According to the biomechanic theory and method, the dynamic mechanism of crop growth under the external force action of multi_environment factors (light, temperature,soil and nutrients etc.) was comprehensively explor...According to the biomechanic theory and method, the dynamic mechanism of crop growth under the external force action of multi_environment factors (light, temperature,soil and nutrients etc.) was comprehensively explored.Continuous_time Markov(CTM) approach was adopted to build the dynamic model of the crop growth system and the simulated numerical method. The growth rate responses to the variation of the external force and the change of biomass saturation value were studied. The crop grew in the semiarid area was taken as an example to carry out the numerical simulation analysis, therefore the results provide the quantity basis for the field management. Comparing the dynamic model with the other plant growth model, the superiority of the former is that it displays multi_dimension of resource utilization by means of combining macroscopic with microcosmic and reveals the process of resource transition. The simulation method of crop growth system is advanced and manipulated. A real simulation result is well identical with field observational results.展开更多
An understanding of dendrite growth is required in order to improve the properties of castings. For this reason, cellular automaton-finite difference(CA-FD) method was used to investigate the dendrite growth during di...An understanding of dendrite growth is required in order to improve the properties of castings. For this reason, cellular automaton-finite difference(CA-FD) method was used to investigate the dendrite growth during directional solidification(DS)process. The solute diffusion model combined with macro temperature field model was established for predicting the dendrite growth behavior. Model validation was performed by the DS experiment, and the cooling curves and grain structures obtained by the experiment presented a reasonable agreement with the simulation results. The competitive growth of dendrites was also simulated by the proposed model, and the competitive behavior of dendrites with different misalignment angles was also discussed in detail.Subsequently, 3D dendrites growth was also investigated by experiment and simulation, and both were in good accordance. The influence on dendrites growth of initial nucleus was investigated by three simulation cases, and the results showed that the initial nuclei just had an effect on the initial growth stage of columnar dendrites, but had little influence on the final dendritic morphology and the primary dendrite arm spacing.展开更多
Numerical analysis and simulation have been an effective means to develop the advanced growth technology and to control the defects type, size and density for silicon crystals of 300 mm and beyond. In the present pape...Numerical analysis and simulation have been an effective means to develop the advanced growth technology and to control the defects type, size and density for silicon crystals of 300 mm and beyond. In the present paper, numerical analysis of the melt flow in the Czochralski （CZ） crystal growth configuration, the three dimensional （3D） modeling, the simulation of melt flow under the magnetic field, the inverse modeling and the time-dependent simulation are reviewed. Finally, comparison of numerical analysis with experimental measurements is discussed.展开更多
The dendrite growth behavior of high-strength steel during slab continuous casting with a traveling-wave magnetic field was studied in this paper. The morphology of the solidification structure and composition distrib...The dendrite growth behavior of high-strength steel during slab continuous casting with a traveling-wave magnetic field was studied in this paper. The morphology of the solidification structure and composition distribution were analyzed. Results showed that the columnar crystals could deflect and break when the traveling-wave magnetic field had low current intensity. With the increase in current intensity, the secondary dendrite arm spacing and solute permeability decreased, and the columnar crystal transformed into an equiaxed crystal. The electromagnetic force caused by the traveling-wave magnetic field changed the temperature gradient and velocity magnitude and promoted the breaking and fusing of dendrites. Dendrite compactness and composition uniformity were arranged in descending order as follows:columnar-toequiaxed transition (high current intensity), columnar crystal zone (low current intensity), columnar-to-equiaxed transition (low current intensity), and equiaxed crystal zone (high current intensity). Verified numerical simulation results combined with the boundary layer theory of solidification front and dendrite breaking–fusing model revealed the dendrite deflection mechanism and growth process. When thermal stress is not considered, and no narrow segment can be found in the dendrite, the velocity magnitude on the solidification front of liquid steel can reach up to 0.041 m/s before the dendrites break.展开更多
A multi-scale continuous-discrete model based on the effects of the p27 gene control is built to simulate the avascular tumor growth. At the tissue level, the continuous Eulerian model is adopted to determine the dist...A multi-scale continuous-discrete model based on the effects of the p27 gene control is built to simulate the avascular tumor growth. At the tissue level, the continuous Eulerian model is adopted to determine the distribution of the concentration of oxygen, the extracellular matrix （ECM）, and the matrix-degradative enzyme （MDE）. At the cellular level, the discrete Lagrangien model is adopted to determine the movement, the proliferation, and the death of single tumor cells （TCs）. At the genetic level, whether a cell is committed to mitosis is determined by solving a set of equations modeling the effects of the p27 gene control. The avascular morphological evolution of the solid tumor growth is simulated, including the radius the oxygen distribution over time, and the expression. of the solid tumor, the number of the TCs, inhibiting effect＇ of the up-regulating p27 gene展开更多
Phase field method offers the prospect of being able to perform realistic numerical experiments on dendrite growth in a metallic system. In this paper, the equiaxed dendrite evolution during the solidification of a pu...Phase field method offers the prospect of being able to perform realistic numerical experiments on dendrite growth in a metallic system. In this paper, the equiaxed dendrite evolution during the solidification of a pure material was numerically simulated using the phase field model. The equiaxed dendrite growth in a two-dimensional square domain of undercooled melt (nickel) with four-fold anisotropy was simulated. The phase field model equations was solved using the explicit finite difference method on a uniform mesh. The formation of various equiaxed dendrite patterns was shown by a series of simulations, and the effect of anisotropy on equiaxed dendrite morphology was investigated.展开更多
Thermally grown oxide(TGO)is a critical factor for the service life of thermal barrier coatings(TBC).Numerical simulations of the growth process of TGO have become an effective means of comprehensively understanding t...Thermally grown oxide(TGO)is a critical factor for the service life of thermal barrier coatings(TBC).Numerical simulations of the growth process of TGO have become an effective means of comprehensively understanding the progressive damage of the TBC system.At present,technologies of numerical simulation to TGO growth include two categories:coupled chemical-mechanical methods and mechanical equivalent methods.The former is based on the diffusion analysis of oxidizing elements,which can describe the influence of bond coat(BC)consumption and phase transformation in the growth process of TGO on the mechanical behavior of each layer of TBC,and has high accuracy for the thickness evolution of TGO,but they cannot describe the lateral growth of TGO and the rumpling phenomenon induced.The latter focuses on describing the final stress and strain state after the growth of a specific TGO rather than the complete growth processes of TGO.Based on the measured TGO thickness growth curve,simulations of thickening and lateral growth can be achieved by directly applying anisotropic volumetric strain to oxidized elements and switching elements properties from the BC to the TGO.展开更多
Numerical results show that an external magnetic field may influence significantly the flow pattern in the molten semiconductor of Czochralski crystal growth. The melt flow could be pronouncedly damped by a magnet. ic...Numerical results show that an external magnetic field may influence significantly the flow pattern in the molten semiconductor of Czochralski crystal growth. The melt flow could be pronouncedly damped by a magnet. ic field with the intensity of several thousands Gauss, while the temperature field is affected only in a less extent by the magnetic field.展开更多
The cavity growth was studied in uniaxial tension of superplastic magnesium alloy. An exponentially increasing cavity growth model was introduced into the numerical simulation effectively. A three dimensional rigid vi...The cavity growth was studied in uniaxial tension of superplastic magnesium alloy. An exponentially increasing cavity growth model was introduced into the numerical simulation effectively. A three dimensional rigid visco plastic finite element method (FEM) program was developed to predict the variation of radius and volume fraction of cavity. Experimental radius and volume fraction of cavity were determined based on the optical microscope observation and analyses. The values obtained by numerical simulation are perfectly in agreement with experimental results. The results are potentially helpful to designing the optimal processing parameters for superplastic forming of materials and to enhance their subsequent mechanical properties.展开更多
Glucose is the mainly nutrient substances in tumor growth,which played an important role in tumor cells' growth,proliferation and immigration.Numerical simulation will help a good understanding for the influence o...Glucose is the mainly nutrient substances in tumor growth,which played an important role in tumor cells' growth,proliferation and immigration.Numerical simulation will help a good understanding for the influence of glucose which affected on a vascular solid tumor growth.We present a hybrid on-Lattice Model to simulate the influence of glucose on a-vascular tumor growth.The hybrid model we developed focuses on five key variables implicated in the invasion process:tumor cells,extracellular matrix,matrix-degradative enzymes,oxygen and glucose.And about the discrete model,we consider cell evolution dynamics on cell level.Results indicate that the number of proliferation and quiescent cells is decreasing by decreasing the initial glucose concentration,consequently increase necrotic area relatively.Thus there is inhabitation effect on tumor growth by decreasing initial glucose concentration.展开更多
Alhagi sparsifolia Shap. （Fabaceae） is a spiny, perennial herb. The species grows in the salinized, arid regions in North China. This study investigated the response characteristics of the root growth and the dis- t...Alhagi sparsifolia Shap. （Fabaceae） is a spiny, perennial herb. The species grows in the salinized, arid regions in North China. This study investigated the response characteristics of the root growth and the dis- tribution of one-year-old A. sparsifolia seedlings to different groundwater depths in controlled plots. The eco- logical adaptability of the root systems of A. sparsifolia seedlings was examined using the artificial digging method. Results showed that： （1） A. sparsifolia seedlings adapted to an increase in groundwater depth mainly through increasing the penetration depth and growth rate of vertical roots. The vertical roots grew rapidly when soil moisture content reached 3%-9%, but slowly when soil moisture content was 13%-20%. The vertical roots stopped growing when soil moisture content reached 30% （the critical soil moisture point）. （2） The morphological plasticity of roots is an important strategy used by A. sparsifolia seedlings to obtain water and adapt to dry soil conditions. When the groundwater table was shallow, horizontal roots quickly expanded and tillering increased in order to compete for light resources, whereas when the groundwater table was deeper, vertical roots developed quickly to exploit space in the deeper soil layers. （3） The decrease in groundwater depth was probably respon- sible for the root distribution in the shallow soil layers. Root biomass and surface area both decreased with soil depth. One strategy of A. sparsifolia seedlings in dealing with the increase in groundwater depth is to increase root biomass in the deep soil layers. The relationship between the root growth/distribution of A. sparsifolia and the depth of groundwater table can be used as guidance for harvesting A. sparsifolia biomass and managing water resources for forage grasses. It is also of ecological significance as it reveals how desert plants adapt to arid environments.展开更多
The growth of mixing zone on an interface induced by Richtmyer-Meshkov(RM)instability occurs frequently in natural phenomena and in engineering applications.Usually,the medium on which the RM instability happens is in...The growth of mixing zone on an interface induced by Richtmyer-Meshkov(RM)instability occurs frequently in natural phenomena and in engineering applications.Usually,the medium on which the RM instability happens is inhomogeneous,the effect of medium inhomogeneity on the growth of the mixing zone during the RM instability is still not clear.Therefore,it is necessary to investigate the RM instability in inhomogeneous medium.Based on a high-order computational scheme,the interactions of a density interface with an incident shock wave(ISW)in inhomogeneous medium are numerically simulated by solving the compressible Navier-Stokes equations.The effect of the inhomogeneity on the interface evolution after the passage of ISW through the interface is investigated.The results show that the interface morphology develops in a distinctive "spike-spike"structure in inhomogeneous medium.Particularly,the spike structure on the bottom of the interface is due to the reverse induction of RM instability by curved ISW or reflected shock wave.With the increase of inhomogeneity,the growth rate of the mixing zone width on interface increases,and the wave patterns caused by interaction between the shock wave and interface are more complex.Compared with RM instability in homogeneous medium,the inhomogeneous distribution of the density in medium further enhances the baroclinic effect and induces larger vorticity in flow field.Therefore,the interface is stretched much more significantly under the induction of enhanced vorticity in inhomogeneous medium.Based on above analyses,a model for predicting the growth of mixing zone width on the interface after the passage of ISW is proposed,in order to provide a useful method for evaluations of perturbation growth behavior during the RM instability in inhomogeneous medium.展开更多
In this study, graphene sheets are prepared under a hydrogen atmosphere without a catalyst, and the growth mechanism of graphene by direct current arc discharge is investigated experimentally and numerically. The size...In this study, graphene sheets are prepared under a hydrogen atmosphere without a catalyst, and the growth mechanism of graphene by direct current arc discharge is investigated experimentally and numerically. The size and layer numbers of graphene sheets increase with the arc current.Distributions of temperature, velocity, and mass fraction of carbon are obtained through numerical simulations. A high current corresponds to a high saturation temperature, evaporation rate, and mass density of carbon clusters. When the carbon vapor is saturated, the saturation temperatures are 3274.9, 3313.9, and 3363.6 K, and the mass densities are 6.4×1022,8.42×1022, and 1.23×1023 m-3 under currents of 150, 200, and 250 A, respectively. A hydrogen-induced marginal growth model is used to explain the growth mechanism. Under a high current, the condensation coefficient and van der Waals force increase owing to the higher saturation temperature and mass density of carbon clusters, which is consistent with experimental results.展开更多
A multiphase cellular automaton model was developed to simulate microstructure evolution of near eutectic spheroidal graphite cast iron(SGI) during its solidification process, and both dendritic austenite and spheroid...A multiphase cellular automaton model was developed to simulate microstructure evolution of near eutectic spheroidal graphite cast iron(SGI) during its solidification process, and both dendritic austenite and spheroidal graphite growth models were adopted. To deduce the mesh anisotropy of cellular automaton method, the composition averaging and geometrical parameter were introduced to simulate the spheroidal graphite growth. Solute balance method and decentered square algorithms were employed to simulate austenite dendrites growth with different crystallographic orientations. The simulated results indicate that the graphite nodule grows in a spherical morphology when the surrounding environment of a single graphite nodule is same. However, for two adjacent graphite nodules, the environment is different. The higher the carbon concentration, the faster the growth of graphite. By comparison with experimental results, it is found that the microstructure evolution of near eutectic spheroidal graphite cast iron during solidification process can be reproduced quantitatively by numerical simulation with this model.展开更多
A lattice Boltzmann （LB）-cellular automaton （CA） model is employed to study the dendrite growth of A1-4.0 wt%Cu- 1.0 wt%Mg alloy. The effects of melt convection, solute diffusion, interface curvature, and preferre...A lattice Boltzmann （LB）-cellular automaton （CA） model is employed to study the dendrite growth of A1-4.0 wt%Cu- 1.0 wt%Mg alloy. The effects of melt convection, solute diffusion, interface curvature, and preferred growth orientation are incorporated into the coupled model by coupling the LB-CA model and the CALPHAD-based phase equilibrium solver, PanEngine. The dendrite growth with single and multiple initial seeds was numerically studied under the conditions of pure diffusion and melt convection. Effects of initial seed number and melt convection strength were characterized by new- defined solidification and concentration entropies, The numerical result shows that the growth behavior of dendJ-ites, the final microstructure, and the micro-segregation are significantly influenced by melt convection during solidification of the ternary alloys. The proposed solidification and concentration entropies are useful characteristics bridging the solidification behavior and the microstructure evolution of alloys.展开更多
Due to the extensive application of Al-Si alloys in the automotive and aerospace industries as structural components, an understanding of their microstructural formation, such as dendrite and(Al+Si) eutectic, is of gr...Due to the extensive application of Al-Si alloys in the automotive and aerospace industries as structural components, an understanding of their microstructural formation, such as dendrite and(Al+Si) eutectic, is of great importance to control the desirable microstructure, so as to modify the performance of castings. Since previous major themes of microstructural simulation are dendrite and regular eutectic growth, few efforts have been paid to simulate the irregular eutectic growth. Therefore, a multiphase cellular automaton(CA) model is developed and applied to simulate the time-dependent Al-Si irregular eutectic growth. Prior to model establishment, related experiments were carried out to investigate the influence of cooling rate and Sr modification on the growth of eutectic Si. This CA model incorporates several aspects, including growth algorithms and nucleation criterion, to achieve the competitive and cooperative growth mechanism for nonfaceted-faceted Al-Si irregular eutectic. The growth kinetics considers thermal undercooling, constitutional undercooling, and curvature undercooling, as well as the anisotropic characteristic of eutectic Si growth. The capturing rule takes into account the effects of modification on the silicon growth behaviors.The simulated results indicate that for unmodified alloy, the higher eutectic undercooling results in the higher eutectic growth velocity, and a more refined eutectic microstructure as well as narrower eutectic lamellar spacing. For modified alloy, the eutectic silicon tends to be obvious fibrous morphology and the morphology of eutectic Si is determined by both chemical modifier and cooling rate. The predicted microstructure of Al-7Si alloy under different solidification conditions shows that this proposed model can successfully reproduce both dendrite and eutectic microstructures.展开更多
Casting microstructure evolution is difficult to describe quantitatively by only a separate simulation of dendrite scale or grain scale, and the numerical simulation of these two scales is difficult to render compatib...Casting microstructure evolution is difficult to describe quantitatively by only a separate simulation of dendrite scale or grain scale, and the numerical simulation of these two scales is difficult to render compatible. A three-dimensional cellular automaton model couplling both dendritic scale and grain scale is developed to simulate the microstructure evolution of the nickel-based single crystal superalloy DD406. Besides, a macro–mesoscopic/microscopic coupling solution algorithm is proposed to improve computational efficiency. The simulation results of dendrite growth and grain growth of the alloy are obtained and compared with the results given in previous reports. The results show that the primary dendritic arm spacing and secondary dendritic arm spacing of the dendritic growth are consistent with the theoretical and experimental results. The mesoscopic grain simulation can be used to obtain results similar to those of microscopic dendrites simulation. It is indicated that the developed model is feasible and effective.展开更多
Thermocapillary-and buoyancy-driven convection in open cavities with differentially heated endwalls is investigated by numerical solutions of the two- dimensional Navier-Stokes equations coupled with the energy equati...Thermocapillary-and buoyancy-driven convection in open cavities with differentially heated endwalls is investigated by numerical solutions of the two- dimensional Navier-Stokes equations coupled with the energy equation. We studied the thermocapillary and buoyancy convection in the cavities, filled with low-Prandtl- number fluids, with two aspect-ratios A=1 and 4, Grashof number up to 10~5 and Reynolds number |Re|≤10~4. Our results show that thermocapillary can have a quite significant effect on the stability of a primarily buoyancy-driven flow, as well as on the flow structures and dynamic behavior for both additive effect (i.e., positive Re) and opposing effect (i.e., negative Re).展开更多
Both a real time optical interferometric experiment and a numerical simulation of two-dimension non-steady state model were employed to study the growth process of aqueous sodium chlorate crystals. The parameters such...Both a real time optical interferometric experiment and a numerical simulation of two-dimension non-steady state model were employed to study the growth process of aqueous sodium chlorate crystals. The parameters such as solution concentration distribution, crystal dimensions, growth rate and velocity field were obtained by both experiment and numerical simulation. The influence of earth gravity during crystal growth process was analyzed. A reasonable theory model corresponding to the present experiment is advanced. The thickness of concentration boundary layer was investigated especially. The results from the experiment and numerical simulation match well.展开更多
Characteristics of root pullout resistance determine the capacity to withstand uprooting and the slope protection ability of plants.However,mechanism underlying the uprooting of taproot-type shrub species in the loess...Characteristics of root pullout resistance determine the capacity to withstand uprooting and the slope protection ability of plants.However,mechanism underlying the uprooting of taproot-type shrub species in the loess area of northeastern Qinghai-Xizang Plateau,China remains unclear.In this study,a common taproot-type shrub,Caragana korshinskii Kom.,in northeastern Qinghai-Xizang Plateau was selected as the research material.Mechanism of root-soil interaction of vertical root of C.korshinskii was investigated via a combination of a single-root pullout test and numerical simulation analysis.The results indicated that,when pulling vertically,axial force of the roots decreased with an increase in buried depth,whereas shear stress at root-soil interface initially increased and then decreased as burial depths increased.At the same buried depth,both axial force and shear stress of the roots increased with the increase in pullout force.Shear stress and plastic zone of the soil surrounding the root were symmetrically distributed along the root system.Plastic zone was located close to the surface and was caused primarily by tensile failure.In nonvertical pulling,symmetry of shear stress and plastic zone of the soil surrounding the root was disrupted.We observed larger shear stress and plastic zones on the side facing the direction of root deflection.Plastic zone included both shear and tensile failure.Axial force of the root system near the surface decreased as deflection angle of the pullout force increased.When different rainfall infiltration depths had the same vertical pulling force,root axial force decreased with the increase of rainfall infiltration depth and total root displacement increased.During rainfall infiltration,shear stress and plastic zone of the soil surrounding the root were prone to propagating deeper into the soil.These findings provide a foundation for further investigation of soil reinforcement and slope protection mechanisms of taproot-type shrub species in the loess area of northeastern Qinghai-Xizang Plateau and similar areas.展开更多
文摘According to the biomechanic theory and method, the dynamic mechanism of crop growth under the external force action of multi_environment factors (light, temperature,soil and nutrients etc.) was comprehensively explored.Continuous_time Markov(CTM) approach was adopted to build the dynamic model of the crop growth system and the simulated numerical method. The growth rate responses to the variation of the external force and the change of biomass saturation value were studied. The crop grew in the semiarid area was taken as an example to carry out the numerical simulation analysis, therefore the results provide the quantity basis for the field management. Comparing the dynamic model with the other plant growth model, the superiority of the former is that it displays multi_dimension of resource utilization by means of combining macroscopic with microcosmic and reveals the process of resource transition. The simulation method of crop growth system is advanced and manipulated. A real simulation result is well identical with field observational results.
基金Project(2017ZX04014001) supported by the National Science and Technology Major Project of ChinaProject(2017YFB0701503) supported by the National Key R&D Program of ChinaProject(51374137) supported by the National Natural Science Foundation of China
文摘An understanding of dendrite growth is required in order to improve the properties of castings. For this reason, cellular automaton-finite difference(CA-FD) method was used to investigate the dendrite growth during directional solidification(DS)process. The solute diffusion model combined with macro temperature field model was established for predicting the dendrite growth behavior. Model validation was performed by the DS experiment, and the cooling curves and grain structures obtained by the experiment presented a reasonable agreement with the simulation results. The competitive growth of dendrites was also simulated by the proposed model, and the competitive behavior of dendrites with different misalignment angles was also discussed in detail.Subsequently, 3D dendrites growth was also investigated by experiment and simulation, and both were in good accordance. The influence on dendrites growth of initial nucleus was investigated by three simulation cases, and the results showed that the initial nuclei just had an effect on the initial growth stage of columnar dendrites, but had little influence on the final dendritic morphology and the primary dendrite arm spacing.
基金the International Scientific and Technical Corporation Major Planning Project (No. 2005DFA5105).
文摘Numerical analysis and simulation have been an effective means to develop the advanced growth technology and to control the defects type, size and density for silicon crystals of 300 mm and beyond. In the present paper, numerical analysis of the melt flow in the Czochralski （CZ） crystal growth configuration, the three dimensional （3D） modeling, the simulation of melt flow under the magnetic field, the inverse modeling and the time-dependent simulation are reviewed. Finally, comparison of numerical analysis with experimental measurements is discussed.
基金financially supported by the National Natural Science Foundation of China (No.51774031)。
文摘The dendrite growth behavior of high-strength steel during slab continuous casting with a traveling-wave magnetic field was studied in this paper. The morphology of the solidification structure and composition distribution were analyzed. Results showed that the columnar crystals could deflect and break when the traveling-wave magnetic field had low current intensity. With the increase in current intensity, the secondary dendrite arm spacing and solute permeability decreased, and the columnar crystal transformed into an equiaxed crystal. The electromagnetic force caused by the traveling-wave magnetic field changed the temperature gradient and velocity magnitude and promoted the breaking and fusing of dendrites. Dendrite compactness and composition uniformity were arranged in descending order as follows:columnar-toequiaxed transition (high current intensity), columnar crystal zone (low current intensity), columnar-to-equiaxed transition (low current intensity), and equiaxed crystal zone (high current intensity). Verified numerical simulation results combined with the boundary layer theory of solidification front and dendrite breaking–fusing model revealed the dendrite deflection mechanism and growth process. When thermal stress is not considered, and no narrow segment can be found in the dendrite, the velocity magnitude on the solidification front of liquid steel can reach up to 0.041 m/s before the dendrites break.
基金Project supported by the National Natural Science Foundation of China （Nos. 10372026 and 10772751）
文摘A multi-scale continuous-discrete model based on the effects of the p27 gene control is built to simulate the avascular tumor growth. At the tissue level, the continuous Eulerian model is adopted to determine the distribution of the concentration of oxygen, the extracellular matrix （ECM）, and the matrix-degradative enzyme （MDE）. At the cellular level, the discrete Lagrangien model is adopted to determine the movement, the proliferation, and the death of single tumor cells （TCs）. At the genetic level, whether a cell is committed to mitosis is determined by solving a set of equations modeling the effects of the p27 gene control. The avascular morphological evolution of the solid tumor growth is simulated, including the radius the oxygen distribution over time, and the expression. of the solid tumor, the number of the TCs, inhibiting effect＇ of the up-regulating p27 gene
文摘Phase field method offers the prospect of being able to perform realistic numerical experiments on dendrite growth in a metallic system. In this paper, the equiaxed dendrite evolution during the solidification of a pure material was numerically simulated using the phase field model. The equiaxed dendrite growth in a two-dimensional square domain of undercooled melt (nickel) with four-fold anisotropy was simulated. The phase field model equations was solved using the explicit finite difference method on a uniform mesh. The formation of various equiaxed dendrite patterns was shown by a series of simulations, and the effect of anisotropy on equiaxed dendrite morphology was investigated.
基金supported by the National Natural Science Foundation of China(Grant No.51905510)National Science and Technology Major Project(J2019-IV-0003-0070).
文摘Thermally grown oxide(TGO)is a critical factor for the service life of thermal barrier coatings(TBC).Numerical simulations of the growth process of TGO have become an effective means of comprehensively understanding the progressive damage of the TBC system.At present,technologies of numerical simulation to TGO growth include two categories:coupled chemical-mechanical methods and mechanical equivalent methods.The former is based on the diffusion analysis of oxidizing elements,which can describe the influence of bond coat(BC)consumption and phase transformation in the growth process of TGO on the mechanical behavior of each layer of TBC,and has high accuracy for the thickness evolution of TGO,but they cannot describe the lateral growth of TGO and the rumpling phenomenon induced.The latter focuses on describing the final stress and strain state after the growth of a specific TGO rather than the complete growth processes of TGO.Based on the measured TGO thickness growth curve,simulations of thickening and lateral growth can be achieved by directly applying anisotropic volumetric strain to oxidized elements and switching elements properties from the BC to the TGO.
基金supported by the National Natural Foundation of China
文摘Numerical results show that an external magnetic field may influence significantly the flow pattern in the molten semiconductor of Czochralski crystal growth. The melt flow could be pronouncedly damped by a magnet. ic field with the intensity of several thousands Gauss, while the temperature field is affected only in a less extent by the magnetic field.
文摘The cavity growth was studied in uniaxial tension of superplastic magnesium alloy. An exponentially increasing cavity growth model was introduced into the numerical simulation effectively. A three dimensional rigid visco plastic finite element method (FEM) program was developed to predict the variation of radius and volume fraction of cavity. Experimental radius and volume fraction of cavity were determined based on the optical microscope observation and analyses. The values obtained by numerical simulation are perfectly in agreement with experimental results. The results are potentially helpful to designing the optimal processing parameters for superplastic forming of materials and to enhance their subsequent mechanical properties.
文摘Glucose is the mainly nutrient substances in tumor growth,which played an important role in tumor cells' growth,proliferation and immigration.Numerical simulation will help a good understanding for the influence of glucose which affected on a vascular solid tumor growth.We present a hybrid on-Lattice Model to simulate the influence of glucose on a-vascular tumor growth.The hybrid model we developed focuses on five key variables implicated in the invasion process:tumor cells,extracellular matrix,matrix-degradative enzymes,oxygen and glucose.And about the discrete model,we consider cell evolution dynamics on cell level.Results indicate that the number of proliferation and quiescent cells is decreasing by decreasing the initial glucose concentration,consequently increase necrotic area relatively.Thus there is inhabitation effect on tumor growth by decreasing initial glucose concentration.
基金supported by the Knowledge Innovation Program of the Chinese Academy of Sciences (KZCX2-EW-316)the National Natural Science Foundation of China (31070477,30870471)the West Light Foundation of the Chinese Academy of Sciences (XBBS201105)
文摘Alhagi sparsifolia Shap. （Fabaceae） is a spiny, perennial herb. The species grows in the salinized, arid regions in North China. This study investigated the response characteristics of the root growth and the dis- tribution of one-year-old A. sparsifolia seedlings to different groundwater depths in controlled plots. The eco- logical adaptability of the root systems of A. sparsifolia seedlings was examined using the artificial digging method. Results showed that： （1） A. sparsifolia seedlings adapted to an increase in groundwater depth mainly through increasing the penetration depth and growth rate of vertical roots. The vertical roots grew rapidly when soil moisture content reached 3%-9%, but slowly when soil moisture content was 13%-20%. The vertical roots stopped growing when soil moisture content reached 30% （the critical soil moisture point）. （2） The morphological plasticity of roots is an important strategy used by A. sparsifolia seedlings to obtain water and adapt to dry soil conditions. When the groundwater table was shallow, horizontal roots quickly expanded and tillering increased in order to compete for light resources, whereas when the groundwater table was deeper, vertical roots developed quickly to exploit space in the deeper soil layers. （3） The decrease in groundwater depth was probably respon- sible for the root distribution in the shallow soil layers. Root biomass and surface area both decreased with soil depth. One strategy of A. sparsifolia seedlings in dealing with the increase in groundwater depth is to increase root biomass in the deep soil layers. The relationship between the root growth/distribution of A. sparsifolia and the depth of groundwater table can be used as guidance for harvesting A. sparsifolia biomass and managing water resources for forage grasses. It is also of ecological significance as it reveals how desert plants adapt to arid environments.
文摘The growth of mixing zone on an interface induced by Richtmyer-Meshkov(RM)instability occurs frequently in natural phenomena and in engineering applications.Usually,the medium on which the RM instability happens is inhomogeneous,the effect of medium inhomogeneity on the growth of the mixing zone during the RM instability is still not clear.Therefore,it is necessary to investigate the RM instability in inhomogeneous medium.Based on a high-order computational scheme,the interactions of a density interface with an incident shock wave(ISW)in inhomogeneous medium are numerically simulated by solving the compressible Navier-Stokes equations.The effect of the inhomogeneity on the interface evolution after the passage of ISW through the interface is investigated.The results show that the interface morphology develops in a distinctive "spike-spike"structure in inhomogeneous medium.Particularly,the spike structure on the bottom of the interface is due to the reverse induction of RM instability by curved ISW or reflected shock wave.With the increase of inhomogeneity,the growth rate of the mixing zone width on interface increases,and the wave patterns caused by interaction between the shock wave and interface are more complex.Compared with RM instability in homogeneous medium,the inhomogeneous distribution of the density in medium further enhances the baroclinic effect and induces larger vorticity in flow field.Therefore,the interface is stretched much more significantly under the induction of enhanced vorticity in inhomogeneous medium.Based on above analyses,a model for predicting the growth of mixing zone width on the interface after the passage of ISW is proposed,in order to provide a useful method for evaluations of perturbation growth behavior during the RM instability in inhomogeneous medium.
基金supported by National Natural Science Foundation of China (No. 11765010)the National Key Research and Development Program of China (No. 2019YFC1907900)+2 种基金the Applied Basic Research Programs of Yunnan Provincial Science and Technology Department (No. 202001AW070004)the Freely Exploring Fund for Academicians in Yunnan Province (No. 2018HA006)the Key Laboratory of Resource Chemistry, Ministry of Education (No. KLRCME2001)
文摘In this study, graphene sheets are prepared under a hydrogen atmosphere without a catalyst, and the growth mechanism of graphene by direct current arc discharge is investigated experimentally and numerically. The size and layer numbers of graphene sheets increase with the arc current.Distributions of temperature, velocity, and mass fraction of carbon are obtained through numerical simulations. A high current corresponds to a high saturation temperature, evaporation rate, and mass density of carbon clusters. When the carbon vapor is saturated, the saturation temperatures are 3274.9, 3313.9, and 3363.6 K, and the mass densities are 6.4×1022,8.42×1022, and 1.23×1023 m-3 under currents of 150, 200, and 250 A, respectively. A hydrogen-induced marginal growth model is used to explain the growth mechanism. Under a high current, the condensation coefficient and van der Waals force increase owing to the higher saturation temperature and mass density of carbon clusters, which is consistent with experimental results.
基金supported by the National Natural Science Foundation of China(51601107)
文摘A multiphase cellular automaton model was developed to simulate microstructure evolution of near eutectic spheroidal graphite cast iron(SGI) during its solidification process, and both dendritic austenite and spheroidal graphite growth models were adopted. To deduce the mesh anisotropy of cellular automaton method, the composition averaging and geometrical parameter were introduced to simulate the spheroidal graphite growth. Solute balance method and decentered square algorithms were employed to simulate austenite dendrites growth with different crystallographic orientations. The simulated results indicate that the graphite nodule grows in a spherical morphology when the surrounding environment of a single graphite nodule is same. However, for two adjacent graphite nodules, the environment is different. The higher the carbon concentration, the faster the growth of graphite. By comparison with experimental results, it is found that the microstructure evolution of near eutectic spheroidal graphite cast iron during solidification process can be reproduced quantitatively by numerical simulation with this model.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51728601 and 51771118)
文摘A lattice Boltzmann （LB）-cellular automaton （CA） model is employed to study the dendrite growth of A1-4.0 wt%Cu- 1.0 wt%Mg alloy. The effects of melt convection, solute diffusion, interface curvature, and preferred growth orientation are incorporated into the coupled model by coupling the LB-CA model and the CALPHAD-based phase equilibrium solver, PanEngine. The dendrite growth with single and multiple initial seeds was numerically studied under the conditions of pure diffusion and melt convection. Effects of initial seed number and melt convection strength were characterized by new- defined solidification and concentration entropies, The numerical result shows that the growth behavior of dendJ-ites, the final microstructure, and the micro-segregation are significantly influenced by melt convection during solidification of the ternary alloys. The proposed solidification and concentration entropies are useful characteristics bridging the solidification behavior and the microstructure evolution of alloys.
基金financially supported by the National Basic Research Program of China(Grant No.2011CB706801)the National Natural Science Foundation of China(Grant No.51374137,51171089)the National Science and Technology Major Projects(Grant No.2012ZX04012-011,2011ZX04014-052)
文摘Due to the extensive application of Al-Si alloys in the automotive and aerospace industries as structural components, an understanding of their microstructural formation, such as dendrite and(Al+Si) eutectic, is of great importance to control the desirable microstructure, so as to modify the performance of castings. Since previous major themes of microstructural simulation are dendrite and regular eutectic growth, few efforts have been paid to simulate the irregular eutectic growth. Therefore, a multiphase cellular automaton(CA) model is developed and applied to simulate the time-dependent Al-Si irregular eutectic growth. Prior to model establishment, related experiments were carried out to investigate the influence of cooling rate and Sr modification on the growth of eutectic Si. This CA model incorporates several aspects, including growth algorithms and nucleation criterion, to achieve the competitive and cooperative growth mechanism for nonfaceted-faceted Al-Si irregular eutectic. The growth kinetics considers thermal undercooling, constitutional undercooling, and curvature undercooling, as well as the anisotropic characteristic of eutectic Si growth. The capturing rule takes into account the effects of modification on the silicon growth behaviors.The simulated results indicate that for unmodified alloy, the higher eutectic undercooling results in the higher eutectic growth velocity, and a more refined eutectic microstructure as well as narrower eutectic lamellar spacing. For modified alloy, the eutectic silicon tends to be obvious fibrous morphology and the morphology of eutectic Si is determined by both chemical modifier and cooling rate. The predicted microstructure of Al-7Si alloy under different solidification conditions shows that this proposed model can successfully reproduce both dendrite and eutectic microstructures.
文摘Casting microstructure evolution is difficult to describe quantitatively by only a separate simulation of dendrite scale or grain scale, and the numerical simulation of these two scales is difficult to render compatible. A three-dimensional cellular automaton model couplling both dendritic scale and grain scale is developed to simulate the microstructure evolution of the nickel-based single crystal superalloy DD406. Besides, a macro–mesoscopic/microscopic coupling solution algorithm is proposed to improve computational efficiency. The simulation results of dendrite growth and grain growth of the alloy are obtained and compared with the results given in previous reports. The results show that the primary dendritic arm spacing and secondary dendritic arm spacing of the dendritic growth are consistent with the theoretical and experimental results. The mesoscopic grain simulation can be used to obtain results similar to those of microscopic dendrites simulation. It is indicated that the developed model is feasible and effective.
文摘Thermocapillary-and buoyancy-driven convection in open cavities with differentially heated endwalls is investigated by numerical solutions of the two- dimensional Navier-Stokes equations coupled with the energy equation. We studied the thermocapillary and buoyancy convection in the cavities, filled with low-Prandtl- number fluids, with two aspect-ratios A=1 and 4, Grashof number up to 10~5 and Reynolds number |Re|≤10~4. Our results show that thermocapillary can have a quite significant effect on the stability of a primarily buoyancy-driven flow, as well as on the flow structures and dynamic behavior for both additive effect (i.e., positive Re) and opposing effect (i.e., negative Re).
基金Project supported by the National Natural Science Foundation of China (No. 10432060)
文摘Both a real time optical interferometric experiment and a numerical simulation of two-dimension non-steady state model were employed to study the growth process of aqueous sodium chlorate crystals. The parameters such as solution concentration distribution, crystal dimensions, growth rate and velocity field were obtained by both experiment and numerical simulation. The influence of earth gravity during crystal growth process was analyzed. A reasonable theory model corresponding to the present experiment is advanced. The thickness of concentration boundary layer was investigated especially. The results from the experiment and numerical simulation match well.
基金funded by the National Natural Science Foundation of China (42002283)
文摘Characteristics of root pullout resistance determine the capacity to withstand uprooting and the slope protection ability of plants.However,mechanism underlying the uprooting of taproot-type shrub species in the loess area of northeastern Qinghai-Xizang Plateau,China remains unclear.In this study,a common taproot-type shrub,Caragana korshinskii Kom.,in northeastern Qinghai-Xizang Plateau was selected as the research material.Mechanism of root-soil interaction of vertical root of C.korshinskii was investigated via a combination of a single-root pullout test and numerical simulation analysis.The results indicated that,when pulling vertically,axial force of the roots decreased with an increase in buried depth,whereas shear stress at root-soil interface initially increased and then decreased as burial depths increased.At the same buried depth,both axial force and shear stress of the roots increased with the increase in pullout force.Shear stress and plastic zone of the soil surrounding the root were symmetrically distributed along the root system.Plastic zone was located close to the surface and was caused primarily by tensile failure.In nonvertical pulling,symmetry of shear stress and plastic zone of the soil surrounding the root was disrupted.We observed larger shear stress and plastic zones on the side facing the direction of root deflection.Plastic zone included both shear and tensile failure.Axial force of the root system near the surface decreased as deflection angle of the pullout force increased.When different rainfall infiltration depths had the same vertical pulling force,root axial force decreased with the increase of rainfall infiltration depth and total root displacement increased.During rainfall infiltration,shear stress and plastic zone of the soil surrounding the root were prone to propagating deeper into the soil.These findings provide a foundation for further investigation of soil reinforcement and slope protection mechanisms of taproot-type shrub species in the loess area of northeastern Qinghai-Xizang Plateau and similar areas.
