deformation strategy on a special cable-net structure of the active reflector system of FAST

A unique large-span cable-net structure, as key unit of the active reflector of FAST, is introduced. The cable-net structure contains huge cable mesh and thousands of down-tied cables driven by hydraulic actuators. The illumination area of cable mesh may change spherical shape to form paraboloid during FAST works, under the condition that hundreds of hydraulic actuators drive coordinately. Therefore deformation strategy is necessary to be discussed in details on how much each actuator should stretch out or draw back to keep shape of paraboloid. Its simulation based on finite element method is further given for demonstration. The regular strategy works well if the illumination area are limited within the spherical mesh. Otherwise, it may induce such structural dangers as slack cable, over-stressed cable or fatigue failure. A new strategy is then developed to crack such problem. It first follows the regular strategy, then checks and finds out all the potentially dangerous cables. The stresses of these dangerous cables are controlled in the safe range via adjusting the related down-tied cables. A comparative simulation result with the measurement on site verifies its effectiveness.