To see the other types of publications on this topic, follow the link: Finite element modal updating.
Dissertations / Theses on the topic 'Finite element modal updating'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Finite element modal updating.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Li, Yi Yuan. "Direct finite element model updating using incomplete modal data inspired from system control." Thesis, University of Macau, 2017. http://umaclib3.umac.mo/record=b3691080.
Full text
2
Gotin, Nathalie. "Finite Element Model Updating for Rotary Machinery." DigitalCommons@CalPoly, 2012. https://digitalcommons.calpoly.edu/theses/864.
Full textAbstract:
The main approach of this thesis was to develop a mathematical model that represents a rotary machine. Experimental data was used to define a finite element model (FEM). In order to obtain the experimental data, the rotary machine had to be balanced. An impact hammer test made it possible to obtain frequency response functions (FRF). The frequency response functions were curvefitted in order to obtain the mode shapes and natural frequencies.
Mathematical models have been created with ABAQUS and Matlab. For the Matlab Model the assumption has been made that the rotor machine consists of a specific number of beam elements. The FEM matrices have been reduced with the Guyan Reduction Method to coincide with the DOFs of the experiment. Applying the method of the least square to an Error Function made it possible to obtain new values for the stiffness and damping of the bearings (). This made it possible to update the mathematical model. By applying the Model Assumption Criterion the theoretical model and those detected from the experimental measurement could be validated. The correlation for Mode Shapes 1 could be improved from 0.6647 to 0.8186 and for Mode Shape 2 from 0.0209 to 0.4208. Therefore, the created method could be proven to work. Additionally the whole theory has been validated with a very simplified model.
3
Hanson, David Mechanical & Manufacturing Engineering Faculty of Engineering UNSW. "Operational modal analysis and model updating with a cyclostationary input." Awarded by:University of New South Wales. School of Mechanical and Manufacturing Engineering, 2006. http://handle.unsw.edu.au/1959.4/31199.
Full textAbstract:
This thesis addresses the problem of identifying the modal properties of a system based only on measurements of the system responses. This situation is frequently encountered in structural dynamics and is particularly relevant for systems where the in-service excitation is not artificially reproducible. The inherent non-linearities in these systems mean that the modal properties estimated using traditional input/output techniques will be different to those exhibited in operation. A common example from the literature is an aircraft in flight where the modal properties are heavily influenced by the operating point, i.e. the combination of load, speed, altitude etc., at which the aircraft is travelling. The process of identifying the modal properties of systems in-service is called Operational Modal Analysis (OMA). Not knowing the input complicates the analysis. Most of the techniques in the literature overcome the lack of knowledge about the unmeasured excitations by assuming they are both spatially and frequentially white, i.e. of equal magnitude and with a flat autospectrum. This thesis presents a new technique for OMA which relaxes these constraints, requiring only that the system is excited by a so called cyclostationary input with a unique cyclic frequency, and that the log spectrum of the second order component of this input is frequentially smooth, as will be explained. Such systems include vehicles with internal combustion engines as the vibration from such an engine exhibits cyclostationary statistics. In this thesis, the technique is applied to a laboratory test rig and a passenger train both using an artificial input, and to a race car using the engine as the excitation. By combining cyclostationary signal processing and the concept of the cepstrum, the technique identifies the resonances and anti-resonances in the transfer functions between each response and the cyclostationary source. These resonances and antiresonances can be used to regenerate Frequency Response Functions (FRFs) and it is shown how the unknown scaling of the system can be recovered by employing finite element model updating in conjunction with this regeneration. In addition, the contribution made to model updating by the anti-resonances is also investigated. Finally, the potential of OMA to inform a model updating process is demonstrated using an experimental case study on a diesel railcar.
4
Ozturk, Murat. "Finite Element Structural Model Updating By Using Experimental Frequency Response Functions." Master's thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/2/12610608/index.pdf.
Full textAbstract:
Initial forms of analytical models created to simulate real engineering structures
may generally yield dynamic response predictions different than those obtained
from experimental tests. Since testing a real structure under every possible
excitation is not practical, it is essential to transform the initial mathematical
model to a model which reflects the characteristics of the actual structure in a
better way. By using structural model updating techniques, the initial
mathematical model is adjusted so that it simulates the experimental
measurements more closely.
In this study, a sensitivity-based finite element (FE) model updating method
using experimental frequency response (FRF) data is presented. This study bases
on a technique developed in an earlier study on the computation of the so-called
Mis-correlation Index (MCI) used for identifying the system matrices which
require updating. MCI values are calculated for each required coordinate, and
non-zero numerical values indicate coordinates carrying error. In this work a
new model updating procedure based on the minimization of this index is
developed. The method uses sensitivity approach. FE models are iteratively
updated by minimizing MCI values using sensitivities. The validation of the
method is realized through some case studies. In order to demonstrate the
application of the method for real systems, a real test data obtained from the
modal test of a scaled aircraft model (GARTEUR SM-AG19) is used. In the
application, the FE model of the scaled aircraft is updated. In the case studies
the generic software developed in this study is used along with some
commercial programs.
5
Levin, Robert Ian. "Dynamic Finite Element model updating using neural networks." Thesis, University of Bristol, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.264075.
Full text
6
Waters, Timothy Paul. "Finite element model updating using frequency response functions." Thesis, University of Bristol, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.294617.
Full text
7
Terrell, Michael John. "Constrained generic substructures in finite element model updating." Thesis, University of Bristol, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.430175.
Full text
8
Greening, Paul David. "Dynamic finite element modelling and updating of loaded structures." Thesis, University of Bristol, 1999. http://hdl.handle.net/1983/5f23c082-ba8b-4860-a81d-ca5e507fd632.
Full text
9
Pilkey, Deborah F. "Computation of a Damping Matrix for Finite Element Model Updating." Diss., Virginia Tech, 1998. http://hdl.handle.net/10919/30453.
Full textAbstract:
The characterization of damping is important in making accurate predictions of both the true response and the frequency response of any device or structure dominated by energy dissipation. The process of modeling damping matrices and experimental verification of those is challenging because damping can not be determined via static tests as can mass and stiffness. Furthermore, damping is more difficult to determine from dynamic measurements than natural frequency. However, damping is extremely important in formulating predictive models of structures. In addition, damping matrix identification may be useful in diagnostics or health monitoring of structures.
The objective of this work is to find a robust, practical procedure to identify damping matrices. All aspects of the damping identification procedure are investigated. The procedures for damping identification presented herein are based on prior knowledge of the finite element or analytical mass matrices and measured eigendata. Alternately, a procedure is based on knowledge of the mass and stiffness matrices and the eigendata. With this in mind, an exploration into model reduction and updating is needed to make the problem more complete for practical applications. Additionally, high performance computing is used as a tool to deal with large problems. High Performance Fortran is exploited for this purpose. Finally, several examples, including one experimental example are used to illustrate the use of these new damping matrix identification algorithms and to explore their robustness.Ph. D.
10
Khodaparast, Hamed Haddad. "Stochastic finite element model updating and its application in aeroelasticity." Thesis, University of Liverpool, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.548785.
Full text
11
Than, Soe Muang. "Vibration-based finite element model updating and structural damage identification." Thesis, University of Greenwich, 2013. http://gala.gre.ac.uk/11451/.
Full textAbstract:
Damage and material deterioration could lead to structural failure with unknown consequences. Structural health monitoring strategy based on vibration measurements for existing aging structures offers a promising technique for effectively managing the deteriorating structures. The main objectives of this research are to develop a procedure for finite element model updating by using incomplete modal data identified from vibration measurements, to develop real time structural damage detecting method by directly using vibration measurements and then identify the damage at detailed location and extend in the structure on the basis of the validated numerical model. A steel frame model structure was constructed in the laboratory for finite element model updating and structural damage detection. Forced vibration testing was undertaken on the model structure and dynamic response such as accelerations were measured by using sensors installed. Modal analyses are then carried out to identify modal parameters such as frequencies, mode shapes and damping from the vibration measurements. Structural damage scenarios were simulated by breaking bracing members of the model structure, and modal parameter of the damaged structures were also identified and analysed. An effective approach for directly updating finite element model from measured incomplete modal data with a regularised iterative algorithm is then presented. The exact relationship between the perturbation of structural parameters and the modal properties of the dynamic structure is developed. Numerical simulation investigations and experimental study of a laboratory tested space steel frame model and practical application to the Canton Tower benchmark problem are undertaken to verify the accuracy and effectiveness of the proposed model updating method. Finally, a new approach for real time structural damage detection by using acceleration measurements is presented. Structural damage is characterised at element level by introducing damage parameters which can indicate the location and severity of damage in the structure. The relationship between the damage parameters and the measured dynamic response is then established from the governing equation of the dynamic structure. Numerical examples of cantilever beams, plane frame, and braced frames are adopted to demonstrate the effectiveness of the proposed method. The new proposed technique performs well and produces stable and reliable results, which could be used for real time damage assessment during the event of earthquake and explosion.
12
Lee, Youngho. "Finite element model updating of loaded and geometrically modified structures." Thesis, University of Bristol, 2006. http://hdl.handle.net/1983/f7493e73-ad88-438c-8b8e-a3e801ec9947.
Full text
13
Hermsdorf, Nathanael. "Optimierung eines FE-Modells auf Grundlage einer experimentellen Modalanalyse." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2008. http://www.nusl.cz/ntk/nusl-264923.
Full textAbstract:
Knowledge about the dynamic behaviour is a basic condition for a secure operation of modern machine tools. Hence numerical methods predicting the dynamic properties are gaining in importance. Usually for complex and coupled structures, the results of dynamic property calculation are yet insufficient. Therefore Finite Element model updating is a tool to improve the hypothetical factor of the analysis. Within the present thesis Finite Element modelling is performed using the example of the “Scherenkinematik”, a machine tool based on hybrid-kinematics. Initially the results of an Experimental Modal Analysis are evaluated by identifying Modal parameters and deriving possible structural modifications. In the second part of the thesis, the machines Finite Element model is created using the FEA-Software ANSYS. Afterwards the Finite Element model updating is performed by coupling ANSYS and the CAE-Software FEMtools. Therefore two approaches are formulated and tracked. It turns out, that there is no improvement of the analytical and experimental models correlation, neighter with nor without a steady reduction of the search domain needed for mode coupling. It is reasoned, that the characteristics and the results of an Finite Element updating process are affected by the quality of the model at start time and the approach as well as the technique chosen for model updating and parameter modification. Therefore the CAE-Software FEMtools is suitable to only a limited extent for Finite Element updating of strongly coupled mechanical structures as a result of the sensitivity analysis used for parameter modification.
14
DeGregory, Christopher P. "Finite element model updating and damage detection using artificial boundary conditions." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1999. http://handle.dtic.mil/100.2/ADA361817.
Full textAbstract:
Thesis (M.S. in Mechanical Engineering) Naval Postgraduate School, March 1999."March 1999". Thesis advisor(s): Joshua H. Gordis. Includes bibliographical references (p. 77). Also available online.
15
Nizamiev, Kamil. "Stochastic Galerkin Model Updating of Randomly Distributed Parameters." University of Akron / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=akron1302884328.
Full text
16
Ng, G. H. T. "Finite element model updating by using natural frequency and mode shape sensitivities." Thesis, Swansea University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.638321.
Full textAbstract:
Three finite element model updating approaches are considered in this thesis. In the first updating approach, a line search method is used in conjunction with the existing two level Gauss-Newton approach. This two level updating approach was used to tackle the problem of shape function discretization and enabled a coarse finite element model to be updated without discretization bias. The purpose of the line search method is to place the updated estimates, which are obtained at each iteration step of the Newton method, in a superior position for the next Newton iteration. Accordingly, convergence can be achieved with the use of line searching in some non-convergent problems. The effectiveness of this updating technique is illustrated by both simulated and experimental case studies. The second approach is concerned with reduction methods for use in finite element model updating. Particular attention is paid to the performance of dynamic condensation and modal truncation schemes. In both cases, subspace iteration and the efficient computation approaches which incorporate the skyline storage method are used in conjunction with the updating method. Moreover, an efficient method is proposed for the computation of eigenvector sensitivities in principal co-ordinates. Two simulated updating problems containing over one thousand degrees of freedom are examined for a variety of cases using different forms of sensitivity data. Another area of interest in the present thesis is the modelling and updating of adhesive, welded and bolted joints. In the case of the adhesive joint, two modelling approaches, referred to as the simplified 'element strip' model and the complex 'full joint' model are examined. For the updating of the welded joint, careful parameterization is found to be critical. The use of nodal offset dimensions is shown to result in an updated joint with physical meaning. When applied to the non-linear adhesive and bolted joints, model updating will produce equivalent linearized representations. The methods and their effectiveness for mechanical joint model updating are demonstrated by experimental case studies.
17
Calvi, Adriano. "Finite element model updating in structural dynamics using design sensitivity and optimisation." Thesis, Cranfield University, 1998. http://dspace.lib.cranfield.ac.uk/handle/1826/10507.
Full textAbstract:
Model
updating is an important issue in engineering. In fact a well-correlated model
provides for accurate evaluation of the structure loads and responses. The main
objectives of the study were to exploit available optimisation programs to create an
error localisation and
updating procedure of nite element models that minimises
the "error" between
experimental and analytical modal data, addressing in particular
the
updating of large scale nite element models with severe requirements on the
mode
shapes correlation.
A new
methodology and procedure that allows the semi-automatic adjustment of a
large nite element dynamic model of a structure to better represent the dynamic
characteristics of an actual structure was developed. The key aspect of the procedure
is a "two
steps" optimisation process to achieve a complete correlation of the modal
data.
Eigenfrequency deviations and mode shapes cross-othogonality (CO) and/or
modal assurance criterion (MAC) are used in the objective functions for the
estimation
problem of the updating parameters, that are the variables for tuning the
analytical model. Theoretical aspects and practical implementation conceming CO
and MAC, and their derivatives, have been fully developed and the advantages of
using these mode correlation indices in the objective function have been largely
commented.
The selection of the updating parameters is a complex issue and can be still
considered a
partially open point. In the new procedure the suggested automated
selection of the
updating parameters by means of a preliminary calculation of the
element modal strain energy and eigenvalue sensitivities is adequate for the
reduction of the
frequency deviations but could not be to improve the correlation
indices of the mode shapes.
The new
procedure was successfully applied four times: to a cantilever beam model,
the Garteur model, the Spacehab dynamic model and the Mini-Pressurised Logistics
Module model. The last application was a real life application on a large scale
structural mathematical model and in this case the procedure was mainly used for
error localisation
purposes. The developed procedure is robust, effective and
efficient, thus the original objectives of the study were largely met.
18
Lee, Soon Gie. "Hybrid Damage Identification Based on Wavelet Transform and Finite Element Model Updating." University of Akron / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=akron1333676433.
Full text
19
Garcia, André Mendes. "Ajuste de modelos estruturais aplicado em problema de contato /." Ilha Solteira : [s.n.], 2006. http://hdl.handle.net/11449/94547.
Full textAbstract:
Orientador: João Antônio PereiraBanca: Amarildo Tabone Paschoalini
Banca: Heraldo Nélio Cambraia
Resumo: O presente trabalho propõe uma metodologia de ajuste de modelos de elementos finitos aplicado a problemas de contato. O ajuste do modelo é realizado através da atualização dos parâmetros físicos e/ou geométricos do modelo bem como dos parâmetros dos elementos de contato. O método utilizado é baseado nas FRF(s) e é formulado a partir de um resíduo de entrada, dado pelo balanço de força do sistema. Um software é implementado para fazer a comparação e correlação dos modelos analítico e experimental, e se necessário, ajustar os parâmetros do modelo analítico. O modelo analítico é gerado pelo software comercial ANSYSâ, e os dados experimentais são obtidos em testes experimentais de análise modal. A metodologia foi avaliada com exemplos numéricos e testes experimentais buscando identificar as potencialidades e limitações do método. Dois testes experimentais foram realizados. O primeiro teste consiste em obter os parâmetros modais de uma estrutura simples do tipo viga. No segundo teste, os parâmetros modais são obtidos de uma estrutura composta por duas peças em contato. O objetivo do primeiro teste é avaliar a potencialidade da metodologia proposta utilizando uma base de dados experimental confiável, já que a estrutura é simples e suas propriedades são bem conhecidas. O segundo teste tem por objetivo avaliar a metodologia para o problema de contato. Os resultados apresentados mostram a funcionalidade da metodologia. O ajuste foi realizado com êxito tanto para a estrutura simples como para a estrutura composta por duas peças em contato.
Abstract: The present work proposes a finite element model updating methodology applied to problems of contact. The updating of the models is accomplished through the updating of the physical and/or geometric parameters of the model as well as the parameters of the contact elements. The approach is a FRF-based method; it is formulated from input residue, given by the equilibrium force of the system. It is implemented a software to makes the comparison and correlation of the analytical and experimental models, and if necessary, to adjust the parameters of the analytic model based in the experimental data, in order to get a more reliable finite element model. The analytical model is created by the commercial software ANSYSâ, and the experimental data are obtained by experimental modal tests. The methodology was evaluated with numeric and experimental data aiming at identifying of the potentialities and limitations of the method. Two experimental tests were developed, the first test consists of the analyses of a beam like structure and the second one, the analysis of a structure composed by two pieces in contact. The aim of the first test is to evaluate the potentiality of the methodology using a reliable experimental base of data, since the structure is simple and its properties are very wellknown. The second test has for objective to evaluate the methodology for problems of contact. The presented results have shown the functionality of the methodology. The adjustment was accomplished with relative success for the simple structure as well as for the structure composed by two pieces in contact.
Mestre
20
Marrè, Badalló Roser. "Implementation and Testing of Two Bee-Based Algorithms in Finite Element Model Updating." Thesis, KTH, Bro- och stålbyggnad, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-140846.
Full textAbstract:
Finite Element Model Updating has recently arisen as an issue of vast importance on the design, construction and maintenance of structures in civil engineering. Many algorithms have been proposed, developed and enhanced in order to accomplish the demands of the updating process, mainly to achieve computationally efficient programs and greater results.The present Master Thesis proposes two new algorithms to be used in Finite Element Model Updating: the Bees Algorithms (BA) and the Artificial Bee Colony algorithm (ABC). Both were first proposed in 2005, are based on the foraging behaviour of bees and have been proved to be efficient algorithms in other fields. The objective of this Master Thesis is, thus, to implement and to test these two newalgorithms in Finite Element Model Updating for a cantilever beam. The Finite Element Model and the algorithms are programmed, followed by the extraction of the experimental frequencies and the updating process. Results, comparison of these two methods and conclusions are given at the end of this report, as well as suggestions for further work.
21
XHIXHA, ELONA. "PASSIVE METHOD FOR DYNAMIC CHARACTERIZATION OF SOIL AND BUILDINGS." Doctoral thesis, Università di Siena, 2017. http://hdl.handle.net/11365/1013203.
Full textAbstract:
The research followed consist mainly on the use of passive methods for dynamic characterization of soil and building. Local Seismic Response of the construction site and Calibration of FE model of a reinforced concrete building have been performed. Passive seismic measurements have been acquired by two portable seismographs synchronized by each other with GPS antenna. Subsequently, structural verifications (global structural response) have been realized using once the response spectrum estimated from Local Seismic Response and once from technical standards. Finally, confronts between results have been realized at the aim to evaluate the importance of local seismic response of soil.
22
Lindholm, Brian Eric. "A Bayesian statistics approach to updating finite element models with frequency response data." Diss., This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-06062008-152108/.
Full text
23
Garcia, André Mendes [UNESP]. "Ajuste de modelos estruturais aplicado em problema de contato." Universidade Estadual Paulista (UNESP), 2006. http://hdl.handle.net/11449/94547.
Full textAbstract:
Made available in DSpace on 2014-06-11T19:27:14Z (GMT). No. of bitstreams: 0
Previous issue date: 2006-10-31Bitstream added on 2014-06-13T19:55:35Z : No. of bitstreams: 1
garcia_am_me_ilha.pdf: 659750 bytes, checksum: 7318de4cdef56cfcd2a84f0bc10c3fbb (MD5)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
O presente trabalho propõe uma metodologia de ajuste de modelos de elementos finitos aplicado a problemas de contato. O ajuste do modelo é realizado através da atualização dos parâmetros físicos e/ou geométricos do modelo bem como dos parâmetros dos elementos de contato. O método utilizado é baseado nas FRF(s) e é formulado a partir de um resíduo de entrada, dado pelo balanço de força do sistema. Um software é implementado para fazer a comparação e correlação dos modelos analítico e experimental, e se necessário, ajustar os parâmetros do modelo analítico. O modelo analítico é gerado pelo software comercial ANSYSâ, e os dados experimentais são obtidos em testes experimentais de análise modal. A metodologia foi avaliada com exemplos numéricos e testes experimentais buscando identificar as potencialidades e limitações do método. Dois testes experimentais foram realizados. O primeiro teste consiste em obter os parâmetros modais de uma estrutura simples do tipo viga. No segundo teste, os parâmetros modais são obtidos de uma estrutura composta por duas peças em contato. O objetivo do primeiro teste é avaliar a potencialidade da metodologia proposta utilizando uma base de dados experimental confiável, já que a estrutura é simples e suas propriedades são bem conhecidas. O segundo teste tem por objetivo avaliar a metodologia para o problema de contato. Os resultados apresentados mostram a funcionalidade da metodologia. O ajuste foi realizado com êxito tanto para a estrutura simples como para a estrutura composta por duas peças em contato.
The present work proposes a finite element model updating methodology applied to problems of contact. The updating of the models is accomplished through the updating of the physical and/or geometric parameters of the model as well as the parameters of the contact elements. The approach is a FRF-based method; it is formulated from input residue, given by the equilibrium force of the system. It is implemented a software to makes the comparison and correlation of the analytical and experimental models, and if necessary, to adjust the parameters of the analytic model based in the experimental data, in order to get a more reliable finite element model. The analytical model is created by the commercial software ANSYSâ, and the experimental data are obtained by experimental modal tests. The methodology was evaluated with numeric and experimental data aiming at identifying of the potentialities and limitations of the method. Two experimental tests were developed, the first test consists of the analyses of a beam like structure and the second one, the analysis of a structure composed by two pieces in contact. The aim of the first test is to evaluate the potentiality of the methodology using a reliable experimental base of data, since the structure is simple and its properties are very wellknown. The second test has for objective to evaluate the methodology for problems of contact. The presented results have shown the functionality of the methodology. The adjustment was accomplished with relative success for the simple structure as well as for the structure composed by two pieces in contact.
24
Renken, Jay A. "Optimal solution selection for sensitivity-based finite element model updating and structural damage detection." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1995. http://handle.dtic.mil/100.2/ADA306053.
Full textAbstract:
Thesis (M.S. in Mechanical Engineering and Mechanical Engineer) Naval Postgraduate School, December 1995.Thesis advisor(s): Joshua H. Gordis. "December 1995." Includes bibliographical references. Also available online.
25
Pampalone, Michael R. "Development, correlation and updating of a finite element model of the OH-6A helicopter." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1996. http://handle.dtic.mil/100.2/ADA333338.
Full text
26
Fernandez, Constance R. S. "Artificial boundary conditions in sensitivity based finite element model updating and structural damage detection." Thesis, Monterey California. Naval Postgraduate School, 2005. http://hdl.handle.net/10945/1786.
Full textAbstract:
A finite element (FE) model is a computational representation of a given structure. In order for the FE model to accurately predict structure response, the model is "updated" or improved. This thesis investigates the use of artificial boundary conditions in sensitivity-based model updating and damage detection. A comparative analysis was conducted on the accuracy of error identification and location with respect to the artificial boundary conditions imposed and the number of modes retained. Results are demonstrated with actual test data from a simple structure.
27
ZHU, SHICHAO. "RECURSIVE MULTI-MODEL UPDATING OF BUILDING STRUCTURE: A NEW SENSITIVITY BASED FINITE ELEMENT APPROACH." Doctoral thesis, Politecnico di Torino, 2016. http://hdl.handle.net/11583/2643111.
Full textAbstract:
An invaluable tool for structural health monitoring and damage detection, parametric system identification through model-updating is an inverse problem, affected by several kinds of modelling assumptions and measurement errors. By minimizing the discrepancy between the measured data and the simulated response, traditional model-updating techniques identify one single optimal model that behaves similarly to the real structure. Due to several sources of errors, this mathematical optimum may be far from the true solution and lead to misleading conclusions about the structural state. Instead of the mere location of the global minimum, it should be therefore preferred the generation of several alternatives, capable to express near-optimal solutions while being as different as possible from each other in physical terms.
The present paper accomplishes this goal through a new recursive, direct-search, multi-model updating technique, where multiple models are first created and separately solved for the respective minimum, and then a selection of quasi-optimal alternatives is retained and classified through data mining and clustering algorithm. The main novelty of the approach consists in the recursive strategy adopted for minimizing the objective function, where convergence towards optimality is sped up by sequentially changing only selected subsets of parameters, depending on their respective influence on the error function. Namely, this approach consists of two steps. First, a sensitivity analysis is performed. The input parameters are allowed to vary within a small interval of fractional variation around a nominal value to compute the partial derivatives numerically. After that, for each parameter the sensitivities to all the responses are summed up, and used as an indicator of sensitivity of the parameter. According to the sensitivity indicators the parameters are divided into an indicated number of subsets given by the user. Then every subset is updated recursively with a specified order according to the sensitivity indicator.
28
Conradie, Johan. "Finite Element Modelling of Off-Road Tyres." Diss., University of Pretoria, 2014. http://hdl.handle.net/2263/45957.
Full textAbstract:
Most tyre models developed to date require a fair amount of data before an accurate representation of the tyre can be obtained. This study entails the development of a simplified, yet accurate, non-linear Finite Element (FE) model of an “off-road” tyre to study the behaviour of the tyre due to radial loading conditions. The study aims to develop a FE tyre model that can solve fast and be accurate enough to be used in multibody dynamic vehicle simulations. A model that is less complex than conventional detailed FE models is developed.
The work explores the use of superimposed finite elements to model the varying stiffness in the respective orthogonal directions of the sidewall and tread of the tyre. Non-linear elements defined by Neo-Hookean or Ogden models and elements with different linear orthogonal stiffnesses are superimposed onto each other to simulate the global material properties of the tread and the sidewall of the tyre investigated.
The geometry of the tyre studied was measured experimentally using laser displacement transducers and digital image correlation techniques. Material properties of segments of the tyre were obtained by performing tensile tests on samples. Since the rubber slipped against the clamps during the experiment, deformation of the segments was also measured using digital image correlation. These geometrical and material properties were used as input to develop a finite element model of an “off-road” tyre.
Measurements were conducted using laser displacement transducers, load cells mounted to actuators, etc. to obtain accurate sidewall deformation profiles and global radial load vs. displacement curves for different radial loading conditions. The data obtained from the results was used to validate the tyre model developed.
Numerous analyses are performed with different combinations of moduli of elasticity in the respective orthogonal directions of the sidewall stiffness and the tread to investigate its influence on the global behaviour of the tyre model.
The main focus of the project was to develop a tyre model from data obtained from laser and photogrammetry measurements in a laboratory that accurately represents tyre behaviour due to radial forces. A finite element model that can simulate the effect of radial forced and obstacles on a tyre was developed. The use of two subsets of elements, superimposed onto each other to simulate global material properties of the rubbers, steel wires, polyester and nylon threads, was investigated.
The combination of material properties that gave the best fit for all the load cases investigated were determined. The finite element model correlated well with the load vs. displacement graphs and sidewall displacement profiles determined experimentally.
The solving time is still fairly high and is still not quite suitable for real-time dynamic simulation. However, it solves faster than more complex tyre models where details of steel wires, etc. are included in the model.
For future studies it is recommended that different element types be investigated in the tyre model.
The study proves that equivalent material properties can be used to simulate the composite properties of the materials in tyres. Most tyres can be divided into a few regions that each has its own material structure right through the region. These regions can be characterized by simple tests and the input can be used as a first estimation of the tyre’s material properties for the model.
Accurate validation criteria should be used to validate the tyre model if time does not allow for excessive testing of the material properties of all the rubber, steel wires, polyester threads, etc. Geometric displacement data at various loading conditions can be used for validation of the tyre model.
The model developed can be used to investigate the effect of different stiffnesses and other material changes in the sidewall or tread of a tyre. Useful insight can be obtained from the finite element model developed for dynamic simulation where the force vs. global displacement data is important.Dissertation (MEng)--University of Pretoria, 2014.
tm2015
Mechanical and Aeronautical Engineering
MEng
Unrestricted
29
Kodikara, Kodikara Arachchige Tharindu Lakshitha. "Structural health monitoring through advanced model updating incorporating uncertainties." Thesis, Queensland University of Technology, 2017. https://eprints.qut.edu.au/110811/1/Kodikara%20Arachchige%20Tharindu%20Lakshitha_Kodikara_Thesis.pdf.
Full textAbstract:
This research developed comprehensive model updating systems for real structures including a hybrid approach which enhanced existing deterministic model updating techniques by providing measures to incorporate uncertainties in a computationally efficient way compared to probabilistic model updating approaches. Further, utilizing the developed hybrid approach a methodology was developed to assess the deterioration of reinforced concrete buildings under serviceability loading conditions. The developed methodologies in the research were successfully validated utilizing two real benchmark structures at Queensland University of Technology equipped with continuous monitoring systems.
30
Karaagacli, Taylan. "Determination Of Dynamically Equivalent Fe Models Of Aircraft Structures By Using Modal Test Data." Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612522/index.pdf.
Full textAbstract:
Reliable flutter analysis of aircraft structures is a major requirement to determine
safe flight envelops. Dynamically equivalent finite element model of an aircraft
structure correlating well with experimental modal is a major requirement for a
reliable flutter analysis. Currently available model updating techniques require
enormous time and engineering work to achieve appropriate finite element models
of aircraft structures. The method developed within the scope of this thesis work
aims to remove important disadvantages of common model updating procedures. In
doing this, the method starts with a simple finite element mesh obtained by
connecting measurement points, used in the Ground Vibration Test of an aircraft
structure, with 3 D Euler-Bernoulli beam elements. Initial estimates of the geometric
and material properties are determined by solving structural identification equations
derived from the mass and stiffness orthogonality of experimental modes. By using
those initial estimates, an initial finite element model is constructed. Starting from
this initial finite element model, structural identification equations are updated and
solved iteratively by using experimental natural frequencies and eigenvectors of the
v
updated finite element model representing the same mode shapes with measured
normal modes. Iterations are continued until eigen solution of the updated finite
element model closely correlates with experimental modal data.
The applicability of the method is illustrated on a scaled aircraft model and a real
aircraft structure. The results are quite satisfactory but the method requires further
improvements to achieve a much better correlation level in case of real aircraft
structures.
31
Graziano, Maria. "Updating of Finite Element Models using static and dynamic optical strains with application to damage assessment." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2016.
Find full textAbstract:
In the recent years, vibration-based structural damage identification has been subject of significant research in structural engineering. The basic idea of vibration-based methods is that damage induces mechanical properties changes that cause anomalies in the dynamic response of the structure, which measures allow to localize damage and its extension. Vibration measured data, such as frequencies and mode shapes, can be used in the Finite Element Model Updating in order to adjust structural parameters sensible at damage (e.g. Young’s Modulus). The novel aspect of this thesis is the introduction into the objective function of accurate measures of strains mode shapes, evaluated through FBG sensors.
After a review of the relevant literature, the case of study, i.e. an irregular prestressed concrete beam destined for roofing of industrial structures, will be presented. The mathematical model was built through FE models, studying static and dynamic behaviour of the element.
Another analytical model was developed, based on the ‘Ritz method’, in order to investigate the possible interaction between the RC beam and the steel supporting table used for testing.
Experimental data, recorded through the contemporary use of different measurement techniques (optical fibers, accelerometers, LVDTs) were compared whit theoretical data, allowing to detect the best model, for which have been outlined the settings for the updating procedure.
32
Hanselowski, Andreas [Verfasser]. "A Fuzzy Arithmetical Approach to Finite Element Model Updating Applied to an Automotive Brake System / Andreas Hanselowski." Aachen : Shaker, 2017. http://d-nb.info/1139583344/34.
Full text
33
Choi, Jiduck. "Investigation of the dynamic behavior of a cable-harnessed structure." Diss., Virginia Tech, 2014. http://hdl.handle.net/10919/49114.
Full textAbstract:
To obtain predictive modeling of a spacecraft, the author investigates the effects of adding cables to a simple structure with the goal of developing an understanding of how cables interacting with a structure. In this research, the author presents predictive and accurate modeling of a cable-harnessed structure by means of the Spectral Element Method (SEM). A double beam model is used to emulate a cable-harnessed structure. SEM modeling can define the location and the number of connections between the two beams in a convenient fashion. The proposed modeling is applied and compared with the conventional FEM. The modeling approach was compared to and validated by measurement data. The validated modeling was implemented to investigate the effect of the number of connections, of the spring stiffness of interconnections, and of mass portion of an attached cable. Damping has an important role in structural design because it reduces the dynamic response, thereby avoiding excessive deflection or stress, fatigue loads, and settling times. Experimental results with some specimens indicate a clear change of damping on the main structure with the inclusion of cable dynamics. The author investigated the modification of the damping of the host structure induced by various attached cables. The identification of a damping matrix is performed using measured data. The effect of the flexibility of a cable harness on damping is observed through experiments with various types of cables. The effect of the number of connections on damping is also investigated by changing the number of connections. Moreover, to overcome the sensitivity to noise in measured data of damping matrix identification approach, various methods are compared with a simulated lumped model and real test results. An improved damping matrix identification approach is proposed and can generate the unique damping matrix over the full frequency range of interest.Ph. D.
34
Nichols, Jonathan Tyler. "Application of Load Updating to a Complex Three Dimensional Frame Structure." Thesis, Virginia Tech, 2017. http://hdl.handle.net/10919/78274.
Full textAbstract:
This thesis presents a novel method for the correlation of FEM results to experimental test results known as the "Load updating method." Specifically, the load updating method uses the math model from the FEM and the strains measured from experimental or flight test data as inputs and then predicts the loads in the FEM which would result in strains that would correlate best to the measured strains in the least squared sense. In this research, the load updating method is applied to the analysis of a complex frame structure whose validation is challenging due to the complex nature of its structural behavior, load distributions, and error derived from residual strains. A FEM created for this structure is used to generate strain data for thirty-two different load cases. These same thirty-two load cases are replicated in an experimental setup consisting of the frame, supporting structure, and thirty actuators which are used to load the frame according to the specifications for each of the thirty-two load conditions. A force-strain matrix is created from the math model in NASTRAN using unit loads which are separately applied to each load point in order to extract strain results for each of the locations of the seventy-four strain gages. The strain data from the structural test and the force-strain matrix is then input into a Matlab code which is created to perform the load updating method. This algorithm delivers a set of coefficients which in turn gives the updated loads. These loads are applied to the FEM and the strain values extracted for correlation to the strains from test data. It is found that the load updating method applied to this structure produces strains which correlate well to the experimental strain data. Although the loads found using the load updating method do not perfectly match those which are applied during the test, this error is primarily attributed to residual strains within the structure. In summary, the load updating method provides a way to predict loads which, when applied to the FEM, would result in strains that correlate best to the experimental strains. Ultimately, this method could prove especially useful for predicting loads in experimental and flight test structures and could aid greatly in the Federal Aviation Administration (FAA) certification process.Master of Science
35
Jayakumar, Vignesh. "Finite Element Model Correlation with Experiment Focusing on Descriptions of Clamped Boundary Condition and Damping." University of Cincinnati / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1592171762884289.
Full text
36
Orlando, Lorenzo. "Finite Element model calibration of a historical railway steel truss bridge by using dynamic monitoring data." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2022.
Find full textAbstract:
This paper proposes a multidisciplinary approach, combining the terrestrial laser scanner and ambient vibration tests to characterize a historical steel truss bridge in Spain: the
Vilagarcia Celosia Bridge. All methods are complemented by advanced numerical simulations and a coarse to fine calibration strategy, based on the Cotter and the non-linear least squares approaches. Results obtained corroborate the robustness of the proposed approach, with a max error in frequencies of 3.6% and an average modal assurance criterion of 0.93.
37
Miguel, Escudero López José. "Traffic-induced vibrations on a two span composite railway bridge : Comparison of theory and measurements." Thesis, KTH, Bro- och stålbyggnad, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-36360.
Full textAbstract:
The economic and technologic development experienced by the society in the last decades has caused the demand of a new type of faster and more comfortable transport. This type of demand has been covered by the air transport, the road transport and the railway transport. This situation where the society demands an improvement in her quality of life is the best situation for the birth of the high speed trains. Different studies carried out in the transport field have demonstrated that for distances between four hundred and one thousand of kilometres, the high speed trains provide a lower travelling times than the rest of the transports. These types of high speed trains have increased the axle loads and the average speeds, thus generally a dynamic analysis is required by the ERRI in all the railway bridges when the train speed is higher than 200 Km/h. Besides, when the train speed is going to be higher than 200 Km/h, the vibrations induced in the bridge can reduce the service life of the vehicles and structure, and generally, this fact leads to become the dynamic effect in the principal factor to take into account in order to design the structure. Therefore, an important knowledge in railway bridges dynamic is required to not to oversize the structures with the consequent economic cost. The purpose of this thesis is to study the possibility of accurately predicting the dynamic response of an existing railway bridge, subjected to the high speed train Gröna Tåget, implementing a simplified 2D finite element model with the aid of the program Abaqus. The bridge chosen is the Lögdeälv Bridge, a two spans composite bridge, located along the Bothnia Line (the new Swedish high-speed line), between the localities of Nordmaling and Rundvik. The measured eigenfrequencies due to bending modes of vibration are used for updating the model and then, these frequencies and the accelerations measured are used to compare and validate the different 2D updated models. The parameters used to update the models are; the damping coefficient of the structure, the mass and the stiffness of the bridge, and the supports stiffness. Finally it is concluded that the best model is achieved when the rotational support stiffness is modified in the two extremes supporters of the bridge.
38
Moravej, Hans. "Vibration-based probabilistic model updating of civil structures using structural health monitoring techniques." Thesis, Queensland University of Technology, 2020. https://eprints.qut.edu.au/203653/1/Hans%20Moravej%20Thesis.pdf.
Full textAbstract:
Information extracted from monitored data is susceptible to uncertainties and not reliable to be used for structural investigations. Finite element model updating (FEMU) is an accredited framework which aims to improve the accuracy of FEMs of real structures. However, FEMU faces barriers to achieving efficiency and addressing uncertainties. This study aims to develop a probabilistic approach based on Modular Bayesian approach (MBA) to address challenges in the application of FEMU. Moreover, this research proposes an integration between MBA and structural reliability analysis to assess the performance of structures during their lifespan. The feasibility of approach is demonstrated on two structures.
39
Wang, Liang. "Innovative damage assessment of steel truss bridges using modal strain energy correlation." Thesis, Queensland University of Technology, 2012. https://eprints.qut.edu.au/53177/1/Liang_Wang_Thesis.pdf.
Full textAbstract:
As a part of vital infrastructure and transportation network, bridge structures must function safely at all times. Bridges are designed to have a long life span. At any point in time, however, some bridges are aged. The ageing of bridge structures, given the rapidly growing demand of heavy and fast inter-city passages and continuous increase of freight transportation, would require diligence on bridge owners to ensure that the infrastructure is healthy at reasonable cost. In recent decades, a new technique, structural health monitoring (SHM), has emerged to meet this challenge. In this new engineering discipline, structural modal identification and damage detection have formed a vital component. Witnessed by an increasing number of publications is that the change in vibration characteristics is widely and deeply investigated to assess structural damage. Although a number of publications have addressed the feasibility of various methods through experimental verifications, few of them have focused on steel truss bridges. Finding a feasible vibration-based damage indicator for steel truss bridges and solving the difficulties in practical modal identification to support damage detection motivated this research project.
This research was to derive an innovative method to assess structural damage in steel truss bridges. First, it proposed a new damage indicator that relies on optimising the correlation between theoretical and measured modal strain energy. The optimisation is powered by a newly proposed multilayer genetic algorithm. In addition, a selection criterion for damage-sensitive modes has been studied to achieve more efficient and accurate damage detection results. Second, in order to support the proposed damage indicator, the research studied the applications of two state-of-the-art modal identification techniques by considering some practical difficulties: the limited instrumentation, the influence of environmental noise, the difficulties in finite element model updating, and the data selection problem in the output-only modal identification methods.
The numerical (by a planer truss model) and experimental (by a laboratory through truss bridge) verifications have proved the effectiveness and feasibility of the proposed damage detection scheme. The modal strain energy-based indicator was found to be sensitive to the damage in steel truss bridges with incomplete measurement. It has shown the damage indicator's potential in practical applications of steel truss bridges. Lastly, the achievement and limitation of this study, and lessons learnt from the modal analysis have been summarised.
40
Monballiu, Franck, and Wouter Schils. "The effect of increasing train lengths on the fatigue lifespan of a bridge." Thesis, KTH, Bro- och stålbyggnad, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-187868.
Full textAbstract:
More and more pressure is exerted on railway infrastructure due to an increasing transportation demand and population density. Instead of expanding the net, a possible solution could lie in the enlargement of the capacity by operating longer trains rather than more short ones. However, close attention has to be paid to the behaviour and the lifetime of the infrastructure under these changed loads. In special bridges are delicate aspects in this matter. In the current thesis the simply supported Banafjäl bridge located on the Bothnia Line in the North of Sweden is studied more in detail with regards to this aspect. It is a high-speed composite railway bridge with a span of 42 m. A detailed 3D finite element (FE) model is made available. However in order to make reliable predictions about the behaviour under increasing train length loads, it had to be further improved. Different methods of calibrating measured response data to an existing FE model, finite element model updating (FEMU), are available and a detailed overview is given at the beginning of this thesis. Next a sensitivity analysis was performed to select the material parameters which are most influential for the result and will be updated. In the following, FEMU is carried out by means of two iterative updating methods, genetic and gradient-based optimization, after which also a combination of these two is implemented. Two objective functions are chosen and it is shown that all methods converge to a global optimal solution. After adjusting the initial model with the updated parameter values, a fatigue analysis on this updated model is carried out for high-speed trains of multiple lengthsby means of the Palmgren-Miner rule. The fatigue is found to increase with increasing train length and in particular when the speed approaches resonance speed. By extension an operating chart is created to indicate the maximum amount of train passages per day in function of speed and train length for a type 4 fatigue train. Furthermore, damping has been shown to have a positive effect on the fatigue, the larger this effect for shorter trains. The static behaviour has been proven not to be a problem and so will solely the weight of trains induce little to no fatigue problems in this particular bridge.
41
Phillips, Peter Louis. "Integrated Multiaxial Experimentation and Constitutive Modeling." University of Dayton / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1492598070791388.
Full text
42
Smith, Chandler B. "Sparsity Constrained Inverse Problems - Application to Vibration-based Structural Health Monitoring." ScholarWorks @ UVM, 2019. https://scholarworks.uvm.edu/graddis/1143.
Full textAbstract:
Vibration-based structural health monitoring (SHM) seeks to detect, quantify, locate, and prognosticate damage by processing vibration signals measured while the structure is operational. The basic premise of vibration-based SHM is that damage will affect the stiffness, mass or energy dissipation properties of the structure and in turn alter its measured dynamic characteristics. In order to make SHM a practical technology it is necessary to perform damage assessment using only a minimum number of permanently installed sensors. Deducing damage at unmeasured regions of the structural domain requires solving an inverse problem that is underdetermined and(or) ill-conditioned. In addition, the effects of local damage on global vibration response may be overshadowed by the effects of modelling error, environmental changes, sensor noise, and unmeasured excitation. These theoretical and practical challenges render the damage identification inverse problem ill-posed, and in some cases unsolvable with conventional inverse methods.
This dissertation proposes and tests a novel interpretation of the damage identification inverse problem. Since damage is inherently local and strictly reduces stiffness and(or) mass, the underdetermined inverse problem can be made uniquely solvable by either imposing sparsity or non-negativity on the solution space. The goal of this research is to leverage this concept in order to prove that damage identification can be performed in practical applications using significantly less measurements than conventional inverse methods require. This dissertation investigates two sparsity inducing methods, L1-norm optimization and the non-negative least squares, in their application to identifying damage from eigenvalues, a minimal sensor-based feature that results in an underdetermined inverse problem. This work presents necessary conditions for solution uniqueness and a method to quantify the bounds on the non-unique solution space. The proposed methods are investigated using a wide range of numerical simulations and validated using a four-story lab-scale frame and a full-scale 17 m long aluminum truss. The findings of this study suggest that leveraging the attributes of both L1-norm optimization and non-negative constrained least squares can provide significant improvement over their standalone applications and over other existing methods of damage detection.
43
Fodor, Ján. "Určování mechanických charakteristik materiálů vícevrstvých struktur s využitím metody zvukové rezonance a modální MKP analýzy." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2017. http://www.nusl.cz/ntk/nusl-318138.
Full textAbstract:
Thesis deals with determination of layerwise mechanical properties of composite ceramics by indirect method, namely Youngs modulus. Based on literature review, it was found that a method to determine elastic properties of one or more components of multi layered composites based on experimental modal analysis and finite element modal analysis, or analytical approach exists. Method based on FE modal analysis was applied to ceramic laminate, where it was attempt to determine youngs modulus of one component. Beyond that, it was attempt to determine Youngs moduli of both components using first two bending resonant frequencies. Results were unsatisfying. Sensitivity analysis showed that layers with unknown Youngs modulus were overly sensitive to small changes in input parameters due to their small relative thickness with respect to thickness of laminate and due to location in laminate. Based on this conclusion, recommendations were made with respect to suitable geometry of test specimens.
44
Salami, Pargoo Navid. "Modeling and calibration of a High Speed Train Railway Bridge based on in-field vibration data." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021.
Find full textAbstract:
Today, high-speed trains railway bridges are monitored and analyzed more stringently and detailed to guarantee the reliability and safety of structure. The increase in speed and loads of trains can impose excessive acceleration and displacement or cause resonance in bridge superstructure, which endangers both the integrity of bridge structure and the safety of passengers using the bridge.
The thesis presents a calibration procedure for a high-fidelity finite element model of a railway bridge to identify the unknown physical parameters using operational modal data. The detailed 3D modelling can decrease the number of uncertainties in the model. The objective is to modify the influential parameters of the bridge model so that its eigenfrequencies and mode shapes matches, as closely as possible, that of the bridge under analysis. The calibration is realized by parametric analysis and manual tuning the uncertain parameters, such as support condition, to the experimental data achieved through Operational Modal Analysis. Furthermore, the optimized finite element model was utilized in moving load simulations with high-speed train loads according to the passages recorded in order to verify the model and assess the possibility of safely increasing the speed of trains travelling over the bridge.
Finally, it is shown that developing a high-fidelity finite element model may help simplifying the model calibration process for a large structure.
45
Zolghadri, Navid. "Short and Long-Term Structural Health Monitoring of Highway Bridges." DigitalCommons@USU, 2017. https://digitalcommons.usu.edu/etd/5626.
Full textAbstract:
Structural Health Monitoring (SHM) is a promising tool for condition assessment of bridge structures. SHM of bridges can be performed for different purposes in long or short-term. A few aspects of short- and long-term monitoring of highway bridges are addressed in this research.
Without quantifying environmental effects, applying vibration-based damage detection techniques may result in false damage identification. As part of a long-term monitoring project, the effect of temperature on vibrational characteristics of two continuously monitored bridges are studied. Natural frequencies of the structures are identified from ambient vibration data using the Natural Excitation Technique (NExT) along with the Eigen System Realization (ERA) algorithm. Variability of identified natural frequencies is investigated based on statistical properties of identified frequencies. Different statistical models are tested and the most accurate model is selected to remove the effect of temperature from the identified frequencies. After removing temperature effects, different damage cases are simulated on calibrated finite-element models. Comparing the effect of simulated damages on natural frequencies showed what levels of damage could be detected with this method.
Evaluating traffic loads can be helpful to different areas including bridge design and assessment, pavement design and maintenance, fatigue analysis, economic studies and enforcement of legal weight limits. In this study, feasibility of using a single-span bridge as a weigh-in-motion tool to quantify the gross vehicle weights (GVW) of trucks is studied. As part of a short-term monitoring project, this bridge was subjected to four sets of high speed, live-load tests. Measured strain data are used to implement bridge weigh-in-motion (B-WIM) algorithms and calculate the corresponding velocities and GVWs. A comparison is made between calculated and static weights, and furthermore, between supposed speeds and estimated speeds of the trucks.
Vibration-based techniques that use finite-element (FE) model updating for SHM of bridges are common for infrastructure applications. This study presents the application of both static and dynamic-based FE model updating of a full scale bridge. Both dynamic and live-load testing were conducted on this bridge and vibration, strain, and deflections were measured at different locations. A FE model is calibrated using different error functions. This model could capture both global and local response of the structure and the performance of the updated model is validated with part of the collected measurements that were not included in the calibration process.
46
Karavelić, Emir. "Stochastic Galerkin finite element method in application to identification problems for failure models parameters in heterogeneous materials." Thesis, Compiègne, 2019. http://www.theses.fr/2019COMP2501.
Full textAbstract:
Cette thèse traite de rupture localisée de structures construites en matériau composite hétérogène, comme le béton, à deux échelles différentes. Ces deux échelles sont connectées par le biais de la mise à l'échelle stochastique, où toute information obtenue à l'échelle méso est utilisée comme connaissance préalable à l'échelle macro. À l'échelle méso, le modèle de réseau est utilisé pour représenter la structure multiphasique du béton, à savoir le ciment et les granulats. L'élément de poutre représenté par une poutre Timoshenko 3D intégrée avec de fortes discontinuités assure un maillage complet indépendance de la propagation des fissures. La géométrie de la taille des agrégats est prise en accord avec la courbe EMPA et Fuller tandis que la distribution de Poisson est utilisée pour la distribution spatiale. Les propriétés des matériaux de chaque phase sont obtenues avec une distribution gaussienne qui prend en compte la zone de transition d'interface (ITZ) par l'affaiblissement du béton. À l'échelle macro, un modèle de plasticité multisurface est choisi qui prend en compte à la fois la contribution d'un écrouissage sous contrainte avec une règle d'écoulement non associative ainsi que des composants d'un modèle d'adoucissement de déformation pour un ensemble complet de différents modes de défaillance 3D. Le modèle de plasticité est représenté par le critère de rendement Drucker-Prager, avec une fonction potentielle plastique similaire régissant le comportement de durcissement tandis que le comportement de ramollissement des contraintes est représenté par le critère de St. Venant. La procédure d'identification du modèle macro-échelle est réalisée de manière séquentielle. En raison du fait que tous les ingrédients du modèle à l'échelle macro ont une interprétation physique, nous avons fait l'étalonnage des paramètres du matériau en fonction de l'étape particulière. Cette approche est utilisée pour la réduction du modèle du modèle méso-échelle au modèle macro-échelle où toutes les échelles sont considérées comme incertaines et un calcul de probabilité est effectué. Lorsque nous modélisons un matériau homogène, chaque paramètre inconnu du modèle réduit est modélisé comme une variable aléatoire tandis que pour un matériau hétérogène, ces paramètres de matériau sont décrits comme des champs aléatoires. Afin de faire des discrétisations appropriées, nous choisissons le raffinement du maillage de méthode p sur le domaine de probabilité et la méthode h sur le domaine spatial. Les sorties du modèle avancé sont construites en utilisant la méthode de Galerkin stochastique fournissant des sorties plus rapidement le modèle avancé complet. La procédure probabiliste d'identification est réalisée avec deux méthodes différentes basées sur le théorème de Bayes qui permet d'incorporer de nouvelles bservations générées dans un programme de chargement particulier. La première méthode Markov Chain Monte Carlo (MCMC) est identifiée comme mettant à jour la mesure, tandis que la deuxième méthode Polynomial Chaos Kalman Filter (PceKF) met à jour la fonction mesurable. Les aspects de mise en œuvre des modèles présentés sont donnés en détail ainsi que leur validation à travers les exemples numériques par rapport aux résultats expérimentaux ou par rapport aux références disponibles dans la littératureThis thesis deals with the localized failure for structures built of heterogeneous composite material, such as concrete, at two different scale. These two scale are latter connected through the stochastic upscaling, where any information obtained at meso-scale are used as prior knowledge at macro-scale. At meso scale, lattice model is used to represent the multi-phase structure of concrete, namely cement and aggregates. The beam element represented by 3D Timoshenko beam embedded with strong discontinuities ensures complete mesh independency of crack propagation. Geometry of aggregate size is taken in agreement with EMPA and Fuller curve while Poisson distribution is used for spatial distribution. Material properties of each phase is obtained with Gaussian distribution which takes into account the Interface Transition Zone (ITZ) through the weakening of concrete. At macro scale multisurface plasticity model is chosen that takes into account both the contribution of a strain hardening with non-associative flow rule as well as a strain softening model components for full set of different 3D failure modes. The plasticity model is represented with Drucker-Prager yield criterion, with similar plastic potential function governing hardening behavior while strain softening behavior is represented with St. Venant criterion. The identification procedure for macro-scale model is perfomed in sequential way. Due to the fact that all ingredients of macro-scale model have physical interpretation we made calibration of material parameters relevant to particular stage. This approach is latter used for model reduction from meso-scale model to macro-scale model where all scales are considered as uncertain and probability computation is performed. When we are modeling homogeneous material each unknown parameter of reduced model is modeled as a random variable while for heterogeneous material, these material parameters are described as random fields. In order to make appropriate discretizations we choose p-method mesh refinement over probability domain and h-method over spatial domain. The forward model outputs are constructed by using Stochastic Galerkin method providing outputs more quickly the the full forward model. The probabilistic procedure of identification is performed with two different methods based on Bayes’s theorem that allows incorporating new observation generated in a particular loading program. The first method Markov Chain Monte Carlo (MCMC) is identified as updating the measure, whereas the second method Polynomial Chaos Kalman Filter (PceKF) is updating the measurable function. The implementation aspects of presented models are given in full detail as well as their validation throughthe numerical examples against the experimental results or against the benchmarks available from literature
47
Lindemann, Sylvester. "Model updating an einem biegeelastischen Rotor." Kassel : Kassel Univ. Press, 2009. http://d-nb.info/994839081/34.
Full text
48
Lindemann, Sylvester. "Model updating an einem biegeelastischen Rotor." Kassel Kassel Univ. Press, 2008. http://d-nb.info/994322720/04.
Full text
49
Friswell, Michael I. "Updating finite element models using measured vibration data." Thesis, Aston University, 1990. http://publications.aston.ac.uk/11893/.
Full textAbstract:
The modelling of mechanical structures using finite element analysis has become an indispensable stage in the design of new components and products. Once the theoretical design has been optimised a prototype may be constructed and tested. What can the engineer do if the measured and theoretically predicted vibration characteristics of the structure are significantly different? This thesis considers the problems of changing the parameters of the finite element model to improve the correlation between a physical structure and its mathematical model. Two new methods are introduced to perform the systematic parameter updating. The first uses the measured modal model to derive the parameter values with the minimum variance. The user must provide estimates for the variance of the theoretical parameter values and the measured data. Previous authors using similar methods have assumed that the estimated parameters and measured modal properties are statistically independent. This will generally be the case during the first iteration but will not be the case subsequently. The second method updates the parameters directly from the frequency response functions. The order of the finite element model of the structure is reduced as a function of the unknown parameters. A method related to a weighted equation error algorithm is used to update the parameters. After each iteration the weighting changes so that on convergence the output error is minimised. The suggested methods are extensively tested using simulated data. An H frame is then used to demonstrate the algorithms on a physical structure.
50
David, Christoph. "Identification de paramètres mécaniques de matériaux composites à partir de corrélation d’images numériques multi-échelles." Thesis, Ecole nationale des Mines d'Albi-Carmaux, 2014. http://www.theses.fr/2014EMAC0012/document.
Full textAbstract:
L’amélioration du caractère prédictif des simulations numériques requiert une meilleure maîtrise des modèles constitutifs. Des procédures d’identification exploitant des mesures de champs ont été développées afin de valider les modèles et d’identifier un jeu de paramètres constitutifs à partir d’un nombre réduit d’essais hétérogènes. Bien évidemment, les résultats de telles procédures dépendent grandement des incertitudes des mesures. Dans cette thèse, une stratégie d’identification de paramètres constitutifs à partir de mesures de champs par corrélation d’images numériques éléments finis (CIN-EF) multi-échelles est proposée et développée. Une variante régularisée du recalage par éléments finis (FEMU-R) est adaptée à cette approche multi-échelles. Elle exploite des champs de déplacements mesurés par CIN-EF d'une part à l’échelle de la structure (fournissant les conditions aux limites pour la simulation EF) et d’autre part à une échelle plus locale (fournissant des champs de déplacements mieux résolus pour la comparaison essais/calculs). Un algorithme de recalage d’images est développé pour faire le lien entre les échelles. D’abord validée à l’aide d’images de synthèse, la procédure est ensuite appliquée à un essai de traction sur plaque trouée réalisé sur un composite stratifié verre/époxy. On montre qu’une telle stratégie permet de diminuer nettement non seulement les incertitudes de mesure mais également les incertitudes d’identification. Finalement, la question d’un mouchetis adapté à cette approche multi-échelles est évoquée et des éléments de solutions sont proposés et testésImproving the prediction of numerical simulations requires a better control of constitutive models. Identification methods exploiting full-field measurements have been developed in order to validate models and to identify a set of constitutive parameters from a reduced number of heterogeneous tests. The results of those methods largely depends on measurement uncertainties. In this PhD thesis, a strategy is proposed and developed for the identification of constitutive parameters from full-field measurements obtained by multiscale finite element digital image correlation (FE-DIC). A Regularised Finite Element Model Updating method (FEMU-R) is adapted to this multiscale approach. It exploits displacement fields measured by FE-DIC at a structural scale (in order to obtain the boundary conditions for FE simulation)and at a local scale (giving a better resolution on the displacement field for the comparison between experiment and simulation). An image registration algorithm is developed to bridge these scales. First validated on synthetic images, the multiscale approach is then applied to an open-hole tensile test of a glass/epoxy composite laminate. It is shown that such a strategy allows to reduce not only the measurement uncertainties but also the identification uncertainties. Finally the question of a speckle pattern suitable for this approach is discussed and some first technical solutions are proposed and tested