Study On Vibrao-acoustic Behavior And Active Control Strategies Of Submerged Complex Hull Coupled Systems

The power machine is one of the main vibration sources for submarines.As it works,the vibration is transmitted to the supporting shell structure,which leads to the radiated noise to the external fluid medium,and then significantly influences the concealment and safety.The active isolation technology can effectively reduce the vibration of the shell resulting in weaken of noise radiation ability for submarines.With the consideration of practical submarine structure,the whole theoretical model of the double-layer active isolation-the shell structure-external fluid medium coupled system is established in the thesis.In order to provide reliable theoretical formulation for the analysis of active isolation system-the shell structure-sound radiation,the design of active isolation systems and control of mechanical noise,simulation and experimental study,the behavior of vibration transmission in the coupled system and the control mechanism of active isolation for the radiated noise from the shell are discussed based on the theoretical analysis.Under the framework,the specific work of this dissertation is presented as follows.Based on the modified Fourier series method and spectral element approach,a general model for coupled shell structures is presented.Due to the uniform description for displacement components of each substructures and the use of three dimensional elastic coupler to coordinate the displacements and forces at the junction,the presented method is of great generality for coupled shell structures.Based on the approach,the whole model consists of conical shell,ring stiffened cylindrical shell,spherical shell,bulkheads and rectangular plate is thereby established.The accuracy and convergence of the present method are validated through comparison to the results from numerical software.Besides,the test platform of plate-cylindrical shell coupled structure is built to validate the accuracy of the present method in the view of frequency-response function.Through simplifying the vibrating power machine and the install base as the rigid bodies,the dynamical formulation of double-layer isolation-shell coupled system is established.Based on the test platform of the plate-cylindrical shell coupled structure,the new platform of the double-layer isolation-cylindrical coupled system is built to validate the accuracy of the present model in the view of experimental study.The characteristics of transmitted power flow in the coupled system and the distribution principle of the kinetic energy on the shell structure are synthetically analyzed.In addition,the effect mechanism of the stiffness of isolators on the behavior of vibration transmission is also discussed.Based on the formulation of the double-layer isolation-shell coupled system,the minimizing power flow strategy and minimizing kinetic energy strategy are deduced by using the least square method.Through various types of the driving force,the influences of mounting location and number of actuators on control effect for these two strategies are synthetically analyzed.Subjected to the distribution principle of the kinetic energy on the shell structure,the new control strategy of minimizing kinetic energy is redesigned to take the kinetic energy of partial structures instead of the whole structure in order to provide achievable design principle for active isolation systems.Considering the fact that the output force of practical actuators can hardly attain the theoretical optimum control force,a constrained solution is achieved through weighting matrix method and its control effect on vibration transmission in the coupled system is discussed to make the present research of practical value.In what follows,a semi-analytical approach through combining the modified Fourier series method and direct boundary element method to build the relationship between radiated pressure at the surface of complex shells in external fluid medium and normal displacement,and thereby to establish the dynamical model of fluid-structure interaction for the whole shell structure for submarines.Through comparison to the results from numerical software,the accuracy and convergence of the present method are validated.the effects of external fluid medium,internal bulkheads,ring stiffeners and double-layer isolation system on vibro-acoutic behavior are analyzed in depth.Based on the formulation of fluid-structure interaction of complex coupled shell structure,the whole model of the double-layer-shell-external fluid field is established.Within the model,the minimizing sound power strategy is deduced in term of external sound radiation from the shell.The influences of the type of driving force and the number as well as the mounting location of actuators on control effect of minimizing sound power strategy are analyzed to discussed the control mechanism of active isolation for coupled shell structure.The control effect of minimizing power flow,kinetic energy of the shell and sound power strategies are synthetically evaluated in term of radiated sound power to provide valuable acoustical design for the practical active isolation system...