• Journal of the Optical Society of Korea
• /
• v.19 no.1
• /
• pp.29-37
• /
• 2015

The wavefront printer records a volume-reflection hologram as a two-dimensional array of elemental holograms from computer-generated holograms (CGHs) displayed on a spatial light modulator (SLM). The wavefront coming from the object is extracted by filtering in the spatial-frequency domain. This paper presents a method to improve color reproduction in a wavefront printer with spatial division of exposures at primary colors, by adaptive partitioning of the SLM in accordance with the color content encoded in the input CGHs, and by the controllable change of exposure times for the recording of primary colors. The method is verified with a color wavefront printer with demagnification of the object beam. The quality of reconstruction achieved by the proposed method proves its efficiency in eliminating the stripe artifacts that are superimposed on reconstructed images in conventional mosaic recording.

• International Journal of Aeronautical and Space Sciences
• /
• v.10 no.2
• /
• pp.77-85
• /
• 2009

A two-dimensional cross-section analysis program based on the finite element method has been developed for composite blades with arbitrary cross-section profiles and material distributions. The modulus weighted approach is used to take into account the non-homogeneous material characteristics of advanced blades. The CLPT (Classical Lamination Plate Theory) is applied to obtain the effective moduli of the composite laminate. The location of shear center for any given cross-sections are determined according to the Trefftz' definition while the torsion constants are obtained using the St. Venant torsion theory. A series of benchmark examples for beams with various cross-sections are illustrated to show the accuracy of the developed cross-section analysis program. The cross section cases include thin-walled C-channel, I-beam, single-cell box, NACA0012 airfoil, and KARI small-scale blades. Overall, a reasonable correlation is obtained in comparison with experiments or finite element analysis results.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.23 no.3
• /
• pp.245-249
• /
• 2010

Two dimensional(2D) pair-photonic crystals (pair-PCs) have been fabricated by a multiple-exposure nanosphere lithography (MENSL) method using the self-assembled nanospheres as lens-mask patterns and the collimated laser beam as a multiple-exposing source. The arrays of the 2D pair-PCs exhibited variable lattice structures and shape the control of rotating angle (${\Theta}$), tilting angle (${\gamma}$) and the exposure conditions. In addition, the base period or filling factor of pair-PCs as well as their shapes could be changed by experimental conditions and nanosphere size. A 1.18-${\mu}m$-thick resist was spincoated on Si substrate and the multiple exposure was carried out at change of ${\gamma}$ and ${\Theta}$. Images of prepared 2D pair-PCs were observed by SEM. We believe that the MENSL method is a suitable useful tool to realize the pair-periodic arrays of large area.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.26 no.7
• /
• pp.1408-1415
• /
• 2002

In this paper, we investigate the effect and the importance of the accuracy of finite element analysis in the shape optimization based on the finite element method and improve the existing finite element which has inaccuracy in some cases. And then, the shape optimization is performed by using the improved finite element. One of the main stream to improve finite element is the prevention of locking phenomenon. In case of bending dominant problems, finite element solutions cannot be reliable because of shear locking phenomenon. In the process of shape optimization, the mesh distortion is large due to the change of the structure outline. So, we have to raise the accuracy of finite element analysis for the large mesh distortion. We cannot guarantee the accurate result unless the finite element itself is accurate or the finite elements are remeshed. So, we approach to more accurate shape optimization to diminish these inaccuracies by improving the existing finite element. The shape optimization using the modified finite element is applied to a two and three dimensional simple beam. Results show that the modified finite element has improved the optimization results.

• Steel and Composite Structures
• /
• v.7 no.1
• /
• pp.1-18
• /
• 2007

Additional cutouts in the floorbeam webs of orthotropic plated bridge decks relieve the highly stressed lower flange of the ribs passing through these floorbeam webs from possible fatigue damage. Conversely, the floorbeam webs themselves suffer from high stress concentrations, especially along the free edges of the additional cutouts. These stresses result from a combination of direct introduction of vertical traffic loads in the weakened web and from the truss action of the floorbeam. The latter differs from a simple beam action due to the presence of the openings and corresponds more to the behaviour of a Vierendeel truss. Close assessment of the appearing stresses, highly relevant for fatigue resistance, requires the use of elaborate finite element modelling. However, a full finite element analysis merely provides the results of total stresses, leaving the researcher or designer the difficult task of finding the origin of these stress components. This paper presents a calculation method for cutout stresses based on a combination of a framework analysis and a two dimensional finite element analysis of much smaller parts of the floorbeam. This method provides more insight in the origin of the stress components, as well as it simplifies any comparison of different additional cutout geometries, independent of the floorbeam topology.

• Smart Structures and Systems
• /
• v.22 no.2
• /
• pp.223-230
• /
• 2018

This study examines a non-contact laser scanning-based ultrasound system, called an angular scan pulse-echo ultrasonic propagation imager (A-PE-UPI), that uses coincided laser beams for ultrasonic sensing and generation. A laser Doppler vibrometer is used for sensing, while a diode pumped solid state (DPSS) Q-switched laser is used for generation of thermoelastic waves. A high-speed raster scanning of up to 10-kHz is achieved using a galvano-motorized mirror scanner that allows for coincided sensing and for the generation beam to perform two-dimensional scanning without causing any harm to the surface under inspection. This process allows for the visualization of longitudinal wave propagation through-the-thickness. A pulse-echo ultrasonic wave propagation imaging algorithm (PE-UWPI) is used for on-the-fly damage visualization of the structure. The presented system is very effective for high-speed, localized, non-contact, and non-destructive inspection of aerospace structures. The system is tested on an aluminum honeycomb sandwich with disbonds and a carbon fiber-reinforced plastic (CFRP) honeycomb sandwich with a layer overlap. Inspection is performed at a 10-kHz scanning speed that takes 16 seconds to scan a $100{\times}100mm^2$ area with a scan interval of 0.25 mm. Finally, a comparison is presented between angular-scanning and a linear-scanning-based pulse-echo UPI system. The results show that the proposed system can successfully visualize defects in the inspected specimens.

• Journal of the Korean Society for Precision Engineering
• /
• v.30 no.8
• /
• pp.878-884
• /
• 2013

Stereolithography can be classified into two main categories according to the cross-sectional shape: scanning type and projection type. Projection stereolithography has significant advantages when making a layer using a single patterned beam, and results in improved speed and accuracy. To implement relatively low-cost projection stereolithography, we developed a system using a commercially available resin, which cures on exposure to visible light. The optimum photoinitiator was investigated, as well as the mixing ratio. The viscosity, shrinkage, curing depth and tensile strength were evaluated through several experiments on fabricated three-dimensional structures, and thus an optimal resin selection system was developed.

• Journal of the Korean Society of Safety
• /
• v.26 no.2
• /
• pp.62-69
• /
• 2011

This paper presents a new simple two-dimensional frame finite element able to accurately estimate the load-carrying capacity of reinforced concrete beams flexurally strengthened externally bonded fiber reinforced polymer (FRP) strips and plates. The proposed analysis model considers distributed plasticity with layer-discretization of the cross-sections and the bond-slip behavior of epoxy layer. The proposed model is used to predict the load-carrying capacity and the applied load-midspan deflection response of RC beams subjected to bending loading. Numerical simulations and experimental measurements are compared based on numerous tests available in the literature and published by different authors. The numerically simulated response agree remarkably well with the corresponding experimental results. Thus, the proposed model is suitable for efficient and accurate modeling and analysis of flexural strengthening of RC beams with externally bonded FRP sheets/plates and for practical use in design-oriented parametric studies.

• Journal of Mechanical Science and Technology
• /
• v.15 no.9
• /
• pp.1311-1318
• /
• 2001

It is necessary to diagnose accurately the characteristics of soot formation and oxidation in a diesel engine. Whereas past measurement techniques for soot concentration give limited information for soot, laser-based two-dimensional imaging diagnostics have a potential to provide temporally and spatially superior resolved measurements of the soot distribution. The technique using laser sheet beam has been applied to an optically accessible diesel engine for the quantitative measurement of soot. The results provided the information for reduction of soot from the diesel engine. Both LIS (Laser Induced Scattering) and LII (Laser Induced Incandescence) techniques were used simultaneously in this study. The images of LIS and LII showed the quantitative distribution of the soot concentration in the diesel engine. In this study, several results were obtained by the simultaneous measurements of LIS and LII technique. The diameter and number density of soot in combustion chamber of the test engine were obtained from ATDC 20 degree to 110 degree. The soot diameter increased about 37% between ATDC 20 degree and 110 degree. The number density of soot, however, decreased significantly between ATDC 40 degree and 70 degree.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.6 no.1
• /
• pp.54-57
• /
• 2005

A soft error rate neutrons is a growing problem fur terrestrial integrated circuits with technology scaling. In the acceleration test with high-density neutron beam, a latch-up prohibits accurate estimations of the soft error rate (SER). This paper presents results of analysis for the latch-up characteristics in the circumstance corresponding to the acceleration SER test for SRAM. Simulation results, using a two-dimensional device simulator, show that the deep p-well structure has better latch-up immunity compared to normal twin and triple well structures. In addition, it is more effective to minimize the distance to ground power compared with controlling a path to the $V_{DD}$ power.