• 한국공작기계학회논문집
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• 제10권1호
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• pp.43-50
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• 2001

Subharmonic resonances of order 1/2 of a continuous rotating shaft with distributed mass are discussed. The restoring force of the shaft exhibits geometric stiffening nonlinearity due to the extension of the shaft center line. It is assumed that a distributed lateral force, such as the gravity, acts on the rotor. The possibility of the occurrence of subharmonic resonances, the shapes of resonance curves, and internal resonance phenomena are investigate.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 제39회 하계학술대회
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• pp.1258-1259
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• 2008

In this paper, the variable tendency of the piezoelectric constant and resonance characteristics of the piezoelectric ceramics due to the electric field is studied. The practical application of piezoelectric ceramics is not only applied in field of small signal. For example, in case of an ultrasonic motor, 120 ${\sim}$ 130Vrms of driving voltage is needed. Therefore, to examine the characteristics of piezoelectric ceramics in large signal contributes to reducing the susceptibility to the multifarious application and securing the ease of the production of control circuit. These contributions may be connected to the expansion of industrial application. We fabricated disk-type piezoelectric ceramic samples by using conventional method and measured the resonance characteristics of these samples under from low to high voltage driving conditions. According to increasing the value of the input voltage, we measured the resonance frequency of the piezoelectric ceramic, and inquired into the cause of these phenomena.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.1767-1772
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• 2008

A microcantilever is a well-known MEMS structure for sensing bio-chemical molecules. When bio-chemical molecules are adsorbed on the microcantilever's surface, resonance frequency shift is generated. There are two issues in this phenomena. The first one is which one between mass change and surface stress change effects is more dominant on the resonance frequency shift. The second one is what will be the performance change when the boundary condition is changed from cantilevers to double clamped beams. We have studied the effect of surface stress change and compared it with that of mass change by using FEM analysis. Furthermore, for microstructures having different boundary conditions, we have studied Q-factor, which determines the detection limit of micro/nano mechanical sensors.

• 정보통신설비학회논문지
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• 제2권1호
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• pp.63-70
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• 2003

공진산란이론은 산란장의 공진현상을 물리적으로 해석해주는 이론으로, 산란장은 공진성분과 비공진성분 즉 배경성분으로 구성되어 있다고 가정한다. 따라서 공진 성분을 산란장으로부터 추출하기 위해서는 정확한 배경성분을 구하는 과정이 필요한데, 본 연구에서는 원통형 유전체와 공동에 의한 산란장으로부터 공진성분을 얻기 위한 배경성분을 제시하고, 수치 계산을 수행하여 타당성을 확인하였다.

• 한국음향학회지
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• 제30권5호
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• pp.249-254
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• 2011

PC의 내장 사운드 카드를 이용하여 음향학 탐구학습을 수행하였다. 사운드 카드는 함수발생기와 오실로스코프에 비해 가격이 저렴하고 학생들의 접근이 용이하다는 장점이 있다. 학생들은 다양한 음향 현상에서 발생하는 소리를 사운드 카드를 이용하여 녹음하고 주파수 스펙트럼을 분석하였다. 소리굽쇠의 맥놀이, Rijke 관에서의 음의 발생, 물을 따를 때에 나는 소리 변화, 소리로 포도주잔 깨기 및 포도주 병마개를 딸 때에 발생하는 소리 등의 현상을 정량적으로 분석하면서 소리의 중첩, 공진 및 정상파에 대한 탐구를 수행하였다.

• 한국자기공명학회논문지
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• 제16권2호
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• pp.111-121
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• 2012

The spin-lattice relaxation times, $T_1$, and spin-spin relaxation times, $T_2$, of the $^{27}Al$ and $^{87}Rb$ nuclei in $RbAl(CrO_4)_2{\cdot}2H_2O$ crystals were investigated. The presence of only one resonance line for the $^{27}Al$ nuclei indicates that the results in a dynamical averaging of the crystal electric field that produces a cubic symmetry field. The changes in the temperature dependence of $T_1$ are related to variations in the symmetry of the octahedra of water molecules surrounding $Al^+$ and $Rb^+$. The $T_1$ values for the $^{27}Al$ and $^{87}Rb$ nuclei are different due to differences in the local environments of these ions. We also compared these $^{27}Al$ and $^{87}Rb$ NMR results with those obtained for $RbAl(CrO_4)_2{\cdot}2H_2O$ crystals. The relaxation mechanisms of $RbAl(XO_4)_2{\cdot}nH_2O$ (X=Cr and S) crystals are characterized by completely different NMR behaviors.

• 한국소음진동공학회논문집
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• 제21권9호
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• pp.813-819
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• 2011

This paper predicted nonlinear dynamic responses of a cantilevered carbon nanotube(CNT) resonator incorporating the electrostatic forces and van der Waals interactions between the CNT cantilever and ground plane. The structural model of CNT includes geometric and inertial nonlinearities to investigate various phenomena of nonlinear responses of the CNT due to the electrostatic excitation. In order to solve this problem, we used Galerkin's approximation and the numerical integration techniques. As a result, the CNT nano-resonator shows the softening effect through saddle-node bifurcation near primary resonance frequency with increasing the applied AC and DC voltages. Also we can predict nonlinear secondary resonances such as superharmonic and subharmonic resonances. The superharmonic resonance of the nano-resonator is influenced by applied AC voltage. The period-doubling bifurcation leads to the subharmonic resonance which occurs when the nano-resonator is actuated by electrostatic forces as parametric excitation.

• Structural Engineering and Mechanics
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• 제75권1호
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• pp.87-100
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• 2020

The present paper investigates the combination resonance behavior of imperfect spiral stiffened functionally graded (SSFG) cylindrical shells with internal and external functionally graded stiffeners under two-term large amplitude excitations. The structure is embedded within a generalized nonlinear viscoelastic foundation, which is composed of a two-parameter Winkler-Pasternak foundation augmented by a Kelvin-Voigt viscoelastic model with a nonlinear cubic stiffness, to account for the vibration hardening/softening phenomena and damping considerations. With regard to classical plate theory of shells, von-Kármán equation and Hook law, the relations of stress-strain are derived for shell and stiffeners. The spiral stiffeners of the cylindrical shell are modeled according to the smeared stiffener technique. According to the Galerkin method, the discretized motion equation is obtained. The combination resonance is obtained by using the multiple scales method. Finally, the influences of the stiffeners angles, foundation type, the nonlinear elastic foundation coefficients, material distribution, and excitation amplitude on the system resonances are investigated comprehensively.

• 한국분무공학회지
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• 제3권4호
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• pp.50-57
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• 1998

The utilization of resonance should be considered to get the maximum effect of ultrasonic to atomize liquid. The ultrasonic generator, transducer, horn, and all attached parts are used to produce the resonance, and specially the characteristics of liquids such as liquid load, property, and etc., for the liquid atomization affinity are considered. In this study, the variable device of liquid load was made and distilled water and city water selected as experimental liquids were sprayed by a twin-fluid spray method and their diameters, distributions, and spray quantum of spray droplets were measured by the light scattering system. And all data were observed, compared and considered relatively. In results, a lot of phenomena of liquid atomization affinity by ultrasonic appeared in accordance with liquid loads, namely head h.

• 동력기계공학회지
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• 제6권4호
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• pp.36-42
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• 2002

In the structures of automobiles and ships which have engines for works, the vibration energies generated by the engines are transferred to dissipation parts through the structures which is welded and bolted with beams and plates. The vibration energies generated by resonance frequencies are the reasons of the resonance phenomena. To solve these problems, up to the present, we have studied to avoid the resonance, and add the higher damping characteristics. However, we need to understand the structural energy flows, to design the structures clearly which have the characteristic of welding. The object of this study is to make differences clear in the characteristics of structures which have some welded part on an homogenous flat plate. In this investigation, we study the flows of structural vibration energy experimently, and then, some knowledge for dynamic structural design is obtained.