• Steel and Composite Structures
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• 제22권4호
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• pp.837-853
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• 2016

This paper presents the experimental and numerical study on the distribution of transverse and longitudinal residual stresses in cold-formed thick-walled structural steel rectangular hollow sections manufactured by indirect technique. Hole-drilling method is employed to measure the magnitude of the transverse and longitudinal surface residual stress distribution, and the effects of the residual stresses are evaluated qualitatively by sectioning method. It is shown that compared to normal cold-formed thin-walled structural hollow sections (SHS), the cold-formed thick-walled SHS has similar level of residual stress in the flat area but higher residual stresses in the corner and welding areas. Both the transverse and longitudinal residual stresses tend to open the section. In order to predict the surface residual stresses in the corners of the cold-formed thick-walled SHS, an analytical model is developed. 2D finite element simulation of the cold bending process is conducted to validate the analytical approach. It is shown that in analyzing bending for thick-walled sections, shifting of neutral axis must be considered, since it would lead to nonlinear and non-symmetrical distribution of stresses through the thickness. This phenomenon leads to the fact that cold-formed thick-walled SHSs has different distribution and magnitude of the residual stresses from the cold-formed thin-walled SHSs.

• 한국ITS학회 논문지
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• 제7권1호
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• pp.68-74
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• 2008

SIW (Substrate Integrated Waveguide) cavity 공진기의 구조는 유전체기판에 다수의 via-hole 을 이용함으로써 나타낼 수 있으며, rectangular waveguide 와 유사한 특성을 갖는다. 그리고 $50-{\Omega}$ 마이크로스트립라인과 SIW cavity 공진기 중앙간의 결합구조를 통하여 대역저지 특성이 나타나도록 하였다. 이러한 특성을 갖는 SIW cavity 공진기를 이용하여 X-band(9.45 GHz) 발진기를 제작하였고, 위상잡음은 100kHz offset에서 -98.1 dBc/Hz 로 측정되었다. SIW cavity 공진기는 높은 QL 값을 갖고, 2차원 구조이기 때문에 저비용에 우수한 위상잡음 특성을 갖는 발진기 설계에 응용할 수 있다.

• Structural Engineering and Mechanics
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• 제85권2호
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• pp.147-161
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• 2023

Based on the ideas of variational differential quadrature (VDQ) and finite element method (FEM), a numerical approach named as VDQFEM is applied herein to study the large deformations of plate-type structures under static loading with arbitrary shape hole made of functionally graded graphene platelet-reinforced composite (FG-GPLRC) in the context of higher-order shear deformation theory (HSDT). The material properties of composite are approximated based upon the modified Halpin-Tsai model and rule of mixture. Furthermore, various FG distribution patterns are considered along the thickness direction of plate for GPLs. Using novel vector/matrix relations, the governing equations are derived through a variational approach. The matricized formulation can be efficiently employed in the coding process of numerical methods. In VDQFEM, the space domain of structure is first transformed into a number of finite elements. Then, the VDQ discretization technique is implemented within each element. As the last step, the assemblage procedure is performed to derive the set of governing equations which is solved via the pseudo arc-length continuation algorithm. Also, since HSDT is used herein, the mixed formulation approach is proposed to accommodate the continuity of first-order derivatives on the common boundaries of elements. Rectangular and circular plates under various boundary conditions with circular/rectangular/elliptical cutout are selected to generate the numerical results. In the numerical examples, the effects of geometrical properties and reinforcement with GPL on the nonlinear maximum deflection-transverse load amplitude curve are studied.

• Steel and Composite Structures
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• 제46권3호
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• pp.353-366
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• 2023

This paper presents a finite-element analysis (FEA) of aluminum alloy rectangular hollow sections (RHSs) and square hollow sections (SHSs) with circular through-openings under three-point and four-point bending. First, a finite-element model (FEM) was developed and validated against the corresponding test results available in the literature. Next, using the validated FE models, a parametric study comprising 180 FE models was conducted. The cross-section width-to-thickness ratio (b/t) ranged from 2 to 5, the hole size ratio (d/h) ranged from 0.2 to 0.8 and the quantity of holes (n) ranged from 2 to 6, respectively. Third, results obtained from laboratory test and FEA were compared with current design strengths calculated in accordance with the North American Specifications (NAS), the modified direct strength method (DSM) and the modified Continuous strength method (CSM). The comparison shows that the modified CSM are conservative by 15% on average for aluminum alloy RHSs and SHSs with circular through-openings subject to bending. Finally, a new design equation is proposed based on the modified CSM after being validated with results obtained from laboratory test and FEA. The proposed design equation can provide accurate predictions of flexural capacities for aluminum alloy RHSs and SHSs with circular through-openings.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.567-567
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• 2013

Surface plasmon resonance is the enhancement of electromagnetic wave caused by oscillation on the metal and dielectric interfaces. Surface plasmons with nanohole arrays provides an enhancedresonance for the specific wavelengths of interests. Asymmetric array of nanoscale structures can enable orientation dependent shift of resonance wavelengths when combined with the control of polarization for incident visible light, thus providing color tunability. Appropriate lattice constants along the direction of polarization in rectangular nanohole arrays can determine the resonance condition generating red (R), green (G), and blue (B) colors and potentially be applied to display applications. In ourprevious report, we have optimized the ion beam nanomachining conditions to fabricate the nanostructures on the metal film. We apply the fabrication conditions to make nanoscale hole arrays using 100 nm thick gold layer on the glass substrate with the optimal design of periodicities along x, y, and diagonal directions of a=440 nm, b=520 nm, c=682 nm, and the hole diameter of d=200 nm. Using the reflective light in dark field mode of optical microscope, we can observe different colors. When the polarizer is paralleled along a, b, or c direction, the represented color is changed to R, G, and B, respectively. We further map the color using i1 to correlate the conditions of the nanohole arrays with their characteristic color.

• 비파괴검사학회지
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• 제25권6호
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• pp.467-474
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• 2005

The expanded multi-Gaussian beam model has recently been developed that can calculate the radiation beam field from a single, rectangular transducer with great computational efficiency. In this study, this model is adopted to calculate the radiation beam field for a phased array transducer with various time delays to achieve steering and/or focusing. The calculation beam fields are compared to those obtained by well known Rayleigh-Sommerfeld integral that provides the exact solution in order to explore the validity of the expanded multi-Gaussian beam model And then, this study proposes a complete ultrasonic measurement model including the expanded beam model, far-field scattering model and system efficiency, Using the proposed model, phased array ultrasonic testing signals for a flat-bottomed hole with/without focusing were performed.

• 한국수자원학회논문집
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• 제34권6호
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• pp.641-649
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• 2001

본 연구에서는 군말뚝 교각 주위에서의 세굴특성을 실험을 통하여 파악하였다. 실험은 4개, 9개, 15개, 35개의 파일로 구성된 군말뚝에 대해 수행하여 파일수, 유속, 접근각에 따른 세굴형상, 최대세굴심의 깊이 및 위치의 변화를 살펴보았다. 실험결과에 의하면, 4개 및 9개로 구성된 군말뚝의 경우 유속비와 상관없이 단일교각의 최대세굴심과 흡사하였고, 15개와 35개로 구성된 군말뚝의 경우 유속비가 증가함에 따라 최대세굴심도 급격히 증가하여 단일교각 세굴심 의 약 2.2배 증가함을 알 수 있었다. 또한 세굴형태는 말뚝간격이 조밀해질수록 원형의 세굴공이 중첩되어 전체적으로 직사각형의 형태를 띠는 것으로 나타났다. 75개의 파일로 구성된 군말뚝에 대한 접근각의 영향을 살펴본 결과 세굴심은 접근각이 35$^{\circ}$에서 최대가 되었으며 이때의 세굴공은 대각선 방향으로 형성됨을 알 수 있었다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2008년도 추계학술대회 논문집
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• pp.401-404
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• 2008

In the present investigation, a high precision thermal imprint system for micro ceramic products was developed and the net-shape manufacturing of multi-layer ceramic reflector for LED (Light Emitting Diode) was conducted with a precision metal die. Workpiece used in the present investigation were the multi-layer laminated ceramic sheets with pre-punched holes. The cavity with arbitrary angle was formed on the circular and rectangular holes of the ceramic sheets. During the imprinting process, the ambient temperature of the imprint system was kept over the transition temperature of the ceramic sheet and then rapidly cooled. The results in this paper show that the present method can be successfully applied to the fabrication of very small size hole array for ceramic reflector in a one step operation.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.801-806
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• 2001

The objective of present study is to find the interaction between volute and impeller of the centrifugal turbomachinery with rectangular cross-sectional volute. Flow measurement were taken in shrouded impeller with 12 backward type blades by using a five-hole pressure probe. The measurements are carried out in 7 flow rate, respectively. Primary function of a centrifugal turbo machinery volute is to serve the flow from the impeller and diffuser to pipe system. For the off-design conditions, Influence of pressure distortion was shown by these measurements. As a result, It has caused the decrease of total efficiency of centrifugal turbomachinery. We have also taken data to design volute by these measurements.

• 한국정밀공학회지
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• 제21권4호
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• pp.32-38
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• 2004

Laser-induced thermochemical wet etching of titanium in phosphoric acid has been investigated to examine the feasibility of this method fur fabrication of microstructures. Cutting, drilling, and milling of titanium foil were carried out while examining the influence of process parameters on etch width, etch depth, and edge straightness. Laser power, scanning speed of workpiece, and etchant concentration were chosen as major process parameters influencing on temperature distribution and reaction rate. Etch width increased almost linearly with laser power showing little dependence on scanning speed while etch depth showed wide variation with both laser power and scanning speed. A well-defined etch profile with good surface quality was obtained at high concentration condition. Fabrication of a hole, micro cantilever beam, and rectangular slot with dimension of tess than 100${\mu}{\textrm}{m}$ has been demonstrated.