Of the cost centres that combine to result in Levelised Cost of Energy (LCOE), O&M costs play a significant part. Several developers have calculated component costs, demonstrating how they can become commercially competitive with other forms of renewable energy. However, there are uncertainties relating to the O&M figures that can only be reduced through lessons learned at sea. This work presents an O&M model calibrated with data from real sea experience of a wave energy device deployed at the Biscay Marine energy Platform (BiMEP): the OPERA O&M Model. Two additional case studies, utilising two other O&M calculation methodologies, are presented for comparison with the OPERA O&M Model. The second case study assumes the inexistence of an O&M model, utilising a Simplified Approach. The third case study applies DTOcean’s (a design tool for ocean energy arrays) O&M module. The results illustrate the potential advantages of utilising real sea data for the calibration and development of an O&M model. The Simplified Approach was observed to overestimate LCOE when compared to the OPERA O&M Model. This work also shows that O&M models can be used for the definition of optimal maintenance plans to assist with OPEX reduction.
The behavior of a subsea pipeline when submitted to external loads is governed by the well predictable physical properties of the pipe and the not-so-well predictable pipe-soil interaction behavior. Understanding of the pipe-soil interaction behavior has advanced over the last years, however, the level of uncertainty in the available models is still high.
This paper presents a series of detailed two-dimensional nonlinear finite element analyses investigating the soil resistance to pipeline lateral displacement. Parametric analyses were used to compare the influence of some important parameters such as the maximum (breakout) resistance, initial stiffness and mobilization displacements for example. Results are compared to the analytical models proposed by Verley, Lund and Bruton [1,2].
The results revealed some aspects not foreseen by the analytical models: The displacement under which the maximum lateral load is mobilized is not straightforwardly linked to the pipeline diameter, as some authors would say; the embedment seems to play a much more important role than the diameter itself in the maximum force derivation. Some other results are discussed through the paper and the main findings are listed in the conclusions.
The assessment of the pipe-soil interaction is an area of continuous research, either by the application of small- and full-scale tests in the attempt to reproduce accurately the interaction of the pipelines and the soil, or by the development of sophisticated numerical simulation models accounting for different sources of nonlinearities.
Motivated to investigate the interaction between subsea pipelines and the soil, with focus in the response under lateral loading, 2-D finite element numerical simulations have been developed applying soil plasticity mechanisms through the extended maximum distortion strain energy criteria [1] and critical state concept [2]. The modified-cam-clay MCC model has been adopted to simulate the soil behavior in large deformations, aiming to numerically reproduce site conditions for selected pipelines ranging from 12 in to 18 in.
The results are presented in terms of the lateral force-displacement curves for numerically representative drained and undrained cases. For the simulations investigated in this work, the agreement of the numerical results with the analytical breakout lateral resistances obtained from the SAFEBUCK guideline [3] formulations have been confirmed for cases where the ratio of initial pipe embedment and pipe diameter is below 0.4.
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