Modal analysis of tethered UAV system under tension

In order to analyze the modal of the tethered UAV system, the motion of the UAV is treated as the boundary condition of the tether, and coupling dynamic model of the tethered UAV system is obtained. Considering the aerodynamic force of the tethered UAV system, the approximate expressions of the equilibrium tension and the equilibrium curvature of the tether are derived. On the basis of rebalancing analysis, the nonlinear equations of the tethered UAV system are linearized, and the normal natural frequencies and modes of the tethered cables are obtained. The influence of cable length and UAV load mass on the normal natural frequency and mode shape of mooring line is studied. It is found that with the increase of cable length and load mass, the forward second-order frequency of mooring method decreases continuously, and the normal second order frequency decreases more than the first order frequency. When the UAV’s load mass is fixed, the first normal mode shape of the mooring line changes little with the increase of the length of the mooring line. When the length of the cable is fixed, with the increase of the UAV load mass, the natural frequencies of the mooring method change little. When the wind excitation frequency of the system is close to the frequency of the system, the resonance of the system can be avoided by changing the length of the cable and load mass of the UAV to maintain the normal operation of the system. These studies provide a theoretical basis for the normal operation of the tethered UAV system.