• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.05a
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• pp.204-209
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• 2004

This paper describes dynamic manipulability analysis of robotic arms moving in viscous fluid. The Manipulability is a functionality of manipulator system in a given configuration and under the limits of joint ability with respect to the tasks required to bt performed. To investigate the manipulability of underwater robotic arms, a modeling and analysis method are presented. The dynamic equation of motion of underwater manipulator is derived from the Lagrange - Euler equation considering with the hydraulic forces caused by added mass, buoyancy and hydraulic drag. The hydraulic drag term in the equation: is established as analytical form using Denavit - Hartenberg (D-H) link coordination of manipulator. Two analytical approaches based on Manipulability Ellipsoid are presented to visualize the manipulability of robotic arm moving in viscous fluid. The one is scaled ellipsoid which transforms the boundary of joint torque to acceleration boundary of end-effector by normalizing the torque in joint space while the other is shifted ellipsoid which depicts total acceleration boundary of end-effector by shifting the ellipsoid in work space. An analysis example of 2-link manipulator with proposed analysis scheme is presented to validate the method.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.829-832
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• 2010

For gas turbine engine starting, external power should be supplied with engine to accelerate to suitable rotational speed for air and fuel ignition conditions. Electric starting system for small gas turbine engine has simple system and light weight, so it is generally used for small aircraft. For system analysis of gas turbine engine electric starting system, Characteristics of battery, start motor, engine drag torque should be analyzed and theirs temperature effects should be considered. In this paper, preliminary design procedure of small gas turbine engine electric starting system and major design parameters were described.

• International Journal of Aeronautical and Space Sciences
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• v.17 no.2
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• pp.167-174
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• 2016

Even though the differential drag type machines of the vertical wind turbines are a bit less efficient than the lift type machines such as Darrieus type machines, they have an advantage of low starting torque. The flapping blade type wind turbine is a specific type of the differential drag machines, and it has no need for orientation as well as quite low starting torque. This work is to develop an innovative 5kW class flapping type vertical wind turbine system which will be applicable to a hybrid power generation system driven by the diesel engine and the wind turbine. The parametric study was carried out to decide an optimum aerodynamic configuration of the wind turbine blade. In order to evaluate the designed blade, the subscale wind tunnel test and the performance test were carried out, and their test results were compared with the analysis results.

• Journal of Biosystems Engineering
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• v.27 no.1
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• pp.19-24
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• 2002

According to the field test, the transient power transmission efficiency of a tractor driveline fluctuated in a range of 56 to 86% and the mean value was about 72.5%. Therefore, the constant efficiency model commonly used for a simulation of power performance was not proper far predicting such a variable of efficiency. In order to predict power efficiency more accurately, new concepts of the maximum efficiency and drag torque were introduced and a new model based on the these concepts was proposed. The difference between measured and model-predicted efficiencies was about 1.5% in average with a standard deviation of 1.1%. The new power efficiency model was expected to enhance the accuracy of predicting power transmission efficiencies of tractor drivelines.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.561-565
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• 2008

Generally, reaction wheels or thrusters are used for attitude control of a satellite. There is a potential method for the attitude control utilizing the plasma flow on the Low Earth Orbit. In the present study, experiments which simulate attitude control of a Low Earth Orbit Satellite using the ionosphere were conducted. In this experiment, a plasma flow was generated by a steady-state Hall type accelerator. However it is known that the Hall type accelerator, which is used as plasma source, produces a torque around its axis called "swirl torque". This torque would affect the attitude control in the above-mentioned experiments. First of all, we conducted the measurement of the swirl torque. Secondly, experiments using a satellite model with negative electrodes were conducted. The negative electrodes generated torque around the axis, and controlled the attitude of the satellite model by changing the applied voltage.

• Journal of Biosystems Engineering
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• v.31 no.4 s.117
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• pp.323-333
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• 2006

Introduction of a direct engine-PTO driveline to agricultural tractors has reduced production cost and increased transmission efficiency of the PTO driveline. However, this type of PTO driveline has caused a severe rattle noise in the PTO gearbox under idle conditions. This study was conducted to investigate the causes of the rattle noise and the effects of driveline parameters on it. A mathematical model was developed for a direct engine-PTO driveline. The model was proved experimentally to be accurate enough to simulate the dynamic characteristics of the PTO driveline motions. The simulation study showed that the rattle noise was caused by collisions between the driving and driven gears in the PTO gearbox due to velocity variation of the gears, which was induced by torque fluctuations from the engine. It was also found that the rattle noise decreased with the drag torque and mass moment of inertia of the engine flywheel. Smaller mass moment of inertia of the driven gears and backlash also reduced the rattle noise. However, increasing the drag torque and mass moment of the engine flywheel or decreasing the backlash and mass moment of inertia of the driven gears were limited practically by their detrimental effects on transmission efficiency, gear strength and smooth meshing of the gears.

• Journal of KSNVE
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• v.4 no.3
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• pp.319-325
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• 1994

The flucturation of the engine torque appears to be the major source of the torsional vibration of the automotive driveline. The reduction of this torsional vibration has become a significant problem, due to an increase in the flucturation of the torque of recent light weighted powered engines, along with the requirements of higher performance. The torsional vibration of the automotive driveline can be reduced by soothing the fluctuation by adjusting the torsional characteristics of the clutch-disc. Computer simulation of the engine- input gear train is a useful investigative tool on studying the torsional characteristics of the clutch-disc. In this paper, a dynamic model for the automotive driveline was developed, and the engine torque and drag torque of the model were evaluated withe experimental data. By executing a simulation using the model, it has become possible to obtain the clutch-disc torsional characteristics when the engine is idling and the clucth-disc torsional characteristics for reducing the torsional vibration has been suggested.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.10
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• pp.2706-2711
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• 1994

In this work, an experimental type of torque converter has been constructed and its characteristics have been evaluated by adapting an electrorheological fluid(ERF) as an operating medium. The device was designed by using the equations which were proposed by Carlson et al. The correlation between the rheological behaviour of an ERF and mechanical parameters of the clutch has been investigated. The torque generated by an ERF in this device is sum of one due to the yield strength by polarizing dispersed particles in dielectric oil and one due to the viscous drag. The experimental results are presented in terms of torque and current density as a function of rotational speed at various electric field strength applied. Experimental results showed that the measured torque was rapidly increased with the increase of the electric field, generally being proportional to the rotational speed of the motor. The measured current was shown to be increased with the increased electric field. Also, the current was decreased with the increase of increased with the increased electric field. Also, the current was decreased with the increase of the rotational speed of the motor and reached plateau region after f = 5 Hz.

• Korean Journal of Applied Biomechanics
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• v.29 no.2
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• pp.43-51
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• 2019

Objective: This study aims to propose an efficient technical model through a kinematic analysis of field hockey drag flick shooting motion in laboratory situations and game situations and to build up the basic data on drag flick shooting technique through a comparative analysis of a Korean specialized shooter and specialized shooters of competing Asian countries. Method: This study selected one Korean female national specialized shooter and seven specialized shooters of competing countries, China, Japan, India, and Malaysia, who participated in the 2018 Asian Hockey Champions Trophy as research subjects. In exercise situations, a 3-D motion analysis utilizing an infrared camera was conducted, while in game situations, an image-based 3-D motion analysis utilizing a digital camera was conducted. Results: The Korean specialized shooter had smaller changes in the angles of the trunk and the stick in game situations than in exercise situations. She had a high angular velocity of the trunk and the stick head, and the maximum speed of the ball was high. The Korean specialized shooter had the maximum angular velocity of the trunk higher than the specialized shooters of the competing countries did, and the angular velocity of the stick head and the maximum speed of the ball were in the average level. Conclusion: As for drag flick shooting in game situations, changes in the angle of the trunk and the stick were small, and the angular velocity was high due to the pressure that the shooters should perform the motion fast with the defenders' interruptions, and this high angular velocity of the trunk and the stick head affected the movement of the ball. Thus, the maximum speed of the ball was higher in game situations than in exercise situations. The Korean specialized shooter had the maximum angular velocity higher than the specialized shooters of the competing countries did; however, the maximum speed of the ball was average, and it turned out that the maximum speed of the ball was associated with the angular velocity of the stick head in P3. Therefore, Korean specialized shooters need complementary training for a change to the torque of the stick head, using the strong torque of the trunk.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.17 no.1
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• pp.23-32
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• 2021

Conventional wind power generators have limited installation sites due to low efficiency due to reverse resistance or high cut-in speed. To compensate for these problems, this study proposed another new type of tilting wind turbine. The key to this method is the structural design of a cylindrical cam with a guide groove that allows the blade to tilt. As the blade rotates by the cam, it tilts according to the angle. In the section that generates torque by receiving drag, the blade is made perpendicular to the wind. And it is a structure that creates a parallel state with the wind in the section where reverse resistance occurs. We prepared six types of cams considering the length of the section subject to drag, reverse resistance, tilting section. The performance was analyzed as the maximum value of the output, torque coefficient, and efficiency coefficient, which is indicated by setting different wind speed and low TSR.