2 DOF System (Heave & Surge)

            The two degree of freedom (DOF) experiment is testing the oscillating cylinder that can move in streamwise (surge) as well as vertical (heave) direction. During March and May of 2023, we did experiments with the gantry system. We did test using the following wave amplitudes: 0.75in, 1.00in and 1.50in. We also had wave frequency varying from 0.4Hz to 1.3Hz. 

            Similar to the one DOF experiments, the cylinder is connected to the carriage through two DOF linear actuator system. Equipped on the cylinder are time synced feedback from force transducer, position encoders, and speed sensors, to identify the applied actuator force to match spring and damping forces for each trial. The cylinder is then placed at nominal depth h/D=0.7 and will oscillate in streamwise and vertical directions. Using this method, we are able to create a “virtual” spring and damper by motor force and can quickly be fixed using a software. The cylinder is then forced by incident, regular (constant frequency) wave produced by a dual flap wave maker w/ actively controlled motion feedback to compensate for wave reflection. By using the embedded force gauges on the cylinder, we can simultaneously measure the corresponding occurring two dimensional horizontal and vertical forces exerted on the cylinder. The power absorbed by the cylinder will be calculated by multiplying the cylinder’s streamwise and vertical velocity, measured by differentiating and filtering the position signal, and the force on the cylinder in the direction of motion, measured by embedding and water-proofed force gauges within the cylinder. The correlation between wave frequency and amplitude, immersion depth, cylinder streamwise and vertical velocity, cylinder radius, and the resulting absorbed energy will make it easier to achieve similar results to the control theoretical modeling of the fluid dynamics features that influence energy absorption by the oscillating horizontal cylinder.