arXiv subjects

Vinod Ramakrishnan

Publications and source records attributed to Vinod Ramakrishnan.

5 recordsLinked to original sources

arXiv2026

Quantifying the effect of resonant amplitude and frequency of phononic material vibrations on the coupled fluid-structure interaction dynamics in separated aerodynamic flows

Phononic materials (PMs) with engineered resonances have been leveraged for fluid-structure interaction (FSI) with fluid flow instabilities, yielding beneficial outcomes such as transition delay, stabilized hypersonic boundary layers, and increased aerodynamic lift. Prior PM-FSI studies primarily identify spatio-temporal flow scales of interest and choose PM structural parameters producing structural dynamics conducive for FSI. However, a fully-coupled FSI system generally produces complex coupled dynamics that is not accurately captured by studying either physical system in isolation. In this context, our prior work established behavioral parameters that govern the coupled PM-FSI dynamics in a separated aerodynamic flow over a limited parameter range. Adopting this framework, this paper explores strongly-coupled high-fidelity PM-FSI simulations over a broader range of two behavioral parameters---truncation resonance frequency and displacement amplitude---to establish their quantitative (linear/cubic) relations to the coupled frequency, lift force, and circulation in the coupled system response. In addition, the results indicate the presence of distinct FSI regimes, depending on the proximity of the truncation resonance frequency or its sub-/super-harmonics to the vortex-shedding frequency. FSI dynamics ranging from multi-/single-frequency dynamics, downshifted coupling frequency due to fluid-added mass effects, generation of non-linear harmonics to convergence of FSI dynamics to the rigid plate case are observed. These results reiterate the importance of the PM frequency and amplitude in determining the coupled FSI dynamics, and the proposed quantitative relations provide a new pathway for designing PMs for aerodynamic flow control to achieve beneficial outcomes, e.g., lift force enhancement.

physics.flu-dyn↗

arXiv2026

Weakly coupled fluid-structure interaction between wall-bounded turbulent flows and defect-embedded phononic subsurfaces

We investigate the interaction between wall-bounded turbulence and defect-embedded phononic subsurface (D-Psub) using a weakly coupled fluid--structure framework, in which the flow and structure are advanced sequentially without sub-iterations. The D-Psub subsurface is modeled as a dynamic wall with a resonance introduced via a localized structural defect, driven by spatially averaged wall-pressure fluctuations from a turbulent channel flow. This configuration enables a controlled study of how a narrow-band structural response interacts with the broadband forcing of near-wall turbulence. Despite broadband turbulent forcing, the D-Psub exhibits a narrow-band response that modifies near-wall dynamics, with representative cases showing suppression of velocity fluctuations, increased coherence of streamwise streaks, and a measurable reduction in turbulent drag. Crucially, the coupled system displays behavior that cannot be replicated by prescribed wall motion: the dominant oscillation frequency shifts away from the designed resonance due to fluid--structure interaction. Additionally, the phase between panels is shown to be governed by the convection of turbulent structures. These results reveal a mechanism by which phononic subsurfaces filter and reorganize turbulent energy through frequency-selective coupling, distinct from conventional compliant or actively forced walls. The findings provide a physical basis for designing passive resonant surfaces that exploit turbulence-structure coupling for flow control.

physics.flu-dyn↗

arXiv2025

A Framework to Systematically Study the Nonlinear Fluid-Structure Interaction of Phononic Materials with Aerodynamic Flows

Phononic materials (PMs) are periodic media that exhibit novel elastodynamic responses. While PMs have made progress in vibration-mitigation applications, recent studies have demonstrated the potential of PMs to passively and adaptively modulate flow behavior through fluid-structure interaction (FSI). For example, PMs have been shown to delay laminar-to-turbulent transition and mitigate unsteadiness in shock-boundary layer interactions. However, a systematic framework to relate the effect of specific PM behaviors to the FSI dynamics is lacking. Such a framework is essential to systematically investigate the complex and nonlinear coupled dynamics of the FSI. Further, parameters that are not typically considered in PM models become critical, such as the vibration amplitude. This article addresses this gap by proposing FSI-relevant ``behavioral'' parameters, distinct from the structural parameters of the PM, but with a clear mapping provided to them. We use high-fidelity, strongly coupled simulations to quantify the FSI between a novel configuration of laminar flow past a flat plate, equipped with a PM. Our study proposes four critical PM behavioral parameters -- effective stiffness, truncation resonance frequency, a quantity representing the dynamic displacement amplitude, and unit cell mass -- that influence the spectral characteristics of the vortex-shedding process inherent to the flat plate system. Results show connections between each parameter and distinct behavior in the lift coefficient in FSI. While the focus of this work is on the PM-FSI dynamics in an aerodynamic flow, we argue that identifying these behavioral parameters is key to unlocking scientific study and design with phononic materials in fluid flows more broadly.

physics.flu-dyn↗

arXiv2025

Pattern Formation in Robotic Mechanical Metamaterial

Spatio-temporal patterns emerging from an initial quiescent, uniform state is a phenomenon observed in many dynamical systems sustained far from thermodynamic equilibrium, the practical application of which has only recently begun to be explored. As the underlying dynamics are typically complex, pattern formation is often theoretically analyzed and understood via phenomenological models, which effectively represent the causal mechanisms, but obscure the link between the small-scale interactions/processes and the observed macroscopic behavior. Moreover, efforts to prescribe the patterning response are often undercut by the experimental inaccessibility of the small-scale constituents/processes. This article demonstrates an artificial system (i.e., a robotic mechanical metamaterial) as an accessible and versatile platform within which to explore and prescribe the patterning response of non-equilibrium systems. Specifically, in varying a feedback parameter within the prescribed reaction kinetics, the robotic mechanical metamaterial alternately develops spatial and temporal oscillations in the displacement field following a perturbation of the initial quiescent, uniform state. The platform is amenable to a first-principles analytical description so that corresponding theoretical results possess qualitative and quantitative significance, and maintain connection to the specific system parameters.

nlin.PS↗

arXiv2025

A Quantitative Study of Energy Localization Characteristics in Defect-embedded Phononic Crystals

Phononic crystals (PnCs) are periodic engineered media that can customize the spatio-temporal characteristics of mechanical energy propagation. PnCs that additionally leverage precisely embedded defects can achieve robust energy localization with desirable spatio-temporal characteristics, opening avenues for critical engineering applications, e.g., energy harvesting, waveguiding, and fluid flow control. Numerous studies have qualitatively explored the localized dynamics via simulations and experiments, investigating the defect resonance frequency as the primary feature. However, the frequency represents only a subset of the relevant characteristics and a systematic approach to quantify the full scope of the defect dynamics remains elusive. This article establishes the frequency, mode shape, and localized velocity (or displacement) amplitude envelope as three significant factors governing the defect resonance dynamics, and quantitatively examines these characteristics using a modified version of the perturbed tridiagonal n-Toeplitz method. The proposed method accurately estimates the resonance characteristics in 1D and 2D defect-embedded PnC lattices with single and multiple defects and elucidates the effects of damping. The method is used to highlight how the key characteristics of defect modes depend on system parameters. Finally, we demonstrate the benefits of defect modes through two defect-based PnCs that can accommodate -- (i) a virtual ground, and (ii) achieve customized acoustic interaction and absorption, and use the proposed method to analyze these scenarios. The proposed strategy can be readily extended to more elaborate PnCs and augments the design space for defect-based PnCs.

physics.app-ph↗