In the study of tubular structures such as pipeline sections, musical wind instruments and human airways, acoustic pulse reflectometry has become established as a useful tool for non-invasively measuring the input impulse response, from which the internal duct dimensions can be calculated.
In this thesis, the theory describing wave propagation in a duct of varying crosssection is outlined, culminating in a discussion of the layer peeling algorithm used to reconstruct a duct’s bore profile from its input impulse response. Experimental measurements of the input impulse responses of various test objects, together with the subsequent bore reconstructions, are then presented.
The problem of offset in input impulse response measurements is discussed and the effect on the bore reconstruction is shown. The offset is found to consist of both a DC component and a sinusoidal component. Methods for eliminating the two offset components are explored and the resultant improvement in the stability and reproducibility of the bore reconstructions is demonstrated.
Two adaptations to the reflectometry technique, designed to extend the bandwidth of input impulse response measurements, are described. The improved high frequency content brought about by these adaptations is shown to lead to bore reconstructions of high axial resolution, allowing rapid changes in cross-sectional area to be more accurately reproduced.
Finally, limitations of the acoustic pulse reflectometry technique (particularly those brought about by the bandwidth improvements) are discussed and potential future ways of overcoming the limitations are proposed.
This paper investigates two robust finite-time controllers for the attitude control of the spacecraft by using a modified terminal sliding mode surface. With the use of terminal sliding mode control and adaptive control, the controllers under input saturation can compensate both external disturbances and the uncertainty of the model parameters. By using the first and the second controller, the closed-loop system is finite-time stability and practical finite-time stability, respectively. As the system model is based on the rotation matrix, both controllers are without unwinding. Numerical simulations are given to demonstrate the effectiveness of the finite-time controllers.
A ZnSe-reduced graphene oxide (ZnSe-rGO) nanocomposite with ZnSe dispersed in rGO is prepared via a one-step hydrothermal method and applied as the anode materials for both lithium and sodium ion batteries (LIBs/SIBs). The as-prepared composite exhibits greatly enhanced reversible capacity, excellent cycling stability and rate capability (530 mA h g-1 after 100 cycles at 500 mA g-1 in LIBs, 259.5 mA h g-1 after 50 cycles at the current density of 100 mA g-1 in SIBs) compared with bare ZnSe in both lithium and sodium storage. The rGO plays an influential role in enhancing the conductivity of the nanocomposites, buffering the volume change and preventing the aggregation of ZnSe particles during the cycling process, thus securing the high structure stability and reversibility of the electrode.
Ion beams with energies in the range 1–2 keV are used to sputter neutral Zr atoms from a polycrystalline surface. Laser induced fluorescence detection is used to obtain angular distributions of sputtered neutrals as a function of ion impact direction, ion mass, ion energy, and spin–orbit state of the exiting atoms. About 40% of the sputtered atoms are excited. Angular distributions depend weakly on ion mass and energy. The angular distributions are fitted well by a modified form of the Roosendaal and Saunders model of sputtering.
An unmanned helicopter dynamic model identification method based on immune particle swarm optimization (PSO) algorithm is approved in this paper.In order to improve the search efficiency of PSO and avoid the premature convergence, the PSO algorithm is combined with the immune algorithm.The unmanned helicopter model parameters are coded as particle, the error of flight test and math simulation model is objective function, and the dynamic model of unmanned helicopter is identified.The simulation result shows that the method has high identification precision and can realistically reflect the dynamic characteristics.
To test high resolution and dynamic performance of star sensor, a method of consideration image motion on Modeling the motion blur of star sensor is proposed. Firstly, image motion geometric model based on the rotation of Starlight vector is studied. Secondly, with the help of the normal distribution of static star image energy model, introducing the star image motion speed, obtaining the energy distribution function of moving stars, implementing high dynamic simulation of star map. Finally, establishing the simulation environment, through adjusting input parameters such as integral time, rate of change of three attitude angle, the launch time, location, then, important simulation data of stars observed by star sensor in orbit can quickly be obtained, such as navigation stars information, value and direction of image motion, intensity distribution, signal to noise ratio. This work is very important to research and evaluate the star image motion compensation algorithm.
According to the impacts of coal power industry to the atmosphere environment in China,this paper proposes a foresting and assessment methodology for coal-fired power technologies in China based on CGE model.The endogenous and exogenous technological progress have been depicted in the model.Then this paper discusses the theory of energy-flow calculation for building energy equilibrium sub-model through analyzing the energy transformation process for coal-fired power industry.Finally,this paper overviews the application and development of advanced coal-fired power technologies in China,and studies the main functional relations of coal-fired power sub-model and its linkage with CGE model.
Isothermal chemical vapor infiltration (CVI) is an important conventional technique for fabrication of ceramic and carbon matrix composites. The major disadvantage of isothermal CVI process is the extremely long processing time required. Therefore the key point of research on isothermal CVI technique is to optimize process parameters and to raise the deposition efficiency. Based on the experimental results, the fuzzy rules were automatically obtained and optimized by genetic algorithm, thus the fuzzy system for isothermal CVI of carbon/carbon composites was established. Through the analysis of the output of training and testing samples, we could draw a conclusion that this system is characterized by higher precision and good generalization ability. With the help of this system the regulation affecting infiltration temperature, fiber content and chamber pressure in isothermal CVI were analyzed. The results show that this system has a good instructive function for formulating of CVI processes in practical application.
Aqueous zinc metal batteries (AZMBs) are an energy storage system that is expected to replace traditional lithium batteries. However, the practical application of AZMBs is hampered by some inherent drawbacks. Herein, an amino acid additive with a screening property is introduced. The additives effectively erode Zn(002) by binding to a specific zinc crystallographic plane, achieving an ordered layered three-dimensional structure anode, and the shielding effect of additives can inhibit the activated H2O and induce uniform Zn deposition. Accordingly, a stable long-term cycling for 3750 h at 1 mA cm–2 and an ultrahigh Coulombic efficiency (99.7%) are obtained. The cell also achieves a cycling life of nearly 1000 h, even at 10 mA cm–2 (cumulative capacity over 5 Ah cm–2). Moreover, a capacity retention of 80% after 1000 cycles and a superior rate are exhibited for Zn//V2O5 cells. The work provides theoretical support for achieving highly reversible Zn anode.
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