An inherent problem of the phase-space discretisation is the spurious separation of energy into the discretised bins. This is called the “Garden Sprinkler Effect” and has been extensively studied in [48,49,20]. (In the Boltzmann transport community this is known as the ray effect.) To showcase this effect in the angular dimension, a large spatial domain (4000km×4000km) is simulated, with a monochromatic wave propagating over a long distance in deep water (d=10000m). For the spatial discretisation a structured triangle mesh is used, with an element edge length of 67km (Fig. 11(a)). The initial wave field, located 500km from the lower and left side has a Gaussian distribution in space, with a significant wave height of Hs=2.5m and a standard deviation of 150km (Fig. 11(b)). Its mean direction is 30° with an angular distribution of cos2⁡(θ) and a frequency of 0.1Hz. The simulation is time-dependent and runs for 5 days with a time-step of 600s.
