• 비파괴검사학회지
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• 제36권2호
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• pp.149-154
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• 2016

The use of nonlinear ultrasonics wave has been accepted as a promising tool for monitoring material states related to microstructural changes, as it has improved sensitivity compared to conventional non-destructive testing approaches. In this paper, third harmonic generation of shear horizontal guided waves propagating in an isotropic plate is investigated using the perturbation method and modal analysis approach. An experimental procedure is proposed to detect the third harmonics of shear horizontal guided waves by electromagnetic transducers. The strongly nonlinear response of shear horizontal guided waves is measured. The accumulative growth of relative acoustic nonlinear response with an increase of propagation distance is detected in this investigation. The experimental results agree with the theoretical prediction, and thus providing another indication of the feasibility of using higher harmonic generation of electromagnetic shear horizontal guided waves for material characterization.

• Structural Engineering and Mechanics
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• 제19권5호
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• pp.535-550
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• 2005

The non-linear static and dynamic response of doubly curved thin isotropic shells has been studied for the step and sinusoidal loadings. Dynamic analogues Von Karman-Donnel type shell equations are used. Clamped immovable and simply supported immovable boundary conditions are considered. The governing nonlinear partial differential equations of the shell are discretized in space and time domains using the harmonic differential quadrature (HDQ) and finite differences (FD) methods, respectively. The accuracy of the proposed HDQ-FD coupled methodology is demonstrated by the numerical examples. Numerical examples demonstrate the satisfactory accuracy, efficiency and versatility of the presented approach.

• Structural Engineering and Mechanics
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• 제35권3호
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• pp.365-377
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• 2010

In the present article, effect of non-uniform excitation due to spatially variation of seismic input on nonlinear response of concrete gravity dams is considered. The reservoir is assumed compressible. Isotropic damage mechanics approach is used to model static and dynamic nonlinear behavior of mass concrete in 2D space. The validity of utilized nonlinear model is considered using available theoretical results under static and dynamic conditions. The tallest monolith of Pine Flat dam is selected as a case study. Two cases are analyzed for considering the effect of limited wave propagation velocity on seismic behavior of the dam-reservoir system in which travelling velocities are chosen as 2000 m/s and infinity. It is found that tensile damage in neck and toe regions and also, in the vicinity of the base increase when the system is excited non-uniformly.

• 한국군사과학기술학회지
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• 제1권1호
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• pp.114-127
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• 1998

A user friendly computer code(EMCOMST; Electro-Magnetic response for COMposite STructures) was developed which provides with computations of the response characteristics such as reflectance and transmittance to the incident wave angles, frequencies, composite thicknesses, ply orientations, and types of backplate as the linearly polarized transverse electro-magnetic wave is emitted to the advanced composite structures. In this investigation were reviewed the electromagnetic characteristics of the continuous orthotropic fiber-reinforced organic matrix composites with or without ferrite fillers, which are actively applied to low-weight and high-strength aircraft structures. Also were calculated the response of the three layered compound structures which have appropriately stacked above-mentioned materials as transmitting layer, absorbing layer, reflection layer, respectively under the specific thickness constraints for mechanical strength design requirements. For the composite structures presented in this study, minimum reflectance value less than -5㏈ can be obtained in the frequency range of 4 to 12 ㎓. In addition, analysis of structures attached isotropic radar absorbing materials(RAM) is facilitated by putting the material properties in the material input card entries adequately.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2002년도 International Meeting on Information Display
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• pp.498-499
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• 2002

In In order to develop liquid crystal mixtures of high response time and high nematic-isotropic transition temperature ($T_{NI}$) for LCD-TV application, novel liquid crystal molecules with a fluoro-isothiocyanate moiety were synthesized. They showed remarkably high $T_{NI}$ over 200 $^{\circ}C$, wide mesophase range of 170 $^{\circ}C$, high dielectric anisotropy of 14 and high optical anisotropy of 0.19. New LC Mixtures of the high $T_{NI}$ ($85{\sim}100 ^{\circ}C$) and fast response time ($8{\sim}10ms$) were blended with the novel fluoro-isothiocyanate containing LC molecules, phenylcyclohexanes, bicyclohexanes and ester compounds. It was also studied on optimum pitch of liquid crystal for high speed twisted nematic LCD-TV applicaton. The LC mixtures show a fast speed of the below one frame rate in real 17" TV panel.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2002년도 International Meeting on Information Display
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• pp.413-414
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• 2002

In In order to develop liquid crystal mixtures of high response time and high nematic-isotropic transition temperature ($T_{NI}$) for LCD-TV application, novel liquid crystal molecules with a fluoroisothiocyanate moiety were synthesized. They showed remarkably high $T_{NI}$ over 200 $^{\circ}C$, wide mesophase range of 170 $^{\circ}C$, high dielectric anisotropy of 14 and high optical anisotropy of 0.19. New LC Mixtures of the high $T_{NI}$ (85${\sim}$100 $^{\circ}C$) and fast response time (8${\sim}$10ms) were blended with the novel fluoroisothiocyanate containing LC molecules, phenylcyclohexanes, bicyclohexanes and ester compounds. It was also studied on optimum pitch of liquid crystal for high speed twisted nematic LCD-TV applicaton. The LC mixtures show a fast speed of the below one frame rate in real 17" TV panel.

• 대한조선학회논문집
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• 제46권2호
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• pp.155-164
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• 2009

In this paper, a spectral finite element method for a rectangular sandwich plate with viscoelastic core having the Levy-type boundary conditions has been plated. The sandwich plate consists of two isotropic and elastic face plates with a surfaced-bonded viscoelastic core. For the analysis, the in-plane and transverse energy in the face plates and only shear energy in the core are considered, respectively. To account for the frequency dependent complex shear modulus of the viscoelastic core, the Golla-Hughes-McTavish model is adopted. To evaluate the validity and accuracy of the proposed method, the frequency response function and dynamic responses of the sandwich plate with all edges simply supported subject to an impact load are calculated and compared with those calculated by a finite element method. Though these calculations, it is confirmed that the proposed method is very reliable and efficient one for vibration analysis of a rectangular sandwich plate with viscoelastic core having the Levy-type boundary conditions.

• Steel and Composite Structures
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• 제29권5호
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• pp.569-578
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• 2018

This paper aims to investigate the transient vibration behavior of functionally graded carbon nanotube (FG-CNT) reinforced nanocomposite plate resting on Pasternak foundation under pulse excitation. The plate is considered to be composed of matrix material and multi-walled carbon nanotubes (MWCNTs) with distribution as per the functional grading concept. The functionally graded distribution patterns in nanocomposite plate are explained more appropriately with the layer-wise variation of carbon nanotubes weight fraction in the thickness coordinate. The layers are stacked up in such a way that it yields uniform and three other types of distribution patterns. The effective material properties of each layer in nanocomposite plate are obtained by modified Halpin-Tsai model and rule of mixtures. The governing equations of an illustrative case of simply-supported nanocomposite plate resting on the Pasternak foundation are derived from third order shear deformation theory and Navier's solution technique. A converge transient response of nanocompiste plate under uniformly distributed load with triangular pulse is obtained by varying number of layer in thickness direction. The validity and accuracy of the present model is also checked by comparing the results with those available in literature for isotropic case. Then, numerical examples are presented to highlight the effects of distribution patterns, foundation stiffness, carbon nanotube parameters and plate aspect ratio on the central deflection response. The results are extended with the consideration of proportional damping in the system and found that nanocomposite plate with distribution III have minimum settling time as compared to the other distributions.

• Journal of Radiation Protection and Research
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• 제36권1호
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• pp.44-51
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• 2011

원자력발전소, 의료용 가속기 등 고선량 지역 및 능동형 열중성자 검출기를 사용하기 힘든 환경에서는 방사화 포일 기반 보너구 스펙트로메터를 사용하여 중성자 에너지 스펙트럼 측정을 수행한다. 중성자 방사화 포일을 보너구의 열중성자 검출기로 사용하는 경우, 중성자 방사화 포일의 위치 변동에 따른 보너구 반응도의 변화 및 중성자 방사화 포일의 질량과 반응도 사이의 상관관계 등 특성연구가 선행되어야만 한다. 본 연구에서는 MCNPX 모사계산을 통하여 중성자 방사화 포일 면에 수직입사하는 경우 중성자 방사화 포일의 위치 의존성이 크다는 사실과 중성자 방사화 포일의 질량과 반응도 사이에 선형관계가 없음을 알 수 있었다. 본 연구를 통하여 중성자 방사화 포일 기반 보너구의 반응함수 계산 방법 및 중성자 방사화 포일 위치 및 질량 차이에 따른 반응도 변화를 연구함으로써 중성자 방사화 포일 기반 보너구의 반응함수 결정방법을 확립하였다. 본 연구결과를 바탕으로 보너구 반응함수를 계산하여 추후 중성자 방사화 포일 기반 보너구 스펙트로메트리에 적용할 예정이다.

• 한국구조물진단유지관리공학회 논문집
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• 제22권5호
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• pp.23-30
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• 2018

최근 들어 건물의 내진 및 내풍 성능을 향상시키기 위하여 감쇠구조에 대한 관심이 높아지고 있다. 감쇠장치 중 저렴한 비용과 높은 에너지소산능력을 발휘하며, 설치와 유지관리가 용이하다는 장점이 있어 강재이력형 감쇠장치를 이용한 수동형 감쇠구조시스템이 널리 사용되고 있다. 본 논문에서는 라멘구조 또는 무량판 구조에 적합한 계단 설치형 카고메 감쇠시스템(SKDS)을 제안하고자 하며, 제안된 감쇠시스템의 지진응답 개선효과에 대하여 해석적으로 검토하고자 한다. 비선형 동적해석결과 최대응답변위, 최대응답가속도 및 밑면전단력 감소로 살펴볼 때 내진구조와 비교하여 더 향상된 거동이 기대된다는 점에서 SKDS의 효과를 확인할 수 있었다.