O aumento das ocorrências de VIM em plataformas flutuantes do tipo \"spar\" e monocoluna serviu de motivação para a investigação dos fundamentos do fenômeno de VIV em cilindros com baixa razão de aspecto e pequena razão de massa. Tal investigação também foi motivada pela necessidade de se preencher lacunas de conhecimento a respeito deste assunto, articularmente por conta da escassa disponibilidade de resultados acerca do VIV em cilindros curtos, bem como pela ausência de modelo fluido que justifique os comportamentos dinâmicos conhecidos. Para o entendimento pretendido, três grupos de experimentos com cilindros dotados de razão de aspecto na faixa 0,1 <= L/D <= 2,0 foram realizados em um canal de água circulante na Escola Politécnica da Universidade de São Paulo, sendo: o primeiro grupo focado nos cilindros curtos estacionários; o segundo nos cilindros curtos de baixa razão de massa, 1,00 <= m* <= 4,36, e dois graus de liberdade; e o grupo final interessado no VIV em cilindros flutuantes, ou seja, razão de massa unitária e seis graus de liberdade. De uma maneira geral, a partir dos resultados aqui obtidos e das comparações com os resultados respectivamente encontrados na literatura, conclui-se que o VIV em cilindros curtos somente acontece se L/D > 0,2. Além de original, a determinação deste valor crítico também identificou outras três regiões com comportamentos fluido-dinâmicos distintos, cada qual marcada por especificidades quanto aos impactos nas amplitudes, frequências e coeficientes de força. Assim sendo, para cilindros com L/D > 2,0 a esteira de von Kármán foi a principal responsável pelas forças sustentação; fato não identificado para os cilindros com 0,5 < L/D < 2,0, onde esta mesma esteira sofreu forte contaminação das estruturas partindo da extremidade livre, principalmente aquelas com vorticidade predominante no plano vertical. Para os cilindros na faixa de 0,2 < L/D <= 0,5, apenas estas últimas estruturas foram responsáveis pelas oscilações de VIV. Finalmente, buscando compreender a origem das forças oscilatórias em cilindros com baixíssima razão de aspecto, \"end-plates\" foram aplicadas e confirmaram que o fenômeno de VIV nestes casos está relacionado à liberação de vórtices junto à extremidade livre, o que indica uma solução interessante para a mitigação do VIM de plataformas. / The increase of VIM occurrences on spar and monocolumn platforms was the motivation to study the vortex-induced vibrations of cylinders with low aspect ratio and small mass ratio under a fundamental perspective. The present work was also motivated by the small number of works in the literature dealing with VIV of cylinders with low aspect ratio, as well as by the scarce concerns about the flow models around this cylinders, which justify the dynamic behaviors observed. Aiming to better understand this problem, three groups of experiments with cylinders of 0.1 <= L/D <= 2.0 were carried out in a recirculating water channel at Escola Politécnica of University of São Paulo, as follow: firstly, the flow around stationary cylinders; secondly, VIV of cylinders with two degrees-of-freedom and 1.00 <= m* <= 4.36. finally, VIV of floating cylinder, thus six degrees-of-freedom. The works concluded that VIV occurs only for cylinders with L/D > 0.2. Besides of being original, this result was also related to the observation of three regions of aspect ratio, each of them with different behaviors of the motion amplitudes, frequency ratios and force coefficients. For cylinders with L/D > 2.0, the von Kármán wake was the mainly responsible for the oscillatory lift forces. On the other hand, the von Kármán wake was contaminated by the effects coming from the free end of cylinders with 0.5 < L/D < 2.0, mainly by the vortex structures with vorticity in the vertical plane. And for cylinders with 0.2 < L/D <=0.5, the vortex structures at the free end were predominant, thus the only one responsible for the oscillatory lift forces. Finally, in order to understand the source for oscillatory lift forces on cylinders with very low aspect ratio, end-plates were applied and confirmed that VIV in these cases is related to the vortex-shedding around the free end, which indicates an interesting solution for VIM mitigation of platforms.

Die experimentellen Untersuchungen zur Strömungs-Struktur-Interaktion kommen zu folgenden Ergebnissen. Die als entrainment bezeichnete Verhaltensweise von Fischen kann durch den gezielten Ausgleich von Auftriebs-, Widerstands- und einer erstmals nachgewiesenen Saugkraft und der damit verbundenen Reduzierung der lokomotorischen Energie erklärt werden. Des Weiteren zeigen die Experimente an einer wellenförmig bewegten Oberfläche, dass die Strömung an einem Wellenberg zyklisch zwischen laminarem und turbulentem Regime wechselt und dass diese Oszillation zur Reduzierung des Form- und Gesamtwiderstandes der geschleppten Oberfläche führt. Dünne, flexible Häutchen hairy flaps an der Rückseite eines Zylinders führen zu einer Änderung der Struktur der Wirbelablösung an diesem. Dadurch wird sowohl die auf den Zylinder wirkende Auftriebskraft als auch die Widerstandskraft um bis zu 65% reduziert. Für die Interaktion zwischen der Strömung um zwei hintereinander positionierte elastische Zylinder und ihrer Kinematik konnte die Synchronisierung (lock-in) ihrer Bewegung mit einer verbundenen Zerstörung der Wirbelstraße hinter dem zweiten Zylinder gezeigt werden. / The experimental investigations presented herein explain the behavioural adaptation of fish called entrainment for the first time. The results confirm a balance of lift-, drag- and a suction-force, explaining the reduction of locomotive energy. Furthermore, flow measurements around an undulating membrane affirm an oscillation between laminar and turbulent flow over one period of the motion and that this oscillation decreases the pressure- and drag-force of the towed membrane. Experiments on thin and flexible flaps attached at the lee-side of a cylinder, show that the flaps alter the natural vortex separation cycle in such a way that the vortices do not shed in a staggered side-by-side arrangement but in line in a row with the cylinder wake axis. Thus, flow fluctuations are reduced by 42% in stream-wise - and 35% in transversal direction at best, compared to a reference case without hairy-flaps. Finally, investigations on the flow around and on the kinematics of two flexible cylinders in a tandem arrangement demonstrate a synchronisation of their motion (lock-in), resulting in the destruction of the vortex-street behind the second cylinder.

O aumento das ocorrências de VIM em plataformas flutuantes do tipo \"spar\" e monocoluna serviu de motivação para a investigação dos fundamentos do fenômeno de VIV em cilindros com baixa razão de aspecto e pequena razão de massa. Tal investigação também foi motivada pela necessidade de se preencher lacunas de conhecimento a respeito deste assunto, articularmente por conta da escassa disponibilidade de resultados acerca do VIV em cilindros curtos, bem como pela ausência de modelo fluido que justifique os comportamentos dinâmicos conhecidos. Para o entendimento pretendido, três grupos de experimentos com cilindros dotados de razão de aspecto na faixa 0,1 <= L/D <= 2,0 foram realizados em um canal de água circulante na Escola Politécnica da Universidade de São Paulo, sendo: o primeiro grupo focado nos cilindros curtos estacionários; o segundo nos cilindros curtos de baixa razão de massa, 1,00 <= m* <= 4,36, e dois graus de liberdade; e o grupo final interessado no VIV em cilindros flutuantes, ou seja, razão de massa unitária e seis graus de liberdade. De uma maneira geral, a partir dos resultados aqui obtidos e das comparações com os resultados respectivamente encontrados na literatura, conclui-se que o VIV em cilindros curtos somente acontece se L/D > 0,2. Além de original, a determinação deste valor crítico também identificou outras três regiões com comportamentos fluido-dinâmicos distintos, cada qual marcada por especificidades quanto aos impactos nas amplitudes, frequências e coeficientes de força. Assim sendo, para cilindros com L/D > 2,0 a esteira de von Kármán foi a principal responsável pelas forças sustentação; fato não identificado para os cilindros com 0,5 < L/D < 2,0, onde esta mesma esteira sofreu forte contaminação das estruturas partindo da extremidade livre, principalmente aquelas com vorticidade predominante no plano vertical. Para os cilindros na faixa de 0,2 < L/D <= 0,5, apenas estas últimas estruturas foram responsáveis pelas oscilações de VIV. Finalmente, buscando compreender a origem das forças oscilatórias em cilindros com baixíssima razão de aspecto, \"end-plates\" foram aplicadas e confirmaram que o fenômeno de VIV nestes casos está relacionado à liberação de vórtices junto à extremidade livre, o que indica uma solução interessante para a mitigação do VIM de plataformas. / The increase of VIM occurrences on spar and monocolumn platforms was the motivation to study the vortex-induced vibrations of cylinders with low aspect ratio and small mass ratio under a fundamental perspective. The present work was also motivated by the small number of works in the literature dealing with VIV of cylinders with low aspect ratio, as well as by the scarce concerns about the flow models around this cylinders, which justify the dynamic behaviors observed. Aiming to better understand this problem, three groups of experiments with cylinders of 0.1 <= L/D <= 2.0 were carried out in a recirculating water channel at Escola Politécnica of University of São Paulo, as follow: firstly, the flow around stationary cylinders; secondly, VIV of cylinders with two degrees-of-freedom and 1.00 <= m* <= 4.36. finally, VIV of floating cylinder, thus six degrees-of-freedom. The works concluded that VIV occurs only for cylinders with L/D > 0.2. Besides of being original, this result was also related to the observation of three regions of aspect ratio, each of them with different behaviors of the motion amplitudes, frequency ratios and force coefficients. For cylinders with L/D > 2.0, the von Kármán wake was the mainly responsible for the oscillatory lift forces. On the other hand, the von Kármán wake was contaminated by the effects coming from the free end of cylinders with 0.5 < L/D < 2.0, mainly by the vortex structures with vorticity in the vertical plane. And for cylinders with 0.2 < L/D <=0.5, the vortex structures at the free end were predominant, thus the only one responsible for the oscillatory lift forces. Finally, in order to understand the source for oscillatory lift forces on cylinders with very low aspect ratio, end-plates were applied and confirmed that VIV in these cases is related to the vortex-shedding around the free end, which indicates an interesting solution for VIM mitigation of platforms.

Die experimentellen Untersuchungen zur Strömungs-Struktur-Interaktion kommen zu folgenden Ergebnissen. Die als entrainment bezeichnete Verhaltensweise von Fischen kann durch den gezielten Ausgleich von Auftriebs-, Widerstands- und einer erstmals nachgewiesenen Saugkraft und der damit verbundenen Reduzierung der lokomotorischen Energie erklärt werden. Des Weiteren zeigen die Experimente an einer wellenförmig bewegten Oberfläche, dass die Strömung an einem Wellenberg zyklisch zwischen laminarem und turbulentem Regime wechselt und dass diese Oszillation zur Reduzierung des Form- und Gesamtwiderstandes der geschleppten Oberfläche führt. Dünne, flexible Häutchen hairy flaps an der Rückseite eines Zylinders führen zu einer Änderung der Struktur der Wirbelablösung an diesem. Dadurch wird sowohl die auf den Zylinder wirkende Auftriebskraft als auch die Widerstandskraft um bis zu 65% reduziert. Für die Interaktion zwischen der Strömung um zwei hintereinander positionierte elastische Zylinder und ihrer Kinematik konnte die Synchronisierung (lock-in) ihrer Bewegung mit einer verbundenen Zerstörung der Wirbelstraße hinter dem zweiten Zylinder gezeigt werden.:Zusammenfassung 1 Conclusions 7 1. Einleitung und Zielsetzung 11 2. Messtechnische Grundlagen 17 2.1. Klassische Particle Image Velocimetry 18 2.2. Scanning Particle Image Velocimetry 20 2.3. Mirror Particle Tracking Velocimetry 21 2.4. Druckberechnung 35 3. Hydrodynamisches Modell des entrainments 37 3.1. Stand der Forschung 38 3.2. Experimenteller Aufbau 42 3.3. Ergebnisse 44 3.4. Zusammenfassung 51 4. Undulatorisch bewegte Oberflächen 53 4.1. Stand der Forschung 54 4.2. Mechanisches Modell 57 4.3. Experimenteller Aufbau 61 4.4. Ergebnisse 65 4.5. Zusammenfassung 74 5. Selbstadaptive elastische Klappen - hairy flaps 77 5.1. Stand der Forschung 78 5.2. Experimenteller Aufbau 82 5.3. Ergebnisse 86 5.4. Zusammenfassung 107 6. Umströmung stumpfer elastischer Körper 109 6.1. Stand der Forschung 110 6.2. Experimenteller Aufbau 116 6.3. Ergebnisse 120 6.4. Zusammenfassung 128 7. Ausblick 131 Abbildungsverzeichnis 135 Tabellenverzeichnis 141 Symbolverzeichnis 142 Literaturverzeichnis 146 A. Anhang 155 / The experimental investigations presented herein explain the behavioural adaptation of fish called entrainment for the first time. The results confirm a balance of lift-, drag- and a suction-force, explaining the reduction of locomotive energy. Furthermore, flow measurements around an undulating membrane affirm an oscillation between laminar and turbulent flow over one period of the motion and that this oscillation decreases the pressure- and drag-force of the towed membrane. Experiments on thin and flexible flaps attached at the lee-side of a cylinder, show that the flaps alter the natural vortex separation cycle in such a way that the vortices do not shed in a staggered side-by-side arrangement but in line in a row with the cylinder wake axis. Thus, flow fluctuations are reduced by 42% in stream-wise - and 35% in transversal direction at best, compared to a reference case without hairy-flaps. Finally, investigations on the flow around and on the kinematics of two flexible cylinders in a tandem arrangement demonstrate a synchronisation of their motion (lock-in), resulting in the destruction of the vortex-street behind the second cylinder.:Zusammenfassung 1 Conclusions 7 1. Einleitung und Zielsetzung 11 2. Messtechnische Grundlagen 17 2.1. Klassische Particle Image Velocimetry 18 2.2. Scanning Particle Image Velocimetry 20 2.3. Mirror Particle Tracking Velocimetry 21 2.4. Druckberechnung 35 3. Hydrodynamisches Modell des entrainments 37 3.1. Stand der Forschung 38 3.2. Experimenteller Aufbau 42 3.3. Ergebnisse 44 3.4. Zusammenfassung 51 4. Undulatorisch bewegte Oberflächen 53 4.1. Stand der Forschung 54 4.2. Mechanisches Modell 57 4.3. Experimenteller Aufbau 61 4.4. Ergebnisse 65 4.5. Zusammenfassung 74 5. Selbstadaptive elastische Klappen - hairy flaps 77 5.1. Stand der Forschung 78 5.2. Experimenteller Aufbau 82 5.3. Ergebnisse 86 5.4. Zusammenfassung 107 6. Umströmung stumpfer elastischer Körper 109 6.1. Stand der Forschung 110 6.2. Experimenteller Aufbau 116 6.3. Ergebnisse 120 6.4. Zusammenfassung 128 7. Ausblick 131 Abbildungsverzeichnis 135 Tabellenverzeichnis 141 Symbolverzeichnis 142 Literaturverzeichnis 146 A. Anhang 155

In this thesis, a miniaturized energy harvester system is developed. The energy harvester converts fluid kinetic energy into electrical energy without using any rotating components. The working principle of the energy harvester is based on the so called vortex-induced vibration. Such systems have the potential to provide energy for wireless sensor networks in the field of inline measurements for gas, oil or water transportation systems. The theoretical background of the vortex-induced vibration (VIV) is studied. Based on the studies, a fluid-structure interaction simulation is carried out to optimize the structure of the energy harvester. As result, the conversion efficiency is significantly improved, which is experimentally confirmed. A series of demonstrators are manufactured according to the simulation and optimization results. It is tested on a self-constructed test bench. To further improve the performance, an electromagnetic generator is proposed, and therefore, a multimethod demonstrator realized. The demonstrators are working in air flow already at a velocity of 2 m/s, and reach the maximum efficiency at 3.6 m/s. This performance ranks among the best published results and is discussed in detail. / In der vorliegenden Arbeit wird ein miniaturisiertes Energiegewinnungssystem entwickelt, das unter Verzicht auf rotierende Komponenten kinetische Strömungsenergie in elektrische Energie umwandelt. Die Funktion dieses Wandlers basiert auf der sogenannten wirbelinduzierten Vibration. Derartige Systeme besitzen unter anderem das Potenzial, drahtlose Sensornetzwerke zur Erfassung von Messdaten in Gas-, Öl- oder Wassertransportsystemen mit Energie zu versorgen zu können. In der Arbeit wird der theoretische Hintergrund der wirbelinduzierten Vibration untersucht und darauf basierend werden Fluid-Struktur-Wechselwirkungssimulationen zur Strukturoptimierung durchgeführt in deren Ergebnis eine theoretische Verbesserung der Effizienz des Wandlers um ein Mehrfaches erreicht wird, die auch praktisch bestätigt wird. Unter Berücksichtigung der Simulations- und Optimierungsergebnisse wurden eine Reihe von Demonstratoren gefertigt, die auf einem selbst konstruierten Prüfstand getestet wurden. Zur weiteren Erhöhung der Leistungsfähigkeit des Wandlers wird ein zusätzlicher elektromagnetischer Generator vorgeschlagen und damit ein Multi-Methoden-Demonstrator technisch realisiert. Die Demonstratoren arbeiten in strömender Luft bereits bei Geschwindigkeiten von 2 m/s und erreichen bei 3,6 m/s ihre maximale Effizienz. Die erreichten Ergebnisse ordnen sich im Vergleich mit denen aus entsprechenden Publikationen vorn ein und werden ausführlich diskutiert.

One of the most prominent factors affecting the performance and longevity of risers is vortex induced vibration (VIV), which can cause severe fatigue damage, especially in risers used in deep waters. The available approaches for analyzing VIV induced fatigue in risers mainly focus on the VIV aspect of the problem; indeed less attention has been paid on the effect of VIV on a riser’s fatigue life and in prediction of fatigue life using various models. This dissertation first demonstrates how one can characterize fatigue of pipes and risers using an equivalent plate specimen as opposed to using a pipe specimen, thereby simplifying the task, yet obtaining good accuracy. Actual variable amplitude loadings (VAL) are used to study the fatigue crack growth in risers’ material with a focus on the various influencing parameters. Extensive experimental investigations are performed, followed by analytical and computational nonlinear finite element analyses. It is shown that the higher harmonics do cause significant fatigue damage, thus their influence should not be ignored. The influence of load interaction effects is also investigated, focusing on the fatigue crack growth retardation effects due to tension overloads, as well as the acceleration effects due to compression underloads. The crack closure concept is then used to explore into both the fatigue retardation and acceleration effects within a VAL scenario. An effective method for calculation of the stress intensity factor is proposed, which considers only the tensile portion of the stress range, while proposing another effective approach for accounting for the influence of compressive stress cycles. Moreover, a two-parameter approach is used in this dissertation, relating the fatigue crack growth rate (FCGR) to the crack tip opening displacement (CTOD). It is shown that the CTOD provides adequate information for calculating the FCGR under VAL, and it can be effectively used to account for the influence of the compressive stress cycles. The experimental investigation also considers the retardation effect resulting from the applied peak tensile overload cycles (TOLC) and the influence of various so-called “clipping” levels, demonstrating the significant influence of the TOLC on crack growth retardation in VAL.

In the flow past bluff bodies for a certain range of velocity a periodical vortex shedding emerges which is known as von Kármán vortex street. This phenomenon causes the periodical alteration of pressure field which affects the body. Should the vortex shedding frequency be similar to the body natural frequency, the amplitude of vibration significantly increases which can lead to fatigue cracking. In the case of water turbines, this phenomenon often affects the stay vanes. Both the vortex shedding frequency and the lift force amplitude can be influenced by the modification of the trailing edge geometry. The aim of this thesis is to use CFD computation in order to find the optimal geometry of the stay vane trailing edge for the specific Francis turbine unit.

In this thesis, a miniaturized energy harvester system is developed. The energy harvester converts fluid kinetic energy into electrical energy without using any rotating components. The working principle of the energy harvester is based on the so called vortex-induced vibration. Such systems have the potential to provide energy for wireless sensor networks in the field of inline measurements for gas, oil or water transportation systems. The theoretical background of the vortex-induced vibration (VIV) is studied. Based on the studies, a fluid-structure interaction simulation is carried out to optimize the structure of the energy harvester. As result, the conversion efficiency is significantly improved, which is experimentally confirmed. A series of demonstrators are manufactured according to the simulation and optimization results. It is tested on a self-constructed test bench. To further improve the performance, an electromagnetic generator is proposed, and therefore, a multimethod demonstrator realized. The demonstrators are working in air flow already at a velocity of 2 m/s, and reach the maximum efficiency at 3.6 m/s. This performance ranks among the best published results and is discussed in detail. / In der vorliegenden Arbeit wird ein miniaturisiertes Energiegewinnungssystem entwickelt, das unter Verzicht auf rotierende Komponenten kinetische Strömungsenergie in elektrische Energie umwandelt. Die Funktion dieses Wandlers basiert auf der sogenannten wirbelinduzierten Vibration. Derartige Systeme besitzen unter anderem das Potenzial, drahtlose Sensornetzwerke zur Erfassung von Messdaten in Gas-, Öl- oder Wassertransportsystemen mit Energie zu versorgen zu können. In der Arbeit wird der theoretische Hintergrund der wirbelinduzierten Vibration untersucht und darauf basierend werden Fluid-Struktur-Wechselwirkungssimulationen zur Strukturoptimierung durchgeführt in deren Ergebnis eine theoretische Verbesserung der Effizienz des Wandlers um ein Mehrfaches erreicht wird, die auch praktisch bestätigt wird. Unter Berücksichtigung der Simulations- und Optimierungsergebnisse wurden eine Reihe von Demonstratoren gefertigt, die auf einem selbst konstruierten Prüfstand getestet wurden. Zur weiteren Erhöhung der Leistungsfähigkeit des Wandlers wird ein zusätzlicher elektromagnetischer Generator vorgeschlagen und damit ein Multi-Methoden-Demonstrator technisch realisiert. Die Demonstratoren arbeiten in strömender Luft bereits bei Geschwindigkeiten von 2 m/s und erreichen bei 3,6 m/s ihre maximale Effizienz. Die erreichten Ergebnisse ordnen sich im Vergleich mit denen aus entsprechenden Publikationen vorn ein und werden ausführlich diskutiert.