Modeling And Dynamic Property Research On Flexible Floating Raft Isolation System

With the purpose of analyzing the dynamic character of floating raft, the isolation performance underthe linear and nonlinear condiction is researched. The linear theory model and simulation arepresented. Through the test method, the results of theory and simulation are validated. In the nonlinearcondition, the dynamic response and global analysis are researched by the method of numericalcalculation and point mapping under cell reference (PMUCR), respectively. Finally, the stability ofperiodic motion is discussed.Theoretical model of flexible floating raft is established by the improving subsystem synthesismethod. Based on the rigid dynamic and impendence theory, the subsystem synthesis method isimproved, which takes the relative reality of the floating raft into account, such as the spatial sixdegree of freedom of rigid power machine, the flexibility of the raft frame and infrastructure, and thesix-direction force acting on the raft and infrastructure. The impendence matrix of the raft frame andinfrastructure is derived from the partial differential equation of the plate. Including the relativemotion and flexible deformation together, the relative motion of the raft frame is analyzed by thesame method of power machine. The equations of whole system are derived by the compatibilitycondition of force and displacement. The distinctions of dynamics properties between the flexible andrigid raft frame are shown by the power flow transmission from power device to infrastructure.Compared with the flexible raft, the rigid raft frame reduces the energy transferred into theinfrastructure. In the design process, the stiffness of the raft frame should increase in order to improvevibration isolation. In the low frequency band, there is no obvious difference between the power flowsof rigid and that of flexible raft frames. When the rev of load device is low, the flexibility of raftframe can be ignored.Simulate research on flexible floating raft is executed by CMD and FEM software. In practice, itis extremely difficult to test the modal of entire floating raft, due to the high cost and the lack ofexperimental equipment, hence the method of numerical calculation and software simulation approachis a preferable alternative. Considering rigid-flexible coupling, CMD and FEM are combined to obtainmore real model, which will be used to verify the validation of the analytical result. The simulationmethod has the advantage of low test cost, short design time and good result. Comparing with FEM,the CMD rigid-flexible coupling method extremely decreases the calculation duration and space of thestorage. At the same time, this method is good at modeling the system with the kinematic pair ofhinge, slip and rotation, and so on. The method of CMD rigid-flexible coupling dynamiccharacteristics analysis not only can test the theoretical solution of the simple structure, but also can simulate the complicated structures.The SALiM isolator is designed, and the isolation performance is tested. Filling gasbag withelastic elements and liquid (Solid and Liquid Mixture, SALiM) instead of air will avoid the airleakage problem, and no longer require the position monitoring and maintaining equipments. As aresult, it effectively reduces the cost of isolation system. The liquid and the corrugated-pipe elementsconstitute the SALiM medium of the vibration isolator. The performance of the vibration isolator isevaluated experimentally and numerically. The result indicates that the vibration isolation effect of theSALiM isolator increases with the number of the corrugated-pipe elements. The stiffness of thegasbag filled with SALiM mixture increases with the pressure of the mixture, but the curve offrequency response function shows that the stiffness presents complicated characteristics. This iscaused by the mechanic properties of the SALiM mixture associated with the gasbag.In the nonlinear condiction, the modeling and calculation on floating raft are researched. Toimprove the isolation effect, a number of vibration isolator with nonlinearity is employed in thefloating raft. Considering that the impendence is the inverse operation of frequency response, thecorrespondence of input and output is no longer preserved. So the ordinary differential equation isderived from the partial differential equation by Galerkin method in the nonlinear condiction. Theeffect of nonlinear isolators on dynamics behaviors of discussed system is given. The multi-scalesmethod and numerical method based on Runge-Kutta are employed to analyze the dynamics responsefor non-resonance states.The simulation method is not overall in the nonlinear condition, and the quantitative analysismethod including the small parameter method, the multiple scales method, KBM method andincremental harmonic balance method is just fit for solving the weak nonlinear system, especially forthe two-dimension or three-dimension system. In fact, most of the dynamics systems have the highdimension and strong nonlinearity, so the main analysis method is based on numerical analysismethods. Through the quantitative analysis and numerical calculation, the basic characteristics of thefloating raft under the symmetric excitation are researched. The first order approximate is obtained bymultiple scales method. The resonance term is internal resonance and combined harmonic resonance.The Runge-Kutta numerical method is used to calculate the nonlinear equations and analyze thedynamic character in non-resonant condition.The global characteristics of floating raft are presented by the PMUCR in the nonlinearcondiction. The calculation under one certain initial condition is unable to reflect the global characterof nonlinear system. So the method of point mapping under cell reference (PMUCR) is employed to analyzed the global character of floating raft mentioned in the preamble, and discussed the severalnecessary principles applied to high-dimensional systems. The impacts from the PMUCR parameter,including the length of calculation time, criterion of persistence of system characteristics and the stepof mapping, on computing efficiency is discussed. The calculation result shows that the period motionis complex and the P-1and P-2motion is discovered in the plane. Finally, the stability of periodicmotion is researched by the shooting method.The experiments show the validity of the basic theory. The experiment structure of floating raftis established, and then the parameters of model are updated by the FEM method. Substituting thepost-correction model parameter into the theoretical model and simulation model, the validity of thetheory and simulation are proved by the experiment method.