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Research Review
PROGRESS IN THE RESEARCH OF HYPERSONIC AND HIGH­ENTHALPY BOUNDARY LAYER INSTABILITIES AND TRANSITION
Chen Xianliang, Fu Song
Boundary layer transition from laminar to turbulence is of vital importance to the design of hypersonic vehicles. With continuous expansion of flight speed and altitude domains, the high-temperature gas effects in hypersonic high-enthalpy boundary layers invalidate the calorically perfect gas assumption. They can thus largely influence the flow transition process. Relevant research is multi-interdisciplinary and multi-physics coupling. In recent years, the hypersonic high-enthalpy boundary layer transition has received increasing interest worldwide owing to rapid development of vehicle design. Recent progress is reviewed in this article. Firstly, commonly used high-temperature gas models are introduced, especially the thermochemical non-equilibrium models. Then, the prevailing computational methods for high-enthalpy flows, including the shock-capturing, shock-fitting and boundary layer equation methods are introduced. The progress in experimental techniques for high-enthalpy wind tunnels and flight tests are also summarized. Afterward, the influences of high-temperature effects on the receptivity, modal growth, transient growth and nonlinear interactions in the transition process are reviewed. Here some phenomena has received wide interests that the third mode and the supersonic mode appear at relatively large growth rates in the streamwise instability. Finally, the progress is summarized, and future researches are briefly prospected.
2022, 54(11): 2937-2957.   doi: 10.6052/0459-1879-22-184
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Fluid Mechanics
IMPACT OF A PLANAR SHOCK ONTO SIDE-BY-SIDE DROPLETS: A 3D NUMERICAL STUDY
Wu Runlong, Li Zhujun, Ding Hang
In this paper we investigate the evolution dynamics of side-by-side droplets after being impacted by a planar shock by using a three-dimensional conservative sharp interface method. Our research mainly focuses on the development of wave structures after the shock impact and the asymmetric interface evolution of single droplet induced by the coupling between the side-by-side droplets. Firstly, we analyze the development of the wave system including those inside and outside the channel between the side-by-side droplets. We find that at the early stage of impact, the intersection of reflected shock waves accounts for the formation of new reflected shock waves and Mach rods. This is quite different from the curved wave front formed by the reflected shock wave on the other side of the droplet transversely opposite to the channel. The difference of the flow field on the two sides of the droplet is responsible for the asymmetric interface evolution of the droplet in the middle stage of the droplet-shock interaction. Secondly, we investigate the interface morphology and its evolution in the middle stage of shock impact, especially when the incident shock wave moves to the downstream of and is far away from the droplets, and report the occurrence of new flow phenomena at the downstream outlet of the channel, such as interface coalescence caused by airflow expansion and subsequent interface fragmentation owing to airflow blockage. Finally, the effect of the gap between the side-by-side droplets on the droplet interaction is studied. We find that the gap size has a significant effect on the occurrence of pressure peaks in the channel. Specifically, a smaller gap not only brings higher pressure peak, but also makes the peak appear at an earlier time.
2022, 54(11): 2958-2969.   doi: 10.6052/0459-1879-22-358
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Fluid Mechanics
ACTIVE FLOW CONTROL OF WAVY CYLINDER BASED ON STEADY BLOWING AND SUCTION
Zou Lin, Zuo Hongcheng, Liu Diwei, Wang Jiahui, Xu Jinli
Based on the control of the near wake flow of a wavy cylinder by steady blowing and suction to enhance the vibration of the cylinder, the effects of the forward blowing and backward suction and the forward and backward suction control modes on the lift and drag characteristics, time-average pressure coefficient, circulation, turbulent kinetic energy and flow field mechanism of a wavy cylinder under different blowing and suction conditions at subcritical Reynolds number (Re = 3000) were numerically studied by large eddy simulation. It is found that the fluctuating lift coefficient of wavy cylinder under the control of forward blowing and backward suction and forward and backward suction is significantly increased under different conditions of blowing and suction momentum coefficient, and the maximum increase is as high as 636% and 391% respectively compared with that of uncontrolled cylinder and wavy cylinder. This may be mainly attributed to the shorter recirculation area of wavy cylinder under the control of blowing and suction, the concentration of high-intensity vortices towards the rear of blunt body, and the shorter vortex formation length, The "riblike vortex" formed by the interaction of spanwise vortex and streamwise vortex becomes larger and longer, and the normalized circulation near the wake increases significantly, resulting in the increase of fluctuating lift coefficient, which may lead to stronger vibration of the cylinder; At the same time, both control methods change the pressure distribution on the surface of the wavy cylinder. Because the front end tends to be streamlined due to the blowing at the front stagnation point of the wavy cylinder, the high-pressure area of the wavy cylinder decreases under different blowing and suction momentum coefficients, but the low-pressure area increases due to the suction at the rear stagnation point, while the high-pressure area of the wavy cylinder is basically unchanged and the low-pressure area increases under different blowing and suction momentum coefficients. The research results can provide basic theoretical support for improving the efficiency of distributed wind energy capture structure in low wind speed areas.
2022, 54(11): 2970-2983.   doi: 10.6052/0459-1879-22-212
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Fluid Mechanics
STUDY OF THE TEMPORAL-SPATIAL FLUCTUATIONS AND EMPIRICAL MODEL OF NEAR SPACE ATMOSPHERIC DENSITY
Zeng Dandan, Wan Tian, Li Shuaihui
Atmospheric density is a fundamental parameter for vehicle designing and flight controlling. In recent years, many researchers have discovered that atmospheric densities in the upper mesosphere and lower thermosphere predicted by the empirical model, such as USSA-76 and NRLMSISE-00, are larger than the measured values. On the other hand, vehicle designing is tending to be more detailed, and engineers hope that the empirical models provide densities under variable latitudes, day-night times and seasons. Based on that, the present work analyzesdependences of near-space atmospheric density on latitude, solar local time and date, by using satellite observed data. Emphasizes are put on density fluctuation patterns and amplitudes. The fluctuation patterns caused by latitude and date vary with altitude, and the amplitudes are largest at 78 km and locally smallest at about 22 km and 92 km. The fluctuation amplitude caused by the solar local time increases monotonically with altitude. Based on the temporal-spatialfluctuationlaw, we proposed the temporal-spatial fluctuation modelfor the near-space atmospheric density, which describes the density fluctuations with latitude, local time and date. The present model describes the temporal-spatial fluctuations better than the existed empirical models at variable altitudes. The confidence coefficient of the present model is much better than NRLMSISE-00 under the same error band. The modeling method in this work is reasonable, and the obtained model could be used in near-space vehicle designing.
2022, 54(11): 2984-2993.   doi: 10.6052/0459-1879-22-231
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Fluid Mechanics
FLUID FLOW AND HEAT TRANSFER CHARACTERISTICS IN THE MULTILAYERED-PARALLEL FRACTURED POROUS CHANNEL
Li Qi, Wang Zhaoyu, Hu Pengfei
Based on the Brinkman-extended Darcy model and the local thermal equilibrium model, the fluid flow and heat transfer characteristics in the multilayered-parallel fractured porous channel are studied. The analytical solutions of velocity field, temperature field in each region of multilayered-parallel fractured porous channel, friction coefficient and Nusselt number are obtained. The effects of the fracture number, Darcy number, hollow ratio and the ratio of effective thermal conductivity on heat transfer characteristics are analyzed. The results show that when Darcy number is small, the Darcy velocity in the porous media which does not change with the porous height increases with the increase of the number of fracture layers, and is not affected by the porous layer position in multilayer porous channel with certain number of fractures. Increasing the number of fracture layers weakens the influence of hollow ratio on pressure drop and increases the fluid pressure drop in the channel, but the increase degree gradually decreases. The increase of the ratio of effective thermal conductivity or decrease of the hollow ratio leads to a stepwise temperature distribution in the multilayered fractured porous channel, while the temperature distribution curves in the multilayered fractured channel tend to be consistent when the thermal conductivity ratio is small or the hollow ratio is large. Furthermore, when the ratio of thermal conductivity is small, the heat transfer effect in multilayered fractured porous channel is better than that in single fractured porous channel at any hollow ratio. However, when the ratio of thermal conductivity is large, there is a critical hollow ratio, which makes the heat transfer effect in the channels with different numbers of fracture layers be the same, and increasing the number of fractured layers has little influence on the heat transfer effect in multilayered fractured porous channel.
2022, 54(11): 2994-3009.   doi: 10.6052/0459-1879-22-285
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Fluid Mechanics
A HIGH-EFFICIENCY AND HIGH-RESOLUTION MAPPED WENO SCHEME AND ITS APPLICATIONS IN THE NUMERICAL SIMULATION OF PROBLEMS WITH COMPLEX FLOWS
Zhong Wei, Jia Leiming, Wang Shufei, Tian Zhou
The traditional mapped weighted essentially non-oscillatory (WENO) schemes commonly suffer from the drawback of low-efficiency, since they usually require the mapping processes resulting in extra computational costs. The goal of the present work is to improve the efficiency of the mapped WENO schemes. By designing a set of approximate constant mapping function which is devised using an approximation of the standard signum function, a novel mapped WENO scheme is proposed. The new mapping function is devised to meet the overall criteria for a proper mapping function required in the design of the WENO-PM6 scheme. The WENO-PM6 scheme was presented to overcome the potential loss of accuracy of the well-validated WENO-M scheme in previously published literature. The new proposed mapped WENO scheme is denoted as WENO-ACM. It maintains almost all advantages of the WENO-PM6 scheme, such as low dissipations and high resolutions. However, it decreases the number of mathematical operations remarkably in every mapping process leading to a significant improvement of efficiency. Theoretical analysis indicates that the new scheme can attain the optimal convergence rate of accuracy regardless of critical points. The investigation of approximate dispersion relation (ADR) shows that the spectral properties of the new scheme are significantly improved. A variety of benchmark-test problems, including accuracy tests, standard shock-tube problem, Mach 3 shock-entropy wave interaction, Woodward-Colella interacting blast waves, 2D Riemann problem, double Mach reflection, forward-facing step problem, Rayleigh-Taylor instability and Kelvin-Helmholtz instability are conducted. Compared to the well-established WENO-JS, WENO-M, WENO-PM6 schemes comprehensively, the present scheme exhibits significantly improved high efficiency, very high resolution and sharp discontinuity capturing. Most importantly, the extra computational cost of WENO-ACM compared to WENO-JS is much lower than those of WENO-M and WENO-PM6. Specifically, WENO-ACM can reduce the extra computational cost compared to WENO-JS more than 80% and 90% against WENO-M and WENO-PM6, respectively.
2022, 54(11): 3010-3031.   doi: 10.6052/0459-1879-22-247
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Fluid Mechanics
VORTEX IDENTIFICATION TECHNOLOGY AND ITS APPLICATION IN THE WAKE FIELD OF MARINE PROPELLER
Yang Lin, Zheng Xing
Vortex identification is a very important problem of fluid and flow, in order to find a reasonable method of vortex identification in the wake of marine propeller, this paper studies the theory of six kinds of vortex recognition technology combined with practice, in which analytic solutions of both Burgers vortex and Lamb-Oseen vortex are also used for necessary explanation. The advantages and disadvantages of various vortex identification methods are discussed in detail at the angle of theory and application. The local low-pressure criterion is intuitive, but it is obviously insufficient after considering viscous and unsteady effects. The path line or streamline criterion obviously cannot satisfy Galileo invariance, which will cause confusion in vortex identification. The magnitude of vorticity criterion needs to specify its threshold value, which has certain uncertainty, and can also incorrectly identify vortex sheets that are not vortices. The complex eigenvalue of the velocity gradient tensor will also have an unrecognized region. The second invariant criterion of the velocity gradient tensor and the second eigenvalue criterion of the symmetric tensor can better identify the vortex core, and these two criteria are sometimes equivalent. The numerical simulation of propeller wake is implemented on the open source software OpenFOAM platform. The large eddy model is modeled by a local dynamic equation, which is better than the dynamic Smagorinsky model to a certain extent. The results of numerical experiment show that, for the vortex identification in the marine propeller wake, the second invariant criterion of the velocity gradient tensor is consistent with the second eigenvalue criterion of the symmetric tensor. However, the local minimum pressure criterion, streamline or path line criterion, vorticity magnitude criterion and complex eigenvalue criterion of velocity gradient tensor have some defects, which are not suitable for vortex identification in the wake of marine propeller.
2022, 54(11): 3032-3041.   doi: 10.6052/0459-1879-22-339
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Fluid Mechanics
EXPERIMENTAL STUDY ON EVOLUTION OF WAKE STRUCTURES IN FLOW PAST THE CIRCULAR CYLINDER PLACED NEAR THE WALL
Qiu Xiang, Wu Haodong, Tao Yizhou, Li Jiahua, Zhou Jiankang, Liu Yulu
The experimental measurement of the flow field around the circular cylinder near the wall is carried out by using the Particle Image Velocimetry. The characteristics of the flow regime under different Reynolds numbers (${Re} = {1500} \sim {5540}$) together with three different gap ratios (${G \mathord{\left/ {\vphantom {G D}} \right. } D}{ \;= 0}{.5}$, ${G \mathord{\left/ {\vphantom {G D}} \right. } D}{\; = 1}{.0}$, ${G \mathord{\left/ {\vphantom {G D}} \right. } D}{ \;= 1}{.5}$) are studied. The experiment results shows that for the case of ${G \mathord{\left/ {\vphantom {G D}} \right. } D}{ \;= 0}{.5}$, with the increasing of Reynolds number, the recirculation zone behind the cylinder is gradually symmetrical about the centerline of the cylinder while its size is decreasing, and the size of the separation bubble on the wall also decreases gradually. The experiment reveals that the cylindrical wake and the gap flow perform differently while the Reynolds numbers ${{Re} _t}$ between ${Re} = {3000} \sim {3200}$. When the Reynolds number is smaller than ${{Re} _t}$, a small separation bubble will form on the front wall of the cylinder, which hinders the flow of upstream fluid through the gap and reduces the intensity of the gap flow, and then deviates from the wall. At ${Re} { \;= 1500}$, the vortex shedding frequency increases with the decrease of the gap ratio. And with the decrease of gap ratio, the vortex shedding frequency increases first and then decreases in a small range (${0}{.185} \leqslant St \leqslant {0}{.227}$) for ${Re} \geqslant {3000}$. The Reynolds number has a significant influence on the flow characteristics, especially for the case of small gap ratios. At ${G \mathord{\left/ {\vphantom {G D}} \right. } D}{ \;= 0}{.5}$, the secondary vortex deviates from the wall and moves upward to the position close to the upper wake vortex, and the vortex merging process appears between the upper wake vortex and the secondary vortex for the ${Re} { \;= 1500}$. As the Reynolds number increases to ${Re} { \;= 5540}$, the secondary vortex does not merge with the upper wake vortex, and the secondary vortex directly interacts with the lower wake vortex. At ${G \mathord{\left/ {\vphantom {G D}} \right. } D}{ \;= 1}{.0}$ and ${G \mathord{\left/ {\vphantom {G D}} \right. } D}{ \;= 1}{.5}$, the energy carried by the secondary vortex is decreasing gradually with the increasing of Reynolds number.
2022, 54(11): 3042-3057.   doi: 10.6052/0459-1879-22-403
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A SCALE-INVARIANT HIGH-ORDER WCNS SCHEME
Zhang Zixuan, Dong Yidao, Huang Ziquan, Kong Lingfa, Liu Wei
For numerical simulation of high-speed flows, it requires that small-scale structures are resolved with high-fidelity, and discontinuities are stably captured without spurious oscillation. These two aspects put forward almost contradictory requirements for numerical schemes. The widely used high-order schemes can satisfy the two demands required above to some extent. However, they all have advantages and disadvantages compared to each other and no one can be considered perfect. For example, high-order schemes are prone to generating numerical oscillations near discontinuities when a small-scale problem is discretized, such as the Reynolds-stress model. To solve this deficiency, a simple, effective and robust modification is introduced to the seventh-order weight compact nonlinear scheme (WCNS) by making use of the descaling function to formulate a scale-invariant WCNS scheme. The descaling function is devised using an average of the function values and introduced into the nonlinear weights of the WCNS7-JS/Z/D schemes to eliminate the scale dependency. The design idea of the scale-invariant WCNS scheme is to make weights independent of the scale factor and the sensitivity parameter. In addition, the shock-capturing ability of the new scheme performs well even for small-scale problems. The new schemes can achieve an essentially non-oscillatory approximation of a discontinuous function (ENO-property), a scale-invariant property with an arbitrary scale of a function (Si-property), and an optimal order of accuracy with smooth function regardless of the critical point (Cp-property). We derive the seventh-order D-type weights. The one-dimensional linear advection equation is solved to verify that WCNS schemes can achieve the optimal (seventh) order of accuracy. We test a series of one- and two-dimensional numerical experiments governed by Euler equations to demonstrate that the scale-invariant WCNS schemes perform well in the shock-capturing ability. Overall, the scale-invariant WCNS schemes provide a new method for improving WCNS schemes and solving nonlinear problems.
2023, 55(1): 1-18.   doi: 10.6052/0459-1879-22-399
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RESEARCH ADVANCES ON THE COLLOCATION METHODS BASED ON THE PHYSICAL-INFORMED KERNEL FUNCTIONS
Fu Zhuojia, Li Mingjuan, Xi Qiang, Xu Wenzhi, Liu Qingguo
In the past few decades, although traditional computational methods such as finite element have been successfully used in many scientific and engineering fields, they still face several challenging problems such as expensive computational cost, low computational efficiency, and difficulty in mesh generation in the numerical simulation of wave propagation under infinite domain, large-scale-ratio structures, engineering inverse problems and moving boundary problems. This paper introduces a class of collocation discretization techniques based on physical-informed kernel function to efficiently solve the above-mentioned problems. The key issue in the physical-informed kernel function collocation methods is to construct the related basis functions, which includes the physical information of the considered differential governing equation. Based on these physical-informed kernel functions, these methods do not need/only need a few collocation nodes to discretize the considered differential governing equations, which may effectively improve the computational efficiency. In this paper, several typical physical-informed kernel functions that satisfy common-used homogeneous differential equations, such as the fundamental solutions, the harmonic functions, the radial Trefftz functions and the T-complete functions and so on, are firstly introduced. After that, the ways to construct the physical-informed kernel functions for nonhomogeneous differential equations, inhomogeneous differential equations, unsteady-state differential equations and implicit differential equations are introduced in turn. Then according to the characteristics of the considered problems, the global collocation scheme or the localized collocation scheme is selected to establish the corresponding physical-informed kernel function collocation method. Finally, four typical examples are given to verify the effectiveness of the physical-informed kernel function collocation methods proposed in this paper.
2022, 54(12): 3352-3365.   doi: 10.6052/0459-1879-22-485
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RESEARCH ON CO2 MICROBUBBLE DISSOLUTION KINETICS AND ENHANCED OIL RECOVERY MECHANISMS
Jia Haowei, Yu Haiyang, Xie Feifan, Yuan Zhou, Xu Ke, Wang Yang
CO2 microbubble is a promising enhanced oil recovery and carbon sequestration method. In this paper, based on microbubbles porous media generation method, a self-designed microbubble generator featuring the porous ceramic membrane was developed. The morphology and dissolution characteristics of CO2 microbubbles at different initial CO2 concentrations were experimentally investigated. The results showed that the CO2 microbubbles prepared at 10 MPa were distributed in the range of 10 ~ 70 μm with an average bubble diameter of 34.43 μm. At 15 MPa, CO2 microbubbles with smaller diameter were generated, with an average bubble radius of 25.03 μm. However, under high salinity condition, microbubbles with average diameter of 277.17 μm were produced. The brine salinity decreased microbubbles stability, which leading to bigger bubble. In a word, the microbubbles diameter was highly affected by the pressure in microbubbles porous medium generation method. Then, the static and dynamic dissolution kinetics of microbubbles in the porous media were investigated by microfluidics. The results of dissolution experiments showed that microbubbles had excellent dissolution efficiency. When contacting with formation water, microbubbles would rapidly dissolve and the undissolved microbubbles were still migrating the porous media in the form of bubbles. CO2 microbubbles could form a migration mode with carbonated water in the front and microbubbles in the rear, after microbubble were injected into the reservoir. For the first time, the enhanced oil recovery mechanisms of CO2 microbubbles were studied under high-temperature high-pressure conditions, which mainly include: ①Microbubbles carry residual oil on the pore wall during migration; ②Microbubbles carry residual oil droplets out of the pores with dead ends through dissolution and oil swelling; ③Break the capillary force balance of residual oil droplets and promote the flow of oil droplets; ④Block the high permeability channel to improve the sweep efficiency. This paper provides valuable guidance for CO2 microbubble to enhanced oil recovery and carbon sequestration.
2023, 55(1): 1-11.   doi: 10.6052/0459-1879-22-507
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ULTRA-LOW FRICTION TIME-CHANGE MODEL AND ENERGY CONVERSION OF DEEP COAL-ROCK INTERFACE
Li Liping, Yu Honghao, Zhang Haitao, Pan Yishan
The ultra-low friction impact ground pressure of deep coal rock is essentially a time-varying process in which a large amount of coal rock mass is instable and sliding along the coal-rock interface, during which the friction and friction coefficient of the coal-rock interface change with time, and at the same time, the energy conversion characteristics of releasing energy from the impact kinetic energy of the coal-rock interfacial with the frictional force of the coal-rock interface. In order to quantitatively describe the energy conversion law of coal rock interface, the dimensional analysis method is introduced, and the elastic coefficient, damping coefficient and pending coefficient of coal rock are experimentally determined, and the expression of the friction coefficient of deep coal rock interface is given. Taking Shenyang Hongyang Three Mines as the research object, through the combination of experimental research and engineering practice, a new index of impact kinetic energy conversion rate is defined, the reliability of the built model is verified, and the law of coal-rock interface friction work to coal-rock impact kinetic energy conversion is quantitatively described. The results show that the interfacial friction coefficient of deep coal rocks decreases linearly with the increase of the amplitude of the impact load, and increases linearly with the increase of the frequency of the impact load. When the impact load amplitude is 5000 N and the impact load frequency is 500 Hz, the ultra-low friction effect occurs when the friction force of deep coal rock interface decreases by 97% and the reduction rate is 38.9 kN/ms ~ 41.38 kN/ms. For the first time, the ultra-low friction effect is quantitatively described in terms of friction reduction amplitude and reduction rate. Combined with the experimental and engineering actual analysis, it is found that the average experimental result of the energy consumption ratio is 0.441, and the calculation result of the "11.11" impact ground pressure of Hongyang Three Mines is 0.488, which is relatively close, which further proves the rationality of the proposed model.
2023, 55(2): 1-13.   doi: 10.6052/0459-1879-22-467
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EXPERIMENTAL INVESTIGATION ON ACTIVE CONTROL TURBULENT BOUNDARY LAYER DRAY REDUCTION BY SYNCHRONOUS AND ASYNCHRONOUS VIBRATION OF DUAL VIBRATORS
Bai Jianxia, Zhao Kaifang, Cheng Xiaoqi, Jiang Nan
In order to achieve the drag reduction effect, the experimental scheme of zero-mass jet active control turbulent boundary layer is designed independently in the paper. Dual piezoelectric (PZT) oscillators as the active control actuators are symmetrically distributed embedded along the spanwise direction of the flat plate in turbulent boundary layer. The experimental investigation is carried out by synchronous (syn) and asynchronous (asyn) vibration active control mode to achieve drag reduction with the periodic vibration of dual PZT oscillators in a wind tunnel. It realizes the periodic interference and modulation to the multi-scale coherent structure in turbulent boundary layer. Furthermore, it reduces the skin friction and realizes drag reduction effect in all controlled cases.The consequence shows that the maximum drag reduction rate of 18.54% is obtained at 100 V, 160 Hz asynchronous vibration case.The multi-scale wavelet analysis of streamwise velocity shows that the energy of the small-scale coherent structure increases while the large-scale coherent structure decreases in all controlled conditions.Meanwhile, it adjusts the energy distribution of the large-scale and small-scale coherent structures in near-wall regions of turbulent boundary layer .The drag reduction effect of the asynchronous controlled case is better than the synchronous controlled case at the same voltage and frequency of vibration. When the vibration frequency of the PZT oscillators is 160 Hz, the PDF curves of the wavelet coefficient show the fluctuation characteristics and the tails of the PDF curve widen significantly. The pulsations of near-wall regions become more ordered and regular and the turbulence weakens intermittently after control in turbulent boundary layer.The results of the conditional phase averaging of small-scale coherent structure show that the periodic perturbations of the PZT oscillators enhance the turbulence intensity of the small-scale coherent structures. Furthermore, drag reduction effect is also achieved by breaking the large-scale coherent structure into the small-scale coherent structure. As the streamwise position is far away from the PZT oscillators, the modulation effect of the coherent structure in turbulent boundary layer gradually weakens.
2023, 55(1): 1-10.   doi: 10.6052/0459-1879-22-248
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INVESTIGATION OF THE TIME EFFICIENCY OF THE SEVENTH-ORDER WENO-S SCHEME
Wu Conghai, Li Hu, Liu Xuliang, Luo Yong, Zhang Shuhai
The WENO-S scheme is a class of weighted essentially non-oscillatory schemes suitable for numerical simulations of problems with discontinuities. The smoothness indicator of this kind of scheme is constant for single-frequency waves, which makes this kind of scheme have exactly the same approximate dispersion relationship with its linear base scheme, and thus has an excellent ability to simulate small-scale waves. Time efficiency is crucial for numerical methods. For a WENO-S scheme, the formula of the smoothness indicator on each sub-stencil has the same formula except for different subscripts. Then some smoothness indicators are the same when calculating adjacent numerical fluxes of linear convection equations. So, a method is proposed to remove redundant computations of smoothness indicators. The premise of this approach is that the quantity used for reconstruction or interpolation on a grid line can be represented as a sequence. According to this requirement, the feasibility and application requirements for several different physical problems are analyzed. The seventh-order WENO-S scheme is employed to illustrate the advantages of the WENO-S schemes, including good properties near extreme points, good stability near discontinuities, and outstanding spectral properties. Then the method of eliminating the computation of the redundant smoothness indicators is introduced. In numerical computation, all smoothness indicators in a grid line are calculated and stored in advance. With this approach, the count of the smoothness indicator calculation is about 1/4 of the original one for the seventh-order WENO-S scheme when there are many grid points. Numerical examples include one-dimensional advection, spherical wave propagation, two-dimensional rotation, small disturbance propagation, and one- and two- dimensional inviscid flow problems. The numerical results show that this scheme can capture a variety of flow structures well and have good time efficiency. Furthermore, the proposed method reduces the computational time by about 20%.
2023, 55(1): 1-15.   doi: 10.6052/0459-1879-22-371
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Zhang Xiong
2022, 54(12): 1-2.   doi: 10.6052/0459-1879-22-557
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SIMULATION OF THE MOTION OF AN ELASTIC HULL IN REGULAR WAVES BASED ON MPS-FEM METHOD
Huang Congyi, Zhao Weiwen, Wan Decheng
A ship always encounters waves and may move with six degrees of freedom in the naval architecture and ocean engineering. The ship can be regarded as a rigid body simply when the motion amplitude is small. However, when the wave gets severe, the ship's motion amplitude get large and the ship hull may deforms a lot. In this situation, ship's elasticity may effects the pressure on the hull and the ship response motion, which cannot be ignored. Therefore, it is of great significance to simulate the motion of an elastic ship in waves and to study the influence of the hull elasticity, which can improve the ship performance and the navigation safety. MPS (Moving Particle Semi-Implicit) method is a mesh free particle method based on Lagrangian representation. This method has its unique advantages in simulating problems with large deformation characteristics of free surfaces. As a traditional structural solution method, Finite Element Method (FEM) has been widely used and has been proved with good stability, accuracy and robustness. In this paper, the advantages of MPS method and FEM method are combined and the in-house fluid-structure interaction solver MPSFEM-SJTU is used to simulate the motions of rigid and elastic hulls in regular waves. The impact of hull elasticity on the hull motion response and the pressure on the hull is analyzed. Firstly, the effect of regular wave length on the motion response of hull is studied by simulating the motion of a rigid hull in regular waves with different wavelengths. Then the motions of rigid and elastic hull in regular waves are simulated respectively. The results show that the motion amplitude of rigid hull, both pitch and heave, are greater than those of the elastic hull. and the pressure near the midship of elastic hull is greater than that of rigid hull. For the pressure distribution on elastic and hull surface, the pressure at the bottom near the midship is greater than that on the rigid hull due to the bending of the elastic ship.
2022, 54(12): 1-14.   doi: 10.6052/0459-1879-22-468
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A True Triaxial Creep Constitutive Model for Rock Considering Hydrochemical Damage
In order to accurately describe the characteristics of each stage of rock creep behavior under the combined action of acid environment and true triaxial stress, based on the chemical kinetic theory of water-rock interaction, a chemical damage factor considering pH and time is defined. The elastic body, nonlinear Kelvin body, linear Kelvin body, and visco-elastic-plastic body (Mogi-Coulomb) are connected in series, and the actual situation under the action of true triaxial stress is considered at the same time, a damage-creep constitutive model considering the coupling of rock acid corrosion and true triaxial stress is established. The parameters of the deduced model are identified and verified with the existing experimental research results. The yield surface equation of rock under true triaxial stress is obtained by data fitting, and the influence of intermediate principal stress on the creep model is discussed. The results show that the derived constitutive model can well reflect creep properties of the rock under acid corrosion The true triaxial creep characteristics under the action have certain rationality and practicability
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MULTI-SCALE MODELING AND SIMULATION OF SKELETAL MUSCLE BIOMECHANICAL PROPERTIES
Aiming at the problems that there is a certain difference between the muscle fiber microstructure model and the image observed under the microscope, the microscopic component biomechanical model cannot effectively capture the mechanical behavior of skeletal muscle during shear deformation, and the high calculation cost of multi-scale numerical models of skeletal muscle. In this thesis, the mechanical properties of skeletal muscle are studied from the perspectives of experiment, multiscale modeling and simulation. Curved-edge Voronoi polygons are proposed as the cross-section of muscle fibers, and the corresponding representative volume element (RVE) is established at the microscale. A new biomechanical model (MMA model) is proposed, and the MMA model is used as the biomechanical model of muscle fibers and connective tissue. Combine the experimental results of skeletal muscle, the RVE models, the biomechanical models of muscle fibers and connective tissue to establish a multiscale numerical model of skeletal muscle. According to the experimental results, the parameters of the biomechanical model are determined, the multiscale homogenization method are used to realize the connection between the microscale and the macro-scale, and the macroscopic mechanical behavior of skeletal muscle is finally obtained.
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EFFECTS OF WAVY ROUGHNESS ON THE STABILITY OF A MACH 6.5 FLAT-PLATE BOUNDARY LAYER
Wang Haopeng, Yuan Xianxu, Chen Xi, Liu Shuyi, Lai Jiang, Liu Xiaodong
Transition from laminar to turbulent flow of the hypersonic boundary layer can increase the wall friction coefficient and heat conduction coefficient by 3-5 times, which has a significant influence on flight performance and safety of hypersonic vehicles. Wavy roughness is a possible passive control method to delay hypersonic boundary layer transition, and is thus of engineering significance. In this paper we investigate the effort of finite-length wavy roughnesses with different locations and heights on the stability of a Mach 6.5 flat-plate boundary layer using direct numerical simulation and linear stability theory(LST). DNS is employed to obtain the laminar base flow, and to study the linear evolution of fixed-frequency disturbances parametrically introduced upstream by blowing and suction. The effects of the relative position of the fast/slow mode synchronization point and the wavy roughness are revealed. It is found that when the wavy roughness is placed upstream of a disturbance’s synchronization point, the disturbance is damped compared to the smooth surface case; when the disturbance’s synchronization point is within or slightly downstream of the wavy roughness, the disturbance is generally enhanced. The effects of heights of wavy roughnesses are also considered. For the wavy roughness with small heights compared to the boundary layer thickness, the effect of wavy roughness is positively correlated with the height of the wavy roughness, while the effect is weakened by the higher wavy roughness. Linear stability theory can predict well the effects of wavy roughness on high-frequency disturbances, but exhibits large discrepancies with DNS in predicting the behaviors of moderate and low-frequency disturbances. This indicates that the receptivity process and the strong non-parallel effect in the vicinity of the wavy roughness neglected by LST should play an important role.
 doi: 10.6052/0459-1879-22-327
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SECONDARY ORIENTATION EFFECTS OF NI-BASED ALLOYS WITH COOLING HOLES: A STRAIN GRADIENT CRYSTAL PLASTICITY FEM STUDY
Xiong Yukai, Zhao Jianfeng, Rao Wei, Huang Zhiyong, Kang Guozheng, Zhang Xu
Single crystal Ni-based alloys possess excellent properties such as high temperature resistance, high strength and high toughness. Thses mechanical properties are affected by secondary orientation and cooling holes induced during complex manufacturing processes. The current research mainly focuses on the deformation mechanism and mechanical response of plates with one hole. While, the plate with multiple holes is often used in engineering. At present, it is urgent to clarify the deformation mechanism of the plate with multiple holes, the secondary orientation effect, and the strain gradient effect caused by cooling holes. In this paper, a nonlocal crystal plasticity constitutive model based on the dislocation mechanism is used to numerically simulate the uniaxial tensile deformation behavior of the Ni-based single crystal plate with cooling holes. A dislocation flux term is derived based on the relationship between the plastic slip gradient and geometrically necessary dislocations, enabling this crystal plasticity model to effectively describe the strain gradient effect. In order to comprehensively reveal the secondary orientation effect of Ni-based alloys with cooling holes, this paper systematically studies the uniaxial tensile deformation behavior of sheets with [100] and [110] orientations (two secondary orientations). The influence of the number of holes on the plastic behavior of the plate with two secondary orientations is investigated. By analyzing the variation of the resolved stress on slip systems, activation of the dominant slip systems and the evolution of geometrically necessary dislocation density during the deformation of Ni-based alloy plates, the effects of plastic slip and its distribution on the strength of Ni-based alloy plates with different secondary orientations are discussed. The results show that the tensile strength of [110] plate is lower than that of [100] plate. Furthermore, the plastic deformation process of the five-hole plate is more complicated than that of the one-hole plate and is easier to be affected by secondary orientation. Finally, the location of the slip gradient is mainly located near the cooling hole and the plastic slip zone. The research results can provide theory basis for the design and service of Ni-based alloys in engineering.
 doi: 10.6052/0459-1879-22-497
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STUDY OF WAVE DISPERSION AND PROPAGATION IN PERIDYNAMICS
Zhu Jinggao, Ren Xiaodan
Periydnamics (PD) is a new nonlocal method reformulated from solid mechanics. It adopts the integral form of governing equation and is naturally suitable to model fragments and cracks under extreme events, thus widely applied in the field of national defense security. However, the nonlocality in PD introduces the dispersion effect and imposes adverse effect on wave propagation, which will greatly restrict its capability in capturing solid behaviors, especially the fractures. For this purpose, we employ the spectral analysis method to study the dispersion behavior of PD system comprehensively. It is found that compared to the low frequencies, the dispersion relation of high frequency components shows an oscillation trend and zero-energy modes, leading to more serious dispersion problems. The dispersion behavior of high frequencies changes with the wave propagation direction and shows 45° symmetry in the spatial wave propagation. As the PD system itself is non-dissipative, the adverse effect of the dispersion problem can not be suppressed. As a result, the simulation accuracy may be greatly influenced. To introduce the numerical dissipation for dispersion effect suppression, the governing equation of viscosity introduction is proposed as a minimum variation of conventional PD. Both the typical deformation in solids and the selective suppression on high frequencies are considered then the corresponding viscous force state is constructed. Finally, a numerical study is conducted to model the shock waves under extreme events and investigate the influence of wave discontinuity. It is indicated that the wave discontinuity aggravates the dispersion problem and shows Gibbs instability in the wave propagation. These can be effectively suppressed by the viscous force state, which verifies the proposed method. This provides an important reference to reproduce the correct wave propagation process and obtain the reasonable solid behavior in PD, thus helps to support and guide the research of national defense security field.
 doi: 10.6052/0459-1879-22-342
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INFLUENCE OF EXPANSION STERNS ON THE FLATTING TRAJECTORY CHARACTERISTICS OF A TRANS-MEDIA VEHICLE DURING HIGH SPEED WATER ENTRY
Liu Xiyan, Luo Kai, Yuan Xulong, Ren Wei
The expansion stern is an important factor affecting the flatting trajectory and its stability of a trans-media vehicle during high speed water entry and turning flat process. In this paper, based on the fluid volume multiphase flow model and dynamic mesh technology, the coupling calculation method of multiphase flow field and trajectory of the trans-media supercavitating vehicle entering water at high speed is established. The accuracy and applicability of the numerical calculation method are verified by the experiments. Through the numerical simulation study on the high speed water entry and turning flat process of the trans-media vehicle, the influence of the expansion stern on the cavity development morphology, hydrodynamic characteristics and trajectory characteristics of the vehicle during the water entry and turning flat process is obtained, and the influence of the cone angle of expansion sterns on the flatting trajectory during high speed water entry is analyzed. The results show that when the vehicle without the expansion stern entering water and turning flat under the different preset rudder angles, the angle of attack increases continuously, eventually leading to the divergence of the flatting trajectory. After the vehicle with the expansion stern entering water, the recovery moment is formed when the expansion stern is wetted, and the stable flatting trajectory is obtained. The vehicles with different expansion stern cone angles (1.5°, 6°, 8°) have formed three different kinds of trajectory characteristics: stable planing, single-sided tail-slapping and double-sided tail-slapping, and all of them can achieve stable flatting trajectory. The principle of stable planing trajectory is the dynamic balance under the coupling effect of the preset rudder angle and expansion stern planing. This trajectory has the smallest comprehensive drag coefficient, the highest flatting efficiency and the smallest dynamic load, which is an ideal flatting trajectory form for the trans-media vehicle during high speed water entry.
 doi: 10.6052/0459-1879-22-427
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THEORETICAL ANALYSIS ON THE CRITICAL FLOW VELOCITY AND VIBRATION MODE OF A TWIN-CHANNEL ROTATING PIPE
Zhang Bo, Zheng Haokai, Sun Dongsheng, Ding Hu, Chen Liqun
Rotating blade is an essential part of aero-engine. It serves in harsh conditions. Its failure is often caused by excessive vibration. To design the blade properly and to ensure the reliability and safety, the vibration characteristics of the blade need to be revealed. The blade is simplified as a cantilever rotating pipe with double cooling channels based on the Euler-Bernoulli beam theory. The influences of channel axis offset on fluid kinetic energy are considered in the present study. The motion governing equation of the blade is established including the bi-gyroscopic effects with the combination of Lagrange principle and assumed mode method. The method of order reduction and dimension expansion is applied to solve the eigenvalue of the system. The influences of the fluid velocity ratio, rotating speed, slenderness et al. on the first three order eigenvalue curves are studied. The present model degenerates into a simply supported pipe conveying fluid with a single channel to compare with the results reported in literature. The correctness of the present modeling method is verified, partly. The velocity ratio of two channels has great influence on the first three order critical flow velocity values. For a given value of the cross-section area of the cooling passage, the critical flow velocity of the twin-channel model is higher than the single-channel model. A circling phenomenon is introduced to on the second and the third eigenvalue curves by the gyroscopic effect due to the rotating motion. The second and the third eigenvalue curves travel through the imaginary axis several times. With the increase of the slenderness ratio, the system’s dynamic behaviors are similar to the non-rotating cantilever pipe. Moreover, due to the gyroscopic effect, the modal response of the lateral displacement presents a traveling wave property. And the damping factor has different enhancement or weakening effects on the first three modes under different parameter conditions.
 doi: 10.6052/0459-1879-22-456
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FULL SOLUTION FOR CHARACTERIZING STRESS FIELDS NEAR THE TIP OF MODE-I CRACK UNDER PLANE AND POWER-LAW PLASTIC CONDITIONS
Wang Zhiqiang, Cai Lixun, Huang Maobo
In the fields of aerospace, ships, oil pipelines and nuclear power, there will be cracks inevitably in structure or component part when running for a long time under extreme conditions. Therefore, it is necessary to explore the features of the stress-strain fields near the crack tip, to study the quasi-static fracture behavior of cracked structures. In this paper, the stress distributions near the tip of mode-I cracked specimens under plane strain and plane stress conditions are studied for power-law hardening material. Based on the energy density equivalence and dimensional analysis, the analytical equation of equivalent stress of representative volume element (RVE) with the median energy density of a finite-dimensions specimen is proposed, and it is defined as the stress factor. Furthermore, for Compact tension (CT) and Single edge bend (SEB) finite size specimens under plane strain and plane stress conditions, the stress factor is used as a characteristic variable, and a special trigonometric function is assumed to characterize Butterfly-Wings type or Scallop type contour lines of the equivalent stress near the mode-I crack tip, and then a semi-analytical model for compact tension specimens and single edge bend specimens under plane strain and plane stress and fully plastic conditions is proposed to describe the stress fields near the crack tip. As shown in comparing results given by finite element analysis to those predicted by the model for stress fields near the crack tip of the two cracked specimens, all agree well with each other. The semi-analytical model of stress field near the crack tip proposed in this paper is simple in form and accurate in result. It can be directly used to predict the stress distribution near the tip of mode-I crack, which is convenient for fracture safety evaluation and theoretical development.
 doi: 10.6052/0459-1879-22-360
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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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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.
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.
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.
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。
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.
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 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.
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.
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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