Structural design of a level-luffing crane through trajectory optimization and strength-based size optimization

The present study explores the trajectory optimization of a double-rocker four-bar mechanism to minimize the amplitude of its trajectory. A numerical model of the levelluffing crane (LLC) is first developed to describe the trajectory mechanism, and the optimal trajectory is then identified after selecting dominant design variables in the context of design of experiments. The numerical optimization solution obtained is compared with measured data. The optimized trajectory design is then applied to the strengthbased deterministic optimization (DO) to minimize the weight of a double-rocker structure under the constraints of stress and deflection. To carry out approximate optimization, a response surface method based on a second-order polynomial is used. Due to the existence of design uncertainties in an actual environment, reliability based design optimization (RBDO) is explored to assess the probabilities of failure in stress and deflection. For the design safety, DO and RBDO solutions are evaluated under severe loading conditions.