The exact solution of Stokes' second problem including start-up process with fractional element

The start-up process of Stokes＇ second problem of a viscoelastic material with fractional element is studied. The fluid above an infinite flat plane is set in motion by a sudden acceleration of the plate to steady oscillation. Exact solutions are obtained by using Laplace transform and Fourier transform. It is found that the relationship between the first peak value and the one of equal-amplitude oscillations depends on the distance from the plate. The amplitude decreases for increasing frequency and increasing distance.

Assessment of the Tessier and BCR sequential extraction procedures for elemental partitioning of Ca, Fe, Mn, Al,and Ti and their application to surface sediments from Chinese continental shelf

Surface sediments can integrate a wide variety of information of seawater in marginal seas, e.g., the Quaternary sedimentary shelf such as the East China Sea（ECS） and Yellow Sea（YS）. The Tessier and BCR sequential extraction procedures（SEPs） have been widely applied for extraction of various geochemical phases from sediments. To choose a suitable SEP for phase extraction of sediments from the above Quaternary sedimentary shelf, efficiency and selectivity experiments were conducted on typical individual minerals and the applicability of each SEP was assessed for natural sediments（the natural sediment standard GSD-9 and three surface sediment samples）. The geochemical represented elements（Ca, Fe, Mn, Al, and Ti） were measured using both SEPs. Both SEPs have good dissolution efficiency and selectivity for the targeted geochemical phases; the optimized extractant volume for each fraction was determined. The Tessier SEP is particularly recommended for the study of adsorption-desorption process. The application of the Tessier SEP to surface sediments can furnish valuable information, including the productivity conditions（via the reducible fraction Mn） and sedimentary environments（via the carbonate fraction Ca）. These results confirm that the Tessier SEP is suitable for elemental fractionation in sediments from the Chinese continental shelf.

A new nonlinear force model to replace the Hertzian contact model in a rigid-rotor ball bearing system

A new nonlinear force model based on experimental data is proposed to replace the classical Hertzian contact model to solve the fractional index nonlinearity in a ball bearing system. Firstly, the radial force and the radial deformation are measured by statics experiments, and the data are fitted respectively by using the Hertzian contact model and the cubic polynomial model. Then~ the two models are compared with the approximation formula appearing in Aeroengine Design Manual. In consequence, the two models are equivalent in an allowable deformation range. After that, the relationship of contact force and contact deformation for single rolling element between the races is cal- culated based on statics equilibrium to obtain the two kinds of nonlinear dynamic models in a rigid-rotor ball bearing system. Finally~ the displacement response and frequency spectrum for the two system models are compared quantitatively at different rotational speeds, and then the structures of frequency-amplitude curves over a wide speed range are compared qualitatively under different levels of radial clearance, amplitude of excitation, and mass of supporting rotor. The results demonstrate that the cubic polynomial model can take place of the Hertzian contact model in a range of deformation.

Effect of Fiber Volume Fraction on Longitudinal Tensile Properties of SiCf/Ti-6Al-4V Composites

The longitudinal tensile properties of SiCf/Ti-6Al-4V composites with different fiber volume fractions were simulated by the Monte Carlo 2-D finite element model. The random distribution of fiber strength was expressed by the two-parameter Weibull function. Meanwhile, contact elements and birth-death elements were used to describe the interfacial sliding process after debonding and fiber breakage（or matrix cracking） respectively, which was realized by subroutine complied in ANSYS-APDL（ANSYS Parametric Design Language）. The experimental results show that the yield stress and ultimate tensile strength of SiCf/Ti-6Al-4V composites increase with increasing fiber volume fraction, while the corresponding strain of them is just on the contrary. In addition, almost the same failure mode is obtained in SiCf/Ti-6Al-4V composites with various fiber volume fractions when the interfacial shear strength is fixed. Finally, the tensile strength predicted by finite element analysis is compared with that predicted by Global load-sharing model, Local load-sharing model and conventional rule of mixtures, thus drawing the conclusion that Local load-sharing model is very perfect for the prediction of the ultimate tensile strength.

Elemental Partitioning Characteristics of Equilibrium Phases in Inconel 718 Alloy at 600-1100℃

The optimization of heat treatment and chemical composition for Inconel 718 alloy has been investigated uninterruptedly because of its excellent mechanical properties and metallurgical workability.The species , chemical compositions and content of equilibrium phases of Inconel 718alloy in the temperature range of 600-1 100℃ were calculated by using thermodynamic software ＂ Thermo-Calc ＂ and the latest relevant datebase of Ni-base superalloys.A concept of elemental partitioning fraction was used to study the partitioning characteristics of alloying elements in each equilibrium phase at different temperatures , such as Ni , Cr , Fe , Nb , Mo , Al , Ti and C , and some calculation results were confirmed under a scanning transmission electron microscope （ STEM ） .The results showed that the elemental partitioning characteristics with the change of temperature revealed the selective partitioning characteristic of alloying elements in equilibrium phases at different temperatures , such as Nb was mainly distributed in δ and γ′phase , C in carbides , Al and Ti in γ′phase and Cr , Mo in Laves phase.At the same time , the effect of the change of component and quantity for each precipitated phase on matrix phase can be helpfully understood , which provided a theoretic foundation to optimize the chemical composition and heat treatment in different environments for Inconel 718alloy.

Effect of number of granulometric fractions on structure and micromechanics of compressed granular packings

The role of number of grain size fractions on structural and mechanical properties of uniaxially com- pressed granular packings with a uniform particle size distribution in terms of number of particles and with various particle size dispersities was studied using the discrete element method. The study addressed packing density, coordination number, contact forces, global stress, and energy dissipation in assemblies composed of frictional spheres. Packing density was found to change with increasing num- ber of granulometric fractions in mixtures with a small ratio of the diameters of the largest to smallest particles. Results indicated a certain value of particle size ratio below which the number of particle size fractions strongly affected packing density. The average coordination number decreased with increasing number of fractions. Detailed analysis of the effect of particle size dispersity on mechanical coordination number, including particles with no less than four contacts, revealed that, contrary to the average coordi- nation number, the mechanical coordination number increased with increasing ratio of the diameters of the largest to smallest particles in the sample. The composition of polydisperse samples strongly affected stress distribution and energy dissipation in granular packings.

Two and three dimensional modeling of fluidized bed with multiple jets in a DEM-CFD framework

Fluidized beds with multiple jets have widespread industrial applications. The objective of this paper is to investigate the jet interactions and hydrodynamics of a fluidized bed with multiple jets. Discrete element modeling coupled with in-house CFD code GenlDLEST has been used to simulate a bed with nine jets. The results are compared with published experiments. Mono dispersed particles of size 550 ~m are used with 1.4 times the minimum fluidization velocity of the particles. Both two and three dimensional computations have been performed. To the best of our knowledge, the results presented in this paper are the first full 3D simulations of a fluidized bed performed with multiple jets. Discrepancies between the experiment and simulations are discussed in the context of the dimensionality of the simulations. The 2D solid fraction profile compares well with the experiment close to the distributor plate. At higher heights, the 2D simulation over-predicts the solid fraction profiles near the walls. The 3D simulation on the other hand is better able to capture the solid fraction profile higher up in the bed compared to that near the distributor plate. Similarly, the normalized particle velocities and the particle fluxes compare well with the experiment closer to the distributor plate for the 2D simulation and the freeboard for the 3D simulation, respectively. A lower expanded bed height is predicted in the 2D simulation compared to the 3D simulation and the experiment. The results obtained from DEM computations show that a 2D simulation can be used to capture essential jetting trends near the distributor plate regions, whereas a full scale 3D simulation is needed to capture the bubbles near the freeboard regions. These serve as validations for the experiment and help us understand the complex jet interaction and solid circulation patterns in a multiple jet fluidized bed system.