Jaakko Heinonen

Modelling Techniques and Case Study of Explicit 3D FE-Simulation of Ridge Loads Against an Offshore Structure

A ridge interaction with an offshore structure, Norstromsgrund lighthouse in the Gulf of Bothnia, was simulated by the finite element method (FEM) utilizing the explicit solution algorithm. The explicit method in a dynamic analysis enabled an efficient way to simulate the failure of a ridge. A shear-cap material model describing the ice rubble mechanical behaviour was developed for the 3-dimensional analysis and implemented into ABAQUS FEM-software as a user material subroutine. The FE-model described the ridge: the sail and keel consisting of ice rubble and the consolidated layer close to the waterline. A selected ridge-interaction event was simulated with a simplified geometry, based on measurements carried out in the STRICE project. The ridge field was idealized to have a constant thickness. The shape of a 3-dimensional structure was modelled using rigid elements. The phenomenological model can be utilized to gain an understanding of how the ridge fails during the interaction with an offshore structure, what the ridge loads are, and how they are distributed against the structure. A parametric study was carried out to study how the mechanical properties, i.e. the cohesion and friction angle of the rubble and the strength of the consolidated layer influence the forces and failure mechanisms.Copyright

Coupled-crushing analysis of a sea ice-wind turbine interaction – feasibility study of FAST simulation software

ABSTRACT The Gulf of Bothnia has the potential for large capacity wind farms because of the relatively high and constant wind velocities. The mostly shallow coastal areas enable cost-efficient foundation and grid connection. However, the sea freezes annually introducing the most significant uncertainties in the support structure design for offshore wind turbines. The magnitude and time variation of sea ice load depends on various factors, like the thickness and velocity of the ice as well as the size and shape of the structure. A feasibility study of the FAST (fatigue, aerodynamics, structures and turbulence) simulation software was carried out investigating the structural performance of offshore wind turbines. Various load combinations and operation modes were studied by taking into account coupling between the ice, wind and structural response. Coupled modelling of ice–structure interaction is a necessary step in terms of cost-efficient structural design.

Application of Confidence Regions to Ice Ridge Keel Data Statistical Assessment

Sets of measurements of underwater ridge parts usually contain a limited amount of data. Outcomes need to be made while relying on small sample sizes. In this event, the chance of making inaccurate estimations increases.This paper proposes to use stochastic confidence regions in the estimation of the unknown parameters of keel depths. A model for a random variable with a lognormal distribution for keel depths is assumed. Regions for the mean and standard deviation of keel depths are obtained from Mood’s and minimum-area confidence regions for parameters of the normally distributed random variable. Conservative safety probability of non-exceeding the critical keel depth in one random interaction of the ridge with structure is estimated.An algorithm for statistically assessment of ice ridge keel data by means of confidence region building is here offered. The assessment of a set of ridge keel depths for the Gulf of Bothnia (Baltic Sea) is performed.Copyright