Journal of Computational Applied Mechanics
Volume:54 Issue: 4, Dec 2023

Modal and frequency response analysis of the piezoelectric energy harvester utilizing the auxetic booster has been performed in this paper. This harvester has composed of a cantilever, auxetic substrate, and piezoelectric layer. The influence of the piezoelectric’s electrical circuit and the harvester’s geometrical properties on the fundamental natural frequency, output voltage, and harvested power of the energy harvester have been investigated. The electrical circuit of this electromechanical system consists of a resistor that influences the energy harvester's output voltage and harvested power. A comprehensive parametric study has been performed to find the optimum resistor of the energy harvester. All the analysis has been performed using the finite element method. Mesh size sensitivity analysis of the models is presented, and the finite element model is verified by previous experimental studies. Furthermore, the effect of this energy harvester's damping ratio on the system's outputs has been investigated. The results show that the system's output alters considerably in different damping ratios, and it is necessary to determine the system's damping ratio of the system. The damping ratio of the auxetic energy harvester has been measured through the experimental investigation. The present study illustrates that harvested power of a trapezoidal auxetic energy harvester in resonant frequency could improve by 260 percent by utilizing the optimum resistor. Also, increasing the auxetic booster's thickness could improve the output voltage and harvested power by 48 percent and 22 percent.

The analysis of the bending behavior of rotating porous disks with exponential thickness variation consisting of viscoelastic functionally graded material is illustrated. The study of bending in the porous disk was done using the first-order shear deformation theory. The porous disk is under the effect of a combination of mechanical stresses and thermal distribution. All material factors for the porous disk change across the thickness as a power law of radius. To solve the mathematical structure by using the semi-analytical technique for displacements in the porous disk, and then to treat the structure model with viscoelastic material by the correspondence principle and Illyushin’s approximation manner. Numerical outcomes including the effect of porosity parameter, inhomogeneity factor, and relaxation time are presented with three different sets of boundary conditions for the solid and hollow disks. A comparison between porous and perfect disk with numerous values of porosity parameters and different inhomogeneity factors have been shown to emphasize the importance of complex mathematical structure in modern engineering mechanical designs.

Mechanical systems with structural symmetries present vibration properties that allow the calculation to be easier and the analysis time to decrease. The paper aims to use the properties involved by the symmetries that exist in mechanical systems for the analysis of the forced response to vibrations. Thus, the study of the properties of systems with symmetries or with identical parts is expanded. Based on a classic model, the characteristic properties that appear in this case are obtained and the advantages of using these properties are revealed. On an example consisting of a truck equipped with two identical engines, the way of applying these properties in the calculation and the resulting advantages is presented.

Using the disk-form multi-layer method (MLM), a semi-analytical thermoelastic solution for pressurized rotating thick cylindrical shells with varying thickness is obtained. The first-order shear deformation theory (FSDT) is used for displacement and bi-directional temperature fields. The thick shell is divided into some virtual disks, and then a set of differential equations for constant thickness are obtained for each virtual disk. The general solution of the thick cylindrical shell is obtained, by applying continuity conditions between the virtual disks. The governing equations, which are a system of differential equations with variable coefficients, have been solved with MLM. Finally, some numerical results are presented to study the effects of mechanical and thermal loading, on the mechanical behavior of the thick cylindrical shell.

Due to the alarming increase in greenhouse gases, switching to clean, renewable energy sources like wind energy has become imperative. As a result, the use of different wind turbines to generate electricity increased worldwide. Meanwhile, Darrieus vertical axis wind turbines (VAWTs) have gained considerable popularity due to their acceptable efficiency. Individual wind turbines are not efficient enough for widespread use and are only suitable for providing domestic energy; therefore, they should be placed in the form of turbine clusters in wind farms. The wind farm configuration and cluster placement have specific considerations, including the rotors' optimal installation distance and rotational direction. In the present study, the rotors installation distance in an array including a cluster of three Darrieus rotors is investigated, and the CFD and Kriging optimization results ensured that the best installation distance is equal to 1.5 times the diameter (1.5D). Also, the CFD results for the rotor's rotational direction at the installation distance of 1.5D showed that when the lower downstream rotor is counter-rotating the leading rotor and clockwise, the overall efficiency of the cluster increases by 67.1%. Additionally, two V-shaped and rhombic configurations are modeled, and the overall efficiency of each turbine in two different configurations is compared separately with the single turbine. In the optimum case, the overall efficiency of turbine A in the V-shaped configuration of three turbines and the rhombic configuration of 12 turbines improved by 54% and 36%, respectively, compared to the single turbine. The study of the streamlines showed that the main reason for improving the performance in the V-shaped configuration is the favorable velocity gradient around the blade, and the decrease in overall efficiency in the V-shaped and rhomboid configurations is wake flow intensity and trapping between the rotors which cause the stagnation zone.

Curved beams are widely used in combination with the linear elements of various civil engineering structures. Many researchers attempted to analyze beam curved in plan, beam curved in elevation, and spatial curved beam using different methods and different approaches and presented analytical exact solution and approximate numerical solution. The analytical exact integration of the governing differential equations is the major difficulty for the analysis of the geometrically non-linear curved beams. To overcome this difficulty, a finite displacement transfer method is proposed to eliminate analytical differentiation and integration, completely. This paper deals with the stiffness matrix of 3D curved beam with varying curvature and varying cross-sectional area. A novel finite displacement transfer method is used to determine displacements of the freely supported node of the cantilever 3D curved beam. The flexibility matrix is derived using the finite displacement transfer method. The stiffness matrix is derived by employing equilibrium and transformation matrix. The finite difference method is used for the numerical solution of the differential equations. Results of the calculation method are compared with the results of other methods in the literature and the FEM based analysis software. For the circular helix with uniformly varying cross-sectional area and 3600 elements, the maximum and minimum percentage difference in the stiffness coefficient is 2.89% and −0.65% respectively. For the elliptic helix with the uniform cross-sectional area and 720 elements, the maximum and minimum percentage difference in the stiffness coefficient is 2.69% and −2.65% respectively. The novel of this study lies in the generation of the stiffness matrix of the 3D curved beams without tedious analytical differentiation and integration of governing equations. The stiffness matrix of the spatial curved beam is applicable to the planer curved beam also.

Today the micro electromechanical systems industry is widely developed. This article aims to study static pull-in instability of a clamped micro-switch which is exerted by an electric potential difference in presence of a longitudinal magnetic field. The size dependent nonlocal couple stress theory in framework of Bernoulli-Euler beam hypothesis is utilized to model a clamped micro-switch. The equilibrium equation of micro-beam in micro-switch is derived using the principle of virtual work. To obtain the dimensionless pull-in voltage of micro-switch, the equilibrium equation is solved by Galerkin method. The effect of longitudinal magnetic field and some geometric parameter of micro-beam on the pull-in voltage is studied, taking into account the effects of a set of size dependent factors with and without considering the fringing field. The results from developed model are validated by comparing them with benchmark results.

This study focuses on the analysis of the bio-thermoelasticity response exhibited by biological tissues when their inner and outer surfaces are free from stress and exposing the outer surface of the skin to harmonic heating with heatlessness of the inner surface of the skin. The investigation employs a refined Green–Lindsay model for a comprehensive understanding of the phenomenon. A system of partial differential equations is written and the solution is obtained using the Laplace transform and numerical inverse Laplace. The current model's results for temperature, displacement, stress, and strain distributions are presented, and it is compared to various (coupled and uncoupled) models from previous literature. The relaxation times effect on the model with other models is clarified, the effect of time, and some vital parameters are also studied, and tabularly to illustrate the effect of blood perfusion on the four distributions.

The existence of friendly programming environments, which allow the transposition of models developed for different mechanical systems into numerical procedures, easy to access, make it necessary to develop models of mechanical systems used in industry. In this work, we propose to do this for an internal combustion engine. The offered model allows the unitary solution of problems of this type, which involves the calculation of the forces appearing in the engine elements. It offers the possibility to analyze different constructive types of engines. The model is a complex model that finally provides the forces existing in different elements of the engine as well as the developed engine torque.

Sandwich structures are widely used in many industries such as marine& submarine, aerospace, automobiles and etc due to its lightweight nature, high bending stiffness, high fatigue resistance and ability to absorb energy. However, the investigations into sandwich structures with 3D printed core are limited in number. These structures can create a meta material behavior with the change of geometry which leads to negative poison ratio of core. Hence, in this article, investigations into sandwich structures with 3D printed core under various loading for comparing their structural responses have been reviewed in detail. Different shapes of 3D printed cores have been reviewed and their specifications are discussed.