一类非线性大滞后系统的智能前馈控制策略与算法

针对工业控制中一类常见的非线性大滞后对象,本文提出一种基于仿人智能策略的前馈组合控制器.前馈控制部分通过在线优化滞后参数估计值来获得被控对象的静态逆模型,逆模型辨识与直接逆控制由两个神经网络分别实现,从而可以在线调整网络权值.基本模糊控制器可在模糊PID和模糊PD控制算法之间进行转换,适用于控制系统的各工作状态.仿人智能控制策略根据输出误差变化的不同阶段调整所使用的控制组合,并具有自寻优功能.仿真表明,这种控制方法可取得较好的控制效果.     

Objective Oriented Multistage Ring Shear Test for Shear Strength of Landslide Soil

Ring shear tests were conducted on five samples of different nature with a modified Imperial College type ring shear machine. The three different testing methods used, (1) individual sample testing for each normal stress, (2) increasing load multistage ring shear test, and (3) reducing load multistage ring shear test, all showed similar effective residual internal friction angle for the samples, irrespective of testing method. However, effective residual shear intercept was different according to the testing methodology. The internal friction angle did not vary, particularly after the first minimum point in the stress displacement curve, although the residual shear intercept decreased with increase in the displacement. The thickness of the shearing zone increased along with the displacement. The remolded peak shear strength for saturated conditions at field dry density varied with the consolidation history. Measurement of remolded peak shear strength was possible in a single sample using the increasing load multistage ring shear test at normal consolidation. The equilibrium water content of the sample after the ring shear test was nearly equal to the plastic limit.     

Efficient Approximation of Unsteady Friction Weighting Functions

A simple method is presented for evaluating wall shear stresses from known flow histories in unsteady pipe flows. The method builds on previous work by Trikha, but has two important differences. One of these enables the method to be used with much larger integration time steps than are acceptable with Trikha’s method. The other, a general procedure for determining approximations to weighting functions, enables it to be used at indefinitely small times (high frequencies). The method is applicable to both laminar and turbulent flows.     

Shear Lag Effect in Simply Supported Prestressed Concrete Box Girder

In this paper, derivation and computed formulas are provided for the shear lag coefficient in a simply supported prestressed concrete box girder under dead load. In the case of prestressed tendons having parabolic configurations, formulas to compute the shear lag effect are also developed. The magnitude of upward loading intensity caused by prestress as well as the relationship between the height of the box girder and the sag of prestressed tendons have been fully treated. Conclusions are drawn that the shear lag effect caused by dead load and prestress force is equivalent to dead load acting alone, provided that the prestressed tendon is set up with a parabolic profile. Shear lag effect caused by movable load is also analyzed according to the eccentricity of the load to the half-width ratio of the box girder. Charts were prepared to predict the shear lag coefficient for live load. Finally, having considered the shear deformation of flanges, the deflection of box girders is studied for both uniformly distributed load and concentrated load. Examples are given for illustrative purpose.     

Concrete Contribution to the Shear Resistance of Fiber Reinforced Polymer Reinforced Concrete Members

Seven beams were tested in bending to determine the concrete contribution to their shear resistance. The beams had similar dimensions and concrete strength and were reinforced with carbon fiber reinforced polymer bars for flexure without transverse reinforcement. They were designed to fail in shear rather than flexure. The test variables were the shear span to depth ratio, varying from 1.82 to 4.5, and the flexural reinforcement ratio, varying from 1.1 to 3.88 times the balanced strain ratio. The test results are analyzed and compared with the corresponding predicted values using the American Concrete Institute, the Canadian Standard, and the Japan Society of Civil Engineers (JSCF) fiber reinforced polymer design recommendations. Based on these results and previous experimental data, it is shown that the ACI recommendations are extremely conservative whereas the Canadian and JSCE recommendations, albeit still conservative, are in closer agreement with the experimental data. Overall the Canadian Standard’s predictions are in better agreement with experimental data than the JSCE predictions.     

工件材料的各向异性对超精密切削变形及已加工表面粗糙度的影响

研究了单晶铜超精密切削时，工件材料的晶体取向对切削变形及表面质量的影响。切削试验结果表明，剪切角、切削力，表面粗糙度随晶体切削方向的不同而有明显的变化。根据超精密切削中切屑形成过程的晶体塑性力学模型，分析了剪切角与切削力随晶体取向的变化规律。理论分析结果与试验结果相符。     

聚合物熔体微尺度剪切黏度测量方法与黏度模型

研究微尺度效应下聚合物熔体黏度时,发现不同入口修正方法获得的剪切黏度随特征尺寸变化的规律不同,这对于聚合物微成型理论和技术尤为重要。采用直径分别为1 000μm、500μm、350μm的毛细管口模,在相同试验条件下分别用零口模法和Bagley法两种入口修正方法,研究高密度聚乙烯(High density polyethylene,HDPE)、短链支化的聚丙烯(Polypropylene,PP)、聚甲基丙烯酸甲脂(Polymethylmethacrylate,PMMA)和聚苯乙烯(Polystyrene,PS)四种材料的剪切黏度变化规律。结果发现,两种方法获得的PMMA和PS黏度随口模直径变化的规律相反,指出传统入口修正方法在测量微尺度黏度时存在局限。基于入口收敛流动特征,提出一种考虑微尺度效应下压力影响的测量方法,并用该方法给出四种材料剪切黏度随口模直径变化的真实规律。试验剪切速度范围内,四种材料剪切黏度均随口模直径的减小而减小,平均变化幅度为9.9%～38.3%,并从分子结构角度揭示四种材料黏度变化程度不同的机理。基于黏度变化规律,采用唯象性方法建立适用于宏—微观尺度下的黏度模型。试验结果表明该模型的理论预测结果与试验结果平均误差小于3.7%,验证了模型的正确性和有效性。     

Retrofit of RC hollow piers with CFRP sheets

Hollow bridge piers, particularly those built before the seventies, often have insufficient shear capacity due to inadequate transverse reinforcement details. Therefore, special attention must be given to this very important aspect when reinforced concrete (RC) piers with hollow sections are analysed and retrofitted. This paper covers the experimental analysis of retrofit solutions using CFRP sheets along the piers’ entire height to prevent shear failure. Experimental cyclic tests were carried out to evaluate the shear retrofit strategy efficiency on a set of RC piers with square hollow sections. This work also covers the study of design procedures for CFRP shear retrofitting and the evaluation of the associated ductility capacity improvement. The various transverse reinforcement detailing scenarios were assessed to determine their shear-failure prevention efficiency. The corresponding cyclic response behavior was also evaluated. The most relevant experimental information is presented in the paper, such as the evolution of the outer damage pattern. Finally, shear retrofit solutions, with a 40% increase over the maximum flexural force, show that this strategy is adequate to allow satisfactory ductility behavior.     

Improvement of adhesive bonding of grit-blasted steel substrates by using diluted resin as a primer

This study reveals the micro-structural details on the metal substrate surface prepared by grit blasting, and then proposes a simple resin pre-coating method aiming at full wetting of the substrate surface for stronger adhesive bonding. The resin pre-coating solution consisting of around 90% acetone and around 10% resin without hardener is used as a primer, which can be sprayed or blushed onto the grit-blasted metal substrate. The acetone solution can carry resin deep into micro-cavities created by grit blasting and effectively coat and wet micro-debris so that micro-voids or gaps between the adhesive joint and metal substrate can be removed. Since the resin pre-coating does not contain hardener and remains wet, the wettability of the substrate is also improved. The normal epoxy adhesive with hardener can then be applied onto the substrate surface. Despite having the primer-like function, the proposed resin pre-coating method still maintains the simplicity of one epoxy resin system. Based on the current study, a resin and acetone solution without hardener does not seem to have adverse effects on the final bonding strengths of adhesive joints, although acetone is known to have detrimental effects on resin and hardener adhesive systems. Four different surface conditions are examined, each having 14 specimens: (1) Grit-Blasted (GB) surface, (2) GB-surface with ultrasonic cleaning, (3) GB-surface with resin Pre-Coating (PC) only, and (4) GB-surface with both ultrasonic cleaning and PC. 25% improvement in the shear strength has been achieved by the resin pre-coating method, even without ultrasonic cleaning, in comparison with 8% improvement after ultrasonic cleaning. These results show GB-surface with PC is beneficial to adhesive bonding, which can be adopted for structural applications even if thorough substrate surface cleaning on site is not possible. The improved wettability of metal substrates after resin pre-coating contributes to the maximum possible utilization of the contact areas over the roughened substrate surfaces and thus leads to the enhanced adhesive bond strength.