Yes / This paper presents the results of laboratory experiments and numerical simulations to investigate the effect of different piggyback pipeline configuration on the morphology of local seabed scour subject to steady currents. Piggyback pipeline configuration investigated includes the commonly used piggyback pipeline, namely a small pipe attached on the top of large pipe and new form of piggyback pipeline proposed in this study in which a small pipe is attached to the large pipe on the upstream and downstream side, respectively. Pressure gradient, drag coefficient, lift coefficient and scour extent around pipelines are measured and analyzed for a range of pipelines and current conditions. Results show that the vortex strength downstream of the commonly used piggyback pipeline is larger than that for a single as well as the new piggyback pipeline under the same condition. This new type piggyback pipeline can effectively reduce the depth and width of the scour hole. In particular, when the ratio of the small pipe diameter over the large pipe diameter is greater than 0.3, little scour under this new type piggyback pipeline occurs for the test conditions. The bed topography downstream of the pipe has also been altered to favor the backfill. / National Natural Science Foundation of China (No. 51279189).

Este trabalho apresenta um estudo experimental acerca da influência da razão de espaçamento e da intensidade de turbulência no escoamento biestável. É estudado o escoamento sobre dois cilindros dispostos lado a lado, para o canal aerodinâmico com intensidade de turbulência inferior a 1%, para o canal aerodinâmico com grade promotora de turbulência com intensidade de turbulência de 8 a 7%, e para uma seção do canal aerodinâmico sem paredes laterais. A técnica experimental aplicada consiste na medição das flutuações de velocidade no canal aerodinâmico utilizando a técnica da anemometria de fio quente. As medições são realizadas com duas sondas, uma fixa e outra móvel que foi posicionada em seis pontos diferentes do escoamento. Os dados medidos são tratados através de ferramentas estatísticas, análise espectral e transformadas de ondaletas. Os resultados confirmam a existência do fenômeno da biestabilidade e mostram como o fenômeno sofre alterações quando exposto às condições de maior intensidade de turbulência e redução da razão de bloqueio pela retirada das paredes laterais em uma seção do canal. Para a condição de maior intensidade de turbulência, os resultados mostram que as trocas de modo se intensificam, e em alguns dos pontos de medição os sinais referentes à sonda móvel não apresentam características de biestabilidade. Para o caso sem paredes laterais, os sinais apresentam características de biestabilidade até o momento em que as paredes são removidas. / This work presents an experimental study, about the influence of the pitch to diameter ratio and the turbulence intensity on a bistable flow. The flow through two cylinders side-by-side is studied in an aerodynamic channel with turbulence intensity lower than 1%, in an aerodynamic channel with a turbulence grid, that increased the turbulence intensity to about 8 to 7%, and a section of the aerodynamic channel without lateral walls. The experimental technique consists in the measurements of the fluctuating velocities in the aerodynamic channel, using hot wire anemometry. The measurements are performed with two probes, one static, and one movable, positioned in six different points of the flow. The acquired data are analysed through statistical, spectral and wavelet tools. The results confirmed the occurrence of the bistable phenomenon and shows how it behaves when exposed to different conditions of turbulence intensity, and reduction of the blockage ratio aspect due to removal of the lateral walls of a channel section. The results for the higher turbulence intensity condition shows that the switches are intensified, some data resulting of the measurements of the second probe, do not show bistable characteristics. In the no-walls section case, the signals showed bistable features, until the moment the walls were removed.

Este trabalho apresenta um estudo experimental acerca da influência da razão de espaçamento e da intensidade de turbulência no escoamento biestável. É estudado o escoamento sobre dois cilindros dispostos lado a lado, para o canal aerodinâmico com intensidade de turbulência inferior a 1%, para o canal aerodinâmico com grade promotora de turbulência com intensidade de turbulência de 8 a 7%, e para uma seção do canal aerodinâmico sem paredes laterais. A técnica experimental aplicada consiste na medição das flutuações de velocidade no canal aerodinâmico utilizando a técnica da anemometria de fio quente. As medições são realizadas com duas sondas, uma fixa e outra móvel que foi posicionada em seis pontos diferentes do escoamento. Os dados medidos são tratados através de ferramentas estatísticas, análise espectral e transformadas de ondaletas. Os resultados confirmam a existência do fenômeno da biestabilidade e mostram como o fenômeno sofre alterações quando exposto às condições de maior intensidade de turbulência e redução da razão de bloqueio pela retirada das paredes laterais em uma seção do canal. Para a condição de maior intensidade de turbulência, os resultados mostram que as trocas de modo se intensificam, e em alguns dos pontos de medição os sinais referentes à sonda móvel não apresentam características de biestabilidade. Para o caso sem paredes laterais, os sinais apresentam características de biestabilidade até o momento em que as paredes são removidas. / This work presents an experimental study, about the influence of the pitch to diameter ratio and the turbulence intensity on a bistable flow. The flow through two cylinders side-by-side is studied in an aerodynamic channel with turbulence intensity lower than 1%, in an aerodynamic channel with a turbulence grid, that increased the turbulence intensity to about 8 to 7%, and a section of the aerodynamic channel without lateral walls. The experimental technique consists in the measurements of the fluctuating velocities in the aerodynamic channel, using hot wire anemometry. The measurements are performed with two probes, one static, and one movable, positioned in six different points of the flow. The acquired data are analysed through statistical, spectral and wavelet tools. The results confirmed the occurrence of the bistable phenomenon and shows how it behaves when exposed to different conditions of turbulence intensity, and reduction of the blockage ratio aspect due to removal of the lateral walls of a channel section. The results for the higher turbulence intensity condition shows that the switches are intensified, some data resulting of the measurements of the second probe, do not show bistable characteristics. In the no-walls section case, the signals showed bistable features, until the moment the walls were removed.

Este trabalho apresenta um estudo experimental acerca da influência da razão de espaçamento e da intensidade de turbulência no escoamento biestável. É estudado o escoamento sobre dois cilindros dispostos lado a lado, para o canal aerodinâmico com intensidade de turbulência inferior a 1%, para o canal aerodinâmico com grade promotora de turbulência com intensidade de turbulência de 8 a 7%, e para uma seção do canal aerodinâmico sem paredes laterais. A técnica experimental aplicada consiste na medição das flutuações de velocidade no canal aerodinâmico utilizando a técnica da anemometria de fio quente. As medições são realizadas com duas sondas, uma fixa e outra móvel que foi posicionada em seis pontos diferentes do escoamento. Os dados medidos são tratados através de ferramentas estatísticas, análise espectral e transformadas de ondaletas. Os resultados confirmam a existência do fenômeno da biestabilidade e mostram como o fenômeno sofre alterações quando exposto às condições de maior intensidade de turbulência e redução da razão de bloqueio pela retirada das paredes laterais em uma seção do canal. Para a condição de maior intensidade de turbulência, os resultados mostram que as trocas de modo se intensificam, e em alguns dos pontos de medição os sinais referentes à sonda móvel não apresentam características de biestabilidade. Para o caso sem paredes laterais, os sinais apresentam características de biestabilidade até o momento em que as paredes são removidas. / This work presents an experimental study, about the influence of the pitch to diameter ratio and the turbulence intensity on a bistable flow. The flow through two cylinders side-by-side is studied in an aerodynamic channel with turbulence intensity lower than 1%, in an aerodynamic channel with a turbulence grid, that increased the turbulence intensity to about 8 to 7%, and a section of the aerodynamic channel without lateral walls. The experimental technique consists in the measurements of the fluctuating velocities in the aerodynamic channel, using hot wire anemometry. The measurements are performed with two probes, one static, and one movable, positioned in six different points of the flow. The acquired data are analysed through statistical, spectral and wavelet tools. The results confirmed the occurrence of the bistable phenomenon and shows how it behaves when exposed to different conditions of turbulence intensity, and reduction of the blockage ratio aspect due to removal of the lateral walls of a channel section. The results for the higher turbulence intensity condition shows that the switches are intensified, some data resulting of the measurements of the second probe, do not show bistable characteristics. In the no-walls section case, the signals showed bistable features, until the moment the walls were removed.

Este trabalho foi estruturado em dois capítulos, utilizando 11 parcelas retangulares e permanentes de 348 m² cada, de um plantio clonal de Eucalyptus camaldulensis e Eucalyptus urophylla na região Sul do Estado do Tocantins. O primeiro capítulo objetivou a melhor forma de ajuste de modelos hipsométricos, analisando a acurácia do melhor modelo, e aplicando-o em uma situação florestal diferente. Os dados foram divididos em um lote de ajuste e outro de aplicação, com três classes de diâmetro e três classes de altura dominante. Inicialmente determinou-se o coeficiente de determinação ajustado em porcentagem (R²aj), erro-padrão da estimativa em porcentagem (Syx%), e análise gráfica residual. Posteriormente realizou-se um teste de identidade de modelos, seguido de um delineamento inteiramente casualizado (DIC) no esquema de parcelas subdivididas, juntamente com o teste de Dunnet. No final da análise, para avaliar a estabilidade dos modelos em um teste de validação, foram utilizados os critérios: coeficiente de determinação da predição (R²), soma de quadrados do resíduo relativo (SQRR), raiz quadrada do erro médio (RQEM), erro médio percentual (EMP). Concluiu-se que a melhor forma de ajuste foi realizar um ajuste por classe, sendo o modelo regional o mais adequado a se utilizar. O segundo capítulo aborda a avaliação de modelos hipsométricos aplicando a técnica de validação cruzada, e a comparação dos resultados com aqueles obtidos no capítulo 1, visando obter o melhor modelo a ser utilizado na região sob diferentes aspectos de seleção. Inicialmente aplicaram-se os critérios de precisão: coeficiente de determinação ajustado, erro padrão da estimativa e análise gráfica residual. Em seguida foram aplicados os critérios de estabilidade realizando a validação cruzada entre os dois lotes de dados, que foram estes: erro médio absoluto, raiz do quadrado médio e soma de quadrados do erro médio. Os modelos selecionados foram submetidos a uma nova análise, utilizando-se os lotes de dados do capítulo 1, onde se aplicou os mesmos critérios de precisão e estabilidade utilizados anteriormente, resultando na comparação entre os capítulos. Concluiu-se que o melhor modelo local foi o 14 de Chapman-Richards, o melhor modelo regional foi o parabólico 03, e na comparação com os modelos selecionados no capítulo 01, o mais adequado para o plantio foi o modelo regional parabólico 3, proveniente do capítulo 02. / Hypsometric relations of clonal eucalyptus in south of Tocantins. This work was structured in two chapters, using 11 rectangular and permanent plots of 348 m² each, from a clonal plantation of Eucalyptus camaldulensis and Eucalyptus urophylla in the southern region of the state of Tocantins. The first chapter aimed at the best way of adjusting hypsometric models, analyzing the accuracy of the best model, and applying it in a different forest situation. The data were divided into one set of adjustment and another of application, with three classes of diameter and three classes of dominant height. The coefficient of determination adjusted in percentage (R²aj), standard error of the estimate in percentage (Syx%), and residual graphical analysis were determined initially. A model identity test was then performed, followed by a completely randomized design (DIC) in the subdivided plot scheme, along with the Dunnet test. At the end of the analysis, to evaluate the stability of the models in a validation test, the following criteria were used: prediction determination coefficient (R²), sum of squares of the residual residue (SQRR), square root mean error (RQEM) mean error (EMP). It was concluded that the best form of adjustment was to perform an adjustment by class, being the regional model the most appropriate to be used. The second chapter deals with the evaluation of hypsometric models applying the cross validation technique, and the comparison of the results with those obtained in chapter 1, aiming to obtain the best model to be used in the region under different aspects of selection. Initially the precision criteria were applied: adjusted coefficient of determination, standard error of the estimate and residual graphical analysis. Then, the stability criteria were applied by performing cross-validation between the two batches of data, which were: absolute mean error, mean square root, and mean square error sum. The selected models were submitted to a new analysis, using the data bundles of chapter 1, where the same criteria of precision and stability previously used were applied, resulting in the comparison between the chapters. It was concluded that the best local model was Chapman-Richards 14, the best regional model was parabolic 03, and in comparison with the models selected in chapter 01, the most suitable for planting was the regional parabolic model 3, of chapter 02.

Isothermal flow development, gap instability, and gap vortex street generation in eccentric annular channels have been studied experimentally. A representative paradigm of a flow in a highly eccentric annular channel was examined for a channel having an inner-to-outer diameter ratio d/D = 0.50 and an eccentricity e = 0.8 for a Reynolds number Re = 7300. Observation of the flow development has identified three distinct regions: the entrance region, the fluctuation-growth region and the rapid-mixing region. Weak quasi-periodic velocity fluctuations were first detected in the downstream part of the entrance region, and grew into very strong ones, reaching peak-to-peak amplitudes in the narrow gap that were nearly 60% of the bulk velocity. The dependence on inlet conditions, d/D, e and Re on the development and structure of flows was also investigated. Experimental conditions covered the ranges: 0 ≤ Re ≤ 19000, 0 ≤ e ≤ 0.9 and d/D = 0.25, 0.50 and 0.75. For Re < 7000, the Strouhal number, the normalized mid-gap axial flow velocity and the axial and cross-flow fluctuation intensities at mid-gap were found to increase with increasing Re and to depend strongly on inlet conditions. At higher Re, however, these parameters reached asymptotic values that were only mildly sensitive to inlet conditions. A map was constructed for the various stages of periodic motions vs. e and Re and it was found that, for e < 0.5 or Re < 1100, the flow was unconditionally stable as far as gap instability is concerned. For e ≤ 0.5, transition to turbulence occurred at Re ≈ 6000, whereas, for 0.6 ≤ e ≤ 0.9, the critical Reynolds number for the formation of periodic motions was found to increase with eccentricity from 1100 for e = 0.6 to 3800 for e = 0.9. The use of an empirically derived "mixing layer Strouhal number" permitted a universal description of gap vortex street periodicity in eccentric annular channels. This study has contributed to our understanding of the physical mechanisms that lead to gap instability and the development of a gap vortex street and the dependence of these flow phenomena on the channel geometry and the dynamic conditions of the flow.

Isothermal flow development, gap instability, and gap vortex street generation in eccentric annular channels have been studied experimentally. A representative paradigm of a flow in a highly eccentric annular channel was examined for a channel having an inner-to-outer diameter ratio d/D = 0.50 and an eccentricity e = 0.8 for a Reynolds number Re = 7300. Observation of the flow development has identified three distinct regions: the entrance region, the fluctuation-growth region and the rapid-mixing region. Weak quasi-periodic velocity fluctuations were first detected in the downstream part of the entrance region, and grew into very strong ones, reaching peak-to-peak amplitudes in the narrow gap that were nearly 60% of the bulk velocity. The dependence on inlet conditions, d/D, e and Re on the development and structure of flows was also investigated. Experimental conditions covered the ranges: 0 ≤ Re ≤ 19000, 0 ≤ e ≤ 0.9 and d/D = 0.25, 0.50 and 0.75. For Re < 7000, the Strouhal number, the normalized mid-gap axial flow velocity and the axial and cross-flow fluctuation intensities at mid-gap were found to increase with increasing Re and to depend strongly on inlet conditions. At higher Re, however, these parameters reached asymptotic values that were only mildly sensitive to inlet conditions. A map was constructed for the various stages of periodic motions vs. e and Re and it was found that, for e < 0.5 or Re < 1100, the flow was unconditionally stable as far as gap instability is concerned. For e ≤ 0.5, transition to turbulence occurred at Re ≈ 6000, whereas, for 0.6 ≤ e ≤ 0.9, the critical Reynolds number for the formation of periodic motions was found to increase with eccentricity from 1100 for e = 0.6 to 3800 for e = 0.9. The use of an empirically derived "mixing layer Strouhal number" permitted a universal description of gap vortex street periodicity in eccentric annular channels. This study has contributed to our understanding of the physical mechanisms that lead to gap instability and the development of a gap vortex street and the dependence of these flow phenomena on the channel geometry and the dynamic conditions of the flow.

The acoustic emissions from supersonic jets represent an area of significant research needs; not only in the field of aero-acoustics, but in industry as well where high pressure let down processes have been known to cause acoustically induced vibrations. A common method to reduce the acoustic emissions of such processes involves dividing the single larger supersonic flow into several smaller ones. Though this is common practice, there is not yet a current model which describes the reduction of acoustic emissions from an array of smaller supersonic jets. Current research which studies supersonic jet arrays are mainly focused on the effects of screech. Though screech is important, due to its high amplitude acoustic pressure, this research focuses on the overall acoustic emissions radiated from supersonic jet arrays which can cause severe acoustic loadings. This research investigated the acoustic emissions and shock formations from several eight by eight arrays of axisymmetric jet experimentally. The array nozzle diameters investigated ranged from 1/8 inch to 1/4 inch and the spacing over diameter ratio ranged from 1.44 to 3. The net pressure ratios investigated ranged from 2 to 24. Results revealed a strong correlation between the acoustic emissions and the shock formations of the flow. Up until a critical net pressure ratio, the overall sound pressure levels were comparable to that of a single jet within an array. At net pressure ratios beyond the critical the overall sound pressure levels transitioned to higher decibel levels; equivalent to a single jet with an equivalent exit area of an entire array. Also, the characteristic acoustic frequency emitted from a nozzle array remained ultrasonic (above 20 kHz) at lower net pressure ratios and then shifted to audible levels (between 20 Hz to 20 kHz) at net pressure ratios beyond the critical. Also, before the critical net pressure ratio the shock cells from the jets within the array remained unmerged, but at net pressure ratios beyond the critical the shock cells merged and formed lattices of weak oblique shocks at first and then strong oblique shocks as the net pressure ratio continued to increase. The critical net pressure ratio was investigated by non-dimensional analysis. The non-dimensional analysis revealed that the critical net pressure ratio was a strong linear function of the spacing over diameter ratio. A linear model was derived which is able to predict the critical net pressure ratio, and in turn, predict a critical shift in the acoustic emissions of a nozzle array.