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AIAA Science and Technology Forum and Exposition (AIAA SciTech)

作者： Cheung, R. C. M. Rezgui, D. Cooper, J. E. Wilson, T. Univ Bristol Dept Aerosp Engn Bristol BS8 1TH Avon England Univ Bristol Dept Aerosp Engn Aerosp Engn Bristol BS8 1TH Avon England Airbus Operat Ltd Loads & Aeroelast Flight Phys Dept Bristol BS34 7PA Avon England

ISBN: (数字)9781624105951

ISBN: (纸本)9781624105951

High aspect ratio wings have been the focus of recent aircraft designs for improving fuel efficiency through induced drag reduction. The lengthened wingspan derived from these designs have led to the introduction of folding wingtips in order to meet airport gate width requirements. Previous numerical and experimental studies have demonstrated that folding wingtips can also provide a gust load alleviation benefit, when the folding wingtips are able to rotate freely about the hinge during the gust encounter. This work examines the dynamic characteristics and behavior of the folding wingtip, and the overall wing in such a configuration. A series of wind tunnel tests was conducted using a specially designed high aspect ratio wing model to establish its modal characteristics through application of a stepped-sine frequency sweep, performed using a gust generator as well as a secondary aerodynamic surface incorporated into the wingtip as the excitation source. In addition, a pseudo-random gust sequence was used as a faster test method through broadband excitation, which yielded results that were in excellent agreement with the stepped-sine methods.

关键词： High Aspect Ratio Low Speed Wind Tunnel Aerodynamic Force Aircraft Design Fuel Efficiency Angle of Attack Accelerometer eigensystem realization algorithm Structural Weight Wing Root

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Two effective methods for impedance estimation in distance relays based on the DC offset removal

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ELECTRIC POWER SYSTEMS RESEARCH 2021年 194卷 107102-107102页

作者： Zamora-Mendez, Alejandro Sotelo-Castanon, Julian Paternina, Mario R. Arrieta Buendia, Paola Torres, Cristian Toledo-Santos, Carlos Velasco, Victor Zelaya-, Francisco Mejia-Ruiz, Gabriel E. Michoacan State Univ Elect Engn Fac Morelia 58030 Michoacan Mexico Univ Guadalajara Mech & Elect Engn Fac Guadalajara 44430 Jalisco Mexico Natl Autonomous Univ Mexico UNAM Mexico City 04510 DF Mexico Ind Univ Santander UIS Bucaramanga 680001 Colombia Univ Tennessee Knoxville TN USA

This paper introduces the eigensystem realization (ER)-based identification algorithm and the Z-domain method (ZDM) to improve the impedance estimation of transmission lines under fault conditions, which is achieved by removing the exponential decaying DC offset from current signals in distance relays. Both methods effectively work employing a one-cycle rectangular window;specifically, the Z-domain method works in less than a fifth of one-cycle window, ensuring timely, accurate, and prompt estimates. To confirm the effectiveness and performance of the proposed algorithms, they are evaluated under steady-state and dynamic conditions by using timedomain simulations performed in PSCAD (c) and DIgSILENT (c) PowerFactory. They also are compared with the wellknown discrete Fourier transform (DFT). The attained results indicate that both the ER-based and Z-domain methods can become a powerful tool to reduce the adverse influence of exponentially decaying DC offsets in distance relays.

关键词： eigensystem realization algorithm Z-domain Phasor estimation Distance relay Impedance estimation DC offset

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The Sensitivity of Leading-Edge Momentum Injection Response to Instantaneous Flow State for an Airfoil in Deep Stall

The Sensitivity of Leading-Edge Momentum Injection Response ...

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AIAA Science and Technology Forum and Exposition (AIAA SciTech)

作者： Asztalos, Katherine J. Dawson, Scott T. M. Williams, David R. IIT MMAE Dept Chicago IL 60616 USA

ISBN: (数字)9781624105951

ISBN: (纸本)9781624105951

In this work, we perform direct numerical simulations of momentum injection near the leading edge of a NACA0009 airfoil at an angle of attack of alpha = 15 degrees. It is found that the lift response is highly dependent upon the instantaneous state of the wake at the time of actuation, which is characterized by the phase of the vortex-shedding limit cycle present in the unactuated system. In particular, we find that actuating at a phase of the limit cycle corresponding to maximum lift gives the largest maximum in transient lift response, which occurs a full vortex-shedding cycle after actuation. Actuating near the lift minimum gives a smaller initial transient lift enhancement, and can lead to a significant reduction in the amplitude of the limit cycle, which persists for around 15 convective time units. As well as characterizing this phase-dependency, we develop a reduced-order model that is able to capture this behavior. This is achieved by applying dynamic mode decomposition to a concatenation of velocity and lift measurements from several training datasets. The resulting models are able to accurately capture the dynamics of the training datasets, and are also able to capture some of the dynamics for actuation at phases not included in the training data.

关键词： Leading Edges Airfoil Strouhal Number Aerodynamic Performance Direct Numerical Simulation Vorticity Laminar Separation Bubble Separated Flows eigensystem realization algorithm Singular Value Decomposition

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Modal identification for superstructure using virtual impulse response

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ADVANCES IN STRUCTURAL ENGINEERING 2019年第16期22卷 3503-3511页

作者： Qu, Chun-Xu Yi, Ting-Hua Li, Hong-Nan Dalian Univ Technol Sch Civil Engn Dalian 116023 Peoples R China Dalian Univ Technol State Key Lab Struct Anal Ind Equipment Dalian Peoples R China

In civil engineering, structural modes are identified with the assumption of stationary white noise, which cannot be satisfied in practical engineering. This article proposes a new method, which contains the virtual impulse response and eigensystem realization algorithm. The formulation of virtual impulse response is derived from the inverse Fourier transform of the ratio of the cross-power to auto-power spectral density functions of the measurement responses, which is based on the concept of frequency response function. During the formulation derivation, a single point excitation is only considered. Frequency response function would not change with different excitations and responses, which means that the excitation cannot influence frequency response function. The impulse response is pointed out to only represent the behavior of superstructure. After obtaining impulse responses, eigensystem realization algorithm is then performed to identify the modes of superstructure. The proposed method is validated by a numerical example. The results show that virtual impulse response can have much better free decayed behavior than natural excitation technique and identify very precise modal parameters for superstructure.

关键词： eigensystem realization algorithm frequency response function modal identification superstructure virtual impulse response

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Modal parameters estimation of an electrical submersible pump installed in a test well using numerical and experimental analysis

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OCEAN ENGINEERING 2019年 176卷 1-7页

作者： Castillo, M. A. Gutierrez, R. H. R. Monteiro, U. A. Minette, R. S. Vaz, L. A. Fed Univ Rio de Janeiro UFRJ Ocean Engn Program PENO Ctr Tecnol Bloco 1-108Cidade Univ BR-20945970 Rio De Janeiro RJ Brazil Petrobras Res & Dev Ctr CENPES PETROBRAS Av Horacio Macedo950Cidade Univ BR-21941915 Rio De Janeiro RJ Brazil

Modal parameters of an Electrical Submersible Pump (ESP) installed in a test well were numerically and experimentally identified. The numerical model was developed using the finite element method. All the masses and stiffness elements necessary to evaluate the lateral vibration of the equipment were considered, as well as the hydrodynamic added mass effect. In the experimental test, an impact hammer was used for exciting the ESP structure near the wellhead, in the production pipe, and not directly at equipment frame. Vibration signals along the ESP were acquired and eigensystem realization algorithm (ERA) method was used to identify the modal properties. Results showed the impact test as a useful method for modal parameters identification of ESP's installed in a test well. However, due to the location where the impacts were applied, the lower vibration modes, outside the operating range, were not excited. On the other hand, the natural frequencies numerically identified were overestimated in comparison with those obtained experimentally.

关键词： Electrical submersible pump Finite element method Modal analysis eigensystem realization algorithm

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A damage identification method for a thin plate structure based on PVDF sensors and strain mode

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PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART C-JOURNAL OF MECHANICAL ENGINEERING SCIENCE 2019年第14期233卷 4881-4895页

作者： Cui, Hongyu Peng, Weiqiang Xu, Xin Hong, Ming Dalian Univ Technol Sch Naval Architecture Engn State Key Lab Struct Anal Ind Equipment Dalian Peoples R China

Damage identification methods for engineering structures based on vibration parameters have the advantages of easy detection and high precision;however, structural strain information is more sensitive to structural damage than displacement information. Traditional resistance strain sensors have low accuracy and poor stability when measuring structural strains. Therefore, this paper uses a highly sensitive polyvinylidene fluoride dynamic strain sensor to identify structural damage in a thin plate. The polyvinylidene fluoride sensor is used to obtain structural strain response information, and structural modal parameters are identified using operational modal identification methods based on the natural excitation technique and the eigensystem realization algorithm. This paper uses a damage index based on mode shape and flexibility. A new damage index based on the LU decomposition of the flexibility matrix is used to identify the damage of the thin plate structure. The effectiveness of the modal identification methods and the new damage index is validated via an elastic thin plate experiment. The results show that the modal identification method and the new damage index proposed in this paper can identify damage in a thin plate structure. Sensor comparison experiments also show that compared with a resistance strain sensor, the polyvinylidene fluoride sensor has higher damage sensitivity, better damage recognition and the ability to recognize farther from the sensor.

关键词： Polyvinylidene fluoride sensor strain modes damage identification thin plate structure natural excitation technique eigensystem realization algorithm

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A comparison among modal parameter extraction methods

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SN APPLIED SCIENCES 2019年第7期1卷 781页

作者： Zrayka, Abdel Kader Mucchi, Emiliano Univ Ferrara Dept Engn Via Saragat 1 I-44122 Ferrara Italy

An effective comparison among several methods for extraction of the modal parameters from the frequency response functions measurements is presented in this research. In particular, several curve fitting methods, which are the peak amplitude method, the circle fit method, the least square complex exponential method, the eigensystem realization algorithm method and the rational fraction polynomial method were implemented in Matlab environment and compared in terms of natural frequencies, modal damping and mode shapes. Measurements were performed on a carcass of the gearbox in free-free condition. A hammer has been used with a periodic impulsive excitation signal. The natural frequencies values obtained by all methods were very similar and the differences between the results were insignificant. The peak amplitude and the circle fit gave good results for the damping ratios. The rational fraction polynomial method did the best job in detecting the damping and frequency values. The results obtained by the least square complex exponential method and the eigensystem realization algorithm method were reasonable for both frequency and damping.

关键词： eigensystem realization algorithm Least square complex exponential Modal analysis methods Rational fraction polynomial Implementation modal analysis by Matlab (R)

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Data-Driven Forecasting of Postflutter Responses of Geometrically Nonlinear Wings

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AIAA JOURNAL 2020年第6期58卷 2726-2736页

作者： Riso, Cristina Ghadami, Amin Cesnik, Carlos E. S. Epureanu, Bogdan I. Univ Michigan Dept Aerosp Engn 1320 Beal Ave Ann Arbor MI 48109 USA Univ Michigan Dept Mech Engn 2350 Hayward St Ann Arbor MI 48109 USA

Ensuring adequate flutter margins is a critical step in aircraft design. However, in the presence of nonlinear effects, subcritical limit-cycle oscillations can arise even before flutter occurs. When nonlinear effects are anticipated, postflutter analyses have to be integrated into aircraft design in addition to flutter computations for preventing this undesirable subcritical behavior. Therefore, there is a need for computationally fast postflutter analysis methods suitable for design applications. This paper investigates a data-driven method to forecast the bifurcation behavior of a geometrically nonlinear wing, demonstrating its suitability to analyze realistic nonlinear aeroelastic systems. The method efficiently forecasts postflutter responses using only a few system transient computations in the preflutter regime. First, the accuracy of forecasted bifurcation diagrams is verified against time-marching results. Next, wing design parameters are varied to investigate their impact on postflutter responses and show the method suitability to parametric studies.

关键词： Nonlinear Aeroelastic Systems Aircraft Design Model Based Analysis Sweep Angle Bending Stiffness Aerodynamic Coefficients Angle of Attack eigensystem realization algorithm Perturbation Method Numerical Simulation

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A Reduced-order model for Aerodynamic Shape Optimization

A Reduced-order model for Aerodynamic Shape Optimization

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AIAA Science and Technology (SciTech) Forum and Exposition

作者： Yao, W. Marques, S. Robinson, T. Armstrong, C. Sun, L. Queens Univ Sch Mech & Aerosp Engn Belfast BT9 5AH Antrim North Ireland Univ Surrey Dept Mech Engn Sci Guildford GU2 7XH Surrey England

ISBN: (数字)9781624105784

ISBN: (纸本)9781624105784

The motivation for the present work is to develop a reduced order model (ROM) for gradient based aerodynamic shape optimization. The fluid Euler equations or full order model (FOM) is converted to a reduced Newton iteration by using the Petrov-Galerkin projection. The reduced order basis (ROB) are extracted by Proper Orthogonal Decomposition (POD) from snapshots collected of the fluid state, along the optimization trajectory. Similarly, the reduced gradient formulation is derived by projecting the FOM state onto the subspace spanned by ROBs. The residual of reduced Newton iteration is used as an indicator to update the snapshots and ROB. The ROM is demonstrated for a subsonic inverse design problem and for airfoil drag minimization at transonic Mach numbers. The results suggest that the constructed ROM is capable of aerodynamic shape optimization while reducing the number of FOM queries with respect to an adjoint gradient based optimization framework. The reduction in computation cost is over one order of magnitude for the subsonic case;however, efficiency deteriorates for the transonic problem, exhibiting a reduction in computational time of about one-third with respect to an optimization using the FOM.

关键词： Aerodynamic Shape Optimization Airfoil Fluid State Euler Equations Transonic Flow Shape Optimization eigensystem realization algorithm Sequential Quadratic Programming Nonlinear Systems MATLAB

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Coupled Flight Mechanics based on Reduced Order Models for use in Tiltrotor Stability Analysis

Coupled Flight Mechanics based on Reduced Order Models for u...

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AIAA Aviation Forum and Exposition

作者： Wakefield, J. E. G. Cassillas, S. M. Gaitondet, A. L. Jones, D. P. Univ Bristol Dept Aerosp Engn Bristol BS8 1TR Avon England

ISBN: (数字)9781624105890

ISBN: (纸本)9781624105890

The development of two coupled stability models is presented. The models are based on the reduced order modelling of an Unsteady Vortex Lattice Method (UVLM) computational fluid dynamics code that provides an explicit wake model, coupled with classical rigid body equations of motion. These have been derived to include all 12 states to accommodate a full dynamic wake response. The model retains the entirety of the linear dynamics of the reduced order aerodynamics in the stability analysis, neglecting the need for aerodynamic derivatives. This allows for rapid and accurate force response and flow solution reconstruction. A new Linear Time Periodic balanced model reduction is developed, as well as an ensemble-averaging approach which may allow for a much lower computational cost than the full periodic stability. Further investigation is required to prove the equivalence of the two approaches. Validation studies have been performed to show the accuracy offered by the coupled model. An investigation into the stability of the XV-15 in comparison to an equivalent classical model was performed, showing similar eigenvalue distributions but with the ensemble-average coupled model producing larger magnitude instabilities. An investigation into the reconstruction of flow solutions during unstable motions was performed, allowing significant insight into the aerodynamics and showing potential for use as a design tool.

关键词： Aircraft Flight Mechanics Tiltrotor Aircraft Aerodynamic Force Vector Computational Fluid Dynamics Computational Fluid Dynamics Code eigensystem realization algorithm Reynolds Averaged Navier Stokes Controllability Gramian Singular Value Decomposition Aircraft Configurations

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