• Korean Journal of Legislative Studies
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• v.24 no.2
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• pp.5-38
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• 2018

A seismic change is under way in diplomatic topography surrounding the Korean Peninsula. A new dynamic is being generated that could lead to a breakthrough in the nuclear stalemate and to an end of hostility between the two Koreas. Moon Administration's bold and creative foreign policy, which is alleged to place South Korea in the "driver's seat", is probably responsible for what is happening on the Korean Peninsula. However, on the other hand, Moon Administration's foreign policy shows a lot of continuity with foreign policy of previous conservative governments. In particular, the Moon government's emphasis on the vitality of the ROK-US alliance and its commitment to close coordination with the US in dealing with nuclear issues of North Korea is the hallmark of the continuity in South Korea's foreign policy. Emphasizing and sharing the notion of the continuities in foreign policy could contribute to social integration by garnering bi-partisan support. It could also spawn sense of stability, predictability, and confidence to diplomatic counterparts in other countries. And it could help avoid the negative effects of expectation-reality gap in the event that the outcome of all the diplomatic endeavor falls short of expectation held by citizens.

• Journal of the Korean Geotechnical Society
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• v.24 no.8
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• pp.35-41
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• 2008

Laminar-shear-boxes are widely used to simulate free-field seismic ground response by using a l-g shaking table or geo centrifuge in geotechnical earthquake engineering. This study numerically modeled and compared the ground responses in the free field, rigid box, and laminar shear box by using a 3-D FEM program. It is found from the numerical simulations that the laminar shear box can simulate the free field ground movement more precisely than the rigid box. However, the laminar shear box underestimated the surface acceleration of the free field ground. It also showed low-frequency characteristics probably because the stiffness and inertia effect of surrounding ground are neglected.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.3A
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• pp.497-512
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• 2006

In this paper, a simple but effective analysis procedure to estimate seismic capacities of multi-span continuous bridge structures is proposed on the basis of modal pushover analysis considering all the dynamic modes of structure. Unlike previous studies, the proposed method eliminates the coupling effects induced from the direct application of modal decomposition by introducing an identical stiffness ratio and an approximate elastic deformed shape. Moreover, in addition to these two introductions, the use of an appropriate distributed load {P} makes it possible to predict the dynamic responses for all kinds of bridge structures through a simpler analysis procedure. Finally, in order to establish the validity and applicability of the proposed method, correlation studies between rigorous nonlinear time history analysis and the proposed method are conducted for multi-span continuous bridges.

• Smart Structures and Systems
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• v.32 no.5
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• pp.281-295
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• 2023

The purpose of this study is to demonstrate and verify the application of phase-control absolute-acceleration-feedback active tuned mass dampers (PCA-ATMD) to multiple-degree-of-freedom (MDOF) building structures. In addition, servo speed control technique has been developed as a replacement for force control in order to mitigate the negative effects caused by friction and inertia. The essence of the proposed PCA-ATMD is to achieve a 90° phase lag for a structure by implementing the desired control force so that the PCA-ATMD can receive the maximum power flow with which to effectively mitigate the structural vibration. An MDOF building structure with a PCA-ATMD and a real-time filter forming a complete system is modeled using a state-space representation and is presented in detail. The feedback measurement for the phase control algorithm of the MDOF structure is compact, with only the absolute acceleration of one structural floor and ATMD's velocity relative to the structure required. A discrete-time direct output-feedback optimization method is introduced to the PCA-ATMD to ensure that the control system is optimized and stable. Numerical simulation and shaking table experiments are conducted on a three-story steel shear building structure to verify the performance of the PCA-ATMD. The results indicate that the absolute acceleration of the structure is well suppressed whether considering peak or root-mean-square responses. The experiment also demonstrates that the control of the PCA-ATMD can be decentralized, so that it is convenient to apply and maintain to real high-rise building structures.

• Structural Engineering and Mechanics
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• v.90 no.1
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• pp.19-26
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• 2024

In recent years, an increasing number of experimental studies have shown that the practical application of mature active control systems requires consideration of robustness criteria in the design process, including the reduction of tracking errors, operational resistance to external disturbances, and measurement noise, as well as robustness and stability. Good uncertainty prediction is thus proposed to solve problems caused by poor parameter selection and to remove the effects of dynamic coupling between degrees of freedom (DOF) in nonlinear systems. To overcome the stability problem, this study develops an advanced adaptive predictive fuzzy controller, which not only solves the programming problem of determining system stability but also uses the law of linear matrix inequality (LMI) to modify the fuzzy problem. The following parameters are used to manipulate the fuzzy controller of the robotic system to improve its control performance. The simulations for system uncertainty in the controller design emphasized the use of acceleration feedback for practical reasons. The simulation results also show that the proposed H∞ controller has excellent performance and reliability, and the effectiveness of the LMI-based method is also recognized. Therefore, this dynamic control method is suitable for seismic protection of civil buildings. The objectives of this document are access to adequate, safe, and affordable housing and basic services, promotion of inclusive and sustainable urbanization, implementation of sustainable disaster-resilient construction, sustainable planning, and sustainable management of human settlements. Simulation results of linear and non-linear structures demonstrate the ability of this method to identify structures and their changes due to damage. Therefore, with the continuous development of artificial intelligence and fuzzy theory, it seems that this goal will be achieved in the near future.

• Geophysics and Geophysical Exploration
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• v.12 no.1
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• pp.132-142
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• 2009

The Tamar rift valley runs through the City of Launceston, Tasmania. Damage has occurred to city buildings due to earthquake activity in Bass Strait. The presence of the ancient valley, the Tamar valley, in-filled with soft sediments that vary rapidly in thickness from 0 to 250mover a few hundreds metres, is thought to induce a 2D resonance pattern, amplifying the surface motions over the valley and in Launceston. Spatially averaged coherency (SPAC), frequency-wavenumber (FK) and horizontal to vertical spectrum ratio (HVSR) microtremor survey methods are combined to identify and characterise site effects over the Tamar valley. Passive seismic array measurements acquired at seven selected sites were analysed with SPAC to estimate shear wave velocity (slowness) depth profiles. SPAC was then combined with HVSR to improve the resolution of these profiles in the sediments to an approximate depth of 125 m. Results show that sediments thicknesses vary significantly throughout Launceston. The top layer is composed of as much as 20m of very soft Quaternary alluvial sediments with a velocity from 50 m/s to 125 m/s. Shear-wave velocities in the deeper Tertiary sediment fill of the Tamar valley, with thicknesses from 0 to 250m vary from 400 m/s to 750 m/s. Results obtained using SPAC are presented at two selected sites (GUN and KPK) that agree well with dispersion curves interpreted with FK analysis. FK interpretation is, however, limited to a narrower range of frequencies than SPAC and seems to overestimate the shear wave velocity at lower frequencies. Observed HVSR are also compared with the results obtained by SPAC, assuming a layered earth model, and provide additional constraints on the shear wave slowness profiles at these sites. The combined SPAC and HVSR analysis confirms the hypothesis of a layered geology at the GUN site and indicates the presence of a 2D resonance pattern across the Tamar valley at the KPK site.

• Economic and Environmental Geology
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• v.44 no.6
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• pp.493-502
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• 2011

We study the deep structure of Korean Peninsula by estimating Moho depth and crustal thickness from using land and oceanic topography and free-air gravity anomaly data. Based on Airy-Heiskanen isostatic hypothesis, the correlated components between the terrain gravity effects and free-air gravity anomalies by wavenumber correlation analysis(WCA) are extracted to estimate the gravity effects that will be resulted from isostatic compensation for the area. With the resulting compensated gravity estimates, Moho depth that is a subsurface between the crust and mantle is estimated by the inversion in an iterative method with the constraints of 20 seismic depth estimates by the receiver function analysis, to minimize the uncertainty of non-uniqueness. Consequently, the average of the resulting crustal thickness estimate of Korean Peninsula is 32.15 km and the standard deviation is 3.12 km. Moho depth of South Korea estimated from this study is compared with the ones from the previous studies, showing they are approximately consistent. And the aspects of Moho undulation from the respective study are in common deep along Taebaek Mountains and Sobaek Mountains and low depth in Gyeongsang Basin relatively. Also, it is discussed that the terrain decorrelated free-air gravity anomalies inferring from the intracrustal characteristics of the crust are compared to the heat flow distributions of South Korea. The low-frequency components of terrain decorrelated Free-air gravity anomalies are highly correlated with the heat flow data, especially in the area of Gyeongsang basin where high heat flow causes to decrease the density of the rocks in the lower crust resulting in lowering the Moho depth by compensation. This result confirms that the high heat sources in this area coming from the upper mantle by Kim et al. (2008).

• Journal of the Computational Structural Engineering Institute of Korea
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• v.20 no.5
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• pp.593-604
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• 2007

Although composite construction has more mechanical advantages compared to noncomposite construction, the design of noncomposite construction for skew bridges with large skew angels has been often checked because composite construction may cause large stresses in the bridge deck. In this study, the analytical model considered dynamic behaviors for noncomposite skew bridges was proposed. Using the proposed analytical model, the validity of the application of noncomposite construction to skew bridges was checked. Also, the effects of interactions between the concrete deck and steel girders such as composite construction, partial composite construction, and noncomposite construction on the dynamic characteristics and dynamic behaviors of simply supported skew bridges were investigated. A series of parametric studies for the total 27 skew bridges was conducted with respect to parameters such as girder spacing, skew angle, and deck aspect ratio. Although the slip at the interfaces between the concrete deck and steel girders results in the reduction of seismic total base shear in the transverse direction due to period elongation, it causes an undesirable behavior of skew bridges by the modification in mode shapes and distributions of stiffness. Shear connectors placed by minimum requirements for partial composite action have an effect on reducing the girder stresses and deck stresses; except case of some skew bridges, the magnitude of the girder stresses and deck stresses obtained from partial composite skew bridges is similar to or slightly more than those acquired from composite skew bridges.

• Proceedings of the Technology Innovation Conference
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• 1997.12a
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• pp.159-176
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• 1997

This paper deals with demand surveys for big science and technology research facilities and equipments to advance national S'||'&'||'T research infrastructure. We perform surveys thrice based on applied Delphi method on the future demand of big S'||'&'||'T research facilities and equipments among Korean scientists and engineers. We employ the concept of big S'||'&'||'T research facilities and equipments as follows: \circled1 The operating size of it is equivalent to that of an institute or research center, and/or \circled2 The users in various disciplines are many, and/or \circled3 The application areas or spill-over effects are large, and/or \circled4 The scale and scope of research objects is equivalent to that of mega science area such as earth.oceanography.space, and/or \circled5 The expenses for installing and operating it are to be supported by government, and/or \circled5 The facilities are expected as necessary for international joint research, and/or \circled7 It is necessary for promoting creative basic science and developing creative technology. We ask the respondents to answer the following questionnaire: - How to prioritize the equipments according to the degree of importance\ulcorner $\square$ Promotion of basic science and mega science, the development of the technologies to enhance the public welfare, the competitiveness of industrial technologies, the job creation for the S'||'&'||'T personnel, and international cooperation. - Who should be in charge of acquisition and operation of the equipments\ulcorner $\square$ Industry, Government Research Institutes, Academy, ERC and SRC. - When shall we acquire the equipment\ulcorner $\square$ Within 2000, 2002, 2007, 2012, and 2017. - How shall we acquire the equipments\ulcorner $\square$ International Joint Development, Domestic Development, Acquisition from Overseas, - How much will the equipment generate spill-over effects to national competitiveness\ulcorner $\square$ Promotion of basic science, contribution to the economy, supply of S'||'&'||'T personnel, and international cooperation. We suggest the following equipments as prioritized candidates after consulting the officers from MOST, MOE, MIC, MOEN and experts from KBSI and STEPI:(table omitted) where, #1, Korea Advanced Liquid Metal Reactor, #2. 800 MHz Superconduction Fourier-Transform Nuclear Magnetic Resonance Spectrometer, #3. Ion Accelerator, #4. Seismic Test Facility, #5. Transonic Wind Tunnel, #6. Radio Telescope for Very Long Baseline Interferometer, #7. 3000t Universal(or Large Structure) Testing Machine, #8. Compost Facility or Plasma Pyrolysis Facility.

• Geophysics and Geophysical Exploration
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• v.21 no.3
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• pp.198-206
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• 2018

In this preliminary study, dehydration of the subducting slab and behavior of the expelled water are numerically modeled using 2-dimensional model scheme. The hydrated minerals in the oceanic crust of the subducting slab experience dehydration by increases in temperature and pressure and expel their water into the overlying mantle wedge. Behavior of the expelled water is governed by both the corner flow in the mantle wedge and porous flow of the expelled water through the pores of the mantle minerals. The effects of convergence rate and age of the subducting slab as well as grain size of the minerals on the dehydration of the subducting slab and behavior of the expelled water are evaluated. The water solubility of the oceanic crust measured from the laboratory experiments is considered for modeling dehydration of the oceanic crust. The model calculations show most of the hydrated minerals in the oceanic crust is dehydrated by a depth of 100 km and the effects of the convergence rate and age of the subducting slab on the dehydration of the subducting slab and behavior of the expelled water are not significant. The larger grain size allows faster porous flow of the expelled water through the oceanic crust, mantle wedge and overlying continental crust and reduces the volume fraction of the expelled water there. The developed technique will be used for future studies on arc volcanism and has a potential implication for the other fields such as seismic tomographic study.