In this paper, we present a deep learning-based reduced-order model (DL-ROM) for the stability prediction of unsteady three-dimensional fluid–structure interaction systems. The proposed DL-ROM has the format of a nonlinear state-space model and employs a recurrent neural network with long short-term memory (LSTM) cells. We consider a canonical fluid–structure system of an elastically mounted sphere coupled with the incompressible fluid flow in a state-space format. Specifically, we develop a nonlinear data-driven coupling for predicting the unsteady forces and the vortex-induced vibration (VIV) lock-in of the freely vibrating sphere in a transverse direction. We design an input–output relationship as a temporal sequence of force and displacement datasets for a low-dimensional approximation of the fluid–structure system. Based on the prior knowledge of the VIV lock-in process, the input function contains a range of frequencies and amplitudes, which significantly affects the system realization ability and enables an efficient DL-ROM without the need for a massive training dataset for the low-dimensional modeling. Once trained, the network provides a nonlinear mapping of input–output dynamics that can predict the coupled fluid–structure dynamics for a longer horizon via the feedback process. By integrating the LSTM network with the eigensystem realization algorithm (ERA), we construct a data-driven state-space model for the reduced-order stability analysis. We investigate the underlying mechanism and stability characteristics of VIV of a freely vibrating sphere via an eigenvalue selection process. Using the reduced-order eigenvalue analysis, we characterize the vibrating sphere-wake lock-in phenomenon and demonstrate that the lock-in responds at preferred vibration frequencies. To understand the frequency lock-in mechanism, we study the eigenvalue trajectories for a range of the reduced oscillation frequencies and the mass ratios. Consistent with the full-order simulations, the frequency lock-in branches are accurately captured by the combined LSTM-ERA procedure. The proposed DL-ROM aligns with the development of physics-based digital twin of engineering systems involving moving boundaries and fluid–structure interactions.
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December 2022
Research Article|
December 28 2022
Deep learning for predicting frequency lock-in of a freely vibrating sphere
Amir Chizfahm
;
Amir Chizfahm
a)
(Formal analysis, Investigation, Methodology, Software, Validation, Visualization, Writing – original draft)
Department of Mechanical Engineering, University of British Columbia
, Vancouver, British Columbia V6T 1Z4, Canada
a)Author to whom correspondence should be addressed: amir.chizfahm@ubc.ca
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Rajeev Jaiman
Rajeev Jaiman
b)
(Conceptualization, Supervision)
Department of Mechanical Engineering, University of British Columbia
, Vancouver, British Columbia V6T 1Z4, Canada
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a)Author to whom correspondence should be addressed: amir.chizfahm@ubc.ca
b)
Electronic mail: rjaiman@mech.ubc.ca
Physics of Fluids 34, 127123 (2022)
Article history
Received:
August 18 2022
Accepted:
November 04 2022
Citation
Amir Chizfahm, Rajeev Jaiman; Deep learning for predicting frequency lock-in of a freely vibrating sphere. Physics of Fluids 1 December 2022; 34 (12): 127123. https://doi.org/10.1063/5.0121630
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