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In this paper, we generate optimal Runge-Kutta stability polynomials for several of ANSYS Fluent's finite volume spatial discretizations. From these stability polynomials we generate Butcher tableaus, and compare the accuracy and ...
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In this paper, we generate optimal Runge-Kutta stability polynomials for several of ANSYS Fluent's finite volume spatial discretizations. From these stability polynomials we generate Butcher tableaus, and compare the accuracy and efficiency of these new schemes to the existing classical temporal schemes currently being used. Theoretical analysis shows that these optimal schemes are expected to be significantly more efficient, allowing larger time step sizes to be used relative to the number of Runge-Kutta stages. These predictions are then verified in practice for several test cases including an isentropic vortex, Taylor-Green vortex, and a T106A turbine cascade. Significant performance improvements were observed for all of these cases, with negligible impact on solution accuracy. Importantly, these improvements are achieved with only minor modifications to the solver.
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This paper presents an effective and practical shape optimization strategy for turbine stages so as to minimize the adverse effects of three-dimensional flow features on the turbine performance. The optimization method combines a ...
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This paper presents an effective and practical shape optimization strategy for turbine stages so as to minimize the adverse effects of three-dimensional flow features on the turbine performance. The optimization method combines a multi-objective genetic algorithm (MOGA), with a Response Surface Approximation (RSA) of the Arti-ficial Neural Network (ANN) type. During the optimization process, the objective functions and constraints are approximated using ANN, which is trained and tested using a few three-dimensional CFD flow simulations that are obtained using the commercial software package Fluent. The optimization objectives include the maximization of the isentropic efficiency, minimization of streamwise vorticity and mini-mization of total pressure loss across the turbine stage while satisfying a number of constraints. They include fixing the inlet total pressure and temperature, the exit pressure, the axial chord and spacing, the inlet and exit flow angles, and the mass flow rate. The blade geometry is given by several two-dimensional blade sections at different radial locations that are joined by a stacking curve in the third direction. The stacking curve, which is the leading physical parameter that con-trols three-dimensional effects in a turbomachine, is parametrically represented using a quadratic rational Bezier curve (QRBC). The pa-rameters of this QRBC are related to the design parameters namely the blade lean, sweep and bow, which are used as the design variables.The described strategy was applied to the optimization of the E/TU3 turbine stage for single and multiple objectives; this optimization strategy proved to be successful, flexible and practical, and resulted in a 1.2% improvement in stage efficiency with as low as five design variables.
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Many state-based specification languages, including the Java Modeling Language (JML), contain at their core specification constructs familiar to most undergraduates: e.g., assertions, pre- and postconditions, and invariants. Unfor...
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Many state-based specification languages, including the Java Modeling Language (JML), contain at their core specification constructs familiar to most undergraduates: e.g., assertions, pre- and postconditions, and invariants. Unfortunately, these constructs are not sufficiently expressive to permit formal modular verification of programs written in modern object-oriented languages like Java. The necessary extra constructs for specifying an object-oriented module include (perhaps the less familiar) frame properties, datagroups, and ghost and model fields. These constructs help specifiers deal with potential problems related to, for example, unexpected side effects, aliasing, class invariants, inheritance, and lack of information hiding. This tutorial paper focuses on JML's realization of these constructs, explaining their meaning while illustrating how they can be used to address the stated problems.
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Recently, a novel time integrator referred to as Paired Explicit Runge-Kutta (P-ERK) schemes, has been proposed for the solution of locally-stiff systems of equations. This approach allows different Runge-Kutta schemes with differ...
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Recently, a novel time integrator referred to as Paired Explicit Runge-Kutta (P-ERK) schemes, has been proposed for the solution of locally-stiff systems of equations. This approach allows different Runge-Kutta schemes with different numbers of active stages to be assigned based on local stiffness criteria. In this paper, we develop P-ERK schemes for finite volume methods. Then, we verify that P-ERK schemes obtain their designed order of accuracy using an isentropic vortex case. We then evaluate performance of P-ERK schemes in a finite volume solver with benchmark simulations including laminar flow over a circular cylinder, turbulent flow over an SD7003 airfoil, and turbulent flow over a T106A turbine blade cascade. Results demonstrate that P-ERK schemes can significantly accelerate simulations and achieve speedup factors in excess of four when compared to a standard explicit temporal scheme, while maintaining accuracy with respect to reference data.
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The aviation industry is turning to novel aircraft concepts and systems to meet challenging environmental targets. New concepts such as hybrid and distributed electric propulsion add increasing complexity to aircraft system archit...
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The aviation industry is turning to novel aircraft concepts and systems to meet challenging environmental targets. New concepts such as hybrid and distributed electric propulsion add increasing complexity to aircraft system architectures. The systems architecting process must thus be modified to identify promising architectures early in the design process. Safety assessment plays a major role in the certification of aircraft systems and thus must be adapted to evaluate novel architectures in early design stages. At the same time, model-based systems engineering (MBSE) is used increasingly for system specification. The safety assessment process is following a similar trend, the so-called Model-Based Safety Assessment (MBSA), which is promising for complex systems architectures. This paper presents how a model-based specification can be used to conduct a Functional Hazard Analysis (FHA), a first step to integrating MBSE with the safety assessment process. A practical framework using the Capella tool is presented. An aircraft brake system example illustrates the effectiveness of the presented methodology using a variety of models and diagrams. Overall, the presented paper improves current MBSE and safety assessment practices for more effective development of future aircraft.
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Decision tables are a useful technique for implementing complex decision logic, and a concise communication device. Model merging is a process that can greatly benefit from the flexibility of control, rapidity of change, and under...
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Decision tables are a useful technique for implementing complex decision logic, and a concise communication device. Model merging is a process that can greatly benefit from the flexibility of control, rapidity of change, and understandability of purpose that tables engender. Heretofore, users have been cut off from the inner workings of merge tools. Among its many features, our model merging tool, Mirador, opens the process of merging to inspection and manipulation. The tool's support for user modification of the decision table rules that drive its conflict detection and resolution, as well as the possibility of adding customized table conditions and actions is the focus of this paper.
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Decision tables are a useful technique for implementing complex decision logic, and a concise communication device. Model merging is a process that can greatly benefit from the flexibility of control, rapidity of change, and under...
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Decision tables are a useful technique for implementing complex decision logic, and a concise communication device. Model merging is a process that can greatly benefit from the flexibility of control, rapidity of change, and understandability of purpose that tables engender. Heretofore, users have been cut off from the inner workings of merge tools. Among its many features, our model merging tool, Mirador, opens the process of merging to inspection and manipulation. The tool's support for user modification of the decision table rules that drive its conflict detection and resolution, as well as the possibility of adding customized table conditions and actions is the focus of this paper.
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