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17 results on '"Oswald, Philipp"'

1. Modeling synchronization in forced turbulent oscillator flows

Author

Herrmann, Benjamin, Oswald, Philipp, Semaan, Richard, and Brunton, Steven L.

Subjects
Physics - Fluid Dynamics
Abstract

Periodically forced, oscillatory fluid flows have been the focus of intense research for decades due to their richness as a nonlinear dynamical system and their relevance to applications in transportation, aeronautics, and energy conversion. Recently, it has been observed that turbulent bluff-body wakes exhibit a subharmonic resonant response when excited with specific spatial symmetries at twice the natural vortex shedding frequency, which is hypothesized to be caused by triadic interactions. The focus of this paper is to provide new physical insight into the dynamics of turbulent oscillator flows, based on improved mechanistic models informed by a comprehensive experimental study of the turbulent wake behind a D-shaped body under periodic forcing. We confirm for the first time the role of resonant triadic interactions in the forced flow by studying the dominant components in the power spectra across multiple excitation frequencies and amplitudes. We then develop an extended Stuart-Landau model for the forced global wake mode, incorporating parametric and non-harmonic forcing. This model captures the system dynamics and reveals the boundaries of multiple synchronization regions. Further, it is possible to identify model coefficients from sparse measurement data, making it applicable to a wide range of turbulent oscillator flows. We believe these generalized synchronization models will be valuable for prediction, control, and understanding of the underlying physics in this ubiquitous class of flows., Comment: 10 pages, 5 figures

Published
2020

3. Closed-Loop Drag Reduction Over a D-Shaped Body Via Coanda Actuation

Author

Shaqarin, Tamir, Oswald, Philipp, Semaan, Richard, Noack, Bernd R., Cavas-Martínez, Francisco, Series Editor, Chaari, Fakher, Series Editor, Gherardini, Francesco, Series Editor, Haddar, Mohamed, Series Editor, Ivanov, Vitalii, Series Editor, Kwon, Young W., Series Editor, Trojanowska, Justyna, Series Editor, Braza, Marianna, editor, Hoarau, Yannick, editor, Zhou, Yu, editor, Lucey, Anthony D., editor, Huang, Lixi, editor, and Stavroulakis, Georgios E., editor

Published
2021
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5. Machine learning drag reduction of car and truck models with multiple actuators and sensors

Author

Noack, Bernd R., Li, Yiqing, Yang, Zhigang, Cornejo Maceda, Guy Yoslan, Lusseyran, François, Oswald, Philipp, Semann, Richard, Harbin Institute of Technology (HIT), Tongji University, Laboratoire Interdisciplinaire des Sciences du Numérique (LISN), Institut National de Recherche en Informatique et en Automatique (Inria)-CentraleSupélec-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), and Technische Universität Braunschweig = Technical University of Braunschweig [Braunschweig]

Subjects
[SPI]Engineering Sciences [physics]
Abstract

International audience; The aerodynamic drag of cars and trucks plays an important role for energy efficiency affecting travel range and operating costs. This drag can be significantly reduced by actuators ranging from passive to closed-loop active devices. A key feature, opportunity and technical challenge is the inherent nonlinearity of the actuation response [1]. For instance, excitation at a given frequency will affect also other frequencies. This frequency cross-talk is hardly accessible in any linear control framework. The challenge is amplified when employing multiple actuators and sensors as well as multiple operating conditions. Recently, Artificial Intelligence (AI) / Machine Learning (ML) has a opened game-changing new avenue [2]: the automated model-free discovery and exploitation of unknown nonlinear actuation mechanisms directly in the plant. In this talk, we present recent advances of machine learning control [3, 5] for car and truck models with multiple actuators and sensors in experiment and in simulations. Examples include 22% drag reduction of a square-back Ahmed body with feedback control, 17% drag reduction of slanted Ahmed body with 10 actuation parameters [4], and the learning of drag / side force control of a truck model during transients. We show that even complex control laws can be optimized in surprisingly short learning times.

Published
2021

6. Variable ECG signs of ischemia during controlled occlusion of the left and right coronary artery in humans

Author

De Marehi, Stefano F., Meier, Pascal, Oswald, Philipp, and Seiler, Christian

Subjects
Collateral circulation -- Research, Coronary arteries -- Research, Ischemia -- Research, Ischemia -- Risk factors, Biological sciences
Abstract

Infarct size (IS) increases with vascular occlusion time, area at risk for infarction, lack of collateral supply, absence of preconditioning, and myocardial demand for [O.sub.2] supply. ECG S-T segment elevation is used as a measure of severity of ischemia and a surrogate for IS. This study in 50 patients with coronary artery disease undergoing a first 120-s balloon occlusion of a stenosis sought to determine whether S-T segment elevation, corrected for the above-mentioned variables, in the left coronary artery (LCA group, n = 36) is different from that in the right coronary artery (RCA group, n = 14) territory. After consideration of all known determinants of IS, particularly mass at risk and collateral supply, the LCA territory is more sensitive than the RCA region to a 2-min period of myocardial ischemia. coronary disease; collateral circulation

Published
2006

8. Closed-loop drag reduction over a D-shaped body via Coanda actuation

Author

Shaqarin, Tamir, Oswald, Philipp, Semaan, Richard, Noack, Bernd, Tafila Technical University, Technische Universität Braunschweig = Technical University of Braunschweig [Braunschweig], Laboratoire d'Informatique pour la Mécanique et les Sciences de l'Ingénieur (LIMSI), Université Paris Saclay (COmUE)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université - UFR d'Ingénierie (UFR 919), Sorbonne Université (SU)-Sorbonne Université (SU)-Université Paris-Saclay-Université Paris-Sud - Paris 11 (UP11), and Noack, Bernd

Subjects
Physics::Fluid Dynamics, Flow control, Closed-loop control, Drag reduction, D-shaped body, [SPI.MECA.MEFL] Engineering Sciences [physics]/Mechanics [physics.med-ph]/Fluids mechanics [physics.class-ph], [SPI.MECA.MEFL]Engineering Sciences [physics]/Mechanics [physics.med-ph]/Fluids mechanics [physics.class-ph]
Abstract

International audience; Up to 40% drag reduction was achieved for a D-shaped cylinder in an experiment with robust model-based closed-loop control. The flow is actuated with on-off jet slots blowing in the stream-wise direction over the top and bottom edge. These jets are deflected inward with Coanda surfaces, thus realizing drag reduction by aerodynamic boat tailing. The flow state is monitored with pressure sensors at the trailing surface. The pressure fluctuation level is found to be closely related to drag. Starting point for control design is an optimized open-loop control, with a Strouhal number of 0.33 and duty cycle of 50%. Successful closed-loop drag reduction was achieved, in terms of improving output stability and enhancing performance in term of settling time.

Published
2019

11. Open- and closed-loop control investigations of unsteady Coanda actuation on a high-lift configuration

Author

El Sayed M., Yosef, primary, Oswald, Philipp, additional, Sattler, Stephan, additional, Kumar, Pradeep, additional, Radespiel, Rolf, additional, Behr, Christian, additional, Sinapius, Michael, additional, Petersen, Jan, additional, Wierach, Peter, additional, Quade, Markus, additional, Abel, Markus, additional, Noack, Bernd R., additional, and Semaan, Richard, additional

Published
2018
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12. Reciprocal relationship between left ventricular filling pressure and the recruitable human coronary collateral circulation

Author

de Marchi, Stefano F., Oswald, Philipp, Windecker, Stephan, Meier, Bernhard, Seiler, Christian, de Marchi, Stefano F., Oswald, Philipp, Windecker, Stephan, Meier, Bernhard, and Seiler, Christian

Abstract

Aims The aim of our study in patients with coronary artery disease (CAD) and present, or absent, myocardial ischaemia during coronary occlusion was to test whether (i) left ventricular (LV) filling pressure is influenced by the collateral circulation and, on the other hand, that (ii) its resistance to flow is directly associated with LV filling pressure. Methods and results In 50 patients with CAD, the following parameters were obtained before and during a 60 s balloon occlusion: LV, aortic (Pao) and coronary pressure (Poccl), flow velocity (Voccl), central venous pressure (CVP), and coronary flow velocity after coronary angioplasty (VØ-occl). The following variables were determined and analysed at 10 s intervals during occlusion, and at 60 s of occlusion: LV end-diastolic pressure (LVEDP), velocity-derived (CFIv) and pressure-derived collateral flow index (CFIp), coronary collateral (Rcoll), and peripheral resistance index to flow (Rperiph). Patients with ECG signs of ischaemia during coronary occlusion (insufficient collaterals, n=33) had higher values of LVEDP over the entire course of occlusion than those without ECG signs of ischaemia during occlusion (sufficient collaterals, n=17). Despite no ischaemia in the latter, there was an increase in LVEDP from 20 to 60 s of occlusion. In patients with insufficient collaterals, CFIv decreased and CFIp increased during occlusion. Beyond an occlusive LVEDP>27 mmHg, Rcoll and Rperiph increased as a function of LVEDP. Conclusion Recruitable collaterals are reciprocally tied to LV filling pressure during occlusion. If poorly developed, they affect it via myocardial ischaemia; if well grown, LV filling pressure still increases gradually during occlusion despite the absence of ischaemia indicating transmission of collateral perfusion pressure to the LV. With low, but not high, collateral flow, resistance to collateral as well as coronary peripheral flow is related to LV filling pressure in the high range

Published
2017

17. Reciprocal relationship between left ventricular filling pressure and the recruitable human coronary collateral circulation

Author

de Marchi, Stefano F., Oswald, Philipp, Windecker, Stephan, Meier, Bernhard, Seiler, Christian, de Marchi, Stefano F., Oswald, Philipp, Windecker, Stephan, Meier, Bernhard, and Seiler, Christian

Abstract

Aims The aim of our study in patients with coronary artery disease (CAD) and present, or absent, myocardial ischaemia during coronary occlusion was to test whether (i) left ventricular (LV) filling pressure is influenced by the collateral circulation and, on the other hand, that (ii) its resistance to flow is directly associated with LV filling pressure. Methods and results In 50 patients with CAD, the following parameters were obtained before and during a 60 s balloon occlusion: LV, aortic (Pao) and coronary pressure (Poccl), flow velocity (Voccl), central venous pressure (CVP), and coronary flow velocity after coronary angioplasty (VØ-occl). The following variables were determined and analysed at 10 s intervals during occlusion, and at 60 s of occlusion: LV end-diastolic pressure (LVEDP), velocity-derived (CFIv) and pressure-derived collateral flow index (CFIp), coronary collateral (Rcoll), and peripheral resistance index to flow (Rperiph). Patients with ECG signs of ischaemia during coronary occlusion (insufficient collaterals, n=33) had higher values of LVEDP over the entire course of occlusion than those without ECG signs of ischaemia during occlusion (sufficient collaterals, n=17). Despite no ischaemia in the latter, there was an increase in LVEDP from 20 to 60 s of occlusion. In patients with insufficient collaterals, CFIv decreased and CFIp increased during occlusion. Beyond an occlusive LVEDP>27 mmHg, Rcoll and Rperiph increased as a function of LVEDP. Conclusion Recruitable collaterals are reciprocally tied to LV filling pressure during occlusion. If poorly developed, they affect it via myocardial ischaemia; if well grown, LV filling pressure still increases gradually during occlusion despite the absence of ischaemia indicating transmission of collateral perfusion pressure to the LV. With low, but not high, collateral flow, resistance to collateral as well as coronary peripheral flow is related to LV filling pressure in the high range

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