消声元件安装位置对消声效果的影响

分别以消声量和管口阶次噪声作为评价指标,研究消声元件安装位置对消声效果的影响规律,设计在直管不同位置安放四分之一波长管的消声量测量试验对消声量评价。结果表明:设计频率声模态下,在反节点处安装波长管消声量最大,与理论分析完全吻合;进一步对消声量进行仿真计算,结果与试验完全相符。对于管口噪声指标评价,设计频率为267 Hz的谐振腔解决某发动机4000 r/min时进气管口存在4阶噪声引起的噪声峰值问题,对比谐振腔安装在进气管路该频率附近的声模态反节点和节点位置的管口4阶噪声,可知谐振腔布置在反节点位置比节点位置噪音降低了24 dB。两个案例充分证明声学系统模态反节点位置是消声元件的最佳布置位置。     

Calculating the Reaction Order and Activation Energy for the Hydrothermal Carbonization of Fructose

The development of accurate kinetic models for hydrothermal carbonization (HTC) faces major difficulties. This is related to the fact that the formation of the solid hydrochar can be regarded as a formation of a second phase from a homogenous solution. The reaction mechanism is not fully understood. From the current state of art, it is obvious that the reaction mechanism is some sort of polymerization reaction, thus, having reaction order higher than one. In order to gain more knowledge about the HTC reaction, fructose is used as a model substance, as it can be regarded as a key intermediate during the hydrothermal processing of carbohydrates. The results indicate that the reaction order is a highly sensitive parameter varying with temperature, reaction time and initial concentration. It can be concluded that the model itself is a strong simplification of the real reaction mechanism, thus more research is necessary to complete the actual knowledge.     

A new control strategy for a higher order proton exchange membrane fuel cell system

In this paper, a new cascade control strategy is proposed for a higher order Proton Exchange Membrane (PEM) Fuel Cell system for improving the performance on the basis of stack voltage. In the proposed strategy, stack voltage is considered as the primary objective and maintaining oxygen excess ratio value as a secondary aim, by manipulating the air compressor voltage. A higher-order PEMFC model is reduced to lower order integer and fractional models using varied model reduction techniques, which are then used to realize the primary as well as secondary controllers. Both integer and fractional order PID controllers are designed for the reduced order models and then implemented for the higher order system. The control performance is evaluated for disturbance rejection, system model mismatch and better controlled output for continuous random disturbance on the basis of Integral Absolute Error and controller effort. The outcome of the proposed control strategy is advantageous in terms of disturbance rejection, robustness, parameter uncertainty and reduction of plant-model mismatch.     

Catalytic dehydrogenation of formic acid-triethanolamine mixture using copper nanoparticles

In a bid to complement the lost reserves from fossils, recent advances in research are tailored towards producing hydrogen as an alternative source of fuel which is aimed at fostering a globally sustainable and reliable energy-economy. In this work, hydrogen was produced from formic acid (FA) using a new technology that involves the use of copper nanoparticles (CuNPs) supported on triethanolamine. The CuNP-catalysts of variant concentrations (i.e. 0.6–1.2 M) were synthesized using the conventional chemical deposition method. Also, a novel approach that bothers on the application of the Differential Method of Analysis (DMA) was used in determining the kinetic parameters for the FA-dehydrogenation. Based on the results, the volume of H₂ produced varied with time, pH, concentration and catalyst-size. At 6 h, the 1 M CuNPs gave the highest volume (815 mL) of hydrogen with corresponding pH, particle size and approximate conversion of 3.19, 1.5 nm and 100% respectively, whereas, over extended periods i.e. over 6 h, the approximate volume-conversions of FA increased insignificantly for all catalysts. According to the investigation, the optimum CuNP-catalyst concentration required to produce 815 mL H₂ in 6 h is 1 M. The decomposition was a first-order-type with a rate constant (k-value) of 1.0041 s⁻¹.     

并联有源滤波器的改进重复控制策略研究

针对三相整流负载产生的6k±1次谐波,提出静止坐标系下的改进型6k±1重复控制策略。同时将比例控制与改进型重复控制相结合,设计改进重复控制并联比例的复合控制结构。为减小改进重复控制中延时环节不为整数的影响,采用基于Lagrange插值近似的FIR滤波器逼近分数延时特性。最后对系统进行稳定性分析和详细设计方法进行推导。通过Matlab仿真验证改进重复控制策略能有效跟踪6k±1次谐波且具有良好的补偿效果,动态响应较快。     

基于Legendre多项式的锂离子电池降阶模型

在Newman模型以及单粒子模型(SPM)的基础上,提出基于Legendre正交多项式的电池模型降阶算法;同时,将固液相物理量的分布纳入模型算法,在提高运算速度的情况下,保证运算精度。以磷酸铁锂(Li Fe PO4)正极锂离子电池为例,对导出的降阶模型进行仿真验证。与全阶模型相比,该模型所计算的电池状态量误差均能保持在2%下。     

Observer‐based fuzzy adaptive quantized control for uncertain nonlinear multiagent systems

This paper focuses on consensus quantized control design problem for uncertain nonlinear multiagent systems with unmeasured states. Every follower can be denoted through a system with unmeasurable states, hysteretic quantized input, and unknown nonlinearities. Fuzzy state observer and Fuzzy logic systems are employed to estimate unmeasured states and approximate unknown nonlinear functions, respectively. The hysteretic quantized input can be split into two bounded nonlinear functions to avoid chattering problem. By combining adaptive backstepping and first‐order filter signals, an observer‐based fuzzy adaptive quantized control scheme is designed for each follower. All signals exist in closed‐loop systems are semiglobally uniformly ultimately bounded, and all followers can accomplish a desired consensus results. Finally, a numerical example is employed to elaborate the effectiveness of proposed control strategy.     

Layered-Perovskite Nanowires with Long-Range Orientational Order for Ultrasensitive Photodetectors

2D layered metal-halide perovskites combine efficient exciton radiative recombination in crystal interior with long-distance free-carrier conduction at layer edges, which are promising candidates for realizing high-performance photovoltaic, light-emission and photodetection devices. The anisotropic electrical conductivity in layered perovskites imposes an additional requirement of orientational control for enabling favorable charge transport. However, rational fabrication of single-crystalline nanostructures with pure crystallographic orientation is still elusive. Herein, large-scale pure (101)-orientated 2D-perovskite single-crystalline nanowire arrays are realized by combining solvent engineering with the capillary-bridge lithography technique. Ordered nucleation at liquid–air interface and unidirectional growth along the dewetting direction are demonstrated by fluorescence microscopy and grazing-incidence X-ray scattering in discrete capillary bridges. In consideration of crystal interior exhibiting high resistance arising from the serial insulating organic barriers and ultrafast dissociation of excitons to generate long-lived free carriers at layer edges, ultrasensitive photodetectors are demonstrated with average responsivity exceeding 1.1 × 10⁴ A W⁻¹ and detectivity exceeding 9.1 × 10¹⁵ Jones.     

The application of fractional order control for an air-based contactless actuation system

Industry pushes towards ever faster and more accurate production of thin substrates. Contactless positioning offers advantages, especially in terms of risk of breakage and contamination. A system is considered designed for contactless positioning by floating a silicon wafer on a thin film of air. This paper focuses on the design of a control system, including actuators, sensors and control method, suitable for this purpose. Two cascaded control loops, with decoupled SISO controllers, are implemented for this moving mass controlled on a mass-spring system, which can be modelled as a fourth order system. The SISO controllers are first designed with classic loopshaping tools, which are then modified using fractional control. Two arguments based on examples in this system are given for the application of fractional control. Firstly, to increase the bandwidth of a regular mass-spring system, and secondly to control a plant which behaves fundamentally fractional, such as the moving mass in this cascaded fourth order system. By merely the application of fractionality, the bandwidths are extended by 14.6 % and 62 %, for the inner and outer loop respectively. A closed-loop positioning bandwidth of the wafer of 60 Hz is achieved, resulting in a positioning error of 104 nm (2σ value), which is limited by sensor noise and pressure disturbances. This paper shows how the extension of classic loopshaping tools with fractional control can directly improve the performance, without adding to the complicatedness of the control system. Moreover it demonstrates a working concept of a novel type of contactless actuator.