• Journal of the Korean Society of Safety
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• v.34 no.4
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• pp.15-21
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• 2019

In order to secure the safety of various machinery, it is very important to develop a technique for accurately and quickly measuring the cracks generated in the mechanical equipment and evaluating the mechanical characteristics. The evaluation of the mechanical properties is accompanied by an appropriate strain measurement according to the material and crack occurrence of the target structure. Especially, when micro cracks are generated, the evaluation method is very important. Digital image correlation is an optical full field displacement measuring method which is using currently with speckles in the interested area. However the evaluation method and conditions of image distributions have to be considered carefully to measure the crack occurrence because the images of the speckle patterns affect the quality of displacement results. In this study, the speckle pattern density is characterized to improve the accuracy of the measurement method. And also the micro crack initiation is detected by the measured displacement in the adopted speckle pattern distribution. It is shown that the proposed method is useful to determine the density pattern distribution for the accurate measurement and crack detection.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.24 no.2
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• pp.251-255
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• 2015

Thermal deformation, such as bending and twisting, occurs among the polymer parts of air-conditioner indoor units because of repetitive temperature change during heating operation. In this study, a numerical method employing finite-element analysis to efficiently simulate the thermal deformation of an assembly is proposed. Firstly, the displacement of an actual assembly produced by thermal deformation was measured using a 3D optical measurement system. The measurement results indicated a general downward sag of the assembly, and the maximum displacement value was approximately 1 mm. The temperature distribution was measured using a thermographic camera, and the results were used as initial-temperature boundary conditions to perform temperature-displacement analysis. The simulation results agreed well with the measured data. To reduce the thermal deformation, the stiffness increased 100%. As the results, the maximum displacement decreased by approximately 5.4% and the twisting deformation of the holder improved significantly.

• Smart Structures and Systems
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• v.30 no.3
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• pp.273-286
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• 2022

In recent years, vision-based monitoring has received great attention. However, structural identification using vision-based displacement measurements is far less established. Especially, simultaneous identification of structural systems and unknown excitation using vision-based displacement measurements is still a challenging task since the unknown excitations do not appear directly in the observation equations. Moreover, measurement accuracy deteriorates over a wider field of view by vision-based monitoring, so, only a portion of the structure is measured instead of targeting a whole structure when using monocular vision. In this paper, the identification of structural system and excitations using vision-based displacement measurements is investigated. It is based on substructure identification approach to treat of problem of limited field of view of vision-based monitoring. For the identification of a target substructure, substructure interaction forces are treated as unknown inputs. A smoothing extended Kalman filter with unknown inputs without direct feedthrough is proposed for the simultaneous identification of substructure and unknown inputs using vision-based displacement measurements. The smoothing makes the identification robust to measurement noises. The proposed algorithm is first validated by the identification of a three-span continuous beam bridge under an impact load. Then, it is investigated by the more difficult identification of a frame and unknown wind excitation. Both examples validate the good performances of the proposed method.

• Smart Structures and Systems
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• v.16 no.3
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• pp.521-535
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• 2015

Vibration-based monitoring is one approach used to perform structural condition assessment. By measuring structural response, such as displacement, dynamic characteristics of a structure may be estimated. Often, the primary dynamic responses in civil structures are below 5 Hz, making accurate low frequency measurement critical for successful dynamic characterization. In addition, static deflection measurements are useful for structural capacity and load rating assessments. This paper presents a DC coupled continuous wave radar to accurately detect both dynamic and static displacement. This low-cost radar sensor provides displacement measurements within a compact, wireless unit appropriate for a range of structural monitoring applications. The hardware components and operating mechanism of the radar are introduced and a series of laboratory experiments are presented to assess the performance characteristics of the radar. The laboratory and field experiments investigate the effect of factors such as target distance, motion amplitude, and motion frequency on the radar's measurement accuracy. The results demonstrate that the radar is capable of both static and dynamic displacement measurements with sub-millimeter accuracy, making it a promising technology for structural health monitoring.

• International conference on construction engineering and project management
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• 2022.06a
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• pp.1250-1251
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• 2022

Measuring management is an important part of preventing the collapse of retaining walls in advance by evaluating their stability with a variety of measuring instruments. The current work of measuring management requires considerable human and material resources since measurement companies need to install measuring instruments at various places on the retaining wall and visit the construction site to collect measurement data and evaluate the stability of the retaining wall. It was investigated that the applicability of the current work of measuring management is poor at small and medium-sized urban construction sites(excavation depth<10m) where measuring management is not essential. Therefore, the purpose of this study is to develop a laser sensor-based hardware to support the wall displacement measurements and their control software applicable to small and medium-sized urban construction sites. The 2D lidar sensor, which is more economical than a 3D laser scanner, is applied as element technology. Additionally, the hardware is mounted on the corner strut of the retaining wall, and it collects point cloud data of the retaining wall by rotating the 2D lidar sensor 360° through a servo motor. Point cloud data collected from the hardware can be transmitted through Wi-Fi to a displacement analysis device (notebook). The hardware control software is designed to control the 2D lidar sensor and servo motor in the displacement analysis device by remote access. The process of analyzing the displacement of a retaining wall using the developed hardware and software is as follows: the construction site manager uses the displacement analysis device to 1)collect the initial point cloud data, and after a certain period 2)comparative point cloud data is collected, and 3)the distance between the initial point and comparison point cloud data is calculated in order. As a result of performing an indoor experiment, the analyses show that a displacement of approximately 15 mm can be identified. In the future, the integrated system of the hardware designed here, and the displacement analysis software to be developed can be applied to small and medium-sized urban construction sites through several field experiments. Therefore, effective management of the displacement of the retaining wall is possible in comparison with the current measuring management work in terms of ease of installation, dismantlement, displacement measurement, and economic feasibility.

• Smart Structures and Systems
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• v.19 no.6
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• pp.679-694
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• 2017

The complexity, enlargement and irregularity of structures and multi-directional dynamic loads acting on the structures can lead to unexpected structural behavior, such as torsion. Continuous torsion of the structure causes unexpected changes in the structure's stress distribution, reduces the performance of the structural members, and shortens the structure's lifespan. Therefore, a method of monitoring the torsional behavior is required to ensure structural safety. Structural torsion typically occurs accompanied by displacement, but no model has yet been developed to measure this type of structural response. This research proposes a model for measuring dynamic torsional response of structure accompanied by displacement and for identifying the torsional modal parameter using vision-based displacement measurement equipment, a motion capture system (MCS). In the present model, dynamic torsional responses including pure rotation and translation displacements are measured and used to calculate the torsional angle and displacements. To apply the proposed model, vibration tests for a shear-type structure were performed. The torsional responses were obtained from measured dynamic displacements. The torsional angle and displacements obtained by the proposed model using MCS were compared with the torsional response measured using laser displacement sensors (LDSs), which have been widely used for displacement measurement. In addition, torsional modal parameters were obtained using the dynamic torsional angle and displacements obtained from the tests.

• The Journal of the Korea Contents Association
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• v.16 no.1
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• pp.362-369
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• 2016

Recently, Last to check the security status of various medium and large bridge structures using various kinds of measurement equipment, but most of the methods are used to measure and check the displacement behavior of the bridge by a certain period. In this study, receive GPS satellite signals that can be observed in real time the whole region, a bridge to automatically measure the displacement and behavior characteristics of the structure in real-time in mm over the 24 hours, the measurement information and transmits the data to the wireless network, by making use, it was applied to the real-time monitoring system in connection with a bridge to be able to automatically notify GNSS fine displacement behavior. In fact, analysis and receives the measurement data to GNSS provided in the upper bridge of the middle and large-sized aging for this purpose, measuring USN and at the same time is converted into a three-dimensional position information of a test study was conducted to monitor the bridge displacement in real time. As a result, a vertical displacement of about 0.027~0.037m at the measurement time of day of the measurement point is that the repeated and confirmed.

• Journal of Internet Computing and Services
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• v.19 no.1
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• pp.105-111
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• 2018

This paper presents the analysis of image quality with FHD(Full HD) resolution camera equipped DIC(Digital Image Correlation) platform for the measurement of the architectural structure's relative displacement. DIC platform was designed based on i.MX6 of Freescale. Displacement measurement based on DIC method, the error is affected by image quality factors as pixel number, brightness, contrast, and SNR[dB](Signal to Noise Ratio). The effect were analyzed. The displacement of ROI(Region Of Interest) area within the image was measured by sub-pixel units based on DIC method. The non-contact telemetry property of DIC method, it can be used to long distance non-contact measurement. The various displacement results was measured and analyzed with the image quality factor adjustment according to the distance(25m, 35m, 50m).

• Journal of the Korean Society for Precision Engineering
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• v.32 no.2
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• pp.191-198
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• 2015

In this paper, six-degree-of-freedom (DoF). Displacement measurement technique using a compact stereo-vision system is proposed. The measuring system consists of a camera, an optical prism, two plane mirrors, and a planar marker on a target. The target was attached on an object so that its six-DoF displacement can be calculated using a proposed coordinates estimating algorithm and stereo images of the marker. A prototype was designed and fabricated for performance test. From the test results, it can be confirmed that the proposed measuring technique can be applied to monitoring and control of various manipulators.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.11 s.242
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• pp.1542-1550
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• 2005

This paper presents the numerical procedure for calculating non-uniform residual stresses based on relieved displacements obtained from incremental hole drilling. The relationship between the in-plane displacement produced by introducing a blind hole and the corresponding residual stress is established. Finite element calculations are described to evaluate the relieved coefficients required for the determination of non-uniform residual stresses. Validity of the proposed method has been tested through three axisymmetric test examples and two three-dimensional examples. As a result of . simulation on the test examples, it is found that this numerical procedure is well adopted to measuring non-uniform residual stress in the full hole depth range of the hole diameter from the surface. The accuracy of the hole drilling method with displacement measurement is discussed, comparing tile method with strain measurement