• Wind and Structures
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• v.20 no.2
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• pp.315-326
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• 2015

To overcome the drawbacks of the traditional contact-type sensor for structural displacement measurement, the vision-based technology with the aid of the digital image processing algorithm has received increasing concerns from the community of structural health monitoring (SHM). The advanced vision-based system has been widely used to measure the structural displacement of civil engineering structures due to its overwhelming merits of non-contact, long-distance, and high-resolution. However, seldom currently-available vision-based systems are capable of realizing the synchronous structural displacement measurement for multiple points on the investigated structure. In this paper, the method for vision-based multi-point structural displacement measurement is presented. A series of moving loading experiments on a scale arch bridge model are carried out to validate the accuracy and reliability of the vision-based system for multi-point structural displacement measurement. The structural displacements of five points on the bridge deck are measured by the vision-based system and compared with those obtained by the linear variable differential transformer (LVDT). The comparative study demonstrates that the vision-based system is deemed to be an effective and reliable means for multi-point structural displacement measurement.

• Journal of the Society of Naval Architects of Korea
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• v.52 no.4
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• pp.315-322
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• 2015

In this paper, the theory of rectangular plate on the elastic foundation is used to get the relation equation between the effective Young’s modulus and the ice sheet deflection by applying the characteristic length concept, since the model ice sheet is rectangular shape in KRISO (Korea Research Institute for Ships and Ocean Engineering) ice basin. The obtained relation equation is equal to that of using the circular plate theory. A device is made and used to measure the deflection of ice plate using LVDT (Linear Variable Differential Transformer) for several loading cases and the procedure of experiments measuring the deflection used for getting the Young’s modulus is explained. In addition, the flexural strength value obtained through flexural strength experiments is compared with that of finite element analysis using the obtained effective Young’s modulus. Also, a nonlinear FEA (Finite Element Analysis) of cantilever ice beam is done with eroding effect and LS-DYNA result shows the fracture of brittle ice under 1 mm/s velocity load.

• Journal of Institute of Control, Robotics and Systems
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• v.20 no.5
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• pp.570-577
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• 2014

This paper describes the design of a force applying system for a smart phone curved glass molding system and its characteristic test. The force applying system is composed of a motor and gear, a rectilinear movement structure, a force sensor, an LVDT (Linear Variable Differential Transformer) sensor, an up and down moving block, and so on. The system precisely controls the applying force and time to the plane glass because the glass can be easily destroyed under applied force, and can be bent imperfectly. As a result of the characteristic test, the curved glass can be manufactured using this system, and the holding time under 0N force, the applying force to the plane glass, the time for applying from 0N to maximum force, and the holding time under maximum force at the manufacture feasible temperature $620^{\circ}C$ were found.

• International Journal of Highway Engineering
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• v.11 no.1
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• pp.135-144
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• 2009

The purpose of this study is to develop a simple and rational crack evaluation system using Marshall tester. Fracture energy were used as a parameter to evaluate the crack resistance of asphalt mixtures. Marshall tester basically measures the vertical deformation obtained from the linear variable differential transformer(LVDT) attached on the specimen's exterior, which can cause a measurement error due to the local deformation near the loading head. Therefore, the validity of the measurement system of Marshall tester should be tested to use it in calculation of fracture energy. Two types of indirect tensile strength tests were performed using four types of asphalt mixtures at two temperature conditions. From the tests, it was shown that local deformation near the loading head had not occurred before a specimen was fractured, so that it did not cause the measurement error of fracture energy. And also from the statistic analysis, the coefficient of variation of vertical deformation measurements obtained on specimen's exterior is less than 15%. Thus, vertical deformation measurements obtained on the specimen's exterior can be used in crack evaluation system using Marshall tester.

• Nuclear Engineering and Technology
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• v.42 no.2
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• pp.203-210
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• 2010

The $\underline{H}igh$ flux $\underline{A}dvanced$ $\underline{N}eutron$ $\underline{A}pplication$ $\underline{R}eact\underline{O}r$ (HANARO), an open-tank-in-pool type reactor, is one of the multi-purpose research reactors in the world. Since the commencement of HANARO's operations in 1995, a significant number of experimental facilities have been developed and installed at HANARO, and continued efforts to develop more facilities are in progress. Owing to the stable operation of the reactor and its frequent utilization, more experimental facilities are being continuously added to satisfy various fields of study and diverse applications. The irradiation testing equipment for nuclear fuels and materials at HANARO can be classified into capsules and the Fuel Test Loop (FTL). Capsules for irradiation tests of nuclear fuels in HANARO have been developed for use under the dry conditions of the coolant and materials at HANARO and are now successfully utilized to perform irradiation tests. The FTL can be used to conduct irradiation testing of a nuclear fuel under the operating conditions of commercial nuclear power plants. During irradiation tests conducted using these capsules in HANARO, instruments such as the thermocouple, Linear Variable Differential Transformer (LVDT), small heater, Fluence Monitor (F/M) and Self-Powered Neutron Detector (SPND) are used to measure various characteristics of the nuclear fuel and irradiated material. This paper describes not only the status of HANARO and the status and perspective of irradiation devices and instrumentation for carrying out nuclear fuel and material tests in HANARO but also some results from instrumentation during irradiation tests.

• Geomechanics and Engineering
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• v.21 no.2
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• pp.95-102
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• 2020

Population concentration in urban areas has led traffic management a central issue. To mitigate traffic congestions, the government has planned to construct large-cross-section tunnels deep underground. This study focuses on estimating the damage caused to frame structures owing to tunnel excavation. When constructing a tunnel network deep underground, it is necessary to divide the main tunnel and connect the divergence tunnel to the ground surface. Ground settlement is caused by excavation of the adjacent divergence tunnel. Therefore, predicting ground settlement using diverse variables is necessary before performing damage estimation. We used the volume loss and cover-tunnel diameter ratio as the variables in this study. Applying the ground settlement values to the settlement induction device, we measured the extent of damage to frame structures due to displacement at specific points. The vertical and horizontal displacements that occur at these points were measured using preattached LVDT (Linear variable differential transformer), and the lateral strain and angular distortion were calculated using these displacements. The lateral strain and angular distortion are key parameters for structural damage estimation. A damage assessment chart comprises the "Negligible", "Very Slight Damage", "Slight Damage", "Moderate to Severe Damage", and "Severe to Very Severe Damage" categories was developed. This table was applied to steel frame and concrete frame structures for comparison.

• Structural Engineering and Mechanics
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• v.73 no.4
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• pp.427-436
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• 2020

The use of final IGS precise orbit and clock products for high-rate GNSS-PPP proved its effectiveness in capturing dynamic displacement of engineering structures caused by earthquakes. However, the main drawback of using the final products is that they are available after approximately two weeks of data collection, which is not suitable for timely measures after an event. In this study, the use of ultra-rapid products (observed part), which are available after a few hours of data collection, and rapid products, which are available in less than 24 hrs, are investigated and their results are compared to the more precise final products. The tests are designed such that harmonic oscillations with different frequencies and amplitudes and ground motion of a simulated real earthquake are generated using a single axis shake table and the PPP was used to capture these movements by monitoring time-change of the table positions. To evaluate the accuracy of PPP using ultra-rapid, rapid and final products, their results were compared with relative GNSS positioning and LVDT (Linear Variable Differential Transformer) data, treated as reference. The results show that the high-rate GNSS-PPP solutions based on the three products can capture frequencies of harmonic oscillations and dynamic displacement with good accuracy. There were slight differences between ultra-rapid, rapid and final products, where some of the tested events indicated that the latter two produced are more accurate and provide better results compared to the ultra-rapid product for monitoring short-term dynamic displacements.

• Structural Engineering and Mechanics
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• v.89 no.6
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• pp.589-599
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• 2024

This study presents the usability of the high-rate single-frequency Precise Point Positioning (SF-PPP) technique based on 20 Hz Global Positioning Systems (GPS)-only observations in detecting dynamic motions. SF-PPP solutions were obtained from post-mission and real-time GNSS corrections. These include the International GNSS Service (IGS)-Final, IGS real-time (RT), real-time MADOCA (Multi-GNSS Advanced Demonstration tool for Orbit and Clock Analysis), and real-time products from the Australian/New Zealand satellite-based augmentation systems (SBAS, known as SouthPAN). SF-PPP results were compared with LVDT (Linear Variable Differential Transformer) sensor and single-frequency relative positioning (SF-RP) solutions. The findings show that the SF-PPP technique successfully detects the harmonic motions, and the real-time products-based PPP solutions were as accurate as the final post-mission products. In the frequency domain, all GNSS-based methods evaluated in this contribution correctly detect the dominant frequency of short-term harmonic oscillations, while the differences in the amplitude values corresponding to the peak frequency do not exceed 1.1 mm. However, evaluations in the time domain show that SF-PPP needs high-pass filtering to detect accurate displacement since SF-PPP solutions include trends and low-frequency fluctuations, mainly due to atmospheric effects. Findings obtained in the time domain indicate that final, real-time, and MADOCA-based PPP results capture short-term dynamic behaviors with an accuracy ranging from 3.4 mm to 8.5 mm, and SBAS-based PPP solutions have several times higher RMSE values compared to other methods. However, after high-pass filtering, the accuracies obtained from PPP methods decreased to a few mm. The outcomes demonstrate the potential of the high-rate SF-PPP method to reliably monitor structural and earthquake-induced ground motions and vibration frequencies of structures.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.3
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• pp.355-373
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• 2017

Tunnelling in urban areas, it is essential to understand existing structure-tunnel interactive behavior. Serviced structures in the city are supported by pile foundation, since they are certainly effected due to tunnelling. In this research, thus, pile load distribution and ground behavior due to tunnelling below grouped pile were investigated using laboratory model test. Grouped pile foundations were considered as 2, 3 row pile and offsets (between pile tip and tunnel crown: 0.5D, 1.0D and 1.5D for generalization to tunnel diameter, D means tunnel diameter). Soil in the tank for laboratory model test was formed by loose sand (relative density: Dr = 30%) and strain gauges were attached to the pile inner shaft to estimate distribution of axial force. Also, settlements of grouped pile and adjacent ground surface depending on the offsets were measured by LVDT and dial gauge, respectively. Tunnelling-induced deformation of underground was measured by close range photogrammetric technique. Numerical analysis was conducted to analyze and compare with results from laboratory model test and close range photogrammetry. For expression of tunnel excavation, the concept of volume loss was applied in this study, it was 1.5%. As a result from this study, far offset, the smaller reduction of pile axial load and was appeared trend of settlement was similar among them. Particulary, ratio of pile load and settlement reduction were larger when the offset is from 0.5D to 1.0D than from 1.0D to 1.5D.

• Journal of Aerospace System Engineering
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• v.12 no.4
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• pp.75-80
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• 2018

The working principle of a satellite camera involves a focusing mechanism for controlling the focus of the optical system, which is essential for proper functioning. However, research on focusing mechanisms of satellite optical systems in Korea is in the beginning stage and developed technology is limited to a thermal control type. Therefore, in this paper, we propose a motor-driven focusing mechanism applicable to small satellite optical systems. The proposed mechanism is designed to generate z-axis displacement in the secondary mirror by a motor. In addition, three flexure hinges have been installed on the supporter for application of preload on the mechanism resulting in minimization of the alignment error arising due to manufacturing tolerance and assembly tolerance within the mechanism. After fabrication of the mechanism, the alignment errors (de-space, de-center, and tilt) were measured with LVDT sensors and laser displacement meters. Conclusively, the proposed focusing mechanism could achieve proper alignment degree, which can be applicable to small satellite optical system.