Validation of Measurement Techniques Used for Slamming

Model test campaigns conducted recent years indicate large wave impact loads on vertical surfaces above the waterline for various types of moored floating structures. The basis for the estimate of characteristic loads is typically slamming pressure measured on a grid of slamming panels. In order to validate the measurements of slamming pressure, drop tests for a slamming section used in slamming tests (see [1] and [2]) have been conducted. The section was dropped in a small water basin at different configurations to resemble impacts from waves with varying front steepness and velocity of wave front. In Lian et al [3], most of the results from the drop tests were presented and compared to theoretical solutions. It was concluded that the peak slamming coefficient is close to the expected theoretical value, but for small impact angles the load measured during the drop becomes significantly lower than theoretical observations and previous tests results, e.g. by Campbell and Weynberg [4]. Possible sources of errors in the tests may be retardation/change of velocity during impact or effect of 3D flow in drop. In the work presented in this paper these findings have been investigated further. An alternative drop test using a cylinder with smaller diameter, and neglectable effect from 3D flow, has been carried out. Numerical simulations of the drop tests, where effect of retardation is accounted for, have been conducted. In November 2019, the drop test with the slamming section was repeated and the mass of the section was varied to study the effect of retardation. In the present paper results from drop tests and numerical calculations are compared and findings are reported.