• 한국소음진동공학회논문집
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• 제15권5호
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• pp.620-628
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• 2005

In this paper, we studied about the dynamic behavior of a cracked rotating cantilever beam. The influences of a rotating angular velocity, the crack depth and the crack position on the dynamic behavior of a cracked cantilever beam have been studied by the numerical method. The equation of motion is derived by using the Lagrange's equation. The cracked cantilever beam is modeled by the Euler-Bernoulli beam theory. The crack is assumed to be in the first mode of fracture and to be always opened during the vibrations. The lateral tip-displacement and the axial tip-deflection of a rotating cantilever beam is more sensitive to the rotating angular velocity than the depth and position of crack. Totally, as the crack depth is increased, the natural frequency of a rotating cantilever beam is decreased in the first and second mode of vibration. When the crack depth is constant, the natural frequencies of a rotating cantilever beam are proportional to the rotating angular velocity in the each direction.

• Journal of Biosystems Engineering
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• 제14권4호
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• pp.221-228
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• 1989

A data acquisition system was designed to measure the forces on a rolling coulter in three coordinated directions, angular velocity of the coulter and travel speed of a soil bin. The data acquisition system consisted of a dynamometer, speed transducers, a signal conditioner, an inter-face board, an Aim-65 microcomputer and a digital data recorder. Strain gages were attached on the surface of the dynamometer and connected to form three Wheatstone bridges, which measure the draft force, the vertical force and the side force on the coulter. An interaction among three dimensional forces was found during the calibration. A matrix procedure was used to correct the forces for this interaction. Rotary shaft encoders were mounted on the coulter and on the soil bin drive to measure the angular velocity of the coulter and the travel speed of the soil bin. The angular velocity and the travel speed were computed by counting the number of pulse signals from the rotary shaft encoders every 0.2 second. The digital signals from the rotary shaft encoders were connected to counters and the analog signals from the dynamometer, after passing through the signal conditioner, were connected to the A/D converter. The microcomputer programs, written in assembly language, were developed to read signals from the transducers, convert them to actual unit, display them upon request and record them on a sigital tape every 0.2 second.

• 동력기계공학회지
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• 제3권1호
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• pp.55-59
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• 1999

Generally, T.G(Tacho-generator, Tachometer) sensor is used widely for sensing the angular velocity in rotary machine. By limitation of T.G sensor's structure, the sensed angular velocity include a periodic noise, and the noise is called "ripple" as an electrical term. To reduce the effecting of the ripple, many kinds of filters are designed and installed, but there is necessary a trade off between response time and adapted frequency band. In this paper, we propose a generalized observer to estimate an angular velocity from the output signal of T.G sensor. The generalized observer is proposed firstly for continue systems, and it is applied to DC servo motor with T.G sensor. For simulation, we measure T.G signals at 60, 400, 570 rpm respectively, and analysis those to obtain the resonance frequency of ripple by FFT method. To verify the effectiveness of the proposed algorithm, we compare the results with those of a RC low frequency band filter.

• 대한기계학회논문집
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• 제16권2호
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• pp.369-381
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• 1992

Characteristics of flow and heat transfer have been studied numerically in a square duct with a periodic pressure gradient. The flow in a duct was assumed to be fully developed and constant heat flux was imposed at the surfaces of a square duct. The distributions of axial velocity and time-space averaged temperature are investigated with angular velocity and amplitude ratio at a given Reynolds number 1000. When the periodic pressure gradient was imposed axially in a duct, the reverse flow may be occurred near the duct wall. The magnitude of this reverse flow increases as the amplitude ratio increases or as the angular frequency decreases. In the ranges of the amplitude ratio and the angular velocity in present investigation, the ratio of the periodic time space averaged temperature to the nonperiodic space averaged temperature has been found to be greater than one. This means that the cooling effect at the duct walls deteriorates with a periodic situation compared with nonperiodic one.

• Journal of Mechanical Science and Technology
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• 제19권6호
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• pp.1253-1267
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• 2005

Misalignment can be an important problem in the integration of GPS/INS. Observability analysis of the alignment errors in the integration of low-grade inertial sensors and multi-antenna GPS is presented in this paper. A control-theoretic approach is adopted to study the observability of time-varying error dynamics models. The relationship between vehicle motions and the observability of the errors in the lever arm and relative attitude between GPS antenna array and IMU is given. It is shown that alignment errors can be made observable through maneuvering. The change of acceleration makes the components of the relative attitude error that are orthogonal to the direction of the acceleration change observable. The change of angular velocity makes the components of the lever arm error that are orthogonal to the direction of the angular velocity observable. The motion of constant angular velocity has no influence on the estimation of the lever arm.

• 한국항공우주학회지
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• 제49권5호
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• pp.389-397
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• 2021

인공위성의 자세제어 구동기인 제어모멘트자이로의 고장에 따른 제어 특성을 분석하였다. 특히, 4개 중에 한 개가 고장난 상황을 고려하였다. 가장 많이 사용되는 피라미드와 box-90 구조를 고려하였으며, 고장 발생 이후의 특이점 및 특이면을 분석하고 비교하였다. 모듈이 고장나고 휠 속도를 줄이는 과정에 대한 동역학 방정식을 유도하였다. 정상인 세 모듈이 고장난 모듈의 모멘텀을 흡수하면서 위성의 각속도를 안정화하는 과정을 분석하였는데, 특이형상에서 나머지 CMG가 교착되거나 과도하게 요동할 수 있는데, 짐벌각 재조정을 통하여 방지할 수 있음을 제시한다.

• 시큐리티연구
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• 제31호
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• pp.187-207
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• 2012

본 연구는 태권도의 기본동작인 주춤서기 자세에서의 주먹 지르기 동작을 3차원 입체영상분석을 통해 유형별로 운동학적 변인인 시간, 속도, 각도, 각속도, 각가속도 등을 분석하여 유형별 특성을 알아보고 올바른 주먹 지르기 동작의 지도방법을 제시하고자 하였다. 이를 위해 대학교 경호무도 태권도 경호무도시범단 3인을 대상으로 실시하였고 다음과 같은 결론은 도출 하였다. 1. 지르기 동작 수행시간 : 각 유형(Type)별 주춤서기 자세에서 주먹 지르기 동작 수행시간은 1구간에서 $0.24{\pm}0.07s$와 $0.42{\pm}0.08s$로 유형(Type)1의 주먹 지르기 동작 수행시간이 빠르게 나타났지만 전체 수행시간에 대한 구간별 비율은 유형(Type)2의 테이크 백(take back)이 더 짧은 것으로 나타났다. 2. 선속도 및 선가속도 변인 : 각 유형(Type)의 국면별 선속도는 모두 다르지만 가장 높은 선속도는 각 유형(Type)의 임팩트 순간 이라 할 수 있으며, 유형(Type)2의 임팩트 순간인 3국면에서 가장 높은 선속도가 나타났다. 3. 관절각 변인 : 유형(Type)별 주먹 지르기 동작이 관절의 각은 임팩트 국면인 유형(Type)1의 주먹 지르기 동작과 유형(Type)2의 주먹 지르기 동작에서 외형적으로 큰 차이가 나지 않지만 유형 (Type)2의 주먹 지르기 동작이 관절각의 변화가 다양해 역동적인 자세를 취하고 있다. 4. 각속도 및 각가속도 변인 : 유형(Type)1의 주먹 지르기 동작이 임팩트 순간인 3국면의 고관절, 견관절, 손목관절 의 각속도는 각각 $0.79{\pm}0.02deg/s$, $0.91{\pm}0.04deg/s$, $5.24{\pm}0.09deg/s$ 로 나타났으며, 유형(Type)2의 주먹 지르기 동작이 임팩트 순간인 4국면의 고관절, 견관절, 손목관절의 각속도는 각각 $1.32{\pm}0.03deg/s$, $0.21{\pm}0.03deg/s$, $4.98{\pm}0.08deg/s$로 나타났다. 유형(Type)2의 임팩트 순간인 3국면의 오른쪽 손목관절의 각가속도의 변화를 보면 $176.24{\pm}1.11deg/s^2$로 유형(Type)1의 임팩트 순간의 각가속도 보다 더 큰 속도의 변화를 보였다.

• 한국운동역학회지
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• 제23권4호
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• pp.327-333
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• 2013

The purpose of this study was to investigate the effects of different types of attentional focus(internal focus vs. external focus) on the dart throwing mechanics. Seven expert dart throwing athletes were assigned to an internal focus group and other seven athletes were assigned to an external focus group. Each group was asked to throw dart either under verbal instruction or without instruction. During dart throwing, accuracy(radial error), consistency(bivariate variable error), dart velocity, acceleration, elbow joint ROM, elbow joint angular velocity, EMD(electromechanical delay), iEMG of biceps brachii and triceps brachii, and CI(coactivation index) were collected and analyzed. Nither instruction type nor instruction itself affected in accuracy and consistency. However, in dart velocity and acceleration, there was an interaction between instruction and attentional focus types. Velocity and acceleration increased in the internal condition, where as they decreased in the external condition. The ROM of elbow joint did not affected by instruction and attention type. However, similar to dart velocity and acceleration, angular velocity increased in internal focus group, while it decreased in external focus group. EMG showed no difference with any condition. In conclusion, internal focus is better than external focus for dart throwing.

• 천문학회보
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• 제36권1호
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• pp.54.2-54.2
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• 2011

It is the conventional wisdom that the Poynting-Robertson effect is essentially the outcome of the interplay between absorption and reemission processes. For a better understanding of the motion of charged particles around a compact star with strong radiation, we reached an alternative interpretation for the Poynting-Robertson effect based on the covariant formalism and found that it is attributed to the combination of the aberration and the Lorentz transformation of the radiation stress-energy tensor. As a general relativistic application of the Poynting-Robertson effect, we studied the dynamics of test particles around the spinning relativistic star with strong radiation. We discovered that the combination of the angular momentum and the finite size of the star generates "radiation counter drag" which exerts on the test particle to enhance its specific angular momentum, contrary to the radiation drag. The balance of the radiation drag and the radiation counter drag renders the particle to hover around the spinning luminous star at the "suspension orbit". The radial position and the angular velocity of the particle on the "suspension orbit" are determined by the angular momentum, the luminosity, and the size of the central star only, and they are independent of the initial position and velocity of the particle.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2003년도 ICCAS
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• pp.1994-1999
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• 2003

This paper discusses dynamic characteristics of motion of a pair of multi-degrees of freedom robot fingers executing grasp of a rigid object and controlling its orientation with the aid of rolling contacts. In particular, the discussions are focused on a problem of gain-tuning of sensory feedback signals proposed from the viewpoint of sensorymotor coordination, which consist of a feedforward term, a feedback term for controlling rotational moment of the object, and another term for controlling its rotational angle. It is found through computer simulations of the overall fingersobject dynamics subject to rolling contact constraints that some dynamic characteristics of torque-angular velocity relation may play an important role likely as reported by experimental results in muscle physiology and therefore selection of damping gains in angular velocity feedback depending on the guess of object mass is crucial. Finally, a guidance of gain-tuning in each feedback term is suggested and its validity is discussed by various computer simulations.