scholarly journals Unveiling modal parameters with forced response using SVD and QR during flutter flight testing

2016 ◽  
Vol 232 (1) ◽  
pp. 68-76
Author(s):  
José Barros-Rodríguez ◽  
José Miguel Fernández Fructuoso ◽  
Roberto Flores Le Roux ◽  
Sebastián Sánchez Prieto ◽  
Oscar Rodríguez Polo
Keyword(s):  
Noise Immunity ◽  
Structural Response ◽  
Forced Response ◽  
Modal Parameters ◽  
Response Signal ◽  
Flight Testing ◽  
Fighter Aircraft ◽  
Response Acquisition ◽  
Analytic Signals ◽  
Forced Excitation

This article presents an algorithm for the identification of modal parameters during flutter flight testing when forced excitation is employed and the aircraft possesses several sensors for structural response acquisition. The main novelty of the method, when compared with other classical modal analysis methods, is that the analysis is carried out in intervals of time instead of in the whole duration of the excitation. It means that, even when the response signal is only partially available, some modal parameters may be still identified. Application to analytic signals as well as structural response of modern fighter aircraft using frequency-swept excitation is provided in order to demonstrate the effectiveness, robustness and noise immunity of the proposed method.

Output-Only Analysis for Modal Parameters Estimation of an Elastically Scaled Ship

2008 ◽  
Vol 52 (01) ◽  
pp. 45-56
Author(s):  
Giuliano Coppotelli ◽  
Daniele Dessi ◽  
Riccardo Mariani ◽  
Marcello Rimondi
Keyword(s):  
Life Prediction ◽  
Structural Response ◽  
Random Excitation ◽  
Parameters Estimation ◽  
Elastic Response ◽  
Modal Parameters ◽  
Practical Application ◽  
Scaled Model ◽  
Output Only ◽  
Ship Speed

The study of the ship structural response assumes an increasing importance as soon as the structures, characterized by much more lightness, are designed and built for faster vessels. This requisite implies a greater flexibility of the structures themselves, the elastic response of which has to be evaluated with accuracy in order to predict the dynamic behavior. In the present paper, a methodology for the identification of the modal parameters from the measurement of only the responses of a vibrating structure has been developed and applied to an elastically scaled model. This output-only technique is successfully applied to the segmented model of a real ship towed in the INSEAN linear basin. The broadband random excitation, provided by the loads exerted by an irregular sea pattern, induces a stochastic response of the model, which is monitored with accelerometers. The obtained results not only outline the parametric dependence of the modal properties on the ship speed, but also suggest a possible practical application of this technique for on-board structural monitoring and fatigue-life prediction.

Aero Engine Performance Evaluation During Missile Firing Test

2017 ◽  
Author(s):  
Sajath Kumar Manoharan ◽  
Kasram Santhosh ◽  
Mahesh P. Padwale ◽  
G. P. Ravishankar
Keyword(s):  
Performance Evaluation ◽  
Engine Performance ◽  
Flight Testing ◽  
Flow Disturbance ◽  
Fighter Aircraft ◽  
Firing Test ◽  
Aero Engine ◽  
Temperature Ramps ◽  
Air Intake ◽  
Model Engine

Evaluation of engine performance during armament firing in fighter aircraft is a vital qualification aspect for airframe engine integration. Ingestion of missile’s efflux into air intake results in rapid increase of engine inlet temperatures (temperature ramps) which cause flow disturbance to the compressor. Temperature distortion caused due to armament firing and its effect on compressor stability during flight testing is evaluated. Accordingly mitigation actions are recommended for stall/surge free operations. Distortion descriptors are assessed using simulation model (engine performance program) and results compared with engine distortion limits.

Operational modal analysis of a nonlinear oscillation system under a harmonic excitation

2020 ◽  
pp. 095440622097755
Author(s):  
Xuchu Jiang ◽  
Feng Jiang ◽  
Biao Zhang
Keyword(s):  
Modal Analysis ◽  
Nonlinear Oscillation ◽  
Normal Modes ◽  
Nonlinear Normal Modes ◽  
Harmonic Excitation ◽  
Forced Response ◽  
Operational Modal Analysis ◽  
Single Frequency ◽  
Modal Parameters ◽  
Oscillation System

Operational modal analysis (OMA) is a procedure that allows the modal parameters of a structure to be extracted from the measured response to an unknown excitation generated during operation. Nonlinearity is inevitably and frequently encountered in OMA. The problem: The traditional OMA method based on linear modal theory cannot be applied to a nonlinear oscillation system. The solution: This paper aims to propose a nonlinear OMA method for nonlinear oscillation systems. The new OMA method is based on the following: (1) a self-excitation phenomenon is caused by nonlinear components; (2) the nonlinear normal modes (NNMs) of the system appear under a single-frequency harmonic excitation; and (3) using forced response data, the symbolic regression method (SR) can be used to automatically search for the NNMs of the system, whose modal parameters are implicit in the expression structure expressing each NNM. The simulation result of a three-degree-of-freedom (3-DOF) nonlinear system verifies the correctness of the proposed OMA method. Then, a disc-rod rotor model is considered, and the proposed OMA method’s capability is further evaluated.

Tower Modal Parameters Identification Based on Polymax Method

2012 ◽  
Vol 229-231 ◽  
pp. 1823-1826
Author(s):  
Wen Wen Yu ◽  
Hao Tian ◽  
Hai Qi Zheng ◽  
Dong Gen Chen
Keyword(s):  
Complex System ◽  
Large Scale ◽  
System Parameter ◽  
Random Excitation ◽  
Modal Parameters ◽  
Response Signal ◽  
Testing Environment ◽  
Tower Structure ◽  
Modal Parameters Identification ◽  
The Ideal

Based on the background of a high tower structure under environment random excitation, large-scale complex system parameter identification based on Polymax method is presented in this paper. Firstly,the system of testing environment excitation response signal for large tower is designed.Secondly,the obtained signal is analysed and intercepted,then the ideal signals are selectted from each experiment. Lastly, the intercepted signal is identified for some parameters based on polymax method.The obtained result shows that the former is effective.

Evaluation of the Lateral Vibration Response of Footbridges under Uncertainty Conditions

2022 ◽  
Author(s):  
Rocío García-Cuevas ◽  
Javier F. Jiménez-Alonso ◽  
Carlos Renedo M.C. ◽  
Francisco Martinez
Keyword(s):  
Distribution Function ◽  
Natural Frequency ◽  
Damping Ratio ◽  
Probabilistic Approach ◽  
Structural Response ◽  
Modal Parameters ◽  
Critical Number ◽  
Lateral Instability ◽  
Lateral Vibrations ◽  
Probabilistic Distribution

<p>The evaluation of the vibration performance of footbridges due to walking pedestrians is an issue of increasing importance in current footbridge design practice. The growing trend of slender footbridges with long spans and light materials has led to serviceability problems in lateral vibrations, which occur when the number of pedestrians reaches a “critical number”. Considering the mode of vibration in which the lateral instability is more likely to develop, the structural response depends on the modal characteristics of the footbridge; in particular, the natural frequency and the damping ratio. These modal parameters are stochastic variables, as it is not possible to determine them without a level of uncertainty. Thus, the purpose of this paper is to obtain the value of the lateral dynamic response of slender footbridges with a certain confidence level under uncertainty conditions. The uncertainties of those modal parameters are considered using a probabilistic approach. Both the natural frequency and the damping ratio are modelled as uncorrelated random variables that follow a predetermined probabilistic distribution function. Consequently, the structural response will also be described by a probabilistic distribution function, which can be estimated through Monte Carlo numerical simulations. As a result, the study allows the footbridge lateral response and the critical number of pedestrians to be calculated for different confidence levels and load scenarios, especially for crowd densities above the “critical number”.</p>

Vibration Control Using Parametric Excitation

1999 ◽  
Author(s):  
Phillip H. Nguyen ◽  
Jerry H. Ginsberg
Keyword(s):  
Natural Frequency ◽  
Parametric Excitation ◽  
Excitation Frequency ◽  
Vertical Direction ◽  
Excitation Amplitude ◽  
Forced Response ◽  
Resonant Forcing ◽  
Parametric Frequency ◽  
Selection Of ◽  
Forced Excitation

Abstract A simple pendulum whose pivot executes harmonic motion in the vertical direction is a prototype for systems subjected to parametric excitation. Forced excitation of this system is represented as a harmonically varying torque whose frequency is taken to be arbitrary. The investigation explores whether, for specified values of the natural frequency and the excitation frequency, it is possible to select an amplitude and frequency for the parametric excitation such that the pendulum’s vibratory rotation is reduced. The analysis supplements numerical integration of the equation of motion with a Fourier series analysis suitable to situations where the parametric frequency is a multiple of the forcing frequency. Studies of the behavior for cases of near-resonant forcing and forced excitation far from the natural frequency lead to a general guideline for selecting the parametric excitation amplitude and frequency. The conclusion is that, with judicious selection of the parametric amplitude, a parametric frequency that is very high relative to the highest contemplated excitation frequency can reduce to forced response at any lower frequency to very small levels.

Structural Modification Software Development for Design Optimization

1995 ◽  
Author(s):  
Xiaoye Gu ◽  
Alison B. Flatau
Keyword(s):  
Structural Response ◽  
Acoustic Power ◽  
Modal Parameters ◽  
Constrained Layer Damping ◽  
Experimental Frequency ◽  
Modal Damping ◽  
Stiffness Matrices ◽  
Structural Responses ◽  
Damping Materials ◽  
Modal Mass

Abstract This paper presents a method for obtaining structural matrices from experimental frequency response function (FRF) data and using these structural matrices to predict the response of the structure to modifications at various locations. The approach taken is designed for subsequent use in optimizing structural modifications to efficiently reduce radiated acoustic power. A series of programs were written for identifying the structural matrices (mass matrices, stiffness matrices and damping matrices) from the measured FRF data. These matrices are used to obtain the modified response of the structure resulting from adding linear springs at different locations on the structure. Experimental results from a beam are presented to verify these programs. Work is in progress on extending this method to incorporate modifications to the structure produced by constrained-layer damping materials. The programs for obtaining the structural matrices and the structural response are composed of approaches used by several prior authors. Potter and Richardson’s [1,2] method is used for obtaining the relative modal parameters (modal mass, modal stiffness and modal damping). Luk and Mitchell’s [3,4] pseudo-inverse method is employed to obtain the structural matrices for cases when the number of modes measured is much less than the number of test points. A method for deriving the absolute value of modal parameters from the measured FRF data is also developed using modal analysis theory. Linear springs are added at various positions to modify the structure. The structural matrices are used to predict the modified structural responses scaled to displacement per unit force. A series of linear spring modifications are modeled and implemented experimentally to verify these programs.

Fan Forced Response Due to Ground Vortex Ingestion

2006 ◽  
Author(s):  
Luca di Mare ◽  
George Simpson ◽  
Abdulnaser I. Sayma
Keyword(s):  
High Cycle Fatigue ◽  
Computational Study ◽  
Structural Response ◽  
Forced Response ◽  
Design Stage ◽  
General Ability ◽  
Engine Order ◽  
Modal Model ◽  
Fan Speed ◽  
Good Agreement

This paper presents a computational study of the formation and ingestion of ground vortices and resulting fan forced response levels in a large turbofan operating near the ground. The model is based on an integrated aeroelasticity numerical method; the aerodynamic part is based on a 3D unstructured Reynolds-Averaged Naveir-Stokes solver. The mechanical model uses linear modal model for the structure, allowing for the direct computation of the structural response during the unsteady simulations. The analysis shows that under certain fan speed and mass flow rate conditions, for a given fan and intake combination, situated at a fixed distance from the ground, an inlet vortex can form near the ground. This inlet vortex is drawn into the intake causing inlet distortions that could excite several low engine order harmonics of the fan. Predictions are compared with measured data showing good agreement in general. Ability to predict the level of response at the design stage allows for implementing design solutions preventing possible failure due to high cycle fatigue.

scholarly journals Sensitivity of Parameter Changes in Structural Damage Detection

1997 ◽  
Vol 4 (1) ◽  
pp. 27-37 ◽  
Author(s):  
C. H. Jenkins ◽  
L. Kjerengtroen ◽  
H. Oestensen
Keyword(s):  
Damage Detection ◽  
Structural Damage ◽  
Structural Response ◽  
Theoretical Models ◽  
Modal Parameters ◽  
Complex Structures ◽  
Static Deflection ◽  
Structural Damage Detection ◽  
Dynamic Measurements ◽  
Static Deflection Measurements

Structural damage detection by nondestructive methods is highly desirable. Changes in modal parameters such as frequency, damping, and mode shape are particularly inviting. Evidence is presented here that reveals that static deflection can, in many cases, be a more sensitive predictor of structural damage than frequency. The reasons for this are illuminated within, and hinge on very fundamental issues about the very nature of structural response. Furthermore, static deflection measurements are often easier to make, with higher levels of accuracy than dynamic measurements. Comparisons are made between theoretical models and experimental results for simple structures, with extensions given to more complex structures.

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