• Journal of Korean Society of Coastal and Ocean Engineers
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• v.31 no.4
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• pp.221-228
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• 2019

Experimental investigation was performed to analyze the flow field characteristics and power generation performance for a shroud tidal power generation system. Electrical power output was compared with the rotational speed of the turbine blade and electric load connected to the generator for various flow velocity. As the electrical load decreased, the speed of the turbine increased rapidly and reached by about 2 times. The power output also increased remarkably with the decrease of load, and then decreased after maximum power point. In addition, the maximum power point appeared at high electrical loads as the experimental flow velocity increased. These results of the flow field characteristics and power generation performance analysis of the shroud tidal power generation system variation with the flow velocity conditions and electrical load are expected to be the basic data necessary for the development of efficient shroud tidal power generation system.

• International Journal of Fluid Machinery and Systems
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• v.6 no.2
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• pp.75-86
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• 2013

The effects of acoustic resonance and volute geometry on phase resonance are studied theoretically and experimentally using a centrifugal fan. One dimensional theoretical model is developed taking account of the reflection from the discharge pipe end. It was found that the phase resonance occurs, even with the effects of acoustic resonance, when the rotational speed of rotor-stator interaction pattern agrees with the sound velocity. This was confirmed by experiments with and without a silencer at the discharge pipe exit. The pressure wave measurements showed that there are certain effects of the cross-sectional area change of the volute which is neglected in the one dimensional model. To clarify the effects of area change, experiments were carried out by using a ring volute with a constant area. It was demonstrated that the phase resonance occurs for both interaction modes travelling towards/away from the volute. The amplitude of travelling wave grows towards the volute exit for the modes rotating towards the volute exit, in the same direction as the impeller. However, a standing wave is developed in the volute for the modes rotating away from the volute exit in the opposite direction as the impeller, as a result of the interaction of a growing wave while travelling towards the tongue and a reflected wave away from the tongue.

• Journal of Korean Society of Transportation
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• v.32 no.1
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• pp.63-72
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• 2014

In this paper, characteristics and types of vehicle accidents involving buses that differ from common passenger cars are analyzed. When heavy vehicles are involved in collision accidents, the external impulse conveyed through bus tire from road surface cannot be ignored, so the conventional rigid-body impact model cannot be applied. As a solution, an analysis model which directly considers the tire impulse or considers the bus as moving barrier has been proposed. Also, as there are many instances in which the location of contact point or coefficients related to rotational motion cannot be estimated, utilization of point-mass collision model has been sought. By applying the proposed analysis model to an actual accident case and comparing with the result of the conventional analysis which does not consider the tire impulse, it is shown that the velocity of bus and other values close to the actual amount can be obtained.

• Journal of Hydrogen and New Energy
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• v.28 no.2
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• pp.212-219
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• 2017

As an environmental pollution and global warming due to an excessive carbon emission are intensified, the importance of renewable energy is in rise today. TCP (Tidal Current Power), one of the renewable energy sources, generates electricity by converting kinetic energy of current into rotational energy of turbine. Also the TCP has a great advantages of predictability and reliability. Because the generating power is proportional to cubic of stream velocity, amplifying current speed by applying duct is highly effective to increase the generating power. SPM (Single Point Mooring) can be applied for the weather vane with various current direction and also augments generating power of the system. In addition, simple installation and retrieval could be a merit of SPM system. By combining duct and SPM, TCP system for relatively low-speed-current and shallow water region can be feasible and economical. In this study, single point moored duct-type TCP system was designed and the motion of submerged structure was investigated in both numerical and experimental method. DNV wadam V4.8-1 and OrcaFlex 10.0a were used for the frequency and time domain motion analysis of system respectively. Duct model scaled by 0.05 of Froude conformity ratio and CWC (Circulate Water Channel) are used for experiment.

• Journal of Sensor Science and Technology
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• v.16 no.1
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• pp.17-23
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• 2007

This paper presents a miniaturized turn-counting sensor (TCS) where the geomagnetism and high-rpm rotation of ammunition are used to detect the turn number of ammunition for applications to small-caliber turn-counting fuzes. The TCS, composed of cores and a coil, has a robust structure with no moving part for increasing the shock survivability in the gunfire environments of ${\sim}30,000$ g's. The TCS is designed on the basis of the simulation results of an electromagnetic analysis tool, $Maxwell^{(R)}$3D. In experimental study, the static TCS test using a solenoid-coil apparatus and the dynamic TCS test (firing test) have been made. The presented TCS has shown that the induction voltage of $6.5{\;}mV_{P-P}$ is generated at the magnetic flux density of 0.05 mT and the rotational velocity of 30,000 rpm. From the measured signal, the TCS has shown the SNR of 44.0 dB, the nonlinearity of 0.59 % and the frequency-normalized sensitivity of $0.26{\pm}0.01{\;}V/T{\cdot}Hz$ in the temperature range of $-30{\sim}+43^{\circ}C$. Firing test has shown that the TCS can be used as a turn-counting sensor for small-caliber ammunition, verifying the shock survivability of TCS in high-g environments.

• Tribology and Lubricants
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• v.36 no.3
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• pp.168-192
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• 2020

In recently designed diesel engines, the running conditions for piston-pin bearings have become severe because of the higher combustion pressure and increased temperature. Moreover, the metal removal from the bushing material has strongly reduced the ability of the antifriction material to accept asperity contacts. Therefore, it is necessary to find ways of reducing wear scar on the connecting-rod small-end bushing and piston-pin boss bearing related to the higher combustion pressure on the power cell of an engine. In this work, the position and level of material removal from the surfaces of the bushing and bearing under such severe operating conditions - for example, maximum power and torque conditions of a passenger car diesel engine - are estimated for several combinations of surface roughness. First, piston-pin rotating motion is investigated by calculating the friction coefficient at piston-pin bearings, the oil film thickness, and the frictional torques induced by hydrodynamic shear stress. Subsequently, the wear scarring on the surfaces of a connecting-rod small-end bushing and two piston-pin boss bearings related to piston-pin rotational motion is numerically calculated under the maximum power and torque operating conditions. This work is helpful to determine the reasonable surface roughness of the bushing and bearing for reducing wear volume occurring at the interface between a bearing and a shaft.

• Tribology and Lubricants
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• v.30 no.3
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• pp.177-182
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• 2014

To stop a high speed train running at the speed of 300 km/h, the disc brake for the train should be able to dissipate enormous kinetic energy of the train into frictional heat energy. Sintered pin-type metals are mostly used for friction materials of high speed brake pads. A pad comprises several friction pins, and the topology, length, flexibility, composition, etc. have a great influence on the tribological properties of the disc brake. In this study, the topology of the friction pins in a pad was our main concern. We presented the optimization of the topology of a railcar brake pad with nine-pin-type friction materials by thermo-mechanical contact analysis. We modeled the brake pad with/without a back plate. To simulate a continuous braking, the pad or friction materials were rotated at constant velocity on the friction surface of the disc. We varied the positions of the nine friction materials to compare the temperature distributions on the disc surface. In a non-optimized brake pad, the distance between two neighboring friction materials in the radial direction from the rotational center of the disc was not equal. In an optimized pad, the distance between two neighboring friction materials in the radial direction was equal. The temperature distribution on the disc surface fluctuated more for the former than the latter. Optimizing the pad reduced the maximum temperature of the brake disc by more than 10%.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.2
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• pp.63-71
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• 2003

This paper presents a robust slewing control of a flexible space structure based on sliding surface design. A sliding surface is designed for a single-axis rest-to-rest slewing in view of target angle, target angular velocity, and root monent of the flexible appendage. In comparison with the Lypunov control law, both controllers guarantee the stability and command tracking capabilities for nominal system. It is also shown that the designed control law provides further robustness to internal/external uncertainties. Extending the results of a single-axis maneuver, a sliding mode control law was sought for an arbitrary three-axis maneuver. Quaternion was used to determine the attitude of a space structure and sliding surfaces were designed for each axis, thereby a robust control law was derived considering the coupling effects between each rotational axis during the maneuver. Several numerical examples were demonstrated to show the effectiveness of the designed control law.

• Bulletin of the Korean Chemical Society
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• v.26 no.9
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• pp.1369-1380
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• 2005

The reaction of methyl radical with iodine molecule on an attractive potential energy surface is studied by classical trajectory procedures. The reaction occurs over a wide range of impact parameters with the majority of reactive events occurring in the backward rebound region on a subpicosecond scale. A small fraction of reactive events take place in the forward hemisphere on a longer time scale. The ensemble average of reaction times is 0.36 ps. The occurrence of reactive events is strongly favored when the incident radical and the target molecule align in the neighborhood of collinear geometry. Since the rotational velocity of I2 is slow, the preferential occurrence of reactive events at the collinear configuration of $CH_3{\ldots}I{\ldots}$I leads to the reaction exhibiting an anisotropic dependence on the orientation of $I_2$. During the collision, there is a rapid flow of energy from the $H_3C{\ldots}$I interaction to the I-I bond. The $CH_3I$ translation and $H_3C$-I vibration share nearly all the energy released in the reaction, and the distribution of the vibrational energy is statistical. The reaction probability is $\cong$0.4 at the $CH_3$ and I2 temperatures maintained at 1000 K and 300 K, respectively. The probability is weakly dependent on the $CH_3\;and\;I_2$ temperatures between 300 K and 1500 K.

• Geophysics and Geophysical Exploration
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• v.18 no.3
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• pp.133-142
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• 2015

Displacement of the Earth's surface due to atmospheric loading has been recognized since a century years ago, and its accurate estimation is required in present day geodesy and surveying, particularly in space geodesy. Atmospheric load deformation in continental region can readily be calculated with the given atmospheric pressure field and the load Green's function, and, in near coastal area, approximate model is used for the calculation. The changes in the Earth's atmospheric circulation and the seasonal variation of atmospheric pressure on two hemispheres of the Earth are the each main causes of variation of the Earth's spin angular velocity and polar motion respectively. Wind and atmospheric pressure do the major role in other periodic and non-periodic perturbations of the positions in the Earth's reference frame and variations in the Earth's spin rotational state. In this reviewing study, the developments of related theories and models are summarized along with brief description of phenomena, and the geodetic perturbing effects of a hypothetical typhoon passing Korea are shown as an example. Finally related existing problems and further necessary studies are discussed in general.