• Aerospace Engineering and Technology
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• v.6 no.1
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• pp.64-73
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• 2007

A Large thermal vacuum chamber (LTVC) for space environment simulation on large satellites was successfully developed and constructed by KARI (Korea Aerospace Research Institute) in Korea with a local company. This chamber has an effective diameter of 8 meters and depth of 10 meters, and is composed of vacuum system, thermal control system, and anti-vibration system. Temperature below $-190^{\circ}C$ is maintained over the thermal shroud wrapping a satellite under $3.7{\times}10^{-5}Pa$ ($5{\times}10^{-7}torr$) vacuum level, and optical test can be done in this chamber by seismic mass with $10^{-5}g_{rms}$ or lower vibration level. In addition, the shroud temperature can be increased up to $123^{\circ}C$ using halogen lamps. Chamber control program based on PLC (Programmable Logic Controller) could control this large thermal vacuum chamber automatically.

• Tunnel and Underground Space
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• v.26 no.5
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• pp.339-347
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• 2016

The world's first underground repository for low- and intermediate- level radioactive waste (SFR1) has been in operation since 1988. SFR1 can accommodate $1,000m^3$ of radioactive waste per year with 4 chambers and 1 silo with a total capacity of $63,000m^3$ of radioactive waste. With extended operation time of 10 of the 12 nuclear power reactors and dismantling of the other 2 nuclear reactors, more nuclear waste need to be disposed in the future. Therefore, Swedish Nuclear Fuel and Waste Management Company (SKB) submitted a license application for a repository extension (SFR3) that consists of 6 additional rock chambers with a capacity of $108,000m^3$ of radioactive waste and for accommodating 9 boiling water reactor tanks. In this study, plans for the extension SFR3 are presented with the geological, geomechanical and hydrogeological issues to be considered.

• Smart Structures and Systems
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• v.22 no.1
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• pp.41-55
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• 2018

Damping ratio and frequency have influence on dynamic serviceability or instability such as vortex-induced vibration and displacement amplification due to earthquake and critical flutter velocity, and it is thus important to make determination of damping ratio and frequency accurate. As bridges are getting longer, small scale model test considering similitude law must be conducted to evaluate damping ratio and frequency. Analysis conditions modified by similitude law are applied to experimental test considering different scale ratios. Generally, Nyquist frequency condition based on natural frequency modified by similitude law has been used to determine sampling rate for different scale ratios, and total time length has been determined by users arbitrarily or by considering similitude law with respect to time for different scale ratios. However, Nyquist frequency condition is not suitable for multimode system with noisy signals. In addition, there is no specified criteria for determination of total time length. Those analysis conditions severely affect accuracy of damping ratio. The focus of this study is made on the determination of minimum analysis conditions for different scale ratios. Influence of signal to noise ratio is studied according to the level of noise level. Free initial value problem is proposed to resolve the condition that is difficult to know original initial value for free vibration. Ambient and free vibration tests were used to analyze the dynamic properties of a system using data collected from tests with a two degree-of-freedom section model and performed on full bridge 3D models of cable stayed bridges. The free decay is estimated with the stochastic subspace identification method that uses displacement data to measure damping ratios under noisy conditions, and the iterative least squares method that adopts low pass filtering and fourth order central differencing. Reasonable results were yielded in numerical and experimental tests.

• Earthquakes and Structures
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• v.8 no.5
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• pp.995-1016
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• 2015

The reliability or the safety index is a measure of how far a structure is from the state of collapse. Also it defined as the probability that a structure will not fail in its lifetime. Having any increase in the reliability index is typically interpreted as increasing in the safety of structures. On the other hand most of researchers acknowledged that one of the most effective means of increasing both the reliability and the safety of structures is to increase the structural redundancy. They also acknowledged that increasing the number of vertical seismic framing will make structural system more reliable and safer against stochastic events such as earthquakes. In this paper the reliability index and the behavior factor of a numbers of three dimensional RC moment resisting frames with the same story area, equal lateral resistant as well as different redundancy has been evaluated numerically using both deterministic and probabilistic approaches. Study on the reliability index and the behavior factor in the case study models of this research illustrated that the changes of these two factors do not have always the same manner due to the increasing of the structural redundancy. In some cases, structures with larger reliability index have smaller behavior factor. Also assuming the same ultimate lateral resistance of structures which causes an increase to a certain level of redundancy can enhance behavior factor of structures. However any further increase in the redundancy of that certain level might decrease the behavior factor. Furthermore, the results of this study illustrate that concerning any increase in the structural redundancy will make the reliability index of structure to be larger.

• Earthquakes and Structures
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• v.6 no.2
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• pp.163-179
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• 2014

Dynamic test with scaled model of a group of intake towers was performed to study the dynamic interaction between water and towers. The test model consists of intake tower or towers, massless foundation near the towers and part of water to simulate the dynamic interaction of tower-water-foundation system. Models with a single tower and 4 towers were tested to find the different influences of the water on the tower dynamic properties, seismic responses as well as dynamic water-tower interaction. It is found that the water has little influence on the resonant frequency in the direction perpendicular to flow due to the normal force transfer role of the water in the contraction joints between towers. By the same effect of the water, maximum accelerations in the same direction on 4 towers tend to close to each other as the water level increased from low to normal level. Moreover, the acceleration responses of the single tower model are larger than the group of towers model in both directions in general. Within 30m from the surface of water, hydrodynamic pressures were quite close for a single tower and group of towers model at two water levels. For points deeper than 30m, the pressures increased about 40 to 55% for the group of towers model than the single tower model at both water levels. In respect to the pressures at different towers, two mid towers experienced higher than two side towers, the deeper, the larger the difference. And the inside hydrodynamic pressures are more dependent on ground motions than the outside.

• KIEAE Journal
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• v.7 no.4
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• pp.147-152
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• 2007

Numerous non-destructive tests(NDT) to assess the safety of real structures have been developed. System identification(SI) techniques using dynamic responses and behaviors of structural systems become an outstanding issue of researchers. However the conventional SI techniques are identified to be non-practical to the complex and tall buildings, due to limitation of the availability of an accurate data that is magnitude or location of external loads. In most SI approaches, the information on input loading and output responses must be known. In many cases, measuring the input information may take most of the resources, and it is very difficult to accurately measure the input information during actual vibrations of practical importance, e.g., earthquakes, winds, micro seismic tremors, and mechanical vibration. However, the desirability and application potential of SI to real structures could be highly improved if an algorithm is available that can estimate structural parameters based on the response data alone without the input information. Thus a technique to estimate structural properties of building without input measurement data and using limited response is essential in structural health monitoring. In this study, shaking table tests on three-story plane frame steel structures were performed. Out-put only model analysis on the measured data was performed, and the dynamic properties were inverse analyzed using least square method in time domain. In results damage detection was performed in each member level, which was performed at story level in conventional SI techniques of frequency domain.

• Explosives and Blasting
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• v.27 no.2
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• pp.48-55
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• 2009

In the process of identifying the earth's crust structures to accurately locate the seismic epicenter, man-made earthquakes need to be generated. Such a large-scale ground vibration can be generated by a deep borehole blasting, but it can also accompany some environmental impacts on the surroundings. In this respect, a borehole test blasting was carried out to determine the maximum charge weight that could be used without affecting the various structures around the blast site. Total 400kg of gelatine-type dynamites was used in the test blast. As a result, a prediction equation for ground vibrations was derived from the measured data. With the allowable level of 3.0 mm/s for residential structures, the maximum charge weight was determined to be 677kg if military structures near the site were considered. But if the military structures were not considered, it was found that up to 2100kg of explosives could be used without affecting old houses in the nearby village.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.18 no.1
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• pp.19-25
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• 2022

Nuclear Power Plants (NPP) should be designed to have sufficient safety margins and to ensure seismic safety against earthquake that may occur during the plant life time. After the 9.12 Gyeongju earthquake accident, the structural integrity of nuclear power plants due to the beyond design basis earthquake is one of key safety issues. Accordingly, it is necessary to conduct structural integrity evaluations for domestic NPPs under beyond design basis earthquake. In this study, the Level 3 LBB (Leak Before Break) evaluation was performed by considering the beyond design basis earthquake for the surge line of a OPR1000 plant of which design basis earthquake was set to be 0.2g. The beyond design basis earthquake corresponding to peak ground acceleration 0.4g at the maximum stress point of the surge line was considered. It was confirmed that the moment behaviors of the hot leg and pressurized surge nozzle were lower than the maximum allowable loading in moment-rotation curve. It was also confirmed that the LBB margin could be secured by comparing the LBB margin through the Level 2 method. It was judged that the margin was secured by reducing the load generated through the compliance of the pipe.

• Journal of Korean Tunnelling and Underground Space Association
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• v.11 no.2
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• pp.163-174
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• 2009

The large underground structure under earthquake is affected more by soil dynamic characteristic and volume of structure than by structural dynamic characteristic itself. Therefore, it is the purpose of research that the aseismic analysis for caverns including various aseismic analysis factors (rock quality-Q value, soil dynamic characteristic, shape ratio $&$ volume, underground structural dynamic characteristic, and aseismic level) are applied by using the numerical analysis program (SAUS; seismic analysis of underground structures). The result of research is stated that maximum strain, maximum moment, and maximum shear are not sensitive with respect to shape ratio. However those values are sensitive with respect to Q value, volume of underground structure and aseismic level. Based on the results of this research, the assessment for the influence factors of aseismic analysis for large underground structure could be possible.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.7 no.4
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• pp.267-285
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• 2002

Dok Island, a Pliocene volcano, lies in the southwestern part of the East Sea. Most the work to date have focused primarily on the petrolography of the island, and as a result, the morphological characteristics and internal structure of the volcanic edifices of the Dok Island remain poorly understood. To provide better constraints on these features, bathymetric data with multibeam echo sounder, 32-channel seismic and 3D gravity modeling were used in this study. Three positive topographic highs are present in the study area, and these highs satisfy the seamount criteria. They are named as Dokdo, Tamhae, and Donghae seamounts. 32-channel seismic survey was conducted to investigate the sediment thickness of the area, which shows that there are no sediments near the summit of seamounts. Away from the seamounts, however, sediment becomes thick(>2000 m) toward the western part of the study area, and sediments in the northern and southern parts are about 1000 m thick. Free-Air gravity anomalies in this study generally follow the bathymetric feature with less than -20 mGal at the western part, but increase towards the seamounts. In the summit of the Dokdo Seamount, anomalies reach over 120 mGal, and in Tamhae and Donghae seamounts, the peak anomaly shows 90 and 70 mGals, respectively. All seamounts have an isolated volcanic conduit in their centre and show regional compensation root with 0.5～1.5 km thickness. The flat-topped summit of the seamounts is probably caused by wave truncation, indicating the sea level at the time of formation of the flat-topped geometry. Comparison between the present-day sea level and subsidence level during the opening of the East Sea suggests that the seamounts in the study area have subsided by 200～300 m after the formation. Furthermore, it implies that the seamounts formed over 12～10 Ma.