@article{ParezanovicCordierSpohnetal.2016,
  author    = {Parezanovic, Vladimir and Cordier, Laurent and Spohn, Andreas and Duriez, Thomas and Noack, Bernd R. and Bonnet, Jean-Paul and Segond, Marc and Abel, Markus and Brunton, Steven L.},
  title     = {Frequency selection by feedback control in a turbulent shear flow},
  series = {Journal of fluid mechanics},
  volume    = {797},
  journal   = {Journal of fluid mechanics},
  publisher = {Cambridge Univ. Press},
  address   = {New York},
  issn      = {0022-1120},
  doi       = {10.1017/jfm.2016.261},
  pages     = {247 -- 283},
  year      = {2016},
  abstract  = {Many previous studies have shown that the turbulent mixing layer under periodic forcing tends to adopt a lock-on state, where the major portion of the fluctuations in the flow are synchronized at the forcing frequency. The goal of this experimental study is to apply closed-loop control in order to provoke the lock-on state, using information from the flow itself. We aim to determine the range of frequencies for which the closed-loop control can establish the lock-on, and what mechanisms are contributing to the selection of a feedback frequency. In order to expand the solution space for optimal closed-loop control laws, we use the genetic programming control (CPC) framework. The best closed-loop control laws obtained by CPC are analysed along with the associated physical mechanisms in the mixing layer flow. The resulting closed-loop control significantly outperforms open-loop forcing in terms of robustness to changes in the free-stream velocities. In addition, the selection of feedback frequencies is not locked to the most amplified local mode, but rather a range of frequencies around it.},
  language  = {en}
}
@article{WinklerAbel2016,
  author    = {Winkler, Michael and Abel, Markus},
  title     = {Optimized setup for two-dimensional convection experiments in thin liquid films},
  series = {Review of scientific instruments : a monthly journal devoted to scientific instruments, apparatus, and techniques},
  volume    = {87},
  journal   = {Review of scientific instruments : a monthly journal devoted to scientific instruments, apparatus, and techniques},
  publisher = {American Institute of Physics},
  address   = {Melville},
  issn      = {0034-6748},
  doi       = {10.1063/1.4950871},
  pages     = {11},
  year      = {2016},
  abstract  = {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-Benard 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 Gamma = 0.16-10. The top and bottom frame elements can be set to specific temperature within T = 15 degrees C to 55 degrees 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. Published by AIP Publishing.},
  language  = {en}
}
@article{QuadeAbelShafietal.2016,
  author    = {Quade, Markus and Abel, Markus and Shafi, Kamran and Niven, Robert K. and Noack, Bernd R.},
  title     = {Prediction of dynamical systems by symbolic regression},
  series = {Physical review : E, Statistical, nonlinear and soft matter physics},
  volume    = {94},
  journal   = {Physical review : E, Statistical, nonlinear and soft matter physics},
  publisher = {American Society for Pharmacology and Experimental Therapeutics},
  address   = {Bethesda},
  issn      = {2470-0045},
  doi       = {10.1103/PhysRevE.94.012214},
  pages     = {15},
  year      = {2016},
  abstract  = {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.},
  language  = {en}
}
@article{WaldripNivenAbeletal.2016,
  author    = {Waldrip, S. H. and Niven, R. K. and Abel, Markus and Schlegel, M.},
  title     = {Maximum Entropy Analysis of Hydraulic Pipe Flow Networks},
  series = {Journal of hydraulic engineering},
  volume    = {142},
  journal   = {Journal of hydraulic engineering},
  publisher = {American Society of Civil Engineers},
  address   = {Reston},
  issn      = {0733-9429},
  doi       = {10.1061/(ASCE)HY.1943-7900.0001126},
  pages     = {332 -- 347},
  year      = {2016},
  language  = {en}
}
@article{FischerBaderAbel2016,
  author    = {Fischer, Jost Leonhardt and Bader, Rolf and Abel, Markus},
  title     = {Aeroacoustical coupling and synchronization of organ pipes},
  series = {The journal of the Acoustical Society of America},
  volume    = {140},
  journal   = {The journal of the Acoustical Society of America},
  publisher = {American Institute of Physics},
  address   = {Melville},
  issn      = {0001-4966},
  doi       = {10.1121/1.4964135},
  pages     = {2344 -- 2351},
  year      = {2016},
  abstract  = {A synchronization experiment on two mutual interacting organ pipes is compared with a theoretical model which takes into account the coupling mechanisms by the underlying first principles of fluid mechanics and aeroacoustics. The focus is on the Arnold-tongue, a mathematical object in the parameter space of detuning and coupling strength which quantitatively captures the interaction of the synchronized sound sources. From the experiment, a nonlinearly shaped Arnold-tongue is obtained, describing the coupling of the synchronized pipe-pipe system. This is in contrast to the linear shaped Arnold-tongue found in a preliminary experiment of the coupled system pipe-loudspeaker. To understand the experimental result, a coarse-grained model of two nonlinear coupled self-sustained oscillators is developed. The model, integrated numerically, is in very good agreement with the synchronization experiment for separation distances of the pipes in the far field and in the intermediate field. The methods introduced open the door for a deeper understanding of the fundamental processes of sound generation and the coupling mechanisms on mutual interacting acoustic oscillators. (C) 2016 Acoustical Society of America.},
  language  = {en}
}
@misc{ParezanovićCordierSpohnetal.2016,
  author    = {Parezanović, Vladimir and Cordier, Laurent and Spohn, Andreas and Duriez, Thomas and Noack, Bernd R. and Bonnet, Jean-Paul and Segond, Marc and Abel, Markus and Brunton, Steven L.},
  title     = {Frequency selection by feedback control in a turbulent shear flow},
  series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  journal   = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  number    = {572},
  issn      = {1866-8372},
  doi       = {10.25932/publishup-41369},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-413693},
  pages     = {37},
  year      = {2016},
  abstract  = {Many previous studies have shown that the turbulent mixing layer under periodic forcing tends to adopt a lock-on state, where the major portion of the fluctuations in the flow are synchronized at the forcing frequency. The goal of this experimental study is to apply closed-loop control in order to provoke the lock-on state, using information from the flow itself. We aim to determine the range of frequencies for which the closed-loop control can establish the lock-on, and what mechanisms are contributing to the selection of a feedback frequency. In order to expand the solution space for optimal closed-loop control laws, we use the genetic programming control (CPC) framework. The best closed-loop control laws obtained by CPC are analysed along with the associated physical mechanisms in the mixing layer flow. The resulting closed-loop control significantly outperforms open-loop forcing in terms of robustness to changes in the free-stream velocities. In addition, the selection of feedback frequencies is not locked to the most amplified local mode, but rather a range of frequencies around it.},
  language  = {en}
}