63 research outputs found

    Direct numerical simulation of a fully developed turbulent square duct flow up to Re-tau=1200

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    Various fundamental studies based on a turbulent duct flow have gained popularity including heat transfer, magnetohydrodynamics as well as particle-laden transportation. An accurate prediction on the turbulent flow field is critical for these researches. However, the database of the mean flow and turbulence statistics is fairly insufficient due to the enormous cost of numerical simulation at high Reynolds number. This paper aims at providing available information by conducting several Direct Numerical Simulations (DNS) on turbulent duct flows at Re-tau = 300, 600, 900 and 1200. A quantitative comparison between current and previous DNS results was performed where a good agreement was achieved at Re-tau = 300. However, further comparisons of the present results with the previous DNS results at Re-tau = 600 obtained with much coarser meshes revealed some discrepancies which can be explained by the insufficient mesh resolution. At last, the mean flow and turbulent statistics at higher Re-tau was presented and the effect of Re-tau on the mean flow and flow dynamics was discussed.Peer ReviewedPostprint (author's final draft

    Particulate immersed boundary method for complex fluid-particle interaction problems with heat transfer

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    In our recent work (Zhang et al., 2015), a Particulate Immersed Boundary Method (PIBM) for simulating fluid-particle multiphase flow was proposed and assessed in both two- and three-dimensional applications. In this study, the PIBM was extended to solve thermal interaction problems between spherical particles and fluid. The Lattice Boltzmann Method (LBM) was adopted to solve the fluid flow and temperature fields, the PIBM was responsible for the no-slip velocity and temperature boundary conditions at the particle surface, and the kinematics and trajectory of the solid particles were evaluated by the Discrete Element Method (DEM). Four case studies were implemented to demonstrate the capability of the current coupling scheme. Firstly, numerical simulation of natural convection in a two-dimensional square cavity with an isothermal concentric annulus was carried out for verification purpose. The current results were found to have good agreement with previous references. Then, sedimentation of two-and three-dimensional isothermal particles in fluid was numerically studied, respectively. The instantaneous temperature distribution in the cavity was captured. The effect of the thermal buoyancy on particle behaviors was discussed. Finally, sedimentation of three-dimensional thermosensitive particles in fluid was numerically investigated. Our results revealed that the LBM-PIBM-DEM is a promising scheme for the solution of complex fluid-particle interaction problems with heat transfer.Peer ReviewedPostprint (author's final draft

    Large-strain self-weight consolidation of dredged sludge

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    Prediction for self-weight consolidation of dredged sludge is important for its reuse in civil engineering applications. In this work, considering the special nonlinear relationships of e – k and e – σ′ for dredged sludge, Gibson’s large strain consolidation equation was modified to simulate the self-weight consolidation process of dredged sludge. Using the finite difference method (FDM), the influences of four main parameters, including initial height, initial void ratio, void ratio at the liquid limit, and specific gravity of soil particles, on the consolidation process of dredged slurry were analyzed. For the aforementioned four parameters, the self-weight consolidation of dredged slurry is most sensitive to the variation of void ratio at the liquid limit, whereas its response to the change of specific gravity of soil particles is relatively subtle. Consolidation behaviors under other commonly used constitutive models were also calculated for comparison. It was found that the total settlement obtained by the present relation is larger than the results obtained using typical nonlinear constitutive relations, and the speed of consolidation is higher

    PIBM: Particulate immersed boundary method for fluid-particle interaction problems

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    It is well known that the number of particles should be scaled up to enable industrial scale simulation. The calculations are more computationally intensive when the motion of the surrounding fluid is considered. Besides the advances in computer hardware and numerical algorithms, the coupling scheme also plays an important role on the computational efficiency. In this study, a particulate immersed boundary method (PIBM) for simulating the fluid–particle multiphase flow was presented and assessed in both two- and three-dimensional applications. The idea behind PIBM derives from the conventional momentum exchange-based Immersed Boundary Method (IBM) by treating each Lagrangian point as a solid particle. This treatment enables Lattice Boltzmann Method (LBM) to be coupled with fine particles residing within a particular grid cell. Compared with the conventional IBM, dozens of times speedup in two-dimensional simulation and hundreds of times in three-dimensional simulation can be expected under the same particle and mesh number. Numerical simulations of particle sedimentation in Newtonian flows were conducted based on a combined LBM–PIBM–Discrete Element Method (DEM) scheme, showing that the PIBM can capture the feature of particulate flows in fluid and is indeed a promising scheme for the solution of the fluid–particle interaction problems

    Discrete element simulation of particle motion in ball mills based on similarity

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    Discrete element (DE) simulation of a ball mill with a large number of particles is challenging when each particle is considered. Similarity principle could be adopted to reduce the number of particles in a simulation whilst still maintaining the accurate flow behaviour of particles. This paper presents a scaling relationship between particle gravitational acceleration, mill diameter and mill rotational speed. A series of scaled simulations of particle motion with different mill diameters are carried out. Consistent motion of a single particle and multiple particles in ball mills with different diameters and rotational speeds verifies the proposed relationship, which could be an effective approach to reduce the size of simulations for ball mills

    Wideband Dual-Element Antenna Array for MIMO Mobile Phone Applications

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    A printed dual-element antenna array for LTE MIMO mobile phone applications is presented in this paper. The two array elements are symmetrically placed with the same dimensions, and each of the them consists of a novel driven strip and a wandering shorting strip. The driven strip is a whole loop, which improves the impedance matching for the upper band. Therefore, the bandwidth coverage is expanded and the antenna size is minimized at the same time. In addition, thanks to the protruded ground on the ground plane, the antenna isolation between the two array elements is significantly enhanced. The proposed planar antenna array successfully covers the seven operating bands of GSM850/900/1800/1900/UMTS2100/LTE2300/2500, and the isolation is more than 10 dB. The prototype was fabricated and tested, with S parameters, efficiency, radiation patterns, envelop correlation coefficient (ECC), and ergodic capacity presented. From the measured results, it is indicated that the antenna array has excellent and reliable performances when it is applied in MIMO applications

    Nanomaterials-Based Colorimetric Immunoassays

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    Colorimetric immunoassays for tumor marker detection have attracted considerable attention due to their simplicity and high efficiency. With the achievements of nanotechnology and nanoscience, nanomaterials-based colorimetric immunoassays have been demonstrated to be promising alternatives to conventional colorimetric enzyme-linked immunoassays. This review is focused on the progress in colorimetric immunoassays with the signal amplification of nanomaterials, including nanomaterials-based artificial enzymes to catalyze the chromogenic reactions, analyte-induced aggregation or size/morphology change of nanomaterials, nanomaterials as the carriers for loading enzyme labels, and chromogenic reactions induced by the constituent elements released from nanomaterials
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