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The paper analyzes the contribution of the sub-particle-scale large-eddy simulation (SPS-LES) turbulent model on the dynamic behavior of the weakly compressible moving-particle semi-implicit (WCMPS) method. To search a robust WCMPS method configuration, the next models are tested: two pressure gradient models, two Laplacian models and the constrained stabilization technique through the control adjustment of the particle velocity by Xu and Jin (Comput Fluids 137:1–14, 2016. https://doi.org/10.1016/j.compfluid.2016.07.014). Then, for these combinations the influence of the SPS-LES turbulent dynamic contributions on the WCMPS method is analyzed. The WCMPS resultant configurations are applied to represent the physics of two different isolated green water events, produced by incoming bores that were generated with the two-dimensional wet dam-break approach. Numerical results captured well the evolution of the green water events, indicating that the WCMPS method can be suitable tool to represent the complex physics of these phenomena, including the breaking features of flow. Moreover, it is shown that even though turbulence is a three-dimensional phenomenon, turbulent contribution can be observable on the velocity field in two dimensions, having a considerable contribution on the adequate representation of green water amounts.

In order to evaluate the dynamic behavior of a FPSO-turret system, experimental tests in engineering wave basin have been performed. During the realization of experimental test large slow yaw rotations were detected in the dynamic behavior of the vessel during regular and irregular wave conditions tests. In order to study this phenomenon, an analytical method was developed in order to predict the maximum yaw angle reached under the slow yaw varying oscillations of a single point moored FPSO-turret system dependent of the regular mean wave drift forces and the turret position. The results for the proposed analytical method were verified by comparing it with experimental and simulated results. Then, the proposed method allows to identify the critical regular wave periods than can provoke large yaw rotations as an alternative for the stability tests by bifurcation analysis. On the other hand, the performed yaw motion simulations take into account the following aspects: the turret position, and the force and momentum associated with the mooring system variations (in function of the FPSO center of gravity positions and regular mean wave drift forces). Analyzing the time domain simulations it is possible to identify that large yaw motion is reached faster when the turret is near the CG and so, as the turret moves away, the yaw motions become slower.

Purpose The paper aims to apply a modified version of the MPS method to a double-dam-breaking test in which high dispersion zones and high natural clusterization zones are present, such as when the water column collapses into two sides and the two solitary waves collide, respectively. Design/methodology/approach The work takes advantage of the mixed source term from the cheaper computational version of the moving particle semi-implicit (MPS) method to reduce one step from the MPS classical algorithm. The proposed test can be successfully simulated by applying modifications to the variance parameter in the Laplacian operator and gradient model. Findings The results show stable behavior in dispersion and clusterization zones. Also, the collision and merging produced by solitary waves was successfully simulated. Research limitations/implications The main limitation in this work was the development of a comparison between the obtained results and the simulations with the original cheaper computational version of the MPS, this limitation is due to the overestimation of inter particle repulsive forces from its gradient model. Practical implications The application of solitary waves is of paramount importance in a number of applications, and this stems from the fact that the interaction of solitary waves with ships and other floating structures could generate highly deformed and complex free surface flows. Social implications For future work, the modified version of the MPS method can be applied in flow over sill base simulations, in close and open channels, and in simulating breaking waves to determine impact pressures by using solitary wave propagation. Originality/value The simulation of interaction of large groups of particles as in the case when two solitary waves collide could cause severe instability problems in pressure, causing the computer analysis to stop. MPS classical algorithm takes into account an explicit step that, in this case, may provoke the problem. For this reason, the cheaper version of MPS method is used to correctly simulate solitary wave interactions.

Sand erosion has been identified as a potential damage and failure mechanism in pipelines/elbows employed to transport gas from wells to terminals. Erosion can cause localized material loss decreasing the structural integrity of pipelines/elbows leading to failure. As a result, sand erosion has been the object of much research work in the oil and gas industry. The prediction of erosion caused by sand transported by hydrocarbons flow is a difficult task due to the large number of variables involved. At present, a great number of empirical models have been developed to predict sand erosion in smaller diameter pipelines under laboratory conditions. Therefore, such formulations generally present uncertainties for their application in larger diameter pipelines employed to transport oil and gas because there is no fundamental basis showing how the empirical formulations can be extrapolated to large diameters pipelines as most of the models have been developed on the basis of elementary laboratory experiments, which may not represent the real sand erosion conditions. Furthermore, most of the analytical/empirical models were developed for specific pipeline/elbows diameters and cannot be employed to predict erosion in different engineering structures. Hence, in the present work a computational fluid dynamic modeling strategy is proposed, which incorporated fundamental physically erosion parameters to predict erosion in larger diameter pipelines/elbows. The methodology was applied to different elbows/pipelines diameters in order to investigate how pipeline's diameter, sand production rate, and sand particles sizes affect the erosion mechanism and the erosion rate. The results showed the importance of including fluid and flow conditions, sand particles trajectory, and self-particles movement. The computational fluid dynaimcs results were compared with those obtained with the most employed empirical models to predict sand erosion in the oil and gas industry models published in the literature, and it was shown that the proposed modeling strategy can be used to predict erosion in larger diameters pipelines/elbows with good results.

The development of methods for damage detection for offshore jacket platforms is useful to prevent structural damage. In this work a methodology for damage identification is applied using the Damage Submatrices Method. The method determines the indicators of damage in terms of stiffness degradation, which allows the identification of damage from changes in structural stiffness values by comparing the baseline (or intact) and damaged conditions. A rectangular system of linear equations was solved to determine damage submatrices that contain information of structural damage associated with each structural element. Singular value decomposition was applied to these submatrices to determine the so-called damage indicators. The stiffness matrix was reconstructed based on limited modal data, using the first three mode shapes of the structure. Finally, results of the proposed method are shown using to a numerical case study of one offshore jacket platform. Several scenarios of damage are considered, and three sensitivity analyses were carried out as well, in order to compare the robustness of the method, which take into account: 1) the variation of the damage severity; 2) the combinations of the first three mode shapes of the platform; and 3) the noise influence in the modal displacements determination.

The water trapped in a moonpool area by a turret-moored Floating Production, Storage and Offloading unit (FPSO) in some cases can give rise to resonant periods due to piston or sloshing modes that cause unstable behaviors in heave and pitch. In this work, experimental tests have been conducted in order to analyze the dynamic effects of water trapped in moonpools and to determine how they affect the global performance of a turret-moored FPSO. Two series of experimental test have been conducted in two different configurations: one using a turret that prevents water inflow, and the other using a turret that allows water inflow between the moonpool and the internal cylinder. The obtained results show that this so-called piston mode appears in the turret model with moonpool area, while at the same time instabilities in dynamic response are observed in FPSO. The experimental results seem to indicate that the piston effect has some contributions in this behavior related to the yaw motion instabilities at regular wave period of 10.0 s.

Breaking waves are a natural phenomenon that can affect infrastructure located near the coast and cause soil erosion problems as well. For this reason, it has been investigated through experiments and numerical simulations for decades. With the advancement of new numerical approaches such as the moving particle semi-implicit (MPS) method that allows a better modeling of the fragmentation process, it is possible now to adequately represent its complex behavior on breaking waves. In this work we apply the MPS method to simulate breaking waves in a slope beach, which is simulated as a two-dimensional numerical tank, where cnoidal waves are generated by using Iwagaki wave theory. To achieve numerical wave generation, we first used an approximation through linear wave theory using piston, flap and a hyperbolic wavemakers with a 1.25-s wave period. Then, a numerical tank was modeled using nonlinear wave theory to simulate a series of different wave periods. Our results show that through the MPS method it is possible to represent the type of wave breaking defined analytically, as well as to determine the predicted wave profile and the momentum for the breaking wave, in the same way wave velocity and pressure under the wave can be approximated to their theoretical values.

Sandwich pipes have been studied as one option to overcome the high pressure problems in deep and ultra-deep waters. They have become a possible alternative solution for submarine infrastructure due to its thermal insulation capacity. This contribute to preventing the pipeline from clogging due to the difference in temperature between reservoir fluids and water at the bottom of the sea. The pipelines in ultra-deepwater are continually exposed to severe operating conditions, such as the effect of high levels of external pressure that can cause local deformation or even collapse of the pipe. Thus, a greater understanding of the mechanical behavior of sandwich pipes is required. This paper presents a FEM-based evaluation of friction and initial imperfection effects on sandwich pipes local buckling. The non-linear evaluation was carried out in FEM of local buckling of two sandwich pipes, with polypropylene and cement as filled annular material. The influence of initial imperfections and the degree of friction, between the annular material and the steel pipes, as well as geometric variations of the pipe were considered. The numerical simulations results indicate a capacity to withstand ultra-deep waters collapsing pressures, around 3000 m, either for polypropylene or cement filled annular material model. In addition, the results indicate that the collapse pressure is inversely proportional to the increase in annular thickness and directly proportional to the decrease in friction which have an impact and contribution on the carrying capacity of the sandwich pipe. Further research will consider a design of experiments analysis of reported effects for different diameter-to-thickness ratios.

The environmental contour concept, in conjunction with the Inverse First Order Reliability Method, is often used to determine the extreme response of marine structural systems. This technique is a powerful option to determine the extreme response associated to a probability of exceedance without the need to perform a long-term analysis, where a large number of short-term simulations are needed. However, there are significant uncertainties involved in its determination, such as the uncertainties related with the probabilistic model used for the environmental variables, as well as the ones related with the threshold selection when the peaks over threshold (POT) method is applied. This paper shows the results of a comparative analysis of the extreme tension of the most loaded mooring line of an FPSO subjected to environmental conditions in deep water, derived from environmental contour lines which were defined with different probabilistic models to represent the significant wave height and different criteria to establish the threshold for the POT methodology. The results showed that the probabilistic model has an important effect on the extreme response of the FPSO and this epistemic uncertainty should be accounted for in the calibration of the design safety factors.

Flexible risers can be subjected to high levels of internal pressure caused by hydrocarbon pressure gradients coming from the reservoir. Therefore, flexible risers can failure by burst of the riser, caused by a pressure armor failure, which were designed to resist the internal pressure or radial loads. This paper presents a burst analysis methodology by performing analytical, 2D and 3D finite element modeling of a section of a flexible riser. In order to obtain reliable results, it was necessary to consider in the finite element modeling both, geometric and physical nonlinearities due to the contact conditions between the two different layers of the riser considered in burst analysis. The results were compared with various existing analytical models with good correlation, and also showed the importance to develop finite element models for a proper burst analysis of flexible risers. The methodology was applied to a flexible riser manufactured with pressure armor with a “Z” profile.

Marine risers are subjected to several types of excitation loads, such as motions induced by the floating production system, external hydrodynamics forces due to currents and waves and internal forces due to the internal fluid flow regularly composed by water, oil and gas. When internal flow conditions as pressure, temperature and flow rate fluctuations appear in a riser, they can induce vibration motion to the system. This paper shows a numerical algorithm to evaluate the vibrations of vertical rigid production risers under internal multiphase flow behavior. The numerical algorithm developed computes the natural frequencies of vertical risers model coupled with a hydrodynamic numerical model. The internal flow was composed of water, oil and gas and was treated as a pseudo-single phase (mixture). The numerical algorithm was developed using difference finite method. The results were compared with information available in the literature.

This paper considers a time-dependent GEV model to assess the extreme value of significant wave. The model incorporates the monthly seasonality of maximum values in a block of time of recorded events. The extreme value distribution parameters are fitted considering the seasonal behavior of the significant wave height using harmonic functions representing annual and semiannual cycles. The model is applied to the records in 10 buoys in the Gulf of Mexico. The obtained results are compared with some of the available results in the literature.

In riser projects it is important to determine modal parameters, such as periods and mode shapes, to evaluate their dynamic behavior. To obtain these parameters of risers, various methods have been developed based on free vibrations theory. These methods do not take into account the variations of the dynamic behavior of the riser in different sea state conditions and also cannot be applied in monitoring activities of risers. In these situations, an alternative method should be investigated because of the need to monitor the structural behavior of future deepwater risers. This work presents a Fourier analysis methodology for the identification of modal parameters; namely natural periods and mode shapes, for a deepwater steel catenary riser (SCR), solely based on acceleration records. A structural model of a riser in 1800 m water depth was considered for the theoretical determination of modal parameters. This theoretical data was compared with the modal parameters identified in different sea states through spectral analyses of simulated acceleration records, assuming the presence of accelerometers at 15 discrete locations along the riser. The main advantage of the proposed methodology is that the estimated modal parameters are solely based on the motion (acceleration) records of the riser, which proves to be an efficient way to identify modal parameters that are being exited. This could be considered for structural health monitoring purposes, especially for damage detection and fatigue analysis.

The design of mooring systems for floating production units usually considers extreme environmental conditions as a primary design parameter. However, in the case of FPSO (Floating, Production, Storage and Offloading) units, the worst response for the mooring system may be associated with other sea state conditions due to the fact that its extreme response may be associated with a resonant period instead of an extreme wave height. The best way to deal with this problem is by performing long-term analysis in order to obtain extreme response estimates. This procedure is computationally very demanding, since many short-term environmental conditions, and their associated stochastic nonlinear time domain numerical simulations of the mooring lines, are required to obtain such estimates. A simplified approach for the long-term analysis is the environmental contour-line design approach. In this paper a Monte Carlo-based integration procedure combined with an interpolation scheme to obtain the parameters of the short-term response distribution is employed to hasten the long-term analysis. Numerical simulations are carried out for an FPSO at three different locations considering a North Sea joint probability distribution for the environmental parameters. The long-term analysis results are compared against those obtained using extreme environmental conditions and environmental contour-line methodology. These results represent the characteristic load effect for the design of mooring systems of floating units using the reliability analysis for mooring line. The results show that the long-term results are usually more critical than those obtained with the other approaches and even different mooring lines can be identified as the critical ones.

The characteristic environmental load effect for the design of mooring systems of floating units can be defined by means of three procedures: (a) the one associated to an extreme sea state with a given return period, (b) the worst one from a set of sea states on a contour line associated to a return period or (c) the extreme one based on response statistics for a long-term period. This work presents the result of a reliability-based partial safety factor calibration study for a LRFD mooring line design criteria considering the three approaches mentioned above. The calibration exercise is applied to three FPSOs considering North Sea environmental conditions and different water depths: 200, 800 and 3000 m. The mooring systems investigated take into account mooring lines made up of chains and polyester ropes. It is shown that, among all cases investigated, the design procedure based on the long-term response is the one that presents less scattered reliability indices around the target level.

The characteristic load effect for the design of mooring systems can be defined by means of three procedures: 1) an extreme sea state with a given return period, 2) a set of sea states on a contour line associated to a return period or 3) extreme response (tension) statistics for a long-term period. This work presents the result of a reliability-based partial safety factor calibration study for a LRFD mooring line design criteria considering the three approaches mentioned above. The calibration exercise is applied to three FPSOs considering North Sea environmental conditions and different water depths: 200m, 800m and 3000m. The mooring systems investigated take into account lines made up of chains and polyester ropes. It is shown that the design procedure based on the long-term response, among all water depths investigated, is the one that presents less scattered reliability indices around the target level.Copyright © 2006 by ASME