• Journal of the Society of Naval Architects of Korea
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• v.36 no.2
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• pp.121-134
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• 1999

In this paper, a ship calculation program is developed, which prof[nuts hydrostatics and volume calculation intact and damage stability and hull variation. Hull form and compartment geometry are expressed with NURBS curve wire-frame model. Hydrostatics and volume calculation are performed directly with the intersection method between section geometry and 3D planar surface. Equilibrium ship position is calculated with hydrostatic equilibrium equation which is linearized by 1st order Taylor series expansion sequentially. The developed program shows more accurate results and easy uses than the latter.

• Journal of the Society of Naval Architects of Korea
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• v.50 no.5
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• pp.349-354
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• 2013

The blades of flexible propellers are formed by overlaying and adhering many layers of thin glass-fiber fabric sheets, are compressed and dried in the rigid mold. The current manufacturing process can not avoid the rather irregular deformation of the blades composed of non-isotropic non-uniform fabric structures, and inevitably introduces the different shape-forming errors between blades. In this paper, several flexible model propellers are precisely measured with three-dimensional optical instrument and compared with the original design geometry. The model propellers with the as-measured geometry are evaluated with the lifting-surface-theory-based propeller analysis code. The open-water performance are presented and discussed. The importance of the manufacturing accuracy is addressed to be able to apply the flexible propellers for propulsion of marine vehicles.

• Transactions of Materials Processing
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• v.25 no.5
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• pp.301-305
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• 2016

The manual modification of stamping die has widely been used in order to reduce springback after sheet metal forming. When UHSS (Ultra High Strength Steel) is used in sheet metal forming, the die design considering springback compensation is more difficult because higher strength sheet has more springback. In this study, the optimization method was used in order to design die geometry considering springback compensation after forming of 1.2GPa UHSS. Die geometries were defined as design variables and the springback distance from the die surface was conducted as object function in optimization process. The optimized die geometry considering springback compensation was performed using finite element and optimization analysis. The simulation results such as thickness distribution and springback amount were compared with measured data using 3D optical measurement system (GOM ARGUS, ATOS). And the prediction of springback amount showed a good agreement within test results.

• The KSFM Journal of Fluid Machinery
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• v.20 no.1
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• pp.21-28
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• 2017

Optimization process of pre-swirl nozzle geometry was conducted to improve the discharge coefficient of pre-swirl system by using CFD. The optimization of pre-swirl nozzle shape covered the converging angle and the location of the converging nozzle. Optimization process included Optimal Latin Hyper-cube Design method to get the experimental points and the Kriging method to create the response surface which gives candidate points. The process was finished when the difference between the predicted value and CFD value of candidate point was less than 0.1 %. This paper compared the Reference model, Initial model which is the first model of optimization and Optimized model to study flow characteristics. Finally, the discharge coefficient of Optimized model is improved about 17 % to the Reference model.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.30 no.4
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• pp.283-288
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• 2017

A spot welded joint is modeled using 3-D finite elements with embedded strong discontinuities. The spot weld is represented by a special cohesive law on the embedded discontinuity surface, instead of meshing its geometry. This strategy naturally eliminates the need of adaptive FEM meshes fitting the local geometry of the spot weld. Mesh independent solutions are guaranteed by explicitly modeling the detailed shape of the spot weld, which is in contrast with the exiting approach using point constraints for the spot weld.

• International Journal of Railway
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• v.3 no.3
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• pp.83-89
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• 2010

This paper attempts to extract the fundamental dynamic properties, i.e. natural frequencies, damping ratios of the 48 m-long, $20^{\circ}$ skewed real bridge with PSC girders wrapped by a steel plate. The forced vibration test is achieved by mounting 12 Hz-capacity of artificial oscillator on the top of bridge deck. The acceleration histories at the 9 different locations of deck surface are recorded using accelerometors. From this full-scaled vibration test, the two possible resonance frequencies are detected at 2.38 Hz and 9.86 Hz of the skewed bridge deck by sweeping a beating frequency up to 12 Hz. The absolute acceleration/energy exhibits much higher in case of higher-order twist mode, 9.86 Hz due to the skewness of bridge deck which leads asymmetric situation of vibration. This implies the test bridge is under swinging vertically in fundamental flexure mode while the bridge is also flickered up and down laterally at 9.86 Hz. This is probably by asymmetric geometry of skewed deck. A detailed 3D beam-shell bridge models using finite elements are performed under a series of train loads for modal dynamic analyses. Thereby, the effect of skewness is examined to clarify the lateral flickering caused by asymmetrical geometry of bridge deck.

• Journal of Electrical Engineering and Technology
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• v.13 no.1
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• pp.400-405
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• 2018

This paper presents a compact ultra-wideband (UWB) flexible monopole antenna design on a paper substrate. The proposed antenna is made of iterations of a circular slot inside an octagonal metallic patch. This fractal-based geometry has been deployed to achieve compactness along with improved bandwidth, measured reflection coefficient -10 dB bandwidth ranging from 2.7 to 15.8 GHz. The overall size of the antenna is $26mm{\times}19mm{\times}0.5mm$, which makes it a compact one. The substrate used is paper and the main features like environment friendly, flexibility, green electronics applications and low cost of fabrication are the key factors for the proposed antenna. The aforementioned UWB prototype is suitable for many wireless communication systems such as WiMAX, WiFi, RFID and WSN applications. Antenna has been tested for the effect of bending by placing it over a curved surface of a very small radius of 10 mm.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.50 no.2
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• pp.59-64
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• 2001

The distribution of current in the conductors influenced by the armature geometry and velocity is an important parameter for determining performance of an electromagnetic launcher(EML). the electric current in the early launching stage tends to flow on the outer surfaces of the conductors, resulting in very high local electric current density. However, the tendency for current to concentrate on the surface is driven by the velocity skin effect later in launching stage. The high current density produces high local heating and, consequently, increases armature wear which causes several defects on EML system. This paper investigates the effects of rail/armature geometry on current density distribution, launcher inductance gradient (L'), and contact force. Three geometrical parameters are used here to characterize the railgun system. These are the ratio of contact length to root length, relative position of contact leading edge to root trailing edge, and the ratio of rail overhang to the rail height. The distribution of current density, L', contact force between various configurations of the armature and the rail are analyzed and compared by using the EMAP3D program.

• Applied Science and Convergence Technology
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• v.27 no.4
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• pp.70-74
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• 2018

We fabricated an anode-type ion source driven by a charge repulsion mechanism and investigated its beam shape controlled by a Whenelt mask integrated at the front face of the source. The ion beam shape was observed to vary by changing the geometry of the Whenelt mask. As the angle of inclination of the Whenelt mask was varied from $40^{\circ}$ to $60^{\circ}$, the etched area at a thin film was reduced from 20 mm to 7.5 mm at the working distance of 286 mm, and the light transmittance through the etched surface was increased from 78% to 80%, respectively. In addition, for the step height difference, ${\Delta}$ between the inner mask and the outer mask of ${\Delta}=0$, -1 mm, and +1 mm, we observed the ion beam shape was formed to be collimated, diverged, and focused, respectively. The focal length of the focused beam was 269 mm. We approved experimentally a simple way of controlling the electric field of the ion beam by changing the geometry of the Whenelt mask such that the initial direction of the ion beam in the plasma region was manipulated effectively.

• Journal of the Society of Naval Architects of Korea
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• v.42 no.2 s.140
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• pp.113-123
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• 2005

A higher order panel method based on B-spline representation for both the geometry and the solution is developed for the analysis of steady flow around marine propellers. The self-influence functions due to the normal dipole and the source are desingularized through the quadratic transformation, and then shown to be evaluated using conventional numerical quadrature. By selecting a proper order for numerical quadrature, the accuracy of the present method can be increased to the machine limit. The far- and near-field influences are shown to be evaluated based on the same far-field approximation, but the near-field solution requires subdividing the panels into smaller subpanels continuously, which can be effectively implemented due to the B-spline representation of the geometry. A null pressure jump Kutta condition at the trailing edge is found to be effective in stabilizing the solution process and in predicting the correct solution. Numerical experiments indicate that the present method is robust and predicts the pressure distribution on the blade surface, including very close to the tip and trailing edge regions, with far fewer panels than existing low order panel methods.