检索结果-南通市图书馆

The effect of surface roughness on rarefied gas flows by lattice Boltzmann method

在线全文

学校读者我要写书评

暂无评论

Chinese Physics B 2008年第12期17卷 4554-4561页

作者：刘超峰倪玉山 department of mechanics and {2. Science Fudan University

This paper studies the roughness effect combining with effects of rarefaction and compressibility by a lattice Boltzmann model for rarefied gas flows at high Knudsen numbers. By discussing the effect of the tangential momentum accommodation coefficient on the rough boundary condition, the lattice Boltzmann simulations of nitrogen and helium flows are performed in a two-dimensional microchannel with rough boundaries. The surface roughness effects in the microchannel on the velocity field, the mass flow rate and the friction coefficient are studied and analysed. Numerical results for the two gases in micro scale show different characteristics from macroscopic flows and demonstrate the feasibility of the lattice Boltzmann model in rarefied gas dynamics.

关键词： surface roughness lattice Boltzmann method rarefied gas flows velocity slip

Harvesting base vibration energy by a piezoelectric inverted beam with pendulum

在线全文

学校读者我要写书评

暂无评论

Chinese Physics B 2019年第1期28卷 594-607页

作者： Jia-Nan Pan Wei-Yang Qin Wang-Zheng Deng Hong-Lei Zhou department of engineering {2. Northwestern Polytechnical University

We proposed a two-degrees-of-freedom inverted piezoelectric beam with pendulum to promote the performance of vibration energy harvesting. This configuration is composed of an inverted elastic beam and a pendulum attached to its free end. The electromechanical equations governing the nonlinear system were derived. The harmonic balance method(HBM)is applied to solve the equation and the results prove that there exists a 1:3 super-harmonic resonance. The simulation results show that owing to the particular nonlinearity, there appears a special bending effect in the amplitude-frequency response, i.e., bending right for the first natural frequency and left for the second natural frequency, which is beneficial for harvesting vibration energy. The HBM results are verified by the entity simulations. Furthermore, over a relatively wide range of power spectral density, it could reach a dense jumping and give a dense high pulse voltage.

关键词： stochastic excitation energy harvesting inverted piezoelectric beam pendulum bi-stable state

A general solution for one dimensional chemo-mechanical coupled hydrogel rod

在线全文

学校读者我要写书评

暂无评论

Acta Mechanica Sinica 2018年第2期34卷 392-399页

作者： Xing-Quan Wang Qing-Sheng Yang department of engineering {2. Beijing University of Technology

Smart hydrogels are environmentally sensitive hydrogels, which can produce a sensitive response to external stimuli, and often exhibit the characteristics of multi filed coupling. In this paper, a hydrogel rod under chemomechanical coupling was analytically studied based on a poroelastical model. The already known constitutive and governing equations were simplified into the one dimensional case, then two different boundary conditions were considered. The expressions of concentration, displacement,chemical potential and stress related to time were obtained in a series form. Examples illustrate the interaction mechanism of chemical and mechanical effect. It was found that there was a balance state in the diffusion of concentration and the diffusion process could lead to the expansion or the stress change of the hydrogel rod.

关键词： Chemo-mechanical coupling Analytical solution One dimensional hydrogel rod

Free vibration of functionally graded material beams with surface-bonded piezoelectric layers in thermal environment

在线全文

学校读者我要写书评

暂无评论

Applied Mathematics and mechanics(English Edition) 2009年第8期30卷 969-982页

作者：李世荣苏厚德程昌钧 department of engineering {2. Lanzhou University of Technology department of mechanics Shanghai University

Free vibration of statically thermal postbuckled functionally graded material （FGM） beams with surface-bonded piezoelectric layers subject to both temperature rise and voltage is studied. By accurately considering the axial extension and based on the Euler-Bernoulli beam theory, geometrically nonlinear dynamic governing equations for FGM beams with surface-bonded piezoelectric layers subject to thermo-electro- mechanical loadings are formulated. It is assumed that the material properties of the middle FGM layer vary continuously as a power law function of the thickness coordinate, and the piezoelectric layers are isotropic and homogenous. By assuming that the amplitude of the beam vibration is small and its response is harmonic, the above mentioned non-linear partial differential equations are reduced to two sets of coupled ordinary differential equations. One is for the postbuckling, and the other is for the linear vibration of the beam superimposed upon the postbuckled configuration. Using a shooting method to solve the two sets of ordinary differential equations with fixed-fixed boundary conditions numerically, the response of postbuckling and free vibration in the vicinity of the postbuckled configuration of the beam with fixed-fixed ends and subject to transversely nonuniform heating and uniform electric field is obtained. Thermo-electric postbuckling equilibrium paths and characteristic curves of the first three natural frequencies versus the temperature, the electricity, and the material gradient parameters are plotted. It is found that the three lowest frequencies of the prebuckled beam decrease with the increase of the temperature, but those of a buckled beam increase monotonically with the temperature rise. The results also show that the tensional force produced in the piezoelectric layers by the voltage can efficiently increase the critical buckling temperature and the natural frequency.

关键词： functionally graded material laminated beams with piezoelectric layers thermal buckling free vibration natural frequency

Effect of electromagnetic boundary condition on dynamo actions

在线全文

学校读者我要写书评

暂无评论

Science China(Physics,mechanics & Astronomy) 2015年第4期58卷 75-83页

作者： XU MingTian department of engineering {2. School of Civil Engineering Shandong University

In this paper, based on the mean field dynamo theory, the influence of the electromagnetic boundary condition on the dynamo actions driven by the small scale turbulent flows in a cylindrical vessel is investigated by the integral equation approach. The numerical results show that the increase of the electrical conductivity or magnetic permeability of the walls of the cylindrical vessel can reduce the critical magnetic Reynolds number. Furthermore, the critical magnetic Reynolds number is more sensi- tive to the varying electrical conductivity of the end wall or magnetic permeability of the side wall. For the anisotropic dynamo which is the mean field model of the Karlsruhe experiment, when the relative electrical conductivity of the side wall or the rel- ative magnetic permeability of the end wall is less than some critical value, the m=l （m is the azimuthal wave number） mag- netic mode is the dominant mode, otherwise the m=0 mode predominates the excited magnetic field. Therefore, by changing the material of the walls of the cylindrical vessel, one can select the magnetic mode excited by the anisotropic dynamo.

关键词： dynamo action mean field dynamo theory electromagnetic boundary condition

Generalized Covariant Derivative with Respect to Time in Flat Space(Ⅱ):Lagrangian Description

在线全文

学校读者我要写书评

暂无评论

Acta Mechanica Solida Sinica 2016年第4期29卷 359-370页

作者： Yajun Yin department of engineering {2. School of Aerospace Engineering Tsinghua University

The previous paper reported a new derivative in the Eulerian description in flat space—the generalized covariant derivative of generalized Eulerian component with respect to time. This paper extends the thought from the Eulerian description to the Lagrangian description:on the basis of the postulate of covariant form invariability in time field, we define a new derivative in the Lagrangian description in flat space—the generalized covariant derivative of generalized Lagrangian component with respect to time. Besides, the covariant differential transformation group is set up. The covariant form invariability of Lagrangian space-time is ascertained.

关键词： Lagrangian description the postulate of covariant form invariability generalized Lagrangian component generalized covariant derivative with respect to time covariant differential transformation group

Generalized covariant differentiation and axiom-based tensor analysis

在线全文

学校读者我要写书评

暂无评论

Applied Mathematics and mechanics(English Edition) 2016年第3期37卷 379-394页

作者： Yajun YIN department of engineering {2. School of Aerospace EngineeringTsinghua University

This paper reports the new progresses in the axiomatization of tensor anal- ysis, including the thought of axiomatization, the concept of generalized components, the axiom of covariant form invariability, the axiomatized definition, the algebraic structure, the transformation group, and the simple calculation of generalized covariant differentia- tions. These progresses strengthen the tendency of the axiomatization of tensor analysis.

关键词： tensor analysis axiom of covariant form invariability generalized compo-nent generalized covariant differentiation covariant differential transformation group

Analysis on high-temperature oxidation and growth stress of iron-based alloy using phase field method

在线全文

学校读者我要写书评

暂无评论

Applied Mathematics and mechanics(English Edition) 2011年第6期32卷 757-764页

作者：杨帆刘彬方岱宁 department of engineering {2. School of AerospaceTsinghua University department of mechanics and Aerospace {2. College of EngineeringPeking University

High-temperature oxidation is an important property to evaluate thermal protection materials. However, since oxidation is a complex process involving microstructure evolution, its quantitative analysis has always been a challenge. In this work, a phase field method （PFM） based on the thermodynamics theory is developed to simulate the oxidation behavior and oxidation induced growth stress. It involves microstructure evolution and solves the problem of quantitatively computational analysis for the oxidation behavior and growth stress. Employing this method, the diffusion process, oxidation performance, and stress evolution axe predicted for Fe-Cr-A1-Y alloys. The numerical results agree well with the experimental data. The linear relationship between the maximum growth stress and the environment oxygen concentration is found. PFM provides a powerful tool to investigate high-temperature oxidation in complex environments.

关键词： high-temperature oxidation phase field method growth stress

Numerical simulation of two-dimensional viscous flows using combined finite element-immersed boundary method

在线全文

学校读者我要写书评

暂无评论

Journal of Hydrodynamics 2015年第5期27卷 658-667页

作者：杨冯超陈效鹏 department of engineering {2. Northwestern Polytechnical University

In this paper, a method that combines the characteristic-based split finite element method（CBS-FEM） and the direct forcing immersed boundary（IB） method is proposed for the simulation of incompressible viscous flows. The structured triangular meshes without regarding the location of the physical boundary of the body is adopted to solve the flow, and the no-slip boundary condition is imposed on the interface. In order to improve the computational efficiency, a grid stretching strategy for the background structured triangular meshes is adopted. The obtained results agree very well with the previous numerical and experimental data. The order of the numerical accuracy is shown to be between 1 and 2. Moreover, the accuracy control by adjusting the number density of the mark points purely at certain stages is explored, and a second power law is obtained. The numerical experiments for the flow around a cylinder behind a backward-facing step show that the location of the cylinder can affect the sizes and the shapes of the corner eddy and the main recirculation region. The proposed method can be applied further to the fluid dynamics with complex geometries, moving boundaries, fluid-structure interactions, etc..

关键词： characteristic-based split immersed boundary(IB) method incompressible flow no-slip condition stretching grid