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The hyperloop aims to become a revolutionary mode of transport, with a maximum envisioned speed of 1200 km/h. However, these speeds, which are much greater than a typical high-speed rail, can induce resonance when the pod’s forcing frequency matches one of the tube’s natural frequencies. This potential resonance can accelerate wear and tear on the track and poses extra challenges for the suspension system, since the air-gap is influenced by vibrations. This increases maintenance costs and potentially reduces the lifespan of the entire system. Prior hyperloop research on tube resonance assumed that a hyperloop tube’s natural frequency was equal to that of a railroad or highway bridge (roughly 5Hz). The forcing frequencies of the pod are calculated as a function of speed, span length, and mode number with the first forcing frequency being between 5-10 Hz. Compared to the 5Hz natural frequency commonly utilized in prior research, the hyperloop tube would achieve resonance before reaching maximum speeds. However, in this study, data acquired from a hammer test conducted on a physical steel hyperloop tube is utilized to determine a more realistic tube natural frequency of roughly 29Hz. This study quantifies when resonance occurs and how a hyperloop tube’s natural frequency fluctuates with varying parameters such as tube material, length, diameter, thickness, and number of spans. The system is modeled as a mass (pod) moving over a Euler-Bernoulli continuous beam (two-degrees-of-freedom per node). To solve the system’s equation of motion and determine the dynamic amplification for each case, a Finite Element Analysis (FEA) is used. From the results, the span length, diameter, and material were found to have the greatest influence on the tube’s natural frequency. Due to concrete having a lower stiffness-to-density ratio, its natural frequency is closer to the pod’s first forcing frequency than the steel tube. However, by choosing a suitable diameter/length ratio of at least 0.09 for steel or 0.11 for concrete, both materials can be suitable for pods traveling at 1200 km/hr in a full-scale hyperloop system.
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