The TUPPERWAVE project is supported by the European Commission’s OceanEraNet program. It aims to design and validate an innovative Oscillating Water Column (OWC) Power Take-Off (PTO) concept at laboratory scale. A conventional OWC typically generates a highly fluctuating bidirectional air flow through a self-rectifying turbine. To reduce the pneumatic power fluctuations through the turbine and the acoustic impact and ultimately increase the device efficiency, the TUPPERWAVE concept generates unidirectional air flow in a closed circuit, which can be converted into electricity via a conventional, high efficiency, unidirectional turbine. The principle is based on the use of a pair of non-return valves, two additional chambers above the water column and a unidirectional turbine harnessing energy from the resulting air flow between the two chambers. The concept was adapted to a floating axisymmetric structure. Numerical time-domain models have been developed by UCC and WavEC to determine the device’s primary conversion from hydrodynamic to pneumatic power. Comparison of the output from the two models showed good agreement and allowed an initial optimization of the PTO main design parameters. A set of design parameters were chosen which maximize the pneumatic average power output flowing through the turbine whilst minimizing the power fluctuations, in regular and irregular sea states. When compared to a conventional OWC with the same structure geometry, the optimised Tupperwave device was shown to produce similar pneumatic average power with much lower fluctuations.