基于摄动法的多条裂纹欧拉梁特征模态分析

基于摄动理论推导了带多条开口裂纹的欧拉梁的特征模态参数的理论计算公式。采用最直接的方式将梁开口裂纹模拟成梁微段内的横截面折减并用δ函数表达了带开口裂纹的梁沿轴线的截面惯矩和线质量等物理参数。基于此,建立了裂纹梁动力微分方程,并采用一阶摄动理论推导得到了梁的模态频率和振型计算公式。简支梁及悬臂梁算例研究表明,该方法具有很好的精度,与有限元模拟结果及实验结果都能很好地吻合。并采用此方法分析了裂纹深度和位置对带多条开口裂纹梁的特征模态参数的影响。结果表明,裂纹对各阶模态频率虽然影响有限,但其引起的各阶频率变化有着明显的模式,可用于结构损伤定位;裂纹对模态振型影响不明显,但对模态曲率影响比较大,可用于结构损伤位置和程度的诊断。     

矩形波导中小导体异物的影响

本文利用矩形谐振腔中的教扰公式结合准静态近似,导出了矩形波导中小导体异物的等效串联电抗和并联电纳。求出了反射系数,传输相移及功率容量降低的表示式.这种表示式在试验中表明是适合的。     

A generalized analytical model for hydrocarbon production using multi-fractured horizontal well with non-uniform permeability distributions

The multi-fractured horizontal well (MFHW) has significantly facilitated the exploitation of unconventional hydrogen-carbon compound reservoirs, which is an abundant source of fossil hydrogen energy. The composite linear flow models were frequently adopted to analytically evaluate the hydrocarbon production using MFHW. Most of the existing composite linear flow models assume uniform permeability in the primary fractures and the Stimulated Reservoir Volume (SRV) region. However, due to the non-uniform proppant distribution in the primary fractures and the heterogeneity in the density of the secondary fractures in SRV region, the permeability field in both regions are non-uniform. For the first time, a generalized analytical model incorporating continuous permeability heterogeneity in both the primary fractures and SRV region is proposed for the hydrocarbon production of MFHW. Any arbitrary permeability distribution functions can be treated as inputs to the proposed model. The mathematical model is solved using the perturbation technique and the Laplace transform method.The good match with the numerical solution verifies the accuracy of the proposed analytical model. Subsequently, the proposed solution is assigned with different modes of permeability heterogeneity to investigate their impacts on well production performances, i.e., cumulative hydrocarbon production and transient bottom-hole pressure (BHP). The results reveal that the incorporation of permeability heterogeneity will enhance the production rate and lower the BHP drawdown compared to the homogeneous case with the same average permeability. Besides, a field case is presented to demonstrate the applicability of the proposed model.     

对光伏的两种输出最大功率点追踪法分析

分析了两种最大功率追踪(MPPT)的方法:扰动观察法(Perturbation and Observation,P&O)与功率反馈法。利用仿真模拟并评估了两种方法的性能,二者功率追踪精确性都可以达到99%以上,但是不同的追踪手段会在追踪时间、系统稳定性、实现成本等方面产生不同的影响。本文旨在仿真结果的基础上,对上述问题进行分析与优化。     

Global optimal solutions to general sensor network localization problem

Sensor network localization problem is to determine the position of the sensor nodes in a network given pairwise distance measurements. Such problem can be formulated as a quartic polynomial minimization via the least squares method. This paper presents a canonical duality theory for solving this challenging problem. It is shown that the nonconvex minimization problem can be reformulated as a concave maximization dual problem over a convex set in a symmetrical matrix space, and hence can be solved efficiently by combining a general (linear or quadratic) perturbation technique with existing optimization techniques. Applications are illustrated by solving some relatively large-scale problems. Our results show that the general sensor network localization problem is not NP-hard unless its canonical dual problem has no solution in its positive definite domain. Fundamental ideas for solving general NP-hard problems are discussed.     

Solving EP singular linear systems

In this article, we deal with EP matrix and EP singular linear systems. We give some properties of EP matrix and its generalized inverse, analyze the solutions of EP systems and make some applications in Navier-Stokes equations.     

Novel control algorithm for MPPT with Boost converters in photovoltaic systems

The great advances in efficiency and performance of photovoltaic modules would not be very useful if they do not work close to their maximum power point (MPP). In this paper a novel Sliding Mode Control (SMC) based algorithm is proposed to be implemented in a DC/DC converter in order to make an autonomous photovoltaic system to work at the MPP. Once that the design of the novel algorithm has been detailed (especially the novel part relative to the current reference signal) and its stability has been demonstrated, its performance has been compared with two of the most commonly used algorithms in this scope, i.e., Perturbation & Observation (P&O) and Incremental Conductance (IC) algorithms, in addition to a PI controller because it is one of the preferred controllers in industrial applications. This comparison has been carried out taking into account both simulated and experimental tests. The first focused on their behavior when sudden changes in irradiance and temperature, while the lasts analyzed them when the load resistance was varying arbitrarily in actual facilities (composed of a photovoltaic module Mitsubishi PV-TD185MF5, a Boost converter, a variable load and a real-time data acquisition card dSPACE DSP1104 used as the interface between the control algorithm implemented in Simulink/Matlab and the real photovoltaic module). After completing tests under different conditions, we found that the proposed SMC based algorithm outperforms the PI controller and the P&O and IC algorithms, especially in experiments carried out using actual facilities.     

区分快慢变子系统的柔性机械臂控制方法

为了提高柔性机械臂控制精度、抑制柔性机械臂末端振动,提出了区分快慢变子系统的组合控制方法。使用拉格朗日方程和假设模态法建立了柔性机械臂动力学方程,利用奇异摄动原理将柔性机械臂系统分解为快变子系统和慢变子系统;鉴于慢变子系统的强非线性和参数不确定性,将反演控制和滑膜变结构相结合,提出了基于反演滑模变结构控制方法的慢变子系统控制;鉴于快变子系统模型不准确问题,而模糊控制对模型精度没有要求,因此设计了快变子系统模糊控制器。经仿真验证可以看出,与传统PID控制相比,机械臂转角最大误差由4.1°下降为0.04°,稳定时间由10s下降为2.5s,末端振动最大值由0.081m下降为0.021m,极大地提高了柔性机械臂控制精度。     

风速、入射角对海面谐振散射的影响

根据微扰法研究波散射,在谐振散射模型基础上导出布拉格散射系数,并分析海表面波对散射系数的影响.考虑海表面斜度的变化,对谐振散射系数进行修正,得出修正后的散射系数,发现散射系数的修正值受海面高度起伏均方根的影响,计算得出海面高度起伏均方根与风速的关系.在30 m深度海域进行试验,入射波角度分别为35°、45°和55°情况...