Optimal control on special Euclidean group via natural gradient algorithm欧几里德群的最优控制问题

Considering the optimal control problem about the control system of the special Euclidean group whose output only depends on its input is meaningful in practical applications. The optimal control considered here is described as the output matrix is as close as possible to the target matrix by adjusting the system input. The geodesic distance is adopted as the measure of the difference between the output matrix and the target matrix, and the trajectory of the control input obtained in the process is achieved. Furthermore, some numerical simulations are shown to illustrate our outcomes based on the natural gradient descent algorithm for optimizing the control system of the special Euclidean group.     

Editorial

Nowadays control systems can find applications in many areas, like aerospace, motion tracking, chemical engineering, physics, biology, economics. To improve control performance is a perpetual goal. With recent progresses of computing technologies, better control performance can be achieved by more judicious control strategies based on more precise and more complicated, such as time-varying, nonlinear, models. Another trend to improve control performance is built upon the divide-and-conquer philosophy, i.e., a complicated control task is cooperatively accomplished by multiple controllers/agents, instead of a single super-powerful controller. This trend is made possible due to great advances in communication, which enable the information exchange among agents and may unite the less powerful agents. The cost for such control performance improvement is higher spatial complexity of control systems. Although high model complexity and spatial complexity can be physically handled by current powerful controllers/agents, the lack of efficient analysis and synthesis methods prevents the performance improvement of control systems with high model or/and spatial complexity. As we know, conventional control methods are mainly developed under the assumptions of linear, time-invariant and centralized models. In order to resolve the issues due to the aforementioned two types of complexities, new methods are expected, which is exactly the major aim of the present special issue.     

A social tag clustering method based on common co-occurrence group similarity

Social tagging systems are widely applied in Web 2.0. Many users use these systems to create, organize, manage, and share Internet resources freely. However, many ambiguous and uncontrolled tags produced by social tagging systems not only worsen users’ experience, but also restrict resources’ retrieval efficiency. Tag clustering can aggregate tags with similar semantics together, and help mitigate the above problems. In this paper, we first present a common co-occurrence group similarity based approach, which employs the ternary relation among users, resources, and tags to measure the semantic relevance between tags. Then we propose a spectral clustering method to address the high dimensionality and sparsity of the annotating data. Finally, experimental results show that the proposed method is useful and efficient.     

A computational model of topological and geometric recovery for visual curve completion

Computational Visual Media - Visual curve completion is a fundamental problem in understanding the principles of the human visual system. This problem is usually divided into two problems: a...     

粉煤灰与硅灰对水泥胶砂抗酸腐蚀性能的影响

通过对7组水泥胶砂受硝酸腐蚀前基准强度及腐蚀后质量损失率和中性化深度的研究,分析了粉煤灰、硅灰对胶砂抗酸腐蚀性能的影响。结果表明:在硝酸腐蚀条件下,随粉煤灰掺量增大,胶砂的质量损失率呈降低趋势,中性化深度呈增大趋势,粉煤灰的掺量为15%时,胶砂抗酸腐蚀性能改善较为明显;随硅灰掺量增大,胶砂的质量损失率呈先降低后增大趋势,中性化深度呈增大趋势,硅灰掺量为5%时,胶砂抗酸腐蚀性能改善较为明显;按单掺最优掺量混掺粉煤灰和硅灰,对胶砂的抗酸腐蚀性能的超叠加效应不显著;对掺加掺合料的胶砂,决定其抗酸腐蚀性能的主要因素是胶凝材料组成而不是强度。     

基于量纲分析的内镶圆柱式毛管局部水头损失研究

为了研究内镶圆柱式毛管局部水头损失规律,本文对常见4种滴灌管进行了灌水试验,同时采用CFD数值分析对4种滴灌管进行了模拟与分析验证,在此基础上,对12种滴灌管进行了模拟研究,通过量纲分析研究了毛管局部水头损失影响因素。结果表明:毛管总水头损失模拟值与实测值吻合度较好;毛管局部水头损失与毛管内径、滴头内径、滴头长度、水流流速、水流运动黏滞系数有关;毛管局部水头损失占沿程水头损失的比值与滴头间距密切相关,以Φ16毛管为例,毛管局部水头损失是沿程水头损失的0.23~1.89倍,毛管层流段水头损失很小,在不需精确计算时可忽略不计。研究结果可为管网水力计算提供参考。     

Implicit Formulation for SPH‐based Viscous Fluids

We propose a stable and efficient particle‐based method for simulating highly viscous fluids that can generate coiling and buckling phenomena and handle variable viscosity. In contrast to previous methods that use explicit integration, our method uses an implicit formulation to improve the robustness of viscosity integration, therefore enabling use of larger time steps and higher viscosities. We use Smoothed Particle Hydrodynamics to solve the full form of viscosity, constructing a sparse linear system with a symmetric positive definite matrix, while exploiting the variational principle that automatically enforces the boundary condition on free surfaces. We also propose a new method for extracting coefficients of the matrix contributed by second‐ring neighbor particles to efficiently solve the linear system using a conjugate gradient solver. Several examples demonstrate the robustness and efficiency of our implicit formulation over previous methods and illustrate the versatility of our method.     

基于ELM的硫熏强度软测量模型

硫熏强度是亚法糖厂澄清工段的关键工艺参数之一;硫熏强度过低会影响澄清效果,过高会造成成品糖二氧化硫残留过高;目前由于缺乏合适的硫熏强度在线测量装置,该参数主要采用人工取样和离线化验的检测方式,化验滞后时间较长,难以根据该指标及时指导实际生产的问题;为此文章采用极限学习机(ELLM)方法建立了硫熏强度软测量模型,并与基于支持向量机(SVM)、径向基函数(RBF)神经网络和反向传播(BP)神经网络的硫熏强度软测量模型进行对比分析;结果显示,基于ELM的硫熏强度软测量模型具有训练收敛速度快、模型精度高和泛化性能好等优点,可以满足实际糖厂澄清工段的要求.