Hybrid wave-wind energy converters are considered an innovative solution to decrease costs in the various phases of installation and operation and lead to a lower Levelized Cost of Energy. Currently, there are different concepts in various Technology Readiness Levels. This paper provides a comprehensive review of existing wave-wind energy converters and the possible nonlinear dynamic assessment tools along with a discussion on their advantages and limitations. This paper broadly reviews and highlights the current level of understanding and knowledge of the relevant phenomena and their effects on the dynamic response of the existing concepts. The synergies between wind and wave energy -converters are discussed and key points for their future research and development are provided. It is shown that more than 60 % of studies are linear based which cannot reflect the highly nonlinear dynamic interaction between multi-bodies. It is demonstrated that the current lack of accurate simulation tools can be compensated by the proposed multilevel micro–macro modelling. This novel approach will allow representing the involved physical phenomena in the simulation of hybrid concepts taking into account the known limitations and lessons learned from the development of single or hybrid concepts and the simulation tools.@en

Generally, it is expected that the total power of N energy converters in an array will be less than N times the power of a single operative converter. The goal of this paper is to enhance the oscillation of the flap-type WEC and consequently the energy extraction of the whole array in front of a coastal structure. Flaps in an array show different response patterns in terms of amplitude and frequency based on their dynamic characteristics, incoming wave frequencies, and the distance between the WECs. Through this work, different dynamic characteristics for each flap in combination with various distances between proximate flaps are investigated. An experimentally validated numerical model developed for the simulation of flap-type WEC operating as single and in an array is used for the simulation. The effects of dynamic characteristics and WEC distances on the response and power production are estimated and discussed in detail for a flap operating in an array of two and five. It is shown that by changing the distance between two flaps, the response is enhanced up to 20%. The findings suggest the most efficient ratio of dynamic characteristics of flaps in an array of two is having a period half to the incoming wave period. However, for an array of five, having staggered flaps with a period equal to the incoming wave period make a 4% increase in the overall response of each flap.@en

The process of finding values of extreme waves and their impacts on wave energy converter (WEC) responses, depends on both wave resources and WEC dynamic characteristics. A wide range of waves can influence the reliability of operation and survivability of a WEC. In this paper, a methodology is described to find specific values of wave heights and periods that can be critical for a flap-type WEC, through the use of an integrated wave-structure approach.The goodness of the fit is studied and the corresponding return periods for ranges that a selected WEC is mostly operating are evaluated. Further discussions for engineering applications and making a clear understanding of the extreme and operational conditions of the WEC are also provided. The critical wave characteristics are defined based on power production and the significant change in the nonlinear dynamic behavior of the device in various ranges.The WEC behavior is represented by an experimentally validated numerical tool considering the nonlinear behaviour of a flap as single and in an array. The study aims to provide insights in the expected behavior and loading on the WEC,affecting its reliability, considering potential catastrophic wave return values that correspond to their power production phase.The finding can be used for determining both efficient operations and limiting environmental conditions or weather windows.@en

Faults in complex systems such as Wave Energy Converters (WECs) are inevitable. WECs are expected to work in harsh environments to produce more power which increases the possibility of major failures. Increasing the reliability of WECs calls for the development of early Fault Detection (FD) algorithms which needs understanding of the enormous modes of failures to prevent the costly downtime of the device. Through this work, a methodology is provided to simulate the effect of malfunction with various levels of complexity dependent on time and velocity of the WEC. The fault signals are applied to an experimentally validated model of an array of flap-type WECs. The assumed failures range from the delayed responses to the complete blocked hinge. It is shown that even a signal of soft fault with 7% change in the response amplitude can change the period of the system. These changes are investigated for the development of a general FD algorithm for WECs.@en

In this paper, we assess numerically the loads applied on PAs of optimally-arranged linear arrays in front of a bottom-mounted vertical wall of finite length under normal operating conditions. The arrays, maximizing the yearly absorbed energy, consist of five, identical, oblate spheroidal heaving PAs and are deployed at three near-shore sites in the Aegean Sea, Greece. The PAs are assumed to be attached on the wall via connection configurations restraining all rigid-body modes except heave. A spectral analysis is performed to quantify loads. The corresponding transfer functions are obtained from a frequency-based hydrodynamic model that solves the diffraction/radiation problem of the multi-body arrangement in the presence of the wall. Results, focusing on surge and sway restraining loads, are, initially, presented for regular waves and, then, for normal operating conditions (irregular waves), highlighting the effect of the arrays’ layouts and of the local wave conditions on the restraining loads. Comparison is also made with equally-spaced arrays to reveal potential positive effects of optimum layouts on structural integrity related issues.@en