• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.296-296
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• 2014

We investigate experimentally and theoretically the splitting of surface plasmon (SP) resonance peaks under TE- and TM-polarized illumination. The SP structure at infrared wavelength is fabricated with a 2-dimensional square periodic array of circular holes penetrating through Au (gold) film. In brief, the processing steps to fabricate the SP structure are as follows. (i) A standard optical lithography was performed to produce to a periodic array of photoresist (PR) circular cylinders. (ii) After the PR pattern, e-beam evaporation was used to deposit a 50-nm thick layer of Au. (iii) A lift-off processing with acetone to remove the PR layer, leading to final structure (pitch, $p=2.2{\mu}m$; aperture size, $d=1.1{\mu}m$) as shown in Fig. 1(a). The transmission is measured using a Nicolet Fourier-transform infrared spectroscopy (FTIR) at the incident angle from $0^{\circ}$ to $36^{\circ}$ with a step of $4^{\circ}$ both in TE and TM polarization. Measured first and second order SP resonances at interface between Au and GaAs exhibit the splitting into two branches under TM-polarized light as shown in Fig. 1(b). However, as the incidence angle under TE polarization is increased, the $1^{st}$ order SP resonance peak blue-shifts slightly while the splitting of $2^{nd}$ order SP resonance peak tends to be larger (not shown here). For the purpose of understanding our experimental results qualitatively, SP resonance peak wavelengths can be calculated from momentum matching condition (black circle depicted in Fig. 2(b)), $k_{sp}=k_{\parallel}{\pm}iG_x{\pm}jG_y$, where $k_{sp}$ is the SP wavevector, $k_{\parallel}$ is the in-plane component of incident light wavevector, i and j are SP coupling order, and G is the grating momentum wavevector. Moreover, for better understanding we performed 3D full field electromagnetic simulations of SP structure using a finite integration technique (CST Microwave Studio). Fig. 1(b) shows an excellent agreement between the experimental, calculated and CST-simulated splitting of SP resonance peaks with various incidence angles under TM-polarized illumination (TE results are not shown here). The simulated z-component electric field (Ez) distribution at incident angle, $4^{\circ}$ and $16^{\circ}$ under TM polarization and at the corresponding SP resonance wavelength is shown in Fig. 1(c). The analysis and comparison of theoretical results with experiment indicates a good agreement of the splitting behavior of the surface plasmon resonance modes at oblique incidence both in TE and TM polarization.

• 한국정보전자통신기술학회논문지
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• 제12권3호
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• pp.299-305
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• 2019

본 연구는 고령화와 젊은층의 이탈로 인한 농경사회에서 고령 및 여성 인력의 애로사항을 해결해주기 위해 시작되었다. 기존에 나와있는 농업용 고소리프트의 경우 전문 자격증 및 조작의 어려움과 평지가 아닌 불균형적인 도로 혹은 작업환경에 노출된 위험성과 여성들도 쉽고 효율적으로 생산적 농업을 할 수 있도록 하기 위하여 선행연구를 바탕으로 진행하였다. 먼저 농업용 포크리프트의 목적인 물체를 이용한 견인 성능 예측 모델을 통하여 시뮬레이션을 진행하고, 견인 성능 모델 수식을 이용하여 실험이 진행되고 있는 경남 김해시의 토양(점착력 34.125kPa, 내부마찰각 35.294deg, 외부마찰각 13.620deg, 부착력 5.750kPa, 평균 원추지수 0-15cm cl, 1001.8kPa)에 맞추었다. 시뮬레이션용 포크리프트의 경우 농업용 전동식 포크리프트의 구동력 및 운동저항 예측 모델링을 수식화하고 이를 바탕으로 모터 제어 드라이브는 AC모터 전용 드라이브인 1232E 모델을 적용, 프로그래밍을 통해 두 개의 드라이버를 각각 마스터와 슬레이브로 구분지어 구동할 수 있도록 하였고 메인 PCB에는 모터구동, 유압구동, 각종 출력을 제어할 수 있도록 시뮬레이션용 모델을 제작하였다. 제작된 시뮬레이션용 모델은 현재 지속적인 시뮬레이션과 수정 및 보완을 진행하고 있으며, 추후 본 연구를 바탕으로 보다 안전하고 효율성이 뛰어난 농업용 전동식 포크리프트의 개발을 위하여 연구를 지속할 예정이다.

• Journal of Mechanical Science and Technology
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• 제15권4호
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• pp.500-509
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• 2001

Offshore subsea pipelines must be stable against external loadings, which are mostly due to waves and currents. To determine the stability of a subsea pipeline on the seabed, the Morrison equation has been applied with prediction of inertia and drag forces. When the pipeline is placed in a trench, the force acting on it is reduced considerably. Therefore, to consider the stability of a pipeline in a trench, one must employ reduction factors. To investigate the stability of various trenches, we numerically simulated flows over various trenches and compared them with experimental data from PIV (Particle Image Velocimetry) measurements. The present results were produced ar Reynolds numbers ranging from 6$\times$10$^3$to 3$\times$10(sub)5 based on the diameter of the cylinder. Quasi-periodic flow patterns computed by large-eddy simulation were compared with experimental data in terms of mean flow characteristics fro typical trench configurations (W/H=1 and H/D=3, 4). The stability for various trench conditions was addressed in terms of mean amplitudes of oscillating lift and drag, and the reduction factor for each case was suggested for pipeline design.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2567-2572
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• 2007

The suppression of fluid force acting on a square prism near plane wall was studied by attaching fences on the corners of the prism. The height of the fence was 10% of the square width and the range of Reynolds number considered was Re=$2.0{\times}10^4$. The experimental parameters were the attaching position and numbers of fences, the space ratios G/B(G/B=0.1${\sim}$1.2) between prism and plane wall. The average drag coefficients were increased and the average lift coefficients were decreased and increased with the space ratios toward plane wall. The drag of the prism was reduced average 7.6% with the space ratios by attaching the normal fence at the rear and upper corner and the horizontal normal fence at the rear and lower corner on the prism. In this case, the separated flow at the front and upper corner was reattached on the upper side of the prism and the vortex streets between the prism and plane wall were appeared more slowly than that of prism without fences.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.89-90
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• 2002

Ball reducer (HERB Drive: High Efficient Wave Rolling Ball Drive) with waved grooves has many advantages over other types of reducers for high-reduction ratio, low noise and low energy loss, etc. The mechanism of force transmission is very similar to that of cam and follower in automobile valve train system especially in contact behaviors. In this study, we have investigated the traces of contact between ball and outer ring, and the dynamic contact behaviors of elastohydodynamic lubrication(EHL) with a certain reduction ratio. In order to verify the contact behaviors between ball and outer ring for the critical endurance lift, the contact velocity and load are computed for a cycle. During some intervals of a cycle, the contact velocity reverses its direction very suddenly. It is expected that changing the contact direction causes undesirable endurance performance because EHL film frequently col lapse at the moment of velocity reversal. From the computational investigation in this work, we hope to predict similar contact damages in other machinery due to this kind of contact behaviors, which is very typical in many contact phenomena.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2011년도 춘계학술대회 논문집
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• pp.1-6
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• 2011

In this study, wind tunnel test were conducted to improve an aerodynamic performance of HEMU400X pantograph system with 4 types of pantograph housing models. Experimental models were 1/4 scaled pantograph system, 1/4 scaled ground plate which is scaled down to real roof shape of HEMU-400x, and 4 types of pantograph housing models. The free stream of wind tunnel were 20, 40, 60, 70m/s. The lift and drag forces were measured with 2-axis load cell. And, Total pressure were measured with rake in the wake region of panhead. In addition, Surface flow visualization by tufts were performed to know flow characteristics around pantograph housing. According to the results of force tests and surface visualizations, pantograph housing shape is important part because the shape affects to pantograph system. Therefore, it is considered that adaption of pantograph housing is more advantageous to decrease drag and acoustic noise.

• 대한조선학회논문집
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• 제49권2호
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• pp.174-181
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• 2012

In this paper, the Flow Control Fin(FCF) optimization has been carried out using computational fluid dynamics(CFD) techniques. This study focused on evaluation for the performance of the FCF attached in the stern part of the ship. The main advantage of FCF is to enhance the resistance performance through the lift generation with a forward force component on the foil section, and the propulsive performance by the uniformity of velocity distribution on the propeller plane. This study intended to evaluate these functions and to find optimized FCF form for minimizing viscous resistance and equalizing wake distribution. Four parameters of FCF are used in the study, which were angle and position of FCF, longitudinal location, transverse location, and span length in the optimization process. KRISO 300K VLCC2(KVLCC2) was chosen for an example ship to demonstrate FCF for optimization. The optimization procedure utilized genetic algorithms (GAs), a gradient-based optimizer for the refinement of the solution, and Non-dominated Sorting GA-II(NSGA-II) for Multiobjective Optimization. The results showed that the optimized FCF could enhance the uniformity of wake distribution at the expense of viscous resistance.

• 한국항공운항학회지
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• 제20권4호
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• pp.50-56
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• 2012

Rotor system is a very important part which produce lift, thrust and control force in helicopter. Component of rotor system must have structural integrity for applied load. The estimation of structural integrity is regarded greatly as important in aerospace field. In this study, the process of structural analysis performed for bearingless main rotor system of helicopter. The composite flexbeam and torque tube of bearingless main rotor are very thick, so 3D layered soild elements of MSC.PATRAN were used to get the finite element analysis results. To estimate structural integrity, non-linear static analysis considering geometric non-linearity is performed. In addition, detailed finete element analysis and non-linear static analysis are performed to consider the stress concentration for fitting effect and contact surface. The estimation process of structural integrity for bearingless main rotor system of helicopter may help the design.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 추계학술대회논문집
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• pp.1276-1279
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• 2007

The main objectives of the Load/Unload are no slider-disk contact and no media damage. But, it remains unsolved technical problems on the unloading process. While the slider climbs up the ramp at the outer edge of the disk, the possibility of the slider-disk contact by lift-off force and rebound of the slider increases. Keeping in mind of these points, to prevent the slider-disk contact, we apply the disk bump on disk outer edge proceeding unload. First, referring to the simulation results, we select the optimal bump shapes to improve unload performance by unload analysis. Second, the disk bump is mechanically manufactured by pressing disk surface using tungsten tips. The bumps are variously processed by changing pressing pressure of tungsten tips. After confirming bump shape by nano-scanner, the optimal bump shape is applied to experimental unload process. Through this experiment, it is conformed that the unload performance was improved by using the optimal disk bump to prevent the slider-disk contact.

• 한국해양공학회지
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• 제25권4호
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• pp.42-47
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• 2011

In this paper, wake equalizing duct (WED) form optimization was carried out using computational fluid dynamics (CFD) techniques. A WED is a ring-shaped flow vane with a foil-type cross-section fitted to a hull in front of the upper propeller area. The main advantage of a WED is the power savings resulting from the uniformity of the velocity distribution on the propeller plane, a reduction in the flow separation at the aft-body, and lift generation with a forward force component on the foil section. This paper intends to evaluate these functions and find an optimized WED form for minimizing the viscous resistance and equalizing the wake distribution. In the optimization process, the study uses four WED parameters: the angle of the section, longitudinal location, and angles of the axes for the half rings against the longitudinal and transverse planes of the ship. KRISO 300K VLCC2 (KVLCC2) is chosen as an example ship to demonstrate the WED optimization. The optimization procedure uses genetic algorithms (GAs), a gradient-based optimizer for the refinement of the solution, and Non-dominated Sorting GA-II(NSGA-II) for Multiobjective Optimization. The results show that the optimized WED can reduce the viscous resistance at the expense of the uniformity of the wake distribution.