A multiscale elasto-plastic damage model is developed to predict the nonlinear behavior of three-dimensional (3D) braided composites. In this model, the sequential multiscale method is applied to ...transfer the effective properties from microscale to mesoscale, and from mesoscale to macroscale. The constituents at the microscale consist of fiber, matrix and interface which are consistent with the mesoscale ones. The fiber is considered to be elastic and brittle, and the elastic damage model is applied to degrade the stiffness. For the epoxy matrix, a coupled elasto-plastic damage model is proposed to integrate the effects of plasticity and damage, and furthermore the paraboloidal yield criterion is adopted to characterize the different types of mechanical behavior in tension and compression. The bilinear constitutive relation based on the cohesive element is used to investigate the properties of interface. A user-defined material subroutine (UMAT) in the nonlinear finite element analysis software ABAQUS is written to implement the proposed model and determine the response for 3D braided composites under quasi-static tension. The numerical simulations are compared with the corresponding experiments and the results show that they agree well with each other.
This paper focuses on the design and analysis of a novel material-efficient permanent-magnet (PM) shape for surface-mounted PM (SPM) motors used in automotive actuators. Most of such applications ...require smooth torque with minimum pulsation for an accurate position control. The proposed PM shape is designed to be sinusoidal and symmetrical in the axial direction for minimizing the amount of rare earth magnets as well as for providing balanced axial electromagnetic force, which turns out to obtain better sinusoidal electromotive force, less cogging torque, and, consequently, smooth electromagnetic torque. The contribution of the novel PM shape to motor characteristics is first estimated by 3-D finite-element method, and all of the simulation results are compared with those of SPM motors with two conventional arched PM shapes: one previously reported sinusoidal PM shape and one step skewed PM shape. Finally, some finite-element analysis results are confirmed by experimental results.
We develop a general interface procedure to couple both structured and unstructured parts of a hybrid mesh in a non-collocated, multi-block fashion. The target is to gain optimal computational ...efficiency in fluid dynamics simulations involving complex geometries. While guaranteeing stability, the proposed procedure is optimized for accuracy and requires minimal algorithmic modifications to already existing schemes. Initial numerical investigations confirm considerable efficiency gains compared to non-hybrid calculations of up to an order of magnitude.
•A new framework for coupling general summation-by-parts schemes is formulated.•The framework is based on summation-by-parts preserving interface operators.•New operators are developed for curvilinear, non-collocated finite difference and finite volume interfaces.•Large efficiency gains are demonstrated for hybrid, non-collocated meshes.
This paper studies finite-time stability analysis and finite-time stabilization of linear systems by bounded linear time-varying feedback. On the one hand, (both local and global) finite-time ...stability of general nonlinear time-varying systems is investigated by the comparison principle and the notion of finite-time escaping functions. Some Lyapunov-like stability theorems are established. On the other hand, finite-time and prescribed-time stabilization of linear systems by bounded linear time-varying feedback are revisited based on the proposed finite-time stability theorems. Two classes of new time-varying high-gain functions are proposed to reduce the regulation time. Some connections of the proposed results to existing results on Lyapunov-inequality based finite-time stability analysis and nonlinear feedback based finite-time stabilization are revealed. The effectiveness of the proposed methods is illustrated by a numerical example.
Several physical phenomena such as transformation of pollutants, energy, particles and many others can be described by the well-known convection–diffusion equation which is a combination of the ...diffusion and advection equations. In this paper, this equation is generalized with the concept of variable-order fractional derivatives. The generalized equation is called variable-order time fractional advection–diffusion equation (V-OTFA–DE). An accurate and robust meshless method based on the moving least squares (MLS) approximation and the finite difference scheme is proposed for its numerical solution on two-dimensional (2-D) arbitrary domains. In the time domain, the finite difference technique with a θ-weighted scheme and in the space domain, the MLS approximation are employed to obtain appropriate semi-discrete solutions. Since the newly developed method is a meshless approach, it does not require any background mesh structure to obtain semi-discrete solutions of the problem under consideration, and the numerical solutions are constructed entirely based on a set of scattered nodes. The proposed method is validated in solving three different examples including two benchmark problems and an applied problem of pollutant distribution in the atmosphere. In all such cases, the obtained results show that the proposed method is very accurate and robust. Moreover, a remarkable property so-called positive scheme for the proposed method is observed in solving concentration transport phenomena.
•The variable-order time fractional advection–diffusion equation in 2-D is defined.•An accurate and robust meshless method is proposed for its numerical solutions.•A variable-order fractional modeling of air pollution is expressed and investigated.•It is shown that the proposed method is a positive scheme.•The proposed method can be extended for other types of variable-order fractional problems.
For wave propagation over distances of many wavelengths, high-order finite difference methods on staggered grids are widely used due to their excellent dispersion properties. However, the enforcement ...of boundary conditions in a stable manner and treatment of interface problems with discontinuous coefficients usually pose many challenges. In this work, we construct a provably stable and high-order-accurate finite difference method on staggered grids that can be applied to a broad class of boundary and interface problems. The staggered grid difference operators are in summation-by-parts form and when combined with a weak enforcement of the boundary conditions, lead to an energy stable method on multiblock grids. The general applicability of the method is demonstrated by simulating an explosive acoustic source, generating waves reflecting against a free surface and material discontinuity.
Summary
Using a hybrid Lagrangian‐Eulerian approach, a level set function–based immersed interface method (LS‐IIM) is proposed for the interaction of a flexible body immersed in a fluid flow. The ...LS‐IIM involves finite volume method for the fluid solver, Galerkin finite element method for the structural solver, and a block‐iterative partitioned method–based fully implicit coupling between the two solvers. The novelty of the proposed method is a level set function–based direct implementation of fluid‐solid interface boundary conditions in both the solvers. Another novelty is the computation of the level set function from a geometric method instead of differential equations commonly used in level set methods—the novel geometric as compared to the traditional method is found to be more accurate and less time‐consuming. The LS‐IIM is demonstrated as second‐order accurate. Verification study is presented first separately for both the solvers and then together for four fluid‐structure interaction (FSI) problems, with different levels of complexity including lid‐driven flow, channel flow, and free‐stream flow. Benchmark solutions are presented for two class of FSI problems: first, easy to set up and less time‐consuming and, second, a reasonably challenging and complex FSI problem involving sharp edges and forced‐motion of the flexible structure. The benchmark solutions are proposed at steady state for the first problem, after a verification study with two open‐source solvers and, at periodic state, after a validation with published experimental results for the second problem. Our benchmark solutions may be useful for verification study in future.
A geometric method–based computation of level set function and its usage for accurate implementation of fluid‐solid interface boundary conditions (BCs) in both the fluid and structural solvers are the novel feature of the proposed method for computational fluid‐structure interaction (CFSI). A simple and another complex FSI benchmark problems are proposed, and the steady and periodic solutions for the respective problems are presented for verification study in future.
Over the past 5 years, a substantial research effort aimed at optimising the design of offshore wind turbines has led to significant reductions in the projected cost of developing offshore wind. ...Optimising the geotechnical design of these structures, through modern analysis techniques such as 3D Finite Element Modelling (FEM), has played a key role in helping to reduce costs. This paper presents a methodology for accurately modelling monopile behaviour using Cone Penetration Test (CPT) data to calibrate the non-linear stress dependent Hardening Soil (HS) model. The methodology is validated by comparing the modelled behaviour to field tests on a range of pile geometries. The paper also demonstrates how the soil-pile reaction response curves can be extracted from the FE model by isolating the stresses on each element of the pile. The contribution of each component to the overall lateral resistance is shown to vary with the pile geometry and is examined using the extracted soil reaction curves.
•The effect of wind speed on PV module is obvious when it increases from 0 to 1m/s.•Ambient temperature plays an important role in PV module’s performance.•The solar cell temperature decreases as ...adjacent cell interval increases.
A three-dimension thermal model of typical polycrystalline photovoltaic (PV) module was performed in finite element software. Based on the model, the temperature distribution of the cell layer and module’s thickness direction were analyzed and simulated. The effects of environmental conditions such as solar irradiance, wind speed, ambient temperature and adjacent cell interval on the temperature distribution of PV module were investigated. The temperature distribution curves showed that the solar cell layer possessed the highest temperature of 331.76K near the solar cell center. The increasing of adjacent solar cell interval decreased PV module temperature. Wider adjacent cell interval is recommended considering the electrical power output of PV module. The results also showed that higher solar irradiance is helpful for the heat dissipation of PV module but results in higher temperature. The effect of wind speed on PV module is obvious when it increases from 0 to 1m/s and higher wind speed is helpful for the improving of PV module electrical efficiency. Lower ambient temperature is helpful for both the heat dissipation and the improving of PV module electrical efficiency, and this effect was obvious especially under high solar irradiance and low wind speed.
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