Investigation On Analysis Methods Of Dynamic Performance For Large Marine Gearbox

This study originates from one of the Key Industrial Projects founded by Zhejiang Province Science and Technology Department:"Investigation and Application of the Key Technologies for Large Marine gearboxes"(2009C11062). The research object is a type of large marine reduction gearboxes matching the medium-speed diesel engines. This project is aimed at developing and improving the dynamic performances of large marine gearboxes which can match the10000～50000-tons large transport ships and warships, for technical reserves of the development for more powerful reduction-gearbox systems, and the formation of dynamic performances for box structural-design and optimization, vibration and noise reduction, shock resistance performance assessment.As one of the most important equipments for the transport ship and warship main power system, the large marine reduction gearbox is developing towards high rotating speed, high efficiency, high stability, light-weight design, low vibration and noise, heavy-duty, short cycle of design and manufacturing, which put towards higher requirements on the dynamic transmission characteristics of gear transmission system and the manufacturing capabilities. In addition, the large marine gear system is designed for both military and civilian use, because of that, the design, construction and improvement should be subjected with relevant military specifications, in which the particular important ones are about the shock resistance performance assessment under the under-water explosion. This paper focuses on a certain models of large marine reduction gearbox systems, by accessing to a large number of domestic and foreign technical materials and academic literatures. By the means of combining theoretical investigations, numerical simulations and experimental studies, and systematically utilizing geared rotor dynamics, gear system dynamics, finite element method, modal analysis theories and techniques, dynamic response analysis methods, vibration test theories and methods, response spectrum analysis methods and etc., this study conducts a comprehensive survey and assessment of the dynamic performances for the large marine gearbox system, and provides theoretical basis and technical solutions for the dynamic performance design methods formation of large-scale marine gearbox systems. The main investigation contents can be summarized as follows:1). Based on finite element theories, coupling geared multi-transmission parallel shafts rotor dynamics model is established. Then the model is utilized to analyze the geared dual parallel shafts in cis-turner working conditions for driving shafts of the large marine gearbox transmission system. The critical speed of coupled and uncoupled system is calculated, and then by analyzing the modal shapes of bending and torsional vibration for the coupled system, the necessity to consider the torsional vibration in the geared rotors is investigated. The critical rotating speeds of the coupled system with different gear meshing stiffness are computed to gain the bending and torsional vibration frequencies changing trends versus meshing stiffness changing. The investigation provides the minimum meshing stiffness for the design of the gearbox transmission system from the perspective of rotor dynamics. After that, the unbalance response is calculated for the drive system, and the sensitivities of different parts for the dual-rotor are studied.2). The refined3D finite element models for components of the large marine gearbox system are built, then the assembled finite element technology is used to integrate the various components in accordance with the original spatial location for the entire gearbox system. Coupling functions, such as inter-node freedom coupling,1D connecting elements,1D spring-damper elements, contacting control coupling and etc are used to build the relationships between bearings, bearing houses, shafts, mating surfaces of gears. Then the computational model of the entire gearbox system is established, including box, bearing houses, shafts, and gears.3). Modal frequencies and modal shapes between0-5000Hz of the large marine gearbox system are analyzed utilizing modal analysis theories. By means of simulated tests before real modal experiments, frequency responses of different parts on the box to force-hammer pulse excitation are extracted to provide a reference of location choices for the real tests. Then hammering method of modal experiments is adopted for modal tests of the large marine gearbox system. The theoretical modal analysis data are compared with experimental modal analysis data, to verify the effectiveness of the theoretical model.4). Based on rotor dynamics, gear system dynamics and finite element method, the inner and outside excitations are studied for the large marine gearbox system. Then, based on modal superposition method of vibration theories, the dynamic response simulation is carried out. By means of comparing the theoretically analyzed response data and experimental vibration data, the rationality of the theoretical model is proved. On this basis, the main vibration frequencies are analyzed, and then the vibration intensity and structural noise are assessed for the gearbox system.5). Based on calculation method of military specification, combined with the vibration parameters of the large marine gearbox system, DDAM design shock spectrum of natural frequencies is produced. Then the DDAM design shock spectrum was fitting into dual-polyline shock response spectrum, which is exerted as excitation of under-water explosion to the foundation of the gearbox system. After that, the response peak values of acceleration, velocity, displacement and stress for the marine gearbox of vertical, athwartship and fore-aft loading directions are computed.6). Mapping relationship between nodes and elements of each sub-system and entire assembly finite element system is established. Synthetic method is derived to combine the static stress under normal working condition and dynamic stress obtained from response spectrum analysis. Then, this method is used to assess the safety performance for the gearbox system under under-water explosion. At last, damping sinusoid method is used to fitting the time domain explosion shock signal from the shock response spectrum, and the time domain signal is utilized to analyze the transient response characteristics of the gearbox system.7). Topology optimization technology was introduced to improve the structural design and optimization for the gearbox. The objective function of dynamic response was derived according to the actual operation condition and dynamic performance analysis method. Multi-constraint and multi-objective optimized model was established according to the SIMP algorithm optimization criteria. After optimization analysis, optimized improvement was done to the gearbox structure.