GGS - Modelling forces and stresses in gigantic granular systems for coastal engineers

The Research Team is based within the Applied Modelling and Computation Group (AMCG) at Imperial in the Department of Earth Science and Engineering. The industrial partners, Sogreah Consultants, and Baird & Associates, are world leaders in Coastal Engineering and have committed considerable financial support. This project exploits the VGW EPSRC project in which numerical models were developed.To meet this century's challenge of extensive and accelerating future coastal change, society will expect coastal engineers to design resilient structures to hold the line against flood and erosion where it is deemed necessary. The first choice construction material and design approach for such structures will often be to use armour layers of massive rocks or concrete units. Currently, designers do not understand the details of how they work, relying heavily on empirical methods. This project will reveal fundamental mechanisms that cause disintegration of these rubble mound coastal structures and breakwaters. With our further enhanced simulation tools we will re-create the construction process, examine inherent heterogeneity, explore unit shapes and their interaction with under-layer rock geometry, examine scale effects, and use vibration and other proxies for wave disturbance, all to study block motion, contact force and stress heterogeneity and risk of concrete unit breakages.The aims are to:(1) Promote a shift in design approach from empirical to scientifically-determined damage and breakage probabilities. This requires modelling the solid geometry together with both the static and transient dynamic stress states within gigantic granular systems of complex-shaped concrete units and rock armour used in coastal structures and breakwaters, during construction, when at rest and as perturbed by external forces. (2) Extend the stress and deformation analysis tools of our world-leading 3D FEMDEM modelling technology that combines the multi-body interaction and motion modelling (i.e. Discrete Element Model, DEM) with the ability to model internal deformation of arbitrary shape (Finite Element Model, FEM) to the point where they can be readily harnessed to deliver a more fundamental understanding of a wide range of environmental and industrial problems.The layers of concrete units and rocks targeted in this coastal research are an extreme case of particulate or granular media intensively studied by physicists, with solid-like behaviour dominating but potentially fluid-like behaviour possible, should they become unravelled in a storm. Scientists have long been able to see stresses in photo-elastically deformed grain pack experiments using any 2D grain shapes, but have had no such property or tool to interrogate our real-world 3D granular systems. This is all about to change following research by the PI and co-workers - the development of a generic 3D computer model based on FEMDEM developed under our VGW EPSRC grant. No other model (presented in the literature) handles multi-body dynamics of complex-shaped deformable particles with greater accuracy, capturing the stress components everywhere in time and space. This project will bring fresh modelling capability to both fundamental science and engineering applications of granular materials. Information about temporal and spatial heterogeneity of stress will become available to underpin the workings at the heart of our currently limited understanding of granular material behaviour that is so vexing the physicists.Applications of numerical models to loading and collapse of silos, mineral and powder processing/handling, avalanching, and geotechnics have all been attempted using DEM. Upgrading DEM to FEMDEM, taking account of deformability, dynamics and the angularity/complexity of particle shape in these multi-body systems will significantly improve simulations, extending applications to unprecedented fields such as biomechanics and nuclear systems, too numerous to list here.

APPLICATION TO COASTAL STRUCTURES targets broader societal needs in times of increasing storminess, sea level rise, and a drive to exploit marine renewables: (a) to develop next generation numerical tools for structure and wave-structure technologies for coastal engineers - hence this addresses the mission of both Energy and Living With Environmental Change (LWEC) research programmes of EPSRC and (b) to provide Industry and Government with more accurate and robust science to innovate in design, help evaluate flood risk and ensure public confidence in the safety of coastal structures well into the 21st century. Rock and concrete unit armoured coastal structures, and structures to protect tidal energy harnessing lagoons, barrages and offshore wind and wave energy farms will use design methods born out of this project's research on granular solids and from fluid/granular structure numerical methods developed in later research phases. It is estimated that across Europe, the value of yearly coastal construction based on rubble mound methods is in excess of 1 billion Euros with breakwater asset values often exceeding 200m and a long-term annual UK flood defence spend requirement of 1b announce by EA (30.06.09). Dr Latham was heavily involved in the Rock Manual (2007) and has well established links with all key UK (and European) stakeholders in rubble structures. They include Government, Infrastructure and Client Organisations: DEFRA/EA, DTI, Local authorities, Network Rail; Consultants: Halcrow, WS Atkins, Royal Haskoning, High-Point Rendel; Contractors: Royal Boskalis Westminster, Van Oord UK, Nuttal; Materials Suppliers: concrete, aggregates, quarry companies e.g. CEMEX. Working with the world's leading unit designers, this project will position UK researchers at the heart of design innovations. With the international pace of numerical modelling, it is reasonable to suggest that within 5-10 years, coastal engineering research groups will use wave-structure numerical models to show realistic armour unit movement and stresses under simulated design wave climates. This may be expected to transfer into routine design practice, often replacing the need for flume models, within say 10-15 years. At key conferences, it will be possible through presentations and exhibits to engage designers and contractors, through visualisation of simulation results, to demonstrate the consequences of different construction practices that either improve or compromise performance in terms of interlocking, stability and dynamic tensile stress development. THE MODELLING TECHNOLOGY RESEARCH into developing further the FEMDEM software will impact on many researchers (PhD, Postdocs whether academic or industry led) of particle or blocky systems interactions, through the software's ability to tackle complex problems and its accessibility, compared with commercial tools. The range of environmental and industrial sectors to benefit from submodel enhancements to the FEMDEM codes already available on VGW are numerous, especially when taken together with the planned further coupling of solids FEMDEM with AMCG's generic fluids codes, FLUIDITY & ICOM. VGW was conceived with a focus on geoscience and geoengineering, but as the FEMDEM/fluids modelling technology becomes more versatile, the potential sectors for exploitation go much wider and include: resilience to extreme events (flood, avalanche), carbon capture, porous/fractured blocky rock-mass engineering, soil engineering, particulate processing, biomechanics and nuclear engineering. To ensure good engagement and communication, following the success of the VGW launch workshop, we will continue to run modelling technology hands-on workshops, use Encora (new European coastal network and Wiki) to promote a workshop and regular group meetings to link with other European Coastal research groups, publish journal and conference papers and webpages and include media relations, through the IC Press Office.