Ambrosys GmbH

Potsdam, Germany

Ambrosys GmbH

Potsdam, Germany

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Gautier N.,CNRS Physics Laboratory | Aider J.-L.,CNRS Physics Laboratory | Duriez T.,CNRS Pprime Institute | Duriez T.,University of Buenos Aires | And 3 more authors.
Journal of Fluid Mechanics | Year: 2015

We present the first closed-loop separation control experiment using a novel, model-free strategy based on genetic programming, which we call 'machine learning control'. The goal is to reduce the recirculation zone of backward-facing step flow at Reh = 1350 manipulated by a slotted jet and optically sensed by online particle image velocimetry. The feedback control law is optimized with respect to a cost functional based on the recirculation area and a penalization of the actuation. This optimization is performed employing genetic programming. After 12 generations comprised of 500 individuals, the algorithm converges to a feedback law which reduces the recirculation zone by 80 %. This machine learning control is benchmarked against the best periodic forcing which excites Kelvin-Helmholtz vortices. The machine learning control yields a new actuation mechanism resonating with the low-frequency flapping mode instability. This feedback control performs similarly to periodic forcing at the design condition but outperforms periodic forcing when the Reynolds number is varied by a factor two. The current study indicates that machine learning control can effectively explore and optimize new feedback actuation mechanisms in numerous experimental applications. © 2015 Cambridge University Press.


Parezanovic V.,CNRS Pprime Institute | Parezanovic V.,Montpellier University | Parezanovic V.,University of Buenos Aires | Laurentie J.-C.,CNRS Pprime Institute | And 12 more authors.
Flow, Turbulence and Combustion | Year: 2015

Open- and closed-loop control of a turbulent mixing layer is experimentally performed in a dedicated large scale, low speed wind-tunnel facility. The flow is manipulated by an array of fluidic micro-valve actuators integrated into the trailing edge of a splitter plate. Sensing is performed using a rake of hot-wire probes downstream of the splitter plate in the mixing layer. The control goal is the manipulation of the local fluctuating energy level. The mixing layer's response to the control is tested with open-loop forcing with a wide range of actuation frequencies. Results are discussed for different closed-loop control approaches, such as: adaptive extremum-seeking and in-time POD mode feedback control. In addition, we propose Machine Learning Control (MLC) as a model-free closed-loop control method. MLC arrives reproducibly at the near-optimal in-time control. © 2014 Springer Science+Business Media Dordrecht.


Stefanakis N.,University of Potsdam | Abel M.,Ambrosys GmbH | Bergner A.,Native Instruments GmbH
Computer Music Journal | Year: 2015

Ordinary differential equations (ODEs) have been studied for centuries as a means to model complex dynamical processes from the real world. Nevertheless, their application to sound synthesis has not yet been fully exploited. In this article we present a systematic approach to sound synthesis based on first-order complex and real ODEs. Using simple time-dependent and nonlinear terms, we illustrate the mapping between ODE coefficients and physically meaningful control parameters such as pitch, pitch bend, decay rate, and attack time. We reveal the connection between nonlinear coupling terms and frequency modulation, and we discuss the implications of this scheme in connection with nonlinear synthesis. The ability to excite a first-order complex ODE with an external input signal is also examined; stochastic or impulsive signals that are physically or synthetically produced can be presented as input to the system, offering additional synthesis possibilities, such as those found in excitation/filter synthesis and filter-based modal synthesis. © 2015 Massachusetts Institute of Technology.


Ahnert K.,University of Potsdam | Ahnert K.,Ambrosys GmbH | Abel M.,University of Potsdam | Abel M.,Ambrosys GmbH | And 3 more authors.
Journal of Materials Chemistry | Year: 2011

Wave energy harvesting could be a substantial renewable energy source without impact on the global climate and ecology, yet practical attempts have struggled with the problems of wear and catastrophic failure. An innovative technology for ocean wave energy harvesting was recently proposed, based on the use of soft capacitors. This study presents a realistic theoretical and numerical model for the quantitative characterization of this harvesting method. Parameter regions with optimal behavior are found, and novel material descriptors are determined, which dramatically simplify analysis. The characteristics of currently available materials are evaluated, and found to merit a very conservative estimate of 10 years for raw material cost recovery. This journal is © The Royal Society of Chemistry.


Quade M.,University of Potsdam | Quade M.,Ambrosys GmbH | Abel M.,University of Potsdam | Shafi K.,University of New South Wales | And 3 more authors.
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2016

We study the modeling and prediction of dynamical systems based on conventional models derived from measurements. Such algorithms are highly desirable in situations where the underlying dynamics are hard to model from physical principles or simplified models need to be found. We focus on symbolic regression methods as a part of machine learning. These algorithms are capable of learning an analytically tractable model from data, a highly valuable property. Symbolic regression methods can be considered as generalized regression methods. We investigate two particular algorithms, the so-called fast function extraction which is a generalized linear regression algorithm, and genetic programming which is a very general method. Both are able to combine functions in a certain way such that a good model for the prediction of the temporal evolution of a dynamical system can be identified. We illustrate the algorithms by finding a prediction for the evolution of a harmonic oscillator based on measurements, by detecting an arriving front in an excitable system, and as a real-world application, the prediction of solar power production based on energy production observations at a given site together with the weather forecast. © 2016 American Physical Society.


Winkler M.,University of Potsdam | Abel M.,University of Potsdam | Abel M.,Ambrosys GmbH
Review of Scientific Instruments | Year: 2016

We present a novel experimental setup to investigate two-dimensional thermal convection in a freestanding thin liquid film. Such films can be produced in a controlled way on the scale of 5-1000 nm. Our primary goal is to investigate convection patterns and the statistics of reversals in Rayleigh-Bénard convection with varying aspect ratio. Additionally, questions regarding the physics of liquid films under controlled conditions can be investigated, like surface forces, or stability under varying thermodynamical parameters. The film is suspended in a frame which can be adjusted in height and width to span an aspect ratio range of Γ = 0.16-10. The top and bottom frame elements can be set to specific temperature within T = 15 °C to 55 °C. A thickness to area ratio of approximately 108 enables only two-dimensional fluid motion in the time scales relevant for turbulent motion. The chemical composition of the film is well-defined and optimized for film stability and reproducibility and in combination with carefully controlled ambient parameters allows the comparison to existing experimental and numerical data. © 2016 Author(s).


Winkler M.,University of Potsdam | Abel M.,University of Potsdam | Abel M.,Ambrosys GmbH
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2015

We study aqueous, freestanding, thin films stabilized by a surfactant with respect to mixing and dynamical systems properties. With this special setup, a two-dimensional fluid can be realized experimentally. The physics of the system involves a complex interplay of thermal convection and interface and gravitational forces. Methodologically, we characterize the system using two classical dynamical systems properties: Lyapunov exponents and entropies. Our experimental setup produces convection with two stable eddies by applying a temperature gradient in one spot that yields weakly turbulent mixing. From dynamical systems theory, one expects a relation of entropies, Lyapunov exponents, a prediction with little experimental support. We can confirm the corresponding statements experimentally, on different scales using different methods. On the small scale the motion and deformation of fluid filaments of equal size (color imaging velocimetry) are used to compute Lyapunov exponents. On the large scale, entropy is computed by tracking the left-right motion of the center fluid jet at the separatrix between the two convection rolls. We thus combine here dynamical systems methods with a concrete application of mixing in a nanoscale freestanding thin film. © 2015 American Physical Society.


Ser-Giacomi E.,University of the Balearic Islands | Vasile R.,Ambrosys GmbH | Recuerda I.,University of the Balearic Islands | Hernandez-Garcia E.,University of the Balearic Islands | Lopez C.,University of the Balearic Islands
Chaos | Year: 2015

Eastern Europe and Western Russia experienced a strong heat wave with devastating consequences in the summer of 2010. This was due to an atmospheric blocking episode that lasted during several weeks. Despite these types of events have been well-investigated over the years, a complete understanding and prediction is still missing. In this work, we present a characterization of this flow pattern based on the study of fluid transport as a Lagrangian flow network, so that the methodology of complex networks can be applied. In particular, the most probable paths (MPPs) linking nodes of this atmospheric network reveal the dominant pathways traced by atmospheric fluid particles.


Ser-Giacomi E.,Institute Fisica Interdisciplinar y Sistemas Complejos CSIC UIB | Vasile R.,Institute Fisica Interdisciplinar y Sistemas Complejos CSIC UIB | Vasile R.,Ambrosys GmbH | Hernandez-Garcia E.,Institute Fisica Interdisciplinar y Sistemas Complejos CSIC UIB | Lopez C.,Institute Fisica Interdisciplinar y Sistemas Complejos CSIC UIB
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2015

We consider paths in weighted and directed temporal networks, introducing tools to compute sets of paths of high probability. We quantify the relative importance of the most probable path between two nodes with respect to the whole set of paths and to a subset of highly probable paths that incorporate most of the connection probability. These concepts are used to provide alternative definitions of betweenness centrality. We apply our formalism to a transport network describing surface flow in the Mediterranean sea. Despite the full transport dynamics is described by a very large number of paths we find that, for realistic time scales, only a very small subset of high probability paths (or even a single most probable one) is enough to characterize global connectivity properties of the network. © 2015 American Physical Society.


PubMed | Ambrosys GmbH and University of the Balearic Islands
Type: Journal Article | Journal: Chaos (Woodbury, N.Y.) | Year: 2015

A Lagrangian flow network is constructed for the atmospheric blocking of Eastern Europe and Western Russia in summer 2010. We compute the most probable paths followed by fluid particles, which reveal the Omega-block skeleton of the event. A hierarchy of sets of highly probable paths is introduced to describe transport pathways when the most probable path alone is not representative enough. These sets of paths have the shape of narrow coherent tubes flowing close to the most probable one. Thus, even when the most probable path is not very significant in terms of its probability, it still identifies the geometry of the transport pathways.

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