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Shayesteh Hafezi

Publications and source records attributed to Shayesteh Hafezi.

2 recordsLinked to original sources

Closed-Loop Adaptive Sampling on a Generative Ocean Model

Adaptive sampling can substantially improve the value of sparse ocean observations by directing mobile robots toward measurements that are most informative for an evolving environment. Recent learned generative ocean models can produce high-resolution forecasts and ensembles at substantially lower computational cost than traditional numerical models, creating an opportunity to use rich predictive forecasts directly in closed-loop robotic sampling. However, these models do not natively provide the explicit uncertainty representations assumed by classical informative-planning methods, and their forecasts often evolve in learned latent spaces rather than directly in physical ocean variables. We develop a multi-robot closed-loop adaptive sampling framework that uses a single learned generative model for forecasting, uncertainty estimation, planning, and measurement assimilation. The model forecasts an ensemble in latent space, decodes it to physical ocean states, and uses ensemble statistics to construct A- or D-optimal sampling objectives. We select sampling locations subject to robot reachability under predicted currents. The collected measurements are assimilated back into the latent state using observation-conditioned diffusion sampling. Across 120 test scenarios A- and D-optimal sampling generally outperforms static, random, and systematic-coverage baselines while adding little planning overhead. Our experiments uncover several scenarios in which model uncertainty diverges from forecast error, motivating future work in uncertainty quantification.

cs.RO↗

Efficient Estimation of Temporal Exceeding Probability for Ship Responses in Broadband Wave Fields

In this paper, we develop an efficient method to evaluate the temporal exceeding probability of ship motion (percentage of time for the ship motion to be above a given high threshold) in an irregular wave field. Our method builds on our previous work of Gong et al. (Applied Ocean Research, 2022), which converts the calculation into a sampling problem in the space of wave group parameters, within which an acquisition-based sequential sampling method is developed to reduce the number of required samples. Two critical advancements are achieved in this paper relative to that work. (1) We develop a new wave group parameterization method, which allows the framework to be applied to general broadband wave fields. (2) We incorporate the variability regarding each parameterized wave group (e.g. varying wave form and initial condition of the ship encountering the group) into the final estimation of a single value of the temporal exceeding probability. Our complete framework is tested for a ship subject to a wave field with a JONSWAP spectrum, for different ship motion dynamical models, spectral bandwidths, and exceeding thresholds. The results show that for most cases our method provides a result with O(15%) error or below within 210 samples, with the ground truth obtained from a continuous simulation that is more than 2300 times more expensive than our method. We also demonstrate the benefits of sequential sampling (with an acquisition function updated due to (2)) compared to standard random or Latin hypercube (LH) samplings, in terms of the mean error of the results.

physics.flu-dyn↗