Thermal buckling analysis of temperature-dependent FG-CNTRC quadrilateral plates

The main objective of the present study is to analyze the thermal buckling of functionally graded carbon nanotube-reinforced composite (FG-CNTRC) quadrilateral plates. Functionally graded patterns are introduced for the distribution of the carbon nanotubes (CNTs) through the thickness direction of the plate. The effective material properties of nanocomposite plate reinforced by CNTs are considered to be temperature-dependent (TD) and estimated using the micromechanical model. By the use of minimum total potential energy principle and based on the first-order shear deformation theory of plates, the stability equations are obtained. In order to use the generalized differential quadrature (GDQ) method and solve the stability equations, the irregular domain of quadrilateral plate is transformed into regular computational domain employing the mapping technique. The efficiency and accuracy of the proposed approach are first validated. Then, a comprehensive parametric study is presented to examine the effects of model parameters on the thermal buckling of FG-CNTRC quadrilateral plates. The results indicate that considering temperature dependency of the material properties plays an important role in the stability of the FG-CNTRC quadrilateral plates subjected to thermal loading.     

Towards development of unsteady near-wall interface boundary conditions for turbulence modeling

In near-wall turbulence modeling it is required to resolve a thin layer nearby the solid boundary, which is characterized by high gradients of the solution. An accurate enough resolution of such a layer can take most computational time. The situation even becomes worse for unsteady problems. To avoid time-consuming computations, a new approach is developed, which is based on a non-overlapping domain decomposition. The boundary condition of Robin type at the interface boundary is achieved via transfer of the boundary condition from the wall. For the first time interface boundary conditions of Robin type are derived for a model nonstationary equation which simulates the key terms of the unsteady boundary layer equations. In the case of stationary solutions the approach is automatically reduced to the technique earlier developed for the steady problems. The considered test cases demonstrate that unsteady effects can be significant for near-wall domain decomposition. In particular, they can be important in the case of the wall-function-based approach.     

宽带电磁散射分析中的ZT-FDTD算法

讨论ZT-FDTD算法,针对其中的不足,提出使用基于Z变换的(FD)2TD算法计算色散半空间上三维有限长介质柱的宽带电磁散射特性.针对在不同极化及入射角情况下的宽带散射,运用(FD)2TD算法进行分析,将频域方程变换到Z域,再返回到时域进行差分计算,并给出仿真结果.     

Short-term traffic flow forecasting: parametric and nonparametric approaches via emotional temporal difference learning

Information signal from real case and natural complex dynamical systems such as traffic flow are usually specified by irregular motions. Chaotic nonlinear dynamics approach is now the most powerful tool for scientists to deal with complexities in real cases, and neural networks and neuro-fuzzy models are widely used for their capabilities in nonlinear modeling of chaotic systems more than the traditional methods. As mentioned, the traffic flow conditions caused the forecasting values of traffic flow to lack robustness and accuracy. In this paper, the traffic flow forecasting is analyzed with emotional concepts and multi-agent systems (MASs) points of view as a new method in this field. The findings enabled the researchers to develop a newly object-oriented method of forecasting traffic flow. Its architecture is based on a temporal difference (TD) Q-learning with a neuro-fuzzy structure, which is the nonparametric approach. The performance of TD Q-learning is improved by emotional learning. The proposed method on the present conditions and the action of the system according to the criteria could forecast traffic signals so that the objectives are reached in minimum time. The ability of presented learning algorithm to prospect gains from future actions and obtain rewards from its past experiences allows emotional TD Q-learning algorithm to improve its decisions for the best possible actions. In addition, to study in a more practical situation, the neuro-fuzzy behaviors could be modeled by MAS. The proposed method (intelligent/nonparametric approach) is compared by parametric approach, autoregressive integrated moving average (ARIMA) method, which is implemented by multi-layer perceptron neural networks and called ARIMANN. Here, the ARIMANN is updated by backpropagation and temporal difference backpropagation for the first time. The simulation results revealed that the studied forecaster could discover the optimal forecasting by means of the Q-learning algorithm. Difficult to handle through parametric and classic methods, the real traffic flow signals used for fitting the algorithms is obtained from a two-lane street I-494 in Minnesota City.     

TD(λ) learning without eligibility traces: a theoretical analysis

A common approach to learning from delayed rewards is to use temporal difference (TD) methods for predicting future reinforcement values. They are parameterized by a recency factor λ which determines whether and how the outcomes from several consecutive time steps contribute to a single prediction update. TD(λ > 0) has been found to usually yield noticeably faster learning than TD(0), but its standard eligibility traces implementation is associated with some well known deficiencies, in particular significantly increased computation expense. This article investigates theoretically two possible ways of implementing TD(λ) without eligibility traces, both proposed by prior work. One is the TTD procedure, which efficiently approximates the effects of eligibility traces by the use of truncated TD(λ) returns. The other is experience replay, which relies on replaying TD prediction updates backwards in time. We provide novel theoretical results related to the former and present an original analysis of the effects of two variations of the latter. The ultimate effect of these investigations is a unified view of the apparently different computational techniques. This contributes to the TD(λ) research in general, by highlighting interesting relationships between several TD-based algorithms and facilitating their further analysis.     

A curved-element unstructured discontinuous Galerkin method on GPUs for the Euler equations

In this work we consider Runge–Kutta discontinuous Galerkin methods for the solution of hyperbolic equations enabling high order discretization in space and time. We aim at an efficient implementation of DG for Euler equations on GPUs. A mesh curvature approach is presented for the proper resolution of the domain boundary. This approach is based on the linear elasticity equations and enables a boundary approximation with arbitrary, high order. In order to demonstrate the performance of the boundary curvature a massively parallel solver on graphics processors is implemented and utilized for the solution of the Euler equations of gas-dynamics.     

A lattice Boltzmann model for electromagnetic waves propagating in a one-dimensional dispersive medium

A first-order extended lattice Boltzmann (LB) model with special forcing terms for one-dimensional Maxwell equations exerting on a dispersive medium, described either by the Debye or Drude model, is proposed in this study. The time dependent dispersive effect is obtained by the inverse Fourier transform of the frequency-domain permittivity and is incorporated into the LB evolution equations via equivalent forcing effects. The Chapman–Enskog multi-scale analysis is employed to ensure that proposed scheme is mathematically consistent with the targeted Maxwell’s equations at the macroscopic limit. Numerical validations are executed through simulating four representative cases to obtain their LB solutions and compare those with the analytical solutions and existing numerical solutions by finite difference time domain (FDTD). All comparisons show that the differences in numerical values are very small. The present model can thus accurately predict the dispersive effects, and demonstrate first order convergence. In addition to its accuracy, the proposed LB model is also easy to implement. Consequently, this new LB scheme is an effective approach for numerical modeling of EM waves in dispersive media.     

人脸语音动画中基于PSOLA的情感语音合成系统

提出一种基于时域基音同步叠加TD-PSOLA算法的情感语音合成系统。根据情感语音库分析总结情感规则,在此基础上利用TD-PSOLA算法对中性语音的韵律参数进行改变,并提出一种能够对基频曲线尾部形状改变的方法,使句子表达出丰富的情感。实验表明,合成出的语音具有明显的情感色彩,证明了该系统能以简单明了的方式实现情感语音的合成,有助于提高人脸语音动画表达的丰富性和生动性。     

利用跟踪微分器构造未知函数的寻优器及求根器

针对函数结构未知的情形,构造出能寻优和求根的非线性动态系统。这些动态系统是用两个跟踪微分器和函数的输入输出过程值模拟数值迭代过程得到的,是对未知函数实现寻优和求根的动态结构。     

Implicit co-simulation method for constraint coupling with improved stability behavior

This paper deals with a novel co-simulation approach for coupling mechanical subsystems in time domain. The submodels are assumed to be coupled by algebraic constraint equations. In contrast to well-known coupling techniques from the literature, the here presented index-1 approach uses a special technique for approximating the coupling variables so that the constraint equations together with the hidden constraints on velocity and acceleration level can be enforced simultaneously at the communication time points. The method discussed here uses second- and third-order approximation polynomials. Because of the high approximation order, the numerical errors are very small, and a good convergence behavior is achieved. A stability analysis is carried out, and it is shown that—despite the fact that higher-order approximation polynomials are applied—also a good numerical stability behavior is observed. Different numerical examples are presented, which illustrate the practical application of the approach.     

Frequency domain design of reduced order observer based H ∞ controllers - a polynomial approach

In this paper a frequency domain solution of the singular H X control problem, where s of the m measurements y ( t ) of the plant are not affected by disturbances, is considered. By applying the polynomial approach to the parameterization of state feedback and of reduced order observers the singular H X control problem is solved for a-n n th order plant using a frequency domain representation of a reduced order observer based H X controller of order n- s . This output feedback controller is directly calculated in the frequency domain by first solving the H X state feedback problem and then solving the singular H X filtering problem for a modified system model, which involves the J -spectral factorization of two polynomial matrix equations. The results presented are obtained by considering the time domain solution first providing good insight in the relations between the time and frequency domain approach to the solution of the singular H X control problem using reduced order observer based controllers.     

An approximation algorithm for the solution of the nonlinear Lane-Emden type equations arising in astrophysics using Hermite functions collocation method

In this paper we propose a collocation method for solving some well-known classes of Lane-Emden type equations which are nonlinear ordinary differential equations on the semi-infinite domain. They are categorized as singular initial value problems. The proposed approach is based on a Hermite function collocation (HFC) method. To illustrate the reliability of the method, some special cases of the equations are solved as test examples. The new method reduces the solution of a problem to the solution of a system of algebraic equations. Hermite functions have prefect properties that make them useful to achieve this goal. We compare the present work with some well-known results and show that the new method is efficient and applicable.     

Solution of systems of Boolean equations via the integer domain

This paper presents a new method for solving systems of Boolean equations. The method is based on converting the equations so that we operate in the integer domain. In the integer domain better and more efficient methodologies for solving equations are available. The conversion leads us to a system of polynomial equations obeying certain characteristics. A method is proposed for solving these equations. The most computationally demanding step is the repeated multiplication of polynomials. We develop a method for this problem that is significantly faster than the standard approach. We also introduce another variant of the method, the so-called hybrid approach, that leads to reduced memory requirements. Theoretical and experimental results indicate the superior performance of the proposed method and its variant compared to the competing methods. The proposed method is also validated by applying it to the problem of hardware verification.     

基于跟踪微分器的基波测量方法研究

电网基波参数特别是基波频率在谐波分析与治理中具有重要的地位,也是电能质量、电能计量以及电力系统控制等领域的重要技术指标。在非同步采样情况下,针对基于频域法测量基波频率存在频谱泄露现象和测算精度不高的问题,提出了基于跟踪微分器(Tracking Differentiator,TD)的基波参数时域测量方法。该方法的主要思想是将检测到的基波信号通过TD来获取基波跟踪信号及其微分跟踪信号,再通过这两个信号的最大幅值即可获取基波的幅值、频率和初相位参数。仿真结果表明,本文方法只需要60%额定工频周期窗口的样本数据即可获得较高精度的基波参数测算值,是一种有效的基波参数测量方法。     

Efficient simulation of liquid–solid flows with high solids fraction in complex geometries

An efficient and inexpensive method for the detailed simulation of liquid/solid flows with a high content of large solid particles is presented. In a finite volume context, a fixed Cartesian grid is used to discretize the equations of motion for the liquid phase. The same fixed grid is also used to represent the location of the solid particles by imposing the velocities on the nodes covered by the particles at any time. The new positions and the new velocities of the particles are updated using Newton’s law so that there is no need to re-mesh the domain. Despite the simplicity of the well-known Cartesian Grid Method, the originality and interest of the present approach lies in its use for coupling the liquid and solid phases, and in the efficient way in which the surface forces governing the motion of the particles are computed. The approach is validated using a series of simple test cases, and, as an illustration, an application relevant to the design of tubular heat exchangers for food processing is highlighted.     

Wavelet based iterative methods for a class of 2D-partial integro differential equations

In this paper, an iterative method based on quasilinearization is presented to solve a class of two dimensional partial integro differential equations that arise in nuclear reactor models and population models. Two different approaches based on Haar and Legendre wavelets are studied to develop numerical methods. In the first approach, time domain is approximated with the help of forward finite difference approach. In the second approach, both time as well as space domains are approximated by wavelets. Appropriate examples are solved using these methods and the obtained results are compared with the methods available in the recent literature.     

Flatness-based feedforward control for parabolic distributed parameter systems with distributed control

This paper deals with distributed parameter systems being described by inhomogeneous parabolic partial differential equations in one space dimension with a distributed control. The distributed control is presented by the right part of an equation, i.e. the source function. The source function can depend on the time as well as spatial variable. The approach for design of a feedforward control for the purpose of exact output tracking is presented. The design of the feedforward control is based on the examination of inverse system dynamics. The proposed technique utilizes the method of the variables separation and the representation of a solution by the power series in the time domain. Some examples and numerical simulations are included and demonstrate the efficiency of the proposed approach for developing the feedforward control.     

一种加速时间差分算法收敛的方法

时间差分算法(Temporal difference methods, TD)是一类模型无关的强化学习算法. 该算法拥有较低的方差和可以在线(On-line)学习的优点, 得到了广泛的应用. 但对于一种给定的TD算法, 往往只能通过调整步长参数或其他超参数来加速收敛, 这也就造成了加速TD算法收敛的方法匮乏. 针对此问题提出了一种利用蒙特卡洛算法(Monte Carlo methods, MC)来加速TD算法收敛的方法(Accelerate TD by MC, ATDMC). 该方法不仅可以适用于绝大部分的TD算法, 而且不需要改变在线学习的方式. 为了证明方法的有效性, 分别在同策略(On-policy)评估、异策略(Off-policy)评估和控制(Control)三个方面进行了实验. 实验结果表明ATDMC方法可以有效地加速各类TD算法.     

Topology optimization of three-dimensional load-bearing structures using boundary elements

A numerical procedure for the topological optimization of three-dimensional linear elastic problems using boundary elements and the Topological Derivative (TD) is presented in this work. The TD is a function which characterizes the sensitivity of a given cost function to the change of the domain topology, like opening a small hole in a continuum. In particular, for this work the total potential strain energy is selected as cost function, and the TD is computed from the stress field by means of the Topological-Shape Sensitivity Method.The optimization problem is solved incrementally. In every step small portions of the model domain are removed by deleting small portions of material associated with the internal points. The new geometry is then remeshed and the resulting boundary element discretization checked (and if necessary fixed) in order to avoid geometrically invalid models. This procedure is repeated until a given stopping criterion is satisfied.The proposed strategy proves to be flexible and robust. A Furthermore, a number of examples are solved and the results discussed and compared to those available in the literature.