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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
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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
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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
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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
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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
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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
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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
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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
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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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微机械陀螺的发展现状 总被引:24,自引:0,他引:24
随着对微电子机械系统(MEMS)的深入研究和取得的进展,属于MEMS研究内容之一的微机械陀螺,在汽车工业需求的推动下,已经成为过去几十年内广泛研究和发展的主题.微机械陀螺与传统机械式陀螺、固体陀螺、光学陀螺等相比,具有成本低、尺寸小、重量轻、可靠性高等优点,其精度正不断得到提高,应用领域也随之不断扩大.本文首先简要介绍了微机械陀螺的定义及特征、性能指标、工作原理、分类以及加工技术,随后对已出现的不同类型微机械陀螺的结构、加工方式、工作原理以及性能进行了综述,最后对微机械陀螺的商业化现状以及发展趋势进行了展望. 相似文献
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本文采用非线性滞后函数模型,对于粘弹性系统的随机振动问题,应用等效线性化和方差分析的方法进行了分析研究,给出了白噪声激励下的响应计算解。 相似文献
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离散系统计算动力学现状 总被引:7,自引:0,他引:7
近10多年来离散系统计算动力学(或称系统动力学的计算方法)在国外发展迅速,本文综述了这个领域国外发展的现状,介绍了计算动力学的任务和研究内容。 相似文献
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网格法的自动检测技术研究 总被引:14,自引:0,他引:14
详细地讨论网格法的自动检测原理及方法,探讨自动网格法应用于细观力学的可能性,并验证性地使用自动网格法测量裂纹尖端的位移场,给出测量精度。 相似文献
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Miao Yingkai 《力学与实践》2015,37(5):658
雨伞是依靠伞柄上弹簧的弹力撑开的, 同时弹簧也将自身举了起来. 在重力的作用下, 弹簧怎么可能自举呢?伞骨和弹簧组成的特殊结构是弹簧能够自举, 雨伞能撑开的关键. 本文与实践相结合, 运用力学知识对雨伞自动撑开的原理进行了分析. 相似文献
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瀑布沟水电站库首右岸深部裂缝成因分析 总被引:4,自引:0,他引:4
水电工程常常建在高山峡谷地带,其天然岸坡通常由坡面向内有一个强卸荷带和弱卸荷带以及相应的强风化和弱风化带,内侧则为完整新鲜的岩石。对涉及的工程岸坡在正常卸荷带以内发育的一系列张性破裂或破裂带,称之为“深拉裂缝”。瀑布沟水电站库首右岸存在两个拉裂变形体,通过对其岸坡深部拉裂缝空间发育分布、变形特征的考察,综合分析造成深部裂缝发育规律与变形特征的因素。在此基础上提出,库首右岸深部拉裂缝是岸坡快速卸荷条件下浅表生改造的产物,其形成时期相当于河谷由宽谷深切为峡谷这一转换时期。 相似文献
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为了提高云纹法的准确度,文中提出了使倍增后的云纹宽度变细并进行显微测量的技术,以及由密集云纹场测算应变的条纹间距插值和小间距均匀法。给出了估计由此法算得的应变的误差及其修正方法。所做的曲杆实验其数据与理论值符合得很好。文中还将云纹法中闪耀光栅与振幅栅相匹配的光学空间滤波系统改进为实时系统,导出其条纹倍增率及云纹图的最佳对比度条件。 相似文献