• Journal of the Optical Society of Korea
• /
• 제19권4호
• /
• pp.363-370
• /
• 2015

The current waveform model of a laser altimeter is based on a Gaussian laser beam of fundamental mode, while the flattened Gaussian beam has many advantages such as nearly constant energy distribution on the center of the cross-section. Following the theory of the flattened Gaussian beam and the waveform theory of the laser altimeter, some of the primary parameters of the received waveform were derived, and a laser altimetry waveform simulator and waveform processing software were programmed and improved under the circumstance of a flattened Gaussian beam. The result showed that the bias between theoretical and simulated waveforms was less than 3% for every order mode, the waveform width and range error would increase as target slope or order number rose. Under higher order mode, the shapes of the received waveforms were no longer Gaussian, and could be fitted more precisely as a generalized Gaussian function with power bigger than 2. The flattened beam got much better performance for a multi-surface target, especially when the small surface is far from the center of the laser footprint. This article provides the waveform theoretical basis for the use of a flattened Gaussian beam in a laser altimeter.

• 한국산업융합학회 논문집
• /
• 제3권1호
• /
• pp.43-51
• /
• 2000

The response statistics of a hinged-clamped beam under broad-band random excitation is investigated. The random excitation is applied at the nodal point of the second mode. By using Galerkin's method the governing equation is reduced to a system of nonautonomous nonlinear ordinary differential equations. A method based upon the Markov vector approach is used to generate a general first-order differential equation in the dynamic moment of response coordinates. By means of the Gaussian and non-Gaussian closure methods the dynamic moment equations for the random responses of the system are reduced to a system of autonomous ordinary differential equations. The case of two mode interaction is considered in order to compare it with the case of three mode interaction. The analytical results for two and three mode interactions are also compared with results obtained by Monte Carlo simulation.

• 한국정밀공학회지
• /
• 제10권4호
• /
• pp.64-72
• /
• 1993

Analytical models for the prediction of the size of hardened zone in laser surface hardening are presented. The models are based on the solutions to the problem of three-dimensional heat flow in plates with infinite thickness. The validity of the model was tested on medium carbon steel for Gaussian mode of beam. Then the model for rectagular beam was used for the predicition of the size of hardened zone on various hardening process parameters. From the calculation results it appeared that the size and shape of the hardened zone are strongly dependent on process parameters such as beam mode, beam size, and traverse speed.

• Coupled systems mechanics
• /
• 제7권1호
• /
• pp.27-42
• /
• 2018

Behavior of soil is usually described with continuum type of failure models such as Mohr-Coulomb or Drucker-Prager model. The main advantage of these models is in a relatively simple and efficient way of predicting the main tendencies and overall behavior of soil in failure analysis of interest for engineering practice. However, the main shortcoming of these models is that they are not able to capture post-peak behavior of soil nor the corresponding failure modes under extreme loading. In this paper we will significantly improve on this state-of-the-art. In particular, we propose the use of a discrete beam lattice model to provide a sharp prediction of inelastic response and failure mechanisms in coupled soil-foundation systems. In the discrete beam lattice model used in this paper, soil is meshed with one-dimensional Timoshenko beam finite elements with embedded strong discontinuities in axial and transverse direction capable of representing crack propagation in mode I and mode II. Mode I relates to crack opening, and mode II relates to crack sliding. To take into account material heterogeneities, we determine fracture limits for each Timoshenko beam with Gaussian random distribution. We compare the results obtained using the discrete beam lattice model against those obtained using the modified three-surface elasto-plastic cap model.

• 한국전산구조공학회논문집
• /
• 제13권4호
• /
• pp.427-436
• /
• 2000

이 논문은 불규칙 가진력을 받는 회전-고정보의 비선형 응답특성을 나타낸다. 불규칙 가진력은 두 번째 고유모드의 절점과 최대변위점에 가했다. 비선형 편미분 방정식과 경계조건으로 표현되는 이 문제를 Galerkin의 방법을 이용하여 연립 비선형 상미분방정식으로 변환하였다. 이 상미분방정식으로부터 Fokker-Planck방정식과 모멘트 방정식을 얻은 후 Gaussian closure 방법 및 non-Gaussian closure 방법을 이용하여 3 모드 근사시 각각 27개 및 209개의 자율 상미분방정식을 구하였다. Gaussian closure 방법과 non-Gaussian closure 방법으로 2 모드 및 3 모드 근사해석을 수행하였고 해석적 결과들은 Monte Carlo 시뮬레이션 결과와 비교되었다. 해석결과 2 모드 근사해와 3 모드 근사해가 거의 일치하였고 2 모드 내부공진만 고려하여도 해석결과에 별 영향을 주지 않는다는 것을 알 수 있다.

• 한국광학회지
• /
• 제4권4호
• /
• pp.428-433
• /
• 1993

공간적으로 Gaussian인 Q-switched Nd:LYAG레이저의 제2고조파 빛살을 일정한 반경의 pinhole로 중심부분만 통과시켜 집광렌즈로 집광시킨 후, 렌즈의 초점면에서 빛살모양을 관찰하여 본 결과 원형 대칭을 갖는 비Gaussian모양을 하고 있음을 확인할 수 있었다. 이 빛살의 집광영역내에서 두께 1mm의 $CS_2$를 이동(z-scan)하여 가며 자체집광효과에 의하여 변화되는 투과도특성을 조사하였다. 측정된 결과를 Fresnel 이론과 1.5% 이내의 오차 범위로 일치함을 알 수 있었고, 자체집광효율이 입사빛의 공간적 모양과 관계함을 확인할 수 있었다.

• 한국통신학회논문지
• /
• 제19권3호
• /
• pp.515-522
• /
• 1994

원뿔형 컬러게이트 급전 혼의 복사특성을 가우시안 빔 모드이론으로 해석한다. 혼 개구면의 전계를 Gaussian-Laguerre모드로 전개하며, 이 모드가 파동방정식의 해임을 밝히고, 모드 확장계수에 의하여 개구면의 전개를 계산함으로써, 종래의 기본모드에 의한 복사특성 해석의 오차를 줄일 수 있게 한다. C-밴드, Ku-밴드 및 밀리미터파 대역에서 동작하는 컬러게이트 혼 안테나의 복사패턴을 계산하였다. 각 벤드에 대하여 계산한 복사패턴은 벡터 포텐실 적분법에 의하여 구한 복사패턴 및 6.175GHz에서의 실측치 등과 잘 일치한다.

• 한국광학회지
• /
• 제7권3호
• /
• pp.200-206
• /
• 1996

When a Gaussian beam is incident to a planar dielectric interface at an angle other than Brewster angle or the critical angle of total reflection, we derive the six nonspecular effects of rotation, lateral shift, focal shift, Rayleigh length change, magnitude and phase changes in the complex amplitude of the reflected beam simultaneously by taking account of the boundary condition. In the derivation we assume a Gaussian beam of fundamental mode to emerge from the interface and then match at the interface the constant, linear, and quadratic variations of the amplitude and phase of the reflected beam with those of the incident beam multiplied by the reflection coefficient. Our calculation shows that the six nonspecular effects can result from a linear variation of the natural logarithm of the reflection coefficient at the interface.

• 한국광학회:학술대회논문집
• /
• 한국광학회 2008년도 하계학술발표회 논문집
• /
• pp.187-189
• /
• 2008

The spatial coherence function of multy-mode beam was measured by using a Sagnac interferometer and self referencing technique. For leaner polarization laser beam passing through a multy-mode fiber, its change value of spatial mode and polarization from stress of faber and input coupling angle. And each spatial mode have each polarizations, when we simulation Wigner distribution function and Spatial Correlation function of spatial multi-mode beam by using Hermit Gaussian modes leaner sum. We measured spatial coherence function of using by multy-mode fiber. One can use this measurement method to study and characterize the property of multy-mode light field coming out of GRIN multy-mode fiber.

• 한국정밀공학회지
• /
• 제12권6호
• /
• pp.87-95
• /
• 1995

In order to predict the case depth and case width in laser transformation hardening, a finite element method was used to analyze the temperature distribution on the material. Laser hardening of the specimens of SM45C and STE11steels was experimented by using the continuous wave CO$_{2}$ laser with the various travel speeds and the defocused Gaussian beam mode. Phosphate coating was adopted on the surface of SM45C to increase the absorption of 10.6 .mu. m laser energy. Experimental data show good agreement with the theoretical predictions. The maximum possible case depth can be predicted for the given laser hardening conditions, such as laser power, and travel speed.