Trajectory Prediction

Objects moving under the influence of external force — whether gravitational, fluid-induced, propulsive, or other — are easily handled using AFT’s overset grid methods. The moving body (or bodies) is resolved with a set of near-field grid blocks that move and/or deform with the body. A second set of blocks resolves the background far-field flow, and remains Earth-fixed at all times. Fluid-induced forces are obtained by integrating the time-accurate RANS solution over each body after every time step. Other (non-fluid) forces are added, and the result used to solve the six degree-of-freedom equations of motion. Near-field body-fitted blocks are updated in time, and the process repeated as long as necessary.

The method can be used for predicting trajectories of dropped and/or powered bodies, to predict forces for populating maneuvering and control models, or for calculating the loads and accelerations experienced by falling bodies. AFT personnel have used this approach to predict the motion of broken parts inside nuclear reactors, to investigate the stability of towed arrays, and to predict loads and trajectories of objects dropped in the deep ocean. The movie at right depicts one of the deep ocean trajectory simulations, and colored bubbles depict flow streak lines. The panel at left shows a far-field Earth-fixed view whereas the panel at right shows a close up moving with the body. Horizontal and vertical hash lines in the close-up are Earth-fixed, and give an idea of relative body motion.