Raúl Guanche

A wind chart to characterize potential offshore wind energy sites

Offshore wind industry needs to improve wind assessment in order to decrease the uncertainty associated to wind resource and its influence on financial requirements. Here, several features related to offshore wind resource assessment are discussed, such as input wind data, estimation of long-term and extreme wind statistics, the wind profile and climate variations.This work proposes an analytical method to characterize wind resource. Final product is a wind chart containing useful wind information that can be applied to any offshore sites. Using long-term time series of meteorological variables (e.g. wind speed and direction at different heights), the methodology is applied to five pilot sites in different countries along European Atlantic corridor and it is used to describe and compare offshore wind behavior.

Wave Interaction With Piled Structures: Application With IH-FOAM

This paper presents a numerical analysis of the interaction of waves with piles. A model called IH-FOAM, based on OpenFOAM®, is used. IH-FOAM is able to simulate and to absorb waves in three-dimensional domains, reducing the computational cost and extending the range of applicability of the CFD modelling to the study of offshore and coastal structures. In this work, a detailed analysis of mono and multi-piled structures is carried out. Several piles layouts are studied Wave run-up and forces have been studied for the multi-piled structures. Those magnitudes have been compared with the single piled structure pointing out the difference in the wave induced hydrodynamics and the non-linear interaction between the waves and the structures. The work contained in this paper presents a first step which will be extended in the future to analyse more complex layouts and the effects of broken waves.Copyright

Experimentally Calibrated Time-Domain Numerical Model for a Fixed OWC Device

Oscillating Water Column technology (OWC) is one of the most promising Wave energy Converter (WEC) technologies. Different OWC devices are nowadays under development: fixed or floating, with one or several chambers. The correct understanding and efficient modelling of the simple problem of a fixed detached OWC is the basis of all of them. For this aim, a combined numerical-experimental working methodology has been followed, since it is believed to be the only way to make a real step forward in this field. Due to the high economic and time costs of experimental and field testing, the use of reliable numerical models is essential, especially during the early stages of the development. For this purpose, numerical models need to be calibrated and validated based on experimental data, ensuring realistic tools for OWC analysis. Computational Fluid Dynamics (CFD) models are widely considered the best way to analyze the dynamics involved in the problem. However, these models are complex and high computational demanding and the accuracy they offer is not necessary for a first approximation to the problem. Therefore, a simplified and faster time-domain model was built for the first stages of WEC analysis.Copyright

Introducing marine climate variability into life cycle management of coastal and offshore structures

Coastal and offshore structures are subject to a life cycle process including several different phases. From the planning and design phase to the re-use or demolition phase marine climate information is extremely important to achieve cost effective functionality and technical quality. The complete life cycle may span over several decades what requires site-specific marine climate information at different time scales and including its natural variability. We present an integrated methodology to generate marine climate information relevant for life cycle management of coastal and offshore structures including short-term, seasonal, long-terms and very longterm information. An application of the methodology to a harbour is presented.

Methodology to Obtain the Life Cycle Mooring Loads on a Semisubmersible Wind Platform

Nowadays there are few methodologies related with the design of mooring systems for floating offshore wind platforms. The ones used until the moment are inherited from the oil and gas industry. Because of that, mooring loads may be incorrectly estimated. This study presents a validated methodology in order to estimate the loads of the moorings of offshore floating platforms along the life cycle of the structure.The methodology is based on an extensive laboratory test data base carried out in a wave basin of the University of Cantabria. The proposed methodology has been applied to a floating semisubmersible platform (similar to the one in Agucadoira by Principle Power).The methodology is composed by a few steps. The first step consist on the selection of the most representative sea states of a long term met-ocean data base through a selection technique named MDA (Maximum dissimilitude algorithm). Afterwards, mooring system loads and platform motion are numerically simulated. SESAM (DNV) numerical model has been used in this particular application. SESAM numerical model was previously calibrated based on the laboratory tests. Finally, based on a multidimensional interpolation technique named Radial Basis Function life cycle mooring system loads were reconstructed.A sensitivity analysis of the methodology were carried out. Based on it, it can be concluded that selecting 1000 sea states with the MaxDiss technique, life cycle mooring loads can be accurately predicted.Copyright

Analysis of the Geometric Tunability of a WEC From a Worldwide Perspective

Nowadays the goal of WEC developers is to reduce the price of the harvested energy for its own technology, via either decreasing the cost of WECs or increasing the power production. In order to increase the power production of a particular WEC, usually the WECs are tuned with the wave climate at the target location. However, in order to achieve the maximum profitability, the WECs must be able to be deployed in a bunch of locations with different wave climates. Therefore WECs must be flexible to be adapted to different kind of locations.The matchability of a device could be achieved via the PTO control or changing the geometric characteristics of a particular device. In this study, an analysis about how the geometric tuning of a generic wave energy converter affects to different climate scenarios is performed.Firstly, a generic wave energy converter is assumed to be formed by an array of floating cylinders that absorb in heave. Three options are proposed in the present study, a cylinder with its natural period on 4 s, typical of enclosed seas, another option with a natural period of 8 s (mean Atlantic swell) and an option that is tunable as a function of the location in order to evaluate the influence of tuning on the power performance.The power matrix is computed with a frequency domain model and then, the converters are evaluated worldwide, taking the met-ocean data from a global reanalysis database (GOW) from Reguero et al (2012). The results are presented in terms of two main indicators, on one hand, the capture width ratio, that evaluates the efficiency of the converter on each location, and the kW/Ton parameter that evaluates the efficiency of the converter on “economic” terms.Finally, tuning a converter for each location of deployment resulted positive in terms of capture width ratio, however regarding the kW/Ton indicator tuning resulted useless due to the heaviness of the structures needed to tune the converter with high peak periods. The number of suitable locations (in terms of an acceptable kW/Ton indicator) was higher as the mass of the structure is reduced, regardless of the natural period of the converter, thanks to a good performance of high natural periods converters.Copyright

Methodology for Performance Assessment of a Two-Body Heave Wave Energy Converter

A wave energy farm composed by several two-body heaving wave energy converters is being developed by IH Cantabria. This study presents a methodology to obtain the power performance of an isolated two-body heaving wave energy converter, previously presented and analyzed by [1]. The methodology relies on a numerical model which represents the motion of the two bodies in the time domain. This time domain model has been built substituting the entire Cummins equation system with a state-space system, thereby avoiding the convolution integral of the radiation force term with a state-space subsystem, previously used in [2] and [3].The performance of the device along its life cycle has been estimated based on a proposed new methodology. The new method is proposed in order to obtain the long term power production of a device with the same computational effort than the classical method based on the power matrix. The proposed method is able to estimate long term power production time series. This long time series is obtained using the MaxDiss selection technique from [4] in order to compute only the power of the most representative sea states and the Radial Basis Function interpolation technique (RBF) to obtain the complete power series.Copyright

Methodology for Integrated Socio-economic Assessment of Multi-use Offshore Platforms

This chapter presents the methodology employed for the Integrated Socio-Economic Assessment (MISEA) of different designs of Multi-Use Offshore Platforms (MUOPs). The methodology allows for the identification, the valuation and the assessment of the potential impacts and their magnitude. The analysis considers a number of feasible designs of MUOP investments, and the likely responses of those impacted by the investment project. The approach provides decision-makers with a valuable tool to assess whether a MUOP project increases the overall social welfare and hence should be undertaken. This is performed under alternative specifications regarding platform design, the discount rate and the stream of net benefits, if a Cost-Benefit Analysis (CBA) is to be followed or a sensitivity analysis of selected criteria in a Multi-Criteria Decision Analysis (MCDA) framework. The methodology can support the implementation of policies aiming at achieving a good environmental status of the EU’s marine waters and the protection of the resource base upon which marine-related economic and social activities depend.

Evaluation of Walk-to-Work Accessibility for a Floating Wind Turbine

There is a growing interest from offshore and energy industry towards floating wind turbines. Since these systems are exposed to harsh metocean conditions, accessibility for inspection and maintenance purposes becomes of primary importance for a safe and cost-effective long-term operation.It is here proposed a methodology for evaluating the accessibility of a floating wind platform, by means of walk-to-work vessels.Two access means are considered: a catamaran equipped with fender and an offshore supply vessels with a motion-compensated gangway. The system composed by the platform and the vessel is modelled as a constrained multi-body system in the frequency domain. This allows to calculate transfer functions for the vessel motions and the contact forces.For given a short-term sea state the maximum crest height of a response variable is calculated assuming that crests heights are Rayleigh distributed, and compared to some threshold to determine whether the platform is accessible or not. For the catamaran, access is possible when the fender does not slip against the landing structure mounted on the floating platform; for the supply vessel, when the relative motions at the gangway tip do not exceed the compensation limits of the hydraulic system. Accessibility is calculated for a sample semisubmersible wind turbine located off the coast of Portugal using hindcast data for the period 1980–2013. Findings indicate that the catamaran and the supply vessel can ensure access for 20% and 76% of the time respectively. However, results are strictly dependent on the vessel types and the walk-to-work constraints.Copyright

Location Targeting for Wave Energy Deployment From an Operation and Maintenance Perspective

When looking for a location for a wave energy converter (WEC) installation, developers usually look for sites with high or very high wave energy resource. From this perspective, countries like Scotland or Ireland have made great effort to include this energy source in their energy mix due to their expected high untapped potential. However, higher resource carries marine operation restrictions. Because of that, the selection of a site for a WEC deployment, the installation, operation and maintenance factors have to be considered from the beginning.In this work an analysis of the suitable locations for the development of wave energy is performed based on the operation and maintenance (O&M) parameters. This study is performed across the globe coastlines taking the met-ocean climate data from Reguero et al (2011) global reanalysis database (GOW) developed at IH Cantabria.Firstly, an analysis of the global availability and accessibility levels is performed all around the globe taking different wave height thresholds into account. Seven specific locations (North-West Denmark, West of Ireland, Chile, North of Spain, West Portugal, South-West Australia and North of Scotland) with high interest on wave energy have been further analyzed and compared.Secondly, the O&M access limits are quantified in terms of the weather windows and the waiting period between available weather windows. A statistical analysis of these parameters is performed within different weather windows lengths (6 h, 12 h and 24 h). The seasonality of these parameters is also analyzed. Finally, a failure analysis will be carried out, simulating the repair operation along the lifecycle of the device for different failure rates and waiting times. The affection of this failure and repair scheme over the power production of a device analyzed previously in Andres et al (2014) will be presented.In this study, some locations with high resource (Spain, Nova Scotia) lead to medium to high accessibilities/availabilities due to the balance between resource and persistence of the weather conditions. Some locations with high resource such as Chile or Australia resulted inaccessible during very long periods of time due to the persistence of severe conditions and then not very recommended for novel converters with uncertain failure rates.Copyright