最新刊期
卷 52 ， 期 5 ， 2018
- 摘要：With due consideration of the tensile-to-compressible strength ratio and intermediate principal stress coefficient, a unified algorithm of elastic and plastic ultimate outer pressures for the casing with close end, open end or plane strain under the outer pressure is obtained following Yu's unified strength theory. Numerical simulation reveals that the elastic ultimate outer pressure increases with the decreasing tensile-to-compressible strength ratio and the increasing intermediate principal stress coefficient. The elastic ultimate outer pressure of the open end casing reaches the maximum, that of the close end casing reaches the minimum, and that of the plane strain casing is between the extremums. The plastic zone radius increases due to the increase of the outer pressure. When the outer pressure increases, the casing diverts from elastic state to elastoplastic state, and the plastic zone radius expands gradually from the inner radius to the outer radius. The plastic ultimate outer pressure increases with the decrease in the tensile-to-compressible strength ratio. The plastic ultimate outer pressure differences among close end, open end and plane strain casings increase with the increasing outer-to-inner radius ratio for the same unified strength theory parameters, and the plastic ultimate outer pressure of casing is greater than the elastic one. The relative error between the computational value of plastic ultimate outer pressure and the measured one lies within the range from -4% to -9%, the relative error between ISO template datum and the measured value lies between -12% and -25%, and the relative error between the commendatory datum from American Petroleum Institute and the measured value lies between -17% and -30%. These comparisons show that the present plastic ultimate outer pressure equation for casing is closer to the experimentally measured value than those in other references.关键词：Yu's unified strength theory;casing;elastic limit;plastic limit;pressure571|5|0更新时间：2025-07-09
- 摘要：This paper presents a method of adaptive grayscale weighted center extraction of light stripe based on skeleton tracking in order to improve the linear structured light three-dimensional surface measurement accuracy. First, a set of fairing and unidirectional skeletons is calculated by mathematical morphological method from the acquired images. Taking the skeleton as a search path, a useful pixel region is set along the normal direction of the skeleton. The grayscale threshold is divided according to the degree of importance of pixel grayscale on the light stripe centerline extraction in the normal section of the skeleton. The value of pixel gray which is more important to centerline extraction is weighted square. Then, the sub-pixel center of the light stripe is calculated according to the gray weighted centroid method. Finally, simulations and experiments are carried out. The simulation results show that the average deviation from the centerline of the light tripe to the fitted curve is less than 0.3 pixels, the standard deviation is less than 0.03 pixels, and the calculation time is 87.6 ms. The experimental results show that the maximum deviation, average deviation and standard deviation extracted by this method are all smaller compared with other methods. The proposed method has some advantages, including high accuracy, stable extraction result and good robustness, whereby a sub-pixel light stripe centerline with fine fairness can be obtained and hence the online measurement requirements could be satisfied.关键词：linear structured light;light stripe center;skeleton tracing;adaptive grayscale weighting;subpixel643|5|6更新时间：2025-07-09
- 摘要：A subwavelength labyrinth acoustic metasurface is proposed to effectively control the physical properties of labyrinth metasurface, and the relationship between each parameter and the acoustic metasurface is discussed in detail. The regulation mechanism of the reflected phase is analyzed emphatically, and the arbitrarily adjustment of the reflected phase is realized. To reveal the physical mechanism of the labyrinth metasurface and the relationship between each parameter and the acoustic metasurface, the influences of each tunable parameter on the sound absorption coefficient and reflected phase of the acoustic metasurface are investigated one by one. The results show that the hole diameter in the cover plate, the side length, and the groove width of labyrinth influence the sound absorption coefficient and reflected phase, whereas the rib width of labyrinth and the plate thickness impose slight influences. Additionally, with the decrease in hole diameter, the peak absorption amplitude remains unchanged, the peak frequency has a blue shift, the reflected phase is effectively regulated by hole diameter, and the reflected phase curve shows a blue shift but the profile and trend remain unchanged. With the decrease in side length, the peak absorption coefficient increases, the peak frequency has a red shift, the reflected phase is effectively controlled by side length, the reflected phase curve shows a red shift, the phase amplitude remains unchanged, and the phase span increases. Moreover, with the decrease in groove width, the peak absorption amplitude increases, the peak frequency has a blue shift, the reflected phase is effectively manipulated by groove width, and the reflected phase curve shows a blue shift but its profile and trend remain unchanged and phase span decreases. A labyrinth structure with ten metasurface cells is designed. These ten cells have identical parameters except for hole diameter. The acoustic metasurface achieves a reflected phase regulation ranging from 0 to 2π. The compact structure is easy to operate, and it can be further expanded into an ultra-thin two-dimensional array plane constructed by metasurface cells to achieve acoustic stealth.关键词：acoustic metasurface;sound absorption coefficient;reflected phase;all-phase regulation;labyrinth449|6|3更新时间：2025-07-09
- 摘要：To statistically consider the dependent failure of meshing tooth-pairs under input torque load, the time varying meshing feature is elaborated, and a reliability analysis method with time varying meshing feature and dependent failure is proposed based on the Monte Carlo simulation. The simulation program is coded taking the static strength failure modes of tooth-root and tooth-surface as the objectives, and the common cause failure with multiple failure modes and time-varying meshing feature are considered in the reliability analysis. The differences between the proposed method and traditional reliability methods are compared. It is found that with the increasing torque action times, the reliability is over-estimated or under-estimated in the traditional methods for lack of considering the dependent failure of tooth-pairs, the time varying feature and the strength uncertainty of each tooth, thus the proposed estimation is more reasonable.关键词：gear reliability;series system;failure dependence;multiple failure mode430|5|0更新时间：2025-07-09
- 摘要：Experimental study and one-dimensional(1D)analysis are conducted to investigate the heat transfer characteristics of moisture removal for hollow stationary blade by steam heating, which involves the condensation heat transfer on heating steam side, the blade wall heat conduction and the boiling heat transfer on main steam side. The influences of the Mach number of main steam and the heating temperature difference are studied, and the comprehensive heat transfer coefficient of the moisture removal by steam heating is fitted according to the experimental data. It indicates that the deviation of comprehensive heat transfer coefficient between the experimental data and the prediction results based on 1D analysis is less than 10%, which could be applied to the engineering design. The increase in the main steam Mach number is favorable for evaporation of the water film on the outer blade surface and hence increases the boiling heat transfer coefficient. When the Mach number is 0.28 or 0.31, the thermal resistance in the main steam boiling process reaches its maximum. When the Mach number is 0.42, the thermal resistance of the solid wall heat conduction becomes the biggest. The comprehensive heat transfer coefficient is mainly affected by the main steam Mach number rather than the heating temperature difference, and it doubles when the Mach number increases from 0.28 to 0.42.关键词：hollow blade;moisture removal by steam heating;heat transfer characteristics;one-dimensional analysis;experimental study458|6|0更新时间：2025-07-09
- 摘要：To develop the microchannel heat sinks with high heat transfer coefficient and low pressure drop, a multi-objective optimization on the geometrical parameters of a single-layer nanofluid-cooled microchannel heat sink with rectangular cross section was performed. The channel aspect ratio α and channel width ratio β were selected as design variables. The optimization objective is to minimize the thermal resistance and pumping power of the heat sink. The K-means clustering analysis was applied for the Pareto optimal solutions, and it was found that there is a tradeoff between the highest and lowest points of the five clusters which can make both pumping power and thermal resistance within the optimal range. The optimal geometrical parameters can be selected based on the requirements of pumping power or thermal resistance in the actual design process. The thermal resistance and pumping power are more sensitive to the width ratio β than to the aspect ratio α. The width ratio β has more significant effect on thermal resistance and pumping power especially when β is greater than 1.15. Compared with the thermal resistance, the pumping power is more sensitive to the design variables. In the design space of variables α and β, the pumping power varies by about 360%, while the thermal resistance only varies by about 135%. The thermal resistance of nanofluid is significantly lower than that of deionized water. The difference of thermal resistance between deionized water and nanofluid increases slowly with the increase of pumping power.关键词：microchannel heat sink;nanofluid;multi-objective optimization;geometrical parameters640|6|4更新时间：2025-07-09
- 摘要：As a commonly used rotary fluid machinery for high-viscosity sludge conveying, the disc-seal single screw pump has a core component of meshing pairs, which is composed of screw rotor and seal disc. So the meshing characteristics of the meshing pairs may significantly affect the performance of the pump body. In order to study the meshing characteristics of disc-seal single screw pump, the structural features and working principle of disc-seal single screw pump are analyzed. And the profile equations of the screw rotor-seal disc meshing pairs are established according to the spatial meshing theory and coordinate transform principle. Using the above profile equations, the meshing characteristics analysis model of an arbitrary sealing disk rotary angle is obtained, and the influencing mechanism of meshing parameters on the meshing characteristics is investigated. The results indicate that the sealing disc shows serious local wear and its lower half will be worn first, and that the meshing angle range of the sealing disc is different at different cross sections. The meshing angle range is the smallest when the central angle is close to π. The effects of the center distance and the sealing disc radius on the meshing angle variation are obvious, but the effects of the edge chamfer radius and eccentricity are small. This research can provide a theoretical basis for the optimal design of meshing pair profiles.关键词：disc-seal single screw pump;meshing pair;profile equation;meshing characteristics353|5|4更新时间：2025-07-09
- 摘要：To put forward a more practical calculation method of wear in spur gears, based on the influence of alternative gear meshing and profile deviation on teeth load, the formula of load distribution among gear teeth is deduced. And then the distributed pressure and velocity of meshing point are calculated on the basis of the Winkler's elastic model and principle of gear meshing. The wear model of spur gear is obtained based on the Archard's wear model. Numerical example shows that the wear of each meshing point on tooth profile accumulates as wearing cycles increase, the wear at the conversion position from single to double teeth-meshing area fluctuates slightly and slowly, the wear changes sharply near the root of the gear, the gear's dynamic load and wear are coupled to grow, and the maximum wear decreases greatly after considering load distribution. This study shows that the load distribution among gear teeth should be considered for wear calculation.关键词：gear;wear;load distribution;Archard's wear model;Winkler elastic model511|5|5更新时间：2025-07-09
- 摘要：The traditional recommendation algorithm based on matrix factorization is facing the problem that in cold start of items, the existing recommendation algorithm does not make full use of the interactive information about item attributes and user's rating behavior, therefore a singular value decomposition recommendation algorithm is proposed(UC-SVD)considering the item attributes and user's rating for items. It adds the item attribute information into the decomposition matrix, and through a comprehensive analysis on the rating data set and attribute data set to get the user preference matrix and item attribute characteristic factor, it adds the user preference characteristic factor to the matrix decomposition. Experimental results on the datasets of Movielens and HetRec2011 show that in comparison with the classic matrix factorization collaborative filtering algorithm, the proposed algorithm can not only solve the problem in cold start of items to some extent, but also under the same condition reduce the root mean square error and the mean absolute error by 3% and 4%, respectively. Especially on the more sparse HetRec2011 dataset, the impact of item attributes on user's rating behavior is more obvious, and this improved algorithm shows greater superiority in recommendation accuracy.关键词：cold start;singular value decomposition;matrix factorization;item attribute414|5|2更新时间：2025-07-09
- 摘要：Influences of different cooling models on blade cooling were investigated, including swirl cooling, impingement cooling and composite cooling, in order to seek for more superior cooling models. The thermal performance of these cooling models was numerically compared under the conditions of same inlet chamber, same number and location of jet nozzles, same swirl chamber and aerodynamic parameters. Moreover, for the new type of composite cooling model, the effects of Reynolds number on the heat transfer performance, the cooling air allocation and the pressure drop were studied. Results indicate that this composite cooling has the highest thermal performance coefficient, i.e., 0.2% and 12.5% higher than that of swirling cooling and impingement cooling, respectively. Its heat transfer performance is slightly lower than swirl cooling and its pressure drop is the lowest among the three cooling models. As the Reynolds number increases, the Nusselt number will significantly rise. At the swirl chamber tip, the heat transfer performance is enhanced because the upstream impingement cooling air impacts the mainstream and decreases the velocity of mainstream. In addition, the upstream clockwise vortex develops along the downstream direction and enhances the heat transfer performance at the swirling chamber tip. The vortices produced by swirl cooling have dramatic effects on the downstream flow structure and have strong resistance against upstream flow. The interaction between swirl cooling and impingement cooling can produce a large-scale vortex pair and single vortex. The cooling air allocation remains stable under different Reynolds numbers. The proportion of cooling air flowing through the impingement jet nozzle is the lowest among all jet nozzles.关键词：swirl cooling;impingement cooling;thermal performance coefficient;flow structure377|5|3更新时间：2025-07-09
- 摘要：Numerical methods are adopted to investigate the heat transfer and film cooling characteristics at three squealer tips with double cavities in a gas turbine first stage rotor blade. At the squealer tips, the ribs are located at 25%, 50% and 75% of axial chord, respectively, and perpendicular to the chord direction, so they are denoted rib25, rib50 and rib75, respectively. The total-to-total isentropic efficiency in the turbine stage, the heat transfer coefficient and the film cooling effectiveness at the blade tip were calculated and also compared with the conventional squealer tip. The results show that, without film cooling, there exists high heat transfer area on the cavity floor near the leading edge for both conventional squealer tip and double-cavity squealer tip. Compared with the conventional squealer tip, the double-cavity squealer tip can improve the total-to-total isentropic efficiency of the turbine stage. Among four squealer tips(conventional squealer tip, rib25, rib50 and rib75), the aerodynamic performance in rib50 turbine stage is the best, the total-to-total isentropic efficiency can be improved by 0.43%. However, the area-averaged heat transfer coefficient at the rotor blade tip is increased by 13.7% compared with the conventional squealer tip. When the film cooling holes are arranged at the rotor tip camber line, the film cooling effect on the tip cavities is significantly improved because more coolant is accumulated in the cavities, which can be attributed to the blade rotation and the limitation of the rib to coolant. Compared with the conventional squealer tip, the three kinds of double-cavity squealer tips perform superior film cooling effect at the tips. Among the four squealer tips, rib50 performs the best film cooling effect at the rotor tip and also has the highest aerodynamic performance in the turbine stage. With film cooling, the total-to-total isentropic efficiency in the turbine stage equipped with rib50 tip can be increased by 0.36%, the area-averaged heat transfer coefficient at the tip is reduced by 14.4% and the area-averaged film cooling effectiveness can be improved by 31.8% in contrast to the conventional squealer tip.关键词：gas turbine;turbine stage;squealer tip;heat transfer;film cooling499|6|7更新时间：2025-07-09
- 摘要：To explore the performance of the wall embedded with capillary-tubes, a scale model of heat distribution of the capillary wall is established, which delivers the ratio of heat exchange from capillary layer to both indoor and outdoor sides according to the simplified transient RC(resistance and capacity)model. The experimental data including the indoor and outdoor air temperatures, the temperature of the inner surface of the capillary wall, the temperature of the capillary layer and the heat fluxes from capillary layer to indoor and outdoor sides are collected to analyze the characteristics of the capillary wall and the heat exchange crossing indoor and outdoor sides subject to the winter conditions. The reasonability of the present scale model is verified, and the one-dimensional heat exchange process of the capillary wall is then discussed. Experimental results show that the capillary radiant air-conditioning system is endowed with good stability, and the fluctuation of the indoor temperature is relatively small. With the increase in the running time of the system, the calculated values of the model are more consistent with the measured results. The proposed model is capable to handily evaluate the performance of the capillary wall in actual applications and to provide a theoretical basis for the further research on indoor load calculation of the radiant air conditioning system.关键词：radiant air conditioning system;capillary-tube embedded wall;scale model of heat exchange distribution;heat flux465|5|1更新时间：2025-07-09
- 摘要：Thermal fatigue study on an aero-engine combustor is carried out for the cracking failure of combustor during its service period. A three-dimensional model of the aero-engine combustor is obtained by three-coordinate scanning reverse modeling, an 1/10 sector of the combustor satisfying the periodic boundary condition is chosen as the computational domain. Considering the interaction between the fluid and solid, a fluid-structure interaction model for the turbulent combustion of the aero-engine combustor is established to simulate the flow field at typical conditions, hence the temperature distribution of the combustor and thermal barrier coating is obtained. The accuracy of the fluid-structure interaction simulation is verified through the comparison between the surface temperature distribution and the macroscopic appearance of the thermal barrier coating of a combustor in service. Based on the results of simulation, nonlinear static analysis is carried out to obtain the plastic strain distribution and hence the maximum strain position corresponding to the actual cracking position of the combustor. Based on Manson-Coffin formula and linear damage rule, the fatigue life of dangerous positions under typical working cycle is calculated. The results show that the temperature of combustor substrate increases gradually with the increasing of engine load, and that the temperature distribution in the downstream region of mixing holes is inhomogeneous under the impact of cold-hot air flows, resulting in large plastic strain and low-cycle fatigue damage. The fatigue life of the dangerous positions under typical working cycle is calculated to be 7 126 cycles.关键词：combustor;fluid-structure interaction;plastic strain;thermal fatigue511|6|5更新时间：2025-07-09
- 摘要：This paper proposes an automatic paroxysmal atrial fibrillation(PAF)detection method based on grey information measurement. Firstly, the discrete wavelet transform(DWT)is applied to decompose an electrocardiogram(ECG)signal into sub-band signals. Then, the difference operation is used for wavelet coefficients to obtain the corresponding one-order central difference plot and gray histogram. Next, the variance, coefficient of variation, and Shannon entropy are extracted from the gray histogram to be the fusion features of atrial fibrillation ECG. Finally, PAF detection is completed automatically by integrating the extracted features with extreme learning machine(ELM). Experimental results on MIT-BIH database show that the average sensitivity, specificity and accuracy of the proposed method reach 93.7%, 94.6% and 94.0%, respectively.关键词：paroxysmal atrial fibrillation;electrocardiogram;discrete wavelet transform;gray histogram;extreme learning machine440|5|0更新时间：2025-07-09
- 摘要：To evaluate the forces on the ankle joint in different situations so as to meet the development requirements of lower limb protection appliances and footwear, a simple lower limb dynamic model is established. The lower limb is simulated by the two-dimensional rigid rod model, in which the ankle joint and the hip joint are simplified as hinge connections, and the muscle forces are expressed by unknown forces at both ends of the calf. Using the measured plantar pressure, the joint torque is determined based on the equilibrium equation of torques. For the dynamic model, the corresponding kinetic equation is derived. Accurate ankle joint force data are obtained through high-speed photography and force platform, and the dynamic data is processed by the action analysis system(APAS). The kinetic model can be used to assess the forces on the ankle joint, and evaluate the force difference among different gaits(such as walking, running and stepping)and between the conditions with and without load. Moreover, the model can be applied to force analysis of ankle joint with wearing different footwear(e.g. running shoes and hiking shoes)or bare feet, and is expected to be applicable to the evaluation of ankle joint force in development of clinical rehabilitation apparatus, lower limb protection appliances, and footwear.关键词：biomechanics;dynamic model;lower limb;ankle joint;force on joint396|5|1更新时间：2025-07-09
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