Adaptive sliding mode control of chaotic dynamical systems with application to synchronization

We address the problem of control and synchronization of a class of uncertain chaotic systems. Our approach follows techniques of sliding mode control and adaptive estimation law. The adaptive algorithm is constructed based on the sliding mode control to ensure perfect tracking and synchronization in presence of system uncertainty and external disturbance. Stability of the closed-loop system is proved using Lyapunov stability theory. Our theoretical findings are supported by simulation results.     

Status of the TOUGH-FLAC simulator and recent applications related to coupled fluid flow and crustal deformations

This paper presents recent advancement in and applications of TOUGH-FLAC, a simulator for multiphase fluid flow and geomechanics. The TOUGH-FLAC simulator links the TOUGH family multiphase fluid and heat transport codes with the commercial FLAC^3D geomechanical simulator. The most significant new TOUGH-FLAC development in the past few years is a revised architecture, enabling a more rigorous and tight coupling procedure with improved computational efficiency. The applications presented in this paper are related to modeling of crustal deformations caused by deep underground fluid movements and pressure changes as a result of both industrial activities (the In Salah CO₂ Storage Project and the Geysers Geothermal Field) and natural events (the 1960s Matsushiro Earthquake Swarm). Finally, the paper provides some perspectives on the future of TOUGH-FLAC in light of its applicability to practical problems and the need for high-performance computing capabilities for field-scale problems, such as industrial-scale CO₂ storage and enhanced geothermal systems. It is concluded that despite some limitations to fully adapting a commercial code such as FLAC^3D for some specialized research and computational needs, TOUGH-FLAC is likely to remain a pragmatic simulation approach, with an increasing number of users in both academia and industry.     

Synthesis and characterisation of fluorescent pyrene‐end‐capped polylactide fibres

Fluorescent markers are critical for tracking the position and movement of molecules both in vivo and in vitro. Conventionally, synthetic dyes are non‐covalently added to polymers for fluorescent tracking, but often diffuse away. Here we demonstrate, for the first time, a facile method for the synthesis of fluorescent poly(lactic acid) nano‐/microfibres for biomedical applications using solution spin blowing. Pyrene‐end‐capped poly(l ‐lactide) (PLLA) derivatives were synthesised using the ring‐opening polymerisation of l ‐lactide and they were characterised using spectroscopic and thermal analyses. Submicrometre‐sized fluorescent fibres were produced from these PLLA derivatives using solution blow spinning techniques generating polymer blends and core–shell fibres. Such system could be further exploited to incorporate electrically conductive carbon allotropes via the pyrene aromaticity, producing fluorescent and electrically active fibres for in vitro monitoring and electrical stimulation. © 2018 Society of Chemical Industry     

Linked multicontinuum and crack tensor approach for modeling of coupled geomechanics, fluid flow and transport in fractured rock

In this paper, we present a linked multicontinuum and crack tensor approach for modeling of coupled geomechanics, fluid flow, and solute transport in fractured rock. We used the crack tensor approach to calculate effective block-scale properties, including anisotropic permeability and elastic tensors, as well as multicontinuum properties relevant to fracture-matrix interactions and matrix diffusion. In the modeling, we considered stress dependent properties, through stress-induced changes in fracture apertures, to update permeability and elastic tensors. We evaluated the effectiveness and accuracy of our multicon-tinuum approach by comparing our modeling results with that of three independent discrete fracture network (DFN) models. In two of the three alternative DFN models, solute transport was simulated by particle tracking, an approach very different from the standard solute transport used in our multicon-tinuum modeling. We compared the results for flow and solute transport through a 20 m × 20 m model domain of fractured rock, including detailed comparison of total flow rate, its distribution, and solute breakthrough curves. In our modeling, we divided the 20 m × 20 m model domain into regular blocks, or continuum elements. We selected a model discretization of 40 × 40 elements (having a side length of 0.5 m) that resulted in a fluid-flow rate equivalent to that of the DFN models. Our simulation results were in reasonably good agreement with the alternative DFN models, for both advective dominated transport (under high hydraulic gradient) and matrix-diffusion retarded transport (under low hydraulic gradient). However, we found pronounced numerical dispersion when using larger grid blocks, a problem that could be remediated by the use of a finer numerical grid resolution, while maintaining a larger grid for evaluation of equivalent properties, i.e. a property grid overlapping the numerical grid. Finally, we encountered some difficulties in using our approach when element sizes were so small that only one or a few fractures intersect an element-this is an area of possible improvement that will be pursued in future research.     

An efficient hybrid approach based on Harris Hawks optimization and imperialist competitive algorithm for structural optimization

In this paper, a new hybrid algorithm is introduced, combining two Harris Hawks Optimizer (HHO) and the Imperialist Competitive Algorithm (ICA) to achieve a better search strategy. HHO is a new population-based, nature-inspired optimization algorithm that mimics Harris Hawks cooperative behavior and chasing style in nature called surprise pounce HHO. It is a robust algorithm in exploitation, but has an unfavorable performance in exploring the search space, while ICA has a better performance in exploration; thus, combining these two algorithms produces an effective hybrid algorithm. The hybrid algorithm is called Imperialist Competitive Harris Hawks Optimization (ICHHO). The proposed hybrid algorithm's effectiveness is examined by comparing other nature-inspired techniques, 23 mathematical benchmark problems, and several well-known structural engineering problems. The results successfully indicate the proposed hybrid algorithm's competitive performance compared to HHO, ICA, and some other well-established algorithms.

     

Chemical sputtering of deuterated carbon surfaces at various surface temperatures

The chemical sputtering of deuterated amorphous carbon (a-C:D) surfaces irradiated by 1-50 eV deuterium atoms at surface temperatures between 300 and 1000 K was studied using classical molecular dynamics. A quasi-stationary state was reached by cumulative bombardment for each energy and temperature. Results were compared with available experimental data and previous modeling results and the applicability of molecular dynamics for thermally generated processes was discussed. An attempt is made to correct the absence of the thermally stimulated desorption/degassing of hydrogen from the MD simulations, which evolve at the longer time scales.     

Analysis of axisymmetric upsetting based on flow pattern observations

A flow-based model for upset forging of cylindrical billets is presented. Four deformation zones are recognized. The size of the elastic zone (Zone I) is determined from empirical equations. Kinematically admissible velocity field equations are obtained for the other three zones. These equations are in terms of two arbitrary parameters which are optimized based on flow pattern observations.From the numerical solution of the velocity and strain rate equations the deformed grid patterns and the localized strains are determined. In general, good agreement with FEM solutions is observed. The phenomenon of side-surface foldover is also predicted with sufficient accuracy by the present solution.     

In situ oxidation of zirconium binary alloys by environmental SEM and analysis by AFM, FIB, and TEM

Binary Zr-alloys containing 1%Fe and 1% Ni (large precipitates) and 1% Cr and 0.6% Nb (small precipitates), as well as a pure Zr sample were exposed in situ at 130 Pa water vapour pressure at 415 °C in an environmental SEM. The surface topography and composition of each sample was characterised before in situ experiments, during and after oxidation. After oxidation the surface was characterised by SEM and EDS, AFM and TEM combined with EDS. Focused ion beam was used to prepare cross sections of the metal-oxide interface and for the preparation of TEM thin foils.The oxidation behaviour of precipitates for these alloying elements can be characterised into two large families, those which show a rapid oxidation and those which induce a delayed oxidation in comparison with the Zr-matrix.At 415 °C after 1 h of oxidation for Zr1%Fe and Zr1%Ni, the formation of protrusions could be detected at the surface, being related to underlying SPP in the oxide. On Zr1%Cr and Zr0.6%Nb unoxidised SPPs were observed in the oxide, close to the metal-oxide interface. These SPPs were, however, oxidised close to the outer surface of the oxide. The surface roughness was increased for all materials after in situ oxidation, however, only for Zr1%Fe and Zr1%Ni protrusions appeared on the surface during oxidation. It was subsequently demonstrated that these latter correspond to the position of SPPs. For Zr1%Fe the surface roughness increased more than in the other materials and on these protrusions small iron oxide crystals have been observed at the surface. These observations confirm that Fe has a different behaviour compared to the other SPP forming elements, and it diffuses out to the free surface of the material.These alloying elements being the constituents of the commercial alloys (Fe and Cr for Zircaloy-4; Fe, Cr and Ni for Zircaloy-2 and Nb for all Nb-containing alloys), this study allows to separate their individual influence and can allow a subsequent comparison to the behaviour of those more complex alloys.     

An investigation of governance frameworks for public projects in Norway and the UK

This paper describes four case studies which formed a key part of an investigation into public investment project governance frameworks in Norway and the UK. The studies looked at how the embedded governance principles worked out in practice, how they affected PM, and how consistent their effects were with their aims. Conclusion is made about the actual effects of the frameworks, and various areas for improvement or further study are highlighted.     

Processing-microstructure relationships for Ti-6Al-2Sn-4Zr-2Mo-0.1Si

The detailed relationships between thermal-mechanical processing parameters and resulting microstructures for Ti-6Al-2Sn-4Zr-2Mo-0.1 Si (Ti-6242) have been established through compression testing and heat treatment. Beginning with either an equiaxed alpha or Widmanstätten alpha preform microstructure, isothermal compression tests were run at strain rates typical of isothermal forging (10^?3 to 10^?1 s^?1) and conventional forging (1 to 100 s^?1). Metallographic investigation of these test specimens in as-deformed and heat treated conditions was used to characterize deformation-induced microstructures and transformations. For the equiaxed alpha microstructure, it was shown that deformation, as well as post-deformation heat treatment, were more effective in promoting microstructures close to the expected equilibrium ones than heat treatment alone, a finding similar to that for other alloy systems. For the metastable Widmanstätten alpha microstructure, the deformation and heat treatment parameters that promote the development of an equilibrium, equiaxed alpha microstructure have been determined. For this microstructure, two separate temperature-strain rate regimes have been identified, and the resulting microstructures correlated with the measured flow stress behavior. For the low temperature regime, deformation is highly nonuniform, and the microstructural features are shown to be similar to those in pearlitic steels and other lamellar alloys. In the higher temperature regime, on the other hand, deformation is much more uniform. The results presented can be applied to select hot forging parameters for the control of final microstructure and properties in Ti-6242 and similarα/β titanium alloys.