Structures and Integrity

De-risking critical aspects for concept selection and enable cost-effective design and fabrication of support structures through reduced uncertainty and application of novel methods.

Work Package 1 is led by Vigdis Olden from SINTEF Industry and Ana Page from NGI. Its focus areas are environmental loads, limetime and performance, design and fabrication.

Anticipated results:

  • Improved methods for prediction of interactions between environmental loads, soil and structure.
  • Decision support platform for lifetime prediction
  • Cost-effective serial production of substructures


Fundamental understanding and accurate models of load, response, and degradation will be a key enabler for design, digitalised operation and lifetime prediction of support structures.

Methodology and research tasks

Environmental loads and response modelling

Hydrodynamic load models, site investigation methodologies and soil structure interaction and integrity.

Integrated design assessment and optimization

Multi-scale aero-hydro-servo-elastic modelling and reliability-based structural design optimisation.

Lifetime, performance, and integrity

Precision in degradation models. This is linked to Work Package 4.


Cost-effective mass production by automation and optimised and light-weight design and materials for secondary structures. Linked to Work Package 2 and 3.

Ambition for innovations

Improved models

Improved models for reliable predictions and better
understanding of interactions between environmental loads, soil, and structure. Accurate knowledge of site conditions and extreme environmental loads is insufficiently applied in early-phase design.

Decision support platform

Decision support platform for life prediction based on advanced model and condition monitoring. Limited understanding and modelling capabilities for material damage during operation.

Cost-effective production

Cost-effective serial production of offshore sub-structures, including a high degree of automation. Manual welding and coating are bottlenecks and cost drivers in fabrication.


Main results from 2022

Numerical simulation of cone penetration tests in silty sands

The offshore wind industry relies heavily on the Cone Penetration Test (CPTu) to measure the in-situ soil conditions and characterise large areas. However, the accuracy of CPT data  interpretation depends on generic correlations. While these correlations work well for sands with limited fine  particles, they are less reliable for soils with higher fines content, like silty sands, partially due to the lack of understanding on how the presence of fine particles affects the measured CPTu response. To address this issue and analyse the influence of fines and drainage on the tip resistance and developed pore pressure in CPTu, researchers in WP1 have combined two known numerical techniques: large-deformation finite element analyses with the “zipper technique” and coupled consolidation analyses.

The results from applying this technique have been compared against CPTu measurements from two locations at an  offshore wind farm site, providing good agreement,  and indicating that this technique may help improving the understanding of the effect of fines content on CPTu response.

Establishing a sand database

The limited capacity of site investigation vessels and laboratories to process and  test soil samples remains a significant bottleneck in the offshore wind industry, causing delays in the  deployment of new offshore wind sites. To address this challenge, researchers in WP1 have taken the initiative to  compile a database of typical sand properties. The primary objective of this database is to provide access to data on  typical soil behaviour for offshore sites.

This will facilitate the development of offshore wind projects,  especially in cases where there are no site-specific laboratory test results available. Our approach involved a combination of existing laboratory tests and newly generated virtual
sand tests to enhance the  coverage of the database. To conduct virtual tests, we used the recently developed Level-Set Discrete Element Method  (LS-DEM). This method  models the interactions  between individual sand grains in an assembly of grains, generating a continuum stress-strain relationship similar to that derived from traditional laboratory tests (see illustration).

Comparison of the stress-strain curves from a virtual LS-DEM test and a triaxial laboratory test for Øysand sand.
Comparison of the stress-strain curves from a virtual LS-DEM test and a triaxial laboratory test for Øysand sand.

Uncertainty analysis of hydrodynamic experiments of floating wind turbines

A numerical study was conducted to evaluate uncertainties in the mooring system of the 12MW INO WINDMOOR semisubmersible floating wind turbine based on the KPN WINDMOOR hydrodynamic experiment. The study investigated uncertainties in the mooring system and their effect on outputs such as mooring line tension and platform responses. Two different approaches were used for the uncertainty analysis: the Taylor Series Method and the Monte Carlo Method. The results will be presented at OMAE2023 in June 2023 and provide valuable insights into the uncertainties associated with the mooring system modelling and its impact on hydrodynamic testing of floating wind turbines.

Materials integrity in the drive train

A state-of-the-art report on design, operation, failures and lifetime of main bearings and gears has been written. Considerable effort to get hold of failed drive train components and relevant material for study of failures and laboratory rolling fatigue experiments have taken place without success. We hope that this can be solved in collaboration with the industry partners in 2023.

Comparison of productivity, LAHW vs. arc welding.
Laser-arc hybrid welding

How efficient is laser-arc hybrid welding?

Laser-arc hybrid welding (LAHW) is an efficient and promising welding technology for manufacturing offshore wind substructures. Inspired by the quest for finding efficient fabrication methods, we performed an initial comparison study in a laboratory to show how efficient LAHW can be compared to conventional welding methods. We found that LAHW may offer 5-24 times higher productivity than conventional arc welding (see the figure above) with half the energy consumption.

Despite the economic and productivity advantages of LAHW, there are challenges with the quality of welds, e.g., cracking at weld centreline and poor microstructure. Improvement of the stability of LAHW process is the key to achieve defect-free welds. Therefore, we have started to investigate the potential of using acoustic emission (AE) technique for LAHW process monitoring. A state-of-the-art review has been performed. The first testing will start in 2023.

Previous results

Establishing a sand database

  • The foundation concept selection for wind turbines often relies on limited information on the soil conditions and some generic correlations. Having access to data and better correlations can facilitate the development of offshore wind projects and de-risk foundation concepts that are sensitive to soil conditions.

Laser welding of thick-walled steel plates

  • For the accelerated deployment of large-scale offshore wind, we need cost-effective, sustainable, and mass-produced substructures. The ability to efficiently perform welding of thick steel plates resulting in a good quality weld with respect to full penetration and material properties is central. A full-penetration, defect-free weld has been achieved.
Figure illustrating the concept of laser-arc hybrid welding
Laser-arc hybrid welding

Identification and description of user cases

In close cooperation with the industry partners, three industrial user cases have been identified.