The flow dynamics of three-phase magmas: the coupling of rheology and permeability via bubble-particle interactions

火山活动与熔岩的流动有着天然的联系，例如岩浆从深水库上升到火山，或者熔岩从火山的侧翼流下。为了评估与火山爆发有关的灾害，尽可能准确地预测和模拟流动过程至关重要。控制岩浆流动特性的一个中心参数是熔体中的气体含量，悬浮在粘性硅酸盐熔体中的晶体和气泡的数量，以及这两相相互作用的程度。在喷发模型中考虑或忽略气泡和固体颗粒的影响会使结果发生数量级的变化，并可能使它们存在致命的缺陷。火山学中的两个关键问题受到晶体和气泡及其相互作用的影响：岩浆或熔岩的整体流动行为，即其流变学，以及气泡连接到连续脱气网络的能力，即其渗透性。该项目的目的是对三相岩浆模拟样品进行实验室实验，并在这些实验的基础上量化气泡和晶体浓度对流变性和渗透率的影响。这将导致“流变本构方程”的公式化，即将悬浮液性质（例如气泡和颗粒浓度）和外力（应力）与所得样品变形相关联的方程。这将使研究结果能够纳入更复杂的喷发模型，并提高其复杂程度，从而提高其准确性。实验包括两个同心圆筒之间的液体气泡颗粒混合物的剪切，其中之一旋转。这项研究的一个重要部分将是可视化的互动过程中发生的，当这样的样品受到剪切。在测量过程中，这些过程将通过透明的外圆柱体观察到。实验结束后，冷冻样品的流动诱导气泡和颗粒纹理将在显微镜下准确表征。所获得的纹理数据将用于重建具有相同纹理属性的“虚拟多孔介质”。对于这种介质，渗透率等参数可以用数值计算。此外，纹理将与斯特龙博利火山天然火山岩的显微断层扫描3D图像进行比较。这将允许在天然岩浆中的剪切历史和渗透性发展过程的推断。尽管三相系统对于自然科学以及工业和商业环境中的许多过程至关重要，但其基本流动特性在很大程度上仍未得到探索。通过这里提出的项目，我打算开发第一套经过验证的包含固体颗粒和气泡的悬浮液的本构方程，并希望为这些系统的精确理解做出贡献。

Volcanic activity is naturally linked to the flow of molten rock, e.g. the rise of magma from a deep reservoir to the volcano, or the flow of lava down the volcano's flanks. For the assessment of hazards associated with a volcanic eruption, it is of pivotal importance to predict and model flow processes as accurately as possible. A central parameter governing the flow properties of a magma is the gas content of he melt, the amount of crystals and bubbles suspended in the viscous silicate melt, and the degree to which these two phases interact. Accounting for, or neglecting the effect of bubbles and solid particles in eruption models can change their results by the orders of magnitudes, and could make them fatally flawed. Two key issues in volcanology are affected by crystals and bubbles, and their interactions: the bulk flow behaviour of the magma or lava, i.e. its rheology, and the ability of bubbles to connect to a continuous degassing network, i.e. its permeability. The objective of this project is to perform laboratory experiments on three-phase magma-analogue samples, and to quantify the influence of bubble and crystal concentrations on rheology and permeability on the basis of these experiments. This will lead to the formulating of a 'rheological constitutive equation', i.e. an equation that relates suspension properties (e.g. bubble & particle concentration) and external forces (stress) to the resulting sample deformation. This will enable the results to be incorporated into more complex eruption models and to enhance their degree of sophistication and thus their accuracy. The experiments comprise shearing of a liquid-bubble-particle mixture between two concentric cylinders, on of which rotates. A vital part of the study will be the visualization of the interactive processes that occur when such a sample is subject to shear. During the measurement, these processes will be observable through a transparent outer cylinder. After the experiment, flow-induced bubble and particle textures of frozen samples will be accurately characterized under the microscope. The textural data obtained will then be used to reconstruct a 'virtual porous medium' with the same textural properties. For this medium, parameters such as permeability can be calculated numerically. Furthermore, the textures will compared to microtomographic 3D images of natural volcanic rocks from Stromboli volcano. This will allow inferences on shear history and permeability development processes in natural magma. Despite its central importance for many processes in natural sciences, as well as in industrial and commercial settings, the fundamental flow properties of three-phase systems remain largely unexplored. With the project proposed here, I intend to develop the first validated set of constitutive equations for suspensions containing both solid particles and bubbles, and by that hope to contribute a substantial portion towards a refined understanding of these systems.