• The Journal of the Acoustical Society of Korea
• /
• v.20 no.1E
• /
• pp.25-30
• /
• 2001

The unstable signature that is defined as frequency change with respect to the time or frequency modulation, is caused by the external loading variation in specific machinery component and Doppler shift etc. In this study, we analyze the generation mechanism of the unstable signature and apply the Extended Kalman filter (EKF) algorithm for its detection. The performance of Extended Kalman Filter is examined for numerical and measured signals and the results show its validity for unstable signature detection.

• Journal of Advanced Marine Engineering and Technology
• /
• v.33 no.5
• /
• pp.721-728
• /
• 2009

PID control is widely used to control stable processes, however, PID control for unstable processes is less common. In this paper, systematic tuning methods are derived to tune the PID controller for unstable FOPTD(Forst Order Plus Time Delay) processes. The proposed PID controllers for set-point tracking and disturbance rejection problem are tuned based on minimizing the performance indexes (IAE, ISE, ITAE) using a real-coded genetic algorithm. Simulation example is given to illustrate the set-point tracking and disturbance rejection performance of the proposed method.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.12 no.8
• /
• pp.3587-3593
• /
• 2011

This study was to investigate the balancing and clinical abilities using stable and unstable surface of stroke patients who surface changes in balance of body. The subjects of this study were 30 stroke patients(16 males and 14 females). They were separated into two groups and did balance reinforcing exercise on stable and unstable surfaces for five times a week for six weeks. To evaluate their balancing ability, they performed functional standing balance test, functional forward arm stretching test. performance-oriented mobility assessment was performed. The balancing exercises were modified from preceding studies and consisted of 6 difference exercises. The functional standing test with open and close eyes and performance-oriented mobility assessment, the unstable surface exercise group and the stable surface exercise group improved significantly. The forward arm stretching test was the unstable surface exercise group improved. This study found that the balancing exercise on unstable surface was more effective than on stable surface for stroke patients. Thus, exercise on unstable surface has more positive effects on the improvement of balancing abilities of stroke patients.

• The Journal of Korean Physical Therapy
• /
• v.28 no.6
• /
• pp.376-380
• /
• 2016

Purpose: This study was to investigate the short-term effects of spiral taping (ST) on performance on the star excursion balance test (SEBT) in individuals with unilateral chronic ankle instability (CAI). Methods: This study was single-group pre - post measures experimental design. The subjects with CAI were 39 (range, 20-31 years; male 16, females 23) were enrolled in the study. The discomfort had in unilateral ankle and Cumberland ankle instability score was 19.56 (${\pm}3.29$). Spiral tape (a width of 3 mm) was applied $3{\times}4$ cross shape on medial malleolus, lateral malleolus and dorsal of talocural joint of unstable ankle. SEBT was measured baseline and 30 min later in stable ankle and unstable ankle. Results: SEBT showed significantly improved after applying the ST (p<0.05, ES=0.74) on unstable ankle. In comparison the difference of stable and unstable ankle, between the pretest and posttest were significant differences (p<0.01, ES=1.88). Conclusion: These results indicated that ST improves performance on the SEBT. Therefore, it suggests that ST may be a suitable intervention to dynamic balance in patients with CAI.

• New & Renewable Energy
• /
• v.18 no.1
• /
• pp.1-16
• /
• 2022

Climatic characteristics were described using the LiDAR (Light Detection and Ranging) and the met-mast on Dongbok·Bukchon region. The influences of meteorological conditions on the power performance of wind turbines were presented using the data of Supervisory Control And Data Acquisition (SCADA) and met-mast of the Dongbok·Bukchon Wind Farm (DBWF) located in Jeju Island. The stability was categorized into three parameters (Richardson number, Turbulence intensity, and Wind shear exponent). DBWF was dominant in unstable atmospheric conditions. At wind speeds of 14 m/s or more, the proportion of slightly unstable conditions accounted for more than 50%. A clear difference in the power output of the wind turbine was exhibited in the category of atmospheric stability and turbulence intensity (TI). Particularly, a more sensitive difference in power performance was showed in the rated wind speeds of the wind turbine and wind regime with high TI. When the flow had a high turbulence at low wind speeds and a low turbulence at rated wind speeds, a higher wind energy potential was produced than that in other conditions. Finally, the high-efficiency of the wind farm was confirmed in the slightly unstable atmospheric stability. However, when the unstable state become stronger, the wind farm efficiency was lower than that in the stable state.

• International Journal of Internet, Broadcasting and Communication
• /
• v.10 no.2
• /
• pp.84-94
• /
• 2018

The purpose of this study was to compare the balance ability at different foot positions using K A T 2000 (Berg, Inc, vista, CA.1994). Thirty (male 15, female 15) normal subjects participated in this study. All subjects were tested at a one leg position or a two leg position that were toe-in $25^{\circ}$, toe-out $25^{\circ}$, and $45^{\circ}$. The starting position was where the subject crossed their arms across the chest and flexed knees slightily. The results of each test were displayed on a screen in a score format, which indicated balance index. These collected data were analyzed by using one way ANOVA, and t-test. The results of this study were as follows: When changing the angle of the foot in the one-foot and two-foot standing positions, there was no statistically significant difference, but the balance performance with the foot rotated by $25^{\circ}$ was better than that with the foot rotated by $45^{\circ}$. When changing the direction of the foot in the one-foot and two-foot standing positions, there was no statistically significant difference, but the balance performance with the foot rotated laterally was better - except for the case when the foot was medially rotated by $25^{\circ}$ in the right-foot static standing position. When the feet were medially rotated by $25^{\circ}$ in the two-foot static standing position, and were medially rotated by $25^{\circ}$ and $45^{\circ}$ in the one-foot static standing position, the balance performance of females was better than that of males. In this study, it was found that the balance performance of the subjects changed when the position of the foot was shifted on an unstable base of support. However, there was little correlation between balance performance and the height, weight and foot length of the subjects. It is necessary to conduct a follow-up study targeting various age groups and those with various diseases using an unstable platform or applying different physical or visual conditions, such as the length of the legs. Physical therapists need to consider the position of the foot in clinical settings for a better balance training or assessment.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.20 no.4
• /
• pp.1491-1500
• /
• 1996

Unstable performance deterioration was found on the performance curve of a small propeller fan with a back plate. To investigate this phenomenon and the effects of the back-plate on the performance of the fan, performance tests and flow measurement using 3-hole pitot tube were carried out. Measurements showed that when the flow rate is small, the radial flow dominates, and when the flow rate is large, the axial flow dominates. Performance characteristic of the propeller fan changes from radial to axial type as the flow rate increases. Unstable performance changes are the result of type change of the flow through the fan.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.21 no.3
• /
• pp.157-164
• /
• 2013

A damper clutch in automatic transmission systems has some advantages of fuel economy and dynamic performance. Although a damper clutch operation improves a fuel economy of the vehicles, a positive operation of a damper clutch in a low vehicle speed induces abnormal vibration. This paper analyzed one of reasons for abnormal vibration by a damper clutch operation in low engine speed ranges. A simulation model was designed to confirm the effects of a damper clutch operation under unstable regions of an engine. A theoretical analysis was carried out about an engine operation stability. Simulation was conducted to depict abnormal vibration by a damper clutch operation in unstable regions of an engine performance curve. The effects of an engine operation region for abnormal vibration by a damper clutch was investigated according to the range and the slope of unstable regions. As a result of simulations, a damper clutch operation would be better to avoid an engine unstable regions.

• International Journal of Control, Automation, and Systems
• /
• v.3 no.spc2
• /
• pp.334-340
• /
• 2005

Based on the stability margin provided by the EEAC, the unstable contingencies can be classified into sets according to their unstable modes. This two-part paper develops a globally optimal algorithm for transient stability control to coordinate preventive actions and emergency actions. In the first part, an algorithm is proposed for a set of contingencies having identical unstable modes. Instead of iterations between discrete emergency actions and continuous preventive actions, the algorithm straightforwardly searches for a globally optimal solution. The procedure includes assessing a set of insufficient emergency schemes identified by the EEAC; calculating the related preventive actions needed for stabilizing the system; and selecting the scheme with the minimum overall costs. Simulations on a Chinese power system highlight its excellent performance. The positive results obtained are explained by analogizing settlements for 0-1 knapsack problems using the multi-points greedy algorithm.

• The Journal of the Acoustical Society of Korea
• /
• v.18 no.2E
• /
• pp.39-44
• /
• 1999

In passive sonar, underwater moving objects are identified by the acoustic sounds they transmit. The spectrum of these sounds show features about the mechanism of the sound source, these features are discrete frequencies on the spectrum and frequency lines on the spectrogram. Variability in the underwater environment produce discontinuous broken or unstable fluctuating frequency lines. In this paper, we propose an efficient algorithm that estimate continuities of the discontinuous frequency lines and extract presence of the unstable frequency lines using neural networks and represent the proposed algorithm shows good performance in estimation and extraction the unstable frequency lines through the experiments.