• Title/Summary/Keyword: stability limit velocity

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A Study on the Combustion Characteristics with Hydrogen Contents of SNG Fuel in Low-Swirl Combustor (저선회 연소기에서 합성천연가스(SNG) 연료의 수소함량에 따른 연소 특성 연구)

  • JEONG, HWANGHUI;KANG, KIJOONG;LEE, KEEMAN
    • Journal of Hydrogen and New Energy
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    • v.28 no.2
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    • pp.181-189
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    • 2017
  • This paper describes experimental results on combustion characteristics with hydrogen contents of synthetic natural gas (SNG) in low swirl combustor. To investigate the effect of hydrogen contents for premixed SNG flame, stability map, CH chemiluminescence images, flame spectrum analysis and emission performances were measured. In the results, as the hydrogen content was increased, the lean flammable limit was expanded and the flame length was decreased. The hydrogen contents affected the flame liftoff height, and it has different tendency according to the equivalence ratio and flame shape. The change of height and length of flame according to hydrogen contents is caused by the fast burning velocity of hydrogen, which can be confirmed by GRI 3.0 reaction mechanism in PREMIX code. The intensity of $OH^*$, $CH^*$ and $C_2^*$ was confirmed by spectrum analysis of flame. As a result, the $CH^*$ intensity was not significantly different according to hydrogen content. The increase of hydrogen contents influenced positively CO and NOx emission performances.

Low Pressure Firing Tests of 75-tonf-Class Channel Cooling Thrust Chamber (75톤급 채널냉각 연소기 저압연소시험)

  • Lim, Byoung-Jik;Han, Yeoung-Min;Kim, Jong-Gyu;Choi, Hwan-Seok
    • Journal of the Korean Society of Propulsion Engineers
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    • v.15 no.1
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    • pp.69-75
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    • 2011
  • Firing tests have been carried out for a technology demonstration model of 75-tonf-class combustor which is to be used on the liquid rocket engine of a Korean space launch vehicle. Firing tests were done at 50% of the nominal flow rate because of incapability of the test facility and limit of the test bed strength. Through the low pressure firing tests of 75-tonf-class channel cooling thrust chamber, operability and stability at the ignition and combustion phases were confirmed. Additionally it was foreseen that the 75-tonf-class thrust chamber would satisfy the performance requirements.

A Study on Self-excitation in Laminar Lifted Coflow-jet Flames (층류 동축류 제트 부상화염에서의 자기진동에 관한 연구)

  • Van, Kyu Ho;Lee, Won June;Park, Jeong;Kim, Tae Hyung;Park, Jong Ho
    • Journal of the Korean Society of Combustion
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    • v.20 no.1
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    • pp.43-51
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    • 2015
  • A study on laminar jet flames in coflow air diluted with helium has been conducted to investigate self-excitations for various propane mole fractions and nozzle exit velocities. The stability map was represented as a function of nozzle exit velocity and fuel mole fraction for propane. The results show that two types of self-excitation were observed : (1) buoyancy-driven self-excitation (hereafter called BDSE) and (2) Lewis-number induced-self-excitation coupled with (1) (hereafter called LCB) near extinction limit for 9.4 mm nozzle diameter. It was shown that with 0.95 mm nozzle diameter, Lewis-number-induced self-excitation (hereafter LISE) and BDSE could be separated. The differences between the two self-excitations were shown and discussed.

An Experimental Study on Combustion Instability in Model Gas Turbine Combustor using Simulated SNG Fuel (모사 SNG 연료를 적용한 모델 가스터빈 연소기의 연소 불안정성에 관한 실험적 연구)

  • Choi, Inchan;Lee, Keeman
    • Journal of the Korean Society of Combustion
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    • v.20 no.1
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    • pp.32-42
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    • 2015
  • The combustion instability was experimentally investigated in model gas turbine combustor with dual swirl burner. When such instability occurs, a strong coupling between pressure oscillation and unsteady heat release excites a self-sustained acoustic wave which results in a loud sound, and can even cause fatal damage to the combustor and entire system. In present study, to understand the combustion instability with a premixed mixture, the detailed periods of pressure and heat release data in unstable flame mode were investigated by various measurement methods at relatively rich condition and lean condition near flammable limits. Also, to prepare the utilization of synthetic natural gas (SNG) fuel in gas turbine system, an investigation was conducted using a simulated SNG including methane as a reference fuel to examine the effects of $H_2$ content on flame stability. These results provide that the instability due to flash-back behaviour like CIVB phenomenon occurred at rich condition, while the repetition of relighting and extinction caused the oscillation of lean condition near flammable limit. From the analysis of $H_2$ content effects, it is also confirmed that the instability frequency is proportional to the laminar burning velocity at both rich and lean condition.

Effects of the Differences in Shoe Heel-height on Balanced Performances (구두 굽 높이의 차이가 균형 수행능력에 미치는 영향)

  • Lee Geon-Cheol;Jeong Hye-MI;Kim Sang-Beom;Kwak Hyun
    • The Journal of Korean Physical Therapy
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    • v.16 no.3
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    • pp.112-124
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    • 2004
  • Purpose : The purpose of this study is to research the effects of the differences in shoe heel height on balanced performances with a balance master. Method : 40 healthy female adults were divided into 2 groups at random. All the female participants were tested by a balance master system. Differences were analyzed according to high heel shoes and low heel shoes. The ability of static postural balance control was measured by modified CTSIB and unilateral stance test, while that of dynamic postural balance control was measured by LOS (limit of stability) and rhythmic weight shift, among the programs of a balance master. Result : 1. There is no significant correlation between the ability of static and dynamic postural balance control before main test without the shoes. 2. Movement velocity and directional control ability were significant correlation compared result of in high heel shoes and low heel shoes group. Conclusion : In conclusion, the test results of the high heeled shoe group and the low heeled shoe group through a balance master system showed that the former one is inferior to the latter one.

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Low Pressure Firing Tests of 75-tonf-Class Channel Cooling Thrust Chamber (75톤급 채널냉각 연소기 저압연소시험)

  • Lim, Byoung-Jik;Han, Yeoung-Min;Kim, Jong-Gyu;Seo, Seong-Hyeon;Ahn, Kyu-Bok;Kim, Mun-Ki;Lee, Kwang-Jin;Choi, Hwan-Seok
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2010.05a
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    • pp.71-74
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    • 2010
  • Using the technology demonstration model of 75-tonf-class combustor which is expected to be used to the rocket engine of a korean space launch vehicle, 2 times of firing tests were carried out. Firing tests were done at 50% of the nominal flow rate because of incapability of the test facility and limit of the test bed strength. Through the low pressure firing tests of 75-tonf-class channel cooling thrust chamber, reliability and stability at the ignition and combustion phases were confirmed. Additionally it was foreseen that the 75-tonf-class thrust chamber would satisfy the performance requirements.

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An Experimental Study on Performance and Emission Characteristics of Hydrogen Mixtures in a CNG Engine (CNG 기관의 수소혼합률 변화에 따른 성능 및 배출가스 특성에 관한 실험적 연구)

  • KIM, INGU;SON, JIHWAN;KIM, JOUNGHWA;KIM, SUNMOON;KIM, JEONGSOO;LEE, SEANGWOCK
    • Journal of Hydrogen and New Energy
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    • v.27 no.4
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    • pp.357-364
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    • 2016
  • Recently, the world faces the environmental problem such as air pollution due to harmful gas discharged from car and abnormal climate due to the green-house gases increased by the discharge of $CO_2$. Compressed Natural Gas (CNG), one of alternative for this problem, is less harmful, compared to the existing fossil fuel, as gaseous fuel, and less carbon in fuel ingredients and carbon dioxide generation rate relatively favorable more than the existing fuel. However, CNG fuel has the weakness of slow flame propagation speed and difficult fast burn. On the other hand, hydrogen does not include carbon in fuel ingredients, and does not discharge harmful gas such as CO and HC. Moreover, it has strength of quick burning velocity and ignition is possible with small ignition energy source and it's has wide Lean Flammability Limit. If using this hydrogen with CNG fuel, the characteristics of output and discharge gas is improved by the mixer's burning velocity improved, and, at the same time, is possible to have stable lean combustion with the reduction of $CO_2$ expected. Therefore, this research tries to identify the characteristics of engine and emission gas when mixing CNG fuel and hydrogen in each portion and burning them in spark igniting engine, and grasp the combustion stability and emission gas characteristics according and use it as the basic data of hydrogen-CNG premixed engine.

Vibration testing using the movement of a 60ton crane for the evaluation the stability of nearby stone cultural heritage. (60톤 크레인의 주행 진동 실험을 통한 인접 석조 문화재의 안정성 평가)

  • Lee, Ga-Yoon;Ra, Young-Eun;Lee, Jong-Hak;Lee, Sung-Min;Lee, Kihak
    • Journal of Korean Association for Spatial Structures
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    • v.24 no.1
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    • pp.47-55
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    • 2024
  • The aim of this study is to evaluate the possibility of damage to cultural assets resulting from vibrations generated by construction vehicle traffic. The cultural heritage's natural vibration frequency was determined to be 150Hz by measurement. The damping ratios were calculated as 4.7% using the logarithmic decrement approach and 4.3% using the half-power method. The vibration measurements obtained during vehicle operation indicated that, despite an increase in vehicle velocity of up to 15 km/h, the vibrations remained below the detectable level of 0.13 mm/sec. When the road is curved and the terrain is sloped, a suitable speed for vehicle operation was found to be around 17 km/h, at which point vibrations were seen. The highest recorded vibration amplitude at this velocity was 0.217 mm/sec, which remains below the stringent regulation limit of 2 mm/sec. Thus, it can be concluded that there is no actual harm caused by vibrations.

Finite element modeling of high Deborah number planar contraction flows with rational function interpolation of the Leonov model

  • Youngdon Kwon;Kim, See-Jo;Kim, Seki
    • Korea-Australia Rheology Journal
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    • v.15 no.3
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    • pp.131-150
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    • 2003
  • A new numerical algorithm of finite element methods is presented to solve high Deborah number flow problems with geometric singularities. The steady inertialess planar 4 : 1 contraction flow is chosen for its test. As a viscoelastic constitutive equation, we have applied the globally stable (dissipative and Hadamard stable) Leonov model that can also properly accommodate important nonlinear viscoelastic phenomena. The streamline upwinding method with discrete elastic-viscous stress splitting is incorporated. New interpolation functions classified as rational interpolation, an alternative formalism to enhance numerical convergence at high Deborah number, are implemented not for the whole set of finite elements but for a few elements attached to the entrance comer, where stress singularity seems to exist. The rational interpolation scheme contains one arbitrary parameter b that controls the singular behavior of the rational functions, and its value is specified to yield the best stabilization effect. The new interpolation method raises the limit of Deborah number by 2∼5 times. Therefore on average, we can obtain convergent solution up to the Deborah number of 200 for which the comer vortex size reaches 1.6 times of the half width of the upstream reservoir. Examining spatial violation of the positive definiteness of the elastic strain tensor, we conjecture that the stabilization effect results from the peculiar behavior of rational functions identified as steep gradient on one domain boundary and linear slope on the other. Whereas the rational interpolation of both elastic strain and velocity distorts solutions significantly, it is shown that the variation of solutions incurred by rational interpolation only of the elastic strain is almost negligible. It is also verified that the rational interpolation deteriorates speed of convergence with respect to mesh refinement.

Rock Mass Stability of the Buddha Statue on a Rock Cliff using Fracture Characteristics and Geological Face-Mapping (마애불 암반의 단열특성과 지질맵핑을 이용한 안정성 해석)

  • Ihm, Myeong Hyeok
    • The Journal of the Convergence on Culture Technology
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    • v.9 no.1
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    • pp.539-544
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    • 2023
  • The subject of this study is the Maae Buddha statue in granodiorite of the Mesozoic Cretaceous period, which is concerned about stability as a standing stone cultural property located in ◯◯-dong, Gyeongsangbuk-do. For stability analysis, three-dimensional face mapping, geological properties of joints, three-dimensional scanning, ultrasonic velocity, polarization microscopy, electron microscopy analysis and XRD analysis were performed. In addition, the safety factor of the Maaebul was calculated by analyzing the damage status investigation, stereographic projection analysis, rock classification, and limit equilibrium analysis. The types and scales of damage and possible collapse by section depend on the degree of weathering of the rock and the orientation and characteristics of the joints, but wedge-failure and toppling-failure are expected to be small-scale. The safety factor of Maaebul in dry and wet conditions is less than 1.2, so stability is concerned. The types of damage were mainly observed, such as exfoliation, cracking, granular decomposition, and vegetation growth. The Maaebul rock is granodiorite, and the surface discoloration materials are K, Fe, and Mg. The 4 sets of joints are developed, J1 is tensile joint and the others are shear joint. The uniaxial compressive strength estimated by ultrasonic exploration is 514kgf/cm2, which corresponds to most soft rocks and some weathered rocks. Rock classification(RMR) is estimated to be grade 5, very poor rock mass. These technique along with the existing methods of safety diagnosis of cultural properties are expected to be a reasonable tool for objective interpretation and stability review of stone cultural properties.