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2020 Vol. 52, No. 3

Display Method:
Jia Ran, Zhao Guiping
As a typical representation in various metallic foams, the aluminum foam is a kind of new material that integrates both structural properties and functional properties. With the improvement of production technology and the development of national economy, the application of the aluminum foam is becoming deeper and wider in the fields of aerospace engineering, transportation, construction engineering, machinery manufacturing and so forth. The complex load conditions in engineering application put forward higher requirements for the accuracy and practicability of the aluminum foam constitutive models. A great deal of experimental research and finite element numerical analysis on aluminum foam have been carried out by scholars both at home and abroad. With the proposal, verification and modification of various research constitutive models and numerical constitutive models, the understanding of researchers on the mechanical properties of aluminum foam becomes deeper and deeper. First of all, the development of experimental research and finite element numerical analysis on the mechanical properties of aluminum foam is briefly summarized in this paper; after that, the research progress and the present situation of constitutive model of aluminum foam both at home and abroad are emphatically reviewed; at last, aiming at the existing problems, the development trend of foam aluminum constitutive model is discussed and prospected. The important research directions in the existing aluminum foam constitutive model system are as follows: supplementing the characteristic parameters that are required for the characterization of constitutive model; introducing the anisotropic material assumption or the transversely isotropic material assumptions into the model building system; clarifying the weight of hydrostatic compression response and uniaxial compression response in material hardening; establishing hardening models which can truly and accurately reflect the hardening process of aluminum foam, such as the kinematic hardening model; introducing the research results of strain rate effect into the constitutive model and so forth.
2020, 52(3): 603-622. doi: 10.6052/0459-1879-20-020
2020, 52(3): 623-624. doi: 10.6052/0459-1879-20-148
Chen Xiaodong, Cui Haixin, Wang Anliang, Ji Shunying
The tensile strength of sea ice is one of the fundamental mechanical properties as well as a key parameter for the design of ships and offshore structures in ice-infected waters. For the determination of the tensile strength of brittle materials, the Brazilian test has advantages on sample preparation and loading procedure compared with the traditional method of uniaxial tension tests. To study the tensile strength of sea ice, the Brazilian tests were carried out on the sea ice with granular structure, which was collected in the Liaodong Bay of Bohai Sea. The load and loading plate displacement were recorded while the final failure pattern was photographed. Besides, the ice texture, salinity, temperature and density were also measured. The tests were performed on the ice samples with various thicknesses, temperatures and loading speeds. To calculate the tensile strength with high precision, the ice deformation is considered to improve the conventional formula. In all the experiments the ice samples failed in splitting manner. It means that the ice sample failed by reaching its tensile strength and the method works as initial expectation. The results show that the tensile strength has weak dependency on the loading speed and sample thickness but strong dependency on the total porosity. The tensile strength increased from 1.0 MPa to 2.8 MPa when total porosity decreased from 75‰ to 10‰. The results were compared with the tensile strength from uniaxial tension tests. It shows that both results have a similar trend where the total porosity and the tensile strength are in a negative relationship. However, the values of tensile strength from granular ice samples were higher than expectation. This study has identified that all the samples failed in expected pattern and the experiments provided reasonable results. It is a potential alternative for the investigation of tensile strength of sea ice.
2020, 52(3): 625-634. doi: 10.6052/0459-1879-20-036
Xin Guowei, Huang Ning, Zhang Jie
The Lan-Xin Railway II from Lanzhou to Xinjiang is the first high-speed railway which passes through the strong wind zones in the world, and it passes through the famous "Yan Dun", "Hundred Miles", "Thirty Miles" and "Dabancheng" wind zones. The total length of the railway is more than 462.4 kilometers, accounting for 65.1${\%}$ of the total length of railway in Xinjiang. Strong winds can do great harm to the operation, maintenance and transportation of railways. In order to resist the damage of strong wind to train, a large number of wind-break walls were built along the Lan-Xin Railway II. The wind-break wall reduces the strong wind damage, but brings a new disaster caused by sand sedimentation. To solve the problem of this engineering practice, this paper puts forward the idea of setting up the second retaining wall at different positions on the leeward side of existing wind-break wall to reduce sand particles sedimentation. The wind tunnel experiment was employed to simulate the wind-sand flow environment. Three typical configurations are considered: 1) single wind-break wall; 2) two walls and the second one locates at the top of the leeward slope of subgrade; 3) two walls and the second one locates at the foot of the leeward slope of subgrade. The decrease rates of the horizontal velocity, number density, horizontal transport flux and deposition rate of sand particles at the height of 0.1 m after the second wall are respectively 8${\%}$$\sim $12${\%}$, 51${\%}$$\sim $69${\%}$, 20${\%}$$\sim $73${\%}$ and 26${\%}$$\sim $38${\%}$, by comparing to the case without the second wall. It is found that the second retaining wall at the foot of the leeward slope of subgrade is optimal. The research result of this paper is helpful to optimize the preventing sand sedimentation measures of existing railway lines and towns in the strong wind zone.
2020, 52(3): 635-644. doi: 10.6052/0459-1879-20-045
Huang Can, Liu Qingquan, Wang Xiaoliang
There are many cascade hydropower dams on the main rivers in China. If cascade dam break happens, the peak flood discharge will be greatly enhanced as compared to the single dam break flood. Therefore, it is important to study the mechanism of peak discharge enhancement of cascade dam break floods. In this study, we developed a well-balanced numerical solver for the one-dimensional shallow water flow model with shock and wetting-drying capturing ability, to study the transformation mechanism of mass and energy in cascade dam break flood. A series of simulations with different combinations of upstream and downstream reservoir capacities imply that a jet-water tower mechanism greatly enhances the peak discharge of cascade dam break flood. The upstream dam break flood adds much mass and momentum into the downstream reservoir, and a tailing jet with large momentum behind replenishes additional mass and momentum continuously into the downstream reservoir during the downstream dam breaks. Based on the jet-water tower mechanism, we propose a novel simplified single dam break flood model with jet and water column for cascade dam break flood. Several simulations show that the new model is able to reproduce almost equivalent peak depth and discharge for small-scale cascade dam break floods. Applications for real-scale cascade dam break flow with dam distance of hundreds of kilometers reveal that the equivalent single dam break model could predict the peak water depth and discharge in cascade dam break flood within acceptable errors, which may provide scientific foundations for flood control and design of cascade dams.
2020, 52(3): 645-655. doi: 10.6052/0459-1879-20-044
Bao Yun, Xi Lingchu
In the environmental fluid mechanics, the turbulent wind field in the atmospheric layer is the driving force and the foundation for the study of the natural environment characteristics such as the wind and sand flow and the wind and snow flow. The calculation simulation of the turbulent wind field is usually used the turbulent boundary layer model, where the large eddy simulation (LES) is an effective computational tool. The parallel computing technology is one of the key technologies for the LES simulation to solve the large-scale turbulent wind field with the high Reynolds number. In the LES simulation of the turbulent wind field, the parallel computing technique of the pressure Poisson equation is the difficult point for the scale parallel calculation. Based on the characteristics of the turbulent wind field flow simulation, the horizontal grids are equidistant spacing and the grids perpendicular to the ground are non-equidistant. Using the FFT decoupling three-dimensional Poisson equation to make it a one-dimensional three-dimensional diagonal equation, and the parallel-able PDD technology is used to solve the three-diagonal equation for solving the difficult problem of the pressure Poisson equation in the scale parallel calculation, and the three-dimensional pressure Poisson equation can be solved directly in parallel. Combined with the other parallel momentum equation calculations, the parallel direct method of LES (PDM-LES) for the turbulent wind field simulation is established. The new method is tested in parallel on the supercomputer, and the parallel computing efficiency is 90${\%}$. The new method can be used for the large-scale parallel calculation for LES simulation of the turbulent wind field. The results show that there is a striped pre-order structure near the wall in the transient velocity distribution. The velocity distribution of the average field conforms to the logarithmic law, and the turbulence characteristic of the wind field is basically reasonable.
2020, 52(3): 656-662. doi: 10.6052/0459-1879-20-052
Wu Mengxi, Yang Jiaxiu, Zhan Zhenggang
The improved limit equilibrium method, which bases on the finite element stress field to analyze the stability of a slope, has an advantage in the analysis of the stability of a slope or a foundation with complex geological composition and strong coupling effect of seepage and effective stresses. In this paper, a virtual power method for slope stability analysis is proposed. The safety factor is calculated by using the ratio of anti-slip power to sliding power on the velocity discontinuities of the sliding mechanism by using the permissible velocity field for maneuvering of the combined rigid body sliding mechanism and the finite element stress field. The stability safety factor of a given sliding mechanism of the slope is obtained by the method of a step by step optimization strategy. Two typical sliding slope cases with weak interlayers are analyzed, including the comparison of the influence to the safety factor results of the stress fields whether static equilibrium only or also hydrostatic allowable. The safety factor in virtual power safety factor method based on linear elastic effective stress field is still a good measure to the stability of a slope even if it is not the best while the stress field is not static permissible. Slope safety factors calculated here are very close to the reference answers in the literature, the sliding mechanisms are consistent with and the safety coefficients are close to that of by the strength reduction finite element method. These show that the proposed method is reasonable. The proposed method is an alternative for the stability analysis of slopes and foundations.
2020, 52(3): 663-672. doi: 10.6052/0459-1879-20-040
Fan Jingyu, Chen Chunyan, Zhao Liang, Wang Daozeng
The mass exchange across sediment-water interface for rough bed depends on not only the hydrodynamic condition, but also the physical feature of the sediment bed and the bedform configuration. To take the comprehensive impact of sediment permeability and microtopography for the rough bed on the mass exchange process across the sediment-water interface into account, quantitative data and variation characteristics of interfacial mass exchange flux and effective diffusion coefficient under different conditions of the sandy beds without and with discrete roughness elements have been measured and obtained by means of laboratory annular flume experiment. A parameterization method has been adopted to analyze the dominant mechanism of interfacial mass exchange within the variation range of non-dimensional controlling parameters. The experimental results indicate that the sediment permeability and microtopography of the rough bed play a key role in the interfacial mass exchange process. An additional bumping exchange driven by the local flow structure around each roughness element increases interfacial mass exchange flux to varying degrees as compared to that for the case of flat bed, and this enhancement effect is closely related to the variations of the sediment permeability and bed roughness. The effective diffusion coefficient tends to increase on the whole with the increasing sediment permeability and bed roughness. Turbulence penetration shows an enhanced effect on the interfacial mass exchange, and the relative importance of the bumping exchange shows an attenuated effect trend. Therefore, an analysis of the dominant interfacial mass exchange mechanism for the rough bed with microtopography should take the comprehensive impact of the sediment permeability and bed roughness into consideration.
2020, 52(3): 673-679. doi: 10.6052/0459-1879-20-037
Wang Wenbo, Huang Ning, Dun Hongchao
When the railway goes through the windy desert area, the sand hazard endangers the railway engineering and normal operation of trains, and a suitable railway form design will reduce the hazard of accumulation of sand particles on railway. In this paper, taking Shashangou area of Dunhuang to Golmud railway as the research object, the multiphase flow method is used to simulate the wind sand movement over a sand dune with a railway in the reverse region, and the influence of wind sand movement on the railway subgrade engineering and bridge engineering located on the leeward slope of sand dunes is studied respectively. The main results of this work show that: The subgrade project significantly reduces the wind speed and divides the reverse area behind the sand dune into two parts, and the diversion effect of the bridge project compresses the reverse area of the leeward slope of the dune; the ballast between the tracks increases the aerodynamic roughness of the railway surface, and there is a small amount of sand deposition between tracks and a huge sand accumulations in both side of the subgrade; the complex interaction between wind field and sand particles makes the accumulated mass profiles of sand particles present non-linear relationship, the wind sweep ability for sand particles on the surface of railway grows faster than the sand accumulation ability with the increasing friction velocity in the bridge case, and this phenomenon is opposite in the subgrade case. According to the conclusion, it can be seen that the bridge engineering is better than the subgrade engineering in preventing the railway from being damaged by wind sand movement. This work offers a theoretical support for the influence of wind sand movement on railway engineering, and provides a new research thought and tool for the railway engineering design in the future.
2020, 52(3): 680-688. doi: 10.6052/0459-1879-20-043
Cheng Pengda, Zhu Xinguang, Feng Chun, Wang Xiaoliang
In environmental hydrodynamics, the release of pollutants from sediments is one of the main problems. Under the condition of hydrodynamics, the resuspension of polluted sediment makes a large number of pollutants released again, resulting in the secondary pollution of water body. Based on a large number of experimental data provided by water channel experiments, a coupled mechanical model of overlying water body, sediment and pollutants is established in this paper. The process of sediment incipient motion and pollutant release are numerically simulated under different velocity of overlying water. The quantitative relationships among velocity, particle volume fraction, pollutant concentration, turbulent kinetic energy and time are obtained by analyzing the relationship between flow field characteristics and pollutant concentration distribution. The results show that the pollutants release process of sediment resuspended is a coupling process composed of overlying water, sediment and pollutants. When the sediment particles are resuspended into the overlying water body, the flow characteristics of overlying water and the release of pollutants are affected rapidly. For the non-adsorption pollutants, the complex characteristics of flow field are the main factors affecting the release of pollutants from resuspended sediment. When the flow field characteristics ($Re$) change, the contribution of convection diffusion and turbulent diffusion is different to pollutant release process. The coupling model of overlying water body, sediment and pollutants is established, and the quantitative relationship between hydrodynamic conditions and sediment pollutant release is studied, which can provide support for the construction of water pollution model in lake and reservoir area.
2020, 52(3): 689-697. doi: 10.6052/0459-1879-20-047
Mao Dong, Tang Qiuming, Gao Qiang
HV insulators take on an important role in power transmission engineering. Because of the rapid development of industrialization, sandstorms and smog often happen. Contamination particles deposit on insulator surface under air flow field, pollution high voltage flashover accidents are prone occur, which seriously affects the safe operation of the power grid. In this paper, to investigate the mechanism of pollution high voltage flashover, a coupling analysis of dynamic accumulation and electric field distortion on insulator surface is explored. A model of gas-solid two phase flow around insulator is established by Euler-Euler approach to simulate the dynamic pollution accumulation process. Thus the distribution of non-uniform contamination layer on the insulator surface is obtained. The surface conductive layer element of the contamination layer is created, and it is used in finite element model of electric field on the polluted insulator, and the electric potential and electric field of the insulator string with non-uniform contamination are analyzed. The results show that: in the case of non-uniform contamination layer, the circumferential position of the polluted layer on the insulator surface has less influence on the trend of its potential distribution, but has greater influence on the position of electric field distortion. With the variation of circumferential position, the deviation of electric field distortion position is different, and maximum deviation occurs on crosswind. The electric field intensity is larger than clean insulator surface with increase of contamination layer conductivity. Furthermore, the field intensity distortion on leeward is the largest.
2020, 52(3): 698-706. doi: 10.6052/0459-1879-20-042
Wei Xinrong, Duan Shaozhen, Sun Jinlong, Wang Wenda
The landslide rolling stone disaster is a prevailing natural hazard in the western mountainous regions of China. The rolling stone disasters featured by burstiness and uncertainty are hard to forecast and prevent the geological disaster. Based on the particle contact theory and considering the random factors in the process of the particle collision, a theoretical model for predicting the velocity of the rolling stone particles after impacting the slope is established. According to the theorem of impulse and momentum moment, the basic equations of rolling stone particles collision are established, and the analytical solutions of the rebound velocity after the rolling stone particles impacting the slope are obtained. The results show that the analytical solutions of the rebound velocity after impacting include the random factors such as slope angle, the velocity and angle of particles on the slope, incident velocity, angle and impact angle. It is found that the model results agree well with the experimental results when the impact angle of incident rolling stone particle impacts the particle on the slope is changed. At the same time, this paper predicts the probability distribution of the rebound velocity, rebound angle and rebound rotational angular velocity after the collision. The results show that the probability distributions of rebound velocity, rebound angle and rebound rotation angular velocity follow Gaussian distribution. When the velocity of particles on the slope and the slope angle change, they have no qualitative influence on the rebound particle velocity, rebound angle and the rebound rotation angular velocity probability distribution, but they have significant influence on the center parameters of probability distribution.
2020, 52(3): 707-715. doi: 10.6052/0459-1879-20-039
Zhan Jun, Zhang Jie, Yang Juancheng, Ni Mingjiu
The motion of solid particles in the liquid is frequently encountered in everyday life and engineering applications. It attracts the devotement of many researchers due to the abundant fluid dynamic phenomena behind the motion of solid particles in the liquid. In the present paper, we experimentally study the falling characteristics of a single prolate sphere particle descending in water under the influence of buoyancy force. The motion tracking platform which consists of two orthogonal high-speed cameras and light sources accompanied by the fluorescence visualization technology is adopted to obtain the paths and vortex structures of the falling prolate sphere particle. The density ratio between the selected prolate sphere and surrounding fluid is 1.2, while the aspect ratio of the selected prolate sphere varies from 2 to 10, the corresponding Archimedes number changes from 400 to 1400, and finally, the terminal Reynolds number is limited in the range from 120 to 1350. During the experiments, we observe five typical types of paths during the falling process of the prolate spheres, which corresponds to small amplitude irregular motion, small-amplitude high-frequency oscillation motion, large-amplitude low-frequency oscillation motion, highly nonlinear motion and rectilinear motion, respectively. And the evolution of the oscillation of velocity and the inclination angle is obtained. Furthermore, we analyze the relationships between the drag coefficient of the freely falling prolate sphere and the Reynolds number during the falling process. Then, by using the fluorescence visualization technique, we identify the different vortex shedding modes, which are responsible for different falling trajectories, and study the influence of vortex shedding on the path of free falling prolate sphere. Finally, comparing with some previous results on the falling characteristics of the slender cylinder, we find the similarities and differences of the motion characteristics between the prolate sphere and the slender cylinder and the potential physical mechanism.
2020, 52(3): 716-727. doi: 10.6052/0459-1879-20-005
Zhang Yantao, Sun Jiao, Gao Ti, a, Fan Ying
Particle image velocimetry (PIV) was used to investigate the effect of solid particles on the wake structure of an isolated hemispherical roughness element placed in a laminar boundary layer of a flat plate. The two-dimensional velocity field information for four operating conditions of single phase and addition of 140 $\mu$m, 200 $\mu$m and 350 $\mu$m polystyrene particles was experimentally collected. The Reynolds number based on hemisphere radius was 994 ($Re_R=RU/\upsilon$). The volume concentration of particles was $3.0\times10^{-5}$. The turbulence statistics such as average velocity profile, comprehensive turbulence intensity and reflux area size under clean water and two-phase conditions are compared to analyze the influence of solid particles on macro characteristics of hemispherical wake flow. The two-dimensional spatial correlation coefficient and power spectral density function of pulsating velocity along the flow direction at different positions along the flow direction are respectively used to analyze the effect of solid particles on the evolution process of wake structure and the shedding frequency of wake structure. The results show that: compared with clear water, the reflux zone gradually increases with the increase of solid particle size; The presence of solid particles increases the comprehensive turbulence intensity and due to the existence of the backflow region, the turbulence intensity in the region before and after the hemispheric backward flow direction position $2R$ presents different changing trends The presence of solid particles reduces the flow direction dimension of the wake structure and the flow direction dimension firstly decreases and then increases with the increase of particle size The presence of solid particles in the wake structure promotes the periodic acceleration and deceleration of the wake structure, and the promotion effect increases first and then decreases with the increase of solid particle size. The presence of solid particles promotes the shedding of wake structure, and the shedding frequency of wake structure increases first and then decreases with the increase of particle size.
2020, 52(3): 728-739. doi: 10.6052/0459-1879-19-353
Chen Yinghong, Wang Yunjiang, Qiao Jichao
Metallic glass is a well-known engineering material that has been attracting tremendous research interest in materials science and condense matter physics. Early studies of the properties and structures of the metallic glasses showed that the dynamic heterogeneity is closely linked to the viscoelasticity and plasticity of metallic glasses. However, the physical landscape between the macroscopic stress relaxation behavior and the mechanical relaxation is still obscure. Different from the deformation mechanism of their crystalline counterparts, the deformation mechanism of metallic glasses is more complicated. To fully understand the mechanical properties of metallic glass, it is necessary to ascertain the structural characteristics of different spatial scales of metallic glass and evolution of structural characteristics with time. The significant importance is the connection between the macroscopic stress relaxation behavior and the dynamic mechanical relaxations (β relaxation, or α relaxation) in metallic glasses. Stress relaxation is a robust technique to characterize the viscoelastic and plastic mechanisms in glasses which can reflect their structural and dynamic heterogeneities. In the current research, La30Ce30Al15Co25 metallic glass was used as a model system, dynamic mechanical processes and stress relaxation behavior were studied. Compared with other traditional metallic glasses, La30Ce30Al15Co25 metallic glass shows a pronounced β relaxation process. The analysis based on the Kohlarausch-Willams-Watts (KWW) equation suggests that the stress relaxation process of metallic glass is a heterogeneous dynamic process. We observed an unusual two-stage stress relaxation phenomenon, consisting of the fast stress-driven event and the slow thermally activated event. The two-stage stress relaxation behavior is attributed the stress-driven event and thermally activated event to short-range atomic rearrangement, and long-range atomic diffusion, respectively. In addition, the analysis of the activation energy spectrum shows that the activation of the stress relaxation unit is not uniform, which corresponds to fluctuations in energy. This research is a step towards building a bridge linking the structural and dynamic heterogeneity of metallic glasses, and strongly supports the physical scenario of β to α relaxation.
2020, 52(3): 740-748. doi: 10.6052/0459-1879-20-013
Lu Guangda, Chen Jianbing
Inspired by peridynamics and the unified phase-field model, a new nonlocal macro-meso-scale consistent damage model has been proposed recently, which provides a new method for the numerical simulation of crack propagation. In the present paper, the criterion for meso-scale damage in this model is modified, and a $\bar{\lambda}-\ell $ damage language is proposed to depict the displacement discontinuity in a cracked solid. In the modified model, the meso-scale damage characterizing the performance degradation of bond between two material points (namely a material point pair), is firstly determined according to the maximum exceedance of deformation of the point pair in terms of the critical elongation quantity during loading history. Then, by the weighted averaging over the meso-scale damage of material point pairs in the influence domain, the macro-scale topologic damage is obtained. Further, by advocating the energetic degradation function, the energy-based damage can be connected to the topologic damage, and in turn can be inserted into the framework of continuum damage mechanics such that governing equations are readily established. The proposed method is a nonlocal model, and it can be numerically implemented by the finite element discretization, where the problem of mesh size sensitivity that occurs in the classical continuum damage mechanics model is circumvented. The modified model is applied to crack modeling problems involving strong nonlinear snap-back property. Examples are studied, showing that the proposed method can not only characterize the crack patterns, but also capture quantitatively the load-deformation curves. The problems to be studied in the future are also discussed.
2020, 52(3): 749-762. doi: 10.6052/0459-1879-19-319
Xu Can, Zhu Ping, Liu Zhao, Tao Wei
Plain woven carbon fiber composites have multi-scale characteristics and spatial randomness in structure. Meanwhile, the mechanical properties of the component materials vary due to different storage conditions, composition phase components and batches. When the stochastic mechanical properties of plain woven carbon fiber composites are predicted with considering of the parameter uncertainty at different scales, there are two main difficulties: first, the large number of random variables makes the accuracy and efficiency of the uncertainty propagation method required; second, a high-precision correlation model is needed to be established because of multi-dimensional correlations. To solve above problems, this paper proposes a multi-scale prediction method based on polynomial chaos expansion and vine Copula for the stochastic mechanical properties of plain woven composites. The random parameters of materials and structures at the microscopic and mesoscopic scales of the plain woven composites are taken into account, and the uncertainties of mechanical properties are studied scale by scale based on the bottom-up hierarchical propagation strategy. In this method, Vine Copula theory is used to construct the multi-dimensional joint probability distribution of correlated random variables, and the non-embedded polynomial chaos expansion is used to realize uncertainty propagation. Results show that the correlation coefficients of the dependence model constructed by the proposed method are almost the same as that of original data and the stochastic prediction of mechanical properties at different scales are realized efficiently and accurately.
2020, 52(3): 763-773. doi: 10.6052/0459-1879-20-002
Wang Shuai, Xu Fei, Dai Zhen, Liu Xiaochuan, Li Xiaocheng, Yang leifeng, Xi Xulong
The distortion of structural impact arising from the use of different materials between the full-size protype and the small-size scaled model is usually compensated by the correction for the velocity or density of the scaled model. However, the traditional correction methods are limited for the application of similarity laws because of some inherent defects such as the needs to test structural response in advance, the dependence for the special constitutive equation and the inability to reflect dynamic process of impact. In the present paper, a direct scaling method for distortion problems is proposed. Based on the best approximation relationships between the predicted flow yield stress of the scaled model and the flow yield stress of the prototype on strain rate interval, the scaling factor for the corrected velocity or the corrected density are obtained directly, and the dynamic similarity relations between the scaled model and the prototype are established. Based on the Norton-Hoff, Cowper-Symonds and Johnson-Cook constitutive models, the influences of material parameters of the strain-rate-sensitive, the reference strain-rate, the yield stress and the density for the dynamic similarity relations are studied. And a crooked plate under impact mass is used to verify the effectiveness of the proposed directly scaling method. The analysis shows that the proposed directly scaling method does not need to test the structural response information in advance, does not depend on the specific form of constitutive equation and emphasis the dynamic similarity characteristics, so that it has the direct, efficient and universal characteristics. The optimal approximation effects of the dynamic similarity relations are mainly controlled by the material strain-rate-sensitive characteristic parameters, while the reference strain-rate, the yield stress and the density have little influence. When the material strain-rate-sensitive characteristic parameters of the scale model are similar to those of the prototype, the best dynamic approximation effects can be obtained.
2020, 52(3): 774-786. doi: 10.6052/0459-1879-19-327
Zhang Xirun, Cai Lixun, Chen Hui
For the hyperelastic problems of materials under indentation conditions, based on the mean-value energy density equivalence principle, semi-theoretical hyperelastic-material indentation models(SHIM) are proposed to describe the relationship among load, depth, indenter dimension and Mooney-Rivlin constitutive parameters under independent indentation with spherical indenter, flat indenter and conical indenter, respectively, and then the indentation method due to dual indenters(IMDI) is presented. The forward verification shows that, based on a series constitutive relation parameters of hyperelastic materials, the force-depth curves of spherical, conical and flat indentation respectively predicted by SHIM are closely consistent with the FEA results; and the reverse verification shows that, based on the force-depth curves under FEA conditional constitutive relation of a series of hyperelastic materials, the Mooney-Rivlin constitutive relations predicted by the dual indentation experimental method are closely consistent with the FEA conditional constitutive relations. For three hyperelastic rubbers, the spherical, flat and conical indentation tests were carried out, three constitutive relationships of the hyperelastic rubbers obtained by IMDI are all in good agreement with the uniaxial tensile results.
2020, 52(3): 787-796. doi: 10.6052/0459-1879-20-023
Ye Xiangping, Duan Zhiwei, Yu Yuying, Geng Huayun, Li Xuemei, Hu Ling, Cai Lingcang, Liu Cangli
Neutron irradiation hardening and embrittlement of metallic materials is very important in the field of nuclear energy and safety. In order to further understand the effects of pre-strain on the plastic deformation and fracture characteristics of neutron irradiated metals and its microscopic mechanism, the tensile stress-strain, plastic instability stress and plastic instability strain of tensile pre-strain high-purity aluminum with different doses were studied in this paper. The results showed that a higher dose results in a higher density and size of voids, a higher yield strength and ultimate tensile stress, a smaller elongation ratio and plastic instability strain, which showed a typical radiation hardening and embrittlement effects, but the plastic instability stress was almost independent of dose. Under the same dose, the high density of dislocation inducing by pre-strain could significantly reduce the size and density of voids, coupling the irradiation annealing effect, that resulted in the pre-strain could reduce the growth rate of yield strength and the falling rate of plastic instability strain, which means the pre-strain could inhibit irradiation hardening and irradiation embrittlement of neutron irradiated high-purity aluminum to a certain degree, but the pre-strain could not improve ductility of high-purity aluminum. Finally, the neutron irradiation embrittlement model for annealed metals basing on Johnson-Cook constitutive model could be directly applied to pre-strain metal materials, and the predicted results of present model agreed well with the experimental data. This means the neutron irradiation embrittlement model for metals basing on Johnson-Cook constitutive model can predict the whole true stress-strain curve, and the fracture true strain of the irradiated annealed and pre-strain metal materials by using the true stress-strain of unirradiated annealed metal and the yield strength of metals with different doses and pre-strain only. That is very important in the field of estimating and predicting safety of nuclear reactor.
2020, 52(3): 797-804. doi: 10.6052/0459-1879-19-370
Wang Enmei, Wu Shunan, Wu Zhigang
Subject to carrying capacity of a launch vehicle, on-orbit assembly technology has become one of the most promising solutions for building ultra-large space structures in the future. The size of the space structure is gradually increasing, and the dynamic characteristics are changing during the assembly process, which brings new challenge to the dynamic modelling and structural active control. Aiming at this issue, an active-control-oriented dynamic modelling method for the on-orbit assembly space structure is proposed in this paper. As the on-orbit assembly mission possess high regularity and repeatability, the basic model database is firstly established for different modules to improve the modelling efficiency, including the module type, the assembly interface, etc. In order to describe the varying on-orbit assembly space structure, the adjacent matrices of modules are defined. The form of intelligent component (IC) oriented to distributed control are then designed, taking the characteristics of the assembly task into consideration. Based upon the finite element modelling method, the 'node freedom degree loading' method is proposed to develop the dynamic models of the IC and the whole space structure, which are adaptively updated along with assembly. Finally, the numerical simulation are carried out on the truss structure under the assembly impact, including the dynamics analysis and the distributed vibration control. The simulation results show that the dynamic characteristics of truss structure experience obvious changes during the process, and the active vibration control is necessary; the modelling method proposed in this paper, with the established basic model database and the 'node freedom degree loading', applies to various on-orbit assembly space structure; According to the adjacency relation matrix, the active-control-oriented dynamic models of the IC can be updated in a limited range during the assembly process, which reduces the complexity of control system and is suitable for distributed active control of on-orbit assembly structure.
2020, 52(3): 805-816. doi: 10.6052/0459-1879-19-375
Jiao Liu, Zhang Baocheng, Zhang Kaisheng, Zhao Bo
In order to study and design a new type of bionic robotic fish with high softness and strong environmental adaptability, imitating the shape of shark and the swimming posture of tuna fish, a bionic robotic fish with hydraulic flexible driving structure is designed. In view of the problem that the single-joint hydraulically driven flexible robotic fish has a C-shaped swing posture that does not conform to the swing rule of tuna fish, a two-joint hydraulic flexible drive is used to simulate the S-shaped swing of the fish, and the internal structure of the bionic fish is designed according to the principle of the hydraulic flexible actuator. According to the theoretical wave equation, the swing amplitude of the robotic fish is determined, the magnitude of the pressure load applied inside the flexible actuator is calculated by numerical simulation, and the driving efficiency of the hydraulic flexible actuator is analyzed and calculated. The software of finite element analysis is used to simulate the autonomous swimming process of the robotic fish in the fluid. And the autonomous cruise process of the two-joint robotic fish and the one-joint roboic fish are simulated and compared to obtain the movement postures, swimming velocity and flow field of the two robotic fishes when they autonomously cruised in the fluid. The results show that at the same frequency and tail-fin swing, the average velocity of the two-joint soft roboic fish cruising is 0.29 BL/s, which is higher than the average velocity of the the one-joint roboic fish 0.15 BL/s. And frome the velocity vector diagram, it can be concluded that the S-type swing of the two-joint roboic fish is closer to the real fish swing attitude, and a series of discrete reverse Karman Vortex Streets will be generated during the movement, so the two-joint bionic fish has a higher propulsion efficiency.
2020, 52(3): 817-827. doi: 10.6052/0459-1879-20-001
Li Shuxia, Guo Shangping, Chen Yueming, Zhang Ningtao, Wu Didi
As an unconventional, clean energy resource, natural gas hydrate is abundant and widely distributed in the subsea and permafrost area. Since the 1990s, permafrost and ocean hydrate production tests have been conducted successively by Canada, the United States, Japan and China. However, many problems such as the producing of sand, low gas production rate and very short stable production time of single well have been found during the production tests. The gas production rate was much less than the demand of the commercial exploitation. The main challenge is that the mechanism of hydrate dissociation, multi-phase, multi-component and multi-field coupling seepage characteristics in the process of hydrate exploitation still remain unclear. According to the multi-field coupling characteristics of hydraulic field, thermal field, chemical field and mechanical field involved in the development of natural gas hydrate, this paper summarizes the effects of hydrate formation/decomposition on the main characteristic parameters of each physical field, including the basic physical parameters of hydrate reservoirs and their dynamic evolution (porosity, hydrate saturation, permeability and relative permeability), thermodynamic parameters (thermal conductivity, specific heat, thermal diffusivity and heat of formation/decomposition of hydrate), kinetic characteristics of hydrate formation and decomposition, mechanical properties of pure hydrate and hydrate-bearing sediments. Finally, the multi-field coupling relationship and interaction in the seepage of natural gas hydrate development are reviewed, and suggestions for the future scientific research and technology development of multi-physics characteristics and coupling seepage in hydrate development are put forward.
2020, 52(3): 828-842. doi: 10.6052/0459-1879-20-050
Yu Weilun, Wu Xiaogang, Li Chaoxin, Sun Yuqin, Zhang Meizhen, Chen Weiyi
In order to accurately describe the fluid flow in osteon, this study developed a method to describe the fluid anisotropic flow based on the density, shape and direction of lacunae. Firstly, the number and distribution of the bone canaliculi around the lacunae were calculated. Secondly, the permeability and porosity were estimated by using the calculated parameters and other microstructure data of bone tissue. Finally, the poroelastic finite element model of osteon was established according to the calculated parameters, and the influence of lacunae shape and direction on the fluid flow behavior in osteon under the axial displacement load was analyzed. The results showed that the lacunae shape and direction had a significant effect on the value and distribution of fluid pressure and velocity in osteon. For the range of parameters investigated, the influence of the lacunae shape on the maximum pressure and flow velocity in the same region of different osteon models can reach 86% and 18%, respectively, and the influence of the lacunae direction on that can reach 125% and 56%, respectively. In addition, the lacunae shape and direction had a great influence on the local pressure and velocity of a single osteon (up to 62% difference in fluid pressure between regions due to the influence of the lacunae shape, and up to 58% and 50% difference in fluid pressure and flow velocity due to the influence of the lacunae direction, respectively). The model showed that the lacunae shape and direction and the three-dimensional distribution of the canaliculus can determine the degree of anisotropy fluid flow in osteon. This study help to accurately quantify the anisotropic flow behavior of interstitial fluid of bone.
2020, 52(3): 843-853. doi: 10.6052/0459-1879-19-357
Feng Shiliang, Zhou Lüwen, Lü Shouqin, Long Mian
Epithelial cells develop adherens junctions via local recruitment of a transmembrane receptor, named E-cadherin, whose activity is dependent on Ca$^{2+}$ signal. Growing evidences indicate the importance of tensile forces within actomyosin cortex, yet a system-level understanding for the mechanosensitive responses of cell-cell contacts remains unclear. Here, we constructed a mechanochemical coupling model, in which the tensile forces presented at adherens junctions participated in the interactions between myosin contractility, actin dynamics and local E-cadherin recruitment, which together, formed a mechanical feedback loop (MFL). The mechanical interactions between a pair of epithelial cells were treated by a motor-clutch mechanism. The in-house developed lattice-Boltzmann particle (LBP)-D1Q3 method, which had been embedded with a simple Monte-Carlo method, was adopted to solve the coupled nonlinear reaction-diffusion equations, which had stochastic reaction terms, and were coupled with the equilibrium differential equation. The numerical simulation results indicate that the spatiotemporal effects of MFL may arise an initial anisotropy in the distribution pattern of E-cadherin, which could be further amplified by "cis" interactions between E-cadherins from the same cell surface. The model thus confirms three distinct phases in the profile of E-cadherin accumulation at the center of contact zone, which are initial, rapid increase, and slowly increase, as observed experimentally. Furthermore, local recruitment of E-cadherin can be mechanically regulated by either the elastic modulus of actomyosin cortex or the extent of cell-cell contact, whereupon the highest E-cadherin density takes place at 1.2 rad. Accordingly, decreasing the elastic modulus of actomyosin cortex may thus act as a triggering mechanism for MFL while the length of cell-cell contact is denoted as a controller of the maturity of adherens junctions.
2020, 52(3): 854-863. doi: 10.6052/0459-1879-20-011
Xu Jipeng, Dong Xinlong, Fu Yingqian, Yu Xinlu, Zhou Fenghua
Brazilian splitting test was widely used in the evaluation of tensile strength of brittle materials, but the results of strength are difference with different loading boundaries, such as flat plates, bearing strips, arc die, and flattened Brazilian disc,which has always been a research focus. In this paper, the splitting test was designed under different loading boundaries of direct flat plates and bearing strips, and analyzed theoretically, carried out experimentally as well. By the high-speed camera and digital image correlation (DIC) method, the process of the evolution of strain field, crack initiation and propagation on the surface of the specimen were studied in the splitting test. The influence of different loading boundaries on the tensile strength and the strain concentration evolution were further discussed. The results show that: (1) The evolution characteristics of strain concentration caused by the nonlinear tensile properties of concrete are sensitive to loading conditions, which lead to strain concentration earlier from the loading ends and evolves to the center of the specimen when loaded by flat plates . In this case, even the experimental condition of "center cracking" is satisfied, its strength still lower than that of bearing strips, the difference can reach 17.9%; (2) As long as the contact angles of bearing strips loading is designed properly, the stress field of the specimen can develop stably than that of direct flat plate loading, which is conductive to ensure strain concentration as well as fracture starting from the center. It is better to meet the requirements of the Brazilian splitting test; (3) It is not sufficient to only verify the validity condition of "center cracking", which must be carefully considered in the test design and analysis. The research results have important reference significance for the design and test analysis of the Brazilian splitting experiment of brittle materials.
2020, 52(3): 864-876. doi: 10.6052/0459-1879-19-303
Chen Qiao, Zhang Kuo, Chen Jilong, Zhang Shaojie, Lü Jun, Zhou Rufu, Wei Fangqiang
When a soil landslide is near the landslide stage, infrasound waves are generated. Infrasound monitoring can be used as a technical means to determine whether a soil landslide is in the approaching stage Considering that the landslide's mechanical method is mainly shear failure, in order to ascertain the response characteristics of infrasound signals during the process of soil landslides, a combined infrasound-force-displacement monitoring system for soil shear experiments was designed and an infrasound monitoring test for soil failure was carried out. Based on the automatic picking up of infrasound events, combined with the theory of progressive failure of cohesive soil, the micro-acoustic mechanism during the shearing process is analyzed. The results show that: (1) The infrasound signals emitted during shear failure of cohesive soil are mainly derived from three aspects: first, from the mutual compression of clay particles in the elastic phase, and then from the tensile fracture of clay colloidal particles in the elastic-plastic phase, finally, it comes from the friction between soil particles during strain softening. (2) The amplitude of the infrasound signal shows a certain regularity at different stages of soil shear loading. The amplitude of the infrasound signal during the elastoplastic phase is the largest. The amplitude of the infrasound signal during the strain softening phase is minimal. The amplitude of the infrasound signal corresponding to the elastic phase is between the elastoplastic phase and the strain softening phase (3) There is a strong correlation between the shear force and the infrasound signal. The peak envelope of the infrasound event matches the shear force trend line. At the same time, the mean square power peak of the infrasound signal is ahead of the thrust peak. The average time is 22.95 s. The research has important theoretical reference value for further using infrasound to carry out monitoring and stability evaluation of soil landslides.
2020, 52(3): 877-889. doi: 10.6052/0459-1879-19-253
Wu Kui, Shao Zhushan, Qin Su
Large deformation problem in soft rocks tunnels at great depth has become a great challenging task for many rock engineers. According to the deformation characteristics of soft rocks under high pressure, yielding supports following the principle of deformation release are able to accommodate rock deformations without being damaged, having been proved to be a feasible and effective solution to deal with such problem. The main purpose of this paper is to theoretically investigate the mechanical response of a deep circular tunnel excavated in rheological rock masses, where yielding supports are applied. Based on the fractional derivative theory the improved fractional Burgers creep model by adopting the Abel viscous element is established to describe the time-dependent deformations of geomaterials. In addition, the correction coefficients of supporting stiffness in different deformation stages are proposed aiming at solving the problem that the traditional supports are unable to take the rock deformation release into account. According to those, this paper derives the analytical solutions for stresses and displacements around the tunnel in different deformation stages, considering the installation delay of support structures. Furthermore, in order to validate the effectiveness and reliability of the theoretical analyses, a well agreement between different solutions and field results can be obtained. Finally, the parametric investigation demonstrates that tunnel displacement and support pressure are greatly influenced by the fractional order of Burgers model representing the deformability of rocks. There exists a linear relationship between tunnel displacement or support pressure and yielding displacement. This linear relationship can also be found between tunnel displacement or support pressure and the correction coefficient of support stiffness. If this correction coefficient ranges in a low level, the change of tunnel displacement or support pressure is not remarkable. This paper may provide a new trail to quickly evaluate the time-dependent deformations of tunnels with yielding supports.
2020, 52(3): 890-900. doi: 10.6052/0459-1879-20-006