• Geophysics and Geophysical Exploration
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• v.4 no.3
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• pp.59-69
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• 2001

Five kinds of modified electrode arrays were proposed to overcome the weak points of the commonly used arrays using dipole and/or pole in two-dimensional resistivity surveys. The modified pole-pole array was suggested to overcome the inefficiency caused by distant earthing in pole-pole array. Four kinds of modified arrays using dipole were designed to enhance the signal-to-noise ratio of the conventional dipole-dipole and pole-dipole arrays through boosting up the measured potential difference. In the numerical experiments using the two-dimensional modeling and inversion, the effects of the ambient electrical noise and the resolving power were examined and the results showed the validity of the modified arrays proposed in this study.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.3
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• pp.32-38
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• 2005

FBG sensors have been studied more actively than any other fiber optic sensor because of good multiplexing capabilities among many fiber optic sensors. The demodulation method of FBG sensors is based on the detection of wavelength shift of their sensor peaks and properties such as strain and temperature can be measured by detecting them. However, the signal stability of FBG sensors can be influenced by the strain gradient induced by structural geometry or cracks on the surface when FBG sensors are embedded into or attached on the structure. In this study, the signal characteristics of reflected spectra of FBG sensors under strain gradient were verified and the relations between the grating length of FBG sensors and the amount of strain gradient were investigated. From the experimental results, the recommended working range of FBG sensors under strain gradients was shown quantitatively with respect to grating lengths of them.

• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.2
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• pp.149-154
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• 2012

The size and distribution of welding residual stress and welding deformation in welding structures have an effect on various sorts of damage like brittle failure, fatigue failure and stress corrosion cracking. So, research for this problem is necessary continuously. In this study, non-destructive technique using laser electronic speckle pattern interferometry, plate of welding specimen according to the external load on the entire behavior of residual stress are presented measurement techniques. Once, welding specimen force tensile loading, using electronic speckle pattern interferometry is measured. welding specimen of base metal and weld zone measure strain from measured result, this using measure elastic modulus. In this study, electronic speckle pattern interferometry use weld zone and base metal parts of the strain differences using were presented in residual stress calculated value, This residual stress value were calculated by numerical calculation. Consequently, weld zone of modulus high approximately 3.7 fold beside base metal and this measured approximately 8.46 MPa.

• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.8
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• pp.178-184
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• 2014

In this study, we develop liquid density sensor by measuring of balanced position between gravity and bouyancy, corresponding to liquid density, using distance measuring by magnetostriction technology. For improvement of accuracy of liquid density sensor system. And we derive the related equation between liquid density and moving distance of density sensor, and make the calibration method for liquid density sensor by magnetostriction technology. Using fabricated liquid density sensing system and derived equation, have measured the density of several liquids. And compare it to measuring results using Oscillating U-tube type high accuracy density meter, having 0.000001 g/cc resolution. The deviation of results between two density measuring systems was less than 0.001 g/cc.

• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.5
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• pp.306-314
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• 2006

Instrumented indentation technique is a new way to evaluate nondestructive such mechanical properties as flow properties, residual stress and fracture toughness by analyzing indentation load-depth curves. This study evaluated quantitatively the flow properties of steels and residual stress of weldments. First, flow properties can be evaluated by defining a representative stress and strain from analysis of deformation behavior beneath the rigid spherical indenter and the parameters obtained from instrumented indentation tests. For estimating residual stress, the deviatoric-stress part of the residual stress affects the indentation load-depth curve, so that by analyzing the difference between the residual-stress-induced indentation curve and residual-stress-free curve, the quantitative residual stress of the target region can be evaluated. The algorithm for flow property evaluation was verified by comparison with uniaxial tensile test and the residual stress evaluation model was compared to mechanical cutting and ED-XRD results.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.38 no.1
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• pp.1-10
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• 2018

It is difficult to predict the early-age cracks of strain restrained concrete members due to environmentally sensitive parameters. A new method is proposed to predict the cracks by test of autogenous deformation and self-induced restrained stress of specimens which simulates early-age crack state by hydration heat of the'Wall-On-Foundation'members. For this purpose, thermal analysis of entire structure considering the environmental condition is performed at first, and the specimens are set up where hydration heat was electronically controlled according to the analysis results. By measuring free deformation and force to compensate the autogenous strain including relaxation, feasibility of cracks can be estimated. The proposed method can predict the occurrence of cracks better than the material test of the early age concrete which has large variance. The method of this study is particularly useful when it is used as a preliminary experiments to predict the crack more precisely before full-scale concrete placement in construction of large structures.

• Journal of the Korean Geotechnical Society
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• v.34 no.11
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• pp.81-92
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• 2018

For a marine bridge foundation construction, a large-circular-steel-pipe has been proposed for supporting vertical load and preventing water infiltration. However, a ship collision can adversely affect the structural stability. This paper presents a fundamental study on dynamic responses of the large-circular-steel-pipe by an impact load. In laboratory experiments, small-scaled steel pipe is installed in a soil tank. The soil height and water level are set to 23 cm and 25~70 cm, respectively. The upper part of the steel pipe is impacted using a hammer to simulate the ship collision. The dynamic responses are measured using accelerometers and strain gauges. Experimental results show that the strain decreases as the measured location is lowered. The higher frequency components appear in the impact load condition compared to the microtremor condition. However, the higher frequency components measured at the strain gauge located below the water level do not appear. For the accelerometer signal, the maximum frequency under the impact load is higher than that of the microtremor. The maximum frequency decreases as water level increases but it is larger than the maximum frequency of the microtremor. This study shows that strain gauge and accelerometer can be useful for evaluating the dynamic responses of large-circular-steel-pipes.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.5A
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• pp.699-707
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• 2008

For most structural evaluation of bridge integrity, it is very important to measure the geometric profile, which is a major factor representing the global behavior of civil structures, especially bridges. In the past, because of the lack of appropriate methods to measure the deflection profile of bridges on site, the measurement of deflection has been restricted to just a few discrete points along the bridge, and the measuring points have been limited to the locations installed with displacement transducers. Thus, some methods for predicting the static deflection by using fiber optic strain sensors has been applied to simply supported bridges. In this study, a method of estimating the static deflection profile by using strains measured from suspension bridges was proposed. Based on the classical deflection theory of suspension bridges, an equation of deflection profile was derived and applied to obtain the actual deflection profile on Namhae suspension bridge. Field load tests were carried out to measure strains from FBG strain sensors attached inside the stiffening girder of the bridge. The predicted deflection profiles were compared with both precise surveying data and numerical analysis results. Thus, it is found that the equation of predicting the deflection profiles proposed in this study could be applicable to suspension bridges and the FBG strain sensors could be reliable on acquiring the strain data from bridges on site.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.1
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• pp.107-119
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• 1991

This dissertation analyzes the running mechanism of flexible and thin tape above rotating head through the experiment. The scope of study is confined to measure the vertical deformation of running tape under hydrodynamic pressure invoking phenomena of elasto-hydrodynamic lubrication between the protruded bump on a rotating cylinder ad the running tape. Experimental system is devised to measure the vertical deflection of the running tape by opto-electronical displacement gauge, which enables to detect microscopic surface deflection of high frequency. Thorough the tests of small specimens of groove and bump, the accuracy and reliability of this experimental method is confirmed and achieved an accuracy within 5%(2.mu.m) error for the microscopic deflection with high frequency. In experimental works, the effects of bump size on flying characteristics of the tape were evaluated and examined. For the vertical deformation of the running tape. the numerical results and its trend agree qualitatively with the experimental ones.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.31 no.2
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• pp.173-180
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• 2013

In this paper, we studied on measurement of soil deformation around the tip of model pile by close-range photogrammetry. The rigorous bundle adjustment method was utilized to monitor the soil deformation in the laboratory model pile-load test as function of incremental penetration of the pile. Control points were installed on the frame of the laboratory model box case and more than 150 target points were inserted inside the soil around the model pile and on the surface. Four overlapping images including three horizontal and one vertical image were acquired by a non-metric camera for each penetration step. The images were processed to automatically locate the control and target points in the images for the self-calibration and the bundle adjustment. During the bundle adjustment, the refraction index of the acrylic case of the laboratory model was accounted for accurate measurement. The experiment showed the proposed approach enabled the automated photogrammetric monitoring of soil deformation around the tip of model pile.