When targeting substantial, potentially dominant optimisation and cost reduction, the categories that contribute the most to the overall techno-economic viability of a wave energy converter (WEC) are of a particular interest.
Overall, the main structure and power take-off system are widely recognised as the main contributors to the Levelised Cost of Energy (LCOE) and the devices’ capital expenditure (CAPEX). The creation of a testing platform addressing the key subsystems of all WEC types and standardised testing procedures is therefore essential for accelerating the devices’ development and reducing their cost.
Drivetrain test rig
The drivetrain rig tests the entire drivetrain of a wave energy converter (WEC), from the input mechanical power to the output electrical, grid-compliant power. This conversion chain includes the following subsystems:
- mechanical drives (gearbox, ball/roller/lead screw, rack-pinion, belt pulley, slider-crank, sprocket chain),
- electrical generators,
- power converters,
- storage systems,
- grid interface units, and
- the control system.
The drivetrain test rig is able to provide either linear or rotary input power with a flexible set-up, in order to adapt the load-speed ratio of the actuation systems to the ones of the device under test.
| Unit | Rated | Peak | |
| Power | kW | 180 | 290 |
| Torque (shaft direct connection) | Nm | 5200 | 8400 |
| Speed (shaft direct connection) | rpm | 330 | 680 |
| Stroke | mm | 4000 | |
The rig can also be used in a hardware-in-the-loop (HIL) setup to emulate the interaction of the subsystem/component under test with the rest of the WEC.
Structural components test rig
The structural components test rig tests several wave energy converter components/subsystems:
- Structural components (as part of the hull),
- Mechanical interfaces,
- Power cables, and
- Sealing systems.
The structural components test rig can actuate one linear degree of freedom at one end and up to five degrees of freedom at the other end (three linear and two rotary). Thanks to the test cell, loads, bending moments and torque can be provided by on-purpose arrangements according to the load application.
Environmental conditions can be replicated by submerging the test sample in synthetic sea water. These features allow for the dynamic testing of large-scale components with realistic motions or loads in a wet environment.
| Unit | Value | |
| Linear actuator peak force | kN | 800 |
| Linear actuator stroke | mm | 500 |
| Bending moment | kNm | 10 |
| Angular displacement | ° | ±40 |
| Test cell inner size | mm | 1450x1250x(h)2500 |
The rig can also be used in a HIL setup to emulate the interaction of the subsystem/component under test with the rest of the WEC.
Novel testing methodologies
The IMPACT consortium has conceptualised a methodological framework that is composed of three layers of different “building blocks”. These consist of:
As an example, the following animation illustrates the building blocks applicable to a Performance test – specifically, to Design Load Case (DLC) 1.1 i.e. Power Generation.
At a high level, accelerated testing aims to assess key metrics related to different evaluation areas of a WEC – e.g. Performance, Reliability or Survivability – in a reduced amount of time. Therefore, two different accelerated testing strategies may essentially be conceived:
In general, QualAT aims to identify and characterise failure profiles by adopting a qualitative approach. Most often, the load applied in QualAT is not directly related to the environmental conditions that the component/subsystem under test will experience in an ocean deployment. Instead, it builds on mapping a range of input conditions that may affect the failure phenomenon.
QuanAT aims to quantify the failure time and/or degradation pattern of the component/subsystem under test at typical usage levels. For example, QuanAT may aim to assess the damage levels, e.g. fatigue, faster than real time, by employing a range of techniques, such as load or resistance manipulation, or by using proxies of the environmental conditions.
