Metamaterials, engineered at the unit-cell level to manipulate wave propagation beyond the limits of conventional materials, rarely combine broadband airborne-sound absorption with structure-borne vibration attenuation in a single lightweight panel. This study proposes a two-dimensional, starfish-inspired multifunctional metamaterial addressing both transmission paths within a compact, mass-efficient unit cell. Its vibro-acoustic performance is characterised through thermoviscous finite element simulation, Bloch–Floquet dispersion analysis, and impedance-tube and shaker-based measurements on additively manufactured specimens. The measured panels achieve an absorption coefficient above 0.5 over a bandwidth of approximately 600 Hz within 400–1600 Hz, with near-unity absorption (α ≈ 0.9–1.0) at the resonant peaks, while dispersion analysis over 0–1200 Hz reveals multiple elastic bandgaps between approximately 610 and 1200 Hz, with measured accelerance reductions of up to 40 dB relative to the below-gap response. The starfish cell operates as a Helmholtz-type resonator, with the base radius R and arm amplitude A conventionally tuning the resonance through the cavity volume across approximately 440–1200 Hz. The distinguishing feature is the pore offset W, which shifts the peak by up to 200 Hz ( ∼ 20%) at constant cavity volume, depth, and neck geometry, by adding inertance without compliance through the arm channels a route unavailable in conventional Helmholtz or lattice-based absorbers; the arm number S affects the resonance only once W is non-zero. The interlocked arrangement yields a core mass per unit area approximately 48.3% lower than an equivalent honeycomb. These results position the design as a lightweight candidate for integrated noise and vibration control in aircraft, railway, and automotive structures.
Understanding the wake dynamics of oscillating fuel-injector needles is critical for optimizing injection performance. To isolate the underlying mechanisms, this study employs an idealized two-dimensional model of a cantilever needle oscillating in planar channel flow. The effects of oscillation parameters, inflow velocity, fluid properties, needle-tip geometry, and bending mode on wake dynamics are systematically investigated, together with the resulting hydrodynamic forces and damping. Increasing oscillation intensity enhances near-tip vorticity and promotes asymmetric shear-layer roll-up, driving the wake from a Kármán-type to a reverse-Kármán-type pattern, whereas increasing inflow velocity or viscosity favors the opposite transition. The combined effects are characterized by the modified Strouhal number (StA) and Reynolds number (Re), with a power-law transition boundary identified in the StA-Re regime map. The transverse hydrodynamic damping changes from positive to negative as inflow velocity increases, indicating a reversal in fluid-structure energy transfer from energy dissipation to energy input. Variations in tip geometry and bending mode do not fundamentally alter the wake mechanism. These findings provide a mechanistic basis for understanding oscillation-induced wake dynamics, and may inform future assessment and optimization of vibration and flow stability in fuel-injector systems.
Flutter suppression in supersonic panel-cavity systems presents a significant challenge due to the strong coupling among aerodynamic loading, structural deformation, and cavity acoustics. Although linear oscillators (LOs) can delay the onset of structural flutter, their effectiveness is limited when the instability behaviors are governed by strong acoustic-structural interactions. This study proposes the use of periodically distributed nonlinear oscillators (NLOs) to regulate aeroelastic-acoustic instabilities in supersonic panel-cavity systems. A fully coupled nonlinear variational framework is developed to incorporate panel geometric nonlinearity, three-dimensional cavity acoustics, and piston-theory aerodynamics. Within this framework, the modal analysis reveals that amplitude-dependent nonlinear stiffness reconfigures the modal interaction, inducing mode veering and localized coalescence, thereby modifying the instability boundaries. Furthermore, an energy-based formulation is established to characterize the underlying mechanism, demonstrating that the embedded NLOs introduce nonlinear energy transfer pathways that transfer energy from the panel to the internal oscillators, where it is stored or dissipated. Numerical results demonstrate that the proposed NLOs can effectively suppress the dominant large-amplitude responses associated with cavity-resonant flutter and structurally dominated flutter over specified dynamic-pressure ranges. The results further indicate that flutter suppression of the panel-cavity system is governed primarily by nonlinear reconfiguration of modal interactions and energy transfer, rather than by simple frequency detuning. The proposed framework provides a basis for designing nonlinear metastructures to regulate multi-physics instabilities in high-speed aeroelastic systems.
