Editor in chief：朱立光
International standard number：ISSN 1008-1542
Unified domestic issue：CN 13-1225/TS
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2015, 36(4):337-343. DOI: 10.7535/hbkd.2015yx04001
Abstract:Surface thermal functional structures are widely used in energy conversion and transmission applications, which is an important research focus in the field of machinery and engineering thermal physics. The status and trends of the development of micro/nano-scale surface thermal functional structures are reviewed from the perspective of processing technology in this paper. Analysis indicates that the effective control of the regularity, hydrothermal stability, solid-liquid interface characteristics of micro/nano-structured surfaces is critical for enhancing heat transfer performance and also challenges the processing technology of micro/nano-scale surface thermal functional structures. Based on the research, the dealloying based in-situ processing technology is introduced, and the status and prospect of as-dealloyed nanoporous metal surface in the application of boiling heat transfer are presented.
2015, 36(4):344-350. DOI: 10.7535/hbkd.2015yx04002
Abstract:During cutting, machine tools are influenced by different heat sources, which induces machine thermal deformation, deviation and thermal error. In different machine errors, thermal error accounts for 40%~70% of total machine errors, which is the main influence factor of machining accuracy. In order to reduce machine thermal error and improve machining precision, there are mainly 3 ways at present: 1) Improving machine thermal stiffness by optimal design of machine structure; 2) Separating heat sources from machine tools; 3) Thermal error compensation, which reduces the influence of thermal distortions by predicting and compensating measures. In order to compensate thermal errors, thermal error modeling is the premise and foundation. Therefore, thermal error modeling technology is introduced in this paper firstly, and its recent development both at home and abroad is analyzed. The main obstacles in thermal error modeling field at present are summerized, and the future of the technology are presented.
2015, 36(4):351-358. DOI: 10.7535/hbkd.2015yx04003
Abstract:Aiming at fault diagnosis problems caused by complex machinery parts, serious background noises and the application limitations of traditional blind signal processing algorithm to the mechanical acoustic signal processing, a failure acoustic diagnosis based on reference signal frequency domain semi-blind extraction is proposed. Key technologies are introduced: Based on frequency-domain blind deconvolution algorithm, the artificial fish swarm algorithm which is good for global optimization is used to construct improved multi-scale morphological filters which is applicable to mechanical failure in order to weaken the background noises; combining the structural parameters of parts to build a reference signal, complex components blind separation is carried out on the signals after noise reduction paragraph by paragraph by reference signal unit semi-blind extraction algorithm; then the improved KL-distance of complex independent components is employed as distance measure to resolve the permutation, and finally the mechanical fault characteristic signals are extracted and separated. The actual acoustic diagnosis of rolling bearing fault in sound field environment results proves the effectiveness of this algorithm.
2015, 36(4):359-367. DOI: 10.7535/hbkd.2015yx04004
Abstract:Firstly, the basic principles, the advantages, the disadvantages and the engineering applications of the conventional TPA, OTPA, OPAX and mixed TPA in recent years are comprehensively analyzed. Meanwhile, the potential applications of power flow in the TPA field are especially discussed. Secondly, focused on the OTPA method, an acoustic transfer path system by spherical radiation transfer path simulation system and a vibration transfer path experiment system by a rectangular plate vibrator excitation are designed considering the effects of the distance from reference points. The results show that the relative error between the OTPA values and the theoretical values as well as the experimental values is less than 5% and 8% respectively. At the same time, OTPA is sensitive to noise. When the noise is lower, the nearer reference points can improve the precision of OTPA method. Therefore, it is needed to arrange sensors and design operating conditions reasonably. Finally, the development trend of TPA method is presented.
2015, 36(4):368-375. DOI: 10.7535/hbkd.2015yx04005
Abstract:Using composite filler is a very potential way to braze dissimilar material, especially braze metals with ceramics. The composite filler which is added varieties of high temperature alloy, carbon fiber and ceramic particles has a suitable coefficient of thermal expansion. The application of composite filler can release the residual stress caused by mismatch of thermal expansion coefficient in the brazing joints and improve the overall performance significantly. According to the traditional classification method of composite materials, the composite filler is divided into micron-reinforced composite filler and nano-reinforced composite filler, of which the feature and research status are discussed in this text. According to the influence of different size reinforced phases on microstructure and mechanical property of the brazing joints, nano-reinforced composite filler has more uniform and better structure compared with micron-reinforced composite filler, and higher joint strengh can be obtained by using it. However, the reinforced mechanism is still an open question, and will become the key area of the future research work.
2015, 36(4):376-381. DOI: 10.7535/hbkd.2015yx04007
Abstract:In view of the Leggett-Williams norm-type theorem due to O'Regan and Zima, by using the properties of the cone and Leray-Schauder degree in Banach space, the existence of positive solutions of the second order boundary value problem with integral boundary condition at resonance is studied. An example is given to illustrate the main results.
2015, 36(4):382-389. DOI: 10.7535/hbkd.2015yx04006
Abstract:In this paper, Leray-Schauder nonlinear alternative theorem is used to study the existence of positive solutions for nth-order integral boundary value problems with p-Laplacian operator on infinite interval （φp(x(n-1)))′(t)+a(t)f(t,x(t),x′(t))=0,〓0
2015, 36(4):390-393. DOI: 10.7535/hbkd.2015yx04008
Abstract:Based on the topological sum, for X being a discrete topological space, we prove that the product topology generated by some topological spaces is equal to the topology of pointwise convergence related to X. For every topology on a Cartesian product, we find an equivalent condition under which every projection from the product to each component is continuous. We propose the definition of functional product spaces, which can be considered as a common framework of the product spaces, the topological sums and the functional spaces (the topology of pointwise convergence).
2015, 36(4):394-400. DOI: 10.7535/hbkd.2015yx04009
Abstract:To study the robust H∞ infinity control for generalized networked control systems with long time delay, it is assumed that the sensors are clock-driver, and controllers and actuators are event-driver in two sampling periods and limited energy of the external disturbance. The augmented state is used to establish uncertain system model of discrete time-varying, and by using Lyapunov function and linear matrix inequalities，the sufficient conditions for dynamic output H∞ infinity feedback control are found out. A simulation example shows the effectiveness of the method.
2015, 36(4):401-406. DOI: 10.7535/hbkd.2015yx04010
Abstract:A wind turbine located in Yunnan is taken as an example in this paper. By using the analytical method and the finite element method, the modal analysis of wind turbine tower is carried out, then the structural dynamic behavior is obtained. Based on the comparison of the results from different calculation methods, the rigidity and the resonance of tower induced by wind wheel rotation are studied. The research shows that, the finite element model is simplified, while the results of this method are rich; the transient resonance inevitably appears for two times in the starting process for the flexible wind tower which has the structure of symmetry basically; while in the normal operation stage, the wind wheel would not induce the resonance for flexible tower. The research provides a theoretical basis for the design of wind turbine tower.
2015, 36(4):407-412. DOI: 10.7535/hbkd.2015yx04011
Abstract:Risk of fatigue failure exists in the tube trailer cylinders under the condition of internal pressure variation and inertial load caused through road transport. In order to estimate the safety state of the cylinders under the action of alternating load, the model of certain geometry sizes is built based on the widely used tube trailer cylinders. The fatigue analysis of tube trailer gas cylinders is made aiming at the action of the internal pressure and the inertial load. The fatigue life distribution of cylinders is obtained under the condition of different loads through the numerical simulation by ANSYS Workbench. The analysis results show that under internal pressure, gas cylinders have limited fatigue life, but can satisfy the requirements; when the inertial load exceeds a certain value, natural gas cylinders of tube trailer is under finite life state, which does not meet the requirements of strength, therefore the inertial load should be controlled.
2015, 36(4):413-418. DOI: 10.7535/hbkd.2015yx04012
Abstract:Al2O3 thin films are deposited on the surface of 304 stainless steel by electrodeposition-pyrolysis, and the effects of electrolyte concentration and electro-deposition voltage on the oxidation behavior of Al2O3 thin film at 900 ℃ are investigated. Macroscopic surface morphologies, XRD analysis and oxidation kinetics curves show that the electrodeposition-Al2O3 thin films reduce the partial pressure of oxygen at the initial oxidation stage on the substrate surface, promoting the selective oxidation, thus the oxidation resistance of 304 stainless steel is significantly improved. The high temperature oxidation resistance of Al2O3 film prepared under voltage of 25 V and aluminum nitrate alcohol solution of 0.10 mol/L is the best.
2015, 36(4):419-424. DOI: 10.7535/hbkd.2015yx04013
Abstract:To analyze the status of selenium-enriched areas, main producing area of foxtail millet and selenium-rich foxtail millet products in China, statistical data, literature, network resources, expert interview, field investigation, etc. are used to acquire data. The data is cleared up and analyzed, and selenium-rich foxtail millets suitable for different regions to plant are screened out, then the development direction is pointed out, which provides a reference for improving the industrialization level of selenium-rich foxtail millet in China.
2015, 36(4):425-430. DOI: 10.7535/hbkd.2015yx04014
Abstract:In order to research fracturing mechanism of coal subjected to liquid nitrogen cooling, submersion tests of liquid nitrogen for natural coal samples are carried out. A laser microscope is employed to observe the extension of native crack and propagation of cracks of coal samples after thermal shock. Then the fracture mechanics theory is used to analyze the extension mechanism of the crack during thermal shock. The main conclusions include: 1) Liquid nitrogen cooling causes temperature tensile stress and the stress concentration. When the stress intensity factor is more than the fracture toughness of coal native crack, the native crack will extend. 2) The temperature tensile stress makes the particle clusters with low tensile strength around the native crack fail and break off, and the destruction of the structure of the coal sample causes microcrack initiation. 3) There is a great effect of cooling time on the stress intensity factor. With the increasing of the temperature gradient and the cooling time, the stress intensity factor increases, with more susceptibility for coal to rupture.
2015, 36(4):431-436. DOI: 10.7535/hbkd.2015yx04015
Abstract:Experimental research on non-isothermal combustion characteristics and dynamics parameters of applied pulverized coal under preheating domestically is conducted with a thermo gravimetric balance. The combustion characteristic parameters such as ignition temperature, peak temperature at maximum weight loss rate, burnout temperature, general burn exponent(G), and maximum combustion rate are studied under different preheating temperatures of 423, 473, 523, 573, 623, 673, 723 and 773 K. The activation energy (E) and frequency factor (A) are also calculated. The results show that for pulverized coal in the North Area, during the preheating process, when temperature varies from 423 K to 773 K, ignition temperature decreases by 240 K mostly, peak temperature at maximum weight loss rate decreases by 263 K at most, maximum weight loss rate increases as 1.29 times, and G increases up to 29.8 times. It shows that there is lining fit result between E and ln A, which proves that the reaction could be regarded as first order reaction. The combustion process behaves greatly when preheating temperature is over 673 K for the pulverized coal.
2015, 36(4):437-444. DOI: 10.7535/hbkd.2015yx04016
Abstract:The second tertiary combined model experiment zone has been developed in Block B, Field L. The percolation feature of the second tertiary combined develop model shows great importance to rational and efficient development of the reservoir. In order to clearly illuminate its percolation feature, the typical reservoir numerical model is built by Eclipse, which is a reservoir numerical simulation software. The percolation features of original and added perforation interval under the second tertiary combined model are studied, and the variation features of general water-cut, recovery percentage, wellbore pressure, reservoir pressure and water saturation on condition of higher injection rate under the second tertiary combined model are analyzed. The research indicates that the second tertiary combined enhances the recovery of remaining oil on top of thick reservoir by developing and enhancing original perforation interval under water drive, then improves development results by polymer flooding, and gains higher recovery rate by synthetic action of water driver and polymer flooding.