Journal of Engineering and Thermal Sciences
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Dynamics of the formation of thin LaNbO4 films using magnetron sputtering
Get PDFDoped lanthanum niobate thin films were deposited using magnetron sputtering technique. W and Mg cathodes were used for doping LaNbO4 thin films. Thin films were deposited on two types of substrates: amorphous optical quartz (SiO2) and polycrystalline Alloy 600 (Ni-Cr-Fe). The structural and morphological analysis was performed using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), atomic force microscope (AFM). The nonequilibrum growth of the thin films and the nonlinear dynamics of the sputtered atoms and their oxides is observed. XRD analysis revealed that Mg promotes crystallite formation in La1-xMgxNbO4 thin films and W inhibits crystallite formation in LaNb1-xWxO4 thin films. EDS analysis showed that La1-xMgxNbO4 and LaNb1-xWxO4 thin films are nonstoichiometric. They have deficit or excess oxygen and Nb (compared to lanthanum). It was noticed that the nonstoichiometry has influence on the morphology of thin films. The cross section of formed thin films analysis showed that grains or fibers are not visible in the thin films with excess oxygen concentration and thin films with deficit of oxygen has fiber type structure. Oxygen concentration also influences the surface morphology. The roughness of the surface increases (0.2 nm ÷ 0.3 nm for La1-xMgxNbO4 and 0.2nm ÷ 0.8 nm for LaNb1-xWxO4) with decreasing oxygen concentration
Preventive maintenance optimization policy based on a three-stage failure process in finite time horizon
Get PDFIn this paper, a preventive maintenance optimization policy based on a three-stage failure process in finite time horizon is proposed. The lifetime of system is divided into three stages by the concept of three-stage failure process, which is corresponding to the three color scheme commonly used in industry. The subsequent inspection interval is halved when the minor defective stage is identified. Once identifying the severe defective stage, maintenance action is carried out. A numerical example is presented to demonstrate the efficiency of the proposed models
Study on the optimization system of supporting schemes for foundation pit
Get PDFAt present, there are various supporting schemes for foundation pit that could be adopted in actual projects; however, there are also certain differences in construction cost and applicability of different schemes. To guarantee reasonable and efficient choice of supporting schemes for foundation pit, it is necessary to implement selection of supporting schemes purposefully. This essay discusses mainly the optimization system of supporting schemes for foundation pit. Through analysis of the affecting factors of supporting schemes of foundation pit, comprehensive optimization system of supporting schemes for foundation pit has been constructed, optimization model of supporting schemes based on TOPSIS has been created and comprehensive optimization system of supporting schemes for foundation pit has also been established
Identification of open crack of beam using model based method
Get PDFThis research aims at identifying the position and depth of the open transverse crack of the beam using the model based method. The stiffness matrix of the cracked beam element and the basic principle of the model based method are introduced. It is discussed to estimate the generalized displacement of all nodes of the beam by the measured displacements of a few degrees of freedom. The relative change rate of the equivalent external load between the intact and cracked elements is compared with that of mode shape, nature frequency and displacement amplitude between the intact and cracked beam. The position and depth of the crack are identified by the model based method in two cases. In first case, the measured displacement is assumed not to include noise. The identification results based on the actual displacement and rotation of all nodes are compared with the results using the estimated generalized displacement. In second case, the measured displacement includes noise and the generalized displacement of all nodes is estimated by the displacement of two measurement points. The simulation results shown there is no error to identify the position, the relative depth identification error of the crack with 1 μm depth is 2.34 % without noise, and the relative depth identification error of the crack with 200 μm depth could be down to about 5 % with the energy signal to noise ratio being about 7.00 before denoising
Detection and identification of mechanical faults by Kalman filtering in electric machines
Get PDFKalman filtering technique is applied on vibration signals to detect eccentricity fault and bearing fault in induction motor. The vibration signals are acquired during load performance tests of healthy and faulty cases of induction motor. The state space equations needed for Kalman filter structure are constructed based on autoregressive model of the signals. The harmonics of fault related frequencies are identified from the spectrum of innovation signal, which is provided from the Kalman filter response, for vibration signal and also it is seen that Kalman filter reduce the noise level
Review of damage problems of the soft substrate interlayer film
Get PDFThis paper reviews the research progress of soft substrate interlayer film, including the applications and the preparation methods of the soft substrate interlayer film, the testing means of the films’ structure and composition and the researches of the film damage, especially the dynamic damage. As well as the future research directions and applications are put forward
Control measures about vibration and noise of pipeline onboard marine vessels
Get PDFThe pipeline noise is an important part of the sources of vibration and noise for high performance marine vessels. It is vital to control the vibration and noise of the onboard pipeline to improve the acoustic stealth and life level in marine vessels. The vibration and noise caused by the onboard pipeline system was analyzed. Some methods and advices were put forwards to reduce the vibration and noise caused by the pipeline system, including the control of vibration, structural noise and fluid noise. In addition, a new concept “pressure-stabilized bladder” was created
A novel time domain structural damage diagnosis method using Jensen-Shannon Divergence
Get PDFStructural vibration response under ambient excitation is a stochastic process. The change in the characteristics of stochastic process can be used to evaluate the state of structure. Jensen-Shannon Divergence (JSD) is a mathematical expression widely used in time series analysis to account for the similarity of measurements. The aim of this article is to extend the JSD index, in conjunction with the Natural Excitation Technique, phase space reconstruction and singular value decomposition, for detecting damage in structures at an early stage. A simulation on the ASCE Benchmark structure with various damage scenarios and a laboratory experiment for a truss-type structure are carried out to validate the proposed JSD damage index. Both numerical and experimental results show that the proposed approach has better performance in contrast to other existing similar damage index such as Cross-entropy, and no mathematical model of the analyzed structure is required a priori
Multi-objective topology optimization for the measuring rod of gun barrel bore detecting system
Get PDFIn this paper, we focus on the measuring rod of the gun barrel bore detecting system. The topology optimization model of the measuring rod is set up based on the variable density continuum structural topology optimization method. In order to minimize the static flexibility and to maximize the low vibration frequency simultaneously, the compromise programming approach is employed to optimize multi-objective topology. Optimization results show that an ideal distribution of material is acquired, which enhances the natural frequency of structure and reduces the structure quality, thus a synchronized multi-objective optimization is achieved. We validate the ultimate optimized topology with statics and dynamics analysis. The results show that both global stiffness and low frequency of the optimized measuring rod have been improved significantly which verify the rationality of the design
Optimum design of a partially-treated MR-fluid sandwich plate
Get PDFThe present study concerns with dynamic characterization and optimal design of a partially treated magneto-rheological (MR) sandwich plate. An aluminum sandwich plate, partially treated with MR fluid (MRF 132DG) was fabricated for dynamic characterization in the laboratory. The MR-filled cavity in the plate was subjected to a uniform magnetic flux using two permanent magnets located at top and bottom of the structure. The dynamic response characteristics of the sandwich plate were experimentally obtained under harmonic force excitations. A finite element model of the partially-treated MR sandwich plate was developed using classical plate theory considering the effect of slippage between the top and bottom layers. The validity of the finite element model was demonstrated by comparing the theoretical results with those of the experiment. An optimization problem was subsequently formulated and solved using genetic algorithm (GA) to identify optimal locations for the MR fluid treatments for realizing maximum variations in stiffness and damping properties of the structure corresponding to the lower three modes of flexural vibration, individually and simultaneously, in response to the applied magnetic field. The effect of shear deformation on the vibration properties of the partially treated sandwich plate was particularly highlighted. The results suggest that the MR fluid treatments can significantly alter the stiffness and damping properties of the sandwich structure under noticeable shear strain, while a partial treatment could yield the changes in stiffness and damping comparable to those of a fully-treated plate