弱化系统耦合度方法与应用

许多工业过程控制系统都具有变量间的耦合,这些系统经常存在一、二个耦合度最大的,只要设法将这一、二个子系统从整体系统分离出来,就可以得到一个弱耦合度的系统。本文介绍一种弱化系统耦合度方法,以及这种方法在球磨机控制中的应用。

Impact of a background velocity field on solidification growth of single-crystal nuclei using the PF-LBM

To promote/inhibit ice formation in the natural environment and industrial systems,the growth and evolution process of ice single-crystal nuclei were simulated using the phase field-lattice Boltzmann method(PF-LBM),and the influence of a background flow field on the growth of single-crystal nucleus dendrites was also analyzed.The results show that the flow field makes dendrite growth asymmetric.The growth of dendrites is more developed on the upstream side than on the downstream side.The dendrite tip growth rate and tip radius are greater on the upstream side than on the downstream side.The solid phase ratio is greater with a background flow field than without one.The higher the flow velocity is,the more developed the dendrites on the upstream side,the faster the dendrites grow,and the higher the dendrite tip growth rate.The dendrites on the backflow side have a lower flow rate and a lower degree of supercooling than those on the upstream side,which inhibits the solidification process,the growth rate is slow,and the dendrites are underdeveloped.

Contouring error modeling and simulation of a four-axis motion control system

A layered modeling method is proposed to resolve the problems resulting from the complexity of the error model of a multi-axis motion control system. In this model, a low level layer can be used as a virtual axis by the high level layer. The first advantage of this model is that the complex error model of a four-axis motion control system can be divided into several simple layers and each layer has different coupling strength to match the real control system. The second advantage lies in the fact that the controller in each layer can be designed specifically for a certain purpose. In this research, a three-layered cross coupling scheme in a four-axis motion control system is proposed to compensate the contouring error of the motion control system. Simulation results show that the maximum contouring error is reduced from 0.208 mm to 0.022 mm and the integration of absolute error is reduced from 0.108 mm to 0.015 mm, which are respectively better than 0.027 mm and 0.037 mm by the traditional method. And in the bottom layer the proposed method also has remarkable ability to achieve high contouring accuracy.

Magnetic Properties of Ferromagnetic Double Layers with Ferrimagnetic Interlayer Coupling at Zero Temperature

Spin-wave theory is used to study magnetic properties of ferromagnetic double layers with a ferrimagnetic interlayer coupling at zero temperature. The spin-wave spectra and four sublattices magnetizations and internal energy are calculated by employing retarded Green function technique. The sublattice magnetizations at ground state are smaller than their classical values, owing to the zero-point quantum fluctuations of the spins.

Generalized Energy-Based Fragmentation Approach for Accurate Binding Energies and Raman Spectra of Methane Hydrate Clusters

Methane hydrates(MHs)play important roles in the fields of chemistry,energy,environmental sciences,etc.In this work,we employ the generalized energy-based fragmentation(GEBF)approach to compute the binding energies and Raman spectra of various MH clusters.For the GEBF binding energies of various MH clusters,we first evaluated the various functionals of density functional theory(DFT),and compared them with the results of explicitly correlated combined coupled-cluster singles and doubles with noniterative triples corrections[CCSD(T)(F12^(*))]method.Our results show that the two best functionals are B3PW91-D3 and B97D,with mean absolute errors of only 0.27 and 0.47 kcal/mol,respectively.Then we employed GEBF-B3PW91-D3 to obtain the structures and Raman spectra of MH clusters with mono-and double-cages.Our results show that the B3PW91-D3 functional can well reproduce the experimental C-H stretching Raman spectra of methane in MH crystals,with errors less than 3 cm^(-1).As the size of the water cages increased,the C-H stretching Raman spectra exhibited a redshift,which is also in agreement with the experimental“loose cage-tight cage”model.In addition,the Raman spectra are only slightly affected by the neighboring environment(cages)of methane.The blueshifts of C-H stretching frequencies are no larger than 3 cm^(-1) for CH_(4) from monocages to doublecages.The Raman spectra of the MH clusters could be combined with the experimental Raman spectra to investigate the structures of methane hydrates in the ocean bottom or in the interior of interstellar icy bodies.Based on the B3PW91-D3 or B97D functional and machine learning models,molecular dynamics simulations could be applied to the nucleation and growth mechanisms,and the phase transitions of methane hydrates.