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The total instantaneous energy transport can be found for polychromatic waves when using the deep water approximation. Expanding this theory to waves in waters of finite depth, we derive an expression for the total instantaneous energy transport for polychromatic fluid gravity waves based on potential theory with linearized free surface boundary conditions. We present the results for time series of wave elevation measured at the Uppsala University wave energy research test site. We show that a significant proportion of the total instantaneous energy transport is not accounted for when using the deep water theory. This is important since many wave energy conversion devices under development will operate in waters that do not fulfil the deep water criteria.

In many wave energy concepts, power output in the MW range requires the simultaneous operation of many wave energy converters. In particular, this is true for small point-absorbers, where a wave energy farm may contain several hundred devices. The total performance of the farm is affected by the hydrodynamic interactions between the individual devices, and reliable tools that can model full farms are needed to study power output and find optimal design parameters. This paper presents a novel method to model the hydrodynamic interactions and power output of very large wave energy farms. The method is based on analytical multiple scattering theory and uses time series of irregular wave amplitudes to compute the instantaneous power of each device. An interaction distance cut-off is introduced to improve the computational cost with acceptable accuracy. As an application of the method, wave energy farms with over 100 devices are studied in the MW range using one month of wave data measured at an off-shore site.

The investigation of various aspects of the wave climate at a wave energy test site is essential for the development of reliable and efficient wave energy conversion technology. This paper presents studies of the wave climate based on nine years of wave observations from the 2005–2013 period measured with a wave measurement buoy at the Lysekil wave energy test site located off the west coast of Sweden. A detailed analysis of the wave statistics is investigated to reveal the characteristics of the wave climate at this specific test site. The long-term extreme waves are estimated from applying the Peak over Threshold (POT) method on the measured wave data. The significant wave height and the maximum wave height at the test site for different return periods are also compared. In this study, a new approach using a mixed-distribution model is proposed to describe the long-term behavior of the significant wave height and it shows an impressive goodness of fit to wave data from the test site. The mixed-distribution model is also applied to measured wave data from four other sites and it provides an illustration of the general applicability of the proposed model. The methodologies used in this paper can be applied to general wave climate analysis of wave energy test sites to estimate extreme waves for the survivability assessment of wave energy converters and characterize the long wave climate to forecast the wave energy resource of the test sites and the energy production of the wave energy converters.

This paper presents design studies of the gravity-based foundation for a linear generator wave energy converter. The wave energy converter is based on a direct driven generator mounted on the gravity-based foundation located at the seabed. The linear generator is connected to a point absorbing buoy on the sea surface via a connection rope. Such a device, developed at Uppsala University, has been in operation on the Swedish west coast since 2006. Study is focused on the analysis of the impact from undesirable motions of the gravity-based foundation, particularly the study of the tip and lifts phenomena with regard to the heave and surge forces. Long-term extreme significant wave heights are extrapolated from the statistical analysis of the measured wave climate data in the test site where the wave energy converter is deployed. The joint distribution of the significant wave height and the zero-crossing period from the measured wave climate is also analyzed to estimate the associated periods with respect to the long-term extreme significant wave height. The 25 years return extreme significant wave height 4.8 m which is associated with its mean zero-crossing period 8.25 s from the joint distribution is chosen to determine the characteristics of the possible maximum wave for the Lysekil test site. The estimated maximum wave 9.2 m is used to estimate the extreme values of the heave and surge forces on the wave energy converter and the gravity-based foundation. The results with respect to the foundation of a new generation wave energy converter about 35 tons with the presented methodology indicate that a heavier foundation which is about 70 tons needs to be designed in terms of considering the stability of the mooring foundation for long term real sea operation. The purpose of this paper is to propose a reliable approach to estimate the appropriate dimensions for gravity-based foundation of the linear generator wave energy converter and provides a theoretical reference to the construction of the gravity-based foundation.