Navegando por Assunto "Modal analysis"

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Acesso aberto (Open Access)
A Comparison of dimensionality reduction and blind source separation techniques for video-based modal identification
(Universidade Federal do Pará, 2023-03-29) PAES, Thaisse Dias; SILVA, Moisés Felipe Mello da; http://lattes.cnpq.br/8154941342611201; COSTA, João Crisóstomo Weyl Albuquerque; http://lattes.cnpq.br/9622051867672434
Understading the dynamic properties of a structural system is indispensable for a reliable study of the structural behavior. Video-based structural dynamics identification has been effectively used as a key method for modal analysis in recent years.With several different approaches, the ones based on the blind source separation strategy have received increased attention for identifying structural characteristics. Blind source separation addresses the problem of separating or extracting the original source waveforms from a sensor array. Although the literature addresses several techniques to perform the source separation, only one of them (named complexity pursuit) is often employed for video-based solutions. This work aims to explore other blind source separation algorithms to perform video-based modal analysis. In order to perform the modal decomposition, a set of blind source separation methods is combined with different dimensionality reduction techniques for full-field high-resolution structural dynamics from video. Specifically, Principal Component Analysis (PCA) and NonnegativeMatrix Factorization (NNMF), two dimensionality reduction techniques, are used for video compression along with six source separation algorithms, resulting in twelve different frameworks tested over a laboratory cantilever beam structure and a bench-scale model of a three-story building structure. The blind source separation techniques used are: Complexity Pursuit (CP), Idependent Component Analysis (ICA), Second Order Blind Identification (SOBI), Second Order Blind Identification with Robust Orthogonalization (SOBIRO), Equivariant Robust Idependent Component Analysis (ERICA) and Algorithm for Multiple Unknown Signals Extraction (AMUSE). The twelve techniques based on dimensionality reduction and blind source separation algorithms are evaluated here using as the criteria comparison their mode shape, modal coordinates and MAC values. The main goal is to provide a range of alternatives for the vide-based structural dynamics evaluation. For specific algorithms, the results indicate that both dimensionality reduction techniques and the blind source separation methods play a major role in the mode estimation performance. In the experiment utilizing the cantilever beam structure, all expected modals were successfully identified using the algorithms based on PCA-CP, PCA-ICA, PCA-SOBIRO, PCA-ERICA, NNMF-CP, NNMFSOBI, NNMF-SOBIRO and NNMF-ERICA. For the second scenario, using the model of a three-story building structure, the methods that correctly perfomed modal analysis are based on PCA-CP, PCA-SOBI, PCA-SOBIRO, PCA-ERICA, NNMF-CP and NNMF-SOBIRO. It is suggested that The effectiveness of combining NNMF and blind source separation methods for modal analysis may be contingent upon the complexity of the system under investigation.
Acesso aberto (Open Access)
Desenvolvimento de um software com interface gráfica para análise e verificação de pontes ferroviárias em concreto armado
(Universidade Federal do Pará, 2010-03-05) QUEIROZ, Rafael Leite de; SOUZA, Remo Magalhães de; http://lattes.cnpq.br/1995895693959225
Development of software with graphical interface for analysis and verification of railway reinforced concrete bridges. The work described here is the development of software capable to do structural analysis with emphasis on bridges. More attention is given to the analysis of railway bridges and the automatic generation of live load in accordance with the vehicles and trains-types user defined by. The software called BridgeLab Laboratory (Bridges) is able to do analysis of extreme importance with respect to the design and verification of civil structures. These analysis are: static analysis, pseudo-dynamic analysis, modal analysis and dynamic analysis. The code at BridgeLab was written in MATLAB® platform, due to some advantages of the language resulting in a shorter time of rogramming. The analyzes performed by the program are based on the direct stiffness method and use finite element of space frame which presents six degrees of freedom per node. In addition to performing the analyzes, BridgeLab performs the structural elements verification from the results of efforts obtained in each analysis according to the Brazilian standards, including verification of fatigue damages that is also verified according to the CEB. The verification is done in an integrated way through the SecLab (Sections Lab). After analysis the visualization results, stress diagrams, deformed configurations and modal shapes are done in the BridgeLab interface itself. The visualization of the deformed configurations of the structure and its modal forms can be done as a bar model or as extruded solids, considering the geometry of the cross section of the elements.
Acesso aberto (Open Access)
Diagnóstico numérico em embarcações de atendimento de atendimento médico-hospitalar visando à otimização vibro-acústica
(Universidade Federal do Pará, 2017-11-10) FERREIRA, Aracelli Suzane Andrade; SOEIRO, Newton Sure; http://lattes.cnpq.br/7303174583088137; https://orcid.org/0000-0003-4224-767X
The use of vessels for hospital care has been one of the main means used by some prefectures belonging to the states of the Legal Amazon to take medical and dental care to communities located in distant locations. These vessels were named by the Ministry of Health of Basic Units of Fluvial Health (UBSF). The design of these units, however, is differentiated in many ways, since it provides for the installation of equipment not present in other conventional vessels. In addition, the service performed in these units requires satisfactory acoustic-vibro-conditions so that health professionals can perform the procedures correctly. This work aims to perform a numerical analysis through the Finite Element Method to evaluate the modal and acoustic properties of the medical service vessel. The work contemplated two analyzes: modal and acoustic. In the modal analysis, the axis, propeller and the structure of the UBSF were considered as objects of study, as these are the main sources of excitation. The acoustic analysis sought to ascertain the main sources of noise emission and its propagation within the UBSF. In this second analysis, it was possible to predict the overall sound pressure level and octave bands inside the vessel. The Ansys and Comsol softwares were used for the modal and acoustic analysis, respectively. After the analyzes, the data obtained with the main national and international standards related to the subject were compared. The results found in this study demonstrated that the reference model proposed by the Ministry of Health did not meet the criteria established by the norms. It is proposed, therefore, as solutions to attenuate the undesired effects from the acoustic-acoustic phenomena, the use of materials with absorptive properties and increase in the structural rigidity of the vessel. Such measures would allow users and crew members to improve the comfort and conditions of basic health care services.
Acesso aberto (Open Access)
Estudo de técnicas de análise modal operacional em sistemas sujeitos a excitações aleatórias com a presença de componente harmônico
(Universidade Federal do Pará, 2006-02-17) CRUZ, Sérgio Luiz Matos da; MESQUITA, Alexandre Luiz Amarante; http://lattes.cnpq.br/3605920981600245
Traditional modal parameter identification usually require measurements of both the input force and the resulting response in laboratory conditions. However, when modal properties are to be identified from large structures in operation, usually the possibilities to control and measure the loading on the structure is rather limited. In this case, the modal testing is usually performed using response data only. Operational Modal Analysis (OMA) or Operational Modal Testing is a method where no artificial excitation needs to be applied to the structure or force signals to be measured. In this case, the modal parameters estimation is based upon the response signals, thereby minimizing the work of preparation for the test. However, standard OMA techniques, such as NExT, are limited to the case when excitation to the system is a white stationary noise. The NexT assumes that the correlation functions are similar to the impulse response functions, and then, traditional time domain identification methods can be applied. However, if harmonic components are present in addition to the white noise, these components can be misunderstood as natural modes in the plot of response spectrum. In this work, it is shown that it is possible identify if a peak in the response spectrum correspond to a natural mode or an operational mode. It is achieved through the application of the probability density function. It is also presented a modification in the LSCE algorithm in such manner that it can support harmonics in the operational excitation. In order to validate the methods presented in this work, it is shown numerical and experimental cases. In the former, results for a mass-spring-damper of five degree of freedom are presented, and in the latter a beam supporting an unbalanced motor is analyzed.
Acesso aberto (Open Access)
Programa computacional com interface gráfica para identificação estocástica de parâmetros modais de estruturas civis: aplicação em pontes e torres de linha de transmissão
(Universidade Federal do Pará, 2007-09-21) AMADOR, Sandro Diord Rescinho; SOUZA, Remo Magalhães de; http://lattes.cnpq.br/1995895693959225
Interest on the dynamic behavior of latticed structures has been increased in the latest decades in Brazil since some accidents with total collapse of some structures, due to excessive vibration, have been occurred in its different regions. In the Amazon region, for instance, where these latticed structures overcome great obstacles such as the rainforest and large rives crossings, cases of collapse of latticed structures have been also reported. This master thesis focuses on the study of the modal behavior of latticed steel structures subjected to ambient vibrations caused by unknown excitation forces. Two study cases are presented: in the first, the modal behavior of a steel overhead transmission line tower is investigated; in the second case, the modal behavior and comfort level of a steel bridge is studied. The study of this last case aims at investigating the level of comfort of the bridge under ambient vibration, caused by wind gusts and vehicle traffic, according to the Brazilian standard NBR 8800 (1986). In both study cases, experimental and theoretical dynamic analyzes were performed to extract the modal parameters of theses structures. In the experimental stage, both structures were monitored using a set of low frequency accelerometers as well as a data acquisition system suitable for vibration tests of civil engineering structures. Since it is very difficult to measure the magnitude of ambient excitation forces, two stochastic subspace identification methods known as SSI-DATA and SSI-COV were employed to extract the modal parameters of the analyzed structures from response data collected in the vibration tests. Among all activities performed in this stage, a Graphical User Interface (GUI) toolbox in Matlab® platform was developed. In this toolbox, the above mentioned stochastic methods were implemented to extract modal parameters of civil engineering structures only from the response data collected in vibration tests. This toolbox consists of three modules: the first is used to process and treat the signals collected in the vibrations tests; the second is designed for allowing user to add the information related to the position and orientation of the accelerometers to the data files; the last module is used to extract the modal parameters from the response data files preprocessed in the first two modules. In the theoretical stage, numerical models were created to simulate de dynamical behavior of the structures under study. By comparing the results from both stages of analysis, it is observed that the experimental and theoretical results are in good agreement for the first modes of vibration. The experimental results showed that the approach developed for output-only modal analysis of civil engineering structures using stochastic state-space based methods was very efficient for identification of the modal parameters of the analyzed structures.