A Study On The Performance Of Leg Mating Unit

As offshore oil and gas exploit is developing to a brand new stage,there will be more and more large offshore platforms being built. This willleads to a much more widely use of float-over installation of large offshoreplatforms. Leg mating unit, LMU for short, acting as the key factor of thefloat-over installation process, will for sure appear in most of the platforms.Thus, researching in performance of LMU and mastering the developingtechnology of that will be of great significance in development of oceanengineering technology of our country.In this thesis, firstly, the key technology of float-over installation wasintroduced. The summary of current situation of research and utilization infloat-over installation was shown. The structure of LMU and currentsituation of research in that was stated.Secondly, the basic theory and methods used in this thesis wasintroduced. ABAQUS, the non-linear finite element software, was used tobuild the FE model and Explicit modulus was used for quasi-static analysis.The scantling was optimized where insufficiency found with respect tostrength. Also, research was carried out for the process of loads acting onLMU, as well as the internal energy absorption rate of sand and rubber.Afterwards, the structure type of LMU was studied, and both staticand dynamic calculation was done for LMU with and without sandboxrespectively. The influence of sandbox on LMU was analyzed based onstress and strain, internal energy absorption rate, velocity and kineticenergy decrease rate. The results indicate that, LMU with sand box canwithstand more loads and transfer the loads to the canister better and moreuniformly; There’s no obvious stress concentration on LMU with sandbox, which will increase the steel usage of canister; LMU with sandbox canreduce the velocity of platform during load transfer and enhance theinternal energy absorption efficiency in float-over process.Last but not least, the static and dynamic analysis on five LMUs withvertical rubber rings differed in layer number was carried out. The LMUswere built with2-6layers of rubber rings. With respect to stress and strain,internal energy absorption rate, velocity and kinetic energy decrease rate,the influence of layer number of rubber rings on performance of LMU wasstudied. The results indicate that, in vertical loading condition, the stiffnessof LMU is in proportion to layer number, while max velocity and kineticenergy, as well as their decrease rate, vary inversely, max stress, however,first decrease then increase as layer number increases. In horizontalloading condition, the layer number has certain influence on performanceof LMU. The internal energy absorption rate of LMU varies inversely withlayer number. Stress exceeding yielding limit occurs in all LMU exceptthat with three layers of rubber rings. However, the influence of layernumber on velocity of LMU can be neglected. The kinetic energy variesinversely with layer number while the internal energy absorption ratekeeps uninfluenced. Concluded from this paper, LMU with three layers ofrubber rings has the best performance.