• 대한기계학회논문집B
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• 제25권3호
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• pp.330-338
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• 2001

This paper is concerned with the effect of cylinder wakes upstream on blade characteristics of compressor cascade(NCA 65 series). At first, it is found that the velocity defect ratio of cylinder wake varies according to the acceleration and deceleration in a flow field but, is conserved nearly constant at flow downstream the cascade, irrespective of the flow path in the cascade. When a cylinder wake flows along near the suction surface of the blade, or impinges on the leading edge, the turbulent velocities are supplied on or inside the outer edge of boundary layer near the leading edge of suction surface, and the transition to a transitional or turbulent boundary layers is induced, so that the laminar separation is prevented, but the profile loss increases. The transition of boundary layer to a transitional or turbulent one is strongly related with the strength of added turbulent velocities near the leading edge on the suction surface, which is influenced by the flow path of a cylinder wake.

• 한국운동역학회지
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• 제14권3호
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• pp.149-163
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• 2004

This study analyzed kinematic variables about the cross step, the delivery and the release for women's javelin athletics recorded over 50m in the 2004 Busan International Athletics Competition. It was used the Kwon3D Motion Analysis Package Ver. 3.1 Program(Kwon, 2000) for analysing the kinematic variables about the distance, the velocity, and the angle, then we had the results as follows; 1 In the Cross step phase, the COG velocity was low because their step length was short. To keep the CM velocity from the approach to the last cross over step contact, the athletes have to keep the longer step length within about 130% of the athletics' height. 2. In the Delivery phase, the athletics' COG height was gradually lower, and the deceleration of the COG was going up. As the same in the cross step, Therefore the athletes have to increase the step length within about 100% of their height, in order to increasing the COG velocity. And it was shown they have to make small angle of the elbow as possible from the right foot contact to the left foot contact in order to being the big acceleration of the upperarm at the release phase. 3. In the release phase, it was shown to being low position of the release point as the COG was low and then the release velocity of the upperarm was low. Specially when the shoulder lean lateral angle is big at the release phase, it was shown they have a excessive release angle. And, when it was shown the high rotation angle of the shoulder, the shoulder was opened forward bigger than the trunk was opened forward. So the transmission of velocity from the proximal segments was a fast change.

• 한국산학기술학회논문지
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• 제17권8호
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• pp.344-351
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• 2016

열차 운영사의 관점에서, 열차 운행에 관한 주요 관심사는 정해진 운행시간의 준수뿐만 아니라, 그와 동시에 열차 운행을 위해 소비되는 에너지 량을 최소화하는 것이다. 일반적인 수동 운전시, 기관사는 운행 노선의 특성에 따라 미리 규정된 최대 속도 프로파일을 기준으로, 노치를 제어함에 따라 규정 속도를 넘지 않도록 열차의 가감속을 조절한다. 이때 규정 속도를 준수하면서 동시에, 전체 운행 중에 소요되는 에너지 량의 절감을 위해, 기관사가 적절한 노치를 선택할 수 있는 구간별 노치 지정 가이드가 있어야 하며, 이는 운행구간에서의 노치 단계 최적화라는 절차를 통해 가능하다. 본 논문에서는 일반적인 운행 환경뿐만 아니라, 열차가 운행 중에 일시적으로 잔여구간의 트랙 정보 또는 규정속도 정보가 변경되는 이벤트 발생시에도 변화된 정보들을 기반으로 실시간으로 잔역구간의 노치 단계를 최적화 할 수 있는 유전 알고리즘을 활용한 실시간 노치 최적화 방안을 제안하였다. 또한 유전 알고리즘을 통해 얻어진 최적해를 적용할 때 에너지 절감 효과와 최적해 수렴특성에 관하여 분석하였다.

• 제어로봇시스템학회논문지
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• 제11권3호
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• pp.214-221
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• 2005

For decades, airships have being developed in Europe (especially German) and America. Airships are planning to be used for advertisements and airliners as well. In Korea, KARI (Korea Aerospace Research Institute) is developing stratospheric communication airship and the similar research is carried out in Japan. Among them, Zeppelin of German has the cutting-edge airship technology with Zeppelin NT. In this paper, the flight performance and stability were evaluated by comparing mathematical theory and the real test. The stability was examined through dynamic modeling and assured by designing controllers at each flight mode. Elevator angle, rudder angle, magnitude of thrust and tilting angle of thrust vector were used as control inputs. Moreover, after measuring the airship velocity, flight direction, magnitude and direction of the wind, attitude angles and trajectories of the airship at each flight mode, the results were compared with the simulation. To get the reasonable data, low-pass filter and band-stop filter were designed to get rid of the sensor noise and engine vibration. The test was accomplished at cruise mode, turning mode, and deceleration. To conclude, with comparing the simulation data and flight test data, it could be known that the dynamic model used in this paper was reasonable.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 추계학술대회 논문집
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• pp.1066-1069
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• 2002

Dynamic postural control varies with the environmental context, specific task and intentions of the subject. In this paper, dynamic postural control against forward-backward perturbations of a platform was estimated using tri-axial accelerometers and a force plate. Ten young healthy volunteers stood upright in comfortable condition on the perturbation system which was controlled by an AC servo motor. With anterior-posterior perturbations, movements of ankle, knee and hip Joints were obtained by tri-axial accelerometers. and ground reaction forces with corresponding displacements of the center of pressure(CoP) by the force plate. The result showed that the ankle moved first and the trunk forward, which implies that the mechanism of the dynamic postural control in forward-backward perturbations, occurred in the procedure of the ankle, the knee and the hip. Knee flexion and hip extension in the period of acceleration, constant velocity and deceleration phase is very important fur the balance recovery. These responses depends on the magnitude and timing of the perturbation. From the present study the accelerometry-system appears to be a promising tool for understanding kinematic accelerative In response to a transient platform perturbation. A more through understanding of balance recovery mechanism may aid in designing methods for reducing falls and the resulting injuries.

• 한국자동차공학회논문집
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• 제7권8호
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• pp.233-247
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• 1999

Traffic accidents are normally caused by late or faulty judgements due to the driver's inaccurate estimation of the distance, velocity, and acceleration from the surrounding vehicles as well as his carelessness or inattention. Thus, the development of collision avoidance systems is motivated by their great potential for increased vehicle safety. A typical collision avoidance system consists of the forward-looking sensor, the criteria for activation of collision warming and avoidance, the collision avoidance maneuvers, and the user interface. This thesis is concerned with the development of a collision warning algorithm in which the driver is warned of approaching collision with the visual and/or the audible signals . The warning algorithm based on fuzzy logic is presented here based on new warning criteria. It has been newly derived from the conventional warning equation by adding a new input variable of the required deceleration to avoid collision. The algorithm is also able to adapt to the individual driver's taste along with the different road conditions by externally controlling the warning intensity. Finally , the proposed algorithm has been validated using computer simulation.

• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1995년도 춘계학술대회
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• pp.113-116
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• 1995

Steady and physiological flows of a Newtonian fluid and blood in the bifurcated arterial vessel are numerically simulated. Distributions of velocity, pressure and wall shear stress in the bifurcated arterial vessel are calculated to investigate the differences between steady and physiological flows. For the given Reynolds number physiological flow characteristics of a Newtonian fluid and blood in the bifurcated arterial vessel are quite different from those of steady flows. No flow separation or flow reversal in the bifurcated region in the downstream after stenosis appears during the acceleration phase. Also, no recirculation region is seen for steady flows. However, during the deceleration phase the flow began to exhibit flow reversal, which is eventually extended to the entire wall region.

• 제어로봇시스템학회논문지
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• 제17권10호
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• pp.1029-1036
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• 2011

An energy-efficient reference walking trajectory generation algorithm is suggested utilizing allowable ZMP (Zero-Moment-Point) region, which maxmizes the energy efficiency for cyclic gaits, based on three-dimensional LIPM (Linear Inverted Pendulum Model) for biped robots. As observed in natural human walking, variable ZMP manipulation is suggested, in which ZMP moves within the allowable region to reduce the joint stress (i.e., rapid acceleration and deceleration of body), and hence to reduce the consumed energy. In addition, opimization of footstep planning is conducted to decide the optimal step-length and body height for a given forward mean velocity to minimize a suitable energy performance - amount of energy required to carry a unit weight a unit distance. In this planning, in order to ensure physically realizable walking trajectory, we also considered geometrical constraints, ZMP stability condition, friction constraint, and yawing moment constraint. Simulations are performed with a 12-DOF 3D biped robot model to verify the effectiveness of the proposed method.

• 대한조선학회논문집
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• 제34권1호
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• pp.41-49
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• 1997

작은 파 기울기(Ak=0.01)를 갖는 Stokes 파/평판의 경계층 및 반류에 대하여 엄밀 및 근사 자유표변 경계조건을 적용하여 Navier-Stokes 식을 수치해석하였다. 거시유동에서는 외부 흐름 압력 변화가 유선방향의 속도 성분을 가속 혹은 감속시키며 교차 유동의 방향 변화를 야기시킨다. 특히 반류는 역(逆)압력기울기 영역에서보다 순(順)압력기울기 영역에서 그 반응이 크며 정수 중에서의 값을 평균치로 하지 않고 편향되는 반류 편향 특성을 갖는다. 미시유동에서는 자유표면 경계조건이 경계층 및 근접/중간 반류영역에서 큰 영향을 미친다. 차수크기 추정은 계산 결과와 잘 일치하였으며 근사 자유표변 경계조건은 상당한 오차를 유발시킴을 알 수 있다.

• 한국운동역학회지
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• 제17권3호
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• pp.31-39
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• 2007

The purpose of this study was to observe the kinematic pattern of elite women 100m hurdler race from start to finish and analyze how the change of horizontal velocity makes an influence on the athletes' performance. The analysis was based on the performance of Korean elite 100m hurdler A and international elite hurdlers B and C. Following results were drawn from the analyzation of elite 100m hurdlers' technical characteristics; During the race, hurdler A made more than 8 m/s of horizontal velocity at the 3rd, 4th, 6th, and the 7th hurdle. The horizontal velocity peaked at the 4th hurdle with 8.23 m/s. On the other hand, hurdler B and hurdler C maintained more than 8 m/s of horizontal velocity from the 2nd hurdle through the 10th hurdle. Hurdler B's fastest horizontal velocity was 8.67 m/s from the 6th to the 7th hurdle and hurdler C's fastest horizontal velocity was 8.85 m/s from the 5th to the 8th hurdle. From the start line to the 3rd hurdle, the times achieved by hurdlers A, B, and C were 4.90 sec, 4.65 sec, and 4.52 sec. In the middle of the race, which is from the 4th hurdle to the 7th hurdle, hurdlers A, B, and C ran in 9.10 sec, 8.60 sec, and 8.38 sec. And the latter part of the race to the 10th hurdle, the times hurdlers A, B, and C hit were 12.32 sec, 11.66 sec, and 11.32 sec. To the finish line, it took 1.15 sec for hurdler A, 1.1 sec for B, and 1.06 sec for C. Hence, to set the record of sub-13 sec, hurdler A should improve her acceleration from the start line to the 1st hurdle with the speed more than 5.4 m/s and should maintain more than 8 m/s of horizontal velocity from the 2nd hurdle through the 10th hurdle. In addition, hurdler A should improve her speed endurance to minimize the deceleration of horizontal velocity from the 4th hurdle to the final hurdle. If hurdler A could shorten 0.05 sec of time in each hurdle section, she would be able to set the record under 13 seconds.