Study On Non-conservative Loss Factor Of Joints Between Ship And Mechanical Equipment

Most of the hull structures are connected with mechanical equipments and instruments by bolts. Damping characteristics of the joint surface of connection structure has a very large impact on the dynamic characteristics of the whole system. If the dynamic response and noise is too large, not only affects the work environment, but also cause failure of instruments and other equipments. The joint surface of connection structure can loss energy, transfer force and power, and the vibration energy can be converted into heat and acoustic energy that can be lost. The energy loss is mainly due to the existence of damping which is so complex that makes it difficult to find effective mathematical models and identification methods to accurately describe and calculate it at present.Finite element analysis of the actual connecting structure in the actual engineering projects mainly applies these two methods:rigid connections and spring connecting. These two approaches are not very good at treating surface damping, In this paper, the joint surface is simulated by contact analysis with preloaded stress. A finite element analysis model of a practical example is established for modal analysis in order to find the impact of coupling damping and preloaded stress on vibration frequencies of the bolted structure.Ship and mechanical equipment connecting structure is a kind of non-conservative coupling system. An important parameter to characterize the energy transfer is non-conservative coupling loss factor. In this paper, these connections will be simplified to a cantilever beam structure with a bolted joint to analyze the transfer of integration power and loss between bolted joint structures by statistical energy analysis method. The computational formula of non-conservative coupling loss factor and internal loss factor is deduced according the integration power balance equation. The energy ratio is obtained by using the contact finite element analysis results. Then the internal loss factor is used to adjust the total loss factor and further obtain the precise coupling loss factor. An actual bolt joint structure is analyzed to conduct simulated numerical calculation. At the same time, the influence of different pre-tightening forces is considered. Analysis results show that this method can effectively reflect the combination of surface damping form and different pre-tightening force affects the result obviously. Some valuable conclusions for engineering applications are thus set forth.