The installation procedure of a torpedo anchor is the release of the torpedo from a high enough position from the sea bottom to allow the device to reach the terminal velocity. A sufficient kinetic energy at the bottom is essential for the penetration. Besides this, the anchor has to reach the bottom in an upright position to maximize the final holding power in all directions. The present work addresses two hydrodynamic aspects for the installation design and analysis. The first is the drag evaluation and the second is the directional stability. If the drag is to be kept small, then the terminal velocity should be high. The work shows that parameters like the mass and the shape are essential for this. On the other hand, the shape and mass distribution have a strong influence on the directional stability. One important parameter is the rear line length connected to the anchor. This line is necessary for further connection with the final mooring line and influences both the terminal velocity and the directional stability. The work addresses all these aspects under the light of an innovative model test setup to be performed in a deep ocean basin. This kind of model testing has been conceived specifically to attend the torpedo anchor evaluation.

The BSR (Buoy for Supporting Risers) concept is composed by a submerged buoy anchored to the sea bottom by tethers and intended to support risers coming from the bottom (probably SCRs — Steel Catenary Risers) and going to the floating platform (probably with flexible jumpers). For the case under analysis here, the main dimensions of the BSR prototype are 27.2 m length × 27.2 m width × 5.0 m depth. The paper describes all final full scale installation step so that the BSR may be considered a suitable technology. The installation indeed was the great challenge of this design due the size of the hull. The present work also evaluates numerically and experimentally a specific new manner to install the BSR with the support of auxiliary mooring lines among with the four tethers connected to it. One of the installation premises was to make use of Anchor Handling Supply Vessels instead of Crane Vessels. After this numerical analysis, the work went on by performing model tests that simulates the operation in a deep water model basin using 1:40 scale. The model test anticipated several problems such as the chain stopper weakness in the operation and others as discussed in this paper. As a conclusion the work was devised the most important parameters during the system installation and suggested ways to improve the methodology. In November 2009 the BSR was installed in 500 m of water depth at Congro field location, Campos Basin, offshore Brazil. The tethers were adjusted in January 2010 and in March 2010 two risers were installed. Thenceforward the last edge of this knowledge was considered over passed.

A Sub-Surface buoy hybrid riser system is considered as a solution for deepwater export systems. Besides the in place static and dynamic loads, the installation operation was analyzed. The development includes the reduced model tests in a (so far) unique Deep Water Ocean Basin. A reduced model in an adequate scale was designed and constructed. It was submitted to an almost full equivalent depth and a comprehensive equivalent environment. The later corresponds to representative Campos Basin currents together with critical high crossing waves, which were made to excite resonance of the FPSO (Floating Production Storage and Offloading) hull. Typical moored FPSOs’ motions are much more than other platforms like Semi-Submersibles or TLPs and therefore the SSB is very adequate, since it resists easily to the cited critical environment conditions. Besides describing the system main characteristics, the paper describes the model testing in detail and present main results. Some problematic aspects has been are clearly appreciated for the first time, anticipating that what could happen in full scale. This therefore, requires a design improvement as also discussed.

The torpedo anchor is a novel kind of device to moor floating offshore structures. It has been proved in practice that this kind of anchoring may be used for both drilling and production offshore activities. For drilling, it is indeed easily recoverable and for large production, it has enough holding power even for large production platforms. There are a lot of soil-interaction aspects to be considered and the installation is one of them. The installation procedure is to release the torpedo from a high enough position from the sea bottom to allow the device to reach the terminal velocity: A correct amount of kinetic energy at the bottom is essential for the penetration. Besides this, the anchor has to reach the bottom in a vertically up right in order to maximize the final holding power in all directions. Therefore, the work addresses two hydrodynamic aspects for the installation design and analysis. The first is the drag minimization and the second is the directional stability. If the drag is be kept to a minimum (without compromising, later on, the soil interaction) then the terminal velocity is higher. The work shows that parameters like the mass and the shape are essential for this. On the other hand, the shape and mass distribution have a strong influence on the directional stability. One important parameter is the rear line length connected to the anchor, which is necessary for further connection with the final mooring line: this parameter influences both the terminal velocity and the directional stability. The presence of the rear line and its role is a novel problem and it seems to have no parallel in other filed applications. The work addresses all this aspects under the light of a novel model testing performed in a model basin that is 15 m deep. It is important to say that this model testing procedure has been conceived to attend specifically the torpedo anchor evaluation. For that matter, the work presents an extrapolating mathematical model. Besides that, an analytical model is shown for the directional stability, together with time domain numerical evaluation. Different model have been used in the tests performed with and without the rear line. Finally, the work presents the model testing design including the use of imaging processing to get the anchor tracking during the launching.

For mooring chains of offshore floating production units, API (American Petroleum Institute) recommends the use of its TxN fatigue curve considering the MBL (Minimum Breaking Load) of an ORQ (Oil Rig Quality) chain even if the chain has a higher grade. DNV (Det Norske Veritas) recommends the use of SxN fatigue curve where the stress is taken using the tension over the nominal area of the chain or wire rope. So it is easy to convert this SxN curve to a TxN curve or vice-versa. The geometry of the chain or wire rope and the material are implicit considered. To develop SxN curve for new accessories design it is necessary the using of FEM (Finite Elements Method) to obtain the distribution of stresses and strains and the stress concentration factor and the SxN curves of the material. The analysis of the tension and the stress concentration factor will be used to obtain the slope and intercept parameters of the fatigue curve. This paper will present the study developed for KS hook and how to obtain the fatigue curve for this accessory based on published papers, rules and recent tests.