• Proceedings of the Korean Society of Precision Engineering Conference
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• 1994.10a
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• pp.893-900
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• 1994

In this study, workspace analysis has been performed for a Clemens Coupling type parallel robotic wrist with four degrees of freedom such as three angular degrees of freedom and 1 plunge motion. Because of plunge motion, this mechanism has no singular point that the general roll-pitch-roll mechanisms have. Also, proposed mechanism performs larger load, faster motion, with less weight and has better structural characteristics such as higher stiffness and strength to weight ratio compared with serial type mechanisms. As a basic step for position control, the closed form solution of forward and inverse kinematics are proposed and workspace is analyzed and plotted by applying triangle tracer method for workspace boundary tracing.

• 한국전산유체공학회:학술대회논문집
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• 2006.05a
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• pp.263-267
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• 2006

The path of a flapping airfoil during upstroke and down-stroke is optimized for maximum thrust and propulsive efficiency. The periodic flapping motion in combined pitch and plunge is described using Non-Uniform B-Splines(NURBS). A gradient based algorithm is employed for optimization of the NURBS parameters. Unsteady, low speed laminar flows are computed using a Navier-Stokes solver in a parallel computing environment based on domain decomposition. It is shown that the thrust generation is significantly improved in comparison to the sinusoidal flapping motion. For a high thrust generation, the airfoil stays at a high effective angle of attack for short durations.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.4
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• pp.123-129
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• 1993

Because the existing scour prediction formulas for plunge pools of pipe culverts and spillways give a wide range of predicted scour depths, it is difficult to estimate actual scour depths. A review of literature showed that wide range of predicted values was caused mostly by lack of thorough analysis of the scour mechanism. In this study, the effects of the parameters govering scour were examined, and the scour potentials were measured. The major variables govering scour were the velocity and size of jet impinging into the plunge pool, the submerged weight of bed material, the ratio of jet size to bed material size, the tail watr depth of the plunge pool, and the angle of jet impact on water surface. The ratio of jet size to bed material size to bed material size was found to be another significant parameter affecting scour for larger bed materials. A densimetric Froude nember of the bed material in incipient motion was formulated. This number represented the scour potential of the jet at the point where the bed material was tested.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.1018-1021
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• 1997

This paper presents a result of simulation and improvement of grinding process for linear motion guide blocks. A simulation software, which is based on cylindrical grinding process. is used to predict the grinding wheel wear during the grinding process. To validate the simulation, the simulation result is compared with the experimental one. Simulation study is extended to obtain an optimal grinding condition for minimizing the grinding wheel wear. The optimal condition is validated through an experiment.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.12
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• pp.1146-1151
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• 2008

In this paper, the effects of torsional flexibility on a flapping airfoil are investigated. The aerodynamic forces of a torsional flexible flapping airfoil is computed using 2-D unsteady vortex panel method. A typical-section aeroelastic model is used for the aeroelsatic calculation of the flapping airfoil. Torsional flexibility and excitation frequency are considered as main effective parameters. Under heavy airfoil condition , the thrust peak is observed at the points where the frequency ratio is about 0.75. Based on this peak criterion, there exists two different motions. One is an inertia driven deformation motion and the other is an oscillation driven deformation motion. Also, in the thrust peak condition, the phase angle is kept 85 degrees, independent of the torsional flexibility and the excitation frequency.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.7
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• pp.9-17
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• 2005

The wake patterns and thrust characteristics of dual flapping airfoils in a biplane configuration are investigated using an unsteady panel method. To trace complicated wake shapes behind airfoils, a core addition scheme, a vortex core model, and the fourth order Runge-Kutta convection scheme are employed. Present results are verified by comparing them with flow visualization, exact solution and published computed results. The thickness and camber of thick airfoils has an effect of decreasing thrust. The airfoils produce maximum thrust when the phase angles between plunging and pitching motions are both 90 and 120 degrees. Thrust increases as the plunge velocity is increased, which is also found as the pitch amplitude is stepped up. Thrust decreases when the distance between the airfoils is less than 0.6c.