PERTURBATION THEORY AND MOMENTS FOR NONLINEAR FREUNDLICH DESORPTION IN A CONTINUOUS-FLOW WELL-STIRRED VESSEL

A regular perturbation expansion is applied to desorption governed by a Freundlich isotherm in a continuous-flow well-stirred vessel. A power series solution is presented, whose convergence is improved by the Shanks transformation. With a symbolic manipulation computer program, the first few temporal moments are derived exactly in closed form from the perturbation scheme.     

可变形机器人协同变形方法

可变形机器人AMOEBA-I的主要特点是具有多种构形方式,但由于受地面条件等影响使得某些构形变换难以实现.为了减小变形阻力,增强机器人对环境的适应性,提出可变形机器人的协同变形方法.建立相应数学模型,分析机器人系统各部分在协同变形过程中的运动和力学特性,实现将变形阻力的一部分转化为变形的动力,完成5种特殊构形之间的相互变换.研究基于摄动分析方法的模型线性化方法,以减小计算复杂度.最后,给出可变形机器人协同变形性能评价指标,并通过仿真和试验验证协同变形方法的有效性,满足机器人变形需要.     

Mathematical model for calculation of thickness of flame sprayed coating of aluminium on S235JR steel

Abstract

In the present work, the method of response surfaces was employed for the purpose of drawing up a mathematical model for the calculation (forecasting) of the thickness of a flame sprayed coating of powdered aluminium on S235JR steel. Experimental work was conducted according to a full central composite design at three levels. The thickness of the coatings made with combinations of input parameters of the procedure according to the experiment plan mentioned was measured in line with the ISO 2064 standard. A mathematical model was derived describing the dependence of the experimentally obtained thickness values on the input parameters of the procedure. The possibility of analysing the influence of the parameters upon the thickness for a certain combination of input parameters has been presented with the use of perturbation plots.     

Perturbation analysis of fuzzy linear systems

This paper deals with the perturbation analysis of fuzzy linear systems. Three cases of perturbation are considered: (a) the right hand side is perturbed while the coefficient matrix remains unchanged; (b) the coefficient matrix is perturbed while the right hand side remains unchanged, and (c) both the coefficient matrix and the right hand side are perturbed. For all of the three cases, the respective relative error bounds for solutions of fuzzy linear system are derived. The results are illustrated by numerical examples.     

Identification of higher-dimensional ill-conditioned systems using extensions of virtual transfer function between inputs

A new formulation is proposed to directly extend the virtual transfer function between inputs (VTFBI) approach to ill-conditioned systems with dimensions higher than 2 × 2. The method requires only a single correlated component and is applicable to moderately large systems of up to around six outputs. To cater for systems with even higher dimensions, an indirect approach is further introduced based on subsystem decomposition in which the design for each subsystem achieves D-optimality in the presence of active output variance constraints. New measures of sensitivity to measurement inaccuracy and parameter changes are also introduced. A detailed case study shows that both direct and indirect extensions of the VTFBI technique outperform competing ones in terms of accuracy in the estimation of singular values, robustness towards the effect of noise as well as effectiveness for application in model based control. An additional advantage of the proposed approaches is that their performance does not depend significantly on the specific design choices made within these methods.     

Experimental study on the detonation propagation behaviors through a small-bore orifice plate in hydrogen-air mixtures

In this study, the regimes of detonation transmission through a single orifice plate were investigated systematically in a 6-m length and 90-mm inner diameter round tube. A series of experiments on the detonation propagation mechanisms in hydrogen-air mixtures were performed. A single obstacle with different orifice size (d) from 10 to 60 mm was adopted to study the effects of the induced perturbations on the detonation propagation. Here, the thickness of orifice plate (δ) was fixed at 10.33 mm. Detonation velocity was determined from the time-of-arrival (TOA) of the detonation wave recorded by eight high-speed piezoelectric pressure transducers (PCB102B06). Detonation cellular size was obtained by the smoked foil technique. The characteristic of detonation velocity evolution were quantitatively analyzed after it passes through a single obstacle, and particular attention was paid to the cases for which the blockage ratio (BR) is greater than 0.9, i.e., the cases of small hole diameter of d < 25 mm. The experimental results showed that, in a smooth tube, only super-critical condition and sub-critical condition can be observed. After the orifice plate is introduced into the tube, critical condition occurs. The detonation re-initiation with distinct cellular structures was experimentally observed. Of note is that when the blockage ratio (BR) values in the range of 0.802–0.96, it was easier to detonate at the fuel-lean side. Finally, the critical condition for detonation propagation through an orifice plate was quantified as d/λ > 1 where λ is the detonation cell size.     

Nonlinear flow-induced vibration of a SWCNT with a geometrical imperfection

Based on the nonlocal continuum theory, transverse vibration of a single-walled carbon nanotube (SWCNT) conveying fluid with immovable support conditions is investigated. Unlike previous similar studies, the SWCNT is assumed to be not perfectly straight and initially includes a slight geometrical curvature as an imperfection. The SWCNT is assumed to be embedded in a Pasternak-type foundation. Hamilton’s principle is applied to drive an efficient governing equation of motion, which covers stretching, large deformation, and imperfection nonlinearities. The perturbation method of multi scales (MMS) is applied and the nonlinear flow-induced frequency ratio is analytically calculated. The obtained results reveal that the imperfection of the nanotube at high flow velocities makes the model severely nonlinear, especially when considering the nonlocal effects. A noteworthy observation is that the nonlinear flow-induced frequency ratio is decreased as the imperfection of the nanotube increases. Whereas through a parametric study, the effects of the flow velocity, nonlocal parameter, the stiffness of the elastic foundation, and the boundary conditions (BCs) on this frequency reduction are calculated and discussed widely.     

Comparative study of variable size perturbation and observation maximum power point trackers for PV systems

Perturbation and observation (P&O) maximum power point tracking (MPPT) algorithms are common in photovoltaic (PV) systems due to its ease of implementation. However, operation with fixed size perturbations results in a trade-off between speed of response and maximum power yield in the steady-state. This paper discusses the use of Fuzzy logic and non-switching zone schemes for implementing variable size perturbations for improved transient and steady-state responses. The potential performance of four different P&O algorithms is investigated by means of simulations. Experimental results are then used to verify how the computational burden of each algorithm and the processing speed of a digital signal processor (DSP) affect the performance of each method in a prototype. The best performance is achieved with a new strategy called non-switching zones in the V_PV × I_PV plane. The power electronics converter operates with duty cycle (D) equal to 0 or 1, depending on which non-MPP region the system operates, pushing the operating point the fastest way possible towards the MPP region, for improved transient response. At the MPP region, a reduced Fuzzy P&O MPPT algorithm optimized for small variations around the MPP is used for reduced oscillations and increased power yield in the steady-state.     

Theoretical considerations of static and dynamic characteristics of air foil thrust bearing with tilt and slip flow

The thrust pad of the rotor is used to sustain the axial force generated due to the pressure difference between the compressor and turbine sides of turbomachinery such as gas turbines, compressors, and turbochargers. Furthermore, this thrust pad has a role to maintain and determines the attitude of the rotor. In a real system, it also helps reinforce the stiffness and damping of the journal bearing. This study was performed for the purpose of analyzing the characteristics of the air foil thrust bearing. The model for the air foil thrust bearing used in this study is composed of two parts: one is an inclined plane, which plays a role in increasing the load carrying capacity using the physical wedge effect, and the other is a flat plane. This study mainly consists of three parts. First, the static characteristics were obtained over the region of the thin air film using the finite-difference method (FDM) and the bump foil characteristics using the finite-element method (FEM). Second, the analysis of the dynamic characteristics was conducted by perturbation method. For more exact calculation, the rarefaction gas coefficients perturbed about the pressure and film thickness were taken into consideration. At last, the static and dynamic characteristics of the tilting condition of the thrust pad were obtained. Furthermore, the load carrying capacity and torque were calculated for both tilting and nontilting conditions. From this study, several results were presented: (1) the stiffness and damping of the bump foil under the condition of the various bump parameters, (2) the load carrying capacity and bearing torque at the tilting state, (3) the bearing performance for various bearing parameters, and (4) the effects considering the rarefaction gas coefficients.     

Sliding-mode repetitive learning control with integral sliding-mode perturbation compensation

This paper proposes a sliding-mode repetitive learning control (SMRLC) scheme with an integral sliding-mode perturbation observer (ISMPO) for repetitive tracking control tasks. The three control strategies which are synthesized to yield excellent tracking performance are: (1) the pole-placement feedback control to specify the desired error dynamics; (2) ISMPO-based feedback compensation as the robust part; and (3) a feedforward learning component that refines the control to improve system performance through repetitive trials. The ISMPO-based feedback compensation ensures that there is only small tracking error during initial learning trials and enhances system insensitivity to exceptional and aperiodic disturbances. The feedforward learning compensation is updated according to a certain switching signal that is equivalent to the compensation error of the feedforward control, yielding fast convergence of the learning process from trial to trial. Experimental results demonstrate the feasibility of the proposed scheme.