• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.1
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• pp.29-35
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• 2019

In this paper, a low-cost dynamic measurement system using the RGB-depth camera, Microsoft $Kinect^{(R)}$ v2, is proposed for measuring time-varying free surface motion of liquid dampers used in building vibration mitigation. Various experimental studies are conducted consecutively: performance evaluation and validation of the $Kinect^{(R)}$ v2, real-time monitoring using the $Kinect^{(R)}$ v2 SDK(software development kits), point cloud acquisition of liquid free surface in the 3D space, comparison with the existing video sensing technology. Utilizing the proposed $Kinect^{(R)}$ v2-based measurement system in this study, dynamic behavior of liquid in a laboratory-scaled small tank under a wide frequency range of input excitation is experimentally analyzed.

• Advances in nano research
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• v.7 no.3
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• pp.191-208
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• 2019

In the present work the dynamic analysis of the functionally graded rectangular nanoplates is studied. The theory of nonlocal elasticity based on the quasi 3D high shear deformation theory (quasi 3D HSDT) has been employed to determine the natural frequencies of the nanosize FG plate. In HSDT a cubic function is employed in terms of thickness coordinate to introduce the influence of transverse shear deformation and stretching thickness. The theory of nonlocal elasticity is utilized to examine the impact of the small scale on the natural frequency of the FG rectangular nanoplate. The equations of motion are deduced by implementing Hamilton's principle. To demonstrate the accuracy of the proposed method, the calculated results in specific cases are compared and examined with available results in the literature and a good agreement is observed. Finally, the influence of the various parameters such as the nonlocal coefficient, the material indexes, the aspect ratio, and the thickness to length ratio on the dynamic properties of the FG nanoplates is illustrated and discussed in detail.

• Journal of Korean Association for Spatial Structures
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• v.19 no.1
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• pp.117-126
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• 2019

Micro-Electro-Mechanical Systems (MEMS) sensors have been widely used in Structural Health Monitoring due to their convenience and lower costs in comparison to conventional sensors. Triggered measurements are relevant in events such as earthquakes because unlike continuous measurements, they only record the structural response once an event happens. This is more cost effective and it makes the data more manageable because only the required measurements from the event are recorded. The most common method of triggering is amplitude triggering. However, lower input amplitudes (less than 0.1g) cannot be triggered by using this method. In this paper, sound triggering was introduced to allow triggered measurements for lower input amplitude values. The performance of the sound triggering and amplitude triggering were compared by a series of shaking-table tests. It was seen that sound-triggering method has a wider frequency (0.5~10Hz) and amplitude (0.01~1.0g) range of measurements. In addition, the sound triggering method performs better than the amplitude triggering method at lower amplitudes. The performance of the amplitude triggering, in terms of the triggering being simultaneous improves at higher input amplitudes.

• Physical Therapy Rehabilitation Science
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• v.8 no.1
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• pp.32-39
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• 2019

Objective: The aim of this study is to investigate the effects of whole body vibratory stimulation on muscle strength, balance, and fall efficacy among super-aged women. Design: Randomized controlled trial. Methods: Twenty-eight super-aged women over 80 years of age were assigned to either the experimental group (n=14) and control group (n=14). The experimental group received an exercise program that used the whole body vibratory stimulation with a frequency of 30 Hz and amplitude of 3 mm, and the control group received an exercise program without vibratory stimulation. Intervention was provided for 4 weeks, 3 sessions per week, and 30 minutes per session. In order to measure lower extremity muscle strength the 30-second chair stand test (CST) was used. The Berg Balance Scale (BBS) was used to measure dynamic balance. Static balance was measured by tracking the path length, velocity, and area of the center of pressure (CoP). The Falls Efficacy Scale (FES) was used to measure the subjects' fear of falling. Results: Both the experimental and control group demonstrated statistically significant increase in muscle strength, dynamic balance, and fall efficacy (p<0.05). Only the experimental group showed significant improvements in static balance before and after the intervention (p<0.05). The experimental group showed significantly greater improvements in CST, BBS, and CoP (path length, velocity) than control group (p<0.05). Conclusions: Whole body vibratory stimulation exercise is shown to be a safe and appropriate physical therapy intervention method to enhance muscle strength, balance, and fall efficacy of super-aged women.

• Journal of Dental Anesthesia and Pain Medicine
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• v.20 no.6
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• pp.397-402
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• 2020

Background: Inferior alveolar nerve block (IANB) is the most common, painful, and anxiety-provoking procedure involving needle insertion for anesthetic solution deposition. DentalVibeⓇ (DV) delivers vibration at a sustained frequency as a counter-stimulation to the site of injection, thereby alleviating pain. The aim of this study was to evaluate and compare the effectiveness of DV and lignocaine hydrochloride 2% gel (Lox 2% jelly) in pain reduction during IANB in children. Methods: A split-mouth randomized clinical trial was designed with a sample of 60 children (age, 6 to 12 years) requiring bilateral IANB for various dental procedures; DV was used while administering IANB and Lox 2% jelly was used as the topical anesthetic before administering IANB at subsequent appointments. During both appointments, pain perception was measured using the sound, eye, motor (SEM) scale and Wong-Baker faces pain rating scale (WBFPRS); oxygen saturation (SpO2) and pulse rate were measured using a pulse oximeter before, during, and after the IANB procedure. The obtained values were tabulated and subjected to statistical analysis. Wilcoxon test was used for intergroup comparison, and Friedman test, for intragroup comparison of measured variables at different treatment phases. Results: The medians and interquartile ranges of the WBFPRS scores recorded during the IANB procedure for DV and Lox 2% jelly were 2 (2-4) and 2 (0-2), respectively (P < 0.05). The SEM scale scores, mean SpO2, and pulse rate did not show any significant differences during the IANB procedure between both treatments. Conclusion: Both DV and Lox 2% jelly were found to be effective in pain reduction during IANB in children.

• Steel and Composite Structures
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• v.39 no.1
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• pp.95-107
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• 2021

In this work, the dynamic response of functionally graded beams on variable elastic foundations is studied using a novel higher-order shear deformation theory (HSDT). Unlike the conventional HSDT, the present one has a new displacement field which introduces undetermined integral variables. The FG beams were assumed to be supported on Winkler-Pasternak type foundations in which the Winkler modulus is supposed to be variable in the length of the beam. The variable rigidity of the elastic foundation is assumed to be linear, parabolic and sinusoidal along the length of the beam. The material properties of the FG porous beam vary according to a power law distribution in terms of the volume fraction of the constituents. The equations of motion are determined using the virtual working principle. For the analytical solution, Navier method is used to solve the governing equations for simply supported porous FG beams. Numerical results of the present theory for the free vibration of FG beams resting on elastic foundations are presented and compared to existing solutions in the literature. A parametric study will be detailed to investigate the effects of several parameters such as gradient index, thickness ratio, porosity factor and foundation parameters on the frequency response of porous FG beams.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.35 no.4
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• pp.353-358
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• 2022

Bulky iron-core potential transformers (PT) are installed in a tank of gas insulated switchgears (GIS) for a system voltage measurement in power substations. In this paper, we studied an electronic voltage transformer (EVT) embedded in a spacer for miniaturization, eco-friendliness, and performance improvement of GIS. The prototype EVT consists of a capacitive probe (CP) that can be embedded in a spacer and a voltage Follower with a high input and a low output impedance. The CP was fabricated in the form of a Flexible-PCB to acquire the insulation performance and to withstand vibration and shock during operation. Voltage ratio of the prototype EVT is about 42,270, and the frequency bandwidth of -3 dB ranges from 0.33 Hz to 3.9 MHz. The voltage ratio error evaluated at about 6%, 12% and 18% of the rated voltage of 170 kV was 0.32%, and the phase error was 12.9 minutes. These results were within the accuracy for the class 0.5 specified in IEC 60044-7 and satisfy even in ranges from 80% to 120% of the rated voltage. If the prototype EVT replaces the conventional iron-core potential transformer, it is expected that the height of the GIS could be reduced by 11% and the amount of SF₆ will be reduced by at least 10%.

• Journal of Environmental Science International
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• v.31 no.10
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• pp.869-881
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• 2022

In this study, a field study was conducted to investigate the relationship between high-resolution remote images and the volumetric moisture, and the number of compaction. Changes in the shape of the surface and soil moisture content were observed and correlated with the number of compactions using roller equipment. As the compaction is repeated, the surface is flattened and the terrain curvature decreases and converges to zero. In particular, the tangential curvature changes as the number of compactions increase. Due to soil compaction, the vegetation index changed from a positive to a negative value, and most of the test site area was homogenized with a negative index. This suggests a decrease in porosity and an increase in volumetric water content associated with increasing soil compaction. Soil moisture, measured using a frequency domain reflectometry(FDR) sensor, tends to increase proportionately with the number of vibration compactions, but the correlation between the number of compactions and soil moisture is unclear. This study suggests that while it is necessary to consider the reproducibility of the experiments performed, the compaction quality of the soil can be evaluated using high-resolution terrain factors and soil moisture.

• Journal of the Korean Society of Industry Convergence
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• v.25 no.5
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• pp.773-782
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• 2022

Estimation of cable tension through proper measurements is one of the essential tasks in evaluating the safety of cable structures. In this paper, a study on cable tension estimation using the built-in accelerometer and camera in a smartphone was conducted. For the experimental study, visual displacement measurement using a smartphone camera and acceleration measurement using a built-in accelerometer were performed in the cable-stayed bridge model. The estimated natural frequencies and transformed tensions from these measurements were compared with the theoretical values and results from the normal visual displacement method. Through comparison, it can be seen that the error between the method using the smartphone and the normal visual displacement is sufficiently small to be acceptable. It has also been shown that those errors are much smaller than the difference between the values calculated by the theoretical model. These results show that the deviation according to the type of measurement method is not large and it is rather important to use an appropriate mathematical model. In conclusion, in the case of cable tension estimation, it can be said that the visual displacement measurement and acceleration using a smartphone can be a sufficiently applicable method, just like the normal visual displacement method. It is also noteworthy that the smartphone accelerometer has a larger magnitude error and has more limitations such as high-frequency sampling instability compared to the visual displacement method, but shows almost the same performance as the visual displacement method in this cable tension estimation.

• The Journal of the Acoustical Society of Korea
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• v.40 no.3
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• pp.192-200
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• 2021

Korean bell is a macroscopically axi-symmetrical structure, but has a slight asymmetry due to complex patterns and casting irregularity. Small asymmetry separates one vibration mode into a mode pair with slight frequency difference. The mode pair interferes and creates a beat. The vivid beat with an appropriate period makes the bell sound magnificent and lively feeling. In this study, we propose a method to make the vivid beat using artificial dumshoi. This method creates the vivid beat by designing artificial dumshoi that overwhelms the bell asymmetry. To this end, the asymmetry of Korean bell is quantified by analyzing the beat period data of a number of Korean bells cast in modern times. Based on the measured beat period data, the magnitude of asymmetry is quantified using an equivalent bell model and artificial dumshoi is applied. The movement of mode pair by dumshoi is predicted through finite element analysis. Finally, a design example of the artificial dumshoi for clear beat is introduced.