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.     

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.     

Application of micro-morphology in the physical characterization of urban road dust

Urban road dust was collected from Vellore City,Tamil Nadu,India,and analyzed.Scanning electron microscopy(SEM)was used to examine road dust from nine sampling locations in the study region.SEM image analysis was used to identify various shape factors of collected dust particles.The equivalent spherical diameter of most particles was between 10μm and 30μm.Fine particles had greater concentrations at locations with higher traffic flow.Particles were categorized into four classes based on their shape factors,viz.,spherical,mineral,elongated,or irregular.Spherical particles had the smallest mean equivalent diameter(1.95μm)and mineral particles had the largest diameter(33.3μm).Spherical particles made up the smallest portion of road dust(0-12%)in the study region and mineral particles made up the largest(45-65%).Elongated and irregular particles,each made up 23-30%of road dust.Electron dispersive X-ray spectroscopy analysis was used to identify the elemental composition of dust particles.Spherical particles were mostly from combustion sources and mineral particles were largely of crustal origin.No individual source was found for irregular and elongated particles.Biological debris was the major source of irregular particles.     

Axially variable-length solid element of absolute nodal coordinate formulation

An axially variable-length solid element with eight nodes is proposed by integrating the arbitrary Lagrangian-Eulerian (ALE) formulation and the absolute nodal coordinate formulation (ANCF). In addition to the nodal positions and slopes of eight nodes, two material coordinates in the axial direction are used as the generalized coordinates. As a consequence, the nodes in the ALE-ANCF are not associated with any specific material points and the axial length of the solid element can be varied over time. These two material coordinates give rise to a variable mass matrix and an additional inertial force vector. Computationally efficient formulae of the additional inertial forces and elastic forces, as well as their Jacobians, are also derived. The dynamic equation of a flexible multibody system (FMBS) with variable-length bodies is presented. The maximum and minimum lengths of the boundary elements of an FMBS have to be appropriately defined to ensure accuracy and non-singularity when solving the dynamic equation. Three numerical examples of static and dynamic problems are given to validate the variable-length solid elements of ALE-ANCF and show their capability.     

Efficient algorithm for 3D bimodulus structures

The bimodulus material is a classical model to describe the elastic behavior of materials with tension-compression asymmetry.Due to the inherently nonlinear properties of bimodular materials,traditional iteration methods suffer from low convergence efficiency and poor adaptability for large-scale structures in engineering.In this paper,a novel 3D algorithm is established by complementing the three shear moduli of the constitutive equation in principal stress coordinates.In contrast to the existing 3D shear modulus constructed based on experience,in this paper the shear modulus is derived theoretically through a limit process.Then,a theoretically self-consistent complemented algorithm is established and implemented in ABAQUS via UMAT;its good stability and convergence efficiency are verified by using benchmark examples.Numerical analysis shows that the calculation error for bimodulus structures using the traditional linear elastic theory is large,which is not in line with reality.     

On the energy conversion in electrokinetic transports

Energy conversion in micro/nano-systems is a subject of current research,among which the electrokinetic energy conversion has attracted extensive attention. However, there exist two different definitions on the electrokinetic energy conversion efficiency in literature. A few researchers defined the efficiency using the pure pressure-driven flow rate, while other groups defined the efficiency based on the flow rate with the inclusion of the effect of the streaming potential field. In this work, b...     

Magnetic nanoparticle drug targeting to patient-specific atherosclerosis: effects of magnetic field intensity and configuration

Nanoparticle-mediated drug delivery is recognized as a promising option for targeted treatment of atherosclerosis. In this paper, the Eulerian-Lagrangian technique is adopted to simulate the delivery of drug-loaded nanoparticles to patient-specific atherosclerotic plaque with the aid of an external magnetic field. Plaques and vascular walls are introduced as porous media formulated by the Darcy-Forchheimer model in this targeted transport process. The results demonstrate that the delivery efficiency of particles to atherosclerosis depends on the external magnetic field, such as configuration and intensity, in which the configuration angle of the current wire is a key factor and the double current wires have advantages over the single current wire. Meanwhile, the delivery efficiency gradually decreases as the distance between the plaque cap and the current wire increases. Further, although augmenting the current or magnetic susceptibility can generally improve the delivery efficiency of nanoparticles, this increase is not apparent when small-sized nanoparticles are employed as drug transport particles. The results obtained can potentially serve as the guideline to optimize regimens for the targeted therapy of atherosclerosis.     

New mixed plate-bending elements with shear strain interpolations

This paper is concerned with two mixed plate-bending elements with shear strain interpolations, a quadrilateral element and an 8-node serendipity-type element based on discussions on the element proposed in Ref.[1]. The shear strains and inner-forces in the natural coordinates are interpolated in an element and then transformed into Cartesian coordinates in accordance with covariant and contravariant tensor transformations, respectively. The quadrilateral element coincides with the element in Ref.[1] when it is rectangular. Numerical examples show that the two new elements are free from shear locking and spurious kinematic modes under regular and irregular meshes and have the advantages of being insensitive to element distortion and able to give fairly accurate results.The Project supported by National Natural Science Foundation of China.     

Geometrically non-linear generalized hybrid element and refined element method of non-conforming modes

A generalized hybrid method of non-conforming modes based on a non-linear generalized variational principles with relaxed interelement continuity requirements, is developed, and the plane quadrilateral geometrically non-linear element is presented, furthermore, non-linear refined element method is devised by orthogonal approach. It is shown that the refined element can improve the computational accuracy for non-conforming modes. The project supported by the National Natural Science Foundation of China     

Development of quadrilateral spline thin plate elements using the B-net method

The quadrilateral discrete Kirchhoff thin plate bending element DKQ is based on the isoparametric element Q8, however, the accuracy of the isoparametric quadrilateral elements will drop significantly due to mesh distortions. In a previous work, we constructed an 8-node quadrilateral spline element L8 using the triangular area coordinates and the Bnet method, which can be insensitive to mesh distortions and possess the second order completeness in the Cartesian coordinates. In this paper, a thin plate spline element is developed based on the spline element L8 and the refined technique. Numerical examples show that the present element indeed possesses higher accuracy than the DKQ element for distorted meshes.     

Corotational nonlinear analyses of laminated shell structures using a 4-node quadrilateral flat shell element with drilling stiffness

A new 4-node quadrilateral flat shell element is developed for geometrically nonlinear analyses of thin and moderately thick laminated shell structures. The fiat shell element is constructed by combining a quadrilateral area co- ordinate method （QAC） based membrane element AGQ6- II, and a Timoshenko beam function （TBF） method based shear deformable plate bending element ARS-Q12. In order to model folded plates and connect with beam elements, the drilling stiffness is added to the element stiffness matrix based on the mixed variational principle. The transverse shear rigidity matrix, based on the first-order shear deformation theory （FSDT）, for the laminated composite plate is evaluated using the transverse equilibrium conditions, while the shear correction factors are not needed. The conventional TBF methods are also modified to efficiently calculate the element stiffness for laminate. The new shell element is extended to large deflection and post-buckling analyses of isotropic and laminated composite shells based on the element independent corotational formulation. Numerical re- sults show that the present shell element has an excellent numerical performance for the test examples, and is applicable to stiffened plates.     

A generalized conforming isoparametric element

Based on the generalized compatibility condition under constant and linear stress field, a quadrilateral generalized conforming isoparametric element, GC-Q6, for plane stress analysis, is developed. The element GC-Q6 can be regarded as an improved form of Wilson’s non-conforming isoparametric element Q6. GC-Q6 can pass the patch test for arbitrary irregular mesh while Q6 can not. GC-Q6 degenerates to Q6 when it is a parallelogram. Numerical examples show that the GC-Q6 element gives more accurate stress solution than the existing non-conforming elements and is less sensitive to geometric distortion.     

Model optimization of hybrid stress general shell element

A 20 DOF (degree of freedom) hybrid stress element based upon Mindlin plate bending theory is developed using the optimizing design method for thin and moderately thick shell. It is of quadrilateral shape with only four corner nodes and can be used for both shallow and deep shells with excellent performance and the shear locking problem no longer exists.The project supported by National Science Foundation of China.     

Coarse-mesh-accuracy improvement of bilinear Q<Subscript>4</Subscript>-plane element by the combined hybrid finite element method

The combined hybrid finite element method is of an intrinsic mechanism of enhancing coarse-mesh-accuracy of lower order displacement schemes. It was confirmed that the combined hybrid scheme without energy error leads to enhancement of accuracy at coarse meshes, and that the combination parameter plays an important role in the enhancement. As an improvement of conforming bilinear Q₄-plane element, the combined hybrid method adopted the most convenient quadrilateral displacements-stress mode, i. e., the mode of compatible isoparametric bilinear displacements and pure constant stresses. By adjusting the combined parameter, the optimized version of the combined hybrid element was obtained and numerical tests indicated that this parameter-adjusted version behaves much better than Q₄-element and is of high accuracy at coarse meshes. Due to elimination of stress parameters at the elemental level, this combined hybrid version is of the same computational cost as that of Q₄-element. Foundation item: the National Tianyuan Yourth Funds of China (TY10126027) Biography: Xie Xiao-ping (1970≈)     

COARSE-MESH-ACCURACY IMPROVEMENT OF BILINEAR Q4-PLANE ELEMENT BY THE COMBINED HYBRID FINITE ELEMENT METHOD

IntroductionByadding‘nodeless’incompatiblebubblemodesandpreservinggeometriccharacteristicofthevariationalprincipleinmechanics,thecombinedhybridmethod[1～4 ]remarkablelyenhancedcoarse_mesh_accuracyofconventionalquadrilateralelementsoflowerorder.ThequadrilateralplaneelasticelementCH(0_1 )proposedinRef.[3 ]isasuccessfulexample.Followingthegeometricpointofviewinmechanicscombinedwithmathematicalanalysis,anovelexpressionofthecombinedhybridvariationalprincipleisintroducedtoclarifyitsintrinsicmecha…     

一个不闭锁和抗畸变的四边形厚板元

构造一个彻底消除剪切闭锁现象并且对网格畸变不敏感的四边形厚薄板通用单元RPAQ。在方法上有三个特点：第一,在厚板挠度和转角的试函数中,采用了合理匹配方案,从而在源头上彻底消除了剪切闭锁现象;第二,采用四边形面积坐标,以代替通常的等参坐标,从而使网格畸变时仍然保持高精度;第三,采用广义协调元做法,使协调条件的采用灵活多样,并保证单元的收敛性。进行了一系列数值例题测试,表明单元RPAQ能自动消除闭锁现象,在由薄板到厚板的不同情况下,在各种网格畸变的情况下,都能体现出良好的精度和数值稳定性。     

On the equivalence of the Wilson element and the generalized hybrid element

In this paper the equivalence of the generalized hybrid element and the modified Wilson element, which is derived by the generalized hybrid method, is proved. The project is supported by the National Natural Science Foundation of China