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Robust fault detection for uncertain discrete-time systems

JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 2002年第2期25卷 291-301页

作者： Wang, HB Lam, J Univ Hong Kong Hong Kong Hong Kong Peoples R China

The fault detection problem under structured uncertainties in the system matrices is considered. The sensitivity of robust fault detection is one of the important issues considered in the fault detection and isolation development. To enhance this characteristic, an unconstrained optimization approach is taken to design a robust fault detection observer. The approach aims at enhancing the fault detection robustness to uncertainties without sacrificing the fault detection sensitivity, which was seldom addressed before. Furthermore, other objectives related to the observer gain and the eigenstructure conditioning of the observer system are also taken into account. The gradient-based optimization approach is facilitated by the explicit gradient expressions derived. numerical simulation has also demonstrated the tradeoffs between different objectives as well as the effectiveness of the present methodology.

关键词： Fault Detection numerical Simulation Observability Gramian MATLAB Vertical Takeoff and Landing Mathematical Models Collective Pitch Control numerical algorithms Aerospace System

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Precise Determination of Reachable Domain for Spacecraft with Single Impulse

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JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 2014年第6期37卷 1767-1779页

作者： Wen, Changxuan Zhao, Yushan Shi, Peng Beihang Univ Sch Astronaut Beijing 100191 Peoples R China

Reachable domain refers to the collection of all positions accessible for a spacecraft under a given initial orbit and fuel constraint with free time of flight. In this study, the fuel constraint is conveniently expressed by a single available velocity impulse. To solve the envelope of the reachable domain, the radius of an accessible target position in a given direction is formulated. By evaluating the extreme values of the accessible radius in the given direction, two reachable boundaries and a reachable line segment are solved. The reachable domain in three-dimensional space is determined by rotating the direction and tracing all the reachable boundaries. The proposed method successfully solves the envelope of the reachable domain for the remaining two unresolved scenarios: the reachable domain with an arbitrary maneuver point and arbitrary impulse direction and the reachable domain with an arbitrary maneuver point and fixed impulse direction. This is the first time the accurate envelope of the reachable domain has been described in three-dimensional space. Acomparison of the results of the proposed numerical simulations with those of the existing method demonstrates the accuracy of the proposed method.

关键词： Maneuverable Spacecraft numerical Simulation Elliptical Orbit Perifocal Coordinate System Keplerian Orbit Earth Orbital Elements numerical algorithms Terminal Velocity Newton's Method

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Reconfiguration of Three-Craft Coulomb Formation Based on Patched-Conic-Section Trajectories

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JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 2016年第3期39卷 474-486页

作者： Xu, Yinan Wang, Shuquan Univ Michigan Dept Mech Engn Ann Arbor MI 48109 USA Chinese Acad Sci Technol & Engn Ctr Space Utilizat Key Lab Space Utilizat Beijing 100094 Peoples R China

This paper investigates the nonequilibrium fixed-shape three-craft Coulomb formation reconfiguration problem. Being aware that using the feedback-control approach might result in the chattering of the charges due to the nonequilibrium nature of the system dynamics, this paper proposes a trajectory planning approach to accomplish the reconfiguration. Entire maneuver trajectories are divided into multiple phases. During each phase, only two of the three craft are charged. In this way, the relative trajectory of the charged spacecraft during a certain phase is a conic section. Entire trajectories are composed of patched conics and/or straight lines. The procedures determining the three-phase maneuver strategy are developed, including a preadjusting phase and two transition phases. numerical simulations demonstrate the effectiveness of the algorithm and the elegance of the charge histories.

关键词： Feedback Control numerical Simulation Specific Angular Momentum Secant Method Earth Kepler's Equation Formation Flying Ion Engines numerical algorithms Three Degrees of Freedom

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Compensating for order variation in mesh refinement for direct transcription methods II: Computational experience

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JOURNAL OF COMPUTATIONAL AND APPLIED MATHEMATICS 2002年第2期143卷 237-261页

作者： Betts, JT Biehn, N Campbell, SL Huffman, WP N Carolina State Univ Coll Phys & Math Sci Dept Math Raleigh NC 27695 USA Boeing Co Math & Engn Anal Seattle WA 98124 USA N Carolina State Univ Operat Res Program Raleigh NC 27695 USA

The numerical theory for Implicit Runge Kutta methods shows that there can be order reduction when these methods are applied to either stiff or differential algebraic equations. A previous paper introduced a way to try and compensate for this order reduction in designing mesh refinement strategies. This paper presents the results from a number of computational studies on the effectiveness of this approach. In addition, we present a new test problem which can be used to examine the efficiency of codes developed for a particular class of applications. (C) 2002 Elsevier Science B.V. All rights reserved.

关键词： optimal control mesh refinement numerical algorithms

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Limit-cycle oscillation induced by nonlinear aerodynamic forces

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AIAA JOURNAL 2002年第11期40卷 2197-2205页

作者： Dotson, KW Baker, RL Sako, BH Aerosp Corp Struct Dynam Dept Los Angeles CA 90009 USA Aerosp Corp Fluid Mech Dept Los Angeles CA 90009 USA

The aerodynamic How state on launch vehicle payload fairings and aircraft wings can change abruptly during transonic flight if the angle of attack reaches a critical value. The nonlinear pressure variation associated with a flow-state change induces transient structural responses that may converge to a limit-cycle oscillation (LCO). In this steady state, the work conducted during the flow-state changes balances the energy dissipation from structural damping. Analysis of this transonic LCO, phenomenon is often conducted using a semi-empirical, unsteady pressure variation in which the levels for the flow states are determined from steady wind-tunnel test data. The presented theory addresses the condition in which the flow-state changes occur near a quasi-steady, nonzero angle of attack. The analysis for the resulting asymmetric forcing function complements the authors' existing derivations for a symmetric forcing function at zero angle of attack. Both the asymmetric and the symmetric analyses develop closed-form equations for the structural response frequency and amplitude. These expressions show that the solution space contains a subcritical Hopf bifurcation when the critical angle of attack equals the quasi-steady angle of attack. They also show that a saddle-node bifurcation, or fold, corresponds to the critical angle of attack beyond which LCO will not occur for a given quasi-steady angle of attack.

关键词： Aerodynamic Damping Critical Angle of Attack Structural Damping Launch Vehicles Structural Response Aircraft Wings Wind Tunnel Tests numerical algorithms Free Vibrations numerical Analysis

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The harmonic linearized Navier-Stokes equations for transition prediction in three-dimensional flows

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COMPUTERS & FLUIDS 2024年 273卷

作者： Paredes, Pedro Choudhari, Meelan Carpenter, Mark H. Li, Fei Natl Inst Aerosp Hampton VA 23666 USA NASA Langley Res Ctr Hampton VA 23681 USA

The conventional method to predict the onset of laminar -turbulent transition in convectively unstable boundary -layer flows is based on the logarithmic amplification ratio, the N -factor, of the linear instability waves. To calculate the N -factor, the flow variables are decomposed into a laminar basic state solution and the linear disturbances, which are assumed to be harmonic in time. The most commonly used linear stability analysis approaches include the locally parallel linear stability theory (LST) and the nonlocal, weakly nonparallel parabolized stability equations (PSE). However, these methods do not account for strong streamwise gradients that are encountered in several configurations of interest, such as those in the vicinity of roughness elements, steps, gaps, or corners. To compute the linear evolution of disturbances along such strongly nonparallel regions, the harmonic linearized Navier-Stokes equations (HLNSE) need to be solved. The discretization of the HLNSE for spanwise/azimuthally inhomogeneous laminar basic states yields a linear system of complex arithmetic with a leading dimension of the order of 107 to 108 even in relatively simple flows. A combined multithread and multiprocessor algorithm is implemented for the direct solution of such linear systems. Results for a supersonic boundary layer over a three-dimensional roughness patch show good agreement with experimental measurements when the evolution of the instability waves over the roughness patch is included via the HLNSE. Additionally, inflow -resolvent analysis based on the HLNSE for discreteroughness -induced disturbances in the nose tip of a blunt cone at Mach 6 demonstrates the importance of including the disturbance amplification along the near vicinity of the roughness element and separation region.

关键词： Boundary layer stability numerical algorithms

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Modeling of slip, twinning and transformation induced plastic deformation for TWIP steel based on crystal plasticity

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INTERNATIONAL JOURNAL OF PLASTICITY 2016年 76卷 186-212页

作者： Sun, C. Y. Guo, N. Fu, M. W. Wang, S. W. Univ Sci & Technol Beijing Sch Mech Engn Beijing 100083 Peoples R China Hong Kong Polytech Univ Dept Mech Engn Kowloon Hong Kong Peoples R China

One of the most critical issues in development of micromechanics models for TWIP steel is to establish the continuum constitutive model which can accurately represent and model the characteristic plastic deformation at macro level. However, the uncertainty in describing the evolution of state variables based on crystal plasticity theory poses a great challenge in handling the complex plastic deformation with different deformation mechanisms and their complicated interactions and interplays at microscopic scale and thus becomes a non-trivial issue. Many attempts to address this issue by coupling slip and twinning or slip and transformation have been proven to be efficient via comparing and corroborating the predicted texture evolution using crystal plasticity theory with experiment. An accurate constitutive model, however, needs to be established to articulate and model the interactions of slip, twinning and transformation, which have been observed in experiment. In this paper, a micromechanics model for modeling of slip, twinning and transformation induced plasticity of twinning-induced plasticity (TWIP) steel is proposed by using the crystal plasticity approach. The model serves as a feasible approach to reflecting the micro deformation mechanisms during the plastic deformation process of TWIP crystals. The phase transformation is introduced and represented by the rate-dependent constitutive model. The algorithms for realization of the developed model are implemented in ABAQUS/Standard platform using UMAT. Furthermore, different deformation mechanisms of the microscopic plastic deformation modes of TWIP steel are analyzed based on the proposed models. The simulation results by using the developed model reveals that both twinning and transformation have an obvious effect on hardening and transformation, which cause the decrease of stress of single crystal, and the sequence of transformation and twinning rotation can be determined according to the proposed model. (C)

关键词： Phase transformation Twinning Crystal plasticity Polycrystalline material numerical algorithms

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Computing the Homology of Semialgebraic Sets. II: General Formulas

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FOUNDATIONS OF COMPUTATIONAL MATHEMATICS 2021年第5期21卷 1279-1316页

作者： Buergisser, Peter Cucker, Felipe Tonelli-Cueto, Josue Tech Univ Berlin Inst Math Berlin Germany City Univ Hong Kong Dept Math Hong Kong Peoples R China Sorbonne Univ Inria Paris Paris France Sorbonne Univ IMJ PRG OURAGAN Team Paris France

We describe and analyze a numerical algorithm for computing the homology (Betti numbers and torsion coefficients) of semialgebraic sets given by Boolean formulas. The algorithm works in weak exponential time. This means that outside a subset of data having exponentially small measure, the cost of the algorithm is single exponential in the size of the data. This extends the work in Part I to arbitrary semialgebraic sets. All previous algorithms proposed for this problem have doubly exponential complexity.

关键词： numerical algorithms Homology groups Weak complexity Semialgebraic sets

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Accuracy of shock capturing in two spatial dimensions

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AIAA JOURNAL 1999年第9期37卷 1072-1079页

作者： Carpenter, MH Casper, JH NASA Langley Res Ctr Aerodynam & Acoust Methods Branch Hampton VA 23681 USA Old Dominion Univ Norfolk VA 23529 USA

An assessment of the accuracy of shock-capturing schemes is made for two-dimensional steady flow around a cylindrical projectile. Both a linear fourth-order method and a nonlinear third-order method are used in this study. This study shows, contrary to conventional wisdom, that captured two-dimensional shocks are asymptotically first order, regardless of the design accuracy of the numerical method. The practical implications of this finding are discussed in the context of the efficacy of high-order numerical methods for discontinuous flows.

关键词： Projectiles Freestream Conditions Rankine Hugoniot Relation Bow Shock Roe Approximate Riemann Solver Stagnation Point numerical algorithms Shock Capturing Method Cartesian Coordinate System Spectral Algorithm

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Large elastoplasticity under static megabar pressures: Formulation and application to compression of samples in diamond anvil cells

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INTERNATIONAL JOURNAL OF PLASTICITY 2016年 84卷 33-57页

作者： Feng, Biao Levitas, Valery I. Hemley, Russell J. Iowa State Univ Dept Aerosp Engn Ames IA 50011 USA Iowa State Univ Dept Aerosp Engn Dept Mech Engn Dept Mat Sci & Engn Ames IA 50011 USA Carnegie Inst Sci Geophys Lab Washington DC 20015 USA

In high pressure research, static megabar pressures are typically produced by compression of a thin sample by two diamonds in various types of diamond anvil cells. This process is accompanied by large plastic deformation (sample thickness is reduced by a factor of 30), and finite elastic deformation of a sample and even the diamond. A thermodynamically consistent system of equations for large elastic and plastic deformation of an isotropic material obeying nonlinear elasticity and pressure dependent yield condition is formulated. The Murnaghan elasticity law and pressure-dependent J(2) plasticity are utilized. The finite-strain third-order elasticity law for cubic crystals is utilized for diamond. A computational algorithm is presented with emphasis on the stress update procedure and derivation of the consistent tangent moduli. It is implemented as a user material subroutine in the finite element code ABAQUS. Material parameters for a rhenium sample, as an example, and a diamond are calibrated based on the experimental and atomistic simulation results in the literature. The evolution of the stress and strain tensor fields in the sample and diamond is studied up to a pressure of 300 GPa. Good correspondence between numerical and experimental pressure distributions at the diamond-sample contact surface is obtained. Because there is a significant scatter of the magnitude of reported third-order single-crystal elastic moduli for diamond, their effect on strains and stresses is studied in detail. With the smaller third-order elastic moduli;the phenomenon of cupping of the diamond-sample contact surface is reproduced, which plays an important role in increasing maximum pressures for a given anvil geometry. The results provide important insight into the mechanical response in diamond anvil cells, interpretation of materials properties under extreme conditions from heterogeneous fields, and optimum design of cells for reaching the maximum static pressure in a volume suffici

关键词： Elastic-plastic material Finite strain numerical algorithms Constitutive behaviors

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