A discussion of a paper with the aforementioned title by Murff and Hamilton, published in this journal (Volume 119, Number 1, January 1993), is presented The discussion focuses on laterally loaded piles in layered soils Maugeri, Castelli, and Motta assert that the authors' method overpredicts the ultimate lateral resistance on the pile Discussion is followed by closure from the authors

P-ultimate for undrained analysis of laterally loaded piles. discussion and closure

A review on recent advancements of substructures for offshore wind turbines

Constitution d'une base de donnees, a partir d'essais triaxiaux non draines et d'essais de cisaillement simple direct sur argile de Drammen, avec combinaison de contraintes de cisaillement statique et dynamiques

Cyclic soil data for design of gravity structures

The installation phase is a critical stage during the lifecycle of an offshore wind turbine. This paper presents a state-of-the-art review of the technical aspects of offshore wind turbine installation. An overview is first presented introducing the classification of offshore wind turbines, installation vessels, rules and regulations, and numerical modelling tools. Then, various installation methods and concepts for bottom-fixed and floating wind turbines are critically discussed, following the order of wind turbine foundations and components. Applications and challenges of the methods are identified. Finally, future developments in four technical areas are envisioned. This review aims to guide research and development activities on offshore wind turbine installation.

Installation of offshore wind turbines: A technical review

Structural vibration monitoring and operational modal analysis of offshore wind turbine structure

Model tests on the bearing capacity of wide-shallow composite bucket foundations for offshore wind turbines in clay

Field experiments on wet tows of an integrated transportation and installation vessel with two bucket foundations for offshore wind turbines

The key in the force transmission between the tower and the foundation for offshore wind turbines is to transfer the large moment and horizontal loads. The finite element model of a large-scale prestressing bucket foundation for offshore wind turbines is set up and the structural characteristics of the arc transition structure of the foundation are analyzed for 40–60 channels (20–30 rows) arranged with prestressing steel strand under the same ultimate load and boundary conditions. The mechanical characteristics of the key parts of the foundation structures are illustrated by the peak of the principal tensile stress, the peak of the principal compressive stress and the distribution areas where the principal tensile stress is larger than 2.00 MPa. It can be concluded that the maximum principal tensile stress of the arc transition decreases with the increasing number of channels, and the amplitude does not change significantly; the maximum principal compressive stress increases with the increasing number of channels and the amplitude changes significantly; however, for the distribution areas where the principal tensile stress is larger than 2.00 MPa, with different channel numbers, the phenomenon is not obvious. Furthermore, the principal tensile stress at the top of the foundation beams fluctuantly increases with the increasing number of channels and for the top cover of the bucket, the principal tensile stress decreases with the increasing number of channels.

Design of large-scale prestressing bucket foundation for offshore wind turbines

In 2010, the first offshore wind turbine with integrated installation was established in Qidong sea area of Jiangsu Province, China, which led to the implementation phase of one-step-installation technique based on the design and construction of large-scale bucket-top-bearing (LSBTB) bucket foundation. The critical technique of LSBTB bucket foundation included self-floating towing, penetration with adjustment of horizontal levelness, removability and one-step-installation. The process of one-step-installation included the prefabrication of LSBTB bucket foundation in onshore construction base, installation and debugging of wind power, overall water transportation of foundation and wind power system, and installation of foundation and offshore wind turbine on the appointed sea area. The cost of one-step-installation technique was about 5 000 Yuan/kW, which was 30%-50% lower than that of the existing technique. The prefabrication of LSBTB bucket foundation took about two months. During the one-step-installation process, the installation and debugging of wind power and overall water transportation need about one to two days in sea area within 35 m depth. After the proposed technique is industrialized, the cost will be further reduced, and the installation capacity is expected to be up to 500 wind turbines per year.

One-step-installation of offshore wind turbine on large-scale bucket-top-bearing bucket foundation

With the current state of offshore wind turbine construction technology, a major marine spread is necessary for the installation of the foundation, tower, and turbine. It is advantageous for offshore installation to be integrated into a single operation. The large-scale composite bucket foundation is the basis for a one-step integrated transportation and installation technique using a specialized transport vessel. The proposed transportation and installation technique will minimize the offshore operation and maximize the proportion of work carried out onshore with consequent benefits in terms of cost, quality, and safety. The self-floating composite bucket foundation is towed into the semicircle groove of the vessel and connected to the wire ropes of a stationary crane. Then the tower and turbine are attached to the foundation at the shore and the entire unit consisting of the foundation, tower, and turbine is loaded out from the quayside, transported to the site and set down on the seabed. During transport, half of the unit's weight is taken by the hoisting system of the vessel, and the remaining half of the weight is supported by air cushions inside the composite bucket foundation. A detailed model is studied to determine the motions of the vessel with two units to confirm the viability and feasibility of such a method of integrated transportation. The draft and air cushion are two effect parameters used to determine the dynamical characteristics of the transportation structure system. The results show that a smaller draft and a greater air cushion positively contribute to a safe transportation process. The viability and feasibility of this method of integrated transportation are confirmed by determining the motions of the various elements proposed by the detailed model.

Hongyan Ding

Papers

Model tests on the bearing capacity of wide-shallow composite bucket foundations for offshore wind turbines in clay

Field experiments on wet tows of an integrated transportation and installation vessel with two bucket foundations for offshore wind turbines

Design of large-scale prestressing bucket foundation for offshore wind turbines

One-step-installation of offshore wind turbine on large-scale bucket-top-bearing bucket foundation

Motion analysis on integrated transportation technique for offshore wind turbines