• The Journal of Korea Robotics Society
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• v.6 no.4
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• pp.308-316
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• 2011

This work deals with development of effective redundancy resolution algorithms for the motion control of manipulator. Differently from the typical kinematically redundant robots that are attached to the fixed ground, the ZMP condition should be taken into account in the manipulator motion in order to guarantee the system stability. In this paper, a new motion planning algorithm for redundant manipulator not fixed to the ground is introduced. A sequential redundancy resolution algorithm is proposed, which ensures the ZMP (Zero Moment Point) stability, the planned operational motion, and additional sub-criteria such as joint limit index. A geometric constraint equation derived by reshaping the existing ZMP equation enables one to employ the sequential redundancy algorithm. The feasibility of the proposed algorithm is verified by simulating a redundant manipulator model.

• Journal of Institute of Control, Robotics and Systems
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• v.11 no.6
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• pp.543-549
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• 2005

This paper deals with modeling and analysis fer the landing motion of a human-body model. First, the dynamic model of a floating human body is derived. The external impulse exerted on the ground as well as the internal impulse experienced at the joints of the human body model is analyzed. Second, a motion planning algorithm exploiting the kinematic redundancy is suggested to ensure stability in terms of ZMP stability condition during a series of landing phases. Four phases of landing motion are investigated. In simulation, the external and internal impulses experienced at the human joints and the ZMP history resulting from the motion planning are analyzed for two different configurations. h desired landing posture is suggested by comparison of the simulation results.

• 제어로봇시스템학회:학술대회논문집
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• 2002.10a
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• pp.85.2-85
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• 2002

If a biped humanoid robot walks stably on even and uneven planes like a human being, it should have a control system capable of compensating for moments generated by motions of its lower-limbs, upper-limbs and head. In this paper, a compensatory motion control method is described for the stability of biped humanoid robots. This control method calculates the combined motion of the trunk and the waist that cancels the generated moments by using an iteration algorithm. During the biped walking, the combined motion is employed only for stability while the motion of the lower-limbs is used only for locomotion. This method is useful for not only a steady walking but also a transient walking. The e...

• International Journal of Naval Architecture and Ocean Engineering
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• v.8 no.4
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• pp.320-329
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• 2016

An implicit method of solving the six degree-of-freedom rigid body motion equations based on the second order Adams-Bashforth-Moulten method was utilised as an improvement over the leapfrog scheme by making modifications to the rigid body motion solver libraries directly. The implementation will depend on predictor-corrector steps still residing within the hybrid Pressure Implicit with Splitting of Operators - Semi-Implicit Method for Pressure Linked Equations (PIMPLE) outer corrector loops to ensure strong coupling between fluid and motion. Aitken's under-relaxation is also introduced in this study to optimise the convergence rate and stability of the coupled solver. The resulting coupled solver ran on a free floating object tutorial test case when converged matches the original solver. It further allows a varying 70%-80% reduction in simulation times compared using a fixed under-relaxation to achieve the required stability.

• Journal of the Korea Institute of Military Science and Technology
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• v.5 no.2
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• pp.37-49
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• 2002

In this paper, flyout stability of missile that is launched in inclined launcher using sabots is analyzed. To include missile bending motion during flyout, FEA model of missile is converted into eight concentrated mass and equivalent stiffness matrix. Six d.o.f ship motion that have influence on flyout stability is modeled and missile firing time is modeled as probability variable to take arbitrary ship attitude into account. Gap between missile and sabot is modeled as normal distribution probability variable and Monte Carlo simulation is performed. As results, the coriolis acceleration effects by ship motion are analyed and statistical results of missile pitch rate are shown.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.13 no.4
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• pp.247-257
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• 2003

This paper presents an analytical method to Investigate the stability of a hydrodynamic journal bearing with rotating herringbone grooves. The dynamic coefficients of the hydrodynamic Journal bearing are calculated using the FEM and the perturbation method. The linear equations of motion can be represented as a parametrically excited system because the dynamic coefficients have time-varying components due to the rotating grooves, even in the steady state. Their solution can be assumed as a Fourier series expansion so that the equations of motion can be rewritten as simultaneous algebraic equations with respect to the Fourier coefficients. Then, stability can be determined by solving Hill's infinite determinant of these algebraic equations. The validity of this research is proved by the comparison of the stability chart with the time response of the whirl radius obtained from the equations of motion. This research shows that the instability of the hydrodynamic journal bearing with rotating herringbone grooves increases with increasing eccentricity and with decreasing groove number, which play the major roles in increasing the average and variation of stiffness coefficients, respectively. It also shows that a high rotational speed is another source of instability by increasing the stiffness coefficients without changing the damping coefficients.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.166-174
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• 2002

This paper presents an analytical method to Investigate the stability of a hydrodynamic journal bearing with rotating herringbone grooves. The dynamic coefficients of the hydrodynamic journal bearing are calculated using the FEM and the perturbation method. The linear equations of motion can be represented as a parametrically excited system because the dynamic coefficients have time-varying components due to the rotating grooves, even in the steady state. Their solution can be assumed as a Fourier series expansion so that the equations of motion can be rewritten as simultaneous algebraic equations with respect to the Fourier coefficients. Then, stability can be determined by solving Hill's infinite determinant of these algebraic equations. The validity of this research is proved by the comparison of the stability chart with the time response of the whirl radius obtained from the equations of motion. This research shows that the instability of the hydrodynamic journal bearing with rotating herringbone grooves increases with increasing eccentricity and with decreasing groove number, which play the major roles in increasing the average and variation of stiffness coefficients, respectively. It also shows that a high rotational speed is another source of instability by increasing the stiffness coefficients without changing the damping coefficients.

• Korean Journal of Applied Biomechanics
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• v.30 no.1
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• pp.7-16
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• 2020

Objective: It is to find factors related to stability through analysis of plantar pressure factors according to the level of instability when performing Snatch. Method: Foot pressure analysis was performed while 10 weightlifters performed 80% of the highest level of Snatch, and motion was classified and analyzed in 3 grades according to the level of instability. Results: First, in Bad Motion, the movement distance of the pressure center in the direction of ML and AP was larger significantly in Phase 2. Second, in Phase 2, the number of zero-crossing in the AP direction was larger statistically significantly in Good Motion. Third, in the bad motion in Phase 3, the number of zero-crossing in the ML direction showed a significantly larger value. Fourth, in Phase 4, it was found that the more stable the lock out motion, the greater the activity of foot controlling in the left and right directions. Fifth, Phase 3, the greater the Maximum/Mean foot pressure value, the more stable the pulling action. Sixth, in Phase 2, the foot pressure was concentrated with a wide distribution in the midfoot and rearfoot. Seventh, the triggering number of the forefoot region was small in the last pull phase. Eighth, the number of triggers in the toe area was significantly higher during Good Motion in Phase 4. Conclusion: Summarizing the factors of instability in Snatch, there was no significant difference in Phase 1 for each condition. In order to enhance the stability in Phase 2, the sensory control ability in the AP direction is required, and focusing the foot pressing motion with a wide distribution in the middle and rear parts increases the instability. In Phase 3, it was found that the more unstable, the more sensory control activity was performed in the ML direction, the stronger the forefoot pressing action should be performed for a stable Snatch. In Phase 4, It is important that the feet sensory control activity in ML directions and the control ability of the toes in order to have stable Lock out motion.

• Journal of the Korean Society of Marine Environment & Safety
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• v.22 no.7
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• pp.800-806
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• 2016

The maneuverability of a tugboat is affected by the slewing motion of a barge while the tug is navigating with the barge in water. Therefore, it is necessary to reduce the slewing motion of the barge to allow for safe towing work. In this study, a water tank experiment was performed to examine the factors affecting the slewing motion of a barge and improve course stability. The characteristics of slewing motion vary according to bow shape. Three barge models, each with a different bow shape, were selected as experimental subjects. A comprehensive analysis was performed to study the effects of various factors on the slewing motion of a barge such as the presence of a skeg and bridle, towing speed, and the length of the towline. The effect of the location of the skeg varied according to bow-hull form. The slewing motion of the barge decreased as the length of the towline increased, and this decrease was even greater when a bridle was connected to the towline. In addition, the slewing motion decreased significantly as the length of the bridle increased. The slewing angles did not show significant change with respect to towing speed.

• Structural Engineering and Mechanics
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• v.18 no.4
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• pp.411-428
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• 2004

In this study, a newly developed unconditionally stable explicit method is employed to solve momentum equations of motion in performing pseudodynamic tests. Due to the explicitness of each time step this pseudodynamic algorithm can be explicitly implemented, and thus its implementation is simple when compared to an implicit pseudodynamic algorithm. In addition, the unconditional stability might be the most promising property of this algorithm in performing pseudodynamic tests. Furthermore, it can have the improved properties if using momentum equations of motion instead of force equations of motion for the step-by-step integration. These characteristics are thoroughly verified analytically and/or numerically. In addition, actual pseudodynamic tests are performed to confirm the superiority of this pseudodynamic algorithm.