微纳尺度结构动力学专刊序

围绕微纳尺度结构跨尺度动力学建模、动力学分析、动力学控制、动力学设计与测量方法等研究主题,本专刊介绍了微纳尺度结构动力学与控制领域的一些最新研究成果.

Research on an inertial piezoelectric actuator for a micro in-pipe robot

A new kind of inertial piezoelectric actuator for a micro in-pipe robot is proposed and studied. The actuator is composed of a body, corresponding to a mass rod, and four elastic legs. Each leg is a composite piezoelectric bimorph beam, made up of a middle metal element, an upper and lower piezoelectric elements. The mechanism is driven by an asymmetric waveform voltage, such as saw-toothed waveform, and utilizes the dynamic relationship between the maximum static friction force and the inertial force. To study the actuator, firstly, the constituent equation of a composite piezoelectric bimorph under both applied voltage and external force was inferred by thermodynamics. Secondly, the dvnamic model of the actuator was established analyzing the relationship between the locomotive states, viz. displacement and velocity, and design parameters, such as piezoelectric strain constant, elastic modulus,length, width and thickness of the piezoelectric element, actuator mass, and driving vohage. At last, the dynamic equation was solved and the theoretical calculation of the inherent frequency was more consistent with the experimental data, which proved the rationality of the model. All these lay a theoretical foundation of the micro actuator parameter optimization and more research on a micro robot.

Modeling of Soot Formation in Gas Burner Using Reduced Chemical Kinetics Coupled with CFD Code

A computational study of soot formation in ethylene/air coflow jet diffusion flame at atmospheric pres-sure was conducted using a reduced mechanism and soot formation model. A 20-step mechanism was derived from the full mechanism using sensitivity analysis,reaction path analysis and quasi steady state(QSS) approximation. The model in premixed flame was validated and with computing savings in diffusion flame was applied by incor-porating into a CFD code. Simulations were performed to explore the effect of coflow air on flame structure and soot formation. Thermal radiation was calculated by a discrete-ordinates method,and soot formation was predicted by a simple two-equation soot model. Model results are in good agreement with those from experiment data and detailed mechanism at atmospheric conditions. The soot nucleation,growth,and oxidation by OH are all enhanced by decrease in coflow air velocity. The peak soot volume fraction region appears in the lower annular region be-tween the peak flame temperature and peak acetylene concentration locations,and the high soot oxidation rate due to the OH attack occurs in the middle annular region because of high temperature.

电机常见问题浅析及对策

结合生产运行与检修实践对生产过程中电机常见的一些问题及解决方案检修工艺标准工艺卡作初步探讨．

Vibration Suppression of Unbalanced Machines UsingLumped Mass Dynamic Vibration Absorber

The vibration of machines due to rotating parts unbalance disturbs the machine functioning and shortens the lifetime of its parts. A dynamic vibration absorber is a favorite solution to suppress the machine vibration since its implementation does not require any modification neither on the machine nor on its installation. The paper considers an unbalanced machine to which a lumped mass dynamic vibration absorber is attached. Firstly, the machine equipped with the absorber is modeled, and the vibration expressions are extracted. Secondly, an original approach to optimize the absorber parameters is presented, and simulation results are advanced, when the absorber is undamped and damped. Thirdly, the absorber optimal parameters allowing the best vibration reduction of the machine are identified, showing bow the absorber should be designed, when the disturbance frequency is stable or unstable. The results are a significant contribution in the vibration control of unbalanced machines.

Hydrodynamic Efficiency Improvement of the High Skew Propeller for the Underwater Vehicle Under Surface and Submerged Conditions

An algorithm based on the Boundary Element Method(BEM)is presented for designing the High Skew Propeller(HSP)used in an Underwater Vehicle(UV).Since UVs operate under two different kinds of working conditions(i.e.surface and submerged conditions),the design of such a propeller is an unwieldy task.This is mainly due to the fact that the resistance forces as well as the vessel efficiency under these conditions are significantly different.Therefore,some factors are necessary for the design of the opti-mum propeller to utilize the power under the mentioned conditions.The design objectives of the optimum propeller are to obtain the highest possible thrust and efficiency with the minimum torque.For the current UV,the main dimensions of the propeller are pre-dicted based on the given required thrust and the defined operating conditions.These dimensions(number of blades,pitch,diameter,expanded area ratio,thickness and camber)are determined through iterative procedure.Because the propeller operates at the stern of the UV where the inflow velocity to the propeller is non-uniform,a 5-blade HSP is preferred for running the UV.Finally,the propel-ler is designed based on the numerical calculations to acquire the improved hydrodynamic efficiency.

Marine Current Turbine Simulator Development Based on Hardware in the Loop Simulation Concept

This paper is a contribution to the development of real time simulators for energy conversion research with respects to the ＂hardware in the loop simulation＂ concept. The focus is on the study of marine current kinetics energy conversion from into electrical energy using a marine current turbine simulator, developed in three stages. In the first stage the marine current turbine is emulated with the help of an induction drive who reproduces at its shaft the characteristics of a real turbine. It is connected with a load break used to force the emulator to respect on its shaft the characteristics of the real turbine. In the second stage, the induction drive is connected on the shaft with a doubly feed induction generator, for the study of energy conversion. The emulator respects the working regime, developed in the previous step, of a real turbine due to the control of the drive. In the third stage the induction machine emulating the turbine is interconnected with the generator and the load break. This assembly is used for the dynamic study of the marine current turbine. The break is used to create extra loads on the shaft and a variable inertial moment.

Recent advances in plasmonic organic photovoltaics

Light trapping based on the localized surface-plasmon resonance(LSPR)effect of metallic nanostructures is a promising strategy to improve the device performance of organic solar cells(OSCs).We review recent advances in plasmonic-enhanced OPVs with solution-processed metallic nanoparticles(NPs).The different types of metallic NPs(sizes,shapes,and hybrids),incorporation positions,and NPs with tunable resonance wavelengths toward broadband enhancement are systematically summarized to give a guideline for the realization of highly efficient plasmonic photovoltaics.

Recent progress in the numerical modeling for organic thin film solar cells

Device modeling is constructive in finding the dependency of devices efficiency on structure parameters and material properties. For the sake of looking into the physics mechanism of organic solar cells (OSCs), as well as predicting their maximum attainable efficiency, numerical modeling is widely utilized to simulate the behavior of OSCs. Although some indispensable parameters are neglected or hypothesized because of inexplicitness in simulation models for OSCs, numerical modeling can describe the kinetic process in OSCs intuitively. This paper summarizes the optical/electrical models in the BHJ solar cell, as well as addresses their corresponding development in recent years on the basis of device physics and its working principle. Applications of numerical modeling and comments on modeling results are summarized. Meanwhile, precision and open questions about every model are discussed.

Pressure fluctuation propagation of a pump turbine at pump mode under low head condition

Pressure fluctuation at the vaneless space and vanes passages is one of the most important problems for the stable operation of a pump turbine. The fluctuation appears in any operating condition. Much research has been done on the pressure fluctuation of hydraulic machinery. However, the details of pressure fluctuation propagation of the pump turbine at the pump mode have not been revealed. The modem pump turbine with high water head requires the runner to be ＂flat＂, which would induce pressure fluctuation more easily than the low head pump turbine. In this article, a high head pump turbine model is used as the re- search object. As the pressure fluctuation at off-design point is more serious than at the design point, the low head condition is chosen as the research condition. Pressure fluctuation at the vaneless space and vanes passages is predicted by the computa- tional fluid dynamics method based on k-co shear stress transport model. The experiment conducted on the test rig of the Har- bin Institute of Large Electrical Machinery is used to verify the simulation method. It proves that the numerical method is a feasible way to research the fluctuation under this operating condition. The pressure fluctuation along the passage direction is analyzed at time and frequency domains. It is affected mainly by the interaction between the runner and vanes. In the circumferential direction, the influence of the special stay vane on the pressure fluctuation is got. The amplitude in the high-pressure side passage of that vane is lower than that in the other side. The study provides a basic understanding of the pressure fluctua- tion of a pump turbine and could be used as a reference to improve the operation stability of it.

Characteristics of the dynamic distribution of suspended particles in the flocculation process

Polyaluminium chloride (PAC) synthetic water was selected as a coagulant and kaolin suspension particles as objects to be removed. Online instruments such as the turbidimeter and particle counter were employed to monitor the flocculation process online and collect test data. The aim of the experiments was to study the dynamic distribution characteristics of suspension particles in the flocculation process. The 3D flow field in the reacting vessel was also simulated at different slow stirring speeds. The experiments showed that particle collision and aggregation in the flocculation process is in compliance with the Sutherland cluster aggregation model. This study further indicated that under appropriate hydrodynamic conditions, the distribution of turbulent flow in the reactor could be improved to increase the odds of effective particle collision and restrain the breakup of formed flocs by vortex shearing force. A good flocculation effect could therefore be produced.