finite element method

In this paper, a high-performance graphene dielectric plasmonic waveguide in the far infrared spectrum is proposed, which is one of the components of integrated photonic and optoelectronic circuits with various applications, including communications, military, medical, etc. The proposed waveguide geometric structure is composed of a rectangular cube layer with a semi-cylindrical ridge underneath (with a high refractive index material), rectangular cube substrate with a semi-cylindrical depression (with a low refractive index material), a sheet of graphene and the substrate of material with low refractive index, that the layers and sublayers are stacked on top of each other, respectively. Here, the surface plasmon polaritons (SPPs) modes are stimulated at the interface of graphene and dielectric. The propagation properties of SPPs modes have been investigated using the finite element method (FEM). The simulation results show that via modifying the geometrical parameters of the structure and tuning the chemical potential of the proposed graphene waveguide, a small normalized mode area ~〖10〗^(-4) and the propagation length ~〖10〗^3 μm are achieved. Therefore, it is recommended that the proposed waveguide can be used as a component of photonic devices due to relatively long propagation length and the strong confinement of light.

The construction of a suitable breakwater is of great importance for the protection of the coast and offshore facilities. When the wave hits the breakwater, part of it is reflected and this part hits the wave that is attacking the structure, which causes water turbulence in front of the breakwater. If the turbulence is severe, it can cause the heel of the breaker to heal over time. Design engineers are forced to use high reliability coefficients in the design in order to solve the problems of stability and bed erosion in front of various breakwaters exposed to high waves. Today, engineers have come up with a suitable solution to solve this problem and reduce the cost of rubble mound breakwater, and that is to use breakwater with optimal porosity. It is now necessary for design engineers to calculate the wave reflectance of porous breakwaters. In this research, using a combination of two finite element numerical methods (FEM) and boundary element method (BEM) for breakwater and fluid modeling has been investigated, so that the finite wave geometry breaker, ‌ Finite components and fluid environments are modeled by the boundary element method. The results show that increasing the porosity increases the reflectance, which will decrease with increasing wavelength.

In this paper, a new design is proposed for a neural-sliding mode controller for a certain class of permanent-magnet synchronous motors to employ in unmanned submarines. Using presented specifications; first, the intended motor is designed and simulated in the Maxwell full-wave software based on the finite element method. Then, the nonlinear model is derived by the neural network using the data obtained from the simulation of the motor in the software. Since the model-based control methods are expensive and error-prone due to the high dependence on the modeling as well as the use of sensors, a sensorless controller is used, and with respect to the proposed nonlinear method, a sliding mode controller is designed for this particular motor. The proposed neural-sliding controller has obtained better results than the PID controller due to its robustness against system uncertainties and external disturbances, the overall closed-loop stability and convergence of error-trace to zero. The simulation results confirm the proper performance of the proposed model and controller.

During the last decades, researchers took active interest in the dynamic behaviour of stiffened shells, because of their practical applications. In this investigation, conventional and super finite elements method are used for linear vibration analysis of these structures. Mindlin plate and Timoshenko beam theory are utilized to formulate plate and stiffeners, respectively. Stiffeners are not limited to be placed on nodal lines, and eccentricity of stiffeners is considered. The accuracy of the formulation is verified, by comparing some of the author's results of specific problems with those available in the literature. Effects of various parameters such as the boundary conditions of plate, along with orientation, type (eccentric, concentric), dimensions and number of stiffeners on free vibration characteristics are studied.