This paper introduces a Theme Issue on discrete-element modelling, based on research presented at an interdisciplinary workshop on this topic organized by the National Institute of Environmental e-Science. The purpose of the workshop, and this collection of papers, is to highlight the opportunities for environmental scientists provided by (primarily) off-lattice methods in the discrete-element family, and to draw on the experiences of research communities in which the use of these methods is more advanced. Applications of these methods may be conceived in a wide range of situations where dynamic processes involve a series of fundamental entities (particles or elements) whose interaction results in emergent macroscale structures. Indeed, the capacity of these methods to reveal emergent properties at the meso- and macroscale, that reflect microscale interactions, is a significant part of their attraction. They assist with the definition of constitutive material properties at scales beyond those at which measurement and theory have been developed, and help us to understand self-organizing behaviours. The paper discusses technical issues including the contact models required to represent collision behaviour, computational aspects of particle tracking and collision detection, and scales at which experimental data are required and choices about modelling style must be made. It then illustrates the applicability of DEM and other forms of individual-based modelling in environmental and related fields as diverse as mineralogy, geomaterials, mass movement and fluvial sediment transport processes, as well as developments in ecology, zoology and the human sciences where the relationship between individual behaviour and group dynamics can be explored using a partially similar methodological framework.
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.
"The accuracy of 3D RANS water surface elevation, bed shear stress and velocity direction and magnitude predictions have been shown to be more accurate than 2D predictions for natural conf luence (Bradbrook et al. 1998; Lane et al. 1999) and natural braided river (Nicholas and Sambrook Smith 1999) settings. Three-dimensional CFD models have been applied primarily in morphological modelling to calculate the stresses exerted on a grain by f luid f low and interactions with other particles (Cleary and Prakash 2004; Hardy 2005; Richards et al. 2004). At this scale, the saltating trajectories of individual grains are modelled. "
[Show abstract][Hide abstract]ABSTRACT: Numerical morphological modelling of braided rivers is increasingly used to explore controls on river pattern and for applied environmental management. This article reviews and presents a taxonomy of braided river morphodynamic models and discusses the challenges facing model development and use, illustrating these challenges with a case example. The taxonomy is contextualised by an initial discussion of the physical mechanisms of braiding. The taxonomy differentiates between reach-scale and catchment-scale models. Reach-scale models are usually physics-based, which are further divided based upon the mathematical approach used to solve equations (analytical or numerical) and their dimensionality (1D, 2D or 3D). Cellular automata models are one type of numerical model that replace at least some physical processes with expedient rules. A 2D physics-based approach encapsulates sufficient process complexity to provide behavioural predictions. Predictions from catchment-scale landscape evolution models have potential for providing boundary conditions. Future progress in physics-based modelling needs to address three challenges: (i) representation of flow and sediment transport; (ii) temporal and spatial scaling; and (iii) model calibration, sensitivity, uncertainty and validation. The key problem for addressing these is the dearth of laboratory or natural experiment datasets. To show that progress can be made by comparing reach-scale predictions to high-resolution observations, a case study of monitoring and modelling, conducted in the Rees River, New Zealand, is presented. Hydraulic predictions of cellular automata and shallow water equation (Delft3d) models are compared to observed inundation extent. The efficacy of high-resolution, multi-temporal morphological data for assessing 2D physics-based morphodynamic model predictions is also demonstrated.
Full-text · Article · Mar 2016 · Geography Compass
"Large-scale DEM simulations have a significant potential in many areas of research and technology, including the environmental sciences to, e.g. simulate land slides or avalanches (Cleary and Prakash, 2004; Richards et al., 2004), the study of complex selforganization phenomena as, e.g. in singing sand dunes (Douady et al., 2006), and research toward answering open questions in the continuum modeling of granular matter (de Gennes, 1999). "
[Show abstract][Hide abstract]ABSTRACT: Purpose - The purpose of this paper is to present large-scale parallel direct numerical simulations of granular flow, using a novel, portable software program for discrete element method (DEM) simulations. Design/methodology/ approach - Since particle methods provide a unifying framework for both discrete and continuous systems, the program is based on the parallel particle mesh (PPM) library, which has already been demonstrated to provide transparent parallelization and state-of-the-art parallel efficiency using particle methods for continuous systems. Findings - By adapting PPM to discrete systems, results are reported from three-dimensional simulations of a sand avalanche down an inclined plane. Originality/value - The paper demonstrates the parallel performance and scalability of the new simulation program using up to 122 million particles on 192 processors, employing adaptive domain decomposition and load balancing techniques.
"In recent years individual-based and multi-agent (Gilbert, 2007; Wooldridge, 2001) approaches to land-use change modelling have begun to be adopted, as they allow a more flexible approach to the representation of people's interaction with the environment: spatial heterogeneity can be more easily included, and the effects of decision making disaggregated (Barthel et al., 2008; Monticino et al., 2007; Matthews et al., 2007; Richards et al., 2004a,b; Parker et al., 2003). The potential for using agent models in ecosystem management has been described by Doran (2001) and has also been reviewed more recently by Bousquet and Le Page (2003). "
[Show abstract][Hide abstract]ABSTRACT: Subsistence farming communities are dependent on the landscape to provide the resource base upon which their societies can be built. A key component of this is the role of climate and the feedback between rainfall, crop growth, land clearance and their coupling to the hydrological cycle. Temporal fluctuations in rainfall alter the spatial distribution of water availability, which in turn is mediated by soil-type, slope and landcover. This pattern ultimately determines the locations within the landscape that can support agriculture and controls sustainability of farming practices. The representation of such a system requires us to couple together the dynamics of human and ecological systems and landscape change, each of which constitutes a significant modelling challenge on its own. Here we present a proto-type coupled modelling system to simulate land-use change by bringing together three simple process models: (a) an agent-based model of subsistence farming; (b) an individual-based model of forest dynamics; and (c) a spatially explicit hydrological model which predicts distributed soil moisture and basin scale water fluxes. Using this modelling system we investigate how demographic changes influence deforestation and assess its impact on forest ecology, stream hydrology and changes in water availability.
Full-text · Article · Feb 2009 · Environmental Modelling and Software