Vibration Control of A Flexible Marine Riser System Subject to Input Dead Zone and Extraneous Disturbances

An observer-based adaptive backstepping boundary control is proposed for vibration control of flexible offshore riser systems with unknown nonlinear input dead zone and uncertain environmental disturbances.The control algorithm can update the control law online through real-time data to make the controller adapt to the environment and improve the control precision.Specifically,based on the adaptive backstepping framework,virtual control laws and Lyapunov functions are designed for each subsystem.Three direction interference observers are designed to track the timevarying boundary disturbance.On this basis,the inverse of the dead zone and linear state transformation are used to compensate for the original system and eliminate the adverse effects of the dead zone.In addition,the stability of the closed-loop system is proven by Lyapunov stability theory.All the system states are bounded,and the vibration offset of the riser converges to a small area of the initial position.Finally,four examples of flexible marine risers are simulated in MATLAB to verify the effectiveness of the proposed controller.

Adaptive Fuzzy Control for a Class of MIMO Nonlinear Systems with Unknown Dead-zones

A design scheme of adaptive fuzzy controller for a class of uncertain MIMO nonlinear systems with unknown dead-zones and a triangular control structure is proposed in this pa-per. The design is based on the principle of sliding mode control and the property of Nussbaum function. The approach does not require a priori knowledge of the signs of the control gains and the upper bounds and lower bounds of dead-zone parameters to be known a priori. By introducing the integral-type Lyapunov function and adopting the adaptive compensation term of the upper bound of the optimal approximation error and the dead-zone disturbance, the closed-loop control system is proved to be semi-globally stable in the sense that all signals involved are bounded, with tracking errors converging to zero.

ADAPTIVE CONTROL OF FLEXIBLE BEAM WITH UNKNOWN DEAD-ZONE IN THE DRIVING MOTOR

Adaptive control of a flexible beam system preceded by an unknown dead-zonein the driving motor is investigated in state space form. By introducing an important lemma forsimplifying error equation between the flexible beam model and the matching reference model, arobust adaptive control scheme is developed by involving the dead-zone inverse terms. The newadaptive control law ensures global stability of the entire system and achieves desired trackingprecision even when the slopes of the dead-zone are not equal. Simulations performed on a typicalflexible beam system illustrate and clarify the validity of this approach.

Adaptive Variable Structure Control of MIMO Nonlinear Systems with Time-varying Delays and Unknown Dead-zones

In this paper, adaptive variable structure neural control is presented for a class of uncertain multi-input multi-output （MIMO） nonlinear systems with state time-varying delays and unknown nonlinear dead-zones. The unknown time-varying delay uncer- tainties are compensated for using appropriate Lyapunov-Krasovskii functionals in the design. The approach removes the assumption of linear function outside the deadband without necessarily constructing a dead-zone inverse as an added contribution. By utilizing the integral-type Lyapunov function and introducing an adaptive compensation term for the upper bound of the residual and optimal approximation error as well as the dead-zone disturbance, the closed-loop control system is proved to be semi-globally uniformly ultimately bounded. In addition, a modified adaptive control algorithm is given in order to avoid the high-frequency chattering phenomenon. Simulation results demonstrate the effectiveness of the approach.

A Flux DC Bias Suppression Scheme of Single-stage Full-bridge PFC Converters Based on Dead Zone Adjustment

由于单级桥式功率因数校正（power factor correction,PFC）AC/DC变换技术电路的特点,导致高频变压器存在偏磁现象,影响了系统正常工作。传统方式通过增加变压器气隙或使用隔直电容来防止变压器出现偏磁,但是该类方案影响了系统性能,并增加了电路的复杂程度。结合有源钳位单级PFC变换器工作特点,提出一种基于死区调节的偏磁抑制策略,通过改变系统的开关时序,能够有效抑制偏磁,具有不增加主电路复杂程度、不影响系统性能、数字控制和模拟控制都能够实现等优点。在提出抑制策略的基础上,设计实现电路,给出死区设计方法及影响规律,最后进行实验研究。理论分析及实验结果表明,该策略能够在不影响系统性能的基础上,有效抑制单级桥式PFC变换器的高频变压器偏磁。

Design of Observer-based Adaptive Controller for Nonlinear Systems with Unmodeled Dynamics and Actuator Dead-zone

This paper presents an up-to-date study on the observer-based control problem for nonlinear systems in the presence of unmodeled dynamics and actuator dead-zone.By introducing a dynamic signal to dominate the unmodeled dynamics and using an adaptive nonlinear damping to counter the effects of the nonlinearities and dead-zone input,the proposed observer and controller can ensure that the closed-loop system is asymptotically stable in the sense of uniform ultimate boundedness.Only one adaptive parameter is needed no matter how many unknown parameters there are.The system investigated is more general and there is no need to solve Linear matrix inequality （LMI）.Moreover,with our method,some assumptions imposed on nonlinear terms and dead-zone input are relaxed.Finally,simulations illustrate the effectiveness of the proposed adaptive control scheme.

Prediction of plastic zone size around circular tunnels in non-hydrostatic stress field

This paper discusses the calculation of plastic zone properties around circular tunnels to rock-masses that satisfy the Hoek–Brown failure criterion in non-hydrostatic condition,and reviews the calculation of plastic zone and displacement,and the basis of the convergence–confinement method in hydrostatic condition.A two-dimensional numerical simulation model was developed to gain understanding of the plastic zone shape.Plastic zone radius in any angles around the tunnel is analyzed and measured,using different values of overburden(four states)and stress ratio(nine states).Plastic zone radius equations were obtained from fitting curve to data which are dependent on the values of stress ratio,angle and plastic zone radius in hydrostatic condition.Finally validation of this equation indicate that results predict the real plastic zone radius appropriately.

Effects of Cylinder Radius,Setover and Heel-Toe Difference on Cylinder-Flat Gauge of a Card

In order to provide manufacturers of carding machines and relevant accessories with theoretical references,how cylinder radius,setover and heel-toe difference affect cylinder-flat gauge of a carding machine was theoretically studied.The relationship between cylinder-flat gauge and cylinder radius,setover and heel-toe difference was geometrically discussed.Numerical calculation and illustration about the relationship were made with MATLAB in accordance with practical settings.A general formula about the relationship is derived.A concept,the small-gauge zone length,has been defined for the first time,and some relevant results thus obtained.Given setover and heel-toe difference,the greater the cylinder radius,the greater the average gauge.If a smaller overall cylinder-flat gauge is desirable,it is not necessary to emphasize the tangential direction of the heel of clothed surface to the cylinder.Their intersection within a small zone is acceptable.In many cases,small-gauge zone can reduce average gauge which may be helpful to the carding action;given cylinder radius and setover,the smaller the heel-toe difference,the more helpful to reduce the overall gauge;given cylinder radius and heel-toe difference,the small-gauge zone length will increase with the increase of setover,so does the difference between the smallest gauge and outlet gauge.

Adaptive variable structure control for large-scale time-delayed systems with unknown nonlinear dead-zone

The problem of adaptive fuzzy control for a class of large-scale, time-delayed systems with unknown nonlinear dead-zone is discussed here. Based on the principle of variable structure control, a design scheme of adaptive, decentralized, variable structure control is proposed. The approach removes the conditions that the dead-zone slopes and boundaries are equal and symmetric, respectively. In addition, it does not require that the assumptions that all parameters of the nonlinear dead-zone model and the lumped uncertainty are known constants. The adaptive compensation terms of the approximation errors axe adopted to minimize the influence of modeling errors and parameter estimation errors. By theoretical analysis, the closed-loop control system is proved to be semiglobally uniformly ultimately bounded, with tracking errors converging to zero. Simulation results demonstrate the effectiveness of the approach.

Parameter estimation for dual-rate sampled Hammerstein systems with dead-zone nonlinearity

The identification of nonlinear systems with multiple sampled rates is a difficult task.The motivation of our paper is to study the parameter estimation problem of Hammerstein systems with dead-zone characteristics by using the dual-rate sampled data.Firstly,the auxiliary model identification principle is used to estimate the unmeasurable variables,and the recursive estimation algorithm is proposed to identify the parameters of the static nonlinear model with the dead-zone function and the parameters of the dynamic linear system model.Then,the convergence of the proposed identification algorithm is analyzed by using the martingale convergence theorem.It is proved theoretically that the estimated parameters can converge to the real values under the condition of continuous excitation.Finally,the validity of the proposed algorithm is proved by the identification of the dual-rate sampled nonlinear systems.

New Dead⁃zone Compensation Approach for Proportional Flow Valve

To solve the dead⁃zone in the output flow curve of the proportional flow valve without displacement sensor,a dead⁃zone compensation approach is proposed in this paper.Instead of detection and feedback of the valve spool position,the proposed approach adopted the pressure drop across the valve metering orifice to accomplish the dead⁃zone compensation.The first step was to test and get the_(max)imum output flow,Q_(max),at a preset reference pressure drop,such asΔP_(0).The next step was to construct the target compensation flow curve,which is a line through(0,0)and(ΔP_(0),Q_(max)).Then a compensation law was designed to approach the target curve.However,the research results show that the above strategy caused over⁃compensation once the actual pressure drop deviated fromΔP_(0).Thus a correction coefficient,β,was presented to correct the initial compensation law as the pressure drop deviated fromΔP_(0).For example,the test results indicate that the corrected compensation approach could reduce the dead⁃zone from 53.9%to 3.5%at a pressure drop of 1 MPa;as the pressure drop was increased to 5 MPa,the dead⁃zone was reduced from 51.7%to 3.5%.Therefore,the following conclusions can be drawn:the proposed compensation approach is feasible,which can effectively reduce the dead⁃zone and improve the output flow static performance of the proportional flow valve without spool displacement feedback.

一种基于超声TOFD法的近表面缺陷检测模式

针对常规超声TOFD法存在近表面检测盲区的问题,提出一种纵波三次反射的TOFDW检测模式.分析了TOFDW模式的声传播特性,并阐明了该模式的检测原理.通过人工缺陷检测,研究了该模式检测信号和图像特征及检测灵敏度和精度.对实际焊缝进行了检测,并通过破坏性试验对无损检测结果进行了验证.结果表明,TOFDW模式能够识别常规模式下无法辨别的近表面缺陷,可有效检测到埋藏深度1.0 mm的人工缺陷;同时,该模式具有较高的量化测量精度,近表面人工缺陷埋藏深度测量的平均绝对误差不超过0.3 mm.

自适应解卷积方法抑制管道TOFD周向扫查盲区

利用超声衍射时差法(TOFD)沿管道外表面实施周向扫查时,受管道曲率和直达纵波脉冲宽度共同影响,在近表面区域形成分层盲区。本文采用自适应解卷积方法,选取与混叠信号主频接近的子带直达纵波信号作为参考信号,进行解卷积与自回归谱外推处理,拓宽有效频带范围,实现时域信号脉冲压缩,并结合周向扫查图像中端点衍射波确定缺陷深度。实验结果表明,对于外壁半径100.0 mm、壁厚30.0 mm,以及外壁半径148.0 mm、壁厚27.0 mm的碳钢管道,在中心频率5 MHz、探头中心距87 mm的检测条件下,自适应解卷积方法能够将管道近表面分层盲区范围减少约60%,且到直达纵波声线距离不小于4.0 mm缺陷的深度定量误差不超过10.6%。同常规频谱分析方法和自回归谱外推方法相比,自适应解卷积方法具有更优的盲区抑制效果,且能够准确定量前者难以检测的缺陷,测量误差不超过5.8%。

近表面缺陷的超声TOFDR和TOFDW检测

针对超声TOFD方法存在近表面检测盲区问题,提出了基于二次波的综合超声衍射反射回波方法(TOFDR)和缺陷W衍射反射方法(TOFDW)的检测模式。分析了TOFDR和TOFDW检测方法的超声传播特性,阐明了2种方法的检测原理,研究了它们的近表面理论检测能力。对于TOFDR检测方法,缺陷越近表面,D扫图像分辨特征越好。对于TOFDW检测方法,总体分辨能力大于TOFDR方法,但对于特别浅的近表面缺陷,声波难以识别,而将这2种检测方法综合应用,通过调整检测工艺参数可对近表面缺陷进行识别。通过对人工缺陷试样的检测,研究了综合2种方法结合条件的新检测模式的信号图像特征以及检测灵敏度,2种检测方法结合产生的D扫图像能很好的发现埋藏深度为1 mm的缺陷。

超声波声束扩散理论在TOFD技术中的应用

对焊缝进行衍射时差法超声检测(TOFD),在其他参数一定的情况下,选用频率较高的探头在一定程度上可以减小表面盲区高度。但从声束扩散理论方面考虑,频率较高的探头其声束覆盖范围小,会导致声束不能覆盖全部焊缝。基于超声波声束扩散理论,结合焊接工艺等因素,得到不同厚度工件的合理探头参数,可为相关人员编制TOFD检测工艺时提供参考。

TOFD检测中扫查方式与检测盲区的关系

非平行扫查、偏置非平行扫查及平行扫查是TOFD检测中常见的三种扫查方式,该三种扫查方式各有其优缺点及用处。通过理论分析及结合实际TOFD检测图像,深入讨论了三种扫查方式与TOFD检测盲区的关系。

TOFD检测盲区的研究及其解决方法

针对TOFD在检测时焊缝上下表面存在盲区容易造成缺陷漏检的问题,对检测盲区进行理论分析,通过试验验证了TOFD检测盲区符合理论计算值,为此设计制作了"TOFD+A"型脉冲反射超声波复合探头,建议采用复合检测的方法来弥补TOFD检测的不足,降低TOFD检测盲区对焊缝检测带来的不利影响。

TOFD检测中采用二次波评定近扫查面缺陷尺寸的方法

在TOFD检测过程中,因直通波宽度而产生的近扫查面盲区对检测影响很大。为精确定量位于近扫查面盲区的缺陷,制作了人工缺陷试块,对其采用常规TOFD以及TOFD二次波分别进行扫查。对比两种扫查方式所得TOFD图像可见,常规TOFD技术对近扫查面缺陷极易漏检且无法定量,而利用TOFD二次波扫查方式得到的图像能够显著分辨出缺陷并能精确定量,因此可弥补常规TOFD检测中对近扫查面缺陷检出能力的不足。

厚壁压力容器近表面TOFD检测研究

从厚壁压力容器近表面缺陷的检出率和缺陷尺寸定位定量的精准性角度出发,开展205 mm厚壁试块超声波衍射时差法(TOFD)上分区检测实验,结合上分区的整体成像结果,验证理论计算得出的通过改变探头间距和入射角来减小上表面盲区的方法是否可靠。实验结果表明,TOFD具有很强的独立发现上表面盲区内缺陷的能力,但无法获得缺陷自身深度和高度的精确定量,结合相控阵技术则可以有效提高近表面检测效果。