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Applied Mathematics and Mechanics(English Edition) 2015年第8期36卷 1033-1044页

作者： A.g.ARANI g.s.jafari Faculty of Mechanical Engineering University of Kashan Institute of Nanoscience & Nanotechnology University of Kashan

The nonlocal nonlinear vibration analysis of embedded laminated micro- plates resting on an elastic matrix as an orthotropic Pasternak medium is investigated. The small size effects of micro/nano-plate are considered based on the Eringen nonlocal theory. Based on the orthotropic Mindlin plate theory along with the von Kármán geo- metric nonlinearity and Hamilton＇s principle, the governing equations are derived. The differential quadrature method （DQM） is applied for obtaining the nonlinear frequency of system. The effects of different parameters such as nonlocal parameters, elastic me- dia, aspect ratios, and boundary conditions are considered on the nonlinear vibration of the micro-plate. Results show that considering elastic medium increases the nonlinear frequency of system. F^lrthermore, the effect of boundary conditions becomes lower at higher nonlocal parameters.

关键词： nonlinear vibration laminated micro-plate orthotropic Pasternak medium,differential quadrature method

Free vibration and transient response of double curved beams connected by intermediate straight beams

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Applied Mathematics and Mechanics(English Edition) 2025年第1期46卷 37-62页

作者： R.A.jafari-TALOOKOLAEI H.gHANDVAR E.JUMAEV s.KHATIR T.CUONg-LE school of Mechanical Engineering Babol Noshirvani University of Technology Department of Mechanical Engineering Faculty of Engineering New Uzbekistan University University of Business and science Center for Engineering Application and Technology solutions Ho Chi Minh City Open University

This paper investigates the free vibration and transient response of interconnected structures including double curved beams and intermediate straight beams,which are all constructed from functionally graded porous(FgP) materials. The strain potential and kinetic energies of each beam along with the work done by the external force are calculated. Additionally, a higher-order beam element is introduced to derive stiffness and mass matrices, along with the force vector. The curved and straight beams are discretized, and their assembled stiffness, mass matrices, and force vectors, are *** conditions at the joints are used to derive the total matrices of the entire structure. subsequently, the natural frequencies and transient response of the system are determined. The accuracy of the mathematical model and the self-developed computer program is validated through the comparison of the obtained results with those of the existing literature and commercial software ANsYs, demonstrating excellent ***, a comprehensive study is conducted to investigate the effects of various parameters on the free vibration and transient response of the considered structure.

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Cross-focusing of two chirped gaussian laser beams and THz wave generation in plasmas of multi-ion species under a weakly relativistic and ponderomotive regime

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Plasma science and Technology 2022年第10期24卷 1-11页

作者： M R jafari MILANI s REZAEI M J jafari Photonics and Quantum Technologies Research school Nuclear Science and Technology Research InstituteTehran 14665-678Iran Plasma and Fusion Research school Nuclear Science and Technology Research InstituteTehran 14399-51113Iran

The generation of terahertz(THz)waves via the beating of two high-intensity chirped gaussian lasers in a multi-ion-species plasma is numerically studied by taking into account the weak relativistic and ponderomotive regime of *** coupled differential equations for beamwidth parameters are extracted by introducing the dielectric function of such plasma and using WKB and paraxial ray *** amplitude of THz radiation at beat frequency resulting from the nonlinear current density induced by the beat ponderomotive force of the cross-focusing of beams was *** impacts of the chirp frequency parameter,initial laser intensity and initial ionic species density(specifically,the presence of singly and doubly charged ions)in the plasma on THz generation were *** numerical results reveal that THz radiation generation strongly depends on the chirp frequency parameter.A specific range of chirp frequencies exists for self-focusing as well as THz generation with a'turning point',where the THz emission reaches its maximum *** results show that the strength of self-focusing and consequently the generated THz radiation are reduced by increasing the density of doubly charged ionic species in the plasma due to the suppression of the nonlinear effects.

关键词： laser–plasma interaction THz generation chirped gaussian laser beams

Lattice Boltzmann method and RANs approach for simulation of turbulent flows and particle transport and deposition

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Particuology 2017年第1期15卷 62-72页

作者： H. sajjadi M. salmanzadeh g. Ahmadi s. jafari Department of Mechanical Engineering Shahid Bahonar University ofKerman Kerrnan lran Department of Mechanical and Aeronautical Engineering Clarkson University Potsdam NY USA Department of Petroleum Engineering Shahid Bahonar University ofKerrnan Kerman lran

Using the lattice-Boltzmann computational approach in conjunction with the Reynolds averaged Navier-stokes （RANs） model, several turbulent flows and the transport and deposition of particles in different passages were studied. The new lattice Boltzmann method （LBM） solved the RANs equations coupled with the standard and renormalization group k-E turbulence models. In particular, the LBM formulation was augmented by the addition of two transport equations for the probability distribution function of populations of k and 8. The discrete random walk model was used to generate the instanta- neous turbulence fluctuations. For turbulent channel flows, the analytical fits to the root mean-square velocity fluctuations obtained by the direct numerical simulation of the turbulent flow were used in the analysis. Attention was given to the proper evaluation of the wall normal turbulent velocity fluctuations particularly near the wall. The simulation results were compared with the available numerical simulation and experimental data. The new LBM-RANs model is shown to provide a reasonably accurate description of turbulent flows and particle transport and deposition at modest computational cost.

关键词： Lattice Boltzmann method Reynolds averaged Navier-stokes Renormalization group model k-ε model Particle transport and deposition

Laser-Plasma Interaction in Presence of an Obliquely External Magnetic Field:Application to Laser Fusion without Radioactivity

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Communications in Theoretical Physics 2016年第8期65卷 237-243页

作者： M.Mobaraki s.jafari Department of Physics University of Guilan

In this paper, the nonlinear interaction of ultra-high power laser beam with fusion plasma at relativistic regime in the presence of obliquely external magnetic field has been studied. Imposing an external magnetic field on plasma can modify the density profile of the plasma so that the thermal conductivity of electrons reduces which is considered to be the decrease of the threshold energy for ignition. To achieve the fusion of Hydrogen–Boron(HB) fuel,the block acceleration model of plasma is employed. Energy production by HB isotopes can be of interest, since its reaction does not generate radioactive tritium. By using the inhibit factor in the block model acceleration of plasma and Maxwell's as well as the momentum transfer equations, the electron density distribution and dielectric permittivity of the plasma medium are obtained. Numerical results indicate that with increasing the intensity of the external magnetic field, the oscillation of the laser magnetic field decreases, while the dielectric permittivity increases. Moreover, the amplitude of the electron density becomes highly peaked and the plasma electrons are strongly bunched with increasing the intensity of external magnetic field. Therefore, the magnetized plasma can act as a positive focusing lens to enhance the fusion process. Besides, we find that with increasing θ-angle(from oblique external magnetic field) between 0 and 90°, the dielectric permittivity increases, while for θ between 90° and 180°, the dielectric permittivity decreases with increasing θ.

关键词： laser-plasma interaction external magnetic field laser fusion HB fuel

Non-harmonic resonance of viscoelastic structures subjected to time-dependent exponentially decreasing transverse distributed loads

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Earthquake Engineering and Engineering Vibration 2023年第3期22卷 825-840页

作者： Nasrin jafari Department of Civil Engineering Isfahan University of TechnologyIsfahan 84156-83111Iran

In this paper,the non-harmonic resonance of Bernoulli viscoelastic beams,Kirchhoff viscoelastic plates,Timoshenko viscoelastic beams,and Mindlin viscoelastic plates subjected to time-dependent exponentially decreasing transverse distributed load is investigated for the first *** constitutive equations are expressed utilizing Boltzmann integral law with a constant bulk *** displacement vector is approximated by employing the separation of variables *** Laplace transformation is used to transfer equations from the time domain to the Laplace domain and vice *** novel point of the proposed method is to express,prove and calculate the critical time in which the displacement will be several times the displacement at time *** addition,this new method calculates the maximum deflection at the critical time,explicitly and exactly,without any need to follow the time-displacement curve with a low computational ***,the proposed method introduces the critical range of time so that the responses are greater than the responses at time zero.

关键词： Bernoulli and Timoshenko viscoelastic beams critical time non-harmonic resonance time-dependent decreasing exponential load Kirchhoff and Mindlin viscoelastic plates

Corrosion Behaviors of Two Types of Commercial stainless steel after Plastic Deformation

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Journal of Materials science & Technology 2010年第9期26卷 833-838页

作者： Esmaeil jafari Materials science and Engineering Department Islamic Azad University Shiraz Branch

The influence of deformation temperature,strain rate and alloying elements such as chromium,nickel,copper,on corrosion resistance of a 304 stainless steel after plastic deformation was *** techniques employed were tensile test at room and elevated temperature,deep drawing tests at various strain rates,X-ray diffraction test and potentiodynamic and cyclic polarization,metallography by optical and scanning electron *** showed that chromium,nickel and copper had a significant effect on corrosion resistance of steel after plastic *** was observed that corrosion resistance after plastic deformation was a function of deformation temperature and alloying elements.

关键词： Corrosion resistance Plastic deformation stainless steel Phase transformation Polarization test

gain calculation of a free-electron laser operating with a non-uniform ion-channel guide

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Chinese Physics B 2011年第9期20卷 187-191页

作者： A.Hasanbeigi H.Mehdian s.jafari Department of Physics and Plasma Research Institute of Tarbiat Moallem University 49 Dr Mofatteh AvenueTehran 15614Iran Department of Physics University of GuilanRasht 41335-1914Iran

Amplification of an electromagnetic wave by a free electron laser （FEL） with a helical wiggler and an ion channel with a periodically varying ion density is examined. The relativistic equation of motion for a single electron in the combined wiggler and the periodic ionbchannel fields is solved and the classes of possible trajectories in this configuration are discussed. The gain equation for the FEL in the low-gain-per-pass lirnit is obtained by adding the effect of the periodic ion channel. Numerical calculation is employed to analyse the gain induced by the effects of the non-uniform ion density. The variation of gain with ion-channel density is demonstrated. It is shown that there is a gain enhancement for group I orbits in the presence of a non-uniform ion-channel but not in a uniform one. It is also shown that periodic ion-channel guiding is used to reach the maximum peak gain in a low ion-channel frequency （low ion density）.

关键词： free electron laser nonuniform ion-channel helical wiggler

Mixed finite element and differential quadrature method for free and forced vibration and buckling analysis of rectangular plates

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Applied Mathematics and Mechanics(English Edition) 2012年第1期33卷 81-98页

作者： s. A. EFTEKHARI A. A. jafari Department of Mechanical Engineering K. N. Toosi University of Technology

This paper presents a combined application of the finite element method （FEM） and the differential quadrature method （DQM） to vibration and buckling problems of rectangular plates. The proposed scheme combines the geometry flexibility of the FEM and the high accuracy and efficiency of the DQM. The accuracy of the present method is demonstrated by comparing the obtained results with those available in the literature. It is shown that highly accurate results can be obtained by using a small number of finite elements and DQM sample points. The proposed method is suitable for the problems considered due to its simplicity and potential for further development.

关键词： finite element method (FEM) differential quadrature method (DQM) rectangular plate free and forced vibration buckling analysis

Thermo-electromechanical behavior of functionally graded piezoelectric hollow cylinder under non-axisymmetric loads

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Applied Mathematics and Mechanics(English Edition) 2015年第7期36卷 939-954页

作者： A.ATRIAN J.jafari FEsHARAKI s.H.NOURBAKHsH Department of Mechanical Engineering Najafabad BranchIslamic Azad University Faculty of Engineering Shahrekord University

This paper presents an analytical solution of a thick walled cylinder composed of a functionally graded piezoelectric material （FgPM） and subjected to a uniform electric field and non-axisymmetric thermo-mechanical loads. All material properties, except Poisson＇s ratio that is assumed to be constant, obey the same power law. An exact solution for the resulting Navier equations is developed by the separation of variables and complex Fourier series. stress and strain distributions and a displacement field through the cylinder are obtained by this technique. To examine the analytical approach, different examples are solved by this method, and the results are discussed.

关键词： functionally graded piezoelectric material (FgPM) thermoelasticity Fourierseries non-axisymmetric