• 대한통합의학회지
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• 제7권3호
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• pp.141-148
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• 2019

Purpose: The present study investigated the effects of 12-week aquatic exercise training on isokinetic muscle function of the shoulder in adolescents with cerebral palsy. Methods: The study included four male and four female adolescents with cerebral palsy. Isokinetic muscle function was measured at an angular velocity of $60^{\circ}/s$, using Biodex System VI Pro. The peak torques of internal rotation and external rotation were measured before and after training. Aquatic exercise training was performed once a day for 120 min, 4 times a week for 12 weeks. Results: The peak torque of external rotation according to body weight and mean power of internal rotation were significantly higher after training (p < 0.05). Conclusion: Our findings suggest that 12-week aquatic training for adolescents with cerebral palsy can improve isokinetic muscle function of the shoulder. Future studies should analyze the changes in isokinetic muscle function of the shoulder in more detail using various aquatic exercise programs to investigate their effects on individuals with cerebral palsy.

• 한국기계가공학회지
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• 제17권5호
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• pp.37-44
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• 2018

In laser material processing for high thermal conductivity, the thermal effect of laser beam shape was examined through computer simulations. In this paper, a circular beam with a focal radius of $500{\mu}m$, an elliptical beam with a major axis of 4 mm and a minor axis of 1 mm, and a rotating beam with a focal radius of $500{\mu}m$ and an angular velocity of 5 rad/sec were compared. Simulation results showed that there was no clear difference in the maximum temperature between the circular focus and the elliptical shape, but the heating and cooling rates were different. The simulation result for a laser beam rotating in a circular pattern with a radius of 5 mm showed an asymmetric temperature rise due to the combination of linear and rotational motion. At points where the rotational and linear speeds combined, the temperature gradually rose and reached the maximum temperature; whereas at points where the rotational and linear speeds were attenuated, the temperature tended to gradually decrease after reaching the maximum temperature. Based on the results of this study, the authors expect to be able to optimize laser material processing by designing patterns of laser beams.

• Steel and Composite Structures
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• 제32권2호
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• pp.225-237
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• 2019

In this research, the dynamic stability and nonlinear vibration behavior of a smart rotating sandwich cylindrical shell is studied. The core of the structure is a functionally graded material (FGM) which is integrated by functionally graded piezoelectric material (FGPM) layers subjected to electric field. The piezoelectric layers at the inner and outer surfaces used as actuator and sensor, respectively. By applying the energy method and Hamilton's principle, the governing equations of sandwich cylindrical shell derived based on first-order shear deformation theory (FSDT). The Galerkin method is used to discriminate the motion equations and the equations are converted to the form of the ordinary differential equations in terms of time. The perturbation method is employed to find the relation between nonlinear frequency and the amplitude of vibration. The main objective of this research is to determine the nonlinear frequencies and nonlinear vibration control by using sensor and actuator layers. The effects of geometrical parameters, power law index of core, sensor and actuator layers, angular velocity and scale transformation parameter on nonlinear frequency-amplitude response diagram and dynamic stability of sandwich cylindrical shell are investigated. The results of this research can be used to design and vibration control of rotating systems in various industries such as aircraft, biomechanics and automobile manufacturing.

• 천문학회보
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• 제44권1호
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• pp.50.2-50.2
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• 2019

Understanding three-dimensional structure and parameters (e.g., radial velocity, angular width, source location and density) of coronal mass ejections (CMEs) is essential for space weather forecast. In this study, we determine CME mean density in solar corona and near the Earth. We select 38 halo CMEs, which have the corresponding interplanetary CMEs (ICMEs), by SOHO/LASCO from 2000 to 2014. To estimate a CME volume, we assume that a CME structure is a full ice-cream cone which is a symmetrical circular cone combined with a hemisphere. We derive CME mean density as a function of radial height, which are approximately fitted to power-law functions. The average of power-law indexes is about 2.1 in the LASCO C3 field of view. We also obtain power-law functions for both CME mean density at 21 solar radii and ICME mean density at 1AU, with the average power-law index of 2.6. We estimate a ratio of CME density to background density based on the Leblanc et al.(1998) at 21 solar radii. Interestingly, the average of the ratios is 4.0, which is the same as a default value used in the WSA-ENLIL model.

• 한국전자통신학회논문지
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• 제16권1호
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• pp.37-44
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• 2021

본 연구는 터렛 서보 시스템에서 사용되는 고가의 절대형 엔코더를 대체하기 위해서 멀티-턴 가능한 센서리스 위치제어기를 구현하였다. 센서리스 제어를 위해서는 모터의 위치 정보가 필수적이다. 따라서, 터렛 서보시스템에서 사용되는 영구자석형 동기 전동기의 수학적 모델로부터 자속 추정기를 구성하였다. 자속 추정기로부터 회전자 자속을 계산하여 회전자의 속도와 위치 정보를 얻었다. 제로-크로싱 기법을 사용하여, 추정한 회전자 자속이 1회전 할 때마다 하나의 펄스를 생성하여 멀티-턴 횟수를 측정하였다. 모의실험과 실험을 통해 제안한 방법의 유용함을 확인하였다.

• 한국기계가공학회지
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• 제21권8호
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• pp.60-65
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• 2022

This study focuses on the driving control design of an index, which is a key component of a rotary transfer machine that is effective in improving productivity and reducing manufacturing costs by shortening cycle time. Although various index studies have been conducted on the rotation of workpieces such as general-purpose machine tools and tilting indices, the development of an index for rotary transfer machines for transfer is insufficient. The index consists of a body, table, hydraulic cylinder, motor, reducer, and curved coupling. The torque of the table for driving was selected, and the angular velocity and torque pattern were simulated using the motor manufacturer's program. The specifications of the drive motor were determined based on the selected torque.

• 대한조선학회논문집
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• 제59권6호
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• pp.338-344
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• 2022

Roll moment usually is ignored when analyzing the maneuverability of surface ships. However, it is well known that the influence of roll moment on maneuverability is significant for ships with small metacentric height such as container ships, passenger ships, etc. In this study, a pure roll test is performed to determine the hydrodynamic derivatives with respect to roll motion as added mass and damping. The target ship is an autonomous surface ship designed to carry containers with a small drift and large freeboard. The commercial code of STAR CCM+ software is applied as a specialized tool in naval hydrodynamic based on RANS equation for simulating the pure roll of the ship. The numerical uncertainty analysis is conducted to verify the numerical accuracy. By distinguishing the in-phase and out-of-phase from hydrodynamic forces and moments due to roll motion, added mass derivatives and damping derivatives relative to roll angular velocity are obtained.

• 한국기계가공학회지
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• 제20권11호
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• pp.43-51
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• 2021

A robust tracking controller design was developed for a rotary motion control system. The friction force versus the angular velocity was measured and modeled as a combination of linear and nonlinear components. By adding a model-based friction compensator to a nominal proportional-integral-derivative controller, it was possible to build a simulated control system model that agreed well with the experimental results. A zero-phase error tracking controller was selected as the feedforward tracking controller and implemented based on the estimated closed-loop transfer function. To provide robustness against external disturbances and modeling uncertainties, a disturbance observer was added in the position feedback loop. The performance improvement of the overall tracking controller structure was verified through simulations and experiments.

• 한국항행학회논문지
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• 제27권1호
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• pp.50-56
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• 2023

관성항법장치는 내장된 관성센서만을 이용하여 외부의 도움 없이 항체의 가속도 및 각속도를 이용하여 항법 정보를 계산한다. 하지만, 장시간 운용 시 관성항법장치는 시간이 지남에 따라 오차가 누적되어 항법 성능이 저하된다. 이러한 관성항법장치의 누적 오차를 줄이기 위하여 관성센서조립체를 일정한 절차로 회전시켜 관성센서 오차가 회전을 통해 상쇄되도록 항법 성능을 개선 시키는 연구가 활발히 진행되고 있다. 본 논문에서는 2축 회전형 관성항법장치의 성능에 영향을 미칠 수 있는 오차 요소를 식별하고 각 오차가 항법 성능에 어떠한 영향을 미치는지 분석하였다. 오차 분석 수행 후 시뮬레이션을 통해 관성항법장치의 항법 성능분석 결과를 제시하였다.

• 수산해양기술연구
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• 제59권2호
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• pp.135-144
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• 2023

In order to provide basic data to increase the efficiency and stability of seamanship at anchoring, the characteristics of the hull motion including dragging anchor due to external forces were observed at Mokpo and Jinhae anchorage for the avoidance of the typhoon. As a result, it is necessary to check the embedding motion and holding power of the anchor according to at initial position to decrease dragging anchor. Dragging anchor at anchorage seems to have been easily caused according to discrepancy between embedded anchor flukes and the towing direction due to the change in wind direction, rather than the wind speed. This discrepancy, thus, should be considered when anchoring. This test vessel with a small radius of curvature of the stem is relatively vulnerable to the influence of wind direction and wind speed, so it is easy to cause a decrease in the holding power due to an increase in the rate of turn. When the current speed is greater than or equal to 1 knot, the range of the rate of turn is reduced resulting in a relatively increased holding power. In addition, during the swing, the tension of the chain was high according to the angular velocity change of heading at three-quarters of the swing length rather than the left and right ends.