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LINEARIZED EULER PREDICTIONS OF UNSTEADY AERODYNAMIC LOADS IN CASCADES (VOL 31, PG 540, 1993)

AIAA JOURNAL 1993年第5期31卷 970-970页

作者： HALL, KC CLARK, WS Duke University Durham North Carolina 27706

A linearized Euler solver for calculating unsteady flows in turbomachinery blade rows due to both incident gusts and vibratory blade motion is presented. Using the linearized Euler technique, one decomposes the flow into a mean (or steady) flow plus an unsteady, harmonically varying, small-disturbance flow. Linear variable coefficient equations describe the small-disturbance behavior of the flow and are solved using a pseudotime time-marching Lax-Wendroff scheme. For the blade-motion problem, a harmonically deforming computational grid that conforms to the motion of vibrating blades eliminates large error producing mean flow gradient terms that would otherwise appear in the unsteady flow tangency boundary condition. Also presented is a new, numerically exact, nonreflecting far-field boundary condition based on an eigenanalysis of the discretized equations. Computed flow solutions demonstrate the computational accuracy and efficiency of the present method. The solution of the linearized Euler equations requires one to two orders of magnitude less computer time than solution of the nonlinear Euler equations using traditional time-accurate time-marching techniques. Furthermore, it is shown that the deformable grid technique significantly improves the accuracy of the solution. © 1993 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.

关键词： Aerodynamic Damping Small Perturbation Flow Euler Equations Turbomachinery Compressor Cascade Perturbation Analysis Conservation of Mass numerical Integration numerical algorithms Specific Heat

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Iterative schemes for linear equations of the second kind and related inverse problems

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APPLIED numerical MATHEMATICS 2024年 200卷 110-123页

作者： Berenguer, M. I. Galan, Ruiz Univ Granada Dept Appl Math Granada Spain Univ Granada Inst Math IMAG ETS Ingn Edificac Granada Spain

This paper consists of two parts. The first one deals with the generation of an iterative algorithm to obtain an approximate solution of a linear equation of the second kind in a Banach space. This generation is based on a perturbed version of the geometric series theorem which, in particular, allows us to find a family of unisolvent linear Fredholm integral equations of the second kind, even when the associated linear operator has norm greater than or equal to 1. When we consider Fredholm equations of this type and linear Volterra integral equations of second kind, the numerical schemes obtained when appropriate Schauder bases are also introduced in the spaces where the equations operate, enable us to approximate their respective solutions iteratively. The second part of this work focuses on the design of a numerical method for solving an inverse problem associated with a linear equation of the second kind in a Banach space, a method which we apply to problems of parameter estimation related to the two classes of integral equations mentioned above. (c) 2023 The Author(s). Published by Elsevier B.V. on behalf of IMACS.

关键词： numerical algorithms Inverse problems Linear Volterra integral equation Linear Fredholm integral equation Schauder bases

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Nonsingular Sliding-Mode Control for Field-of-View Constrained Impact Time Guidance

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JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 2018年第5期41卷 1214-1222页

作者： Chen, Xiaotian Wang, Jinzhi Peking Univ State Key Lab Turbulence & Complex Syst Dept Mech & Engn Sci Coll Engn Beijing 100871 Peoples R China

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A FAST, TIME-ACCURATE, UNSTEADY FULL POTENTIAL SCHEME

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AIAA JOURNAL 1987年第2期25卷 230-238页

作者： SHANKAR, V IDE, H GORSKI, J UNIV CALIF LOS ANGELES DEPT MATHLOS ANGELESCA 90024

The unsteady form of the full potential equation is solved in conservation form by an implicit method based on approximate factorization. At each time level, internal Newton iterations are performed to achieve time accuracy and computational efficiency. A local time linearization procedure is introduced to provide a good initial guess for the Newton iteration. A flux biasing technique is applied to generate proper forms of the artificial viscosity to treat hyperbolic regions with shocks and sonic lines present. The wake is modeled by a cut behind the trailing edge across which the density is matched at any instant of time by solving the vorticity convection equation. The far field is modeled using the Riemann invariants to simulate nonreflecting boundary conditions. The resulting unsteady method performs well and, even at low reduced frequency levels of 0.1 or less, requires fewer than 100 time steps per cycle at transonic Mach numbers. © 1987 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.

关键词： Freestream Mach Number Trailing Edges Viscosity Implicit Methods Convection Vorticity Supersonic Flow Pitching Airfoil Lift Coefficient numerical algorithms

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Coupled porous porous plasticity Continuum damage mechanics approaches for modelling temperature driven ductile-to-brittle transition fracture in ferritic steels

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INTERNATIONAL JOURNAL OF PLASTICITY 2016年 77卷 246-261页

作者： Turtuk, I. C. Deliktas, B. Uludag Univ Dept Civil Engn TR-16059 Bursa Turkey

Following;(a) the observation that micro-void and micro-crack driven failure mechanisms co-exist in metallic alloys and (b) the two damage state variable definition given in Chaboche et al. (2006), two coupled porous plasticity and continuum damage mechanics approaches to assess temperature driven ductile-to-brittle transition fracture in ferritic steels have been developed. Based on hypo-elastic formulation of Gurson-Tvergaard-Needleman (GTN) thermoplasticity to account for ductile failure following void growth, continuum damage mechanics formalism have been coupled in order to account for micro-crack driven brittle fracture. Keeping GTN thermoplasticity as a basis for ductile fracture, Leckie-Hayhurst creep rupture criterion has been modified and proposed to account for brittle damage, thus cleavage, in the first model. The second approach, which is proposed following the motivation that plasticity exists in and below the lower transition region, replaces Leckie-Hayhurst model with plasticity driven damage evolution law of Lemaitre et al. (2000). Unlike commonly used cleavage models such as Ritchie et al. (1973) and Beremin (1983), both of the proposed models have been aimed to take into account blended effects of micro-voids and micro-cracks in order to capture energy dissipation and softening accompanying and prior to brittle fracture. numerical implementation has been done for ABAQUS/Explicit and uses staggered solution based on plastic flow-damage correction structure, while its validation has been performed modeling Small Punch Fracture Experiments for P91 ferritic steel, published by Turba et al. (2011). (C) 2015 Elsevier Ltd. All rights reserved.

关键词： Fracture mechanisms Finite strain Porous material numerical algorithms Small punch testing

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Predicting elastic anisotropy of dual-phase steels based on crystal mechanics and microstructure

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INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES 2019年 151卷 639-649页

作者： Cantara, Aaron M. Zecevic, Milovan Eghtesad, Adnan Poulin, Camille M. Knezevic, Marko Univ New Hampshire Dept Mech Engn 33 Acad WayKingsbury HallW119 Durham NH 03824 USA

This work utilizes mean-field self-consistent and full-field fast Fourier transform-based homogenizations to study the effective elastic behavior of several steels: three dual-phase (DP), DP 590, DP 980, and DP 1180, and one martensitic (MS), MS 1700. Crystallographic textures and phase fractions of these steels are characterized using electron microscopy along with electron-backscattered diffraction to initialize the models. A comprehensive set of Young's modulus and Poisson's ratio data, measured at the ambient temperature as a function of orientation with respect to the rolling direction for each steel sheet, is used to calibrate and validate the models. The calibration of the models enabled us to estimate the single crystal elastic constants for both the martensitic phase and ferrite, while calculating the orientation dependent effective properties. Half of the data was used in the calibration. Subsequent predictions of the orientation dependent effective elastic properties for the remaining data verified that the estimated single crystal properties are reliable. As the steels exhibit a different level of anisotropy in their effective behavior, good predictions allowed us to discuss the role of texture, grain structure, phase fraction and distribution on the effective properties. The results of this work represent a significant incentive to introduce elastic anisotropy in numerical tools for simulating metal forming processes of dual-phase steels, in particular those processes involving springback, using the texture informed crystal mechanics-based models to more accurately estimate the effective elastic properties required by such simulations.

关键词： Microstructures Elastic material Anisotropic material numerical algorithms Dual-phase steel

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Crack front waves

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JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS 1998年第3期46卷 467-487页

作者： Morrissey, JW Rice, JR Harvard Univ Div Engn & Appl Sci Cambridge MA 02138 USA Harvard Univ Dept Earth & Planetary Sci Cambridge MA 02138 USA

We present simulations of 3 D dynamic fracture which suggest that a persistent elastic wave is generated in response to a localized perturbation of a propagating crack front, e.g., by a local heterogeneity of critical fracture energy. The wave propagates along the moving crack front and spreads, relative to its origin point on the fractured surface, at a speed slightly below the Rayleigh speed. The simulations were done using the spectral elastodynamic methodology of Geubelle and Rice (1995). They model failure by a displacement-weakening cohesive model, which corresponds in the singular crack limit to crack growth at a critical fracture energy. Confirmation that crack front waves with properties like in our simulation do exist has been provided by Ramanathan and Fisher (1997). Through a derivation based on the linearized perturbation analysis of dynamic singular tensile crack growth by Willis and Movchan (1995), those authors found by numerical evaluation that a transfer function thereby introduced has a simple pole at a certain omega/k ratio, corresponding to a non-dispersive wave. Further, we show that as a consequence of these persistent waves, when a crack grows through a region of small random fluctuations in fracture energy, the variances of both the local propagation velocity and the deformed slope of the crack Front increase, according to linearized perturbation theory. in direct proportion to distance of growth into the randomly heterogeneous region. That rate of disordering is more rapid than the growth of the variances with the logarithm of distance established by Perrin and Rice (1994) for a model elastodynamic fracture theory based on a scalar wave equation. That scalar case, which shows slowly decaying (as t(-1/2)) rather than persistent crack front waves, is analyzed here too. (C) 1998 Elsevier Science Ltd. All rights reserved.

关键词： dynamic fracture crack mechanics stress waves numerical algorithms

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COMPUTATION OF STEADY AND UNSTEADY CONTROL SURFACE LOADS IN TRANSONIC FLOW

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AIAA JOURNAL 1991年第11期29卷 1906-1911页

作者： BHARADVAJ, BK Douglas Aircraft Company Long Beach California 90846

A computational procedure for the analysis of loads due to steady and oscillatory control surface deflections is presented. The numerical algorithm is based on a time accurate solution of the transonic full potential equation in a body-fitted coordinate system. Control surface deflection and motion are modeled using an equivalent body velocity that circumvents the need for generating time-dependent grids and interpolation between planes and discontinuity. Viscous effects, including mild separation, are modeled using an interactive inverse boundary layer and the transpiration velocity approach. numerical results are presented for a three-dimensional transport aircraft wing with supercritical sections, for control surfaces located at the trailing edge and the leading edge, for steady as well as oscillatory deflections. Results are compared with experimental data as well as with linear theory.

关键词： Subcritical Flow Boundary Layer Analysis Trailing Edges Control Surfaces numerical algorithms Transport Aircraft Freestream Mach Number High Aspect Ratio Viscosity Supercritical Wings

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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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Robust fault detection for uncertain discrete-time systems

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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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