• Journal of computational fluids engineering
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• v.20 no.2
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• pp.96-102
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• 2015

In this study, the green water phenomena on rectangular shaped structure is numerically simulated by STAR-CCM+ to investigate the flow pattern including the velocity profiles in bubbly water flow. 5 phases of the formation of green water in front of and over the rectangular shaped structure is simulated at the design condition which is scaled down by 1:125 from FPSO operating in GOM. All numerical results are compared with the experimental results performed in a two dimensional wave flume. The water deformation due to the green water are obtained by the high speed CCD camera with employing the shadow graphy technique, which is allowed to take the bubbly water flow into images. A series of image taken by shadow graphy technique is analyzed with MQD method to calculate the velocity in bubbly water flow.

• Proceedings of the Korean Society of Medical Physics Conference
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• 2002.09a
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• pp.415-417
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• 2002

Images of microcalcification specks showed large variation in conventional radiographs of phantoms which are approved for mammography image quality standard by the American College of Radiology (ACR). This kind of variation is not appropriate for image quality standards because the number of specks are visually counted in images and that number is important in image quality evaluation. Our study using synchrotron radiation (SR) imaging revealed the overlapping of micro-sized air bubble(s) to some specks, and also the structural deformation or crackings. Eight phantoms approved by ACR from two different makers and an air-bubble phantom were examined. SR imaging was performed at a synchrotron radiation facility, SPring-8, in Japan. The image-detector was a fluorescent-screen optical-lens coupling system using a CCD camera with a spatial resolution of 6 $\square$m. Objects when imaged with longer sample-to-detector distance show edge enhancement due to a difference in refraction indices, that is refraction enhancement. Refraction-enhanced SR images revealed that some of specks carried foreign objects, which were proven to be air. In phantoms provided by one maker, attaching/overlapping airs were observed for 62 out of 150 specks (41%) , with a higher incidence for the smallest specks. A speck becomes hardly visible in a conventional radiograph when air(s) overlaps the majority part of a speck, though depending on the size of the air-inclusion and on its configuration. Those airs might have been adsorbed on a speck surface before being embedded and then introduced into the matrix together with specks. Our study using SR imaging has clearly shown the nature of defects in some mammography phantoms which seriously degrade the quality as an image standard.

• Journal of the Society of Naval Architects of Korea
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• v.39 no.3
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• pp.18-27
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• 2002

In order to improve the accuracy of the solution near the boundary in an analysis of viscous flow around an arbitrary boundary which move and be deformed using an Eulerian concept, a level-set based grid deformation method is introduced to concentrate grid points near the boundary. This paper presents a new monitor function which can easily control the level of the concentration of grid points along the boundary. Computations for steady flow around a semi-circular cylinder mounted on the bottom of the flow domain were carried out to check the improvement of the solution using the adaptive grid system with an immersed boundary method. The present numerical results show a good agreement with the solutions obtained by a body fitted grid system and more accurate solutions than those computed with non-adaptive grid system. For the validation of mechanical usefulness of the present method, an expanded analysis of flow around multi-body fixed in the flow domain was carried out. Finally, the present moving adaptive grid method was applied to a two-dimensional bubble rise problem. The computed results show well adapted grid points around the boundary of the bubble at every time and a good agreement with the result calculated by fixed grid system.

• Transactions of the KSME C: Technology and Education
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• v.3 no.4
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• pp.265-271
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• 2015

The bonding process should be achieved in vacuum environment to avoid air bubble. In this study, we studied about pressure uniformity that became an issue in thermo compression bonding usually. Uniform press is realized by the method that use air spring and metal form spring. The concept of uniform press using air spring is removed except pressing direction in the press processing so angle between the vector of pressure surface and the pressure axis is parallel automatically. Air spring compensate the errors of machining and assembly. Metal form compensate the thermal deformation and flatness error.

• Journal of Powder Materials
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• v.27 no.1
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• pp.37-43
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• 2020

The Fe-22wt.%Cr-6wt.%Al foams were fabricated via the powder alloying process in this study. The structural characteristics, microstructure, and mechanical properties of Fe-Cr-Al foams with different average pore sizes were investigated. Result of the structural analysis shows that the average pore sizes were measured as 474 ㎛ (450 foam) and 1220 ㎛ (1200 foam). Regardless of the pore size, Fe-Cr-Al foams had a Weaire-Phelan bubble structure, and α-ferrite was the major constituent phase. Tensile and compressive tests were conducted with an initial strain rate of 10^-3/s. Tensile yield strengths were 3.4 MPa (450 foam) and 1.4 MPa (1200 foam). Note that the total elongation of 1200 foam was higher than that of 450 foam. Furthermore, their compressive yield strengths were 2.5 MPa (450 foam) and 1.1 MPa (1200 foam), respectively. Different compressive deformation behaviors according to the pore sizes of the Fe-Cr-Al foams were characterized: strain hardening for the 450 foam and constant flow stress after a slight stress drop for the 1200 foam. The effect of structural characteristics on the mechanical properties was also discussed.