Real-Time Sea-State Estimation From Measurement Of A Ship’s Motion in Waves

Speaker: Drs. Jason M. Dahl and Stephan T. Grilli, University of Rhode Island
Date: Sep 13, 2019; Time: 2:30pm Location: UTEB 175

Abstract: In standard seakeeping simulations of a ship in irregular seas, the rigid body motions of the ship are computed using a set of semi-analytic integro-differential equations, which model the response of the ship including non-linear and history dependent forces.    Using this type of model allows one to model the response of the ship in incident irregular waves, corresponding to a sea state defined by its significant wave height, H_s, peak spectral period, T_p, dominant wave direction, θ₀, and spectrum type, while allowing fairly quick simulation of the response using standard numerical integration methods.  In this work, we develop and apply such a model to compute ship motions for a large number of sea states. Then, we perform the inverse problem of determining the governing sea state parameters by training a Neural Network, based on the time histories of ship response in roll, pitch, and heave computed with the model. The estimator is then validated against physical model test experiments conducted using irregular waves generated in a towing tank to demonstrate that the numerical model is sufficient for training the Neural Network using simulated data.  The main rationale for this work is to develop a low-cost method for small vessels to estimate local sea state conditions in order to avoid operations in dangerous sea states, however the same techniques could be applied in general to transiting vessels to obtain local and continuous sea state measurements for general science purposes or other uses. 

Biographical Sketches: Jason M. Dahl is an Associate Professor in the Department of Ocean Engineering at the University of Rhode Island.  Dr. Dahl (PhD, Ocean Engineering, MIT; B.S., Naval Architecture and Marine Engineering, Webb Institute) is an expert in fluid-structure interactions and floating body dynamics, with particular expertise in the flow-induced vibration of underwater structures. Dr. Dahl has extensive experience as an experimentalist with towing tank operations, dynamic testing, and quantitative flow visualization.

Stephan T. Grilli is a Distinguished Professor and Chair, in the Department of Ocean Engineering at the University of Rhode Island.  Dr. Grilli (PhD, Ocean Engineering, M.S. Physical Oceanography, M.S. Civil Engineering, University of Liège) has a broad background in Computational Fluids Dynamics related to free surface and wave-structure interaction problems in coastal, naval and ocean engineering, and oceanography. Dr. Grilli has over 30 years of experience with developing higher-order boundary element models and viscous simulations for the solution of free surface potential flows for wave propagation and wave-structure interactions including the modeling of tsunami wave propagation, ship seakeeping in waves, wave breaking, and wave energy systems.