Research Of Dynamical Properties And Stability For Submerged Mooring Monitoring Platform

The submerged mooring monitoring platform is a new type engineering structure ofriverway and harbor, and it is a support platform of equipment and image collect instrument forsubmerged monitoring system. The buoy and mooring cable of the submerged mooringmonitoring platform are very long and the ratio of diameter and length are very large. Theirdynamical property will change greatly by nonlinearity wave force and fluid force; they willpresent nonlinearity large displacement and rotation, these will influence the security andstability of the platform. So study the nonlinearity dynamical response and stability by waveforce and fluid force were very important.The dissertation chose the submerged mooring monitoring platform as study object,analyzed the dynamical property and environment load in detail, combined with mooringmonitoring platform function characteristics and performance requirements, then established thenonlinearity fluid-solid coupling dynamical equation and finite element model, studied thestability criterion and influencing factor、the nonlinearity dynamical response and the impactresponse of buoy and mooring cable by chaos theory and Hopkinson impact loading theory. Themain works of the dissertation are below:（1） The wave and fluid load of submerged mooring monitoring platformFirst I studied the velocity distribution rule of the water area where the platform fixed, thendetermined the fixed area according to the measure data of hydrology environment, calculatedthe fluid load of mooring platform by Morison theory; simulated the vortex field of square crosssection、circular cross section and ellipse cross section buoy by CFD software, through theanalysis the conclusion could be got that in the same stream surface area of buoy situation, thestreaming field of bluff section was complex and the drag coefficient was large, with the sectioncurvature change mild, the streaming field changed observably, the distributed pressure of buoysurface decreased, it’s beneficial to the whole stress situation of buoy and it could enhance itsstability.（2） The nonlinearity vibration model of submerged mooring monitoring platformIn order to overcome and avoid resonance, studied the natural frequency of vibration forsubmerged mooring monitoring platform, let the vortex frequency far from to the naturalfrequency, the buoy between the two mooring cable was chose to be analyzed, studied theresponse by distance of two mooring cable、the mass of per unit length of buoy and the diameterof buoy, the conclusion indicated that the distance influence the natural frequency of buoy wasmost and the mass of per unit length was least. So, when designed the mooring monitoringplatform, the diameter of buoy and the distance of mooring cable were chosen as the maincontrol factors, if the velocity of fluid was known, we can chose the suitable diameter of buoy tomake the vortex frequency far from to the natural frequency, it could decrease the damage byresonance.（3） The stability of submerged mooring monitoring platformAimed at the problem of stability by flow vertex-induced action for submerged mooring monitoring platform, the fluid-solid coupling nonlinear dynamic equation was set up by takinginto account the deformation of floating body on vibration. Done the nonlinear characteristicqualitative analysis by harmonic wave equilibrium method and researched the stability criteriaand influencing factors by Melnikov method. Studied the influence for stability of mooring cablesupport distance、fluid velocity and the diameter of buoy on the stipulation that the systememerged chaotic state, and calculated the critical value of support distance, the results shown thatthe stability first decreased slow and then increase rapid with the diameter of buoy, the stabilityof system would decrease along with the increase of support distance, after the support distanceexceed the critical value, a little increase would make the mooring platform’s vibration deviatethe vibration track、cause local instability and even damaged the structure.（4） The dynamical response and impact tension of mooring cable for submerged mooringmonitoring platformThe dynamical model of submerged mooring monitoring platform on impacting and afterimpacting was formulated aimed at impact tension of mooring cable and the dynamical responseby the action of flow force, based on Hopkinson impact load theory, taken into account thecatenoid effect of mooring cable and revised the difference of tension and chordwise directionaction force by equivalent modulus of elasticity. And solved the equation by hydraulics theoryand structural mechanics theory of oceaneering, studied the action force characteristic ofmooring cable and motion characteristic of buoy. Calculated the equation according to a specificexample and hydrological environment, through the result the conclusion could be got that thebuoy would engender biggish heave and swaying displacement, but the swaying displacementgot stable quickly and the heaven displacement got vibration for the vortex-induced action by theflow, because the vortex-induced action and the impact action between buoy and the mooringcable, the tension changed greatly when the mooring cable was relaxation-tension.