higher emissions of harmful exhaust gases. Hydrogen blended with natural gas can extend the lean burn limit while maintaining stable, efficient combustion and achieving lower NOx, hydrocarbon and green house gas emissions. In this study, the effect of hydrogen addition on an engine performance and NOx emission characteristics was investigated in a heavy duty natural gas engine. The results showed that thermal efficiency was increased and NOx emissions were reduced due to the expansion of lean operation range under stable operation. NOx emission can be significantly reduced with the retard of spark advance timing.

• Korean Journal of Materials Research
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• v.20 no.11
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• pp.559-569
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• 2010

The liquid-phase sintering method was used to prepare a glass lens forming core composed of SiC-$Al_2O_3-Y_2O_3$. Spark plasma sintering was used to obtain dense sintered bodies. The sintering characteristics of different SiC sources and compositions of additives were studied. Results revealed that, owing to its initial larger surface area, $\alpha$-SiC offers sinterability that is superior to that of $\beta$-SiC. A maximum density of $3.32\;g/cm^3$ (theoretical density [TD] of 99.7%) was obtained in $\alpha$-SiC-10 wt% ($6Al_2O_3-4Y_2O_3$) sintered at $1850^{\circ}C$ without high-energy ball milling. The maximum hardness and compression stress of the sintered body reached 2870 Hv and 1110 MPa, respectively. The optimum ultra-precision machining parameters were a grinding speed of 1243 m/min, work spindle rotation rate of 100 rpm, feed rate of 0.5 mm/min, and depth of cut of $0.2\;{\mu}m$. The surface roughnesses of the thus prepared final products were Ra = 4.3 nm and Rt = 55.3 nm for the aspheric lens forming core and Ra = 4.4 nm and Rt = 41.9 for the spherical lens forming core. These values were found to be sufficiently low, and the cores showed good compatibility between SiC and the diamond-like carbon (DLC) coating material. Thus, these glass lens forming cores have great potential for application in the lens industry.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.5 s.122
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• pp.456-463
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• 2007

It is important to improve the initial launch conditions of golf ball at impact between golf club and ball to get a long flight distance. The flight distance is greatly influenced by the initial launch conditions such as ball speed, launch angle and back spin rate. It is also important to analyze the mechanism of ball spin to improve the initial conditions of golf ball. Back spin rate is created by the contact time and force. Previous studies showed that the contact force is determined as the resultant force of the reaction forces normal and tangential to the club face at the contact point. The normal force causes the compression and restitution of ball, and the tangential force creates the spin. Especially, the tangential force is known to take either positive or negative values as the ball rolls and slides along the club face during impact. Although the positive and negative tangential forces are known to create and reduce the back spin rate, respectively, the mechanism of ball spin creation has not yet been discussed in detail in the literature. In this paper, the influence of the contact force between golf club and ball is investigated to analyze the mechanism of impact. For this purpose, the contact force and time at impact between golf club head and ball are computed using FEM and compared with previous results. In addition, we investigate the impact phenomenon between golf club head and ball by FEM and clarify the mechanism of ball spin creation accurately, particularly focusing on the effect of negative tangential force on ball spin rate.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.1017-1022
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• 2007

It is important to improve the initial launch conditions of golf ball at impact between golf club and ball to get a long flight distance. The flight distance is greatly influenced by the initial launch conditions such as ball speed, launch angle and back spin rate. It is also important to analyze the mechanism of ball spin to improve the initial conditions of golf ball. Back spin rate is created by the contact time and force. Previous studies showed that the contact force is determined as the resultant force of the reaction forces normal and tangential to the club face at the contact point. The normal force causes the compression and restitution of ball, and the tangential force creates the spin. Especially, the tangential force is known to take either positive or negative values as the ball rolls and slides along the club face during impact. Although the positive and negative tangential forces are known to create and reduce the back spin rate, respectively, the mechanism of ball spin creation has not yet been discussed in detail in the literature. In this paper, the influence of the contact force between golf club and ball is investigated to analyze the mechanism of impact. For this purpose, the contact force and time at impact between golf club head and ball are computed using FEM and compared with previous results. In addition, we investigate the impact phenomenon between golf club head and ball by FEM and clarify the mechanism of ball spin creation accurately, particularly focusing on the effect of negative tangential force on ball spin rate.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.7
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• pp.552-560
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• 2014

Pulse Detonation Engine(PDE) has been investigated as a next generation propulsion system with the advantages of the higher thermal efficiency by the compression effect and the wide operation ranges from zero speed at ground. In the present study, an efficient theoretical PDE performance prediction program was developed for realistic propellants based on the Endo's theory combining the Chapman-Jouguet detonation theory and expansion process of burnt gas in a constant area tube. The program was validated through the comparison with the experimental data obtained by a ballistic pendulum measurement. PDE performance analyses were carried out for various hydrocarbon fuels and oxidizer compositions by changing the mixture equivalence ratio and initial conditions. Theoretical PDE performance database could be established as a result of the analyses.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.12
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• pp.1031-1038
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• 2017

In order to improve the performance of the air breathing engines, it is important to maximize the total pressure recovery through air intake. In this study, we investigated whether the Oswatitsch method, which guarantees the maximum pressure recovery for supersonic intake, is effective at hypersonic speed by compressing the intake air with the same intensity at each ramp. The non-linearity of the shock wave normal Mach number at each ramp stage was analyzed by comparing the compression ramp angle and the number of ramp to the inflow Mach number in terms of compressible thermodynamics and the operation limits of the inlet. Based on this analysis, the Oswaitisch technique yields valid conditions not only in supersonic but also hypersonic flight regime.

• Proceedings of the Korea Contents Association Conference
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• 2003.11a
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• pp.161-166
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• 2003

In this paper, we propose a novel method of design and implementation for the multimedia monitoring system using Web Camera. Recently WebCam is variously applied to many different areas and implemented as an improved performance using convenient functions of Web in this Internet era. Multimedia moving pictures has been popularly used in a variety of ways in different areas of monitoring systems in order to enhance the performance and the service with their data compression capability and the speed of the communication network these days. The design method of WebCam system presented in this paper might offer not only a convenient function of the monitoring system but great application capabilities. It can be used for a real time application of the multimedia picture and audio transmission so that the monitoring system can manage the security information in the sense for the reality. Tn addition, the monitoring system may be used as an inreal-time application using data storage and retrieval features of the Web. We offer both functions of monitoring in this structured form of implemented system.