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2013 Vol. 34, No. 4
Published:
论文
325
ANALYSIS ON THE AEROELASTIC DYNAMIC STABILITY OF A ROTATING SANDWICH ANNULAR PLATE WITH VISCOELASTIC CORE LAYER
;;Youhe Zhou
An aeroelastic dynamic model for a rotating sandwich annular plate with a viscoelastic core layer is developed in this paper. Based on the Hamilton’s principle, all fundamental equations and boundary conditions for the rotating annular plate are derived, through comprehensive analysis of the aerodynamic forces acting on the plate and the complex modulus properties of the viscoelastic core layer. The effects of geometrical and material parameters on the respective frequency and damping of the forward and backward traveling waves, as well as the dynamic stability for the rotating sandwich plate are numerically analyzed by means of the Galerkin’s method. The results demonstrate that the critical and flutter speed of the rotating sandwich plate can be improved by certain proper geometrical and material parameters of the viscoelastic core layer.
2013 Vol. 34 (4): 325-332 [
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252
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333
ENERGY HARVESTING BASED ON LOCALLY RESONANT PHONONIC CRYSTALS FOR LOW FREQUENCY VIBRATIONS
In this paper, a novel locally resonant structure with energy harvesting capabilities is proposed, based on the analysis of bandgap mechanisms and energy localization effect in locally resonant phononic crystals. The vibration characteristics and energy harvesting capabilities of the structure are investigated using finite element methods (FEM). According to the resonant modes and the simplified "mass-spring" system model, the first seven-order resonant frequencies of the structure can be reduced to the frequency range of 50~250 Hz by changing material and geometric parameters. With a developed multi-core structure, dozens, perhaps hundreds, of resonant frequencies appear in the frequency range below 250 Hz and the lowest frequency is 20 Hz. Based on the harmonic response analysis of finite structures, these low and broadband resonance properties as well as the piezoelectric energy harvesting capabilities are confirmed to satisfy the low and broadband frequency requirements of the energy harvesting from ambient vibrations. These structures will be helpful for the self-powered microsystems, such as portable electronic devices, wireless sensor, microelectromechanical systems (MEMS) and so on, to extract energy from ambient low frequency vibrations.
2013 Vol. 34 (4): 333-341 [
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366
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342
Topology optimization of closed liquid cell materials based on extended multiscale finite element method
A topology optimization method based on extended multiscale finite element method is developed to design the closed liquid cell materials. The main goal of the methodology is to discuss the optimal layout of the closed liquid cells, which can be considered as the basic element of the closed liquid cell structure. Firstly, the multiscale topology optimizations focus on finding the optimal distributions of closed liquid cells in terms of minimum compliance of the whole structure, in which the design domain is discretized by the multiscale coarse elements and a “SIMP-like” density-based approach is employed. Subsequently, due to the fact that the closed liquid cell materials can be used to design compliant mechanisms, the topology optimization problems of such kind of compliant mechanism are investigated based on the multiscale methods. Finally, software implementation is based on SiPESC and numerical examples are carried out to validate the accuracy of the multiscale topology optimization method for the closed liquid cell materials.
2013 Vol. 34 (4): 342-351 [
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324
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352
The zonal disintegration mechanism of isotropic rock masses around a deep circular tunnel? subjected to dynamic unloading
A new mechanical model is proposed to investigate the zonal disintegration mechanism of isotropic rock masses around a deep circular tunnel subjected to dynamic unloading under hydrostatic pressure condition as well as the total elastic stress-field distributions. Effects of unloading rate and dynamic mechanical parameters of isotropic deep rock masses on the zonal disintegration phenomenon of the surrounding rock masses around a deep circular tunnel are taken into account.The number and size of fractured and non-fractured zones is determined using the Hoek-Brown criterion. Numerical computation is carried out. It is found from numerical results that the number and size of fractured and non-fractured zones significantly depend on unloading rate and dynamic mechanical parameters of deep rock masses.
2013 Vol. 34 (4): 352-360 [
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235
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361
NONLINEAR DYNAMIC RESPONSE OF SIMPLY-SUPPORTED FUNCTIONALLY GRADED RECTANGULAR PLATES
The nonlinear dynamic response of simply-supported functionally graded rectangular plates subjected to a transverse harmonic excitation is studied. Equivalent material properties of functionally graded material are described as power-law distribution functions. The ordinary differential governing equation for generalized coordinate of system is deduced based on the Galerkin method. Using averaging method, the amplitude-frequency response of system is obtained, and the nonlinear principal resonance of functionally graded rectangular thin plates is analyzed. Numerical example validates the averaging method; the multivaluedness and jump phenomenon in principal resonance response of functionally graded plates are revealed. Meanwhile, it is found that the initial conditions may change the response amplitude of principal resonance of functionally graded plates. Finally, the effect of power-law exponent of functionally graded material on the response amplitude of system is discussed.
2013 Vol. 34 (4): 361-366 [
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286
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367
Simulation analysis of IPMC 8-legged walking reptile
The 8-legged walking reptile model was designed with laminated IPMC as sheet-form leg asymmetrically distributing on the two sides. The power driver was achieved by inputting voltage wave. Using rigid-flexible hybrid technology, the touch-model of flexible sheet-form leg and rigid ground was determined. The reasonable walking gait was designed so as to get the driving power to make the reptile moving forward continuously. The entire analysis was carried out completely by finite element analysis software ANSYS and ADAMS. Geometric model and up to 32-order mode was obtained in ANSYS, while the movement analysis of the 8-legged walking reptile was performed in ADAMS. Parameter study found that the smaller power-driven and high drive frequency can not only make the walking reptile maintain a certain speed, but also increase its loading capacity and keep its stability quite well.
2013 Vol. 34 (4): 367-373 [
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289
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374
Effective mechanical property of nano coated fiber reinforced composites due to interface stress
Based on the theory of Gurtin-Murdoch surface/interface theory and the generalized self-consistent method, the closed-form solution of the effective anti-plane shear modulus of the nano coated fiber reinforced composites is obtained. The effects of wall thickness, mechanical property and interfacial property of the coating on the effective property of the composites are discussed. The numerical results reveal that the effective modulus is size dependent when the size of the coating is on the order of nanometer. For a fixed fiber volume fraction, the thinner the wall thickness is and the smaller the fiber radius is, the greater of the deviation is with the classical results. The influences of the fiber stiffness and coating interfacial property on the effective modulus are dependent on the coating stiffness, i.e., a very soft or very hard coating can shield the contribution of the fiber stiffness to the effective modulus of composites, and a very hard coating shields the surface/interface effect of the nano composites.
2013 Vol. 34 (4): 374-379 [
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309
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简报
380
A piecewise temperal expanding algorithm to solve viscoelastic problems with large deformation
Zhi Han;
Abstract: By utilizing an expanding technique, this paper presents a piecewised adaptive algorithm in time domain to solve viscoelastic problems with large deformation, and develops an explicit recursive Update-Lagrange FE formula. The iteration, except at the initial time interval where a large deformation elastic problem is needed to solve, is not required at any other time interval. A self-adaptive computing can be realized by controlling the computing accuracy via the increase of expanding powers. Numerical verification provides satisfactory results.
2013 Vol. 34 (4): 380-387 [
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234
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388
Thermal Fatigue Reliability Analysis for Space Structures Composed of Thin-walled Tube
The fatigue reliability of space structures composed of thin-walled tube element has been analyzed under alternating thermal load. Taking into account the fatigue damage due to both average temperature and temperature difference in cross section, an analytical method is proposed by using the models of residual strength and fatigue cumulative damage. First of all, according to the principle of fatigue cumulative damage equal, the frequency of multi-level disturbance stress load caused by temperature difference in cross section is equivalent to the times of constant amplitude stress load action under average temperature, thus both thermal stress loads will be unified for a constant amplitude load, then fatigue reliability can be analyzed by applying the residual strength model based on the theory of dynamic stress-strength interference, finally, the dynamic reliability of the structure in the comprehensive consideration of both thermal fatigue state is obtained. This method not only avoids the direct use of the critical damage value of the cumulated fatigue damage theory which is difficult to determine the problem, but also reflect the real situation of fatigue damage of metal. In the end, take Hubble Space Telescope as an example ,the dynamic reliability of the main beam with the role of cycle fatigue thermal load is analyzed ,and some meaningful conclusions are drawed.
2013 Vol. 34 (4): 388-395 [
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260
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396
Effect of random void defects on the mechanical properties of 3D braided composites
As for three-dimensional braided composites manufactured by the resin transfer molding (RTM) process, it is difficult to avoid the formation of void defects in the composites. Firstly, the generation mechanism of the void defects in the process of RTM was analyzed. The void defects mainly include the dry patches in the fiber-bundle and the voids in the resin matrix pocket. Then, a simple model for describing the random void defects distribution was presented. Based on the unit cell model containing the random void defects, a new finite element model was put forward to predict the effective elastic properties. Considering the random distribution of void defects, the probability statistics analysis was done by establishing the samples. Finally, the effect of the void volume fraction on the elastic properties was discussed in detail. The presented model can be utilized to predict the mechanical properties of 3D braided composites with random void defects. Keywords: braided composites; elastic properties; void volume fraction; random defects; probability statistics
2013 Vol. 34 (4): 396-400 [
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247
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401
Calculation of the Stress Intensity Factors of Three Dimensional Interface Crack Under Mechanical and Thermal Loading Using Universal Weight Function Method
Crack propogation in bimaterials and composites tends to occur at the interface when they withstand mechanical and thermal loadings, most cracks in engineering practice are three dimensional cracks, the traditional numerical methods such as finite element method and boundary element method for determination of transient stress intensity factor of interface crack under mechanical and thermal loadings are inefficient due to large amount of calculation. The universal weight function (UWF) is only dependent on the crack configuration and body geometry, and is independent of temperature fields and time, which avoids the repeated determinations of stress field for individual time instants and has an enhanced efficiency. The UWF method is especially suitable for determining the variation of transient stress intensity factors of an interface cracked body subjected to thermal and mechanical shock. The basic equation and finite element implementation of the UWF method for three dimensional Mode I, Mode II and Mode III interface cracks subjected to thermal and mechanical loadings is given in this paper based on Betti’s reciprocal theorem. Numerical results show that the UWF method is of good accuracy and satisfies the engineering application demand.
2013 Vol. 34 (4): 401-409 [
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291
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410
Dynamic Stress Concentrations in Thick Plates With an Arbitrary Cutout by Using the Refined Theory
Abstract: In this paper, based on complex variables and conformal mapping methods, using the refined dynamic equation of plates[9], elastic wave scattering and dynamic stress concentrations in plates with an arbitrary cutout were studied. Applying the orthogonal function expansion method, the problem to be solved can be reduced into the solution of a set of infinite algebraic equations. As examples, under free boundary conditions, numerical results of dynamic moment concentration factors in thick plates with a circular, elliptic cutout were computed, and then, the influences of the thickness ratio to the cutout radius on dynamic moment distributions were also analyzed. The results indicate that the parameters such as incident wave number, thickness of plates and elliptic eccentricity ratio have a great effect on dynamic moment distributions. It is shown that at a higher frequency, the numerical results, which are from the Mindlin theory and the refined theory, respectively, are different. The results are more accurate because the refined equation is derivative without using any engineering hypotheses.
2013 Vol. 34 (4): 410-416 [
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269
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417
MAGNETO-ELASTIC COUPLED DYNAMICS THEORETICAL MODEL OF AXIALLY MOVING CURRENT-CONDUCTING THIN PLATE
The problem of dynamics theoretical modeling for axially moving current-conducting thin plate in magnetic field is investigated and the basic magneto-elastic coupled vibration equations and corresponding relational expressions were derived. Kinetic energy, strain energy and virtual work done by external force of the thin plate are obtained when geometric nonlinearity was taken into account. The nonlinear magneto-elastic coupled vibration equations of an axially moving thin plate in magnetic field were deduced by using Hamilton principle, and boundary conditions of force and displacement were also obtained. Based on the Maxwell equations, the corresponding electromagnetic constitutive relations and boundary conditions, the electrodynamics equations and electromagnetic forces expressions of axially moving current-conducting thin plate in general magnetic field were derived. In particular, the expressions of vibration equations, electrodynamics equations and electromagnetic forces were simplified in terms of longitudinal, transverse magnetic field and strip thin plate. The results are expected to be a theoretical reference for further analysis of this case.
2013 Vol. 34 (4): 417-425 [
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269
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426
Dynamic Analysis of the Scattering of SH-wave by Circular Lining near Bimaterial Interface in Half-space
The scattering of SH-wave by circular lining near bimaterial interface in half-space and dynamic stress concentration are studied, based on the complex function method and Green’s function method. The solution of present problem is given by “image” method. Firstly, a suitable Green’s function is constructed, which is the essential solution of displacement field for an elastic right-angle plane with a circular lining impacted by anti-plane harmonic line source loading at horizontal surface. Secondly, the method of “conjunction” is used to construct the scattering model of SH-wave, then a series of Fredholm integral equations of first kind for determining the unknown forces can be set up through continuity conditions that are expressed in terms of the Green's function. Finally, the numerical examples showed that the concentration of dynamic stress depended on the incident frequency and angle of SH-wave, the geometrical position of circular cavity, and the different media combination parameters.
2013 Vol. 34 (4): 426-432 [
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265
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