The Study Of Connection Mode And Dynamics Characteristics For Very Large Floating Platforms

The very large floating plat form is a t ype of special marine engineering equipment which is composed of several connected float ing modules.The research and development of this equipment is of great significance for defending the nat ional sovereignt y,the deep sea resources explo itat ion and the future marine immigrat ion.This doctoral thesis focuses on the studies of the connect ion mode and dynamic characterist ic for the very large float ing plat form.The connector is a key component for the modular float ing systems,and the connect ion load may exceed 10000 tons.How to improve the heavy-load bearing capacit y of float ing body connector has become an unsolved technical bott leneck in ocean engineering.Based on the nonlinear network dynamics analysis method,a series of theoret ical and technical studies on flexible connectors have been carried out.According to the system response stabilit y and load constraints,this the sis studies the key technologies such as st iffness combinat ions and opt imal layout of flexible connectors,and proposes a set o f customized optimal st iffness and layout scheme for the specific funct ional requirements of VLFS.Combined wit h the above result s,this thesis proposes a new type of face-contact connect ion model.Through the numerical and experimental comparison with the traditional hinged connectors,the significant advantages of the face-contact connect ion model in reducing the stress level of t he connect ion regio n are verified.The studies in this paper are significant for the new connector design of the very large floating platform.The main research contents are listed as follows.A nonlinear network dynamics model of the mult i-modular float ing system has been established.This model consists of the linear wave theory,rigid module flexible connector model,wave load model and coupling model of connectors.Different from the tradit ional model,this network dynamics model has a topology matrix w hich can be used to represent the modules are connected or not.Only by changing the elements of the topology matrix,the network model could be suitable for any topological t ype of float ing platform.In addit ion,the detailed modeling process of coupling model o f connectors can reflect the real material and geometric characterist ics of the connector.This thesis also carried out a basin experiment to verify the network dynamics model results.The results show that the network dynamics model is reliable in the response predict ion.The flexible connector is outperformance than the rigidly hinged connectors in reducing connect ion loads.The configuration of the flexible connector st iffness in each coordinate direction is a key technology.According to the syst em response stabilit y and load constraints,a set of customized theoret ical analysis method for solving the opt imal st iffness combinat ion of flexible connectors is proposed.Sensit ivit y analysis of connector load parameters has been done by using the orthogonal experimental design method.The connector st iffness combinat ion is opt imized by using the parameters with high sensit ivit y.The linear weighted sum method is used to conduct the mult i-objective optimizat ion.The weights of the opt imized target depend on the actual engineering requirements of the very large flo ating plat form.A new flexible connector design is proposed based on the optimal st iffness combinat ion in previous research.The strength reliabilit y of the design is verified by finite element s imulat ion,and the equivalent st iffness of the model is used to simulate the responses of float ing modules by using the network dynamics model.The reasonable layout of connectors on the end face of floating body is also one of the key technologies of connector design,which relates to the locat ion and the number of the connectors.A solut ion to solve the opt imal layout of the connector on the float ing modules' end face is proposed.Considering there are many parameters related to the connector layout,the orthogonal experimental design also has been used to analyze the sensit ivit y of the layout parameters of the connectors.By using the parameters with the high sensit ivit y,this thesis opt imizes the targets related to connector strength,cost performance and so on.The linear weighted sum method is used to assign different weights to each target.The values of the weight depend on the designer's decisio n,and this method can be used to customized solve the opt imal layout of the connector.The present connectors hardly meet the requirements of structural strength at connect ion.It has become a major technical obstacle in the connector design.This thesis proposes a new t ype of face-contact connector which consists of a huge flexible cushion and a series of cables.The core idea is to disperse the huge connect ion load to the whole end face of modules,so as to significant ly reduce the local stress level at connect ion areas.By adopt ing the finite element method and network dynamics analysis method,the load distribut ion and maximum stress level of the connect io n area caused by the module movements are evaluated.By analyzing the stress levels under extreme sea condit io ns,it is found that the face-contact connector has significant advantages over tradit ional hing ed connectors in the stress level.The flume experiments of a five-modular semi-submersible plat form connected with the rigid hinged connector and the face-contact connector are carried out.The experiment results show that the mult i-mo dular platform connected by the two different connectors does not have a significant difference in the response amplitude.Through the finite element simulat ion,it is found that the face-contact connector could reduce the stress level on rigidly hinged connectors by one orde r of magnitude.This face-contact connector design provides a reliable new idea for the flexible connector design.For providing addit ional power supply to the mult i-modular float ing platform working in the offshore,this thesis proposes a new nonlinear wa ve energy conversio n device which could be applied to the mult i-modular float ing plat form.Through the numerical simulat ion of the two-modular float ing system,the influence of the structural parameters of this new nonlinear wave energy conversio n device o n the mot ion mode of models is discussed in detail.By comparing wit h the tradit ional linear wave energy conversio n device,the new nonlinear wave energy conversio n could increase the efficiency of wave energy conversio n by more than two t imes and broaden the useful frequencies,which are better to work in the offshore.