Abstract
Harnessing wave energy is a new concept that requires the development of new technologies able to extract energy from the waves and transmit it to the shore. A large number of technologies are proposed and given the complexity of the task and the high cost of offshore work, a staged development path is required involving indoor and offshore testing at various scales. This offers a large reduction in the development costs of device testing in hydrodynamic facilities and low energy offshore test sites. This leads to the validation of the operation principle, verification of numerical model result, model optimisation, operation training, etc.
In order to ensure the reduced scale provides an accurate representation of the full scale model, a number of techniques can be applied. Two main scaling methods, called Froude and Reynolds, are commonly used for the scaling of hydrodynamic structures. The full design of a scaled model must follow the chosen scaling method and be chosen taking into account suitable materials which can vary with the scales.
This document aims at reviewing the techniques used for scaling, designing and building models for the best representation of the full scale prototype characteristics in controlled ocean test facilities. It provides a description of the full scale prototype characteristics and the scaling methods available. It then provides useful information on the design techniques and the last section concentrates on the verification methods to assess the quality of the model built. This work is based on experience from MARINET partners and documents such as (Grégory S. Payne 2009), (Luís Mallen, D2.13, Collation of model construction methods 2012) and (ITTC 2014).
The most common scaling method for WEC testing is using the Froude similitude explained in this document and the most appropriate scale depends mainly on the stage of development of the device, the equipment available and related costs. When the approximate scale is chosen, the characteristics of the deployment location and/or the material cost and availability may be used to select the final modelling scale.
For the model design, at the chosen scale, a large number of parameters are presented in this report and must be taken into account. It includes the test objectives (optimisation or validation), characteristics of the materials and instrumentation available. All the design parameters must be accurately set and measured in order to ensure repeatability of the results at all scales of testing. This document also suggests and describes a number of verification methods for the most commonly used parameters, weight and weight distribution, power take off systems, instrumentation and mooring lines.
Although the weight and weight distribution is a critical part in the design and construction of floating or underwater models in motion, this is not relevant for the modelling of fixed devices.