• Journal of the Korean Wood Science and Technology
• /
• 제27권3호
• /
• pp.1-6
• /
• 1999

복잡한 구조를 지니는 바이올린 동체 설계 및 음질 평가률 위한 기본정보를 마련코자 바이올린 주요소재인 European spruce 및 European maple의 강제진동(强制振動) 의한 선형(線型) 휨진동(振動) 모드를 조사하고 소재밀도 및 절삭방향에 따른 진동모드별 공진(共振)주파수 변위를 분석하였다. 연구 결과 저비중재임에도 불구하고 spruce가 maple에 비해 더 높은 공진(共振) 주파수률 지님으로써 보다 우수한 음향특성을 지니는 것으로 나타났다. 또 spruce의 경우 접선방향으로 절삭된 판목재에 비해 방사방향 절삭된 정목재의 주파수 편차가 작아 균일한 음질을 위해서는 전반(前板)주요부품 가공시 정목판재를 사용하는 것이 바람직한 것으로 판단되었다. 그리고 두 수종 공히 소재밀도와 공진(共振)주파수간의 관계는 양의 상관관계를 나타냈으며, 절삭방향별로는 정목재의 상관계수가 판목재에 비해 놓게 나타났다.

• Bulletin of the Korean Chemical Society
• /
• 제25권9호
• /
• pp.1314-1320
• /
• 2004

The adsorption and configuration of CO molecules adsorbed on W (110) and W (100) surfaces have been calculated by the atomic superposition and electron delocalization molecular orbital (ASED-MO) method. Referred to as the ASED-MO method, it has been used in the present study to calculate the geometries, binding energies, vibrational frequencies, orbital energies, reduced overlap population (ROP), and charges. From these results adsorption properties of ${\alpha}$-state and ${\beta}$-state were deduced. The calculated binding energies are in good agreement with the experimental result. On the W (110), the calculated average binding energies are 2.56 eV for the end-on configuration and 3.20 eV for the lying-down configuration. Calculated vibrational frequency is 1927 $cm^{-1}$ at a 1-fold site and 1161 $cm^{-1}$ at a long-bridge (2) site. These results are in reasonable agreement with experimental values. On the W(100) surface, calculated average binding energies of the end-on and the lying-down are 2.54 eV and 4.02 eV respectively. The differences for binding energy and configuration on the surfaces are explained on the basis of surface-atom coordination and atom-atom spacing. In the favored lyingdown CO configuration on the W(110) and W(100) surfaces, 4 ${\sigma}$ and 1 ${\pi}$ donation interactions, coupled with the familiar 5 ${\sigma}$ donation to the surfaces and back-donations to the CO 2 ${\pi}^{\ast}$ orbital, are responsible for adsorption to the surface.

• 대한화학회지
• /
• 제63권3호
• /
• pp.151-159
• /
• 2019

본 연구는 밀도 범함수 이론(DFT) 가운데 하나인 B3LYP 방법을 $6-31G^{**}$, cc-pVDZ, cc-pVTZ의 바탕함수 집합(basis set)과 함께 사용하여 전자 공여성 분자(D)로 카바졸(carbazol) 그리고 전자 구인성 분자(A)로 dicyanobenzene, diphenyl sulfone, benzonitrile 등의 조합으로 이루어진 열 활성화 지연형광(TADF) 후보 물질에 대하여 분자구조를 최적화하고 진동주파수를 계산하였다. 또한 최적화된 분자 구조에 대하여 HOMO와 LUMO 에너지 차이를 계산하였으며, 나아가 시간 의존 밀도 범함수 이론(TD-DFT)을 사용하여 분자의 최대 흡수 및 방출 파장(${\lambda}_{max}$) 그리고 단일항과 삼중항 들뜬 상태의 에너지 차이(${\Delta}E_{ST}$) 등을 계산하여 열 활성 지연형광(TADF) 소재로서의 가능성을 예측하였다.

• Steel and Composite Structures
• /
• 제51권1호
• /
• pp.73-91
• /
• 2024

This paper has focused on presenting vibration analysis of trapezoidal sandwich plates with a damaged core and FG wavy CNT-reinforced face sheets. A damage model is introduced to provide an analytical description of an irreversible rheological process that causes the decay of the mechanical properties, in terms of engineering constants. An isotropic damage is considered for the core of the sandwich structure. The classical theory concerning the mechanical efficiency of a matrix embedding finite length fibers has been modified by introducing the tube-to-tube random contact, which explicitly accounts for the progressive reduction of the tubes' effective aspect ratio as the filler content increases. The First-order shear deformation theory of plate is utilized to establish governing partial differential equations and boundary conditions for the trapezoidal plate. The governing equations together with related boundary conditions are discretized using a mapping-generalized differential quadrature (GDQ) method in spatial domain. Then natural frequencies of the trapezoidal sandwich plates are obtained using GDQ method. Validity of the current study is evaluated by comparing its numerical results with those available in the literature. After demonstrating the convergence and accuracy of the method, different parametric studies for laminated trapezoidal structure including carbon nanotubes waviness (0≤w≤1), CNT aspect ratio (0≤AR≤4000), face sheet to core thickness ratio (0.1 ≤ ${\frac{h_f}{h_c}}$ ≤ 0.5), trapezoidal side angles (30° ≤ α, β ≤ 90°) and damaged parameter (0 ≤ D < 1) are carried out. It is explicated that the damaged core and weight fraction, carbon nanotubes (CNTs) waviness and CNT aspect ratio can significantly affect the vibrational behavior of the sandwich structure. Results show that by increasing the values of waviness index (w), normalized natural frequency of the structure decreases, and the straight CNT (w=0) gives the highest frequency. For an overall comprehension on vibration of laminated trapezoidal plates, some selected vibration mode shapes were graphically represented in this study.

• 대한화학회지
• /
• 제40권4호
• /
• pp.219-228
• /
• 1996

ab initio 방법을 이용하여 hexahydroxbenzene triscarbonate($C_9O_9$)와 이와 유사한 화합물($C_9O_9,C_9O_6S_3,C_9O_3S_9$)들의 평형구조(equilibrium geometry)와 에너지를 HF와 MP2 level에서 구하였다. 계산결과 이들 화합물은 모드 $C_{3v}$ bowl형 구조보다는 $D_{3h}$ 평면형구조가 더 안정함을 알 수 있었다. $HF/3-21G^*$ level에서 조화진동수(harmonic vibrational frequency)를 계산하였고 각각의 진동방식(vibrational mode)을 비교, 분석하였으며, $HF/63G^*$ level에서 구한 Mulliken population과 natural population을 이용하여 화합물들의 결합특성에 대하여 연구하였다. 또한 이들 화합물들의 열분해 의해서 생성되는 $C_6O_6$과 $C_6S_6$의 전자구조와 결합특성에 대한 연구를 HF와 MP2 level에서 하였다. 그리고 화합물들이 열분해하여 $C_6O_6,\;C_6S_6$, CO, 그리고 CS로 분리될 때의 필요한 에너지를 $HF/3-21G^*$ level에서 계산하여 열분해에 필요한 대략적인 에너지 장벽을 예상하여 보았다.

• 한국소음진동공학회논문집
• /
• 제20권5호
• /
• pp.492-501
• /
• 2010

Equations of motion of thin-walled composite H-type cross-section beams incorporating a number of nonclassical effects of transverse shear and primary and secondary warping, and anisotropy of constituent materials are derived. The vibrational characteristics of a composite thin-walled beam exhibiting the circumferentially asymmetric stiffness system(CAS) and the circumferentially uniform stiffness system(CUS) are exploited in connection with the bending-transverse shear coupling and the bending-twist coupling resulting from directional properties of fiber reinforced composite materials.

• Structural Engineering and Mechanics
• /
• 제67권5호
• /
• pp.517-525
• /
• 2018

In this study, we investigate the vibration of single-walled carbon nanotubes embedded in a polymeric matrix using nonlocal elasticity theories with account arbitrary boundary conditions effects. A Winkler type elastic foundation is employed to model the interaction of nanobeam and the surrounding elastic medium. Influence of all parameters such as nonlocal small-scale effects, Winkler modulus parameter, vibration mode and aspect ratio of nanobeam on the vibration frequency are analyzed and discussed. The mechanical properties of carbon nanotubes and polymer matrix are treated and an analytical solution is derived using the governing equations of the nonlocal Euler-Bernoulli beam models. Solutions have been compared with those obtained in the literature and The results obtained show that the non-dimensional natural frequency is significantly affected by the small-scale coefficient, the vibrational mode number and the elastic medium.

• Smart Structures and Systems
• /
• 제25권4호
• /
• pp.393-399
• /
• 2020

In this paper, the design method and experimental validation for the two-degree-of-freedom (2DOF) electromagnetic energy harvester are presented. The harvester consists of the rigid body suspended by four tension springs and electromagnetic transducers. Once the two resonant frequencies and the mass properties are specified, both the constant and the positions for the springs can be determined in the closed form. The designed harvester can locate two resonant peaks close to each other and forms the extended frequency bandwidth for power harvesting. Halbach magnet array is also introduced to enhance the output power. In the experiment, two resonant frequencies are measured at 34.9 and 37.6 Hz and the frequency bandwidth improves to 5 Hz at the voltage level of 207.9 mV. The normalized peak power of 4.587 mW/G² is obtained at the optimal load resistor of 367 Ω.

• Steel and Composite Structures
• /
• 제22권2호
• /
• pp.277-299
• /
• 2016

In this paper, free vibration, forced vibration, resonance and stress wave propagation behavior in nanocomposite plates reinforced by wavy carbon nanotube (CNT) are studied by a mesh-free method based on first order shear deformation theory (FSDT). The plates are resting on Winkler-Pasternak elastic foundation and subjected to periodic or impact loading. The distributions of CNTs are considered functionally graded (FG) or uniform along the thickness and their mechanical properties are estimated by an extended rule of mixture. In the mesh-free analysis, moving least squares (MLS) shape functions are used for approximation of displacement field in the weak form of motion equation and the transformation method is used for imposition of essential boundary conditions. Effects of CNT distribution, volume fraction, aspect ratio and waviness, and also effects of elastic foundation coefficients, plate thickness and time depended loading are examined on the vibrational and stresses wave propagation responses of the nanocomposite plates reinforced by wavy CNT.

• Steel and Composite Structures
• /
• 제35권6호
• /
• pp.765-777
• /
• 2020

In the context of classic conical shell formulation, nonlinear forced vibration analysis of truncated conical shells and annular plates made of multi-scale epoxy/CNT/fiberglass composites has been presented. The composite material is reinforced by carbon nanotube (CNT) and also fiberglass for which the material properties are defined according to a 3D Mori-Tanaka micromechanical scheme. By utilizing the Jacobi elliptic functions, the frequency-deflection curves of truncated conical shells and annular plates related to their forced vibrations have been derived. The main focus is to study the influences of CNT amount, fiberglass volume, open angle, fiber angle, truncated distance and force magnitude on forced vibrational behaviors of multi-scale truncated conical shells and annular plates.