PROGRAMMABLE BANDGAPS IN META-STRUCTURES WITH DYNAMIC VIBRATION RESONATORS

Elastic wave propagation is controlled using metastructures with dynamic vibration resonators (DVRs). These meta-structures exhibit bandgaps whose location is determined by the attributes of the DVRs, especially their resonant frequency. However, in passive meta-structures, the bandgap location is fixed, which limits their ability to attenuate vibrations over a wide frequency range. To overcome this limitation, this study introduces a novel approach to achieve a wide programmable bandgap using a DVR with two states: high-frequency and low-frequency states. A new n-bit nomenclature for the meta-structure is introduced to absorb vibrations over a wide frequency bandwidth by switching between various n-bit configurations. The programmability of these meta-structures is assessed, and the results are validated with experiments. This novel approach allows for a wide programmable bandgap, which significantly improves the effectiveness of meta-structures in attenuating vibrations and acoustics over a broad frequency range. In conclusion, this study presents a new approach to achieving programmable bandgap meta-structures with dynamic vibration resonators, which can significantly improve their ability to mitigate vibrations and sound in various applications, including transportation, buildings, and machinery. This innovation has the potential to address several engineering challenges and contribute to the development of more efficient and effective NVH systems

DATA-DRIVEN ESTIMATION OF BANDGAP FREQUENCIES IN METASTRUCTURES FOR ELASTIC WAVE ABSORPTION

This study investigates the elastic wave absorption behavior of metastructures in the bandgap frequency region. The bandgap region is estimated using data-driven methods based on the Frequency Response Function (FRF) of the unit cell of the metastructure. To achieve this, the unit cell is discretized using 1-D finite bar elements, and the numerical FRFs are calculated to dynamically link multiple unit cells using Component Mode Synthesis (CMS). The location of the bandgap is determined through the FRF of the multi-unit cell structure, which is referred to as Dynamically Linked Element Grade Oscillators (DLEGOs) due to the dynamic coupling between unit cells. The study also estimates the dispersion relation of the structure from the mode shapes of the finite structure. This approach is validated through the estimation of the bandgap from dispersion relations calculated using the traditional Finite Element Method. This comprehensive and validated method provides a way to estimate the edge frequencies of the bandgap in metastructures. The findings of this study contribute to the development of new metastructure designs that can inhibit elastic wave propagation in specific frequency ranges. Such designs have potential applications in various industries, including aerospace, defense, and transportation. In conclusion, this study highlights the importance of understanding the dynamic behavior of metastructures in modern engineering and their impact on various industries

ESTIMATION OF STRESS STATE IN AN AXIALLY LOADED BEAM USING MODAL DATA

Residual stresses are found to play a vital role in the dynamic behavior of the beam. These stresses are sometimes induced unintentionally due to manufacturing processes where temperate plays a role, while at other times, beams are subjected to stresses to alter their dynamic behavior for a particular application. Owing to the ubiquitous presence of the stressed beam, the estimation of its stress state becomes imperative to prevent structural failures. This study employs an approach to estimate the stress state of a beam from the natural frequencies and mode shapes. Using the modal data, the wave-numbers are calculated, and hence a dispersion relation is established. Modal analysis for a beam subjected to axial load is performed in a standard finite element software package, and the natural frequencies and the mode shapes are extracted. The analysis is performed for different values of loads, both compressive and tensile. The dispersion relation for the load cases is calculated, and the relationship between the wave-number, natural frequency, and load value is established using a curve-fitting approach. It was found that the discussed approach estimated the load value accurately. The discussed approach can be utilized to estimate the buckling of structures and stress states in a beam directly from the experimental data of the axially loaded beam

Vibration Isolation in 3D Printer Using Meta-Structures

Reducing vibrations in a 3D printer is crucial in improving the quality of printed prototypes. Ideally, the noise from the actuators in 3D printers should not hinder the print quality. However, isolating the printer surface from vibrations is challenging. Therefore, in this paper, a novel vibration-isolating frame is designed for building a novel 3D printer. Such a structure would absorb external vibrations and isolate the print-plate, thereby improving the print quality. The proposed frame is a meta-structure that absorbs vibrations over a frequency bandwidth. The structure is built with assembling multiple identical unit cells. Each unit cell is an assembly of 1D beams of varying cross-sections. The current paper’s objective is to design a fame that produces in-plane and out-of-plane bandgaps. Finite element models iterate over multiple designs, which are validated in the lab through robust experimentation. The paper discusses the design methodology and the corresponding results

PARAMETRIC-FEEL ALGORITHM: DEVELOPING A PARAMETRIC VECTORFITTING MODEL FOR EVENT LOCALIZATION IN CALIBRATED STRUCTURES

For smart structures, especially in the context of human activity, the force exerted and the location it happened is of significant relevance. This paper revisits and improves the performance in localizing and characterizing an input force with precalibrated structures through vibration measurement. The Force Estimation and Event Localization (FEEL) Algorithm have been discussed as a means of calculating the force of an impact and pinpointing its location. Unlike other time-of-flight approaches, FEEL does not require time synchronization, instead using transfer functions between possible impact locations and sensor locations to estimate force and localize impact. However, this approach is limited to locations where transfer functions are available. To overcome this limitation, a rowing hammer test was used to determine Frequency Response Functions (FRFs) at various points on a beam with a uniform rectangular cross-section. The Vector-Fitting algorithm was then used to improve the FRF approximation by moving poles to more advantageous locations, enhancing convergence, and lowering noise. Using the curve fitting approach, residues and FRFs were interpolated for additional locations. The extended FEEL algorithm was then used to localize impacts and estimate forces at these additional locations. This method can be used in applications such as tracking customer movement in retail establishments, detecting falls, tracking rehabilitation progress, and estimating building occupancy

NOVEL PUMPING MECHANISM FOR HEAT SINKS WITH FLUID MEDIUM USING STEADY STATE TRAVELING WAVES

The use of steady-state traveling waves as a novel pumping mechanism in liquid-cooled heat sinks offers a controlled and efficient method for fluid flow and heat removal without the need for an external fluid transfer pump. This experimental study demonstrates how traveling waves can be harnessed in a beam submerged in quiescent water using two force input methods, with the waves used to remove heat from a ceramic-based Positive Temperature Cofficient (PTC) heating element. The study analyzed the heating and cooling profiles of the heating element under two different conditions which are still water cooling and forced liquid convection cooling using steady-state traveling waves. The findings showed that a steady-state traveling wave could be an effective pumping mechanism for liquid-cooled heat sinks, resulting in lower maximum temperatures and equilibrium times than still-water cooling. These results suggest that optimizing the parameters like voltage and frequency could improve the performance of liquid-cooled heat sinks for various designs and operating conditions

ACOUSTIC META-STRUCTURE TRANSMISSION LOSS CHARACTERIZATION VIA AN IMPEDANCE TUBE AND THE TRANSFER MATRIX APPROACH

This paper proposes a new meta-structure bandgap depth measurement method that considers energy absorption rather than discrete structural response. By applying measurement techniques previously reserved for acoustic property characterization, this novel method aims to characterize acoustic metastructures by their transmission loss (TL). Transmission loss is the ratio of incident energy to transmitted energy from a structure. One extensively defined testing method for determining acoustic transmission loss involves using an impedance tube or a tube outfitted with transducers flush to its inside wall on either side of a sample holder, along with a source and termination on either end of the tube. Using the transfer matrix approach and transfer functions computed from the impedance tube transducers, the pressure and particle velocity at one point in space and time can be related to that of another point in space and time. In the end, a transfer matrix can be determined, which contains information about how much energy is absorbed, reflected, and transmitted by a structure over an entire range of frequencies. By outfitting an impedance tube to accept acoustic meta-structure samples, this same method can determine the transmission loss versus frequency exhibited by such a structure. This information can be used to directly observe and measure the band gap depth of an acoustic meta-structure

DYNAMIC MODE DECOMPOSITION APPROACH FOR ESTIMATING THE SHAPE OF A CABLE

This study investigates the dynamic behavior of a flexible cable with heterogeneous stiffness using a data-driven approach. The study aims to develop accurate models that describe intricate structures with rigid or flexible components. To achieve this, reflective markers were attached to the cable at equal spacing and the motion was manually excited and captured using an 8 camera setup and OptiTrack\u27s Motive software. Cable displacement data at marker locations were used as initial conditions for various Dynamic Mode Decomposition (DMD) models. The performance of the data-driven cable model is compared against the performance of the DMD modeling approach, fitting the dynamics of single- and multidegreeof-freedom systems with added white noise. In this work, the authors have considered using time delays and Wavelets-based DMD. The study found that the wavelet-based DMD (WDMD) model was the most accurate method for reconstructing the response of the cable in the test cases. Researchers suggest that this data-driven approach can be applied to predict the dynamic behavior of nonlinear systems, with potential applications in civil engineering, aerospace, and robotics. Overall, this study presents a promising approach for developing accurate models of complex structures with rigid or flexible components. The findings of this study may be valuable in designing structures that can withstand dynamic loads and vibrations