• Smart Structures and Systems
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• 제22권3호
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• pp.277-290
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• 2018

In this paper, wavelet finite element model (WFEM) updating technique is employed to detect sub-element damage in thin plate structures progressively. The procedure of WFEM-based detection method, which can detect sub-element damage gradually, is established. This method involves the optimization of an objective function that combines frequencies and modal assurance criteria (MAC). During the damage detection process, the scales of wavelet elements in the concerned regions are adaptively enhanced or reduced to remain compatible with the gradually identified damage scenarios, while the modal properties from the tests remains the same, i.e., no measurement point replacement or addition are needed. Numerical and experimental examples were conducted to examine the effectiveness of the proposed method. A scanning Doppler laser vibrometer system was employed to measure the plate mode shapes in the experimental study. The results indicate that the proposed method can detect structural damage with satisfactory accuracy by using minimal degrees-of-freedoms (DOFs) in the model and minimal updating parameters in optimization.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1996년도 한국자동제어학술회의논문집(국내학술편); 포항공과대학교, 포항; 24-26 Oct. 1996
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• pp.1352-1355
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• 1996

The control of diamond turning is usually achieved through a laser-interferometer feedback of slide position. If the tool post is rigid and the material removal process is relatively static, then such a non-collocated position feedback control scheme may surface. However, as the accuracy requirement gets tighter and desired surface contours become more complex, the need for a direct tool-tip sensing becomes inevitable. The physical constraints of the machining process prohibit any reasonable implementation of a tool-tip motion measurement. It is proposed that the measured force normal to the face of the workpiece can be filtered through an appropriate admittance transfer function to result in the estimated depth of cut. This can be compared to the desired depth of cut to generate the adjustment control action in addition to position feedback control. In this work, the design methodology on the admittance model-based control with a conventional controller is presented. The recursive least-squares algorithm with forgetting factor is proposed to identify the parameters and update the cutting process in real time. The normal cutting forces are measured to identify the cutting dynamics in the real diamond turning process using the precision dynamometer. Based on the parameter estimation of cutting dynamics and the admittance model-based nanodynamic control scheme, simulation results are shown.

• 대한전자공학회논문지SD
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• 제37권2호
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• pp.38-45
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• 2000

광연결 시스템의 SPICE 모델링과 이를 이용한 시스템 성능 분석에 관한 연구를 수행하였다. 먼저, 광소자의 등가회로 모델을 구현하고, 송·수신단의 회로를 설계하여 안정적인 SPICE 시뮬레이션 결과를 얻었다. SPICE 시뮬레이션 결과로 eye 다이어그램을 얻을 수 있고, 이를 토대로 BER을 계산할 수 있었다. 바이어스 조건에 따라서 turn-on 지연으로 인한 jitter 현상을 볼 수 있고, 전송율, BER, 송신단의 전력 소모, 바이어스 조건의 상호 관계를 통해 시스템의 최적화를 이룰 수 있다. 광연결 시스템의 SPICE를 이용한 최적화 방법은 Gigabit Ethernet, ATM등의 응용 분야에서 LD 구동회로와 수신단의 회로 설계에 유용하게 쓰일 것으로 기대된다.

• 한국결정학회지
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• 제11권1호
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• pp.16-21
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• 2000

(Yb/sub x/Y/sub 1-x/)Ca₄O(BO₃)₃ single crystals where x=0.3,8,15,20% were grown by Czochralski Method. The crystals grown under the optimum conditions were transparent and colorless with good crystal form. Using polarizing microscope, crystal defects such as parasite crystals and bubbles were detected depending on the composition of melts and pulling rates. The optimum growth parameters for high quality of single crystals were 15∼20 rpm of rotation rate and 2mm/h of pulling rate at the flow rate of 2 l/min of Nitrogen gas. The relationship between crystal axes and optical axes was investigated by optical crystallographic method, polarization technique and single crystal X-ray method. From the spectroscopic measurements, it was confirmed that there were strong absorption bands at 900 and 976.4 nm and strong emission band at 976.4 nm in Yb/sup 3+/ ion doped YCa₄O(BO₃)₃ crystal. For the application of second harmonic generation of 1.064 ㎛ laser, non-linear optical devices with θ=32.32° and Ψ=0°, λ/10 of flatness and the size of 6x8x5.73 mm were fabricated from the grown YCa₄O(BO₃)₃ crystal.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2003년도 추계학술대회 논문집
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• pp.67-70
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• 2003

Hard disk drives (HDD) in computer are used extensively as data storage capacity. The trend in the computer industry to produce smaller disk drives rotating at higher speeds requires an improved understanding of fluid motion in the space between disks. Laser sheet and digital camera was used for 2-dimensional visualization of the unsteady flow between the center pair of two co-rotating disks in air with a cylindrical enclosure (or shroud). Geometric parameters are gap height (H) between disks, and gap distance (G) between disk tip and shroud. The lobe-structured boundary between inner region and outer region was detected by inserted particles, and the number of dominant vortices was determined clearly It is found from flow visualization that the number of vortex cells can be correlated with Reynolds number based on H which is defined as $Re_H={\Omega}RH/v$ ranging from $3.18\times10^3\;to\;1.43\times10^4$, and decreases as the disk speed increases. The lobe pattern by vortex cells is changed to a circular pattern for the wide gap than narrow one.

• 대한기계학회논문집
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• 제18권4호
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• pp.920-932
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• 1994

The combustion phenomena of a reciprocating engine is one of the most important processes affecting performance and emissions. One effective way to improve the engine combustion is to control the motion of the charge inside a cylinder by means of optimum induction system design, because the flame speed is mainly determined by the turbulence at compression(TDC) process in S.I. engine. It is believed that the tumble and swirl motion generated during intake breaks down into small-scale turbulence in the compression stroke of the cycle. However, the exact nature of their relationship is not well known. This paper describes cycle resolved LDV measurement of turbulent flow inside the cylinder of a 4-valve engine under motoring(non-firing) conditions, and studies the effect of intake port configurations on the turbulence characteristics using following parameters ; Eulerian temporal autocorrelation coefficient, turbulence energy spectral density function, Taylor micro time scale, integral time scale, and integral length scale.

• Journal of Mechanical Science and Technology
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• 제17권12호
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• pp.2107-2115
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• 2003

A supersonic dual coaxial jet has been employed popularly for various industrial purposes, such as gasdynamic laser, supersonic ejector, noise control and enhancement of mixing. Detailed characteristics of supersonic dual coaxial jets issuing from an inner supersonic nozzle and outer sonic nozzles with various ejection angles are experimentally investigated. Three important parameters, such as pressure ratios of the inner and outer nozzles, and outer nozzle ejection angle, are chosen for a better understanding of jet structures in the present study. The results obtained from the present experimental study show that the Mach disk diameter becomes smaller, and the Mach disk moves toward the nozzle exit, and the length of the first shock cell decreases with the pressure ratio of the outer nozzle. It was also found that the highly underexpanded outer jet produces a new oblique shock wave, which makes jet structure much more complicated. On the other hand the outer jet ejection angle affects the structure of the inner jet structure less than the pressure ratio of the outer nozzle, relatively.

• Journal of Mechanical Science and Technology
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• 제17권12호
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• pp.2053-2065
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• 2003

The current trend in automotive finishing industry is to use more electrostatic rotating bell (ESRB) need space to their higher transfer efficiency. The flow physics related with the transfer efficiency is strongly influenced by operating parameters. In order to improve their high transfer efficiency without compromising the coating quality, a better understanding is necessary to the ESRB application of metallic basecoat painting for the automobile exterior. This paper presents the results from experimental investigation of the ESRB spray to apply water-borne painting. The visualization, the droplet size, and velocity measurements of the spray flow were conducted under the operating conditions such as liquid flow rate, shaping airflow rate, bell rotational speed, and electrostatic voltage setting. The optical techniques used in here were a microscopic and light sheet visualization by a copper vapor laser, and a phase Doppler particle analyzer (PDPA) system. Water was used as paint surrogate for simplicity. The results show that the bell rotating speed is the most important influencing parameter for atomization processes. Liquid flow rate and shaping airflow rate significantly influence the spray structure. Based on the microscopic visualization, the atomization process occurs in ligament breakup mode, which is one of three atomization modes in rotating atomizer. In the spray transport zone, droplets tend to distribute according to size with the larger drops on the outer periphery of spray. In addition, the results of present study provide detailed information on the paint spray structure and transfer processes.

• 한국광학회지
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• 제15권6호
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• pp.495-502
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• 2004

파장가변 필터를 목적으로 plane-concave 거울쌍으로 구성된 Fabry-Perot 공진기에 대한 해석모델을 제안하고, 이를 실제 제작과정에서의 변수 값을 적용하여 해석한 결과를 제시하였다. 공진기의 결합손실과 거울의 손실이 필터의 삽입손실에 가장 큰 변수로 작용하며, plane-concave 거울쌍 구성을 이용하여 finesse가 600, FSR이 57 nm, 삽입손실 (insertion loss)이 3 dB 이하인 필터를 구현하기 위해서는 손실이 0.09% 이하인 거울을 사용하여 공진기의 결합손실이 0.1% 이하가 되도록 오목거울의 곡률반경과 정렬상태를 조절하여야 하는 것으로 밝혀졌다.

• Journal of the Optical Society of Korea
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• 제14권4호
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• pp.431-437
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• 2010

A stack of gradient-index (GRIN) rod lenses cannot be used for coherent anti-Stokes Raman scattering (CARS) microendoscopy for insertion to internal organs through a surgical keyhole with minimal invasiveness. That's because GRIN lens has large amount of inherent chromatic aberrations in spite of absolutely requiring a common focus for pump and Stokes beam with each frequency of ${\omega}_p$ and ${\omega}_S$. For this endoscopic purpose, we need to develop a long slender probe-type objective, namely probe-type microscope objective (PMO). In this paper, we introduce the structure, the working principle, and the design techniques of PMO which is composed of a probe-type lens module (PLM) and an adaptor lens module (ALM). PLM is first designed for a long slender type and ALM is successively designed by using several design parameters from PLM for eliminating optical discords between scanning unit and PLM. A combined module is optimized again to eliminate some coupling disparities between PLM and ALM for the best PMO. As a result, we can obtain a long slender PMO with perfectly diffraction-limited performance for pump beam of 817 nm and Stokes beam of 1064 nm.