STRUCTURAL LIFE-CYCLE ENHANCEMENT OF NEXT-GENERATION ONSHORE AND OFFSHORE WIND FARMS
Lead Research Organisation:
University of Brighton
Department Name: Sch of Environment and Technology
Abstract
The proposed research aims to develop an innovative mitigation device to protect the next-generation onshore and offshore wind farms from dynamic loading caused by extreme natural events.
In 2020, 20% of the UK's electricity was obtained from wind using both onshore and offshore windfarms. In order to increase this percentage and help the UK address its climate change target, new wind farms, with taller and larger wind turbines, and situated in more extreme locations are planned. Projections of growth also indicate the expansion into emerging markets and construction of new wind farms in developing countries. Therefore, these next-generation wind turbines will have to cope with harsher climate conditions induced by stronger storms and taller sea waves, and extreme events such as earthquakes and tsunamis. Several simplifying assumptions used for the design of previous generations of wind turbines can no longer be applied and new critical factors and uncertainties linked to power-generation efficiency and structural safety will emerge, affecting their resilience and life-cycle. The particular area of focus of this research is the traditional transition piece of a wind turbine, which is a structural element that connects the tower with its foundation and will have to tolerate extreme stresses induced by dynamic loading during extreme natural events. The aim is to replace the traditional connector with a novel mechanical joint of hourglass shape, termed an Hourglass Lattice Structure (HLS). This innovation will combine the unique features of two proven technologies extremely effective in seismic engineering, namely the "reduced beam section" approach and the "rocking foundation" design. In particular, the proposed HLS device, because of its hourglass shape, will facilitate the rocking behaviour in order to create a highly dissipating "fuse" which will protect the wind tower and foundation.
Performance of the novel proposed device on the structural life-cycle risk will be assessed through analytical, numerical, and experimental investigation by using, as a measure of efficiency, the levelized cost of energy (LCOE), namely the cost per unit of energy based on amortized capital cost over the project life.
In addition, experimental testing of offshore small-scale wind turbines will be carried out by means of an innovative test rig, the first-ever underwater shake-table hosted in a hydraulic flume that will be deployed, calibrated, and used to simulate multi-hazard scenarios such as those recently discovered and dubbed "stormquakes".
The successful outcome of this timely project will allow next-generation wind turbines to be more resilient and cost effective so that wind energy can develop as a competitive renewable energy resource with less need for government subsidy. The inclusion of industrial partners in all stages of the project ensures that the technical developments will be included in commercial devices for a medium-long term impact.
In 2020, 20% of the UK's electricity was obtained from wind using both onshore and offshore windfarms. In order to increase this percentage and help the UK address its climate change target, new wind farms, with taller and larger wind turbines, and situated in more extreme locations are planned. Projections of growth also indicate the expansion into emerging markets and construction of new wind farms in developing countries. Therefore, these next-generation wind turbines will have to cope with harsher climate conditions induced by stronger storms and taller sea waves, and extreme events such as earthquakes and tsunamis. Several simplifying assumptions used for the design of previous generations of wind turbines can no longer be applied and new critical factors and uncertainties linked to power-generation efficiency and structural safety will emerge, affecting their resilience and life-cycle. The particular area of focus of this research is the traditional transition piece of a wind turbine, which is a structural element that connects the tower with its foundation and will have to tolerate extreme stresses induced by dynamic loading during extreme natural events. The aim is to replace the traditional connector with a novel mechanical joint of hourglass shape, termed an Hourglass Lattice Structure (HLS). This innovation will combine the unique features of two proven technologies extremely effective in seismic engineering, namely the "reduced beam section" approach and the "rocking foundation" design. In particular, the proposed HLS device, because of its hourglass shape, will facilitate the rocking behaviour in order to create a highly dissipating "fuse" which will protect the wind tower and foundation.
Performance of the novel proposed device on the structural life-cycle risk will be assessed through analytical, numerical, and experimental investigation by using, as a measure of efficiency, the levelized cost of energy (LCOE), namely the cost per unit of energy based on amortized capital cost over the project life.
In addition, experimental testing of offshore small-scale wind turbines will be carried out by means of an innovative test rig, the first-ever underwater shake-table hosted in a hydraulic flume that will be deployed, calibrated, and used to simulate multi-hazard scenarios such as those recently discovered and dubbed "stormquakes".
The successful outcome of this timely project will allow next-generation wind turbines to be more resilient and cost effective so that wind energy can develop as a competitive renewable energy resource with less need for government subsidy. The inclusion of industrial partners in all stages of the project ensures that the technical developments will be included in commercial devices for a medium-long term impact.
Publications
Rostami R
(2023)
A novel reduced column section approach for the seismic protection of wind turbines
in Engineering Structures
Tombari A
(2024)
A rigorous possibility approach for the geotechnical reliability assessment supported by external database and local experience
in Computers and Geotechnics
| Description | Achievement 1) The research project pursued the development of a novel design approach to the connecting element between the wind turbine tower and its foundation, denoted transition piece, for the mitigation of the vibrations induced by wind and earthquakes. The novel approach called "Reduced Column Section" (RCS) is based on creating a "mechanical fuse" to protect the remaining structural components. Initially, the RCS has been shaped as an hourglass. The geometry (section reduction), the thickness of the steel wall as well as the steel grade are the main design parameters of the RCS. According to the type of wind turbine, either shifting the period or creating a plastic hinge in the reduced section can be obtained for reliable dynamic protection of the tower and foundation. Numerical analyses have been carried out on a real onshore wind turbine located in Italy which has been real-time monitored during the first part of the project. This research has been carried out with the Italian project partner, ErgoWind s.r.l., which provided technical support and access to the investigated onshore wind turbine. The results highlighted that the RCS can be effective in working as a passive mitigating device localizing the peak stresses on the reduced section and, if possible, by shifting the fundamental period of the tower. In the analyzed case study, a reduction of the effective stresses on the tower of about 70% has been obtained; this has an important impact on reducing the use of material (boosting sustainability and reducing costs) and/or increasing structural safety. This topic will continue with the development of the Hourglass Lattice Structure by exploiting the RCS approach. Numerical analyses will be conducted on next-generation offshore wind turbines to instruct developers on the benefits of the proposed idea. A few questions have been opened in this research, can the RCS be applied to buildings? can the RCS be used in soft-soft design of wind turbines? Can the fatigue on the RCS be an issue? Some of these questions will be replied to during and after the duration of the project. In terms of critical aspects generated by the RCS is the difficulty of combining the very different inputs of wind and seismic loading; protecting the structure from both is a difficult task and more investigation on the combination of these two actions must be investigated thoroughly. Achievement 2) The optimal design of the RCS requires the assessment of the structural reliability. In this research, the impact of the uncertainty in characterizing the soil properties has been investigated to perform a reliable design. Because of the complex nature of the soil and the lower number of tests used for each geotechnical investigation, adopting traditional probability approaches can lead to large errors in the assessment of the probability of failure of the geotechnical foundation. In this research, a data-driven reliability approach based on the Possibility Theory has been developed. The method is consistent with the target safety levels provided by the building codes and quantifies in a rigours fashion the local experience and engineering judgment in the reliability assessment. The research has been conducted with the support of the British Geological Survey providing access to their geotechnical databases as well as technical support. The data has been analysed through the possibility theory and elaborated to create design possibility numbers to be used for the reliability assessment. The proposed method, albeit based on an emerging theory, has been devised to be applied with a simple step-by-step procedure to allow practitioners to adopt it without being familiar with the mathematical theory itself. This research strand will continue by analyzing databases and providing new metrics for the uncertainty quantification analysis. Moreover, the method will be extended to consider large systems and verify its advantages compared to the traditional Monte Carlo Simulation. Achievement 3) The research has been focused on the correct modelling of the soil-pile interaction considering soil hardening and degradation. A new approach based on the Discrete Element Method has been proposed to calibrate the main parameters of the cyclic hardening/degradation of sandy soils. This is fundamental for a correct assessment of structural safety. This research is opening to new collaborations that has just started or will begin in the near future; a first collaborative research is starting between the Principal Investigator and COWI A/S, Denmark based on the modelling of offshore geotechnical foundations considering seismic events and nonlinear soils. has opened three important new research fields that will be continuing after the duration of the project. |
| Exploitation Route | The concept of the "Reduced Column Section" approach can be used by wind turbine designers to protect the next-generation wind turbine located in earthquake-prone areas. Therefore, the knowledge generated by this research can be taken forward by practitioners in the Wind Industry as well as by academics in Wind and Seismic Engineering. As a matter of fact, the method can be even used for columns of steel buildings; therefore new studies are required to optimize the RCS to steel structures and experimental testing could be conducted. Therefore, a new research question has been opened up and it can be used for applying for additional research grants with experts in steel design. The data-driven possibilistic approach can be used by academics for comparison with traditional Bayesian methods. Data-driven approaches are fundamental for enabling digitalisation and use of Artificial Intelligence in geotechnical engineering Use of the Discrete Element Method for calibrating soil degradation and impact of the Wind Turbine fatigue is a open-research topic that needs further studies to become a realistic method used by practitioners. |
| Sectors | Construction Creative Economy Digital/Communication/Information Technologies (including Software) Energy Environment |
| Description | Investigation into cyclic soil-pile degradation has been fundamental in gaining expertise to attract the interest of academic and non-academic parties. This has led to a first collaboration with COWI A/S, Denmark, for the modelling of offshore wind foundations under seismic loading. This research is useful for developing future projects in earthquake-prone areas. |
| First Year Of Impact | 2024 |
| Sector | Construction |
| Impact Types | Economic Policy & public services |
| Description | COWIfonden Fast&Furious |
| Amount | 100,000 kr. (DKK) |
| Funding ID | DKM/knl/F-165.08 |
| Organisation | Cowi Foundation |
| Sector | Private |
| Country | Denmark |
| Start | 02/2024 |
| End | 07/2024 |
| Description | Linkedin Post |
| Form Of Engagement Activity | Engagement focused website, blog or social media channel |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Professional Practitioners |
| Results and Impact | 2545 impressions of the research finding. |
| Year(s) Of Engagement Activity | 2023 |
| URL | https://www.linkedin.com/pulse/can-wind-turbine-transition-piece-designed-mitigate-tombari/ |