• Structural Engineering and Mechanics
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• 제9권5호
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• pp.449-467
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• 2000

The natural frequencies and the corresponding mode shapes of a non-uniform beam carrying multiple point masses are determined by using the analytical-and-numerical-combined method. To confirm the reliability of the last approach, all the presented results are compared with those obtained from the existing literature or the conventional finite element method and close agreement is achieved. For a "uniform" beam, the natural frequencies and mode shapes of the "clamped-hinged" beam are exactly equal to those of the "hinged-clamped" beam so that one eigenvalue equation is available for two boundary conditions, but this is not true for a "non-uniform" beam. To improve this drawback, a simple transformation function ${\varphi}({\xi})=(e+{\xi}{\alpha})^2$ is presented. Where ${\xi}=x/L$ is the ratio of the axial coordinate x to the beam length L, ${\alpha}$ is a taper constant for the non-uniform beam, e=1.0 for "positive" taper and e=1.0+$|{\alpha}|$ for "negative" taper (where $|{\alpha}|$ is the absolute value of ${\alpha}$). Based on the last function, the eigenvalue equation for a non-uniform beam with "positive" taper (with increasingly varying stiffness) is also available for that with "negative" taper (with decreasingly varying stiffness) so that half of the effort may be saved. For the purpose of comparison, the eigenvalue equations for a positively-tapered beam with five types of boundary conditions are derived. Besides, a general expression for the "normal" mode shapes of the non-uniform beam is also presented.

• Composites Research
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• 제12권1호
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• pp.1-10
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• 1999

복합재 적층판의 기계적 특성값 $E_1,\;E_2,\;V_{12},\;G_{12}$을 설계변수로 하는 변수식별을 수행하여 동적 거동을 보다 정확하게 예측할 수 있는 동적 모델을 확보하였다. 간단한 진동실험을 통해 고유진동수를 측정한 후 대상구조물에 대한 고유치의 실험값과 수치해석값 사이의 오차들의 합으로 목적함수를 구성하였다. 목적함수를 최소화하기 위해 최적화 방법으로 conjugate gradient method를 사용하였다. 최적화 과정 중 설계변수를 증감시키기 위해 민감도 해석이 수행된다. 민감도 해석을 통해 변수식별 결과도 설명할 수 있었다. 변수식별 결과의 타당성을 검토하기 위해 식별전후의 모드형상을 비교하였다. 식별된 기계적 특성값을 사용하여 보다 정확하게 복합재 적층판의 고유진동수를 예측할 수 있었다. 결과의 적용을 위해 식별된 기계적 특성값을 사용하여 다른 적층순서를 가진 복합재 적층판의 고유진동수를 예측해 보고 실험결과와 비교해 보았다.

• 한국자동차공학회논문집
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• 제19권3호
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• pp.29-37
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• 2011

The modal characteristics of a compressor wheel of an automotive turbocharger have been investigated using an experimental method based on an acoustic frequency response function, p/f(${\omega}$), where p is sound pressure radiated from a structure, and f is impact force. First, a well-defined annular disc with narrow radial slots was examined to check whether the vibro-acoustic test could precisely determine natural quencies and vibration modes of structures showing that the vibro-acoustic test proposed in this paper was comparable to the conventional modal test with an accelerometer and the numerical analysis. The conventional method has been found to be inappropriate for compressor wheel because of additional mass due to the accelerometer and additional damping from the accelerometer cable alter the dynamic responses of the wheel blades. odal characteristics of the wheel have been defined using vibro-acoustic test and verified with the results from another conventional method using a laser vibrometer. Natural quencies and mode shapes of a turbocharger wheel, which can't be precisely obtained with onventional method, could be defined accurately without the additional effects from sensor and cable. Proposed method can be applied to small structures where conventional sensors and cables could generate troubles.

• 대한조선학회논문집
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• 제50권1호
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• pp.1-7
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• 2013

The high-skewed and/or composite propellers of current interests to reduce the ship vibration and to increase the acoustic performance are likely to be exposed to the unexpected structural problems. One typical example is that the added mass effect on the propellers working in the non-uniform wake field reduces the natural frequency of the propeller leading to the resonance with the low-frequency excitation of the external forces. To avoid this resonance problem during the design stage, the technique of fluid-structure interaction has been developed, but the higher-order effect of the blade geometry deformation is not yet considered in evaluating the added mass effects. In this paper the fluid boundary-value problem is formulated by the potential-based panel method in the inviscid fluid region with the velocity inflow due to the body deformation, and the structural response of the solid body under the hydrodynamic loading is solved by applying the finite element method which implements the 20-node iso-parametric element model. The fluid-structure problem is solved iteratively. A basic fluid-sturcture interaction study is performed with the simple rectangular plates of thin thickness with various planform submerged in the water of infinite extent. The computations show good correlation with the experimental results of Linholm, et al. (1965).

• 한국구조물진단유지관리공학회 논문집
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• 제22권6호
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• pp.148-156
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• 2018

교량 구조물 거동의 건전성 평가는 하중재하-처짐의 정적특성과 충격계수와 고유진동수 등의 동적특성으로 평가하는 것이 일반적이며, 이를 수치해석적 방법으로 비교 분석하는 것이 합리적인 방법이라 할 수 있다. 사용하중에 대한 거동은 탄성영역에서 이루어지므로 실물구조체와 수치해석의 결과는 일체성을 보이지만, 동적특성의 경우 특히, 진동학적 분석에 있어서는 구조물의 기하형상과 사용재료의 이질성에 기인하여 실물 구조체의 결과와 다소 차이를 보인다. 이러한 오차를 수렴시키기 위하여 본 연구는 실물 모형체의 실험결과를 바탕으로 다양한 수치해석적 모델을 제시하고 그 예민도를 분석함으로써, 교량 구조물 평가를 위한 실용적인 모델링 기법을 도출하여 안정적인 예비 해석 결과를 제공하는데 그 목적이 있다. 프리스트레스트 콘크리트 구조물의 긴장재를 환산단면으로 치환한 모델을 기반으로 긴장재의 탄성적 특성을 반영한 모델과 수정된 탄성계수를 적용한 모델의 고유진동수가 실물 모형체의 그것과 가장 유사한 결과를 얻을 수 있었다.

• 대한후두음성언어의학회지
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• 제24권2호
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• pp.107-111
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• 2013

Objectives : We developed two-dimensional (2D) scanning videokyomography to evaluate the mucosal wave of whole vocal cords in real time to overcome the limit of preexisting stroboscopy and line scanning videokymography which could not evaluate it. Methods : We implemented a continuous light source with high brightness, a high-definition CMOS camera, and capture board for saving the data. We created the software program to analyze the image data from the system. The test of the functionality of the 2D scanning videokymography camera was performed in one of the authors (P.H.J 32 years old male). Vocal cord images were obtained during normal phonation and falsetto phonation. Images were obtained also during cough, diplophonia. Results : The system made it possible to measure objective parameters, including fundamental frequency, amplitude, regularity, mucosal wave, and phase difference, medial and lateral peak, opening versus closing duration related to vocal fold vibration. Simultaneously, it enabled analysis of the whole mucosal wave of the entire vocal fold in real time. 2D scanning videokymography was also effective for evaluating the dynamic status of the vocal fold when the subject phonated aperiodic voice. Conclusion : In conclusion, 2D scanning videokymography can support the analysis of the whole mucosal wave of the entire vocal cord with objective vocal parameters, overcoming the limitations of stroboscopy and previous line scanning videokymography techniques.

• Advances in nano research
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• 제7권3호
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• pp.191-208
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• 2019

In the present work the dynamic analysis of the functionally graded rectangular nanoplates is studied. The theory of nonlocal elasticity based on the quasi 3D high shear deformation theory (quasi 3D HSDT) has been employed to determine the natural frequencies of the nanosize FG plate. In HSDT a cubic function is employed in terms of thickness coordinate to introduce the influence of transverse shear deformation and stretching thickness. The theory of nonlocal elasticity is utilized to examine the impact of the small scale on the natural frequency of the FG rectangular nanoplate. The equations of motion are deduced by implementing Hamilton's principle. To demonstrate the accuracy of the proposed method, the calculated results in specific cases are compared and examined with available results in the literature and a good agreement is observed. Finally, the influence of the various parameters such as the nonlocal coefficient, the material indexes, the aspect ratio, and the thickness to length ratio on the dynamic properties of the FG nanoplates is illustrated and discussed in detail.

• Structural Engineering and Mechanics
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• 제7권2호
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• pp.181-202
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• 1999

Dynamic response of axisymmetric arbitrary laminated composite cylindrical shell of finite length, using three-dimensional elasticity equations are studied. The shell is simply supported at both ends. The highly coupled partial differential equations are reduced to ordinary differential equations (ODE) with variable coefficients by means of trigonometric function expansion in axial direction. For cylindrical shell under dynamic load, the resulting differential equations are solved by Galerkin finite element method, In this solution, the continuity conditions between any two layer is satisfied. It is found that the difference between elasticity solution (ES) and higher order shear deformation theory (HSD) become higher for a symmetric laminations than their unsymmetric counterpart. That is due to the effect of bending-streching coupling. It is also found that due to the discontinuity of inplane stresses at the interface of the laminate, the slope of transverse normal and shear stresses aren't continuous across the interface. For free vibration analysis, through dividing each layer into thin laminas, the variable coefficients in ODE become constants and the resulting equations can be solved exactly. It is shown that the natural frequency of symmetric angle-ply are generally higher than their antisymmetric counterpart. Also the results are in good agreement with similar results found in literatures.

• Structural Engineering and Mechanics
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• 제65권5호
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• pp.523-533
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• 2018

In this study, the dynamic response of a functionally graded material (FGM) circular plate in contact with incompressible fluid under the harmonic load is investigated. Analysis of the plate is based on First-order Shear Deformation Plate Theory (FSDT). The governing equation of the oscillatory behavior of the fluid is obtained by solving Laplace equation and satisfying its boundary conditions. A new set of admissible functions, which satisfy both geometrical and natural boundary conditions, are developed for the free vibration analysis of moderately thick circular plate. The Chebyshev-Ritz Method is employed together with this set of admissible functions to determine the vibrational behaviors. The modal superposition approach is used to determine the dynamic response of the plate exposed to harmonic loading. Numerical results of the force vibrations and the effects of the different geometrical parameters on the dynamic response of the plate are investigated. Finally, the results of this research in the limit case are compared and validated with the results of other researches and finite element model (FEM).

• Structural Engineering and Mechanics
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• 제65권5호
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• pp.505-511
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• 2018

Recently, a new foundation model called "Dynamic foundation model" was proposed for the dynamic analysis of structures on the foundation. This model includes a linear elastic spring, shear layer, viscous damping and the special effects of mass density parameter of foundation during vibration. However, the relationship of foundation property parameters with the experimental parameter of the influence of foundation mass also has not been established in previous research. Hence, the purpose of the paper presents a simple experimental model in order to establish relationships between foundation properties such as stiffness, depth of foundation and experimental parameter of the influence of foundation mass. The simple experimental model is described by a steel plate connected with solid rubber layer as a single degree of freedom system including an elastic spring connected with lumped mass. Based on natural circular frequencies of the experimental models determined from FFT analysis plots of the time history of acceleration data, the experimental parameter of the influence of foundation mass is obtained and the above relationships are also discussed.