| The multi-modular floating structure with flexible connection is a cutting-edge platform in ocean engineering,emerged from the horizon of the national strategic goals in naval defense and natural resource development.This doctoral thesis aims at the dynamic forecast of a super-scale multi-modular floating airport,and related scientific and technical problems.By introducing the most advanced network theory,t he nonlinear dynamic characteristics of the floating airport is investigated.The study covers the methodology development of network modeling,the nonlinear dynamic characteristics of the floating airport with different connections,the global stability of the floating airport based on the mechanism of ?amplitude death? and critical conditions,the modeling method for an entire floating airport with connected floating modules and flexible runway structure,and its application for an embedded wave energy harvest farm.This study provides a new perspective for the engineering safety design of the floating airport.The methodology developed from this thesis is not limited to the ocean engineering but also extended to other engineering fields with network structure alike.The main results of this thesis are listed as follows.Nonlinear network modeling method for multi-module floating airport is developed by using rigid module flexible connector(RMFC)based on the dynamic model of a single floating body,coupling model of connector and the constraint model of the mooring system.Different from the traditional modeling method,th e network model is suitable for any topological type of floating platform by introducing a topology matrix.The network model can perform the nonlinear dynamic forecast of the floating airport and estimate the loads of flexible connectors in different wave conditions.The conceptual designs of connectors,the key parts of the floating airport,are proposed with different topology configurations.The effects of connector designs on dynamic behaviors of chain-type floating airport are analyzed in various operator conditions.With different connector stiffness and wave conditions,the complex dynamic phenomena,such as response jump,synergetic effects,phase locking synchronization,beating vibration,torus oscillation and multi-stability oscillation,are revealed.The results show that the ideal connector should have proper stiffness constraint in every degree of freedom,which could provide a theoretical guideline for engineering design.Amplitude death(AD)phenomenon is observed,and the important relationship between the very weak oscillatory state for AD and wave period is discovered.Based on this clue,the fundamental solution for revealing the mechanism of the occurrence of AD is derived.Further,the semi-analytical critical condition for the onset of AD is formulated based on the fundamental solution and bifurcation theor y,which enables to identify the AD design space for non-autonomous systems.The stability of the floating airport is analyzed based on the AD condition and a set of AD diagrams are drawn in the parameter space of wave period and connector stiffness.The AD diagrams plays the role of the theoretical reference for the stability design of the floating airport.AD is a new concept of the stability design for complex engineering systems.A standard network modeling method for three-dimensional multi-module floating airport is developed,suitable for arbitrary topology multi-module floating structures with any topology connection.This method can be generally extendable to other engineering systems with network structure alike.As a typical application,a chain-type airport model in full sea condition is considered for numerical simulation.The effects of oblique wave on nonlinear dynamic response and connector load are analyzed.The stability parametric regions for the floating airport in the condition of various wave parameters and coupling strength are studied,which provides a theoretical basis for nonlinear dynamic stability design of floating airport in complex sea condition.At last,the dynamic response and connector load of floating airport under irregular wave excitation are also analyzed.The modeling method for the floating airport with discrete modules coupled with continuum flexible runway is developed.A network model of a multi-module floating platform incorporated with a runway structure,viewed as a non-autonomous network with discrete-continuum oscillators,is developed and then is converted to network model coupled with completely discrete oscillators f or the convenience of dynamic analysis.The mechanism of AD phenomenon is analyzed using the averaging method.The dynamic stability of floating airport is investigated based on the AD mechanism and the effects of runway stiffness and wave condition on AD stability is analyzed.Various complex dynamics are revealed via numerical analysis.This method has general scientific characteristics and can be extended to floating wave farm and other engineering application fields.Dynamic characteristics and energy absorption efficiency for very large floating wave energy harvesting system are analyzed.The wa ve energy converters,to be installed in between floating module and operating platform,can achieve dual benefits,not only provide additional power supply to the floating airport but also improve the stability of the platform.The governing equation of floating airport with embedded wave energy harvesting system is formulated by using Hamilton's principle and Galerkin discretization method.The effects of wave condition,connector stiffness,damper for the energy convector on the efficiency of wave energy absorption are analyzed via numerical simulation.The energy absorption efficiency of multiple oscillators coupled with platform can be doubly enhanced in comparison with that of equivalent wave energy convector modules without platform. |
PDF Full Text Request