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.

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.

Distributed systems such as cables, beams, plates, etc., are widely used in many electro-mechanical devices. The efficiency of such devices largely depends on precise dynamics of the structural components, as in micro-electro-mechanical (MEMs) devices. Therefore, better sensing of the dynamics of such components and thereafter necessary actuation are the keys to increase precision of such devices. This work designs an optimal distributed actuator of a linear beam using its vibration modes. General boundary conditions are considered with a finite element frame work so that the transducer design is applicable for any vibrating beam. Piezoelectric composites are considered as actuators and the signal is considered proportional to the excited response of the targeted mode for optimization. Finally, the optimal shaped transducer is used to control an externally excited beam with cantilever boundary condition. The voltage inputs required to control shaped modal actuator is compared with a regular rectangular shaped piezoelectric actuator. Results are reported at the end.

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.

Flexible structures are continuum modeled as infinite degrees of freedom. Most of the time finite element models are made with large number of degrees-of-freedom to analyse flexible structures. Continuous monitoring, analysis and control of dynamics of flexible structures need simulation of large degrees of freedom in real time. This is computationally expensive and realtime control fails. This study focuses on the development of a reduced order framework for dynamics of flexible structures and use the reduced order model for controlling the structure. Essentially, in the proposed framework, full order state space obtained from finite element modeling of the flexible structure has been reduced to lower subspace using a reduced order algorithm keeping the dynamical characteristic intact. The transformation matrix for reduction has been calculated using system equivalent reduction expansion process (SEREP). Traditionally, full order dynamical system is being used to find the gain matrix to suppress the uncontrolled dynamics associated with the dynamical system. Here in this methodology, the reduced dimension of state space of the system is used for estimating the gain matrix using optimal linear quadratic regulator (LQR). The gain obtained through the reduced system is subsequently used as a feedback to the attached actuators which produce the required force to control the system. A numerical example of a flexible cantilever beam has been shown to investigate the effectiveness of the algorithm.

Workspace, the set of all possible positions reached by the end effector, must be large for a continuum robot for safe steerability. Magnetically actuated soft robots have high workspace due to their millimetre-scale size and large flexibility, enabling them to navigate constrained environments. When subjected to an external magnetic field, they undergo large deflections by interacting with magnetic particles. This work develops closed-form (assuming 2D planar) and numerical solutions to rotation and deflection for uniformly magnetised elastica at an angle using Cosserat rod theory. They are derived in terms of the elliptic function and shooting method, respectively, and are in good agreement with the experimental results provided in the literature. Deflection and rotation plots are presented for various input conditions. The analytical solutions show pitchfork bifurcation when the external field is antiparallel to the magnetic direction with a peak normalised half workspace of 0.103. In contrast, perturbed pitchfork bifurcation is observed for the other angles; increasing the workspace to 0.416 is not yet studied in the existing literature.

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.

Advent of low-powered, wireless and miniature sensors with semi-conductor revolution necessitated innovation in energy supply and solutions. One such innovation is using ambient energy to power sensors with little power requirement. This study analyses the potential of a bi-stable nonlinear harvester for possible broadband energy harvesting with sufficient power output. An inverted cantilever beam with tip mass that shows chaotic vibrations is analysed. In this paper, a time-delayed feedback control is used to stabilize this system into the unstable periodic orbits (UPOs) embedded inside chaotic attractor. Two situations are considered to compare; (a) the system dynamics without power harvesting mechanism and (b) with power harvesting feature. Focus is upon the capability of enhancing the efficiency of the harvester using feedback and finally effect of control parameters on the dynamics of the system is reported.

This study focusses on probabilistic modelling of the bladed disc system and numerical estimation of the distributions of the response quantities of the system. Stochastic finite element model of the system consisting of all the assemblies and the hub is developed and reported. The spatial inhomogeneity of mistuned structures is modelled as non-Gaussian random field. Experimentally, the system parameters can be measured at the specified locations of the bladed disk structure. In this analysis, a synthetic data is generated which represent this measured data set. Further, Nataf transformation is implemented to each component of the data set to get the polynomial chaos expansion framework of the system parameters. Since, the random field of the system parameter is approximated as correlated random variables, Spearman's rank correlation coefficient is used in this manuscript to obtain that correlation among the random parameters across the domain. The approximated probability density function obtained through the aforementioned methodology is compared with the target probability density function of the parameter using Kullback - Liebler (KL) entropy as a metric. Also, the same KL entropy is used as a metric to check the convergence of polynomial chaos terms in the expansion. Next, the proposed polynomial chaos method is integrated with commercial finite element software to quantify the propagation of randomness associated with system parameters into the response quantities. Subsequently, the statistical processing helps in estimating the probabilistic measure of the required response quantities. The results obtained through the conventional Monte Carlo (MC) simulations have been used as the benchmark to compare the response characteristics obtained through the proposed algorithm.