Carlos Levi - Academia.edu (original) (raw)

Papers by Carlos Levi

Applied Ocean Research, 2016

Wave-current flow is a phenomenon that is present in many practical engineering situations. Over ... more Wave-current flow is a phenomenon that is present in many practical engineering situations. Over the past several decades, this type of flow has been increasingly investigated under controlled laboratory conditions. This paper presents a numerical study of wave-current flow in the ocean basin of the LabOceano (COPPE/UFRJ). A homogeneous multiphase model based on the RANS equations and the k-ε turbulence model implemented in ANSYS-CFX code were used. A cross section of the ocean basin was represented. A regular wave with a height of 0.08 m and a period of 1.80 s (i.e., a wave steepness of H/L = 0.016), propagating on favourable currents, was simulated. The behaviour of the free surface elevation over time and the streamlines along the basin for wave and wave-current flows were presented. The numerical results were compared to the non-viscous theory given by the Rayleigh equation applied to the problem of wave-current interaction. Good agreement was found between the wave length estimated by the numerical results and the analytical solutions, with a deviation of less than 2%.

The present paper discusses an experimental technique to measure the correlation length related t... more The present paper discusses an experimental technique to measure the correlation length related to typical flexible model of marine riser. The relative correlation coefficient and correlation length were compared for rigid and flexible cylinders. The results show that for each cylinder there was a specific subcritical Reynolds number where the correlation coefficient and correlation length had local maxima. Phase drift along spanwise positions were analyzed, and as expected, the RMS of them increased for large separation, meanwhile, the distribution of Probability Density Function PDF demonstrated that the flexible cylinder had a totally different vortex shedding profiles when compared with the rigid case.

Ocean Engineering

Abstract The controllability and maneuverability of an Autonomous Underwater Vehicle (AUV) in pra... more Abstract The controllability and maneuverability of an Autonomous Underwater Vehicle (AUV) in practical applications need to be properly validated and assessed before the prototype is finalized for manufacturing. With regard to mathematical system model of the AUV, hydrodynamic coefficients have a dominant effect on the quality of vehicle pre-testing and evaluation, which is crucial to be estimated with adequate accuracy to curb the uncertainty from modeling simplifications. The standard time domain discrete Extended Kalman Filter (EKF) and Unscented Kalman Filter (UKF) algorithms are two promising numerical approximation approaches for hydrodynamic identification technique with favourable computational complexity and acceptable estimation precision. In this paper, a study with respect to time domain discrete optimized UKF (OUKF) algorithm based on recursive tuning rule and update gradient descent lemma for a typical prototype known as NPS AUV II will be proposed to enhance adaptability and prediction performance of the identification approach with appropriate verification. In addition, Auto Regressive Moving Average (ARMA) noisy model needs to be included into three Kalman Filter (KF) algorithms to further improve the estimation precision and perturbations inhibiting performance. Pre-processing numerical model validation and non-dimensional viscous linear damping coefficient identification based on three KF algorithms will be implemented respectively to provide an assistant pre-assessment for the vehicle. In accordance with comparable outputs and estimation-experiment errors, the OUKF identification algorithm is certified to be more precise and superior compared with EKF and UKF approaches in the presence of ARMA noisy model.

Applied Ocean Research

Abstract Mechanical restoration of a point absorber (PA) wave energy converter (WEC) featured a n... more Abstract Mechanical restoration of a point absorber (PA) wave energy converter (WEC) featured a nonlinear stiffness system built by conventional mechanical compression springs (NSMech). Numerical simulations conducted here considered irregular waves in a specific sea site. Results showed considerable improvement for a given suitable spring configuration (length and stiffness parameters). However, practical implementation of NSMech imposed limiting constraints on the geometrical and physical characteristics of the mechanical compression springs. Such constraints limited very much the feasible region of NSMech configurations, restricting significantly applications for wave energy converter. One alternative approach using pneumatic cylinder springs proved to overcome such a limitation aggregating obvious advantages with fewer elements and bringing more enhancement to the WEC performance.

ABSTRACT Dynamic response of a vertical flexible cylinder vibrating at low mode numbers with comb... more ABSTRACT Dynamic response of a vertical flexible cylinder vibrating at low mode numbers with combined x􀀀y motion are investigated in this paper. The uniform flow was simulated by towing the flexible cylinder along the tank in still water, therefore the turbulence intensity of the free flow is negligible in order to obtain more reliable results. The dominant frequencies, maximum attainable amplitude, modal analysis and x􀀀y trajectory in cross-flow and in-line directions have been reported and compared with literatures, some good agreements and justifiable discrepancies are obtained. These results could benefit the future experimental and numerical work in this area.

In 2009, the general development plan for the Federal University of Rio de Janeiro (Plano Diretor... more In 2009, the general development plan for the Federal University of Rio de Janeiro (Plano Diretor UFRJ 2020 in Portuguese) was approved for the period between 2009 and 2020. A significant effort was made to incorporate in-house innovative solutions as much as possible. Such strategy was supposed to (1) directly benefit the University with solutions created within its own research programs; (2) serve as a privileged showroom of its potential contributions to the community; and (3) pioneer applications that may be adopted in urban areas in the near future. UFRJ’s main campus is located in an island, with an area of circa 5.2 km2, 5 km in length and 1 km in width. Its daily population is estimated in 60,000 persons, including students, faculty, technical, administrative and support workers, and visitors. More than 25,000 vehicles circulate every day along its main avenues. Besides the university buildings and installations, 15 other research centres are also located in the campus. Thes...

Journal of Marine Science and Application

Lower efficiencies induce higher energy costs and pose a barrier to wave energy devices’ commerci... more Lower efficiencies induce higher energy costs and pose a barrier to wave energy devices’ commercial applications. Therefore, the efficiency enhancement of wave energy converters has received much attention in recent decades. The reported research presents the double snap-through mechanism applied to a hemispheric point absorber type wave energy converter (WEC) to improve the energy absorption performance. The double snap-through mechanism comprises four oblique springs mounted in an X-configuration. This provides the WEC with different dynamic stability behaviors depending on the particular geometric and physical parameters employed. The efficiency of these different WEC behaviors (linear, bistable, and tristable) was initially evaluated under the action of regular waves. The results for bistable or tristable responses indicated significant improvements in the WEC’s energy capture efficiency. Furthermore, the WEC frequency bandwidth was shown to be significantly enlarged when the tr...

Ocean Engineering

Abstract The dynamic behaviours of subsea pipe-valve structures—the principal components of subse... more Abstract The dynamic behaviours of subsea pipe-valve structures—the principal components of subsea equipment—are of critical concern for the control of the lowering through the splash zone during installation. Nonlinear interactions between waves and pipe-valve combinations are challenging the investigation of the wave forces acting on large-dimension structures. This paper proposes a numerical model to study the nonlinear hydrodynamic performance of partially submerged pipe-valve structures. A two-dimensional (2D) numerical water tank (NWT) was established to efficiently generate high-accuracy incident waves, and a semi-immersed horizontal cylinder was applied to the numerical simulations of wave-structure interaction (WSI) to study the mesh and time convergence. The numerical model was validated with a comparative analysis of the modelling results with experimental data, other numerical results, and theoretical results. Numerical simulations of the interaction between Stokes-II waves and subsea pipe-valve structures were performed, and the effects of the valve height ratio, valve length ratio, and valve spacing were investigated. The subsea pipe-valve structure is a kind of multi-scale structure, the wave forces exhibited stronger nonlinearity when acting on the partially submerged valves than on the completely submerged pipe. Changes in valve structure and distribution significantly increased the overall change in the wave forces acting on the valves. The stronger nonlinearity was primarily derived from phenomena such as wave reflection, wave blockage, and wave run-up. The numerical results provide references for the structure and strength designs and offshore installations of large subsea equipment like subsea manifolds.

Ocean Engineering

Abstract As one of the renewable and clean energy sources, wave energy has high density and all-d... more Abstract As one of the renewable and clean energy sources, wave energy has high density and all-day availability characteristics. However, the development of wave energy converters has been hampered, mainly because of the low efficiency induced high levelized energy costs. The present study introduces an improved bistable mechanism composed of three linear springs, aiming to enhance the performance of a point absorber employed as a wave energy converter. The improved bistable mechanism features an asymmetric configuration of three linear stiffness springs: one horizontal and two obliques on a vertical plane. Numerical simulations based on Cummins equations in the time domain describe the point absorber dynamic behavior in regular and irregular waves. The improved bistable wave energy converter featured a wider low equivalent stiffness range than linear and conventional bistable counterparts, improving its ability to frequency shifting. Its lower potential barrier greatly improves the capture width ratio and frequency bandwidth at low excitations. Such characteristics facilitate the improved bistable wave energy converter to achieve higher efficiency than its linear and conventional bistable counterparts at low frequencies, and enhance its robustness against power-take-off damping detuning and sea state changes. These features altogether make the improved bistable mechanism an efficient alternative to explore the benefits of the bistable dynamics applied to wave energy converters.

Energies

This study, firstly, provides an up-to-date global review of the potential, technologies, prototy... more This study, firstly, provides an up-to-date global review of the potential, technologies, prototypes, installed capacities, and projects related to ocean renewable energy including wave, tidal, and thermal, and salinity gradient sources. Secondly, as a case study, we present a preliminary assessment of the wave, ocean current, and thermal gradient sources along the Brazilian coastline. The global status of the technological maturity of the projects, their different stages of development, and the current global installed capacity for different sources indicate the most promising technologies considering the trend of global interest. In Brazil, despite the extensive coastline and the fact that almost 82% of the Brazilian electricity matrix is renewable, ocean renewable energy resources are still unexplored. The results, using oceanographic fields produced by numerical models, show the significant potential of ocean thermal and wave energy sources in the northern and southern regions o...

Applied Ocean Research

Abstract A nonlinear stiffness mechanism installed in a floating point absorber (FPA) in regular ... more Abstract A nonlinear stiffness mechanism installed in a floating point absorber (FPA) in regular waves allowed for studying the influence of the nonlinear behavior on wave energy harvesting. Static analysis of nonlinear stiffness system and time domain numerical simulations based on Cummins’ equation evaluated the effects of power take-off (PTO) damping, system stiffness and geometry dimensions. The results may apply to the evaluation of the balance between energy harvesting performance and practical design limitations. The nonlinear stiffness system improved the efficiency of wave energy harvesting, increasing mean power, by both pushing up the natural period, and broadening resonance, therefore proving more competitiveness.

Marine Systems & Ocean Technology

Researchers have spent significant effort to understand the complicated flow around bluff bodies ... more Researchers have spent significant effort to understand the complicated flow around bluff bodies to control or even eliminate the Vortex Induced Vibration (VIV) occurrence. Numerical simulations have been unsuccessful to predict the VIV amplitudes mainly because of the diffusive nature of the numerical methods. The present two-dimensional numerical investigation is a continuation of previous efforts trying to predict correct amplitudes of the VIV oscillations. The upwind TVD Roe-Sweby scheme is used to solve the slightly compressible Reynolds Average Navier-Stokes equations written in general curvilinear coordinates. For comparisons, the SST and the k-ε turbulence models are used to simulate the turbulent flow in the wake of a circular cylinder. The numerical results obtained in the present work agree remarkably well with experimental data obtained from the literature. The k-ε turbulence model showed better agreement with experiment than the SST turbulence model.

Dynamic response of a vertical flexible cylinder vibrating at low mode numbers with combined x – ... more Dynamic response of a vertical flexible cylinder vibrating at low mode numbers with combined x – y motion are investigated in this paper. The uniform flow was simulated by towing the flexible cylinder along the tank in still water, therefore the turbulence intensity of the free flow is negligible in order to obtain more reliable results. The dominant frequencies, maximum attainable amplitude, modal analysis and x – y trajectory in cross-flow and in-line directions have been reported and compared with literatures, some good agreements and justifiable discrepancies are obtained. These results could benefit the future experimental and numerical work in this area.Copyright © 2012 by ASME

RESUMEN El presente trabajo describe la modificación del sistema de propulsión de un catamarán de... more RESUMEN El presente trabajo describe la modificación del sistema de propulsión de un catamarán de pasajeros, debido al cambio de los motores principales por otros de mayor potencia. Nuevas hélices y relaciones de reducción son diseñadas para poder alcanzar la mayor eficiencia posible. Se analiza también la factibilidad del uso de las hélices originales con los nuevos motores. La Resistencia al Avance del catamarán es dividida utilizando el método de Hughes. La componente de la Resistencia por Formación de Olas es determinada usando el Método de los Paneles. Debido a la esbeltez de los cascos del catamarán, la Resistencia Viscosa es aproximada a la Resistencia de una Placa Plana y se considera que no existen efectos de interferencia viscosa entre los cascos. Otras componentes de la Resistencia al Avance como la Resistencia de Apéndices, Rugosidad y Viento son consideradas. La aplicación de factores de seguridad como margen de mar, motor y rotación son incluidas en el cálculo de las h...

29th International Conference on Ocean, Offshore and Arctic Engineering: Volume 6, 2010

ABSTRACT The vortex induced vibration (VIV) on a circular cylinder is investigated by the numeric... more ABSTRACT The vortex induced vibration (VIV) on a circular cylinder is investigated by the numerical solution of the two dimensional Reynolds average Navier-Stokes equations. An upwind and Total Variation Diminishing (TVD) conservative scheme is used to solve the governing equations written in curvilinear coordinates and the k-ε turbulence model is used to simulate the turbulent flow in the wake of the body. The cylinder is supported by a spring and a damper and free to vibrate in the transverse direction. Results are obtained for the phase angle, amplitude, and frequency for an elastically mounted rigid cylinder subjected to vortex shedding and support motion. The numerical results showed the strong influence of the support motion on the response amplitude. This kind of scenario is found in the attachment between platform and riser. The motion of platforms on the ocean free surface can cause this kind of excitation and amplify the vortex induced vibration response amplitude of risers.

Computational Simulations and Applications, 2011

Volume 4: Terry Jones Pipeline Technology; Ocean Space Utilization; CFD and VIV Symposium, 2006

The present stage of viscous flow numerical analysis combined with computer technology latest adv... more The present stage of viscous flow numerical analysis combined with computer technology latest advances made viable the mathematical treatment of many robust and complex engineering problems of practical interest. Some numerical problems which solutions would be just unthinkable not more than ten years ago may be now dealt with in a reliable and fairly accurate manner. A truly example of this kind of problem would be the calculation of hydrodynamic loads acting on yawing ships. The solution of such a problem raises practical interest due to applications, for instance, as in the case of stationary FPSO/FSO ships facing sea currents, commonly used in offshore deep-water oil production. In the present solution, the complete incompressible Navier–Stokes (N-S) equations are solved by means of an algorithm that applies the Beam and Warming [1] approximated factorization scheme to simulate the flow around a Wigley’s hull. The numerical code was implemented using Message Passage Interface (M...

Applied Ocean Research, 2016

Wave-current flow is a phenomenon that is present in many practical engineering situations. Over ... more Wave-current flow is a phenomenon that is present in many practical engineering situations. Over the past several decades, this type of flow has been increasingly investigated under controlled laboratory conditions. This paper presents a numerical study of wave-current flow in the ocean basin of the LabOceano (COPPE/UFRJ). A homogeneous multiphase model based on the RANS equations and the k-ε turbulence model implemented in ANSYS-CFX code were used. A cross section of the ocean basin was represented. A regular wave with a height of 0.08 m and a period of 1.80 s (i.e., a wave steepness of H/L = 0.016), propagating on favourable currents, was simulated. The behaviour of the free surface elevation over time and the streamlines along the basin for wave and wave-current flows were presented. The numerical results were compared to the non-viscous theory given by the Rayleigh equation applied to the problem of wave-current interaction. Good agreement was found between the wave length estimated by the numerical results and the analytical solutions, with a deviation of less than 2%.

The present paper discusses an experimental technique to measure the correlation length related t... more The present paper discusses an experimental technique to measure the correlation length related to typical flexible model of marine riser. The relative correlation coefficient and correlation length were compared for rigid and flexible cylinders. The results show that for each cylinder there was a specific subcritical Reynolds number where the correlation coefficient and correlation length had local maxima. Phase drift along spanwise positions were analyzed, and as expected, the RMS of them increased for large separation, meanwhile, the distribution of Probability Density Function PDF demonstrated that the flexible cylinder had a totally different vortex shedding profiles when compared with the rigid case.

Ocean Engineering

Abstract The controllability and maneuverability of an Autonomous Underwater Vehicle (AUV) in pra... more Abstract The controllability and maneuverability of an Autonomous Underwater Vehicle (AUV) in practical applications need to be properly validated and assessed before the prototype is finalized for manufacturing. With regard to mathematical system model of the AUV, hydrodynamic coefficients have a dominant effect on the quality of vehicle pre-testing and evaluation, which is crucial to be estimated with adequate accuracy to curb the uncertainty from modeling simplifications. The standard time domain discrete Extended Kalman Filter (EKF) and Unscented Kalman Filter (UKF) algorithms are two promising numerical approximation approaches for hydrodynamic identification technique with favourable computational complexity and acceptable estimation precision. In this paper, a study with respect to time domain discrete optimized UKF (OUKF) algorithm based on recursive tuning rule and update gradient descent lemma for a typical prototype known as NPS AUV II will be proposed to enhance adaptability and prediction performance of the identification approach with appropriate verification. In addition, Auto Regressive Moving Average (ARMA) noisy model needs to be included into three Kalman Filter (KF) algorithms to further improve the estimation precision and perturbations inhibiting performance. Pre-processing numerical model validation and non-dimensional viscous linear damping coefficient identification based on three KF algorithms will be implemented respectively to provide an assistant pre-assessment for the vehicle. In accordance with comparable outputs and estimation-experiment errors, the OUKF identification algorithm is certified to be more precise and superior compared with EKF and UKF approaches in the presence of ARMA noisy model.

Applied Ocean Research

Abstract Mechanical restoration of a point absorber (PA) wave energy converter (WEC) featured a n... more Abstract Mechanical restoration of a point absorber (PA) wave energy converter (WEC) featured a nonlinear stiffness system built by conventional mechanical compression springs (NSMech). Numerical simulations conducted here considered irregular waves in a specific sea site. Results showed considerable improvement for a given suitable spring configuration (length and stiffness parameters). However, practical implementation of NSMech imposed limiting constraints on the geometrical and physical characteristics of the mechanical compression springs. Such constraints limited very much the feasible region of NSMech configurations, restricting significantly applications for wave energy converter. One alternative approach using pneumatic cylinder springs proved to overcome such a limitation aggregating obvious advantages with fewer elements and bringing more enhancement to the WEC performance.

ABSTRACT Dynamic response of a vertical flexible cylinder vibrating at low mode numbers with comb... more ABSTRACT Dynamic response of a vertical flexible cylinder vibrating at low mode numbers with combined x􀀀y motion are investigated in this paper. The uniform flow was simulated by towing the flexible cylinder along the tank in still water, therefore the turbulence intensity of the free flow is negligible in order to obtain more reliable results. The dominant frequencies, maximum attainable amplitude, modal analysis and x􀀀y trajectory in cross-flow and in-line directions have been reported and compared with literatures, some good agreements and justifiable discrepancies are obtained. These results could benefit the future experimental and numerical work in this area.

In 2009, the general development plan for the Federal University of Rio de Janeiro (Plano Diretor... more In 2009, the general development plan for the Federal University of Rio de Janeiro (Plano Diretor UFRJ 2020 in Portuguese) was approved for the period between 2009 and 2020. A significant effort was made to incorporate in-house innovative solutions as much as possible. Such strategy was supposed to (1) directly benefit the University with solutions created within its own research programs; (2) serve as a privileged showroom of its potential contributions to the community; and (3) pioneer applications that may be adopted in urban areas in the near future. UFRJ’s main campus is located in an island, with an area of circa 5.2 km2, 5 km in length and 1 km in width. Its daily population is estimated in 60,000 persons, including students, faculty, technical, administrative and support workers, and visitors. More than 25,000 vehicles circulate every day along its main avenues. Besides the university buildings and installations, 15 other research centres are also located in the campus. Thes...

Journal of Marine Science and Application

Lower efficiencies induce higher energy costs and pose a barrier to wave energy devices’ commerci... more Lower efficiencies induce higher energy costs and pose a barrier to wave energy devices’ commercial applications. Therefore, the efficiency enhancement of wave energy converters has received much attention in recent decades. The reported research presents the double snap-through mechanism applied to a hemispheric point absorber type wave energy converter (WEC) to improve the energy absorption performance. The double snap-through mechanism comprises four oblique springs mounted in an X-configuration. This provides the WEC with different dynamic stability behaviors depending on the particular geometric and physical parameters employed. The efficiency of these different WEC behaviors (linear, bistable, and tristable) was initially evaluated under the action of regular waves. The results for bistable or tristable responses indicated significant improvements in the WEC’s energy capture efficiency. Furthermore, the WEC frequency bandwidth was shown to be significantly enlarged when the tr...

Ocean Engineering

Abstract The dynamic behaviours of subsea pipe-valve structures—the principal components of subse... more Abstract The dynamic behaviours of subsea pipe-valve structures—the principal components of subsea equipment—are of critical concern for the control of the lowering through the splash zone during installation. Nonlinear interactions between waves and pipe-valve combinations are challenging the investigation of the wave forces acting on large-dimension structures. This paper proposes a numerical model to study the nonlinear hydrodynamic performance of partially submerged pipe-valve structures. A two-dimensional (2D) numerical water tank (NWT) was established to efficiently generate high-accuracy incident waves, and a semi-immersed horizontal cylinder was applied to the numerical simulations of wave-structure interaction (WSI) to study the mesh and time convergence. The numerical model was validated with a comparative analysis of the modelling results with experimental data, other numerical results, and theoretical results. Numerical simulations of the interaction between Stokes-II waves and subsea pipe-valve structures were performed, and the effects of the valve height ratio, valve length ratio, and valve spacing were investigated. The subsea pipe-valve structure is a kind of multi-scale structure, the wave forces exhibited stronger nonlinearity when acting on the partially submerged valves than on the completely submerged pipe. Changes in valve structure and distribution significantly increased the overall change in the wave forces acting on the valves. The stronger nonlinearity was primarily derived from phenomena such as wave reflection, wave blockage, and wave run-up. The numerical results provide references for the structure and strength designs and offshore installations of large subsea equipment like subsea manifolds.

Ocean Engineering

Abstract As one of the renewable and clean energy sources, wave energy has high density and all-d... more Abstract As one of the renewable and clean energy sources, wave energy has high density and all-day availability characteristics. However, the development of wave energy converters has been hampered, mainly because of the low efficiency induced high levelized energy costs. The present study introduces an improved bistable mechanism composed of three linear springs, aiming to enhance the performance of a point absorber employed as a wave energy converter. The improved bistable mechanism features an asymmetric configuration of three linear stiffness springs: one horizontal and two obliques on a vertical plane. Numerical simulations based on Cummins equations in the time domain describe the point absorber dynamic behavior in regular and irregular waves. The improved bistable wave energy converter featured a wider low equivalent stiffness range than linear and conventional bistable counterparts, improving its ability to frequency shifting. Its lower potential barrier greatly improves the capture width ratio and frequency bandwidth at low excitations. Such characteristics facilitate the improved bistable wave energy converter to achieve higher efficiency than its linear and conventional bistable counterparts at low frequencies, and enhance its robustness against power-take-off damping detuning and sea state changes. These features altogether make the improved bistable mechanism an efficient alternative to explore the benefits of the bistable dynamics applied to wave energy converters.

Energies

This study, firstly, provides an up-to-date global review of the potential, technologies, prototy... more This study, firstly, provides an up-to-date global review of the potential, technologies, prototypes, installed capacities, and projects related to ocean renewable energy including wave, tidal, and thermal, and salinity gradient sources. Secondly, as a case study, we present a preliminary assessment of the wave, ocean current, and thermal gradient sources along the Brazilian coastline. The global status of the technological maturity of the projects, their different stages of development, and the current global installed capacity for different sources indicate the most promising technologies considering the trend of global interest. In Brazil, despite the extensive coastline and the fact that almost 82% of the Brazilian electricity matrix is renewable, ocean renewable energy resources are still unexplored. The results, using oceanographic fields produced by numerical models, show the significant potential of ocean thermal and wave energy sources in the northern and southern regions o...

Applied Ocean Research

Abstract A nonlinear stiffness mechanism installed in a floating point absorber (FPA) in regular ... more Abstract A nonlinear stiffness mechanism installed in a floating point absorber (FPA) in regular waves allowed for studying the influence of the nonlinear behavior on wave energy harvesting. Static analysis of nonlinear stiffness system and time domain numerical simulations based on Cummins’ equation evaluated the effects of power take-off (PTO) damping, system stiffness and geometry dimensions. The results may apply to the evaluation of the balance between energy harvesting performance and practical design limitations. The nonlinear stiffness system improved the efficiency of wave energy harvesting, increasing mean power, by both pushing up the natural period, and broadening resonance, therefore proving more competitiveness.

Marine Systems & Ocean Technology

Researchers have spent significant effort to understand the complicated flow around bluff bodies ... more Researchers have spent significant effort to understand the complicated flow around bluff bodies to control or even eliminate the Vortex Induced Vibration (VIV) occurrence. Numerical simulations have been unsuccessful to predict the VIV amplitudes mainly because of the diffusive nature of the numerical methods. The present two-dimensional numerical investigation is a continuation of previous efforts trying to predict correct amplitudes of the VIV oscillations. The upwind TVD Roe-Sweby scheme is used to solve the slightly compressible Reynolds Average Navier-Stokes equations written in general curvilinear coordinates. For comparisons, the SST and the k-ε turbulence models are used to simulate the turbulent flow in the wake of a circular cylinder. The numerical results obtained in the present work agree remarkably well with experimental data obtained from the literature. The k-ε turbulence model showed better agreement with experiment than the SST turbulence model.

Dynamic response of a vertical flexible cylinder vibrating at low mode numbers with combined x – ... more Dynamic response of a vertical flexible cylinder vibrating at low mode numbers with combined x – y motion are investigated in this paper. The uniform flow was simulated by towing the flexible cylinder along the tank in still water, therefore the turbulence intensity of the free flow is negligible in order to obtain more reliable results. The dominant frequencies, maximum attainable amplitude, modal analysis and x – y trajectory in cross-flow and in-line directions have been reported and compared with literatures, some good agreements and justifiable discrepancies are obtained. These results could benefit the future experimental and numerical work in this area.Copyright © 2012 by ASME

RESUMEN El presente trabajo describe la modificación del sistema de propulsión de un catamarán de... more RESUMEN El presente trabajo describe la modificación del sistema de propulsión de un catamarán de pasajeros, debido al cambio de los motores principales por otros de mayor potencia. Nuevas hélices y relaciones de reducción son diseñadas para poder alcanzar la mayor eficiencia posible. Se analiza también la factibilidad del uso de las hélices originales con los nuevos motores. La Resistencia al Avance del catamarán es dividida utilizando el método de Hughes. La componente de la Resistencia por Formación de Olas es determinada usando el Método de los Paneles. Debido a la esbeltez de los cascos del catamarán, la Resistencia Viscosa es aproximada a la Resistencia de una Placa Plana y se considera que no existen efectos de interferencia viscosa entre los cascos. Otras componentes de la Resistencia al Avance como la Resistencia de Apéndices, Rugosidad y Viento son consideradas. La aplicación de factores de seguridad como margen de mar, motor y rotación son incluidas en el cálculo de las h...

29th International Conference on Ocean, Offshore and Arctic Engineering: Volume 6, 2010

ABSTRACT The vortex induced vibration (VIV) on a circular cylinder is investigated by the numeric... more ABSTRACT The vortex induced vibration (VIV) on a circular cylinder is investigated by the numerical solution of the two dimensional Reynolds average Navier-Stokes equations. An upwind and Total Variation Diminishing (TVD) conservative scheme is used to solve the governing equations written in curvilinear coordinates and the k-ε turbulence model is used to simulate the turbulent flow in the wake of the body. The cylinder is supported by a spring and a damper and free to vibrate in the transverse direction. Results are obtained for the phase angle, amplitude, and frequency for an elastically mounted rigid cylinder subjected to vortex shedding and support motion. The numerical results showed the strong influence of the support motion on the response amplitude. This kind of scenario is found in the attachment between platform and riser. The motion of platforms on the ocean free surface can cause this kind of excitation and amplify the vortex induced vibration response amplitude of risers.

Computational Simulations and Applications, 2011

Volume 4: Terry Jones Pipeline Technology; Ocean Space Utilization; CFD and VIV Symposium, 2006

The present stage of viscous flow numerical analysis combined with computer technology latest adv... more The present stage of viscous flow numerical analysis combined with computer technology latest advances made viable the mathematical treatment of many robust and complex engineering problems of practical interest. Some numerical problems which solutions would be just unthinkable not more than ten years ago may be now dealt with in a reliable and fairly accurate manner. A truly example of this kind of problem would be the calculation of hydrodynamic loads acting on yawing ships. The solution of such a problem raises practical interest due to applications, for instance, as in the case of stationary FPSO/FSO ships facing sea currents, commonly used in offshore deep-water oil production. In the present solution, the complete incompressible Navier–Stokes (N-S) equations are solved by means of an algorithm that applies the Beam and Warming [1] approximated factorization scheme to simulate the flow around a Wigley’s hull. The numerical code was implemented using Message Passage Interface (M...