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.     

Smart computing approach for design and scale-up of conical spouted beds with open-sided draft tubes

Open-sided draft tubes provide an optimal gas distribution through a cross flow pattern between the spout and the annulus in conical spouted beds.The design,optimization,control,and scale-up of the spouted beds require precise information on operating and peak pressure drops.In this study,a multi-layer perceptron(MLP)neural network was employed for accurate prediction of these hydrodynamic characteristics.A relatively huge number of experiments were accomplished and the most influential dimensionless groups were extracted using the Buckingham-pi theorem.Then,the dimensionless groups were used for developing the MLP model for simultaneous estimation of operating and peak pressure drops.The iterative constructive technique confirmed that 4-14-2 is the best structure for the MLP model in terms of absolute average relative deviation(AARD%),mean square error(MSE),and regression coefficient(R²).The developed MLP approach has an excellent capacity to predict the transformed operating(MSE=0.00039,AARD%=1.30,and R²=0.76099)and peak(MSE=0.22933,AARD%=11.88,and R2=0.89867)pressure drops.     

Analytical solution for the stress field of hierarchical defects:multiscale framework and applications

Hierarchical defects are defined as adjacent defects at different length scales.Involved are the two scales where the stress field distribution is interrelated.Based on the complex variable method and conformal mapping,a multiscale framework for solving the problems of hierarchical defects is formulated.The separated representations of mapping function,the governing equations of potentials,and the stress field are subsequently obtained.The proposed multiscale framework can be used to solve a variety of simplified engineering problems.The case in point is the analytical solution of a macroscopic elliptic hole with a microscopic circular edge defect.The results indicate that the microscopic defect aggregates the stress concentration on the macroscopic defect and likely leads to global propagation and rupture.Multiple micro-defects have interactive effects on the distribution of the stress field.The level of stress concentration may be reduced by the coalescence of micro-defects.This work provides a unified method to analytically investigate the influence of edge micro-defects within the scope of multiscale hierarchy.The formulated multiscale approach can also be potentially applied to materials with hierarchical defects,such as additive manufacturing and bio-inspired materials.     

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.     

Nonlinear Performance of MEMS Vibratory Ring Gyroscope

Micro-electro-mechanical system(MEMS)gyroscopes are an important sort of inertial sensor for identifying parameters of spinning structures,such as the spinning speed and angular deviation,based on the Coriolis effect.In this paper,the nonlinear mechanism of MEMS vibratory ring gyroscopes is analyzed by applying a fully coupled nonlinear model,in which the gyroscopic coupling and geometrically and structurally nonlinear couplings are all taken into account.The coupled differential equations governing the drive and sense motions are established via the Lagrangian equations.Numerical simulation is conducted,and the key nonlinear components and energy transfer behaviors between the drive and sense modes are elucidated.It is revealed that the cubic rigidity nonlinearity is another significant factor leading to the coupling between the drive and sense modes other than the gyroscopic coupling.Perturbation analysis is also carried out by using the method of multiple scales.The nonlinear frequency-amplitude responses of the drive and sense vibrations are obtained,and comprehensive parametric studies are performed.The significant effects of system damping,excitation amplitude,drive amplitude and spinning speed on the responses are discussed,which will facilitate to improve the nonlinear performance and sensitivity of the gyroscope.     

Effective enhanced model for a large deformable soft pneumatic actuator

Soft pneumatic actuators have been widely used for implementing sophisticated and dexterous movements,due to numerous fascinating features compared with their rigid counterparts.Relatively speaking,modeling and analysis of an entire soft pneumatic actuator considering contact interaction between two adjacent air chambers is extremely rare,which is exactly what we are particularly interested in.Therefore,in order to establish an accurate mechanical model and analyze the overall configuration and stress distribution for the soft pneumatic actuator with large deflection,we consider the contact interaction of soft materials rather than hard materials,to produce an effective enhanced model for soft contact of a large deformable pneumatic actuator.In this article,a multiple-point contact approach is developed to circumvent the mutual penetration problem between adjacent air chambers of the soft actuator that occurs with the single-point contact approach employed in linear elastic rigid materials.In contrast to the previous simplified rod-based model that did not focus on contact interaction which was adopted to clarify the entire deformation of the actuator,the present model not only elaborates nonlinear large deformation and overall configuration variations,but also accurately delineates stress distribution law inside the chamber structure and the stress concentration phenomenon.By means of a corresponding static experiment,a comparison of the simulation results with experimental data validates the effectiveness and accuracy of this model employing a multiple-point contact approach.Excellent simulation of the actual bending deformation of the soft actuator is obtained,while mutual penetration is successfully circumvented,whereas the model with single-point contact cannot achieve those goals.Finally,as compared with the rod-based model,the results obtained using the proposed model are more consistent with experimental data,and simulation precision is improved.     

The effect of hemicellulose on the interparticle frictional behavior of lignocellulosic biomass particulates

Lignocellulosic biomass material sourced from plants and herbaceous sources is considered as a prospective feedstock of inexpensive,potentially carbon-neutral energy.Lignocellulosic biomass is structurally built on cellulose,hemicellulose,and lignin,which are present in varying concentrations based on the feedstock type and play distinct and not well understood mechanical functions in the flow behavior.The frictional characteristics of lignocellulosic biomass particulates influence their flow behavior in biorefineries.Thus,it is important to fundamentally investigate the relative contribution of cellulose,hemicellulose,and lignin to the frictional behavior.However,these three biopolymers are interwoven into a complex matrix in the lignocellulosic biomass,thus making it hard to quantify the contribution of each biopolymer.In this study,we selectively remove hemicellulose from switchgrass and investigate the effects of its diminishing concentration on the coefficient of friction.We observed that the angle of repose and,therefore,the coefficient of friction for a loose assembly of the control and treated switchgrass samples decrease with decreasing hemicellulose content.This indicates the frictional resistance to flow for biomass particulate assemblies is at least proportional to the hemicellulose content.We also established that the observed changes in the frictional behavior were not due to particle morphological characteristics.     

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.