• Journal of the Korean GEO-environmental Society
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• v.12 no.1
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• pp.27-33
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• 2011

In general, the shear strength of a clay specimen under the direct shear test and the triaxial compression test increases with an increase in the shear rate. This study investigates the effects of shear rate and silt content on the stress-strain behavior of remolded Gwangyang clay, by changing the shear rate and the silt content. Based on the results of the triaxial compression tests, the equi-strain line of remolded Gwangyang clay shows initially positive slope and then becomes flat at certain strain level. As the strain level where the equistrain becomes flat is different depending on the soil with different silt contents, this can be considered as the inherent property of soil.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.6
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• pp.607-614
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• 2015

In this research, the structural analysis and safety evaluation for Sungnyemun -No.1 national treasure of Korea- was performed. Roof loads were calculated in detail, and structural analysis model was constructed using Midas Gen ver.820. Static structural analysis under vertical loads was performed and safety of main structural members and serviceability of main horizontal members were evaluated. To evaluate dynamic characteristics of Sungnyemun, both field measurements by impact hammer test and eigenvalue analysis by structural analysis software were performed and the results were compared. Sungnyemun showed rooms in their structural capacity.

• Journal of the Earthquake Engineering Society of Korea
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• v.5 no.4
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• pp.27-38
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• 2001

A mechanical lumped parameter model is proposed for the dynamic modeling of a semi-infinite reservoir. A semi-analytic transmitting boundary is derived for a semi-infinite 2-D reservoir of constant depth. The characteristics of the solution are examined in both frequency and time domains. Mass, damping and spring coefficients of the mechanical model are obtained to preserve the major features of the solution such as eigenfrequencies and the shapes of Bessel functions that appear as kernels in the convolution integrals. The lumped parameter model in its final form consists of two masses, a spring and two dampers for each eigenfrequency. Application examples demonstrated that the new lumped parameter model could be used for the time domain analysis of dam-reservoir systems.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.4
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• pp.64-69
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• 2002

Dynamic analysis of laminated beams with a embedded damping layer under tension or compression axial load is investigated. Improved Layer-Wise Zig-Zag Beam Theory and Interdependent Kinematic Relation using the governing equations of motion are incorporated to model the laminated beams with a damping layer and a corresponding beam zig-zag finite element is developed. Flexural frequencies and modal loss factors under tension or compression axial load are calculated based on Complex Eigenvalue Method. The effects of the axial tension and compression load on the frequencies and loss factors are discussed.

• Proceedings of the Korea Water Resources Association Conference
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• 2006.05a
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• pp.1732-1736
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• 2006

여수로는 월류시 한계류 상태와 고유속의 사류상태가 복합적으로 일어나는 복잡한 흐름형태를 가지고 있어 여수로의 단면설계시 수리적인면뿐만 아니라 구조적인 측면에서도 안정해야 하며 경제성이 고려되어야 한다. 그래서 고유속의 흐름을 갖는 여수로에 축소부를 고려할 경우 충격파에 의한 수위상승과 하류의 흐름 교란 등 수리학적인 불안정이 발생하기 때문에 설계시 경제적인 장점이 있음에도 불구하고 단면축소부를 고려하여 여수로를 설계하는 것은 현실적으로 많은 어려움이 있다. 본 연구에서는 단면축소를 고려한 여수로 설계를 위하여 3차원 수치모형인 Flow-3D를 이용하여 충격파로 인하여 발생하는 교차파 저감을 모의하기 위하여 수치실험을 실시하였다. 교차파 저감을 위해 축소부내에서 교차파가 발생하도록 축소부의 각도는 유입흐름 특성을 고려하여 적정하게 설정하였다. 수치실험결과 축소부의 각도가 작을수록 첫번째 교차파의 수위는 크게 발생하지 않으나 단면축소후 교차파가 하류로 전파되어 불안정한 흐름이 연속적으로 발생하고, 과대하게 설정할 경우 첫번째 발생하는 교차파에 의해 중앙부의 수위가 크게 상승하는 결과를 보였다. 또한 본 연구에서는 축소부단면내 회절판(diffractor) 설치전 후의 수리학적 거동을 모의하여 회절판의 흐름개선 효과를 검증하였다.

• ETRI Journal
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• v.13 no.2
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• pp.42-53
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• 1991

고유전율 적충세라믹 커패시터 소재인 $BaTiO_3$ 자기물은 일반적으로 큐리오도인 약 $120^{\circ}C$부근에서 유전율이 최고 약 10,000정도로 증가한 다음 급격히 감소하므로 적절한 이동체를 첨가하여 큐리온도를 상온으로 이동시켜 상온에서 최대 유전율을 이용하여야 한다. 그리고$BaTiO_3$ 자기물은 $1300^{\circ}C$이상의 고온소결시 고가인 Pd전극이 요구된다. 그러나 자기물의 소결온도를 저온화화면 저가의 Ag합금으로 전극재료를 대체할 수 있다. 본 연구에서는 이동제로서 $CaSnO_3$ 를 이용하여 큐리온도를 상온으로 이동시켰다. 또한 소결온도를 저온화하기 위하여 $BaTiO_3$ 세라믹에 여러가지 산화물을 첨가하여 소결현상을 살펴보았다. 실험결과 첨가제를 넣지 않은 경우 소결온도는 $1350^{\circ}C$의 고온이 필요한 반면, $CuO,B_2O_3$는 $1050^{\circ}C$의 낮은 온도에서도 치밀화와 입도성장이 잘 일어났다. 특히 $B_2$$O_3$ 를 첨가한 경우는 $1250^{\circ}C$이상에서 소결할 때 절연저항이 낮아 유전손실이 큰 문제점을 보였지만, 최대 유전율이 11,000 정도로 높고, 양호한 유전율의 온도변화 특성을 나타내어 우수한 고유전율 소재의 첨가제로 응용될 가능성을 보였다

• Journal of the Computational Structural Engineering Institute of Korea
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• v.19 no.4 s.74
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• pp.441-447
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• 2006

This paper deals with the application of the numerical differentiation in the structural analyses. Derivative values of the geometry of structure are definitely needed for analysing the structural behavior. In this study, free vibration problems of arches are chosen for verifying the numerical differential technique in the structural analyses. The curvature parameters composed with the derivatives of arch geometry obtained herein are quite agreed with those of analytical method. Also, natural frequencies with curvature parameters obtained by using the forward fifth polynomial method are quite agreed with those in the literature. The numerical differentiation technique can be practically utilized in the structural analyses.

• Computational Structural Engineering
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• v.11 no.1
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• pp.227-235
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• 1998

A method of calculating the natural frequency corresponding to the first mode of vibration of beams and tower structures, with irregular cross-sections and with arbitrary boundary conditions was developed and reported by D. H. Kim in 1974. This method has been developed for two-dimensional problems including the laminated composite plates and was proved to be very effective for the plates with arbitrary boundary conditions and irregular sections. In this paper, the result of application of this method to the building slabs with passive and active control devices is presented. Finite difference method is used to obtain the deflection influence surfaces needed for this vibration analysis in this paper. The influence of the modulus of the foundation on the natural frequency is thoroughly studied.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.4B
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• pp.377-384
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• 2009

In order to reduce computing time significantly for a large matrix in EFEM of linear waves propagation over ripple beds, each of which is approximated to a multi-step topography, a partition method is presented to calculate reflection coefficients. By use of 10 evanescent modes in the model, the most accurate numerical solutions have been obtained up to date, which show different behaviors of computed reflection coefficient in some cases against the existing results. Both computing time and memory of the present partition model for solving a large matrix are still so much demanding that it is needed to develop an efficient method.

• Journal of the Earthquake Engineering Society of Korea
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• v.16 no.3
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• pp.23-33
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• 2012

Dynamic response measurements from natural excitation were carried out for three 18-story office buildings to determine their inherent properties. The beam-column frame system was adopted as a typical structural form, but a core wall was added to resist the lateral force more effectively, resulting in a mixed configuration. To extract modal parameters such as natural frequencies, mode shapes and damping ratios from a series of vibration records at each floor, the most advanced operational system identification methods based on frequency- and time-domain like FDD, pLSCF and SSI were applied. Extracted frequencies and mode shapes from the different identification methods showed a greater consistency for three buildings, however the three lower frequencies extracted were 1.2 to 1.7 times as stiff as those obtained using the initial FE models. Comparing the extracted fundamental periods with those estimated from the code equations and FE analysis, the FE analysis results showed the most flexible behavior, and the most simple equation that considers the building height as the only parameter correlated fairly well with test results. It is recognized that such a discrepancy arises from the fact that the present tests exclude the stiffness decreasing factors like concrete cracking, while the FE models ignore the stiffness increasing factors, such as the contribution of non-structural elements and the actual material properties used.