Experimental Validation of a Real-Time Hybrid Mooring System for Wave Energy Systems Using a Linear Test Bed

Abstract

As wave energy continues to emerge as a viable renewable energy source, the need for accurate and scalable testing of wave energy converters (WECs) becomes increasingly important. Wave tank testing is a standard approach for validating scaled models of WECs. However, replicating the forces and dynamics of real-world mooring systems at laboratory scale remains a significant challenge. While physical geometries of WECs can be scaled with relative ease, traditional methods for simulating mooring forces—such as using springs—fail to capture the nonlinear and dynamic behaviors of full-scale mooring systems. These methods are also unsuitable for replicating complex configurations, such as catenary moorings, or demonstrating critical failure events like line breakage.

To address these limitations, a novel hybrid simulation approach is proposed. This method integrates hardware-in-the-loop testing with MoorDyn, an open-source lumped-mass model for simulating mooring dynamics in marine structures. The hybrid simulation loop works by sending displacement data from a physical model to MoorDyn. MoorDyn then reads the displacement data and calculates the instantaneous mooring force for a full-depth mooring line. This mooring force is then sent back to the experimental setup where actuators will apply the full-depth mooring force to the experimental model. This process repeats for each time step so that the physical experiment experiences full-depth mooring forces throughout the run. Unlike simpler methods of simulating mooring lines, MoorDyn is able to replicate realistic nonlinear dynamics of mooring lines. Early-stage testing will be conducted on a linear test bed to validate the hybrid simulation system's single degree-of-freedom response, including system communication, computational speed, and motor reactivity. These tests lay the foundation for the system’s application in more complex wave tank environments.

Real-time hybrid simulation systems have shown feasible computational speed for experimental testing of marine energy technology. However, the application of MoorDyn in hardware-in-the-loop setups remains relatively unexplored in the wave energy sector. This research represents a critical step toward validating the potential of a hybrid simulation system utilizing MoorDyn. Time-accurate results from the linear test bed will confirm the viability of this approach as an analog for equivalent wave tank testing, paving the way for broader adoption in the field.

The hybrid simulation system offers significant opportunities for advancing WEC mooring design. By enabling the testing of advanced mooring systems—including those with nonlinear characteristics and configurations intended for extreme conditions—hybrid simulation will facilitate optimal mooring designs for diverse deployment scenarios. This approach could lead to cost savings in WEC design and testing while improving environmental outcomes by streamlining the development of wave energy technologies. Looking forward, hybrid simulation has the potential to become a standard tool for marine energy developers, driving innovation and supporting the growth of the wave energy industry.