Flexoelectric effect on thickness-shear vibration of a rectangular piezoelectric crystal plate

Thickness-shear (TSh) vibration of a rectangular piezoelectric crystal plate is studied with the consideration of flexoelectric effect in this paper. The developed theoretical model is based on the assumed displacement function which includes the anti-symmetric mode through thickness and symmetric mode in length. The constitutive equation with flexoelectricity, governing equations and boundary conditions are derived from the Gibbs energy density function and variational principle. For the effect of flexoelectricity, we only consider the shear strain gradient in the thickness direction so as to simply the mathematical model. Thus, two flexoelectric coefficients are used in the present model. The electric potential functions are also obtained for different electric boundary conditions. The present results clearly show that the flexoelectric effect has significant effect on vibration frequencies of thickness-shear modes of thin piezoelectric crystal plate. It is also found that the flexoelectric coefficients and length to thickness ratio have influence on the thickness-shear modes. The results tell that flexoelectricity cannot be neglected for design of small size piezoelectric resonators.

Investigation on vibration of the functionally graded material–stepped cylindrical shell coupled with annular plate in thermal environment

This article is concerned with thermal vibration behaviors of the functionally graded material–stepped cylindrical shell coupled with annular plate, including free vibration, transient response, and steady state response. The stepped cylindrical shell is divided into N s segments at locations of thickness and radius variations, which is coupled with N p annular plates. The boundary and coupling conditions are achieved by introducing the artificial virtual spring technology. Under the framework of FSDT, the displacement function of arbitrary shell segment and annular plate is expanded with Chebyshev polynomials and Fourier series for circumferential direction. Compared with results obtained by the finite element method and the references, a series of numerical examples and validations are presented to verify the convergence and accuracy of the current method. The effects of the relevant parameters containing the geometric parameters, boundary conditions, various loadings, and the thermal environment are investigated in detail.

A Unified Solution for the Vibration Analysis of Lattice Sandwich Beams with General Elastic Supports

Free vibration analyses of lattice sandwich beams with general elastic supports have rarely been discussed in this field’s literature. In this paper, a unified method is proposed to study the free vibration characteristics of lattice sandwich beams under various boundary conditions. The proposed method is to convert the three truss cores of lattice sandwich beams into an equivalent homogeneous layer and introduce two different types of constraint springs to simulate the general elastic support boundary at both ends of lattice sandwich beams. By changing the rigidity of the boundary restraint spring, various boundary conditions can be easily obtained without modifying the solving algorithm and solving process. In order to overcome all the discontinuities or jumps associated with the elastic boundary support conditions, the displacement function of lattice sandwich beams is usually obtained as an improved Fourier cosine series along with four sine terms. On this basis, the unknown series coefficients of the displacement function are treated as the generalized coordinates and solved using the Rayleigh–Ritz method. The correctness of the present method is verified through comparison with existing literature. The calculation results of the present method are highly accurate, indicating that the present method is suitable for analyzing the vibration characteristics of lattice sandwich beams with general elastic supports. In addition, the effects of beam length, panel thickness, core height, radius and truss inclination on the natural frequencies of lattice sandwich beams with arbitrary boundary conditions have been discussed in this paper.

Numerical Analysis of Thick Isotropic and Transversely Isotropic Plates in Bending using FE Based New Inverse Shear Deformation Theory

In this work, using new inverse trigonometric kinematic displacement function, the bending solution of simply supported isotropic and transversely isotopic thin, moderately thin and thick square plates with aspect ratio variations is given. The paper introduces a new inverse trigonometric shear deformation theory (nITSDT) for the bi-directional bending study, which is variationally compatible. The transverse shear stress can be obtained directly from the constitutive relationships on the top and bottom surfaces of the plate that satisfy the shear stress free surface conditions, so the theory does not need a factor for shear correction. The dynamic version of the virtual work principle is used to obtain the governing equations and boundary conditions of the theory. The Finite Element (FE) solution has been developed using MATLAB code based on the present theory for simply supported laminated composite plates. In order to illustrate the efficiency of the proposed theory, the results of displacements and stresses are compared with those of other refined theories and exact solution. The findings obtained from the use of the theory are found to agree well with the precise results of elasticity.

A semi-analytical elastic stress solution for circular rock stratum based on the theory of curved beam

The circular rock stratum are inevitably encountered in underground mining engineering, which causes waste of resources and dynamic instability. Based on the elastic theory of curved beam and finite-difference computation, a displacement function is presented in polar coordinates for solving two partial differential equations with the boundary conditions in mixed type in elastic, isotropic and homogeneous rock. A semi-analytical elastic stress solution for circular rock stratum is obtained according to the governing equation and stress components in terms of displacement function. The variations of stress distribution with different influencing factors are analyzed, which may lead to a better understanding of the stability of circular rock stratum after coal extractions. Finally, this semi-analytical elastic stress solution is applied to the fold structure in No.2502 mining area and points out the dangerous sites during coal extractions, which provides the basis of construction and safety in coal mine engineering.

Dynamic Analysis of Multi-Stepped Functionally Graded Carbon Nanotube Reinforced Composite Plate with General Boundary Condition

This study presents the multi-stepped functionally graded carbon nanotube reinforced composite (FG-CNTRC) plate model for the first time, and its free and forced vibration is analyzed by employing the domain decomposition method. The segmentation technique is employed to discretize the structure along the length direction. The artificial spring technique is applied to the structural boundary and piecewise interface for satisfying the boundary conditions and the combined conditions between subplates. Based on this, the boundary conditions of subdomains could be considered as a free boundary constraint, reducing the difficulty in constructing the allowable displacement function. Since all the structures of subdomains are identical, the allowable displacement functions of them can be uniformly constructed using the two-dimensional ultraspherical polynomial expansion. The potential energy function of the plate is derived from the first-order shear deformation theory (FSDT). The allowable displacement function is substituted into the potential energy function, and then the natural frequencies and mode shapes of the multi-stepped FG-CNTRC plate are decided by using the Rayleigh–Ritz method. The accuracy and reliability of the proposed method are confirmed by the results of the previous literature and finite element method (FEM). On this basis, the influences of the geometric and material parameters on free and forced vibration of the multi-stepped FG-CNTRC plate are also studied.

A Smoothed GFEM Based on Taylor Expansion and Constrained MLS for Analysis of Reissner–Mindlin Plate

Based on the Taylor Expansion and constrained moving least square function, a smoothed GFEM (SGFEM) is proposed in this paper for static, free vibration and buckling analysis of Reissner–Mindlin plate. The displacement function based on SGFEM is composed of classical linear finite element shape function and nodal displacement function, which are obtained by introducing the gradient smoothed meshfree approximation in Taylor expansion of nodal displacement function. A constrained moving least square function is proposed for constituting meshfree nodal displacement function. The merits of the proposed SGFEM, including high accuracy, rapid error convergence, insensitive to mesh distortion, free of shear-locking problem, no extra DOFs and temporal stability, etc., are demonstrated by several typical examples and comparisons with other numerical methods.

Investigation of the characteristics of turbulent flow and heat transfer induced by a vibrating piezoelectric fan on asymmetrical concave surfaces

This paper aims at performing an investigation numerically on the turbulent flow and thermal performances for an asymmetrical concave surface integrated with a slim vibrating piezoelectric fan. The dynamic mesh technique using a user defined function to describe the displacement function of vibrating cantilever beam is employed to model the deformation of the slim piezoelectric fan in time. Meanwhile, the SST k-ω turbulence model is chosen to capture the turbulence behavior of the flow and heat transfer. Two important factors, the relative curvature of the both sides of semicircular surfaces ( RK) and the dimensionless distance of fan offset along y-axis (Δ y/ APP) are taken into considerations during the simulation process. A considerable increase of local time-average heat transfer coefficients is observed in the vicinity of vibration envelope. The results show that the relative curvature ( RK) has a strong influence on the flow and heat transfer at both ends of the asymmetrical concave surface when its value is larger than 2. And by adjusting the dimensionless offset distance of the piezoelectric fan (Δ y/ APP), the area-averaged convective heat transfer coefficient can be increased by 20% on a small zone surrounding the fan with WPF × App (S1). The conclusions of this paper implement a theoretical attempt for expanding the application scenarios of piezoelectric fan.

Dynamic Analysis of Line Gear Pair Based on Numerical Manifold Method

As a kind of tiny gear based on space curve meshing theory, the line gear is very suitable for miniaturized machines due to its compact size and low weight. However, the line gear usually suffers from serious vibration problems since its line teeth are designed as twisted three-dimensional cantilevers to provide conjugated meshing curves. A dynamic model of the line gear pair is established in this paper using the numerical manifold method (NMM) to alleviate its vibration conditions, which can simultaneously provide mathematical and physical covers. The displacement function is first derived for the line teeth, and the dynamic equations of the manifold element are acquired. After inspecting the reasons that cause meshing excitation, the dynamic response of the line teeth is attained in all three orthogonal directions. The attained dynamic response shows that the vibration in the axial gear direction is more significant than that in the curvature direction. Furthermore, the vibration differential equations of the line teeth are solved through a detailed example, and the relationship between the design parameters and the natural frequency is revealed. The vibration characteristics of the first four order of the line gear are revealed through the method of NMM and compared with the result that is carried out through the commercial finite element method (FEM). The comparison shows that NMM can efficiently relieve the vibration problems of the line gear.