Recent advancements in metamaterials have brought about exciting innovations aimed at controlling low-frequency vibrations, particularly within ship propulsion systems. Researchers have developed bionic quasi-zero stiffness (QZS) metamaterials, which exhibit low-frequency band gaps, showing great promise for reducing unwanted longitudinal vibrations generated by the rotation of ship propellers.
The propulsion system of surface ships, primarily driven by their propellers, creates pulsations as it navigates through uneven wake fields caused by the hull shape. This pulsation results in vibrations transmitted through the shafting to the ship hull, exacerbated by the effects of unsteady flow. These vibrations not only impact the structural integrity of the vessel but can also significantly hinder its acoustic stealth performance, posing challenges for military operations.
To tackle this issue, researchers have proposed the integration of novel QZS metamaterials, which employ local resonance mechanisms to attenuate vibrations more effectively compared to traditional methods. A fundamental aspect of this approach is the design of the metamaterial's unit cells to replicate biological structures known for their vibration-absorbing qualities. By mimicking natural adaptations, such as the limb shapes of animals, these QZS materials attain unique mechanical properties beneficial for vibration isolation.
The study incorporated detailed mechanical modeling, which utilized parameters to characterize the effects of both damping and stiffness on the system's performance. Damping is known to broaden the band gap, potentially allowing for wider control over vibrations, whereas the stiffness ratios and mass ratios directly influence the operational frequency of the band gaps.
By applying the Harmonic Balance method, the researchers developed equations to determine the dispersion relationship for longitudinal waves, resulting in the identification of specific frequency ranges, or band gaps, within which wave propagation is significantly reduced. Simulations confirmed the theoretical predictions, displaying low-frequency band gaps centered around 7.5 Hz—ideal for mitigating the vibrations experienced by ship shafting systems.
Notably, the incorporation of these QZS metamaterials presents opportunities to not only prevent the detrimental effects of vibrations on vessel integrity but also improve stealth capabilities by reducing underwater noise emissions. This innovative research introduces new avenues for maritime engineering, potentially informing the design of quieter, more efficient propulsion systems.
Overall, the development of bionic QZS metamaterials marks an important step forward in vibration control research, with promising applications not just limited to marine environments but potentially extending to various fields where vibration dampening is desired.