Study On The Hull Strength Calculation Method Of Semi-submersible Vessels In Load-out Operation

The rapid development of marine engineering equipment market haspresented a higher challenge to marine transport. Because theself-propelled semi-submersible vessel is especially suitable for thetransport of large marine engineering equipment due to its goodperformance, it has a good market now and in the foreseeable future.However, because of the high value and time cost of the largeequipment semi-submersible vessel usually carries, the technical difficultyof semi-submersible vessels, and the current lack of perfect rules forsemi-submersible vessels, starting from the hull strength, in order toensure security in operation of the semi-submersible vessel, as well aspromoting the development of specifications, it is necessary to carry out adetailed analysis of hull strength of the semi-submersible vesselconsidering the characteristics of semi-submersible vessels, and putforward a suitable semi-submersible vessel hull strength assessmentmethod. The main work contents and conclusions are listed as follows:(1) For the typical float-on and slip load-out patterns ofsemi-submersible vessels, analysis points out that the phenomenon ofcontact will redistribute the cargo load. And then the contact load iscalculated respectively by the theoretical method and the finite elementmethod. At last the impacts of stiffness of the support structures relative tothe cargo on the contact load are showed by finite element analysis. (2) The basic assumptions are firstly established according to thesemi-submersible vessels’ actual loading operations. Analysis followedshows that the dangerous state of the hull strength can be involved inseveral critical conditions, and therefore a key step in the strengthcalculation is to determine the dangerous working conditions in load-outoperations. Through qualitative and preliminary quantitative analysis,computing conditions have been developed in the paper forsemi-submersible vessel float-on and slip load-out (including sternload-out and side load-out).(3) Taking the process that a38,000DWT semi-submersible vesselfloating-on a15,000tons jack-up platform for an example, cargo-supporting structure-semi-submersible vessel finite element model isestablished, and the finite element analysis is developed in accordancewith the preliminarily developed float-on calculation conditions. Bycomparing and analysis of the calculation results, it is found that thesemi-submersible vessel hull strength proves to be the most dangerouswhen the cargo just lifted out of water and the vessel reaching its structuraldraft (or designated draft).