• Journal of the Earthquake Engineering Society of Korea
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• v.11 no.3 s.55
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• pp.1-10
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• 2007

In general, the tension forces of hanger cable in suspension bridges play an important role in evaluating the bridge conditions. The vibration method, as a conventional one, has been widely applied to estimate the tension forces by using the measured frequencies on hanger cables. However, the vibration method is not applicable to short hanger cables because the fiequencies of short cables are severely sensitive to flexural rigidity. Thus, in this study, the tension forces of short hanger cables, of which the length is shorter than 10 meters, were estimated through back analysis of the cable fiequencies measured from Gwang-An suspension bridge in Korea. Direct approach to back analysis is adopted using the univariate method among the direct search methods as an optimization technique. The univariate method is able to search the optimal tension forces without regard to the initial ones and has a rapid convergence rate. To verify the feasibility of back analysis, the results from back analysis and vibration method are compared with the design tension forces. From the comparison, it can be inferred that back analysis results are more reasonable agreement with the design tension forces of short hanger cable. Therefore, it is concluded that back analysis applied in this study is an appropriate tool for estimating tension forces of short hanger cables.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.32 no.1
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• pp.55-68
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• 2020

In order to investigate the hydraulic characteristics of a boundary layer streaming over the beach cusps appeared in swells prevailing mild seas, we numerically simulated the shoaling process of Edge waves over the beach cusp. Synchronous Edge waves known to sustain the beach cusps could successfully be duplicated by generating two obliquely colliding Edge waves in front of beach cusps. The amplitude A_B and length L_B of Beach Cusp were elected to be 1.25 m and 18 m, respectively based on the measured data along the Mang-Bang beach. Numerical results show that boundary layer streaming was formed at every phase of shoaling process without exception, and the maximum boundary layer streaming was observed to occur at the crest of sand bar. In RUN 1 where the shortest waves were deployed, the maximum boundary layer streaming was observed to be around 0.32 m/s, which far exceeds the amplitude of free stream by two times. It is also noted that the maximum boundary layer streaming mentioned above greatly differs from the analytical solution by Longuet-Higgins (1957) based on wave Reynolds stress. In doing so, we also identify the recovery procedure of natural beaches in swells prevailing mild seas, which can be summarized such as: as the infra-gravity waves formed in swells by the resonance wave-wave interaction arrives near the breaking line, the sediments ascending near the free surface by the Phase II waves orbital motion were carried toward the pinnacle of foreshore by the shoreward flow commenced at the steep front of breaking waves, and were deposited near the pinnacle of foreshore due to the infiltration.

• The Journal of Korean Society for Radiation Therapy
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• v.29 no.1
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• pp.93-101
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• 2017

Purpose: In breast cancer radiotherapy, brass mesh bolus has been recently studied to overcome disadvantage of conventional bolus. The purpose of this study is to investigate the stability of first introduced the brass mesh in the country, and evaluate the skin surface dose of that. Materials and Methods: The measurement of skin surface dose was evaluated to verify similar thickness of the Brass mesh bolus that compared conformal tissue equivalent bolus with 5 mm thickness. We used 6 MV photons on an ELEKTA VERSA linear accelerator and optically stimulated luminescent dosimeter (OSLD). In addition, two opposed beam using IMRT phantom was applied to comparative study of brass mesh bolus between tissue equivalent bolus. Results: The results showed that similar thickness of the Brass mesh bolus was 3 mm compared with 5 mm tissue equivalent bolus by measuring the skin surface dose of solid phantom. The surface dose for IMRT thorax phantom using 3 mm brass mesh bolus was about 1.069 times greater than that using tissue equivalent bolus. Conclusion: In this study, we found that the brass mesh bolus improved better reduction of skin sparing effect and dose uniformity than tissue equivalent bolus. However evaluation for various clinic cases should be investigated.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.1
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• pp.208-215
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• 2020

This study investigated the relationship among gait variables and physical fitness variables for Korean elderly people. Two hundred elderly people aged 65 to 85, (100 men and 100 women) participated in this study. They performed senior fitness test consisting of 6 tests, 3 additional physical tests (vertical jump, one leg stand, and grip force), body composition measures, and gait test. The gait test used shoes having an inertia measurement device in the outer-soles. The results indicated that the stride length, 6-min walking, lean body mass, and dumbbell curls were significantly affected by age (the above 75 group vs. the below 75 group). Among 33 measured parameters, the principal component analysis (PCA) revealed five PCs such as gait characteristics, physical features, gait variability, and fitness levels. In addition, the correlation analysis showed that the preferred walking speed was significantly, positively associated with stride length and single support time, whereas it was negatively associated with double support time and gait variability.(Ed note: please confirm my modification) In conclusion, sarcopenia should be avoided in elderly people, and resistance exercise is highly recommended to help elderly people maintain their gait ability.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.5
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• pp.1-9
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• 2016

Railroad bridges account for 25% of the entire high-speed rail network. Railway bridges are subject to gradual structural degradation or fatigue accumulation due to consistent and repeating excitation by fast moving trains. Wireless sensing technology has opened up a new avenue for bridge health monitoring owing to its low-cost, high fidelity, and multiple sensing capability. On the other hand, measuring the transient response during train passage is quite challenging that the current wireless sensor system cannot be applied due to the intrinsic time delay of the sensor network. Therefore, this paper presents a framework for monitoring such transient responses with wireless sensing systems using 1) real-time excessive vibration monitoring through ultra-low-power MEMS accelerometers, and 2) post-event time synchronization scheme. The ultra-low power accelerometer continuously monitors the vibration and trigger network when excessive vibrations are detected. The entire network of wireless smart sensors starts sensing through triggering and the post-event time synchronization is conducted to compensate for the time error on the measured responses. The results of this study highlight the potential of detecting the impact load and triggering the entire network, as well as the effectiveness of the post-event time synchronized scheme for compensating for the time error. A numerical and experimental study was carried out to validate the proposed sensing hardware and time synchronization method.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.6
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• pp.1124-1131
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• 2006

The recent medical treatment guidelines and the development of information technology make hospitals reduce the expense in surrounding environment and it requires improving the quality of medical treatment of the hospital. Moreover, MIS, PACS(Picture Archiving and Communication System), OCS, EMR are also developing. Medical Information System is evolved toward integration of medical IT and situation is changing with increasing high speed in the ICT convergence. Mobile component refers to construct wireless system of hospital which has constructed in existing environment. Through RFID development in existing system, anyone can log on easily to internet whenever and wherever. It is the core technology to implement automatic medical processing system. This paper provides a basic review of RFID model, PACS application component services. In addition, designed and implemented database server's component program and client program of mobile application that recognized RFID tag and patient data in the ubiquitous environments. This system implemented mobile PACS that performed patient data based db environments, and so reduced delay time of requisition, medical treatment, lab.

• Journal of Korean Society of Transportation
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• v.22 no.6
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• pp.145-157
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• 2004

Microscopic freeway simulation models project the uncertain values of performance measures for subject traffic conditions by explaining drivers' driving behavior with lane changing and car-following models. However, the existing lane changing models are limited to gap acceptance oriented passive behavior of drivers and not able to capture more-or-less aggressive driving behavior(e.g. cut-in lane changing) ordinarily obseved in field. This paper suggests the definition of cut-inlane changing and presents its characteristics based on the findings from two different freeway on- and off-ramp sections. In addition, this paper proposes a new lane changing model capable of handling both passive and active drivers' driving behavior for better performance of simulations. The proposed lane changing model was tested with Hanyang Simulatin (HYTSIM), a microscopic freeway simulation program developed for this study. The HYTSIM simulation results reflecting the performance of the proposed lane changing model were compared against the field data. The test results showed that the distribution of gaps collected when vehicles change lanes were statistically identical to the field data at 95% confidence level.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.11
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• pp.2105-2110
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• 2008

Embedding the compact wearable units to monitor the health status of a person has been analysed as a convenient solution for the home health care. This paper presents a method to detect fall from the other activities of daily living and also to classify those activities. This kind of ambulatory monitoring of the elderly and people with limited mobility can not only provide their general health status but also alarms whenever an emergency such as fall or gait has been occurred and a help is needed. A timely assistance in such a situation can reduce the loss of life. This work shows a detailed analysis of the data received from a chest worn sensor unit embedding a 3-axis accelerometer and depicts which features are important for the classification of human activities. How to arrange and reduce the features to a new feature set so that it can be classified using a simple classifier and also improving the classification resolution. Principal component analysis (PCA) has been used for modifying the feature set and afterwards for reducing the size of the same. Finally a Neural network classifier has been used to analyse the classification accuracies. The accuracy for detection of fall events was found to be 86%. The overall accuracy for the classification of Activities or daily living (ADL) and fall was around 94%.

• Journal of the Society of Disaster Information
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• v.17 no.4
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• pp.747-754
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• 2021

Purpose: Seismic safety evaluation of a curved bridge must be performed since the curved bridges exhibit the complex behavior rather than the straight bridges, due to geometrical characteristics. In order to conduct the probabilistic seismic assessment of the curved bridge, Seismic fragility evaluation was performed using the uncertainty of the steel material properties of a curved bridge girde, in this study. Method: The finite element (FE) model using ABAQUS platform of the curved bridge girder was constructed, and the statistical parameters of steel materials presented in previous studies were used. 100 steel material models were sampled using the Latin Hypercube Sampling method. As an input ground motion in this study, seismic fragility evaluation was performed by the normalized scale of the Gyeongju earthquake to 0.2g, 0.5g, 0.8g, 1.2g, and 1.5g. Result: As a result of the seismic fragility evaluation of the curved girder, it was found that there was no failure up to 0.03g corresponding to the limit state of allowable stress design, but the failure was started from 0.11g associated with using limit state design. Conclusion: In this study, seismic fragility evaluation was performed considering steel materials uncertainties. Further it must be considered the seismic fragility of the curved bridge using both the uncertainties of input motions and material properties.

• Journal of Climate Change Research
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• v.4 no.4
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• pp.359-369
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• 2013

In this paper, correlations between driving parameters and $CO_2$ of light-duty vehicles have been analyzed. Three test vehicles equipped with PEMS (Portable Emission Measurement System) have been driven in real-road in urban areas of Seoul. Averaged vehicle speed, RPA(Relative Positive Acceleration) and stop ratio have been selected as main driving parameters. The analysis have been conducted in interrupted and uninterrupted road types. Averaged values in various driving conditions have been calculated with distance based moving averaging window method. The multiple linear regression method have been applied to account for correlation between driving parameters and $CO_2$ emissions. This approach has shown statistically that $CO_2$ emission per distance (g/km) have tendencies to be increased as decreased averaged vehicle speed and increased RPA and stop ratio. Compared with uninterrupted traffic, interrupted traffic have shown the lower vehicle speed and the higher RPA and stop ratio. These characteristics of driving parameters in interrupted traffic should cause the higher $CO_2$ emission per distance.