In-line inspection of ferromagnetic gas or oil pipe lines having pipe wall defects is typically accomplished using magnetic flux leakage (MFL) technique. An efficient modelling and computational scheme for forward model, during the process of solving inverse problems in magnetostatic non-destructive evaluation using finite-element method is presented. The shape, size and place of defect are determined considering the nonlinearity of the pipe material using genetic algorithm as the optimisation technique. It is shown that the reduced model improves the FE computations significantly. The methodology for construction of defect shapes from particular MFL signals has been explained.

This paper presents a robust artificial time delay based attitude regulation control of a small spacecraft under the influence of parametric uncertainties, surrounding disturbances, and time-varying actuator faults. In the artificial time delay (ATD) approach, the input-output information of the previous time instant is utilized to estimate the uncertain dynamical parts. The proposed attitude controller is designed by integrating the time delay approach with a feedback control technique. Under the proposed composite control scheme, the system states are proved to be uniformly ultimately bounded (UUB) stable using the Lyapunov analysis. Moreover, the problem of unwinding in the quaternion representation, due to which the spacecraft consumes more time and energy, is also resolved under the proposed scheme. The performance of the proposed control methodology has been validated using numerical simulations. Furthermore, two different control schemes are also compared to illustrate the efficacy of the proposed strategy.

The active magnetic bearings (AMB) play an essential role in supporting the shaft of fast rotating machines and controlling the displacements in the rotors due to the deviation in the shaft. In this paper, an adaptive integral third-order sliding mode control (AITOSMC) is proposed. The controller suppresses the deviations in the rotor and rejects the system uncertainties and unknown disturbances present in the five DOF AMB system. The application of AITOSMC alleviates the problem of high-frequency switching called chattering, which would otherwise restrict the practical application of sliding mode control (SMC). Moreover, adaptive laws are also incorporated in the proposed approach for estimating the controller gains. Further, it also prevents the problem of overestimation and avoids the use of a priori assumption about the upper bound knowledge of total disturbance. The Lyapunov and homogeneity theories are exploited for the stability proof, which guarantees the finite-time convergence of closed-loop and output signals. The numerical analysis of the proposed strategy illustrates the effective performance. Furthermore, the comparative analysis with the existing control schemes demonstrates the efficacy of the proposed controller.

The re-entry phase of the reusable launch vehicle (RLV) is a challenging optimal control problem because of its high nonlinearity and numerical sensitivity. In this paper, a recently proposed metaheuristic optimization algorithm, Sine-Cosine Algorithm(SCA) is employed to solve the re-entry trajectory problem for space shuttle vehicle. A cost function which maximizes the cross range along with satisfying certain boundary conditions is selected for the problem. Control inputs are parameterized with defined ranges for the implementation of SCA to solve the optimal control problem. The results demonstrate the optimal trajectory. The results obtained show efficiency and applicability of SCA for solving the trajectory optimal control problem.