• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2005.06a
• /
• pp.1332-1336
• /
• 2005

It could make the LIghtweight Piezoelectric Composite Actuator (LIPCA) damageable by the cyclic large deformation. If the progressive microvoid coalescence of LIPCA interlaminar took place, the decrease of the stiffness and the weakness of stress transmission and fiber bridging effect would make the fatigue characteristics worse suddenly. Therefore, it is required to study the variation of fatigue behavior and interlaminar condition in LIPCA under resonant frequencies. These studies such as the changeable fatigue phase and interlaminar behavior of LIPCA affected by the resonant frequencies should be carried out due to the strong anisotropy of CFRP layer. Hence, these studies are as follows. 1) The residual stresses distribution of interlaminar in LIPCA using the Classical Lamination Theory (CLT). 2) Comparative analysis of interlaminar behavior for the intact LIPCA versus LIPCA containing an artificial delamination during resonant frequency.

• Journal of electromagnetic engineering and science
• /
• v.9 no.4
• /
• pp.211-217
• /
• 2009

A three-dimensional locally one-dimensional multiresolution time-domain(LOD-MRTD) method is introduced and unconditional stability is proved analytically. The updating formulations have fewer terms on the right-hand side than those of an alternating direction implicit MRTD(ADI-MRTD). The validation of the method is presented using the resonance frequency problem of an empty cavity. The reduction of the numerical dispersion technique is also combined with the proposed method. The numerical examples show that the combined method can improve the accuracy significantly.

• Nuclear Engineering and Technology
• /
• v.49 no.6
• /
• pp.1114-1124
• /
• 2017

Acceleration/preconditioning strategies available in the SCEPTRE radiation transport code are described. A flexible transport synthetic acceleration (TSA) algorithm that uses a low-order discrete-ordinates ($S_N$) or spherical-harmonics ($P_N$) solve to accelerate convergence of a high-order $S_N$ source-iteration (SI) solve is described. Convergence of the low-order solves can be further accelerated by applying off-the-shelf incomplete-factorization or algebraic-multigrid methods. Also available is an algorithm that uses a generalized minimum residual (GMRES) iterative method rather than SI for convergence, using a parallel sweep-based solver to build up a Krylov subspace. TSA has been applied as a preconditioner to accelerate the convergence of the GMRES iterations. The methods are applied to several problems involving electron transport and problems with artificial cross sections with large scattering ratios. These methods were compared and evaluated by considering material discontinuities and scattering anisotropy. Observed accelerations obtained are highly problem dependent, but speedup factors around 10 have been observed in typical applications.

• Tunnel and Underground Space
• /
• v.19 no.3
• /
• pp.213-225
• /
• 2009

The purpose of the study is to evaluate the effects of chemical weathering on the granite and orthogneiss in Wonju area based on accelerated artificial chemical weathering. The rock samples were scrutinized the variation of index properties and ion exchanges caused by artificial chemical weathering which was implemented with leaching test for 170 days using double soxhlet extractor. The differential weathering and decrease of p wave velocity were obtained by weathering process without significant changes of porosity. In case of granite samples, the uniaxial compression strength was reduced by 20% and 16% for the F-grade and SW-grade, respectively. For MW-grade granite, however, was not able to examine the effect of strength reduction due to lack of sample number. Also, for orthogneiss, it is difficult to compare the values of uniaxial compressive strength between before and after the test because of its strong anisotropy.

• Explosives and Blasting
• /
• v.23 no.1
• /
• pp.9-17
• /
• 2005

This study is to clarify the comparative relationship and mechanical anisotropy of granite distributed in the Nam-weon on the subject of weathered rock mass sea water surroundings. Artificial weathering test is defined as a test, which controls the weathering rate and agents by controlling the weathering rate and agents by artificial environmental of salt water. Increased weathering degree is large indicated by weathering salt water, such as apparent specific gravity, absorption, porosity, uniaxial compression strength, P-wave velocity, slake durability, shore hardness, indirect tensile strength(brazilian test) and cohesion were measured. As the Weathering salt water proceeds, cracks develope increasingly. A number the cracks affect the rock deformation. Therefore, stress-strain curve of weathered salt water rock in one confined state are quite differ from weathered fresh water rock those. A reason of their deformation type is the formation of micro-cracks and potential porosity caused by artificial weathering test.

• Tunnel and Underground Space
• /
• v.31 no.4
• /
• pp.211-220
• /
• 2021

Tunnel collapse often occurs during deep underground tunneling (> 40 m depth) in South Korea. Natural cavities as well as water supply pipes, sewer pipes, electric power cables, artificial cavities created by subway construction are complexly distributed in the artificial ground in the shallow depths of the urban area. For deep tunnel excavation, it is necessary to understand the properties of the ground which is characterized by porous elements and various geological structures, and their influence on the stability of the ground. This study analyzed geological factors for risk assessment in deep excavation in South Korea based on domestic and overseas case study. As a result, a total of 7 categories and 38 factors were derived. Factors with high weights were fault and fault clay, differential stress, rock type, groundwater and mud inrush, uniaxial compressive strength, cross-sectional area of tunnel, overburden thickness, karst and valley terrain, fold, limestone alternation, fluctuation of groundwater table, tunnel depth, dyke, RQD, joint characteristics, anisotropy, rockburst and so forth.

• Annual Conference on Human and Language Technology
• /
• 2022.10a
• /
• pp.360-365
• /
• 2022

문장 표현(sentence representation)은 자연어처리 분야 내의 다양한 문제 해결 및 응용 개발에 있어 유용하게 활용될 수 있는 주요한 도구 중 하나이다. 하지만 최근 널리 도입되고 있는 사전 학습 언어 모델(pre-trained language model)로부터 도출한 문장 표현은 이방성(anisotropy)이 뚜렷한 등 그 고유의 특성으로 인해 문장 유사도(Semantic Textual Similarity; STS) 측정과 같은 태스크에서 기대 이하의 성능을 보이는 것으로 알려져 있다. 이러한 문제를 해결하기 위해 대조 학습(contrastive learning)을 사전 학습 언어 모델에 적용하는 연구가 문헌에서 활발히 진행되어 왔으며, 그중에서도 레이블이 없는 데이터를 활용하는 비지도 대조 학습 방법이 주목을 받고 있다. 하지만 대다수의 기존 연구들은 주로 영어 문장 표현 개선에 집중하였으며, 이에 대응되는 한국어 문장 표현에 관한 연구는 상대적으로 부족한 실정이다. 이에 본 논문에서는 대표적인 비지도 대조 학습 방법(ConSERT, SimCSE)을 다양한 한국어 사전 학습 언어 모델(KoBERT, KR-BERT, KLUE-BERT)에 적용하여 문장 유사도 태스크(KorSTS, KLUE-STS)에 대해 평가하였다. 그 결과, 한국어의 경우에도 일반적으로 영어의 경우와 유사한 경향성을 보이는 것을 확인하였으며, 이에 더하여 다음과 같은 새로운 사실을 관측하였다. 첫째, 사용한 비지도 대조 학습 방법 모두에서 KLUE-BERT가 KoBERT, KR-BERT보다 더 안정적이고 나은 성능을 보였다. 둘째, ConSERT에서 소개하는 여러 데이터 증강 방법 중 token shuffling 방법이 전반적으로 높은 성능을 보였다. 셋째, 두 가지 비지도 대조 학습 방법 모두 검증 데이터로 활용한 KLUE-STS 학습 데이터에 대해 성능이 과적합되는 현상을 발견하였다. 결론적으로, 본 연구에서는 한국어 문장 표현 또한 영어의 경우와 마찬가지로 비지도 대조 학습의 적용을 통해 그 성능을 개선할 수 있음을 검증하였으며, 이와 같은 결과가 향후 한국어 문장 표현 연구 발전에 초석이 되기를 기대한다.

• Journal of the Korean earth science society
• /
• v.29 no.5
• /
• pp.396-407
• /
• 2008

Hydrogeologic properties of a well field around middle mountainous areas in Pyosun, Jeju volcanic island were examined based on water level monitoring, geologic logging and pumping test data. Due to the alternating basaltic layers with varying permeability in the subsurface, it is difficult to analyze the hydraulic responses to artificial pumping and/or natural precipitation. The least permeable layer, detrital materials with clay, is found at a depth of 200 m below surface, but it is not an upper confining bed for lower main aquifer. Nevertheless, this layer may serve as a natural barrier to vertical percolation and to contaminant migration. Water levels of the production wells are dominantly affected by pumping frequently, while those of the remote observation wells are controlled by ambient precipitation. Results of pumping tests revealed a possible existence of horizontal anisotropy of transmissivity. However, some results of this study include inherent limitations enforced by field conditions such as the consistent of groundwater production and the set of time periods for the cessation of the pumping prior to pumping tests.

• Geomechanics and Engineering
• /
• v.31 no.3
• /
• pp.291-304
• /
• 2022

Maximum shear modulus (G_max or G₀) is an important soil property useful for many engineering applications, such as the analysis of soil-structure interactions, soil stability, liquefaction evaluation, ground deformation and performance of seismic design. In the current study, bender element (BE) tests are used to evaluate the effect of the void ratio, effective confining pressure, grading characteristics (D₅₀, C_u and C_c), anisotropic consolidation and initial fabric anisotropy produced during specimen preparation on the G_max of sand-gravel mixtures. Based on the tests results, an empirical equation is proposed to predict G_max in granular soils, evaluated by the experimental data. The artificial neural network (ANN) and Adaptive Neuro Fuzzy Inference System (ANFIS) models were also applied. Coefficient of determination (R²) and Root Mean Square Error (RMSE) between predicted and measured values of G_max were calculated for the empirical equation, ANN and ANFIS. The results indicate that all methods accuracy is high; however, ANFIS achieves the highest accuracy amongst the presented methods.

• Tunnel and Underground Space
• /
• v.26 no.6
• /
• pp.516-523
• /
• 2016

Roughness of a joint surface is one of the most important parameters that affects the mechanical and hydraulic behavior of rock mass. Therefore, various studies on making constitutive model and/or roughness quantification have been conducted in experimental and empirical manners. Advances in recent 3D printing technology can be utilized to generate a joint surface with a specific roughness. In this study, a reliable technique to generate a rough joint surface was introduced and its quantitative assessment was made. Random midpoint displacement method was applied to generate a joint surface and the distribution of $Z_2$ was investigated to assess its roughness. As a result, a certain roughness can be embodied by controlling input parameters and furthermore it was able to generate a joint surface with specific roughness anisotropy.