• Steel and Composite Structures
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• v.28 no.5
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• pp.607-615
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• 2018

The dynamic behavior of the deployment and folding process of a foldable boom based on the Miura origami pattern is investigated in this paper. Firstly, mechanical behavior of a single storey during the motion is studied numerically. Then the deployment and folding of a multi-storey boom is discussed. Moreover, the influence of the geometry parameters and the number of Miura-ori elements n on the dynamic behavior of the boom is also studied. Finally, the influence of the imperfection on the dynamic behavior is investigated. The results show that the angles between the diagonal folds and horizontal folds will have great effect on the strains during the motion. A bistable configuration can be obtained by choosing proper fold angles for a given multi-storey boom. The influence of the imperfection on the folding behavior of the foldable mast is significant.

• The Journal of the Acoustical Society of Korea
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• v.31 no.1
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• pp.51-61
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• 2012

In this research, we have analyzed the trend of radiation pattern variation in relation to the change of design variables such as source interval and source number for conformal array transducers arranged in equi-angle, equi-interval, and geodesic dome forms. Through statistical multiple regression analysis of the results, we derived functional forms of the side lobe level and the beamwidth in terms of the design variables. Futhermore, the structure of the array transducer was optimized to achieve the smallest side lobe level while satisfying the requirements on beam width by the GA (genetic algorithm) method. Based on the optimized results, we have determined the equi-interval form as the optimal array geometry among the three conformal array geometries.

• Journal of Korea Multimedia Society
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• v.17 no.1
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• pp.34-42
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• 2014

In this paper an embedding algorithm based on commute time is implemented by organizing patches according to the graph-based metric, and its performance is analyzed by comparing with the results of principal component analysis embedding. It is usual that the dimensionality reduction be done within some acceptable approximation error. However this paper shows the proposed manifold embedding method generates the intrinsic geometry corresponding to the signal despite severe approximation error, so that it can be applied to the areas such as pattern classification or machine learning.

• Journal of Korea Foundry Society
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• v.29 no.1
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• pp.33-37
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• 2009

Cartesian grid system has mainly been used in the casting simulation even though it does not nicely represent sloped and curved surfaces. These distorted boundaries cause several problems. A special treatment is necessary to clear these problems. In this paper, we propose a new method that can consider the cutting cells which are cut by casting and mold based on the partial cell treatment (PCT). This method provides a better representation of geometry surface and will be used in the computation of velocities that are defined on the cell boundaries in the Cartesian grid system. Various test examples for several casting process were computed and validated. The analysis results of more accurate fluid flow pattern and less momentum loss owing to the stepped boundaries in the Cartesian grid system were confirmed. By using the cut cell method, performance of computation gets better because of reducing the whole number of meshes.

• Electrical & Electronic Materials
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• v.9 no.6
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• pp.593-599
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• 1996

Laser scribing of silicon plays an important role in metallization including the grid pattern and the front surface geometry which means aspect ratio of metal contacts. To make a front metal electrode of buried contact solar cell, we used ND:YAG lasers that deliver average 3-4W at TEM$\_$00/ mode power to sample stage. The Q-switched Nd:YAG laser of 1.064 gm wavelength was used for silicon scribing with 20-40.mu.m width and 20-200.mu.m depth capabilities. After silicon slag etching, the groove width and depth for buried contact solar cell are -20.mu.m and 30-50.mu.m respectively. Using MEL 40 Nd:YAG laser system, we can scribe the silicon surface with 18-23.mu.m width and 20-200.mu.m depth controlled by krypton arc lamp power, scan speed, pulse frequency and beam focusing. We fabricated a buried contact Silicon Solar Cell which had an energy conversion efficiency of 18.8 %. In this case, the groove width and depth are 20.mu.m and 50.mu.m respectively.

• International Journal of Fluid Machinery and Systems
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• v.7 no.1
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• pp.1-6
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• 2014

The propellant acquisition vane (PAV) is a key part of a vane type surface tension propellant management device (PMD), which can manage the propellant effectively. In the present paper, the fluid transportation behaviors for five PAVs with different sections were investigated by using microgravity drop tower test. Further, numerical simulation for the propellant flow in a PMD under microgravity condition was also carried out based on VOF model, and showed the similar flow pattern for PAVs to the experiment. It is noted that the section geometry of PAVs is one of the main factors affecting the fluid transportation behavior of PMD. PAVs with bottom length ratio of 5/6 and 1/2 have larger propellant transportation velocity. Based on the experiments, there were two stages during the process of propellant transportation under microgravity environment: liquid relocation and steady transportation stage. It is also recognized that there is a linear correlation between liquid transportation velocity and relative time's square root. Those results can not only provide a guideline for optimization of new vane type PMDs, but also are helpful for fluid control applications in space environment.

• Composites Research
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• v.28 no.3
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• pp.136-141
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• 2015

The stitching process has been widely utilized for the improvement of through-thickness property of the conventional laminated composites. This paper reports the effects of stitching on the flexural and interlaminar shear properties of multi-axial warp knitted (MWK) composites in order to identify the mechanical property improvements. In order to minimize the geometric uncertainties associated with the stacking pattern of fabrics, the regular lay-up was considered in the examination of the stitching effect. The key parameters are as follows: the stitch spacings, the stitching types, the stitching location, and the location of compression fixture nose. These parameters have little effect on the flexural and interlaminar shear properties, except for the case of stitching location. However, the geometry variations caused by the stitching resulted in minor changes to the mechanical properties consistently. Stitching on the $0^{\circ}$ fibers showed the lowest flexural strength and modulus (12% reduction for both properties). The stitch spacing of 5 mm resulted in 8% reduction for the case of interlaminar strength compared with that of 10 mm spacing.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.11 s.254
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• pp.1107-1116
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• 2006

The droplet ejection process driven by an evaporating bubble in a thermal inkjet printhead is investigated by numerically solving the conservation equations for mass, momentum and energy. The phase interfaces are tracked by a level set method which is modified to include the effect of phase change at the interface and extended for multiphase flows with irregular solid boundaries. The compressibility effect of a bubble is also included in the analysis to appropriately describe the bubble expansion behaviour associated with the high pressure caused by bubble nucleation. The whole process of bubble growth and collapse as well as droplet ejection during thermal inkjet printing is simulated without employing a simplified semi-empirical bubble growth model. Based on the numerical results, the jet breaking and droplet formation behaviour is observed to depend strongly on the bubble growth and collapse pattern. Also, the effects of liquid viscosity, surface tension and nozzle geometry are quantified from the calculated bubble growth rate and ink droplet ejection distance.

• The Mathematical Education
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• v.53 no.4
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• pp.493-507
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• 2014

The purpose of this study is to analyze how high school students form and interpret the mental image in the process of solving regular polyhedron problems. For this purpose, a set of problems about the regular polyhedron's vertex is developed on the base of the regular polyhedron's duality and circulation. and applied to 2 students of the 12th graders in D high school. After 2 hours of teaching and learning and another 2 hours of mental image-analysis process, the following research findings are obtained. Fisrt, a student who recorded medium high-level grade in the national scholastic test can build the dynamic image or the patten image in the process of solving regular polyhedron's vertex problems by utilizing the 3D geometry program. However, the other student who recorded low-level grade can build the concrete-pictorial image. Second, pattern image or dynamic image can help students solve the regular polyhedron's vertex problems by proper transformation of informations and the mental images while the concrete-pictorial image does not help. Hence, it is recommended that the mathematics teachers should develop teaching and learning materials about the regular polyhedron's duality and circulation and also give students suitable questions to build the various mental images.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.191-195
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• 2003

The formation degree of sustain (ITO pattern) decides quality of PDP (plasma display panel). For this reason. it makes efforts in search defects more than 30 ${\mu}{\textrm}{m}$. Now, the existing inspection process is dependent upon naked eye or SEM equipment in off-line PDP manufacturing process. In this study developed prototype inspection system of PDP ITO glass. This system creates information that detects and sorts kind of defect automatically. Design ed inspection technology adopts line-scan method by slip-beam formation for the minimum of inspection time and image processing algorithm is embodied in detection ability of developed system. Designed algorithm had to make good use of kernel matrix which draws up an approach to geometry. A characteristic of area-shaped defects, as pin hole, substance, protrusion et al, are extracted from blob analysis method. Defects, as open, short, spots, et al, are distinguished by line type inspection algorithm. In experiment results, we could have ensured ability of inspection that can be detected with reliability of up to 95% in about 60 seconds