In this paper, we apply the recursive genetic programming (RGP) approach to the cognition of a system, and then proceed to the detecting procedure for structural changes in the system whose components are of long memo...In this paper, we apply the recursive genetic programming (RGP) approach to the cognition of a system, and then proceed to the detecting procedure for structural changes in the system whose components are of long memory. This approach is adaptive and model-free, which can simulate the individual activities of the system's participants, therefore, it has strong ability to recognize the operating mechanism of the system. Based on the previous cognition about the system, a testing statistic is developed for the detection of structural changes in the system. Furthermore, an example is presented to illustrate the validity and practical value of the proposed.展开更多
In this paper, a new derivative free trust region method is developed based on the conic interpolation model for the unconstrained optimization. The conic interpolation model is built by means of the quadratic model f...In this paper, a new derivative free trust region method is developed based on the conic interpolation model for the unconstrained optimization. The conic interpolation model is built by means of the quadratic model function, the collinear scaling formula, quadratic approximation and interpolation. All the parameters in this model are determined by objective function interpolation condition. A new derivative free method is developed based upon this model and the global convergence of this new method is proved without any information on gradient.展开更多
The bubbles rise up and burst at the free surface is a complex two-phase process.A free energy lattice Boltzmann method(LBM)model is adopted in this paper to study this phenomenon.The interface capturing technique[Zhe...The bubbles rise up and burst at the free surface is a complex two-phase process.A free energy lattice Boltzmann method(LBM)model is adopted in this paper to study this phenomenon.The interface capturing technique[Zheng et al.,2006]is used to deal with the high density ratio problem.The Laplace law and the air-water interface capturing ability are validated for the multiphase model.The interaction between the single bubble or multiple bubbles and the free surface are studied by the multiphase model.The force acting on the bubble and the evolution of the free surface is studied.Meanwhile,effect of the initial distance between two adjacent bubbles on interaction effects of multiple bubbles is investigated as well.展开更多
For the growth and departure of bubbles from an orifice, a free energy lattice Boltzmann model is adopted to deal with this complex multiphase flow phenomenon. A virtual layer is set at the boundary of the flow domain...For the growth and departure of bubbles from an orifice, a free energy lattice Boltzmann model is adopted to deal with this complex multiphase flow phenomenon. A virtual layer is set at the boundary of the flow domain to deal with the no-slip boundary condition. Effects of the viscosity, surface tension, gas inertial force and buoyancy on the characteristics of bubbles when they grow and departure from an orifice in quiescent liquid are studied. The releasing period and departure diameter of the bubble are influenced by the residual gas at the orifice, and the interaction between bubbles is taken into consideration. The relations between the releasing period or departure diameter and the gravity acceleration show fair agreements with previous numerical and theoretical results. And the influence of the gas outflow velocity on bubble formation is discussed as well. For the bubbles growing in cross-flow field, effects of the cross-flow speed and the gas outflow velocity on the bubble formation are discussed, which is related to the application in ship resistance reduction. And optimal choice of the ship speed and gas outflow velocity is studied. Cases in this paper also prove that this high density ratio LBM model has its flexibility and effectiveness on multiphase flow simulations.展开更多
Abstract A transonic, high Reynolds number natural laminar flow airfoil is designed and studied. The γ-θ transition model is combined with the shear stress transport （SST） k-w turbulence model to predict the trans...Abstract A transonic, high Reynolds number natural laminar flow airfoil is designed and studied. The γ-θ transition model is combined with the shear stress transport （SST） k-w turbulence model to predict the transition region for a laminar-turbulent boundary layer. The non-uniform free-form deformation （NFFD） method based on the non-uniform rational B-spline （NURBS） basis function is introduced to the airfoil parameterization. The non-dominated sorting genetic algorithm-II （NSGA-II） is used as the search algo- rithm, and the surrogate model based on the Kriging models is introduced to improve the efficiency of the optimization system. The optimization system is set up based on the above technologies, and the robust design about the uncertainty of the Mach number is carried out for NASA0412 airfoil. The optimized airfoil is analyzed and compared with the original airfoil. The results show that natural laminar flow can be achieved on a supercritical airfoil to improve the aerodynamic characteristic of airfoils.展开更多
传统激光软钎焊依赖人工经验调整参数,难以应对复杂产品结构和温度动态变化,基于模型的方法又高度依赖模型精度,实用性受限.为解决上述问题,文中提出了一种基于迭代学习的激光软钎焊温度控制方法.无需建立精确数学模型,利用历史焊接数...传统激光软钎焊依赖人工经验调整参数,难以应对复杂产品结构和温度动态变化,基于模型的方法又高度依赖模型精度,实用性受限.为解决上述问题,文中提出了一种基于迭代学习的激光软钎焊温度控制方法.无需建立精确数学模型,利用历史焊接数据进行迭代优化,逐步修正控制功率,使实际温度曲线在无需人工干预的情况下逐步逼近目标温度曲线,从而增强控制系统的自适应能力与鲁棒性.结果表明,仅需2次迭代,在实际温度曲线与目标温度曲线的均方根误差和最大绝对误差方面,即优于传统PID(proportional integral derivative)控制方法.迭代3次后,温度控制的精度、稳定性和工艺适应性均得到显著提升,表现出较强的收敛性与控制性能.为激光软钎焊在多变复杂工况下实现高精度、高一致性的温度控制提供了有效解决思路.展开更多
为解决一类有向拓扑结构下模型未知的非线性多智能体系统的聚类一致性问题,考虑到传统无模型自适应控制(MFAC)算法中存在的收敛速度慢等问题,提出了一种基于梯度下降的无模型聚类一致性控制算法。首先,在无模型算法中引入自适应矩估计(a...为解决一类有向拓扑结构下模型未知的非线性多智能体系统的聚类一致性问题,考虑到传统无模型自适应控制(MFAC)算法中存在的收敛速度慢等问题,提出了一种基于梯度下降的无模型聚类一致性控制算法。首先,在无模型算法中引入自适应矩估计(adaptive moment estimation,Adam)梯度下降优化方法,利用梯度的矩估计自适应地调整学习率并更新MFAC中的伪偏导数,加快并提高了模型的准确性。然后,在系统拓扑结构和聚类耦合强度约束下定义多智能体聚类误差。在此基础上,设计了基于Adam-MFAC的多智能体聚类一致性控制协议。此外,对Adam-MFAC方法的稳定性和收敛性进行了分析和证明。最后,分别考虑了具有固定拓扑和切换拓扑的系统,对所提出的方法进行仿真,证明了所提出的控制策略在多智能体聚类一致性问题上的有效性和优越性。展开更多
文摘In this paper, we apply the recursive genetic programming (RGP) approach to the cognition of a system, and then proceed to the detecting procedure for structural changes in the system whose components are of long memory. This approach is adaptive and model-free, which can simulate the individual activities of the system's participants, therefore, it has strong ability to recognize the operating mechanism of the system. Based on the previous cognition about the system, a testing statistic is developed for the detection of structural changes in the system. Furthermore, an example is presented to illustrate the validity and practical value of the proposed.
基金This work was supported by the National Natural Science Foundation of China(10071037)
文摘In this paper, a new derivative free trust region method is developed based on the conic interpolation model for the unconstrained optimization. The conic interpolation model is built by means of the quadratic model function, the collinear scaling formula, quadratic approximation and interpolation. All the parameters in this model are determined by objective function interpolation condition. A new derivative free method is developed based upon this model and the global convergence of this new method is proved without any information on gradient.
基金supported by the National Natural Science Foundation of China (11672081)
文摘The bubbles rise up and burst at the free surface is a complex two-phase process.A free energy lattice Boltzmann method(LBM)model is adopted in this paper to study this phenomenon.The interface capturing technique[Zheng et al.,2006]is used to deal with the high density ratio problem.The Laplace law and the air-water interface capturing ability are validated for the multiphase model.The interaction between the single bubble or multiple bubbles and the free surface are studied by the multiphase model.The force acting on the bubble and the evolution of the free surface is studied.Meanwhile,effect of the initial distance between two adjacent bubbles on interaction effects of multiple bubbles is investigated as well.
基金financially supported by the National Key R&D Program of China(Grant No.2018YFC0308900)the Industrial Technology Development Program(Grant No.JCKY2018604C010)Shenzhen Special Fund for Future Industries(Grant No.JCYJ20160331163751413)
文摘For the growth and departure of bubbles from an orifice, a free energy lattice Boltzmann model is adopted to deal with this complex multiphase flow phenomenon. A virtual layer is set at the boundary of the flow domain to deal with the no-slip boundary condition. Effects of the viscosity, surface tension, gas inertial force and buoyancy on the characteristics of bubbles when they grow and departure from an orifice in quiescent liquid are studied. The releasing period and departure diameter of the bubble are influenced by the residual gas at the orifice, and the interaction between bubbles is taken into consideration. The relations between the releasing period or departure diameter and the gravity acceleration show fair agreements with previous numerical and theoretical results. And the influence of the gas outflow velocity on bubble formation is discussed as well. For the bubbles growing in cross-flow field, effects of the cross-flow speed and the gas outflow velocity on the bubble formation are discussed, which is related to the application in ship resistance reduction. And optimal choice of the ship speed and gas outflow velocity is studied. Cases in this paper also prove that this high density ratio LBM model has its flexibility and effectiveness on multiphase flow simulations.
文摘Abstract A transonic, high Reynolds number natural laminar flow airfoil is designed and studied. The γ-θ transition model is combined with the shear stress transport （SST） k-w turbulence model to predict the transition region for a laminar-turbulent boundary layer. The non-uniform free-form deformation （NFFD） method based on the non-uniform rational B-spline （NURBS） basis function is introduced to the airfoil parameterization. The non-dominated sorting genetic algorithm-II （NSGA-II） is used as the search algo- rithm, and the surrogate model based on the Kriging models is introduced to improve the efficiency of the optimization system. The optimization system is set up based on the above technologies, and the robust design about the uncertainty of the Mach number is carried out for NASA0412 airfoil. The optimized airfoil is analyzed and compared with the original airfoil. The results show that natural laminar flow can be achieved on a supercritical airfoil to improve the aerodynamic characteristic of airfoils.
文摘传统激光软钎焊依赖人工经验调整参数,难以应对复杂产品结构和温度动态变化,基于模型的方法又高度依赖模型精度,实用性受限.为解决上述问题,文中提出了一种基于迭代学习的激光软钎焊温度控制方法.无需建立精确数学模型,利用历史焊接数据进行迭代优化,逐步修正控制功率,使实际温度曲线在无需人工干预的情况下逐步逼近目标温度曲线,从而增强控制系统的自适应能力与鲁棒性.结果表明,仅需2次迭代,在实际温度曲线与目标温度曲线的均方根误差和最大绝对误差方面,即优于传统PID(proportional integral derivative)控制方法.迭代3次后,温度控制的精度、稳定性和工艺适应性均得到显著提升,表现出较强的收敛性与控制性能.为激光软钎焊在多变复杂工况下实现高精度、高一致性的温度控制提供了有效解决思路.
文摘为解决一类有向拓扑结构下模型未知的非线性多智能体系统的聚类一致性问题,考虑到传统无模型自适应控制(MFAC)算法中存在的收敛速度慢等问题,提出了一种基于梯度下降的无模型聚类一致性控制算法。首先,在无模型算法中引入自适应矩估计(adaptive moment estimation,Adam)梯度下降优化方法,利用梯度的矩估计自适应地调整学习率并更新MFAC中的伪偏导数,加快并提高了模型的准确性。然后,在系统拓扑结构和聚类耦合强度约束下定义多智能体聚类误差。在此基础上,设计了基于Adam-MFAC的多智能体聚类一致性控制协议。此外,对Adam-MFAC方法的稳定性和收敛性进行了分析和证明。最后,分别考虑了具有固定拓扑和切换拓扑的系统,对所提出的方法进行仿真,证明了所提出的控制策略在多智能体聚类一致性问题上的有效性和优越性。
