最新刊期
卷 44 ， 期 3 ， 2010
- 摘要：On the basis of the equation for predicting self-diffusion coefficients of Lennard Jones chain fluid proposed in our previous work, the van der Waals mixing rule to calculate the equilibrium properties is adopted to the calculation of the transport properties in this paper. A new correlation to predict the mutual diffusion coefficient of binary LJC fluid is proposed. The present correlation has no binary adjusted parameter and its physical meaning is more explicit. The calculation results agree with the experimental data of 12 binary LJC systems over the wide ranges of temperature and composition with an average absolute deviation of 6.98%, indicating the higher accuracy and effectiveness of the new equation.关键词：binary liquid system;mutual diffusion coefficient;Lennard-Jones chain fluid;van der Waals mixing rule3684|4|10更新时间：2025-05-01
- 摘要：The heat transfer performance of open-celled aluminum foam heat sinks under axial fan impinging cooling flow is experimentally studied. Three open-celled aluminum foam samples with different pore sizes and identical porosity(ε=0.92)were tested. The overall thermal resistance and temperature difference on the base plate of the heat sink were measured and compared with those of the conventional plain-fin heat sink. The results obtained show that, with only 50% of the total volume and weight of the conventional fin heat sink, the aluminum foam heat sink can achieve a similar cooling performance and more uniform temperature distribution on the heated base plate. The aluminum foam heat sink has further potential for optimization in terms of foam thickness, pore density and porosity, leading to a further enhancement of its overall heat dissipation performance under axial fan impinging cooling for power electronics.关键词：aluminum foam heat sink;electronic cooling;axial flow fan;impingement cooling3272|4|1更新时间：2025-05-01
- 摘要：The flow field of a small gas turbine cascade was numerically simulated with the preconditioning method at low Reynolds number varying from 4.40×104 to 2.55×105. Both the cases with and without tip clearance were considered in the simulation. The numerical results of the loss caused by the tip clearance agree well with the experimental data and the values predicted by the Denton formula. It is indicated that this loss will not change with the increase of the Reynolds number but the intensity of the passage vortex increases with the decrease of the Reynolds number. The tip leakage flow will weaken with the increase of the passage vortex because of the interaction between the passage vortex and the tip leakage vortex, and the position of the tip leakage vortex is more close to the middle of the passage. In addition, the distributions of the total pressure loss and the flow angle at the exit of the cascade are influenced by the intensity and the position of the tip leakage vortex.关键词：gas turbine;tip leakage flow;low Reynolds number;preconditioning method;numerical simulation3662|4|3更新时间：2025-05-01
- 摘要：The effects of sealing clearance, pressure ratio and rotational speed on the discharge behavior of a typical labyrinth seal are numerically investigated. The Reynolds-averaged Navier-Stokes equations and the standard k-ε turbulent model are adopted to obtain the leakage flow characteristics of the labyrinth seal under the conditions of three sealing gaps, four pressure ratios and four rotational speeds. The relative leakage flow coefficient CD/CD0 and velocity ratio U/Caxare employed to analyze the effects of the rotational speed on the discharge behavior. CD/CD0 is defined as the ratio of leakage rate at rotation to the leakage rate at rest. U/Cax denotes the ratio of the circumferential velocity to the axial flow velocity. Numerical simulation results show that there exists a critical velocity ratio of 1.0. The effect of the rotational speed on the relative leakage flow coefficient can be ignored when the velocity ratio is less than 1.0. If the velocity ratio is greater than 1.0, the relative leakage flow coefficient decreases with the increase of the rotational speed, and the leakage flow rate of the labyrinth seal at the high rotational speed of more than 6 000 r/min decreases by 5.1%. The leakage coefficient increases linearly with pressure ratio at the fixed sealing clearance. In addition, the leakage coefficient decreases with the decrease of gap width at the same rotational speed.关键词：labyrinth seal;discharge behavior;numerical simulation3405|4|20更新时间：2025-05-01
- 摘要：From the augment Young-Laplace equation and the Wayner's interface mass flux equation, the influence of system operating parameters, geometry parameters and working fluid properties on the heat and mass transfer of an evaporating meniscus, as well as its stability, was investigated using the numerical analysis on a thin-film heat and mass transfer model in the present work. The results show that the meniscus with higher superheat degree or higher meniscus temperature has a greater capability of heat and mass transfer, but its stability is lower. The influence of geometry parameters on interface heat and transfer is slight while the effect of working fluid properties is significant. Generally, higher heat and mass transfer capability occurs along with lower stability, which should be carefully considered in the design of a capillary pumped loop system.关键词：capillary pumped two phase devices;evaporating meniscus;heat and mass transfer2913|4|7更新时间：2025-05-01
- 摘要：The mechanism of temperature oscillation in a loop heat pipe was analyzed on the basis of the instability of two-phase flow at the entrance of a condenser, and the results show that the instability of two-phase flow is one of the sources of temperature oscillation. The experimental results indicate that temperature oscillation occurs as the heat load of the loop heat pipe system is in a range of 12-60 W while the system can operate stably when the load is outside the range, matching the theoretical analysis. Further, the severity of temperature oscillation of the loop heat pipe increases obviously with the increase of charging ratio of working fluid. In addition, compared with the loop heat pipe with methanol as working fluid, the system using acetone with lower latent heat has a smaller range of heat load in which temperature oscillation exists and the severity of temperature oscillation decreases clearly.关键词：loop heat pipe;temperature oscillation;two phase flow;theoretical research2925|4|2更新时间：2025-05-01
- 摘要：One deficiency of the traditional adaptive stochastic resonance is that only a single parameter can be optimized while the other parameters in the system being fixed. A new adaptive stochastic resonance based on genetic algorithm, which realizes multi-parameter synchronous optimization, is proposed. The signal-noise-ratio of the output of the bi-stable system is determined as the fitness function of genetic algorithm and multi-parameters in stochastic resonance system are selected adaptively. As a result, weak periodical components in original signals are sufficiently amplified. Simultaneously, the optimization algorithm, combined with frequency-shifted and re-scaling stochastic resonance, enables to achieve the stochastic resonance under the conditions of great parameters. The proposed method is evaluated by simulation data and vibration signals measured on defective bearings with outer race fault. The results show that weak periodical components with high frequency buried in strong noise are well extracted in case of small number of sample points.关键词：stochastic resonance;genetic algorithm;multi-parameter synchronous optimization;weak signal detection3423|4|16更新时间：2025-05-01
- 摘要：To improve on-line modeling precision of support vector regression(SVR)in uncertain control systems, by analyzing the effects of training data sets distribution and outliers, it is demonstrated that the precision can be effectively improved by increasing data density at neighborhood of outliers. A modeling method using multirate sampling is presented based on on-line SVR. In this method, multirate sampling is chosen to increase local data density, and a local-data-intensive sliding time window is established to reduce the training data number and eliminate outliers by taking advantage of the good performance of SVR in small sample. The method is applied to a multichannel electrohydraulic force servo synchronous loading system to predict the load output. Compared with the traditional single rate sampling method, the results indicatethe better robustness and prediction accuracy. The prediction mean absolute percentage error gets 0.66% while only two training samples are added.关键词：support vector regression;multirate sampling;outlier2853|4|1更新时间：2025-05-01
- 摘要：Aiming at resolving the problem that linear models are not able to express the influence of the nonlinear phenomena in servo drive system, such as stick-slip friction, dead-zone etc, on condition of low-velocity or changing of directions, the Hammerstein model which contains static nonlinearity and dynamic linearity is adopted to describe servo system instead of linear model. The nonlinear characteristic of servo system is approximated by static nonlinearity, where two-segment polynomial is used to describe asymmetrical characteristics of friction. The recursive least square method is performed to estimate the parameters of model with multi-frequency sinusoidal input signal and velocity output signal of the servo system. The comparison of the model output between the linear model and the Hammerstein model in identification experiments indicates that the Hammerstein model can effectively represent the nonlinear characteristics of servo system, the error of the Hammerstein model output can be reduced by 90% of that of the linear model to greatly improving, the identification accuracy and precisely predicting the dynamic response of system in nonlinear states.关键词：servo system;Hammerstein model;nonlinear parameter identification3556|4|6更新时间：2025-05-01
- 摘要：To solve the problems in adjusting and controlling shapes of developable surfaces, following the important idea of duality between points and planes in 3D projective space, two direct explicit and efficient methods of computer-aided design for developable surfaces are proposed. Constructing a class of cubic extension Bézier(CE-Bézier)basis functions with two shape parameters α,γ, the corresponding developable CE-Bézier surfaces with multiple shape control parameters are represented. The developable CE-Bézier surfaces inherit the outstanding properties of the Bézier surfaces, with a good performance on adjusting their local shapes by changing the two shape control parameters. In the particular case where α and γ are equal to 1, the developable CE-Bézier surface is a developable Bézier surface. Finally, some applications in developable surfaces design are discussed. The modeling examples illustrate that the developable CE-Bézier surfaces provide two valuable ways for the design of developable surfaces.关键词：developable surface;duality;shape parameter;CE-Bézier curve3131|4|3更新时间：2025-05-01
- 摘要：Software testing is unable to meet the verification needs of process scheduling for multi-core CPU, therefore a theorem proving approach with projection temporal logic(PTL)is adapted to verify the process scheduler. A general model supporting the most commonly used scheduling algorithms for multi-core CPU is constructed by a PTL formula S, and the desired property of the system is described by a PTL formula P, then whether the system possesses the property can be identified by proving whether or not S implying P is a theorem based on the axiomatization of PTL. As a case study, the correctness of the processes scheduling with the multilevel feedback queue scheduling algorithm over a two-core CPU is proved, which indicates that the proposed approach can be used to verify system properties of process scheduling over multi-core CPU and hence to ensure the reliability of the process scheduler. Since the process scheduler over multi-core CPU has the typical features of concurrent system, the method can also be applied to verify general concurrent systems.关键词：projection temporal logic;process scheduling;theorem proving;multi-core CPU;scheduling verification2883|4|1更新时间：2025-05-01
- 摘要：Sound admittance of porous material is deduced on the basis of Wilson numerical method. A numerical method for calculating the absorption property of porous metal at high sound pressure level(SPL)is developed by using a standard fourth-order Runge-Kutta algorithm. It is found that an exponential distribution in Wilson method for identifying the distance between discrete points of calculating meshes is unnecessary in the proposed method, and the sound absorption properties of porous metal at high sound pressure levels can be well evaluated with smaller number of meshes. The SPL of incident wave exerts greater influence on the acoustic resistance of porous metal than on the acoustic reactance in the case of porous material without air gap. However, for the case of porous material with an air gap, the influence of reactance on the acoustic properties of porous metal is enhanced gradually.关键词：high sound intensity;porous metal;sound admittance;numerical calculation3250|4|4更新时间：2025-05-01
- 摘要：Inertial radial friction welding process was adopted to weld 35CrMnSi and T3. The interface microcosmic binding characteristics were observed by SEM. The element diffusion near the interface was detected by EDS. The results show the tightly connected contact surface of 35CrMnSi/T3 with obviously wavy occlusion at flywheel rotation speed of 3 000 r/min. The elements diffusion and dissolution through the interface occur, and the metallurgical bonding forms. The diffusion distance of Fe atoms into copper matrix gets to 33 μm and Cu atoms into Fe matrix about 3 μm. In addition, the adverse effect of oxygen on friction welded joints is inhibited by the evident plastic deformation of the contact surfaces in radial friction welding process.关键词：friction welding;35CrMnSi/T3;interface;diffusion15|5|1更新时间：2025-05-01
- 摘要：Facing a huge memory space and long calculating period in finite element calculation for large thick-wall welded structure, three predictor models based on software ANSYS with simplification of bead number, moving heat source, and both of them respectively are presented. Under the three simplifications, the residual stress and the process stress of the welded cylinder with angle-inserting elbow and thickness of 125 mm are evaluated, and as a result, the similarities and differences for the welding stress are obtained. It shows that the residual stress in simplified bead model has greater error than that by simplified moving heat source model in direction of bead filled, and the stress in simplified moving heat source model has greater error than that by simplified bead model in the same bead plane. The process peak stress increases in case of simplified moving heat source model, and the process stress of the joint with many beads or a very long welding time is affected more significantly by the simplified bead model.关键词：large thick-wall;fast prediction;stress evolution3287|5|1更新时间：2025-05-01
- 摘要：A high speed rotary machine rotor-bearing system collaborative design knowledge repository is constructed by ontological method and technology, and the functions of knowledge base prototype system are verified. The ontological models are made for multi-disciplinary field design knowledge of high speed rotary machine rotor-bearing system and ontology web language format design knowledge ontology repository is developed based on protégé ontology development platform. Then the complex product collaborative design knowledge repository is established with Jena technical framework, by mapping and data transferring from ontology repository to knowledge repository. Taking with the design of two-span rotor test-bed as an engineering example, the knowledge repository prototype system functions of tribology design and collaborative analysis module of simulated and experimental data are verified by implementing knowledge sharing, reuse and interoperability of heterogeneous system.关键词：knowledge repository;ontology;rotor-bearing system;collaborative design3981|4|6更新时间：2025-05-01
- 摘要：A new multiwavelet is constructed according to the signal feature, which utilizes mulitiwavelet lifting, taking kurtosis as the optimal object and genetic algorithm as the optimal strategy. The new multiwavelet is substituted for the filter in spectral kurtosis(SK)and the kurtogram is improved accordingly. The multiwavelet spectral kurtosis is proposed based on the conventional SK, which makes up the SK in filter limitation and improves the resolution of spectral analysis. The examples for rolling bearing in test rig and locomotive result indicate the improved accuracy of frequency-band-selection and the signal-to-noise-ratio of signal filtered.关键词：multiwavelet;adaptive construction;spectral kurtosis;rolling bearing;fault diagnosis3679|5|29更新时间：2025-05-01
- 摘要：To improve the output capability of piezoelectric pump, a dual-chamber piezoelectric pump in parallel connection with passive check valve was designed, and the experimental prototype driven by piezoelectric bimorph was processed. The output properties of dual-chamber piezoelectric pump in parallel connection was analyzed theoretically with liquid and gas as the media for different piezoelectric vibrator driven modes(synchronous drive and synchronous drive).The results show that the output capability of pump with two oscillators under asynchronous-driven gets better than that by synchronous drive for delivering liquid, and the maximum output flow was 1330 ml/min under 110 V drive voltage and within operating frequency range approaches less than 400 Hz. The output capability of pump with two oscillators under asynchronous drive gets close to synchronous-driven for delivering gas with maximum output flow 950 ml/min. Thus dual-chamber piezoelectric pump in parallel connection determines the optimum delivering fluid mode.关键词：bimorph;piezoelectric pump;parallel connection;gas;liquid3108|4|6更新时间：2025-05-01
- 摘要：Reliability of the furnace in an existing industrial continuous catalytic reforming unit was investigated with the fuzzy fault tree analysis method. A fault tree was developed considering failure of the reforming furnace to be a top event. Thirty-one minimum cut sets were achieved by qualitative analysis with the ascending method. The concept of fuzzy number of the fuzzy sets theory was applied to describe the probability of basic event occurrence in the fault tree, and the fuzzy failure probabilities of the middle events and the top event were calculated with fuzzy AND and OR operators. Among all middle events the probability of tube failure is highest, and the tube failure probability in the radiant chamber is clearly higher than that in convection chamber, showing that the radiant chamber tube is a weak part in the furnace. The results show that the fuzzy fault tree proposed is an effective method of reliability analysis for petrochemical equipments and its calculation results are more reasonable than those of the conventional fault tree.关键词：reforming furnace;reliability;fuzzy fault tree3283|4|1更新时间：2025-05-01
- 摘要：To improve the rate and accuracy of weld defect segmentation in radiographic images, a segmentation method based on water-flooding principle is proposed. According to the principle water flows downwards to the low-lying-land and runs over when it is full, the region of a defect and its neighbor are flooded and the threshold value is determined in terms of the growth of the flooded area. The waveform analysis of gray level profiles is used to detect a defect and get the seed point. Then, a flooding process is carried out starting from the seed point, where a line by line search strategy is employed. Once flooding, the threshold is determined by analyzing the relative increment of the flooded area. The experimental results show that the computation cost of the proposed method is 5.3% and 25% of that of Alaknanda method and Kaftandjian method, and the segmentation error gets 27.33% and 53.14%.关键词：radiographic image;defect segmentation;flooding;line by line search strategy3187|4|1更新时间：2025-05-01
- 摘要：The reason of non-physical profiles of the lid driven flow in a closed circular cavity was analyzed to avoid singularity in solving a non-axisymmetrical fluid flow problem using a polar cylindrical grid. A new numerical method was proposed to treat these singularity elements by decomposing the pressure gradient term. The present method can obviously avoid the singularity without increasing the calculation amount. Compared with the unstructured grid, the same level of accuracy can be obtained using the present method with much fewer cells in a Cartesian coordinate system. Unlike the conventional methods, this method does not need special treatment of the cells. Our results indicate that the present method will reduce the difficulty of adopting the finite volume method and ensure its feasibility by orthogonal decomposition treatment of the pressure gradient term in the discretization scheme at the singularity cells.关键词：finite volume method;singularity;polar coordinate system2758|4|0更新时间：2025-05-01
- 摘要：The unexpected cracking of the crankshafts in a six-crank reciprocating compressor occurred frequently. The severe vibration of the compressor and the scuffing of the 1st and 2nd crank bearings existed after the diameter of the main shaft was magnified. In this paper, modal and dynamic response of the initial crankshaft and the crankshaft with the diameter magnified are analyzed with ANSYS finite element analysis software. The results show that the cracking of crankshafts results from fatigue damage and torsional vibration. Given the diameter of the main shaft magnified, if two plate flanges connecting the 2nd shaft and the 3rd shaft are integrated by hot assembling, the rotating inertia-mass of the modified crankshafts will be enlarged and the frequency ratio r will increase, leading to disappearance of the sympathetic vibration.关键词：crankshaft torsional vibration;fatigue damage;modal analysis;dynamic response3275|4|4更新时间：2025-05-01
- 摘要：According to the current development of refrigerated transport industry of China and wide promotion of liquefied natural gas(LNG)vehicles, the advantages and feasibility to recover LNG cold energy for refrigerated truck were analyzed, and cooling capacity demand was theoretically calculated. A process of a direct-cooled refrigerated truck recovering LNG cold energy was proposed. A steady state experiment on a direct-cooled cold energy recovery of a refrigerated truck was conducted, in which liquid nitrogen was used instead of LNG. The experimental results show that the system could operate well and cold energy recovered during the LNG gasification process could match the demand of cold storage. The temperature could drop to -20 ℃ in the carriage, and the temperature difference between the measuring points was all below 4 ℃. In addition, the temperature drop rate and uniformity of the temperature field in the carriage could meet the relevant technical standard.关键词：liquefied natural gas;low temperature cold storage vehicle;cold energy recovering;temperature field;energy saving3245|4|3更新时间：2025-05-01
- 摘要：Predicting noise-induced vibration from acoustic loads experienced in launch environment was investigated with the coupled finite element method and boundary element algorithm. The conventional numerical simulation of a reverberant field as a launch acoustic environment was introduced. Following the reciprocity theorem used in the coupled FE-BE model, the structural response due to reverberant acoustic excitation was substituted by the sound pressure caused by force excitation on the structure, then the output response power spectrum density of the coupled model subjected to reverberant environment was evaluated based on the stochastic analysis principle. To verify the accuracy and efficiency of the proposed method,it was used to simulate a force-excited structure. The simulation results were in good agreement with the solutions from the conventional methods.关键词：reverberant acoustic field;reciprocity theorem;stochastic analysis;sound-vibration coupling analysis;numerical simulation.3324|4|0更新时间：2025-05-01
- 摘要：La1-xSrxCoO3-δ(LSCO)is a promising cathode material for solid oxide fuel cells(SOFCs). The properties of the LSCO cathode are significantly influenced by its oxygen content. In this paper, La0.5Sr0.5CoO3-δ coatings are prepared by both flame spraying and plasma spraying. Annealing treatment of the LSCO coatings is performed at 1 000 ℃ for 3 hours. Oxygen contents of different samples are investigated by iodine titration. The effects of spray condition and annealing treatment on the oxygen content of the La0.5Sr0.5CoO3-δ are investigated. The results show that oxygen contents in the as-sprayed coatings get significantly lower than that in the starting powder owing to heating to a high temperature of spray particles by high temperature flame. The escaped oxygen of plasma-sprayed La0.5Sr0.5CoO3-δ is more than that of flame-sprayed one. The oxygen content significantly increases after annealing treatment. It is clear that the deficit oxygen can be recovered through annealing treatment. The lattice distortion occurs in the thermally sprayed coatings due to large concentration of oxygen vacancies, which induces tetragonal phase formation. It is also found that recovery of oxygen through annealing treatment leads to a recovery phase transformation from tetragonal phase to perovskite cubic phase.关键词：La0.5Sr0.5CoO3-δ;plasma spraying;flame spraying;oxygen content;iodine titration2818|4|1更新时间：2025-05-01
- 摘要：The surface wettability and surface structure of poly(tetrafluoroethylene)(PTFE)treated with remote O2 plasma were studied. The contact angles of the samples were measured and the critical surface tensions γC were determined on the basis of the Zisman's plots. The values of the surface free energy γS, and its dispersion force γdS, dipole force γpS, and hydrogen bonding force γhS were evaluated by the extended Fowkes equation. In addition, the analysis was performed on the relation of the distribution of reactive species in remote O2 plasma and the surface free energy. The results show that the surface wettability of remote O2 plasma treated PTFE is determined only by the polar force(γpS+γhS), especially by theγhS. A mixed atmosphere constituted by all reactive species or super pure and high free radicals concentration in remote O2plasma facilitates the increase of polar force(γpS+γhS), but the surface free energy is mainly influenced by the concentration of charged particles. X-ray photoelectron spectroscopy(XPS)indicates that the C—F bonds on the PTFE surface are broken by the O2 plasma treatment, and then the C—O and C=O are yielded effectively, leading to a higher surface wettability.关键词：remote oxygen plasma;PTFE;surface wettability;surface free energy2986|4|2更新时间：2025-05-01
- 摘要：With ERDAS IMAGINE and the fragstats3.3 landscape pattern analysis system, dynamics and its impacting factors of the land use/land cover and landscape pattern in Hongjiannao watershed were quantitatively analyzed with some landscape indices. The results show that during 1986-2002, the areas of dense shrub, forest/infield and other water types increased by 15.45%, 30.33%, and 106.16%, respectively. The areas of arable land, dune shrub and the lakes decreased by 40.05%,10.10%, and 24.33%, respectively, showing that the lakes were seriously degraded and the dune sparse shrub and cultivated land primarily transformed to dense shrub and forest meadow. Some landscape pattern indices increased, such as the total number of patches, shape index, diversity index, but the average patch area decreased, indicating that the degree of watershed landscape fragmentation and the landscape types increased. With the implementation of the returning farmland to forest(grass)project, the landscape fragmentation was mitigated during 1999-2002. Our conclusion is that the construction of reservoirs upstream and agricultural irrigation lead primarily to the reduction of lake area and human socio-economic activity has the main influence on the landscape pattern changes in the Hongjiannao watershed.关键词：Hongjiannao watershed;land use/land cover;landscape patterns2900|4|4更新时间：2025-05-01
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