H2020Индивидуална стипендия2017–2019

TransTurb · Large Deviations and Rare Transitions in Turbulent flows

„Хоризонт 2020“ — Действия „Мария Склодовска-Кюри“

Период: 2017-12-01 → 2019-11-30
Финансиране от ЕС: 123 138 €
Участници: 1
Схема: MSCA-IF-EF-ST

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Накратко на български

Турбулентните потоци, като например струйните течения в атмосферата, се променят внезапно и непредвидимо. Разбирането на тези редки събития помага при прогнозирането на екстремни климатични явления и при проектирането на по-издръжливи вятърни турбини.

Този кратък обзор е генериран от изкуствен интелект

Кратко обяснение, генерирано от езиков модел по текста на CORDIS. Оригиналът е по-долу.

Резултати накратко

Large Deviations and Rare Transitions in Turbulent flows

Turbulent flows, like planetary atmospheres or flow around an airfoil, undergo strong fluctuations. Sometimes, those fluctuations may flip the system to an entirely different flow configuration. Such transitions seem to occur at random times, in an unpredictable manner. These extreme events are crucial for weather, climate, and many engineering applications. One may think for instance about the occurrence of heat waves or cold spells in the mid-latitudes, related to fluctuations of the strong turbulent jet going around the planet, the Jet Stream, which have a large impact on society and global economy. Similarly the most important factor for designing devices like wind turbines is not the average mechanical forces they will be subjected to, but rather the strongest ones. Finally, the existence of tipping points, leading to abrupt climate change, is a major question for climate projections in the 21st century. Because turbulent flows have in general several metastable attractors, it can be expected that such abrupt transitions exist in the ocean and atmosphere, due solely to their turbulent nature. There are two overarching difficulties in these problems: one is essentially technical, the other more fundamental. The first deadlock is that we are interested in rare events, for which, by definition, we have few observations. Direct numerical simulations of the system do not really alleviate the problem, because models for turbulent flows or the climate system are computationally expensive. Specific algorithms have been developed over the past few years to solve this sampling problem. The first main goal of the project was to show that they can be adapted to address relevant questions for rare events in turbulent flows. The second major aspect of the problem is to understand which properties of rare events are predictable, and which properties are not. For noise-induced transitions, for instance, transition times are unpredictable, but the dynamics of the transition is: the path to the rare event is always the same. The second main goal of the project was to test whether such ideas, inspired from statistical physics, hold for complex systems such as turbulent flows and climate models. To start with, we intended to establish on a solid basis if noise-induced transitions between bistable states existed at all in the atmosphere.

Текст от CORDIS, на английски · Данни: CORDIS, © Европейски съюз

Цел на проекта

Many out-of-equilibrium systems undergo transitions from one quasi-stationary state to a radically different one.Turbulent flows, for instance, exhibit sudden switches between attractors.It is crucial to understand this phenomenon, both for theoretical reasons and for potential applications to industrial or geophysical flows.Indeed, abrupt transitions or tipping points are a critical component of climate dynamics, which is a topic of major importance for society as a whole, in addition to being a scientific subject of uttermost current interest.Over the past decades, outstanding progress has been achieved in non-equilibrium statistical physics thanks to the theory of large deviations, which provides a natural generalization of the core concepts of equilibrium statistical mechanics: like entropy or free energy, large deviation rate functions encode all the relevant statistical information about an observable, such as its most probable values but also the probability of small and large fluctuations and the transitions between steady-states.However, large deviation computations have been up to now mostly restricted to relatively simple systems.This project will further develop cutting-edge analytical and numerical tools to compute large deviations in complex systems such as turbulent flows and the climate.The new ingredients we will consider are on the one hand, time-dependent attractors, and on the other hand, a complex field structure, since both are key features of geophysical flows.The goal of the project is at the same time to be able to predict some universal features of rare but high-impact transitions in turbulent attractors or, ultimately, the climate, and to promote novel techniques in rare event simulations which are applicable in an increasingly large spectrum of problems.Due to the combination of skills from the parties involved, the project will build a fruitful bridge between the statistical mechanics and the climate communities.

Оригинален текст от CORDIS (на английски).

Участници

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