Wall Shear Stress (WSS) has been demonstrated to be a biomarker of the development of atheroscler... more Wall Shear Stress (WSS) has been demonstrated to be a biomarker of the development of atherosclerosis. In vivo assessment of WSS is still challenging, but 4D Flow MRI represents a promising tool to provide 3D velocity data from which WSS can be calculated. In this study, a system based on Laser Doppler Velocimetry (LDV) was developed to validate new improvements of 4D Flow MRI acquisitions and derived WSS computing. A hydraulic circuit was manufactured to allow both 4D Flow MRI and LDV velocity measurements. WSS profiles were calculated with one 2D and one 3D method. Results indicated an excellent agreement between MRI and LDV velocity data, and thus the set-up enabled the evaluation of the improved performances of 3D with respect to the 2D-WSS computation method. To provide a concrete example of the efficacy of this method, the influence of the spatial resolution of MRI data on derived 3D-WSS profiles was investigated. This investigation showed that, with acquisition times compatib...
The prediction of ship motions in extreme seastates is very complex as it involves strong nonline... more The prediction of ship motions in extreme seastates is very complex as it involves strong nonlinearities. It deals with high motions of the ship and implies strong mooring system loads. These seastates are usually modeled in tank tests but an alternative in the near future could be CFD computations. In this article, all required steps to setup and verify the hydrodynamic and numerical model are performed. The setup of the hydrodynamic and numerical model enable us to show that CFD computations of motion RAOS and pitch decay tests provide results in agreement with diffraction-radiation results. Wave only simulations enable us to verify that irregular waves are accurately modelled in the CFD domain. Since the wavemaker motion used in tank tests to generate irregular waves is not available, a process of linear back propagation is set up from the wave elevation on a wave probe in tank tests. High Order Spectral (HOS) simulations are performed to reproduce the seastate measured in tank tests. Finally, a test was performed to model the ship motions in irregular extreme waves with ICARE solver coupled to the computed HOS wave field through Spectral Wave Explicit Navier Stokes Equations (SWENSE).
HOS-ocean is an efficient High-Order Spectral code developed to solve the deterministic propagati... more HOS-ocean is an efficient High-Order Spectral code developed to solve the deterministic propagation of nonlinear wavefields in open ocean. HOS-ocean is released as open-source, developed and distributed under the terms of GNU General Public License (GPLv3). Along with the source code, a documentation under wiki format is available which makes easy the compilation and execution of the source files. The code has been shown to be accurate and efficient.
The study of energetic free-surface flows is challenging because of the large range of interface ... more The study of energetic free-surface flows is challenging because of the large range of interface scales involved due to multiple fragmentations and reconnections of the air-water interface with the formation of drops and bubbles. Because of their complexity the investigation of such phenomena through numerical simulation largely increased during recent years. Actually, in the last decades different numerical models have been developed to study these flows, especially in the context of particle methods. In the latter a single-phase approximation is usually adopted to reduce the computational costs and the model complexity. While it is well known that the role of air largely affects the local flow evolution, it is still not clear whether this single-phase approximation is able to predict global flow features like the evolution of the global mechanical energy dissipation. The present work is dedicated to this topic through the study of a selected problem simulated with both single-phase and two-phase models. It is shown that, interestingly, even though flow evolutions are different, energy evolutions can be similar when including or not the presence of air. This is remarkable since, in the problem considered, with the two-phase model about half of the energy is lost in the air phase while in the one-phase model the energy is mainly dissipated by cavity collapses.
This paper is devoted to the numerical simulation of water diffraction in viscous flow. An origin... more This paper is devoted to the numerical simulation of water diffraction in viscous flow. An original approach using a diffracted flow defined as the difference between total and incident flows is followed. The incident flow is defined explicitly using nonlinear potential flow theory; Navier-Stokes equations and nonlinear free surface boundary conditions are solved for the diffracted flow only. This procedure, which is very efficient in terms of computing time and accuracy, was primarily developed by Ferrant (1996) for 3D non linear wave-body interactions in potential theory.
This chapter presents our progress on developing efficient nonlinear potential flow models for th... more This chapter presents our progress on developing efficient nonlinear potential flow models for the simulation of 2D or 3D gravity wave propagation in wave tanks and oceanic domains. Spectral methods are used in combination with either second order perturbation series or fully-nonlinear High-Order Spectral method. Such techniques involve quick FFT resolution permitting accurate simulations of wave fields at low cost. Both second order and fully nonlinear Numerical Wave Tanks are developed. Such models feature all the physical characteristics of a wavetank (snake wave-maker, experimentally calibrated absorbing zone, etc.). Several validation results are presented where numerical simulations are successfully compared to experiments on different 2D and 3D complex sea-states. A periodic domain HOS modelling of open ocean wavefields is then applied to simulate long-time evolutions of 3D ocean in order to study the formation of freak waves. An investigation of the influence of directionali...
Wall Shear Stress (WSS) has been demonstrated to be a biomarker of the development of atheroscler... more Wall Shear Stress (WSS) has been demonstrated to be a biomarker of the development of atherosclerosis. In vivo assessment of WSS is still challenging, but 4D Flow MRI represents a promising tool to provide 3D velocity data from which WSS can be calculated. In this study, a system based on Laser Doppler Velocimetry (LDV) was developed to validate new improvements of 4D Flow MRI acquisitions and derived WSS computing. A hydraulic circuit was manufactured to allow both 4D Flow MRI and LDV velocity measurements. WSS profiles were calculated with one 2D and one 3D method. Results indicated an excellent agreement between MRI and LDV velocity data, and thus the set-up enabled the evaluation of the improved performances of 3D with respect to the 2D-WSS computation method. To provide a concrete example of the efficacy of this method, the influence of the spatial resolution of MRI data on derived 3D-WSS profiles was investigated. This investigation showed that, with acquisition times compatib...
The prediction of ship motions in extreme seastates is very complex as it involves strong nonline... more The prediction of ship motions in extreme seastates is very complex as it involves strong nonlinearities. It deals with high motions of the ship and implies strong mooring system loads. These seastates are usually modeled in tank tests but an alternative in the near future could be CFD computations. In this article, all required steps to setup and verify the hydrodynamic and numerical model are performed. The setup of the hydrodynamic and numerical model enable us to show that CFD computations of motion RAOS and pitch decay tests provide results in agreement with diffraction-radiation results. Wave only simulations enable us to verify that irregular waves are accurately modelled in the CFD domain. Since the wavemaker motion used in tank tests to generate irregular waves is not available, a process of linear back propagation is set up from the wave elevation on a wave probe in tank tests. High Order Spectral (HOS) simulations are performed to reproduce the seastate measured in tank tests. Finally, a test was performed to model the ship motions in irregular extreme waves with ICARE solver coupled to the computed HOS wave field through Spectral Wave Explicit Navier Stokes Equations (SWENSE).
HOS-ocean is an efficient High-Order Spectral code developed to solve the deterministic propagati... more HOS-ocean is an efficient High-Order Spectral code developed to solve the deterministic propagation of nonlinear wavefields in open ocean. HOS-ocean is released as open-source, developed and distributed under the terms of GNU General Public License (GPLv3). Along with the source code, a documentation under wiki format is available which makes easy the compilation and execution of the source files. The code has been shown to be accurate and efficient.
The study of energetic free-surface flows is challenging because of the large range of interface ... more The study of energetic free-surface flows is challenging because of the large range of interface scales involved due to multiple fragmentations and reconnections of the air-water interface with the formation of drops and bubbles. Because of their complexity the investigation of such phenomena through numerical simulation largely increased during recent years. Actually, in the last decades different numerical models have been developed to study these flows, especially in the context of particle methods. In the latter a single-phase approximation is usually adopted to reduce the computational costs and the model complexity. While it is well known that the role of air largely affects the local flow evolution, it is still not clear whether this single-phase approximation is able to predict global flow features like the evolution of the global mechanical energy dissipation. The present work is dedicated to this topic through the study of a selected problem simulated with both single-phase and two-phase models. It is shown that, interestingly, even though flow evolutions are different, energy evolutions can be similar when including or not the presence of air. This is remarkable since, in the problem considered, with the two-phase model about half of the energy is lost in the air phase while in the one-phase model the energy is mainly dissipated by cavity collapses.
This paper is devoted to the numerical simulation of water diffraction in viscous flow. An origin... more This paper is devoted to the numerical simulation of water diffraction in viscous flow. An original approach using a diffracted flow defined as the difference between total and incident flows is followed. The incident flow is defined explicitly using nonlinear potential flow theory; Navier-Stokes equations and nonlinear free surface boundary conditions are solved for the diffracted flow only. This procedure, which is very efficient in terms of computing time and accuracy, was primarily developed by Ferrant (1996) for 3D non linear wave-body interactions in potential theory.
This chapter presents our progress on developing efficient nonlinear potential flow models for th... more This chapter presents our progress on developing efficient nonlinear potential flow models for the simulation of 2D or 3D gravity wave propagation in wave tanks and oceanic domains. Spectral methods are used in combination with either second order perturbation series or fully-nonlinear High-Order Spectral method. Such techniques involve quick FFT resolution permitting accurate simulations of wave fields at low cost. Both second order and fully nonlinear Numerical Wave Tanks are developed. Such models feature all the physical characteristics of a wavetank (snake wave-maker, experimentally calibrated absorbing zone, etc.). Several validation results are presented where numerical simulations are successfully compared to experiments on different 2D and 3D complex sea-states. A periodic domain HOS modelling of open ocean wavefields is then applied to simulate long-time evolutions of 3D ocean in order to study the formation of freak waves. An investigation of the influence of directionali...
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Papers by David Le Touzé