Orientador: Dilson Amancio Alves / Banca: Carlos Roberto Minussi / Banca: Luiz Carlos Pereira da Silva / Resumo: O objetivo do trabalho proposto é o de apresentar aplicações práticas da técnica de análise modal na avaliação da estabilidade de tensão e à redução da perda total de potência reativa na transmissão. A análise modal tem demonstrado ser uma ferramenta de análise estática muito útil que pode ser utilizada para identificar áreas propensas à instabilidade de tensão. Seus resultados são usados para identificar as medidas de reforço mais adequadas para aumentar a margem de estabilidade de tensão de sistemas elétricos de potência. A melhor localização para a instalação de compensação reativa shunt e série é determinada baseada nos fatores de participação de barra e de ramos, respectivamente. Outros objetivos deste trabalho são os de apresentar uma metodologia alternativa para a alocação de bancos de capacitores shunt, e o efeito da compensação de bancos de capacitores série na margem de carregamento. Os objetivos são à redução da perda total de potência reativa na transmissão e o aumento na margem de carregamento do sistema. Os valores dos montantes de compensação reativa shunt a serem alocados são determinados com base nas curvas de perda total de potência reativa na transmissão versus magnitude de tensão da barra. No caso da compensação série, o valor da reatância capacitiva escolhido é limitado pelo valor prático de compensação que é da ordem de 80%. Também são investigados os efeitos individuais que cada um destes procedimentos traz para o sistema. Entre os efeitos investigados estão: a redução das perdas reativas, a variação na margem de estabilidade estática de tensão, e a melhoria do perfil de tensão. Os resultados obtidos para os sistemas do IEEE (14, 57 e 118 barras) mostram que o procedimento conduz a uma sensível redução da perda total de potência... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The objective of the proposed work is to present practical applications of the modal analysis technique applied to voltage stability assessment and reactive power losses reduction. Modal analysis has proven to be a useful steady-state analysis approach which can be applied to identify areas prone to voltage instability. Its results are used to identify the most effective remedial actions to increase system voltage stability margin. The best location for placing shunt and series capacitor is determined based on the bus and branch participations factors respectively. Other goals of the proposed work are to present an alternative procedure to the allocation of shunt capacitor, and the effects of series capacitor compensation on the system loading margin. The objectives are the total reactive power losses reduction in the transmission and the loading margin increase. The values of shunt reactive compensation to be allocated are determined based on the curve of total transmission reactive power losses versus bus voltage magnitude. In case of series compensation, the chosen reactive capacitance values are limited by a practical upper limit of series compensation degree of 80%. The individual effects that each one of these procedures brings for the system are also investigated. Among the investigated effects are: the reduction in the total reactive power losses, the changes in the static voltage stability margin, and the improvement of voltage profile. The results obtained for the IEEE system (14, 57 and 118 bus) show that the procedure leads to a sensible reduction of total reactive power losses and simultaneously, an improvement in the voltage profile and load margin increase. / Mestre

Abstract not available

In this study, a systematic approach was adopted to investigate, numerically and experimentally, localised defects and/or damage in timber bridges, such as rot, using modal based damage detection techniques. An existing damage detection method namely damage index (DI) method that utilises modal strain energy before and after damaged state was adopted. One contribution of this study was to modify the Dl method by an additional step of normalising the modal curvature, which would minimise the dominance of higher modes. In the numerical models, a comparative study of the effects of numerical integration techniques used in a damage detection process was carried out. The results show that when mode shape curvature integrations use the rectangular rule for the numerical integration, it yields better results than the trapezoidal rule. In the numerical examples using a finite element model of timber beam, the modified DI (MDI) methods were found to perform better than its original form for locating'" single and multiple damage scenarios. For the DI methods, two types of formulations were adopted and modified, and they are denoted as modified damage index I (MDI-I) and modified damage index II (MDI-II). Another modal based damage detection method, namely changes in flexibility (CIF), was adopted for locating damage. It was found that the ClF method performed reasonably well for single damage but not multiple damage scenarios. As part of the study, the modified damage index methods were utilised for evaluating severity of damage. For the :MDI-I method, the formulation was not derived to evaluate damage severity directly. Instead, a hybrid of the MDI-I and CIF methods (HMC), was proposed for evaluating severity of damage in terms of loss of '1' (moment of inertia). Using three levels of damage, i.e. light (L), medium (M) and severe (S), the HMC method is able to predict the medium and severe damage quite well, but it is less efficient for light damage scenarios. For the MDI-II method, further manipulation of the algorithm can predict the severity of damage in terms of loss of'I'. This method is able to predict the medium and severe damage quite well but is not as good for the light damage. Both methods, HMC and MDI-II, for predicting severity of damage, required some adjustment using a weighting factor in order to obtain reasonable results. An experimental modal analysis (EMA) test program of timber beams was undertaken. This was done to verify the robustness of the modified damage index methods for detecting location and estimating severity of damage. The laboratory investigation was conducted on the corresponding changes of modal parameters due to loss of section. The MDI methods were used to detect location of damage and to evaluate the severity of damage in the test beams. A mode shape reconstruction technique was utilised to enhance the capability of the damage detection algorithms with limited number of sensors. The test results and analysis show that location of damage is quite accurately estimated with the available sensors. The methods demonstrate that they are less mode dependant and can detect damage with a higher degree of confidence. The MDI methods also show that they are able to predict the severe damage well, but it is less accurate for the medium damage and not as good for light damage. The damage index II (DI-II) method extended to plate-like structures (DI-II-P) was adopted and evaluated for detecting damage. Based on finite element analysis (FEA) results of a laboratory timber bridge, the DI-II-P method which utilises two dimensional (2-D) mode shape curvature was employed to detect location of damage. The results show that the tnethod based on 2-D mode shape curvature is able to locate damage quite well, numerically. A supplementary work using the DI-II-P method in a timber plate model was carried out. The results also show that the method was able to predict the damage location well. A process of updating a laboratory timber bridge, analytically, is presented. A finite element model was developed and updated with experimental modal data. Material properties of timber beam (girders) and plywood (deck) as well as the screw connection between deck and girder were experimentally investigated. These test results were then used for the finite element modelling. The model has been developed sequentially starting with a preliminary model having very simple features. It followed by the advanced model calibrated with the experimental modal data employing a global objective function, consisting of errors of natural frequencies and modal assurance criterion. The calibrated finite element model shows a good correlation to the experimental model with minor adjustments to the real material properties and boundary conditions. The calibrated model can reasonably be used to study the damaged behaviour of the laboratory timber bridge. The bridge model was then used to verify the numerical results for detecting damage. The bridge was inflicted with various damage scenarios with loss of section similar to the timber beam models. The limited number of data was expanded using the 2-D cubic spline. Using the reconstructed data for detecting damage yields better results than just using 'as is' data. Using the undanlaged and dmnaged modal data, the D I-II -P method was employed to detect the location of damage. The results of using the first nine modes showed that generally the severe damage is able to be located by the method. It performs reasonably well for the medium damage but does not perform as good in the light damage scenarios. However, in some cases the method can present some problems in identifying severe damage, which may be due to lack of normalisation of mode shape curvature. Complementary work was undertaken using the method 'On a timber plate, experimentally. The results showed that the damage detection process in the timber plate is less efficient compared to the laboratory timber bridge. A comprehensive comparative study was carried out based on the results of the numerical and experimental investigation of damage detection on timber beam, laboratory timber bridge and timber plate. For the timber beam, both damage detection methods, MDI-I and MDI-II, were capable of detecting medium and severe damage in the numerical and experimental studies. However, the light damage was not identified well using the experimental data in the presence of noise. To estimate damage severity in the timber beam, the HMC method performed well for the medium and severe damage. The method did not work well in estimating severity of light damage. Similar conclusions can be drawn in using the MDI-II method to estimate the damage severity. The results of applying the DI-II-P method (using 9 modes) to locate damage in the laboratory timber bridge showed that numerical and experimental data are capable of detecting all severe damage for damage cases with less than three damage locations. While for light and medium damage, the experimental data did not work well as compared to the numerical one. For the timber plate (a complementary work), the numerical and experimental results also showed that they are able to detect the severe damage well. However, there were serious false positives appearing in the light damage cases in the experimental results.

Thesis (M.Eng.)--Memorial University of Newfoundland, 2001. / Bibliography: leaves 135-140.

Thesis (M.S. in Mechanical Engineering)--Naval Postgraduate School, June 2003. / Thesis advisor(s): Young Shin, Ilbae Ham. Includes bibliographical references (p. 63). Also available online.

No description available.

Previous work on modal analysis of mooring lines has been performed from different theoretical formulations. Most studies have focused on mooring lines of a single homogeneous material, and the effect of added mass and damping produced by the water has not been examined deeply. The variational formulation approach, employed in this research to perform a modal analysis, has been useful to study the behavior of several realistic mooring lines. The cases presented are composed from segments of materials with different mechanical characteristics, more similar to those in current offshore projects. In the newly proposed formulation, damping produced by transverse motion of the mooring line through the surrounding water has been added to the modal analysis. The modal analysis formulation applied in this work has been verified with calculations from commercial software and the results are sufficiently accurate to understand the global behavior of the dynamics of mooring lines with the damping produced by the sea water. Inclusion of linearized drag damping in the modal analysis showed that the modal periods of the mooring systems studied depend on the amplitude of the transverse motion of the mooring line. When more amplitude in the motion is expected more damping is obtained. Two realistic designs of mooring lines were compared: one made up with a main insert of steel rope, called “Steel System”, and one composed by a main insert of polyester, named “Polyester System”. Comparing the natural periods of both systems, the Steel System appears to be safer because its fundamental natural period is more distant from the wave excitation periods produced by storms. The same happens considering the wave excitation periods produced by prevailing seas. In this case the natural periods of the Polyester System are nearer to the wave excitation periods causing fatigue loads. The transverse mode shapes for lateral motions of the mooring lines are observed to be continuous and smooth across material transitions, such as transitions between chain and wire rope and transitions between chain and polyester rope. This behavior is not always observed in the tangential mode shapes for the Polyester System where significant differences in dynamic tension seem to be present in the specific cases studied.

A study of vibrations and sound radiation in upright and grand pianos has been made to determine whether the piano may be improved by altering the materials of the component parts which are traditionally fabricated in timber. Modal analysis and sound level measurements of an upright piano has shown that the radiation from the case is at least 20 dB lower than the radiation from the soundboard, and therefore the case is not a significant determinant of piano tone. A method was developed for separating piano sound and vibrations into broadband and tonal components and used to compare the performance of upright and grand pianos. Using this method it was found that the broadband vibration level was twice as high in the uprights as in the grands. A finite element model of an upright piano was developed and used to demonstrate that replacing the keybed with a higher impedance material than conventionally used would reduce the key vibration level, and hence bring the uprights closer in performance to grand pianos, and improve the 'feel' of the instrument for the player. The keybed of one of a pair of identical pianos was replaced with high density fibreboard, and subsequent objective measurements showed that the broadband component of key vibrations was reduced by 3.2 dB while the radiated sound was unchanged. A controlled subjective comparison between the modified and unmodified pianos undertaken by experienced players showed that a statistically significant number preferred the modified piano, and that the upright piano had been improved. / Acoustics Research Centre, Department of Mechanical Engineering, Foundation for Research Science and Technology, Fletcher Wood Panels.

A study of vibrations and sound radiation in upright and grand pianos has been made to determine whether the piano may be improved by altering the materials of the component parts which are traditionally fabricated in timber. Modal analysis and sound level measurements of an upright piano has shown that the radiation from the case is at least 20 dB lower than the radiation from the soundboard, and therefore the case is not a significant determinant of piano tone. A method was developed for separating piano sound and vibrations into broadband and tonal components and used to compare the performance of upright and grand pianos. Using this method it was found that the broadband vibration level was twice as high in the uprights as in the grands. A finite element model of an upright piano was developed and used to demonstrate that replacing the keybed with a higher impedance material than conventionally used would reduce the key vibration level, and hence bring the uprights closer in performance to grand pianos, and improve the 'feel' of the instrument for the player. The keybed of one of a pair of identical pianos was replaced with high density fibreboard, and subsequent objective measurements showed that the broadband component of key vibrations was reduced by 3.2 dB while the radiated sound was unchanged. A controlled subjective comparison between the modified and unmodified pianos undertaken by experienced players showed that a statistically significant number preferred the modified piano, and that the upright piano had been improved. / Acoustics Research Centre, Department of Mechanical Engineering, Foundation for Research Science and Technology, Fletcher Wood Panels.

A study of vibrations and sound radiation in upright and grand pianos has been made to determine whether the piano may be improved by altering the materials of the component parts which are traditionally fabricated in timber. Modal analysis and sound level measurements of an upright piano has shown that the radiation from the case is at least 20 dB lower than the radiation from the soundboard, and therefore the case is not a significant determinant of piano tone. A method was developed for separating piano sound and vibrations into broadband and tonal components and used to compare the performance of upright and grand pianos. Using this method it was found that the broadband vibration level was twice as high in the uprights as in the grands. A finite element model of an upright piano was developed and used to demonstrate that replacing the keybed with a higher impedance material than conventionally used would reduce the key vibration level, and hence bring the uprights closer in performance to grand pianos, and improve the 'feel' of the instrument for the player. The keybed of one of a pair of identical pianos was replaced with high density fibreboard, and subsequent objective measurements showed that the broadband component of key vibrations was reduced by 3.2 dB while the radiated sound was unchanged. A controlled subjective comparison between the modified and unmodified pianos undertaken by experienced players showed that a statistically significant number preferred the modified piano, and that the upright piano had been improved. / Acoustics Research Centre, Department of Mechanical Engineering, Foundation for Research Science and Technology, Fletcher Wood Panels.