Department of Applied Mechanics

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Damage detection in complicated engineering systems from vibration measurements typically involves the use of algorithms that are built on the principles of bayesian dynamic state estimation. These methods invariably required the solution of the forward problem a fairly large number of times. For complex engineering systems that are numerically modeled using Finite Element (FE), this can be computationally intensive especially when a single FE run for the problem takes a large time. To alleviate this problem, there is a need for the development of Reduced Order Models (ROMs) that significantly reduce the computational cost associated with solving the forward problem, for a given measure without sacrificing the accuracy. The present study discusses three ROM methods with specific reference to a simple problem. These methods include well-known Component Mode Synthesis (CMS) and System Equivalent Reduction Expansion Process (SEREP) which are applicable only for linear systems, as well as Principal Component Analysis (PCA)—the method which is more general and can be used for nonlinear systems as well. A comparison of the performance of all these methods is carried out for a stepped beam. The FE based results obtained from the full model is treated as the benchmark. © 2021, Springer Nature Singapore Pte Ltd.

World University root node

Lecture Notes in Mechanical Engineering

Analysis of Stepped Beam Using Reduced Order Models

This study focusses on the vibration control of linear large scale engineering structures, modelled as continuous system, with varying system parameters. Because of manufacturing limitations or/and measurement errors, system parameters need to be modelled as random variables. Here, system parameters are modelled as non-Gaussian random variables. Mathematically, continuous system is governed by partial differential equations and solved using approximation methods. High fidelity finite element model is the starting point of the analysis. Since numerical approximation involves large number of degrees-of-freedom, solving the system in real time is computationally expensive and application of control algorithm is cumbersome. In this study, a reduced order model is developed to reduce the state space dimension of the problem and further integrated with the control algorithm. Next, controller gain is obtained using linear quadratic regulator in reduced subspace which is used as a feedback to the actuators to produce the required control force for vibration control. A numerical example of flexible cantilever beam is solved to demonstrate the efficacy of the algorithm and probabilistic characterisation is carried out using Monte Carlo simulation. © 2020 The Society of Instrument and Control Engineers - SICE.

2020 59th Annual Conference of the Society of Instrument and Control Engineers of Japan, SICE 2020

ROM integrated vibration control of stochastically parametered flexible structures

Magnetostrictive materials that couple mechanical and magnetic domains have been widely explored for use in sensors and actuators. These materials often exhibit a nonlinear material response under applied magnetic fields, which limits the use of linear constitutive models. Furthermore, the nonlinear constitutive relations tend to be implicit in nature. Hence, a finite element scheme that can handle the implicit relationship between the mechanical (stresses and strains) and magnetic (magnetic flux density and magnetic field) quantities is proposed in order to arrive at solutions to boundary value problems. In the proposed scheme, while the physical requirements of equilibrium and strain–displacement relation are satisfied point-wise, the constitutive relations hold in a weak integral sense. A fully coupled magnetostrictive plane stress rectangular element is developed based on the proposed scheme and its efficacy in arriving at solutions to coupled field boundary value problems is illustrated by subjecting the element to standard loading conditions. © 2020, Springer-Verlag GmbH Germany, part of Springer Nature.

Department Of Civil Engineering

Computational Mechanics

Finite element formulation for implicit magnetostrictive constitutive relations

Magnetostrictive materials are potential candidates for many applications such as sensors, actuators, transducers, and other magnetoelectric applications. Cobalt ferrite (CoFe 2 O 4) has proven to be favorable in comparison with commonly used magnetostrictive materials due to its high magnetostriction coefficient and low cost. This work deals with the synthesis of CoFe 2 O 4 and subsequent characterization of its magnetostrictive properties. Hydrothermal route was adopted for the synthesis, and the effect of sintering and measurement temperatures on the magnetostrictive response of the synthesized samples was also established. Bipolar magnetostriction has been observed in pure CoFe 2 O 4 for the first time, and its control by means of the sintering temperature has been elucidated. The results thus reveal that the temperature is an important parameter in determining the magnetostrictive characteristics of CoFe 2 O 4. The switching from bipolar to unipolar magnetostriction under elevated sintering and measurement temperatures was also observed, and this was owed to the crystal anisotropy of the material. The effect of prestress on the magnetostriction was also studied, wherein it was observed that the application of a compressive prestress resulted in broadening of the magnetostriction loops. The reported bipolar magnetostrictive characteristics are quite interesting and hence can prove to be cost-effective in comparison with existing magnetostrictive materials. © 2020 Author(s).

Fulltext

Journal of Applied Physics

Bipolar magnetostriction in CoFe2O4: Effect of sintering, measurement temperature, and prestress

This manuscript discusses a magnetically coupled nonlinear hybrid piezo-electromagnetic energy harvester under harmonic base motion. Linear energy harvester works optimally when the natural frequency of the harvester meets the resonating frequency, elsewhere harvested power falls drastically. Most of the ambient vibration sources are random in nature. Hence, considering the realistic application, narrowband linear vibration energy harvesters are inefficient. Alternatively, nonlinear energy harvesters are capable of producing the electrical power over a broad frequency range. Hence, to acquire the optimum power in the broader frequency range, a magnetically coupled hybrid piezo-electromagnetic energy harvester is developed. In this current work, a tip loaded unimorph piezo cantilever beam configuration is used to scavenge electrical energy from the strain developed in the piezoelectric patch and spring-magnetic mass attached to another end of the cantilever beam with solenoid arrangements are used to scavenge electrical energy from the relative motion between magnetic mass and solenoid. This hybrid harvester is coupled with magnetic oscillators to introduces nonlinearity in the developed harvester. This paper compares, the energy harvested from the hybrid harvester with that of conventional piezoelectric and electromagnetic harvesters for both linear and nonlinear systems. © Springer Nature Singapore Pte Ltd 2020.

A nonlinear hybrid energy harvester

This manuscript analyzes the performance of a tristable vibration energy harvester under Gaussian white noise excitation. Broadband vibration energy harvesting has attracted significant research attention and is targeted toward obtaining large power output over a wide range of frequencies. Nonlinearity can be introduced into vibration energy harvesting systems through multi-stability. In cantilever-type vibration energy harvesters, multi-stability could be achieved by the introduction of magnetic interactions. When two external magnets are used, the harvester can have up to three stable static equilibrium positions. The harvester with two stable states has been explored widely, both theoretically and experimentally. Recently, the harvester with three stable states is shown to perform better than its bistable counterpart in the presence of a linearly increasing harmonic sweep excitation. Ambient vibrations are random in nature, and the performance of tristable energy harvesters under such excitations needs to be studied. To begin with, we study the performance of tristable energy harvesters under Gaussian white noise excitation through numerical simulations. The simulations show that beyond a certain critical amplitude of excitation, the harvesters undergo inter-well oscillations and harvest more power. This implies that if the variance of the random ambient excitation is known, then the harvester could be optimized so that the mean harvested power is maximized. © Springer Nature Singapore Pte Ltd 2020.

Analysis of tristable energy harvesters under random excitations

An energy harvesting device built on the lines of capitalizing the linear resonance of the system works well only when the natural frequency is close to the excitation frequency. To overcome this limitation of the linear harvester, this work investigates the prospect of using an array of mistuned cantilevers for broadband energy harvesting. The common device configuration of inverted beams with tip masses has been adopted in this study. The considered system is highly nonlinear for tip masses beyond Euler buckling load, and it has two potential wells on either side of the unstable zero position. The non-linear characteristics of the harvester are studied as a preliminary investigation to identify the values of mistuning parameters used in the current work. Numerical simulations have been carried out to understand the influence of mistuning parameters such as length of the beams and tip masses on the frequency band of the harvester power. Comparative studies on the power bandwidth of array of mistuned linear and non-linear harvesters are performed. Observations show that an array of non-linear harvesters enhanced the frequency bandwidth of the power more than that of its linear counterpart. © Springer Nature Singapore Pte Ltd 2020.

Broadband Piezoelectric Energy Harvesting Using an Array of Mistuned Inverted Cantilever Beams

In this study, wake of an elliptic cylinder is analyzed in the presence of a fluid–fluid interface. The interactions between the interface and flow affect each other and hence different wake dynamics and interface topologies are observed. The numerical solver developed for this study has immersed boundary method (IBM) coupled with level-set method (LSM). The proximity of the elliptical cylinder to the interface (H/D), Froude number (Fr), and angle of incidence (AOI) are the parameters considered. Three different Froude number regimes are considered for this study, namely, subcritical (Fr &lt; 1), critical (Fr = 1.0), and supercritical (Fr &gt;1) regime. In this paper, the interface topology, wake dynamics, and force values are compared for the variation of these parameters.

Shear Layer Interactions With Fluid–Fluid Interface in the Wake of an Elliptical Cylinder

This work involves an experimental investigation of the static and fatigue behavior of patch repaired laminates under flexural loading. At first, a static flexural study is conducted for two types of parent laminates comprising 4-plies ([0°]4 &amp; [45°]4) and 8-plies ([0°]8 &amp; [45°]8) of woven carbon fiber. The repair is conducted by two types of patches with stacking sequence [0°]2 and [45°]2. Three different repair configurations involving patch bonded on the compressive side, tensile side, and both the sides of the parent specimens, have been tested. Digital image correlation has been employed to capture the deflection of the specimens. In order to understand the vulnerability of patch repaired laminates to cyclic loading, the load controlled constant amplitude fatigue tests have been conducted on 8-ply repaired laminates. Different failure modes, distinctive to each type of repair configurations have been observed. The results of this work provide more insight to the influence of various parameters viz. number of plies, fiber orientation, patch placement, and so forth, on the flexural behavior of repaired laminates. © 2020 Society of Plastics Engineers

Polymer Composites

Flexural static and fatigue response of patch repaired laminated composites for different patch-parent configurations

The nonstationarity measure of surface Electromyography (sEMG) signals provide an index for muscle fatigue conditions. In this paper, a new framework has been proposed for the analysis of sEMG signal using Instantaneous Spectral Centroid (ISC). The novelty of the proposed work is use of topological signal processing method to quantify the nonstationarity of sEMG signal. For this, the signals are recorded from the biceps brachii muscles of 25 healthy subjects in isometric contraction. The analytical signals corresponding to nonfatigue and fatigue segments are computed using Hilbert Transform. Further, topological features such as center of gravity (CoG), triangular area function (TAF) and ISC are calculated from the geometrical representation of a transformed signal. The result indicates the increase of TAF in fatigue condition and the significant right shift of CoG in x-axis for 80% of subjects. Importantly, the ISC estimate is decreased by 17% upon fatiguing for 84% of subjects. The obtained results show statistical significance with p < 0.05. It is observed that the shape parameters are varied in accordance with the changes observed in global characteristics of sEMG signals during muscle fatigue. The preliminary results show that the topological features are able to quantify the nonstationarity in sEMG signal. Therefore, the proposed method can be used as a fatigue index for diagnosing various neuromuscular disorders.Clinical Relevance - This method can be used to establish metrics of muscle fatigue for the benefit of physicians especially in the field of fitness, sports, pre and post-surgery surveillance and rehabilitation. © 2020 IEEE.