Measuring energy dissipation rates in a wave tank

The effectiveness of dispersants is typically evaluated at various scales ranging from the smallest (10 cm, typical of flask tests in the laboratory) to the largest (10's to 100's of meters, typical of field scale open water dispersion tests). This study aims at evaluating dispersant effectiveness at intermediate or pilot scale. The hypothesis is that the energy dissipation rate per unit mass, ε, plays a major role in the effectiveness of a dispersant. Therefore, it is stipulated that in fairly general conditions, conservation ε between the wave tank scale and that of the field scale is sufficient to accurately evaluate the effectiveness of a dispersant to disperse oil droplets. A wave tank measuring 16 m long × 0.6 m wide × 2 m deep was constructed on the premises of the Bedford Institute of Oceanography, Halifax, Nova Scotia. Waves were generated using a flap-type wavemaker. Conditions of the breaking waves were created using a dispersive focusing technique in which the wave maker is started at high frequency and then the frequency decreased to create breaking waves. Experiments defining the velocity profile and energy dissipation rates in the wave tank were conducted at 2 different induced breaking-wave energies. Energy in the wave tank was measured with an Acoustic Doppler Velocimeter (ADV) coupled to a data acquisition system. Energy in the lab flasks was measured with a Hot Wire Anemometer.