Numerical investigation of the fall rate of a sea-monitoring probe

The errors in eXpendable BathyThermograph (XBT) fall rate equations are demonstrated to be responsible for a time-varying warm bias in the global ocean temperature by many investigators. In this paper, a numerical model based on the Reynolds averaged Navier–Stokes (RANS) equations and the equation of motion for rigid body has been applied to investigate the fall rate of a sea-monitoring probe. The free surface and its interaction with the probe were simulated by the Volume of fluids (VOF) method, and the movement of the probe was tracked using Newmark's integration. The numerical model has been validated against experimental data of water entry of a sphere. Following the validation, the model was applied to simulate whole descending process of probe after it was released from surface, and time histories of displacement and velocity were obtained. Results indicated that drop height and mass reduction (due to wire payout) have a great influence on the fall rate and terminal velocity of the probe. Factors affecting the terminal velocity of the probe were also discussed.

► We examine the hydrodynamic performance of a sea probe using a numerical model.
► We study the time history of velocity and displacement of the probe with different drop heights.
► Mass reduction due to wire payout has an accumulated influence on fall rate.