Faculty Publications
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Item Performance enhancement in polymer electrolyte membrane fuel cell with flow traps and field gradients: A Numerical Study(Elsevier Ltd, 2024) Padavu, P.; Koorata, P.K.; Kattimani, S.; Gaonkar, D.N.Efficient reactant distribution and water removal are critical during polymer electrolyte fuel cell (PEFC) operation. The bipolar plate and its corresponding flow field design are vital among the PEFC components for enhancing reactant transport and water removal. The issues arising in the PEFC during the high current operation, such as reactant starvation and water removal, can be alleviated by improving the flow channel geometry. In this study, we analyze the variation in overall PEFC performance and corresponding reactant transport phenomenon for two independent design cases. The converging gradient design without channel traps at 0.4 V operating voltage exhibited a current density increment of 6.85% against the conventional design. Moreover, at 0.4 V, including channel traps enhanced the current density, as we observed a current density increment of 7.1% for the converging design with channel traps against the conventional design without channel traps. Likewise, at 0.4 V, the diverging design with channel traps exhibited a current density increment of 5.85% against the diverging design with no channel traps. Further, enhanced reactant distribution is observed in the catalyst layer upon introducing channel traps in the flow field design. © 2024 Hydrogen Energy Publications LLCItem Flutter prediction for unmanned long endurance aircraft using virtual structural model and experimental modes(SAGE Publications Ltd, 2025) Sampath, A.K.; Kattimani, S.Aeroelastic stability is an important consideration in the design and certification processes of modern, flexible aircraft. This includes demonstration of freedom from flutter at all combinations of airspeed and altitude within the flight envelope. This paper presents the analysis and clearance of flutter characteristics for an unmanned medium altitude long endurance aircraft by two distinct methods. The traditional method based on a theoretical Finite Element (FE) model was adopted prior to the conduct of Ground Vibration Tests (GVT) where as the more recent method utilized a Virtual Structural Model (VSM) built on the experimental modal parameters that were obtained from the GVT. The Direct Matrix Abstraction Program (DMAP) feature of MSC NASTRAN was used to create the VSM whose nodes correspond to the GVT accelerometer locations, and to insert the GVT modes into the model. In both approaches the unsteady airloads were generated using the Doublet Lattice Method (DLM). The GVT/VSM based analyses closely mirrored the original FE model analysis and confirmed the existence of sufficient flutter margins, thereby enabling the flight certification of the aircraft. The VSM route to flutter analysis is outlined in this paper as an alternative to using a GVT-tuned FE model. This is beneficial (i) if no FE model is available as it happens with bought out aircraft, or (ii) if the configurations of interest are too few to justify the effort of FE model tuning. © IMechE 2025Item Effect of piezoelectric ceramic on natural frequency, structural, and thermal properties of additively manufactured PLA/BTO composite structure(Elsevier Ltd, 2025) Senthil Murugan, S.S.; Kattimani, S.This study investigates the fabrication and characterisation of filaments and 3D-printed samples using polylactic acid (PLA) and PLA/BTO (Barium Titanate) composites via fused deposition additive manufacturing (FDAM). PLA/BTO composite filaments were prepared by blending PLA granules with BTO particles using hot extrusion. Samples were 3D printed under controlled parameters and analyzed for dynamic, thermal, and structural properties. The inclusion of BTO significantly enhanced natural frequency (11 Hz-first peak) and structural rigidity compared to pure PLA (8 Hz-first peak), particularly under cantilever beam configurations. Microstructural analysis via optical and field emission scanning electron microscopy (FESEM) revealed uniform particle dispersion and good layer adhesion in composites with a peak width of 340 ?m. Energy-dispersive X-ray diffraction (EDS) study insisted that the presence of BTO improves functionality with minimal reinforcement with other trace elements. X-ray diffraction (XRD) confirmed increased crystallinity in PLA/BTO samples and improved alignment of the crystalline regions post-FDAM process, while Fourier transform infrared spectroscopy (FTIR) demonstrated molecular interactions between PLA and BTO and highlights the structural modifications in the composite due to the act of BTO reinforcement as nucleating agent. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) highlighted enhanced thermal stability and modified crystallinity due to BTO incorporation. Printed PLA/BTO demonstrates the highest resistance to thermal degradation than pure PLA, with degradation onset at an elevated temperature. Results validate the suitability of PLA/BTO composites for applications requiring tailored dynamic, thermal, and structural properties, emphasizing the FDAM process's potential for advanced material development. © 2025 Elsevier Ltd and Techna Group S.r.l.Item Non-linear thermal stability and free vibration behavior of sandwich beams with auxetic re-entrant aluminum cores and graphene origami-enhanced facings(Elsevier Ltd, 2025) Shashiraj; Pitchaimani, J.; Kattimani, S.Revolutionizing advanced sandwich structures, this study delves into the non-linear thermal stability behavior and free vibration characteristics of auxetic aluminum re-entrant core sandwich beams enhanced with graphene origami (GOri) metamaterial facings, subjected to spatially varying thermal environment. The sandwich beams are modeled as layered structures incorporating complex geometric non-linearities, using a higher-order shear deformation framework and non-linear strain–displacement kinematics based on von Kármán assumptions. The governing equations of motion are addressed through the Ritz formulation, enabling an in-depth investigation of how variations in graphene origami layout, concentration, and fold geometry within the face sheets influence the structural performance. Additionally, the influence of various core Poisson's ratio configurations-negative (NPR), zero (ZPR), and positive (PPR)-along with the effects of core angle and thickness ratio, are systematically explored. The results highlight that core topology critically influences post-buckling resistance and non-linear vibrational characteristics. Furthermore, the integration of graphene origami significantly enhances stiffness and structural stability, demonstrating its potential for next-generation aerospace, automotive, and high-performance engineering applications. To the best of the authors’ knowledge, this is the first study to explore the coupled effects of auxetic re-entrant aluminum cores and graphene origami-enhanced facings on the non-linear thermal and dynamic behavior of sandwich beams. © 2025 Elsevier Ltd