• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.43-46
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• 2005

Micro molding technology is a promising mass production technology for polymer based microstructures. Mass production technologies such as the micro injection/compression molding, hot embossing, and micro reaction molding are already in use. In the present study, we have developed a numerical analysis system to simulate three-dimensional non-isothermal cavity filling for hot embossing, with a special emphasis on the free surface capturing. Precise free surface capturing has been successfully accomplished with the level set method, which is solved by means of the Runge-Kutta discontinuous Galerkin (RKDG) method. The RKDG method turns out to be excellent from the viewpoint of both numerical stability and accuracy of volume conservation. The Stokes equations are solved by the stabilized finite element method using the equal order tri-linear interpolation function. To prevent possible numerical oscillation in temperature Held we employ the streamline upwind Petrov-Galerkin (SUPG) method. With the developed code we investigated the detailed change of free surface shape in time during the mold filling. In the filling simulation of a simple rectangular cavity with repeating protruded parts, we find out that filling patterns are significantly influenced by the geometric characteristics such as the thickness of base plate and the aspect ratio and pitch of repeating microstructures. The numerical analysis system enables us to understand the basic flow and material deformation taking place during the cavity filling stage in microstructure fabrications.

• Applied Chemistry for Engineering
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• v.30 no.5
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• pp.639-642
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• 2019

Hydroxyapatite (HAP) containing hexadecyltrimethylammonium chloride (CTAC) as a cationic surfactant was prepared by a precipitation method. X-ray diffraction (XRD), transmission electron microscopy (TEM) and micropore physisorption analyzer were used for characterizing the crystal phase, morphology and specific surface area of HAP and CTAC-HAP. After thermal treatment, the specific surface area of both pure HAP and CTAC-HAP were reduced. The sharp rod morphology of CTAC-HAP was changed into a round shape with a smaller aspect ratio after the heat treatment. The morphological change by thermal treatment was also observed in pure HAP. Therefore, the morphological change and decrease of the specific surface area suggested that pores from the removal of CTAC during thermal treatment were not retained.

• Journal of the Society of Naval Architects of Korea
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• v.31 no.1
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• pp.121-132
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• 1994

The aim of the present paper is to clarify the damage characteristics fur ship bottom stiffened platings in grounding. For this purpose, a series of tests are performed. A rigid wedge is quasi-statically pushed into the high tensile steel plates with two stiffeners. The aspect ratio of plates(a/B) is in the range from 1.0 to 2.5 and the thickness of plates is in the range from 3.4 to 7.0mm. Also other parameters, namely the shape of wedge tip, wedge angle and property/direction of stiffeners are varied. The test is carried out using the 100ton universal test machine. During the loading. both applied force and length of cutting(penetration) resulting in the grounding force-penetration response are measured.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.40 no.3
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• pp.206-213
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• 2004

As far as an opening device of fishing gears is concerned, applications of a kite are under development around the world. The typical examples are found in the opening device of the stow net on anchor and the buoyancy material of the trawl. While the stow net on anchor has proved its capability for the past 20 years, the trawl has not been wildly used since it has been first introduced for the commercial use only without sufficient studies and thus has revealed many drawbacks. Therefore, the fundamental hydrodynamics of the kite itself need to ne studied further. Models of plate and canvas kite were deployed in the circulating water tank for the mechanical test. For this situation lift and drag tests were performed considering a change in the shape of objects, which resulted in a different aspect ratio of rectangle and trapezoid. The results obtained from the above approaches are summarized as follows, where aspect ratio, attack angle, lift coefficient and maximum lift coefficient are denoted as A, B, $C_L$ and $C_{Lmax}$ respectively : 1. Given the triangular plate, $C_{Lmax}$ was produced as 1.26${\sim}$1.32 with A${\leq}$1 and 38$^{\circ}$B${\leq}$42$^{\circ}$. And when A${\geq}$1.5 and 20$^{\circ}$${\leq}$B${\leq}$50$^{\circ}$, $C_L$ was around 0.85. Given the inverted triangular plate, $C_{Lmax}$ was 1.46${\sim}$1.56 with A${\leq}$1 and 36$^{\circ}$B${\leq}$38$^{\circ}$. And When A${\geq}$1.5 and 22$^{\circ}$B${\leq}$26$^{\circ}$, $C_{Lmax}$ was 1.05${\sim}$1.21. Given the triangular kite, $C_{Lmax}$ was produced as 1.67${\sim}$1.77 with A${\leq}$1 and 46$^{\circ}$B${\leq}$48$^{\circ}$. And when A${\geq}$1.5 and 20$^{\circ}$B${\leq}$50$^{\circ}$, $C_L$ was around 1.10. Given the inverted triangular kite, $C_{Lmax}$ was 1.44${\sim}$1.68 with A${\leq}$1 and 28$^{\circ}$B${\leq}$32$^{\circ}$. And when A${\geq}$1.5 and 18$^{\circ}$B${\leq}$24$^{\circ}$, $C_{Lmax}$ was 1.03${\sim}$1.18. 2. For a model with A=1/2, an increase in B caused an increase in $C_L$ until $C_L$ has reached the maximum. Then there was a tendency of a very gradual decrease or no change in the value of $C_L$. For a model with A=2/3, the tendency of $C_L$ was similar to the case of a model with A=1/2. For a model with A=1, an increase in B caused an increase in $C_L$ until $C_L$ has reached the maximum. And the tendency of $C_L$ didn't change dramatically. For a model with A=1.5, the tendency of $C_L$ as a function of B was changed very small as 0.75${\sim}$1.22 with 20$^{\circ}$B${\leq}$50$^{\circ}$. For a model with A=2, the tendency of $C_L$ as a function of B was almost the same in the triangular model. There was no considerable change in the models with 20$^{\circ}$B${\leq}$50$^{\circ}$. 3. The inverted model's $C_L$ as a function of increase of B reached the maximum rapidly, then decreased gradually compared to the non-inverted models. Others were decreased dramatically. 4. The action point of dynamic pressure in accordance with the attack angle was close to the rear area of the model with small attack angle, and with large attack angle, the action point was close to the front part of the model. 5. There was camber vertex in the position in which the fluid pressure was generated, and the triangular canvas had large value of camber vertex when the aspect ratio was high, while the inverted triangular canvas was versa. 6. All canvas kite had larger camber ratio when the aspect ratio was high, and the triangular canvas had larger one when the attack angle was high, while the inverted triangluar canvas was versa.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.40 no.3
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• pp.196-205
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• 2004

As far as an opening device of fishing gears is concerned, applications of a kite are under development around the world. The typical examples are found in the opening device of the stow net on anchor and the buoyancy material of the trawl. While the stow net on anchor has proved its capability for the past 20 years, the trawl has not been wildly used since it has been first introduced for the commercial use only without sufficient studies and thus has revealed many drawbacks. Therefore, the fundamental hydrodynamics of the kite itself need to ne studied further. Models of plate and canvas kite were deployed in the circulating water tank for the mechanical test. For this situation lift and drag tests were performed considering a change in the shape of objects, which resulted in a different aspect ratio of rectangle and trapezoid. The results obtained from the above approaches are summarized as follows, where aspect ratio, attack angle, lift coefficient and maximum lift coefficient are denoted as A, B, $C_L$ and $C_{Lmax}$ respectively : 1. Given the rectangular plate, $C_{Lmax}$ was produced as 1.46${\sim}$1.54 with A${\leq}$1 and 40$^{\circ}$${\leq}$B${\leq}$42$^{\circ}$. And when A${\geq}$1.5 and 20$^{\circ}$${\leq}$B${\leq}$22$^{\circ}$, $C_{Lmax}$ was 10.7${\sim}$1.11. Given the rectangular canvas, $C_{Lmax}$ was 1.75${\sim}$1.91 with A${\leq}$1 and 32$^{\circ}$${\leq}$B${\leq}$40$^{\circ}$. And when A${\geq}$1.5 and 18$^{\circ}$${\leq}$B${\leq}$22$^{\circ}$, $C_{Lmax}$ was 1.24${\sim}$1.40. Given the trapezoid kite, $C_{Lmax}$ was produced as 1.65${\sim}$1.89 with A${\leq}$1.5 and 34$^{\circ}$${\leq}$B${\leq}$44$^{\circ}$. And when A=2 and B=14${\sim}$48, $C_L$ was around 1. Given the inverted trapezoid kite, $C_{Lmax}$ was 1.57${\sim}$1.74 with A${\leq}$1.5 and 24$^{\circ}$${\leq}$B${\leq}$36$^{\circ}$. And when A=2, $C_{Lmax}$ was 1.21 with B=18$^{\circ}$. 2. For a model with A=1/2, an increase in B caused an increase in $C_L$ until $C_L$ has reached the maximum. Then there was a tendency of a gradual decrease in the value of $C_L$ and in particular, the rectangular kite showed a more rapid decrease. For a model with A=2/3, the tendency of $C_L$ was similar to the case of a model with A=1/2 but the tendency was a more rapid decrease than those of the previous models. For a model with A=1, and increase in B caused an increase in $C_L$ until $C_L$ has reached the maximum. Soon after the tendency of $C_L$ decreased dramatically. For a model with A=1.5, the tendency of $C_L$ as a function of B was various. For a model with A=2, the tendency of $C_L$ as a function of B was almost the same in the rectangular and trapezoid model. There was no considerable change in the models with 20$^{\circ}$${\leq}$B${\leq}$50$^{\circ}$. 3. The tendency of kite model's $C_L$ in accordance with increase of B was increased rapidly than plate models until $C_L$ has reached the maximum. Then $C_L$ in the kite model was decreased dramatically but in the plate model was decreased gradually. The value of $C_{Lmax}$ in the kite model was higher than that of the plate model, and the kite model's attack angel at $C_{Lmax}$ was smaller than the plate model's. 4. In the relationship between aspect ratio and lift force, the attack angle which had the maximum lift coefficient was large at the small aspect ratio models, At the large aspect ratio models, the attack angle was small. 5. There was camber vertex in the position in which the fluid pressure was generated, and the rectangular & trapezoid canvas had larger value of camber vertex when the aspect ratio was high, while the inverted trapezoid canvas was versa. 6. All canvas kite had larger camber ratio when the aspect ratio was high, and the rectangular & trapezoid canvas had larger one when the attack angle was high.

• Steel and Composite Structures
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• v.29 no.3
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• pp.379-389
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• 2018

In this research, the explicit closed-form local buckling solution of steel plates in contact with concrete, with both loaded and unloaded edges elastically restrained against rotation and subjected to eccentric compression is presented. The Rayleigh-Rize approach is applied to establish the eigenvalue problem for the local buckling performance. Buckling shape which combines trigonometric and biquadratic functions is introduced according to that used by Qin et al. (2017) on steel plate buckling under uniform compression. Explicit solutions for predicting the local buckling stress of steel plate are obtained in terms of the rotational stiffness. Based on different boundary conditions, simply yet explicit local buckling solutions are discussed in details. The proposed formulas are validated against previous research and finite element results. The influences of the loading stress gradient parameter, the aspect ratio, and the rotational stiffness on the local buckling stress resultants of steel plates with different boundary conditions were evaluated. This work can be considered as an alternative to apply a different buckling shape function to study the buckling problem of steel plate under eccentric compression comparing to the work by Qin et al. (2018), and the results are found to be in consistent with those in Qin et al. (2018).

• Applied Chemistry for Engineering
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• v.10 no.5
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• pp.789-795
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• 1999

In this study, carbon fiber reinforced cement composites(CFRCs) reinforced with short noncircular type carbon fibers were fabricated and properties(drying shrinkage, resistance to freezing and thawing, and fracture toughness) were compared with those of the CFRCs reinforced with circular type carbon fibers. It was found that these properties greatly depended on the shape and length of carbon fibers. The drying shrinkage of CFRCs reinforced with C-type carbon fiber was superior to other CFRCs. This effect was increased with a high aspect ratio of fiber. The resistance to freezing and thawing was increased with the fiber length and fiber volume percent, but there was on remarkable effect to fiber shape. Fracture toughness and resistance to crack propagation of CFRCs reinforced with C-CFs were improved compared with other CFRCs. It was believed that the more absorption of fracture energy into the larger interface caused an increase in fracture toughness and resistance to crack propagation.

• Journal of Korean Society of Steel Construction
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• v.22 no.1
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• pp.43-53
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• 2010

Seismic isolation is one of the most widely implemented and accepted seismic protection systems to limit or avoid damages from unforeseeable earthquakes. As an energy absorption device, however, the supplemental lead itself tends to pollute the environment. Consequently, it is predicted that the use of lead would be controlled. Considering the pollution caused by lead, several researchers are interested in the viability of using steel in place of lead. In this study, first, based on the results of a non-linear finite element analysis, the excellent deformation capacity of a very tough steel damper was demonstrated by comparing it with that of the SS400 damper and determining the effects of main parameters (the aspect ratio, thickness, and width) on the deformation capacity. Second, an optimum shape and design equation for a U-shaped damper with an opening based on stress distribution was suggested.

• Journal of Korea Foundry Society
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• v.15 no.6
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• pp.574-587
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• 1995

The $SiC_p-reinforced$ preforms fabricated by spray casting process were hot-extruded and subsequently T6-treated, and the morphology of the silicon phase and the grain size for these preforms and extruded samples were examined by Image Analyzer. Experimental observation revealed that with increase in volume percent of SiC particles, the grain size and silicon phase of the $Al-Si/SiC_p$ composites become finer, the shape of Si phase is changed from blocky to granular type, and aspect ratio of Si phase tend to become unity. Wear-tests with various sliding velocities, show that the wear resistance of spray cast specimen is increased remarkably compare to the permanent mold cast specimen at the sliding velocity range of $1.98{\sim}2.38m/sec$.. Microstructural observations for the worn surfaces of specimens revealed that wear resistance of Al-Si alloys at certain sliding velocities could be improved not only by the fine grain size of aluminum matrix but also the fine size and granular shape of silicon phases. The wear resistance of $SiC_p$ reinforced aluminum composites was found to be sensitive to the volume percentage of the reinforcing particles. The worn surfaces with various sliding velocities, show that change in wear mechanism seems to occur at the sliding velocity of near 2m/sec for all samples, and such a change in mechanism is delayed with increase in $SiC_p$ volume fraction.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.2
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• pp.97-108
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• 2015

In the design of sailing yachts, para-glider, or high-sky wind power, etc., the analysis of side-wind aerodynamic forces exerted on a cambered 3-D model is very important to predict the performance of various machinery systems. To understand the essential flow physics around the three-dimensional shape, simplified rigid-body models are proposed in this study. Four parameters such as free stream velocity, angle of attack, aspect ratio, and camber are considered as the independent variables. Lift and drag coefficients are computed with CFD technique using ANSYS-CFX, and the results with the visualization of post-processed flow fields are analyzed in the viewpoint of fluid dynamics.