In the last decades, renewable energies gained an increasing interest due to the environmental awareness of people, especially in the developed countries. Moreover sustainable resources represent a long-term investment full of possibilities of use.
In the Netherlands a technology which is getting more and more popular to produce green energy is represented by offshore wind turbines (OWT). However, during the installation of the structural elements for these systems, the risk of noise pollution and animal harm is an issue that has to be considered.
Previous works developed models to predict the noise emission and propagation during the construction phase, however the uncertainty related to the environmental properties has not been yet fully investigated.
Since the model characteristics are uncertain, so will be the prediction of the noise.
This thesis aims to fill this gap, investigating in the underwater soil property uncertainties and the resulting variation in sound predictions. The main goal of this work is to settle a sounding methodology to model the soil characteristics and interpret the sound levels.
In the first part of this work, the soil uncertainties are treated.
A framework on how to use measurements from cone penetration tests (CPT) and obtain mechanical and dynamic soil features is presented.
By means of statistical approaches, the procedure to define the optimal depth for different homogeneous layers (given the software used for the noise prediction) is described. Another topic dealt with is the definition of proper characteristic distributions and the choice of the optimal one representing the available empirical measurements.
Finally a procedure to generate random samples for the analyses that will follow is shown.
An important feature presented is the use of the correlation between the properties to define copulas. The samples then are not completely random and independent, but instead combinations that are more likely to appear are obtained.
In the second part, the results of several analyses are presented.
The steps to treat the sound levels and obtain the probability density (and cumulative) distributions are discussed. These results will help in estimating the probability of exceeding a particular defined sound level.
With this information, additional measures and precautions, as noise barriers, may be adopted in the installation of the pile to prevent exceeding the threshold.
The correlation between soil properties and obtained sound levels is investigated, in order to highlight if there are soil properties that greatly affect the outcomes.
The insight obtained may help in determining which particular features need a careful estimation, both by more accurate measurements or new techniques. Another benefit related to the detection of parameters not affecting significantly the sound levels, is the reduction of simulations necessary to cover enough combinations. That is because if a property
can be neglected in the generation of samples and be taken as a fixed value, less combinations are needed to be considered.
Finally, a comparison between the obtained estimations and empirical measurements in the North Sea is made, to test the validity of the framework proposed.