Bungee jumping cord design using a simple model
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A simple energy model of a bungee jump is used to generate strain guidelines and practical design equations for the sizing of an all-rubber bungee cord. The cord is represented as a massless linear spring of elastic modulusE. A design strain between two and three (2<ε<3) is recommended to ensure a balance between lowg-forces in the cord (F/mg<3) and high factor of safety (f s >10). Cord design is essentially a two-step process. In the first step, the cord crossectional area is proportionally matched to the jumper's weight to ensure the specified design strain. In the second step, cord length is matched to the structure height so the jumper does not strike the ground. In a typical bungee jump using a body harness, the cord elongates 200% and exerts a maximum tensile force of three times the jumper's body weight. The ability of this model to predict strain accurately is enhanced by taking into account the viscoelastic nature of rubber.
Keywordsdynamics factor of safety g-force modelling natural rubber viscoelastic
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