• International Journal of Fluid Machinery and Systems
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• v.3 no.2
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• pp.129-136
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• 2010

The attachment of inducer upstream of main impeller is an effective method to improve the suction performance of turbopump. However, various types of cavitation instabilities are known to occur even at the designed flow rate as well as in the partial flow rate region. The cavitation surge occurring at partial flow rates is known to be strongly associated with the inlet back flow. In the present study, in order to understand the detailed structure of internal flow of inducer, we firstly carried out the experimental and numerical studies of non-cavitating flow, focusing on the flow field near the inlet throat section and inside the blade passage of a two bladed inducer at a partial flow rate. The steady flow simulation with cavitation model was also made to investigate the difference of flow field between in the cavitating and no-cavitating conditions.

• Transactions of the Korean Society of Automotive Engineers
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• v.7 no.9
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• pp.63-74
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• 1999

When a fuel was injected with opening the intake valve of a port fuel injection engine, the spray atomization and flow characteristics in the intake port have a strong influence on the mixture formation of a combustion chamber. Thus , this study was to clarify the spray flow characteristics of the air-assist gasoline spray with fine dropkets across the suction air stream in model intake port. For the simulated opening intake valve in port, suction air stream was varied to 10m/s ∼30m/s. And fuel pressur ewas fixed to 300kPa, but air assist pressure was varied to 0∼25kPa for a vairable spray conditions. Spray flow trajectory was investigated by means of laser sheet visualization and the measurements of droplet sizes and velocities were made by PDPA system. Measured droplets within the spray flow field were subdivided into five size groups and then, the flow characteristics of droplet size groups were investigated to the spray across a suction air stream.

• Journal of Mechanical Science and Technology
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• v.18 no.8
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• pp.1401-1417
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• 2004

Experimental and computational studies were performed to determine the effects of different blade designs on a flow pattern inside a double-spindle counter rotating mower deck. In the experimental study, two different blade models were tested by measuring air velocities using a forward-scatter LDV system. The velocity measurements were taken at several different azimuth and axial sections inside the deck. The measured velocity distributions clarified the air flow pattern caused by the rotating blades and demonstrated the effects of deck and blade designs. A high-speed video camera and a sound level meter were used for flow visualization and noise level measurement. In the computational works, two-dimensional blade shapes at several arbitrary radial sections have been selected for flow computations around the blade model. For three-dimensional computation applied a non-inertia coordinate system, a flow field around the entire three-dimensional blade shape is used to evaluate flow patterns in order to take radial flow interactions into account. The computational results were compared with the experimental results.

• Journal of Electrical Engineering and Technology
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• v.7 no.5
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• pp.797-806
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• 2012

Fault detection and isolation (FDI) algorithms provide fault monitoring methods in GPS measurement to isolate abnormal signals from the GPS satellites or the acquired signal in receiver. In order to monitor the occurred faults, FDI generates test statistics and decides the case that is beyond a designed threshold as a fault. For such problem of fault detection and isolation, this paper presents and evaluates position domain integrity monitoring methods by formulating various pseudorange prediction methods and investigating the resulting test statistics. In particular, precise measurements like carrier phase and Doppler rate are employed under the assumption of fault free carrier signal. The presented position domain algorithm contains the following process; first a common pseudorange prediction formula is defined with the proposed variations in pseudorange differential update. Next, a threshold computation is proposed with the test statistics distribution considering the elevation angle. Then, by examining the test statistics, fault detection and isolation is done for each satellite channel. To verify the performance, simulations using the presented fault detection methods are done for an ideal and real fault case, respectively.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.12A
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• pp.1198-1204
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• 2006

In this paper, we extend SVR-MMSE detection scheme which is proposed in MIMO system to MIMO-OFDM system, and evaluate performance of the system in frequency selective fading channel. First of all, we explain about typical MIMO-OFDM system and detection scheme of constant modulus signals in this system. And compare proposed SVR-MMSE with Zero Forcing, Minimum Mean Square Error which is conventional detection scheme. we identify that the performance of the proposed system is shown different by varying doppler frequency in frequency selective fading channel using jakes channel model. The result of detection performance by the proposed SVR-MMSE in this simulation, it shows that proposed algorithm have a good performance in MIMO-OFDM systems.

• Journal of The Korean Astronomical Society
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• v.42 no.6
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• pp.145-153
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• 2009

We present measurements of diffuse interstellar $H_2$ absorption lines in the continuum spectra of 10 early-type stars. The data were observed with the Berkeley Extreme and Far-Ultraviolet Spectrometer (BEFS) of the ORFEUS telescope on board the ORFEUS-SPAS I and II space-shuttle missions in 1993 and 1996, respectively. The spectra extend from the interstellar cutoff at 912 $\AA$ to about 1200 $\AA$ with a resolution of ~ 3000 and statistical signal-to-noise ratios between 10 and 65. Adopting Doppler broadening velocities from high-resolution optical observations, we obtain the $H_2$ column densities of rotational levels J" = 0 through 5 for each line of sight. The kinetic temperatures derived from J" = 0 and 1 states show a small variation around the mean value of 80 K, except for the component toward HD 219188, which has a temperature of 211 K. Based on a synthetic interstellar cloud model described in our previous work, we derive the incident UV intensity IUV and the hydrogen density $n_H$ of the observed components to be -0.4 $\leq$ log $I_{UV}\leq2.2$ and $6.3{\leq}n_H2500cm^{-3}$, respectively.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.7
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• pp.905-914
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• 2001

A large eddy simulation(LES) is performed for turbulent flow around a bluff body inside a sudden expansion cylinder chamber, a configuration which resembles a premixed gas turbine combustor. To promote turbulent mixing and to accommodate flame stability, a flame holder is installed inside the combustion chamber. The Smagorinsky model is employed and the calculated Reynolds number is 5,000 based on the bulk velocity and the diameter of the inlet pipe. The simulation code is constructed by using a general coordinate system based on the physical contravariant velocity components. The predicted turbulent statistics are evaluated by comparing them with the laser-doppler velocimetry (LDV) measurement data. The agreement of LES with the experimental data is shown to be satisfactory. Emphasis is placed on the time-dependent evolutions of turbulent vortical structure behind the flame holder. The numerical flow visualizations depict the behavior of large-scale vortices. The turbulent mixing process behind the flame holder is analyzed by visualizing the sectional views of vortical structure.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.717-720
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• 2002

The present study is to evaluate the performances of flow velocity and wall shear stress in the stenosed coronary artery using human in vivo hemodynamic Parameters and computer simulation. Initial and follow-up coronary angiographics in the patients with angulated coronary stenosis are performed. Follow-up coronary angiogram demonstrated significant difference in the percent of diameter in the stenosed coronary between two groups ($Group\;1:\;40.3{\%},\;Group\;2:\;25.5{\%}$). Flow-velocity wave obtained from in vivo intracoronary Doppler ultrasound data is used for the boundary condition for the computer simulation. Spatial and temporal variations of flow velocity vector and recirculation area are drawn throughout the selected segment of coronary models. The WSS of pre- and post-intracoronary stenting are calculated from three-dimensional computer simulation. Then negative shear stresses area on 3D simulation we noted on the inner wall of the post-stenotic area before stenting. The negative WSS is disappeared after stenting. High spatial and temporal WSS before stenting fell into within physiologic WSS after stenting. This finding was prominent in Model 2. The present study suggest that hemodynamic forces exerted by pulsatile coronary circulation termed WSS might affect on the evolution of atherosclerosis within the angulated vascular curvature. The local recirculation area which has low or negative WSS, might lead to progression of atherosclerosis.

• Journal of the Society of Naval Architects of Korea
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• v.53 no.4
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• pp.300-306
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• 2016

The gas ventilated by supercavitation splits into smaller bubbles and follows the water passage of the cavitation tunnel. The bubbles quickly return to the test section by rather high speed flow, and interrupt the observation of the supercavitation. To secure clear observation in the test section, the bubble collecting section(settling chamber) of large volume is prepared to collect bubbles in the water passage ahead of the test section. The bubble collecting section should provide enough buoyancy effect to the bubbles for proper bubble collecting. However, rather high-speed oncoming flow produces non-uniform velocity distribution and deteriorates buoyancy effect in the bubble collecting section. In the present study, the bubble collecting space and three porous plates are designed and analyzed through numerical methods, and the bubble collecting function is experimentally validated by 1/10-scaled model in terms of the formation of uniformly low velocity distribution in the bubble collecting section.

• Current Optics and Photonics
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• v.1 no.6
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• pp.598-603
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• 2017

Traditional three-dimensional (3-D) laser imaging systems are based on real aperture imaging technology, whose resolution decreases as the range increases. In this paper, we develop a novel 3-D imaging technique based on the synthetic aperture technology in which the imaging resolution is significantly improved and does not degrade with the increase of the range. We consider an imaging laser radar (ladar) system using the floodlight transmitting mode and multi-beam receiving mode. High 3-D imaging resolutions are achieved by matched filtering the linear frequency modulated (LFM) signals respectively in range, synthetic aperture along-track, and the real aperture across-track. In this paper, a novel 3-D imaging signal model is given first. Because of the motion during the transmission of a sweep, the Doppler shift induced by the continuous motion is taken into account. And then, a proper algorithm for the 3-D imaging geometry is given. Finally, simulation results validate the effectiveness of the proposed technique.