• Journal of Aerospace System Engineering
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• v.18 no.3
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• pp.8-16
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• 2024

Because hydrogen has very low density, a different storage method is required to store the same amount of energy as fossil fuel. One way to increase the density of hydrogen is through liquefaction. However, since the liquefied temperature of hydrogen is extremely low at -252 ℃, it is easily vaporized by external heat input. When liquid hydrogen is vaporized, a self-pressurizing phenomenon occurs in which the pressure inside the hydrogen tank increases, so when designing the tank, this rising pressure must be carefully predicted. Therefore, in this paper, the internal pressure of a cryogenic liquid fuel tank was predicted according to the liquid hydrogen filling ratio. A one-dimensional thermodynamic model was applied to predict the pressure rise inside the tank. The thermodynamic model considered heat transfer, vaporization of liquid hydrogen, and fuel discharging. Finally, it was confirmed that there was a significant difference in pressure behavior and maximum rise pressure depending on the filling ratio of liquid hydrogen in the fuel tank.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2005.11a
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• pp.341-345
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• 2005

This paper is for the combustion characteristics of gas generator which drive 1.5MW-class turbo pump and runs in fuel-rich combustion regime with LOx/kerosene as propellant. The outline of development procedure of real scale high pressure gas generator is introduced and the relation between O/F ratio and outlet temperature and the molecular weight and specific heat ratio of combustion gas are described. The relation between O/F ratio and temperature is newly obtained at higher pressure and the molecular weight and specific heat ratio is modified and their validity is confirmed by the mass relation equation.

• Journal of computational fluids engineering
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• v.5 no.2
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• pp.38-46
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• 2000

It has been indicated that the rotor/stator interaction has distinct causes of unsteadiness, such as the viscous vortex shedding, wake/stator interaction and potential rotor/stator interaction. In this paper, the mechanism of unsteady potential interaction in one stage axial compressor is numerically investigated for blade row ratio 1:1 and 2:3 at design point and for blade row ratio 2:3 at off-design point in two-dimensional view point. The numerical technique used is the upwind scheme of Van-Leer's Flux Vector Splitting(FVS) and Cubic spline interpolation is applied on zonal interface. In this study the flow unsteadiness due to potential interaction are found to be larger in blade row ratio 2:3 than in 1:1. The total pressure rise in blade row ratio 2:3 is closer to the real value in design point than that in 1:1. The change of unsteady pressure amplitude according to the variation of stator exit pressure is very small.

• Coupled systems mechanics
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• v.7 no.4
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• pp.395-406
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• 2018

This paper proposes a linear damping model of tire-soil system using semi-empirical method. A test rig was designed and developed to measure the vertical equivalent linear damping ratio of tire only and tire-soil system using Free-Vibration Logarithmic Decay Method. The test was performed with two kinds of tractor tires using a combination of five inflation pressure levels, two soil depths and four soil moisture contents in the paddy soil. The results revealed that the linear damping ratio of tires increased with decreasing tire inflation pressure; the linear damping ratio of tire-soil system also increased with decreasing tire inflation pressure and increased with the increasing soil depth (observed at 80 and 120 mm). It also increased with a relative increase of soil moisture contents (observed at 37.9%, 48.8%, 66.7% and 77.4%). The results also indicated that the damping ratio of tire-soil system was higher than that of tire only. A linear damping model of tire-soil system is proposed as a damping model in parallel which is established based on experimental results and vibration theory. This model will have a great significance in study of tractor vibration.

• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.3
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• pp.172-178
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• 2008

An object of this study is to confirm performance characteristics of the vortex tube apparatus for substitution of the intercooler in a common-rail diesel engine. The turbo pressure, the intake air flow rate and the ${\Delta}T_c$ decrease ratio of the intercooler were measured in a experimental engine. The vortex tube apparatus was made after confirmation of the geometric phenomena in fundamental experiments. To investigate energy separation characteristics of the vortex tube, the measured turbo pressure was applied to the vortex tube inlet and the ${\Delta}T_c$ decrease ratio was compared with one of the intercooler in the cold air mass flow ratio similar to the intake air flow rate of the experimental engine. From the results, we found that the energy separation ratio is increased according to of the inlet pressure and the ${\Delta}T_c$ decrease ratio of the vortex tube apparatus is higher than one of the intercooler at low engine speed and engine load of medium and low.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.3 s.258
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• pp.264-272
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• 2007

The aim of this study is to investigate the effects of nozzle orifice shapes and the nozzle length-to-diameter ratio(L/D) on the nozzle cavitation formation inside the orifice and the external flow pattern. The nozzle used in this work was tested the taper orifice nozzle and the rectangular orifice nozzle which was made from the transparent acrylic acid resin. For studying the effect of the nozzle L/D ratio, it was used to three L/D ratios of 3.33, 10, and 20. The cavitation flow of nozzle was visualized by using the ICCD camera and optical system. This work revealed that the flow rate and discharge coefficient($C_d$) of the taper orifice nozzle was larger than those of the rectangular orifice nozzle at the same injection pressure. The cavitation flow was observed in the nozzle orifice at the low injection pressure and the breakup of liquid jet was promoted as the L/D ratio is decreased. The cavitation of biodiesel fuel was formed at the lower injection pressure than that of diesel fuel because of higher viscosity and density.

• Geomechanics and Engineering
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• v.38 no.2
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• pp.191-203
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• 2024

One of the issues with clayey soils, particularly those with significant quantities of organic matter, is the creep settling problem. Clay soils can be strengthened using a variety of techniques, one of which is the use of stone columns. Prior research involved foundation loading when the soil beds were ready and confined in one-dimensional consolidation chambers. In this study, a particular methodology is used to get around the model's frictional resistance issue. Initially, specimens were prepared via static compaction, and they were then re-consolidated inside a sizable triaxial cell while under isotropic pressure. With this configuration, the confining pressure can be adjusted, the pore water pressure beneath the foundation can be measured, and the spacemen's lateral border may be freely moved. This paper's important conclusions include the observation that secondary settlement declines with area replacement ratio. Because of the composite ground's increasing stiffness, the length to diameter ratio (l/d) and the stone column to sample height ratio (Hc/Hs) both increase. The degree of improvement varies from 12.4 to 55% according to area replacement ratio and (l/d) ratio.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.10
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• pp.1193-1201
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• 2004

The effect of equivalence ratio and fuel/air mixing quality on the phase-resolved gas temperatures at different phases of the oscillating pressure cycle was experimentally investigated. An atmospheric pressure, optically accessible and laboratory-scale dump combustor operating on methane with heat release rate of 1.59kW was used. Temperature measurements were made using coherent anti-Stokes Raman spectroscopy (CARS) at several spatial locations fur typical unstable combustion conditions. Analysis was conducted using parameters such as phase-resolved averaged temperature, normalized standard deviation and temperature probability distribution functions (PDFs). Also the probability on the occurrence of high temperature (over 1900K) was investigated to get the information on the perturbation of equivalence ratio and NOx emission characteristics. It was shown that most of temperature histograms exhibit Gaussian profile which has short breadth of temperature fluctuation at equivalence ratio of 0.6, while beta profile was predominant for the cases of other equivalence ratios (${\Phi}$=0.55, 0.50). It was also shown that phase-resolved averaged temperature oscillated in phase with pressure cycle, while normalized standard deviations which represent temporal turbulent intensity of temperature showed nearly constant value around 0.1. The characteristics on the occurrence of high temperature also displayed periodic wave form which was very similar to the pressure signal. And the amplitude of this profile went larger as the fuel/air mixing quality became poorer. These also provided additional information on the perturbation of equivalence ratio at flame as well as NOx emission characteristics.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.1458-1465
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• 2010

A lot of dredging and reclaming projects are recently under way in Korea for the efficient use of limiting land space. Saemanguem area is special case of reclaiming by dredged soil. In case of a confined disposal of dredged soils by a pump dredger, generally coarse grained soils are separated from fines with dropping at the near part of the pump dredger. This kind of seperation of fine contents could be a factor of liquefaction by earthquake. In Korea, recently, earthquakes with magnitude of 3.0 or higher are distinctively increasing in 1990. In this study, cyclic shear characterics of Saemanguem Dredged sand depending on fine content were analyzed. A series of undrained cyclic triaxial test with cyclic stress ratio ($\sigma_d/{2\sigma_{{\upsilon}c}}'$) were performed on both isotropic consolidated specimen and sand with fine contents of 0%, 5%, 15%, 30%, 40% under the effective vertical stress of 100kPa and 50% and 60%, 70% of relative density for fine content of 0%, respectively. In the test results, cyclic shear strength increased by increasing of cyclic stress ratio($\sigma_d/{2\sigma_{{\upsilon}c}}'$) with increasing the relative density at the same number of cyclic under the effective confining pressure of 100kPa. It is almost highest the double amplitude(DA) 1%, 3%, 5%, 7.5% and 10% at fine content of 15% between Cyclic stress ratio($\sigma_d/{2\sigma_{{\upsilon}c}}'$) value at cyclic number five and fine content. Number of cyclic is 30 under the effective vertical stress of 100kPa, 70% of relative density for fine content of 15%. when the cyclic stress ratio at each relative density was compared at cyclic number five, the double amplitude(DA) 1%, 3%, 5%, 7.5% and 10%, and the pore-pressure ratio (${\Delta}u/{\sigma'}_c$) 0.95 value were compared; under the relative density of 70% and the effective confining pressure of 100kPa. The pore-pressure ratio (${\Delta}u/{\sigma'}_c$) 0.95 value showed a similar trend to the double amplitude (DA) 5% line.

• Plant Journal
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• v.10 no.3
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• pp.39-44
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• 2014

The gas turbine thermal efficiency has been predicted when the compressor pressure ratio increases from the previously set 13.5. Thermal efficiency has been predicted from 14.2 up to 18.2 at which the turbine work reaches its maximum value on the assumption that isentropic efficiency of the compressor and the turbine are constant using the operating data at the pressure ratio of 13.5. 35.11% of thermal efficiency has been acquired by the performance test when the pressure ratio increased to 16.2 since replacing the compressor low pressure stages. It's been approved that predicting thermal efficiency using the operating data at the pressure ratio of 13.5 is useful within 7.86% of tolerance as the figure measured by the performance test.