• Journal of the Optical Society of Korea
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• v.20 no.1
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• pp.180-187
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• 2016

The independent operation of a color filter for incident polarization is demonstrated using a guided-mode resonance (GMR) filter employing a metal-insulator-metal (MIM) waveguide. To achieve independent operation, a rectangular MIM grating is proposed as a wave-guide resonator. The design considerations are discussed and include how to determine the grating period and slit width. Power flow distribution is observed with slit width variation. Blue-green, green-red, and blue-red filters for corresponding x- and y-polarizations are demonstrated as application examples with numerical simulation with rectangle-shaped MIM grating. As a practical application, feasibility as a chromatic polarizer is discussed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.771-772
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• 2014

In this paper, the integrated design method of suction muffler in compressor was studied. There are three things to consider when designing this. First, the transmission loss was maximized to consider the noise reduction. Second, dissipation energy of fluid flow was minimized for energy efficiency. Finally, acoustical resonance frequency of suction muffler was controlled because energy efficiency can be increased by supercharging of refrigerant. Therefore, suction muffler was designed to have the specific resonance frequency. The input impedance was used for designing target acoustical resonance frequency. Topology optimization was used for optimization method.

• Journal of the Korean Society of Laryngology, Phoniatrics and Logopedics
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• v.28 no.1
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• pp.14-16
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• 2017

Pop singers frequently use breathy voice to express diverse emotion. Such method is the major factor that divides vocalization in pop and classical music. Using breathy voice too much for a long time could make singer short-winded, which might cause the voice injured. In order to prevent the problem, singers need to find resonance balance between high notes and low notes and among vowels. Moreover, they should take more attention when producing resonance in consonants with much air flow. Along with finding resonance balance, if skilled at controlling the volume of voice, singers can use the breathy voice selectively at the desired part, adjusting close quotient freely. Through this kind of approach, pop singers can develope their unique style of vocalization and avoid the vocal damage.

• Journal of Power System Engineering
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• v.6 no.4
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• pp.36-42
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• 2002

In the structures of automobiles and ships which have engines for works, the vibration energies generated by the engines are transferred to dissipation parts through the structures which is welded and bolted with beams and plates. The vibration energies generated by resonance frequencies are the reasons of the resonance phenomena. To solve these problems, up to the present, we have studied to avoid the resonance, and add the higher damping characteristics. However, we need to understand the structural energy flows, to design the structures clearly which have the characteristic of welding. The object of this study is to make differences clear in the characteristics of structures which have some welded part on an homogenous flat plate. In this investigation, we study the flows of structural vibration energy experimently, and then, some knowledge for dynamic structural design is obtained.

• International Journal of Vascular Biomedical Engineering
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• v.1 no.2
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• pp.36-41
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• 2003

Both flow visualizations and computational fluid dynamics were performed to determine hemodynamics in a total cavopulmonary connection (TCPC) model for surgically correcting congenital heart defects. From magnetic resonance images, an anatomically correct glass model was fabricated to visualize steady flow. The total flow rates were 4, 6 and 8L/min and flow rates from SVC and IVC were 40:60. The flow split ratio between LPA and RPA was varied by 70:30, 60:40 and 50:50. A pressure-based finite-volume software was used to solve steady flow dynamics in TCPC models. Results showed that superior vena cava(SVC) and inferior vena cava(IVC) flow merged directly to the intra-atrial conduit, creating two large vortices. Significant swirl motions were observed in the intra-atrial conduit and pulmonary arteries. Flow collision or swirling flow resulted in energy loss in TCPC models. In addition, a large intra-atrial channel or a sharp bend in TCPC geometries could influence on energy losses. Energy conservation was efficient when flow rates in pulmonary branches were balanced. In order to increase energy efficiency in Fontan operations, it is necessary to remove a flow collision in the intra-atrial channel and a sharp bend in the pulmonary bifurcation.

• Proceedings of the KIEE Conference
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• 1996.07a
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• pp.479-481
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• 1996

This paper describes a simulation model to analyze the dynamic performance of Unified Power Flow Controller which ran flexibly adjust the active and reactive power flow through the ac transmission line. An equivalent circuit to analyze the basic principle for the whole system operation was developed and a control system for the Unified Power Flow Controller was derived using vector control method. A computer simulation model with EMTP code was also conceived to evaluate the performance of the Unified power Flow Controller. The simulation results show that Unified Power flow Controller is very effective for controlling the power flow and damping the subsynchronous resonance in the power system.

• The Journal of the Acoustical Society of Korea
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• v.16 no.6
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• pp.68-75
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• 1997

In this study, to investigate vibration response of piping systems due to pulsation flow, a transfer matrix method is presented. Fluid-pipe interaction is formulated using wave equation for flow velocity and pressure, which depends on position and time. From the wave equation, transfer matrix is obtained. The dynamic responses of piping systems induced by pulsation flow appeared to depend upon fluctuation fluid velocity and pressure occurrnece from pulsation, and beating phenomena were observed near the resonance. Consequently, the dynamic behaviors of piping systems appeared to the same as response characteristics of the inside flow pattern of the pipe, and are determined by the inside fluid flow.

• Journal of radiological science and technology
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• v.25 no.1
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• pp.55-62
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• 2002

Aneurysm-mimicking findings were frequently visualized due to hemodynamical causes of dephasing effects around area of A-com artery during magnetic resonance angiography(MRA) and these kind of phenomena have not been clearly known yet. We investigated the hemodynamical patterns of dephasing effect around area of the A-com artery that might be a cause of false intracranial aneurysms on MRA. For experimental study, We used hand-made silicon phantoms of the asymmetric A-com artery as like a bifurcation configuration. In a closed circulatory system with UHDC computer driven cardiac pump system. MRA and fast digital subfraction angiography(DSA) involved the use of these phantoms. Flow patterns were evaluated with axial and coronal imaging of MRA(2D-TOF, 3D-TOF) and DSA of Phantoms constructed from an automated closed-type circulatory system filled with glycerol solution [circulation fluid(glycerol:water = 1:1.4)]. These findings were then compared with those obtained from computational fluid dynamic(CFD) for inter-experimental correlation study. Imaging findings of MRA, DSA and CFD on inflow zone according to the following: a) MRA demonstrated high signal intensity zone as inflow zone on silicon phantom; b) Patterns of DSA were well matched with MRA on trajectory of inflow zone; and c) CFD were well matched with MRA on the pattern of main flow. Imaging findings of MRA. DSA and CFD on turbulent flow zone according to the following: a) MRA demonstrated hyposignal intensity zone at shoulder and axillar zone of main inflow; b) DSA delineated prominent vortex flow at the same area. The hemodynamical causes of signal defect, which could Induce the false aneurysm on MRA, turned out to be dephasing effects at axilla area of bifurcation from turbulent flow as the results of MRA, DSA and CFD.

• Investigative Magnetic Resonance Imaging
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• v.5 no.1
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• pp.38-42
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• 2001

Dark band artifacts are often observed in angiograms of arteries obtained by 2D time-of-flight (TOF) angiography with saturation of veins by presaturation RF pulses. At some arteries the arterial blood velocity varies in a triphasic pattern during a cardiac cycle. The arterial blood, that is saturated by presaturation RF pulses in the saturation band, can flow back into the imaging slice during the retrograde flow phase of the triphasic variation. When such saturated retrograde flow occurs during the acquisition of the central part of the K space, a signal void can result in base images and consequently dark band artifacts can appear in angiograms. This phenomenon is experimentally demonstrated by varying the gap between the imaging slice and the saturation band. Furthermore, a new pulse sequence is proposed to eliminate the dark band artifacts by changing the profile of the saturation band front a rectangle to a ramp.

• Investigative Magnetic Resonance Imaging
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• v.5 no.2
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• pp.116-122
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• 2001

Purpose : To find sensitivity of MRI imaging methods to slow flow phantom study was performed with conventional Spin-Echo, gradient echo based Phase Contrast, fast GRASS, and heavily T2-weighted Fast Spin Echo pulse sequences. Materials and Methods : A siphon driven flow phantom was constructed with a ventriculo-peritoneal shunt catheter and a GE phantom to achieve continuous variable flow. Four different pulse sequences including Spin-Echo, Phase Contrast, GRASS and Heavily T2-weighted Fast Spin Echo were evaluated to depict slow flow in the range from 0.08 ml/min to 1.7 ml/min and to compare signal intensities between static fluid and flowing fluid. Results : In the slow flow above 0.17 ml/min conventional Spin-Echo showed superior apparent contrast between static and flowing fluid while GRASS was more sensitive to the very slow flow below 0.17 ml/mim. It was not accurate to calculate flow and velocity below 0.1 ml/min with a modified PC imaging. Conclusion : Four different MR pulse sequences demonstrated different sensitivity to the range of slow flow from 0.08 ml/min to 1.7 ml/min. This finding may be clinically useful to measure CSF shunt flow or detecting CSF collection and thrombosis.