Aiming at the inherent bottleneck of low efficiency and narrow frequency band of energy capture for traditional linear hinged module floating wave energy converters (WEC), a simple negative stiffness mechanism for hinged two-module floating WEC was proposed, which could be used as a passive method to improve the energy capture efficiency. Firstly, a simple and compact negative stiffness device was proposed, which was realized by placing simple stretch elastic elements between articulated floating bodies. Secondly a dynamic model of two-module nonlinear WEC in the time domain was established based on linear wave theory and Cummins equation. At the same time, the convolution integral term induced by wave radiation force was replaced by the state space model to improve the calculation speed. Finally, the numerical simulation of the two-module nonlinear WEC was carried out, and its energy capture characteristics under regular waves were analyzed. The numerical results show that the equivalent natural frequency of the system can be effectively reduced by introducing the nonlinear negative stiffness mechanism. When the negative stiffness mechanism was adjusted to appropriate parameters, the elastic force of the system can form an elliptical potential well in the phase plane of pitch motion, and its long axis is close to the mode direction of pitch motion of the floating module. Thus the pitch motion of the two modules tends to anti-phase and the nonlinear negative stiffness mechanism plays the role of phase control. Due to the above mechanism, the nonlinear negative stiffness mechanism with appropriate parameters can effectively improve the energy capture efficiency and broaden the energy absorption band.
| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |