• Journal of International Academy of Physical Therapy Research
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• v.6 no.2
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• pp.891-895
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• 2015

We investigated the effects of a Virtual reality(VR) program on the proprioception and instability of functional ankle instability(FAI) patients. Among the 20s old individuals who lived in Republic of Korea; 20 people were selected through a public participation process. The 20 participants were then randomly divided into two groups, one of strength exercise(n=10) and one of balance exercise(n=10). Of the patients who had experienced an ankle sprain in the past and currently felt ankle instability, those who recorded 24 points or less on the Cumberland ankle instability tool(CAIT) were determined to have FAI. We selected the strength exercise and balance exercise in the Nintendo Wii Fit Plus as a VR program. The subjects used the program on the Wii Balance Board three times per week for 20 minutes and total 10-minute warm-up and down for four weeks. Proprioception and CAIT of the balance exercise group were improved significantly after the exercise compared to before the exercise(p<.05). Authors recommend that the balance exercise in the VR program be used as an aid for physical therapeutic intervention.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.05a
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• pp.83-87
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• 2009

Ramjet engine is weak for low frequency combustion instability because of their long air flow passage. A model combustor which has fuel injector and V-gutter shaped flame holder was designed and fabricated in order to simulate a combustion mechanism of ramjet engine, and it could demonstrate combustion instability which might occur in ramjet combustor. The frequency of the instability was very similar to that of acoustic resonance frequency of combustor, and it proved that a typical combustion instability by thermo-acoustic coupling occurred.

• Journal of Communications and Networks
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• v.3 no.4
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• pp.342-350
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• 2001

The Internet routing instability, or the rapid fluctuation of network reachability information, is an important problem currently facing the Internet engineering community. High levels of network instability can lead to packet loss, increased network latency, and delayed routing convergence. At the extreme, high levels of routing instability can lead to the loss of internal connectivity in wide-area networks. In this paper, we investigate the variation of domain degree and domain count of the inter-domain network over time by using linear regression model in order to analyze the topology variation of inter-domain network. We Also propose an efficient policy management model to reduce the instability in the inter-domain routing system. The proposed model can be used to identify whether a routing policy is adequate to reduce convergence time that is required to return to a normal state when BGP routing instability happens. Experimental analysis shows that the proposed model can be used to set up routing policy in domains for the purpose of minimizing the effects and the propagation of BGP routing instability.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.92.2-92.2
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• 2012

Previous simulations posed a problem that they used reduced ion to electron mass ratios to save computation time. It was assumed that ion and electron dynamics are sufficiently separated, but it was not clearly verified. In this study, we examine the effect of ion to electron mass ratios on the generation of ion holes by ion beam driven instability. Ion holes are generated via electron holes in an applied electric field with the given initial condition. First, the ion acoustic instability is excited and nonlinearly develops. After the ion acoustic instability nonlinearly develops, the ion two-stream instability is excited and develops into ion holes. This implies that the previously suggested ion beam driven instability is strongly affected by the coupling between ions and electrons and the ion to electron mass ratio is important on the development of the instability. The energy transition and detail variation is different as reduced mass ratio under the same observation value based on FAST satellite. Although, the parameters are rescaled by conserving the kinetic energy to obtain the proper results, the nonlinear evolution is not perfectly identical.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.9
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• pp.1218-1229
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• 1997

The diffusional-thermal instability of diffusion flames in the premixed-flame regime is studied in a constant-density two-dimensional counterflow diffusion-flame configuration, to investigate the instability mechanism by which periodic wrinkling, travelling or pulsating of the reaction sheet can occur. Attention is focused on flames with small departures of the Lewis number from unity and with small values of the stoichiometric mixture fraction, so that the premixed-flame regime can be employed for activation-energy asymptotics. Cellular patterns will occur near quasisteady extinction when the Lewis number of the more completely consumed reactant is less than a critical value( ~ =0.7). Parametric studies for the instability onset conditions show that flames with smaller values of the Lewis number and stoichiometric mixture fraction and with larger values of the Zel'dovich number tend to be more unstable. For Lewis number greater than unity, near-extinction flame are found to exhibit either travelling instability or pulsating instability.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.853-858
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• 2001

The knowledge of flame structure is essential for control of combustion instability phenomena. Some results of an experimental study on mechanism of naturally occurring combustion oscillations with a single dominant frequency are presented. Tests were conducted in a laboratory-scale dump combustor at atmospheric pressure. Sound level meter was used to track the pressure wave inside the combustor. The observed instability was a longitudinal mode with a frequency of $\sim341.8Hz$. Instability map was obtained at the condition of inlet temperature of $360^{\circ}C$, mean velocities of $8.5\sim10.8m/s$ and well premixed mixture. It showed that combustion instability was susceptible to occur in the lean conditions. In this study, unstable flame was observed from stoichiometric to 0.7 in overall equivalence ratio. At selected unstable conditions, phase-resolved OH chemiluminescence images were captured to investigate flame structure with various mean velocities. As mean velocity is increased, the flame grows and global heat release was changed. Due to these effects, combustion instability can be maintained at more lean air-fuel ratio. Also, these results give an insight to the controlling mechanism for an increasing heat release at maximum pressure.

• Structural Engineering and Mechanics
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• v.65 no.1
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• pp.121-128
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• 2018

Three structure-dependent integration methods with no numerical dissipation have been successfully developed for time integration. Although these three integration methods generally have the same numerical properties, such as unconditional stability, second-order accuracy, explicit formulation, no overshoot and no numerical damping, there still exist some different numerical properties. It is found that TLM can only have unconditional stability for linear elastic and stiffness softening systems for zero viscous damping while for nonzero viscous damping it only has unconditional stability for linear elastic systems. Whereas, both CEM and CRM can have unconditional stability for linear elastic and stiffness softening systems for both zero and nonzero viscous damping. However, the most significantly different property among the three integration methods is a weak instability. In fact, both CRM and TLM have a weak instability, which will lead to an adverse overshoot or even a numerical instability in the high frequency responses to nonzero initial conditions. Whereas, CEM possesses no such an adverse weak instability. As a result, the performance of CEM is much better than for CRM and TLM. Notice that a weak instability property of CRM and TLM might severely limit its practical applications.

• 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.

• Clinics in Shoulder and Elbow
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• v.3 no.1
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• pp.10-19
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• 2000

The aims of this retrospective study were to evaluate the results of inferior capsular shift operation which were approached anteriorly or posteriorly according to a main instability direction in contact sports population who had multidirectional shoulder instability. Fifty-three shoulders in 47 athletes who engaged in contact sports underwent an anterior or posterior inferior capsular shift procedure for the correction of multidirectional instability of the shoulder joint. The surgical approach was selected according to the predominant direction of the instability. Follow up was average of 42 months(24∼73 months). After anterior inferior capsular shift, anterior dislocation was recurred in three shoulders, posterior dislocation in one, and inferior dislocation in two shoulders. After posterior inferior capsular shift, one dislocation occurred anteriorly, one inferiorly and one posteriorly. The excessive tightening of capsule or improper diagnosis could be causative factors for the development of dislocation in the opposite direction to the preoperative major instability. Of six patients who could not return to their sports, five had bilateral repairs. Successful repair based on the criteria of the American shoulder and elbow association was achieved in 92% of anterior repairs, and 81 % of posterior repairs.

• Journal of the Korean Society of Combustion
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• v.20 no.4
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• pp.10-18
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• 2015

Combustion instability is a major issue in design and maintenance of gas turbine combustors for efficient operation with low emissions. With the thermoacoustic view point the instability is induced by the interaction of the unsteady heat release of the combustion process and the change in the acoustic pressure in the combustion chamber. In an effort to study the combustion dynamics of gas turbine combustors, Morgans et al (2014) have developed OSCILOS (open source combustion instability low order simulator) code and it is currently available online. In this study the code has been utilized to predict the combustion instability of a reported case for lean premixed gas turbine combustion, and then its prediction results have been compared with the corresponding experimental data. It turned out that both the predicted and the experimental combustion instability results agree well. Further the effects of some typical inlet acoustic boundary conditions on the prediction have been investigated briefly. It is believed that the validity and effectiveness of the open source code is reconfirmed through this benchmark test.