Paulo T. T. Esperança

Computational Techniques for Stabilized Edge-Based Finite Element Simulation of Nonlinear Free-Surface Flows

Free-surface flows occur in several problems in hydrodynamics, such as fuel or water sloshing in tanks, waves breaking in ships, offshore platforms, harbors, and coastal areas. The computation of such highly nonlinear flows is challenging, since free-surfaces commonly present merging, fragmentation, and breaking parts, leading to the use of interface-capturing Eulerian approaches. In such methods the surface between two fluids is captured by the use of a marking function, which is transported in a flow field. In this work we discuss computational techniques for efficient implementation of 3D incompressible streamline-upwind/Petrov–Galerkin (SUPG)/pressure-stabilizing/Petrov–Galerkin finite element methods to cope with free-surface problems with the volume-of-fluid method (Elias, and Coutinho, 2007, “Stabilized Edge-Based Finite Element Simulation of Free-Surface Flows,” Int. J. Numer. Methods Fluids, 54, pp. 965–993). The pure advection equation for the scalar marking function was solved by a fully implicit parallel edge-based SUPG finite element formulation. Global mass conservation is enforced, adding or removing mass proportionally to the absolute value of the normal velocity of the interface. We introduce parallel edge-based data structures, a parallel dynamic deactivation algorithm to solve the marking function equation only in a small region around the interface. The implementation is targeted to distributed memory systems with cache-based processors. The performance and accuracy of the proposed solution method is tested in the simulation of the water impact on a square cylinder and in the propagation of a solitary wave.

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

An Experimental Approach for the Offshore Launching of Jack-Ups

Recently, as part of the building contract for the new Brazilian jack-up drilling platforms, an operational challenge was raised: to launch these units from the building site, where neither dry dock nor launching ground ways exist. Economically, the best alternative was to launch these jack-ups using the available barges used commonly for jacket launch. Due to the marked differences between a jacket and a jack-up, the implementation of this novel launch operation required a careful feasibility study. Model tests were required to measure the motions of the barge and the jack-up and to evaluate the loads on the barge rocker arms. The present paper discusses the experimental approach, test setup, calibration procedures, and some results from the hydrodynamics perspective.

An Investigation on the Excitation of Yaw Parametric Resonance of a Tension Leg Platform

The paper summarizes some aspects of a series of model experiments conducted with a Tension Leg Platform (in fact a Tension Leg Wellhead Platform) in close proximity with a FPSO emphasizing the types of coupled motions taking place. It is observed that as the yaw motion develops increasing amplitudes the sway motion is reduced, pointing out to an interesting exchange of energy between the sway and yaw modes. This should be recognized as a revealing aspect of strongly non-linear coupled parametric resonant motions. A mathematical model is proposed to describe the main aspects of the two-body moored system and hydrodynamic interactions. In principle a 12-DOF model is contemplated. Numerical simulations are compared to the time series obtained from the experiments showing adequate agreement. However, in this paper the essential coupling of sway and yaw is distinguished in order to typify the Mathieu-type instability as being the main mechanism behind the onset of large yaw motions of the TLP unit.Copyright

A Nonlinear Numerical Algorithm for Time-Domain Hydrodynamic Simulations of Vessel Motions in the Presence of Waves

Linear approaches have been traditionally employed to simulate the dynamic behavior of floating vessels and its interaction with regular or irregular waves. Some difficulties arise when large waves and vessel motions occur. Under these circumstances, the linear assumptions to compute the restoring and wave forces, which are computed on the mean position of body and water surface, are not capable of accurately representing the physics of the interactions between waves and vessels.Hydrostatic analysis of generic hull forms has already been implemented with a geometrical face representation of the hull and also internal ballast and oil tanks [1]. With the goal of improving the modeling the non-linear computation of hydrostatic in waves (at the instantaneous free surface) is implemented, thus using a generic geometric modeling of the hull to perform hydrodynamic simulations of vessel motions in the presence of waves. Additionally, for the computation of the instantaneous non-linear Froude-Krylov force (6 DOF time-domain model) the contribution of each geometrical face to the global Froude-Krylov force is calculated at the exact relative position of the vessel and the incident waves. After computing the relative position of each face, possibly being cut at the free surface, the pressure at the wetted face centers determines the contribution to the integral calculation.The paper presents the main aspects of the proposed methodology and highlights its capabilities and differences with respect to the linear approach. Complementarily, comparisons with model experiments are discussed.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

Development of a Training Simulator for Oil Spill Response

The paper describes the development of a training simulator for boats used on Oil Spill response at sea. The simulator models the dynamics of tug boats pulling an oil boom under waves, wind and current. The boom is modeled as a flexible line connected by lumped masses and its flotation characteristics and loads are calculated by Morison equation. A simplified model is used to simulate the oil itself and its interface with the boom line. The verification process was applied and its outcomes are discussed. Also, some case study scenarios are presented and the results are used to evaluate the applicability of the simulator as a training system.Copyright

Experimental Assessment of the Offshore Launching Operation of a Jack-Up Unit

Recently, an experimental campaign was carried out to assess the feasibility of the launching operation of two jack-up units using a barge as the launching platform. This experimental study was divided in four stages. In stages 1 to 3, a series of preliminary model tests were performed in order to provide scientific understanding of the mechanics of the operation, and investigate systematically the influence of launching parameters. The experimental approach developed for testing this operation and the results of the preliminary launching tests have been discussed in detail in a previous paper [1]. Based on the analyses of the experimental results of stages 1 to 3 and, the results of numerical simulation tools, in stage 4, a final launching condition was designed and a new set of model tests were specified to check the safety of the operation. This paper presents the results and analyses of the experimental tests in stage 4. The conditions tested in this stage covered the expected real launching condition and possible deviations in some launch parameters. The tests results include the 6-DOF motions and trajectories of the launched jack-up and the launch barge, and the reaction forces on the barge rocker arms. Later on, the success of the launching operations of P-59 and P-60 jack-up units confirmed the experimental investigation results and the feasibility of this novel launching procedure. Furthermore, it can be concluded that the experimental approach efficiently served as a tool for the assessment of high risk operations.© 2014 ASME

Uncertainty Analysis for Inclining Tests

In this paper, we addressed the qualitative consequences on uncertainty for the execution of a inclining test of a Semi-submergible platform with mooring system and risers at production site and compared the results to the ones taken from typical inclining test procedures at sheltered waters, as defined by ASTM F1321. To accomplish that, we applied Uncertainty Analysis according to ISO procedures, by evaluating propagation of uncertainties from the measurements until the final calculations. We discussed the use of measurement devices for the variables of concern and performed some numerical simulations to address the mooring system restoring effects and its implications on uncertainty analysis. We used data from two semi-subs with different displacements and found small influence on final uncertainty from the addition of mooring system and risers. At end, we discussed how new technologies on data acquisition and filtering of signals can become an important tool to help in the safety of the offshore floating production units, by facilitating the verification of the updated center of gravity of them after important interventions.Copyright

Development of Deep Water Multicolumn Buoy

A new conceptual design of a deepwater MONOBUOY, named DeepWater MultiColumn Buoy (DWMCB), patent PCT/BR2011/000133, was developed by PETROBRAS/CENPES. The DWMCB was designed to be part of an offloading system for a Spread Moored Floating Production Offloading Unit (FPSO). The offloading system principle consists of Oil being exported from the FPSO to a Shutle tanker passing through Offloading Oil Lines (OOLs) that are supported by the DWMCB. The system is designed to operate at a water depth of 2,200 meters, with expected in site life duration of 25 years. The geometry of DWMCB was defined after an optimization process in order to minimize its motions. This paper describes the development of this concept and discusses the results from some design verifications done with the help of a model tests campaign. An equivalent traditional shaped monobuoy was also tested for comparison purposes.Copyright