Capturing the invisible


High-speed video allows us to capture processes which occur too fast to be visible to the naked eye. This technology is especially valuable for the model tests we carry out at MARIN.


High-speed video is valuable for studying waves


B Fedde Bloemhof &


Frans Hendrik Lafeber f.bloemhof@marin.nl


14 report


y filming at a high frame rate, we can study details of dynamic processes such as cavitation on a


propeller. For example, when recording at 2,500 frames per second (fps) the film can be slowed down to 25 fps while still giving a useful, smooth video with enough time-resolution.


Most model tests are carried out following Froude scaling. This means that time is also scaled in the test; for a model-scale of 1:25


the test is a factor 5 faster than at full-scale! However, this means that the dynamic processes happen faster and become more difficult to observe.


Propeller cavitation We already use high-speed observation systems for a large range of tests. One of the main applications is the observation of cavitation on a ship propeller. This is a highly dynamic process; cavitation grows and retreats every time a blade passes through the hull wake. Cavitation


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