Comparison of trajectories of a lifeboat during drop as found from model tests and simulations with Dropsim


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large number of tests are, however, required to predict the behaviour for all the conditions the lifeboat may end up in. Dropsim is able to predict the behaviour of a freefall lifeboat during the drop, submerged, surfacing and sailing phases for a wide range of conditions.


The mathematical model underlying Dropsim is completely non-linear and considers instantaneous submergence. All forces and moments in six degrees of freedom are calculated instantaneously, based on a summation of impact forces, cross flow drag forces, generated lift, Coriolis forces, as well as buoyancy, propulsion and steering forces and resistance.


As Dropsim is a simplified tool, it is vital to determine that the software is adequate for performing thousands of lifeboat drops, yielding robust predictions with sufficient accuracy. In order to show the performance of the simulation tool, an extensive validation procedure was established, based on the available model test data and data from other simulation tools. From this comparison, the accuracy of the predictions was determined and the program was validated.


Water impact of bullet shape 10 report


Model tests As part of the lifeboat projects, a large amount of model tests were carried out in MARIN’s Seakeeping and Manoeuvring Basin and Depressurised Wave Basin. The tests were used to study the behaviour of lifeboats in different (limiting) conditions, to show compliance of newly built lifeboats with the DNV standard and for the validation of Dropsim. Performed model tests included: - Captive and free running manoeuvring and seakeeping tests


- Resistance and powering tests - Integrated drop and sailaway tests - Drop, water entry and exit tests with an elementary shaped lifeboat (bullet)


In particular the integrated drop and sailaway tests and the tests with the bullet-shaped model proved to be technically challenging and required dedicated test setups. During these tests, the model was completely free sailing and steered by an autopilot but completely autonomous by wireless control. An optical measurement system, which was installed flush in the hull of the model, was used to track the LED targets. Accelerometers inside the model and pressure gauges installed in the hull measured the accelerations and pressures, respectively.


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