• Current Optics and Photonics
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• v.1 no.4
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• pp.278-283
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• 2017

We theoretically study the dynamics of water tetramer in intense femtosecond laser pulses with different frequencies. The simulations are carried out by incorporating the molecular dynamics method non-adiabatically into the time-dependent local-density approximation (TDLDA-MD). Three typical scenarios of water tetramer including the normal vibration with enlarged OH bonds, free OH bonds breaking and the pure Coulomb explosion are presented by investigating the electronic and ionic dynamics. The result indicates that the ionization is enhanced and the corresponding fragmentation effect as well as the damping of the dipole moment are found more notably when increasing the laser frequency especially when the frequency falls in the resonant region of the absorption spectra. The study of the level depletion reveals that the ratio of the emission amount from different levels can be controlled by changing the laser frequency referring to the Keldysh parameter.

• Proceedings of the KSR Conference
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• 2004.10a
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• pp.906-915
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• 2004

Derivation procedures of exact dynamic stiffness matrices of thin-walled curved beams subjected to axial forces are rigorously presented for the spatial free vibration analysis. An exact dynamic stiffness matrix is established from governing equations for a uniform curved beam element with nonsymmetric thin-walled cross section. Firstly this numerical technique is accomplished via a generalized linear eigenvalue problem by introducing 14 displacement parameters and a system of linear algebraic equations with complex matrices. Thus, displacement functions of dispalcement parameters are exactly derived and finally exact stiffness matrices are determined using clement force-displacement relationships. The natural frequencies of the nonsymmetric thin-walled curved beam are evaluated and compared with analytical solutions or results by ABAQUS's shell elements in order to demonstrate the validity of this study.

• Structural Engineering and Mechanics
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• v.57 no.2
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• pp.221-238
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• 2016

One of the objectives of this study is to implement the direct calculation of the torsional moment of inertia for non-circular cross-sections, which is based on the St. Venant torsion formulation and the finite element method. Recently the proposed method provides a unique calculation of the torsional rigidity of simply and multiply connected cross-sections. Next, free vibration analyses of cylindrical and non-cylindrical helices with non-circular cross-sections are solved by a curved two-nodded mixed finite element based on the Timoshenko beam theory. Some thin-thick closed or open sections are handled and the natural frequencies of cylindrical and non-cylindrical helices are compared with the literature and the commercial finite element program SAP2000.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.8
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• pp.2546-2554
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• 1996

In order to investigate the characteristics of sound-structure interaction problems, we modeled a rectangular cavity and the flexible wall of the cavity. Because the governing equations of motion are coupled through velocity terms, we could redefine them using the velocity potential. We calculated the natural frequencies of plate using orthogonal polynomial functions which satisfy the boundary conditions in the Rayleigh-Ritz Method. As the result, comparisons of theory and experiment show good agreement. and using orthogonal polynomial functions which satisfy the boundary conditions in the Rayleigh-Ritz method show useful method for sound-structure interaction problems too.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.9
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• pp.1457-1462
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• 2003

The problem of reducing the level of vibrations in structures arises in various branches of technology. For the calculation of systems equipped with DVAs, the frequencies of the protected system's free vibrations are determined first. In most practical problems system have to be considered continuous systems. It is important to obtain the detailed information about not the first frequency and the mode but anothers corresponding to it. So, this paper describes the method to obtain the accurate information about the combined discrete system. This information is obtained from the combined system's receptance. This paper shows the convenience when design the dynamic vibration absorber with the combined system's receptance.

• Journal of the Korea institute for structural maintenance and inspection
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• v.2 no.4
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• pp.217-223
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• 1998

본 논문에서는 원형연단이 단순지지 되어 있을 때 단순과 자유의 방사연단 조건을 갖는 부채꼴형 평판의 휨진동에 대한 엄밀한 해석방법을 제시한다. Ritz방법을 이용하여 수직진동변위를 두가지 적합 함수식으로 가정하였다. 이러한 두가지의 적합 함수식은 (1) 수학적으로 완전한 대수삼각다항함수와, (2) 둔각 모서리에서의 휨모멘트 특이도를 고려하는 모서리함수로 구성되어있다. 본 연구에서는 방사연단의 둔각 모서리를 이루는 부채꼴형 각도의 범위에 따른 엄밀한 진동수 및 수직진동 변위의 전형적인 등고선을 제시하였다.

• Journal of Power System Engineering
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• v.9 no.3
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• pp.58-65
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• 2005

This paper deals with the free vibrations of truncated conical shell with uniform thickness by the transfer influence coefficient method. The classical thin shell theory based upon the $Fl\ddot{u}gge$ theory is assumed and the governing equations of a conical shell are written as a coupled set of first order differential equations using the transfer matrix. The Runge-Kutta-Gill integration and bisection method are used to solve the governing differential equations and to compute the eigenvalues respectively. The natural frequencies and corresponding mode shapes are calculated numerically for the truncated conical shell with any combination of boundary conditions at the edges. And all boundary conditions and the intermediate supports between conical shell and foundation could be treated only by adequately varying the values of the spring constants. Numerical results are compared with existing exact and numerical solutions of other methods.

• Journal of the Korea institute for structural maintenance and inspection
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• v.3 no.3
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• pp.167-176
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• 1999

This paper is concerned with the damage detection of existing 2 and 3-dimensional truss structures based on free vibration equation and extended Kalman filter. The local damage is characterized in terms of the stiffness degradation of damaged members. As the observed data, the natural frequencies and mode shapes of damaged truss structure model are adopted. Both location and stiffness of damaged parts of members in truss structures can be estimated by the proposed inverse solution procedure. The applicability and effectiveness of proposed inverse solution procedure are demonstrated through the numerical examples.

• Structural Engineering and Mechanics
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• v.27 no.3
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• pp.333-345
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• 2007

In this study, the nonlinear vibrations of stepped beams having different boundary conditions were investigated. The equations of motions were obtained using Hamilton's principle and made non dimensional. The stretching effect induced non-linear terms to the equations. Forcing and damping terms were also included in the equations. The dimensionless equations were solved for six different set of boundary conditions. A perturbation method was applied to the equations of motions. The first terms of the perturbation series lead to the linear problem. Natural frequencies for the linear problem were calculated exactly for different boundary conditions. Second order non-linear terms of the perturbation series behave as corrections to the linear problem. Amplitude and phase modulation equations were obtained. Non-linear free and forced vibrations were investigated in detail. The effects of the position and magnitude of the step, as well as effects of different boundary conditions on the vibrations, were determined.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.35 no.10
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• pp.135-142
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• 2019

Ant colony optimization(ACO) technique is utilized in truss size optimization with frequency constraints. Total weight of truss to be minimized is considered as the objective function and multiple natural frequencies are adopted as constraints. The modified traveling salesman problem(TSP) is adopted and total length of the TSP tour is interpreted as the weight of the structure. The present ACO-based design optimization procedure uses discrete design variables and the penalty function is introduced to enforce design constraints during optimization process. Three numerical examples are carried out to verify the capability of ACO in truss optimization with frequency constraints. From numerical results, the present ACO is a very effective way of finding optimum design of truss structures in free vibration. Finally, we provide the present numerical results as future reference solutions.