INCIPIENT MOTION OF BREAKWATER ARMOR UNITS

Abstract

This paper describes observations made of incipient motion on both stone and sphere armor layers. Velocity measurements were made during these experiments both inside and just outside the armor layer. It is shown that the vertical convective acceleration across the armor layer is proportional to the square of the vertical velocity. An incipient lifting motion criterion is derived based on Morison forcing for the dominant mode of motion: vertical lift under the steep breaking-wave face. The experimental observations and measurements are used to validate the incipient motion criterion for breakwater armor.