A model of capillary cohesion for numerical simulations of 3D polydisperse granular media

We present a 3D discrete‐element approach for numerical investigation of wet granular media. This approach relies on the basic laws of contact and Coulomb friction enriched by a capillary force law between particles. We show that the latter can be expressed as a simple explicit function of the gap and volume of the liquid bridge connecting a pair of spherical particles. The length scales involved in this expression are analyzed by comparing with direct integration of the Laplace–Young equation. We illustrate and validate this approach by application to direct shear and simple compression loadings. The shear and compression strengths obtained from simulations reproduce well the experimental measurements under similar material and boundary conditions. Our findings clearly show that the number density of liquid bonds in the bulk is a decisive parameter for the overall cohesion of wet granular materials. A homogeneous distribution of the liquid within the bridge debonding distance, even at low volume contents, leads to the highest cohesion. The latter is independent of the liquid content as far as the liquid remains in the pendular state and the number density of liquid bonds remains constant. Copyright © 2007 John Wiley & Sons, Ltd.     

煤层地震波振幅切片解释煤层变薄带及应用实例

本方法根据薄煤层厚度与其振幅基本呈线性关系的原理,利用三维地震资料解释系统提取煤层反射波振幅参数,对生成的彩色平面振幅图进行分析,进而圈定出煤层变薄带的范围。并以实例说明了该技术方法在解释煤层变薄带方面的应用效果。     

Next steps in geoengineering scenario research: limited deployment scenarios and beyond

Climate engineering has received increasing attention, but its discussion has remained on the sidelines of mainstream climate policy. The policy relevance of this previously exotic option is poised to rise because of the gap between the temperature goals of the Paris Agreement and slow global mitigation efforts. It is therefore crucial to understand the risks and benefits of the proposed schemes, and the social implications of policy choices. Assessment of the risks and benefits of solar geoengineering strongly depends on scenarios, but previous scenarios have not reflected the full range of social choices. In light of concerns over risks, a newer set of scenarios is desirable, which represents both uncertainties and social choices more fully. Borrowing and extending lessons from recent literature on the new community climate scenario process, we envision a possible scenario-building process that combines interdisciplinary scholarship with the involvement of stakeholders and citizens. The resultant scenarios would better characterize uncertainties of, and policy choices for, solar geoengineering, and foster critical appraisal of its risks and benefits. Such societal choices might include not only total ban and large-scale deployment, but also limited deployment, which has received less attention in the scenario literature. The interaction between scenario and governance research would be able to highlight the central issues at stake, including ethical, social, and political dimensions.

Key policy insights

• A more comprehensive assessment of solar geoengineering is necessary to evaluate its risks and benefits, necessitating new scenario research

• It is crucial to reflect the full span of policy choices and uncertainties with interdisciplinary collaboration in such scenarios

• Such societal choices might include not only total ban and large-scale deployment, but also limited deployment, which has received less attention in the scenario literature

• Participatory scenario research would enable incorporating the concerns and opinions of stakeholders and citizens in scenario creation

     

The Loci of Satellite Positions: A Constellation Design Approach

In special cases in which satellite constellations can be described by a limited set of parameters, a correlation between the latter and the constellation characteristics (i.e. shape and kinematics of the satellite configurations) has been investigated. Such cases may be a useful starting point for designing more complex constellations in order to achieve better the desired performances. Therefore, this proves to be one way to fix an initial set of parameters once the desired behaviour of the constellation has been established on the basis of the operational purposes required. This revised version was published online in August 2006 with corrections to the Cover Date.     

Indirect-approach method for specified-end points seismic ray tracing in three dimensional inhomogeneous media

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A quasi three-dimensional model for flow and transport in unsaturated and saturated zones: 1. Implementation of the quasi two-dimensional case

A quasi three-dimensional (QUASI 3-D) model is presented for simulating the subsurface water flow and solute transport in the unsaturated and in the saturated zones of soil. The model is based on the assumptions of vertical flow in the unsaturated zone and essentially horizontal groundwater flow. The 1-D Richards equation for the unsaturated zone is coupled at the phreatic surface with the 2-D flow equation for the saturated zone. The latter was obtained by averaging 3-D flow equation in the saturated zone over the aquifer thickness. Unlike the Boussinesq equation for a leaky-phreatic aquifer, the developed model does not contain a storage term with specific yield and a source term for natural replenishment. Instead it includes a water flux term at the phreatic surface through which the Richards equation is linked with the groundwater flow equation. The vertical water flux in the saturated zone is evaluated on the basis of the fluid mass balance equation while the horizontal fluxes, in that equation, are prescribed by Darcy law. A 3-D transport equation is used to simulate the solute migration. A numerical algorithm to solve the problem for the general quasi 3-D case was developed. The developed methodology was exemplified for the quasi 2-D cross-sectional case (QUASI2D). Simulations for three synthetic problems demonstrate good agreement between the results obtained by QUASI2D and two fully 2-D flow and transport codes (SUTRA and 2DSOIL). Yet, simulations with the QUASI2D code were several times faster than those by the SUTRA and the 2DSOIL codes.     

用EOF展开和人工神经网络方法预测ENSO的研究

本文利用EOF展开技术和人工神经网络方法进行了预测ENSO的研究，研究结果表明，二种方法的结合对预测ENSO有较好的效果，但预报效果依赖于预报时效，依赖于预报因子的合理选取。     

油气资源补充评价方法探讨

我国近海含油气盆地的勘探现状是油气普查阶段基本完成 ,但勘探程度差别较大。同一含油气盆地内 ,有利区带 (凹陷 )勘探程度较高 ,发现了相当数量的油气田和含油气构造 ,而油气条件较差的坳 (凹 )陷 ,勘探程度较低。当前油气资源补充评价的主要任务是在前人评价的基础上 ,如何通过勘探程度较高地区丰富的资料 ,用多种方法求取、验证评价关键参数 ,指导勘探程度低的地区油气资源评价 ,这就是本文的目的和要探讨的评价方法。     

A Finite-Difference Approach to the Time-Dependent Mild-Slope Equation

A finite-difference approach is used to develop a time-dependent mild-slope equation incorporating the effects of bottom dissipation and nonlinearity.The Euler predictor-corrector method and the three-point finite-difference method with varying spatial steps are adopted to discretize the time derivatives and the two-dimensional horizontal ones,respectively,thus leading both the time and spatial derivatives to the second-order accuracy.The boundary conditions for the present model are treated on the basis of the general conditions for open and fixed boundaries with an arbitrary reflection coefficient and phase shift.Both the linear and nonlinear versions of the numerical model are applied to the wave propagation and transformation over an elliptic shoal on a sloping beach,respectively,and the linear version is applied to the simulation of wave propagation in a fully open rectangular harbor.From comparison of numerical results with theoretical or experimental ones,it is found that they are in reasonable agreement.