A kind of catamaran crane with hoisting truss as connecting bridge structure has recently emerged on Qiantang River due to the prominent requirement of lifting and salvage in inland river and the difficulty of ship repair imposed by the situation of more ships than factories. The strength check of this new structure that is beyond the rules is a new problem in the ship inspection and certification. On the basis of relevant specifications, the analysis methods of the total longitudinal and local strength, total transverse and torsional strength, hoisting truss strength and supporting structure strength for this type of ship are presented and applied to the structural analysis of a 700 t crane ship. This method can be applied to the design and check of the same type of ship.

The topology optimization method can find the best path of the load transmission and the best type of the load bearing on the premise of ensuring the requirements of the design specifications. The compromise programming method is a method commonly used in the topology optimization deign of the structure under multiple operating conditions. However, the designers need to perform topology optimization trial calculations under different volume fraction constraints during the topology optimization design, which often costs more time. An improved compromise programming method is then proposed to save time. The multi-operating-condition topology optimization design is carried out for the longitudinal frame of a cantilever platform in the offshore engineering structure based on the secondary development of the HyperMesh software. A clear longitudinal frame configuration is given from the perspective of structural design according to the final topology optimization configuration.