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1.
The effect of particle shape modification on the segregation reduction of enzyme granules in laundry detergent powder mixtures was investigated,both experimentally and computationally using Deseret Element Method(DEM).The shape of modified enzyme particles was in such a way that the large and dense enzyme particles were layered by other fine particles in the detergent powder,by means of a process known in the literature as“seeded granulation”.It is found that the homogeneity of modified enzyme particles could be improved significantly comparing to the original spherical enzyme particles in powder mixtures.Overall,the results of this research demonstrated that the segregation-induced properties of the dense/spherical enzyme particles could be lowered by altering their shape,which could enable the enzyme particles to behave almost similar to other ingredients during the pile formation process. 相似文献
2.
Kambiz Divsalar 《Acta Mechanica Sinica》2020,36(1):44-56
The main aims of this study are to investigate the hydrodynamic performance of an autonomous underwater vehicle(AUV),calculate its hydrodynamic coefficients,and consider the flow characteristics of underwater bodies.In addition,three important parts of the SUBOFF bare hull,namely the main body,nose,and tail,are modified and redesigned to improve its hydrodynamic performance.A three-dimensional(3D)simulation is carried out using the computational fluid dynamics(CFD)method.To simulate turbulence,the k-ωshear stress transport(SST)model is employed,due to its good prediction capability at reasonable computational cost.Considering the effects of the length-to-diameter ratio(LTDR)and the nose and tail shapes on the hydrodynamic coefficients,it is concluded that a hull shape with bullet nose and sharp tail with LTDR equal to 7.14 performs better than the SUBOFF model.The final proposed model shows lower drag by about 14.9%at u=1.5 m·s^-1.Moreover,it produces 8 times more lift than the SUBOFF model at u=6.1 m·s^-1.These effects are due to the attachment of the fluid flow at the tail area of the hull,which weakens the wake region. 相似文献
3.
The mathematical model of a semiconductor device is governed by a system of quasi-linear partial differential equations.The electric potential equation is approximated by a mixed finite element method,and the concentration equations are approximated by a standard Galerkin method.We estimate the error of the numerical solutions in the sense of the Lqnorm.To linearize the full discrete scheme of the problem,we present an efficient two-grid method based on the idea of Newton iteration.The main procedures are to solve the small scaled nonlinear equations on the coarse grid and then deal with the linear equations on the fine grid.Error estimation for the two-grid solutions is analyzed in detail.It is shown that this method still achieves asymptotically optimal approximations as long as a mesh size satisfies H=O(h^1/2).Numerical experiments are given to illustrate the efficiency of the two-grid method. 相似文献
4.
In this study,the optical flow method is used to measure the velocity distribution of a granular flow in a rectangular quasi-two-dimensional silo.Using the velocity gradient,a free-fall arch(FFA)is obtained and its geometric characteristics are calculated.A parabola-shaped FFA structure is discovered above the orifice in the steady flow state.The shape of the FFA affects the flow rate through the orifice.Furthermore,as jamming begins to occur,the geometry of the FFA disappears gradually from both sides and then from the middle;finally,the FFA disappears completely in the state of jamming.As the boundary between finite-stress and stress-free regions,the FFA facilitates further studies regarding the discontinuity of the stress area above the orifice. 相似文献
5.
The existing drag models are mostly based on the assumption of homogenous fluidization.However,the use of a homogeneous drag model to predict a heterogeneous granular flow system will cause a deviation.In this study,we developed a drag force model based on the assumption of heterogeneous fluidization.To prevent weakening of the heterogeneous characteristics in the drag force formula,we propose a finite average statistical method to filter the information of the heterogeneous granular cluster.The filtered information was used to fit the modified drag formula,which can reflect the heterogeneity of the granular cluster considering different configurations.A comparison shows that the new proposed drag formula filtered by the finite average statistical method fits well with energy minimization multi-scale simulation results. 相似文献
6.
The turbulent combustion flow modeling is performed to study the effects of CO_2 addition to the fuel and oxidizer streams on the thermochemical characteristics of a swirl stabilized diffusion flame. A flamelet approach along with three well-known turbulence models is utilized to model the turbulent combustion flow field. The k-ω shear stress transport(SST) model shows the best agreement with the experimental measurements compared with other models. Therefore, the k-ω SST model is used to study the effects of CO_2 dilution on the flame structure and strength, temperature distribution, and CO concentration. To determine the chemical effects of CO_2 dilution, a fictitious species is replaced with the regular CO_2 in both the fuel stream and the oxidizer stream. The results indicate that the flame temperature decreases when CO_2 is added to either the fuel or the oxidizer stream. The flame length reduction is observed at all levels of CO_2 dilution. The H radical concentration indicating the flame strength decreases, following by the thermochemical effects of CO_2 dilution processes. In comparison with the fictitious species dilution, the chemical effects of CO_2 addition enhance the CO mass fraction. The numerical simulations show that when the dilution level is higher, the rate of the flame length reduction is more significant at low swirl numbers. 相似文献
7.
Static output feedback stabilization for second-order singular systems using model reduction methods
In this paper,the static output feedback stabilization for large-scale unstable second-order singular systems is investigated.First,the upper bound of all unstable eigenvalues of second-order singular systems is derived.Then,by using the argument principle,a computable stability criterion is proposed to check the stability of secondorder singular systems.Furthermore,by applying model reduction methods to original systems,a static output feedback design algorithm for stabilizing second-order singular systems is presented.A simulation example is provided to illustrate the effectiveness of the design algorithm. 相似文献
8.
A new theory developed from extended high-order sandwich panel theory(EHSAPT)is set up to assess the static response of sandwich panels by considering the geometrical and material nonlinearities simultaneously.The geometrical nonlinearity is considered by adopting the Green-Lagrange-type strain for the face sheets and core.The material nonlinearity is included as a piecewise function matched to the experimental stress-strain curve using a polynomial fitting technique.A Ritz technique is applied to solve the governing equations.The results show that the stress stiffening feature is well captured in the geometric nonlinear analysis.The effect of the geometric nonlinearity in the face sheets on the displacement response is more significant when the stiffness ratio of the face sheets to the core is large.The geometric nonlinearity decreases the shear stress and increases the normal stress in the sandwich core.By comparison with open literature and finite element simulations,the present nonlinear EHSAPT is shown to be sufficiently precise for estimating the nonlinear static response of sandwich beams by considering the geometric and material nonlinearities simultaneously. 相似文献
9.
第七届全国周培源大学生力学竞赛试题 总被引:2,自引:2,他引:0
《力学与实践》编辑部 《力学与实践》2009,31(4)
一、小球在高脚玻璃杯中的运动(20分)
一半球形高脚玻璃杯,半径r=5cm,其质量m1=0.3kg,杯底座半径R=5cm,厚度不计,杯脚高度h=10cm.如果有一个质量m2=0.1kg的光滑小球自杯子的边缘由静止释放后沿杯的内侧滑下,小球的半径忽略不计. 相似文献
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12.
To verify the theoretical models of varying transversely isotropic stress-strain relations of dentin established in the preceding
work (Part I), we perform a set of experiments. Because of the very fine tooth size, it usually seems to be difficult to directly
measure the inhomogeneous and anisotropic parameters of dentin. In this paper, by the digital speckle correlation method,
tensile experiments are made on the small dentin samples either parallel or perpendicular to the dentin tubules. With the
theoretically predicted elastic stress-strain relations, an optimization method is proposed to fit the strain curve adapted
to the experimental data. The results show that the theoretical elastic stress-strain relations coincides very well with the
experimental observations. The determined Young's modulus and Poisson's ratio of dentin matrix are 29.5 GPa and 0.44, respectively,
in the optimization sense.
The project supported by the National Natural Science Foundation of China (19525207) 相似文献
13.
Based on the three dimensional elastic theory, the state equation of the axisymmetric free vibration of transversely isotropic
circular plates is established. Taking the advantage of finite Hankel transform, two exact solutions are derived for two boundary
conditions, i. e. the rigid-slipping boundary and elastic simply supported boundary. Finally, numerical results are presented
and compared with those of FEM.
The project is supported by the National Natural Science Foundation of China and the Zhejiang Provincial Natural Science Foundation. 相似文献
14.
In this paper, a systematic approach is proposed to obtain the macroscopic elastic-plastic constitutive relation of particle
reinforced composites (PRC). The strain energy density of PRC is analyzed based on the cell model, and the analytical formula
for the macro-constitutive relation of PRC is obtained. The strength effects of volume fraction of the particle and the strain
hardening exponent of matrix material on the macro-constitutive relation are investigated, the relation curve of strain versus
stress of PRC is calculated in detail. The present results are consistent with the results given in the existing references.
The project supported by the National Natural Science Foundation of China (No. 19704100) and National Science Foundation of
Chinese Academy of Sciences (Project KJ951-1-20). 相似文献
15.
BEM for simulation of a 2D elastic body with randomly distributed circular inclusions 总被引:7,自引:0,他引:7
Based on our 2D BEM software THBEM2 which can be applied to the simulation of an elastic body with randomly distributed identical
circular holes, a scheme of BEM for the simulation of elastic bodies with randomly distributed circular inclusions is proposed.
The numerical examples given show that the boundary element method is more accurate and more effective than the finite element
method for such a problem. The scheme presented can also be successfully used to estimate the effective elastic properties
of composite materials.
Project supported by the National Natural Science Foundation of China (No. 19772025). 相似文献
16.
Cavitation in hookean elastic membranes 总被引:1,自引:0,他引:1
An exact solution to cavitation is found in tension of a class of Cauchy elastic membranes. The constitutive relationship
of materials is based on Hookean elastic law and finite logarithmic strain measure. A variable transformation is used in solving
the two-point boundary-value problem of nonlinear ordinary differential equation. A simple formula to calculate the critical
stretch for cavitation is derived. As the numerical results, the bifurcation curves describing void nucleation and suddenly
rapidly growth of the cavity are obtained. The boundary layers of displacements and stresses near the cavity wall are observed.
The cata-strophic transition from homogeneous to cavitated deformation and the jumping of stress distribution are discussed.
The result of the energy comparison shows the cavitated deformation has lower energy than the homogeneous one, thus the state
of cavitated deformation is relatively stable. All investigations illustrate that cavitation reflects a local behavior of
materials.
Project supported by the National Natural Science Foundation of China (No. 19802012) the Scientific Research Foundation for
Returned Overseas Chinese Scholars, and the Scientific Research Foundation for Key Teachers in Chinese Universities. 相似文献
17.
When the thicknesses of thin films reduce to microns or even nanometers, surface energy and surface interaction often play a significant role in their deformation behavior and surface morphology. The spinodal surface instability induced by the van der Waals force in a soft elastic thin film perfectly bonded to a rigid substrate is investigated theoretically using the bifurcation theory of elastic structures. The analytical solution is derived for the critical condition of spinodal surface morphology instability by accounting for the competition of the van der Waals interaction energy, elastic strain energy and surface energy. Detailed examinations on the effect of surface energy, thickness and elastic properties of the film show that the characteristic wavelength of the deformation bifurcation mode depends on the film thickness via an exponential relation, with the power index in the range from 0.749 to 1.0. The theoretical solution has a good agreement with relevant experiment results. 相似文献
18.
An embedded cell model is presented to obtain the effective elastic moduli for three-dimensional two-phase composites which
is an exact analytic formula without any simplified approximation and can be expressed in an explicit form. For the different
cells such as spherical inclusions and cracks surrounded by sphere and oblate ellipsoidal matrix, the effective elastic moduli
are evaluated and the results are compared with those from various micromechanics models. These results show that the present
model is direct, simple and efficient to deal with three-dimensional two-phase composites.
The project supported by the National Natural Science Foundation of China (No. 19704100) and the National Natural Science
Foundation of Chinese Academy of Sciences (No. KJ951-1-201) 相似文献
19.
A continuous variable optimization method and a topological optimization method are proposed for the vibration control of piezoelectric truss structures by means of the optimal placements of active bars. In this optimization model, a zero-one discrete variable is defined in order to solve the optimal placement of piezoelectric active bars. At the same time, the feedback gains are also optimized as continuous design variables. A two-phase procedure is proposed to solve the optimization problem. The sequential linear programming algorithm is used to solve optimization problem and the sensitivity analysis is carried out for objective and constraint functions to make linear approximations. On the basis of the Newmark time integration of structural transient dynamic responses, a new sensitivity analysis method is developed in this paper for the vibration control problem of piezoelectric truss structures with respect to various kinds of design variables. Numerical examples are given in the paper to demonstrate the effectiveness of the methods. 相似文献
20.
The weak point of the generalized self-consistent method (GSCM) is that its solution for the effective shear moduli involves
determining the complicated displacement and strain fields in constitutents. Furthermore, the effective moduli estimated by
GSCM cannot be expressed in an explicit form. Instead of following the procedure of GSCM, in this paper a generalized self-consistent
Mori-Tanaka method (GSCMTM) is developed by means of Hill's interface condition and the assumption that the strain in the
inclusion is uniform. A comparison with the existing theoretical and experimental results shows that the present GSCMTM is
sufficiently accurate to predict the effective moduli of the coated inclusion-based composite materials. Moreover, it is interesting
to find that the application of Hill's interface condition in volumetric domain is equivalent to the Mori-Tanaka average field
approximation.
This project was supported by the National Natural Science Foundation of China and China Postdoctoral Science Foundation. 相似文献