## 1 Introduction  
Accurate numerical models of physical systems are vital resources for the design and optimization of complex systems. They aid in understanding the effects on the system before undergoing physical design changes or implementing ideas such as new control strategies. Although many studies have validated wave energy converter (WEC) numerical models against scaled prototype experimental data, there remains a notable lack of validation using data from full-scale deployed WECs. A summary of studies with WEC validation against numerical analyses, real sea data, and mooring systems is presented in [1], where the authors note that not only are there a limited number of WECs that have been deployed at full-scale, but the measured data from them are typically not publicly available. To address this gap, two numerical models have been developed that represent Monterey Bay Aquarium Research Institute's Wave Energy Converter, the _MBARI-WEC_, which has been operating for six-month periods since 2014 [2].  
The MBARI-WEC is a two-body point absorber consisting of a surface buoy and a submerged heave cone connected together by an electro-hydraulic power take-off (PTO) system as shown in Figure 1. The relative heave motion between the surface buoy and heave cone actuates the PTO piston, driving a hydraulic motor directly coupled to an electric motor/generator. The electric power generated is transmitted to a battery or a load dump heater if the batteries cannot accept the power. Battery power can be utilized on-board for sensors, data acquisition, data logging, data transmission, and auxiliary systems.  
An air spring provides a restoring force against the weight of the heave cone. The heave cone doors can open and close to alter the system's drag in the event of severe sea states. See [3] for further device description, as well as [4] for more details regarding the PTO design and operation.  
Two numerical models of the MBARI-WEC are considered in this study, and it is important to note that the fundamental nature of the two models are different, as described below. One model was created using _WEC-Sim_, Wave Energy Converter Simulator, utilizing Matlab, Simulink, and Simscape Multibody [5]. This model is a combination of two individual numerical models, the hydrodynamics and the PTO system, and is intended to serve as a component-based model of the MBARI-WEC as its inputs are derived from data or specifications of the physical system. A second numerical model for the MBARI-WEC was developed as a software interface project using the ROS 2 (Robotic Operating System) framework [6] and _Gazebo_ as the simulation environment [7]. ROS 2 serves as the software platform in both the _Gazebo_ model and the physical MBARI-WEC hardware, therefore using ROS 2 features in simulation is identical to coding interactions with the physical system. The _Gazebo_ model is intended to be used as a digital twin of the MBARI-WEC, allowing users to work with the same interface as the real hardware and develop and test their work before deployment on the real system [2]. The goal of this paper was to analyze the accuracy of the _WEC-Sim_ and _Gazebo_ models when comparing the field data recorded by the MBARI-WEC to the outputs, thus providing insight into the trade-offs and benefits between the use of one model over the other. These parameters were obtained via a Sofar Spotter buoy and data being reported from the MBARI-WEC itself.  
Figure 1: The MBARI-WEC portrayed in _Gazebo_. Labeled from top to bottom are the surface buoy, PTO, tether, and heave cone. Relative motion between the surface buoy and heave cone actuate the PTO piston which drives a hydraulic/electric motor. An air spring driven by the piston provides the necessary restoring force.