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Research Review
ADVANCES IN THE DYNAMICS OF ORIGAMI STRUCTURES AND ORIGAMI METAMATERIALS
Fang Hongbin, Wu Haiping, Liu Zuolin, Zhang Qiwei, Xu Jian
Recently, due to the infinite design space, outstanding capability in changing shape, dimension, and topology, as well as the folding-induced extraordinary mechanical properties, origami structures and origami metamaterials have rapidly become the research frontiers and hot spots in the fields of mathematics, physics, and engineering. Origami structures and origami metamaterials have extensive application prospects in various fields, including aerospace, medical, and robotic engineering. Typical examples are the large-scale deployable aerospace structures, reconfigurable self-folding robots, and micro-scale foldable devices. As the scope of engineering applications continues to expand, the dynamics of origami structures and origami metamaterials become increasingly prominent, which not only involves dynamic modeling and parameter identification but also relates to the dynamic mechanism analyses and experimental tests. The origami dynamics research is facing many new challenges and opportunities brought by the complex spatial geometric relations, the rich deformation modes, and the folding-induced global strong nonlinear constitutive profiles. In this review, the research background and significance of origami structures and origami metamaterials are firstly surveyed, followed by a brief introduction to the fundamental definitions, assumptions, and categorization of origami. The geometric design, kinematic and static properties of the origami structures and origami metamaterials are also summarized in brief. Afterward, the recent research progress on the dynamics of origami structures and origami metamaterials are systematically reviewed, from the following aspects: (1) dynamic modeling and parameter identification methods; (2) theoretical, finite element, and experimental approaches for dynamic analysis; (3) folding-induced dynamic behaviors, including bi-stable and multi-stable dynamic behaviors, transient dynamic behaviors, and wave propagation dynamic behaviors, etc.; (4) typical dynamic applications. Finally, several open problems are addressed for future studies.
2022, 54(1): 1-38.   doi: 10.6052/0459-1879-21-478
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Fluid Mechanics
ANALYSES ON GENERATION MECHANISM OF SKIN FRICTION IN HIGH ENTHALPY TURBULENT BOUNDARY LAYER
Liu Pengxin, Sun Dong, Li Chen, Guo Qilong, Yuan Xianxu
When flying in low or medium attitude at very high Mach number, the surface of new hypersonic vehicles will encounter the interaction between turbulence and chemical non-equilibrium, which makes the flying environment more complicated. Generation mechanism of skin friction in such high enthalpy turbulent boundary layer is the fundamental scientific problem. The clarification of this mechanism can serve guidance for the drag reduction design, which has a significant engineering practical value. This work chose the flow condition after the leading shock of a cone in hypersonic flight, and performed direct numerical simulation (DNS) of turbulent boundary including chemical non-equilibrium effect. The low enthalpy case under the same boundary condition was set as a comparison. The RD (Renard & Deck) decomposition was utilized to analyse the dominant generation process of skin friction. The profiles of the integrand functions of main contributors were compared in detail. The influence of chemical non-equilibrium on the generation mechanism of skin friction was investigated. Furtherly, quadrant analysis technique was utilized to analyse the dominant flow events of turbulence kinetic energy production term in RD decomposition. The results show that the steaks scales of skin friction fluctuation are reduced both in streamwise and spanwise directions due to the chemical non-equilibrium effect. The molecular viscous dissipation term and the turbulence kinetic energy production term are the two main contributors to the generation of skin friction. The former mainly works in the near wall region, and the influence of high enthalpy is applied through its average portion. The profile of the integrand function of the molecular viscous dissipation term is different between high- and low enthalpy cases. The results of quadrant analysis show that the ejection and sweep events are the dominant processes for the latter term.
2022, 54(1): 39-47.   doi: 10.6052/0459-1879-21-490
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Fluid Mechanics
MEASUREMENT METHOD OF EMBEDDED TEMPERATURE SENSITIVE PAINT UNDER HYPERSONIC HIGH ENTHALPY CONDITIONS
Yuan Chaokai, Jiang Zonglin
The heat flux measurement results of point sensors cannot fully reveal the detailed heat flux distribution characteristics, especially for the areas with large heat flux gradient and complex heat flux distribution. Measurement methods of heat flux field are needed to meet the demand. The method of temperature sensitive paint has been widely used to measure heat flux field. However, the stagnation temperature of the test condition is much lower than the real flight condition. The radiation effect under hypersonic high enthalpy conditions seriously limits the application of temperature sensitive paint. To solve this problem, the embedded temperature sensitive paint method is proposed. The heat flux field is determined by the solution of the inverse heat conduction problem with inner wall temperature history measured by temperature sensitive paint. In this paper, the measurement principle, system composition, data processing method, design principle and advantages of the embedded temperature sensitive paint method are introduced in detail. The feasibility of this method is verified by numerical simulation with typical heat flux distribution. Also, the influence of temperature measurement accuracy and noise on the measurement results are analyzed. The embedded temperature sensitive paint method can be applied in the hypersonic real flight condition to reveal the detailed characteristics of the heat flux field. This method extends the application of temperature sensitive paint and solves the problem of heat flux field measurement under hypersonic high enthalpy conditions.
2022, 54(1): 48-58.   doi: 10.6052/0459-1879-21-279
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Fluid Mechanics
WAKE RECOGNITION OF A BLUNT BODY BASED ON CONVOLUTIONAL NEURAL NETWORK
Du Xiangbo, Chen Shaoqiang, Hou Jingyao, Zhang Fan, Hu Haibao, Ren Feng
Wake structures of different blunt bodies with identical characteristic length are similar, this is quite challenging to be distinguished using solely human eyes. Here, we propose a blunt body wake recognition method based on the convolutional neural network (CNN), which is then verified to be highly accurate with various types of blunt bodies models in vertical soap-film water tunnel experiments. The experimental platform is composed of a self-built vertical soap-film device, three typical blunt body models (square cylinder, circular cylinder, and triangle cylinder), and an image acquisition system. Based on the optical interference method, this image processing modulus can realize continuous high-fidelity photography of blunt body wakes with different incoming velocities. The CNN recognition model is built up with input layer, convolutional layer, pooling layer, fully-connected layer, and classification layer. Among them, the convolutional layer and the pooling layer are used to extract the deep feature information of wakes, while the fully-connected layer and the classification layer together can finally determine the category or Reynolds numbers of the input wake image. By importing a data set with 9000 wake images into the CNN model, a wake feature recognition model capable of classifying various body shapes is established in a data-driven manner. Results show that the shape recognition accuracy is 97.6% at the same Reynolds number (300 wake images), and 96% at different Reynolds numbers (1200 wake images). Even when wake images with different shapes and Reynolds numbers are mixed together, the recognition accuracy in terms of both shape and Reynolds number can still reach 91% (1500 mixed wake images). The proposed method provides a solid reference for future applications of artificial intelligence in extracting physical information from blunt body wakes.
2022, 54(1): 59-67.   doi: 10.6052/0459-1879-21-404
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Fluid Mechanics
STUDY ON THE VORTEX-INDUCED VIBRATION CHARACTERISTICS OF TWO TANDEM CYLINDERS AT LOW REYNOLDS NUMBER
Tu Jiahuang, Huang Linxi, He Yongkang, Lü Haiyu, Liang Jingqun
Based on the four-step semi-implicit characteristic line splitting operator finite element method, the vortex-induced vibration problem of two-degree-of-freedom tandem arrangement of double cylinders is numerically simulated, and the spacing ratio, shear ratio, natural frequency ratio and reduced velocity are analyzed. The influence of four parameters on the dynamic response of cylindrical structure.The study found:natural frequency ratio and shear ratio have a greater impact on the vibration amplitude of upstream cylinder. However, the impact of the natural frequency ratio and shear ratio on the downstream cylinder is small.The upstream cylinder reaches the maximum reduction speed in the two degrees of freedom direction is different, but the downstream cylinder is basically synchronized. The resonance area of the upstream cylinder is significantly wider than that of the downstream cylinder. Meanwhile, the time of upstream cylinder enter and exit the resonance area is earlier than that of the downstream cylinder. On the other hand, the two cylinders mainly complete the phase transition in the in-lock region. With the increase of the frequency ratio, the rate of the energy transfer from the fluid to the cylinder slow down, resulting in the slower rate of the cylinder complete the transition of in-phase to anti-phase. In the shear flow case, the phase difference between lift and displacement will appear “platform period” at the space ratio is more than 3.5. When the spacing ratio further increases beyond the critical value, with the increase of the reduced velocity, the more clutter frequency appears in the fluid force power spectral density curve, which leads to the phenomenon of energy “feedback”.Finally, in the uniform flow case, the main frequency value in the lift-drag power spectral density curve is twice the relationship, but as the shear rate increases, the fluid force power spectral density curve will basically coincide.
2022, 54(1): 68-82.   doi: 10.6052/0459-1879-21-381
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Fluid Mechanics
DESIGN OF MULTISTAGE COMPRESSION WAVERIDER BASED ON THE LOCAL-TURNING OSCULATING CONES METHOD
Zheng Xiaogang, Zhu Chengxiang, You Yancheng
Due to its outstanding aerodynamic performance, the waverider is considered as one of the effective ways to break through the current “lift-to-drag barrier”. It has become the research hotspot for hypersonic vehicle design. However, the traditional waverider is widely generated by a single shock wave, which cause the lack of compression efficiency. To solve the aforementioned problem, a multistage compression waverider design method for non-axisymmetric shock waves, has been proposed in this paper based the local-turning osculating cones method. With the help of multiple non-axisymmetric shock waves, the pre-compression effect of the waverider forebody is able to be fully exerted, and new design ideas for the design of hypersonic vehicles under complicated geometric conditions can be provided as well. The double compression waverider with two elliptic cone shock waves was specified as an example to introduce the new proposed method in detail. Three types of double elliptic cone compression waveriders with different eccentricities were designed under the same conditions. The numerical results demonstrate that under the inviscid conditions, the wall pressure obtained by the proposed design method is basically consistent with the CFD result. The maximum error of the corresponding aerodynamic parameters is about 0.3%, which proves the reliability of this new proposed design method. Compared with the double conical compression waverider, the waverider with eccentricity larger than one has better compression performance and lift-drag characteristics, but lower total pressure recovery coefficient and volumetric efficiency. In contrast, the double compression waverider with eccentricity less than one has larger total pressure recovery coefficient and volumetric efficiency, but lower compression performance and lift-to-drag characteristics. Additionally, the shock structure of the waverider under the viscous conditions remain essentially the same, and the corresponding two elliptic cone shock waves basically intersect at the bottom section. It reveals that this kind of waverider still owns wonderful “wave-ride” characteristics when the viscosity is taken into consideration.
2022, 54(1): 83-93.   doi: 10.6052/0459-1879-21-357
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Fluid Mechanics
COMPRESSIBLE COUETTE FLOW AND ITS HEAT TRANSFER UNDER VIBRATIONAL NONEQUILIBRIUM EFFECTS
Luo Jian, Wang Zhihui
Most of the new-generation hypersonic cruise vehicles have sharp leading edges and thin wings, and the flow and heat transfer downstream the stagnation point are characterized by the strong shear effects and significant nonequilibrium effects. Because of the demand on the total heat load prediction and the experimental data identification, there is an increasing engineering interest in the strongly sheared nonequilibrium flow and aerodynamic heating problems. In this paper, the theoretical modeling method, as well as the direct simulation Monte Carlo (DSMC) method, is used to study the aerodynamic force and heating performance of the compressible Couette flow under the vibrational nonequilibrium effects. Firstly, based on the reference temperature method, a theoretical formula of the reference temperature for the compressible Couette flow is deduced under the calorically perfect gas model. Then, analyses are conducted of the vibrational nonequilibrium effects on the reference temperature and the Reynolds analogy. The dimensionless criterion for the vibrational nonequilibrium effects is proposed, and the criterion is further employed to design formulas for prediction of the skin-friction and heat transfer. Finally, the theoretical results are validated and calibrated by the DSMC results. Both the analytical and numerical results in this study indicate that, the vibrational nonequilibrium effects reduce the skin-friction of the compressible Couette flow, but meanwhile, the Reynolds analogy is still valid as long as the analogy ratio is corrected to take into account of the vibrational energy transfer. The present study could enrich our understanding of the vibrational nonequilibrium shear flow, and specifically, the nonequilibrium flow criterion could be extended to investigate more practical aerodynamic heating problems which significantly involve the thermal nonequilibrium effects.
2022, 54(1): 83-93.   doi: 10.6052/0459-1879-21-414
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Fluid Mechanics
AN IMMERSED BOUNDARY LATTICE BOLTZMANN METHOD BASED ON IMPLICIT DIFFUSE DIRECT-FORCING SCHEME
Tong Ying, Xia Jian, Chen Long, Xue Haotian
When the immersed boundary-lattice Boltzmann (IB-LB) model with the direct-forcing scheme is used to analyze the viscous fluid dynamics of the flow around a moving boundary, the interaction interface and the boundary force format directly affect the numerical accuracy and computational efficiency of the flow solver. Based on the implicit diffuse interface, an improved IB-LB model with the direct-forcing scheme was presented. The boundary force expression is derived based on Eulerian/Lagrangian variable identities. The interaction interface described by the transfer matrix couples the asynchronous movement between Lagrangian points. Use Richardson iteration to numerically solve the linear equations related to the boundary force and the non-slip velocity constraint. It not only overcomes the calculation efficiency problem caused by matrix inversion in the traditional velocity correction scheme, but also gets rid of the dependence of algorithm stability and Lagrangian point distribution. According to the Taylor-Green flow with analytical solution, the numerical accuracy of the present model is evaluated. The results show that the improved IB model can retain the second-order numerical accuracy of the background LB model. The numerical results of the flow over a stationary cylinder and an oscillating cylinder show that the model can provide reliable numerical predictions in the flow simulation involving complex geometries and moving interfaces. The IB-LB model yielded the force identity can effectively suppress the non-physical oscillation of the predicted hydrodynamic forces. The simulation of the flow around the undulating airfoil verifies the practicability of the current model, and can be further popularized in the fluid-structure coupling simulation of large-deformation flexible bodies.
2022, 54(1): 94-105.   doi: 10.6052/0459-1879-21-315
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CODIMENSION-2 BIFURCATION ANALYSIS OF MACROSCOPIC TRAFFIC FLOW MODEL
Fan Shuangshuang, Liu Danyang, Duan Lixia
The traffic flow characteristics are an important factor in mixed traffic flow modeling. The bifurcation in the traffic flow model is one of the issues related to the complex traffic phenomena. The bifurcation phenomenon of traffic flow models involves complex dynamic characteristics and is rarely studied. Therefore, an optimal velocity model is proposed to study the effects of driver’s memory on driving behavior. Based on the optimal velocity continuous traffic flow model with memory, we analyze and predict complex traffic phenomena by using nonlinear dynamics. The conditions for the existence of saddle-node (LP) bifurcation are derived. We numerically obtain codim-1 Hopf (H) bifurcation, saddle-node (LP) bifurcation and homoclinic (HC) bifurcation, and codim-2 generalized Hopf (GH) bifurcation, cusp (CP) bifurcation and Bogdanov-Takens (BT) bifurcation. According to the characteristics of two-parameter bifurcation regions, the influence of memory parameters on the one-parameter bifurcation structures is studied, and the influence of different bifurcation structures on traffic flow is analyzed. The phase plane is used to describe the variational characteristics of the trajectories near the equilibrium point. Selecting the Hopf bifurcation and saddle-node bifurcation as the starting point of density evolution, we describe the uniform flow, stable and unstable crowded flow and stop-and-go phenomena. Further, these outcomes can improve the understanding of go-and-stop waves and local clusters observed on highways. The results show that the driver’s memory plays an important role in the stability of the traffic flow. Dynamic behavior can well explain the complex phenomenon of congested traffic. The source of traffic congestion can be better understood by considering the impact of codim-2 bifurcation. The results in this paper can provide some theoretical methods for the suppress traffic congestion.
2022, 54(2): 1-13.   doi: 10.6052/0459-1879-21-509
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THE THEORETICAL METHOD TO INCREASE THE THRUST OF HIGH MACH NUMBER SCRAMJETS
Han Xin, Liu Yunfeng, Zhang Zijian, Zhang Wenshuo, Ma Kaifu
The oblique detonation engines and shock-induced combustion ramjets have been proved to be practicable for high flight Mach number air-breathing engines in recent years. However, whether the oblique detonation engines and shock-induced combustion ramjets have enough thrust or not is unknown yet. In this paper, the combustion characteristics and propulsive performance of scramjets are discussed theoretically. Firstly, the mechanism of engine unstart of scramjets is discussed from the point of view of shock/shock interaction and deflagration-to-detonation transition. The results show that engine unstart process is very similar to the deflagration-to-detonation transition process. In the combustor of scramjets, the maximum velocity of the deflagration wave is very close to the detonation velocity. Therefore, the C-J detonation velocity is defined as the stable operation boundary of scramjets. Secondly, the formula of thrust produced by the divergent nozzle is put forth and key parameters influencing thrust are obtained. According to the thrust formula, supersonic combustion is beneficial for increasing the thrust. The main way to increase the thrust is to increase the pressure of combustion products. The propulsive performance of scramjets is theoretically analyzed by using C-J detonation theory, which is the critical condition when the engine is thermally choked. Finally, the theoretical method to increase the thrust is discussed. For high flight Mach number scramjets Ma ≥ 12, the velocity in the isolator is much faster than the C-J detonation velocity in the combustor and the problem of engine unstart disappears. Therefore, extra fuel and oxidizer can be injected into the combustor to increase the thrust further as long as the shock wave generated by the high pressure combustion products is slower than the air velocity in the isolator. The theoretical results agree well with the existing experimental and numerical results, which can be used as a baseline for the development of high Mach number scramjets.
2022, 54(2): 1-11.   doi: 10.6052/0459-1879-21-350
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Research progress on high-Mach-number scramjet engine technologies
Yue Lianjie, Zhang Xu, Zhang Qifan, Chen Keting, Li Jingping, Chen Hao, Yao Wei, Zhong Fengquan, Li Fei, Wang Chun, Chen Hong
Hypersonic airbreathing flights are highly valued in both the fields of space transportation and national aerospace safety, and the scramjet engines are pivotal propulsion devices for these flights. The scramjet engines for flight Mach numbers within the range between 4.0 and 7.0 have been extensively studied and well developed in recent years, and the extension to the scramjet engines for higher flight Mach numbers within the range between 8.0 and 10.0 or even higher are sure to be a competing focus for near-space competitions in the following decades. The current paper analyzes and summarizes the recent research advances of scramjet engines with flight Mach numbers within the range between 8.0 and 10.0 + . First of all, the key scientific problems and technologies of the higher Mach number scramjet engines are highlighted, including the high-temperature dissociation and thermochemical nonequilibrium effects, mixing and combustion enhancement technologies in ultra-high-speed flows, the matching of hypersonic combustion and inflow compression and the operating modes, the high-enthalpy low Reynolds number boundary-layer flows and the boundary-layer flow control methods, the thermal protection technologies of high-enthalpy low-density combustion inflows, and the ground test facility technologies for high-Mach number scramjet engines, respectively. Second, the experimental apparatus related to high-enthalpy shock tunnels and the shock tunnel driving technologies and typical ground and flight experiments of the high-Mach number scramjet engines home and aboard in recent years are introduced. Third, research advances including overall performance analyses of thrusts and thermal protections, the prominent high-enthalpy dissociation and thermochemical nonequilibrium effects in high-Mach-number scramjet engines, and mixing and combustion enhancement technologies in the ultra-high-speed flows are reviewed, so as to assess the feasibilities of high-Mach-number scramjet engines, and to discuss the features of engines’ key technologies. Finally, the summary is presented and several suggestions are proposed for further studies of the higher Mach number scramjet engines.
2022, 54(2): 1-26.   doi: 10.6052/0459-1879-21-547
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STUDY ON NONLINEAR COUPLED VIBRATIONS OF DAMAGED SUSPENDED CABLES WITH SYMMETRY-BREAKING
Zhao Yaobing, Zheng Panpan, Chen Lincong, Kang Houjun
Symmetry is one of the five aesthetic characteristics in the vibration theory, but the symmetry-breaking is also inevitable. This paper takes a common vulnerable structure in engineering-the suspended cable-as an example, and the influences of symmetry-breaking on the planar coupled vibrations have been investigated when the asymmetric damage is occurred. Firstly, the in-plane nonlinear dynamical model of damaged suspended cable has been established, and the nonlinear infinite dimensional differential equations have been obtained by using the Galerkin method. The method of multiple scales has been adopted to obtain the modulation equations of the nonlinear systems’ in-plane coupled vibrations. The resonant curves of undamaged and damaged suspended cables including the first nine modes have been obtained by using the numerical methods, and the stabilities of solutions have also been determined. The largest Lyapunov exponent has been calculated to determine the system’s chaotic motions. The numerical results show that the classical parabolic curves have been often adopted to simulate the suspended cables’ static configurations. However, when the asymmetric damage occurs, the piecewise functions should be used to accurately describe the damaged cables’ static configurations. The symmetry-breaking causes crossover points between two natural frequencies of suspended cables to turn into veering points, and the symmetric/anti-symmetric mode shapes before damage are changed into the asymmetric ones after damaged. The nonlinear interaction coefficients are changed significantly, resulting in significant changes in internal resonant responses. When the excitation is directly applied to the higher-order modes, the single-mode solutions and internal resonant ones are obvious in the undamaged system, while the damaged system does not present the obvious single-mode solutions. The bifurcations and chaos of the damaged system are also changed obviously, and some chaotic motions around the period-doubling bifurcation are observed as to the damaged system.
2022, 54(2): 1-11.   doi: 10.6052/0459-1879-21-542
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MOMENTUM DECOMPOSITION AND ENERGY TRANSFER CHARACTERISTICS OF OPEN CAVITY FLOW
Han Shuaibin, Luo Yong, Li Hu, Wu Conghai, Zhang Shuhai
Cavity structure is extensively employed in the aerospace vehicle components and ground vehicles. The complex characteristics of the flow and acoustic fields is one of the key problems that must be considered in the design of the associated practical engineering. In the cavity flow, the hydro-acoustic interaction plays an important role in the self-sustained oscillation. Accurate identification and decomposition of the hydrodynamic and acoustic mode is the key to improving the understanding of the hydro-acoustic interaction and the associated energy transfer mechanism. In this paper, the two-dimensional Navier-Stokes equation is directly solved to conduct numerical simulation of open cavity flow with inflow Mach number of 0.8 to obtain the high-order accuracy unsteady flow field. Adopting P. E. Doak’s momentum potential theory, the momentum of the flow is decomposed into three parts of the hydrodynamic vortical component, the hydrodynamic entropic component and the acoustic component. The physical properties and the associated energy transfer characteristics of each component are analyzed. The results show that the hydrodynamic vortical and entropic components exist only in the near field, which are convected downstream with the main flow at the speed of shear layer convection. The spatial distribution of the vortical and entropic components are concentrated in the shear layer and resembles each other. The hydrodynamic energy carried by the vortical component is transported from the inside of the shear layer to the outside of the shear layer and to the rear-end of the cavity while the energy carried by the entropic component is continuously transported to the shear layer and then dissipated there. The acoustic component exists in both the near and far field, and the spatial distribution of the acoustic component exhibits a classical compression-divergence pattern. The acoustic energy is radiated from the rear-end of the cavity and propagates to the upstream and the far field at the speed of sound.
2022, 54(2): 1-10.   doi: 10.6052/0459-1879-21-569
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Numerical investigation on the water-entry cavity feature and flow structure of a spinning sphere based on large-eddy simulation
Yan Chenyi, Chen Ying
The water-entry process of spinning sphere has great significance to the research of the up-to-date load reduction method of water-entry based on pre-launched object. In the present work, large-eddy simulation method is used together with the homogeneous multiphase flow model and VOF algorithm of interface capturing, to simulate the water-entry free motion of a fast-spinning sphere with hydrophobic coating at low Froude number, thus to investigate the water-entry cavity evolution, the flow structure and the hydrodynamic features. The free motion of the sphere is achieved through the dynamic mesh and sliding mesh techniques. The reliability and accuracy of the numerical simulation results are validated by comparison with previously published experimental results with good agreement on the transient cavity shape and the motion of the sphere. The spinning motion induces a lift force on the sphere and the trajectory of the sphere has significant curvature along its descent. A persistent wedge of fluid is emerged across the center of the cavity due to the fluid along the surface dragged by the sphere. The velocity and spin rate were normalized with the impact velocity and spin rate to analyze the numerical results. It shows that the spin rate has significant influence on the cavity evolution and hydrodynamic characteristics. Both of those cavity shapes have asymmetrical splash curtain and collapse asymmetrically. As spin rate increases, the horizontal velocity and the maximum lift force increase, while the maximum lift force is also limited by the impact velocity. The spin rate increase also leads to a stronger wedge of fluid forming. As a result, the pinch-off pressure maximum decreases and less vortex structures are observed. And also, the spin rate increase leads to lower side pressure during the initial impact phase. However, the vertical dynamic characteristics of spheres, like vertical velocity, acceleration and immersion depth of pinch-off, are less affected by the spin rate. Moreover, the sphere spin rate is less affected by the impact spin rate increase before cavity pinch-off.
2022, 54(3): 1-14.   doi: 10.6052/0459-1879-21-634
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5/6 DOFS CB SHELL ELEMENTS BASED ON THE LOCAL FRAME OF SE(3) GROUP
Zhang Teng, Liu Cheng, Zhang Zhijuan, Liu Shaokui
The modeling method based on the local frame of Lie group (LFLG) for flexible multibody dynamics can naturally eliminate the geometric nonlinearity of the overall rigid motion, so that the generalized internal forces and inertial forces as well as their Jacobian matrices are invariant under the arbitrary rigid body motion. In this paper, a novel 5 Dofs CB shell element based on the LFLG is proposed by integrating the idea of the LFLG and the continuum-based (CB) shell theory. Compared with the geometrically exact shell element based on the LFLG, the proposed shell element greatly simplifies the complexity caused by the interpolation, and the discretized strain tensors naturally satisfy the objectivity. At the same time, the finite element discretization and variational operations are commutative, which further simplifies the computation of the generalized internal forces and their Jacobian matrices. To deal with the composite structure conveniently, the relationship between the mid-surface motion and the drilling Dofs is established by the polar decomposition of the mid-surface deformation gradient tensor on the basis of the 5 Dofs CB shell element. Then, a 6 Dofs CB shell element based on the LFLG is proposed. To improve the convergence accuracy of the proposed elements, the two-field Hellinger–Reissner variational principle and the assumed natural strain (ANS) method are used to alleviate the in-plane and transverse shear locking, respectively. Several static examples are presented to verify the convergence accuracy of the 6 Dofs CB shell element. A dynamic example is presented to demonstrate that the 6 Dofs CB shell element can eliminate the geometric nonlinearity of the overall rigid motion.
2022, 54(3): 1-16.   doi: 10.6052/0459-1879-21-584
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SERVICE LIFE EVALUATION OF TRACTION MOTOR BEARINGS IN COMPLICATED VIBRATION ENVIRONMENT OF A LOCOMOTIVE
Liu Yuqing, Chen Zaigang, Ge Xin, Wang Kaiyun
Traction motor is the power source of the railway locomotive, therefore, the stability and reliability of the locomotive transmission system are directly affected by the service lives of its key components (e.g., the support bearings, etc). For the heavy haul locomotive, the traditional evaluation methods are mainly based on the fixed load conditions, therefore, it is difficult to accurately evaluate the service lives of motor bearings under complex external excitations such as track random irregularities. Based on the vehicle-track coupling dynamics, a locomotive-track coupled dynamics model with traction power transmission system considering the specific structures of the traction motor and rolling bearing is established. In addition, the effect of the impact wheel-rail interaction and gear engagement is considered in this study. Besides, the service lives of traction motor bearings in the complex vibration environment of a locomotive are assessed based on the linear damage accumulation criterion and ISO 281 standard. Results indicate that the vertical wheel-rail interactive force, gear meshing force, the centrifugal force of rotor, and unbalanced magnetic pull increase obviously under the external excitation induced by the track random irregularity. In the complex vibration environment of the locomotive, the interactions between the roller and race in motor bearings are intensified, and the corresponding fatigue lives of the driving end and non-driving end motor bearings are shortened. Furthermore, with the continuous deterioration of the line state and the improvement of the locomotive running speed, the predicted life mileages of the motor bearings decrease in the increasingly harsh service environment. Because of the large external dynamic loads, the service life of the driving end bearing is shorter than that of the non-driving end one. This evaluation method proposed in this study can provide a theoretical guidance for the design, selection, and service life prediction of motor bearings used in the locomotive.
2022, 54(3): 1-10.   doi: 10.6052/0459-1879-21-545
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RESEARCH PROGRESS OF ADAPTIVE CONTROL METHODS FOR COMPRESSOR FLOW STABILITY
Xu Dengke, Dong Xu, Xu Ruize, Li Jia, Sun Dakun, Sun Xiaofeng
Adaptive control of compressor flow stability is a key technology of intelligent aeroengine in the future. Basic research needs to answer three concerns: How to describe the system stability? How to change the system stability? How to monitor the system stability? Therefore, our team has carried out systematic and in-depth research work in three aspects: general theory of compressor flow stability, stability margin enhancement method based on wall impedance boundary and real-time stall warning technology. 1) The developed general theory of flow instability in turbomachinery not only can consider the flow non-uniformity and blade geometry, but also has high calculation efficiency and great prediction accuracy, which provides a reliable evaluation tool for the integrated design of compressor aerodynamics and stability. 2) The developed SPS (Stall Precursor-Suppressed) casing treatment and foam metal casing treatment based on wall impedance boundary control strategy have made substantial progress in enhancing stability margin and reducing noise while maintaining the aerodynamic performance of the compressor system. Equivalent distributed source method is employed to establish the stall inception prediction model considering the effect of casing, which is able to make sensitivity analysis on crucial structural parameters of SPS casing treatment and foam metal casing treatment so as to provide the clear theoretical design criterion. The experimental results show that SPS casing treatment achieves the purpose of stability enhancement by restraining the nonlinear evolution of stall precursor wave, while maintaining the pressure ratio and efficiency characteristics of the compressor; Foam metal casing treatment has favorable engineering application prospects for its double effects of improving stability and reducing noise. 3) The developed real-time stall warning approach based on aeroacoustic principle increases the stall warning time to more than seconds, and can monitor the system stability online. Combining the above theoretical prediction method, stability enhancement technology and real-time stall warning approach, the closed-loop feedback adaptive control method is developed, which provides an adaptive stability control technology for the future intelligent aeroengine.
 doi: 10.6052/0459-1879-21-560
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A REVIEW OF THE FOURTH NATIONAL SYMPOSIUM ON BIOMECHANICS FOR YOUNG SCHOLARS
Wu Yu, Li Dechang, Ji Baohua
This review briefly introduces the Fourth National Symposium on Biomechanics for Young Scholars. It summarizes the scientific presentations delivered by the invited experts and young scholars.
 doi: 10.6052/0459-1879-21-012
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REVIEW OF NEURAL NETWORK-BASED METHODS FOR SOLVING PARTIAL DIFFERENTIAL EQUATIONS
Zha Wenshu, Li Daolun, Shen Luhang, Zhang Wen, Liu Xuliang
Neural networks are widely used as a powerful information processing tool in the fields of computer vision, biomedicine, and oil-gas engineering, triggering technological changes. Due to the powerful learning ability, deep learning networks can not only discover physical laws but also solve partial differential equations (PDEs). In recent years, PDE solving based on deep learning has been a new research hotspot. Following the terms of traditional PDE analytical solution, this paper calls the method of solving PDE by neural network as PDE intelligent solution or PDE neural-network solution. This paper briefly introduces the development history of PDE intelligent solution, and then discusses the development of recovering unknown PDEs and solving known PDEs. The main focus of this paper is on a neural network solution method for a known PDE. It is divided into three categories according to the way of constructing loss functions. The first is data-driven method, which mainly learns PDEs from partially known data and can be applied to recovering physical equations, discovering unknown equations, parameter inversion, etc. The second is physical-constraint method, i.e., data-driven supplemented by physical constraints, which is manifested by adding physical laws such as governing equation to the loss function, thus reducing the network's reliance on labeled data and improving the generalization ability and application value. The third is physics-driven method (purely physical constraints), which solves PDEs by physical laws without any labeled data. However, such methods are currently only applied to solve simple PDEs and still need to be improved for complex physics. This paper introduces the research progress of intelligent solution of PDEs from these three aspects, involving various network structures such as fully-connected neural networks, convolutional neural networks, recurrent neural networks, etc. Finally, we summarize the research progress of PDE intelligent solutions, and outline the corresponding application scenarios and future research outlook.
 doi: 10.6052/0459-1879-21-617
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Reactionless terminal sliding mode control of space robot with joint dead-zone
Zhang Zhihao, Yu Xiaoyan
As the present Reaction Null Space planning for the incomplete kinematic properties of the space manipulator during the general operation involvesn either the impact of joint dead-zones on the system nor the relationship between the manipulator and the target to be grasped, it can not ensure the effectiveness of the tracking control in the presence of joint dead-zone. In this paper, the study of Reaction Null Space planning and control in the final period before intercepting a target of a free-floating three-link space manipulator with joint dead-zone is focused. First, the dynamic model of a free-floating three-link space manipulator with joint dead-zone is established by the second Lagrange equation, in which the position and attitude of the carrier are uncontrolled. Then, the Reaction Null Space mathematical model of the free-floating three-link space manipulator with joint dead-zone is derived, and the vector norm constraint algorithm of the Reaction Null Space is studied. Furthermore, a nonsingular fast terminal sliding mode control algorithm with anti-interference and high convergence is proposed, in which it combines the double power reaching rate of variable coefficient with the nonsingular fast terminal sliding mode surface to improve the convergence speed and interference immunity. The dead-zone of the joint may reduce the control accuracy of the space robot system. In order to eliminate the influence of the free-floating three-link space manipulator’s joint dead-zone, an adaptive dead-zone compensator is designed. This compensator can approach the upper bound of dead-zone characteristics by self-adaptive control to eliminate the effect of the joint dead-zone on the system and to ensure the effectiveness of the tracking control. Finally, based on the Lyapunov function method the stability of the system is proved, and numerical simulation is carried out. The simulation results show the desired reactionless trajectories are tracked with the base’s attitude reactionless and the effectiveness of the proposed planning and control algorithm is demonstrated.
 doi: 10.6052/0459-1879-21-494
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DILATANCY ANALYSIS OF GRANULAR MATERIALS BASED ON MESOSCOPIC TOPOLOGICAL EVOLUTIONS
Liu Jiaying, Zhou Wei, Ji Xiang, Wei Gang, Yuan Siying, Li Xinjun
Dilatancy is one of the most important characteristics for frictional granular materials, especially for geo materials. It is widely accepted that the mechanism of dilatancy could be related to the evolution of the internal topological structure within the granular system. Based on meso-structural data of granular assemblies, features of the internal topological structure evolution in the granular system can be captured, which could further help to correlate the mesoscopic topological evolution and the macroscopic deformation properties including dilatancy. In this paper, the discrete element method (DEM) was used to conduct biaxial tests on dense, medium-dense and loose frictional granular materials, respectively. According to those DEM data from macroscopic to microscopic levels, the topological mechanism for dilatancy of granular materials are investigated in terms of network parameters (e.g., coordination number and clustering coefficient) and deformation features of 3 types of mesoscopic structures induced by topological exchanges. The results show that the significant strain softening and dilatancy occur for dense granular samples under biaxial loading, which is related to the topological and geometric changes of mesoscopic structures. The medium dense sample also exhibits dilatancy features but the degree is less evident, and the loose sample only shows contractancy and strain hardening during the shearing process. The contact network could be tessellated to force loop structures with the polygon shapes, and further classified into new, lost and constant categories by considering the topological exchanges. The anisotropy and composition evolutions of three groups of force loop structures are different, and loops with larger size could exhibit higher geometrical anisotropy. Under deviatoric loads, the new loop structures are easily related to higher dilatancy, and the dilatancy mechanism of the overall granular system could be influenced by the comprehensive effects of the topological evolutions of new meso structures and geometrical evolutions of constant meso structures.
 doi: 10.6052/0459-1879-21-521
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STUDY ON DYNAMICS OF PLANETARY TRANSMISSION GEAR CONSIDERING WEAR AND DYNAMICS COUPLING
Ning Zhiyuan, Bai Zhengfeng, Jiang Xin, Wang Siyu
The planetary gear wear leads to the nonlinear increase of gear tooth clearance, decrease of the transmission accuracy, and increase of the tooth surface impact force, which will cause the aggravation of the vibration of the gear transmission system. Therefore, it is necessary to analyze the tooth surface wear and dynamic characteristics of planetary gears. In this paper, the nonlinear dynamic coupling calculation model of gear nonlinear wear and gear backlash is established and the gear wear characteristics of the planetary transmission is investigated. Firstly, the nonlinear dynamic model of gear meshing is established. And then, the nonlinear meshing force of gear motion is obtained. Secondly, the wear distribution law of gear tooth surface is presented by combining the nonlinear meshing force with the wear model of gear tooth surface. Further, the tooth surface is reconstructed according to the tooth clearance after wear, and the dynamics model of the gear is updated. Finally, the trend of dynamic meshing force and wear characteristics of planetary gear transmission can be obtained. The gear tooth vibration responses of the gear transmission system are presented. The numerical calculation results show that the increases of the planetary gear wear mainly affect the gear force in the alternating single-double tooth meshing. Moreover, the sun-planetary meshing tooth is more sensitive to wear, and the meshing condition of the tooth surface deteriorates greatly, which is the main reason causing the deterioration of planetary gear transmission. The presented work provides a theoretical basis for the working performance evaluation and reliability prediction of planetary gear transmission system.
 doi: 10.6052/0459-1879-21-554
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Numerical study on Water Entry Process of Supercavitating Projectile by Considering Bidirectional Fluid Structure Interaction effect
Supercavitating projectiles travel underwater at high speed and long distances through the supercavitation drag reduction technology, which is an effective means to counter close-range underwater threats. In order to expand the defense range and increase the lethality, the supercavitating projectile has a high launch speed. The high-speed supercavitating projectile is subjected to a great impact load during water entry process, and a significant structural deformation occurs on the projectile. There is an interaction between the structural deformation and the flow field. Resultantly, the regular simulation research method based on the rigid body assumption is no longer applicable. To study the structural deformation of the high-speed supercavitating projectile and its influence on the hydrodynamic characteristics, a bidirectional fluid-structurer interaction simulation model of the high-speed projectile is established by coupling the fluid dynamics solver and the structural dynamics solver. The accuracy of the numerical method to calculate the supercavitation flow field and the fluid structure interaction are validated by comparing with the published results. Numerical simulation investigations on the supercavitation flow field and the structural deformation characteristics of the high-speed projectile during water entry at different initial angles of attack are carried out with the bidirectional fluid-structure interaction method. By comparing the calculation results of the fluid-structure interaction model and the rigid body model, the influence of structural bending deformation of the supercavitating projectile on its hydrodynamic load is obtained. Research results show that the fluid-structure interaction effect has a significant influence on the supercavity and hydrodynamic load. When considering the fluid-structure interaction effect, there is positive feedback between the hydrodynamic load and the bending deformation of the supercavitating projectiles; the stress, strain and the hydrodynamic load of high-speed supercavitating projectiles increase significantly with the increase of the initial angle of attack. The structure of the projectile is safe when the initial velocity is 1400m/s and the initial angle of attack is below 2°.
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Research on Intelligent Identification Algorithms for Short-term Aerodynamics of Hypersonic Wind Tunnels
Wang Qinchao, Li Shichao, Gao Hongli, Ma Guilin, Wu Guang, Duan Zhiqin
Pulse combustion wind tunnel force measurement is an important step in the research and development process of hypersonic aircraft, and with the development of hypersonic aircraft technology, large-scale and heavy-load aircraft test models has become the trend of hypersonic pulse combustion wind force test. During the effective test time of several hundred milliseconds, Large-scale force measurement system stiffness weakened and other issues will seriously lead to poor aerodynamic identification accuracy. The large-scale measurement model poses a challenge to the accurate aerodynamic identification of the short-term pulse combustion wind tunnel. To solve this problem, A new intelligent aerodynamic identification algorithm based on traditional signal processing combined with deep learning is presented in this paper. The algorithm framework is mainly divided into two stages for signal processing: (1) signal decomposition (2) data training. In the signal decomposition stage, the original data is decomposed into different modal sub-signals through variational modal decomposition(VMD). In the training stage, the effective features in the remaining datasets containing characteristic sub-signals are extracted by deep learning model, and the real aerodynamic signals are obtained. In addition, in order to enhance the robustness and applicability of the algorithm, different optimization methods are used to optimize the hyperparameters in the algorithm at different stages of the algorithm framework to obtain the optimal parameter combination. This algorithm model has obtained relatively ideal results in terms of aerodynamic recognition accuracy and anti-interference. Finally, the algorithm is validated on a suspended force test bench, and the results show that the algorithm model can effectively identify and filter out the interference components that are difficult to eliminate by the traditional methods brought by the large-scale model. Finally, the algorithm is successfully applied to the large scale model force measurement system of pulse combustion wind tunnel. Accuracy of aerodynamic identification of large-scale model force measurement system is effectively improved.
 doi: 10.6052/0459-1879-21-484
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REVIEW OF MATERIALS AND STRUCTURES IN SOFT ROBOTICS
Li Tiefeng, Li Guorui, Liang Yiming, Cheng Tingyu, Yang Xuxu, Huang Zhilong
2016, 48(4): 756-766.   doi: 10.6052/0459-1879-16-159
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摘要:
软体机器人是一类新型机器人,具有结构柔软度高,环境适应性好,亲和性强,功能多样等特点,有着十分广阔的研究和应用前景. 智能材料在软体机器人结构设计及实际应用中扮演了重要的角色,其特殊的驱动机制极大拓展了软体机器人的功能. 介绍了软体机器人的发展和研究现状,按其应用场合及功能总结了几种典型的软体机器人. 从仿生机理的角度,介绍了蠕虫、弯曲爬行虫、鱼类游动等几类仿生运动机理以及其相应的软体机器人. 还按不同驱动类型将软体机器人归纳为气动、形状记忆合金、离子交换聚合物金属复合材料、介电高弹体、响应水凝胶、化学燃烧驱动等类型. 介绍了软体机器人的制作方法与工艺,分析了目前软体机器人研究的主要挑战,提出对未来研究的展望.
ESSENTIAL ISSUES AND THEIR RESEARCH PROGRESS IN TUNNEL AND UNDERGROUND ENGINEERING
Zhang Dingli
2017, 49(1): 3-21.   doi: 10.6052/0459-1879-16-348
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摘要:
作为隧道及地下工程学科的3个基本问题,隧道围岩稳定性、支护——围岩相互作用和结构体系的动力响应一直都是本学科研究的核心问题,本文围绕上述问题重点分析了隧道围岩力学特性及其载荷效应,建立了深浅层围岩结构力学模型,并通过分析深层围岩中结构层稳定性得到了围岩特性曲线的解析公式,提出了围岩结构性特点及载荷效应的计算方法;通过对隧道支护与围岩作用关系的分析,将支护与围岩的动态作用分为4个阶段:即自由变形、超前支护、初期支护和二次衬砌阶段.由此提出了动态作用全过程的描述方法;基于广义与狭义载荷的理念,提出隧道支护具有调动和协助围岩承载基本功能的观点,明确了两种功能的实现方式,即通过围岩加固、超前加固及锚杆支护实现调动围岩承载,通过支护结构协助围岩承载;针对复杂的隧道支护结构体系,提出了多目标、分阶段协同作用动态优化概念,可使各种支护结构的施作实现时间和空间上的协调,提高可靠性;针对极不稳定的复杂隧道围岩的安全性特点,建立了3种模式的安全事故机理模型,基于工程响应特点提出了安全性分级的新理念,并形成了分级指标体系和分级方法;针对水下隧道及富水围岩条件,建立了3种模式的隧道突涌水机理模型,提出了基于围岩变形控制的安全性控制理论和方法.最后,对本学科发展的热点和核心问题进行了分析和展望.
MECHANICAL MECHANISM AND DEVELOPMENT TREND OF WATER-INRUSH DISASTERS IN KARST TUNNELS
Li Shucai, Wang Kang, Li Liping, Zhou Zongqing, Shi Shaoshuai, Liu Shang
2017, 49(1): 22-30.   doi: 10.6052/0459-1879-16-345
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摘要:
岩溶隧道突水灾害具有“强突发、高水压、大流量、多类型”等显著特点,其灾变演化过程复杂、动力失稳规律尚不清楚.本文系统提出了不同类型突水灾害的发生条件、判据及安全厚度分析方法,剖析了近期研究进展及发展趋势.首先,给出了隧道突水灾害的概念、类型及构成三要素,从系统论角度分析了隧道突水的灾变过程;其次,总结了隧道突水灾害致灾机理、力学模型、失稳判据和最小安全厚度等方面的近期研究成果;最后,从构成三要素角度分析了隧道突水致灾机理方面的现状与问题,并提出了今后的发展趋势与方向,主要有:(1)灾害源固液气三相置换机制与释能模式,(2)突水通道多相物质迁移与流态演化规律,(3)隔水阻泥结构动力灾变演化机理,(4)突水通道破裂形成过程的模拟分析方法等.
SURVEY ON UNCALIBRATED ROBOT VISUAL SERVOING CONTROL
Tao Bo, Gong Zeyu, Ding Han
2016, 48(4): 767-783.   doi: 10.6052/0459-1879-16-161
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摘要:
视觉伺服控制是机器人系统重要的控制手段. 相比传统的在标定条件下使用的视觉伺服系统,无标定视觉伺服系统具有更高的灵活性与适应性,是机器人伺服控制系统未来重要的发展方向和研究热点. 本文从目标函数选择、控制器设计、运动轨迹规划三方面综述了无标定视觉伺服控制系统近年来的主要研究进展. 首先根据目标函数的形式,分析了基于位置的视觉伺服、基于图像的视觉伺服以及混合视觉伺服各自的特点与应用;在控制器设计方面,根据是否在设计过程中考虑机器人的非线性动力学特性,分别介绍了考虑机器人运动学与考虑机器人动力学的无标定视觉伺服控制器的设计,重点突出了雅克比矩阵的构造与估计方法;针对无标定视觉伺服系统运动轨迹可能存在的问题,从空间轨迹优化与障碍规避的角度,阐述了已有的可行解决方案. 最后,基于当前的研究进展展望了无标定视觉伺服的未来研究方向.
A CRITICAL REVIEW ON CRITERIA OF FRACTURE MECHANICS
Ji Xing
2016, 48(4): 741-753.   doi: 10.6052/0459-1879-16-069
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摘要:
从Inglis 和Griffith 的著名论文到Irwin 和Rice 等的奠基性贡献,对断裂力学中的线弹性断裂力学的K判据,界面断裂力学的G判据,和弹塑性断裂力学的J 判据作了扼要的综述. 介绍了在界面断裂力学G判据的基础上提出的界面断裂力学的K判据,以说明断裂力学的判据存在改进的可能性. 在综述中归纳出断裂力学判据中目前还没有较好解决的几个问题. 在总结以往断裂力学研究经验的基础上,指出裂纹端应力奇异性的源是对断裂力学判据存在的问题作进一步研究的切入点. 探讨了裂纹端应变间断的奇点是裂纹端应力奇异性的源的问题,从而对裂纹端应力强度因子的物理意义进行了讨论. 最后,阐述了进行可靠的裂纹端应力场的弹塑性分析是改进弹塑性断裂力学判据的关键,而进行可靠的裂纹端应力场的弹塑性分析的前提是要通过裂纹端应力奇异性的源的研究来获得作用在裂纹端的造成裂纹端应变间断的有限值应力.
RESEARCH PROGRESS IN AUXETIC MATERIALS AND STRUCTURES
Xin Ren, Xiangyu Zhang, Yimin Xie
2019, 51(3): 656-689.   doi: 10.6052/0459-1879-18-381
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摘要:
负泊松比材料和结构具有特殊的力学性能,在单轴压力(拉力)作用下发生横向收缩(膨胀).其在抗剪承载力、抗断裂性、能量吸收和压陷阻力等方面比传统材料更有优势,因而负泊松比材料在医疗设备、传感器、防护设备、航空航海及国防工程等领域有广泛的应用前景,但目前负泊松比材料的应用与普及仍面临一些挑战.本文广泛讨论了国内外关于负泊松比材料的研究成果并介绍了负泊松比材料的最新进展,将负泊松比材料大体概括为以下4类:天然负泊松比材料、胞状负泊松比材料、金属负泊松比材料、多重和复合负泊松比材料.主要介绍了各种负泊松比材料的内部结构、负泊松比机理、力学性能以及在各行各业的新发明、新应用.针对目前负泊松比材料研究理论和实验成果多,而实际应用仍然较少的情况,指出了负泊松比材料的缺点及其推广所面临的挑战.目前负泊松比材料面临的主要问题是制造成本高、孔隙率大而承载力不足以及仅适用于小应变情况等.本文针对此情况详细介绍了金属负泊松比材料及其设计和制作的方法,改善负泊松比材料的不足并推广其应用.
REVIEW OF RESEARCH PROGRESSES OF THE QUANTIFYING JOINT ROUGHNESS COEFFICIENT
Chen Shijiang, Zhu Wancheng, Wang Chuangye, Zhang Fei
2017, 49(2): 239-256.   doi: 10.6052/0459-1879-16-255
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摘要:
1978年,Barton提出的节理粗糙度系数(joint roughness coefficient,JRC)被国际岩石力学学会作为评估节理粗糙度的标准方法.然而该方法存在人为估值的主观性缺陷.就此,国内外学者围绕岩体结构面粗糙度定量化表征开展了大量的研究工作.首先,从二维节理轮廓线到三维岩体结构面,系统地阐述了其粗糙度定量化表征方法研究进展,并总结了各方法参数与JRC的关系;评价了各表征参数的本质特性及其适用性;指出了各方法参数获取过程中存在的问题,主要有:采样间隔的影响,三角形单元划分的影响,如何确定综合参数法中各参数的权重;针对这些问题,给出了笔者的一些想法、建议.与此同时,对结构面粗糙度表征的两个热点问题,即各向异性和尺寸效应的研究也进行了详细总结分析.最后,笔者认为:(1)分形维数因是描述自然界复杂几何体的一种简洁有力的工具,其仍是结构面粗糙度定量描述的有效方法;(2)3D打印技术的应用,有望在开展结构面各向异性、尺寸效应研究方面取得突破性进展.
REVIEW ON NONLINEAR VIBRATION AND MODELING OF LARGE SPAN CABLE-STAYED BRIDGE
Kang Houjun, Guo Tieding, Zhao Yueyu
2016, 48(3): 519-535.   doi: 10.6052/0459-1879-15-436
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摘要:
斜拉桥的非线性动力学问题一直都是力学、结构和桥梁领域的研究热点.随着新材料(如碳纤维增强聚合物索)和新施工工艺的发展,斜拉桥的跨越能力不断得到提高,从而在桥梁建设中更具有竞争力.然而,斜拉桥跨度的增大和新材料的应用使结构变得更轻和更柔,使结构的非线性振动问题比以往更为突出,可能危及桥梁安全.基于课题组近年来对斜拉桥非线性动力学的研究,围绕大跨度斜拉桥的非线性建模理论及动力学问题,较为详细地评述近十年来国内外的研究进展情况.主要从斜拉索非线性动力学模型、梁的非线性动力学模型、索-梁组合结构的非线性动力学模型、斜拉桥整体非线性动力学模型与理论、以及斜拉桥的非线性振动实验等几个方面对斜拉桥非线性建模方法、力学模型、数学模型、求解方法及相应研究成果进行评述和讨论.研究结果表明,斜拉桥由于多柔性索和大跨度梁的耦合问题,以及环境载荷的复杂性,导致其具有丰富的非线性动力学行为.同时由于高维非线性系统求解方法的欠缺,整体斜拉桥非线性动力学行为又相当复杂,深入研究面临很大困难.最后,基于未来斜拉桥的发展趋势和可能面临的突出问题,对斜拉桥非线性振动问题今后的发展方向进行了探讨和展望.
SOME RECENT PROGRESSES IN NONLINEAR PASSIVE ISOLATIONS OF VIBRATIONS
Lu Zeqi, Chen Liqun
2017, 49(3): 550-564.   doi: 10.6052/0459-1879-17-064
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摘要:
工程中航空航天、船舶与海洋结构物及其上装备和精密仪器易受极端环境干扰和破坏,使得非线性隔振理论在近十年来迅猛发展;针对日益严峻的隔振和抗冲击等要求,工程师和科学家们已发展出各种不同的非线性隔振系统,包括主动、半主动、被动和复合隔振。利用非线性改善的被动隔振兼具传统被动隔振的鲁棒性和主动隔振的高效性成为振动控制领域的先进技术。本文主要综述了非线性隔振理论和应用的近十年进展,包括非线性隔振设计、建模、分析、仿真和实验。在隔振系统的构建中,既考虑了刚度非线性又考虑了阻尼非线性;动力学响应的研究中,既有确定性分析又有随机分析。首先提出了适用于非线性隔振系统改进的评价方式;其次综述了高静态低动态刚度隔振及其加强形式非线性阻尼加强和双层非线性隔振,混沌反控制技术、内共振影响、非线性能量阱应用等振动机制利用型隔振和非线性隔振功能材料。最后,对非线性隔振研究发展的热点和关键性问题进行了分析和展望。
ADVANCES IN DYNAMICS AND VIBRATION CONTROL OF LARGE-SCALE FLEXIBLE SPACECRAFT
Cao Dengqing, Bai Kunchao, Ding Hu, Zhou Xubin, Pan Zhongwen, Chen Liqun, Zhan Shige
2019, 51(1): 1-13.   doi: 10.6052/0459-1879-18-054
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摘要:
随着航天重大工程的逐步实施,航天器正朝着超高速、超大尺度、多功能的方向发展,其面临的发射和运行环境也更加恶劣.航天器发射过程中的振动及其主/被动控制、在轨运行中大型柔性航天器动力学建模与动态响应分析、结构振动与飞行器姿态的混合控制等问题越来越复杂且难于处理;航天器结构的大型化和柔性化(如大阵面天线和太阳翼等)也对其地面试验和半实物仿真提出了挑战.本文着重介绍大型柔性航天器涉及到的动力学与振动控制问题,包括航天器发射过程中的整星隔振,大型柔性结构动力学建模与振动响应分析,大型柔性航天器的结构振动与姿轨控耦合动力学及其混合控制等.提炼出航天动力学与控制领域中亟待解决的若干基础科学问题,包括:多刚柔体系统动力学建模与模型降阶(涉及大变形柔性体动力学建模、多求解器合作仿真、模型降阶、组合结构动力学建模的解析方法等);复杂结构状态空间模型构建方法与能控性(涉及状态空间模型构建的理论与实验方法、复杂结构振动控制系统的能观性与能控性等);航天器姿态运动与大型柔性结构振动的混合控制律设计(涉及姿态机动与结构振动的鲁棒混合控制、执行机构与压电控制器的协同控制等).
A MODIFIED KUBOTA CAVITATION MODEL FOR COMPUTATIONS OF CRYOGENIC CAVITATING FLOWS
Shi Suguo, Wang Guoyu
2012, 44(2): 269-277.   doi: 10.6052/0459-1879-2012-2-20120210
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Abstract:
In order to predict the cavitating flow characteristics in cryogenic fluids more exactly, a revised cavitation model considering the thermal effect with modified the evaporation and condensation source terms is established, which is based on Kubota cavitation model. The computations for cavitating flows in liquid nitrogen are conducted around an axisymmetric ogive by employing Kubota cavitation model and the revised cavitation model, respectively. The computational results are compared with the experimental data to evaluate the revised cavitation model. It is found that for the results of the revised cavitation model due to considering the thermal effects, the evaporation becomes smaller and the condensation becomes larger, the cavity length is shorter and the cavity interface becomes more porous compared with the results of original Kubota model. The results of the revised cavitation model are more accordant with the experimental data, and it dictates that the revised cavitation model can describe the process of mass transport more accurately in the cavitation process in cryogenic fluids and it is applicable for computations of cavitating flows in cryogenic fluids flow.
ANALYSIS OF VELOCITY ANNULAR EFFECT OF OSCILLATORY FLOW INSIDE PARALLEL PLATE CHANNEL
Tang Ke, Zhang Yu, Tang Wentao, Jin Tao, Zhang Xuejun
2012, 44(2): 252-258.   doi: 10.6052/0459-1879-2012-2-20120208
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Abstract:
This study focuses on the velocity-annular-effect (VAE) of compressible oscillatory flow inside parallel plate channel. By analyzing the mechanism of VAE, we conclude that VAE, which inevitably occurs in viscous oscillatory pipe flow, is most visible at the phase when the centerline velocity reaches zero. In order to quantitatively evaluate the VAE, coefficient of velocity annular effect (CVAE) was proposed as an index parameter, based on the slope of velocity profile when the centerline velocity reaches zero. Numerical computations with the index parameter CVAE were conducted to analyze the impacts of dimensionless parameters, i.e., Valensi number Va and maximum Reynolds number Remax, on the VAE of oscillatory flow inside parallel plate channel.

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