Tailoring particle shape for enhancing the homogeneity of powder mixtures:Experimental study and DEM modelling

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.     

Improving the hydrodynamic performance of the SUBOFF bare hull model: a CFD approach

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.     

Analysis of a two-grid method for semiconductor device problem

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.     

Shape of free-fall arch in quasi-2D silo

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.     

A drag force formula for heterogeneous granular flow systems based on finite average statistical method

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.     

A numerical investigation of CO2 dilution on the thermochemical characteristics of a swirl stabilized diffusion flame

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.     

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.     

Geometric and material nonlinearities of sandwich beams under static loads

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.     

第七届全国周培源大学生力学竞赛试题

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.     

Comparative study of two fluid model and dense discrete phase model for simulations of gas-solid hydrodynamics in circulating fluidized beds

Computational fluid dynamics(CFD)has become a valuable tool to study the complex gas-solid hydrodynamics in the circulating fluidized bed(CFB).Based on the two fluid model(TFM)under the Eulerian-Eulerian framework and the dense discrete phase model(DDPM)under the Eulerian-Lagrangian framework,this work conducts the comparative study of the gas-solid hydrodynamics in a CFB riser by these two different models.Results show that DDPM could be used to predict gas-solid hydrodynamics in the circulating fluidized bed,and there are differences between TFM and DDPM,especially in the radial distribution profiles of solid phase.Sensitivity analysis results show that the gas-solid drag model exhibits significant effects on the results for both the two models.The specularity coefficient and the restitution coefficient in the TFM,as well as the reflection coefficient and the parcel number in the DDPM,exhibit less impact on the simulated results.     

地基沉降计算新方法的探索

目前地基沉降理论计算方法基本上把沉降分段计算,事实上,主、次固结沉降是同时发生的。本文在实践基础上提出用静力触探法和瞬态R波法进行地基沉降计算,通过理论推导并与实测资料进行对比,论证了这两种方法都是快捷有效且具有发展前途的方法。     

Helmholtz方程的中值定理

本文提出并证明了二维和三维Ｈｅｌｍｈｏｌｔｚ方程的中值定理。令λ→０就得到二维和三维Ｌａｐｌａｃｅ方程的中值定理。     

基于CFD的气动力建模及其在气动弹性中的应用

CFD技术为带有气动力非线性的气动弹性分析提供了一种研究途径,但是基于CFD的气动弹性直接数值模拟方法的计算量很大,不便开展定性分析和参数设计.基于CFD的非定常气动力模型的降阶技术为缓解计算效率与计算精度之间的矛盾以及系统的复杂性与易分析、易设计性之间的矛盾提供了行之有效的技术途径.综述了近年来发展的两类基于CFD技术的非定常气动力降阶技术和一种非线性气动力的谐波平衡方法,以及这些方法在非线性气动弹性研究中的运用.对比了各种方法的优越性并作了进一步的展望.      

岩石可爆性神经网络研究

应用人工神经网络系统理论，采用机器学习的方法，建立了岩石的可爆性指数与岩体的爆炸漏斗体积Ｖ、大块率Ｋ＿１、平均合格率Ｋ＿２、小块率Ｋ＿３和波阻抗Ｚ之间的非线性映射关系，并将其用神经网络、网络连接权值矩阵和节点阈值向量分布式表达出来。对于新的岩石，网络采用并行推理的方法预报出其可爆性。实践表明，神经网络方法科学、具有较强的非线性动态处理的能力。     

爆破地震效应若干问题的探讨

对爆破地震效应的若干问题进行了研究，提出了一些新的观点。内容包括:微差爆破问题；焊破地震动转动分量的推算；地震荷载的计算；基于多维反应谱方法的内力组合。     

复合地基承载特性的弹塑性分析

对桩及承台采用线弹性有限元模型,对承台下桩周土采用弹塑性有限元模型,对群桩以外的土体采用线弹性无限元模型,在桩土接触面上设置接触面单元,利用三维弹塑性有限元对桩%D土%D承台相互作用进行了分析。得出了如下结论 :承台下桩顶反力总体表现出角桩最大,边桩次之,中桩最小的分布规律,随着作用在承台上的荷载增大,桩顶反力趋于均匀分布,承台下桩侧摩阻力是由桩端向桩顶逐渐发展的,承台对桩上部侧摩擦阻力存在“削弱作用”。为了验证本文方法的可行性,对承台下有九桩的情况进行了静载试验,将试验结果与本文计算结果进行了比较。     

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探讨了载荷重构技术在智能化复合材料结构健康监测中的应用，着重针对一个自感 知复合材料层合板的载荷重构进行了研究. 首先，基于弹性波动理论和层合板理论，建立了 低速冲击载荷作用下正交铺层层合板的前向波动模型的状态空间表达式；通过构造误差指标 $J$, 应用优化求逆重构了载荷时程和载荷的作用点，并应用算例对以上方法进行了验证.     

基于信息融合技术的结构模型修正研究

提出基于信息融合技术的结构模型修正法.在概率思维条件下,采用二次响应面代替有限元模型,通过调整融合系数实现先验信息和实测信息的融合,并利用响应面自身特性和精度要求进行迭代修正.该方法计算量小,程序化高,易于工程应用,还可推广至非线性等复杂情况.某抽水蓄能电站地下厂房结构的有限元模型修正结果验证了该方法的有效性.     

漂浮载体上机械臂的工作空间

本文讨论载于航天器的机械臂的工作空间问题，导出机械臂位形计算的普遍公式。对不同载体控制方案的机械臂工作空间进行分析和对比，并提出了为扩大工作空间的机械设计原则，最后讨论了负载对工作空间的影响。     

利用摩擦纳米发电机的流体能量俘获研究新进展

环境中的流体 (包括气体和液体) 动能是十分丰富且重要的清洁能源之一, 流体能量可通过不同的能量俘获技术 (电磁发电技术、压电能量俘获技术) 被转化为电能并供人们使用. 自2012年王中林研究团队发明摩擦纳米发电机 (triboelectric nanogenerator, TENG) 以来, TENG已成为了最重要的能量, 俘获技术之一, 并应用于流体能量俘获研究中. 论文综述了当前用于流体能量俘获的摩擦纳米发电机 (fluidic energy harvesting TENG, FEH-TENG) 的研究现状. 介绍了 FEH-TENG 中摩擦电材料之间的电荷转移原理以及基本的工作模式. 在气流动能俘获方面, 流致振动 (如涡激振动、驰振、颤振和尾流驰振等)是一种有效的将流体动力转化为机械能的物理机制, 基于该机制, 总结了FEH-TENG在风能和流致振动能量俘获中的研究进展以及各类能量俘获结构. 液体动能俘获方面总结了 FEH-TENG 在波浪和雨滴能量俘获中的研究进展. 介绍了基于 FEH-TENG的混合能量俘获系统和摩擦电材料优化在提升FEH-TENG流体能量俘获效率方面的研究. 接着介绍了FEH-TENG在不同领域中的应用. 最后讨论了目前 FEH-TENG 在流体能量俘获中存在的问题并提出了一些展望. 论文工作有助于推动FEH-TENG在流体能量俘获领域的发展以及促进相关研究人员对该领域的认识.