Fast Water Waves in Stationary Surface Disk Arrays

Traditionally, the phase and group velocities of water waves can be increased by increasing water depth but possess upper bounds, which are related to the gravitational acceleration and difficult to exceed. Here, we theoretically propose and experimentally demonstrate that when water is covered with a periodic array of stationary rigid disks, both the gravitational acceleration and reduced water depth can be effectively increased in the lowest frequency band. As a result, fast water waves can occur in the system, with both the phase and group velocities exceeding those in water without disks. Unusual effects, such as total reflection at oblique incidence and unidirectional transmission of water waves, are further realized.