• Bulletin of the Society of Naval Architects of Korea
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• v.22 no.2
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• pp.12-26
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• 1985

This paper describes the experimental method to predict the propeller induced fluctuating pressure on the hull surface. Cavitations of the three model propellers with varying degree of skews, $0^{\circ},\;36^{\circ}\;and\;72^{\circ}$, were observed and the fluctuating pressure induced by the cavitating propellers in the flat plate above these propellers were measured simultaneously at 9 points in the wake field generated by the wire-mesh screens. Another model propeller designed for the dummy model ship was tested in a similar way behind the dummy model ship. The effects of skew variation on the cavitation patterns and fluctuating pressures were illustrated, and the influence of tip-clearances on the fluctuating pressures was also demonstrated. As a result, it is shown that the level of fluctuating pressure and cavity extent could be controlled to some extent by introducing the skews and tip clearances.

• Structural Engineering and Mechanics
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• v.4 no.3
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• pp.303-312
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• 1996

The dynamic behavior of an Euler beam with multiple point constraints traversed by a moving concentrated mass, a "moving-force moving-mass" problem, is analyzed and compared with the corresponding simplified "moving-force" problem. The equation of motion in matrix form is formulated using Lagrangian approach and the assumed mode method. The effects of the presence of intermediate point constraints in reducing the fluctuation of the contact force between the mass and the beam and the possible separation of the mass from the beam are investigated. The equation of motion and the numerical results are expressed in dimensionless form. The numerical results presented are therefore applicable for a large combination of system parameters.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.37 no.11
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• pp.762-771
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• 1988

This paper presents the experimental study to confirm the basic properties extract the operating problems of SMES. A new fast control system including u-computer and 12pulse power converter are designed and fabricated. The experiment of 25KJ SMES discharge and charge is carried out by I-C (Inductor-Converter) unit using a new proposed control system. The proposed control algorithm is proved by the simulations and control properties tests. It is also confirmed experimetally that SMES connected I-C unit controlled by this control scheme has an effects on compansating freguency fluctuation by independent active power control.

• International Journal of Fluid Machinery and Systems
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• v.1 no.1
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• pp.92-100
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• 2008

The main objective of this study was to clarify the origin of the unsteady flows arising in a mixed-flow vaneless diffuser system and also the effects of physical components of the system. The testing equipment consists of a straight tube, a swirl generator, and a mixed-flow vaneless diffuser. Pressure fluctuations of the flow through the tube and diffuser were measured by using a semiconductor-type pressure transducer and analyzed by an FFT analyzer. In the experiment, the velocity ratio (axial velocity/peripheral velocity) of the internal flow, and the geometric parameters of the diffuser were varied. Two kinds of unsteady flows were measured according to the combination of the components, and the origin of each unsteady flow was clarified. The fundamental frequencies of unsteady flows arose were examined by two-dimensional small perturbation analysis.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.9
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• pp.2454-2462
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• 1994

The effects of thermal stratification on the flow of a stratified fluid past a heated circular cylinder were examined in a wind tunnel. Turbulent intensities, rms values of temperature and turbulent convective heat flux distributions in the heated cylinder wake with and without thermal stratification were measured by using a hot-wire and cold-wire combination probe. A phase averaging method was also used to estimated coherent motion in the near wake. It is found that the vertical turbulent motion in the stably stratified flow case dissipates faster than that of the neutral case, i.e., vertical growth of vortical structure is suppressed under the strongly stratified condition. The coherent motion of temperature makes a large contribution like velocity coherent motion. However, the coherent motions of temperature fluctuation become very different with the change of experimental conditions, though the velocity coherent motions are quite similar in all experimental conditions.

• Journal of Advanced Marine Engineering and Technology
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• v.28 no.7
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• pp.1111-1122
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• 2004

An idea to suppress the self-excited combustion oscillation was applied to the flames. The characteristics of unsteady combustion were examined and the unsteady combustion was driven by forced pulsating mixture supply that can modulate its amplitude and frequency. The self-excited combustion oscillation having weaker flow velocity fluctuation intensity than that of the forced pulsating supply can be suppressed by this method. The effects of the forced pulsation amplitude and frequency on controlling self-excited combustion oscillations were also investigated comparing with the steady mixture supply. The unsteady combustion used in this experiment plays an important role in controlling self-excited combustion oscillation. Symptoms of self-excited combustion oscillation were also studied in order to predict the onset of combustion oscillation before it proceeded to a catastrophic failure For the purpose, the unique measures to observe the onset of self-excited combustion oscillations based on the careful statistics of fluctuating properties in flames, such as pressure or emission of OH radicals, have been proposed.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1875-1880
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• 2003

Measurements of wind flow and pressure fluctuations induced by train passing on station platform have been conducted. Test conventional trains have a different nose shapes - bluff nose and wedged nose. The bluff nose train influence peak value of pressure fluctuations on station platform three times more than the wedged nose train for train speed of 108 km/h. Also, air flow induced by the bluff nose train passing is three times more than the wedged nose train passing. Current study shows that the gust induced by the bluff nose conventional train may threaten a passenger's safety on station platform in proximity to train passage.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.12 no.6
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• pp.14-21
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• 2003

With the increased use of lasers in industrial welding applications, techniques for monitoring and controlling these processes become increasingly important. It is very important that we understand the dynamic behaviors of the laser induced Plume in welding, because the laser induced plume has considerable effects on welding efficiency and the quality of materials. As the plume fluctuation was associated with keyhole instability, unstable vapor plume indicated the process was unstable and would result in poor welds. An Infrared Thermal-vision Camera can be utilized compensate for incurracies encountered in real-time monitoring during laser welding. We have results that instabilities of plume are closely related with hot cracking and defect of laser welding.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.663-666
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• 2002

Hard disk drived (HDD) in computer are used extensively as data storage capacity. The trend in the computer industry to produce smaller disk drives rotating at higher speeds requires an improved understanding of fluid motion in the space between disks. The distribution of pressure disturbance on disks has relation to flow structure. To investigate the flow structure, time-resolved hot-wire measurements of the circumferential velocity component were obtained for the flow between the center pair of four disks of common radius $R_2$ coretating at angular velocity ${\Omega}$ in a fixed cylindrical enclosure. Hot-wire supporter acts as an obstruction in this case. The effects of rotating speed and size of hot-wire supporter diameter between disks on the flow driven by disks were investigated. Velocity spectra at the fixed space were measured to obtain the structure of inner and outer region in flow field.

• Proceedings of the KSR Conference
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• 2000.11a
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• pp.382-389
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• 2000

The purpose of present study is to investigate for reducing pressure fluctuations in tile case of installing tile air-shafts on the side wall of the tunnel with small cross-sectional area on conventional line. Experiments were performed with a 1/61-scale moving model rig for the tunnel of 0.764km length in the condition of tunnel cross-section area of 28 ㎡ According to the results, the maximum pressure fluctuation is reduced by 45% for 19 air-shafts. This results have the speed-up effects of about 33.4km/h for the train running in tunnel.