Force-Based Real-Time Hybrid Testing: Force Actuation System

Real-time hybrid model testing is the name given to the real-time coupling of experimental and numerical testing methods. It is based on dividing complex structures into two system parts; one that is simulated numerically, and one that is tested physically. The two systems will interact in real-time through a network of sensors and actuators. This exploits the advantages of numerical simulation while still capturing the most uncertain physical phenomena by physical testing. For real-time hybrid model testing in ocean engineering, forces that are not properly reconstructed physically are simulated numerically and applied to the physical part using actuators. A force-actuation system for use in real-time hybrid model testing is developed. The force-actuation system consists of a position controlled DC-servomotor, torque spring, wheel, and wire. Fast and accurate actuation of forces on moving structures is needed, and challenges related to this type of actuation are discussed. Time delays, actuator dynamics, and process noise are some of the main challenges. Identification of the force actuation system is done to evaluate the performance. The control algorithm consists of a feedforward controller, exploiting the linear stiffness properties of the torque spring, and a feedback PI controller compensating for uncertainties in the model. An analysis of the actuation system and force controller is carried out. The system show limited performance, mainly because of time delays and inadequate performance of the actuator.