Over the past few decades, visualization and application researchers have been investigating vortices and have developed several algorithms for detecting vortex-like structures in the flow. These techniques can adequately identify vortices in most computational datasets, each with its own degree of accuracy. However, despite these efforts, there still does not exist an entirely reliable vortex detection method that does not require significant user intervention. The objective of this research is to solve this problem by introducing a novel vortex analysis technique that provides more accurate results by optimizing the threshold for several computationally-efficient, local vortex detectors, before merging them using the Bayesian method into a more robust detector that assimilates global domain knowledge based on labeling performed by an expert. Results show that when choosing the threshold well, combining the methods does not improve accuracy; whereas, if the threshold is chosen poorly, combining the methods produces significant improvement.

A maior parte do sinal propagante para oeste nos oceanos é explicada pelas ondas de Rossby baroclínicas. Porém, vórtices de mesoescala podem interferir na identificação dessas ondas. A maior adversidade em se distinguir o sinal dessas feições é que os vórtices parecem propagar-se com uma velocidade aproximada à velocidade de fase das ondas. Um dos objetivos do presente trabalho é caracterizar os sinais propagantes para oeste em termos da sua velocidade de fase no Atlântico. A análise se baseia em de dados das anomalias da altura da superfície do mar (ASM) e da temperatura de superfície do mar (TSM) derivados dos altímetros TOPEX/Poseidon e Jason-1 e radiômetro TRMM/TMI. As anomalias de ASM e TSM foram filtradas por um conjunto de filtros de resposta impulsiva finita (FIR) para eliminar o sinais sazonais, interanuais e sinais de alta frequência. A análise de correlação cruzada entre as matrizes zonais-temporais de ASM e TSM foi feita para limitar as conclusões aos sinais presentes simultaneamente em ambas as bases de dados. A velocidade de fase das ondas de Rossby foi estimada via transformada de Radon aplicada às matrizes de correlação cruzada. Um máximo local solitário sobre a origem foi observado nos diagramas de correlação e associado à presença de vórtices de mesoescala. Porém este máximo se alonga com a mesma inclinação correspondente à velocidade de fase das ondas de Rossby. Isto sugere que estes vórtices podem propagar-se sobrepostos às ondas. As velocidades de propagação dos vórtices são estimadas através do ajuste de uma função de decaimento exponencial no tempo e na distância zonal. Análises preliminares da transformada de Fourier mostraram que os sinais propagantes para oeste são predominantemente anuais, embora picos de frequências semi-anuais são observadas nestes espectros. Em decorrência da evidência de que os sinais propagantes para oeste são compostos simultaneamente por vórtices e ondas de Rossby, um filtro baseado na transformada de Radon e sua inversa foi desenvolvido para separar o sinal de feições com simetria circular. O filtro de vórtice circular foi aplicado em três áreas onde se localizam a Corrente das Agulhas, Confluências Brasil-Malvinas e Corrente do Golfo. Com base na análise visual pode-se afirmar que o filtro identificou com sucesso vórtices circulares nas três áreas estudadas, tanto nos dados de ASM como nos de TSM. As velocidades de fase das ondas de Rossby foram ligeiramente mais rápidas, em média, que as velocidades dos vórtices em todas as três áreas, cerca de 10% na ASM e 13% na TSM. As velocidades calculadas após a aplicação do filtro de vórtice circular apresentaram um viés positivo em relação as obtidas via correlações cruzadas. A maior diferença na estimativa das velocidades dos vórtices foi de 21% e nas ondas 25%, ambas na região da Corrente das Agulhas. Baseado nas evidências apresentadas é possível afirmar que vórtices podem se propagar com velocidades semelhantes à velocidade das ondas de Rossby do primeiro modo baroclínico. O lag das correlações cruzadas indicaram que o processo físico que relaciona a variabilidade nos dados de ASM à dos TSM é a advecção causada pela passagem de uma onda planet´aria do primeiro modo baroclínico. Esta advecção pode ser horizontal ou vertical dependendo do processo dominante que ocorre numa dada região. / In the oceans, most of the westward propagating signal is explained by baroclinic Rossby waves. However, mesoscale vortices can interfere in the identification of these waves. The main observational issue is to distinguish eddies from the wave-like propagating signals, since the former propagates with a speed that approximately matches the phase speed of baroclinic Rossby waves. The objective of the present study is to characterize the westward propagating signals in terms of their propagation speeds in the Atlantic. The analysis is based on satellite derived sea surface height (SSH) and sea surface temperature (SST) anomalies from the TOPEX/Poseidon and Jason-1 altimeters and TRMM/TMI radiometer records. The SSH and SST anomaly maps were filtered with a set of finite impulse response filters to eliminate the seasonal and interannual cycles and high frequency signals. The cross-correlation analysis between SSH and SST longitude-time matrices was performed to limit the conclusions to the features that appear simultaneously in both datasets. The of Rossby wave phase speed was estimated via Radon transform applied to the longitude-time cross-correlation matrices. A single local maximum was was observed at the origin of the cross-correlation diagrams and associated to mesoscale vortices. However, this maximum spreads along the same slope that characterizes the the westward Rossby wave phase speed. This suggests that vortices propagate superimposed to Rossby waves. The propagating speed of the vortices is estimated from the linear fit of an exponential decay function. A preliminary Fourier analysis show that the westward propagating signals are predominantly annual, yet peaks in the semiannual frequencies are observed. The evidence that the westward propagating signals are composed simultaneously of vortices and Rossby waves motivated the development of a filter based in the Radon transform and its inverse, to isolate the signal associated to circularly symmetric features. This circular vortex filter was applied in three areas that portray the Agulhas Current, the Brazil-Malvinas Confluence, and the Gulf Stream. Based on visual analysis one can affirm that the circular filter sucessfully identified vortices in three areas, both in the SSH and in the SST data. The phase speeds of Rossby waves were, on average, slightly faster than vortices speeds in the three areas, approximately 10% in SSH and 13% in SST. The speeds calculated after the circular vortex filter was applied presented a positive bias in relation to those obtain from cross correlations. The largest difference in the vortices speeds was 21% and in the wave speeds 25%, both in Agulhas Current region. Based on the present evidences it is possible to state that vortices can propagate with speeds similar to those of first-mode baroclinic Rossby waves. The cross-correlation lag suggests that the physical process that links the variability of the SSH to that of the SST is the advection generated by the passage of a first-mode baroclinic planetary wave. This advection can be horizontal or vertical depending of the dominant process in a given region.

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A new experimental setup for studies on wake flow instability and its control that successfully has been designed and manufactured, is introduced and de- scribed. The main body is a dual-sided flat plate with an elliptic leading edge and a blunt trailing edge. Permeable surfaces enable boundary layer suction and/or blowing that introduce the unique feature of adjusting the inlet condition of the wake created behind the plate. This, in combination with a trailing edge that is easily modified, makes it an ideal experiment for studies of different control methods for the wake flow instability as well as extensive parameter studies. Experimental validation of the setup has been performed by means of measurements of the wake symmetry and boundary layer velocity profiles at the trailing edge. Some preliminary results on the Strouhal number versus different inlet conditions are reported. Additionally, an in-house vortex detection (VD) program has been developed in order to detect, analyse and compare small-scale vortical structures in instantaneous velocity fields from flow measurements. This will be a powerful tool for comparison of wake characteristics for varying inlet conditions and control methods in the new experimental setup. Measurements from three completely separate experimental setups with different geometries and flow cases, have been analysed by the VD-program.          i.     In order to obtain improved ventilation we have studied the effect of pulsating inflow into a closed volume compared to having the inflow at a constant flow rate. We show that the number of small-scale eddies is significantly increased and that the stagnation zones are reduced in size, which enhances the mixing.         ii.     Instantaneous velocity fields in the wake behind a porous cylinder subjected to suction or blowing through the entire cylinder surface have also been analysed using the VD-program. The results show that the major change for different levels of blowing or suction is the location of vortices while the most common vortex size and strength are essentially unchanged.        iii.     Another study on how the geometry of a V-shaped mixer in a pipe flow affects the mixing have also been examined, where no general differences were found between different thicknesses, why a thickness that is favourable from an acoustic point of view can be chosen.   We also propose a new method, using global mode analysis on experimental data, showing that randomly ordered snapshots of the velocity field behind the porous cylinder can be re-ordered and phase-averaged. / QC 20111108 / Active control of vortex shedding behind bluff bodies

A maior parte do sinal propagante para oeste nos oceanos é explicada pelas ondas de Rossby baroclínicas. Porém, vórtices de mesoescala podem interferir na identificação dessas ondas. A maior adversidade em se distinguir o sinal dessas feições é que os vórtices parecem propagar-se com uma velocidade aproximada à velocidade de fase das ondas. Um dos objetivos do presente trabalho é caracterizar os sinais propagantes para oeste em termos da sua velocidade de fase no Atlântico. A análise se baseia em de dados das anomalias da altura da superfície do mar (ASM) e da temperatura de superfície do mar (TSM) derivados dos altímetros TOPEX/Poseidon e Jason-1 e radiômetro TRMM/TMI. As anomalias de ASM e TSM foram filtradas por um conjunto de filtros de resposta impulsiva finita (FIR) para eliminar o sinais sazonais, interanuais e sinais de alta frequência. A análise de correlação cruzada entre as matrizes zonais-temporais de ASM e TSM foi feita para limitar as conclusões aos sinais presentes simultaneamente em ambas as bases de dados. A velocidade de fase das ondas de Rossby foi estimada via transformada de Radon aplicada às matrizes de correlação cruzada. Um máximo local solitário sobre a origem foi observado nos diagramas de correlação e associado à presença de vórtices de mesoescala. Porém este máximo se alonga com a mesma inclinação correspondente à velocidade de fase das ondas de Rossby. Isto sugere que estes vórtices podem propagar-se sobrepostos às ondas. As velocidades de propagação dos vórtices são estimadas através do ajuste de uma função de decaimento exponencial no tempo e na distância zonal. Análises preliminares da transformada de Fourier mostraram que os sinais propagantes para oeste são predominantemente anuais, embora picos de frequências semi-anuais são observadas nestes espectros. Em decorrência da evidência de que os sinais propagantes para oeste são compostos simultaneamente por vórtices e ondas de Rossby, um filtro baseado na transformada de Radon e sua inversa foi desenvolvido para separar o sinal de feições com simetria circular. O filtro de vórtice circular foi aplicado em três áreas onde se localizam a Corrente das Agulhas, Confluências Brasil-Malvinas e Corrente do Golfo. Com base na análise visual pode-se afirmar que o filtro identificou com sucesso vórtices circulares nas três áreas estudadas, tanto nos dados de ASM como nos de TSM. As velocidades de fase das ondas de Rossby foram ligeiramente mais rápidas, em média, que as velocidades dos vórtices em todas as três áreas, cerca de 10% na ASM e 13% na TSM. As velocidades calculadas após a aplicação do filtro de vórtice circular apresentaram um viés positivo em relação as obtidas via correlações cruzadas. A maior diferença na estimativa das velocidades dos vórtices foi de 21% e nas ondas 25%, ambas na região da Corrente das Agulhas. Baseado nas evidências apresentadas é possível afirmar que vórtices podem se propagar com velocidades semelhantes à velocidade das ondas de Rossby do primeiro modo baroclínico. O lag das correlações cruzadas indicaram que o processo físico que relaciona a variabilidade nos dados de ASM à dos TSM é a advecção causada pela passagem de uma onda planet´aria do primeiro modo baroclínico. Esta advecção pode ser horizontal ou vertical dependendo do processo dominante que ocorre numa dada região. / In the oceans, most of the westward propagating signal is explained by baroclinic Rossby waves. However, mesoscale vortices can interfere in the identification of these waves. The main observational issue is to distinguish eddies from the wave-like propagating signals, since the former propagates with a speed that approximately matches the phase speed of baroclinic Rossby waves. The objective of the present study is to characterize the westward propagating signals in terms of their propagation speeds in the Atlantic. The analysis is based on satellite derived sea surface height (SSH) and sea surface temperature (SST) anomalies from the TOPEX/Poseidon and Jason-1 altimeters and TRMM/TMI radiometer records. The SSH and SST anomaly maps were filtered with a set of finite impulse response filters to eliminate the seasonal and interannual cycles and high frequency signals. The cross-correlation analysis between SSH and SST longitude-time matrices was performed to limit the conclusions to the features that appear simultaneously in both datasets. The of Rossby wave phase speed was estimated via Radon transform applied to the longitude-time cross-correlation matrices. A single local maximum was was observed at the origin of the cross-correlation diagrams and associated to mesoscale vortices. However, this maximum spreads along the same slope that characterizes the the westward Rossby wave phase speed. This suggests that vortices propagate superimposed to Rossby waves. The propagating speed of the vortices is estimated from the linear fit of an exponential decay function. A preliminary Fourier analysis show that the westward propagating signals are predominantly annual, yet peaks in the semiannual frequencies are observed. The evidence that the westward propagating signals are composed simultaneously of vortices and Rossby waves motivated the development of a filter based in the Radon transform and its inverse, to isolate the signal associated to circularly symmetric features. This circular vortex filter was applied in three areas that portray the Agulhas Current, the Brazil-Malvinas Confluence, and the Gulf Stream. Based on visual analysis one can affirm that the circular filter sucessfully identified vortices in three areas, both in the SSH and in the SST data. The phase speeds of Rossby waves were, on average, slightly faster than vortices speeds in the three areas, approximately 10% in SSH and 13% in SST. The speeds calculated after the circular vortex filter was applied presented a positive bias in relation to those obtain from cross correlations. The largest difference in the vortices speeds was 21% and in the wave speeds 25%, both in Agulhas Current region. Based on the present evidences it is possible to state that vortices can propagate with speeds similar to those of first-mode baroclinic Rossby waves. The cross-correlation lag suggests that the physical process that links the variability of the SSH to that of the SST is the advection generated by the passage of a first-mode baroclinic planetary wave. This advection can be horizontal or vertical depending of the dominant process in a given region.