Free-surface Waves

Water waves are ubiquitous on our oceans, seas and lakes. During hurricane storm conditions they can become large enough to sink ships at sea and destroy coastal defenses as they break on the shore with potentially catastrophic results. But also during more moderate conditions waves play a very important role in our environment, for instance in the shipping conditions at harbor channels, associated downtime in marine operations, dynamic loading of structures requiring design wave conditions. Furthermore, they transport material inside the water through the non-linear Stokes drift and streaming within the wave boundary layer at the bed. This has important consequences for the transport of pollutants like oil, but also harmful algae and biological connectivity. Once arrived at the shore the waves break within the surf zone, creating opportunities for popular activities like surfing.

At breaking large amounts of sediment are being stirred up that are subsequently transported by wave-generated currents. These include longshore currents shaping our sandy coastlines, hazardous rip currents catching involuntary swimmers and return flows carrying sediments to deeper water eroding our coasts. At the same time a significant part of the wave energy is transformed into infragravity waves with periods of order 1 minute that contribute significantly to the run-up and overtopping and this adversely affect our coastal safety.  These infragravity waves can also result in harbor resonance creating large forces on mooring lines. It is therefore imperative to understand how waves are being generated, propagated and dissipated within the coastal system. We specifically focus on the wave transition from deep water to the coast to be able to assess coastal safety in all the aspects mentioned before. These coastal regions require special attention as the interaction with the bathymetry, currents, stratification and also vegetation lead to complex non-linear interactions affecting the evolution of the wind and infragravity waves.

This knowledge is embedded in state of the art numerical models that we (co-)develop like SWAN, SWASH, FINLAB, H2Ocean and XBeach. These models are continuously improved with new scientific insights obtained from research involving laboratory and field experiments that are an integral part of our research approach including both in-situ (fixed sensors) and roving (e.g. GPS-drifters and drones) instruments.

© 2017 TU Delft

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