레이저의 탄성 매질 흡수에 의해 발생하는 열 및 기계적 효과에 관한 연구

Abstract

In this study, simulations of the thermal and mechanical effects induced by pulsed-laser absorption in an elastic medium were performed and a method for determining the optical and thermal properties of an absorbing medium was demonstrated. For the simulations of the thermal effects, ANSYS Fluent (ANSYS Incorporated, USA), computational fluid dynamics (CFD) software, was utilized. The elastic medium, assumed to be in the form of a circular plate, used for the simulations has a thickness of 2.2 mm and a radius of 15 mm. Axisymmetric analysis is applied for the simulations for considering the geometrical symmetry of the medium. For the simulations of the mechanical effects, ANSYS Mechanical (ANSYS Incorporated, USA), a structural analysis tool, was utilized. Spatio-temporal distributions of the temperature increase obtained from the simulations of the thermal effects were used as the input data for the structural simulations, and the results of the displacement and acceleration of the central point on the rear surface of the elastic medium were obtained. When a single pulse (pulse width: 8 ns) was incident on the medium, the central point on the front surface attained the maximum temperature increase immediately after the incidence of the laser pulse, and then the temperature gradually decreased due to thermal diffusion. The magnitudes of the displacement and acceleration linearly increased with increasing laser-pulse energy. When repetitive pulses were incident on the medium, an abrupt temperature increase occurred immediately after the incidence of each laser pulse and the temperature gradually decreased during the period between adjacent pulses. While the magnitude of the displacement increased cumulatively after the incidence of each laser pulse, the same waveform of the acceleration appeared periodically whenever each laser pulse was incident on the medium. The simulated results were in fairly good qualitative agreement with the experimental results measured using an acceleration sensor. While simulating the thermal effects, we found that the maximum temperature increase of the medium depends on the absorption coefficient and the decay time constant of the temperature depends on both the absorption coefficient and the thermal conductivity. The absorption coefficient and thermal conductivity of the medium were determined by fitting the simulated results with measured ones for the temperature change data obtained using an infrared camera. We believe that the results presented in this thesis can provide useful information for research on evoking tactile sensations by using a pulsed laser and an absorbing elastic medium. A study in which effective parameters for the laser and medium are determined through simulations is in progress.