Nonintrusive Dynamic Pressure Monitoring of Sloshing Liquid Using a Hierarchically Microstructured Flexible Sensor

Monitoring dynamic pressure in sloshing liquids is critical for the safety of storage, transportation, and aerospace systems, as uncontrolled sloshing can increase structural loads and cause vehicle instability or containment failure. Conventionally, such measurements are done using rigid pressure transducers that are flush-mounted through drilled ports. This process disturbs the flow, limits the repositioning of sensors, and is unsuitable for curved or flexible tank surfaces. In this study, a hierarchically microstructured flexible pressure sensor (FlexiHMS) was employed to monitor slosh-induced wall pressures and benchmarked against a commercial piezoelectric (PZT) sensor. Controlled sloshing experiments were conducted in a lab-developed rectangular tank at 22%, 30%, and 70% fill volumes under base excitation from 0.8 to 1.2 times the first-mode natural frequency. Free-decay tests validated the test protocol, where dominant frequencies deviated from theoretical values by less than 5%. FlexiHMS successfully captured peak dynamic pressures ranging over (0.3-127) Pa and closely followed the expected resonant amplification behavior. Frequency-domain analysis using fast Fourier transforms and steady-state boxplots revealed pronounced nonlinear pressure characteristics near resonance, with increased dispersion and intermittency. While both sensors demonstrated repeatable cycle-to-cycle responses across multiple trials, FlexiHMS continued to exhibit a measurable pressure response under conditions where the PZT response diminished, especially at higher fill volumes. Our results highlight the potential of flexible pressure sensors like FlexiHMS for conformal, nonintrusive, dynamic pressure monitoring in fluid-structure interaction systems where conventional rigid sensor mounting is impractical.