• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.6
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• pp.795-801
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• 1999

An experimental investigation has been conducted with the objective of studying the mixing mechanism near the nozzle exit in a tone-excited jet diffusion flame. The fuel jet was pulsed by means of a loudspeaker-driven cavity. The excitation frequencies were chosen for the two cases of the non-resonant and resonant frequency identified as a fuel tube resonance due to acoustic excitation. The effect of tone-excitations on mixing pattern near the nozzle exit and flame was visualized using various techniques, including schlieren photograph and laser light scattering photograph from $TiO_2$ seed particles. In order to clarify the details of the flame feature observed by visualization methods, hotwire measurements have been made. Excitation at the resonant frequency makes strong mixing near the nozzle. In this case, the fuel jet flow in the vicinity of nozzle exit breaks up into disturbed fuel parcels. This phenomena affects greatly the combustion characteristics of the tone excited jet and presumably occurs by flow separation from the wall inside the fuel nozzle. As a result, in the resonant frequency the flame length reduces greatly.

• Biomedical Science Letters
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• v.11 no.2
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• pp.129-134
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• 2005

Three different deconvolution techniques for quantifying cerebral blood flow (CBF) from whole brain $T2^{\ast}-weighted$ bolus tracking images were implemented (parametric Fourier transform P-FT, parametric single value decomposition P-SVD and nonparametric single value decomposition NP-SVD). The techniques were tested on 206 regions from 38 hyperacute stroke patients. In the P-FT and P-SVD techniques, the tissue and arterial concentration time curves were fit to a gamma variate function and the resulting CBF values correlated very well $(CBF_{P-FT}\;=\;1.02{\cdot}CBF_{p-SVD},\;r^2\;=\;0.96)$. The NP-SVD CBF values correlated well with the P-FT CBF values only when a sufficient number of time series volumes were acquired to minimize tracer time curve truncation $(CBF_{P-FT}\;=\;0.92{\cdot}CBF_{NP-SVD},\;r^2\;=\;0.88)$. The correlation between the fitted CBV and the unfitted CBV values was also maximized in regions with minimal tracer time curve truncation $(CBV_{fit}\;=\;1.00{\cdot}CBV_{ Unfit},\;^r^2\;=\;0.89)$. When a sufficient number of time series volumes could not be acquired (due to scanner limitations) to avoid tracer time curve truncation, the P-FT and P-SVD techniques gave more reliable estimates of CBF than the NP-SVD technique.

• Wind and Structures
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• v.18 no.1
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• pp.57-67
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• 2014

For a building with a dominant windward wall opening, the wind-induced internal pressure response can be described by a second-order non-linear differential equation. However, there are two ill-defined parameters in the governing equation: the inertial coefficient $C_I$ and the loss coefficient $C_L$. Lack of knowledge of these two parameters restricts the practical use of the governing equation. This study was primarily focused on finding an accurate reference value for $C_I$, and the paper presents a systematic investigation of the factors influencing the inertial coefficient for a wind-tunnel model building including: opening configuration and location, wind speed and direction, approaching flow turbulence, the model material, and the installation method. A numerical model was used to simulate the volume deformation under internal pressure, and to predict the bulk modulus of an experimental model. In considering the structural flexibility, an alternative approach was proposed to ensure accurate internal volume distortions, so that similarity of internal pressure responses between model-scale and full-scale building was maintained. The research showed 0.8 to be a reasonable standard value for the inertial coefficient.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1643-1648
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• 2004

When a shock wave propagates into a Helmholtz resonator, very complicated wave phenomena are formed both inside and outside the resonator tube. Shock wave reflection, shock focusing phenomena and shock-vortex interactions cause strong pressure fluctuations inside the resonator, consequently leading to powerful sound emission. In the present study, the wave phenomena inside and outside the Helmholtz resonator are, in detail, investigated with a help of CFD. The Mach number of the incident shock wave is varied below 2.0 and several types of resonators are tested to investigate the influence of resonator geometry on the wave phenomena. A TVD scheme is employed to solve the axisymmetric, compressible, Euler equations. The results obtained show that the configuration of the Helmholtz resonator significantly affects the peak pressure of shock wave focusing, its location, the amplitude of the discharged wave and resonance frequency.

• Journal of the Korea Society for Simulation
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• v.7 no.2
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• pp.115-123
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• 1998

A simulation is performed to investigate the effect of the pipe supports on the change of the natural frequencies of curved pipe systems containing fluid flow, for different elbow angles and geometry of the pipe systems. Based upon the Hamilton's principle, the equations of motions are derived, and the finite element equation is constructed to solve the corresponding eigenvalue problem. The angles of elbows do not affect the change of the fundamental natural frequency, but affect the change of the third or higher natural frequencies. Without any support, the change of the fundamental natural frequency due to the geometric change is smaller than the change of the second or higher natural frequencies. The more curve parts exist in the pipe system, the less change of lower frequency range, compared with the change of higher frequency range, is observed. Spring supports can be used to reduce the fundamental natural frequency, without change of the second or higher natural frequencies. To avoid resonance, which is critically dangerous from the view point of structural dynamics, the mechanical properties such as stiffness or the location of pipe supports are need to be changed to isolate the natural frequencies from the frequency range of dominant vibration modes.

• Transactions of the Society of Information Storage Systems
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• v.3 no.4
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• pp.196-201
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• 2007

As the demand for the lap-top computer has been increased, most users ask quiet environment to work comfortably. Therefore, noise problems of an ODD are of great interest. For the high speed ODD, the flow induced noise is caused by the turbulent flow[1], which is known to be a major source of overall noise of a slim type ODD. In this study, we introduce a new attempt to reduce the noise level using the concept of Helmholtz resonator[2].The experimental analysis is carried out for several cases at different resonance frequencies and different hole patterns. The results show reductions in the noise level from the acoustic noise absorption point of view.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.3
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• pp.547-554
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• 1992

Response characteristics and false counts of laser and white light optical particle counters (OPC) have been studied as a function of particle size using monodisperse polystylen laterx (PSL) particles. Theoretical light scattering calculations for He-Ne laser based counter have been compared with the experimental results and thus good agreements have been found. The light scattering intensity in monochromatic light shows an oscillatory character for the transparent and spherical particles of PSL due to Mie resonance. Because of this effect, the response of the LAS-X OPC showed almost same responses in the diameter ranges of 0.4mu.m to 0.6mu.m and 0.7mu.m to 1.0mu.m for PSL particles. A laser optical particle counter with high flow rate applied for clean room has been studied to identify the noise sources. Three different manufacturer's clean room optical particle counters alos have been tested to measure the background noise level.

• International Journal of Naval Architecture and Ocean Engineering
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• v.12 no.1
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• pp.552-568
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• 2020

After long-term service in deep ocean, pipelines are usually suffered from corrosions, which may greatly influence the Vortex-Induced Vibration (VIV) behavior of pipes. Thus, we investigate the VIV of defective pipelines. The geometric nonlinearity due to large deformation of pipes and nonlinearity in vortex-induced force are simulated. This nonlinear vibration system is simulated with finite element method and solved by direct integration method with incremental algorithm. Two kinds of defects, corrosion pits and volumetric flaws, and their effects of depth and range on VIV responses are investigated. A new finite element is developed to simulate corrosion pits. Defects are found to aggravate VIV displacement response only if environmental flow rate is less than resonance flow rate. As the defect depth grows, the stress responses increase, however, the increase of the defect range reduces the stress response at corroded part. The volumetric flaws affect VIV response stronger than the corrosion pits.

• Investigative Magnetic Resonance Imaging
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• v.16 no.1
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• pp.47-54
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• 2012

Purpose : This study was performed to evaluate the characteristics of rat mesenchymal stem cells (RMSCs) transduced with human ferritin gene and investigate $in$ $vitro$ MRI detectability of ferritin-transduced RMSCs. Materials and Methods: The RMSCs expressing both myc-tagged human ferritin heavy chain subunit (myc-FTH) and green fluorescence protein (GFP) were transduced with lentiviurs. Transduced cells were sorted by GFP expression using a fluorescence-activated cell sorter. Myc-FTH and GFP expression in transduced cells were detected by immunofluorescence staining. The cell proliferative ability and viability were assessed by MTT assay. The RMSC surface markers (CD29+/CD45-) were analyzed by flow cytometry. The intracellular iron amount was measured spectrophotometically and the presence of ferritin-iron accumulation was detected by Prussian blue staining. $In$ $vitro$ magnetic resonance imaging (MRI) study of cell phantoms was done on 9.4 T MR scanner to evaluate the feasibility of imaging the ferritin-transduced RMSCs. Results: The myc-FTH and GFP genes were stably transduced into RMSCs. No significant differences were observed in terms of biologic properties in transduced RMSCs compared with non-transduced RMSCs. Ferritin-transduced RMSCs exhibited increased iron accumulation ability and showed significantly lower $T_2$ relaxation time than non-transduced RMSCs. Conclusion: Ferritin gene as MR reporter gene could be used for non-invasive tracking and visualization of therapeutic mesenchymal stem cells by MRI.

• Investigative Magnetic Resonance Imaging
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• v.18 no.4
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• pp.290-302
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• 2014

Purpose : Susceptibility-weighted magnetic resonance (MR) sequence is three-dimensional (3D), spoiled gradient-echo pulse sequences that provide a high sensitivity for the detection of blood degradation products, calcifications, and iron deposits. This pictorial review is aimed at illustrating and discussing its main clinical applications. Materials and Methods: SWI is based on high-resolution, 3D, fully velocity-compensated gradient-echo sequences using both magnitude and phase images. To enhance the visibility of the venous structures, the magnitude images are multiplied with a phase mask generated from the filtered phase data, which are displayed at best after post-processing of the 3D dataset with the minimal intensity projection algorithm. A total of 200 patients underwent MR examinations that included SWI on a 3 tesla MR imager were enrolled. Results: SWI is very useful in detecting multiple brain disorders. Among the 200 patients, 80 showed developmental venous anomaly, 22 showed cavernous malformation, 12 showed calcifications in various conditions, 21 showed cerebrovascular accident with susceptibility vessel sign or microbleeds, 52 showed brain tumors, 2 showed diffuse axonal injury, 3 showed arteriovenous malformation, 5 showed dural arteriovenous fistula, 1 showed moyamoya disease, and 2 showed Parkinson's disease. Conclusion: SWI is useful in detecting occult low flow vascular lesions, calcification and microbleed and characterising diverse brain disorders.