最新刊期
卷 51 ， 期 9 ， 2017
- 摘要：Aiming at the modelling for the molecular representation of high-sodium coal char to characterize the complex physico-chemical properties, an image-guided construction strategy of molecular model based on coupling stack and pore size distributions for high-sodium coal char(about 40 000 atoms)was proposed using HRTEM micrographs. Simplified modelling programs Fringe3D and Vol3D based on Perl language were developed. A macromolecular model of coal char with pore size distribution and various sodium compositions was constructed. The approach proposed in the present study is highly automatic and controllable, and easy to couple complex structures. Various sodium distributions were considered in the modelling of coal char. The constructed macromolecular 3D coal char model and molecular dynamics simulation are beneficial for further elucidating the migration behavior and microscopic reaction mechanisms of sodium.关键词：coal char;molecular model construction;pore size distribution;alkali metal sodium;stacking distribution836|6|2更新时间：2025-07-09
- 摘要：To improve the uniformity of traditional impinging jet heat transfer, a new type of jet structure with some circumferential spiral channels set inside the normal nozzle, like the internal thread, is proposed in this paper. First, several numerical methods are adopted to process the experimental data of the swirling impinging jet from a swirl generator, and the data are referenced from a published literature. Results show that the RNG k-ε turbulence model is more suitable for simulation of the swirling impingement jet. Then, the effects of such parameters as Reynolds number(4 000-12 000), impact distance(1-8 times of equivalent diameter)and helix angle(0°-75°)on the heat transfer performance of such threaded hole are studied. The research is focused on the flow field and heat transfer characteristics. The experimental results indicate that the heat transfer rate and the uniformity of impinging target will increase with the Reynolds number, and the local Nusselt number will increase first and then decrease with the increasing impact distance. Meanwhile, the double-peak feature of the local Nusselt number will change to single-peak shape, and the maximum local Nusselt number can be obtained at the 4-fold equivalent diameter. The local Nusselt number at the center point will increase with the helix angle, but the heat transfer uniformity will be worse. In addition, it is found that the helix angle corresponding to the best heat transfer performance also changes with different impact distances.关键词：swirling impinging jet;impingement cooling;heat transfer uniformity;threaded nozzle785|6|1更新时间：2025-07-09
- 摘要：The impact dynamics of droplets of different liquids onto solid surfaces with different roughness was investigated by using the high-speed microphotography. The influences of viscosity, surface tension and surface roughness on the non-dimensional maximum spreading diameter and the critical Weber number for transition from spreading to splashing were discussed. The results showed that the non-dimensional maximum spreading diameter decreases with the increasing liquid viscosity, and higher surface tension makes droplet more possible to retract after impacting on the solid surface. It was also observed that water is the only liquid that retracts in the experiment since it has obviously higher surface tension than other three liquids. The droplet needs to wet larger surface and will have higher viscous dissipation with the increase of surface roughness, leading to the decrease of the maximum spreading diameter at the same Weber number. The relationship of the maximum spreading diameter with Weber number, Ohnesorge number and surface roughness was obtained by introducing surface roughness to Laan's equation. The “finger-like” disturbance around the rim becomes more obvious with the increase of surface roughness, which makes the droplet more likely to splash after impact onto the solid surface and leads to lower critical Weber number for transition from spreading to splashing. In addition, the surface roughness influences the critical Weber number more significantly for the liquids with smaller Ohnesorge number.关键词：droplet;impact;surface roughness887|5|3更新时间：2025-07-09
- 摘要：The pyrolysis and kinetic characteristics of ammonium salts in solid ammonium selective catalytic reduction(SCR)system are investigated to provide theoretical and technical supports for design of solid ammonia SCR gaseous ammonia production and supply system. The pyrolysis characteristics of three kinds of ammonium salts, including decomposition temperatures and rates, are analyzed by thermogravimetric test and decomposition equilibrium pressure test, and the decomposition kinetics parameters of ammonium carbamate and ammonium carbonate are calculated with isothermal method and integral method. The thermal decomposition of ammonium carbonate and ammonium carbamate are completed at constant temperature to determine the relationship between the residual mass ratio and the heating time, and the rate constants and reaction orders are obtained by the mass ratio versus reaction time in thermogravimetric analysis curves. The results show that the decomposition rate of ammonium carbamate gets higher than that of ammonium carbonate and ammonium bicarbonate; the reaction order of ammonium carbamate is 1/2, and that of ammonium carbonate is 2/3; the activation energy of ammonium carbamate and ammonium carbonate reaches respectively 56 kJ/mol and 62 kJ/mol; ammonium carbamate and ammonium carbonate are suitable to be the source of the reducing agent of SSCR system, and the advantage of ammonium carbamate is more obvious. Compared with urea SCR technology, solid-state ammonium SCR technology can provide more sufficient amount of reducing agent when the engine is at low exhaust temperature, so that the conversion efficiency of low-temperature NOx is effectively improved.关键词：solid-state ammonium;selective catalytic reduction;ammonium salt;pyrolysis characteristics;kinetic parameter812|5|1更新时间：2025-07-09
- 摘要：Polycyclic aromatic hydrocarbons(PAHs)emitted from a gasoline direct injection(GDI)engine during start were extracted via Soxhlet extraction system and analyzed by GS-MS. Three kinds of fuel, gasoline, gasoline blended with 10% volume fraction ethanol(E10), and gasoline blended with 15% volume fraction methanol(M15), were considered. The results show that compared with gasoline, PAHs mass concentration of the exhaust extraction from the engine fueled with E10 decreases by 39.03% and 23.78% under 20 ℃ and 80 ℃ coolant start conditions, respectively; PAHs mass concentration from the engine fueled with M15 decreases by 30.17% and 66.06%, respectively. Toxicity of PAHs was assessed under different coolant's temperature start conditions. Under 20 ℃ coolant start condition, benzo(a)pyrene equivalent toxicity values of PAHs from the engine fueled with E10 and M10 decrease by 23.25% and 21.47% compared with gasoline; under 80 ℃ coolant start condition, benzo(a)pyrene equivalent toxicity values of PAHs from the engine fueled with E10 and M10 decrease by 33.26% and 50.46% compared with gasoline. In contrast to 20 ℃ coolant start condition, benzo(a)pyrene equivalent toxicity values of PAHs from the engine fueled with gasoline, E10 and M15 decrease the values by 44.25%, 50.80% and 64.84% respectively under 80 ℃ coolant start condition.关键词：gasoline direct injection engine;oxygenated fuel;polycyclic aromatic hydrocarbons;start698|5|0更新时间：2025-07-09
- 摘要：Following the finite element analysis and the experimental verification, the vertical stiffness of thrust rod for heavy-duty vehicles is analyzed, the influence of rubber compressibility on the simulation result is taken into consideration, and the structure of the thrust rod is optimized. Uniaxial tension test for rubber specimens is conducted to obtain the strain-stress data, by which the parameters of the deviatoric term are fitted. The parameters of the volumetric term are described by Poisson's ratio. And the compressibility can be adjusted by changing the value of Poisson's ratio. It shows that the compressibility exerts an important effect on the finite element simulation result, and the stiffness of the thrust rod increases with Poisson's ratio increasing. The stiffness of the thrust rod increases linearly when Poisson's ratio is less than 0.495, and it increases rapidly as Poisson's ratio is larger than 0.495. When Poisson's ratio is 0.492, the results of simulation and experiment coincide well. It indicates that modification of rubber compressibility by adjusting Poisson's ratio is reasonable.关键词：thrust rod;finite element analysis;rubber;compressibility638|6|4更新时间：2025-07-09
- 摘要：To conduct tolerance analysis of gears more effectively and reasonably, a new tolerance analysis modeling approach for gears based on small displacement torsor(SDT)and response surface method is proposed. Taking the installation tolerance of a gear for example, the mathematical model for installation tolerance of the gear is built based on SDT theory and in accordance with gear precision standard. Based on this model and tooth contact analysis(TCA), a simulation program considering the errors is coded and the effects of different variation factors on transmission error are analyzed. A second-order response surface approximate model of gear transmission error is built based on Latin hypercube sampling and the least squares method, hence the tolerance analysis model of gears is obtained. An example is analyzed and the result indicates that the proposed method has high modeling accuracy and good practicability, and may provide a reference for gear tolerance analysis and synthesis.关键词：gear;tolerance analysis;tolerance modeling;small displacement torsor;response surface method713|6|5更新时间：2025-07-09
- 摘要：According to the basic theory of the vector form intrinsic finite element(VFIFE)and its element type and current applications, basic theoretic formulas of the hexahedral entity element are derived by calculating reverse movement and element inner forces, which extends VFIFE application to complex solid structures and engineering fields. For the collision-contact behavior of solid surfaces, the master-slave algorithm and inside-outside algorithm are used to perform global search and local search between the particle and hexahedral mesh surface of the outer entity surface, and a penalty method based on the central differential formula is presented for the analysis of collision response. Taking a pair of spiral bevel gears for example, its model is established and analyzed by VFIFE, and the results are compared with that of finite element method(FEM). Comparison shows that the stress, contact force and contact pattern agree well with the FEM results, and the VFIFE method is efficient for analyzing solid structures with a relatively sparse grid.关键词：spiral bevel gear;vector form intrinsic finite element;hexahedral entity element;contact stress;meshing performance701|6|5更新时间：2025-07-09
- 摘要：The friction and wear behaviors of copper-based graphite seal material used in liquid rocket engine were investigated by means of pin-on-disk machine. The effects of load, velocity and temperature rise on friction and wear behaviors of the copper-graphite material were analyzed. Results show that: 1)It is not easy to form copper-graphite transfer film under water lubrication condition, so the friction coefficient under water lubrication condition is higher than that under dry friction; 2)Under the condition of water lubrication, the wear mechanism is adhesive wear and abrasive wear, and properly increasing load and decreasing velocity can reduce the wear rate of the copper-based graphite material; and 3)Under the condition of dry friction, the wear mechanism is adhesive wear, and properly decreasing load and increasing speed can help reduce the wear rate of copper-based graphite material.关键词：seal material;copper-based graphite;friction and wear behavior;wear mechanism636|6|2更新时间：2025-07-09
- 摘要：To explore the human body thermal comfort under radiative cooling air conditioning system, the heat transfer mechanism of radiative cooling air conditioning system is investigated. The relationship of the thermal comfort indicator with the human body's sensible heat loss and the ratio of radiative heat loss to convective heat loss is achieved. Both experimental and numerical results show that the human body thermal comfort index, i.e., predicted mean vote(PMV), is approximately linear with the sensible heat loss of human body under the radiative cooling air conditioning system. Thus, the human body thermal comfort could be directly evaluated by the human body thermal balance according to the obtained linear relationship. Furthermore, it is found that the ratio of radiative heat loss to convective heat loss of human body has no effect on PMV. Therefore, on the basis of maintaining human body thermal comfort, it is conceivable that the higher ratio of radiative heat loss to convective heat loss, which means larger radiative area or higher air supply temperature, could be beneficial to energy conservation. This study may provide a reference for both assessment of human body thermal comfort and system design of radiative cooling air conditioning system.关键词：radiative cooling air conditioning system;human body thermal comfort;human body thermal balance;sensible heat loss710|6|2更新时间：2025-07-09
- 摘要：To reveal the force chain evolution and dynamic state under granular flow lubrication, an analytical model of granular flow lubrication between sheared parallel plates is established based on the discrete element theory of continuum mechanics. Using this analytical model, the contact force distribution rule, the force chain evolution rule and dynamic state, as well as the force chain distribution and its influence on the granular flow lubrication system, are studied. Numerical analytical results show that the probability distributions of normal contact force, tangential contact force, and contact between granular lubrication medium all obey the power law; the load bearing and dynamic characteristics of granular lubrication system are mainly influenced by normal contact force; and the dynamic state of granular lubrication medium can be transformed into four states of jamming state, quasi-static state, slow flow and fast flow. Under these four flow states, the magnitude of total force chain is large in the jamming state, quasi-static state and slow flow state, but small in the fast flow state. When the dynamic state of granular lubrication medium transforms from fast flow state to slow flow state or quasi-static state, the number of weak force chains is deceased and the number of strong and super force chains is increased. And in the meantime, the flow speed of granular lubrication medium as well as the deconstruction and reconstruction speeds of force chains slows down.关键词：granular flow lubrication;force chain evolution;kinetic;contact force;discrete element method922|5|4更新时间：2025-07-09
- 摘要：To improve the control accuracy of brushed DC motor at low speeds, a novel control system using disturbance observer and sliding mode control is developed. It aims at compensating the nonlinear friction and load disturbances. First, since the friction changes fast with the variation of motor speed, it is very difficult to estimate it online. Therefore, the Stribeck friction model is used for computing the friction, and the parameters of this model are identified offline. Then, a disturbance observer is designed for estimating the model errors and load disturbances. It is proved that the estimated errors can converge to a prescribed range after a finite time. Finally, the estimated errors are taken as the amplitude bounded disturbance inputs, and an adaptive slide mode controller is designed to guarantee the robustness of this system. The switching gain estimated by the adaptive technique is just related to the upper bounds of the estimated errors, therefore, the demand of high-gain feedback for high accuracy is avoided since the switching gain is reduced with this method. The designed controller is evaluated through experimental tests. Compared with the PI and traditional slide-mode control methods, the steady-state output error of this controller is reduced to 46% and 63% of the two methods' errors, respectively; its response time is 0.15 s, and the input chattering is also reduced. It shows that the designed controller could effectively suppress the effects of the friction and load disturbances on the control over the brushed DC motor.关键词：brushed DC motor;disturbance observer;adaptive slide mode controller;Lyapunov stability785|5|5更新时间：2025-07-09
- 摘要：To understand the fatigue damage behavior and residual strength of composite sandwich T-joint subject to bending loads, the bending fatigue tests were performed, including the static bending failure tests before and after the fatigue tests on fatigue loading test machine and universal material testing machine. The static bending failure tests were carried out before fatigue loading to obtain the initial failure load of the structure, and the damage characteristic mode was observed. The experimental results show that the stiffness of the composite sandwich T-joint presents a progressive degradation, and the acceleration trend increases with the rise of the peak load; The shear damage of foam core is the main damage mode of the composite sandwich T-joint on the side of the horizontal panel; The degradation of mechanical property of the foam leads to a progressive decrease in the structural stiffness. Further comparative analysis shows that the stiffness and the ultimate bearable bending moment of the composite sandwich T-joint after 105 fatigue loading circles are approximately equal to that before fatigue loading is imposed under the condition that the fatigue peak load is 70% of the initial failure load.关键词：composite;T-joint;bending load;fatigue damage;residual strength652|5|0更新时间：2025-07-09
- 摘要：To study the influence of geometric parameters on the propulsion performance of three-dimensional bionic motion wings, a general large-scale solver based on IB-LBM algorithm for Tianhe-II supercomputer is developed. To implement this process, the immersed boundary method is used to construct a force function on the surface of the wing. Then the force function is spread to the neighbor fluid mesh with interpolation function. The lattice Boltzmann method is used to perform fluid computation and update the velocity field. Four different wings, i.e., ellipsoidal wing, plate wing, NACA0012 wing and cuboid wing, are investigated to explore how the geometric shapes of the wings influence the thrust coefficient and vortex structure. The numerical results show that the vortex induced by the ellipsoidal wing is fully structured and close to the surface of the wing, so its propulsion performance is best. The vortex structures of NACA0012 wing and plate wing are similar, and hence have similar propulsion performance. The vortex structure of cuboid wing, however, is small and far from the wing surface, leading to a worst propulsion performance. So, in design of bionic airplane, the cuboid wing should be excluded. Although the performance of ellipsoidal wing is best, it requires a high-quality mass distribution in connection parts, so the plate wing would be a proper choice as a result of tradeoff.关键词：bionic motion wing;immersed boundary method;lattice Boltzmann method;propulsion performance;geometric parameter825|5|4更新时间：2025-07-09
- 摘要：Adjoint method based design optimization is currently a hot topic in the field of fluid machinery, which has the advantage that the computation cost is almost independent of the number of design variables. In view of that few efforts in previous researches have been devoted to the inverse aerodynamic design of cascades with flow separation by means of the adjoint method, an optimization method for aerodynamic inverse problem of cascade, which includes blade geometry parameterization, grid generation, flow solving, adjoint field solving and optimizing, is proposed. From the point of view of weakening the flow separation, the aerodynamic inverse design of a cascade is completed by giving a desirable surface pressure distribution on the blade. The results show that the suction profile of the obtained blade becomes flatter than the initial design, and the flow separation near the trailing edge is weakened at two investigated attack angles. This approach is beneficial for the development of aerodynamic design technology of cascades with higher efficiency and wider operating range.关键词：cascade;geometry parameterization;adjoint method;inverse problem;design optimization653|5|3更新时间：2025-07-09
- 摘要：The effect of non-uniform inlet flow temperature and pressure conditions due to stator/rotor interaction and supplementary steam on fluid excited rotordynamic characteristics of blade tip labyrinth seal was numerically investigated by unsteady Reynolds-averaged Navier-Stokes(URANS)solution based on the multi-frequency elliptical orbit rotor whirling model and dynamic mesh technique. The rotordynamic coefficients of blade tip labyrinth seal were calculated at three different inlet preswirl ratios of 0.2, 0.5 and 0.7. The rotordynamic characteristics of the blade tip labyrinth seal were comparatively analyzed under the conditions of non-uniform and uniform inlet flow temperature and pressure. The obtained results show that the increasing inlet preswirl ratio weakens rotor stability of labyrinth seal; the discrepancies of the circumferential swirl strength and pressure under non-uniform inlet and uniform inlet conditions are gradually reduced with the increasing inlet swirl ratio, and the differences of rotordynamic characteristics under the two conditions are also reduced when inlet preswirl ratio increases. At least a reduction of 82.7% in cross-coupling stiffness Kxy, an increase of more than 30.7% in cross-coupling damping Cxy of the blade tip labyrinth seal under non-uniform inlet conditions are observed at inlet preswirl ratio of 0.2 compared with uniform inlet conditions. When inlet preswirl ratio increases to 0.5, the effective damping under non-uniform inlet condition is only 8.4%-12.4% lower than that of uniform inlet condition at whirling frequencies from 50 Hz to 100 Hz. The same rotordynamic coefficients of the blade tip labyrinth seal are captured for the non-uniform and uniform inlet conditions at inlet preswirl ratio 0.7, so the effect of the inlet flow condition on the rotordynamic characteristics can be omitted at higher inlet preswirl ratio.关键词：labyrinth seal;non-uniform inlet;fluid excitation;rotordynamic characteristics675|5|12更新时间：2025-07-09
- 摘要：Dynamic acceleration simulation on three-axis centrifuge is important to test some precision instruments' performance under high G-load conditions. In order to select proper kinematic parameters to carry out dynamic acceleration simulations, a desired G-load curve is symmetrically constructed so that the kinematic parameters could be calculated inversely. First, the centrifuge system's kinematics model is established through the motion synthesis method and matrix rotation method. Then, kinematic parameters' calculation formulas are derived based on the kinematics modeling. The rotation angle, angle velocity and angle acceleration of each revolute joint are obtained by recursive method. To verify the algorithm, the G-load generated by RecurDyn, which uses the algorithm's results as input, is contrasted with the desired G-load. The result shows that the algorithm is viable and the maximum absolute error is less than 0.1g.关键词：three-axis centrifuge;kinematics model;3D acceleration simulation;inversion of motion parameters723|6|1更新时间：2025-07-09
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