Nylon fibre rope moorings for wave energy converters
The wave energy market has traditionally employed mooring concepts adopted from the mature technology of the oil and gas industry. However, this approach may not always be appropriate to satisfy the particular requirements of Wave Energy Converter (WEC) mooring systems, especially the need for very compliant moorings. Specific challenges are: the huge 1st order motion induced forces generated by storm waves in shallow water; the potential for slack-snap loading on a mooring; and, the fatigue performance of the mooring components. This paper describes the benefits of employing high compliance fibre rope in mooring systems of less than 100 m water depth. Nylon fibre ropes are a very attractive proposition because of their low modulus and cost but have previously been thought to have a poor wet fatigue performance. A specially designed long-lay-length Superline subrope has been tested both for compliance and for wet fatigue performance. The rope compliance is about twice that of parallel-subrope construction polyester rope. The fatigue performance is less than that of parallel-subrope polyester rope but is comparable to that of conventional construction polyester rope and to that of the chain and steel wire ropes which must also be used as mooring components. The high compliance of the nylon subrope construction together with the more than adequate fatigue performance demonstrated in this study qualify such nylon ropes as ideal for WEC mooring systems.
Validation of a Tool for the Initial Dynamic Design of Mooring Systems for Large Floating Wave Energy Converters
Mooring of floating wave energy converters is an important topic in renewable research since it highly influences the overall cost of the wave energy converter and thereby the cost of energy. In addition, several wave energy converter failures have been observed due to insufficient mooring systems. When designing these systems, it is necessary to ensure the applicability of the design tool and to establish an understanding of the error between model and prototype. The present paper presents the outcome of an experimental test campaign and construction of a numerical model using the open-source boundary element method code NEMOH and the commercial time-domain mooring analysis tool OrcaFlex. The work used the wind/wave energy converter Floating Power Plant as a case study, which is defined as a large floating structure with a passive mooring system. The investigated mooring consists of a three-legged turret system with synthetic lines, and it was tested for both operational and extreme events. In order to understand the difference between the model and experimental results, no tuning of the model was done, besides adding drag elements with values found from a simplified methodology. This resembles initial design cases where no experimental data are available. Generally good agreement was found for the tensions in the lines when the drag element was applied, with some overestimation of the motions. The main cause of difference was found to be underestimation of linear damping. A model was tested with additional linear damping, and it illustrated that a final analysis needs to use experimental data to achieve the best results. However, the analyses showed that the investigated model can be used without tuning in initial investigations of mooring systems, and it is expected that this approach can be applied to other similar systems.
Frequency selective surface design for blinds applications
In this paper, the reconfigurable blind structure with frequency selective surfaces(FSS) for the building applications are presented. Frequency transmission characteristics for different angles of the proposed blind-FSSs are investigated and verified through simulation and measurement. The simulation results show that we can implement the reconfigurable blind-FSS for multiband wireless applications. To verify the proposed paper, two kinds of blind-FSSs, crossed dipole FSS and circular ring FSS are fabricated and measurements are performed for different angles. The proposed structure in this paper which is very simple, can be easily applied to any planar surface for wireless security applications at low cost.