Physical Modelling of Coastal Structures

While computational modelling is increasingly being used in place of physical modelling in many fields of engineering, physical modelling still finds an important role in coastal engineering. In the designing and testing of coastal engineering structures such as breakwaters, sea walls and revetments, the complex interactions between waves, sediments and the structural components need to be assessed and quantified. Owing to the high complexity, current numerical and analytical techniques cannot be applied to get a comprehensive solution within a practical time-frame. For this reason despite the relatively high cost involved, physical modelling is relied upon for an accurate assessment of how the real world structure will behave. Usually the final step in the design process of a coastal structure, it serves as a verification of the design calculations and is also a key step in the final project approval.

Physical modelling for coastal structures can be broadly classified into 2D or wave flume testing and 3D or wave basin testing. As the name suggests, 2D tests involve direct wave impact channeled along a long, narrow wave tank known as the flume. Flume tests are mainly used to assess the structural stability of the engineered design, Displacement of structural components, wave over topping and overall structural integrity are monitored over different types of wave attack. 3D tests involve an accurately scaled down construction of the seafloor, or bathymetry over which oceanic conditions of the locality are recreated. It is used to test the structure over waves from different directions and magnitudes. It helps to identify critical locations of the structure. 

The following is a video of a wave flume test carried out at the Lanka Hydraulic Institute (LHI) in Sri Lanka.

Although physical modelling is preferred over computational methods at present, this situation is likely to change in the near future. With increasingly powerful computers and efficient numerical methods being developed, the time taken to run complex simulations have come down significantly. A very promising computational method which could be used for these types of testing is, Smoothed Particle Hydrodynamics (SPH) first developed by Gingold and Monaghan (1977). A mesh free method which models the behavior of a set of particles under a given set of constitutive relations, SPH has already been used in oceanographic research. SPH can also be used to model wave structure interactions and other complex phenomena making it the ideal method for evaluating designs of coastal structures.