Speaker 2 :  Yeunwoo Cho  (Korea Advanced Institute of Science and Technology)
    Date & Time : October 15th (Fri.), 2021 / 10:50-11:30PM (Tokyo (JST)) 
    Title : Hysteresis phenomena in gravity-capillary waves on deep water generated 
         by a moving two-dimensional/three-dimensional air-blowing/air-suction forcing
    Abstract : 
         Hysteresis phenomena in forced gravity-capillary waves on deep water where 
       the minimum phase speed c_min = 23cm/s are experimentally investigated. Four 
       kinds of forcings are considered: two-dimensional/three-dimensional 
       air-blowing/air-suction forcings. For a still-water initial condition, 
       as the forcing speed increases from zero towards a certain target speed (U), 
       there exists a certain critical speed (U_crit) at which the transition from 
       linear to nonlinear states occurs. When U < U_crit, steady linear localized 
       waves are observed (state I). When U_crit < U < c_min, steady nonlinear 
       localized waves, including steep gravity-capillary solitary waves, are 
       observed (state II). When U is nearly equal to c_min, periodic shedding 
       phenomena of nonlinear localized depressions are observed (state III). 
       When U > c_min, steady linear non-local waves are observed (state IV). 
       Next, with these state-II, III and IV waves as new initial conditions, 
       as the forcing speed is decreased towards a certain target speed (U_final), 
       a certain critical speed (U_crit_2) is identified at which the transition from 
       nonlinear to linear states occurs. When U_crit_2 < U_final < U_crit, relatively 
       steeper steady nonlinear localized waves, including steeper gravity-capillary 
       solitary waves, are observed. When U_final < U_crit_2 , linear state-I waves 
       are observed. These are hysteresis phenomena, which show jump transitions from 
       linear to nonlinear states and from nonlinear to linear states at two different
       critical speeds. For air-blowing cases, experimental results are compared with 
       simulation results based on a theoretical model equation. They agree with each 
       other very well except that the experimentally identified critical speed 
       (U_crit_2) is different from the theoretically predicted one.
       *This abstract is excerpted from Park & Cho (JFM, 2020, vol. 885, A20).