Design, Construction, and Installation of Off-Shore Wind Turbine With Tripod Suction Bucket Foundation

As part of the national off-shore wind power development project by the government of Korea, the very first off-shore wind turbine utilizing tri-pod suction buckets for its sub-surface foundation has been successfully completed. This off-shore wind turbine with a capacity of 3MW has been designed, constructed, and installed in late 2016. It is located approximately 200 meters offshore with a water depth of approximately 10 meters. Sub-surface soil consists of interbedded clay and sand layers. Details of the design, construction, and installation of this wind turbine with tripod suction bucket foundation system are described and discussed.

Summary and Conclusions of the Full Life-Cycle of the WindFloat FOWT Prototype Project

The WindFloat prototype is a semisubmersible type foundation supporting a 2 MW, 3 bladed, horizontal axis Vestas V-80 turbine. The 8-year project is near its completion. After 3 years of planning, engineering and fabrication, the prototype was installed in 2011 in the northern Portugal Atlantic waters. Following 5 years of operations and electricity production, the unit was decommissioned in the summer of 2016. This paper retraces the prototype project going back to the early objectives, focusing on its 5-year performance and lessons learned. The overall assessment of the impact of the prototype on the incoming pre-commercial projects is discussed. Some emphasis is placed on both the decommissioning of the unit and the economics of the project, as these have not yet been published.

On the Axial Holding Capacity of Torpedo Bases in Clay

A torpedo base is a type of conductor casing that embeds into the seabed mainly by free fall using its own weight as driving energy. One of the advantages of this concept is to install the conductor casing before the dynamic positioned (DP) drillship arrival at the location. This reduces the time of the well drilling leading to significant cost saving. However, the need to withstand the challenging loads of the ultra-deep water scenarios pushed the typical torpedo base design to its limit and, consequently, modifications to its original geometry and more accurate design models are needed. Therefore, in this work, a new torpedo base, designed to sustain high axial loads in very soft clays, is analyzed with a three-dimensional finite element (FE) model. This model accounts for the setup-effects of the soil with the use of a previously proposed analytical approach to estimate the stress state of the soil at any time after the installation of the base. The results obtained indicate that the axial holding capacity of the base varies along time. The holding capacity increase rapidly at the beginning of the installation, but this rate reduces after the first days. Depending on soil characteristics, full axial capacity may be reached more than one year after the installation of the base. Moreover, the use of more than four fins welded to the shaft of the conductor casing modifies the shear zone along the base, but does not contribute to a significant increase in the axial holding capacity.

Advanced Approaches for Coupled Deformation-Seepage-Analyses of Suction Caisson Installation

In this paper the installation procedure of suction caissons is investigated by means of coupled seepage large deformation analysis performed with finite element methods. The modelling techniques employed to enable simulations of the penetration of a caisson into the soil under offshore conditions, i. e. several tens of meters below the water level. The numerical model includes a u-p-formulation, which is used to calculate the excess pore pressures and effective stresses from the total stresses. The Coupled-Eulerian-Lagrangian (CEL) approach available in conjunction with the Abaqus/Explicit solver is used. The calculation results are compared to centrifuge tests that were carried out recently at the Centre for Offshore Foundation Systems (COFS). This sheds light on the potential and the limitations of the presented numerical techniques. This paper concludes with a brief discussion of alternative numerical approaches that could be capable of the simulation of caisson installation.

An Automated Approach for Designing Monopiles Subjected to Lateral Loads

This paper describes an automated algorithm for determining the length and diameter of monopile foundations subject to lateral loads with the aim of minimising the pile weight, whilst satisfying both ultimate and serviceability limit states. The algorithm works by wrapping an optimisation routine around a finite element p - y model for laterally loaded piles. The objective function is expressed as a function representing the pile volume, while the ultimate limit state and serviceability limit states are expressed as optimisation constraints. The approach was found to be accurate and near instantaneous when compared to manual design procedures and may improve design outcomes and reduce design time and costs.

Simplified Hydrodynamic Design Procedure of a Submerged Floating Tube Bridge Across the Digernessund of Norway

The paper will look into the hydrodynamic loads and responses on the proposed Submerged Floating Tube Bridge (SFTB) through the Digernessund by the Norwegian Public Roads Administration (Statens vegvesen, NPRA). The aim is to show how different hydrodynamics aspects during the prelimiary design can be simply addressed under the given environmental conditions. Different SFTB systems are introduced as the first step. A simplified method based on modal analysis is introduced and implemented for evaluation of the motions and stress, bending moments along the bridge. Firstly, a 2D Boundary Element Method (BEM) solver is developed and verified, which is further used for solving the hydrodynamics coefficients of different bridge cross sections. The 3D hydrodynamic coefficients of pontoons are solved by the commercial software AQWA. The analysis procedure of the simplified method for the global SFTB responses is presented. The Eigen periods of the Bjørnefjord SFTB is re-calculated by the present model as a first validation of the implementation. The loads and responses of the bridge under given wave conditions are then estimated. The evaluation of the possibility of vortex induced vibrations of the current SFTB design is given.

Experience From Introduction of the Design Code NS 9415 to the Aquaculture Industry in Norway and Expanding the Scope to Cover Also Operations

This paper presents the current state of regulations, guidelines and the engineering in the Norwegian aquaculture industry. The statistics of fish escapes is evaluated and the need for further developments of the regulations, in planned revisions, of the Norwegian standard, are laid. Simplified case studies are shown to present the main forces acting on fish farms.

Manoeuvring Validation Analysis of the M/F Landegode

A framework is described in which a manoeuvring simulator can be built up from model tests. It is applied to a modern LNG powered RORO ferry, the M/F Landegode, with model tests and computational results being used to make full-scale predictions. These predictions are tested against full-scale manoeuvring performance measurements, and are shown to be of a high quality.

Numerical Modelling and Analysis of a Hybrid-Spar Floating Wind Turbine

In this paper, numerical modelling and analysis of a hybrid-spar floating wind turbine is presented. The hybrid-spar consists of steel at the upper part and the precast prestressed concrete (PC) at the lower part. Such a configuration is referred to as a hybrid-spar in this paper. The hybrid spar was successfully installed offshore of Kabashima Island, Goto city, Nagasaki prefecture, Japan on October 18, 2013 (see OMAE2015-41544 [1] for details). In this paper, some details on numerical modelling of the hybrid-spar for design load analysis are presented. Then, the validation of the numerical analysis model is presented for a full-scale hybrid-spar model with 2-MW wind turbine.