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Multibody vehicle widely exists in the fields of aerospace and weapon system. There are three main types for the multibody vehicle system. Firstly, multiple vehicles are in close proximity flight that do not touch each other, such as formation flight and towed flight. Secendly, multibody vehicle are in contact with each other or combined to flight as a whole, such as aircraft-store carriage, the booster-flight of multistage vehicles, etc. Finally, multibody vehicle is in the relative motion after recovery or separation, such as aircraft-store separation, stage separation of multistage vehicles, etc. Multibody interference or interaction universally exists in the flowfield of multibody vehicle during steady or unsteady flight and dynamic separation, which makes the flow physics or characteristics of multibody vehicle different from isolated-body vehicle, especially in supersonic and hypersonic flow. There are multiple shock-wave reflection and diffraction, interference or interaction between shock-wave and vortex, shock-wave and boundary layer among multibody vehicle, which can significantly change the aerodynamic characteristics of multibody vehicle. The concept of “multibody aerodynamics” is advocated to summarize the field of multibody vehicle, and its basic connotation, application fields and flow characteristics of typical multibody configurations are explained, in order to point out the direction and ideas on aerodynamics and separation dynamics of multibody vehicle for the future research.
2022, 54(6): 1461-1484.   doi: 10.6052/0459-1879-22-096
Shock/boundary-layer separation is a typical turbulence non-equilibrium flow in the field of aeronautical aerodynamics. Accurate simulation of shock separated flow is of great significance for aerodynamic performance evaluation and optimization of transonic aircraft. The definition of eddy viscosity coefficient in conventional eddy-viscosity turbulence models (EVM), however, is not suitable for non-equilibrium flow. The Bradshaw assumption introduced by k-ω SST turbulence model for this purpose instead restricts the generation of Reynolds stress when applied to three-dimensional flow with strong adverse pressure gradient and large separation, which results in the invalidity of k-ω SST model as well as other commonly used EVMs for this kind of flow. Moreover, the existing nonlinear constitutive relation of Reynolds stress cannot effectively improve the simulation accuracy. To this end, two shock separated flow correction methods respectively based on Bradshaw assumption and length scale are proposed for k-ω SST model. The former correction relaxes the limitation of Reynolds stress generation by increasing Bradshaw constant. While based on the concept of turbulence length scale, the latter correction constructs a modified function for the dissipation term of the ω equation by using the mixing length theory, the generation-dissipation ratio of turbulent kinetic energy and a newly defined ratio of length scale to improve the modeling length scale in three-dimensional shock separated flow. The two methods both get better simulation results for the transonic flow of ONERA M6 wing at high angle of attack than those of Reynolds stress model. Further Reynolds stress analysis reveals that the concept of "major Reynolds-stress component" in three-dimensional shock separated flow is no longer tenable since the magnitude of each Reynolds-stress component is close. The grid convergence analysis, and verifications on other angles of attack and the wall-function law of turbulent boundary layer on the flat plate further confirm the validity, applicability and universality of the proposed correction methods.
2022, 54(6): 1485-1501.   doi: 10.6052/0459-1879-22-065
So far, the smoothed particle hydrodynamics (SPH) method has been widely applied in the study of the interactions between water waves and structures. However, nonphysical energy dissipation is a still problem which challenges the simulation of wave-body interactions at large-scale and long duration. For example, in the SPH simulation of wave propagation to a long distance, the wave height could gradually become much smaller than the one generated near the wave maker. To tackle this problem, in this work a kernel correction algorithm is applied to the pressure gradient term in the SPH model, aiming to prevent nonphysical energy dissipation in long time simulations. The kernel correction algorithm is able to ensure the symmetry of the interaction between particle pairs, and therefore, compared with other corrective methods, the present corrected algorithm ensures the conservation of linear momentum and also avoids the complicated treatment at the free surface. Two numerical cases, i.e., the oscillating droplet and wave propagation in a numerical wave tank, are presented to test the accuracy and validity of present corrected SPH algorithm. For the oscillating droplet case, the corrected algorithm is shown to accurately simulate the evolution of the droplet shape, and the kinetic energy is dissipated much slower than traditional SPH models. Through the simulations of regular and irregular wave propagations as well as validations with experimental data, the capability of the corrected SPH algorithm to reduce nonphysical energy attenuation is demonstrated, even for wave propagation at long-term and long-distance conditions. In addition, this algorithm will be shown to be optimal for the SPH simulation at small smooth length, which contributes to save SPH computational cost significantly at three dimensional simulations.
2022, 54(6): 1502-1515.   doi: 10.6052/0459-1879-22-041
Spreading and rebounding of drop on solid substrate are of great significance in industry and scientific research, where the evolution of morphology of a drop is investigated frequently. It is normally believed that a spread drop retracts in inertia-capillary regime with a speed deduced by a Taylor-Culick procedure. Experimental and finite element method studies were conducted, which show that a drop retracts on moderately wettable plate with a low speed after the aforementioned inertia-capillary retraction. The speed has a value as low as 1/10 of the first retracting stage. The mechanism is explored according to the experiments and additional numerical simulations. It is found that the low-speed retraction depends on the density and capillary of the liquid, rather than the viscosity and wall condition (including the wettability and slip characters). It is revealed that the process is still dominated by capillary-inertial effects. The findings are also validated on the liquid with viscosity as high as 10 times of the original one in simulations. The research is valuable for studying droplet dynamics and relative industrial processes.
2022, 54(6): 1516-1522.   doi: 10.6052/0459-1879-21-663
When hypersonic vehicles reenter the atmosphere, the surface thermal protection materials will ablate under the action of high temperature airflow. In the process, the ablative particles will entrance the high temperature airflow and affect boundary-layer transition and turbulence characteristics downstream. Those phenomena will also happen in an arc-heated wind tunnel when conducting material thermal response experiments. Therefore, it is a significant basic scientific problem to study the transport behavior of inertial ablative particles under aerodynamic load. In this article, we analyzed the flow condition and particle exfoliation process very near a hypersonic vehicle wall with dimensional theory. After a series of reasonable assumptions and simplifications, we modelled the ablative particle exfoliation and transport process as one spherical inertial particle in Couette flow and adopted the particle resolved-direct numerical simulation (PR-DNS) method to study it. As a result, the particle exfoliation and transport characteristics were revealed and a normalized expression of particle start-up velocity was obtained, which would provide theoretical basis for accurate prediction of particle mass loss in the future. The research findings show that as the particle fluid density ratio${\rho _r}$increases, the particle inertia St increases, and the horizontal and normal velocities of particle decrease. The larger the particle diameter is, the larger the particle inertia St is, and the horizontal velocity of the particle decreases. However, the normal velocity and displacement of the larger particle are increased. The reason is maybe larger particles receive larger Saffman lift force. Besides, the normal displacement of ablative particles is much smaller than the horizontal displacement, so the particles are mainly transported horizontally. In order to find the unified law underlying all the regularities, we defined the start-up velocity and found that the normalized particle start-up velocity is a function of the particle and fluid inertia, i.e., the particle horizontal transport velocity is the velocity of fluid or neutral buoyant particle minus the inertia correction term.
2022, 54(6): 1523-1532.   doi: 10.6052/0459-1879-21-604
Numerical simulations of high-fidelity aerospace engines are usually based on the rapid chemical reaction flame surface assumption, that is, the characteristic scale of supersonic combustion reaction is smaller than the turbulent Kolmogorov scale. This model method has good simulation results for hydrogen fuel, but further research is needed for hydrocarbon fuels such as ethylene. Limited by the extreme environment special nonintrusive measurement techniques, experimental investigations on the discrimination of supersonic combustion flame mode have not been presented in literature. The applicability of the supersonic combustion flame surface model and understandings of the regimes of supersonic combustion restricts the development of high fidelity numerical simulation methods. Based on the in house designed MHz endoscope optical fiber sensor, experiments are designed to study the regimes of supersonic combustion of a dual-mode scramjet combustor. The minimum Shannon entropy of the chemiluminescence signal is used to define the characteristic time of supersonic combustion. The flow characteristic time of supersonic combustion is estimated according to the theoretical method and the incoming flow conditions. Combined with the partition combustion theory, the partition situation of hydrocarbon fuel combustion in a dual-mode scramjet is analyzed. Through combustion zoning and comparison with Taylor scale .The data presented in this paper suggests the supersonic combustion in the vortex framelet regime in a typical flight envelope (Re$\cong$50000; Da∈1.80-2.60, B zone), suggesting the strong influence of turbulence,With different sizes relative to the Taylor scale, vortex structures corresponding to different scales dominate the process. In addition, parametric evaluation on the influence of equivalence ratio, flux ratio and Mach number during a simulated acceleration is presented in this paper. The experiment found that the combustion gradually increased with the increase of the equivalence ratio within a certain range, and the enhancement effect was obviously stronger than that of the flux ratio; the change of the flux ratio would cause the combustion to bifurcate; the change of the incoming Mach number was important for The effect of combustion is more obvious, and it also shows that the effect mechanism of incoming flow is an important direction for future research on turbulent combustion theory.
2022, 54(6): 1533-1547.   doi: 10.6052/0459-1879-21-686
When the scramjet combustor works under high Mach number conditions, the total enthalpy of the inlet air is very high, and auto-ignition becomes an important physical and chemical process to maintain flame stability. This paper develops an auto-ignition tabulated method based on chemical kinetics, referring to the dimensions reduction means of the flamelet/progress variable model. The complex and multi-dimensional chemical reactions is reduced by defining the mixture fraction and progress variables, and the database method is successfully integrated into the existing large eddy simulation solver. After testing and verification, the method possesses the ability to simulate and describe the supersonic auto-ignition and flame. Numerical simulation is carried out for supersonic combustion induced by auto-ignition in two configuration. This method effectively reduces the amount of calculation in the process of solving chemical reactions by looking up the database. When the detailed chemical reaction mechanism is used, the auto-ignition behavior and flame structure can be accurately reproduced, and the predicted temperature and the distribution of important components are in good agreement with the experiment.
2022, 54(6): 1548-1556.   doi: 10.6052/0459-1879-21-635
The collapse of static granular pile under gravity is the basis for understanding many human processes and natural phenomena. There are some difficulties for the traditional simulation methods, such as large number of single particle tracking, obvious rheological characteristics, and complex phase evolution of macro simulation. Based on the physical mechanism of different phases in granular media, the concept of full phases is defined and divided into three regions. According to the stress-strain relationship and volume fraction of granular media, the existing theories describing each phase are effectively combined by determining the coupling relationship and transformation criteria between different phases, and the coupling model theory describing all phase states of granular media is established. Then the physical model of granular media is solved with the strategy of coupling smoothed discrete particle hydrodynamics and discrete element method. The coupling and transformation algorithm between different phase particles is clarified and the particle size independence of the diameter selection of the initial SDPH particles is tested. The numerical simulation of collapse process of granular pile under different aspect ratio is realized. The calculated results are in good agreement with the experimental results. At the same time, compared with the discrete element method, the amount of calculation is controlled. It not only captures the different phenomena of deposition after granular pile collapse under the influence of different parameters, but also obtains the effects of different conditions and parameters on the spreading characteristics of granular pile after collapse are obtained, which provides effective support for revealing the complex motion mechanism of granular media widely existing in industry and nature.
2022, 54(6): 1572-1589.   doi: 10.6052/0459-1879-22-001
Simplification and assumptions are usually made in the process of vehicle dynamics modeling, resulting in the model can not accurately reflect the actual dynamic characteristics of the vehicle under some working conditions, which affects the control accuracy and even safety. In view of this, this paper proposes a data-driven nonlinear modeling and control method, establishes a new neural network multi-step prediction model of vehicle lateral dynamics, and realizes the tracking control of reference trajectory of intelligent vehicle. Firstly, based on the analysis of vehicle single-track model and considering tire nonlinearity and longitudinal load transfer, a neural network lateral dynamics model is designed based on encoder decoder structure. Among them, the serial arrangement is used to expand the differential equation to describe the incomplete dynamic information, and the hidden layer neurons learn the highly nonlinear and strong coupling characteristics of the vehicle, so as to improve the global calculation accuracy of the model. Use the constructed data set for model training and testing, the results show that, compared with the physical model, the proposed model has higher modeling accuracy under different road adhesion coefficients, and has the ability to implicitly predict road friction conditions. Secondly, using the proposed model to design trajectory tracking control algorithm, according to the vehicle steady-state steering assumption, the required front wheel steering angle and steady-state sideslip angle are calculated, and the steady-state sideslip angle is incorporated into the steering feedback based on path error to realize the reference trajectory tracking control. Finally, comparative analysis of tests under different working conditions is carried out with Simulink / CarSim co-simulation and HiL experiments to evaluate the proposed control algorithm based on neural network model. The results show that the model can realize the accurate tracking control effect of intelligent vehicle at high speed, and has good lateral stability.
2022, 54(7): 1-13.   doi: 10.6052/0459-1879-21-667
In aerodynamic shape optimization design and aircraft performance analysis, the cost of directly using numerical simulation or wind tunnel experiments to obtain aerodynamic forces is high. Building surrogate model is an important way to improve the efficiency of shape optimization and performance analysis. However, in the process of building the model, researchers only focus on the aerodynamic force and moment information after integration. In this paper, the accuracy and generalization of modeling are improved by making full use of the pressure distribution information generated in the sampling process, thereby reducing the cost of sample acquisition. In this paper, an aerodynamic modeling method integrating pressure distribution information under the framework of small sample is proposed. Firstly, the pressure distribution information and aerodynamic coefficients of airfoil surface under different flow parameters are obtained by numerical simulation or wind tunnel experiments. Secondly, the pressure distribution information is extracted by proper orthogonal decomposition technology to obtain the POD coefficients corresponding to the distribution information under different input parameters. Then, the pressure distribution information is modeled by Kriging algorithm combined with input parameters. The pressure distribution information is integrated to obtain the prediction model of low precision aerodynamic coefficients. Finally, the low precision aerodynamic coefficients are combined with the input parameters to construct a high precision aerodynamic prediction model by Kriging algorithm. The method is verified by the same-state variable airfoil example and the CAS350 airfoil variable-state example. Compared with the traditional Kriging model, this method can effectively improve the prediction accuracy of aerodynamic force and the robustness of the model, and reduce the data amount of learning samples.
2022, 54(9): 1-11.   doi: 10.6052/0459-1879-22-170
Modern spacecraft usually carry large amounts of liquid propellant. In the process of attitude change, the liquid fuel may slosh violently due to the action of inertial force and gravity, resulting in additional sloshing force, which will have an important impact on the spacecraft. In order to obtain the law of liquid sloshing and meet the requirements of on-board computer real-time calculation, a dynamic model for equivalent liquid sloshing is studied and verified in this paper. Firstly, the moving pulsating ball model (MPBM) of large liquid sloshing motion is extended to the gravity environment. Based on the Newton-Euler dynamic equation of the moving pulsating ball and the energy relation in the process of "breathing movement", the expression of the normal component of the sloshing force is derived. In addition, the equivalent model of liquid not involved in sloshing is introduced to make the calculation of liquid centroid position more accurate. Compared with the experimental data in the references and the calculation results of CFD (Computational fluid dynamics) software, the effectiveness of the improved MPBM under large amplitude sloshing and zero momentum maneuver is verified. Also, based on the equivalent model, the effects of different time series of impulse excitation on liquid sloshing response in spacecraft are studied. Finally, an experimental platform for precise measurement of liquid sloshing force is designed and built to verify that the MPBM can also well reflect the variation trend of sloshing force in the liquid sloshing of equivalent non spherical tank. The research work of this paper has important reference value for the further study of rigid-liquid coupling dynamic behavior of liquid filled spacecraft in gravity environment.
2022, 54(9): 1-9.   doi: 10.6052/0459-1879-22-187
Vortex-induced vibration (VIV) of cylindrical structures is a very common phenomenon in daily life. Cylinder structures, such as pipelines in ocean engineering, high-rise buildings, stay cables in civil engineering and heat exchangers in nuclear engineering, etc. are frequently affected by vortex-induced vibrations, which can induce fatigue damage and make the failure of structures. At present, the VIV mechanism of cylindrical structures in vertical incoming flow has been comprehensively understood. However, when the cylinder structure is inclined in the flow field, the wake flow of the inclined cylinder is significantly different from that of the vertical one, and the fluid-structure interaction mechanism is more complex. Earlier, Independence Principle (IP) was proposed to simplify the problem of flow around an inclined stationary cylinder. In the assumption of the Independence Principle, the incoming flow velocity can be decomposed into one part that is vertical to the cylinder axis, and the other that is parallel to the cylinder axis. Only the velocity component vertical to the cylinder axis is considered and the influence of the velocity component parallel to the cylinder axis is ignored. In recent years, a large number of experimental and numerical studies have been carried out to investigate the VIV characteristics of an inclined cylinder and the applicability of Independence Principle. To deepen the understanding of the VIV characteristics and mechanisms of inclined cylinder, this paper summarizes and expounds the response characteristic, wake flow characteristic and hydrodynamic characteristic in “the flow around an inclined stationary cylinder, vortex-induced vibration of an inclined rigid cylinder, vortex-induced vibration of an inclined flexible cylinder and VIV suppression of an inclined cylinder”. The scope of the application of Independence Principle, the VIV mechanisms and VIV suppression of inclined cylindrical structures are discussed in depth, and the future research direction of this problem is prospected.
2022, 54(9): 1-18.   doi: 10.6052/0459-1879-22-186
In recent years, various large space structures are gradually implemented in the aerospace industry of China. Thus, the corresponding thermally induced vibration problems are drawn more and more attentions. Under this background, it is necessary to clarify the underling mechanism of the thermally induced vibration phenomenon and the corresponding critical issues in the analysis and design. Based on the research work of the authors, this article gives a comprehensive review of the related problems and mainly focuses on some special aspects in the thermally induced vibration analysis of complex engineering structures, which are compose of many thin-walled bars. Firstly, this article introduces a Fourier finite element that decomposes the temperature into the average part and the perturbation part. In this way, the thermal conduction equation under thermal radiation can be decoupled into the corresponding two parts due to the orthogonal property of the Fourier series. Thus, the transient temperature field of closed-section or open-section thin-walled bars can be efficiently analyzed. Based on this kind of element, both linear and nonlinear methods for the thermally induced vibration analysis are presented with the emphasis on the thermal-dynamic coupling effect. In order to give the analytical form of the necessary condition of the thermally induced vibration, this paper analyzes the properties of the transient temperature and the oscillation displacement in the mode space, and thus it obtains a general criterion to evaluate the intensity of the thermally induced vibration. Based on these work, the dynamic stability of the thermally induced vibration is further discussed by not only the mechanism reflected in the thermal flutter criterion of a cantilever bar, but also the thermal flutter analysis of complex engineering structures. Finally, the conclusion part briefly addresses some important factors in the underground testing and the method of suppressing the thermally induced responses. Some research topics need further investigating in the future are also envisaged.
2022, 54(9): 1-16.   doi: 10.6052/0459-1879-22-171
Binary composite plate is one of the common elements in metamaterial plate structure. A semi-analytical model of the free vibration of the structure is proposed for the binary composite plate composed of a matrix and an embedded body with different material parameters, and its vibration characteristics are studied. The plate is decomposed into two sub-regions based on the domain decomposition method and the distribution of binary materials. The non-smoothness of the local displacement and strain caused by the sudden change of stiffness in the composite plate is described by adding a local trial function to the mode shape function. Based on the essential boundary conditions of the binary composite plate and the condition of compatibility for the displacement at the joint of the two sub-regions, a new mode shape function is constructed. Based on the classical thin plate theory, the Ritz method with special trial functions is used to calculate the natural frequencies and modes of the binary material plate under different geometric configurations. The influence of the size and location of the embedded body on the vibration characteristics of the structure is investigated. The accuracy of this method is verified by the convergence analysis and the finite element simulation results. The results show that the classical global trial function will lead to inaccurate results when analyzing the modes with vibration localization, while the additional local trial function can significantly improve the convergence speed of the Ritz method and the accuracy of the results; the effect of the embedded body position on the low-order natural frequencies is not obvious, but it can significantly change the distribution of the low-order mode shape nodal lines and the region where vibration localization occurs.
2022, 54(7): 1-9.   doi: 10.6052/0459-1879-22-160
The objective of this paper is to investigate the transient evolution and dynamic characteristic of liquid nitrogen single bubble. In the experiment, electric spark transient discharge (EDM) was used to stimulate the evaporation of liquid nitrogen to form a single bubble, and the evolution process of the single bubble was captured by a high-speed camera with high resolution. In order to further reveal the unique physical properties of low-temperature media and the strong thermodynamic effects on the evolution of the single bubble, the unsteady evolution process and dynamic characteristics of single bubble in liquid nitrogen at 77.41 K and water at 298.36 K under the same ambient pressure were analyzed. And quantitative data such as the radius of bubble and interfacial velocity were obtained experimentally to elucidate the unsteady characteristics of the spherical and non-spherical evolution of liquid nitrogen single bubble. The results show that: (1) The size of a single bubble in liquid nitrogen is smaller than that of ambient water at the same input voltage. The maximum radius of the liquid nitrogen bubble is about 0.69 times that of the ambient water bubble, when the input voltage is 400. The evolution of a single bubble in liquid nitrogen experiences an expansion stage, a contraction stage, an oscillation stage, and a up phase, respectively; (2) The shrinkage stage of liquid nitrogen vacuoles is mainly dominated by the heat conduction at the phase interface, and there is no obvious collapse phenomenon. The minimum radius of liquid nitrogen bubble is about 5.5 times bigger than that of the ambient water bubble during the shrinkage stage; (3) The heat transfer at the phase interface is enhanced during the early stage of the oscillation stage, the surface roughening effects is amplified over the bubble surface resulting from Rayleigh-Taylor instability coupled with the thermal effects. And small broken bubbles exist near the bubble surface during the oscillation stage. When the input voltage is higher, the number of small bubbles at the bottom of the vacuole increases significantly; (4) Due to the large buoyancy coefficient of the liquid nitrogen bubble, the overall upward migration of liquid nitrogen bubble is significant in the late stage of liquid nitrogen. The bottom of the liquid nitrogen vacuole shrinks more quickly to create a depression, driving the vacuole to into a ring shape.
2022, 54(9): 1-14.   doi: 10.6052/0459-1879-22-144
The vulnerability analysis is a vital part of the seismic probabilistic risk assessment of nuclear power plants. However, due to the complexity of nuclear power structures and the larger calculation scale, the vulnerability analysis of NPP equipment is very time consuming when considering soil-structure interaction (SSI). In order to develop an efficient vulnerability analysis method, this paper adopts a partition calculation method applied to NPP SSI analysis, and establishes an artificial neural network (ANN) using limited SSI analysis results to substitute the FEM process. Based on the regression method with log-normal assumption and Monte Carlo method to analyze the equipment vulnerability. The ANN numerical simulation includes the following contents. (1) Establish the best ANN model through cross-validation to substitute the FEM process, and the most relevant ground motion parameters are selected as the ANN input based on the semi-partial correlation coefficient. (2) Quantification and investigation of the ANN prediction uncertainty. It includes the aleatory uncertainty caused by the simplification of the seismic inputs and the epistemic uncertainty from the limited size of the training data. (3) Computation of fragility curves with Monte Carlo method and the regression method with log-normal assumption based on the prediction data of ANN model. This paper explores the impact on fragility curves induced by different seismic intensity measures and uncertainty of soil material. Meanwhile, the results verify the basic rationality of the lognormal assumption and provide a possible direction for the vulnerability analysis of NPP equipment.
2022, 54(7): 1-12.   doi: 10.6052/0459-1879-21-466
Due to its extreme value characteristics, the Gauss principle is not only universal in principle, but also has great application value, such as the design and analysis of robots, approximate solutions of nonlinear vibration equations and dynamics of multi-body systems, etc. This paper deals with the generalized Gauss principle for mechanical systems with variable mass and its extension to higher order nonholonomic mechanics. Firstly, Gauss’s principle of least compulsion for mechanical system with variable mass is established, and extended to second order linear nonholonomic constrained systems by constructing modified compulsion function. Secondly, the generalized Gauss principle of mechanical system with variable mass for arbitrary order cases is proposed, and generalized Gauss’s principle of least compulsion is established, and the generalized compulsion function is constructed to extend the principle to high order nonholonomic constrained systems with variable mass. It is shown that for variable-mass mechanical system with bilateral ideal high-order nonholonomic constraints, the acceleration of real motion minimizes the generalized compulsion function under the Gauss variation in every instant among all the possible accelerations compatible with the constraints in the acceleration space. At the end of this paper, the differential equations of motion of a burning uniform sphere moving along a rough horizontal plane and the variable-mass Hamel problem are derived by applying the generalized Gauss’s principle of least compulsion.
Under the impacted of solar heat flux, the satellite antenna in orbit is prone to thermally induced vibration or inaccurate pointing. In this study, a modeling and model order reduction method for rigid flexible thermal coupling multibody system based on improved component mode synthesis method is proposed. The displacement and temperature field of the flexible antenna are discretized by the unified element shape function of the absolute node coordinate formulation (ANCF). The reference node is used to describe the central rigid bodies. In addition, the solar radiation input and the surface emitting radiation are considered in the system equation. Then, the Taylor expansion is used to linearized the dynamic and heat transfer equations. Afterwards, the improved component mode synthesis method is used to divide the substructure and reduce the degrees of freedom of the system. The substructures are connected by constraint equations to ensure the continuity between the structures. Finally, four numerical examples are given to verify the effectiveness of the proposed method. Without losing accuracy, the system scale is reduced and the computational efficiency is greatly improved.
Traction control system (TCS) based on road adhesion coefficient estimation is designed for the tractor. To track the time-varying nonlinear system, a fuzzy control theory and an attenuated memory filter are introduced into untraced Kalman filter, and the fuzzy forgetting factor unscented Kalman filter (FFUKF) is proposed to estimate road adhesion coefficient, which improves the tracking performance of the algorithm. Traction control includes torque control and braking control. For the TCS torque control, the road adhesion coefficient and the vehicle acceleration when the slip rate of the driving wheel is near the target slip rate are used to calculate the target base torque. According to the vehicle state and chattering parameters, the dynamic weight coefficient is obtained by the correlation function of extension set. The target base torques are designed by extension fusion of the torques calculated by the above methods. Then, the error between the actual slip rate and the target slip rate is used as the input, and the target feedback torque is obtained by using the fuzzy self-tuning PI controller. In terms of braking control, the pressure controls based on the PI controller are designed on two typical road surfaces. Test results show that the proposed algorithm can track the tire-road friction coefficient more quickly. The proposed control strategy can effectively restrain the excessive slip of the driving wheels, improving vehicle dynamic performance significantly.
Indentation scaling law is a general mechanics and physical conclusion for the determination of mechanical properties of solid materials by indentation test method. It has important theoretical significance and is a methodological study to explore the potential mechanics and physical laws of mechanical properties of materials. In this review paper, the main contents are introduced systematically and briefly as follows: a review of the research on the indentation scaling law of traditional solid materials by using the traditional mechanics theory; A review of the research on the trans-scale indentation scaling law of advanced solid materials by using the theory of trans-scale mechanics. The main conclusions are summarized as follows: the traditional indentation scaling law for solid materials can be completely described by a spatial surface. If the value range of a class of dimensionless independent parameters is known, the spatial surface can degenerate into a family of planar curves; The trans-scale indentation scaling law of advanced solid materials (new materials) can be completely described by a three-dimensional function relationship. If the value range of some independent dimensionless parameter is known, the three-dimensional function relationship will degenerate into a series of spatial surface families. The future research on indentation scaling law for researchers in this research region will be likely still to be focused on the establishment of trans-scale indentation scaling law for new materials, aiming to fundamentally solve the theoretical problems that it is difficult to establish the mechanical properties standard for new materials. In addition, they will be also likely focus on the establishment of multi-scale and trans-scale indentation scaling laws for various functional new materials. The chapters of this review paper are as follows: as the introduction of the research background; Some studies on indentation scaling law of traditional solid materials; The important role of dimensional analysis in the establishment of indentation scaling law; The theory of trans-scale mechanics for characterizing the trans-scale mechanical behavior of advanced solid materials; Characterization of trans-scale indentation scaling law; The future development of trans-scale hardness scaling law.
Due to the advantages of large storage ratio, high controllability, reconfigurability, easy assembly and diversified design, the origami structure has broad application prospects in the fields of aerospace, biomedicine, architecture, robotics, material science, etc. With the development of origami structure engineering, the dynamic research for the origami structure with low stiffness becomes more important. In this paper, a general bar-and-hinge dynamics model is developed, in which a non-rigid origami structure is equivalent to a spatial truss structure with rotational spring. Considering the geometric nonlinearity of the material, a bar element based on Ogden hyperelastic constitutive model is used to simulate the creases and virtual creases of the non-rigid origami structure, which can deal with the non-rigid origami structure with large overall motions and large deformations. A nonlinear rotational spring is introduced to reflect the bending resistance of the crease. Compared with the traditional rotational spring constitutive model, the modified nonlinear rotational spring constitutive model proposed in this paper has stronger versatility and robustness, and can effectively avoid the mutual penetration between the folding surfaces in contact-impact dynamics. Based on the principle of virtual work, the dynamic equations of the non-rigid origami multibody system considering the damping effect are established, which are solved by the variable-step generalized-α method. Finally, a series of numerical examples of three classical origami structures are presented to verify the accuracy and efficiency of the bar-and-hinge dynamics model proposed in this paper. Furthermore, by adding virtual creases and correcting the initial configuration, the locking problem of the unfolding and folding process in the rigid origami model is effectively resolved. Compared with the rigid origami model, the bar-and-hinge dynamics model can continue to perform further calculation and provide the fully deployed configuration with large deformation. On this basis, the complex dynamic behaviors of the non-rigid origami structure are revealed, and the mechanics characteristics of multi-stable, transient dynamics and wave dynamics are analyzed.
The damper is connected to the structure by setting the braces, but in order to simplify the analysis, the bracing stiffness is regarded as infinite, that is, the influence of braces on the random response of energy dissipation structure is not considered. Therefore, it is necessary to consider the influence of the braces with finite stiffness on the response of the structure. To analyze the response of the generalized Maxwell energy dissipation isolated structure considering the influence of the braces under the Hu Yuxian spectrum excitation, a concise analytic solution is proposed. The non-classical damping system is composed of the equivalent constitutive relation of the generalized Maxwell damper with braces, the structural motion equation and the Hu Yuxian spectral filtering equation. The complex modal method is used to decouple the system, and the Duhamel integral expression of the system series response based on white noise excitation is obtained through different response modes. Based on the properties of Dirac function, the system series response covariance is simplified into non-integral expression. According to Wiener-Khinchin relationship, the system series response power spectrum and ground acceleration power spectrum are obtained. Based on the definition of spectral moments, the 0 ~ 2 order spectral moments of system series response are obtained. The example verifies the correctness and efficiency of the proposed method in the bracing system by comparing with the pseudo excitation method, and discusses the influence of different bracing stiffness on damping effect of damper.
The ion concentration polarization phenomenon caused by ion selective surface provides a new idea for the development of micro-nano fluidic technology. When voltage is applied to the electrolyte solution with ions selective surface, the passing current will undergo complex nonlinear evolution. It triggers electric convection when the bias voltage is high enough. In this work, a multi block lattice Boltzmann Method algorithm is proposed to simulate this problem. The above multi block model overcomes shortcomings of uniform grid in the boundary layer of ion concentration. The information exchange equations of lattice Boltzmann distribution function between different grid blocks are given and the voltage current characteristic curve is obtained by simulation. The current increases first and then saturates with the increase of voltage, which is in good agreement with the theoretical solution. Further research shows that after convection occurs, the flow tends to form large rolls under a low voltage, and the intensity increases exponentially. While under a higher voltage, multi small rolls form first and then merge into larger rolls. The ions transport efficiency is higher when the large rolls are formed. It is worth noting that our multi blocks method also suitable for other numerical studies of electrohydrodynamic.
Under the pressure of energy and environmental protection, electric vehicle and intelligent driving have been attached great attention. The wheel vibration of electric vehicle driven by hub motors is severe, which has the more interaction with the bridge pavement. Current studies are mainly aimed at traditional vehicles, while there are few works on the dynamic interaction between electric wheels with bridge and vibration of multi-vehicle-bridge coupling system based on intelligent driving fleets. In this paper, considering the multi-point contact relationship between the wheel and bridge deck, the coupling dynamic characteristics of two intelligent driving of hub motors electric vehicles crossing the bridge are studied. The influences of motor mass, motor excitation, tire and suspension stiffness nonlinearity, vehicle distance and speed on vibration response of system, as well as the influences of bridge irregularities excitation and triple coupling excitation on ride comfort of electric vehicle are analyzed. The results show that, the vehicle distance and speed are important factors which affecting the vibration characteristics, and should be pay more attention to the dynamic design of vehicle-bridge coupling system. The more flat the bridge deck is, the more significant of influence of motor excitation and bridge deck secondary excitation on vehicle ride comfort and road friendliness are. When the vehicle is driving on a flat bridge deck, the influence of the two kinds of excitation on the hub motors electric vehicle should not be ignored. The proposed model is expected to provide a theoretical reference for the study of coupling vibration of intelligent driving electric vehicles and bridge.
2016, 48(4): 756-766.   doi: 10.6052/0459-1879-16-159

2017, 49(1): 3-21.   doi: 10.6052/0459-1879-16-348

2017, 49(1): 22-30.   doi: 10.6052/0459-1879-16-345

2016, 48(4): 767-783.   doi: 10.6052/0459-1879-16-161

2019, 51(3): 656-689.   doi: 10.6052/0459-1879-18-381

2017, 49(3): 550-564.   doi: 10.6052/0459-1879-17-064

2019, 51(1): 1-13.   doi: 10.6052/0459-1879-18-054

2016, 48(3): 519-535.   doi: 10.6052/0459-1879-15-436

2016, 48(4): 741-753.   doi: 10.6052/0459-1879-16-069

2017, 49(2): 239-256.   doi: 10.6052/0459-1879-16-255

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.
2012, 44(2): 269-277.   doi: 10.6052/0459-1879-2012-2-20120210
Abstract PDF(35)
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.
2012, 44(2): 252-258.   doi: 10.6052/0459-1879-2012-2-20120208
Abstract PDF(17)
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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