Keynote talks

• Tal Cohen (MIT, USA)

Title: Growth, instability, and failure: bringing order into the chaos of natural phenomena

Abstract: Natural phenomena such as growth, instability, and failure, can be highly dependent upon stochastic mechanisms at the microscale, which may be activated, for example, by the existence of initial imperfections, the action of molecular motors, or the diffusion of constituents. Yet, at the macroscale, astonishing order is often observed. In this talk, I will discuss our recent attempts to bring a deterministic understanding to explain such processes by focusing on growth of cavities in soft materials and their transition into cracks.

• Luis Cueto-Felgueroso (U Politecnica de Madrid, Spain)

Title: Wetting, hysteresis and phase transitions in multiphase flow through permeable media: insights from modeling

Abstract: Multiphase flow in porous and fractured media involves a complex sequence of pore-scale events, from the smooth, reversible displacement of interfaces to abrupt interfacial reconfigurations and rapid pore invasion cascades. Two-phase displacements are controlled by the wetting properties of the system, the viscosity contrast between the fluids, and the relative balance between capillary and viscous forces. Using results from numerical modeling and upscaling, I will discuss how these abrupt and collective interfacial displacements (Haines jumps) can be simulated at the pore scale, and incorporated into continuum (Darcy) scale theories of porous media flow. I will consider fully immiscible, as well as partially miscible systems. The former are described using the 3D Cahn-Hilliard-Stokes equations, while the latter are modeled using a Navier-Stokes-Korteweg formulation for multicomponent systems, with fluid mixtures described by cubic equations of state.

• Xiaojing (Ruby) Fu (UC Berkeley, USA)

Title: Instabilities and Phase Transitions in Multiphase Flow through Porous Media-- a story told by gas hydrates

Abstract: Flow and transport through porous media is ubiquitous in nature. They are key processes behind subsurface resources such as groundwater, oil and gas and geothermal energy. They also mediate corrosion and ageing of porous engineering materials as well as geohazards such as landslides, volcanic eruptions and earthquakes.

Central to many of these processes is the strong coupling between porous media flows and phase transitions—the creation or destruction of fluid or solid driven by thermodynamics. Multiphase flow with phase transitions often leads to dynamic systems that are far from thermodynamic equilibrium. In this talk, I will describe an example of nonequilibrium phenomena encountered in methane clathrate (gas hydrate) in multiphase environments, and new continuum mathematical descriptions based on phase-field methods to model them. Motivated by field and laboratory observations, I will describe how the spontaneous formation of a solid hydrate crust on a moving gas-liquid interface gives rise to a new type of flow instability we term crustal fingering. I will further show that this solid-modulated gas percolation mechanism is crucial to our understanding of methane venting in the world’s oceans, gas hydrate dissociation as a trigger to landslides, and energy extraction from gas hydrate deposits.

• Tobias Keller (U Glasgow, UK)

Title: Modelling magma transport with rock failure: the effective-viscosity approach

Abstract: There is abundant geological evidence of magma transport interacting with rock failure recorded in features such as magma-filled dikes, sills, tears, shear bands, tubes, and more. The basic rheological behaviour of rock can be approximated as an effective visco-elastic medium. In the course of visco-elastic deformation, stress can accumulate to a critical threshold or yield stress, where rock begins to fail. The result of failure range from strongly localised ductile creep to discrete brittle fracture. It has long been known that the yield stress is lowered significantly by pore liquid pressure. Hence, the presence of melt in partially molten rock can promote the onset of failure even at comparatively low shear stress. Modelling failure in a continuum mechanics framework can be challenging. Failure not only introduces strong non-linearity, but the resulting localisation or discontinuity of deformation can be difficult to resolve without either accepting strong resolution dependence or resorting to intrusive regularisation schemes. One approach to modelling magma transport interacting with rock failure is to augment a McKenzian viscous two-phase flow model by approximating elasticity and plastic failure as adaptive viscosity weakening. In this presentation, I will introduce this effective-viscosity approach, highlight some of its challenges and limitations, but also demonstrate opportunities and possible applications of the method.

• Ludovic Pauchard (CNRS–University Paris Sud, France)

Title: Mechanical instabilities induced by drying complex fluids

Abstract: Most coatings are made by depositing a volatile liquid that contains dispersed nanoparticles or polymers. The liquid is then evaporated until a dry film is obtained. During the drying, hydrodynamical and/or mechanical instabilities can develop. In particular, mechanical instabilities can result in heterogeneities, typically cracks or wrinkles, that influence the quality of the final product. Such structures can take place at a wide range of scales and lead to a large variety of morphologies that appears to be the signature of the matter. They influence the quality of a final coating as well as exhibit a plausible powerful tool to highlight the physical properties of dairy colloids. In particular, crack patterns can be of great interest in the domain of conservation/restoration of paintings. Indeed, the crack patterns, whether they formed at the earlier stage or developing later in the life of the painting, reveal the mechanical and physical properties and can give information about the methods used by the artist. Following this issue, quantitative analysis of crack morphology (crack spacing, cracks orientation, crack opening,…) is investigated using tunable model systems from brittle to tough. In particular, since a key objective in art conservation deals with the potential evolution of a crack pattern with further stresses, the stability of a crack network is investigated under successive wetting/drying cycles.