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This paper addresses the problem of traditional sliding mode control design subject to the mismatched disturbance. Existing methods fail to provide an efficient and simple solution. To counteract the unmatched disturbance in the system, a new sliding mode control strategy based on a non-smooth integral sliding manifold is proposed. The proposed sliding manifold has two important features. First, it acts like a reduced order disturbance observer since it estimates the mismatched disturbances by itself without any requirement of an additional observer design. Secondly, the system always starts from the sliding surface, hence, there is no reaching phase dynamics. Thus, the system trajectory is insensitive towards the disturbance from the initial point. The proposed method is tested on a coupled tank system to demonstrate its effectiveness. Both the simulation and experimental results are provided. • A non-smooth integral sliding manifold is proposed with modified sliding mode control design. • Act as reduced order disturbance observer to estimate mismatched disturbances without any additional observer design. • System trajectory is insensitive towards the disturbance as there is no reaching phase dynamics. • Proposed work is tested on a coupled tank system to demonstrate its effectiveness. [ABSTRACT FROM AUTHOR]

A new approach for asymptotic stabilization of a general input-affine nonlinear system is presented. This relies upon the results of Matrosov's theorem to decompose the n th dimensional space. The construction of the [K,KL] sector for a nonlinear system is done with the suitable choice of control-Lyapunov function. The study of a nonlinear system is viewed from the perspective of comparison function for uniformity in solution. By means of designed sector, we design a switching controller which is well suited in the condition that shows its presence only outside of [K,KL] sector. Thus, it yields a stabilization scheme which saves the superfluous control termed as Lazy or Hands-Off control. Finally, we demonstrate the proposed approach which yields an asymptotically stable results for the simulation of an illustrative example. • The definition of [K,KL] sector with a K ∞ class function. • The equivalence definition of [K,KL] sector with the comparison of two K ∞ class functions. • The elementary [K,KL] sector based on the above equivalence definition. • The design specification of elementary [K,KL] sector. • A new approach to design [K,KL] sector. [ABSTRACT FROM AUTHOR]

Abstract This paper studies the formation of multiple mobile agents with double integrator dynamics and their target tracking. An algorithm consisting of an observer and a feedback control law of the nonsmooth type is proposed for the purpose of achieving finite-time formation and target tracking. The development is based on the Multi-input Multi-output (MIMO) super-twisting like approach aiming at finite time convergence without chattering. In addition to the formation; tracking, chattering prevention and robustness is also provided by the sliding mode mechanism which is demonstrated by simulations. Highlights • Formation of multiple mobile agents and their target tracking is studied. • An observer based feedback control algorithm for finite-time tracking is proposed. • The design is based on the Multi-input Multi-output super twisting like approach. • Tracking and chattering prevention of the robust system are shown by simulations. [ABSTRACT FROM AUTHOR]

This paper introduces a new approach to designing a disturbance observer called a modified extended state observer (ESO). The existing ESO technique ensures that the trajectories of estimation error dynamics globally asymptotically converge to zero in the absence of time varying disturbances. However, for perturbed systems, where time varying disturbances affect system behavior, these trajectories never reach zero but rather remain bounded around the origin within a constant value. Consequently, this discrepancy leads to challenges in accurately estimating state trajectories and discerning information about disturbances. This, in turn, complicates the precise estimation of state dynamics and disturbances and poses difficulties in designing control laws for stability analysis of the system. Unlike existing ESO methods, the distinguishing characteristic of this modified ESO is its capability to achieve global and asymptotic convergence of observation error in the presence of unknown bounded time varying disturbances. This unique property enables the exact estimation of state trajectories. Information about the bounded time varying disturbances is obtained and significantly attenuate more efficiently compared to existing ESO techniques. Based on the estimated disturbances, any classical controller can be designed for the system to achieve set-point tracking subject to time varying disturbances. To validate the performance of the proposed modified ESO, the model of a coupled-tank setup is simulated for the stabilization problem and its experimental setup is demonstrated for the tracking problem. For carrying out the experiment on a real-time hardware setup, an input of step change at every 60 s with water level variation of ± 2 cm from initial set value of 15 cm to achieve the set-point tracking of the water levels in the both the tanks along with good transient performance in the presence of time-varying external disturbances. • Development of modified extended state observer in presence of unknown disturbances. • The observation error converges to zero globally and asymptotically. • Achieves higher accuracy for disturbance estimation and complete elimination. • Proposed work is tested on a coupled tank system to demonstrate its effectiveness. [ABSTRACT FROM AUTHOR]

In the past mooring chain failure probabilities have been much higher than the design failure probabilities. The high failure rates are attributed to prolonged exposure to various degradation mechanisms in harsh offshore conditions. In addition to understanding failure mechanisms, researchers have stressed on reducing the risk of failures through regular and reliable inspections. Current inspection techniques involve both in-air and in-water inspections. However, current in-air inspections are time consuming and expensive, while in-water inspection techniques are not yet reliable. The present paper proposes a condition monitoring and strength estimation methodology based on three-dimensional (3D) scans of links. The study first identifies and estimates changes in simple geometrical features of chain links using finite element (FE) modeling for condition monitoring. The methodology has two stages: 3D general imaging (3D-GI) to identify degraded chain links using feature monitoring, followed by 3D detailed imaging (3D-DI) of the identified weak links. The weak links 3D point clouds could be further converted to solid FE models for residual strength estimation by employing a suitable material degradation model. The geometrical feature monitoring methodology is verified by 3D scans of an undeformed and a deformed studded link. • In-water three-dimensional (3D) imaging for condition assessment of mooring chains. • Identification of geometrical features which could be monitored during the underwater 3D inspections. • Scanning of chain links to generate 3D point clouds and conversion to solid Finite Element (FE) models for analysis. • Strength estimation of degraded chain links using FE models generated using 3D point cloud data. [ABSTRACT FROM AUTHOR]

Mooring chains in many offshore floating facilities have failed due to overloading under extreme environmental events. The ductile failure in chains due to overloading has not been addressed in past studies. Therefore, the present study aims to analyze the ductile failure in chain links using micromechanics and phenomenology based numerical models. The material damage model parameters are established using material stress-strain plots obtained from tensile tests on coupons, extracted from a R3 grade steel chain link. The validation of material degradation models is achieved by comparing results from numerical studies and monotonic loading tests on mooring chain links of 76 mm nominal diameter. The material models successfully capture the failure mode and strength of the chain links. • Non-linear behavior estimation of 76 mm stud chain specimens of R3 grade steel using monotonic loading tests. • Material strength tests on tensile coupon specimens extracted from R3 grade steel stud chain link. • Identification and calibration of micromechanics and phenomenology based material failure models. • Use of material damage models in conjunction with elastic-plastic material definition established using material tests. • ABAQUS/Explicit analysis is utilized for ductile fracture modeling in the stud chain links. [ABSTRACT FROM AUTHOR]