### Browsing by Author "Reddy, Batmanathan"

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- ItemOpen AccessIsogeometric Analysis: Fundamentals and details of implementation. From first steps to two-dimensional non-linear problems(2018) Burger, Heidi; Ismail, Ernesto; Reddy, BatmanathanIsogeometric analysis (IGA) is a computational analysis technique that can serve as an alternative to the traditional finite element method (FEM) in approximating solutions to differential equations. IGA is not necessarily more efficient that traditional FEM, but because of its nature, can naturally handle a greater variety of complex geometries. IGA is based on the use of NURBS (non-uniform rational B-splines), mathematical descriptions of geometry which are the standard of representing geometry in computer aided design (CAD) modeling software. IGA therefore links the CAD world to the world of analysis. Traditional FEM was developed before NURBS, in the 1950s and therefore developed quite separately. This project focuses on the fundamentals and implementation of IGA for problems, including one-dimensional, two-dimensional scalar, two-dimensional vector-valued and simple non-linear problems. For each new problem, the underlying mathematics is developed and the implementation is discussed in detail. One of the major contributions of this project is considered to be the detail in which the implementation of the Neumann boundary condition is described. There is none of this level of detail in any of the available literature. All problems solved are demonstrative and was written in a modular way that is easy to read and understand. Furthermore, how to extract NURBS data from CAD software is discussed, which would prove useful for future problems with more complex geometry. While the work done in this project is not considered novel, the thoroughness in which the project was approached is hoped to be useful for future projects. From this project, the work can be expanded to more complex geometries, multi-patch problems with the help of CAD programs or more complex non-linear problems.
- ItemOpen AccessMathematical and computational modelling of the dynamic behaviour of direct current plasma arcs(2010) Reddy, BatmanathanThe problem of direct-current plasma arc behaviour, interaction, and dynamics is considered in the context of metallurgical DC arc furnace applications. Particular attention is paid to the transient flow behaviour of arc systems. A mathematical formulation of the physics used to describe the arc system is presented, and includes the spatial and temporal evolution of fluid flow, heat transfer, and electromagnetism. Based on this formulation, a numerical model is developed using a finite difference approach on a regular cartesian grid in both two and three dimensions, with a special focus on robust stability, high resolution modelling, and high performance. A collection of results produced using the numerical model to study pilot plant-scale furnaces is then presented. These address a range of process and design variables and their effect on the numerical model's results. Where possible, the qualitative behaviour of the model is compared to available experimental data. A number of novel effects and phenomena are seen in the dynamic behaviour of the DC plasma arc model for both single and multiple arc systems, which may lead to improved understanding, control, and manipulation of such systems where they occur in industrial applications.
- ItemOpen AccessMicromechanical modelling of advanced hierarchical composites(2020) Griffiths, Emma; Reddy, Batmanathan; Bargmann, SwantjeNanoporous metals are uniquely interesting materials. Their high ductility and impressive strength in compression make them a favourable candidate for use in structural applications. However, these materials under-perform when tested in tension. This issue may be addressed by impregnating the nanoporous metal with a polymer. In this work the behaviour of a polymer impregnated nanoporous gold (NPG) composite is explored using the finite element method in three different scenarios: linear elasticity, fracture and electrically stimulated actuation. Using representative volume elements (RVEs), previously unexplored relationships between the macroscopic material response and its microstructure as well as interesting mechanisms and deformation strategies are explored. Firstly the homogenization and micromechanical response under compression of a gold/epoxy nanocomposite is investigated. Investigation into the stress-strain response within the material reveals a complex interaction between the constituents resulting in both compressive and tensile strains. With specific focus on the loading modes of the individual ligaments, significant axial and bending loading as well as an unexpectedly large amount of shear stress is seen. Following this the improved ductility and resistance to fracture of a gold/polymer nanocomposite compared to the pure NPG material is revealed using computational compact-tension tests. It is observed that the polymer stabilizes the gold thus preventing ductile fracture. Several toughening mechanisms are also revealed. Previously unexplored effects of increasing the volume fraction on the ductility and strength of the composite are also explored. The functionality of the gold/polymer nanocomposite as an actuator material is then investigated. A coupled chemo-electro-mechanical material model is adopted to model the electrically stimulated deformation. This is carried out in Abaqus using a novel staggered explicit-implicit solution scheme. Simulation of several RVEs with different gold volume fractions show that while the gold provides strength and support, increasing its volume fraction hinders both the ion transport speed and the total deformation of the nanocomposite. A complex interaction between the stress response and the gold volume fraction is also observed.
- ItemOpen AccessMultiscale modelling of sutures in a high-performing biological protective structure: the turtle shell(2022) Alheit, Benjamin; Reddy, Batmanathan; Bargmann, SwantjeMany natural protective structures, such as alligator armour, turtle shells, and the skulls of many animals including humans, contain networks of sutures; those are, soft tissue that bonds adjacent stiff plates typically made of bone. Such protective structures ought to withstand large loads associated with predator attacks. If one considers the optimization process of evolution and the ubiquity of suture networks in natural protective structures, it is reasonable to hypothesize that sutures improve the mechanical behaviour of protective structures during predator attacks. However, the effect of sutures in such loading scenarios is not well understood. We address this by using computational models of turtle shells where special attention is paid to the influence of the network of sutures. Additionally, we elucidate the structure-function relationship using parametric studies varying the suture geometry. Computational experiments are carried out at the suture scale to elucidate its mechanical behaviour and at the shell scale to elucidate the effect that sutures have on the shell. Among other insights, we show that: the compliance of the shell during small deformations can be increased by increasing the height of the interlocking bone protrusions and suture thickness; the bone plates interlock for sufficiently large deformations of sutures with sufficiently long protrusions; suture geometry can be used to tailor stress-wave propagation; and the presence of sutures can reduce the maximum strain energy density, a key indicator for a material failure, during a predator attack by 31 times. The work presented paves the way for the inclusion of sutures in biomimetic protective structures such as helmets and body armour. Computational solid mechanics aspects include multiscale modelling, model order reduction, and finite strain constitutive modelling aspects, such as viscoelasticity, hyperelasticity, and anisotropy.
- ItemOpen AccessOn the Evaluation of Common Design Metrics for the Optimization of Non-Axisymmetric Endwall Contours for a 1-stage Turbine Rotor(2018) Bergh, Jonathan; Reddy, Batmanathan; Snedden, GaelWith the continued economic and socio-political pressure on aircraft manufacturers to produce more profitable and environmentally-friendly aircraft, the drive towards increasingly more efficient aircraft engines remains of prime importance to aircraft engine manufacturers. While the majority of axial flow turbomachines use cylindrically shaped endwalls between the blades on the hub or shroud, non-axisymmetric endwall contouring is a reasonably recent technique which relaxes this constraint, and allows the geometry of the endwalls to depart from that of a plain cylinder. Although a number of studies have shown non-axisymmetric endwall contouring to be an effective mechanism for the reduction of secondary flows (and the losses associated with them), within the open literature there still remains a general lack of detailed information relating to the optimal design of these devices. Among some of the most important issues which remain unresolved, are uncertainties such as: “What is the best way to identify and thereafter quantify the strength of turbine secondary flows?”, and thereafter, as a natural progression from this, “Of the metrics which are currently found within the literature, which are best for use in the design of secondary loss mitigating endwall contours for a real turbine?”. Some of the reasons for the lack of information as described above, result from the undertaking of many of the investigations into the design of endwall contours by or on behalf of the major engine manufacturers, and therefore, a general inability or perhaps even unwillingness to divulge many of the specific details related to the methodologies and quantities used as a result of the commercial sensitivity of these investigations. In addition to this, as a result of the relatively large number and diverse nature of groups involved in non-axisymmetric endwall contouring research, within the literature which has been made available, there exists a wide variety of different test geometries as well as conditions which have been used, making a neutral determination of the most successful approach to endwall contouring considerably more difficult. This thesis documents the design and testing of a number of different non-axisymmetric endwall configurations intended to produce flow conditions optimized using a selection of the metrics commonly found in the literature, for the rotor of a low speed, research turbine, whose baseline as well as performance using contoured endwalls has been reported on previously, in order to establish which of these metrics is the most effective. As part of this process, a fully validated computational fluid dynamics model of the turbine downstream of the first nozzle was developed and incorporated into an automated non-axisymmetric end- wall design routine, capable of producing endwall contours optimized for various objective functions. Numerical testing showed that, in order to distinguish accurately between the various endwall configurations, relatively fine computational meshes were required and therefore, as a result of corresponding computational expense associated with these meshes, the implementation of a surrogate modelling procedure in which part of this computational cost is offset by mathematical modelling, was necessary. Altogether, a total of 8 endwall designs were produced - 6 using a single metric each as the basis of their objective functions (the ‘simple’ designs) and a further 2 so-called ‘compound’ designs. Of the simple designs, the best performing endwalls in terms of improvements to the rotor exit efficiency were the ηtt-, Cske- & βdev-based designs, which were based in turn on the rotor total-total efficiency (ηtt), coefficient of secondary kinetic energy (Cske) and flow deviation from design angle (βdev) respectively. All three of these designs were predicted to result in very similar changes to the secondary flow characteristics although the increasing bias towards flow correction was found to have an inverse correlation with the overall efficiencies predicted for each rotor. Of these designs, the numerical predictions for both the ηtt- & Cske-based designs (which were included in the experimental subset), were found to be validated, at both the rotor exit as well as downstream measurement planes. Further to this (with the exception of the Cp0,rel-based case), although the remainder of the simple designs (i.e. the SKEH & ηde-based designs) were also predicted to improve the overall rotor efficiency, either the form or the performance of these endwalls resulted in the final corresponding designs for these metrics being considered unsatisfactory. Finally, the two ‘compound’ metrics were both formulated to to include a term designed to target the secondary flow within the target blade row, as well as an additional term which was designed to promote improvement in the flow into the downstream blade row. While both designs produced using the compound design objective functions were predicted to improve both the conditions for the target blade row, as well as the flow quality at the exit of the blade row, flow separations at the exit of the contoured regions for both designs resulted in only partial validation of each design when tested experimentally. Finally, although both designs were once again predicted to perform very well at the ‘mixed-out’ measurement plane, these predictions were found to be only partially validated by the experiment.