Brazilian subsea exploration is increasing specially after the post salt petroleum field discovery. Several challenges have been imposed for the production of those fields. In this scenery, the transport of oil and gas from the production field to the continent is a problem, especially when the fields are located at a great distance from the coast. A possible solution could be the use of subsea pipeline systems, for the transportation of the fluids produced from the petroleum wells. For the pipeline system design it is highly recommended the evaluation of the transient flow, considering the water hammer phenomenon. The definition for this phenomenon is given by the pressure variation due to operation singularities in the pipe system. The disruption in the flow originated by the operation of valves or failure of a pump can be listed as some of the main causes of the water hammer. The basic equations to model the water hammer in fluid mechanics comes from two partial differential equations, the equation of continuity and momentum. The solution of those equations can be obtained by different numerical methods. In this context, this work seeks to contrast results obtained by finite difference method (FDM), the method of characteristics (MOC) and finite elements method (FEM) solutions for the water hammer problem. Those numerical methods were implemented and used to solve a simple system, which are composed of an infinite reservoir, a pipeline and a valve. In this case the valve is closed, originating the water hammer phenomenon. Although it can be considered a simple problem, it allows the evaluation of those numerical methods. Performance, convergence and accuracy were evaluated in order to support the choice of the best numerical method for the development of a numerical simulator used in complex and greater pipeline system design.

Nowadays, hybrid risers systems have been continuously adopted for deep and ultra-deep water petroleum fields. This riser system consists of a submersible buoy connected to flexible and rigid risers. Commonly, the buoy is installed 200 meters depth from the free surface to avoid the wave forces. Therefore, the main forces acting in this part of the system is due to the current flow. In this case, the VIM force is one of the forces that induce oscillations in the buoy, which can cause significantly fatigue damage to the riser system. In this scenario, understand the VIM response of the buoys is important for the system design. In this work, the semi-empirical approach presented by Tsukada et al. (2014), Numerical Simulation of VIM Response of a Submersible Buoy Using a Semi-Empirical Approach, OMAE2014–24187, is applied to perform a parametric study varying the riser length and the properties and dimensions of the buoy of a FSHR system. The main objective of this study is to show the trends of the response due to the variation of this parameters, which assists in understanding the real riser system response presented later in this paper. The real riser system properties and dimensions are obtained from the technical literature and used in the simulations. The results of amplitude and frequency of oscillation of the buoy are compatible with the results of FSHR model test experiments.