Marcelo A. Vitola

Influence of Sloshing on the Transfer of Water Between Neighbouring Compartments Considering Three Different Opening Configurations

Model tests to generate validation data for the codes predicting the sloshing and progression of water through an opening in case of a damaged ship were planned and performed. Behaviour of the flooding water after the damage is greatly dependent on the internal compartment geometries and vessel motions. Vessels angular position and motions in turn are affected by the flooding water. Thus accurate prediction of this strongly coupled flooding phenomenon requires simultaneous solving of the ship motions and behaviour of the internal water. In order to produce validation data for calculation methods for internal flood water behaviour, tests for water motion between two connected neighbouring compartments were designed. Model tests concentrated purely on the internal sloshing motion under forced compartment motions, thus uncoupling the vessel response.Copyright

Numerical Simulations of Regular Waves in a Hydrodynamic Laboratory Basin

Hydrodynamic behavior of offshore floating structures is of fundamental practical importance to engineers and designers. Physical modelling of offshore structures in hydrodynamic laboratory is a common practice in this field. Due to the increasing in the computer power and the development of the numerical algorithms, the use of the numerical wave tanks (NWT) have become a complementary tool to the model tests. The knowledge of the drawbacks of numerical model is an important issue for engineers and researchers, especially in the models whose governing equations do not have exact solution. This work presents the application of numerical model to simulate the generation and propagation of regular waves in the LabOcean Basin (LabOceano/ COPPE/UFRJ) using the commercial code Ansys-CFX. A cross-section of the offshore basin have been used. Waves have been generated by flap type wavemaker. Period wave in the range from 1.75 to 3.00 seconds have been simulated. For all tests, the analytical wave steepness is smaller than 0.017. Numerical results have been compared with Stokes wave theory and experimental data obtained in the offshore basin. Both the behavior of the free surface and the reflection coefficient have been evaluated. Good agreement was found for the wave profile, mean wave height and mean wave period. Divergences between numerical and experimental results were found evaluating the reflection parameters.Copyright

Uncertainty Analysis of Numerical Wave Modelling With Relevance to the Dynamics of Oil Booms

This paper presents the first attempt to estimate the numerical uncertainty in wave propagation studies. This work was motivated by a current project at LabOceano (COPPE/UFRJ) related to studying the dynamic behaviour of oil containment booms on waves and currents. To study the dynamics of an oil boom, the influence of the viscous effect needs to be taken into consideration due to the geometry of the boom. Numerically, this can be achieved using software that solves the Navier-Stokes equation. However, prior to evaluating the wave-structure interaction using a viscous model, it is important to evaluate how the numerical model represents the wave flow only, which is the focus of the present paper. Thus, a model based on the continuity and momentum equations available in the software package StarCCM+ is used to simulate the wave propagation. The computational domain is discretized using a trimmer mesh. The results obtained for a regular wave with a wave steepness (H/L) equal to 0.025 are presented. The numerical uncertainties in the mean wave height and in the mean wave period are estimated along the domain using the methodology proposed by [8]. The wave elevation is also compared with the second-order Stokes wave solution.Copyright

Experimental Investigation of Dynamic Response of a Flexible Cylinder in a Transverse Flow

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

Numerical Study of the Influence of Initial Condition in Vortex Induced Vibration of a Circular Cylinder With Two Degree of Freedom

The vortex-induced vibration (VIV) is a classical problem in ocean engineering. Intensive research on this field for flow around a circular cylinder has been observed, due to practical application, mainly the design of risers, cables and pipelines with free span. The relevance of this phenomenon is related to the structure failure, consequence of large displacement or fatigue. In the present study the influence of initial condition on the vortex induced vibration (VIV) of a circular cylinder with two degree of freedom is investigated by the numerical solution of the slightly compressible formulation of 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. The k–e turbulence model is used to simulate the turbulent flow in the wake of the cylinder. Two different initial conditions have been tested, free-stream and continuous reduced velocity increase (using the previous reduced velocity as initial condition for the next value). Results for the phase angle, amplitude, frequency, and lift coefficient are presented. The numerical results have been compared with experimental data of Jauvtis and Williamson [1]. The results indicate that the history of cylinder movement has a important impact in the amplitude oscillation observed in-line and cross-flow, principally in the reduced velocity range associated with the upper branch. Results obtained for the initial and lower branch seems to be independent of the initial condition. Further investigation are necessary to understand the difference observed such as the absence of the jump in the cross-flow oscillation between the initial and upper branch and the absence of in-line oscillation for reduced velocity in the range of 1–4 and the peak of in-line oscillation at reduced velocity 6.0.Copyright

Reynolds Number Effect on Vortex-Induced Vibration on a Two-Dimensional Circular Cylinder With Low Mass-Damping Parameter

The vortex induced vibration (VIV) on a circular cylinder with low mass-damping parameter and low Reynolds number is investigated numerically as basis for applications on dynamics of risers used in the offshore oil and gas industry and as a first step before tackling the harder high Reynolds number problem. The cylinder is supported by a spring and a damper and free to vibrate in the transverse direction. The numerical solution of the Reynolds average Navier-Stokes equations written in curvilinear coordinates is obtained using an upwind and Total Variation Diminishing conservative scheme and the k-e turbulence model is used to simulate the turbulent flow in the wake of the body. Results were obtained for the phase angle, response amplitude, frequency, and lift coefficient for a variation of reduced velocity from 2 to 12 and three different proportional variations of Reynolds number, 2000–6000, 2000–12000, and 2000–24000. The numerical results indicate the strong effect of the Reynolds number range on the response amplitude, lift coefficient, and frequency of oscillation for a low mass-damping parameter.Copyright

Validation of Vortex Induced Vibration With One Degree of Freedom

The vortex induced vibration is an important problem for the offshore industry, due to the frequent use of structures, such as risers and umbilicals. In the last decade, the use of numerical methods to study the vortex induced vibration has increased. Some disagreement between numerical and experimental results has been verified in the literature. In the present work, the numerical model solves the Reynolds average Navier-Stokes equations using an upwind and a Total Variation Diminishing (TVD) conservative scheme, written in curvilinear coordinates. The turbulent flow in the wake of the cylinder has been modelled using the k–e model. The cylinder is supported by a spring and a damper and free to vibrate in the transverse direction. Results obtained for phase angle, amplitude, frequency, and lift coefficient are compared to experimental data from Morse et al. [1]. The results indicate that the two dimensional simulation represents better the behaviour of cylinder displacement obtained experimentally using the unattached or attached end plate setup used by Morse et al. [1]. These results suggest that some difference between experimental and numerical data could be associated with the end condition used in the experiments. For the case using the unattached or attached end plate the difference in the peak amplitude between experimental and present results seems to be related with the initial condition adopted.Copyright

The Response of an Elastically Mounted Rigid Cylinder Subjected to Vortex Shedding and Support Motion

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–e 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.Copyright

A Numerical Investigation of the Response of an Elastically Mounted Rigid Cylinder With Two Degrees of Freedom

The vortex induced vibration (VIV) on a circular cylinder is investigated by the numerical solution of the 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–e 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 and in-line directions. In previous work, numerical results for the amplitude of oscillation, vortex shedding frequency, and phase angle between lift and displacement were compared to experimental data obtained from Khalak and Williamson (1996) to validate the code for VIV simulations in the transverse direction. In the present work, results are obtained for phase angle, amplitude, frequency, and lift coefficient and compared to experimental data from Jauvtis and Williamson (2003) for an elastically mounted rigid cylinder with two degrees of freedom. Differences in the amplitude of oscillation between experimental and numerical data were observed for both direction. It seems that the fluid flow memory effect is an important aspect that should be taken in consideration on numerical simulation to reproduce the experimental results for VIV with 2DOF as pointed out by Moe and Wu [1].© 2010 ASME

Forced Oscillation of a Circular Cylinder

Circular structures are frequently found in offshore industrial application, such as risers, umbilicals, spars, and TLP platforms. Theses structures are frequently subjected to vortex induced vibration. Sometimes, they are also subjected to forced vibration. In the present paper, the forced vibration of a circular cylinder is investigated by the numerical solution of the Reynolds Average Navier-Stokes (RANS) equations. An upwind and Total Variation Diminishing (TVD) conservative scheme is used to solve the governing equations written in curvilinear coordinates. The k–e turbulence model is used to simulate the turbulent flow in the wake of the body, when necessary. The cylinder is forced to oscillate only in the transverse direction of the mean flow with low Reynolds number and low amplitude ratio. The numerical results of the lift and drag coefficients were compared with numerical data obtained from Benevenutti and Silvestrini [1] and Meneghini and Bearman [2] to validate the code for forced vibration. The numerical results indicate that the implemented code is able to reproduce the experimental data capturing quite well the lock-in boundary, and results of practical interest are obtained, such as mean drag, RMS lift and lock-in range and.Copyright