scholarly journals Wavelet-based analysis of time-variant adaptive structures

2018 ◽  
Vol 376 (2126) ◽  
pp. 20170245 ◽  
Author(s):  
Kajetan Dziedziech ◽  
Alexander Nowak ◽  
Alexander Hasse ◽  
Tadeusz Uhl ◽  
Wiesław J. Staszewski
Keyword(s):  
Frequency Response Function ◽  
Natural Frequencies ◽  
Fibre Composite ◽  
Structural Response ◽  
Structural Stiffness ◽  
Theme Issue ◽  
Adaptive Structures ◽  
Output Characteristics ◽  
Variant System

Wavelet analysis is applied to identify the time-variant dynamics of adaptive structures. The wavelet-based power spectrum of the structural response, wavelet-based frequency response function (FRF) and wavelet-based coherence are used to identify continuously and abruptly varying natural frequencies. A cantilever plate with surface-bonded macro fibre composite—which alters the structural stiffness—is used to demonstrate the application of the methods. The results show that the wavelet-based input–output characteristics—i.e. the FRF and coherence—can identify correctly the dynamics of the analysed time-variant system and reveal the varying natural frequency. The wavelet-based coherence can be used not only for the assessment of the quality of the wavelet-based FRF but also for the identification. This article is part of the theme issue ‘Redundancy rules: the continuous wavelet transform comes of age’.

Modal Analysis and Optimization of Spindle Box of Turn-Milling Center Based on Finite Element Method

2012 ◽  
Vol 226-228 ◽  
pp. 281-284
Author(s):  
Li Da Zhu ◽  
Xiao Bang Wang ◽  
Tiao Biao Yu ◽  
Wan Shan Wang
Keyword(s):  
Finite Element ◽  
Natural Frequencies ◽  
Element Model ◽  
Ansys Software ◽  
Design Requirement ◽  
Design Quality ◽  
Machining Center ◽  
Main Components ◽  
Turn Milling

The dynamic characteristics of machine tool may directly affect its machining capability, which is analyzed to improve the machining precision and efficiency. In this paper, the 3D finite element model of main components turn-milling center is established by using ANSYS software, and then spindle box of turn-milling center is analyzed and optimized; the natural frequencies and vibration models are obtained after analysis, which guarantee the design requirement of the machining center. Therefore it is significant to improve the design quality of machining center by using FEA software in the design process.

A New Methodology for the Accurate and Consistent Identification of Modal Parameters Using Multi-FRF Analysis

1995 ◽  
Author(s):  
R. M. Lin ◽  
S.-F. Ling
Keyword(s):  
Eigenvalue Problem ◽  
Loss Factor ◽  
Frequency Response Function ◽  
Natural Frequencies ◽  
Identification Problem ◽  
Modal Parameters ◽  
Frequency Range ◽  
Case Examples ◽  
Measured Frequency Response ◽  
Damping Loss Factor

Abstract A new method for the estimation of modal parameters is presented in this paper. Unlike the majority of the existing methods which involve complicated curve fitting and interpolative procedures, the proposed method calculates the modal parameters by solving eigenvalue problem of an equivalent eigensystem derived from measured frequency response function (FRF) data. It is developed based on the practical assumption that only one incomplete column of the FRF matrix of the test structure has been measured in a frequency range of interest. All the measured FRFs are used simultaneously to construct the equivalent eigensystem matrices from which natural frequencies, damping loss factor and modeshape vectors of interest can be directly solved. Since the identification problem is reduced to an eigenvalue problem of an equivalent system, natural frequencies and damping loss factors identified are consistent. Further procedures for normalizing the identified eigenvectors so that they become mass-normalized are developed. Numerical case examples are given to demonstrate the practicality of the proposed method and results obtained are indeed very promising. It is believed that with the availability of such identification method, modal analysts’ dream of intelligent and full automatic modal analysis will become a reality.

Verified fuselage section water impact modelling

2019 ◽  
Vol 123 (1268) ◽  
pp. 1740-1754 ◽  
Author(s):  
Y. Song ◽  
B. Horton ◽  
J. Bayandor
Keyword(s):  
Large Scale ◽  
Structural Response ◽  
High Fidelity ◽  
Water Impact ◽  
Impact Modelling ◽  
Drop Tests ◽  
Section Model ◽  
Aircraft Crashworthiness ◽  
Bodies Of Water

ABSTRACTAlong many flight corridors, bodies of water serve as preferred emergency landing options. Thus, relevant scenarios must be investigated to improve aircraft crashworthiness in the event of an impact landing on water. Enhancing the damage tolerance of aircraft structures through repetitive experiments can, however, prove highly uneconomical. Such large-scale trials can be influenced by many factors of uncertainty adversely affecting the quality of the results. Therefore, the work presented in this study focuses in particular on evaluating a computational methodology perfected for aircraft water ditching using Coupled Lagrangian-Eulerian (CLE) that allows detailed prediction of structural response of a verified deformable fuselage section during such events. Validation of the fluid-structure interactive (FSI) strategy developed is conducted, thoroughly comparing the method against the analytical and experimental results of multiple wedge drop tests. Finally, the validated FSI strategy is applied to a high-fidelity fuselage section model impacting water to simulate and assess a realistic ditching scenario.

scholarly journals Bird strike on aircraft radome: Dynamic characterisation of quartz fibre composite sandwich for accurate, predictive impact simulations

2018 ◽  
Vol 183 ◽  
pp. 01007
Author(s):  
Sebastian Heimbs ◽  
Tim Wagner ◽  
Heinz Meister ◽  
Clemens Brand ◽  
Mircea Calomfirescu
Keyword(s):  
High Velocity ◽  
Satellite Communication ◽  
Fibre Composite ◽  
Structural Response ◽  
High Rate ◽  
Bird Strike ◽  
Strain Rate Effects ◽  
Quartz Fibre ◽  
Remotely Piloted Aircraft ◽  
Aircraft System

This study assesses the bird strike resistance of the satellite communication (SatCom) radome of a medium altitude, long endurance (MALE) remotely piloted aircraft system (RPAS), which is designed as a lightweight sandwich structure with thin quartz fibre composite skins and a cellular honeycomb core. In order to perform accurate, predictive numerical bird strike simulations, the building block approach was applied, involving extensive experimental characterisation and model validation of the materials and structures from simple coupon level up to full-scale radome level. Coupon tests of the quartz fibre composite skin material under high-rate dynamic loading revealed significant strain rate effects, which needed to be taken into account in the simulation model in order to predict the structural response under high-velocity bird strike loading. In summary, this work presents a systematic and detailed approach for obtaining validated modelling methods for high-velocity impact analyses, which could be used efficiently for various design and parameter studies during the development of the SatCom radome.

Positioning of bearings for curved continuous spread-box girder bridges

2002 ◽  
Vol 29 (5) ◽  
pp. 641-652 ◽  
Author(s):  
Magdy Samaan ◽  
Khaled Sennah ◽  
John B Kennedy
Keyword(s):  
Finite Element ◽  
Natural Frequencies ◽  
Structural Response ◽  
Element Model ◽  
Extensive Study ◽  
Mode Shapes ◽  
Box Girder ◽  
Girder Bridges ◽  
Bridge Superstructure ◽  
Girder Bridge

The type and arrangement of bearings for a bridge superstructure are important considerations in bridge design. For a curved continuous spread-box girder bridge, the support conditions for the bridge superstructure may significantly influence the distribution factors for maximum stresses, reactions, and shear forces as well as the bridge natural frequencies and mode shapes. Current design practices in North America recommend very few guidelines for bearing arrangements and types. This paper describes an extensive study carried out using an experimentally calibrated finite element model, in which curved continuous prototype bridges were analyzed to determine their structural response. Six different types and arrangements of support bearings were studied to determine their effect on the maximum stress and reaction distributions as well as on the natural frequencies of such bridges. The results were used to suggest the most favourable bearing arrangement and type.Key words: bridge bearings, composite, continuous, curved bridges, design, distribution factors, finite element, spread-box.

An Identification Approach of Dynamic Contact Parameters for Toolholder-Spindle Joint Base on Frequency Response Function

2012 ◽  
Vol 538-541 ◽  
pp. 748-753
Author(s):  
Guo Ping An ◽  
Xin Yu Liu ◽  
Yong Sheng Zhao ◽  
Li Gang Cai
Keyword(s):  
Frequency Response ◽  
Response Function ◽  
Frequency Response Function ◽  
Dynamic Contact ◽  
Work Piece ◽  
Spindle System ◽  
Manufacturing Efficiency ◽  
Identification Approach ◽  
Contact Parameters

The joint of the toolholder-spindle is the most weakness structure in the system of toolholder-spindle. It affects the manufacturing efficiency and the surface quality of work piece. It is important to identify the dynamic contact parameters for evaluating the connectivity of the toolholder-spindle system. The article introduces an approach to identify the dynamic contact parameters of toolholder-spindle joint base on frequency response function (FRF). Using the BT40 toolholder-spindle system, we can get the dynamic contact parameters curve of toolholder-spindle by the previous approach. The translational and rotational contact parameters can be obtained by sensitivity analysis. By comparing the simulation results with those of experimentation, it can prove the validity of identified dynamic contact parameters. The research results can provide a theoretical basis for the optimization of toolholder.

Thermal Robustness Assessment of a Rigidized Space Inflatable Boom via Experimental Modal Analysis and Finite Element Modeling

2010 ◽  
Author(s):  
Matthew Daly ◽  
Armaghan Salehian ◽  
Alireza Doosthoseini
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Frequency Response Function ◽  
Good Accuracy ◽  
Natural Frequencies ◽  
Beam Theory ◽  
Element Model ◽  
Modal Testing ◽  
Environmental Temperatures ◽  
Robustness Assessment

The following paper presents the results of a thermal robustness assessment of a rigidized space inflatable boom. Modal testing is performed at three different environmental temperatures; spanning a range of 38°C, with the purpose of characterizing dynamic behavior and assessing changes in bending frequencies. Experimental results show that the natural frequencies of the boom shift only marginally within the tested bandwidth. A finite element model is developed in parallel with experiments to determine compatibility with beam theory. The resulting simulation shows that linear beam theory can be used to predict bending frequencies and frequency response function magnitudes with very good accuracy.

Wind-induced instability of structures

1971 ◽  
Vol 269 (1199) ◽  
pp. 395-413 ◽  
Keyword(s):  
Wind Speed ◽  
Cross Sections ◽  
Natural Frequencies ◽  
Structural Response ◽  
Cross Sectional ◽  
Periodic Surface ◽  
Speed Range ◽  
Aerodynamic Instability ◽  
Sectional Shape ◽  
Transverse Galloping

Forms of wind-induced instability of structures are described, and two of these, typical of long bodies with bluff cross-sections, are selected for more detailed consideration. The first is vortex-induced bending oscillation, a type of resonant response to the periodic surface pressure loading caused by the discrete wake vortex street formed from the shear layers separating from the bluff cross-section. Oscillation phenomena are described, including capture of the vortex frequency by the structural response frequency over a discrete wind speed range and amplification and phase shift of the loading over this range. The second form is transverse galloping, arising from aerodynamic instability of the bluff cross-sectional shape, so that small-amplitude oscillations generate forces which increase the amplitudes to large values. Oscillation phenomena are described, including the occurrence at very nearly natural frequencies, and the relatively large amplitudes (compared to vortex-induced oscillations) increasing with wind speed beyond a critical wind speed dependent on the level o fstructural damping. Effects of body and wind parameters on both forms of oscillation are considered, and methods of analysis and suppression for susceptible structures are described. Some probable future requirements and prospects are considered.

Derivation of New Transcendental Member Stiffness Determinant for Vibrating Frames

2003 ◽  
Vol 03 (02) ◽  
pp. 299-305 ◽  
Author(s):  
F. W. Williams ◽  
D. Kennedy
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Stiffness Matrix ◽  
Infinite Order ◽  
Natural Frequencies ◽  
Dynamic Stiffness ◽  
Structural Stiffness ◽  
Trial And Error ◽  
Stiffness Matrices ◽  
Vibration Problems

Transcendental dynamic member stiffness matrices for vibration problems arise from solving the governing differential equations to avoid the conventional finite element method (FEM) discretization errors. Assembling them into the overall dynamic structural stiffness matrix gives a transcendental eigenproblem, whose eigenvalues (natural frequencies or their squares) are found with certainty using the Wittrick–Williams algorithm. This paper gives equations for the recently discovered transcendental member stiffness determinant, which equals the appropriately normalized FEM dynamic stiffness matrix determinant of a clamped ended member modelled by infinitely many elements. Multiplying the overall transcendental stiffness matrix determinant by the member stiffness determinants removes its poles to improve curve following eigensolution methods. The present paper gives the first ever derivation of the Bernoulli–Euler member stiffness determinant, which was previously found by trial-and-error and then verified. The derivation uses the total equivalence of the transcendental formulation and an infinite order FEM formulation, which incidentally gives insights into conventional FEM results.

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