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Mesh generation using unstructured computational meshes and elliptic partial differential equation smoothing

AIAA JOURNAL 2006年第6期44卷 1277-1286页

作者： Karman, SL Anderson, WK Sahasrabudhe, M Univ Tennessee Grad Sch Computat Engn Chattanooga TN 37403 USA

A novel approach for generating unstructured meshes using elliptic smoothing is presented. Like structured mesh-generation methods, the approach begins with the construction of a computational mesh. The computational mesh is used to solve elliptic partial differential equations that control, grid point distributions and improve mesh quality. Two types of elliptic partial differential equations are employed: modified linear-elastic theory and Winslow equations, with or without forcing functions. Results are included to illustrate the use of these methods for unstructured mesh generation, mesh untangling, and mesh movement and viscous mesh creation.

关键词： Unstructured Grid Differential Equations Poisson's Ratio Linear Elasticity Aspect Ratio Tetrahedral Element Statistical Analysis NASA Langley Research Center Structural Mechanics solution algorithm

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Tractable conflict risk accumulation in quadratic space for autonomous vehicles

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JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 2006年第1期29卷 39-48页

作者： Jones, T Univ Stellenbosch ZA-7602 Stellenbosch South Africa

Recent developments have shown that conflict avoidance may be cast as a probabilistic state-space problem. The probabilistic accumulation of risk because of exposure to a hazard over a period of time is an essential and often neglected and misunderstood aspect of the process of conflict risk calculation. How such risk accumulation may be accurately approximated in real time is demonstrated. The research reverts to theoretical basics and illustrates how risk accumulation for a one- and two-vehicle scenario is a first passage time problem. It is illustrated how exact quadratic state-order reduction may be combined with simple and accurate first passage time approximations. In this way, a tractable and accurate receding horizon solution is provided with the recognition of the time dependence of risk accumulation. The solution algorithm is implemented as a relatively straight-forward four-step discrete-time propagation and accumulation of risk. Small calculation errors are characterized to first order-second moment and always lead to a slight upper-bound solution, thereby improving safety. Simulation results indicate a high degree of risk calculation accuracy, calculable in real time.

关键词： solution algorithm Traffic Alert and Collision Avoidance System Cumulative Distribution Function Monte Carlo Simulation Linear Time Invariant Alerting System Pilot Federal Aviation Administration Air Traffic Management System Unscented Kalman Filter

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Target exploration for disconnected feasible regions in enterprise-driven multilevel product design

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AIAA JOURNAL 2006年第1期44卷 67-77页

作者： Kim, HM Kumar, DKD Chen, W Papalambros, PY Univ Illinois Dept Gen Engn Urbana IL 61801 USA Northwestern Univ Dept Mech Engn Evanston IL 60208 USA Univ Michigan Dept Mech Engn Ann Arbor MI 48109 USA

Enterprise-level business decisions are linked with engineering product decisions by integrating enterprise utility optimization and engineering design optimization under a hierarchical, multilevel, decision-based design framework. The enterprise problem sets attribute targets, that is, specifications, for engineering product development, which then optimizes product performance within the feasible design space to match the targets with minimum deviations. When the feasible domain imposed by engineering product development is disconnected in the space of attribute targets, an engineering design with the minimum deviation from the targets may not correspond to the design with the maximum utility value, even though the design is a converged solution from the multilevel optimization. To address this issue, a new algorithm is developed, which systematically explores the target space to lead the engineering product development to a feasible and optimal design in the enterprise context. Analytical examples and an automotive suspension design case study are presented to demonstrate the effectiveness of the proposed methodology.

关键词： Suspension Design Decision Based Design Enterprise Level Business Decisions MDO Sequential Quadratic Programming solution algorithm Nonlinear Programming Manufacturing Cost Search algorithm Production Planning

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Parallel overset-grid Euler solution of generic wing pylon and finned store

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JOURNAL OF AIRCRAFT 2005年第5期42卷 1337-1339页

作者： Tarhan, E Kavsaoglu, MS Turkish Aircraft Ind Inc TUSAS Technol Dev Dept TR-06520 Ankara Turkey Istanbul Tech Univ Dept Aeronaut Engn TR-34469 Istanbul Turkey

A three-dimensional finite differencing scheme, multiblock structured Euler and thin-layer Navier-Stokes solver was modified to enhance overset grid capability and to run in a parallel-computing environment. A wing-store configuration and Eglin WPFS configuration were employed as the test cases for the validation purposes. Numerical solutions were carried out at two different platforms. The magnitude of the expansion was overpredicted in the downstream around the pylon. The comparison of the pressure distribution on the store showed soome discrepancies when compared with the experimental data in the regions aft of the store close to the pylon and wing.

关键词： Message Passing Interface Pressure Coefficient Search algorithm Angle of Attack Parallel Computing Environment Navier Stokes Equations Freestream Mach Number solution algorithm Wind Tunnel Tests Pitching Airfoil

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Estimation of a spacecraft's attitude dynamics parameters by using flight data

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JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 2005年第4期28卷 594-603页

作者： Psiaki, ML Cornell Univ Sibley Sch Mech & Aerosp Engn Ithaca NY 14853 USA

An algorithm that uses flight data to estimate the parameters in an attitude dynamics model of a spacecraft has been developed. The new algorithm's estimates can enhance the fidelity of Enter equation models that are used to implement attitude determination and control functions. The algorithm's estimation equation is an integrated version of Euler's equation expressed in inertial coordinates. It uses three-axis attitude data and three-axis rate-gyro data to yield a set of linear equations in the unknown dynamics parameters, which include moments and products of inertia and scale factors, alignments, and biases for all reaction wheels and magnetic torque rods. The estimation problem statement includes the statistics of unmodeled torques and sensor errors, and it incorporates a scalar quadratic constraint to overcome the unobservability of the parameters' overall scaling. The sensor errors enter the model equation in a multiplicative fashion, which yields a total least-squares problem. The solution algorithm employs a guarded Newton iteration and recursive factorizations that deal efficiently with the problem's dynamic structure. The algorithm has been applied to the Wilkinson Microwave Anisotropy Probe spacecraft, and the resulting parameter estimates reduce torque modeling errors by a factor of 5-7.

关键词： Spacecraft Attitude Flight Data Control Moment Gyros Euler Equations solution algorithm Sensors Wilkinson Microwave Anisotropy Probe Singular Value Decomposition Numerical Integration Attitude Determination and Control System

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Mathematical modeling of the stress-strain state in rock and artificial masses during slice chamber mining of underpit reserves in the "Internatsionalnaya" kimberlite pipe

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JOURNAL OF MINING SCIENCE 2005年第3期41卷 215-224页

作者： Konstantinova, SA Chernopazov, SA Ural Sci Res Perm Russia Planning Inst Halurgy Perm Russia

The statement and solution algorithm are proposed for the problem on the stress-strain state of a kimberlite body, filling massif, and enclosing rock during slice chamber mining with filling. The equations of nonlinea... 详细信息

关键词： stress-strain state filling model hereditary viscoelasticity solution algorithm

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Finite element-based boundary treatment in the hybrid particle method

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AIAA JOURNAL 2005年第7期43卷 1626-1628页

作者： Huang, H Saigal, S Dyka, CT Univ S Florida Tampa FL 33620 USA USN Ctr Surface Warfare Dahlgren VA 22448 USA

The treatment based on the finite element method (FEM) in which the motion points of the hybrid particle method (HPM) that lie on natural boundaries is presented. The HPM uses as its basis the differential form of equations for the conservation of momentum, mass, and energy. The formulation employs the motion points (mps) and the stress points (sps) to facilitate computation. The resulting approach considers boundary motion points as finite element nodes, while the neighboring stress points are considered as the integration points of an explicit finite element method (FEM) formulation.

关键词： Shape Functions Specific Volume Conservation Equations Elastic Modulus Plane Strain Smoothed Particle Hydrodynamics Predictor Corrector Method Conservation of Mass solution algorithm Work Hardening

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A modular mixed-integer non-linear programming algorithm for synthesis of chemical processes

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CANADIAN JOURNAL OF CHEMICAL ENGINEERING 2004年第5期82卷 1029-1036页

作者： Li, HH Qian, Y Zheng, SQ Cheng, HN S China Univ Technol Sch Chem Engn Guangzhou 510640 Peoples R China Qingdao Univ Sci & Technol Qingdao 266042 Peoples R China

A modular approach to the formulation and a solution of mixed-integer non-linear programming (MINLP) problems are presented, which reduce the size of MINLP and the computational expenses effectively. The method decomposes the synthesis task into three hierarchical levels-the superstructure, the structure, and the modules, with the layer of modules being the most critical to the problem solution. The strategy has been implemented in a simulation environment in which the variables of interest are defined as implicit functions of the optimization variables. The implicit relationships are handled using a data-oriented process simulation technique (DOPS) that significantly simplify the simulation. The method has been effectively applied to two case studies, one from literature for the synthesis of hydrodesalkylation, and another from industrial process manufacturing methylene diphenylene diisocyanates.

关键词： process synthesis modular simulator environment MINLP solution algorithm

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Compact methodology for computing limit-cycle oscillations in aeroelasticity

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JOURNAL OF AIRCRAFT 2003年第5期40卷 955-963页

作者： Epureanu, BI Dowell, EH Univ Michigan Dept Mech Engn Ann Arbor MI 48109 USA Duke Univ Dept Mech Engn & Mat Sci Durham NC 27708 USA

A technique for computing limit-cycle oscillations of aeroelastic systems is presented. This technique can be used also for constructing and identifying reduced-order models that characterize accurately limit-cycle oscillations. The models presented use a spatial model reduction combined with a nonlinear identification technique. The finite difference in time method, a methodology similar to a finite element in time, is discussed. The specific novel aspects of the proposed method are noted. Numerical examples analyzing the dynamics of a panel forced by a buffeting aerodynamic load demonstrate the performance of the proposed methods.

关键词： Nonlinear Aeroelastic Systems Computing Aerodynamic Force Frequency Domain Mathematical Models Harmonic Balance solution algorithm Newton Raphson Method Nonlinear Dynamics Benard Convection

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Thrust generation caused by flapping airfoils in a biplane configuration

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JOURNAL OF AIRCRAFT 2003年第3期40卷 509-515页

作者： Tuncer, IH Kaya, M Middle E Tech Univ Dept Aerosp Engn TR-06531 Ankara Turkey

Unsteady, viscous flows over flapping airfoils in a biplane configuration are computed on moving overset grids. The overset grid solutions are obtained in parallel in a distributed memory environment. Unsteady flowfields are described by particle traces: Time-averaged thrust values are obtained from the integration of the unsteady drag coefficient. It is shown that airfoils in a biplane configuration and oscillating in a combined pitch and plunge motion with a proper phase shift between them produce 20-40% more thrust than a single flapping airfoil. Turbulence in the flow further augments the thrust generation. For a maximum thrust at a given flapping frequency, an optimization of the flapping motion parameters is needed.

关键词： Freestream Velocity Biplane Flapping Airfoil Vortices Flapping Wing solution algorithm Computer Cluster Spalart Allmaras Turbulence Model Propulsion Technology Aerodynamic Performance

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