• Proceedings of the KSR Conference
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• 2005.11a
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• pp.418-423
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• 2005

In designing underground structure such as tunnels, estimating geotechnical characteristics of the ground is one of the most important and difficult tasks. In this paper, a methodology that can identify geotechnical parameters using only field-measured relative convergence displacements is presented. By using only relative convergence measurement data, inevitable errors in absolute convergence estimation can be avoided and in turn the parameter estimation process can be simplified. The methodology utilizes sensitivity relationship between static displacement measurements and geotechnical parameters. The feasibility and applicability of the proposed methodology is verified via a 3-d numerical example of a tunnel structure.

• Smart Structures and Systems
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• v.32 no.4
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• pp.207-218
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• 2023

Real-time monitoring of the behavior of reinforced soil retaining wall (RSW) is required for safety checks. In this study, a targetless displacement measurement technology (TDMT) consisting of an image registration module and a displacement calculation module was proposed to monitor the behavior of RSW, in which facing displacement and settlement typically occur. Laboratory and field experiments were conducted to compare the measuring performance of natural target (NT) with the performance of artificial target (AT). Feature count- and location-based performance metrics and displacement calculation performance were analyzed to determine their correlations. The results of laboratory and field experiments showed that the feature location-based performance metric was more relevant to the displacement calculation performance than the feature count-based performance metric. The mean relative errors of the TDMT were less than 1.69 % and 5.50 % for the laboratory and field experiments, respectively. The proposed TDMT can accurately monitor the behavior of RSW for real-time safety checks.

• Journal of the Korean GEO-environmental Society
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• v.15 no.1
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• pp.43-51
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• 2014

Angular distortion due to differential settlement is one of the critical factors which influences on the stability and serviceability of a structure. The angular distortion criterion proposed by Bjerrum is generally used in practice. However, the measurement system used in field especially a road embankment site did not properly represent the angular distortion of a structure. The problem was related to the shortage and not proper installation of measurement gauges, and the incorrect understanding of the basic concept of angular distortion in interpretation of measurement data. These things were reveled by analyzing the measured data in the road embankment site. An improved measurement system has been suggested as a so-called "relative displacement measurement system" between columns with automatic measurement.

• Journal of Mechanical Science and Technology
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• v.18 no.10
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• pp.1712-1721
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• 2004

A method of measuring the thermal diffusivity of semi-infinite solid material at room temperature using photothermal displacement is proposed. In previous works, within the constant thickness of material, the thermal diffusivity was determined by the magnitude and phase of deformation gradient as the relative position between the pump and probe beams. In this study, however, a complete theoretical treatment of the photothermal displacement technique has been performed for thermal diffusivity measurement in semi-infinite solid materials. The influence of parameters, such as, radius and modulation frequency of the pump beam and the thermal diffusivity, was studied. We propose a simple analysis method based on the zero -crossing position of real part of deformation gradient and the minimum position of phase as the relative position between two beams. It is independent of parameters such as power of pump beam, absorption coefficient, reflectivity, Poisson's ratio, and thermal expansion coefficient.

• Smart Structures and Systems
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• v.14 no.5
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• pp.943-960
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• 2014

A visually servoed paired structured light system (ViSP) was recently proposed as a novel estimation method of the 6-DOF (Degree-Of-Freedom) relative displacement in civil structures. In order to apply the ViSP to massive structures, multiple ViSP modules should be installed in a cascaded manner. In this configuration, the estimation errors are propagated through the ViSP modules. In order to resolve this problem, a displacement estimation error back-propagation (DEEP) method was proposed. However, the DEEP method has some disadvantages: the displacement range of each ViSP module must be constrained and displacement errors are corrected sequentially, and thus the entire estimation errors are not considered concurrently. To address this problem, a pose-graph optimized displacement estimation (PODE) method is proposed in this paper. The PODE method is based on a graph-based optimization technique that considers entire errors at the same time. Moreover, this method does not require any constraints on the movement of the ViSP modules. Simulations and experiments are conducted to validate the performance of the proposed method. The results show that the PODE method reduces the propagation errors in comparison with a previous work.

• Korean Journal of Optics and Photonics
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• v.8 no.4
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• pp.267-276
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• 1997

We set up a four-wave holographic interferometer using a symmetric dual-beam illumination which is to measure in-plane and out-of-plane displacement simultaneously. In order to acquire the displacement phase map we applied the phase-shifting method and removed the noise of the phase map with least-squares fitting. In this approach the access to information relative to both the difference and sum of phases existing in the two arms of four-wave holographic interferometer was allowed. As a result, in-plane and out-of-plane displacement was measured to the accuracy of λ/40 and λ/100, respectively at λ=632.8nm

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2003.03a
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• pp.238-246
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• 2003

By using simulated ground motions, which is sum of earthquake signals and noise, we measured the distortion of response spectra due to noise. We found that the distortion is more closely related to the signal-to-noise (S/N) ratio of root-mean-square (RMS) measurement than that of conventional peak measurement. Given a S/M ratio, the distortion of absolute acceleration response spectra is independent on the earthquake magnitude, while that of relative displacement response spectra has a strong dependence on the earthquake magnitude. This means that, when we calculate response spectra from time histories, we can efficiently predict the distortion of acceleration response spectra simply by measuring the RMS SJN ratios, or the distortion of displacement response spectra by combining the RMS S/N ratios and the earthquake magnitudes.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.2
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• pp.302-309
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• 2002

A new method of measuring the thermal diffusivity of solid material at room temperature using photothermal displacement is proposed. The influence of the parameters, such as radius and modulation frequency of the pump beam and the sample thickness, was studied. In previous works, thermal diffusivity was determined by the deformation angle and phase angle as the relative position between the heating and probe beams. In this study, however, we proposed the new analysis method based on the real part of deformation angle as the relative position between two beams. From the zero-crossing position of real part of deformation angle with respect to the pump beam, the thermal diffusivity of the materials can be obtained. The experimental values for different samples obtained by applying the new method are in good agreement with the literature values.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.9
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• pp.1033-1039
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• 2012

Artificial joints are used when joints lose their function because of either the destruction or damage of the composing bones of the joints. To evaluate the primary stability of a femur-implant system, the relative displacement caused by a repeated load is measured immediately after the insertion of the artificial joint. For more accurate stability evaluation, the accurate measurement of the penetration displacement of the artificial joint to the bone and the rotation angle of the artificial joint is essential. In this study, to evaluate the primary stability of the femur-implant system, we propose a new relative displacement measurement method. By using this new method, we comparatively evaluate the primary stability for various surgical methods and the varying stiffness of the cadaver femur-implant itself.

• Journal of Power System Engineering
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• v.15 no.1
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• pp.72-77
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• 2011

The handling ability of containers at the terminal strongly depends on the performance of the cargo handling system such as RTGC(Rubber Tired Gantry Crane). This paper introduces a new guide line position measurement method using a camera for the RTGC which plays a important role in the harbor area. Because the line tracking is the basic technique for control system design of RTGC, it is necessary to develop a useful and reliable measurement system. If the displacement and angle of the RTGC relative to a guide line as trajectory to follow is obtained, the position of RTGC is calculated. Therefore, in this paper, a camera-based measurement system is introduced. The proposed measurement system is robust against light fluctuation and cracks of the guideline. This system consists of a camera and a PC which are installed at the lower side of the RTGC. Two edges of the guide line are detected from an input image taken by the camera, and these positions are determined in a Hough parameter space by using the Hough transformation method. From the experimental results, high accurate standard deviations were found as 0.98 pixel of the displacement and 0.24 degree of the angle, including robustness against lighting fluctuation and cracks of the guide line also.