Ph.D. (Engg): Acoustic Black Holes and Architected Designs for Vibration and Wave Control in Composite and Sandwich Structures

Lightweight composite panels and sandwich structures are vital in aerospace and mechanical engineering due to their high stiffness-to-weight ratios. However, minimizing structural mass often compromises dynamic performance, leading to severe issues like excessive vibration, noise transmission, flutter, and uncontrolled wave propagation. This research investigates the integration of acoustic black holes (ABHs) as a passive mechanism to mitigate these dynamic challenges by tailoring structural thickness. Furthermore, it explores how cellular core architectures and the fiber tailoring of composite laminates can be engineered in tandem to optimize overall dynamic behaviour. To achieve this, a three-dimensional homogenization approach is established to determine the effective material properties of various cellular cores, which are then integrated into a sandwich-plate framework. The preliminary findings reveal that core geometry simultaneously dictates stiffness, vibration modes, and flutter resistance, establishing a foundational understanding of how cellular architecture can complement ABH designs.
The core of this dissertation focuses on modelling and analyzing ABHs embedded within carbon-fiber-reinforced polymer (CFRP) laminated plates and sandwich configurations. To address the computational demands of optimizing these structures, computationally efficient Gaussian expansion methods are developed to simulate realistic ABH profiles with finite residual thickness and localized damping layer treatments. This framework enables a comprehensive parametric study on how ABH geometry, spatial distribution, laminate stacking sequences, core topologies, temperature, and moisture affect structural vibration. The numerical predictions show strong agreement with finite-element validation models while drastically reducing computational overhead. Crucially, the results indicate that effective vibration mitigation depends on the synergistic interaction between the ABH arrangement, laminate layout, and target frequency ranges, rather than geometric modification alone.
Finally, the research extends to acoustic and wave-steering applications to evaluate the broader structural-acoustic behaviour. By coupling a CFRP-ABH plate to an enclosed acoustic cavity, a specialized model is formulated to predict both panel kinematics and internal sound pressure. The analysis reveals a critical decoupling phenomenon: while ABHs successfully modify the system’s resonant behaviour and suppress structural vibration, this reduction does not automatically translate to lowered cavity sound pressure, emphasizing the necessity of distinct structural and acoustic optimization. The study concludes with an investigation into periodic CFRP arrays featuring circular and annular ABHs to control flexural-wave propagation. Utilizing an anisotropic reconstructed Gaussian expansion method, dispersion curves and group-velocity profiles are mapped, demonstrating that combining laminate anisotropy with ABH geometry enables precise wave steering and self-collimation over specific frequency bands. Together, these methodologies and insights offer a robust framework for designing high-performance, lightweight structures without the weight penalties of traditional damping treatments.
Keywords: Acoustic black holes; CFRP laminates; cellular sandwich structures; vibration control; structural–acoustic coupling; Gaussian expansion method; phononic crystals; flexural-wave steering and self-collimation.

Speaker: Singepogu Chinna Babu

Research Supervisor: Prof. Dineshkumar Harursampath