This paper studies Double-Helix Tensegrity (DHT) payload carriers for applications in payload protection of air deliveries. The DHT carriers are formed by a central payload, internal tensile strings that connect the central payload to the boundary of the carrier, surface tensile strings forming the boundary of the carrier, and compressive bars forming a double-helix pattern. Such an arrangement of strings and bars allows for load attenuation of the central payload when the carrier experiences impact against a ground during free fall (e.g., during an air delivery). Carriers with cylindrical and ellipsoidal shapes are considered. To allow for both impact energy absorption and dissipation, the strings of the DHT carriers are formed by a viscoelastic material (Nylon) and the bars are formed by an elastic material (Titanium). An explicit implementation of a dynamic model for tensegrity structures previously created by the authors is used to assess the impact load attenuation capabilities of the DHT carriers. An optimization study of the DHT carriers considering a 5 kg payload is provided. The design parameters include topological variables such as the number of double-helix periodic units along the axial and circumferential directions of the DHT carriers (i.e., the complexities of the carriers) and size variables such as the radii of the strings and bars. The optimization objective consists of minimizing the mass of the DHT carrier under constraints including that the payload does not exceed an acceleration of 10 times the gravity of Earth and the strings and bars do not undergo yield or buckling failure. The most favorable results obtained from the optimization process that minimized mass while satisfying all the constraints correspond to a cylindrical DHT carrier of 12.68 kg and an ellipsoidal DHT carrier of 9.47 kg.
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