• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2008.04a
• /
• pp.766-771
• /
• 2008

In this paper, the vibration of high speed trains and the irregularity of railway are examined using a wavelet-based frequency response function. To investigate their characteristics, non-stationary acceleration data are acquired and processed using the wavelet transform. Also, the railway irregularity is examined by acquiring the data from the on-board laser-based measurement system. The correlation between the train vibration and the railway irregularity has been investigated. From the analysis, the wavelet-based frequency response function is a promised method for the dynamic characteristics of high speed trains.

• Proceedings of the Korean Vacuum Society Conference
• /
• 1999.07a
• /
• pp.102-102
• /
• 1999

Visible photoluminescence(PL) in si-implanted SiO2 films on crystaline silicon were observed. Thermal oxide films of 1 ${\mu}{\textrm}{m}$ thickness on P-type crystal silicon were made and si+ ions were implanted with 200keV acceleration voltage on ti. Argon laser (wavelength 488nm) and PM tube were used for PL measurements. As annealing time increased at low temperature, the visible PL intensity are increased and the peak positions are changed. On the other hand, with increasing annealing time at high temperature, the visible PL intensity are disappeared. From the PL peaks and intensity changes, XRD results, and TEM observations, we will discuss the origin of PL in Si+-implanted SiO2 films with oxygen righ defects and silicon rich defects.

• Journal of Welding and Joining
• /
• v.11 no.1
• /
• pp.73-79
• /
• 1993

The phenomenon of metal transfer has been investigated for different transfer modes using a digital high speed motion analyzer and an arc shadow-graphing system based on a laser source and related optical system. It was observed that the pinch instability phenomenon did not occur for the globular transfer mode, since the liquid globule was then spherical rateher than a cylindrical liquid bar. On increasing the ratio of carbon dioxide to argon, the transition current from globular to spray transfer generally increased, but it is interesting that the transition was observed to occur at the lowest current in a 5% CO$_{2}$-95% argon gas mixture. For pure carbon dioxide and helium shielding gases, the drop frequency increased slowly with increasing current. At high currents or an argon based shielding gas, the length of liquid bar decreased as the carbon dioxide content increased. The acceleration of a droplet within the arc was determined using the gas drag force theory and was found to be greater than the experimental results.

• Journal of the Korean Society for Precision Engineering
• /
• v.9 no.4
• /
• pp.136-146
• /
• 1992

This paper provides the end-point positioning of a single-link flexible robot arm by inverse dynamics. The system is composed of a flexible arm, the mobile ballscrew stage as an arm base, a DC servomotor as an actuator, and a computer. Actuator voltages required for the model of a flexible arm to follow a given tip trajectory are formulated on the basis of the Bermoullie-Euler beam theory and solved by applying the Laplace transform method, and computed by the numerical inversion method proposed by Weeks. The mobile stage as the arm base is shifted so that the end-point follows the desired trajectories. Then the trajectory of end-point is measured by the laser displacement sensor. Here, two kinds of functions are chosen for the given tip trajectories. One is what is called the bang-bang acceleration profile and the other is the Gaussian velocity profile.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.13 no.4
• /
• pp.187-198
• /
• 2003

Zinc selenide (ZnSe) single crystals hold promise for many electro-optics, acousto-optic and green laser generation applications. This material is prepared in closed ampoules by the physical vapor transport (PVT) growth method based on the dissociative sublimation. We investigate the effects of diffusive-convection on the crystal growth rate of ZnSe with a low vapor pressure system in a horizontal configuration. Our results show that for the ratios of partial pressures, s=0.2 and 2.9, the growth rate increases with the Peclet number and the temperature differences between the source and crystal. As the ratio of partial pressures approaches the stoichiometric value of 2, the rate increases. The mass fluk based on one dimensional (1D model) flow for low vapor pressure system fall within the range of the predictions (2D model) obtained by solving the coupled set of conservation equations, which indicates the flow fields would be advective-diffusive. Therefore, the rate and the flow fields are independent of gravity acceleration levels.

• Journal of the Korean Society for Precision Engineering
• /
• v.21 no.5
• /
• pp.142-148
• /
• 2004

In this paper, to detect exciting frequency on the latticed fence structure, fiber optic sensor using Sagnac interferometer was fabricated and tested. The latticed structure fabricated with dimension of 180 cm wide and 180 cm high, the optical fiber, 50 m in length, distributed and fixed on the latticed structure. Single mode fiber, a laser with 1,550 m wavelength, and $3{\times}3$ coupler were used. Excited vibration signal applied to the latticed structure from 200 Hz to 1 KHz. The detected optical signals were compared to the detected acceleration signals and analyzed on the time and frequency domain. Based on the experimental results, fiber optic sensor using Sagnac interferometer detected exciting frequency, effectively. This system can be applied to the structural health monitoring system.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.26 no.4
• /
• pp.271-274
• /
• 2013

Inclinometer sensors are widely applied in many fields. Especially in the field of construction of high-rise buildings also measure the horizontal and vertical help has been applied to monitor. Recent micro electro-mechanical system(MEMS) technology with the development of the many sensors have been developed. In this paper, a MEMS inclinometer is based on a MEMS accelerometer. The sensor can measure the angle of inclination using the relationship between static acceleration and gravity acceleration from an accelerometer. From this principle, inclinometer has been developed that has more accurate. The accuracy is proved by the experiment with laser displacement. Results in the experiment express high-accuracy, stability and economics of MEMS inclinometer. In conclusion, wireless MEMS inclinometer sensor is expected to be applicable in the areas of construction and many other industries with accurate and convenient monitoring system.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.45 no.5
• /
• pp.376-385
• /
• 2017

In this paper, a method for the estimation of structural displacements using structure's mode shapes and accelerations is suggested to reduce the disadvantages of acceleration time integration method. Acceleration time integration method requires accurate information on initial conditions, and errors caused by noise can be accumulated during time integration. To avoid these problems, the method for the estimation of structural displacements based on mode superposition method is developed and two vibration experiments for cantilever beam are conducted to verify this method. Static displacements and dynamic displacements of beam structure are estimated using measured accelerations from experiments and mode shapes of cantilever beam, and they are compared with measured displacements using laser displacement sensor. From these results, the validity and usefulness of this method are verified.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.14 no.6
• /
• pp.254-262
• /
• 2010

In order to evaluate vibration serviceability by means of non-contact vibration meter, serviceability of existing bridge were experimentally evaluated by using laser vibration meter. Test results were analyzed and compared with evaluation results acquired by using accelerometer and LVDT. To testify accuracy of laser vibration meter measured natural frequency were compared with that acquired by using accelerometer. According to test and comparison results it is showed that serviceability can be evaluated properly enough from the tolerance curve of Reiher-Meister for the estimated acceleration that can be calculated by the numerical differentiation of measured velocity. But because of cumulative numerical error occurred during integration of measured velocity in the time domain serviceability grade could be different from the result acquired by LVDT.

• Journal of Aerospace System Engineering
• /
• v.16 no.4
• /
• pp.60-67
• /
• 2022

An Electro-Optical Tracking System (EOTS) is an electric optical system with EO/IR cameras, laser sensors, and an IMU. The EOTS calculates coordinates of targets, using attitude and acceleration measured by the IMU. In particular for an armed aircraft, the performance of the weapon system depends on how quickly and accurately it acquires the target coordinates. The IMU should be operated after alignment is complete, to meet the coordinate accuracy required by the weapon system so the initial stabilization time of the IMU should be reduced, by quickly measuring the attitude and acceleration. Alignment is the process of determining the initial attitude by resolving the attitude error of the IMU, and the IMU of mission equipment such as an airborne EOTS, uses velocity matching based on the velocity from GPS/INS for aircraft navigation. In this paper, a method is presented to improve the transfer alignment performance of the airborne EOTS, by maneuvering aircraft and the mission equipment. First, the performance factor of the alignment was identified, as a heading error through the velocity matching model and simulation results. Then acceleration maneuvers and attitude changes were necessary, to correct the error. As a result of flight tests applied to an EOTS on a OOO aircraft system, the transfer alignment performance was improved as the duration time was decreased, by more than five times when the aircraft accelerated by more than 0.2g and the EOTS was moving until 6.7deg/s.