Has it already been 12 years since Elon Musk proposed the concept of high-speed train travel, namely Hyperloop, that would whisk passengers from Los Angeles to San Francisco in ~30 minutes at near-supersonic speed? Musk chose to rolled the concept out as open source. Companies like Virgin Hyperloop and HyperloopTT started working on prototypes but gave up, citing engineering challenges. For one thing, the prototypes were encountering excessive vibration.
China, on the other hand, has made ultra-high-speed a national research priority, aiming to redefine high-speed land travel, and has thrown all its might towards solving the engineering problems. China’s Aerospace Science and Industry Corporation (CASIC) engineers have swapped the original concept’s “cushion of air” for magnetic levitation, or mag-lev, which will also be of use for low-cost space launches. Projects like the Shanxi test line are showing progress towards a solution, according to China’s news services.
Magnetic levitation, or mag-lev, was considered for the original Hyperloop but ruled out to keep the cost low.
A South China Morning Post (SCMP) article reports that the vibration has been reduced to tolerable levels, citing a national peer-reviewed rail journal. ASIC engineers reasoned the probable cause and used simulation and supercomputers to find the resonant modes of vibration. Their conclusion: without the stability provided by the physical contact between wheels and track, the train cars were unrestrained and therefore free to vibrate, the vibration most noticeable at lower frequencies with occurring in the plane perpendicular to the forward motion. Their solution: 1) stabilize the train cars with “sky‑hook” damping, which simulates a virtual “sky anchor” and 2)smoothing out low-frequency motion and PID control optimized via a genetic-algorithm, NSGA-II) that adapts to micro-movement of the track relative to the train car in near real time.
Theory was tested on a 1/10 scale model. The result was a Sperling Index[i] score below 2.5, which is read as “pronounced but tolerable” level of vibration.
CASIC does not claim all problems are solved, however. Scaling this suspension system to full-size train cars will further test the high-speed train, as will emergency braking and less-than-optimum track conditions in the real world.
_____
[i] A numerical value calculated from frequencies and RMS of accelerations over those frequencies that