Ring-Net Subdivision Equivalent Model of Flexible Protection System

The ring-net is an important interception component in passive flexible protection systems, and it has obvious nonlinear dynamic characteristics. Constructing a mechanical model of the ring network is the key problem in the theoretical study of the flexible protection structure. To propose an equivalent mechanical model of the ring net, an full-scale impact test was conducted with an actual structure, and the regional deformation characteristics of the ring-net and typical deformation state of the ring-net were obtained. Then, the load-displacement relationships of the net ring under typical deformation states were obtained using a tension test and numerical simulation calculation; on these bases, a subdivision equivalent calculation model was established.. Finally, the accuracy of the model was verified by comparison with the breaking and dynamic impact tests. Results show that the deformation of the ring net has obvious regional characteristics, and the ring-net (basic unit of the net) displays three typical deformation states (each with two-stage characteristics). Based on this, an ‘X’ type 4-truss element, connected to the centre of the circle with the initial length of the ring radius, is used to simulate a single ring. The load-displacement relationship of the ring in a typical deformation state is treated as equivalent to the stress-strain relationship of the truss element, and the corresponding nodes are connected to form the element model of the entire ring-net. A comparison with the static and dynamic tests indicates that the model calculation error is less than 10%.