• The Journal of the Acoustical Society of Korea
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• v.25 no.8
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• pp.389-394
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• 2006

Mid-Frequency bistatic reverberation level is modeled using ray theoretic algorithms. The algorithm assumes multiple forward/backward scatter along with reciprocity in the Propagation paths. The environments modeled are assumed to be range independent in bathymetry, bottom scattering and surface scattering. Mid-Frequency bistatic scattering algorithm is used as a scattering model. A comparison of predicted reverberation versus time with measured data is presented to verify the bistatic reverberation model. The result demonstrates that it is possible to obtain reasonable reverberation Predictions in experimental site.

• Journal of the Korea Concrete Institute
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• v.15 no.2
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• pp.225-233
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• 2003

Even though a lot of advanced researches on analysis, design, and performance evaluation of reinforced concrete (RC) under seismic action have been carried out, there has been only a few study on seismic analysis of underground RC structures surrounding soil medium. Since the underground RC structures interact with surrounding soil medium, a path-dependent soil model which can predict the soil response is necessary for analyzing behavior of the structure inside soil medium. The behavior of interfacial zone between the RC structure and the surrounding medium should be also considered for more accurate seismic analysis of the RC structure. In this paper, an averaged constitutive model of concrete and reinforcing bars for RC structure and path-dependent Ohsaki's model for soil are applied, and an elasto-plastic interface model having thickness is proposed for seismic analysis of underground RC structures. A finite element analysis technique is developed by applying aforementioned constitutive equations and is verified by predicting both static and dynamic behaviors of RC structures. Then, failure mechanisms of underground RC structure under seismic action are numerically derived through seismic analysis of underground RC station structure under different seismic forces. Finally, the changes of failure mode and the damage level of the structures are also analytically derived for different design cases of underground RC structures.

• Korean Journal of Optics and Photonics
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• v.28 no.6
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• pp.304-313
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• 2017

The finite element analysis for optimizing a mirror system consisting of a large-diameter mirror and flexures requires numerous, repetitive calculations and corrections of the actual model to satisfy the given design conditions. In general, modification of this real model is conducted by reconfiguring nodes of the elements. The reconfiguration is very time-consuming work, to fix the continuity of each of the newly formed component nodes at the interfaces. But the process is a very important factor in determining the analysis time. To save time in modeling and actual computation, and to attain faster convergence, we present a new opto-mechanical analysis using non-shared node connections at each of the interfaces of the optical components. By comparing the results between the new element model and a conventional element model with shared node connections, we found that the opto-mechanical performance was almost the same, but the time to reach the given condition was drastically reduced.

• Journal of the Korean Geotechnical Society
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• v.36 no.12
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• pp.117-124
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• 2020

The present research focuses on a methodology to describe shearing response of clay with respect to temperature. An increase of temperature shifts the normal consolidation line to move down in the plane of void ratio and mean effective stress. The critical state line, however, does not move as much as the normal consolidation line in accordance with temperature increase. As temperature increase, therefore, the difference between the critical state mean effective stress and the pre-consolidation pressure reduces. To reflect this easily, the present study applies a bounding surface consisting of two parts divided by the critical state mean effective stress. This study calibrated a bounding surface for the soft Bangkok clay and performed elemental simulation for undrained triaxial compression tests. The elemental simulation showed that the model can describe the mechanical response upon temperature of clay without complex hardening and evolution rules compared to the experimental data.

• Journal of Korean Tunnelling and Underground Space Association
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• v.14 no.4
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• pp.321-336
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• 2012

The shear behavior at the particle/surface interface such as rock joint can determine the mechanical behavior of whole structure. Therefore, a fundamental understanding of the mechanisms governing its behavior and accurately estimation of the interface strength is essential. In this paper, PFC, a numerical analysis program of discrete element method was used to investigate the effects of the surface roughness crushing on interface strength. The surface roughness was characterized by smooth, intermediate, and rough surface, respectively. Particle shape was classified into one ball model of circular shape and 3 ball model of triangular shape. The surface shape was modelled by wall model of non-crushing surface and ball model of crushing surface. The results showed that as the bonding strength of ball model decreases, lower interface strength is induced. After the surface roughness crushing was occurred, the interface strength tended to converge and higher bonding strength induced lower surface roughness crushing. Higher friction angle was induced in wall model and higher surface roughness induced the higher friction angle. From these findings, it is verified that the surface roughness and surface roughness crushing effect on the particle/surface interface shear behavior.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.30 no.6
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• pp.515-522
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• 2017

In this paper, an isogeometric analysis for multipatch problem is investigated, in which two or more geometries are connected at the interface in a conforming or non-conforming conditions. To express higher continuity at the patch interface, two approaches such as Nitsche based method and master-slave method are formulated for the linear elasticity problem and discretized using the isogeometric approach using NURBS basis functions. A short comparison between two approaches in formulations reveals the pros and cons of them with the applicability in the isogeometric multipatch problem. In addition, a NURBS based stress recovery is adopted to express a better stress continuity through the post-processing. Numerical examples indicate the effectiveness of Nitsche method in the non-conforming patch, following the exact solution well. For the stress concentration problem with the conforming patch, introduced two methodologies show comparative results, meanwhile the NURBS based stress recovery presents an improved smooth stress contour in the whole domain including the patch interface.

• Journal of Energy Engineering
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• v.10 no.4
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• pp.349-356
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• 2001

Phenomenon of direct contact condensation (DCC) heat transfer between steam and water is characterized by the transport of heat and mass through a moving steam/water interface. Since the DCC heat transfer provides some advantageous features in the viewpoint of enhanced heat transfer, it is widely applied to the diversified industries. This study proposes a simple condensation model on the stable steam jets discharging into a quenching tank with subcooled water from a single horizontal pipe for the prediction of the steam jet shapes. The model was derived from the mass, momentum and energy equations as well as thermal balance equation with condensing characteristics at the steam/water interface for the axi-symmetric coordinates. The extremely large heat transfer rate at the steam/water interface was reflected in the effective thermal conductivity estimated from the previous experimental results. The results were compared with the experimental ones. The predicted steam jet shape(i. e. radius and length) by the model was increasing as the steam mass flux and the pool temperature were increasing, which was similar to the trend observed in the experiment.

• Journal of the Korea Concrete Institute
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• v.18 no.1 s.91
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• pp.91-100
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• 2006

This paper presents an analytical model for evaluation of crack widths in structural concrete members. The model is mathematically derived from the actual bond stress-slip relationships between the reinforcement and the surrounding concrete, and the relationships summarized in CEB-FIP Model Code 1990 are employed in this study together with the assumption of a linear slip distribution along the interface at the stabilized cracking stage. With these, the actual strains of the steel and the concrete are integrated respectively along the embedment length between the adjacent cracks so as to obtain the difference in the axial elongation. The model is applied to the test specimens available in literatures, and the predicted values are shown to be in good agreement with the experimentally measured data.

• Journal of the Korean Society for Railway
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• v.12 no.6
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• pp.944-952
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• 2009

This paper presents an analytical model for calculation of crack widths in reinforced concrete structures. The model is mathematically derived from the actual bond stress-slip relationships between the reinforcement and the surrounding concrete, and the relationships summarized in CEB-FIP Model Code 1990 and Eurocode 2 are employed in this study together with the numerical analysis result of a linear slip distribution along the interface at the stabilized cracking stage. With these, the actual strains of the steel and the concrete are integrated respectively along the embedment length between the adjacent cracks so as to obtain the difference in the axial elongation. The model is applied to the test results available in literatures, and the predicted values are shown to be in good agreement with the experimentally measured data.

• Proceedings of the Korean Quaternary Association Conference
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• 2004.06a
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• pp.7-7
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• 2004

한국 남동해역 대륙붕에서 취득된 고해상 탄성파 탐사자료와 퇴적물 시료의 분석에 의하면 후 제4기 퇴적층은 마지막 빙하기 이후의 해수면 변화에 의해 조절되는 저해수면계열, 해침계열, 고해수면계열로 구성된다. 시퀀스 경계면 위의 저해수면계열(층서단위 I)은 마지막 빙하기 동안 퇴적된 니질사 혹은 사질니 퇴적물로 구성되며 대륙붕단과 해곡의 외해역에 분포한다. 해침면과 최대 해침면 사이에 위치하는 해침계열(층서단위 II)은 지난 15,000-6,000년 사이에 퇴적되었으며 주로 사질퇴적물로 구성된다. 해침계열은 연구해역 전반에 걸쳐 넓게 분포하지만 저해수면계열과 고해수면계열에 비해 박층으로 분포한다. 이러한 해침계열은 분포특성에 따라 3개의 소퇴적단위로 세분된다. 즉, 대륙붕단의 초기해침계열(Unit IIa), 중간대륙붕의 중기해침계열(Unit IIb), 내대륙붕의 후기해침계열(Unit IIc)등으로 이들은 후배열층서의 특성을 가진다. 최대해침면 상부에 놓이는 고해수면계열(층서단위 III)은 해수면이 현 수준에 도달한 지난 약 6,000년 이후에 퇴적된 현생 니질 퇴적물로 구성되며 내대륙붕의 연안을 따라 제한적으로 분포한다.