• Journal of Advanced Marine Engineering and Technology
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• v.40 no.8
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• pp.704-709
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• 2016

Wave energy generation systems can be divided into oscillating water chamber type, over topping device type and wave activating body type. The wave activating body type converts wave energy to kinetic energy, and the power generation amount increases as the motion of an activating body increases. In this paper, the wave energy convertor consists of a main body, which has an H-shape, and the activating body. These are connected by a bar-type bridge. By the incident wave, when the activating body moves with vertical motion this motion is consequently converted into rotational motion. The twisting moment and angular velocity at a shaft of convertor are calculated according to various conditions of the incident wave and the shape of the activating body. This can be used as a basic idea for determining the design of wave activating body type convertor.

• Journal of the Korean Society of Visualization
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• v.10 no.1
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• pp.15-20
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• 2012

PCV(Positive Crankcase Ventilation) system is designed to remove blowby gas. In this system, a PCV valve is attached in a manifold suction tube to control the flow rate of blowby gas which generates various operating conditions of an automotive engine. As this valve plays a crucial role, the demand in its design is high owing to the small size and high velocity. For this reason, a numerical investigation was carried out to understand both the spool dynamic motion and internal fluid flow characteristics. As a result, the spool dynamic characteristics(i.e. displacement, velocity, acting force), increase in direct proportion to the magnitude of the pressure difference and indicate periodic oscillating motions. Moreover, the velocity at the orifice region decreases according to the increase in differential pressure due to energy loss caused by the sudden decrease of flow area at the orifice region and the increase of flow volume in front of the spool head. Finally, the mass flow rate at the outlet decreases with the increase of spool displacement.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.810-812
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• 2008

Previously study on structural design of the main wing of the twenty-seat class WIG(Wing in Ground Effect) craft. In the final design, three spars construction was selected for safety in the critical flight load, and the Carbon-Epoxy material was selected for lightness and structural stability. In this study, the forced vibration analysis was performed on the composite main wing structure of the twenty-seat class WIG craft with two-stroke pusher type reciprocating engine. The vibration analysis based on the finite element method was performed using a commercial FEM code, MSC/NASTRAN. Excitations for the frequency response analysis were assumed as the H-mode(horizontal mode), the V-mode(vertical mode) and the X-mode(twisted mode) which are typical main vibration modes of engine. And excitations for the transient response analysis were assumed as the L-mode(longitudinal mode) with the oscillating propeller thrust which occurs in operation. According to the result of forced vibration analysis, structural design was modified to reduce the vibrations.

• Journal of the Korean Society of Industry Convergence
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• v.23 no.6_2
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• pp.999-1006
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• 2020

This study was conducted to develop an efficiency prediction program of a hydraulic secondary energy converter for calculating annual power generation of a Wavestar type wave power generator. Using the period and wave height obtained from the frequency domain analysis, the behavior of the floating body was obtained by assuming the sin function. The piston displacement and speed of the hydraulic cylinder were calculated considering the behavior of the floating body and the shape of the mechanism. The numerical simulation of the hydraulic system was performed by physically modeling the hydraulic cylinders, check valves, hydraulic motors, which are the main devices. In the future, this analysis program will be used to develop a program for estimating annual power generation of a moveable body type wave power generation device.

• Journal of IKEEE
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• v.17 no.1
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• pp.10-15
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• 2013

This paper, we analyzed that the measured data of the radiated power spectrum of electromagnetic waves of the normal spark ignition system and the spark ignition system with feed through type ceramic condenser. The results show that the strength of power spectrum radiated from the system with feed through type ceramic condenser is weaker than the normal system, and the density of power spectrum radiated from the system with feed through type ceramic condenser is smaller than the normal system. From these results, the feed through type ceramic condenser can reduce the electromagnetic waves radiating from the spark ignition system which is the spurious emission, and it can be concluded that the ignition coil of the spark ignition system generating high voltage pulse is equivalent to the radio frequency oscillator which is oscillating high frequency from a electronic point of view.

• Transactions of the Korean hydrogen and new energy society
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• v.26 no.6
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• pp.638-644
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• 2015

This paper describes the continuing effort to analysis and design on dynamic and electrical behavior of gamma-type free piston Stirling engine/generator with dual-opposed linear generator for domestic micro-CHP (Combined Heat and Power) system. The double acting Stirling engine/generator has one displacer and two power piston which are supported by flexure springs. Two power pistons oscillate with symmetric sinusoidal displacement and are connected with moving magnet type linear generators for power generation. To operate Stirling engine/generator, combustion heat of natural gas is supplied to hot-end and heat is rejected from cold-end by cooling water. The temperature difference across the displacer induces the oscillating motion, and it can be explained with mass-spring vibration system. The purpose of this paper is to describe the design process of linear generator for the double acting free-piston Stirling engine.

• Journal of the Korean Wood Science and Technology
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• v.43 no.5
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• pp.682-690
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• 2015

The bonding performance of two types of wood adhesives, namely phenol-resorcinol-formaldehyde (PRF) resin and melamine-urea-formaldehyde (MUF) resin for glued laminated timber manufactured by high frequency (HF) heating was evaluated. The HF heating system consists of HF oscillator with dielectric heating system for curing adhesives, and hydraulic press system for clamping glued laminated timber. The designed frequency and output power of the HF system was as 5 MHz and 60 kW, respectively. To verify dielectric heating mechanism under HF oscillation, the heat loss factors of laminae and adhesives were measured. The results show that it is possible to selectively heat adhesives for their curing due to the remarkably higher loss factor of the adhesives than those of wood laminae. The temperature of adhesive in the bonding line reached up to the set temperature within a few seconds by high frequency oscillating, which advanced the curing of adhesive afterwards. The bonding performance, such as shear strength of bonding line, water soaking delamination, and boiling water soaking delamination of PRF resin met the requirement of Korean Standard (KS), however the MUF resin did not meet the KS requirement of boiling water soaking delamination. These results indicate that the HF heating system is successful to manufacture glued laminated timbers with PRF resins to meet the bonding requirements.

• Ocean and Polar Research
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• v.39 no.3
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• pp.169-179
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• 2017

The "GeoDrifter" is a newly-developed surface drifter with high temporal resolution. It is the first time that high-frequency drifters have been deployed in the East/Japan Sea. The purpose of this study is to introduce the phenomena experienced by these drifters flowing along with the Tsushima Current across the East/Japan Sea, focusing on high-frequency variability, and to discuss them in comparison with previous observations. The observed basin-scale circulation of the Tsushima Current generally coincides well with the known schematic circulation. The GeoDrifter trajectories also show inertial oscillations almost everywhere in the oceanic regions of the East/Japan Sea, strong semi-diurnal tidal currents in the western part of Korea Strait, diurnal currents much stronger than semi-diurnal currents in the upstream region of the Nearshore Branch off the Japanese coast, and many warm eddies in the Yamato Basin, all comparable to the observational results reported in the previous studies. An interesting point is that the semi-diurnal tidal currents undergo a great spatial variation in the western part of the Korea Strait. The observed features that cannot be explained are, among others, strong counter-clockwise motions with oscillating period about 51 hours appearing in the upstream region of the Nearshore Branch off the Japanese coast and the different tidal behaviors between upstream and downstream regions of the latter.

• Journal of Advanced Marine Engineering and Technology
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• v.41 no.1
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• pp.105-110
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• 2017

This paper introduces a heave compensation system for offshore crane when it subjected to unexpected disturbances such as ocean waves, tidal currents or winds and their external force. The dynamic model consists of a crane which is considered to behave in the same manner as a rigid body, a hydraulic driven winch, an elastic rope and a payload. To keep the payload from moving upwards and downwards, PD(Proportional-Derivative) control was applied by using linearization. In order to achieve a better performance, the sliding mode control and the nonlinear generalized predictive control algorithm was applied according to the time-delay. As a result, the oscillating amplitude of the payload was reduced by the control algorithm. Considering the time-delay involved in the system to be one second, nonlinear generalized predictive controller with a robust controller was a suitable control algorithm for this heave compensation system because it made the position of te payload reach the desired position with the minimum error. This paper presented a control algorithm using the robust control and its simulation results.

• Journal of Advanced Navigation Technology
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• v.20 no.3
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• pp.175-181
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• 2016

This paper introduces a heave compensation system for offshore crane when it gets unexpected disturbances and external force. The dynamic model consists of crane assumed to be the rigid body, hydraulic driven winch, elastic rope and payload. To keep the payload from moving up and down, PD control algorithm is applied. By using the control, the oscillating amplitude of the payload is reduced. Also by using the estimated values involved with time-delay, the relative motion of payload in heave direction is dramatically shortened. This paper shows using the control algorithm with estimated value having time-delay 0.1 second is enough to heave compensation system.