• 한국소음진동공학회논문집
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• 제15권6호
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• pp.706-711
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• 2005

Torsional oscillations of a system incorporating a Hooke's joint are investigated by studying a simple similar nonlinear 2-degree-of-freedom model, which has linear and quadratic nonlinear parametric excitations. The simple system is identified to have the possibilities of primary, sub harmonic and combination resonances. The case of simultaneous primary and combination resonances is selected for perturbation analysis to have the reduced amplitude-equations of motion. The same procedure is applied to the system incorporating a Hooke's joint.

• 대한수학회보
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• 제38권2호
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• pp.337-346
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• 2001

A linearization owing to Oseen originally is performed to study the recirculating Navier-Stokes flows at high Reynolds numbers. The procedure is generalized to produce higher order asymptotic expansion for the flow velocity. We call this the Oseen-type expansion of the given flow. As a concrete example, the velocity of a steady Navier-Stockes flow due to a swimming flexible sheet in two-dimensional infinite strip domain is calculated by an asymptotic expansion technic with two-parameters, the Reynolds number R and the perturbation parameter $\varepsilon$ first and then R secondly. The asymptotic result is up to second order in $\varepsilon$.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1996년도 가을 학술발표회 논문집
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• pp.62-69
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• 1996

Most dynamic systems have various random properties in excitation and system parameters. In this paper, a procedure fur response analysis is proposed for the linear dynamic system with random properties in both excitation and system parameters. The system parameter and response with random properties are modeled by perturbation technique, aand then response analysis is formulated by probabilistic and vibration theories. And probabilistic FEM is also used for the calculation of mean response which is difficult by the proposed response model. As an application example, the transient response is calculated for a sdof system with random mass and spring constant subjected to stationary white-noise excitation and the results are compared to those of numerical simulation.

• 대한기계학회논문집A
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• 제20권5호
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• pp.1436-1444
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• 1996

The problem ofinstability of laminated circular cylindrical shell under the action of torsio or lateral pressure is investigated. The analysis is based on the Sander's theory for finite deformations of thin shell. The buckling is elastic for thin compoisite shell nad the geometry is assumed to be free of initial imperfections. The equilibrium equations are obrained by usitn the p[erturbation technique. Solution procedure is based on the Galerkin mehtod. The computer program for numerical results is made for several stacking sequence, length-to-radius ratio, and radius-to-thickness ratio. The numerical results of buckling load are present.

• 대한기계학회논문집
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• 제2권3호
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• pp.62-68
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• 1978

The influences of the large amplitude free vibrations of simply supported Timoshenko beams with ends restrained to remain a fixed distance apart and with no axial restraints, which cause a longitudinal elastic force and a longitudinal inertia force, respectively, are investigated. The equations of motion derived by an appropriate linearizarion of the nonlinear strain- displacement relation have nonlinear terms arising from large curvature, longitudinal elastic force and longitudinal inertia force. The fourth order nonlinear partial differential equations for the deflection, can be reduced to the nonlinear ordinary differential equations by means of Galerkin procedure and a modal expansion. The general response and frequensy-amplitude relations are derived by the perturbation method of strained parameters. Comparison with previously published results is made.

• Structural Engineering and Mechanics
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• 제61권5호
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• pp.657-661
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• 2017

In this paper, it has been tried to propose a new semi analytical approach for solving nonlinear vibration of conservative systems. Hamiltonian approach is presented and applied to high nonlinear vibration systems. Hamiltonian approach leads us to high accurate solution using only one iteration. The method doesn't need any small perturbation and sufficiently accurate to both linear and nonlinear problems in engineering. The results are compared with numerical solution using Runge-Kutta-algorithm. The procedure of numerical solution are presented in detail. Hamiltonian approach could be simply apply to other powerfully non-natural oscillations and it could be found widely feasible in engineering and science.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1995년도 Proceedings of the Korea Automation Control Conference, 10th (KACC); Seoul, Korea; 23-25 Oct. 1995
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• pp.332-335
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• 1995

A simple and effective method for improving Euclidean norm condition number for chemical processing system is presented. The singular value sensitivities of Freudenberg et al. (1982) is used to estimate the behavior of singular values of process transfer function matrix when design parameter is changed, then the condition number can be calculated straightforwardly. The method requires explicit dependencies of each transfer function matrix elements on design parameters. These dependencies can be obtained either by symbolic differentiation in the form of explicit function of design parameters, or by numerical perturbation studies for units with large and complicated models. Gerschgorin-type lower bound for minimum singular value is introduced to detect the large divergencies near singular point due to linearity of sensitivities. The case studies are performed to show the efficiency of the proposed method.

• 소음진동
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• 제8권3호
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• pp.408-419
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• 1998

Dynamic characteristics are investigated when a nonlinear system showing periodic and chaotic responses under harmonic excitation is exposed to random perturbation. Approach for both qulitative and quantitative analysis of the noise effect in a nonlinear system under harmonic excitation is presented. For the qualitative analysis, Lyapunov exponents are calculated and Poincar map is illustrated. For the quatitative analysis. Fokker-Planck equatin is solved numerical by means of a Path-integral solution procedure. Eigenvalue problem obtained from the numerical caculation is solved and the relation of eigenvalue, eigenvector and chaotic motion is investigated.

• Journal of Power Electronics
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• 제16권2호
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• pp.695-703
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• 2016

A fuel cell power conditioning system for online diagnosis and load leveling under the condition of varying load is developed in this study. The proposed system comprises a unidirectional boost converter and a bidirectional buck-boost converter with a battery. The system operates in two different modes. In normal mode, the bidirectional converter is utilized for load leveling; in diagnostic mode, it is utilized to control load voltage while the boost converter generates perturbation current to implement the online diagnosis function through in-situ electrochemical impedance spectroscopy (EIS). The proposed method can perform EIS for a fuel cell under varying-load conditions with no influence on the load. The validity and feasibility of the proposed system are verified by experiments, and the design procedure of the proposed system is detailed.

• 한국연소학회지
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• 제21권3호
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• pp.16-23
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• 2016

In this study, skeletal mechanisms are produced by directed relation graph with specified threshold value and sensitivity analysis based on species database from the directed relation graph. Skeletal mechanism is optimized through the elimination of unimportant reaction steps by computational singular perturbation importance index. Reduction is performed for the detailed mechanism of methyl butanoate consisting of 264 species and 1219 elementary reactions. Validation shows acceptable agreement for auto-ignition delays in wide parametric ranges of pressure, temperature and equivalence ratio. Methyl butanoate has been proposed as a simple biodiesel surrogate although the alkyl chain consists of four carbon atoms. The resulting surrogate mechanism for n-heptane and MB consists of 76 species and 226 reaction steps including those for NOx.