Flow visualization is the direct observation of fluid flow. Moving fluids form complex patterns and understanding and visualizing those patterns is an important aspect in aerospace industry. The previously existing research and results were taken into consideration for design parameters and calculation for dimensions of various parts of the wind tunnel. Design calculations allow wind velocities in the range of 1-3 m/s at the test section. The design includes a rectangular test section of 0.06m x 0.30m cross-section for accommodation of test object of width 0.06m. The design was made in SolidWorks and was fabricated with basic materials like plywood and acrylic sheets. PC cabinet fans were used for flow circulation. Liquid wax is utilized for the purpose of smoke generation and rubber and PVC pipes were utilized for smoke containment and delivery system. Profiles that were used for testing included cylinder, sphere, cuboid, NACA airfoils and flat plate.@en

This study reports the presence of an interface mode in the one-dimensional topologically arranged mechanical metamaterials using mechanical dome shaped metastructures which can be exhibited by hourglass configurations. The paper proposes the method of obtaining a localized interface mode within the bandgap using the hourglass shaped resonating elements in the one dimensional topologically arranged chain. Implementing a wide range of different re-entrant angles on the patterns imprinted on dome shaped hourglass metastructure ranging from negative to positive re-entrant angle would lead to lattice dependent stiffness characteristics in the system. The primary unit cell considered in this system is diatomic unit cell having identical masses and alternating spring stiffness driven by the dome shaped hourglass metastructure. Moreover, the variation in the stiffness of hourglass metastructure is also dependent on the height to thickness ratio which is also explored in this study to restrict the stiffness of hourglass unit in the linear regime which is easily obtainable in small deformation range. The interface unit cell is placed in the one-dimensional chain in such a way that inversion symmetry is broken using the different classes of hourglass lattice metastructures within the unit cell. The frequency response function of the one dimensional topologically protected chain is analytically computed and the interface mode is observed locally within the bandgap. The possibility of wave propagation at specific frequencies within the bandgaps is strategically achieved by defining lattice-dependent stiffness parameters at the interface modes. The considered configurations define a framework for introducing lattice-based imperfections in the continuous elastic structures that makes it potential engineering relevance.

@en

Background: The architected mechanical metastructures have garnered significant research attention for various engineering applications due to their remarkable mechanical properties and unique deformation behavior. The lattice-based micro-structured materials have shown enhanced mechanical properties and the ability to control wave propagation, making them ideal for multifunctional applications. Objective: We report the family of lattice-based hourglass metastructures within the optimal design scope and its geometrical parameter selection. The lattice-based energy absorption performance and their damping characteristics have been classified based on different constitutive lattices. Methods: Herein, the uniaxial compressive response and lattice-based energy absorption capacity of a novel hybrid configuration, hourglass-shaped, consists of auxetic and honeycomb-based lattice, are systematically investigated through theoretical, finite element simulation and experimental methods. The proposed hourglass-shaped unit cell is a combination of two oppositely oriented coaxial domes that give more flexibility to control dynamic response and enhance lattice functionality passively. An additive manufacturing route has fabricated a series of hourglass-shaped lattice metastructures with nylon-based material. Results: It was found from the experimental data that the Ideal energy absorption efficiency parameter (E _i) is highest for the case of the auxetic-based hourglass with the increment of 22% and 35% than the solid shell and honeycomb lattice-based metastructure, respectively. The specific energy absorption parameters data have also been evaluated and compared with the numerical computational results. Conclusion: The combination of numerical simulation, additive layer manufacturing (3D printing), and experimental testing are implemented to quantitatively determine the lattice-based energy absorption properties and justify their evaluation. This study suggests the utilization of novel hourglass lattice-based metastructure for multifunctional engineering applications.

@en

Nonreciprocity and topologically protected wave propagation have significant implications on how energy and information are transmitted or guided within materials to control or mitigate its effects. The major challenge in tailoring interface mode arises from challenges related to the customizability and linearity of interface lattice, moreover, there is a scarce of experimental analysis reported in the literature. Our study has focused on obtaining topologically protected nontrivial interface modes at a specific frequency by breaking the inversion symmetry through novel hourglass metastructure both theoretically and experimentally. Detailed work on wave transmission, dispersion, and bandgap analysis are carried out considering topological metamaterials. New cellular configurations based on regular honeycomb and auxetic cells, and variations of their geometric parameters responsible for interface mode tuning are reported here. A generalized theoretical scheme for different combinations of the hourglass lattice is derived at the interface, and consequent energy harvesting and damping prospects are reported. Analytical modeling of topological metamaterial lattice along with numerical simulation, additive layer manufacturing (3D printing), and finally experimental validations are carried out to justify the behavior and reveal the underlying physics responsible for its unique behavior. Three types of configurations including hourglass lattice at the interface define a general framework for introducing lattice-based imperfections in the continuous elastic structure for potential engineering applications. The localized topological interface mode obtained within the bandgap can be tuned significantly with the help of latticed hourglass and may be utilized for the purpose of wave guiding, wave focusing, and energy harvesting within the isolation zone.@en

In this work, the vibration transmissibility behavior of novel dome shaped auxetic structures with different cellular configurations are simulated using Abaqus 6.14 and subsequently studied experimentally. The dynamic behavior of domes and hourglass shape auxetic structures are studied within the frequency bandwidth of 5-500 Hz by using base excitation technique. The auxetic samples are subjected to broadband excitation at low dynamic strain, followed by sine sweep around the resonance of the system. The dynamic and modal behaviors are experimentally analyzed by using 3D Laser Doppler Vibrometer. The system is shown to develop specific wave propagation and attenuation bands, outline of which is important for developing strategies for damping/energy harvesting. Further, analysis has been carried out to analyze the mechanical wave propagation behavior when the system is subjected to broadband excitation frequency at low dynamic strains. Here, we have arranged a large periodic repeating units of hourglass shape auxetics with lumped mass inside it placed at the center. The equivalent spring-mass-damper mechanical circuit has been developed for the shake of simplifying our system. The Non-linear stiffness of hourglass structure depend upon constitutive cellular cells i.e. auxetic, regular honeycomb and plane, which is evident for getting broader bandgap formation than the linear one. The lumped mass is considered here as locally resonating metamaterial enabling low-frequency vibration attenuation. Furthermore, the analysis is being done for bandgap expressions depending upon the added mass ratio and target frequency. Further study is proposed for attenuation and transmission band analysis to steer the waves which roots the idea of vibration sink, in which we can damp the mechanical waves effectively at a specific location. The Auxetic meta-materials are envisaged to have a significant role in wave attenuation and wave steering, and can be used effectively for vibration control.@en