• Journal of the Korean Society of Marine Environment & Safety
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• v.25 no.7
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• pp.898-905
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• 2019

As the positive feedback between the absorption of chromophoric dissolved organic matter (CDOM) and acceleration of ice melt can impact the aquatic biota and dynamic heat budget, long-term monitoring of the CDOM variation in the polar ocean is necessary. However, the monitoring of CDOM is not easy because of harsh weather and difficult access, especially in the Antarctic Ocean. Therefore, the purpose of this study was to find a suitable long-term monitoring site for CDOM variation; we selected Maxwell Bay and Marian Cove at Sejong Base and horizontal and vertical distributions of CDOM were measured. After a 72 hr time-series measurement test of the CDOM variation at Sejong Dock and Sejong Cape in Maxwell Bay, Sejong Dock was selected, as it does not haveland discharge effects. The seasonal variation of CDOM was evident and the average CDOM concentration of Maxwell Bay was comparable with the adjacent sea. The CDOM at Sejong Dock from February to November 2010 was the highest in the fall and winter and the lowest during spring and summer. Thus, based on our one-year CDOM data, we suggest that Sejong Dock in Maxwell Bay is suitable for long-term monitoring of CDOM as an indicator of photochemical and biological environmental change and an important factor in determining the heating budget in the Antarctic Ocean.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.40 no.1
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• pp.1-11
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• 2020

Medium to large post structures installed along the roadside without proper protection can lead to serious vehicle damage and occupant injury at the impact. In North America and Europe, splitting systems such as slip base or breakaway device are used to reduce impacts. But the system has the risk of secondary accident when the splitted post falls down to the traffic or pedestrian. Sliding Post have been proposed as a way to solve this problem. By studying the crash test results of the 1.3ton and 0.9ton vehicle with 60 km/h and 80 km/h to a Rigidly Fixed Post (RFP) and Sliding Post (SP), danger of the conventional RFP and crashworthiness of the SP have been proven. While collision analysis only from the acceleration measured at the center of the vehicle assumes the motion of the post is the same as that of the vehicle, in this paper, by adding high speed film data to the analysis with vehicle acceleration could have separate the post motion from the vehicle motion. It gives better explanations on the movement of post and vehicle in each distinctive time step and provides basics to the crashworthy post design.

• Design & Manufacturing
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• v.14 no.3
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• pp.8-16
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• 2020

In this study, the vibration signal of the mold was measured and analyzed to monitoring the process time and characteristics during injection molding. A 5 inch light guide plate mold was used to injection molding and the vibration signal was measured by MPU6050 acceleration sensor module attached the surface of fixed mold base. Conditions except for injection speed and packing pressure were set to the same value and the change of the vibration signal of the mold according to injection speed and packing pressure was analyzed. As a result, the vibration signal had a large change at three points: "Injection start", "V/P switchover", and "Packing end". The time difference between "injection start" and "V/P switchover" means the injection time in the injection molding process, and the time difference between "V/P switchover" and "Packing end" means the packing time. When the injection time and packing time obtained from the vibration signal of the mold are compared with the time recorded in the injection molding machine, the error of the injection time was 2.19±0.69% and the error of the packing time was 1.39±0.83%, which was the same level as the actual value. Additionally, the amplitude at the time of "injection start" increased as the injection speed increased. In "V/P switchover", the amplitude tended to be proportional to the pressure difference between the maximum injection pressure and the packing pressure and the amplitude at the "packing end" tended to the pressure difference between the packing pressure and the back pressure. Therefore, based on the result of this study, the injection time and packing time of each cycle can be monitored by measuring the vibration signal of the mold. Also, it was confirmed that the level and trend of process variables such as the injection speed, maximum injection pressure, and packing pressure can be evaluated as the change of the mold vibration during injection molding.

• Journal of the Earthquake Engineering Society of Korea
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• v.12 no.5
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• pp.11-21
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• 2008

In recent years, time history analysis has been the method generally used for the seismic analysis of tall buildings with damping devices. When T is the natural period of the first vibration mode of the structure, the sum of the spectral acceleration of the earthquake ground motion is usually adjusted to that of the design response spectrum in the period ranging from 0.2T to 1.5T to meet the requirements of design code. However, when the ground motion is scaled according to the design code, the differences in the responses obtained by response spectrum analysis (RSA) and time history analysis (THA) of the structures increase as the natural period of the structure becomes longer. When time history analysis is performed by using ground accelerations that are scaled according to the design code, base shear is similar to that obtained from RSA, but other responses, such as displacements, drifts and member forces, are underestimated compared to RSA. If these results are adjusted by multiplying with the scale-up factor, the scaled responses become much smaller. Therefore, a scaling method of ground motions corresponding with the design code is proposed in this study, as a way of assisting structural engineers in generating artificial ground motions.

• Geotechnical Engineering
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• v.7 no.1
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• pp.41-52
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• 1991

A study of the effects of dynamic pile-soil-structure interactions on the response of super- structures, supported by group piles, are presented in this paper. The dynamic impedance functions of single pile generated by soil-pile interactions are obtained and compared among others using the methods proposed by Novak, Gazetas, and Kuhlemeyer, and using the equivalent cantilever method. Group pile effects are also considered by the following approaches : neglecting interaction effects : group efficiency ratio concept : static interaction approach . and dynamic interaction approach. The responses of a nuclear containment structure are obtained by using the elastic half-space analysis, based on the impedance functions mentioned above. Main conclusions drawn from this study are as follows : 1. The numerical results of the impedance functions calculated by each method were quite different : the Novak's was the smallest, and the Kuhlemeyer's the highest. Considering group effects, similar values in each approach were obtained for the stiffness : the difference was very big for the damping. 2. The top displacement of the structure was reduced by 20% or more by pile installations. However, the base shear force, the base moment, and the resonance frequency were increased by more than two times due to stiffening effect of the ground by pile installations. 3. Whether frequency dependant impedence functions or frequency independant functions were used, the responses of the structure were not so much affected by the choice of the impedance functions. 4. The reduction effect of the top displacement increased with the increase of the maximum ground acceleration.

• Journal of the Earthquake Engineering Society of Korea
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• v.5 no.5
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• pp.73-83
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• 2001

The mass and stiffness of upper wall-lower frame system(mixed building structures) change sharply at transfer floor due to different structural system in upper and lower part. These mixed building structures generally show the stiffness, weight or geometric vertical irregularities. The purpose of this study is to investigate the response characteristics of these structures by push-over analysis and nonlinear time history analysis. For four types of analysed models, only the variation of upper wall stories was considered. The conclusions of this study are following; (1) In the push-over analysis, yielding hinges in beams and columns of lower frame occurred at the base shear of similar magnitude in all models. But as the number of stories of upper wall increases, yielding hinges at ends of coupling beams were observed in the small magnitude of base shear. (2) In the nonlinear time history analysis, yielding of lower frame occurred at beams with as small ground acceleration as 55gal, and in upper walls yielding was concentrated on coupling beams and shear walls near the transfer floor. (3) As the number of stories of upper walls decreases, the story stiffness of the lower frames decreased relatively and the occurrence of soft stories in the lower frame was observed.

• Journal of the Korean Geosynthetics Society
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• v.12 no.4
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• pp.133-141
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• 2013

This paper describes the earthquake risk evaluation of 15 sites of architectural heritages, which are considered ground conditions of sites in Seoul. In order to acquire the input data of earthquake response analysis, surface wave exploration was performed at the site. Earthquake response analysis and 3D earthquake safety evaluation were carried out under the base of scenario earthquakes. Ground displacements of areas, which are located on architectural heritages, are showed about 0.5 mm ~ 9.7 mm, and it was analyzed to small affected by earthquakes. In case of Naksungdae three-story stone pagoda, ground displacement is similar to the others. However, displacement of three-story stone pagoda with granite is 30 mm on the top, because the greatest occurrence of that is caused by stress release at seismic wave effect.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.31 no.3
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• pp.141-145
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• 2018

The paper presents a new dynamic displacement measurement system. The developed displacement measurement system consists of a sensor module, a base module and a computation module. The sensor module, which contains a force-balanced accelerometer and low-price RTK-GNSS, measures the high-precision acceleration with sampling frequency of 100Hz, the low-precision displacement and velocity with sampling frequency of 10Hz. The measured data is transferred to the computation module through LAN cable, and precise displacement is estimated in real-time with 100Hz sampling frequency through a two stage Kalman filter. The field test was conducted at San Francisco-Oaklmand Bay bridge, CA, USA to verify the precision of the developed system, and it showed the RMSE was 1.68mm.

• Journal of the Earthquake Engineering Society of Korea
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• v.20 no.4
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• pp.223-234
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• 2016

To investigate earthquake responses of structures with basements affected by soil deposits, centrifuge tests were performed using an in-flight earthquake simulator. The test specimen was composed of a single-degree-of-freedom structure model, a basement and sub-soil deposits in a centrifuge container. The test parameters were the dynamic period of the structure model, boundary conditions of the basement, existence of soil deposits, centrifugal acceleration level, and type and level of input earthquake accelerations. When soil deposits did not exist, the earthquake responses of the structures with fixed basement were significantly greater than those of the structure without basement. Also, the earthquake responses of the structures with the fixed basement surrounded by soil deposits were amplified, but the amplifications were smaller than those of the structures without basement. The earthquake responses of the structures with the half-embedded basement in the soil deposits were greater than those estimated by the fixed base model using the measured free-field ground motion. The test showed that the basement and the soil deposit should be simultaneously considered in the numerical analysis model, and the stiffness of the half-embedded was not effective.

• Applied Chemistry for Engineering
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• v.7 no.5
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• pp.963-969
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• 1996

Cure characteristics of DGEBA(diglycidyl ether of bisphenol A)/dicy(dicyandiamide) system containing diuron(3-(3,4-dichloro phenyl) -1,1-dimethylurea) as an accelerator was investigated. The system has shelf life of six months because dicy is insoluble in liquid/solid resins at room temperature. It is generally known that dicy is an adequate curing agent for one component adhesive due to its highly latent property. With increasing the amount of added dicy, reaction heat of DGEBA/dicy system increased and degree of conversion was not varied. For DGEBA/dicy/diuron system, cure temperature decreased about $40^{\circ}C$ and cure reaction became fast by the addition of diuron which activates dicy. $T_g$ of the mixed resin decreased with the amount of accelerator. which was interpreated with molecular structure forming loose chain. Cure kinetics of DGEBA/dicy and DGEBA/dicy/diuron system were explained using Kamal's autocatalytic reaction model. The effect of acceleration was confirmed with that reaction model.