最新刊期
卷 52 ， 期 1 ， 2018
- 摘要：In conventional failure modes and effects analysis(FMEA), the relations between component failures and system faults are analyzed and determined by domain experts, which is tedious, error-prone, and difficult to obtain the probabilities of the faults. In this paper, formal methods are introduced to FMEA for electromechanical systems and an approach to probabilistic FMEA(PFMEA)for electromechanical systems based on probabilistic model checking is proposed. Based on the state transitions in electromechanical systems, probabilistic model and its formal representation for the behavior process of the systems are studied and the formal probabilistic models for PFMEA are established. Continuous stochastic logic(CSL)formulas are employed to make formal specification of the potential faults in electromechanical systems, and the formal probabilistic specifications of potential fault are given. Formal verification is conducted for the system probabilistic models and potential faults, thereby the relations between the component failures and the potential system faults are identified. Moreover, the probabilities of the faults caused by component failures are calculated, so the efficiency and accuracy of the PFMEA are improved. By means of the approach presented in the paper, the causal relations between component failures and system faults are determined quickly and accurately, and the probabilities of the system faults are computed automatically. This approach is applied to the feed system of a CNC machine tool, and the system faults caused by limit switches and the probabilities of the faults are identified successfully, which demonstrates the feasibility of this approach.关键词：electromechanical system;failure mode and effects analysis;probabilistic failure mode and effects analysis;probabilistic model checking;reliability evaluation563|5|2更新时间：2025-07-09
- 摘要：To achieve high-efficiency cooling performance and good uniformity of impinging jet, a new type of nozzle structure is proposed. The new nozzle has four circumferential spiral channels symmetrically distributed inside a normal smooth nozzle, similar to an internal threads. The influences of this nozzle on heat transfer characteristics of impinged surface under different helix angles(0°, 15°, 30°, 45°), Reynolds numbers(6 000-30 000)and impact distances(1 to 8 times the equivalent diameter)were studied experimentally. And the heat transfer rule of the impinged surface was revealed. The experimental results indicate that a big helix angle can enhance slightly the heat transfer coefficient on the impinged surface. Compared with the conventional impinging jet from the smooth circular hole and the hole with four straight channels, the swirling impinging jets from the designed nozzles are effective to enhance the overall heat transfer coefficient on the impinged surface under the same conditions. At the impact distances of 2 times and 4 times the equivalent diameter, Nusselt numbers of the 45-degree thread hole are 7.4% and 11.4% higher than that of conventional impinging jet at the stagnation area, respectively. The heat transfer coefficient on the impinged surface is non-linearly increased with the increase of Reynolds number. The maximal value of Nusselt number under a relative large Reynolds number occurs at the location of 0.7 times the equivalent diameter outside the stagnation point. With the increase of the impact distance, the effect of the swirling flow on the target surface heat transfer is weakened or even disappeared.关键词：swirling impinging jets;impingement cooling;uniformity of heat transfer;thread nozzle649|5|3更新时间：2025-07-09
- 摘要：To study the heat transfer performance at the shell side of the titanium alloy spiral twisted tube heat exchanger with high viscosity heat transfer oil, experimental research was conducted on the laminar flow(Re<2 000)and transition flow(2 000关键词：twisted tube heat exchanger;laminar flow;transition flow;experiment434|6|5更新时间：2025-07-09
- 摘要：To explore the heat and mass transfer characteristics during the phase change in metal foams, a test rig with solid/liquid phase change heat transfer visualization device was designed and established. The effects of pore structure parameters on solidification process were measured. Results show that the involvement of open-cells in metal foam can significantly enhance the solidification process. The deterioration of phase change heat transfer can be compensated by the enhanced heat conduction with metal foam. The full solidification time can be reduced by 48.86%(pore density of 1 181 m-1 and porosity of 0.90)and 60.97%(pore density of 1 181 m-1 and porosity of 0.97), respectively, in comparison with the case of pure water. Porosity plays a vital role in solidification process but the influence of pore density upon solidification can be neglected. The full solidification time can be further reduced by 20% when the porosity decreases from 0.97 to 0.90. The visualization demonstrated an inclined solidification front, which indicated the contribution of local natural convection in the fluid phase. Local thermal equilibrium between metallic ligaments and the saturating PCM(distilled water)was experimentally observed.关键词：phase change heat transfer;metal foam;solidification;experimental study460|5|4更新时间：2025-07-09
- 摘要：To research the effect of different parameters on the water spraying rate for an energy storage system of isothermal compressed air, a novel method was proposed to study the quasi-isothermal compression using a compression process with the polytropic exponent close to 1, where the water vapor, liquid water and air in the final state were assumed as an ideal mixture. The water spraying rate under different state parameters was researched according to the saturated water vapor pressure formula, the Dalton partial pressure theory and the thermodynamic parameters of the components. The results show that the heat transfer proportion increases with the pressure ratio and the water spraying rate. When the pressure ratio is 10 and the rotation speed is 100 r/min, the water spraying rate increases from 5.73 kg/s to 8.68 kg/s, and the proportion of heat transfer is increased by 5%. The pressure ratio, heat transfer efficiency and final temperature all have effects on the mass ratio of air to water. Moreover, results also show that when other conditions are constant, the rotation speed has almost no effect on the ratio of air to water. When the pressure ratio increases to 10, the heat transfer efficiency is 95% and the final temperature is 50 ℃, the mass ratio of air to water maintains at 0.86 when the rotation speed is 60, 100, 150 r/min, respectively. In all, lower pressure is unfavorable to the thermal storage of water.关键词：energy storage of compressed air;isothermal compression;heat storage;saturated water vapor pressure497|5|4更新时间：2025-07-09
- 摘要：The influence of mushroom-shaped tooth wear on leakage performance and fluid excited rotordynamic characteristics of labyrinth seal was numerically investigated by means of the unsteady Reynolds-averaged Navier-Stokes(URANS)equation based on the multi-frequency elliptical orbit rotor whirling model and dynamic mesh technique. The leakage performance, flow fields and rotordynamic coefficients of labyrinth seal with unworn clearance of 0.3 mm and after-damage clearances of 0.4, 0.5 and 0.6 mm were calculated. The obtained results indicate that a mushroom-shaped tooth wear causes an increase of vena contracta area in sealing clearance, thus leakage flow rate is increased with the worn clearance and a linear increase is expected when after-damage clearance is over 0.4 mm. In addition, a mushroom-shaped tooth wear results in an obvious increase in direct stiffness and a drop of cross-coupling stiffness and direct damping, but direct damping will be no longer affected by worn clearance when the worn clearance is above 0.5 mm. Also, the stability is reduced as a result of a drop in effective damping with the increase of worn clearance, but is still within a stable range.511|5|12更新时间：2025-07-09
- 摘要：To study the influence of inclined angle on the film cooling characteristics under high mainstream turbulence intensity, cylindrical holes with inclined angles 30° and 60° were studied using the transient liquid crystal measurement technique under high mainstream turbulence intensity(11.82%), and the result was compared with the result under low mainstream turbulence intensity. The results indicate that the film cooling effectiveness decreases with the increase of inclined angle. With the increase of mainstream turbulence intensity, the film cooling effectiveness increases in upstream region and decreases in downstream region, and in addition, the film cooling effectiveness distributes more uniform in the lateral direction. With the increase of blowing ratio, the heat transfer ratio is enhanced obviously for all cylindrical holes. At small blowing ratio, the heat transfer coefficient ratio decreases gradually along the flowing direction. And the heat transfer coefficient ratio has an undulation feature at large blowing ratios. The increase of the inclined angle leads to an enhancement of heat transfer intensity at the same blowing ratio. But the increase of the mainstream turbulence intensity may result in lower heat transfer intensity at the same blowing ratio. With the increase of blowing ratio, the mainstream turbulence intensity-induced differences of the film cooling parameters between two kinds of inclined-angle holes grow under two mainstream turbulence intensities in downstream region, while the influence of mainstream turbulence intensity is more complex in upstream region.关键词：film cooling;mainstream turbulence intensity;inclined angle;cooling effectiveness;heat transfer coefficient ratio527|5|1更新时间：2025-07-09
- 摘要：To optimize the start-up process of steam turbine, a semi-analytical recursive calculation model of rotor temperature field is developed. Considering the change of heat transfer coefficient with time, the start-up process is divided into multiple heating processes with constant heat transfer coefficient in the algorithm. The value of heat transfer coefficient of each heating process is taken as the initial value of heat transfer coefficient at the beginning of the process. The temperature field at the end of each process is fitted as 4th-order polynomial, and the 4th-order polynomial will be the initial temperature field of the next temperature rising process. Then, the transient temperature field of the next temperature rising process is calculated through the Laplace transform method. To verify the accuracy and efficiency of the semi-analytical recursive model, finite element method and recursive model are used to calculate the temperature field and stress field of the rotor during cold start of a 660 MW turbine unit. The calculation results show that the trend of the thermal stress calculated by two models is the same. The thermal stress calculated by two models differs by 0.11%, and the computation time of the recursive model is about 2.8% of the finite element model. An objective function of rotor start-up optimization is constructed by the semi-analytical recursive model, and the genetic algorithm is used to optimize the rotor cold start-up of a 660 MW unit. After optimization, the maximum thermal stress of the rotor is reduced by 19.4% and the starting time is reduced by 4.9%.关键词：rotor;thermal stress;start-up optimization;genetic algorithm540|5|0更新时间：2025-07-09
- 摘要：To study the pyrolysis/gasification characteristics of biomass under high temperature conditions, in particular the formation mechanism of soot during the process, rapid pyrolysis of wheat straw and poplars sawdust was conducted in a lab-scale drop-tube furnace(DTF)at 900-1 300 ℃. Three-phase products including gas, liquid and solid were collected and characterized to study the influences of temperature and biomass origin. Special attention was paid to the soot formation during the pyrolysis. The results showed that the yields of soot from wheat straw and poplars sawdust were 0.28%-2.40% and 0.34%-6.30%(dry biomass)respectively, with an increasing trend with the temperature, while the yield of char was 2.8%-7.3% and 0.29%-2.9% respectively, with a decreasing trend. More soot was formed due to the high level of lignin and cellulose components in sawdust, and more char was produced due to the high ash and extracts contents in wheat straw. Raising temperature favored the production of uncondensed gas: for wheat straw the production rate of uncondensed gas ranged from 47%-69% and for sawdust the data were between 59%-77%. It was found that temperature has a significant effect on tar destruction. The tar dominated by aromatic compounds is decomposed completely at 1 200 ℃. When the pyrolysis temperature is relatively low(900-1 100 ℃), the soot is formed through the combined mechanism of light hydrocarbon decomposition and heavy tar polycondensation. However when temperature is higher than 1 100 ℃, most of the soot is formed by the decomposition of light hydrocarbon.关键词：biomass;pyrolysis;three-phase products;soot;formation mechanism541|5|5更新时间：2025-07-09
- 摘要：To improve the heat dissipation performance of vehicle radiator, based on the single fan configuration of a traditional passenger car, this paper designs five different matrix fan configurations, and numerically analyzes of the effect of different configurations on the heat dissipation performance of radiator. With the differential control strategies introduced, a further optimization of the thermal management on the vehicle front end is conducted. The final results indicate that different matrix fan configurations have different effects on the heat dissipation performance of radiator, the matrix fan(N=6)is the optimal configuration due to the largest heat dissipation achieved. As the fans run in low-temperature region at higher speed, this matrix fan can decrease the hot air recirculation at idle and lower the average temperature in underhood, thus effectively improving the thermal environment of underhood. In the idle condition, when the rotation speed ratio α=3, the heat dissipation reaches 6.61 kW, which is improved by 1.71% compared with the uniform speed condition; and similarly, in the low-speed condition, when the rotation speed ratio α=1.8, the heat dissipation reaches 10.73 kW, which is improved by 1.2%. Moreover, the fans running in low-temperature region at higher speed also can suppress the flow separation in underhood and beneath the engine board, and decrease the flow resistance in underhood as the vehicle runs at a low speed.关键词：matrix fan;radiator;heat dissipation performance;differential control533|5|1更新时间：2025-07-09
- 摘要：To improve the efficiency of design and optimization of permanent magnet motors and avoid lengthy finite element modeling and computing time, an analytical model of surface-mounted permanent magnet motor with auxiliary slots is built. The Laplace equations or Poisson equations are established in each subdomain with the vector magnetic bit as a function in the two-dimensional polar coordinates, and the vector magnetic bit expression of each subdomain is solved according to the separation variable method. The relevant harmonic coefficients are obtained using the boundary conditions of each subdomain. The air gap flux density, cogging torque, flux linkage and back-electromotive force(EMF)of the model are deduced under no-load condition, then the air gap flux density, cogging torque, flux linkage and EMF of a 32-pole-48-slot external rotor in-wheel permanent magnet motor used for electric vehicles are calculated under no-load condition. The accuracy and validity of the analytical model are verified by finite element method and cogging torque experiment. In addition, the cogging torque of the in-wheel motor is optimized on the basis of this analytical model, and is consequently reduced by 37.2%.关键词：permanent magnet in-wheel motor;analytical model;auxiliary slots;cogging torque weakening532|5|3更新时间：2025-07-09
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Journal Bearing Properties and Dynamic Responses under Transient Impact Load and Elastic Deformation
摘要：In consideration of transient impact load and elastic deformation of bearing pad, the lubrication properties and dynamic response of journal bearing supporting the propulsion shaft of ships under the action of wind and waves are simulated. The pad of journal bearing is elastic metal-plastic pad(EMP), made of polytetrafluoroethylene(PTFE). The variations of the minimum oil film thickness and maximum oil film pressure, as well as the journal orbits in time history are investigated. Solving the Reynolds equation with finite element method, the oil-film force is converted to nodal forces of pad to calculate the elastic deformation; solving the kinetic equation of journal with Euler method, the dynamic journal orbits are obtained. Comparison of the properties between rigid bearing and EMP bearing indicates that the elastic deformation of EMP bearing cannot be neglected, and the deformation could enhance the loading capacity. Through comparative analysis on the properties and dynamic journal orbits of EMP journal bearing under the transient impact loads from four directions, it is found that adjusting the direction of the bearing static load and decreasing the angle between the directions of transient impact load and the eccentric of journal can increase the minimum oil film thickness and reduce the maximum oil film pressure, hence the displacement response amplitudes of journal orbits are decreased. Consequently, the lubricating condition, the deformation of the journal pad and the operating stability are improved.关键词：journal bearing;transient impact load;elastic deformation;dynamic responses516|5|8更新时间：2025-07-09 -
A Mixed Elasto-Hydrodynamic Lubrication Model for Studying Tribological Properties of Rough Surfaces
摘要：To investigate the influence of asperities on tribological properties in mixed elasto-hydrodynamic lubrication(EHL), a numerical model which can present the local contact state of the rough surface is developed. This model can produce a virtual rough surface in Gaussion distribution, and with the use of average flow Reynolds equation and the K-E elasto-plastic model, the hydrodynamic pressure and the contact pressure can be predicted, respectively. Fast Fourier transform(FFT)method is used to compute the elastic deformation of substrate. The influences of virtual asperities, nominal load, roughness and asperity curvature radius on the tribological properties of EHL are also discussed through plotting corresponding Stribeck curves and film thickness shapes. The results show that the contact of asperities induces the deformation of substrate, which subsequently increases the film thickness and reduces the hydrodynamic pressure. Thus, the load rate of oil film and the friction coefficient are increased accordingly. With the increase of nominal bearing load, the friction coefficient is decreased at low speed, implying that the transition point from boundary lubrication regime to mixed lubrication regime occurs at lower speeds. Smaller roughness implies the movement of the Stribeck curves towards left. The increase of asperity curvature radius accelerates the transformation from boundary lubrication to mixed lubrication. However, the transition from mixed lubrication to hydrodynamic lubrication seems not to be obviously influenced by the asperity curvature radius.关键词：tribology;mixed elasto-hydrodynamic lubrication;rough surface;modeling545|6|11更新时间：2025-07-09 - 摘要：A novel prediction method of riveting deformation of aircraft panels is proposed to solve the problems of low prediction accuracy and long calculation time in existing prediction methods. Through the analysis on the panel assembly process, the major causes of the panel deformation are identified. Combining with the DOF expanding method, the additional stress arising in the normal connection method is avoided. Then the method is used to establish a local-global mapping model. Based on this model, the complex stress-strain state around the rivet hole is transferred to the thin shell model of panel in a relatively simple way. Finally, the prediction of riveting deformation of large panel is achieved. The results show that, compared with dynamic explicit finite element model, the average calculation time of a single rivet is decreased from 55 minutes to 15 minutes, and the deformation distribution and magnitude of ten-rivet structure are basically identical. Comparing the predicted results with experimental results of a aircraft panel, the deviation of maximum deformation values is 0.062 mm, the deviation of average deformation values is 0.01 mm, and the correlation coefficient between them is 0.898. The proposed method improves the computational efficiency and is proved effective. This study may provide a theoretical basis for the control of riveting deformation.关键词：aircraft panel;riveting deformation;local-global mapping model;numerical simulation;riveting experiment469|6|3更新时间：2025-07-09
- 摘要：In view of the nonlinearity and difficulty in control of absorption chiller, a set point optimization method based on inverse neural network model is proposed. Firstly, taking an 11.5 kW single-effect lithium bromide absorption chiller as the research object, an artificial neural network method is used to establish a model of the unit. Through the analysis of the chiller, a network model with a 5-6-2 structure is established. The correlation coefficient of the neural network model is more than 0.99 and the root mean square error is less than 0.2%, so the experimental data are well fitted. Subsequently, the sensitivity analysis of each input parameter of the chiller is conducted to select the hot water supply temperature and the cooling water flow rate as the control input parameters to be estimated. Finally, as the control output of the system, the chilled water output temperature is optimized. The optimal control input parameters of the chilling system are estimated by combination of an improved particle swarm optimization and the inverse neural network algorithm. Through the analysis of experiment and simulation, the calculation time of this method is within 30 s, which is shorter than the stable time of absorption chiller. Moreover, the error between target output and simulation calculation is less than 0.02%. These results show that the proposed scheme is suitable for online control of absorption chiller.关键词：absorption chiller;neural network;particle swarm optimization;online estimation480|6|1更新时间：2025-07-09
- 摘要：To characterize the sound absorbing properties of gradient porous metal fibers at high temperature, a theoretical model is developed by introducing the temperature-dependent parameters of air into the Johnson-Allard model. This model is favorably validated by experiments on porous metal fibers at high temperatures. Further, employing acoustic impedance transfer formulation, another theoretical model for multi-layered gradient metal fibers at high temperature is established. By adopting an optimization strategy, the multi-layered gradient metal fibers are optimized for superior sound absorption. The results reveal that the sound absorbing capacity of the material at high temperature is slightly worse than that in normal temperature. With the increase of porosity or fiber diameter, the sound absorption decreases in low frequency range but increases in medium frequency range. The sound absorption capability of the gradient structure is better than that of homogeneous structure with the same thickness, and the optimal sound absorption can be achieved in given specific conditions. This research is helpful for the application and design of the gradient porous metal fibers in high temperature environments.关键词：porous metal fiber;gradient structure;high temperature;sound absorbing property683|5|5更新时间：2025-07-09
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