• Computational Structural Engineering
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• v.10 no.1
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• pp.149-158
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• 1997

This paper presents the illustration of application under attached point mass to the special orthotropic plates with a pair of opposite edges simply supported and the other pair of opposite edges free. Design engineers need to calculate the natural frequencies of such elements but obtaining exact solution to such problems is very much difficult. Pretlove reported a method of analysis of beams with attached masses using the concept of effective mass. This method, however, is useful only for certain simple types of beam. Therefore, considering the method has been developed by D. H. Kim(1974) is simple, accurate, and very effective for the plates with arbitrary boundary conditions and irregular sections, this paper calculates the natural frequencies of composite laminated plate under attached point mass/masses.

• Journal of the Korean Geotechnical Society
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• v.17 no.5
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• pp.107-114
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• 2001

비검측공 시험법을 현장타설말뚝의 건전도 평가 목적으로 적용함에 있어서 시험법의 적용성을 향상시키기 위한 연구가 진행되어 오고 있다. 본 논문에서는 같은 맥락에서 수행되어 온 일련의 해석적 연구 결과 중 시험법의 해상도에 관한 문제와 말뚝 주변 및 선단지반의 강성이 비검측공 시험결과에 미치는 영향에 관해 다루었다. 본 논문에서 수행한 연구결과에 의하면 충격응답기법의 해상도를 평가하기 위해서는 말뚝재료에 대한 지반의 강성비($V_{s}$ /$V_{c}$)와 말뚝의 길이에 대한 직경의 비(L/D)에 의존하는 기존 평가기준에 부가하여 말뚝의 상대적인 체적변화가 필히 고려되어야 한다는 결론을 얻었다. 한편, 말뚝이 수평으로 층이 진 주변 지반을 통과하여 말뚝선단부를 지지하는 지반(선단지반)에 근입되거나 지지되는 경우에 말뚝의 자유단 혹은 고정단 경계 조건은 주변 지반과 선단 지반의 강성비와 선단 지반에 대한 말뚝의 근입깊이에 따라 변화한다는 사실을 규명하였다. 말뚝의 건전도 평가 시에 사용하게 되는 말뚝의 공진주파수가 이들 조건에 따라 변화하므로 결과적으로 시험결과분석에 있어서 이들 영향이 필히 고려되어야 한다는 결론을 얻었다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.19 no.4 s.74
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• pp.399-406
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• 2006

The natural frequencies of Al square plates with a brass inclusion were analyzed by the rule of mixtures. The rule of mixtures is the method to derive natural frequency mutiplying effective inplane wane speed and nondimensional frequency parameters. Numerical models were Al square plates with an inclusion with cantilever type, 2 clamped edge-2 free edge type, 3 clamped edge-1 free edge type and fully clamped edge type. In cantilever type plates, 2 clamped edge-2 free edge type plates and 3 clamped edge-1 free edge plates with an inclusion, good agreement within 10% obtained from rule of mixtures' results and numerical analysis results within inclusion area ratio 1/9. It was found that the natural frequencies of the cantilever type, 2 clamped edge-2 free edge type and 3 clamped edge-1 free edge type plates with an inclusion decrease as the size of inclusion increases when inclusion is located center of plates. And when the density of inclusion is less than the plates, natural frequency of plates with an inclusion increases as the size of inclusion increases.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.6 s.123
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• pp.531-538
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• 2007

A new method for free nitration analysis using series functions is proposed to obtain the eigenvalues of arbitrarily shaped, polygonal plates with clamped edges. Since a general solution used in the method satisfies the equation of motion for the transverse vibration of a plate, the method offers very accurate eigenvalues, compared to FEM or BEM results. In addition, the method can minimize the amount of numerical calculation because it has the advantage of not needing to divide the plate of interest. Two case studies show that the proposed method is valid and accurate when the eigenvalues by the proposed method are compared to those by FEM (NASTRAN) or another analytical method.

• Journal of the Korean Geotechnical Society
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• v.18 no.4
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• pp.21-32
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• 2002

Small and full scale model tests were performed to obtain the transient responses of shafts subjected to elastic impact by impact-echo test. Four end conditions of drilled shafts were considered: (1) free, (2) fixed, (3) rock-socketed, and (4) soft bottom. In small scale model tests, mock-up shafts were fabricated to simulate these four drilled shafts using poly-urethane and plastic material. Additionally, skin frictions between shaft and rock were changed to find out the effect of side contact on dynamic responses. All impact responses were tested in the air. Subsequently, full scale model tests were also carried out on concrete shafts that were in free and rock-socketed condition. The end conditions of the drilled shafts could be identified with good reliability by the waveforms from both small and full scale model tests. The results obtained in this study will provide an improved understanding of the impact responses for end conditions, especially for rock-socketed drilled shafts that are frequently designed and built in Korea.

• Journal of the Korean Geotechnical Society
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• v.32 no.9
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• pp.51-62
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• 2016

Parametric studies for various site conditions by using 3d numerical model were carried out in order to estimate dynamic behavior of soil-pile-structure system in dry soil deposits. Proposed model was analyzed in time domain using FLAC3D which is commercial finite difference code to properly simulate nonlinear response of soil under strong earthquake. Mohr-Coulomb criterion was adopted as soil constitutive model. Soil nonlinearity was considered by adopting the hysteretic damping model, and an interface model which can simulate separation and slip between soil and pile was adopted. Simplified continuum modeling was used as boundary condition to reduce analysis time. Also, initial shear modulus and yield depth were appropriately determined for accurate simulation of system's nonlinear behavior. Parametric study was performed by varying weight of superstructure, pile length, pile head fixity, soil relative density with proposed numerical model. From the results of parametric study, it is identified that inertial force induced by superstructure is dominant on dynamic behavior of soil-pile-structure system and effect of kinematic force induced by soil movement was relatively small. Difference in dynamic behavior according to the pile length and pile head fixity was also numerically investigated.

• Proceedings of the KIEE Conference
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• 2006.10a
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• pp.50-52
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• 2006

본 논문은 고성능 다결정 실리콘(Poly-Si) 박막 트랜지스터 (Thin Film Transistor)에서 단일 수직 그레인 경계(Single Perpendlcular Grain Boundary)가 고온 캐리어 스트레스(Hot Carrier Stress) 및 정전류 안정성 평가에서 어떠한 효과를 보이는가에 대해서 살펴보았다. 고온 캐리어 스트레스 하에서($V_G=V_{TH}+1V,\;V_D$ =12V),그레이 경계가 없는 다결정 실리콘 TFT와 비교했을 때 그레인 경계를 가지고 있는 다결정 실리를 TFT는 전기 전도(Electric Conduction)에 작용하는 자유 캐리어(Free Carrier)의 개수가 적기 때문에 상대적으로 더욱 우수한 전기적 특성을 나타낸다. 먼저 1000초 동안 고온 캐리어 스트레스를 가해준 결과 단일 그레인 경계를 가진 다결정 실리콘에서의 트랜스 컨덕턴스(Transconductance)의 이동 정도는 5% 미만으로 확인되었다. 반면에 같은 스트레스 조건 하에서 그레인 경계가 존재하지 않는 다결정 실리콘의 경우에는 그 이동 정도가 약 25%에 달하는 것으로 측정되었다. 다음으로 정전류 스트레스(Constant Current Stress) 인가시, 수직형 그레인 경계가 채널 영역 내에 존재하지 않는 다결정 실리콘 TFT는 드레인 접합 부분의 전계 세기를 비교했을 때, 그레인 경계를 가지고 있는 다결정 실리콘 TFT보다 상대적으로 낮은 원 인 때문에 적게 열화되는(Degraded) 특성을 확인할 수 있었다.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.36 no.2
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• pp.70-79
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• 2024

In this study, we introduce a linear spectral method capable of simulating wave generation and transformation caused by a moving bottom in a 3-dimensional space. The governing equations are linear dynamic free-surface boundary conditions and linear kinematic free-surface boundary conditions, which are solved in Fourier space. Solved velocity potential and free-surface displacement should satisfy continuity equation and kinematic bottom boundary condition. For numerical analysis, a 4th order Runge-Kutta method was utilized to analyze the time integral. The results obtained in Fourier space can be converted into velocity potential and free-surface displacement in a real space using inverse Fourier transform. Regular waves generated by various types of moving bottoms were simulated with the linear spectral method. Additionally, obliquely generated regular waves using specified bottom movements were simulated. The results obtained from the spectral method were compared to analytical solutions, showing good agreement between the two.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.3A
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• pp.181-187
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• 2011

This paper deals with free vibrations of the Timoshenko beam supported by two elastomeric bearings at two far ends. The ordinary differential equation governing free vibrations of such beam is derived, in which both effects of rotatory inertia and shear deformation are included as the Timoshenko beam theory. Also, boundary conditions of the free end are derived based on the Timoshenko beam theory. The ordinary differential equation is solved by the numerical methods for calculating natural frequencies and mode shapes. Both effects of the rotatory inertia and shear deformation on natural frequencies are extensively discussed. Also, relationships between natural frequencies and slenderness ratio, foundation modulus and bearing length are presented. Typical mode shapes of bending moment and shear force as well as deflection are given in figures which show the positions of maximum amplitudes and nodal points.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.31 no.2
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• pp.71-78
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• 2018

This paper presents the assembling of multiple patches based on the single patch isogeometric formulation for the shear deformable shell element given in the previous study. The geometrically exact shell formulation has been accomplished with the shell theory based formulation and the generalized curvilinear coordinate system directly derived from the given NURBS geometry. For the knot elements matching across adjacent surfaces, the zero-th and first parametric continuity conditions are considered and the corresponding coupling constraints are implemented by a master-slave formulation between adjacent patches. The constraints are then enforced by a substitution method for condensation of the slave variables, thereby reducing the model size. Through numerical investigations, the important features of the first parametric continuity condition are confirmed. The performance of the multi-patch shell models is also examined comparing the rate of convergence of response coefficients for the zero and first order continuity conditions and continuity in coupling boundary between two patches is confirmed.