Faculty Publications
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Item Experimental study on the dynamic properties of magneto-rheological materials(Institute of Physics Publishing helen.craven@iop.org, 2018) Rajpal, R.; Lijesh, K.P.; Kant, M.; Gangadharan, K.V.Magneto-rheological elastomer (MRE), is considered to be a smart material, which transFigure their rheological properties with the external applied magnetic field. Due to this novel property, MREs are extensively employed to control the vibration of a system at resonant frequency. Presently, MREs are integrated in a structure through a layer by layer technique and the bigger drawback of this technology is that, in the presence of high transverse shear stresses, de-lamination occurs which may result in failure of the system. To overcome the aforementioned problem, a novel method is proposed to merge the MREs with Fused Deposition Method (FDM). FDM is used to develop the primary structure with cavities using a FDM compatible material and MRE i.e. secondary material is filled in the cavities. It is postulated that the proposed methodology has the capability of reducing the possibility of de-lamination. Now, to investigate the dynamic performance of the developed structure, an experimental test setup was developed by fixing one end of the beam and supplying the desired magnetic field to the beam using an electromagnet. From the test results, It was concluded that, with the increase in the applied magnetic field, the isolation effect of the structure enhanced and it reduced with the shift of electromagnet from the free end to fixed end of the beam. Further, in the case of MRE, high magnetic field is required for achieving satisfactory performance, which results in increase of the electromagnet weight, in turn making the system bulkier. Therefore, the present work endeavours to replace the MRE with MR Fluid (MRF) in the same primary structure and perform a comparison study between MRE and MRF, for the same applied magnetic field. From the experimental results it was envisaged that the MRF depicted better isolation capability than MRE. © Published under licence by IOP Publishing Ltd.Item Influence of nature of core on vibro acoustic behavior of sandwich aerospace structures(Elsevier Masson SAS 62 rue Camille Desmoulins Issy les Moulineaux Cedex 92442, 2016) Arunkumar, M.P.; Jeyaraj, P.; Gangadharan, K.V.; Mailan Chinnapandi, M.C.This paper presents the study of influence of core geometry on vibration and acoustic response characteristics of sandwich panels which are used as aerospace structures. Sandwich panels considered in this research work are: (a) Honeycomb core, (b) Truss and Z core, (c) Foam core. The present study has found that (i) For a honeycomb core sandwich panel in due consideration to space constraint, the better acoustic comfort can be achieved by reducing the core height and increasing the face sheet thickness. (ii) It is demonstrated that, for a honeycomb core sandwich panel, vibration and acoustic response is not sensitive to the cell size. (iii) It is observed that, triangular core gives better acoustic comfort for the truss core sandwich panel compared to other type of core. (iv) For foam core sandwich panels, it is observed that sandwich panel with carbon-epoxy (high stiffness) face sheet radiates less sound in the lower frequency range (0–100 Hz). While the sandwich panel with Titanium (high density) face sheet radiates less sound at the higher frequencies. In order to reduce the preprocessing time and computational effort throughout the analysis in the present study, equivalent 2D elastic properties are calculated and used to find out the vibration and acoustic response characteristics. © 2016 Elsevier Masson SASItem Parametric studies on bending stiffness and damping ratio of Sandwich structures(Elsevier B.V., 2018) Rajpal, R.; Lijesh, L.; Gangadharan, K.V.Sandwich structures are extensively used in aviation industries to reduce the overall weight of the system. Although the mechanical behavior of these structures has been widely studied, the performance of core shape in vibration response has been minimally explored. This study focuses on understanding the various influences of sandwich structures considering the following parameters: (i) nature of core shape, (ii) number of infill shapes, and (iii) orientation of cores, which affect the dynamic behavior of sandwich structures. Nine sandwich structures comprising three different core shapes, hexagon, triangle, and square shapes, in three different orientations, namely 0° 45° and 90° were considered for the present study. These structures in the beginning were put by modal analysis using finite element method (FEM). All the nine structures were printed using the fused deposition method to validate the FEM findings, while the DEWE soft data acquisition system was used to estimate the modal parameters (i) natural frequency and (ii) damping ratio. Natural frequency and damping ratio were estimated using FRF and Nyquist circle plot, respectively. This study demonstrates that although the square core orientated at 0° exhibited superior stiffness in bending loads, the hexagonal core orientated at 0° displayed an admirable combination of both stiffness and damping properties. © 2018 Elsevier B.V.Item Experimental investigation of 3D-printed polymer-based MR sandwich beam under discretized magnetic field(Springer Verlag service@springer.de, 2018) Rajpal, R.; Lijesh, K.P.; Gangadharan, K.V.Smart materials are being employed in dynamic systems to tune the stiffness and damping of the structure by using external stimuli. Magnetorheological elastomers (MREs) are considered to be as one of the smart materials because of their characteristics of altering the dynamic properties under the external magnetic field. So far, MRE sandwich beams have been developed by embedding them between two parent structures. In the present work, a novel technique of embedding MR materials is presented to create complex sandwich structures. This technique will replace the conventional embedding technique which uses adhesives to bind the MR materials with the parent structure. The vibration characteristics of the developed sandwich beams are estimated by conducting harmonic analysis to a predefined band of frequency range under the different directions of magnetic field. Sinusoidal signals of desired frequency and amplitude were proffered using NI educational laboratory virtual instrumentation suite to an amplified piezoactuator for exciting the MR sandwich beam. A non-contact-type laser displacement sensor is used in this study to avoid the additional mass of the sensor on the beam. The results indicate that the smart materials can be efficiently embedded with the sandwich beam without using the adhesives. It is also found that by changing the direction of magnetic field, the range of the variation in stiffness of MR sandwich beam can be increased to enhance the isolation effect at fundamental natural frequency. © 2018, The Brazilian Society of Mechanical Sciences and Engineering.Item Numerical and Experimental Investigations on Robust Output Feedback Control for Active Vibration Attenuation of Flexible Smart System(Institute of Electrical and Electronics Engineers Inc., 2023) Parameswaran, A.P.; Padmasali, A.N.; Gangadharan, K.V.This paper investigates the prototyping and implementation of an output feedback-based robust controller on a Field Programmable Gate Array (FPGA) platform. The Smart System under Test (SSuT) in this submission is a flexible cantilever beam bonded with Piezoelectric (PZT 5H) patches that act as a sensor as well as an actuator (perturbance creation as well as control actuation). For ease of modeling and subsequent controller design in the laboratory studies, the low-frequency dynamics of the smart system are approximated to only a Single Degree of Freedom (SDOF) in terms of flexural vibrations. The SSuT is modeled analytically through finite element modeling and experimentally through sub-space system identification process. The developed models' accuracy is compared with the experimental results of non - parametric modeling. The developed models are then used to conduct the simulation studies with the designed robust output feedback controller in the closed loop. Apart from the simulation studies, the designed controller was also prototyped on an FPGA platform using LabVIEW FPGA with the associated hardware in loop to carry out the experimental validation of its performance. The robustness and efficiency of the prototype controller to control the system vibrations in real-time were proved through extensive tests at single resonant frequencies and a range of frequencies encompassing the dominant resonant regions in the flexural mode. Findings from this study are further used to ensure satisfactory active vibration control of smart cantilever systems in various heavy/aerospace industries by approximating them to suitable benchmark systems in the laboratory. © 2013 IEEE.