PROCESSES LEADING TO INFRA-GRAVITY PERIOD OSCILLATIONS AND CURRENTS IN PORTS AND MARINAS
AbstractIn this paper, we take the broad definition of tsunami ('harbour wave') to describe oscillations in the infragravity (IG) periods (between 30 and 300s) in ports and marinas that often lead to interruption in harbour operations due to excessive vessel movements. The main processes that lead to these oscillations (also called seiches) are examined through the analysis of field measurements of water levels and currents from Western Australia. In a port or marina with lengths of the order of 500m and depths of the order of 10m, the natural oscillation periods are of the order of a few minutes. Changes in water levels in the coastal ocean adjacent to the port can setup oscillations within the port at its natural frequency. This results in water level fluctuations and strong horizontal currents within the port. If the incoming forcing is close to the natural frequency of oscillation resonance conditions may arise resulting in increased agitation inside the port. In addition if the harbour oscillation periods coincide with natural period of moored vessels, harbour operations can be severely interrupted due to strong vessel movements damaging to mooring lines and fenders.
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