柴油加氢工艺动态仿真研究与应用

柴油加氢工艺是通过加氢反应来提高油品质量,对于环境保护和大气污染防治起着至关重要的作用.由于柴油的组成纷繁复杂,使得柴油组分难以确定,一直以来是加氢工艺动态仿真模拟中的难点问题.为解决上述问题,采用真实组分法确定了柴油组成,建立了组分分率模型,进而实现了柴油加氢工艺的全流程动态仿真.仿真结果与实际相吻合,证明了该方法用于柴油加氢工艺的动态仿真是行之有效的.     

Mechanical analysis of hollow fiber membrane integrity in water reuse applications

In order to gain insight into membrane fiber failure (i.e., loss of integrity), properties of five hollow fiber membranes and four hollow fiber modules were evaluated. Specifically, membrane material, membrane symmetry, fiber modulus of elasticity, fiber diameter and thickness, module potting technique, module flow pattern (inside-out or outside-in), and coliform breakthrough were investigated. The approach combined evaluation of the above properties with mathematical modeling of structure-fluid interactions to comprehensively evaluate the properties most important for maintaining hollow fiber membrane integrity. Tensile strength testing revealed that the strongest fiber was an asymmetric polyacrylonitrile membrane fiber. The weakest fiber was a symmetric polyethylene membrane fiber. Pilot plant testing on the four membrane modules revealed that membrane symmetry may be a more important factor than potting technique for hollow fiber integrity. Results from the SEM and tensile testing were used as input to a finite element analysis model used to evaluate time-dependent structure-fluid interactions. It was found that additional stresses at the juncture of the potting material and the hollow fiber membranes exist. These stresses likely lead to the formation of fractures.     

On-line multi-variable predictive control of molar mass and particle size distributions in free-radical emulsion copolymerization

A multi-variable model predictive control (MPC) was formulated to solve control problems associated with a combination of regulation and targeting desired set-points. We investigated the simultaneous control of key polymer properties: the particle size (PSD) and molecular weight distribution (MWD) by manipulating the flow rates of the monomers (styrene, MMA), surfactant, initiator and the temperature of the reactor. A multi-input-multi-output (MIMO) formulation was constructed for the constrained optimal control problem to maximize the width of the PSD (with M_n at a constant set-point), and to maximize the average molar mass. The strategy developed within a gPROMS-API-DCS environment allowed real-time implementation of model-based control of the process. The optimal control problem was implemented via an interface to a dynamic optimization code. Major improvements in process operation and polymer property control resulted on the implementation of our multi-variable MPC algorithm. The manipulation of the four flow rates and the temperature increased the degree of freedom in the system and achieved tighter PSD and MWD control. The on-line performance of MPC for MWD and PSD control was found to be satisfactory.     

Viscoelastic characterization of moderately concentrated polystyrene solutions by dynamic light scattering

The dynamic light scattering measurements were performed for moderately concentrated entangled solutions of atactic polystyrene in benzene (BZ) at 25.0 °C, in cyclohexane (CH) at 34.5 °C (Θ), and in diethyl malonate (DEM) at 35.0 °C (Θ) to characterize their viscoelastic properties. The results have shown that while the mutual diffusion coefficient D increases in the BZ solutions and decreases in the CH and DEM solutions with increasing polymer mass concentration c, the friction coefficient ζ for the three solutions increases with c showing the same power-law behavior irrespective of the weight-average molecular weight M_w and solvent quality. It has been found that the instantaneous longitudinal modulus L₀ for the CH and DEM solutions increases in proportion to c², obeying the familiar relation for the plateau value (4/3)G_N of the longitudinal stress relaxation modulus, but the L₀ values for these solutions are somewhat smaller than the values predicted from the relation. The terminal relaxation time τ_m for the two Θ solvent systems has been found to follow the power-law τ_m∝c^2.7, showing good correspondence to the relation established by rheological measurements.     

基于不同线路条件下的车辆动力学性能分析

随着我国在既有线上的线路改造和载运量的不断增加,对线路参数的设计要求也随之提高。应用动力学方法建立车辆-轨道系统动力学模型,研究不同曲线半径和线路激励对车辆动力学性能的影响。研究结果表明：增加曲线半径有利于增加车辆曲线通过安全性,车辆经过曲线线路连接处时脱轨概率变大,驶入曲线时的脱轨系数明显高于驶出曲线,重点考虑曲线线路连接位置处的车辆通过速度以及车辆运行状态;适当增加曲线半径可以减少轮轨间磨耗,有效降低磨耗速度;轨道激励变化对车辆临界速度的影响较大,应根据实际运行工况模拟得出最佳临界速度范围。     

柔性石墨纸轧机动刚度薄弱部位辨识与优化

借助谐响应分析辨识出柔性石墨纸轧机动刚度的薄弱环节,并利用灵敏度分析方法建立该环节的优化数学模型,进而实现对整机动刚度的提升。通过对各部件刚度提升前后的柔性石墨纸轧机进行模态分析,并对比各部件对整机固有频率的影响,辨识出薄弱部位为底座,故以底座为优化对象;将牌坊Y向共振频率对底座尺寸的灵敏度曲线拟合得出优化目标函数,以Y向共振频率为优化目标,质量为约束条件建立优化方程并求解;对比优化前后整机的动刚度,得出:在质量不增加的情况下,整机薄弱频率提升了24.1%,Y向振幅降低了15.9%。为提高优化效率提供了理论依据和参考。     

Anti-disturbance dynamic surface control scheme for a class of uncertain nonlinear systems with asymmetric dead-zone nonlinearity

This study proposes anti-disturbance dynamic surface control scheme for nonlinear strict-feedback systems subjected simultaneously to unknown asymmetric dead-zone nonlinearity, unmatched external disturbance and uncertain nonlinear dynamics. Radial basis function-neural network (RBF-NN) is invoked to approximate the uncertain dynamics of the system, and the dead-zone nonlinearity is represented as a time-varying system with a bounded disturbance. The nonlinear disturbance observer (NDO) is proposed to estimate the unmatched external disturbance which further will be used to compensate the effect of the disturbance. Then, by integrating RBF-NN, NDO and dynamic surface control (DSC) approaches, the proposed anti-disturbance control scheme is designed. Stability analysis of the closed-loop system shows that all signals of the closed-loop system are semi-globally uniformly ultimately bounded and the tracking error can be made arbitrarily small by proper selection of the design parameters. In comparison with the existing methods, the proposed scheme deals with the unmatched external disturbance, uncertain dynamics and unknown asymmetric dead-zone nonlinearity, simultaneously; it avoids the "explosion of complexity" problem and develops the simple control law without singularity concern. Furthermore, some imposed assumptions to the dead-zone input and disturbances are relaxed. Simulation and comparison results verify the effectiveness of the proposed approach.     

The dynamic contact area of elastomers at different velocities

The friction in tribo-systems that contain viscoelastic materials, such as elastomers, is relevant for a large number of applications. Examples include tyres, hoses, transmission and conveyor belts. To quantify the friction in these applications, one must first understand the contact behaviour of such viscoelastic materials, both in static and in dynamic situations. This work discusses an experimental study into the change of the contact area with the sliding velocity and relates the change in contact area with the mechanical properties of the elastomer. The results show that for a tribo-system containing an elastomer, there is a threshold velocity, above which the size of the contact area significantly reduces.     

复数形式的FFT相位谱及转子偏心运动分析

本文首先对精密转子的回转误差进行了数学描述，并首次提出利用FFT复数表达式的相位谱来解析转子回转误差中“偏心运动”的主要成因，文章还提出了相应的转子回转精度的“两端双向测量法”。