1.

2015-03-19

Particle methods for multiscale and multiphysics. World Scientific

M. B. Liu, G. R. Liu

Abstract:

粒子是构成物质的基本单元，基于粒子的计算方法是模拟简单乃至复杂介质的一个自然选择，也被广泛视为新一代计算方法，在研究多相、多尺度、多物理场等复杂问题方面具有特殊优势。该书从微观尺度、介观尺度到宏观尺度介绍了分子动力学（molecular dynamics，MD）、耗散粒子动力学(dissipative particle dynamics，DPD)以及光滑粒子动力学（smoothed particle hydrodynamics，SPH)等三种粒子类方法的基本理论、数值方法及内在联系。该书也结合刘谋斌研究员及合作者多年的研究工作，阐述了相关粒子方法的一些最新理论模型与数值方法，并给出了科学与工程领域的众多应用，包括微流动和生物流动（微液滴动力行为、高分子悬浮与输运、细胞变形、粘附与运移等），环境与地质流动（多孔介质与裂隙网络中多相流动、溃坝、泥石流等），自由液面流动（波浪砰击、液体晃荡、结构出入水、溢油拦截等）。该书所展示的理论模型、数值方法及示范案例将有助于推动粒子类数值方法与应用方面的研究工作。

Reference:

M. B. Liu, G. R. Liu (2015) Particle methods for multiscale and multiphysics. World Scientific (ISBN: 978-981-238-456-0).

2.

2015-02-15

An SPH model for multiphase flows with complex interfaces and large density differences

Liu Moubin, et al.

Abstract:

In this paper, an improved SPH model for multiphase flows with complex interfaces and large density differences is developed. The multiphase SPH model is based on the assumption of pressure continuity over the interfaces and avoids directly using the information of neighboring particles’ densities or masses in solving governing equations. In order to improve computational accuracy and to obtain smooth pressure fields, a corrected density re-initialization is applied. A coupled dynamic solid boundary treatment (SBT) is implemented both to reduce numerical oscillations and to prevent unphysical particle penetration in the boundary area. The density correction and coupled dynamics SBT algorithms are modified to adapt to the density discontinuity on fluid interfaces in multiphase simulation. A cut-off value of the particle density is set to avoid negative pressure, which can lead to severe numerical difficulties and may even terminate the simulations. Three representative numerical examples, including a Rayleigh–Taylor instability test, a non-Boussinesq problem and a dam breaking simulation, are presented and compared with analytical results or experimental data. It is demonstrated that the present SPH model is capable of modeling complex multiphase flows with large interfacial deformations and density ratios.

Reference:

Chen Z, Zong Z, Liu M B, et al. An SPH model for multiphase flows with complex interfaces and large density differences[J]. Journal of Computational Physics, 2015, 283: 169-188.

3.

2015-10-14

Export production fluctuations in the eastern equatorial Pacific during the Pliocene-Pleistocene: Reconstruction using barite accumulation rates

Zhou Liping, et al.

Abstract:

Export production is an important component of the carbon cycle, modulating the climate system by transferring CO2 from the atmosphere to the deep ocean via the biological pump. Here we use barite accumulation rates to reconstruct export production in the eastern equatorial Pacific over the past 4.3 Ma. We find that export production fluctuated considerably on multiple time scales. Export production was on average higher (51 g C m−2 yr−1) during the Pliocene than the Pleistocene (40 g C m−2 yr−1), decreasing between 3 and 1 Ma (from more than 60 to 20 g C m−2 yr−1) followed by an increase over the last million years. These trends likely reflect basin-scale changes in nutrient inventory and ocean circulation. Our record reveals decoupling between export production and temperatures on these long (million years) time scale. On orbital time scales, export production was generally higher during cold periods (glacial maxima) between 4.3 and 1.1 Ma. This could be due to stronger wind stress and higher upwelling rates during glacial periods. A shift in the timing of maximum export production to deglaciations is seen in the last 1.1 million years. Results from this study suggest that, in the eastern equatorial Pacific, mechanisms that affect nutrient supply and/or ecosystem structure and in turn carbon export on orbital time scales differ from those operating on longer time scales and that processes linking export production and climate-modulated oceanic conditions changed about 1.1 million years ago. These observations should be accounted for in climate models to ensure better predictions of future climate change.

Reference:

Ma Z, Ravelo A C, Liu Z, et al. Export production fluctuations in the eastern equatorial Pacific during the Pliocene‐Pleistocene: Reconstruction using barite accumulation rates[J]. Paleoceanography, 2015, 30(11): 1455-1469.

4.

2015

A comparative study of different baffles on mitigating liquid sloshing in a rectangular tank due to a horizontal excitation

Liu Moubin, et al.

Abstract:

The purpose of this paper is to investigate different baffles on mitigating liquid sloshing in a rectangular tank due to a horizontal excitation and to find out the optimal selection of sloshing mitigation for practical applications. Design/methodology/approach - The numerical study is conducted by using a proven improved smoothed particle hydrodynamics (SPH), which is convenient in tracking free surfaces and capable of obtaining smooth and correct pressure field. Findings - Liquid sloshing effects in a rectangular tank with vertical middle baffles, horizontal baffles, T-shape baffles and porous baffles are investigated together with those without any baffles. It is found that the existence of baffles can mitigate sloshing effects and the mitigation performance depends on the shape, structure and location of the baffles. Considering the balance of sloshing mitigation performance and the complexity in structure and design, the I shaped and T shaped baffles can be good choices to mitigate sloshing effects. Practical implications - The presented methodology and findings can be helpful in practical engineering applications, especially in ocean engineering and problems with large sloshing effects. Originality/value - The SPH method is a meshfree, Lagrangian particle method, and therefore it is an attractive approach for modeling liquid sloshing with material interfaces, free surfaces and moving boundaries. In most previous literature, only simple baffles are investigated. In this paper, more complicated baffles are investigated, which can be helpful in practical applications and engineering designs.

Reference:

Shao J, Li S, Li Z, et al. A comparative study of different baffles on mitigating liquid sloshing in a rectangular tank due to a horizontal excitation[J]. Engineering Computations, 2015, 32(4): 1172-1190.