scholarly journals Scaling Mode Shapes in Output-Only Structure by a Mass-Change-Based Method

2017 ◽  
Vol 2017 ◽  
pp. 1-11 ◽  
Author(s):  
Liangliang Yu ◽  
Hanwen Song
Keyword(s):  
Modal Analysis ◽  
Mass Distribution ◽  
Null Space ◽  
Mass Matrix ◽  
Small Mass ◽  
Mass Change ◽  
Mode Shapes ◽  
Distribution Matrix ◽  
Distribution Vector ◽  
Output Only

A mass-change-based method based on output-only data for the rescaling of mode shapes in operational modal analysis (OMA) is introduced. The mass distribution matrix, which is defined as a diagonal matrix whose diagonal elements represent the ratios among the diagonal elements of the mass matrix, is calculated using the unscaled mode shapes. Based on the theory of null space, the mass distribution vector or mass distribution matrix is obtained. A small mass with calibrated weight is added to a certain location of the structure, and then the mass distribution vector of the modified structure is estimated. The mass matrix is identified according to the difference of the mass distribution vectors between the original and modified structures. Additionally, the universal set of modes is unnecessary when calculating the mass distribution matrix, indicating that modal truncation is allowed in the proposed method. The mass-scaled mode shapes estimated in OMA according to the proposed method are compared with those obtained by experimental modal analysis. A simulation is employed to validate the feasibility of the method. Finally, the method is tested on output-only data from an experiment on a five-storey structure, and the results confirm the effectiveness of the method.

scholarly journals Reduced Mass-Weighted Proper Decomposition for Modal Analysis

2011 ◽  
Vol 133 (2) ◽  
Author(s):  
Venkata K. Yadalam ◽  
B. F. Feeny
Keyword(s):  
Modal Analysis ◽  
Mass Distribution ◽  
Mass Matrix ◽  
Linear Interpolation ◽  
Modal Identification ◽  
Distributed Parameter ◽  
Arbitrary Mass ◽  
Spring System ◽  
Mass Spring ◽  
Proper Orthogonal

A method of modal analysis by a mass-weighted proper orthogonal decomposition for multi-degree-of-freedom and distributed-parameter systems of arbitrary mass distribution is outlined. The method involves reduced-order modeling of the system mass distribution so that the discretized mass matrix dimension matches the number of sensed quantities, and hence the dimension of the response ensemble and correlation matrix. In this case, the linear interpolation of unsensed displacements is used to reduce the size of the mass matrix. The idea is applied to the modal identification of a mass-spring system and an exponential rod.

Output-Only Modal Analysis of an Internal Unreachable Module Embedded in a Space Electronic Equipment

2012 ◽  
Author(s):  
Lassaad Ben Fekih ◽  
Georges Kouroussis ◽  
David Wattiaux ◽  
Olivier Verlinden ◽  
Christophe De Fruytier
Keyword(s):  
Finite Element ◽  
Modal Analysis ◽  
Degrees Of Freedom ◽  
Transverse Direction ◽  
Mode Shapes ◽  
Fe Model ◽  
Fe Method ◽  
Numeric Model ◽  
Stiffness Matrices ◽  
Output Only

An approach is proposed to identify the modal properties of a subsystem made up of an arbitrary chosen inner module of embedded space equipment. An experimental modal analysis was carried out along the equipment transverse direction with references taken onto its outer housing. In parallel, a numerical model using the finite element (FE) method was developed to correlate with the measured results. A static Guyan reduction has led to a set of master degrees of freedom in which the experimental mode shapes were expanded. An updating technique consisting in minimizing the dynamic residual induced by the FE model and the measurements has been investigated. A last verification has consisted in solving the numeric model composed of the new mass and stiffness matrices obtained by means of a minimization of the error in the constitutive equation method.

Improved Results in Structural Dynamic Calculations by Linking Finite Element Analysis (FEA) and Experimental Modal Analysis (EMA)

1995 ◽  
Author(s):  
Ulrich Gabbert ◽  
Manfred Zehn ◽  
Friedrich Wahl
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Modal Analysis ◽  
Numerical Models ◽  
Mass Matrix ◽  
Computer Time ◽  
Experimental Modal Analysis ◽  
Mode Shapes ◽  
Element Analysis ◽  
Structural Dynamic

Abstract The paper deals with improvements of accuracy of structural dynamic calculations by using both the advantages of Finite Element Analysis (FEA) and Experimental Modal Analysis (EMA). The basis for such improvements are reasonable mechanical and numerical models and accurate frequency response measurements (eigenfrequencies and mode shapes). The paper deals first with reasons for and estimations of errors in numerical and experimental analysis. It can be shown by theory and experiment that neither FEA nor EMA models are unique, due to inevitable incompleteness of the mode shapes and eigenfrequencies from a vibration test. Verification and updating of FE models by linking FEA with EMA are discussed in the paper and mainly focussed on FE models with a large number of degrees of freedom. Hence an update method has been introduced, which leads to an improved model in a relatively small quantity of computer time. It can be shown, that based on measured eigenfrequencies and calculated eigenvectors, an updating of FE-models for real engineering problems, by changing the mass matrix only, is a very efficient procedure with a surprisingly good quality updated model.

FLUTTER CALCULATION BASED ON GVT-RESULTS AND THEORETICAL MASS MODEL

Aviation ◽  
2009 ◽  
Vol 13 (4) ◽  
pp. 122-129 ◽  
Author(s):  
Wojciech Chajec
Keyword(s):  
Mass Distribution ◽  
Normal Modes ◽  
Ground Vibration ◽  
Small Mass ◽  
Mode Shapes ◽  
Mass Model ◽  
Stiffness Properties ◽  
Theoretical Mass ◽  
Vibration Tests ◽  
Calculation Software

Ground vibration tests (GVT) are a typical source of data for flutter prediction. In this paper, a simple, lowcost method to calculate flutter is presented. In this method, measured frequencies, mode shapes of an airplane are used and, additionally, the theoretical mass model of it. If the theoretical mass model is used, it is possible to calculate generalized masses of modes and cross mass couplings between them. The mass couplings of normal modes should be zero. Orthogonalization is correction of the mode shapes to lead the couplings to zero. The possible orthogonalization methods are presented in chapter 2. Based on eigenmodes of airplane configuration during GVT, it is possible to determine the eigenmodes of the same free airplane after a relatively small mass change, i.e. for another mass distribution that was not investigated by GVT. In the procedure presented in chapter 3, it is assumed that geometric and stiffness properties do not change. The methodology was used in the own flutter calculation software that is useful for flutter prediction of light airplanes and sailplanes. Santrauka Dažnuminiai bandymai žemėje yra tipinis informacijos šaltinis flaterio skaičiavimui. Šiame straipsnyje pateikiamas paprastas ir pigus flaterio skaičiavimo metodas. Šiame metode naudojamos lėktuvo išmatuotų dažnuminių modų formos ir teorinis lėktuvo masių modelis. Naudojant teorinį masių modelį galima apskaičiuoti apibendrintas modų mases ir masių ryšius tarp jų. Normalinių modų masių ryšys turi būti lygus nuliui. Ortogonalizavimu koreguojamos modų formos, siekiant ryšius sumažinti iki nulio. Galimi ortogonalizavimo metodai pateikti antrame skyriuje. Remiantis lėktuvo laisvųjų svyravimo modomis, gautomis dažnuminių bandymų žemėje metu, galima nustatyti kitokio masių pasiskirstymo įtaką laisvųjų svyravimų modoms. Procedūroje, pateiktoje trečiame skyriuje, manoma, kad geometrinės ir standumo savybės nesikeičia. Ši metodologija buvo panaudota savoje programinėje įrangoje flateriui skaičiuoti, kurią galima naudoti lengvų lėktuvų ir sklandytuvų flaterio skaičiavimui.

scholarly journals Analysis of the stiffness sensitivity of a sorting arm mechanism based on a generalized modal mass distributing matrix

2018 ◽  
Vol 10 (11) ◽  
pp. 168781401881063
Author(s):  
Xuchu Jiang ◽  
Bin Li ◽  
Hongqi Liu ◽  
Songping He ◽  
Xinyong Mao ◽  
...  
Keyword(s):  
Modal Analysis ◽  
Mass Distribution ◽  
High Speed ◽  
Degrees Of Freedom ◽  
Light Emitting Diode ◽  
Positional Accuracy ◽  
Operation Conditions ◽  
The Matrix ◽  
Distribution Matrix ◽  
Modal Mass

A light-emitting diode chip sorting machine, which operates at high frequencies, exhibits reciprocating motion with multiple degrees of freedom and is characterized by quick starts and stops over a short range at a high frequency. The stiffness sensitivity of the chip sorter directly influences the positional accuracy of the sorting arm. However, existing experimental modal analysis methods cannot effectively identify the structural stiffness sensitivity under high-speed operation conditions. In this article, a method based on the modal mass distribution matrix is used to analyze the stiffness sensitivity of the sorting arm system. This method retrieves the modal parameters by modal analysis, after which the modal mass distribution matrix is obtained. The size of each element in the column of the matrix represents the energy distribution and stiffness sensitivity of the system under the mode. The stiffness-sensitive components of the sorting arm machine are accurately and quickly identified, thereby providing the guiding principle and basis for the dynamic optimization of the sorting arm mechanism.

Scaling Mode Shapes in Output-Only Systems by a Consecutive Mass Change Method

2010 ◽  
Vol 51 (6) ◽  
pp. 995-1005 ◽  
Author(s):  
P. Fernández ◽  
P. Reynolds ◽  
M. López-Aenlle
Keyword(s):  
Mass Change ◽  
Mode Shapes ◽  
Output Only

scholarly journals Laboratory investigation of a bridge scour monitoring method using decentralized modal analysis

2021 ◽  
pp. 147592172098512
Author(s):  
Muhammad Arslan Khan ◽  
Daniel P McCrum ◽  
Luke J Prendergast ◽  
Eugene J OBrien ◽  
Paul C Fitzgerald ◽  
...  
Keyword(s):  
Modal Analysis ◽  
Mode Shape ◽  
Experimental Tests ◽  
Linear Increase ◽  
Mode Shapes ◽  
Bridge Scour ◽  
Scaled Model ◽  
Global Mode ◽  
Monitoring Method ◽  
Output Only

Scour is a significant issue for bridges worldwide that influences the global stiffness of bridge structures and hence alters the dynamic behaviour of these systems. For the first time, this article presents a new approach to detect bridge scour at shallow pad foundations, using a decentralized modal analysis approach through re-deployable accelerometers to extract modal information. A numerical model of a bridge with four simply supported spans on piers is created to test the approach. Scour is modelled as a reduction in foundation stiffness under a given pier. A passing half-car vehicle model is simulated to excite the bridge in phases of measurement to obtain segments of the mode shape using output-only modal analysis. Two points of the bridge are used to obtain modal amplitudes in each phase, which are combined to estimate the global mode shape. A damage indicator is postulated based on fitting curves to the mode shapes, using maximum likelihood, which can locate scour damage. The root mean square difference between the healthy and scoured mode shape curves exhibits an almost linear increase with increasing foundation stiffness loss under scour. Experimental tests have been carried out on a scaled model bridge to validate the approach presented in this article.

scholarly journals Reduced Mass-Weighted Proper Decomposition for Modal Analysis

2008 ◽  
Author(s):  
Venkata K. Yadalam ◽  
B. F. Feeny
Keyword(s):  
Modal Analysis ◽  
Mass Distribution ◽  
Mass Matrix ◽  
Linear Interpolation ◽  
Modal Identification ◽  
Lumped Mass ◽  
Arbitrary Mass ◽  
Spring System ◽  
Mass Spring ◽  
Proper Orthogonal

A method of modal analysis by proper orthogonal decomposition for large-order systems of arbitrary mass distribution is outlined. The method involves reduced-order modeling of the system mass distribution so that the discretized mass matrix dimension matches the number of sensed quantities, and hence the dimension of the response ensemble and correlation matrix. In this case, the linear interpolation of unsensed displacements is used to perform an effective lumped mass homogenization. The idea is applied to the modal identification of a mass-spring system and an exponential rod.

Sign in / Sign up

Export Citation Format

Share Document