Optimal design and performance analysis of a hybrid system combing a floating wind platform and wave energy converters

•Combined floating platform and WECs system can provide a cost-effective solution.•An accurate method is developed to optimize size and layout of WECs on a platform.•Larger WECs capture more wave energy in a limited region and a specific sea state.•Added WECs reduce the maximum horizontal force and pitch moment on the platform.•The synergy between wave and wind energy utilization on floating platform is shown.