International Journal of Applied Mechanics

The influences of crack and delamination on the natural frequency and strain energy release rate of the laminated doubly curved shell structure are computed via a commercial finite element tool (ABAQUS). The effect of individual damages (crack and delamination) is modeled using the virtual crack closure technique (VCCT), considering the curvature effect. Initially, the model validity is established by comparing the results with the available results in the open domain. Additionally, the model validity has been verified via in-house experimentation for frequency responses. Further, the natural frequency and strain energy release rate (SERR) have been calculated for the structure to examine the influences of the individual or combined effect of damages by varying the design-dependent input geometrical parameters. The inclusive characteristics of the current model in conjunction with geometrical configurations are summarized for subsequent references.

In this paper, an improved dissipative particle dynamics (DPD) model is proposed to simulate magnetorheological (MR) suspension by using the cubic spline function to represent the interactions between magnetic and fluid particles. The model’s accuracy has been verified and validated through carrying out a number of simulations on simple fluids and MR fluids, in which both qualitative and quantitative agreements are observed between the DPD simulation results and the experimental findings and theoretical models in the existing literature. A series of numerical experiments are then conducted on MR fluids, thereby the microstructure evolution and flow properties of MR fluids in Couette and Poiseuille flows are investigated and the effects of some critical factors are particularly explored. Simulation results reveal that the plug region size, which relates to the yield stress of MR fluids, shows an increasing trend with the increase of magnetic field strength, particle volume fraction, particle mass but a decreasing trend with the increase of Mason number and pressure gradient; however, it remains almost unchanged with varying temperature.

We investigate the effect of horizontal periodic oscillation on the interfacial instability of two immiscible and viscous fluids of different densities in a fully saturated porous media. A linear stability analysis of the viscous and time-dependent basic flow leads to a periodic oscillator describing the evolution of the interfacial perturbation amplitude. The horizontal oscillation leads to the occurrence of two types of instability, the Kelvin–Helmholtz’s instability and the parametric resonance. These instabilities appear at the frontier between water and petroleum and have a practical interest in oil reservoir engineering. The results show that, an increase of the oscillation frequency destabilizes the Kelvin–Helmholtz instability and displaces the parametric instability regions toward the short wavelength perturbation. Also, we examine mainly how the other physical parameters of the system affect the instabilities for various permeability and porosity values of the porous medium as well as for relative heights of the two fluid layers.

This paper explores a new method for vibration control and energy harvesting by coupling a nonlinear energy sink (NES) with a cantilever beam containing giant magnetostrictive material. A mathematical model of the principal linear system under the action of an external harmonic force is established, and the dynamic equation of the system is derived using Newton’s second law, Hamilton’s principle, and nonlinear boundary conditions. The displacement responses of the system as functions of time and of frequency are obtained by using the Runge–Kutta method and harmonic balance method. The analytic results are found to be consistent with the numerical solution, confirming the accuracy and reliability of the calculated results. The frequency response and time response of the system with and without NES coupling, and with other parameters unchanged, were compared. The results show that the proposed structure can achieve excellent vibration suppression. The energy harvesting effect of the system as a function of time is also analyzed by the Runge–Kutta method, comparing results for different values of parameters such as NES mass, nonlinear spring stiffness, and damping coefficient. The results indicate that the proposed structure can achieve the desired effects of vibration reduction and energy harvesting, and that results can be optimized by adjusting the relevant parameters.

In this study, the optimization of free vibration and flutter analysis of a composite plate with the implementation of different boundary conditions is investigated. The governing equations of a composite plate are obtained using the first shear deformation theory (FSDT) of plates. The first-order piston theory is utilized to simulate aerodynamic loads, including arbitrary yaw angle over the panel area. The coupled method of genetic algorithm with well-known generalized differential quadrature (GDQ) method is then developed to obtain optimal layup, which led to maximum fundamental frequency and optimized critical flutter aerodynamic pressure. To achieve this aim, the free vibration and flutter analysis of a composite plate will be conducted via the obtained eigenvalue problem by establishing the discretized governing equations and applying boundary conditions. The obtained results are compared and validated with the available results in the literature, which show high accuracy and a fast rate of convergence. Also, the influence of changing in the yaw angle, number of layers, thickness-to-length ratio, boundary conditions and turning symmetric layup to asymmetric layup is studied.

TubeNet has the simplest possible tubular configuration with the uniform number of neurons in all layers and enables explicit inversion. To create a TubeNet, dimension-reduction is a prerequisite for the inverse problems so that the numbers of neurons in the input and output layerscan be made the same. This study introduces a novel procedure to construct inverse TubeNets. The proposed procedure has three major sequential steps. (1) An autoencoder will be used to extract the necessary number of features from a large number of features in a high-dimensional space; (2) Constraints will be imposed to the autoencoder guided by the concepts of the principal component analysis (PCA), so that the extracted features possess the important orthogonality; (3) An L2 regularizer is proposed to adequately impose these constraints on the off-diagonal entries in the weight matrix of the autoencoder, ensuring quality orthogonality. The benchmark problems of inverse identification of material constants of composite laminated plates are used to evaluate the effect of the present TubeNet procedure with the constraint autoencoder, standard autoencoder and PCA, implemented in TubeNet. The study shows that the present constrained autoencoder can effectively overcome the shortcomings of PCA and standard autoencoder, and offers an effective way for dimension-reduction for inverse TubeNet.

By semi-analytical modifications to Mackenzie’s equation, a new third-order relation between bulk modulus and porosity is developed for porous materials. Compared with Mackenzie’s equation, the proposed equation takes into consideration critical porosity and real geometry represented by the assembly of hollow spheres. It has been shown that the proposed equation is in better agreement with 10 sets of published data than Mackenzie’s equation and that has an advantage in predicting the matrix bulk modulus even lack of the data of dense porous specimens. In addition, the proposed equation can describe the bulk modulus of porous materials with critical porosity well. However, Mackenzie’s equation cannot work.

As a new model, functionally graded piezoelectric (FGP) sandwich plate with negative Poisson’s ratio honeycomb core (auxetic core) is considered in this paper. Buckling analysis of the FGP sandwich plate is investigated based on a novel four-unknown shear deformation plate theory. The electrical and mechanical properties of the face layers are continuously varied through the thickness of the layers. This variation is achieved using a power law distribution in terms of the constituents volume fraction. The core layer composed of hexagonal honeycomb cells with negative Poisson’s ratio was made of a metallic material. The sandwich plate is exposed to uniaxial or biaxial compressive loads as well as electric voltage. Five stability differential equations are established based on the principle of virtual work including mechanical and electric loads. The obtained buckling load is compared with that available in the literature. Impacts of various parameters like the power law index, load parameter, external applied voltage, core thickness, boundary conditions and plate geometry on the buckling load of the smart composite plates with auxetic core are investigated. From the numerical results, one can find that the increase of electric voltage and core thickness decreases the buckling load.

Traditional creep models cannot describe the nonlinear creep characteristics of rock; thus, considerable efforts have been made to establish better rock creep models. However, many of the previously presented improved models are too complicated, leading to difficulties in mathematical derivation and engineering application. To address this problem, this study proposes a simple model that can comprehensively describe rock creep characteristics and that can be effectively applied in practical engineering. Based on the variable-order fractional derivatives and continuum damage mechanics, an improved Burgers creep model is established. The use of this proposed model can be divided into two stages based on whether the accumulated creep strain of the rock reaches the threshold of starting accelerated creep. Then, both the one-dimensional and three-dimensional constitutive equations of the improved model are provided. In addition, the compression creep test results of six groups of rock samples are used to verify the effectiveness and reliability of the improved Burgers model proposed in this study. Furthermore, an analytical solution for tunnel displacement is derived on the basis of the improved model. This analytical solution is applied to the time-dependent displacement prediction of an auxiliary tunnel in Jinping hydropower station, and a good agreement between the theoretical results and monitoring data is achieved. The outcome of this study can provide useful guidance for related engineering designs.

Averaging approaches have been widely used to estimate continuum stress in granular materials to facilitate the assimilation of granular materials’ behavior into a continuum mechanics framework. At present, selection criteria for the appropriate averaging approach are still poorly understood. This paper compares the stresses computed by two popular averaging approaches, i.e., volume average approach (VAA) and boundary average approach (BAA) in order to investigate relative errors between the two approaches under various conditions. The comparisons between VAA and BAA under a static condition were first carried out based on the rigid particle analytical framework proposed by Rothenburg, L. [1980] “Micromechanics of idealized granular systems,” Ph.D. thesis, Carleton University, Ottawa, followed by discrete element modelling (DEM) simulations using PFC3D under a quasi-static condition. The results of theoretical comparison suggested that the relative error in the computed stresses by VAA with an omission of overlap could be grossly estimated by the ratio of overlap to length of contact branch, while the relative error in the computed stresses by VAA with an omission of external contacts could be grossly estimated by the ratio of maximum particle diameter to specimen size. At the ratio of maximum particle diameter to specimen size of 5, which is usually taken as the minimum recommended ratio to minimize boundary effect, the relative error caused by omitting the external contacts was as high as 20%. Numerical comparisons suggested that the relative errors of the two approaches under a quasi-static condition were significantly influenced by the strain energy ratio defined in this study. The VAA was recommended as a preferred computation method over the BAA when the strain energy ratio was considerably lower than unity.

The vibration of the composite towering structure as tower crane is obvious under dynamic load, so that it is very necessary to study the dynamic characteristics of the composite towering structure. The tower crane and the hoisting rope are considered flexible, and the lifted object is treated as a rigid body. Considering the pendulum motion of the payload, the rigid flexible coupling model of crane system is established by Lagrangian equation. The dynamic characteristics of the composite towering structure under the action of pendulum are studied numerically. In order to study the dynamic characteristics of the composite towering structure under different working conditions, simulations are carried out under various conditions with different lifting ranges, various hoisting ratios and swing directions of payload. According to the computation results, the influence of different parameters on the dynamic response of the composite towering structure is revealed.