We report the development of a finite-element-based solver to compute transport of mass, momentum and energy during evaporation of a sessile droplet on a heated surface. The evaporation is assumed to be quasi-steady a...
详细信息
We report the development of a finite-element-based solver to compute transport of mass, momentum and energy during evaporation of a sessile droplet on a heated surface. The evaporation is assumed to be quasi-steady and diffusion-limited. The heat transfer between the droplet and substrate and mass transfer of liquid-vapor are solved using a two-way coupling. In particular, here, we develop and implement the formulation of fluid flow inside the droplet in the model. The continuity and Navier-Stokes equations are solved in axisymmetric, cylindrical coordinates. Jump velocity boundary condition is applied on the liquid-gas interface using the evaporation mass flux. The governing equations are discretized in the framework of the Galerkin weight residual approach. A mesh of finite triangular elements with six nodes is utilized, and quadratic shape functions are used to obtain the second-order accurate numerical solution. Two formulations, namely, penalty function and velocity pressure, are employed to obtain discretized equations. The numerical results are the same using both methods, and the latter is around 30-50% faster than the former for the cases of refined grid. Computed flow fields are in excellent agreement with published results. The solver's capability is demonstrated by solving the internal flow field for a case of a heated substrate.
This study investigates a parallel-in-space-and-time finite-element method (PinSTFEM) in time-periodic magnetic field analyses that take magnetic hysteresis into account. The developed PinSTFEM is obtained from a comb...
详细信息
This study investigates a parallel-in-space-and-time finite-element method (PinSTFEM) in time-periodic magnetic field analyses that take magnetic hysteresis into account. The developed PinSTFEM is obtained from a combination of the domain decomposition method (DDM) and parallel time-periodic explicit-error-correction (PTP-EEC) method. In addition, the magnetization history of each element is corrected appropriately based on time-series data for flux density vectors within the framework of the PTP-EEC method. The parallel performance of the developed PinSTFEM is verified by the 3-D magnetic field analyses of a ring core specimen and a practical interior permanent magnet synchronous motor (IPMSM) fed by a pulsewidth modulation (PWM) inverter.
PurposeLangevin transducers are ultrasonic transducers that convert electrical into mechanical energy through the piezoelectric effect. This class of transducers achieves the highest efficiency in their mechanical res...
详细信息
PurposeLangevin transducers are ultrasonic transducers that convert electrical into mechanical energy through the piezoelectric effect. This class of transducers achieves the highest efficiency in their mechanical resonance. Studies have shown that the resonant frequency changes with temperature. The aim of this contribution is to reproduce this temperature-dependence resonance frequency as accurately as possible with FEM ***, the temperature-dependent resonance behavior of Langevin transducers is examined experimentally. A FEM model is created on the basis of temperature-dependent measured material coefficients. Using parameter correlations and optimization algorithms, the FEM model is fitted and validated by experimental results. Six variants of Langevin transducers are examined in the range from 30 degrees C to 80 degrees C with resonance frequencies between 34 and 38 kHz. They differ in three geometries and two *** experimental results show that the resonance frequencies decrease with increasing temperatures by 5.0-19.4 Hz/degrees C, depending on the material and geometry. As decisive parameters for the model fitting of the FEM results, three function-dependent stiffness coefficients of the piezoelectric material PZT8 and the Young's moduli of the metallic materials are determined by parameter *** the targeted fitting of these function-dependent parameters, the calculation of the resonance frequencies of Langevin transducers can be qualitatively and quantitatively improved, independent of shape and material.
In this study, the effects in terms of electric stress of composite voltages on a high-voltage disconnector were investigated. The main purpose of this study is to determine and evaluate the effects of the conditions ...
详细信息
In this study, the effects in terms of electric stress of composite voltages on a high-voltage disconnector were investigated. The main purpose of this study is to determine and evaluate the effects of the conditions that may occur in real working conditions but out of the type tests. As for the disconnector model, one phase of a center-break disconnector was considered. In order to examine the effects of composite voltages on high-voltage disconnectors, a model is defined in the Comsol Multiphysics program. Different types of voltages such as operating voltage, 50 Hz test voltage, lightning impulse voltage, and composite voltage, were applied to the 170 kV disconnector model separately. After applying a composite voltage consisting of power frequency voltage and lightning impulse voltage to the disconnector, electric potential and electric field distributions were obtained. It has been observed that the maximum electric potential and the maximum electric field strength values on the disconnector are higher when composite voltage is applied than when non- composite voltage is applied to the disconnector. It is observed that the intensity of the electric field lines increases near the contacts of the current-carrying arm and the main contacts of the disconnector.
This paper is the first that proposes an extended hybrid analytical method (HAM) based on a two-dimensional (2-D) coupling between the semi-analytical Maxwell-Fourier analysis and finite-element method (FEM) in polar ...
详细信息
This paper is the first that proposes an extended hybrid analytical method (HAM) based on a two-dimensional (2-D) coupling between the semi-analytical Maxwell-Fourier analysis and finite-element method (FEM) in polar coordinates. The proposed model is applied to any rotating electrical machines. The main objective of this paper is to establish the magnetic field solution in the whole machine by coupling an exact analytical model (AM), proposed for all regions having relative magnetic permeability equal to unity, with a FEM in ferromagnetic regions. The AM and FEM are coupled in both directions (r, ?) in the edge separating teeth regions and all its adjacent regions by applied boundary conditions (BCs). The developed HAM gives accurate results on the magnetic flux density distribution and the cogging torque whatever the operating conditions, the magnetic or geometric parameters. All results obtained give very satisfactory agreement with 2-D finite-element analysis (FEA).
In this paper, the coupled advection-dominated diffusion-reaction equations which arise in the prevention of groundwater contamination problem are approximated by usual finiteelementmethod (FEM). It is clear that by...
详细信息
In this paper, the coupled advection-dominated diffusion-reaction equations which arise in the prevention of groundwater contamination problem are approximated by usual finiteelementmethod (FEM). It is clear that by increasing the number of elements to improve computational accuracy, we have to incur a lot of costs. The main presented idea is to reduce the used CPU time for employing the finite-element method by combining that with a technique which reduces the dimension of the problem. To this end, we apply the proper orthogonal decomposition (POD) technique to the usual FEM for the prevention of groundwater contamination problem to reduce CPU time with acceptable accuracy. Numerical examples are provided to illustrate efficiency and validity of the proposed method.
In this paper, we propose an efficient finite-element method based on dimension reduction scheme to solve the fourth-order elliptic equation in a circular domain. First of all, by using polar coordinate transformation...
详细信息
In this paper, we propose an efficient finite-element method based on dimension reduction scheme to solve the fourth-order elliptic equation in a circular domain. First of all, by using polar coordinate transformation and Fourier basis function expansion, the necessary pole conditions are derived and the original problem is decomposed into a series of equivalent one-dimensional fourth-order problems. Based on the pole conditions, the appropriate weighted Sobolev spaces are introduced and the error estimate of finite-element solution is proved for each one-dimensional fourth-order problem. Then we construct the cubic Hermite interpolation basis functions and derive the matrix form corresponding to the discrete scheme. Furthermore, the sparsity of mass matrix and stiffness matrix are illustrated. Finally, we provide some numerical experiments, and the numerical results show that our method is very effective.
In this article, we present a systematic numerical study for second-order linear wave equation using weak Galerkin finite-element methods (WG-FEMs). Various degrees of polynomials are used to construct weak Galerkin f...
详细信息
In this article, we present a systematic numerical study for second-order linear wave equation using weak Galerkin finite-element methods (WG-FEMs). Various degrees of polynomials are used to construct weak Galerkin finite-element spaces. Error estimates in L-2 norm as well as in discrete H-1 norm have been established for general weak Galerkin space (P-k (K), P-j (partial derivative K), [P-l (K)](2)), where k, j&l are non-negative integers with k >= 1. Time discretization for fully discrete scheme is based on second order in time Newmark scheme. Finally, we provide several numerical results to confirm theoretical findings.
The Darwin model for electromagnetic quasistatic (EMQS) field analysis is of particular interest for the analysis of power electronic devices, such as power transformers and wireless power transfer systems. This model...
详细信息
The Darwin model for electromagnetic quasistatic (EMQS) field analysis is of particular interest for the analysis of power electronic devices, such as power transformers and wireless power transfer systems. This model is an approach that neglects the second derivative term in time of the displacement current and considers the electrostatic field. This approximation allows conventional techniques for magneto-quasistatic (MQS) field analysis, such as considering nonlinear magnetic material properties and coupled circuit analysis, to be appropriated, and capacitance effects to be included. Several methods have been proposed for frequency-domain (FD) analysis. This is because it is difficult to properly derive a formulation of time domain (TD) analysis. We have already proposed a potential formulation in FD analysis and succeeded in obtaining appropriate calculation results. In this study, we propose a TD analysis of the low-frequency stabilization formulation in the finiteelementmethod. The proposed formulation is based on the Coulomb-type gauge condition, which defines no additional variables and redundant variables to improve the convergence characteristics. In addition, the system matrix can be made symmetric for solving by general preconditioners with iterative solvers.
In this work, to improve the static behavior of aerostatic journal bearings, we examine the effect of pockets with different shapes, including the square, rectangular 1, rectangular 2, and circular, manufactured on th...
详细信息
In this work, to improve the static behavior of aerostatic journal bearings, we examine the effect of pockets with different shapes, including the square, rectangular 1, rectangular 2, and circular, manufactured on the surface of the aerostatic journal bearing. The effects of the pocket shapes, pocket area S over bar , eccentricity ratio e, orifice diameter d(f), average gas film thickness h(0), and misalignment angles phi(x) and phi(y) on the static performance are investigated using simulations. The Reynolds equation is solved by the finite-element method in this work. Simulations reveal that the pocket area S over bar , eccentricity ratio e, gas film thickness h(0), orifice diameter d(f), and misalignment angles phi(x) and phi(y) have a significant influence on the load force F and the stiffness K. In general, rectangular 2 pocket bearings are found to perform somewhat better than bearings with other pocket shapes, with the pocket depth set to one-half of h(0), when the pocket area S over bar varies from one-twelfth to one. The pocket area S over bar should be set according to the average gas film thickness h(0) and the orifice diameter d(f) to achieve a better static performance for the bearings. For bearings operated with misalignment angles phi(x) and phi(y), different pocket areas S over bar should be set according to the pocket shapes for the optimal design.
暂无评论