• 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.

• Journal of International Academy of Physical Therapy Research
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• v.11 no.1
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• pp.1950-1953
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• 2020

Background: Ankle instability usually occurs after stroke, and contributes to unsafe walking and associated risk of falling in the affected patients. Objective: To investigate the effects of kinesiology taping (KT) on gait and balance ability (center of pressure, CoP) in patients with ankle instability after stroke. Design: One group, pre-post design. Methods: A total of 11 patients with ankle instability after stroke were enrolled. In all subjects, the gait and balance ability were assessed under 2 conditions: KT and barefoot. Gait and balance ability was assessed using GAITRite system and FDM-S platform. Results: Comparison between KT and barefoot condition, KT condition was significantly higher in velocity, cadence, step length, and stride length than barefoot condition (P<.05). KT condition was significantly lower in CoP path length and sway speed than barefoot condition (P<.05). Conclusion: KT indicated potential as a helpful method for walking and balancing ability in patients with ankle instability after stroke. Therefore, this study recommends KT as an option applicable to the stroke with ankle instability.

• Journal of the Korean Society of Combustion
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• v.7 no.1
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• pp.23-30
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• 2002

Instability of oblique detonation waves (ODW) at off-attaching condition was investigated through a series of numerical simulations. Two-dimensional wedge of finite length was considered in $H_2/O_2/N_2$ mixtures at superdetonative condition. Numerical simulation was carried out with a compressible fluid dynamics code and a detailed hydrogen-oxygen combustion mechanism. Present result reveals that there is a chemical kinetic limit of the ODW detachment, in addition to the theoretical limit predicted by Rankine-Hugoniot theory with equilibrium chemistry. Result also presents that ODW still attaches at a wedge as an oblique shock-induced flame showing periodically unstable motion, if the Rankine-Hugoniot limit of detachment is satisfied but the chemical kinetic limit is not. Mechanism of the periodic instability is considered as interactions of shock and reaction waves coupled with chemical kinetic effects. From the investigation of characteristic chemical time, condition of the periodic instability is identified as follows; at the detaching condition of the Rankine-Hugoniot theory, (1) flow residence time is smaller than the chemical characteristic time, behind the detached shock wave with heat addition, (2) flow residence time should be greater than the chemical characteristic time, behind an oblique shock wave without heat addition.

• Journal of the Korean Society of Safety
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• v.12 no.3
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• pp.52-59
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• 1997

Hill's anisotropy theory and isotropy theory under the deformed profile assumed two separate cases(that is circular and ellipitical) are applied to predict the plastic deformation characteristics of bulge, the strain and polar height under instability condition, using thin square diaphragms of stainless steel, mild steel, brass, copper and aluminum. In this study it was found that the pressure-polar height curves, and the polar height-the polar radius of curvature curve, under anisotropy theory and isotropy theory, assuming a circle profile, agree well with the experimental results, and the equivalent strains of the instability condition under anisotropy theory are better good agreement with the experimental results than those of the instability condition under isotropy theory. Beside, FLCo(plane Strain Intercept) obtained by Bethlehem FLC method and standard FLC method (modified) agree well with the experimental result.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2001.04a
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• pp.17-20
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• 2001

Combustion characteristics of KSR-III liquid rocket engine are investigated numerically in the standpoints of engine performance and acoustic instability. In the present calculation, engine performance for design and off-design conditions is estimated effectively with reasonable error. Numerical results of acoustic instability show that engine operation for the design condition has sufficient stability margin, but for a certain off-design condition, acoustic instability can be triggered by artificial pressure perturbation. The present results are in a good agreement with the available experimental results and can be adopted for the prediction of engine performance and stability, depending on the specific operating condition.

• Journal of Korean Association for Spatial Structures
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• v.14 no.1
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• pp.85-91
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• 2014

The purpose of this paper is to study comparative of dynamic instability characteristic of Geiger-typed cable dome structures by load condition, which is well-known among the cable dome structures that are the lightweight hybrid structure using compression and tension element continuously. Dynamic buckling process in the phase plane is very important thing for understanding why unstable phenomena are sensitively originated in nonlinear dynamic by various initial conditions. But there is no paper for the dynamic instability of hybrid cable dome by Sinusoidal Excitations, many papers which deal with the dynamic instability for shell-structures under the step load have been published. As a result of Geiger-typed cable dome, which shows chaotic behavior in dynamic nonlinear analysis with initial imperfection.

• Proceeding of KASS Symposium
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• 2008.05a
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• pp.80-85
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• 2008

This paper investigate the structure instability properties of the shelled space frame structure. The large structure must have thin thickness for build the large space structure there fore structure instability review is important when we do structural design. The structure instability of the shelled structure accept it sensitively by varied conditions. This come to a nonlinear problem with be concomitant large deformation. In this study, it is compared unstable behavior according to lode and boundary condition of the shelled space frame structure through numerical method which considered geometrical nonlinear and grasped influence for the instability phenomenon and investigated the fundamental collapse mechanism.

• The Journal of Korean Physical Therapy
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• v.31 no.4
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• pp.176-183
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• 2019

Purpose: The purpose of this study was to investigate the short term effects of ASEJ (ankle strengthening with emphasis on jumping) for 3weeks on strength, mechanical properties, and balance and to compare the balance with and without HH(high-heel) condition. Methods: ASEJ (a combined exercise of squat, heel raise up, and jumping) were performed for the subjects in 11 female ankle instability young females ($21.7{\pm}2.0yrs$ Cumberland ankle instability score $19{\pm}6.5$). To investigate the effect of ASEJ, investigator used dynamometer for measuring strength, MyotonPRO for measuring mechanical properties(tone, stiffness, and elasticity of the muscles), I-Balance test for static balance, and Y-balance test for dynamic balance between the condition with and without HH condition. All data were normally distributed and analyzed using the SPSS 22.0 statistical program. Comparing pre- and post-intervention and the condition with and without HH conditions data were examined using the paired t-test. The level of significance was chosen as 0.05 for all the analyses. Results: 3wks of ASEJ would strengthen leg muscles and increasing muscle tone and stiffness in most muscles however there was decreasing muscle elasticity of gastrocnemious. In addition, the ASEJ improves the static balance for ankle instability young females and increases the dynamic balance when wearing the heels especially. Conclusions: the ASEJ could recommend to improve the strength and balance for ankle instability young females. Also, measuring the balance with HH conditions well represents the risk of ankle damage in female.

• Journal of the Korean Society of Combustion
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• v.18 no.2
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• pp.42-50
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• 2013

Linear stability analysis of radiating counterflow diffusion flames is numerically conducted to examine the instability characteristics of cellular patterns. Lewis number is assumed to be 0.5 to consider diffusional-thermal instability. Near kinetic limit extinction regime, growth rates of disturbances always have real eigen-values and neutral stability condition of planar disturbances perfectly falls into quasi-steady extinction. Cellular instability of disturbance with transverse direction occurs just before steady extinction. However, near radiative limit extinction regime, the eigenvalues are complex and pulsating instability of planar disturbances appears prior to steady extinction. Cellular instability occurs before the onset of planar pulsating instability, which means the extension of flammability.

• Proceedings of the KSME Conference
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• 2001.06c
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• pp.311-315
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• 2001

In this paper synchronous whirl of bearing is employed as control algorithm of actively controlled hydrodynamic journal bearing to suppress the whirl instability and unbalance response of a rotor-bearing system. Also, the cavitation algorithm implementing the Jakobsson-Floberg-Olsson boundary condition is adopted to predict cavitation regions in the fluid film more accurately than conventional analysis which uses the Reynolds condition. The stability and unbalance responses of a rotor-bearing system are investigated for various control gain and phase difference between the bearing and journal motion. It is shown that the unbalance response of a rotor-bearing system can be greatly improved by synchronous whirl of the bearing, and there is an optimum phase difference, which gives the minimum unbalance response of the system, at given operating condition. It is also found that the speed at onset of instability can be greatly increased by synchronous whirl of the bearing.