• Journal of the Korean Society of Propulsion Engineers
• /
• v.12 no.3
• /
• pp.49-59
• /
• 2008

In this study, the design method of a 155 mm Solid Fuel Ramjet projectile is proposed and a flight performance analysis program through mathematical modelling is developed. Through flight performance analysis, ramjet performance during flight, which is comprised of thrust, specific impulse, pressure recovery ratio, location of shock waves, and magnitude of drag, was predicted. The results show that compared to Rocket Assisted Projectile(RAP), the range was increased by 90 %. Furthermore, how variations in nozzle exit area ratio and the intake area cause variations in range was observed. This research on modeling and simulation methodology will provide useful data for future development of solid fuel ramjet projectiles.

• The Transactions of the Korean Institute of Electrical Engineers C
• /
• v.50 no.6
• /
• pp.288-295
• /
• 2001

Predischarges in nonuniform electric field stressed by lightning impulse voltagesin SF(sub)6-$N_2$mixtures are initiated by streamer coronas. Due to field ehnancement at a protrusion point of electrodes new ionization processes occur and a precursor, which leads to a first leader, is created. The leader proceeds step by step to the opposite electrode and the final jump bridges the test gap. It was found that the predischarge is propagated with a leader mechanism of stepwise expansion from the predischarge current waveforms measured by a shunt. The predischarge current is closely related to the amplitude and polarity of applied voltages, the gas pressure and the gap geometry. The time intervals between step leaders for the positive and negative polarities were inversely proportional to V.P$^2$. When the gas pressure increases in the positive polarity, statistical time lag to statistical time lag to streamer corona inception increase slightly, but the formative time lag to flashover is significantly decreased.

• Proceedings of the KIEE Conference
• /
• 2007.11a
• /
• pp.165-166
• /
• 2007

In these days $SF_6$ mixtures and alternative gas have been studied because of global warming and liquefying at low temperature and high pressure. At present work the breakdown characteristics of $SF_6/CF_4$ mixture in non-uniform field was performed. The experiments were carried out under positive and negative standard lightning impulse (SLT) voltages. The point-plane electrode was used with 3 mm gap distance in the test chamber. The $SF_6/CF_4$ mixture which contain 20% of $SF_6$ was compared with pure $SF_6$ and $CF_4$ gas. Experimental gas pressure ranged from 0.1 to 0.4 MPa. The breakdown voltage under negative SLI is higher than the breakdown voltage under positive voltage. And the breakdown voltage of $SF_6$ 20%, $CF_4$ 80% mixture is similar to that of pure $SF_6$.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.57 no.4
• /
• pp.635-640
• /
• 2008

New gas mixtures are now finding applications such as interrupting media for high-voltage circuit breakers. These mixtures consist of a high content of carbon tetrafluoride($CF_4$) added to sulfur hexafluoride($SF_6$). Nowdays $SF_6$ has been established for the use in gas insulated substations due to its high insulation withstand level and good arc quenching capability. At this paper Breakdown characteristics were investigated for $SF_6/CF_4$ mixtures when AC voltage and standard lightning impulse voltage(LI) was applied in a needle-plane electrodes. And partial discharge(PD) experiments were carried out in the test chamber which was made in needle-plane electrode. And ${\Phi}$-Q-N distribution of partial discharge signals was analyzed. The total pressure of the $SF_6/CF_4$ mixtures was varied within the range of 0.1-0.5 Mpa in the test chamber. The breakdown voltage in needle-plane electrode displayed N shape characteristics for increasing the content of $SF_6$ at positive impulse voltage and the PD inception voltage was increased slightly when pressure of $SF_6/CF_4$ Mixtures was increased. Maximum PD inception voltage is showed in 80% SF6/20%$CF_4$.

• Journal of Advanced Marine Engineering and Technology
• /
• v.37 no.8
• /
• pp.886-892
• /
• 2013

Hydraulic hose assemblies are used as piping components for construction machinery, automobile, aircraft, industrial machinery, machine tools, and machinery for ships. Then the reliability of hose assemblies is important because total hydraulic system, which used to deliver the fluid power ($P^*Q$) needed to flexibility in the piping system, is not operated if the hose assembly failed in the system. The data of the accelerated life test estimated through the shape parameter(${\beta}$) resulting of the Weibull distribution analysis. This study has tried to reduce the test time resulting from varying impulse pressure range and the flexing diameter. Accelerated life test model for the test results was adopted the GLL(generalized log linear) and the accelerated indexes are identified as 6.64 for the pressure and 4.46 for flexing radius. Also, it found that shape parameter is 6.19, scale parameter(${\eta}$) is $1.035{\times}108$, which were adopted the pressure 35 MPa and the flexing diameter R100 mm in the used condition.

• Journal of Applied Reliability
• /
• v.14 no.4
• /
• pp.243-247
• /
• 2014

The Spinal cage is the cage-shaped implantable medical device used to treat structural abnormalities caused by degenerative intervertebral disks. In order to secure enough space to provide the mechanical stability and the intervertebral fusion, after removing the intervertebral disc, the Spinal cage is transplanted between the intervertebral space. A hammer is used to push the spinal cage into a narrow space during the spinal cage transplant surgery. Due to the impact and pressure, damage occurs frequently on the spinal cage. In this study, a test model is constructed to measure the value of impulse generally applied on the Spinal cage. The figures of internal impulse before and after the improvement of the Spinal cage are then compared to suggest direction to improve the reliability of the spinal cage.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.61 no.10
• /
• pp.1471-1476
• /
• 2012

A study on the dielectric characteristics of the Glass Fiber Reinforced Plastic (GFRP) is important for designing a reliable high voltage superconducting machines such as transmission superconducting fault current limiters, superconducting cables, and superconducting transformers. In this paper, dielectric experiments of the GFRP under lightning impulse voltage are conducted in liquid nitrogen($LN_2$) according to various experimental conditions such as the thicknesses of the GFRP, the diameters of electrode systems and the pressures. The dielectric characteristics of the GFRP are analyzed by using a Finite Elements Method(FEM) according to various field utilization factors. It has been reported that the electrical insulation design of the GFRP would be conducted by considering the mean electric field intensity($E_{mean}$) distributed inside the GFRP. In this study, it is found that the dielectric performance of the GFRP could be explained by not only $E_{mean}$ but also the maximum electric field intensity ($E_{max}$). Finally, the empirical formulae of the GFRP to estimate an electrical breakdown voltage at sparkover under the lightning impulse condition are deduced. It is expected that the presented experimental results in this paper are helpful to design electrically reliable high voltage superconducting machines using the GFRP as an insulation material.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2011.11a
• /
• pp.116-121
• /
• 2011

Performance of Secondary Injection Thrust Vector Control system is investigated under various secondary injection operating conditions. 3-dimensional converging-diverging nozzle having 8 secondary injection nozzles is used in this numerical study. Total pressure of flow inside the nozzle is about 70bars, and total temperature set to 300K for cold flow simulation. Effect of secondary injection flow rate and injection nozzle configuration is considered in this research. Simulation is conducted with commercial CFD code Ansys Fluent v13. Spalart-Allmaras(1-equation)model is used for turbulence modeling with AUSM+ scheme. Various performance factors as Axial thrust, side force, system specific impulse ratio are considered and explained for system performance evaluation.

• 연구논문집
• /
• s.34
• /
• pp.79-85
• /
• 2004

There are several types of life test method for hose assemblies. The two major tests used for hose assemblies are impulse test and burst test. And magnification adjustment of impulse pressure, heating of testing oil and repetitive motions of bending and straightening of testing hose are also performed for accelerating the life. According to the manufacture process of hose and swaging process of fitting, there is a difference in the life of hose assemblies from minimum 7 times to maximum 40 times during the life test in the same functioning condition. Like this, the life test of hose which has a wide scope of life distribution gives a problem that observation should take a long time to find out the existence of the bursting from the beginning of the test to the completion of bursting of hose assemblies. Therefore, this research proposes a process of concentrating on the defective section of hose assemblies and maximizing the life acceleration by giving 'Knockdown stress' to hose assemblies just until before the hose assemblies get out of order.

• Journal of Electrical Engineering and Technology
• /
• v.10 no.3
• /
• pp.1181-1187
• /
• 2015

Sulfur hexafluoride (SF₆) gas is used widely in electric power equipment such as Gas Insulated Switchgear (GIS), Gas Insulation transmission Line (GIL), and Gas Circuit Breaker (GCB). But applications of SF₆ should be restricted because SF6 gas is one of the greenhouse effect gases. To reduce use of SF₆ gas, a study on eco-friendly alternative insulation medium is needed. In this paper, we investigated lightning impulse (LI) breakdown of dry-air which is attracting attention as an ecofriendly alternative gas and the LI breakdown of hybrid insulation combined with dry-air and solid insulation (Room-Temperature Vulcanizing Silicone Rubber-RTV SIR) and dry-air in inhomogeneous fields according to gap distance and pressure. The experiment results showed that the LI breakdown strength of hybrid insulation system was higher than that of dry-air insulation system. It was verified that the development of technology related to eco-friendly power apparatus compact such GIS, GCB and GIL can be used as basic research data.