TY - JOUR A1 - Parezanovic, Vladimir A1 - Cordier, Laurent A1 - Spohn, Andreas A1 - Duriez, Thomas A1 - Noack, Bernd R. A1 - Bonnet, Jean-Paul A1 - Segond, Marc A1 - Abel, Markus A1 - Brunton, Steven L. T1 - Frequency selection by feedback control in a turbulent shear flow JF - Journal of fluid mechanics N2 - 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. KW - free shear layers KW - instability control KW - turbulence control Y1 - 2016 U6 - https://doi.org/10.1017/jfm.2016.261 SN - 0022-1120 SN - 1469-7645 VL - 797 SP - 247 EP - 283 PB - Cambridge Univ. Press CY - New York ER - TY - JOUR A1 - Parezanovic, Vladimir A1 - Laurentie, Jean-Charles A1 - Fourment, Carine A1 - Delville, Joel A1 - Bonnet, Jean-Paul A1 - Spohn, Andreas A1 - Duriez, Thomas A1 - Cordier, Laurent A1 - Noack, Bernd R. A1 - Abel, Markus A1 - Segond, Marc A1 - Shaqarin, Tamir A1 - Brunton, Steven L. T1 - Mixing layer manipulation experiment from open-loop forcing to closed-loop machine learning control JF - Flow, turbulence and combustion : an international journal published in association with ERCOFTAC KW - Shear flow KW - Turbulence KW - Active flow control KW - Extremum seeking KW - POD KW - Machine learning KW - Genetic programming Y1 - 2015 U6 - https://doi.org/10.1007/s10494-014-9581-1 SN - 1386-6184 SN - 1573-1987 VL - 94 IS - 1 SP - 155 EP - 173 PB - Springer CY - Dordrecht ER - TY - GEN A1 - Parezanović, Vladimir A1 - Cordier, Laurent A1 - Spohn, Andreas A1 - Duriez, Thomas A1 - Noack, Bernd R. A1 - Bonnet, Jean-Paul A1 - Segond, Marc A1 - Abel, Markus A1 - Brunton, Steven L. T1 - Frequency selection by feedback control in a turbulent shear flow T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - 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. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 572 KW - free shear layers KW - instability control KW - turbulence control Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-413693 SN - 1866-8372 IS - 572 ER - TY - JOUR A1 - Bouakline, Foudhil A1 - Althorpe, Stuart C. A1 - Larregaray, Pascal A1 - Bonnet, Laurent T1 - Strong geometric-phase effects in the hydrogen-exchange reaction at high collision energies : II. quasiclassical trajectory analysis N2 - Recent calculations on the hydrogen-exchange reaction [Bouakline et al., J. Chem. Phys. 128, 124322 (2008)], have found strong geometric phase (GP) effects in the state-to-state differential cross-sections (DCS), at energies above the energetic minimum of the conical intersection (CI) seam, which cancel out in the integral cross-sections (ICS). In this article, we explain the origin of this cancellation and make other predictions about the nature of the reaction mechanisms at these high energies by carrying out quasiclassical trajectory (QCT) calculations. Detailed comparisons are made with the quantum results by splitting the quantum and the QCT cross-sections into contributions from reaction paths that wind in different senses around the CI and that scatter the products in the nearside and farside directions. Reaction paths that traverse one transition state (1-TS) scatter their products in just the nearside direction, whereas paths that traverse two transition states (2-TS) scatter in both the nearside and farside directions. However, the nearside 2-TS products scatter into a different region of angular phase-space than the 1-TS products, which explains why the GP effects cancel out in the ICS. Analysis of the QCT results also suggests that two separate reaction mechanisms may be responsible for the 2-TS scattering at high energies. Y1 - 2010 UR - http://www.informaworld.com/openurl?genre=journal&issn=0026-8976 U6 - https://doi.org/10.1080/00268971003610218 SN - 0026-8976 ER -