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Coherent nonlinear structures in dense electron positron plasma

Chinese Physics B 2013年第2期22卷 335-340页

作者： S.A.Khan Z.Wazir National Centre for Physics Quaid-i-Azam University CampusIslamabad 45320Pakistan Department of Physics Riphah International UniversityIslamabadPakistan

It is shown that rarefactive-type double layer structures exist in ultradense electron-positron *** this purpose,an extended Korteweg de Vries equation is derived and solved analytically in the low amplitude limit by employing the appropriate fluid equations.A strong influence of quantum degeneracy pressure of electrons and positrons,quantum diffraction effects and concentration of background positive ions on double layer is *** is also pointed out that the amplitude and steepness of the double layer increases with an increase in ion concentration or ion charge *** results are examined numerically for some interesting cases of dense plasmas with illustrations.

关键词： degenerate plasma nonlinear structures double layers

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Orthogonal expansion of ground motion and PDEM-based seismic response analysis of nonlinear structures

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Earthquake Engineering and Engineering Vibration 2009年第3期8卷 313-328页

作者： Li Jie Liu Zhangjun Chen Jianbing State Key Laboratory of Disaster Reduction in Civil Engineering Tongji University Shanghai 200092 China College of Civil ＆ Hydroelectric Engineering China Three Gorges University Yichang 443002 China

This paper introduces an orthogonal expansion method for general stochastic processes. In the method, a normalized orthogonal function of time variable t is first introduced to carry out the decomposition of a stochastic process and then a correlated matrix decomposition technique, which transforms a correlated random vector into a vector of standard uncorrelated random variables, is used to complete a double orthogonal decomposition of the stochastic processes. Considering the relationship between the Hartley transform and Fourier transform of a real-valued function, it is suggested that the first orthogonal expansion in the above process is carried out using the Hartley basis function instead of the trigonometric basis function in practical applications. The seismic ground motion is investigated using the above method. In order to capture the main probabilistic characteristics of the seismic ground motion, it is proposed to directly carry out the orthogonal expansion of the seismic displacements. The case study shows that the proposed method is feasible to represent the seismic ground motion with only a few random variables. In the second part of the paper, the probability density evolution method （PDEM） is employed to study the stochastic response of nonlinear structures subjected to earthquake excitations. In the PDEM, a completely uncoupled one-dimensional partial differential equation, the generalized density evolution equation, plays a central role in governing the stochastic seismic responses of the nonlinear structure. The solution to this equation will yield the instantaneous probability density function of the responses. Computational algorithms to solve the probability density evolution equation are described. An example, which deals with a nonlinear frame structure subjected to stochastic ground motions, is illustrated to validate the above approach.

关键词： seismic ground motion stochastic processes orthogonal expansion probability density evolution method nonlinear structures stochastic response analysis

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THE APPLICATIONS OF GENERALIZED VARIATIONAL PRINCIPLES IN nonlinear STRUCTURAL ANALYSIS

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Applied Mathematics and Mechanics(English Edition) 1993年第5期14卷 417-428页

作者：成祥生 Tongji University Shanghai

This paper discusses the generalized variational principles founded by the technique of Lagrangian multipliers in structural mechanics and analyzes the nonlinear statically indeterminate structures. It is assumed that the stress-strain relationship of the materials of structures has the form of namely, the physical equations of structures have the shape of exponential functions. Several examples are given to illustrate the statically indeterminate structures such as the trusses, beams, frames and torsional bars.

关键词： generalized variational principle nonlinear structures statically indeterminate structures

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Design and Control nonlinear Dynamic Response Optimization of Flexible Mechanical Systems

Design and Control Nonlinear Dynamic Response Optimization o...

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The Fourth World Congress of Structural and Multidisciplinary Optimization

作者： Paulo Pires Moita Jorge Pinto Pereira Jo o Barradas Cardoso Escola Superior de Tecnologia de Setúbal Campus do IPS 2914-508 SetúbalPortugal Escola Superior de Tecnologia de Setúbal Campus do IPS 2914-508 SetúbalPortugal Instituto Superior Técnico Departamento de Engenharia Mec（a|＾）nica Av. Rovisco Pais1049-001 LisboaPortugal

＜正＞A design and control sensitivity analysis and multicriteria optimization formulation is derived for flexible mechanical systems. This formulation is implemented in an optimum design code and it is applied to the nonlinear response of an impact absorber and to a flexible vehicle chassis with suspension. Structural dimensions as well as lumped damping and stiffness characteristics plus control driven forces, are considered as decision variables. The dynamic response and its sensitivity are discretized via space and time finite elements, and are integrated globally or step-by-step. Direct differentiation and adjoint system approaches are used to calculate the sensitivities. nonlinear programming and optimality criteria are used for the optimization process.

关键词： Optimization nonlinear structures Dynamic Response Space-Time Finite Elements

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