no code implementations • 27 Jun 2023 • Stephen Guth, Alireza Mojahed, Themistoklis P. Sapsis
Machine learning methods for the construction of data-driven reduced order model models are used in an increasing variety of engineering domains, especially as a supplement to expensive computational fluid dynamics for design problems.
1 code implementation • 10 Sep 2022 • JiaQi Zhang, Louis Cammarata, Chandler Squires, Themistoklis P. Sapsis, Caroline Uhler
Here, we develop a causal active learning strategy to identify interventions that are optimal, as measured by the discrepancy between the post-interventional mean of the distribution and a desired target mean.
no code implementations • 27 Aug 2022 • Ethan Pickering, Themistoklis P. Sapsis
This ensures that key information is never wasted in testing or validation.
no code implementations • 5 Apr 2022 • Ethan Pickering, Stephen Guth, George Em Karniadakis, Themistoklis P. Sapsis
This model-agnostic framework pairs a BED scheme that actively selects data for quantifying extreme events with an ensemble of DNOs that approximate infinite-dimensional nonlinear operators.
no code implementations • 9 Mar 2022 • Ethan Pickering, Themistoklis P. Sapsis
We propose two bounded comparison metrics that may be implemented to arbitrary dimensions in regression tasks.
no code implementations • 15 Feb 2021 • Alexis-Tzianni G. Charalampopoulos, Themistoklis P. Sapsis
Overall the adoption of the constraint results in an average improvement of 26% for one-dimensional closures and 29% for two-dimensional closures, being notably larger for flows that were not used for training.
Fluid Dynamics
1 code implementation • 18 May 2020 • Samuel H. Rudy, Themistoklis P. Sapsis
This work considers methods for imposing sparsity in Bayesian regression with applications in nonlinear system identification.
1 code implementation • 9 Oct 2019 • Pantelis R. Vlachas, Jaideep Pathak, Brian R. Hunt, Themistoklis P. Sapsis, Michelle Girvan, Edward Ott, Petros Koumoutsakos
We examine the efficiency of Recurrent Neural Networks in forecasting the spatiotemporal dynamics of high dimensional and reduced order complex systems using Reservoir Computing (RC) and Backpropagation through time (BPTT) for gated network architectures.
1 code implementation • 24 Jul 2019 • Antoine Blanchard, Themistoklis P. Sapsis
For a large class of dynamical systems, the optimally time-dependent (OTD) modes, a set of deformable orthonormal tangent vectors that track directions of instabilities along any trajectory, are known to depend "pointwise" on the state of the system on the attractor, and not on the history of the trajectory.
no code implementations • 17 Jul 2019 • Themistoklis P. Sapsis
For many important problems the quantity of interest is an unknown function of the parameters, which is a random vector with known statistics.
no code implementations • 19 Apr 2018 • Mustafa A. Mohamad, Themistoklis P. Sapsis
The 'next-best' design point is sequentially determined through an optimization procedure that selects the point in parameter space that maximally reduces uncertainty between the estimated bounds of the pdf prediction.
1 code implementation • 9 Mar 2018 • Zhong Yi Wan, Pantelis R. Vlachas, Petros Koumoutsakos, Themistoklis P. Sapsis
In this way, the data-driven model improves the imperfect model in regions where data is available, while for locations where data is sparse the imperfect model still provides a baseline for the prediction of the system dynamics.
Chaotic Dynamics Computational Physics
no code implementations • 21 Feb 2018 • Pantelis R. Vlachas, Wonmin Byeon, Zhong Y. Wan, Themistoklis P. Sapsis, Petros Koumoutsakos
We introduce a data-driven forecasting method for high-dimensional chaotic systems using long short-term memory (LSTM) recurrent neural networks.