• Journal of Mechanical Science and Technology
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• 제18권7호
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• pp.1086-1093
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• 2004

The modal characteristics of constrained multibody systems undergoing constant accelerated motions are investigated in this paper. Relative coordinates are employed to derive the equations of motion, which are generally nonlinear in terms of the coordinates. The dynamic equilibrium position of a constrained multibody system needs to be obtained from the nonlinear equations of motion, which are then linearized at the dynamic equilibrium position. The mass and the stiffness matrices for the modal analysis can be obtained from the linearized equations of motion. To verify the effectiveness and the accuracy of the proposed method, two numerical examples are solved and the results obtained by using the proposed method are compared with those obtained by analytical and other numerical methods. The proposed method is found to be accurate as well as effective in predicting the modal characteristics of constrained multibody systems undergoing constant accelerated motions.

• Journal of Hydrospace Technology
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• 제1권1호
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• pp.57-65
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• 1995

For the mechanism of ship capsizing, we can generally consider that it\`s caused due to pure loss of stability, parametric oscillation(low cycle resonance) of ship in waves and the broaching phenomena. Among them, low cycle resonance occurs due to the dynamic change of righting arm with respect to the relative position of ship to waves. The dynamic change depends on the encounter period of a ship in following waves. This paper discusses the following items : (1) An analytical expression of GZ curve varying with respect to the relative position of ship to waves, (2) Non-linear equation of motion describing low cycle resonance, (3) The effects of righting arm, stability range and encounter period on low cycle resonance.

• 한국항공우주학회지
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• 제43권4호
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• pp.289-295
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• 2015

본 논문은 지상에서 단안 영상센서를 이용하여 항공기의 상대 위치를 측정하는 방법에 대하여 기술하는데, 알고 있는 항공기의 날개전폭과 카메라의 광학 파라미터를 이용하여 상대 거리 및 상대 위치를 측정하는 방법을 제시하였다. 또한 항공기 영상을 추출하기 위하여 차영상 기법을 이용하는 방법을 제시하였다. 이러한 기술은 ILS를 대신할 영상기반 자동착륙 시스템으로 이용될 수 있다. 상대 위치 및 거리 측정 성능을 검증하기 위하여 경비행기와 GPS를 이용하여 성능을 검증하였으며 1.85m의 평균제곱근 오차가 발생함을 확인하였다.

• 한국자기학회지
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• 제23권3호
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• pp.89-93
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• 2013

본 연구에서는 홀센서의 감도를 높이기 위해 사용되는 자속집속기의 두께, 홀소자와의 상대적 위치, 모서리 형상에 따르는 발생 자계를 유한요소법을 이용하여 계산하였다. 자속집속기의 두께가 얇을수록 발생 자계가 커지는 것을 알 수 있었고, 이 경향은 반자계를 고려한 겉보기 상대투자율의 두께의존성과 유사하다는 것을 알 수 있었다. 홀소자와의 상대적 위치에 따라 최대의 자계를 발생시키는 자속집속기의 최적의 두께가 변화하는 것을 알 수 있었다. 자속집속기와 홀소자의 간격이 가까울 경우, 자속집속기의 모서리 형상에 경사가 없는 것이 유리하지만, 자속집속기와 홀소자의 간격이 멀어질수록 자속집속기의 모서리를 경사지게 하는 것이 유리하다는 것을 알 수 있었다.

• 한국운동역학회지
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• 제15권1호
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• pp.1-18
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• 2005

The purpose of this study was to evaluate performance characteristics. in the success of team attack during volleyball competition. For this, real game was analyzed using S-VHS video camera for three dimensional cinematography. The contents of this research were receive to set time, set to spike time, setter moving distance, ball position during set and attacker's relative ball position during jump and spike, and open area at spike. Among the various kinematical factors considered in this study, the ball height relative spiker and open area were found to be related to offensive performance. This finding implies that although their direct impact were not significant the other factors could have indirect impact on offensive performance by increasing open area. Thus, receiver, setter, assistant attacker, and main attacker should practice for successful performance in each stage. Lastly, it is necessary to develop kinematic variables to evaluate performance characteristics of players. Further study may consider the best defense position against the attack of the opponent player.

• 대한한의학회지
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• 제28권3호통권71호
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• pp.13-22
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• 2007

Objectives : To obtain pulse information, oriental medical doctors usually use the three finger pulse diagnosis method. Although the diagnostic positions are very important, the exact positions are not known because of the uncertain conversion of measures of length (bun, chon, chuk) and misunderstanding of the related concepts of oriental medicine. In this study, we proposed relative positions for the detection of three pulses with a pulse analyzer. Methods : The proposal was made based mainly on several literature reviews, especially the original texts, and the examination of anthropometric characteristics of 78 individuals. Results : The Kwan is the spot where the radial pulse can be felt well near the eminent head of the radius at wrist, high bone. The position of Chon should be apart from Kwan by 6/10 distance between the high bone and wrist joint of each individual. Finally, the position of Chuk is apart from Kwan by 6.5/100 distance between the high bone and the elbow joint of each individual. Conclusions : Adapting those proposed positions for measuring three pulses can provide more consistent information to what an oriental doctor obtains than a pulse analyzer applied to other positions.

• 한국생산제조학회지
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• 제22권6호
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• pp.1010-1017
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• 2013

Two-axial electrodynamic forces generated on a conductive plate by a partially shielded magnet wheel are strongly coupled through the rotational speed of the wheel. To control the spatial position of the plate using magnet wheels, the forces should be handled independently. Thus, three methods are proposed in this paper. First, considering that a relative ratio between two forces is independent of the length of the air-gap from the top of the wheel, it is possible to indirectly control the in-plane position of the plate using only the normal forces. In doing so, the control inputs for in-plane motion are converted into the target positions for out-of-plane motion. Second, the tangential direction of the open area of the shield plate and the rotational speed of the wheel become the new control variables. Third, the absolute magnitude of the open area is varied, instead of rotating the open area. The forces are determined simply by using a linear controller, and the relative ratio between the forces creates a unique wheel speed. The above methods were verified experimentally.

• Journal of Mechanical Science and Technology
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• 제15권8호
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• pp.1097-1107
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• 2001

In this paper, the wall following navigation algorithm of the mobile robot using a mono vision system is described. The key points of the mobile robot navigation system are effective acquisition of the environmental information and fast recognition of the robot position. Also, from this information, the mobile robot should be appropriately controlled to follow a desired path. For the recognition of the relative position and orientation of the robot to the wall, the features of the corridor structure are extracted using the mono vision system, then the relative position, the offset distance and steering angle of the robot from the wall, is derived for a simple corridor geometry. For the alleviation of the computation burden of the image processing, the Kalman filter is used to reduce search region in the image space for line detection. Next, the robot is controlled by this information to follow the desired path. The wall following control scheme by the PD control scheme is composed of two control parts, the approaching control and the orientation control, and each control is performed by steering and forward-driving motion of the robot. To verify the effectiveness of the proposed algorithm, the real time navigation experiments are performed. Through the result of the experiments, the effectiveness and flexibility of the suggested algorithm are verified in comparison with a pure encoder-guided mobile robot navigation system.

• 대한물리의학회지
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• 제18권3호
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• pp.113-119
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• 2023

PURPOSE: This study aimed to determine the effects of using a smartphone in the sitting position on the pelvic posture and the low back pressure pain threshold (PPT). METHODS: Thirty participants (15 women and 15 men) were recruited for this study. The participants were asked to sit in a normal sitting position without using a smartphone, followed by sitting while watching a video using a smartphone. The pelvic posture was measured using the back range of motion II (BROM II) device and a palpation meter. We measured PPT using the digital pressure algometer. RESULTS: Pelvic posterior tilting was significantly greater when sitting while using a smartphone relative to sitting without using a smartphone (p < .05). There was no significant difference in the height of the iliac crest when sitting while using a smartphone compared to sitting without using a smartphone (p > .05). The PPTs of L1, L3, and L5 were significantly lower when sitting while using a smartphone relative to sitting without using a smartphone (p < .05). CONCLUSION: Based on these results, it can be concluded that frequent smartphone use while sitting may potentially increase the risk of developing low back problems.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2012년도 추계학술대회 논문집
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• pp.215-216
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• 2012