جستجوی مقالات مرتبط با کلیدواژه "روش المان محدود" در نشریات گروه "مهندسی دریا"

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.

Propeller-induced vibration of a marine vessel is one of the most complex issues of fluid and structure and the interaction between them. In the present article, numerical simulations of fluid flow around the propeller are performed first and the characteristic curves of propeller hydrodynamic performance in open water conditions are plotted for various advance ratios. It is observed that the maximum relative error of numerical simulations relative to experimental data in various advance ratios is about 7%. Then, the numerical vibration simulations of the solid propeller are performed. To achieve the results independently from the computational grid, the modal analysis results for calculating the vibrational natural frequencies for five different computational grids are compared to each other. Three different popular propeller materials i.e. brass, nickel aluminum bronze, and stainless steel are considered, and the results of numerical vibrational simulations such as natural frequencies and vibrational mode shapes using the modal analysis are compared for these propellers. Quantitatively, the magnitudes of natural frequencies for stainless steel and nickel-aluminum bronze propellers are 33% and 14% more than that of the brass propeller, respectively. In other words, brass is the most vulnerable and stainless steel is the most durable propeller material against resonance.

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.

Launching pads are among the essential elements of missiles and their main function is to prepare missiles for launch. Tower launchers dimension and configuration depend on effective loads, dimension and weight of the missile. In the majority of tower launchers, two bars connected to each other with crossbar connectors are considered to be the basic parts. Therefore, it is essential to calculate accelerations (forces) applied from ship to structure of the tower launcher. Space frame element is used for designing and a finite element code has been written in MATLAB Software to calculate stress and deformities of the structure. A Genetic algorithm which is codified in MATLAB has been used for optimization. All of the written codes have been compared to experimental data and results confirm the accuracy and exactness of the outcome. In this design weight of the tower launcher was the target equation, displacement and yield stress were constraints and geometrical specifications of the cross section were variables.

From historical point of view, equations that have the capability of modeling the dispersion and nonlinearity characteristics of waves were first used by Peregrine in 1967 to analyze the experimental results of solitary waves. In year 1972, Peregrine, based on the equations that he had developed in year 1967, derived a new system of equations for modeling the waves in shallow waters. These equations later became the foundations for derivation of shallow water system of equations like that of Madsen-Sorensen in 1992. In the present article, an effort has been made to offer a suitable finite element method for numerical solution of Peregrine system of equations (1972) which would have the capability of solving other shallow water system of equations that would be derived based on the Peregrine system of equations.

Solitary wave is a two-dimensional and nonlinear gravity wave that was observed for the first time by John Scott Russell in 1894 during researches in a channel and First was named translating Wave. Modeling of solitary wave propagation in a long channel with constant depth is a suitable test to assess the stability and accuracy rate of governing equation’s dispersion and nonlinear terms recruitment and provide dynamic equilibrium. In this study, a numerical model based on the extended boussinesq equations derived by Beji and Nadaoka as a suitable system of governing equations based on standard Galerkin finite element method is presented. The time integration is performed using the semi-implicit method. Flat triangular elements with linear Interpolation functions are employed for the two horizontal velocity components and the water surface elevation. In order to evaluate the ability of one and two-dimensional numerical model, solitary wave propagation is simulated in a channel. The model is capable of giving satisfactory predictions in all cases.