• 한국환경생태학회지
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• 제33권5호
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• pp.565-577
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• 2019

설악산 분비나무 개체군의 쇠퇴징후에 대한 요인과 군락의 변화 양상을 파악하기 위하여 귀때기청봉, 관모능선, 설악폭포지역에 고정조사구를 설치하였으며, 군락구조, 개체군동태, 비대생장 및 활력도 등을 2009년부터 모니터링 하였다. 설악폭포지를 제외한 3개 조사지는 아교목층이 수관층을 형성하는 3층구조를 보였다. 목본수종의 중요치에서는 분비나무, 눈측백, 신갈나무, 사스래나무, 당단풍나무 등이 주요 종으로 분포하였으며, 설악폭포지에 분포하는 분비나무의 중요치는 2009년 45.3%에서 2018년 36.8%로 가장 크게 감소하였다. 생육목의 개체수($DBH{\geq}5cm$)는 귀때기청봉2와 관모능선에서 각각 1,800개체/ha와 1,700개체/ha로 가장 많았으며, 지난 10년 동안 고사율은 귀때기청봉1과 설악폭포지에서 각각 38.3%와 35.3%로 매우 높게 나타났다. 분비나무 개체군의 흉고직경급 분포에서는 귀때기청봉1 지역에서 가장 안정적인 역 J자형의 분포를 보였다. 분비나무의 연평균 비대생장은 0.96~1.73mm/year 였으며, 활력도가 감소 추세를 보인 귀때기청봉2, 관모능선, 설악폭포 지역에서 비대생장은 대체로 생장이 저하되는 추세를 나타내었다. 향후 모니터링 과정이 지속적으로 이루어진다면, 아고산 식생의 보전과 관리를 위한 기초자료 확보가 가능할 것으로 생각된다.

• International Journal of Aeronautical and Space Sciences
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• 제8권1호
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• pp.10-20
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• 2007

For spacecraft attitude control, reaction wheel (RW) steering laws with more than three wheels for three-axis attitude control can be derived by using a control allocation (CA) approach.1-2 The CA technique deals with a problem of distributing a given control demand to available sets of actuators.3-4 There are many references for CA with applications to aerospace systems. For spacecraft, the control torque command for three body-fixed reference frames can be constructed by a combination of multiple wheels, usually four-wheel pyramid sets. Multi-wheel configurations can be exploited to satisfy a body-axis control torque requirement while satisfying objectives such as minimum control energy.1-2 In general, the reaction wheel steering laws determine required torque command for each wheel in the form of matrix pseudo-inverse. In general, the attitude control command is generated in the form of a feedback control. The spacecraft body angular rate measured by gyros is used to estimate angular displacement also.⁵ Combination of the body angular rate and attitude parameters such as quaternion and MRPs(Modified Rodrigues Parameters) is typically used in synthesizing the control command which should be produced by RWs.¹ The attitude sensor signals are usually corrupted by noise; gyros tend to contain errors such as drift and random noise. The attitude determination system can estimate such errors, and provide best true signals for feedback control.⁶ Even if the attitude determination system, for instance, sophisticated algorithm such as the EKF(Extended Kalman Filter) algorithm⁶, can eliminate the errors efficiently, it is quite probable that the control command still contains noise sources. The noise and/or other high frequency components in the control command would cause the wheel speed to change in an undesirable manner. The closed-loop system, governed by the feedback control law, is also directly affected by the noise due to imperfect sensor characteristics. The noise components in the sensor signal should be mitigated so that the control command is isolated from the noise effect. This can be done by adding a filter to the sensor output or preventing rapid change in the control command. Dynamic control allocation(DCA), recently studied by Härkegård, is to distribute the control command in the sense of dynamics⁴: the allocation is made over a certain time interval, not a fixed time instant. The dynamic behavior of the control command is taken into account in the course of distributing the control command. Not only the control command requirement, but also variation of the control command over a sampling interval is included in the performance criterion to be optimized. The result is a control command in the form of a finite difference equation over the given time interval.⁴ It results in a filter dynamics by taking the previous control command into account for the synthesis of current control command. Stability of the proposed dynamic control allocation (CA) approach was proved to ensure the control command is bounded at the steady-state. In this study, we extended the results presented in Ref. 4 by adding a two-step dynamic CA term in deriving the control allocation law. Also, the strict equality constraint, between the virtual and actual control inputs, is relaxed in order to construct control command with a smooth profile. The proposed DCA technique is applied to a spacecraft attitude control problem. The sensor noise and/or irregular signals, which are existent in most of spacecraft attitude sensors, can be handled effectively by the proposed approach.

• 한국운동역학회지
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• 제21권3호
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• pp.317-325
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• 2011

The purpose of this study was to investigate the contributions of body joints to the kinetic energy of the clubhead in the golf swing. Three dimensional swing analysis was conducted on the seven KPGA golfers. The subjects were asked to swing with 45 inches of driver. The work done by body joints were computed by utilizing the inverse dynamics method. The order of work done by the body joints was lumbar > left hip > right shoulder > left wrist > right wrist > right hip at the first phase. At the second phase, the order of work done by the body joints was trunk > left elbow > right wrist > right shoulder > left wrist > right wrist. At the third phase, the order of work done by body joints was lumbar > right shoulder > left shoulder > left elbow > right wrist > right elbow. The sum of the work done by the body joints was lumbar > shoulder > wrist on the average. The kinetic energy of the club head was 430.11${\pm}$24.35 J and the subject's swing efficiency was shown as 31.82${\pm}$4.86% on the average. The contributions of body joints to the kinetic energy of the clubhead was the order of lumbar > upper right shoulder > left elbow > right wrist during the down swing.

• Journal of Biosystems Engineering
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• 제39권4호
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• pp.389-399
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• 2014

Purpose: This study was aimed at developing a tractor-driving simulator for the safety training of agricultural tractor operators. Methods: The developed simulator consists of five principal components: mock operator control devices, a data acquisition and processing device, a motion platform, a visual system that displays a computer model of the tractor, a motion platform, and a virtual environment. The control devices of a real tractor cabin were successfully converted into mock operator control devices in which sensors were used for relevant measurements. A 3D computer model of the tractor was also implemented using 3ds Max, tractor dynamics, and the physics of Unity 3D. The visual system consisted of two graphic cards and four monitors for the simultaneous display of the four different sides of a 3D object to the operator. The motion platform was designed with two rotational degrees of freedom to reduce cost, and inverse kinematics was used to calculate the required motor positions and to rotate the platform. The generated virtual environment consisted of roads, traffic signals, buildings, rice paddies, and fields. Results: The effectiveness of the simulator was evaluated by a performance test survey administered to 128 agricultural machinery instructors, 116 of whom considered the simulator as having potential for improving safety training. Conclusions: From the study results, it is concluded that the developed simulator can be effectively used for the safety training of agricultural tractor operators.

• 해양환경안전학회지
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• 제19권6호
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• pp.637-642
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• 2013

본 연구는 피예인선의 거동을 결정짓는 예인선의 힘과 작용지점의 해석에 대해 언급하고 있다. 예인대상선박의 간략화된 동역학방정식을 바탕으로 선형화기법을 적용하여 목적으로 하는 피예인선의 자세와 위치를 달성하기 위한 예인력과 예인력이 가해져야 하는 지점을 도출하였다. 이를 위해 LQR제어기법을 적용하였으며, 수치적인 시뮬레이션을 수행하였다. 리카치방정식을 이용하여 피예인선의 자세제어를 위한 제어기 이득과 자세제어에 필요한 무게중심에서의 힘을 도출하였고, 도출한 힘과 예인지점의 역학적인 관계는 의사역행렬을 이용하여 구하였다. 이러한 해석기법을 바탕으로 피예인선을 초기위치로부터 목표위치로 예인할 때 예인지점 및 예인방식에 따른 예인력을 구할 수 있었다. 최종적으로 선박을 예인하기 위한 예인력은 예인지점과 방향에 밀접하게 연관되어 있는 것을 확인할 수 있었고 이러한 연구결과는 사고선박의 구난작업 시 예인선의 배치에도 적용이 가능할 것이다.

• Wind and Structures
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• 제20권4호
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• pp.509-525
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• 2015

A three-dimensional aerodynamic model and a vehicle dynamics model are established to investigate the effect of noise barrier on the dynamic performance of a high-speed train running on an embankment in crosswind in this paper. Based on the developed model, flow structures around the train with and without noise barrier are compared. Effect of the noise barrier height on the train dynamic performance is studied. Then, comparisons between the dynamic performance indexes of the train running on the windward track and on the leeward track are made. The calculated results show that the noise barrier has significant effects on the structure of the flow field around the train in crosswind and thus on the dynamic performance of the high-speed train. The dynamic performance of the train on the windward track is better than that on the leeward track. In addition, various heights of the noise barrier will have different effects on the train dynamic performance. The dynamic performance indexes keep decreasing with the increase of the noise barrier height before the height reaches a certain value, while these indexes have an inverse trend when the height is above this value. These results suggest that optimization on the noise barrier height is possible and demonstrate that the designed noise barrier height of the existing China Railway High-speed line analysed in this article is reasonable from the view point of the flow field structure and train dynamic performance although the noise barrier is always designed based on the noise-related standard.

• 대한안전경영과학회지
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• 제11권2호
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• pp.103-110
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• 2009

The purpose of this study is to suggest a proper tread of stairs using kinematic factors and moments of the lower-limb joints in the stair decent with the 3 different treads with boimechanical method in ergonomics. 9 subjects (body masses; $59.41{\pm}7.49$, $64.03{\pm}6.65$, $67.26:{\pm}7.58$, heights; $160.50{\pm}6.35$ ages; $31.22{\pm}2.99$; parity; $1.67{\pm}0.71$) participated in three experiments that were divided by physiological symptoms (the early (0-15 weeks), middle (16-27 weeks) and last (18-39 weeks). and they walked at self-selected pace on 4 staircases 3 trials. As extending the pregnancy period, cadence was shorter but cycle time were longer more and more. As extending treads of stair decent during pregnancy, speed, stride lengths and cycle time were increased. As extending the treads of stair decent, hip and ankle moments increased but knee moments decreased in sagittal plane. There were increasing or decreasing of moments by means of treads. These changes may account for relation between the treads of stair and moments in pregnant women. The main changes of pregnant women were joint moments and kinematic factors during pregnancy period because pregnancy makes them physical changes. It is possible that joints have connection with compensation each other to maximize stability and to control gait motion. In conclusion, we suggest that the tread of stair is longer than 26cm tread. and exercise programs to improve muscle activity were necessary where joint moments were small.

• Journal of Advanced Marine Engineering and Technology
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• 제39권9호
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• pp.918-922
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• 2015

선박으로부터 배출되는 오염원과 온실가스에 대한 국제적 규제가 점점 더 강화되어 감에 따라, 액화 천연 가스를 선박의 연료로 사용하는데 대한 관심이 높아져 가고 있다. 본 연구는 액화 천연 가스 연료 선박에서 사용되는 두 가지 방식의 연료 가스 공급 장치에 대하여 폭발 잠재 위험 분석을 수행하였다. 8500 TEU 급 컨테이너 선박을 목표 선박으로 선정하여, 액화 천연 가스 저장 탱크를 설계하였고 각 연료 공급 방식의 운전을 위한 압력 조건을 가정하였다. 누출공의 크기를 세 개의 범주로 분류하여, 각 누출공 크기 범주에 대한 누출 빈도를 산출하였고, 대표 누출공의 크기와 누출량을 추산하였다. 방출률의 증가와 누출 빈도는 역비례 관계를 보였으며, 펌프 방식 연료 공급 장치에서는 누출 빈도가 높게 나타났고, 가압 방식 연료 공급 장치에서는 방출률이 높게 나타났다. 전산 유체 역학 시뮬레이션을 통하여 폭발 잠재 위험 분석을 수행하고 각 연료 공급 장치에 대한 결과를 비교하였다.

• The Journal of Korean Physical Therapy
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• 제22권2호
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• pp.15-23
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• 2010

Purpose: This study was done to establish reference data for temporo-spatial, kinematic and kinetic parameters for normal Koreans as they age. Methods: Normal adults and children without a previous history of musculoskeletal problems were enrolled in this study. The normal subjects were divided by age into three groups: Group I: children ($11.95{\pm}0.29$ years); Group II: young adults ($23.90{\pm}3.67$ years); Group III: older adults ($71.40{\pm}4.08$ years). The temporo-spatial and kinematic data were measured using 6 MX3 cameras while each subject walked through a 10 m walkway at a self-selected speed. The kinetic data were measured using 2 force plates and were calculated by inverse dynamics. Results: Motion patterns are typically associated with a specific phase of the gait cycle. Our results were as follows: 1. There were significant differences between the different age groups in temporo-spatial parameters such as cadence, double support, time of foot off, stride length, step length, and walking speed. 2. There were significant differences between the groups in kinematic parameters such as range of motion (ROM) of the hip, knee and ankle in the sagittal plane, ROM of the pelvis, hip and knee in the coronal plane and ROM of the pelvis, hip and ankle in the transverse plane. 3. There were significant differences between the groups in kinetic parameters such as joint moments of force, joint mechanical power generation or absorption and ground reaction forces. Conclusion: The results of this study can be utilized (a) as a reference for kinematic and kinetic data of gait analysis in normal Koreans, and (b) as an aide in evaluating and treating patients who have problems relating to gait.

• 한국운동역학회지
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• 제22권1호
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• pp.43-53
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• 2012

The purpose of this study was to quantitatively examine the biomechanical variables of Fouette turns for expert and beginner ballet dancers and to determine the difference in the variables between the two groups. sixteen female ballet dancers participated in this study. They were divided into an expert group(age, $25.38{\pm}1.92$ years; height, $168.38{\pm}4.66$ cm; mass, $49.63{\pm}4.41$ kg) and a beginner group(age, $20.88{\pm}1.13$ years; height, $161.63{\pm}7.42$ cm; mass, $48.88{\pm}3.64$ kg) depending on their ballet experience. Descriptive data were expressed as mean ${\pm}$ standard deviation (SD) for all variables including the duration, displacement of the center of the body, velocity of the center of the body, angle of the body segments, angular velocity of the body segments, ground reaction force, lower extremity torque, muscle activity, body weight, age, and body mass. An independence t-test was conducted to determine how the following variables differed between the beginners and experts: duration, displacement of the center of the body, velocity of the center of the body, angle of the body segments, angular velocity of the body segments, ground reaction force, lower extremity torque, and muscle activity. All comparisons were made at the p<0.05 significance level. The results show that the experts scored high on the biomechanical variables, although all the variables were not significant. Significant differences were found in the angle of body segments, angular velocity of the body segments, lower extremity torque, and muscle activity(p<0.05). The findings of this study demonstrate that the experts have the required skill to make an improved Fouette turn. The findings may also help ballet dancers to learn and understand the Fouette turn.