• Journal of Mechanical Science and Technology
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• 제15권7호
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• pp.951-961
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• 2001

The present article presents an extension to the computational model for spray/wall interaction and liquid film processes that has been dealt with in the earlier studies (Lee and Ryou, 2000a). The extensions incorporate film spread due to impingement forces and dynamic motion induced by film inertia to predict the dynamic characteristics of wall films effectively. The film model includes the impingement pressure of droplets, tangential momentum transfer due to the impinging droplets on the film surface and the gas shear force at the film surface. Validation of the spray/wall interaction model and the film model was carried out for non-evaporative diesel sprays against several sources of experimental data. The computational model for spray/wall interactions was in good agreement with experimental data for both spray radius and height. The film model in the present work was better than the previous static film model, indicating that the dynamic effects of film motion should be considered for wall films. On the overall the present film model was acceptable for predication of the film radius and thickness.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2005년도 후기학술대회논문집
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• pp.254-255
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• 2005

The effect of surrounding air velocity on the soot deposition process from a diffusion flame to a solid wall was investigated in a microgravity environment to attain in-situ observations of the process. An ethylene($C_2H_4$) diffusion flame was formed around a cylindrical rod burner in surrounding air velocity of $v_{air}$=2.5, 5, and 10 cm/s with oxygen concentration of 35 % and wall temperature of 300 K. Laser extinction was adopted to determine the soot volume fraction distribution between the flame and burner wall. The experimental results show that the soot particle distribution region moves closer to the surface of the wall with increasing surrounding air velocity. A numerical simulation was also performed to understand the motion of soot particles in the flame and the characteristics of the soot deposition to the wall. The results successfully predicted the differences in the motion of soot particles by different surrounding air velocity near the burner surface and are in good agreement with observed soot behavior in microgravity. A comparison of the calculations and experimental results led to the conclusion that a consideration of the thermophoretic effect is essential to understand the soot deposition on walls.

• Nuclear Engineering and Technology
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• 제47권4호
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• pp.416-423
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• 2015

It had been disputed how to apply wall drag to the dispersed phase in the framework of the conventional two-fluid model for two-phase flows. Recently, Kim et al. [1] introduced the volume-averaged momentum equation based on the equation of a solid/fluid particle motion. They showed theoretically that for dispersed two-phase flows, the overall two-phase pressure drop by wall friction must be apportioned to each phase, in proportion to each phase fraction. In this study, the validity of the proposed wall drag model is demonstrated though one-dimensional (1D) simulations. In addition, it is shown that the existing form loss model incorrectly predicts the motion of the dispersed phase. A new form loss model is proposed to overcome that problem. The newly proposed form loss model is tested in the region covering the lower plenum and the core in a nuclear power plant. As a result, it is shown that the new models can correctly predict the relative velocity of the dispersed phase to the surrounding fluid velocity in the core with spacer grids.

• 대한핵의학회지
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• 제32권6호
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• pp.509-515
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• 1998

목적: 관동맥확장 성형술과 같은 재관류술전의 급성심근경색 환자에서 T1-201 부하-재분포 관류 SPECT 영상에서의 역재분포의 빈도를 알아보고 T1-201 재주사 후 섭취증가 여부에 따른 생존심근여부를 좌심실 벽운동의 호전 유무를 관찰하여 임상적의의를 알아보고자 하였다. 대상 및 방법: 급성심근경색으로 입원한 환자 42명을 대상으로 하였으며 T1-201 부하-4시간 재분포-24시간 재주사법에 의한 심근관류 SPECT를 관동맥확장 성형술 전에 시행하였고 좌심실 벽운동의 평가를 위해 심초음파를 SPECT 실시 전에 시행하였다. 또한 좌심실 벽운동 이상의 호전유무를 평가하기 위해 급성심근경색 후 4개월경에 추적관찰을 하였다. 심근관류는 육안적 평가에 의해서 정상을 0, 섭취 없음을 3점으로 4단계 분류하였다. 심근벽의 이상은 정상을 1, 이상운동을 4점으로 5단계 분류하였다. 결과: 42명 환자 전체심근영역 총 672개 영역 중 36개 영역(5%)에서 부하-재분포 영상에서 역재분포가 관찰되었다. 이중 좌심실 벽운동이 심초음파상 이상을 보인 19개영역 중에서 11개가 재주사 후 섭취 증가가 있었고. 이 중 10개 영역(90%)이 심초음파상 좌심실 벽운동이상이 4개월 후에 호전이 있어 생존심근임을 나타냈다. 재주사 후 섭취증가가 없었던 8개 영역 중 5개(62%) 영역은 좌심실 벽운동의 호전이 없었다. 재주사 후 섭취정도에 따라서는 재주사시 정상관류 및 경도관류감소를 보인 10개 영역 중 9개 영역에서 좌심실 벽운동의 호전이 있어 90%의 양성 예측도를 보였다. 중증도 관류감소 및 관류결손을 보인 9개 영역 중 4개 영역은 호전을 5개 영역은 호전이 없어서 56% (5/9)의 음성 예측도를 보였다. 결론: 급성심근경색 후 역재분포를 보인 영역에 T1-201 재주사는 생존심근의 여부를 판단하는데 높은 양성예측도를 갖는 유용한 검사이다.

• 한국지진공학회논문집
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• 제20권3호
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• pp.155-162
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• 2016

Observations of the damages to high-rise reinforced concrete (RC) wall building structures caused by by recent earthquakes in Chile ($M_w$ 8.8, February 2010) and New Zealand (February 2011, $M_L$ 6.3) have generally exceeded expectations. Firstly, this study estimated the seismic damage levels of 15-story RC box-type wall building structures using the analytical models calibrated by the results of a shaking table test on a 1:5 scale 10-story RC box-type wall building model. Then, the seismic fragility analysis of the prototype model was conducted by using the SAC/FEMA method and the incremental dynamic analysis (IDA). To compensate for the uncertainties and variability of ground motion and its impacts on the prototype model, in the SAC/FEMA method, a total of 61 ground motion records were selected from 20 earthquakes, with a magnitude ranging from 5.9 to 8.8 and an epicentral distance ranging from 5 to 105km. In the IDA, a total of 11 ground motion records were used based on the uniform hazard response spectrum representing a return period of 2,475 years. As a result, the probabilities that the limits of the serviceability, damage control, and collapse prevention would be exceeded were as follows: from the SAC/FEMA method: 79%, 0.3%, and 0%, respectively; and from the IDA: 57%, 1.7%, and 0%, respectively.

• 한국지진공학회논문집
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• 제24권6호
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• pp.293-303
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• 2020

Seismic fragility was assessed for non-seismic reinforced concrete shear walls in Korean high-rise apartment buildings in order to implement an earthquake damage prediction system. Seismic hazard was defined with an earthquake scenario, in which ground motion intensity was varied with respect to prescribed seismic center distances given an earthquake magnitude. Ground motion response spectra were computed using Korean ground motion attenuation equations to match accelerograms. Seismic fragility functions were developed using nonlinear static and dynamic analysis for comparison. Differences in seismic fragility between damage state criteria including inter-story drifts and the performance of individual structural members were investigated. The analyzed building had an exceptionally long period for the fundamental mode in the longitudinal direction and corresponding contribution of higher modes because of a prominently insufficient wall quantity in such direction. The results showed that nonlinear static analyses based on a single mode tend to underestimate structural damage. Moreover, detailed assessments of structural members are recommended for seismic fragility assessment of a relatively low performance level such as collapse prevention. On the other hand, inter-story drift is a more appropriate criterion for a relatively high performance level such as immediate occupancy.

• Structural Engineering and Mechanics
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• 제62권2호
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• pp.163-170
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• 2017

This study presents a particle-wall filtration model for predicting the particle motion behavior in a typical rotational flow field-filtration in blower system of cooker hood. Based on computational fluid dynamics model, air flow and particles has been simulated by Lagrangian-particle/ Eulerian-gas approaches and get verified by experiment data from a manufacturer. Airflow volume, particle diameter and local structure, which are related to the particle filtration has been studied. Results indicates that: (1) there exists an optimal airflow volume of $1243m^3/h$ related to the most appropriate filtration rate; (2) Diameter of particle is the significant property related to the filtration rate. Big size particles can represent the filtration performance of blower; (3) More than 86% grease particles are caught by impeller blades firstly, and then splashed onto the corresponding location of worm box internal wall. These results would help to study the micro-particle motion behavior and evaluate the filtration rate and structure design of blower.

• 한국가시화정보학회지
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• 제3권1호
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• pp.3-19
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• 2005

Novel optical techniques are presented for three-dimensional tracking of nanoparticles; Optical Serial Sectioning Microscopy (OSSM) and Ratiometric Total Internal Reflection Fluorescent Microscopy (R-TIRFM). OSSM measures optically diffracted particle images, the so-called Point Spread Function (PSF), and dotermines the defocusing or line-of-sight location of the imaged particle measured from the focal plane. The line-of-sight Brownian motion detection using the OSSM technique is proposed in lieu of the more cumbersome two-dimensional Brownian motion tracking on the imaging plane as a potentially more effective tool to nonintrusively map the temperature fields for nanoparticle suspension fluids. On the other hand, R-TIRFM is presented to experimentally examine the classic theory on the near-wall hindered Brownian diffusive motion. An evanescent wave field from the total internal reflection of a 488-nm bandwidth of an argon-ion laser is used to provide a thin illumination field of an order of a few hundred nanometers from the wall. The experimental results show good agreement with the lateral hindrance theory, but show discrepancies from the normal hindrance theory. It is conjectured that the discrepancies can be attributed to the additional hindering effects, including electrostatic and electro-osmotic interactions between the negatively charged tracer particles and the glass surface.

• 한국해양공학회지
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• 제6권2호
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• pp.46-54
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• 1992

In this paper, behavior of rectangular storage structures under earthquake loadings are investigated. Linear sloshing is assumed in this study. The effect of the wall flexibility is considered. Eulerian and lagrangian approaches are presented. The Eulerian approach is carried out by solving the boundary value problem for the fluid motion. In the lagrangian approach, the fluid as well as the storage structure is modelled by the finite element method. The fluid region is discretized by using fluid elements. The (1 $\times$ 1)-reduced integration is carried out for constructing the stiffness matrices of the fluid elements. Seismic analysis of the coupled system is carried out by the response spectra method. The numerical results show that the fluid forces on the wall obtained by two approaches are in good agreements. By including the effect of the wall flexibility, the forces due to fluid motion can be increased very significantly.

• 한국유체기계학회 논문집
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• 제12권4호
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• pp.37-43
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• 2009

In the present study, the flow characteristics of a peristaltic micropump were numerically analyzed. A channel wall motion of the micropump was simulated using a moving mesh technique. A sine wave pattern was assumed to simulate the peristaltic motion of wall. The present numerical method was verified by comparing the result with the available numerical data. The effects of the operating conditions which include the maximum displacement and frequency of the channel wall and the phase difference between top and bottom walls on the flow characteristics were investigated. From these numerical results, the pressure-flowrate characteristic curve was obtained for various maximum displacement and frequencies.