Formation of corner waves in the wake of a partially submerged bluff body

We study theoretically and numerically the downstream flow near the corner of a bluff body partially submerged at a deadrise depth Δh into a uniform stream of velocity U, in the presence of gravity, g. When the Froude number, Fr=U/√gΔh, is large, a three-dimensional steady plunging wave, which is referred to as a corner wave, forms near the corner, developing downstream in a similar way to a two-dimensional plunging wave evolving in time. We have performed an asymptotic analysis of the flow near this corner to describe the wave's initial evolution and to clarify the physical mechanism that leads to its formation. Using the two-dimensions-plus-time approximation, the problem reduces to one similar to dam-break flow with a wet bed in front of the dam. The analysis shows that, at leading order, the problem admits a self-similar formulation when the size of the wave is small compared with the height difference Δh. The essential feature of the self-similar solution is the formation of a mushroom-shaped jet from which two smaller lateral jets stem. However, numerical simulations show that this self-similar solution is questionable from the physical point of view, as the two lateral jets plunge onto the free surface, leading to a self-intersecting flow. The physical mechanism leading to the formation of the mushroom-shaped structure is discussed

Olas de Esquina aguas abajo de una placa parcialmente sumergida

In this dissertation, the high-Reynolds-number flow near the corner of a vertical at plate partially submerged across an uniform stream has been studied using a combination of experimental, numerical and analytical tools. In this configuration, a three dimensional wave forms at the corner of the plate which evolves downstream in a similar way as a time-evolving two dimensional plunging or spilling breaker, depending the occurrence of one or the other type of breaker on the flow conditions. Experiments have been performed submerging a flat plate perpendicular to the free stream in the test section of a recirculating water channel. Experimental results show that the formation and the initial development of the wave is nearly unaffected by the presence of the channel walls and bottom even when their distance to the corner, where the wave originates, is of the order of the size of the wave itself. This is a remarkable observation, that suggests that the formation of the corner wave is a local process in a sense that it is only influenced by the characteristics of the velocity field very near the corner. Moreover, it has been observed that the jet formed when the corner wave adopts the plunging breaker configuration follows a nearly ballistic trajectory, has is the case in two-dimensional unsteady plunging breakers. Theoretical analysis shows that, taking advantage of the slender nature of the flow, the 3D steady problem can be transformed into a two dimensional unsteady one using the so called 2D+T approximation. Together with the high Reynolds number of the flow, the 2D+T approximation makes the problem amenable to be simulated numerically using a Boundary Element Method (BEM). Moreover, a pressure-impulse asymptotic analysis of the flow near the origin of the corner wave has been performed in order to describe the initial evolution of the wave and to clarify the physical mechanisms that lead to its formation. The analysis shows that the flow near the corner exhibits a self similar behavior at short times. The problem considered in this dissertation is of interest in naval hydrodynamics as well as oceanography. Indeed, the flow resembles to the one found at the dry stern of high-speed surface vessels. The similarities between the waves formed in the wake of such ships and our laboratory breakers will be investigated. This experiment also shares many features with deep water waves in the ocean, and thus it will be applied to the study of their breaking process. A criterion for the transition between overturning laboratory waves and spilling ones is proposed. ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------En esta tesis se ha estudiado el flujo a altos números de Reynolds aguas abajo de la esquina de una placa vertical parcialmente sumergida en una corriente uniforme, usando para tal fin una combinación de herramientas experimentales, numéricas y analíticas. Este flujo se caracteriza por la aparición de una ola estacionaria, que permanece unida a la esquina de la placa. Tanto la amplitud como la pendiente del frente de la ola crecen a medida que la ola evoluciona aguas abajo de la placa, dando lugar ya sea, a una rotura de la ola en la cual la cresta se derrama sobre la propia ola, o a una rotura en forma de tubo. Para estudiar este flujo experimentalmente, se sumergió una placa perpendicularmente a una corriente uniforme en un canal de recirculación. Los resultados experimentales demuestran que la presencia de las paredes y el suelo del canal no afectan a la formación y el desarrollo inicial de la ola, incluso cuando dichas paredes se encuentran a distancias del orden de magnitud de la propia ola. Esta es una observación importante dado que sugiere que la formación de la ola es un proceso local, en el sentido de que solamente se ve afectado por el campo de velocidades cerca de la esquina. Complementariamente se ha observado que, cuando la ola rompe en forma de tubo, la cresta de la ola sigue una trayectoria balística, al igual que en las olas en aguas profundas. El análisis teórico muestra que, haciendo uso de la naturaleza esbelta del flujo, el problema tridimensional estacionario se puede transformar en un problema bidimensional no estacionario mediante el uso de la, así llamada, aproximaci on 2D+T. Combinando los altos números de Reynolds encontrados en el flujo con el uso de dicha aproximación, el problema puede ser tratado numéricamente mediante un método de elementos de contorno. Para investigar el mecanismo físico que conduce a la formación de la ola y su posterior desarrollo, un análisis asintótico de la presión impulsiva en el flujo se ha llevado a cabo, capturándose con fiabilidad la evolución, a tiempos cortos, de la cresta de la ola, la cual se demuestra que exhibe un comportamiento auto semejante en las etapas iniciales. El problema considerado en esta tesis es de gran interés tanto en oceanografía como en el campo de la investigación naval. De hecho, este flujo recuerda al que se encuentra aguas abajo de las popas de espejo en barcos de superficie de alta velocidad. En esta tesis se investiga la semejanza entre las olas que se forman en la estela de dichos barcos y las generadas en el laboratorio. Adicionalmente, se observa que las olas obtenidas en el laboratorio también comparten muchas características de las olas en aguas profundas, por lo que se propone un criterio para separar ambos regímenes de rotura.This work has been sponsored by the ONR through grant N00014-05-1-0121

Persistent Pulmonary Hypertension in Corrected Valvular Heart Disease: Hemodynamic Insights and Long‐Term Survival

Insuficiència cardíaca; Hipertensió pulmonar; Malaltia valvular cardíacaInsuficiencia cardiaca; Hipertensión pulmonar; Enfermedad valvular cardíacaHeart failure; Pulmonary hypertension; Valvular heart diseaseBackground The determinants and consequences of pulmonary hypertension after successfully corrected valvular heart disease remain poorly understood. We aim to clarify the hemodynamic bases and risk factors for mortality in patients with this condition. Methods and Results We analyzed long‐term follow‐up data of 222 patients with pulmonary hypertension and valvular heart disease successfully corrected at least 1 year before enrollment who had undergone comprehensive hemodynamic and imaging characterization as per the SIOVAC (Sildenafil for Improving Outcomes After Valvular Correction) clinical trial. Median (interquartile range) mean pulmonary pressure was 37 mm Hg (32–44 mm Hg) and pulmonary artery wedge pressure was 23 mm Hg (18–26 mm Hg). Most patients were classified either as having combined precapillary and postcapillary or isolated postcapillary pulmonary hypertension. After a median follow‐up of 4.5 years, 91 deaths accounted for 4.21 higher‐than‐expected mortality in the age‐matched population. Risk factors for mortality were male sex, older age, diabetes mellitus, World Health Organization functional class III and higher pulmonary vascular resistance—either measured by catheterization or approximated from ultrasound data. Higher pulmonary vascular resistance was related to diabetes mellitus and smaller residual aortic and mitral valve areas. In turn, the latter correlated with prosthetic nominal size. Six‐month changes in the composite clinical score and in the 6‐minute walk test distance were related to survival. Conclusions Persistent valvular heart disease–pulmonary hypertension is an ominous disease that is almost universally associated with elevated pulmonary artery wedge pressure. Pulmonary vascular resistance is a major determinant of mortality in this condition and is related to diabetes mellitus and the residual effective area of the corrected valve. These findings have important implications for individualizing valve correction procedures.This study was funded by the Instituto de Salud Carlos III, Ministerio de Ciencia e Innovación, Spain, the European Union–European Regional Development Fund (EC07/90772 and PI19/00649), and the Consorcio de Investigación Biomédica en Red de Enfermedades Cardiovasculares (CIBERCV)

Pulmonary vein flow split effects in patient-specific simulations of left atrial flow

Disruptions to left atrial (LA) blood flow, such as those caused by atrial fibrillation (AF), can lead to thrombosis in the left atrial appendage (LAA) and an increased risk of systemic embolism. LA hemodynamics are influenced by various factors, including LA anatomy and function, and pulmonary vein (PV) inflow conditions. In particular, the PV flow split can vary significantly among and within patients depending on multiple factors. In this study, we investigated how changes in PV flow split affect LA flow transport, focusing for the first time on blood stasis in the LAA, using a high-fidelity patient-specific computational fluid dynamics (CFD) model. We use an Immersed Boundary Method, simulating the flow in a fixed, uniform Cartesian mesh and imposing the movement of the LA walls with a moving Lagrangian mesh generated from 4D Computerized Tomography images. We analyzed LA anatomies from eight patients with varying atrial function, including three with AF and either a LAA thrombus or a history of Transient Ischemic Attacks (TIAs). Using four different flow splits (60/40% and 55/45% through right and left PVs, even flow rate, and same velocity through each PV), we found that flow patterns are sensitive to PV flow split variations, particularly in planes parallel to the mitral valve. Changes in PV flow split also had a significant impact on blood stasis and could contribute to increased risk for thrombosis inside the LAA, particularly in patients with AF and previous LAA thrombus or a history of TIAs. Our study highlights the importance of considering patient-specific PV flow split variations when assessing LA hemodynamics and identifying patients at increased risk for thrombosis and stroke. This knowledge is relevant to planning clinical procedures such as AF ablation or the implementation of LAA occluders.This work was partially supported by Comunidad de Madrid (Synergy Grant Y2018/BIO-4858 PREFI-CM), Spanish Research Agency (AEI, grant number PID2019-107279RB-I00), Instituto de Salud Carlos III (grant numbers PI15/02211-ISBITAMI and DTS/1900063-ISBIFLOW), and by the EU-European Regional Development Fund. Funding for open access charge: Universidad de Málaga /CBU

Estimating fish passage over velocity barriers for non-uniform flow conditions: A case study in flat-V gauging weirs

Producción CientíficaWhen the flow velocity over a river structure exceeds the swimming capacity of fish, it behaves as a velocity barrier. Depending on the hydrodynamic circumstances of the structure as well as the fish’s swimming ability and motivation, the barrier can be permanent, partial, or intermittent. This is the case of flat-V gauging weirs, a common type of velocity barrier in Spanish rivers and in other European rivers. Flat-V weirs are broadly used as they provide precise information about river discharge for water resource management under different hydraulic scenarios, especially during low flow conditions. However, depending on their size, local river morphology, and the river flow scenario, they can produce excessive velocities and thus, reduce or hinder fish upstream movements. Due to their variable geometry, velocity barriers exhibit a non-uniform flow velocity field, which means that flow velocity varies along the barrier. Therefore, any predictive swimming model to assess the barrier effect on fish must consider the spatial variation to achieve a valuable forecast. This work aims to estimate fish passage over Flat-V weirs by linking their 3D hydraulic performance with the swimming capacity of fish. For this, a predictive model is developed using as target species the Iberian barbel (Luciobarbus bocagei), combining research on their swimming ability with 3D models of the structure. Results of the model show the river conditions and weir dimensions that permit the ascent of this species through the sloped wall of the weir. This information has direct implications for the design and assessment of velocity barriers as well as for the retrofitting of velocity barriers, making them compatible with the fish migration.Consejo Europeo de Investigación, European Union’s Horizon 2020 - (Grant 101032024

Efficient multi-fidelity computation of blood coagulation under flow

Clot formation is a crucial process that prevents bleeding, but can lead to severe disorders when imbalanced. This process is regulated by the coagulation cascade, a biochemical network that controls the enzyme thrombin, which converts soluble fibrinogen into the fibrin fibers that constitute clots. Coagulation cascade models are typically complex and involve dozens of partial differential equations (PDEs) representing various chemical species’ transport, reaction kinetics, and diffusion. Solving these PDE systems computationally is challenging, due to their large size and multi-scale nature. We propose a multi-fidelity strategy to increase the efficiency of coagulation cascade simulations. Leveraging the slower dynamics of molecular diffusion, we transform the governing PDEs into ordinary differential equations (ODEs) representing the evolution of species concentrations versus blood residence time. We then Taylor-expand the ODE solution around the zero-diffusivity limit to obtain spatiotemporal maps of species concentrations in terms of the statistical moments of residence time, , and provide the governing PDEs for . This strategy replaces a high-fidelity system of N PDEs representing the coagulation cascade of N chemical species by N ODEs and p PDEs governing the residence time statistical moments. The multi-fidelity order (p) allows balancing accuracy and computational cost providing a speedup of over N/p compared to high-fidelity models. Moreover, this cost becomes independent of the number of chemical species in the large computational meshes typical of the arterial and cardiac chamber simulations. Using a coagulation network with N = 9 and an idealized aneurysm geometry with a pulsatile flow as a benchmark, we demonstrate favorable accuracy for low-order models of p = 1 and p = 2. The thrombin concentration in these models departs from the high-fidelity solution by under 20% (p = 1) and 2% (p = 2) after 20 cardiac cycles. These multi-fidelity models could enable new coagulation analyses in complex flow scenarios and extensive reaction networks. Furthermore, it could be generalized to advance our understanding of other reacting systems affected by flow.MGH, MGV and OF have been partially supported by the Spanish Research Agency and the European Regional Development Fund, under grant number PID2019-107279RB-I00. MGH, MGV, PML, JB and OF have been partially supported by the Comunidad de Madrid and the European Regional Development Fund, under grant number Y2018/BIO-4858 PREFI-CM, and by the Instituto de Salud Carlos III and the European Regional Development Fund, under grant numbers PI15/02211-ISBITAMI and DTS/1900063-ISBIFLOW. AG, EMcV, AK and JCdA have been partially supported by the US National Institutes of Health, under grant 1R01HL160024. JCdA has been partially supported by the US National Insitutes of Health, under grant number 1R01HL158667

Pulmonary vein flow split effects in patient-specific simulations of left atrial flow

Disruptions to left atrial (LA) blood flow, such as those caused by atrial fibrillation (AF), can lead to thrombosis in the left atrial appendage (LAA) and an increased risk of systemic embolism. LA hemodynamics are influenced by various factors, including LA anatomy and function, and pulmonary vein (PV) inflow conditions. In particular, the PV flow split can vary significantly among and within patients depending on multiple factors. In this study, we investigated how changes in PV flow split affect LA flow transport, focusing for the first time on blood stasis in the LAA, using a high-fidelity patient-specific computational fluid dynamics (CFD) model. We use an Immersed Boundary Method, simulating the flow in a fixed, uniform Cartesian mesh and imposing the movement of the LA walls with a moving Lagrangian mesh generated from 4D Computerized Tomography images. We analyzed LA anatomies from eight patients with varying atrial function, including three with AF and either a LAA thrombus or a history of Transient Ischemic Attacks (TIAs). Using four different flow splits (60/40% and 55/45% through right and left PVs, even flow rate, and same velocity through each PV), we found that flow patterns are sensitive to PV flow split variations, particularly in planes parallel to the mitral valve. Changes in PV flow split also had a significant impact on blood stasis and could contribute to increased risk for thrombosis inside the LAA, particularly in patients with AF and previous LAA thrombus or a history of TIAs. Our study highlights the importance of considering patient-specific PV flow split variations when assessing LA hemodynamics and identifying patients at increased risk for thrombosis and stroke. This knowledge is relevant to planning clinical procedures such as AF ablation or the implementation of LAA occluders.This work was partially supported by Comunidad de Madrid (Synergy Grant Y2018/BIO-4858 PREFI-CM), Spanish Research Agency (AEI, grant number PID2019-107279RB-I00), Instituto de Salud Carlos III (grant numbers PI15/02211-ISBITAMI and DTS/1900063-ISBIFLOW), and by the EU-European Regional Development Fund . Funding for open access charge: Universidad de Málaga / CBUA

Demonstration of Patient-Specific Simulations to Assess Left Atrial Appendage Thrombogenesis Risk

Atrial fibrillation (AF) alters left atrial (LA) hemodynamics, which can lead to thrombosis in the left atrial appendage (LAA), systemic embolism and stroke. A personalized risk-stratification of AF patients for stroke would permit improved balancing of preventive anticoagulation therapies against bleeding risk. We investigated how LA anatomy and function impact LA and LAA hemodynamics, and explored whether patient-specific analysis by computational fluid dynamics (CFD) can predict the risk of LAA thrombosis. We analyzed 4D-CT acquisitions of LA wall motion with an in-house immersed-boundary CFD solver. We considered six patients with diverse atrial function, three with either a LAA thrombus (removed digitally before running the simulations) or a history of transient ischemic attacks (LAAT/TIA-pos), and three without a LAA thrombus or TIA (LAAT/TIA-neg). We found that blood inside the left atrial appendage of LAAT/TIA-pos patients had marked alterations in residence time and kinetic energy when compared with LAAT/TIA-neg patients. In addition, we showed how the LA conduit, reservoir and booster functions distinctly affect LA and LAA hemodynamics. Finally, fixed-wall and moving-wall simulations produced different LA hemodynamics and residence time predictions for each patient. Consequently, fixed-wall simulations risk-stratified our small cohort for LAA thrombosis worse than moving-wall simulations, particularly patients with intermediate LAA residence time. Overall, these results suggest that both wall kinetics and LAA morphology contribute to LAA blood stasis and thrombosis.This work was partially supported by the Comunidad de Madrid (Sinergias Y2018/BIO-4858 PREFI-CM), Cátedra Excelencia UC3M-Santander, Ministry of Education of Spain (Salvador de Madariaga program), the US NHLBI (NCAI-UCCAI-2017-06-6), the United States American Heart Association (AHA 20POST35200401), and the 2019 UCSD GEM Program. Computational time provided by XSEDE (Comet) and RES (Altamira) is gratefully acknowledged

Assessment of diastolic chamber properties of the right ventricle by global fitting of pressure-volume data and conformational analysis of 3D + T echocardiographic sequences

Assessment of diastolic chamber properties of the right ventricle by global fitting of pressure-volume data and conformational analysis of 3D + T echocardiographic sequence

A clinical method for mapping and quantifying blood stasis in the left ventricle

In patients at risk of intraventrcular thrombosis, the benefits of chronic anticoagulation therapy need to be balanced with the pro-hemorrhagic effects of therapy. Blood stasis in the cardiac chambers is a recognized risk factor for intracardiac thrombosis and potential cardiogenic embolic events. In this work, we present a novel flow image-based method to assess the location and extent of intraventricular stasis regions inside the left ventricle (LV) by digital processing flow-velocity images obtained either by phase-contrast magnetic resonance (PCMR) or 2D color-Doppler velocimetry (echo-CDV). This approach is based on quantifying the distribution of the blood Residence Time (TR) from time-resolved blood velocity fields in the LV. We tested the new method in illustrative examples of normal hearts, patients with dilated cardiomyopathy and one patient before and after the implantation of a left ventricular assist device (LVAD). The method allowed us to assess in-vivo the location and extent of the stasis regions in the LV. Original metrics were developed to integrate flow properties into simple scalars suitable for a robust and personalized assessment of the risk of thrombosis. From a clinical perspective, this work introduces the new paradigm that quantitative flow dynamics can provide the basis to obtain subclinical markers of intraventricular thrombosis risk. The early prediction of LV blood stasis may result in decrease strokes by appropriate use of anticoagulant therapy for the purpose of primary and secondary prevention. It may also have a significant impact on LVAD device design and operation set-up