Shaikh Faruque Ali

In the recent past, bistable laminates have been widely studied for their potential in wing morphing applications. The existence of multiple stable states makes them extremely viable as structural elements. However, for successful deployment, these laminates must be integrated into a larger mechanism. For integration, the bistable laminates are required to be clamped to a larger structure without the loss of bistability. In this work, an attempt has been made to understand the effect of integration (i.e., using different structural constraints and clamping) on the bistability and the snapthrough performance of a special class of hybrid bistable symmetric laminates (HBSLs). The structural analysis has been carried out using FEA software ABAQUS. Subsequently, a conceptual design of a morphing wing is proposed based on the insights gained from the numerical analysis that uses two HBSLs as skin with a corrugated core. Finally, using the analysis guidelines, two HBSL skins and a circular corrugated core are manufactured and integrated to show the possibility of using such bistable laminates as skin.

Nano-piezoelectric energy harvesters, due to their ability to convert mechanical vibrations to electrical current, are apt candidates for self-powered NEMs devices. Further, these are strain based electrical potential generators and can be used in tactile devices for accurate position sensing. ZnO, due to its piezoelectric properties and semiconducting nature is the ideal candidate for such applications. This paper proposes an analytical model to explain the potentials generated due to ZnO nano-films on being subjected to different forms of static loading. The model also incorporates the effect of different boundary conditions imposed on the nano-film. A perturbation theory based approach has been used to generate the analytical model. Initially, the strains are calculated ignoring the piezoelectric effect. Later, the electromechanical coupling is taken into consideration and the potentials have been calculated as a second order effect. The finite element simulation results agree with the theory to an accuracy of 5%. The profiles for piezoelectric potential distribution agree also well with the simulations. These piezoelectric potential profiles can also be used in smart materials for obtaining the required deformation in a specimen by applying a similar electrical potential across it.

The traditional [0/90]T laminate has two stable equilibrium shapes, and it is possible to go from one shape to the other by means of an external force. In the past, researchers have attempted to obtain the snap-through between the two equilibrium states using smart actuators like shape memory alloy (SMA) wires and macro-fiber composite (MFC) patches. The integration of these actuators adds several complications. Moreover these smart actuators are generally attached to the surface of the laminate hence influencing the structural performance substantially. Recently, non contact magnetic actuation was experimentally demonstrated to be a viable method of reversible snap-through. A non-contact actuation using magnetic fields provides an elegant means of achieving reversible snapping without affecting the bistability characteristics of the laminate. In this work, a numerical model has been developed to aid the design of non-contact systems comprising of a ferromagnetic material actuated by a solenoid. The developed model uses a Rayleigh-Ritz based potential minimization to capture the magnetic snap-through of a hybrid [Fe/0/90/Fe]T laminate. The model accurately captures the bistability of the multi-sectioned hybrid layup and can be used for the design of coils to provide the necessary actuation currents.

The current aircraft industry, specially unmanned aerial vehicles, is shifting from fixed wing vehicles to morphed wing. Morphing wings can create smoother aerodynamic surfaces, making an aircraft more agile and efficient than an aircraft that flies with many discrete moving surfaces. In present study, a double corrugated variable camber configuration of morphing wing with trailing edge morphing sections are proposed. The two configurations available from literature; one Fish Bone Active camber concept and other is variable camber morphing wing composed of single corrugated structure is considered for comparison of structural and aerodynamic analysis. The structural analysis of all prototype models is done using finite element analysis with actuation mechanism. Aerodynamic analysis is done using two methods; one analytical approach based on thin airfoil theory, and the other one is numerically using XFOIL, which couples a potential-flow panel method with viscous boundary-layer solver. A comparison is done on the basis of stress and deformation developed in various parts of the models. The results show that the double corrugated variable camber morphing configuration can take more structural load without harmful deformation. The aerodynamic analysis also shows that the aerodynamic efficiency of double corrugated variable camber morphing configuration is higher compared to other configurations.

In this article two numerical approaches for the shape prediction of a composite wing panel under the combined actuation of a Shape memory alloy (SMA) wire and a Macro fiber composite (MFC) bimorph has been developed. The first approach is a Euler-Bernouilli beam theory based linear finite element iterative scheme and the second approach is a Timoshenko beam theory based nonlinear finite element iterative scheme that takes into account the von Karman strains. The force due to the SMA wire is modeled as a follower force. It is shown that both the techniques developed are capable taking into account this non conservative follower force, while accounting for any additional arbitrary loading. The numerical schemes developed in this paper are validated using the existing techniques while elucidating the lacuna in the existing methods.

Camber morphing is an effective way to control the lift generated in any airfoil and potentially improve airfoil efficiency (lift-drag ratio). This can be especially useful for fixed wing UAVs undergoing different flying manoeuvres and flight phases. This work investigates the aerodynamic characteristics of NACA0012 airfoil morphed by the Single Corrugated Variable Camber (SCVC) morphing and Double Corrugated Variable Camber (DCVC) morphing approach. The airfoil is reconstructed from the camber line using a Radial Basis Function (RBF) based interpolation method (J. H. S. Fincham and M. I. Friswell, “Aerodynamic optimisation of a camber morphing aerofoil,” Aerosp. Sci. Technol., 2015). The aerodynamic analysis is done by employing two different finite volume solvers: OpenFOAM and ANSYS-Fluent, and a panel method code (XFoil). Results reveal that the aerodynamic coefficients predicted by the two finite-volume solvers using a fully turbulent flow assumption are similar but differ from those predicted by XFoil. The aerodynamic performance of morphed airfoils are nearly equal or lower than that of the baseline airfoil at lower values of coefficient of lift whilst at large values of the morphed airfoils display superior aerodynamic performance. At identical morphing angles, the aerodynamic characteristics of SCVC and DCVC airfoils are almost identical. Finally, it is observed for a fixed angle of attack, that an optimum morphing angle exists for which the aerodynamic efficiency becomes maximum.

This manuscript deals with the creation and stabilization of limit cycles in the Lorenz attractor with the help of orbit closure technique. Chaos control techniques such as the OGY and OPF techniques apply small perturbations to a system parameter to stabilize an unstable periodic orbit present in a chaotic attractor. But it may happen that the system parameters may not be available for control. For example, in structural systems, it is difficult to alter their geometry and material properties in real-time, so as to suppress chaos. In such cases, use of state feedback control will provide ease of implementation. The orbit closure technique is a novel method of controlling chaos wherein a finite time control effort is applied to the system states, once per period, to bring back the chaotic trajectory to a desired periodic orbit so as to stabilize it. In this manuscript, the orbit closure technique is applied to create and stabilize limit cycles of different time periods in the Lorenz attractor. The control effort required for closure of the orbits is provided through feedback linearization. As a pilot study, the efficacy of the proposed technique is demonstrated through numerical simulations in this manuscript. Further, the influence of the control gain on the shape and time period of the stabilized orbit is studied and reported.