Numerical and experimental verification of a theoretical model of ripple formation in ice growth under supercooled water film flow

Little is known about morphological instability of a solidification front during the crystal growth of a thin film of flowing supercooled liquid with a free surface: for example, the ring-like ripples on the surface of icicles. The length scale of the ripples is nearly 1 cm. Two theoretical models for the ripple formation mechanism have been proposed. However, these models lead to quite different results because of differences in the boundary conditions at the solid-liquid interface and liquid-air surface. The validity of the assumption used in the two models is numerically investigated and some of the theoretical predictions are compared with experiments.Comment: 30 pages, 9 figure

libcloudph++ 0.2: single-moment bulk, double-moment bulk, and particle-based warm-rain microphysics library in C++

This paper introduces a library of algorithms for representing cloud microphysics in numerical models. The library is written in C++, hence the name libcloudph++. In the current release, the library covers three warm-rain schemes: the single- and double-moment bulk schemes, and the particle-based scheme with Monte-Carlo coalescence. The three schemes are intended for modelling frameworks of different dimensionality and complexity ranging from parcel models to multi-dimensional cloud-resolving (e.g. large-eddy) simulations. A two-dimensional prescribed-flow framework is used in example simulations presented in the paper with the aim of highlighting the library features. The libcloudph++ and all its mandatory dependencies are free and open-source software. The Boost.units library is used for zero-overhead dimensional analysis of the code at compile time. The particle-based scheme is implemented using the Thrust library that allows to leverage the power of graphics processing units (GPU), retaining the possibility to compile the unchanged code for execution on single or multiple standard processors (CPUs). The paper includes complete description of the programming interface (API) of the library and a performance analysis including comparison of GPU and CPU setups.Comment: The library description has been updated to the new library API (i.e. v0.1 -> v0.2 update). The key difference is that the model state variables are now mixing ratios as opposed to densities. The particle-based scheme was supplemented with the "particle recycling" process. Numerous editorial corrections were mad

A spatially distributed model for the dynamic prediction of sediment erosion and transport in mountainous forested watersheds

Erosion and sediment transport in a temperate forested watershed are predicted with a new sediment model that represents the main sources of sediment generation in forested environments (mass wasting, hillslope erosion, and road surface erosion) within the distributed hydrology-soil-vegetation model (DHSVM) environment. The model produces slope failures on the basis of a factor-of-safety analysis with the infinite slope model through use of stochastically generated soil and vegetation parameters. Failed material is routed downslope with a rule-based scheme that determines sediment delivery to streams. Sediment from hillslopes and road surfaces is also transported to the channel network. A simple channel routing scheme is implemented to predict basin sediment yield. We demonstrate through an initial application of this model to the Rainy Creek catchment, a tributary of the Wenatchee River, which drains the east slopes of the Cascade Mountains, that the model produces plausible sediment yield and ratios of landsliding and surface erosion when compared to published rates for similar catchments in the Pacific Northwest. A road removal scenario and a basin-wide fire scenario are both evaluated with the model

Environmental Objects for Authoring Procedural Scenes

International audienceWe propose a novel approach for authoring large scenes with automatic enhancement of objects to create geometric decoration details such as snow cover, icicles, fallen leaves, grass tufts or even trash. We introduce environmental objects that extend an input object geometry with a set of procedural effects that defines how the object reacts to the environment, and by a set of scalar fields that defines the influence of the object over of the environment. The user controls the scene by modifying environmental variables, such as temperature or humidity fields. The scene definition is hierarchical: objects can be grouped and their behaviours can be set at each level of the hierarchy. Our per object definition allows us to optimize and accelerate the effects computation, which also enables us to generate large scenes with many geometric details at a very high level of detail. In our implementation, a complex urban scene of 10 000 m², represented with details of less than 1 cm, can be locally modified and entirely regenerated in a few seconds

Convective-absolute nature of ripple instabilities on ice and icicles

Film hydrodynamics is crucial in water-driven morphological pattern formation. A prominent example is given by icicle ripples and ice ripples, which are regular patterns developing on freezing-melting inclined surfaces bounding open-channel flows. By a suitable mathematical model based on conservation principles and the use of the cuspmap method, in this paper we address the convective-absolute nature of these two kinds of instabilities. The obtained results show that icicle ripples, which develop at inverted (overhang) conditions, have subcentimetric wavelengths which are unstable when the Reynolds number of the liquid flow (Re) is small and the supercooling is intensive. With the increase in Re, the instability switches from absolute to convective. Ice ripples instead exhibit the opposite dependance on Re and are highly affected by the surface slope. In addition, the evaluation of the so-called absolute wave number, which is responsible for the asymptotic impulse response, suggests a different interpretation of some recent experiments about ice ripples

Physically-based simulation of ice formation

The geometric and optical complexity of ice has been a constant source of wonder and inspiration for scientists and artists. It is a defining seasonal characteristic, so modeling it convincingly is a crucial component of any synthetic winter scene. Like wind and fire, it is also considered elemental, so it has found considerable use as a dramatic tool in visual effects. However, its complex appearance makes it difficult for an artist to model by hand, so physically-based simulation methods are necessary. In this dissertation, I present several methods for visually simulating ice formation. A general description of ice formation has been known for over a hundred years and is referred to as the Stefan Problem. There is no known general solution to the Stefan Problem, but several numerical methods have successfully simulated many of its features. I will focus on three such methods in this dissertation: phase field methods, diffusion limited aggregation, and level set methods. Many different variants of the Stefan problem exist, and each presents unique challenges. Phase field methods excel at simulating the Stefan problem with surface tension anisotropy. Surface tension gives snowflakes their characteristic six arms, so phase field methods provide a way of simulating medium scale detail such as frost and snowflakes. However, phase field methods track the ice as an implicit surface, so it tends to smear away small-scale detail. In order to restore this detail, I present a hybrid method that combines phase fields with diffusion limited aggregation (DLA). DLA is a fractal growth algorithm that simulates the quasi-steady state, zero surface tension Stefan problem, and does not suffer from smearing problems. I demonstrate that combining these two algorithms can produce visual features that neither method could capture alone. Finally, I present a method of simulating icicle formation. Icicle formation corresponds to the thin-film, quasi-steady state Stefan problem, and neither phase fields nor DLA are directly applicable. I instead use level set methods, an alternate implicit front tracking strategy. I derive the necessary velocity equations for level set simulation, and also propose an efficient method of simulating ripple formation across the surface of the icicles

Linear and weakly nonlinear analyses on morphological instabilities

L'abstract è presente nell'allegato / the abstract is in the attachmen

Trailing Fire: Working in the Woods and the Future of Forests in a Chaotic Climate

Our national conversation about wildfire is shifting. As wildland fires become larger, more frequent, more severe, and more expensive—and as climate change and land-use patterns drive the trend toward more fire—we’re scrambling to find a different paradigm for engaging with fire. Scientists now call this age of increasingly extreme burning the Pyrocene, and we’re just beginning to grapple with its impacts on the way we work, play, and live on the land. As a longtime trail worker for the U.S. Forest Service, I’ve spent hundreds of days clearing trails in burned forests. In Trailing Fire, I draw on these experiences to show how we have yet to reckon with wildfire’s longer-term effects on outdoor recreation, and to explore what that means for how humans connect with wild spaces. As outdoor recreation surges across the country, putting public lands in the spotlight and prompting important conversations about equity, inclusion, and access in the outdoors, federal recreation budgets keep shrinking, forcing smaller crews to keep up with the impacts of exploding use. Meanwhile, more fire means trail-maintenance workloads are growing, as the effects of severe burns persist for years, if not decades. While approaches to preparing for and fighting wildfire are changing at both a policy and community level, federal land managers have no comprehensive strategy for addressing the impacts of fire on recreation and trails. And that’s a problem, because recreation provides a portal through which vast numbers of Americans connect with wild spaces. Extreme fire regimes, by limiting access to the outdoors, threaten opportunities for understanding fire’s historic and future role in our shared landscapes. I illustrate these complexities by sharing vivid stories from my years of restoring burned trails, at the same time tracing my evolving understanding of reciprocity between communities, landscapes, and the fires that shape them. Trailing Fire weaves personal narrative with ecological and political context, offering an intimate and original perspective on living and working in the Pyrocene

Thinking from materials in Andy Goldsworthy’s environmental artworks

By adopting posthuman ecology as its methodological framework, the author of this paper examines how British environmental artist Andy Goldsworthy’s conceptualization of nature can radically undermine the nature/culture dichotomy. To do this, the author will survey the first and the second waves of environmental art movement, also known as Representational and Performative Environmental Art, in order to situate Goldsworthy’s small-scale works within the latter. Then, by embracing Tim Ingold’s idea of “thinking through making” within materialist ecology, the author puts forward that Goldsworthy’s environmental art can resist the old-age hylomorphic model by using intuitiveness and improvisation as its strategy. In doing so, Goldsworthy eschews from turning nature into a representation that is to be manipulated by human subjectivity from afar, precisely by thinking from natural materials rather than about them, thus inviting us to conceive all human and nonhuman organisms as an intricate conglomerate of “leaky things” in an endless flux of ecological becoming.Modern and Contemporary Studie