Abstract

One contribution of 14 to a theme issue 'Toward the development of high-fidelity models of wall turbulence at large Reynolds number' . Field observations and laboratory experiments suggest that at high Reynolds numbers Re the outer region of turbulent boundary layers selforganizes into quasi-uniform momentum zones (UMZs) separated by internal shear layers termed 'vortical fissures' (VFs). Motivated by this emergent structure, a conceptual model is proposed with dynamical components that collectively have the potential to generate a self-sustaining interaction between a single VF and adjacent UMZs. A large-Re asymptotic analysis of the governing incompressible Navier-Stokes equation is performed to derive reduced equation sets for the streamwise-averaged and streamwise-fluctuating flow within the VF and UMZs. The simplified equations reveal the dominant physics within-and isolate possible coupling mechanisms among-these different regions of the flow.This article is part of the themed issue 'Toward the development of high-fidelity models of wall turbulence at large Reynolds number'.

Sea ice dynamics exhibit granular behavior as individual floes and fracture networks become particularly evident at length scales O(10–100) km and smaller. However, climate models do not resolve floes and represent sea ice as a continuum, while existing floe‐scale sea ice models tend to oversimplify floes using discrete elements of predefined simple shapes. The idealized nature of climate and discrete element sea ice models presents a challenge of comparing the model output with floe‐scale sea ice observations. Here we present SubZero, a conceptually new sea ice model geared to explicitly simulate the life cycles of individual floes by using complex discrete elements with time‐evolving shapes. This unique model uses parameterizations of floe‐scale processes, such as collisions, fractures, ridging, and welding, to simulate a wide range of evolving floe shapes and sizes. We demonstrate the novel capabilities of the SubZero model in idealized experiments, including uniaxial compression, the summer‐time sea ice flow through the Nares Strait, and winter‐time sea ice growth. The model naturally reproduces the statistical behavior of the observed sea ice, such as the power‐law appearance of the floe size distribution and the long‐tailed ice thickness distribution. The SubZero model could provide a valuable alternative to existing discrete element and continuous sea ice models for simulations of floe interactions.

Sea ice dynamics span a wide range of scales and exhibit granular behavior as individual floes and fracture networks become evident at length scales O(10--100) km and smaller. Existing floe-scale sea ice models use bonded elements of predefined simple shapes like disks or tetrahedra to represent more complex floe geometries. However, floe-scale modeling remains challenging due to its typically high computational cost and difficulties in reconciling the idealized nature of discrete elements with complex floe-scale observations. Here we present SubZero, a conceptually new sea ice model geared to explicitly simulate the lifecycles of individual floes by using complex discrete elements with time-evolving shapes. This unique model uses parameterizations of floe-scale processes, such as collisions, fractures, ridging, and welding, to bypass the high computational costs of resolving intra-floe bonded elements. We demonstrate the novel capabilities brought by the SubZero model in idealized experiments, including the summer-time sea ice flow through the Nares Strait and a winter-time equilibration of floe size and ice thickness distributions. The SubZero model could provide a valuable alternative to existing discrete element and continuous sea ice models for simulations of floe interactions.

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