• 한국전산유체공학회:학술대회논문집
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• 2008.10a
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• pp.367-373
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• 2008

Spinning detonations propagating in a circular tube were numerically investigated with a one-step irreversible reaction model governed by Arrhenius kinetics. Activation energy is used as parameter as 10, 20, 27 and 35, and the specific heat ratio and the heat release are fixed as 1.2 and 50. The time evolution of the simulation results was utilized to reveal the propagation mechanism of single-headed spinning detonation. The track angle of soot record on the tube wall was numerically reproduced with various levels of activation energy, and the simulated unique angle was the same as that of the previous reports. The maximum pressure histories of the shock front on the tube wall showed stable pitch at Ea=10, periodical unstable pitch at Ea=20 and 27 and unstable pitch consisting of stable, periodical unstable and weak modes at Ea=35, respectively. In the weak mode, there is no Mach leg on the shock front, where the pressure level is much lower than the other modes. The shock front shapes and the pressure profiles on the tube wall clarified the mechanisms of these stable and unstable modes. In the stable pitch at Ea=10, the maximum pressure history on the tube wall remained nearly constant, and the steady single Mach leg on the shock front rotated at a constant speed. The high and low frequency pressure oscillations appeared in the periodical unstable pitch at Ea=20 and 27 of the maximum pressure history. The high frequency was one cycle of a self-induced oscillation by generation and decay in complex Mach interaction due to the variation in intensity of the transverse wave behind the shock front. Eventually, sequential high frequency oscillations formed the low frequency behavior because the frequency behavior was not always the same for each cycle. In unstable pitch at Ea=35, there are stable, periodical unstable and weak modes in one cycle of the low frequency oscillation in the maximum pressure history, and the pressure amplitude of low frequency was much larger than the others. The pressure peak appeared after weak mode, and the stable, periodical unstable and weak modes were sequentially observed with pressure decay. A series of simulations of spinning detonations clarified that the unsteady mechanism behind the shock front depending on the activation energy.

• Journal of information and communication convergence engineering
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• v.15 no.4
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• pp.244-249
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• 2017

Wearable sensor-based gait analysis has been widely conducted to analyze various aspects of human ambulation abilities under the free-living condition. However, there have been few research efforts on using wearable sensors to analyze human walking on an unstable surface such as on a ship during a sea voyage. Since the motion of a ship on the unstable sea surface imposes significant differences in walking strategies, investigation is suggested to find better performing wearable sensor-based gait analysis algorithms on this unstable environment. This study aimed to compare two representative gait event algorithms including time domain and frequency domain analyses for detecting heel strike on an unstable platform. As results, although two methods did not miss any heel strike, the frequency domain analysis method perform better when comparing heel strike timing. The finding suggests that the frequency analysis is recommended to efficiently detect gait event in the unstable walking environment.

• Journal of the Korean Ceramic Society
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• v.22 no.3
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• pp.60-66
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• 1985

The formation mechanism of unstable alkali and its existing states in the clinker were studied. The relation of unstable alkali content vs. other water-soluble components porosity and the distributionof potassium were investigated. The results are as follows :1) Two states of unstable alkali seem to exist in clinker ie compounds of $K_2O-Al_2O_3$ system and free $K_2O$ 2) The content of water-soluble $Al_2O_3$ tends to increase with increase of unstable alkali content, 3) Most of alkalies in clinker are concentrated in liquid phase at high temperature. Therefore it is possible to make various $K_2O-Al_2O_3$ system compounds according to the content of $K_2O$ in the liquid phase of clinker. In this experiment we found out a $K_2O-Al_2O_3$ compound of high $Al_2O_3$ content (34%) and high $K_2O$ content (33%) in clinker with 1.09% unstable alkali. 4) The porosity of clinker tends to increase with increase of unstable alkali content. 5) The amount of trapped alkali vapor may increase in closed pore in the clinker with high alkali and low $SO_3$ condecent. Therefore free $K_2O$ is the condensed alkali on the wall of closed pore in the clinker.

• Journal of International Academy of Physical Therapy Research
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• v.5 no.1
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• pp.641-646
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• 2014

The purpose of this study is to observe how balance exercise on an unstable platform and on a stable platform affects balance ability. The subjects were 35 adults in their 20s and were randomly assigned to a stable platform group and an unstable platform group. They performed balance exercise three times per week for six weeks. Balance exercise introduced by previous research was modified and complemented for use in this study. Balance ability of the subjects was measured through center of pressure(COP) area, medial-lateral displacement, and anterior-posterior displacement using a portable balance platform BT4. There was significant difference in the COP area between the unstable platform exercise group and the stable platform exercise group. In comparison in differences between the unstable platform exercise group and the stable platform exercise group after the exercise, there was significant difference in anterior-posterior movement. Therefore, exercise on an unstable platform is more effective than exercise on a stable platform in strengthening balance ability.

• Journal of the Korea institute for structural maintenance and inspection
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• v.6 no.3
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• pp.119-128
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• 2002

This study discusses the issues related to the accuracy of deflection measurement and unstable energy in the testing of FRC. Some deflection methods may include large extraneous deformations. A faulty load-deflection curve will be obtained if an unstable deflection measuring system is used, and inaccurate toughness evaluation can result from this faulty curve. Some load-deflection curve of FRC may be attributed to unstable region of the load-deflection curve. If the unstable region is not correctly evaluated toughness indices from the curve would inappropriately represent true indices. In this paper, the discussion will focus on the effects of the deflection measuring system both on the measurement of the load-deflection response of FRC and the evaluation of FRC toughness and the effects of the unstable region and the management method of unstable region on toughness evaluation of FRC. It is observed that ASTM toughness indices which is based on measured deflection at first cracking is influenced significantly by extraneous deformation of deflection measurement. Extraneous deformation in deflection measurement, however result in negligible errors in toughness evaluation if JSCE and JCI definitions are used.

• Journal of International Academy of Physical Therapy Research
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• v.8 no.1
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• pp.1077-1083
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• 2017

The purpose of this study was to investigate the effects of stable and unstable bridging exercises on the EMG activity of abdominal muscles. Twenty healthy women participated in this study and the muscle activities of left-right rectus abdominis (RA), external oblique (EO), and internal oblique (IO) muscles were recorded during 4 bridging exercises (unilateral/ bilateral, stable/unstable). The activity of the right EO muscle was the highest during unilateral exercise in unstable condition, and left EO muscle also produced the same result. The activity of the right IO muscle was the highest during unilateral exercise in an unstable condition, and left IO muscle also produced the same result. The activity of the right RA muscle was the highest during unilateral exercise in a stable condition, and left RA muscle produced the same result. Unstable/unilateral (USUL) represented the highest activity among the 4 exercises. EO/IO muscles represented the highest activity during the USUL exercise, and RA did so during the stable/unilateral exercise. These results suggest that specific posture (USUL) can be administered targeting a specific side of abdominal muscles.

• Journal of the Korean Society of Physical Medicine
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• v.7 no.3
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• pp.251-258
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• 2012

Purpose : The purpose of this study is to provide an efficient and basis for muscle activity of Quadriceps muscles and balance in anterior cruciate ligament reconstruction patients through unstable surface exercise and stable surface exercise. Methods : This study included 30 anterior cruciate ligament reconstruction patients belonging to A hospital and D orthopedic surgery clinic of province who attended the program for 30 minutes at a time and three times a week for 4 weeks. Of these 15 attended the unstable surface exercise program and 15 the stable surface exercise program. To increase muscle activity (%MVIC) and balance (WPL), the unstable surface exercise. Results : The %MVIC of lower extrmity muscle(RF, VL, VM) increased from before training to after training in the case of the participants who performed the unstable surface exercise, and the whole path length (WPL) decreased from before the training to after the training(p<.05). Conclusion : In conclusion, unstable surface exercise program helps to improve the balancing ability and musle activity in a anterior cruciate ligament recunstruction patients who requires both muscle activity and balance than stable surface exercise program.

• Journal of The Korean Society of Integrative Medicine
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• v.7 no.3
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• pp.197-204
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• 2019

Purpose: The purpose of this study was to investigate the effects of the plank exercise to strengthen the core muscles on the muscle thickness of external and internal obliques and transverse abdominis muscle depending on the form of the support surface. Methods: This study was randomized to 12 males and 12 females in their 20s and conducted three times a week for 4 weeks. The subjects were divided into the two groups and performed flank exercise on a stable surface (stable surface group) and an unstable surface (unstable surface group). A mat was used as a stable surface, and an TOGU used as a unstable surface. Results : In both stable and unstable surface, the thickness changes of the transverse abdominis and external and internal oblique muscle increased (p<.05). In the unstable surface, there was a greater increase in the thickness change of the transverse abdominis and external oblique muscles in the flank exercise than in the stable surface (p.<05). Among them, the greatest increase was found in the external abdominal muscle (p<.05). Conclusion : This study found that the flank exercise was more effective in strengthening the abdominal muscles on an unstable surface, when compared with the outcomes on a stable one. It is also thought to have the most effect on the muscle activity of the external oblique muscle on unstable surface.

• Nuclear Engineering and Technology
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• v.54 no.5
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• pp.1851-1859
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• 2022

Experimental research on flow characteristics of open natural circulation system was performed, to figure out the mechanism of the open natural circulation behaviors. The influence factors, such as the heating power, the inlet subcooled and the level of cooling tank on the flow characteristics of the system were examined. It was shown that within the scope of the experimental conditions, there are five flow types: single-phase stable flow, flash and geyser coexisting unstable flow, flash stable flow, flash unstable flow, and flash and boiling coexisting unstable flow. The geyser flow in flash and geyser coexisting unstable flow is different from classic geysers flow. The flow oscillation period and amplitude of the former are more regular, is a newly discovered flow pattern. By drawing the flow instability boundary diagram and sorting out the flow types, it is found that the two-phase unstable flow is mainly characterized by boiling and flash, which determine the behavior of open natural circulation respectively or jointly. Moreover, compared with full liquid level system, non-full liquid level system is more prone to boiling phenomenon, and the range of heat flux density and undercooling degree corresponding to unstable flow is larger.

• Proceedings of the KIEE Conference
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• 1989.11a
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• pp.254-257
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• 1989

In general, unstable phenomena of induction motor are oftenly appeared at low speed and light load. This paper discribes eigenic unstable regions of I.M. itself by computer simulations and the results are compared to experimental ones. And also the optimal design parameters of I.M. which the unstable reg ion can be minimized are determined.