WENO scheme with static grid adaptation for tracking steep moving fronts

The numerical solution of a hyperbolic or a convection-dominated parabolic partial differential equation is challenging due to the large local gradients that are present in the solution. A possible method to track the sharp fronts that are associated with large gradients is to adapt the grid and this can be done dynamically or statically, i.e. at discrete points of time during the simulation. In this paper, a novel approach that is based on combining the high-order WENO scheme with a static moving grid method is presented. The proposed algorithm is tested on the viscid Burgers’ equation, the linear advection equation and the population balance equation that describes particle growth in emulsion polymerization. Enhancements in the performance are observed in all case studies when compared with the conventional WENO scheme on a uniform grid making it a promising alternative when dealing with similar problems.     

催化油浆泵预热系统改造

通过对催化装置油浆泵预热阀闸板磨损原因进行分析,并根据分析结果对其预热系统进行技术改造,取得了良好效果。     

High-efficiency dynamic supply CMOS audio power amplifier for low-power applications

This paper describes the analysis and design of a dynamic supply CMOS audio power amplifier for low-power applications. The dynamic supply technique is used to increase the efficiency of a class AB power amplifier. The polarization of its output stage is adaptive so that the maximum efficiency enhancement can be achieved without jeopardizing the linearity of the system. Two types of adaptive polarization are proposed and compared. A concept of power supplies switching is also proposed. Simulation results are presented showing that an efficiency of 53.6% at a total harmonic distortion (THD) of less than 0.1% can be achieved, whereas the maximal theoretical value for a class AB amplifier is approximately 33.3%.     

基于自适应粒子群算法的目标位置测量方法

针对现有目标位置测量算法复杂和标准粒子群算法收敛速度慢的缺点,提出了一种基于自适应粒子群算法的目标位置测量方法。该方法通过自适应惯性权重平衡PSO的全局搜索和局部改良能力,通过自适应变异策略提高算法摆脱局部极值和局部寻优的能力,实现了目标位置的快速测量。仿真结果表明,该方法在测量时差精度为100ns的条件下,目标位置测量精度小于100m,且能够有效地避免早熟收敛问题,具有较快的收敛速度。     

切削加工有限元仿真技术研究进展

基于有限元仿真技术强大的数值分析能力,它已成为定量研究金属切削加工过程的有效手段,该技术对减少制造成本,缩短产品制造周期和提高产品质量具有重要意义。因此,对切削加工有限元仿真的一些关键技术:材料本构模型、动态自适应网格技术和切屑分离标准作了重点介绍,并对其研究现状和发展趋势进行了深入探讨。     

Image noise reduction using Wiener filtering with pseudo-inverse

We present a preliminary design and experimental results of a Gaussian noise reduction method for ultrasound images. Our method utilizes a Wiener filtering algorithm with pseudo-inverse technique. The method is capable of solving the Gaussian noise problem in ultrasound image by setup a constant dB of noise function. The key idea of the Wiener filtering algorithm is to process the given ultrasound signal by making the filtering less sensitive to slight changes in input conditions. In this paper, we investigate the possibility of employing this approach for pre-processing ultrasound image application. The application of the proposed method for reducing Gaussian noise is demonstrated by four examples. Meanwhile, we also made the comparisons with median filter, mean filter and adaptive filter; the results reveal that the proposed method has the best noise filtering capability than other three methods. The results also show that the proposed method produces recovery images with quiet high peak-signal-to-noise ratio.     

载波混沌Newton法在并联机构位置正解中的应用

针对Logistic混沌序列在(0,1)区间内的概率分布不均匀的特点,提出了基于幂函数的Logistic自适应载波混沌映射。新映射的概率分布较均匀,具有良好的遍历性。提出了基于Logistic自适应载波混沌映射的Newton迭代算法,即应用Newton迭代法求解非线性方程组时,以具有良好遍历性的Logistic载波混沌序列作为初始点。新方法可快速求出非线性方程组的多数(甚至全部)解,且计算过程简洁、效率高。根据杆长约束条件,建立了求6-DOF对称结构6-RUS并联机器人机构位置正解的非线性方程组,并应用新方法求解该方程组。数值实例表明,新方法可快速求出并联机构的全部位置正解,且应用位置反解验证了位置正解方法的正确性。     

加工中心龙门磁悬浮高度的滑模-H_∞控制

针对龙门数控加工中心中移动横梁的悬浮高度进行了研究。在龙门移动式数控机床中,可采用磁浮技术悬浮横梁消除摩擦提高加工精度。为保持悬浮系统的稳定性和精确性,提出了自适应积分滑模控制器并结合鲁棒H∞控制理论的控制方案。针对系统参数摄动和未建模动态设计了积分滑模变结构控制器;为降低滑模控制器抖振的发生,采用自适应控制对控制律的不确定值进行估测;考虑到刀具切削部件引起的系统质量变化以及外力干扰等对系统的影响,在控制中结合了H∞的控制理论,以增加系统的鲁棒性。仿真研究结果表明,此控制器具有很强的抑制扰动的能力和高刚度,可以实现稳定悬浮。     

基于Simulink的仿手指自适应柔性夹具支腿液压系统仿真

悬臂支腿系统是仿手指自适应柔性夹具的重要组成部分。建立支腿液压系统的数学模型与仿真模型,分析系统的稳定性。改变模型的主要参数,对系统进行仿真。仿真结果表明:系统稳定性和动态性能受泄漏系数和放大器增益系数的影响较大;采用PID控制后,系统的性能得到进一步的改善。     

基于滑模控制的模型参考自适应异步电机无速度传感器控制

针对异步电机无速度传感器控制中用传统模型参考自适应理论估计转速时存在复杂的PI增益系数调节的实际问题,提出了一种基于趋近律的滑模模型参考自适应系统,并利用Lyapunov理论推导出一种新的速度估计自适应律以确保系统稳定性和快速性.同时,该方法对外部扰动和噪声具有强鲁棒性,且对抖振具有明显的抑制效果.通过Simulink仿真实验也验证了该方法响应速度快,控制精度高的优良性能.