Water waves generated by a moving bottom

Tsunamis are often generated by a moving sea bottom. This paper deals with the case where the tsunami source is an earthquake. The linearized water-wave equations are solved analytically for various sea bottom motions. Numerical results based on the analytical solutions are shown for the free-surface profiles, the horizontal and vertical velocities as well as the bottom pressure.Comment: 41 pages, 13 figures. Accepted for publication in a book: "Tsunami and Nonlinear Waves", Kundu, Anjan (Editor), Springer 2007, Approx. 325 p., 170 illus., Hardcover, ISBN: 978-3-540-71255-8, available: May 200

Transport time scales in soil erosion modelling

Unlike sediment transport in rivers, erosion of agricultural soil must overcome its cohesive strength to move soil particles into suspension. Soil particle size variability also leads to fall velocities covering many orders of magnitude, and hence to different suspended travel distances in overland flow. Consequently, there is a large range of inherent time scales involved in transport of eroded soil. For conditions where there is a constant rainfall rate and detachment is the dominant erosion mechanism, we use the Hairsine-Rose (HR) model to analyze these timescales, to determine their magnitude (bounds) and to provide simple approximations for them. We show that each particle size produces both fast and slow timescales. The fast timescale controls the rapid adjustment away from experimental initial conditions – this happens so quickly that it cannot be measured in practice. The slow time scales control the subsequent transition to steady state and are so large that true steady state is rarely achieved in laboratory experiments. Both the fastest and slowest time scales are governed by the largest particle size class. Physically, these correspond to the rate of vertical movement between suspension and the soil bed, and the time to achieve steady state, respectively. For typical distributions of size classes, we also find that there is often a single dominant time scale that governs the growth in the total mass of sediment in the non-cohesive deposited layer. This finding allows a considerable simplification of the HR model leading to analytical expressions for the evolution of suspended and deposited layer concentrations

An agent-based framework for modelling social influence on travel behaviour

Recent travel forecasting models have focussed upon the fact that travel is derived from the activities in which people participate, such as work, school, shopping, sport, leisure, and social events. Non-discretionary activities such as work and school may be explained by the traveller's sociodemographic characteristics and generalised travel costs, as well as long-term decisions such as a decision to move to a particular town. Participation in social and leisure activities is determined by one's friends and the groups that one is a member of, i.e., their household, their workplace/school, sporting groups, voluntary organisations and clubs. These acquaintances form part of an individual's social network: a representation of the people one interacts with. This demonstrates a shift in the activity-travel modelling field from “where” to “what” and now towards “who with”. On top of this, our changing use of ICT is influencing our activity and travel patterns, as some activities can now be replaced by online activities, and online activities can lead to actual travel. Some researchers are already looking beyond households to the influence of social networks. However, we are not aware of any agent-based urban models considering activity-travel choice of individuals. Existing work is in the conceptual or early implementation phases. The aim of this project is to develop and validate a model combining social (“who with”) and spatial (“where”) networks for investigating and predicting social activities. In this paper, we describe the design of our model. Agent-based modelling is a good fit for our model. Our system consists of different people, their relationships and interactions with each other, and their activities in and possible movement around the environment. The topology is not homogeneous and clusters may form. We have used a combination of the metamodels found in mature agent-oriented software engineering methodologies to design our model, focussing on system goals, the environment, acquaintances, roles, and services. The design successfully caters for the description of the environment, the nature of activities, and the dynamics of individuals and their networks. The individuals in our model each have an agenda, and interact and negotiate with others to schedule social activities, in particular negotiating about the nature of the activity, participants, time, and location. Existing models do not capture the actual joint decision making process behind activity scheduling, and although some work on joint decisions has been undertaken, these models focus on outcomes of interactions within households and have not considered personal social networks at large. We use existing multi-issue negotiation theory to describe an interaction design, which is shown to satisfy a number of basic properties, such as termination, liveness, and safety. Due to the current interest in predicting social activities and the changing nature of social activities due to our use of ICT, this type of model is of increasing importance to planners who need to be able to predict social activities and travel. The model is currently being implemented in Java, and will be validated using an extensive dataset of people's activity participation and personal networks, collected in Eindhoven, Netherlands. Future work includes more empirical experimentation with the protocols and implementation of and experimentation with the entire model

Comparing modelling frameworks : a workshop approach

Of concern to the environmental modelling community is the proliferation of individual, and individualistic, models and the time associated with common model development tasks such as data transformation, coding of models, and visualisation. One way of addressing this problem is the adoption of modelling frameworks. These frameworks, or environments, support modular model development through provision of libraries of core environmental modelling modules, as well as reusable tools for data manipulation, analysis and visualisation. Such frameworks have a range of features and requirements related to the architecture, protocols and methods of operation, and it is difficult to compare the modelling workload and performance of alternative frameworks without using them to undertake identical, or similar modelling tasks. This paper describes the outcomes of a workshop to compare three frameworks - the Spatial Modelling Environment (SME), Tarsier and the Integrated Component Modelling System (ICMS). A simple environmental problem linking hillslope flow and soil erosion processes with a receiving water store was designed and then implemented in the three frameworks. It was found that the SME and Tarsier contained many components well suited to handling complex spatial and temporal models, with ICMS being an integrated framework tailored for smaller scale problems. Of the three tested frameworks, the SME proved superior in supporting problem description, Tarsier provided more flexibility in linking and validating the model components, and ICMS served as an effective prototyping tool. The test problem, and associated data and parameters, are described in detail to allow others to undertake this test.No Full Tex